JP2000302876A - Production of water absorptive resin powder, water absorptive resin powder and its use - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a process for producing water absorptive resin powder having high liquid permeability and, at the same time, high water absorbability, water absorptive powder and its use. SOLUTION: A process for producing water absorptive resin powder by obtaining water absorptive crosslinked polymer particles through an aqueous solution polymerization step comprises a step of abrading the crosslinked polymer particles to increase the bulk density up to not less than 0.72 (g/ml). The water absorptive resin powder is in an indefinite crushed shape and has a bulk density of not less than 0.74 (g/ml) and a water absorption ratio for a 0.9 wt.% physiological saline under a pressure of 0.7 psi (4.83 kPa) of not lower than 20 (g/g). An absorber comprises the water absorptive resin powder and a fiber base material. An absorbent article comprises an absorption layer composed of the absorber.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for producing a water-absorbent resin powder, a water-absorbent resin powder, and uses thereof.

[0002]

2. Description of the Related Art In recent years, sanitary materials such as disposable diapers and sanitary napkins, so-called incontinence pads, have been used as constituent materials thereof.
Water absorbing resin (water absorbing agent) for the purpose of absorbing body fluid
Is widely used. As the above water absorbent resin,
For example, polyacrylic acid partially neutralized cross-linked product, starch-acrylic acid graft polymer hydrolyzate, vinyl acetate-acrylate copolymer saponified product, acrylonitrile copolymer or hydrolyzed acrylamide copolymer or These crosslinked products and crosslinked products of cationic monomers are known.

[0003] The above-mentioned water-absorbing resin should have the following characteristics: excellent water absorption amount, water absorption speed, gel strength, and suction power for sucking water from a base material containing an aqueous liquid when in contact with an aqueous liquid such as a body fluid. And so on. A water-absorbent resin exhibiting excellent performance (absorption characteristics) when used in sanitary materials such as disposable diapers and sanitary napkins. Various absorbers and absorbent articles have been proposed. Examples of the above-mentioned conventional water-absorbent resin or an absorbent or absorbent article using the water-absorbent resin include, for example, a water-absorbent resin having a specific gel capacity, shear modulus, and extractable polymer content (US Pat. No. 4,654,039). No.), a water-absorbing resin having specified water absorption amount, water-absorbing speed and gel strength, and a disposable diaper and sanitary napkin using the water-absorbing resin (JP-A-60-185550, JP-A-60-185551) JP, JP-A-60-185804,
U.S. Pat. No. 4,666,975), specific water absorption and water absorption rate,
A disposable diaper using a water-absorbing resin having gel stability (Japanese Patent Application Laid-Open No. 60-185805), a water-absorbing article using a water-absorbing resin whose water absorption, suction power, and water-soluble component content are specified ( 1963-2
No. 1902), a water-absorbing sanitary article containing a water-absorbing resin having specified water absorption, water absorption under pressure, and gel breaking strength
No. 63-99861), a paper diaper containing a water-absorbent resin whose water absorption amount and water absorption rate under pressure are specified (Japanese Patent Application Laid-Open No. 2-34167), water absorption amount under pressure (AUL) and its particle size were specified. Water-absorbing agent containing water-absorbing resin (European Patent No. 339,461)
No.), water-absorbing agent containing 60 to 100% by weight of a water-absorbing resin whose water absorption rate (FSR) and water absorption under pressure for 5 minutes are specified (European Patent No. 443,627), deformation under load (DUL)
Absorbent (EP 532,002) containing at least 30% by weight or more of a water-absorbent resin having a specified water absorption index (WI), and a resin having a pressure absorption index (PAI) and a 16-hour extractability level of 30%. Absorbent articles (European Patent No. 615,735) using a water-absorbing resin composition comprising a superabsorbent material having a specific water absorption capacity, water absorption rate and liquid permeability under pressure (US Pat. No. 5,985,944), diffusion Water-absorbing agent having a specific absorption capacity (US Pat. No. 5760080), water-absorbing agent composition having a specific diffusion absorption index (European Patent No. 761241), absorption characteristics under pressure (PUP), and physiological saline flow attraction (SFC) )
Absorber using a hydrogel characterized by US Patent No.
No. 5562646) is known. In addition, the absorbent resin powder has a problem that the physical property is deteriorated due to surface destruction when (pneumatic) transportation or after being incorporated into the absorbent article after the production process or the production, but the impact resistance is small with little physical property decrease. Water-absorbing resins are also known (European Patent No. 812873).

[0004]

By applying the above-mentioned various improvements to the water-absorbing resin, the characteristics (water-absorbing properties) when the resin is used in an absorbent body or an absorbent article containing the same can be obtained. The water absorption capacity under pressure, water absorption capacity under pressure, etc.) have been steadily improved as compared with those before improvement, and application to paper diapers having high water absorption has been made. However, the liquid permeability between the particles of the gel after the resin has absorbed water, which is important in actual daily use, is still at an insufficient level.
It cannot be said that the entire water-absorbent resin contained in the absorbent article is fully utilized. Furthermore, in order to ensure the liquid permeability of the gel under high pressure (for example, 0.3 psi (2.07 kPa) corresponding to the load of an infant), it is necessary to increase the crosslink density of the gel and sacrifice the water absorption performance. was there.

Accordingly, an object of the present invention is to provide a method for producing a water-absorbent resin powder having high liquid permeability under pressure and having high water absorbability both under pressure and under no pressure. An object of the present invention is to provide a powder, an absorbent body and an absorbent article using the same. Another object of the present invention is to provide a water-absorbent resin powder which is excellent in impact resistance with little deterioration in physical properties when it is incorporated into an absorbent article by (pneumatic) transport after the production process or production.

[0006]

Means for Solving the Problems The present inventor has made intensive studies to achieve the above object. As a result, the liquid permeability of the water-absorbing resin is insufficient because the resin particles are irregularly crushed, and the surface has angular portions and folds, and therefore, usually tens of thousands to tens of thousands. It was considered that the space through which the liquid could pass between the particles in an absorbent or an absorbent article containing 10,000 or more of the resin particles was not uniform. In addition, because the corners and folds of the particle surface are weak,
It was thought that the impact resistance was reduced. Then, as a means for eliminating the above-mentioned cause, the idea of surface cross-linking after polishing the surface of the resin particles was conceived, and when the resin particles were surface-cross-linked after actual polishing, the water absorption maintained the conventional level. As it was, it was found that the liquid permeability under pressure was significantly improved as compared with the conventional case. In addition, the water-absorbent resin powder whose surface is polished is found to be a water-absorbent resin powder having excellent impact resistance with little deterioration in physical properties during (pneumatic) transport or incorporation into an absorbent article after the production process or production. Was. further,
It has also been found that a novel water-absorbent resin powder having high water absorbency and high bulk specific gravity can be obtained by using the above method. In addition, the water-absorbent resin powder having a high bulk specific gravity in an amorphous crushed shape has a surprisingly improved liquid permeability under pressure between particles, despite the fact that the space when filled is small. I found it. The present invention has been completed as described above.

That is, the amorphous crushed water-absorbent resin powder of the present invention has a bulk specific gravity of 0.74 (g / ml) or more,
And 0.7 psi against 0.9 wt% saline
(4.83 kPa) Water absorption capacity under pressure of 20 (g / g)
It is characterized by the above. The absorbent body of the present invention is characterized by comprising the irregularly crushed water-absorbent resin powder of the present invention and a fiber base material. The absorbent article of the present invention is characterized by comprising an absorbent layer comprising the absorbent of the present invention. Another absorbent article of the present invention is a diaper comprising an absorbent layer comprising the absorbent of the present invention, wherein the proportion of the irregularly crushed water-absorbent resin powder in the absorbent is 30% by weight or more. It is characterized by the following.

[0008] The method for producing the irregularly crushed water-absorbent resin powder of the present invention is a method for producing water-absorbent resin powder, wherein water-absorbent crosslinked polymer particles are obtained through an aqueous solution polymerization step. Is characterized by including a step of polishing until is increased to 0.72 (g / ml) or more.

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in detail. (Method for Producing Water Absorbent Resin Powder) FIG. 1 shows an example of a process for producing the water absorbent resin powder of the present invention. However, the production process of the water-absorbent resin powder of the present invention is not limited to this. The method for producing a water-absorbent resin powder according to the present invention is the method for producing a water-absorbent resin powder which obtains water-absorbent crosslinked polymer particles through an aqueous solution polymerization step. ml) or more.

[0010] The water-absorbent resin powder of the present invention is in an irregularly crushed state. Amorphous crushed particles are water-absorbent resin powders obtained by crushing a gel or a dried product (preferably a dried product) of a crosslinked polymer obtained through aqueous solution polymerization, and crushed particles having an irregular shape. (For example, FIG. 2
(Particles having shapes as shown in (A) and (B)). Hereinafter, the irregularly crushed water-absorbent resin powder in the present invention is simply referred to as a water-absorbent resin powder. The crosslinked polymer particles used in the production of the water-absorbent resin powder of the present invention absorb 50 to 1000 times as much water in ion-exchanged water to form an anionic, nonionic or cationic hydrogel. It is a conventionally known crosslinked polymer, or obtained by drying the polymer, if necessary, and usually pulverizing before and / or after drying. Examples of such a crosslinked polymer include a crosslinked product of a partially neutralized polyacrylic acid, a hydrolyzate of a starch-acrylonitrile graft polymer, a hydrolyzate of a starch-acrylic acid graft polymer, and vinyl acetate-acrylate copolymer. One or two or more of a combined saponified product, a hydrolyzate of an acrylonitrile copolymer or an acrylamide copolymer or a crosslinked product thereof, a carboxyl group-containing crosslinked polyvinyl alcohol modified product, a crosslinked isobutylene-maleic anhydride copolymer, or the like. Can be mentioned. These crosslinked polymers can be used alone or as a mixture. Among them, one having a carboxyl group or a mixture thereof is preferable. Typically, acrylic acid and / or a salt thereof (neutralized product) is used as a main component. The main component is a polymer obtained by polymerizing / crosslinking a monomer to be formed. As the crosslinked polymer, an uncrosslinked water-soluble component in the crosslinked polymer is preferably 20% by weight or less, more preferably 15% by weight or less.
% Or less, more preferably 12% by weight or less, particularly preferably 10% by weight or less.

The acrylates include alkali metal salts of sodium, potassium, lithium and the like of acrylic acid;
Examples thereof include an ammonium salt and an amine salt. The crosslinked polymer has, as its constituent units, 0 mol% to 50 mol% of acrylic acid and 100 mol% of acrylate.
To 50 mol% (however, the total amount of both is 100 mol%), preferably 10 mol% to 40 mol% of acrylic acid and 90 mol% to 60 mol% of acrylate (however, both Is more preferably 100 mol%). Neutralization of the crosslinked polymer for forming the salt may be performed in a monomer state before polymerization, or may be performed in a polymer state during or after polymerization, or may be performed in combination. Although neutralization in the state of a polymer may have the advantage that the soluble component is reduced, the neutralization requires a considerably long time. It is preferable to neutralize in a state.

