absorber

Abstract

One embodiment of the present invention relates to an absorber comprising water-absorbing resin particles, wherein the water-absorbing resin particles include water-absorbing resin particles (A) which have a water absorption rate by the Vortex method of 55 to 150 seconds and a non-pressure DW 5 minute value of 36 mL / g or less, and the content of the water-absorbing resin particles (A) based on the total amount of the water-absorbing resin particles is 9 to 90 mass%.

Description

[Technical Field]

[0001] The present invention relates to an absorbent body. [Background technology]

[0002] Conventionally, absorbent articles for absorbing liquids whose main component is water, such as urine, have used absorbents containing water-absorbent resin particles. For example, Patent Document 1 discloses a method for producing water-absorbent resin particles having a particle size suitable for use in absorbent articles such as diapers, and Patent Document 2 discloses a method for using a hydrogel-forming absorbent polymer having specific saline flow conductivity, pressure resistance, etc., as an absorbent member effective for storing aqueous body fluids. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 06-345819 [Patent Document 2] Special Publication No. 09-510889 Summary of the Invention [Problem to be solved by the invention]

[0004] An important performance requirement for absorbent articles is that they are less likely to leak liquid even when worn for long periods of time. One possible method for suppressing liquid leakage is to use water-absorbent resin particles with a high water absorption rate (large water retention capacity after water absorption) as a constituent material of the absorbent body. However, water-absorbent resin particles with a high water absorption rate have poor liquid diffusibility, and as a result, they are unable to sufficiently suppress liquid leakage from absorbent articles. Specifically, when water-absorbent resin particles swell with liquid, the gaps that originally existed between the water-absorbent resin particles are filled with the swollen gel-like water-absorbent resin particles, making it difficult for liquid to pass through the gaps. This phenomenon is generally referred to as the gel-blocking phenomenon. As a result, the diffusibility of liquid within the absorbent body decreases, the entire amount of water-absorbent resin particles contained in the absorbent body cannot be effectively utilized, and liquid that has not been absorbed by the water-absorbent resin particles is more likely to leak from the absorbent body.

[0005] In order to suppress the gel-blocking phenomenon, if water-absorbent resin particles with a slow water-absorption rate (which retains a small amount of water after absorbing water) are used as a constituent material of the absorbent body, the gel-blocking phenomenon is less likely to occur and liquid is more likely to diffuse within the absorbent body. However, if water-absorbent resin particles with a slow water-absorption rate are used, the rate at which the absorbent body absorbs liquid (absorption rate) is likely to become excessively slow. Furthermore, water-absorbent resin particles with a slow water-absorption rate are likely to cause liquid backflow (leakage of liquid once absorbed by the water-absorbent resin particles) when pressurized.

[0006] An object of the present invention is to provide an absorbent body that combines excellent liquid diffusion, a small amount of return, and a fast absorption rate. [Means for solving the problem]

[0007] One aspect of the present invention relates to an absorbent body containing water-absorbent resin particles, the water-absorbent resin particles containing water-absorbent resin particles (A) having a water absorption speed of 55 to 150 seconds as measured by a Vortex method and a 5-minute value of no-pressure DW of 36 mL / g or less, and the content of the water-absorbent resin particles (A) is 9 to 90 mass% based on the total amount of the water-absorbent resin particles. [Effects of the Invention]

[0008] According to the present invention, it is possible to provide an absorbent body that combines excellent liquid diffusibility, a small amount of return, and a fast absorption rate. [Brief explanation of the drawings]

[0009] [Figure 1] FIG. 1 is a cross-sectional view showing an example of an absorbent article. [Figure 2] FIG. 1 is a schematic diagram showing a device for measuring the pressureless DW of water-absorbent resin particles. DETAILED DESCRIPTION OF THE INVENTION

[0010] Hereinafter, several embodiments of the present invention will be described in detail, but the present invention is not limited to the following embodiments.

[0011] In this specification, "acrylic" and "methacrylic" are collectively referred to as "(meth)acrylic." Similarly, "acrylate" and "methacrylate" are also referred to as "(meth)acrylate." "(Poly)" refers to both cases with and without the prefix "poly." In the numerical ranges described in this specification, the upper or lower limit of a certain numerical range can be arbitrarily combined with the upper or lower limit of another numerical range. In the numerical ranges described in this specification, the upper or lower limit of the numerical range may be replaced with a value shown in the Examples. The materials exemplified in this specification may be used alone or in combination of two or more. When multiple substances corresponding to each component are present in the composition, the content of each component refers to the total amount of the multiple substances present in the composition, unless otherwise specified. "Room temperature" refers to 25±2°C. The term "layer" encompasses structures that are formed over the entire surface as well as structures that are formed only partially when observed in a plan view. "Saline" refers to a 0.9% by mass aqueous solution of sodium chloride.

[0012] [Absorbent] The absorbent body according to the present embodiment contains water-absorbent resin particles (A) having a water absorption speed of 55 to 150 seconds by the Vortex method and a 5-minute no-pressure DW value of 36 mL / g or less. The content of the water-absorbent resin particles (A) in the absorbent body is 9 to 90 mass % based on the total amount of the water-absorbent resin particles.

[0013] When the water-absorbent resin particles (A) have a water-absorption rate of 55 seconds or more, the occurrence of gel blocking can be easily suppressed. When the water-absorbent resin particles (A) have a water-absorption rate of 150 seconds or less, the water-absorbent resin particles (A) have excellent water-absorbency and are easy to improve the dry feeling. Since the effects of the present invention are more easily exhibited, the water-absorbent resin particles (A) may have a water-absorption rate of 58 seconds or more, 60 seconds or more, or 61 seconds or more, and preferably 63 seconds or more, 65 seconds or more, or 67 seconds or more. Furthermore, the water-absorption rate may be 130 seconds or less, 110 seconds or less, or 90 seconds or less, and preferably 80 seconds or less, 75 seconds or less, or 70 seconds or less. The water-absorption rate by the Vortex method is measured in accordance with Japanese Industrial Standard JIS K 7224 (1996), as described in the Examples below.

