JP3350193B2 - Crosslinking agent, water-absorbing resin using the crosslinking agent, and method for producing the same - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a water-absorbing resin, a method for producing the same, and a crosslinking agent used for the same. More specifically, the gel has high durability, is excellent in diffusibility and liquid permeability of an aqueous liquid, and exhibits excellent performance even when used as a sanitary material, a method for producing the same, and a method for producing the same. It relates to a crosslinking agent .

[0002]

2. Description of the Related Art In recent years, water-absorbing resins for absorbing body fluids have been widely used as sanitary materials such as disposable diapers and sanitary napkins.

Examples of the above water-absorbing resin include cross-linked polyacrylic acid partially neutralized products (JP-A-55-84304,
JP-A-55-108407, JP-A-55-133413),
Hydrolyzate of starch-acrylonitrile graft polymer (JP-A-46-43995), neutralized product of starch-acrylic acid graft polymer (JP-A-51-125468), vinyl acetate-acrylate Saponified polymer (JP-A-52
-14689), a hydrolyzate of an acrylonitrile copolymer or an acrylamide copolymer (JP-A-53-15959) or a crosslinked product thereof, or a cross-linked product of a cationic monomer (JP-A-58-154709) And JP-A-58-154710) are known. At present, among the above crosslinked polymers, a crosslinked polymer obtained by copolymerizing a hydrophilic unsaturated monomer having a carboxyl group such as acrylic acid in the presence of a crosslinking agent is a raw material. Is also the mainstream of water-absorbing resins because they are inexpensive, have excellent water-absorbing properties, and have no fear of spoilage.

[0004] Desirable characteristics of the above-mentioned water-absorbent resin include a high water absorption ratio when contacted with an aqueous liquid, an excellent water absorption rate, the durability of a swollen gel, the diffusivity and liquid permeability of an aqueous liquid, and the properties of an aqueous liquid. For example, a suction force for sucking water from the contained base material may be used.

On the other hand, in recent years, hygienic materials such as disposable diapers and sanitary napkins have become more sophisticated and thinner, and the amount of water-absorbing resin used tends to increase. Among the above properties, gels having further improved physical properties such as gel durability, aqueous liquid diffusivity and liquid permeability have been desired. It is a well-known fact that the cross-linking agent used at the time of the production has an important effect on the water absorption properties of such a water-absorbent resin.

In the case of producing a water-absorbing resin industrially, the crosslinking agent used is easily available industrially, is inexpensive, has affinity with a hydrophilic unsaturated monomer, and has high polymerizability. It must be excellent and highly secure. As such, industrially, copolymerizable with a hydrophilic unsaturated monomer having a carboxyl group, unsaturated carboxylic acid esters of a polyhydric alcohol having a plurality of polymerizable unsaturated groups, for example, Examples include poly (oxyalkylene glycol) di (meth) acrylate, (poly) propylene glycol di (meth) acrylate, trimethylolpropane tri (meth) acrylate, pentaerythritol tetra (meth) acrylate, dipentaerythritol hexa (meth) acrylate, and the like. can do.

In the case of using such a compound as a cross-linking agent to produce a water-absorbing resin having high gel durability and excellent diffusion of an aqueous liquid, the amount of the cross-linking agent used is generally increased. Need to be done. Although there is almost a positive correlation between the amount of the cross-linking agent used and the durability of the gel, the copolymerizability, affinity, and dissolution of the cross-linking agent and the hydrophilic unsaturated monomer having a carboxyl group described above. If the amount is more than a certain amount, the reaction efficiency of the crosslinking agent is reduced. That is, when the amount is more than a certain amount, the effect of increasing the durability of the gel is not seen in proportion to the amount of the crosslinking agent, and the effect of reducing the amount of the water-soluble component that affects the diffusivity and liquid permeability is not seen. And the like. Therefore, in order to obtain a water-absorbent resin having high durability of the target gel, there is a problem that the amount of the cross-linking agent must be excessively increased.

In order to improve the copolymerizability, affinity, solubility, etc., of such a crosslinking agent and a hydrophilic unsaturated monomer, a method in which a surfactant is present at the time of polymerization (Japanese Patent Publication No. 61-1986). Three
No. 6763), a method in which a dispersant is present (Japanese Unexamined Patent Publication No. 1-1469)
No. 02) has been reported so far. However, even in these methods, a surfactant and a dispersant as the third component remain in the obtained water-absorbent resin, and these surfactants and dispersants cause a reduction in the water-absorbing ability of the water-absorbent resin. It is not always a preferred method.

[0009]

The cross-linking agent, which is industrially easily and inexpensively available, generally has a low purity and is a mixture of a plurality of components. Therefore, when the amount of the crosslinking agent used is increased, there is a problem that various properties of the water-absorbing resin are reduced. Conventionally, the performance deterioration of the water-absorbing resin is caused by the fact that the crosslinking agent contains a plurality of unsaturated carboxylic esters of polyhydric alcohols, so that the unsaturated carboxylic esters of these polyhydric alcohols and the hydrophilic unsaturated monomer It was thought to be due to the formation of various copolymers with the body. However, the inventors of the present application have conducted intensive studies to determine the cause of the deterioration in the performance of the water-absorbent resin. As a result, the crosslinking agent contains a high boiling component having two or more polyhydric alcohol skeletons in the molecule in a certain amount or more. Then, it was found that the performance of the water absorbent resin was reduced. That is, it has been found that the above-mentioned problems can be solved by controlling the content of the high boiling component in the crosslinking agent.

