WO2021132266A1

WO2021132266A1 - Absorbent resin particles, absorber, absorbent sheet, absorbent article, and method for producing absorbent resin particles

Info

Publication number: WO2021132266A1
Application number: PCT/JP2020/048009
Authority: WO
Inventors: 瞭平田
Original assignee: 住友精化株式会社
Priority date: 2019-12-23
Filing date: 2020-12-22
Publication date: 2021-07-01
Also published as: JPWO2021132266A1

Abstract

Disclosed are absorbent resin particles having, on the surface of each of the particles, two or more portions having different shapes.

Description

Method for manufacturing water-absorbent resin particles, absorber, water-absorbent sheet, absorbent article, water-absorbent resin particles

The present invention relates to a method for producing water-absorbent resin particles, an absorber, a water-absorbent sheet, an absorbent article, and water-absorbent resin particles.

Conventionally, an absorber containing water-absorbent resin particles has been used as an absorbent article for absorbing a liquid containing water as a main component such as urine. In order to improve the production efficiency of the water-absorbent resin particles, the water-absorbent resin particles are aggregated and granulated (for example, Patent Document 1). Further, for example, Patent Document 2 discloses a method for producing a water-absorbent resin, which comprises a step of mixing two or more kinds of water-absorbent resins having different blood absorption rates in order to improve the blood absorbency of the water-absorbent resin. ..

Japanese Patent Publication No. 2008-533213 JP-A-11-246625

In the conventional absorbent article using water-absorbent resin particles, there is room for improvement in that the liquid to be absorbed leaks out of the absorbent article.

An object of the present invention is to provide water-absorbent resin particles that provide an absorbent article in which liquid leakage is suppressed.

One aspect of the present invention relates to water-absorbent resin particles having two or more differently shaped portions on the surface of one particle.

The water-absorbent resin particles preferably have a spherical portion and an irregularly shaped portion on at least a part of the surface of one particle.

The water-absorbent resin particles have at least a part of the surface of one particle having a portion having an unevenness of 1 μm or more and 20 μm or less and a portion having an unevenness of more than 20 μm and 200 μm or less as measured by a laser microscope. It may be there.

The water-absorbent resin particles may have a shape in which primary particles are aggregated.

Another aspect of the present invention relates to water-absorbent resin particles in which primary particles are aggregated and the average unevenness of the particles measured by a digital microscope is 120 to 180 μm.

The water-absorbent resin particles may have a medium particle size of 300 to 600 μm and a water absorption rate of 5 to 20 seconds by the Vortex method.

The water-absorbent resin particles may have a physiological saline water retention amount of 20 to 60 g / g and a water absorption amount under load at 4.14 kPa of 10 ml / g or more.

The present invention also provides an absorber containing the above water-absorbent resin particles.

The present invention also provides a water absorption sheet provided with the above absorber.

The water absorbing sheet may further include a core wrap sheet, and the absorbent body may be arranged inside the core wrap sheet.

The present invention also provides an absorbent article comprising the water absorbing sheet.

Another aspect of the present invention relates to a method for producing water-absorbent resin particles, which comprises aggregating and granulating primary particles, wherein the primary particles have two or more shapes.

In the above method, it is preferable that the primary particles include spherical particles and irregularly shaped particles.

In the above method, the mixing ratio of the spherical particles and the irregularly shaped particles is preferably 70:30 to 20:80.

INDUSTRIAL APPLICABILITY The present invention provides water-absorbent resin particles that provide an absorbent article in which liquid leakage is suppressed.

It is a schematic cross-sectional view which shows one Embodiment of a water absorption sheet. It is a schematic plan view which shows an example of the adhesive pattern formed on the core wrap sheet. It is a schematic cross-sectional view which shows one Embodiment of an absorbent article. It is a top view which shows an example of a stirring blade (a flat plate blade which has a slit in a flat plate part). It is a scanning electron micrograph which shows the water-absorbing resin particle of Example 3. FIG. It is a graph which shows the measurement example of the average unevenness of a particle. It is a schematic diagram which shows the measuring apparatus of the water absorption amount under load of a water-absorbing resin particle. It is a schematic diagram which shows the measuring apparatus of non-pressurized DW of a water-absorbent resin particle. It is a schematic diagram which shows the method of evaluating the liquid leakage property.

Hereinafter, embodiments of the present invention will be described in detail. However, the present invention is not limited to the following embodiments, and can be variously modified and implemented within the scope of the gist thereof.

In this specification, "acrylic" and "methacryl" are collectively referred to as "(meth) acrylic". Similarly, "acrylate" and "methacrylate" are also referred to as "(meth) acrylate". "(Poly)" shall mean both with and without the "poly" prefix. In the numerical range described stepwise in the present specification, the upper limit value or the lower limit value of the numerical range of one step can be arbitrarily combined with the upper limit value or the lower limit value of the numerical range of another step. In the numerical range described in the present specification, the upper limit value or the lower limit value of the numerical range may be replaced with the value shown in the examples. "Water-soluble" means that it exhibits a solubility in water of 5% by mass or more at 25 ° C. The materials exemplified in the present specification may be used alone or in combination of two or more. The content of each component in the composition means the total amount of the plurality of substances present in the composition when a plurality of substances corresponding to each component are present in the composition, unless otherwise specified. "Saline" refers to a 0.9% by mass sodium chloride aqueous solution.

One aspect of this embodiment relates to water-absorbent resin particles having two or more differently shaped portions on the surface of one particle. In the present specification, two or more different shapes are visually distinguished from each other when one particle is magnified (for example, 10 to 200 times) and observed by a microscope such as an optical microscope, a digital microscope, or a scanning electron microscope. It refers to what can be done, and does not include the shape of parts that cannot be observed from the outside, such as the inside of particles. The two or more different shapes may be, for example, a spherical shape, an indefinite shape, or the like.

By having two or more kinds of differently shaped portions on the surface of one particle, the water-absorbent resin particles of the present embodiment can suppress liquid leakage when applied to an absorbent article. Although the cause for obtaining such an effect is not always clear, the present inventor speculates as follows. However, the mechanism is not limited to the following contents. That is, since one water-absorbent resin particle has a plurality of shapes on the surface, the absorption performance due to each shape is appropriately balanced and both performances are exhibited, so that liquid leakage property is exhibited. Is thought to be suppressed. Such an effect was not confirmed when the particles having two or more different shapes were simply mixed, that is, when two or more different shapes were on the surface of different different particles.

In the present specification, the spherical shape includes a true spherical shape, a substantially spherical shape, and an elliptical surface shape. Further, the spherical portion has a spherical shape as a whole, but a part thereof may be chipped and may have holes and / or recesses.

In the present specification, the indefinite shape is a non-homogeneous shape that is not spherical, and may be, for example, spongy, cauliflower, amorphous, scaly, crushed, or granular. The portion of the water-absorbent resin particles having an indefinite shape may have an indefinite shape at the time of polymerization obtained by, for example, a polymerization method such as reverse phase suspension polymerization. It may be a crushed product obtained by crushing a water-absorbent resin obtained by a polymerization method such as phase polymerization or aqueous solution polymerization, or an agglomerate of the crushed product.

The water-absorbent resin particles according to the present embodiment preferably have at least a spherical portion and an irregularly shaped portion on the surface of one particle.

In the water-absorbent resin particles according to the present embodiment, at least a part of the surface of one particle has an unevenness measured by a laser microscope (hereinafter, also referred to as “shape-specific unevenness”) of 1 μm or more and 20 μm or less. (Hereinafter, also referred to as a "low unevenness portion") and a portion having an unevenness of more than 20 μm and 200 μm or less (hereinafter, also referred to as a “high unevenness portion”).

Details of the method for measuring the degree of unevenness by shape will be shown in Examples described later, but the outline is as follows. The water-absorbent resin particles used for the measurement are in a dry state before use. The degree of unevenness for each shape is measured within a portion having the same type of shape so as not to include a different type of shape portion. When measuring the degree of unevenness of the spherical portion, the profile line used for the measurement is set on only one sphere so as not to straddle the boundary of the sphere. The unevenness is measured along the profile line. The profile line shall be a circle with a diameter of 30 to 35 μm at each location, and 90% or more of the total length of the waveform curve obtained thereby shall be used. The degree of unevenness for each shape is the average value of the values measured at five or more points for the same shape portion.

The low unevenness portion of the water-absorbent resin particles may have an unevenness measured by a laser microscope of 3 μm or more or 5 μm or more, and may be 20 μm or less, 18 μm or less, 15 μm or less, or 10 μm or less. The low unevenness portion of the water-absorbent resin particles may have an unevenness measured by a laser microscope of 3 to 20 μm, 5 to 18 μm, 5 to 15 μm, 5 to 13 μm, or 5 to 10 μm. The low unevenness portion may be spherical.

The high unevenness portion of the water-absorbent resin particles may have unevenness measured by a laser microscope of 25 μm or more, 30 μm or more, 40 μm or more, 45 μm or more, 50 μm or more or 55 μm or more, and 180 μm or less, 150 μm or less, 120 μm. Hereinafter, it may be 100 μm or less, 90 μm or less, 80 μm or less, or 70 μm or less. The high unevenness portion of the water-absorbent resin particles may have irregularities measured by a laser microscope of 25 to 200 μm, 30 to 180 μm, 30 to 150 μm, 30 to 120 μm, 40 to 120 μm, or 40 to 80 μm. The high unevenness portion may have an indefinite shape.

It is preferable that the water-absorbent resin particles according to the present embodiment have a spherical portion composed of all or a part of a sphere having a diameter of 30 to 100 μm on at least a part of the surface thereof. The water-absorbent resin particles preferably have a spherical portion having a sphere diameter of 30 to 80 μm, 30 to 60 μm, or 30 to 40 μm on at least a part of the surface thereof.

The water-absorbent resin particles having two or more kinds of differently shaped portions on the surface of one particle may have a shape in which the primary particles are aggregated. Such water-absorbent resin particles can be produced, for example, by aggregating and granulating two or more types of primary particles having different shapes. Details of the manufacturing method will be described later.

Another aspect of the present embodiment relates to water-absorbent resin particles in which primary particles are aggregated and the average unevenness of the particles measured by a digital microscope is 120 to 180 μm.

The detailed measurement method of the average unevenness of the particles is shown in Examples described later, but the outline is as follows. The water-absorbent resin particles used for the measurement are in a dry state before use. The profile line used for the measurement shall be a circle having a diameter in the range of 270 to 320 μm at each location, and 90% or more of the total length of the waveform curve obtained thereby shall be used. The unevenness is measured along the profile line. The degree of unevenness is the sum of the absolute values of the highest peak elevation and the lowest valley bottom elevation, which have the largest elevation difference with respect to the reference line when the average line of the waveform curve is used as the reference line. is there. The degree of unevenness is measured for 12 particles, and the average value of 10 points excluding the maximum value and the minimum value among them is taken as the average degree of unevenness of the particles.

As a digital microscope that measures the average degree of unevenness of particles, a microscope that can measure the degree of unevenness on the surface of an object non-destructively is used. As such a measuring device, for example, a digital microscope such as VHX-5000 or VHX-7000 manufactured by KEYENCE Corporation can be used.

The present inventor has found that water-absorbent resin particles having an aggregated shape of primary particles and having an average unevenness of particles in an appropriate range of 120 to 180 μm exhibit excellent absorption performance. The surface of the water-absorbent resin particles is not too smooth and not too rough. Since the water-absorbent resin particles have a shape in which the primary particles are aggregated and the average unevenness of the particles is 120 to 180 μm, the liquid leakage property can be suppressed when applied to an absorbent article. Although the cause for obtaining such an effect is not always clear, the present inventor speculates as follows. However, the mechanism is not limited to the following contents. That is, when the average unevenness of the particles is within a predetermined range, the water-absorbent resin particles and the fibers are well entangled, the water-absorbent resin particles are easily fixed in the absorbent article, and the water-absorbing resin particles have an appropriate water absorption rate. It is considered that it is easy to suppress liquid leakage because it is easy to do.

The average unevenness of the particles may be 125 μm or more, 130 μm or more, 135 μm or more, 140 μm or more, 145 μm or more, 150 μm or more, 155 μm or more, 160 μm or more, or 165 μm or more. The average unevenness of the particles may be 175 μm or less, 170 μm or less, 165 μm or less, 160 μm or less, 155 μm or less, or 150 μm or less. The average unevenness of the particles may be 130 to 180 μm, 135 to 175 μm, or 140 to 170 μm.

The water-absorbent resin particles having an aggregated shape of the primary particles and having an average unevenness of the particles in the range of 120 to 180 μm may have two or more different shaped portions on the surface of the single particles. Often, at least a part of the surface of one particle may have a spherical part and an irregularly shaped part, and at least a part of the surface of one particle has an unevenness measured by a laser microscope of 1 μm or more and 20 μm. It may have a portion having a degree of unevenness of more than 20 μm and a portion having a degree of unevenness of more than 200 μm or less.

