absorbent articles

Abstract

To provide an absorbent article capable of suppressing expansion of an absorption part, while maintaining absorption performance such as diffusion properties of absorbed aqueous liquid, in use of a thin absorbent article.SOLUTION: An absorbent article comprises: a liquid impermeable back sheet; an absorber including water absorptive resin particles; and a liquid permeable top sheet in this order, a diffusion auxiliary sheet is provided between the top sheet and the absorber, the diffusion auxiliary sheet is a liquid permeable nonwoven fabric whose basis weight amount is 25 to 100 g / m2, and the water absorptive resin is particulate poly(meth)acrylic acid(acrylate) absorptive resin which is expressed by a following formula (1) and whose expansion gel compression ratio is 3% or greater, where the expansion gel compression ratio (%)=(D1-D2) / D1×100 (formula 1). Where, D1 is a thickness of the expansion gel layer (mm) formed by the water absorptive resin 16, when a piston 12 whose diameter is 59 mm and a cell 11 having a mesh shaped bottom 15 and an inner diameter of 60 mm, are prepared, the cell 11 where 1.0 g of the water absorptive resin 16 is dispersed on the bottom 15, is mounted in a Petri dish 13 storing therein, 0.9 mass% of a sodium chloride aqueous solution for making the water absorptive resin 16 absorb the 0.9 mass% of sodium chloride aqueous solution for 5 minutes, D2 is a thickness (mm) of the expansion gel layer formed by the water absorptive resin 16, when the cell 11 is mounted on a sieve whose aperture is 4750 μm, then a weight 14 is mounted on the piston 12 so as to apply 0.7 psi of a load to the expansion gel layer, then the cell 11 is left to stand for 10 minutes, then the weight 14 is detached, then the same operation is repeated 10 times.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to an absorbent article, and more specifically to an absorbent article having an absorbent body containing a poly(meth)acrylic acid (salt)-based water-absorbent resin. [Background technology]

[0002] Known absorbent articles include sanitary materials such as disposable diapers, sanitary napkins, and incontinence pads that absorb body fluids. In recent years, water-absorbent resins have been widely used as water-absorbing agents in these sanitary materials, as constituent materials thereof, from the viewpoint of absorbing body fluids. Known examples of such water-absorbent resins include hydrolyzates of starch-acrylonitrile graft copolymers, neutralized starch-acrylic acid graft polymers, saponified vinyl acetate-acrylic acid ester copolymers, and crosslinked polymers of partially neutralized (meth)acrylic acid. However, from the viewpoint of water-absorbing performance, poly(meth)acrylic acid (salt)-based water-absorbent resins using (meth)acrylic acid and / or its salts as the main monomer component are most widely produced industrially.

[0003] Water-absorbent resins with excellent gel elasticity are known to suppress gel blocking. For example, Patent Documents 1 to 5 disclose water-absorbent resins that, when used in absorbents, have excellent elasticity after absorbing water. Absorbent articles equipped with absorbents containing the water-absorbent resins described in Patent Documents 1 to 5 can maintain sufficiently high elasticity even when the proportion of fibrous material in the absorbent core of the absorbent article is low (high-concentration core), allowing them to be made thinner without compromising absorption performance.

[0004] It is also known that a liquid-diffusing sheet is used in absorbent articles to enhance liquid diffusion. For example, Patent Document 6 discloses an absorbent sheet that promotes the diffusion of absorbed liquid in the surface direction. Revenue The absorbent article is an absorbent article in which a liquid-diffusing sheet is interposed between a liquid-permeable top sheet and an absorbent body. Revenue A sexual article is disclosed. [Prior art document] [Patent documents] [Prior art documents] [Patent documents]

[0005] [Patent Document 1] International Publication WO2019 / 189485 [Patent Document 2] Patent 4880144 [Patent Document 3] Patent 03107909 [Patent Document 4] Japanese Patent Application Publication No. 9-3123 [Patent Document 5] International Publication WO2019 / 189445 [Patent Document 6] Japanese Patent Application Laid-Open No. 2015-154881 Summary of the Invention [Problem to be solved by the invention]

[0006] In the absorbent articles containing the water-absorbent resin having excellent elasticity described in the above-mentioned prior art, the absorbent body remains in a swollen state when the absorbent article is worn due to the water-absorbent resin swelling due to liquid absorption (water absorption), which causes discomfort to the user.

[0007] One embodiment of the present invention has been made in consideration of the above-mentioned problems, and its purpose is to provide an absorbent article that, when absorbing aqueous liquids such as urine during use, can suppress swelling of the absorbent body while maintaining absorption performance such as the diffusibility of the absorbed aqueous liquid. [Means for solving the problem]

[0008] The present inventors have independently discovered that, in order to provide an absorbent article that has excellent absorption performance, such as the diffusibility of absorbed aqueous liquids when absorbing aqueous liquids such as urine during use, and that suppresses swelling of the absorbent body, it is preferable to use, as components of the absorbent article, a poly(meth)acrylic acid (salt)-based water-absorbent resin having a high compressibility of the swollen gel, and a liquid-permeable nonwoven fabric having a basis weight within a specific range, and have completed the present invention.

[0009] That is, an absorbent article according to one embodiment of the present invention is an absorbent article comprising a liquid-impermeable back sheet, an absorbent body containing water-absorbent resin particles, and a liquid-permeable top sheet in this order, and a diffusion auxiliary sheet is provided between the top sheet and the absorbent body, and the diffusion auxiliary sheet has a basis weight of 25 to 100 g / m 2 and the water-absorbent resin is a poly(meth)acrylic acid (salt)-based water-absorbent resin having a swelling gel compression ratio of 3% or more, which is represented by the following (Equation 1): Swollen gel compressibility [%] = (D1 - D2) / D1 × 100 (Equation 1) (Here, D1 is the thickness [mm] of a swollen gel layer formed by the water absorbent resin when a cell comprising a piston with a diameter of 59 mm and a cell with an inner diameter of 60 mm having a mesh-like bottom, with 1.0 g of the water absorbent resin sprayed on the bottom, is placed in a Petri dish containing a 0.9 mass % sodium chloride aqueous solution, and the water absorbent resin is allowed to absorb the 0.9 mass % sodium chloride aqueous solution for 5 minutes; and D2 is the thickness [mm] of the swollen gel layer formed by the water absorbent resin after an operation of placing the cell on a sieve with a mesh size of 4750 μm, placing a weight on the piston so that a load of 0.7 psi is applied to the swollen gel layer, leaving the cell to stand for 10 seconds, and then removing the weight, is repeated 10 times.)

[0010] In an absorbent article according to one embodiment of the present invention, the water-absorbent resin is an aggregate of spherical particles.

[0011] In the absorbent article according to one embodiment of the present invention, the water-absorbent resin has a mass median particle diameter (D50) of 50 to 700 μm.

[0012] In an absorbent article according to one embodiment of the present invention, the water-absorbent resin has D2 of less than 15 mm.

[0013] In an absorbent article according to one embodiment of the present invention, the water-absorbent resin has D1 of less than 15 mm.

[0014] In the absorbent article according to one embodiment of the present invention, the absorbency under pressure (AAP) of the water-absorbent resin is 18 g / g or more.

[0015] In an absorbent article according to one embodiment of the present invention, the absorbent body is either (1) an absorbent body that does not contain hydrophilic fibers, or (2) an absorbent body that further contains hydrophilic fibers and in which the mass of the water-absorbent resin is 50% by mass or more out of a total of 100% by mass of the water-absorbent resin and the hydrophilic fibers. [Effects of the Invention]

[0016] According to one embodiment of the present invention, it is possible to provide an absorbent article that has excellent absorption performance, such as the diffusibility of the absorbed aqueous liquid, when absorbing aqueous liquid such as urine during use, and that suppresses swelling of the absorbent part. [Brief explanation of the drawings]

[0017] [Figure 1] FIG. 1 is a perspective view showing the external configuration of a measuring device for swollen gel compressibility as viewed from one direction. [Figure 2] FIG. 1 is a cross-sectional view showing a part of a device for measuring the compressibility of a swollen gel. [Figure 3] FIG. 2 is a diagram showing measurement points when measuring the thickness of an absorbent article in an example. [Figure 4] FIG. 2 is a cross-sectional view of an absorbent article produced in an example. DETAILED DESCRIPTION OF THE INVENTION

[0018] The present invention will now be described with reference to the best mode thereof. It should be understood that the terms used in this specification are used in the same manner as commonly used in the art unless otherwise specified. Therefore, unless otherwise defined, all technical and scientific 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 event of any conflict, the present specification (including definitions) shall prevail. The present invention is not limited to the following embodiments, and various modifications may be made within the scope of the claims.

[0019] An absorbent article according to one embodiment of the present invention is an absorbent article including, in this order, a liquid-impermeable back sheet, an absorbent body containing water-absorbent resin particles, and a liquid-permeable top sheet, A diffusion-assisting sheet is provided between the top sheet and the absorbent body, The diffusion auxiliary sheet has a basis weight of 25 to 100 g / m 2 It is a liquid-permeable nonwoven fabric, The water-absorbent resin has a swelling gel compressibility of 3% or more, which is represented by the following formula (1): Swollen gel compressibility [%] = (D1 - D2) / D1 × 100 (Equation 1) (Here, D1 is the thickness [mm] of a swollen gel layer formed by the water absorbent resin when a cell comprising a piston with a diameter of 59 mm and a cell with an inner diameter of 60 mm having a mesh-like bottom, with 1.0 g of the water absorbent resin sprayed on the bottom, is placed in a Petri dish containing a 0.9 mass % sodium chloride aqueous solution, and the water absorbent resin is allowed to absorb the 0.9 mass % sodium chloride aqueous solution for 5 minutes; and D2 is the thickness [mm] of the swollen gel layer formed by the water absorbent resin after an operation of placing the cell on a sieve with a mesh size of 4750 μm, placing a weight on the piston so that a load of 0.7 psi is applied to the swollen gel layer, leaving the cell to stand for 10 seconds, and then removing the weight, is repeated 10 times.)

[0020] In the absorbent article, by selecting a water-absorbent resin with a high swollen gel compressibility, the thickness of the swollen gel layer formed by the water-absorbent resin is reduced when the absorbent article absorbs liquid under a load simulating use, thereby providing a thin absorbent article even after use. Furthermore, even when liquid is locally introduced, the inclusion of the diffusion auxiliary sheet allows the absorbed aqueous liquid to be uniformly dispersed throughout the absorbent, thereby preventing the absorbent article from becoming thicker in parts. In particular, when a load is applied to the swollen gel layer formed by the water-absorbent resin, the gaps between the gels that serve as paths for the absorbed aqueous liquid narrow, making it easy for the diffusibility of the absorbed aqueous liquid to decrease. In one embodiment of the present invention, since the diffusibility of the absorbed aqueous liquid of the water-absorbent resin alone is limited, the use of the diffusion auxiliary sheet can suppress the decrease in diffusibility and more effectively improve the diffusibility of the absorbed aqueous liquid. Furthermore, in one embodiment of the present invention, the use of a nonwoven fabric with the above-mentioned basis weight as the diffusion auxiliary sheet can further improve the diffusibility of the absorbed aqueous liquid without excessively increasing the thickness of the material itself.

[0021] [1] Definitions [1-1] Water-absorbing resin The term "water-absorbent resin" as used herein refers to a water-swellable and water-insoluble polymer gelling agent that satisfies the following physical properties: "Water-swellable" refers to a polymer gelling agent that has a CRC of 5 g / g or more as defined in ERT441.2-02, and "water-insoluble" refers to a polymer gelling agent that has an Ext of 50 wt% or less as defined in ERT470.2-02.

[0022] The water-absorbing resin can be appropriately designed depending on its application and is not particularly limited, but is preferably a hydrophilic cross-linked polymer obtained by cross-linking an unsaturated monomer having a carboxyl group. The water-absorbing resin is not limited to a form in which the entire amount (100 mass%) is a polymer, and may be in the form of a water-absorbing resin composition containing additives and the like within a range that satisfies the physical properties (CRC, Ext).

[0023] Furthermore, the water-absorbent resin in the present invention is not limited to a final product, but may also refer to an intermediate in the production process of a water-absorbent resin (for example, a hydrogel-like crosslinked polymer (hydrogel polymer) after polymerization, a dried polymer after drying, a water-absorbent resin powder before surface crosslinking, etc.), and all of these, together with the water-absorbent resin composition, are collectively referred to as a "water-absorbent resin".

[0024] The shape of the water-absorbent resin in one embodiment of the present invention may be a sheet, fiber, film, particle, gel, or the like. The shape of the water-absorbent resin in one embodiment of the present invention is preferably a particle. The water-absorbent resin in one embodiment of the present invention is more preferably a particulate poly(meth)acrylic acid (salt)-based water-absorbent resin.

[0025] [1-2] "EDANA" and "ERT" "EDANA" is an abbreviation for European Disposables and Nonwovens Associations, and "ERT" is an abbreviation for EDANA Recommended Test Methods, a European standard (almost a global standard) for measuring the properties of water-absorbent resins. In the present invention, unless otherwise specified, the physical properties of a water-absorbent resin are measured in accordance with the original ERT (revised in 2002 / publicly known document).

[0026] [1-3] Other In this specification, the range "X to Y" means "X or more and Y or less."

[0027] In this specification, unless otherwise specified, "ppm" means "ppm by mass."

[0028] In this specification, "acid (salt)" means "acid and / or its salt." "(Meth)acrylic" means "acrylic and / or methacrylic." "Poly(meth)acrylic acid (salt)-based water-absorbing resin" means a water-absorbing resin containing a repeating unit derived from (meth)acrylic acid (salt) as a main component, and specifically refers to a water-absorbing resin containing preferably 50 to 100 mol%, more preferably 70 to 100 mol%, even more preferably 90 to 100 mol%, and particularly preferably substantially 100 mol% of (meth)acrylic acid (salt) in the total monomers (excluding crosslinking agents) used in polymerization.

[0029] In this specification, the unit of volume "liter" may be written as "l" or "L".

[0030] In this specification, "weight" and "mass," "wt %" and "mass %," and "parts by weight" and "parts by mass" are treated as synonyms.

[0031] [2] Water-absorbing resin [2-1] Shape of water-absorbent resin The water-absorbent resin contained in the absorbent article according to one embodiment of the present invention (hereinafter also referred to as "the water-absorbent resin of the present invention") is preferably in a particulate form, and specifically, preferably in an irregularly crushed form, a spherical form, a football form, an aggregate form, or the like. Among these, since a high gel compressibility can be obtained when the water-absorbent resin has a spherical particle shape, particularly when the water-absorbent resin has an aggregate form, the water-absorbent resin is preferably in the form of aggregated particles of spherical particles (for example, spherical particles containing a poly(meth)acrylic acid (salt)-based water-absorbent resin). Note that spherical particles of the water-absorbent resin can also be referred to as primary particles, and aggregated particles of the water-absorbent resin can also be referred to as aggregated secondary particles formed by agglomeration of spherical primary particles. Here, "spherical" includes not only a perfect sphere but also an approximately spherical shape with an aspect ratio of 1.0 to 1.2.

[0032] [2-2] CRC "CRC" is an abbreviation for Centrifuge Retention Capacity, which means the water absorption capacity of a water-absorbent resin under no pressure.

