JP3466222B2 - Method for producing water absorbent resin - Google Patents

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a method for producing a water absorbent resin. More specifically, the present invention has a high absorption capacity,
The present invention relates to a method for producing a water-absorbent resin having a small amount of water-soluble components and excellent stability over time.

[0002]

2. Description of the Related Art Water-absorbent resins have hitherto been used in various water-absorbing materials such as paper diapers (or disposable diapers), sanitary products and soil water retention agents. Examples of such a water-absorbent resin include a hydrolyzate of a starch-acrylonitrile graft copolymer, a neutralized product of a starch-acrylic acid graft copolymer, a cross-linked acrylic acid or acrylate polymer, and a partial cross-linked polyethylene oxide. And carboxymethyl cellulose cross-linked products are known.

Among the above-mentioned crosslinked polymers, at present, a crosslinked polymer obtained by copolymerizing a water-soluble monoethylenically unsaturated monomer such as acrylic acid in the presence of a crosslinkable monomer is a raw material. Moreover, it is inexpensive, has excellent water absorption properties, and is not worried about spoilage, and thus has become the mainstream of water-absorbent resins (JP-A-60-24807 and US Pat. No. 4).
351922).

[0004]

However, in these water-absorbent resins, the amount of water-soluble component (component soluble in water) usually increases as the absorption capacity increases. When such a water-absorbent resin containing a large amount of water-soluble components is used for a long time, for example, in a diaper, the problem of sliming on the surface of the diaper, or poor liquid permeability and practical water absorption capacity and liquid diffusivity Therefore, there is a problem that leakage is likely to occur. On the contrary, if the amount of the cross-linking agent used is increased in order to reduce the water-soluble component in the water absorbent resin, the absorption capacity will be reduced and the range of use of the water absorbent resin will be limited.

In addition to the problem of the water-soluble component, there is a problem of stability of the swollen gel over time. For example, when used in a diaper or the like, there is a problem that the swollen gel of the water-absorbent resin that has absorbed urine deteriorates with time (fluidization of the gel), leading to deterioration of the absorption characteristics. In addition, even if it is used for a long time such as for agricultural and horticultural use, it may be deteriorated or decomposed.
As a known method for preventing the deterioration and decomposition of the swollen gel of the water-absorbent resin, a method of incorporating an oxygen-containing reducing inorganic salt or a radical chain inhibitor into the water-absorbent resin (Japanese Patent Laid-Open No. 63-118375). JP-A-63-152667
No.), a method of incorporating an oxidizing agent (Japanese Patent Laid-Open No. 63-1530).
No. 60), and a method of incorporating a sulfur-containing reducing agent (JP-A-6-61)
3-272349). However, all of these methods are methods of adding an additive for deterioration prevention to the water absorbent resin, and adding other additives means that these water absorbent resins are used for sanitary materials and the like. Therefore, it was not always preferable in terms of safety.

[0006] Therefore, there is also a method of increasing the crosslink density of the water-absorbent resin by using a large amount of the cross-linking agent to increase the gel strength and improve the stability over time. However, these water-absorbent resins are sufficiently stable over time. In order to impart the property, there is a problem that the water absorption capacity becomes extremely low due to the high crosslinking.

[0007]

Means for Solving the Problems As a result of intensive studies to solve the above problems, the present inventors have found that a water-soluble ethylenically unsaturated monomer is used in the presence of a crosslinking agent having a specific structure. It was found that the polymer obtained by polymerization has a high absorption capacity only when it is heat-treated in a certain temperature range, has a small amount of water-soluble components, and can be a water-absorbent resin having excellent stability over time. Completed the invention.

That is, the present invention provides a method for producing a water-absorbent resin in which a water-soluble monoethylenically unsaturated monomer is polymerized in an aqueous solution in the presence of a cross-linking agent, and the resulting polymer is heat-treated. Having at least two polymerizable unsaturated groups as a unit, and at least one unit represented by the chemical formula (1) between the at least two polymerizable unsaturated groups.

[0009]

[Chemical 6]

[0010] (however, ^{R 1} in the chemical formula (1), following one
At least selected from the group consisting of general formulas (a) to (c)
It is one kind of alkylene group. ) Having a molecular weight of 600
The cross-linking agent (I) of 0 or less is used in a proportion of 0.01 to 0.3 mol% with respect to the water-soluble monoethylenically unsaturated monomer, and the heat treatment of the polymer is carried out by the polymer. It relates to a method for producing a water absorbent resin, which is carried out at a heat treatment temperature of 160 to 230 ° C. in the presence of a crosslinking agent (III) having at least two reactive groups capable of reacting with a functional group.

