JPH0713096B2 - Method for producing polyvinyl acetoacetal resin - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for producing a polyvinyl acetoacetal resin, and more particularly to a method for producing a polyvinyl acetoacetal resin having a high degree of acetalization and a small particle size variation.

[Conventional technology]

Polyvinyl acetal resin is known as a resin having excellent heat resistance. This resin is obtained by condensing polyvinyl alcohol with an aldehyde (formaldehyde, acetaldehyde, butyraldehyde, etc.). In particular, it is known that the smaller the number of carbon atoms forming the acetal ring of polyvinyl acetal, the higher the glass transition temperature and the better the heat resistance (“mechanical properties of polymer”).
p.19, Kagaku Doujin, 1965). However, polyvinyl formal, which has the smallest number of carbon atoms in the acetal ring, has a specific solubility in a solvent, and the usable solvent is limited. For example, polyvinyl formal having a high degree of formalization is soluble only in limited solvents such as methylene chloride, methylene chloride-chloroform, methanol, glycol, formalin and benzene-alcohol. therefore,
It is desired to use a polyvinyl acetoacetal resin as a heat resistant resin.

In this condensation reaction in which acetaldehyde is subjected to condensation reaction with polyvinyl alcohol to obtain polyvinyl acetoacetal resin, it is difficult to obtain a high quality acetalized product (acetalization degree of 60 mol% or more) because of low reactivity of acetaldehyde. Polyvinyl acetoacetal resin, which has a low degree of acetalization, is water-soluble and becomes water-insoluble as acetalization proceeds. Therefore, the polyvinyl acetoacetal resin is usually marketed as a water-soluble acetal (low acetal compound). Such water-soluble polyvinyl acetoacetal resin is not used as a heat resistant resin.

Even if the reaction temperature is raised to increase the reactivity of acetaldehyde in order to obtain a polyvinyl acetoacetal resin with a high degree of acetalization, if the reaction temperature rises, the solubility limit point of the acetal compound (the limit degree of acetalization that makes water insoluble) Decreases, causing precipitation of low-acetal compounds. The precipitated low acetal compound is in the form of huge particles, and it is difficult for acetaldehyde to attack, so the acetalization does not proceed any further. Therefore, the desired high acetal compound cannot be obtained. Moreover, purification of this giant particulate acetal compound is difficult because the acid catalyst remains in the particles. The variation in the degree of acetalization within the particles also increases.

(Problems to be Solved by the Invention) The present invention is to solve the above-mentioned conventional problems, and an object thereof is to obtain a high degree of acetalization (60 mol% or more, preferably 65 mol% or more, more preferably Is 70 mol%
The above is to provide a method for producing a polyvinyl acetoacetal resin. Another object of the present invention is to provide a method for producing a polyvinyl acetoacetal resin having no large particles and having a small variation in particle diameter. Still another object of the present invention is to provide a method for producing a polyvinyl acetoacetal resin having a small variation in acetalization degree. Still another object of the present invention is to provide a method for producing a polyvinyl acetoacetal resin without coloring. Still another object of the present invention is to provide a method for producing a polyvinyl acetoacetal resin having good solvent solubility.

(Means for Solving the Problem) In the production of a polyvinyl acetoacetal resin, the present invention is a method in which, in the presence of an acid catalyst, acetalization is slowly progressed at a low temperature in an aqueous phase to precipitate a partial acetalized product. By keeping it at a high temperature, a polyvinyl acetacetal resin with a high degree of acetalization can be obtained. By adjusting the amount of the acid catalyst and the reaction temperature, there is little variation in particle size, no coloring, and good solvent solubility. It was completed based on the inventor's finding that a good polyvinyl acetoacetal resin can be obtained.

