WO2019188648A1 - Water absorbent resin particles and production method therefor - Google Patents

Abstract

Provided are water absorbent resin particles that have both a high apparent density and a high absorption rate without causing a reduction in mechanical strength. The present invention is water absorbent resin particles in which, with respect to sieved particles in the range of 300-600 μm, the volume ratio of particles having a particle defective degree (CONV) defined by formula (1) of 1% or less, is 50% or less, and the volume ratio of particles having a CONV of 8% or more, is 5% or less. (1): CONV (%) = {B/(A + B)} × 100 (A represents the projected area of a particle of interest obtained by an image analysis method, and B represents a value obtained by subtracting the projected area represented by A from a projected area surrounded by an envelope connecting protruding portions of the particle of interest obtained by an image analysis method.)

Description

Water-absorbent resin particles and method for producing the same

The present invention relates to a water-absorbent resin particle and a method for producing the same.

For hygiene materials such as paper diapers, sanitary napkins, and incontinence pads, a mixture of hydrophilic fibers such as pulp and a water-absorbent resin mainly composed of acrylic acid (salt) is widely used as an absorbent. From the viewpoint of improving QOL (quality of life) in recent years, the demand for these sanitary materials has been shifting to lighter and thinner materials, and accordingly, the use of hydrophilic fibers has been desired to be reduced. . For this reason, the water-absorbing resin itself has been required to have the role of liquid diffusibility and initial absorption in the absorbent body, which has been carried out by hydrophilic fibers so far. It is requested.

As a method for improving the absorption rate, a method of physically increasing the surface area of the water-absorbing resin is generally used. For example, a method of decreasing the apparent density by increasing the drying speed of the water absorbent resin (Patent Document 1) and a method of decreasing the apparent density by internally foaming in the drying step of the water absorbent resin are known. A technique (Patent Document 3) for granulating water-absorbing resin particles is also known. However, in any case, the mechanical strength of the particles is weak, and fine powder is easily generated in the manufacturing process of the diaper. The fine powder causes gel blocking during the diaper manufacturing process, which causes a problem of clogging of the process. Furthermore, a method of improving the absorption rate by reducing the particle size of the water-absorbent resin particles in the sieving step (Patent Document 4) is also known, but when the particle size of the water-absorbent resin is reduced, the moisture absorption resistance decreases, Similar to the above, there is a problem that causes clogging of the process in the diaper manufacturing process.

JP 2013-132434 A Special table 2015-508836 gazette Special table 2008-533213 JP 2006-143972 A

An object of the present invention is to provide water-absorbing resin particles having both an apparent density and an absorption speed without reducing mechanical strength.

In the present invention, particles having a particle defect degree (CONV) defined by the following formula (1) of 1% or less among particles screened in a range of 300 to 600 μm using a JIS standard sieve are 50% by volume. % Or less and particles having a particle defect degree (CONV) of 8% or more are water-absorbent resin particles having a volume ratio of 5% or less.
CONV (%) = {B / (A + B)} × 100 (1) In the formula (1), CONV represents the particle defect degree, A represents the projected area of the target particle obtained by the image analysis method, and B Represents a value obtained by subtracting the projected area of the target particle indicated by A from the projected area surrounded by the envelope connecting the convex portions of the target particle obtained by the image analysis method. In addition, the present invention provides a monomer composition comprising a water-soluble vinyl monomer (a1) and / or a vinyl monomer (a2) that becomes a water-soluble vinyl monomer (a1) by hydrolysis and an internal crosslinking agent (b) as essential constituent units. A polymerization step for polymerizing the product to obtain a hydrogel of the crosslinked polymer (A), a step of subdividing the hydrogel of the crosslinked polymer (A), and kneading and chopping the subdivided gel at a gel temperature of 40 ° C to 120 ° C And a step of surface-crosslinking the surface of the resin particles (B) containing the crosslinked polymer (A) with a surface crosslinking agent (c).

The water-absorbent resin particles of the present invention and the water-absorbent resin particles obtained by the production method of the present invention are formed by forming irregularities on the surface of the water-absorbent resin particles and with respect to particles at a certain controlled ratio. The apparent density and the absorption speed can be compatible without reducing the mechanical strength. Therefore, a diaper can be manufactured stably even under high humidity, and exhibits excellent absorption performance (for example, liquid diffusibility, absorption speed, absorption amount, etc.) even in various usage situations.

It is a schematic diagram explaining the method of calculating | requiring a particle | grain defect | deletion degree (CONV). (1) shows a particle projection area. (2) shows a projection area surrounded by an envelope connecting the convex portions of the particle projection area. It is the figure which represented typically the cross-sectional view of the filtration cylindrical tube for measuring a gel flow rate. It is the perspective view which represented typically the pressurization axis | shaft for measuring a gel liquid flow rate, and a weight.

The water-absorbent resin particles of the present invention are particles having a particle deficiency (CONV) defined by the following formula (1) of 1% or less among particles screened in a range of 300 to 600 μm using a JIS standard sieve. The volume ratio is 50% or less. Further, among the particles screened in the range of 300 to 600 μm, the volume ratio of particles having a particle defect degree of 8% or more is 5% or less.
CONV (%) = {B / (A + B)} × 100 (1)
In Formula (1), CONV represents the degree of particle defect, A represents the projected area of the target particle obtained by the image analysis method, and B represents the envelope connecting the convex portions of the target particle obtained by the image analysis method. This represents a value obtained by subtracting the projected area of the target particle indicated by A from the projected area surrounded by the line, and represents the area of the missing portion of the particle. The degree of particle deficiency is 0% or more and less than 100%, and the closer to 0%, the smoother the surface with less irregularities in the particles.
FIG. 1 is a schematic diagram for explaining a method for obtaining a particle defect degree. The projected area (A) of the target particle is obtained from the “particle projected area” in FIG. Next, the projection area (A + B) surrounded by the envelope connecting the convex portions of the particle projection area is obtained as an area including the A portion which is the projection area (A) of the target particle and the B portion which is the missing portion. It is done. From these values, the area of part B is obtained.

If the volume ratio of particles having a particle defect degree of 1% or less is 50% or less among the particles screened in the range of 300 to 600 μm using a JIS standard sieve, the proportion of particles having a smooth surface is small. Since the water-absorbent resin particles have sufficient irregularities, it exhibits good absorption performance, exhibits excellent absorption performance when made into an absorbent article, is less likely to cause leakage, and has good anti-fogging properties. Preferably it is 46% or less, More preferably, it is 40% or less. On the other hand, the larger the value of the particle deficiency, the more the unevenness of the particles and the faster the absorption speed. However, the breakage of the water-absorbent resin particles increases and the fine powder increases in the diaper manufacturing process. Among the particles screened in the range of 600 μm, the volume ratio of particles having a particle defect degree of 8% or more is 5% or less, preferably 3% or less, more preferably 2% or less. Moreover, it is preferable that the volume ratio with respect to all the particles of the particle | grain defect degree of 8% or more is 5% or less. Thereby, it can suppress that the mechanical strength of a water-absorbent resin particle falls.

The water-absorbent resin particles of the present invention may be of any type as long as they have the above-mentioned characteristics, but preferably the water-soluble vinyl monomer (a1) and / or the water-soluble vinyl monomer (a1) by hydrolysis. It is a crosslinked polymer (A) obtained by polymerizing a monomer composition having the vinyl monomer (a2) and the internal crosslinking agent (b) as essential constituent units, and more preferably contains a crosslinked polymer (A). Water-absorbent resin particles obtained by surface-crosslinking the surface of the resin particles (B) to be surface-treated with the surface cross-linking agent (c).

The water-soluble vinyl monomer (a1) in the present invention is not particularly limited, and known monomers, for example, at least one water-soluble substituent and an ethylenic group disclosed in paragraphs 0007 to 0023 of Japanese Patent No. 3648553 are disclosed. Vinyl monomers having a saturated group (for example, anionic vinyl monomers, nonionic vinyl monomers and cationic vinyl monomers), anionic vinyl monomers disclosed in JP-A-2003-16583, paragraphs 0009 to 0024, nonionic Selected from the group consisting of a carboxylic group, a sulfo group, a phosphono group, a hydroxyl group, a carbamoyl group, an amino group and an ammonio group disclosed in paragraphs 0041 to 0051 of JP-A-2005-75982 At least one Vinyl monomer having can be used.

