JPH0710893B2 - Super absorbent resin manufacturing method - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a super absorbent resin.

[0002]

2. Description of the Related Art Highly water-absorbent resins have been put into practical use as liquid absorbing materials 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 their amazing water absorption capacity. In recent years, its application is not limited to hygiene products, and is widely spreading to fields such as agriculture, horticulture, food and medical fields.

The highly water-absorbent resin is obtained by crosslinking a polymerizable monomer containing acrylic acid as a main component with a crosslinking agent, for example, a hydrolyzate of starch / acrylonitrile graft copolymer, or a starch / acrylic acid graft copolymer part. Known are hydrates, 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.
Among these, a polyacrylic acid-based water-absorbing polymer compound composed of a polymer or copolymer having a monomer unit of acrylic acid or an acrylic acid salt in the main chain, such as polyacrylic acid, polyacrylic acid salt, acrylic acid and acrylic acid salt Copolymers with and the like are widely known.

[0004]

In the production of the super absorbent polymer as described above, in order to improve the gel strength of the super absorbent polymer, N, N'-methylenebisacrylamide (hereinafter referred to as MBAA) is used as a crosslinking agent. Was added to the polymerization system to carry out polymerization. However, when MBAA is used for crosslinking, even if the amount of MBAA added is increased, uniform crosslinking does not occur, so that a superabsorbent resin having sufficiently high water absorption performance cannot be obtained and gel strength is also increased. There was a problem in that a uniform gel body could not be obtained because it became inferior and it was difficult to control the heat generation during polymerization.

Further, when MBAA is used as a cross-linking agent, there is a drawback that the polymerization initiation time becomes long. The main object of the present invention is to have high gel strength with uniform crosslinking,
Another object of the present invention is to provide a method for producing a highly water-absorbent resin, which can easily obtain a highly water-absorbent resin that is a uniform gel body without adversely affecting the polymerization reaction.

[0006]

Means and Actions for Solving the Problems In the method for producing a super absorbent polymer of the present invention, a polymerizable monomer having a carboxyl group, which is neutralized by 20% or more with an alkali metal salt or an ammonium salt, is polymerized. In the above, the reaction product of epihalohydrin and ammonium or amines is added as a cross-linking agent.

By using the cross-linking agent of the present invention, it becomes possible to shorten the polymerization initiation time and the heat generation during the polymerization as compared with the case of using a conventional cross-linking agent such as MBAA. As a result, the polymerization reaction proceeds smoothly, uniform crosslinking is possible, and a highly water-absorbent resin having improved gel strength and uniformity of gel body can be obtained. Hereinafter, the method of the present invention will be described in detail.

The polymerizable monomer used in the present invention has a carboxyl group, and examples thereof include various polymerizable organic acids such as acrylic acid, methacrylic acid, maleic acid, etc. What is used as a component is preferable. At least 20% or more, preferably 60% or more of the carboxyl group of the polymerizable monomer is neutralized with an alkali metal salt or an ammonium salt in order to smoothly carry out the reaction with the crosslinking agent. It is necessary. Examples of the alkali metal salt include sodium salt, potassium salt, lithium salt and the like.

As the polymerizable monomer in the present invention, the polymerizable monomer having a carboxyl group may be used alone or in admixture of two or more kinds, and further, the characteristics such as hydrophilicity are improved. For this purpose, it may be copolymerized with acrylamide, N-vinylpyrrolidone, 2-hydroxyethyl methacrylate or the like. The cross-linking agent in the present invention is a reaction product of epihalohydrin with ammonia or amines. This reaction product reacts with the —COOM group (in the formula, M is a hydrogen atom, an alkali metal salt or an ammonium salt) of the polymerizable monomer, and crosslinks during polymerization.

Examples of the above epihalohydrin include epichlorohydrin, epibromohydrin and epiiodohydrin. Examples of the amines include monoamines such as ethylamine, methylamine and propylamine; diamines such as triethylenediamine, bis-2-aminoethylether, N, N-dimethylethylenediamine, piperazine and ethylenediamine; N-aminoethyl. Examples are triamines such as piperazine and diethylenetriamine, and diamines are particularly preferably used.

