JP2002069127A - Method for producing polyvinyl acetal resin - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for producing a polyvinyl acetal resin whereby the produced resin is difficult to coagulate. SOLUTION: In the method for producing the resin by the reaction of a polyvinyl alcohol resin and an aldehyde, it is characterized in that an acid having pH of 2 or more in 2% aqueous solution at 25 deg.C is used as a catalyst and the reaction temperature is 20 deg.C or more.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD The present invention relates to a method for producing a polyvinyl acetal resin.

[0002]

2. Description of the Related Art Polyvinyl acetal resins have a high affinity for inorganic materials, and are widely used for copper foil adhesives for printed circuits, safety glass interlayers, ceramic binders, etc. by utilizing their properties. As a production method, a polyvinyl alcohol as a raw material is uniformly dissolved in water, then an acid is added as a catalyst, and an aldehyde is further added to start an acetalization reaction. A typical example is a solvent method in which an acetalization reaction is started using an acid as a catalyst in a homogeneous system, and furthermore, a homogeneous method combining these methods is used. I have.

In the aqueous medium method, the polyvinyl acetal resin is gradually precipitated because the water solubility decreases as the acetalization reaction proceeds. However, when the precipitated particles are aggregated, the acid used as a catalyst is neutralized. There are problems such as insufficient removal of impurities such as alkali metal salts generated at the time, and difficulty in handling.

In order to suppress such agglomeration of precipitated particles, various reaction conditions have been improved so far, and a method using a surfactant in combination has been proposed. For example, JP
In JP-A-47795 and Patent No. 2980947, there is a description that an acetalization reaction is started while maintaining at 5 to 12 ° C. in the presence of an anionic surfactant such as sodium dodecylbenzenesulfonate and hydrochloric acid as a catalyst,
JP-A-59-81312 describes that a polyvinyl acetal having a uniform particle size is produced in the presence of a special modified nonionic surfactant and hydrochloric acid as a catalyst.

[0005] However, in the conventional aqueous medium method represented by these known examples, hydrochloric acid, which is a strong acid, is basically required as a catalyst, and the reaction is carried out in a low temperature range where a refrigerator at 20 ° C or lower is required. Unless started, it is impossible to sufficiently prevent the resulting particles from agglomeration or enlargement even when a surfactant is used in combination.

[0006]

DISCLOSURE OF THE INVENTION The present invention has been made in view of such prior art, and the use of a specific acid as a catalyst in a specific temperature range as a catalyst in an acetalization reaction makes it possible to produce particles. An object of the present invention is to provide a method for producing a polyvinyl acetal-based resin that is difficult to aggregate.

[0007]

That is, the present invention provides a reaction between a polyvinyl alcohol resin and an aldehyde,
In a method for producing a polyvinyl acetal resin,
A method for producing a polyvinyl acetal resin, wherein an acid whose pH of a 2% aqueous solution at 25 ° C. is 2 or more is used as a catalyst and a reaction temperature is 20 ° C. or more, wherein the acid used as a catalyst is A method for producing a polyvinyl acetal resin, which is an organic acid.

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION The production method of the present invention involves mixing a raw material polyvinyl alcohol resin with an aldehyde, and an acid as a catalyst, and then heating the mixture to cause an acetalization reaction to proceed to form particles. , Acid used as a catalyst, and temperature conditions.

The acid used as a catalyst in the present invention is 25 ° C.
A 2% aqueous solution having a pH of 2 or more is used, preferably in a range of 2.5 to 6, and more preferably in a range of 2.5 to 6.
A range of 4 is particularly preferred. If the pH is less than 2, the effect of the acid is too strong, and the particles of the polyvinyl acetal-based resin formed as the acetalization reaction proceeds tend to aggregate, which is not preferable. When the pH is high, the effect as a catalyst is poor.

The type of the acid used as a catalyst in the present invention is not particularly limited, but is a so-called weak acid type, for example, citric acid, glyoxylic acid, malic acid, succinic acid, gluconic acid, ascorbic acid, tartaric acid, lactic acid, mandelic acid. , Carbonic acid and the like. Among them, organic acids are preferable in that they are easy to control the reaction and hardly cause a change such as coloring when remaining in the resin.

The amount of the acid used as a catalyst in the present invention is preferably 0.1 to 30% by mass, more preferably 1 to 1% by mass, based on the starting polyvinyl alcohol resin.
5% by mass.

The reaction temperature during the acetalization reaction according to the production method of the present invention is at least 20 ° C., preferably at least 25 ° C.
Particularly preferably, it is 30 ° C. or higher. If the reaction temperature is lower than 20 ° C., the progress of the acetalization reaction is slow, which is not preferable. The upper limit of the reaction temperature is not particularly limited, but is preferably 200 ° C. or lower, particularly preferably 150 ° C. or lower for controlling side reactions.

