JP3262711B2 - Method for producing polyvinyl acetal resin solution - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for producing a polyvinyl acetal resin solution, and more particularly, to a method for producing a polyvinyl acetal resin using a precipitation method.

[0002]

2. Description of the Related Art Conventionally, as a method for producing a polyvinyl acetal resin, a precipitation method and a dissolution method are widely known.

In the precipitation method, an acid catalyst is added to an aqueous solution of polyvinyl alcohol, and an aldehyde compound is added and reacted to form a polyvinyl acetal resin. After the polyvinyl acetal resin is precipitated, steps such as washing and drying are performed. After that, polyvinyl acetal resin is obtained.

[0004] In the dissolution method, polyvinyl alcohol is dispersed in an organic solvent, an acid catalyst is added, an aldehyde compound is added and reacted, and then a polyvinyl acetal resin is precipitated, followed by washing and drying. After that, polyvinyl acetal resin is obtained.

In particular, when an aromatic aldehyde is used as the aldehyde compound, it is said that the precipitation method is preferably used among the above two methods (Japanese Patent Application Laid-Open No. Sho 63-163).
No. 2,210,772). This is thought to be because when the dissolution method is used, the aromatic aldehyde, which is an aldehyde compound, is very easily dissolved in an organic solvent and hardly participates in the reaction with polyvinyl alcohol, so that the acetalization reaction does not easily proceed. Have been.

[0006] Conventionally, when producing a polyvinyl acetal resin by a dissolution method or a precipitation method, the acid catalyst is added to the reaction system so as to have a concentration of 0.5 to 4% by weight. Accordingly, when the reaction is stopped by adding a neutralizing agent at the end of the reaction, an excessive salt is generated by the neutralization. Therefore, in obtaining the dried polyvinyl acetal resin, it was necessary to sufficiently remove the generated excess salt by washing with water.

On the other hand, when producing a polyvinyl acetal resin solution, a dry polyvinyl acetal resin obtained by the above-mentioned precipitation method or dissolution method is dissolved in a target solvent.

However, in the case of a polyvinyl acetal resin having a degree of acetalization of 10 mol% or less, hydrophilicity is too strong. While dissolving the polyvinyl acetal resin in the solvent after the resin flows out with water or after washing and drying, there is a problem that a considerable amount of the polyvinyl acetal resin adheres to the reaction tank or the washing tank and the yield decreases. there were.

Therefore, it is considered that the polyvinyl acetal resin solution on which the polyvinyl acetal resin is precipitated may be used as it is, for example, as a solution for forming a coating film, without performing the washing and drying steps. In this case, the polyvinyl acetal resin does not flow out with the water due to the water washing, and the amount of the polyvinyl acetal resin attached to the reaction tank or the water washing tank can be reduced. However, since the obtained polyvinyl acetal resin solution contains an excess salt generated by neutralization of the acid catalyst, when the coating is applied with the solution, the coating is affected by the salt. There was a problem that it became cloudy.

It is conceivable that the reaction is carried out at a very low acid catalyst concentration in order to prevent the excess salt produced by the neutralization of the acid catalyst from being contained. Since the acetal resin precipitates as one sponge-like mass, the reaction speed between the outer layer portion and the inner layer portion of the mass differs, and a polyvinyl acetal resin having a different degree of acetalization between the outer layer portion and the inner layer portion can be obtained.
Therefore, when the coating film is coated with the polyvinyl acetal resin solution, there is a problem that the water resistance is slightly inferior due to the effect of the low acetalized product in the inner layer portion of the precipitated resin.

An object of the present invention is to provide a polyvinyl acetal which can be efficiently produced by utilizing a precipitation method, and which can form a coating film excellent in both transparency and water resistance when the coating film is formed. An object of the present invention is to provide a method for producing a resin solution.

[0012]

SUMMARY OF THE INVENTION The present invention has been made to achieve the above object, and a polyvinyl acetal resin obtained by an acetalization reaction between polyvinyl alcohol and an aromatic aldehyde is a mixed solvent of water and alcohol. A method for producing a polyvinyl acetal resin solution dissolved in polyvinyl alcohol, wherein an acid catalyst is added in an aqueous polyvinyl alcohol solution so that the acid catalyst concentration becomes 0.005 to 0.03% by weight, and the polyvinyl alcohol and the aromatic compound are dissolved. By reacting with aldehyde, a particulate polyvinyl acetal resin having a particle size of 10 mm or less is produced, and alcohol is added so that the weight ratio of water: alcohol in the solution is 80:20 to 20:80. A method for producing a polyvinyl acetal resin solution, characterized by dissolving an acetal resin.

