JPH11349687A - Particulate water-containing gel polymer and preparation of water absorption resin - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a particulate water-containing gel polymer capable of being uniformly and quickly dried and to provide a process for efficiently preparing high quality water absorption resins. SOLUTION: This particulate water-containing gel polymer can be obtained by polymerizing a water soluble ethylenically unsaturated monomer, then pulverizing the resulting polymer and, preferably, classifying the pulverized polymer. The average particle diameter is within the range of 0.8 to 5 mm and, at the same time, the particle distribution is a logarithmic standard deviation σζ of not more than 1.5. By this property, extremely better drying than before can be realized, and a high quality water absorption resin can efficiently be obtained by drying this particulate water-containing gel polymer.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a particulate hydrogel polymer which is preferably used as a material of a water-absorbent resin, and a method of drying the particulate hydrogel polymer to obtain a water absorption rate and a water absorption capacity. And a method for efficiently producing a water-absorbent resin having excellent water resistance.

[0002]

2. Description of the Related Art It is well known that a water-containing gel polymer (hereinafter simply referred to as a water-containing gel) can be obtained as a water-absorbing polymer by aqueous solution polymerization of a water-soluble ethylenically unsaturated monomer. I have. This hydrogel is obtained as a semi-solid and highly elastic gel-like material, which is dried to a powder state to be used as a water-absorbing resin, that is, a water-absorbing agent.

[0003] The hydrogel is often obtained as a lump or as an aggregate of hydrogel particles. If such a hydrogel is dried as it is, the drying efficiency decreases,
Usually, a process of once crushing particles having a size within a predetermined range using a crusher such as a kneader or a meat chopper and then drying the crushed particles is performed.

[0004]

However, in the prior art,
The particle size distribution of the particles of the hydrogel was not considered much, and the hydrogel was merely crushed finely. Therefore, the obtained particulate hydrogel becomes a mixture of particles of various sizes, and the particle size distribution becomes very wide. As described above, when the particle size distribution of the particulate hydrogel is broadened, the hydrogel is not dried uniformly.

[0005] In other words, if the size of the particulate hydrogel is not substantially constant, in the drying step, the small particles are dried first to become a dried product of the hydrogel, but the larger particles are reduced to smaller particles. Is not dried quickly. Therefore, if drying is performed on the basis of small particles, large particles will remain as undried substances, and in the pulverizing step after drying, the disadvantage that the undried substances adhere to the pulverizer and hinder pulverization. Will be invited. Further, if the undried material is mixed into the water absorbent resin as the final product, the physical properties of the water absorbent resin will be reduced.

On the other hand, when drying is performed on the basis of large particles, it takes a very long time until the large particles are completely dried, and during the long drying, the small particles are dried. Is disadvantageously over-dried. Therefore, the production of the water-absorbent resin cannot be performed efficiently, and the overdried particles are mixed into the water-absorbent resin as a final product, so that the physical properties of the water-absorbent resin also deteriorate.

Further, when the hydrogel is ground with a kneader or meat chopper, the hydrogel is kneaded with the grinding. For this reason, unevenness due to kneading occurs on the surface of the primary particles of the obtained hydrogel, and the surface area increases.
If such surface irregularities occur in the primary particles, the irregularities are very easily entangled with each other, so that the primary particles easily aggregate. Moreover, since the entangled irregularities are in contact with each other so as to mesh with each other, it is very difficult to dissociate the aggregated primary particles.

When a large external force is applied to the aggregates of the primary particles, which are difficult to dissociate, when the aggregates are dissociated from each other, the frequency at which the primary particles themselves are pulverized by the external force is extremely high. Get higher. as a result,
In addition to the primary particles of a desired size, a large amount of fine powder is generated due to the pulverization of the primary particles. The generation of the fine powder causes a problem of deteriorating the performance as a water-absorbing resin composed of the primary particles. In addition, since the fine powder itself cannot be used as the water-absorbing resin, there is a problem that the yield in the production of the water-absorbing resin is reduced.

The present invention has been made in view of the above problems, and an object of the present invention is to enable uniform and rapid drying without the primary particles after pulverization being aggregated.
A particulate hydrogel polymer that becomes a high-quality water-absorbent resin,
It is an object of the present invention to provide a method for producing a water-absorbent resin, which efficiently produces a high-quality water-absorbent resin using the particulate hydrogel polymer.

[0010]

Means for Solving the Problems The present inventors have found that a particulate hydrogel polymer obtained by polymerizing a water-soluble ethylenically unsaturated monomer, preferably in the presence of a crosslinking agent, and then pulverizing the polymer, Having an average particle size within a predetermined range, and
If the particle size distribution has a predetermined logarithmic standard deviation value, extremely good drying is possible, and if this particulate hydrogel is used, it is possible to efficiently produce a high-quality water-absorbing resin. They have found and completed the present invention.

Further, if the particulate hydrogel has a square shape and a smooth surface, it is possible to suppress aggregation of the particulate hydrogel,
As a result, they have found that a high-quality water-absorbent resin can be produced more efficiently, and have completed the present invention.

That is, in order to solve the above-mentioned problems, the particulate hydrogel polymer according to the first aspect of the present invention is obtained by polymerizing a water-soluble ethylenically unsaturated monomer and then pulverizing it at least. The particulate hydrogel polymer is characterized in that the average particle size is in the range of 0.8 to 5 mm, and the particle size distribution is 1.5 or less in logarithmic standard deviation σζ.

According to the first aspect of the present invention, since the shape of the particles of the hydrogel polymer becomes very uniform as a whole, when the hydrogel polymer is dried, some of the particles are dried. Does not dry out or become difficult to dry. Therefore, even when the conventionally used drying method is used, the hydrogel polymer can be dried more uniformly than before. Further, since the shape of the particles is uniform, it is not necessary to set the drying time to a long time corresponding to the large particles, and the drying time can be shortened. As described above, since the particle size distribution of the hydrogel polymer is uniform, it is possible to perform extremely better drying than before.

The particulate hydrogel polymer according to the second aspect of the present invention is intended to solve the above-mentioned problems.
In addition to the constitution described above, the solid content is further characterized in the range of 20 to 50%.

According to the second aspect of the present invention, since the water content of the particulate hydrogel polymer is in an optimum range for drying, the particulate hydrogel polymer can be dried more favorably. Can be.

[0016] The particulate hydrogel polymer according to the third aspect of the present invention is intended to solve the above-mentioned problems.
Or, in addition to the configuration described in 2, the angle of repose is 38 °.
It is characterized by the following.

According to the structure of the third aspect, the particles of the particulate hydrogel polymer are unlikely to be caught between the particles, and the fluidity of the whole particles is enhanced. Therefore, the particulate hydrogel polymer is angular, has no irregularities on the surface, is almost transparent, and has particles of a uniform size as a whole. Therefore, drying can be performed more favorably.

According to a fourth aspect of the present invention, there is provided a method for producing a water-absorbent resin having an average particle size of 0.1 to achieve the above object.
The method is characterized in that the pulverized particulate hydrogel polymer having a particle size distribution within a range of 8 to 5 mm and a logarithmic standard deviation σζ of 1.5 or less is dried.

According to the method of the fourth aspect, since the particle size distribution of the particulate hydrogel polymer serving as the water-absorbing resin is uniform, drying can be performed uniformly and quickly. Therefore, the production of the water absorbent resin can be made more efficient.
In addition, particles that become over-dried or undried hardly occur. For this reason, it is possible to avoid inconveniences that occur in the step after drying due to generation of undried matter, and to avoid deterioration in physical properties of the obtained water-absorbent resin, thereby obtaining a high-quality water-absorbent resin. .

According to a fifth aspect of the present invention, there is provided a particulate hydrogel polymer obtained by polymerizing a water-soluble ethylenically unsaturated monomer and then pulverizing the polymer at least. In the hydrogel polymer, the average particle size is in the range of 0.5 to 5 mm, and
It is characterized in that the particle size distribution is 1.5 or less in logarithmic standard deviation σζ.

According to a sixth aspect of the present invention, there is provided a particulate hydrogel polymer according to the present invention. It is characterized by having a substantially rectangular parallelepiped shape.

According to the fifth or sixth aspect of the present invention, the shape of the particulate hydrogel polymer is generally uniform, so that the particles are less likely to aggregate. Therefore, while drying is performed very well, in a drying step or the like, particles are prevented from aggregating to form an aggregate, and even if an aggregate is formed, a weak external force is applied to the aggregate. It can be easily dissociated into primary particles only by adding.

Therefore, if a water-absorbing resin is produced using the particulate hydrogel polymer of the present invention, generation of fine powder of the hydrogel polymer which cannot be used as a water-absorbing resin is suppressed. As a result, a high-quality water-absorbent resin can be obtained with a high yield, and the burden of removing and collecting fine powder can be reduced, and the production efficiency of the water-absorbent resin can be improved.

[0024]

DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described below. Note that the present invention is not limited to this.

