JPH0768305B2 - 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 in particular, a resin having a high degree of acetalization and a small particle size variation can be obtained in a relatively short time. It relates to a method for producing a polyvinyl acetoacetal resin.

(Prior Art) The production method of polyvinyl acetoacetal resin has not been studied as much as polyvinyl butyral resin,
At present, the reaction conditions are not well known.

According to the knowledge of the present inventors, the problems in the production method of the polyvinyl acetoacetal resin are as follows.

Due to the low reactivity between acetaldehyde and polyvinyl alcohol, it takes a longer time to precipitate in the aqueous phase as compared with polyvinyl butyral resin.

Further, since the low acetalized product obtained by the initial reaction of polyvinyl alcohol and acetaldehyde has water solubility, the water molecule in the aqueous phase is bound to the unreacted hydroxyl group of the acetalized product in a hydrated state, resulting in an attack from acetaldehyde. It is considered that the hydroxyl groups are protected, which makes it difficult to obtain a resin having a high degree of acetalization.

As a method of increasing the degree of acetalization of this polyvinyl acetoacetal resin, the amount of the acid catalyst used is increased, and the low acetalized product is a water-soluble polyvinyl acetoacetal resin peculiar property, after adding an aldehyde, A method in which the low acetal compound and acetaldehyde are further reacted by holding at a predetermined temperature for a certain time or more can be mentioned.

(Problems to be Solved by the Invention) In the above method, a polyvinyl acetal resin having a relatively high degree of acetalization can be obtained, but the obtained resin has a drawback that the particle size greatly varies.

The cause of the variation in the particle size of the resin is presumed as follows.

Fluctuations in temperature during the reaction of polyvinyl alcohol and acetaldehyde change the degree of increase in the degree of acetalization, and changes in the degree of increase in the degree of acetalization change the size of the primary particles of the precipitated resin. The change in the size of the primary particles is the main factor that determines the subsequent particle size distribution of the resin particles.

Therefore, in order to narrow the particle size distribution of the obtained resin,
The reaction temperature must be strictly controlled, but in order to strictly control such a reaction temperature, it is necessary to control all internal and external factors such as heat of stirring, outside air temperature, heat of reaction, There is a drawback that the equipment cost becomes high.

The present invention solves the above drawbacks, and its purpose is to:
A method for producing a polyvinyl acetoacetal resin capable of producing a polyvinyl acetoacetal resin having a high degree of acetalization and a narrow particle size distribution in a relatively short time with relatively inexpensive equipment that does not require strict temperature control. To provide.

(Means for Solving the Problem) The method for producing a polyvinyl acetoacetal resin of the present invention is a method for producing a polyvinyl acetoacetal resin by reacting polyvinyl alcohol and acetaldehyde in an aqueous phase in the presence of an acid catalyst. Then, before the mixing of all of the acetaldehyde with polyvinyl alcohol,
Alternatively, a step of mixing the total amount of acetaldehyde with polyvinyl alcohol and at the same time mixing 0.002 mol to 0.2 mol of an aldehyde having 3 or more carbon atoms with 2 mol of vinyl alcohol units in polyvinyl alcohol, polyvinyl alcohol, acetaldehyde, and 3 or more carbon atoms. And a step of precipitating an acetalized product by the reaction with the aldehyde, thereby achieving the above object.

The present invention will be described in detail below.

First, polyvinyl alcohol is completely dissolved in water, and an acid catalyst is added to this water to prepare a polyvinyl alcohol aqueous solution. Polyvinyl alcohol has a degree of polymerization of 30
Those having a saponification degree of 88.0 to 99.5 mol% are preferably used, and those having a saponification degree of 88.0 to 99.5 mol% are usually used. The amount of polyvinyl alcohol dissolved in water is preferably 4 to 15% by weight based on the aqueous solution. The addition amount of the acid catalyst is usually 4 to 10% by weight based on the aqueous solution. If the amount of the acid catalyst added is less than 4% by weight of the aqueous solution, acetalization generally does not proceed sufficiently and the production time becomes long, and if it exceeds 10% by weight, acetaldehyde is converted to aldol due to excess acid. Due to condensation, the resulting polyvinyl acetoacetal resin may be colored. Examples of the acid catalyst that can be used include hydrochloric acid, sulfuric acid and nitric acid, and hydrochloric acid is particularly preferable.

