JPH0639488B2 - Super absorbent resin modification method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial field of application> The present invention relates to a method for modifying a highly water-absorbent resin, and more specifically, to a water absorption capacity without lowering the gel strength and without applying pressure ( Modification of super absorbent resin that can increase the water absorption capacity under pressure (hereinafter referred to as "pressurized water absorption capacity") without decreasing the "pressureless water absorption capacity") Concerning the law.

<Prior art> Highly water-absorbent resin has been put into practical use as a liquid-absorbing material to replace pulp and water-absorbent paper at the beginning of the attention of sanitary ware manufacturers such as diapers and sanitary products due to its amazing water absorption capacity. In recent years, its application is not limited to sanitary products, and is widely spreading to agriculture, horticulture, food products, medical products and the like.

By the way, in the case of super absorbent resin used for sanitary goods,
In many cases, not only the unpressurized water absorption capacity is also large, but also the pressurized water absorption capacity is required in practical use. For example, in the disposable diaper industry, the water absorption amount in a state where the weight of the baby is replaced by the resin is used as one measure of the water absorption evaluation.

However, in the conventional water-absorbent resin,
There is no one having a sufficiently high water absorption capacity under pressure.

Therefore, conventionally, when a superabsorbent resin is used for such an application, a crosslinking agent such as epichlorohydrin, ethylene glycol = diglycidyl ether (hereinafter referred to as "EGDGE") is used in order to improve its pressurized water absorbency. It has been carried out to further improve the water absorption property under pressure by further crosslinking.

<Problems to be Solved by the Invention> However, in order to improve the pressurized water absorbency of the super absorbent polymer using the above-mentioned technique, a large amount of a cross-linking agent is required, which is not economical.

Further, when such a cross-linking agent is used in a large amount, there arises a problem that the cross-linking reaction proceeds too much and the unabsorbed water absorption capacity becomes small, or the structure of the entire gel becomes brittle. When the structure of the gel becomes brittle, there is a risk that the liquid that has once absorbed water will leak, and when it is used for sanitary products, etc.
The resin may cause so-called misalignment, and the original water absorption effect may not be obtained.

Therefore, as a result of intensive studies by the present inventors to solve the above problems, a super absorbent polymer having a specific functional group in its side chain is crosslinked by using a reaction product of epihalohydrin and ammonia or amines. , Without the above problems,
It was found that the pressurized water absorbency can be improved.

<Means for Solving the Problems> The present invention has been made based on the above findings, and the gist of the present invention is to provide a water-insoluble compound having a —COOM group (M is a hydrogen atom or an alkali metal atom) in a side chain. It is a method for modifying a superabsorbent resin, which comprises cross-linking the superabsorbent resin with a reaction product of epihalohydrin and ammonia or amines.

Hereinafter, the method of the present invention will be described in detail.

The superabsorbent resin that can be used in the method of the present invention may be any water-insoluble superabsorbent resin having the above-mentioned —COOM group in the side chain, such as a hydrolyzate of starch / acrylonitrile graft copolymer or starch / acrylic acid graft copolymer. Partially neutralized products, saponified products of vinyl acetate / acrylic acid ester copolymers, carboxymethyl cellulose, isobutylene / maleic anhydride copolymers, partially neutralized products of polyacrylic acid, and crosslinked products of these polymers. it can. A polyacrylic acid-based water-absorbing polymer compound consisting of a polymer or copolymer having a monomer unit of acrylic acid or an acrylic acid salt in its main chain is particularly preferable. For example, polyacrylic acid, polyacrylic acid salt, acrylic acid and acrylic acid salt And the like.
Here, examples of the salt portion of the polyacrylic acid salt and the acrylic acid salt include alkali metal salts such as sodium salt, potassium salt, and lithium salt. Further, in order to improve properties such as hydrophilicity, it is a copolymer of a polymer having a monomer unit of acrylic acid or acrylate in its main chain with acrylamide, N-vinylpyrrolidone, 2-hydroxyethyl methacrylate or the like. It may be.

