JPH09110930A - Production of polyvinyl acetal resin - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a process for producing a polyvinyl acetal resin having a low degree of polymn. industrially easily at a low cost. SOLUTION: Polyvinyl alcohol is subjected to the bond cleavage of the main chain with an oxidizing agent and to reduction to lower the degree of polymn. and is then acetalized with an aldehyde.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a method for producing a polyvinyl acetal resin having a low degree of polymerization.

[0002]

2. Description of the Related Art Polyvinyl acetal resins typified by polyvinyl butyral resins differ greatly in their characteristics due to changes in the degree of acetalization and the degree of polymerization. Due to their different properties, laminated glass interlayers, adhesives, paints,
It is widely used in various applications such as ink, ceramics binder, and paper coating material. Among them, paint, ink,
A polyvinyl butyral resin for a ceramics binder is required to be a low viscosity type in which the viscosity of a solution having a concentration of 10% by weight is 50 mPa · s or less from the viewpoint of easy handling. However, at present, the melt viscosity or solution viscosity of polyvinyl butyral resin is mostly determined by the degree of polymerization of polyvinyl alcohol (hereinafter abbreviated as PVA) used as a raw material.

PVA used as a raw material for polyvinyl acetal resin is industrially prepared by saponifying polyvinyl acetate obtained by solution polymerization using methanol as a solvent with an alkali catalyst. There is. However, it is known that a general-purpose PVA industrially obtained by this method has a degree of polymerization of 400 or more in terms of economy and quality. As a method for producing a PVA having a polymerization degree lower than this, a chain transfer agent such as aldehydes and mercaptans may be used together during the polymerization of vinyl acetate (Japanese Patent Publication No. 1-40043).
A method in which a solvent having a high chain transfer constant such as ethanol or isopropanol is used in place of methanol (Japanese Patent Publication No. 52-1.
No. 7874) has been proposed.

[0004]

However, when a chain transfer agent is used in combination or a solvent having a high chain transfer constant is used, PVA which originally uses methanol as a solvent.
In order to prevent the production process of the above from being contaminated with these solvents, it is necessary to newly install auxiliary equipment, and the produced low polymerization degree PVA becomes very expensive, and the polyvinyl acetal resin There was a problem that the use as a raw material was restricted.

In view of the above circumstances, the present invention industrially manufactures a desired low degree of polymerization of PVA at a low cost to industrially manufacture a desired low degree of polymerization of polyvinyl acetal resin at a low cost. The purpose is.

[0006]

The method for producing a polyvinyl acetal resin of the present invention achieves the above object, and the main chain is cleaved with an oxidizing agent and a reduction treatment is carried out to reduce the degree of polymerization. It is characterized in that PVA is acetalized with aldehydes.

[0007]

BEST MODE FOR CARRYING OUT THE INVENTION P used as a raw material in the present invention
As the VA, a commercially available one having a polymerization degree of 400 or more is generally used. Further, PVA used here is α-olefins, alkyl vinyl ethers, as long as the effects of the present invention are not impaired.
(Meth) acrylic acid or a derivative thereof, unsaturated dicarboxylic acid or a derivative thereof, or the like, or a known monomer copolymerizable with vinyl acetate is copolymerized, or PVA is used as an epoxy group-containing compound or an isocyanate group-containing compound. The modified PVA obtained by post-reacting the compound containing the reactive group of 1 by a known method may be used.

The oxidizing agent used for lowering the degree of polymerization of the raw material PVA may be any one that oxidatively cleaves the molecular main chain of PVA, and examples thereof include hydrogen peroxide, ozone, periodic acid or salts thereof, and peroxide. Oxidizing agents such as hydrogen peroxide, ozone, etc., such as manganic acid or salts thereof, randomly cleave the molecular main chain of PVA, whereas periodic acid or its salts are usually present in the PVA molecular main chain. It is particularly effective because it selectively cleaves a 1,2-glycol bond contained in an amount of 1 to 2 mol%.

The addition amount of the oxidizing agent used in the present invention can be changed according to the desired degree of polymerization of PVA, whereby PVA having an arbitrary low degree of polymerization can be easily obtained. Considering the cost of PVA, even if the degree of polymerization of PVA is the degree of polymerization obtained with commercially available PVA, it may be obtained by lowering the degree of polymerization of inexpensive high degree of polymerization PVA. , Can be selected in a wide range.
The degree of polymerization of PVA is preferably 40 to 380, particularly 50 to 250.

PVA whose main chain is oxidatively cleaved by the oxidizing agent used in the present invention has an aldehyde group at the end,
As it is, it is chemically unstable and it is necessary to treat with a reducing agent. The reducing agent used here may be any one capable of reducing a known aldehyde group, and examples thereof include metal hydrides such as lithium aluminum hydride and sodium borohydride, and sulfite salts such as sodium hydrogen sulfite. However, of these, sulfite is preferable.

As the aldehyde for acetalizing the polyvinyl alcohol thus obtained with aldehydes, various aldehydes can be used, but those having 1 to 10 carbon atoms are particularly desirable. For example, formaldehyde, acetaldehyde, propionaldehyde, n-butyraldehyde, isobutyraldehyde, n-octyl aldehyde, benzaldehyde and the like can be mentioned. An acid catalyst is usually used for the acetalization reaction.