Accordingly, an object of the present invention is to solve the above-mentioned problems, to provide a gel with high durability, a small amount of water-soluble components, excellent diffusion and permeability of an aqueous liquid, and use as a sanitary material. An object of the present invention is to provide a water-absorbent resin which exhibits excellent performance even when the resin is used. Further, to provide a method for producing a water-absorbent resin capable of producing a water-absorbent resin without using a third component such as a surfactant or a dispersant, and without excessively using a crosslinking agent. is there.

[0011]

Means for Solving the Problems In order to achieve the above object, the inventors of the present invention have prepared a method of preparing a hydrophilic unsaturated monomer having a carboxyl group in the presence of a crosslinking agent having two or more polymerizable unsaturated bonds. the method of producing water-absorbent resin is polymerized in, and the
As a result of intensive studies on the cross-linking agent used in the production method, when the cross-linking agent used is an esterified product of a trivalent or higher alcohol and an unsaturated carboxylic acid, of the above esterified products, Controlling the amount of esterified product (main component of cross-linking agent) in which the ratio of the molecular weight is in a specific range to the molecular weight of the compound when all the hydroxyl groups form an ester bond with the unsaturated carboxylic acid are controlled in a specific range. By doing so, the copolymerizability, affinity, solubility, etc. of the crosslinking agent and the hydrophilic unsaturated monomer having a carboxyl group are improved, the durability of the gel is high, the amount of the water-soluble component is small, and the aqueous liquid is small. A water-absorbent resin that has excellent diffusibility and liquid permeability, and also shows excellent performance when used for sanitary materials,
The present inventors have found that it can be easily produced without the presence of a third component such as a surfactant or a dispersant and without excessively using a crosslinking agent, and have completed the present invention.

That is, the present invention provides a method for producing a water-absorbent resin, which comprises polymerizing a hydrophilic unsaturated monomer having a carboxyl group in the presence of a crosslinking agent having two or more polymerizable unsaturated bonds, As the crosslinking agent, the number of carbon atoms is 6 or less and 3
When the molecular weight of a compound consisting of an esterified product of an alcohol having a valency of 3 or more and an unsaturated carboxylic acid, and all the hydroxyl groups of the alcohol having a valency of 3 or more form an ester bond with the unsaturated carboxylic acid, 1 A compound having a ratio of the molecular weight to the molecular weight of the compound of at least 0.7 and less than 1.3 contains 90% by weight or more of the main component of the crosslinking agent , and
High boiling components having two or more alcohol skeletons
In addition, a cross-linking agent contained in a range of less than 10% by weight is used.

[0013]

Furthermore, the viscosity of the crosslinking agent is 10 cps ( 0.01 Pa ·
s) to 60 cps (0.06 Pa · s) or less (25 ° C).

Further, it is characterized in that the alcohol having 6 or less carbon atoms and a valency of 3 or more is trimethylolpropane, and the unsaturated carboxylic acid is acrylic acid. Furthermore, the amount of the main component of the crosslinking agent is 0.01 mol% or more and 5 mol% or less based on the hydrophilic unsaturated monomer.

Further, the present invention is a water-absorbing resin obtained by any one of the above-mentioned production methods. Further, the present invention provides
A cross-linking agent that can be used in any of the above-mentioned production methods.
You.

Hereinafter, the present invention will be described in detail. The hydrophilic unsaturated monomer having a carboxyl group used as a raw material in the present invention is not particularly limited, but specific examples include, for example, acrylic acid, methacrylic acid, maleic acid, and maleic anhydride. , Fumaric acid,
Crotonic acid, itaconic acid, sorbic acid, cinnamic acid, and neutralized products thereof. These hydrophilic unsaturated monomers may be used alone or as a mixture of two or more. Of these, acrylic acid, methacrylic acid, and their neutralized products are preferred.

In general, the affinity and solubility between the hydrophilic unsaturated monomer and the crosslinking agent tend to decrease when the carboxyl group of the hydrophilic unsaturated monomer is neutralized. However, in the present invention, when the hydrophilic unsaturated monomer is neutralized, the tendency becomes more remarkable. Therefore,
Of the acrylic acid and methacrylic acid, those in which 30 mol% to 90 mol% of all carboxyl groups are neutralized are preferable, those in which 50 mol% to 80 mol% are neutralized are more preferable, and those in which 60 mol % To 75 mol% are particularly preferred.

