WO2021049465A1 - Method for improving amount of water absorption under load, method for manufacturing cross-linked polymer particles, and method for manufacturing water-absorbing resin particles - Google Patents

Abstract

Provided is a method for improving the amount of water absorption of water-absorbing resin particles (10a) under a load, the water-absorbing resin particles (10a) being obtained by implementing cross-linking along cross-linked polymer particles, wherein the method is provided with a pulverization step for pulverizing a cross-linked polymer that has structural units derived from an ethylenic unsaturated monomer to obtain cross-linked polymer particles that satisfy (a) to (c).　(a) The proportion of particles having a particle diameter of less than 500 μm in the cross-linked polymer particles is 50 mass% or greater.　(b) The proportion of particles having a particle diameter of less than 106 μm in the cross-linked polymer particles is 20 mass% or less.　(c) The proportion of particles having a particle diameter of at least 106 μm but less than 250 μm in the cross-linked polymer particles is 40 mass% or less.

Description

Method for improving water absorption under load, method for producing crosslinked polymer particles, and method for producing water-absorbent resin particles

The present invention relates to a method for improving water absorption under load, a method for producing crosslinked polymer particles, and a method for producing 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 (for example, urine) (see, for example, Patent Document 1 below). The water-absorbent resin particles are obtained, for example, by crushing a crosslinked polymer having a structural unit derived from an ethylenically unsaturated monomer to obtain crosslinked polymer particles, and then subjecting the crosslinked polymer particles to crosslinking. Obtainable.

Japanese Unexamined Patent Publication No. 06-345819

When a liquid containing water as a main component is provided to an absorbent article, if the liquid is not sufficiently absorbed by the absorbent body of the absorbent article, the excess liquid flows on the surface of the absorbent article and the absorbent article is used. Problems such as leakage to the outside may occur. Therefore, the water-absorbent resin particles constituting the absorber are required to have an excellent water absorption amount. In particular, when an absorbent article such as a diaper is attached to the user, a load is applied to the water-absorbent resin particles, and the water absorption amount of the water-absorbent resin particles in such a loaded state is improved. It is required to make it.

One aspect of the present invention is to provide a method for improving the amount of water absorption under load of water-absorbent resin particles. Another aspect of the present invention is to provide a method for producing crosslinked polymer particles capable of obtaining water-absorbent resin particles having an excellent amount of water absorption under load. Another aspect of the present invention is to provide a method for producing water-absorbent resin particles having an excellent amount of water absorption under load.

The present inventor has found that even water-absorbent resin particles having excellent water absorption performance (for example, CRC (Centrifuge Crosslink Polymer)) different from the water absorption amount under load may not be able to obtain a sufficient water absorption amount under load. By adjusting the conditions of the crushing treatment using the particle size of the particles constituting the crosslinked polymer particles obtained by the crushing treatment as an index, the crosslinked polymer is crushed under appropriate conditions under the load of the water-absorbent resin particles. It was found that the amount of water absorption can be improved.

One aspect of the present invention is a method for improving the amount of water absorption under load of water-absorbent resin particles obtained by cross-linking the cross-linked polymer particles, and has a structural unit derived from an ethylenically unsaturated monomer. Provided is a method for improving water absorption under load, which comprises a crushing step of obtaining crosslinked polymer particles satisfying the following (a) to (c) by crushing the crosslinked polymer.
(A) The proportion of particles having a particle diameter of less than 500 μm in the crosslinked polymer particles is 50% by mass or more.
(B) The proportion of particles having a particle diameter of less than 106 μm in the crosslinked polymer particles is 20% by mass or less.
(C) The proportion of particles having a particle diameter of 106 μm or more and less than 250 μm in the crosslinked polymer particles is 40% by mass or less.

Another aspect of the present invention is a pulverization step of pulverizing a crosslinked polymer having a structural unit derived from an ethylenically unsaturated monomer to obtain crosslinked polymer particles satisfying the following (a) to (c). Provided is a method for producing crosslinked polymer particles.
(A) The proportion of particles having a particle diameter of less than 500 μm in the crosslinked polymer particles is 50% by mass or more.
(B) The proportion of particles having a particle diameter of less than 106 μm in the crosslinked polymer particles is 20% by mass or less.
(C) The proportion of particles having a particle diameter of 106 μm or more and less than 250 μm in the crosslinked polymer particles is 40% by mass or less.

Another aspect of the present invention provides a method for producing water-absorbent resin particles, which comprises a step of performing additional cross-linking on the cross-linked polymer particles obtained by the above-mentioned method for producing cross-linked polymer particles.

According to the above-mentioned method for improving the amount of water absorption under load, the method for producing crosslinked polymer particles, and the method for producing water-absorbent resin particles, it is possible to improve the amount of water absorption under load of the water-absorbent resin particles, and the load can be improved. It is possible to obtain water-absorbent resin particles having an excellent amount of lower water absorption.

By the way, when producing crosslinked polymer particles for obtaining water-absorbent resin particles, the particle size of the particles contained in the crosslinked polymer particles is classified after the crosslinked polymer is crushed to obtain the crosslinked polymer particles. It may be adjusted by particle size adjustment processing such as processing. On the other hand, the present inventor has complicated the manufacturing process of the water-absorbent resin particles by adding the particle size adjusting treatment, and has an excellent amount of water absorption under load even if the particle size adjusting treatment is performed after pulverization. The idea was to obtain crosslinked polymer particles capable of obtaining water-absorbent resin particles having an excellent amount of water absorption under load by a simple method, paying attention to the fact that the particles may not be obtained. It has been found that crosslinked polymer particles (crosslinked polymer particles satisfying the above-mentioned (a) to (c)) that give water absorption under load are obtained in the pulverization step. According to the above-mentioned method for improving the amount of water absorption under load and the method for producing crosslinked polymer particles, the amount of water absorption under load of the water-absorbent resin particles is improved by a simple method without performing particle size adjustment treatment after the pulverization step. It is possible to obtain water-absorbent resin particles having an excellent amount of water absorption under load by a simple method.

According to one aspect of the present invention, it is possible to provide a method for improving the amount of water absorption under load of the water-absorbent resin particles. According to another aspect of the present invention, it is possible to provide a method for producing crosslinked polymer particles capable of obtaining water-absorbent resin particles having an excellent amount of water absorption under load. According to another aspect of the present invention, it is possible to provide a method for producing water-absorbent resin particles having an excellent amount of water absorption under load.

It is sectional drawing which shows an example of an absorbent article. It is the schematic which shows the measuring apparatus of the water absorption amount under load of a water-absorbing resin particle.

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". "Polyethylene glycol" and "ethylene glycol" are collectively referred to as "(poly) ethylene glycol". The same applies to other expressions including "(poly)". 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. With respect to at least one (meth) acrylic acid compound selected from the group consisting of (meth) acrylic acid and salts thereof, what are "content of (meth) acrylic acid compound" and "total mass of (meth) acrylic acid compound"? , Acrylic acid, acrylate, methacrylic acid and methacrylic acid total amount. "Room temperature" means 25 ° C ± 2 ° C.

The method for improving the amount of water absorption under load according to the present embodiment is a method for improving the amount of water absorption under load of the water-absorbent resin particles obtained by subjecting the crosslinked polymer particles to cross-linking. The method for producing crosslinked polymer particles according to the present embodiment is a method for producing crosslinked polymer particles capable of obtaining water-absorbent resin particles by subjecting crosslinking. The method for improving the amount of water absorbed under load and the method for producing crosslinked polymer particles according to the present embodiment are to pulverize a crosslinked polymer having a structural unit derived from an ethylenically unsaturated monomer. A pulverization step for obtaining crosslinked polymer particles (crushed product) satisfying the following (a) to (c) is provided. The crosslinked polymer particles according to the present embodiment are crosslinked polymer particles from which water-absorbent resin particles can be obtained by performing additional cross-linking, and have a structural unit derived from an ethylenically unsaturated monomer. The following (a) to (c) are satisfied.
(A) The proportion of particles having a particle diameter of less than 500 μm in the crosslinked polymer particles is 50% by mass or more.
(B) The proportion of particles having a particle diameter of less than 106 μm in the crosslinked polymer particles is 20% by mass or less.
(C) The proportion of particles having a particle diameter of 106 μm or more and less than 250 μm in the crosslinked polymer particles is 40% by mass or less.

