Water-absorbent resin particles and absorbent

Abstract

The present invention relates to a water-absorbent resin particle in which a contact angle with 0.9 mass% saline at 25±2°C is 100 degrees or more, and an absorbent containing the water-absorbent resin particle.

Description

TECHNICAL FIELD

[0001] The present application relates to a water-absorbent resin particle and an absorbent. BACKGROUND

[0002] Water-absorbent resin particles are widely used in various fields such as sanitary materials such as paper diapers, sanitary products, and simple toilets, agricultural and horticultural materials such as water-retaining agents and soil conditioners, industrial materials such as water-blocking agents and dew-preventing agents, and the like. Absorbent articles for absorbing a liquid mainly composed of water (for example, urine) use an absorbent containing water-absorbent resin particles (for example, refer to Patent Documents 1 and 2).

[0003] Prior Art Documents

[0004] Patent Documents

[0005] Patent Document 1: Japanese Patent Application Laid-Open No. 2006-199805

[0006] Patent Document 2: Japanese Patent Application Laid-Open No. 2016-28117 SUMMARY

[0007] Technical Problem to be Solved by the Invention

[0008] Water-absorbent resin particles in an absorbent are required not only to have a high water absorption amount but also to have excellent liquid diffusivity. The present inventors and others have found that an absorbent containing water-absorbent resin particles having high liquid permeability has excellent liquid diffusivity, but has a tendency for the backflow amount of absorbed liquid to increase.

[0009] An object of the present application is to provide a water-absorbent resin particle that, when used in an absorbent, can have both excellent liquid diffusivity and a sufficient backflow amount in actual use.

[0010] Means for Solving the Technical Problem

[0011] One aspect of the present application relates to a water-absorbent resin particle in which the contact angle with 0.9 mass% saline solution at 25 ± 2°C is 100 degrees or more.

[0012] Another aspect of the present application relates to an absorbent having the above water-absorbent resin particle.

[0013] Effects of the Invention

[0014] According to the present application, it is possible to provide a water-absorbent resin particle that, when used in an absorbent, can have both excellent liquid diffusivity and a sufficient backflow amount in actual use. BRIEF DESCRIPTION OF DRAWINGS

[0015] Figure 1 is a cross-sectional view showing an example of an absorbent article.

[0016] Figure 2 is a schematic diagram showing a measuring method of a diffusion distance of a test liquid. DETAILED DESCRIPTION

[0017] Hereinafter, several embodiments of the present application will be described in detail. However, the present application is not limited to the following embodiments.

[0018] In the present specification, "acrylic acid" and "methacrylic acid" are collectively expressed as "(meth)acrylic acid". "Acrylate" and "methacrylate" are also collectively expressed as "(meth)acrylate". "(Poly)" means both cases with and without the prefix "poly". In the numerical range recited in stages in the present specification, the upper limit value or the lower limit value of the numerical range of a certain stage can be arbitrarily combined with the upper limit value or the lower limit value of the numerical range of another stage. In the numerical range recited in the present specification, the upper limit value or the lower limit value of the numerical range can be replaced with the value shown in the examples. The materials exemplified in the present specification can be used alone or in combination of two or more. Regarding the content of each component in the composition, when a plurality of substances corresponding to each component is present in the composition, the total amount of the plurality of substances present in the composition is meant, unless otherwise specified. "Physiological saline" means a 0.9 mass% sodium chloride aqueous solution. "Room temperature" means 25 ± 2°C. The term "layer" includes not only a shape structure formed on the entire surface when viewed as a plan view, but also a shape structure formed on a part.

[0019] [Water-absorbent resin particles]

[0020] The water-absorbent resin particles according to the present embodiment have a contact angle of 100 degrees or more with respect to 0.9 mass% saline water (physiological saline at room temperature) at 25 ± 2°C. By using water-absorbent resin particles having a high contact angle for an absorbent, water is repelled at an initial stage of contact of the water-absorbent resin particles with a liquid, and it is difficult to start water absorption, but the liquid easily spreads. Then, since water absorption starts in a state where the liquid is sufficiently spread, it is presumed that an increase in the amount of back penetration can be suppressed.

[0021] From the viewpoint of combining excellent liquid spreadability and an actual use sufficient amount of back penetration, the water-absorbent resin particles according to the present embodiment have a contact angle of 100 degrees or more. Furthermore, the water-absorbent resin particles can have a contact angle of 102 degrees or more, 104 degrees or more, or 108 degrees or more, and can have a contact angle of 130 degrees or less, 128 degrees or less, 125 degrees or less, or 120 degrees or less. Furthermore, from the viewpoint of combining excellent liquid spreadability and an excellent amount of back penetration, the water-absorbent resin particles can have a contact angle of 118 degrees or less, 115 degrees or less, or 114 degrees or less. In this case, the lower limit value of the contact angle can be the value exemplified above.

[0022] The contact angle was a value determined according to JIS R 3257 (1999) "Test method for wettability of glass surface of a substrate". The contact angle in the present embodiment can be determined using a test performed in the following order of i) and ii).

[0023] i) At 25 ± 2°C, a droplet equivalent to 0.01 g of physiological saline was added to the surface of the water-absorbent resin particles, and the water-absorbent resin particles were brought into contact with the droplet.

[0024] ii) The contact angle of the droplet was determined at a time 0.1 seconds after the droplet came into contact with the surface of the water-absorbent resin particles.