[0033] The CRC of the water absorbent resin of the present invention is preferably 30 g / g or more, more preferably 32 g / g or more, and further preferably 34 g / g or more. There is no particular limitation on the upper limit of the CRC, and the higher the CRC of the water absorbent resin, the more preferable it is, but from the viewpoint of the balance between other physical properties of the water absorbent resin and the CRC, it is preferably 50 g / g or less, more preferably 48 g / g or less, and further preferably 46 g / g or less.

[0034] If the CRC is 30 g / g or more, the water-absorbent resin has a sufficient absorption capacity and can be suitably used as an absorbent body for absorbent articles such as disposable diapers. Furthermore, if the CRC is 50 g / g or less, a decrease in the rate at which the water-absorbent resin absorbs body fluids such as urine and blood is prevented, and the water-absorbent resin is suitable for use in high-absorption-rate disposable diapers and the like. The CRC value can be controlled by changing the type and amount of an internal cross-linking agent, a surface cross-linking agent, etc. An example of a method for measuring the CRC will be described in detail in the Examples.

[0035] [2-3] Ext "Ext" is an abbreviation for Extractables, and refers to the amount of extractables extracted from the water-absorbent resin. The water-soluble content is measured in accordance with the EDANA method (ERT470.2-02).

[0036] The Ext of the water absorbent resin of the present invention is preferably 30% by mass or less, more preferably 20% by mass or less, and further preferably 10% by mass or less. The lower limit of Ext is 0% by mass, but from the viewpoint of the balance between other physical properties of the water absorbent resin and Ext, it is preferably 2% by mass or more, more preferably 4% by mass or more.

[0037] When the Ext is 30% by mass or less, a decrease in the rate at which the water-absorbent resin absorbs body fluids such as urine and blood is prevented, and the water-absorbent resin is suitable for use in high-absorption-rate disposable diapers, etc. The value of Ext can be controlled by changing the type and amount of a polymerization initiator, an internal crosslinking agent, a surface crosslinking agent, etc., and can also be controlled by using a chain transfer agent in the polymerization step.

[0038] [2-4] AAP "AAP" is an abbreviation for Absorption Against Pressure, and means the water absorption capacity of a water-absorbent resin under pressure. In the present invention, AAP is measured in accordance with the EDANA method (ERT442.2-02) except that the load condition is changed to 4.83 kPa (0.7 psi). Specifically, 0.9 g of a water-absorbent resin is swelled under a pressure of 4.83 kPa for 1 hour using a 0.9 mass % (mass / mass %) sodium chloride aqueous solution, and then AAP (absorption capacity under pressure) (unit: g / g) is measured.

[0039] From the viewpoint of water absorption properties when used in sanitary materials, the AAP of the water-absorbent resin of the present invention is preferably 18 g / g or more, more preferably 20 g / g or more, and even more preferably 23 g / g or more. The upper limit of the AAP of the water-absorbent resin is not particularly limited, but is preferably 40 g / g or less.

[0040] [2-5] Moisture content The "moisture content" is measured in accordance with the EDANA method (ERT430.2-02), except that the sample amount is changed to 1.0 g and the drying temperature is changed to 180° C. An example of the method for measuring moisture content will be described in detail in the Examples.

[0041] The water content of the water-absorbent resin of the present invention is not particularly limited, but is preferably 1% by mass to 20% by mass, more preferably 1% by mass to 15% by mass, even more preferably 2% by mass to 13% by mass, even more preferably 5% by mass to 13% by mass, even more preferably 8% by mass to 13% by mass, and particularly preferably 10% by mass to 13% by mass. When the water content is 1% by mass to 20% by mass, a decrease in the rate at which the water-absorbent resin absorbs body fluids such as urine and blood is prevented, and the water-absorbent resin is suitable for use in high-absorption-rate disposable diapers and the like.

[0042] [2-6] Mass average particle diameter (D50) The "mass-average particle diameter (D50)" is defined as "(3) Mass-Average Particle Diameter (D50) and Logarithmic Standard Deviation" in columns 27 and 28 of U.S. Patent No. 7,638,570. It is measured in accordance with the "(σζ) of Particle Diameter Distribution" standard.

[0043] The mass median particle diameter (D50) of the water-absorbent resin of the present invention is preferably 50 μm to 700 μm, more preferably 50 μm to 500 μm, and even more preferably 100 μm to 400 μm. Furthermore, the proportion of particles having a mass median particle diameter of less than 45 μm in 100 mass% of the water-absorbent resin is preferably 40 mass% or less, more preferably 30 mass% or less, even more preferably 20 mass% or less, and particularly preferably 10 mass% or less. When the mass median particle diameter is 200 μm or more, dust is reduced and handling is easy. Furthermore, when the mass median particle diameter is 700 μm or less, a decrease in the rate at which the water-absorbent resin absorbs body fluids such as urine and blood is prevented, and the water-absorbent resin is suitable for use in high-absorption-rate disposable diapers and the like.

[0044] [2-7] Number average particle diameter When the water-absorbent resin is in the form of aggregate particles (secondary particles), the number-average particle size of the primary particles (e.g., spherical particles) constituting the aggregates (the aggregate particles) is measured using an electron microscope. The number-average particle size of the primary particles of the water-absorbent resin is preferably 5 μm to 800 μm, more preferably 8 μm to 500 μm, even more preferably 10 μm to 300 μm, still more preferably 10 μm to 200 μm, and particularly preferably 30 μm to 200 μm. An example of a method for measuring the number-average particle size will be described in detail in the Examples.

[0045] [2-8] Bulk density "Bulk density" is measured in accordance with the EDANA method (ERT460.2-02).

[0046] The bulk density of the water-absorbent resin of the present invention is preferably 0.68 g / cm 3 ~1.00g / cm3 , preferably 0.69 g / cm 3 ~0.95g / cm 3 , and most preferably 0.68 g / cm 3 ~0.90g / cm 3 The bulk density is 0.68 to 1.00 g / cm 3 If so, the rate at which the water-absorbent resin absorbs body fluids such as urine and blood is prevented from decreasing, and the water-absorbent resin is suitable for use in high-absorption-rate disposable diapers and the like.

[0047] [2-9] Liquid permeability The "liquid permeability" of the water-absorbent resin in the present invention refers to the flowability of a liquid passing between particles of swollen gel under load or without load, and a representative measurement method is GBP (Gel Bed Permeability). "GBP" refers to the liquid permeability of a 0.9% by mass aqueous sodium chloride solution through a water-absorbent resin under load or in free swelling, and is measured in accordance with the GBP test method disclosed in International Publication No. 2005 / 016393. However, in the present invention, the particle size of the water-absorbent resin is measured without classification into particles of 300 μm or more and 600 μm or less. It is preferable that the absorbent core exhibits liquid permeability even when the swelling is suppressed, and the GBP of the water-absorbent resin is preferably 5×10 -9 cm 2 , more preferably 10×10 -9 cm 2 , and more preferably 15×10 -9 cm 2 is.

[0048] [2-10] Swollen gel compressibility The "swelled gel compressibility" in the present invention is a novel physical property value representing the change in thickness (compressibility) of a swollen gel of a water-absorbent resin when a load is repeatedly applied to the swollen gel of the water-absorbent resin in a cell with a mesh-like bottom. The "swelled gel compressibility" is measured by the method described below. A water-absorbent resin having a high "swelled gel compressibility" is preferred, for example, in a thin absorbent sheet for light incontinence, because the swollen gel layer of the water-absorbent resin is compressed when a load is repeatedly applied, thereby suppressing swelling of the absorbent core even during long-term use. The "swelled gel compressibility" is 3.0% or more, preferably 3.5% or more, more preferably 4.0% or more, even more preferably 4.5% or more, and particularly preferably 5.0% or more. From the viewpoint of maintaining the absorption performance of the swollen gel of the water-absorbent resin, the upper limit of the swelled gel compressibility is preferably 30% or less, 25% or less, and 20% or less, in that order.

[0049] [2-11] Gel thickness before compression D1 In measuring the "swelled gel compressibility" described above, the thickness D1 of the gel before compression is preferably low, from the viewpoint of preventing discomfort caused by excessive swelling of the absorbent core when the water-absorbent resin is used in an absorbent article. The thickness D1 of the gel before compression is preferably 20 mm or less, more preferably 15 mm or less, and even more preferably less than 15 mm. There is no particular lower limit for D1, but it is sufficient as long as it is above 0 mm, and it is preferably 5 mm or more, more preferably 10 mm or more, and even more preferably 12 mm or more.

[0050] [2-12] Gel thickness after compression D2 In measuring the "swelled gel compressibility" described above, the thickness D2 of the gel after compression is preferably low, from the viewpoint of preventing discomfort caused by swelling of the absorbent core when the water-absorbent resin is used in an absorbent article and a load (body weight) is applied. The "thickness D2 of the gel after compression" is preferably 18 mm or less, more preferably 15 mm or less, and even more preferably less than 15 mm. There is no particular lower limit for D2, but it is sufficient as long as it is above 0 mm, and it is preferably 5 mm or more, more preferably 10 mm or more, and even more preferably 12 mm or more.

[0051] The apparatus for measuring swollen gel compressibility will be described with reference to Figs. 1 and 2. Fig. 1 is a perspective view showing the external configuration of the apparatus for measuring swollen gel compressibility as seen from one direction. Fig. 2 is a cross-sectional view showing a part of the apparatus for measuring swollen gel compressibility. As shown in Fig. 1, the apparatus for measuring swollen gel compressibility comprises a cell 11, a piston 12, a Petri dish 13, and a weight 14. As shown in Fig. 2, the inner diameter of the cell 11 is 60 mm, and the diameter of the piston 12 is 59 mm. Also, as shown in Fig. 2, the cell 11 has a bottom 15, which is a stainless steel mesh formed with a mesh opening of 36 µm (i.e., 400 mesh).

[0052] A method for measuring the swollen gel compressibility will be described with reference to FIGS. 1 and 2. First, as shown in FIG. 2, a water-absorbent resin 16 is sprayed onto the bottom 15 of a cell 11 having an inner diameter of 60 mm and equipped with a mesh-like bottom 15. Next, as shown in FIG. 2, a piston 12 having a diameter of 59 mm is placed into the cell 11 from above the sprayed water-absorbent resin 16. Next, as shown in FIG. 1, the cell 11 having the piston 12 and the water-absorbent resin 16 is placed in a petri dish 13 and left to stand for 5 minutes. Here, although not shown in FIG. 1, a 0.9% by mass aqueous sodium chloride solution is present in the petri dish 13. Therefore, this operation allows the water-absorbent resin 16 to absorb the 0.9% by mass aqueous sodium chloride solution for 5 minutes, and the water-absorbent resin 16 thereby forms a swollen gel layer (swollen gel layer). In Fig. 1, weight 14 is depicted on top of piston 12 present inside cell 11 placed in petri dish 13, but in the actual measurement of swollen gel compressibility, when cell 11 having piston 12 and water-absorbent resin 16 is placed in petri dish 13 containing a 0.9 mass % sodium chloride aqueous solution, weight 14 is not placed on piston 12. As will be described later, weight 14 is placed on piston 12 in cell 11 placed on a sieve. In Fig. 1, the state when weight 14 is placed on piston 12 in cell 11 placed on a sieve is merely shown for convenience by using piston 12 in cell 11 placed in petri dish 13.

[0053] After forming a swollen gel layer on the water-absorbent resin 16 in the cell 11, the thickness [mm] of the swollen gel layer is measured and designated D1. Next, the cell 11 having the swollen gel layer and piston 12 on the water-absorbent resin 16 is removed from the Petri dish 13 and placed on a sieve with a mesh size of 4750 μm. Next, (1) an operation of placing a weight 14 on the piston 12 in the cell 11 and leaving the cell 11 for 10 seconds so that a load of 0.7 psi is applied to the swollen gel layer of the water-absorbent resin 16, and (2) thereafter, an operation of removing the weight 14 is repeated 10 times. Thereafter, the thickness [mm] of the swollen gel layer formed by the water-absorbent resin 16 is measured and designated D2.

[0054] Next, the compressibility of the swollen gel is calculated from D1 and D2 according to the following formula (1): Swollen gel compressibility [%] = (D1 - D2) / D1 × 100 (Equation 1). [2-13] Additives included In the present invention, the water-absorbent resin may contain additives to exhibit various functions. Specific examples of the additives include surfactants, compounds having phosphorus atoms, oxidizing agents, organic reducing agents, inorganic reducing agents, water-insoluble inorganic fine particles, chelating agents, polyvalent metal salts, organic powders such as metal soaps, deodorants, antibacterial agents, pulp, and thermoplastic fibers. The amount of the additives used (added amount) is appropriately determined depending on the application of the resulting water-absorbent resin, and is 5% by mass or less, preferably 3% by mass or less, and more preferably 1% by mass or less, based on the water-absorbent resin (e.g., water-absorbent resin powder). The lower limit is 0.001% by mass or more, preferably 0.01% by mass or more, based on the water-absorbent resin (e.g., water-absorbent resin powder). The compounds disclosed in "(5) Water-Insoluble Inorganic Fine Particles" of International Patent Publication No. 2011 / 040530 are applicable to the present invention as the water-insoluble inorganic fine particles.

[0055] [3] Method for producing water-absorbent resin The method for producing the water-absorbent resin of the present invention may be any of aqueous solution polymerization, reversed-phase suspension polymerization, gas-phase droplet polymerization, and other polymerization methods, but it is preferable to adopt reversed-phase suspension polymerization because it is easy to control the physical properties of the water-absorbent resin of the present invention. Hereinafter, reversed-phase suspension polymerization will be described as an example of the method for producing the water-absorbent resin of the present invention. In particular, unlike typical reversed-phase suspension polymerization, which includes an azeotropic dehydration step in a hydrophobic organic solvent after polymerization and a surface cross-linking step in a dispersion system, a preferred embodiment of the method for producing the water-absorbent resin of the present invention will be described by taking as an example a production method including a separation step of a reversed-phase suspension polymerization gel, a gel sizing step, a drying step of a hydrogel (preferably hot air drying), and a surface cross-linking step (preferably powder surface treatment).

[0056] The method for producing a water-absorbent resin according to the present invention is not particularly limited, but preferably includes a polymerization step of polymerizing a monomer in a state where droplets containing the monomer are dispersed or suspended in a hydrophobic organic solvent to obtain a hydrogel polymer.

[0057] A preferred method for producing a water-absorbent resin (polymerization method) is, for example, a method in which droplets containing a monomer are dispersed or suspended in a liquid phase consisting of a hydrophobic organic solvent and the monomer is polymerized to obtain a hydrogel polymer. In other words, a method in which a hydrogel polymer is obtained by reverse-phase suspension polymerization is used. This polymerization method may be batch or continuous. A batch production method is a production method in which an aqueous monomer solution is added or dropped into a hydrophobic organic solvent in a reactor, and mixed to disperse or suspend droplets of the aqueous monomer solution in the hydrophobic organic solvent, and then polymerize the monomer to obtain a hydrogel polymer. On the other hand, a continuous production method is a method in which an aqueous monomer solution is continuously fed into a hydrophobic organic solvent in a reactor, droplets of the aqueous monomer solution are dispersed or suspended in the hydrophobic organic solvent, and then the monomer is polymerized. The hydrogel polymer formed by the polymerization reaction and the hydrophobic organic solvent are continuously discharged from the reactor. A preferred embodiment of the present invention is batch reverse-phase suspension polymerization. The method for producing a water-absorbent resin according to the present invention may include a separation step of separating the hydrogel polymer obtained in the polymerization step from the hydrophobic organic solvent.