In the method for producing water-absorbent resin particles according to the present embodiment, the crosslinked polymer particles according to the present embodiment or the crosslinked polymer particles obtained by the method for producing the crosslinked polymer particles according to the present embodiment are crosslinked. It is provided with a cross-linking step to be applied.

According to the method for improving the amount of water absorption under load according to the present embodiment, the crosslinked polymer particles according to the present embodiment and the method for producing the same, and the method for producing the water-absorbent resin particles according to the present embodiment, the water-absorbent resin particles It is possible to improve the amount of water absorption under load, and it is possible to obtain water-absorbent resin particles having an excellent amount of water absorption under load. The reason why the amount of water absorption under load can be improved is not clear, but the present inventor speculates as follows. However, the cause is not limited to the following contents.
That is, when the crosslinked polymer is pulverized under inappropriate conditions, the crosslinked polymer particles are damaged and a sufficient amount of water absorption under a load cannot be obtained. On the other hand, according to the present embodiment, the crosslinked polymer is pulverized under appropriate conditions by adjusting the conditions of the pulverization treatment using the particle size of the particles constituting the crosslinked polymer particles obtained by the pulverization treatment as an index. Damage to the crosslinked polymer particles can be suppressed and the amount of water absorbed under load can be improved.
In order to obtain an excellent amount of water absorption under load of the water-absorbent resin particles, it is desirable that an excessively large amount of particles does not exist, and therefore it is desirable that the proportion of particles having a particle diameter of less than 500 μm is large.
On the other hand, particles having a small diameter such as particles having a particle diameter of less than 106 μm and particles having a particle diameter of 106 μm or more and less than 250 μm may be obtained by reducing the diameter by pulverizing a large number of times in the pulverization step. Therefore, since such small-diameter particles (for example, the surface of the particles) may be excessively damaged, it is easy to improve the water absorption under load by reducing the number of small-diameter particles.
Further, in order to improve the amount of water absorption under load, it is desirable that the cross-linking proceeds uniformly over the entire cross-linked polymer particles when the cross-linked polymer particles are subjected to additional cross-linking. Since particles having a particle size of less than 106 μm tend to have a high absorption rate of the cross-linking agent, if the proportion of particles having a particle size of less than 106 μm is too large, the cross-linking may not proceed uniformly. Therefore, it is desirable that the proportion of particles having a particle diameter of less than 106 μm is small.

According to the method for improving the amount of water absorption under load according to the present embodiment, and the crosslinked polymer particles and the method for producing the same according to the present embodiment, water absorption is performed without performing particle size adjustment treatment such as classification treatment after the pulverization step. It is possible to improve the water absorption amount of the sex resin particles under load by a simple method, and it is possible to obtain water-absorbent resin particles having an excellent water absorption amount under load by a simple method.

In the pulverization step, the crosslinked polymer having a structural unit derived from the ethylenically unsaturated monomer is pulverized to obtain crosslinked polymer particles satisfying the above-mentioned (a) to (c). In the pulverization step, crosslinked polymer particles satisfying the above-mentioned (a) to (c) can be obtained by adjusting the type of the pulverizer, the pulverization conditions, and the like.

In the crushing step, the crosslinked polymer can be crushed using a screen (net member, punching plate, etc.) having openings (through holes; mesh). The present embodiment may be, for example, an embodiment in which the crosslinked polymer is pulverized while passing the crosslinked polymer through the screen in the pulverization step. In this case, by passing the crosslinked polymer through the screen from one side to the other side of the screen, the particles constituting the crosslinked polymer particles can be obtained on the other side of the screen. Further, the particle size can be adjusted while crushing the crosslinked polymer, and particles having a diameter corresponding to the opening diameter of the opening of the screen can be obtained on the other side of the screen. By adjusting the opening diameter of the opening of the screen, the particle size and particle size distribution of the particles contained in the crosslinked polymer particles can be adjusted. The opening of the screen has an opening diameter larger than the diameter of at least a part of the crosslinked polymer to be pulverized. The opening diameter (hole diameter) of the screen opening may be, for example, 0.08 to 10 mm, 0.50 to 2.0 mm, or 0.75 to 1.5 mm. The screen may be annular (for example, annular), plate-shaped, or the like.

The present embodiment may be, for example, an embodiment in which the crosslinked polymer is pulverized while passing the crosslinked polymer through the screen by applying a centrifugal force to the crosslinked polymer in the pulverization step. In this case, the crosslinked polymer can be impact pulverized by colliding the crosslinked polymer with a screen or another member (for example, a rotating member described later) by centrifugal force. In this embodiment, for example, the screen is cyclic, and in the pulverization step, the crosslinked polymer is subjected to centrifugal force (centrifugal force from the inner peripheral side to the outer peripheral side) on the inner peripheral side of the screen. May be an embodiment in which the crosslinked polymer is pulverized while passing the crosslinked polymer through a screen. In this case, by passing the crosslinked polymer through the screen from the inner peripheral side to the outer peripheral side of the screen, the particles constituting the crosslinked polymer particles can be obtained on the outer peripheral side of the screen. Further, the particle size can be adjusted while crushing the crosslinked polymer by impact pulverization, and particles having a diameter corresponding to the opening diameter of the opening of the screen can be obtained on the outer peripheral side of the screen.

The crusher used in the crushing step may have, for example, a sample table to which the crosslinked polymer is supplied and an annular screen surrounding the sample table. The sample table may be rotatable, and centrifugal force may be applied to the crosslinked polymer by rotating the sample table. For example, centrifugal force can be applied to the crosslinked polymer by rotating the sample table around the central axis (axis orthogonal to the circumferential direction) of the annular screen.

In addition to the sample table and the annular screen, the crusher may include a rotating member (for example, a blade member) that can rotate along the inner wall of the annular screen. In this case, the crosslinked polymer is easily impact-milled by colliding the crosslinked polymer with the rotating member by centrifugal force while rotating the rotating member. The rotating member may be located near the inner wall of the screen. In this case, it is possible to apply a shearing force to the crosslinked polymer existing between the rotating member and the inner wall of the screen, and the crosslinked polymer can be easily crushed. The rotating member may be a member that extends along the central axis of the annular screen. The rotating member may be integrated with the sample table or may be separate from the sample table. The rotating member may be rotatable with the sample table. A plurality (for example, 6) of rotating members may be arranged at intervals on the outer peripheral portion of the sample table. The rotation speed of each of the sample table and the rotating member may be, for example, 6000 to 18000 rpm.

As the crusher, a product name manufactured by Verder Scientific Co., Ltd .: ZM200; a product name manufactured by Fritsch Japan Co., Ltd .: P-14 rotor speed mill (Pulveristte 14) or the like can be used. In the crushing step, a crusher in which the particles that have passed through the screen are not further adjusted in particle size can be used.

Regarding (a) above, the proportion of particles having a particle diameter of less than 500 μm in the crosslinked polymer particles according to the present embodiment is 50% by mass or more based on the total mass of the crosslinked polymer particles, and is in the following range. It's okay. The proportion of particles with a particle diameter of less than 500 μm is more than 50% by mass, 55% by mass or more, 60% by mass or more, more than 60% by mass, 65% by mass or more, more than 65% by mass, or 67% by mass or more. It may be there. The proportion of particles with a particle size of less than 500 μm is 90% by mass or less, less than 90% by mass, 85% by mass or less, 80% by mass or less, less than 80% by mass, 75% by mass or less, 70% by mass or less, or 70% by mass. May be less than. From these viewpoints, the proportion of particles having a particle diameter of less than 500 μm may be 50 to 90% by mass.