The hydrophilic unsaturated monomer having a carboxyl group used as a raw material in the present invention may contain another hydrophilic unsaturated monomer, if necessary.
The other hydrophilic unsaturated monomer is not particularly limited, but specific examples thereof include vinyl sulfonic acid, styrene sulfonic acid, and 2- (meth) acrylamide-2-methylpropane sulfone. Anionic unsaturated monomers such as acid, 2- (meth) acryloylethanesulfonic acid, 2- (meth) acryloylpropanesulfonic acid and salts thereof; acrylamide, methacrylamide, N-ethyl (meth) acrylamide, Nn -Propyl (meth) acrylamide, N-isopropyl (meth) acrylamide, N, N-dimethyl (meth) acrylamide, 2-hydroxyethyl (meth) acrylate, 2-hydroxypropyl (meth) acrylate, methoxypolyethylene glycol (meth) acrylate ,
Nonionic hydrophilic group-containing unsaturated monomers such as polyethylene glycol mono (meth) acrylate, vinylpyridine, N-vinylpyrrolidone, N-acryloylpiperidine, N-acryloylpyrrolidine; N, N-dimethylaminoethyl (meth) acrylate , N, N-diethylaminoethyl (meth) acrylate, N, N-dimethylaminopropyl (meth) acrylate, N, N-dimethylaminopropyl (meth) acrylate, and cationically unsaturated monofunctional compounds such as quaternary salts thereof. And the like. When these other hydrophilic unsaturated monomers are used, they are preferably used in an amount of less than 50% by weight based on the total amount of the hydrophilic unsaturated monomers having a carboxyl group.

In the present invention, the crosslinking agent used in the polymerization is an esterification reaction between an alcohol having 6 or less carbon atoms and a trivalent or higher alcohol and an unsaturated carboxylic acid, or a crosslinking agent having 6 carbon atoms or less.
The following is obtained by a transesterification reaction between a trivalent or higher-valent alcohol and an unsaturated carboxylic acid ester. And
The cross-linking agent has a molecular weight relative to the molecular weight of the compound, where the molecular weight of the compound is 1 when all the hydroxyl groups of the alcohol having 6 or less carbon atoms and 3 or more carbon atoms form an ester bond with the unsaturated carboxylic acid. Ratio of 0.7 or more, 1.3
In a range of 0.9 or less, preferably 90% by weight or more, preferably 95% or more, from the viewpoint of durability and water-soluble content of the resulting water-absorbent resin.
% By weight or more. If the molecular weight ratio is out of the above range, or if the main component of the crosslinking agent is less than 90% by weight, the effect of the present invention cannot be sufficiently obtained, which is not preferable.

The crosslinking agent contains a high-boiling component having two or more trivalent or higher alcohol skeletons in the molecule in a range of more than 0 and less than 10% by weight, or It consists only of components that do not have at least two trivalent or higher alcohol skeletons. When the cross-linking agent contains the high boiling component, the viscosity increases, but the viscosity of the cross-linking agent used in the present invention is 10 cps (0.01 Pas ) or more, and 60 cps (0.06 Pas). It is desirable to be within the following range (25 ° C). If the amount of the high-boiling component is outside the above range, or if the viscosity of the crosslinking agent exceeds 60 cps (0.06 Pas) , the effect of the present invention cannot be sufficiently obtained, which is not preferable. . The method for measuring the viscosity will be described later.

That is, since the above-mentioned cross-linking agent has a high content of the main component of the cross-linking agent of 90% by weight or more, it is possible to improve the performance of the resulting water-absorbent resin such as the durability and the amount of water-soluble components of the gel. Has become. It is not clear why the performance is improved in this way, but when the content of the crosslinking agent main component in the crosslinking agent increases,
It is presumed that the affinity and solubility for the hydrophilic unsaturated monomer having a carboxyl group are drastically increased, thereby forming a uniform crosslinked structure. When the content of the main component of the cross-linking agent is less than 90% by weight, the performance of the gel of the water-absorbent resin, such as the durability and the amount of the water-soluble component, becomes poor, but this makes it difficult to form a uniform cross-linked structure. It is presumed that it is because.

Generally, industrially available unsaturated carboxylic esters such as acrylates having a plurality of functional groups (hereinafter, referred to as polyfunctional) are usually prepared from polyhydric alcohols and unsaturated carboxylic acids. Or an ester exchange reaction between a polyhydric alcohol and an unsaturated carboxylic acid ester. However,
Since these unsaturated carboxylic esters are polyfunctional, it is difficult to produce at high selectivity the desired product, that is, a product in which all of the hydroxyl groups of the polyhydric alcohol are esterified. Therefore, compounds commercially available as polyfunctional unsaturated carboxylic acid esters generally have low purity and are a mixture of a plurality of components.

For example, the inventors of the present invention have analyzed the composition of several commercially available trimethylolpropane triacrylates, and found that any of them contains 20% to 25% of a compound which is considered to be an intermediate or a by-product. Thus, the target product, trimethylolpropane triacrylate, contained at most 80%. Therefore,
Even if such an industrially available unsaturated carboxylic acid ester having a low purity is used as a crosslinking agent, the effects obtained in the present invention cannot be expected.

The crosslinking agent used in the present invention is a commercially available polyfunctional unsaturated carboxylic acid ester.
For example, a separation and purification method by column chromatography,
It is obtained by increasing the content of the main component of the crosslinking agent by a separation and purification method using an adsorbent such as silica gel, zeolite, activated carbon or the like, or a simple separation and purification method such as extraction with an organic solvent.

The alcohols having 6 or less carbon atoms and having 3 or more carbon atoms that can be used in preparing the crosslinking agent of the present invention are not particularly limited, but include glycerin, trimethylolethane, and tetramethylolethane. , Trimethylolpropane, tetrahydroxyethane, pentaerythritol and the like are desirable. Of these, trimethylolpropane is particularly preferred. Examples of the unsaturated carboxylic acid that can be used when preparing the crosslinking agent include the above-mentioned hydrophilic unsaturated monomer having a carboxyl group, and acrylic acid is particularly preferable.

