JPH03179008A - Production of water-absorptive resin of excellent durability - Google Patents

Abstract

PURPOSE:To obtain the title resin excellent in the durability and liquid permeability of a swollen gel and showing a high water absorption rate even to physiologic saline by subjecting an aqueous solution containing a water-soluble, ethylenically unsaturated monomer, a crosslinking agent and a water-soluble chain transfer agent each in a specified amount to aqueous solution polymerization. CONSTITUTION:An aqueous monomer solution of a concentration of from 30wt.% to the saturation concentration containing a water-soluble, ethylenically unsaturated monomer (e.g. acrylic acid/sodium acrylate mixture), 0.005-5mol%, based on this monomer, crosslinking agent (e.g. trimethylolpropane tri-acrylate) and 0.001-1mol%, based on this monomer, water-soluble chain transfer agent (e.g. sodium hypophosphite) is subjected to aqueous solution polymerization.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to a method for producing a water-absorbing resin with excellent durability. More specifically, the present invention relates to a method for producing a water-absorbing resin that has excellent water absorption capacity, water absorption rate, and durability during swelling, has less stickiness in the swollen gel, and has excellent liquid permeability.

Such water-absorbing resins are not only cheap and easy to produce and have excellent safety, but also have excellent water-absorbing ability, so they can be used as sanitary materials such as sanitary products and disposable diapers, and as water-retaining agents for agriculture, horticulture, and greening. Furthermore, it can be widely used as a material for a wide range of absorbent articles.

[Conventional technology]

In recent years, water-absorbing resins that absorb several tens to hundreds of times their own weight in water have been developed and are widely used in the fields of impact, such as disposable diapers and sanitary napkins, as well as in the fields of agriculture, forestry, and civil engineering.

Examples of such water-absorbing resins include crosslinked partially neutralized polyacrylic acid (Japanese Patent Application Laid-open No. 84304/1983), starch-
Hydrolyzate of acrylonitrile graft polymer (Japanese Patent Publication No. 49-43395), neutralized product of starch-acrylic acid ester copolymer (Japanese Patent Publication No. 51-125468), saponification of vinyl acetate-acrylic acid ester copolymer Things (Unexamined Japanese Patent Publication No. 5
2-14689), hydrolyzate of acrylonitrile copolymer or acrylamide copolymer (Japanese Patent Publication No. 1983-
No. 15959) or crosslinked products thereof are known.

Desired properties for these water-absorbing resins include high absorption capacity and excellent water absorption speed when in contact with aqueous liquids, and excellent suction power for sucking up liquids from substrates containing aqueous liquids.

However, depending on the use of the water-absorbing resin, durability and stability over time of the swollen gel are required in addition to the above-mentioned properties. For example, when conventional water-absorbing resins are used as sanitary materials such as disposable diapers, the swollen gel of the water-absorbing resin that absorbs urine deteriorates and decomposes over time. It deteriorated with use and could cause decomposition.

Deterioration of the swelling gel of water-absorbing resin, which has been known so far,
A method for preventing decomposition is to add oxygen-containing reducing inorganic salts, radical chain inhibitors, etc. to the water-absorbing resin (JP-A-63-118375, JP-A-63-152667).
, a method of containing an oxidizing agent (Japanese Patent Application Laid-Open No. 63-153060
No.), a method of incorporating a sulfur-containing reducing agent (Japanese Patent Application Laid-open No. 1983-
272349). However, all of these methods involve adding additives to the water-absorbing resin to prevent deterioration, and adding other additives means
Considering that these water-absorbing resins are used for sanitary materials and the like, they are not necessarily desirable from the standpoint of safety.

Therefore, there is a method to increase the gel strength and improve the durability by increasing the crosslinking density of the water-absorbing resin by using a large amount of cross-linking agent, but in order to have sufficient durability, these water-absorbing resins must be highly cross-linked. Therefore, the actual situation was that the water absorption capacity was extremely low.

As described above, at present, a water-absorbing resin with excellent safety, high water absorption capacity, and excellent durability has not been obtained.

In addition to the above-mentioned durability, problems such as stickiness of the swollen gel and decreased liquid permeability may arise when the gel is incorporated into a diaper or the like. Water-absorbing resin has a water-soluble portion (hereinafter referred to as water-soluble portion), and because of these water-soluble portions, the swollen gel may become sticky after absorbing water, and may be difficult to absorb on absorbent articles such as diapers. When incorporated, this stickiness reduces fluid permeability and may cause leakage when new urine is excreted. The water-soluble content generally has a positive correlation with the water absorption capacity, and in order to reduce the water-soluble content, it is necessary to increase the crosslinking density of the water-absorbing resin. The reality is that the water absorption capacity also decreases.

However, it is well known that the greater the amount of crosslinking agent blended in such water-absorbing resins, the better the durability, but the problem is that the water absorption capacity decreases as the amount of crosslinking agent increases. there were.

Furthermore, a technique has been disclosed in which the water absorption capacity is improved by using a chain transfer agent during the production of a water absorbent resin. (U
S P 4698404). However, in this case, although the water absorption capacity for water and physiological saline is certainly improved, there is almost no increase in the water absorption capacity for human urine.

[Problem to be solved by the invention]

The present invention has been made in view of the above-mentioned current situation.

Therefore, an object of the present invention is to provide a method for producing a water-absorbing resin with excellent durability.

Another object of the present invention is to exhibit a high water absorption capacity for both physiological saline and especially human urine, to exhibit excellent durability when used in disposable diapers, and to reduce the amount of water returned by the diaper. It is an object of the present invention to provide a method for producing a water-absorbing resin which has less sticky feeling and has excellent liquid permeability.