Regarding (b) above, the proportion of particles having a particle diameter of less than 106 μm (more than 0 μm and less than 106 μm) in the crosslinked polymer particles according to the present embodiment is 20% by mass or less based on the total mass of the crosslinked polymer particles. Yes, it may be in the following range. The proportion of particles with a particle size of less than 106 μm is less than 20% by mass, 17.5% by mass or less, 15% by mass or less, 12.5% by mass or less, 10% by mass or less, less than 10% by mass, and 9.9% by mass or less. , 9.8% by mass or less, 9.7% by mass or less, 9.6% by mass or less, or 9.5% by mass or less. The proportion of particles with a particle size of less than 106 μm is 0% by mass or more, more than 0% by mass, 1% by mass or more, 2% by mass or more, 3% by mass or more, 4% by mass or more, 5% by mass or more, 6% by mass or more. , 7% by mass or more, 8% by mass or more, or 9% by mass or more. From these viewpoints, the proportion of particles having a particle diameter of less than 106 μm may be 0 to 20% by mass.

Regarding (c) above, the proportion of particles having a particle diameter of 106 μm or more and less than 250 μm in the crosslinked polymer particles according to the present embodiment is the total of the crosslinked polymer particles from the viewpoint of improving the water absorption amount under load of the water-absorbent resin particles. It is 40% by mass or less based on the mass. The proportion of particles having a particle diameter of 106 μm or more and less than 250 μm is less than 40% by mass, 35% by mass or less, and 35, based on the total mass of the crosslinked polymer particles, from the viewpoint of easily improving the amount of water absorption under load of the water-absorbent resin particles. It may be less than mass%, 30% by mass or less, less than 30% by mass, 25% by mass or less, less than 25% by mass, or 24% by mass or less. The proportion of particles with a particle size of 106 μm or more and less than 250 μm is 0% by mass or more, more than 0% by mass, 1% by mass or more, 5% by mass or more, 10% by mass or more, 15% by mass or more, 20% by mass or more, or It may be 23% by mass or more. From these viewpoints, the proportion of particles having a particle diameter of 106 μm or more and less than 250 μm may be 0 to 40% by mass, and may be 20 to 40% by mass.

The proportion of particles having a particle diameter of 250 μm or more and less than 500 μm in the crosslinked polymer particles according to the present embodiment may be in the following range based on the total mass of the crosslinked polymer particles. The proportion of particles having a particle diameter of 250 μm or more and less than 500 μm may be 50% by mass or less, less than 50% by mass, 45% by mass or less, 40% by mass or less, or 36% by mass or less. The proportion of particles with a particle size of 250 μm or more and less than 500 μm is 0% by mass or more, more than 0% by mass, 1% by mass or more, 5% by mass or more, 10% by mass or more, 15% by mass or more, 20% by mass or more, 25% by mass. % Or more, 30% by mass or more, or 35% by mass or more. From these viewpoints, the proportion of particles having a particle diameter of 250 μm or more and less than 500 μm may be 0 to 50% by mass.

The proportion of particles having a particle diameter of 500 μm or more and less than 850 μm in the crosslinked polymer particles according to the present embodiment may be in the following range based on the total mass of the crosslinked polymer particles. The proportion of particles having a particle diameter of 500 μm or more and less than 850 μm may be 50% by mass or less, less than 50% by mass, 45% by mass or less, 40% by mass or less, 35% by mass or less, or 30% by mass or less. The proportion of particles with a particle diameter of 500 μm or more and less than 850 μm is 0% by mass or more, more than 0% by mass, 1% by mass or more, 5% by mass or more, 10% by mass or more, 15% by mass or more, 20% by mass or more, 25% by mass. % Or more, or 29% by mass or more. From these viewpoints, the proportion of particles having a particle diameter of 500 μm or more and less than 850 μm may be 0 to 50% by mass.

The proportion of particles having a particle diameter of 850 μm or more in the crosslinked polymer particles according to the present embodiment may be in the following range based on the total mass of the crosslinked polymer particles. The proportion of particles having a particle diameter of 850 μm or more may be 10% by mass or less, less than 10% by mass, 8% by mass or less, 6% by mass or less, 5% by mass or less, 4% by mass or less, or 3% by mass or less. .. The proportion of particles having a particle diameter of 850 μm or more may be 0% by mass or more, more than 0% by mass, 1% by mass or more, 2% by mass or more, or 2.5% by mass or more. From these viewpoints, the proportion of particles having a particle diameter of 850 μm or more may be 0 to 10% by mass.

The medium particle size of the crosslinked polymer particles according to this embodiment is preferably in the following range. The medium particle size may be 250 μm or more, 280 μm or more, 300 μm or more, 330 μm or more, or 350 μm or more. The medium particle size may be 600 μm or less, 550 μm or less, 500 μm or less, 450 μm or less, 400 μm or less, 380 μm or less, or 360 μm or less. From these viewpoints, the medium particle size may be 250 to 600 μm. The medium particle size can be measured by the method described in Examples described later. For the medium particle size, the measured value at room temperature can be used.

The method for producing a crosslinked polymer (crosslinked polymer that is pulverized in the pulverization step) includes a polymerization step of polymerizing a monomer composition containing an ethylenically unsaturated monomer. In the polymerization step, a crosslinked polymer gel may be obtained by polymerizing a monomer composition containing an ethylenically unsaturated monomer.

The monomer composition may contain water, an organic solvent, and the like. The monomer composition may be a monomer aqueous solution. Examples of the polymerization method of the monomer composition include an aqueous solution polymerization method, a bulk polymerization method, a precipitation polymerization method and the like. Among these, the aqueous solution polymerization method is preferable from the viewpoint that good water absorption performance (CRC, water absorption under load, etc.) can be easily obtained and the polymerization reaction can be easily controlled. In the following, a case where the aqueous solution polymerization method is used as an example of the polymerization method will be described.

As the ethylenically unsaturated monomer, a water-soluble ethylenically unsaturated monomer can be used. Examples of the ethylenically unsaturated monomer include α, β-unsaturated carboxylic acids such as (meth) acrylic acid, maleic acid, maleic anhydride and fumaric acid, and carboxylic acid-based monomers such as salts thereof; Nonionic monomers such as meta) acrylamide, N, N-dimethyl (meth) acrylamide, 2-hydroxyethyl (meth) acrylate, N-methylol (meth) acrylamide, polyethylene glycol mono (meth) acrylate; N, N -Amino group-containing unsaturated monomers such as diethylaminoethyl (meth) acrylate, N, N-diethylaminopropyl (meth) acrylate, diethylaminopropyl (meth) acrylamide, and quaternary products thereof; vinyl sulfonic acid, styrene sulfone. Examples thereof include acids, 2- (meth) acrylamide-2-methylpropanesulfonic acid, 2- (meth) acryloylethanesulfonic acid, and sulfonic acid-based monomers such as salts thereof. The ethylenically unsaturated monomer can contain at least one (meth) acrylic acid compound selected from the group consisting of (meth) acrylic acid and salts thereof. The ethylenically unsaturated monomer may contain both (meth) acrylic acid and a salt of (meth) acrylic acid. Examples of salts of α, β-unsaturated carboxylic acid ((meth) acrylic acid, etc.) include alkali metal salts (sodium salt, potassium salt, etc.), alkaline earth metal salts (calcium salt, etc.) and the like.

The ethylenically unsaturated monomer having an acid group (for example, (meth) acrylic acid) may have an acid group neutralized in advance with an alkaline neutralizer. 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 in the form of an aqueous solution in order to simplify the neutralization operation. The acid group may be neutralized before the polymerization of the ethylenically unsaturated monomer as a raw material, or during or after the polymerization.