[0025] With respect to the water-absorbent resin particles involved in the present embodiment, the water absorption speed based on the Vortex method is 55 seconds or more, and the effect of the present application is more likely to be produced. The water absorption speed of the water-absorbent resin particles can be 56 seconds or more, 58 seconds or more, 60 seconds or more, or 61 seconds or more, and can also be 180 seconds or less, 150 seconds or less, 120 seconds or less, 100 seconds or less, 95 seconds or less, or 92 seconds or less. The water absorption speed based on the Vortex method was determined in accordance with (Japanese Industrial Standard JIS K 7224 (1996)). Specifically, 2.0 ± 0.002 g of water-absorbent resin particles were added to 50 ± 0.1 g of physiological saline stirred at 600 rpm (rpm = min -1 ) in a 100 mL beaker having a flat bottom surface, and the water absorption speed was obtained in seconds from the time of addition of the water-absorbent resin particles until the vortex disappeared and the liquid surface became flat.

[0026] The water retention amount of the water-absorbent resin particles with respect to physiological saline can be, for example, 32 g / g or more, 34 g / g or more, or 35 g / g or more, and can also be 60 g / g or less, 55 g / g or less, 50 g / g or less, 45 g / g or less, or 43 g / g or less. Furthermore, from the viewpoint of excellent liquid diffusivity and excellent water retention amount, the water retention amount of the water-absorbent resin particles with respect to physiological saline can be 37 g / g or more, 39 g / g or more, or 40 g / g or more. In this case, the upper limit of the water retention amount can be the values listed above. In addition, the water retention amount with respect to physiological saline was determined by the method described in the Examples below.

[0027] The water-absorbent resin particles involved in the present embodiment are not particularly limited as long as the contact angle with respect to physiological saline at room temperature is 100 degrees or more. The contact angle can be adjusted, for example, by (1) adjusting the amount and / or HLB of the surfactant that can be used in the polymerization step of the inverse suspension polymerization, (2) forming a coating layer that covers at least a part of the surface of the polymer particles having water absorbency, and (3) using both of the above (1) and (2). Hereinafter, the method of (2) will be described.

[0028] The polymer particles are not particularly limited as long as they are composed of a resin having water absorbency. The polymer particles may, for example, contain a crosslinked polymer formed by polymerization of a monomer containing an ethylenically unsaturated monomer. The crosslinked polymer can have a monomer unit derived from the ethylenically unsaturated monomer. The polymer particles may, for example, be produced by a method including a step of polymerizing a monomer containing an ethylenically unsaturated monomer. As the polymerization method, there can be mentioned a reverse phase suspension polymerization method, an aqueous solution polymerization method, a bulk polymerization method, a precipitation polymerization method, and the like.

[0029] The ethylenically unsaturated monomer can be a water-soluble ethylenically unsaturated monomer (for example, an ethylenically unsaturated monomer having a solubility of 1 g or more in 100 g of water at 98°C). As the ethylenically unsaturated monomer, there can be mentioned, for example, (meth)acrylic acid and a salt thereof, 2-(meth)acrylamido-2-methylpropane sulfonic acid and a salt thereof, (meth)acrylamide, N,N-dimethyl(meth)acrylamide, 2-(meth)acrylhydroxyethyl ester, N-hydroxymethyl(meth)acrylamide, polyethylene glycol mono(meth)acrylate, N,N-diethylaminoethyl(meth)acrylate, N,N-diethylaminopropyl(meth)acrylate, and diethylaminopropyl(meth)acrylamide. When the ethylenically unsaturated monomer has an amino group, the amino group can be quaternized. The ethylenically unsaturated monomer can be used alone or in combination of two or more.

[0030] The ethylenically unsaturated monomer can contain at least one compound selected from the group consisting of (meth)acrylic acid and a salt thereof, acrylamide, methacrylamide, and N,N-dimethylacrylamide, from the viewpoint of industrial availability. The ethylenically unsaturated monomer can also contain at least one compound selected from the group consisting of (meth)acrylic acid and a salt thereof, and acrylamide.

[0031] When the ethylenically unsaturated monomer has an acidic group, it can be used in the polymerization reaction after neutralization of the acidic group. The degree of neutralization in the ethylenically unsaturated monomer can be 10 to 100 mol%, 50 to 90 mol%, or 60 to 80 mol% of the acidic group in the ethylenically unsaturated monomer.

[0032] As the monomer used to obtain the polymer particles, a monomer other than the above-described ethylenically unsaturated monomer can be used. Such a monomer may, for example, be mixed in an aqueous solution containing the above-described ethylenically unsaturated monomer and used. The amount of the ethylenically unsaturated monomer used can be 70 to 100 mol% relative to the total amount of the monomers (total amount of the monomers used to obtain the water-absorbent resin particles. For example, total amount of the monomers that impart the structure unit of the crosslinked polymer. The same applies hereinafter).

[0033] While cross-linking based on self-cross-linking can occur at the time of polymerization, the cross-linking of the polymer particles can also be promoted by using an internal cross-linking agent. If an internal cross-linking agent is used, the water absorption properties (water retention capacity, etc.) of the water-absorbent resin particles can be easily controlled. The internal cross-linking agent is generally added to the reaction liquid at the time of polymerization. As the internal cross-linking agent, for example, polyglycidyl compounds such as (poly)ethylene glycol diglycidyl ether, (poly)propylene glycol diglycidyl ether, (poly)glycerol diglycidyl ether, (poly)glycerol triglycidyl ether, (poly)propylene glycol polyglycidyl ether, and polyglycerol polyglycidyl ether can be given.

[0034] The polymer particles can be particles that have undergone cross-linking in the vicinity of the surface (surface cross-linking). The polymer particles can be composed only of cross-linked polymer particles, and for example, can also include a gel stabilizer, a metal chelating agent, a flowability improver (lubricant), and the like. These components can be disposed in the interior of the cross-linked polymer particles, on the surface of the cross-linked polymer particles, or both.