The particulate hydrogel polymer according to the present invention is obtained by subjecting an ethylenically unsaturated monomer to aqueous solution polymerization, preferably in the presence of a trace amount of a crosslinking agent, to form a hydrogel polymer or hydrogel crosslinkable polymer. It is obtained after a coalescence is obtained and this hydrogel polymer or hydrogel crosslinked polymer is pulverized and preferably classified. The average particle diameter of the particulate hydrogel polymer is in the range of 0.5 to 5 mm, or 0.1 to 5 mm.
It is in the range of 8 to 5 mm, and the particle size distribution of the particles is 1.5 or less in logarithmic standard deviation σζ.

The method for producing a water-absorbent resin according to the present invention is a method for producing the above-mentioned particulate hydrogel polymer and drying the particulate hydrogel polymer.

The above-mentioned hydrogel polymer or hydrogel crosslinked polymer is hereinafter simply referred to simply as hydrogel. Unless otherwise specified, these hydrogels are all lumpy or aggregated hydrogels. On the other hand, the hydrogel according to the present invention is in the form of particles, which is hereinafter referred to as a particulate hydrogel, and is distinguished from the above-mentioned massive or aggregated hydrogel.

The ethylenically unsaturated monomer used as a raw material of the hydrogel is a water-soluble monomer,
Specifically, for example, (meth) acrylic acid, β-acryloyloxypropionic acid, maleic acid, maleic anhydride, fumaric acid, crotonic acid, itaconic acid, cinnamic acid,
2- (meth) acryloylethanesulfonic acid, 2- (meth) acryloylpropanesulfonic acid, 2- (meth) acrylamide-2-methylpropanesulfonic acid, vinylsulfonic acid, styrenesulfonic acid, allylsulfonic acid,
Acid group-containing monomers such as vinylphosphonic acid, 2- (meth) acryloyloxyethyl phosphoric acid, (meth) acryloxyalkanesulfonic acid, and alkali metal salts, alkaline earth metal salts, ammonium salts, and alkylamines thereof. Salts; dialkylaminoalkyl (meth) acrylates such as N, N-dimethylaminoethyl (meth) acrylate, N, N-dimethylaminopropyl (meth) acrylate, N, N-dimethylaminopropyl (meth) acrylamide and the like; Grades (eg, reactants with alkyl hydride, reactants with dialkyl sulfate, etc.); dialkylaminohydroxyalkyl (meth)
Acrylates and their quaternaries; N-alkylvinylpyridinium halides; hydroxymethyl (meth)
Hydroxyalkyl (meth) acrylates such as acrylate, 2-hydroxyethyl methacrylate, and 2-hydroxypropyl (meth) acrylate; acrylamide, methacrylamide, N-ethyl (meth) acrylamide, Nn-propyl (meth) acrylamide, N -Isopropyl (meth) acrylamide, N, N
-Dimethyl (meth) acrylamide; alkoxypolyethylene glycol (meth) acrylate such as methoxypolyethylene glycol (meth) acrylate, polyethylene glycol mono (meth) acrylate; vinylpyridine, N-vinylpyridine, N-vinylpyrrolidone,
N-acryloylpiperidine; N-vinylacetamide; and the like. One of these ethylenically unsaturated monomers may be used alone, or two or more thereof may be appropriately mixed.

When a monomer containing an acrylate monomer as a main component among the above-mentioned ethylenically unsaturated monomers is used, the water-absorbing performance and safety of the obtained hydrogel are further improved. It is preferred. Here, the acrylate-based monomer indicates acrylic acid and / or a water-soluble salt of acrylic acid.

The water-soluble salts of acrylic acid are defined as having a neutralization ratio of 30 mol% to 100 mol%, preferably 5 mol%.
An alkali metal salt, an alkaline earth metal salt, an ammonium salt, a hydroxyammonium salt, an amine salt, and an alkylamine salt of acrylic acid in the range of 0 mol% to 99 mol% are shown. Of the water-soluble salts exemplified above, sodium salts and potassium salts are particularly preferred.

These acrylate monomers may be used alone or in combination of two or more. The average molecular weight (degree of polymerization) of the water-absorbent resin is not particularly limited.

The above-mentioned hydrogel can be obtained by polymerizing a monomer composition containing the above-mentioned ethylenically unsaturated monomer as a main component in the presence of a crosslinking agent. Further, the monomer composition contains another monomer (copolymerizable monomer) copolymerizable with the ethylenically unsaturated monomer to such an extent that the hydrophilicity of the obtained hydrogel is not impaired. May be.

Specific examples of the copolymerizable monomer include (meth) acrylates such as methyl (meth) acrylate, ethyl (meth) acrylate, and butyl (meth) acrylate; vinyl acetate, propion, and the like. And hydrophobic monomers such as vinyl acid. These copolymerizable monomers may be used alone,
Further, two or more kinds may be appropriately mixed and used.

Examples of the crosslinking agent used in polymerizing the above monomer component include a compound having a plurality of vinyl groups in the molecule; a functional group capable of reacting with a carboxyl group or a sulfonic acid group in the molecule. Compounds containing a plurality of groups; and the like. These crosslinking agents may be used alone or in combination of two or more.

Examples of the compound having a plurality of vinyl groups in the molecule include, for example, N, N-methylenebis (meth) acrylamide, (poly) ethylene glycol di (meth) acrylate, and (poly) propylene glycol diamine. (Meth) acrylate, trimethylolpropane tri (meth) acrylate, trimethylolpropane di (meth) acrylate, glycerin tri (meth) acrylate, glycerin acrylate methacrylate, ethylene oxide modified trimethylolpropane tri (meth) acrylate, pentaerythritol tetra ( (Meth) acrylate, dipentaerythritol hexa (meth) acrylate, N, N-diallylacrylamide,
Examples include triallyl cyanurate, triallyl isocyanurate, triallyl phosphate, triallylamine, diallyloxyacetic acid, bis (N-vinylcarboxylic amide), tetraallyloxyethane, and the like.

Compounds having a plurality of functional groups capable of reacting with a carboxyl group or a sulfonic acid group in the molecule include (poly) ethylene glycol, diethylene glycol, propylene glycol, triethylene glycol,
Tetraethylene glycol, 1,3-propanediol, dipropylene glycol, 2,2,4-trimethyl-1,3-pentanediol, polypropylene glycol, (poly) glycerin, 2-butene-1,4-diol, 1, 4-butanediol, 1,5-pentanediol, 1,6-hexanediol, 1,2-cyclohexanedimethanol, 1,2-cyclohexanol, trimethylolpropane, diethanolamine, triethanolamine, polyoxypropylene, oxyethylene Polyhydric alcohol compounds such as oxypropylene block copolymer, pentaerythritol and sorbitol; (poly) ethylene glycol diglycidyl ether, (poly) glycerol polyglycidyl ether, diglycerol polyglycidyl ether And epoxy compounds such as (poly) propylene glycol diglycidyl ether and glycidol; polyamine compounds such as ethylenediamine, diethylenetriamine, triethylenetetramine, tetraethylenepentamine, pentaethylenehexamine, polyamidepolyamine and polyethyleneimine; Condensates of amines and haloepoxy compounds; polyvalent isocyanate compounds such as 2,4-tolylene diisocyanate and hexamethylene diisocyanate;
Polyvalent oxazoline compounds such as 1,2-ethylenebisoxazoline; silane coupling agents such as γ-glycidoxypropyltrimethoxysilane, γ-aminopropyltrimethoxysilane; 1,3-dioxolan-2-one; Methyl-1,3-dioxolan-2-one,
4,5-dimethyl-1,3-dioxolan-2-one,
4,4-dimethyl-1,3-dioxolan-2-one,
4-ethyl-1,3-dioxolan-2-one, 4-hydroxymethyl-1,3-dioxolan-2-one,
1,3-dioxan-2-one, 4-methyl-1,3-
Alkylene carbonate compounds such as dioxan-2-one, 4,6-dimethyl-1,3-dioxan-2-one and 1,3-dioxopan-2-one; haloepoxy compounds such as epichlorohydrin; zinc, calcium, Hydroxides or chlorides of magnesium, aluminum, iron, zirconium and the like.

The amount of the cross-linking agent used is not particularly limited, but may be in the range of 0.
It is preferably in the range of 0001 mol% to 10 mol%, more preferably in the range of 0.001 mol% to 1 mol%.

In the present invention, examples of the method for polymerizing the above monomer component include aqueous solution polymerization, standing polymerization on a vat or a belt, and polymerization in a kneader. Of these, stationary polymerization on a belt is preferred. In addition, when the above ethylenically unsaturated monomer is subjected to aqueous solution polymerization, either continuous polymerization or batch polymerization may be employed, and any of normal pressure, reduced pressure, and increased pressure may be used. It may be performed under pressure. Note that the polymerization reaction is preferably performed under a stream of an inert gas such as nitrogen, helium, argon, or carbon dioxide.

