JPH0834894A - Poly(acrylic acid) composite - Google Patents

Abstract

PURPOSE:To obtain a poly(acrylic acid) composite having high water absorption and Kindustrially advantageously obtain the composite without passing through an aqueous gel state. CONSTITUTION:The composite comprises a particulate organic support having an alkali supported thereon and a crosslinked poly(acrylic acid). It is obtained by polymerizing acrylic acid and a crosslinking agent therefor in a nonaqueous solvent in which acrylic acid is soluble but poly(acrylic acid) is substantially insoluble in the presence of a particulate organic support having an alkali supported thereon.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a novel polyacrylic acid composite and a method for producing the same. Specifically, a polyacrylic acid complex having a high water-absorbing ability composed of specific organic carrier particles and a polyacrylic acid crosslinked product and the polyacrylic acid complex are industrially advantageous without passing through the state of an aqueous gel. The present invention provides a manufacturing method which can be obtained.

[0002]

2. Description of the Related Art In recent years, the uses of superabsorbent polymers have diversified, and various kinds of superabsorbent polymers have been produced and used. Among them, polyacrylic acid-based highly water-absorbent polymers have been established in production technology and are most often used.

The method for producing the superabsorbent polymer is roughly classified as follows.

A method in which a gel polymer is obtained by adding a cross-linking agent to an aqueous solution of an acrylate and polymerizing, and drying the contained water.

A method in which an aqueous acrylate solution is subjected to reverse phase suspension polymerization in an organic solvent to obtain swollen gel particles, and the contained water is dried.

A method of graft-polymerizing acrylonitrile onto an organic substance such as starch and then hydrolyzing it to dry the water contained in the product.

The superabsorbent polymer obtained by the above method is obtained as a polymer which uniformly contains a salt of a carboxyl group such as -COONa.

[0008]

However, in the above-mentioned method for producing a superabsorbent polymer, the state of the polymer after polymerization or hydrolysis is a gel containing a large amount of water, which is more than that of the gel polymer. In order to obtain the product, a drying process for drying the water is required.

Such a gel polymer has a high affinity for water and a large latent heat of vaporization of water (540 cal).
Therefore, it takes a lot of energy and time to dry and remove the water.

Therefore, at present, the above-mentioned water drying step significantly increases the production cost of the superabsorbent polymer, and the superabsorbent polymer is used as a hygiene product which is a relatively high value-added product. It has been one of the main causes used.

Therefore, in the future, further reduction of the manufacturing cost is desired in order to further develop the applications for agriculture, civil engineering, industrial use and the like.

[0012]

Means for Solving the Problems The inventors of the present invention have conducted extensive studies in order to solve the above-mentioned problems, and as a result, at least a part of the surface of the organic carrier particles carrying an alkali was formed by a polyacrylic acid crosslinked product. The coated polyacrylic acid complex exhibits high water absorption upon contact with water, and the polyacrylic acid complex contains acrylic acid and a crosslinking agent thereof in an alkaline solution in a specific non-aqueous solvent. By polymerizing in the co-presence of organic carrier particles carrying, it is possible to obtain the desired product without passing through an aqueous gel, and find that the energy required for the drying step can be significantly reduced.
The present invention has been completed.

That is, the present invention provides a polyacrylic acid composite comprising organic carrier particles carrying an alkali and a polyacrylic acid crosslinked product, and acrylic acid and a crosslinking agent thereof.
Provided is a method for producing a polyacrylic acid complex, which comprises polymerizing in the presence of organic carrier particles carrying an alkali in a solvent that dissolves acrylic acid and does not substantially dissolve polyacrylic acid. It is a thing.

In the present invention, the organic carrier particles carrying an alkali (hereinafter also referred to as “alkali-supporting particles”) are
There is no particular limitation as long as the organic carrier particles carry the alkali in a state where the alkali can be eluted by contact with water. As the organic carrier particles, water-soluble or water-swellable organic substances are preferably used for improving the water absorption rate of the obtained polyacrylic acid composite. Examples of such organic substances include carbohydrate-containing substances such as starch and flour such as wheat flour; cellulose; water-soluble polymers such as polyvinyl alcohol.

On the other hand, as the alkali, caustic soda and potassium caustic are generally used.