A vinyl monomer (a2) (hereinafter also referred to as a hydrolyzable vinyl monomer (a2)) that becomes a water-soluble vinyl monomer (a1) by hydrolysis is not particularly limited, and is known (for example, 0024 to 0025 of Japanese Patent No. 3648553). A vinyl monomer having at least one hydrolyzable substituent which becomes a water-soluble substituent by hydrolysis disclosed in paragraphs, and at least one hydrolyzate disclosed in paragraphs 0052 to 0055 of JP-A-2005-75982. A vinyl monomer of a degradable substituent (a vinyl monomer having a 1,3-oxo-2-oxapropylene (—CO—O—CO—) group, an acyl group, a cyano group, etc.)) can be used. The water-soluble vinyl monomer means a vinyl monomer having a property of dissolving at least 100 g in 100 g of water at 25 ° C. The term “hydrolyzable” refers to the property of being hydrolyzed by the action of 50 ° C. water and, if necessary, the catalyst (acid or base) to make it water-soluble. The hydrolysis of the hydrolyzable vinyl monomer may be performed either during polymerization, after polymerization, or both of them, but is preferably after polymerization from the viewpoint of the molecular weight of the water-absorbent resin particles obtained.

Of these, the water-soluble vinyl monomer (a1) is preferable from the viewpoint of absorption characteristics. The water-soluble vinyl monomer (a1) is preferably an anionic vinyl monomer, more preferably a carboxy (salt) group, a sulfo (salt) group, an amino group, a carbamoyl group, an ammonio group, or a mono-, di- or tri-alkyl. It is a vinyl monomer having an ammonio group. Among these, a vinyl monomer having a carboxy (salt) group or a carbamoyl group is more preferable, (meth) acrylic acid (salt) and (meth) acrylamide, more preferably (meth) acrylic acid (salt), Most preferred is acrylic acid (salt).

The “carboxy (salt) group” means “carboxy group” or “carboxylate group”, and the “sulfo (salt) group” means “sulfo group” or “sulfonate group”. Moreover, (meth) acrylic acid (salt) means acrylic acid, acrylate, methacrylic acid or methacrylate, and (meth) acrylamide means acrylamide or methacrylamide. Examples of the salt include an alkali metal (such as lithium, sodium and potassium) salt, an alkaline earth metal (such as magnesium and calcium) salt or an ammonium (NH ₄ ) salt. Among these salts, alkali metal salts and ammonium salts are preferable from the viewpoint of absorption characteristics and the like, more preferably alkali metal salts, and particularly preferably sodium salts.

When either the water-soluble vinyl monomer (a1) or the hydrolyzable vinyl monomer (a2) is used as a structural unit, each may be used alone as a structural unit, or two or more kinds may be used as a structural unit as necessary. The same applies when the water-soluble vinyl monomer (a1) and the hydrolyzable vinyl monomer (a2) are used as constituent units. When the water-soluble vinyl monomer (a1) and the hydrolyzable vinyl monomer (a2) are used as structural units, the molar ratio (a1 / a2) of these is preferably 75/25 to 99/1, more preferably 85/15 to 95/5, particularly preferably 90/10 to 93/7, and most preferably 91/9 to 92/8. Within this range, the absorption performance is further improved.

As a structural unit of the crosslinked polymer (A), in addition to the water-soluble vinyl monomer (a1) and the hydrolyzable vinyl monomer (a2), other vinyl monomers (a3) copolymerizable therewith are used as the structural unit. Can do.

Other vinyl monomers (a3) that can be copolymerized are not particularly limited and are known (for example, hydrophobic vinyl monomers disclosed in paragraphs 0028 to 0029 of Japanese Patent No. 3648553, Japanese Patent Laid-Open No. 2003-165883, (Vinyl monomers disclosed in paragraph 0058 of JP-A-2005-75982) can be used, and the following vinyl monomers (i) to (iii) can be used.
(I) Aromatic ethylenic monomer having 8 to 30 carbon atoms Styrene such as styrene, α-methylstyrene, vinyltoluene and hydroxystyrene, and halogen substituted products of styrene such as vinylnaphthalene and dichlorostyrene.
(Ii) C2-C20 aliphatic ethylene monomer Alkene [ethylene, propylene, butene, isobutylene, pentene, heptene, diisobutylene, octene, dodecene, octadecene, etc.]; and alkadiene [butadiene, isoprene, etc.], etc.
(Iii) Cycloaliphatic ethylene monomer having 5 to 15 carbon atoms Monoethylenically unsaturated monomer [pinene, limonene, indene and the like]; Polyethylene vinyl polymerizable monomer [cyclopentadiene, bicyclopentadiene, ethylidene norbornene and the like] and the like.

When the other vinyl monomer (a3) is used as a constituent unit, the content (mol%) of the other vinyl monomer (a3) unit is that of the water-soluble vinyl monomer (a1) unit and the hydrolyzable vinyl monomer (a2) unit. Based on the number of moles, it is preferably 0.01 to 5, more preferably 0.05 to 3, even more preferably 0.08 to 2, and particularly preferably 0.1 to 1.5. In spite of the above, it is most preferable that the content of other vinyl monomer (a3) units is 0 mol% from the viewpoint of absorption characteristics and the like.

The internal cross-linking agent (b) (hereinafter, also simply referred to as cross-linking agent (b)) is not particularly limited, and is known (for example, 2 ethylenically unsaturated groups disclosed in paragraphs 0031 to 0034 of Japanese Patent No. 3648553). At least one functional group capable of reacting with a water-soluble substituent, having at least one functional group capable of reacting with a water-soluble substituent, and having at least one functional group capable of reacting with a water-soluble substituent. A cross-linking agent having two, a cross-linking agent having two or more ethylenically unsaturated groups, and a cross-linking having an ethylenically unsaturated group and a reactive functional group disclosed in paragraphs 0028 to 0031 of JP-A No. 2003-165883 And a crosslinking agent having two or more reactive substituents, a crosslinkable vinyl monomer disclosed in paragraph 0059 of JP-A-2005-75982, and JP-A-2005-2005 Crosslinking agents such 5759 JP-0015-0016 crosslinking vinyl monomers disclosed in paragraph) may be used. Among these, from the viewpoint of absorption performance and the like, a crosslinking agent having two or more ethylenically unsaturated groups is preferable, and more preferable is triallyl cyanurate, triallyl isocyanurate, and a poly (poly (2) having 2 to 10 carbon atoms). Meta) allyl ethers, particularly preferred are triallyl cyanurate, triallyl isocyanurate, tetraallyloxyethane and pentaerythritol triallyl ether, most preferred pentaerythritol triallyl ether. A crosslinking agent (b) may be used individually by 1 type, or may use 2 or more types together.

The content (mol%) of the crosslinking agent (b) unit is (a1) to when the other vinyl monomer (a3) of the water-soluble vinyl monomer (a1) unit and the hydrolyzable vinyl monomer (a2) unit is used. Based on the total number of moles of (a3), 0.001 to 5 is preferable, 0.005 to 3 is more preferable, and 0.01 to 1 is particularly preferable. Within this range, the absorption performance is further improved.

Examples of the method for producing the crosslinked polymer (A) include known solution polymerization (adiabatic polymerization, thin film polymerization, spray polymerization method, etc .; JP-A-55-133413, etc.), known suspension polymerization method and reverse phase suspension. If necessary, a hydrogel polymer (consisting of a crosslinked polymer and water) obtained by suspension polymerization (Japanese Patent Publication No. Sho 54-30710, Japanese Patent Publication No. 56-26909, Japanese Patent Publication No. 1-5808, etc.) is required. It can be obtained by heat drying and grinding. The cross-linked polymer (A) may be a single type or a mixture of two or more types.

Among the polymerization methods, the solution polymerization method is preferable, and it is advantageous in terms of production cost because it is not necessary to use an organic solvent. Therefore, the aqueous solution polymerization method is particularly preferable, and the water retention amount is large and water-soluble. An aqueous solution adiabatic polymerization method is most preferred because a water-absorbing resin with a small amount of components can be obtained and temperature control during polymerization is unnecessary.

When aqueous solution polymerization is performed, a mixed solvent containing water and an organic solvent can be used. Examples of the organic solvent include methanol, ethanol, acetone, methyl ethyl ketone, N, N-dimethylformamide, dimethyl sulfoxide, and two or more of these. A mixture of
When aqueous solution polymerization is performed, the amount (% by weight) of the organic solvent used is preferably 40 or less, more preferably 30 or less, based on the weight of water.

In the case of using a catalyst for the polymerization, a conventionally known radical polymerization catalyst can be used, for example, an azo compound [azobisisobutyronitrile, azobiscyanovaleric acid and 2,2′-azobis (2-amidinopropane) hydrochloride. Etc.], inorganic peroxides (hydrogen peroxide, ammonium persulfate, potassium persulfate, sodium persulfate, etc.), organic peroxides [benzoyl peroxide, di-t-butyl peroxide, cumene hydroperoxide, succinic acid peroxide, etc. Oxides and di (2-ethoxyethyl) peroxydicarbonate, etc.] and redox catalysts (alkali metal sulfites or bisulfites, ammonium sulfites, ammonium bisulfites, ascorbic acids and the like, and alkali metal persulfates, Oxidation of ammonium persulfate, hydrogen peroxide and organic peroxides And the like). These catalysts may be used alone or in combination of two or more thereof.
The amount (% by weight) of the radical polymerization catalyst used is that of the water-soluble vinyl monomer (a1) and the hydrolyzable vinyl monomer (a2), in the case of using other vinyl monomers (a3) (a1) to (a3), Based on the total weight, it is preferably 0.0005 to 5, more preferably 0.001 to 2.

