JPH06239929A - Production of polyvinyl acetal resin - Google Patents

Abstract

PURPOSE:To obtain the subject resin, having a uniform particle diameter and high acetalization degree without any blocking or sticking to walls by reacting a PVA solution with an aldehyde in the presence of an acidic catalyst according to a specific method. CONSTITUTION:An aqueous solution of PVA (preferably having 200-10000 average polymerization degree and >=88mol% saponification degree) is mixed with an aldehyde (preferably acetaldehyde, propionaldehyde, etc.) at a temperature of 20 deg.C to <= the boiling point of the aldehyde so as to provide 100-180 mol% aldehyde based on 100mol% residual hydroxyl group in the PVA. The resultant mixture solution is then mixed with an acidic catalyst (e.g. hydrochloric acid or sulfuric acid) at 70-95 deg.C to carry out the reaction. Furthermore, the aqueous solution of the PVA is preferably mixed with the aldehyde by a method for charging the PVA into hot water at >=80 deg.C, dissolving the PVA therein, cooling the obtained aqueous solution, regulating the cooled aqueous solution to a temperature within the range of 20 deg.C to the boiling point of the aldehyde and then charging the aldehyde into the aqueous solution of the PVA.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing polyvinyl acetal, and more particularly, it has a high degree of acetalization of about 80 mol% or more, which is considered to be difficult to produce with an aqueous solvent, and has a small degree. The present invention relates to a method for producing a polyvinyl acetal resin having a particle size.

[0002]

2. Description of the Related Art Polyvinyl acetal resins typified by polyvinyl butyral have long been excellent in transparency, adhesion to glass, metal, etc., mechanical strength, etc. It is used as a resin for printed circuit board adhesives. One of the reasons why polyvinyl acetal resin is used for these applications is
It has excellent adhesion to metal and glass. And this excellent adhesiveness is due to the fact that the polyvinyl acetal resin has essentially many hydroxyl groups.

However, according to the conventional method for producing polyvinyl butyral, it is difficult to produce a polyvinyl acetal resin having a high degree of acetalization, and particularly when the reaction solvent is water or a mixed system mainly containing water, for example, JP-A-56 is used. As described in JP-A-92142, an industrial method for obtaining a highly acetalized polyvinyl butyral whose acetalization degree is about 75 mol% and whose acetalization degree exceeds about 80 mol% is known. There wasn't.

The reason for this is that in the precipitation method, which is a conventional water-based synthesis method, it is necessary to increase the degree of acetalization while forming fine particles, so the reaction temperature was set in the range of 10 to 50 ° C., and , Aldehyde added 7
This is because only about 0 mol% was used.

However, in order to obtain a highly acetalized resin by the conventional precipitation method, the reaction is carried out at a high temperature (Japanese Examined Patent Publication No. 38-
25040), and when the amount of aldehyde was increased, precipitated particles of acetal became very large or coalescence occurred in one lump, which hindered the increase in the degree of acetalization, so that a high acetal resin could not be obtained. .

[0006]

As described above, the method of mixing the mixed solution of the polyvinyl alcohol aqueous solution, the catalyst and the aldehyde has the drawback that large particles are generated due to the blocking of the produced resin, and the degree of acetalization is increased. There are difficulties that cannot be raised. Moreover, in order to obtain a resin having a stable particle size, it is necessary to add a large amount of a surfactant to the reaction system. If this is not sufficiently removed during resin purification, problems such as clouding and yellowing of the resin will occur. Occurs.

The present invention has been made in view of the above points, and an object thereof is a specific reaction in a condensation reaction of polyvinyl alcohol and an aldehyde in an aqueous solvent which has been conventionally industrially carried out. It is an object of the present invention to provide a method for producing a polyvinyl acetal resin having an acetalization degree of 80 mol% or more by setting conditions so that blocking of the resin and adhesion to the wall are eliminated to obtain uniform particles.

[0008]

Means for Solving the Problems As a result of various investigations for solving the above-mentioned drawbacks, the present inventors have found that the acetalization reaction can be achieved by raising the reaction temperature higher than usual and making the amount of aldehyde excessive. The present invention has been completed based on the finding that a polyvinyl acetal resin having a uniform small particle size and an acetalization degree of 80 mol% or more can be produced by increasing the speed to increase the solid-liquid reactivity.

