JP2000297117A - Preparation of polyvinyl acetal resin - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a preparation process of a polyvinyl acetal resin which gives a high conversion rate of aldehydes, especially aromatic aldehydes in acetalization, yields a resin showing an excellent hue and rationalizes the purification process when preparing a polyvinyl acetal resin by allowing a polyvinyl alcohol to undergo acetalization with aldehydes containing aromatic aldehydes. SOLUTION: In the objective process, a polyvinyl alcohol is allowed to undergo acetalization with aldehydes containing aromatic aldehydes in an organic solvent which azeotropes with water in the presence of an acid catalyst. Here, the acetalization is carried out while removing water by azeotroping it with the organic solvent to maintain the amount of water present within the reaction system at the end of acetalization within from 5 to 30 pts.wt. against 100 pts.wt. polyvinyl alcohol used.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD The present invention relates to a method for producing a polyvinyl acetal resin, and more particularly, to an acetalization reaction of an aldehyde containing an aromatic aldehyde with polyvinyl alcohol to produce a polyvinyl acetal resin. In particular, the present invention relates to a method for producing a polyvinyl acetal resin in which the conversion rate of an acetalization reaction of an aromatic aldehyde is high, the color of the obtained resin is excellent, and the purification step can be rationalized.

[0002]

2. Description of the Related Art Polyvinyl acetal resins obtained by condensation reaction of polyvinyl alcohol and aldehydes by acetalization can have various physical properties depending on the selection of aldehydes, and can be used in various applications such as paints, film materials and sheets. Used.

[0003] As a method for producing the same, an aldehyde is acetalized in an aqueous polyvinyl alcohol solution in the presence of an acid catalyst, and the aldehyde is precipitated and precipitated to obtain a polyvinyl acetal resin. In the presence of an acid catalyst in the reaction of aldehydes in the acetalization reaction, a solution obtained by adding a poor solvent to the resulting solution to precipitate to obtain a polyvinyl acetal resin, and the like, further, in the former precipitation method, A method for increasing the degree of acetalization of a resin obtained by using an excess of aldehydes with respect to polyvinyl alcohol,
For example, according to JP-A-6-239929,
In the latter dissolution method, similarly, a method of obtaining a polyvinyl acetal resin by using an excess of aldehydes with respect to polyvinyl alcohol is disclosed in, for example, JP-A-5-15-1.
No. 40217, each of which has been proposed.
A method that eliminates the use of a catalyst by using an excess of aldehydes with respect to polyvinyl alcohol and performing an acetalization reaction while removing water produced as an azeotrope with the aldehydes outside the reaction system, for example, JP 60
-79011 and the like.

[0004] However, all of these methods inherently have a problem that the conversion of aldehydes, particularly aromatic aldehydes, into acetal is low, and the purification step of the resulting resin is accompanied by the use of excess aldehydes. However, there is also a problem that such processes become complicated, and it is presently required to improve them. Further, according to the study of the present inventors, it has been found that in removing the by-produced water to the outside of the reaction system as in the above method, there is a problem that the color of the obtained resin sometimes deteriorates.

[0005]

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned prior art. Accordingly, the present invention provides an acetalization reaction between polyvinyl alcohol and an aldehyde containing an aromatic aldehyde to form a polyvinyl acetal resin. To provide a method for producing a polyvinyl acetal resin, which has a high acetalization reaction conversion rate of aldehydes, particularly aromatic aldehydes, and an excellent hue of the obtained resin, and can streamline the purification process. With the goal.

[0006]

Means for Solving the Problems As a result of intensive studies to achieve the above object, the present inventors have decided to use the above-mentioned dissolving method in which a reaction is carried out in a solution of polyvinyl alcohol in an organic solvent, and to use the dissolving method in a reaction system. It is found that the above object can be achieved by removing water as an azeotrope with the organic solvent out of the system so that the amount of water to be in a specific range reaches the present invention, that is, the present invention provides: A method for acetalizing polyvinyl alcohol and an aldehyde containing an aromatic aldehyde in the presence of an acid catalyst in an organic solvent capable of azeotroping with water, wherein water present in the reaction system at the end of the acetalization reaction is removed. The charge amount of the polyvinyl alcohol 10
The gist of the present invention is a method for producing a polyvinyl acetal resin which is subjected to an acetalization reaction while being removed from the reaction system by azeotropic distillation with the organic solvent so as to be 5 to 30 parts by weight with respect to 0 part by weight.

