JP3145459B2 - Method for producing water absorbent resin - Google Patents

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. More specifically, a water-absorbent resin that has a strong particle structure during water-absorption and swelling despite being reused as a fine powder of the water-absorbent resin, and that has excellent handleability and various water-absorbing properties, is economical. The present invention also relates to a method for producing it in an advantageous manner.

[0002]

2. Description of the Related Art In recent years, water-absorbent resins have been used in various fields such as sanitary materials such as disposable diapers and menstrual cotton, agricultural and horticultural water retention agents, and industrial dehydrating agents. In general, when a water-absorbent resin is used for these various uses, there is an optimum water-absorbent resin particle size depending on the use.

However, in the past, the water-absorbent resin actually contained a considerable proportion of fine powder finer than the intended optimum particle size. Therefore, in using such a water-absorbing resin, the following problems can be considered.

(1) Dust is apt to be generated at the time of work, which causes deterioration of work environment and reduction of the amount.

[0005] (2) Mamako is easily formed during absorption, and diffusion of the liquid is hindered, so that when used in a disposable diaper or the like, leakage tends to occur.

(3) Poor mixability and dispersibility when mixed with other substances, for example, it is difficult to uniformly mix with soil.

(4) Since the fluidity of the powder is poor, the formation of a bridge in the hopper, the flash phenomenon and the like are likely to occur.

As a method for solving these problems, a technique of granulating a water-absorbent resin and a technique of reusing fine powder of a water-absorbent resin have been reported. For example, as a granulation technique, a method of granulating a water-absorbent resin fine powder with water or a binder in which a water-soluble polymer or an inorganic powder is used in combination with water (Japanese Patent Laid-Open No. 61-97,3)
No. 33 and JP-A-61-101,536), a method in which a water-absorbent resin fine powder is dispersed in a non-aqueous liquid, an aqueous solution of a monomer is added to absorb the powder, and then granulated by polymerization. No. 62-230,813), by adding a water-absorbent resin fine powder to an organic solvent containing a water-containing gel of a water-absorbent resin obtained by a reversed-phase suspension polymerization method, followed by azeotropic dehydration. Granulation method (JP-A-63-210108)
No.), as a technique for recycling fine powder, a water-absorbent resin fine powder is swollen with a sufficient amount of water to produce an amorphous gel, and then the continuous amorphous gel is used. Crushing and drying (US-A-4,950,692),
A method of adding a crosslinking agent aqueous solution to a water-absorbent resin fine powder to form a gel-like mass, followed by a crosslinking reaction, followed by drying and pulverization (EP-A-0,401,044). Is partially hydrated by contact with spray water, and simultaneously with the spraying, the fine powder and water are substantially completely hydrated without agglomeration of the fine powder and discharged from the mixing area. Mixing at such a high shear stress and then kneading the viscous material and said hydrated fine powder with a moderate shear stress in another mixing zone so as to produce a substantially homogeneous admixed product. (EP-A-0,417,761) and the like are known.

However, the above-mentioned Japanese Patent Application Laid-Open No. 61-9 / 1986
In the method of JP-A-7,333 and JP-A-61-101,536, the strength of the formed granules is not sufficient, and part of the granules is broken during the production line or transportation, and fine powder is formed. There was a case to play. In the method disclosed in Japanese Patent Application Laid-Open No. 62-230,813, it is difficult for all the water-absorbing resins to uniformly absorb the aqueous monomer solution, the rate of forming granules is low, and Is excessively penetrated into the resin powder and polymerized, resulting in a decrease in the absorption capacity of the water-absorbing resin.
In the method of JP-A-63-210,108, a granulated product is obtained, but the granulation strength is low, and a fine gel is regenerated upon swelling with water, which hinders liquid permeability and diffusion. There was a problem that only can be obtained.

Also, US-A-4,950,692, E
PA-0,401,044 and EP-A-0,41
The method described in No. 7,761 requires that the water-absorbent resin fine powder is once swollen by adding water or an aqueous solution of a crosslinking agent, and then dried again, which not only makes the operation complicated and difficult, but also makes the operation complicated and difficult. But it was economically disadvantageous. Further, when the dry particles formed from only the water-absorbent resin fine powder obtained in US-A-4,950,692 are swollen, most of the fine powder used becomes a fine gel and is regenerated. In addition, it is inferior in liquid permeability and diffusivity. Further, according to the method of EP-A-0,401,044,
The cross-linking agent penetrates into the water-absorbent resin fine powder together with a large amount of water, and as a result of performing a cross-linking reaction, the obtained dry particles have a disadvantage that the absorption capacity is extremely reduced.

[0011]

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a novel method for producing a water absorbent resin.

Another object of the present invention is to have a strong particle structure even when swelling with water, despite the fact that the fine powder of the water-absorbing resin, which has not been achieved by the conventional method, is reused. Another object of the present invention is to provide a method for economically and advantageously producing a water-absorbent resin excellent in various water-absorbing properties such as water absorption capacity and liquid permeability.

[0013]

Means for Solving the Problems The inventors of the present invention have conducted intensive studies to obtain a water-absorbing resin in order to meet the above-mentioned object. After mixing the fine powder of the water-absorbent resin in a substantially dry state with an average particle diameter smaller than the average particle diameter in a dry state of the water-absorbent gel on the surface of the water-containing gel of the water-absorbent resin having a water content and a temperature range, By further increasing the polymerization rate of the hydrogel, the fine powder of the water-absorbing resin is firmly bonded to the surface portion thereof, and the fine powder or the fine powder is formed even during the factory line or transportation, or when the resin swells. It has a strong particle structure from which the fine gel derived does not easily regenerate, and a water-absorbent resin excellent in various water-absorbing properties can be easily obtained, and the water-absorbent resin having the above properties obtained in this manner Is a base polymer and its particles By cross-linking the vicinity of the surface with a cross-linking agent, it has the same particle strength as primary particles even under shearing force at the time of swelling, fine gel derived from fine powder does not easily regenerate, absorption capacity and liquid permeability It has been found that a water-absorbing resin having excellent cross-linking properties near the particle surface can be obtained, and the present invention has been completed.

That is, these objects are aimed at achieving a conversion of 60
~ 99%, average particle size 0.1 ~ 200mm, water content 30
100 parts by weight of a water-absorbent resin hydrogel (A) obtained by aqueous solution polymerization and having a temperature of 40 to 110 ° C. and a smaller average particle diameter when the water-absorbent resin hydrogel (A) is dried. After mixing 1 to 50 parts by weight of a water-absorbent resin fine powder (B) having an average particle size and being substantially dry, the polymerization rate of the water-absorbent resin hydrogel (A) is increased to a polymerization rate or more at the time of mixing. And a method for producing a water absorbent resin.

[0015] Further, these objects are to achieve a conversion of 60 to 99.
%, Average particle size 0.1 to 200 mm, water content 30 to 90
100 parts by weight of a water-absorbent resin hydrogel (A) obtained by aqueous polymerization and having an average particle size smaller than the average particle diameter when the water-absorbent resin hydrogel (A) is dried After mixing 1 to 50 parts by weight of the water-absorbent resin fine powder (B) having a diameter and a substantially dry state, the polymerization rate of the water-absorbent resin-containing gel (A) is increased to the polymerization rate at the time of mixing or more. It is also achieved by a method for producing a water-absorbent resin in which the vicinity of the particle surface is crosslinked by mixing the obtained water-absorbent resin as a base polymer with a crosslinking agent (D) to cause a crosslinking reaction.

[0016]

The water-absorbent resin hydrogel (A) which can be used in the present invention has an irregular shape due to aqueous solution polymerization. The polymerization rate during the polymerization is in the range of 60 to 99%, and the average particle size is Has a water content of 30 to 90% by weight subdivided into 0.1 to 200 mm and a temperature of 40 to 110%.
It is in the range of ° C. When a water-in-oil type hydrogel obtained by reverse phase suspension polymerization is used, the shape is spherical, and these hydrogels generally have a dispersing agent such as a surfactant used on the surface during polymerization. Remains, so that a water-absorbent resin having a strong particle structure cannot be obtained even during water-absorption swelling, which is the object of the present invention. In addition, it is essential that the water-absorbent resin hydrogel (A) be in a polymerization rate range of 60 to 99%. When the polymerization rate is less than 60%, the monomer is excessively penetrated into the water-absorbent resin fine powder (B) to be used, and an excessively cross-linked structure is formed by a graft reaction or the like, so that the resultant is not absorbed. Magnification decreases. When the polymerization rate exceeds 99%, the bonding with the water-absorbent resin fine powder (B) on the surface of the hydrogel is weak, and the obtained water-absorbent resin is easy to regenerate the fine powder when swelling with water. Becomes Preferably, the degree of polymerization is 80 to 98%.

