JPS601204A - Production of highly water-absorptive resin - Google Patents

Abstract

PURPOSE:To obtain a highly water-absorptive resin excellent in salt resistance and rate of water absorption, by adjusting the water content of a hydrophilic polymer obtained by polymerising a specified polymerizable monomer with the aid of a specified polymerization initiator to a value within a specified range and crosslinking the polymer with a specified crosslinking agent. CONSTITUTION:A hydrophilic polymer is produced by polymerizing a polymerizable monomer having a carboxyl or/and carboxylate group [e.g., (meth)acrylic acid] with the aid of a polymerization initiator comprising a combination of a persulfate (e.g., sodium persulfate) with a hydroperoxide (e.g., hydrogen peroxide). After the water content of this polymer is adjusted to 10-40wt%, this polymer is crosslinked with a crosslinking agent having at least two functional groups reactive with the carboxyl and/or carboxylate groups (e.g., ethylene glycol diglycidyl ether) to produce a highly water-absorptive resin. By the use of the above combination as a polymerization initiator, the produced resin can show excellent salt resistance and rate of water absorption and find wide applications including various sanitary materials.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing a superabsorbent resin, and more particularly to a method for producing a superabsorbent resin having excellent salt resistance and water absorption rate.

Conventionally, paper, pulp, sponge, etc. have been used as non-water-absorbing/water-retaining materials for hygiene materials such as sanitary napkins and disposable diapers, or in the agricultural field. If pressure is applied to the water,
A large portion of it is squeezed out.

In recent years, as alternatives to these materials, starch-7-crylonitrile graft polymer hydrolysates, carboxymethyl cellulose crosslinked products, polyethylene oxide partially crosslinked products, polyacrylate partially crosslinked products, and vinyl alcohol-acrylate copolymer. Water-absorbing materials such as polymers have been proposed, but all of them have drawbacks such as low water-absorbing ability, or even if they have high water-absorbing ability, the water absorption rate is slow and the dispersibility in water is poor. .

The present inventors have already proposed a water-absorbing material with excellent water-absorbing performance (M Kokai No. 54-30710), and have also proposed a further improved water-absorbing material (Japanese Unexamined Patent Publication No. 57-158209).
．． JP-A-57-158210), since these water-absorbing materials are also polymer electrolytes, there is a problem in that their performance in salt solutions is significantly reduced. If this drawback is solved, it is clear that the range of applications will be further expanded to various uses, including sanitary napkins, disposable diapers, underbats, etc., and the emergence of iron water materials with excellent salt resistance. desired. □ The present inventors have conducted various studies in order to obtain a super water-absorbing resin that has even better salt resistance and water absorption rate than the various previously known water-absorbing materials, and has found that the water content is 10 to 10%. It has already been proposed that the objective can be achieved by crosslinking a hydrophilic polymer having carboxyl groups or carboxylate groups adjusted to 40% by weight (Japanese Patent Application No. 1983- 155097
), and as a result of intensive research in order to further improve the performance, we found that a polymerizable monomer having a carboxyl group or/and a carboxylate group as a parent aqueous polymer was used as a polymerization initiator [using a combination of persulfate and hydroperoxide]. When using a hydrophilic polymer obtained by polymerization or copolymerization,
It was discovered that the final resin obtained by crosslinking this was dramatically superior in salt resistance and water absorption rate, and the present invention was completed (7).

That is, the present invention provides a hydrophilic polymer obtained by polymerizing a polymerizable monomer having a carboxyl group or/and a carboxylate group using a combination of a persulfate and a hydroperoxide as a polymerization initiator or by copolymerizing it with other monomers. After adjusting the water content in the polymer to 10 to 40% by weight, the polymer is crosslinked with a crosslinking agent having two or more functional groups capable of reacting with carboxyl groups and/or carboxylate groups. The present invention provides a method for producing a water-absorbing resin.

