Water-absorbent sheet and absorbent article including same

Abstract

To provide a novel water-absorbing sheet capable of significantly reducing liquid release from the water-absorbing sheet caused by return even when liquid is intermittently introduced a plurality of times (particularly, 3 or more times).SOLUTION: A water-absorbing sheet comprises a first substrate, a second substrate, and a water-absorbing layer positioned between the first substrate and the second substrate. The water-absorbing sheet is such that: the water-absorbing layer contains a particulate absorbent; the surface of the first substrate forms a water-absorbing surface for directly absorbing liquid; and a ratio of a thickness (mm) of the first substrate to a thickness (mm) of the second substrate [first substrate thickness (mm) / second substrate thickness (mm)] is 1.5 or more and less than 14.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a water-absorbent sheet and an absorbent article including the same. [Background technology]

[0002] Super absorbent polymers (SAPs) are water-swellable, water-insoluble polymer gelling agents that are used in a variety of applications, including hygiene materials such as disposable diapers, sanitary napkins, and adult incontinence products, soil water retention agents in agricultural and horticultural applications, and industrial water-stopping agents.

[0003] These absorbent articles are generally manufactured in paper diaper manufacturing plants as absorbent bodies that are individually molded for each absorbent article by mixing absorbent resin and fibrous material, and are processed into absorbent bodies of various shapes (for example, hourglass-shaped, fox-shaped, oval, etc. when viewed in plan) depending on the purpose. These manufacturing methods for absorbent bodies are the mainstream for current paper diapers, since they can be processed into any shape because they are individually molded, and the amount of fiber and absorbent resin can be easily adjusted for each absorbent article.

[0004] However, in recent years, paper diapers have begun to be manufactured using absorbents (called water-absorbent sheets, usually cut into rectangles about 10 cm wide and several tens of cm long) made by cutting a long water-absorbent sheet with water-absorbent resin fixed between two sheets during the manufacturing process of sanitary materials. By purchasing or manufacturing a long continuous water-absorbent sheet, paper diaper manufacturers can simplify the manufacturing process of paper diapers, and furthermore, by not using pulp, they can make paper diapers thinner. Water-absorbent sheets are configured by sandwiching and fixing water-absorbent resin particles between upper and lower sheets (particularly nonwoven sheets), and usually after manufacturing a long continuous sheet, the long continuous sheet is cut into rectangles about 10 cm wide and several tens of cm long, which are then incorporated into paper diapers (for example, International Publication No. WO 2010 / 143635).

[0005] Unlike conventional sanitary materials (disposable diapers), disposable diapers made with absorbent sheets have a short history, and the reality is that there has been almost no development of absorbent resins suitable for absorbent sheets or proposals for parameters for them, and the absorbent resins used in conventional disposable diapers are used as is for absorbent sheets. Summary of the Invention [Problem to be solved by the invention]

[0006] The inventors have found that, due to the structure of the water-absorbent sheet, which is mainly thin, the absorbed liquid is easily released in the direction of the absorbed liquid introduction by applying pressure to the water-absorbent sheet, which is called "backflow". "Backflow" is also called "re-wet". The inventors have found that the occurrence of backflow is more prominent when the liquid is introduced intermittently multiple times (especially three or more times) and the amount of introduced liquid is large. When backflow occurs, the skin in contact with the water-absorbent sheet comes into contact with the backflowed liquid and is exposed to a highly humid state. This not only causes discomfort to the user, but also makes the skin in contact with the water-absorbent sheet more susceptible to rashes.

[0007] The present invention has been made in consideration of the above circumstances, and aims to provide a novel water-absorbent sheet that can significantly reduce liquid release from the water-absorbent sheet due to backflow, even if liquid is intermittently introduced multiple times (particularly, three or more times). [Means for solving the problem]

[0008] The present inventors have conducted extensive research to solve the above problems. As a result, they have found that the above problems can be solved by a water-absorbent sheet having a first substrate, a second substrate, and a water-absorbent layer located between the first substrate and the second substrate, the water-absorbent layer containing a particulate water-absorbing agent, the surface of the first substrate forming a liquid-absorbent surface that directly absorbs liquid, and the ratio of the thickness (mm) of the first substrate to the thickness (mm) of the second substrate (thickness (mm) of the first substrate / thickness (mm) of the second substrate) is 1.5 or more and less than 14.

[0009] Furthermore, a water-absorbent sheet according to another embodiment of the present invention is a water-absorbent sheet having a first substrate, a second substrate, and a water-absorbent layer located between the first substrate and the second substrate, wherein the water-absorbent layer contains a particulate water-absorbing agent, the water-absorbent layer is not disposed on the first substrate, and the ratio of the thickness (mm) of the first substrate to the thickness (mm) of the second substrate (thickness (mm) of the first substrate / thickness (mm) of the second substrate) is 1.5 or more and less than 14.

[0010] Furthermore, a water-absorbent sheet according to another embodiment of the present invention is a water-absorbent sheet having a first substrate, a second substrate, and a water-absorbent layer located between the first substrate and the second substrate, wherein the water-absorbent layer contains a particulate water-absorbing agent, the water-absorbent layer is not disposed on the first substrate, the thickness of the first substrate is 0.7 mm or more and 5 mm or less, and the ratio of the thickness (mm) of the first substrate to the thickness (mm) of the second substrate (thickness (mm) of the first substrate / thickness (mm) of the second substrate) is 1.5 or more and less than 14.

[0011] A water-absorbent sheet according to still another embodiment of the present invention includes a first substrate, a second substrate, a water-absorbent layer located between the first substrate and the second substrate, and a wrapping sheet disposed on a surface of the first substrate, wherein the water-absorbent layer contains a particulate water-absorbing agent, the surface of the wrapping sheet forms a liquid-absorbent surface that directly absorbs liquid, and the ratio of the thickness of the first substrate to the thickness of the second substrate (thickness of the first substrate (mm) / thickness of the second substrate (mm)) is 1.5 or more and less than 14. [Brief description of the drawings]

[0012] [Figure 1] 1 is a schematic diagram illustrating a cross section of a water-absorbent sheet according to one embodiment of the present invention. [Diagram 2] FIG. 4 is a schematic diagram showing a cross section of a water-absorbent sheet according to another embodiment of the present invention. [Diagram 3] FIG. 4 is a schematic diagram showing a cross section of a water-absorbent sheet according to another embodiment of the present invention. [Figure 4] FIG. 4 is a schematic diagram showing a cross section of a water-absorbent sheet according to another embodiment of the present invention. [Diagram 5] FIG. 2 is a schematic diagram illustrating a method for measuring the permeability of a particulate water-absorbing agent through a nonwoven fabric. [Figure 6] FIG. 2 is a plan view and a right side view showing a sample used in the evaluation of a specific rewetting amount, and shows a state in which the water-absorbent sheet produced in the example is wrapped in a liquid-impermeable sheet. [Figure 7] 1A and 1B are a plan view and a front view of a liquid injection tube used in evaluating a specific return amount. [Figure 8] FIG. 2 is a front view showing a state in which a liquid injection tube is placed on the water-absorbent sheet used in the examples of the present application in the specific rewet amount evaluation. [Figure 9] FIG. 13 is a front view showing a state in which a sodium chloride aqueous solution is poured into a water-absorbent sheet from a liquid injection tube using a funnel in a specific rewet amount evaluation. [Figure 10] FIG. 1 is a schematic diagram showing an apparatus used for evaluating the amount of leakage in the surface direction. [Figure 11] FIG. 2 is a schematic diagram illustrating a method for measuring the raised area ratio of a nonwoven fabric. [Figure 12] 1A and 1B are a plan view and a front view of a liquid injection tube used in evaluating a specific return amount under pressure. [Figure 13] FIG. 13 is a front view showing a state in which a liquid injection tube is placed on the absorbent sheet used in the examples of the present application in the evaluation of the specific rewetting amount under pressure. [Figure 14] FIG. 13 is a front view showing a state in which a sodium chloride aqueous solution is poured into a water-absorbent sheet from a liquid injection tube using a funnel in an evaluation of a specific rewet amount under pressure. [Figure 15] FIG. 2 is a schematic diagram showing a cross section of a water-absorbent sheet for illustrating the form of a particulate water-absorbing agent and gaps in the water-absorbent sheet produced in the Examples. [Figure 16] FIG. 2 is a schematic diagram showing a cross section of a water-absorbent sheet for illustrating the form of a particulate water-absorbing agent and gaps in the water-absorbent sheet produced in the Examples. [Figure 17] FIG. 2 is a schematic diagram illustrating a method for measuring the elongation of a nonwoven fabric. [Figure 18] FIG. 1 is a schematic diagram illustrating a cross section of a water-absorbent sheet according to a first embodiment of the present invention. [Figure 19] FIG. 4 is a schematic diagram showing a cross section of a water-absorbent sheet according to a second embodiment of the present invention. [Figure 20] FIG. 2 is a schematic diagram showing a cross section of a water-absorbent sheet for illustrating the form of a particulate water-absorbing agent and gaps in the water-absorbent sheet produced in the Examples. [Figure 21] FIG. 2 is a schematic diagram showing a cross section of a water-absorbent sheet for illustrating the form of a particulate water-absorbing agent and gaps in the water-absorbent sheet produced in the Examples. [Figure 22] FIG. 2 is a schematic diagram illustrating a method for measuring the elongation of a nonwoven fabric. [Figure 23] FIG. 2 is a schematic diagram illustrating a method for measuring the permeability of a particulate water-absorbing agent through a nonwoven fabric. [Figure 24] FIG. 2 is a plan view and a right side view showing a sample used in the evaluation of a specific rewetting amount, and shows a state in which the water-absorbent sheet produced in the example is wrapped in a liquid-impermeable sheet. [Diagram 25] 1A and 1B are a plan view and a front view of a liquid injection tube used in evaluating a specific return amount. [Figure 26] FIG. 2 is a front view showing a state in which a liquid injection tube is placed on the water-absorbent sheet used in the examples of the present application in the specific rewet amount evaluation. [Figure 27] FIG. 13 is a front view showing a state in which a sodium chloride aqueous solution is poured into a water-absorbent sheet from a liquid injection tube using a funnel in a specific rewet amount evaluation. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0013] The present invention will be described below while showing the best mode. Throughout this specification, the expression of the singular form should be understood to include the concept of the plural form, unless otherwise specified. Therefore, the singular article (for example, in the case of English, "a", "an", "the", etc.) should be understood to include the concept of the plural form, unless otherwise specified. In addition, it should be understood that the terms used in this specification are used in the sense commonly used in the field, unless otherwise specified. Therefore, unless otherwise defined, all technical terms and scientific and technical terms used in this specification have the same meaning as commonly understood by those skilled in the art to which this invention belongs. In the case of conflict, this specification (including definitions) will take precedence. The present invention is not limited to the following embodiments, and various modifications can be made within the scope of the claims.

[0014] [First invention] The first invention will be described. The water-absorbent sheet of the first invention is a water-absorbent sheet having a first substrate, a second substrate, and a water-absorbent layer located between the first substrate and the second substrate, the water-absorbent layer contains a particulate water-absorbing agent, the surface of the first substrate forms a liquid-absorbent surface that directly absorbs liquid, and the ratio of the thickness (mm) of the first substrate to the thickness (mm) of the second substrate (thickness (mm) of the first substrate / thickness (mm) of the second substrate) is 1.5 or more and less than 14.

[0015] 1. Definitions of Terms [1-1. Water-absorbent sheet] The "water-absorbent sheet" in the present invention refers to a structure in which a water-absorbent resin (particulate water-absorbing agent) is supported between two or more long substrates. The water-absorbent sheet may use an adhesive or a hot melt adhesive to bond the substrates together and / or to bond the substrate and the particulate water-absorbing agent. The water-absorbent sheet may contain other components (fiber components, antibacterial agents, deodorants, etc.) in addition to the particulate water-absorbing agent. There is a water-absorbent sheet that contains other sheets other than the two substrates that sandwich the particulate water-absorbing agent. In this embodiment, there may be a water-absorbent sheet that contains other sheets other than the two substrates that sandwich the particulate water-absorbing agent, etc., only if it does not hinder the solution of the problem of the present invention. A water-absorbent sheet in which the particulate water-absorbing agent, etc. is sandwiched between two substrates is a preferred embodiment.

[0016] Usually, the absorbent sheet is in the form of a continuous sheet or a roll of the continuous sheet. When using the absorbent sheet, the continuous sheet is cut into an appropriate shape (such as a rectangle) and then incorporated into an absorbent article (such as a paper diaper, a sanitary napkin, or a pad for incontinent people). Absorbent articles such as paper diapers (disposable diapers), sanitary napkins, and pads for incontinent people have an absorbent body that absorbs and retains bodily fluids such as urine and menstrual blood excreted from the body, a flexible liquid-permeable front sheet arranged on the side that contacts the body, and a liquid-impermeable back sheet arranged on the side opposite to the side that contacts the body. The absorbent sheet can be used as the absorbent body. Conventional paper diapers are absorbent articles that are individually molded for each paper diaper and have a shape that fits the buttocks. Therefore, such absorbents have technical properties that are different from the absorbent sheet of the present invention.

[0017] [1-2. Water-absorbing resin] In this specification, the term "water-absorbent resin" refers to a polymer gelling agent having a water swelling coefficient (CRC) of 5 g / g or more as defined by ERT441.2-02 and a water-soluble component (Ext) of 50 mass % or less as defined by ERT470.2-02.

[0018] The water-absorbent resin is preferably a hydrophilic cross-linked polymer obtained by cross-linking and polymerizing an unsaturated monomer having a carboxyl group. The shape of the water-absorbent resin may be a sheet, a fiber, a film, a particle, a gel, or the like. The water-absorbent sheet according to one embodiment of the present invention uses a particle-shaped water-absorbent resin.

[0019] In this specification, the term "water-absorbent resin" is not limited to an embodiment in which the total amount (100% by mass) is the water-absorbent resin alone. As long as the above-mentioned CRC and Ext are satisfied, the water-absorbent resin composition may contain additives. In addition, in this specification, the term "water-absorbent resin" is a concept that also includes intermediates in the manufacturing process of the water-absorbent resin. For example, a hydrogel-like crosslinked polymer after polymerization, a dried polymer after drying, a water-absorbent resin powder before surface crosslinking, etc. may also be referred to as a "water-absorbent resin".

[0020] Thus, in this specification, in addition to the water-absorbing resin itself, the water-absorbing resin composition and the intermediate may be collectively referred to as the "water-absorbing resin".

[0021] [1-3. Water absorbents, particulate water absorbents] In this specification, the term "water absorbing agent" refers to an absorbent gelling agent containing a water absorbent resin as a main component for absorbing an aqueous liquid. Here, the aqueous liquid is not limited to water, but is any liquid containing water. The aqueous liquid absorbed by the water absorbent sheet according to one embodiment of the present invention is urine, menstrual blood, sweat, and other body fluids.

[0022] In this specification, the term "particulate water absorbing agent" means a particulate (powdered) water absorbing agent (corresponding to a particulate water absorbing resin since the water absorbing agent contains a water absorbing resin as a main component). The concept of "particulate water absorbing agent" includes both a single particulate water absorbing agent and an aggregate of a plurality of particulate water absorbing agents. In this specification, "particulate" means having a particle shape. Here, "particle" refers to a relatively small divided body of a substance, and has a size of several Å to several mm (see "Particle", McGraw-Hill Scientific and Technical Dictionary 3rd Edition, edited by McGraw-Hill Scientific and Technical Dictionary Editorial Committee, Nikkan Kogyo Shimbun, 1996, p. 1929). In the present invention, the shape of the water absorbing agent is not limited to a particulate water absorbing agent. In this specification, the present invention will be described using a particulate water absorbing agent as an example, but "particulate water absorbing agent" can be read as "water absorbing agent". In this specification, the "particulate water absorbing agent" may be simply referred to as the "water absorbing agent".

[0023] In the water absorbent sheet of the present invention, the particulate water absorbing agent has a weight average particle diameter of 200 to 600 μm. If the particulate water absorbing agent has a weight average particle diameter of less than 200 μm, the handling property may be deteriorated. If the particulate water absorbing agent has a weight average particle diameter of more than 600 μm, the texture of the water absorbent sheet may be deteriorated. In the water absorbent sheet according to one embodiment of the present invention, the particulate water absorbing agent has a weight average particle diameter of preferably 250 to 500 μm, more preferably 300 to 450 μm. In the water absorbent sheet of the present invention, it is preferable that 95% by mass or more of the whole particulate water absorbing agent has a particle diameter of 850 μm or less, more preferably 98% by mass or more of the whole particulate water absorbing agent has a particle diameter of 850 μm or less, and further preferably that substantially 100% by mass of the whole particulate water absorbing agent has a particle diameter of 850 μm or less. In the examples of the present application, substantially 100% by mass of the whole particulate water absorbing agent has a particle diameter of 850 μm or less. In this specification, the weight-average particle diameter is calculated in the same manner as "(3) Mass-Average Particle Diameter (D50) and Logarithmic Standard Deviation (σζ) of Particle Diameter Distribution" described in U.S. Pat. No. 7,638,570 based on the PSD obtained according to the measurement method for "PSD" specified in ERT420.2-02.

[0024] The particulate water absorbing agent contains a water absorbent resin as a polymer (also called a particulate water absorbing resin or water absorbent resin particles) as a main component. The particulate water absorbing agent contains 60 to 100 mass %, preferably 70 to 100 mass %, more preferably 80 to 100 mass %, further preferably 90 to 100 mass %, and particularly preferably 95 to 100 mass % of the water absorbent resin as a polymer. The remainder of the particulate water absorbing agent may contain water, additives (inorganic fine particles, polyvalent metal cations, etc.), etc., as desired. The particulate water absorbing agent used in the examples of the present application contains 80 to 100 mass % of the water absorbent resin.

[0025] That is, the upper limit of the water absorbent resin in the particulate water absorbing agent is, for example, 100 mass%, 99 mass%, 97 mass%, 95 mass%, or 90 mass%, and preferably further contains 0 to 10 mass% of components other than the water absorbent resin, particularly water, additives (inorganic fine particles, polyvalent metal cations), etc.

[0026] The particulate water absorbing agent preferably has a water content of 0.2 to 30 mass %. As explained above, the particulate water absorbing agent also includes a water absorbing resin composition in which components such as water and additives are integrated with and / or mixed with the water absorbing resin.

[0027] Examples of the water-absorbing resin that is the main component of the particulate water-absorbing agent include polyacrylic acid (salt)-based resin, polysulfonic acid (salt)-based resin, maleic anhydride (salt)-based resin, polyacrylamide-based resin, polyvinyl alcohol-based resin, polyethylene oxide-based resin, polyaspartic acid (salt)-based resin, polyglutamic acid (salt)-based resin, polyalginic acid (salt)-based resin, starch-based resin, and cellulose-based resin. Among these, polyacrylic acid (salt)-based resin is preferably used as the water-absorbing resin.

[0028] [1-4. Polyacrylic acid (salt)] In this specification, "polyacrylic acid (salt)" refers to polyacrylic acid and / or its salt. The polyacrylic acid (salt) is a polymer containing repeating units of acrylic acid and / or its salt (hereinafter referred to as "acrylic acid (salt)") as a main component, and further containing a graft component as an optional component. The polyacrylic acid (salt) is obtained by polymerization of acrylic acid (salt), hydrolysis of polyacrylamide, polyacrylonitrile, etc. Preferably, the polyacrylic acid (salt) is obtained by polymerization of acrylic acid (salt).

[0029] Here, "containing as a main component" means that the amount of acrylic acid (salt) used when polymerizing polyacrylic acid (salt) is usually 50 to 100 mol %, preferably 70 to 100 mol %, more preferably 90 to 100 mol %, and even more preferably substantially 100 mol %, based on the total amount of monomers (excluding the internal crosslinking agent) used in the polymerization.

[0030] [1-5. EDANA and ERT] "EDANA" is an abbreviation for European Disposables and Nonwovens Associations. "ERT" is an abbreviation for EDANA Recommended Test Methods, a European standard (effectively a global standard) for measuring water-absorbent resins. In this specification, unless otherwise specified, the physical properties of water-absorbent resins are measured in accordance with the 2002 edition of ERT.

[0031] [1-6.Other] In this specification, the range "X to Y" means "X or more and Y or less."

[0032] In this specification, unless otherwise noted, the unit of mass "t (ton)" means "metric ton." "ppm" means "ppm by mass." "Mass" and "weight," "parts by mass" and "parts by weight," "% by mass" and "% by weight," "ppm by mass" and "ppm by weight" are each treated as having the same meaning.

[0033] In this specification, "acid (salt)" means "acid and / or its salt." "(Meth)acrylic" means "acrylic and / or methacrylic."

[0034] In this specification, the unit of volume "liter" may be abbreviated as "l" or "L". "% by mass" may be abbreviated as "wt%". When measuring trace components, values ​​below the detection limit are abbreviated as ND (Non Detected).

[0035] [2. Water-absorbent sheet] The water-absorbent sheet of the present invention has a first substrate, a second substrate, and a water-absorbent layer located between the first substrate and the second substrate, wherein the water-absorbent layer contains a particulate water-absorbing agent, a surface of the first substrate forms a liquid-absorbent surface that directly absorbs liquid, and a ratio of a thickness (mm) of the first substrate to a thickness (mm) of the second substrate (thickness (mm) of the first substrate / thickness (mm) of the second substrate) is 1.5 or more and less than 14.

[0036] With this configuration, even if the amount of liquid introduced is large due to the intermittent introduction of liquid several times (particularly, three or more times), the liquid discharge from the absorbent sheet due to backflow can be significantly reduced. In the absorbent sheet of the present invention, the thickness (mm) of the first substrate forming the liquid-absorbing surface that directly absorbs liquid is 1.5 to less than 14 mm relative to the thickness (mm) of the second substrate. That is, the first substrate is significantly thicker than the second substrate. The liquid-absorbing surface that directly absorbs liquid is formed on the surface of the first substrate that is significantly thicker than the second substrate. Here, in this specification, "directly" does not include a form in which liquid that has permeated other substrates or the like is sequentially absorbed. In this specification, even when a wrapping sheet described later is placed on the surface of the first substrate, the form in which the surface of the first substrate forms a liquid-absorbing surface that directly absorbs liquid is included.

[0037] In another embodiment of the present invention, the surface of the first substrate is a liquid-absorbing surface that directly absorbs liquid, and therefore no water-absorbing layer is disposed on the first substrate. Thus, the water-absorbent sheet according to one embodiment of the present invention is a water-absorbent sheet having a first substrate, a second substrate, and a water-absorbent layer located between the first substrate and the second substrate, in which the water-absorbent layer contains a particulate water-absorbing agent, no water-absorbent layer is disposed on the first substrate, and the ratio of the thickness of the first substrate to the thickness of the second substrate (thickness of the first substrate (mm) / thickness of the second substrate (mm)) is 1.5 or more and less than 14. In this embodiment, even if a part of the particulate water-absorbing agent contained in the water-absorbent layer passes through the first substrate and moves to the first substrate and is partially exposed, this is not considered to be the case where a water-absorbent layer is disposed. The cause of the movement is assumed to be, for example, vibrations caused by transportation or conveyance of the water-absorbent sheet as a final product. The case where a particulate water absorbing agent is intentionally scattered or placed on the first base material is not within the scope of this embodiment.

[0038] The present inventors have found that in a conventional absorbent sheet (for example, an absorbent sheet in which the thickness of the first substrate and the second substrate are the same in order to obtain a thin absorbent sheet), the amount of return is significantly large in the measurement of the amount of return under specific conditions in the examples of the present application (also referred to as "specific return amount evaluation" in this specification). In other words, if liquid is intermittently introduced multiple times (particularly, three or more times), in a normal configuration, the amount of liquid exceeds the set absorption amount, and excessive "return" occurs. In contrast, in the present invention, the first substrate on the liquid introduction side is made significantly thicker than the second substrate, so that the distance between the liquid absorption surface of the first substrate and the absorbent layer can be increased, and thus the liquid introduced from the liquid absorption surface can be efficiently sent to the lower absorbent layer that performs the absorbent function without stagnation on the liquid absorption surface (and further, without the introduced liquid being locally stagnated). Specifically, when liquid passes through the first substrate, the liquid has high diffusibility in the surface direction, and the diffused liquid (e.g., urine) migrates widely and thoroughly over the entire surface of the absorbent layer. That is, when the absorbed liquid reaches the absorbent layer, the liquid is diffused in the surface direction, and therefore, even if a large amount of liquid is introduced into the absorbent layer, the absorbent layer absorbs the liquid that has spread in the surface direction, not locally. Therefore, the absorbent layer can sufficiently absorb and retain liquid. It is also considered that the liquid diffusion function of hydrophilic pulp contained in conventional absorbents is imparted to the first substrate. And once the liquid is absorbed into the absorbent layer, since the first substrate is significantly thick, it is possible to significantly reduce the liquid absorbed by the absorbent layer returning to the liquid absorption surface of the first substrate, and thus it is possible to suppress the liquid that has returned rising to the skin (contacting the skin). On the other hand, even if the second substrate is significantly thicker than the first substrate, the expected effect of the present invention cannot be obtained. The reason for this is unclear; in other words, this effect is unexpected even for those skilled in the art.

[0039] In the water-absorbent sheet, the water-absorbing function in the water-absorbent layer is mainly performed by the water-absorbing agent. In particular, in the water-absorbent sheet, which has a different structure from conventional absorbent articles in which pulp is present in the water-absorbent layer, the role of the water-absorbent agent becomes even more important. In particular, in the present invention, since the first substrate is significantly thick, the liquid once introduced into the water-absorbent agent does not easily return to the liquid-absorbing surface of the first substrate. Here, in addition to backflow, there is also leakage in the surface direction (lateral leakage), and the lateral leakage is a phenomenon in which liquid that cannot be instantly absorbed after reaching the water-absorbent layer leaks out in the surface direction from the water-absorbent sheet. In the present invention, by taking advantage of the fact that the particulate water-absorbing agent is formed in a sheet (layer) shape, the liquid diffusion in the surface direction of the water-absorbent layer is maximized, thereby suppressing backflow to the first substrate and suppressing leakage in the surface direction (lateral leakage) from the water-absorbent sheet. Specifically, in the present invention, since the first substrate is significantly thicker than the second substrate, when liquid passes through the first substrate, the liquid has high diffusibility in the surface direction, and the particulate water absorbing agent, which has a significantly high absorption rate and functions like a tank, absorbs the diffused liquid (e.g., urine) widely and thoroughly in the surface direction. That is, when the absorbed liquid reaches the water absorption layer, the liquid is diffused in the surface direction, and therefore, even if a large amount of liquid is introduced into the water absorption layer, the water absorption layer absorbs the liquid that has spread in the surface direction, not locally. Therefore, the water absorption layer can sufficiently absorb and hold the liquid, and leakage in the surface direction from the water absorbent sheet is significantly low. And even if the liquid that the water absorption layer could not absorb tries to return, the first substrate is significantly thicker than the second substrate, so that the liquid can be prevented from rising to the skin. Therefore, the "specific return amount evaluation" can be made excellent, and leakage in the surface direction can be prevented. Here, it should be noted that absorbent sheets and absorbent articles designed to suppress the amount of backflow under general conditions do not necessarily achieve excellent results in the "specific backflow evaluation" of this application. In addition, the absorbent sheet according to one embodiment of the present invention is suitable as an absorbent article (e.g., a diaper) to be used during the daytime or other times when an infant who has just started to learn to run and whose bladder is still small is actively moving around, but the form of use is not limited to this. In addition, the mechanisms described in this specification do not limit the technical scope of the claims of this application.

[0040] Hereinafter, an embodiment of the present invention will be described with reference to the attached drawings. In the description of the drawings, the same elements are given the same reference numerals, and duplicated explanations will be omitted. In addition, the dimensional ratios of the drawings are exaggerated for the convenience of explanation, and may differ from the actual ratios.

[0041] First, the configuration of the water-absorbent sheet will be described with reference to Figures 1 to 4. Figure 1 is a schematic cross-sectional view of a water-absorbent sheet 10 according to one embodiment of the present invention. Figures 2 to 4 are schematic cross-sectional views of a water-absorbent sheet 10 according to another embodiment of the present invention.

[0042] In Fig. 1, the arrow indicates the direction in which the liquid to be absorbed is introduced. The first substrate 11 is located on the side where the liquid to be absorbed (liquid to be absorbed) is introduced relative to the water-absorbent layer 12. In other words, the first substrate 11 is disposed on the side where the liquid is discharged (for example, the skin side in the case of a paper diaper). This allows the first substrate 11 to form a liquid-absorbent surface that directly absorbs the liquid. The water-absorbent layer 12 is disposed between the first substrate 11 and the second substrate 13.

[0043] In FIG. 1, the water-absorbing layer 12 includes a particulate water-absorbing agent 14. In the embodiment of FIG. 1, the water-absorbing layer 12 shows a state in which the particulate water-absorbing agent 14 exists between the first substrate 11 and the second substrate 13. The water-absorbing layer 12 includes the particulate water-absorbing agent 14 in contact with (or fixed to) the first substrate 11 and the particulate water-absorbing agent 14 in contact with (or fixed to) the second substrate 13. A part of the particulate water-absorbing agent 14 may not be in contact with (or may not be fixed to) each substrate 11, 13. It may be detached from each substrate 11, 13. Therefore, the water-absorbing "layer" does not only refer to a continuous body such as a sheet, but may be in any form as long as it exists between the first substrate 11 and the second substrate 13 with a certain thickness. When the particulate water-absorbing agent 14 is fixed to each substrate 11, 13, for example, an adhesive may be used. The method of manufacturing the water-absorbent sheet using an adhesive will be described in detail in [3.].

[0044] The particulate water absorbing agent 14 may be present in the first substrate 11. The particulate water absorbing agent 14 in the first substrate 11 may be, for example, a particulate water absorbing agent 14 in contact with (or fixed to) the first substrate 11, or a particulate water absorbing agent 14 in contact with (or fixed to) the second substrate 13 that is detached and captured in the first substrate 11. When the particulate water absorbing agent 14 is present in the first substrate 11, the content of the particulate water absorbing agent 14 in the first substrate 11 is preferably 5% or more, more preferably 10% or more, even more preferably 20% or more, and even more preferably 30% or more, relative to the particulate water absorbing agent 14 contained in the entire water absorbent sheet 10. The upper limit is not particularly limited, but is preferably 90% or less, 70% or less, and 50% or less. In this specification, the content ratio of the particulate water absorbing agent 14 in the first substrate 11 to the particulate water absorbing agent 14 contained in the entire water absorbent sheet 10 is calculated by the method in the examples described later.

[0045] The water-absorbent sheet 10 has a wrapping sheet 16. The wrapping sheet 16 has the following purposes: to maintain the shape of the water-absorbent sheet 10, which is a structure in which the particulate water-absorbing agent 14 is supported between the first substrate 11 and the second substrate 13; to prevent the particulate water-absorbing agent 14 supported between the first substrate 11 and the second substrate 13 from spilling (falling off) from the absorbent (water-absorbent sheet 10); and to prevent the particulate water-absorbing agent 14 from directly contacting the skin when the particulate water-absorbing agent 14 passes through the first substrate 11 and migrates to the outer surface (liquid-absorbing surface that directly absorbs liquid) of the first substrate 11. When the wrapping sheet 16 is not provided, for example, there is a method of sealing by bonding the substrates 11 and 13 together, a method of suppressing migration to the outer surface (liquid-absorbing surface that directly absorbs liquid) of the first substrate 11 by surface treatment, and the like. As a method for preventing the particulate water absorbing agent 14 from falling off the water absorbent sheet 10 while maintaining the effect of the present invention, it is preferable to provide a wrapping sheet 16 .