[0058] The method for producing a water-absorbent resin according to the present invention includes, for example, an optional step of preparing an aqueous monomer solution; an optional dispersing step; a polymerization step; an optional separation step; an optional gel sizing step; a drying step; and a hydrophilization treatment step. After the drying step, the method may optionally include a cooling step, a pulverizing step, a classification step, a surface cross-linking step, a water-containing (rewetting) step, a step of adding other additives, a sizing step, a fine powder removing step, a granulation step, and a fine powder recycling step. The method may further include a transporting step, a storing step, a packaging step, a storage step, and the like.

[0059] Each step will be described below.

[0060] [3-1] Monomer aqueous solution preparation process The aqueous monomer solution is an aqueous solution containing a monomer that is a raw material for the water-absorbent resin, and is a solution that is dispersed or suspended in a hydrophobic organic solvent to carry out reversed-phase suspension polymerization.

[0061] The solvent for the aqueous monomer solution is preferably water or a mixture of water and a water-soluble organic solvent (e.g., alcohol, etc.), and more preferably water. In the case of a mixture of water and a water-soluble organic solvent, the water-soluble organic solvent (e.g., alcohol, etc.) is preferably 30% by mass or less, more preferably 5% by mass or less, of the mixture (100% by mass).

[0062] As the monomer, a water-soluble ethylenically unsaturated monomer is preferably used. Examples of the water-soluble ethylenically unsaturated monomer include (meth)acrylic acid, (anhydrous) maleic acid, itaconic acid, cinnamic acid, vinyl sulfonic acid, allyl toluene sulfonic acid, vinyl toluene sulfonic acid, styrene sulfonic acid, 2-(meth)acrylamido-2-methylpropane sulfonic acid, 2-(meth)acryloylethane sulfonic acid, 2-(meth)acryloylpropane sulfonic acid, 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 2-hydroxyethyl (meth)acryloyl phosphate, methoxypolyethylene glycol (meth)acrylate, polyethylene glycol mono(meth)acrylate, and other acid group-containing unsaturated monomers; (meth)acrylamide, N-ethyl (meth)acrylate, N-methyl ... Examples of the unsaturated monomers include amide group-containing unsaturated monomers such as acrylamide, N,N-dimethyl(meth)acrylamide, Nn-propyl(meth)acrylamide, N-isopropyl(meth)acrylamide, vinylpyridine, N-vinylpyrrolidone, N-acryloylpiperidine, N-acryloylpyrrolidine, and N-vinylacetamide; amino group-containing unsaturated monomers such as N,N-dimethylaminoethyl(meth)acrylate, N,N-dimethylaminopropyl(meth)acrylate, N,N-dimethylaminopropyl(meth)acrylamide, and N,N-diethylaminoethyl(meth)acrylate; mercapto group-containing unsaturated monomers; phenolic hydroxyl group-containing unsaturated monomers; and lactam group-containing unsaturated monomers such as N-vinylpyrrolidone.

[0063] When a water-soluble ethylenically unsaturated monomer is used, a polymerization inhibitor may be added to the aqueous monomer solution, if necessary, in consideration of the stability of the water-soluble ethylenically unsaturated monomer.

[0064] When a water-absorbing resin is produced using an acid group-containing unsaturated monomer having an acid group such as a carboxyl group among the water-soluble ethylenically unsaturated monomers, a neutralized salt in which the acid group is neutralized can be used. In this case, the salt (neutralized salt) of the acid group-containing unsaturated monomer is preferably a salt with a monovalent cation, more preferably at least one selected from alkali metal salts, ammonium salts, and amine salts, still more preferably an alkali metal salt, still more preferably at least one selected from sodium salts, lithium salts, and potassium salts, and particularly preferably a sodium salt.

[0065] Among these, from the viewpoint of the water absorption performance of the obtained water absorbent resin, the water-soluble ethylenically unsaturated monomer is preferably an acid group-containing unsaturated monomer and / or a salt thereof, more preferably (meth)acrylic acid (salt), maleic anhydride (salt), itaconic acid (salt) and / or cinnamic acid (salt), still more preferably (meth)acrylic acid (salt), and particularly preferably acrylic acid (salt).

[0066] When an acid group-containing unsaturated monomer is used as a monomer, it is preferable to use a combination of the acid group-containing unsaturated monomer and a neutralized salt of the acid group-containing unsaturated monomer from the viewpoint of the water absorption performance of the resulting water absorbent resin. When an acid group-containing unsaturated monomer and a neutralized salt of the acid group-containing unsaturated monomer are used in combination, from the viewpoint of water absorption performance, the number of moles of the neutralized salt relative to the total number of moles of the acid group-containing unsaturated monomer and its neutralized salt (100 mol%) (hereinafter referred to as "neutralization rate") is preferably 40 mol% or more, more preferably 40 mol% to 95 mol%, even more preferably 50 mol% to 90 mol%, even more preferably 55 mol% to 85 mol%, and particularly preferably 60 mol% to 80 mol%.

[0067] In the production method according to the present invention, in preparing the aqueous monomer solution, any one of the exemplified monomers may be used alone, or any two or more of the monomers may be used in appropriate mixture. Furthermore, as long as the object of the present invention is achieved, the exemplified monomers may be further mixed with a monomer other than the exemplified monomers.

[0068] In the preparation of the aqueous monomer solution, when two or more kinds of monomers are used in combination, the monomer used for polymerization preferably contains (meth)acrylic acid (salt) as a main component. In this case, the ratio of (meth)acrylic acid (salt) to the total monomers (100 mol%) used for polymerization is usually 50 mol% or more, preferably 70 mol% or more, more preferably 80 mol% or more, and even more preferably 90 mol% or more (upper limit is 100 mol%), from the viewpoint of the water absorption performance of the obtained water absorbent resin.

[0069] In preparing the aqueous monomer solution, an internal crosslinking agent can be used as needed. Examples of the internal crosslinking agent include conventionally known internal crosslinking agents having two or more polymerizable unsaturated groups or two or more reactive groups in one molecule. Examples of the internal crosslinking agent include N,N'-methylenebis(meth)acrylamide, (poly)ethylene glycol di(meth)acrylate, (poly)propylene glycol di(meth)acrylate, trimethylolpropane tri(meth)acrylate, trimethylolpropane di(meth)acrylate, glycerin tri(meth)acrylate, glycerin acrylate methacrylate, ethylene oxide-modified trimethylolpropane tri(meth)acrylate, pentaerythritol tetra(meth)acrylate, dipentaerythritol hexa(meth)acrylate, and the like. Examples of the internal crosslinking agent include (meth)acrylate, triallyl cyanurate, triallyl isocyanurate, triallyl phosphate, triallylamine, poly(meth)allyloxyalkane, (poly)ethylene glycol diglycidyl ether, glycerol diglycidyl ether, ethylene glycol, polyethylene glycol, propylene glycol, glycerin, 1,4-butanediol, pentaerythritol, ethylenediamine, ethylene carbonate, propylene carbonate, polyethyleneimine, glycidyl (meth)acrylate, etc. These internal crosslinking agents may be used alone or in combination of two or more.

[0070] Although it may be appropriately determined depending on the desired physical properties of the water absorbent resin, the amount of the internal crosslinking agent used is usually 0.0001 to 5 mol %, more preferably 0.001 to 3 mol %, and even more preferably 0.005 to 1.5 mol %, relative to the total amount of monomers used in polymerization (100 mol %).

[0071] In addition, the following substances (hereinafter referred to as "other substances") may be added to the aqueous monomer solution.

[0072] Specific examples of other substances include chain transfer agents such as thiols, thiolic acids, secondary alcohols, amines, and hypophosphites; blowing agents such as carbonates, bicarbonates, azo compounds, and bubbles; chelating agents such as metal salts of ethylenediaminetetraacetic acid and metal salts of diethylenetriaminepentaacetic acid; polyacrylic acid (salts) and crosslinked products thereof; starch; cellulose; starch-cellulose derivatives; hydroxyethyl cellulose; polyvinyl alcohol; etc. One of the other substances may be used alone, or two or more may be used in combination.

[0073] The amount of other substances used is not particularly limited, but the total concentration of other substances is preferably 10% by mass or less, more preferably 1% by mass or less, and even more preferably 0.1% by mass or less, relative to the total amount of monomers used in the polymerization (100% by mass).

[0074] The following describes the case where polyacrylic acid (salts) and their crosslinked products, starch, cellulose, starch-cellulose derivatives, and / or polyvinyl alcohol are used as other substances. The total concentration of these polyacrylic acid (salts) and their crosslinked products, starch, cellulose, starch-cellulose derivatives, hydroxyethyl cellulose, and polyvinyl alcohol is preferably 30% by mass or less, more preferably 20% by mass or less, and even more preferably 10% by mass or less, based on the total amount of monomers used in the polymerization (100% by mass).

[0075] The dissolved oxygen in the aqueous monomer solution may be reduced by raising the temperature or by replacing the oxygen with an inert gas.

[0076] "Polymerization initiator" A polymerization initiator may be used in preparing the aqueous monomer solution. When a polymerization initiator is used in preparing the aqueous monomer solution, gelation or an increase in viscosity of the aqueous monomer solution may occur. Therefore, the polymerization initiator is preferably added to the aqueous monomer solution by (1) immediately before dispersing and / or suspending the aqueous monomer solution in a hydrophobic organic solvent, (2) cooling the aqueous monomer solution and mixing it with the polymerization initiator at a temperature lower than room temperature (for example, 20°C or lower, preferably around 0°C), or (3) subjecting the aqueous monomer solution and the polymerization initiator to the dispersion step while line mixing. A thermally decomposable polymerization initiator is preferably used as the polymerization initiator. The thermally decomposable polymerization initiator refers to a compound that decomposes when heated to generate radicals. From the viewpoints of the storage stability of the thermally decomposable polymerization initiator and the production efficiency of the water-absorbent resin, a water-soluble compound having a 10-hour half-life temperature of preferably 0°C to 120°C, more preferably 30°C to 100°C, and even more preferably 50°C to 80°C is preferably used as the polymerization initiator.

[0077] From the viewpoint of ease of handling and the physical properties of the water-absorbing resin, the polymerization initiator is preferably a water-soluble polymerization initiator, and more preferably a water-soluble radical polymerization initiator.

[0078] Examples of water-soluble radical polymerization initiators include persulfates such as potassium persulfate, ammonium persulfate, and sodium persulfate; peroxides such as methyl ethyl ketone peroxide, methyl isobutyl ketone peroxide, di-t-butyl peroxide, t-butylcumyl peroxide, t-butyl peroxyacetate, t-butylperoxyisobutyrate, t-butylperoxypivalate, and hydrogen peroxide; and water-soluble azo compounds such as 2,2'-azobis(2-amidinopropane) dihydrochloride, 2,2'-azobis[2-(N-phenylamidino)propane] dihydrochloride, and 2,2'-azobis[2-(2-imidazolin-2-yl)propane] dihydrochloride. These polymerization initiators may be used alone or in combination of two or more. Among these, preferably used are persulfates or water-soluble azo compounds, more preferably sodium persulfate, potassium persulfate, ammonium persulfate, or 2,2'-azobis(2-amidinopropane) dihydrochloride, and even more preferably sodium persulfate.

[0079] The amount of the thermally decomposable polymerization initiator used is appropriately set depending on the types of monomers and polymerization initiator, and is not particularly limited, but from the viewpoint of production efficiency, it is preferably 0.001 g / mol or more, more preferably 0.005 g / mol or more, and even more preferably 0.01 g / mol or more, relative to the total amount of monomers used in polymerization (1 mol). Also, from the viewpoint of improving the water absorption performance of the water absorbent resin, the amount of the thermally decomposable polymerization initiator used is preferably 2 g / mol or less, more preferably 1 g / mol or less, relative to the total amount of monomers used in polymerization (1 mol).

[0080] The thermally decomposable polymerization initiator can also be used in combination with other polymerization initiators, such as a photodecomposable polymerization initiator, if necessary. Specific examples of the photodecomposable polymerization initiator include benzoin derivatives, benzyl derivatives, acetophenone derivatives, and benzophenone derivatives.

[0081] Furthermore, the thermally decomposable polymerization initiator can be used in combination with a reducing agent to form a redox polymerization initiator. In the redox polymerization initiator, the thermally decomposable polymerization initiator functions as an oxidizing agent. The reducing agent to be used is not particularly limited, but examples thereof include (bis)sulfites such as sodium sulfite and sodium hydrogen sulfite; reducing metal salts such as ferrous salts; L-ascorbic acid (salts), and amines.

[0082] "Monomer concentration in aqueous monomer solution" In the present invention, the concentration of the monomer in the aqueous monomer solution (100% by mass) is selected depending on the selected monomer and the type of hydrophobic organic solvent, etc., but in terms of production efficiency, the lower limit is preferably 10% by mass or more, more preferably 20% by mass or more, and even more preferably 30% by mass or more, and the upper limit is preferably 100% by mass or less, more preferably 90% by mass or less, even more preferably 80% by mass or less, and even more preferably 70% by mass or less.

[0083] As long as the object of the present invention is not impaired, it is also possible to blend additives such as an internal crosslinking agent, a surfactant, a density adjuster, a thickener, a chelating agent, etc. The type and amount of the additive can be appropriately selected depending on the combination of the monomer and the hydrophobic organic solvent used.

[0084] [3-2] Dispersion process The dispersion step is a step of dispersing or suspending droplets containing a monomer (e.g., droplets of an aqueous monomer solution) in a hydrophobic organic solvent. Hereinafter, the term "dispersion" is intended to encompass suspension. More specifically, the aqueous monomer solution is added to a hydrophobic organic solvent and mixed and stirred to disperse the droplets containing the monomer. In the dispersion step, for example, a stirrer equipped with a stirring blade (e.g., a propeller blade, a paddle blade, an anchor blade, a turbine blade, a Pfaudle blade, a ribbon blade, or a flat blade) may be used. When using a stirrer equipped with such a stirring blade, the dispersed droplet size (the droplet size of the dispersed aqueous monomer solution) can be adjusted by the type, blade diameter, and rotation speed of the stirring blade. This stirrer is particularly suitable for use in batch-type reverse-phase suspension polymerization. Dispersions can also be obtained by methods described in International Publication Nos. 2009 / 025235 and 2013 / 018571. When continuous reverse phase suspension polymerization is carried out, the dispersing step preferably comprises continuously supplying an aqueous monomer solution and a hydrophobic organic solvent separately to a dispersing device to produce droplets containing the monomer dispersed in the hydrophobic organic solvent.

[0085] When continuous reversed-phase suspension polymerization is carried out, examples of the dispersing device used in the dispersing step include, but are not particularly limited to, a spray nozzle, a high-speed rotary shear type agitator (rotary mixer type, turbo mixer type, disk type, double cylinder type, etc.), a cylindrical nozzle such as a needle, an orifice plate having a large number of holes directly formed in a plate, a spray nozzle, and a centrifugal atomizer such as a rotating wheel.

[0086] "Hydrophobic organic solvent" Preferred hydrophobic organic solvents include at least one organic solvent selected from the group consisting of aliphatic hydrocarbons, alicyclic hydrocarbons, aromatic hydrocarbons, and halogenated hydrocarbons. Specific examples include aliphatic hydrocarbons such as n-pentane, n-hexane, n-heptane, and n-octane; alicyclic hydrocarbons such as cyclohexane, methylcyclohexane, cyclooctane, and decalin; aromatic hydrocarbons such as benzene, toluene, and xylene; and halogenated hydrocarbons such as chlorobenzene, bromobenzene, carbon tetrachloride, and 1,2-dichloroethane. Among these, n-hexane, n-heptane, and cyclohexane are preferred from the viewpoints of availability and quality stability. It is also possible to use a mixed solvent of two or more hydrophobic organic solvents.