[0035] The shape of the polymer particles is not particularly limited, and for example, can be substantially spherical, scattered, particulate, or a shape in which primary particles having these shapes are agglomerated.

[0036] The median particle diameter of the polymer particles can be 130 to 800 μm, 200 to 850 μm, 250 to 700 μm, 300 to 600 μm, or 300 to 450 μm. The polymer particles can have the desired particle size distribution at the time of being obtained by the manufacturing method described later, but the particle size distribution can also be adjusted by performing an operation such as particle size adjustment using classification based on a sieve.

[0037] The coating layer preferably includes a water-insoluble component. In the present specification, the water-insoluble component can include not only a substance that is completely insoluble in water, but also a substance that exhibits slight solubility in water (a water-soluble substance). The solubility of the water-insoluble component with respect to 100 g of water is, for example, less than 10 g, preferably less than 5 g, more preferably less than 3 g, and further preferably less than 1 g at 25°C.

[0038] From the viewpoint of easily adjusting the contact angle of the water-absorbent resin particles, as the water-insoluble component, at least one selected from the group consisting of polyurethane, polyolefin, polyester, polyamide, polystyrene, polycarbonate, polyacrylate, polyaldehyde, and acid-modified products of these is preferably used, at least one selected from the group consisting of polyolefin, polyurethane, polyester, and acid-modified products of these is more preferably used, at least one selected from the group consisting of polyolefin, polyurethane, and acid-modified products of these is further preferably used, and acid-modified polyolefin and / or polyurethane is particularly preferably used.

[0039] In the case where the water-insoluble component is modified by an acid, the water-insoluble component can be modified by at least one acid anhydride selected from the group consisting of maleic anhydride, succinic anhydride, and phthalic anhydride. The modification target based on the acid anhydride is preferably a polyolefin, more preferably at least one selected from the group consisting of polyethylene, polypropylene, and ethylene / propylene copolymer, further preferably ethylene / propylene copolymer. Also, the acid anhydride used for the modification is preferably maleic anhydride.

[0040] The polyurethane is a reaction product of a polyol and a polyisocyanate. As the polyol, for example, polyether polyol, polyester polyol, polybutadiene polyol, and hydrogenated polybutadiene polyol can be given. As the polyisocyanate, for example, aromatic isocyanate such as diphenylmethane diisocyanate, dimethyldiphenylmethane diisocyanate, toluene diisocyanate, xylylene diisocyanate, and p-phenylene diisocyanate; alicyclic isocyanate such as dicyclohexylmethane diisocyanate and isophorone diisocyanate; and aliphatic isocyanate such as hexamethylene diisocyanate can be given.

[0041] In the case where the polymer particles form a coating layer, the polymer particles and the coating material can be mixed, and the coating layer can be formed on at least a part of the surface of the polymer particles. The coating material can be, for example, a component capable of forming the above-described coating layer or a forming material of the component. For example, in the case where the coating layer contains polyurethane, the coating material can contain the polyurethane itself, or can contain a polyol and a polyisocyanate as forming materials of the polyurethane.

[0042] The method of forming the coating layer is not particularly limited. For example, after the polymer particles are put in a dispersed state, the coating material can be brought into contact with the polymer particles in the dispersed state to form the coating layer. Specifically, in the case where the coating material is dissolved in a dispersion medium in which the polymer particles are dispersed, the polymer particles and the coating material can be added to the dispersion medium, and the coating layer can be formed on the surface of the polymer particles. Also, in the case where a polyol and a polyisocyanate are used as the coating material, the polymer particles can be brought into contact with the polyol by mixing an aqueous solution of the polyol in a dispersion liquid of the polymer particles, and then a liquid containing the polyisocyanate can be mixed to polymerize the polyol and the polyisocyanate, so that the coating layer containing polyurethane can be formed on the surface of the polymer particles.

[0043] The contact angle of the water-absorbent resin particles can be adjusted by appropriately changing the proportion of the coating material used to form the coating layer. The proportion of the coating material varies depending on the coating material, but can be, for example, 0.01% by mass or more, 0.1% by mass or more, or 0.4% by mass or more, and can also be 20% by mass or less, 18% by mass or less, or 16.7% by mass or less. In particular, in the case where the coating layer contains polyurethane, the proportion of the coating material can be 1.5% by mass or less or 1.3% by mass or less. Also, from the viewpoint of achieving both excellent liquid spreading properties and excellent rewet amount, in the case where the coating layer contains polyurethane, the proportion of the coating material can be 1.0% by mass or less or 0.9% by mass or less. In these cases, the lower limit of the proportion of the coating material can be the value listed above. In addition, the proportion of the coating material is calculated by the method described in the Examples below.

[0044] The dispersion medium can contain a hydrocarbon-based solvent. As the hydrocarbon-based solvent, for example, there can be mentioned: straight-chain aliphatic hydrocarbons such as n-hexane, n-heptane, 2-methylhexane, 3-methylhexane, 2,3-dimethylpentane, 3-ethylpentane, and n-octane; alicyclic hydrocarbons such as cyclohexane, methylcyclohexane, cyclopentane, methylcyclopentane, trans-1,2-dimethylcyclopentane, cis-1,3-dimethylcyclopentane, and trans-1,3-dimethylcyclopentane; and aromatic hydrocarbons such as benzene, toluene, and xylene.

[0045] [absorbent]

[0046] The absorbent according to the present embodiment contains the water-absorbent resin particles according to the present embodiment. The absorbent can contain a fibrous material, for example, be a mixture containing the water-absorbent resin particles and the fibrous material. As the structure of the absorbent, for example, there can be mentioned a structure in which the water-absorbent resin particles and the fibrous material are uniformly mixed, a structure in which the water-absorbent resin particles are interposed between the fibrous material formed in a sheet shape or a layer shape, and other structures.

