JPS6126575B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a foamable thermoplastic resin composition, and more particularly to a novel foamable resin composition that makes it possible to provide a thermoplastic resin molded article with a high expansion ratio. Conventionally, foam molding of thermoplastic resins uses chemical blowing agents, physical blowing agents, etc.
Various types of resins are used, and each is selected depending on the purpose of the thermoplastic resin, processing and molding conditions, etc. In the case of thermoplastic resins such as polypropylene and nylon, which show a sudden drop in viscosity when heated and melted during processing, it is difficult to incorporate and retain foam in the resin, making it difficult to create uniform molded products with a high expansion ratio. difficult to obtain. In particular, in the case of thermally decomposable blowing agents such as azodicarbonamide and oxybisbenzenesulfonyl hydrazide, which are widely used chemical blowing agents, the decomposition reaction involves heat generation, so it is necessary to mold products with a higher expansion ratio. making it difficult. As one of the countermeasures against this problem, a proposal to use alkoxymethylurea as a blowing agent is known. This is because no heat is generated during the main decomposition reaction, so when used, for example, in extrusion foam molding where polypropylene is the main component, temperature control is easy and it is easy to obtain molded products with a foaming rate that is more than twice as large. be. However, since alkoxymethylurea has a low decomposition temperature, when used for high melting point thermoplastic resins, the thermal decomposition reaction begins before the resin plasticizes, resulting in the generated gas escaping before it dissolves into the molten resin. , the blowing agent is likely to be wasted. The present inventors have spent many years searching and studying a blowing agent that overcomes these difficulties and has advantages similar to those of alkoxymethylurea, and as a result, they have arrived at the present invention. The present invention is a foamable thermoplastic resin composition characterized in that 0.1 to 10 parts by weight of one or more alkoxymethylmelamines having the structural formula () are added to 100 parts by weight of the thermoplastic resin. Here, ^R1 to ^{R5 are} -H or _-CH2 - ^OR7R6 , ^R7 is -H or a _C1-4 alkyl group. Like alkoxymethyl urea, the blowing agent used in the present invention, alkoxymethyl melamine, generates little heat during the main decomposition reaction, and its decomposition temperature is 250°C.
Since the decomposition temperature is extremely high for a thermally decomposable foaming agent, it is suitable for foam molding of thermoplastic resins such as polycarbonate, where the applicable molding temperature is around this temperature. Furthermore, the blowing agent according to the present invention can lower the decomposition start temperature by coexisting with an acidic catalyst that exhibits acidity near the application temperature during molding, such as para-toluenesulfonic acid.
By increasing or decreasing the amount of this catalyst added, the decomposition start temperature can be adjusted as in Examples 2 to 4 to be described later, and can be adapted to the molding temperature of various thermoplastic resin compositions such as polyolefin. The thermoplastic resins used in the composition of the present invention include various thermoplastic resins such as homopolymers and copolymers such as polyethylene, polypropylene, polyamide, polycarbonate, polyacetal, and polyphenylene oxide, and mixtures of two or more thereof. It may also contain fillers such as calcium carbonate, talc, asbestos, silica, etc. as appropriate. Examples of blowing agents according to the present invention include methoxymethyl, ethoxymethyl, propoxymethyl, isopropoxymethyl, butoxymethyl of melamine,
isobutoxymethyl, sec-butoxymethyl,
Examples include mono-, di-, tri-, tetra-, penta-, and hexa-substituted tert-butoxymethyl,
Trimethoxymethylmelamine, hexamethoxymethylmelamine, etc. are generally easily available on the market. Generally, commercially available alkoxymethylmelamine is often a mixture of substances with similar numbers of functional groups, and may also contain condensed oligomers as impurities, but it can be used for the purpose of the present invention. No problem. The blending ratio of alkoxymethyl melamine is 0.1 to 10 parts by weight per 100 parts by weight of the thermoplastic resin. If it is less than 0.1 part by weight, the foaming effect is small, and it is hardly effective for reducing the weight of the thermoplastic resin or preventing sink marks during molding. It's pretty useless. If the amount is 10 parts by weight or more, the cells of the foam to be molded become interconnected, resulting in so-called open-cell foam, which causes foaming gas to escape from the foam, which is undesirable because the expansion ratio is reduced. The acidic catalyst that accelerates the decomposition of alkoxymethyl melamine at high temperatures may be any catalyst that exhibits acidity at the molding temperature of the thermoplastic composition, that is, any catalyst that provides protons to alkoxymethyl melamine at high temperatures. Specifically, various typical inorganic acids and organic acids (carboxylic acids, sulfonic acids)
In addition to those that are acidic even at room temperature, such as acidic salts such as acidic sodium sulfate, there are latent catalysts that are close to neutral at room temperature but become acidic due to thermal decomposition or the like when heated. Latent catalysts include carboxylic acid esters such as oxalic acid dimethyl ester, acid anhydrides such as maleic anhydride, organic halides such as monochloroacetic acid sodium salt, and amines such as triethanolamine hydrochloride. There are hydrochlorides, etc.
In addition to the above, as a latent catalyst, when heated and pressurized,
There are ammonium salts and urea derivatives such as ammonium chloride and ammonium sulfate that act as catalysts to liberate acidic substances by reaction with formaldehyde generated from alkoxymethylmelamine and methylol groups contained in decomposition residues. Generally, as the acidic catalyst used in the present invention, when the foamable resin composition needs to be stored after being blended, it is preferable to use a latent catalyst in order to suppress decomposition of alkoxymethylmelamine during storage. No special operations are required when formulating the foamable thermoplastic resin composition according to the present invention, and it is usually a viscous liquid at room temperature. The alkoxymethyl melamine may be simply mixed directly with the other components of the composition (mainly the base resin), or it may be mixed and kneaded with other low melting point thermoplastic resins to form master pellets and then foam molded. It may be mixed with the base resin for use. When mixing liquid alkoxymethyl melamine with the base resin, due to the viscous nature of alkoxymethyl melamine, it is necessary to minimize raw material loss and fluctuations in the blending ratio due to adhesion to the walls of the blender. In terms of the procedure for feeding raw materials into the machine, it is preferable to feed solids (pellets or powder) first and liquid alkoxymethylmelamine later.
The compounding machine is a commonly used Henschel mixer,
A ribbon blender, drum blender, etc. may be used, but in consideration of homogeneous dispersion, one capable of high rotational stirring such as a Henschel mixer is preferable. The present invention will be explained below with reference to Examples. Example 1 To 100 parts by weight of polycarbonate (medium viscosity grade), 2 parts by weight of Cymel 303 (trade name: hexamethoxymethyl melamine is the main component; raw material for paint manufactured by Mitsui Toatsu Chemical Co., Ltd.) and 1.4 parts by weight of hydrated silica were added. Mixed with a mixer. A 40 m/mφ extruder with L/D=22 and a compression ratio of 2.4 was equipped with a fishtail die having a lip length of 150 m/m and a lip gap of 2 m/m, and the above compounded composition was extruded and foamed at an extrusion resin temperature of 270°C. The obtained sheet has a smooth surface and an apparent specific gravity of
It was 0.4. Comparative Example 1 When the same extrusion molding as in Example 1 was carried out using a composition in which 2 parts by weight of azodicarbonamide was added instead of Cymel 303, the sheet hardly foamed and the apparent specific gravity was 1.1. Examples 2 to 4 Compositions as shown in Table 1 were prepared and extrusion foam molded using the extruder used in Example 1.