[0087] In the present invention, a dispersing aid such as a surfactant or a polymer additive may be added to the hydrophobic organic solvent as needed, as long as the object of the present invention is not impaired. The type of dispersing aid is appropriately selected depending on the combination of the hydrophobic organic solvent and the monomer used, and examples of dispersing aids that can be used include the following surfactants and polymer additives.

[0088] Specific examples of the surfactant include sucrose fatty acid esters, polyglycerin fatty acid esters, sorbitan fatty acid esters, polyoxyethylene sorbitan fatty acid esters, polyoxyethylene glycerin fatty acid esters, sorbitol fatty acid esters, polyoxyethylene sorbitol fatty acid esters, polyoxyethylene alkyl ethers, polyoxyethylene alkylphenyl ethers, polyoxyethylene castor oil, polyoxyethylene hydrogenated castor oil, alkylaryl formaldehyde condensed polyoxyethylene ethers, polyoxyethylene polyoxypropylene block copolymers, polyoxyethylene polyoxypropyl alkyl ethers, polyethylene glycol fatty acid esters, alkyl glucosides, N-alkyl gluconamides, polyoxyethylene fatty acid amides, polyoxyethylene alkylamines, phosphate esters of polyoxyethylene alkyl ethers, and phosphate esters of polyoxyethylene alkyl allyl ethers. Two or more of these surfactants may be used in combination. Polymerizable surfactants having polymerizability may also be used. Specific examples of the polymerizable surfactant include compounds having the following structure:

[0089] [ka]

[0090] In the formula, R 1 and R 2 are each independently hydrogen, methyl, or ethyl, and n is an integer of 3 to 20. Among the above surfactants, fatty acid esters such as sucrose fatty acid esters, polyglycerol fatty acid esters, sorbitan fatty acid esters, polyoxyethylene sorbitan fatty acid esters, polyoxyethylene glycerol fatty acid esters, sorbitol fatty acid esters, polyoxyethylene sorbitol fatty acid esters, and polyethylene glycol fatty acid esters are preferred, and sucrose fatty acid esters are particularly preferred.

[0091] The HLB value of the surfactant used in the present invention is preferably in the range of 1-20, more preferably 1-10, and even more preferably 3-6.

[0092] Specific examples of the polymer additive include maleic anhydride-modified polyethylene, maleic anhydride-modified polypropylene, maleic anhydride-modified ethylene-propylene copolymer, maleic anhydride-modified ethylene-propylene-diene terpolymer (EPDM), maleic anhydride-modified polybutadiene, maleic anhydride-ethylene copolymer, maleic anhydride-propylene copolymer, maleic anhydride-ethylene-propylene copolymer, maleic anhydride-butadiene copolymer, polyethylene, polypropylene, ethylene-propylene copolymer, oxidized polyethylene, oxidized polypropylene, oxidized ethylene-propylene copolymer, ethylene-acrylic acid copolymer, ethyl cellulose, hydroxyethyl cellulose, etc. Among these, from the viewpoint of dispersion stability of the aqueous monomer solution, maleic anhydride-modified polyethylene, maleic anhydride-modified polypropylene, maleic anhydride-modified ethylene-propylene copolymer, maleic anhydride-ethylene copolymer, maleic anhydride-propylene copolymer, maleic anhydride-ethylene-propylene copolymer, polyethylene, polypropylene, ethylene-propylene copolymer, oxidized polyethylene, oxidized polypropylene, and oxidized ethylene-propylene copolymer are preferred. Two or more of these may be used in combination. These polymer additives may also be used in combination with the surfactants. Among these, it is preferable to use a polymer additive, and it is more preferable to use a maleic anhydride-modified ethylene-propylene copolymer. In another preferred embodiment, the polymer additive is used alone without using a surfactant.

[0093] The amount of the dispersing aid used is appropriately set depending on the polymerization form, the type of aqueous monomer solution and the hydrophobic organic solvent, etc. Specifically, the concentration of the dispersing aid in the hydrophobic organic solvent (100% by mass) is preferably 0.0001 to 2% by mass, and more preferably 0.0005 to 1% by mass.

[0094] [3-3] Polymerization process The polymerization step is a step in which the monomers in the droplets containing the monomers obtained in the dispersion step are polymerized to obtain a hydrogel polymer (hereinafter also simply referred to as a hydrogel).

[0095] "Reactor" The reaction apparatus used in the polymerization step may be the same as the dispersing apparatus used in the dispersing step, or may be a different apparatus. In the case of batch-type reversed-phase suspension polymerization, the apparatus used in the dispersing step can be used as the reaction apparatus, which is preferable in terms of workability. When the reaction apparatus is a different apparatus from the dispersing apparatus, the monomer dispersion obtained in the dispersing step is supplied to the reaction apparatus.

[0096] The shape of the reactor in which the polymerization reaction is carried out is not particularly limited, and known reactors can be used. As described above, a stirring device that can be suitably used in the dispersion step can also be suitably used in the polymerization reaction. In the case of a continuous production method, the reactor is preferably shaped so that the monomer (aqueous solution) can undergo the polymerization reaction while moving as a droplet-like dispersed phase in the hydrophobic organic solvent that is the continuous phase formed in the reactor. Examples of such reactors include reactors in which tubular reaction tubes are arranged vertically, horizontally, or spirally. In this embodiment, the monomer (aqueous solution) is supplied into the hydrophobic organic solvent moving within the reaction section (reaction tube), so that droplets of the monomer aqueous solution move together with the hydrophobic organic solvent without stagnating. This prevents contact between monomer reactants with different polymerization rates.

[0097] Furthermore, the reaction apparatus may be equipped with a temperature adjusting means (for example, a heating means) so that the continuous phase inside the reaction apparatus can be heated or cooled from the outside, as required.

[0098] "Polymerization temperature" The polymerization temperature, which is the reaction temperature in the polymerization step, may be set appropriately depending on the type and amount of polymerization initiator used, but is preferably 20°C to 100°C, and more preferably 40°C to 90°C. Polymerization temperatures higher than 100°C are not preferred because a rapid polymerization reaction occurs. The polymerization temperature refers to the temperature of the hydrophobic organic solvent, which is the dispersion medium (hereinafter referred to as "Td").

[0099] In the polymerization step, since the monomer (aqueous solution) is dispersed in the hydrophobic organic solvent in the form of droplets, the temperature of the aqueous monomer solution is rapidly increased by heat transfer from the hydrophobic organic solvent. If the polymerization initiator contained in the droplets is a thermally decomposable polymerization initiator, the thermally decomposable polymerization initiator decomposes as the temperature rises, generating radicals. The generated radicals then initiate a polymerization reaction, and as the polymerization reaction progresses, a hydrogel is formed.

[0100] In the case of a continuous production method, the formed hydrogel moves inside the reactor with the moving continuous phase and is discharged from the reactor together with the hydrophobic organic solvent that forms the continuous phase.

[0101] When the aqueous monomer solution contains a thermally decomposable polymerization initiator, the Td is, from the viewpoint of the polymerization rate, preferably 70° C. or higher, more preferably 75° C. or higher, and even more preferably 80° C. or higher. There are no particular limitations on the upper limit of Td, but from the viewpoint of safety, it is appropriately selected within a range that does not exceed the boiling point of the hydrophobic organic solvent that forms the continuous phase.

[0102] "Multi-stage reversed-phase suspension polymerization" In the production method of the present invention, from the viewpoint of obtaining an appropriate aggregate particle size (particle size of aggregate-like particles), multi-stage polymerization may be performed. Specifically, after the completion of the first-stage polymerization step, the above-mentioned aqueous monomer solution may be further added to carry out a polymerization reaction, etc. In the multi-stage polymerization, the reaction solution may be appropriately stirred.

[0103] "Inorganic fine particles" In the production method of the present invention, inorganic fine particles may be added to the hydrogel polymer during and / or after the completion of polymerization in order to obtain an appropriate aggregate particle size.

[0104] Examples of inorganic fine particles that can be used in the present invention include silicon dioxide, aluminum oxide, titanium dioxide, calcium phosphate, calcium carbonate, magnesium phosphate, calcium sulfate, diatomaceous earth, bentonite, zeolite, and other metal oxides. Silicon dioxide, aluminum oxide, and titanium dioxide are particularly preferred.

[0105] The amount of inorganic fine particles added is generally 0.001 to 1 part by mass, preferably 0.001 to 0.5 parts by mass, per 100 parts by mass of the hydrogel polymer, to obtain good results. By adding inorganic fine particles in this range, the effect of adding inorganic fine particles is efficiently expressed, and the influence of inorganic fine particles on water absorption performance is also small, which is preferable.

[0106] [3-4] Separation process The separation step is a step of separating the hydrogel polymer obtained in the polymerization step from the hydrophobic organic solvent. The type and structure of the apparatus used in the separation step are not particularly limited, and for example, known apparatuses used for filtration, sedimentation, centrifugation, squeezing, etc. can be used. Alternatively, the hydrogel polymer and the hydrophobic organic solvent may be separated by heating the mixture of the hydrogel polymer and the hydrophobic organic solvent at normal or reduced pressure using a stirring apparatus having stirring blades used in the polymerization step, and distilling the mixture. In batch-type reversed-phase suspension polymerization, distillation at normal or reduced pressure is preferably carried out.

[0107] [3-5] Gel sizing process In the gel sizing step, the hydrogel polymer separated from the hydrophobic organic solvent in the separation step is sized using a gel sizing device having an extrusion section and a perforated plate. This results in a sized hydrogel polymer (hereinafter, the hydrogel after gel sizing will be referred to as sized gel). The gel sizing step is an optional step. By including the gel sizing step, it becomes easier to control the compressibility of the swollen gel of the water-absorbent resin.

[0108] The hydrogel polymer subjected to this gel sizing step is in the form of a single gel sphere or an aggregate of gel spheres. There is no particular lower limit to the average particle size of the hydrogel polymer, but it is preferably 0.01 mm or more, more preferably 0.03 mm or more, even more preferably 0.05 mm or more, and even more preferably 0.1 mm or more. There is no particular upper limit to the average particle size, but it is preferably 20 mm or less, more preferably 10 mm or less. When the hydrogel polymer is in the form of a single particle, the particle size is referred to as the primary particle size of the hydrogel polymer. When the hydrogel polymer is in the form of an aggregate, the particle size of each gel sphere constituting the aggregate is referred to as the primary particle size of the hydrogel polymer. In the present invention, the average primary particle size of the hydrogel polymer is not particularly limited, but from the viewpoint of being able to suppress the generation of fine powder in the drying step, it is preferably 5 to 2000 μm, more preferably 5 to 1000 μm, even more preferably 5 to 800 μm, still more preferably 8 to 500 μm, still more preferably 10 to 300 μm, and particularly preferably 10 to 200 μm.

[0109] Incidentally, a device having a cutter may be installed before the gel particle size adjusting device having the extrusion section and the perforated plate to break down large aggregates of the hydrogel polymer.

[0110] "Hydrated gel temperature" The lower limit of the temperature of the hydrogel entering (feeding into) the gel sizing device is not particularly limited, but from the viewpoint of granulation efficiency and suppression of damage to the hydrogel, it is preferably 80° C. or higher, more preferably 90° C. or higher. The upper limit of the temperature of the hydrogel when fed into the gel sizing device is not particularly limited, but is generally 100° C. or lower.

[0111] "Gel granulation device" As used herein, "gel sizing" refers to the process of producing particles of approximately uniform shape and size from a wet powder raw material by extruding the wet powder mass through small holes in a perforated plate into a cylindrical shape. In other words, by using a perforated plate, the hydrogel that has become excessively coarse aggregates in the preceding solvent separation step is broken down, and the hydrogel in the form of small single particles is appropriately aggregated. Therefore, this step makes it possible to obtain a hydrogel (sized gel) in a granulated form with a relatively uniform particle size. The sized gel may contain single-particle hydrogel.

[0112] The "gel sizing device having an extrusion section and a perforated plate" used in the gel sizing step is not particularly limited as long as it has an extrusion section and a perforated plate (die or screen), the extrusion section usually has an extrusion member that extrudes and supplies the contents toward the perforated plate, and is an apparatus (e.g., an extruder) that can produce particles of a certain size by extruding the material through the perforated plate. Also, a plurality of the above-mentioned devices may be prepared and used by arranging the plurality of devices in series.

[0113] Furthermore, the shape of the holes in the perforated plate (die or screen) is not particularly limited and can be arbitrarily selected from shapes suitable for use, such as circles, ellipses, polygons (e.g., hexagons), and triangles. However, from the viewpoint of sizing strength, circles and ellipses are preferred. The hole diameter of the perforated plate is also not particularly limited, but is preferably 1.5 mm or less, more preferably 1.0 mm or less, and even more preferably 0.8 mm or less. By keeping the hole diameter below this upper limit, the size of the resulting sieved gel is prevented from increasing more than necessary, and the amount of fine powder generated during drying using an agitator dryer in the downstream process can be reduced. The hole diameter is preferably 0.3 to 1.5 mm, more preferably 0.3 to 0.8 mm. If the hole diameter of the perforated plate is 0.3 mm or more, efficient extrusion can be achieved during the extrusion operation.

[0114] The hole diameter is defined as follows: First, if the hole is not perfectly round, the geometric mean value of the minor axis and major axis of the hole is used as the hole diameter. Furthermore, if the hole diameters of the holes in the perforated plate are different, the hole diameters of all the holes are calculated, and the geometric mean value is used as the hole diameter of the holes in the perforated plate. Furthermore, if the hole diameter of the perforated plate changes from the extrusion action portion side to the opposite side (the hole diameter changes in the thickness direction of the perforated plate), the value that gives the smallest hole diameter among them is used.

[0115] In this step, additives may be further added to the hydrogel polymer. Examples of additives that can be added in this step include polymerization initiators, oxidizing agents, reducing agents, chelating agents, thickeners, surfactants, crosslinking agents, acids, bases, foaming agents, organic or inorganic fine particles, polyvalent metal salts, etc. Among these, additives that can control the degree of aggregation, such as thickeners such as starch, cellulose, starch-cellulose derivatives, and polyvinyl alcohol, surfactants, fine powders of water-absorbent resins, crosslinking agents, and polyvalent metal salts, are preferred.

[0116] [3-6] Drying process The drying step is a step of drying the hydrogel. In the present invention, the drying method in the drying step is not particularly limited. The drying method may be azeotropic dehydration in a hydrophobic dispersion solvent used in conventional reverse phase suspension polymerization. However, as a more suitable method for obtaining the water-absorbent resin of the present invention by reverse phase suspension polymerization, both stirring drying and static drying can be preferably used instead of azeotropic dehydration. However, stirring drying is preferred in order to maintain the particle size of the gel controlled in the gel sizing step. In the drying step, an apparatus equipped with a heating means for heating the hydrogel may be used. Furthermore, when stirring drying is used, a rotary dryer equipped with a rotary container may be used as the drying apparatus.

[0117] The dried polymer made of particles obtained in this drying step can be directly used as a water-absorbent resin for various applications. When a water-absorbent resin is produced by this production method, the dried polymer obtained in the drying step can also be subjected to a surface-crosslinking step described later. In this case, the dried polymer to be subjected to the surface-crosslinking step described later is also referred to as a "water-absorbent resin powder" for convenience.