[Chemical formula 20] The present invention also provides an acid group-containing monomer and the acid group-containing unit amount.
Body metal, ammonium and amine salts, nonions
Hydrophilic group-containing monomer, amino group-containing monomer and
A small amount selected from the group consisting of quaternized products of mino group-containing monomers.
At least one water-soluble monoethylenically unsaturated monomer (however
Monomers that do not contain hypophosphorous acid and thiomalic acid)
Aqueous solution polymerization in the presence of a cross-linking agent, heating the resulting polymer
In the method for producing a water absorbent resin to be treated, with the crosslinking agent
And has at least two polymerizable unsaturated groups,
At least one between the at least two polymerizable unsaturated groups
Unit represented by chemical formula (1)

[Chemical formula 21] (However, R1 in the chemical formula (1) is an alkane having 2 to 4 carbon atoms.
It is a xylene group. ) Having a molecular weight of 6000 or less
The crosslinking agent (I) is a water-soluble monoethylenically unsaturated monomer
Used in a proportion of 0.01 to 0.3 mol% with respect to the body, and
The heat treatment of the polymer may react with the functional groups of the polymer.
Of a crosslinking agent (III) having at least two reactive groups
In the presence of heat treatment temperatures of 160-230 ° C.
And a method for producing a water-absorbent resin.

[0011]

The water-soluble monoethylenically unsaturated monomer used in the present invention has one ethylenically unsaturated group,
It is not particularly limited as long as it is a water-soluble monomer, and examples thereof include (meth) acrylic acid, itaconic acid, 2- (meth) acryloylethanesulfonic acid, 2- (meth) acryloylpropanesulfonic acid, 2- ( (Meth) acrylamide
Acid group-containing monomer such as 2-methylpropanesulfonic acid, vinylsulfonic acid, styrenesulfonic acid; metal salt, ammonium salt or amine salt of the acid group-containing monomer; (meth)
Nonionic hydrophilic group-containing monomers such as acrylamide and alkoxypolyethylene glycol (meth) acrylate; amino group-containing monomers such as diethylaminoethyl (meth) acrylate, diethylaminopropyl (meth) acrylate and dimethylaminopropyl (meth) acrylamide A quaternized product of the amino group-containing monomer and the like, and one or more selected from these groups can be used.

A preferred water-soluble monoethylenically unsaturated monomer is a monomer containing acrylic acid and at least 50% by weight or more of at least one selected from alkali metal salts, ammonium salts and amine salts thereof. Here, the salt preferably has a neutralization ratio of 30 to 80%. Neutralization may be performed after polymerization.

Further, other monomers may be used in combination so long as the performance of the resulting water-absorbent resin is not significantly impaired, and further natural or synthetic polymers such as starch, cellulose and polyvinyl alcohol may be used. You may polymerize in addition to a water-soluble monoethylenically unsaturated monomer as a grafting component. Other monomers that can be used in combination with the water-soluble monoethylenically unsaturated monomer include, for example, methyl (meth) acrylate, ethyl (meth) acrylate, butyl (meth).
Examples thereof include acrylate, vinyl acetate, vinyl propionate, and the like, and these may be used in combination of two or more kinds.

The cross-linking agent (hereinafter referred to as cross-linking agent (I)) used in the present invention has at least one unit represented by the following chemical formula (1) in the molecule.

[0015]

[Chemical 6]

(However, R ¹ in the chemical formula (1) has 2 carbon atoms.
To 4 alkylene groups. ) Between at least two polymerizable unsaturated groups. Where the carbon number is 2
The alkylene group of 4 may have either a straight chain structure or a branched structure, and examples thereof include compounds represented by the following general formulas (a) to (c).

[0017]

[Chemical 7]

And the like. The molecular weight of the cross-linking agent (I) is preferably not more than 6000, especially 214 to 50
00 is preferable, and 214 to 2500 is most preferable.

A typical example of such a crosslinking agent (I) is represented by the following chemical formula (2).