[0014] When the 5-minute value of the no-pressure DW of the water-absorbent resin particles (A) is 36 mL / g or less, the amount of water absorbed in the initial stage of water absorption is reduced, thereby increasing urine diffusibility, leading to an improvement in the absorption rate and the absorbent utilization (the utilization of the entire water-absorbent resin particles contained in the absorbent). From the viewpoint of achieving both excellent liquid diffusibility and excellent return flow, the 5-minute value of the no-pressure DW of the water-absorbent resin particles (A) may be 35 mL / g or less, 34 mL / g or less, or 33 mL / g or less, preferably 30 mL / g or less, 20 mL / g or less, or 15 mL / g or less, and more preferably 10 mL / g or less, 8 mL / g or less, or 5 mL / g or less. The lower limit of the 5-minute value of the no-pressure DW may be 1 mL / g or more. The 5-minute value of the no-pressure DW is measured by the method described in the Examples below. The 5-minute value of no-pressure DW is the water absorption rate expressed as the amount of saline solution absorbed by the water-absorbent resin particles within 5 minutes after contact with the saline solution under no pressure. The no-pressure DW is expressed as the absorption amount [mL] per 1 g of water-absorbent resin particles before absorbing the saline solution.

[0015] The water-retention capacity of the water-absorbent resin particles (A) for saline may be, for example, 16 g / g or more, 18 g / g or more, or 20 g / g or more, from the viewpoint of more easily achieving both excellent liquid diffusibility and excellent return flow. The water-retention capacity for saline may be 50 g / g or less, 45 g / g or less, or 40 g / g or less, preferably 35 g / g or less or 30 g / g or less, and more preferably 25 g / g or less or 22 g / g or less. The water-retention capacity for saline is measured by the method described in the Examples below.

[0016] The absorbent according to the present embodiment contains 9 to 90% by mass of water-absorbent resin particles (A) based on the total amount of water-absorbent resin particles, thereby achieving excellent liquid diffusibility, a small amount of return, and a fast absorption rate. From the viewpoint of an excellent amount of return and a fast absorption rate, the content of the water-absorbent resin particles (A) may be 10% by mass or more, 12% by mass or more, or 16% by mass or more, preferably 20% by mass or more, 30% by mass or more, or 33% by mass or more, and more preferably 50% by mass or more, 55% by mass or more, 60% by mass or more, or 66% by mass or more. From the viewpoint of achieving both excellent liquid diffusibility and a fast absorption rate, the content of the water-absorbent resin particles (A) may be 88% by mass or less, 86% by mass or less, 85% by mass or less, or 84% by mass or less.

[0017] The constitution of the water-absorbent resin particles (A) is not particularly limited as long as the resin satisfies the above-mentioned water absorption rate and 5-minute value of no-pressure DW. The water-absorbent resin particles (A) may be, for example, coated resin particles having a water-insoluble coating layer that covers at least a part of the surface of the water-absorbent resin particles.

[0018] The water-absorbent resin particles constituting the coated resin particles are not particularly limited as long as they are made of a resin having water-absorbing properties, and may include, for example, a crosslinked polymer formed by polymerization of a monomer containing an ethylenically unsaturated monomer. The crosslinked polymer may have a monomer unit derived from the ethylenically unsaturated monomer. The water-absorbent resin particles can be produced, for example, by a method including a step of polymerizing a monomer containing an ethylenically unsaturated monomer. Examples of the polymerization method include reverse-phase suspension polymerization, aqueous solution polymerization, bulk polymerization, and precipitation polymerization.

[0019] The ethylenically unsaturated monomer may be a water-soluble ethylenically unsaturated monomer (an ethylenically unsaturated monomer having a solubility of 1 g or more in 100 g of water at 98°C). Examples of water-soluble ethylenically unsaturated monomers include (meth)acrylic acid and its salts, 2-(meth)acrylamido-2-methylpropanesulfonic acid and its salts, (meth)acrylamide, N,N-dimethyl(meth)acrylamide, 2-hydroxyethyl(meth)acrylate, N-methylol(meth)acrylamide, polyethylene glycol mono(meth)acrylate, N,N-diethylaminoethyl(meth)acrylate, N,N-diethylaminopropyl(meth)acrylate, and diethylaminopropyl(meth)acrylamide. When the ethylenically unsaturated monomer has an amino group, the amino group may be quaternized. The ethylenically unsaturated monomer may be used alone or in combination of two or more.

[0020] When the ethylenically unsaturated monomer has an acid group, the acid group may be neutralized with an alkaline neutralizing agent before the polymerization reaction. The degree of neutralization of the ethylenically unsaturated monomer with the alkaline neutralizing agent may be, for example, 10 to 100 mol %, 50 to 90 mol %, or 60 to 80 mol % of the acid group in the ethylenically unsaturated monomer.

[0021] From the viewpoint of industrial ease of availability, the ethylenically unsaturated monomer may include at least one compound selected from the group consisting of (meth)acrylic acid and its salts, acrylamide, methacrylamide, and N,N-dimethylacrylamide. The ethylenically unsaturated monomer may include at least one compound selected from the group consisting of (meth)acrylic acid and its salts, and acrylamide.

[0022] As a monomer for obtaining water-absorbing resin particles, a monomer other than the above-mentioned ethylenically unsaturated monomer may be used. Such a monomer may be used, for example, by mixing with an aqueous solution containing the above-mentioned ethylenically unsaturated monomer. The amount of the ethylenically unsaturated monomer used may be 70 to 100 mol% based on the total amount of monomers. The proportion of (meth)acrylic acid and its salts may be 70 to 100 mol% based on the total amount of monomers.

[0023] Self-crosslinking may occur during polymerization, but crosslinking may be promoted by using an internal crosslinking agent. The use of an internal crosslinking agent makes it easy to control the water absorption properties (water retention capacity, etc.) of the water-absorbent resin particles. The internal crosslinking agent is usually added to the reaction solution during the polymerization reaction.

[0024] The water-absorbent resin particles may be crosslinked near the surface (surface crosslinked). The water-absorbent resin particles may be composed of polymer particles (crosslinked polymers) alone, or may further contain various additional components selected from, for example, gel stabilizers, metal chelating agents, and flow improvers (lubricants). The additional components may be located inside the polymer particles, on the surfaces of the polymer particles, or both. The additional component may be a flow improver (lubricant). The flow improver may contain inorganic particles. Examples of inorganic particles include silica particles such as amorphous silica.

[0025] The shape of the water-absorbent resin particles is not particularly limited, and may be, for example, substantially spherical, crushed or granular, or may be an aggregate of primary particles having these shapes.

