JPH05178919A - Highly water-absorbing resin and its production - Google Patents

Abstract

PURPOSE:To obtain a highly water-absorbing resin without using any organic solvent or surfactant by radical-copolymerizing an acrylic acid monomer with a water-soluble cross-linking agent in the presence of a specified chain transfer agent and a polymerization initiator. CONSTITUTION:An acrylic acid monomer is radical-copolymerized with a water- soluble cross-linking agent in the persence of a compound of the formula (wherein n is 4-8) or its salt and a polymerization initiator. The obtained copolymer is dried and ground to obtain the purpose highly water-absorbing resin. As a salt of the methacrylic acid to be used, an alkali metal salt is particularly desirable. In order to fully exhibit the effect of the compound of the formula as a chain transfer agent, a process which comprises slowly adding an initiator solution and a solution containing the acrylic acid monomer and the cross- linking agent to an aqueous solution the compound of the formula or its salt and conducting polymerization is desirable.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a highly water-absorbent resin and a method for producing the same. More specifically, the present invention relates to a superabsorbent resin which is a copolymer of an acrylic acid-based monomer and a water-soluble cross-linking agent and contains a phenol sulfonic acid cyclic derivative in the molecule, and a method for producing the same.

[0002]

2. Description of the Related Art Super absorbent polymers have been put to practical use in paper diapers, sanitary products, dew condensation prevention agents, greening, agricultural and horticultural applications, etc.
Moreover, its range of application is expanding. As the super absorbent polymer, starch-hydrolyzate of acrylonitrile graft copolymer, carboxymethyl cellulose crosslinked product,
Polyacrylate cross-linked products, acrylate-vinyl alcohol copolymers, polyethylene cross-linked products and the like are known.
Among them, polyacrylic acid salt-based super absorbent polymers are widely used because they are excellent in terms of chemical stability and water absorption capacity, and various methods are also available for producing super absorbent polymers of this type. Is proposed. However, it is quite difficult to prepare a highly water-absorbent resin having a large water-absorbing capacity and a high water-absorption rate, and the polymer is likely to adhere to the wall of the polymerization vessel from the viewpoint of work, and bulk polymerization is likely to occur. There is also a problem with sex.

[0003]

As a method for solving such a problem, JP-A-2-153907 proposes a reverse phase suspension polymerization method using a specific surfactant. In this method, at the time of producing a polyacrylate superabsorbent resin, in order to prevent the adhesion of the polymer to the wall of the polymerization vessel and to operate stably, the radical polymerization of the acrylate is initiated in the presence of the crosslinking agent. Hydrocarbon solvent-
Reversed phase suspension polymerization is carried out with a surfactant such as sorbitan fatty acid ester in an aqueous system, but since highly flammable cyclohexane or normal hexane is used, there is a problem in safety during production. There is a problem that the manufacturing cost becomes high because a complicated manufacturing device is required. The present invention was devised to solve the above-mentioned drawbacks of the prior art, and is excellent in water absorption performance such as water absorption capacity and water absorption speed, and a polyacrylic acid-based high-polymerizable material that can be produced without using an organic solvent or a surfactant. An object is to provide a water absorbent resin and a method for producing the same.

[0004]

The superabsorbent resin of the present invention, which has been made to solve the above-mentioned problems, has the following general formula (1) which acts as a chain transfer agent. A copolymer obtained by radically copolymerizing an acrylic acid-based monomer and a water-soluble crosslinking agent in an aqueous system in the presence of a compound represented by the formula (n represents an integer of 4 to 8) and / or a salt thereof. A compound consisting of a polymer and represented by the general formula (1) and /
Or its salt is incorporated into the molecule by a chain transfer reaction,
It becomes a constituent of the copolymer. Further, the method for producing the superabsorbent resin of the present invention is the above-described method for producing the superabsorbent resin, which comprises adding an acrylic acid-based monomer in the presence of a compound represented by the general formula (1) and / or a salt thereof. The method comprises radically copolymerizing a water-soluble crosslinking agent with a polymerization initiator, drying the resulting copolymer, and pulverizing.

The present invention having the above-mentioned constitution, the compounds represented by the general formula (1) and salts thereof used in the present invention are known compounds, and are disclosed in, for example, JP-A-61-83156. And can be prepared by the method described in the publication. Further, the present inventors have found that the compound represented by the general formula (1) and a salt thereof have radical scavenging ability and can be an aqueous antioxidant, and have already applied for such use. (Japanese Patent Application No. 2-216969)
issue).