[0118] "Additives" As long as the effects of the present invention are not impaired, additives may be added to the hydrogel. The additives may be added to the hydrogel while the hydrogel is being heated by a heating means and / or while the hydrogel is being stirred (rotated) in a rotating container, or may be added to the hydrogel before the drying step (before the hydrogel is heated by a heating means and / or before the hydrogel is being stirred (rotated) in a rotating container). Furthermore, the additives may be added to the hydrogel in any step before the drying step. The additives can reduce excessive adhesion between hydrogel particles during drying, making it possible to obtain a water-absorbent resin with an excellent water absorption rate.

[0119] An example of an additive that can be added to the hydrogel is a drying aid.

[0120] Specifically, from the viewpoint of industrial efficiency, it is preferable to add a drying aid to the hydrogel when handling particulate hydrogels having a diameter of 1 mm or less. In particular, by adding a drying aid to the hydrogel before the drying step of the present invention, a water-absorbent resin with an excellent water absorption rate can be obtained. That is, a preferred embodiment of the present invention includes adding a drying aid to the hydrogel polymer.

[0121] Drying aid The drying aid is added for the purpose of maintaining the fluidity of the hydrogel during stirring and drying, and examples of the drying aid include surfactants and polymer lubricants. As the drying aid, a polymer lubricant and a surfactant may be used in combination.

[0122] The amount of drying aid added is appropriately determined depending on the water content of the drying aid and the type of gel fluidizer. The total amount of drying aid added is preferably 0.001% to 0.5% by mass, more preferably 0.01% to 0.3% by mass, and even more preferably 0.02% to 0.2% by mass, relative to the solid content (100% by mass) of the hydrogel. In a preferred embodiment of the present invention, the hydrogel polymer in the drying step contains less than 0.08% by mass of drying aid relative to the solid content (100% by mass) of the hydrogel polymer. By drying the hydrogel obtained by reversed-phase suspension polymerization using a rotary dryer as in this embodiment, the hydrogel is less likely to fuse, making it easier to adjust the particle size by crushing or the like. Therefore, when the hydrogel is dried using a rotary dryer, the amount of drying aid used can be reduced.

[0123] The drying aid is preferably added to the hydrogel polymer in a step prior to the drying step. Specific examples include (1) adding the drying aid to the hydrogel separated from the hydrophobic organic solvent in the separation step, (2) adding the drying aid to the sized gel before the drying step, (3) adding the drying aid to the aqueous monomer solution in the monomer solution preparation step, and (4) adding the drying aid to the hydrophobic organic solvent in the dispersion step. The drying aid is more preferably added in a step immediately prior to the drying step, and even more preferably between the step prior to the drying step (e.g., the gel sizing step) and the step prior to the drying step. Furthermore, it is also a preferred embodiment to add the drying aid to the hydrogel polymer after the step prior to the drying step (e.g., the gel sizing step), or between the step prior to the drying step (e.g., the gel sizing step) and the step prior to the drying step (e.g., the gel sizing step) and the step prior to the drying step. The drying aid may be added before the drying step by, for example, adding the hydrogel polymer and the drying aid to a dryer, or adding the drying aid to the hydrogel polymer before the hydrogel polymer is added to the dryer, etc. The drying aid may overlap with the surfactant and / or polymer additive used as a dispersion aid in the dispersion step.

[0124] Specific examples of surfactants used in drying aids include: (1) sucrose fatty acid esters, polyglycerin fatty acid esters, sorbitan fatty acid esters, polyoxyethylene sorbitan fatty acid esters, polyoxyethylene glycerin fatty acid esters, sorbitol fatty acid esters, polyoxyethylene sorbitol fatty acid esters, polyoxyethylene alkyl ethers, polyoxyethylene alkylphenyl ethers, polyoxyethylene castor oil, polyoxyethylene hydrogenated castor oil, alkylaryl formaldehyde condensed polyoxyethylene ethers, polyoxyethylene polyoxypropylene block copolymers, polyoxyethylene polyoxypropyl alkyl ethers, polyethylene glycol fatty acid esters, alkyl glucosides, N-alkyl gluconamides, polyoxyethylene fatty acid amides, polyoxyethylene alkylamines, phosphate esters of polyoxyethylene alkyl ethers, and phosphate esters of polyoxyethylene alkyl allyl ethers. (2) alkyldialkylaminoacetic acid betaines such as capryldimethylaminoacetic acid betaine, lauryldimethylaminoacetic acid betaine, myristyldimethylaminoacetic acid betaine, and stearyldimethylaminoacetic acid betaine; alkylamidopropyl betaines such as lauric acid amidopropyl betaine, coconut oil fatty acid amidopropyl betaine, and palm kernel oil fatty acid amidopropyl betaine; alkylhydroxysulfobetaines such as laurylhydroxysulfobetaine; and amphoteric surfactants such as alkylcarboxymethylhydroxyethylimidazolinium betaine and 2-alkyl-N-carboxymethyl-N-hydroxyethylimidazolinium betaine; (3) anionic surfactants such as alkylaminodiacetate monoalkali metals such as laurylaminodiacetate monosodium, laurylaminodiacetate potassium, and myristylaminodiacetate sodium; and (4) cationic surfactants such as long-chain alkyldimethylaminoethyl quaternary salts. Two or more of these may be used in combination.

[0125] Specific examples of polymeric lubricants include maleic anhydride-modified polyethylene, maleic anhydride-modified polypropylene, maleic anhydride-modified ethylene-propylene copolymer, maleic anhydride-modified ethylene-propylene-diene terpolymer (EPDM), maleic anhydride-modified polybutadiene, maleic anhydride-ethylene copolymer, maleic anhydride-propylene copolymer, maleic anhydride-ethylene-propylene copolymer, maleic anhydride-butadiene copolymer, polyethylene, polypropylene, ethylene-propylene copolymer, oxidized polyethylene, oxidized polypropylene, oxidized ethylene-propylene copolymer, ethylene-acrylic acid copolymer, ethyl cellulose, hydroxyethyl cellulose, and polyalkylene oxides such as polyethylene glycol. The molecular weight (weight average molecular weight) of these polymeric lubricants is preferably selected from the range of 2 to 2,000,000, more preferably 4 to 1,000,000. Two or more of these may be used in combination.

[0126] "Particle size distribution of dried polymer" The particle size distribution of the dried polymer obtained in the drying step is such that the proportion of particles with a diameter of 850 μm or more (the proportion of particles that did not pass through a sieve with an opening diameter of 850 μm) is preferably 50% by mass or less, more preferably 45% by mass or less, and even more preferably 40% by mass or less, based on 100% by mass of the dried polymer. According to the method of this embodiment, by combining this with drying using an agitator dryer, the formation of coarse particles is significantly suppressed, making it possible to keep the proportion of particles with a diameter of 850 μm or more within the preferred range. Furthermore, the proportion of particles with a diameter of 1400 μm or more (the proportion of particles that did not pass through a sieve with an opening diameter of 1400 μm) based on 100% by mass of the dried polymer is preferably 40% by mass or less, more preferably 35% by mass or less, and even more preferably 30% by mass or less.

[0127] [3-7] Surface crosslinking process The water-absorbent resin (for example, water-absorbent resin powder) obtained through the drying step (and any subsequent step) is preferably surface-crosslinked with a surface crosslinking agent. This surface crosslinking is a treatment for providing a portion with high crosslink density in the surface layer (a portion several tens of μm from the surface of the water-absorbent resin (for example, water-absorbent resin powder)) of the water-absorbent resin (for example, water-absorbent resin powder). By carrying out the surface crosslinking treatment, various water-absorbing properties of the water-absorbent resin can be improved. Here, by appropriately adjusting the crosslink density, particularly excellent absorbency under load can be obtained.

[0128] In the present invention, known surface cross-linking techniques are appropriately applied, including surface cross-linking in a state dispersed in a hydrophobic organic solvent, which is carried out in conventional reversed-phase suspension polymerization, and surface cross-linking to a powder in a dry state, which is generally carried out in aqueous solution polymerization, but in the present invention, from the viewpoint of improving the absorption capacity under pressure, surface cross-linking to a water absorbent resin that has been subjected to a gel separation step and a drying step is preferred. In addition, the surface cross-linking agent used in this step is also indicated as a "post-cross-linking agent" in known techniques in order to distinguish it from the internal cross-linking agent used in the step of preparing an aqueous monomer solution.

[0129] In the present invention, the surface cross-linking step may be carried out after the drying step or during the drying step. In known surface cross-linking steps, a surface cross-linking agent is generally mixed with a hydrogel polymer (e.g., a hydrogel cross-linked polymer) or a dried polymer thereof (e.g., a cross-linked polymer), and the mixture is heated to carry out a cross-linking reaction. In the present invention, however, these steps may be separately provided after the drying step, or a surface cross-linking agent may be added to the hydrogel polymer in the drying step to carry out the surface cross-linking reaction of the polymer and drying simultaneously. Furthermore, when a water-absorbent resin is produced by a batch-type reversed-phase suspension polymerization method, the hydrophobic organic solvent and the hydrogel polymer can be separated by distillation in the separation step after the polymerization reaction. However, a surface-cross-linked water-absorbent resin (e.g., water-absorbent resin particles) can also be obtained by adding a surface cross-linking agent to the hydrogel polymer even during the separation step.

[0130] [3-8] Other processes The method for producing a water-absorbent resin according to the present invention may include, in addition to the above-mentioned steps, a cooling step, a pulverizing step, a water-containing (rewetting) step, a step of adding other additives, a classification step, a sizing step, and a fine powder recycling step, as needed. In addition, the method may further include a transporting step, a storing step, a packaging step, a preservation step, etc.

[0131] (cooling process) In the cooling step, which is optionally performed, the particulate dry polymer obtained in the drying step can be cooled using a known cooling means to obtain a particulate dry polymer cooled to a desired temperature.

[0132] (Crushing process) It is preferable to carry out a pulverization step in which the particulate dried polymer obtained in the drying step (and any subsequent cooling step) is pulverized. By passing through the pulverization step, a water-absorbent resin (for example, a water-absorbent resin powder) having a controlled particle size or particle size distribution is obtained. In the pulverization step, for example, a high-speed rotary pulverizer such as a roll mill, a hammer mill, a screw mill, or a pin mill, a vibration mill, a knuckle-type pulverizer, a cylindrical mixer, or the like is appropriately selected and used as a pulverization means.

[0133] (Rewetting process) The rewetting step, which is optionally performed, is a step of adding at least one additive selected from the group consisting of a polyvalent metal salt, a cationic polymer, a chelating agent, an inorganic reducing agent, and an α-hydroxycarboxylic acid compound to the water-absorbent resin (e.g., water-absorbent resin particles) obtained in the surface-crosslinking step. The additive is preferably added to the water-absorbent resin (e.g., water-absorbent resin particles) in the form of an aqueous solution or a dispersion (slurry). The additive may be added or mixed simultaneously with the above-mentioned surface-crosslinking agent solution. Specifically, the method described in "(2-7) Rewetting Step" in International Patent Publication No. 2015 / 053372 is also applicable to the present invention.

[0134] (Other additive addition process) In the present invention, additives other than those mentioned above can be added to the water-absorbent resin to impart various functions. Specific examples of such additives include surfactants, compounds containing phosphorus atoms, oxidizing agents, organic reducing agents, water-insoluble inorganic fine particles, organic powders such as metal soaps, deodorants, antibacterial agents, pulp, and thermoplastic fibers. The water-insoluble inorganic fine particles disclosed in International Patent Publication No. 2011 / 040530, "(5) Water-insoluble inorganic fine particles," are applicable to the present invention. Among these additives, polyvalent metal salts, cationic polymers, and inorganic fine particles that improve liquid permeability are preferably added to the water-absorbent resin, particularly to prevent deterioration of the water-absorbent properties when the swollen gel is compressed.

[0135] (Sizing process) The "size regulating step" means a step of loosening a water absorbent resin (for example, a water absorbent resin powder) that has been loosely aggregated through the surface cross-linking step, to regulate the particle size. This size regulating step includes a fine powder removing step and a classification step that follow the surface cross-linking step. The size regulating step is preferably carried out from the viewpoint of regulating the particle size of the water absorbent resin and obtaining stable water absorption properties.

[0136] (Fine powder reuse process) The "fine powder reuse step" means a step of supplying fine powder of a hydrogel or a water absorbent resin generated by sieve classification or the like in each of the steps to any of the steps as it is or after granulating the fine powder. The fine powder reuse step is preferably carried out from the viewpoint of reducing production loss of the water absorbent resin.

[0137] [4] Absorbent articles and their manufacturing methods An absorbent article according to one embodiment of the present invention comprises a liquid-impermeable back sheet, an absorbent body containing the water-absorbent resin particles of the present invention, and a liquid-permeable top sheet in this order, and a diffusion auxiliary sheet is provided between the top sheet and the absorbent body, and the diffusion auxiliary sheet has a basis weight of 25 to 100 g / m 2 It is a liquid-permeable nonwoven fabric.

[0138] The absorbent article according to one embodiment of the present invention has the effect of exhibiting excellent absorption performance, such as the diffusibility of the absorbed aqueous liquid, when absorbing an aqueous liquid such as urine during use, and suppressing swelling of the water-absorbent section. More specifically, the absorbent article according to one embodiment of the present invention has the effect of suitably suppressing swelling of the absorbent body even during long-term use, preventing discomfort to the user, and exhibiting excellent absorption performance, such as the diffusibility of the absorbed aqueous liquid, when absorbing an aqueous liquid such as urine during use.

[0139] In one embodiment of the present invention, the diffusion auxiliary sheet is not particularly limited and may be any known nonwoven fabric that can be used as a liquid-permeable nonwoven fabric for an absorbent article, as long as it is a liquid-permeable nonwoven fabric having a basis weight within the range described below. The diffusion auxiliary sheet may be, for example, an air-through nonwoven fabric, a point-bonded nonwoven fabric, a spunbonded nonwoven fabric, or a spunlace nonwoven fabric. Furthermore, a composite nonwoven fabric of these may also be used as the diffusion auxiliary sheet. Examples of the composite nonwoven fabric include spunbond / meltblown / meltblown / spunbond nonwoven fabrics (SMMS nonwoven fabrics). The diffusion auxiliary sheet is preferably hydrophilized with a surfactant.

[0140] The material constituting the diffusion-assisting sheet is not particularly limited, and examples thereof include synthetic fibers such as polypropylene, polyethylene, and polyester.

[0141] As described above, in an absorbent article according to one embodiment of the present invention, the gel layer formed when the water-absorbent resin absorbs water and swells is compressed during use. When the gel layer is compressed, gaps within the gel layer that could serve as paths for aqueous liquids are crushed, which reduces the diffusibility of the absorbed aqueous liquid within the absorbent body that includes the gel layer and may cause the aqueous liquid to seep out of the absorbent body. For this reason, the diffusion auxiliary sheet is provided between the top sheet and the absorbent body.

[0142] In an absorbent article according to one embodiment of the present invention, when the diffusion auxiliary sheet is a liquid-permeable nonwoven fabric having a basis weight of a specific value or more, it is believed that liquid is more easily diffused within the diffusion auxiliary sheet, and that the absorbent article can achieve excellent diffusion of absorbed aqueous liquids.

[0143] Here, the basis weight of the liquid-permeable nonwoven fabric serving as the diffusion-assisting sheet is the weight per unit area of ​​the liquid-permeable nonwoven fabric.

