JPH0819163B2 - Manufacturing method of super absorbent material - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial field of application] The present invention is a production method for extremely efficiently producing a highly water-absorbent material that is widely used in medical hygiene materials, civil engineering construction, agricultural materials and the like. It is about. More specifically, the present invention relates to a production method which can carry out polymerization, crosslinking, drying and pulverization steps for producing a superabsorbent material in one step and can provide extremely high productivity and excellent quality. is there.

[Conventional technology]

Conventionally, as the water-absorbing material, polyacrylic acid salt type, starch-acrylic acid graft polymer, acrylic acid-vinyl alcohol copolymer, polyethylene oxide type, isobutylene-maleic anhydride copolymer, PVA-maleic acid ester type Known are copolymers, carboxymethyl cellulose-based polymers, starch-acrylonitrile graft polymers, and the like.

In order to produce these water-absorbing materials, generally, complicated steps such as polymerization, crosslinking, drying, pulverization, hydrolysis and the like must be performed. In particular, the water-absorbing material obtained by carrying out a polymerization reaction such as aqueous solution polymerization, suspension polymerization, reverse phase emulsion polymerization, reverse phase suspension polymerization contains a large amount of water,
Removing water is an important point. Removal of water requires a large amount of energy consumption, and efficiency improvement has been a problem for those skilled in the art. JP-A-58-71907
Japanese Unexamined Patent Publication (Kokai) No. 59-18712 discloses, as one of methods for improving this, a method of evaporating water by utilizing reaction heat during polymerization. In this method, it was difficult to say that the removal of water was complete, and it was necessary to supplement energy. In addition, the form of the water-absorbent material obtained is rough, and a crushing step is necessary to obtain a product. Therefore, there are drawbacks such that the process is complicated, the productivity is low, and the cost is high for industrial production.

[Problems to be Solved by the Invention]

An object of the present invention is to overcome the drawbacks of the conventional methods for producing a water-absorbing material and to provide a production method in which the steps of polymerization, crosslinking, drying and pulverization can be carried out in one step.

[Means for solving the problem]

The present inventors, in view of such a current situation, as a result of repeated intensive studies, by spraying a mixture of a suitable monomer, catalyst, crosslinking agent and solvent into a container set to specific conditions It was found that polymerization, crosslinking, drying and pulverization can be carried out in one step, and the present invention has been completed. JP 58-7
As disclosed in Japanese Patent No. 1907, the method using a spraying method has many problems in terms of drying efficiency and quality stability, and in the case of a highly water-absorbing material, the reaction such as polymerization and crosslinking is rapid. It has been considered by those skilled in the art that it cannot be used at all due to troubles such as clogging in the piping.

 Hereinafter, the present invention will be described in detail.

The gist of the present invention is to control a mixture consisting essentially of a monomer, a water-soluble peroxide catalyst, a cross-linking agent and a solvent thereof within a temperature or a residence time at which fluidity is not lost. From the spraying device, the maximum temperature is above the starting temperature of the crosslinking reaction, above the boiling point of the solvent, and below the decomposition temperature of the monomer, and sprayed into a container to carry out reaction, pulverization, and drying. It is a method for producing a highly water-absorbing material, which is characterized in that it is performed in one step.

As the monomer used here, a vinyl compound is used, and preferably a water-soluble vinyl compound is used. As the water-soluble vinyl compound, acrylic acid, acrylic acid salts, methacrylic acid, methacrylic acid salts, and acrylamide are particularly preferably used, and these may be used alone or in combination of two or more. Most preferably, a combination of acrylic acid or acrylates and acrylamide is utilized. With this combination, a highly water-absorbent material having excellent performance, in particular, absorption capacity for seawater can be obtained.

Usually, the ratio of acrylic acid or acrylates to acrylamide is preferably 10 to 90% by weight, and more preferably 15 to 85% by weight. By setting it within this range, it is possible to obtain a water-absorbing material having an excellent absorbing ability for any of water, ion water and seawater.

As the polymerization catalyst, a radical catalyst used for usual polymerization of vinyl compounds can be used. Usually, a water-soluble catalyst is used. Preferably, water-soluble peroxides, most preferably water-soluble inorganic peroxides, such as potassium persulfate, ammonium persulfate,
Hydrogen peroxide or the like is used. These water-soluble catalysts are
It is useful for uniformly causing the polymerization reaction and the cross-linking reaction and expressing the stability of performance. These water-soluble inorganic peroxides are generally used as a redox catalyst in combination with a reducing substance such as sulfite or an amine. However, in the present invention, the use of a catalyst substantially composed of a water-soluble peroxide is one of the greatest features. Preferably, the peroxide catalyst is used alone. This is effective in suppressing the progress of polymerization and cross-linking reaction and preventing troubles such as clogging due to gelation in the piping and the spraying device. In the method of the present invention, the weight ratio is usually 0.01 to 3 with respect to the monomer.
% Catalyst is used, preferably 0.05 to 1%. If an amount outside this range is used, the reaction may be too fast, causing troubles due to gelation, or the reaction may be too slow, or may occur nonuniformly, resulting in poor performance.