That is, in the method for producing a polyvinyl acetal resin according to the present invention, an aqueous polyvinyl alcohol solution and an aldehyde are mixed with the residual hydroxyl group 1 of the polyvinyl alcohol.
The step of mixing the aldehyde in an amount of 100 to 180 mol% with respect to 00 mol% in a temperature range of 20 ° C to the boiling point of the aldehyde or less, and then the obtained mixed liquid and the catalyst are mixed.
And a step of mixing in a temperature range of 0 to 95 ° C.

The degree of polymerization of polyvinyl alcohol, which is one of the starting materials, is not particularly limited, but one having an average degree of polymerization of 200 to 10,000, which is usually used for producing a polyvinyl acetal resin, is suitable. The saponification degree of polyvinyl alcohol is preferably 88 mol% or more.

The concentration of polyvinyl alcohol in the aqueous solution is appropriately determined within the range of 0.1 to 50% by weight, which is usually applied. If this concentration is less than 0.1% by weight, it may be economically disadvantageous. Moreover, this concentration is 50% by weight.
If it exceeds, the reversible reactivity may decrease due to the interaction of the hydroxyl groups with each other due to the high concentration of the polyvinyl acetal resin. However, this concentration range does not limit the method of the present invention.

As the aldehyde which is the other raw material, an aldehyde usually used for acetalization of polyvinyl alcohol is used. From the viewpoint of solubility in a solvent, an aldehyde having 1 to 10 carbon atoms is particularly preferable. For example, formaldehyde, acetaldehyde, propionaldehyde, n-butyraldehyde, isobutyraldehyde, 2-ethylbutyraldehyde, n-hexylaldehyde, n-octylaldehyde, 2-ethylhexylaldehyde, n-nonylaldehyde, n-decylaldehyde, cinnamaldehyde. Are exemplified. These may be used alone or in combination of two or more.
More suitable aldehydes include acetaldehyde, propionaldehyde, n-butyraldehyde, isobutyraldehyde, valeraldehyde, 2-ethylbutyraldehyde, n-hexylaldehyde and the like.

The amount of aldehyde charged is 100 to 100 mol% of the residual hydroxyl groups in the aqueous polyvinyl alcohol solution.
It is 180 mol%, and more preferably 110 to 150 mol%. The reason for this is that if the amount of aldehyde charged is less than 100 mol%, the degree of acetalization is less than 80 mol%, and if it exceeds 180 mol%, intermolecular acetalization occurs and the resin becomes harder. This is because the resin becomes difficult to dissolve in the solvent.

As the acid catalyst, an inorganic acid such as hydrochloric acid, sulfuric acid, trifluoroacetic acid or paratoluenesulfonic acid, or an organic acid such as acetic acid is used appropriately. The concentration of the acid catalyst can be set within a wide range of 0.02 to 10% by weight with respect to the solvent. If the concentration of the acid catalyst is less than 0.02% by weight,
The effect of donating protons as a catalyst is poor, and even if it exceeds 10% by weight, there is no additional effect in terms of catalyst efficiency and it is uneconomical. However, this concentration range does not limit the method of the present invention.

The temperature range in which the aqueous solution of polyvinyl alcohol and the aldehyde are mixed is not less than 20 ° C. and not more than the boiling point of the aldehyde. More preferably, the upper limit of the mixing temperature is about 10 ° C. lower than the boiling point of the aldehyde. is there. The reason for this is that if the mixing temperature of the aqueous polyvinyl alcohol solution and the aldehyde is lower than 20 ° C., a microgel may be generated in the polyvinyl alcohol, and a non-uniform resin that appears in the solvent solubility may be generated. If the boiling point of the aldehyde is exceeded, volatilization requires a large excess amount of the aldehyde charged, or a reaction under pressure is required.

To mix the polyvinyl alcohol and the aldehyde, first, the polyvinyl alcohol is put into and dissolved in warm water of 80 ° C. or higher, and then the obtained aqueous solution is cooled to 20.
It is preferable that the temperature is adjusted to be in the range of ° C to the boiling point of the aldehyde, and the aldehyde is added to and dispersed in this polyvinyl alcohol aqueous solution.