The salt of the compound represented by the general formula (1) is, for example, an alkali metal salt (for example, sodium salt,
Inorganic metal salts such as potassium salts) and alkaline earth metal salts (eg magnesium salts, calcium salts etc.), ammonium salts, organic base salts (eg trimethylamine salts, triethylamine salts, ethanolamine salts, triethanolamine salts) , Piperazine salt, piperidine salt, morpholine salt, N-methylmorpholine salt, pyridine salt, picoline salt, N-methylpyridinium salt, etc.), salts with amino acids (eg, lysine salt, arginine salt, etc.) and the like. , Alkali metal salts are preferred. In addition, the salt of the compound represented by the general formula (1) includes both a compound in which all the sulfo groups of the compound represented by the general formula (1) are neutralized and a compound in which a part thereof is neutralized. Included. A part of the phenolic hydroxyl group of the compound represented by the general formula (1) may be neutralized.

Acrylic acid-based monomers used in the superabsorbent resin of the present invention include acrylic acid and methacrylic acid, and salts thereof. Examples of the salts include the salts exemplified above. Alkali metal salts are particularly preferably used. As the water-soluble cross-linking agent, any one can be used as long as it is a water-soluble monomer capable of radical polymerization and can be a cross-linking agent, but N, N ′ having excellent copolymerizability with an acrylic acid-based monomer. -Methylenebisacrylamide and ethylene glycol diacrylate are preferably used.

The superabsorbent resin of the present invention contains an acrylic acid-based monomer and a water-soluble crosslinking agent in a conventional manner in the presence of a compound represented by the general formula (1) which is a chain transfer agent and / or a salt thereof. According to the same manner, radical copolymerization is carried out in a water solvent using a polymerization initiator under an inert gas atmosphere, and the obtained copolymer is dried and then pulverized. The above-mentioned polymerization can be carried out in accordance with ordinary radical polymerization, and any initiator can be used as long as it is used for aqueous radical polymerization, for example, a persulfate-based initiator (for example, , Potassium persulfate, ammonium persulfate, etc.), redox type initiators (eg, hydrogen peroxide-first
Iron salts, etc.), azo initiators [eg, azobis- (2-amidinopropane) hydrochloride, etc.] and the like. As the charging ratio of each of the above components, the amount of the water-soluble crosslinking agent with respect to the total amount of acrylic acid-based monomers is about 0.001 to 0.03 times the molar amount,
The amount is preferably about 0.003 to 0.01 times by mole, and if it is less than 0.001 times by mole, the degree of crosslinking may be insufficient, and if it exceeds 0.03 times by mole, crosslinking may be excessively performed and water absorption performance may be deteriorated. Further, the total amount of the compound represented by the general formula (1) and a salt thereof with respect to the total amount of the acrylic acid-based monomer is about 0.001 to 0.03 times mol, preferably about 0.003 to 0.01 times mol, and water absorption is less than 0.001 times mol. The performance is inferior, and if it exceeds 0.03 times by mole, it is disadvantageous in terms of production cost, and there is a possibility that it is excessively crosslinked and water absorption performance is deteriorated. Further, the water-soluble cross-linking agent is added in an amount of 0.05 to
The amount is about 10 times mol, preferably about 0.1 to 5 times mol, more preferably about 0.5 to 2 times mol. If it is less than 0.05 times mol, the degree of crosslinking is insufficient, and if it exceeds 10 times mol, water absorption performance may be poor. .. The acrylic acid-based monomer used is preferably a combination of a free acid and a salt (preferably an alkali metal salt such as a sodium salt or a potassium salt), and the content of the salt in the total acrylic acid-based monomer is 50-95 mol%
Degree, more preferably about 60 to 90 mol%.
If the salt content is less than 50 mol%, the water absorption capacity may be poor,
If it exceeds 95 mol%, the polymerization may be inhibited.

During polymerization, in order to fully exert the action of the compound represented by the general formula (1) as a chain transfer agent, the compound represented by the general formula (1) and / or a salt thereof is added to an aqueous solution. A method of gradually adding a solution containing an acrylic acid-based monomer and a water-soluble crosslinking agent together with the agent solution to polymerize is preferable. More specifically, a predetermined amount of the compound represented by the general formula (1) and / or its salt is dissolved in water, and the temperature is raised to 80 to 90 ° C under a nitrogen stream. To this solution, at the same temperature, an aqueous solution in which a predetermined amount of acrylic acid-based monomer and a water-soluble crosslinking agent are dissolved and an aqueous solution in which an initiator is dissolved are slowly dropped at the same time to start polymerization. After completion of the dropping, the copolymer is obtained by aging at the same temperature (usually about 30 minutes to 1.5 hours). The monomer concentration in the polymerization system is finally about 5 to 50% by weight, preferably 10 to
40% by weight, and the final concentration of the initiator is 0.01
˜3 wt%, preferably 0.1 ˜1 wt%. The obtained copolymer solution may be neutralized with an acid group present in the copolymer by using a basic substance such as sodium hydroxide, if necessary. The copolymer solution thus obtained is concentrated, then dried and pulverized to obtain a highly water-absorbent resin. The above drying can be carried out according to a conventional method, but it is preferably carried out by heating and drying. Crosslinking of the copolymer is promoted by heating, and the water absorption capacity can be improved. Examples of the heat-drying include a method of heat-treating the copolymer at about 60 to 90 ° C, preferably about 70 to 80 ° C under reduced pressure. The thus dried copolymer is pulverized into an appropriate particle size in the form of powder or particles by a conventional method using a pulverizer or the like to obtain a highly water-absorbent resin.