The method for producing a polyvinyl acetoacetal resin of the present invention is a method for producing a polyvinyl acetoacetal resin by the reaction of polyvinyl alcohol and acetaldehyde in an aqueous phase in the presence of 4 to 10% by weight of an acid catalyst. Is started at a temperature of 8 to 17 ° C for 30 minutes or more to start the precipitation of the acetal compound, and then the reaction system is maintained at a temperature of 25 to 40 ° C, whereby the above object is achieved. It

Polyvinyl acetoacetal has higher solubility in water than polyvinyl butyral. For example, the solubility limit of polyvinyl butyral in water at 20 ° C (the degree of acetalization that makes water insoluble) is 20 to 25 mol%, while the solubility limit of polyvinyl acetoacetal is 45 to 45 mol%.
It is 60 mol%. The melting point decreases with increasing temperature. On the other hand, acetaldehyde has a lower reactivity to polyvinyl alcohol than butyraldehyde.
Therefore, in the production of polyvinyl acetoacetal resin,
In order to obtain a highly acetalized product, it is necessary to gradually promote acetalization in a state where polyvinyl acetoacetal is dissolved in water to make it highly acetalized. Therefore, in the production of the polyvinyl acetoacetal resin of the present invention, after adding an acid catalyst and acetaldehyde to polyvinyl alcohol, the mixture is kept at a low temperature for a certain period of time to gradually increase the acetal to precipitate an acetalized product. There is.
If the acetalized product precipitates quickly, lower the reaction temperature to raise the solubility limit and ensure a holding time of at least 30 minutes before the start of precipitation.

In the method of the present invention, the mode of adding acetaldehyde to polyvinyl alcohol is not particularly limited. That is, it may be added all at once, dividedly or continuously.

In the present invention, “holding the reaction system at 8 to 17 ° C. for 30 minutes or more” means reaction conditions after adding acetaldehyde capable of substantially reacting with polyvinyl alcohol to the polyvinyl alcohol. In the case of addition or continuous addition, it means the reaction conditions after the addition of the last amount of acetaldehyde that can substantially react with polyvinyl alcohol. In other words, when adding the total amount of acetaldehyde to polyvinyl alcohol at once, after adding the acetaldehyde, this mixed solution is heated at 8 to 17 ° C.
Hold for at least 30 minutes. When the total amount of acetaldehyde is divided into small portions and each of the divided acetaldehyde is intermittently added to polyvinyl alcohol after a predetermined time, or when acetaldehyde is continuously added in small amounts during the predetermined time, polyvinyl alcohol is added. After the addition of all the amount of acetaldehyde which can react substantially with, the mixture is kept at 8 to 17 ° C for 30 minutes or more.

The amount of acid catalyst is preferably in the range of 4 to 10% by weight. If the amount is less than 4% by weight, the acetalization reaction does not proceed sufficiently, and a polyvinyl acetoacetal resin having a desired degree of acetalization cannot be obtained. Due to the low degree of acetalization, the particles are blocked into large particles. If the amount exceeds 10% by weight, acetaldehyde causes aldol condensation with an excess of acid, and thus the obtained polyvinyl acetoacetal resin may be colored. Examples of acid catalysts include hydrochloric acid, sulfuric acid, and nitric acid.

The amount of acetaldehyde is 0.7 to 2.2 mol, preferably 2 to 2 mol of polyvinyl alcohol (the number of hydroxyl groups).
It is set to 1.0 to 2.2 mol. If the amount is less than 0.7 mol, the acetalization reaction does not proceed sufficiently, and a polyvinyl acetoacetal resin having a desired degree of acetalization cannot be obtained. If it exceeds 2.2 mol, the amount of acetaldehyde in the reaction system becomes excessive, and the solubility limit point of the acetal compound rises. Therefore, it takes a long time to deposit the acetal compound, and the obtained polyvinyl acetoacetal resin varies in particle size.

The reaction takes place in the aqueous phase. In alcohol such as methanol, acetalization equilibrium is established, and a polyvinyl acetacetal resin having a high degree of acetalization cannot be obtained.