[0046] The wrapping sheet 16 is disposed on the first substrate 11, and is folded over so as to enclose the entire water-absorbing layer 12 and the second substrate 13. Thus, the wrapping sheet 16 covers the entire first substrate 11, the water-absorbing layer 12, and the second substrate 13. With such a configuration, it is possible to suppress the particulate water-absorbing agent 14 from falling off from the water-absorbing sheet 10. The wrapping sheet 16 does not need to cover the entire first substrate 11, the water-absorbing layer 12, and the second substrate 13. For example, the wrapping sheet 16 may be disposed on the first substrate 11, folded over so as to enclose the side of the water-absorbing layer 12 and the side of the second substrate 13, and folded over the side of the second substrate 13 opposite to the surface that absorbs liquid (i.e., the surface on which the water-absorbing layer 12 is provided). That is, one end of the wrapping sheet 16 overlaps the other end of the wrapping sheet 16 on the surface of the second substrate 13 opposite to the surface on which the water absorbent layer 12 is provided. In this case, the wrapping sheet 16 covers the liquid-absorbing surface and side surfaces of the first substrate 11, the side surfaces of the water absorbent layer 12, and the side surfaces of the second substrate 13, and covers the whole or part of the surface of the second substrate 13 opposite to the surface on which the water absorbent layer 12 is provided.

[0047] Here, the wrapping sheet 16 may have one end and the other end separated on the surface of the second substrate 13 opposite to the surface on which the water-absorbent layer 12 is provided. For example, in FIG. 2, the wrapping sheet 16 is placed on the first substrate 11 and folded so as to enclose the side surface of the water-absorbent layer 12 and the side surface of the second substrate 13, and one end and the other end of the wrapping sheet 16 are placed apart on the surface opposite to the liquid-absorbing surface of the second substrate 13 that directly absorbs liquid (i.e., the surface on which the water-absorbent layer 12 is provided). In this case, the wrapping sheet 16 covers the liquid-absorbing surface and the side surface of the first substrate 11, the side surface of the water-absorbent layer 12, and the side surface of the second substrate 13, and covers a part of the surface of the second substrate 13 opposite to the surface on which the water-absorbent layer 12 is provided.

[0048] The wrapping sheet 16 is not a required component of the water-absorbent sheet 10 of the present invention, but by providing the water-absorbent sheet 10 of the present invention with the wrapping sheet 16 in such a configuration, it is possible to prevent the particulate water-absorbing agent 14 from falling off from the water-absorbent sheet 10.

[0049] Therefore, the water-absorbent sheet 10 according to one embodiment of the present invention preferably has at least a wrapping sheet 16 disposed on the surface of the first substrate 11. As described above, in the present specification, even when the water-absorbent sheet 10 has the wrapping sheet 16, the first substrate 11 forms a liquid-absorbent surface that directly absorbs liquid. For example, in the case where the water-absorbent sheet 10 has the wrapping sheet 16, the case where the wrapping sheet 16 forms a liquid-absorbent surface that directly absorbs liquid can be rephrased as follows; the water-absorbent sheet has a first substrate, a second substrate, a water-absorbent layer located between the first substrate and the second substrate, and a wrapping sheet disposed on the surface of the first substrate, the water-absorbent layer contains a particulate water-absorbing agent, the surface of the wrapping sheet forms a liquid-absorbent surface that directly absorbs liquid, and the ratio of the thickness of the first substrate to the thickness of the second substrate (thickness of the first substrate (mm) / thickness of the second substrate (mm)) is 1.5 or more and less than 14.

[0050] The wrapping sheet 16 may be fixed to the base materials 11 and 13 by using, for example, an adhesive.

[0051] In the present invention, the first substrate 11 and the particulate water absorbing agent 14 in the water absorbing layer 12 are preferably in contact with each other directly or via an adhesive, and / or the second substrate 13 and the particulate water absorbing agent 14 in the water absorbing layer 12 are preferably in contact with each other directly or via an adhesive. Thus, the water absorbent sheet of the present invention has a simple configuration substantially consisting of only the first substrate, the second substrate, the particulate water absorbing agent sandwiched between the first substrate and the second substrate, an adhesive for fixing the particulate water absorbing agent to at least one of the first substrate and the second substrate, and a wrapping sheet for wrapping a part or all of these as necessary (it is not excluded that the particulate water absorbing agent may contain additives described in this specification). A more preferred embodiment is a simple configuration consisting of only a first substrate, a second substrate, a particulate water absorbing agent sandwiched between the first substrate and the second substrate, an adhesive between the particulate water absorbing agent and the second substrate for fixing the particulate water absorbing agent to the second substrate, and a wrapping sheet for wrapping all of these. That is, the water absorbent sheet of the present invention is one that can effectively reduce the specific return amount despite its simple configuration.

[0052] In the present invention, the ratio of the thickness (mm) of the first substrate to the thickness (mm) of the second substrate (thickness (mm) of the first substrate / thickness (mm) of the second substrate) is 1.5 or more and less than 14. When the ratio of the thickness (mm) of the first substrate to the thickness (mm) of the second substrate is less than 1.5, the distance between the liquid-absorbing surface of the first substrate and the water-absorbing layer and the second substrate is not sufficiently secured, and the liquid that has once reached the water-absorbing layer and the second substrate may return. In addition, when the ratio of the thickness (mm) of the first substrate to the thickness (mm) of the second substrate is 14 or more, the liquid-absorbing surface of the first substrate is separated from the water-absorbing layer, and therefore leakage in the surface direction may occur before the liquid absorbed from the liquid-absorbing surface of the first substrate reaches the water-absorbing layer.

[0053] The lower limit of the ratio of the thickness (mm) of the first substrate to the thickness (mm) of the second substrate is preferably 1.7 or more, more preferably 2.5 or more, even more preferably 3.2 or more, even more preferably 3.4 or more, particularly preferably 3.5 or more, and most preferably 3.6 or more. The upper limit of the ratio of the thickness (mm) of the first substrate to the thickness (mm) of the second substrate is preferably 12 or less, more preferably 10 or less, even more preferably 9 or less, and even more preferably 8 or less. By setting the ratio of the thickness (mm) of the first substrate to the thickness (mm) of the second substrate in such a range, the reversal can be significantly reduced.

[0054] In the water-absorbent sheet according to one embodiment of the present invention, the ratio of the thickness (mm) of the first substrate to the thickness (mm) of the second substrate is 1.5 or more and less than 14. In addition, in the water-absorbent sheet according to one embodiment of the present invention, the ratio of the thickness (mm) of the first substrate to the thickness (mm) of the second substrate is preferably 1.7 or more and less than 14, more preferably 3 or more and 12 or less, and even more preferably 3.4 or more and 10 or less.

[0055] The water-absorbent sheet according to one embodiment of the present invention may have a bulky form due to the low density of the first substrate, but can be thinner than the absorbent used in conventional absorbent articles. When the water-absorbent sheet is used in a paper diaper, the thickness is preferably 15 mm or less, more preferably 10 mm or less, even more preferably 7 mm or less, particularly preferably 5 mm or less, and most preferably 4 mm or less, for example, at 40% RH to 50% RH. On the other hand, the lower limit of the thickness is preferably 0.2 mm or more, more preferably 0.3 mm or more, and even more preferably 0.5 mm or more, in consideration of the strength of the water-absorbent sheet and the diameter of the particulate water-absorbing agent. The thickness of the water-absorbent sheet used in the examples of the present application was 2 to 5 mm.

[0056] The thicknesses of the first substrate, the second substrate, the wrapping sheet, and the water-absorbent sheet in this application were measured using a large-type dial thickness gauge (thickness measuring device) (manufactured by Ozaki Manufacturing Co., Ltd., model number: JB, measuring probe: anvil top and bottom φ50 mm). The number of measurement points was set to 5 different points on the sheet to be measured, and each point was measured twice, and the measured value was the average value of the total 5 points. When measuring the thickness, the hand was slowly released from the handle so as to apply as little pressure as possible to the sheet to be measured, and the thickness was measured. As a specific procedure, the sheet to be measured was attached flatly on a plate with a constant thickness so as not to cause wrinkles or distortions at the measurement points of the sheet to be measured, and the plate was set on the lower measuring probe of the thickness measuring device. Next, the upper measuring probe of the thickness measuring device was brought close to a height position of 2 to 3 mm from the sheet to be measured, and then the hand was slowly released from the handle, and the thickness of the sheet to be measured and the plate together was measured. The thickness of the sheet to be measured is determined by the formula: T1=T2-T0 (T0: plate thickness (mm), T1: sheet thickness (mm), T2: thicknesses of the sheet and plate to be measured (mm)).

[0057] The content of the particulate water absorbing agent contained in the water absorbent sheet is preferably 50 to 400 g / m 2 and more preferably 100 to 350 g / m 2 and more preferably 125 to 250 g / m 2 It is.

[0058] The ratio of the area containing the particulate water absorbing agent (hereinafter also referred to as "the ratio of the area containing the particulate water absorbing agent 14") in the surface of the first substrate on the water absorption layer side (the surface on which the particulate water absorbing agent is arranged) is preferably more than 75% in area, more preferably more than 80%, and even more preferably more than 90%. The upper limit of the ratio of the area containing the particulate water absorbing agent in the surface of the first substrate on the water absorption layer side is not particularly limited, but is practically 99.5% or less in area. By providing the particulate water absorbing agent in such a range, the particulate water absorbing agent is arranged in a balanced manner, and the effect of reducing the amount of return is further exhibited. The ratio of the area containing the particulate water absorbing agent in the surface of the first substrate on the water absorption layer side is the same as the ratio of the area containing the particulate water absorbing agent in the surface of the second substrate on the water absorption layer side (the surface on which the particulate water absorbing agent is arranged).

[0059] Here, the ratio of the area containing the particulate water absorbing agent on the surface of the first substrate facing the water absorbing layer can be controlled by adjusting the area where the particulate water absorbing agent is dispersed during production of the water absorbent sheet.

[0060] Also, by photographing and analyzing the cross section of the produced water absorbent sheet by an X-ray CT device (inspeXio SMX-100CT), the ratio of the area containing the particulate water absorbing agent on the surface of the water absorbent layer side of the first substrate can be calculated. Specifically, the cross section of the water absorbent sheet is photographed, and the interface between the first substrate or the second substrate and the water absorbent layer is classified into an area where the particulate water absorbing agent is present and an area where the particulate water absorbing agent is not present, and the respective areas are summed up and the ratio is calculated, whereby the ratio of the area containing the particulate water absorbing agent can be calculated. Note that, three or more cross sections in the short direction of the water absorbent sheet are photographed, the ratio of the area containing the particulate water absorbing agent is calculated, and the average value of the ratios of the area containing the particulate water absorbing agent obtained from each cross section is defined as the "ratio of the area containing the particulate water absorbing agent".

[0061] In order to further impart liquid permeability, diffusibility, flexibility, etc. to the water-absorbent sheet, the surface of the water-absorbent sheet (the surface of the first substrate or the surface of the wrapping sheet described below) may be appropriately embossed. The area to be embossed may be the entire surface of the water-absorbent sheet, or a part of it. By providing a continuous embossed area in the longitudinal direction of the water-absorbent sheet, liquid can be easily diffused in the longitudinal direction. For example, by providing a continuous embossed area in the longitudinal direction, the area serves as a passage (liquid transport passage) for flowing a large amount of liquid. The embossed area may be provided in a straight line, a curved line, or a wavy line.

[0062] The particulate water absorbing agent may be dispersed over the entire surface of the water absorbent sheet, or a part of the water absorbent sheet may have a region where the particulate water absorbing agent is not present. That is, in the water absorbent layer between the first substrate and the second substrate, the particulate water absorbing agent may be dispersed over the entire surface of the water absorbent layer, or a part of the water absorbent layer may have a region where the particulate water absorbing agent is not present.

[0063] Here, an embodiment in which a part of the water absorbent layer between the first substrate and the second substrate has a part of the water absorbent layer that does not contain a particulate water absorbing agent will be described. The embodiment in which a part of the water absorbent layer has a particulate water absorbing agent-free region is a state in which a part of the water absorbent layer between the first substrate and the second substrate, in which a particulate water absorbing agent-containing region is disposed across a gap that does not substantially contain the particulate water absorbing agent. When a part of the water absorbent layer has a particulate water absorbing agent-free region, the particulate water absorbing agent-free region is preferably provided in a channel shape (stripes) in the longitudinal direction of the water absorbent sheet. In this way, by providing the particulate water absorbing agent-free region continuously in the longitudinal direction, the region plays the role of a passage (liquid transport passage) for flowing a large amount of liquid. The particulate water absorbing agent-free region may be provided in a straight line, a curved line, or a wavy line.

[0064] When a part of the water-absorbing layer is provided with a particulate water-absorbing agent-free region, the first substrate is preferably stretchable, and the elongation rate of the first substrate is more preferably 10% or more. In one embodiment, the water-absorbing sheet of the present invention is such that, in the water-absorbing layer between the first substrate and the second substrate, a region containing the particulate water-absorbing agent is disposed across a gap that does not substantially contain the particulate water-absorbing agent, and the elongation rate of the first substrate is 10% or more. For example, the particulate water-absorbing agent is not sprayed over the entire surface of the first substrate or the second substrate, but the particulate water-absorbing agent is sprayed across a part of the first substrate or the second substrate that is provided with a particulate water-absorbing agent-free region. As a result, the particulate water-absorbing agent is disposed across a gap that does not substantially contain the particulate water-absorbing agent.

[0065] In the conventional water-absorbent sheet configuration, the water-absorbent resin particles that absorb liquid swell, weakening the fixation of the water-absorbent resin particles to the upper and lower sheets, and the water-absorbent resin particles may move within the sheet. This causes the water-absorbent resin particles to become biased within the sheet, causing the shape of the water-absorbent sheet to be distorted. In this case, the liquid absorption of the water-absorbent sheet becomes biased, causing leakage. In some cases, the water-absorbent resin particles may fall out of the sheet to the outside.

[0066] In one embodiment of the water-absorbent sheet of the present invention, when the elongation percentage of the first substrate is 10% or more and a part of the water-absorbent layer has an area where the particulate water-absorbing agent is not present, not only can the specific return amount be effectively reduced, but also the sheet shape is maintained even after absorbing liquid (the sheet has high shape retention).

[0067] Hereinafter, with reference to FIG. 3, a description will be given of an embodiment in which a region containing a particulate water absorbing agent in a water absorbent layer between a first substrate and a second substrate is disposed across a gap that does not substantially contain a particulate water absorbing agent, and the elongation of the first substrate is 10% or more. FIG. 3 is a schematic diagram showing a cross section of a water absorbent sheet 10 according to another embodiment of the present invention. FIG. 3 shows three embodiments ((a) to (c)) of the water absorbent sheet 10. In FIG. 3(a) to (c), the arrows indicate the direction in which the liquid to be absorbed is introduced. The first substrate 11 is located on the side where the liquid to be absorbed (liquid to be absorbed) is introduced with respect to the water absorbent layer 12. That is, the first substrate 11 is disposed on the liquid discharge side (for example, the skin side in the case of a paper diaper). The water absorbent layer 12 is disposed between the first substrate 11 and the second substrate 13.

[0068] In Fig. 3(a) to (c), the water absorbent layer 12 includes a particulate water absorbing agent 14. In the forms of Fig. 3(a) to (c), the water absorbent layer 12 shows a state in which the particulate water absorbing agent 14 exists between the first substrate 11 and the second substrate 13. A part of the particulate water absorbing agent 14 may be detached from each substrate 11, 13. The particulate water absorbing agent 14 (the region including the particulate water absorbing agent 14) is arranged across a gap 15 that does not substantially include the particulate water absorbing agent 14. Therefore, the water absorption "layer" does not only refer to a continuous body such as a sheet, but may be any form that exists between the first substrate 11 and the second substrate 13 with a certain thickness and length. For example, the water absorbent layer 12 may exist intermittently between the first substrate 11 and the second substrate 13 with a certain thickness and length. When the particulate water absorbing agent 14 is fixed to the substrate 11 and / or 13, for example, an adhesive may be used. The method of manufacturing the water-absorbent sheet using an adhesive will be described in detail in [3.].

[0069] Here, in FIG. 3(a), the gap 15 is formed between the first substrate 11 and the second substrate 13, but the gap 15 in the present invention also includes the forms of FIG. 3(b) and FIG. 3(c). In FIG. 3(b), the first substrate 11 and the second substrate 13 come into contact with each other, so that the region containing the particulate water absorbing agent 14 is separated. Although the first substrate and the second substrate are in contact with each other, the liquid passage is maintained, so that the gap is considered. In addition, the first substrate 11 (and the second substrate 13 in some cases) enters the water absorption layer 12, so that the water absorption layer 12 is separated, and therefore, in this form, the water absorption layer 12 exists intermittently. In FIG. 3(c), the end of the first substrate 11 and the end of the second substrate 13 are overlapped with each other, so that the end of the water absorbent sheet 10 is closed by the first substrate 11 and the second substrate 13. Even in this case, the first substrate 11 (and possibly the first substrate 11 and the second substrate 13) penetrates into the end portion of the water absorbent layer 12, resulting in a state in which the water absorbent layer 12 is not present at the end portion of the water absorbent layer 12.

[0070] The particulate water absorbing agent 14 may be present in the first substrate 11. The particulate water absorbing agent 14 in the first substrate 11 may be, for example, a particulate water absorbing agent 14 in contact with (or fixed to) the first substrate 11, or a particulate water absorbing agent 14 in contact with (or fixed to) the second substrate 13 that is detached and captured in the first substrate 11. When the particulate water absorbing agent 14 is present in the first substrate 11, the content of the particulate water absorbing agent 14 in the first substrate 11 is preferably 5% or more, more preferably 10% or more, even more preferably 20% or more, and even more preferably 30% or more, relative to the particulate water absorbing agent 14 contained in the entire water absorbent sheet 10. The upper limit is not particularly limited, but is preferably 90% or less, 70% or less, and 50% or less. In this specification, the content ratio of the particulate water absorbing agent 14 in the first substrate 11 to the particulate water absorbing agent 14 contained in the entire water absorbent sheet 10 is calculated by the method of the examples described later.

[0071] Since the particulate water absorbing agent 14 is not spread or arranged in the region of the gap 15, the region of the gap 15 does not substantially contain the particulate water absorbing agent 14. The region of the gap 15 may contain additives other than the particulate water absorbing agent 14. For example, the gap 15 may be formed by contacting the first base material 11 and the second base material 13 directly or via an adhesive. Since the first base material 11 has elasticity, when a region containing the particulate water absorbing agent 14 exists on the second base material 13, the first base material 11 expands and contracts following the region containing the particulate water absorbing agent 14. Therefore, the first base material 11 has a shape that covers the region containing the particulate water absorbing agent 14 on the region containing the particulate water absorbing agent 14, and on the gap 15, it has a shape that sinks toward the second base material 13 after following the upper side surface of the region containing the particulate water absorbing agent 14.

[0072] In the water absorbent sheet of the present invention, the ratio (Lb / La) of the thickness (Lb) from the liquid absorbing surface of the first substrate 11 to the surface of the water absorbing layer 12 side of the second substrate 13 in the region containing the particulate water absorbing agent 14 to the thickness (La) from the liquid absorbing surface of the first substrate 11 to the surface of the water absorbing layer 12 side of the second substrate 13 in the gap 15 is preferably 1.05 or less. Since the first substrate 11 has elasticity, the first substrate 11 has a shape following the shape of the region containing the particulate water absorbing agent 14 (i.e., the shape of the particulate water absorbing agent 14 on the side of the particulate water absorbing agent 14 in contact with the first substrate 11) (i.e., it expands and contracts following the shape). Therefore, the first base material 11 can be in close contact with the particulate water absorbing agent 14 (the region including the particulate water absorbing agent 14), and as a result, the first base material 11 is integrated with the particulate water absorbing agent 14 (the region including the particulate water absorbing agent 14). In this case, the difference between the thickness of La and the thickness of Lb is small, and therefore Lb / La is 1.05 or less. In this case, the shape of the region including the particulate water absorbing agent 14 is highly retained. Therefore, even after the particulate water absorbing agent 14 swells, the gaps 15 are highly retained, and the return can be further reduced. Note that Lb / La is usually 1 or more.

[0073] In the water absorbent sheet 10, the gaps 15 are formed by providing a region where the particulate water absorbing agent 14 does not exist on a part of the second base material 13. The gaps 15 (i.e., the region where the particulate water absorbing agent 14 does not exist) are continuously provided along one direction on the liquid absorbing surface of the first base material 11, so that the function as a liquid passage can be more effectively exhibited. The shape of the continuously provided gaps 15 may be, for example, linear, curved, or wavy, but it is preferable that these gaps 15 are provided linearly and in parallel. Therefore, in the water absorbent sheet 10, the region where the particulate water absorbing agent 14 is included and the gaps 15 preferably have a shape extending along one direction (the surface direction perpendicular to the direction in which the liquid is absorbed) on the liquid absorbing surface of the first base material 11, and are arranged in parallel. That is, the region where the particulate water absorbing agent 14 is included is arranged in a streaky (striped) state. As a result, the gaps 15 are also formed in a striped pattern, so that even when the particulate water absorbing agent 14 swells, the gaps 15 are easily maintained, and as a result, backflow can be further reduced. Here, the "one direction" may be any direction parallel to the surface direction of the liquid-absorbing surface of the first substrate 11, excluding the thickness direction, that is, any of the longitudinal direction, transverse direction, and directions inclined to these directions of the liquid-absorbing surface of the first substrate 11. From the viewpoint of the balance between the role of the gaps 15 and the role of the particulate water absorbing agent 14, in the water absorbent sheet 10, the regions including the particulate water absorbing agent 14 and the gaps 15 preferably have a shape extending along the longitudinal direction of the liquid-absorbing surface of the first substrate 11 and are arranged in parallel.

[0074] The ratio of the area including the particulate water absorbing agent 14 on the surface of the first base material 11 facing the water absorbent layer 12 (the surface on which the particulate water absorbing agent 14 is disposed) is preferably 90% or less in area, more preferably 80% or less, and even more preferably 75% or less. The ratio of the area including the particulate water absorbing agent 14 on the surface of the first base material 11 facing the water absorbent layer 12 is preferably 10% or more in area, and more preferably 20% or more. By providing the particulate water absorbing agent 14 in such a range, the balance between the role of the gap 15 and the role of the particulate water absorbing agent 14 is appropriately achieved, and the effect of reducing the amount of return is further exhibited. The ratio of the area including the particulate water absorbing agent 14 on the surface of the first base material 11 facing the water absorbent layer 12 is similar to the ratio of the area including the particulate water absorbing agent 14 on the surface of the second base material 13 facing the water absorbent layer 12 (the surface on which the particulate water absorbing agent 14 is disposed).

[0075] The water-absorbent sheet 10 has a wrapping sheet 16. The wrapping sheet 16 has the following purposes: to maintain the shape of the water-absorbent sheet 10, which is a structure in which the particulate water-absorbing agent 14 is supported between the first substrate 11 and the second substrate 13; to prevent the particulate water-absorbing agent 14 supported between the first substrate 11 and the second substrate 13 from spilling (falling off) from the absorbent (water-absorbent sheet 10); and to prevent the particulate water-absorbing agent 14 from directly contacting the skin when the particulate water-absorbing agent 14 permeates the first substrate 11 and migrates to the outer surface (surface that directly contacts liquid) of the first substrate 11. When the wrapping sheet 16 is not provided, for example, there is a method of sealing by bonding the substrates 11 and 13 to each other, a method of suppressing migration to the outer surface of the first substrate 11 by surface treatment of the first substrate 11, and the like. As a method for preventing the particulate water absorbing agent 14 from falling off from the water absorbent sheet 10 while maintaining the effect of the present invention, it is preferable to have a wrapping sheet 16. The structure of the wrapping sheet 16 has been described with reference to Figs. 1 and 2 and will not be described here.

[0076] Therefore, the water-absorbent sheet 10 of the present invention preferably has at least a wrapping sheet 16 that is placed on the surface of the first substrate 11 (ie, on the liquid-absorbing surface of the first substrate 11). As described above, in this specification, even when the wrapping sheet 16 is included, the first substrate 11 forms a liquid-absorbing surface that directly absorbs liquid. For example, in the case of a water-absorbent sheet having a wrapping sheet 16, when the wrapping sheet 16 forms a liquid-absorbing surface that directly absorbs liquid, the water-absorbent sheet has a first substrate, a second substrate, a water-absorbent layer located between the first substrate and the second substrate, and a wrapping sheet disposed on a surface of the first substrate, the water-absorbent layer contains a particulate water-absorbing agent, an area containing the particulate water-absorbing agent is disposed apart from the area containing the particulate water-absorbing agent by a gap that does not substantially contain the particulate water-absorbing agent, the surface of the wrapping sheet forms a liquid-absorbent surface that directly absorbs liquid, the ratio of the thickness of the first substrate to the thickness of the second substrate (thickness of the first substrate (mm) / thickness of the second substrate (mm)) is 1.5 or more and less than 14, and the first substrate has an elongation rate of 10% or more.

[0077] In the water absorbent sheet 10 of the present invention, the first substrate 11 and the particulate water absorbing agent 14 in the water absorbent layer 12 are preferably in contact with each other directly or via an adhesive, and / or the second substrate 13 and the particulate water absorbing agent 14 in the water absorbent layer 12 are preferably in contact with each other directly or via an adhesive. Thus, the water absorbent sheet of the present invention has a simple configuration essentially consisting of only the first substrate, the second substrate, the particulate water absorbing agent sandwiched between the first substrate and the second substrate, an adhesive for fixing the particulate water absorbing agent to at least one of the first substrate and the second substrate, and a wrapping sheet for wrapping a part or all of these as necessary (it is not excluded that the water absorbent sheet may contain additives described in this specification that may be contained in the particulate water absorbing agent). A more preferred embodiment is a simple configuration consisting of only a first substrate, a second substrate, a particulate water absorbing agent sandwiched between the first substrate and the second substrate, an adhesive between the particulate water absorbing agent and the second substrate for fixing the particulate water absorbing agent to the second substrate, and a wrapping sheet for wrapping all of these. That is, the water absorbent sheet of the present invention is one that can effectively reduce the specific return amount despite its simple configuration.

[0078] In the present invention, the elongation percentage of the first substrate is 10% or more, preferably 15% or more, more preferably 17% or more, even more preferably 20% or more, and even more preferably 22% or more. The upper limit of the elongation percentage of the first substrate is not particularly limited, but is preferably 60% or less. When the elongation percentage of the first substrate is in such a range, the first substrate is easily adapted to the shape of the particulate water absorbing agent, and as a result, the shape retention of the water absorbent sheet is further improved and the amount of return can be further reduced. The elongation percentage of the first substrate is a value measured by the method described in the examples below. In this specification, the "elongation percentage of the nonwoven fabric (first substrate)" is a numerical value when the elongation percentage is measured in the most elongated direction. In addition, the elongation percentage of the first substrate can be controlled by the bulk density, basis weight, material, mesh structure, manufacturing process conditions, and the like.

[0079] In the present invention, the stretch direction of the first substrate is not particularly limited as long as it is stretched in any one direction parallel to the surface direction of the first substrate, except the thickness direction. For example, in the case of a rectangular absorbent sheet, it is sufficient that it is stretched at an elongation rate within the above range in any one direction from any angle direction, such as the long side direction, short side direction, or diagonal direction of the sheet plane. The same applies to square, elliptical, or circular absorbent sheets. Preferably, the substrate is capable of stretching in any direction (isotropically).

[0080] In the present invention, the surface of the first substrate 11 may be brushed to further impart liquid permeability, diffusibility, flexibility, and the like to the water-absorbent sheet 10. That is, in one embodiment of the present invention, the surface of the first substrate 11 opposite to the liquid-absorbing surface that directly absorbs liquid, i.e., the surface on which the water-absorbent layer 12 is provided (the surface on the water-absorbent layer 12 side), is brushed. In this specification, "brushed" refers to a state in which the surface fibers are fluffy.

[0081] In one embodiment of the water-absorbent sheet of the present invention, when the surface of the first substrate facing the water-absorbing layer is raised, not only can the specific return amount be effectively reduced, but also the particulate water-absorbing agent can be effectively prevented from falling off from the water-absorbent sheet after the water-absorbent sheet has absorbed liquid.

[0082] Here, an embodiment in which the surface of the first substrate 11 on the water-absorbing layer 12 side is raised will be described. FIG. 4 shows a water-absorbent sheet having a first substrate 11 with a raised surface on the water-absorbing layer 12 side. As shown in FIG. 4, the fibers of the first substrate 11 are raised toward the water-absorbing layer 12 on the surface on the water-absorbing layer 12 side. A part of the raised fibers of the first substrate 11 exceeds the particulate water-absorbing agent 14 and contacts and adheres to the second substrate 13 to which an adhesive is applied. Therefore, even after the particulate water-absorbing agent 14 absorbs water and swells, the first substrate 11 and the second substrate 13 can continue to be adhered to each other via the raised fibers of the first substrate 11, and thus the particulate water-absorbing agent 14 between the first substrate 11 and the second substrate 13 can be held. Therefore, by bonding the first substrate 11 and the second substrate 13 together, the particulate water-absorbing agent 14 is retained even after the water-absorbent sheet 10 has absorbed water, and the rate of gel falling off can be reduced.

[0083] In one embodiment, the surface of the first substrate 11 facing the water absorbent layer 12 is raised, and the first substrate does not support the particulate water absorbing agent 14 with an adhesive. That is, the first substrate 11 and the particulate water absorbing agent 14 in the water absorbent layer 12 are in direct contact with each other. In this case, the particulate water absorbing agent 14 is fixed to the second substrate 13 with an adhesive. Therefore, in one embodiment, it is preferable that the first substrate 11 and the particulate water absorbing agent 14 in the water absorbent layer 12 are in direct contact with each other, and it is preferable that the second substrate 13 and the particulate water absorbing agent 14 in the water absorbent layer 12 are in contact with each other via an adhesive.

[0084] Although the details of the reason why it is preferable that the surface of the first substrate 11 facing the water absorbent layer 12 is raised and the first substrate does not support the particulate water absorbing agent 14 with an adhesive are unclear, the effect is proven by the specific return amount in the examples. That is, the form in which no adhesive is applied to the raised surface of the first substrate 11 facing the water absorbent layer 12 and the first substrate does not support the particulate water absorbing agent 14 with an adhesive is preferable because it reduces the specific return amount compared to the form in which an adhesive is applied to the raised surface of the first substrate 11 facing the water absorbent layer 12 and the first substrate supports the particulate water absorbing agent 14 with an adhesive.

[0085] Here, the adhesive applied to the surface of the second substrate 13 on the water-absorbing layer 12 side, i.e., the adhesive on the second substrate 13, is preferably a hot melt adhesive. When the adhesive is a hot melt adhesive, the adhesion between the raised fibers of the first substrate 11 and the second substrate 13 is good, and the first substrate 11 and the second substrate 13 continue to adhere to each other even after the water-absorbent sheet 10 has absorbed water, and the particulate water-absorbing agent 14 between the first substrate 11 and the second substrate 13 is maintained.

[0086] The water-absorbent sheet 10 has a wrapping sheet 16. The wrapping sheet 16 is not an essential component of the water-absorbent sheet 10 according to the present invention, but by providing the first base material 11, the surface of which facing the water-absorbing layer 12 is raised, and the wrapping sheet 16 in the water-absorbent sheet 10, it is possible to effectively prevent the particulate water-absorbing agent 14 from falling off from the water-absorbent sheet 10. The configuration of the wrapping sheet 16 has been described above and will not be described here.