The monomer for obtaining the crosslinked polymer used in the present invention may contain a monomer other than the above-mentioned acrylic acid (salt) if necessary. The monomer other than acrylic acid (salt) is not particularly limited, but specifically, for example, methacrylic acid, maleic acid, vinylsulfonic acid, styrenesulfonic acid, 2- (meth) acrylamide- Anionic unsaturated monomers such as 2-methylpropanesulfonic acid, 2- (meth) acryloylethanesulfonic acid, 2- (meth) acryloylpropanesulfonic acid and salts thereof; acrylamide, methacrylamide, N-ethyl (meth) Acrylamide, Nn-propyl (meth)
Acrylamide, N-isopropyl (meth) acrylamide, N, N-dimethyl (meth) acrylamide, 2-
Hydroxyethyl (meth) acrylate, 2-hydroxypropyl (meth) acrylate, methoxypolyethylene glycol (meth) acrylate, polyethylene glycol mono (meth) acrylate, vinylpyridine, N
-Vinylpyrrolidone, N-acryloylpiperidine, N
Nonionic unsaturated monomers containing a hydrophilic group such as acryloylpyrrolidine and N-vinylacetamide; N, N-dimethylaminoethyl (meth) acrylate, N, N-diethylaminoethyl (meth) acrylate, N, N-dimethyl Examples include cationic unsaturated monomers such as aminopropyl (meth) acrylate, N, N-dimethylaminopropyl (meth) acrylamide, and quaternary salts thereof. These monomers may be used alone or as a mixture of two or more.

In the present invention, when a monomer other than acrylic acid (salt) is used, the monomer other than acrylic acid (salt) is used in the total amount of acrylic acid and its salt used as a main component. On the other hand, it is preferably at most 30 mol%, more preferably at most 10 mol%. By using a monomer other than the acrylic acid (salt) in the above ratio,
The absorption characteristics of the water-absorbent resin powder finally obtained are further improved, and the water-absorbent resin powder can be obtained at a lower cost. When polymerizing the above-mentioned monomer to obtain the crosslinked polymer used in the present invention, bulk polymerization or precipitation polymerization can be performed, but performance and ease of control of polymerization, and swelling gel can be further improved. From the viewpoint of liquid permeability, aqueous polymerization of the above monomer in an aqueous solution is preferable. When the monomer is used as an aqueous solution, the concentration of the monomer in the aqueous solution (hereinafter, referred to as an aqueous monomer solution) is not particularly limited, but may be from 10% by weight to 70% by weight. It is preferably within the range, more preferably within the range of 20% by weight to 40% by weight. Also, when performing the aqueous solution polymerization,
Solvents other than water may be used in combination as needed, and the type of the solvent used in combination is not particularly limited.

As a method of aqueous solution polymerization, the aqueous monomer solution is polymerized while crushing the obtained hydrogel in a double-arm kneader, or the aqueous monomer solution is supplied in a predetermined container or on a driven belt. And a method of pulverizing a gel obtained by polymerization with a meat chopper or the like. When the above polymerization is initiated, for example, potassium persulfate, ammonium persulfate, sodium persulfate, t-butyl hydroperoxide, hydrogen peroxide, 2,2'-azobis (2-amidinopropane) dihydrochloride, etc. A radical polymerization initiator can be used.

Further, a redox initiator can be obtained by using a combination of these reducing agents which promote the decomposition of the polymerization initiator and combining them. Examples of the reducing agent include (bis) sulfite (salt) such as sodium sulfite and sodium hydrogen sulfite, L-ascorbic acid (salt), reducing metals (salt) such as ferrous salt, and amines. Although it is mentioned, it is not particularly limited. The amount of the polymerization initiator used is usually 0.001 mol% to 2 mol%, preferably 0.01 mol% to 0.1 mol%.
When the use amount of these polymerization initiators is less than 0.001 mol%, unreacted monomers increase, and thus the amount of residual monomers in the obtained polymer increases, which is not preferable.
On the other hand, when the use amount of these polymerization initiators exceeds 2 mol%, the amount of water-soluble components in the obtained polymer increases, which may not be preferable.

The polymerization reaction may be initiated by irradiating the reaction system with an active energy ray such as radiation, an electron beam, or an ultraviolet ray, or the polymerization initiator may be used in combination. In addition, the reaction temperature in the said polymerization reaction is although it does not specifically limit, The range of 15-110 degreeC is preferable, and the range of 20-90 degreeC is more preferable. Also,
The reaction time is also not particularly limited, and may be appropriately set according to the type of the monomer and the polymerization initiator, the reaction temperature, and the like. The crosslinked polymer used in the present invention may be a self-crosslinking type that does not use a crosslinking agent,
Those obtained by copolymerizing or reacting an internal crosslinking agent having two or more polymerizable unsaturated groups or two or more reactive groups in one molecule are more preferable.

Specific examples of these internal crosslinking agents include, for example, N, N-methylenebis (meth) acrylamide,
(Poly) ethylene glycol di (meth) acrylate,
(Poly) propylene glycol di (meth) acrylate, trimethylolpropane tri (meth) acrylate, glycerin tri (meth) acrylate, glycerin acrylate methacrylate, ethylene oxide modified trimethylolpropane tri (meth) acrylate, pentaerythritol hexa (meth) acrylate , Triallyl cyanurate, triallyl isocyanurate, triallyl phosphate, triallylamine, poly (meth) allyloxyalkane, (poly) ethylene glycol diglycidyl ether, glycerol diglycidyl ether, ethylene glycol, polyethylene glycol,
Examples thereof include propylene glycol, glycerin, pentaerythritol, ethylenediamine, ethylene carbonate, propylene carbonate, polyethyleneimine, and glycidyl (meth) acrylate.

These internal crosslinking agents may be used alone or as a mixture of two or more. Further, these internal crosslinking agents may be added to the reaction system all at once, or may be added in portions. When at least one or two or more internal crosslinking agents are used, a compound having two or more polymerizable unsaturated groups is polymerized in consideration of the absorption characteristics and the like of the water-absorbent resin powder finally obtained. It is preferable to use it at times. The amount of the internal crosslinking agent used is preferably in the range of 0.005 mol% to 2 mol%, and more preferably in the range of 0.02 mol% to 0.5 mol%, based on the monomer. More preferably, it is more preferably in the range of 0.04 mol% to 0.2 mol%. If the amount of the internal crosslinking agent used is less than 0.005 mol%, or if it is more than 2 mol%, sufficient absorption characteristics may not be obtained.

When a crosslinked structure is introduced into a polymer using the above internal crosslinking agent, the internal crosslinking agent is added to the reaction system before or during the polymerization of the monomer, after the polymerization, or after the neutralization. May be added. In the above polymerization, various foaming agents such as carbonic acid (hydrogen) salt, carbon dioxide, azo compound, and inert organic solvent; starch / cellulose, starch / cellulose derivatives, polyvinyl alcohol, polyacrylic acid ( A hydrophilic polymer such as a salt) and a crosslinked polyacrylic acid (salt); various surfactants; a chelating agent; and a chain transfer agent such as hypophosphorous acid (salt) may be added.

When the crosslinked polymer is obtained by aqueous solution polymerization and is in a gel state, that is, when the crosslinked polymer is a hydrogel crosslinked polymer, the crosslinked polymer is dried, if necessary, before drying and before drying. And / or later usually pulverized to obtain an irregularly crushed crosslinked polymer. The water content of the crosslinked polymer that can be used in the present invention is not particularly limited, but the water content is preferably 0.1% by weight or more and less than 40% by weight, more preferably 0.2% by weight or more and 20% by weight or less, furthermore Preferably it is 0.5% by weight or more and 10% by weight or less. The average particle size of the crosslinked polymer that can be used in the production method of the present invention is usually 10 μm to 1500 μm, preferably 10 μm.
μm to 1000 μm, more preferably 50 μm to 800
μm, even more preferably more than 75 μm and 700 μm
m or less, particularly preferably more than 150 μm and 600 μm
These are:

Next, polishing of the crosslinked polymer particles, which is a feature of the method for producing a water absorbent resin powder of the present invention, will be described. FIG. 2B shows an example of the shape of the water-absorbent resin powder obtained by the production method of the present invention. The definition of "polishing" in the present invention refers to a mechanical unit operation for reducing the specific surface area by applying external force to break or rub the polymer particles. Therefore, when compared at the same particle size distribution, "polishing" is a different concept from "grinding" in which an increase in specific surface area occurs.

In other words, in the present invention, “crushing” refers to a gel formed by aqueous solution polymerization or, preferably, a solid substance obtained by drying the gel.
A mechanical operation that breaks down by an external force such as a breaking force and reduces the particle size. Pulverization is mainly performed on the whole or inside of the particles. On the other hand, the term "polishing" in the present invention refers to a mechanical operation for smoothing the surface of a particle by removing convex portions from particles having a sharp or sharp portion obtained by grinding. ,
Polishing is mainly performed on the surface of the particles. The method for producing a water-absorbent resin powder of the present invention includes a step of polishing (surface) the crosslinked polymer particles until the bulk specific gravity increases to 0.72 (g / ml) or more. . Here, the bulk specific gravity refers to the bulk specific gravity of the particles after removing fine powder generated by grinding (shaved). Further, the removed fine powder may be collected and reused if necessary. (A method for collecting fine powder of a water-absorbent resin is described in, for example, US Pat. No. 4,950,
No. 692, U.S. Pat.No. 5,064,582, U.S. Pat.No. 5,264,495
No. 5,478,879, EP 812,873, EP 885,917, EP 844,270, etc.).

The term "fine powder" used herein refers to, for example, 10
The particles have a certain particle size or less, such as 0 μm or less, preferably 150 μm or less, and more preferably 212 μm or less. In addition, as a method of removing fine powder, a method of sieving using a sieve or a method of removing by a gas stream can be used.
When removing the fine powder, it is difficult to completely remove the fine powder due to classification efficiency and the like. Therefore, usually, 50 wt% or more, preferably 70 wt% or more of the target fine powder,
More preferably, 90 wt% or more may be removed. In the present invention, it is preferable that the crosslinked polymer particles obtained by the above method are polished, and after the polishing, a surface treatment described later is performed. The particle shape of the crosslinked polymer obtained by the above-mentioned method is irregularly crushed, and includes a square portion and a pleated portion (FIG. 2).
(A) and FIG. 9), and the polishing operation results in a relatively rounded shape (see FIGS. 2B and 8).

By the polishing according to the present invention, the polymer particles become more rounded and have a uniform shape. Therefore, the bulk specific gravity of the polymer after polishing is higher than that before polishing, and The specific gravity is preferably 0.72 g / ml or more,
More preferably, 0.72 to 0.95 g / ml, still more preferably 0.73 to 0.90 g / ml, still more preferably 0.74 to 0.90 g / ml, and still more preferably 0.1 to 0.9 g / ml.
75-0.90 g / ml, even more preferably 0.7
6-0.90 g / ml, particularly preferably 0.78-0.
90 g / ml, most preferably 0.79-0.90 g / ml
ml. If the bulk specific gravity after polishing is lower than 0.72 g / ml, the liquid permeability of the finally obtained absorbent or absorbent article is not sufficiently improved, and the impact resistance of the resulting water-absorbent resin powder ( (Process damage). On the other hand, if it is higher than 0.95 g / ml, it may be difficult to secure a liquid passage space between the gels at the time of swelling. In addition, the value of the bulk specific gravity in the present invention was measured in a state where the solid content (wet basis) of the polymer was 95% by weight or more.

The “bulk specific gravity” (unit: g / ml) is
This is a value representing the total weight of the aggregate of particles when the container is filled into a container having a fixed volume as the weight per unit volume. And when the container is filled with particles, gaps (voids) between the particles
, The bulk specific gravity is a value represented by mass per volume of the particles, such as “density” or “true specific gravity” (unit: g / c
The value is substantially lower than that of m ³ ). In addition, the bulk specific gravity is a value that is affected by the method of filling particles (roughly and densely packed), and furthermore, a certain amount of deviation occurs depending on the type of measuring device (bulk specific gravity meter).