The water-absorbent resin particles having an aggregated shape of the primary particles and having an average unevenness of the particles in the range of 120 to 180 μm, for example, aggregate and granulate the primary particles having two or more different shapes. Can be obtained by The two or more different shapes are preferably spherical and indefinite, for example.

In the present specification, the particles having a shape in which the primary particles are aggregated have at least a part of the shape of the primary particles used as a raw material on the particle surface to the extent that they can be visually observed, but the primary particles are also used. It means that a plurality of primary particles are integrally formed without being separated into the units of.

The medium particle size of the water-absorbent resin particles according to the present embodiment is preferably 300 to 600 μm from the viewpoint of easily obtaining higher absorption performance in the water-absorbent sheet. The medium particle size of the water-absorbent resin particles may be 350 μm or more, 380 μm or more, or 400 μm or more, and may be 550 μm or less, or 500 μm or less.

The water-absorbent resin particles according to the present embodiment preferably have a water absorption rate of 5 to 20 seconds by the Vortex method from the viewpoint of easily obtaining higher absorption performance in the water-absorbent sheet. A detailed measurement method of the water absorption rate by the Vortex method will be shown in Examples described later. The water absorption rate may be 6 seconds or more, 7 seconds or more, or 8 seconds or more, and may be 18 seconds or less, 16 seconds or less, 15 seconds or less, 14 seconds or less, 14 seconds or less, or 12 seconds or less. Good.

The water-absorbent resin particles according to the present embodiment preferably have a physiological saline water retention amount of 20 to 60 g / g from the viewpoint of easily obtaining higher absorption performance in the water-absorbent sheet. A detailed measurement method of the physiological saline water retention amount will be shown in Examples described later. The amount of saline water retained may be 23 g / g or more, 25 g / g or more, 27 g / g or more, or 30 g / g or more, and 55 g / g or less, 50 g / g or less, or 45 g / g or less. May be good.

The water-absorbent resin particles according to the present embodiment preferably have a water absorption amount of 10 ml / g or more under load at 4.14 kPa from the viewpoint of easily obtaining higher absorption performance in the water-absorbent sheet. The amount of water absorption under load at 4.14 kPa may be 12 ml / g or more, 14 ml / g or more, 16 ml / g or more, 20 ml / g or more, 24 ml / g or more, 40 ml / g or less, 35 ml / g or less, 30 ml. It may be / g or less, 25 ml / g or less, 20 ml / g or less, or 18 ml / g or less.

The water-absorbent resin particles according to the present embodiment have a non-pressurized DW 0.5 minute value of 1 ml / g or more, 3 ml / g or more, or 4 ml / g or more from the viewpoint of easily obtaining higher absorption performance in the water-absorbent sheet. It may be 15 ml / g or less, 13 ml / g or less, 11 ml / g or less, or 9 ml / g or less. The water-absorbent resin particles according to the present embodiment have non-pressurized DW 2-minute values of 15 ml / g or more, 20 ml / g or more, 24 ml / g or more, and 30 ml / g from the viewpoint of easily obtaining higher absorption performance in the water-absorbing sheet. The above may be 35 ml / g or more, or 40 ml / g or more, and may be 50 ml / g or less, 45 ml / g or less, 40 ml / g or less, 35 ml / g or less, or 30 ml / g or less. The water-absorbent resin particles according to the present embodiment have non-pressurized DW 5-minute values of 30 ml / g or more, 35 ml / g or more, 40 ml / g or more, and 45 ml / g from the viewpoint of easily obtaining higher absorption performance in the water-absorbing sheet. It may be more than or equal to 50 ml / g or more, and may be 65 ml / g or less, 60 ml / g or less, or 55 ml / g or less.

Yet another aspect of the present embodiment relates to a method for producing water-absorbent resin particles, which comprises aggregating and granulating primary particles, wherein the primary particles have two or more shapes. The shape of the primary particles is preferably spherical or indefinite. As used herein, the term "spherical" includes a true spherical shape, a substantially spherical shape, and an ellipsoidal shape, and may be partially chipped, and may have holes and / or recesses.

As the granulation method, a method is used in which the granulation strength is obtained so that most of the formed particles do not decompose into primary particles in normal use. Further, as the granulation method, a method is used in which at least a part of each of the shapes derived from the primary particles having two or more kinds of shapes can be left on the surface of the formed particles. The primary particles used for granulation may be dry particles, but it is preferable that at least a part of the primary particles is in the form of a hydrogel, and it is more preferable that all of the primary particles used are in the form of a hydrogel. When mixing the primary particles for granulation, water for promoting aggregation can be added. The added water may contain a cross-linking agent or the like, and for example, an aqueous solution of the post-polymerization cross-linking agent described later may be used. Further, in order to efficiently perform granulation, it is preferable to add a coagulant such as a powdered inorganic coagulant when mixing the primary particles.

Examples of the powdered inorganic flocculant include silica, zeolite, bentonite, aluminum oxide, talc, titanium dioxide, kaolin, clay, and hydrotalcite. From the viewpoint of excellent aggregating effect, the aggregating agent is preferably at least one selected from the group consisting of silica, aluminum oxide, talc and kaolin.

The amount of the flocculant added is preferably 0.001 to 1 part by mass, more preferably 0.005 to 0.5 part by mass, based on 100 parts by mass of the ethylenically unsaturated monomer used for the polymerization. 01 to 0.2 parts by mass is more preferable.

When a flocculant is used, it is preferable to use it as a dispersion liquid in which the flocculant is dispersed in a solvent in advance because the flocculant is uniformly mixed with the primary particles. When a flocculant is used, it is preferable that the primary particles to be used are mixed first, and then the flocculant is added.

Granulation can be performed using various stirrers having stirring blades. As the stirring blade, flat plate blades, lattice blades, paddle blades, propeller blades, anchor blades, turbine blades, Faudler blades, ribbon blades, full zone blades, max blend blades and the like can be used. The flat plate blade has a shaft (stirring shaft) and a flat plate portion (stirring portion) arranged around the shaft. Further, the flat plate portion may have a slit or the like. When a flat plate blade is used as the stirring blade, granulation tends to be performed more uniformly.

At the time of granulation, it is preferable to mix the primary particles with each other and, if necessary, a flocculant in a hydrocarbon dispersion medium. After the particles having a shape in which the primary particles are aggregated are obtained by granulation, the solvent and water may be removed and surface cross-linking may be carried out as appropriate.

When spherical particles and irregularly shaped particles are used as the primary particles used for granulation, the mixing ratio (mass standard) thereof is preferably 70:30 to 20:80 as the solid content. When the mixing ratio is within the above range, the water absorption performance of each primary particle can be appropriately exhibited, and the water absorption performance of the formed particles can be further enhanced, which is preferable. The mixing ratio of spherical particles and irregularly shaped particles may be 60:40 to 20:80, 55:45 to 20:80, 50:50 to 20:80, or 50:50 to 25:75. ..

When a crushed product of a water-absorbent resin is used as the irregularly shaped particles, a crushed product that has been previously aggregated only with the crushed product may be further aggregated with spherical particles to granulate, and the crushed product may be aggregated with spherical particles. It may be used directly in.

The medium particle size of the primary particles used for granulation may be, for example, 20 to 250 μm, 30 to 200 μm, 40 to 180 μm, or 50 to 160 μm.

By the above granulation method, water-absorbent resin particles having a spherical portion and an irregularly shaped portion on at least a part of the surface of one particle can be obtained.

Spherical particles as primary particles can be obtained, for example, by setting the HLB of the surfactant used at the time of polymerization to 7 or less in the reverse phase suspension polymerization method. Spherical particles can also be obtained by a vapor phase polymerization method. In the case of the reverse phase suspension polymerization method, the irregularly shaped particles can be obtained by setting the HLB of the surfactant used at the time of polymerization to 8 or more. The irregularly shaped particles can also be obtained by crushing a water-absorbent resin obtained by various polymerization methods such as a reverse phase suspension polymerization method, an aqueous solution polymerization method, and a gas phase polymerization method, or by aggregating crushed products.

The water-absorbent resin particles according to the present embodiment and the primary particles used for the production thereof include, for example, as polymer particles, a crosslinked polymer formed by polymerization of a monomer containing an ethylenically unsaturated monomer. You can stay. The crosslinked polymer has a structural unit derived from an ethylenically unsaturated monomer. As the ethylenically unsaturated monomer, a water-soluble ethylenically unsaturated monomer can be used. In the following, as a method for polymerizing an ethylenically unsaturated monomer, a reverse phase suspension polymerization method will be described as an example.

The ethylenically unsaturated monomer is preferably water-soluble, for example, (meth) acrylic acid and a salt thereof, 2- (meth) acrylamide-2-methylpropanesulfonic acid and a salt thereof, (meth) acrylamide, N. , N-dimethyl (meth) acrylamide, 2-hydroxyethyl (meth) acrylate, N-methylol (meth) acrylamide, polyethylene glycol mono (meth) acrylate, N, N-diethylaminoethyl (meth) acrylate, N, N-diethylamino Examples thereof include propyl (meth) acrylate and diethylaminopropyl (meth) acrylamide. When the ethylenically unsaturated monomer has an amino group, the amino group may be quaternized. The ethylenically unsaturated monomer may be used alone or in combination of two or more. Functional groups such as the carboxyl group and amino group of the above-mentioned monomers can function as functional groups capable of cross-linking in the surface cross-linking step described later.

Among these, from the viewpoint of industrial availability, the ethylenically unsaturated monomer is selected from the group consisting of (meth) acrylic acid and its salts, acrylamide, methacrylamide, and N, N-dimethylacrylamide. It is preferable to contain at least one compound selected, and more preferably to contain at least one compound selected from the group consisting of (meth) acrylic acid and salts thereof, and acrylamide. From the viewpoint of further enhancing the water absorption property, the ethylenically unsaturated monomer further preferably contains at least one compound selected from the group consisting of (meth) acrylic acid and salts thereof. That is, the water-absorbent resin particles preferably have a structural unit derived from at least one selected from the group consisting of (meth) acrylic acid and salts thereof.

As the monomer for obtaining the water-absorbent resin particles, a monomer other than the above-mentioned ethylenically unsaturated monomer may be used. Such a monomer can be used, for example, by mixing with an aqueous solution containing the above-mentioned ethylenically unsaturated monomer. The amount of the ethylenically unsaturated monomer used is preferably 70 to 100 mol% with respect to the total amount of the monomers. Above all, the ratio of (meth) acrylic acid and a salt thereof is more preferably 70 to 100 mol% with respect to the total amount of the monomers.

The ethylenically unsaturated monomer is usually preferably used as an aqueous solution. The concentration of the ethylenically unsaturated monomer in the aqueous solution containing the ethylenically unsaturated monomer (hereinafter, simply referred to as “monomer aqueous solution”) is preferably 20% by mass or more and preferably 25 to 70% by mass. Is more preferable, and 30 to 55% by mass is further preferable. Examples of the water used in the aqueous solution include tap water, distilled water, ion-exchanged water and the like.

When the ethylenically unsaturated monomer has an acid group, the monomer aqueous solution may be used by neutralizing the acid group with an alkaline neutralizer. The degree of neutralization of the ethylenically unsaturated monomer by the alkaline neutralizing agent increases the osmotic pressure of the obtained water-absorbent resin particles and further enhances the water absorption characteristics. It is preferably 10 to 100 mol%, more preferably 50 to 90 mol%, and even more preferably 60 to 80 mol% of the group. Examples of the alkaline neutralizing agent include alkali metal salts such as sodium hydroxide, sodium carbonate, sodium hydrogen carbonate, potassium hydroxide and potassium carbonate; ammonia and the like. The alkaline neutralizer may be used alone or in combination of two or more. The alkaline neutralizer may be used in the form of an aqueous solution to simplify the neutralization operation. Neutralization of the acid group of the ethylenically unsaturated monomer can be performed, for example, by adding an aqueous solution of sodium hydroxide, potassium hydroxide or the like to the above-mentioned monomer aqueous solution and mixing them.

In the reverse phase suspension polymerization method, the monomer aqueous solution is dispersed in a hydrocarbon dispersion medium in the presence of a surfactant, and the ethylenically unsaturated monomer is polymerized using a radical polymerization initiator or the like. Can be done.

Examples of the surfactant used in the polymerization include nonionic surfactants and anionic surfactants. Nonionic surfactants include sorbitan fatty acid ester, (poly) glycerin fatty acid ester, sucrose fatty acid ester, polyoxyethylene sorbitan fatty acid ester, polyoxyethylene glycerin fatty acid ester, sorbitol fatty acid ester, polyoxyethylene sorbitol fatty acid ester, and poly. Oxyethylene alkyl ether, polyoxyethylene alkyl phenyl ether, polyoxyethylene castor oil, polyoxyethylene hydrogenated castor oil, alkylallyl formaldehyde condensed polyoxyethylene ether, polyoxyethylene polyoxypropylene block copolymer, polyoxyethylene polyoxypropyl alkyl Examples include ether and polyethylene glycol fatty acid ester. Anionic surfactants include fatty acid salts, alkylbenzene sulfonates, alkylmethyl taurates, polyoxyethylene alkylphenyl ether sulfates, polyoxyethylene alkyl ether sulfonates, and polyoxyethylene alkyl ether phosphates. , Phosphate ester of polyoxyethylene alkyl allyl ether and the like. The surfactant may be used alone or in combination of two or more. The type of surfactant does not matter when producing spherical particles and irregularly shaped particles separately.

