JPH07224204A - Production of water-absorbing resin - Google Patents

Abstract

PURPOSE:To produce easily and inexpensively a water-absorbing resin modified by surface treatment and having high water absorption capacity even under elevated pressure while reducing the loss due to the reaction for surface treatment. CONSTITUTION:Heated water-absorbing carboxylic resin powder having such a particle size that at least 90wt.% of the particles can pass a sieve mesh with an opening of 850mum but can not pass a sieve mesh with an opening of 250mum is mixed and reacted with a cross-linking agent, whereupon the formation of agglomerates of resin particles that interfere with the reaction during the surface treatment can be reduced, and the waterabsorbing resin having high water absorbing capacity even under elevated pressure and high water absorption rate can be produced.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a water absorbent resin modified by subjecting a water absorbent resin to a surface treatment. More specifically, the present invention reduces reaction loss during surface treatment, and can easily and inexpensively produce a water-absorbent resin having a high water-absorbing ability even under pressure,
The resin with modified properties obtained by the present invention is widely used as a sanitary product, a civil engineering chemical, and an agricultural chemical.

[0002]

2. Description of the Related Art In recent years, water absorbent resins have been used for sanitary napkins,
It is used as a sanitary agent such as paper diapers and breast milk pads, an agricultural agent such as a water retention agent for agricultural and horticultural purposes, a sludge solidifying agent, and a civil engineering agent for drilling mud. Specific examples of such a water absorbent resin include starch-
Hydrolyzate of acrylonitrile graft copolymer, neutralized product of starch-acrylic acid graft copolymer, polyvinyl alcohol crosslinked polymer, hydrolyzate of vinyl acetate-acrylic acid ester copolymer, or crosslinked product thereof, poly Acrylate-based crosslinked products and maleic anhydride-based crosslinked products are known.

Among the applications of the water-absorbent resin, the one that is widely used at present is the sanitary paper diapers and the like.
It is a product, and the performance that is particularly expected for this resin in this application includes a water absorption capacity that absorbs body fluid even under pressure, a high water absorption capacity that can absorb a large amount of the body fluid, and a water retention capacity that does not reverse the absorbed body fluid. Etc. However, the water absorption capacity and the water absorption capacity under pressure have a contradictory relationship, that is, if the water absorption capacity under pressure is improved, the water absorption capacity decreases, and conversely, if the water absorption capacity is increased, the water absorption capacity under pressure decreases. There is a relationship. Further, the water retention capacity is such that the performance is not sufficiently exhibited unless both physical properties of the water absorption capacity and the water absorption capacity under pressure are high.

As a method for maintaining the water absorption capacity and improving the water absorption capacity under pressure, there is a method in which only the vicinity of the surface of the water absorbent resin having a high water absorption capacity is uniformly crosslinked, and a difference in the crosslinking gradient between the surface and the inside is provided. Are known. For example, a method of dispersing a water-absorbent resin in a hydrophilic organic solvent or a mixed solvent of water and a hydrophilic organic solvent and crosslinking with a crosslinking agent (JP-A-57-44).
627, JP-A-58-42602), a method in which a water-absorbent resin powder is directly mixed with a cross-linking agent or an aqueous solution of the cross-linking agent, and heat-treated as necessary to cross-link the surface (JP-A-58-18).
0233, JP-A-59-62665, JP-A-61-46.
241) and the like are known.

However, in the above method using a mixed solvent of a hydrophilic organic solvent and water, there is a high possibility that the cross-linking agent will be dissolved in the solvent and the surface of the water-absorbent resin can be uniformly cross-linked. Due to heating in the process and the drying process for removing the organic solvent, there is a high risk of causing an explosion and a fire, and it can be said that it is a preferable method for industrial implementation due to safety problems such as environmental hygiene due to waste gas. There is no such thing. In addition, there is a problem from the economical point of view that an expensive organic solvent is used. Further, directly mixing the cross-linking agent to the water-absorbent resin, the latter method can be industrially implemented at low cost, but it is difficult to uniformly permeate the water-absorbent resin only with the cross-linking agent. However, since there are many viscous liquids in the effective crosslinking agent and it is difficult to mix them uniformly, there is a problem that the vicinity of the resin surface cannot be sufficiently crosslinked. Further, in the method of spraying on the resin surface as an aqueous solution of the crosslinking agent, the possibility that the crosslinking agent permeates the entire surface of the water-absorbent resin together with water, and the possibility of sufficiently crosslinking the resin surface increases, while swelling due to water absorption swells. Agglomeration of the resin particles caused by the agglomeration occurs, and since this agglomerate hinders uniform mixing, it is difficult to uniformly cross-link all the resin particle surfaces, which is a method having problems. Is. In addition, the water-absorbent resin of the agglomerates generated during this crosslinking reaction causes the concentration gradient of the crosslinking agent on the particle surface because the aqueous solution of the crosslinking agent is taken in between the resins, and the extremely low water absorption capacity due to crosslinking is obtained. Contrary to the part (1), the cross-linking is insufficient and a part having a low water absorption capacity under pressure is likely to be mixed, and it is difficult to obtain a product having sufficient water absorption capacity. Furthermore, these agglomerates almost always have a particle size of more than 1000 μm, and it is difficult to say that such particles have a sufficient water absorption rate, and such agglomerates remain in the product. Doing so is not preferable in terms of water absorption capacity and water absorption speed. In order to solve this problem, these agglomerates are classified and removed, or the classified and removed ones are re-crushed and returned to the product, but those operations are economical and workable. This is a big problem in terms of points.