At the start of the polymerization in the above polymerization reaction, for example, a polymerization initiator or an activation energy ray such as a radiation, an electron beam, an ultraviolet ray, or an electromagnetic ray can be used. Specific examples of the polymerization initiator include inorganic compounds such as sodium persulfate, ammonium persulfate, potassium persulfate, and hydrogen peroxide; and t-butyl hydroperoxide, benzoyl peroxide, cumene hydroperoxide, and the like. Organic peroxide; 2,2′-azobis (N, N′-methyleneisobutylamidine) or a salt thereof, 2,2′-azobis (2-methylpropionamidine) or a salt thereof, 2,2′-azobis (2 -Amidinopropane) or a salt thereof, 4,4'-azobis-
Radical polymerization initiators such as azo compounds such as 4-cyanovaleric acid;

These polymerization initiators may be used alone or in combination of two or more. When a peroxide is used as the polymerization initiator, for example, redox polymerization may be performed using a reducing agent such as a sulfite, a bisulfite, or L-ascorbic acid in combination.

In the present invention, if the hydrogel obtained by polymerizing the above monomer component contains bubbles therein,
It is particularly preferable because the water absorbing performance of the obtained water absorbing resin can be improved. The hydrogel containing bubbles therein can be easily obtained by polymerizing the monomer component in the presence of a crosslinking agent so as to contain bubbles. As such a polymerization method, a polymerization method in the presence of an azo-based initiator; a carbonate as a foaming agent (JP-A-5-23)
7378, JP-A-7-185331); a polymerization method in which a water-insoluble blowing agent such as pentane or trifluoroethane is dispersed in a monomer (US Pat. No. 5,328,935; US Patent 533
No. 8766); a polymerization method using a solid particulate foaming agent (WO 96/17884); a method of polymerizing while dispersing an inert gas in the presence of a surfactant; Various methods can be employed.

When polymerizing the above monomer components in the presence of a crosslinking agent, it is preferable to use water as a solvent. That is, it is preferable that the monomer component and the cross-linking agent be an aqueous solution. This is to improve the water absorbing performance of the obtained water-absorbing resin and to efficiently perform foaming with a foaming agent.

The above aqueous solution (hereinafter referred to as an aqueous monomer solution)
The concentration of the monomer component therein is more preferably in the range of 20% by weight to 60% by weight. When the concentration of the monomer component is less than 20% by weight, the amount of the water-soluble component of the obtained water-absorbent resin may increase, and the foaming by the foaming agent becomes insufficient, so that the water absorption rate can be improved. It may not be possible. On the other hand, if the concentration of the monomer component exceeds 60% by weight, it may be difficult to control the reaction temperature and foaming by the foaming agent.

As a solvent for the aqueous monomer solution, water and
An organic solvent soluble in water can be used in combination. Specific examples of the organic solvent include methyl alcohol, ethyl alcohol, acetone, dimethyl sulfoxide, ethylene glycol monomethyl ether, glycerin, (poly) ethylene glycol, (poly) propylene glycol, and alkylene carbonate. These organic solvents may be used alone or in combination of two or more.

The foaming agent added to the above monomer aqueous solution is as follows:
Those that disperse or dissolve in the aqueous monomer solution can be used. As the foaming agent, specifically, for example, n-pentane, 2-methylpropane, 2,2-dimethylpropane, hexane, heptane, benzene, substituted benzene, chloromethane, chlorofluoromethane,
Volatile organic compounds dispersed or dissolved in the above monomer aqueous solution such as 1,1,2-trichlorotrifluoromethane, methanol, ethanol, isopropanol, acetone, azodicarbonamide, azobisisobutyronitrile; sodium bicarbonate; Carbonates such as ammonium carbonate, ammonium bicarbonate, basic magnesium carbonate and calcium carbonate; ammonium nitrite; dry ice; and acrylates of amino group-containing azo compounds. The foaming agents may be used alone or in combination of two or more.

The amount of the foaming agent to be used with respect to the monomer may be appropriately set according to the combination of the monomer and the foaming agent, and is not particularly limited. However, the amount is more preferably in the range of 0.001 to 10 parts by weight based on 100 parts by weight of the monomer. If the amount of the foaming agent is out of the above range, the resulting water-absorbent resin may have insufficient water-absorbing performance.

The water content of the hydrogel in the form of a lump or aggregate obtained as described above is generally 10% by weight.
To 90% by weight, preferably 20% to 8% by weight.
The range is 0% by weight. If the water content is less than 10% by weight,
In some cases, it may be difficult to pulverize the hydrogel, or in the case of a hydrogel containing bubbles, the bubbles may be crushed. On the other hand, if the water content is higher than 90% by weight, it takes too much time to dry the particles after pulverization.

The obtained massive hydrogel is pulverized to obtain a particulate hydrogel. The pulverization method includes a vertical cutting machine (cutting mill or rotoplex), a kneader, a guillotine cutter, a slicer, and a roll. Various pulverizing means such as a cutter, a shredder, and scissors can be used. The pulverizing means is not particularly limited, but it is particularly preferable to use a vertical cutter in order to obtain the particulate hydrogel according to the present invention more efficiently.

The above-mentioned vertical cutter grinds the hydrogel by shearing the fixed blade and the rotary blade, preferably in the presence of a surfactant. Therefore, if pulverization is performed using this vertical cutting machine, the mechanical external force applied to the hydrogel can be reduced, and a rectangular and transparent particulate hydrogel having few irregularities on the surface can be obtained. it can. As described below, it is more preferable to classify the pulverized hydrogel, which is a pulverized product, simultaneously with the pulverization.

The vertical cutting machine has a pulverizing section having at least an inlet and an outlet. Then, the water-containing gel is continuously and gradually fed into the pulverizing section from the above-mentioned inlet,
Crush continuously. Then, the pulverized product obtained by the pulverization is discharged from the discharge port. It is more efficient to discharge the pulverized product while sucking it with a blower or the like.

The configuration of the pulverizing section provided in the vertical cutting machine will be specifically described. As shown in FIGS. 1A and 1B, the pulverizing unit 2 has a cylindrical casing 11, and in the casing 11, that is, in the pulverizing unit 2, an outer wall of the casing 11 is provided in a circumferential direction. Fixed blade 13 fixed along
... are provided (three in FIGS. 1A and 1B). A rotating shaft 16 that is driven to rotate by a motor is provided at the center of the casing 11. further,
As shown in FIG. 1 (b), a stagnation area 17 may be provided in the pulverizing section 2.

The rotating shaft 16 is provided in parallel with the fixed blades 13. Around the rotating shaft 16, a plurality of rotating blades 12 (usually 2 to 5 blades, FIG.
(Three in (b)) are provided at equal intervals and radially outward of the rotating shaft 16. The fixed blade 13 described above ...
Is provided so as to extend in the axial direction of the rotating shaft 16. The rotating blades 12 and the fixed blades 13 have their opposing surfaces substantially parallel to each other with a certain interval.

The gap between the rotary blade 12 and the fixed blade 13 facing the rotary blade 12 is preferably 0.1 mm or more and 3 mm or less, more preferably 0.5 mm or more and 2 mm or less. When the gap is narrower than 0.1 mm, extra mechanical external force is applied to the particulate hydrogel,
The particulate hydrogel may be kneaded. In addition, there is a possibility that the rotating blade 12 comes into contact with the fixed blade 13 during rotation.

On the other hand, the size of the particulate hydrogel is determined by the gap between the rotary blade 12 and the fixed blade 13, and if the gap is larger than 3 mm, the particulate hydrogel is pulverized to a large size. As a result, the hydrated gel in the form of a lump or aggregate is less likely to be crushed.

The peripheral speed of the rotary blade 12 is preferably in the range of 0.1 m / sec to 50 m / sec, and is preferably 1 m / sec.
More preferably, it is in the range of not less than 20 m / sec. If the peripheral speed is lower than 0.1 m / sec, the crushing amount (processing amount) of the hydrogel per unit time extremely decreases, which is not preferable. On the other hand, if the peripheral speed is higher than 50 m / sec or more, the particulate hydrogels re-attach to each other before being discharged from the screen 14 and agglomerate, so that smooth discharge cannot be performed. Therefore, the production efficiency is lowered, which is not preferable.

In the pulverization of the massive hydrogel,
It is preferable to add a surfactant. This surfactant needs to be present on the surface of the hydrogel. By the presence of the surfactant on the surface of the hydrogel,
The surface of the hydrogel can be subjected to a surface treatment. The hydrogel subjected to the surface treatment is smoothly pulverized by the lubricating effect of the surfactant without receiving unnecessary mechanical external force from the blades.

Therefore, at the time when the hydrogel is subjected to shearing by the rotary blade 12 and the fixed blade 13, the surfactant must already be present on the surface of the hydrogel. Therefore, it is preferable that the surfactant is added when crushing the hydrogel or after crushing the hydrogel. Alternatively, a surfactant may be added at the same time that the crushed hydrogel is crushed.

As the surfactant, for example, an anionic surfactant, a nonionic surfactant, a cationic surfactant, or an amphoteric surfactant can be used.