From the viewpoint that the W / O type reverse phase suspension is in a good state, water-absorbent resin particles having a suitable particle size can be easily obtained, and industrially available, the surfactant is a sorbitan fatty acid ester. It preferably contains at least one compound selected from the group consisting of polyglycerin fatty acid esters and sucrose fatty acid esters.

The amount of the surfactant used is preferably 0.05 to 10 parts by mass with respect to 100 parts by mass of the monomer aqueous solution from the viewpoint of obtaining a sufficient effect on the amount used and from the viewpoint of economic efficiency. .08 to 5 parts by mass is more preferable, and 0.1 to 3 parts by mass is further preferable.

In reverse phase suspension polymerization, a polymer-based dispersant may be used in combination with the above-mentioned surfactant. Examples of the polymer dispersant include maleic anhydride-modified polyethylene, maleic anhydride-modified polypropylene, maleic anhydride-modified ethylene / propylene copolymer, maleic anhydride-modified EPDM (ethylene / propylene / diene / terpolymer), and 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 Examples thereof include coalescence, oxidized polyethylene, oxidized polypropylene, oxidized ethylene / propylene copolymer, ethylene / acrylic acid copolymer, ethyl cellulose, ethyl hydroxyethyl cellulose and the like. The polymer-based dispersant may be used alone or in combination of two or more. As the polymer-based dispersant, from the viewpoint of excellent dispersion stability of the monomer, maleic anhydride-modified polyethylene, maleic anhydride-modified polypropylene, maleic anhydride-modified ethylene / propylene copolymer, and maleic anhydride / ethylene copolymer weight. Combined, maleic anhydride / propylene copolymer, maleic anhydride / ethylene / propylene copolymer, polyethylene, polypropylene, ethylene / propylene copolymer, oxidized polyethylene, oxidized polypropylene, and oxidized ethylene / propylene copolymer At least one selected from the group consisting of coalescing is preferable.

The amount of the polymer-based dispersant used is preferably 0.05 to 10 parts by mass with respect to 100 parts by mass of the monomer aqueous solution from the viewpoint of obtaining a sufficient effect on the amount used and from the viewpoint of economic efficiency. , 0.08 to 5 parts by mass is more preferable, and 0.1 to 3 parts by mass is further preferable.

The hydrocarbon dispersion medium may contain at least one compound selected from the group consisting of chain aliphatic hydrocarbons having 6 to 8 carbon atoms and alicyclic hydrocarbons having 6 to 8 carbon atoms. Hydrocarbon dispersion media include chain aliphatic hydrocarbons such as n-hexane, n-heptane, 2-methylhexane, 3-methylhexane, 2,3-dimethylpentane, 3-ethylpentane, and n-octane; cyclohexane. , Methylcyclohexane, cyclopentane, methylcyclopentane, trans-1,2-dimethylcyclopentane, cis-1,3-dimethylcyclopentane, trans-1,3-dimethylcyclopentane and other alicyclic hydrocarbons; benzene, Examples include aromatic hydrocarbons such as toluene and xylene. The hydrocarbon dispersion medium may be used alone or in combination of two or more.

The hydrocarbon dispersion medium may contain at least one selected from the group consisting of n-heptane and cyclohexane from the viewpoint of being industrially easily available and having stable quality. From the same viewpoint, as the mixture of the above-mentioned hydrocarbon dispersion medium, for example, commercially available ExxonHeptane (manufactured by ExxonMobil: containing 75 to 85% of n-heptane and isomeric hydrocarbons) is used. You may.

The amount of the hydrocarbon dispersion medium used is preferably 30 to 1000 parts by mass and 40 to 500 parts by mass with respect to 100 parts by mass of the monomer aqueous solution from the viewpoint of appropriately removing the heat of polymerization and easily controlling the polymerization temperature. Is more preferable, and 50 to 400 parts by mass is further preferable. When the amount of the hydrocarbon dispersion medium used is 30 parts by mass or more, the polymerization temperature tends to be easily controlled. When the amount of the hydrocarbon dispersion medium used is 1000 parts by mass or less, the productivity of polymerization tends to be improved, which is economical.

The radical polymerization initiator is preferably water-soluble, for example, persulfates such as potassium persulfate, ammonium persulfate, sodium persulfate; methyl ethyl ketone peroxide, methyl isobutyl ketone peroxide, di-t-butyl peroxide, t. -Peroxides such as butyl cumylperoxide, t-butylperoxyacetate, t-butylperoxyisobutyrate, t-butylperoxypivalate, hydrogen peroxide; 2,2'-azobis (2-amidinopropane) ) 2 hydrochloride, 2,2'-azobis [2- (N-phenylamidino) propane] 2 hydrochloride, 2,2'-azobis [2- (N-allylamidino) propane] 2 hydrochloride, 2,2 '-Azobis [2- (2-imidazolin-2-yl) propane] dihydrochloride, 2,2'-azobis {2- [1- (2-hydroxyethyl) -2-imidazolin-2-yl] propane} Dihydrochloride, 2,2'-azobis {2-methyl-N- [1,1-bis (hydroxymethyl) -2-hydroxyethyl] propionamide}, 2,2'-azobis [2-methyl-N- (2-Hydroxyethyl) -propionamide], azo compounds such as 4,4'-azobis (4-cyanovaleric acid) and the like can be mentioned. The radical polymerization initiator may be used alone or in combination of two or more. Examples of the radical polymerization initiator include potassium persulfate, ammonium persulfate, sodium persulfate, 2,2'-azobis (2-amidinopropane) dihydrochloride, and 2,2'-azobis [2- (2-imidazolin-2-). Il) Propane] 2 hydrochloride and 2,2'-azobis {2- [1- (2-hydroxyethyl) -2-imidazolin-2-yl] propane} 2 hydrochloride at least selected from the group. Is preferable.

The amount of the radical polymerization initiator used may be 0.05 to 10 mmol per 1 mol of the ethylenically unsaturated monomer. When the amount of the radical polymerization initiator used is 0.05 mmol or more, the polymerization reaction does not require a long time and is efficient. When the amount of the radical polymerization initiator used is 10 mmol or less, it is easy to suppress the occurrence of a rapid polymerization reaction.

The above-mentioned radical polymerization initiator can also be used as a redox polymerization initiator in combination with a reducing agent such as sodium sulfite, sodium hydrogen sulfite, ferrous sulfate, and L-ascorbic acid.

At the time of the polymerization reaction, the monomer aqueous solution used for the polymerization may contain a chain transfer agent. Examples of the chain transfer agent include hypophosphates, thiols, thiolic acids, secondary alcohols, amines and the like.

When performing reverse phase suspension polymerization, the monomer aqueous solution used for the polymerization may contain a thickener in order to control the particle size of the water-absorbent resin particles. Examples of the thickener include hydroxyethyl cellulose, hydroxypropyl cellulose, methyl cellulose, carboxymethyl cellulose, polyethylene glycol, polyacrylamide, polyethyleneimine, dextrin, sodium alginate, polyvinyl alcohol, polyvinylpyrrolidone, polyethylene oxide and the like. If the stirring speed at the time of polymerization is the same, the higher the viscosity of the aqueous monomer solution, the larger the medium particle size of the obtained particles tends to be.

Cross-linking by self-cross-linking may occur during polymerization, but cross-linking may be performed by using an internal cross-linking agent. When an internal cross-linking agent is used, it is easy to control the water absorption characteristics of the water-absorbent resin particles. The internal cross-linking agent is usually added to the reaction solution during the polymerization reaction. Examples of the internal cross-linking agent include di or tri (meth) acrylic acid esters of polyols such as ethylene glycol, propylene glycol, trimethylolpropane, glycerin, polyoxyethylene glycol, polyoxypropylene glycol, and polyglycerin; Unsaturated polyesters obtained by reacting polyols with unsaturated acids (maleic acid, fumaric acid, etc.); bis (meth) acrylamides such as N, N'-methylenebis (meth) acrylamide; polyepoxides and (meth) Di or tri (meth) acrylic acid esters obtained by reacting with acrylic acid; di (meth) obtained by reacting polyisocyanate (tolylene diisocyanate, hexamethylene diisocyanate, etc.) with hydroxyethyl (meth) acrylate. ) Acrylic acid carbamil esters; compounds having two or more polymerizable unsaturated groups such as allylated starch, allylated cellulose, diallyl phthalate, N, N', N "-triallyl isocyanurate, divinylbenzene; Poly such as (poly) ethylene glycol diglycidyl ether, (poly) propylene glycol diglycidyl ether, (poly) glycerin diglycidyl ether, (poly) glycerin triglycidyl ether, (poly) propylene glycol polyglycidyl ether, polyglycerol polyglycidyl ether, etc. Glycidyl compounds; haloepoxy compounds such as epichlorohydrin, epibromhydrin, α-methylepichlorohydrin; 2 reactive functional groups such as isocyanate compounds (2,4-tolylene diisocyanate, hexamethylene diisocyanate, etc.) Examples thereof include compounds having more than one. The internal cross-linking agent may be used alone or in combination of two or more. As the internal cross-linking agent, a polyglycidyl compound is preferable, and a diglycidyl ether compound is used. Is more preferable, and at least one selected from the group consisting of (poly) ethylene glycol diglycidyl ether, (poly) propylene glycol diglycidyl ether, and (poly) glycerin diglycidyl ether is further preferable.

The amount of the internal cross-linking agent used is from the viewpoint of suppressing liquid leakage in the absorbent article, and the water-soluble property is suppressed by appropriately cross-linking the obtained polymer, so that a sufficient water absorption amount can be easily obtained. From the viewpoint, 30 mmol or less is preferable, 0.01 to 10 mmol is more preferable, 0.012 to 5 mmol is further preferable, and 0.015 to 1 mmol is particularly preferable, per 1 mol of the ethylenically unsaturated monomer. 0.02 to 0.1 mmol is highly preferred, and 0.025 to 0.08 mmol is very preferred.

An aqueous phase containing an ethylenically unsaturated monomer, a radical polymerization initiator and an internal cross-linking agent if necessary, and an oil phase containing a hydrocarbon dispersion medium, a surfactant and a polymer-based dispersant if necessary. Can be heated under stirring in a mixed state to carry out reverse phase suspension polymerization in an aqueous system in oil.

When performing reverse phase suspension polymerization, a monomer aqueous solution containing an ethylenically unsaturated monomer is used as a hydrocarbon dispersion medium in the presence of a surfactant (more polymer-based dispersant if necessary). Disperse. At this time, the timing of adding the surfactant, the polymer-based dispersant, or the like may be either before or after the addition of the monomer aqueous solution, as long as it is before the start of the polymerization reaction.

Among them, from the viewpoint of easily reducing the amount of the hydrocarbon dispersion medium remaining in the obtained water-absorbent resin, the surfactant is prepared after the monomer aqueous solution is dispersed in the hydrocarbon dispersion medium in which the polymer-based dispersant is dispersed. It is preferable to further disperse the above and then carry out the polymerization.

Reverse phase suspension polymerization can be carried out in one stage or in multiple stages of two or more stages. Reversed phase suspension polymerization may be carried out in 2 to 3 steps from the viewpoint of increasing productivity.

When reverse-phase suspension polymerization is carried out in two or more stages, the reaction mixture obtained in the first-step polymerization reaction after the first-step reverse-phase suspension polymerization is subjected to an ethylenically unsaturated single amount. The body may be added and mixed, and the reverse phase suspension polymerization of the second and subsequent steps may be carried out in the same manner as in the first step. In the reverse phase suspension polymerization in each stage after the second stage, in addition to the ethylenically unsaturated monomer, the above-mentioned radical polymerization initiator and / or internal cross-linking agent is used in the reverse phase in each stage after the second stage. Based on the amount of ethylenically unsaturated monomer added during suspension polymerization, reverse phase suspension polymerization is carried out by adding within the range of the molar ratio of each component to the above-mentioned ethylenically unsaturated monomer. Is preferable. An internal cross-linking agent may be used in the reverse phase suspension polymerization in each of the second and subsequent stages, if necessary. When an internal cross-linking agent is used, it is added within the range of the molar ratio of each component to the above-mentioned ethylenically unsaturated monomer based on the amount of the ethylenically unsaturated monomer provided in each stage, and the suspension is reversed. It is preferable to carry out turbid polymerization.