When the polymerization method is a suspension polymerization method or a reverse phase suspension polymerization method, the polymerization may be performed in the presence of a conventionally known dispersant or surfactant, if necessary. In the case of the reverse phase suspension polymerization method, polymerization can be carried out using a conventionally known hydrocarbon solvent such as xylene, normal hexane and normal heptane.

The polymerization start temperature can be appropriately adjusted depending on the type of catalyst used, but is preferably 0 to 100 ° C., more preferably 5 to 80 ° C.

When a solvent (such as an organic solvent and water) is used for polymerization, it is preferable to distill off the solvent after polymerization. When the solvent contains an organic solvent, the content (% by weight) of the organic solvent after distillation is preferably 0 to 10, more preferably 0 to 5, particularly preferably based on the weight of the crosslinked polymer (A). Is 0-3, most preferably 0-1. Within this range, the absorption performance of the water-absorbent resin particles is further improved.

When water is contained in the solvent, the water content (% by weight) after the distillation is preferably 0 to 20, more preferably 1 to 10, particularly preferably 2 to 9, based on the weight of the crosslinked polymer (A). Most preferably, it is 3-8. Within this range, the absorption performance is further improved.

In addition, the content and water content of the organic solvent were measured using an infrared moisture meter [JE400 manufactured by KETT Co., Ltd .: 120 ± 5 ° C., 30 minutes, atmospheric humidity before heating 50 ± 10% RH, lamp specifications 100V, 40W ] Is obtained from the weight loss of the measurement sample when heated.

The water-containing gel polymer obtained by polymerization can be kneaded and shredded and dried to obtain a crosslinked polymer (A). The kneading chopping in the present invention is a step of making the hydrated gel fine while repeating the cutting of the hydrated gel by shearing force (shear) and the coalescence of the cut hydrated gel particles. A hydrogel in which the gel particles are aggregated is obtained, and irregularities can be formed on the surface of the water-absorbent resin particles. The size (longest diameter) of the gel after kneading is preferably 50 μm to 10 cm, more preferably 100 μm to 2 cm, and particularly preferably 1 mm to 1 cm. Within this range, the drying property in the drying process is further improved.

The kneading shredding can be performed by a known method, and kneading shredding using a kneading shredding device (for example, a kneader, a universal mixer, a uniaxial or biaxial kneading extruder, a mincing machine, and a meat chopper). I can decline. The temperature of the hydrogel during kneading is preferably 40 to 120 ° C, more preferably 60 to 100 ° C. Within this range, adhesion of the water-containing gel in the kneading shredding device can be prevented and the water-containing gel can be treated uniformly, so that the degree of particle deficiency of the water-absorbent resin particles described above tends to be uniform. Further, from the viewpoint of uniformly forming the unevenness of the water-absorbent resin particles as a whole, the kneading shredding may be performed a plurality of times, and the number of kneading shredding is preferably 1 to 4 times, more preferably 2 to 3 times. is there. In addition, the kneading shredding apparatus in the case of processing a plurality of times may be the same type or a combination of different types.

The hydrogel polymer obtained by polymerization is preferably subdivided before kneading and chopping. In the present invention, the subdivision is a step of cutting the water-containing gel into fine pieces while maintaining the structure inside the water-containing gel, and is different from the kneading chopping described above from the viewpoint of the internal structure. By subdividing before the kneading shredding step, excessive stress applied to the water-containing gel during the kneading shredding step can be relaxed and deterioration of the water-containing gel polymer can be suppressed. It is possible to prevent an extreme increase in the degree of particle deficiency of the water absorbent resin particles.

There is no particular limitation on the method of subdividing, for example, it may be subdivided with scissors, or a frozen water-containing gel is pulverized (for example, a hammer-type pulverizer, an impact-type pulverizer, a roll-type pulverizer, and a shet airflow-type pulverizer). ).

The size (longest diameter) of the gel after subdivision is preferably 50 μm to 10 cm, more preferably 100 μm to 2 cm, and particularly preferably 500 μm to 1 cm.

When an acid group-containing monomer such as acrylic acid or methacrylic acid is used as the water-soluble vinyl monomer (a1), an alkali is added to the crosslinked polymer (A) containing an acid group obtained after polymerization in the form of a hydrogel. It can also be neutralized. The degree of neutralization of the acid groups of the crosslinked polymer (A) is preferably 50 to 80 mol% with respect to the total number of moles of acid groups. When the degree of neutralization is less than 50 mol%, the resulting water-containing gel polymer has high tackiness, the workability during production and use deteriorates, or the water retention amount of the resulting water-absorbent resin particles decreases. There is. On the other hand, when the degree of neutralization exceeds 80 mol%, the pH of the obtained water-absorbent resin is increased, and there is a concern about the safety of human skin, or the liquid permeability of the water-absorbent resin particles may be lowered. As the alkali, those known in the art {Japanese Patent No. 3205168 etc.} can be used. Among these, from the viewpoint of water absorption performance, lithium hydroxide, sodium hydroxide, and potassium hydroxide are preferable, sodium hydroxide and potassium hydroxide are more preferable, and sodium hydroxide is particularly preferable. As the method of adding alkali, from the viewpoint of uniformity of neutralization, preferably before the step of kneading the hydrated gel or during the step of kneading the hydrated gel, more preferably the step of kneading the hydrated gel It is preferable to add an alkali before, more preferably, after the step of subdividing the hydrated gel and before the step of kneading and chopping the hydrated gel. In addition, as an alkali, it can add as the aqueous solution of the said alkali.

As a method of distilling off the solvent (including water) in the hydrogel, a method of distilling (drying) with hot air at a temperature of 80 to 230 ° C., a thin film drying method using a drum dryer or the like heated to 100 to 230 ° C. (Heating) reduced pressure drying method, freeze drying method, infrared drying method, decantation, filtration and the like can be applied.

The kneaded hydrated gel is chopped and then dried to obtain a crosslinked polymer (A), which can be further pulverized. The pulverization method is not particularly limited, and a pulverizer (for example, a hammer pulverizer, an impact pulverizer, a roll pulverizer, and a shet airflow pulverizer) can be used. The pulverized crosslinked polymer can be adjusted in particle size by sieving or the like, if necessary.

The weight average particle diameter (μm) of the crosslinked polymer (A) screened as necessary is preferably 100 to 800, more preferably 200 to 700, next preferably 250 to 600, particularly preferably 300 to 500, most preferably Preferably it is 350-450. Within this range, the absorption performance is further improved.

The weight average particle size was measured using a low-tap test sieve shaker and a standard sieve (JIS Z8801-1: 2006), Perry's Chemical Engineers Handbook, 6th edition (Mac Glow Hill Book, 1984). , Page 21). That is, JIS standard sieves are combined in the order of 1000 μm, 850 μm, 710 μm, 500 μm, 425 μm, 355 μm, 250 μm, 150 μm, 125 μm, 75 μm and 45 μm, and a tray from the top. About 50 g of the measured particles are put in the uppermost screen and shaken for 5 minutes with a low-tap test sieve shaker. Weigh the measured particles on each sieve and pan, and calculate the weight fraction of the particles on each sieve with the total as 100% by weight. This value is the logarithmic probability paper [horizontal axis is sieve aperture (particle size ), The vertical axis is plotted in the weight fraction], and then a line connecting the points is drawn to obtain the particle diameter corresponding to the weight fraction of 50% by weight, which is defined as the weight average particle diameter.

In addition, since the absorption performance is better when the content of fine particles contained in the crosslinked polymer (A) is smaller, the content (% by weight) of fine particles of 150 μm or less in the total weight of the crosslinked polymer (A) is 3.0 or less is preferable, More preferably, it is 1.0 or less. The content of the fine particles can be determined using a graph created when determining the above-mentioned weight average particle diameter.

The shape of the crosslinked polymer (A) is not particularly limited, and examples thereof include an irregular crushed shape, a flake shape, a pearl shape, and a rice grain shape. Among these, from the viewpoint of good entanglement with the fibrous material for use as a disposable diaper and no fear of dropping off from the fibrous material, an irregularly crushed shape is preferable.

The crosslinked polymer (A) or the polymer gel may be treated with a hydrophobic substance as required by the method described in JP2013-231199A.