[Means and effects for solving the problem] The present inventors,
As a result of intensive studies to solve the above problems, we found that (1) specific amounts of crosslinking agent (B) and water-soluble chain transfer agent (C1)
By polymerizing a water-soluble ethylenically unsaturated monomer (A) aqueous solution containing the following in a specific concentration range, durability is improved while maintaining a high water absorption capacity, and the molecular weight of the water-soluble component is reduced. (2) Furthermore, the water-absorbing resin (D) obtained by the production method of (1) above can be obtained with good productivity, and the sticky feeling and liquid permeability of the gel are also improved as the gel decreases. By cross-linking the vicinity of the surface of D) with a hydrophilic cross-linking agent (E), an even more excellent effect of improving water absorption properties is exhibited, and while maintaining a high water absorption capacity, the gel becomes more durable, has a sticky feel, and has improved liquid permeability. Water-absorbing resin with improved water-absorbing properties (
The present invention was completed based on the discovery that F) can be obtained.

That is, the present invention provides +7 water-soluble ethylenically unsaturated monomers (Al and the monomers (
3 containing 0.005 to 5 mol% of the crosslinking agent (B) and 0.001 to 1 mol% of the water-soluble chain transfer agent (C) based on A).
The monomer (A) aqueous solution with a concentration of 0% by weight to saturation is
A method for producing a water-absorbing resin (D) with excellent durability, which is characterized by carrying out aqueous solution polymerization.

and a water-soluble ethylenically unsaturated monomer (A) and the monomer (
3 containing a crosslinking agent (BIo, 005 to 5 mol%, and a water-soluble chain transfer agent (C) 0.001 to 1 mol%, based on A).
The monomer (A) aqueous solution with a concentration of 0% by weight to saturation is
, a water absorbent with excellent durability characterized by crosslinking the surface vicinity of the water absorbent resin (D) obtained by aqueous solution polymerization with a hydrophilic crosslinking agent (E) that can react with a functional group in the water absorbent resin. Method for producing resin (F).

It is related to.

The present invention will be explained in more detail.

Water-soluble ethylenically unsaturated monomer (A) used in the present invention
Hereinafter, the monomer (A)) is one having a functional group, such as acrylic acid, methacrylic acid, maleic acid, fumaric acid, crotonic acid, itaconic acid, vinylbenzenesulfonic acid, 2-(meth)acrylamide- 2-methylpropanesulfonic acid 2-(meth)acryloylethanesulfonic acid, 2-(meth)acryloylpropanesulfonic acid, and their alkali metal salts, ammonium salts, acrylamide, methacrylamide, 2-hydroxyethyl (meth)acrylate, Methoxypolyethylene glycol (meth)acrylate, N, N-dimethylaminoethyl (meth)acrylate, N.

N-diethylaminopropyl (meth)acrylate,
Examples include N,N-diethylaminopropyl (meth)acrylamide and quaternary salts thereof, and at least one selected from these groups can be used.

Among the above monomers (A), it is preferable to use acrylic acid as the main component from the viewpoint of the performance and cost of the resulting water absorbent resin, and in this case, acrylic acid and its alkali salts and/or The content of ammonium salt is preferably 50% by weight or more in the monomer (A),
More preferably, the content is 75% by weight or more.

Further, in the present invention, in order to obtain a water-absorbing resin with excellent durability, it is essential to use a specific amount of a crosslinking agent CB) having two or more polymerizable unsaturated groups or reactive functional groups in the molecule.

Examples of these crosslinking agents (B) include compounds having two or more polymerizable unsaturated groups in the molecule, such as N, N'
- Methylene bisacrylamide, (poly>ethylene glycol di(meth)acrylate, (poly)brobylene glycol di(meth)acrylate, glycerin tri(
Examples include meth)acrylate, glycerin acrylate methacrylate, (meth)acrylic acid polyvalent metal salt trimethylolpropane tri(meth)acrylate, triallylamine, triallyl cyanurate, triallyl isocyanurate, triallyl phosphate, and the like.

Examples of those having reactive functional groups include polyhydric alcohols such as monomeric glycol, diethylene glycol, triethylene glycol, polyethylene glycol, propylene glycol, dipropylene glycol, polypropylene glycol, and glycerin: (poly)ethylene Polyvalent glycidyl compounds such as glycol diglycidyl ether and glycerol polyglycidyl ether; polyvalent amines such as ethylenediamine and polyethyleneimine;
In addition, there are polyvalent oxazoline compounds, haloepoxy compounds, polyvalent incyanates, polyvalent metal salts, etc. Also, compounds having both a polymerizable unsaturated group and a reactive functional group in the molecule include glycidyl (meth)acrylate, N -Methylol (meth)acrylamide etc. can be exemplified.

Among these crosslinking agents (B), it is particularly preferable to use a compound having two or more polymerizable unsaturated groups in the molecule from the viewpoint of the durability and water absorption characteristics of the resulting water absorbent resin.

The amount of these crosslinking agents (B) used in the present invention is determined by adjusting the amount of the water-soluble chain transfer agent (
Compared to the amount of crosslinking agent used under the same conditions except that C) is not used, the amount is 2 to 100 times, more preferably 4 to 1
It is 0 times the mole. Specifically, the amount of the crosslinking agent (B) used is 0.005 to 5 mol% based on the monomer (A). If the amount of crosslinking agent (B) used is less than 0.005 mol%, the resulting water absorbent resin will have a high water absorption capacity, but will have poor durability, and will have a large amount of water-soluble bone and a high molecular weight. The gel becomes sticky and has poor liquid permeability. Moreover, if it is used in an amount exceeding 5 mol %, the water absorption capacity becomes extremely low. The amount of the crosslinking agent used depends on the amount of the water-soluble chain transfer agent (C) described below, but is preferably 0.02 to 1 mol%, more preferably 0.04 to 1 mol%.
0.4 mol%, even more preferably 0.08 to 0
．． It is 2 mol%.