[0087] Therefore, the water-absorbent sheet 10 of the present invention preferably has at least a wrapping sheet 16 that is placed on the surface of the first substrate 11 (ie, on the liquid-absorbing surface of the first substrate 11). As described above, in this specification, even when the wrapping sheet 16 is included, the first substrate 11 forms a liquid-absorbing surface that directly absorbs liquid. For example, in the case of a water-absorbent sheet having a wrapping sheet 16, when the wrapping sheet 16 forms a liquid-absorbing surface that directly absorbs liquid, this can be expressed as follows: a water-absorbent sheet having a first substrate, a second substrate, a water-absorbent layer located between the first substrate and the second substrate, and a wrapping sheet disposed on a surface of the first substrate, the water-absorbent layer contains a particulate water-absorbing agent, the surface of the wrapping sheet forms a liquid-absorbent surface that directly absorbs liquid, the ratio of the thickness of the first substrate to the thickness of the second substrate (thickness of the first substrate (mm) / thickness of the second substrate (mm)) is 1.5 or more and less than 14, and the surface of the first substrate 11 on which the water-absorbent layer 12 is provided (the surface on the water-absorbent layer 12 side) is raised.

[0088] In the water absorbent sheet 10 of the present invention, the first substrate 11 and the particulate water absorbing agent 14 in the water absorbent layer 12 are preferably in contact with each other directly or via an adhesive, more preferably directly. And / or, the second substrate 13 and the particulate water absorbing agent 14 in the water absorbent layer 12 are preferably in contact with each other directly or via an adhesive, more preferably via an adhesive. Thus, the water absorbent sheet of the present invention has a simple structure consisting essentially of only the first substrate; the second substrate; the particulate water absorbing agent sandwiched between the first substrate and the second substrate; an adhesive for fixing the particulate water absorbing agent to at least one of the first substrate and the second substrate; and a wrapping sheet for wrapping a part or all of these as necessary (it is not excluded that the particulate water absorbing agent may contain additives described in this specification). A more preferred embodiment is a simple configuration consisting of only a first substrate, a second substrate, a particulate water absorbing agent sandwiched between the first substrate and the second substrate, an adhesive between the particulate water absorbing agent and the second substrate for fixing the particulate water absorbing agent to the second substrate, and a wrapping sheet for wrapping all of these. That is, the water absorbent sheet of the present invention is one that can effectively reduce the specific return amount despite its simple configuration.

[0089] In the water-absorbent sheet 10 having the first base material 11 with the surface on the water-absorbent layer 12 side raised, the particulate water-absorbing agent 14 can be effectively prevented from falling off from the water-absorbent sheet 10. Therefore, the content of the particulate water-absorbing agent 14 contained in the water-absorbent sheet 10 is set to 200 g / m 2 Therefore, in the water-absorbent sheet 10 having the first base material 11 with the surface on the water-absorbent layer 12 side raised, the content of the particulate water-absorbing agent 14 contained in the water-absorbent sheet 10 is preferably 200 g / m 2 More than 230g / m 2 More than 250g / m 2 More than 270g / m 2 More than 280g / m 2 More than 300g / m 2 In this case, the upper limit of the content of the particulate water-absorbing agent 14 contained in the water-absorbent sheet 10 is not particularly limited, but from the viewpoint of retention of the water-absorbing agent 14, it is preferably 360 g / m2 Less than 350g / m 2 Less than 325 g / m, more preferably 325 g / m 2 The following is the result.

[0090] In addition, in the water-absorbent sheet 10 having the first substrate 11 with the napped surface on the water-absorbent layer 12 side, the particulate water-absorbing agent 14 can be effectively prevented from falling off from the water-absorbent sheet 10, and therefore the amount of adhesive (preferably hot melt adhesive) can be reduced. Therefore, in the water-absorbent sheet 10 having the first substrate 11 with the napped surface on the water-absorbent layer 12 side, the content of the adhesive sprayed on the second substrate 13 is preferably 1 to 50 g / m 2 and more preferably 5 to 50 g / m 2 and even more preferably 10 to 45 g / m 2 and particularly preferably 15 to 30 g / m 2 and most preferably 15 to 25 g / m 2 It is.

[0091] In one embodiment, the mass ratio of the particulate water absorbing agent to the adhesive is preferably 80:20 to 99:1, more preferably 85:15 to 98:2, even more preferably 90:10 to 98:2, particularly preferably 91:9 to 97:3, and most preferably 92:8 to 96:4. By raising the surface of the water absorbing layer side of the first substrate, the raised fibers of the first substrate and the particulate water absorbing agent are entangled, and the particulate water absorbing agent is held by the first substrate, so that the amount of adhesive relative to the particulate water absorbing agent can be reduced. This further exerts the effect of reducing the specific return amount.

[0092] In the water-absorbent sheet, when the surface of the first substrate facing the water-absorbing layer is raised, the raised surface preferably has a raised surface area ratio of 5% or more in a raised surface area measurement test. The raised surface area ratio of the first substrate is preferably 5% or more, 7% or more, and 10% or more in this order. The upper limit of the raised surface area ratio of the first substrate is not particularly limited, but is preferably 30% or less, more preferably 28% or less, and even more preferably 25% or less, from the viewpoint of swelling control of the particulate water-absorbing agent. In this specification, the raised surface area ratio in the raised surface area measurement test is calculated by the method described in the Examples below.

[0093] In one embodiment of the water absorbent sheet of the present invention, when the surface of the first substrate facing the water absorbent layer is raised, not only can the specific return amount be effectively reduced, but also the particulate water absorbing agent can be effectively prevented from falling off from the water absorbent sheet. For example, the particulate water absorbing agent falling off rate calculated in the examples of the present invention is preferably 10% by mass or less, more preferably 5% by mass or less, and even more preferably 3% by mass or less. Such an effect is effectively achieved by raising the surface of the first substrate facing the water absorbent layer.

[0094] The present invention is not limited to the above-described embodiment, but can be modified in various ways within the scope of the claims.

[0095] Each of the components constituting the water-absorbent sheet will now be described in detail.

[0096] [2-1. First base material] The first substrate is a water-permeable sheet located on the side where the liquid to be absorbed is introduced. The liquid to be absorbed is not limited to water, but may be urine, blood, sweat, feces, waste liquid, moisture, steam, ice, a mixture of water and an organic solvent and / or an inorganic solvent, rainwater, groundwater, etc., and is not particularly limited as long as it contains water. Preferred examples include urine, menstrual blood, sweat, and other body fluids.

[0097] The first substrate is a water-permeable sheet and is positioned on the side where liquid is absorbed, so that the performance of the water-absorbent sheet, which is the effect of the present invention (e.g., amount of return, leakage in the surface direction, etc.), can be fully exhibited. The water permeability of the water-permeable sheet is 1×10 -5 The water permeability coefficient is preferably 1×10 cm / sec or more. -4 cm / sec or more, and even more preferably 1×10 -3 cm / sec or more, and particularly preferably 1×10 -2 cm / sec or more, most preferably 1×10 -1 The permeability coefficient of the first substrate used in the examples of the present application is 1×10 -5 cm / sec or more.

[0098] In the present invention, the first substrate has a bulk density of 0.1 g / cm 3 It is preferable that the density is 0.08 g / cm or less. 3 More preferably, it is 0.05 g / cm or less. 3 The bulk density of the first substrate is preferably 0.001 g / cm or less. 3 More preferably, it is 0.005 g / cm 3 More preferably, it is 0.01 g / cm 3 That is all. In this specification, the bulk density is the mass per unit volume, and is not the density when the substrate is compressed under high pressure (when voids are eliminated), but is the density obtained from the volume of the substrate including the volume of voids. When the bulk density of the first substrate is 0.1 g / cm 3or less means that the first substrate is light. Bulky means that the substrate is significantly thick with a low bulk density. In the present invention, the bulky first substrate allows the absorbed liquid in contact with the liquid-absorbing surface of the first substrate to flow quickly into the lower layer, the water-absorbing layer, and the second substrate, and the liquid remaining on the liquid-absorbing surface of the first substrate can be reduced. Furthermore, when the absorbed liquid reaches the water-absorbing layer, the liquid is diffused in the surface direction. Therefore, even if a large amount of liquid is introduced into the water-absorbing layer, the water-absorbing layer absorbs the liquid that has spread in the surface direction, not locally. That is, the bulky first substrate has low water absorption, high liquid permeability, and high liquid diffusibility. This can reduce the amount of backflow in the water-absorbent sheet. The humidity of the liquid-absorbing surface of the first substrate can be suppressed, and discomfort to the skin can be reduced. The bulk density of the first substrate is preferably 0.1 g / cm 3 In the present specification, the bulk density is a value calculated in the examples described later.

[0099] In the present invention, the first substrate has a basis weight of 3 to 80 g / m 2 It is preferable that the thickness is 5 to 70 g / m 2 More preferably, it is 10 to 60 g / m 2 By setting the basis weight of the first base material in such a range, the amount of backflow can be further reduced, and the particulate water-absorbing agent can be easily incorporated into the first base material, resulting in further improved shape retention of the water-absorbent sheet.

[0100] The thickness of the first substrate is, for example, at 40% RH to 50% RH, preferably 0.7 mm or more, more preferably 1.0 mm or more, even more preferably 1.2 mm or more, particularly preferably 1.3 mm or more, and most preferably 1.4 mm or more. The upper limit of the thickness of the first substrate is, for example, at 40% RH to 50% RH, preferably 5 mm or less, more preferably 4 mm or less, even more preferably 3 mm or less, particularly preferably 2.5 mm or less, and most preferably 2 mm or less. By making the thickness of the first substrate within this range, a sufficient distance can be secured between the liquid-absorbing surface of the first substrate and the water-absorbing layer and the second substrate, and the liquid that has once reached the water-absorbing layer and the second substrate can be significantly reduced from returning, and leakage in the surface direction can be reduced.

[0101] The thickness, bulk density, and basis weight of the first substrate can be controlled by the material constituting the first substrate, the manufacturing method of the first substrate, and the like, and the thickness and bulk density of the first substrate are determined by the balance between these factors.

[0102] The first base material has a transmittance of the particulate water absorbing agent (transmittance of the particulate water absorbing agent through the first base material) of preferably 40% by mass or more, more preferably 50% by mass or more, further preferably 60% by mass or more, 70% by mass or more, particularly preferably 80% by mass or more, and most preferably 90% by mass or more. The upper limit of the transmittance is not particularly limited, but is preferably 97% by mass or less. When the transmittance of the particulate water absorbing agent through the first base material is in such a range, the particulate water absorbing agent easily penetrates into the first base material on the side of the first base material that contacts the water absorbing layer. This enables the particulate water absorbing agent to absorb the moisture contained in the first base material, and backflow is further reduced. In this specification, the transmittance of the particulate water absorbing agent to the first substrate is the ratio of the particulate water absorbing agent that passes through the first substrate, and is determined by the weight of the particulate water absorbing agent that passes through the first substrate when the particulate water absorbing agent present on the first substrate is sieved under a predetermined condition described later, and is specifically a value calculated by the method described in the Examples described later. Here, when the first substrate is a nonwoven fabric, the transmittance of the first substrate can be adjusted to a desired range by appropriately adjusting the properties of the members constituting the first substrate, the surface condition, the complexity of the mesh structure, the fiber diameter, the fusion state between the fibers, the basis weight, the thickness, etc. For example, when the first substrate is an air-through nonwoven fabric as described later, the transmittance can be adjusted by changing the heat treatment conditions, the fiber diameter, and the density of the air-through nonwoven fabric.

[0103] In one embodiment, the first substrate has a raised surface facing the water-absorbing layer.

[0104] "Materials that make up the base material" Examples of materials constituting the first substrate include paper (sanitary paper, such as tissue paper, toilet paper, and towel paper), net, nonwoven fabric, woven fabric, film, etc. Among these, from the viewpoint of water permeability, nonwoven fabric is preferably used for at least the first substrate.

[0105] The nonwoven fabric used is not particularly limited, but from the standpoint of liquid permeability, flexibility, and strength when made into a water-absorbent sheet, examples include nonwoven fabrics made of polyolefin fibers such as polyethylene (PE) and polypropylene (PP), polyester fibers such as polyethylene terephthalate (PET), polytrimethylene terephthalate (PTT), and polyethylene naphthalate (PEN), polyamide fibers such as nylon, rayon fibers, and other synthetic fibers, as well as nonwoven fabrics made from a mixture of cotton, silk, hemp, pulp (cellulose) fibers, etc.

[0106] The material of the nonwoven fabric that can be used as the first substrate is preferably rayon fiber, polyolefin fiber, polyester fiber, pulp fiber, or a mixture of these fibers, and more preferably polyolefin fiber. These fibers may be hydrophilized.

[0107] Furthermore, the nonwoven fabric that can be used as the first substrate is not particularly limited and may be obtained by any method, such as the air-through method, the airlaid method, the spunbond method, or the spunlace method. However, it is preferable that the nonwoven fabric is obtained by the air-through method or the airlaid method, and it is preferable that the nonwoven fabric is obtained by the air-through method (air-through nonwoven fabric).

[0108] The air-through method is a process in which hot air is blown onto heat-sealable composite fibers such as PE / PP and PE / PET to perform heat fusion and increase the amount of air contained between the fibers, thereby increasing the bulk and decreasing the density. The air-laid method is a method of making a nonwoven fabric by uniformly dispersing pulp fibers in an air flow and absorbing them on a wire mesh, and since air is used to disperse the pulp fibers, it is possible to increase the bulk and decrease the density. By using an air-through nonwoven fabric as the first substrate, the liquid to be absorbed is easily introduced into the first substrate after contacting the liquid-absorbing surface of the first substrate. In other words, by using an air-through nonwoven fabric as the first substrate, the first substrate can be made to have low water absorption and high liquid permeability, and the amount of backflow in the absorbent sheet can be significantly reduced.

[0109] [2-2. Second substrate] The second substrate is a water-permeable sheet, and is positioned on the opposite side to the side that absorbs liquid, so that the performance of the water-absorbent sheet, which is the effect of the present invention (e.g., amount of return, leakage in the surface direction, etc.), can be fully exhibited. The water permeability of the water-permeable sheet is 1×10 -5 The water permeability coefficient is preferably 1×10 cm / sec or more. -4 cm / sec or more, and even more preferably 1×10 -3 cm / sec or more, and particularly preferably 1×10 -2 cm / sec or more, most preferably 1×10 -1 cm / sec or more.

[0110] The thickness of the second substrate is preferably 0.05 mm or more, more preferably 0.08 mm or more, even more preferably 0.1 mm or more, particularly preferably 0.2 mm or more, and most preferably 0.3 mm or more, for example, at 40% RH to 50% RH. The thickness of the second substrate is preferably 0.9 mm or less, more preferably 0.8 mm or less, even more preferably 0.7 mm or less, particularly preferably 0.6 mm or less, and most preferably 0.5 mm or less, for example, at 40% RH to 50% RH.

[0111] Here, according to one embodiment of the present invention, the thickness of the first substrate is 0.7 mm or more and 5 mm or less, and the thickness of the second substrate is 0.05 mm or more and 0.9 mm or less. By adjusting the thicknesses of the first substrate and the second substrate within the above ranges, the intended effect of the present invention can be efficiently achieved. Also, according to one embodiment of the present invention, preferably the thickness of the first substrate is 1.0 mm or more and 4 mm or less, and the thickness of the second substrate is 0.08 mm or more and 0.8 mm or less, more preferably the thickness of the first substrate is 1.2 mm or more and 3 mm or less, and the thickness of the second substrate is 0.1 mm or more and 0.7 mm or less, even more preferably the thickness of the first substrate is 1.3 mm or more and 2.5 mm or less, and the thickness of the second substrate is 0.2 mm or more and 0.6 mm or less, and particularly preferably the thickness of the first substrate is 1.4 mm or more and 2 mm or less, and the thickness of the second substrate is 0.3 mm or more and 0.5 mm or less.

[0112] In the present invention, the bulk density of the second substrate is 1 g / cm 3 It is preferable that the density is 0.5 g / cm or less. 3 More preferably, it is 0.3 g / cm or less. 3 More preferably, the bulk density of the second substrate is 0.05 g / cm or less. 3 More preferably, it is 0.07 g / cm 3 More preferably, it is 0.08 g / cm 3 That is all. When the bulk density of the second base material is in this range, the second base material can easily retain the liquid introduced therein, and backflow can be reduced.

[0113] In the present invention, the second substrate has a basis weight of 5 to 100 g / m 2 It is preferable that the thickness is 10 to 70 g / m 2 More preferably, it is 15 to 65 g / m 2 It is even more preferable that:

[0114] The thickness, bulk density, and basis weight of the second substrate can be controlled by the material constituting the second substrate and the manufacturing method of the second substrate, and the thickness and bulk density of the second substrate are determined by the balance between these factors.

[0115] The porosity of the first substrate, the second substrate, and the wrapping sheet (e.g., nonwoven fabric) can be measured by the following formula: 2 ), the thickness B (mm) of the substrate (or wrapping sheet), the density C (g / cm) of the material (e.g., polyolefin) used in the substrate (or wrapping sheet), 3 ) Porosity of substrate (or sheet) (%) = 100-{(A / 10000) / (B / 10)} / C*100

[0116] The second substrate has a liquid diffusion area of ​​1000 mm 2 It is preferable that the length is 3000 mm or more. 2 More preferably, it is 6000 mm or more. 2 More preferably, it is 7000 mm or more. 2 The upper limit of the liquid diffusion area of ​​the second substrate is not particularly limited, but it is preferably 10,000 mm or more. 2 It is preferable that the liquid diffusion area of ​​the second substrate is within the above range, when the absorbed liquid reaches the second substrate, the liquid can be sufficiently diffused in the surface direction in the second substrate. As a result, even if a large amount of liquid that has passed through the water absorbing layer is introduced into the second substrate, the second substrate absorbs the liquid while spreading in the surface direction, not locally. Therefore, the second substrate can sufficiently absorb and retain the liquid, the amount of backflow in the water absorbent sheet can be significantly reduced, and leakage in the surface direction can be significantly reduced.

[0117] Here, the liquid diffusion area means the area in the surface direction in which the liquid diffuses when the liquid contacts the substrate (e.g., nonwoven fabric) and / or when the liquid passes through the substrate in a direction perpendicular to the surface direction of the substrate, and is a value calculated by the method described in the Examples below. The larger the liquid diffusion area of ​​the substrate, the higher the liquid diffusion property of the substrate in the surface direction.

[0118] "Materials that make up the base material" The material constituting the second substrate is preferably a nonwoven fabric. The material of the nonwoven fabric may be the same as that of the first substrate, and for example, rayon fiber, polyolefin fiber, polyester fiber, pulp fiber, or a mixture of these fibers is preferable, and polyolefin fiber is more preferable.

[0119] The nonwoven fabric that can be used as the second substrate is not particularly limited and may be obtained by any method such as the air-through method, the airlaid method, the spunbond method, or the spunlace method, but is preferably obtained by the airlaid method (airlaid nonwoven fabric) or the spunlace method (spunlace nonwoven fabric). The spunlace method is a method in which fibers are entangled by a high-pressure water flow and does not use an adhesive. By using an airlaid or spunlace nonwoven fabric as the second substrate, the amount of return in the water-absorbent sheet can be significantly reduced, and leakage in the surface direction can be significantly reduced.

[0120] [2-3. Water absorption layer] The water-absorbent layer of the water-absorbent sheet according to one embodiment of the present invention has a particulate water-absorbing agent. In the water-absorbent sheet according to one embodiment of the present invention, it is preferable that no other substrate such as a nonwoven fabric is present in the water-absorbent layer.

[0121] (Particulate water absorbing agent) The water-absorbing layer contains a particulate water-absorbing agent. Unless otherwise specified, when the water-absorbing agent is a mixture of multiple types of particulate water-absorbing agents, the following description is an explanation of the physical properties of the mixture. In other words, the physical properties of the particulate water-absorbing agent are the physical properties when all the particulate water-absorbing agents contained in the water-absorbing layer are mixed together. The physical properties of the particulate water-absorbing agent may be measured by taking out only the particulate water-absorbing agent from the water-absorbing sheet so that no cotton-like pulp or the like is mixed in.

[0122] "surface tension" Surface tension is the work (free energy) required to increase the surface area of ​​a solid or liquid, expressed per unit area. The surface tension referred to in this application refers to the surface tension of the aqueous solution when the particulate water absorbing agent is dispersed in a 0.90 mass % sodium chloride aqueous solution. The surface tension of the water absorbing agent is measured by the following procedure. That is, 50 ml of physiological saline adjusted to 20°C is placed in a thoroughly washed 100 ml beaker, and the surface tension of the physiological saline is first measured using a surface tensiometer (K11 automatic surface tensiometer manufactured by KRUSS). Next, a thoroughly washed 25 mm long fluororesin rotor and 0.5 g of the particulate water absorbing agent are placed in the beaker containing the physiological saline adjusted to 20°C after the surface tension measurement, and the mixture is stirred for 4 minutes under the condition of 500 rpm. After 4 minutes, the stirring is stopped, and after the particulate water absorbing agent containing the water is settled, the surface tension of the supernatant liquid is measured again by performing the same operation. In the present invention, a plate method using a platinum plate is adopted, and the plate is thoroughly washed with deionized water and heated and washed with a gas burner before each measurement.

[0123] In the water absorbent sheet according to one embodiment of the present invention, the surface tension of the particulate water absorbing agent is preferably 60 mN / m or more, 65 mN / m or more, 66 mN / m or more, 67 mN / m or more, 69 mN / m or more, 70 mN / m or more, 71 mN / m or more, and most preferably 72 mN / m or more. When the particulate water absorbing agent is applied to the water absorbent sheet, the effect of the surface tension is more likely to appear than in conventional paper diapers, and when the surface tension satisfies the above conditions, the amount of return in the water absorbent sheet can be reduced, and leakage in the surface direction can be reduced.

[0124] In the water-absorbent sheet according to one embodiment of the present invention, the upper limit of the surface tension of the particulate water-absorbing agent is not particularly limited, but is practically 73 mN / m or less.

[0125] In the water absorbent sheet according to one embodiment of the present invention, the CRC (absorption capacity without load) of the particulate water absorbing agent is preferably 30 g / g or more, 32 g / g or more, 33 g / g or more, 34 g / g or more, and most preferably 35 g / g or more. When the CRC of the particulate water absorbing agent satisfies the above conditions, the amount of return in the water absorbent sheet can be reduced. The CRC of the particulate water absorbing agent is an abbreviation of Centrifuge Retention Capacity (centrifuge retention capacity) defined by ERT441.2-02, and means the absorption capacity without load (sometimes called "absorption capacity") of the particulate water absorbing agent. Specifically, the CRC refers to the absorption capacity (unit: g / g) after immersing 0.2 g of the particulate water absorbing agent in a nonwoven bag for 30 minutes in a large excess of 0.9% by mass sodium chloride aqueous solution to allow free swelling, and then draining the water with a centrifuge (250 G).

[0126] In the water absorbent sheet according to one embodiment of the present invention, the AAP (absorption capacity against pressure) of the particulate water absorbing agent is, in the following order, preferably 25 g / g or more, more preferably 28 g / g or more, particularly preferably 30 g / g or more, and most preferably 33 g / g or more, from the viewpoint of improving the performance of the water absorbent sheet (reducing the amount of rewetting). The AAP of the particulate water absorbing agent is an abbreviation of Absorption Against Pressure defined by ERT442.2-02, and means the water absorption capacity against pressure of the particulate water absorbing agent. Specifically, 0.9 g of the particulate water absorbing agent is subjected to a large excess of 0.9 mass % sodium chloride aqueous solution at 2.06 kPa (21 g / cm) for 1 hour. 2 This refers to the water absorption capacity (unit: g / g) after swelling under a load of 0.3 psi (0.2 psi). In addition, ERT442.2-02 states it as Absorption Under Pressure (AUP), but this is essentially the same thing.

[0127] In the water absorbent sheet according to one embodiment of the present invention, the DRC5min (immersion retention capacity 5 minutes value) of the particulate water absorbing agent is preferably 25 to 50 g / g, more preferably 30 to 45 g / g, and particularly preferably 30 to 40 g / g, in the following order, from the viewpoint of improving the performance of the water absorbent sheet (reducing the specific return amount). The DRC5min of the particulate water absorbing agent means the water absorption capacity under no pressure for 5 minutes, and the larger the DRC5min value, the faster the absorption speed. For a detailed explanation of the DRC5min of the water absorbing agent, the descriptions in paragraphs "0151" to "0152", "0328", and "0484" to "0487" (including FIG. 1) of the specification of US Patent Application Publication No. 2019 / 0111411 are incorporated herein by reference.

[0128] In the water absorbent sheet according to one embodiment of the present invention, the GPR of the particulate water absorbing agent is preferably 20 g / min or more, more preferably 50 g / min or more, even more preferably 70 g / min or more, even more preferably 100 g / min or more, and particularly preferably 150 g / min or more, because it is excellent in the effect of shortening the water absorption time in the pressure specific reversion amount evaluation described later, that is, improving the water absorption speed. That is, when the GPR of the particulate water absorbing agent is 20 g / min or more, the water absorption time can be shortened in the pressure specific reversion amount evaluation, and therefore the water absorption speed is improved. This can reduce the discomfort of the user. Such an effect is effectively expressed by raising the surface of the first base material on the water absorption layer side. There is no particular upper limit for the GPR of the particulate water absorbing agent, but it is preferably 1000 g / min or less. The GPR of the particulate water absorbing agent is an abbreviation for Gel Permeation Rate, and refers to the flow rate (unit: g / min) of the liquid passing between the particles of the swollen gel when the particulate water absorbing agent is swollen under a load. For a detailed description of the GPR measurement method, the description in paragraphs "0237" to "0239" (including Figure 5) of the specification of International Publication No. 2019 / 074094 is incorporated by reference into this specification.

[0129] "Particle shape" In the water absorbent sheet according to one embodiment of the present invention, the particulate water absorbing agent is not limited in its particle shape, and may be, for example, a spherical particulate water absorbing agent (and its granulated product). In a preferred embodiment, the particulate water absorbing agent is preferably in an irregularly pulverized form. Here, the term "irregularly pulverized form" refers to particles in a pulverized form that are not uniform in shape. This is because the irregularly pulverized form can be easily fixed to a substrate compared with spherical particles obtained by reversed-phase suspension polymerization or gas-phase polymerization. The particulate water absorbing agent according to one embodiment of the present invention is preferably a pulverized product obtained in aqueous solution polymerization. On the other hand, in the case where the pulverization step is not performed, typically spherical particles or granulated products of spherical particles obtained by reversed-phase suspension polymerization or droplet polymerization in which a polymerization monomer is sprayed and polymerized are not in an irregularly pulverized form. In the embodiment of the present invention, when the particulate water absorbing agent has an irregularly pulverized form, the shape of the water absorbent sheet is more easily maintained compared with those having a high average roundness (for example, spherical). In the embodiment of the present invention, the average circularity of the particulate water absorbing agent is preferably 0.70 or less, more preferably 0.60 or less, and further preferably 0.55 or less.

[0130] The calculation method of the average circularity is as follows. 100 or more particulate water absorbing agents were randomly selected, and each particulate water absorbing agent was photographed with an electron microscope (VE-9800 manufactured by Keyence Corporation) (magnification: 50 times) to obtain an image of the particulate water absorbing agent, and the perimeter and area of ​​each particle were calculated using the attached image analysis software. The following formula:

[0131]

number

[0132] The circularity of each particle is obtained, and the average of the obtained values ​​is calculated as the average circularity.

[0133] "Particle size" The particle diameter of the particulate water absorbing agent (or particulate water absorbent resin, water absorbent resin particles) according to one embodiment of the present invention is a weight average particle diameter obtained according to a measurement method of "PSD" specified in ERT420.2-02, and may be 150 to 600 μm.

[0134] The method for producing the particulate water absorbing agent is not particularly limited as long as it is a method for producing a water absorbing agent having desired physical properties, and the particulate water absorbing agent can be produced appropriately by taking into consideration, for example, publications described in the examples.

[0135] [2-4. Wrapping Sheet] The water-absorbent sheet according to one embodiment of the present invention preferably has at least a wrapping sheet arranged on the surface of the first substrate. The wrapping sheet may be arranged on the surface of the first substrate, but it is more preferable that the wrapping sheet is arranged so as to cover the side surface of the first substrate and the side surface of the water-absorbing layer, and it is even more preferable that the wrapping sheet covers the side surface of the first substrate, the side surface of the water-absorbing layer, and the side surface of the second substrate, and partially or entirely covers the side surface of the second substrate opposite to the side where the liquid to be absorbed is introduced.

[0136] In a preferred embodiment of the present invention, the water-absorbent sheet includes a wrapping sheet, which is a water-permeable sheet and is located at least on the surface (the side that absorbs liquid) of the first substrate.

[0137] The thickness of the wrapping sheet is preferably 0.001 mm or more, more preferably 0.005 mm or more, even more preferably 0.01 mm or more, particularly preferably 0.1 mm or more, and most preferably 0.2 mm or more, for example, at 40% RH to 50% RH. The thickness of the wrapping sheet is preferably less than 0.9 mm, more preferably 0.8 mm or less, even more preferably 0.7 mm or less, particularly preferably 0.6 mm or less, and most preferably 0.5 mm or less, for example, at 40% RH to 50% RH.

[0138] In the present invention, the bulk density of the wrapping sheet is 1 g / cm 3 It is preferable that the density is 0.5 g / cm or less. 3 More preferably, it is 0.3 g / cm or less. 3 The bulk density of the wrapping sheet is preferably 0.1 g / cm or less. 3More preferably, it is 0.12 g / cm 3 More preferably, it is 0.13 g / cm 3 That's all.

[0139] In the present invention, the wrapping sheet has a basis weight of 5 to 100 g / m 2 It is preferable that the thickness is 5 to 70 g / m 2 More preferably, it is 10 to 65 g / m 2 It is even more preferable that:

[0140] The thickness, bulk density, and basis weight of the wrapping sheet can be controlled by the material constituting the wrapping sheet, the manufacturing method of the wrapping sheet, etc., and the thickness and bulk density of the wrapping sheet are determined by the balance between these factors.

[0141] "Materials that make up wrapping sheets" The material constituting the wrapping sheet is not particularly limited as long as it can achieve the purpose of providing the wrapping sheet described above, but examples include paper (sanitary paper, such as tissue paper, toilet paper, and towel paper), net, nonwoven fabric, woven fabric, film, etc.

[0142] The nonwoven fabric used is not particularly limited, but from the standpoint of liquid permeability, flexibility, and strength when made into a water-absorbent sheet, examples include nonwoven fabrics made of polyolefin fibers such as polyethylene (PE) and polypropylene (PP), polyester fibers such as polyethylene terephthalate (PET), polytrimethylene terephthalate (PTT), and polyethylene naphthalate (PEN), polyamide fibers such as nylon, rayon fibers, and other synthetic fibers, as well as nonwoven fabrics made from a mixture of cotton, silk, hemp, pulp (cellulose) fibers, etc.

[0143] The material of the nonwoven fabric that can be used as the wrapping sheet is preferably rayon fiber, polyolefin fiber, polyester fiber, pulp fiber, or a mixture of these fibers, and more preferably polyolefin fiber. These fibers may be hydrophilized.

[0144] The nonwoven fabric that can be used as the wrapping sheet is not particularly limited, and may be obtained by any method such as the air-through method, the air-laid method, the spunbond method, or the spunlace method, but is preferably obtained by the spunbond method (spunbond nonwoven fabric). A wrapping sheet having water repellency is preferable so that the urine absorbed in the absorbent sheet does not seep out of the sheet (so-called backflow) even when weight is applied (pressurized), such as when an infant wearing an absorbent article such as a paper diaper is sitting on the absorbent sheet, and for example, a spunbond nonwoven fabric is preferable. The method for producing a spunbond nonwoven fabric is a method in which continuous long fibers obtained by melting and spinning a raw material resin are directly accumulated to form a fleece. Examples of raw material resins include polyethylene, polypropylene, and polylactic acid.