The crosslinked polymer (A) is preferably surface-crosslinked. By surface crosslinking, the gel strength can be further improved, and the water retention amount and the absorption amount under load that are desirable in actual use can be satisfied.

As a method of surface cross-linking the cross-linked polymer (A), a conventionally known method, for example, after forming a water-absorbing resin in the form of particles, mixing a surface cross-linking agent (c), a mixed solution of water and a solvent, and heating reaction The method of doing is mentioned. Examples of the mixing method include spraying the mixed solution onto the crosslinked polymer (A) or dipping the crosslinked polymer (A) into the mixed solution. Preferably, the crosslinked polymer (A) is mixed with the crosslinked polymer (A). In this method, the mixed solution is sprayed and mixed.

Examples of the surface cross-linking agent (c) include polyglycidyl compounds such as ethylene glycol diglycidyl ether, glycerol diglycidyl ether and polyglycerol polyglycidyl ether, polyhydric alcohols such as glycerin and ethylene glycol, ethylene carbonate, polyamine and polyvalent A metal compound etc. are mentioned. Among these, a polyglycidyl compound is preferable in that a crosslinking reaction can be performed at a relatively low temperature. These surface crosslinking agents may be used alone or in combination of two or more.

The amount of the surface crosslinking agent (c) used is preferably 0.001 to 5% by weight, more preferably 0.005 to 2% by weight, based on the weight of the water-absorbent resin before crosslinking. When the amount of the surface cross-linking agent (c) used is less than 0.001% by weight, the degree of surface cross-linking is insufficient, and the effect of improving the amount of absorption under load may be insufficient. On the other hand, when the amount of the surface cross-linking agent (c) used exceeds 5% by weight, the degree of cross-linking of the surface becomes excessive, and the water retention amount may decrease.

The amount of water used for surface crosslinking is preferably 0.5 to 10% by weight, more preferably 1 to 7% by weight, based on the weight of the water absorbent resin before crosslinking. When the amount of water used is less than 0.5% by weight, the degree of penetration of the surface cross-linking agent (c) into the water-absorbent resin particles becomes insufficient, and the effect of improving the amount of absorption under load may be poor. On the other hand, when the amount of water used exceeds 10% by weight, penetration of the surface cross-linking agent (c) into the inside becomes excessive, and although an improvement in the amount of absorption under load is observed, the amount of water retained may decrease.

As the solvent used in combination with water at the time of surface cross-linking, conventionally known solvents can be used, the degree of penetration of the surface cross-linking agent (c) into the water-absorbent resin particles, and the reactivity of the surface cross-linking agent (c). However, it is preferably a hydrophilic organic solvent that can be dissolved in water such as methanol, diethylene glycol, and propylene glycol. A solvent may be used independently and may use 2 or more types together.
The amount of the solvent used can be appropriately adjusted depending on the type of the solvent, but is preferably 1 to 10% by weight based on the weight of the water-absorbent resin before surface crosslinking. Further, the ratio of the solvent to water can be arbitrarily adjusted, but it is preferably 20 to 80% by weight, more preferably 30 to 70% by weight based on the weight.

In order to carry out surface cross-linking, a mixed solution of the surface cross-linking agent (c), water and a solvent is mixed with water-absorbent resin particles by a conventionally known method, and a heating reaction is performed. The reaction temperature is preferably 100 to 230 ° C, more preferably 120 to 180 ° C. The reaction time can be appropriately adjusted depending on the reaction temperature, but it is preferably 3 to 60 minutes, more preferably 10 to 45 minutes. The particulate water-absorbing resin obtained by surface cross-linking can be further subjected to surface cross-linking using the same or different type of surface cross-linking agent as the first used surface cross-linking agent.

After surface cross-linking, the particle size may be adjusted by sieving if necessary.

The water-absorbent resin particles of the present invention may further contain a polyvalent metal salt (d). For this reason, the production method of the present invention described later further comprises a step of mixing with the polyvalent metal salt (d). May be included. By containing the polyvalent metal salt (d), the blocking resistance and liquid permeability of the water-absorbent resin particles are improved. Examples of the polyvalent metal salt (d) include a salt of at least one metal selected from the group consisting of magnesium, calcium, zirconium, aluminum, and titanium and the above inorganic acid or organic acid.

As the polyvalent metal salt (d), from the viewpoint of easy availability and solubility, inorganic acid salts of aluminum and inorganic acid salts of titanium are preferable, and aluminum sulfate, aluminum chloride, potassium aluminum sulfate and sulfuric acid are more preferable. Sodium aluminum, particularly preferred are aluminum sulfate and sodium aluminum sulfate, and most preferred is sodium aluminum sulfate. These may be used alone or in combination of two or more.

The use amount (% by weight) of the polyvalent metal salt (d) is preferably 0.01 to 5 based on the weight of the crosslinked polymer (A) from the viewpoint of absorption performance and anti-blocking property, more preferably 0. 05 to 4, particularly preferably 0.1 to 3.

Although there is no restriction | limiting in particular as timing which mixes with a polyvalent metal salt (d), it mixes after drying the said hydrogel polymer and obtaining the crosslinked polymer from a viewpoint of absorption performance and blocking resistance. preferable.

The surface of the water-absorbent resin particles of the present invention can be further coated with an inorganic powder (D). Examples of the inorganic powder (D) include hydrophilic inorganic particles (D1) and hydrophobic inorganic particles (D2).
Examples of the hydrophilic inorganic particles (D1) include particles such as glass, silica gel, silica, and clay.
Examples of the hydrophobic inorganic particles (D2) include particles of carbon fiber, kaolin, talc, mica, bentonite, sericite, asbestos, shirasu, and the like.
Of these, hydrophilic inorganic particles (D1) are preferred, and silica is most preferred.

The shape of the hydrophilic inorganic particles (D1) and the hydrophobic inorganic particles (D2) may be any of an irregular shape (crushed shape), a true spherical shape, a film shape, a rod shape, a fiber shape, etc., but an irregular shape (crushed shape). Alternatively, a true spherical shape is preferable, and a true spherical shape is more preferable.

The content (% by weight) of the inorganic powder (D) is preferably 0.01 to 3.0, more preferably 0.05 to 1.0, and then preferably based on the weight of the crosslinked polymer (A). Is 0.1 to 0.8, particularly preferably 0.2 to 0.7, and most preferably 0.3 to 0.6. Within this range, the anti-fogging property of the absorbent article is further improved.

The water-absorbent resin particles of the present invention may contain other additives (for example, known preservatives, fungicides, antibacterial agents, antioxidants, ultraviolet rays (for example, JP-A-2003-225565, JP-A-2006-131767, etc.) An absorbent, a colorant, a fragrance, a deodorant, an organic fibrous material, etc.}. When these additives are contained, the content (% by weight) of the additive is preferably 0.001 to 10, more preferably 0.01 to 5, particularly preferably based on the weight of the crosslinked polymer (A1). Preferably it is 0.05 to 1, most preferably 0.1 to 0.5.

The weight average particle diameter (μm) of the water-absorbent resin particles of the present invention is preferably 100 to 800, more preferably 200 to 700, next preferably 250 to 600, particularly preferably 300 to 500, most preferably 350 to 450. If it is larger than this range, the absorption rate may be slow, and if it is smaller than this range, the liquid permeability is deteriorated to cause spot absorption and gel blocking, and both easily cause liquid leakage. The content of fine particles is preferably small, and the content of particles of 150 μm or less is preferably 3.0% by weight or less, more preferably 1.0% by weight or less. When there are many fine particles, spot absorption and gel blocking may occur, which may easily cause leakage, and may cause clogging of the process in the diaper manufacturing process.

The weight ratio of particles having a particle diameter of 300 to 600 μm to the total weight of the water-absorbent resin particles of the present invention is preferably 50% by weight or more, more preferably 60% by weight, and particularly preferably 70% by weight. The upper limit is preferably as high as possible, but is not particularly limited, but is preferably 100% by weight or less, more preferably 90% by weight or less from the viewpoint of productivity.

The particle shape of the water-absorbent resin particles of the present invention is not particularly limited, and examples thereof include an irregular crushed shape, a flake shape, a pearl shape, and a rice grain shape. Among these, from the viewpoint of good entanglement with the fibrous material for use as a disposable diaper and no fear of dropping off from the fibrous material, an irregularly crushed shape is preferable.

The apparent density (g / ml) of the water absorbent resin particles of the present invention is preferably 0.5 to 0.7, more preferably 0.52 to 0.69, and particularly preferably 0.54 to 0.68. . Within this range, the anti-fogging property of the absorbent article is further improved. The apparent density of the water absorbent resin particles is measured at 25 ° C. according to JIS K7365: 1999.