In the method of the present invention, a reaction product of epihalohydrin and ammonia or amines is used. These reaction products react with the above-mentioned —COOM group which the superabsorbent resin has in the side chain to crosslink the superabsorbent resin. Further, since the super absorbent polymer is usually crosslinked in the form of particles or powder, it is crosslinked from the surface of the particles or powder.

As the above epihalohydrin, epichlorohydrin,
Examples include epibromohydrin and epiiodohydrin.

The amines include monoamines such as ethylamine, methylamine and propylamine; triethylenediamine, bis-2-aminoethyl ether, N, N-
Examples include diamines such as dimethylethylenediamine, piperazine, and ethylenediamine; triamines such as N-aminoethylpiperazine and diethylenetriamine, and diamines are particularly preferable.

The reaction of epihalohydrin with ammonia or amines is preferably carried out in advance in a solution of water or alcohol while controlling the temperature.

The above-mentioned ammonia or amines is epihalohydrin 1
The amount used is preferably 0.01 to 4 mol, and more preferably 0.1 to 1.0 mol, based on mol. This is because when the amount of ammonia or amines used is outside the above range (0.01 to 4 mol), the crosslinking effect is lost.

The water or alcohol solution is used in an amount of preferably 1 to 50 parts by weight, more preferably 5 to 20 parts by weight, based on 1 part by weight of epihalohydrin. This is because if the amount is less than 1 part by weight, the epihalohydrin will not be dissolved, and if the amount exceeds 50 parts by weight, a great amount of heat energy is required for drying and it is uneconomical.

The alcohol is preferably a monohydric liquid alcohol, preferably methanol, ethanol, propanol or butanol.

Further, a water-soluble surfactant may be added to the above solution to uniformly disperse the reaction product of epihalohydrin and ammonia or amines. Thereby, the gel strength can be enhanced without impairing the water absorption property.

Examples of the water-soluble surfactant include polyvinyl alcohol, polyethylene oxide, polyethylene glycol, polypropylene glycol, and nonionic surfactants such as polyoxyethylene alkyl ether (alkyl group having 12 to 18 carbon atoms). Of these, polyethylene glycol is particularly preferable.

The crosslinking liquid containing the reaction product of epihalohydrin and ammonia or amines can be used in an appropriate amount depending on the desired water absorption capacity, gel strength and the like. Usually, it is preferably used in an amount of 0.01 to 20 parts by weight, more preferably 0.1 to 2.0 parts by weight, based on 100 parts by weight of the super absorbent polymer. this is,
If the amount is less than 0.01 part by weight, the crosslinking effect is not sufficiently exhibited, and during the crosslinking treatment, the powdery water-absorbent resin aggregates into a mammoth-shaped lump, which makes it difficult to uniformly perform the crosslinking treatment. On the other hand, when it exceeds 20 parts by weight, the crosslinking density becomes too high and the water absorption capacity decreases.

In the method for modifying a superabsorbent resin according to the present invention, the superabsorbent resin is cross-linked with the above-mentioned crosslinking liquid, but water or another alcohol is further added if necessary, and cross-linked in the presence of water and alcohol. Is done.

As this alcohol, polyethylene glycol, butanediol, pentanediol, hexanediol,
Examples include methyl carbitol, carbitol, dibutyl carbitol, 1-methoxy-2-propanol, 2-methoxypropoxypropanol and the like.

Various methods are conceivable as the crosslinking method. For example, a superabsorbent resin is accommodated in a mixer, a cross-linking liquid in which a predetermined reaction product is dispersed in water, is added dropwise or sprayed while stirring a treatment liquid prepared by further adding water and alcohol,
After thoroughly mixing and crosslinking, it is dried in a dryer. In addition, by adding alcohol to the cross-linking liquid or the treatment liquid, so-called mamako (probable gathering of resin particles) can be prevented at the time of cross-linking.