In the present invention, the method for producing the alkali-supported particles is not particularly limited, but a typical production method will be exemplified, in which an alcohol solution of alkali is uniformly dispersed over the organic carrier particles, or the organic carrier is used. After immersing the particles in an alkali alcohol solution, the alcohol is filtered off if necessary, and the alcohol is dried and removed.

The amount of alkali supported on the above-mentioned alkali-supported particles is not particularly limited, but is generally 1 to 20 g / 1.
A range of 0 g organic supported particles is preferred.

The particle size of the alkali-supporting particles varies depending on the form of the polyacrylic acid complex to be obtained and is not specifically limited, but is generally 1 to 1000 μm,
In particular, those having a particle size of 10 to 200 μm are used.

In the present invention, the crosslinked polyacrylic acid is swelled by contact with water, and the polyacrylic acid alkali salt formed by the reaction with alkali ions eluted from the alkali-supporting particles is not dissolved in water. Polyacrylic acid crosslinked to is preferably used.

Generally, the degree of the above-mentioned crosslinking can be specified by the ratio of acrylic acid, which is a raw material for the polyacrylic acid crosslinked product, and the crosslinking agent. The acid molar ratio is 0.002-
About 0.05 is suitable.

In the polyacrylic acid composite of the present invention,
The polyacrylic acid may contain a copolymer with other copolymerizable monomers within a range that does not significantly impair the effects of the present invention.

Examples of such monomers include components made of hydrophilic monomers such as methoxy polyethylene glycol monoacrylate, methoxy polyethylene glycol monomethacrylate, polyethylene glycol monoacrylate and polyethylene glycol monomethacrylate.

In the present invention, the embodiment in which the polyacrylic acid complex is constituted by the alkali-supporting particles and the polyacrylic acid crosslinked product is such that when the polyacrylic acid complex is brought into contact with water,
It is preferable that the alkali elutes more quickly than the alkali-carrying particles and the alkali reacts efficiently with the polyacrylic acid crosslinked product.

For example, an embodiment in which a part of the surface of the alkali-supporting particles is covered with the polyacrylic acid cross-linked product so that it is exposed from the polyacrylic acid cross-linking product, or the entire surface of the alkali-supporting particles is covered with the polyacrylic acid cross-linking product. The embodiment mentioned above is included. In the aspect of coating the alkali-supported particles with the polyacrylic acid crosslinked product, the aspect in which the polyacrylic acid crosslinked product is coated so that a part of the surface of the alkali-supported particles is exposed from the polyacrylic acid crosslinked product, It is particularly preferable because the alkaline ions are rapidly eluted by the contact.

In the above-mentioned coating mode, the alkali-supporting particles may be a single particle or an agglomerated particle thereof coated with a polyacrylic acid crosslinked body, or the alkali-supported particles may be coated in a state of being dispersed in the polyacrylic acid crosslinked body. It may be done.

In the present invention, the ratio of the alkali-supporting particles in the polyacrylic acid composite and the polyacrylic acid crosslinked product is such that the molar ratio of the alkali amount in the alkali-supported particles / acrylic acid unit of the polyacrylic acid crosslinked product is 0. .2 to 0.7
It is preferable to adjust the ratio so that

The present inventor estimates the water absorption effect of the polyacrylic acid composite of the present invention as follows. That is, when contacted with water or an aqueous solution, the polyacrylic acid crosslinked body starts to swell, and at the same time, the alkali ion eluted from the alkali-supporting particles produces an alkali salt unit of acrylic acid in the polyacrylic acid crosslinked body, It promotes the swelling of the crosslinked polyacrylic acid and exhibits good water absorption.

The production of the polyacrylic acid composite of the present invention comprises
A method of carrying out cross-linking polymerization of acrylic acid in a non-aqueous solvent capable of preventing the elution of alkali from the alkali-supporting particles is adopted without particular limitation.

A preferred method for producing a polyacrylic acid composite having a structure in which at least a part of alkali-supporting particles is coated with a crosslinked polyacrylic acid, which is a typical embodiment of the polyacrylic acid composite of the present invention, will be illustrated. For example, acrylic acid and a crosslinking agent, and if necessary, other polymerizable copolymerizable components,
There may be mentioned a method of polymerizing in a non-aqueous solvent in which acrylic acid is dissolved and in which polyacrylic acid is not substantially dissolved, in the presence of organic carrier particles carrying an alkali.