Among the above surfactants, examples of the anionic surfactant include mixed fatty acid sodium soap, semi-hardened tallow fatty acid sodium soap, sodium stearate soap, potassium oleate soap, castor oil potassium soap and the like. Fatty acid salts; alkyl sulfate esters such as sodium lauryl sulfate, higher alcohol sodium sulfate and triethanolamine lauryl sulfate; alkylbenzene sulfonates such as sodium dodecylbenzenesulfonate; alkylnaphthalene sulfonates such as sodium alkylnaphthalenesulfonate; Alkyl sulfosuccinates such as sodium dialkyl sulfosuccinate; alkyl diphenyl ether disulfonates such as sodium alkyl diphenyl ether disulfonate; alkyl Alkyl phosphates such as potassium phosphate; polyoxyethylene alkyls such as sodium polyoxyethylene lauryl ether sulfate, sodium polyoxyethylene alkyl ether sulfate, triethanolamine polyoxyethylene alkyl ether sulfate and sodium polyoxyethylene alkyl phenyl ether sulfate (Or alkyl allyl) sulfate; special reactive anionic surfactant; special carboxylic acid surfactant;
Naphthalenesulfonic acid formalin condensate such as sodium salt of β-naphthalenesulfonic acid formalin condensate, sodium salt of special aromatic sulfonic acid formalin condensate;
Special polycarboxylic acid type polymer surfactants; polyoxyethylene alkyl phosphates; and the like.

Examples of the nonionic surfactant include polyolefin oxides such as polyethylene glycol, polypropylene glycol and polyethylene glycol-polypropylene glycol block copolymer; polyoxyethylene lauryl ether, polyoxyethylene cetyl ether, Polyoxyethylene stearyl ether, polyoxyethylene oleyl ether,
Polyoxyethylene alkyl ethers such as polyoxyethylene higher alcohol ethers, polyoxyethylene alkyl aryl ethers such as polyoxyethylene nonylphenyl ether; polyoxyethylene derivatives; sorbitan monolaurate, sorbitan monopalmitate, sorbitan monostearate, and sorbitan Sorbitan fatty acid esters such as tristearate, sorbitan monooleate, sorbitan trioleate, sorbitan sesquioleate, sorbitan distearate; polyoxyethylene sorbitan monolaurate, polyoxyethylene sorbitan monopalmitate, polyoxyethylene sorbitan monostearate , Polyoxyethylene sorbitan tristearate, polyoxyethylene sorbitan monooleate Polyoxyethylene sorbitan fatty acid esters such as polyoxyethylene sorbitan trioleate; polyoxyethylene sorbitol fatty acid esters such as polyoxyethylene sorbite tetraoleate; glycerol monostearate, glycerol monooleate, self-emulsifying glycerol monostearate Glycerin fatty acid esters of: polyoxyethylene fatty acid esters such as polyethylene glycol monolaurate, polyethylene glycol monostearate, polyethylene glycol distearate, polyethylene glycol monooleate; polyoxyethylene alkylamine; polyoxyethylene hydrogenated castor oil; alkyl Alkanolamide; and the like.

Examples of the cationic surfactant and the amphoteric surfactant include alkylamine salts such as coconutamine acetate and stearylamine acetate; lauryltrimethylammonium chloride, stearyltrimethylammonium chloride, and cetyltrimethylammonium. Quaternary ammonium salts such as chloride, distearyldimethylammonium chloride, alkylbenzyldimethylammonium chloride; alkylbetaines such as laurylbetaine, stearylbetaine, laurylcarboxymethylhydroxyethylimidazoliniumbetaine; amine oxides such as lauryldimethylamine oxide; And the like.

In addition to the above surfactants, it is also possible to use a fluorine-based surfactant or a siloxane-based surfactant.

Among the above surfactants, polypropylene glycol or polyethylene glycol-polypropylene glycol block copolymer is particularly preferred. These surfactants can be added in a small amount when added to the hydrogel. In addition, even when these surfactants are subjected to a surface treatment on the surface of the hydrogel after the addition, they do not impair the physical properties of the hydrogel (for example, water absorption under pressure, etc.). Further, these surfactants are preferable because of high safety in use.

The amount of the above surfactant added depends on the amount of the hydrogel 10
It is in the range of 0.001 to 10 parts by weight, preferably 0.01 to 5 parts by weight, and more preferably 0.1 to 5 parts by weight with respect to 0 parts by weight.
More preferably, it is in the range of 2 parts by weight. The above addition amount is 0.0
If the amount is less than 01 parts by weight, the particulate hydrogel obtained by pulverization reaggregates. On the other hand, if the addition amount is more than 10 parts by weight, not only the effect corresponding to the addition is not obtained, but also the physical properties of the water absorbent resin of the final product may be reduced.

The rotary blade 12 and the fixed blade 13 having the above configuration
When the above-mentioned surfactant is further added in the shearing, the smoother pulverization becomes possible due to its lubricating effect. Therefore, the particulate hydrogel according to the present invention, which has a square and transparent shape and has a uniform size, can be efficiently obtained.

The particulate hydrogel crushed by the vertical cutting machine with the addition of the surfactant is mixed with the screen 14
It is particularly preferable that the particles be classified into particles having a predetermined size. This screen 14 is shown in FIG.
As shown in FIG. 1B, the rotary blade 12 is provided in an arc shape on the outer peripheral side, and further, as shown in FIG. 1A, provided on the entire outer peripheral side in a circular shape. Is particularly preferred. As described above, when the screen 14 is provided in an arc shape on the outer peripheral side of the rotary blade 12, particularly, in a circular shape on the entire surface, the pulverized particulate hydrogel is subjected to excessive shearing and mechanical external force by the rotary blade 12. Since it is not added and is immediately classified and discharged from the outlet 3 outside the screen 14 to the outside of the vertical cutting machine, good pulverization becomes possible.

The screen 14 is not particularly limited. For example, 50 screens / 100 cm ²
It is preferable that a plurality of holes are formed in a range of 800 holes / 100 cm ² or less. Further, the porosity of the screen 14 is preferably 30% or more and less than 60%.

If the number of holes per unit area and the opening ratio are out of the above ranges, it is not preferable because the classification of the particulate hydrogel may not be performed effectively. The aperture ratio is a percentage of the total area of the screen 14 and the total area of a plurality of holes formed in the screen 14. Further, the shape of the holes formed in the screen 14 is not particularly limited, and may be a circle or a square such as a square or a hexagon.

Further, it is preferable that the screen 14 is coated with Teflon. Thereby, it is possible to suppress the adhesion of the clumpy or agglomerated hydrogel or the particulate hydrogel having high adhesiveness to the screen 14. Therefore, the occurrence of clogging of the screen 14 is avoided, and more efficient pulverization is possible.

The gap between the rotary blade 12 and the screen 14 is preferably such that the rotary blade 12 does not contact the screen 14. Specifically, 0.1
It is preferably within the range of not less than 5 mm and not more than 5 mm,
More preferably, it is in the range of 0.5 mm or more and 3 mm or less. If the gap is smaller than 0.1 mm, unnecessary mechanical external force is applied to the particulate hydrogel, and the particulate hydrogel may be crushed. Further, there is a possibility that the rotary blade 12 may come into contact with the screen 14 during rotation. On the other hand, when the gap is larger than 5 mm, the particulate hydrogel is difficult to be discharged to the outside of the screen 14, and the treatment efficiency is reduced.

The average particle size (size) of the particulate hydrogel obtained by the above-mentioned pulverizing method, preferably using a vertical cutter, is much sharper than in the prior art. That is, the size of the particles of the particulate hydrogel is
It is very uniform. As will be described later, the shape of the particles is transparent with a smooth angular surface and a repose angle of 38 ° or less. The particulate hydrogel having such a configuration can be dried uniformly, and a water-absorbent resin having good properties can be obtained.

The above particulate hydrogel will be specifically described. First, when the generation of fine powder described later is considered to some extent, the average particle size of the particulate hydrogel is in the range of 0.8 mm or more and 5 mm or less, preferably 1 mm.
In the range of not less than 4 mm and more preferably not more than 1 m
m and 3 mm or less.

The calculation of the average particle size can be performed as follows. First, the obtained particulate hydrogel is classified by, for example, a sieve, and the weight on the classified sieve is weighed. Next, the logarithmic probability paper was used with the vertical axis being the upper percentage of the integrated sieve and the horizontal axis being the sieve opening, and the logarithmic probability paper was subjected to a predetermined formula to obtain particles corresponding to solid content α weight%. The particle size distribution of the hydrated gel is plotted. And
The particle size corresponding to 50% by weight on the integrated sieve on this plot is defined as the average particle size.

The predetermined equation used when plotting the particle size distribution on log probability paper is such that the weight of the sample of the particulate hydrogel used is w ₀ , the weight of the particulate hydrogel after classification is w, and the classification is w. When the opening of the used sieve is r and the opening of the sieve corresponding to the solid content α weight% is R (α), the following equation (1) is obtained.