The temperature of the polymerization reaction varies depending on the radical polymerization initiator used, but by rapidly advancing the polymerization and shortening the polymerization time, the efficiency is improved and the heat of polymerization is easily removed to carry out the reaction smoothly. From the viewpoint, 20 to 150 ° C. is preferable, and 40 to 120 ° C. is more preferable. The reaction time is usually 0.5-4 hours. The completion of the polymerization reaction can be confirmed, for example, by stopping the temperature rise in the reaction system. As a result, the polymer of the ethylenically unsaturated monomer is usually obtained in the state of a hydrogel.

The polymerization reaction can be carried out using various stirrers having stirring blades. As the stirring blade, flat plate blades, lattice blades, paddle blades, propeller blades, anchor blades, turbine blades, Faudler blades, ribbon blades, full zone blades, max blend blades and the like can be used.

After polymerization, cross-linking may be performed by adding a cross-linking agent to the obtained hydrogel polymer and heating it. By performing cross-linking after the polymerization, the degree of cross-linking of the hydrogel polymer can be increased to further improve the water absorption characteristics. As the post-polymerization cross-linking agent, the same type as the surface cross-linking agent described later can be used.

The time for adding the cross-linking agent after polymerization may be after the polymerization of the ethylenically unsaturated monomer used for polymerization. The post-polymerization cross-linking agent contains water in consideration of heat generation during and after polymerization, retention due to process delay, opening of the system when the cross-linking agent is added, and fluctuation of water content due to addition of water accompanying the addition of the cross-linking agent. From the viewpoint of rate (described later), it is preferable to add in the region of [moisture content immediately after polymerization ± 3% by mass]. Further, by adding the post-polymerization cross-linking agent aqueous solution to the post-polymerization hydrogel polymer, the post-polymerization cross-linking agent aqueous solution can also serve as a granulator for aggregating the primary particles.

After obtaining the hydrogel-like polymer as the primary particles, granulation is performed by aggregation as described above, and the hydrogel-like polymer in the form in which the primary particles are aggregated can be obtained.

Subsequently, by carrying out drying to remove water from the obtained hydrogel-like polymer, polymer particles (for example, polymer particles having a structural unit derived from an ethylenically unsaturated monomer) can be obtained. As a drying method, for example, (a) a hydrogel-like polymer is dispersed in a hydrocarbon dispersion medium, and co-boiling distillation is performed by heating from the outside, and the hydrocarbon dispersion medium is refluxed to remove water. Examples thereof include (b) a method of taking out the hydrogel polymer by decantation and drying under reduced pressure, and (c) a method of filtering the hydrogel polymer with a filter and drying under reduced pressure. Above all, it is preferable to use the method (a) because of the simplicity in the manufacturing process.

The particle size of the water-absorbent resin particles obtained by adjusting the number of rotations of the stirrer during the polymerization reaction or granulation, or by adding a flocculant into the system after the polymerization reaction or in the early stage of drying. Can be adjusted.

In the production of water-absorbent resin particles, surface cross-linking of the surface portion (surface and vicinity of the surface) of the hydrogel polymer using a cross-linking agent in the drying step (moisture removing step) after the granulation step or the subsequent steps. Is preferably performed. By performing surface cross-linking, it is easy to control the water absorption characteristics. The surface cross-linking is preferably performed at a timing when the water-containing gel polymer has a specific water content. The time of surface cross-linking is preferably when the water content of the hydrogel polymer is 5 to 50% by mass, more preferably 10 to 40% by mass, and even more preferably 15 to 35% by mass.

The water content (mass%) of the water-containing gel polymer is calculated by the following formula.
Moisture content = [Ww / (Ww + Ws)] x 100
Ww: A flocculant, a surface cross-linking agent, etc. are mixed in an amount obtained by subtracting the amount of water discharged to the outside of the system by a step such as a drying step from the amount of water contained in the monomer aqueous solution before polymerization in the entire polymerization step. The amount of water in the hydrogel polymer to which the amount of water used as needed is added.
Ws: A solid content calculated from the amount of materials such as an ethylenically unsaturated monomer, a cross-linking agent, and an initiator that constitute a hydrogel polymer.

Examples of the cross-linking agent (surface cross-linking agent) for performing surface cross-linking include compounds having two or more reactive functional groups. Examples of the surface cross-linking agent include polyols such as ethylene glycol, propylene glycol, 1,4-butanediol, trimethylolpropane, glycerin, polyoxyethylene glycol, polyoxypropylene glycol, and polyglycerin; (poly) ethylene glycol diglycidyl ether. , (Poly) Glycerin diglycidyl ether, (Poly) Glycerin triglycidyl ether, Trimethylol propantriglycidyl ether (Poly) propylene glycol Polyglycidyl ether, (Poly) Oxetane Polyglycidyl ether and other polyglycidyl compounds; Epichlorohydrin, Haloepoxy compounds such as epibromhydrin and α-methylepichlorohydrin; isocyanate compounds such as 2,4-tolylene diisocyanate and hexamethylenediisocyanate; 3-methyl-3-oxetanemethanol, 3-ethyl-3-oxetanemethanol , 3-butyl-3-oxetane methanol, 3-methyl-3-oxetane ethanol, 3-ethyl-3-oxetane ethanol, 3-butyl-3-oxetane ethanol and other oxetane compounds; 1,2-ethylenebisoxazoline and the like. Examples thereof include oxazoline compounds; carbonate compounds such as ethylene carbonate; hydroxyalkylamide compounds such as bis [N, N-di (β-hydroxyethyl)] adipamide. The surface cross-linking agent may be used alone or in combination of two or more. As the surface cross-linking agent, a polyglycidyl compound is preferable, and (poly) ethylene glycol diglycidyl ether, (poly) glycerin diglycidyl ether, (poly) glycerin triglycidyl ether, (poly) propylene glycol polyglycidyl ether, and polyglycerol are used. At least one selected from the group consisting of polyglycidyl ether is more preferable.

The amount of the surface cross-linking agent used is preferably 0.01 to 20 mmol, preferably 0.05 to 10 to 1 mol of the ethylenically unsaturated monomer used for polymerization, from the viewpoint that suitable water absorption characteristics can be easily obtained. Millimole is more preferable, 0.1 to 5 mmol is further preferable, 0.15 to 2 mmol is particularly preferable, and 0.2 to 0.8 mmol is extremely preferable.

After surface cross-linking, water and a hydrocarbon dispersion medium are distilled off by a known method, and the polymer particles are dried under heating and reduced pressure to obtain polymer particles which are dry products with surface cross-linking.

The water-absorbent resin particles according to the present embodiment may be composed of only polymer particles, and for example, a gel stabilizer and a metal chelating agent (ethylenediaminetetraacetic acid and a salt thereof, diethylenetriamine-5 acetic acid and a salt thereof, for example, diethylenetriamine). 5 Sodium acetate, etc.), additional components such as a fluidity improver (lubricant) for polymer particles can be further included. Additional components may be placed inside the polymer particles, on the surface of the polymer particles, or both.

The water-absorbent resin particles may contain a plurality of inorganic particles arranged on the surface of the polymer particles. For example, by mixing the polymer particles and the inorganic particles, the inorganic particles can be arranged on the surface of the polymer particles. The inorganic particles may be silica particles such as amorphous silica.

When the water-absorbent resin particles include inorganic particles arranged on the surface of the polymer particles, the content of the inorganic particles may be in the following range based on the total mass of the polymer particles. The content of the inorganic particles may be 0.05% by mass or more, 0.1% by mass or more, 0.15% by mass or more, or 0.2% by mass or more. The content of the inorganic particles may be 5.0% by mass or less, 3.0% by mass or less, 1.0% by mass or less, 0.5% by mass or less, or 0.3% by mass or less.

The water-absorbent resin particles according to the present embodiment have excellent absorbency of body fluids such as urine and blood, and for example, disposable diapers, sanitary napkins, light incontinence pads, sanitary products such as tampons, pet sheets, dogs or cats. It can be applied to fields such as animal excrement treatment materials such as toilet formulations.

The water-absorbent resin particles are suitable for, for example, a water-absorbent sheet. FIG. 1 is a cross-sectional view showing an example of a water absorption sheet. The water absorbing sheet 50 shown in FIG. 1 has an absorber 10 and two

core wrap sheets

20a and 20b. The

core wrap sheets

20a and 20b are arranged on both sides of the absorber 10. In other words, the absorber 10 is arranged inside the

core wrap sheets

20a and 20b. The absorber 10 is held in shape by being sandwiched between the two

core wrap sheets

20a and 20b. The

core wrap sheets

20a and 20b may be two sheets, one folded sheet, or one bag body.

The water absorbing sheet 50 may further have an adhesive 21 interposed between the core wrap sheet 20a and the absorber 10. FIG. 2 is a plan view showing an example of an adhesive pattern formed on the core wrap sheet. The adhesive 21 shown in FIG. 2 forms a pattern composed of a plurality of linear portions arranged at intervals on the core wrap sheet 20a. However, the pattern of the adhesive 21 is not limited to this. The adhesive 21 may be interposed not only between the core wrap sheet 20a and the absorber 10 but also between the core wrap sheet 20b and the absorber 10. The adhesive 21 is not particularly limited, and may be, for example, a hot melt adhesive.

The absorber 10 has the water-absorbent resin particles 10a according to the above-described embodiment and the fiber layer 10b containing a fibrous material. The absorber 10 does not have to have the fiber layer 10b. The content of the water-absorbent resin particles in the absorber may be 70 to 100% by mass, 80 to 100% by mass, or 90 to 100% by mass based on the mass of the absorber 10.

The content of the water-absorbent resin particles in the absorber 10 is, for example, 30 g or more, 50 g or more, 70 g or more, 80 g or more, 90 g or more, 100 g or more, per ^{1 m 2 of the absorbent body 10 from the viewpoint of easily obtaining sufficient water absorption performance.} Alternatively, it may be 120 g or more, and may be 1000 g or less, 800 g or less, 700 g or less, 600 g or less, 500 g or less, 400 g or less, and 300 g or less.

The thickness of the absorber 10 is not particularly limited, but may be, for example, 20 mm or less, 15 mm or less, 10 mm or less, 5 mm or less, 4 mm or less, or 3 mm or less in a dry state, and may be 0.1 mm or more or 0.3 mm or less. It may be the above. The mass per unit area of the absorber 10 may be 1000 g / m ² or less, 800 g / m ² or less, 600 g / m ² or less, or 100 g / m ² or more.

The fibrous material constituting the fiber layer 10b can be, for example, a cellulosic fiber, a synthetic fiber, or a combination thereof. Examples of cellulosic fibers include crushed wood pulp, cotton, cotton linters, rayon and cellulosic acetate. Examples of synthetic fibers include polyamide fibers, polyester fibers, and polyolefin fibers. The fibrous material may be hydrophilic fibers (for example, pulp).

The absorber 10 (or fiber layer 10b) may further contain an inorganic powder (for example, amorphous silica), a deodorant, an antibacterial agent, a fragrance, and the like. When the water-absorbent resin particles 10a contain inorganic particles, the absorber 10 may contain inorganic powder in addition to the inorganic particles in the water-absorbent resin particles 10a.

The

core wrap sheets

20a and 20b may be, for example, a non-woven fabric. The two

core wrap sheets

20a and 20b can be the same or different non-woven fabrics. The non-woven fabric may be a non-woven fabric composed of short fibers (that is, staples) (short-fiber non-woven fabric) or a non-woven fabric composed of long fibers (that is, filaments) (long-fiber non-woven fabric). Staples are not limited to this, but generally may have a fiber length of several hundred mm or less.

The

core wrap sheets

20a and 20b are laminated including a thermal bond non-woven fabric, an air-through non-woven fabric, a resin bond non-woven fabric, a spunbond non-woven fabric, a melt blow non-woven fabric, an air-laid non-woven fabric, a spunlace non-woven fabric, a point bond non-woven fabric, or two or more kinds of non-woven fabrics selected from these. It can be a body.

The non-woven fabric used as the

core wrap sheets

20a and 20b can be a non-woven fabric formed of synthetic fibers, natural fibers, or a combination thereof. Examples of synthetic fibers include polyolefins such as polyethylene (PE) and polypropylene (PP), polyesters such as polyethylene terephthalate (PET), polytrimethylene terephthalate (PTT) and polyethylene naphthalate (PEN), polyamides such as nylon, and Examples thereof include fibers containing a synthetic resin selected from rayon. Examples of natural fibers include fibers containing cotton, silk, hemp, or pulp (cellulose). The fibers forming the non-woven fabric may be polyolefin fibers, polyester fibers or a combination thereof. The

core wrap sheets

20a and 20b may be tissue paper.

In the water absorbing sheet 50, for example, the water absorbing resin particles 10a or a mixture containing the water absorbing resin particles 10a and the fibrous material is sandwiched between the

core wrap sheets

20a and 20b, and the formed structure is heated as necessary. It can be obtained by the method of pressurizing. If necessary, the adhesive 21 is arranged between the

core wrap sheets

20a and 20b and the water-absorbent resin particles 10a or a mixture containing the same.