The water-absorbent resin particles of the present invention preferably have a 0.9% by weight physiological saline water retention of 30 to 50 g / g. The water retention amount can be measured by the method described later, and is preferably 33 to 49 g / g, more preferably 36 to 48 g / g, further preferably 39 to 47 g / g, from the viewpoint of suppressing leakage of the absorbent article. Particularly preferred. If it is less than 30 g / g, leakage is likely to occur during repeated use. Moreover, since it will become easy to block when it exceeds 50 g / g, it is not preferable. The amount of water retention can be appropriately adjusted by the kind and amount of the crosslinking agent (b) and the surface crosslinking agent (c). Therefore, for example, when it is necessary to increase the water retention amount, it can be easily realized by reducing the amount of the crosslinking agent (b) and the surface crosslinking agent (c) used.

The water-absorbent resin particles of the present invention preferably have an absorption rate (seconds) measured by the vortex method of 50 or less and an absorption rate (seconds) measured by the lockup method of 130 or less. The vortex method can be measured by the method described later, and is preferably 48 or less, more preferably 46 or less, and particularly preferably 44 or less from the viewpoint of suppressing leakage of the absorbent article. The lock-up method can be measured by the method described later, and is preferably 130 or less, more preferably 120 or less, and particularly preferably 110 or less from the viewpoint of suppressing leakage of the absorbent article.

The water-absorbent resin particles of the present invention preferably have an absorption amount under load of 10 to 27 g / g. The amount of absorption under load can be measured by the method described later, and is preferably 13 to 27, more preferably 16 to 27, and particularly preferably 19 to 27 from the viewpoint of absorption characteristics.

The gel flow rate (ml / min) of the water-absorbent resin particles of the present invention is preferably 5 to 250. The gel flow rate can be measured by the method described later, and is more preferably 10 to 230, and particularly preferably 30 to 210, from the viewpoint of absorption characteristics.

The amount (%) of increase in the fine particle content after the breakability test of the water-absorbent resin particles of the present invention is preferably 0.0 to 3.0. The amount of increase in the content of fine particles after the breakability test can be measured by the method described later. From the viewpoint of mechanical strength, it is more preferably 0.0 to 2.0, particularly preferably 0.0 to 1.5. It is.

The water-absorbent resin particles of the present invention include a water-soluble vinyl monomer (a1) and / or a vinyl monomer (a2) that becomes a water-soluble vinyl monomer (a1) by hydrolysis and an internal crosslinking agent (b) as essential constituent units. A polymerization step of polymerizing the monomer composition to obtain a hydrogel of the cross-linked polymer (A), a step of subdividing the hydrogel of the cross-linked polymer (A), and the subdivided gel at a gel temperature of 40 ° C. to 120 ° C. It is preferably produced by a method for producing water-absorbent resin particles, comprising a step of kneading and chopping, and a step of surface-crosslinking the surface of the resin particles (B) containing the crosslinked polymer (A) with a surface crosslinking agent (c). be able to. In the production method of the present invention, by subdividing before the kneading shredding step, the shape of the water-absorbent resin particles can be maintained, and the mechanical strength of the water-absorbent resin particles can be prevented from being lowered. The absorption performance of the resin particles is improved.

The absorber of the present invention contains the water absorbent resin particles of the present invention. As the absorber, water-absorbing resin particles may be used alone or may be used together with other materials as an absorber.
Examples of other materials include fibrous materials. The structure and production method of the absorbent when used together with the fibrous material are the same as those known (JP 2003-225565 A, JP 2006-131767 A, JP 2005-097569 A, etc.). is there.

Preferred as the fibrous material are cellulose fibers, organic synthetic fibers, and a mixture of cellulose fibers and organic synthetic fibers.

Examples of the cellulosic fibers include natural fibers such as fluff pulp, and cellulosic chemical fibers such as viscose rayon, acetate, and cupra. There are no particular restrictions on the raw materials (conifers, hardwoods, etc.), production methods (chemical pulp, semi-chemical pulp, mechanical pulp, CTMP, etc.), bleaching methods, etc. of this cellulose-based natural fiber.

Examples of organic synthetic fibers include polypropylene fibers, polyethylene fibers, polyamide fibers, polyacrylonitrile fibers, polyester fibers, polyvinyl alcohol fibers, polyurethane fibers, and heat-fusible composite fibers (the above fibers having different melting points). And a fiber obtained by compounding at least two of the above into a sheath core type, an eccentric type, a parallel type, and the like, a fiber obtained by blending at least two kinds of the above fibers, and a fiber obtained by modifying the surface layer of the above fibers).

Among these fibrous materials, preferred are cellulose-based natural fibers, polypropylene-based fibers, polyethylene-based fibers, polyester-based fibers, heat-fusible conjugate fibers, and mixed fibers thereof, and more preferable are obtained. The fluff pulp, the heat-fusible conjugate fiber, and the mixed fiber thereof are preferable in that the water-absorbing agent has excellent shape retention after water absorption.

The length and thickness of the fibrous material are not particularly limited and can be suitably used as long as the length is 1 to 200 mm and the thickness is in the range of 0.1 to 100 denier. The shape is not particularly limited as long as it is fibrous, and examples thereof include a thin cylindrical shape, a split yarn shape, a staple shape, a filament shape, and a web shape.

When the water-absorbent resin particles are used as an absorbent together with the fibrous material, the weight ratio of the water-absorbent resin particles to the fibers (the weight of the water-absorbent resin particles / the weight of the fibers) is preferably 40/60 to 90/10, more preferably Is 70/30 to 80/20.

The absorbent article of the present invention uses the above absorber. The absorbent article is applicable not only to sanitary articles such as disposable diapers and sanitary napkins, but also to those used for various uses such as absorbent and retention agents for various aqueous liquids and gelling agents described later. . The manufacturing method and the like of the absorbent article are the same as known ones (described in JP 2003-225565 A, JP 2006-131767 A, JP 2005-097569 A, etc.).

Hereinafter, although an example and a comparative example explain the present invention further, the present invention is not limited to these. Hereinafter, unless otherwise specified, parts indicate parts by weight and% indicates% by weight.
Particle deficiency, water retention, absorption rate measured by vortex method, absorption rate measured by lock-up method, absorption amount under load, gel flow rate is 25 ± 2 ° C, humidity is 50 ± 10% in a room. Each was measured by the following method. Note that the temperature of the physiological saline used was adjusted to 25 ° C. ± 2 ° C. in advance.

<Measuring Method of Particle Defect Degree> The particle defect degree of the water-absorbent resin particles was measured using a Camsizer (registered trademark) image analysis system (manufactured by Retsch Technology GmbH). From the sample feeder at the top of the device, 5.00 g of the measurement sample screened in the range of 300 to 600 μm using a standard sieve (JIS Z8801-1: 2006) is freely dropped little by little, and the falling measurement sample is continuously collected with a CCD camera. Taken on. The degree of particle defect of the measurement sample was derived by analyzing the captured image. The arithmetic average value of the degree of particle defect derived with an analysis point N = 3 was defined as the particle defect degree of the present invention. Moreover, the measurement with respect to all the particles was measured like the above except not sieving.

<Measurement method of water retention amount>
1.00 g of a measurement sample is placed in a tea bag (20 cm long, 10 cm wide) made of a nylon net having a mesh size of 63 μm (JIS Z8801-1: 2006), and 1,000 ml of physiological saline (saline concentration 0.9%). The sample was immersed for 1 hour without stirring and then pulled up, suspended for 15 minutes and drained. Thereafter, each tea bag was placed in a centrifuge, centrifuged at 150 G for 90 seconds to remove excess physiological saline, and the weight (h1) including the tea bag was measured to obtain the water retention amount from the following formula. In addition, the temperature of the used physiological saline and measurement atmosphere was 25 degreeC +/- 2 degreeC.
Water retention amount (g / g) = (h1) − (h2)
(H2) is the weight of the tea bag measured by the same operation as described above when there is no measurement sample.

<Absorption rate measured by vortex method>
Physiological salt in which 2.000 g of a measurement sample screened in the range of 300 to 600 μm using a standard sieve is stirred at a rotation speed of 600 rotations per minute in a 100 ml tall beaker having a flat bottom as defined in JIS R 3503 The time (unit: second) required to absorb 50 g of water was measured according to JIS K7224-1996, and the absorption rate was measured by the vortex method.