On the other hand, a method in which an aqueous solution of a cross-linking agent is mixed with a water-absorbent resin powder in the presence of an inert inorganic powder or sucrose fatty acid ester to carry out a reaction (JP-A-60-16395).
6, JP-A-60-255814, JP-A-3-2820
Although 3) is known, this method certainly suppresses agglomeration between resin particles due to the effect of the inorganic powder and the sucrose fatty acid ester, and it is highly possible that the aqueous solution of the crosslinking agent is uniformly mixed. In the case of, if the amount of the inorganic powder required to suppress the agglomeration between the resin particles is present before the reaction, the crosslinking agent aqueous solution is also absorbed in the inorganic powder to inhibit the crosslinking reaction, and the water absorption with sufficient performance is obtained. It is difficult to obtain a water-soluble resin, and if the required amount of inorganic powder is used to suppress the agglomeration of resin particles, dust is likely to be generated from the water-absorbent resin obtained, which causes environmental problems. Occurs.
In the latter case, expensive sucrose fatty acid ester must be used, which is not suitable for industrial practice.

Further, the water absorbent resin is continuously dispersed in the air without using the inorganic powder, and the cross-linking agent aqueous solution is 500 μm.
A method of forming droplets of m or less and mixing them (Japanese Patent Laid-Open No. 3-8400
4) is known, the contact force between the cross-linking agent and the resin is insufficient due to the wind force generated when the water-absorbent resin is continuously dispersed in the air when the droplet has a fine particle size of less than 200 μm. In particular, when it is carried out on an industrial scale, a large amount of gas and power are required to disperse the resin powder, but in such a state fine droplets can be absorbed by the water-absorbent resin. It is almost impossible to make uniform contact. Further, when the heating is carried out under heating, the fine droplets evaporate the water before reaching the resin surface, which makes it difficult to perform sufficient crosslinking. Further, in the case where the particle diameter of the droplet is in the range of 200 to 500 μm, agglomeration occurs between the resin particles depending on the shape of the water absorbent resin and the state at the time of adding the aqueous solution of the cross-linking agent, so that the object is sufficiently achieved. Difficult to do.

[0008]

As described above, various methods of cross-linking the vicinity of the surface of the water-absorbent resin to improve the contradictory properties in a well-balanced manner have been tried, but all have the above-mentioned problems. Therefore, it is a difficult method to obtain a water-absorbent resin exhibiting a sufficient improvement effect.

An object of the present invention is to improve the above problems and provide an effective method for obtaining a water-absorbent resin having a high water-absorption capacity even under pressure while maintaining a high water-absorption capacity. . Further, the present invention reduces the agglomerates of particles that were by-produced during the surface treatment of the water-absorbent resin and can omit the treatment step of the agglomerates, which is industrially economical and has improved properties. It is an object of the present invention to provide a method for producing a quality water absorbent resin. A further object of the present invention is that it can be effectively carried out even in the case where a hydrophilic organic solvent or a flow aid fine particle that causes dust is not used in the surface treatment step, has excellent industrial safety, and is environmentally friendly. Another object of the present invention is to provide a method for producing a modified water-absorbent resin that does not have any problems.

[0010]

In order to solve the above-mentioned problems, the inventors of the present invention have conducted extensive studies and found that the agglomeration between resin particles during the surface treatment reaction of the water-absorbent resin powder has a powder temperature near room temperature, that is, 20. Particles around -30 ° C with a particle size of 250
It was found that particles easily pass through a sieve net of μm, and the particle size is adjusted so that 10 wt% or more of particles passing through the sieve of 250 μm mesh do not exist in the water absorbent resin powder. The present invention has been completed by finding that the above-mentioned problems can be solved and a desired water-absorbent resin can be obtained by reacting the resin with a surface cross-linking agent at a high temperature.

That is, according to the present invention, 90% by weight of particles having a carboxyl group in the molecular structure and passing through a sieve mesh having an opening of 850 μm but not passing through a sieve mesh having an opening of 250 μm is heated water absorption. The present invention relates to a method for producing a modified water absorbent resin, which comprises mixing a reactive resin powder and a cross-linking agent and reacting them.