In the method for producing a polyvinyl acetal resin solution of the present invention, as described above, the acid catalyst is used in an amount of 0.005%.
０．０0.03% by weight.
Since the amount is very small as compared with the conventional method, the amount of salt generated by neutralization for stopping the acetalization reaction becomes very small. Therefore, it is possible to prevent a problem due to an excessive salt, that is, turbidity of the coating film when the coating film is applied, without performing the washing step. Further, since the washing step is not performed, the polyvinyl acetal resin does not flow out together with the water.
A solution of a polyvinyl acetal resin having excellent hydrophilicity of 0 mol% or less can be efficiently produced.

As a method for obtaining a particulate polyvinyl acetal resin having a particle size of 10 mm or less, after the above-mentioned acid catalyst is charged, aromatic aldehydes are collectively charged at 45 to 65 ° C. It can be obtained by lowering the temperature at the time of adding the group aldehyde by 5 ° C. or more. The reason why a particulate resin is obtained by the above conditions is not clear, but a certain reaction speed is required to obtain the particulate resin, and if the reaction speed is higher than that, the resin aggregates during precipitation. If the reaction speed is slower than this, the degree of acetalization of the resin at the time of precipitation is low, so that the particles grow while coalescing and a sponge-like resin is generated. It is thought that there is not.

Hereinafter, the present invention will be described in detail. In the present invention, first, an acid catalyst is added to a polyvinyl alcohol aqueous solution so as to have a concentration of 0.005 to 0.03% by weight based on the whole system.

The polyvinyl alcohol is not particularly limited, but has a polymerization degree of 200 to 350.
0, it is preferable to use those having a saponification degree of 75 to 99.8 mol%. When the degree of polymerization is less than 200, the synthesis of polyvinyl alcohol tends to be difficult. On the contrary, when the degree of polymerization exceeds 3500, the viscosity may become too high when an aqueous solution is used. In addition, the degree of saponification is 75 mol%
If it is less than 1, the solubility of the polyvinyl acetal resin in water may be insufficient, and conversely, the degree of saponification may be 9 or less.
If it exceeds 9.8 mol%, the synthesis of polyvinyl alcohol may be difficult.

In the present invention, as the polyvinyl alcohol, two or more kinds of polyvinyl alcohols having different degrees of polymerization may be mixed and used, and in this case, two or more kinds of polyvinyl alcohols having an apparent degree of polymerization falling within the above range may be used. It is preferable to use polyvinyl alcohols having different degrees of polymerization.

Examples of the acid usable as the acid catalyst include inorganic acids such as hydrochloric acid, sulfuric acid and nitric acid; and organic acids such as acetic acid, benzoic acid, paratoluenesulfonic acid, uric acid and barbituric acid. May be used alone or in combination of two or more.

The acid catalyst is used in an amount of 0.0
It is added so as to be 0.5 to 0.03% by weight. When the amount of the acid catalyst is less than 0.005% by weight, the acetalization reaction hardly proceeds, and when the amount exceeds 0.03% by weight, the amount of the salt generated by the neutralization of the acid catalyst in the subsequent step increases. This is because the solution becomes turbid or the film becomes white and turbid when a coating film is formed using the solution.

The aromatic aldehyde used for acetalization of the polyvinyl alcohol is not particularly limited, but may be benzaldehyde, 2-methylbenzaldehyde, 3-methylbenzaldehyde, 4-methylbenzaldehyde, other alkyl-substituted benzaldehydes; chlorbenzaldehyde , Other halogen-substituted benzaldehydes; phenylacetobenzaldehyde, β
-Phenylpropionaldehyde, other phenyl-substituted alkyl aldehydes, and the like, and further, aromatic aldehydes having a substituent such as a hydroxy group, an alkoxy group, an amino group, and a cyano group on the aromatic ring. May be used alone or in combination of two or more.

The concentration of the aqueous polyvinyl alcohol solution is such that the viscosity of the aqueous solution at 20 ° C. is 10,000 mPa · s
It is preferable that the range be s or less. This is because if the viscosity of the aqueous solution at 20 ° C. exceeds 10,000 mPa · s, the viscosity becomes high and the synthesis becomes difficult.