Examples of the cross-linking agent used in the present invention include formalin, ethylenediamine, glyoxal, glycerin, water-soluble diepoxide, inorganic metal salts, organic metal salts, N, N′-methylenebisacrylamide, N, N′-methylenebismethacrylamide and the like. Is preferably used. Particularly frequently used are water-soluble divinyl compounds such as N, N'-methylenebisacrylamide, but not limited to these. The amount of cross-linking agent used in the method of the present invention is preferably in the range of 0.01 to 3% by weight with respect to the monomer. If it exceeds this range, the water absorption performance will decrease, and if it is below this range, the gel strength when absorbing water will be insufficient, and in either case, the performance as a water absorbing material will be insufficient, making it difficult to use as a product.

Next, the above-mentioned monomer, catalyst and crosslinking agent are mixed with water. In this case, it is preferable that the monomer, the catalyst and the crosslinking agent are dissolved in water. Even if the monomer, the catalyst, and the crosslinking agent are not dissolved by themselves, it is preferable that they are dissolved by mixing. Further, in order to improve the solubility of these, in order to improve the reaction, the drying efficiency, etc.,
You may mix other solvents, such as methanol, ethanol, and acetone. Here, the weight ratio of the monomer in water alone or in water and the solvent is preferably 5 to 80%, and more preferably 20 to 70%. If a weight ratio lower than this range is used, not only will the reaction and drying not be carried out satisfactorily, but it will not be possible to obtain a good quality product, but also undried products will accumulate in the equipment and It leads to the above trouble.

Also, when using a weight ratio higher than this range,
The monomer is not sufficiently dissolved, and a stable quality product cannot be obtained.

Subsequently, the mixture is sprayed from a controlled spraying device within a temperature or residence time at which fluidity is not lost. In the method of the present invention, temperatures below 80 ° C are preferably used,
Suitably temperatures below 60 ° C. are used. Use above this temperature is accompanied by gelation due to the progress of polymerization and crosslinking reaction,
The mixture loses its fluidity and causes troubles such as clogging. In consideration of drying efficiency, cooling cost, reaction efficiency, etc., the lower limit temperature is preferably -15 ° C or higher, and preferably 0 ° C or higher. Furthermore, in order to increase the drying efficiency or for the reason of the device, when the temperature is raised above the above temperature range, or when the fluidity of the mixture is lost even within the temperature range, the mixture in the spraying device is used. Residence time should be set within a time period in which the flowability of the mixture is not lost. Here, the residence time in the spraying device is defined as the substantial residence time inside the main body for carrying out the spraying, and does not include the residence time in the piping section. Further, when there is a portion where the temperature is controlled in a temperature range where the crosslinking reaction does not occur, the residence time of this portion is excluded. In the method of the present invention, it is usually set to 20 seconds or less, more preferably 5 seconds or less, and most preferably 3 seconds or less. If the residence time is longer than this, polymerization and crosslinking reaction proceed, gelation of the mixture occurs, and troubles such as clogging of the spraying device occur. Here, as a spraying device to be used, a spraying device that sprays the mixture at a gas pressure or a spraying device that uses centrifugal force is used, but the spraying device is not particularly limited.

The spraying is carried out in a container whose maximum temperature is higher than the starting temperature of the crosslinking reaction and higher than the boiling point of the solvent, and lower than the decomposition temperature of the monomer. In the method of the present invention, a temperature range of 100 to 300 ° C. is usually used, and preferably
A temperature range of 150 ° C to 200 ° C is used. If the maximum temperature does not reach this temperature, not only the drying becomes insufficient, but also the polymerization reaction or the cross-linking reaction of the monomer are not sufficient, so that a high quality water-absorbing material cannot be obtained. The temperature in the container is preferably uniform in consideration of the efficiency of polymerization, crosslinking, and drying, but a temperature gradient may be given due to restrictions on the device. This temperature is not particularly limited, but it is advantageous from the viewpoint of reaction and drying efficiency to set it near the boiling point of the solvent constituting the mixture. Usually, a temperature of 60 ° C. or higher is used, preferably 80 ° C. or higher. Most preferably, it is 100 ° C or higher.

The mixture sprayed into the container needs to remain in the space inside the container while the polymerization, crosslinking and drying are completed. Although it depends on the particle size of the sprayed mixture and the concentration of the monomer contained in the mixture, it is usually 5 seconds or more, preferably 10 to
A range of 60 seconds is used. If it is too short, the polymerization, crosslinking reaction and drying will be insufficient. The length is not particularly limited, but when the temperature inside the container is high, the water-absorbing material may be accelerated to be denatured and the performance may be deteriorated.

The water absorbent resin thus obtained is deposited under the container. This is taken out and used as a product. Alternatively, connect cyclones and forcibly collect them to make products.