As an apparatus for measuring the bulk specific gravity, for example,
Apparatus indicated by JIS K-3362, JIS K-6
721, ASTM D 1895-69
And the device indicated by edana APPARENT D
Devices such as ENSITY 460, 1-99 are mentioned, but the measured values of these devices do not always indicate the same value, and cannot be compared unconditionally. For example, the above edana APPARENT DE
The value measured by the apparatus indicated by NSITY 460, 1-99 tends to show a somewhat higher value than the value measured by the apparatus used in the present invention (the apparatus indicated by JIS K-3362). In addition, the value differs depending on the measurement conditions. For example, when the measurement container is filled with the water-absorbent resin powder, the measurement value is increased by applying vibration or hitting the measurement device. In the present invention, the measurement was performed without applying vibration or hitting the measurement container during filling. As the value of the bulk specific gravity in the present invention, a value obtained by a measuring device and a measuring method described in Examples described later is employed.

By the polishing according to the present invention, the polymer particles are more rounded and have a uniform shape. Therefore, the decrease in the average particle diameter (D50) of the polymer after polishing from before polishing is smaller in the case of pulverization. It is less than that, preferably 40% or less, more preferably 30% or less, and more preferably 25% or less.
Polishing exceeding 40% is not preferred because the water absorption rate decreases and the amount of fine powder generated increases. The apparatus used for performing the polishing according to the present invention is not particularly limited,
A device capable of polishing the particle surface by mechanically stirring the particles is preferable, and a homogenizer or a pin mill is particularly preferable in that effective polishing can be achieved, and a high-speed homogenizer is more preferably used. A homogenizer is usually a mixing device that converts a solid and liquid or a liquid and liquid two-phase system into a suspension or an emulsion. In the present invention, however, it has been found that the homogenizer is effective for polishing crosslinked polymer particles. Was.

For example, in the present invention, when the crosslinked polymer particles are polished using a homogenizer, the rotation speed is 10
The rotation speed is preferably from 2000 to 20000 rpm, and more preferably 3 rpm.
000-10000 rpm, and the time is 30 seconds-5.
The time is preferably, more preferably 1 minute to 3 hours, even more preferably 3 minutes to 2 hours. By the polishing according to the present invention, the crosslinked polymer particles are rounded and have a uniform shape as described above. And the liquid permeability (under pressure) between the particles is improved, despite the reduced voids between the particles.

Further, the polishing according to the present invention increases the bulk specific gravity (g / ml) of the water-absorbent resin powder as described above. In addition, the same container can be filled with a large amount of the water-absorbing resin powder, and there is also a merit in terms of transportation. Further, by the polishing according to the present invention, since the angular portion of the polymer particles and the portion of the shape of the folds are removed,
Damage to the resin (so-called process damage) due to collision between resin particles or collision between the resin and the device in the process of manufacturing the resin is reduced, and a decrease in physical properties of the resin due to the damage can be suppressed. Further, not only against process damage, but also during transportation after production, during production of a water-absorbent article, and in actual use of a disposable diaper or the like, resin damage can be reduced, and a decrease in physical properties can be suppressed. In addition, the polished particles (water-absorbent resin powder) have improved mixing properties with the surface cross-linking agent as compared with conventional particles (water-absorbent resin powder), and have less lumps (aggregates) during mixing. Since the crosslinking can be performed uniformly, the absorption characteristics and the process damage resistance of the obtained water-absorbent resin powder are improved.

In the method for producing a water-absorbent resin powder of the present invention,
It is preferable to include a step of further mixing a surface cross-linking agent with the polished cross-linked polymer particles (water-absorbent resin powder) obtained as described above and subjecting the cross-linked polymer particles to a surface cross-linking process. By cross-linking the surface, it is possible to reduce agglomeration between the particles or to improve the absorption characteristics under pressure, and to further apply a surface cross-linking treatment to the polished cross-linked polymer (water-absorbent resin powder). Thereby, liquid permeability under pressure can be improved without impairing absorption characteristics under pressure. Examples of the surface crosslinking agent that can be used in the present invention include ethylene glycol, diethylene glycol, propylene glycol, triethylene glycol, tetraethylene glycol, polyethylene glycol, 1,3-propanediol, dipropylene glycol, 2,2,4 Trimethyl-1,3-pentanediol, polypropylene glycol, glycerin, polyglycerin, glycerophosphoric acid, 2-butene-1,4-diol, 1,3-butanediol, 1,4-butanediol, 1,5-pentane Diol, 1,6-hexanediol, 1,2-cyclohexanedimethanol, 1,2-cyclohexanol,
Polyhydric alcohol compounds such as trimethylolpropane, diethanolamine, triethanolamine, polyoxypropylene, oxyethylene-oxypropylene block copolymer, pentaerythritol, sorbitol; ethylene glycol diglycidyl ether, polyethylene glycol diglycidyl ether, glycerol polyglycidyl Epoxy compounds such as ether, diglycerol polyglycidyl ether, polyglycerol polyglycidyl ether, propylene glycol diglycidyl ether, polypropylene glycol diglycidyl ether, glycidol; ethylenediamine, diethylenetriamine, triethylenetetramine, tetraethylenepentamine, pentaethylenehexamine, polyethylene Polyamines such as imines Compounds and their inorganic or organic salts (e.g., aztinium salts); polyvalent isocyanate compounds such as 2,4-tolylene diisocyanate and hexamethylene diisocyanate; 1,2-ethylenebisoxazoline, polyisopropenyloxazoline and the like Polyvalent oxazoline compounds such as copolymers; 1,3-dioxolan-2-one, 4-methyl-1,3-dioxolan-2-
On, 4,5-dimethyl-1,3-dioxolan-2-
On, 4,4-dimethyl-1,3-dioxolan-2-
On, 4-ethyl-1,3-dioxolan-2-one,
4-hydroxymethyl-1,3-dioxolan-2-one, 1,3-dioxan-2-one, 4-methyl-1,
3-dioxan-2-one, 4,6-dimethyl-1,3
-Dioxan-2-one, 1,3-dioxopan-2-
Alkylene carbonate compounds such as ON; haloepoxy compounds such as epichlorohydrin, epibromhydrin, α-methylepichlorohydrin, and polyvalent amine adducts thereof (eg, Hercules-made Kaimen; registered trademark); γ-glycol Sidoxypropyltrimethoxysilane,
silane coupling agents such as γ-aminopropyltriethoxysilane; and polyvalent metal compounds such as hydroxides and chlorides such as zinc, calcium, magnesium, aluminum, iron and zirconium. In consideration of safety when an unreacted surface cross-linking agent remains among these, polyhydric alcohols and alkylene carbonate compounds are preferable. Particularly, those containing a polyhydric alcohol are preferable as the surface cross-linking agent.

These surface crosslinking agents may be used alone or in combination of two or more. When two or more surface crosslinking agents are used in combination, the solubility parameter (S
By combining the first surface cross-linking agent and the second surface cross-linking agent having different P values), a water-absorbing resin having even more excellent absorption characteristics can be obtained. The above-mentioned solubility parameter is a value generally used as a factor indicating the polarity of a compound. The first surface cross-linking agent has a solubility parameter of 12.5 (ca) capable of reacting with a carboxyl group of a cross-linked polymer (water-absorbent resin powder).
l / cm ³ ) ^1/2 (0.0256 (J / m ³ ) ^1/2 ) or more, for example, ethylene glycol, propylene glycol, glycerin, ethylene carbonate,
Propylene carbonate and the like correspond. The second surface cross-linking agent has a solubility parameter of 12.5 which can react with a carboxyl group of a cross-linked polymer (water-absorbent resin powder).
(Cal / cm ³ ) ^1/2 (0.0256 (J / m ³ )
^1/2 )), such as glycerol polyglycidyl ether, (poly) glycerol polyglycidyl ether, ethylene glycol diglycidyl ether, 1,3-butanediol, trimethylolpropane, 1,3-propanediol, 6-hexanediol, diethylene glycol, triethylene glycol, tetraethylene glycol, 1,4-butanediol and the like are applicable.

The amount of the surface cross-linking agent used as needed for the cross-linked polymer (water-absorbent resin powder) after the polishing treatment in the present invention depends on the combination of the cross-linked polymer (water-absorbent resin powder) and the surface cross-linking agent. Although it depends, 100 parts by weight of the crosslinked polymer (water-absorbent resin powder) in a dry state is 0.00.0% by weight.
Within the range of 05 to 10 parts by weight, more preferably 0.05 to 10 parts by weight.
It may be within the range of 5 parts by weight. When the first surface cross-linking agent and the second surface cross-linking agent are used in combination, the amount of the first surface cross-linking agent is preferably 0.01 to 8 parts by weight, more preferably 0.1 to 5 parts by weight. The amount of the second surface cross-linking agent to be used is preferably 0.001 to 1 part by weight, more preferably 0.005 to 0.5 part by weight. By using the surface cross-linking agent within the above range, the absorption characteristics for body fluids (aqueous liquids) such as urine, sweat, menstrual blood, etc. can be further improved. The amount of the surface crosslinking agent used is 0.0
If the amount is less than 05 parts by weight, the crosslink density near the surface of the crosslinked polymer (water-absorbent resin powder) cannot be almost increased, and the absorption characteristics may not be improved. When the amount of the surface cross-linking agent is more than 10 parts by weight, the surface cross-linking agent becomes excessive, which is uneconomical, and it is difficult to control the cross-linking density to an appropriate value, and the water absorption capacity is not improved. There is fear.

In the present invention, when the crosslinked polymer (water-absorbent resin powder) after the polishing treatment is mixed with the surface crosslinking agent, it is preferable to use water. At this time, the amount of water used varies depending on the type, particle size, and water content of the crosslinked polymer, but is 0.5 to 10 parts by weight based on 100 parts by weight of the solid content of the crosslinked polymer (water-absorbent resin powder). Parts by weight, preferably 0.5 to
The range is 3 parts by weight. If the amount of water used exceeds 10% by weight, the water absorption capacity may decrease. If the amount is less than 0.5% by weight, the water absorption capacity under pressure may not be improved. In the present invention, when a crosslinked polymer (water-absorbent resin powder) and a surface crosslinking agent are mixed, a hydrophilic organic solvent may be used. Examples of the hydrophilic organic solvent used include methyl alcohol, ethyl alcohol, propyl alcohol, isopropyl alcohol, butyl alcohol, isobutyl alcohol, t-butyl alcohol, propylene glycol, and other alcohols; ketones such as acetone; dioxane, alkoxy (poly) Ethers such as ethylene glycol and tetrahydrofuran; amides such as N, N-dimethylformamide; and sulfoxides such as dimethyl sulfoxide. The amount of the organic solvent used depends on the type and particle size of the crosslinked polymer (water-absorbent resin powder), but is usually 0 to 10 parts by weight, preferably 100 parts by weight, based on 100 parts by weight of the crosslinked polymer (water-absorbent resin powder). 0-5 parts by weight, more preferably 0.1
-5 parts by weight.

In the present invention, the crosslinked polymer (water-absorbent resin powder) and the surface crosslinking agent are mixed in a state where the crosslinked polymer (water-absorbent resin powder) is dispersed in an organic solvent such as cyclohexane or pentane. The method may be, for example, a method in which water and / or a hydrophilic organic solvent and a surface cross-linking agent are preliminarily mixed as necessary, and then the mixture is sprayed or mixed dropwise onto the cross-linked polymer. The method is preferably a spraying method, and the size of the droplet to be sprayed is preferably 300 μm or less, more preferably 200 μm or less. When water is used for mixing, a water-insoluble fine particle powder and a surfactant may coexist.