The reaction temperature and reaction time in the above-mentioned cross-linking are not particularly limited, and it can be carried out at an appropriate temperature depending on the type of cross-linking liquid, the desired water absorption capacity, gel strength and the like. Usually 0-9
The reaction is carried out at a temperature of 0 ° C. for 30 minutes to 20 hours.

The mixer used is not particularly limited in the present invention,
A conventional mixer such as a Nauter mixer, a ribbon blender, a conical blender, a Henschel mixer, and a Reiki mixer can be used.

Calcium chloride, zinc nitrate, etc. may be added at an appropriate stage of mixing in order to improve fluidity, cross-linking characteristics and the like during mixing.

Further, the drying may be carried out by a conventional dryer, and a hot air circulating dryer, a reduced pressure dryer and the like may be used to simultaneously mix and dry the crosslinking solution and the super absorbent resin.

<Examples> Hereinafter, the present invention will be described in detail based on Examples. It should be added that the present invention is not limited to the following examples.

In addition,% in the following is weight%.

A. Preparation of super absorbent polymer to be modified 80% acrylic acid 75 parts by weight, 48.6% sodium hydroxide 48.0 parts by weight and ion-exchanged water 48.6 parts by weight are mixed to obtain a 70% neutralized acrylic resin. An acid salt aqueous solution was prepared. To 1028 g of this aqueous acrylate solution, 5 g of a 1% N, N′-methylenebisacrylamide aqueous solution was added to remove oxygen dissolved in the aqueous solution so that the polymerization proceeds smoothly. After substitution, 36 g of a 2% aqueous K ₂ S ₂ O ₈ peroxodisulfate solution, 21.6 g of a 2% aqueous K ₂ S ₂ O ₅ pyrosulfite solution and a 40% aqueous glyoxal solution diluted 50 times with water to obtain a diluted solution 14. .4
g was added to obtain a mixed solution. Next, this mixed solution was poured into a vat (internal Teflon coating) having a length of 48 cm and a width of 37 cm, and polymerized for 20 minutes in a hot air circulation dryer at 42 ° C., and the length was 48 cm, the width was 37 cm, and the thickness was 5 to 6 mm. A hydrogel was obtained. The obtained water-containing gel was dried with a drum dryer having a surface temperature of 130 ° C. to obtain a flake-like resin, which was crushed with a pin mill and then classified to obtain a 16 to 200 mesh highly water-absorbent resin powder.

B. Preparation of cross-linking liquid (1) Preparation of epichlorohydrin-ammonia-based cross-linking liquid Epichlorohydrin 3 g, 25% aqueous ammonia 3.4
g and 27.4 g of water were mixed with stirring, and a standing reaction was carried out at a temperature of 50 ° C. for 15 hours to prepare a crosslinking solution.

(2) Preparation of Epichlorohydrin-Ammonia Crosslinking Solution Epichlorohydrin 3 g, 25% aqueous ammonia 3.4
g, 12.9 g of water, and 14.5 g of polyethylene glycol (average molecular weight 4000) were stirred and mixed, and the mixture was allowed to stand for 15 hours at a temperature of 50 ° C. to prepare a crosslinking solution.

(3) Preparation of Epichlorohydrin-Ethylenediamine Crosslinking Solution Epichlorohydrin 3 g, ethylenediamine 0.49
g and methanol (30.0 g) were mixed with stirring, and the mixture was allowed to stand at room temperature for 15 hours at a temperature of 50 ° C. to prepare a crosslinking solution.

(4) Preparation of Epichlorohydrin-Diethylenetriamine Crosslinking Solution Epichlorohydrin 3 g, diethylenetriamine 0.6
7 g and 30.0 g of methanol were mixed with stirring, and the reaction was allowed to stand for 15 hours at a temperature of 50 ° C. to prepare a crosslinking solution.

In addition, when amines are used for the preparation of the cross-linking liquid in the examples (Examples 5 to 8), when methanol is used,
It is preferable because the crosslinking proceeds sufficiently.