At the time of the reaction, after the acid catalyst is charged, the aromatic aldehyde is charged at 45 to 65 ° C. at a time, and the temperature is lowered by at least 5 ° C. within 30 minutes to 40 to 60 ° C. within 30 minutes. The reaction temperature is preferably set to about 3 to 10 hours. When the reaction temperature is lower than 40 ° C., the amount of the acid catalyst is very small, so that the reaction may not progress easily to the target degree of acetalization,
If the temperature exceeds 60 ° C., the acetalization reaction proceeds more than necessary, so that a polyvinyl acetal resin having a non-uniform acetalization degree may be generated. When the reaction time is less than 3 hours, the amount of the acid catalyst is very small, so that the acetalization reaction may hardly proceed,
If the time exceeds 10 hours, the reaction is completed and the acetalization reaction often does not proceed any more.

In the present invention, the polyvinyl acetal resin is produced as a particulate polyvinyl acetal resin having a particle size of 10 mm or less. The particle size is set to 10 mm or less because, when the particle size exceeds 10 mm, since the degree of acetalization differs between the outer layer portion and the inner layer portion of the particles, the water resistance is poor when the coating film is ground with a polyvinyl acetal resin solution. It is.

In the present invention, in order to stop the acetalization reaction, a neutralizing agent for neutralizing the acid catalyst is preferably added to the reaction system. The neutralizing agent is not particularly limited, and generally, a hydroxide such as an alkali metal or an alkaline earth metal, or an alkylene oxide such as ethylene oxide or propylene oxide is used. May be used alone, 2
More than one species may be used in combination. The amount of the neutralizing agent is not particularly limited as long as the pH of the reaction solution can be adjusted to 6 to 8,
Usually, neutralization is performed by adding an equal amount of a neutralizing agent to the acid catalyst.

In the present invention, after the polyvinyl acetal resin is formed by the acetalization, the weight ratio of water: alcohol in the solution is 80:20 to 20: 8.
Alcohol is added so as to be 0, and the polyvinyl acetal resin is dissolved. Examples of the alcohol in this case include methanol, ethanol, isopropyl alcohol, isobutyl alcohol, n-butyl alcohol and the like, and these alcohols may be used alone or in combination of two or more. .

As described above, the amount of the alcohol to be added is such that the ratio of water: alcohol of the solvent is 80:20 to 20:20 by weight.
It is chosen to be 80. If the content of water in the mixed solvent exceeds 80% by weight or less than 20% by weight, the polyvinyl acetal resin cannot be dissolved.

The degree of acetalization of the polyvinyl acetal resin is preferably 10 mol% or less, regardless of whether a single aldehyde or a mixed aldehyde is used. If it exceeds 10 mol%, the water resistance becomes relatively high. Therefore, even if the water is washed in the conventional method, the water resistance is high and the polyvinyl acetal resin hardly flows out together with the water. Therefore, when the present invention is used for producing a polyvinyl acetal resin solution having an acetalization degree of 10 mol% or less, the effect of the present invention is large. When the acetalization degree exceeds 10 mol%, the polyvinyl acetal resin becomes difficult to dissolve in the mixed solvent containing water and alcohol at the above ratio.

In the production method of the present invention, since the amount of the acid catalyst is very small as 0.005 to 0.03% by weight as described above, the obtained polyvinyl acetal resin can be washed and dried without water. Even if alcohol is added to and dissolved in the reaction system, the transparency of the polyvinyl acetal resin solution is not easily impaired. In addition, even when a coating film is applied using the polyvinyl acetal resin solution, a coating film having excellent transparency can be obtained.

Further, since the washing and drying steps can be omitted in the production of the polyvinyl acetal resin solution, the effluent and the reaction tank are not affected even though the polyvinyl acetal resin has a high degree of acetalization of 10 mol% or less. The decrease in the yield due to adhesion to the surface is unlikely to occur.

In the present invention, the resin to be precipitated is precipitated as a particulate polyvinyl acetal resin having a particle size of 10 mm or less. Therefore, since the degree of acetalization is uniform in the whole resin, even when the polyvinyl acetal resin solution is used to form a coating film, the coating film has excellent water resistance.

[0031]

The present invention will be clarified by the following non-limiting examples and comparative examples.