In addition to the above-mentioned crosslinking agent (B), a method of forming crosslinks by graft polymerization may be used in combination. As such a method, an aqueous monomer (A) solution is polymerized in the presence of a hydrophilic polymer such as cellulose, starch, or polyvinyl alcohol,
Examples include a method of forming crosslinks due to graft polymerization during polymerization, and these water-soluble polymers are preferably used in an amount of 1 to 50% by weight based on the monomer (A).

In the present invention, a specific amount of water-soluble chain transfer agent (C) is used, a specific amount of water-soluble chain transfer agent (C) is selected, and compared to the usual manufacturing method,
By using a large amount of cross-linking agent (100 times the mole) and performing polymerization as a highly cross-linked polymer, it has excellent durability, exhibits a high water absorption capacity not only for physiological saline but also for human urine, and has a high water-soluble content. Because of its low molecular weight, it is possible to obtain an excellent water-absorbing resin that has few negative effects such as a sticky gel feel or a decrease in legality.

The water-soluble chain transfer agent (C) used in the present invention is not particularly limited as long as it dissolves in water or a water-soluble ethylenically unsaturated monomer, and includes thiols, thiol acids,
alcohols, amines, hypophosphites, etc., specifically mercaptoethanol, mercaptopropanol, dodecylmercaptan, thioglycolic acid, thiomalic acid, 3-mercaptopropionic acid,
Isopropanol, sodium hypophosphite, formic acid, and their salts are used, and one or more types selected from these groups are used, but hypophosphites such as sodium hypophosphite are used due to their effectiveness. It is preferable.

The amount of water-soluble chain transfer agent (C) used depends on the type and amount of water-soluble chain transfer agent used, and the concentration of the monomer (A) aqueous solution.
The amount is 0.00] to 1 mol %, preferably 0.005 to 0.3 mol %, based on the monomer (A), which is not preferable because the water absorption capacity becomes too low.

Moreover, if it is used in an amount exceeding 1 mol %, the water-soluble content will increase and the durability will actually decrease, which is not preferable.

The monomer used in the present invention (A> The concentration of the aqueous solution is in the range of 30% by weight to saturated concentration, more preferably 35% by weight to saturated concentration. At a concentration of 30% by weight, the concentration is in the range of 30% by weight to saturated concentration. This is unfavorable from an industrial point of view because the productivity decreases and the drying process also takes time.

In conventional polymerization methods, when polymerization is performed near saturation concentration to improve productivity, unnecessary reactions such as self-crosslinking occur and the water absorption capacity decreases, which limits the amount of crosslinking agent (B) that can be used during polymerization. Only a water absorbent resin with poor durability was obtained. However, according to the method of the present invention, by selecting the amount of the water-soluble chain transfer agent (C) used, the self-crosslinking reaction is suppressed, and the amount of the crosslinking agent CB) used can be increased, resulting in a high water absorption capacity with excellent durability. Water-absorbing resin can be produced at high concentration and with good productivity.

Further, a thickener may be used in the monomer (A) aqueous solution if necessary. Examples of such thickeners include polyvinylpyrrolidone, polyacrylamide, methylcellulose,
Examples include hydroxyethylcellulose.

In the present invention, known polymerization techniques such as aqueous solution polymerization, reverse phase suspension polymerization, precipitation polymerization, bulk polymerization, ultraviolet ray or electron beam polymerization can be used to polymerize the monomer (A) aqueous solution to obtain the water absorbent resin. Among them, such as polymerization with active energies such as
Aqueous solution polymerization is used as a method to obtain water-absorbing resins that are excellent in terms of performance, productivity, and cost. As a method for carrying out aqueous solution polymerization, for example, cast polymerization carried out in a mold (Tokuko Kouko 4
8-42466), a method of polymerizing on a belt conveyor (JP-A-58-49714), a method of polymerizing in a kneader or the like having stirring blades capable of dividing the hydrogel polymer into small pieces (JP-A-57-1999), 34101), etc. can be exemplified.

When such aqueous polymerization is performed, in order to proceed with a uniform chain transfer reaction using the water-soluble chain transfer agent (C) and a uniform crosslinking reaction using the crosslinking agent (B), to obtain a water absorbent resin with better performance. It is preferable that the heat of polymerization be removed uniformly. For this purpose, rather than using a polymerization method in which the polymer gel is integrated, the polymer gel in the reaction system is stirred during all or part of the time from the start to the end of polymerization, preferably the entire time, to uniformly remove the polymerization heat. Therefore, it is preferable that the polymerization reaction is carried out in a reaction vessel having a rotating stirring blade. There are no particular restrictions on the reaction vessel having a rotating stirring blade, but one that has a large stirring force for the polymer gel is preferable, and examples include a reactor that uses a rotating stirring blade to apply shearing force to the polymer gel that is produced as the polymerization progresses. In addition, in order to increase the stirring power, it is more preferable to use a plurality of rotating stirring blades. Examples of the reactor include a -shaft kneader, a -shaft extruder, a double-arm kneader, and a three-shaft kneader.
Examples include. Further, it is preferable to use a double-arm kneader because the polymerized gel can be finely divided and stirred uniformly throughout the entire polymerization period, and the heat of polymerization can be uniformly removed, resulting in a water-absorbing resin with better performance.