The required performance of water-absorbing polymers has been CI)
2) Water absorption rate and 3) Gel strength are mentioned, but a positive correlation is recognized between these performances, and conventional water-absorbing polymers are established on the balance of these. The performance of each was slightly sacrificed. However, according to the method of the present invention, it is possible to improve these drawbacks and to produce a highly water-absorbing resin that satisfies various performances required of a super-absorbent polymer.

Important points for achieving the purpose of the present invention are the use of persulfate and hydroperoxide together as a polymerization initiator while synthesizing a hydrophilic polymer having carboxyl groups and/or carboxylate groups, and the resulting hydrophilic polymer. After adjusting the water content in the polymer to a specific range of 10 to 40% by weight, the polymer is subjected to a crosslinking reaction.

Examples of the monomer having a carboxyl group and/or carboxylate group in the present invention include heptacrylic acid or a salt thereof, methacrylic acid or a salt thereof, and these can be preferably used in the present invention. In addition to these, comonomers such as maleic acid, itaconic acid, acryl 1mide, 2-acrylamido-2-methylpropanesulfone, 2-(meth)7-acryloylethanesulfonic acid, and 2-hydroxyethyl (meth)7-acrylate are added. can be copolymerized within a range that does not reduce the performance of the water-absorbing polymer.

There is no particular question regarding the polymerization method, but since the present invention requires that the water content in the hydrophilic polymer produced be within a specific range as described above, a dehydration step is usually required after the polymer is synthesized. shall be. Therefore, from the viewpoint of workability and the like, the reverse phase suspension polymerization method is preferable.

An important point in the method of the present invention is to use a persulfate and a hydroperoxide together as a polymerization initiator during polymerization as described above. The present inventors had previously proposed a method for obtaining a superabsorbent polymer by using two types of initiators in combination during polymerization (Japanese Patent Application Laid-open No. 161-408-1983), but the polymer obtained by this method has a high Although it is water-absorbing, it has a poor water-absorbing speed, so it has a major drawback when used in sanitary materials such as sanitary napkins and disposable diapers, making it virtually impossible to use. However, in the present invention, by subjecting the hydrophilic polymer produced as described above to a crosslinking reaction under special conditions, a polymer with high water absorption and excellent water absorption speed can be obtained, and the above drawbacks can also be solved. .

Persulfates used in the present invention include sodium persulfate, potassium persulfate, ammonium persulfate, etc. Hydroperoxides include hydrogen peroxide, t-
Examples include butyl hydroperoxide and cumene hydroperoxide. Any combination of initiators may be used as long as the amount of persulfate is 0.01 to 1% by weight and the amount of hydroperoxide is 0.01 to 2% by weight based on the monomer. As mentioned above, the second important point of the present invention is that the cross-linking reaction is carried out when the water content in the hydrophilic polymer is within a specific range (10
~40% by weight) a! After adjusting it, it is just one line.

Conventionally, methods for producing water-absorbing polymers in which a crosslinking reaction is carried out after polymerization are known. For example, Japanese Patent Laid-Open No. 57-44627 discloses a method in which polyacrylates are crosslinked in a mixed solvent of water and a hydrophilic organic solvent. It is written that
-28505 publication describes polyacrylic acid (or its salt)
A method for crosslinking in the presence of water is described. However, the water content in these water-containing polymers is 50% by weight or more, especially the latter has a water content of 70% by weight or more,
At such a water content, the δ effect of the present invention cannot be achieved.

Usually, the hydrophilic polymer has a monomer content of 45% by weight or less,
That is, it is obtained by polymerizing in an aqueous solution containing water of 55% by weight or more. Therefore, in further implementation of the present invention, hydrophilic polyesters obtained by conventional methods are used.

It is necessary to control the water content in the refrigeration.

According to the invention, this water content is in the range of 10 to 40% by weight (full weight of the hydrophilic polymer hydrate), more preferably 15 to 35's, ii%.

If the water content in the hydrophilic polymer is outside the above range, the water absorption amount and/or water absorption rate will be poor, and the effects of the present invention will not be obtained.