[0020]

[Chemical 8]

(However, R ² and R ^{3 in the} chemical formula (2) are
Are each independently hydrogen or methyl, and n is 2 to 10
It is 0, preferably 2 to 50. And a compound having the structure represented by the following chemical formula (3)

[0022]

[Chemical 9]

[However, R ² and R ^{3 in the} chemical formula (3) are
Are each independently hydrogen or a methyl group, and X is 1 to
100, preferably 1 to 50 -CH2CH2
Structure 2 unit (A) represented by O-, 1 to 20, preferably 1 to 10 -R ⁴ O- (wherein R ⁴ has 3 to 10 carbon atoms).
4 is an alkylene group. ) Structural unit (B)
Is a divalent organic group linearly bonded in an arbitrary sequence, or X is 1 to 5, preferably 1 to 3
Structural unit (C) represented by (CO-CH = CH-CO-O)-, 2 to 100, preferably 4 to 50 CH ₂
Structural unit (D) represented by CH ₂ O- and 0 to 20
, Preferably 0 to 10 structural units (E) represented by —R ⁵ O— (wherein R ⁵ is an alkylene group having 3 to 4 carbon atoms) are linear in any sequence. It is a bonded divalent organic group. ] It is a compound which has a structure represented.

Here, the alkylene group having 3 to 4 carbon atoms may be linear, branched, or structured similarly to R ¹ described above.

Examples of the crosslinking agent (I) include polyethylene glycol di (meth) acrylate, polyethylene glycol-polypropylene glycol block copolymer di (meth) acrylate, polyethylene glycol-
Polypropylene glycol random copolymer di (meth) acrylate, fumaric acid di [polyethylene glycol mono (meth) acrylate] ester, maleic acid di [polyethylene glycol mono (meth) acrylate]
There are esters, etc.

In the present invention, a conventionally known cross-linking agent may be used as the second cross-linking agent (hereinafter referred to as the cross-linking agent (II)) in a small amount according to the cross-linking agent (I).
The amount used is generally 0.01 mol% or less based on the water-soluble ethylenically unsaturated monomer.

The crosslinking agent (I) is 0.0 to the water-soluble monoethylenically unsaturated monomer in view of the object of the present invention.
It is essential that it be used in a proportion of 1 to 0.3 mol%. If the amount of the cross-linking agent used is less than 0.01 mol%, the water-soluble component of the resulting water-absorbent resin may increase, and if it exceeds 0.3 mol%, the water-absorbent resin may absorb water even if heat treatment is added. The improvement of the characteristics may be insufficient. Preferably,
It is 0.03 to 0.2 mol%.

In the present invention, any method may be used to polymerize the water-soluble monoethylenically unsaturated monomer in the presence of the crosslinking agent (I). An aqueous solution of a monomer component containing a monomer is used as the crosslinking agent (I).
The method of polymerizing in the presence of As the polymerization method, various methods such as aqueous solution polymerization, reverse phase suspension polymerization, and precipitation polymerization can be adopted. Among them, the aqueous solution polymerization method or the reverse phase suspension polymerization method is preferable from the viewpoint of workability during polymerization and the water absorption characteristics of the resulting water absorbent resin. Further, at the time of initiation of polymerization, a method of polymerizing using a radical polymerization initiator; a method of polymerizing by irradiating radiation, an electron beam, or ultraviolet rays (in the case of ultraviolet irradiation, a photopolymerization initiator may also be used. There is a normal method such as As the radical polymerization initiator, persulfates such as potassium persulfate, sodium persulfate and ammonium persulfate which are commonly used water-soluble radical polymerization initiators; hydrogen peroxide, t
-Hydroperoxides such as butyl hydroperoxide and cumene hydroperoxide; and azo compounds such as 2,2'-azobis-2-amidinopropane hydrochloride. These radical polymerization initiators may be used alone or in a mixture of two or more, and further, sulfite, L-ascorbic acid,
Redox initiator systems can also be used in combination with reducing agents such as ferrous salts. The amount of the radical polymerization initiator used is preferably 0.01 to 1.0% by weight, more preferably 0.005 to 0.5% by weight, based on the monomers.