In the present invention, radical polymerization initiators used in aqueous solution polymerization are particularly limited as long as they are water-soluble; hydroperoxides such as hydroperoxide and cumene hydroperoxide; Azo compounds such as (propane) dihydrochloride; others include ceric salts, permanganates, and the like. Among them, from the viewpoint of the performance of the obtained water absorbent resin and the safety of decomposition products,
One or more selected from the group consisting of persulfates, hydrogen peroxide, and azo compounds are preferred.

Further, when the radical polymerization initiator is an oxidizing radical polymerization initiator, it may be used as a redox initiator in combination with a reducing agent. Examples of the reducing agent used include sulfite (hydrogen) salts such as sodium sulfite and sodium hydrogen sulfite; thiosulfates such as sodium thiosulfate; dithionites; metal salts such as cuprous sulfate and ferrous sulfate; Examples include organic reducing agents such as β-ascorbic acid; amines such as aniline and monoethanolamine.

The amount of the radical polymerization initiator used can vary widely, but it is usually preferably in the range of 0.001 to 2 mol%, more preferably 0.0001 to 2 mol%, based on the monomer (A).
It is in the range of 1 to 0.5 mol%. This usage amount is 0.00
If it is less than 1 mol %, the polymerization time and induction period will become long, and the amount of residual monomer will also tend to increase, which is not preferable. In addition, in conventional polymerization methods, increasing the amount of polymerization initiator to reduce residual monomers, shorten the induction period, and shorten polymerization time causes unnecessary reactions such as self-crosslinking and reduces water absorption capacity, so the amount of initiator that can be used is However, according to the method of the present invention, these drawbacks are improved and a high-performance water absorbent resin can be obtained even if the amount of initiator is increased. However, even if it is used in an amount greater than 2 mol %, not only will the effect commensurate with the amount added be small, but it will also become difficult to control the polymerization reaction, which is not preferable.

The water-absorbent resin obtained in the present invention may be polymerized at a high concentration and dried and polymerized simultaneously using the polymerization heat, or depending on the water content after polymerization, the obtained water-containing gel may be further dried to form a water-absorbent resin. May be used as As a drying method, a known drying method can be used, such as a method using azeotropic dehydration in an organic solvent, a forced draft oven, a vacuum dryer, a microwave dryer, an infrared dryer, or a belt heated to a predetermined temperature. Alternatively, a drying method using a drum dryer or the like can be mentioned. If these drying methods are used to heat the hydrogel after polymerization to 80° C. or higher, the hydrophilic resin may deteriorate further, so care must be taken.

In addition, the water-absorbing resin obtained by polymerizing and drying as described above is
It is used after being crushed and/or classified if necessary.

Furthermore, the present invention also provides a method for producing a water absorbent resin (F) in which the vicinity of the surface of the water absorbent resin (D) obtained by the above production method is crosslinked with a specific hydrophilic crosslinking agent (E). Water absorbent resin (D) obtained by the above manufacturing method
shows a remarkable improvement in water absorption properties compared to conventional water absorbent resins, and the water absorbent resin (F) that has been crosslinked near the surface has more durability than the water absorbent resin (CD) that has not been crosslinked near the surface. It has excellent water absorption properties.

The hydrophilic crosslinking agent (E) used in the present invention is a compound (E-1) having two or more functional groups capable of reacting with a carboxyl group in one molecule and/or a polyvalent metal salt (E-1).
2). For example, when the water-absorbing resin (D) has a carboxyl group, the compound (E-1) may include ethylene glycol, diethylene glycol, triethylene glycol, tetraethylene glycol, polyethylene glycol, 1.4-butanediol, 1.5 - Polyhydric alcohol compounds such as bentanediol, 1,6-hexanediol, neopentyl glycol, propylene glycol, glycerin, polyglycerin, trimethylolpropane, pentaerythritol, sorbitol, polyvinyl alcohol; ethylene glycol diglycidyl ether, polyethylene glycol di Polyvalent glycidyl ether compounds such as glycidyl ether, glycerol polyglycidyl ether, diglycerol polyglycidyl ether, polyglycerol polyglycidyl ether, propylene glycol diglycidyl ether, polypropylene glycol diglycidyl ether; ethylene diamine,
Polyvalent amine compounds such as diethylenetriamine, triethylenetetramine, polyethyleneimine; polyvalent oxazoline compounds such as 1,2-ethylenebisoxazoline and polyisopropenyloxazoline; haloepoxy compounds such as shrimp chlorohydrin; other polyvalent aziridine compounds, Examples include polyvalent incyanate compounds, and examples of the polyvalent metal salt (E-2) include hydroxides and chlorides of zinc, calcium, magnesium, aluminum, iron, zirconium, and the like. It is preferable to use one or more types from these groups, and among them, compound (E-1)
It is preferable to essentially use polyvalent alcohols, polyvalent glycidyl compounds, and polyvalent amines as the hydrophilic crosslinking agent (E) from the viewpoint of the surface crosslinking effect. In addition, as a hydrophilic crosslinking agent (E), compound (E-1
> and a polyvalent metal salt (E-2) may be used in combination to improve the miscibility.

The amount of the hydrophilic crosslinking agent (E) used in the present invention is 0.005 to 5 parts by weight, preferably 0.005 to 5 parts by weight, based on 100 parts by weight of the water absorbent resin (D) obtained by the above manufacturing method ．．
If the amount of the proportionate crosslinking agent (E) in the range of 0.01 to 1 part by weight exceeds 5 parts by weight, it will not only be uneconomical, but also unreacted hydrophilic crosslinking agent (E) will be used in the obtained water absorbent resin ( In addition to the possibility that the water-absorbing resin (F) may remain in the water-absorbing resin (F), an excessive amount of the water-absorbing resin (F) to achieve an appropriate crosslinking effect will reduce the water absorption capacity of the water-absorbing resin (F), which is not preferable. Furthermore, if the amount is as small as less than 0,005 parts by weight, it is difficult to obtain the effects of the present invention.

