JP2877255B2 - Manufacturing method of water absorbent resin with excellent durability - Google Patents

Description

The present invention relates to a method for producing a water absorbent resin having excellent durability. More specifically, the present invention relates to a method for producing a water-absorbent resin which is excellent in water absorption capacity, water absorption rate, durability during swelling, has low stickiness of a swollen gel, and has excellent liquid permeability.

Such a water-absorbing resin is not only excellent in safety and can be easily manufactured at low cost, because it has excellent water absorption capacity,
It can be widely used as a sanitary material such as sanitary products and disposable diapers, as a water retention agent for agriculture and horticulture and greening, and as a material for a wide range of absorbent articles.

[Conventional technology]

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

Examples of such a water-absorbing resin include a crosslinked product of a partially neutralized polyacrylic acid (JP-A-55-84304) and a hydrolyzate of a starch-acrylonitrile graft polymer (JP-B-49-433).
95), a starch-acrylate copolymer neutralized product (JP-A-51-125468), a vinyl acetate-acrylate copolymer saponified product (JP-A-52-14689), and acrylonitrile copolymer. Hydrolysates of polymers or acrylamide copolymers (JP-B-53-15959) or cross-linked products thereof are known.

Desirable characteristics of these water-absorbent resins include a high absorption capacity upon contact with an aqueous liquid, an excellent water absorption rate, and an excellent suction force for sucking up a liquid from a substrate containing the aqueous liquid.

However, depending on the use of the water-absorbing resin, in particular, the durability and aging stability of the swollen gel are required in addition to the above properties. For example, when a conventional water-absorbent resin is used for a sanitary material in a disposable diaper or the like, the swelling gel of the water-absorbent resin that has absorbed urine may be degraded over time, or may be used for a long time in agricultural and horticultural applications. Degradation may occur during use, causing decomposition.

As a method for preventing deterioration and decomposition of a swelling gel of a water-absorbent resin which has been known so far, a method of incorporating an oxygen-containing reducing inorganic salt or a radical chain inhibitor into the water-absorbent resin (JP-A-63-118375) JP-A-63-152667), a method containing an oxidizing agent (JP-A-63-153060), and a method containing a sulfur-containing reducing agent (JP-A-63-272349). However, any of these methods is a method of adding an additive for preventing deterioration to the water-absorbent resin, and adding another additive means that the water-absorbent resin is used for a sanitary material or the like. However, it was not always preferable in terms 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 the crosslinking agent.However, these water-absorbing resins have to be highly crosslinked in order to have sufficient durability. As a result, the water absorption ratio became extremely low. As you can see, currently,
A water-absorbing resin having a high water absorption ratio and excellent durability has not been obtained.

Moreover, in addition to the above-mentioned durability, when the swelling gel is incorporated in a diaper or the like, the swelling gel may have problems such as stickiness and reduced liquid permeability. The water-absorbent resin has a water-soluble portion (hereinafter, referred to as a water-soluble component). Due to these water-soluble components, the swelling gel after water absorption is applied to absorbent articles such as sticky or diapers. When incorporated, this stickiness reduces the liquid permeability and may cause leakage when new urine is discharged. In general, the water-soluble content is positively correlated with the water absorption capacity.To reduce the water-soluble content, the cross-linking density of the water-absorbent resin must be increased. The fact was that the water absorption ratio also decreased.

Although it is known that durability increases as the amount of the cross-linking agent is increased in such a water-absorbent resin, the problem is that the water-absorbing power decreases as the amount of the cross-linking agent increases. there were. In addition, a technique for improving the water absorption ratio by using a chain transfer agent during the production of a water-absorbent resin has been disclosed (USP4698404). However, in this case, the water absorption capacity for water or physiological saline is certainly improved, but almost no increase is observed for human urine.

[Problems to be solved by the invention]

The present invention has been made in view of the above situation. Accordingly, an object of the present invention is to provide a method for producing a water absorbent resin having excellent durability.

Another object of the present invention is to exhibit a high water absorption capacity with respect to physiological saline and particularly with respect to human urine, exhibit excellent durability when used in disposable diapers, and return amount in the diaper. It is an object of the present invention to provide a method for producing a water-absorbent resin which has a small amount of gel and has less stickiness of the gel and is excellent in liquid permeability.

[Means and Actions for Solving the Problems]

The present inventors have conducted intensive studies in order to solve the above-mentioned problems. As a result, (1) a water-soluble ethylenically unsaturated monomer containing a specific amount of a crosslinking agent (B) and a water-soluble chain transfer agent (C) ( A)
By polymerizing the aqueous solution in a specific concentration range,
A good water-absorbent resin (D) with improved durability while maintaining a high water absorption ratio, and with improved gel stickiness and liquid permeability as the molecular weight of the water-soluble component is reduced, can be obtained with good productivity. (2) By further crosslinking the vicinity of the surface of the water-absorbent resin (D) obtained by the production method of the above (1) with a hydrophilic crosslinking agent (E), a more excellent effect of improving water-absorbing properties is exhibited;
The present inventors have found that a water-absorbent resin (F) having improved durability, improved gel stickiness and liquid permeability, and excellent water-absorbing properties can be obtained while maintaining a high water absorption ratio, thereby completing the present invention.