When the polymer is synthesized by the aqueous solution polymerization method or the reverse phase suspension polymerization method, it is generally preferable to use the monomer as an aqueous solution. The monomer concentration in the monomer aqueous solution can be selected over a wide range, but generally 20% by weight or more,
It is preferably from 25% by weight or more to a saturated concentration. If necessary, an organic solvent may be present at this time.
As such an organic solvent, for example, methanol,
Alcohols that are compatible with water, such as ethanol, propanol, butanol; Ethers that are compatible with water, such as tetrahydrofuran and dioxane; Ketones that are compatible with water, such as acetone and methyl ethyl ketone; Water and phases, such as acetonitrile Soluble nitriles; N, N
Examples include amides that are compatible with water, such as dibutylformamide.

The polymerization temperature can be variously changed depending on the kind of the radical polymerization initiator to be used, but it is usually 0.
˜150 ° C., preferably 10˜100 ° C. The atmospheric pressure during the polymerization can be appropriately set in the range of reduced pressure to increased pressure.

Type of radical polymerization initiator used above
The polymerization temperature may be controlled by combining the amount and the atmospheric pressure.

In the present invention, the polymer obtained by the polymerization is
It is essential to perform heat treatment within a specific temperature range of 60 to 230 ° C. When the heat treatment is lower than 160 ° C. or higher than 230 ° C., the absorption capacity of the resulting water absorbent resin is low, and the amount of the water-soluble component produced is large relative to the absorption capacity. Preferably, the heat treatment temperature is 180 to
It is 200 ° C. When the heat treatment is carried out, the polymer is preferably in a water-containing state. More preferably, the water content before the heat treatment is 30 to 95% by weight, and further preferably 6
It is 0 to 95% by weight.

As a specific method of heat treatment in the above-mentioned specific temperature range when the polymer is in a water-containing state, for example, a method of drying the water-containing polymer at the same time as the heat treatment,
Water is added to the polymer to adjust the water content to an optimum value, and then heat treatment is performed, the water content of the polymer is reduced at a temperature lower than 160 ° C., and then this resin is heat treated, and water content is contained. And the like, for example, by subjecting the polymer to heat treatment in a state where the water content is hardly reduced.

The water-absorbent resin obtained by the heat treatment may be dried if necessary, and further crushed and classified as necessary to obtain a product.

For the heat treatment of the present invention, an ordinary dryer, a heating oven or the like can be used. For example, a groove type stirring dryer, a rotary dryer, a disk dryer, a kneading dryer, a hot air dryer, Examples thereof include a fluidized bed dryer, a gas stream dryer, an infrared dryer, a dielectric heating dryer and the like.

In order to more clearly attain the object of the present invention, the absorption capacity of the resin obtained when heated at a temperature outside the specific temperature range of the present invention is less than 55 times, more preferably less than 50 times. And the absorption capacity of the water-absorbent resin obtained by heat treatment in the specific temperature range of the present invention is 5
It is preferable to select the polymerization conditions of the polymer so as to be 5 times or more. When the absorption capacity of the resin is 55 times or more when the polymer is heated at a temperature outside the specific temperature range of the present invention, the water-soluble component is removed by heat treatment at the specific temperature range of the present invention. There is a tendency that the water absorption resin tends to increase, and as a result, a water absorbent resin having a high absorption capacity and a small amount of a water-soluble component, which is the object of the present invention, cannot be obtained. In order to make the absorption capacity of the resin less than 55 times when heated at a temperature outside the specific temperature range of the present invention, the type and / or the amount of the cross-linking agent (I) used in obtaining the polymer are appropriately adjusted. It may be adjusted or a means of using another second crosslinking agent together.

When the polymer is heat-treated in the specific temperature range of the present invention, a third crosslinking agent having two or more functional groups capable of reacting with the functional group of the polymer in advance (hereinafter referred to as a crosslinking agent ( It is also possible to increase the crosslink density in the vicinity of the surface of the polymer particles and further improve the water absorption characteristics and the stability over time during swelling by mixing with (III)) and reacting at the surface portion simultaneously with the heat treatment. In this case, the cross-linking agent (III) that can be used is, for example,
When the water absorbent resin has a carboxyl group, polyhydric alcohols, polyhydric glycidyl ethers, polyhydric amines, polyhydric aziridines, polyhydric isocyanates, alkylene carbonates, polyhydric metal salts, etc. Can be mentioned. The preferable amount of the crosslinking agent (III) is 0.005 to 5 parts by weight, based on 100 parts by weight of the solid content of the polymer.
It is preferably 0.01 to 1 part by weight.

