JPH04359903A - Production of water-soluble polyvinyl acetal resin - Google Patents

Abstract

PURPOSE:To produce the title resin without using any catalyst comprising an inorganic acid such as hydrochloric or sulfuric acid and without causing metal corrosion of the associated apparatuses. CONSTITUTION:A process for producing a water-soluble polyvinyl acetal resin comprising treating sodium acetate remaining in polyvinyl alcohol with a cation exchange resin to form acetic acid, acetalizing the polyvinyl alcohol with an aldehyde by using the formed acetic acid as a catalyst, and neutralizing the product with ammonia.

Description

[Detailed description of the invention]

0001

[Industrial Application Field] The present invention relates to a method for producing water-soluble polyvinyl acetal resin, and more particularly, to a water-soluble polyvinyl acetal resin that ion-exchanges sodium acetate remaining in raw material polyvinyl alcohol and uses it as a catalyst. This invention relates to a method for producing resin.

0002

BACKGROUND OF THE INVENTION Heretofore, polyvinyl alcohol has been widely used as a binder for various films and ceramics. However, films made of polyvinyl alcohol are relatively hard, and depending on the application, a more flexible film is desired. Furthermore, when used as a binder for ceramics, polyvinyl alcohol is relatively hard, so there is a problem in that it is not easy to handle.

[0003] Therefore, as a solution to the above-mentioned problems, for example, Japanese Patent Laid-Open No. 156112/1983 discloses
Polyvinyl acetal resins that dissolve rapidly in cold water have been proposed. Here, for polyvinyl alcohol with a saponification degree of 98 mol% or more, that is, completely saponified polyvinyl alcohol, the average polymerization degree is Polyvinyl acetal resin is constructed by acetalizing a material with a relatively low value.

[0004] In the method for producing polyvinyl acetal of the above-mentioned prior art, first, polyvinyl alcohol is dissolved in water,
For example, in the presence of an inorganic acid such as hydrochloric acid or sulfuric acid, a predetermined amount of aldehyde is reacted to achieve the desired degree of acetalization, and then neutralized with an alkali such as sodium hydroxide.

[0005]

[Problems to be Solved by the Invention] In the production method of the prior art described above, an inorganic acid such as hydrochloric acid or sulfuric acid was used as a catalyst for obtaining polyvinyl acetal resin. That is, acetalization of polyvinyl alcohol by aldehyde is promoted by protons in the inorganic acid. After acetalization, a water-soluble polyvinyl acetal resin was obtained by neutralizing with an alkali such as sodium hydroxide.

However, the above-mentioned prior art manufacturing method uses an inorganic acid such as hydrochloric acid or sulfuric acid, and therefore has the problem of significant metal corrosion in peripheral equipment. Furthermore, it has not been possible to recover and reuse the inorganic acid used as a catalyst. Furthermore, the aqueous solution of water-soluble polyvinyl acetal resin obtained by the above method contains impurities such as sodium ions and chloride ions. Therefore, purification by reprecipitation is used to remove these impurities. That is, an organic solvent as a poor solvent for the resin is added to an aqueous polyvinyl acetal resin solution, impurities such as ions are dissolved in water, and the resin is precipitated, thereby separating the impurities from the resin. however,
Such methods not only require the use of hazardous organic solvents, but also pose problems in the post-treatment of the water-organic solvent mixture.

Therefore, the present invention solves the above-mentioned problems of the conventional water-soluble polyvinyl acetal resin production method, makes metal corrosion of peripheral devices less likely to occur, and allows easy treatment of impurities such as inorganic ions. The purpose of the present invention is to provide a method for producing water-soluble polyvinyl acetal resin.

[0008]

[Means for Solving the Problems] The present inventors have made intensive studies to achieve the above-mentioned problems and obtain a water-soluble polyvinyl acetal resin having appropriate flexibility. The present inventors have discovered that the problems of the prior art can be overcome by ion-exchanging sodium acetate with a cation exchange resin and using the resulting acetic acid as a catalyst, leading to the present invention.