Example 1 200 g of polyvinyl alcohol having a polymerization degree of 2,000 and a saponification degree of 88 mol% was added to 1500 g of pure water, and dissolved while stirring at a temperature of 90 ° C. for about 2 hours. The resulting solution is
The mixture was cooled to 55 ° C, 0.3 g of hydrochloric acid having a concentration of 35% by weight was added, and further cooled to 55 ° C. As a result, a precipitate was formed in the solution. This reaction solution is 1 mm x 1 mm
The size was changed from 1 mm to 10 mm x 10 mm at 1 mm intervals and poured into a sieve, and the size at which no precipitate remained on the sieve was measured as the maximum particle size.
It was below.

Thereafter, the mixture was cooled to a liquid temperature of 20 ° C., and 920 g of isopropyl alcohol was added with stirring.
A resin having a particle size of 2 mm or less is completely dissolved. Thereafter, 1.2 g of a 10% by weight aqueous sodium hydroxide solution is added, and water-isopropyl alcohol (a ratio of water and isopropyl alcohol) of an 8% by weight polyvinyl acetal resin is added. 6: 4) by weight ratio to obtain a clear solution.

The resulting transparent solution was applied to a polyethylene film, dried, and then peeled off from the polyethylene film to produce a transparent film. This transparent film is
MSO-d was dissolved in ₆ (dimethylsulfoxide), ¹³ C
When the degree of acetalization was measured using -NMR (nuclear magnetic resonance spectrum), the degree of acetalization was 8 mol%.

As the evaluation of Example 1, the transparency and the equilibrium water content of the coating film were evaluated, and the yield was calculated. (1) Evaluation of transparency of coating film The transparent solution obtained as described above was dried on a 100 μm-thick polyethylene terephthalate film to a thickness of 2 μm.
It was applied so as to have a thickness of 0 μm. The transparency of the film thus formed was visually observed. This visual observation was evaluated on a three-point scale using the following symbols. …: Colorless and transparent without any turbidity or cloudiness. Δ: Partly whitish and cloudy. ×: The whole is fairly cloudy.

(2) Evaluation of Equilibrium Water Content of Coated Film The transparent solution obtained as described above was dried on a 100 μm-thick polyethylene terephthalate film to a thickness of 2 μm.
It was applied so as to have a thickness of 0 μm. This was cut into a 10 × 10 cm square, dried well again, and then heated to a temperature of 20 ° C. and a humidity of 8
It was left in a room of 0% RH for one week. The equilibrium water content was determined by considering the change in weight of the film at this time as the water content.

(3) Yield The substantial amount of resin was calculated from the amount of the polyvinyl acetal solution obtained as described above and its solid content, and the reaction was carried out using the amount of resin and the degree of acetalization measured above. The amount of polyvinyl alcohol was calculated. The amount of the polyvinyl alcohol was divided by the amount of the polyvinyl alcohol used during the preparation of the reaction, and the yield of the polyvinyl acetal resin obtained by the reaction was determined. The results of the evaluation of the transparency of the coating film, the equilibrium moisture content and the yield are shown in Table 1 below.

Examples 2 to 6 As shown in Table 1 below, a polyvinyl acetal resin solution was prepared in the same manner as in Example 1 except that the types of polyvinyl alcohol, aldehyde and alcohol and the amounts used thereof were changed. Then, evaluation was performed in the same manner as in Example 1. The results are shown in Table 1 below.

Comparative Example 1 200 g of polyvinyl alcohol having a polymerization degree of 2,000 and a saponification degree of 88 mol% was added to 1500 g of pure water, and the mixture was stirred at a temperature of 90 ° C. for about 2 hours to dissolve. The obtained solution is heated at 40 ° C.
, And 50 g of hydrochloric acid having a concentration of 35% by weight was added thereto.
Further cool to 30 ° C. and add benzaldehyde 27
g was added dropwise over 1 hour, and an acetalization reaction was performed at 25 ° C. for 3 hours. As a result, a sponge-like precipitate was obtained.

Thereafter, the mixture was cooled to a liquid temperature of 20 ° C., and 720 g of isopropyl alcohol was added with stirring.
Dissolve the sponge-like resin completely, and then
192 g of an aqueous solution of sodium hydroxide at a concentration of 8% by weight was added to obtain a solution of a polyvinyl acetal resin at a concentration of 8% by weight in water-isopropyl alcohol (the ratio of water to isopropyl alcohol was 7: 3 by weight). This solution was cloudy. The polyvinyl acetal resin solution obtained as described above was evaluated in the same manner as in Example 1. The results are shown in Table 2 below.