The degree of neutralization of the ethylenically unsaturated monomer by the alkaline neutralizing agent is from the viewpoint that good water absorption performance (CRC, water absorption under load, etc.) can be easily obtained by increasing the osmotic pressure, and in excess alkalinity. From the viewpoint of suppressing defects caused by the presence of the Japanese agent, 10 to 100 mol%, 30 to 90 mol%, 40 to 85 mol%, or 50 to 80 mol% is preferable. The "neutralization degree" is the neutralization degree for all the acid groups of the ethylenically unsaturated monomer.

The content of the (meth) acrylic acid compound is preferably in the following range based on the total mass of the monomer composition. The content of the (meth) acrylic acid compound is 10% by mass or more, 15% by mass or more, 20% by mass or more, 25% by mass or more, 30% by mass or more, or 35% by mass or more from the viewpoint of easily increasing productivity. Is preferable. The content of the (meth) acrylic acid compound is 60% by mass or less, 55% by mass or less, 50% by mass or less, less than 50% by mass, 45% by mass from the viewpoint of easily improving the water absorption performance (CRC, water absorption under load, etc.). % Or less, or 40% by mass or less is preferable. From these viewpoints, the content of the (meth) acrylic acid compound is preferably 10 to 60% by mass.

The content of the (meth) acrylic acid compound is the total amount of the monomers contained in the monomer composition and / or the total amount of the ethylenically unsaturated monomer contained in the monomer composition. The following range is preferable with reference to. The content of the (meth) acrylic acid compound is preferably 50 mol% or more, 70 mol% or more, 90 mol% or more, 95 mol% or more, 97 mol% or more, or 99 mol% or more. The monomer contained in the monomer composition and / or the ethylenically unsaturated monomer contained in the monomer composition is substantially composed of a (meth) acrylic acid compound (substantially). In addition, 100 mol% of the monomer contained in the monomer composition and / or the ethylenically unsaturated monomer contained in the monomer composition is a (meth) acrylic acid compound). It may be.

The monomer composition may contain a polymerization initiator. The polymerization of the monomer contained in the monomer composition may be started by adding a polymerization initiator to the monomer composition and, if necessary, heating, irradiating with light or the like. Examples of the polymerization initiator include a photopolymerization initiator and a radical polymerization initiator, and a water-soluble radical polymerization initiator is preferable. The polymerization initiator preferably contains at least one selected from the group consisting of azo compounds and peroxides from the viewpoint of easily enhancing water absorption performance (CRC, water absorption under load, etc.).

Examples of the azo compound include 2,2'-azobis [2- (N-phenylamidino) propane] dihydrochloride and 2,2'-azobis {2- [N- (4-chlorophenyl) amidino] propane} dihydrochloride. Salt, 2,2'-azobis {2- [N- (4-hydroxyphenyl) amidino] propane} dihydrochloride, 2,2'-azobis [2- (N-benzylamidino) propane] dihydrochloride, 2 , 2'-azobis [2- (N-allylamidino) propane] dihydrochloride, 2,2'-azobis (2-amidinopropane) dihydrochloride, 2,2'-azobis {2- [N- (2) -Hydroxyethyl) amidino] propane} dihydrochloride, 2,2'-azobis [2- (5-methyl-2-imidazolin-2-yl) propane] dihydrochloride, 2,2'-azobis [2-( 2-imidazolin-2-yl) propane] dihydrochloride, 2,2'-azobis [2- (4,5,6,7-tetrahydro-1H-1,3-diazepine-2-yl) propane] dihydrochloride Salt, 2,2'-azobis [2- (5-hydroxy-3,4,5,6-tetrahydropyrimidine-2-yl) propane] dihydrochloride, 2,2'-azobis {2- [1-( 2-Hydroxyethyl) -2-imidazolin-2-yl] propane} dihydrochloride, 2,2'-azobis [2- (2-imidazolin-2-yl) propane] disulfate dihydrate, 2, 2'-azobis [N- (2-carboxyethyl) -2-methylpropion amidine] tetrahydrate, 2,2'-azobis [2-methyl-N- (2-hydroxyethyl) propionamide] and the like can be mentioned. Be done. The azo compounds are 2,2'-azobis (2-methylpropionamide) dihydrochloride and 2,2'-azobis (2) from the viewpoint that good water absorption performance (CRC, water absorption under load, etc.) can be easily obtained. -Amidinopropane) dihydrochloride, 2,2'-azobis {2- [1- (2-hydroxyethyl) -2-imidazolin-2-yl] propane} dihydrochloride, and 2,2'-azobis [ It is preferable to contain at least one selected from the group consisting of N- (2-carboxyethyl) -2-methylpropion amidine] tetrahydrate.

Peroxides include persulfates such as potassium persulfate, ammonium persulfate, sodium persulfate; methyl ethyl ketone peroxide, methyl isobutyl ketone peroxide, di-t-butyl peroxide, t-butyl cumyl peroxide, t-butyl. Examples thereof include organic peroxides such as peroxyacetate, t-butylperoxyisobutyrate, and t-butylperoxypivalate. The peroxide preferably contains at least one selected from the group consisting of potassium persulfate, ammonium persulfate, and sodium persulfate from the viewpoint of easily obtaining good water absorption performance (CRC, water absorption under load, etc.). ..

The content of the polymerization initiator is preferably in the following range with respect to 1 mol of the ethylenically unsaturated monomer (for example, (meth) acrylic acid compound). The content of the polymerization initiator is 0.001 mmol or more, 0.003 mmol or more, 0.015 from the viewpoint of easily improving the water absorption performance (CRC, water absorption under load, etc.) and shortening the polymerization reaction time. It is preferably mmol or more, 0.03 mmol or more, 0.06 mmol or more, 0.08 mmol or more, or 0.1 mmol or more. The content of the polymerization initiator is 5 mmol or less, 4 mmol or less, 2 mmol or less, 1 from the viewpoint of easily improving the water absorption performance (CRC, water absorption under load, etc.) and easily avoiding a rapid polymerization reaction. It is preferably mmol or less, 0.5 mmol or less, 0.3 mmol or less, 0.25 mmol or less, 0.2 mmol or less, or 0.15 mmol or less. From these viewpoints, the content of the polymerization initiator is preferably 0.001 to 5 mmol.

The monomer composition may contain a reducing agent. Examples of the reducing agent include sodium sulfite, sodium hydrogen sulfite, ferrous sulfate, L-ascorbic acid and the like. A polymerization initiator and a reducing agent may be used in combination.

The monomer composition may contain an oxidizing agent. Examples of the oxidizing agent include hydrogen peroxide, sodium perborate, perphosphoric acid and salts thereof, potassium permanganate and the like.

The monomer composition may contain an internal cross-linking agent. By using the internal cross-linking agent, the obtained cross-linked polymer can have a cross-linked structure by the internal cross-linking agent in addition to the self-cross-linking structure by the polymerization reaction as the internal cross-linking structure.

Examples of the internal cross-linking agent include compounds having two or more reactive functional groups (for example, polymerizable unsaturated groups). Examples of the internal cross-linking agent include di or tri (meth) acrylic acid esters of polyols such as (poly) ethylene glycol, (poly) propylene glycol, trimethylolpropane, glycerin polyoxyethylene glycol, polyoxypropylene glycol, and (poly) glycerin. Class: Unsaturated polyesters obtained by reacting the above-mentioned polyol with an unsaturated acid (maleic acid, fumaric acid, etc.); (poly) ethylene glycol diglycidyl ether, (poly) propylene glycol diglycidyl ether, (poly) glycerin Glycidyl group-containing compounds such as diglycidyl ether and glycidyl (meth) acrylate; bisacrylamides such as N, N'-methylenebis (meth) acrylamide; di or tri (meth) obtained by reacting polyepoxide with (meth) acrylic acid. Meta) acrylic acid esters; di (meth) acrylic acid carbamil esters obtained by reacting polyisocyanates (tolylene diisocyanate, hexamethylene diisocyanate, etc.) with hydroxyethyl (meth) acrylic acid; allylated starch; allyl Cellified cellulose; diallyl phthalate; N, N', N "-triallyl isocyanurate; divinylbenzene; pentaerythritol; ethylenediamine; polyethyleneimine, etc. The internal cross-linking agent has water absorption performance (CRC, water absorption under load, etc.). It is selected from the group consisting of (poly) ethylene glycol diglycidyl ether, (poly) propylene glycol diglycidyl ether, and (poly) glycerin diglycidyl ether from the viewpoint of being easy to increase and having excellent reactivity at low temperature. It is preferable to contain at least one kind.