[0047] As the fibrous material, for example, there can be mentioned: wood pulp that has been finely pulverized; cotton; cotton flock; rayon; cellulose-based fibers such as cellulose acetate; synthetic fibers such as polyamide, polyester, and polyolefin; and mixtures of these fibers. The fibrous material can be used alone or in combination of two or more. As the fibrous material, a hydrophilic fiber can be used.

[0048] In order to improve the form retention of the absorbent before and during use, the fibers can be adhered to each other by adding an adhesiveness adhesive to the fibrous material. As the adhesiveness adhesive, there can be mentioned, for example, a hot-melt synthetic fiber, a hot-melt adhesive, and an adhesiveness emulsion. The adhesiveness adhesive can be used alone or in combination of two or more.

[0049] As the hot-melt synthetic fiber, for example, there are mentioned a full-melt type adhesive such as polyethylene, polypropylene, ethylene-propylene copolymer, and the like; a non-full-melt type adhesive such as a side-by-side or core-sheath structure of polypropylene and polyethylene; and the like. In the above non-full-melt type adhesive, only the polyethylene portion can be hot-melted.

[0050] As the hot-melt adhesive, for example, there are mentioned a mixture of a base polymer such as ethylene-vinyl acetate copolymer, styrene-isoprene-styrene block copolymer, styrene-butadiene-styrene block copolymer, styrene-ethylene-butylene-styrene block copolymer, styrene-ethylene-propylene-styrene block copolymer, amorphous polypropylene, and the like, and a tackifier, a plasticizer, an antioxidant, and the like.

[0051] As the adhesive emulsion, for example, there are mentioned a polymer of a monomer selected from at least one of the group consisting of methyl methacrylate, styrene, acrylonitrile, 2-ethylhexyl acrylate, butyl acrylate, butadiene, ethylene, and vinyl acetate.

[0052] The absorbent of the present embodiment can contain inorganic powder (for example, amorphous silica), deodorant, antibacterial agent, pigment, dye, perfume, pressure-sensitive adhesive, and the like. When the water-absorbent resin particles contain inorganic particles, the absorbent can contain inorganic powder different from the inorganic particles in the water-absorbent resin particles.

[0053] The absorbent of the present embodiment can have, for example, a sheet shape. The thickness of the absorbent (for example, the thickness of the sheet-shaped absorbent) can be 0.1 to 20 mm or 0.3 to 15 mm.

[0054] [absorbent article]

[0055] The absorbent article of the present embodiment is provided with the absorbent of the present embodiment. As other components of the absorbent article, there are mentioned a core wrap that maintains the shape of the absorbent and prevents the components of the absorbent from falling off or flowing, a liquid-permeable sheet material arranged at the outermost portion on the side where the liquid of the liquid-absorbing object is immersed, and a liquid-impermeable sheet material arranged at the outermost portion on the side opposite to the side where the liquid of the liquid-absorbing object is immersed, and the like. As the absorbent article, there are mentioned a diaper (for example, a paper diaper), a toilet training pant, an incontinence pad, a sanitary material (sanitary napkin, sanitary tampon, and the like), a sweat-absorbing pad, a pet pad, a simple toilet component, an animal excrement treatment material, and the like.

[0056] Figure 1 is a cross-sectional view showing an example of an absorbent article. Figure 1The absorbent article 100 shown includes an absorbent body 10, core sheets 20a and 20b, a liquid-permeable sheet 30, and a liquid-impermeable sheet 40. The liquid-impermeable sheet 40, core sheet 20b, absorbent body 10, core sheet 20a, and liquid-permeable sheet 30 are sequentially stacked in the absorbent article 100. Figure 1 The diagram shows a section where there is a gap between components, but components can also be placed tightly together without this gap.

[0057] The absorbent 10 has water-absorbing resin particles 10a as described in this embodiment and a fiber layer 10b containing fibrous material. The water-absorbing resin particles 10a are dispersed within the fiber layer 10b.

[0058] The core-packing sheet 20a is disposed on one side of the absorber 10 in a state of contact with the absorber 10. Figure 1 The core sheet 20b is disposed on the other side of the absorber 10 in contact with the absorber 10. Figure 1 (The absorber 10 is located on the lower side of the absorber 10). The absorber 10 is disposed between the core sheet 20a and the core sheet 20b. Examples of core sheets 20a and 20b include paper towels, nonwoven fabrics, woven fabrics, synthetic resin films with liquid permeability pores, and mesh sheets with mesh openings. Core sheets 20a and 20b, for example, have a main surface area of ​​the same size as the absorber 10.

[0059] The liquid-permeable sheet 30 is disposed on the outermost side of the absorbent material where the liquid is immersed. The liquid-permeable sheet 30 is disposed on the core-packing sheet 20a in contact with it. Examples of liquid-permeable sheets 30 include nonwoven fabrics and porous sheets made of synthetic resins such as polyethylene, polypropylene, polyester, and polyamide. The liquid-impermeable sheet 40 is disposed on the outermost side of the absorbent article 100 opposite to the liquid-permeable sheet 30. The liquid-impermeable sheet 40 is disposed on the underside of the core-packing sheet 20b in contact with it. Examples of liquid-impermeable sheets 40 include sheets made of synthetic resins such as polyethylene, polypropylene, and polyvinyl chloride, and sheets made of composite materials of these synthetic resins and nonwoven fabrics. The liquid-permeable sheet 30 and the liquid-impermeable sheet 40, for example, have a main surface that is wider than the main surface of the absorber 10, and the outer edges of the liquid-permeable sheet 30 and the liquid-impermeable sheet 40 extend to the periphery of the absorber 10 and the core packing sheets 20a and 20b.