[0145] According to one embodiment of the present invention, the manufacturing method of the first substrate, the manufacturing method of the second substrate, and the manufacturing method of the wrapping sheet are different. By appropriately changing the manufacturing methods of each member constituting the water-absorbent sheet in this manner, the desired effect of the present invention can be efficiently achieved. According to one embodiment of the present invention, the first substrate is an air-through nonwoven fabric, the second substrate is an air-laid nonwoven fabric or a spunlace nonwoven fabric, and the wrapping sheet is a spunbond nonwoven fabric, which are different nonwoven fabrics. With this embodiment, the desired effect of the present invention can be efficiently achieved.

[0146] 3. Method for producing water-absorbent sheet The method for producing a water-absorbent sheet according to one embodiment of the present invention includes at least one of the steps of (1) spraying a particulate water-absorbing agent on a first substrate and (2) spraying a particulate water-absorbing agent on a second substrate. More specific examples of the production method include the following production methods (a) to (d).

[0147] When the first base material has a raised surface, one surface of the first base material may be raised before the manufacturing methods (a) to (d).

[0148] The method for raising the water-absorbing surface of the first substrate is not particularly limited, and any known method can be used, for example, a method using a needle, thistle seeds (teasels), brush (brush hair), etc. Industrially, the first substrate can be raised by rotating a roller wrapped with cardboard or thistle seeds and running a cloth over it to scratch off fibers from the spun yarn on the surface of the fabric.

[0149] For example, in the method using a brush, 60 cm of nonwoven fabric is placed on a horizontal surface, and 10 kg weights larger than the width of the nonwoven fabric are placed on both ends of the nonwoven fabric in the direction of its length to fix the nonwoven fabric. A brush is inserted vertically at a point 10 cm from the end of the nonwoven fabric in the direction of its length to be wound. The brush is inserted so that the long side of the brush is in the width direction of the nonwoven fabric until the tip of the brush (the tip of the bristles) touches the horizontal surface, and then the brush is moved horizontally 40 cm in the direction of the length to be wound. The brush and weights are removed from the nonwoven fabric, and the nonwoven fabric on the side where the brush was moved is cut off to obtain a raised nonwoven fabric.

[0150] As conditions for obtaining a raised nonwoven fabric, for example, the following conditions are preferable. ·Brush Product name: 25mm x 0.1m Seal brush (PBT / blue), Manufacturer: ESCO Bristle length: 25mm, Bristle diameter: 0.2mm Brush length: 100mm, brush width: 5mm, material: PBT Brush movement speed: 16m / min=0.27m / s.

[0151] (a) A particulate water absorbing agent is uniformly sprayed on a first substrate. An adhesive is uniformly sprayed on a second substrate. The first substrate is superimposed so that the surface on which the particulate water absorbing agent is sprayed faces the surface on which the adhesive is sprayed on the second substrate, and the substrates are pressed together. The pressing is preferably performed by heating and pressing at a temperature near the melting temperature of the adhesive.

[0152] (b) After the adhesive is uniformly sprayed on the second base material, the particulate water absorbing agent is uniformly sprayed on the second base material. The first base material is placed on the surface of the second base material on which the particulate water absorbing agent is sprayed, and the first base material and the second base material are heated and pressed together.

[0153] (c) A particulate water absorbing agent and preferably an adhesive are sprayed on the second substrate, and the particulate water absorbing agent is fixed to such an extent that it does not dissipate by passing through a heating furnace. The first substrate is placed on the surface of the second substrate on which the particulate water absorbing agent is sprayed, and is heat-pressed to bond the first substrate to the second substrate.

[0154] (d) After the adhesive is melt-applied onto the second substrate, the particulate water-absorbing agent is uniformly spread thereon to form a layer. The first substrate is placed on the surface of the second substrate on which the particulate water-absorbing agent is spread, and the first substrate is pressed together using a roll press or the like.

[0155] Among these methods, the method (d) is preferred from the viewpoint of uniformly applying the adhesive. Note that the methods (a) to (d) can also be used in combination to produce a water-absorbent sheet.

[0156] In the case where the particulate water absorbing agent-free region is provided in the water absorbing layer, the particulate water absorbing agent may be sprayed in stripes in the above-mentioned methods (a) to (d). Specifically, the particulate water absorbing agent may be sprayed on the adhesive sprayed in stripes on a substrate (e.g., a first substrate), and another substrate may be placed on the surface of the substrate on which the particulate water absorbing agent is sprayed, and then heat-pressed. Alternatively, the adhesive may be sprayed in stripes on a substrate (e.g., a second substrate) facing the substrate on which the particulate water absorbing agent is sprayed in stripes, and the two substrates may be placed on top of each other so that the surface on which the particulate water absorbing agent is sprayed and the surface on which the adhesive is sprayed face each other, and then heat-pressed. That is, the following manufacturing methods (a') to (d') may be mentioned.

[0157] (a') A particulate water absorbing agent is sprayed in stripes on a first substrate. An adhesive is sprayed uniformly on a second substrate. The first substrate is superimposed so that the surface on which the particulate water absorbing agent is sprayed faces the surface on which the adhesive is sprayed on the second substrate, and the substrates are pressed together. The pressing is preferably performed by heating and pressing at a temperature near the melting temperature of the adhesive.

[0158] (b') After applying an adhesive in stripes onto a second substrate, a particulate water absorbing agent is uniformly applied onto the second substrate. The first substrate is placed on the surface of the second substrate on which the particulate water absorbing agent is applied, and the two substrates are heated and pressed together.

[0159] (c') On the second base material, the particulate water absorbing agent is sprayed in stripes, and preferably an adhesive is sprayed uniformly, and the particulate water absorbing agent is fixed to such an extent that it does not dissipate by passing through a heating furnace. The first base material is placed on the surface of the second base material on which the particulate water absorbing agent is sprayed, and is heated and pressed to be bonded.

[0160] (d') After the adhesive is melt-applied onto the second substrate, the particulate water absorbing agent is sprayed in stripes to form a layer. The first substrate is placed on the surface of the second substrate on which the particulate water absorbing agent is sprayed, and the first substrate is pressed together using a roll press or the like.

[0161] Here, in the present invention, the method of spraying the particulate water absorbing agent in stripes is not particularly limited, and for example, the particulate water absorbing agent can be sprayed in stripes by using a template. Specifically, a plate having the same size as the water absorbent sheet and cut out in a striped pattern with a constant width and length is used as the template. This template is placed on the substrate on which the particulate water absorbing agent is to be sprayed, and the particulate water absorbing agent is sprayed into the cut-out holes. After spraying the particulate water absorbing agent, the template is removed, leaving the particulate water absorbing agent sprayed in stripes on the substrate.

[0162] Also, the particulate water absorbing agent can be sprayed in stripes on the substrate by applying an adhesive in stripes by screen printing or the like, spraying the particulate water absorbing agent on the substrate, and then brushing off any particulate water absorbing agent on the substrate that is not in contact with the adhesive, thereby spraying the particulate water absorbing agent in stripes on the substrate.

[0163] In the embodiment in which the water-absorbent sheet is provided with a wrapping sheet as shown in Fig. 1 to Fig. 4, the method includes a step (3) of covering the first substrate, the water-absorbent layer, and the second substrate with a wrapping sheet arranged on the first substrate. For example, the sheet obtained by the above steps (a) or (b) in which the first substrate, the water-absorbent layer, and the second substrate are bonded together is placed on the wrapping sheet with the first substrate facing down, adhesive is sprayed on the upper surface of the second substrate (the surface on which the water-absorbent layer is not bonded), and the excess portion of the wrapping sheet protruding from the first substrate is folded and wrapped so that the adhesive surface of the second substrate comes into contact with the wrapping sheet, and the second substrate is turned upside down and then bonded together under pressure to obtain a water-absorbent sheet provided with a wrapping sheet.

[0164] As a step other than those described above, the absorbent sheet may be embossed in order to improve the texture of the absorbent sheet and to enhance the liquid absorption performance. The embossing may be performed simultaneously when the first substrate and the second substrate are pressed together, or may be performed after the sheet is manufactured. The wrapping sheet may also be embossed.

[0165] In the method for producing a water-absorbent sheet according to one embodiment of the present invention, additives (deodorant, fiber, antibacterial agent, gel stabilizer, etc.) may be appropriately blended. The blending amount of the additives is preferably 0 to 50 mass % and more preferably 1 to 10 mass % based on the mass of the particulate water-absorbing agent. In the above-mentioned production method, the particulate water-absorbing agent in which the additives are mixed in advance may be used, or the additives may be added during the production process.

[0166] The dimensions of the water-absorbent sheet produced can be designed appropriately. Usually, the width is 3 to 10 m, and the length is several tens to several thousand meters (in the form of a continuous sheet or roll). The produced water-absorbent sheet is cut according to the purpose (the size of the absorbent body to be used) and used.

[0167] In addition to the above-mentioned examples, methods for producing water-absorbent sheets are disclosed, for example, in the following patent documents: WO 2012 / 174026, WO 2013 / 078109, WO 2015 / 041784, WO 2011 / 117187, WO 2012 / 001117, WO 2012 / 024445, WO 2010 / 004894, WO 2010 / 004895, WO 2010 / 076857, WO 2010 / 082373, WO 2010 / 113754, WO 2010 / 143635, WO 2011 / 043256, WO 2011 / 0 86841, WO 2011 / 086842, WO 2011 / 086843, WO 2011 / 086844, WO 2011 / 117997, WO 2011 / 118409, WO 2011 / 136087, WO 2012 / 043546, WO 2013 / 09 No. 9634, International Publication No. 2013 / 099635, JP 2010-115406, JP 2002-345883, JP 6-315501, JP 6-190003, JP 6-190002, JP 6-190001, JP 2-252558, JP 2-252560, and JP 2-252561. The methods of producing water-absorbent sheets disclosed in these documents are also referred to as appropriate.

[0168] In the water-absorbent sheet according to one embodiment of the present invention, the method of bonding the substrates together or the substrate and the particulate water-absorbing agent may be (i) pressure bonding, (ii) water, water-soluble polymer, or various binders dissolved or dispersed in a solvent, (iii) heat sealing the substrates together at the melting point of the material of the substrate itself, or (iv) bonding using an adhesive. The substrates together or the substrate and the particulate water-absorbing agent are preferably bonded using (iv) an adhesive.

[0169] The adhesive used may be a solution type, but in view of the labor required for removing the solvent, the problem of the remaining solvent, and the problem of productivity, a hot melt adhesive is preferred, which has high productivity and does not have the problem of the remaining solvent. In the present invention, the hot melt adhesive may be contained in advance on the surface of the substrate or the particulate water absorbing agent, or the hot melt adhesive may be used separately in the manufacturing process of the water absorbent sheet. The form and melting point of the hot melt adhesive can be appropriately selected, and may be particulate, fibrous, net, or film, or may be liquid melted by heating. From the viewpoint of applying the adhesive uniformly, it is preferable to spray the molten hot melt adhesive.

[0170] In a preferred embodiment, when the surface of the first substrate facing the water-absorbing layer is raised, the hot melt adhesive is sprayed onto the second substrate. The first substrate sprayed with the particulate water-absorbing agent and the second substrate sprayed with the hot melt adhesive are superimposed such that the surface sprayed with the particulate water-absorbing agent and the surface sprayed with the hot melt adhesive face each other, and then pressed together to produce a water-absorbent sheet.

[0171] The hot melt adhesive used in the present invention can be appropriately selected, but preferably, one or more types selected from ethylene-vinyl acetate copolymer adhesives, styrene-based elastomer adhesives, polyolefin-based adhesives, polyester-based adhesives, etc. can be appropriately used.

[0172] Specifically, examples of polyolefin-based adhesives include polyethylene, polypropylene, and atactic polypropylene; examples of styrene-based elastomer adhesives include styrene block copolymers such as styrene-isoprene block copolymer (SIS), styrene-butadiene block copolymer (SBS), styrene-isobutylene block copolymer (SIBS), and styrene-ethylene-butylene-styrene block copolymer (SEBS); examples of polyester-based adhesives include polyethylene terephthalate (PET), polybutylene terephthalate (PBT), and copolymer polyester; examples of ethylene-vinyl acetate copolymer adhesives include ethylene-vinyl acetate copolymer (EVA) adhesives; ethylene-ethyl acrylate copolymer (EEA), ethylene-butyl acrylate copolymer (EBA), and the like.

[0173] Commercially available hot melt adhesives include, for example, JaourMelt 3889U (manufactured by JAOUR HOT MELT ADHESIVE, main components: styrene block copolymer, hydrocarbon resin, white mineral oil), MORESCO MELT TN-640Z (manufactured by MORESCO CORPORATION), MORESCO MELT TN-781Z (manufactured by MORESCO CORPORATION), MORESCO MELT TN-262Z (manufactured by MORESCO CORPORATION), and the like.

[0174] In the water-absorbent sheet and / or its manufacturing method according to one embodiment of the present invention, the water-absorbent sheet preferably contains an adhesive, the adhesive is preferably a hot melt adhesive, and the amount (content) of the adhesive (e.g., hot melt adhesive) used is preferably 3.0 times or less, more preferably 0.01 to 2.5 times, and even more preferably 0.05 to 2.0 times, the mass of the particulate water-absorbing agent. If the content of the adhesive (particularly hot melt adhesive) is too high, not only is it disadvantageous in terms of cost and mass of the water-absorbent sheet (mass increase of the paper diaper), but it may also be that the particulate water-absorbing agent is restricted in swelling, thereby reducing the water-absorbing ability of the water-absorbent sheet.

[0175] [4. Absorbent Articles] The absorbent article according to one embodiment of the present invention has a structure in which the water-absorbent sheet described in [2] is sandwiched between a liquid-permeable sheet and a liquid-impermeable sheet. Here, the liquid-permeable sheet is located on the first substrate side, and the liquid-impermeable sheet is located on the second substrate side. That is, the absorbent article according to one embodiment of the present invention is formed by sandwiching the water-absorbent sheet of the present invention between a liquid-permeable sheet and a liquid-impermeable sheet, and the liquid-permeable sheet is located on the first substrate side, and the liquid-impermeable sheet is located on the second substrate side. Specific examples of absorbent articles include paper diapers, incontinence pads, sanitary napkins, pet sheets, food drip sheets, and waterproofing agents for power cables.

[0176] As the liquid permeable sheet and the liquid impermeable sheet, any sheet known in the technical field of absorbent articles can be used without any particular limitation. The absorbent article can be manufactured by a known method. EXAMPLES

[0177] The present invention will be described in more detail with reference to the following examples and comparative examples. However, the technical scope of the present invention is not limited to the following examples. In the following examples, unless otherwise specified, the operations were carried out under the conditions of room temperature (25°C) and relative humidity of 40 to 50% RH.

[0178] [Example A] <Production Example> [Production Example 1] By referring to the manufacturing examples, examples, and comparative examples described in the following patents, the CRC was appropriately adjusted by the amount of the internal crosslinking agent to obtain particulate water absorbing agents (1) to (3) made of polyacrylic acid (salt) resin. The physical properties of the obtained particulate water absorbing agents are shown in Table 1.

[0179] International Publication No. 2014 / 034897 International Publication No. 2017 / 170605 International Publication No. 2016 / 204302 International Publication No. 2014 / 054656 International Publication No. 2015 / 152299 International Publication No. 2018 / 062539 International Publication No. 2012 / 043821.

[0180] [Production Example of Acrylic Acid] Commercially available acrylic acid (2000 ppm acrylic acid dimer, 500 ppm acetic acid, 500 ppm propionic acid, 200 ppm p-methoxyphenol) was supplied to the bottom of a high-boiling impurity separation tower having 50 perforated trays without a weir, distilled at a reflux ratio of 1, and after removing dimers (acrylic acid dimers) composed of maleic acid and acrylic acid, crystallization was performed to obtain acrylic acid (20 ppm acrylic acid dimer, 50 ppm acetic acid, 50 ppm propionic acid, 1 ppm or less furfural, 1 ppm or less protoanemonin), and 50 ppm p-methoxyphenol was added after distillation.

[0181] [Method for producing aqueous sodium acrylate solution] According to Example 9 of US Patent No. 5,210,298, 1,390 g of the above acrylic acid was neutralized with 48% caustic soda at 20 to 40° C. to obtain a 100% neutralized aqueous sodium acrylate solution with a concentration of 37%.

[0182] <Particulate water absorbing agent (1)> A reaction solution was prepared by dissolving 4.11 g of polyethylene glycol diacrylate (average number of moles of ethylene oxide added: 9) in 5500 g (monomer concentration: 36.0% by mass) of an aqueous solution of sodium acrylate having a neutralization rate of 75 mol% obtained by mixing the acrylic acid obtained in the above-mentioned acrylic acid production example, the aqueous sodium acrylate solution obtained by the above-mentioned method for producing an aqueous sodium acrylate solution using the acrylic acid, and deionized water. Next, the reaction solution was supplied to a reactor formed by attaching a lid to a jacketed stainless steel double-arm kneader having an internal volume of 10 L and two sigma-type blades, and the system was replaced with nitrogen gas while maintaining the reaction solution at 30°C to remove dissolved oxygen in the reaction solution. Next, 28.66 g of a 10% by mass aqueous solution of sodium persulfate and 35.28 g of a 1% by mass aqueous solution of L-ascorbic acid were added while stirring the reaction solution, and polymerization started about 1 minute later. A hydrogel polymer was taken out 40 minutes after the start of polymerization. The obtained hydrogel polymer was fragmented into particles of about 2 to 4 mm. The fragmented hydrogel polymer was spread on a wire net with a mesh size of 50 mesh (300 μm) and dried with hot air at 175° C. for 65 minutes. The dried product was then pulverized using a roll mill, and further classified and mixed using a wire net with a mesh size of 600 μm to obtain an irregularly pulverized water absorbent resin (1-1) having an average particle size of 350 μm.

[0183] 100 parts by mass of the obtained water absorbent resin (1-1) was mixed by spraying with 4.03 parts by mass of a surface cross-linking agent aqueous solution consisting of 0.03 parts by mass of ethylene glycol diglycidyl ether, 1.0 parts by mass of propylene glycol, and 3.0 parts by mass of water. The above mixture was heat-treated for 40 minutes at a heat medium temperature of 100°C using a paddle-type mixing heat treatment machine to obtain a surface cross-linked water absorbent resin (1-2). 100 parts by mass of the obtained surface cross-linked water absorbent resin (1-2) was mixed by spraying with 3.0 parts by mass of water, cured at 60°C for 1 hour in a sealed container, and then passed through a sieve with an opening of 710 μm to obtain a water absorbent resin (1-3). 0.3 parts by mass of Aerosil 90G (hydrophilic amorphous silica, manufactured by Nippon Aerosil Co., Ltd.) was added to the water absorbent resin (1-3) and mixed to obtain a water absorbent resin, which was used as a particulate water absorbent (1).

[0184] <Particulate water absorbent (2)> 5.01 g of polyethylene glycol diacrylate (average number of moles of ethylene oxide added: 9) was dissolved in 5500 g (monomer concentration: 36.0% by mass) of an aqueous solution of sodium acrylate having a neutralization rate of 75 mol% obtained by mixing the acrylic acid obtained in the above-mentioned acrylic acid production example, the aqueous sodium acrylate solution obtained by the above-mentioned method for producing an aqueous sodium acrylate solution using the acrylic acid, and deionized water to obtain a reaction solution. Next, the reaction solution was supplied to a reactor formed by attaching a lid to a jacketed stainless steel double-arm kneader having an internal volume of 10 L and two sigma-type blades, and the system was replaced with nitrogen gas while maintaining the reaction solution at 30°C to remove dissolved oxygen in the reaction solution. Next, 29.07 g of a 10% by mass aqueous solution of sodium persulfate and 35.78 g of a 1% by mass aqueous solution of L-ascorbic acid were added while stirring the reaction solution, and polymerization started about 1 minute later. 40 minutes after the start of polymerization, a hydrogel polymer was taken out. The obtained hydrogel polymer was fragmented into particles of about 2 to 4 mm. The fragmented hydrogel polymer was spread on a wire net with a mesh size of 50 mesh (300 μm) and dried with hot air at 175° C. for 65 minutes. The dried product was then pulverized using a roll mill, and further classified and mixed using a wire net with a mesh size of 600 μm to obtain an irregularly pulverized water absorbent resin (2-1) having an average particle size of 350 μm.

[0185] 100 parts by mass of the obtained water absorbent resin (2-1) was mixed by spraying with 4.03 parts by mass of a surface cross-linking agent aqueous solution consisting of 0.03 parts by mass of ethylene glycol diglycidyl ether, 1.0 parts by mass of propylene glycol, and 3.0 parts by mass of water. The mixture was heat-treated for 40 minutes at a heat medium temperature of 100°C using a paddle-type mixing heat treatment machine to obtain a surface cross-linked water absorbent resin (2-2). 100 parts by mass of the obtained surface cross-linked water absorbent resin (2-2) was mixed by spraying with 3.0 parts by mass of water, cured at 60°C for 1 hour in a sealed container, and then passed through a sieve with a mesh size of 710 μm to obtain a water absorbent resin (2-3). 0.3 parts by mass of Aerosil 90G (hydrophilic amorphous silica, manufactured by Nippon Aerosil Co., Ltd.) was added to the water absorbent resin (2-3) and mixed to obtain a water absorbent resin as a particulate water absorbent (2).

[0186] <Particulate water absorbing agent (3)> 3.77 g of polyethylene glycol diacrylate (average number of moles of ethylene oxide added: 9) was dissolved in 5500 g (monomer concentration: 38.0% by mass) of an aqueous solution of sodium acrylate having a neutralization rate of 75 mol% obtained by mixing the acrylic acid obtained in the above-mentioned acrylic acid production example, the aqueous sodium acrylate solution obtained by the above-mentioned method for producing an aqueous sodium acrylate solution using the acrylic acid, and deionized water to obtain a reaction solution. Next, the reaction solution was supplied to a reactor formed by attaching a lid to a jacketed stainless steel double-arm kneader having an internal volume of 10 L and two sigma-type blades, and the system was replaced with nitrogen gas while maintaining the reaction solution at 30°C to remove dissolved oxygen in the reaction solution. Next, 30.68 g of a 10% by mass aqueous solution of sodium persulfate and 37.76 g of a 1% by mass aqueous solution of L-ascorbic acid were added while stirring the reaction solution, and polymerization started about 1 minute later. 40 minutes after the start of polymerization, a hydrogel polymer was taken out. The obtained hydrogel polymer was fragmented into particles of about 2 to 4 mm. The fragmented hydrogel polymer was spread on a wire net with a mesh size of 50 mesh (300 μm) and dried with hot air at 175° C. for 65 minutes. The dried product was then pulverized using a roll mill, and further classified and mixed using a wire net with a mesh size of 600 μm to obtain an irregularly pulverized water absorbent resin (3-1) having an average particle size of 350 μm.

[0187] To 100 parts by mass of the obtained water-absorbing resin (3-1), 3.83 parts by mass of an aqueous solution of a surface crosslinking agent composed of 0.03 parts by mass of ethylene glycol diglycidyl ether, 0.3 parts by mass of 1,4-butanediol, 0.5 parts by mass of propylene glycol, and 3.0 parts by mass of water was spray-mixed. The above mixture was heat-treated at a heat medium temperature of 195°C for 40 minutes using a paddle-type mixing and heat-treating machine to obtain a surface-crosslinked water-absorbing resin (3-2). To 100 parts by mass of the obtained surface-crosslinked water-absorbing resin (3-2), 1.0 part by mass of water was spray-mixed, cured at 60°C for 1 hour in a sealed container, and then passed through a sieve with an opening of 710 μm to obtain a water-absorbing resin (3-3). A water-absorbing resin obtained by adding 0.3 part by mass of Aerosil 200 (hydrophilic amorphous silica, manufactured by Nippon Aerosil Co., Ltd.) to the water-absorbing resin (3-3) and mixing was used as the particulate water absorbent (3).

[0188] [Removal of Water-Absorbing Resin from Commercially Available Paper Diapers] <Particulate Water Absorbent (4)> The water-absorbing resin was taken out from commercially available paper diapers (Moony Air Fit (L size, Lot No. 201512163072), manufactured by Unicharm, purchased in May 2016). At the time of removal, only the water-absorbing resin was taken out so that cotton-like pulp and the like were not mixed. The removed water-absorbing resin had a particle shape in which spherical particles were granulated. This water-absorbing resin was used as the particulate water absorbent (4).

[0189] [Method for Measuring Physical Properties of Particulate Water Absorbent] <Weight-Average Particle Diameter> The particle diameter of the particulate water absorbent (or particulate water-absorbing resin, water-absorbing resin particles) according to an embodiment of the present invention is the weight-average particle diameter obtained according to the measurement method of "PSD" defined in ERT420.2-02. The weight-average particle diameters of the respective particulate water absorbents are shown in Table 1.

[0190] <CRC (Water Absorption Ratio under Unpressurized Conditions) (ERT441.2-02)> 0.2g of the particulate water absorbing agent (weight before water absorption) is placed in a nonwoven bag, and then immersed in a large excess of 0.9% by mass sodium chloride aqueous solution for 30 minutes to allow free swelling, and then the weight of the particulate water absorbing agent after water absorption is measured after draining the water with a centrifuge (250G). The water absorption ratio (unit: g / g) is calculated by "(weight of particulate water absorbing agent after water absorption - weight of particulate water absorbing agent before water absorption) / (weight of particulate water absorbing agent before water absorption) x 100". The CRC of each particulate water absorbing agent is shown in Table 1.

[0191] <Surface tension> In the present invention, the surface tension means the surface tension of an aqueous solution when the particulate water absorbing agent is dispersed in a 0.90 mass % sodium chloride aqueous solution.

[0192] 50 ml of physiological saline adjusted to 20°C is placed in a thoroughly washed 100 ml beaker, and the surface tension of the physiological saline is measured using a surface tensiometer (K11 automatic surface tensiometer manufactured by KRUSS). Note that in the present invention, a plate method using a platinum plate is adopted, and the plate is thoroughly washed with deionized water and heated and washed with a gas burner before each measurement.

[0193] Next, a thoroughly washed 25 mm long fluororesin rotor and 0.5 g of the particulate water absorbing agent are placed in a beaker containing the physiological saline after surface tension measurement, adjusted to 20°C, and stirred for 4 minutes at 500 rpm. After 4 minutes, the stirring is stopped and the water-absorbed particulate water absorbing agent settles, and the surface tension of the supernatant liquid is measured again by carrying out the same operation. Here, the surface tension of the particulate water absorbing agent (unit: mN / m) is obtained from the surface tension of the supernatant liquid when the particulate water absorbing agent is dispersed in physiological saline. The surface tension of each particulate water absorbing agent is shown in Table 1.

[0194] [Example] [Example 1] Nonwoven fabric E, 10cm long and 40cm wide (mainly made of pulp fiber. Thickness: 0.4mm. Made using the airlaid method. Corresponds to the second base material. Weight: 47g / m 2) and evenly spread 0.5 to 0.7 g of an adhesive containing styrene-butadiene rubber (Spray Glue 77, manufactured by 3M Japan Ltd.) (spray amount: 12.5 to 17.5 g / m 2 ), and then 9.0 g (spraying amount: 225 g / m) of particulate water absorbing agent (1) was sprayed on the adhesive sprayed surface. 2 ) was distributed evenly.

[0195] Next, a piece of air-through nonwoven fabric A (corresponding to the first substrate) containing olefin as the main component and having a thickness of 1.4 mm was cut into a length of 10 cm and a width of 40 cm. The basis weight was 41 g / m 2 ) was placed on the surface of the nonwoven fabric E on which the particulate water-absorbing agent had been sprayed, and pressed to obtain an intermediate sheet X.

[0196] Next, cut a spunbond nonwoven fabric (equivalent to a wrapping sheet, basis weight: 13 g / m) with a thickness of 0.1 mm, whose main component is olefin, into a length of 24 cm and a width of 40 cm. 2 , Bulk density 0.13g / cm 3 ) was laid out, and the intermediate sheet X was placed so that the nonwoven fabric A side of the intermediate sheet X faced and contacted the spunbond nonwoven fabric.

[0197] Next, 0.1 to 0.2 g of an adhesive containing styrene-butadiene rubber (Spray Glue 77, manufactured by 3M Japan Ltd.) was uniformly sprayed onto the surface (upper surface) of the nonwoven fabric E side of the intermediate sheet X, and then the excess portion of the spunbond nonwoven fabric was folded and wrapped so that the nonwoven fabric E (the surface of the intermediate sheet X facing the nonwoven fabric E) and the spunbond nonwoven fabric were in contact with each other, and the sheet was turned upside down and then pressed to obtain a water-absorbent sheet (1).

[0198] [Example 2] A spunbond nonwoven fabric (corresponding to a wrapping sheet) having a thickness of 0.1 mm and mainly composed of olefin, cut to a length of 24 cm and a width of 40 cm, was laid on top of the spunbond nonwoven fabric, and an air-through nonwoven fabric A (corresponding to a first substrate) having a thickness of 1.4 mm and mainly composed of olefin, cut to a length of 10 cm and a width of 40 cm, was placed on the spunbond nonwoven fabric. 9.0 g (spray amount: 225 g / m) of the particulate water-absorbing agent (1) was applied to the surface of the nonwoven fabric A. 2 ) was distributed evenly.

[0199] Next, nonwoven fabric E (mainly made of pulp fiber, thickness 0.4 mm, produced by the airlaid method) was cut to a length of 10 cm and width of 40 cm. It corresponds to the second base material. Basis weight: 47 g / m 2 0.5 to 0.7 g of an adhesive containing styrene butadiene rubber (Spray Glue 77, manufactured by 3M Japan Ltd.) was evenly sprayed onto the surface of the board (spray amount: 12.5 to 17.5 g / m). 2 After that, the surface of the nonwoven fabric A on which the particulate water absorbent was sprayed and the surface of the nonwoven fabric E on which the adhesive was sprayed were placed face to face (contacted), pressed together, and then 0.1 to 0.2 g of an adhesive containing styrene butadiene rubber (Spray Glue 77, manufactured by 3M Japan Ltd.) was sprayed evenly onto the nonwoven fabric E (spray amount: 2.5 to 5.0 g / m2). 2 ), an intermediate sheet Y was obtained.

[0200] Next, the excess portion of the spunbond nonwoven fabric located at the bottom layer was folded and wrapped so that the spunbond nonwoven fabric was in contact with the nonwoven fabric E of the intermediate sheet Y (the surface of the intermediate sheet Y facing the nonwoven fabric E), and the sheet was turned upside down and then pressed to obtain the water-absorbent sheet (2).

[0201] [Example 3] A water-absorbent sheet (3) was obtained in the same manner as in Example 2, except that the particulate water-absorbing agent (2) was used instead of the particulate water-absorbing agent (1).

[0202] [Example 4] A water-absorbent sheet (4) was obtained in the same manner as in Example 2, except that the particulate water-absorbing agent (3) was used instead of the particulate water-absorbing agent (1).

[0203] [Example 5] A water-absorbent sheet (5) was obtained in the same manner as in Example 2, except that the particulate water-absorbing agent (4) was used instead of the particulate water-absorbing agent (1).

[0204] [Example 6] Instead of air-through nonwoven fabric A, air-through nonwoven fabric B (basis weight: 43 g / m) with a thickness of 2.0 mm was used. 2 A water-absorbent sheet (6) was obtained in the same manner as in Example 2, except that the above-mentioned cellulose acetate sheet (1) was used.