The present invention will be described in more detail below. The water-absorbent resin applied to the present invention has a carboxyl group in its molecular structure, and is, for example, a hydrolyzate of starch-acrylonitrile graft copolymer, a neutralized product of starch-acrylic acid graft copolymer, acrylonitrile. Hydrolyzate of copolymer or acrylamide copolymer,
Examples thereof include hydrolysates of vinyl acetate-acrylic acid ester copolymers, crosslinked products thereof, polyacrylic acid salt-based crosslinked products, and maleic anhydride-based copolymer crosslinked products.

Among such water-absorbent resins, preferred for the present invention are unsaturated carboxylic acid or its salt monomer alone or in combination of two or more kinds or other unsaturated monomers.
(Co) is a polymer obtained by polymerizing, unsaturated carboxylic acid salt-based monomer, acrylic acid, methacrylic acid, itaconic acid, maleic acid or its metal salts such as sodium, potassium. To be Other unsaturated monomers include 2-acrylamido-2-methylpropanesulfonic acid; (meth) acrylic acid esters such as (meth) acrylamide, acrylonitrile, methyl (meth) acrylate; vinyl acetate; diethylaminoethyl
Alkylaminoalkyl (meth) such as (meth) acrylate
Examples thereof include acrylates and quaternary ammonium salts obtained by quaternizing them with an alkyl halide such as methyl chloride, or tertiary amine salts treated with hydrochloric acid, sulfuric acid, etc. It is more preferable that the saturated carboxylic acid salt-based monomers are (co) polymerized,
Particularly preferably, the ratio of acrylic acid and acrylate is 0.
-80: 100 to 20 mol% of an acrylate monomer. Of course, polyacrylic acid obtained by polymerizing acrylic acid may be partially neutralized so that the above molar ratio is obtained.

Further, as the water-absorbent resin applied to the present invention, a polymer having no cross-linking structure can be effectively used, but when polymerizing the above-mentioned monomer, two or more unsaturated groups or reactive functional groups are used. It is more preferable that a small amount of a crosslinking agent having a group is reacted to form a crosslinked body having a crosslinked structure. Examples of the cross-linking agent used during this polymerization include N, N'-
Methylene bis (meth) acrylamide, N-methylol (meth) acrylamide, (poly) ethylene glycol di (meth) acrylate, (poly) propylene glycol di (meth) acrylate, glycerin tri (meth) acrylate, glycerin di (meth) acrylate, (Meth) acrylic acid polyvalent metal salt rate, trimethylolpropane tri (meth) acrylate, triallylamine, triallyl phosphate, glycidyl (meth) acrylate, (poly) ethylene glycol diglycidyl ether, glycerin tri
(Di) glycidyl ether etc. can be mentioned. Moreover, you may use these crosslinking agents in mixture of 2 or more types.
The amount of these cross-linking agents used is generally 0.001 to 0.5% by weight, preferably 0.01.
It is about 0.3% by weight.

The polymerization initiator used in the polymerization includes water-soluble radical initiators generally used, such as peroxides such as sodium persulfate and ammonium persulfate, hydrogen peroxide, t-butyl hydroperoxide and the like. Examples thereof include azo compounds such as hydroperoxide and 2,2′-azobis-2-amidinopropane hydrochloride. These polymerization initiators can be used as a mixture of two or more kinds, and further, redox initiation using a sulfite such as sodium sulfite, L-ascorbic acid, erythorbic acid and a reducing agent for the salt in combination. Agent systems can also be used. The amount of the polymerization initiator added is generally 0.005 to the monomer.
It is 0.5% by weight.

The water-absorbent resin powder used in the present invention has a particle size distribution containing 90% by weight or more of particles which pass through a sieve mesh having a particle size of 850 μm but do not pass through a sieve mesh having a mesh size of 250 μm. I have. 10% by weight of particles having a particle size that passes through a sieve mesh of 250 μm
When present in a larger amount, it promotes agglomeration between resin particles during the surface treatment reaction, which hinders cross-linking in the vicinity of the resin surface or cross-links in a non-uniform state, thus exhibiting no sufficient effect. By adjusting the particle size of the water-absorbent resin powder, which is a characteristic of the above, the characteristic that the surface treatment reaction can be carried out uniformly without using an aggregation inhibitor such as an inorganic powder is impaired. On the other hand, if more than 10% by weight of particles having a particle size that does not pass through the sieve mesh with an opening of 850 μm are present, the water absorption rate of the resulting water-absorbent resin will be slow, and the water absorption capacity and the water absorption capacity under pressure will not be a problem. However, a preferable product for use as a sanitary article cannot be obtained.