〔The invention's effect〕

Conventionally, it has been the current situation that the steps of polymerizing, crosslinking, drying and pulverizing water-absorbent materials are carried out in separate steps. Even the improved method requires two steps of polymerization, crosslinking, drying and pulverization. Performing these steps in separate steps requires excessive capital investment and human investment, which leads to an increase in cost and is a cause of concern for those skilled in the art.

According to the method of the present invention, each of these steps of polymerization, crosslinking, drying, and pulverization can be carried out in one step, a significant cost reduction can be expected, and its utility value is extremely high for those skilled in the art. is there. Furthermore, when the water absorbing property of the water absorbent material obtained by the method of the present invention was examined, it was found that it has an extremely excellent water absorbing property. This is an effect that the present inventors initially did not expect.

Hereinafter, the present invention will be described in more detail with reference to Examples.

Example 1 The weight ratio of sodium acrylate and acrylamide is
Each monomer was dissolved in water at room temperature so as to be 40/60. The weight ratio of the monomers in the aqueous solution was 30%. N, N'-methylenebisacrylamide was dissolved in this solution so that the weight ratio of the N, N'-methylenebisacrylamide to the monomer was 0.05%. Immediately before spraying from the spraying device, ammonium persulfate was dissolved in the solution at room temperature so that the weight ratio of the monomer was 0.3% to obtain a mixed solution. This mixture was sprayed from a centrifugal sprayer into a container in which the maximum temperature was 180 ° C and the temperature around the outlet was controlled to 115 ° C. At this time, the residence time of the mixed liquid in the spray device was 1.5 seconds, and the rotation speed of the spray device was 24000 rpm. The retention time of the spray particles in the container was 25 seconds. When the obtained water absorbing material was examined, the average particle diameter was 30.5 μm, and the water content was
The water absorption capacity was 0.5% by weight, the water absorption capacity was 300 times, and the sea water absorption capacity was 30 times, showing extremely excellent water absorption performance.

Comparative Example 1 Ammonium sulfite was dissolved in the mixture of Example 1 so that the weight ratio to the monomer was 1%. When an attempt was made to spray from the centrifugal spraying device under the same conditions as in Example 1, the mixed solution was clogged in the spraying device, and spraying was not possible. Approximately 5 for mixed liquid (room temperature) that is not in the spray device
It gelled after a minute.

Comparative Example 2 The mixture of Example 1 was sprayed from a centrifugal sprayer into a container in which the maximum temperature was controlled at 120 ° C and the temperature near the outlet was controlled at 90 ° C. At this time, the other conditions were the same as in Example 1. When the obtained water absorbing material was examined, the water content was 25% by weight, and the drying was not sufficient. In addition, when the water-absorbing material was added to a large amount of water and left for 2 hours and then the water was analyzed by gas chromatography, 5% by weight of unreacted monomer was present in the water-absorbing material, and it could not be used as a product. Met. Further, when the container was opened and viewed, a large amount of the undried water-absorbing material adhered to the wall of the container.

Example 2 The same mixed liquid as in Example 1 was sprayed from a spraying device of a system in which the gas pressure was sprayed under the same conditions.

The residence time of the sprayed particles in the container was 20 seconds. The dried particles were collected by a cyclone. When the obtained water absorbing material was examined, the average particle diameter was 51 μm and the water content was 1.
5% by weight, water absorption capacity was 295 times, and sea water absorption capacity was 29.5 times.

Example 3 The weight ratio of sodium acrylate and acrylamide is
Each monomer was dissolved in water at room temperature so as to be 60/40. The weight ratio of the monomers in the aqueous solution was 50%. N, N'-methylenebisacrylamide was dissolved in this solution so that the weight ratio of the N, N'-methylenebisacrylamide to the monomer was 0.05%. Immediately before spraying from the spraying device, ammonium persulfate was dissolved at room temperature so that the weight ratio was 0.3% with respect to the monomer to obtain a mixed solution. This mixed solution was used in Example 1.
Spraying was carried out under the same conditions as above to obtain a dry water absorbent material. This water absorbent material has an average particle size of 36.5 μm and a water content of 0.4%.
Met. The water absorption capacity for water was 500 times, and the water absorption capacity for seawater was 40 times.

Claims (3)

[Claims] 1. A mixture of a monomer, a water-soluble peroxide catalyst, a cross-linking agent and water, which is controlled by a spraying device controlled at a temperature or a residence time at which fluidity is not lost, Spraying in a container whose maximum temperature is above the starting temperature of the crosslinking reaction, above the boiling point of the solvent, and below the decomposition temperature of the monomer, and carrying out the reaction, pulverization, and drying in one step. A method for producing a highly water-absorbent material characterized by: 2. The method according to claim 1, wherein the catalyst is an inorganic water-soluble peroxide. 3. The method according to claim 1, wherein the monomer is at least one selected from acrylic acid, acrylic acid salts, methacrylic acid, methacrylic acid salts and acrylamide.