R (α) = (w ₀ / w) ^1/3 × r (1) The distribution of the average particle size of the particulate hydrogel is evaluated by a logarithmic standard deviation σζ. This σζ is calculated from the above-mentioned plot by calculating the particle size (X ₁ ) and the particle size R = 15.9% (X ₂ ) when the integrated sieve% is R = 84.1%. _{From 1} and X ₂ , the following equation (2)
Is calculated by

Σζ = (１ ／) ln (X ₂ / X ₁ ) (2) The logarithmic standard deviation δζ is preferably 1.5 or less, more preferably 1.0 or less. It is more preferably 0.8 or less. If the logarithmic standard deviation value is within this range, the particle size distribution of the particulate hydrogel is very sharp, indicating that uniform particles are obtained as a whole.

The particulate hydrogel has a solid content of 20% to 5%.
It is preferably within a range of 0%, and more preferably within a range of 25% to 40%. If the solid content of the particulate hydrogel is out of the above range, good drying cannot be achieved, which is not preferable.

The shape of the particulate hydrogel will be described in more detail. The shape of the particulate hydrogel obtained by pulverization by the vertical cutting machine is square, and its surface is a smooth surface with very few irregularities. In other words, the shape of the particulate hydrogel according to the present invention is a substantially polyhedral shape such as a substantially parallelepiped shape or a substantially rectangular parallelepiped shape whose main peripheral surface is a smooth surface. Therefore, when the particulate hydrogel is irradiated with light, the light is not scattered due to surface irregularities, so that the particles are observed to be almost transparent.

Conventionally, for example, when a hydrogel is pulverized by a kneader or a meat chopper, the hydrogel is kneaded with the pulverization. For this reason, the surface of the primary particles (particle-like hydrogel) of the obtained hydrogel has irregularities due to kneading, and the surface area increases. When such primary particles are irradiated with light, the light is scattered due to unevenness. Therefore, the conventional particulate hydrogel is observed in a cloudy state.

When the surface of the particulate hydrogel has a lot of irregularities and is cloudy, the particles are apt to be caught and the fluidity of the whole particles is reduced. In other words, the irregularities are very easily entangled with each other, so that the primary particles are easily aggregated, and the entangled irregularities are in contact with each other so as to mesh with each other. Therefore, it is very difficult to dissociate the aggregated primary particles. Further, due to the occurrence of this aggregation, drying cannot be performed well.

When a large external force is applied to the aggregates of the primary particles which are difficult to dissociate, the primary particles themselves are dissociated from each other, and the primary particles themselves are frequently pulverized by the external force. . As a result, in addition to the primary particles of a desired size, a large amount of fine powder accompanying the pulverization of the primary particles is generated. The generation of the fine powder not only lowers the performance of the water-absorbent resin but also lowers the yield in the production of the water-absorbent resin.

On the other hand, in the present invention, as described above, the hydrogel in the form of a lump or agglomerate is cut sharply as if cut with scissors, without being kneaded, by the vertical cutting machine. . Therefore, the surface of the obtained particulate hydrogel has a substantially smooth flat surface, that is, a smooth surface even with some irregularities and curved surfaces.

For this reason, the particulate hydrogel is less likely to be caught between the primary particles, and the primary particles are less likely to aggregate after drying. Further, even if the particles coagulate, they are easily dissociated only by applying a light external force. Therefore, when dissociating the primary particles, the amount of generated fine powder can be extremely reduced.

Therefore, when the particulate hydrogel according to the present invention is used, the amount of fine powder generated in the process of producing the water-absorbent resin can be reduced, and the burden of removing or collecting the fine powder is greatly reduced. can do. Further, since the entire primary particles are homogeneous, drying can be performed more favorably. As a result, the production efficiency of the water absorbent resin can be further improved.

In the present invention, fine particles of the dried particulate hydrogel having a particle size of less than 150 μm, more preferably less than 200 μm are used. 150μ particle size
The particulate hydrogel having a particle size of less than m cannot be used at least as a water absorbent resin. In addition, the particle size is 150 to 200
Although the particulate hydrogel within the range of μm can be used as the water-absorbing resin, the presence of the particulate hydrogel in this range is not preferable because the particle size distribution of the particulate hydrogel is widened. .

Therefore, in the particulate hydrogel according to the present invention, the lower limit of the particle size after drying is preferably 150 μm, more preferably 200 μm. On the other hand, the upper limit of the particle size after drying is more preferably 850 μm when used for sanitary materials such as disposable diapers and napkins. That is, the particle size of the particulate hydrogel according to the present invention after drying is 150 μm or more and 850 μm or more.
It is preferably in the range of not more than μm, and particularly preferably in the range of not less than 200 μm and not more than 850 μm.

In the present invention, it is particularly preferable to obtain a particulate hydrogel by pulverization using a vertical cutter.
At this time, the particle size of the particulate hydrogel was 0.8 m
0.5 mm wider than the range from m to 5 mm
It may be in the range of not less than 5 mm or more. In particular, in order to obtain a water-absorbent resin having a particle size within the above range after drying, the particle size of the particulate hydrogel is preferably 0.5 mm or more and 3 mm or less, more preferably 0.5 mm or more and 1 mm or less. Is within.

When a particulate hydrogel is obtained by using a meat chopper or a kneader, as described above, when the aggregates of the particulate hydrogel are crushed, the primary particles of the particulate hydrogel are themselves. Pulverized by external force to generate fine powder.
Therefore, the particle diameter of the primary particles themselves tends to be small. In contrast, when a particulate hydrogel is obtained using a vertical cutting machine, as described above, even when the aggregated particulate hydrogel is crushed, the primary particles themselves are hardly crushed and are simply dissociated. Just do it. Therefore, the particle size of the primary particles hardly changes. As a result, a water-absorbent resin having a small particle size and a sharp particle size distribution can be obtained.

Therefore, when the particle size of the particulate hydrogel after drying is in the range of 150 μm to 850 μm,
When fine powder is generated, a slightly larger range (0.8 to 5 mm) is set in anticipation of a decrease in particle size.
If the pulverization is carried out by a vertical cutting machine, it is not necessary to consider the generation of fine powder. Therefore, the particle size of the undried particulate hydrogel may be further smaller than the range of 0.8 mm or more and 5 mm or less. it can. Therefore, the average particle size of the particulate hydrogel according to the present invention may be in the range of 0.5 mm or more and 5 mm or less.

The hydrogel crushed in the present invention is a hydrogel obtained by polymerizing a water-soluble ethylenically unsaturated monomer in the presence of an internal crosslinking agent, and has a solid content of 25 to
It is 50%, preferably 30 to 45%. Since the hydrogel has a cross-linked structure, it is pulverized without kneading when pulverized by a vertical pulverizer, as shown in FIG. 5,
A substantially polyhedral particulate hydrogel 21 having a plurality of smooth surfaces 20 on the surface is obtained.

The water absorption capacity of the above hydrogel was 20 to 20.
It is within the range of 60 times, more preferably within the range of 30 to 50 times. If the water absorption ratio is less than 20 times, the water absorption ratio after drying is low, which is not preferable when used for sanitary materials such as disposable diapers. If the water absorption ratio is larger than 60 times, the hydrogel becomes soft, so that the hydrogel is kneaded at the time of pulverization, and a polyhedral hydrogel having a smooth surface may not be obtained. The water absorption capacity (in terms of solid content) of the hydrogel was determined by immersing the hydrogel in a tea bag for 24 hours in a physiological saline solution, and then centrifuging it at 1300.
Measured after draining the liquid at rpm for 3 minutes.

In the present embodiment, the angle of repose is used as an index indirectly indicating that the surface of the particulate hydrogel 21 is smooth and the particle size distribution is sharp. The angle of repose will be described. As shown in FIG. 2, the particulate hydrogel 2 obtained by pulverization is used.
1 is a length 15c on which a fluororesin impregnated film 22 is stuck.
m, spread evenly on a plate 23 having a width of 6 cm. next,
One end of the plate 23 is gradually lifted, and the particulate hydrogel 2
1 Measure the height H at which the whole begins to run off. Then, the repose angle θ is calculated from the measured height H based on the following equation (3).

Θ = sin ⁻¹ (H / 20) (3) The smaller the angle of repose is, the smaller the particulate hydrogel 2
1 will flow smoothly. Particulate hydrogel 21
Flowing smoothly means that the particulate hydrogel 2
1 shows that the particle surface has few irregularities and the frictional force between the particulate hydrogels 21 or the particulate hydrogel 21 and the plate 23 derived from the irregularities is small.

If the particle size distribution is sharp, that is, if the particle size of the particulate hydrogel is uniform, the fluidity of the whole particle is improved. If the particle size is not uniform,
For example, small particles may enter the gaps between the large particles, thereby impeding the fluidity of the whole particles. However, such a phenomenon does not occur if the size of the particles is uniform. Therefore, the smaller the angle of repose, the smoother the surface of the particulate hydrogel and the sharper the particle size distribution.