As a main component of the crosslinking agent, the alcohol having 6 or less carbon atoms and a trivalent or higher alcohol is used as an alcohol component.
Examples of the polyfunctional unsaturated carboxylic acid esters having the unsaturated carboxylic acid as an acid component include, in addition, for example,
A mixture of glycerin tri (meth) acrylate and glycerin di (meth) acrylate, a mixture of trimethylolethane tri (meth) acrylate and trimethylolethanedi (meth) acrylate, a mixture of tetramethylolethanetetra (meth) acrylate and tetramethylolethane ( A mixture of (meth) acrylate, a mixture of trimethylolpropane tri (meth) acrylate and trimethylolpropane di (meth) acrylate, a mixture of tetrahydroxyethanetetra (meth) acrylate and tetrahydroxyethanetri (meth) acrylate, and the like can be given.

The effect of the present invention can be obtained by using, as a main component of the crosslinking agent, one having low affinity and solubility with a hydrophilic unsaturated monomer having a carboxyl group (particularly in a neutralized form). Are remarkably easy to appear. Further, as a main component of the crosslinking agent,
Those having three or more polymerizable unsaturated bonds are particularly preferable from the viewpoint of improving the durability of the gel of the resulting water-absorbent resin and the performance such as the amount of water-soluble components.

The main component of the crosslinking agent in the present invention is an esterified product of a polyhydric alcohol having 6 or less carbon atoms and 3 or more carbon atoms and an unsaturated carboxylic acid. When the main component of the cross-linking agent is produced by an esterification reaction, even if an esterification intermediate such as a monoester or a diester is formed, the range defined above as a product corresponding to the main component of the cross-linking agent is obtained. The reaction product obtained by a single esterification reaction step can be used as it is as a cross-linking agent in the present invention. At that time, even if by-products not corresponding to the cross-linking agent main component, for example, high boiling components are generated,
As long as the production amount does not deviate from the object of the present invention,
Even if such a by-product is used as a cross-linking agent, it can be used without any problem.

The amount of the crosslinking agent used is preferably from 0.01 mol% to 5 mol%, more preferably from 0.05 mol% to 1 mol%, based on the amount of the hydrophilic unsaturated monomer having a carboxyl group. It is preferred that In addition, a small amount of a second crosslinking agent other than the above crosslinking agent may be used at the time of polymerization to the extent that the effects of the present invention are not impaired. Examples of the second crosslinking agent include methylene bisacrylamide, (poly) ethylene glycol di (meth) acrylate, (poly) ethylene glycol diglycidyl ether, glycerol diglycidyl ether, ethylene glycol, polyethylene glycol, propylene glycol, glycerin,
Examples include pentaerythritol, ethylene carbonate, propylene carbonate, ethylene diamine, polyethylene imine, glycidyl (meth) acrylate, and the like.

For the purpose of obtaining a graft copolymer, starch, cellulose, their derivatives, and water-soluble polymers such as polyacrylic acid and polyvinyl alcohol are present in an aqueous solution of the above-mentioned hydrophilic unsaturated monomer. May be.

In the present invention, when the above-mentioned hydrophilic unsaturated monomer having a carboxyl group is polymerized in the presence of a crosslinking agent, bulk polymerization or precipitation polymerization can be carried out. From the viewpoint of ease of control and the like, aqueous solution polymerization and reverse phase suspension polymerization in which a hydrophilic unsaturated monomer is made into an aqueous solution are preferable, and among them, aqueous solution polymerization without using an organic solvent is more preferable. In this case, the concentration of the hydrophilic unsaturated monomer in the aqueous solution is from 20% by weight to a saturated concentration, and more preferably about 25% by weight to 40% by weight in order to achieve the effects of the present invention.

At the start of the polymerization, potassium persulfate,
Radical polymerization initiators such as ammonium persulfate, sodium persulfate, t-butyl hydroperoxide, hydrogen peroxide, 2,2′-azobis (2-amidinopropane) dihydrochloride, and active energy rays such as ultraviolet rays and electron beams Can be used. When an oxidative radical polymerization initiator is used, redox polymerization may be performed by using a reducing agent such as sodium sulfite, sodium hydrogen sulfite, ferrous sulfate, or L-ascorbic acid in combination.

The water content of the water-absorbent resin is 0.1% to 50%, preferably 1% to 20%, more preferably 1% so that the obtained water-absorbent resin can be handled as a particulate powder. % To 10%, and for this purpose, a drying step is usually provided following the polymerization step.

In the present invention, in the above production process, it is preferable to heat-treat the polymer obtained by polymerization at 80 to 250 ° C. More preferably, heat treatment is performed at 150 ° C to 220 ° C. If the heat treatment temperature exceeds 250 ℃,
There is a possibility that the water-absorbing resin may be deteriorated, and if the temperature is lower than 80 ° C., the strength of the gel may be insufficient with respect to a target value. The above-mentioned heat treatment can be performed using a usual dryer or a heating furnace, and includes a hot air conduction type dryer, a groove type mixing dryer, a rotary dryer, a disk dryer, a fluidized bed dryer, and a gas stream type dryer. , And an infrared dryer.

The shape of the resulting water-absorbent resin may be various, such as irregularly crushed, spherical, fibrous, rod-like, substantially spherical, and the like. Considering the application to sanitary materials such as difficulty in work, it is an amorphous crushed shape obtained by aqueous solution polymerization, and its average particle size is 100 μm to 1000 μm, especially 300 μm to 600 μm.
μm is most preferred.