The particle size used in the present invention is 850 mesh.
A water-absorbent resin powder having a particle size distribution containing 90% by weight or more of particles that pass through a sieve mesh of μm but not through a sieve mesh of 250 μm is aqueous solution polymerization, reverse phase suspension polymerization,
Any of those prepared by various polymerization methods such as precipitation polymerization and bulk polymerization may be used, and the particle shape of the water-absorbent resin obtained is, for example, a bead shape obtained by reverse phase suspension polymerization,
There is no particular limitation such as flakes obtained by drum-drying a highly water-containing water-absorbent gel, and indefinite shapes obtained by pulverizing massive water-absorbent resin, but aqueous solution polymerization produces particles having a particle size of 250 μm or more. It is a preferable method as a method for producing the water-absorbent resin applied to the present invention, since an indefinite shape having good workability and economy is prepared.

The concentration of the monomer in the aqueous solution when the water-absorbent resin is produced by the aqueous solution polymerization can be arbitrarily set up to the saturated concentration of the monomer, but is generally 20% by weight or more, preferably 25% by weight or more. , And more preferably 30% by weight or more. A higher monomer concentration is economically advantageous because the hydrogel (crosslinked polymer in a water-containing state) after polymerization can be easily chopped and dehydrated. Polymerization at a monomer concentration of 35% by weight or more at atmospheric pressure is apt to cause sudden polymerization, which is dangerous, and the resulting hydrogel also self-destructs due to vapor pressure. The reason is unknown, but the obtained water-absorbent resin Therefore, when the polymerization is carried out at a monomer concentration of 35% by weight or more, it is preferable to apply a pressure capable of preventing boiling of water in the monomer in a pressure-resistant container.

The hydrogel of the water-absorbent resin obtained by the aqueous solution polymerization is shredded and then dried by an ordinary method to form a lumpy crushed powder having a major axis of 5 mm or more. As a shredding method, a device capable of cutting and extruding a rubber-like elastic body can be used, and examples thereof include a cutter type shredder, a chopper type shredder, and a kneader type shredder. As a drying method, an ordinary dryer or a heating furnace can be used, and for example, a hot air dryer, a fluidized bed dryer, a gas stream dryer, an infrared dryer, a dielectric heating dryer or the like is used.

The dried lumpy water-absorbent resin powder is further pulverized, and if necessary, classified to have a particle size of 850 μm.
The water-absorbent resin powder has a particle size distribution containing 90% by weight or more of particles that pass through the sieve net of No. 1 but do not pass through the sieve net of 250 μm. As the crushing method, a device for crushing coarsely crushed particles such as ordinary ores can be used, and for example, a direct pressure crusher such as a jaw crusher or a cone crusher, a disk crusher such as a rotary crusher or an attrition mill. Examples thereof include impact crushers such as hammer mills and pulverizers, roller type crushers such as ring roller mills, ring roll mills and ball roller mills, and cylinder type crushers such as ball mills and rod mills. Of these, a direct pressure type crusher and a roller type crusher are preferable because they are less likely to generate fine powder having a particle size of 250 μm or less, have good workability, and are easy to operate continuously. Further, it is more preferable to use two or more of these pulverizers in combination without being crushed, because the pulverizers can be pulverized with almost no generation of fine powder having a particle diameter of 250 μm or less, and therefore from the viewpoint of economy and workability.

In the present invention, the cross-linking agent to be reacted with the water absorbent resin powder (hereinafter referred to as a surface cross-linking agent in distinction from the cross-linking agent at the time of polymerization) is preferably hydrophilic, and more preferably a water-soluble compound. There is no particular limitation as long as it is a water-soluble compound, and examples thereof include (poly) ethylene glycol diglycidyl ether, (poly) glycerol polyglycidyl ether, diglycerol polyglycidyl ether, and (poly) propylene glycol diglycidyl ether. , Polyhydric glycidyl ethers such as pentaerythritol polyglycidyl ether; polyhydric alcohols such as (poly) ethylene glycol, diethylene glycol, (poly) glycerin, diethanolamine, polyoxypropylene, pentaerythritol, sorbitol; epichlorohydrin, α-meth Haloepoxy compounds such as Rukuroruhidorin ethylenediamine, diethylenetriamine, polyethyleneimine, polyamines such as triethylenetetramine; aluminum chloride, magnesium chloride,
Examples thereof include polyvalent metal salts such as aluminum sulfate and magnesium sulfate; polyvalent isocyanates such as 2,4-toluylene diisocyanate and hexamethylene diisocyanate; and polyvalent aldehydes such as glutaraldehyde and glyoxal. Among them, especially preferred is
They are polyhydric glycidyl ethers and polyhydric alcohols.