<Absorption rate measured by lock-up method>
1.000 g of the measurement sample was placed in a 100 ml tall beaker having a flat bottom as defined in JIS R 3503. At this time, the upper surface of the water absorbent resin placed in the beaker was made horizontal. Next, 40 g of physiological saline adjusted to 23 ° C. ± 2 ° C. was weighed into a 100 ml glass beaker and poured quickly and carefully into a 100 ml beaker containing a water absorbent resin. Time measurement was started at the same time as the poured physiological saline contacted the water-absorbent resin. When the beaker filled with physiological saline is turned sideways at an angle of about 90 °, the end point is the point at which the fluid does not ooze from the surface of the water-absorbent resin, and this time (unit: seconds) is the lock-up method. The absorption rate measured in

<Measurement method of absorption under load>
Measurement using a standard sieve in a cylindrical plastic tube (inner diameter: 25 mm, height: 34 mm) with a nylon mesh of 63 μm mesh (JIS Z8801-1: 2006) pasted on the bottom. Weigh 0.16 g of sample, arrange the cylindrical plastic tube vertically and arrange the measurement sample on the nylon net so as to have a substantially uniform thickness, and then place a weight on the measurement sample (weight: 310.6 g, outer Diameter: 24.5 mm). After measuring the weight (M1) of the entire cylindrical plastic tube, a cylindrical plastic containing a measurement sample and a weight in a petri dish (diameter: 12 cm) containing 60 ml of physiological saline (salt concentration 0.9%). The tube was set up vertically and immersed with the nylon mesh side as the bottom surface and allowed to stand for 60 minutes. After 60 minutes, the cylindrical plastic tube was pulled up from the petri dish, and the slant was tilted to collect the water adhering to the bottom in one place and dropped as water droplets. The weight (M2) of the entire cylindrical plastic tube was weighed, and the absorbed amount under load was determined from the following equation. In addition, the temperature of the used physiological saline and measurement atmosphere was 25 degreeC +/- 2 degreeC.
Absorption under load (g / g) = {(M2) − (M1)} / 0.16

<Measurement method of gel flow rate>
Measurement was performed by the following operation using the instrument shown in FIGS.
Swelled gel particles 2 were prepared by immersing 0.32 g of the measurement sample in 150 ml of physiological saline 1 (salt concentration of 0.9%) for 30 minutes. The cylinder 3 standing upright {diameter (inner diameter) 25.4 mm, length 40 cm, scale line 4 and scale line 5 are provided at a position of 60 ml and 40 ml from the bottom, respectively. } At the bottom of the filtration cylinder having a wire mesh 6 (mesh opening 106 μm, JIS Z8801-1: 2006) and an openable / closable cock 7 (inner diameter of the liquid passing part 5 mm), After the prepared swollen gel particles 2 are transferred together with physiological saline, a circular wire mesh having a pressure shaft 9 (weight 22 g, length 47 cm) which is bonded perpendicularly to the wire mesh surface on the swollen gel particles 2. 8 (aperture 150 μm, diameter 25 mm) was placed so that the wire mesh and swollen gel particles were in contact with each other, and a weight 10 (88.5 g) was placed on the pressure shaft 9 and allowed to stand for 1 minute. Subsequently, the cock 7 is opened, the time (T1; second) required for the liquid level in the filtration cylindrical tube to change from the 60 ml scale line 4 to the 40 ml scale line 5 is measured, and the gel flow rate (ml / min) is calculated from the following equation. Asked.
Gel flow rate (ml / min) = 20 ml × 60 / (T1-T2)
The temperature of the physiological saline used and the measurement atmosphere is 25 ° C. ± 2 ° C., and T2 is the time measured by the same operation as described above when there is no measurement sample.

<Example 1> Acrylic acid (a1) {Mitsubishi Chemical Co., Ltd., purity 100%} 131 parts, Internal crosslinking agent (b-1) {Pentaerythritol triallyl ether, Osaka Soda Co., Ltd.} 0.44 parts and 362 parts of deionized water was kept at 3 ° C. with stirring and mixing. After flowing nitrogen into this mixture to reduce the dissolved oxygen amount to 1 ppm or less, 0.5 part of 1% aqueous hydrogen peroxide solution, 1 part of 2% aqueous ascorbic acid solution and 2% 2,2′-azobisamidinopropane Polymerization was started by adding and mixing 0.1 part of a dihydrochloride aqueous solution. After the temperature of the mixture reached 80 ° C., a water-containing gel was obtained by polymerization at 80 ± 2 ° C. for about 5 hours.

Next, this hydrogel was subdivided into about 1 mm square with scissors, and 162 parts of 45% aqueous sodium hydroxide solution was added. Further, after kneading and cutting four times at a gel temperature of 80 ° C. with a mincing machine (ROYAL 12VR-400K) having a diameter of 16 mm, the dried product is obtained by drying with a ventilation dryer {150 ° C., wind speed 2 m / sec}. It was. After the dried product is pulverized with a juicer mixer (Osterizer BLENDER manufactured by Oster), the dried product is screened and adjusted to a particle size range of 710 to 150 μm (400 μm as a weight average particle size) to include crosslinked polymer particles Resin particles were obtained.

Next, 100 parts of the obtained resin particles were stirred at a high speed (high speed stirring turbulizer manufactured by Hosokawa Micron (registered trademark; hereinafter the same): rotation speed: 2000 rpm), and then sodium aluminum sulfate alum as inorganic acid salt (d) was added thereto. Add 0.6 parts by weight of 12 hydrate, 0.08 parts by weight of ethylene glycol diglycidyl ether as surface cross-linking agent and 3.3 parts by weight of 45% propylene glycol aqueous solution as solvent. After uniform mixing, the mixture was allowed to stand at 130 ° C. for 60 minutes and dried to obtain water-absorbing resin particles (P-1) of the present invention. The weight ratio of the particles having a particle diameter of 300 to 600 μm to the total weight of the water absorbent resin particles (P-1) was 71% by weight.

<Example 2>
Water-absorbent resin particles (P-2) were obtained in the same manner as in Example 1 except that the hydrogel was subdivided into 5 mm squares with scissors. The weight ratio of the particles having a particle diameter of 300 to 600 μm to the total weight of the water absorbent resin particles (P-2) was 70% by weight.

<Example 3> The water-absorbing property was the same as in Example 1 except that the neutralized hydrous gel was kneaded and chopped four times at a gel temperature of 80 ° C with a minced machine (ROYAL 12VR-400K) having a diameter of 8 mm. Resin particles (P-3) were obtained. The weight ratio of the particles having a particle diameter of 300 to 600 μm to the total weight of the water absorbent resin particles (P-3) was 70% by weight.

<Example 4> The water-absorbing property was the same as in Example 1 except that the neutralized hydrogel was kneaded and chopped twice at a gel temperature of 80 ° C. with a minced machine (ROYAL 12VR-400K) having a diameter of 16 mm. Resin particles (P-4) were obtained. The weight ratio of the particles having a particle diameter of 300 to 600 μm to the total weight of the water absorbent resin particles (P-4) was 71% by weight.

<Example 5>
Water-absorbent resin particles (P-5) were obtained in the same manner as in Example 1 except that the hydrogel kneading shredding temperature was set to 60 ° C. The weight ratio of the particles having a particle diameter of 300 to 600 μm to the total weight of the water absorbent resin particles (P-5) was 71% by weight.

<Example 6>
Water-absorbent resin particles (P-6) were obtained in the same manner as in Example 1 except that the kneading shredding temperature of the hydrogel was set to 100 ° C. The weight ratio of the particles having a particle diameter of 300 to 600 μm to the total weight of the water absorbent resin particles (P-6) was 71% by weight.

<Example 7>
The hydrogel subdivision size is about 1 mm square to about 5 mm square, the diameter of the minced machine 16 mm is 8 mm, and the hydrogel kneading shredding temperature 80 ° C. is 100 ° C. Water-absorbing resin particles (P-7) were obtained. The weight ratio of the particles having a particle diameter of 300 to 600 μm to the total weight of the water absorbent resin particles (P-7) was 71% by weight.

<Example 8> Acrylic acid (a1) {Mitsubishi Chemical Co., Ltd., purity 100%} 131 parts, Internal crosslinking agent (b-1) {Pentaerythritol triallyl ether, Osaka Soda Co., Ltd.} 0.44 parts and 362 parts of deionized water was kept at 3 ° C. with stirring and mixing. After flowing nitrogen into this mixture to reduce the dissolved oxygen amount to 1 ppm or less, 0.5 part of 1% aqueous hydrogen peroxide solution, 1 part of 2% aqueous ascorbic acid solution and 2% 2,2′-azobisamidinopropane Polymerization was started by adding and mixing 0.1 part of a dihydrochloride aqueous solution. After the temperature of the mixture reached 80 ° C., a water-containing gel was obtained by polymerization at 80 ± 2 ° C. for about 5 hours.

Next, this hydrogel was subdivided into about 5 mm squares with scissors, and 162 parts of 45% aqueous sodium hydroxide solution was added. Furthermore, after kneading and chopping four times at a gel temperature of 100 ° C. with a mincing machine (ROYAL 12VR-400K) having a diameter of 8 mm, a kneader (desktop kneader PNV-1, Co., Ltd.) The whole amount was charged into Irie Shokai, and dried for 60 minutes at a rotation speed of 40 rpm and a jacket temperature of 180 ° C. to obtain a dried product containing a crosslinked polymer. After the dried product is pulverized with a juicer mixer (Osterizer BLENDER manufactured by Oster), the dried product is screened and adjusted to a particle size range of 710 to 150 μm (400 μm as a weight average particle size) to include crosslinked polymer particles Resin particles were obtained.