That is, the method for producing a water-soluble polyvinyl acetal resin according to the invention described in claim 1 includes the steps of ion-exchanging sodium acetate, which is a residue in polyvinyl alcohol, with a cation exchange resin to produce acetic acid;
The method is characterized by comprising a step of acetalizing polyvinyl alcohol with an aldehyde using the generated acetic acid as a catalyst. Moreover, the invention according to claim 2 further includes a step of neutralizing with ammonia after the acetalization.

In the first and second aspects of the invention, first, sodium acetate remaining in polyvinyl alcohol is ion-exchanged by a cation exchange resin to produce acetic acid. The cation exchange resin used is preferably a strongly acidic cation exchange resin. As the strongly acidic cation exchange resin, a so-called polystyrene sulfonic acid type resin, which is a copolymer of styrene and divinylbenzene into which 1 to 2 mmol/ml of sulfonic acid groups are introduced, is usually used.

Ion exchange using a cation exchange resin can be carried out by a column method, a batch method, or the like. The column method is a method in which a column is filled with a cation exchange resin and an aqueous polyvinyl alcohol solution is passed through the column. In the column method, usually 0.5~
Sodium acetate, contained in a concentration of 1.5% by weight, is ion-exchanged into acetic acid.

The batch method is a method in which a cation exchange resin is introduced into an aqueous polyvinyl alcohol solution to perform ion exchange. In this case, the aldehyde to be used in the next step may be added to the cation exchange resin at the same time and reacted with stirring. In the batch method, sodium acetate, which is contained as an impurity in polyvinyl alcohol at a concentration of 0.5 to 1.5% by weight, is ion-exchanged by a cation exchange resin to produce acetic acid. In the batch method, since the cation exchange resin is added to the polyvinyl alcohol aqueous solution, not only the acetic acid produced as described above but also the protons in the ion exchange groups of the cation exchange resin are used as a catalyst. That is, the present invention uses acetic acid produced by ion exchange with a cation exchange resin as a catalyst, but not only the acetic acid produced in this way but also the protons in the ion exchange groups of the cation exchange resin This also includes methods of using it as a catalyst.

[0013] The polyvinyl alcohol aqueous solution used for the above ion exchange usually contains 1 to 30% by weight.
, preferably adjusted to a concentration of 5 to 20% by weight. The concentration of polyvinyl alcohol aqueous solution is 30
This is because if it exceeds % by weight, the viscosity becomes too high and the aqueous polyvinyl alcohol solution adheres to the cation exchange resin, coating the ion exchange groups and reducing the activity of the cation exchange resin. On the other hand, if the concentration of the aqueous polyvinyl alcohol solution is less than 1% by weight, the amount of acetic acid produced is too small and the acetalization takes a very long time because the concentration of acetic acid present in the reaction system is low.

In the production method of the present invention, polyvinyl alcohol is acetalized with an aldehyde using the acetic acid produced as described above as a catalyst. In the column method, this acetalization is performed by introducing an aldehyde into an aqueous polyvinyl alcohol solution containing acetic acid recovered from a column, and reacting the aldehyde with polyvinyl alcohol in the presence of acetic acid. In addition, in the batch method, a cation exchange resin is added and stirred to proceed with the ion exchange reaction to produce acetic acid, and then the aldehyde is added to a polyvinyl alcohol aqueous solution, or a cation exchange resin is added to the polyvinyl alcohol aqueous solution. Any method may be employed in which the resin and aldehyde are simultaneously introduced and stirred to advance the ion exchange reaction and acetalization.