The reaction system of polyvinyl alcohol to which an acid catalyst is added and acetaldehyde in the aqueous phase is maintained at 8 to 17 ° C for 30 minutes or longer, preferably 1 to 6 hours. As a result, the acetalization proceeds slowly, and the acetalized product is deposited. 8
When the temperature is lower than ℃, it takes a long time for the acetalization product to precipitate, and the obtained polyvinyl acetoacetal resin varies in particle size. Above 17 ° C, the solubility limit of the acetal compound decreases, causing precipitation of the low acetal compound. The precipitated low acetal compound is in the form of huge particles, and it is difficult for acetaldehyde to attack it, so the acetalization does not proceed any further. for that reason,
A polyvinyl acetacetal resin having a high degree of acetalization cannot be obtained.

The average particle size of the precipitated acetal compound is usually 25 to 75
μm. If it is less than 25 μm, the resin obtained will be scattered when it is used and the workability will be reduced.
When it exceeds 75 μm, the acetalization does not proceed any more at the next constant temperature holding, and the desired high acetalization product cannot be obtained. The acid catalyst remains in the particles, making purification difficult.

The reaction system in which the acetal compound was deposited was then 25-40 ° C.
The temperature is usually kept constant for 2 to 8 hours. When the temperature is lower than 25 ° C, a high acetalized product can be obtained, but it contains a large amount of a low acetalized product, and the distribution of acetalization degree of the obtained polyvinyl acetoacetal resin becomes wide. Above 40 ° C, acetaldehyde volatilizes into the gas phase of the reaction system, and the degree of acetalization rather decreases. Volatilization of acetaldehyde contaminates the area around the reaction system. The solvent solubility of the obtained polyvinyl acetoacetal resin also becomes low due to deacetalization or intermolecular acetal formation. In particular, it becomes insoluble in non-alcoholic solvents (such as methyl ethyl ketone).

The degree of polymerization of polyvinyl alcohol is preferably 500-3500. When the degree of polymerization of polyvinyl alcohol is low, the reaction rate of acetalization is high. Therefore, even if the reaction temperature is raised and the melting point is lowered to accelerate the precipitation of the acetal compound, a high acetal compound can be obtained. The residual acetyl group of polyvinyl alcohol is preferably 0.5 to 12 mol%. The concentration of polyvinyl alcohol in the reaction system is not particularly limited, but is usually 4 to 10% by weight.

(Examples) The present invention will be described below with reference to Examples.

Example 1 2790 g of pure water was placed in the separable flask of Example 5, and 220 g of polyvinyl alcohol (polymerization degree: 2400, saponification degree: 98.8 mol%) was added thereto and completely dissolved. Next, the liquid temperature of this aqueous solution was maintained at 20 ° C., and 35 wt% hydrochloric acid was added to this.
650g was added. The amount of hydrochloric acid was 6% by weight. Liquid temperature 11 ℃
Then, 143 g of acetaldehyde was appropriately added and reacted, and a colorless powder was deposited. The amount of acetaldehyde is
It was 1.3 mol based on 2 mol of polyvinyl alcohol.
At this time, the time from the addition of acetaldehyde to the precipitation was 2 hours. The temperature of the reaction system was raised to 30 ° C, and the temperature was kept constant for 5 hours, followed by neutralization by washing with water to remove the catalyst and unreacted aldehyde, and a polyvinyl acetoacetal resin was obtained. This polyvinyl acetoacetal resin has a degree of acetalization of
It was 75.0 mol%. The average particle size of this resin is about
It was 40 μm. The results are shown in the table below.

Example 2 A polyvinyl acetoacetal resin was produced in the same manner as in Example 1 except that the amount of acetaldehyde was 88 g (0.8 mol based on 2 mol of polyvinyl alcohol). The time from the addition of acetaldehyde to the precipitation was 2 hours. The obtained polyvinyl acetoacetal resin has an acetalization degree of 69.3 mol% and an average particle size of about 40 μm.
Met. The results are shown in the table below.