The water absorption sheet 50 may have two layers of the absorber 10 by further providing the absorber 10 and the core wrap sheet on the surface of the core wrap sheet 20b opposite to the surface on which the absorber 10 exists. Good. Since the water-absorbent resin particles according to the present embodiment are particularly excellent in suppressing leakage, they have high absorption performance even in a water-absorbent sheet having a single-layer absorption layer, and can suppress liquid leakage.

The content of the water-absorbent resin particles in the water-absorbent sheet 50 is, for example, 30 g or more, 50 g or more, 70 g or more, 80 g or more, 90 g or more, 100 g or more, per ^{1 m 2 of the absorber 10 from the viewpoint of easily obtaining sufficient water absorption performance.} Alternatively, it may be 120 g or more, and may be 1000 g or less, 800 g or less, 700 g or less, 600 g or less, 500 g or less, 400 g or less, and 300 g or less.

The water absorption sheet 50 is used, for example, for producing various absorbent articles. Examples of absorbent articles include diapers (eg paper diapers), toilet training pants, incontinence pads, sanitary materials (sanitary napkins, tampons, etc.), sweat pads, pet sheets, toilet components, and animal waste treatment materials. Can be mentioned.

FIG. 3 is a cross-sectional view showing an example of an absorbent article. The absorbent article 100 shown in FIG. 3 includes a water absorbing sheet 50, a liquid permeable sheet 30, and a liquid permeable sheet 40. In other words, the water absorbing sheet 50 is sandwiched between the liquid permeable sheet 30 and the liquid impermeable sheet 40.

The liquid permeable sheet 30 is arranged at the position of the outermost layer on the side where the liquid to be absorbed enters. The liquid permeable sheet 30 is arranged on the outside of the core wrap sheet 20b in contact with the core wrap sheet 20b. The liquid permeable sheet 40 is arranged at the position of the outermost layer on the side opposite to the liquid permeable sheet 30 in the absorbent article 100. The liquid impermeable sheet 40 is arranged on the outside of the core wrap sheet 20a in a state of being in contact with the core wrap sheet 20a. The liquid permeable sheet 30 and the liquid permeable sheet 40 have a main surface wider than the main surface of the water absorbing sheet 50, and the outer edges of the liquid permeable sheet 30 and the liquid permeable sheet 40 are absorbers. It extends around 10 and the

core wrap sheets

20a and 20b. However, the magnitude relationship between the absorbent body 10, the

core wrap sheets

20a and 20b, the liquid permeable sheet 30, and the liquid permeable sheet 40 is not particularly limited, and is appropriately adjusted according to the use of the absorbent article and the like. ..

The liquid permeable sheet 30 may be a non-woven fabric. The non-woven fabric used as the liquid permeable sheet 30 may have appropriate hydrophilicity from the viewpoint of the liquid absorption performance of the absorbent article. From this point of view, the liquid permeable sheet 30 is obtained from the pulp and paper test method No. 1 by the Paper and Pulp Technology Association. A non-woven fabric having a hydrophilicity of 5 to 200 measured according to the measuring method of 68 (2000) may be used. The hydrophilicity of the non-woven fabric may be 10 to 150. Pulp and paper test method No. For details of 68, for example, WO2011 / 086843 can be referred to.

The non-woven fabric having hydrophilicity may be formed of fibers showing appropriate hydrophilicity such as rayon fiber, or obtained by hydrophilizing a hydrophobic chemical fiber such as polyolefin fiber or polyester fiber. It may be formed of rayon fibers. Examples of a method for obtaining a non-woven fabric containing hydrophobic chemical fibers that have been hydrophilized include a method for obtaining a non-woven fabric by a spunbond method using a mixture of hydrophobic chemical fibers and a hydrophilic agent, and hydrophobic chemistry. Examples thereof include a method of accommodating a hydrophilic agent when producing a spunbonded non-woven fabric from fibers, and a method of impregnating a spunbonded non-woven fabric obtained by using hydrophobic chemical fibers with a hydrophilicizing agent. Examples of the hydrophilizing agent include anionic surfactants such as aliphatic sulfonates and higher alcohol sulfates, cationic surfactants such as quaternary ammonium salts, polyethylene glycol fatty acid esters, polyglycerin fatty acid esters, and sorbitan fatty acids. Nonionic surfactants such as esters, silicone-based surfactants such as polyoxyalkylene-modified silicones, and stain-releasing agents made of polyester-based, polyamide-based, acrylic-based, and urethane-based resins are used.

The amount of texture (mass per unit area) of the non-woven fabric used as the liquid permeable sheet 30 is from the viewpoint of imparting good liquid permeability, flexibility, strength and cushioning property to the absorbent article, and the liquid of the absorbent article. From the viewpoint of increasing the permeation rate, it may be 5 to 200 g / m ² , 8 to 150 g / m ² , or 10 to 100 g / m ² . The thickness of the liquid permeable sheet 30 may be 20 to 1400 μm, 50 to 1200 μm, or 80 to 1000 μm.

The liquid impermeable sheet 40 prevents the liquid absorbed by the absorber 10 from leaking to the outside from the liquid impermeable sheet 40 side. The liquid impermeable sheet 40 may be a resin sheet or a non-woven fabric. The resin sheet may be a sheet made of a synthetic resin such as polyethylene, polypropylene, or polyvinyl chloride. The non-woven fabric may be a spunbond / meltblow / spunbond (SMS) non-woven fabric in which a water-resistant melt-blow non-woven fabric is sandwiched between high-strength spunbond non-woven fabrics. The liquid impermeable sheet 40 may be a composite sheet of a resin sheet and a non-woven fabric (for example, a spunbonded non-woven fabric or a spunlaced non-woven fabric). The liquid impermeable sheet 40 may have breathability from the viewpoint that stuffiness at the time of wearing is reduced and discomfort given to the wearer can be reduced. As the liquid impermeable sheet 40 having breathability, for example, a sheet of low density polyethylene (LDPE) resin can be used.

From the viewpoint of ensuring flexibility so as not to impair the wearing feeling of the absorbent article, the basis weight (mass per unit area) of the liquid impermeable sheet 40 may be ^{10 to 50 g / m 2.}

The absorbent article 100 can be manufactured, for example, by a method including arranging the water absorbing sheet 50 between the liquid permeable sheet 30 and the liquid permeable sheet 40. A laminated body in which the liquid permeable sheet 40, the water absorbing sheet 50, and the liquid permeable sheet 30 are laminated in this order is pressurized as necessary. Alternatively, the liquid permeable sheet 30, the core wrap sheet 20b, the water-absorbent resin particles 10a, or the mixture containing the water-absorbent resin particles 10a and the fibrous material, and the core wrap sheet 20a and the liquid impermeable sheet 40 are used. The absorbent article 100 can also be obtained by arranging in this order and pressurizing the formed structure while heating if necessary. A non-woven fabric may be arranged between the liquid permeable sheet 30 and the core wrap sheet 20b for the purpose of diffusing the liquid.

Hereinafter, the content of the present invention will be described in more detail with reference to Examples and Comparative Examples, but the present invention is not limited to the following Examples.

<Example 1>
[Production of hydrogel polymer a]
A round-bottomed cylindrical separable flask with an inner diameter of 11 cm and a capacity of 2 L, equipped with a reflux condenser, a dropping funnel, a nitrogen gas introduction pipe, and a stirring blade having four inclined paddle blades with a blade diameter of 5 cm in two stages as a stirrer. Prepared. In the flask, 293 g of n-heptane as a hydrocarbon dispersion medium is added, and 0.736 g of a maleic anhydride-modified ethylene-propylene copolymer (Mitsui Chemicals, Inc., High Wax 1105A) is added and mixed as a polymer-based dispersant. did. The dispersant was dissolved in n-heptane by heating the mixture in the flask to 80 ° C. with stirring, and then cooled to 50 ° C.

In a beaker with an internal volume of 300 mL, 92.0 g (1.03 mol) of an 80.5 mass% acrylic acid aqueous solution as a water-soluble ethylenically unsaturated monomer was placed, and while being cooled from the outside, 20.9 mass% was added. Neutralization of 75 mol% was carried out by dropping 147.7 g of an aqueous sodium hydroxide solution. Then, 0.092 g of hydroxylethyl cellulose (Sumitomo Seika Co., Ltd., HEC AW-15F) as a thickener, 0.0736 g (0.272 mmol) of potassium persulfate as a water-soluble radical polymerization initiator, and ethylene as an internal cross-linking agent. A first-stage monomer aqueous solution was prepared by adding 0.010 g (0.057 mmol) of glycol diglycidyl ether and dissolving it.

The first-stage monomer aqueous solution was added to the flask and stirred for 10 minutes. Separately, 0.736 g of sucrose stearic acid ester (Mitsubishi Chemical Foods Co., Ltd., Ryoto Sugar Ester S-370, HLB: 3) as a surfactant is dissolved in 6.62 g of n-heptane by heating to dissolve the surfactant solution. Was prepared. The surfactant solution was further added to the flask, and the inside of the system was sufficiently replaced with nitrogen while stirring at a stirring speed of 550 rpm. Then, the flask was immersed in a water bath at 70 ° C. for heating, and polymerization was carried out for 60 minutes to obtain a slurry containing a spherical hydrogel polymer a.

[Production of hydrogel polymer b]
Round-bottomed cylindrical separable flask with four side wall baffles with an inner diameter of 11 cm and an internal volume of 2 L equipped with a reflux condenser, a dropping funnel, a nitrogen gas introduction pipe, and a stirrer (baffle length: 10 cm, baffle width: 7 mm) ) Was prepared. As the stirrer, one having a stirrer blade having two stages of four inclined paddle blades (surface treated with fluororesin) having a blade diameter of 5 cm was used. To the flask, 451.4 g of n-heptane as a hydrocarbon dispersion medium was added, and 1.29 g of sorbitan monolaurate (Nonion LP-20R, HLB value: 8.6, manufactured by NOF CORPORATION) was added as a surfactant. The mixture was obtained by addition. The sorbitan monolaurate was dissolved in n-heptane by heating the mixture to 50 ° C. while stirring at a stirring speed of 300 rpm. The mixture was then cooled to 40 ° C.

Next, 92.0 g (acrylic acid: 1.03 mol) of an 80.5 mass% acrylic acid aqueous solution was placed in an Erlenmeyer flask having an internal volume of 500 mL. Subsequently, 147.7 g of a 20.9 mass% sodium hydroxide aqueous solution was added dropwise from the outside while cooling with ice to neutralize the acrylic acid, thereby obtaining an aqueous solution of a partially neutralized acrylic acid. Next, a monomer aqueous solution was prepared by adding 0.1012 g (0.374 mmol) of potassium persulfate as a water-soluble radical polymerization initiator to the acrylic acid partially neutralized aqueous solution and then dissolving the mixture.

After adding the above-mentioned monomer aqueous solution to the above-mentioned flask, the inside of the system was sufficiently replaced with nitrogen. Then, while stirring the mixture in the flask at a rotation speed of 700 rpm of the stirrer, the flask is immersed in a water bath at 70 ° C. and held for 60 minutes to complete the polymerization. A slurry containing b was obtained.

[Granulation]
A round-bottomed cylindrical separable flask having an inner diameter of 11 cm and a volume of 2 L equipped with a reflux condenser, a dropping funnel, a nitrogen gas introduction pipe, and a stirrer was prepared. The stirrer was equipped with a stirrer blade 200 whose outline is shown in FIG. The stirring blade 200 includes a shaft 200a and a flat plate portion 200b. The flat plate portion 200b is welded to the shaft 200a and has a curved tip. The flat plate portion 200b is formed with four slits S extending along the axial direction of the shaft 200a. The four slits S are arranged in the width direction of the flat plate portion 200b, the width of the two inner slits S is 1 cm, and the width of the two outer slits S is 0.5 cm. The length of the flat plate portion 200b is about 10 cm, and the width of the flat plate portion 200b is about 6 cm.

In the flask, a slurry containing 220 g of n-heptane and a slurry containing a hydrogel polymer a filtered from n-heptane using a JIS standard sieve having a mesh size of 75 μm, and a JIS standard sieve having a mesh size of 75 μm were used. -185 g of a slurry containing the hydrogel polymer b filtered from heptane was added, and the slurry was immersed in an oil bath at 80 ° C. while stirring at a stirring speed of 1000 rpm. Separately, a dispersion was prepared by dispersing 0.092 g of amorphous silica (Oriental Silicas Corporation, Toxile NP-S) as a powdery inorganic flocculant in 100 g of n-heptane. The dispersion liquid was added to the flask and mixed for 10 minutes to aggregate the hydrogel polymer a and the hydrogel polymer b. Mixing ratio of hydrogel polymer a and hydrogel polymer b (theoretical ratio calculated based on the results of measuring the content of water-absorbent resin solids contained in each slurry by separately heating and drying, and so on. ) Is 50:50.