[0060] The size relationship between the absorbent body 10, core sheets 20a and 20b, liquid-permeable sheet 30, and liquid-impermeable sheet 40 is not particularly limited and can be adjusted appropriately according to the intended use of the absorbent article. Furthermore, the method by which the core sheets 20a and 20b maintain the shape of the absorbent body 10 is not particularly limited, such as... Figure 1 As shown, the absorber can be encapsulated using multiple core sheets or a single core sheet.

[0061] According to the present embodiment, a water-absorbing resin particle, an absorbent, or an absorbent article, and a liquid absorption method using the same can be provided. The liquid absorption method according to the present embodiment includes a step of bringing a liquid to be absorbed into contact with the water-absorbing resin particle, the absorbent, or the absorbent article according to the present embodiment.

[0062] Examples

[0063] The present application will be described more specifically below with reference to examples. However, the present application is not limited to these examples.

[0064] < Polymer particle >

[0065] [Manufacturing Example 1]

[0066] (Polymerization of the first stage)

[0067] A round-bottom cylindrical detachable flask having an inner diameter of 11 cm and a content volume of 2 L was prepared, which was equipped with a reflux condenser, a dropping funnel, a nitrogen gas introduction tube, and a stirring machine (stirring blade having a 2-stage 4-blade inclined paddle blade with a wing diameter of 5 cm). In the flask, n-heptane 293 g and maleic anhydride-modified ethylene-propylene copolymer (Hi-WAX 1105A by Mitsui Chemicals, Inc.) 0.736 g as a dispersant were put in and mixed. While the mixture in the flask was stirred, the temperature was raised to 80°C, and after the dispersant was dissolved in the n-heptane, the mixture was cooled to 50°C.

[0068] In a beaker having a content volume of 300 mL, an aqueous solution of 80.5 mass% of acrylic acid 92.0 g (acrylic acid: 1.03 mol) was put as a water-soluble ethylenically unsaturated monomer, and while being externally cooled, an aqueous solution of 20.9 mass% of sodium hydroxide 147.7 g was added dropwise into the beaker to neutralize 75 mol% of the acrylic acid. Next, hydroxyethyl cellulose 0.092 g (HECAW-15F by Sumitomo Seika Chemicals Company, Limited) was added as a thickening agent, potassium persulfate 0.0736 g (0.272 mmol) was added as a radical polymerization initiator, and ethylene glycol diglycidyl ether 0.010 g (0.057 mmol) was added as an internal crosslinking agent, and dissolved to prepare an aqueous solution of the first stage.

[0069] After the aqueous solution of the first stage was added to the above-mentioned detachable flask, stirring was performed for 10 minutes. Next, a surfactant solution in which sucrose stearate (Ryoto Sugar Ester S-370, HLB: 3, of Mitsubishi-Chemical Foods Corporation) 0.736 g was dissolved as a surfactant in n-heptane 6.62 g was added to the flask to obtain a reaction liquid. While the reaction liquid was stirred at 550 rpm with a stirrer, the inside of the system was sufficiently replaced with nitrogen. After that, the flask was immersed in a water bath at 70°C and the reaction liquid was warmed to perform a polymerization reaction for 60 minutes, whereby a polymerization slurry of the first stage was obtained.

[0070] (Polymerization of the second stage)

[0071] In a beaker with a content volume of 500 mL, 80.5 mass% of an aqueous solution of acrylic acid 128.8 g (acrylic acid: 1.43 moles) was placed, and while being externally cooled, 27 mass% of an aqueous solution of sodium hydroxide 159.0 g was added dropwise to neutralize 75 mole% of the acrylic acid. By adding potassium persulfate 0.103 g (0.381 millimoles) as a radical polymerization initiator, and ethylene glycol diglycidyl ether 0.0116 g (0.067 millimoles) as an internal crosslinking agent to the beaker in which the neutralized aqueous solution of acrylic acid was placed and dissolving these, an aqueous solution of the second stage was prepared.

[0072] While the rotation speed of the stirrer was set to 1000 rpm to stir, the polymerization slurry of the first stage in the above-mentioned flask was cooled to 25°C, and the total amount of the aqueous solution of the second stage was added. After the inside of the flask was replaced with nitrogen for 30 minutes, the flask was again immersed in a water bath at 70°C and the reaction liquid was warmed to perform a polymerization reaction of the second stage for 60 minutes, whereby a water-containing gel-like polymer was obtained. After that, the above-mentioned flask was immersed in an oil bath set to 125°C, and 257.7 g of water was drawn out to the outside of the system by azeotropic distillation of n-heptane and water. Next, the flask was lifted to a state in which the lower part thereof was slightly in contact with the oil bath, and the inside temperature was adjusted to 83°C. After that, in the flask, 2 mass% of an aqueous solution of ethylene glycol diglycidyl ether 4.42 g (0.507 millimoles) was added as a surface crosslinking agent, and the inside temperature was maintained at 83°C for 2 hours.

[0073] After that, the flask was again immersed in the oil bath, and n-heptane was removed by drying at 125°C, whereby a dried product (polymer) was obtained. The dried product was passed through a sieve with a pore size of 850 μm to obtain 220.8 g of polymer particles A. The median particle diameter of the polymer particles A was 357 μm.

[0074] [Manufacture Example 2]

[0075] In addition to 254.4 g of water drawn out to the outside of the system by azeotropic distillation of n-heptane and water from the aqueous gel polymer after polymerization in the second stage, 220.8 g of polymer particles B were obtained in the same manner as in Production Example 1. The median particle diameter of the polymer particles B was 364 μm.