[0015] As the above-mentioned aldehyde, appropriate aldehydes conventionally used for acetalizing polyvinyl alcohol can be used, such as formaldehyde, acetaldehyde, and butyraldehyde. The water-soluble polyvinyl acetal resin obtained by the present invention is
The degree of polymerization is 300-3500, and the degree of saponification is 75-3500.
When 99.8 mol% polyvinyl alcohol is made into acetoacetalization degree A mol% (however, A≧0) and butyralization degree B mol% (however, B≧0) with acetaldehyde and/or butyraldehyde, 10≦(A
It can be obtained by acetalization within the range of +3B)≦50. When the degree of acetalization by acetaldehyde and/or butyraldehyde shown in the above formula is lower than about 10 mol %, the resulting polyvinyl acetal resin is water-soluble but has poor flexibility and is of little practical value. On the other hand, when it exceeds 50 mol%, it becomes water-insoluble, and in the case of a batch method, it becomes difficult to separate it from the cation exchange resin.

In the second aspect of the invention, following the acetalization described above, the obtained water-soluble polyvinyl acetal resin aqueous solution is neutralized with ammonia. In this case, when the cation exchange resin and aldehyde are simultaneously introduced in the batch method described above to proceed with the ion exchange reaction and acetalization, ammonia is introduced into the reaction system after the acetalization is completed, and then the cation exchange resin and aldehyde are introduced into the reaction system. The exchanged resin may be recovered.

[0017]

[Operation] In the present invention, sodium acetate that inevitably remains in polyvinyl alcohol is converted to acetic acid by ion exchange, and the acetalization of polyvinyl alcohol is carried out by using the acetic acid thus obtained as a catalyst. be exposed. Therefore, since there is no need to newly add a catalyst made of an inorganic acid such as hydrochloric acid to the raw material polyvinyl alcohol, metal corrosion of peripheral devices can be prevented. Furthermore, the used cation exchange resin can be reused by regenerating it.

Furthermore, in the invention as set forth in claim 2, since the water-soluble polyvinyl acetal resin aqueous solution is neutralized with ammonia after acetalization, impurity inorganic ions such as sodium ions can be removed.

[0019]

[Description of Examples] Hereinafter, the present invention will be explained in more detail with reference to Examples, but the present invention is not limited to the following Examples. Example 1 Polyvinyl alcohol 2 with degree of polymerization = 2000, degree of saponification = 88 mol%, residual sodium acetate concentration = 1.0% by weight
00g was added to 1600g of water and stirred at a temperature of 90°C for about 2 hours to dissolve. Next, the above polyvinyl alcohol aqueous solution was cooled to 45°C and passed through a column filled with 50 ml of cation exchange resin (manufactured by Mitsubishi Kasei Corporation, trade name: Diaion SK1B) at a flow rate of SV10, and pH = approximately 3. ．．
An aqueous polyvinyl alcohol solution of No. 5 was obtained. After that, the obtained polyvinyl alcohol aqueous solution was cooled to 35°C, and 20g of butyraldehyde with a purity of 99% was added.
After reacting at 5° C. for 8 hours, a cloudy white reaction mixture was obtained.

The reaction mixture obtained was cooled to 20°C,
17 g of aqueous ammonia with a concentration of 5% by weight were added under stirring to obtain a clear solution. The obtained transparent solution was cast onto a polyethylene film and dried to obtain a transparent film. The obtained film was dissolved in DMSO-d6 and 1
When the degree of acetalization was measured using 3C-NMR, the degree of butyralization was 10 mol%. Further, 5 g of the above transparent solution was sampled and dried under vacuum at 70° C. for 3 hours, and the sodium ion concentration in the obtained solid was measured using an atomic absorption spectrometer and found to be 3 ppm.

Example 2 Polyvinyl alcohol having a degree of polymerization of 500, a degree of saponification of 98 mol%, and a residual sodium acetate concentration of 1.2% by weight was used, and 43 g of acetaldehyde was used in place of 20 g of butyraldehyde. A polyvinyl acetoacetal aqueous solution having a degree of acetoacetalization of 31 mol % was obtained in the same manner as in Example 1 except for the following. Further, a solid was obtained in the same manner as in Example 1 using the polyvinyl acetoacetal aqueous solution, and the sodium ion concentration in the solid was measured and found to be 7 ppm.