The content of the internal cross-linking agent is preferably in the following range with respect to 1 mol of the ethylenically unsaturated monomer (for example, (meth) acrylic acid compound). The content of the internal cross-linking agent is 0.0005 mmol or more, 0.001 mmol or more, 0.002 mmol or more, 0.005 mmol from the viewpoint that good water absorption performance (CRC, water absorption under load, etc.) can be easily obtained. As mentioned above, 0.01 mmol or more, 0.015 mmol or more, 0.02 mmol or more, or 0.025 mmol or more is preferable. The content of the internal cross-linking agent is 0.3 mmol or less, 0.25 mmol or less, 0.2 mmol or less, 0.18 mmol from the viewpoint that good water absorption performance (CRC, water absorption under load, etc.) can be easily obtained. Below, less than 0.18 mmol, less than 0.17 mmol, less than 0.16 mmol, less than 0.15 mmol, less than 0.1 mmol, less than 0.06 mmol, less than 0.06 mmol, less than 0.05 mmol, It is preferably less than 0.05 mmol, 0.04 mmol or less, or 0.03 mmol or less. From these viewpoints, the content of the internal cross-linking agent is preferably 0.0005 to 0.3 mmol.

If necessary, the monomer composition may contain additives such as a chain transfer agent, a thickener, and an inorganic filler as components different from the above-mentioned components. Examples of the chain transfer agent include thiols, thiol acids, secondary alcohols, hypophosphorous acid, phosphorous acid, achlorine and the like. Examples of the thickener include carboxymethyl cellulose, hydroxyethyl cellulose, hydroxypropyl cellulose, methyl cellulose, polyethylene glycol, polyacrylic acid, neutralized polyacrylic acid, polyacrylamide and the like. Examples of the inorganic filler include metal oxides, ceramics, and viscous minerals.

As a polymerization method for aqueous solution polymerization, a static polymerization method in which the monomer composition is polymerized without stirring (for example, a static state); a stirring polymerization method in which the monomer composition is polymerized while stirring in a reaction apparatus. And so on. In the static polymerization method, when the polymerization is completed, a single block-shaped gel occupying substantially the same volume as the monomer composition present in the reaction vessel is obtained.

The form of polymerization may be batch, semi-continuous, continuous, or the like. For example, when the static polymerization method is carried out by continuous polymerization, the polymerization reaction can be carried out while continuously supplying the monomer composition to the continuous polymerization apparatus to continuously obtain a gel.

The polymerization temperature varies depending on the polymerization initiator used, but from the viewpoint of rapidly advancing the polymerization, increasing the productivity by shortening the polymerization time, removing the heat of polymerization, and facilitating the smooth reaction, 0 to 0 to It is preferably 130 ° C. or 10 to 110 ° C. The polymerization time is appropriately set depending on the type and amount of the polymerization initiator used, the reaction temperature, and the like, but is preferably 1 to 200 minutes or 5 to 100 minutes.

The method for producing the crosslinked polymer may include a coarse crushing step and a drying step after the polymerization step.

The coarse crushing step is, for example, a step of coarsely crushing the crosslinked polymer (for example, a crosslinked polymer gel) obtained in the polymerization step to obtain a coarsely crushed product (for example, a gel coarse crushed product). As the crushing apparatus in the crushing step, for example, a kneader (pressurized kneader, double-armed kneader, etc.), a meat chopper, a cutter mill, a pharma mill, or the like can be used.

The drying step is a step of drying the crushed product obtained in the crushing step to obtain a dried product. In the drying step, a dried product (for example, a gel dried product) can be obtained by removing the liquid component (water or the like) in the pyroclastic material by heating and / or blowing air. The drying method may be natural drying, heat drying, vacuum drying or the like. The drying temperature is, for example, 70 to 250 ° C.

The crosslinked polymer particles according to the present embodiment (crosslinked polymer particles obtained in the pulverization step) include a crosslinked polymer having a structural unit derived from an ethylenically unsaturated monomer (for example, a (meth) acrylic acid compound). .. The crosslinked polymer particles according to the present embodiment include a gel stabilizer, a metal chelating agent (ethylenediamine tetraacetic acid and its salt, diethylenetriamine 5 acetic acid and its salt (for example, diethylenetriamine 5 sodium acetate), etc.), and a fluidity improver (lubricant). Other components such as may be further contained. Other components may be located inside, on the surface, or both of the crosslinked polymers.

The crosslinked polymer particles according to the present embodiment may contain inorganic particles arranged on the surface of the crosslinked polymer. For example, by mixing the crosslinked polymer and the inorganic particles, the inorganic particles can be arranged on the surface of the crosslinked polymer. Examples of the inorganic particles include silica particles such as amorphous silica.

The water-absorbent resin particles according to the present embodiment can be obtained by cross-linking the crosslinked polymer particles obtained in the pulverization step (crosslinking step). The cross-linking may be surface cross-linking to the cross-linked polymer particles. The cross-linking can be performed, for example, by reacting a cross-linking agent (for example, a surface cross-linking agent) with the cross-linked polymer particles. By performing additional cross-linking using a cross-linking agent, the cross-linking density of the cross-linked polymer particles (for example, the cross-linking density near the surface of the cross-linked polymer particles) is increased, so that the water absorption performance (CRC, water absorption under load, water absorption rate, etc.) ) Is easy to increase. When comparing the amount of water absorption under load of the water-absorbent resin particles, the amount of the cross-linking agent used may be adjusted in order to adjust the CRC of the water-absorbent resin particles equally.

Examples of the cross-linking agent include compounds containing two or more functional groups (reactive functional groups) having reactivity with functional groups derived from ethylenically unsaturated monomers. Examples of the 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, Polyglycidyl compounds such as (poly) glycerin diglycidyl ether, (poly) glycerin triglycidyl ether, (poly) propylene glycol polyglycidyl ether, (poly) glycerol polyglycidyl ether; epichlorohydrin, epibromhydrin, α-methylepicrolhydrin, etc. Haloepoxy compounds; compounds having two or more reactive functional groups such as isocyanate compounds (2,4-tolylene diisocyanate, hexamethylene diisocyanate, etc.); 3-methyl-3-oxetane methanol, 3-ethyl-3-oxetane Oxetane compounds such as methanol, 3-butyl-3-oxetane methanol, 3-methyl-3-oxetane ethanol, 3-ethyl-3-oxetane ethanol, 3-butyl-3-oxetane ethanol; 1,2-ethylenebisoxazoline and the like. Oxetane compounds; carbonate compounds such as ethylene carbonate; hydroxyalkylamide compounds such as bis [N, N-di (β-hydroxyethyl)] adipamide and the like.

The water-absorbent resin particles according to the present embodiment have a gel stabilizer on the surface thereof; a metal chelating agent (ethylenediaminetetraacetic acid and its salt thereof, diethylenetriamine-5 acetic acid and its salt (for example, diethylenetriamine-5 sodium acetate), etc.); It may contain inorganic particles of an agent (lubricant). For example, by mixing the post-crosslinked particles and the inorganic particles, the inorganic particles can be arranged on the surface of the post-crosslinked particles. Examples of the inorganic particles include silica particles such as amorphous silica.