The amount of these surface-crosslinking agents used varies depending on the type, but is usually 0.01 to 2 with respect to the water-absorbent resin.
0% by weight is suitable, preferably 0.05 to 10% by weight. If this amount is less than 0.01% by weight, the effect of the present invention cannot be sufficiently exhibited, and if it is used in excess of 20% by weight, the water absorption capacity may be significantly reduced.

Regarding the method for mixing the surface-crosslinking agent and the water-absorbent resin used in the present invention, the surface-crosslinking agent and the resin powder can be mixed in a uniform ratio regardless of where they are sampled in the reaction system. Then, any method can be adopted. For example, (A) a method of simultaneously dispersing the surface-crosslinking agent and the water-absorbent resin in an inert hydrophilic organic solvent, (B) quantitatively flowing the surface-crosslinking agent into a liquid stream in which the surface-crosslinking agent is quantitatively sprayed. Method of contacting the water-absorbent resin powder in parallel or countercurrent state (C) Method of contacting a certain amount of the water-absorbent resin powder flowing with a certain amount of the surface cross-linking agent (D) On a belt Examples include a method of showering a certain amount of the surface-crosslinking agent on a certain amount of the water-absorbent resin powder that is laid and vibrated. However, since the present invention is characterized in that the surface treatment can be carried out without using an expensive organic solvent having a risk of ignition and explosion, the surface cross-linking agent and the water-absorbing agent are mixed in the inert hydrophilic organic solvent (A). It is preferable to avoid the method of simultaneously dispersing the organic resin, and it is effective and preferable to carry out the method (B), (C), (D) or the like without using an organic solvent.

In the methods (B), (C), (D), etc., the surface cross-linking agent is usually added in order to uniformly mix the surface cross-linking agent and the water absorbent resin or carry out the surface cross-linking reaction. It is added to the water-absorbent resin powder in a droplet state. In order to carry out the mixing and the surface crosslinking reaction more effectively, the surface crosslinking agent is usually used as a dilute solution. The solvent used for diluting can be used without limitation as long as it dissolves the surface cross-linking agent and does not affect the performance of the water absorbent resin. Examples of the solvent include water, lower alcohols such as methyl alcohol and ethyl alcohol; ketones such as acetone and methyl ethyl ketone; ethers such as dioxane and tetrahydrofuran. These may be used alone or as a mixture of two or more, but in this case as well, considering the economical efficiency and safety, water alone should be used rather than using an expensive organic solvent that easily catches fire or explodes. It is preferable to use.

The amount of water used varies depending on the amount of the surface cross-linking agent used.
-30% by weight is suitable, preferably 5-30% by weight
Is. When this amount is less than 1% by weight, the effect of dilution does not appear, and when it is used in excess of 30% by weight, even if the particle diameter of the water-absorbent resin powder is adjusted, the amount of resin particles between the resin particles during the surface treatment reaction is increased. Aggregation proceeds and the effect of the invention is not exhibited.

In this case, the droplets of the surface-crosslinking agent aqueous solution preferably have an average diameter in the range of 200 to 600 μm, more preferably 300 to 500 μm.
It is to be in the range of. The average diameter of this droplet is 200μ
When it is less than m, the wind force generated during dispersion and mixing of the water-absorbent resin powder causes the water-absorbent resin powder to fly to the outside of the mixing device wall or the system, or when mixed with the water-absorbent resin powder in the heated reaction system, The solvent water may evaporate before reaching the water-absorbent resin powder and hinder surface cross-linking, which is not preferable.
On the other hand, if the average diameter of the liquid droplets is 600 μm or more, it is not preferable because it may promote aggregation between resin particles or inhibit uniform cross-linking of the resin surface. Average diameter 200-600μ
There are no particular restrictions on the method of forming droplets in the range of m as long as the liquid can be atomized, but in general, a spray type or shower ring type is preferable.

In the present invention, the surface cross-linking agent is mixed with the water-absorbent resin powder in a heated state. A preferred method is to mix the surface cross-linking agent as an aqueous solution with the water-absorbent resin powder in a heated state in a droplet state. The temperature of the water-absorbent resin powder in this heated state is preferably 50 ° C. or higher at the temperature of the powder itself, and more preferably 80 to 150 ° C. When the temperature of the water-absorbent resin powder is lower than 50 ° C., when the surface-crosslinking agent or the surface-crosslinking agent aqueous solution is mixed with the water-absorbent resin powder in the form of droplets, the water-absorbent resin particles are promoted to agglomerate to form a smooth surface. It may interfere with the crosslinking reaction.