A preferred mixing device used for the mixing is
It is necessary to be able to produce large mixing forces to ensure uniform mixing. Examples of the mixing device that can be used in the present invention include, for example, a cylindrical mixer, a double-wall conical mixer, a high-speed stirring mixer, a V-shaped mixer, a ribbon mixer, a screw mixer, and a fluid mixer. A mold furnace rotary disk type mixer, a gas stream type mixer, a double arm type kneader, an internal mixer, a pulverization type kneader, a rotary type mixer, a screw type extruder and the like are preferable. In the method for producing a water-absorbent resin powder of the present invention, the crosslinked polymer (water-absorbent resin powder) polished is
Preferably, after mixing with a surface cross-linking agent, a heat treatment is performed as necessary when cross-linking the vicinity of the surface of the water-absorbent resin powder.

When the heat treatment is performed in the present invention, the treatment time is preferably 1 minute to 180 minutes, more preferably 3 minutes to 120 minutes, and still more preferably 5 minutes to 100 minutes. The processing temperature is preferably in the range of 80 to 250 ° C, and 100 to 210 ° C.
Is more preferable, and the range of 120 to 200 ° C. is still more preferable. When the heating temperature is lower than 80 ° C., the heat treatment takes a long time to cause a decrease in productivity, and further, uniform crosslinking is not achieved, and there is a possibility that an excellent water-absorbing resin powder may not be obtained. If the treatment temperature exceeds 250 ° C., the obtained water-absorbent resin powder may be damaged, and it may be difficult to obtain one having excellent water absorption ratio.

The heat treatment can be carried out using a conventional dryer or heating furnace, and includes a groove-type mixing dryer, a rotary dryer, a disk dryer, a fluidized-bed dryer, a gas-flow dryer, and an infrared dryer. Illustrated. By performing the surface cross-linking, preferably, the water absorption capacity under a pressure of 0.7 psi (4.83 kPa) against 0.9% by weight of physiological saline is 20 (g / g) or more, more preferably 23 (g / g). ) Or more, more preferably 25 (g / g) or more, even more preferably 27 (g / g) or more, particularly preferably 28 (g / g) or more.
(G / g) or more water-absorbent resin powder. In addition, the physical properties are physical properties before undergoing a mechanical damage test described later, but the water-absorbent resin powder of the present invention is different from the conventional one, and the physical properties are maintained even after being subjected to mechanical damage, or An excellent water-absorbing resin powder that hardly decreases.

In the above method for producing a water-absorbent resin powder according to the present invention, if necessary, a deodorant, an antibacterial agent, a fragrance, an inorganic powder such as silicon dioxide or titanium oxide, a foaming agent, a pigment, Dyes, hydrophilic short fibers, plasticizers, adhesives, surfactants, fertilizers, oxidizing agents, reducing agents, water, salts, chelating agents, fungicides, hydrophilic polymers such as polyethylene glycol and polyethylene imine, paraffins, etc. The method may include a step of imparting various functions to the water-absorbing resin powder, for example, by adding a hydrophobic polymer, a thermoplastic resin such as polyethylene or polypropylene, or a thermosetting resin such as a polyester resin or a urea resin. (Water-absorbent resin powder) The amorphous crushed water-absorbent resin powder according to the present invention has a bulk specific gravity of 0.74 (g / ml) or more,
And 0.7 psi against 0.9 wt% saline
(4.83 kPa) Water absorption capacity under pressure of 20 (g / g)
It is characterized by the above, and can be obtained by, for example, the manufacturing method according to the present invention described above, but is not limited by the manufacturing method.

The conventional amorphous crushed water-absorbent resin powder is 0.7 psi with respect to 0.9% by weight of physiological saline.
(4.83 kPa) Water absorption capacity under pressure of 20 (g / g)
In the case described above, only those having a bulk specific gravity of less than 0.74 (g / ml) are disclosed, and the amorphous crushed water-absorbent resin powder according to the present invention is a novel resin. When the bulk specific gravity is 0.74 (g / ml) or more, the space through which the liquid can pass is uniformly distributed throughout the resin, so that the liquid permeability improves.
On the other hand, a water-absorbent resin having a relatively small particle diameter or a spherical shape obtained by reverse-phase suspension polymerization is difficult to immobilize on pulp, is unsuitable for water-absorbent articles, and tends to be closest packed. In addition, the space between the particles that can pass through is too small, and the liquid permeability (under pressure) decreases. Therefore,
The water-absorbent resin powder according to the present invention is a resin having both improved water absorbency and improved liquid permeability (under pressure). Conventionally, in order to ensure the liquid permeability of a gel under high pressure, it is necessary to increase the crosslink density of the gel or to sacrifice the absorption property by adding an additive. In order to ensure water absorption capacity), it was difficult to achieve both water absorption and liquid permeability (under pressure) because liquid permeability was sacrificed, but the water-absorbent resin powder of the present invention required It is made possible.

When the bulk specific gravity is 0.74 (g / ml) or more, there is also an advantage in terms of transportation, such as a compact container (bag) for containing the obtained water-absorbent resin powder. Furthermore, since the resin particles have less extra unevenness, there is an advantage in that the resin particles are less likely to be damaged in the process and in actual use when transferring the resin in the process of manufacturing the water-absorbent resin powder or manufacturing the diaper. Also have. By setting the bulk specific gravity to 0.74 (g / ml) or more,
The present invention has also found an unexpected advantage that the water-soluble content of the water-absorbent resin powder is also reduced. In the amorphous crushed water-absorbent resin powder according to the present invention, the bulk specific gravity is preferably 0.75 (g / ml) or more in terms of improving liquid permeability under pressure and reducing process damage. It is more preferably 0.76 (g / ml) or more, and still more preferably 0.1 g (g / ml).
78 (g / ml) or more, particularly preferably 0.79 (g / ml)
ml) or more. The upper limit of the bulk specific gravity is preferably 0.95 (g / ml) or less, more preferably 0.90 (g / ml).
(G / ml) or less. The upper limit is 0.95 (g / ml)
If it exceeds, the particles will be too densely packed, and the liquid permeability (under pressure) may be reduced, which is not preferable.

In the present invention, 0.3 psi (2.07 k
Pa) The liquid permeability under pressure is the liquid permeability between particles of the water-absorbent resin powder in an absorbent article such as a diaper in consideration of the weight of an infant. However, such 0.3 psi
(2.07 kPa) Liquid permeability under pressure is 0.3 psi
(2.07 kPa) It has been found that this cannot be achieved with a water-absorbent resin powder having only a high water absorption capacity under pressure. Conventionally, a water-absorbing resin powder having a water absorption capacity of 20 (g / g) or more under a pressure of 0.3 psi (2.07 kPa) or a bulk specific gravity of about 0.4 to a maximum of 0.7 (g / ml) A water-absorbent resin powder that has undergone a pulverizing step to a certain degree has been known (for example, in Examples of JP-A-61-200102, a bulk specific gravity of 0.1 was used).
40-0.46 (g / ml) of water-absorbent resin powder is disclosed). However, in general, the water absorption capacity under pressure is reduced by 0.3 psi due to a decrease as the load increases.
(2.07 kPa) Even if the water-absorbent resin powder has a high water absorption capacity under pressure, the water absorption capacity under 0.7 psi (4.83 kPa) pressure is not always high. Same 0.3
Even if the water-absorbent resin powder exhibits a water absorption capacity under pressure of psi, depending on the manufacturing method and the polymer structure, 0.7 psi
Indicate different values.

Therefore, the present inventor has proposed that 0.3 psi (2.
07 kPa) In order to improve the liquid permeability under pressure, the water absorption ratio of the water-absorbent resin powder under 0.7 psi (4.83 kPa) under pressure is increased, and the bulk specific gravity is further increased.
This task has been achieved. That is, in the present invention, the bulk specific gravity of the water-absorbent resin powder is increased by polishing the crosslinked polymer (surface) by the above method, and
By increasing the water absorption capacity under pressure of 0.7 psi (4.83 kPa) from that of the prior art, 0.3 psi (2.07 kPa)
Pa) The liquid permeability under pressure was improved, and the process damage of the water-absorbent resin powder was further reduced.

Further, in the irregularly crushed water-absorbent resin powder according to the present invention, 0.1% by weight of 0.9% by weight physiological saline is used.
The water absorption capacity under a pressure of 7 psi (4.83 kPa) is preferably 23 (g / g) or more, more preferably 25 (g / g).
g) or more, more preferably 27 (g / g) or more, particularly preferably 28 (g / g) or more. In addition, the physical properties are physical properties before undergoing a mechanical damage test described below, but the water-absorbent resin powder of the present invention is different from the conventional one, and even after mechanical damage, the physical properties are maintained. Alternatively, it is an excellent water-absorbing resin powder that hardly decreases. The irregularly crushed water-absorbent resin powder according to the present invention is preferably the one in which the surface vicinity of the resin powder is cross-linked, for the same reason as described in the description of the above-mentioned production method, and furthermore, the cross-linking is performed. Is preferably performed using a surface crosslinking agent containing a polyhydric alcohol. The type of the surface cross-linking agent and the method of surface cross-linking are the same as described above.

The average particle size of the water-absorbent resin powder obtained in the present invention is preferably 150 to 600 μm, more preferably 300 to 600 μm. The fine powder having a size of 150 μm or less is usually at most 10% by weight, preferably at most 5% by weight, based on the total amount of the water-absorbent resin powder. The amorphous crushed water-absorbent resin powder according to the present invention preferably has a lightness (brightness index) L value of at least 85 measured using a spectroscopic colorimeter or the like, and exhibits a chromaticity (chromaticity index). The value and the b value are preferably in the range of ± 2 for the a value and in the range of 0 to 9 for the b value. When the L value, a value, and b value are out of the above ranges, the surface of the water-absorbent resin powder tends to be colored in brown, and particularly, the water-absorbent resin concentration (% by weight) in the absorber is low. If it is too high, the particles of the water-absorbent resin may look like yellow spots in the absorber, which is not preferred by consumers. Such lightness and chromaticity depend on the raw materials (monomer,
It is determined by the initiator and its purity, the production conditions (heating temperature and time), etc., but the above-mentioned conditions of the present invention may be appropriately performed.