In the present invention, the water-absorbing resin thus obtained may be mixed with a third cross-linking agent capable of reacting with a carboxyl group to further cross-link the vicinity of the surface. As the third crosslinking agent that can be used, usually,
Known cross-linking agents used for this purpose are exemplified. Specifically, for example, ethylene glycol, diethylene glycol, propylene glycol, triethylene glycol, tetraethylene glycol, polyethylene glycol, propylene glycol, 1,3-propanediol, dipropylene glycol, 2,2,4-trimethyl-1, 3-pentadiol, polypropylene glycol, glycerin, polyglycerin, 2-butene-1,4
-Diol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, 1,2-cyclohexanedimethanol, 1,2-cyclohexanol, trimethylolpropane, diethanolamine, triethanolamine, poly Polyhydric alcohol compounds such as oxypropylene, oxyethyleneoxypropylene block copolymer, pentaerythritol and sorbitol;
Polyhydric epoxy compounds such as ethylene glycol diglycidyl ether, polyethylene diglycidyl ether, glycerol polyglycidyl ether, diglycerol polyglycidyl ether, polyglycerol polyglycidyl ether, propylene glycol diglycidyl ether, and polypropylene glycol diglycidyl ether; ethylenediamine, diethylenetriamine, Polyvalent amine compounds such as triethylenetetramine, tetraethylenepentamine, pentaethylenehexamine and polyethyleneimine; polyvalent isocyanate compounds such as 2,4-tolylenediisocyanate and hexamethylene diisocyanate;
Polyvalent oxazoline compounds such as 1,2-ethylenebisoxazoline; 1,3-dioxolan-2-one, 4-methyl-1,3-dioxolan-2-one, 4,5-dimethyl-1,3-dioxolan- 2-one, 4,4-dimethyl-1,3-dioxolan-2-one, 4-ethyl-
1,3-dioxolan-2-one, 4-hydroxymethyl-1,3-dioxolan-2-one, 1,3-dioxan-2-one, 4-methyl-1,3-dioxane-2
-One, 4,6-dimethyl-1,3-dioxane-2-
Alkylene carbonate compounds such as on, 1,3-dioxopan-2-one; haloepoxy compounds such as epichlorohydrin, epibromohydrin, α-methylepichlorohydrin; zinc, calcium, magnesium, aluminum, iron, zirconium And polyvalent metal compounds such as chlorides.

When mixing the third crosslinking agent for crosslinking near the surface, it is preferable to add water simultaneously or separately. When mixing the third crosslinking agent,
So-called water-insoluble fine powder, a surfactant, a hydrophilic organic solvent, or the like may be used.

The water-absorbent resin obtained by the present invention further comprises a deodorant, a fragrance, an inorganic powder, a foaming agent, a pigment, a dye, a hydrophilic short fiber, a synthetic fiber, a fertilizer, an oxidizing agent, a reducing agent, water, salts and the like. It may be added. By adding these, various functions can be imparted to the water-absorbing resin, so that it can be applied to various fields in addition to the above-mentioned sanitary materials such as disposable diapers and sanitary napkins.

[0040]

According to the above method, it is possible to produce a water-absorbing resin without the presence of a third component such as a surfactant or a dispersant and without excessively using a crosslinking agent. In addition, the water-absorbent resin obtained by the above method has high gel durability, a small amount of a water-soluble component, excellent diffusion and liquid permeability of an aqueous liquid, and is excellent even when used as a sanitary material. Can show performance. The above water-absorbing resin can be particularly suitably used for sanitary materials such as disposable diapers and sanitary napkins even when the amount of the water-absorbing resin is increased.

[0041]

The present invention will be described in more detail with reference to the following Examples and Comparative Examples, but the present invention is not limited thereto. The various properties of the water-absorbent resin are as follows:
It was measured by the following method.

(A) Water absorption capacity A non-woven tea bag type bag (40 mm
× 150 mm) and immersed in a 0.9% by weight aqueous sodium chloride solution (physiological saline). Thirty minutes later, the tea bag-type bag was pulled out and drained for a certain time, and then the weight W ₁ of the tea bag-type bag was measured. Also conducted without using the water-absorbent resin The same operation was weighed W ₀ at that time. From these weights W ₁ · W ₀ , the water absorption capacity (g / g) was calculated according to the following equation.

[0043]

(Equation 1)

(B) Gel Durability 2.0 g of a water-absorbent resin was placed in a 100-ml polypropylene container (diameter: 50 mm) with a lid, and 50 ml of urine collected from five adults was added to the water-absorbent resin to swell. After standing at 40 ° C. for 24 hours, the container was turned sideways, and the distance (mm) over which the swollen gel flowed and moved per minute was measured. The shorter the moving distance, the more stable the swollen gel is against urine and the more durable it is.

(C) Amount of Water-Soluble Component 0.500 g of the water-absorbent resin was dispersed in 1000 ml of deionized water, stirred for 16 hours, then filtered with a filter paper, and the amount (%) of the water-soluble component was determined by colloid titration. Was.