Example 3 Polyvinyl chloride was prepared in the same manner as in Example 1 except that 220 g of acetaldehyde (2.0 mol per 2 mol of polyvinyl alcohol), the reaction temperature was 10 ° C., and the constant temperature after resin precipitation was 35 ° C. for 5 hours. An acetoacetal resin was produced. The time from the addition of acetaldehyde to the precipitation is 3
It was time. The obtained polyvinyl acetoacetal resin had an acetalization degree of 77.1 mol% and an average particle size of about 40 μm. The results are shown in the table below.

Example 4 The reaction temperature was 9 ° C., and the constant temperature after resin precipitation was 35 ° C., 5
A polyvinyl acetoacetal resin was produced in the same manner as in Example 1 except that the time was set. The time from the addition of acetaldehyde to the precipitation was 6 hours. The obtained polyvinyl acetoacetal resin has a degree of acetalization.
The average particle size was 75.0 mol%, and the average particle size was about 25 μm. The results are shown in the table below.

Example 5 The reaction temperature was 16 ° C., and the constant temperature after resin precipitation was 35 ° C.
A polyvinyl acetoacetal resin was produced in the same manner as in Example 1 except that the time was set. The time from the addition of acetaldehyde to the precipitation was 30 minutes. The obtained polyvinyl acetoacetal resin had an acetalization degree of 74.6 mol% and an average particle size of about 75 μm.
The results are shown in the table below.

Example 6 Example 1 was repeated except that the amount of hydrochloric acid was 420 g (4% by weight), the reaction temperature was 12 ° C., and the constant temperature after resin precipitation was 25 ° C. for 5 hours.
A polyvinyl acetoacetal resin was produced in the same manner as in. The time from the addition of acetaldehyde to the precipitation is
It was 4.5 hours. The obtained polyvinyl acetoacetal resin had an acetalization degree of 66.1 mol% and an average particle size of about 40 μm. The results are shown in the table below.

Example 7 2400 g of pure water, 1200 g (10% by weight) of hydrochloric acid, 220 g of acetaldehyde (2.0 mol per 2 mol of polyvinyl alcohol)
Mol), the reaction temperature was 9 ° C., and the polyvinyl acetoacetal resin was produced in the same manner as in Example 1 except that the temperature was kept constant after the resin precipitation was 40 ° C. for 8 hours. The time from the addition of acetaldehyde to the precipitation was 1 hour. The obtained polyvinyl acetoacetal resin had an acetalization degree of 79.4 mol% and an average particle size of about 40 μm. The results are shown in the table below.

Example 8 A polyvinyl acetoacetal resin was prepared in the same manner as in Example 1 except that polyvinyl alcohol having a degree of polymerization of 500 and a saponification degree of 98.8 mol% was used, the amount of hydrochloric acid was 420 g (4% by weight), and the reaction temperature was 16 ° C. Was manufactured. The time from the addition of acetaldehyde to the precipitation was 1 hour. The obtained polyvinyl acetoacetal resin had an acetalization degree of 70.8 mol% and an average particle size of about 40 μm. The results are shown in the table below.

Example 9 A polyvinyl acetoacetal resin was produced in the same manner as in Example 1 except that polyvinyl alcohol having a polymerization degree of 3500 and a saponification degree of 98.8 mol% was used. The time from the addition of acetaldehyde to the precipitation was 5 hours. The obtained polyvinyl acetoacetal resin has a degree of acetalization.
75.3 mol%, and the average particle size was 45 μm. The results are shown in the table below.

Example 10 A polyvinyl acetoacetal resin was produced in the same manner as in Example 1 except that polyvinyl alcohol having a polymerization degree of 2400 and a saponification degree of 88.0 mol% was used. The time from the addition of acetaldehyde to the precipitation was 2 hours. The obtained polyvinyl acetoacetal resin has a degree of acetalization.
The average particle size was 66.9 mol%, and the average particle size was about 40 μm. The results are shown in the table below.