The raw material polyvinyl alcohol resin used in the present invention is not particularly limited, but a vinyl alcohol-vinyl acetate copolymer obtained by partially saponifying polyvinyl acetate is preferable. In particular, the saponification rate is 80-99.5.
Molar% vinyl alcohol-vinyl acetate copolymer is preferred. The average degree of polymerization of the vinyl alcohol-vinyl acetate copolymer is 50 to 5,000, particularly 100 to 400.
0 is preferred.

The aldehyde to be reacted with the polyvinyl alcohol polymer in the present invention includes aliphatic aldehydes such as acetaldehyde, propionaldehyde, n-butyraldehyde, isobutyraldehyde, pentylaldehyde, n-hexylaldehyde, cyclohexylaldehyde and octylaldehyde. And aromatic aldehydes such as benzaldehyde, benzyl aldehyde and naphthyl aldehyde.

In the present invention, besides the above-mentioned aldehydes, ketones having a functional group such as glyoxylic acid and diacetone alcohol can be used, and if necessary, a surfactant may be used. Can also be used in combination.

After the acetalization reaction, a dry powder is obtained through filtration, washing and drying steps. Further, it is also possible to neutralize the acid used as a catalyst, if necessary.

According to the present invention, at a particle size suitable for workability,
In addition, a polyvinyl acetal resin having good properties such as solubility and adhesiveness can be produced.

[0018]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below with reference to embodiments.
Unless otherwise specified, “parts” and “%” represent parts by mass and% by mass, respectively. (Example 1) 40 ion-exchanged water was placed in a vessel equipped with a stirrer.
0 parts, and charged with a polyvinyl alcohol resin (degree of polymerization 17).
100 parts of vinyl alcohol (98.0%, vinyl acetate 2.0%) were added with stirring. Thereafter, the internal temperature was raised from room temperature to 90 ° C., and the polyvinyl alcohol resin was dissolved over 2 hours while maintaining the temperature at 90 ° C. After cooling this aqueous solution to 50 ° C., a citric acid for industrial use [Iwata Chemical, 2% aqueous solution pH at 25 ° C.] was used as a catalyst.
= 2.2] and uniformly mixed at 50 ° C. for 30 minutes. Then, while maintaining the internal temperature at 50 ° C., 53 parts of butyl aldehyde was added dropwise, and the mixture was stirred for 3 hours. As a result, white polyvinyl butyral resin powder was precipitated. After cooling to room temperature, the mixture was neutralized with sodium hydrogen carbonate, and the resulting resin was filtered, washed with water, and dried to obtain a granular polyvinyl acetal resin.

When the obtained polyvinyl acetal resin was analyzed, 21.0% of vinyl alcohol units, 1.5% of vinyl acetate units and 7% of vinyl butyral units were obtained.
7.5%, and the average particle size was 250 μm. Further, 5% in a mixed solvent of an equal amount of ethanol / toluene
The solution viscosity at the resin concentration was 55 mPa · s (20 ° C.), and the transparency of the solution was 40 cm or more.

The composition of the polyvinyl acetal resin was analyzed by 1H-NMR, and the average particle size was determined by a standard sieve (JIS Z).
8801), and the solution viscosity is measured using a B-type viscometer.
Solution transparency was measured by the Nessler tube method (JIS K 6728). The pH value was measured with a glass electrode type hydrogen ion concentration meter (HM-5ES, manufactured by Toa Denpa Kogyo KK).

(Examples 2 and 3, Comparative Examples 1 and 2) A polyvinyl acetal resin was produced in the same manner as in Example 1 except that the kind of acid used as the catalyst and the reaction temperature were changed, and the characteristics were evaluated. went. The production conditions are shown in Table 1, and the physical property evaluation results are shown in Table 2.

[0022]

[Table 1]

[0023]

[Table 2]

[0024]

The polyvinyl acetal resin obtained by the production method of the present invention is not a fine powder but a granular powder, so that it is excellent in handleability at the time of dissolving work and transparency of the solution. Are good.

Claims (2)

[Claims] 1. A method for producing a polyvinyl acetal resin by reacting a polyvinyl alcohol resin with an aldehyde, wherein an acid having a pH of 2 or more at 25 ° C. in a 2% aqueous solution is used as a catalyst, and the reaction temperature is Is 2
Method for producing polyvinyl acetal resin characterized by being at least 0 ° C. 2. The method for producing a polyvinyl acetal resin according to claim 1, wherein the acid used as the catalyst is an organic acid.