[0007]

BEST MODE FOR CARRYING OUT THE INVENTION In the method for producing a polyvinyl acetal resin of the present invention, the polyvinyl alcohol as a raw material may be a homopolymer or a copolymer containing a vinyl carboxylate unit having 3 to 20 carbon atoms. Specifically, for example, it is obtained by hydrolyzing polyvinyl acetate, ethylene-vinyl acetate copolymer, or the like, preferably at a ratio of 90 mol% or more, and the molecular weight is not particularly limited. , 2000 to 300,000 are preferred.

The aldehyde as a raw material contains at least an aromatic aldehyde, and the aromatic aldehyde is preferably represented by the following general formula (I).

[0009]

Embedded image O ＝ CH— (R ¹ ) _n —R ² (I)

[In the formula (I), R ¹ is an alkylene group having 1 to 4 carbon atoms which may have a substituent, or an alkylene group having 1 to 4 carbon atoms which may have a substituent. Represents an alkenylene group;
² represents an aryl group which may have a substituent, and n
Is 0 or 1. ]

Here, specific examples of the aromatic aldehyde represented by the general formula (I) include benzaldehyde, phenylacetaldehyde, α-phenylpropionaldehyde, and β-phenylpropionaldehyde. Examples of the substituent include an alkyl group such as a methyl group, an ethyl group, and a butyl group, and a halogen atom such as chlorine. Among them, phenylacetaldehyde is preferable.

The aldehydes other than the aromatic aldehyde include aliphatic aldehydes, and the aliphatic aldehyde is preferably represented by the following general formula (II).

[0013]

Embedded image O ＝ CH—R ³ (II)

[In the formula (II), R ³ is a hydrogen atom, an alkyl group having 1 to 4 carbon atoms which may have a substituent, or a C 1 to 4 carbon atom which may have a substituent. An alkenyl group of ]

Here, specific examples of the aliphatic aldehyde represented by the general formula (II) include formaldehyde, acetaldehyde, propionaldehyde, butyraldehyde, and the like. Groups, an alkyl group such as an ethyl group and a butyl group, a halogen atom such as chlorine and the like, and among them, butyraldehyde is preferable.

As the acid catalyst, hydrochloric acid, sulfuric acid, nitric acid,
Phosphoric acid, mineral acids such as boric acid, and heteropoly acids such as tungstophosphoric acid, molybdophosphoric acid, tungstosilicic acid, and molybdosilicic acid,
And inorganic acids such as partially neutralized salts thereof; organic sulfonic acids such as methanesulfonic acid and p-toluenesulfonic acid; organic carboxylic acids such as formic acid, acetic acid, lauric acid and oleic acid; and strongly acidic ion exchange. Organic acids such as resins are used, among which mineral acids and organic sulfonic acids are preferred, and sulfuric acid, methanesulfonic acid and p-toluenesulfonic acid are particularly preferred.

The process for producing a polyvinyl acetal according to the present invention is a process for acetalizing the polyvinyl alcohol and an aldehyde containing an aromatic aldehyde in an organic solvent in the presence of the acid catalyst. A water azeotrope is used, and water present in the reaction system at the end of the acetalization reaction is co-existed with the organic solvent in an amount of 5 to 30 parts by weight based on 100 parts by weight of the polyvinyl alcohol. It is essential to carry out an acetalization reaction while boiling and removing it outside the reaction system.

Specific examples of the organic solvent in the present invention include aromatic hydrocarbons such as benzene, toluene and xylene, among which toluene is particularly preferred.

In the present invention, as a method of removing water present in the reaction system by azeotropic distillation with the organic solvent and removing the water outside the reaction system, specifically, for example, after charging the raw materials,
Under normal pressure or reduced pressure, 20 to 90 ° C, preferably 40 to 70 ° C
Under the reaction temperature range of ° C., water present in the reaction system such as reaction by-product water and water used for diluting the catalyst is distilled off as an azeotrope with the organic solvent, and this is subjected to liquid-liquid separation. This is based on a method in which only the organic solvent is returned into the reaction system and water is removed outside the reaction system.

At this time, in the present invention, at the end of the acetalization reaction, the total theoretical amount of water present in the system such as reaction by-product water and water used for diluting the catalyst is calculated based on the charged amount of the polyvinyl alcohol of 100 wt. It is essential that the amount be in the range of 5 to 30 parts by weight,
It is preferred to be in the range of 5 parts by weight. If the theoretical amount of water is above the above range, the conversion of aldehydes, particularly aromatic aldehydes, into acetalization reaction will be low. On the other hand, if the theoretical amount of water is below the above range, the hue of the obtained resin will be deteriorated.