Next, the thus obtained mixed solution of polyvinyl alcohol and aldehyde is mixed with the catalyst in the temperature range of 70 to 95 ° C. This mixing method may be any method, and for example, the following method can be adopted.

70-95 ° C. with a small amount of catalyst added
In warm water, the above mixed solution of polyvinyl alcohol and aldehyde and an appropriate amount of catalyst are added. The above mixture and the catalyst are added to warm water at 70 to 95 ° C. The above mixed solution is added to 70 to 95 ° C. warm water containing a catalyst. Here, in order to add the mixed liquid or the catalyst to the liquid, it is preferable to drop the mixed liquid or the catalyst while stirring the liquid, and it is particularly preferable to add the mixed liquid or the catalyst over 60 to 180 minutes. When the mixing temperature of the mixed solution and the catalyst is less than 70 ° C., the acetalization reaction rate is slow and the acetalization degree is 80.
If the mol% or more of the acetal resin cannot be obtained, and if the temperature is lower than the room temperature, the above-described microgel formation occurs.
On the contrary, when the temperature of the mixture of the above-mentioned mixed solution and the catalyst exceeds 95 ° C., water as the reaction mother liquor evaporates remarkably, and the generated resin is softened. Adherence occurs.

In the reaction process, purposeful additives such as a dispersant for preventing particle coalescence, a surfactant, and an antioxidant for preventing oxidation during the reaction may be appropriately added.

[0020]

According to the method of the present invention, a polyvinyl acetal resin having a high degree of acetalization is produced, and the distribution of the degree of acetalization is narrow. This is because by adding polyvinyl alcohol and aldehyde to the reaction tank in a mixed state, particles are precipitated and acetalization by a heterogeneous system occurs, as compared with the case where polyvinyl alcohol and aldehyde are separately charged into the reaction tank. In the process of progressing, the particle formation and reaction rate are fast, and because the polyvinyl alcohol has a high efficiency as a dispersant on the particle surface,
It is considered that coalescence of the produced particles is prevented even though the reaction temperature is high (the reaction speed is fast). Further, when a dispersant or a surfactant is added to the reaction system in the production method of the present invention, polyvinyl acetal having a more uniform particle size can be obtained.

[0021]

EXAMPLES Next, the present invention will be specifically described with reference to some examples of the present invention.

The particle size of the obtained polyvinyl butyral resin was evaluated and the degree of butyralization was measured by the following methods.

<Evaluation of Particle Size> The particle size was evaluated by the weight% of resin particles passing through meshes of different sizes. <Measurement of degree of butyralization> The degree of butyralization was measured by the proton nuclear magnetic resonance spectrum of the following method.

A 2% by weight heavy water-benzene solution of polyvinyl butyral resin was prepared, and a small amount of tetramethylsilane [(CH ₃ ) ₄ Si] was added as a standard substance.
The spectrum was measured at 3 ° C. From the obtained measurement chart, the attribution and integral intensity of each absorption peak as described in Table 1, fitting the values of the integrated intensity of the (I _A and I _B) in the formula below, was calculated butyral degree.

[0025]

[Table 1] <Formula> butyralization degree _{= {2I A / (3I B} -4I A)} × 1
00 (mol%) <Example 1> Step i) To 2900 g of pure water, 193 g of polyvinyl alcohol having a polymerization degree of 1700 and a saponification degree of 99.2 mol% was added and dissolved by heating. The temperature of this aqueous solution was adjusted to 30 ° C., 300 g of n-butyraldehyde was added thereto, and the mixture was stirred and mixed for 10 minutes. Step ii) This mixed solution and 200 g of 3.5% hydrochloric acid are added,
Simultaneously, each was dropped into a reaction tank containing 500 g of 0.2% hydrochloric acid and kept at 90 ° C. The dropping was performed so as to be completed simultaneously in 120 minutes. Thus, after depositing polyvinyl butyral, the reaction system was held at a temperature of 90 ° C. for 90 minutes to complete the reaction.

Step iii) Then, the unreacted aldehyde is washed away by washing with excess water, the solution is neutralized to pH 7 to 8 by adding an aqueous solution of sodium carbonate, and salts are removed.
After drying, a white powder of polyvinyl butyral resin was obtained.