That is, the present invention relates to a water-soluble ethylenically unsaturated monomer (A) and a crosslinking agent (B) 0.005 to 5 mol%, a water-soluble chain transfer agent (C) 0.001 to 30% by weight containing 1 mol%
A method for producing a water-absorbent resin (D) having excellent durability, comprising subjecting the aqueous solution of the monomer (A) to a saturated concentration to polymerize in an aqueous solution.

And 0.005 to 5 mol% of a crosslinking agent (B) and 0.001 to 1 mol% of a water-soluble chain transfer agent (C) based on the water-soluble ethylenically unsaturated monomer (A) and the monomer (A). Contains 30% by weight
The vicinity of the surface of the water-absorbent resin (D) obtained by subjecting the aqueous solution of the monomer (A) to a saturated concentration is polymerized with an aqueous solution, and cross-linked with a hydrophilic cross-linking agent (E) capable of reacting with a functional group in the water-absorbent resin. A method for producing a water-absorbent resin (F) having excellent durability, characterized in that:

 It is about.

 The present invention will be described in more detail.

Water-soluble ethylenically unsaturated monomer (A) used in the present invention
(Hereinafter, the monomer (A)) has a functional group, for example, acrylic acid, methacrylic acid, maleic acid,
Fumaric acid, crotonic acid, itaconic acid, vinylbenzenesulfonic acid, 2- (meth) acrylamido-2-methylpropanesulfonic acid, 2- (meth) acryloylethanesulfonic acid, 2- (meth) acryloylpropanesulfonic acid, and the like 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, N, N-diethylamino Propyl (meth) acrylamide and their quaternary salts can be mentioned, and at least one selected from these groups can be used.

Above all, among the above monomers (A), it is preferable to use acrylic acid as a main component from the viewpoint of the performance and cost of the obtained water-absorbent resin, in which case acrylic acid and its alkali metal salt and / or ammonium The content of the salt is preferably 50% by weight or more, more preferably 75% by weight or more in the monomer (A).

In order to obtain a water absorbent resin having excellent durability in the present invention, it is essential to use a specific amount of a crosslinking agent (B) having two or more polymerizable unsaturated groups or reactive functional groups in a molecule. As these crosslinking agents (B), for example, as compounds having two or more polymerizable unsaturated groups in the molecule, for example, N,
N'-methylenebisacrylamide, (poly) ethylene glycol di (meth) acrylate, (poly) propylene glycol di (meth) acrylate, glycerin tri (meth) acrylate, glycerin acrylate methacrylate, (meth) acrylic acid polyvalent metal salt, Examples include trimethylolpropane tri (meth) acrylate, triallylamine, triallyl cyanurate, triallyl isocyanurate, triallyl phosphate and the like. Examples of those having a reactive functional group include, for example,
When the monomer (A) has a carboxyl group, polyhydric alcohols such as ethylene glycol, diethylene glycol, triethyl glycol, polyethylene glycol, propylene glycol, dipropylene glycol, polypropylene glycol, and glycerin; Polyvalent glycidyl compounds such as glycidyl ether and glycerol polyglycidyl ether; polyvalent amines such as ethylenediamine and polyethyleneimine; other polyvalent oxazoline compounds, haloepoxy compounds,
Glycidyl (meth) acrylate, N-methylol (meth) acrylamide, etc. are exemplified as those having a polyvalent isocyanate and a polyvalent metal salt, and having both a polymerizable unsaturated group and a reactive functional group in the molecule. Can be done. 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 viewpoints of durability and water absorbing properties of the resulting water-absorbent resin.

The amount of the cross-linking agent (B) used in the present invention is the same as that of the cross-linking agent under the same conditions except that the water-soluble chain transfer agent (C) is not used in order to obtain the desired water absorption capacity. 2 to 100 times mol, more preferably 4 to 10 times,
It is twice the mole. Specifically, the amount of the crosslinking agent (B) used is 0.005 to 5 mol% based on the monomer (A). When the amount of the crosslinking agent (B) used is less than 0.005 mol%, the obtained water-absorbing resin has a high water absorption ratio, but is inferior in durability and has a large amount of water-soluble components and a high molecular weight, so that the gel has a high water absorption. It is inferior in stickiness and liquid permeability. Further, when the amount is more than 5 mol%, the water absorption capacity becomes extremely low. The amount of the crosslinking agent depends on the amount of the water-soluble chain transfer agent (C) to be described later, but is preferably 0.02 to 1 mol%, more preferably 0.04 to 0.4 mol%.
Still more preferably, it is 0.08 to 0.2 mol%.

In addition to the crosslinking agent (B), a method of forming a crosslinking by graft polymerization may be used in combination. Examples of such a method include a method in which an aqueous solution of the monomer (A) is polymerized in the presence of a hydrophilic polymer such as cellulose, starch, or polyvinyl alcohol, and a crosslink resulting from graft polymerization is formed during the polymerization. The water-soluble polymer is a monomer (A)
Is preferably used in the range of 1 to 50% by weight.