Further, when the cross-linking agent (III) is mixed with the polymer or the water-absorbent resin after heat treatment, water or a hydrophilic organic solvent is used for the purpose of controlling penetration of the cross-linking agent (III) into the polymer. Is preferably used. Examples of the hydrophilic organic solvent include alcohols such as methanol, ethanol and propanol; ethers such as tetrahydrofuran and dioxane; ketones such as acetone and methyl ethyl ketone; nitriles such as acetonitrile,
One or a mixture of two or more of these may be used. Further, the crosslinking with the crosslinking agent (III) may be performed on the water absorbent resin obtained after the heat treatment.

The water-absorbent resin obtained by the production method of the present invention has a higher absorption capacity than conventional water-absorbent resins, less water-soluble components, and excellent stability over time.
There is little stickiness when swelling, good liquid permeability, and
These performances are maintained for a long time. Therefore, it can be widely used for sanitary materials, civil engineering, agriculture and horticulture.

[0040]

EXAMPLES Specific examples and comparative examples of the present invention will be shown below, but the present invention is not limited to the following examples. The absorption capacity, the amount of water-soluble components, the stickiness of the gel, and the temporal stability of the gel of the water absorbent resins obtained in Examples and Comparative Examples were determined as follows. (A) Absorption capacity About 0.200 g of the obtained water-absorbent resin powder was precisely weighed and uniformly placed in a non-woven tea bag type bag (40 mm x 50 mm), and immersed in 0.9% saline solution, The weight after 30 minutes was measured. The absorption capacity of the water-absorbent resin was calculated according to the following mathematical formula (1), with the liquid absorption weight of only the tea bag type bag as the blank.

[0041]

[Equation 1]

(B) Water-soluble component amount 0.500 g of the water-absorbent resin powder was dispersed in 1000 ml of deionized water, stirred for 12 hours, and then filtered with a filter paper,
The solid content of the filtrate was measured and the amount of water-soluble components was determined according to the following mathematical formula (2).

[0043]

[Equation 2]

(C) Stickiness of gel The stickiness of the swollen gel after measuring the absorption capacity in (a) was evaluated by touch.

(D) Stability of gel over time 2.0 g of the water-absorbent resin powder was swollen with 50 g of human urine sampled from 10 adult males and left at 37 ° C. for 6 hours, 12 hours, 18 hours. The appearance of the swollen gel after the lapse of time was observed. The deterioration state was judged by three-level evaluation from ◯ to Δ to ×.

◯: The shape of the swollen gel is maintained.
Δ: The shape of the swollen gel is partially broken. X: The shape of the swollen gel is collapsed and becomes a muddy fluid state.

Example 1 A stainless steel double-arm kneader with a jacket having an internal volume of 10 liters and provided with two sigma (Σ) blades, and an acrylic acid salt containing 75 mol% of sodium acrylate and 25 mol% of acrylic acid. 5500 g of an aqueous solution of a system monomer (monomer concentration 30% by weight) and 8.09 g of polyethylene glycol diacrylate (average number of ethylene oxide units 7) as crosslinking agent (I) (0.1 mol% of monomer) In addition, nitrogen gas was blown into the reaction system to replace it with nitrogen.

While warming the jacket with warm water of 35 ° C., ammonium persulfate 2.5 was added as a polymerization initiator.
g and 2.5 g of sodium hydrogen sulfite were added, and the polymerization was started while stirring the sigma blade in the kneader at 65 r, p, m. The polymerization reaction was carried out for 1 hour. After the reaction is completed, 2000 g of the hydrous gel that has been subdivided is opened by 0.3 mm
It was placed on a wire mesh of No. 1 and dried with hot air at a temperature of 180 ° C. for 2 hours. The dried product was crushed using a hammer mill to obtain a water absorbent resin. This product had an absorption capacity of 58.9 g / g and a water-soluble component of 8.3% (see Table 1).

Comparative Example 1 A water absorbent resin was obtained in the same manner as in Example 1, except that the hydrogel was dried in hot air at a temperature of 150 ° C. for 2 hours. This product had an absorption capacity of 48.7 g / g and a water-soluble component of 8.2% (see Table 1).

Comparative Example 2 The procedure of Example 1 was repeated except that the crosslinking agent (I) was replaced by 9.92 g of polypropylene glycol diacrylate (average number of propylene oxide units: 7) (0.1 mol% based on the monomer). The same procedure as in Example 1 was carried out to obtain a water absorbent resin. This product has an absorption capacity of 48.3 g / g and a water-soluble component of 1
It was 1.1% (see Table 1).