In the present invention, water absorbent resin (D) and hydrophilic crosslinking agent (E)
When mixing with water and/or hydrophilic organic solvent (G)
may also be used.

In the present invention, the amount of water used is 1 d of water absorbent resin (D)
20 parts by weight per 900 parts by weight, preferably 0°5-1
The proportion is in the range of 0 parts by weight.

Further, as the hydrophilic organic solvent (G), for example, methanol,
Lower alcohols such as ethanol, n-propertool, 1so-propertool, n-butanol, 1so-butanol, t-butanol; Ketones such as acetone, methyl ethyl ketone, methyl butyl ketone; Ethers such as dioxane, tetrahydrofuran, N , amides such as N-dimethylformamide; and sulfoxides such as dimethyl sulfoxide; the amount used is 0 to 20 parts by weight, preferably 0 to 8 parts by weight, based on 100 parts by weight of the water absorbent resin (D). This is the percentage of the range.

In the present invention, the water absorbent resin (D) is mixed with a hydrophilic crosslinking agent (E).
Examples of methods for crosslinking near the surface of the water absorbent resin include the following methods.

(+) A method of spraying or dropwise mixing a liquid mixture of a hydrophilic crosslinking agent (ε) and, if necessary, water (steam) and/or a hydrophilic organic solvent (G), onto the water absorbent resin (D).

Or, (II) the water absorbent resin (D) is dispersed/suspended in a polymerization-inactive hydrophobic organic solvent, and the hydrophilic crosslinking agent (E) and, if necessary, water and/or the hydrophilic organic solvent (G) are added. A method of adding under stirring.

In this case, a method of emulsifying and suspending the hydrophilic crosslinking agent (E) in a hydrophobic organic solvent using a specific surfactant in advance and adding the emulsion to a dispersion suspension of the water absorbent resin CD) is preferred.

Or (m) water absorbent resin (D) is mixed with water and hydrophilic organic solvent (G
) is dispersed in a mixed solvent and a hydrophilic crosslinking agent (E) is added.

Examples include.

A mixture obtained by mixing the water absorbent resin (D) obtained by the method of the present invention with the hydrophilic crosslinking agent (E) and, if necessary, water and/or a hydrophilic organic solvent (G) as described above. For heat treatment, a normal heater or heating furnace can be used. Examples include a groove-type stirring dryer, a rotary dryer, a disc dryer, a wet dryer, a fluidized bed dryer, a flash dryer, an infrared dryer, a dielectric heating dryer, and the like. Also (I
After adding the hydrophilic crosslinking agent (E) to the water-absorbing resin (Dl) in an organic solvent by method I), the mixture may be directly heated and reacted in the organic solvent.

Although the heat treatment temperature depends on the type of hydrophilic crosslinking agent (E) used, it is preferably in the range of 40 to 250°C, more preferably in the range of 90 to 220°C.

If it is lower than 40°C, not only will the reaction take a long time and productivity will decrease, but also a portion of the hydrophilic crosslinking agent (E) may become unreacted and remain in the resulting water absorbent resin (F), which is not preferable. . At high temperatures exceeding 250℃, water absorbent resin fD
) Please note that thermal deterioration may occur depending on the type of material.

Incidentally, the surface-crosslinked water-absorbing resin (F) or the surface-uncrosslinked water-absorbing resin (D) may be crushed and granulated if necessary.

[Effects of the Invention] The water-absorbing resin obtained by the present invention has excellent durability of a swollen gel that could not be obtained by conventional methods, has a high water absorption capacity even in physiological saline and especially human urine, and is water resistant. It is a safe water-absorbing resin that has a low molecular weight of the dissolved component, and has significantly improved stickiness and liquid permeability of the swollen gel. According to the method of the present invention, such an excellent water-absorbing resin can be obtained by combining a water-soluble ethylenically unsaturated monomer (A) with a specific amount of a crosslinking agent (B) and a specific amount of a water-soluble chain transfer agent (fly ) can be easily produced by simply carrying out aqueous polymerization in the presence of the water-absorbent resin (D).
By crosslinking the vicinity of the surface with a specific hydrophilic crosslinking agent (E), a water absorbent resin (F) with significantly improved water absorption rate and durability can be obtained. These water-absorbing resins (D) and (F) can be produced at low cost and have unprecedented water-absorbing properties, so they are used for sanitary materials, food, and civil engineering. In order to obtain a water-absorbing resin, polymerization was carried out with a reduced amount of cross-linking agent, resulting in poor durability of the swollen gel. However, with the method of the present invention, even if a large amount of cross-linking agent is used, the swelling The gel exhibits excellent durability.

(2) It exhibits a high water absorption capacity for human urine, which was not possible with conventional water absorbent resins.

(3) Even if the i-mer used is polymerized at a high concentration near the saturation concentration, a high-performance water-absorbing resin with suppressed unnecessary reactions such as self-crosslinking can be obtained, so polymerization can be performed at a high concentration and high productivity can be achieved. It can be manufactured by nature.

(4) The water-absorbing resin of the present invention exhibits a high water absorption capacity and does not have any adverse effects.

(5) By crosslinking near the surface, it shows an improvement effect on water absorption properties that could not be obtained by surface crosslinking of conventional water absorbent resins,
It also shows superior durability and water absorption speed.