[0076] [Production Example 3]

[0077] In a beaker having an inner volume of 2 L, 400.0 g of an aqueous solution of acrylic acid (acrylic acid: 4.46 moles) was placed as a water-soluble ethylenically unsaturated monomer, and while externally cooling, 480.6 g of a 28.2 mass% aqueous solution of sodium hydroxide was added dropwise to the beaker, whereby 75 moles% of the acrylic acid was neutralized. Subsequently, 0.66 g (2.23 millimoles) of trimethylolpropane triacrylate and 133.1 g of ion exchange water were added as an internal crosslinking agent and dissolved, and a reaction liquid was prepared.

[0078] The reaction liquid, which had been replaced with nitrogen for 30 minutes, was supplied to a reactor formed by installing a cover to a double-arm type kneader made of stainless steel with a volume of 5 L having 2 pieces of sigma type blades, and while maintaining 30°C, the inside of the reactor was replaced with nitrogen. Subsequently, after adding 1.47 g (pervosulfate: 1.93 millimoles) of 30 mass% ammonium persulfate and 1.10 g (L-ascorbic acid: 0.125 millimoles) of 2 mass% L-ascorbic acid as a polymerization initiator while stirring the reaction liquid at a rotation speed of 30 rpm, polymerization was started after about 1 minute. The polymerization reaction was carried out at 30°C for 60 minutes, and an aqueous gel-like polymer was obtained. The aqueous gel-like polymer was refined to a diameter of about 5 mm.

[0079] The refined aqueous gel-like polymer was uniformly spread on a fluorine resin-coated tank, and hot air drying was carried out at 150°C for 90 minutes to obtain a dried product. The dried product was pulverized using a high-speed pulverizer (ZM-200; manufactured by Retsch). The pulverized powder was passed through a sieve having a mesh size of 850 μm, and an amorphous and irregularly fragmented polymer particle precursor having an average particle diameter of 425 μm was obtained.

[0080] As a surface crosslinking agent, a surface crosslinking agent solution containing 10 parts by mass of propylene glycol and 0.5 parts by mass of ethylene glycol diglycidyl ether, 30 parts by mass of water, and 10 parts by mass of isopropyl alcohol was prepared.

[0081] Into a round-bottom cylindrical detachable flask of 11 cm in inner diameter and 2 L in content volume, which was provided with a stirrer having a Teflon-made anchor blade, was put 40 g of the polymer resin precursor, and while stirring at a rotation speed of 500 rpm, 4.04 g of the surface crosslinking agent solution was added dropwise and mixed for 1 minute. The mixture was dried by hot air at 180°C for 40 minutes to obtain polymer particles C. The median particle diameter of the polymer particles C was 430 μm.

[0082] (Median particle diameter)

[0083] The particle size distribution of the water-absorbing resin particles 5 g was measured using a continuous full-automatic sonic vibration type sieve measuring device (Robot shifter RPS-205, manufactured by SEISHIN ENTERPRISE Co., Ltd.), sieves of JIS standard pore diameters of 850 μm, 710 μm, 600 μm, 500 μm, 400 μm, 300 μm, 250 μm, and 150 μm, and a receiving tray. With respect to the particle size distribution, the relationship between the pore diameter of the sieve and the cumulative value of the mass percentage of the particles remaining on the sieve was plotted on a logarithmic probability paper by performing the accumulation on the sieve in the order of the particle diameter from large to small. The plotted points on the probability paper were connected by a straight line, and the particle diameter corresponding to the cumulative mass percentage of 50 mass% was obtained as the median particle diameter.

[0084] <Water-absorbing resin particles>

[0085] [Example 1]

[0086] A round-bottom cylindrical detachable flask of 11 cm in inner diameter and 2 L in content volume, which was provided with a reflux condenser, a dropping funnel, a nitrogen gas introduction tube, and a stirrer (stirring blade having a 2-stage 4-blade inclined paddle blade with a wing diameter of 5 cm), was prepared. Into the flask were put n-heptane 480 g and polymer particles A 40 g, and stirring was performed at 1000 rpm to obtain a n-heptane dispersion liquid of the polymer particles A. After adding a mixture (1) of distilled water 1.52 g and polyether polyol (EXCENOL 750ED, manufactured by AGC Inc.) 0.08 g to the dispersion liquid and stirring for 30 minutes, a mixture (2) of acetone 0.86 g and toluene diisocyanate 0.095 g was further added and stirred for 120 minutes. Subsequently, the flask was immersed in an oil bath set at 125°C, and water was drawn out to the outside of the system while refluxing n-heptane by azeotropic distillation of n-heptane and water.

[0087] Thereafter, the n-heptane was removed by drying at 125°C to thereby obtain a dried product. The dried product was passed through a sieve of pore diameter 850 μm to obtain water-absorbing resin particles 36 g having a coating layer containing polyurethane.

[0088] [Example 2]

[0089] The water-absorbent resin particles 36 g were obtained in the same manner as in Example 1 except that the mixture (1) was changed to a mixture of distilled water 3.04 g and polyether polyol (EXCENOL 750ED) 0.16 g, and the mixture (2) was changed to a mixture of acetone 1.72 g and toluene diisocyanate 0.19 g.

[0090] [Example 3]

[0091] The water-absorbent resin particles 36 g were obtained in the same manner as in Example 1 except that the mixture (1) was changed to a mixture of distilled water 4.56 g and polyether polyol (EXCENOL 750ED) 0.24 g, and the mixture (2) was changed to a mixture of acetone 2.57 g and toluene diisocyanate 0.29 g.