In the present invention, the amount of the polyvinyl alcohol and the aldehyde containing an aromatic aldehyde is 0.9 to 1.2 moles per 2 moles of the hydroxyl groups contained in the former polyvinyl alcohol. The aldehydes are preferably 10 to 100 mol% of an aromatic aldehyde and 90 to 0 mol% of an aliphatic aldehyde, and 20 to 90 mol% of an aromatic aldehyde and 80 to 10 mol of an aliphatic aldehyde. % Is more preferable. The preparation of these aldehydes is not limited to batch, but may be performed continuously or separately in small quantities.

The amount of the organic solvent used is preferably 1 to 7 times, more preferably 2 to 5 times the weight of the total amount of the polyvinyl alcohol and the aldehyde containing the aromatic aldehyde. More preferably,

[0023] Separation and purification of the polyvinyl acetal resin from the reaction solution after the completion of the acetalization reaction include, for example, neutralization and filtration of the reaction solution, if necessary, followed by adding a poor solvent for the polyvinyl acetal resin to precipitate the resin. The separation is performed, and if necessary, the operation of re-dissolving the precipitated resin in the organic solvent used for the reaction and re-precipitating with a poor solvent is repeated.

The polyvinyl acetal resin obtained by the production method of the present invention has particularly excellent hue, and can be used not only for various applications such as conventionally used paints, film materials, sheets and the like, but also for the constitution of a thermal transfer recording image receiving body and the like. It is also useful as a material.

[0025]

EXAMPLES Hereinafter, the present invention will be described more specifically with reference to examples, but the present invention is not limited to the following examples unless it exceeds the gist of the present invention.

Example 1 To a 1 liter flask equipped with a stirrer was added toluene 233.2.
g, 40.0 g of polyvinyl alcohol, 39.0 g of phenylacetaldehyde (corresponding to 0.703 mol with respect to 2 mol of hydroxyl groups contained in polyvinyl alcohol), and 13.2 g of n-butyraldehyde (2 mol of hydroxyl groups contained in polyvinyl alcohol). Was added and mixed, and then 10.9 g of 50% sulfuric acid was mixed.
Was added, and the temperature was raised to 55 to 60 ° C to start the acetalization reaction under normal pressure. After 2 hours, it was confirmed that the conversion of n-butyraldehyde became 90% or more, and the temperature was maintained. The pressure was reduced to 100 to 200 torr, and distillation of an azeotropic mixture of toluene and water in the system was started. A Dean stack tube was used for the distilling portion, and the upper layer toluene phase of the liquid-liquid separated distillate was overflowed and returned into the flask, so that only the lower aqueous phase was accumulated in the distilling portion.

After carrying out the acetalization reaction under reduced pressure in this state for 3 hours, the amount of distilled water was 9 ml (the theoretical amount of water in the reaction system was 10 wt.
This corresponds to 11.6 parts by weight for 0 parts by weight. ) Was confirmed, and a solution prepared by dissolving 14.5 g of sodium acetate in 214.2 g of methanol was added to the reaction solution to neutralize the reaction solution, followed by filtration to remove insolubles. The conversion calculated by quantifying the unreacted components of phenylacetaldehyde and n-butyraldehyde in the neutralized reaction solution was 83.6% for phenylacetaldehyde and 9 for n-butyraldehyde.
5.5%, and the residual amount of unreacted phenylacetaldehyde in the reaction solution was 1.13%.

Subsequently, a neutralized and filtered reaction solution was charged in its entirety into a 2-liter separable flask equipped with a stirrer and a baffle.
g was gradually added, and after about 30 minutes, stirring was stopped. The separated upper layer liquid was removed by suction from the upper part of the flask, and then the toluene was added to the high viscosity liquid phase (mochi phase) containing the polyvinyl acetal resin separated in the lower layer. After adding and dissolving 300 g, this purification operation was repeated twice, and then the concentration was adjusted to finally obtain a 20% polyvinyl acetal resin toluene solution. The polyvinyl acetal resin in this solution is 6
6.9 g, residual amount of unreacted phenylacetaldehyde is 1
It was 36 ppm, and the hue by the Hazen color number of JIS K0071-1 was 50 APHA.