Next, 100 parts of the obtained resin particles were stirred at a high speed (high speed stirring turbulizer manufactured by Hosokawa Micron: rotation speed: 2000 rpm), and sodium aluminum sulfate alum 12 hydrate as an inorganic acid salt (d) was added to the mixture in an amount of 0.001. 6 parts by weight, a mixed solution in which 0.08 part by weight of ethylene glycol diglycidyl ether as a surface cross-linking agent and 3.3 parts by weight of 45% propylene glycol aqueous solution as a solvent were mixed and mixed uniformly. The mixture was allowed to stand at 60 ° C. for 60 minutes for drying to obtain water absorbent resin particles (P-8) of the present invention. The weight ratio of the particles having a particle diameter of 300 to 600 μm to the total weight of the water absorbent resin particles (P-8) was 70% by weight.

<Example 9> Acrylic acid (a1) {manufactured by Mitsubishi Chemical Corporation, purity 100%} 131 parts, internal cross-linking agent (b-2) {polyethylene glycol diacrylate (Mw = 508), manufactured by Shin-Nakamura Chemical Co., Ltd. } 0.4 parts, 162 parts of 45% aqueous sodium hydroxide, and 362 parts of deionized water were kept at 3 ° C. with stirring and mixing. After flowing nitrogen into this mixture to reduce the dissolved oxygen amount to 1 ppm or less, 0.5 part of 1% aqueous hydrogen peroxide solution, 1 part of 2% aqueous ascorbic acid solution and 2% 2,2′-azobisamidinopropane Polymerization was started by adding and mixing 0.1 part of a dihydrochloride aqueous solution. After the temperature of the mixture reached 80 ° C., a water-containing gel was obtained by polymerization at 80 ± 2 ° C. for about 5 hours.

Next, this hydrogel was subdivided into approximately 1 mm squares with scissors, kneaded and cut four times at a gel temperature of 80 ° C. with a minced machine (ROYAL 12VR-400K) having a diameter of 16 mm, and then ventilated dryer {150 ° C. And dried at a wind speed of 2 m / sec} to obtain a dried product. After the dried product is pulverized with a juicer mixer (Osterizer BLENDER manufactured by Oster), the dried product is screened and adjusted to a particle size range of 710 to 150 μm (400 μm as a weight average particle size) to include crosslinked polymer particles Resin particles were obtained.

Next, 100 parts of the obtained resin particles were stirred at a high speed (high speed stirring turbulizer manufactured by Hosokawa Micron: rotation speed: 2000 rpm), and sodium aluminum sulfate alum 12 hydrate as an inorganic acid salt (d) was added to the mixture in an amount of 0.001. 6 parts by weight, a mixed solution in which 0.08 part by weight of ethylene glycol diglycidyl ether as a surface cross-linking agent and 3.3 parts by weight of 45% propylene glycol aqueous solution as a solvent were mixed and mixed uniformly. The mixture was allowed to stand at 60 ° C. for 60 minutes to dry to obtain water absorbent resin particles (P-9) of the present invention. The weight ratio of the particles having a particle diameter of 300 to 600 μm to the total weight of the water absorbent resin particles (P-9) was 70% by weight.

<Example 10>
Water-absorbent resin particles (P-10) were obtained in the same manner as in Example 9, except that the hydrogel was subdivided into 5 mm squares with scissors. The weight ratio of the particles having a particle diameter of 300 to 600 μm to the total weight of the water absorbent resin particles (P-10) was 71% by weight.

<Example 11> Except that the hydrogel subdivided into approximately 1 mm square was kneaded and shredded four times at a gel temperature of 80 ° C with a minced machine (ROYAL 12VR-400K) having a diameter of 8 mm. Thus, water-absorbing resin particles (P-11) were obtained. The weight ratio of the particles having a particle diameter of 300 to 600 μm to the total weight of the water absorbent resin particles (P-11) was 70% by weight.

<Example 12> Except that the hydrogel subdivided into approximately 1 mm square was kneaded and cut twice at a gel temperature of 80 ° C with a minced machine (ROYAL 12VR-400K) having a 16 mm diameter. Thus, water absorbent resin particles (P-12) were obtained. The weight ratio of the particles having a particle diameter of 300 to 600 μm to the total weight of the water absorbent resin particles (P-12) was 71% by weight.

<Comparative Example 1> The neutralized water-containing gel was dried with a ventilation dryer {150 ° C, wind speed 2 m / sec} without kneading and chopping with a minced machine (ROYAL 12VR-400K) to obtain a dried product. Except that, comparative water-absorbent resin particles (R-1) were obtained in the same manner as in Example 1. The weight ratio of the particles having a particle diameter of 300 to 600 μm to the total weight of the water absorbent resin particles (R-1) was 71% by weight.

<Comparative Example 2> The hydrogel subdivided into approximately 1 mm square was kneaded and chopped with a minced machine (ROYAL 12VR-400K), and dried with a ventilation dryer {150 ° C, wind speed 2 m / sec} and dried. A comparative water-absorbent resin particle (R-2) was obtained in the same manner as in Example 9, except that the product was obtained. The weight ratio of the particles having a particle diameter of 300 to 600 μm to the total weight of the water absorbent resin particles (R-2) was 71% by weight.

<Comparative Example 3> The method disclosed in paragraphs 0088 to 0091 of JP-T-2017-222875 was traced to obtain a dried hydrated gel. That is, 100 g of acrylic acid, 0.5 g of polyethylene glycol diacrylate (Mw = 523) as a crosslinking agent, 0.033 g of diphenyl (2,4,6-trimethylbenzoyl) -phosphine oxide as a UV initiator, 50% aqueous sodium hydroxide solution (NaOH) 83.3 g) and 89.8 g of water were mixed to prepare a monomer aqueous solution composition having a monomer concentration of 45% by weight. Next, after the monomer aqueous solution composition is charged through a supply unit of a polymerization vessel composed of a conveyor belt that continuously moves, UV irradiation is performed by a UV irradiation device (irradiation amount: ² mW / cm ² ), and UV polymerization is performed for 2 minutes. To proceed to produce a hydrogel polymer. The hydrated gel polymer was transferred to a cutting machine and then cut to 0.2 cm. At this time, the water content of the cut hydrogel polymer was 50% by weight.

Next, the hydrogel polymer was dried for 30 minutes with a hot air dryer at a temperature of 160 ° C. to obtain a dried product. After the dried product is pulverized with a juicer mixer (Osterizer BLENDER manufactured by Oster), the dried product is screened and adjusted to a particle size range of 710 to 150 μm (400 μm as a weight average particle size) to include crosslinked polymer particles Resin particles were obtained.

Next, 100 parts of the obtained resin particles were stirred at a high speed (high speed stirring turbulizer manufactured by Hosokawa Micron: rotation speed: 2000 rpm), and sodium aluminum sulfate alum 12 hydrate as an inorganic acid salt (d) was added to the mixture in an amount of 0.001. 6 parts by weight, a mixed solution in which 0.08 part by weight of ethylene glycol diglycidyl ether as a surface cross-linking agent and 3.3 parts by weight of 45% propylene glycol aqueous solution as a solvent were mixed and mixed uniformly. The mixture was allowed to stand at 60 ° C. for 60 minutes for drying to obtain comparative water absorbent resin particles (R-3). The weight ratio of the particles having a particle diameter of 300 to 600 μm to the total weight of the water absorbent resin particles (R-3) was 70% by weight.

<Comparative example 4>
Water-absorbing resin particles (R-4) for comparison were obtained by tracing the method disclosed in paragraphs 0075 to 0077 of JP-A-2018-16750. Namely, acrylic acid (a1) {Mitsubishi Chemical Co., Ltd., purity 100%} 270 parts, internal cross-linking agent (b-1) {pentaerythritol triallyl ether, Osaka Soda Co., Ltd.} 0.98 parts and ion-exchanged water 712 parts were kept at 3 ° C. with stirring and mixing. After flowing nitrogen into this mixture to reduce the dissolved oxygen amount to 1 ppm or less, 1.1 parts of 1% aqueous hydrogen peroxide solution, 2.0 parts of 2% aqueous ascorbic acid solution, and 2% 2,2′-azobis Polymerization was initiated by adding and mixing 13.5 parts of an amidinopropane dihydrochloride aqueous solution. After the temperature of the mixture reached 80 ° C., it was aged at 80 ± 2 ° C. for about 5 hours to obtain a water-containing gel.