The water-absorbent resin particles according to the present embodiment can retain water and can absorb body fluids such as urine, sweat, and blood (for example, menstrual blood). The water-absorbent resin particles according to the present embodiment can be used as a constituent component of the absorber. This embodiment can be used in the fields of, for example, sanitary materials such as disposable diapers and sanitary products; agricultural and horticultural materials such as water retention agents and soil conditioners; and industrial materials such as water stop agents and dew condensation inhibitors.

The CRC of the water-absorbent resin particles according to the present embodiment is 10 g / g or more, 15 g / g or more, 20 g / g or more, 25 g / g or more, 30 g / g or more, 32 g / g or more, or 34 g / g or more. It may be there. The CRC of the water-absorbent resin particles may be 60 g / g or less, 55 g / g or less, 50 g / g or less, 45 g / g or less, 40 g / g or less, or 35 g / g or less. From these viewpoints, the CRC of the water-absorbent resin particles may be 10 to 60 g / g. CRC is an abbreviation for Centrifuge Retention Capacity (centrifuge holding capacity). The CRC of the water-absorbent resin particles can be measured by the method described in Examples described later with reference to the EDANA method (NWSP 241.0.R2 (15), page.769-778). As a water absorption ratio when a non-woven bag containing 0.2 g of water-absorbent resin particles in a dry state is immersed in 1000 g of physiological saline for 30 minutes and then centrifuged using a centrifuge to drain water. Obtainable. As the CRC of the water-absorbent resin particles, a measured value at room temperature can be used.

The method for improving the water absorption under load according to the present embodiment may include the above-mentioned cross-linking step and a measurement step for measuring the water absorption under load of the water-absorbent resin particles after the crushing step. The amount of water absorption of the water-absorbent resin particles under load is preferably 21 mL / g or more, 21.5 mL / g or more, or 22 mL / g or more. The amount of water absorption of the water-absorbent resin particles under load is preferably 35 mL / g or less, or 30 mL / g or less. The amount of water absorption under load can be measured by the method described in Examples described later. As the water absorption amount of the water-absorbent resin particles under load, a measured value at room temperature can be used.

The absorber according to the present embodiment contains the water-absorbent resin particles according to the present embodiment. The absorber according to the present embodiment may contain a fibrous substance, for example, a mixture containing water-absorbent resin particles and the fibrous substance. The structure of the absorber may be, for example, a structure in which the water-absorbent resin particles and the fibrous material are uniformly mixed, and the water-absorbent resin particles are sandwiched between the fibrous material formed in a sheet or layer. It may be a configuration or another configuration.

Examples of the fibrous material include finely pulverized wood pulp; cotton; cotton linter; rayon; cellulosic fibers such as cellulose acetate; synthetic fibers such as polyamide, polyester and polyolefin; and a mixture of these fibers. As the fibrous material, hydrophilic fibers can be used.

In order to improve the morphological retention before and during use of the absorber, the fibers may be adhered to each other by adding an adhesive binder to the fibrous material. Examples of the adhesive binder include heat-sealing synthetic fibers, hot melt adhesives, and adhesive emulsions.

Examples of the heat-bondable synthetic fiber include a total fusion type binder such as polyethylene, polypropylene, and an ethylene-propylene copolymer; a non-total fusion type binder having a side-by-side or core-sheath structure of polypropylene and polyethylene. In the above-mentioned non-total fusion type binder, only the polyethylene portion can be heat-sealed.

Examples of the hot melt adhesive include ethylene-vinyl acetate copolymer, styrene-isoprene-styrene block copolymer, styrene-butadiene-styrene block copolymer, styrene-ethylene-butylene-styrene block copolymer, and styrene-ethylene-propylene-styrene block copolymer. , A mixture of a base polymer such as amorphous polypropylene and a tackifier, a plasticizer, an antioxidant and the like.

Examples of the adhesive emulsion include polymers of at least one monomer selected from the group consisting of methyl methacrylate, styrene, acrylonitrile, 2-ethylhexyl acrylate, butyl acrylate, butadiene, ethylene, and vinyl acetate.

The absorber according to the present embodiment may contain inorganic particles (for example, amorphous silica), a deodorant, an antibacterial agent, a pigment, a dye, a fragrance, an adhesive and the like. When the water-absorbent resin particles contain inorganic particles, the absorber may contain inorganic particles in addition to the inorganic particles in the water-absorbent resin particles.

The shape of the absorber according to this embodiment may be, for example, a sheet shape. The thickness of the absorber (for example, the thickness of the sheet-shaped absorber) may be 0.1 to 20 mm or 0.3 to 15 mm.

The content of the water-absorbent resin particles in the absorber is 2 to 95% by mass, 10 to 80% by mass, or 20 to 20 to 95% by mass with respect to the total of the water-absorbent resin particles and the fibrous material from the viewpoint of easily obtaining sufficient absorption characteristics. It may be 60% by mass.

The content of the water-absorbent resin particles in the absorber is preferably 100 to 1000 g, 150 to 800 g, or 200 to 700 g per ^{1 m 2 of the absorber from the viewpoint of easily obtaining sufficient absorption characteristics.} The content of the fibrous material in the absorber is preferably 50 to 800 g, 100 to 600 g, or 150 to 500 g per ^{1 m 2 of} the absorber from the viewpoint of easily obtaining sufficient absorption characteristics.

The absorbent article according to the present embodiment includes an absorber according to the present embodiment. As another constituent member of the absorbent article according to the present embodiment, a core wrap that retains the shape of the absorber and prevents the constituent member of the absorber from falling off or flowing; Liquid permeable sheet to be arranged; Examples thereof include a liquid permeable sheet arranged on the outermost side opposite to the side on which the liquid to be absorbed enters. Examples of absorbent articles include diapers (for example, paper diapers), toilet training pants, incontinence pads, sanitary materials (sanitary napkins, tampons, etc.), sweat pads, pet sheets, toilet members, animal excrement treatment materials, and the like. ..

FIG. 1 is a cross-sectional view showing an example of an absorbent article. The absorbent article 100 shown in FIG. 1 includes an absorbent body 10, core wraps 20a and 20b, a liquid permeable sheet 30, and a liquid permeable sheet 40. In the absorbent article 100, the liquid permeable sheet 40, the core wrap 20b, the absorbent body 10, the core wrap 20a, and the liquid permeable sheet 30 are laminated in this order. In FIG. 1, there is a portion shown so that there is a gap between the members, but the members may be in close contact with each other without the gap.

The absorber 10 has a water-absorbent resin particle 10a and a fiber layer 10b containing a fibrous material. The water-absorbent resin particles 10a are dispersed in the fiber layer 10b.

The core wrap 20a is arranged on one side of the absorber 10 (upper side of the absorber 10 in FIG. 1) in contact with the absorber 10. The core wrap 20b is arranged on the other side of the absorber 10 (lower side of the absorber 10 in FIG. 1) in contact with the absorber 10. The absorber 10 is arranged between the core wrap 20a and the core wrap 20b. Examples of the core wraps 20a and 20b include tissues, non-woven fabrics, woven fabrics, synthetic resin films having liquid permeation holes, net-like sheets having a mesh, and the like. The core wrap 20a and the core wrap 20b have, for example, a main surface having the same size as the absorber 10.

The liquid permeable sheet 30 is arranged on the outermost side on the side where the liquid to be absorbed enters. The liquid permeable sheet 30 is arranged on the core wrap 20a in contact with the core wrap 20a. Examples of the liquid permeable sheet 30 include non-woven fabrics made of synthetic resins such as polyethylene, polypropylene, polyester and polyamide, and porous sheets. The liquid permeable sheet 40 is arranged on the outermost side of the absorbent article 100 on the opposite side of the liquid permeable sheet 30. The liquid impermeable sheet 40 is arranged under the core wrap 20b in contact with the core wrap 20b. Examples of the liquid impermeable sheet 40 include a sheet made of a synthetic resin such as polyethylene, polypropylene, and polyvinyl chloride, and a sheet made of a composite material of these synthetic resins and a non-woven fabric. The liquid permeable sheet 30 and the liquid permeable sheet 40 have, for example, a main surface wider than the main surface of the absorber 10, and the outer edges of the liquid permeable sheet 30 and the liquid permeable sheet 40 are It extends around the absorber 10 and the core wraps 20a, 20b.