After aggregation, the flask was immersed in an oil bath set at 125 ° C., and 100.0 g of water was extracted from the system while refluxing n-heptane by azeotropic distillation of n-heptane and water. Then, 4.14 g (0.475 mmol) of a 2% by mass ethylene glycol diglycidyl ether aqueous solution was added to the flask as a surface cross-linking agent, and the flask was kept at 83 ° C. for 2 hours.

Then, n-heptane and water were heated in an oil bath at 125 ° C. to evaporate and dry to obtain a dried product of polymer particles. The polymer particles were passed through a sieve having an opening of 850 μm to obtain 59.9 g of water-absorbent resin particles A. The medium particle size of the water-absorbent resin particles A was 486 μm. Each of the water-absorbent resin particles A had a spherical portion and an irregularly shaped portion.

<Example 2>
The amount of 2% by mass ethylene glycol diglycidyl ether aqueous solution added after aggregation was changed to 8.28 g (0.951 mmol), and the mixture was extracted by azeotropic distillation of n-heptane and water. 51.8 g of water-absorbent resin particles B were obtained in the same manner as in Example 1 except that the amount of water was changed to 101.6 g. The medium particle size of the water-absorbent resin particles B was 517 μm. Each of the water-absorbent resin particles B had a spherical portion and an irregularly shaped portion.

<Example 3>
The amount of the hydrogel polymer a added during granulation was changed to 100 g, the amount of the hydrogel polymer b was changed to 222 g, and the water extracted by azeotropic distillation of n-heptane and water. 75.6 g of water-absorbent resin particles C was obtained in the same manner as in Example 1 except that the amount was changed to 114.0 g. The mixing ratio (mass basis) of the hydrogel polymer a and the hydrogel polymer b is 40:60. The medium particle size of the water-absorbent resin particles was 453 μm. Each of the water-absorbent resin particles C had a spherical portion and an irregularly shaped portion. A scanning electron micrograph of the water-absorbent resin particles C is shown in FIG.

<Example 4>
The amount of the hydrogel polymer a added during granulation was changed to 75 g, the amount of the hydrogel polymer b was changed to 259 g, and the water extracted by azeotropic distillation of n-heptane and water. 69.9 g of water-absorbent resin particles D was obtained in the same manner as in Example 1 except that the amount was changed to 106.3 g. The mixing ratio (mass basis) of the hydrogel polymer a and the hydrogel polymer b is 30:70. The medium particle size of the water-absorbent resin particles was 424 μm. Each of the water-absorbent resin particles D had a spherical portion and an irregularly shaped portion.

<Comparative example 1>
[Manufacturing of spherical particles]
A slurry containing the hydrogel polymer was obtained in the same manner as in the hydrogel polymer a of Example 1. The flask containing the slurry was immersed in an oil bath set at 125 ° C., and 117.8 g of water was extracted from the system while refluxing n-heptane by azeotropic distillation of n-heptane and water. Then, 4.42 g (0.507 mmol) of a 2% by mass ethylene glycol diglycidyl ether aqueous solution was added to the flask as a surface cross-linking agent, and the flask was kept at 83 ° C. for 2 hours.

Then, n-heptane and water were heated in an oil bath at 125 ° C. to evaporate and dry to obtain a dried product of polymer particles. The polymer particles were passed through a sieve having an opening of 850 μm to obtain 90.5 g of spherical water-absorbent resin particles E. The medium particle size of the water-absorbent resin particles E was 55 μm.

[Manufacturing of amorphous particles]
A slurry containing the hydrogel polymer was obtained in the same manner as in the hydrogel polymer b of Example 1. The flask containing the slurry was immersed in an oil bath at 125 ° C., and 96.7 g of water was extracted from the system while refluxing n-heptane by azeotropic distillation of n-heptane and water. Then, 4.14 g (ethylene glycol diglycidyl ether: 0.475 mmol) of 2% by mass of an ethylene glycol diglycidyl ether aqueous solution was added as a surface cross-linking agent, and the mixture was maintained at an internal temperature of 83 ± 2 ° C. for 2 hours.

Then, water and n-heptane were heated in an oil bath at 125 ° C. to evaporate, and dried until almost no evaporation from the system was distilled off to obtain a dried product of polymer particles. By passing the polymer particles through a sieve having an opening of 850 μm, 90.6 g of water-absorbent resin particles F having an indefinite shape were obtained. The medium particle size of the water-absorbent resin particles F was 156 μm.

Comparative Example 1 was a mixture of water-absorbent resin particles E and water-absorbent resin particles F at a mass ratio of 50:50.

<Comparative example 2>
[Manufacturing of spherical particles]
A round-bottomed cylindrical separable flask with an inner diameter of 11 cm and a capacity of 2 L, equipped with a reflux condenser, a dropping funnel, a nitrogen gas introduction pipe, and a stirring blade having four inclined paddle blades with a blade diameter of 5 cm in two stages as a stirrer. Prepared. In the flask, 293 g of n-heptane as a hydrocarbon dispersion medium is added, and 0.736 g of a maleic anhydride-modified ethylene-propylene copolymer (Mitsui Chemicals, Inc., High Wax 1105A) is added and mixed as a polymer-based dispersant. did. The dispersant was dissolved in n-heptane by heating the mixture in the flask to 80 ° C. with stirring, and then cooled to 50 ° C.

In a beaker with an internal volume of 300 mL, 92.0 g (1.03 mol) of an 80.5 mass% acrylic acid aqueous solution as a water-soluble ethylenically unsaturated monomer was placed, and while being cooled from the outside, 20.9 mass% was added. Neutralization of 75 mol% was carried out by dropping 147.7 g of an aqueous sodium hydroxide solution. After that, 1.38 g of hydroxylethyl cellulose (Sumitomo Seika Co., Ltd., HEC AW-15F) was used as a thickener, and 0.110 g of 2,2'-azobis (2-amidinopropane) dihydrochloride as a water-soluble radical polymerization initiator (. 0.407 mmol) and 0.0046 g (0.026 mmol) of ethylene glycol diglycidyl ether as an internal cross-linking agent were added to the beaker and dissolved to prepare a first-stage monomer aqueous solution.

The first-stage monomer aqueous solution was added to the flask and stirred for 10 minutes. Separately, 0.736 g of sucrose stearic acid ester (Mitsubishi Chemical Foods Co., Ltd., Ryoto Sugar Ester S-370, HLB: 3) as a surfactant is dissolved in 6.62 g of n-heptane by heating to dissolve the surfactant solution. Was prepared. The surfactant solution was further added to the flask, and the inside of the system was sufficiently replaced with nitrogen while stirring at a stirring speed of 400 rpm. Then, the flask was immersed in a water bath at 70 ° C. and heated, and polymerization was carried out for 60 minutes to obtain a slurry containing a hydrogel polymer.

The flask containing the slurry was immersed in an oil bath set at 125 ° C., and 108.2 water was extracted from the system while refluxing n-heptane by azeotropic distillation of n-heptane and water. Then, 4.60 g (0.528 mmol) of a 2% by mass ethylene glycol diglycidyl ether aqueous solution was added to the flask as a surface cross-linking agent, and the flask was kept at 83 ° C. for 2 hours.

Then, n-heptane and water were heated in an oil bath at 125 ° C. to evaporate and dry to obtain a dried product of polymer particles. The polymer particles were passed through a sieve having an opening of 850 μm to obtain 91.2 spherical water-absorbent resin particles G. The medium particle size of the water-absorbent resin particles G was 381 μm.

[Manufacturing of amorphous particles]
A hydrogel polymer was obtained in the same manner as in the hydrogel polymer b of Example 1. Separately, 0.092 g of amorphous silica (Oriental Silicas Corporation, Toxile NP-S) as a powdery inorganic flocculant was dispersed in 100 g of n-heptane to obtain a dispersion liquid. While stirring at a rotation speed of 1000 rpm of a stirrer, the above dispersion was added to a polymerization solution containing a hydrogel polymer, n-heptane and a surfactant, and mixed for 10 minutes. Then, the flask was immersed in an oil bath at 125 ° C., and 98.0 g of water was extracted from the system while refluxing n-heptane by azeotropic distillation of n-heptane and water. Then, 4.14 g (ethylene glycol diglycidyl ether: 0.475 mmol) of 2% by mass of an ethylene glycol diglycidyl ether aqueous solution was added to the flask as a surface cross-linking agent, and the mixture was kept at an internal temperature of 83 ± 2 ° C. for 2 hours. ..

Then, water and n-heptane were heated in an oil bath at 125 ° C. to evaporate, and dried until almost no evaporation from the system was distilled off to obtain a dried product of polymer particles. By passing the polymer particles through a sieve having an opening of 850 μm, 90.1 g of water-absorbent resin particles H having an indefinite shape was obtained. The medium particle size of the water-absorbent resin particles H was 352 μm.

Comparative Example 2 was a mixture of water-absorbent resin particles G and water-absorbent resin particles H at a mass ratio of 50:50.

<Comparative example 3>
The water-absorbent resin particles H having an indefinite shape obtained in Comparative Example 2 were used alone as Comparative Example 3.

<Comparative example 4>
A round-bottomed cylindrical separable flask with an inner diameter of 11 cm and a capacity of 2 L, equipped with a reflux condenser, a dropping funnel, a nitrogen gas introduction pipe, and a stirring blade having four inclined paddle blades with a blade diameter of 5 cm in two stages as a stirrer. Prepared. In the flask, 293 g of n-heptane as a hydrocarbon dispersion medium is added, and 0.736 g of a maleic anhydride-modified ethylene-propylene copolymer (Mitsui Chemicals, Inc., High Wax 1105A) is added and mixed as a polymer-based dispersant. did. The dispersant was dissolved in n-heptane by heating the mixture in the flask to 80 ° C. with stirring, and then cooled to 50 ° C.

In a beaker with an internal volume of 300 mL, 92.0 g (1.03 mol) of an 80.5 mass% acrylic acid aqueous solution as a water-soluble ethylenically unsaturated monomer was placed, and while being cooled from the outside, 20.9 mass% was added. Neutralization of 75 mol% was carried out by dropping 147.7 g of an aqueous sodium hydroxide solution. Then, 0.092 g of hydroxylethyl cellulose (Sumitomo Seika Co., Ltd., HEC AW-15F) as a thickener, 0.0736 g (0.272 mmol) of potassium persulfate as a water-soluble radical polymerization initiator, and ethylene as an internal cross-linking agent. A first-stage monomer aqueous solution was prepared by adding 0.010 g (0.057 mmol) of glycol diglycidyl ether to the above beaker and dissolving it.

The first-stage monomer aqueous solution was added to the flask and stirred for 10 minutes. Separately, 0.736 g of sucrose stearic acid ester (Mitsubishi Chemical Foods Co., Ltd., Ryoto Sugar Ester S-370, HLB: 3) as a surfactant is dissolved in 6.62 g of n-heptane by heating to dissolve the surfactant solution. Was prepared. The surfactant solution was further added to the flask, and the inside of the system was sufficiently replaced with nitrogen while stirring at a rotation speed of a stirrer of 500 rpm. Then, the flask was immersed in a water bath at 70 ° C. for heating, and polymerization was carried out for 60 minutes to obtain a first-stage polymerization slurry liquid.

128.8 g (1.44 mol) of an 80.5 mass% acrylic acid aqueous solution as a water-soluble ethylenically unsaturated monomer was placed in a beaker having an internal volume of 500 mL, and 27 mass% sodium hydroxide was cooled from the outside. Neutralization of 75 mol% was carried out by dropping 159.0 g of the aqueous solution. Then, 0.090 g (0.333 mmol) of potassium persulfate as a water-soluble radical polymerization initiator and 0.0116 g (0.067 mmol) of ethylene glycol diglycidyl ether as an internal cross-linking agent were added to the beaker to dissolve them. A second-stage monomer aqueous solution was prepared.

After cooling the inside of the flask system to 25 ° C. while stirring at a stirring speed of 1000 rpm, the entire amount of the monomer aqueous solution in the second stage was added to the polymerized slurry solution in the first stage. Then, the inside of the system was replaced with nitrogen for 30 minutes, the flask was again immersed in a water bath at 70 ° C. for heating, and the polymerization reaction was carried out for 60 minutes to obtain a slurry containing a hydrogel polymer.

The flask containing the above slurry was immersed in an oil bath set at 125 ° C., and 248.2 g of water was extracted from the system while refluxing n-heptane by azeotropic distillation of n-heptane and water. Then, 4.42 g (0.507 mmol) of a 2% by mass ethylene glycol diglycidyl ether aqueous solution was added to the flask as a surface cross-linking agent, and the flask was kept at 83 ° C. for 2 hours.