Next, the polyvinyl alcohol aqueous solution thus prepared is mixed with acetaldehyde and an aldehyde having 3 or more carbon atoms to react the polyvinyl alcohol with acetaldehyde and the aldehyde having 3 or more carbon atoms. The aldehyde having 3 or more carbon atoms is mixed with the aqueous solution of polyvinyl alcohol before or after the entire amount of acetaldehyde is completely mixed with the aqueous solution of polyvinyl alcohol, and is mixed with the aqueous solution to react with polyvinyl alcohol.

Here, as a form in which polyvinyl alcohol is mixed with acetaldehyde and an aldehyde having 3 or more carbon atoms, for example, the following method can be adopted.

The total amount of aldehyde having 3 or more carbon atoms is added to the aqueous polyvinyl alcohol solution in the tank, and after a predetermined time, the total amount of acetaldehyde is added to the tank for the reaction.

By simultaneously charging the total amount of aldehyde having 3 or more carbon atoms and the total amount of acetaldehyde into the polyvinyl alcohol aqueous solution contained in the tank, the polyvinyl alcohol and the aldehyde having 3 or more carbon atoms and acetaldehyde are subjected to the reaction together.

Here, when the aldehyde having 3 or more carbon atoms and the acetaldehyde are charged at the same time, the following cases are included.

Except the above case, when acetaldehyde is charged immediately after the aldehyde having 3 or more carbon atoms is charged into the tank, when aldehyde having 3 or more carbon atoms is charged immediately after the acetaldehyde is charged in the tank, and For example, when an aldehyde having 3 or more carbon atoms and acetaldehyde are charged together within a predetermined time, or when a mixed aldehyde obtained by mixing an aldehyde having 3 or more carbon atoms and acetaldehyde is charged into a tank.

Acetaldehyde is charged into the polyvinyl alcohol aqueous solution placed in the tank over a predetermined time, and an aldehyde having 3 or more carbon atoms is charged into the tank while the acetaldehyde is charged. Or vice versa.

When adding polyvinyl alcohol to aldehyde or / and acetaldehyde having 3 or more carbon atoms in a tank.

In addition, it is preferable that the respective liquids contained in the tank are constantly stirred and mixed by an ordinary stirring device, but when the respective liquids are charged, or when the reaction including the charging is stopped, the stirring is stopped, The stirring speed may be slowed down.

Examples of the aldehyde having 3 or more carbon atoms that can be used in the present invention include, but are not limited to, propionaldehyde, butyraldehyde, 2-ethylhexylaldehyde, cyclohexylaldehyde, benzaldehyde, and benzacetaldehyde. As the aldehyde having 3 or more carbon atoms, the above-mentioned aldehydes may be used alone or in combination. The addition amount of the aldehyde having 3 or more carbon atoms is 0.002 mol to 0.2 mol, preferably 0.005 mol to 0.15 mol based on 2 mol of the vinyl alcohol unit in the polyvinyl alcohol.

When the addition amount is less than 0.002 mol, the effect of narrowing the particle size distribution of the polyvinyl acetoacetal resin obtained as described below is small. If it exceeds 0.2 mol,
Since the proportion of the acetalized portion of the resin due to acetaldehyde is relatively decreased, it is difficult to obtain the characteristics of the polyvinyl acetoacetal resin.

The amount of acetaldehyde added is preferably 0.7 to 2.2 mol per 2 mol of the vinyl alcohol unit in order to obtain good physical properties. Further, the reaction temperature is preferably carried out in the range of 8 to 17 ° C.