The crosslinking agent used in the present invention may be any compound having two or more functional groups that can react with carboxyl groups (or carboxylate groups). Examples of such crosslinking agents include ethylene glycol diglycidyl ether, Polyglycidyl ethers such as polyethylene glycol diglycidyl ether and glycerin triglycidyl ether, haloepoxy compounds such as epichlorohydrin and α-methylchlorohydrin, polyaldehydes such as geltaraldehyde and glyoxal, polyols such as glycerin, pentaerythritol, and ethylene glycol fat; Examples include polyamines such as ethylene diamine, and preferably polyglycidyl ethers such as ethylene glycol diglycidyl ether.

The amount of the crosslinking agent added varies depending on the type of crosslinking agent and the type of polymer, but the appropriate range is usually 0.01 to 5.0% by weight based on the polymer. If the amount of the crosslinking agent added is less than 0.01% by weight, the effect of the addition will not be sufficiently expressed; O]t'JfL%, the crosslinking density increases, leading to a decrease in water absorption, which is not the intention of the present invention. When the reverse phase suspension polymerization method is adopted as a polymerization method, sorbitan fatty acid esters such as nrubitan monoster 7-rate and sorbitan monolaurate are used as protective colloids, and celluloses such as ethyl cellulose, benzyl cellulose, and ethyl hydroxyethyl cellulose are used as polymer dispersants. 7) Cellulose esters, maleated polybutadiene, maleated polyethylene, maleated α-olefins, etc. can be mentioned.

By using the method of the present invention, it is possible to obtain a water-absorbing material with excellent salt resistance and water absorption rate, which is very advantageous for use as a water-retaining agent for agriculture and a water-absorbing agent for sanitary materials. The superabsorbent resin obtained by the method of the present invention can be advantageously used in the field of disposable diapers, which must absorb large amounts of urine quickly, and sanitary napkins, which must absorb blood. Possible, Leakage - 1 Discomfort 5
It may be possible to eliminate the need to leave behind.

EXAMPLES The present invention will be specifically explained below with reference to Examples and Comparative Examples, but the present invention is not limited to these Examples.

In addition, the amount of water absorption in the following Examples and Comparative Examples is a value determined by the following operation. That is, about 1 g of polymer was dispersed in a large excess of physiological saline, sufficiently swollen, and then
The weight (W) of the swollen polymer obtained was measured, and this value was calculated as the initial polymer weight tij: (
No) It is the value obtained by dividing by te.

In other words, water absorption amount (,9/,9)=w/w, ).

The water absorption rate was expressed as the amount of physiological saline absorbed by 0.6 g of polymer in 10 minutes.

Examples 1 to 3 In a 500 WT 4-necked round bottom flask equipped with a stirrer, reflux condenser, dropping funnel and nitrogen gas inlet tube, cyclohexane 2 Some and ethyl cellulose N-100 were added.
1,0Ii was charged and the temperature was raised to 75°C. Separately, in an Erlenmeyer flask, acrylic acid 30I was neutralized with 52.4% of a 25.6% by weight aqueous solution of caustic soda. The monomer concentration in the monomer aqueous solution was 45% by weight (water content 55% by weight). Next, 0.1 g of potassium persulfate and a 30% by weight hydrogen peroxide solution were added. ．． 9, 0.18
# was added and dissolved. This aqueous monomer solution was dropwise polymerized in the fourth flask under a nitrogen atmosphere for 1.5 hours, and then maintained at 70 DEG to 75 DEG C. for 0.5 hour to complete the polymerization. After this, the water content in the polymer suspended in cyclohexane was reduced to 25% by weight by azeotropic dehydration.
They were controlled to 20% by weight and 15-fold weight, respectively.

After this, 7 ml of an aqueous solution of 0.02 ethylene glycol diglycidyl ether and 1 rn/f of water were dissolved in each.
After addition at 3°C and holding at this temperature for 2 hours, the cyclohexane was removed and the polymer was dried at 806-100°C under reduced pressure to obtain a water-absorbing polymer.