[0026] The median particle diameter of the water-absorbent resin particles may be 100 to 800 μm, 150 to 700 μm, 200 to 600 μm, or 250 to 500 μm. The median particle diameter can be measured by the following method.

[0027] <Measuring method for median particle size> JIS standard sieves were stacked in the following order from top to bottom: a 600 μm mesh sieve, a 500 μm mesh sieve, a 425 μm mesh sieve, a 300 μm mesh sieve, a 250 μm mesh sieve, a 180 μm mesh sieve, a 150 μm mesh sieve, and a tray. 50 g of water-absorbent resin particles were placed on the top sieve and classified in accordance with JIS Z 8815 (1994) using a Rotap shaker (manufactured by Iida Seisakusho Co., Ltd.). After classification, the mass of the particles remaining on each sieve was calculated as a mass percentage of the total mass to determine the particle size distribution. The particles remaining on the sieves were integrated in descending order of particle size, and the relationship between the sieve opening size and the integrated value of the mass percentage of the particles remaining on the sieves was plotted on logarithmic probability paper. By connecting the plots on the probability paper with a straight line, the particle size corresponding to a cumulative mass percentage of 50 mass % is obtained as the median particle size.

[0028] The water-insoluble coating layer constituting the coated resin particles is a layer containing a water-insoluble component. In this specification, the water-insoluble component may include not only a substance that is completely insoluble in water, but also a substance that is slightly soluble in water (a poorly water-soluble substance). The solubility of the water-insoluble component in 100 g of water at 98°C is, for example, less than 10 g, preferably less than 5 g, more preferably less than 3 g, and even more preferably less than 1 g.

[0029] The coating layer may be a layer containing at least one water-insoluble component selected from water-insoluble organic compounds and water-insoluble inorganic compounds.

[0030] Examples of water-insoluble organic compounds include polyurethane, polyolefin, polyester, polyamide, polystyrene, polycarbonate, polyacrylate, polyacetal, and acid-modified versions thereof. The water-insoluble organic compound preferably contains at least one selected from the group consisting of polyolefin, polyurethane, polyester, and acid-modified versions thereof, more preferably contains at least one selected from the group consisting of polyolefin, polyurethane, and acid-modified versions thereof, and even more preferably contains acid-modified polyolefin and / or polyurethane. These organic compounds may be used alone or in combination.

[0031] When the water-insoluble component is acid-modified, the water-insoluble component may be modified with at least one acid anhydride selected from the group consisting of maleic anhydride, succinic anhydride, and phthalic anhydride. The material to be modified with the acid anhydride is preferably a polyolefin, more preferably at least one selected from the group consisting of polyethylene, polypropylene, and an ethylene-propylene copolymer, and even more preferably an ethylene-propylene copolymer. Furthermore, the acid anhydride used for modification is preferably maleic anhydride.

[0032] Polyurethane is a reaction product of a polyol and a polyisocyanate. Examples of polyols include polyether polyols, polyester polyols, polybutadiene polyols, and hydrogenated polybutadiene polyols. Examples of polyisocyanates include aromatic isocyanates such as diphenylmethane diisocyanate, dimethyldiphenylmethane diisocyanate, tolylene diisocyanate, xylylene diisocyanate, and p-phenylene diisocyanate; alicyclic isocyanates such as dicyclohexylmethane diisocyanate and isophorone diisocyanate; and aliphatic isocyanates such as hexamethylene diisocyanate.

[0033] Examples of water-insoluble inorganic compounds include light anhydrous silicic acid, calcium silicate, silicon dioxide (silica), talc, silicon monoxide, and synthetic hydrotalcite. These inorganic compounds may be used alone or in combination. Since a coating layer formed therefrom can exhibit relatively high water permeability, at least one of silicon dioxide and talc is preferably used, and silicon dioxide is more preferably used. Silicon dioxide may be hydrophilic or hydrophobic, but is preferably hydrophobic because it can easily achieve the water absorption rate and 5-minute value of the unpressurized DW of the water-absorbent resin particles described above.

[0034] When forming a coating layer on water-absorbent resin particles, the water-absorbent resin particles may be mixed with a coating material to form a coating layer on at least a part of the surface of the water-absorbent resin particles. The coating material is, for example, a component capable of forming the above-mentioned coating layer or a material for forming the component. For example, when the coating layer contains polyurethane, the coating material may contain polyurethane itself, or may contain polyol and polyisocyanate, which are materials for forming the polyurethane.

[0035] The method for forming the coating layer is not particularly limited. For example, after dispersing water-absorbent resin particles, a coating material can be brought into contact with the dispersed water-absorbent resin particles to form a coating layer. Specifically, when the coating material is soluble in a dispersion medium for dispersing polymer particles, the water-absorbent resin particles and the coating material may be added to the dispersion medium to form a coating layer on the surface of the water-absorbent resin particles. Furthermore, when a polyol and a polyisocyanate are used as the coating material, an aqueous solution of the polyol may be mixed with a dispersion of water-absorbent resin particles to bring the water-absorbent resin particles and the polyol into contact, and then a liquid containing the polyisocyanate may be added to polymerize the polyol and the polyisocyanate, thereby forming a coating layer containing polyurethane on the surface of the polymer particles.

[0036] The dispersion medium may contain a hydrocarbon solvent, such as: chain aliphatic hydrocarbons such as n-hexane, n-heptane, 2-methylhexane, 3-methylhexane, 2,3-dimethylpentane, 3-ethylpentane, and n-octane; alicyclic hydrocarbons such as cyclohexane, methylcyclohexane, cyclopentane, methylcyclopentane, trans-1,2-dimethylcyclopentane, cis-1,3-dimethylcyclopentane, and trans-1,3-dimethylcyclopentane; and aromatic hydrocarbons such as benzene, toluene, and xylene.

[0037] When a solid inorganic compound is used as the coating material, a particle compositing device can be used to press the coating material onto the surface of water-absorbent resin particles to form a coating layer. Specifically, a predetermined amount of water-absorbent resin particles and a solid inorganic compound are charged into the particle compositing device. Thereafter, stress (compressive stress and shear stress) is applied to the water-absorbent resin particles and the inorganic compound by rotating an agitator blade provided in the device, and the inorganic compound is pressed onto the surface of the water-absorbent resin particles by the stress, thereby producing coated resin particles.