When polyvinyl alcohol is reacted with an aldehyde having 3 or more carbon atoms and acetaldehyde in this way, the acetalization gradually progresses and the acetalization product as a reaction product changes from water-soluble to water-insoluble. Compounds are relatively easily deposited. Here, when the reaction temperature is lower than 8 ° C, it takes a long time to precipitate the acetal compound, and the particle diameter of the obtained polyvinyl acetoacetal resin tends to vary, and when the reaction temperature exceeds 17 ° C. Since the solubility limit point of the acetal compound is lowered, the low acetal compound tends to be precipitated. This low acetalized product is in the form of huge particles, and since acetaldehyde is more difficult to react with it, acetalization does not proceed any further, and therefore, a polyvinyl acetacetal resin having a high degree of acetalization cannot be obtained. .

The temperature of the reaction system after deposition of the acetal compound is not particularly limited, but it is preferable to keep the temperature in the temperature range of 25 to 40 ° C. for 1 to 2 hours or more.

Then, the acid catalyst is neutralized, the salt is removed, and the unreacted aldehyde is removed by a commonly used method, and a polyvinyl acetacetal resin in a powder form is obtained through a drying step.
The degree of acetalization of the polyvinyl acetoacetal resin thus produced is generally 65 mol% or more,
The proportion of acetalized moieties with acetaldehyde is typically about 85% or more by weight of the total acetalized moieties. The average particle size of the particles is generally 30 to 60 μm. Further, as an index showing the particle size distribution of the particles, when the proportions of coarse particles of 100 μm or more and fine particles of 10 μm or less contained in this resin are measured, the respective particles are 0.5% by weight or less of the total amount of the resin. The various conditions of the reaction described above can be appropriately changed, and even if the conditions are outside the range of the reaction conditions, they do not depart from the spirit of the present invention.

As described above, by adding an aldehyde having 3 or more carbon atoms to polyvinyl alcohol, a vinyl acetal ring is formed by the aldehyde having 3 or more carbon atoms, and the acetalized portion produced here is hydrophobic. Compared to the case of reacting only polyvinyl alcohol and acetaldehyde, the acetalized product is more likely to be deposited and the acetalized product having a uniform particle size is more likely to be deposited.

This is because the addition of an aldehyde having 3 or more carbon atoms forms a hydrophobic acetalized portion, lowers the solubility limit point (the limit degree of water acetalization) of water in the entire acetalized product, and is uniform at an early stage. It is presumed that this is due to the deposition of the acetal compound while forming nuclei.

(Example) Hereinafter, the present invention will be described in detail based on examples.

In the composition analysis of the resin, first, in accordance with JIS K 6728 "Polyvinyl butyral test method", the weight% of the portion acetalized with two kinds of aldehydes was calculated by the measuring method. Similarly, the proportion (% by weight) of the vinyl acetate portion was calculated based on JIS K 6728, and the vinyl alcohol portion was calculated by subtracting the above two components from 100.

On the other hand, the resin was prepared into a film having a thickness of about several tens of μm by a casting method or the like, and the ratio of the acetalized portion of each aldehyde in the mixed aldehyde was calculated from its infrared absorption spectrum.

The polymerization degree of polyvinyl alcohol is 1700 in Example 4,
Except for using 1000 in Example 7, 2400 was used in all, including the comparative examples.

Example 1 2810 g of pure water in a 5 liter separable flask equipped with a stirring blade
Then, 220 g of polyvinyl alcohol (polymerization degree 2400, saponification degree 98.8 mol%) is added to this, and the mixture is stirred,
Polyvinyl alcohol was completely dissolved in water. next,
Keep this solution at 20 ° C and add 645 g of 35 wt% hydrochloric acid.
Was added. Then, the liquid temperature was lowered to 10 ° C., and 3.6 g of butyraldehyde (0.02 mol based on 2 mol of vinyl alcohol unit) was added to the flask. After the addition, the mixture was allowed to stand for 5 minutes, and then 143 g of acetaldehyde was added to the flask. After 50 minutes, an acetalized product was deposited. Subsequently, the temperature of this reaction system was raised to 35 ° C. and kept at this temperature for 4 hours, followed by washing with water and neutralization to remove the catalyst, salt and unreacted aldehyde contained in the solution. An acetoacetal resin was obtained.