The viscosity of the crosslinking agent was measured by the following method. That is, by circulating hot water in a thermostat, 25 ° C
1 ml of a cross-linking agent is put into a sample container held in a sample, and a viscosity measuring device (manufactured by Tokyo Keiki Co., Ltd .: VISCONIC E)
(MD type), and after one minute, the viscosity under the set conditions was measured. The crosslinking agent was prepared by the following method.

[Preparation Method 1] 1 L4 equipped with a stirrer, a water separation tube with a cooling tube, a thermometer, and an air blowing tube
134 g of trimethylolpropane, 238 g of acrylic acid, 170 g of toluene, 24 g of p-toluenesulfonic acid and 0.6 g of hydroquinone were added to a one-necked flask, and the flask was heated at 130 ° C. while blowing air.

The reaction product was traced by gel permeation chromatography (GPC) and gas chromatography (GC) while distilling off the reaction product water by azeotropic dehydration with toluene, and trimethylolpropane triacrylate and trimethylolpropane were used. When the total content of methylolpropane diacrylate reached 81% by weight, the reaction was stopped.

Next, the reaction solution was transferred to a separating funnel, and 10% N
Unreacted acrylic acid was neutralized and separated with 500 g of aOH water and 300 g of 5% NaOH water, and then washed several times with 500 g of water until the washing became neutral. Thereafter, 0.06 g of hydroquinone monomethyl ether was added to the organic layer, and toluene was distilled off under reduced pressure to obtain a reaction product.

As a result of analyzing the reaction product using GPC and GC, the content of trimethylolpropane triacrylate and trimethylolpropane diacrylate corresponding to the main component of the crosslinking agent was 85% by weight in total.

Subsequently, silica gel (manufactured by Merk: No.
7734) Using a glass column filled with 600 g and having an inner diameter of 80 mm and a length of 500 mm, hexane / ethyl acetate = 10/1 (v
ol / vol) was used as a developing solvent for column chromatography, and 20 g of the above reaction product was separated into each component. As a result, trimethylolpropane triacrylate (a compound in which all hydroxyl groups of trimethylolpropane are ester-bonded to acrylic acid. Molecular weight 296. Molecular weight ratio of the present invention)
1.0) 15.5 g (purity 99%) were obtained.

Incidentally, chloroform / methanol = 25/1
Using (vol / vol) as a developing solvent, the component adsorbed on the silica gel was eluted, and the solvent was distilled off from the eluted portion, whereby 4 g of an organic substance was obtained. As a result of analyzing the organic matter using GPC, it was estimated that the compound had a molecular weight of 400 to 1,000. From these molecular weight ranges, these were presumed to be multimers (molecular weight ratio: 1.35 to 3.88, condensate) such as trimethylolpropane triacrylate, trimethylolpropane diacrylate, or trimethylolpropane monoacrylate. That is, the organic substance is a high boiling component.

[Preparation method 2] Column chromatography was carried out in the same manner as in Preparation method 1 using hexane / ethyl acetate = 3/2 (vol / vol) as a developing solvent, and the reaction product obtained in Preparation method 1 was obtained. From 30 g, 1.5 g (purity: 99%) of trimethylolpropane diacrylate (molecular weight ratio: 0.82) was obtained.

Next, a hydrophilic unsaturated monomer having a carboxyl group was polymerized using the crosslinking agent obtained by the above Preparation Methods 1 and 2.

Example 1 To 425 g of acrylic acid as a hydrophilic unsaturated monomer was added trimethylolpropane triacrylate (purity 99) obtained in Preparation Method 1 as a crosslinking agent.
%) Of 4.88 g was dissolved, and 4,500 g of a 37% by weight aqueous solution of sodium acrylate and 540 g of ion-exchanged water were added to prepare a reaction solution. Next, an internal volume of 10 L having two sigma type blades
The above reaction solution is supplied to a reactor formed by attaching a lid to a jacketed stainless steel double-arm kneader of
While maintaining the temperature at 22 ° C., the system was replaced with nitrogen gas. Subsequently, the reaction solution was stirred while being maintained at 22 ° C., and sodium persulfate 2.83
g and L-ascorbic acid 0.12 g were added to initiate polymerization. Then, 40 minutes after the start of the polymerization, the hydrogel polymer was taken out.

The obtained hydrogel polymer was subdivided into finely divided products. The finely divided products were spread on a 50-mesh wire net and dried with hot air at 150 ° C. for 90 minutes. Next, the dried product was pulverized by using a vibration mill, and further classified by a 20-mesh wire net to obtain a water content of 8% and an average particle size of 370.
A μm amorphous crushed water-absorbent resin was obtained. The amount and viscosity of the cross-linking agent, the contents of the main component of the cross-linking agent and the high boiling components, the water absorption capacity of the obtained water-absorbent resin, the durability of the gel, and the amount of the water-soluble component (hereinafter simply referred to as the result) It is described according to Table 1.

As is apparent from the results, a water-absorbent resin having high gel durability, a small amount of water-soluble components, and excellent performance in diffusing and permeating an aqueous liquid was obtained.

Example 2 As a cross-linking agent, the trimethylolpropane triacrylate obtained in Preparation Method 1 (purity
A water-absorbent resin was obtained in the same manner as in Example 1, except that a mixture of 4.64 g (99%) and 0.24 g of the above-mentioned organic substance (crosslinking agent main component content: 95%) was used. Table 1 shows the obtained results.
It is described in accordance with.