The water-absorbent resin hydrogel (A) has an average particle diameter in the range of 0.1 to 200 mm. In order to obtain particles having such a particle size, a hydrogel obtained by aqueous solution polymerization is mechanically crushed and cut while being polymerized, or after a polymerization rate reaches 60 to 99%, mechanically. A method of crushing or cutting can be adopted.

When the average particle size exceeds 200 mm, the surface area of the water-absorbent resin hydrogel (A) becomes small, and the water-absorbent resin fine powder (B) sufficiently exists on the surface of the water-absorbent resin water-containing gel (A). Since it is not obtained, the obtained water-absorbent resin is also easy to regenerate the fine powder at the time of swelling by water absorption. Usually, the water-absorbent resin hydrogel (A) has an average particle diameter of 0.1 m.
It is difficult to crush and cut to less than m. Preferably, the average particle size is in the range of 0.5 to 20 mm.

The water content of the water-absorbent resin water-containing gel (A) is 30 to 90% by weight. Water content 30 to 90
In order to obtain a water-absorbent resin-containing gel (A) having a concentration of 10% by weight, an aqueous monomer solution having a monomer concentration of about 10 to 70% by weight may be subjected to aqueous solution polymerization by a known method. The polymerization may be carried out in a range outside the concentration range, and the water content may be adjusted so as to be in the above-mentioned water content range. When the water content is less than 30% by weight, the water-absorbent resin fine powder (B)
And the bond becomes weaker. On the other hand, when the water content exceeds 90% by weight, drying becomes difficult, which is not preferable. Preferably, the water content is 55 to 75% by weight.

The temperature of the water-absorbent resin hydrogel (A) is in the range of 40 to 110 ° C. 40 ℃
If it is less than 10, the fixability of the hydrogel particles increases, and the mixing with the water-absorbent resin fine powder (B) becomes insufficient, and the performance may be lowered. Further, if the temperature of the hydrogel rises above 110 ° C., the gel will boil at normal pressure, which may make mixing difficult.

The water-absorbent resin hydrogel (A) is not particularly limited as long as it absorbs water or an aqueous liquid and swells, but is generally obtained by polymerizing a water-soluble unsaturated monomer. .

Examples of these water-soluble unsaturated monomers include (meth) acrylic acid, (anhydride) maleic acid, fumaric acid, crotonic acid, itaconic acid, 2- (meth) acryloylethanesulfonic acid, Anionic monomers such as-(meth) acryloylpropanesulfonic acid, 2- (meth) acrylamide-2-methylpropanesulfonic acid, vinylsulfonic acid and styrenesulfonic acid, and salts thereof, (meth) acrylamide, N-substituted ( Nonionic hydrophilic group-containing monomers such as meth) acrylamide, 2-hydroxyethyl (meth) acrylate, 2-hydroxypropyl (meth) acrylate, methoxypolyethylene glycol (meth) acrylate, and polyethylene glycol (meth) acrylate; N-dimethylaminoethyl (meth) acrylate, N, N-di Amino group-containing unsaturated monomers such as tylaminopropyl (meth) acrylate and N, N-dimethylaminopropyl (meth) acrylamide, and quaternized products thereof, and acrylics such as methyl (meth) acrylate and ethyl (meth) acrylate Acid esters and the like can be mentioned, and one or more of these can be selected and used. However, considering various water absorbing properties of the finally obtained water absorbing resin, (meth) acrylic acid (Salt), 2- (meth) acryloylethanesulfonic acid (salt), 2- (meth) acrylamide-2-methylpropanesulfonic acid (salt), (meth) acrylamide, methoxypolyethylene glycol (meth) acrylate,
One or more selected from the group consisting of N, N-dimethylaminoethyl (meth) acrylate or a quaternary compound thereof is preferable, and one containing (meth) acrylic acid (salt) as an essential component is more preferable. In this case, it is most preferable that 30 to 90% of the (meth) acrylic acid is neutralized with a basic substance.

The water-absorbent resin-containing gel (A) may be a self-crosslinkable gel obtained without using a crosslinking agent, but may be a water-absorbing resin having a polymerizable unsaturated group and / or a reactive functional group. The resin hydrogel (A) may be obtained by using the gel strength in a range where the gel strength reaches a desired standard.

Examples of these crosslinking agents include, for example, N,
N'-methylenebis (meth) acrylamide, (poly)
Ethylene glycol di (meth) acrylate, glycerin tri (meth) acrylate, trimethylolpropane tri (meth) acrylate, triallylamine, triallyl cyanurate, triallyl isocyanurate, glycidyl (meth) acrylate, (poly) ethylene glycol, diethylene glycol , (Poly) glycerin, propylene glycol, diethanolamine, trimethylolpropane, pentaerythritol, (poly) ethylene glycol diglycidyl ether, (poly) glycerol polyglycidyl ether, epichlorohydrin, ethylenediamine, polyethyleneimine, (poly) aluminum chloride , Aluminum sulfate, calcium chloride, magnesium sulfate, and the like. Or more can be used species.

In order to obtain the water-absorbent resin hydrogel (A), the water-soluble unsaturated monomer is polymerized in the presence of a hydrophilic polymer such as starch, cellulose, polyvinyl alcohol or the like, thereby simultaneously obtaining the polymerization. A graft bond or a complex may be formed. When polymerizing these water-absorbent resin hydrogels (A), ammonium persulfate, potassium persulfate, sodium persulfate, hydrogen peroxide, t-butyl hydroperoxide, 2,2'-azobis are used as polymerization initiators. Water-soluble radical polymerization initiators such as amidinopropane dihydrochloride may be used, and among them, persulfates such as ammonium persulfate, potassium persulfate, and sodium persulfate may be used. Is preferred in order to further increase the polymerization rate after mixing.

The water-absorbent resin fine powder (B) which can be used in the present invention is the above-mentioned water-absorbent resin hydrogel (A)
Has an average particle size smaller than the average particle size when it is in a dry state, and is in a substantially dry state. These water-absorbent resin fine powders (B) are generally prepared by using a water-soluble unsaturated monomer containing a crosslinking agent as necessary as a starting material of the water-absorbent resin-containing gel (A) by a known method. It is a part of fine powder having a small particle size which is mixed in the water-absorbing agent obtained by polymerization and drying, and is not suitable for the intended use. Obtained by classification.

The water-absorbent resin fine powder (B) is in a substantially dry state, and has a smaller particle diameter than the average particle diameter when the water-absorbent resin hydrogel (A) is in a dry state. is necessary. When the water-absorbent resin fine powder (B) absorbs water and is in a swelling state, the energy required for the subsequent drying step is increased, which is not only economically disadvantageous, but also the water-absorbent resin hydrogel (A) The permeation of the monomer components and the like does not occur, and the bonding strength with the water-absorbent resin hydrogel (A) is weakened. The water content in the water-absorbent resin fine powder (B) is preferably as small as possible, but it is actually difficult to reduce the water content to 0% by weight, and usually the water content is preferably about 1 to 10% by weight. belongs to.

When the average particle diameter of the water-absorbent resin fine powder (B) is larger than the average particle diameter of the water-absorbent resin hydrogel (A) in a dry state, the water-absorbent resin hydrogel (A) And the water-absorbent resin fine powder (B) cannot be sufficiently mixed and bonded, so that the resulting water-absorbent resin hardly has a strong particle structure.

The average particle size of the water-absorbent resin fine powder (B) varies depending on the average particle size of the water-absorbent resin hydrogel (A), but preferably when the water-absorbent resin hydrogel (A) is dried. 0.001 to 20% of the average particle diameter of
More preferably, it has an average particle diameter of 0.01 to 10%.