The irregularly crushed water-absorbent resin powder according to the present invention or the water-absorbent resin powder obtained by the production method of the present invention has a small decrease in physical properties due to process damage (mechanical damage), and has little mechanical damage. The water absorption capacity after the test (described later in Examples) is preferably 25 (g).
/ G) or more, more preferably 30 (g / g) or more, and even more preferably 35 (g / g) or more. The water-soluble component is the same as the above-mentioned range, and is preferably 20% by weight or less, more preferably 15% by weight or less, further preferably 12% by weight or less, and still more preferably 10% by weight.
It is as follows. (Absorbent Body) The absorbent body according to the present invention is characterized by comprising the irregularly crushed water-absorbent resin powder according to the present invention and a fiber base material such as a hydrophilic fiber. When the absorber is made of, for example, a water-absorbent resin powder and hydrophilic fibers, the structure of the absorber may be, for example, a structure including a uniform mixture of the water-absorbent resin powder and the hydrophilic fibers. It is preferable in that the effects of the present invention can be sufficiently exhibited. In this case, the weight ratio of the water-absorbent resin powder to the hydrophilic fiber is usually 2
0:80 to 90:10, preferably 3
0:70 to 90:10, more preferably 40:70.
60-80: 20, more preferably 5
The range is from 0:50 to 80:20. Since the surface of the water-absorbent resin powder of the present invention is polished and excellent in liquid permeability, the ratio of the water-absorbent resin powder is 30% by weight or more in order to maximize its characteristics. Preferably,
More preferably, it is at least 40% by weight. Examples of such a material include a structure in which a water-absorbent resin powder and a hydrophilic fiber are uniformly mixed; a method in which a water-absorbent resin powder and a hydrophilic fiber are uniformly mixed to form a layer, and a layer is formed thereon. A structure in which hydrophilic fibers are laminated; a structure in which a water-absorbent resin powder and a hydrophilic fiber are uniformly mixed to form a layer, and the water-absorbent resin powder is sandwiched between the layer and the hydrophilic fibers formed in a layer. Can be exemplified. In addition, a configuration in which a water-absorbing resin powder is sandwiched between hydrophilic fibers formed in layers may be used. Further, the absorber may have a configuration in which a specific amount of water is mixed with the water-absorbent resin powder to form the water-absorbent resin powder into a sheet. The configuration of the absorber is not limited to the above-described configuration.

Examples of the above-mentioned fiber base material include, for example, cellulose fibers such as mechanical pulp, chemical pulp, semi-chemical pulp and dissolved pulp obtained from wood, and hydrophilic fibers such as artificial cellulose fibers such as rayon and acetate. No. Among the fibers exemplified above, cellulose fibers are preferred. Further, the hydrophilic fibers may contain synthetic fibers such as polyamide, polyester, and polyolefin. In addition, the fiber base material is not limited to the fibers exemplified above. When the ratio of the fiber base material such as hydrophilic fibers in the absorber is relatively small, the absorbers, that is, the hydrophilic fibers may be bonded to each other using an adhesive binder. By adhering the hydrophilic fibers to each other, the strength and shape retention of the absorber before and during use of the absorber can be increased.

Examples of the adhesive binder include heat-fusible fibers such as polyolefin fibers such as polyethylene, polypropylene, ethylene-propylene copolymer, and 1-butene-ethylene copolymer, and emulsions having adhesive properties. . These adhesive binders may be used alone or as a mixture of two or more. The weight ratio of the hydrophilic fiber to the adhesive binder is 50/50.
９９99/1 is preferred, and 70 / 30〜95 / 5.
Is more preferable, and the range of 80/20 to 95/5 is still more preferable. Since the absorbent according to the present invention is manufactured using the water-absorbent resin powder that is resistant to the process damage according to the present invention, the decrease in physical properties during the manufacture of the absorbent is small, and therefore, high absorbency and high liquid permeability are achieved. The effects of the water-absorbent resin powder of the present invention, such as compatibility, can be exhibited even in the absorber. (Absorptive article) The absorbent article according to the present invention is characterized by comprising an absorbent layer comprising the above-described absorber according to the present invention.

The absorbent article according to the present invention preferably comprises
An absorbent layer made of such an absorber is sandwiched between a liquid-permeable top sheet and a liquid-impermeable back sheet. Nonwoven fabric, cellulose, which helps liquid diffusion
A diffusion layer made of crosslinked cellulose or the like can be provided. Since the absorbent article according to the present invention has the absorbent layer composed of the absorbent having the above configuration, it has both excellent absorption characteristics and excellent liquid permeability as described above. Specific examples of the absorbent article include, but are not particularly limited to, sanitary materials such as disposable diapers and sanitary napkins, so-called incontinence pads. Since the absorbent article has excellent absorption characteristics and liquid permeability, for example, when the absorbent article is a paper diaper, it can prevent urine from leaking and impart a so-called dry feeling. Can be. In particular, when the absorbent article of the present invention is a diaper, the absorbent article comprises an absorbent layer comprising the absorbent of the present invention, and the proportion of the irregularly crushed water-absorbent resin powder in the absorbent is not less than 30% by weight. It is preferable that the diaper can sufficiently exhibit the performance as a diaper having excellent liquid permeability, more preferably 40% by weight or more, further preferably 50% by weight or more, and particularly preferably 60% by weight or more.

The above-mentioned liquid-permeable sheet (hereinafter, referred to as a liquid-permeable sheet) is made of a material having a property of transmitting an aqueous liquid. Examples of the material of the liquid permeable sheet include a nonwoven fabric, a woven fabric, and a porous synthetic resin film made of polyethylene, polypropylene, polyester, polyamide, or the like. The liquid-impermeable sheet (hereinafter, referred to as a liquid-impermeable sheet) is made of a material having a property of impermeable to an aqueous liquid. As a material of the liquid impermeable sheet, for example, a synthetic resin film made of polyethylene, polypropylene, ethylene vinyl acetate, polyvinyl chloride, or the like; a film made of a composite material of these synthetic resin and nonwoven fabric; And the like.
Note that the liquid impermeable sheet may have a property of transmitting vapor.

The structure of the absorption layer is not particularly limited, as long as it has the above-mentioned absorber. Further, the method for producing the absorbing layer is not particularly limited. further,
The method for sandwiching the absorbent layer between the liquid-permeable sheet and the liquid-impermeable sheet, that is, the method for producing an absorbent article is not particularly limited. In addition, a deodorant, a fragrance, various inorganic powders, a foaming agent, a pigment, a dye, a hydrophilic short fiber, a fertilizer, an oxidizing agent, a reducing agent, a chelating agent, water, salts and the like are further added to the above absorber, Thereby, various functions may be given to the absorber or the absorbent article. The absorbent article according to the present invention,
Since the absorbent is made using the water-absorbent resin powder according to the present invention described above, the effects of the water-absorbent resin powder of the present invention, such as high absorbency and high liquid permeability, can be exhibited.

[0051]

The present invention will be described in more detail with reference to examples and comparative examples, but the present invention is not limited to these examples. In addition, various properties of the polymer and the water-absorbing resin powder were measured by the following methods. Further, when the physical properties of the water-absorbent resin powder are measured, the water-absorbent resin powder may have a water content if necessary, if the water-absorbent resin powder has absorbed moisture due to distribution, storage, or compounding with an absorbent article. It is preferable to correct. For example, when the water content (based on moisture content) of the water-absorbent resin powder is less than 5% by weight, the measured value may be used as it is without correcting the moisture content, but the moisture content (based on moisture content) may be reduced due to moisture absorption or the like. When the content is 5% by weight or more, a value obtained by correcting the moisture content of the following measured value (for example, 5% by weight) is used, or the water-absorbent resin powder which has been absorbed in the measurement is dried in advance (for example, windless drying at 60 ° C.). (Drying under reduced pressure in a vessel). (Water Absorption Ratio Under No Pressure) 0.2 g of the water-absorbent resin powder was uniformly placed in a nonwoven bag (60 mm × 60 mm) and immersed in 0.9% by weight saline. After 60 minutes, the bag was pulled out, and after draining at 250 G for 3 minutes using a centrifuge, the weight W1 (g) of the bag was measured. Further, the same operation was performed without using the water-absorbing resin powder, and the weight W0
(G) was measured. From these W1 and W0, the water absorption capacity under no pressure (g / g) was calculated according to the following equation.

Water absorption capacity under no pressure (g / g) = (W1
(G) -W0 (g)) / weight of water-absorbent resin powder (g) (Water absorption under pressure) First, a measuring apparatus used for measuring water absorption under pressure will be described with reference to FIG. As shown in FIG. 3, the measuring device includes a balance 11, a container 12 having a predetermined capacity placed on the balance 11, and an outside air suction pipe 13.
, A conduit 14, a glass filter 16, and a measuring unit 15 mounted on the glass filter 16.

The container 12 has an opening 12 at its top.
a has an opening 12b on the side surface thereof. An outside air suction pipe 13 is fitted into the opening 12a of the container 12, while a conduit 14 is attached to the opening 12b. The container 12 contains a predetermined amount of physiological saline 22. The lower end of the outside air suction pipe 13 is submerged in the physiological saline 22. The outside air suction pipe 13
It is provided to keep the pressure in the container 12 approximately at atmospheric pressure. The above glass filter 16 is formed to have a diameter of 55 mm. The container 12 and the glass filter 16 communicate with each other by a conduit 14 made of silicone resin. In addition, the glass filter 16 is
The position and height with respect to 2 are fixed.

The measuring section 15 includes a filter paper 17, a support cylinder 18, and a wire mesh 1 attached to the bottom of the support cylinder 18.
9 and a weight 20. And the measuring unit 15
Is a filter paper 17 on a glass filter 16 and a wire mesh 19 on the bottom.
Are placed in this order, and a weight 20 is placed inside the support cylinder 18, that is, on a wire mesh 19. The wire mesh 19 is made of stainless steel,
It is formed to 400 mesh (38 μm mesh).
The height of the upper surface of the wire mesh 19, that is, the height of the contact surface between the wire mesh 19 and the water-absorbent resin powder 21 is set to be equal to the height of the lower end surface 13a of the outside air suction pipe 13. Then, a predetermined amount and a predetermined size of the water-absorbing resin powder are uniformly spread on the wire net 19. Weight 2
0 is 0.0 with respect to the water-absorbent resin powder 21 on the wire mesh 19.
The weight is adjusted so that a load of 7 psi (4.83 kPa) can be applied uniformly.

The water absorption capacity of the water-absorbent resin powder 21 under pressure was measured using the measuring apparatus having the above-mentioned structure. The measuring method will be described below. First, a predetermined amount of 0.
A 9% by weight physiological saline solution 22 was put in, and a predetermined preparation operation such as fitting the outside air suction pipe 13 was performed. Next, the filter paper 17 is placed on the glass filter 16, and in parallel with the placing operation, 0.9 g of the water-absorbent resin powder is uniformly dispersed inside the support cylinder 18, that is, on the wire net 19. The weight 20 was placed on the water absorbent resin powder 21. Next, the wire mesh 19 of the support cylinder 18 on which the water-absorbent resin powder 21 and the weight 20 were placed was placed on the filter paper 17 such that the center portion thereof coincided with the center portion of the glass filter 16.

Then, the weight (g) of the physiological saline 22 absorbed by the water-absorbent resin powder 21 was measured with the balance 11 over a period of 60 minutes from the time when the support cylinder 18 was placed on the filter paper 17. Asked from. The same operation is performed without using the water-absorbent resin powder 21, and the blank weight, that is, the weight (g) of the physiological saline 22 absorbed by the filter paper 17 and the like other than the water-absorbent resin powder 21 is measured by the balance 11. It was determined from the measured value and used as a blank value. Next, the weight (g) of the physiological saline 22 actually absorbed by the water-absorbent resin powder 21 is corrected by subtracting the blank value from the water-absorbent resin powder 2.
The water absorption capacity (g / g) under pressure was calculated by dividing the weight by 0.9 (0.9 g). (Liquid flow under pressure) Using the apparatus shown in FIG. 4, the water-absorbent resin powder (0.900 g) uniformly placed in the container 40 was placed under a pressure of 0.3 psi (2.07 kPa) in artificial urine (1). ,
Swell for 60 minutes, then 0.3 psi (2.07 kP
Under the pressure of a), the amount (g) of the 0.69% by weight aqueous solution of sodium chloride 33 that passed through the swollen gel 44 (mainly between the particles) for 10 minutes was measured.