[0038] The absorbent body according to this embodiment contains water-absorbent resin particles (B) that are different from the water-absorbent resin particles (A). The water-absorbent resin particles (B) have a water absorption rate measured by a Vortex method or a 5-minute value of non-pressurized DW that is different from that of the water-absorbent resin particles (A). As the water-absorbent resin particles (B), conventional water-absorbent resin particles may be used, and for example, water-absorbent resin particles before forming a coating layer with the above-mentioned coated resin particles may be used.

[0039] The water absorption capacity of the water-absorbent resin particles (B) is not particularly limited, provided that at least one of the water absorption rate measured by the Vortex method and the 5-minute value of the non-pressure DW is different from that of the water-absorbent resin particles (A). The water-absorbent resin particles (B) at least satisfy either a water absorption rate measured by the Vortex method of less than 55 seconds, a water absorption rate measured by the Vortex method of more than 150 seconds, or a 5-minute value of the non-pressure DW of more than 36 mL / g.

[0040] The water absorption rate of the water-absorbent resin particles (B) measured by the Vortex method may be, for example, 20 seconds or more or 25 seconds or more, or 160 seconds or less, 155 seconds or less, or 153 seconds or less, or 60 seconds or less, 55 seconds or less, or 53 seconds or less. The 5-minute value of the no-pressure DW of the water-absorbent resin particles (B) may be 5 mL / g or more or 9 mL / g or more, preferably 35 mL / g or more, 38 mL / g or more, 40 mL / g or more, or 45 mL / g or more, and more preferably 50 mL / g or more or 54 mL / g or more. The 5-minute value of the no-pressure DW of the water-absorbent resin particles (B) may be 65 mL / g or less or 60 mL / g, and preferably 55 mL / g or less or 54 mL / g or less.

[0041] The water-retention capacity of the water-absorbent resin particles (B) for physiological saline may be 35 g / g or more, 38 g / g or more, or 40 g / g or more, and may be 60 g / g or less, 55 g / g or less, or 50 g / g or less.

[0042] The absorbent body according to the present embodiment may contain fibrous material, for example, a mixture containing water-absorbent resin particles and fibrous material. The absorbent body may have a configuration in which the water-absorbent resin particles and fibrous material are uniformly mixed, a configuration in which the water-absorbent resin particles are sandwiched between fibrous material formed in a sheet or layer shape, or another configuration.

[0043] Examples of fibrous materials include finely ground wood pulp, cotton, cotton linters, rayon, cellulosic fibers such as cellulose acetate, synthetic fibers such as polyamide, polyester, and polyolefin, and mixtures of these fibers.The fibrous materials may be used alone or in combination of two or more.Hydrophilic fibers can be used as the fibrous material.

[0044] To improve the shape retention of the absorbent body before and during use, an adhesive binder may be added to the fibrous material to bond the fibers together. Examples of adhesive binders include heat-fusible synthetic fibers, hot-melt adhesives, and adhesive emulsions. The adhesive binders may be used alone or in combination of two or more.

[0045] Examples of heat-fusible synthetic fibers include full-melt binders such as polyethylene, polypropylene, and ethylene-propylene copolymers; and non-full-melt binders having a side-by-side or core-sheath structure of polypropylene and polyethylene. In the above-mentioned non-full-melt binders, only the polyethylene portion can be heat-fused.

[0046] Examples of hot melt adhesives include mixtures of base polymers such as ethylene-vinyl acetate copolymer, styrene-isoprene-styrene block copolymer, styrene-butadiene-styrene block copolymer, styrene-ethylene-butylene-styrene block copolymer, styrene-ethylene-propylene-styrene block copolymer, and amorphous polypropylene with tackifiers, plasticizers, antioxidants, and the like.

[0047] The adhesive emulsion may be, for example, a polymer of at least one monomer selected from the group consisting of methyl methacrylate, styrene, acrylonitrile, 2-ethylhexyl acrylate, butyl acrylate, butadiene, ethylene, and vinyl acetate.

[0048] The absorbent body according to the present embodiment may contain inorganic powder (for example, amorphous silica), a deodorant, an antibacterial agent, a pigment, a dye, a fragrance, an adhesive, etc. When the water-absorbent resin particles contain inorganic particles, the absorbent body may contain the inorganic powder separately from the inorganic particles in the water-absorbent resin particles.

[0049] The absorbent body according to this embodiment may be, for example, in the form of a sheet, and the thickness of the absorbent body (for example, the thickness of a sheet-shaped absorbent body) may be 0.1 to 20 mm or 0.3 to 15 mm.

[0050] [Absorbent articles] The absorbent article according to this embodiment includes the absorbent body according to this embodiment. Other components of the absorbent article include a core wrap that maintains the shape of the absorbent body and prevents the components of the absorbent body from falling off or flowing; a liquid-permeable sheet that is placed on the outermost side on the side where the liquid to be absorbed penetrates; and a liquid-impermeable sheet that is placed on the outermost side on the side opposite the side where the liquid to be absorbed penetrates. Examples of absorbent articles include diapers (e.g., disposable diapers), toilet training pants, incontinence pads, sanitary materials (sanitary napkins, tampons, etc.), sweat pads, pet sheets, parts for portable toilets, and animal waste disposal materials.

[0051] Fig. 1 is a cross-sectional view showing an example of an absorbent article. The absorbent article 100 shown in Fig. 1 comprises an absorbent body 10, core wrap sheets 20a and 20b, a liquid-permeable sheet 30, and a liquid-impermeable sheet 40. In the absorbent article 100, the liquid-impermeable sheet 40, the core wrap sheet 20b, the absorbent body 10, the core wrap sheet 20a, and the liquid-permeable sheet 30 are layered in this order. In Fig. 1, some parts are shown as having gaps between the members, but the members may be in close contact with each other without any gaps.

[0052] The absorbent body 10 has water-absorbent resin particles 10a and a fiber layer 10b containing fibrous material. The water-absorbent resin particles 10a are dispersed in the fiber layer 10b. The water-absorbent resin particles 10a are a mixture of water-absorbent resin particles (A) and water-absorbent resin particles (B).