Example 3 As a cross-linking agent, trimethylolpropane triacrylate (purity) obtained in Preparation Method 1 was used.
A water-absorbent resin was obtained in the same manner as in Example 1, except that a mixture (99%) of 4.39 g and the above organic substance (0.49 g) was used (the main component content of the crosslinking agent was 90%). Table 1 shows the obtained results.
It is described in accordance with.

Example 4 As a cross-linking agent, trimethylolpropane triacrylate (purity) obtained in Preparation Method 1 was used.
(99%) The same operation as in Example 1 was carried out except that 6.98 g was used to obtain a water-absorbent resin. The obtained results are shown in Table 1.

Example 5 As a crosslinking agent, trimethylolpropane triacrylate (purity) obtained in Preparation Method 1 was used.
A water-absorbent resin was obtained by performing the same operation as in Example 1 except that a mixture of 6.63 g (99%) and 0.35 g of the above-mentioned organic substance (crosslinking agent main component content: 95%) was used. Table 1 shows the obtained results.
It is described in accordance with.

Example 6 As a crosslinking agent, trimethylolpropane triacrylate (purity) obtained in Preparation Method 1 was used.
A water-absorbent resin was obtained in the same manner as in Example 1 except that a mixture (99%) of 6.28 g and the above-mentioned organic substance (0.7 g) was used (the content of the main component of the crosslinking agent was 90%). Table 1 shows the obtained results.
It is described in accordance with.

Example 7 As a cross-linking agent, trimethylolpropane triacrylate (purity) obtained in Preparation Method 1 was used.
Except that 3.49 g of 99%) was used, the same operation as in Example 1 was performed to obtain a water-absorbing resin. The obtained results are shown in Table 1.

Example 8 As a cross-linking agent, the trimethylolpropane triacrylate obtained in Preparation Method 1 (purity
(99%) A water-absorbent resin was obtained in the same manner as in Example 1 except that a mixture of 3.32 g of the organic substance and 0.17 g of the above-mentioned organic substance (crosslinking agent main component content: 95%) was used. Table 1 shows the obtained results.
It is described in accordance with.

Example 9 As a cross-linking agent, the trimethylolpropane triacrylate obtained in Preparation Method 1 (purity
A water-absorbent resin was obtained in the same manner as in Example 1, except that a mixture of 3.14 g (99%) and 0.35 g of the above organic substance (the main component content of the crosslinking agent was 90%) was used. Table 1 shows the obtained results.
It is described in accordance with.

Example 10 As cross-linking agents, 4.15 g of trimethylolpropane triacrylate (purity 99%) obtained by Preparation Method 1, and trimethylolpropane diacrylate (purity 99%) obtained by Preparation Method 2 A water-absorbent resin was obtained by performing the same operation as in Example 1 except that a mixture with 0.73 g (99% of the main component of the crosslinking agent) was used. The obtained results are shown in Table 1.

Example 11 As cross-linking agents, 2.97 g of trimethylolpropane triacrylate (purity 99%) obtained by Preparation Method 1, and trimethylolpropane diacrylate (purity 99%) obtained by Preparation Method 2 A water-absorbent resin was obtained by performing the same operation as in Example 1 except that a mixture with 0.52 g (99% of a crosslinking agent main component content) was used. The obtained results are shown in Table 1.

Example 12 As cross-linking agents, 5.93 g of trimethylolpropane triacrylate (purity 99%) obtained by Preparation Method 1, and trimethylolpropane diacrylate (purity 99%) obtained by Preparation Method 2 A water-absorbent resin was obtained in the same manner as in Example 1, except that a mixture with 1.05 g (99% of the main component of the crosslinking agent) was used. The obtained results are shown in Table 1.

As is evident from the results of Examples 2 to 12, as in Example 1, the gel has high durability, a small amount of water-soluble components, and excellent performance in diffusing and permeating aqueous liquids. Was obtained.

Comparative Example 1 Instead of the crosslinking agent of the present invention in Example 1, 4.88 g of a commercially available product, trimethylolpropane triacrylate (manufactured by Rhone Poulin, content of the main component of the crosslinking agent: 80%) was used. Except for the above, the same operation as in Example 1 was performed to obtain a water absorbent resin. The obtained results are shown in Table 1.

Comparative Example 2 A mixture of 2.69 g of trimethylolpropane triacrylate (purity: 99%) obtained in Preparation Method 1 and 0.80 g of the above organic substance was used in place of the crosslinking agent of the present invention in Example 1. The same operation as in Example 1 was carried out except that the crosslinker main component content was 76%) to obtain a water absorbent resin. The obtained results are shown in Table 1.

[Comparative Example 3] A mixture of 4.23 g of trimethylolpropane triacrylate (purity 99%) obtained in Preparation Method 1 and 2.75 g of the above organic substance instead of the crosslinking agent of the present invention in Example 1 ( A water-absorbent resin was obtained by performing the same operation as in Example 1 except that the crosslinker main component content was 60%. The obtained results are shown in Table 1.

Comparative Example 4 In place of the crosslinking agent of the present invention in Example 7, the reaction product obtained in Preparation Method 1 (ie,
The same operation as in Example 7 was carried out, except that 3.49 g of a reaction product having a total content of trimethylolpropane triacrylate and trimethylolpropane diacrylate of 85% by weight was used as a crosslinking agent, to obtain a water-absorbent resin. Was.
The obtained results are shown in Table 1.