[0205] [Example 7] Instead of air-through nonwoven fabric A, air-through nonwoven fabric C with a thickness of 1.5 mm (basis weight: 37 g / m 2 A water-absorbent sheet (7) was obtained in the same manner as in Example 2, except that the above-mentioned cellulose acetate sheet (1) was used.

[0206] [Example 8] Instead of air-through nonwoven fabric A, air-through nonwoven fabric D with a thickness of 1.5 mm (basis weight: 45 g / m 2 A water-absorbent sheet (8) was obtained in the same manner as in Example 2, except that the above-mentioned cellulose acetate sheet (1) was used.

[0207] [Example 9] Instead of nonwoven fabric E, spunlace nonwoven fabric F (made of PET resin and pulp, with a thickness of 0.4 mm and a basis weight of 45 g / m2) was used. 2 A water-absorbent sheet (9) was obtained in the same manner as in Example 2, except that the above-mentioned water-absorbent sheet (9) was used.

[0208] [Example 10] Instead of nonwoven fabric A, we used air-through nonwoven fabric G (weight: 20 g / m) with a thickness of 0.7 mm. 2 A water-absorbent sheet (10) was obtained in the same manner as in Example 2, except that the above-mentioned cellulose acetate sheet (10) was used.

[0209] [Comparative Example 1] An air-through nonwoven fabric A of 1.4 mm thickness, mainly composed of olefin, cut to 10 cm length and 40 cm width, was placed on the surface of the nonwoven fabric A, and 4.5 g of the particulate water absorbing agent (1) (spray amount: 112.5 g / m) was applied. 2 ) was distributed evenly.

[0210] Next, nonwoven fabric E (mainly made of pulp fiber, thickness 0.4 mm, produced by the airlaid method) was cut to a length of 10 cm and width of 40 cm. It corresponds to the second base material. Basis weight: 47 g / m 20.5 to 0.7 g of an adhesive containing styrene butadiene rubber (Spray Glue 77, manufactured by 3M Japan Ltd.) was evenly sprayed onto the surface of the board (spray amount: 12.5 to 17.5 g / m). 2 Thereafter, the surface of nonwoven fabric A on which the particulate water absorbing agent was sprayed and the surface of nonwoven fabric E on which the adhesive was sprayed were placed face to face (contacted) and pressed together.

[0211] Next, 4.5 g of the particulate water absorbing agent (1) (spray amount: 112.5 g / m) was sprayed onto the surface of the nonwoven fabric A on the side not facing the particulate water absorbing agent (1). 2 ) was distributed evenly.

[0212] Next, nonwoven fabric E (similar to nonwoven fabric E used above (thickness 0.4 mm) corresponding to the first substrate) was cut to a length of 10 cm and a width of 40 cm. On the surface of the fabric, 0.5 to 0.7 g of an adhesive containing styrene-butadiene rubber (Spray Glue 77, manufactured by 3M Japan Ltd.) was uniformly sprayed (amount sprayed: 12.5 to 17.5 g / m 2 Thereafter, the surface of the nonwoven fabric A on which the particulate water absorbing agent was sprayed and the surface of the nonwoven fabric E on which the adhesive was sprayed were placed face to face (contacted), and pressed together to obtain an intermediate sheet Z.

[0213] Finally, 0.1 to 0.2 g of adhesive containing styrene-butadiene rubber (Spray Glue 77, manufactured by 3M Japan Ltd.) was uniformly sprayed (spray amount: 2.5 to 5.0 g / m) on the nonwoven fabric E of the intermediate sheet Z (the side of the nonwoven fabric on which the particulate water absorbent was sprayed the first time). 2 ), and then the sheet was cut to a size of 24 cm length and 40 cm width, wrapped in a 0.1 mm thick spunbond nonwoven fabric mainly composed of olefin, and pressed to obtain a water-absorbent sheet (11).

[0214] In Comparative Example 1, the transmittance of the particulate water absorbing agent of the nonwoven fabric E corresponding to the first substrate was 0.3 mass%, and the content of the particulate water absorbing agent was 0%. In the water absorbent sheet obtained in Comparative Example 1, the ratio of "thickness of the first substrate / thickness of the second substrate" was 1.

[0215] [Comparative Example 2] A spunbond nonwoven fabric (corresponding to a wrapping sheet) having a thickness of 0.1 mm and mainly composed of olefin, cut to a length of 24 cm and a width of 40 cm, was laid on top of the spunbond nonwoven fabric, and an air-through nonwoven fabric A (corresponding to a first substrate) having a thickness of 1.4 mm and mainly composed of olefin, cut to a length of 10 cm and a width of 40 cm, was placed on the spunbond nonwoven fabric. 9.0 g (spray amount: 225 g / m) of the particulate water-absorbing agent (1) was applied to the surface of the nonwoven fabric A. 2 ) was distributed evenly.

[0216] Next, 0.5 to 0.7 g of an adhesive containing styrene-butadiene rubber (Spray Glue 77, manufactured by 3M Japan Ltd.) was uniformly sprayed (amount sprayed: 12.5 to 17.5 g / m) on the surface of a 1.4 mm-thick air-through nonwoven fabric A (corresponding to the second substrate; hereinafter, for convenience, this nonwoven fabric A2) cut into a size of 10 cm length and 40 cm width. 2 Thereafter, the surface of the nonwoven fabric A2 on which the adhesive has been sprayed and the surface of the nonwoven fabric A on which the particulate water absorbing agent has been sprayed are placed face to face (contacted) and pressed together. Then, 0.1 to 0.2 g of an adhesive containing styrene butadiene rubber (Spray Glue 77, manufactured by 3M Japan Ltd.) is sprayed uniformly onto the nonwoven fabric A2 (spray amount: 2.5 to 5.0 g / m2). 2 ), to obtain intermediate sheet Z2.

[0217] Next, the excess portion of the spunbond nonwoven fabric located at the bottom layer was folded and wrapped so that the intermediate sheet Z2 and the spunbond nonwoven fabric were in contact with each other, and then the intermediate sheet Z2 was turned upside down and pressed to obtain a water-absorbent sheet (12).

[0218] [Comparative Example 3] A spunbond nonwoven fabric (corresponding to a wrapping sheet) having a thickness of 0.1 mm and mainly composed of olefin, cut to a length of 24 cm and a width of 40 cm, was laid on top of the spunbond nonwoven fabric, and an air-through nonwoven fabric A (corresponding to a first substrate) having a thickness of 1.4 mm and mainly composed of olefin, cut to a length of 10 cm and a width of 40 cm, was placed on the spunbond nonwoven fabric. 9.0 g (spray amount: 225 g / m) of the particulate water-absorbing agent (1) was applied to the surface of the nonwoven fabric A. 2 ) was distributed evenly.

[0219] Next, the remaining part of the spunbond nonwoven fabric located at the bottom layer was folded and wrapped so that the surface of the nonwoven fabric on which the particulate water absorbing agent (1) was scattered was in contact with the spunbond nonwoven fabric, and after turning it upside down, it was pressed and bonded to obtain a water absorbent sheet (13). Note that only the part of the spunbond nonwoven fabric that was in contact with the surface of the nonwoven fabric on which the particulate water absorbing agent (1) was scattered was uniformly sprayed with 0.5 to 0.7 g of an adhesive containing styrene butadiene rubber (Spray Glue 77, 3M Japan Ltd.) before wrapping.

[0220] [Comparative Example 4] Instead of air-through nonwoven fabric A, spunlace nonwoven fabric F (made of PET resin and pulp, with a thickness of 0.4 mm and a basis weight of 45 g / m2) was used. 2 A water-absorbent sheet (14) was obtained in the same manner as in Example 2, except that a water-absorbent sheet (14) was used.

[0221] In Comparative Example 4, the transmittance of the particulate water absorbing agent of the nonwoven fabric F corresponding to the first substrate was 1 mass %, and the content of the particulate water absorbing agent was 0%. In the water absorbent sheet obtained in Comparative Example 4, the ratio of "thickness of the first substrate / thickness of the second substrate" was 1.

[0222] The nonwoven fabrics A to G used in this example were all water-permeable sheets.

[0223] [Method of measuring physical properties of nonwoven fabric] The thickness, bulk density, liquid diffusion area, and permeability of the particulate water absorbing agent through the nonwoven fabric of the nonwoven fabrics A to F used in Examples 1 to 10 and Comparative Examples 1 to 4 were measured according to the following methods.

[0224] <Measurement of thickness of nonwoven fabric> Measurements were taken using a large-type dial thickness gauge (thickness measuring device) (manufactured by Ozaki Seisakusho Co., Ltd., model number: JB, gauge head: anvil top and bottom φ50 mm). Measurements were taken five times at different points, and the measured value was the average of the five points. When measuring the thickness, the hand was slowly released from the handle so as to apply as little pressure as possible to the nonwoven fabric, and the thickness was measured.

[0225] <How to calculate the bulk density of nonwoven fabric> The weight of the nonwoven fabric cut into a size of 10 cm or more in length and 40 cm or more in width was measured. The volume of the nonwoven fabric was calculated by multiplying the length and width of the nonwoven fabric by the thickness measured in the <Thickness Measurement>, and the weight of the nonwoven fabric was divided by the volume of the nonwoven fabric to calculate the bulk density.

[0226] <Method for measuring the liquid diffusion area of ​​nonwoven fabric> A 30 cm diameter sieve with a mesh size of 2 mm and linearity of 0.9 mm was placed on a flat surface, and a nonwoven fabric cut into a 10 cm square (second substrate) was placed on it. A 0.50 mm diameter needle was attached to a 1 ml syringe, and 1.00 g of saline containing 20 ppm of Blue No. 1 Reagent was measured and the saline from the syringe was injected vertically into the center of the nonwoven fabric on the sieve. At this time, the sieve mesh and the flat surface were sufficiently separated so that the saline that had passed through the nonwoven fabric and mesh did not come into contact with the mesh. When the nonwoven fabric absorbed the saline and the diffusion of the liquid was completed, the area over which the saline had diffused was measured.

[0227] <Permeability of particulate water absorbent through nonwoven fabric> A nonwoven fabric (first substrate 11) cut to a diameter of 80 mm is placed in a JIS standard sieve (The IIDA TESTING SIEVE: inner diameter 80 mm; JIS Z8801-1 (2000)) having a mesh 32 with an opening of 850 μm or a sieve 31 equivalent to the JIS standard sieve, as shown in FIG. 5, and the periphery is secured with tape 33 (ensuring an area of ​​at least 75 mm in diameter through which particles can pass). The nonwoven fabric (first substrate 11) may be removed from a water-absorbent sheet by the method described below. 10.0 g of the particulate water absorbing agent 14 (weight average particle diameter: 367 μm, particle size distribution: 6.1% from 850 μm to 600 μm, 14.5% from 600 μm to 500 μm, 50% from 500 μm to 300 μm, 27.6% from 300 μm to 150 μm, 1.9% from 150 μm to 45 μm, 0.1% below 45 μm) was put into the sieve 31 from above (the direction of the arrow in FIG. 5 ) and shaken for 5 minutes under the conditions of room temperature (20 to 25° C.) and relative humidity 50% RH using a low tap type sieve shaker (ES-65 type sieve shaker manufactured by Iida Manufacturing Co., Ltd.; rotation speed 230 rpm, impact speed 130 rpm). After shaking, the mass (W(g)) of the nonwoven fabric (first substrate 11) and the particulate water absorbing agent 14 that passed through the mesh 32 of the sieve 31 corresponding to the JIS standard sieve (i.e., the particulate water absorbing agent 14 present in the portion 31a below the mesh 32 of the sieve 31) was measured, and the transmittance of the particulate water absorbing agent was calculated according to the following formula (i). The measurement was performed three times, and the average value was calculated. In Table 1, the transmittance (mass%) of the particulate water absorbing agent is indicated as "Transmittance (mass%)".

[0228]

number

[0229] <Method of Removing Particulate Water Absorbing Agent from Water Absorbent Sheet> The particulate water absorbing agent (the intermediate sheet and the particulate water absorbing agent when the intermediate sheet is included) was taken out by peeling off the upper nonwoven fabric and the lower nonwoven fabric from the water absorbent sheet. The particulate water absorbing agent attached to the upper and lower nonwoven fabrics and the intermediate sheet was also taken out. When peeling off the upper and lower nonwoven fabrics, the water absorbent sheet was cooled, and the adhesive (hot melt adhesive or spray glue) that attached the nonwoven fabric and the particulate water absorbing agent was sufficiently weakened before peeling off. By following this procedure, the nonwoven fabric can be taken out without changing the fiber or structure thickness, and the transmittance can be accurately measured. The water absorbent sheet can be cooled by various means such as placing it in a thermostatic chamber at -10°C or less for a certain period of time, spraying it with a cooling spray, or pouring liquid nitrogen, but there is no particular limitation as long as it is performed under conditions that do not change the fiber, structure, or thickness of the nonwoven fabric and do not cause the particulate water absorbing agent contained in the water absorbent sheet to absorb moisture.

[0230] In addition, when the particulate water absorbing agent taken out has absorbed moisture, the moisture content may be adjusted to 10 mass % or less, preferably 5±2 mass %, for example, by drying, and the transmittance and various physical properties specified in the present application may be measured. The drying conditions for adjusting the moisture content are not particularly limited as long as they do not cause decomposition or denaturation of the water absorbent resin (particulate water absorbing agent), but reduced pressure drying is preferable.

[0231] <Measurement of the content of the particulate water absorbing agent in the upper nonwoven fabric (corresponding to the first base material)> The upper nonwoven fabric was cut into a square of 10 mm length and 10 mm width (with the thickness unchanged) and measured using a microfocus X-ray CT system inspeXio SMX-100CT manufactured by Shimadzu Corporation. The measurement conditions are as follows:

[0232] [X-ray CT scan] Image width (pixels): 512 Image vertical size (pixels): 512 X-ray tube voltage (kV): 50 X-ray tube current (μA): 40 Inch size(inch):4.0 X-ray filter: None SDD (distance between the focal point of the X-ray source and the X-ray detector) (mm): 700 SRD (distance between the focal point of the X-ray source and the center of rotation of the measurement sample) (mm): 550 Scanning mode 1:CBCT Scanning mode 2: Normal scanning Scan angle: Full scan View count:2400 Average number: 5 Smoothing: YZ Slice thickness (mm): 0.166 BHC data: None Precision mode: Yes FOV XY (Maximum shooting area XY) (mm): 50.3 FOV Z (maximum shooting area Z) (mm): 40.0.

[0233] Next, the X-ray CT data was analyzed using Win ROOF, an analysis software made by Mitani Shoji Co., Ltd., in the following procedure.

[0234] (1) Open Win ROOF and select the image (JPEG) you want to analyze that was saved in the X-ray CT scan.

[0235] (2) Click (select) the following on the screen: Binary Processing, Automatic Binarization, Mode Method, Threshold (adjust as necessary), and Execute.

[0236] (3) A polygonal ROI is selected to surround the particulate water-absorbing agent in the first base material (upper nonwoven fabric), and the area of ​​the particulate water-absorbing agent is calculated.

[0237] (4) In the same manner as in (3), the total area of ​​the particulate water-absorbing agent in the water-absorbent sheet is calculated.

[0238] From the calculation results, the content ratio (%) of the particulate water absorbing agent in the first base material was calculated according to the following formula.

[0239] Content ratio (%) of particulate water absorbing agent in first base material=area (I) of particulate water absorbing agent in first base material / total area (II) of particulate water absorbing agent×100 That is, the content ratio of the particulate water absorbing agent in the first base material is expressed as an area % relative to the total area of ​​the particulate water absorbing agent. Note that, since the particulate water absorbing agent is present, even if present, on the surface of the first base material on the side where the absorbed liquid is introduced, it is less than several % and therefore can be considered as not being present.

[0240] [Method of evaluating water-absorbent sheets] <Return amount (specific return amount evaluation)> As shown in Fig. 6, the absorbent sheet 10, which was made to be 10 cm long and 40 cm wide, was wrapped in a liquid-impermeable sheet 21, which was 14 cm long and 40 cm wide, so that an opening was formed at the top. The absorbent sheet 10 wrapped in the liquid-impermeable sheet 21 was placed on a flat surface, and a liquid injection tube 41 (Fig. 7) was placed on top of it in the center of the absorbent sheet 10, as shown in Fig. 8. In this state, 80 g of a 0.9 wt % aqueous sodium chloride solution at 23°C was poured into the liquid injection tube 41 using a funnel 42 capable of pouring liquid at a flow rate of 7 ml / sec (Fig. 9). In this case, the liquid was poured into the absorbent sheet 10 exposed from the liquid-impermeable sheet 21. Ten minutes after the liquid was poured in, twenty sheets of filter paper 43 (type No. 2, manufactured by ADVANTEC; circular, 110 mm diameter) whose weight had been measured in advance were placed in the center of the absorbent sheet 10, and a circular weight 44 (1200 g) with a diameter of 100 mm was further placed on top and held for one minute. After one minute, the weight 44 was removed, and the first amount of backflow (g) was measured from the weight increase of the filter paper 43. One minute after the weight 44 was removed, the same procedure (pouring in liquid → 10 minutes after pouring, placing filter paper 43 and weight 44 (1200 g) and holding for one minute → holding for one minute → removing the weight, measuring the amount of backflow) was repeated, and the second amount of backflow (g) and the third amount of backflow (g) were measured. The total of the measured amounts of backflow from the first to third times are shown in Table 1.

[0241] <Leakage amount (diagonal evaluation)> The leakage rate was measured using the device shown in FIG.

[0242] In outline, this is a mechanism that uses a commercially available experimental stand 60 and pipes 61 to tilt and fix an acrylic plate 63, then pours saline solution vertically from above using a funnel onto an absorbent sheet fixed onto the plate, and measures the amount of leakage. The detailed specifications are shown below.

[0243] The acrylic plate 63 had a length of 400 mm in the direction of the inclined surface, and was fixed by the stand 60 so that the angle it made with the horizontal was 20°. The acrylic plate 63 had a width of 200 mm and a thickness of 3 mm. The surface of the acrylic plate 63 was smooth, so liquid did not accumulate or be absorbed by the plate. Using the stand 60, a funnel 64 was fixed vertically above the inclined acrylic plate 63. The funnel 64 used was one that could input liquid at a rate of 7 mL / sec.

[0244] A metal tray 65 was placed under the acrylic plate 63 to receive all the test liquid that leaked out and record its mass to an accuracy of 0.1 g.

[0245] The inclined leakage test using such an apparatus was carried out as follows: As shown in FIG.

[0246] A mark was made 1.5 cm below the top end of the water-absorbent sheet, and the inlet of the funnel was fixed vertically above the mark at a distance of 15±2 mm.

[0247] 20 mL of saline was poured into the dropping funnel 64 at once. The amount of test liquid that flowed down the inclined acrylic plate 63 without being absorbed by the absorbent sheet 66 and entered the metal tray 65 was measured and recorded as the first leakage amount (mL) in the surface direction. After 10 minutes, 20 mL of saline was poured in the same way and the second leakage amount was measured, and after another 10 minutes, 20 mL of saline was poured in the same way and the third leakage amount was measured. The leakage amount in the table is the total value of the first to third leakage amounts.

[0248] Table 1 shows the configurations and evaluation results of the water-absorbent sheets of Examples 1 to 10 and Comparative Examples 1 to 4.

[0249] [Table 1]

[0250] From the above results, the water-absorbent sheets of Examples 1 to 10 had a significantly smaller amount of return water than the water-absorbent sheets of Comparative Examples 1 to 4, and also had a significantly reduced leakage from the water-absorbent sheets.

[0251] On the other hand, in Comparative Example 1, which had a multi-layer structure, and in Comparative Examples 2 and 4, in which the thickness ratio between the first base material and the second base material was 1, the amount of return increased significantly.

[0252] [Example 11] A spunbond nonwoven fabric (corresponding to a wrapping sheet) having a thickness of 0.1 mm and mainly composed of polyolefin fiber, cut to a length of 24 cm and a width of 40 cm, was laid down, and in the center of the spunbond nonwoven fabric, a brushed air-through nonwoven fabric A (corresponding to a first substrate) having a thickness of 1.4 mm and mainly composed of polyolefin fiber, cut to a length of 10 cm and a width of 40 cm, was placed. 9.0 g (spreading amount: 225 g / m) of the particulate water-absorbing agent (2) was applied to the brushed surface of the nonwoven fabric A. 2 The nonwoven fabric A was raised in the manner described below.

[0253] Next, nonwoven fabric E (mainly made of pulp fiber, thickness 0.4 mm, produced by the airlaid method) was cut to a length of 10 cm and width of 40 cm. It corresponds to the second base material. Basis weight: 47 g / m 2 0.8 g of hot melt adhesive (JaourMelt3889U, manufactured by JAOUR HOT MELT ADHESIVE, main components: styrene block copolymer, hydrocarbon resin, white mineral oil) heated to 135°C and made into a liquid was uniformly spread on the surface of the board (spray amount: 20.0 g / m 2 Thereafter, the surface of the nonwoven fabric A on which the particulate water absorbing agent was sprayed and the surface of the nonwoven fabric E on which the adhesive was sprayed were placed face to face (contacted) and pressed together to obtain an intermediate sheet Y.

[0254] On the surface of the nonwoven fabric E of the intermediate sheet Y, 0.3 g of a hot melt adhesive (JaourMelt3889U, manufactured by JAOUR HOT MELT ADHESIVE, main components: styrene block copolymer, hydrocarbon resin, white mineral oil) heated to 135°C and made into a liquid was sprayed (spray amount: 7.5 g / m 2 Next, the remaining portion of the spunbond nonwoven fabric was folded and wrapped so that the surface of the nonwoven fabric E of the intermediate sheet Y was in contact with the spunbond nonwoven fabric, and the intermediate sheet Y was turned upside down and then pressed to obtain a water-absorbent sheet (21).

[0255] [Example 12] The amount of particulate water absorbent applied was 12.0 g (application amount: 300 g / m 2 ) was used to obtain a water-absorbent sheet (22).

[0256] [Example 13] A water-absorbent sheet (23) was obtained in the same manner as in Example 12, except that nonwoven fabric A that had not been subjected to nap-raising treatment was used instead of nonwoven fabric A that had been subjected to nap-raising treatment.

[0257] [Example 14] The adhesive to be sprayed onto the nonwoven fabric E was 0.8 g (spray amount: 20.0 g / m) of an adhesive containing styrene butadiene rubber (Spray Glue 77, manufactured by 3M Japan Ltd.). 2 ) was used to obtain a water-absorbent sheet (24).

[0258] [Example 15] A water-absorbent sheet (25) was obtained in the same manner as in Example 12, except that a particulate water-absorbing agent (5) obtained by the following production method was used.

[0259] <Particulate water absorbent (5)> 5.03 g of polyethylene glycol diacrylate (average number of moles of ethylene oxide added: 9) was dissolved in 5500 g (monomer concentration: 38% by mass) of an aqueous solution of sodium acrylate having a neutralization rate of 75 mol% obtained by mixing the acrylic acid obtained in the above-mentioned acrylic acid production example, the aqueous sodium acrylate solution obtained by the above-mentioned method for producing an aqueous sodium acrylate solution using the acrylic acid, and deionized water to obtain a reaction solution. Next, the reaction solution was supplied to a reactor formed by attaching a lid to a jacketed stainless steel double-arm kneader having an internal volume of 10 L and two sigma-type blades, and the system was replaced with nitrogen gas while maintaining the reaction solution at 30°C to remove dissolved oxygen in the reaction solution. Next, 30.68 g of a 10% by mass aqueous solution of sodium persulfate and 37.76 g of a 1% by mass aqueous solution of L-ascorbic acid were added while stirring the reaction solution, and polymerization started about 1 minute later. 40 minutes after the start of polymerization, a hydrogel polymer was taken out. The obtained hydrogel polymer was fragmented into particles of about 2 to 4 mm. The fragmented hydrogel polymer was spread on a wire net with a mesh size of 50 mesh (300 μm) and dried with hot air at 175° C. for 65 minutes. The dried product was then pulverized using a roll mill, and further classified and mixed using a wire net with a mesh size of 600 μm to obtain an irregularly pulverized water absorbent resin (5-1) having an average particle size of 380 μm.

[0260] 100 parts by mass of the obtained water absorbent resin (5-1) was mixed by spraying with 3.83 parts by mass of a surface cross-linking agent aqueous solution consisting of 0.03 parts by mass of ethylene glycol diglycidyl ether, 0.3 parts by mass of 1,4-butanediol, 0.5 parts by mass of propylene glycol, and 3.0 parts by mass of water. The mixture was heat-treated for 40 minutes at a heat medium temperature of 210°C using a paddle-type mixing heat treatment machine to obtain a surface cross-linked water absorbent resin (5-2). 100 parts by mass of the obtained surface cross-linked water absorbent resin (5-2) was mixed by spraying with 1.0 part by mass of water, cured at 60°C for 1 hour in a sealed container, and then passed through a sieve with an opening of 710 μm to obtain a water absorbent resin (5-3). 0.3 parts by mass of Aerosil 200 (hydrophilic amorphous silica, manufactured by Nippon Aerosil Co., Ltd.) was added to the water absorbent resin (5-3) and mixed to obtain a water absorbent resin as a particulate water absorbent (5).

[0261] [Example 16] A water-absorbent sheet (26) was obtained in the same manner as in Example 12, except that a particulate water-absorbing agent (6) obtained by the following production method was used.

[0262] <Particulate water absorbing agent (6)> A reaction solution was prepared by dissolving 4.11 g of polyethylene glycol diacrylate (average number of moles of ethylene oxide added: 9) in 5500 g (monomer concentration: 36.0% by mass) of an aqueous solution of sodium acrylate having a neutralization rate of 75 mol% obtained by mixing the acrylic acid obtained in the above-mentioned acrylic acid production example, the aqueous sodium acrylate solution obtained by the above-mentioned method for producing an aqueous sodium acrylate solution using the acrylic acid, and deionized water. Next, the reaction solution was supplied to a reactor formed by attaching a lid to a jacketed stainless steel double-arm kneader having an internal volume of 10 L and two sigma-type blades, and the system was replaced with nitrogen gas while maintaining the reaction solution at 30°C to remove dissolved oxygen in the reaction solution. Next, 28.66 g of a 10% by mass aqueous solution of sodium persulfate and 35.28 g of a 1% by mass aqueous solution of L-ascorbic acid were added while stirring the reaction solution, and polymerization started about 1 minute later.

[0263] After 40 minutes from the start of polymerization, 181.5 g of water-absorbent resin fine powder of 150 μm or less was added, and the gel was crushed for 10 minutes by rotating the kneader blade at high speed (130 rpm), and then the hydrogel polymer was taken out. The obtained hydrogel polymer was fragmented into particles of about 1 to 2 mm. The fragmented hydrogel polymer was spread on a wire mesh of 50 mesh (opening size 300 μm) and dried with hot air at 175 ° C. for 65 minutes. Next, the dried product was pulverized using a roll mill, and further classified and mixed using a wire mesh with an opening of 600 μm to obtain an irregularly crushed water-absorbent resin (6-1) with an average particle size of 350 μm.

[0264] 100 parts by mass of the obtained water absorbent resin (6-1) was mixed by spraying with 4.03 parts by mass of a surface cross-linking agent aqueous solution consisting of 0.03 parts by mass of ethylene glycol diglycidyl ether, 1.0 parts by mass of propylene glycol, and 3.0 parts by mass of water. The mixture was heat-treated for 40 minutes at a heat medium temperature of 100°C using a paddle-type mixing heat treatment machine to obtain a surface cross-linked water absorbent resin (6-2). 100 parts by mass of the obtained surface cross-linked water absorbent resin (6-2) was mixed by spraying with 3.0 parts by mass of water, cured at 60°C for 1 hour in a sealed container, and then passed through a sieve with an opening of 710 μm to obtain a water absorbent resin (6-3). 0.3 parts by mass of Aerosil 90G (hydrophilic amorphous silica, manufactured by Nippon Aerosil Co., Ltd.) was added to the water absorbent resin (6-3) and mixed to obtain a water absorbent resin as a particulate water absorbent (6).

[0265] [Example 17] A water-absorbent sheet (27) was obtained in the same manner as in Example 12, except that a particulate water-absorbing agent (7) obtained by the following production method was used.

[0266] <Particulate water absorbing agent (7)> A 2-L polypropylene container was charged with 351.7 g of acrylic acid, 0.860 g (0.034 mol % relative to the carboxyl group-containing unsaturated monomer) of polyethylene glycol diacrylate (molecular weight 523) as an internal crosslinking agent, 2.15 g of a 1.0 wt % aqueous solution of trisodium diethylenetriaminepentaacetate (DTPA·3Na), 149.0 g of a 48.5 wt % aqueous solution of sodium hydroxide, and 336.2 g of deionized water (ion-exchanged water) and mixed to prepare an aqueous monomer solution (a').

[0267] Next, the monomer aqueous solution (a') was cooled while stirring. When the liquid temperature reached 40.0°C, 144.8 g of 48.5 wt% aqueous sodium hydroxide solution adjusted to 40°C was added and mixed to prepare the monomer aqueous solution (a). At this time, the temperature of the monomer aqueous solution (a) rose to 78.2°C due to the heat of neutralization in the second stage immediately after preparation. Immediately after starting to mix the 48.5 wt% aqueous sodium hydroxide solution, precipitates were observed, but they gradually dissolved and became a transparent homogeneous solution.

[0268] Next, 15.49 g of 4.0 wt % aqueous sodium persulfate solution was added to the stirred aqueous monomer solution (a), and the mixture was immediately poured into a stainless steel bat-shaped container (bottom surface 340×340 mm, height 25 mm, inner surface; Teflon (registered trademark) coating) in an open-air system. The time from the start of the second neutralization to pouring the aqueous monomer solution (a) into the bat-shaped container was 55 seconds, and the bat-shaped container was heated using a hot plate (NEO HOTPLATE HI-1000 / Iuchi Seiei-do Co., Ltd.) until the surface temperature reached 40° C.

[0269] The polymerization reaction started 60 seconds after the monomer aqueous solution (a) was poured into the bat-shaped container. The polymerization reaction proceeded by expanding and foaming in all directions while generating steam, and then contracted to a size slightly larger than the bat-shaped container. Three minutes after the start of the polymerization reaction, a hydrogel-like crosslinked polymer (hereinafter referred to as "hydrogel") (7-1) was taken out. The series of operations was carried out in an open-to-air system.

[0270] The hydrogel (7-1) obtained by the polymerization reaction was cut into strips and fed to a screw extruder for gel crushing to obtain a particulate hydrogel (7-2). The screw extruder was equipped with a perforated plate at the tip with a diameter of 100 mm, a hole diameter of 11.0 mm, 40 holes, an aperture ratio of 62.5%, and a thickness of 10 mm, and the outer diameter of the screw shaft was 86 mm.

[0271] The gel crushing was carried out by simultaneously feeding the rectangular hydrous gel (7-1) and steam from separate feed ports at a rate of 4640 g / min and 83 g / min, respectively, with the screw shaft of the screw extruder rotating at 130 rpm.

[0272] This particulate hydrogel (7-2) was spread on a 50-mesh wire net, dried with hot air at 190°C for 30 minutes, and the dried product was pulverized using a roll mill (WML type roll pulverizer / Inokuchi Giken Co., Ltd.), and further sieved with JIS sieves having openings of 850μm, 600μm, 500μm, 300μm, and 150μm, and then mixed to obtain an irregularly pulverized precursor water absorbent resin (A) having a weight average particle diameter (D50) of 305μm and a logarithmic standard deviation (σζ) of particle size distribution of 0.35. The centrifuge retention capacity (CRC) of the precursor water absorbent resin (A) was 48.4 (g / g).