The water-absorbent resin obtained in the present invention is easy to handle as a powder as it is, but in order to adjust the powder fluidity, fine particles acting as a flow aid are added to the surface treatment in the present invention. Mixing afterwards is also appropriately performed. The fine particles to be used are not particularly limited as long as they are substances that absorb moisture after addition and are not sticky, for example, polymethylmethacrylate, polyvinyl chloride, polystyrene, polyethylene, ABS resin, polycarbonate, polypropylene, and other organic compound-based substances. Examples thereof include fine particles, or inorganic fine particles such as silicon dioxide (silica), alumina, titanium oxide, magnesium oxide, aluminum silicate, and magnesium silicate. Furthermore, not only the powder fluidity of the water-absorbent resin, but also crystalline fine particles having a layered structure such as hydrotalcite that suppresses the elution of residual monomers in the resin can be mentioned.

The particle size of these fine particles is preferably 100 μm or less, and more preferably 50 μm or less. Further, the addition amount of these fine particles, the particle size of the fine particles,
Although it varies depending on the specific surface area, it is usually 0.01 to 10% by weight, preferably 0.1 to 5% by weight based on the obtained water absorbent resin.
It is in the range of% by weight. If the fine particles used are within the range, without decreasing the water absorption capacity and the water absorption capacity under pressure of the water absorbent resin obtained in the present invention, depending on the powder fluidity and the added fine particles, the water absorbent resin It is possible to obtain a water-absorbent resin having excellent safety that suppresses elution of residual monomers therein. If this amount exceeds 10% by weight, not only the water absorption capacity under pressure and the water absorption capacity will decrease, but also these fine particles will scatter as dust during handling of the powder, which is not preferable for environmental hygiene. .

[0030]

[Function] Particles at a temperature near room temperature are likely to aggregate, why heated water-absorbent resin particles are difficult to aggregate, and why particles passing through a sieving net having a particle size of 250 μm are likely to aggregate. However, according to the present invention in which the water-absorbent resin particles having a specific heated particle diameter are used, the water-absorbent resin can be easily modified, that is, the characteristics can be improved.

[0031]

The present invention will be described in detail below with reference to examples, but the scope of the present invention is not limited to these examples. In the following examples, weight% will be referred to as "%" unless otherwise specified. Example 1 An aqueous acrylate monomer solution composed of 4574 g of 36% sodium acrylate aqueous solution and 98% of 425 g acrylic acid was placed in a temperature-adjustable pressure-resistant container having an internal volume of 10 L.
2.1 g of N, N′-methylenebisacrylamide was added, and the monomer temperature was adjusted to 20 ° C. while blowing nitrogen gas. When nitrogen substitution was completed, 1.0 g of ammonium persulfate and 0.2 g of L-ascorbic acid were added as polymerization initiators, and at the same time, the pressure in the container was increased to 5 kg / cm ² . Polymerization was started in 3 minutes after the addition of the polymerization initiator, and the temperature of the reaction system reached the maximum in 30 minutes. The obtained water-containing gel polymer was taken out of the container, firstly roughly cut into about 5 cm square with a cutter, and further cut into about 5 mm diameter with a meat chopper. The shredded hydrogel was dried with a hot air dryer at a temperature of 130 ° C. for 60 minutes to obtain a water-absorbent resin powder (A-1) of about 2 mm square. By crushing this with a roll crusher, the particle size is 150 μm to 1000 μm.
Water-absorbent resin powder (B-1) having a range of μm was obtained.

A cylindrical container 1 made of all stainless steel, having a raw material inlet 3 with an inner diameter of 20 cm and a height of 40 cm shown in FIG. 1 and a hot air blowing inlet 4, and a jacket 2 around the cylinder for heating. A fluidized-drying type apparatus, which was attached and equipped with a pressure spray nozzle 5 for spraying the surface cross-linking agent aqueous solution and a net 6 impervious to the water absorbent resin, was used for the surface reaction. 1000 g of the water-absorbent resin powder (B-1) obtained above was put into this apparatus, and the water-absorbent resin powder (B-1) was made to flow while vibrating with a jacket heated to 120 ° C. and a slight amount of hot air at 120 ° C. to vibrate. -1) was heated. When the temperature of the water absorbent resin powder (B-1) reaches 80 ° C., an aqueous solution consisting of 3 g of polyethylene glycol diglycidyl ether (n = 9) and 150 g of water is pressurized and spray nozzle while the water absorbent resin is vibrating and flowing. The mixture was sprayed for 10 minutes and mixed with the water absorbent resin powder (B-1). After spraying, the surface cross-linking agent and the water-absorbent resin powder (B-1) reacted instantly, and the reaction was completed within 5 minutes while containing water.

Then, subsequently, in order to remove water, hot air at 120 ° C. was increased to 4 Nm ³ / Hr to vigorously flow the water-absorbent resin, while absorbing the surface-crosslinking agent aqueous solution (B-1). ) Was dried to obtain a surface-treated water absorbent resin (1).