Example-4 Polymerization was carried out according to Example-1. However, instead of ethyl cellulose N-100, maleic acid-modified polyethylene wax (H1-wax 1 manufactured by Mitsui Petrochemical Industries, Ltd.) was used.
105 A molecular weight 1,400, density 0.94, acid value 60
) 1.8.9, and 7 instead of hydrogen peroxide.
0.2.9% by weight t-butyl hydroperoxide was used. After the polymerization was completed, the water content in the polymer was controlled to 20% by weight by azeotropic dehydration, and then an aqueous solution of glycerin diglycidyl ether 0.0511 dissolved in 1 ml of water was added at 73°C and maintained at this temperature for 3 hours. After that, the cyclohexane was removed and the polymer was heated at 80° to 100°.
It was dried under reduced pressure at °C to obtain a water-absorbing polymer.

Example-5 The preparation method of Example-1 except that the monomer concentration in the monomer aqueous solution was set to 35 times the highest, and 0.0051 of N,N'-methylenebisacryl 7mide was additionally dissolved. A water-absorbing polymer was obtained in the same manner as in 1.

Example-6 Example-1 except that n-hexantholyte was used as the internal solvent in the charging process of Example-1, and 1.8 g of nrubitan monosterate 7 was used instead of ethyl cellulose N-100 (7).
A water-absorbing polymer was obtained in the same manner as in 1.

Example-7 Caustic soda 1 in which acrylic acid 3011 was dissolved in 39 g of water
It was neutralized in step 3.4.9, and the monomer concentration in the monomer aqueous solution became 45%. Furthermore, 0.1 g of sodium persulfate, 3
0.03 I of 0% hydrogen peroxide was added and dissolved. This aqueous monomer solution was poured into a thin film between two Teflon plates and held at 65° C. for 3 hours to polymerize. The resulting polymer gel was cut into two cod pieces, and then dried in a hot air dryer until the water content reached 28 parts.

The polymer was placed in a Nigu, and an aqueous solution of 0.03 F of ethylene glycol diglycidyl ether dissolved in 1 ml of water was sprayed thereon, and the mixture was kept at 70°C for 1 hour.
The resulting polymer was dried under reduced pressure at 0° C. to 80° C. and pulverized to obtain a water-absorbing polymer having a center particle size of 100 to 250 μm.

Comparative Example-1 Polymerization was carried out according to Example-1. However, the same operation as in Example 1 was carried out without adding 30% by weight hydrogen peroxide to obtain a water-absorbing polymer.

Comparative Example-2 Polymerization was carried out according to Example-1. However, 0.02 g of ethylene glycol diglycidyl ether was added to the monomer aqueous solution to carry out a crosslinking reaction simultaneously with the polymerization.

After the polymerization is complete, cyclohexane is removed and the polymer is reduced to 80%
It was dried under reduced pressure at @-100°C to obtain a water-absorbing polymer.

Comparative Example-5 In the charging method in Example-1, the polymerization initiators were 0.1 g of potassium persulfate and 0.09 g of ammonium persulfate.
A water-absorbing polymer was obtained in the same manner as in Example-1 except for the difference.

Table 1 shows the water absorption amount and water absorption rate of each water absorbing poly 1- obtained in Examples 1 to 6 and Comparative Examples 1 to 3.

It is clear from Table 1 how the polymer obtained by the present invention exhibits excellent absorption performance in salt resistance and water absorption rate.

Table-1

Claims (1)

[Scope of Claims] 1. A hydrophilic polymer obtained by polymerizing or copolymerizing a polymerizable monomer having a carboxyl group or/and a carboxylate group using a persulfate and a hydroperoxide in combination as a polymerization initiator. The water content inside is 10-4
1. A method for producing a super absorbent resin, which comprises adjusting the water content to 0% by weight, and then crosslinking the resin with a crosslinking agent having two or more carboxylate sulfone functional groups. 2. The method for producing a super absorbent resin according to claim 1, wherein the hydrophilic polymer is a polymer or copolymer of acrylic acid or an alkali metal salt of acrylic acid. (v) The method for producing a superabsorbent resin according to claim 1, wherein the crosslinking agent is polyglycidyl ether.