(Example 1) 150 g of a super absorbent polymer was placed in a tabletop mixer, and 12.9 g of water and 2.43 of a cross-linking solution were stirred in this.
g, 1,3-butanediol (1.50 g) was added to the treatment liquid over 1 minute. After the addition, the mixture was stirred and mixed for 3 minutes, and then dried at a temperature of 140 ° C. for 30 minutes to obtain a highly water-absorbent resin with improved water absorbency under pressure.

(Example 2) As a treatment liquid, 6.4 g of water, 9.7 g of a crosslinking liquid, and 1,3
A highly water-absorbent resin having improved water absorbability under pressure was obtained in the same manner as in Example 1 except that a mixed solution containing 1.5 g of butanediol was used.

(Example 3) As a treatment liquid, 13.9 g of water, 2.43 g of a cross-linking liquid,
A highly water-absorbent resin having improved pressurized water absorbency was obtained in the same manner as in Example 1 except that a mixed solution of 1.5 g of 1,3-butanediol was used.

(Example 4) As a treatment liquid, water 10.6 g, cross-linking liquid 9.7 g, 1,
A highly water-absorbent resin having improved water absorbability under pressure was obtained in the same manner as in Example 1 except that a mixed solution containing 1.5 g of 3-butanediol was used.

(Example 5) Pressurized water absorption was performed in the same manner as in Example 1 except that a mixed liquid of 15.0 g of water, 0.61 g of a cross-linking liquid, and 1.5 g of 1,3-butanediol was used as a treatment liquid. A highly water-absorbent resin having improved properties was obtained.

(Example 6) As a treatment liquid, water 15.9 g, a cross-linking liquid 2.42 g,
A highly water-absorbent resin having improved pressurized water absorbency was obtained in the same manner as in Example 1 except that a mixed solution of 1.5 g of 1,3-butanediol was used.

(Example 7) As a treatment liquid, water 15.0 g, crosslinking liquid 0.61 g,
A highly water-absorbent resin having improved pressurized water absorbency was obtained in the same manner as in Example 1 except that a mixed solution of 1.5 g of 1,3-butanediol was used.

(Example 8) As a treatment liquid, water 15.0 g, cross-linking liquid 2.44 g,
A highly water-absorbent resin having improved pressurized water absorbency was obtained in the same manner as in Example 1 except that a mixed solution of 1.5 g of 1,3-butanediol was used.

(Comparative Example 1) As a treatment liquid, water 15 g, epichlorohydrin 0.86
A highly water-absorbent resin having improved water absorbency under pressure was obtained in the same manner as in Example 1 except that a mixed solution containing 1.5 g of 1,3-butanediol was used.

(Comparative Example 2) As the treatment liquid, 15 g of water, 0.05 g of EGDGE, 1,
A highly water-absorbent resin having improved water absorbability under pressure was obtained in the same manner as in Example 1 except that a mixed solution containing 1.5 g of 3-butanediol was used.

(Comparative Example 3) As the treatment liquid, 15 g of water, 0.25 g of EGDGE, 1,
A highly water-absorbent resin having improved water absorbability under pressure was obtained in the same manner as in Example 1 except that a mixed solution containing 1.5 g of 3-butanediol was used.

C. Measurement of gel strength, non-pressurized water absorption capacity, and pressurized water absorption capacity The performance tests of the following a) to c) were performed on each of the superabsorbent resins obtained in Examples 1 to 8 and Comparative Examples 1 to 3 above.

a) Measurement of gel strength 97.5 g of 0.9% saline was stored in a 200 m beaker, and 2.5 g of each superabsorbent resin was added to the mixture while stirring with a magnetic stirrer to cause gelation. After leaving this gel in a thermostatic chamber for 24 hours, first, a JIS standard ball-bearing steel ball (SUS) with a diameter of 3/16 inch, and then a steel ball with a diameter increased by 1/16 inch from that Place on the gel surface in sequence. This operation is continued until the steel balls settle in the gel. However, the steel balls that have not settled should be removed before the next steel ball is placed. In this way, the maximum diameter (M / 16 inch) M of the steel balls that did not settle was defined as the gel strength.

b) Measurement of non-pressurized water absorption capacity 1 g of the highly water-absorbent resin is put in 97.5 g of 0.9% saline solution and left for 10 minutes to absorb water. Then, the mixture was transferred onto a pre-weighed 80-mesh wire net (whose weight is Yg), drained for 5 minutes, and the hydrogel was weighed together with the wire net (this weight is Xg). The non-pressurized water absorption capacity was obtained.