[0010]

EFFECTS OF THE INVENTION The highly water-absorbent resin of the present invention is excellent in water absorption capacity, water absorption speed, etc., exhibits high water absorption characteristics even in water containing salts, and can be manufactured more easily. Also,
According to the method for producing a superabsorbent resin of the present invention, the superabsorbent resin can be produced safely and simply without using any hydrocarbon solvent that may cause a fire or explosion.

[0011]

The present invention will be described in more detail based on the following examples, comparative examples and test examples, but the present invention is not limited to these examples. In the following examples, the sodium salt of the compound represented by the general formula (1) was used. The properties of the compounds used are shown in Table 1. In Table 1 and the following description, CALX-SN is used as the abbreviation for the sodium salt of the compound represented by the general formula (1), and sodium in the compound represented by the general formula (1), wherein n is 4. The salt is represented by CALX-S4, and similarly, the sodium salt of the compound in which n is 6 is CALX-S.
6, the sodium salt of the compound in which n is 8 is CALX-S
Displayed at 8.

[0012]

[Table 1]

Example 1 20.0 g of water and 1.271 g of CALX-S4 in a reaction vessel equipped with a stirrer, a thermometer, a dropping device and a reflux condenser.
Was charged and the temperature was raised to 82 to 84 ° C. under a nitrogen stream,
Separately prepared water 77.6g, sodium acrylate (AAN
a) 18.28 g, acrylic acid (AA) 6 g and N,
N'-methylenebisacrylamide (MBAD) 0.2
Separately, a homogeneous mixed transparent aqueous solution containing 127 g and 4 g of a 5% by weight ammonium persulfate aqueous solution at 82 to 84 ° C.
It was added dropwise in 2 hours. As the dropping proceeds, the polymerization reaction proceeds, and the viscosity of the reaction system increases. 8 after the dropping
An aqueous copolymer solution was obtained by aging the polymerization reaction at 2 to 84 ° C. for 1 hour. The reaction system was light yellow, transparent, viscous, and homogeneous in water.

A portion of the reaction system was sampled at 70 ° C.
When the polymerization rate was determined by drying under reduced pressure to a constant weight, the polymerization was almost quantitative, and was 99% or more. The solid content concentration was about 20% by weight, and the pH was 6-7. In addition,
The charged molar composition of this reaction system is as follows. After concentrating the copolymer solution obtained above, 70-80
It was dried under reduced pressure to constant weight at ℃. The dried solid substance was crushed in a mortar to obtain a pale yellow granular polymer (about the size of rough sugar).

Example 2 In Example 1, [MBAD] / [CALX-S4]
Copolymerization was performed in the same manner as in Example 1 except that the molar ratio of was 0.25, and drying and pulverization were performed in the same manner to obtain a polymer.

Example 3 Copolymerization was carried out in the same manner as in Example 1, except that CALX-S4 was mixed in the acrylic acid monomer-MBAD-water solution without adding it in water and dissolved uniformly.
Further, similarly, drying and pulverization were performed to obtain a polymer.

Comparative Example 1 Copolymerization was carried out in the same manner as in Example 1 except that the polymerization reaction was carried out without using CALX-S4 and MBAD, and drying and crushing were carried out in the same manner as in Example 1. Got united.

Test Example 1 (Water absorption test 1) Regarding the polymers obtained in Examples 1 to 3 and Comparative Example 1,
A water absorption capacity test for salt water was performed. The water absorption capacity was measured by the following method. Measurement method of water absorption amount Sample [Xg (about 1 g)] was put into a commercially available tea bag filter of 9 cm x 7 cm, and after soaking in 0.9% saline for a certain period of time, after taking out and no drop of water was observed (About 1 minute), including the tea bag filter, measure the weight [Yg]. Separately, as a blank test, the weight [Zg] after the same dipping operation with only the tea bag filter is measured. These measured values X, Y and Z
The water absorption amount (times) was calculated based on the following formula. The measurement was repeated until water absorption equilibrium was reached. The measurement results are shown in Table 2. Water absorption (times) = (YZ) / X