In the present invention, it is essential to use a specific amount of the water-soluble chain transfer agent (C).

According to the method of the present invention, a specific amount of the water-soluble chain transfer agent (C) is selected, and polymerization is carried out as a highly cross-linked polymer by using a cross-linking agent in a large amount of 2 to 100 times as much as that of a normal production method. Excellent durability, high absorption capacity not only for physiological saline but also for human urine, and low molecular weight of water-soluble component, which has adverse effects such as gel stickiness and reduced liquid permeability. Excellent water-absorbing resin, such as low water content.

The water-soluble chain transfer agent (C) used in the present invention includes:
There is no particular limitation as long as it can be dissolved in water or a water-soluble ethylenically unsaturated monomer, and examples thereof include thiols, thiolic acids, secondary alcohols, amines, and hypophosphites. Typically, mercaptoethanol,
Mercaptopropanol, dodecylmercaptan, thioglycolic acid, thiomalic acid, 3-mercaptopropionic acid, isopropanol, sodium hypophosphite, formic acid,
And salts thereof, and one or more selected from these groups are used, and it is preferable to use a hypophosphite such as sodium hypophosphite from the viewpoint of the effect.

The amount of the water-soluble chain transfer agent (C) used depends on the type and amount of the water-soluble chain transfer agent and the concentration of the aqueous solution of the monomer (A), but is 0.001 to 1 mol based on the monomer (A). %, Preferably 0.005 to 0.3 mol%. This usage is 0.001
If the amount is less than mol%, the amount of the crosslinking agent (B) used in the present invention is not preferred because the crosslinking density is high and the water absorption is too low. If it is used in excess of 1 mol%, the water-soluble content increases and the durability is rather lowered, which is not preferable.

The concentration of the aqueous solution of the monomer (A) used in the present invention is in the range of 30% by weight to saturated concentration, more preferably 35% by weight to saturated concentration. If the concentration is less than 30% by weight, the productivity per unit reaction volume decreases, and the drying step requires time, and the productivity decreases, which is not preferable from an industrial viewpoint. In the conventional polymerization method, if the polymerization is carried out near the saturation concentration in order to improve the productivity, unnecessary reactions such as self-crosslinking occur and the water absorption capacity decreases, so that the amount of the crosslinking agent (B) that can be used at the time of polymerization is limited. Only a water-absorbent resin having poor durability was obtained. However, according to the method of the present invention, the self-crosslinking reaction is suppressed by selecting the amount of the water-soluble chain transfer agent (C) to be used, and the amount of the cross-linking agent (B) can be increased. Can be produced at a high concentration with high productivity.

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

In the present invention, as a polymerization method for polymerizing an aqueous solution of the monomer (A) to obtain a water-absorbing resin, there are known polymerization techniques such as aqueous solution polymerization, reversed-phase suspension polymerization, precipitation polymerization, bulk polymerization, ultraviolet light and electron beam. In polymerization by active energy such as,
Aqueous solution polymerization is used as a method for obtaining a water-absorbent resin excellent in performance, productivity and cost. As a method of carrying out the aqueous solution polymerization, for example, a cast polymerization carried out in a mold (Japanese Patent Publication No.
-42466), polymerization on a belt conveyor
58-49714), and a method of polymerizing in a kneader having a stirring blade capable of subdividing a hydrogel polymer (Japanese Patent Application Laid-Open No. 57-34101).

When such aqueous solution polymerization is carried out, a uniform chain transfer reaction with the water-soluble chain transfer agent (C) or a uniform cross-linking reaction with the cross-linking agent (B) proceeds to obtain a water absorbent resin having better performance. Preferably, the heat of polymerization is uniformly removed. For this purpose, the polymerization gel is not a polymerization method in which the polymerization gel is integrated, but the polymerization gel of the reaction system is stirred for the entire time from the start to the end of the polymerization, or preferably for the whole time, and the polymerization heat is uniformly removed. It is preferable that the polymerization reaction is carried out in a reaction vessel having a rotary stirring blade. The reaction vessel having a rotary stirring blade is not particularly limited, but preferably has a large stirring force for the polymer gel, and a reactor in which the polymer gel generated as the polymerization proceeds with a shear force by the rotary stirring blade is also exemplified. Can,
Further, in order to increase the stirring power, it is more preferable that the number of rotary stirring blades is plural. Examples of the reactor include a single-screw kneader, a single-screw extruder, a double-arm kneader, and a triple-screw kneader. Also, if you use a double-armed kneader,
It is preferable because the polymer gel is finely divided and uniformly stirred over the entire time of the polymerization and the polymerization heat can be uniformly removed, so that a water-absorbent resin having more excellent performance can be obtained.

In the present invention, the radical polymerization initiator used in the aqueous solution polymerization is not particularly limited as long as it is water-soluble, and for example, persulfates such as potassium persulfate, ammonium persulfate and sodium persulfate; hydrogen peroxide; Hydroperoxides such as -butyl hydroperoxide and cumene hydroperoxide; azo compounds such as 2,2'-azobis (2-amidinopropane) dihydrochloride; and other ceric salts and permanganates. Can be Among these, one or more selected from the group consisting of persulfate, hydrogen peroxide, and azo compound are preferable from the viewpoint of the performance of the obtained water-absorbent resin, the safety of decomposition products, and the like.