When the finally obtained water-absorbent resin is used as a sanitary material such as a disposable diaper, for example, 1 to 149
It may be preferable to remove portions of the fine powder that are in the particle size range of μm. In this case, 90-100% by weight of the water-absorbent resin fine powder (B) may have a particle diameter of 1 to 149 μm. ) May be set to an optimum value.

The amount of the water-absorbent resin fine powder (B) used is 1 to 50 parts by weight based on 100 parts by weight of the water-absorbent resin hydrogel (A). If the amount exceeds 50 parts by weight, the water-absorbent resin fine powder (B) cannot sufficiently contact the surface of the water-absorbent resin hydrogel (A), and a sufficient bond cannot be formed. On the other hand, if the amount is less than 1 part by weight, the effect corresponding to the method of the present invention cannot be obtained. Preferably 5 to 2
0 parts by weight.

The composition of the water-absorbent resin fine powder (B) and the water-absorbent resin hydrogel (A) may be the same or different. Considering the case where the operation of the present invention is repeated as described above, the same composition is preferable.

The polymerization method for obtaining the water-absorbent resin fine powder (B) may be the same as or different from the polymerization method for obtaining the water-absorbent resin hydrogel (A). In view of the properties, those obtained by aqueous solution polymerization are more preferable.

Further, as the water-absorbent resin fine powder (B), a powder whose surface is cross-linked may be used. When a crosslinked product is used, a water-absorbent resin hydrogel (A)
May occur more uniformly, and the bond may be strengthened.

For mixing the water-absorbent resin hydrogel (A) and the water-absorbent resin fine powder (B), conventionally known mixers such as a V-type mixer, a ribbon-type mixer, a paddle-type mixer and a screw-type mixer are used. A mixer, kneader, pressurized kneader, or the like can be used. However, in order to achieve sufficient mixing and maximize the effects of the present invention, the particles of the water-absorbent resin hydrogel (A) are deformed with a mixer having a large shearing force. The method of mixing while receiving is preferable. According to the method of mixing the water-absorbent resin-containing gel (A) while stirring and subdividing it during mixing, the water-absorbent resin fine powder (B) is efficiently attached to the newly formed cut gel surface, Or it is more preferable because it can be kneaded.

As a mixer that meets these objectives,
Examples include a kneader and a pressure kneader. If the polymerization of the water-absorbent resin hydrogel (A) is also carried out in a reactor such as a kneader, the hydrogel can be crushed and fragmented so as to have a desired average particle size as the polymerization proceeds. When the water-absorbent resin fine powder (B) is mixed with the resin hydrogel (A), there is no need to use a separate apparatus, and the present invention can be carried out in a series of processes.

In mixing, a method in which the water-absorbent resin fine powder (B) is intermittently and continuously charged while stirring the water-absorbent resin-containing gel (A), a method in which the water-absorbent resin fine powder (B) is charged at once, and a method in which water is absorbed in reverse. A method in which the water-absorbent resin hydrogel (A) is charged into the water-absorbent resin fine powder (B) and then stirred, continuously while simultaneously feeding the water-absorbent resin hydrogel (A) and the water-absorbent resin fine powder (B). A method of mixing can be exemplified. However, in the case of using a continuous mixing method, the feed must be terminated within a range where the polymerization rate of the water-absorbent resin hydrogel (A) is within the range specified in the present invention. Further, it is more preferable that the mixing is performed in an inert gas such as nitrogen so as not to hinder the operation for increasing the polymerization rate performed later.

During this mixing, the water-absorbent resin hydrogel (A) is prevented from sticking to each other, the mixing is performed efficiently, and the water-absorbent resin hydrogel (A) and the water-absorbent resin fine powder (B) are mixed. In order to make the integration of
It is preferable to keep the temperature at 0 to 100 ° C.

In the present invention, the operation of increasing the polymerization rate later by adding a polymerization initiator, a reducing agent, etc., at the time of mixing the water-absorbent resin hydrogel (A) and the water-absorbent resin fine powder (B). May be easier. Further, at the time of mixing, a water-insoluble particulate inorganic substance, for example, silicon dioxide, titanium dioxide, aluminum oxide, talc, zeolite, bentonite, hydrotalcite, montmorillonite, etc. may be interposed. As a result, the particle structure of the obtained water-absorbent resin may become stronger.

The present invention can be achieved only by mixing the water-absorbent resin hydrogel (A) and the water-absorbent resin fine powder (B) by the above-mentioned method, and then increasing the polymerization rate to at least the polymerization rate at the time of mixing. For this purpose, there can be mentioned, for example, a method in which the mixture is heated and aged at an optimum temperature while keeping the water content at an appropriate level, and a method in which the mixture is heated and dried under conditions that increase the polymerization rate. If the operation of further increasing the polymerization rate is not performed as described above, a water-absorbent resin having a strong particle structure that does not regenerate fine powder even at the time of water absorption and swelling as the object of the present invention cannot be obtained. In order to improve the strength and maximize the efficiency of the present invention, it is preferable to increase the polymerization rate of the finally obtained water-absorbent resin to 99.9 to 100%.

The water-absorbent resin thus obtained in the present invention may be further subjected to drying, pulverization, classification and the like, if necessary, so as to have a desired particle size.

Further, when the water-absorbent resin powder (C) in a substantially dry state corresponding to the particle size range of the water-absorbent resin fine powder (B) which is not suitable for the intended use is produced again by a process such as classification, The water-absorbent resin powder (C) is further mixed with the water-absorbent resin hydrogel (A) obtained by a new polymerization step as a water-absorbent resin fine powder (B). Is repeated twice or more to continuously and efficiently produce a water-absorbent resin having a very narrow particle size distribution, a strong particle structure without regenerating fine powder, and showing no difference in properties between batches. be able to.

According to the present invention, the water-absorbing resin thus obtained is used as a base polymer, and the water-absorbing resin as the base polymer is further mixed with a crosslinking agent (D) to cause a cross-linking reaction in the vicinity of the particle surface. The present invention also provides a method for producing a water-absorbent resin in which the vicinity of the obtained particle surface is crosslinked.

The thus obtained water-absorbent resin having a crosslinked area near the particle surface has a stronger particle structure than a water-absorbing resin having no crosslinked area near the particle surface.
Even under the shearing force at the time of water absorption swelling, its particle structure is not destroyed, it has the same strength as primary particles, there is little regeneration of fine gel derived from fine powder, water absorption such as absorption capacity and liquid permeability Various characteristics are further improved.

In this case, as the water-absorbing resin as the base polymer, after mixing the water-absorbing resin fine powder (B) and the water-absorbing resin hydrogel (A), the polymerization rate of the water-absorbing resin hydrogel (A) After drying, if necessary, drying is performed, and the water content is preferably adjusted to 20% by weight or less, and further, if necessary, pulverization and classification are performed, and those having an average particle diameter of 200 to 600 μm are more preferable. If the water content is higher than 20% by weight, the crosslinking agent (D)
May excessively penetrate into the resin particles, resulting in a decrease in absorption capacity.

When the water-absorbing resin as the base polymer obtained in advance contains the water-absorbing resin powder (C) in a substantially dry state corresponding to the particle size range of the fine powder of the water-absorbing resin (B), this is used. By the removal, the mixing with the crosslinking agent (D) can be uniformly performed, and the particle structure of the water-absorbent resin particles in which the vicinity of the obtained particle surface is cross-linked becomes strong.
In addition, the content of the fine powder may decrease.

Further, the water-absorbing resin as the base polymer preferably has a carboxyl group from the viewpoints of various water-absorbing properties, ease of performing a subsequent crosslinking reaction, and strength of the formed particles. As described above, it is preferable to have a polymerized unit derived from (meth) acrylic acid.