The water-absorbent resin powder (B-1) and the surface-treated water-absorbent resin (1) have the following properties: (a) particle size distribution, (b) salt water absorption capacity, (c) water absorption under pressure after 30 minutes. The amount was evaluated by the following method, and the results are shown in Table 1. (a) Particle size distribution: Opening 1000 μm (16 mesh), 850
μm (18 mesh), 500 μm (30 mesh), 355 μm
(42 mesh), 250 μm (60 mesh), 150 μm (10
0 mesh) and 100 μm (149 mesh) size JIS standard sieve and pan of 20 cm in diameter are stacked, and 100 g of water-absorbent resin powder (B-1) or surface-treated water-absorbent resin (1) is placed on the uppermost sieve. ) Was placed and vibrated with a classifier for 10 minutes. The weight collected on each sieve was weighed and expressed in% by weight. (B) Absorption capacity of salt water: 0.5 g of water-absorbent resin powder (B-1) or surface-treated water-absorbent resin (1) was precisely weighed, 20
The mixture was placed in a 10 cm × 10 cm tea bag type bag made of a 0 mesh nylon filter cloth, and immersed in 200 ml of a 0.9% sodium chloride aqueous solution (physiological saline) for 60 minutes. After that, the teabag bag was pulled up, drained for 10 minutes, flank correction of the teabag bag was performed, and the weight of the swollen gel was measured and calculated by the following formula 1.

[0035]

[Equation 1]

(C) Water absorption under pressure: The water absorption under pressure is shown in FIG.
It measured using the apparatus shown in. Burette with measuring tube 10
At the measuring tube 11, the thin tube 1 with an inner diameter of 2 mm
2 is inserted to the center of the buret to take in air as small air bubbles, and a Teflon tube 15 is connected to the tip 14 of the buret to make a glass filter 1 having a diameter of 60 mm.
6 was attached. Artificial urine (2% urea, 0.
Fill 9% sodium chloride, 500ppm calcium chloride and 1000ppm magnesium sulfate), plug the top of the buret 17 and filter plate 1 of the glass filter.
9 The upper surface and the air intake thin tube 12 were fixed on the same plane. A filter paper, a sample of 0.2 g of the water-absorbent resin powder (B-1) or the surface-treated water-absorbent resin (1) is placed on the upper surface of the filter plate 19, and a filter paper is placed on the sample, and the diameter of the bottom surface is 60.
A weight 21 having a pressure of 20 g / cm ^{2 in} mm was placed at the same time, and 30 minutes after placing these weights, the volume of water absorbed by the water absorbent resin (1) was measured and calculated by the following mathematical formula 2.

[0037]

[Equation 2]

Example 2 Water-absorbent resin powder of about 2 mm square after drying in Example 1
The same operation as in Example 1 was carried out except that (A-1) was pulverized in combination with a roll pulverizer to obtain a water absorbent resin powder (B-2) having a particle diameter in the range of 150 μm to 1000 μm. Repeatedly, a water absorbent resin (2) was obtained. This was evaluated in the same manner as in Example 1, and the results are shown in Table 1.

Example 3 Water-absorbent resin powder of about 2 mm square after drying in Example 1
The same operation as in Example 1 was carried out except that (A-1) was pulverized in combination with a roll pulverizer to obtain a water absorbent resin powder (B-3) having a particle diameter in the range of 150 μm to 1000 μm. Repeatedly, a water absorbent resin (3) was obtained. This was evaluated in the same manner as in Example 1, and the results are shown in Table 1.

Example 4 The water-absorbent resin powder (B-2) obtained in Example 2 was sieved to remove particles having a particle size of 500 μm or more and less than 150 μm to obtain a water-absorbing resin in the range of 150 μm to 500 μm. The same operation as in Example 1 was repeated except that the resin powder (B-4) was obtained to obtain a water absorbent resin (4). This was evaluated in the same manner as in Example 1, and the results are shown in Table 1.

Example 5 Example 1 was repeated except that the water absorbent resin powder (B-3) obtained in Example 3 was spray mixed with the aqueous solution of the crosslinking agent when the temperature of the water absorbent resin powder reached 100 ° C. The same operation as above was repeated to obtain a water absorbent resin (5). This was evaluated in the same manner as in Example 1, and the results are shown in Table 1.

Example 6 Example 1 was repeated except that the water absorbent resin powder (B-3) obtained in Example 3 was spray mixed with the aqueous solution of the crosslinking agent when the temperature of the water absorbent resin powder reached 40 ° C. The same operation as above was repeated to obtain a water absorbent resin (6). This was evaluated in the same manner as in Example 1, and the results are shown in Table 1.

Example 7 To the water-absorbent resin powder (1) obtained in Example 1, 0.5% of silica (Tokusil Tokuyama Soda Co., Ltd.) was added and mixed to adjust the powder fluidity, and the water-absorbent property was obtained. The resin (7) was evaluated in the same manner as in Example 1, and the results are shown in Table 1.