[0273] A surface crosslinking agent solution consisting of 0.03 parts by weight of ethylene glycol diglycidyl ether, 1.5 parts by weight of propylene glycol, and 3.5 parts by weight of deionized water was uniformly mixed with 100 parts by weight of the precursor water absorbent resin (A), and the mixture was heated at 100°C for about 30 minutes so that the CRC of the obtained water absorbent resin (1) was about 35 [g / g]. After cooling, an aqueous solution consisting of 1 part by weight of deionized water and 0.05 parts by weight of diethylenetriaminepentaacetic acid·trisodium (DTPA·3Na) was uniformly mixed with 100 parts by weight of the water absorbent resin. After drying at 60°C for 1 hour, the mixture was passed through a JIS standard sieve with an opening of 850 μm, and 0.3 parts by weight of silicon dioxide (trade name: Reoloseal QS-20, manufactured by Tokuyama Corporation) was mixed. The mixture was prepared by putting 30 g of the water-absorbent resin together with silicon dioxide into a 225 mL mayonnaise bottle and mixing for 60 minutes by vibration using a Turbula Shaker Mixer T2F (manufactured by Shinmaru Enterprises Co., Ltd.) to obtain water-absorbent resin particles (7).

[0274] [Example 18] A 0.1 mm thick spunbond nonwoven fabric (corresponding to a wrapping sheet) made primarily of polyolefin fiber and cut to 24 cm length and 40 cm width was laid out, and a 1.4 mm thick, raised air-through nonwoven fabric A (corresponding to a first substrate) made primarily of polyolefin fiber and cut to 10 cm length and 40 cm width was placed in the center of the spunbond nonwoven fabric. 0.8 g of hot melt adhesive (JaourMelt3889U, manufactured by JAOUR HOT MELT ADHESIVE, main components: styrene block copolymer, hydrocarbon resin, white mineral oil) heated to 135°C and made into a liquid was uniformly spread (spraying amount: 20.0 g / m) on the raised surface of nonwoven fabric A. 2 ), and then 12.0 g (spreading amount: 300 g / m) of particulate water absorbing agent (2) was applied to the raised surface of nonwoven fabric A to which the adhesive was attached. 2 ) was distributed evenly.

[0275] Next, nonwoven fabric E (mainly made of pulp fiber, thickness 0.4 mm, produced by the airlaid method) was cut to a length of 10 cm and width of 40 cm. It corresponds to the second base material. Basis weight: 47 g / m 2 ) and nonwoven fabric A were placed together so that the surfaces onto which the adhesive and particulate water absorbing agent had been sprayed faced each other (contacted each other), and then pressed together to obtain intermediate sheet Y.

[0276] On the surface of the nonwoven fabric E of the intermediate sheet Y, 0.3 g of a hot melt adhesive (JaourMelt3889U, manufactured by JAOUR HOT MELT ADHESIVE, main components: styrene block copolymer, hydrocarbon resin, white mineral oil) that had been heated to 135°C and turned into a liquid was uniformly spread (spray amount: 7.5 g / m 2 Next, the remaining portion of the spunbond nonwoven fabric was folded and wrapped so that the surface of the nonwoven fabric E of the intermediate sheet Y was in contact with the spunbond nonwoven fabric, and the intermediate sheet Y was turned upside down and then pressed to bond the surface to obtain a water-absorbent sheet (28).

[0277] <Brushing process> The nonwoven fabric is placed on a table with a horizontal, smooth surface, and 10 kg weights are placed on both ends of the nonwoven fabric in the long axis direction to fix the nonwoven fabric. A brush (length: 100 mm, bristle length: 25 mm, brush material: polybutylene terephthalate resin, brush diameter: 0.2 mm) is held from above perpendicular to the long axis of the nonwoven fabric and lowered vertically downward toward the surface of the nonwoven fabric, and while pressing the nonwoven fabric with the tip of the brush, it is inserted until it touches the surface of the table. Then, the brush is moved horizontally to the desired length in the long axis direction of the nonwoven fabric without applying a load. The brush and weights are removed, and the nonwoven fabric in the part where the brush was moved is cut off to obtain a raised nonwoven fabric.

[0278] <Measuring method of raised area ratio> The brushed nonwoven fabric is cut to a size of 20 cm x 10 cm, and a smooth plastic plate 3 cm wide is inserted beneath the nonwoven fabric perpendicular to the long axis of the nonwoven fabric (see Figure 11(a)). Next, the nonwoven fabric is lifted vertically upwards by about 10 cm, and the plastic plate is held horizontal. Both ends of the long axis of the hanging nonwoven fabric are clamped from below with a clip weighing 70 g and with a clamping opening of at least 10 cm (see Figure 11(b)). A photograph is taken of the top surface of the nonwoven fabric stretched over the plastic plate from a direction perpendicular to the short axis of the nonwoven fabric (taken from the direction of the arrow in Figure 11(b)).

[0279] The photographs were imported into the image analysis software WinRoof (ver.6.1) and subjected to "monochrome image processing" from the "image processing" tab. After that, the raised area (5 mm above the surface of the nonwoven fabric) was selected using a rectangular ROI as shown in Figure 11(c), and "Automatic binarization" was selected from the "binary processing" tab, and the threshold value was adjusted so that only the raised fibers could be selected. From the "measurement" tab, "area ratio" was selected from "total area / number" and executed to calculate the raised area ratio of the nonwoven fabric.

[0280] <Evaluation of specific return amount under pressure> As shown in Fig. 6, the absorbent sheet 10, which was made to be 10 cm long and 40 cm wide, was wrapped in a liquid-impermeable sheet 21, which was 14 cm long and 40 cm wide, so that an opening was formed at the top. The absorbent sheet 10 wrapped in the liquid-impermeable sheet 21 was placed on a flat surface, and a liquid-injection tube 45 (a plastic tube with an inner diameter of 26 mm, an outer diameter of 30 mm, a length of 150 mm, and a weight of 34 g attached thereto, an inner diameter of 30 mm, an outer diameter of 60 mm, a length of 62 mm, and a weight of 1030 g, Fig. 12) was placed on top of the absorbent sheet 10 at the center as shown in Fig. 13. In this state, 80 g of an aqueous solution containing 0.9 wt % sodium chloride and 0.002 wt % Food Blue No. 1 (Tokyo Chemical Industry Co., Ltd.) at 23°C was injected into the liquid-injection tube 45 using a funnel 42 capable of injecting liquid at a flow rate of 7 ml / sec (Fig. 14). The time from the moment the aqueous solution was poured in until the aqueous solution in the liquid-injection tube 45 was completely absorbed by the absorbent sheet 10 was measured. In this case, the liquid was poured into the absorbent sheet 10 exposed from the liquid-impermeable sheet 21. 10 minutes after the liquid was poured in, 20 sheets of filter paper 43 (type No. 2, manufactured by ADVANTEC; circular with a diameter of 110 mm) whose weight had been measured in advance were placed in the center of the absorbent sheet 10, and a circular weight 44 (1200 g) with a diameter of 100 mm was further placed on top and held for 1 minute. After 1 minute, the weight 44 was removed, and the first backflow amount (g) was measured from the weight increase of the filter paper 43. One minute after removing the weight 44, the same procedure (adding liquid → measuring the liquid absorption time → 10 minutes after adding, placing filter paper 43 and weight 44 (1200 g) and holding for 1 minute → holding for 1 minute → removing the weight and measuring the backflow amount) was repeated, and the backflow amount was measured for the second time (g) and the third time (g). The measured absorption time and the total backflow amount from the first to third times are shown in Table 1.

[0281] <Rate of particulate water absorbing agent falling off> The drop rate of the particulate water absorbing agent was calculated as follows. After measuring the weight of a 40cm x 10cm water absorbent sheet, the surface on the second substrate side and the entire side surface, as well as the surface on the first substrate side extending from the outer periphery toward the inside by 1cm, were covered with a vinyl sheet and fixed with tape. 300ml of physiological saline (0.9% aqueous sodium chloride solution) was evenly poured onto the surface of the water absorbent sheet covered with the vinyl sheet. 10 minutes after pouring the physiological saline, the vinyl sheet covering the water absorbent sheet was removed, and the water absorbent sheet was placed in a vinyl bag (OK bag No. 18, 53cm x 38cm, manufactured by Okura Kogyo Co., Ltd.). A muff (ASS ONE, muff with claws, 360° rotation type) was attached to each of the two support rods of an electromagnetic sieve shaker (Retsch, AS200), and one SUS pipe (diameter 13 mm, inner diameter 10 mm, length 290 mm) was fixed parallel to the ground with each muff, and the water-absorbing sheet together with the plastic bag was clamped with a large clip (clamping mouth 150 mm) attached to the SUS pipe, and vibrated with a vibration amplitude of 3 mm for 1 minute. The water-absorbing sheet together with the plastic bag was removed from the large clip of the electromagnetic sieve shaker, and the weight of the particulate water-absorbing agent that had fallen from the water-absorbing sheet into the plastic bag was measured. The falling rate of the particulate water-absorbing agent was measured by the following formula. In the following formula, the weight of the physiological saline solution is 300 g. Particulate water absorbent shedding rate (%) = Fallen particulate water-absorbing agent (g) / (weight of water-absorbent sheet (g) + weight of physiological saline (g)) × 100.

[0282] Table 2 shows the configurations and evaluation results of the water-absorbent sheets of Examples 11 to 18.

[0283] [Table 2]

[0284] [Example B] In the following examples, a single-layer structure in which a laminate in which a first substrate is laminated on a water-absorbing layer (region containing a particulate water-absorbing agent) is laminated on a second substrate in a single layer, and a two-layer structure in which a laminate in which a first substrate is laminated on a water-absorbing layer (region containing a particulate water-absorbing agent) is laminated on a second substrate in two layers are disclosed. In both the single-layer structure and the two-layer structure, the term "upper nonwoven fabric" refers to the first substrate having a liquid-absorbing surface that directly absorbs liquid, and the term "lower nonwoven fabric" refers to the second substrate. In the two-layer structure, the substrate other than the first substrate having a liquid-absorbing surface that directly absorbs liquid is an intermediate substrate, and is referred to as "intermediate nonwoven fabric" herein.

[0285] <Production Example> [Production Example 1] By referring to the manufacturing examples, examples, and comparative examples described in the following patents, the CRC was appropriately adjusted by the amount of the internal crosslinking agent to obtain particulate water absorbing agents (1) and (2) made of polyacrylic acid (salt) resin. The physical properties of the obtained particulate water absorbing agents are shown in Table 3.

[0286] International Publication No. 2014 / 034897 International Publication No. 2017 / 170605 International Publication No. 2016 / 204302 International Publication No. 2014 / 054656 International Publication No. 2015 / 152299 International Publication No. 2018 / 062539 International Publication No. 2012 / 043821.

[0287] [Production Example of Acrylic Acid] Commercially available acrylic acid (2000 ppm acrylic acid dimer, 500 ppm acetic acid, 500 ppm propionic acid, 200 ppm p-methoxyphenol) was supplied to the bottom of a high-boiling impurity separation tower having 50 perforated trays without a weir, distilled at a reflux ratio of 1, and after removing dimers (acrylic acid dimers) composed of maleic acid and acrylic acid, crystallization was performed to obtain acrylic acid (20 ppm acrylic acid dimer, 50 ppm acetic acid, 50 ppm propionic acid, 1 ppm or less furfural, 1 ppm or less protoanemonin), and 50 ppm p-methoxyphenol was added after distillation.

[0288] [Method for producing aqueous sodium acrylate solution] According to Example 9 of US Patent No. 5,210,298, 1,390 g of the above acrylic acid was neutralized with 48% caustic soda at 20 to 40° C. to obtain a 100% neutralized aqueous sodium acrylate solution with a concentration of 37%.

[0289] <Particulate water absorbing agent (1)> The acrylic acid obtained in the above-mentioned acrylic acid production example, the aqueous sodium acrylate solution obtained by the above-mentioned method for producing an aqueous sodium acrylate solution using the acrylic acid, and deionized water were mixed to obtain an aqueous sodium acrylate solution having a neutralization rate of 75 mol%, and 5500 g (monomer concentration 35.5 mass%) of the aqueous sodium acrylate solution was dissolved with 4.00 g of polyethylene glycol diacrylate (average number of moles of ethylene oxide added: 9) to obtain a reaction solution. Next, the reaction solution was supplied to a reactor formed by attaching a lid to a jacketed stainless steel double-arm kneader having an internal volume of 10 L and two sigma-type blades, and the system was replaced with nitrogen gas while maintaining the reaction solution at 30°C to remove dissolved oxygen in the reaction solution. Next, 28.66 g of a 10 mass% aqueous sodium persulfate solution and 35.28 g of a 1 mass% aqueous L-ascorbic acid solution were added while stirring the reaction solution, and polymerization started about 1 minute later. 40 minutes after the start of polymerization, 181.5 g of water-absorbent resin fine powder of 150 μm or less was added, and the kneader blade was rotated at high speed (130 rpm) for 10 minutes to break down the gel, and the hydrogel polymer was taken out. The obtained hydrogel polymer was fragmented into particles of about 1 to 2 mm.

[0290] This subdivided water-containing gel polymer was spread on a wire mesh of 50 mesh (mesh size: 300 μm) and dried with hot air at 175°C for 65 minutes. Next, the dried product was pulverized using a roll mill, and further classified and formulated with a wire mesh having an opening of 600 μm to obtain an amorphous crushed water-absorbing resin (1-1) with an average particle size of 350 μm. To 100 parts by mass of the obtained water-absorbing resin (1-1), 4.03 parts by mass of an aqueous solution of a surface cross-linking agent composed of 0.03 parts by mass of ethylene glycol diglycidyl ether, 1.0 part by mass of propylene glycol, and 3.0 parts by mass of water was spray-mixed. The above mixture was heat-treated at a heat medium temperature of 100°C for 40 minutes using a paddle-type mixing heat-treating machine to obtain a surface-cross-linked water-absorbing resin (1-2). To 100 parts by mass of the obtained surface-cross-linked water-absorbing resin (1-2), 3.0 parts by mass of water was spray-mixed, cured at 60°C for 1 hour in a sealed container, and then passed through a sieve with an opening of 710 μm to obtain a water-absorbing resin (1-3). A water-absorbing resin obtained by adding 0.3 part by mass of Aerosil 90G (hydrophilic amorphous silica, manufactured by Nippon Aerosil Co., Ltd.) to the water-absorbing resin (1-3) and mixing was designated as the particulate water absorbent (1).

[0291] 〔Measurement method for physical properties of particulate water absorbent〕 <Weight average particle size> The particle size of the particulate water absorbent (or particulate water-absorbing resin, water-absorbing resin particles) according to one embodiment of the present invention is the weight average particle size obtained according to the measurement method of "PSD" defined in ERT420.2-02. The weight average particle size of each particulate water absorbent is shown in Table 3.

[0292] <CRC (water absorption ratio under no pressure) (ERT441.2-02)> After putting 0.2 g (weight before water absorption) of the particulate water absorbent into a bag made of non-woven fabric, it was immersed in a large excess of 0.9 mass% sodium chloride aqueous solution for 30 minutes for free swelling, and then the weight of the particulate water absorbent after draining with a centrifuge (250G) was measured. The water absorption ratio (unit: g / g) is obtained by "(weight of the particulate water absorbent after water absorption - weight of the particulate water absorbent before water absorption) / (weight of the particulate water absorbent before water absorption) × 100". The CRC of each particulate water absorbent is shown in Tables 4 and 6.

[0293] <Surface tension> In the present invention, the surface tension means the surface tension of an aqueous solution when the particulate water absorbing agent is dispersed in a 0.90 mass % sodium chloride aqueous solution.

[0294] 50 ml of physiological saline adjusted to 20°C is placed in a thoroughly washed 100 ml beaker, and the surface tension of the physiological saline is measured using a surface tensiometer (K11 automatic surface tensiometer manufactured by KRUSS). Note that in the present invention, a plate method using a platinum plate is adopted, and the plate is thoroughly washed with deionized water and heated and washed with a gas burner before each measurement.

[0295] Next, a thoroughly washed 25 mm long fluororesin rotor and 0.5 g of the particulate water absorbing agent are put into a beaker containing the physiological saline after surface tension measurement adjusted to 20°C, and stirred for 4 minutes at 500 rpm. After 4 minutes, the stirring is stopped, and after the particulate water absorbing agent containing water settles, the surface tension of the supernatant liquid is measured again by carrying out the same operation. Here, the surface tension of the particulate water absorbing agent (unit: mN / m) is obtained from the surface tension of the supernatant liquid when the particulate water absorbing agent is dispersed in the physiological saline. The surface tension of each particulate water absorbing agent is shown in Tables 4 and 6.

[0296] [Example] <Preparing the pattern> In order to spread the particulate water absorbing agent on the nonwoven fabric in stripes, templates 1 to 6 were prepared. Templates 1 to 6 were made of paper measuring 14 cm in length and 44 cm in width, and holes were made in the areas where the particulate water absorbing agent was present, so that the areas where the particulate water absorbing agent was present and the areas where the particulate water absorbing agent was not present were formed linearly along the longitudinal direction. In templates 1 to 6, a 2 cm outer periphery was used as a frame, and the paper was not cut (that is, the template was punched in the areas where the particulate water absorbing agent was present, starting from the end in the short side direction, in the areas excluding the frame, to form holes). Shapes (S-1) to (S-6) formed by templates 1 to 6 will be described with reference to Figs. 15(a) to 15(c) and Figs. 16(a) to 16(c). Figs. 15(a) to 15(c) and Figs. 16(a) to 16(c) are schematic cross-sectional views of a single-layered water absorbent sheet cut along the short side direction. In the shapes (S-1) to (S-6), the region including the particulate water absorbing agent 14 and the gaps 15 are formed symmetrically with respect to the center in the short side direction of the water absorbent sheet. Therefore, the region ratio of the "particulate water absorbing agent 14" to the "gaps 15" shown below may be from either the left or right side along the short side direction.

[0297] 15(a) shows the (S-1) shape formed by the template 1. In the (S-1) shape, "particulate water absorbing agent 14: 15 mm, gap 15: 25 mm, particulate water absorbing agent 14: 20 mm, gap 15: 25 mm, particulate water absorbing agent 14: 15 mm" is formed in this order along the short side direction between the first base material 11 and the second base material 13.

[0298] 15(b) shows the (S-2) shape formed by the template 2. In the (S-2) shape, "particulate water absorbing agent 14: 20 mm, gap 15: 20 mm, particulate water absorbing agent 14: 20 mm, gap 15: 20 mm, particulate water absorbing agent 14: 20 mm" is formed in this order along the short side direction between the first base material 11 and the second base material 13.

[0299] 15(c) shows the (S-3) shape formed by the template 3. In the (S-3) shape, "particulate water absorbing agent 14: 10 mm, gap 15: 35 mm, particulate water absorbing agent 14: 10 mm, gap 15: 35 mm, particulate water absorbing agent 14: 10 mm" is formed in this order along the short side direction between the first base material 11 and the second base material 13.

[0300] 16(a) shows the (S-4) shape formed by the template 4. In the (S-4) shape, "particulate water absorbing agent 14: 25 mm, gap 15: 10 mm, particulate water absorbing agent 14: 30 mm, gap 15: 10 mm, particulate water absorbing agent 14: 25 mm" is formed in this order along the short side direction between the first base material 11 and the second base material 13.

[0301] 16(b) shows the (S-5) shape formed by the template 5. In the (S-5) shape, "particulate water absorbing agent 14: 17.5 mm, gap 15: 10 mm, particulate water absorbing agent 14: 17.5 mm, gap 15: 10 mm, particulate water absorbing agent 14: 17.5 mm, gap 15: 10 mm, particulate water absorbing agent 14: 17.5 mm, gap 15: 10 mm, particulate water absorbing agent 14: 17.5 mm" is formed in this order along the short side direction between the first base material 11 and the second base material 13.

[0302] 16(c) shows the (S-6) shape formed by the template 6. In the (S-6) shape, "particulate water absorbing agent 14:10mm, gap 15:5mm, particulate water absorbing agent 14:10mm, gap 15:5mm, particulate water absorbing agent 14:10mm, gap 15:5mm, particulate water absorbing agent 14:10mm, gap 15:5mm, particulate water absorbing agent 14:10mm, gap 15:5mm, particulate water absorbing agent 14:10mm, gap 15:5mm, particulate water absorbing agent 14:10mm, gap 15:5mm, particulate water absorbing agent 14:10mm" are formed in this order along the short side direction between the first base material 11 and the second base material 13.

[0303] [Example 1] Template 1 (see Fig. 15(a)) was placed on nonwoven fabric A (produced by the air-through method, mainly composed of olefin, 1.4 mm thick, equivalent to intermediate nonwoven fabric) cut to 10 cm length and 40 cm width. Template 1 had three rectangular holes, and the position was adjusted so that the nonwoven fabric A underneath template 1 could be seen as much as possible through the holes. The area ratio of each hole to the total area of ​​all the holes in template 1 was calculated, and 4.5 g of particulate water-absorbing agent (1) (spray amount: 112.5 g / m2) was applied. 2 ) was divided and measured according to the area ratio of each hole, and was uniformly sprayed onto the nonwoven fabric A visible from each hole. When a part of the particulate water absorbing agent (1) was sprayed onto the template, the template 1 was tilted toward the nonwoven fabric A onto which the particulate water absorbing agent (1) was sprayed, so that the particulate water absorbing agent fell into the holes of the template 1. Then, the template 1 was removed from the nonwoven fabric A.

[0304] Separate from the nonwoven fabric A, a piece of nonwoven fabric A (the same as the nonwoven fabric A (thickness: 1.4 mm). Hereinafter, this is referred to as nonwoven fabric A2. This corresponds to the first base material (upper nonwoven fabric)) was cut to a length of 10 cm and a width of 40 cm. On this piece of nonwoven fabric A, 0.7 to 0.9 g of an adhesive containing styrene-butadiene rubber (Spray Glue 77, manufactured by 3M Japan Ltd.) was uniformly sprayed (spraying amount: 17.5 to 21.5 g / m), and then the surface of the nonwoven fabric A sprayed with the particulate water absorbent (1) and the surface of the nonwoven fabric A2 sprayed with the adhesive were placed face to face (contacted), and pressed together.

[0305] A template 1 (see FIG. 15(a)) was placed on the surface of the nonwoven fabric A on the side not facing the particulate water absorbing agent (1). The position was adjusted so that the nonwoven fabric A under the template 1 could be seen to the maximum extent from the three rectangular holes in the template 1. The area ratio of each hole to the total area of ​​all the holes in the template 1 was calculated, and 4.5 g of the particulate water absorbing agent (1) was measured out according to the area ratio of each hole, and uniformly sprayed onto the nonwoven fabric A visible from each hole. When a part of the particulate water absorbing agent (1) was sprayed onto the template, the template 1 was tilted toward the nonwoven fabric A to which the particulate water absorbing agent (1) was sprayed, and the particulate water absorbing agent was dropped into the hole in the template 1. Then, the template 1 was removed from the nonwoven fabric A.

[0306] Nonwoven fabric E, 10cm long and 40cm wide (made using the airlaid method. The main component is pulp fiber. Thickness: 0.4mm. Weight: 47g / m 2 After uniformly spraying 0.7 to 0.9 g of the adhesive onto the second substrate (corresponding to the lower nonwoven fabric), the surface of the nonwoven fabric A sprayed with the particulate water absorbing agent (1) and the surface of the nonwoven fabric E sprayed with the adhesive were placed face to face (contacted), and pressed together to obtain an intermediate sheet X.

[0307] Finally, the intermediate sheet X was cut into a length of 24 cm and a width of 40 cm to form nonwoven fabric F (made by the spunbond method. The main component is olefin, the thickness is 0.1 mm, and the basis weight is 13 g / m 2 Bulk density: 0.15g / cm 3 The absorbent sheet (1) was obtained by wrapping the absorbent sheet (1).

[0308] [Example 2] A nonwoven fabric F (corresponding to a wrapping sheet) cut to 24 cm in length and 40 cm in width was laid down, and a nonwoven fabric A (corresponding to a first base material) cut to 10 cm in length and 40 cm in width was placed on top of the nonwoven fabric F. Then, a template 1 (see FIG. 15(a)) was placed on the surface of the nonwoven fabric A. The position was adjusted so that the nonwoven fabric A under the template 1 could be seen to the maximum extent from the three rectangular holes in the template 1. The area ratio of each hole to the total area of ​​all the holes in the template 1 was calculated, and 9.0 g of the particulate water-absorbing agent (1) (spraying amount: 225 g / m) was applied. 2 ) was divided and measured according to the area ratio of each hole, and was uniformly sprayed onto the nonwoven fabric A visible from each hole. When a part of the particulate water absorbing agent (1) was sprayed onto the template, the template 1 was tilted toward the nonwoven fabric A onto which the particulate water absorbing agent (1) was sprayed, so that the particulate water absorbing agent fell into the holes of the template 1. Then, the template 1 was removed from the nonwoven fabric A.

[0309] On a nonwoven fabric E (corresponding to the second substrate) having a length of 10 cm and a width of 40 cm, 0.7 to 0.9 g of an adhesive containing styrene-butadiene rubber (Spray Glue 77, manufactured by 3M Japan Ltd.) was uniformly sprayed (spraying amount: 17.5 to 21.5 g / m), and then the surface of the nonwoven fabric A sprayed with the particulate water absorbent (1) and the surface of the nonwoven fabric E sprayed with the adhesive were placed face to face (contacted), and pressed together to obtain an intermediate sheet Y.

[0310] Finally, the intermediate sheet Y was wrapped in the nonwoven fabric F and pressed to obtain the water-absorbent sheet (2).

[0311] [Example 3] A water-absorbent sheet (3) was obtained in the same manner as in Example 2, except that the air-through nonwoven fabric A was replaced with the air-through nonwoven fabric G having a thickness of 0.7 mm.

[0312] [Example 4] A water-absorbent sheet (4) was obtained in the same manner as in Example 2, except that the paper template 2 (see FIG. 15(b)) was used instead of the paper template 1.

[0313] [Example 5] A water-absorbent sheet (5) was obtained in the same manner as in Example 2, except that the paper template 3 (see FIG. 15(c)) was used instead of the paper template 1.

[0314] [Example 6] A water-absorbent sheet (6) was obtained in the same manner as in Example 2, except that the paper template 4 (see FIG. 16(a)) was used instead of the paper template 1.

[0315] [Example 7] A water-absorbent sheet (7) was obtained in the same manner as in Example 2, except that the paper template 5 (see FIG. 16(b)) was used instead of the paper template 1.

[0316] [Example 8] A water-absorbent sheet (8) was obtained in the same manner as in Example 2, except that the paper template 6 (see FIG. 16(c)) was used instead of the paper template 1.

[0317] [Example 9] A water-absorbent sheet (9) was obtained in the same manner as in Example 2, except that nonwoven fabric A was replaced with nonwoven fabric B (produced by the air-through method, mainly composed of olefin, thickness 2.0 mm).

[0318] [Example 10] A water-absorbent sheet (10) was obtained in the same manner as in Example 2, except that nonwoven fabric C (prepared by the air-through method, mainly composed of olefin, thickness 1.5 mm) was used instead of nonwoven fabric A.

[0319] [Comparative Example 1] On the nonwoven fabric A cut to a length of 10 cm and a width of 40 cm, 4.5 g of the particulate water absorbing agent (1) was evenly spread.

[0320] On a nonwoven fabric E (corresponding to a first base material) having a length of 10 cm and a width of 40 cm, 0.7 to 0.9 g of an adhesive containing styrene-butadiene rubber (Spray Glue 77, manufactured by 3M Japan Ltd.) was uniformly sprayed (spraying amount: 17.5 to 21.5 g / m), and then the surface of the nonwoven fabric A sprayed with the particulate water absorbent (1) and the surface of the nonwoven fabric E sprayed with the adhesive were placed face to face (contacted), and pressed together.

[0321] 4.5 g of the particulate water absorbing agent (1) was evenly spread on the surface of the nonwoven fabric A on the side not facing the particulate water absorbing agent (1).

[0322] Separate from the nonwoven fabric E, 0.7 to 0.9 g of the adhesive was uniformly sprayed onto a nonwoven fabric E (hereinafter referred to as nonwoven fabric E2, which corresponds to a second substrate) measuring 10 cm in length and 40 cm in width, and then the surface of the nonwoven fabric A sprayed with the particulate water-absorbing agent (1) and the surface of the nonwoven fabric E2 sprayed with the adhesive were placed face to face (contacted), and pressed together to obtain an intermediate sheet Z. Finally, the intermediate sheet Z was wrapped in nonwoven fabric F and pressed together to obtain a water-absorbent sheet (11).

[0323] [Comparative Example 2] A water-absorbent sheet (12) was obtained in the same manner as in Example 1, except that the template 1 was not used and the particulate water-absorbing agent (1) was uniformly spread over the entire surface of the nonwoven fabric A.

[0324] [Comparative Example 3] Except for using the nonwoven fabric E instead of the nonwoven fabric A2, the water-absorbent sheet (13) was obtained in the same manner as in Example 1. As for the intermediate nonwoven fabric, the nonwoven fabric A was used.

[0325] [Comparative Example 4] A water-absorbent sheet (14) was obtained in the same manner as in Example 2, except that nonwoven fabric E was used instead of nonwoven fabric A.

[0326] The nonwoven fabrics A to C and G used in this example were all water-permeable sheets.

[0327] [Method of measuring physical properties of nonwoven fabric] The elongation, thickness, bulk density, liquid diffusion area, and permeability of the particulate water absorbing agent to the nonwoven fabric of the nonwoven fabrics A to C, E and G used in Example 1, Examples 2 to 10 and Comparative Examples 1 to 4 were measured according to the following methods.

[0328] [Method of measuring elongation rate] The nonwoven fabric for measuring the elongation rate was cut into a rectangle with a long side of 100 mm and a short side of 30 mm. At this time, the long side is the width direction of the nonwoven fabric roll, and the short side is the winding length direction of the nonwoven fabric roll. In this embodiment, the nonwoven fabric used for the water-absorbent sheet has a length (short side) of 100 mm and a width (long side) of 400 mm, and the length (short side) is the width direction of the nonwoven fabric roll, and the width (long side) is the winding length direction of the nonwoven fabric roll. As shown in FIG. 17(a), a guide line was drawn 5 mm from both ends of the cut nonwoven fabric for measuring the elongation rate so that it was parallel to the short side. Each piece was clamped with a double clip so that it overlapped the guide line (FIG. 17(b)). The double clip used had a claw length of 30 mm or more. A weight was attached to one of the double clips, and the weight of the double clip with the weight attached and the weight was 110 g. At room temperature, the double clip without the weight was held and the weight attached to the other double clip was lifted so that it was floating in the air, and the nonwoven fabric was kept in this stretched state by the weight of the double clip and the weight for 20 seconds. Immediately after that, the length of the long side of the nonwoven fabric was measured while it was still floating in the air (Figure 17(c)). The ratio of the length of the long side after it was suspended in the air to the length of the long side before it was suspended in the air (100 mm) was calculated using the following formula to determine the degree to which the length had stretched after it was suspended in the air, and this was taken as the elongation rate.

[0329]

number

[0330] <Measurement of thickness of nonwoven fabric> Measurements were taken using a large-type dial thickness gauge (thickness measuring device) (manufactured by Ozaki Seisakusho Co., Ltd., model number: JB, gauge head: anvil top and bottom φ50 mm). Measurements were taken five times at different points, and the measured value was the average of the five points. When measuring the thickness, the hand was slowly released from the handle so as to apply as little pressure as possible to the nonwoven fabric, and the thickness was measured.