[0053] The core wrap sheet 20a is arranged on one side of the absorbent body 10 (the upper side of the absorbent body 10 in FIG. 1) while in contact with the absorbent body 10. The core wrap sheet 20b is arranged on the other side of the absorbent body 10 (the lower side of the absorbent body 10 in FIG. 1) while in contact with the absorbent body 10. The absorbent body 10 is arranged between the core wrap sheets 20a and 20b. Examples of the core wrap sheets 20a and 20b include tissue, nonwoven fabric, woven fabric, synthetic resin films with liquid-permeable holes, and net-like sheets with mesh. The core wrap sheets 20a and 20b have, for example, a main surface of the same size as the absorbent body 10.

[0054] The liquid-permeable sheet 30 is disposed on the outermost side where the liquid to be absorbed penetrates. The liquid-permeable sheet 30 is disposed on the core wrap sheet 20a in contact with the core wrap sheet 20a. Examples of the liquid-permeable sheet 30 include nonwoven fabrics and porous sheets made of synthetic resins such as polyethylene, polypropylene, polyester, and polyamide.

[0055] The liquid-impermeable sheet 40 is disposed at the outermost side of the absorbent article 100, opposite the liquid-permeable sheet 30. The liquid-impermeable sheet 40 is disposed below the core wrap sheet 20b in a state of contact with the core wrap sheet 20b. Examples of the liquid-impermeable sheet 40 include sheets made of synthetic resins such as polyethylene, polypropylene, and polyvinyl chloride, and sheets made of composite materials of these synthetic resins and nonwoven fabric.

[0056] The liquid-permeable sheet 30 and the liquid-impermeable sheet 40 have, for example, a main surface that is wider than the main surface of the absorbent body 10, and the outer edges of the liquid-permeable sheet 30 and the liquid-impermeable sheet 40 extend around the absorbent body 10 and the core wrap sheets 20a, 20b.

[0057] The size relationships among the absorbent body 10, core wrap sheets 20a and 20b, liquid-permeable sheet 30, and liquid-impermeable sheet 40 are not particularly limited and are adjusted as appropriate depending on the intended use of the absorbent article, etc. Furthermore, the method for maintaining the shape of the absorbent body 10 using the core wrap sheets 20a and 20b is not particularly limited, and the absorbent body may be wrapped with multiple core wrap sheets as shown in Figure 1, or may be wrapped with a single core wrap sheet.

[0058] The lower limit of the diffusion length of an absorbent article using the absorbent body according to this embodiment may be 25 cm or more, 28 cm or more, or 30 cm or more, and the upper limit of the diffusion length may be 40 cm or less or 35 cm or less. The upper limit of the return amount of the absorbent article may be 4.0 g or less, 3.0 g or less, 2.0 g or less, or 1.0 g or less, and the lower limit of the return amount may be 0.01 g or 0.05 g. The upper limit of the absorption speed of the absorbent article may be 65 seconds or less, 60 seconds or less, 55 seconds or less, or 50 seconds or less, and the lower limit of the absorption speed may be 1 second or more, 5 seconds or more, or 10 seconds or more. The lower limit of the diffusion area of ​​the absorbent article may be 300 cm. 2 Above, 315cm 2 More than 350cm 2 or more, or 400cm 2 The upper limit of the diffusion area is 480 cm 2 or less than 450cm 2 Each of the above-mentioned performances of the absorbent article is measured by the method described in the examples below. [Example]

[0059] The present invention will be described in more detail below with reference to examples, although the present invention is not limited to these examples.

[0060] [Preparation of water-absorbent resin particles] (Production Example 1) A round-bottom, cylindrical, separable flask with an inner diameter of 11 cm and an internal volume of 2 L was prepared, equipped with a reflux condenser, a dropping funnel, a nitrogen gas inlet tube, and a stirrer. The stirrer had a two-stage, four-paddle blade arrangement with a blade diameter of 5 cm. 293 g of n-heptane and 0.736 g of maleic anhydride-modified ethylene-propylene copolymer (Hiwax 1105A, Mitsui Chemicals, Inc.) as a dispersant were added to the flask and mixed. The mixture in the flask was stirred at 300 rpm while heating to 80 °C to dissolve the dispersant in n-heptane. The resulting solution was then cooled to 50 °C.

[0061] A 300 mL beaker was charged with 92.0 g of an 80.5% by weight aqueous solution of acrylic acid (1.03 mol of acrylic acid) as a water-soluble ethylenically unsaturated monomer. While cooling, 147.7 g of a 20.9% by weight aqueous solution of sodium hydroxide was added dropwise to the beaker to neutralize the 75 mol% acrylic acid. Next, 0.092 g of hydroxyethyl cellulose (Sumitomo Seika Chemicals Co., Ltd., HEC AW-15F) was added as a thickener, 0.0736 g (0.272 mmol) of potassium persulfate as a radical polymerization initiator, and 0.010 g (0.057 mmol) of ethylene glycol diglycidyl ether as an internal crosslinker. The first aqueous solution was prepared by dissolving the solution.

[0062] The first-stage aqueous solution was added to the separable flask and stirred for 10 minutes. Next, a surfactant solution prepared by dissolving 0.736 g of sucrose stearate (Ryoto Sugar Ester S-370, HLB: 3, Mitsubishi Chemical Foods Corporation) in 6.62 g of n-heptane was added to the flask to obtain a reaction solution. The system was thoroughly purged with nitrogen while stirring the reaction solution at a stirrer speed of 550 rpm. The flask was then immersed in a 70°C water bath to heat the reaction solution, and the polymerization reaction was allowed to proceed for 60 minutes to obtain a first-stage polymerization slurry.

[0063] A 500 mL beaker was charged with 128.8 g of an 80.5% by weight acrylic acid solution (1.43 mol of acrylic acid). While cooling from the outside, 159.0 g of a 27% by weight sodium hydroxide solution was added dropwise to neutralize the 75 mol% acrylic acid. To the beaker containing the neutralized acrylic acid solution, 0.103 g (0.381 mmol) of potassium persulfate as a radical polymerization initiator and 0.0116 g (0.067 mmol) of ethylene glycol diglycidyl ether as an internal crosslinking agent were added and dissolved to prepare the second aqueous solution.