As is clear from the results of Comparative Examples 1 to 4,
When an industrially available low-purity crosslinking agent was used, Examples 1 to 12 obtained using the crosslinking agent of the present invention were used.
Only a water-absorbent resin exhibiting poorer performance in gel durability, water-soluble component amount, aqueous liquid diffusivity, and liquid permeability than the water-absorbent resin described above was obtained.

[0075]

[Table 1]

[0076]

According to the above method, it is possible to produce a water-absorbent resin without the presence of a third component such as a surfactant or a dispersant and without excessively using a crosslinking agent. Become. Therefore, the above method has an effect that it is suitably used as a method for producing a water-absorbing resin.

The water-absorbent resin obtained by the above-mentioned method has high gel durability, a small amount of water-soluble components, is excellent in diffusibility and liquid permeability of aqueous liquids, and has a low water-absorbing property when used as a sanitary material. Also has an effect that excellent performance can be exhibited. The above water-absorbing resin can be particularly suitably used for sanitary materials such as disposable diapers and sanitary napkins even when the amount of the water-absorbing resin is increased.

────────────────────────────────────────────────── ─── Continued on the front page (72) Inventor Hideaki Nagano 992, Nishioki, Okihama-shi, Abashiri-ku, Himeji-shi, Hyogo Nippon Shokubai Co., Ltd. (72) Inventor Hideyuki Kubo 992, Nishioki, Okihama-ji, Abashiri-ku, Himeji-shi, Hyogo (56) References JP-A-3-179008 (JP, A) JP-A-2-209906 (JP, A) JP-A-63-275608 (JP, A) (58) Fields investigated (Int. Cl. ^7, DB name) C08F 220/06 C08F 220/20 CA (STN ) REGISTRY (STN)

Claims (11)

(57) [Claims] 1. A method for producing a water-absorbent resin, comprising polymerizing a hydrophilic unsaturated monomer having a carboxyl group in the presence of a crosslinking agent having two or more polymerizable unsaturated bonds, wherein the crosslinking agent is When it is composed of an ester of an alcohol having 6 or less carbon atoms and having a valency of 3 or more and an unsaturated carboxylic acid, and all the hydroxyl groups of the alcohol having a valency of 3 or more form an ester bond with the unsaturated carboxylic acid. Assuming that the compound of formula (1) has a molecular weight of 1, the compound contains 90% by weight or more of the main component of a crosslinking agent having a ratio of the molecular weight to the molecular weight of 0.7 or more and less than 1.3 , and has the alcohol in the molecule.
High boiling component having two or more skeletons
% Of a water-absorbent resin, comprising using a crosslinking agent contained in an amount of less than 10% . 2. The crosslinking agent has a viscosity of 10 cps (0.01 Pa · s) or more,
2. The method for producing a water-absorbent resin according to claim 1, wherein the temperature is in the range of not more than 60 cps (0.06 Pa · s) (25 ° C.). 3. and the number of carbon atoms is at most 6 trihydric or higher alcohol is trimethylol propane, and claim 1 or unsaturated carboxylic acid is characterized in that the acrylic acid
Or the method for producing a water-absorbent resin according to 2 . The amount of wherein the crosslinking agent mainly composed, the hydrophilic unsaturated monomer to 0.01 mol% or more, 5 claims 1 to equal to or less than the molar% any one of 3 3. The method for producing a water-absorbent resin according to item 1. 5. The obtained water-absorbent resin has an average particle size of 300 μm.
The method for producing a water-absorbent resin according to any one of claims 1 to 4 , wherein the thickness is from 600 to 600 µm. 6. A resulting water-absorbing resin is mixed with a third cross-linking agent capable of reacting with a carboxyl group, any one of claims 1 to 5, characterized in that to further crosslink the surface neighborhood 3. The method for producing a water-absorbent resin according to item 1. 7. The method of claim 1 to water-absorbent resin obtained by any of the manufacturing methods 6. 8. A sanitary material containing the water absorbent resin according to claim 7 . 9. A hydrophilic unsaturated monomer having a carboxyl group
Of cross-linking agent having two or more polymerizable unsaturated bonds
Can be used in the production of water-absorbent resin to be polymerized under
A crosslinking agent, wherein the crosslinking agent has two or more polymerizable unsaturated bonds.
It comprises an ester of an alcohol having 6 or less carbon atoms and having a valency of 3 or more and an unsaturated carboxylic acid, and all hydroxyl groups of the alcohol having a valency of 3 or more form an ester bond with the unsaturated carboxylic acid Assuming that the molecular weight of the compound when formed is 1, the ratio of the molecular weight to the molecular weight of the compound is not less than 0.7 and less than 1.3, the cross-linking agent main component is not less than 90% by weight, and the alcohol skeleton is contained in the molecule. 2 or more
Having a high boiling component in a range of more than 0 and less than 10% by weight
Crosslinking agent characterized by containing. 10. A viscosity of 10 cps (0.01 Pa · s) or more, 60 cps.
10. The crosslinking agent according to claim 9 , wherein the temperature is in the range of (0.06 Pa · s) or less (25 ° C.). 11. and the number of carbon atoms is at most 6 trihydric or higher alcohol is trimethylolpropane, claim 9 or an unsaturated carboxylic acid is characterized in that the acrylic acid
10. The crosslinking agent according to 10 .