The crosslinking agent (D) is not particularly limited as long as it reacts with the functional group of the water absorbing resin. For example, when the water absorbent resin has a carboxyl group, ethylene glycol, diethylene glycol, triethylene glycol, polyethylene glycol, glycerin, polyglycerin, propylene glycol, diethanolamine, triethanolamine, polypropylene glycol polyvinyl alcohol, pentaerythritol , 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, sorbitol, sorbitan, mannitol, mannitan, polyhydric alcohols such as sucrose, glucose, etc., ethylene glycol diglycidyl ether, polyethylene glycol di Polyvalent glycidyl compounds such as glycidyl ether and glycerin triglycidyl ether; and haloepoxy such as epichlorohydrin and α-methylchlorohydrin Compounds, polyaldehydes such as glutaraldehyde and glyoxal, polyamine compounds such as ethylenediamine and polyethyleneimine, calcium hydroxide, calcium chloride, calcium carbonate, calcium oxide, magnesium borax, magnesium oxide, aluminum chloride, zinc chloride and chloride Hydroxides, halides, carbonates, oxides, borates such as borax, and polyvalent metal compounds such as aluminum isopropylate, etc. of metals of the 2A group, 3B group and 8 group of the periodic table such as nickel; One or more of these can be appropriately selected and used in consideration of reactivity. Among these, when the water-absorbent resin as the base polymer has a carboxyl group, the crosslinking agent (D) is often used because of the strength of the particle structure of the water-absorbent resin in which the vicinity of the particle surface is crosslinked. It is preferable to use a polyhydric alcohol compound, a polyhydric glycidyl compound or the like, and among them, a polyhydric alcohol compound is most preferable. Among them, glycerin, trimethylolpropane, pentaerythritol and the like are preferable in consideration of permeability to the vicinity of the particle surface.

The amount of the crosslinking agent (D) used in the present invention is preferably 0.01 to 10 parts by weight, more preferably 0.1 to 5 parts by weight, based on 100 parts by weight of the water-absorbent resin as the base polymer. Part is the proportion of the range. When the amount is within this range, a water-absorbing resin having a strong particle structure even under a shear force at the time of water absorption swelling and excellent in handleability and water absorption properties, in which the vicinity of the particle surface is crosslinked, can be obtained. However, when the amount exceeds 10 parts by weight, not only is it uneconomical, but also the ratio of the water-absorbing resin is reduced, so that the absorption amount is reduced. Conversely 0.01
If the amount is less than less than parts by weight, it is difficult to obtain the effect of improving the particle strength as compared with the water-absorbing resin as the base polymer. In this case, water or a hydrophilic organic solvent is used when mixing the crosslinking agent (D) to control the penetration of the crosslinking agent (D) into the water-absorbent resin as a base polymer and to optimize the particle strength. Is preferred. In this case, the crosslinking agent may be prepared in advance as an aqueous solution or a mixed solution of water and a hydrophilic organic solvent and added to the water-absorbing resin as the base polymer. In this case, the amount of water used depends on the amount of the crosslinking agent (D) or hydrophilic organic solvent used, but is generally 0.1 to 25% by weight, preferably 100 to 25 parts by weight of the water-absorbing resin as the base polymer. Is 0.5 to 10% by weight. When the amount of water is less than 0.1% by weight, the crosslinking agent (D) hardly permeates into the resin, and the effect of improving the particle strength is hardly obtained. If it exceeds 25% by weight, the absorption capacity of the obtained water-absorbent resin may decrease.

In the present invention, an ordinary mixer can be used for mixing the water-absorbing resin as the base polymer and the crosslinking agent (D). For example, a V-type mixer, a ribbon-type mixer, a screw-type mixer, a rotating disk-type mixer, an air-flow-type mixer, and the like. For the heat treatment of the mixture of the water-absorbent resin as the base polymer and the crosslinking agent (D), a usual dryer or heating furnace, for example, a groove-type stirring dryer, a rotary dryer, a fluidized-bed dryer, a flash dryer, An infrared dryer or the like can be used. In order to accelerate the crosslinking reaction, it is generally preferable to perform heating, and the temperature is usually 40 ° C to 250 ° C.
It is about ° C. In particular, when a polyhydric alcohol compound is used as the crosslinking agent (D), the heat treatment temperature is 90 ° C. or higher and 230 ° C.
The temperature is preferably lower than 120 ° C, more preferably higher than 120 ° C and lower than 210 ° C. Further, the mixing and the heat treatment may be performed simultaneously. The crosslinked water-absorbent resin of the present invention obtained in this manner is not crosslinked in the vicinity of the particle surface, and has a fine powder even under a shearing force during swelling compared to the water-absorbent resin as the base polymer. It has a strong particle structure with almost no regeneration and has excellent water absorption properties.

The thus obtained water-absorbent resin having a crosslinked surface area contains a substantially dry water-absorbent resin powder (C ′) corresponding to the water-absorbent resin fine powder (B). If so, it is preferable to remove it,
Furthermore, by mixing the water-absorbent resin hydrogel (A) as the water-absorbent resin fine powder (B) with the water-absorbent resin hydrogel (A) and repeating the same operation twice or more, it has a very narrow particle size distribution, a strong particle structure, and excellent water absorption properties. A water-absorbent resin in which the vicinity of the particle surface is crosslinked can be continuously and efficiently produced.

The water-absorbing resin thus obtained according to the present invention may be further modified in surface properties by a known method. Also, the obtained water-absorbent resin and water-soluble polymer, deodorant, fragrance, drug, plant growth aid, bactericide, preservative, foaming agent, pigment, dye, carbon black, activated carbon,
By mixing hydrophilic short fibers or the like, a new function can be imparted to the obtained water-absorbent resin.

[0053]

The present invention will be described in detail with reference to the following examples, but the scope of the present invention is not limited by these examples. The polymerization rate of the hydrogel, the average particle diameter of the hydrogel, and the average particle diameter when the hydrogel was in a dry state were determined by the following methods. The rate of increase in fine powder upon impact and the rate of change in particle size upon swelling were measured by the following methods.

(A) Polymerization rate of water-containing gel 0.5 g of the sampled water-containing gel was dispersed in 1000 ml of deionized water, and after stirring for 2 hours, the dispersion was filtered with filter paper to determine the amount of residual monomer in the filtrate. The measurement was performed using high performance liquid chromatography to determine the amount of residual monomers in the hydrogel.
The polymerization rate of the hydrogel was determined from the residual monomer amount by using the following equation (1).

[0055]

(Equation 1)

(B) Average particle size of hydrogel 5 g of the sampled hydrogel is put into 1200 g of a 20% by weight aqueous sodium chloride solution, and the stirrer tip is rotated at 300 rpm and stirred for 60 minutes. After completion of the stirring, a standard sieve (mesh size: 9.5 mm, 2.5 mm, 0.
85mm, 0.60mm, 0.30mm, 0.075m
m) in order, and the whole amount of the gel is put into the sieve, and a further 20 g of a 20% by weight aqueous sodium chloride solution (1000 g) is passed through the sieve.
, And the hydrogel was classified by the water flow. The weight (ω) of the gel on each classified sieve was weighed.
The converted mesh size R (α) of each sieve was determined according to the following formula 2 in consideration of the weight change of the gel in a 20% by weight aqueous sodium chloride solution. The converted sieve opening R (α) of the sieve determined on logarithmic probability paper and the weight% of the gel on the sieve are plotted, and the particle size corresponding to 50% by weight is read from the obtained graph to obtain the water content. The average particle diameter (rG) of the gel was used.

[0057]

(Equation 2)

(C) Average Particle Diameter in Dry State From the average particle diameter (rG) of the hydrogel obtained in (b) above, the average particle diameter in a dry state using the following equation (3) rD) was determined.

[0059]

(Equation 3)

(1) Absorption capacity About 0.2 g of a water-absorbent resin is uniformly placed in a non-woven tea bag bag (40 mm × 150 mm), and the tea bag bag is placed in a large excess saline solution (0.9 wt. (Aqueous sodium chloride solution) for 30 minutes to swell, pull up, drain, and measure the weight. Further, the absorption capacity was calculated according to the following formula 4 using the weight when only the empty tea bag bag was sucked in the same procedure as the blank as a blank.

[0061]

(Equation 4)

(2) Liquid Permeability Particles of the obtained water-absorbent resin having a size of 600 to 850 μm were fractionated and used as measurement samples. 0.500 g of a sample was put into a glass tube having an inner diameter of 16 mm and a length of 18 cm, which was capped with a silicon rubber stopper at the lower part, and 30 ml of artificial urine was poured. Next, the silicon rubber stopper at the bottom was removed, placed vertically on a 48-mesh sieve placed on a beaker, and the silicon rubber stopper at the top was removed and left for 10 minutes.