[0331] <How to calculate the bulk density of nonwoven fabric> The weight of the nonwoven fabric cut into a size of 10 cm or more in length and 40 cm or more in width was measured. The volume of the nonwoven fabric was calculated by multiplying the length and width of the nonwoven fabric by the thickness measured in the <Thickness Measurement>, and the weight of the nonwoven fabric was divided by the volume of the nonwoven fabric to calculate the bulk density.

[0332] <Method for measuring the liquid diffusion area of ​​nonwoven fabric> A 30 cm diameter sieve with a mesh size of 2 mm and linearity of 0.9 mm was placed on a flat surface, and a nonwoven fabric cut into a 10 cm square (second substrate) was placed on it. A 0.50 mm diameter needle was attached to a 1 ml syringe, and 1.00 g of saline containing 20 ppm of Blue No. 1 Reagent was measured and the saline from the syringe was injected vertically into the center of the nonwoven fabric on the sieve. At this time, the sieve mesh and the flat surface were sufficiently separated so that the saline that had passed through the nonwoven fabric and mesh did not come into contact with the mesh. When the nonwoven fabric absorbed the saline and the diffusion of the liquid was completed, the area over which the saline had diffused was measured.

[0333] <Permeability of particulate water absorbent through nonwoven fabric> A nonwoven fabric (first substrate 11) cut to a diameter of 80 mm is placed in a JIS standard sieve (The IIDA TESTING SIEVE: inner diameter 80 mm; JIS Z8801-1 (2000)) having a mesh 32 with an opening of 850 μm or a sieve 31 equivalent to the JIS standard sieve, as shown in FIG. 5, and the periphery is secured with tape 33 (ensuring an area of ​​at least 75 mm in diameter through which particles can pass). The nonwoven fabric (first substrate 11) may be removed from a water-absorbent sheet by the method described below. 10.0 g of the particulate water absorbing agent 14 (weight average particle diameter: 367 μm, particle size distribution: 6.1% from 850 μm to 600 μm, 14.5% from 600 μm to 500 μm, 50% from 500 μm to 300 μm, 27.6% from 300 μm to 150 μm, 1.9% from 150 μm to 45 μm, 0.1% below 45 μm) was put into the sieve 31 from above (the direction of the arrow in FIG. 5 ) and shaken for 5 minutes under the conditions of room temperature (20 to 25° C.) and relative humidity 50% RH using a low tap type sieve shaker (ES-65 type sieve shaker manufactured by Iida Manufacturing Co., Ltd.; rotation speed 230 rpm, impact speed 130 rpm). After shaking, the mass (W(g)) of the nonwoven fabric (first substrate 11) and the particulate water absorbing agent 14 that passed through the mesh 32 of the sieve 31 corresponding to the JIS standard sieve (i.e., the particulate water absorbing agent 14 present in the portion 31a below the mesh 32 of the sieve 31) was measured, and the transmittance of the particulate water absorbing agent 14 was calculated according to the following formula (i). The measurement was performed twice, and the average value was calculated.

[0334]

number

[0335] The particulate water absorbing agent used in the measurement of the transmittance is a particulate water absorbing agent containing 90% by weight or more of a particulate water absorbing agent having a weight average particle diameter of 300 to 450 μm and a particle size distribution of 850 μm to 150 μm. Therefore, the transmittance of the particulate water absorbing agent through the first base material calculated in this example corresponds to the transmittance of a specific particulate water absorbing agent through the first base material.

[0336] <Method of Removing Particulate Water Absorbing Agent from Water Absorbent Sheet> The particulate water absorbing agent (the intermediate nonwoven fabric and the particulate water absorbing agent when the intermediate nonwoven fabric is included) was taken out by peeling off the upper nonwoven fabric and the lower nonwoven fabric from the water absorbent sheet. The particulate water absorbing agent attached to the upper and lower nonwoven fabrics and the intermediate nonwoven fabric was also taken out. When peeling off the upper and lower nonwoven fabrics, the water absorbent sheet was cooled, and the adhesive (hot melt adhesive or spray glue) that attached the nonwoven fabric and the particulate water absorbing agent was sufficiently weakened before peeling off. By following this procedure, the nonwoven fabric can be taken out without changing the fiber or structure thickness, and the transmittance can be accurately measured. The water absorbent sheet can be cooled by various means such as placing it in a thermostatic chamber at -10°C or less for a certain period of time, spraying it with a cooling spray, or pouring liquid nitrogen, but there is no particular limitation as long as it is performed under conditions that do not change the fiber, structure, or thickness of the nonwoven fabric and do not cause the particulate water absorbing agent contained in the water absorbent sheet to absorb moisture.

[0337] In addition, when the particulate water absorbing agent taken out has absorbed moisture, the moisture content may be adjusted to 10 mass % or less, preferably 5±2 mass %, for example, by drying, and the transmittance and various physical properties specified in the present application may be measured. The drying conditions for adjusting the moisture content are not particularly limited as long as they do not cause decomposition or denaturation of the water absorbent resin (particulate water absorbing agent), but reduced pressure drying is preferable.

[0338] <Measurement of the content of particulate water absorbing agent in the upper nonwoven fabric> The upper nonwoven fabric was cut into a square of 10 mm length and 10 mm width (with the thickness unchanged) and measured using a microfocus X-ray CT system inspeXio SMX-100CT manufactured by Shimadzu Corporation. The measurement conditions are as follows:

[0339] [X-ray CT scan] Image width (pixels): 512 Image vertical size (pixels): 512 X-ray tube voltage (kV): 50 X-ray tube current (μA): 40 Inch size(inch):4.0 X-ray filter: None SDD (distance between the focal point of the X-ray source and the X-ray detector) (mm): 700 SRD (distance between the focal point of the X-ray source and the center of rotation of the measurement sample) (mm): 550 Scanning mode 1:CBCT Scanning mode 2: Normal scanning Scan angle: Full scan View count:2400 Average number: 5 Smoothing: YZ Slice thickness (mm): 0.166 BHC data: None Precision mode: Yes FOV XY (Maximum shooting area XY) (mm): 50.3 FOV Z (maximum shooting area Z) (mm): 40.0.

[0340] Next, the X-ray CT data was analyzed using Win ROOF, an analysis software made by Mitani Shoji Co., Ltd., in the following procedure.

[0341] (1) Open Win ROOF and select the image (JPEG) you want to analyze that was saved in the X-ray CT scan.

[0342] (2) Click (select) the following on the screen: Binary Processing, Automatic Binarization, Mode Method, Threshold (adjust as necessary), and Execute.

[0343] (3) A polygonal ROI is selected to surround the particulate water-absorbing agent in the first base material (upper nonwoven fabric), and the area of ​​the particulate water-absorbing agent is calculated.

[0344] (4) In the same manner as in (3), the total area of ​​the particulate water-absorbing agent in the water-absorbent sheet is calculated.

[0345] From the calculation results, the content ratio (%) of the particulate water absorbing agent in the first base material was calculated according to the following formula.

[0346] Content ratio (%) of particulate water absorbing agent in first base material=area (I) of particulate water absorbing agent in first base material / total area (II) of particulate water absorbing agent×100 That is, the content of the particulate water absorbing agent in the first substrate is expressed as an area % relative to the total area of ​​the particulate water absorbing agent. The particulate water absorbing agent is present on the liquid absorbing surface of the first substrate that directly absorbs the liquid (the surface of the upper nonwoven fabric to which the liquid to be absorbed is introduced) in an amount of less than a few percent even if it is present, and therefore can be considered not to be present. In the following examples, the content of the particulate water absorbing agent in the first substrate was 5% or more relative to the particulate water absorbing agent contained in the entire water absorbent sheet.

[0347] [Method of evaluating water-absorbent sheets] <Return amount (specific return amount evaluation)> As shown in Fig. 6, the absorbent sheet 10, which was made to be 10 cm long and 40 cm wide, was wrapped in a liquid-impermeable sheet 21, which was 14 cm long and 40 cm wide, so that an opening was formed at the top. The absorbent sheet 10 wrapped in the liquid-impermeable sheet 21 was placed on a flat surface, and a liquid injection tube 41 (Fig. 7) was placed on top of it in the center of the absorbent sheet 10, as shown in Fig. 8. In this state, 80 g of a 0.9 wt % aqueous sodium chloride solution at 23°C was poured into the liquid injection tube 41 using a funnel 42 capable of pouring liquid at a flow rate of 7 ml / sec (Fig. 9). In this case, the liquid was poured into the absorbent sheet 10 exposed from the liquid-impermeable sheet 21 at the sheet 22. Ten minutes after the liquid was poured in, twenty sheets of filter paper 43 (type No. 2, manufactured by ADVANTEC; circular, 110 mm diameter) whose weight had been measured in advance were placed on the center of sheet 22, i.e., the center of absorbent sheet 10, and a circular weight 44 (1200 g) with a diameter of 100 mm was further placed on it and held for one minute. After one minute, weight 44 was removed, and the first amount of backflow (g) was measured from the weight increase of filter paper 43. One minute after the weight 44 was removed, the same procedure (liquid was poured in → 10 minutes after pouring, filter paper 43 and weight 44 (1200 g) were placed and held for one minute → held for one minute → weight was removed, and the amount of backflow was measured) was repeated, and the second amount of backflow (g) and the third amount of backflow (g) were measured. The totals of the measured amounts of backflow from the first to third times are shown in Tables 4 and 6.

[0348] <How to calculate thickness ratio (Lb / La)> La is the thickness from the liquid-absorbent surface of the upper nonwoven fabric (the liquid-absorbent surface of the first substrate) in the gap to the surface of the water-absorbent layer side of the lower nonwoven fabric (the second substrate), and Lb is the thickness from the liquid-absorbent surface of the upper nonwoven fabric (the liquid-absorbent surface of the first substrate) to the surface of the water-absorbent layer side of the lower nonwoven fabric (the second substrate) in the region containing the particulate water-absorbing agent.

[0349] [Thickness measurement of absorbent sheet using X-ray CT] The absorbent sheet was photographed using X-ray CT by fixing both ends of a 180 mm-long cut piece of absorbent sheet to a plastic plate 350 mm long, 100 mm wide, and 3 mm thick with packing tape, and placing the plastic plate perpendicular to the thickness direction on the internal plate of an X-ray device (Shimadzu Corporation, inspeXio SMX-100CT), and measuring the center of the absorbent sheet under the following conditions.

[0350] Equipment used: inspeXio SMX-100CT (manufactured by Shimadzu Corporation) X-ray tube voltage (kV): 80 X-ray tube current (μA): 40 Inch size: 4.0 X-ray filter: None SOD(mm):700 SRD(mm):550 View count: 2400 Average number: 5×1 Slice thickness (mm): 0.166 CT mode 1:CBCT CT Mode 2: Normal operation Scanning Angle: Full Scan BHC Data: None Center Adjust: Yes Fine mode: Yes FOV (XY)(mm):50.3 FOV (Z)(mm):20.0 Voxel size (mm / voxel): 0.098 The captured stereoscopic image was divided into 203 cross-sectional views in the length direction, and the thickness of the water-absorbent sheet was measured from the 50th, 100th, and 150th images. When measuring the thickness, the thickness from the liquid-absorbent surface of the upper nonwoven fabric in the gap below the upper nonwoven fabric to the surface of the water-absorbent layer side of the lower nonwoven fabric was taken as La, and the thickness from the liquid-absorbent surface of the upper nonwoven fabric to the surface of the water-absorbent layer side of the lower nonwoven fabric in the region containing the particulate water-absorbing agent below the upper nonwoven fabric was taken as Lb.

[0351] <Evaluation of shape retention> After evaluating the <return amount> of the water-absorbent sheet, the water-absorbent sheet was cut in the width direction at the center, and the area not containing the particulate water-absorbing agent (i.e., gaps) was visually confirmed. At this time, the particulate water-absorbing agent present in the gaps was confirmed and evaluated according to the following evaluation criteria. Evaluation criteria ○: The area containing the particulate water absorbing agent is separated by gaps. (That is, there is no member in the gap, or the gap is mainly filled with a substrate that supports the water-absorbing layer (that is, in the case of a single-layer structure, the upper nonwoven fabric and the lower nonwoven fabric; in the case of a two-layer structure, the upper nonwoven fabric, the middle nonwoven fabric, and the lower nonwoven fabric). ×: The ratio of the gaps is small, and the regions including the particulate water absorbing agents arranged in parallel are connected to each other (not separated by gaps) (That is, the particulate water-absorbing agent has entered into the area that was previously the gap, and the proportion of the base material that supports the water-absorbing layer has decreased).

[0352] Tables 3 to 6 below show the configurations of the water-absorbent sheets produced in Examples 1 to 10 and Comparative Examples 1 to 4, the evaluation results of the physical properties of the substrates used in each water-absorbent sheet, and the evaluation results of the water-absorbent sheets. In Tables 3 to 6, SAP means a particulate water-absorbing agent. In Tables 3 and 5, the SAP-disposed area (%) means the area ratio of the area containing the particulate water-absorbing agent to the total area of ​​the substrate on which the particulate water-absorbing agent is disposed in the surface direction of the upper nonwoven fabric, and the SAP-free area (%) means the area ratio of the area not containing the particulate water-absorbing agent (i.e., gaps) to the total area of ​​the substrate on which the particulate water-absorbing agent is disposed in the surface direction of the upper nonwoven fabric. Here, the substrate on which the particulate water-absorbing agent is disposed means a substrate on which the particulate water-absorbing agent is sprayed. In this embodiment, the upper nonwoven fabric, the middle nonwoven fabric, and the lower nonwoven fabric are the same size.

[0353] [Table 3]

[0354] [Table 4]

[0355] [Table 5]

[0356] [Table 6]

[0357] From the above results, the water-absorbent sheets of Examples 2 to 10 had higher shape retention and significantly less reversion compared to the water-absorbent sheets of Comparative Examples 1 to 4. That is, it was confirmed that in the single-layer and double-layer water-absorbent sheets, the amount of reversion could be reduced and shape retention was high by providing gaps in the water-absorbent layer using an upper nonwoven fabric having elasticity.

[0358] In this embodiment, the two-layer form tends to have a larger amount of return compared to the single-layer form. One of the reasons for this is that the amount of particulate water absorbing agent in the upper nonwoven fabric of the two-layer form (i.e., the amount of particulate water absorbing agent located between the upper nonwoven fabric and the middle nonwoven fabric) is smaller than the amount of particulate water absorbing agent in the upper nonwoven fabric of the single-layer form (i.e., the amount of particulate water absorbing agent located between the upper nonwoven fabric and the lower nonwoven fabric). Therefore, it is considered difficult to make a general comparison of the difference in the reduction effect of the amount of return between the single-layer form and the two-layer form.

[0359] This application is based on Japanese Patent Application No. 2019-215887 filed on November 28, 2019 and Japanese Patent Application No. 2019-215888 filed on November 28, 2019, the disclosures of which are incorporated herein by reference in their entirety. [Explanation of symbols] 10 Water-absorbent sheet 11 first substrate, 12 water absorption layer, 13 second substrate; 14 Particulate water absorbing agent, 15 gap, 16 wrapping sheets, 21 Liquid impermeable sheet, 31 sieve, 31a: the portion below the mesh of the sieve; 32 mesh, 33 Tape, 41 Liquid injection tube, 42 funnel, 60 stands, 61 Pipes, 63 Acrylic plate, 64 funnel, 65 Metal tray.

[0360] [Second Invention] Next, the second invention will be described. The water-absorbent sheet of the second invention is a water-absorbent sheet having a first substrate, a second substrate, and a water-absorbent layer located between the first substrate and the second substrate, the water-absorbent layer contains a particulate water-absorbing agent, the region containing the particulate water-absorbing agent is disposed separated by a gap that does not substantially contain the particulate water-absorbing agent, the surface of the first substrate forms a liquid-absorbing surface that directly absorbs liquid, and the first substrate has an elongation rate of 10% or more. [Document name] Statement [Name of invention] Absorbent sheet and absorbent article containing same [Technical field] The present invention relates to a water-absorbent sheet and an absorbent article including the same.

[0361] [Background technology] Super absorbent polymers (SAPs) are water-swellable, water-insoluble polymer gelling agents that are used in a variety of applications, including hygiene materials such as disposable diapers, sanitary napkins, and adult incontinence products, soil water retention agents in agricultural and horticultural applications, and industrial water-stopping agents.

[0362] These absorbent articles are generally manufactured in paper diaper manufacturing plants as absorbent bodies that are individually molded for each absorbent article by mixing absorbent resin and fibrous material, and are processed into absorbent bodies of various shapes (for example, hourglass-shaped, fox-shaped, oval, etc. when viewed in plan) depending on the purpose. These manufacturing methods for absorbent bodies are the mainstream for current paper diapers, since they can be processed into any shape because they are individually molded, and the amount of fiber and absorbent resin can be easily adjusted for each absorbent article.

[0363] However, in recent years, paper diapers have begun to be manufactured using absorbents (called water-absorbent sheets, usually cut into rectangles about 10 cm wide and several tens of cm long) made by cutting a long water-absorbent sheet with water-absorbent resin fixed between two sheets during the manufacturing process of sanitary materials. By purchasing or manufacturing a long continuous water-absorbent sheet, paper diaper manufacturers can simplify the manufacturing process of paper diapers, and furthermore, by not using pulp, they can make paper diapers thinner. Water-absorbent sheets are configured by sandwiching and fixing water-absorbent resin particles between upper and lower sheets (particularly nonwoven sheets), and usually after manufacturing a long continuous sheet, the long continuous sheet is cut into rectangles about 10 cm wide and several tens of cm long, which are then incorporated into paper diapers (for example, International Publication No. WO 2010 / 143635).

[0364] Unlike conventional sanitary materials (disposable diapers), disposable diapers made with absorbent sheets have a short history, and the reality is that there has been almost no development of absorbent resins suitable for absorbent sheets or proposals for parameters for them, and the absorbent resins used in conventional disposable diapers are used as is for absorbent sheets.

[0365] [Summary of the Invention] [Problem to be solved by the invention] The inventors have found that, due to the structure of the water-absorbent sheet, which is mainly thin, the absorbed liquid is easily released in the direction of the absorbed liquid introduction by applying pressure to the water-absorbent sheet, which is called "backflow". "Backflow" is also called "re-wet". The inventors have found that the occurrence of backflow is more noticeable when the amount of liquid introduced is large due to the intermittent introduction of liquid multiple times (especially three or more times). When backflow occurs, the skin in contact with the water-absorbent sheet comes into contact with the backflowed liquid and is exposed to a highly humid state. This not only causes discomfort to the user, but also makes the skin in contact with the water-absorbent sheet more susceptible to rashes.

[0366] In addition, in such a conventional water-absorbent sheet configuration, the water-absorbent resin particles that absorb liquid swell, weakening the fixation of the water-absorbent resin particles to the upper and lower sheets, and the water-absorbent resin particles may move within the sheet. This causes the water-absorbent resin particles to become biased within the sheet, causing the shape of the water-absorbent sheet to be distorted. In this case, the liquid absorption of the water-absorbent sheet becomes biased, causing leakage. In some cases, the water-absorbent resin particles may fall out of the sheet to the outside.

[0367] The present invention has been made in consideration of the above circumstances, and aims to provide a novel water-absorbent sheet that can significantly reduce liquid release from the water-absorbent sheet due to backflow, even when liquid is intermittently introduced multiple times (particularly, three or more times), and that maintains its sheet shape even after absorbing liquid (has high sheet shape retention).

[0368] [Means for solving the problem] The present inventors have conducted intensive research to solve the above-mentioned problems. As a result, they have found that the above-mentioned problems can be solved by a water-absorbent sheet having a first substrate, a second substrate, and a water-absorbent layer located between the first substrate and the second substrate, the water-absorbent layer contains a particulate water-absorbing agent, an area containing the particulate water-absorbing agent is disposed apart from the area by a gap that does not substantially contain the particulate water-absorbing agent, the surface of the first substrate forms a liquid-absorbing surface that directly absorbs liquid, and the first substrate has an elongation rate of 10% or more.

[0369] In addition, in another embodiment of the water-absorbent sheet of the present invention, only the laminate in which the first substrate is laminated on the water-absorbent layer is laminated on the second substrate.

[0370] Furthermore, in another aspect of the water-absorbent sheet of the present invention, a laminate in which the first substrate is laminated on the water-absorbent layer, and a construct in which an intermediate substrate is laminated on the water-absorbent layer are laminated on the second substrate.

[0371] [Brief description of the drawings] FIG. 18 is a schematic diagram illustrating a cross section of a water-absorbent sheet according to a first embodiment of the present invention.

[0372] FIG. 19 is a schematic diagram showing a cross section of a water-absorbent sheet according to a second embodiment of the present invention.

[0373] FIG. 20 is a schematic diagram showing a cross section of a water-absorbent sheet for illustrating the form of a particulate water-absorbing agent and gaps in the water-absorbent sheet produced in an Example.

[0374] FIG. 21 is a schematic diagram showing a cross section of a water-absorbent sheet for illustrating the form of a particulate water-absorbing agent and gaps in the water-absorbent sheet produced in an Example.

[0375] FIG. 22 is a schematic diagram illustrating a method for measuring the elongation of a nonwoven fabric.

[0376] FIG. 23 is a schematic diagram illustrating a method for measuring the permeability of a particulate water-absorbing agent to a nonwoven fabric.

[0377] FIG. 24 is a plan view and a right side view showing a sample used in evaluating the amount of return, illustrating how the water-absorbent sheet produced in the examples is wrapped in a liquid-impermeable sheet.

[0378] FIG. 25 is a plan view and a front view of the liquid injection tube used in evaluating the amount of backflow.

[0379] FIG. 26 is a front view showing a liquid injection tube placed on the water-absorbent sheet used in an embodiment of the present application.

[0380] FIG. 27 is a front view showing how a sodium chloride aqueous solution is poured into a water-absorbent sheet from a liquid pouring tube using a funnel.

[0381] [Mode for carrying out the invention] The present invention will be described below while showing the best mode. Throughout this specification, the expression of the singular form should be understood to include the concept of the plural form, unless otherwise specified. Therefore, the singular article (for example, in the case of English, "a", "an", "the", etc.) should be understood to include the concept of the plural form, unless otherwise specified. In addition, it should be understood that the terms used in this specification are used in the sense commonly used in the field, unless otherwise specified. Therefore, unless otherwise defined, all technical terms and scientific and technical terms used in this specification have the same meaning as commonly understood by those skilled in the art to which this invention belongs. In the case of conflict, this specification (including definitions) will take precedence. The present invention is not limited to the following embodiments, and various modifications can be made within the scope of the claims.

[0382] 1. Definitions of Terms The definitions of [1-1. Water-absorbent sheet], [1-2. Water-absorbent resin], [1-3. Water-absorbing agent, particulate water-absorbing agent], [1-4. Polyacrylic acid (salt)], [1-5. EDANA and ERT], and [1-6. Others] in the first invention are similarly applied to the second invention. Therefore, although omitted here, these definitions are incorporated by reference into the second invention.

[0383] [2. Water-absorbent sheet] The water-absorbent sheet of the present invention has a first substrate, a second substrate, and a water-absorbent layer located between the first substrate and the second substrate, wherein the water-absorbent layer contains a particulate water-absorbing agent, and an area containing the particulate water-absorbing agent is disposed separated by a gap that does not substantially contain the particulate water-absorbing agent, the surface of the first substrate forms a liquid-absorbent surface that directly absorbs liquid, and the first substrate has an elongation percentage of 10% or more.

[0384] With this configuration, even if the amount of liquid introduced is large due to the intermittent introduction of liquid several times (particularly, three or more times), the liquid discharge from the absorbent sheet due to backflow can be significantly reduced, and the shape retention after the liquid is absorbed is high. In the absorbent sheet of the present invention, the elongation rate of the first substrate forming the liquid-absorbing surface that directly absorbs the liquid is 10% or more. That is, the first substrate has elasticity. The liquid-absorbing surface that directly absorbs the liquid is formed on the surface of the first substrate having elasticity. Here, in this specification, the "liquid-absorbing surface" means the surface of the substrate that absorbs the liquid, that is, the surface of the substrate that is introduced with the liquid. In addition, in this specification, the term "directly" does not include a form in which the liquid that has permeated other substrates is sequentially absorbed. In this specification, even when a wrapping sheet described later is arranged on the surface of the first substrate, the form in which the surface of the first substrate forms the liquid-absorbing surface that directly absorbs the liquid is included.

[0385] In the first embodiment of the present invention, the surface of the first substrate is a liquid-absorbing surface that directly absorbs liquid, and therefore no water-absorbing layer is disposed on the first substrate. Thus, the water-absorbent sheet according to one embodiment of the present invention is a water-absorbent sheet having a first substrate, a second substrate, and a water-absorbent layer located between the first substrate and the second substrate, the water-absorbent layer contains a particulate water-absorbing agent, the water-absorbent layer is not disposed on the first substrate, the region containing the particulate water-absorbing agent is disposed across a gap that does not substantially contain the particulate water-absorbing agent, and the first substrate has an elongation rate of 10% or more. In this embodiment, even if a part of the particulate water-absorbing agent contained in the water-absorbent layer passes through the first substrate and moves to the first substrate and is partially exposed, this is not considered to be the case. The cause of the movement is assumed to be, for example, vibrations caused by the water-absorbent sheet becoming a final product and being transported or carried. The case where a particulate water absorbing agent is intentionally scattered or placed on the first base material is not within the scope of this embodiment.

[0386] The present inventors have found that in conventional absorbent sheets (for example, an absorbent sheet having a guide groove (corresponding to a gap) in an absorbent layer located between a first substrate and a second substrate, such as the absorbent sheet described in Chinese Patent Application Publication No. 105380752), the amount of return is reduced but the shape retention is poor when the amount of return is measured under specific conditions in the examples of the present application (also referred to as "specific amount of return evaluation" in this specification).

[0387] Here, the gaps existing between the regions containing the particulate water absorbing agent can function as a liquid passage when the liquid is introduced from the first substrate to the water absorbing layer. That is, due to the existence of the liquid passage, the liquid introduced from the liquid absorbing surface can be efficiently sent to the lower water absorbing layer that has the water absorbing function without being retained on the liquid absorbing surface (furthermore, the introduced liquid does not locally stagnate). Specifically, the liquid (e.g., urine) that has passed through the first substrate is introduced into the entire surface of the water absorbing layer and the gaps. The liquid introduced into the gaps is easily diffused because there is no particulate water absorbing agent that prevents the liquid from passing through the region containing the particulate water absorbing agent and the absorption by the particulate water absorbing agent is also gentle. As a result of the diffusion of the liquid, it is possible to prevent the occurrence of a bias in the amount of liquid absorption, such as a large amount of liquid absorption by the particulate water absorbing agent at the portion where the liquid is introduced and a small amount of liquid absorption by the particulate water absorbing agent at the portion away from the liquid introduction portion. Therefore, it is possible to prevent the particulate water absorbing agent from being saturated and swollen, that is, from being unable to absorb liquid and increasing the amount of backflow. As a result, it is considered that the amount of backflow can be reduced.

[0388] However, for example, when the particulate water absorbing agent absorbs liquid and swells, the volume of the region containing the particulate water absorbing agent increases, so that the swollen particulate water absorbing agent penetrates into the region that was previously a gap, and the gap decreases. In this case, if liquid is intermittently introduced multiple times, the liquid absorption capacity is considered to gradually decrease as the gap decreases. When liquid is released from the water absorbing layer, the liquid becomes difficult to pass through the gap as the gap decreases, and the particulate water absorbing agent tends to partially swell to saturation, so that the amount of liquid that flows back to the liquid absorbing surface of the first base material gradually increases. As a result, the liquid that flows back rises up to the skin (comes into contact with the skin), causing discomfort.

[0389] Furthermore, in the configuration of a conventional water-absorbent sheet having gaps in the water-absorbent layer (for example, the water-absorbent sheet described in Chinese Patent Application Publication No. 105380752), the swelling of the particulate water-absorbing agent weakens the fixation of the particulate water-absorbing agent to the first substrate and / or the second substrate, and the particulate water-absorbing agent may move in the water-absorbent layer. This causes the particulate water-absorbing agent to become biased in the water-absorbent layer, causing the shape of the water-absorbent sheet to be distorted (reduced shape retention).

[0390] In contrast, the water absorbent sheet of the present invention is considered to be able to buffer the increase in the volume of the region containing the particulate water absorbing agent because the first substrate has elasticity. That is, when the particulate water absorbing agent swells, the first substrate stretches in response to the swelling, thereby suppressing the reduction in the gap, and thus maintaining the shape of the gap. As a result, even if liquid is intermittently introduced multiple times, the amount of backflow can be reduced without reducing the liquid diffusion ability. In addition, since the first substrate stretches and contracts to buffer the swelling of the particulate water absorbing agent, the fixation of the particulate water absorbing agent to the first substrate and / or the second substrate does not weaken. Specifically, the first substrate in contact with the particulate water absorbing agent stretches into a shape following the swollen particulate water absorbing agent as the particulate water absorbing agent swells. As a result, the first substrate and the particulate water absorbing agent are entangled, and the particulate water absorbing agent is held more firmly between the first substrate and the second substrate. Therefore, the water-absorbent sheet of the present invention can suppress the migration of the particulate water-absorbing agent from the region in the water-absorbent layer where the particulate water-absorbing agent is contained, and can maintain the shape of the water-absorbent sheet, so that the shape retention is high. In the embodiment of the present invention, a multilayered (two-layered) water-absorbent sheet in which a laminate in which a first substrate is laminated on a water-absorbent layer and a structure in which an intermediate substrate is laminated on a water-absorbent layer are laminated on a second substrate (with the water-absorbent layer positioned on the second substrate) is laminated on the second substrate, and a single-layered water-absorbent sheet in which a laminate in which a first substrate is laminated on a water-absorbent layer is laminated on the second substrate, the single-layered water-absorbent sheet has a greater effect of reducing backflow. The reason for this is unclear, and in other words, it can be said to be an unexpected effect even for a person skilled in the art.

[0391] In the water-absorbent sheet, the water-absorbing function in the water-absorbent layer is mainly performed by the water-absorbing agent (particulate water-absorbing agent). In particular, in the water-absorbent sheet, which has a different configuration from conventional absorbent articles in which pulp is present in the water-absorbent layer, the role of the water-absorbent agent becomes even more important. In particular, in the present invention, since the first base material has elasticity, the shape of the gap provided between the water-absorbent layer and the area containing the particulate water-absorbing agent can be maintained, and liquid once introduced into the water-absorbent agent is unlikely to return to the liquid-absorbing surface of the first base material. Therefore, the shape of the water-absorbent sheet can be maintained (i.e., high shape retention) and the "specific return amount evaluation" can be excellent. Here, it should be noted that water-absorbent sheets and absorbent articles designed to suppress the amount of return under general conditions do not necessarily give excellent results in the "specific return amount evaluation" of the present application. In addition, the water-absorbent sheet according to one embodiment of the present invention is suitable as an absorbent article (e.g., a diaper) to be used during the time period when an infant who has just started to learn to run and whose bladder is still small is actively moving around during the daytime, but of course the use form is not limited to this. Furthermore, the mechanisms described in this specification do not limit the technical scope of the claims of this application.

[0392] Hereinafter, an embodiment of the present invention will be described with reference to the attached drawings. In the description of the drawings, the same elements are given the same reference numerals, and duplicated explanations will be omitted. In addition, the dimensional ratios of the drawings are exaggerated for the convenience of explanation, and may differ from the actual ratios.

[0393] The water-absorbent sheet according to the first embodiment of the present invention is formed by laminating only a laminate in which a first substrate is laminated on a water-absorbent layer, on a second substrate. That is, in the first embodiment, the water-absorbent layer is sandwiched between the first substrate and the second substrate. The first embodiment will be described with reference to FIG. 18.