[0144] Therefore, in the absorbent article according to one embodiment of the present invention, from the viewpoint of diffusing the absorbed aqueous liquid, the diffusion-assisting sheet has a basis weight of 25 to 100 g / m 2 , preferably 30 to 50 g / m 2 It is a liquid-permeable nonwoven fabric.

[0145] The thickness of the diffusion auxiliary sheet is preferably 0.1 mm or more and less than 0.5 mm. By reducing the thickness of the diffusion auxiliary sheet, it is possible to reduce the thickness of the absorbent article before use and during use (when absorbing water). Furthermore, a diffusion auxiliary sheet having both a basis weight within the above range and a thickness within the above range is a diffusion auxiliary sheet with a high fiber density. Therefore, the absorbent article according to one embodiment of the present invention Revenue In an absorbent article, it is particularly preferable in terms of the diffusibility of the absorbed aqueous liquid in the absorbent article to provide a diffusion auxiliary sheet having both a basis weight within the aforementioned range and a thickness within the aforementioned range, since the absorbed aqueous liquid is quickly diffused in the plane direction of the diffusion auxiliary sheet by capillary force.

[0146] In one embodiment of the present invention, the liquid-permeable top sheet may be any known nonwoven fabric that can be used as a liquid-permeable top sheet constituting an absorbent article, as long as the basis weight is within the range described below, and is not particularly limited. The liquid-permeable top sheet may be, for example, an air-through nonwoven fabric, a point-bonded nonwoven fabric, a spunbonded nonwoven fabric, or a spunlace nonwoven fabric. Furthermore, composite nonwoven fabrics of these may also be used. For example, a spunbond / meltblown / meltblown / spunbonded nonwoven fabric (SMMS nonwoven fabric) may be mentioned. These are preferably hydrophilized with a surfactant.

[0147] The material constituting the liquid-permeable top sheet is not particularly limited, and examples thereof include synthetic fibers such as polypropylene, polyethylene, and polyester.

[0148] The basis weight of the liquid-permeable top sheet is preferably 10 to 30 g / m 2 , more preferably 10 to 20 g / m 2 , . When the basis weight of the liquid-permeable top sheet is within the above-mentioned range, the absorbed aqueous liquid is smoothly absorbed in the lower layer, i.e., the absorbent body or the like located below the liquid-permeable top sheet, and the wetted area of ​​the liquid-permeable top sheet does not spread. This makes it possible to provide comfort to the user of the absorbent article. Furthermore, the thickness of the liquid-permeable top sheet is preferably 0.1 to 0.5 mm, more preferably 0.15 to 0.3 mm. In the absorbent article according to one embodiment of the present invention, when the basis weight and thickness of the liquid-permeable top sheet are within the above-mentioned ranges, the absorbent article has the effect of being soft to the touch.

[0149] In one embodiment of the present invention, the back sheet may be any known sheet that can be used as a liquid-impermeable sheet constituting an absorbent article, and is not particularly limited. The liquid-impermeable back sheet may be, for example, a thin plastic film such as a polyethylene film. Among such plastic films, a breathable film is preferred in order to provide comfort to the user of the absorbent article.

[0150] The absorbent body according to one embodiment of the present invention may contain hydrophilic fibers in addition to the water-absorbent resin. The absorbent body may also contain additives in addition to the water-absorbent resin and hydrophilic fibers. The additives may be additives that are generally contained in absorbent bodies in absorbent articles, and are not particularly limited. Specific examples of the additives include inorganic powders (e.g., amorphous silica), deodorants, pigments, dyes, antibacterial agents, fragrances, and adhesives. When the water-absorbent resin contains inorganic particles, the absorbent body may contain an inorganic powder in addition to the inorganic particles in the water-absorbent resin. Examples of the inorganic powder include silicon dioxide, zeolite, kaolin, and clay.

[0151] The method for producing the absorbent body in one embodiment of the present invention can be any method commonly known for producing absorbent bodies in absorbent articles, and is not particularly limited. Specific examples of the method for producing the absorbent body include a method of mixing the water-absorbent resin of the present invention with optional hydrophilic fibers to obtain a mixture and then molding the mixture; a method of forming a layer of hydrophilic fibers and then spraying the water-absorbent resin of the present invention on the layer of hydrophilic fibers; and a method of spraying the water-absorbent resin of the present invention in layers to form a layer of absorbent resin and then placing a layer of hydrophilic fibers on the layer of water-absorbent resin. The absorbent body produced in this manner may be a uniform mixture of the water-absorbent resin of the present invention and the hydrophilic fibers, or the water-absorbent resin of the present invention and the hydrophilic fibers may each form a layer and be in contact with each other. When the water-absorbent resin of the present invention and the hydrophilic fibers each form a layer, the water-absorbent resin of the present invention and the hydrophilic fibers may each form one layer, or at least one of the water-absorbent resin of the present invention and the hydrophilic fibers may form multiple layers, with the layers of the water-absorbent resin of the present invention and the layers of the hydrophilic fibers being alternately stacked. Even when the water-absorbent resin of the present invention and the hydrophilic fibers form separate layers, the water-absorbent resin of the present invention may be mixed into the hydrophilic fiber layer. In the absorbent core of the absorbent article according to one embodiment of the present invention, it is preferable to have a hydrophilic fiber layer on the back sheet side and a water-absorbent resin layer on the top sheet side, because the water-absorbent resin will be mixed into the hydrophilic fiber layer when the absorbent article is in use, from the viewpoints of the thickness of the absorbent article and the diffusibility of absorbed aqueous liquid.

[0152] The hydrophilic fiber is not particularly limited, and examples thereof include pulp fiber, cotton linter crosslinked cellulose fiber, rayon, cotton, wool, acetate, vinylon, etc. Furthermore, in one embodiment of the present invention, the hydrophilic fiber is preferably an air-laid hydrophilic fiber listed above.

[0153] Furthermore, absorbent materials such as pulp fibers can also be used as the hydrophilic fibers. In this case, the content of the water-absorbent resin in 100% by mass of the absorbent body (core concentration) is preferably 30% by mass to 100% by mass, more preferably 40% by mass to 100% by mass, even more preferably 50% by mass to 100% by mass, still more preferably 60% by mass to 100% by mass, particularly preferably 70% by mass to 100% by mass, and most preferably 75% by mass to 95% by mass. However, in the present invention, the hydrophilic fibers used in the absorbent body do not include cloth-like fibers (woven fabrics or nonwoven fabrics).

[0154] By setting the core concentration within the above range, when the absorbent is used in the upper layer of an absorbent article, the absorbent article can be maintained in a clean white state. Furthermore, since the absorbent having a core concentration within the above range has excellent diffusibility of body fluids such as urine and blood, efficient liquid distribution is achieved, and an improvement in the absorption capacity of the absorbent article according to one embodiment of the present invention can be expected.

[0155] More ingredients body In other words, the absorbent body in one embodiment of the present invention may be an absorbent body that contains the water-absorbent resin in one embodiment of the present invention but does not contain hydrophilic fibers, or the absorbent body in one embodiment of the present invention may be an absorbent body that contains the water-absorbent resin in one embodiment of the present invention and hydrophilic fibers, and the mass of the water-absorbent resin is 50 mass% or more in 100 mass% in total of the water-absorbent resin and the hydrophilic fibers.

[0156] When the absorbent body contains the water-absorbent resin and hydrophilic fibers according to one embodiment of the present invention, the mass proportion of the water-absorbent resin is preferably 50% by mass or more and less than 100% by mass, more preferably 60% by mass or more and less than 100% by mass, more preferably 70% by mass or more and less than 100% by mass, more preferably 80% by mass or more and less than 100% by mass, even more preferably 90% by mass or more and less than 100% by mass, and particularly preferably 90% by mass to 95% by mass, based on 100% by mass of the total of the water-absorbent resin and the hydrophilic fibers. When the mass proportion of the water-absorbent resin in the absorbent body according to one embodiment of the present invention is within the above range, it has the following advantages: (1) the thickness of the absorbent article according to one embodiment of the present invention before use can be reduced while maintaining the liquid absorption capacity, and / or (2) the absorbent body has excellent diffusibility of body fluids such as urine and blood, and therefore efficient liquid distribution is achieved, making it less likely to cause localized swelling, and the absorbent article according to one embodiment of the present invention can be expected to have a reduced thickness and an increased absorption capacity during use.

[0157] In the absorbent body, the amount (basis weight) of the water-absorbent resin used is preferably 50 to 300 g / m 2 relative to the area where the water-absorbent resin is present. 2 , more preferably 100 to 200 g / m 2 When the amount of the water-absorbent resin used is within the above range, there is an advantage that the thickness of the absorbent article can be reduced between before use and during use (when absorbing water) while maintaining the liquid absorption capacity of the absorbent article. The water-absorbent resin-existing region is a region in the absorbent body where the water-absorbent resin is present. The absorbent article of the present invention is intended to have the water-absorbent resin dispersed to form a layer, and the basis weight is the mass of the water-absorbent resin per area of ​​the water-absorbent resin layer.

[0158] In addition to the above-mentioned configuration, the absorbent article according to one embodiment of the present invention may have a core wrap or three-dimensional gathers that cover at least one surface of the absorbent body in order to maintain the shape of the absorbent body.

[0159] The core wrap of the absorbent article according to one embodiment of the present invention may be tissue paper, particularly crepe paper; nonwoven fabric, particularly air-through nonwoven fabric, point-bonded nonwoven fabric, spunbonded nonwoven fabric, spunlace nonwoven fabric, etc., made of synthetic fibers such as polypropylene, polyethylene, or polyester. Furthermore, the core wrap may be a composite nonwoven fabric of these. Examples of the composite nonwoven fabric include spunbond / meltblown / spunbond (SMS nonwoven fabric) and spunbond / meltblown / meltblown / spunbond nonwoven fabric (SMMS nonwoven fabric). These core wraps are preferably hydrophilized with a surfactant. The core wrap may also serve as the diffusion-assisting sheet.

[0160] The thickness of the absorbent core in the absorbent article according to one embodiment of the present invention is preferably 1 mm to 10 mm, more preferably 1 mm to 5 mm, and the overall thickness of the absorbent article according to one embodiment of the present invention is preferably 1.2 mm to 15 mm, more preferably 1.2 mm to 10 mm. [Example]

[0161] The present invention will be described in more detail with reference to the following examples and comparative examples. However, the present invention is not limited to these examples. Examples obtained by appropriately combining the technical means described in each example are also included within the scope of the present invention. Although the terms "parts" and "%" are sometimes used in the examples, they represent "parts by mass" or "% by mass" unless otherwise specified. Unless otherwise specified, each operation is performed at room temperature (e.g., 25°C). Electrical equipment used in the production examples, examples, and comparative examples (including measurements of the physical properties of the water-absorbent resin) used a 200V or 100V, 60Hz power supply unless otherwise noted.

[0162] <Evaluation method> [Number average particle diameter] A scanning electron microscope (SEM) photograph of the water-absorbent resin or water-absorbent resin powder was taken. 50 primary particles located in front of the aggregate particles (secondary particles) were randomly selected from the photograph, and the major axis and minor axis of each primary particle were measured. The product of the measured values ​​was averaged (the geometric mean value of the measured values) to obtain the primary particle diameter. The primary particle diameter of each of the 50 primary particles was calculated, and the average of the obtained values ​​was defined as the average primary particle diameter of the water-absorbent resin.

[0163] [Moisture content] The moisture content was measured in accordance with the EDANA method (ERT430.2-02). For the measurement, the mass of the sample (water-absorbent resin or water-absorbent resin powder) was changed to 1.0 g, the drying temperature to 180°C, and the drying time to 3 hours. Specifically, 1.0 g of the sample (water-absorbent resin or water-absorbent resin powder) was placed in an aluminum cup with a bottom diameter of 50 mm, and then the total mass W1 (g) of the aluminum cup (aluminum cup containing water-absorbent resin or water-absorbent resin powder) was accurately weighed. Next, the aluminum cup (aluminum cup containing water-absorbent resin or water-absorbent resin powder) was placed in an oven set at an ambient temperature of 180°C. After 3 hours, the aluminum cup (aluminum cup containing water-absorbent resin or water-absorbent resin powder) was removed from the oven, and the total mass W2 (g) was accurately weighed. When the mass of the sample (water absorbent resin or water absorbent resin powder) used in this measurement is M (1.0 g), the water content (mass %) of the sample was calculated according to the following (Equation 2). Moisture content (mass%) = {(W1-W2) / M}×100 (Formula 2).

[0164] [Mass average particle diameter (D50)] The mass-average particle diameter (D50) was measured according to the method described in columns 27 and 28 of U.S. Pat. No. 7,638,570, under "(3) Mass-Average Particle Diameter (D50) and Logarithmic Standard Deviation (σζ) of Particle Diameter Distribution."

[0165] [CRC] CRC (centrifuge retention capacity) was measured in accordance with the EDANA method (ERT441.2-02). Specifically, 0.2 g of the water-absorbent resin was placed in a nonwoven bag, and the nonwoven bag was immersed in a large excess of 0.9 mass % sodium chloride aqueous solution for 30 minutes to allow the water-absorbent resin to freely swell. Thereafter, the water-absorbent resin was centrifuged (250 G) for 3 minutes to drain the water, and then the water absorption capacity (unit: g / g) was determined.

[0166] [AAP] The absorbency against pressure (AAP) was measured in accordance with the EDANA method (ERT442.2-02), except that the load condition was changed to 4.83 kPa (0.7 psi).

[0167] [Ext] The Ext (water-soluble content) of the water-absorbent resin obtained in this production example was measured in accordance with the EDANA method (ERT470.2-02).

[0168] [Bulk density] The bulk density of the water-absorbent resin of the present invention was measured in accordance with the EDANA method (T460.2-02).

[0169] [Swelled gel compressibility] The swollen gel compressibility of the water-absorbent resin of the present invention was measured by the following procedure: The measuring device used for measuring the swollen gel compressibility will be described with reference to FIGS.

[0170] 1.0 g of water-absorbent resin 16 was uniformly sprayed onto the bottom 15 of a cell 11 having an inner diameter of 60 mm, the bottom 15 of which was formed of a stainless steel mesh (openings 36 μm = 400 mesh). Next, a piston 12 having a diameter of 59 mm and weighing 108 g was placed in the cell 11 from above the water-absorbent resin 16. Thereafter, the cell 11 was placed in a 19.8 cm × 19.8 cm Petri dish 13 containing 180 g of a 0.9 mass % (mass / mass %) sodium chloride aqueous solution at 25°C, and the water-absorbent resin 16 was allowed to absorb the 0.9 mass % sodium chloride aqueous solution for 5 minutes. This operation caused the water-absorbent resin 16 to swell and form a swollen gel layer. Thereafter, the thickness (D1 [mm]) of the swollen gel layer formed by the swollen water-absorbent resin 16 was measured. Next, the cell 11, with the piston 12 still attached, was placed on a JIS standard sieve with a mesh size of 4750 μm, and a 1283 g weight 14 was placed on the piston so that a load of 0.7 psi was applied to the swollen gel. The cell was left standing for 10 seconds, and then the weight 14 was removed. This operation was repeated 10 times. Immediately after removing the weight 14, the load was applied for another 10 seconds. Thereafter, the thickness (D2 [mm]) of the swollen gel layer formed by the swollen water-absorbent resin 16 was measured, and the swollen gel compressibility was calculated using the following (Equation 1). Swollen gel compressibility [%] = (D1 - D2) / D1 × 100 (Equation 1).