Table 1 shows the evaluation results of the particle size of the obtained polyvinyl butyral resin and the measurement results of the degree of butyralization.

<Example 2> In step ii) of Example 1, except that a mixed solution of polyvinyl alcohol and n-butyraldehyde and 150 g of trifluoroacetic acid were added dropwise to a solution containing 0.4% trifluoroacetic acid. A polyvinyl acetal was obtained in the same manner as in Example 1. The results of particle size evaluation and butyralization degree measurement are shown in Table 1.

Example 3 A polyvinyl acetal was obtained in the same manner as in Example 1 except that the temperature of the reaction vessel was maintained at 70 ° C. in step ii) of Example 1. The results of particle size evaluation and butyralization degree measurement are shown in Table 1.

Example 4 A polyvinyl acetal was obtained in the same manner as in Example 2 except that the temperature of the reaction vessel was maintained at 70 ° C. in step ii) of Example 2. The results of particle size evaluation and butyralization degree measurement are shown in Table 1.

<Example 5> In step i) of Example 1, as the aldehyde, propionaldehyde (Bp4
A polyvinyl acetal was obtained in the same manner as in Example 1 except that 320 g (9 ° C.) was used. The results of particle size evaluation and butyralization degree measurement are shown in Table 1.

Example 6 In step i) of Example 1, n-hexyl aldehyde (Bp) was used as the aldehyde.
Polyvinyl acetal was obtained in the same manner as in Example 1 except that 320 g of (131 ° C.) was used. The results of particle size evaluation and butyralization degree measurement are shown in Table 1.

Example 7 In step i) of Example 1, isobutyraldehyde (Bp6) was used as the aldehyde.
Polyvinyl acetal was obtained in the same manner as in Example 1 except that 300 g (3 to 64 ° C.) was used. The results of particle size evaluation and butyralization degree measurement are shown in Table 1.

Comparative Example 1 A polymerization degree of 17 was added to 2900 g of pure water.
00 and 193 g of polyvinyl alcohol having a saponification degree of 99.2 mol% were added and dissolved by heating. The temperature of this aqueous solution was adjusted to 30 ° C., 200 g of 35% hydrochloric acid and 300 g of n-butyraldehyde were added, and the reaction was carried out for 6 hours. The treatment after the completion of the reaction was performed in the same manner as in step iii) of Example 1. As a result, with the progress of the reaction, the resin was blocked and became a lump, and the reaction was stopped because it was wrapped around the stirring spring and an excessive load was applied.

Comparative Example 2 200 g of 3.5% hydrochloric acid was mixed with the aqueous polyvinyl alcohol solution prepared in the same manner as in Example 1, and the temperature of the mixed solution was kept at 80 ° C. This mixture and n
-Butyraldehyde (300 g) was simultaneously added dropwise to a reaction tank kept at 90 ° C over 120 minutes. The other operations were the same as in Example 1. The results of particle size evaluation and butyralization degree measurement are shown in Table 1.

Comparative Example 3 A polyvinyl acetal was obtained in the same manner as in Example 1 except that the temperature of the reaction vessel was maintained at 50 ° C. in step ii) of Example 1. As a result, as the reaction progressed, block formation and adhesion to the layer wall were remarkable, and only sponge-like resin was obtained.

[0037]

[Table 2]

[0038]

According to the present invention, it is possible to obtain a polyvinyl acetal having a uniform small particle size, which has an acetalization degree of 80 mol% or more, does not cause blocking of the produced resin and does not adhere to the wall. Moreover, since a resin having a stable particle size can be obtained without adding a surfactant and other additives to the reaction system, the problems of clouding and yellowing of the resin do not occur. Also, there is little variation in the degree of acetalization due to manufacturing conditions.

Claims (1)

[Claims] 1. A step of mixing an aqueous polyvinyl alcohol solution and an aldehyde at a ratio of 100 to 180 mol% of aldehyde to 100 mol% of residual hydroxyl groups of polyvinyl alcohol in a temperature range of 20 ° C. to a boiling point of the aldehyde or lower. Then, the manufacturing method of polyvinyl acetal characterized by including the process of mixing the obtained mixed liquid and a catalyst in a temperature range of 70-95 degreeC.