When the radical polymerization initiator is an oxidizing radical polymerization initiator, a reducing agent may be used in combination as a redox initiator. As the reducing agent to be used, for example, sulfurous acid (hydrogen) such as sodium sulfite and sodium hydrogen sulfite
Salts; thiosulfates such as sodium thiosulfate; dithionite; metal salts such as cuprous sulfate and ferrous sulfate; organic reducing agents such as l-ascorbic acid; amines such as aniline and monoethanolamine Is mentioned.

The amount of the radical polymerization initiator used can be in a wide range, but is usually preferably in the range of 0.001 to 2 mol%, more preferably 0.01 to 0.1 mol%, based on the monomer (A).
It is in the range of 5 mol%. If the amount is less than 0.001 mol%, the polymerization time and the induction period are prolonged, and the amount of residual monomers tends to increase. In the conventional polymerization method,
To reduce the residual monomer, shorten the induction period, and shorten the polymerization time,
When the amount of the polymerization initiator is increased, an unnecessary reaction such as self-crosslinking occurs and the water absorption capacity is reduced, so that the amount of the initiator that can be used has been limited, but according to the direction of the present invention, such a disadvantage is improved. Even if the amount of the initiator is increased, a high-performance water-absorbing resin can be obtained. However, if you use more than 2 mol%,
Not only is there a small effect corresponding to the amount added, but also it becomes 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 drying and polymerization may be simultaneously performed by the heat of polymerization, or depending on the water content after polymerization, the obtained water-containing gel may be further dried to obtain a water-absorbent resin. You may use as. As a drying method, a known drying method can be used, for example, a method by azeotropic dehydration in an organic solvent, a forced air oven, a reduced-pressure dryer, a microwave dryer, an infrared dryer, and a belt heated to a predetermined temperature. Alternatively, a drying method using a drum dryer or the like may be used. By using these drying methods, it is preferable to dry the hydrogel after polymerization at 80 ° C or higher, more preferably at 80 to 230 ° C. If it is lower than 80 ° C., it takes a long time for drying, which is not preferable from the viewpoint of productivity. If the temperature exceeds 230 ° C., care must be taken because the water-absorbing resin may deteriorate.

The water-absorbent resin obtained by polymerization and drying as described above is used after being pulverized and / or classified if necessary.

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-mentioned production method is crosslinked with a specific hydrophilic crosslinking agent (E).
The water-absorbent resin (D) obtained by the production method of the present invention exhibits a remarkable effect of improving water-absorbing properties as compared with the conventional water-absorbent resin, and the water-absorbent resin (F) having a crosslinked surface area.
Is more excellent in durability and water absorption properties than the water absorbent resin (D) before cross-linking the vicinity of the surface.

As the hydrophilic crosslinking agent (E) used in the present invention, a compound (E-1) having at least two functional groups capable of reacting with a carboxyl group in one molecule and / or a polyvalent metal salt (E)
-2). For example, when the water absorbent resin (D) has a carboxyl group, the compound (E-1) may be ethylene glycol, diethylene glycol, triethylene glycol, tetraethylene glycol, polyethylene glycol, 1,4-butanediol, 1,5 -Pentanediol, 1,6-hexanediol, neopentyl glycol, propylene glycol, glycerin, polyglycerin, trimethylolpropane, pentaerythritol,
Polyhydric alcohol compounds such as sorbitol and polyvinyl alcohol; ethylene glycol diglycidyl ether;
Polyethylene glycol diglycidyl ether, glycerol polyglycidyl ether, diglycerol polyglycidyl ether, polyglycerol polyglycidyl ether, propylene glycol diglycidyl ether,
Polyvalent glycidyl ether compounds such as polypropylene glycol diglycidyl ether; polyvalent amine compounds such as ethylenediamine, diethylenetriamine, triethylenetetramine and polyethyleneimine; polyvalent oxazoline compounds such as 1,2-ethylenebisoxazoline and polyisopropenyloxazoline; epi; Haloepoxy compounds such as chlorohydrin; other polyvalent aziridine compounds, polyvalent isocyanate compounds and the like; and polyvalent metal salts (E-
Examples of 2) include hydroxides and chlorides of zinc, calcium, magnesium, aluminum, iron, zirconium and the like. One or more of these groups are preferably used, and among them, compound (E-1) is preferably used. Particularly, polyhydric alcohols, polyglycidyl compounds, and polyamines are used as hydrophilic compounds. Crosslinking agent (E)
Is preferred from the viewpoint of the surface crosslinking effect. Further, the compound (E-1) and the polyvalent metal salt (E-2) may be used in combination as the hydrophilic crosslinking agent (E) to improve the mixing property.