In the apparatus shown in FIG. 4, a glass tube 32 is inserted into a tank 31, and the lower end of the glass tube 32 is filled with a 0.69 wt% sodium chloride aqueous solution 33 by a swelling gel 44 in a cell 41. Positioned so that it could be maintained at a height of 5 cm above the bottom. The 0.69% by weight aqueous sodium chloride solution 33 in the tank 31 is
To the cell 41. Under the cell 41, a container 48 for collecting the passed liquid was arranged, and the collection container 48 was set on a fine balance 49. Cell 41
Has an inner diameter of 6 cm, and No. A 400 stainless steel wire mesh (mesh size 38 μm) 42 was provided. At the bottom of the piston 46, there is a hole 47 sufficient for liquid to pass. At the bottom, a glass filter 45 with good permeability is attached so that the water-absorbent resin powder or its swollen gel does not enter the hole 47. Was. The cell 41 was placed on a table on which the cell was placed, and the surface of the table in contact with the cell was placed on a stainless steel wire netting 43 that did not hinder the liquid permeation.

The measured value was obtained by reading the amount of liquid (g) flowing for 10 minutes after opening the cock 35 with a precision balance. Artificial urine (1) is 0.25 g of calcium chloride dihydrate,
Potassium chloride 2.0 g, magnesium chloride hexahydrate 0.50 g, sodium sulfate 2.0 g, ammonium dihydrogen phosphate 0.85 g, diammonium hydrogen phosphate 0.1 g.
What added 15 g and 994.25 g of pure water was used. (Mechanical damage test) In a glass container (mayonnaise bottle manufactured by Yamamura Glass Co., Ltd., trade name: A-29) shown in FIG. 10 g of glass beads). This was dispersed in a dispersing machine shown in FIG.
88 test disperser), and was fixed by being clamped between clamps provided, and a vibration having a vibration rotation speed of 750 cpm at 100 V / 60 Hz was applied for 30 minutes. As a result, the container fixed to the dispersing machine tilts left and right by 12.5 ° (total 25 °) with respect to the mounting surface of the clamp in the dispersing machine, and simultaneously vibrates 8 mm (total 16 mm) forward and backward. This gives an impact to the water-absorbent resin powder inside the container.

The above-mentioned impact is a force empirically determined as a representative of the impact applied to the water-absorbent resin powder during the manufacturing process of the water-absorbent resin powder. It can be widely applied to damages. (Bulk specific gravity) The bulk specific gravity was measured according to JIS K 3362 using a bulk specific gravity measuring instrument (manufactured by Kuramochi Scientific Instruments Co., Ltd.) shown in FIG. After 120 g of a sufficiently mixed sample (water-absorbent resin particles) was put into the funnel 62 with the damper 61 closed, the damper 61 was quickly opened, and the sample was dropped into the receiver 63. The sample raised from the receiver
After being ground with a glass rod, the receiver containing the sample was accurately weighed to 0.1 g, and the bulk specific gravity was calculated by the following equation. In addition, the solid content (wet amount basis) of the water-absorbent resin powder at the time of measuring the bulk specific gravity was measured at 95% by weight or more. The temperature at the time of measurement was 25 ± 2 ° C., and the relative humidity was 30 to 50%. The solid content (wet amount basis) of the water-absorbent resin powder is 9
When the content is less than 5% by weight, it is preferable to conduct measurement after drying under reduced pressure in a windless drier at 60 ° C. to make the solid content (wet weight basis) 95% by weight or more.

S = (CA) / B S: Bulk specific gravity (g / ml) A: Weight of receiver (g) B: Internal volume of receiver (100 ml) C: Reception of receiver containing sample Weight (g) (Specific surface area) The specific surface area of the water-absorbent resin powder is represented by “BET
(Brunauer-Emmett-Teller) one-point method ". As a measuring device, "specimen fully automatic specific surface area measuring device 4-sorb U-1" (manufactured by Yuasa Ionics) was used. First, about 5 g of a water-absorbing resin powder (a sample is particles previously classified into a range of 850 to 212 or 850 to 150 μm by a sieve) is placed in a microcell (TYPE: QS-400) having an internal capacity of about 13 cm ³ , The microcell containing the sample was heated to 150 ° C. under a gas stream to sufficiently deaerate and dehydrate the sample. Next, the microcell containing the sample was cooled to -200 ° C. under a mixed gas flow of helium gas and 0.1% krypton gas, and the mixed gas was adsorbed to the sample until equilibrium was reached. Thereafter, the temperature of the microcell containing the sample was returned to room temperature, the mixed gas was desorbed from the sample, and the specific surface area of the water-absorbent resin powder was determined from the amount of desorbed krypton mixed gas. The adsorption / desorption step of the microcell containing the sample was performed three times, and the specific surface area (m ² / g) of the water-absorbent resin powder was determined from the average amount. (Weight average particle size)
Particle size distribution of particles classified in the range of 0 to 212 or 850 to 150 μm (for example, 600 μm, 500 μm,
25 μm, 300 μm, 212 μm, 150 μm, 10
6 μm) were plotted on log probability paper. Thereby, the weight average particle diameter (D50) was read. (Water content) 1.000 g of the water-absorbent resin powder is 52 mm in inner diameter
In an aluminum cup of
Heat drying for hours. The moisture content (% by weight) was determined using the loss on drying (g) of the powder as moisture. (Evaluation of color of water-absorbent resin powder) Lightness (brightness index) L value, chromaticity (chromaticity index) a of water-absorbent resin powder
The value and b value are measured with a spectroscopic color difference meter (SZ-Σ80 COLOR MEASURING S) manufactured by Nippon Denshoku Industries Co., Ltd.
YSTEM), setting conditions (reflection measurement / supplied powder / paste sample table (30 mmφ) / powder as standard)
Standard round white plate for paste NO. 2 / 30Φ floodlight pipe)
, The surface color of the water-absorbent resin powder was measured. (Absorption Rate of Absorber: Core Acquisition) 11.4 g of the water-absorbent resin powder and 6.2 g of wood pulp were dry-mixed using a mixer. 260 mm × 1
An absorber (the ratio of the water-absorbent resin powder in the absorber was 65% by weight) was produced by forming the web into a web having a size of 50 mm.

On the other hand, 1.9% by weight of urea and 0.8% of NaCl
% By weight, 0.1% by weight of CaCl ₂ and MgSO ₄
Artificial urine (2) having a composition of 0.1% by weight (the rest being water)
Was prepared. A load of 18 g / cm ² was uniformly applied to the entire absorber, and a cylinder having a diameter of 30 mm and a height of 120 mm was pressed against the center of the absorber, and the cylinder was set upright. Then, 50 g of the artificial urine (2) at 25 ° C. was quickly poured (at once) into the cylinder, and from the time when the artificial urine (2) was started to be poured, the artificial urine (2) in the cylinder was completely absorbed from the center to the entire absorber. Measure the time until
The second absorption rate (second) was used. Then, the same measurement was repeated twice at 50 minute intervals using the absorber used for the above measurement, and the second absorption speed (second) and the third absorption speed (second) were measured.

The liquid diffusivity of the absorber can be evaluated as higher as the absorption speed is higher, that is, as the number of seconds is shorter. (Performance evaluation of absorbent article: Kewpie doll test) 65 parts by weight of water-absorbent resin powder and 35 parts by weight of wood pulp were dry-mixed using a mixer. The resulting mixture was air-formed on a wire screen formed into a 400 mesh (mesh size: 38 μm) using a batch-type air-forming apparatus to form a web having a size of 120 mm × 400 mm. Further, the web is pressed at a pressure of 2 kg / cm ²
By pressing for 5 seconds, the basis weight is about 0.047g
/ Cm ² (65% by weight of water-absorbent resin powder in the absorber).

Subsequently, a back sheet (liquid-impermeable sheet) made of liquid-impervious polypropylene and having a so-called leg gather, the absorber, and a top sheet (liquid-permeable sheet) made of liquid-pervious polypropylene ) Were adhered to each other in this order using a double-sided tape, and two so-called tape fasteners were attached to the adhered product to obtain an absorbent article (diaper). The absorbent article is mounted on a so-called Kewpie doll (55 cm in length and 5 kg in weight). After the doll is placed in a prone state, a tube is inserted between the absorbent article and the doll to correspond to a position for urinating in the human body. In each position, 50 g of 0.9% by weight physiological saline was sequentially injected at intervals of 20 minutes. When the injected physiological saline was not absorbed by the absorbent article and leaked to the outside, the injection operation was terminated, and the total amount (g) of the physiological saline injected up to this time was measured.

The above measured values were repeated four times, and the obtained 4
The average of the two measured values was determined, and this value was taken as the amount of absorption (g). The larger the amount of absorption, the better the performance of the absorbent article was evaluated. (Soluble Amount) 0.5 g of the water-absorbent resin powder was dispersed in 1000 ml of deionized water, stirred for 16 hours, and the swollen gel was filtered with filter paper. Then, the water-soluble polymer in the obtained filtrate, that is, the amount of soluble matter eluted from the water-absorbent resin powder (% by weight, relative to the water-absorbent resin powder) was measured by colloid titration.

Reference Example 1 Acrylic having a neutralization ratio of 75 mol% in a reactor formed by attaching a lid to a jacketed stainless steel double-armed kneader having two sigma-type blades and having a capacity of 10 liters and having a capacity of 10 liters. To 5500 g of an aqueous solution of sodium acidate (monomer concentration 33% by weight) was added 2.50 of polyethylene glycol diacrylate.
When 2.4 g of ammonium persulfate and 0.12 g of L-ascorbic acid were added with stirring to the reaction solution in which g had been dissolved, polymerization started about 1 minute later. And
While pulverizing the formed gel, polymerization was carried out at 30 to 80 ° C., and 60 minutes after the start of the polymerization, the hydrogel crosslinked polymer (1) was taken out.

The obtained hydrogel crosslinked polymer (1) was
The diameter was subdivided to about 5 mm or less. The finely divided hydrogel crosslinked polymer (1) is spread on a 50-mesh (mesh opening: 300 μm) wire mesh and dried with hot air at 150 ° C. for 90 minutes to obtain a water-absorbent resin (A) as a crosslinked polymer. I got Reference Example 2 In a reaction vessel equipped with a stainless steel vat and a thermometer and a lid, polyethylene glycol diacrylate was added to an aqueous solution of sodium acrylate having a neutralization ratio of 65 mol% in an amount of 2000 g (monomer concentration: 35% by weight). 3.97 g of a 5% by weight aqueous sodium persulfate solution was added to the reaction solution in which 1.97 g was dissolved.
And a 0.5% by weight aqueous solution of L-ascorbic acid 2.92
g, 5% by weight 2,3′-azobis (2-amidinopropane) dibasic acid salt (trade name: V-50, manufactured by Wako Pure Chemical Industries, Ltd.) 3.24 g, 0.35% by weight aqueous hydrogen peroxide solution 3.34 g was added with stirring and the reaction solution was degassed with nitrogen, and polymerization started about 1 minute later. And
Polymerization is performed while cooling the lower surface of the reaction vessel to 10 ° C.
Ten minutes after the start of the polymerization, the peak temperature of the exotherm (82 °
C) has been reached. Then, the lower surface of the reactor was heated at 60 ° C. for 20 minutes.
After heating for 1 minute, the hydrogel crosslinked polymer (2) was taken out.