[Table] As shown in the apparent specific gravity of the extrusion test results in Table 1, the expansion ratio varies depending on the amount of acidic catalyst added to the foamable resin composition. This is because the decomposition temperature of the blowing agent changes depending on the amount of acidic catalyst added. In Example 2, the decomposition temperature was too high and a sufficient amount of gas generation could not be obtained, and in order to increase the amount of gas generation, high temperature extrusion was performed. If this is done, the melt tension of the resin composition decreases, the generated gas cannot be retained in the molten composition, and the expansion ratio decreases. on the other hand,
In Example 4, since the blowing agent starts to decompose below the melting point of the resin composition, the generated gas escapes before being incorporated into the molten composition, and a decrease in the foaming ratio was also observed. On the other hand, in Example 3, the decomposition temperature of the blowing agent matched the melting behavior of the resin composition, and a sheet with a practical high expansion ratio was obtained. As is clear from Examples 2 to 4, there is one suitable blowing agent decomposition temperature for one resin composition, and the suitable temperature differs depending on the type of resin and composition ratio. The blowing agent according to the present invention is extremely advantageous because the decomposition temperature can be finely adjusted by adjusting the amount of acidic catalyst added.

Claims (1)

[Claims] 1. Structural formula for 100 parts by weight of thermoplastic resin (In the formula, R ¹ to R ⁵ are each independently hydrogen, −CH ₂
-O- ^R7 , and ^R6 and ^R7 each independently represent hydrogen or a _C1-4 alkyl group. ) Foamable thermoplastic resin composition 2, characterized in that the foamable thermoplastic resin composition contains 0.1 to 10 parts by weight of one or more alkoxymethylmelamines represented by The foamable thermoplastic resin composition according to claim 1, which contains an acidic catalyst that promotes decomposition at high temperatures.