That is, when acrylic acid and a crosslinking agent are polymerized in the presence of alkali-supporting particles in a solvent in which acrylic acid and a crosslinking agent are dissolved but polyacrylic acid is not dissolved, polyacrylic acid produced is insoluble. Phase separation occurs, and the use of a cross-linking agent accelerates the phase separation. Further, the phase-separated crosslinked polyacrylic acid radical or crosslinked polyacrylic acid is deposited on the surface of the alkali-supporting particles having large polarity and covers the surface. Then, the powder is separated by filtration and the solvent is removed by drying to obtain a powdery polyacrylic acid complex in which the alkali-carrying particles and the polyacrylic acid crosslinked body coexist.

In the present invention, as the cross-linking agent, a known cross-linking agent such as a commonly used divinyl compound or trivinyl compound can be used. Examples of typical crosslinking agents include divinylbenzene, 1,2-distyrylethane, polyethylene glycol diacrylate, polyethylene glycol dimethacrylate, polypropylene glycol diacrylate, polypropylene glycol
Examples thereof include dimethacrylate.

The non-aqueous solvent can be used without particular limitation as long as it dissolves acrylic acid and a cross-linking agent and does not dissolve polyacrylic acid.
These non-aqueous solvents can be used alone or in combination.

Among such non-aqueous solvents, those having a relatively low boiling point are more desirable in order to facilitate removal of the solvent.
Of these, suitable non-aqueous solvents are exemplified by benzene,
Examples thereof include toluene, cyclohexane, ethyl ether, acetone and the like, or a mixed solvent thereof.

When using the above-mentioned non-aqueous solvent, it is desirable to experimentally confirm in advance whether or not the obtained polyacrylic acid complex product can maintain the powder state and select it.

In the present invention, a method of polymerizing acrylic acid and its cross-linking agent in a non-aqueous solvent in the presence of alkali-supporting particles is as follows: acrylic acid and its cross-linking agent in a state where the alkali-supporting particles are dispersed in a non-aqueous solvent. The method of polymerizing is preferred.

The dispersion concentration of the above-mentioned alkali-supported particles may be any concentration that allows stirring at the final polymerization stage. Generally,
Depending on the particle size of the alkali-supported particles, etc., 3 to 20 g
A concentration of about / 100 ml solvent is used. Further, the amount of the alkali-supported particles used with respect to acrylic acid may be set so as to be a suitable ratio in the polyacrylic acid composite.

In the polymerization reaction, the acrylic acid and the cross-linking agent may be added to the non-aqueous solvent in the total amount, or may be added continuously or intermittently.

Further, the polymerization reaction is generally carried out by adding a polymerization initiator to the system. As the polymerization initiator, an ordinary radical polymerization initiator can be used and is not particularly limited. For example, azobisisobutyronitrile, benzoyl peroxide or the like may be used alone. It is also possible to use redox polymerization initiators such as benzoyl-p-tolyldiethanolamine oxide.

Furthermore, at the time of polymerization, it is possible to appropriately add the above-mentioned monomer copolymerizable with acrylic acid together with acrylic acid.

In the polymerization reaction, a temperature lower than the boiling point of the non-aqueous solvent under the reaction conditions is generally adopted.

[0041]

As can be understood from the above description, the polyacrylic acid composite of the present invention has a special structure, which is composed of alkali-supporting particles and polyacrylic acid cross-linked product, which has never existed before, It exhibits the property of exhibiting excellent water absorption by contact with an aqueous solution.

The method of the present invention for producing the polyacrylic acid composite has the following features.

(1) The polyacrylic acid complex obtained is not swollen with water because it is obtained by reacting in a non-aqueous solvent. Therefore, it is not necessary to dry the water having large latent heat of vaporization in the final step, and the polyacrylic acid complex can be obtained extremely efficiently and economically.

(2) The polyacrylic acid composite obtained is
Since it is powdery corresponding to the size of the alkali-supporting particles,
No grinding process is required.

(3) By adjusting the amount ratio of the alkali-supported particles and acrylic acid, the ratio of the acrylic acid unit and the acrylic acid alkali salt unit in the product can be adjusted as desired, and the resulting poly It is possible to arbitrarily adjust the water absorption of the acrylic acid complex.