The angle of repose of the particulate hydrogel according to the present invention is preferably 38 ° or less, more preferably 36 ° or less. If the angle of repose is 38 ° or less, it can be determined that the particulate hydrogel has a substantially polyhedral shape having a smooth surface as a whole (see FIG. 5). That is, when the angle of repose is 38 ° or less, it can be determined that the surface of the particulate hydrogel is smooth and the particle size distribution is sharp.

As described above, the particulate hydrogel according to the present invention has a uniform particle size distribution of the particulate hydrogel, and has a surface with few irregularities and is a transparent particle. Is performed very uniformly. Therefore, the small particles do not overdry and the large particles do not remain undried, so that much better drying than before can be achieved. As a result, a high quality water absorbent resin can be obtained. Further, the drying time can be made shorter than before, so that the production efficiency of the water-absorbing resin can be improved.

Next, the method for producing a water-absorbent resin according to the present invention is a method using the above-mentioned particulate hydrogel, and the production process is as shown in FIG. It has at least each step of pulverization and classification.

More specifically, the particulate hydrogel according to the present invention obtained by the above-described method is first dried in the drying step of step 1 (hereinafter, step is abbreviated as S). The drying method at this time is not particularly limited, and for example, a conventional drying method using a band dryer, a stirring dryer, a fluidized bed dryer, or the like can be suitably used.

The particulate hydrogel obtained in the drying step is pulverized by the pulverizing step of S2 so as to have a size within a predetermined range. The pulverization method at this time is not limited, and a conventional pulverization method using a roll mill or the like can be suitably used.

The pulverized product obtained in the pulverization step is classified in the classification step of S3, but the classification method is not particularly limited. For example, sieving using a sieve is preferably used. And after each process of S1-S3 is completed, a water-absorbing resin is obtained.

Here, the particulate hydrogel has a uniform particle shape and a sharp particle size distribution.
In the drying step of S1, uniform drying can be performed as a whole. Therefore, no undried matter is generated and small particles are not excessively dried as in the related art.

As a result, in the pulverizing step of S2, undried particles do not adhere to the pulverizer, so that there is no inconvenience that hinders pulverization. Therefore, the production of the water absorbent resin can be made more efficient. Further, after the classification step of S3, since the undried matter and the over-dried matter are not mixed into the obtained water-absorbent resin, the water-absorbent resin can be of high quality.

Further, in the drying step of S1, since the drying can be performed quickly as described above, the production of the water-absorbing resin can be made more efficient. Further, by appropriately setting the pulverization and classification of the original particulate hydrogel, the S
The desired water-absorbing resin can be obtained only by drying in step 1. That is, since each of the steps S2 and S3 can be omitted, the production of the water-absorbing resin can be more efficient.

For example, as the conventional particulate hydrogel is dried in the drying step of S1 to lose water, the primary particles of the particulate hydrogel agglomerate and the primary particles are less likely to dissociate. Become. On the other hand, the particulate hydrogel according to the present invention does not easily aggregate as described above. As a result, it is sufficiently possible to omit the steps S2 and S3.

However, even the particulate hydrogel according to the present invention may be slightly aggregated in the drying step of S1. However, since the particulate hydrogel is easily dissociated even if agglomerated, it can be returned to primary particles only by applying a light external force without being pulverized in the pulverization step. Therefore, as shown in FIG. 4, in the method for producing a water-absorbent resin according to the present invention, a crushing step for returning the aggregated particulate hydrogel to the original primary particles is performed instead of the crushing step. Is highly preferred.

A method for producing a water-absorbing resin including the crushing step will be described. First, as shown in FIG. 4, a drying step is performed as S11 in the same manner as in the method for producing a water absorbent resin shown in FIG. Thereafter, the aggregate of the particulate hydrogel obtained in the drying step is crushed in the crushing step of S12 to dissociate into primary particles. It should be noted that applying the external force to the aggregate of the particulate hydrogel to loosen the aggregate and dissociate it to return to the primary particles is referred to as "crushing".

As the crushing method used in the crushing step, the above-described crushing method using a roll mill can be used. However, the aggregates can be easily crushed without applying a large external force,
If a large external force is applied, fine powder may be generated. Therefore, a method in which a small external force is applied is preferable.

As a method of applying a small external force, for example, a method of crushing using a single-shaft mixer equipped with a gently rotatable stirring blade can be mentioned. As a single-shaft mixer equipped with this stirring blade, a conventionally used one can be suitably used, but it is very preferable that the rotation speed of the stirring blade can be reduced to a sufficiently low value. . This is because if the rotation speed is too high, the primary particles themselves may be disintegrated to generate fine powder. However, the specific number of rotations of the rotating blades is not particularly limited because it differs depending on each device.

The crushing step may be performed simultaneously with the drying step, and may be a drying / crushing step. In this case, examples of the drying method include a method using a stirring dryer or a fluidized bed dryer. It is preferable to perform the crushing step and the drying step at the same time because the method for producing the water-absorbent resin can be further simplified.

The pulverized product obtained in the crushing step is S13
Classification in the classification process. Here, in the disintegration step of S12, the aggregate of the particulate hydrogel is easily and surely dissociated into primary particles, and the dissociated primary particles have a more uniform shape. Therefore, most of the crushed material obtained by the crushing step has a particle size within a predetermined range,
The amount of particles larger or smaller than a predetermined range (that is, fine particles) can be extremely reduced. for that reason,
In the method for producing a water-absorbent resin according to the present invention, this classification step can be omitted as appropriate.

In the classifying step of S13, when particles having a particle size not smaller than a predetermined range are obtained to some extent,
Further, a pulverizing step of pulverizing the particles may be added as S14. The classification process is performed again on the particles obtained after the pulverization process (that is, the process returns to S13). Then, S11 to S13 (or S11 to S1)
After each step up to 4), a water-absorbing resin is obtained.

In the present invention, a water-absorbent resin having a particle size according to the intended use of the water-absorbent resin can be easily obtained by drying and crushing the hydrogel. Particles or agglomerates larger than the desired particle size are pulverized. In this pulverization, the water-absorbent resin having the target particle size can be separated by classification or the like, so that the amount of the water-absorbent resin pulverized by the pulverizer can be reduced. As a result, the amount of generated fine powder can be reduced, and the addition of a pulverizer can be reduced.

Thus, the method for producing a water-absorbent resin according to the present invention uses the particulate hydrogel according to the present invention. Therefore, the production of the water-absorbent resin can be made more efficient than before, and a high-quality water-absorbent resin can be obtained.

The water-absorbing resin obtained by the production method according to the present invention as described above has excellent water-absorbing performance, and can be used, for example, in sanitary materials such as paper diapers, sanitary napkins, incontinence pads, wound protection materials, wound healing materials and the like. Materials (body fluid absorbent articles); Absorbent articles such as urine for pets; water-retaining materials for building materials and soil;
Materials for civil engineering and construction such as packing materials, gel blisters, etc .; Food products such as drip absorbing materials, freshness preserving materials, and cold insulators; Various industrial products such as oil-water separating materials, anti-condensation materials, and coagulants; Plants and soil, etc. It has been suitably used for various purposes such as agricultural and horticultural articles such as water retention materials.

[0115]

EXAMPLES The method for producing the water-absorbent resin of the present invention will be described more specifically based on the following examples and comparative examples, but the present invention is not limited to these examples and comparative examples.

In the following examples and comparative examples, the angle of repose was performed in the same manner as in the method described in the above embodiment. In addition, the water absorption capacity of the water-absorbent resin (or hydrogel),
The particle size distribution of the particulate hydrogel and the logarithmic standard deviation of the particle size distribution were measured as follows. (Water Absorption Ratio of Water Absorbent Resin) About 2.0 g of the water absorbent resin (or dried hydrogel) was accurately weighed, placed in a 5 cm square non-woven tea bag, and sealed by heat sealing. This tea bag was immersed in artificial urine at room temperature. After 1 hour, the tea bag is pulled up, and after draining the solution at 1300 rpm for 3 minutes using a centrifuge,
The weight W ₁ (g) of the tea bag was measured. Separately,
The same scanning was performed without enclosing the water absorbent resin in the tea bag, and the weight W ₀ (g) of the tea bag at that time was determined as a blank. The water absorption capacity was calculated based on the following equation.

[0117]

(Equation 1)

Table 1 shows the composition of the artificial urine and the amounts thereof.

[0119]

[Table 1]

(Measurement of Particle Size Distribution of Particulate Hydrogel and Logarithmic Standard Deviation of Particle Size Distribution) First, 30 g of a sample having a solid content of α% by weight was subjected to 1000 g of a 20% by weight aqueous NaCl solution.
And stirred for 120 minutes by rotating the stirrer chip at 300 rpm. After the completion of the stirring, the six types of sieves (9.
5mm, 2.0mm, 0.85mm, 0.6mm, 0.
3mm, 0.075mm)
Further, 6000 g of a 20% by weight aqueous solution of NaCl was charged and classified. The sample on the classified sieve was drained sufficiently and weighed.