Comparative Examples 2 and 3 As shown in Table 1, a polyvinyl acetal resin solution was obtained in the same manner as in Comparative Example 1 except that the types and amounts of polyvinyl alcohol, aldehyde and alcohol were changed. The evaluation was performed in the same manner as described above. The results are shown in Table 2 below.

Comparative Example 4 A spongy precipitate was obtained in the same manner as in Comparative Example 1.
192 g of a 10% by weight aqueous sodium hydroxide solution was added for neutralization. Next, 1000 g of pure water was added thereto, and after sufficiently stirring, 2000 g of water was removed by decantation. Subsequently, after adding 2000 g of pure water and stirring well, a process of removing water by decantation is performed in a total of 3 steps.
Repeated times. Thereafter, isopropyl alcohol was added to completely dissolve the resin to obtain a transparent 8% by weight polyvinyl acetal resin solution in water-isopropyl alcohol (the weight ratio of water to isopropyl alcohol was 7: 3). The obtained polyvinyl acetal resin solution was evaluated in the same manner as in Example 1. The results are shown in Table 2 below.

Comparative Examples 5 and 6 As shown in Table 2, a polyvinyl acetal resin solution was prepared in the same manner as in Comparative Example 4, except that the types of polyvinyl alcohol, aldehyde and alcohol, and the amounts used were changed. Evaluation was performed in the same manner as in Example 1. The results are shown in Table 2 below.

Comparative Example 7 The reaction was carried out in the same manner as in Comparative Example 4, neutralization and decantation were performed, and then the polyvinyl acetal resin was dried. After drying, the dried polyvinyl acetal resin is added to a mixed solvent of water and isopropyl alcohol (the ratio of water to isopropyl alcohol is 6: 4 by weight), completely dissolved under stirring, and a transparent 8 wt% A water-isopropyl alcohol solution of a polyvinyl acetal resin (the ratio of water to isopropyl alcohol was 6: 4 by weight) was obtained. The obtained polyvinyl acetal resin solution was used in Example 1.
The evaluation was performed in the same manner as described above. The results are shown in Table 2 below.

Comparative Examples 8 and 9 As shown in Table 2, a polyvinyl acetal resin solution was obtained in the same manner as in Comparative Example 7, except that the types of polyvinyl alcohol, aldehyde and alcohol, and the amounts used were changed. Evaluation was performed in the same manner as in Example 1. The results are shown in Table 2 below.

Comparative Example 10 200 g of polyvinyl alcohol having a degree of polymerization of 2,000 and a degree of saponification of 88 mol% was added to 1500 g of pure water and dissolved with stirring at a temperature of 90 ° C. for about 2 hours. The resulting solution is
After cooling to 35 ° C., 0.3 g of hydrochloric acid having a concentration of 35% by weight was added, and further cooled to 50 ° C., 27 g of benzaldehyde was added dropwise over 1 hour, and an acetalization reaction was performed at 45 ° C. for 5 hours. As a result, a sponge-like precipitate was formed in the solution.

Thereafter, the mixture was cooled to a liquid temperature of 20 ° C., and 920 g of isopropyl alcohol was added with stirring.
Dissolve the sponge-like resin completely, and then
A 1.2% by weight aqueous sodium hydroxide solution was added to obtain an 8% by weight aqueous solution of polyvinyl acetal resin in water-isopropyl alcohol (the ratio of water to isopropyl alcohol was 6: 4 by weight). The obtained polyvinyl acetal resin solution was evaluated in the same manner as in Example 1. The results are shown in Table 2 below.

Comparative Examples 11 and 12 As shown in Table 2, a polyvinyl acetal resin solution was obtained in the same manner as in Comparative Example 10 except that the types of polyvinyl alcohol, aldehyde and alcohol, and the amounts used were changed. Evaluation was performed in the same manner as in Example 1. The results are shown in Table 2 below.

[0049]

[Table 1]

[0050]

[Table 2]

In Comparative Examples 1 to 3, the concentration of the acid catalyst was 1.0
Due to the high weight percent, the polyvinyl acetal resin solution was cloudy, and the transparency of the film was greatly impaired. Also, the yield was only 96%.