Various known methods can be used as a method for producing a polyvinyl acetal resin by acetalizing the above-mentioned low polymerization degree polyvinyl alcohol with aldehydes. For example, in the case of polyvinyl butyral resin, the low-polymerization degree PVA obtained by the method of the present invention is dissolved by heating in water, an acid catalyst and butyraldehyde are added, most of the reaction is allowed to proceed, and aging is carried out appropriately. In addition, the temperature of the reaction system is further raised to maintain the high temperature to complete the reaction, and then neutralization, washing with water and drying are carried out by a conventional method. The degree of acetalization can be determined according to the purpose.

The obtained acetalized product contains, if necessary, known plasticizers, adhesive strength modifiers,
Antioxidants and ultraviolet absorbers can also be added. According to the method of the present invention, a low polymerization type acetal resin for paints, inks and ceramics binders can be industrially produced easily and at low cost.

[0014]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be specifically described below based on embodiments.

Example 1 a) Preparation of low degree of polymerization PVA 400 g of a 10% by weight aqueous solution of PVA having a degree of polymerization of 500 and an oxidation degree of 99.3 mol% was prepared, and 0.6 g of sodium periodate was added thereto. , React at 60 ℃ for 1 hour
After cleaving the main chain of VA, 0.7 g of sodium hydrogen sulfite was added as a reducing agent, reacted for 1 hour, and cooled to room temperature. The degree of polymerization of the obtained PVA was 240.

B) Reaction with butyraldehyde 300 g of an aqueous PVA solution having a degree of polymerization of 240 obtained in a) is added to 50 g.
After the temperature was increased to 15 ° C., 15 g of hydrochloric acid having a concentration of 35% by weight and 20 g of n-butyraldehyde were added, and the reaction was allowed to proceed.
The reaction system was kept at 50 ° C. for 4 hours after the precipitation of sodium chloride. Then, the mixture was cooled to room temperature, neutralized with sodium hydrogen carbonate, and the produced resin was washed with water and dried. The obtained reaction product had an acetalization degree of 65 mol% and a viscosity of a 10% by weight ethanol / toluene (1 part by weight / 1 part by weight) mixed solution was 2%.
It was 2 mPa · s (20 ° C.).

Example 2 a) Preparation of low degree of polymerization PVA 400 g of a 5% by weight aqueous solution of PVA having a degree of polymerization of 1600 and a degree of saponification of 99.4 mol% was prepared and pH was adjusted with sodium hydroxide.
After adjusting to 13, add hydrogen peroxide solution so that hydrogen peroxide becomes 3% by weight, and react at 60 ° C. for 3 hours to produce PV.
After cleaving the main chain of A, 2.0 g of sodium hydrogen sulfite was added as a reducing agent, and the mixture was reacted for 1 hour and then cooled. The degree of polymerization of the obtained PVA was 220.

B) Reaction with octyl aldehyde Same as Example 1 except that 300 g of an aqueous PVA solution having a degree of polymerization of 220 obtained in a) was used and 5 g of octyl aldehyde was added instead of n-butyraldehyde in Example 1. Was reacted, neutralized, washed with water and dried. The obtained reaction product had a degree of acetalization of 9.5 mol% and a viscosity of a 10 wt% isopropanol / water (4 parts by weight / 6 parts by weight) mixed solution was 19 mPa · s (20 ° C.). It was

Comparative Example 1 In the reaction of Example 1b) with butyraldehyde,
Not treated with sodium periodate as PVA. The same reaction as in Example 1, b) butyraldehyde was performed except that PVA having a polymerization degree of 500 and an oxidation degree of 99.3 mol% was used, followed by neutralization, washing with water, and drying. The degree of acetalization of the obtained reaction product was 64 mol%, 10% by weight of ethanol /
The viscosity of the mixed solution of toluene (1 part by weight / 1 part by weight) is 11
It was 0 mPa · s (20 ° C.).

Comparative Example 2 In the preparation of the low degree of polymerization PVA of Example 2 b), PV
After treating A with hydrogen peroxide and then subjecting it to the reaction with octyl aldehyde in b), which was not subjected to reduction treatment by adding sodium bisulfite, the reaction was carried out in the same manner as in Example 2, and The viscosity of the solution increased. The obtained reaction product was ethanol / toluene (1 part by weight / 1
(Parts by weight) When dissolved and used in the mixed solution, a large amount of insoluble matter was generated, so that the viscosity of the solution could not be measured.

[0021]

As is apparent from the above description, according to the present invention, a PVA having a polymerization degree that can be obtained at a low cost, such as a commercially available PVA, is treated with an appropriate oxidizing agent and subjected to a reduction treatment to obtain a desired product. By acetalizing PVA having a low degree of polymerization, a polyvinyl acetal resin having a desired low degree of polymerization can be industrially manufactured at low cost.

Claims (1)

[Claims] 1. A method for producing a polyvinyl acetal resin, characterized in that a main chain is cleaved with an oxidizing agent, and reduction treatment is carried out to reduce the degree of polymerization of polyvinyl alcohol with aldehydes.