The weight of the particulate hydrogel after the classification and drainage is denoted by w, the opening of the sieve is denoted by r, and the sample weight w
Assuming that ₁ = 30 g, the equation (1) described in the above embodiment is used.
, The particle size distribution of the particulate hydrogel was plotted on log probability paper. The particle diameter corresponding to 50% by weight of% R on the integrated sieve of the plot was defined as the average particle diameter of the particulate hydrogel. Equation (1) is shown below.

R (α) = (30 / w) ^1/3 × r (1) From the above plot,% R on the integrated sieve is 84.1%.
% (Referred to as X ₁₎ on the cumulative sieve% R = 15.9
% (Referred to as X ₂ ), and the logarithmic standard deviation σζ was determined by the equation (2) described in the above embodiment. Equation (2) is shown below.

Σζ = (１ ／) ln (X ₂ / X ₁ ) (2) [Example 1] 65% neutralized sodium acrylate and polyethylene glycol diacrylate (average number of ethylene oxide units: 8) Was prepared in the form of an aqueous monomer solution containing 0.04 mol% (based on sodium acrylate). At this time, the concentration of sodium acrylate was 35% by weight. Nitrogen was blown into the monomer aqueous solution to reduce the dissolved oxygen concentration in the aqueous solution to 0.1 ppm or less.

Then, a water-soluble azo initiator (manufactured by Wako Pure Chemical Industries, Ltd .; product number V-50) 0.02 g / mol (based on sodium acrylate monomer), L-ascorbic acid 0.002 g / mol (based on acrylic) (A sodium acrylate monomer) and 0.001 g / mol of hydrogen peroxide (based on a sodium acrylate monomer) were added in that order to carry out polymerization. The polymerization initiation temperature was 22 ° C, and the temperature reached 80 ° C after 10 minutes.

The hydrogel after polymerization was crushed to a 25 mm square with a guillotine cutter. To this crushed hydrogel, a polyethylene glycol-polypropylene glycol block copolymer having a molecular weight of about 3,000 was added by 0.5% by weight (based on solid content), and the pore diameter was 3 mm, the opening ratio was 34%, and the number of pores was 48.
Pulverization was carried out by a vertical cutting machine having a screen of 0 pieces / 100 cm ² .

By this pulverization, a particulate hydrogel (1) according to the present invention was obtained. The average particle size of the particulate hydrogel (1) was 950 μm. Further, the particle size when R = 15.9% was 400 μm, and the particle size when R = 84.1% was 1510 μm, so that σζ = 0.66. When the angle of repose of this particulate hydrogel (1) was measured twice, it was 36.2 ° and 34.8 °.
Further, the water absorption capacity of the particulate hydrogel (1) was 38 times.

When the particulate hydrogel (1) was dried at 160 ° C. for 60 minutes, no undried product was obtained.
Further, even when the particulate hydrogel (1) was pulverized, there was no adhesion of the rubbery undried substance to the pulverizer. The water absorption capacity of the water absorbent resin (1) obtained after the above-mentioned pulverization and drying is 6
It was 5 times and the soluble content was 12%.

[Example 2] In Example 1, the screen having a hole diameter of 6 mm and an aperture ratio of 51 were used instead of the screen having a hole diameter of 3 mm.
%, A particulate hydrogel (2) according to the present invention was obtained in the same manner as in Example 1 except that a screen having 180 holes / 100 cm ² was used.

The average particle size of the particulate hydrogel (2) is 1
It was 600 μm. The particle size at R = 15.9% was 800 μm, and the particle size at R = 84.1% was 2400 μm, so σζ = 0.55.
The angle of repose of this particulate hydrogel (2) was measured twice, and was 35.1 ° and 33.4 °.

When the particulate hydrogel (2) was dried at 160 ° C. for 60 minutes, no undried product was obtained.
Furthermore, even if this particulate hydrogel (2) is pulverized,
There was no adhesion of the rubbery undried substance to the pulverizer. The water absorption ratio of the water-absorbent resin (2) obtained after the above-mentioned pulverization and drying was 65 times, and the soluble matter was 12%.

[Comparative Example 1] In Example 1, the hydrogel was pulverized with a double bowl type kneader to obtain comparative particulate hydrogel (1). The average particle size of the comparative particulate hydrogel (1) was 1.8 mm. Also, R = 1
The particle size at 5.9% is 320 μm, and R = 84.
Since the particle size at 1% was 8000 μm, σζ =
It was 1.6. Further, 2% of the particles had a particle diameter of 10 mm or more. In addition, when the angle of repose of this comparative particulate hydrogel (1) was measured twice, it was 40.0 ° and 41.0 °.

The comparative particulate hydrogel (1) was mixed with 160
Drying at 60 ° C. for 60 minutes produced undried material. Further, when the comparative particulate hydrogel (1) was pulverized, the rubbery hydrogel was adhered to the inside of the pulverizer, which hindered the pulverization. Further, a comparative water-absorbent resin (1) was obtained after the pulverization and drying. The water absorption capacity of this comparative water absorbent resin (1) was 65 times, and the soluble matter was 13%.

Comparative Example 2 The hydrogel was crushed with a meat chopper (diameter 9.5 mm) in the same manner as in Example 1 to obtain a comparative particulate hydrogel (2). The average particle size of the comparative particulate hydrogel (2) is 1.8.
mm. When R = 15.9%, the particle size is 4%.
00 μm, and the particle size when R = 84.1% is 500.
Since it was 0 μm, σζ = 1.26. Further, when the angle of repose of this comparative particulate hydrogel (2) was measured twice, it was 40.5 ° and 38.7 °.

This comparative particulate hydrogel (2) was mixed with 160
Drying at 60 ° C. for 60 minutes produced undried material. Further, when the comparative particulate hydrogel (2) was pulverized, the rubbery hydrogel was adhered to the inside of the pulverizer, which hindered the pulverization. After the above-mentioned pulverization and drying, a comparative water-absorbent resin (2) was obtained. The water absorption capacity of this comparative water absorbent resin (2) was 65 times, and the soluble matter was 15%.

Further, in the following Example 3 and Comparative Examples 3 and 4, the uniform number n obtained by the following Rosin-Rammlar plot was used as an index indicating the particle size distribution of the obtained water-absorbent resin.

The crushed water-absorbent resin was classified with a sieve, and the integrated% R on the sieve and the particle diameter Dp were plotted on a graph according to the following equation (3). The slope of this plot was determined by the least-squares method, and the uniform number n was calculated.

Loglog (100 / R) = nlog Dp-C (Example 3) 0.1% of 70% neutralized sodium acrylate and polyethylene glycol diacrylate (average number of ethylene oxide units: 8) An aqueous monomer solution containing mol% (relative to sodium acrylate) was prepared. At this time, the concentration of sodium acrylate was 39% by weight. Nitrogen was blown into the monomer aqueous solution to reduce the dissolved oxygen concentration in the aqueous solution to 0.5 ppm or less.

Then, 0.12 g / mol of sodium persulfate (based on the monomer of sodium acrylate) and 0.0005 g / mol of L-ascorbic acid (based on the monomer of sodium acrylate) were sequentially added to carry out polymerization. The polymerization initiation temperature was 18 ° C., and after 12 minutes, the temperature reached 90 ° C.

The hydrogel after polymerization was crushed into a 30 mm square by a guillotine cutter. To the crushed hydrogel, 1% by weight (based on solid content) of a polyethylene glycol-polypropylene glycol block copolymer having a molecular weight of about 3,000 was added, and pulverized by a vertical cutter in the same manner as in Example 1. Then, the obtained pulverized product was further pulverized by a vertical cutter having a screen with a hole diameter of 1.5 mm, an opening ratio of 23%, and a number of holes of 1300/100 cm ² .

By this pulverization, a particulate hydrogel (3) according to the present invention was obtained. The average particle size of the particulate hydrogel (3) was 710 μm. In addition, σ５ = 0.45. Further, the average particle size in terms of solid content was 520 μm. The water absorption capacity of the particulate hydrogel (3) was 25 times. This particulate hydrogel (3) is heated at 170 ° C. for 4 hours.
When dried with a hot-air dryer for 0 minutes, no undried product was obtained. Further, the aggregate obtained after drying was stirred in a Loedige mixer, and the aggregate was broken into primary particles.

[0141] The obtained crushed product was screened with a sieve opening of 85.
Classification was carried out by sieves of 0 μm and 212 μm. At this time, the upper portion of the 212 μm sieve (850/212 μm) passed through the 850 μm sieve was obtained as the water absorbent resin (3) according to the present invention. This 850/212 μm
The ratio of the upper portion of the sieve was 79% by weight, and the ratio of the crushed material (ie, fine powder) passed through the 212 μm sieve was 0.4%.
% By weight. The average particle size was 700 μm. The uniform number n of the Rosin-Rammlar plot showing the sharpness of the particle size distribution was 4.4. The water absorption ratio of the water absorbent resin (3) was 42 times, and the soluble matter was 4%.