[0171] "Measurement of nonwoven fabric thickness" The thickness of the nonwoven fabric was measured using a large-type dial thickness gauge (thickness measuring device) (manufactured by Ozaki Seisakusho Co., Ltd., model number: JB, measuring probe: anvil upper and lower φ50 mm). The upper measuring probe of the thickness measuring device was brought close to a height of 2 to 3 mm from the nonwoven fabric, and then the handle was slowly released to measure the thickness of the nonwoven fabric.

[0172] "Thickness of absorbent article (before swelling, after swelling and after compression)" For the absorbent articles manufactured in the examples and comparative examples described below, the thickness after swelling and compression was measured by the methods shown in (a) to (e) below. The thickness of the absorbent article measured in (a), (c), and (e) below was calculated by measuring the thickness at each of the five locations marked in Figure 3 and then averaging the thicknesses measured at each of the five locations. (a) The absorbent articles manufactured in the Examples and Comparative Examples were sandwiched between two acrylic plates from the top and bottom. In this state, the thickness of the absorbent article was measured using a large-type dial thickness gauge (thickness measuring device) (manufactured by Ozaki Seisakusho Co., Ltd., model number: JB, measuring probe: anvil top and bottom φ50 mm), and the thickness of the acrylic plate was subtracted from the measured value to obtain the thickness before swelling. The acrylic plate had a length of 12 cm, a width of 23 cm, a thickness of 0.3 cm, and a weight of 115 g. In the absorbent article, the liquid-permeable top sheet side was facing upward. (b) After temporarily removing the acrylic plate on the upper side of the absorbent article, 29 g of a 0.9 mass % sodium chloride aqueous solution was slowly added to the entire absorbent body of the absorbent article over 1 to 2 minutes, and the absorbent article was left to stand for 5 minutes from the start of the addition of the 0.9 mass % sodium chloride aqueous solution, thereby swelling the water-absorbing resin constituting the absorbent body, and a swollen absorbent article was obtained. (c) The removed acrylic plate was placed back on top of the swollen absorbent article, and the swollen absorbent article was sandwiched between the two acrylic plates. The thickness of the swollen absorbent article sandwiched between the two acrylic plates was measured using a large-type dial thickness gauge (thickness measuring device) (manufactured by Ozaki Seisakusho Co., Ltd., model number: JB, measuring probe: anvil upper and lower φ50 mm), and the thickness of the acrylic plate was subtracted from the measured value to obtain the thickness after swelling. (d) A weight of 2314 g was placed on the acrylic plate on the upper side of the swollen absorbent article, and the swollen absorbent article was left to stand for 10 minutes, and then a compression operation was performed on the swollen absorbent article. (e) After the above-mentioned compression operation, the weight was removed to obtain a compressed absorbent article sandwiched between the two acrylic plates. The thickness of the compressed absorbent article sandwiched between the two acrylic plates was measured using a large-type dial thickness gauge (thickness measuring device) (manufactured by Ozaki Seisakusho Co., Ltd., model number: JB, measuring probe: anvil upper and lower φ50 mm), and the thickness of the acrylic plates was subtracted from the measured value to obtain the thickness after compression.

[0173] "Diffusion length" After measuring the thickness after compression, the upper acrylic plate was removed. Then, 1 ml of a 0.9% by mass sodium chloride solution containing 0.002% by mass of Blue No. 1 was added to the compressed absorbent article from directly above the center over 5 seconds using a syringe (syringe needle gauge: 21G). After allowing to stand for 30 seconds, the longest length of the blue-dyed portion of the compressed absorbent article, i.e., the portion into which the 0.9% by mass sodium chloride aqueous solution had diffused, was measured using a ruler and defined as the diffusion length. The longest length of the portion into which the 0.9% by mass sodium chloride aqueous solution had diffused refers to the length of the longest straight line passing through the center of the absorbent article and connecting the two ends of the blue-dyed portion 30 seconds after the addition of the blue-dyed 0.9% by mass sodium chloride aqueous solution.

[0174] [Production of water-absorbent resin] [Manufacturing Example 1] 800 g of n-heptane was placed in a 2000 ml four-neck separable flask equipped with a stirrer, reflux condenser, thermometer, nitrogen gas inlet tube, and dropping funnel. 0.88 g of maleic anhydride-modified ethylene-propylene copolymer (Hiwax® HW2203A, manufactured by Mitsui Chemicals, Inc.) was added as a dispersing aid. The maleic anhydride-modified ethylene-propylene copolymer was dissolved in n-heptane to obtain a heptane solution. Nitrogen gas was then blown into the resulting heptane solution to remove dissolved oxygen.

[0175] Separately, a monomer aqueous solution (1) consisting of 127 g of sodium acrylate, 36 g of acrylic acid, 0.097 g of polyethylene glycol diacrylate (n=9), 0.008 g of pentasodium diethylenetriaminepentaacetate, 0.67 g of hydroxyethyl cellulose as a thickener, and 215 g of ion-exchanged water was prepared in a flask, and nitrogen gas was blown into the monomer aqueous solution (1) to expel dissolved oxygen from the monomer aqueous solution (1). Next, 1.2 g of a 15% (mass / mass%) aqueous solution of sodium persulfate was added to the monomer aqueous solution (1) in the flask, and the entire amount of the resulting solution was added to the separable flask. The mixture in the separable flask was stirred at 210 rpm to disperse the monomer aqueous solution (1) in the heptane solution. The bath temperature was then raised to 60°C to initiate the polymerization reaction, and after maintaining this bath temperature at 60°C for 2 hours, the polymerization was stopped, the mixture was filtered by suction, and the residue was air-dried overnight to obtain a hydrogel polymer (1). The hydrogel polymer (1) had an average primary particle size of 180 µm.

[0176] Next, the hydrogel polymer (1) (gel temperature: 90°C) was placed in a gel sizing device having a screw and a perforated plate with a hole diameter of 0.8 mm, and discharged from the gel sizing device to obtain a sizing gel (1).

[0177] Subsequently, the granulated gel (1) was dried using a cylindrical container rotary dryer. Specifically, the rotary container provided in the cylindrical container rotary dryer was rotated at 75 rpm in an atmosphere at a temperature of 200°C, and the heated granulated gel (1) was supplied to the cylindrical container rotary dryer and dried to obtain a dried polymer (1). The moisture content of the dried polymer (1) was 10% by mass.

[0178] Subsequently, the dried polymer (1) was fed to a roll mill (pulverizer) and pulverized to adjust the particle size, and further classified using a sieve with an opening particle size of 150 μm to obtain a water absorbent resin powder (1). The mass average particle size of the water absorbent resin powder (1) was 380 μm.

[0179]

[0223] A surface crosslinking agent solution composed of 0.03 part by mass of ethylene glycol diglycidyl ether, 0.385 part by mass of ethylene carbonate, 0.644 part by mass of propylene glycol and 2.6 parts by mass of ion exchanged water was sprayed with a sprayer relative to 100 parts by mass of the water absorbent resin powder (1), and the mixture was mixed uniformly using a high-speed continuous mixer.

[0180] The obtained mixture was introduced into a heat treatment machine whose atmospheric temperature was adjusted to 195°C ± 2°C, and subjected to heat treatment for 30 minutes, and then the powder temperature was forcibly cooled to 60°C, thereby obtaining a surface-crosslinked water absorbent resin powder (1).

[0181] A surface cross-linking agent solution consisting of 1.17 parts by mass of a 27.5% by mass aqueous aluminum sulfate solution (8% by mass in terms of aluminum oxide), 0.196 parts by mass of a 60% by mass aqueous sodium lactate solution, and 0.029 parts by mass of propylene glycol was further uniformly mixed with 100 parts by mass of the surface cross-linked water absorbent resin powder (1). Further, 10.0% by mass of water was uniformly mixed with 100 parts by mass of the water absorbent resin powder (1) after mixing.

[0182] Thereafter, the mixture was crushed (sized) until it passed through a JIS standard sieve with a mesh size of 710 μm, thereby obtaining a water-absorbent resin (1). The obtained water-absorbent resin (1) was in the form of particles, more specifically, aggregate particles of spherical particles. The physical properties of the obtained water-absorbent resin (1) are shown in Tables 1 to 3.

[0183] [Production Example 2] 800 g of cyclohexane was placed in a 2000 ml four-neck separable flask equipped with a stirrer, reflux condenser, thermometer, nitrogen gas inlet tube, and dropping funnel, and 0.6 g of a sucrose fatty acid ester (DK Ester (registered trademark) F-50 / Dai-ichi Kogyo Seiyaku Co., Ltd., HLB=6) was added as a dispersing aid to dissolve the sucrose fatty acid ester in cyclohexane to obtain a cyclohexane solution. Nitrogen gas was then blown into the resulting cyclohexane solution to expel dissolved oxygen in the cyclohexane solution.

[0184] Separately, a monomer aqueous solution (2) was prepared in a flask containing 141 g of sodium acrylate, 36 g of acrylic acid, 0.022 g of N,N'-methylenebisacrylamide, 0.71 g of hydroxyethyl cellulose as a thickener, and 327.65 g of ion-exchanged water. Nitrogen gas was blown into the monomer aqueous solution (2) to expel dissolved oxygen. Next, 0.95 g of a 15% aqueous solution of sodium persulfate was added to the monomer aqueous solution (2) in the flask, and the entire resulting solution was added to the separable flask. The mixture in the separable flask was stirred at 370 rpm to disperse the monomer aqueous solution (2) in the cyclohexane solution. The bath temperature was then raised to 60°C to initiate the polymerization reaction. The bath temperature was maintained at 60°C for 2 hours, after which the polymerization was stopped. The mixture was filtered by suction, and the residue was air-dried overnight to obtain a hydrogel polymer (2). The average primary particle size of the hydrogel polymer (2) was 195 μm.

[0185] Next, the hydrogel polymer (2) (gel temperature: 90°C) was placed in a gel sizing device having a screw and a perforated plate with a hole diameter of 0.8 mm, and discharged from the gel sizing device to obtain a sizing gel (2).

[0186] Next, 3.2 kg of the granulated gel (2) obtained above was placed in the warming cabinet. As a result of heating in the warming cabinet, the temperature of the granulated gel (2) became 80°C when it was fed into the dryer.

[0187] Subsequently, the granulated gel (2) was dried using a cylindrical container rotary dryer. Specifically, the rotary container provided in the cylindrical container rotary dryer was rotated at 75 rpm in an atmosphere at a temperature of 200°C, and the heated granulated gel (2) was supplied to the cylindrical container rotary dryer and dried to obtain a dried polymer (2). The moisture content of the dried polymer (2) was 8% by mass.

[0188] Subsequently, the dried polymer (2) was fed to a roll mill (pulverizer) and pulverized to adjust the particle size, and further classified using a sieve with an opening particle size of 150 μm to obtain a water absorbent resin powder (2). The mass average particle size of the water absorbent resin powder (2) was 110 μm.

[0189] A surface crosslinking agent solution composed of 0.1 part by mass of ethylene glycol diglycidyl ether, 1.0 part by mass of isopropyl alcohol and 3.0 parts by mass of ion-exchanged water was sprayed with a sprayer onto 100 parts by mass of the water absorbent resin powder (2), and the mixture was uniformly mixed using a high-speed continuous mixer.

[0190] The obtained mixture was introduced into a heat treatment machine whose atmospheric temperature was adjusted to 100°C, and subjected to heat treatment for 40 minutes, and then the powder temperature was forcibly cooled to 60°C, thereby obtaining a surface-crosslinked water absorbent resin powder (2).

[0191] With respect to 100 parts by mass of the surface-crosslinked water absorbent resin powder (2), a surface crosslinking agent solution consisting of 1.17 parts by mass of a 27.5% by mass aqueous aluminum sulfate solution (8% by mass in terms of aluminum oxide), 0.196 parts by mass of a 60% by mass aqueous sodium lactate solution, and 0.029 parts by mass of propylene glycol was further uniformly mixed.

[0192] Thereafter, the mixture was crushed (sized) until it passed through a JIS standard sieve with a mesh size of 300 μm, thereby obtaining a water-absorbent resin (2). The obtained water-absorbent resin (2) was in the form of particles, more specifically, spherical particles. The physical properties of the obtained water-absorbent resin (2) are shown in Tables 1 to 3.

[0193] [Production Example 3] 500 g of n-heptane was placed in a 2000 mL five-necked cylindrical round-bottom flask equipped with a stirrer, reflux condenser, dropping funnel, thermometer, and nitrogen gas inlet tube, and 0.92 g of sucrose fatty acid ester (S-370 / Mitsubishi Chemical Corporation, HLB=3) was added as a dispersing aid. The mixture was then heated to dissolve the sucrose fatty acid ester in n-heptane, yielding a heptane solution. The resulting heptane solution was then cooled to 55°C.

[0194] Separately, 73.6 g of acrylic acid was placed in a 500 mL Erlenmeyer flask, and while cooling the flask from the outside, 102.2 g of a 30 mass % (mass / mass %) aqueous sodium hydroxide solution was added dropwise to the Erlenmeyer flask to neutralize 75 mol % of the acrylic acid. Furthermore, 0.71 g of hydroxyethyl cellulose as a thickener, 68.6 g of ion-exchanged water, 0.11 g of potassium persulfate, and 0.0092 g of ethylene glycol diglycidyl ether were added to the Erlenmeyer flask to prepare a monomer solution (3A) for the first-stage polymerization.

[0195] The entire amount of this aqueous monomer solution (3A) for the first-stage polymerization was added to the five-neck cylindrical round-bottom flask while stirring at 450 rpm, and the aqueous monomer solution (3A) was dispersed in the heptane solution. Next, the system was thoroughly purged with nitrogen, and the temperature was raised. The bath temperature was maintained at 70°C, and the polymerization reaction was carried out for 1 hour. The polymerized slurry was then cooled to room temperature.

[0196] Into another 500 mL Erlenmeyer flask, 95.28 g of acrylic acid was placed, and while cooling, 132.2 g of a 30 mass % aqueous sodium hydroxide solution was added dropwise to the Erlenmeyer flask to neutralize 75 mol % of the acrylic acid. Furthermore, 51.2 g of ion-exchanged water, 0.14 g of potassium persulfate, and 0.0357 g of ethylene glycol diglycidyl ether were added to the Erlenmeyer flask to prepare an aqueous monomer solution (3B) for the second-stage polymerization, which was then cooled in an ice-water bath.

[0197] The entire amount of this aqueous monomer solution (3B) for second-stage polymerization was added to the polymerization slurry, and the system was again thoroughly purged with nitrogen. The bath temperature was then raised to 70°C to initiate the polymerization reaction. After the polymerization reaction was carried out for 2 hours, the mixture was filtered by suction filtration, and the residue was air-dried overnight to obtain a hydrogel polymer (3). The primary particle diameter of the hydrogel polymer (3) was 70 μm.

[0198] Next, the hydrogel polymer (3) (gel temperature: 90°C) was placed in a gel sizing device having a screw and a perforated plate with a hole diameter of 0.8 mm, and discharged from the gel sizing device to obtain a sizing gel (3).

[0199] Subsequently, the granulated gel (3) was dried using a cylindrical container rotary dryer. Specifically, the rotary container provided in the cylindrical container rotary dryer was rotated at 75 rpm in an atmosphere at a temperature of 200°C, and the heated granulated gel (3) was supplied to the cylindrical container rotary dryer and dried to obtain a dried polymer (3). The moisture content of the dried polymer (3) was 7% by mass.