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 reaction temperature is 0 to 90 ° C. and the reaction time is 0.5 to 20 hours. It is appropriate that it is a degree. The ammonia or amines are used in a proportion of 0.01 to 4 mol, preferably 0.1 to 1 mol, per 1 mol of epihalohydrin. This is because the amount of ammonia or amines used is in the above range (0.01 to
This is because the cross-linking effect is lost when the amount is out of 4 mol).

The water or alcohol is used in an amount of 50 parts by weight or less, preferably 5 to 20 parts by weight, based on 1 part by weight of epihalohydrin. If the amount of water or alcohol exceeds 50 parts by weight, a great amount of heat energy is required for drying, which is uneconomical. The alcohol is preferably a monohydric liquid alcohol, preferably methanol, ethanol, propanol or butanol.

Further, a 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 surfactant include polyvinyl alcohol, polyethylene oxide, polyethylene glycol, polypropylene glycol, and nonionic surfactants (eg, polyoxyethylene alkyl ether (alkyl group having 12 to 18 carbon atoms)). Of these, it is particularly preferable to use polyethylene glycol.

The amount of the crosslinking agent, which is a reaction product of epihalohydrin and ammonia or amines, can be appropriately determined according to the desired water absorption capacity, gel strength and the like.
In the polymerizable monomer containing acrylic acid as a main component, it is preferable to use the crosslinking agent in an amount of 0.005 to 20 parts by weight with respect to 100 parts by weight of acrylic acid. If the addition amount of the cross-linking agent is less than 0.005 parts by weight, the crosslinking will be insufficient, and if it exceeds 20 parts by weight, the crosslinking will be excessive and the water absorption will be reduced.

For the polymerization, any ordinary polymerization method can be adopted. For example, the above-mentioned crosslinking agent and a predetermined amount of a polymerization initiator are added to an acrylate solution to initiate the polymerization to obtain a hydrogel. The resulting hydrogel is dried, then crushed and classified,
It is a super absorbent polymer powder or particles having a predetermined particle size or particle size.

[0016]

EXAMPLES The method for producing the superabsorbent resin of the present invention will be described in detail below with reference to examples. The present invention is not limited to the following examples. Reference Example 1 [Preparation of Epichlorohydrin-Ammonia Crosslinking Solution] Epichlorohydrin 6.0 g, 25% aqueous ammonia 1.4
7 g and 60 g of methanol are mixed by stirring, and 1 at 50 ° C.
The reaction was allowed to stand for 5 hours to obtain a cross-linking solution (A). Reference Example 2 [Preparation of epichlorohydrin-diethylenetriamine-based cross-linking solution] 6.0 g of epichlorohydrin, 1.34 g of diethylenetriamine and 60 g of methanol were stirred and mixed, and allowed to stand for 15 hours at 50 ° C to carry out a cross-linking solution (B ) Got. Example 1 75 parts by weight of 80% acrylic acid, 48.0 parts by weight of 48.6% sodium hydroxide and 48.6 parts by weight of ion-exchanged water were mixed to prepare an aqueous acrylate solution having a neutralization degree of 70%. The epichlorohydrin-ammonia-based cross-linking solution (A) obtained in Reference Example 1 was added to 1028 g of this aqueous acrylate solution.
After adding 0.80 g and purging with nitrogen, 36 g of a 2% peroxodisulfate (k ₂ S ₂ O ₈ ) aqueous solution, 21.6 g of a 2% pyrosulfite (k ₂ S ₂ O ₅ ) aqueous solution and 40% glyoxal A water-diluted solution (50-fold diluted) of 14.4 g of the aqueous solution was added to obtain a mixed solution. Next, this mixed solution is poured into a bat (inner surface 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 a length of 48 cm, a width of 37 cm, and a thickness of 0.5 to A 0.6 cm hydrogel was obtained. The obtained water-containing gel was dried with a drum dryer at a surface temperature of 130 ° C. to form 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. Example 2 A highly water-absorbent resin powder was obtained in the same manner as in Example 1 except that the amount of the cross-linking liquid (A) obtained in Reference Example 1 was 2.00 g. Example 3 A highly water-absorbent resin powder was obtained in the same manner as in Example 1 except that the addition amount of the cross-linking liquid (A) obtained in Reference Example 1 was 4.00 g. Example 4 Instead of the crosslinking liquid (A), the crosslinking liquid (B) obtained in Reference Example 2
A highly water-absorbent resin powder was obtained in the same manner as in Example 1 except that 0.81 g was added. Example 5 Instead of the crosslinking solution (A), the crosslinking solution (B) obtained in Reference Example 2
A highly water-absorbent resin powder was obtained in the same manner as in Example 1 except that 2.03 g was added. Example 6 Instead of the crosslinking liquid (A), the crosslinking liquid (B) obtained in Reference Example 2
A highly water-absorbent resin powder was obtained in the same manner as in Example 1 except that 4.07 g was added. Comparative Example 1 A highly water-absorbent resin powder was obtained in the same manner as in Example 1 except that the crosslinking liquid was not added. Comparative Example 2 Instead of the crosslinking liquid (A), MBAA0.05 was used as a crosslinking agent.
A highly water-absorbent resin powder was obtained in the same manner as in Example 1 except that g was added. Comparative Example 3 Instead of the crosslinking liquid (A), MBAA0.10 was used as a crosslinking agent.
A highly water-absorbent resin powder was obtained in the same manner as in Example 1 except that g was added. Comparative Example 4 Instead of the cross-linking liquid (A), MBAA 0.20 was used as a cross-linking agent.
A highly water-absorbent resin powder was obtained in the same manner as in Example 1 except that g was added.