[0064] While stirring at a stirrer speed of 1000 rpm, the first-stage polymerization slurry in the flask was cooled to 25°C, and the entire amount of the second-stage aqueous solution was added. After purging the flask with nitrogen for 30 minutes, the flask was again immersed in a 70°C water bath to raise the temperature of the reaction solution, and the second-stage polymerization reaction was carried out for 60 minutes to obtain a hydrogel polymer. The flask was then immersed in an oil bath set at 125°C, and 257.7 g of water was extracted from the system by azeotropic distillation of n-heptane and water. Next, 4.42 g (0.507 mmol) of a 2% by weight aqueous solution of ethylene glycol diglycidyl ether was added as a surface crosslinking agent to the flask, and the mixture was maintained at 83°C for 2 hours.

[0065] Furthermore, the flask was immersed in an oil bath at 125°C to remove (dry) n-heptane, thereby obtaining polymer particles (dried material). The polymer particles were passed through an 850µm JIS standard sieve to obtain 228.0g of water-absorbent resin particles (B1). The above operation was repeated to produce 2kg of water-absorbent resin particles (B1) having a median particle size of 352µm.

[0066] (Production Example 2) A mixture of 4 g of polyether polyol (AGC, EXCENOL 750ED) and 76 g of distilled water (1) (80 g) was prepared. A mixture of 4.76 g of tolylene-2,4-disulfonate and 42.84 g of acetone (2) (47.6 g) was prepared.

[0067] Next, the same flask as in Production Example 1 was prepared. 40 g of water-absorbent resin particles (B1) and 480 g of n-heptane were added to the flask to obtain a dispersion. Mixed liquid (1) was added to the dispersion and stirred at room temperature for 30 minutes, and then mixed liquid (2) was added and stirred at room temperature for 120 minutes, allowing a sequential polymerization reaction to proceed on the surface of the water-absorbent resin particles (B1) to obtain a reaction product. Next, the reaction product was heated in an oil bath at 125°C, and 76 g of water and acetone were extracted from the system by azeotropic distillation of n-heptane and water while refluxing n-heptane.

[0068] Thereafter, the flask was immersed in an oil bath at 125°C to remove (dry) n-heptane, acetone, and water, thereby obtaining a dried product. The dried product was passed through a JIS standard sieve with an opening of 850 µm, thereby obtaining 38.2 g of water absorbent resin particles (A1) having a coating layer containing polyurethane.

[0069] (Production Example 3) The same flask as in Production Example 1 was prepared. 250 g of n-heptane, 100 g of water-absorbent resin particles (B1), and 20 g of maleic anhydride-modified ethylene-propylene copolymer (Hiwax 1105A, Mitsui Chemicals, Inc.) were placed in the flask, and the mixture was stirred at 1,000 rpm while being heated to 85°C and stirred for 10 minutes.

[0070] The n-heptane was then removed by drying in an oil bath at 125°C to obtain a dried product. The dried product was passed through a JIS standard sieve with an opening of 850 μm to obtain 111.52 g of water-absorbent resin particles (A2) having a coating layer containing maleic anhydride-modified ethylene-propylene copolymer.

[0071] (Production Example 4) 100 g of water-absorbent resin particles (B1) and 5.0 g of hydrophobic silica, Nipsil (Tosoh Silica Corporation, product number: SS-30P), were added to a 2 L round-bottom cylindrical separable flask. Next, the flask was immersed in a 125°C oil bath while dispersing at a rotation speed of 150 rpm using a silicone anchor blade, and mixed for 20 minutes while maintaining the internal temperature at 100°C.

[0072] Thereafter, the round-bottom flask was removed from the 125°C oil bath, and the mixture was allowed to cool to room temperature while stirring with a silicon anchor blade, thereby obtaining a precursor of coated resin particles. This precursor was passed through a JIS standard sieve with an opening of 850 µm, thereby obtaining 102.21 g of water-absorbent resin particles (A3) having a coating layer containing hydrophobic silica.

[0073] (Production Example 5) An absorbent mixture composed of water-absorbent resin particles and pulp was taken out from a commercially available baby diaper in Japan (Unicharm Corporation, product name: Mooney Air Fit, L size, tape type). Next, the pulp was removed from the absorbent mixture to obtain approximately 40 g of water-absorbent resin particles (B2).

[0074] (Production Example 6) An absorbent mixture composed of water-absorbent resin particles and pulp was taken out from a baby diaper (Kao Corporation, product name: Merries Suhada Sarasara Air Through, L size, tape type) commercially available in Japan. Next, the pulp was removed from the absorbent mixture to obtain approximately 42 g of water-absorbent resin particles (B3).

[0075] (Production Example 7) 101.75 g of water absorbent resin particles (B4) having a coating layer containing amorphous silica was obtained in the same manner as in Production Example 4, except that the hydrophobic silica was changed to Toxil (Oriental Silicas Corporation, product number: NP-S), which is hydrophilic silica.

[0076] (Production Example 8) The same flask as in Preparation Example 1 was prepared. 293 g of n-heptane and 0.736 g of maleic anhydride-modified ethylene-propylene copolymer (Hiwax 1105A, Mitsui Chemicals, Inc.) as a dispersant were added to the flask and mixed. The mixture in the flask was stirred at 300 rpm and heated to 80°C to dissolve the dispersant in the n-heptane, and the resulting solution was then cooled to 50°C.

[0077] A 300 mL beaker was charged with 92.0 g of 80.5 wt% acrylic acid (1.03 mol) as a water-soluble ethylenically unsaturated monomer. While cooling, 147.7 g of 20.9 wt% sodium hydroxide solution was added dropwise to the beaker to neutralize the 75 mol% acrylic acid. Next, 1.376 g of hydroxyethyl cellulose (Sumitomo Seika Chemicals Co., Ltd., HEC AW-15F) was added as a thickener, 0.0184 g (0.068 mmol) of potassium persulfate as a radical polymerization initiator, 0.0920 g (0.339 mmol) of 2,2'-azobis(2-methylpropionamidine) dihydrochloride as a water-soluble azo polymerization initiator, and 0.0101 g (0.057 mmol) of ethylene glycol diglycidyl ether as an internal crosslinker.

[0078] The first-stage aqueous solution was added to the separable flask and stirred for 10 minutes. Next, a surfactant solution prepared by dissolving 0.736 g of sucrose stearate (Ryoto Sugar Ester S-370, HLB: 3, Mitsubishi Chemical Foods Corporation) in 6.62 g of n-heptane was added to the flask to obtain a reaction solution. The reaction solution was stirred at a stirrer speed of 400 rpm while the system was thoroughly purged with nitrogen. The flask was then immersed in a 66°C water bath to heat the reaction solution. The polymerization reaction was allowed to proceed for 60 minutes while maintaining the temperature at 56°C, yielding a first-stage polymerization slurry.