The amount of the hydrophilic crosslinking agent (E) used in the present invention is:
The water-absorbent resin (D) 100 obtained by the above-mentioned production method
0.005 to 5 parts by weight, preferably 0.01 to 5 parts by weight,
The ratio is within a range of 1 part by weight, and if the amount is within this range, a surface-crosslinked water-absorbent resin (F) excellent in various properties can be obtained. When the amount of the hydrophilic cross-linking agent (E) exceeds 5 parts by weight, not only is it uneconomical, but also the possibility that unreacted hydrophilic cross-linking agent (E) remains in the obtained water-absorbent resin (F). In addition, the water absorption ratio of the resulting water-absorbent resin (F) becomes excessive in order to achieve an appropriate crosslinking effect, which is not preferable. If the amount is less than 0.005 parts by weight, the effect of the present invention is hardly obtained.

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

In the present invention, the amount of water used is in the range of 0 to 20 parts by weight, preferably 0.5 to 10 parts by weight, per 100 parts by weight of the water absorbent resin (D).

Examples of the hydrophilic organic solvent (G) include lower alcohols such as methanol, ethanol, n-propanol, iso-propanol, n-butanol, iso-butanol and t-butanol; ketones such as acetone, methyl ethyl ketone and methyl butyl ketone. Ethers such as dioxane and tetrahydrofuran; amides such as N, N-dimethylformamide; and sulfoxides such as dimethylsulfoxide. The amount of the compound is 0 to 100 parts by weight of the water-absorbent resin (D). ~ 20 parts by weight, preferably 0
８8 parts by weight.

In the present invention, the following method is exemplified as a method of mixing the water-absorbent resin (D) with the hydrophilic crosslinking agent (E) to crosslink the vicinity of the surface of the water-absorbent resin.

(I) A method of spraying or mixing a liquid mixture of a hydrophilic cross-linking agent (E) and, if necessary, water (steam) and / or a hydrophilic organic solvent (G) onto the water-absorbent resin (D).

Or (II) a water-absorbent resin (D) is dispersed and suspended in a polymerization-inactive hydrophobic organic solvent, and a hydrophilic crosslinking agent (E) and, if necessary, water and / or a hydrophilic organic solvent (G) Under stirring.

In this case, a method in which the hydrophilic crosslinking agent (E) is emulsified and suspended in a hydrophobic organic solvent in advance using a specific surfactant, and the emulsion is added to the dispersion suspension of the water absorbent resin (D). Is preferred.

Or (III) water-absorbent resin (D) with water and hydrophilic organic solvent (G)
A hydrophilic cross-linking agent (E).

 And the like.

As described above, the water-absorbent resin (D) and the hydrophilic crosslinking agent (E) obtained by the method of the present invention and, if necessary,
In order to heat-treat the mixture obtained by mixing water and / or the hydrophilic organic solvent (G), an ordinary heater or heating furnace can be used. For example, a channel-type stirring dryer, a rotary dryer, a disk dryer, a Netsuwa dryer, a fluidized-bed dryer, a flash dryer, an infrared dryer, a dielectric heating dryer, and the like. Alternatively, after the hydrophilic cross-linking agent (E) is added to the water-absorbent resin (D) in an organic solvent by the method (II), the reaction may be carried out by directly heating in the organic solvent.

The heat treatment temperature is preferably from 40 to 250 ° C, more preferably from 90 to 220 ° C, depending on the kind of the hydrophilic crosslinking agent (E) used and the like. If the temperature is lower than 40 ° C., the reaction takes a long time and not only the productivity is lowered, but also a part of the hydrophilic crosslinking agent (E) becomes unreacted and the resulting water-absorbent resin (F)
May be left undesirably. At a high temperature exceeding 250 ° C., care must be taken because thermal degradation may occur depending on the type of the water absorbent resin (D).

The surface-crosslinked water-absorbent resin (F) or the surface-noncrosslinked water-absorbent resin (D) may be crushed and granulated as necessary.

〔The invention's effect〕

The water-absorbent resin obtained by the present invention is not obtained by the conventional method, has excellent swelling gel durability, has a high water absorption capacity even for physiological saline and especially human urine, and has a molecular weight of water-soluble component. It is a safe water-absorbent resin that is low and has greatly improved swelling gel tackiness and liquid permeability. According to the method of the present invention, such an excellent water-absorbing resin is obtained by converting a water-soluble ethylenically unsaturated monomer (A) into a specific amount of a crosslinking agent (B) and a specific amount of a water-soluble chain transfer agent (C). It can be easily produced simply by performing aqueous solution polymerization in the presence of a water-absorbent resin (D), and the vicinity of the surface of the obtained water-absorbent resin (D) is cross-linked with a specific hydrophilic cross-linking agent (E). An improved water absorbent resin (F) is obtained. Since such water-absorbent resins (D) and (F) can be manufactured at low cost and have excellent water-absorbing properties which have not been seen before,
It can be widely used in fields such as sanitary materials, food, civil engineering, and agriculture.

As described above, the water-absorbent resin obtained by the production method of the present invention is as follows: (1) Conventionally, polymerization was carried out with a reduced amount of a cross-linking agent in order to obtain a water-absorbent resin having a high water absorption capacity. However, in the method of the present invention, even when a large number of crosslinking agents are used, the swollen gel shows excellent durability because of high water absorption.

(2) It shows a high water absorption capacity for human urine, which could not be obtained with the conventional water-absorbing resin.