[0394] FIG. 18 is a schematic diagram showing a cross section of the water-absorbent sheet 10 according to the first embodiment of the present invention. Three forms ((a) to (c)) of the water-absorbent sheet 10 are shown in FIG. 18. In FIG. 18(a) to (c), the arrows indicate the direction in which the liquid to be absorbed is introduced. The first substrate 11 is located on the side where the liquid to be absorbed (liquid to be absorbed) is introduced relative to the water-absorbent layer 12. That is, the first substrate is disposed on the side from which the liquid is discharged (for example, the skin side in the case of a paper diaper). The water-absorbent layer 12 is disposed between the first substrate 11 and the second substrate 13. That is, the laminate 18 in which the first substrate 11 is laminated on the water-absorbent layer 12 is laminated on the second substrate 13.

[0395] In Fig. 18(a)-(c), the water absorbent layer 12 includes a particulate water absorbing agent 14. In the forms of Fig. 18(a)-(c), the water absorbent layer 12 shows a state in which the particulate water absorbing agent 14 exists between the first substrate 11 and the second substrate 13. A part of the particulate water absorbing agent 14 may be detached from each substrate 11, 13. The particulate water absorbing agent 14 (the region including the particulate water absorbing agent 14) is disposed across a gap 15 that does not substantially include the particulate water absorbing agent 14. Therefore, the water absorption "layer" does not only refer to a continuous body such as a sheet, but may be any form that exists between the first substrate 11 and the second substrate 13 with a certain thickness and length. For example, the water absorbent layer 12 may exist intermittently between the first substrate 11 and the second substrate 13 with a certain thickness and length. For example, an adhesive may be used to fix the particulate water absorbing agent 14 to the substrate 11 and / or 13. The method of producing a water absorbent sheet using an adhesive will be described in detail in [3.].

[0396] Here, in FIG. 18(a), the gap 15 is formed between the first substrate 11 and the second substrate 13, but the gap 15 in the present invention also includes the forms of FIG. 18(b) and FIG. 18(c). In FIG. 18(b), the first substrate 11 and the second substrate 13 come into contact with each other, so that the region containing the particulate water absorbing agent 14 is separated. Although the first substrate and the second substrate are in contact with each other, the liquid passage is maintained, so that the gap is considered. In addition, the first substrate 11 (and the second substrate 13 in some cases) enters the water absorption layer 12, so that the water absorption layer 12 is separated, and therefore, in this form, the water absorption layer 12 exists intermittently. In FIG. 18(c), the end of the first substrate 11 and the end of the second substrate 13 are overlapped with each other, so that the end of the water absorbent sheet 10 is closed by the first substrate 11 and the second substrate 13. Even in this case, the first substrate 11 (and possibly the first substrate 11 and the second substrate 13) penetrates into the end portion of the water-absorbing layer 12, so that the water-absorbing layer 12 is not present at the end portion of the water-absorbing layer 12. The configuration of the water-absorbing layer 12 and the gap 15 is similarly applied to the second embodiment described later.

[0397] The particulate water absorbing agent 14 may be present in the first substrate 11. The particulate water absorbing agent 14 in the first substrate 11 may be, for example, a particulate water absorbing agent 14 in contact with (or fixed to) the first substrate 11, or a particulate water absorbing agent 14 in contact with (or fixed to) the second substrate 13 that is detached and captured in the first substrate 11. When the particulate water absorbing agent 14 is present in the first substrate 11, the content of the particulate water absorbing agent 14 in the first substrate 11 is preferably 5% or more, more preferably 10% or more, even more preferably 20% or more, and even more preferably 30% or more, relative to the particulate water absorbing agent 14 contained in the entire water absorbent sheet 10. The upper limit is not particularly limited, but is preferably 90% or less, 70% or less, and 50% or less. In this specification, the content ratio of the particulate water absorbing agent 14 in the first substrate 11 to the particulate water absorbing agent 14 contained in the entire water absorbent sheet 10 is calculated by the method of the examples described later.

[0398] Since the particulate water absorbing agent 14 is not spread or arranged in the region of the gap 15, the region of the gap 15 does not substantially contain the particulate water absorbing agent 14. The region of the gap 15 may contain additives other than the particulate water absorbing agent 14. For example, the gap 15 may be formed by contacting the first base material 11 and the second base material 13 directly or via an adhesive. Since the first base material 11 has elasticity, when a region containing the particulate water absorbing agent 14 exists on the second base material 13, the first base material 11 expands and contracts following the region containing the particulate water absorbing agent 14. Therefore, the first base material 11 has a shape that covers the region containing the particulate water absorbing agent 14 on the region containing the particulate water absorbing agent 14, and on the gap 15, it has a shape that sinks toward the second base material 13 after following the upper side surface of the region containing the particulate water absorbing agent 14.

[0399] In the water absorbent sheet according to the first embodiment of the present invention, the ratio (Lb / La) of the thickness (Lb) from the liquid absorbing surface of the first substrate 11 to the surface of the water absorbing layer 12 side of the second substrate in the region containing the particulate water absorbing agent 14 to the thickness (La) from the liquid absorbing surface of the first substrate 11 to the surface of the water absorbing layer side of the second substrate 13 in the gap 15 is preferably 1.05 or less. Since the first substrate 11 has elasticity, the part of the first substrate 11 in contact with the particulate water absorbing agent 14 has a shape following the shape of the region containing the particulate water absorbing agent 14 (i.e., the shape of the particulate water absorbing agent 14 on the side of the particulate water absorbing agent 14 in contact with the first substrate 11) (i.e., it expands and contracts following the shape). Therefore, the first base material 11 can be in close contact with the particulate water absorbing agent 14 (the region including the particulate water absorbing agent 14), and as a result, the first base material 11 is integrated with the particulate water absorbing agent 14 (the region including the particulate water absorbing agent 14). In this case, the difference between the thickness of La and the thickness of Lb is small, and therefore Lb / La is 1.05 or less. In this case, the shape of the region including the particulate water absorbing agent 14 is highly retained. Therefore, even after the particulate water absorbing agent 14 swells, the gaps 15 are highly retained, and the return can be further reduced. Note that Lb / La is usually 1 or more.

[0400] In the water absorbent sheet 10, the gaps 15 are formed by providing a region where the particulate water absorbing agent 14 does not exist on a part of the second base material 13. The gaps 15 (i.e., the region where the particulate water absorbing agent 14 does not exist) are continuously provided along one direction on the liquid absorbing surface of the first base material 11, so that the function as a liquid passage can be more effectively exhibited. The shape of the continuously provided gaps 15 may be, for example, linear, curved, or wavy, but it is preferable that these gaps 15 are provided linearly and in parallel. Therefore, in the water absorbent sheet 10, the region where the particulate water absorbing agent 14 is included and the gaps 15 preferably have a shape extending along one direction (the surface direction perpendicular to the direction in which the liquid is absorbed) on the liquid absorbing surface of the first base material 11, and are arranged in parallel. That is, the region where the particulate water absorbing agent 14 is included is arranged in a streaky (striped) state. As a result, the gaps 15 are also formed in a striped pattern, so that even when the particulate water absorbing agent 14 swells, the gaps 15 are easily maintained, and as a result, backflow can be further reduced. Here, the "one direction" may be any direction parallel to the surface direction of the liquid-absorbing surface of the first substrate 11, excluding the thickness direction, that is, any of the longitudinal direction, transverse direction, and directions inclined to these directions of the liquid-absorbing surface of the first substrate 11. From the viewpoint of the balance between the role of the gaps 15 and the role of the particulate water absorbing agent 14, in the water absorbent sheet 10, the regions including the particulate water absorbing agent 14 and the gaps 15 preferably have a shape extending along the longitudinal direction of the liquid-absorbing surface of the first substrate 11 and are arranged in parallel.

[0401] The ratio of the area containing the particulate water absorbing agent 14 on the surface of the first base material 11 facing the water absorbent layer 12 (the surface on which the particulate water absorbing agent 14 is disposed) (hereinafter, also referred to as "the ratio of the area containing the particulate water absorbing agent 14") is preferably 90% or less in area, more preferably 80% or less, and even more preferably 75% or less. The ratio of the area containing the particulate water absorbing agent 14 on the surface of the first base material 11 facing the water absorbent layer 12 is preferably 10% or more in area, and more preferably 20% or more. By providing the particulate water absorbing agent 14 in such a range, the balance between the role of the gap 15 and the role of the particulate water absorbing agent 14 becomes appropriate, and the effect of reducing the amount of return is further exhibited. The ratio of the area containing the particulate water absorbing agent 14 on the surface of the first base material 11 facing the water absorbent layer 12 is similar to the ratio of the area containing the particulate water absorbing agent 14 on the surface of the second base material 13 facing the water absorbent layer 12 (the surface on which the particulate water absorbing agent 14 is disposed).

[0402] Here, the ratio of the area containing the particulate water absorbing agent 14 on the surface of the first substrate 11 facing the water absorbing layer 12 can be controlled by adjusting the area where the particulate water absorbing agent 14 is dispersed during the production of the water absorbent sheet 10.

[0403] Also, for example, by photographing and analyzing a cross section obtained by cutting the produced water absorbent sheet 10 with an X-ray CT device (inspeXio SMX-100CT), the ratio of the area containing the particulate water absorbing agent 14 on the surface of the first base material 11 on the water absorbent layer 12 side can be calculated. Specifically, the cross section of the water absorbent sheet 10 is photographed, and the interface between the first base material 11 or the second base material 13 and the water absorbent layer 12 is classified into an area where the particulate water absorbing agent 14 is present and an area where the particulate water absorbing agent 14 is not present, and the respective areas are summed up and the ratio is calculated, whereby the ratio of the area containing the particulate water absorbing agent 14 can be calculated. Note that three or more cross sections in the short length direction of the water absorbent sheet 10 are photographed, the ratio of the area containing the particulate water absorbing agent 14 is calculated, and the average value of the ratios of the area containing the particulate water absorbing agent 14 obtained from each cross section is defined as the "ratio of the area containing the particulate water absorbing agent 14".

[0404] The content of the particulate water absorbing agent 14 contained in the water absorbent sheet 10 is preferably 200 to 360 g / m 2 and more preferably 250 to 350 g / m 2 and more preferably 300 to 325 g / m 2 It is.

[0405] The water-absorbent sheet 10 has a wrapping sheet 16. The wrapping sheet 16 has the following purposes: to maintain the shape of the water-absorbent sheet 10, which is a structure in which the particulate water-absorbing agent 14 is supported between the first substrate 11 and the second substrate 13; to prevent the particulate water-absorbing agent 14 supported between the first substrate 11 and the second substrate 13 from spilling (falling off) from the absorbent (water-absorbent sheet 10); and to prevent the particulate water-absorbing agent 14 from directly contacting the skin when the particulate water-absorbing agent 14 permeates the first substrate 11 and migrates to the outer surface (surface that directly contacts liquid) of the first substrate 11. When the wrapping sheet 16 is not provided, for example, there is a method of sealing by bonding the substrates 11 and 13 to each other, a method of suppressing migration to the outer surface of the first substrate 11 by surface treatment of the first substrate 11, and the like. As a method for preventing the particulate water absorbing agent 14 from falling off the water absorbent sheet 10 while maintaining the effect of the present invention, it is preferable to provide a wrapping sheet 16 .

[0406] The wrapping sheet 16 is disposed on the first substrate 11, and is folded over so as to enclose the entire water-absorbing layer 12 and the second substrate 13. Thus, the wrapping sheet 16 covers the entire first substrate 11, the water-absorbing layer 12, and the second substrate 13. With such a configuration, it is possible to suppress the particulate water-absorbing agent 14 from falling off from the water-absorbing sheet 10. The wrapping sheet 16 does not need to cover the entire first substrate 11, the water-absorbing layer 12, and the second substrate 13. For example, the wrapping sheet 16 may be disposed on the first substrate 11, folded over so as to enclose the side of the water-absorbing layer 12 and the side of the second substrate 13, and folded over the side of the second substrate 13 opposite to the surface that absorbs liquid (i.e., the surface on which the water-absorbing layer 12 is provided). That is, one end of the wrapping sheet 16 overlaps with the other end of the wrapping sheet 16 on the surface of the second substrate 13 opposite to the surface on which the water-absorbing layer 12 is provided. In this case, the wrapping sheet 16 covers the first substrate 11, the water-absorbing layer 12, and the side surface of the second substrate 13, and covers the whole or part of the surface of the second substrate 13 opposite to the surface on which the water-absorbing layer 12 is provided. For example, the wrapping sheet 16 may be disposed on the first substrate 11 and folded so as to enclose the side surface of the water-absorbing layer 12 and the side surface of the second substrate 13, and one end of the wrapping sheet 16 may be disposed apart from the other end of the wrapping sheet 16 on the surface of the second substrate 13 opposite to the surface to be absorbed (i.e., the surface on which the water-absorbing layer 12 is provided). In this case, the wrapping sheet 16 covers the liquid-absorbing surface and side surfaces of the first substrate 11, the side surfaces of the water-absorbing layer 12, and the side surfaces of the second substrate 13, and also covers a part of the surface of the second substrate 13 opposite to the surface on which the water-absorbing layer 12 is provided. Although the wrapping sheet 16 is not an essential component of the water-absorbent sheet according to the present invention, by providing the water-absorbent sheet 10 according to the present invention with the wrapping sheet 16 in such a configuration, it is possible to suppress the particulate water-absorbing agent 14 from falling off from the water-absorbent sheet 10.

[0407] Therefore, the water-absorbent sheet 10 according to the first embodiment of the present invention preferably has at least a wrapping sheet 16 arranged on the surface of the first substrate 11 (i.e., on the liquid-absorbing surface of the first substrate 11). As described above, in this specification, even when the water-absorbent sheet 10 has the wrapping sheet 16, the first substrate 11 forms a liquid-absorbent surface that directly absorbs liquid. For example, in the case of the water-absorbent sheet 10 having the wrapping sheet 16, when the wrapping sheet 16 forms a liquid-absorbent surface that directly absorbs liquid, it can be rephrased as follows; the water-absorbent sheet has a first substrate, a second substrate, a water-absorbent layer located between the first substrate and the second substrate, and a wrapping sheet arranged on the surface of the first substrate, the water-absorbent layer contains a particulate water-absorbing agent, the region containing the particulate water-absorbing agent is arranged with a gap that does not substantially contain the particulate water-absorbing agent, the surface of the wrapping sheet forms a liquid-absorbent surface that directly absorbs liquid, and the first substrate has an elongation rate of 10% or more.

[0408] The wrapping sheet 16 may be fixed to the base materials 11 and 13 by using, for example, an adhesive.

[0409] In the water absorbent sheet 10 according to the first embodiment of the present invention, the first substrate 11 and the particulate water absorbing agent 14 in the water absorbent layer 12 are preferably in contact with each other directly or via an adhesive, and / or the second substrate 13 and the particulate water absorbing agent 14 in the water absorbent layer 12 are preferably in contact with each other directly or via an adhesive. Thus, the water absorbent sheet of the present invention has a simple configuration substantially consisting of only the first substrate, the second substrate, the particulate water absorbing agent sandwiched between the first substrate and the second substrate, an adhesive for fixing the particulate water absorbing agent to at least one of the first substrate and the second substrate, and a wrapping sheet for wrapping a part or all of these as necessary (it is not excluded that the particulate water absorbing agent may contain additives described in this specification). A more preferred embodiment is a simple configuration consisting of only a first substrate, a second substrate, a particulate water absorbing agent sandwiched between the first substrate and the second substrate, an adhesive between the particulate water absorbing agent and the second substrate for fixing the particulate water absorbing agent to the second substrate, and a wrapping sheet for wrapping all of these. That is, the water absorbent sheet of the present invention is one that can effectively reduce the specific return amount despite its simple configuration.

[0410] The water-absorbent sheet according to the second embodiment of the present invention is formed by laminating a laminate in which a first substrate is laminated on a water-absorbent layer A, and a structure in which an intermediate substrate is laminated on a water-absorbent layer B (with the water-absorbent layer positioned on the second substrate) on the second substrate. Hereinafter, the second embodiment will be described based on Fig. 19, but the requirements for the second embodiment to be applicable to the same configuration as the first embodiment will be omitted. Fig. 19 is a schematic diagram showing a cross section of a water-absorbent sheet 20 according to the second embodiment of the present invention.

[0411] 19, the water-absorbent sheet 20 is formed by laminating, in order from the direction in which the liquid to be absorbed is introduced (the direction of the arrow in FIG. 19), a first substrate 11a, a water-absorbent layer 12a (water-absorbent layer A), an intermediate substrate 11b, and a water-absorbent layer 12b (water-absorbent layer B) on a second substrate 13. That is, the water-absorbent sheet 20 is formed by laminating, on the second substrate 13, a laminate 18a in which the first substrate 11a is laminated on the water-absorbent layer 12a, and a construct 18b in which the intermediate substrate 11b is laminated on the water-absorbent layer 12b, with the water-absorbent layers 12a and 12b positioned on the second substrate 13. Hereinafter, the particulate water absorbing agent 14 in the laminate 18a will be referred to as the particulate water absorbing agent 14a, and the gaps 15 in the construct 18b will be referred to as the particulate water absorbing agent 14b, and the gaps 15 in the construct 18b will be referred to as the particulate water absorbing agent 14b, and the gaps 15 in the construct 18b will be referred to as the gaps 15b. Since the first base material 11a in the second embodiment is similar to the first base material 11 in the first embodiment, it may be abbreviated to the first base material 11. Also, the particulate water absorbing agent 14a and the gaps 15a in the second embodiment may be simply referred to as the particulate water absorbing agent 14 and the gaps 15.

[0412] The water absorbing layers 12a and 12b are respectively composed of particulate water absorbing agents 14a and 14b, similarly to the first embodiment. Specifically, the water absorbing layer 12a is composed of the particulate water absorbing agent 14a adhered to the first substrate 11a and the particulate water absorbing agent 14a adhered to the intermediate substrate 11b, and the water absorbing layer 12b is composed of the particulate water absorbing agent 14b adhered to the intermediate substrate 11b and the particulate water absorbing agent 14b adhered to the second substrate 13. In the water absorbing layers 12a and 12b, the regions including the particulate water absorbing agents 14a and 14b are arranged to be separated by gaps 15a and 15b, respectively.

[0413] In the water-absorbent sheet 20, the gaps 15a, 15b (areas where the particulate water-absorbing agent 14 is not present) provided on the intermediate substrate 11b and on a part of the second substrate 13 preferably have the same form as the water-absorbent sheet 10 according to the first embodiment. That is, the areas where the particulate water-absorbing agents 14a, 14b are present and the gaps 15a, 15b preferably have a shape extending along one direction on the liquid-absorbing surface of the first substrate and are arranged in parallel.

[0414] In Fig. 19, the region in which the particulate water absorbing agent 14a is included in the laminate 18a and the region in which the particulate water absorbing agent 14b is included in the constituent 18b are arranged with the same thickness and width so as to overlap in the surface direction of the first base material 11a (i.e., at the same position in the direction perpendicular to the liquid absorbing surface of the first base material 11a), but the positional relationship, thickness, and width relationship are not limited to this. For example, the region in which the particulate water absorbing agent 14a is included in the laminate 18a and the region in which the particulate water absorbing agent 14b is included in the constituent 18b may be arranged so as to be shifted from each other so as not to overlap in the surface direction. Also, the region in which the particulate water absorbing agent 14a is included in the laminate 18a may be made wider or narrower, thicker or thinner than the region in which the particulate water absorbing agent 14b is included in the constituent 18b.

[0415] Particulate water absorbing agents 14a and 14b may be present in the first substrate 11a and the intermediate substrate 11b. For example, the particulate water absorbing agent 14a may be present in the first substrate 11a, while the particulate water absorbing agent 14a may be present on the liquid absorbing surface of the intermediate substrate 11b, and the particulate water absorbing agent 14b may be present on the second substrate 13 side of the intermediate substrate 11b.

[0416] In the water-absorbent sheet 20 according to the second embodiment of the present invention, the first substrate 11, the water-absorbent layer 12, the particulate water-absorbing agent 14, and the gaps 15 in the first embodiment are replaced with the first substrate 11a, the water-absorbent layer 12b, the particulate water-absorbing agent 14a, and the gaps 15a of the laminate 18a arranged on the side where the liquid is introduced, respectively. (1) Content of the particulate water absorbing agent 14 in the first substrate 11 (2) The ratio (Lb / La) of the thickness (Lb) from the liquid absorption surface of the first substrate 11 to the surface of the second substrate 13 on the water absorption layer 12 side in the region containing the particulate water absorbing agent 14 to the thickness (La) from the liquid absorption surface of the first substrate 11 to the surface of the second substrate 13 on the water absorption layer 12 side in the gap 15.

[0417] In the two-layer form (2), the region containing the particulate water absorbing agents 14a, 14b in the laminate 18a and the construct 18b and the gaps 15a, 15b may be formed without overlapping in the surface direction of the first base material 11a. In this case, the gap 15 "in the gap 15" serving as the basis of La is the gap 15a close to the liquid absorbing surface of the first base material 11a (i.e., in the laminate 11a), and the region containing the particulate water absorbing agent 14 "in the region containing the particulate water absorbing agent 14" serving as the basis of Lb is the region containing the particulate water absorbing agent 14a close to the liquid absorbing surface of the first base material 11a (i.e., in the laminate 11a).

[0418] That is, in the water-absorbent sheet 20 according to the second embodiment of the present invention, when the particulate water-absorbing agent 14 is present in the first base material 11a, the content of the particulate water-absorbing agent 14 in the first base material 11a is preferably 5% or more relative to the particulate water-absorbing agent 14 contained in the entire water-absorbent sheet 20.

[0419] In the water absorbent sheet 20 according to the second embodiment of the present invention, the ratio (Lb / La) of the thickness (Lb) from the liquid absorbing surface of the first substrate 11a in the region containing the particulate water absorbing agent 14a to the surface of the water absorbent layer 12b of the second substrate 13 in the gap 15a to the thickness (La) from the liquid absorbing surface of the first substrate 11a to the surface of the water absorbent layer 12b of the second substrate 13 is preferably 1.05 or less. For the content ratio of the particulate water absorbing agent 14a in the first substrate 11a and Lb / La, the preferred ranges of the water absorbent sheet 10 according to the first embodiment can be applied to the water absorbent sheet 20 in the same manner.

[0420] The water-absorbent sheet 20 has a wrapping sheet 16. The wrapping sheet 16 is placed on the first substrate 11a and folded over so as to entirely wrap the laminate 18a, the construct 18b, and the second substrate 13. Therefore, the water-absorbent sheet 20 according to the second embodiment of the present invention preferably has at least the wrapping sheet 16 placed on the surface of the first substrate 11a (i.e., the liquid-absorbing surface of the first substrate).

[0421] In the present specification, the term can be rephrased as follows: a water-absorbent sheet having a first substrate, an intermediate substrate, a second substrate, a water-absorbent layer, and a wrapping sheet, in which a laminate in which the first substrate is laminated on the water-absorbent layer, and a construct in which the intermediate substrate is laminated on the water-absorbent layer are laminated on a second substrate with the water-absorbent layer positioned on the second substrate side, the wrapping sheet is disposed on a surface of the first substrate, the water-absorbent layer contains a particulate water-absorbing agent, and an area in which the particulate water-absorbing agent is contained is disposed apart from the gap that does not substantially contain the particulate water-absorbing agent, the surface of the wrapping sheet forms a liquid-absorbent surface that directly absorbs liquid, and the first substrate has an elongation rate of 10% or more.

[0422] In the water-absorbent sheet 20 according to the second embodiment of the present invention, the first substrate 11a and the particulate water-absorbing agent 14a in the water-absorbent layer 12a are preferably in contact with each other directly or via an adhesive, the intermediate substrate 11b and the particulate water-absorbing agent 14a in the water-absorbent layer 12a are preferably in contact with each other directly or via an adhesive, the intermediate substrate 11b and the particulate water-absorbing agent 14b in the water-absorbent layer 12b are preferably in contact with each other directly or via an adhesive, and / or the second substrate 13 and the particulate water-absorbing agent 14b in the water-absorbent layer 12b are preferably in contact with each other directly or via an adhesive.

[0423] In the water absorbent sheet 20 according to the second embodiment, the ratio of the area containing the particulate water absorbing agent 14a on the surface of the first substrate 11a facing the water absorbent layer 12a (the surface on which the particulate water absorbing agent 14a is disposed) and the ratio of the area containing the particulate water absorbing agent 14b on the water absorbent layer 12b side of the intermediate substrate 11b (the surface on which the particulate water absorbing agent 14b is disposed) are preferably 90% or less in area, more preferably 80% or less, and even more preferably 75% or less. Moreover, the ratio of the area containing the particulate water absorbing agent 14a on the surface of the first substrate 11a facing the water absorbent layer 12a and the ratio of the area containing the particulate water absorbing agent 14b on the water absorbent layer 12b side of the intermediate substrate 11b are preferably 10% or more in area, and more preferably 20% or more. By providing the particulate water absorbing agents 14a, 14b in such a range, the role of the gaps 15a, 15b and the role of the particulate water absorbing agents 14a, 14b are properly balanced, and the effect of reducing the amount of return is further exerted. Note that the ratio of the area including the particulate water absorbing agent 14a on the surface of the first base material 11a facing the water absorbent layer 12a is similar to the ratio of the area including the particulate water absorbing agent 14a on the surface of the intermediate base material 11b facing the water absorbent layer 12a (the surface on which the particulate water absorbing agent 14a is arranged), and the ratio of the area including the particulate water absorbing agent 14b on the water absorbent layer 12b of the intermediate base material 11b is similar to the ratio of the area including the particulate water absorbing agent 14b on the water absorbent layer 12b of the second base material 13 (the surface on which the particulate water absorbing agent 14b is arranged).

[0424] In the water absorbent sheet 20, the ratio of the area in which the particulate water absorbing agents 14a, 14b are present in the first base material 11 or the second base material 13 can be calculated in the same manner as in the water absorbent sheet .

[0425] The content of the particulate water absorbing agent 14 in the water absorbent sheet 20 is preferably 200 to 360 g / m 2 and more preferably 210 to 350 g / m 2 and more preferably 225 to 325 g / m 2In the water absorbent sheet 20, the total amount of the particulate water absorbing agents 14a, 12b present in the water absorbent layers 12a, 12b may be adjusted to be within the above range, and the amount of the particulate water absorbing agents 14a, 12b present in the water absorbent layers 12a, 12b is preferably 2:1 to 1:2, and more preferably 1.5:1 to 1:1.5.

[0426] In the water-absorbent sheets 10 and 20 according to the first and second embodiments of the present invention, according to one embodiment, the first substrate 11 may be in a bulky form (significantly thick form with low bulk density), but it is possible to make it thinner than absorbents used in conventional absorbent articles. When the water-absorbent sheets 10 and 20 are used in paper diapers, the thickness is preferably 15 mm or less, more preferably 10 mm or less, even more preferably 7 mm or less, particularly preferably 5 mm or less, and most preferably 4 mm or less, for example, at 40% RH to 50% RH. On the other hand, the lower limit of the thickness is preferably 0.2 mm or more, more preferably 0.3 mm or more, and even more preferably 0.5 mm or more, in consideration of the strength of the water-absorbent sheets 10 and 20 and the diameter of the particulate water-absorbing agent 14. The thickness of the water-absorbent sheets 10 and 20 used in the examples of the present application was 2 to 5 mm.

[0427] The thicknesses of the first substrate 11, the intermediate substrate 11b, the second substrate 13, the wrapping sheet 16, and the absorbent sheets 10 and 20 in this application were measured using a large-type dial thickness gauge (thickness measuring device) (manufactured by Ozaki Manufacturing Co., Ltd., model number: JB, measuring probe: anvil top and bottom φ50 mm). The number of measurement points was set to 5 different points on the sheet to be measured, and each point was measured twice, and the measured value was the average value of the total 5 points. When measuring the thickness, the hand was slowly released from the handle so as to apply as little pressure as possible to the sheet to be measured, and the thickness was measured. As a specific procedure, the sheet to be measured was attached flat on a plate with a constant thickness so as not to cause wrinkles or distortions at the measurement points of the sheet to be measured, and the plate was set on the lower measuring probe of the thickness measuring device. Next, the upper measuring probe of the thickness measuring device was brought close to a height position of 2 to 3 mm from the sheet to be measured, and then the hand was slowly released from the handle, and the thickness of the sheet to be measured and the plate tog...

Claims

1. A first substrate; A second substrate; a water-absorbing layer located between the first substrate and the second substrate; A water-absorbent sheet having the water absorbing layer includes a particulate water absorbing agent, and a region including the particulate water absorbing agent is disposed with a gap that does not substantially include the particulate water absorbing agent therebetween; a surface of the first substrate forms a liquid-absorbing surface that directly absorbs liquid; The first base material has an elongation percentage of 10% or more and 60% or less, The water-absorbent sheet has an area ratio of the particulate water-absorbing agent of 20% or more and 75% or less.

2. The basis weight of the first substrate is 10 to 60 g / m 2 The water-absorbent sheet according to claim 1 ,

3. The bulk density of the first substrate is 0.1 g / cm 3 3. The water-absorbent sheet according to claim 1 or 2, wherein:

4. The water-absorbent sheet according to any one of claims 1 to 3, wherein the first substrate is an air-through nonwoven fabric.

5. An absorbent sheet as described in any one of claims 1 to 4, comprising a laminate in which the first substrate is laminated on the absorbent layer A, and a construct in which an intermediate substrate is laminated on the absorbent layer B, which are laminated on the second substrate.

6. The water-absorbent sheet according to any one of claims 1 to 5, wherein only a laminate in which the first base material is laminated on the water-absorbent layer is laminated on the second base material.

7. 7. The water-absorbent sheet according to claim 6, wherein a ratio (Lb / La) of a thickness (Lb) from the liquid-absorption surface of the first substrate to the surface of the water-absorption layer side of the second substrate in a region containing the particulate water-absorbing agent to a thickness (La) from the liquid-absorption surface of the first substrate to the surface of the water-absorption layer side of the second substrate in the gap is 1.05 or less.

8. The water-absorbent sheet according to any one of claims 1 to 7, wherein the second substrate is a spunlace nonwoven fabric.

9. The water absorbent sheet according to any one of claims 1 to 8, wherein the first base material contains the particulate water absorbing agent, and a content ratio of the particulate water absorbing agent in the first base material is 5% or more with respect to the particulate water absorbing agent contained in the entire water absorbent sheet.

10. The water-absorbent sheet according to any one of claims 1 to 9, wherein the particulate water-absorbing agent has a transmittance of 40 mass % or more through the first substrate.

11. The water-absorbent sheet according to any one of claims 1 to 10, wherein the region containing the particulate water-absorbing agent and the gaps have a shape extending along one direction on the liquid-absorbent surface of the first substrate and are arranged in parallel.

12. The water-absorbent sheet according to any one of claims 1 to 11, comprising at least a wrapping sheet disposed on a surface of the first substrate.

13. The water-absorbent sheet according to any one of claims 1 to 12, wherein the particulate water-absorbing agent has a CRC of 30 g / g or more.

14. The water-absorbent sheet contains an adhesive, The water-absorbent sheet according to any one of claims 1 to 13, wherein the amount of the adhesive used is 0.05 to 2.0 times the mass of the particulate water-absorbing agent.

15. An absorbent article comprising the water-absorbent sheet according to any one of claims 1 to 14 sandwiched between a liquid-permeable sheet and a liquid-impermeable sheet, the liquid-permeable sheet being positioned on the first substrate side and the liquid-impermeable sheet being positioned on the second substrate side.

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