[0200] Subsequently, the dried polymer (3) was fed to a roll mill (pulverizer) and pulverized to adjust the particle size, and further classified using a sieve with an opening particle size of 150 μm to obtain a water absorbent resin powder (3). The mass average particle size of the water absorbent resin powder (3) was 400 μm.

[0201] Subsequently, a surface crosslinking agent solution composed of 0.18 parts by mass of ethylene glycol diglycidyl ether, 1.5 parts by mass of propylene glycol and 5.0 parts by mass of ion exchanged water was sprayed with a sprayer onto 100 parts by mass of the water absorbent resin powder (3), and the mixture was uniformly mixed using a high-speed continuous mixer.

[0202] The obtained mixture was introduced into a heat treatment machine whose atmospheric temperature was adjusted to 100°C, and subjected to heat treatment for 40 minutes, and then the powder temperature was forcibly cooled to 60°C, thereby obtaining a surface-crosslinked water absorbent resin powder (3).

[0203] With respect to 100 parts by mass of the surface-crosslinked water absorbent resin powder (3), a surface crosslinking agent solution consisting of 1.17 parts by mass of a 27.5% by mass (mass / mass%) aqueous aluminum sulfate solution (8% by mass in terms of aluminum oxide), 0.196 parts by mass of a 60% by mass aqueous sodium lactate solution, and 0.029 parts by mass of propylene glycol was further uniformly mixed.

[0204] Thereafter, the mixture was crushed (sized) until it passed through a JIS standard sieve with an opening of 710 μm, thereby obtaining a water-absorbent resin (3). The obtained water-absorbent resin (3) was in the form of particles, more specifically, aggregate particles of spherical particles. The physical properties of the obtained water-absorbent resin (3) are shown in Tables 1 to 3.

[0205] [Production Example 4] A water-absorbent resin was obtained by aqueous solution polymerization. Specifically, 296 g of a 48.5 mass% aqueous solution of sodium hydroxide, 354 g of acrylic acid, 1.00 g of polyethylene glycol diacrylate (average number of ethylene oxide units: 9), 21.66 g of a 0.1 mass% aqueous solution of diethylenetriaminepentaacetic acid pentasodium, and 319 g of ion-exchanged water were placed in a 1 L polypropylene container and stirred to prepare a comparative aqueous monomer solution (1) consisting of these raw materials.

[0206] Stirring of the comparative monomer aqueous solution (1) was continued, and the comparative monomer aqueous solution (1) was heated. When the liquid temperature of the comparative monomer aqueous solution (1) reached 78°C, 15.8 g of a 3.8 wt% aqueous solution of sodium persulfate was added to the comparative monomer aqueous solution (1). The resulting mixture was immediately poured into a stainless steel vat-type reactor (bottom: 340 x 340 mm, height: 25 mm, inner surface: Teflon (registered trademark) coating) in an open-to-air system, and the polymerization reaction began shortly thereafter. The stainless steel vat-type reactor was preset to a surface temperature of 50°C using a hot plate (NEO HOTPLATE HI-1000 / Iuchi Seieido Co., Ltd.).

[0207] The polymerization reaction proceeded by expanding and foaming in all directions toward the top of the vat-type reactor while generating steam, and then contracted to a size slightly larger than the bottom of the reactor. The polymer obtained by this operation was designated comparative hydrogel polymer (1). The polymerization reaction (expansion and contraction) was completed in about 1 minute, but the comparative hydrogel polymer (1) was retained in the reactor for an additional 3 minutes. This series of operations was carried out in an open-air system.

[0208] The obtained comparative hydrogel polymer (1) was pulverized using a meat chopper (No. 32 type / manufactured by Hiraga Manufacturing Co., Ltd.) equipped with a die having a die hole diameter of 9.5 mm. The gel pulverization was carried out by feeding 2.4 (kg / min) of the comparative hydrogel polymer (1) and 5.0 (kg / h) of steam into the meat chopper with the screw shaft rotation speed of the meat chopper set to 130 rpm.

[0209] The comparative hydrogel polymer (1) was then dried using a hot air dryer to obtain a comparative dried polymer (1). The drying was carried out by spreading the comparative hydrogel polymer (1) pulverized with a meat chopper on a stainless steel wire mesh with a mesh size of 850 μm, and passing hot air at 180° C. through the polymer for 30 minutes.

[0210] The comparative dried polymer (1) was pulverized using a roll mill (WML type roll pulverizer / manufactured by Inokuchi Giken Co., Ltd.), and then classified using JIS standard sieves with mesh sizes of 850 μm and 150 μm to obtain an irregularly pulverized comparative water absorbent resin powder (1). The mass average particle diameter of the comparative water absorbent resin powder (1) was 340 μm.

[0211] A surface cross-linking agent solution consisting of 0.024 parts by mass of ethylene glycol diglycidyl ether, 0.308 parts by mass of ethylene carbonate, 0.515 parts by mass of propylene glycol, and 2.08 parts by mass of ion-exchanged water was uniformly mixed with 100 parts by mass of the comparative water absorbent resin powder (1). The obtained mixture was introduced into a heat treatment chamber adjusted to an atmospheric temperature of 190°C ± 2°C, and subjected to heat treatment for 30 minutes, and then the powder temperature was forcibly cooled to 60°C, thereby obtaining a surface-cross-linked comparative water absorbent resin powder (1).

[0212] 100 parts by mass of the surface-crosslinked comparative water absorbent resin powder (1) was uniformly mixed with a solution consisting of 0.022 parts by mass of 45% by mass of diethylenetriaminepentaacetic acid trisodium salt and 1 part by mass of ion-exchanged water to obtain comparative water absorbent resin particles (1).

[0213] 0.35 parts by mass of fine particle silicon dioxide (Reolosil (registered trademark) QS-20 / manufactured by Oriental Silicas Corporation) was added to and mixed with 100 parts by mass of the obtained comparative water absorbent resin particles (1) to obtain a comparative water absorbent resin (1). The physical properties of the obtained comparative water absorbent resin particles (1) are shown in Tables 1 to 3.

[0214] [Table 1]

[0215] [Table 2]

[0216] Tables 1 and 2 reveal the following: The water-absorbent resins (1) to (3) of Production Examples 1 to 3 have swollen gel compressibility of 3% or more, and correspond to the water-absorbent resins of the present invention. On the other hand, the comparative water-absorbent resin (1) of Production Example 4 has small absolute values ​​of the swollen gel thicknesses D1 and D2, but the swollen gel compressibility (%) is negative, and the thickness D2 after loading is actually larger than the thickness D1 before loading. Therefore, the comparative water-absorbent resin (1) of Production Example 4 does not correspond to the water-absorbent resin of the present invention.

[0217] [Manufacture of absorbent articles] [Example 1] As shown in FIG. 3, 1.0 g of the water-absorbent resin (1) produced in Production Example 1 was uniformly sprayed on the inner side of a square measuring 8 cm long x 8 cm wide, with 1.5 cm spaced apart from each edge of an SMMS nonwoven fabric (material: polypropylene, corresponding to the core wrap below the absorbent body) measuring 11 cm long x 11 cm wide x 0.19 mm thick. Here, the part where the water-absorbent resin (1) was sprayed corresponds to the absorbent body. The core concentration of the absorbent body was 100% by mass. Thereafter, a spunlace nonwoven fabric (basis weight: 40 g / m ) measuring 8 cm long x 8 cm wide x 0.43 mm thick, which is a liquid-permeable nonwoven fabric, was sprayed on the part where the water-absorbent resin (1) was sprayed. 2(material: nonwoven fabric mainly composed of polypropylene and polyethylene) was placed on top of the liquid-permeable nonwoven fabric. The liquid-permeable nonwoven fabric corresponds to the diffusion-assisting sheet. Next, the SMMS nonwoven fabric was placed on top of the liquid-permeable nonwoven fabric and sandwiched between them. The portions of the SMMS nonwoven fabric 1.0 cm away from the edges of each of the four sides (the portions indicated by the broken lines in Figure 3) were compressed and heat-sealed with a heat sealer to obtain a laminate. The SMMS nonwoven fabric placed on top of the liquid-permeable nonwoven fabric corresponds to the liquid-permeable top sheet. Finally, the laminate was placed with the top sheet facing up in the center of a polyethylene film measuring 12 cm in length, 17 cm in width, and 0.03 mm in thickness (a No. 7 OK bag manufactured by Okura Kogyo Co., Ltd., cut into a size of 12 cm in length and 17 cm in width), thereby producing an absorbent article. The polyethylene film corresponds to the liquid-impermeable back sheet. The produced absorbent article was designated absorbent article (1).

[0218] [Example 2] An absorbent article was produced in the same manner as in Example 1, except that the water-absorbent resin (2) produced in Production Example 2 was used instead of the water-absorbent resin (1). The produced absorbent article was designated as absorbent article (2).

[0219] [Example 3] An absorbent article was produced in the same manner as in Example 1, except that the water-absorbent resin (3) produced in Production Example 3 was used instead of the water-absorbent resin (1). The produced absorbent article was designated as absorbent article (3).

[0220] [Comparative Example 1] An absorbent article was produced in the same manner as in Example 1, except that the comparative water-absorbent resin (1) produced in Production Example 4 was used instead of the water-absorbent resin (1). The produced absorbent article was designated as the comparative absorbent article (1).

[0221] Comparative Example 2 As a diffusion-assisting sheet, a spunbond nonwoven fabric having a thickness of 0.28 mm (basis weight: 21 g / m) was used instead of the spunlace nonwoven fabric. 2An absorbent article was manufactured in the same manner as in Example 3, except that a nonwoven fabric mainly composed of polypropylene and polyethylene was used. The manufactured absorbent article was designated as comparative absorbent article (2).

[0222] Comparative Example 3 As a diffusion-assisting sheet, a spunbond nonwoven fabric having a thickness of 0.18 mm (basis weight: 13 g / m) was used instead of the spunlace nonwoven fabric. 2 An absorbent article was manufactured in the same manner as in Example 3, except that a nonwoven fabric mainly composed of polypropylene and polyethylene was used. The manufactured absorbent article was designated as comparative absorbent article (3).

[0223] [result] The absorbents produced in Examples 1 to 3 Revenue Absorbent articles (1) to (3) and comparative absorbent articles (1) to (3) manufactured in Comparative Examples 1 to 3 Revenue The thickness and diffusion length of the properties articles (1) to (3) were measured by the above-mentioned method, and the results are shown in Table 4 below.

[0224] [Table 3]

[0225] As shown in Table 3, the absorbent articles produced in Examples 1 to 3, which contain a water-absorbent resin corresponding to the water-absorbent resin of the present invention, are more suitably compressed by the compression operation and have a smaller thickness after compression than the absorbent article produced in Comparative Example 1, which contains a water-absorbent resin that does not correspond to the water-absorbent resin of the present invention. Therefore, it was found that the absorbent article according to one embodiment of the present invention can suitably suppress swelling of the water-absorbent part by containing the water-absorbent resin of the present invention.

[0226] In addition, as a diffusion auxiliary sheet, the basis weight is 25 to 100 g / m 2 The absorbent articles manufactured in Examples 1 to 3 used a liquid-permeable nonwoven fabric having a basis weight of 25 g / m as a diffusion-assisting sheet. 2The diffusion length is longer than that of the absorbent articles manufactured in Comparative Examples 2 and 3, in which a liquid-permeable nonwoven fabric of less than 25 g / m2, i.e., outside the aforementioned range, is used. Therefore, the absorbent article according to one embodiment of the present invention uses a diffusion-assisting sheet having a basis weight of 25 to 100 g / m2. 2 It was found that the use of a liquid-permeable nonwoven fabric within this range resulted in excellent diffusion of absorbed aqueous liquids.

[0227] In view of the above, an absorbent article according to one embodiment of the present invention comprises the water-absorbent resin of the present invention and a diffusion-assisting sheet having a basis weight of 25 to 100 g / m 2 It has been found that the use of a liquid-permeable nonwoven fabric within this range has the effect of providing excellent absorption performance, such as the diffusibility of the absorbed aqueous liquid, when absorbing aqueous liquids such as urine during use, and suppressing swelling of the absorbent part. [Industrial Applicability]

[0228] The absorbent article according to one embodiment of the present invention has excellent absorption performance, such as the diffusibility of the absorbed aqueous liquid, when absorbing an aqueous liquid such as urine during use, and suppresses swelling of the absorbent part. Therefore, the absorbent article according to one embodiment of the present invention can be suitably used for applications such as disposable diapers (for infants and adults), sanitary napkins, and incontinence pads. [Explanation of symbols]

[0229] 10: Apparatus for measuring compressibility of swollen gel 11: Cell 12: Piston 13: Petri dish 14: Weight 15: Bottom 16: Water-absorbing resin 17: Liquid-permeable top sheet 18: Diffusion auxiliary sheet 19: Absorbent 19a: Water-absorbing resin 20: Core Wrap 21: Liquid-impermeable back sheet

Claims

1. An absorbent article comprising, in this order, a liquid-impermeable back sheet, an absorbent body containing water-absorbent resin particles, and a liquid-permeable top sheet, A diffusion-assisting sheet is provided between the top sheet and the absorbent body, The diffusion-assisting sheet has a basis weight of 25 to 100 g / m ２ It is a liquid-permeable nonwoven fabric, The water-absorbent resin is a particulate poly(meth)acrylic acid (salt)-based water-absorbent resin, and has a swelling gel compression ratio represented by the following (Equation 1) of 3% or more and 20% or less, An absorbent article, wherein the poly(meth)acrylic acid (salt)-based water-absorbing resin contains 50 mol% or more of structural units derived from acrylic acid and sodium acrylate relative to the total structural units derived from monomers: Swollen gel compressibility [%] = (D1 - D2) / D1 × 100 (Equation 1) (Here, D1 is the thickness [mm] of a swollen gel layer formed by the water absorbent resin when a cell comprising a piston with a diameter of 59 mm and a cell with an inner diameter of 60 mm having a mesh-like bottom, with 1.0 g of the water absorbent resin scattered on the bottom, is placed in a Petri dish containing a 0.9 mass % sodium chloride aqueous solution, and the water absorbent resin is allowed to absorb the 0.9 mass % sodium chloride aqueous solution for 5 minutes; and D2 is the thickness [mm] of the swollen gel layer formed by the water absorbent resin after an operation of placing the cell on a sieve with a mesh size of 4750 μm, placing a weight on the piston so that a load of 0.7 psi is applied to the swollen gel layer, leaving the cell to stand for 10 seconds, and then removing the weight, is repeated 10 times.)

2. The absorbent article according to claim 1 , wherein the water-absorbing resin is an aggregate of spherical particles.

3. The absorbent article according to claim 1 or 2, wherein the water-absorbent resin has a mass average particle diameter (D50) of 50 to 700 μm.

4. The absorbent article according to any one of claims 1 to 3, wherein the water-absorbent resin has a D2 of less than 15 mm.

5. The absorbent article according to any one of claims 1 to 4, wherein the water-absorbent resin has a D1 of less than 15 mm.

6. The absorbent article according to any one of claims 1 to 5, wherein the absorbency under pressure (AAP) of the water-absorbent resin is 18 g / g or more.

7. The absorbent article according to any one of claims 1 to 6, wherein the absorbent is either (1) an absorbent that does not contain hydrophilic fibers, or (2) an absorbent that further contains hydrophilic fibers and in which the mass of the water-absorbent resin is 50 mass% or more of a total of 100 mass% of the water-absorbent resin and the hydrophilic fibers.

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