As shown in Table 2, the water-absorbing ability of the polymer obtained in Comparative Example 1 was small, but all the polymers of the present invention showed high water-absorbing ability. More specifically, the polymer obtained in Comparative Example 1 had the CALX-S4 and MBA
A polyacrylic acid-based polymer obtained by polymerizing by the same operation as in Example 1 without using D, and its equilibrium water absorption capacity was markedly inferior at 11.0 after 24 hours. In addition, CALX-S
When radical polymerization was carried out in the same manner as in Example 1 except that MBAD was added without using No. 4, the water absorption capacity obtained in Comparative Example 1 was similar to that of the polymer. On the other hand, Examples 1 and 2
The polymer obtained in (1) showed a water absorption capacity of about 40 times or more. It is said that the polyacrylic acid-based highly water-absorbent resin preferably has a water absorption capacity of 0.9% or more with respect to saline solution of 40 times or more (see, for example, JP-A-1-292004). The polymer obtained in No. 2 has excellent water absorption, and in particular, the molar ratio of MBAD / CALX-S4 is 1 /
It was revealed that the polymer obtained in Example 1, which is No. 1, has excellent water absorption performance. The water absorption capacity of the polymer obtained in Example 3 is 21 times, which is slightly inferior to the polymers obtained in Examples 1 and 2. Examples 1 and 2
Then, the monomer aqueous solution and the initiator aqueous solution are added dropwise to the CALX-S4 aqueous solution to perform radical polymerization.
Then, a solution obtained by mixing and uniformly dissolving CALX-S4 in an aqueous solution of a monomer is added dropwise to perform radical copolymerization. Therefore, these facts indicate that the protons of the methylene chain of the CALX-S4 skeleton undergo a radical chain transfer reaction, resulting in CALX-
-Acrylic acid monomer by S4 skeleton radical-MB
Example 1 suggests that the cross-linking of the AD copolymer is improved.
It was revealed that the methods described in 1 and 2 were preferable to the method described in Example 3. In addition, instead of CALX-S4 in Example 1, CALX-S6 and CA
The polymer obtained in the same manner as in Example 1 except that LX-S8 was used also showed the same high water absorption as the polymer obtained in Example 1.

Test Example 2 (Water Absorption Capacity Test 2) The polymers obtained in Examples 1 and 2 were subjected to a water absorption capacity test for tap water. The test method was the same as above. The results are shown in Table 3. As shown in Table 3,
It was found that the polymers obtained in Examples 1 and 2 exhibited 500 to 300 times higher water absorption than tap water.

[0021]

[Table 3]

It is not clear what mechanism the high water absorbing effect of the CALX-S4-acrylic acid type monomer-MBAD copolymer is due to, but as described above,
It is considered that this is due to the property of the polymer in which X-S4 is bonded to the main chain of the copolymer by the radical chain transfer reaction. As the reason, first, it was shown in Japanese Patent Application No. 2-21963 that the cyclic structure is stably maintained in the aqueous radical polymerization reaction of CALX-SN at a temperature of 70 to 90 ° C. Furthermore, CAL is performed by the same operation as Comparative Example 1 or Comparative Example 1.
The same amount of CALX-S4 as used in Example 1 was mixed and dissolved in the polymer obtained by radical polymerization in a system in which only MBAD was added without adding X-S4, dried, and then pulverized to obtain. The obtained polymer composition showed only a water absorption capacity similar to that of Comparative Example 1. Therefore, from these facts, the polymers obtained in Examples 1 to 3 are qualitatively,
Acrylic acid-based monomer-MBAD copolymer and CALX-
Acrylic acid-based monomer-not just a mixture of S4
It suggests that CALX-S4 is bonded to the MBAD copolymer main chain by radical chain transfer reaction. Therefore, such a CALX-SN-acrylic acid-based monomer-M
It is presumed that the polymer obtained in the BAD system exhibits high water absorption performance by expanding the cavity of CALX-SN for the inclusion ability and increasing the liquidity due to MBAD bridging.

[Table 2]

Claims (4)

[Claims] 1. The general formula (1) (In the formula, n represents an integer of 4 to 8), which is polymerized in the presence of a compound represented by the formula or a salt thereof, and which has a high water-absorbing property, comprising a copolymer of an acrylic acid-based monomer and a water-soluble crosslinking agent. resin. 2. The general formula (1) (In the formula, n represents an integer of 4 to 8) or in the presence of a salt thereof, an acrylic acid-based monomer and a water-soluble crosslinking agent are radically copolymerized using a polymerization initiator to obtain A method for producing a highly water-absorbent resin, which comprises drying and pulverizing the obtained copolymer. 3. The radical copolymerization by dropping an aqueous solution containing an acrylic acid-based monomer and a water-soluble crosslinking agent and an aqueous solution of a polymerization initiator into an aqueous solution of a compound represented by the general formula (1) or a salt thereof. A method for producing the superabsorbent resin described. 4. After heating and drying the obtained copolymer,
The method for producing a highly water-absorbent resin according to claim 2 or 3, which comprises pulverizing.