10 ml of artificial urine was added from the upper part of the glass tube, and the number of seconds required for the meniscus of the artificial urine to gradually drop and reach the upper surface of the gel was measured. The smaller the value is, the stronger the particle strength of the water-absorbent resin is, and the fine particle gel does not deviate from the swelling gel and is not regenerated.When this water-absorbent resin is used for a sanitary material, the liquid diffusibility is excellent. Show.

The artificial urine was prepared by using 7 g of potassium chloride, 7 g of sodium sulfate, and 2.975 of ammonium dihydrogen phosphate.
g, 0.525 g of diammonium hydrogen phosphate, 0.875 g of potassium chloride (dihydrate), and 1.75 g of magnesium chloride (hexahydrate), and ion-exchanged water was added to the mixture, for a total of 3.5 kg.
Was used.

(3) Increase rate of fine powder upon impact In a 225 ml container, 30 g of water-absorbent resin having a particle size range of 600 to 850 μm and 5 g of glass beads having a diameter of 5 mm
And shake it with a paint shaker for 30 minutes.
The production amount (%) of particles having a size of 49 μm or less was measured.

The smaller the value, the more difficult it is to regenerate the fine powder upon impact, indicating that the powder has a strong particle structure.

(4) Rate of change in particle size upon swelling Two 100 ml beakers each containing 75 g of artificial urine are prepared, and 1 g of a water-absorbent resin having a particle size range of 600 to 850 μm is added to each beaker. This water-absorbent resin dispersion was kept for 1 hour in a stationary state and the other was stirred for 1 hour at 500 rpm using a magnetic stirrer, and then each swollen gel was 10 mesh (1700 μm) and 200 Classification was performed by flowing a total of 1 liter of artificial urine from above the wire mesh using a mesh (74 μm) wire mesh. The particle size change rate at the time of swelling was determined as in the following Expression 5.

[0068]

(Equation 5)

The smaller these values are, the smaller the gel is, even under a swelling still state and under a shearing force, indicating that the fine gel is not regenerated and has a strong particle structure.

Reference Example 1 A 10-liter jacketed stainless steel double-arm kneader having two sigma-type blades and a 4400 g aqueous solution of a monomer component composed of 75 mol% of sodium acrylate and 25 mol% of acrylic acid was placed in a stainless steel double-arm kneader having a capacity of 10 liters. (Concentration of monomer component 3
7% by weight) and 2.72 g of trimethylolpropane triacrylate (0.05 mol% relative to the monomer component) as a cross-linking agent, and nitrogen gas was blown into the reaction system to replace the inside of the reaction system with nitrogen. Next, while rotating the two sigma-type blades and heating the reaction system by passing warm water of 30 ° C. through the jacket, 1.10 g of sodium persulfate and 1.10 g of sodium bisulfite were added as initiators. did. The aqueous monomer solution formed a soft hydrogel as the polymerization proceeded, and was gradually subdivided by the rotation of the blades. Forty minutes after the start of the polymerization, the hydrogel polymer was about 1.9.
It was subdivided to an average particle size of mm. The obtained polymer gel was dried with hot air on a wire mesh at a temperature of 150 ° C. for 2 hours. The dried product was pulverized using a hammer mill equipped with an 8 mm screen, and classified with a 20-mesh wire net to obtain a reference water-absorbent resin powder (1).

Example 1 In Reference Example 1, the water-absorbent resin hydrogel (A-1) 17 minutes after the start of the polymerization reaction was added to the water-absorbent resin fine powder (B-
1) [Water absorbent resin powder before classification in Reference Example 1
The particle size obtained by passing through a 00 mesh wire mesh is 1 to 1
49 μm, powder having an average particle diameter of 95 μm] The same operation as in Reference Example 1 except that 325 g is continuously charged over 5 minutes and mixed with the water-absorbent resin hydrogel (A-1) during the polymerization reaction. Was repeated. The polymerization rate of the water-absorbent resin-containing gel (A-1) at the start of charging was 96.3%, and the average particle size was 2.3 mm (average particle size 1.7 when dried).
mm), the water content was 61.4% by weight, and the temperature was 81 ° C.
After the addition was completed, the hydrogel (A-1) was further subdivided by continuing mixing for 10 minutes under a shearing force.
At the end of the mixing, the temperature in the system was 77 ° C. The obtained polymer gel was dried with hot air at a temperature of 150 ° C. for 2 hours to increase the polymerization rate of the water-absorbent resin hydrogel (A-1), and then pulverized and classified in the same manner as in Reference Example 1. Water-absorbing resin (I-1) was obtained. The polymerization rate of the water absorbent resin (I-1) was 99.95%. Table 1 shows properties of the water absorbent resin (I-1).

Example 2 In Example 1, the addition amount of the water-absorbent resin fine powder (B-1) was changed to 650 g, and the addition time of the water-absorbent resin fine powder (B-1) was changed to 20 after the polymerization reaction started. The same operation as in Example 1 was repeated, except that the continuous charging was continued for 7 minutes from the end of the period. In addition, the water-absorbent resin hydrate gel (A-
The polymerization rate of 2) is 97.1%, and the average particle size is 1.7 mm.
(Average particle diameter 1.2 mm when dried), water content 62.0% by weight, temperature 77 ° C. After completion of the introduction, the mixture was further mixed for 2 minutes under a shearing force, whereby the hydrogel (A-2) was further subdivided. At the end of the mixing, the temperature in the system was 72 ° C. The obtained polymer gel was mixed with 150
Reference Example 1 After increasing the polymerization rate of the water-absorbent resin hydrogel (A-2) by drying with hot air at a temperature of 2 ° C. for 2 hours.
Pulverization and classification were performed in the same manner as in the above to obtain a water-absorbent resin (I-2). The polymerization rate of this water absorbent resin (I-2) is 99.97%
Met. Table 1 shows properties of the water absorbent resin (I-2).

Example 3 In Example 1, the amount of the water-absorbent resin fine powder (B-1) added was 975 g, and the time of addition of the water-absorbent resin fine powder (B-1) was 14 The same operation as in Example 1 was repeated, except that the continuous charging was continued for 10 minutes after 10 minutes. In addition, the water-absorbent resin hydrate gel (A-
The polymerization rate of 3) is 95.9%, the average particle diameter is 3.6 mm (the average particle diameter when dried is 2.6 mm), and the water content is 6
1.1% by weight, temperature 86 ° C. After completion of the introduction, the mixture was further continued to be mixed under a shearing force for 5 minutes, whereby the hydrogel (A-3) was further subdivided. At the end of the mixing, the temperature in the system was 80 ° C. 150 ° C.
After increasing the polymerization rate of the water-absorbent resin hydrogel (A-3) by drying with hot air for 2 hours under the temperature conditions described above, pulverization and classification were performed in the same manner as in Reference Example 1 to obtain a water-absorbent resin (I-3). Was.
The polymerization rate of the water absorbent resin (I-3) was 99.97%. Table 1 shows properties of the water absorbent resin (I-3).