The resulting hydrogel crosslinked polymer (2) was pulverized with a meat chopper (Hiraga Seisakusho Co., Ltd., two blades, die diameter: 9.5 mm) so that the gel diameter became about 5 mm or less. The pulverized hydrogel crosslinked polymer (2) is spread on a 50-mesh (mesh size: 300 μm) wire mesh and dried with hot air at 170 ° C. for 40 minutes to remove the water-absorbent resin (B) as a crosslinked polymer. Obtained. Reference Example 3 In a reaction vessel equipped with a stainless steel vat and a thermometer and a lid, polyethylene glycol diacrylate was added to an aqueous solution of sodium acrylate having a neutralization rate of 70 mol% in an amount of 2000 g (monomer concentration: 39% by weight). 4.33 g of the reaction solution was dissolved in a 20% by weight aqueous solution of sodium persulfate 5.33 g
g and 0.5% by weight L-ascorbic acid aqueous solution 3.2
When 0 g was added with stirring and the reaction solution was degassed with nitrogen, polymerization started about 4 minutes later. Then, the polymerization was carried out while cooling the lower surface of the reaction vessel to 15 ° C., and the peak temperature of the heat generation (93 ° C.) was reached 16 minutes after the polymerization started. Thereafter, the lower surface of the reactor was heated at 80 ° C. for 20 minutes, and then the hydrogel crosslinked polymer (3) was taken out.

The obtained hydrogel crosslinked polymer (3) was pulverized with a meat chopper (Hiraga Seisakusho Co., Ltd., two blades, die diameter 16 mm) so that the gel diameter was about 5 mm or less. This ground hydrogel crosslinked polymer (3)
Spread on a 50 mesh (mesh opening 300 μm) wire mesh,
The resultant was dried with hot air at 170 ° C. for 40 minutes to obtain a water-absorbent resin (C) as a crosslinked polymer. -Example 1-The water-absorbing resin (A) which is the crosslinked polymer obtained in Reference Example 1
Was crushed by a hammer mill (Rostor: hole diameter: 3 mm), and 150 g of a water-absorbing resin was put into a homogenizer (manufactured by Nippon Seiki Co., Ltd., high-speed homogenizer, Model: MX-7) and polished at 6,000 rpm for about 1 hour. The obtained water-absorbent resin is passed through a JIS standard sieve (opening 850, 21).
2 μm) and classified to a particle size of 850 to 212 μm. Table 1 shows the measurement results of the water absorption capacity under no pressure, the soluble content, the bulk specific gravity, and the average particle diameter of the obtained amorphous crushed water-absorbent resin powder (1). FIG. 8 shows an electron micrograph showing the particle structure of the obtained irregularly crushed water-absorbent resin powder (1).

Example 2 Water-absorbing resin (A) which is the crosslinked polymer obtained in Reference Example 1
Was ground with a roll granulator (Model: GRN1041 manufactured by Nippon Granulator Co., Ltd.), and 150 g of a water-absorbent resin was put into a homogenizer (manufactured by Nippon Seiki Co., Ltd., high-speed homogenizer, Model: MX-7), and the number of rotations was 6,000 rpm. For 25 minutes. The obtained water-absorbent resin is passed through a JIS standard sieve (opening 850, 21).
2 μm) and classified to a particle size of 850 to 212 μm. Table 1 shows the results of the measurement of the water absorption capacity under no pressure, the soluble content, the bulk specific gravity, and the average particle size of the obtained amorphous crushed water-absorbent resin powder (2).

Example 3 Water-absorbing resin (B) which is the crosslinked polymer obtained in Reference Example 2
After manually dissolving 150 g of the water-absorbent resin, a homogenizer (manufactured by Nippon Seiki Co., Ltd., high-speed homogenizer, Model: M
X-7), and polished at 6000 rpm for about 1 hour. The obtained water-absorbent resin was sieved with a JIS standard sieve (mesh opening 850, 212 μm) and classified to a particle size of 850 to 212 μm. Table 1 shows the results of the measurement of the water absorption capacity under no pressure, the soluble content, the bulk specific gravity, and the average particle size of the obtained amorphous crushed water-absorbent resin powder (3).

Example 4 The water-absorbent resin (B) which is the crosslinked polymer obtained in Reference Example 2
After manually dissolving 150 g of the water-absorbent resin, a homogenizer (manufactured by Nippon Seiki Co., Ltd., high-speed homogenizer, Model: M
X-7) and polished at 6000 rpm for about 15 minutes. The obtained water-absorbent resin is sieved with a JIS standard sieve (850, 212 μm opening), 850 to 212 μm
Was classified. Table 1 shows the measurement results of the water absorption capacity under no pressure, the soluble matter content, the bulk specific gravity, and the average particle size of the obtained amorphous crushed water-absorbent resin powder (4).

Example 5 The water-absorbent resin (C) which is the crosslinked polymer obtained in Reference Example 3
Was ground with a hammer mill (Rostor: hole diameter 3 mm), and then 180 g of the water-absorbent resin was put into a homogenizer (manufactured by Nippon Seiki Co., Ltd., high-speed homogenizer, Model: MX-7), and polished at 6,000 rpm for about 1.5 hours. did. The obtained water-absorbent resin is passed through a JIS standard sieve (opening 850,
(212 μm) and classified to a particle size of 850 to 212 μm. The obtained irregularly crushed water-absorbent resin powder (5)
Table 1 shows the measurement results of the water absorption capacity under no pressure, the soluble content, the bulk specific gravity, and the average particle diameter of the sample. Further, the specific surface area of the obtained irregularly crushed water-absorbent resin powder (5) was measured to be 0.011 m ² / g.

Comparative Example 1 The water-absorbing resin (A) which is the crosslinked polymer obtained in Reference Example 1
Is ground with a hammer mill (Rostor: hole diameter 3 mm), and the obtained water-absorbent resin is sieved with a JIS standard sieve (mesh size 8).
50,212 μm) and classified to a particle size of 850 to 212 μm. Table 1 shows the measurement results of the water absorption capacity under no pressure, the soluble content, the bulk specific gravity, and the average particle diameter of the obtained amorphous crushed comparative water-absorbent resin powder (1). FIG. 9 shows an electron micrograph showing the particle structure of the obtained irregularly crushed comparative water-absorbent resin powder (1). -Comparative Example 2-Water-absorbing resin (B) which is the crosslinked polymer obtained in Reference Example 2
Is ground with a hammer mill (Rostor: hole diameter 3 mm), and the obtained water-absorbent resin is sieved with a JIS standard sieve (mesh size 8).
50,212 μm) and classified to a particle size of 850 to 212 μm. Table 1 shows the measurement results of the water absorption capacity under no pressure, the soluble content, the bulk specific gravity, and the average particle diameter of the obtained amorphous crushed comparative water-absorbent resin powder (2).

Comparative Example 3 The water-absorbent resin (C) which is the crosslinked polymer obtained in Reference Example 3
Is ground with a hammer mill (Rostor: hole diameter 3 mm), and the obtained water-absorbent resin is sieved with a JIS standard sieve (mesh size 8).
50,212 μm) and classified to a particle size of 850 to 212 μm. Table 1 shows the measurement results of the water absorption capacity under no pressure, the soluble content, the bulk specific gravity, and the average particle diameter of the obtained amorphous crushed comparative water-absorbent resin powder (3). Further, the specific surface area of the obtained irregularly crushed comparative water-absorbent resin powder (3) was measured, and was 0.023 m ² / g.

[0075]

[Table 1] Table 1 shows a comparison of physical properties before surface crosslinking. Example 1 including a step of polishing the water-absorbent resin (A) (bulk specific gravity 0.8
3 (g / ml)) and Example 2 (bulk specific gravity 0.77 (g / m
l)) is Comparative Example 1 without polishing (bulk specific gravity 0.66 (g /
ml)), the amount of soluble matter is reduced. The water absorption capacity under no pressure is the value after immersion for 1 hour, and the saturation value was 46 (g / g), which is equivalent. Example 3 including a step of polishing the water absorbent resin (B) (bulk specific gravity 0.87
(G / ml)), Example 4 (bulk specific gravity 0.73 (g / m
l)) was used in Comparative Example 2 where no polishing was performed (bulk specific gravity 0.66 (g /
ml)), the amount of soluble matter is reduced. In addition, the water absorption capacity under no pressure is a value after immersion for 1 hour, and the saturation value was 53 (g / g) which is equivalent.

In Example 5 (bulk specific gravity 0.87 (g / ml)) including the step of polishing the water-absorbent resin (C), Comparative Example 3 (bulk specific gravity 0.64 (g / ml)) without polishing was used. ), The specific surface area is about half (0.023 (m ² / g) 0.2%).
011 (m ² / g)) and the amount of soluble matter is also reduced. -Example 6- The amorphous crushed water-absorbent resin powder obtained in Example 1 (1)
100 parts by weight, 0.03 parts by weight of ethylene glycol diglycidyl ether, 1 part by weight of propylene glycol,
A surface crosslinking agent consisting of 3 parts by weight of water and 1 part by weight of 2-propanol was mixed. The mixture was heat-treated at 185 ° C. for 30 minutes to obtain irregularly crushed water-absorbent resin powder (6). Table 2 shows the results of measuring the water absorption capacity under no pressure, the water absorption capacity under pressure, the flow rate under pressure, the solid content, and the bulk specific gravity of the obtained amorphous crushed water-absorbent resin powder (6).

Example 7 Amorphous crushed water-absorbent resin powder obtained in Example 2 (2)
100 parts by weight, 0.03 parts by weight of ethylene glycol diglycidyl ether, 1 part by weight of propylene glycol,
A surface crosslinking agent consisting of 3 parts by weight of water and 1 part by weight of 2-propanol was mixed. The mixture was heat-treated at 185 ° C. for 30 minutes to obtain irregularly crushed water-absorbent resin powder (7). Table 2 shows the results of measurement of the water absorption capacity under no pressure, the water absorption capacity under pressure, the flow rate under pressure, the solid content, and the bulk specific gravity of the obtained irregularly crushed water-absorbent resin powder (7).

Example 8 Amorphous crushed water-absorbent resin powder obtained in Example 3 (3)
100 parts by weight, 0.03 parts by weight of ethylene glycol diglycidyl ether, 1 part by weight of propylene glycol,
A surface crosslinking agent consisting of 3 parts by weight of water and 1 part by weight of 2-propanol was mixed. The mixture was heat-treated at 185 ° C. for 30 minutes to obtain irregularly crushed water-absorbent resin powder (8). Table 2 shows the results of measuring the water absorption capacity under no pressure, the water absorption capacity under pressure, the liquid flow rate under pressure, the solid content, and the bulk specific gravity of the obtained amorphous crushed water-absorbent resin powder (8).

Example 9 Amorphous crushed water-absorbent resin powder (4) obtained in Example 4
100 parts by weight, 0.03 parts by weight of ethylene glycol diglycidyl ether, 1 part by weight of propylene glycol,
A surface crosslinking agent consisting of 3 parts by weight of water and 1 part by weight of 2-propanol was mixed. The mixture was heat-treated at 185 ° C. for 30 minutes to obtain irregularly crushed water-absorbent resin powder (9). Table 2 shows the measurement results of the water absorption capacity under no pressure, the water absorption capacity under pressure, the liquid flow rate under pressure, the solid content, and the bulk specific gravity of the obtained amorphous crushed water-absorbent resin powder (9).