Table 1 shows the type and amount of the crosslinking agent, the maximum temperature during the polymerization reaction, and the polymerization initiation time in each of the examples and comparative examples. Further, the gel strength, water absorption capacity and gel uniformity of the obtained super absorbent polymer powder were examined. The results are also shown in Table 1. The respective measuring methods are as follows. (1) Gel strength 96.0 g of 0.9% saline solution was placed in a 200 ml beaker, and 4.0 g of a superabsorbent resin powder as a sample was added thereto while stirring with a magnetic stirrer to cause gelation. After leaving this gel in a thermostatic chamber for 24 hours,
A JIS standard ball bearing steel ball (SUS) having an inch diameter is next placed on the gel surface in order of 1/16 inch. 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. Thus, the maximum diameter of a steel ball that did not settle (M / 16 inch)
The value of M was taken as the gel strength. (2) Measurement of water absorption ratio 1 g of 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). And the water absorption capacity without pressure was determined.

Water absorption ratio = XY-1 (3) Evaluation of uniformity of gel Bursting traces of bubbles having a diameter of 0.5 to 2 cm formed on the surface of the gel are visually observed and evaluated according to the following criteria. did. ○: Surface is uniform △: Partially bumped (explosion traces of bubbles are less than half of surface area) ×: Explosive boiling (explosion traces of bubbles occur on almost entire surface area)

[0019]

[Table 1]

As shown in the table, in Comparative Examples 2 to 4, MB
As the amount of AA added increases, the temperature during polymerization rises, causing bumping, impairing the homogeneity of the gel, and further increasing the polymerization start time. On the other hand, in Examples 1 to 6, the temperature during the polymerization and the polymerization start time were
Almost constant regardless of the amount of cross-linking agent added, and MB
It was low as compared with Comparative Examples 2 to 4 in which AA was used as a crosslinking agent, indicating that the polymerization reaction proceeded smoothly without bumping. As a result, in Examples 1 to 6, the gel strength, the water absorption performance, and the uniformity of the gel were all good, indicating that uniform crosslinking was performed.

On the other hand, in Comparative Example 1 containing no cross-linking agent, the temperature during polymerization and the polymerization initiation time were almost the same as those in Example, but since no cross-linking was carried out, the gel strength of Examples and other Comparative Examples was Markedly inferior to.

[0022]

EFFECTS OF THE INVENTION According to the method of the present invention, since the polymerizable monomer is uniformly crosslinked, the water absorption performance is excellent, the gel strength is excellent, and the initiation of polymerization is adversely affected by the presence of the crosslinking agent. It is carried out promptly without receiving the heat and the exothermic control at the time of polymerization is easy, so that there is an effect that a uniform gel body can be obtained.

Claims (2)

[Claims] 1. When polymerizing a polymerizable monomer having a carboxyl group, which is neutralized by 20% or more with an alkali metal salt or an ammonium salt, a reaction product of epihalohydrin and ammonium or amine is added as a crosslinking agent. A method for producing a highly water-absorbent resin, comprising: 2. The polymerizable monomer has a carboxyl group of 2
The method for producing a super absorbent polymer according to claim 1, wherein 0% or more is mainly composed of acrylic acid neutralized with an alkali metal salt or an ammonium salt.