Example 3 Polyvinyl alcohol having a degree of polymerization of 1000, a degree of saponification of 98 mol% and a residual sodium acetate concentration of 0.8% by weight was used, and butyraldehyde 10 was used as the aldehyde.
An aqueous polyvinyl acetal solution having a degree of butyralization of 5 mol % and a degree of acetoacetalization of 6 mol % was obtained in the same manner as in Example 1, except that g and 9 g of acetaldehyde were used.

[0023] Furthermore, a solid substance was obtained from the polyvinyl acetal aqueous solution obtained as described above in the same manner as in Example 1, and the sodium ion concentration in the solid substance was measured and found to be 6 ppm.

Example 4 Polyvinyl alcohol 2 with degree of polymerization = 2000, degree of saponification = 88 mol%, residual sodium acetate concentration = 1.0% by weight
00g was added to 1600g of water and stirred at a temperature of 90°C for about 2 hours to dissolve. The obtained polyvinyl alcohol aqueous solution was cooled to 45°C, and a cation exchange resin (manufactured by Mitsubishi Chemical Corporation,
50 ml of Diaion PK216 (trade name) was added to the polyvinyl alcohol aqueous solution and further cooled to 35°C. Next, 99% pure butyraldehyde 2 was added to the polyvinyl alcohol aqueous solution containing the cation exchange resin.
0 g was added and the reaction was carried out at 35° C. for 6 hours to obtain a cloudy white reaction mixture.

The obtained mixture was cooled to 20° C., and 17 g of aqueous ammonia with a concentration of 5% by weight was added while stirring.
The cation exchange resin was then recovered by filtration to obtain a clear solution. The obtained transparent solution was cast onto a polyethylene film and dried to obtain a transparent film. This transparent film was dissolved in DMSO-d6 and 13C-NMR
When the degree of acetalization was measured using , the degree of butyralization was 10 mol %.

[0026] Furthermore, a solid was obtained from the transparent solution obtained as described above in the same manner as in Example 1, and the sodium ion concentration in the solid was measured, and it was found to be 4 ppm.
Met. Therefore, in Example 4, compared to Example 1, 2
It can be seen that the desired water-soluble polyvinyl acetal resin can be obtained in a short period of time.

Example 5 Except for using polyvinyl alcohol having a degree of polymerization of 2400, a degree of saponification of 80 mol%, and a residual sodium acetate concentration of 0.8% by weight, and using 17 g of acetaldehyde as the aldehyde. In the same manner as in Example 4, an aqueous solution of polyvinyl acetoacetal having a degree of acetoacetalization of 12 mol % was obtained. In addition, regarding the polyvinyl acetoacetal aqueous solution obtained as above,
A solid was obtained in the same manner as in Example 1, and the sodium ion concentration in the solid was measured and found to be 3 ppm.

Example 6 Polyvinyl alcohol having a degree of polymerization of 300, a degree of saponification of 98 mol%, and a residual sodium acetate concentration of 1.2% by weight was used, and 11 g of butyraldehyde and 36 g of acetaldehyde were used as aldehydes. Except for this, an aqueous polyvinyl acetal solution having a degree of butyralization of 6 mol% and a degree of acetoacetalization of 25 mol% was obtained in the same manner as in Example 4.

[0029] Furthermore, a solid substance was obtained from the polyvinyl acetal aqueous solution obtained as described above in the same manner as in Example 1, and the sodium ion concentration in the solid substance was measured and found to be 8 ppm.

Comparative Example 1 Polyvinyl alcohol 2 with degree of polymerization = 2000, degree of saponification = 88 mol%, residual sodium acetate concentration = 1.0% by weight
00g was added to 1600g of water and stirred at a temperature of 90°C for about 2 hours to dissolve. Thereafter, the mixture was cooled to 45°C, 50 g of 35% by weight hydrochloric acid was added thereto, and the mixture was further cooled to 35°C. Next, 20g of butyraldehyde with a purity of 99%
was added and reacted at 35°C for 3 hours to obtain a cloudy white reaction mixture.