Then, n-heptane and water were heated in an oil bath at 125 ° C. to evaporate and dry to obtain a dried product of polymer particles. The polymer particles are passed through a sieve having an opening of 850 μm, and 0.2% by mass of amorphous silica (Oriental Silicas Corporation, Toxile NP-S) with respect to the mass of the polymer particles is mixed with the polymer particles. , 230.8 g of water-absorbent resin particles I having a shape in which spherical primary particles were aggregated were obtained. The medium particle size of the water-absorbent resin particles I was 363 μm.

<Roughness by shape>
With respect to the water-absorbent resin particles of Example 1, the degree of unevenness for each shape was measured by the following method using a laser microscope (manufactured by KEYENCE CORPORATION, VK-X150). The water-absorbent resin particles A obtained in Example 1 were further classified, and particles having a medium particle diameter in the range of 300 to 355 μm were used as shape-specific unevenness measurement samples. The measurement sample was in a dry state before water absorption and was stored at a humidity of 40%. For the illumination of the shape analysis laser microscope, the observation application was set to "bright field" and the shape measurement was set to "dark field". The magnification of the lens was set to 20 times. A 3D image of the sample was taken with a laser color confocal image.

A circular profile line (circumference of about 100 to 105 μm) having a diameter in the range of 31.8 to 33.4 μm was set on the acquired image of the water-absorbent resin particles. The unevenness of the particle surface is measured along this profile line. In one particle, spherical parts were measured at 5 points and irregularly shaped parts were measured at 5 places. When measuring the spherical portion, the profile line was set so as not to protrude from the spherical portion of one sphere, and the boundary between the spheres was not included. When measuring the irregularly shaped portion, only the irregularly shaped portion was set so that the profile line did not include the spherical portion.

90% or more of the total length of the waveform curve showing the unevenness of the particles measured along the profile line was extracted, and the maximum height roughness Rz at the extracted portion was measured. Specifically, the average line of the waveform curve in the extracted portion is drawn, and the sum of the absolute values of the highest peak elevation and the lowest valley bottom elevation of the extracted portion of the waveform curve is maximized with reference to the average line. It was calculated as height roughness Rz. The average line is automatically set so that the area surrounded by the average line and the waveform curve above the average line and the area surrounded by the average line and the waveform curve below the average line are equal. For each of the spherical part and the irregular shape part, the average of the measured values at five places was obtained as the degree of unevenness for each shape. The results are shown in Table 1.

Among the water-absorbent resin particles of Example 1, the spherical portion had a shape-specific unevenness of 1 μm or more and 20 μm or less, and the irregular shape portion had a shape-specific unevenness of more than 20 μm and 200 μm or less. As for the water-absorbent resin particles of Examples 2 to 4, since the spherical portion and the irregularly shaped portion each have substantially the same shape as the water-absorbent resin particles of Example 1, the degree of unevenness for each shape is determined in Example 1. Shows substantially the same value as.

The details of the laser microscope used are as follows.
Made by KEYENCE CORPORATION, VK-X150 (with the following functions)
Observation image: Ultra-high-definition color CCD image, 16-bit laser color cofocal image, cofocal + ND filter optical system, C-laser differential interference image Measurement laser light source: Wavelength: Red semiconductor laser 658 nm, maximum output: 0.95 mW, class : Class 2 (JISC6802)
Microscope function: Autofocus function, Depth synthesis function, Dimension measurement function, Automatic edge detection function, HDR function Analysis function: Shape analysis function, Profile / Step / Angle volume / Surface surface / R / Roughness (JIS / ISO) / Film Thickness (line / surface), teaching function, automatic measurement function, comparative analysis function, template function Software: Autofocus software, pixel shift software, automatic upper / lower limit setting software

<Average unevenness of particles>
With respect to the water-absorbent resin particles of Examples 1, 3 and 4, and Comparative Examples 2 and 4, the average unevenness of the particles was measured by the following method using a digital microscope (manufactured by KEYENCE CORPORATION, VHX-5000).

The water-absorbent resin particles of the examples or comparative examples were further classified, and the particles having a medium particle size in the range of 300 to 355 μm were used as the unevenness measurement sample. The measurement sample was in a dry state before use and was stored at a humidity of 40%. The settings of the digital microscope were set to epi-illumination: 10, ring illumination, and VH-Z20R lens magnification: 200 times. Depth synthesis was performed using "quick synthesis & 3D" as the program of the above digital microscope, and a 3D image of the surface of the water-absorbent resin particles was taken. A circular profile line (circumference of about 850 to 1000 μm) having a diameter in the range of 270 to 320 μm was set on the acquired image of the water-absorbent resin particles. At the time of setting, the center of the circular profile line was aligned with the center of the water-absorbent resin particles, and the profile line was prevented from protruding from the water-absorbent resin particles.

90% or more of the total length of the waveform curve showing the unevenness of the particles measured along the profile line was extracted, and the average line of the waveform curve in the extracted portion was drawn. In the average line, the area surrounded by the average line and the waveform curve above the average line and the area surrounded by the average line and the waveform curve below the average line are almost equal (0.95 ≤ one ÷ other ≤ 1.05). ). FIG. 6 is an example of a graph showing a waveform curve and an average line. The line indicated by the arrowhead in the graph is the average line. The broken line in the vertical direction is a line indicating the range of the sampling points of the waveform curve. The average line is drawn so as to connect the points where the waveform curve and the vertical broken line intersect. The sampling point of the waveform curve is set at a position where the average line satisfies the above area condition.

Of the extracted parts of the waveform curve, the sum of the absolute values of the highest peak elevation and the lowest valley bottom elevation based on the average line was taken as the degree of unevenness. The degree of unevenness was measured for 12 samples, and the average value of 10 points excluding the maximum value and the minimum value was taken as the average degree of unevenness of the particles.

The details of the digital microscope used are as follows.
・ VHX-5000 manufactured by KEYENCE CORPORATION (with the following functions)
Video engine (23-inch IPS full HD LCD built-in), live depth composition function, real-time super-resolution HDR function, shooting setting reproduction function, ultra-high-speed image connection function, 50-frame CMOS camera (high-spec multi-scan camera head (VHX-5100)) )))
TRIPLE'R lens (ultra-compact high-performance Z lens TR [20-200] (VH-Z20T), lens joint for VH-Z20T (VHX-J20T))
・ Free-angle observation stand (XYZ electric stage (VHX-S550))
・ 3D shape measurement software (VHX-H4M)

<Evaluation of water-absorbent resin particles>
For the water-absorbent resin particles of the above Examples and Comparative Examples or a mixture thereof, the average particle size, the amount of physiological saline water retained, the amount of water absorbed under load, the water absorption rate, and the non-pressurized DW were measured.

[Medium particle size]
The medium particle size of the particles was measured in an environment of room temperature (25 ± 2 ° C.) and humidity of 50 ± 10% according to the following procedure. Using a continuous fully automatic sonic vibration type sieving measuring instrument (Robot Shifter RPS-205, manufactured by Seishin Enterprise Co., Ltd.), using JIS standard 850 μm, 600 μm, 500 μm, 425 μm, 300 μm, 250 μm and 180 μm sieves, and a saucer. , The particle size distribution of 5 g of water-absorbent resin particles was measured. The relationship between the mesh size of the sieve and the integrated value of the mass percentage of the particles remaining on the sieve was plotted on a logarithmic probability paper by integrating on the sieve in order from the one having the largest particle size with respect to this particle size distribution. By connecting the plots on the probability paper with a straight line, the particle size corresponding to the cumulative mass percentage of 50% by mass was obtained as the medium particle size.

[Water retention]
The water retention amount (room temperature, 25 ± 2 ° C.) of the physiological saline of the water-absorbent resin particles was measured by the following procedure. First, a cotton bag (Membroad No. 60, width 100 mm × length 200 mm) weighing 2.0 g of water-absorbent resin particles was placed in a beaker having an internal volume of 500 mL. After pouring 500 g of physiological saline into a cotton bag containing water-absorbent resin particles at a time so that mamako cannot be made, tie the upper part of the cotton bag with a rubber band and let it stand for 30 minutes to swell the water-absorbent resin particles. I let you. After 30 minutes, the cotton bag was dehydrated for 1 minute using a dehydrator (manufactured by Kokusan Co., Ltd., product number: H-122) set to have a centrifugal force of 167 G, and then contained a swollen gel after dehydration. The mass Wa [g] of the cotton bag was measured. The same operation was performed without adding the water-absorbent resin particles, the empty mass Wb [g] of the cotton bag when wet was measured, and the water retention amount of the physiological saline of the water-absorbent resin particles was calculated from the following formula. The results are shown in Table 3.
Water retention [g / g] = (Wa-Wb) /2.0

[Water absorption under load]
The amount of water absorption (room temperature, 25 ° C. ± 2 ° C.) of the physiological saline under the load of the water-absorbent resin particles was measured using the measuring device Y shown in FIG. 7. The measuring device Y is composed of a burette unit 61, a conduit 62, a measuring table 63, and a measuring unit 64 placed on the measuring table 63. The burette portion 61 has a burette 61a extending in the vertical direction, a rubber stopper 61b arranged at the upper end of the burette 61a, a cock 61c arranged at the lower end of the burette 61a, and one end extending into the burette 61a in the vicinity of the cock 61c. It has an air introduction pipe 61d and a cock 61e arranged on the other end side of the air introduction pipe 61d. The conduit 62 is attached between the burette portion 61 and the measuring table 63. The inner diameter of the conduit 62 is 6 mm. A hole having a diameter of 2 mm is formed in the central portion of the measuring table 63, and the conduit 62 is connected to the hole. The measuring unit 64 has a cylinder 64a (made of acrylic resin), a nylon mesh 64b adhered to the bottom of the cylinder 64a, and a weight 64c. The inner diameter of the cylinder 64a is 20 mm. The opening of the nylon mesh 64b is 75 μm (200 mesh). Then, at the time of measurement, the water-absorbent resin particles 65 to be measured are uniformly sprinkled on the nylon mesh 64b. The diameter of the weight 64c is 19 mm, and the mass of the weight 64c is 119.6 g. The weight 64c is placed on the water-absorbent resin particles 65, and a load of 4.14 kPa can be applied to the water-absorbent resin particles 65.

After 0.100 g of the water-absorbent resin particles 65 were placed in the cylinder 64a of the measuring device Y, the weight 64c was placed and the measurement was started. Since the same volume of air as the physiological saline absorbed by the water-absorbent resin particles 65 is quickly and smoothly supplied to the inside of the burette 61a from the air introduction pipe, the water level of the physiological saline inside the burette 61a is reduced. However, the amount of physiological saline absorbed by the water-absorbent resin particles 65 is obtained. The scale of the burette 61a is engraved from top to bottom in increments of 0 mL to 0.5 mL, and the scale Va of the burette 61a before the start of water absorption and the burette 61a 60 minutes after the start of water absorption are used as the water level of the physiological saline. The scale Vb of was read, and the amount of water absorption under load was calculated from the following formula. The results are shown in Table 3.
Water absorption under load [mL / g] = (Vb-Va) /0.1

[Water absorption rate]
The water absorption rate of the physiological saline of the water-absorbent resin particles was measured by the following procedure based on the Vortex method. First, 50 ± 0.1 g of a 0.9 mass% sodium chloride aqueous solution (physiological saline) adjusted to a temperature of 25 ± 0.2 ° C. in a constant temperature water tank was weighed in a beaker having an internal volume of 100 mL. Next, a vortex was generated by stirring at a rotation speed of 600 rpm using a magnetic stirrer bar (8 mmφ × 30 mm, without ring). 2.0 ± 0.002 g of water-absorbent resin particles were added to the aqueous sodium chloride solution at one time. The time [seconds] from the addition of the water-absorbent resin particles to the time when the vortex on the liquid surface converged was measured, and the time was obtained as the water absorption rate of the water-absorbent resin particles. The results are shown in Table 3.

[Unpressurized DW]
The non-pressurized DW of the water-absorbent resin particles was measured using the measuring device Z shown in FIG. The measurement was carried out 5 times for one type of water-absorbent resin particles, and the average value of the measured values at three points excluding the minimum value and the maximum value was obtained.

The measuring device Z has a burette portion 71, a conduit 72, a flat plate-shaped measuring table 73, a nylon mesh 74, a pedestal 75, and a clamp 76. The burette portion 71 was connected to a burette 71a on which a scale was written, a rubber stopper 71b for sealing the opening at the upper part of the burette 71a, a cock 71c connected to the tip of the lower part of the burette 71a, and a lower part of the burette 71a. It has an air introduction pipe 71d and a cock 71e. The burette portion 71 is fixed by a clamp 76. The measuring table 73 has a through hole 73a having a diameter of 2 mm formed in the central portion thereof, and is supported by a frame 75 having a variable height. The through hole 73a of the measuring table 73 and the cock 71c of the burette portion 71 are connected by a conduit 72. The inner diameter of the conduit 72 is 6 mm.