[0046]

EXAMPLES Examples will be shown below to more specifically describe the present invention, but the present invention is not limited to these examples.

Example 1 5 g of starch containing 2 g of caustic soda (average particle diameter 100 μm), 15 g of acrylic acid, polyethylene glycol diacrylate (average molecular weight of 45 in 300 ml of benzene)
0) 1 g was added, and the mixture was polymerized in a nitrogen atmosphere at 40 ° C. with stirring.

As the polymerization initiator, a redox system containing 0.2 g of benzoyl peroxide and 0.2 g of diethanol paratoluylamine was used.

After 2 hours, the polymerized product was filtered off and dried under reduced pressure to obtain 21 g of a powdery water-absorbent polyacrylic acid complex without passing through a gel state.

In the above operation, the polyacrylic acid complex was not swollen, and filtration and drying were extremely easy.

Further, as a result of observing the obtained polyacrylic acid composite with an electron microscope, it was found that the particle surface had a structure partially covered with the polyacrylic acid crosslinked product.

Furthermore, the obtained polyacrylic acid complex 0.
After dipping 5 g in 300 ml of 0.9% saline, the water absorption was measured by a filtration method. As a result, the liquid absorption was 60 g / g polyacrylic acid complex, and the pH of the saline after immersion was 4. It was 5.

Example 2 Starch containing 3.6 g of caustic soda (average particle size 80 μm)
Suspension of 10 g in 300 ml of benzene, acrylic acid 1
5 g polyethylene glycol monoacrylate (average molecular weight 450) 4 g and divinylbenzene 3 g were added,
Using the same redox polymerization initiator as in Example 1, 50
Polymerization was carried out for 3 hours under a nitrogen atmosphere at ℃.

By filtering and drying the product, 26 g of a powdery polyacrylic acid complex was obtained without passing through a gel state.

In the above operation, the polyacrylic acid complex was not swollen and it was extremely easy to filter and dry.

Further, the obtained polyacrylic acid complex 0.
The liquid absorption of the polyacrylic acid complex measured by the filtration method after immersing 5 g in 300 ml of 0.9% saline solution was 72 g / g polyacrylic acid complex, The pH was 4.9.

Example 3 10 g of wheat flour (average particle size 100 μm) containing 4 g of caustic soda was suspended in 300 ml of benzene, and further 10 g of acrylic acid, 3 g of methoxy polyethylene glycol monomethacrylate (average molecular weight 1070), and polyethylene glycol diacrylate. (Average molecular weight 508)
Polymerization was performed under the same conditions as in Example 1 except that 0.7 g was added and the same polymerization initiator as in Example was used and the polymerization temperature was 40 to 45 ° C.

Then, by filtration and drying, 17 g of a powdery polyacrylic acid complex was obtained without going through a gel state.

In the above operation, the polyacrylic acid complex was not swollen and it was extremely easy to filter and dry.

Furthermore, the obtained polyacrylic acid complex 0.
After soaking 5 g in 300 ml of 0.9% NaCl aqueous solution, the amount of liquid absorbed by the filtration method was 70 g / g polyacrylic acid complex.

Example 4 Corn starch containing 6 g of caustic soda as an alkali-supporting particle in 300 ml of acetone (average particle size: 10
0 μm) 15 g, acrylic acid 15 g, polyethylene glycol diacrylate 1.5 g, benzoyl peroxide 0.
After adding 3 g and 0.3 g of p-toluyl-diethanolamine and polymerizing at 45 ° C. for 3.5 hours in a nitrogen atmosphere,
By filtering and drying, 30 g of a powdery polyacrylic acid complex was obtained without passing through a gel state.

After immersing 0.5 g of the obtained polyacrylic acid complex in 300 ml of 0.5% NaCl aqueous solution,
The amount of liquid absorbed by the filtration method was 60 g / g polyacrylic acid complex, and the pH of the saline solution after immersion was 5.5.

Claims (2)

[Claims] 1. A polyacrylic acid composite comprising organic carrier particles carrying an alkali and a crosslinked polyacrylic acid. 2. Polymerization of acrylic acid and its cross-linking agent in a non-aqueous solvent that dissolves acrylic acid and does not substantially dissolve polyacrylic acid in the presence of organic carrier particles carrying an alkali. A method for producing a polyacrylic acid complex, comprising: