JPH0623214B2 - Method for neutralizing hydrous gel polymer - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for neutralizing a hydrogel polymer. More specifically, it does not reduce the physical properties of the polymer when neutralizing a part or all of the acid groups of the hydrogel polymer containing an acid group,
Moreover, the present invention relates to a neutralization method capable of efficiently neutralizing.

(Prior art and problems to be solved) In recent years, water-absorbing polymers that absorb several tens to several hundreds of times their own weight of water have been developed, and sanitary products such as sanitary napkins and paper seams are used as agricultural products. It is used as a water retention / water absorption material in the industrial and civil engineering fields.

Many of such water-absorbent polymers have an acid group, and the synthesis method thereof is generally produced through a water-containing gel polymer obtained by polymerizing an acid group-containing monomer in an aqueous solution. It is known that an acid group-containing monomer is polymerized in an aqueous solution and the resulting polymer is neutralized with a substance exhibiting alkalinity such as an alkali metal hydroxide. At this time, in order to make the neutralization uniform, it was necessary to subdivide the polymer so as to have a sufficient surface area and contact it with an alkaline substance. As a method for mechanically subdividing the hydrogel polymer, there are methods such as cutting and extrusion, but in any case, since the hydrogel polymer has a strong rubber-like elasticity, a large amount of energy is required. There was a problem.

Furthermore, it has been found that when a strong alkaline substance is used during neutralization, the physical properties of the resulting polymer are degraded due to hydrolysis of the cross-linking points and the like.

Therefore, there has been a demand for an efficient method for neutralizing a hydrogel polymer which does not deteriorate the physical properties of the polymer and which is efficient.

(Means for Solving Problems) As a result of intensive research conducted by the present inventors in view of the above circumstances,
Containing an acid group, when neutralizing a part or all of the acid groups of the hydrogel polymer having a crosslinked structure, the hydrogel polymer in a container having a plurality of rotating stirring shafts of the stirring shaft A method for neutralizing a hydrogel polymer characterized by adding a salt of a weak acid while subdividing by shearing force by rotation to perform neutralization does not lower the physical properties of the polymer and yet efficiently neutralizes the polymer. The inventors have found out what can be done and have completed the present invention.

The hydrogel polymer containing an acid group and having a crosslinked structure can be obtained by various methods. For example, a hydrogel polymer containing an acid group and a crosslinkable monomer having two or more polymerizable double bonds in the molecule can be obtained. By copolymerization, starch, cellulose,
Examples thereof include those in which an acid group-containing monomer is subjected to aqueous solution polymerization in the presence of a hydrophilic polymer such as polyvinyl alcohol to simultaneously form a graft bond or a complex.

Examples of the acid group-containing monomer used when the hydrogel polymer is obtained by the method exemplified above include acrylic acid, methacrylic acid, 2-acrylamido-2-methylpropanesulfonic acid, and 2- (meth) acryloylethanesulfonic acid. , 2- (meth) acryloylpropanesulfonic acid, maleic acid, itaconic acid and the like, and one or more of them can be used.

Examples of the crosslinkable monomer include ethylene glycol, diethylene glycol, triethylene glycol,
Propylene glycol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, neopentyl glycol, trimethylolpropane and pentaerythritol diacrylate or dimethacrylate,
Triacrylate or trimethacrylate of trimethylolpropane and pentaerythritol, tetraacrylate or tetramethacrylate of pentaerythritol, N, N'-methylenebisacrylamide, N, N '
-Methylenebismethacrylamide, triallyl isocyanurate, triallylamine and the like can be mentioned, and one or more of these can be used.

The container having a plurality of rotary stirring shafts used in the present invention,
It is necessary that a shearing force can be applied to the hydrous gel polymer by rotating the rotary stirring shaft. It is necessary to have a plurality of rotary stirring shafts, and a double-arm kneader is preferable in such a container because the hydrogel polymer can be efficiently subdivided. When using the kneader, the two rotary stirring shafts are used by rotating them in opposite directions at a constant speed or a non-uniform speed. In the case of constant speed, the two rotating stirring shafts are used in a state where the radii of rotation of the two rotating stirring shafts overlap each other. The rotary stirring shaft may be of sigma type, S type, Banbury type or fishtail type.

According to the method of the present invention, the hydrogel polymer containing an acid group and having a crosslinked structure is atomized in a device such as the above kneader upon neutralization. Although the particle size varies depending on the state of the hydrogel polymer, a particle size of 3 cm or less can be usually obtained. The obtained water-containing gel-like polymer particles have not only small adhesion between particles, but also very good releasability from the inner wall of the polymerization container and stirring blades, and good flowability.

Neutralization of the water-containing gel-like polymer can be easily achieved by adding a salt of a weak acid to the water-containing gel-like polymer atomized as described above to neutralize a part or all of the acid groups. . As the weak acid salt, a conventionally known inorganic or organic weak acid salt can be used, and specific examples thereof include ammonium carbonate, sodium carbonate, potassium carbonate, potassium sodium carbonate, ammonium hydrogen carbonate, and sodium hydrogen carbonate. Potassium hydrogen carbonate, ammonium phosphate, sodium phosphate, potassium phosphate, ammonium borate, sodium borate, potassium borate, ammonium oxalate, sodium oxalate, potassium oxalate, ammonium acetate, sodium acetate, potassium acetate, etc. Among these, one kind or a mixture of two or more kinds can be used. Among these weak acid salts, carbonates are preferable because they are industrially easily available and have good neutralization efficiency, and strong alkali salts of carbonic acid, such as sodium carbonate, potassium carbonate, sodium hydrogen carbonate, and potassium hydrogen carbonate, are particularly preferable.

The weak acid salt may be added in the form of an aqueous solution or slurry, but may be directly added in the form of powder or powder such as granules. According to the method of the present invention, the water-containing gel-like polymer is sufficiently finely divided, and since the finely divided water-containing gel-like polymer and the salt of the weak acid are also sufficiently mixed, The acid group-containing hydrated gel polymer can be neutralized even if the salt is directly added as a powder without going through the step of forming an aqueous solution or slurry. Further, since the hydrogel polymer finely pulverized as described above is sufficiently mixed, it is not necessary to make the feeding method particularly uniform even when the salt of the weak acid is added as a powder.

The time after the addition of the salt of the weak acid until the predetermined neutralization is achieved varies depending on the particle size of the hydrogel polymer and the amount of acid groups, but is usually 10 to 60 minutes. At that time, after adding a salt of a weak acid, the lid of the container is closed to raise the temperature of the system to promote evaporation of water from the hydrogel polymer, and the system is steamed to achieve neutralization quickly. Become.

As described above, according to the neutralization method of the present invention, there is no decrease in the solid content of the hydrogel polymer as compared with the conventional method of neutralizing by adding an alkaline substance in the form of an aqueous solution. It is possible to reduce the burden of the drying process that will follow. Furthermore, in the conventionally known neutralization method, that is, a method of neutralizing by adding a strong alkaline substance such as sodium hydroxide or potassium hydroxide, the cross-linking points forming the cross-linking structure can be obtained by cleavage by hydrolysis. While there were problems such as deterioration of the physical properties of the polymer to be obtained, such problems do not occur according to the method of the present invention.

Further, when a carbonate is used as a salt of a weak acid, the acid radical becomes carbon dioxide gas, which is easily removed from the hydrogel polymer and the drying efficiency is remarkably increased.

Even after neutralization is completed by adding a salt of a weak acid according to the method of the present invention, the hydrogel polymer particles not only have low adhesiveness between particles, but also have releasability from the inner wall of the polymerization container or a stirring blade. It is extremely good, has good fluidity, and is extremely easy to handle when it needs to be taken out of the polymerization vessel or dried. Therefore, in order to take out the gelled polymer particles from the polymerization container, the polymerization container is tilted or turned over to flow out, or a method in which a screw is provided at the bottom of the polymerization container in addition to the rotary stirring shaft and extrusion is performed easily. be able to.

(Examples) The present invention will be described in more detail below with reference to Examples and Comparative Examples, but the scope of the present invention is not limited by these Examples. Unless otherwise specified,% in the examples and comparative examples means% by weight, and part means part by weight.

Further, the water absorption capacity and water-soluble content described in these examples refer to numerical values measured by the following test methods.

Water absorption ratio 0.2g of polymer is a non-woven tea bag bag (40mm ×
150 mm) and soak it in 0.9% saline solution for 30
The weight after minutes was measured, and the water absorption capacity was determined according to the following formula.

Water-soluble component 0.5 g of polymer was dispersed in 1000 ml of deionized water to prepare 1
After stirring for 2 hours, the mixture was passed with a No. 2 paper and the solid content of the solution was measured to determine the water-soluble content according to the following formula.

Example 1 Internal volume 2, opening 100 mm x 100 mm, depth 200 mm
In a jacketed stainless steel rectangular parallelepiped container, acrylic acid 180 parts, trimethylolpropane triacrylate
An aqueous monomer solution consisting of 0.53 part and 900 parts of water was charged, and nitrogen gas was blown into the reaction system to replace it with nitrogen. Then, the jacket was heated by passing warm water of 20 ° C., 0.25 parts of ammonium persulfate and 0.25 part of sodium hydrogen sulfite were added as a polymerization initiator, and stationary bulk polymerization was carried out. Polymerization started 15 minutes after the addition of the polymerization initiator, and the monomer aqueous solution became a transparent gel as the polymerization proceeded. After 30 minutes from the addition of the polymerization initiator, the temperature in the rectangular parallelepiped container made of stainless steel increased to 60 ° C. and started to decrease thereafter. Then, the gel was heated to a temperature of 60 ° C. for 60 minutes, and the hydrogel polymer was taken out. Obtained approx. 100 mm x 100 mm x 10
0 mm of water-containing gel-like polymer, inner volume 2, opening 160
mm x 150 mm, depth 135 mm, blade rotation diameter 70 mm, transferred to a jacketed stainless steel double-arm kneader with two blades, covered and then two sigma blades at 67 and 56 rpm, respectively. Rotate at speed,
The water-containing gel polymer was subdivided while heating the jacket with warm water at 80 ° C. When stirring was continued for 10 minutes, fine particles having a diameter of about 5 mm were subdivided. Then, the lid was removed, and 99.4 parts of powdered anhydrous sodium carbonate was added over 10 minutes. (The neutralization rate of the polymer is 75 mol%.) The lid was capped again and stirring was continued for 20 minutes. When the lid was removed and the phenolphthalein solution was added dropwise, no red color was observed at any place.

The finely granulated product of the hydrogel polymer thus obtained was placed on a 50-mesh wire net and dried with hot air at a temperature of 150 ° C. for 1 hour. The water content of the dried product was 3%. The dried product was pulverized using a vibration mill, the water absorption capacity and the water-soluble content of the obtained powder (hereinafter referred to as absorbent (1)) were measured, and the results are shown in Table 1.

Comparative Example 1 Polymerization and neutralization were carried out by repeating the same operations as in Example 1 except that 166.7 parts of a 45% sodium hydroxide solution was used instead of the powdery anhydrous sodium carbonate in Example 1. When the phenolphthalein solution was dropped, no red color was observed at any place.

The resulting water-containing gel polymer was placed on a 50-mesh wire net and dried with hot air at a temperature of 150 ° C. for 1 hour. The water content of the dried product was 10.1%. The dried product was pulverized using a vibration mill, the water absorption capacity and the water-soluble content of the obtained powder (hereinafter referred to as comparative absorbent (1)) were measured, and the results are shown in Table 1.

Example 2 137 parts of corn starch was dispersed in 660 parts of water and gelatinized by stirring at 60 ° C. for 1 hour. Acrylic acid (200 parts) and trimethylolpropane triacrylate (1.54 parts) were added to the obtained starch liquid, and the mixture was transferred to the polymerization container used in Example 1. Nitrogen gas was blown in to replace nitrogen in the reaction system. The jacket was heated by passing warm water of 20 ° C., 0.3 parts of ammonium persulfate and 0.3 part of sodium bisulfite were added as polymerization initiators, and stationary bulk polymerization was carried out. Polymerization started 10 minutes after the addition of the polymerization initiator, and the monomer aqueous solution became a gel as the polymerization proceeded. 26 minutes after the polymerization initiator was added, the temperature in the polymerization vessel was 70
The temperature rose to ℃, and then began to fall. Then, the gel was heated to a temperature of 60 ° C. for 60 minutes, and the hydrogel polymer was taken out. The obtained hydrogel polymer of about 100 mm × 100 mm × 100 mm was transferred to the kneader used in Example 1, and the hydrogel polymer was subdivided by the same operation as in Example 1. When stirring was continued for 10 minutes, fine particles having a diameter of about 5 mm were subdivided.
Then remove the lid, 59.6% sodium carbonate aqueous slurry
197.4 parts were added over 12 minutes. (The neutralization rate of the polymer is 80 mol%.) The lid is closed again and stirring is continued for 25 minutes. When the lid was removed and the phenolphthalein solution was added dropwise, no red color was observed at any place.

The finely granulated product of the hydrogel polymer thus obtained was placed on a 50-mesh wire net and dried with hot air at a temperature of 150 ° C. for 1 hour. The water content of the dried product was 3%. The dried product was pulverized using a vibration mill, the water absorption capacity and the water-soluble content of the obtained powder (hereinafter referred to as absorbent (2)) were measured, and the results are shown in Table 1.

Comparative Example 2 Polymerization and neutralization were carried out by repeating the same operations as in Example 2, except that 197.4 parts of a 45% sodium hydroxide solution was used instead of the 59.6% sodium carbonate aqueous slurry in Example 2. When the phenolphthalein solution was dropped, no red color was observed at any place.

The obtained hydrogel polymer was placed on a 550 mesh wire net and dried with hot air at a temperature of 150 ° C. for 1 hour. The water content of the dried product was 8.2%. The dried product was pulverized using a vibration mill, the water absorption capacity and the water-soluble content of the obtained powder (hereinafter referred to as comparative absorbent (2)) were measured, and the results are shown in Table 1.

(Effects of the Invention) As is clear from the above-mentioned Examples and Comparative Examples, the polymers obtained by applying the neutralization method of the present invention do not show a decrease in physical properties due to neutralization. That is, it is possible to obtain an absorbent having a high water absorption capacity and a low water-soluble content. Furthermore, as an additional effect, the drying efficiency is good and the dryer is not burdened.

Claims (4)

[Claims] 1. When neutralizing a part or all of the acid groups of a hydrogel polymer containing an acid group and forming a crosslinked structure, the hydrogel polymer is contained in a container having a plurality of rotary stirring shafts. A method for neutralizing a water-containing gel polymer, characterized in that a weak acid salt is added while being subdivided by shearing force caused by rotation of the stirring shaft to neutralize. 2. The method for neutralizing a hydrogel polymer according to claim 1, wherein the container having a plurality of rotary stirring shafts is a double-arm kneader. 3. The method for neutralizing a hydrogel polymer according to claim 1, wherein the weak acid salt is added as a powder. 4. The method for neutralizing a hydrogel polymer according to claim 1, wherein the weak acid salt is a carbonate.