In Comparative Examples 4 to 6, similarly, the concentration of hydrochloric acid as an acid catalyst was as high as 1.0% by weight, and neutralization was carried out by using a large amount of aqueous sodium hydroxide solution. Perhaps, the water washing process had to be performed many times. Therefore, the yield was as low as 84% or less.

Also in Comparative Examples 7 to 9, the concentration of hydrochloric acid as an acid catalyst was as high as 1.0% by weight, and therefore, after the reaction, a large amount of aqueous sodium hydroxide was used to neutralize the same as in Comparative Example 4. . Therefore, a large amount of salt was generated, and the water washing treatment was repeated, so that the yield was reduced to 77% or less.

On the other hand, Examples 1 to 6 and Comparative Example 10
In Nos. To 12, the concentration of the acid catalyst was as low as 0.01% by weight or less, and therefore, the salt was obtained by dissolving the polyvinyl acetal resin formed by adding the alcohol according to the present invention, probably because the salt generated by the neutralization was small. The polyvinyl acetal resin solution was transparent, and the resulting coating film had good transparency. Further, since the washing and drying steps were not performed, the yield was as high as 98%.

On the other hand, with respect to the equilibrium water content, Comparative Examples 1 to 1
2 is a sponge-like mass upon precipitation of the resin, and has a high water resistance of 14% or more due to the low acetalized material contained in the inner layer portion.
% Or less, the equilibrium water content was low and the water resistance was good.

[0056]

As described above, according to the production method of the present invention, the acetalization reaction is carried out under the above-mentioned specific conditions while the amount of the acid catalyst is made extremely small as 0.005 to 0.03% by weight. Therefore, the obtained polyvinyl acetal resin is
No need to dry. Therefore, since the polyvinyl acetal resin solution is obtained by adding the alcohol without passing through the washing and drying steps, the yield of the polyvinyl acetal resin solution can be increased, and the salt generated by the neutralization is reduced, The transparency of the polyvinyl acetal resin solution is enhanced, and the transparency of a coating film formed by using the polyvinyl acetal resin solution is also enhanced.

In the present invention, since the precipitated resin formed by the acetalization reaction is a particulate polyvinyl acetal resin having a particle size of 10 mm or less, a coating film or the like formed using the polyvinyl acetal resin solution can be used. The equilibrium water content can be kept low, and the water resistance can be increased.

Further, a polyvinyl acetal resin having a degree of acetalization of 10 mol% or less does not dissolve alone in water,
Although it does not dissolve in an alcohol-based organic solvent alone, it can be dissolved in the water-alcohol mixed solvent by the method of the present invention. Therefore, a solution of a polyvinyl acetal resin having both hydrophilicity and water resistance can be obtained.

Thus, the polyvinyl acetal resin solution obtained by the production method of the present invention can be suitably used for a recording material of a printer or an XY plotter by coating it on a support such as paper or film. Yes, especially
It is suitable as a transparent recording material suitable for an overhead projector for recording by an ink jet system or a pen system, or as a transparent recording material for a color mosaic filter used in other color displays such as slides and liquid crystals. In addition to the recording material, it can be suitably used as an antifogging material for vinyl houses, strippable paint, and the like.

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-62-156112 (JP, A) JP-A-6-211920 (JP, A) JP-A-63-46279 (JP, A) 221077 (JP, A) JP-A-4-55404 (JP, A) JP-A-6-239929 (JP, A) JP-A-2-123104 (JP, A) (58) Fields investigated (Int. ⁷ , DB name) C08F 8/00-8/50 C08F 16/06

Claims (1)

(57) [Claims] 1. A method for producing a polyvinyl acetal resin solution in which a polyvinyl acetal resin obtained by an acetalization reaction between polyvinyl alcohol and an aromatic aldehyde is dissolved in a mixed solvent of water and an alcohol. Acid catalyst concentration of 0.0
An acid catalyst is added so as to be 0.5 to 0.03% by weight to react the polyvinyl alcohol with the aromatic aldehyde to produce a particulate polyvinyl acetal resin having a particle size of 10 mm or less. Water in the solution: alcohol Is 80:20 by weight.
20. A method for producing a polyvinyl acetal resin solution, comprising adding an alcohol to dissolve the polyvinyl acetal resin at a ratio of 20:80.