(3) Even if the monomer used is polymerized at a high concentration close to the saturation concentration, a high-performance water-absorbent resin in which unnecessary reactions such as self-crosslinking are suppressed can be obtained. It can be manufactured by nature.

(4) Although the water-absorbent resin of the present invention exhibits a high water absorption capacity, the water-soluble component has a low molecular weight, and thus has an adverse effect such as stickiness of the swollen gel and a decrease in liquid permeability due to the water-soluble component. Absent.

(5) By cross-linking the vicinity of the surface, an effect of improving water-absorbing properties, which cannot be obtained by surface cross-linking of the conventional water-absorbent resin, is exhibited.
Furthermore, it shows excellent durability and water absorption rate.

(6) Conventionally, if the amount of the polymerization initiator was increased to reduce the residual monomer, shorten the induction period, or shorten the polymerization time, an unnecessary reaction such as self-crosslinking occurred and a product having a high water absorption ratio could not be obtained. Even if the amount of the agent is increased, a product having a high water absorption can be obtained, resulting in a low residual monomer amount.

 And so on.

(Examples) Hereinafter, the present invention will be described with reference to examples, but the scope of the present invention is not limited only to these examples.
In addition, various physical properties of the water-absorbing resin described in the examples are values measured by the following test methods.

 Parts represent parts by weight.

(1) Absorption Ratio of Physiological Saline 1.0 g of a water-absorbent resin was immersed in a beaker containing 150 ml of 0.9% by weight aqueous sodium chloride solution and slowly stirred with a magnetic stirrer. After 6 hours, the swelled gel was filtered through a wire net, and after swelling, the weight of the swelled gel was measured, and the water absorption capacity was calculated by the following equation.

(2) Water absorption capacity of human urine The water absorption capacity of human urine was measured in the same manner except that human urine sampled from 10 adult males was used instead of the physiological saline of (1).

(3) Water-soluble component 0.5 g of water-absorbent resin is dispersed in 1000 ml of deionized water,
After a period of time, the solution was filtered through filter paper, and the solid content in the filtrate was measured to determine the water-soluble content according to the following formula.

(4) Molecular Weight of Water-Soluble Content The molecular weight of the water-soluble content sampled by the method (3) was determined by gel permeation chromatography using various sodium polyacrylates of known molecular weight as a standard.

(5) Durability of swollen gel Cut a commercially available children's diaper (weight: 72 g) consisting of non-woven fabric, flocculent pulp, water-absorbing paper and waterproof film, and cut 2.5 g of polymer evenly between flocculent pulp and absorbent paper Spray
120 ml of human urine of an adult was added and left at 37 ° C., and after 6, 12, and 18 hours, the diaper was opened and the state of the swollen gel in the diaper was observed. The determination of the deterioration state was performed on a three-point scale of △ to △ to ×.

；: The shape of the swollen gel is maintained.

Δ: The shape of the swollen gel was partially broken.

X: The shape of the swollen gel collapsed, and it became a muddy fluid state.

(6) Return amount above covered 10 sheets of paper towel 23cm * 23cm was folded in two over the nonwoven fabric 18 hours after diaper for children using the durability test swollen gel, 1 minute the pressure of 40 g / cm ² The amount of urine that had returned to the paper towel was measured.

(7) Stickiness of Swollen Gel The stickiness (dry feeling) of the swollen gel after measuring the water absorption ratio in (1) was measured by touch. Judgment of dry feeling was evaluated on a three-point scale of △ to △ to ×.

；: The swollen gel is quite smooth and dry.

Δ: Swelled gel was partially tacky.

X: The swollen gel is sticky and the hands are slimy.

(8) Liquid Permeability of Swollen Gel As shown in FIG. 1, 1.0 g of a water-absorbent resin is placed in a petri dish 1 having an inner diameter of 53 mm, and 10 ml of human urine is poured to obtain a swollen gel 2. A paper towel 3 having a diameter of 53 mm is placed on the swelling gel 2, and as shown in FIG. 1, a disc-shaped acrylic resin tester 4 having a cylindrical portion protruding at the center is placed. After standing at room temperature for 1 hour, 6 ml of human urine is poured from the inlet 5, and the time until all human urine is absorbed in the polymer is measured, and this is used as the liquid permeability of the swollen gel.

(Example 1) 414 g of acrylic acid and 37% by weight of sodium acrylate
4380 g of an aqueous solution, and 6.815 g of trimethylolpropane triacrylate as a cross-linking agent (B) (with respect to the monomer (A) 0.1%).
1 mol%), 0.195 g of sodium hypophosphite hydrate as a water-soluble chain transfer agent (C) (0.008 mol% of monomer (A)), 670 g of ion-exchanged water, 37% concentration, neutralization rate 75%
After obtaining a monomer aqueous solution of the above, dissolved oxygen was expelled by blowing nitrogen gas.