The reaction mixture was cooled to 20° C., and 190 g of a 10% strength by weight aqueous sodium hydroxide solution was added thereto while stirring.
was added to obtain a clear solution. This solution was cast onto a polyethylene film and dried to obtain a transparent film. This film was dissolved in DMSO-d6 and 13C-
When the degree of acetalization was measured using NMR, the degree of butyralization was 10 mol%. Furthermore, 5 g of the above transparent solution was sampled and dried under vacuum at 70° C. for 3 hours, and the sodium ion concentration in the obtained solid content was measured using an atomic absorption spectrometer and found to be 58,000 ppm.

Comparative Example 2 Polyvinyl alcohol having a degree of polymerization of 2000, a degree of saponification of 98 mol%, and a residual sodium acetate concentration of 1.2% by weight was used, and 43 g of acetaldehyde was used in place of 20 g of butyraldehyde. Comparative example 1 except for
In the same manner as above, an aqueous solution of polyvinyl acetoacetal having a degree of acetoacetalization of 31 mol% was obtained. Further, using the polyvinyl acetoacetal aqueous solution, a solid content was obtained in the same manner as in Comparative Example 1, and the sodium ion concentration in the solid content was measured and found to be 59,000 ppm.

Furthermore, 1000 g of isopropyl alcohol was added to 500 g of the 11% by weight polyvinyl acetoacetal aqueous solution thus obtained to precipitate the resin, and the solid content was obtained in the same manner as in Comparative Example 1. When we measured the sodium ion concentration inside, it was approximately 3000p.
It was pm.

[0034]

As described above, in the present invention, acetic acid is obtained by ion-exchanging sodium acetate remaining in polyvinyl alcohol, and the acetic acid is used as a catalyst for acetalization. Therefore, in the conventional method, it was necessary to add a catalyst consisting of an inorganic acid such as hydrochloric acid or sulfuric acid, but according to the present invention, it is possible to produce water-soluble polyvinyl acetal resin without adding a separate catalyst. .

[0035] Therefore, metal corrosion of the peripheral equipment due to hydrochloric acid, inorganic acid, etc. is less likely to occur, so that the frequency of complicated cleaning work and repair work of the manufacturing equipment can be reduced. Moreover, since the water-soluble polyvinyl acetal resin aqueous solution is neutralized with ammonia after acetalization, a highly purified water-soluble polyvinyl acetal resin containing almost no inorganic ions such as sodium ions can be easily obtained. Furthermore, the used cation exchange resin can be reused by regenerating it.

Therefore, according to the present invention, water-soluble polyvinyl acetal resin can be provided efficiently and at low cost. In the polyvinyl acetal resin obtained according to the present invention, crystallization, which is the main cause of the hardness of polyvinyl alcohol, and the formation of intermolecular hydrogen bonds between hydroxyl groups are inhibited due to the steric hindrance effect of the acetal ring. Therefore, since the polyvinyl acetal resin obtained by the present invention is flexible and water-soluble, it does not cause environmental problems due to the use of organic solvents.
It can be suitably used for various purposes.

Furthermore, since it is possible to obtain a highly pure water-soluble polyvinyl acetal resin that does not contain impurity ions such as inorganic ions, the polyvinyl acetal resin obtained by the present invention can be used, for example, in ceramics used in the production of ceramic capacitors. It can be suitably used as a water-soluble binder for green sheets. Similarly, it can also be used as a coating agent for aqueous inkjet recording, an additive for imparting hydrophilicity, and the like.

Claims (2)

[Claims] 1. A step of ion-exchanging sodium acetate remaining in polyvinyl alcohol with a cation exchange resin to generate acetic acid, and acetalizing the polyvinyl alcohol with an aldehyde using the generated acetic acid as a catalyst. A method for producing a water-soluble polyvinyl acetal resin, comprising the steps of: 2. A step of ion-exchanging sodium acetate remaining in polyvinyl alcohol with a cation exchange resin to generate acetic acid, and acetalizing the polyvinyl alcohol with an aldehyde using the generated acetic acid as a catalyst. and a step of neutralizing with ammonia after the acetalization.