Example 11 Example 1 was repeated except that polyvinyl alcohol having a polymerization degree of 1700 and a saponification degree of 99.2 mol% was used and the reaction temperature was 10 ° C.
A polyvinyl acetoacetal resin was produced in the same manner as in. The time from the addition of acetaldehyde to the precipitation is 3
It was time. The polyvinyl acetoacetal resin obtained had an acetalization degree of 74.8% and an average particle size of about 30.
was μm. The results are shown in the table below.

Example 12 A polyvinyl acetoacetal resin was produced in the same manner as in Example 1 except that acetaldehyde was 71.5 g (0.65 mol based on 2 mol of polyvinyl alcohol) and the reaction temperature was 16 ° C. The time from the addition of acetaldehyde to the precipitation was 6 hours. The obtained polyvinyl acetoacetal resin had an acetalization degree of 62.5 mol% and an average particle size of about 195 μm. The results are shown in the table below.

Example 13 A polyvinyl acetoacetal resin was produced in the same manner as in Example 1 except that 264 g of acetaldehyde (2.4 mol based on 2 mol of polyvinyl alcohol) and the reaction temperature were 10 ° C. The time from the addition of acetaldehyde to the precipitation was 9 hours. The obtained polyvinyl acetoacetal resin had an acetalization degree of 78.4 mol% and an average particle size of about 70 μm. However, the particle size of this resin was found to vary from 30 to 100 μm. The results are shown in the table below.

Comparative Example 1 Example 1 except that the amount of hydrochloric acid was 200 g (2% by weight)
A polyvinyl acetoacetal resin was produced in the same manner as in. The time from the addition of acetaldehyde to precipitation is 2
It was 0 hours. The obtained polyvinyl acetoacetal resin had an acetalization degree of 60.3 mol% and an average particle size of several mm. This resin was blocked. The results are shown in the table below.

Comparative Example 2 A polyvinyl acetoacetal resin was produced in the same manner as in Example 1 except that the amount of pure water was 2250 g, the amount of hydrochloric acid was 1400 g (12% by weight), and the reaction temperature was 10 ° C. The time from the addition of acetaldehyde to the precipitation was 30 minutes. The obtained polyvinyl acetoacetal resin had an acetalization degree of 77.2 mol% and an average particle size of about 40 μm. However, this resin was colored pale yellow as a whole. The results are shown in the table below.

Comparative Example 3 An attempt was made to produce a polyvinyl acetoacetal resin in the same manner as in Example 1 except that the reaction temperature was 6 ° C. However, no resin precipitation was observed even after 24 hours.
It is considered that this is because the reaction temperature is low and the solubility limit concentration of the acetal compound is too high.

Comparative Example 4 A polyvinyl acetoacetal resin was produced in the same manner as in Example 1 except that the reaction temperature was 19 ° C. The time from the addition of acetaldehyde to the precipitation was 6 minutes. The obtained polyvinyl acetoacetal resin has an acetalization degree of 70.0 mol% and an average particle size of about 400 μm.
Met. The particle size of this resin was large, varying from 200 to 500 μm. The results are shown in the table below.

Comparative Example 5 Except that the constant temperature after resin precipitation was 50 ° C. for 3 hours,
A polyvinyl acetoacetal resin was produced in the same manner as in Example 1. The time from the addition of acetaldehyde to the precipitation was 2 hours. The obtained polyvinyl acetoacetal resin had an acetalization degree of 71.5 mol% and an average particle size of about 60 μm.

The degree of acetalization was lower than that of the resin obtained in Example 1. This is probably because acetaldehyde was volatilized in the gas phase of the reaction system, resulting in deacetalization. The obtained polyvinyl acetoacetal resin was insoluble in a non-alcoholic solvent (such as methyl ethyl ketone). This is presumed to have been insolubilized by the intermolecular acetalization accompanying the deacetalization. The results are shown in the table below.