Next, while this hydrated gel was chopped with a mincing machine (12VR-400K manufactured by ROYAL), 220 parts of a 49% sodium hydroxide aqueous solution was added and mixed and neutralized to obtain a neutralized gel. The diameter of the eye plate used at this time was 16 mm, and was chopped four times. The gel temperature was 60 ° C. Further, the neutralized water-containing gel was air-dried using a ventilation dryer (manufactured by Inoue Metal) under the conditions of a supply temperature of 150 ° C. and a wind speed of 1.5 m / sec until the water content became 4% to obtain a dried product. It was. The dried product was pulverized with a juicer mixer (Osterizer BLENDER manufactured by Oster), and then sieved to adjust the particle size to a particle size range of 710 to 150 μm to obtain resin particles containing a crosslinked polymer.

Subsequently, 100 parts of the obtained resin particles were stirred at a high speed (high speed stirring turbulizer manufactured by Hosokawa Micron: rotation speed 2000 rpm), and 0.12 part of ethylene glycol diglycidyl ether as a surface cross-linking agent and 1.0 of propylene glycol were added thereto. Part, Klebosol 30cal25 (colloidal silica manufactured by AZ Material Co., Ltd.) 1.0 part as water-insoluble inorganic fine particles and 1.7 parts of ion-exchanged water, and sodium aluminum sulfate 12 hydrate as inorganic acid salt (d) A mixture of 0.6 part of the product, 0.6 part of propylene glycol and 1.5 part of ion-exchanged water was added at the same time, mixed uniformly, then heated at 135 ° C. for 30 minutes, and surface-crosslinked resin particles (R-4) was obtained. The weight ratio of the particles having a particle diameter of 300 to 600 μm to the total weight of the water absorbent resin particles (R-4) was 71% by weight.

<Comparative Example 5>
Regarding the drying conditions of the neutralized hydrous gel, water-absorbent resin particles (R-5) were obtained in the same manner as in Comparative Example 4 except that the supply temperature was 150 ° C. and the wind speed was 1.5 m / sec. Got. The weight ratio of the particles having a particle diameter of 300 to 600 μm to the total weight of the water absorbent resin particles (R-5) was 70% by weight.

Subsequently, in order to evaluate the mechanical strength of the water-absorbing resin particles, the water-absorbing resin particles obtained in Example 1, Example 8, Comparative Example 4 and Comparative Example 5 were used, and the breakability was as follows. The increase in fine particle content after the test was evaluated.

<Increase in fine particle content after breakability test>
50 g of a measurement sample was sieved with a 150 μm JIS standard sieve (JIS Z8801-1: 2006) to remove particles of 150 μm or less. The total amount of particles of 150 μm or more remaining on the sieve was put into a 3 L round bottom flask (manufactured by AS ONE), and a nylon net (JIS Z8801- 1: 2000), and a four-mouth separable cover (ASONE main pipe TS29 / 42, side pipe TS24 / 40, 24/40, 15/35) was set thereon. Next, set the stainless steel pipe (outer diameter 6 mm, inner diameter 4 mm) to the main pipe TS29 / 42 of the four-neck separable cover so that it passes through the nylon net and the tip is 45 mm from the bottom of the round bottom flask. did. The other end of the stainless steel tube was equipped with a urethane tube (length 1500 mm, inner diameter 8.5 mm) and connected to an air line capable of achieving a pressure of 0.3 MPa or more. Next, the air line is opened at a pressure of 0.2 MPa, and after air blowing for 10 minutes, the measurement sample is taken out, sieved with a 150 μm JIS standard sieve (JIS Z8801-1: 2006), and the weight of particles of 150 μm or less relative to the total weight. The percentage (%) was taken as the amount of increase in the fine particle content.

Particle defect degree (1) for the water absorbent resin particles (P-1) to (P-12) of Examples 1 to 12 and the water absorbent resin particles (R-1) to (R-5) of Comparative Examples 1 to 5 % Or less, 8% or more (screened particles and whole grains)), apparent density (g / ml), weight average particle diameter (μm), performance (water retention (g / g), absorption rate measured by vortex method ( (Second), absorption rate (second), absorption amount under load (g / g) and gel flow rate (ml / min)) measured by the lock-up method are shown in Table 1. In addition, Table 2 shows the evaluation results of the increase in the fine particle content after the breakage test for the water absorbent resin particles (P-1), (P-8), (R-4), and (R-5).

From the results shown in Table 1, the water-absorbent resin particles of the present invention have a volume ratio of 50% or less in terms of the volume ratio of the particles having a particle deficiency of 1% or less compared to the water-absorbent resin particles of Comparative Examples 1 to 3. It can be seen that the absorption rate measured by the vortex method and the lock-up method is greatly improved. In Comparative Examples 4 and 5, the proportion of particles having a particle defect degree of 8% or more does not satisfy the requirements of the present invention. Although Comparative Examples 4 and 5 are not inferior to the Examples in the performance listed in Table 1, as shown in Table 2, the increase in the content of fine particles after the breakability test is large. That is, from the results of Table 2, as typically shown in Examples 1 and 8, the water absorbent resin particles of the present invention have a particle defect degree of 8% or more compared to the water absorbent resin particles of Comparative Examples 4 and 5. It can be seen that the ratio of the particles is 5% or less by volume ratio, the increase in the fine particle content after the breakability test is suppressed, and the decrease in mechanical strength can be suppressed. Furthermore, since there is no large difference in apparent density and average particle diameter in the whole Examples and Comparative Examples, and no difference due to the polymerization method, it can be seen that the shape of the particle surface greatly contributes to the absorption rate.

The water-absorbent resin particles of the present invention form irregularities on the surface of the water-absorbent resin particles, and are formed with respect to particles at a constant controlled ratio, so that the apparent density and absorption are reduced without reducing the mechanical strength. Since both speeds are compatible, it can be used for absorbent articles with high absorption speed, excellent reversibility and surface dryness without causing troubles in the manufacturing process of various absorbent bodies, and is suitably used for sanitary goods.

DESCRIPTION OF SYMBOLS 1 Saline 2 Hydrous gel particle 3 Cylinder 4 Scale line of 60 ml position from bottom 5 Scale line of 40 ml position from bottom 6 Wire mesh 7 Cock 8 Circular wire mesh 9 Pressurizing shaft 10 Weight

Claims (11)

1. Among the particles screened in the range of 300 to 600 μm using a JIS standard sieve, the particles having a particle defect degree (CONV) defined by the following formula (1) of 1% or less are 50% or less by volume. Water-absorbent resin particles in which particles having a particle defect degree (CONV) of 8% or more are 5% or less by volume.
   CONV (%) = {B / (A + B)} × 100 (1)
   (In Formula (1), CONV represents the particle defect degree, A represents the projected area of the target particle obtained by the image analysis method, and B connected the convex portions of the target particle obtained by the image analysis method. (A value obtained by subtracting the projected area of the target particle indicated by A from the projected area surrounded by the envelope).
2. The water-absorbent resin particles according to claim 1, wherein the apparent density is 0.5 to 0.7 g / ml.
3. The water-absorbent resin particles according to claim 1 or 2, wherein the water retention amount of 0.9% by weight physiological saline is 30 to 50 g / g per unit weight.
4. The water-absorbent resin particle according to any one of claims 1 to 3, wherein an absorption rate (second) measured by a vortex method is 50 or less and an absorption rate (second) measured by a lockup method is 130 or less. .
5. The water-absorbent resin particles according to any one of claims 1 to 4, wherein the absorbed amount under load is 10 to 27 g / g.
6. The water-absorbent resin particles according to any one of claims 1 to 5, wherein the gel flow rate is 5 to 250 ml / min.
7. Water-soluble vinyl monomer (a1) and / or vinyl monomer (a2) which becomes water-soluble vinyl monomer (a1) by hydrolysis and a monomer composition having an internal crosslinking agent (b) as essential constituent units are polymerized and crosslinked. A step of polymerizing the hydrogel of the polymer (A), a step of subdividing the hydrogel of the cross-linked polymer (A), a step of further kneading the subdivided gel at a gel temperature of 40 ° C. to 120 ° C., And a step of surface cross-linking the surface of the resin particles (B) containing the polymer (A) with a surface cross-linking agent (c).
8. The method according to claim 7, further comprising the step of mixing the polyvalent metal salt (d) in an amount of 0.01 to 5% by weight based on the weight of the crosslinked polymer (A) after drying the hydrogel to obtain a crosslinked polymer. The manufacturing method as described.
9. The production method according to claim 8, wherein the polyvalent metal salt (d) is an inorganic acid salt of aluminum.
10. An absorber comprising the water-absorbent resin particles according to any one of claims 1 to 6.
11. An absorbent article comprising the absorbent body according to claim 10.
    

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