Comparative Example 3 A water absorbent resin was obtained in the same manner as in Comparative Example 2 except that the hydrogel was dried in hot air at a temperature of 150 ° C. for 2 hours. The absorption capacity of this product was 46.0 g / g, and the water-soluble component was 10.2% (see Table 1).

Example 2 7.52 g (0.07 mol%) of the crosslinking agent (I) used in Example 1 was used as the crosslinking agent represented by the following chemical formula (5).

[0053]

[Chemical 10]

A water absorbing resin was obtained in the same manner as in Example 1 except that the above was adopted. The absorption capacity of this product is 62.2 g /
g, water-soluble component was 8.3% (see Table 1).

Comparative Example 4 A water absorbent resin was obtained in the same manner as in Example 1, except that the hydrogel was dried in hot air at a temperature of 150 ° C. for 2 hours. The absorption capacity of this product was 52.7 g / g, and the water-soluble component was 8.1% (see Table 1).

From Examples 1 and 2 and Comparative Examples 1 to 4, the absorption capacity is low when the heat treatment temperature is 150 ° C. and when a crosslinking agent other than the crosslinking agent (I) used in the present invention is used.

Example 3 In Example 1, the crosslinking agent (I) used was 9.66 g (0.07 mol%) of the crosslinking agent represented by the following chemical formula (6).

[0058]

[Chemical 11]

A water absorbing resin was obtained in the same manner as in Example 1 except that the above was carried out. The absorption capacity of this product is 56.4 g /
g, water-soluble component was 10.3% (see Table 2).

Comparative Example 5 In Example 3, the amount of the crosslinking agent (I) used was 4.
A water absorbent resin was obtained in the same manner except that the amount of the water-containing gel was changed to 14 g (0.03 mol% based on the monomer) and the hydrogel was dried with hot air at a temperature of 150 ° C. for 2 hours. The absorption capacity of this product is 55.2.
The g / g and water-soluble components were 18.4%. The gel is sticky and has poor stability over time in urine (see Table 2).

Comparative Example 6 1.66 g of trimethylolpropane triacrylate instead of the crosslinking agent (I) used in Example 3
The same procedure is performed except that (0.03 mol% relative to the monomer),
A water absorbent resin was obtained. The absorption capacity of this product is 56.2 g /
g, the water-soluble component was 20.2%. The gel is sticky and the stability of the gel over time is poor (see Table 2).

From Example 3 and Comparative Examples 5 to 6, when it was attempted to obtain a water-absorbent resin having almost the same absorption capacity by a method other than the present invention, the water-soluble component increased, the gel became sticky, and the gel Poor stability over time.

Example 4 5500 g of an aqueous solution of a monomer component containing 75 mol% of potassium acrylate, 20 mol% of acrylic acid and 5 mol% of acrylamide was added to the same double-arm kneader as in Example 1.
(Monomer concentration 35% by weight), as a cross-linking agent (I),
14.1 g of the compound represented by the following chemical formula (7) (0.1 mol% based on the monomer)

[0064]

[Chemical 12]

Then, nitrogen gas was blown into the reaction system to replace the atmosphere in the reaction system with nitrogen.

Then, 2.0 g of sodium persulfate and 0.1 g of L-ascorbic acid were added as polymerization initiators,
Polymerization was started while stirring the sigma type blade in the kneader at 65r, p, m.

After completion of the reaction, the subdivided gel was opened with a mesh size of 0.
It was placed on a 3 mm wire mesh and dried with hot air at a temperature of 200 ° C. for 1 hour. The dried product was crushed using a hammer mill to obtain a water absorbent resin. The absorption capacity of this product is 59.2 g /
g, water-soluble component was 12.4% (see Table 3).

Example 5 Example 5 was repeated except that the cross-linking agent (I) used was 60.5 g of polyethylene glycol diacrylate (average number of ethylene oxide units: 45) (0.15 mol% based on the monomer). The same procedure as in Example 4 was carried out to obtain a water absorbent resin. The absorption capacity of this product was 57.3 g / g, and the water-soluble component was 12.1% (see Table 3).