Example 4 In a 10-liter jacketed stainless steel double-arm kneader having two sigma-type blades and an inner volume of 10 liters, 4400 g of an aqueous solution of a monomer component composed of 75 mol% of sodium acrylate and 25 mol% of acrylic acid was added. (Concentration of monomer component 3
7% by weight) and 1.13 g of N, N'-methylenebisacrylamide (0.04 mol% based on the monomer component) as a crosslinking agent, and nitrogen gas was blown into the reaction system to replace the inside of the reaction system with nitrogen. Next, while rotating the two sigma-type blades and heating the reaction system by passing warm water of 30 ° C. through the jacket, 1.10 g of sodium persulfate and 1.10 g of sodium bisulfite were added as initiators. did. After the polymerization is started, the water-absorbent resin fine powder (B-2) is passed through the water-absorbent resin hydrogel (A-4) 25 minutes later. The pre-classified water-absorbent resin powder in Reference Example 1 passes through a 200 mesh wire mesh. 490 g of a powder having a particle diameter of 1 to 75 μm and an average particle diameter of 65 μm] was continuously charged over 6 minutes and mixed with the water-absorbent resin hydrogel (A-4). The polymerization rate of the water-absorbent resin-containing gel (A-4) at the start of charging was 9
8.0%, average particle size 0.7 mm (average particle size 0.5 mm when dried), water content 60.5% by weight,
The temperature was 69 ° C. After the end of the charging, 6
By continuing the mixing for minutes, the hydrogel (A-4)
It was further subdivided. At the end of mixing, the temperature in the system is 62 ° C
Met. The obtained polymer gel was dried with hot air at 150 ° C. for 2 hours to increase the polymerization rate of the water-absorbent resin hydrogel (A-4), and then pulverized and classified in the same manner as in Reference Example 1. Water-absorbing resin (I-4) was obtained. The polymerization rate of the water absorbent resin (I-4) was 99.94%. Table 1 shows properties of the water absorbent resin (I-4).

REFERENCE EXAMPLE 2 In the same manner as in Reference Example 1, 4400 g of an aqueous solution of a monomer component having the same composition as used in Reference Example 1 and N, N'-methylenebisacrylamide as a crosslinking agent 4.2
5 g (0.15 mol% relative to the monomer component) was added, and polymerization was performed in the same manner as in Reference Example 1. The aqueous monomer solution produced a soft hydrogel as the polymerization proceeded, and was gradually subdivided by the rotation of the blades. Thirty minutes after the start of the polymerization, the hydrogel polymer was finely divided into an average particle diameter of about 5 mm. The obtained polymer gel was dried with hot air on a wire mesh at a temperature of 150 ° C. for 2 hours. This dried product is pulverized using a hammer mill equipped with a 15 mm screen,
By classifying with a 10.5 mesh wire mesh, a water-absorbent resin powder for reference (2) was obtained.

Example 5 In Reference Example 2, the water-absorbent resin hydrogel (A-5) 7 minutes after the start of the polymerization reaction was added to the water-absorbent resin fine powder (B-3).
[The particle diameter of the water-absorbent resin powder before classification in Reference Example 2 obtained by passing the powder through a 32 mesh wire mesh is 1 to 500 µm.
m, powder having an average particle diameter of 290 μm] The same operation as in Reference Example 2 except that 590 g is continuously charged over 8 minutes and mixed with the water-absorbent resin hydrogel (A-5) during the polymerization reaction. Was repeated. The polymerization rate of the water-absorbent resin-containing gel (A-5) at the start of charging was 86.4%, and the average particle diameter was 1
5 mm (average particle diameter 11 mm when dried),
The water content was 62.4% by weight, and the temperature was 75 ° C. After the addition, the hydrogel (A-5) was further subdivided by continuing mixing under a shearing force for 10 minutes. At the end of the mixing, the temperature in the system was 74 ° C. The obtained polymer gel was dried with hot air at a temperature of 150 ° C. for 2 hours to increase the polymerization rate of the water-absorbent resin hydrogel (A-5), and then pulverized and classified in the same manner as in Reference Example 1. Water absorbent resin (I
-5) was obtained. The polymerization rate of this water-absorbing resin (I-5) is 9
9.97%. Table 1 shows properties of the water absorbent resin (I-5).

Example 6 The same procedure as in Reference Example 1 was carried out except that the water-absorbent resin hydrogel (A-6) was added to the water-absorbent resin fine powder (B-1) 5 minutes after the initiation of the polymerization reaction.
[The water absorbent resin powder before classification in Reference Example 1 was 100
Particle size obtained by passing through a mesh wire mesh is 1 to 149
powder having an average particle diameter of 95 μm] and the same operation as in Reference Example 1 except that 325 g is continuously charged over 5 minutes and mixed with the water-absorbent resin hydrogel (A-6) during the polymerization reaction. Was repeated. The polymerization rate of the water-absorbent resin-containing gel (A-6) at the start of the introduction was 74.2%, and the average particle diameter was 3%.
5 mm (average particle diameter of 25 mm when dried),
The water content was 61.8% by weight and the temperature was 62 ° C. After the addition, the hydrogel (A-6) was further subdivided by continuing mixing under a shearing force for 10 minutes. At the end of the mixing, the temperature in the system was 60 ° C. The resulting polymer gel was dried with hot air at a temperature of 150 ° C. for 2 hours to increase the polymerization rate of the water-absorbent resin hydrogel (A-6), and then pulverized and classified in the same manner as in Reference Example 1. Water absorbent resin (I
-6) was obtained. The polymerization rate of this water-absorbing resin (I-6) is 9
9.96%. Table 1 shows properties of the water absorbent resin (I-6).

Example 7 In the same manner as in Reference Example 1, 4400 g of an aqueous solution of a monomer component composed of 75 mol% of sodium acrylate and 25 mol% of acrylic acid (concentration of monomer component: 20% by weight) was placed in a double-arm kneader. And 2.30 g of N, N'-methylenebisacrylamide as a cross-linking agent (0.15 mol% based on monomer components)
And the inside of the reaction system was purged with nitrogen by blowing nitrogen gas. Then, while rotating the two sigma type blades and heating the inside of the reaction system by passing warm water of 40 ° C. through the jacket, sodium persulfate 1.10 was used as an initiator.
g and 1.10 g of sodium bisulfite were added. The aqueous monomer solution formed a soft hydrogel as the polymerization proceeded, and was gradually subdivided by the rotation of the blades. After the polymerization starts, the water-absorbent resin fine powder (B-1) is passed through the water-absorbent resin hydrogel (A-7) 35 minutes later. The water-absorbent resin powder before classification in Reference Example 1 is passed through a 100-mesh wire mesh. The particle size obtained by the above is 1 to 149 μm, and the average particle size is 95 μm.
The same operation as in Reference Example 1 was repeated except that 1730 g of the powder was continuously charged over 15 minutes and mixed with the water-absorbent resin hydrogel (A-7) during the polymerization reaction. In addition,
The polymerization rate of the water-absorbent resin water-containing gel (A-7) at the start of charging was 97.8%, the average particle size was 1.8 mm (average particle size in a dry state, 1.1 mm), and the water content was 80.2. Wt%, temperature 45 ° C. After completion of the addition, the mixture is further mixed for 30 minutes under a shearing force to thereby obtain a hydrogel (A-7).
Was further subdivided. At the end of mixing, the temperature in the system is 4
It was 0 ° C. The resulting polymer gel was dried with hot air at a temperature of 150 ° C. for 2 hours to increase the polymerization rate of the water-absorbent resin hydrogel (A-7), and then pulverized and classified in the same manner as in Reference Example 1. A water-absorbing resin (I-7) was obtained. The polymerization rate of this water absorbent resin (I-7) was 99.95%.
Table 1 shows properties of the water absorbent resin (I-7).

Example 8 In the same manner as in Reference Example 1, 4000 g of an aqueous solution of a monomer component composed of 55 mol% of sodium acrylate and 45 mol% of acrylic acid (concentration of the monomer component was 48% by weight) in a double-arm kneader. And 3.42 g of N, N'-methylenebisacrylamide as a cross-linking agent (0.10 mol% based on monomer components)
And the inside of the reaction system was purged with nitrogen by blowing nitrogen gas. Then, while rotating the two sigma-type blades and passing warm water of 15 ° C. through the jacket, 0.69 g of sodium persulfate and 0.1% of sodium bisulfite were used as initiators.
69 g were added. The aqueous monomer solution formed a soft hydrogel as the polymerization proceeded, and was gradually subdivided by the rotation of the blades. After the polymerization is started, the water-absorbent resin fine powder (B-1) is passed through the water-absorbent resin hydrogel (A-8) 20 minutes later. The water-absorbent resin powder before classification in Reference Example 1 is passed through a 100-mesh wire mesh. Particle size obtained by letting it be 1 to 149 μm
In the same manner as in Reference Example 1 except that 190 g of powder having an average particle diameter of 95 μm] is continuously charged over 5 minutes and mixed with the water-absorbent resin hydrogel (A-8) during the polymerization reaction. Repeated. The polymerization rate of the water-absorbent resin-containing gel (A-8) at the start of charging was 98.7%, and the average particle size was 5.3.
mm (average particle size of 4.1 mm when dried),
The water content was 52.3% by weight and the temperature was 90 ° C. After the addition, the hydrogel (A-8) was further subdivided by continuing mixing for 15 minutes under a shearing force. At the end of the mixing, the temperature in the system was 86 ° C. The obtained polymer gel was dried with hot air at a temperature of 150 ° C. for 2 hours to increase the polymerization rate of the water-absorbent resin hydrogel (A-8), and then pulverized and classified in the same manner as in Reference Example 1. Water absorbent resin (I
-8) was obtained. The polymerization rate of this water absorbent resin (I-8) is 9
9.98%. Table 1 shows properties of the water absorbent resin (I-8).

