JPH0542463B2 - - Google Patents

Description

[Detailed description of the invention]

[Technical Field of the Invention] The present invention relates to a phenolic resin molding material that allows molded products with a small shrinkage rate to be obtained and has excellent moisture resistance. [Technical background of the invention and its problems] Conventionally, phenolic resin molding materials containing phenolic resin as a main component have been widely applied to electrical and mechanical parts due to their excellent electrical and mechanical properties. In addition, general-purpose phenolic resin molding materials filled with wood flour and pulp base materials have been widely used because of their low cost, moldability, and weight reduction. However, since such general-purpose phenolic resin molding materials use wood flour, pulp, etc., the shrinkage rate during molding, the heat shrinkage rate of molded products, and the water absorption of molded products are large, making it difficult to use them for electrical and mechanical parts. In many cases, its use was impossible, especially in applications involving precision parts. Therefore, methods for reducing the shrinkage rate of molded products using low-density phenolic resin molding materials include (a) reducing the usual resin/filler (wood flour, pulp) ratio; (b) wood flour, There was a method of filling inorganic hollow bodies (shirasu balloons, glass balloons) instead of pulp fillers. In the case of (a), although the specific gravity and shrinkage are low, the fluidity of the material is reduced, moldability is deteriorated, and moisture resistance (water absorption resistance) is reduced. Again (b)
In the case of , it has a lower specific gravity than ordinary inorganic fillers,
Although the shrinkage is low, there is a limit beyond which the moldability, electrical properties, and mechanical strength are significantly reduced. [Object of the Invention] The object of the present invention was made in view of the above-mentioned drawbacks, and it is an object of the present invention to reduce the shrinkage rate during molding and of molded products,
The present invention also aims to provide a low specific gravity phenolic resin molding material that has excellent moisture resistance. [Summary of the Invention] As a result of intensive research to achieve the above object, the present invention provides that a phenolic resin molding material with low shrinkage, moisture resistance, and low specific gravity can be obtained by filling with polyvinyl acetal resin. This is what we discovered. That is, the present invention comprises (A) a phenolic resin, and (B) a general formula A polyvinyl acetal resin represented by
This is a phenolic resin molding material characterized by containing the following. The phenolic resin (A) used in the present invention includes phenols such as phenol and cresol, or phenols modified with molasses, lignin, xylene, naphthalene, and petroleum aromatic hydrocarbons, and formalin or paraformaldehyde as appropriate. Novolak-type phenolic resin condensates, resol-type phenolic resin condensates, or resol-type phenolic resin condensates and novolak-type phenolic resin condensates obtained by blending them in a molar ratio and reacting them under a catalyst, etc. Used alone or in combination. Examples of the polyvinyl acetal resin (B) used in the present invention include polyvinyl formal resin, polyvinyl acetal resin, polyvinyl butyral resin, etc., and these resins may be used alone or as a mixture of two or more thereof. The softening point of the polyvinyl acetal resin is preferably similar to that of the phenol resin used in combination, for example, in the case of polyvinyl butyral resin, the average degree of polymerization is preferably about 200 to 400. It is also assumed that polyvinyl acetal resin has good compatibility with phenolic resin and imparts the dimensional stability and moisture resistance of the resin to the molding material, resulting in low shrinkage and excellent moisture resistance. The blending ratio of the polyvinyl acetal resin is preferably 0.1 to 30% by weight based on the molding material. If the amount is less than 0.1% by weight, the shrinkage will be low.
It has no effect on moisture resistance, and its content is 30% by weight.
If it exceeds this value, the moldability and curing properties deteriorate, making it unsuitable for practical use. A more preferable blending ratio is in the range of 3 to 20% by weight. The phenolic resin molding material of the present invention is characterized by containing (A) a phenolic resin and (B) a polyvinyl acetal resin, but in addition to these, wood flour, pulp, a hardening agent, a coloring agent, curing accelerator,
Flame retardants, mold release agents, lubricants, coupling agents, plasticizers, etc. can be added. The phenolic resin molding material of the present invention is usually produced as follows. First, a predetermined amount of phenolic resin, polyvinyl acetal resin, wood flour, and other additives as necessary are mixed and dispersed uniformly, then heated and kneaded in a kneader, then cooled and solidified, and then crushed into appropriate sizes by a pulverizer. Pulverize to produce phenolic resin molding material. The phenolic resin molding material thus obtained can be widely used as electrical parts and mechanical parts. [Effects of the Invention] The phenolic resin molding material of the present invention has a low shrinkage rate during molding and molded products despite its low specific gravity, and is a molding material with excellent moisture resistance.
It is particularly suitable for use in precision molded parts. [Examples of the Invention] Next, the present invention will be specifically explained using Examples, but the present invention is not limited by the Examples. In the following Examples and Comparative Examples, "%" means "% by weight". Example 1 40% novolac type phenolic resin, 5% polyvinyl butyral resin, 35% wood flour, 8% hexamethylenetetramine, and 12% other additives were mixed at room temperature, then kneaded at 90°C to 110°C and cooled. rear,
It was pulverized to produce a phenolic resin molding material. This molding material was injection molded into a mold heated to 170°C and cured to form a molded product. The molding shrinkage rate, specific gravity, and water absorption rate of the obtained molded product are determined according to JIS standards.
-Test was conducted according to K-6911. These results are shown in Table 1. Comparative example Novolac type phenolic resin 45%, wood flour 35%,
Hexamethylenetetramine 8%, other additives 12
% was operated in the same manner as in the examples to produce a phenolic resin molding material. Next, a molded article was made using this molding material in the same manner as in the example, and molding shrinkage, specific gravity, and water absorption were tested in the same manner. These results are shown in Table 1.

[Table] As is clear from Table 1, it can be seen that the phenolic resin molding material of the present invention has excellent molding shrinkage and water absorption.

Claims (1)

[Claims] 1 (A) phenolic resin, (B) general formula A polyvinyl acetal resin represented by
A phenolic resin molding material characterized by containing the following. 2. The phenolic resin molding material according to claim 1, wherein the polyvinyl acetal resin is contained in an amount of 0.1 to 30% by weight based on the molding material.