[0079] Next, while stirring at a rotation speed of 1000 rpm, the flask was immersed in an oil bath set to 125°C, and 108.12 g of water was extracted from the system by azeotropic distillation of n-heptane and water. Thereafter, 4.60 g (0.528 mmol) of a 2 mass% aqueous solution of ethylene glycol diglycidyl ether was added as a surface cross-linking agent to the flask, and the mixture was maintained at 83°C for 2 hours.

[0080] Furthermore, the flask was immersed in an oil bath at 125°C to remove (dry) n-heptane, thereby obtaining polymer particles (dried material). The polymer particles were passed through a JIS standard sieve with an opening of 850 µm, thereby obtaining 99.95 g of water-absorbent resin particles (B5).

[0081] [Evaluation of water-absorbent resin particles] The water-absorbent resin particles were evaluated as follows, and the results are shown in Table 1.

[0082] (1) Water retention capacity The water retention capacity (room temperature) of the water-absorbent resin particles in physiological saline was measured using the following procedure. First, a cotton bag (membrane broadcloth No. 60, 100 mm wide x 200 mm long) containing 2.0 g of water-absorbent resin particles was weighed out and placed in a 500 mL beaker. 500 g of physiological saline was poured into the cotton bag containing the water-absorbent resin particles all at once, taking care not to smear the bag. The top of the cotton bag was then tied with a rubber band and allowed to stand for 30 minutes to allow the water-absorbent resin particles to swell. After 30 minutes had elapsed, the cotton bag was dehydrated for 1 minute using a dehydrator (manufactured by Kokusan Co., Ltd., product number: H-122) set to a centrifugal force of 167 G, and the mass (Wa [g]) of the cotton bag containing the swollen gel after dehydration was measured. The same procedure was performed without adding the water-absorbent resin particles, and the empty mass (Wb [g]) of the cotton bag when wet was measured. The water retention capacity of the water-absorbent resin particles in physiological saline was calculated using the following formula. Water retention amount [g / g]=(Wa-Wb) / 2.0

[0083] (2) Water absorption rate by the Vortex method 50.0 g of physiological saline was added to a 100 mL beaker containing a rotor (8 mm × 30 mm, without ring), and the beaker was kept at 25°C in a thermostatic bath. Next, 2.0 g of water-absorbent resin particles for evaluation were added to the vortex of physiological saline stirred at 600 rpm, and measurement with a stopwatch was started at the same time. The time when the vortex disappeared and the liquid level became horizontal was set as the end point, and the time (seconds) up to that point was taken as the water absorption rate.

[0084] (3) Unpressurized DW The unpressurized DW of the water-absorbent resin particles was measured using a measuring device Z shown in FIG. 2. The measuring device Z has a burette unit 71, a conduit 72, a flat measurement table 73, a nylon mesh 74, a stand 75, and a clamp 76. The burette unit 71 has a burette 71a with a scale, a rubber stopper 71b that seals the opening at the top of the burette 71a, a cock 71c connected to the tip of the bottom of the burette 71a, and an air introduction tube 71d and a cock 71e connected to the bottom of the burette 71a. The burette unit 71 is fixed with a clamp 76. The measurement table 73 has a through-hole 73a with a diameter of 2 mm formed in its center, and is supported by a height-adjustable stand 75. The through-hole 73a of the measurement table 73 and the cock 71c of the burette unit 71 are connected by a conduit 72. The inner diameter of the conduit 72 is 6 mm.

[0085] The measurements were performed in an environment with a temperature of 25°C and a humidity of 50±10%. First, the stopcocks 71c and 71e of the burette part 71 were closed, and saline solution 77 adjusted to 25°C was poured into the burette 71a through the opening at the top of the burette 71a. After sealing the opening of the burette 71a with a rubber stopper 71b, the stopcocks 71c and 71e were opened. The inside of the conduit 72 was filled with saline solution 77 while preventing air bubbles from entering. The height of the measurement table 73 was adjusted so that the height of the water surface of the saline solution 77 that had reached the through-hole 73a was the same as the height of the upper surface of the measurement table 73. After the adjustment, the height of the water surface of the saline solution 77 in the burette 71a was read using the scale on the burette 71a, and this position was designated as the zero point (the reading at 0 seconds).

[0086] A nylon mesh 74 (40 mm × 40 mm, 250 mesh, thickness: approximately 50 μm) was laid near the through-hole 73 a on the measurement table 73, and a cylinder with an inner diameter of 30 mm and a height of 20 mm was placed in the center of the nylon mesh 74. 1.00 g of water-absorbent resin particles 78 were uniformly dispersed in the cylinder, and then the cylinder was carefully removed to obtain a sample in which the water-absorbent resin particles 78 were dispersed in a circular pattern in the center of the nylon mesh 74. Next, the nylon mesh 74 on which the water-absorbent resin particles 78 were placed was moved quickly so that its center was positioned at the position of the through-hole 73 a, without scattering the water-absorbent resin particles 78, and measurement was started. The time when air bubbles were first introduced into the burette 71 a from the air inlet tube 71 d was defined as the start of water absorption (0 seconds).

[0087] The amount of reduction in the saline solution 77 in the burette 71a (i.e., the amount of saline solution 77 absorbed by the water-absorbent resin particles 78) was sequentially read in increments of 0.1 mL, and the amount of reduction in the amount of saline solution 77 Wc [g] 5 minutes after the start of water absorption by the water-absorbent resin particles 78 was read. From Wc, the 5-minute value of the no-pressure DW was calculated using the following formula. The no-pressure DW is the amount of water absorbed per 1.00 g of the water-absorbent resin particles 78. No-pressure DW value [mL / g] = Wc / 1.00

[0088] [Table 1]

[0089] [Fabrication of absorber] Using an airflow type mixer (Autech Co., Ltd., Pad Former), water-absorbent resin particles in the blending amounts (g) shown in Table 2 or Table 3 and 8.0 g of crushed pulp (Leonia Co., Ltd., Rayflock) were uniformly mixed by air papermaking to prepare an absorbent core measuring 40 cm x 12 cm. Next, a sheet measuring 42 cm x 14 cm and weighing 16 g / m was cut into 100 pieces. 2 The absorbent body was placed on a tissue paper of 16 g / m2 in basis weight and 0.6 g of ion-exchanged water was sprayed onto the tissue paper using a spray bottle. 2A tissue paper of 42 cm × 22 cm in size and having a mesh size of 2 mm was placed on the above-mentioned absorbent body, and a press (small air press, Imoto Machinery Works) was used to press the entire body under a load of 141 kPa for 30 seconds, thereby producing an absorbent body having a water-absorbent resin particle content of 60 mass %.