Example 2 The amount of distilled water at the end of the acetalization reaction was set to 8 ml (the theoretical amount of water in the reaction system was 14.1 parts by weight based on 100 parts by weight of the charged amount of polyvinyl alcohol). Other than that, each operation was performed in the same manner as in Example 1. The conversion of phenylacetaldehyde in the neutralized and filtered reaction solution was 78.8%, the conversion of n-butyraldehyde was 93.1%, and the polyvinyl acetal resin in the purified 20% toluene solution was 65%. 0.4 g,
The remaining amount of unreacted phenylacetaldehyde is 178 pp
m, and the hue according to the Hazen color number of JIS K0071-1 was 30 APHA.

Comparative Example 1 The amount of distilled water at the end of the acetalization reaction was 12 ml (theoretical water amount in the reaction system was 4.1 parts by weight based on 100 parts by weight of the charged amount of polyvinyl alcohol).
Each operation was performed in the same manner as in Example 1 except that
The conversion rate of phenylacetaldehyde in the neutralized and filtered reaction solution was 96.2%, the conversion rate of n-butyraldehyde was 98.6%, and the polyvinyl acetal resin in the purified 20% toluene solution was 66%. 0.5 g, the residual amount of unreacted phenylacetaldehyde was 56 ppm, and the hue based on the Hazen color number of JIS K0071-1 was 200 APHA.

Comparative Example 2 An acetalization reaction was carried out under normal pressure for 5 hours, and water in the reaction system was not removed at all (the theoretical amount of water in the reaction system was
It is 34.1 parts by weight based on 100 parts by weight of the charged amount of polyvinyl alcohol. Other operations were performed in the same manner as in Example 1 except for the above. The conversion rate of phenylacetaldehyde in the neutralized and filtered reaction solution was 61.8%, the conversion rate of n-butyraldehyde was 96.4%, and the residual amount of unreacted phenylacetaldehyde was 2.61%. The amount of the polyvinyl acetal resin in the subsequent 20% toluene solution was 64.4 g, the residual amount of unreacted phenylacetaldehyde was 323 ppm, and JIS K0071-1.
Was 40 APHA based on the Hazen color number.

[0032]

According to the present invention, in the production of a polyvinyl acetal resin by acetalizing polyvinyl alcohol and an aldehyde containing an aromatic aldehyde, the acetalization reaction conversion of aldehydes, especially aromatic aldehydes, is high. Further, it is possible to provide a method for producing a polyvinyl acetal resin in which the obtained resin is excellent in hue and in which the purification step can be rationalized.

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Miyuki Miura 1 Toho-cho, Yokkaichi-shi, Mie Mitsubishi Chemical Corporation's Yoichi Office F-term (reference) 4J100 AB02Q AD02P BC59H CA01 CA04 CA31 HA43 HB25 HB44 HB52 HB58 HB61 HB63 HC16 HC17 HC18 HC19 HC20 HC27 HC71 HE14 JA01 JA07 JA15

Claims (6)

[Claims] 1. A method for acetalizing an aldehyde containing an aromatic aldehyde with polyvinyl alcohol in the presence of an acid catalyst in an organic solvent capable of azeotroping with water,
The water present in the reaction system at the end of the acetalization reaction is azeotropically removed with the organic solvent so as to be 5 to 30 parts by weight with respect to the charged amount of the polyvinyl alcohol of 100 parts by weight, and is removed outside the reaction system. , A method for producing a polyvinyl acetal resin, which comprises causing an acetalization reaction. 2. The polyvinyl acetal resin according to claim 1, wherein the charged amount of the organic solvent is 1 to 7 times the weight of the total charged amount of the polyvinyl alcohol and the aldehyde containing the aromatic aldehyde. Production method. 3. The method for producing a polyvinyl acetal resin according to claim 1, wherein the acid catalyst is sulfuric acid. 4. The amount of aldehydes charged is 0.9 to 1.2 with respect to 2 moles of hydroxyl groups contained in polyvinyl alcohol.
The method for producing a polyvinyl acetal resin according to any one of claims 1 to 3, which is a mole. 5. An aldehyde comprising an aromatic aldehyde and an aliphatic aldehyde, wherein the proportion of the charged aldehydes is 10 to 100 mol% of the aromatic aldehyde and 9
The method for producing a polyvinyl acetal resin according to any one of claims 1 to 4, wherein the amount is 0 to 0 mol%. 6. The method for producing a polyvinyl acetal resin according to claim 1, wherein the aromatic aldehyde is represented by the following general formula (I). Embedded image O ＝ CH— (R ¹ ) _n —R ² (I) wherein R ¹ is an alkylene group having 1 to 4 carbon atoms which may have a substituent, or It represents an alkenylene group having 1 to 4 carbon atoms which may have a substituent, R ² represents an aryl group which may have a substituent, and n is 0 or 1. ]