Example 9 To 100 parts by weight of the water-absorbent resin (I-1) obtained in Example 1, an aqueous liquid composed of 0.5 part of glycerin, 2 parts of water and 0.5 part of isopropyl alcohol was added as a crosslinking agent. And mixed with a screw mixer, and the resulting mixture was heated to 200 ° C.
The water-absorbent resin (II-1) was obtained by performing a crosslinking reaction by heating in a dryer for 20 minutes. Water absorbent resin (II
Table 1 shows the performances of -1).

Example 10 The water-absorbent resin (I-1) obtained in Example 1 was further treated with 10
The particles were classified using a 0-mesh wire mesh (150 μm mesh), and the water-absorbing resin (I-
1 ') An aqueous liquid comprising 1 part of trimethylolpropane as a crosslinking agent, 4 parts of water and 1 part of ethanol was added to 100 parts by weight, and the jacket was charged into a ribbon blender heated to 190 ° C. with a heating medium and heated for 30 minutes. By mixing, a crosslinking reaction was carried out to obtain a water absorbent resin (II-2). Table 1 shows properties of the water absorbent resin (II-2).

Example 11 An aqueous liquid comprising 0.05 parts of ethylene glycol diglycidyl ether, 8 parts of water and 1 part of methanol as a crosslinking agent was added to 100 parts by weight of the water-absorbent resin (I-2) obtained in Example 2. Each of them was quantitatively and continuously supplied to a paddle dryer heated by a heating medium at 150 ° C., mixed and heated to perform a crosslinking reaction, thereby obtaining a water-absorbent resin (II-3). Water absorbent resin (II-
Table 1 shows the performances of 3).

Example 12 In Reference Example 1, the water-absorbent resin hydrogel (A-9) was added 18 minutes after the initiation of the polymerization reaction, and the water-absorbent resin fine powder (B-
4) [Water absorbent resin (II-1) obtained in Example 9]
Is a powder having a particle diameter of 1 to 149 µm and an average particle diameter of 75 µm obtained by passing through a 100 mesh wire mesh] 32
The same operation as in Reference Example 1 was repeated except that 5 g was continuously charged over 5 minutes and mixed with the water-absorbent resin hydrogel (A-9) during the polymerization reaction. The polymerization rate of the water-absorbent resin water-containing gel (A-9) at the start of charging was 96.7%, the average particle diameter was 2.4 mm (average particle diameter in a dry state, 1.7 mm), and the water content was 61. 0.2% by weight, temperature 80 ° C. After the addition, the hydrogel (A-9) was further subdivided by continuing mixing under a shearing force for 10 minutes. At the end of the mixing, the temperature in the system was 76 ° C. The resulting polymer gel was dried with hot air at 150 ° C. for 2 hours to increase the polymerization rate of the water-absorbent resin hydrogel (A-9), and then pulverized in the same manner as in Reference Example 1 to obtain a 20-mesh mesh. The resulting mixture was classified with a metal mesh (aperture: 850 μm) to obtain a water-absorbent resin (I-9). The polymerization rate of the water absorbent resin (I-9) was 99.95%. Next, the water absorbent resin (I
-9) 100 parts by weight of glycerin 0.5 as a crosslinking agent
, 2 parts of water and 0.5 parts of isopropyl alcohol, and mixed by a screw-type mixer. The resulting mixture was placed in a drier at 200 ° C. and heated for 20 minutes to form a water-absorbent resin ( II-4) was obtained. The water absorbent resin (II
-4) was classified using a 100-mesh wire mesh (mesh size: 149 μm), and the resin remaining on the 100-mesh wire mesh was designated as a water-absorbent resin (II-4 ′). Water absorbent resin (II-4 ')
Are shown in Table 1.

Comparative Example 1 1600 g of the dried product in Reference Example 1 was returned to the double-arm kneader of the reactor, and 2600 g of deionized water at 98 ° C. was added and heated to uniformly swell. The obtained water-absorbent resin hydrogel (A-10) has a polymerization rate of 99.95%, an average particle diameter of 1.9 mm (average particle diameter when dried), and a water content of 61.9% by weight. And the temperature was 78 ° C. Example 1 was prepared using the water-absorbent resin hydrogel (A-10).
325 g of the same water-absorbent resin fine powder (B-1) as used in
For 5 minutes, and the water-absorbent resin hydrogel (A-
10). At the end of the mixing, the temperature in the system was 75 ° C. The obtained polymer gel was dried in the same manner as in Reference Example 1,
By performing pulverization and classification, a comparative water-absorbent resin (I) was obtained. The polymerization rate of this dried product was 99.96%. Table 1 shows various properties of the comparative water absorbent resin (I).

Comparative Example 2 250 g of the same water-absorbent resin fine powder (B-1) as used in Example 1 was added to 750 g of pure water and kneaded.
An integrated continuous rice cake-like swollen hydrogel was obtained. This hydrogel was finely torn and left in a drier at 95 ° C. for 3 hours to dry. This dried product was pulverized under the same conditions as in Reference Example 1,
After classification, a comparative water-absorbent resin powder (2) was obtained. Table 1 shows properties of the comparative water-absorbent resin powder (2).

Comparative Example 3 500 g of the water-absorbent resin fine powder (B-1) used in Example 1 was added to 1000 g of pure water and kneaded to obtain an integrated continuous rice cake-like swollen hydrogel. . This was finely divided using a meat chopper, 1000 g of the finely divided gel obtained and 4000 g of the hydrogel polymer obtained in Reference Example 1 were mixed by hand, and dried and pulverized in the same manner as in Reference Example 1. By performing the classification, a comparative water-absorbent resin powder (3) was obtained. Table 1 shows properties of the comparative water-absorbent resin powder (3).

Comparative Example 4 The reference water-absorbent resin powder (1) obtained in Reference Example 1 was
Classification was performed using a 00 mesh wire mesh. Powders passing through a 100-mesh wire net and powders remaining on the 100-mesh wire net were mixed to obtain a water-absorbent resin powder A having 15% of particles of 1 to 149 μm. After 100 parts of the water-absorbent resin powder A and 5 parts of water are uniformly mixed using a sand turbo (manufactured by Hosokawa Micron Corporation), the mixture is pulverized and granulated using a flash mill (manufactured by Fuji Paudal Co., Ltd.) and used for comparison. Water-absorbing resin (4) was obtained. Table 1 shows the properties of the comparative water absorbent resin (4).
It was shown to.

Comparative Example 5 An aqueous liquid in which 7.5 g of ethylene glycol diglycidyl ether was dissolved in 500 g of pure water and 500 g of the water-absorbent resin fine powder (B-1) used in Example 1 were kneaded using a kneader. As a result, an integrated gel-like hydrate was obtained. The hydrous gel was finely crushed in a kneader to obtain a gel having a water content of 49.5% by weight and an average particle diameter of 2.5 mm (average particle diameter of 2.0 mm when dried). The obtained gel was dried with hot air at a temperature of 90 ° C. for 2 hours and pulverized and classified in the same manner as in Reference Example 1 to obtain a comparative water absorbent resin (5). Table 1 shows various properties of the comparative water absorbent resin (5).
It was shown to.