[0090] [Absorbent articles] On the top surface of the absorbent body, a sheet of paper of the same size as the absorbent body and weighing 22 g / m 2 An absorbent article was produced by placing a polyethylene air-through porous liquid-permeable sheet of the above-mentioned type on the bottom surface of an absorbent body, and a polyethylene liquid-impermeable sheet of the same size and basis weight on the bottom surface of the absorbent body. The following evaluations were carried out using the absorbent article.

[0091] (Preparation of test solution) A test solution was prepared by mixing 9866.0 g of distilled water, 100.0 g of sodium chloride, 3.0 g of calcium chloride dihydrate, 6.0 g of magnesium chloride hexahydrate, 25.0 g of 1 mass % Triton X solution (a mixture of Triton X-100 and water manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.), and 0.25 g of Food Blue No. 1 (for coloring).

[0092] (Absorption rate) The test was conducted in a room conditioned at 25°C and 50% humidity (RH). The absorbent article was placed on a horizontal table, and a liquid-injection cylinder (weight: 60 g) with an opening of 3 cm inner diameter was placed at the center of the absorbent article. Next, 150 mL of test liquid was quickly poured into the cylinder. The time from the start of the test liquid injection until the test liquid was completely absorbed into the absorbent article was measured, and this was taken as the absorption rate (seconds).

[0093] (return amount) The cylinder was removed, and 5 minutes after the test liquid was added, approximately 75 g of filter paper (ADVANTEC No. 51A, 100 mm x 100 mm) with a pre-measured mass was placed near the center of the absorbent article, and a weight of approximately 0.7 psi (100 mm x 100 mm base, 5.0 kg) was quickly placed on top of it and the load was applied for 5 minutes. After that, the weight and filter paper were removed, and the mass of the test liquid absorbed by the filter paper was measured. The increase in the mass of the filter paper before and after the test was taken as the return amount (g).

[0094] (diffusibility) Ten minutes after the test liquid was introduced, a 50-cm-long plastic ruler was used to measure the distance the liquid had spread in the absorbent article, and this distance was designated the diffusion length (cm). The diffusion length was measured by peeling off the polyethylene air-through porous liquid-permeable sheet from the absorbent article to expose the absorbent body so that the diffused test liquid could be clearly seen. The diffusion length was the partial length of the stain formed on the surface of the absorbent body, specifically, the length of the portion of the stain formed on the surface of the absorbent body that passed through the test liquid introduction point (the portion corresponding to the center of the cylinder when the test liquid was introduced) and extended parallel to the long side of the absorbent body.

[0095] Next, a Unipack (Seisan Nippon Co., Ltd., product number: L-4, polyethylene material, dimensions: 480 mm × 340 mm, thickness: 0.04 mm) was used to cut out a Unipack along the outline of the stain formed on the absorbent surface, to prepare Film A (Fa), and its mass was measured. Furthermore, the same Unipack was used to cut out a film measuring 100 mm long × 100 mm wide (area 10,000 mm). 2 ), 10 sheets of film B were prepared, and the masses were measured to determine the average mass (Fb) per sheet of film B. The diffusion area (cm2) in the absorbent article was calculated using the following formula: 2 ) was calculated. Diffusion area (cm 2 ) = {(Fa / Fb) × Area of ​​Fb (10000mm 2 )} / 100

[0096] [Table 2]

[0097] [Table 3] [Explanation of symbols]

[0098] 10...absorbent body, 10a, 78...water-absorbent resin particles, 10b...fiber layer, 20a, 20b...core wrap sheet, 30...liquid-permeable sheet, 40...liquid-impermeable sheet, 71...burette part, 71a...burette, 71b...rubber stopper, 71c, 71e...cock, 71d...air introduction tube, 72...conduit, 73...measuring table, 74...nylon mesh, 73a...through hole, 75...stand, 76...clamp, 77...saline solution, 100...absorbent article, Z...measuring device.

Claims

1. An absorbent body containing water-absorbent resin particles, the water-absorbent resin particles contain water-absorbent resin particles (A) having a water absorption rate of 55 to 150 seconds as measured by a Vortex method and a 5-minute value of no-pressure DW of 36 mL / g or less, and water-absorbent resin particles (B) different from the water-absorbent resin particles (A), the water-absorbent resin particles (B) satisfy at least one of a water absorption rate measured by a Vortex method of less than 55 seconds, a water absorption rate measured by a Vortex method of more than 150 seconds, and a 5-minute value of no-pressure DW of more than 36 mL / g; An absorbent body, wherein the content of the water-absorbent resin particles (A) is 9 to 84 mass % based on the total amount of the water-absorbent resin particles.

2. 2. The absorbent according to claim 1, wherein the water-absorbent resin particles (A) are coated resin particles having a water-insoluble coating layer that covers at least a part of the surface of the water-absorbent resin particles, and the content of the water-absorbent resin particles (A) is 20 to 84 mass% based on the total amount of the water-absorbent resin particles.

3. 3. The absorbent body according to claim 2, wherein the coating layer is a layer containing at least one water-insoluble component selected from the group consisting of water-insoluble organic compounds and water-insoluble inorganic compounds.

4. 4. The absorbent body according to claim 3, wherein the water-insoluble organic compound comprises at least one organic compound selected from the group consisting of polyurethane, polyolefin, polyester, polyamide, polystyrene, polycarbonate, polyacrylate, polyacetal, and acid-modified products thereof.

5. 4. The absorbent body according to claim 3, wherein the water-insoluble inorganic compound comprises at least one inorganic compound selected from the group consisting of light anhydrous silicic acid, calcium silicate, silicon dioxide, talc, silicon monoxide, and synthetic hydrotalcite.

Images