[0092] [Example 4]

[0093] The same flask as in Example 1 was prepared. In the flask, n-heptane 250 g, polymer particles A 100 g, and maleic anhydride-modified ethylene / propylene copolymer (Mitsui Chemicals, Inc., High Wax 1105A) 20 g were put in, and while stirring at 1000 rpm, the temperature was raised to 85°C and stirring was performed for 10 minutes.

[0094] After that, n-heptane was removed by drying at 125°C, and thus a dried product was obtained. The dried product was passed through a sieve having a pore size of 850 μm, and water-absorbent resin particles having a coating layer containing the maleic anhydride-modified ethylene / propylene copolymer were obtained 112 g.

[0095] [Comparative Example 1]

[0096] Polymer particles A were used as the water-absorbent resin particles.

[0097] [Comparative Example 2]

[0098] Polymer particles B were used as the water-absorbent resin particles.

[0099] [Comparative Example 3]

[0100] Water-absorbent resin particles 30 g were collected from a child diaper "Goo.N Comfortable Breathable Paper Diaper, Boy, L size" of Daio Paper Corporation. The median particle diameter of the water-absorbent resin particles was 388 μm.

[0101] [Comparative Example 4]

[0102] Polymer particles C were used as the water-absorbent resin particles.

[0103] The following evaluations were performed on the water-absorbent resin particles. The results are shown in Tables 1 and 2.

[0104] (Ratio of coating material)

[0105] The ratio of coating material in the production of the water-absorbent resin particles was calculated by the following formula.

[0106] Ratio of coating material (% by mass) = {mass of coating material supplied to form the coating layer / (mass of polymer particles supplied to form the coating layer + mass of coating material supplied to form the coating layer)} x 100

[0107] (Water retention)

[0108] The water retention (room temperature) of the water-absorbent resin particles with physiological saline was measured by the following procedure. First, a cotton bag (broadcloth No. 60, 100 mm wide x 200 mm long) into which 2.0 g of the water-absorbent resin particles had been weighed was set in a beaker with a content volume of 500 mL. Physiological saline 500 g was injected into the cotton bag containing the water-absorbent resin particles in such a manner that no lumps were formed, and then the upper portion of the cotton bag was bound with a rubber band, and left to stand for 30 minutes, thereby allowing the water-absorbent resin particles to swell. The cotton bag after 30 minutes was dehydrated for 1 minute using a dehydrator (KOKUSAN Co., Ltd., product No. H-122) set so that the centrifugal force became 167 G, and the mass Wa [g] of the cotton bag containing the swollen gel after dehydration was measured. The same operation was performed without adding the water-absorbent resin particles, and the empty mass Wb [g] of the cotton bag when wet was measured, and the water retention of the water-absorbent resin particles with physiological saline was calculated from the following formula.

[0109] Water retention [g / g] = (Wa - Wb) / 2.0

[0110] (Water absorption speed based on Vortex method)

[0111] In a 100 mL beaker into which a rotor (8 mm x 30 mm, without a ring) was put, physiological saline 50 g was added, and kept at 25°C in a thermostat. Next, 2.0 g of the water-absorbent resin particles for evaluation was put into the vortex of the physiological saline stirred at 600 rpm, and the measurement based on a stopwatch was started. The time (seconds) until the vortex disappeared and the liquid surface became horizontal was taken as the endpoint, and the time (seconds) until then was taken as the water absorption speed.

[0112] (Passability)

[0113] The measurement was performed at room temperature. Into a cylindrical container (1) made of Plexiglas having an inner diameter of 26 mm, an outer diameter of 40 mm, and a height of 80 mm, to which a nylon screen sheet (250 mesh) was attached, 0.20 g of water absorbent resin particles classified to have a size of 250 to 500 μm was uniformly put, and a cylindrical container (2) made of Plexiglas having an inner diameter of 19 mm, an outer diameter of 25 mm, and a height of 120 mm, to which the same nylon screen sheet was attached, was inserted from the upper portion as a measurement portion. The screen side of the measurement portion was immersed in a culture dish having an inner diameter of about 90 mm in which 30 g of physiological saline was put, and was allowed to swell for 30 minutes, and a swollen gel was formed.

[0114] Next, the entire measurement portion was moved to an empty culture dish, a 200 g weight was slowly placed on the upper portion of the cylindrical container (2), and the swollen gel was loaded for 3 minutes.

[0115] On the empty culture dish (We) on which the mass had been measured, a metal mesh having a size of 100 mm x 100 mm and having a lattice-shaped opening portion of 2 mm square was placed, and the measurement portion including the swollen gel was also placed. Next, while 20 g of physiological saline was added from the upper portion of the cylindrical container (2), a stopwatch was started. The mass (Wf) of the culture dish including the physiological saline that flowed out through the swollen gel was measured for 30 seconds (0.5 minutes) from the time of the addition, and the permeation rate (g / minute) was calculated by the following equation.

[0116] Permeation rate (g / minute) = (Wf - We) / 0.5

[0117] (Contact angle)

[0118] The measurement of the contact angle was performed in an environment having a temperature of 25°C and a humidity of 50°C ± 10%. A glass slice (25 mm x 75 mm) to which a double-sided tape (NICE TACK manufactured by NICHIBAN CO., LTD.: 10 mm x 75 mm) was attached so that the adhesive surface was exposed was prepared. First, 1.0 g of water absorbent resin particles was uniformly scattered on the double-sided tape attached to the slice. Thereafter, the slice was vertically erected and the remaining water absorbent resin particles were removed to prepare a measurement sample.