The degree of acetalization of the obtained resin was 75.3 mol%.
The average particle size of this resin was 35 μm. Coarse particles of 100 μm or more contained in this resin are 0.1% by weight of the total amount of resin, and fine particles of 10 μm or less are 0.1% by weight of the total amount of resin.
Met.

Examples 2 to 7 As shown in Table 1, the degree of polymerization of polyvinyl alcohol, the reaction temperature, the number of moles of acetaldehyde added to 2 moles of the vinyl alcohol unit, the type of aldehyde having 3 or more carbon atoms and the amount added, and the time of introduction of acetaldehyde. A particulate polyvinyl acetoacetal resin was produced in the same manner as in Example 1 except that the timing of introducing the aldehyde having 3 or more carbon atoms based on the above was changed. However, the aqueous solution concentration of the hydrochloric acid catalyst was 5% by weight in Examples 3 and 7,
Then, all were set to 6% by weight except 4% by weight. Also,
The average particle size, coarse particles and fine particles of the obtained resin were measured in the same manner as in Example 1. The results are summarized in Table 1.

Comparative Example 1 Example 1 was repeated except that the amount of butyraldehyde added was 0.001 mol with respect to 2 mol of the vinyl alcohol unit.
A polyvinyl acetoacetal resin was produced in the same manner as in.

The average particle size, coarse particles and fine particles of the obtained resin were measured in the same manner as in Example 1. The results are shown in Table 1. The average particle size of the resin of Comparative Example 1 is almost the same as the average particle size of each Example, but the proportion of coarse particles and fine particles contained in the resin of Comparative Example 1 is higher than that of each Example. It can be seen that the particle size distribution of the resin is wide. In addition, the time required for precipitation is long.

Comparative Example 2 A polyvinyl acetoacetal resin was produced in the same manner as in Example 1 except that it was carried out without adding butyraldehyde. The average particle size of the resin of Comparative Example 2 is almost the same as the average particle size of each Example, but the proportion of coarse particles and fine particles contained in the resin of Comparative Example 2 is higher than that of each Example. ,
It can be seen that the resin particle size distribution is wide. Moreover, the time required for precipitation is long.

(Effect of the Invention) As described above, according to the present invention, since the predetermined amount of the aldehyde having 3 or more carbon atoms is added to the polyvinyl alcohol, a substantially uniform particle size is obtained without being significantly affected by the reaction temperature. The acetalized product can be deposited in a short time to narrow the particle size distribution of the polyvinyl acetoacetal resin.

Therefore, unlike the conventional case, a polyvinyl acetoacetal resin having a high degree of acetalization and a narrow particle size distribution can be obtained in a short time without requiring expensive equipment for strictly controlling the reaction temperature.

Claims (1)

[Claims] 1. A method for producing a polyvinyl acetoacetal resin by reacting polyvinyl alcohol and acetaldehyde in an aqueous phase in the presence of an acid catalyst, which comprises mixing the entire amount of acetaldehyde with polyvinyl alcohol, or At the same time as mixing the total amount of acetaldehyde with polyvinyl alcohol, a step of mixing 0.002 mol to 0.2 mol of an aldehyde having 3 or more carbon atoms with 2 mol of vinyl alcohol units in polyvinyl alcohol, polyvinyl alcohol, acetaldehyde, and 3 or more carbon atoms. A method for producing a polyvinyl acetoacetal resin, which comprises a step of depositing an acetalized product by a reaction with an aldehyde.