(6) Conventionally, when increasing the amount of polymerization initiator to reduce residual monomer, induction period, and shorten polymerization time, unnecessary reactions such as self-crosslinking occurred, making it impossible to obtain a product with high water absorption capacity. Even if the amount of the agent is increased, a high water absorption rate can be obtained, resulting in a low amount of residual monomer.

It has excellent advantages such as:

(Examples) The present invention will be described below with reference to Examples, but the scope of the present invention is not limited only to these Examples. still,
The physical properties of the water-absorbing resin described in the Examples are the values measured by the following test method.

In addition, parts indicate parts by weight.

(1) Water absorption capacity of physiological saline 1.0 g of a water absorbent resin was immersed in a beaker containing 150 ml of a 0.9% by weight thorium chloride aqueous solution and slowly stirred with a magnetic stirrer. After 6 hours, the swollen gel was filtered through a wire mesh, the weight of the swollen gel after sufficiently draining water was measured, and the water absorption capacity was calculated using the following formula.

Weight of swollen gel (2) Water absorption capacity of human urine (1) The same procedure was performed except that human urine sampled from 10 adult males was used instead of physiological saline, and the water absorption capacity of human urine was measured.

(3) Water-soluble content: Disperse 0.5 g of water-absorbing resin in 10100O deionized water, filter it with filter paper after 12 hours, measure the solid content in the filtrate, and calculate the water-soluble content according to the following formula. Ta.

Weight of filtrate (g) *Solid content of filtrate (%) (4) Molecular weight of water-soluble component By gel permeation chromatography using various sodium polyacrylates with known molecular weights as standards, (3) The molecular weight of the water-soluble components sampled was determined using the method described above.

(5) Durability of swollen gel A commercially available children's diaper (weighing 72 g) consisting of non-woven fabric, cotton bulb, water-absorbing paper and waterproof film was cut in half, and 2.5 g of polymer was evenly distributed between the cotton bulb and the water-absorbing paper. 120ml of adult human urine was added and left at 37°C.
After 12 hours and 18 hours, the diaper was opened and the state of the swollen gel inside was observed. The deterioration state is judged as ○~Δ~×
A three-level evaluation was made.

○: The shape of the swollen gel is maintained.

△D The shape of the swollen gel is partially distorted.

×: The shape of the swollen gel is distorted and becomes mushy and fluid.

(6) Amount of recovery: 23 cm * 23 cm folded in half on the non-woven fabric of a child's diaper after 18 hours used in the durability test of the above swelling gel.
Cover with 10 paper towels of 40 g/cm"
The amount of urine that returned to the paper towel was measured by applying pressure for 1 minute.

(7) After measuring the water absorption capacity with the swollen gel Betokki (1), the swollen gel Betokki (
Dry feeling) was measured by touch. Judging the dry feeling
Evaluation was made in three stages: ◯ to Δ to X.

○: The swollen gel has a very smooth and dry feel.

Δ: Part of the swollen gel is sticky.

×: The swollen gel is sticky and hands are sticky.

(8) Liquid permeability of swollen gel As shown in FIG. 1, 1.0 g of a water-absorbing resin is placed in a Petri dish 1 with an inner diameter of 53 mm, and 10 ml of human urine is poured into it to obtain a swollen gel 2. A paper towel 3 with a diameter of 53n++n was placed on top of the swollen gel 2, and a disk-shaped acrylic resin tester 4 with a protruding cylindrical portion in the center was placed on top of the swollen gel 2, as shown in FIG. After leaving it to stand, 6 ml of human urine was poured into the inlet 5, and the time until all of the human urine was absorbed into the polymer was measured, and this was taken as the liquid permeability of the swollen gel.

(Example 1) 414 g of acrylic acid, 4380 g of a 37% by weight aqueous solution of sodium acrylate, and 6.815 g of trimethylolpropane triacrylate as the crosslinking agent (B) (based on monomer (A10.1 mol%)), water-soluble chain Transfer agent (C)
0.195 g of sodium hypophosphite monohydrate (0.008 mol% of monomer (A)), 670 g of ion-exchanged water
After obtaining a monomer aqueous solution with a concentration of 37% and a neutralization rate of 75% using g, nitrogen gas was blown in to drive out dissolved oxygen.

Attach a lid to a jacketed stainless steel double-arm polisher having two sigma-type blades with an internal volume of 102 cm.
The above monomer (A) aqueous solution was introduced into this reactor, and nitrogen gas was blown into the reactor to replace the inside of the reaction system with nitrogen. Next, rotate the two sigma type blades and add 35 to the jacket.
2.62 g of ammonium persulfate and 0.0 g of sodium hydrogen sulfite were added as polymerization initiators while heating through hot water at
Polymerization was initiated by adding 12 g. At the peak of polymerization, the hydrogel polymer was fragmented into pieces with a diameter of about 5 mm, and after further stirring, the lid was removed 60 minutes after polymerization was started, and the gel was taken out. The resulting finely granulated water-containing gel polymer was spread on a 50-mesh wire mesh and dried with hot air at a temperature of 170° C. for 50 minutes. This dried material was ground with a hammer-type grinder and sieved through a 20-mesh wire mesh.

(Example 2) In Example 1, the amount of the water-soluble chain transfer agent (C) sodium hypophosphite l-hydrate used was 1.

A water-absorbing resin (2) was obtained in the same manner except that 219 g (0.05 mol % of monomer (A)) was used.

This water absorbent resin (2) was similarly evaluated and the results are shown in Table 1.