COMPARATIVE EXAMPLE 7 In Example 4, 0.72 g of methylenebisacrylamide was used instead of the crosslinking agent (I) used.
(03 mol%), except that the same procedure as in Example 4 was carried out to obtain a water absorbent resin. The absorption capacity of this product is 55.9 g / g,
The water-soluble component was 20.4%. The gel is sticky and has poor stability over time in urine (see Table 3). Comparative Example 8 In Example 4, after the reaction was completed, 1
A water-absorbent resin was obtained in the same manner as in Example 4, except that hot-air drying was performed at a temperature of 20 ° C for 4 hours. This product has an absorption capacity of 4
The content of water-soluble component was 6.2 g / g, 11.8%. Absorption capacity is lower than in Example 4 (see Table 3).

Example 6 As a solution of the crosslinking agent (III) in 100 parts by weight of the water absorbent resin obtained in Example 1, 0.3 part of glycerin and 2 parts of water were added.
Part, an aqueous liquid consisting of 8 parts of isopropyl alcohol was added, and the resulting mixture was placed in a dryer at 180 ° C. for 2 minutes.
A water-absorbent resin was obtained by heating for 0 minutes to carry out a crosslinking reaction. The absorption capacity of this product was 58 times, and the stability of the gel over time was good (see Table 4).

Comparative Example 9 A water absorbent resin was obtained in the same manner as in Example 6 except that the water absorbent resin obtained in Comparative Example 6 was used.
The absorption capacity of this product is 55 times, and the stability of the gel over time is
Although slightly improved as compared with Comparative Example 6, it was still unstable. Further, the gel was sticky (see Table 4).

Comparative Example 10 The procedure of Example 6 was repeated except that the solution of the cross-linking agent (II) was mixed with the water absorbent resin obtained in Comparative Example 6 and the mixture was heated for 40 minutes. A resin was obtained. Although this gel had good stability over time, the gel was sticky. The absorption capacity was 47 times (see Table 4).

[0073]

[Table 1]

[0074]

[Table 2]

[0075]

[Table 3]

[0076]

[Table 4]

[0077]

The method for producing a water-absorbent resin of the present invention is further obtained by copolymerizing a water-soluble monoethylenically unsaturated monomer in the presence of a crosslinking agent (I) having the above-mentioned specific structure. The resin is heat-treated at a temperature of 160 to 230 ° C.

According to this method, a water absorbent resin having a high absorption capacity, a small amount of water-soluble components and excellent gel stability over time can be obtained.

Continuation of front page (51) Int.Cl. ⁷ Identification code FI // C08L 33:02 C08L 33:02 (72) Inventor Yoshio Irie 1 992 Nishi-oki, Akihama, Aboshi-ku, Himeji-shi, Hyogo Nihon Catalysis Himeji Laboratory Co., Ltd. (56) References JP-A-3-179008 (JP, A) (58) Fields investigated (Int.Cl. ⁷ , DB name) C08F 8 / 00-8 / 50

Claims (9)