The magnitude relationship between the absorbent body 10, the core wraps 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. Further, the method of retaining the shape of the absorber 10 using the core wraps 20a and 20b is not particularly limited, and as shown in FIG. 1, the absorber may be wrapped by a plurality of core wraps, and the absorber is wrapped by one core wrap. But it may be.

The absorber may be adhered to the top sheet. When the absorber is sandwiched or covered by the core wrap, it is preferable that at least the core wrap and the top sheet are adhered, and the core wrap and the top sheet are adhered and the core wrap and the absorber are adhered to each other. Is more preferable. As a method of adhering the absorber, a hot melt adhesive is applied to the top sheet at predetermined intervals in a striped shape, a spiral shape, etc. in the width direction and adhered; starch, carboxymethyl cellulose, polyvinyl alcohol, polyvinylpyrrolidone, etc. Examples thereof include a method of adhering using a water-soluble binder such as a water-soluble polymer. Further, when the absorber contains heat-sealing synthetic fibers, a method of adhering by heat-sealing of the heat-sealing synthetic fibers may be adopted.

According to the present embodiment, it is possible to provide a liquid absorbing method using the water-absorbent resin particles, the absorber or the absorbent article according to the present embodiment. The liquid absorbing method according to the present embodiment includes a step of bringing the liquid to be absorbed into contact with the water-absorbent resin particles, the absorber or the absorbent article according to the present embodiment. According to this embodiment, it is possible to provide an application of water-absorbent resin particles, an absorber and an absorbent article to a liquid absorbent.

According to the present embodiment, it is possible to provide a method for producing an absorber using the above-mentioned water-absorbent resin particles. The method for producing an absorber according to the present embodiment includes a process for producing water-absorbent resin particles for obtaining the above-mentioned water-absorbent resin particles. The method for producing an absorber according to the present embodiment may include a step of mixing the water-absorbent resin particles and the fibrous material after the step of producing the water-absorbent resin particles. According to the present embodiment, it is possible to provide a method for producing an absorbent article using the absorber obtained by the above-mentioned method for producing an absorber. The method for producing an absorbent article according to the present embodiment includes an absorber manufacturing step for obtaining an absorber by the above-mentioned method for manufacturing an absorber. The method for producing an absorbent article according to the present embodiment may include a step of obtaining an absorbent article by using the absorber and other constituent members of the absorbent article after the absorbent body manufacturing step. For example, an absorbent article is obtained by laminating the absorber and other constituent members of the absorbent article with each other.

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.

<Preparation of water-absorbent resin particles>
(Example 1)
Stirrer (diameter: 8 mm, length: 40 mm) in the center of a stainless steel bat with a fluororesin-coated inner surface (outer dimensions of opening: 210 mm x 170 mm, inner dimensions of bottom surface: 170 x 130 mm, height: 30 mm) , Without ring) was put in. Partial neutralization solution of sodium acrylate (monomer used for polymerization, monomer concentration: 45% by mass, neutralization rate of sodium acrylate: 75 mol%) 340.0 g, ethylene glycol diglycidyl ether 0.0077 g (inside) A cross-linking agent (0.044 mmol) and 59.0 g of ion-exchanged water were added, and then the mixture was uniformly mixed by rotating the stirrer to obtain a mixture. Then, the upper part of the stainless steel vat was covered with a polyethylene film. After adjusting the temperature of the mixture in the stainless steel pad to 25 ° C., the amount of dissolved oxygen was adjusted to 0.1 ppm or less by substituting nitrogen in the mixture. Then, under stirring at 300 rpm, 3.09 g of a 2 mass% potassium persulfate aqueous solution (potassium persulfate: 0.229 mmol) and 0.65 g of a 0.5 mass% L-ascorbic acid aqueous solution were added dropwise in this order. A monomer aqueous solution was prepared. The concentration of the partially neutralized sodium acrylate in the aqueous monomer solution was 38% by mass. A 0.5 mass% L-ascorbic acid aqueous solution was added dropwise, and polymerization started 2 minutes later. After reaching the maximum temperature 22 minutes after the start of polymerization, the temperature began to decrease. The obtained product was immersed in a water bath at 75 ° C. in a container and aged for 20 minutes to obtain a gel (gel after polymerization).

After polymerization after aging, the entire amount of the gel was taken out from the container, and then cut in a grid pattern at 5 cm intervals. The entire amount of the cut post-polymerization gel was sequentially put into a meat chopper (model number: 12VR-750SDX, manufactured by Kiren Royal Co., Ltd.), and the post-polymerization gel was coarsely crushed. The diameter of the hole (circular) of the plate located at the outlet of the meat chopper was 6.4 mm, and the density of the holes was 40 holes / 36.30 cm ² . Rough crushing was performed until no crushed material (coarse crushed gel, hydrogel crushed material) came out from the plate of the meat chopper. Next, the pyroclastic material was dried with hot air at 180 ° C. for 30 minutes to obtain a dried product (crosslinked polymer dried product).

20 g of the dried product was placed in a low-density polyethylene bag (size: 120 mm x 85 mm under the zipper, thickness: 0.04 mm). By reciprocating a 4.0 kg roller (stainless steel, diameter: 10.5 cm, width: 6.0 cm) three times on a low-density polyethylene bag, the dried material is crushed to a size that fits into the inlet of the crusher. A crushed product (crosslinked polymer crushed product) was obtained.

Cross-linking by crushing 20 g of crushed material using an ultracentrifuge crusher (manufactured by Verder Scientific Co., Ltd., product name: ZM200, 6-blade rotor, rotor rotation speed: 6000 rpm, screen trapezoidal hole: 1.00 mm) Polymer particles were obtained. The particle size distribution and medium particle size of the crosslinked polymer particles were measured by the procedure described later.

5.0 g of the above-mentioned crosslinked polymer particles was weighed in a round-bottomed cylindrical separable flask having an inner diameter of 11 cm equipped with a fluororesin anchor-shaped stirring blade. Next, while stirring at 400 rpm, a cross-linking agent solution obtained by mixing 0.0125 g of ethylene glycol diglycidyl ether, 0.750 g of water, 0.25 g of propylene glycol, and 0.25 g of isopropyl alcohol was applied to a pasteur pipette. The mixture was obtained by dropping into a separable flask. Cross-linking was performed by immersing the separable flask in an oil bath at 180 ° C. and heating the mixture while stirring the mixture for 40 minutes. After cooling to room temperature, the mixture was passed through a mesh of 850 μm to obtain 4.5 g of water-absorbent resin particles.

(Comparative Example 1)
A crushed material was obtained by the same method as in Example 1. Next, 20 g of the pyroclastic material was pulverized for 12 seconds using a small crusher (Osaka Chemical Co., Ltd., product name: Wonder Blender WB-1) to obtain crosslinked polymer particles. The particle size distribution and medium particle size of the crosslinked polymer particles were measured by the procedure described later. Then, after performing additional cross-linking by the same method as in Example 1, 4.2 g of water-absorbent resin particles was obtained by passing the mixture through a mesh of 850 μm.

(Comparative Example 2)
Crosslinked polymer particles were produced by the same method as in Comparative Example 1 to obtain crosslinked polymer particles 1. The crosslinked polymer particles 1 were classified with a sieve having an opening of 850 μm, 500 μm, 250 μm, and 106 μm, and a saucer. Crosslinked polymer particles 2 were obtained by remixing the classified particles in a required amount so that the particle size distribution was similar to that of the particles of Example 1. The particle size distribution and the medium particle size of the crosslinked polymer particles 2 were measured by the procedure described later. Then, after performing additional cross-linking by the same method as in Example 1, 4.3 g of water-absorbent resin particles was obtained by passing the mixture through a mesh of 850 μm.