Comparative Example 6 1 part of trimethylolpropane as a crosslinking agent and 100 parts of water were added to 100 parts by weight of the comparative water-absorbent resin (2) obtained in Comparative Example 2.
And an aqueous liquid composed of 1 part of ethanol, and the jacket was placed in a ribbon blender heated to 190 ° C. with a heating medium, and heated and mixed for 30 minutes. ) Got. Table 1 shows properties of the comparative water absorbent resin (6).

Comparative Example 7 In the same manner as in Reference Example 1, the water-absorbent resin hydrogel (A-11) two minutes after the initiation of the polymerization reaction was added to the water-absorbent resin fine powder (B-
1) The same operation as in Reference Example 1 was repeated except that 325 g was continuously charged over 10 minutes and mixed with the water-absorbent resin hydrogel (A-11) during the polymerization reaction. In addition, the polymerization rate of the water-absorbent resin hydrogel (A-11) at the start of charging was 3
0.5%, average particle diameter 40 mm (average particle diameter 29 mm when dried), water content 61.3% by weight, temperature 4
2 ° C. After completion of the introduction, the hydrogel (A-11) was further subdivided by continuing mixing for 15 minutes under a shearing force. The obtained polymer gel was dried with hot air at a temperature of 150 ° C. for 2 hours and pulverized in the same manner as in Reference Example 1.
Classify with a 0-mesh wire mesh and compare water-absorbent resin (7)
I got The polymerization rate of this comparative water-soluble resin (7) is 99.
It was 50%. Table 1 shows properties of the comparative water-absorbent resin powder (7).

Comparative Example 8 In Example 1, the addition amount of the water-absorbent resin fine powder (B-1) was changed to 4400 g, and the water-absorbent resin fine powder (B-
The addition time of 1) is changed from 15 minutes after the start of the polymerization reaction to 15 minutes.
The same operation as in Example 1 was repeated except that the continuous charging was performed for 0 minutes. In addition, the polymerization rate of the water-absorbent resin hydrogel (A-12) at the start of charging was 92.3%, and the average particle diameter was 5.
2 mm (average particle diameter of 3.7 mm when dried),
The water content was 61.8% by weight and the temperature was 82 ° C. After the end of the dosing, by further mixing for 2 minutes under shearing force,
The hydrogel (A-12) was further subdivided. At the end of the mixing, the temperature in the system was 78 ° C. The obtained polymer gel was dried with hot air at 150 ° C. for 2 hours to increase the polymerization rate of the water-absorbent resin hydrogel (A-12), and then pulverized and classified in the same manner as in Reference Example 1 for comparison. Water absorbent resin (8) was obtained. The polymerization rate of this comparative water absorbent resin (8) was 99.95%. Table 1 shows properties of the comparative water absorbent resin (8).

[0092]

[Table 1]

As is evident from Table 1, the water-absorbent resins (I-1 to I-8) obtained according to the present invention, despite the addition of undesired fine powder having a small particle size during polymerization. Without
It has a strong particle structure, hardly regenerates fine powder or gel derived from fine powder even at impact or swelling due to water absorption, and has a good working environment etc. during factory line, transportation, use of various applications And excellent in various water absorption properties such as absorption capacity, liquid permeability, and diffusivity. In addition, the water-absorbing resin (II-1 to II-
It was confirmed that 4 ′) can maintain its strong particle structure even under the shearing force during swelling, in addition to the above properties.

[0094]

The water-absorbent resin obtained by the method of the present invention has a strong particle structure despite the reuse of fine powder of the water-absorbent resin, and has a strong particle structure even upon impact or swelling due to water absorption. Because the structure can be maintained, it is difficult to regenerate the fine powder even during the factory line, transportation, and use of various applications, not only the working environment etc. can always be good, but also the absorption capacity and liquid permeability It also has excellent water absorption properties such as diffusivity, including hygienic materials, agricultural and horticultural, and industrial water retention agents.
It is very good for use in a wide range of fields.

Continuing from the front page (72) Inventor Yoshio Irie 992, Nishioki, Okihama-shi, Aboshi-ku, Himeji-shi, Hyogo Japan Nippon Shokubai Himeji Laboratory Co., Ltd. (58) Field surveyed (Int. Cl. ⁷ , DB name) C08F 2/00- 2/60

Claims (18)

(57) [Claims] 1. A polymerization rate of 60 to 99% and an average particle diameter of 0.1.
~ 200mm, water content 30 ~ 90% by weight and temperature 40
100 parts by weight of a water-absorbent resin hydrogel (A) obtained by aqueous solution polymerization and having an average particle diameter smaller than the average particle diameter when the water-absorbent resin hydrogel (A) is in a dry state, and having a substantially dry state. Water-absorbent resin fine powder in a state (B)
A method for producing a water-absorbent resin, which comprises mixing 1 to 50 parts by weight of a water-absorbent resin and then increasing the polymerization rate of the water-absorbent resin-containing gel (A) to the polymerization rate at the time of mixing. 2. The water-absorbent resin fine powder (B) has a water content of 0.1%.
The method according to claim 1, wherein the amount is 1 to 10% by weight. 3. The method according to claim 1, wherein the mixing is performed under shear. 4. The method of claim 1 wherein the temperature range is maintained between 50 and 100 ° C. during mixing. 5. The method according to claim 1, wherein the polymerization of the water-absorbent resin hydrogel (A) is carried out using a persulfate as a polymerization initiator. 6. The method according to claim 1, wherein a new polymerization initiator is added during mixing. 7. The method according to claim 1, wherein a water-insoluble particulate inorganic powder is added during mixing. 8. The water-absorbent resin hydrogel (A) is dried after increasing the polymerization rate to at least the polymerization rate at the time of mixing, and then classified and classified into a substantially dry state corresponding to the particle size range of the water-absorbent resin fine powder (B). The method according to claim 1, wherein the water-absorbent resin powder (C) is removed. 9. The method according to claim 8 , wherein the substantially dry water-absorbent resin powder (C) corresponding to the particle size range of the water-absorbent resin fine powder (B) is reused as the water-absorbent resin fine powder (B). . 10. A polymerization degree of 60 to 99%, and an average particle diameter of 0.1.
1 to 200 mm, water content 30 to 90% by weight and temperature 4
100 parts by weight of a water-absorbent resin hydrogel (A) having an aqueous solution polymerization having a temperature of 0 to 110 ° C. and an average particle diameter smaller and substantially smaller than the average particle diameter when the water-absorbent resin hydrogel (A) is dried. Dry water-absorbent resin fine powder (B)
After mixing with 1 to 50 parts by weight, the water-absorbent resin as a base polymer obtained by increasing the polymerization rate of the water-absorbent resin-containing gel (A) to a polymerization rate at the time of mixing or more is used as a crosslinking agent (D). And producing a water-absorbent resin in which the vicinity of the particle surface is cross-linked by mixing and cross-linking reaction. 11. The method according to claim 10 , wherein the water-absorbent resin as the base polymer has a carboxyl group. 12. The method according to claim 11 , wherein the crosslinking agent (D) is a compound capable of reacting with a carboxyl group. 13. The method according to claim 10 , wherein the water content of the water-absorbent resin as the base polymer is 20% by weight or less. 14. The method according to claim 10 , wherein the water-absorbent resin as the base polymer has an average particle size of 200 to 600 μm. 15. The particle size of the water-absorbent resin fine powder (B) from the water-absorbent resin as the base polymer by drying after increasing the polymerization rate of the water-absorbent resin hydrogel (A) to the polymerization rate at the time of mixing and then classification. The method according to claim 10 , wherein the water-absorbent resin powder (C) in a substantially dry state corresponding to the range is removed, and further a crosslinking agent (D) is mixed to carry out a crosslinking reaction. 16. A substantially dry water-absorbent resin powder (C) corresponding to the particle size range of the water-absorbent resin fine powder (B) removed from the water-absorbent resin as a base polymer, 16. The method of claim 15 , wherein the method is reused as (B). 17. A water-absorbent resin powder (C ′) corresponding to the particle size range of the water-absorbent resin fine powder (B) by mixing a water-absorbent resin as a base polymer with a cross-linking agent (D) and performing a cross-linking reaction, followed by classification. 11. The method according to claim 10 , wherein) is removed. 18. The method according to claim 17 , wherein the water-absorbent resin powder (C ′) is reused as the water-absorbent resin fine powder (B).