(57) [Claims] 1. A method for producing a water-absorbent resin, which comprises subjecting a water-soluble monoethylenically unsaturated monomer to aqueous solution polymerization in the presence of a cross-linking agent, and subjecting the resulting polymer to heat treatment, wherein at least two crosslinking agents are used. And a unit represented by the chemical formula (1) having at least two polymerizable unsaturated groups between the at least two polymerizable unsaturated groups. (However, R ¹ in the chemical formula (1) is represented by the following general formula (a) to
It is at least one alkylene group selected from the group consisting of (c) . Is used in a proportion of 0.01 to 0.3 mol% with respect to the water-soluble monoethylenically unsaturated monomer, and a heat treatment of the polymer is carried out. Is carried out at a heat treatment temperature of 160 to 230 ° C. in the presence of a cross-linking agent (III) having at least two reactive groups capable of reacting with a functional group of the polymer. . [Chemical 2] 2. An acid group-containing monomer and the acid group-containing monomer
Metal salts, ammonium salts and amine salts, nonionic
Hydrophilic group-containing monomer, amino group-containing monomer and the amino group
A small amount selected from the group consisting of quaternized products of non-group-containing monomers.
At least one water-soluble monoethylenically unsaturated monomer (however
Monomers that do not contain hypophosphorous acid and thiomalic acid)
Aqueous solution polymerization in the presence of a cross-linking agent, heating the resulting polymer
In the method for producing a water absorbent resin to be treated , at least two polymerizable unsaturated groups are contained as the crosslinking agent.
And between the at least two polymerizable unsaturated groups
At least one unit represented by the chemical formula (1) : (However, R1 in the chemical formula (1) is an alkane having 2 to 4 carbon atoms.
It is a xylene group. ) Having a molecular weight of 6000 or less
The crosslinking agent (I) is a water-soluble monoethylenically unsaturated monomer
Used in a proportion of 0.01 to 0.3 mol% with respect to the body, and
The heat treatment of the polymer may react with the functional groups of the polymer.
Of a crosslinking agent (III) having at least two reactive groups
In the presence of heat treatment temperatures of 160-230 ° C.
And a method for producing a water-absorbent resin. 3. A polymer having a water content of 160 to 230
After heat treatment at ℃, further heat treatment of the polymer
Reduce the number of reactive groups that can react with the functional groups of the polymer
In the presence of a cross-linking agent having two
The method according to claim 1, wherein heat treatment is performed. 4. A polymer having a water content of 160 to 230.
Absorption capacity of polymer after heat treatment by heat treatment at ℃
Manufacturing according to any one of claims 1 to 3, which improves the
Method. 5. A polymer having a water content of 160 to 230.
Improving the absorption capacity by heat treatment at ℃ increases the solid content of the polymer.
It is 1 g / g or more per one, Any one of Claims 1-4.
The method described in. 6. The cross- linking agent (I) has the following chemical formula (2) : (However, R2 and R3 in the chemical formula (2) are each
Vertically represents hydrogen or a methyl group, and n is 2 to 100.
It ) The structure according to any one of claims 2 to 5 having a structure represented by
The method according to one. 7. The cross- linking agent (I) has the following chemical formula (3) : [However, R2 and R3 in the chemical formula (3) are each
Vertically represents hydrogen or a methyl group, and X is 1 to 100
Structural unit (A) represented by -CH2CH2O-, 1-
20 -R4O- (where R4 is an alkyl group having 3 to 4 carbon atoms)
It is a xylene group. ) Is a structural unit (B)
Is the divalent organic group linearly bonded in the desired sequence?
In other words, X is 1 to 5-(CO-CH = CH-CO-
O)-, a structural unit (C) represented by 2 to 100 -C
Structural unit (D) represented by H2CH2O- and 0 to 2
0 -R5O- (where R5 is an alkyl group having 3 to 4 carbon atoms)
It is a len group. ) The structural unit (E) represented by
It is a divalent organic group linearly linked in a row. ]]
The structure according to claim 1, which has a structure
How to list. 8. A method for producing a water-absorbent resin in which a water-soluble monoethylenically unsaturated monomer is polymerized in the presence of a cross-linking agent, and the resulting polymer is heat-treated, wherein at least two cross-linking agents are used. A unit having a polymerizable unsaturated group and at least one unit represented by the chemical formula (1) between the at least two polymerizable unsaturated groups: (However, R ¹ in the chemical formula (1) is represented by the following general formula (a) to
(C) [Chemical formula 7] It is at least one alkylene group selected from the group consisting of: Is used in a proportion of 0.01 to 0.3 mol% with respect to the water-soluble monoethylenically unsaturated monomer, and the heat treatment temperature of the polymer is 160 to 2
A method for producing a water absorbent resin, which is at 30 ° C. 9. An acid group-containing monomer and the acid group-containing monomer
Metal salts, ammonium salts and amine salts, nonionic
Hydrophilic group-containing monomer, amino group-containing monomer and the amino group
Of at least one water-soluble monoethylenically unsaturated monomer selected from the group consisting of quaternized non-group-containing monomers (provided that it does not contain hypophosphorous acid and thiomalic acid) In a method for producing a water-absorbent resin, which comprises polymerizing an aqueous solution in the presence of the polymer and heat-treating the obtained polymer, the polymer has at least two polymerizable unsaturated groups as the cross-linking agent,
At least one between the at least two polymerizable unsaturated groups
A unit represented by the chemical formula (1) (However, R ¹ in the chemical formula (1) is an alkylene group having 2 to 4 carbon atoms.) The crosslinking agent (I) is added to the water-soluble monoethylenically unsaturated monomer in an amount of 0.01 to It is used in a proportion of 0.3 mol%, the polymer to be heat treated is in a water-containing state, and the temperature of the heat treatment of the polymer is 180 to 20.
It is 0 degreeC, The manufacturing method of the water absorbent resin characterized by the above-mentioned.