[0119] The microscope (VHX-5000 manufactured by KEYENCE CORPORATION) was composed of a worktable for placing a sample which can be moved up and down, and a free angle observation stand having an observation fixed part which can be moved up to 90 degrees downward when set to 0 degrees in parallel with the worktable. The measurement of the contact angle was performed using the above microscope, a micropipette (Pipetman capacity 100-1000 μL manufactured by Gilson Incorporated), and a pipette tip (Eppendorf ep T.I.P.S. Standard 50-1000 μL) by the following steps.

[0120] The observation part of the microscope was adjusted to be horizontal with the worktable part, and a sample for measurement was placed at the center of the worktable part. The front end part of the pipette tip attached to the micropipette was set at a height of 7 ± 1 mm from the surface of the sample for measurement along the vertical distance. At a smooth part of the surface of the sample, one drop (0.01 g) of saline measured by the micropipette was added, and a dynamic image of the absorption of the liquid onto the surface of the sample for measurement was photographed. The image at a time of t = 0.1 (seconds) from the time when the liquid landed on the surface of the sample (the time was set to t = 0 (seconds)) was extracted, and the angle of a straight line connecting the left and right end points and the apex of the contact surface between the above saline droplet and the surface of the double-sided tape with respect to the surface of the double-sided tape was measured using the function of the microscope, and the angle was set to θ / 2. The contact angle θ was calculated by magnifying it by 2 times. The value obtained by repeating the measurement 5 times and averaging was used as the contact angle of the water-absorbing resin particles. The reading method of the angle was based on JIS R 3257 (1999) "Test method for wettability of glass surface".

[0121] <Absorbent>

[0122] A sheet-shaped absorbent core having a size of 40 cm x 12 cm was produced using 12.0 g of water-absorbing resin particles and 8 g of a ground pulp (Reiflock manufactured by Leonia Corporation) which were uniformly mixed by air-creping. Next, the upper and lower surfaces of the absorbent core were sandwiched by two paper towels having a basis weight of 16 g / m 2 at a state where the entire body was pressed by applying a load of 141 kPa for 30 seconds, to produce an absorbent having a content of water-absorbing resin particles of 60 mass%.

[0123] <Absorbent article>

[0124] On the upper surface of the absorbent, a paper towel having a basis weight of 22 g / m 2An absorbent article was produced by sandwiching an absorbent body between a breathable, porous, liquid-permeable sheet of polyethylene and an impermeable sheet of polyethylene of the same size and basis weight. The absorbent article was then used and evaluated. The results are shown in Tables 1 and 2.

[0125] (Preparation of the test solution)

[0126] The test solution was prepared by mixing 9866.0 g of distilled water, 100.0 g of sodium chloride, 3.0 g of calcium chloride dihydrate, 6.0 g of magnesium chloride hexahydrate, 25.0 g of 1% Triton X solution (a mixture of Triton X-100 manufactured by FUJIFILM Wako Pure Chemical Corp. and water), and 0.25 g of edible blue No. 1 (for coloring).

[0127] (Recirculation rate)

[0128] The backflow test was conducted indoors at 25°C and 50% RH. The absorbent material was placed on a level surface. A liquid-filling cylinder with an opening of 3 cm inner diameter was placed in the center of the absorbent material, and 80 mL of test solution was poured into the cylinder. The cylinder was removed, and the absorbent material was left to stand as is. Thirty minutes after the first addition of test solution, the same procedure was performed in the same position using the cylinder. This procedure was repeated a total of five times.

[0129] Sixty minutes after the fifth application of the test solution, 40 sheets of 10cm square filter paper with a pre-determined mass (Wd(g)) were placed near the application point on the absorbent material. A 5kg weight with a 10cm x 10cm base was then placed on top of each sheet. After 5 minutes of this loading, the mass (W(g)) of the filter paper was measured, and the increase in mass was recorded as the reabsorption amount (g).

[0130] Recirculation amount (g) = W - Wd

[0131] (Diffusion)

[0132] Sixty minutes after the fifth application of the test solution, the absorbent was removed from the absorbent material, and the length of the test solution spread was measured. Specifically, as follows... Figure 2 The diffusion distance of the test liquid in the long side direction passing through the center of the absorbent (the part of the absorbent article corresponding to the position where the test liquid is placed) and the diffusion distance of the test liquid in the long side direction passing through the inner side of the absorbent from the ends in the width direction of each absorbent towards the center within 2 cm are measured, and the average of these three values ​​is taken as the diffusion distance (cm).

[0133] [Table 1]

[0134]

[0135] [Table 2]

[0136] Comparative Example 1 2 3 4 Coating layer - - - - Contact angle (degrees) 87 74 40 51 Water absorption speed (seconds) 38 40 53 100 Water retention (g / g) 40 31 37 33 Liquid permeation speed (g / min) 4 19 13 16 Re-wet amount (g) 46 60 57 59 Diffusion distance (cm) 31 36 35 38

[0137] Explanation of symbols

[0138] 10 - absorbent body, 10a - water-absorbent resin particles, 10b - fibrous layer, 20a, 20b - core wrap sheet, 30 - liquid-permeable sheet, 40 - liquid- impermeable sheet.

Claims

1. A water-absorbent resin particle, wherein a contact angle with 0.9 mass% saline at 25±2°C is 114 degrees or more and 130 degrees or less, and a water absorption speed based on a Vortex method is 55 seconds or more and 180 seconds or less, the water-absorbent resin particle has a polymer particle having water absorbency, and a coating layer that coats at least a part of a surface of the polymer particle, the coating layer contains a polyurethane, a median particle diameter of the polymer particle is 200 to 850 μm.

2. The water-absorbent resin particle according to claim 1, wherein the water absorption speed based on the Vortex method is 58 seconds or more.

3. An absorbent body containing the water-absorbent resin particle according to claim 1 or 2.

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