<Particle size distribution>
Using a continuous fully automatic sonic vibration type sieving measuring instrument (Robot Shifter RPS-205, manufactured by Seishin Enterprise Co., Ltd.), crosslink with JIS standard 850 μm, 710 μm, 600 μm, 500 μm, 300 μm, 250 μm and 106 μm sieves and a saucer. The particle size distribution of 5 g of the polymer particles was measured. Calculate the mass percentage of the total mass in the particle size range of "more than 0 μm and less than 106 μm", "106 μm or more and less than 250 μm", "250 μm or more and less than 500 μm", "500 μm or more and less than 850 μm", and "850 μm or more", and the particle size distribution. Asked. The mass percentage of "500 μm or more and less than 850 μm" was calculated based on the total amount of particles remaining on the sieves of 710 μm, 600 μm and 500 μm. The results are shown in Table 1.

<Medium particle size>
Regarding the above-mentioned particle size distribution, the masses of the particles remaining on the sieve are integrated in order from the one with the largest particle size, and the relationship between the mesh size of the sieve and the integrated value of the mass percentage of the particles remaining on the sieve is calculated as a logarithmic probability paper. Plotted in. 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. The results are shown in Table 1.

<CRC>
The CRC of the water-absorbent resin particles was measured by the following procedure with reference to the EDANA method (NWSP 241.0.R2 (15), page.769-778).

A non-woven fabric with a size of 60 mm x 170 mm (product name: Heat Pack MWA-18, manufactured by Nippon Paper Papylia Co., Ltd.) was folded in half in the longitudinal direction to adjust the size to 60 mm x 85 mm. A 60 mm × 85 mm non-woven fabric bag was produced by crimping the non-woven fabrics to each other on both sides extending in the longitudinal direction with a heat seal (a crimped portion having a width of 5 mm was formed on both sides along the longitudinal direction). 0.2 g of the above-mentioned water-absorbent resin particles were contained in the non-woven fabric bag. Then, the non-woven fabric bag was closed by crimping the remaining one side extending in the lateral direction with a heat seal.

The entire non-woven fabric bag was completely moistened by floating the non-woven fabric bag on 1000 g of physiological saline contained in a stainless steel vat (240 mm × 320 mm × 45 mm) without folding the non-woven fabric bag. One minute after the non-woven fabric bag was put into the physiological saline solution, the non-woven fabric bag was immersed in the physiological saline solution with a spatula to obtain a non-woven fabric bag containing the gel.

Thirty minutes after the non-woven fabric bag was put into the physiological saline solution (a total of 1 minute of floating time and 29 minutes of immersion time), the non-woven fabric bag was taken out from the physiological saline solution. Then, the non-woven fabric bag was put in a centrifuge (manufactured by Kokusan Co., Ltd., model number: H-122). After the centrifugal force in the centrifuge reached 250 G, the non-woven fabric bag was dehydrated for 3 minutes. After dehydration, it was weighed mass M _a nonwoven bag containing the mass of gel. Subjecting the above procedure similar relative woven bags without accommodating the water-absorbent resin particles, the mass was measured M _b of the nonwoven fabric bag. The CRC was calculated based on the following formula. M _c is the precisely weighed value of the mass 0.2g of water-absorbent resin particles used for the measurement. The results are shown in Table 1.
CRC [g / g] = {(M _a- M _b ) -M _c } / M _c

<Water absorption under load>
The water absorption amount (room temperature) of the physiological saline under the load (pressurization) of the water-absorbent resin particles was measured using the measuring device Y shown in FIG. 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 (plexiglass)), 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 1.
Water absorption under load [mL / g] = (Vb-Va) /0.1

According to Table 1, it is confirmed that the amount of water absorption under load of the water-absorbent resin particles is improved when the crosslinked polymer particles satisfying the above-mentioned (a) to (c) are obtained in the pulverization step.

10 ... Absorbent, 10a, 65 ... Water-absorbent resin particles, 10b ... Fiber layer, 20a, 20b ... Core wrap, 30 ... Liquid permeable sheet, 40 ... Liquid permeable sheet, 61 ... Burette part, 61a ... Burette, 61b ... Rubber stopper, 61c, 61e ... Cock, 61d ... Air introduction pipe, 62 ... Conduit, 63 ... Measuring table, 64 ... Measuring unit, 64a ... Cylindrical, 64b ... Nylon mesh, 64c ... Weight, 100 ... Absorbent article, Y …measuring device.

Claims (11)

1. It is a method for improving the amount of water absorption under the load of the water-absorbent resin particles obtained by performing additional cross-linking on the crosslinked polymer particles.
   Improvement of water absorption under load by comprising a pulverization step of obtaining crosslinked polymer particles satisfying the following (a) to (c) by pulverizing a crosslinked polymer having a structural unit derived from an ethylenically unsaturated monomer. Method.
   (A) The proportion of particles having a particle diameter of less than 500 μm in the crosslinked polymer particles is 50% by mass or more.
   (B) The proportion of particles having a particle diameter of less than 106 μm in the crosslinked polymer particles is 20% by mass or less.
   (C) The proportion of particles having a particle diameter of 106 μm or more and less than 250 μm in the crosslinked polymer particles is 40% by mass or less.
2. The method for improving water absorption under load according to claim 1, wherein the proportion of particles having a particle diameter of 106 μm or more and less than 250 μm in the crosslinked polymer particles is 20 to 40% by mass.
3. The method for improving water absorption under load according to claim 1 or 2, wherein the ethylenically unsaturated monomer contains at least one selected from the group consisting of (meth) acrylic acid and a salt thereof.
4. The method for improving water absorption under load according to any one of claims 1 to 3, wherein in the pulverization step, the crosslinked polymer is pulverized while passing the crosslinked polymer through a screen.
5. The screen is annular
   The fourth aspect of the present invention, wherein in the pulverization step, a centrifugal force is applied to the crosslinked polymer on the inner peripheral side of the screen to pulverize the crosslinked polymer while passing the crosslinked polymer through the screen. How to improve water absorption under load.
6. Production of crosslinked polymer particles comprising a pulverization step of pulverizing a crosslinked polymer having a structural unit derived from an ethylenically unsaturated monomer to obtain crosslinked polymer particles satisfying the following (a) to (c). Method.
   (A) The proportion of particles having a particle diameter of less than 500 μm in the crosslinked polymer particles is 50% by mass or more.
   (B) The proportion of particles having a particle diameter of less than 106 μm in the crosslinked polymer particles is 20% by mass or less.
   (C) The proportion of particles having a particle diameter of 106 μm or more and less than 250 μm in the crosslinked polymer particles is 40% by mass or less.
7. The method for producing crosslinked polymer particles according to claim 6, wherein the proportion of particles having a particle size of 106 μm or more and less than 250 μm in the crosslinked polymer particles is 20 to 40% by mass.
8. The method for producing crosslinked polymer particles according to claim 6 or 7, wherein the ethylenically unsaturated monomer contains at least one selected from the group consisting of (meth) acrylic acid and a salt thereof.
9. The method for producing crosslinked polymer particles according to any one of claims 6 to 8, wherein in the pulverization step, the crosslinked polymer is pulverized while passing the crosslinked polymer through a screen.
10. The screen is annular
    The ninth aspect of the invention, wherein in the pulverization step, a centrifugal force is applied to the crosslinked polymer on the inner peripheral side of the screen to pulverize the crosslinked polymer while passing the crosslinked polymer through the screen. A method for producing crosslinked polymer particles.
11. A method for producing water-absorbent resin particles, comprising a step of performing additional cross-linking on the cross-linked polymer particles obtained by the method for producing cross-linked polymer particles according to any one of claims 6 to 10.
    
    

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