Non-pressurized water absorption capacity = XY-1 c) Measurement of pressurized water absorption capacity FIG. 1 is a schematic cross-sectional view of an apparatus manufactured by the present inventors for measuring the amount of water absorption under pressure. This pressurized water absorption measuring device has a substrate (1) and a weight (2) as main constituent members. The base body (1) is provided with a cylindrical portion (1a) and a support portion (1b) provided on the upper surface thereof with its upper surface horizontal in a substantially central portion thereof, and supporting the superabsorbent resin (3) indicated by the alternate long and short dash line in the figure. ) And.

The support portion (1b) is provided with a plurality of drain holes (1c) for draining the water discharged from the superabsorbent resin (3) during pressurization.

The weight (2) is detachably fitted to the cylindrical portion (1a) of the base body (1), and is for applying a constant pressure to the superabsorbent resin (3). A water supply hole (2a) for supplying saline solution to (3) and absorbing water penetrates the center of the cross section in the axial direction.

In the pressurized water absorption measuring device having the above-mentioned configuration, each of the upper and lower surfaces of each superabsorbent resin to be measured (3) has Kimwipes (4) on the inside, and the wire mesh (5) is arranged on the outside, Weight (2)
With a pressure of 51.0 g / cm ² applied to the superabsorbent resin (3), 0.9% of the superabsorbent resin (3) is supplied from the water supply hole (2a) provided in the weight (2). 20 g of saline solution was injected, and after 10 minutes, it was taken out from the device and drained, and then the water absorption amount of the superabsorbent resin (3) was measured. ) Was calculated and made into the water absorption capacity under pressure.

As shown in the table, when treated by using the conventional modification method (Comparative Examples 1 to 3), when the amount of the cross-linking agent used is increased (Comparative Example 3 with respect to Comparative Example 2), the water absorbency against pressure is increased. Is improved but the non-pressurized water absorbency is deteriorated. On the other hand, when modified by the method of the present invention (Examples 1 to 8), the amount of the cross-linking agent is increased to increase the water absorbency under pressure. Even if the above conditions are improved (Example 1 is Example 2; Example 3 is Example 4; Example 5 is Example 6; Example 7 is Example 8). It was found that the water absorption did not deteriorate.

<Effects of the Invention> As described above, the method of the present invention provides a reforming method capable of improving the pressurized water absorbency of a super absorbent polymer without impairing the unpressurized water absorbency. The present invention has excellent unique effects.

[Brief description of drawings]

FIG. 1 is a schematic cross-sectional view of an apparatus for measuring the amount of pressurized water absorption. (1) ... Substrate, (1a) ... Cylindrical part, (1b) ... Support part, (1c) ... Drainage hole, (2) ... Weight, (2a) ... Water supply hole, (3) ... Super absorbent resin,
(4) ... Kimwipe, (5) ... Wire mesh.

Claims (3)

[Claims] 1. A water-insoluble superabsorbent resin having a --COOM group (M is a hydrogen atom or an alkali metal atom) in a side chain is crosslinked by a reaction product of epihalohydrin with ammonia or amines. A method for modifying super absorbent polymer. 2. The method for modifying a super absorbent polymer according to claim 1, wherein the reaction product is obtained by reacting epihalohydrin with ammonia or amines in a solution of water or alcohol. 3. The method for modifying a super absorbent polymer according to claim 1, wherein at least the surface of the super absorbent polymer powder is crosslinked.