(Example 3) 21.988 g (0.2 mol % based on monomer), and the amount used of water-soluble chain transfer agent (C) sodium hypophosphite monohydrate was 2.44 g (based on monomer (A) 0°1 mol%)
A water absorbent resin (3) was obtained in the same manner except for the following steps.

This water absorbent resin (3) was similarly evaluated and the results are shown in Table 1.

(Example 4) In Example 1, 54.97 g of the crosslinking agent (B) polyethylene glycol diacrylate (n = 8) used
(0.5" mol% relative to monomer), and the amount of water-soluble chain transfer agent (C) sodium hypophosphite monohydrate used was 9.7"
A water-absorbing resin (4) was obtained in the same manner except that the amount was 6 g (0.4 mol % based on monomer (A)).

This water absorbent resin (4) was similarly evaluated and the results are shown in Table 1.

(Example 5) In Example 1, the crosslinking agent (B) used was 2.152 g of NN'-methylenebisacrylamide (relative to monomer fA).
)0.06 mol%) and a water-soluble chain transfer agent (C)
A water-absorbing resin (5) was obtained in the same manner except that 3.45 g of thiomalic acid (0.1 mol % relative to monomer (A)) was used.

This water absorbent resin (5) was similarly evaluated and the results are shown in Table 1.

(Example 6) In Example 1, the amount of ion-exchanged water used was 50g.
The concentration of monomer (A) water-soluble acid was changed to 42%, and the crosslinking agent (B) used was polyethylene 1''7 glycol diacrylate (n = 14, 17.07 g (
0.1 mol% relative to monomer (A)) and the amount of water-soluble chain transfer agent (C) thiomalic acid used was 0.69 g (0.02 mol% relative to monomer (A)). A water absorbent resin (6) was obtained in the same manner.

This water absorbent resin (6) was similarly evaluated and the results are shown in Table 1.

(Example 7) 40 g of corn starch and 600 g of ion-exchanged water were placed in a reaction chamber equipped with a stirring rod, a nitrogen gas blowing tube, and a temperature meter, and after stirring at 55° C. for 1 hour,
Cooled to 0°C. 300g of acrylic acid in this starch aqueous solution
, 1.92 g of N,N'-methylenebisacrylamide as the crosslinking agent (B) (0.3 mol% relative to monomer (A))
, 0.94 thiomalic acid as water-soluble chain transfer agent (C)
g (0.15 mol % relative to monomer (A)) was dissolved to obtain a monomer aqueous solution with a concentration of 33% and a neutralization rate of 0%.

This monomer aqueous solution was heated to 35°C, 0.20 g of sodium persulfate was used as a polymerization initiator, and 0.2 g of 12-ascorbic acid was used as a polymerization initiator.
04 g was added and polymerized for 3 hours without stirring.

389 g of a 30% by weight aqueous caustic soda solution was added to the obtained hydrogel polymer to give a neutralization rate of 70%, and the mixture was further dried and ground in the same manner as in Example 1 to obtain a water absorbent resin (7).

This water absorbent resin (7) was similarly evaluated and the results are shown in Table 1.

(Example 8) 22.2 g of deionized water was added to 72 g of acrylic acid, and this was used as a neutralizing agent to prepare 49.9 g of potassium hydroxide with a purity of 85%.
5g and N as crosslinker (B).

0.1 g of N'-methylenebisacrylamide (0.065 mol % based on monomer (A)), 0.225 g thiomalic acid (based on monomer (A10.
15 mol%) was added sequentially to achieve a concentration of 70% and a neutralization rate of 75%.
An aqueous monomer solution was prepared.

This monomer aqueous solution was kept at 70°C and kept under a nitrogen stream to a thickness of about 5 mm, and then added with 0.1 ammonium persulfate.
g and 0.02 g of sodium bisulfite were added to carry out polymerization. Polymerization started immediately, and after 10 minutes, the almost dry polymer gel was taken out and further dried and crushed in the same manner as in Example 1 to obtain a water absorbent resin (8).

This water absorbent resin (8) was similarly evaluated and the results are shown in Table 1.

(Example 9) To 100 parts of the water absorbent resin (5) obtained in Example 1, 0.1 part of ethylene glycol diglycidyl ether, 5 parts of water,
1 part of isopropyl alcohol was mixed, and the resulting mixture was heated in a dryer at 100° C. for 30 minutes to obtain a water absorbent resin (9).

Table 1 shows the analysis results of the water absorbent resin (9) thus obtained.

(Example 10) 1 part of glycerin, 6 parts of water, and 1 part of acetone were added to 100 parts of the water-absorbing resin (2) obtained in Example 2, and the mixture was placed in a blender heated to 230°C using a heat medium. , mixing and heat treatment were performed to obtain a water absorbent resin (IO).

The analysis results of the water absorbent resin (10) thus obtained are shown in Table 1.

(Example 11) To 100 parts of the water absorbent resin (3) obtained in Example 3, 0.00 parts of ethylene glycol diglycidyl ether was added. A treatment solution consisting of 1 part water, 3 parts water, and 6 parts methanol was mixed. The resulting mixture was heat-treated at 130° C. for 1 hour in a dryer to obtain a water-absorbing resin (11).

Table 1 shows the analysis results of the water absorbent resin (11) thus obtained.

(Example 12) 100 parts of the water absorbent resin (4) obtained in Example 4 was mixed with 10 parts of a treated aqueous solution consisting of 1 part of aluminum sulfate, 1 part of glycerin, and 8 parts of water. The resulting mixture was heat-treated at 200° C. for 30 minutes to obtain a water absorbent resin (12).

Table 1 shows the analysis results of the water absorbent resin (12) thus obtained.