Example 10 Amorphous crushed water-absorbent resin powder (5) obtained in Example 5
A surface cross-linking agent consisting of 1 part by weight of 1,4-butanediol, 3 parts by weight of water, and 1 part by weight of 2-propanol was mixed with 100 parts by weight. The mixture was heat-treated at 195 ° C. for 25 minutes to obtain an irregularly crushed water-absorbent resin powder (10). Table 2 shows the results of measuring the water absorption capacity under no pressure, the water absorption capacity under pressure, the liquid flow rate under pressure, the solid content, and the bulk specific gravity of the obtained amorphous crushed water-absorbent resin powder (10). Comparative Example 4 0.03 parts by weight of ethylene glycol diglycidyl ether, 1 part by weight of propylene glycol, and 3 parts by weight of water were added to 100 parts by weight of the amorphous crushed comparative water-absorbent resin powder (1) obtained in Comparative Example 1. , 1 part by weight of 2-propanol was mixed. The above mixture at 185 ° C.
The mixture was heat-treated for 1 minute to obtain an irregularly crushed comparative water absorbent resin powder (4). Table 2 shows the results of measuring the water absorption capacity under no pressure, the water absorption capacity under pressure, the liquid flow rate under pressure, the solid content, and the bulk specific gravity of the obtained amorphous crushed comparative water-absorbent resin powder (4).

Comparative Example 5- 100 parts by weight of the irregularly crushed comparative water-absorbent resin powder (2) obtained in Comparative Example 2 were mixed with 0.03 part by weight of ethylene glycol diglycidyl ether, 1 part by weight of propylene glycol, and water A surface crosslinking agent consisting of 3 parts by weight and 1 part by weight of 2-propanol was mixed. The above mixture at 185 ° C.
The mixture was subjected to a heat treatment for 5 minutes to obtain an irregular crushed comparative water-absorbent resin powder (5). Table 2 shows the results of measuring the water absorption capacity under no pressure, the water absorption capacity under pressure, the liquid flow rate under pressure, the solid content, and the bulk specific gravity of the obtained amorphous crushed comparative water-absorbent resin powder (5).

Comparative Example 6 100 parts by weight of the irregularly crushed comparative water-absorbent resin powder (3) obtained in Comparative Example 3 were mixed with 1 part by weight of 1,4-butanediol, 3 parts by weight of water, and 2-propanol. One part by weight of a surface crosslinking agent was mixed. The mixture was heat-treated at 195 ° C. for 25 minutes to obtain irregularly crushed comparative water-absorbent resin powder (6). Table 2 shows the measurement results of the water absorption capacity under no pressure, the water absorption capacity under pressure, the liquid flow rate under pressure, the solid content, and the bulk specific gravity of the obtained amorphous crushed comparative water-absorbent resin powder (6).

[0083]

[Table 2] Table 2 shows a comparison of physical properties after surface crosslinking. Example 6 including a step of polishing the water absorbent resin (A) (bulk specific gravity 0.8
3 (g / ml)) and Example 7 (bulk specific gravity 0.77 (g / m
l)) is Comparative Example 4 (bulk specific gravity 0.68 (g /
The flow rate under pressure is more than doubled as compared with (ml))). Further, Example 8 (bulk specific gravity 0.86 (g / ml)) and Example 9 (bulk specific gravity 0.75 (g / ml)) including the step of polishing the water-absorbent resin (B) were not polished. Example 5
As compared with (bulk specific gravity 0.67 (g / ml)), the amount of liquid passing under pressure is improved about twice. Furthermore, water-absorbing resin (C)
Example 10 (bulk specific gravity 0.85 (g)
/ Ml)) is Comparative Example 6 (bulk specific gravity 0.64)
(G / ml)), the flow rate under pressure is improved by 72 (g).

Comparative Example 7 100 parts by weight of the irregularly crushed comparative water-absorbent resin powder (1) obtained in Comparative Example 1 were mixed with 0.015 part by weight of ethylene glycol diglycidyl ether and 0.5 part by weight of propylene glycol. , Water 1.5 parts by weight, 2-propanol 0.
45 parts by weight of a surface crosslinking agent were mixed. The mixture was heat-treated at 180 ° C. for 15 minutes to obtain irregularly crushed comparative water-absorbent resin powder (7). The water absorption capacity under no pressure, the water absorption capacity under pressure, the flow rate under pressure, the solid content, and the bulk specific gravity of the obtained amorphous crushed comparative water-absorbent resin powder (7) were measured.
In particular, regarding the water absorption capacity under pressure, two types of loads (0.
3 psi and 0.7 psi). The water absorption under pressure of 0.3 psi (2.07 kPa) was measured by applying a load of 0.7 psi (4.
83 kPa) to 0.3 psi (2.07 kPa). The results are shown in Table 3.

[0085]

[Table 3] The amorphous crushed comparative water-absorbent resin powder (7) of Comparative Example 7 (bulk specific gravity 0.67 (g / ml)) was 0.3 psi (2.0 psi).
Although the water absorption capacity under pressure of 7 kPa) is 33 (g / g), the water absorption capacity under pressure of 0.7 psi (4.83 kPa) is as low as 12 (g / g). It was found that the liquid permeability under pressure was greatly reduced (Example 6: 375 (g), Comparative Example 7: 40 (g)). -Examples 11 to 15 and Comparative Examples 8 to 10-Each of the water-absorbent resin powders obtained in Examples 6 to 10 and Comparative Examples 4 to 6 was subjected to a mechanical damage test. The results are shown in Table 4.

[0086]

[Table 4] Table 4 shows a result of a mechanical damage test performed after surface crosslinking, and a bulk specific gravity of 0.74 compared to Table 2 before impact.
(G / ml) or more, the amorphous crushed water-absorbent resin powders (6) to (10) of the present invention have little or no deterioration in physical properties even when mechanically damaged. On the other hand, the amorphous crushed comparative water-absorbent resin powders (4) to (6) of the present invention having a bulk specific gravity of less than 0.74 (g / ml).
In the method, the water absorption capacity under pressure and the amount of liquid flow under pressure are greatly reduced due to mechanical damage. The amorphous crushed water-absorbent resin powder of the present invention is an excellent one with little deterioration in physical properties during the production process, transportation after production, and production of an absorbent article.

-Example 16, Comparative Example 11-For each of the water-absorbent resin powders obtained in Example 6 and Comparative Example 4, measurement of the absorption rate (core acquisition) of the absorber and performance of the absorbent article Evaluation (Kewpie doll test) was performed. These measuring or evaluating methods are as described above. Table 5 shows the results.

[0088]

[Table 5] Table 5 shows the performance evaluation of the absorbent body and the absorbent article (diaper). The absorbent body using the irregularly crushed water-absorbent resin powder (6) of Example 6 is the same as the amorphous body of Comparative Example 4. Compared to the absorbent using the crushed comparative water-absorbent resin powder (4), especially
The number of seconds required for the third and third liquid absorption is less than half, and the absorption speed of the absorber is greatly improved. Also,
The absorbent article (diaper) using the irregularly crushed comparative water absorbent resin powder (6) of Example 6 is an absorbent article (diaper) using the irregularly crushed comparative water absorbent resin powder (4) of Comparative Example 4. ), The total absorption (g) of the absorbent article is also improved.

-Example 17- The irregularly shaped crushed water-absorbent resin powder (6) of Examples 6 to 10
For (10), the color was evaluated. As a result, all of the water-absorbent resin powders had L values of 85 or more (about 88), a values within the range of ± 2 (about −0.6), and b values of It was in the range of 0-9 (about 6).

[0090]

According to the method for producing a water-absorbent resin powder of the present invention, while maintaining the conventional high level of water absorption, the liquid permeability is greatly improved as compared with the conventional one, and it is resistant to mechanical damage. Become. Further, the water-absorbing resin powder obtained by the production method of the present invention is a novel resin powder having high water absorption and high bulk specific gravity.

[Brief description of the drawings]

FIG. 1 is a process chart showing a typical example of a process for producing a water-absorbent resin powder of the present invention.

FIG. 2 is an image diagram showing the shape of a resin powder after pulverization (before polishing) (A) and after polishing (B) in the present invention.

FIG. 3 is a schematic sectional view of a measuring device used for measuring a water absorption capacity under pressure.

FIG. 4 is a schematic cross-sectional view of a measuring device used for measuring a liquid passing amount under pressure.

FIG. 5 is a schematic side view (a) and a schematic plan view (b) of a glass container used for a mechanical damage test.

FIG. 6 is a schematic view of a disperser used for a mechanical damage test.

FIG. 7 is a schematic diagram of an apparatus for measuring bulk specific gravity.

FIG. 8 is an electron micrograph showing the particle structure of the resin powder obtained in Example 1.

FIG. 9 is an electron micrograph showing the particle structure of the resin powder obtained in Comparative Example 1.

[Explanation of symbols]

 REFERENCE SIGNS LIST 11 balance 12 container 12a top opening 12b side opening 13 outside air suction pipe 13a lower end surface of outside air suction pipe 14 conduit 15 measuring unit 16 glass filter 17 filter paper 18 support cylinder 19 wire net 20 weight 21 water-absorbent resin powder 22 physiological saline 31 Tank 32 Glass tube 33 0.69% by weight aqueous sodium chloride solution 34 L-shaped tube with cock 35 Cock 40 Container 41 Cell 42 Stainless steel wire mesh 43 Stainless steel wire mesh 44 Swelling gel 45 Glass filter 46 Piston 47 Hole in piston 48 Collection Container 49 Upper plate balance 51 Glass container 52 Disperser 53 Upper clamp 54 Lower clamp 61 Damper 62 Funnel 63 Receiver

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) C08J 3/24 CER C08J 3/24 CERZ 5/04 CER 5/04 CER // A61F 13/53 A61F 5 / 44 H 13/49 C08L 101/14 5/44 A41B 13/02 D A61L 15/60 A61F 13/18 307A C08L 101/14 (72) Inventor Koji Miyake 992, Nishioki, Okihama-shi, Aboshi-ku, Himeji-shi, Hyogo 1 Co., Ltd. Inside Nippon Shokubai (72) Inventor Yoshio Irie 992, Nishioki, Kohama-shi, Abashiri-ku, Himeji-shi, Hyogo 1 Inside Nippon Shokubai Co., Ltd.

Claims (8)

[Claims] 1. A bulk specific gravity of 0.74 (g / ml) or more, and 0.7 ps to 0.9% by weight of physiological saline.
i (4.83 kPa) water absorption capacity under pressure of 20 (g /
g) An amorphous crushed water-absorbent resin powder as described above. 2. An absorber comprising the irregularly crushed water-absorbent resin powder according to claim 1 and a fiber base material. 3. An absorbent article comprising an absorbent layer comprising the absorbent according to claim 2. 4. An absorbent article as a diaper, comprising an absorbent layer comprising the absorbent body according to claim 2, wherein the proportion of the irregularly crushed water-absorbent resin powder in the absorbent body is 30% by weight or more. 5. A method for producing a water-absorbent resin powder, wherein water-absorbent crosslinked polymer particles are obtained through an aqueous solution polymerization step, until the bulk specific gravity of the crosslinked polymer particles increases to 0.72 (g / ml) or more. A method for producing an irregularly crushed water-absorbent resin powder, comprising a step of polishing. 6. The method according to claim 1, wherein the step of obtaining the crosslinked polymer particles by pulverization includes the step of performing the pulverization simultaneously with the polishing.
A method for producing the irregularly crushed water-absorbent resin powder according to claim 5. 7. The method for producing an irregularly crushed water-absorbent resin powder according to claim 5, wherein the polishing is performed under conditions such that the specific surface area of the crosslinked polymer particles is reduced. 8. The method for producing an irregularly crushed water-absorbent resin powder according to claim 5, further comprising a step of crosslinking the vicinity of the surface of the water-absorbent resin powder after the polishing.