Comparative Example 1 Water-absorbent resin powder of about 2 mm square after drying in Example 1
The same operation as in Example 1 was carried out except that (A-1) was pulverized in combination with a roll pulverizer to obtain a water-absorbent resin powder (C-1) having a particle size in the range of several tens of μm to 850 μm. Repeatedly, a water absorbent resin (Comparative 1) was obtained. This was evaluated in the same manner as in Example 1, and the results are shown in Table 1.

Comparative Example 2 About 2 mm square water-absorbent resin powder after drying in Example 1
(A-1) is crushed with a mill-type crusher to obtain a particle size of 500μ.
A water-absorbent resin powder having a particle size of m or less was obtained. The same operation as in Example 1 was repeated except that the water-absorbent resin powder (C-2) having a particle size of 355 μm or more and less than 100 μm was removed by sieving to remove particles having a particle size of 355 μm or more and less than 100 μm. , A water absorbent resin (Comparative 2) was obtained. This is Example 1
The same evaluation as above was performed, and the results are shown in Table 1.

Comparative Example 3 Water-absorbent resin powder of about 2 mm square after drying in Example 1
The same operation as in Example 1 was carried out except that (A-1) was pulverized in combination with a roll pulverizer to obtain a water-absorbent resin powder (C-3) containing 10% or more of particles having a particle diameter of 850 μm or more. Repeatedly, a water absorbent resin (Comparative 3) was obtained. This was evaluated in the same manner as in Example 1, and the results are shown in Table 1.

Comparative Example 4 In Comparative Example 1, 0.5% of silica (Tokushiru Tokuyama Soda Co., Ltd.) was added to and mixed with the water-absorbent resin powder (C-1) before spray mixing the surface-crosslinking agent aqueous solution. The same operation as in Comparative Example 1 was repeated to obtain a water absorbent resin (Comparative 4). This was evaluated in the same manner as in Example 1, and the results are shown in Table 1.

[0048]

[Table 1]

[0049]

According to the method of the present invention. It is possible to reduce the amount of aggregates formed between resin particles that inhibit the reaction during surface reaction of the water-absorbent resin, and to obtain a water-absorbent resin having a high water-absorbing capacity even under pressure while maintaining a high water-absorption capacity. Further, the method of the present invention can be carried out even without using fine particles of a flow aid which causes a hydrophilic organic solvent or dust, so that it is industrially safe and excellent in economic efficiency, and there is no problem in environmental hygiene. Is. Therefore, the water-absorbent resin obtained by the present invention is widely used not only as a raw material for sanitary products such as high-performance and highly safe paper diapers and sanitary napkins, but also in the agricultural field, civil engineering field, medical field, etc. It can be used.

[Brief description of drawings]

FIG. 1 is a cross-sectional view of a surface crosslinking reaction device used in the present invention.

FIG. 2 is a cross-sectional view of a water absorption measuring device under pressure used in the present invention.

[Explanation of numbers]

 DESCRIPTION OF SYMBOLS 1 ... Surface reaction apparatus 2 ... Jacket 3 ... Raw material input port 4 ... Heated air injection port 5 ... Spray nozzle 6 ... Net 10 ... Burette with measuring tube 11 ... Burette measuring pipe 12 ... Air intake thin tube 13 ... Air intake 14 ... Bullet tip 15 ... Teflon tube 16 ... Glass filter 17 ... Burette upper part 18 ... Plug 19 ... ..Glass filter plate 20 ... Layer consisting of filter paper, sample, filter paper 21 ... Weight

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Takashi Aoyama 1-1 Funami-cho, Minato-ku, Nagoya-shi, Aichi Toagosei Chemical Industry Co., Ltd. Nagoya Research Institute (72) Inventor Minoru Okada Minato-shi, Aichi Prefecture 1 of Funami-cho, Ward-ward Toagosei Chemical Industry Co., Ltd. Nagoya Research Institute (72) Inventor, Hotaro Yasuda 23, 23, Showa-cho, Minato-ku, Nagoya, Aichi Prefecture Toagosei Chemical Industry Co., Ltd. Nagoya Plant (72 ) Inventor Yoshikazu Mori 23 Toagosei Synthetic Chemical Industry Co., Ltd.Nagoya factory at 17 Showa-cho, Minato-ku, Nagoya city, Aichi prefecture

Claims (2)

[Claims] 1. A heated water-absorbent resin powder having 90% by weight or more of particles having a carboxyl group in its molecular structure and passing through a sieve mesh having an opening of 850 μm, but not passing through a sieve mesh having an opening of 250 μm. A method for producing a modified water-absorbent resin, comprising: 2. The water absorbent resin powder according to claim 1, wherein the water absorbent resin powder is 50.degree.
A method for producing a modified water-absorbent resin, which is heated as described above.