(Comparative Example 1) In Example 1, the amount of crosslinking agent (B) used was 00273
Comparative water absorbent resin (1) was obtained in the same manner except that g (0.004 mol% relative to monomer (A)).

Table 1 shows the analysis results of the comparative water absorbent resin (1) thus obtained.

(Comparative Example 2) A comparative water absorbent resin (2) was obtained in the same manner as in Example 1 except that the water-soluble chain transfer agent (C) sodium hypophosphite monohydrate was not added.

Table 1 shows the analysis results of the comparative water absorbent resin (2) thus obtained.

(Comparative Example 3) In Example 1, the water-soluble chain transfer agent (C1 sodium hypophosphite monohydrate was not added, and the amount of crosslinking agent (B) used was 3.41.g (relative to the monomer ( Comparative water-absorbing resin (3) was obtained in the same manner except that A) was 0.05 mol %).

Table 1 shows the analysis results of the comparative water absorbent resin (3) thus obtained.

(Comparative Example 4) In Example 1, the water-soluble chain transfer agent (C) sodium hypophosphite 1-eternal was not added, and the crosslinking agent (B) was replaced with N, N'
A comparative water-absorbent resin (4) was obtained in the same manner except that 17.73 g of -methylenebisacrylamide (0.5 mol % based on monomer (A)) was used.

Table 1 shows the analysis results of the comparative water absorbent resin (4) thus obtained.

(Comparative Example 5) A comparative water absorbent resin (5) was obtained in the same manner as in Example 7 except that the crosslinking agent (B) was not added.

Table 1 shows the analysis results of the comparative water absorbent resin (5) thus obtained.

(Comparative Examples 6 to 8) Comparative water absorbent resins (6) to (8) were obtained.

Table 1 shows the analysis results of the comparative water absorbent resins (6) to (8) thus obtained.

[Brief explanation of drawings]

FIG. 1 shows an apparatus for testing the legality of a swollen gel. 1... Petri dish 2... Swelling gel 3... Vapor towel 4... Acrylic resin tester 5...
Inlet

Claims (1)

[Scope of Claims] 1. A water-soluble ethylenically unsaturated monomer (A) and 0.005 to 5 mol% of a crosslinking agent (B) and a water-soluble chain transfer agent (based on the monomer (A)). C) Production of a highly durable water-absorbing resin (D) characterized by aqueous polymerization of an aqueous solution of the monomer (A) containing 0.001 to 1 mol% and having a concentration of 30% to saturation. Method. 2. Water-soluble ethylenically unsaturated monomer (A) and 0.005 to 5 mol% of crosslinking agent (B) and 0.001 to 5 mol% of water-soluble chain transfer agent (C) based on the monomer (A) A functional group in the water absorbent resin (D) is formed near the surface of the water absorbent resin (D) obtained by aqueous polymerization of an aqueous solution of the monomer (A) containing 1 mol % at a concentration of 30 wt.% to saturated concentration. A method for producing a water absorbent resin (F) with excellent durability, which comprises crosslinking with a reactive hydrophilic crosslinking agent (E). 3. The manufacturing method according to claim 1 or 2, wherein the water-soluble chain transfer agent (C) is a hypophosphite. 4. Claim 1, wherein the amount of crosslinking agent (B) used is 0.02 to 1 mol% based on the water-soluble ethylenically unsaturated monomer (A).
Or the manufacturing method described in 2. 5. The manufacturing method according to claim 1 or 2, wherein the concentration of the water-soluble ethylenically unsaturated monomer (A) aqueous solution is 35% by weight to saturated concentration. 6. The production method according to claim 1 or 2, wherein the water-soluble ethylenically unsaturated monomer (A) contains at least 50% by weight of acrylic acid and an alkali metal salt and/or ammonium salt of acrylic acid. 7. The production method according to claim 1 or 2, wherein the aqueous solution of the water-soluble ethylenically unsaturated monomer (A) is polymerized in a reactor having a rotating stirring shaft. 8. The manufacturing method according to claim 7, wherein the reaction vessel having a rotating stirring blade has a plurality of rotating stirring blades. 9. The manufacturing method according to claim 8, wherein the reaction vessel having a plurality of rotating stirring shafts is a double-arm kneader. 10. The manufacturing method according to claim 9, wherein the amount of the crosslinking agent (B) used is 0.04 to 0.4 mol% based on the water-soluble ethylenically unsaturated monomer (A). 11. Water 0 to 100 parts by weight of water absorbent resin (D)
In the presence of 20 parts by weight and 0 to 20 parts by weight of a hydrophilic organic solvent (G), a compound (E-1) having two or more functional groups capable of reacting with a carboxyl group and/or a polyvalent metal salt (
E-2) 0.005 to 5 parts by weight of at least one hydrophilic crosslinking agent (E) selected from the group consisting of
3. The manufacturing method according to claim 2, which comprises heating at ~250<0>C. 12. The manufacturing method according to claim 11, wherein the hydrophilic crosslinking agent (E) is the compound (E-1). 13. The compound (E-1) according to claim 12, wherein the compound (E-1) is one or more compounds selected from the group consisting of polyhydric alcohol compounds, polyhydric glycidyl ether compounds, polyvalent oxazoline compounds, and polyvalent amine compounds. Production method. 14. Water content is 0.0% per 100 parts by weight of water absorbent resin (D).
12. The method according to claim 11, wherein the amount is 5 to 10 parts by weight. 15. Hydrophilic organic solvent (G) is water absorbent resin (D) 101
The manufacturing method according to claim 11, wherein the method is used in an amount of 0 to 8 parts by weight. 16. The manufacturing method according to claim 11, wherein the heating is performed at a temperature of 90 to 220°C.