A lid is attached to a jacketed stainless steel double-armed kneader (kneader) having two sigma-type blades having an inner volume of 10 l, and the above-mentioned aqueous solution of the monomer (A) is fed into the reactor,
The inside of the reaction system was replaced with nitrogen by blowing nitrogen gas. Next, rotate the two sigma-type blades,
The polymerization was initiated by adding 2.62 g of ammonium persulfate and 0.12 g of sodium bisulfite as a polymerization initiator while heating through warm water at 35 ° C. At the time of the polymerization peak, the hydrogel polymer was subdivided into a diameter of about 5 mm. Further, stirring was continued to start the polymerization, and after 60 minutes, the lid was removed, and the gel was taken out. The obtained finely divided hydrogel polymer was spread on a 50-mesh wire net and dried with hot air at a temperature of 170 ° C. for 50 minutes. The dried product was pulverized with a mold pulverizer with a hammer and sieved with a 20-mesh wire net to obtain a water-absorbent resin (1) having passed through a 20-mesh wire.

Various physical properties of the water absorbent resin (1) were evaluated, and
It is shown in the table.

(Example 2) The water-soluble chain transfer agent (C) used in Example 1
A water-absorbent resin (2) was obtained in the same manner except that the amount of sodium hypophosphite monohydrate used was changed to 1.219 g (based on the monomer (A) 0.05 mol%).

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

(Example 3) In Example 1, the crosslinking agent (B) used was polyethylene glycol diacrylate (n = 8; average number of ethylene oxide units) of 21.988 g (based on 0.2 mol% of monomer), and was water-soluble. A water-absorbent resin (3) was obtained in the same manner except that the amount of the chain transfer agent (C) sodium hypophosphite monohydrate was changed to 2.44 g (based on the monomer (A) 0.1 mol%).

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

(Example 4) In Example 1, the amount of the crosslinking agent (B) used was 54.97 g (0.5 mol% with respect to the monomer) of polyethylene glycol diacrylate (n = 8), and the water-soluble chain transfer agent (C ) A water-absorbent resin (4) was obtained in the same manner except that the amount of sodium hypophosphite monohydrate was changed to 9.76 g (based on the monomer (A) 0.4 mol%).

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 N, N'-
2.152 g of methylenebisacrylamide (based on monomer (A) 0.
06 mol%) and 3.45 g of thiomalic acid (0.1 mol% with respect to monomer (A)) as the water-soluble chain transfer agent (C) to obtain a water-absorbent resin (5).

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 exchange water used was 50 g.
The concentration of the aqueous solution of the monomer (A) was changed to 42%, and the crosslinking agent (B) used was 17.07 g of polyethylene glycol diacrylate (n = 14) (based on 0.1 mol% of the monomer (A)). And a water-absorbent resin (6) was obtained in the same manner except that the amount of the water-soluble chain transfer agent (C) thiomalic acid was changed to 0.69 g (based on the monomer (A) 0.02 mol%).

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 charged into a reactor equipped with a stirring rod, a nitrogen gas blowing tube and a thermometer, stirred at 55 ° C. for 1 hour, and cooled to 30 ° C. 300 g of acrylic acid was added to this aqueous starch solution, and N, N 'was used as a crosslinking agent (B).
1.92 g of methylenebisacrylamide (based on monomer (A)
0.34 mol%) and 0.94 g of thiomalic acid (0.15 mol% relative to monomer (A)) as a water-soluble chain transfer agent (C)
A monomer aqueous solution having a concentration of 33% and a neutralization rate of 0% was obtained.

The aqueous monomer solution was heated to 35 ° C., and 0.20 g of sodium persulfate and 0.04 g of 1-ascorbic acid were added as polymerization initiators, and the mixture was polymerized with stirring for 3 hours. To the resulting hydrogel polymer was added 389 g of a 30% by weight aqueous solution of caustic soda to obtain a neutralization ratio of 70%, followed by drying and pulverization 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 49.5 g of 85% pure potassium hydroxide was used as a neutralizing agent and N, N'-methylenebisacrylamide was used as a crosslinking agent (B).
0.1 g (based on monomer (A) 0.065 mol%), and 0.225 g of thiomalic acid as water-soluble chain transfer agent (C) (based on monomer (A) 0.
15 mol%) was added in order to prepare a monomer aqueous solution having a concentration of 70% and a neutralization rate of 75%.

This monomer aqueous solution was kept at 70 ° C. and kept under a nitrogen stream to a thickness of about 5 mm, and then 0.1 g of ammonium persulfate and 0.02 g of sodium bisulfite were further added to carry out polymerization.
The polymerization was started immediately, and after 10 minutes, the almost dried polymer gel was taken out and further dried and pulverized 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 and 1 part of isopropanol alcohol were mixed, and the obtained mixture was placed in a dryer. Heat treatment was performed 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) To 100 parts of the water-absorbent resin (2) obtained in Example 2, 1 part of glycerin, 6 parts of water and 1 part of acetone were added, and the jacket was charged into a blender heated to 230 ° C with a heating medium. The mixture was mixed and heated to obtain a water-absorbent resin (10).

Table 1 shows the analysis results of the water absorbent resin (10) thus obtained.

Example 11 To 100 parts of the water-absorbent resin (3) obtained in Example 3, a treatment solution comprising 0.1 part of ethylene glycol diglycidyl ether, 3 parts of water and 6 parts of methanol was mixed. The obtained mixture was subjected to heat treatment at 130 ° C. for 1 hour in a dryer to obtain a water-absorbent resin (11).