[Comparative Example 3] To the crushed horny hydrogel obtained in Example 3 was added 1% by weight (based on solid content) of a polyethylene glycol-polypropylene glycol block copolymer, and the pore size was 1. It was pulverized with a meat chopper having a die having a diameter of 2 mm and an opening ratio of 35% to obtain a comparative particulate hydrogel (3). The comparative particulate hydrogel (3) was dried with a hot air drier at 170 ° C. for 40 minutes. The dried aggregate was stirred in a Loedige mixer in the same manner as in Example 3 to break up the aggregate.

The obtained crushed product was classified in the same manner as in Example 3, and the fraction on the 850/212 μm sieve was obtained as a comparative water absorbent resin (3). The ratio of the fraction on the 850/212 μm sieve was 59% by weight, and the percentage of the crushed material (ie, fine powder) passed by 212 μm was 32% by weight. The average particle size was 1300 μm. The uniform number n of the Rosin-Rammlar plot showing the sharpness of the particle size distribution was 2.0. The water absorption capacity of the comparative water absorbent resin (3) is 42 times,
The soluble matter was 5%.

[Comparative Example 4] 1% of a polyethylene glycol-polypropylene glycol block copolymer was added to the crushed square hydrogel obtained in Example 3, and the mixture was stirred for 20 minutes in a kneader and pulverized. Thus, a comparative particulate hydrogel (4) was obtained. Thereafter, a crushed product was obtained in the same manner as in Example 3.

The obtained crushed product was classified in the same manner as in Example 3 to obtain a portion on a 850/212 μm sieve as a comparative water absorbent resin (4). The ratio of the fraction on the 850/212 μm sieve was 38% by weight, and the ratio of the crushed product (that is, fine powder) passed 212 μm was 1% by weight. The average particle size was 1300 μm. The uniform number n of the Rosin-Rammlar plot showing the sharpness of the particle size distribution was 2.1. The water absorption capacity of the comparative water absorbent resin (4) is 41 times,
The soluble matter was 5%.

From the above Examples and Comparative Examples, the particulate hydrogels (1) and (2) according to the present invention have a sharper particle size distribution than the comparative particulate hydrogels (1) and (2). It can be seen that the particles have a uniform particle size.

In addition, a comparison was made between the particulate hydrogel (3) according to the present invention, the comparative particulate hydrogel obtained with a meat chopper (3), and the comparative particulate hydrogel (4) obtained with a kneader. The particulate hydrogel (3) according to the present invention has a sharp average particle size and a large even number,
It can be seen that the particles have a more uniform average particle size.

Further, comparing the shapes of the particulate hydrogel, as shown in FIG. 6 (a), the particulate hydrogel (3) according to the present invention is transparent and its main peripheral surface is smooth. 6 (see FIG. 5).
As shown in (b) and (c), each of the other comparative particulate hydrogels (3) and (4) has its surface kneaded to form irregularities,
It turns out that it became cloudy. FIG. 6B shows the comparative particulate hydrogel (4), and FIG. 6C shows the comparative particulate hydrogel (3).

Further, when comparing the shapes, the particulate hydrogel (3) according to the present invention has a substantially rectangular parallelepiped shape while the shape of each particle is substantially unified, while the other comparative particulate hydrous gel has the same shape. It can be seen that in each of the gels (3) and (4), the shape of each particle is irregular. FIG.
(D) is a ruler scale of the same scale as in FIGS. 6 (a) to (c), and one scale indicates 1 mm.

Further, in the water absorbent resin (3) obtained by the production method according to the present invention, almost no fine powder was generated, but in the production process of the comparative water absorbent resin (3) obtained by the meat chopper, Significant fines were generated. In the production process of the comparative water absorbent resin (4) obtained by the kneader, the amount of generated fine powder was small, but the particle size distribution was not as sharp as that of the water absorbent resin (3), and the average particle size was uniform. Did not become.

As described above, the particulate hydrogel polymer according to the present invention has a sharp particle size distribution, and is formed into transparent particles having a square shape and no irregularities on the surface of the particles. It is. In addition, when a water-absorbent resin is produced using this particulate hydrogel polymer, drying can be performed favorably, and undried matter is not generated. Various inconveniences that occur can be avoided. As a result, a high-quality water-absorbent resin can be efficiently produced.

[0152]

As described above, the particulate hydrogel polymer according to the first aspect of the present invention is obtained by polymerizing a water-soluble ethylenically unsaturated monomer and then pulverizing it at least. In the polymer, the average particle size is in the range of 0.8 to 5 mm, and the particle size distribution is 1.5 or less in logarithmic standard deviation σζ.

As described above, the particulate hydrogel polymer according to the second aspect of the present invention has a solid content in the range of 20 to 50% in addition to the constitution according to the first aspect. Configuration.

As described above, the particulate hydrogel polymer according to the third aspect of the present invention has a repose angle of 38 ° or less in addition to the configuration according to the first or second aspect. Configuration.

[0155] Therefore, each of the above constitutions has an effect that extremely excellent drying is possible as compared with the conventional particulate hydrogel polymer.

In the method for producing a water-absorbent resin according to claim 4 of the present invention, as described above, the average particle size is in the range of 0.8 to 5 mm, and the particle size distribution is logarithmic standard deviation σζ. Is a method of drying a pulverized particulate hydrogel polymer having a particle size of 1.5 or less.

Therefore, in the above-mentioned method, the drying step is performed efficiently, and the occurrence of overdrying or undrying is suppressed. For this reason, it is possible to avoid inconvenience in the process after drying caused by undried materials and the like, and to obtain an effect of obtaining a high-quality water-absorbing resin.

As described above, the particulate hydrogel polymer according to the fifth aspect of the present invention is obtained by polymerizing a water-soluble ethylenically unsaturated monomer and then pulverizing it at least. In the union, the average particle size is in the range of 0.5 to 5 mm, and the particle size distribution is 1.5 or less in logarithmic standard deviation σζ.

As described above, the particulate hydrogel polymer according to the sixth aspect of the present invention has a substantially rectangular parallelepiped shape whose main peripheral surface is a smooth surface, in addition to the configuration according to the fifth aspect. This is the configuration.

Therefore, in the above configuration, uniform drying is possible, and the generation of fine powder of the hydrogel polymer which cannot be used as the water-absorbing resin is suppressed. It is possible to obtain a high yield, reduce the burden of removing and collecting fine powder, and improve the production efficiency of the water absorbent resin.

[Brief description of the drawings]

FIG. 1A is a cross-sectional view showing the internal structure of a pulverizing unit in a vertical cutting machine used when producing a particulate hydrogel polymer according to one embodiment of the present invention;
(B) is sectional drawing which shows another example of the internal structure of the grinding | pulverization part in the vertical cutting machine shown to Fig.1 (a).

FIG. 2 is an explanatory diagram showing a measurement system for measuring the angle of repose of the particulate hydrogel polymer according to the present invention.

FIG. 3 is a process chart showing an example of a method for producing a water absorbent resin according to one embodiment of the present invention.

4 is a process chart showing another example of the method for producing the water absorbent resin shown in FIG.

FIG. 5 is a schematic view showing a shape of a particulate hydrogel according to the present invention.

FIGS. 6 (a) to 6 (c) are photographs substituted for drawings showing the states of the particulate hydrogel according to one embodiment of the present invention and a conventional particulate hydrogel observed by an optical microscope; (D) is a drawing substitute photograph showing a ruler scale observed by an optical microscope at the same scale as (a) to (c).

[Explanation of symbols]

 2 crushing part 12 rotating blade 13 fixed blade 14 screen 21 particulate hydrogel

 ────────────────────────────────────────────────── ─── Continued on the front page (72) The inventor Kazuki Kimura 992, Nishioki, Okihama-shi, Aboshi-ku, Himeji-shi, Hyogo

Claims (6)

[Claims] 1. A particulate hydrogel polymer obtained by polymerizing a water-soluble ethylenically unsaturated monomer and then pulverizing the polymer at least, having an average particle size in the range of 0.8 to 5 mm, and A particulate hydrogel polymer having a particle size distribution of 1.5 or less in logarithmic standard deviation σζ. 2. The particulate hydrogel polymer according to claim 1, wherein the solid content is in the range of 20 to 50%. 3. The particulate hydrogel polymer according to claim 1, wherein the angle of repose is 38 ° or less. 4. A pulverized particulate hydrogel polymer having an average particle size in the range of 0.8 to 5 mm and a particle size distribution of 1.5 or less in logarithmic standard deviation σζ. Drying the water-absorbent resin. 5. A particulate hydrogel polymer obtained by polymerizing a water-soluble ethylenically unsaturated monomer and then pulverizing the polymer at least, having an average particle size in a range of 0.5 to 5 mm, and A particulate hydrogel polymer having a particle size distribution of 1.5 or less in logarithmic standard deviation σζ. 6. The particulate hydrogel polymer according to claim 5, wherein the main peripheral surface has a polyhedral shape comprising a smooth surface.