Comparative Example 6 except that the amount of hydrochloric acid was 1408 g (13% by weight), the reaction temperature was 10 ° C., and the constant temperature after resin precipitation was 60 ° C. for 3 hours,
A polyvinyl acetoacetal resin was produced in the same manner as in Example 1. The time from the addition of acetaldehyde to the precipitation was 30 minutes. The obtained polyvinyl acetoacetal resin had an acetalization degree of 68.4 mol% and an average particle size of about 70 μm. However, this resin was colored pale yellow as a whole.

The degree of acetalization was lower than that of the resin obtained in Example 1. This is probably because acetaldehyde was volatilized in the gas phase of the reaction system, resulting in deacetalization. The obtained polyvinyl acetoacetal resin was insoluble in a non-alcoholic solvent (such as methyl ethyl ketone). This is presumed to have been insolubilized by the intermolecular acetalization that accompanies the deacetalization. The results are shown in the table below.

As is clear from Examples and Comparative Examples, according to the method for producing a polyvinyl acetoacetal resin of the present invention, a polyvinyl acetoacetal resin having a high degree of acetalization can be obtained. This resin has a small variation in particle size and is not colored. Moreover, the solvent solubility is good. If the amount of hydrochloric acid is 2% by weight, a polyvinyl acetoacetal resin having a high degree of acetalization cannot be obtained. Due to the low degree of acetalization,
The particles become blocks and become huge particles. The amount of hydrochloric acid is 12
At weight%, the obtained polyvinyl acetoacetal resin is colored light yellow as a whole. If the reaction temperature is 6 ° C, the solubility limit concentration of the acetal compound is too high.
No resin precipitation is observed over time. Reaction temperature
When the temperature is set to 19 ° C, the average particle size increases and the particle size also varies. The constant temperature holding temperature during resin deposition is 50 ° C
At 60 ° C, the degree of acetalization rather decreases due to deacetalization. Moreover, the obtained resin becomes insoluble in a non-alcoholic solvent (such as methyl ethyl ketone).

(Effects of the Invention) According to the present invention, as described above, in the production of polyvinyl acetoacetal resin, in order to adjust the reaction temperature and the isothermal holding conditions in the presence of a certain amount of catalyst, polyvinyl acetal having a high degree of acetalization is obtained. A resin is obtained. This resin does not have huge particles, has a small variation in particle size, and is not colored. Therefore, purification is easy. It has good solvent solubility and is also soluble in non-alcoholic solvents (such as methyl ethyl ketone). Aldehydes do not evaporate during the manufacturing process, and there is no problem in terms of environmental pollution.

As a result, the polyvinyl acetoacetal resin obtained by the method of the present invention is useful as a heat resistant resin.

 ─────────────────────────────────────────────────── ─── Continuation of front page (72) Inventor Masanori Akada 4-25-14 Kugahara, Ota-ku, Tokyo (72) Inventor Katsuhiro Kamakari 6 Wakaba Dormitory, Takumi-cho, Ichitaka, Shinjuku-ku, Tokyo

Claims (4)

[Claims] 1. A method for producing a polyvinyl acetoacetal resin by reacting polyvinyl alcohol with acetaldehyde in an aqueous phase in the presence of 4 to 10% by weight of an acid catalyst, wherein the reaction system is heated to 8 to 17 ° C. After starting the precipitation of the acetal compound by holding it for 30 minutes or more,
A method for producing a polyvinyl acetoacetal resin, which comprises keeping the temperature at ℃. 2. The method for producing a polyvinyl acetoacetal resin according to claim 1, wherein the acid catalyst is at least one of hydrochloric acid, sulfuric acid and nitric acid. 3. With respect to 2 mol of the polyvinyl alcohol,
The method for producing a polyvinyl acetoacetal resin according to claim 1, wherein the acetaldehyde is used in the reaction at a ratio of 0.7 to 2.2 mol. 4. The method for producing a polyvinyl acetoacetal resin according to claim 1, wherein the degree of acetalization is 60 mol% or more, preferably 65 mol% or more, and more preferably 70 mol% or more.