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

Example 12 To 100 parts of the water-absorbent resin (4) obtained in Example 4, 10 parts of a treatment aqueous solution comprising 1 part of aluminum sulfate, 1 part of glycerin and 8 parts of water were mixed. The obtained mixture was subjected to a heat treatment 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) The amount of the crosslinking agent (B) used in Example 1 was changed to 0.273 g.
(Comparative water-absorbing resin (1)) was obtained in the same manner except that (based on monomer (A) 0.004 mol%).

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 amount of the crosslinking agent (B) used was 3.41 g (based on the monomer (A)) without adding the water-soluble chain transfer agent (C) and sodium hypophosphite monohydrate. 0.005 mol%) to obtain a comparative water-absorbent resin (3).

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

(Comparative Example 4) In Example 1, the crosslinking agent (B) was changed to N, N 'without adding the water-soluble chain transfer agent (C) sodium hypophosphite monohydrate.
17.73 g of methylenebisacrylamide (based on monomer (A)
0.5 mol%) to obtain a comparative water-absorbent resin (4).

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 (1) to obtained in Comparative Examples 1 to 3.
(3) was subjected to the same surface crosslinking treatment operation as in Example 9 to obtain comparative water-absorbent resins (6) to (8).

Comparative water-absorbing resins (6) to (8) thus obtained
Table 1 shows the analysis results.

[Brief description of the drawings]

FIG. 1 shows an apparatus for testing the liquid permeability of a swollen gel. 1 ... Petri dish 2 ... Swelling gel 3 ... Paper towel 4 ... Acrylic resin tester 5 ... Filler

──────────────────────────────────────────────────続 き Continuing from the front page (72) Inventor Tadao Shimomura 5-8 Nishiburi-cho, Suita-shi, Osaka Inside the Central Research Laboratory of Nippon Shokubai Chemical Co., Ltd. (56) References JP-A-2-34167 (JP, A JP-A-2-300210 (JP, A) JP-A-1-146902 (JP, A) JP-A-1-201312 (JP, A) JP-A-63-61005 (JP, A) (58) Field (Int.Cl. ⁶ , DB name) C08F 8/00-8/50 C08F 2/00-2/60

Claims (10)

(57) [Claims] 1. A water-soluble ethylenically unsaturated monomer (A) and 0.005 to 5 mol% of a crosslinking agent (B) and 0.001 to 1 mol% of a water-soluble chain transfer agent (C) based on the monomer (A). An aqueous solution of the monomer (A) having a concentration of 30% by weight to a saturated concentration containing
Excellent durability characterized by crosslinking the vicinity of the surface of the water-absorbent resin (D) obtained by aqueous solution polymerization with a hydrophilic crosslinking agent (E) capable of reacting with a functional group in the water-absorbent resin (D). A method for producing the water absorbent resin (F). 2. The method according to claim 1, wherein the water-soluble chain transfer agent (C) is hypophosphite. 3. The process according to claim 1, wherein the amount of the crosslinking agent (B) used is 0.02 to 1 mol% based on the water-soluble ethylenically unsaturated monomer (A). 4. The process according to claim 1, wherein the aqueous solution of the water-soluble ethylenically unsaturated monomer (A) is polymerized in a reactor having a rotary stirring shaft. 5. An absorbency against physiological saline of 40 to 54 g / g.
A water-absorbent resin (D) having an absorption capacity for human urine of 28 to 36 g / g and a molecular weight of water-soluble component of 120,000 or less
A method for producing a water-absorbent resin (F), which comprises crosslinking the vicinity of the surface with a hydrophilic crosslinking agent (E) capable of reacting with a functional group in the water-absorbent resin (D). 6. The absorption capacity for physiological saline is 40 to 54 g / g.
The absorption capacity for human urine is 28 to 36 g / g, and the durability of the swollen gel is 12 hours. A method for producing a water-absorbent resin (F), which comprises crosslinking with a hydrophilic crosslinking agent (E) capable of reacting with the functional group in D). 7. The particle surface is cross-linked, has an absorption capacity of 41 to 51 g / g for physiological saline, an absorption capacity of 35 to 38 g / g for human urine, and a molecular weight of 80,000 for the water-soluble component. A water-absorbent resin characterized by the following. 8. The particle surface has been cross-linked and has an absorption capacity of 41 to 51 g / g for physiological saline, an absorption capacity of 35 to 38 g / g for human urine, and a durability of the swollen gel after 12 hours. A water-absorbent resin, wherein the shape of the swollen gel is maintained. 9. The particle surface is cross-linked, has an absorption capacity of 41 to 51 g / g for physiological saline, an absorption capacity of 35 to 38 g / g for human urine, and a molecular weight of 80,000 for the water-soluble component. An absorbent article containing the following water absorbent resin. 10. The particle surface has been cross-linked and has an absorbency against physiological saline of 41 to 51 g / g, an absorbency against human urine of 35 to 38 g / g, and a swelling gel having a durability of 12 hours. An absorbent article containing a water-absorbent resin in which the shape of a swollen gel is maintained.