The measurement was performed in an environment with a temperature of 25 ° C and a humidity of 60 ± 10%. First, the cock 71c and the cock 71e of the burette portion 71 were closed, and the physiological saline 77 adjusted to 25 ° C. was put into the burette 71a through the opening at the upper part of the burette 71a. After sealing the opening of the burette 71a with the rubber stopper 71b, the cock 71c and the cock 71e were opened. The inside of the conduit 72 was filled with saline 77 to prevent air bubbles from entering. The height of the measuring table 73 was adjusted so that the height of the water surface of the physiological saline 77 that reached the inside of the through hole 73a was the same as the height of the upper surface of the measuring table 73. After the adjustment, the height of the water surface of the physiological saline 77 in the burette 71a was read by the scale of the burette 71a, and the position was set as the zero point (reading value at 0 seconds).

A nylon mesh 74 (100 mm × 100 mm, 250 mesh, thickness: about 50 μm) was laid in the vicinity of the through hole 73a on the measuring table 73, and a cylinder having an inner diameter of 30 mm and a height of 20 mm was placed in the center thereof. 1.00 g of water-absorbent resin particles 78 were uniformly sprayed on this cylinder. Then, the cylinder was carefully removed to obtain a sample in which the water-absorbent resin particles 78 were dispersed in a circle in the central portion of the nylon mesh 74. Next, the nylon mesh 74 on which the water-absorbent resin particles 78 were placed was quickly moved so that the center thereof was at the position of the through hole 73a so that the water-absorbent resin particles 78 did not dissipate, and the measurement was started. The time when air bubbles were first introduced into the burette 71a from the air introduction pipe 71d was defined as the start of water absorption (0 seconds).

The decrease amount of the physiological saline 77 in the burette 71a (that is, the amount of the physiological saline 77 absorbed by the water-absorbent resin particles 78) is sequentially read in units of 0.1 mL, and calculated from the start of water absorption of the water-absorbent resin particles 78. After 10 minutes, the weight loss Wc [g] of the physiological saline 77 was read. From Wc, the 10-minute value of non-pressurized DW was calculated by the following formula. The non-pressurized DW is the amount of water absorbed per 1.00 g of the water-absorbent resin particles 78.
Unpressurized DW value [mL / g] = Wc / 1.00

<Preparation of water absorption sheet for evaluation>
[Evaluation Example 1]
^Two air-laid non-woven fabrics (KNH, product number 6190516-1A01) having a basis weight of 40 g / m 2 were cut into two pieces having a size of 40 cm × 12 cm to obtain air-laid non-woven fabrics 1 and 2, respectively. Hot-melt adhesive to air-laid non-woven fabric 1 with a hot-melt coating machine (Henkel Japan Ltd., pump: Marshal150, table: XA-DT, tank set temperature: 150 ° C, hose set temperature: 165 ° C, gun head set temperature: 170 ° C). 0.16 g of the agent (Henkel Japan Ltd., ME-765E) was applied. As shown in FIG. 2, the application pattern of the hot melt adhesive was 12 spiral stripes at 10 mm intervals. Water-absorbent resin particles obtained in Example 1 using an air-flow type mixing device (Padformer manufactured by Otec Co., Ltd.) in an area of 40 cm × 12 cm on the side coated with the hot melt adhesive of the air-laid nonwoven fabric 1. A7.2 g was evenly sprayed.

0.16 g of hot melt adhesive was applied to the air-laid non-woven fabric 2 using a hot melt coating machine in the same manner as described above. A laminate was obtained by stacking the surfaces of the air-laid nonwoven fabric 1 on which the water-absorbent resin particles A were sprayed so as to face the surfaces of the air-laid nonwoven fabric 2 to which the hot melt adhesive was applied, with both ends aligned. A water-absorbing sheet is formed by sandwiching the laminate with release paper and pressing it together under the conditions of 110 ° C. and 0.1 MPa using a laminating machine (Hashima Co., Ltd., Straight Liner Fusion Press, model HP-600LFS). Was produced.

[Evaluation Examples 2 to 4]
Evaluation Examples 2, 3 and 4 are the same as those in Evaluation Example 1 except that the water-absorbent resin particles A are changed to the water-absorbent resin particles B, C and D produced in Examples 2, 3 and 4. Water absorption sheets were prepared respectively.

[Evaluation Comparison Example 1]
(Mixing of water-absorbent resin particles)
50 g of the water-absorbent resin particles E and 50 g of the water-absorbent resin particles manufactured in Comparative Example 1 are placed in a stainless steel mixing container having a capacity of 1 L, and mixed with a cross rotary mixer (Meiwa Kogyo Co., Ltd., CM-3 type) for 30 minutes. A mixture of water-absorbent resin particles was obtained. The medium particle size of the mixture was 123 μm.

(Making a water absorption sheet)
A water-absorbent sheet was produced in the same manner as in Evaluation Example 1 except that the water-absorbent resin particles A were changed to the mixture of the water-absorbent resin particles.

[Evaluation Comparison Example 2]
A water-absorbent sheet was produced in the same manner as in Evaluation Comparative Example 1 except that the water-absorbent resin particles E and F were changed to the water-absorbent resin particles G and H produced in Comparative Example 2. The medium particle size of the mixture of the water-absorbent resin particles G and H was 366 μm.

[Evaluation Comparison Example 3]
A spunlace non-woven fabric having a basis weight of 35 g / m ² (manufactured by Kuraray Co., Ltd., 70% rayon, 20% PET, 10% PP / PE) was cut into a size of 40 × 12 cm. The cut spunlace non-woven fabric was coated with a hot melt adhesive and sprayed with 1.44 g of the water-absorbent resin particles H produced in Comparative Example 2 in the same manner as in Evaluation Example 1.

^Two spunbonded non-woven fabrics (LIVSEN manufactured by Toray Industries, Inc.) having a basis weight of 17 g / m 2 were cut into two pieces having a size of 40 cm × 12 cm to obtain spunbonded nonwoven fabrics 1 and 2, respectively. 0.16 g of a hot melt adhesive was applied to the spunbonded nonwoven fabric 1 using a hot melt coating machine in the same manner as in Evaluation Example 1. The surface of the spunbonded nonwoven fabric 1 to which the hot melt was attached was faced with the surface of the spunlaced nonwoven fabric on which the water-absorbent resin particles H were sprayed, and both ends were aligned, sandwiched between release papers, and turned upside down. Then, the release paper was removed.

0.16 g of hot melt adhesive was applied to the surface of the spunlace non-woven fabric opposite to the surface on which the water-absorbent resin particles H were sprayed, in the same manner as above, using a hot melt coating machine. Using an airflow type mixer, 5.76 g of the water-absorbent resin particles I produced in Comparative Example 4 were uniformly sprayed over a 40 cm × 12 cm area of the spunlace non-woven fabric on the side to which the hot melt adhesive was applied immediately before. I let you.

0.16 g of hot melt adhesive was applied to the spunbonded non-woven fabric 2 using a hot melt coating machine in the same manner as above. A laminate was obtained by aligning both ends of the spunlaced nonwoven fabric with the surface on which the water-absorbent resin particles I were sprayed facing the surface of the spunbonded nonwoven fabric 2 coated with the hot melt adhesive. A water-absorbent sheet was prepared by sandwiching the laminated pair with a release paper and pressing the laminating machine under the conditions of 110 ° C. and 0.1 MPa in the same manner as in Evaluation Example 1 to bond them together.

<Evaluation of water absorption sheet>
[Preparation of artificial urine]
Sodium chloride, calcium chloride and magnesium sulfate were dissolved in ion-exchanged water at the following concentrations. Artificial urine (test solution) was prepared by further adding Blue No. 1 having the following concentration to the obtained solution. The following concentrations are based on the total mass of artificial urine.
(Artificial urine composition)
NaCl: 0.780% by mass
CaCl ₂ : 0.022% by mass
0054 ₄ : 0.038% by mass
Blue No. 1: 0.002% by mass

[Gradient absorption test]
FIG. 9 is a schematic view showing a method for evaluating the liquid leakage property of the water absorption sheet. A support plate 1 having a flat main surface and a length of 45 cm (here, an acrylic resin plate; hereinafter also referred to as an “inclined surface S1”) is fixed by a gantry 81 in a state of being inclined at 45 ± 2 degrees with respect to the horizontal plane S0. did. In a room having a temperature of 25 ± 2 ° C., a water absorption sheet 50 for testing was attached on the inclined surface S1 of the fixed support plate 1 so that the longitudinal direction thereof was along the longitudinal direction of the support plate 1. Next, a test solution (artificial urine) adjusted to 25 ± 1 ° C. was dropped from the dropping funnel 82 arranged vertically above the water absorption sheet 50 toward a position 8 cm above the center of the water absorption sheet 50. 80 mL of the test solution was added dropwise at a rate of 8 mL / sec. The distance between the tip of the dropping funnel 82 and the water absorbing sheet 50 was 10 ± 1 mm. The test solution was repeatedly added under the same conditions at intervals of 10 minutes from the start of the first addition of the test solution, and the test solution was added until leakage was observed.

When the test liquid that was not absorbed by the water absorption sheet 50 leaked from the lower part of the support plate 1, the leaked test liquid was collected in the metal tray 84 arranged below the support plate 1. The weight (g) of the recovered test solution was measured with a balance 83, and the value was recorded as the amount of leakage. By subtracting the leakage amount from the total input amount of the test solution, the absorption amount until the leakage occurred was calculated. It is judged that the larger this value is, the less likely it is that liquid will leak when worn. The results are shown in Table 4.

Evaluation using the water-absorbent resin particles obtained in the example The water-absorbent sheet of the example has a small total leakage amount when artificial urine is added three times, and even a single-layer structure water-absorbent sheet sufficiently suppresses leakage. It was confirmed that On the other hand, the water-absorbing sheets of Evaluation Comparative Examples 1 and 2 using the water-absorbent resin particles of Comparative Example 1 or 2 had a large amount of leakage. In addition, the water-absorbing sheet of Evaluation Comparative Example 3 in which the water-absorbent resin particles of Comparative Examples 3 and 4 were used in a two-layer structure also had a large amount of leakage.

1 ... Support plate, 10 ... Absorbent, 10a ... Water-absorbent resin particles, 10b ... Fiber layer, 20a ... Core wrap sheet, 20b ... Core wrap sheet, 21 ... Adhesive, 30 ... Liquid permeable sheet, 40 ... Liquid impervious Permeable sheet, 50 ... water absorption sheet, 61, 71 ... burette part, 61a, 71a ... burette, 61b, 71b ... rubber stopper, 61c, 71c, 71e ... cock, 61d, 71d ... air introduction pipe, 61e ... cock, 62 , 72 ... Conduit, 63, 73 ... Measuring table, 64 ... Measuring unit, 64a ... Cylindrical, 64b, 74 ... Nylon mesh, 64c ... Weight, 73a ... Through hole, 75 ... Stand, 76 ... Clamp, 77 ... Physiological saline , 81 ... gantry, 82 ... dripping funnel, 83 ... balance, 84 ... metal tray, 100 ... absorbent article, 200 ... stirring blade, 200a ... shaft, 200b ... flat plate, S ... slit, S ₀ ... horizontal plane, S ₁ ... Inclined surface, Y, Z ... Measuring device.

Claims

Water-absorbent resin particles having two or more differently shaped parts on the surface of one particle.
The water-absorbent resin particle according to claim 1, which has a spherical portion and an irregularly shaped portion on at least a part of the surface of one particle.
The first or second claim, wherein at least a part of the surface of one particle has a portion having an unevenness of 1 μm or more and 20 μm or less and a portion having an unevenness of more than 20 μm and 200 μm or less as measured by a laser microscope. Water-absorbent resin particles.
The water-absorbent resin particle according to any one of claims 1 to 3, which has a shape in which the primary particles are aggregated.
Water-absorbent resin particles in which the primary particles are aggregated, and the average unevenness of the particles measured by a digital microscope is 120 to 180 μm.
The water-absorbent resin particle according to any one of claims 1 to 5, wherein the medium particle size is 300 to 600 μm, and the water absorption rate by the Vortex method is 5 to 20 seconds.
The water-absorbent resin particles according to any one of claims 1 to 6, wherein the saline water retention amount is 20 to 60 g / g, and the water absorption amount under load at 4.14 kPa is 10 ml / g or more.
An absorber containing the water-absorbent resin particles according to any one of claims 1 to 7.
A water absorption sheet comprising the absorber according to claim 8.
The water-absorbing sheet according to claim 9, further comprising a core wrap sheet and having the absorber arranged inside the core wrap sheet.
An absorbent article comprising the water-absorbing sheet according to claim 9 or 10.
A method for producing water-absorbent resin particles, which comprises aggregating and granulating primary particles, wherein the primary particles have two or more types of shapes.
The method according to claim 12, wherein the primary particles include spherical particles and irregularly shaped particles.
The method according to claim 13, wherein the mixing ratio of the spherical particles and the irregularly shaped particles is 70:30 to 20:80.