JPH0118092B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing a highly expanded styrene-maleic anhydride copolymer resin foam.

In general, extrusion molding is an example of a method for manufacturing thermoplastic resin foam, in which a molten plasticized resin composition containing a blowing agent is extruded from a high pressure state into a normal pressure atmosphere, and the pressure changes A method is used to obtain a desired molded product by expanding it.

Polystyrene, polyethylene, and the like are well known as typical general-purpose thermoplastic resins used in such methods. In particular, polystyrene has a small temperature dependence of its melt viscosity and can be extruded at low temperatures, making it easy to select a blowing agent.At the same time, it is easy to obtain a viscosity suitable for foaming, so evaporative blowing agents are used. By using this, a highly foamed body can be formed relatively easily. As the blowing agent, inert gas such as carbon dioxide, nitrogen gas, helium gas, etc.; saturated aliphatic hydrocarbon having 8 or less carbon atoms such as methane, ethane, butane, etc.;
Saturated alicyclic hydrocarbons such as cyclohexane, ethylcyclopentane, etc.; aromatic hydrocarbons, such as benzene, xylene, etc.; ketones, such as acetone, methyl ethyl ketone, etc.; and petroleum ether.

Using an evaporative blowing agent requires expensive equipment to quantitatively introduce high-pressure gas from a cylinder into the extruder, and consideration must be given to the risk of explosion and poisoning due to leakage of blowing agent gas. is also necessary.

On the other hand, there is a decomposable foaming agent that requires little consideration for expensive equipment or dangers such as explosion and poisoning. Examples of inorganic decomposable blowing agents include sodium hydrogen carbonate, ammonium carbonate,
ammonium bicarbonate, sodium borohydride,
Examples include light metals (Mg, Zn, Al, etc.), and examples of organic decomposition foaming agents include azodicarbonamide, azobisformamide, isobutyronitrile, diazoaminobenzene, and N,N'-dinitrosopentamethylene. Tetramine, N,N'-dimethyl N,N'-dinitroterephthalamide, benzenesulfonyl hydrazide, p-toluenesulfonyl hydrazide, p,p'-oxybisbenzenesulfonyl hydrazide, etc. are used. However, with this method, bubbles are generated by the separation and association of gas dissolved in the resin, so it does not work to rapidly solidify the bubble membrane, and the permeability of the generated gas is high, so it is not easy to obtain highly foamed products. .

However, as a result of intensive research in order to obtain a highly foamed product without using an evaporative foaming agent, the present inventors found that styrene-maleic anhydride copolymer resin and group a metals of the periodic table and/or group a metals of the periodic table. Group metals (hereinafter both are also referred to as "alkali metals")
We have discovered that by extrusion molding a resin composition that has been dry-blended in advance with a carboxylic acid salt of , arrived at the present invention.

Specifically, the present invention uses 0.1% by weight to 0.1% by weight of an alkali metal carboxylate salt that has been powdered in advance.
10% by weight, more preferably 0.5% to 5% by weight, and 99.9% to 90% by weight of a styrene-maleic anhydride copolymer resin coated with a small amount of oil;
More preferably, 99.5% to 95% by weight of the styrene-maleic anhydride copolymer resin and the alkali metal carboxylic acid are dry blended and then melted and heated to obtain a foam by, for example, extrusion molding or injection molding. It is characterized by obtaining a highly foamed product by the foaming gas produced by the reaction with the acid salt.

Here, the styrene-maleic anhydride copolymer resin refers to a resin obtained by thermally polymerizing a styrene monomer and a maleic anhydride monomer in the presence of a chain transfer agent and a radical generator. For example, molar ratio 1.4-4.9 preferably 4.6-17.0
A styrene monomer/maleic anhydride monomer mixture, a known and commonly used radical generator and a chain transfer agent are added to a ketone solvent such as acetone or methyl isobutyl ketone, and heated to 60 to 180°C, preferably 75°C.
Thermal polymerization is carried out at a temperature of ~140°C. The resulting polymer is precipitated using a poor solvent such as petroleum benzene or methanol. It is also possible to use granules obtained by adding an antioxidant or the like as necessary and granulating them using an extruder or the like.

The alkali metals that form the alkali metal carboxylic acids mentioned above refer to group a metals and group a metals of the periodic table, and the former metals include lithium, sodium, or potassium, and the latter metals include magnesium, Calcium or strontium are typical, and representative examples of carboxylic acids include aliphatic monocarboxylic acids such as formic acid, acetic acid, propionic acid, butyric acid, caprylic acid, capric acid, lauric acid, stearic acid or myristic acid; Aliphatic saturated or unsaturated dicarboxylic acids such as oxalic acid, malonic acid, succinic acid, glutaric acid, maleic acid, fumaric acid or glutaconic acid; oxymonocarboxylic acids such as glycolic acid, lactic acid, ethylene lactic acid or glyceric acid; malic acid , oxypolycarboxylic acids such as tartaric acid or citric acid; or aromatic carboxylic acids such as benzoic acid or terephthalic acid.

These alkali metal carboxylates may be used alone or in combination with each other.

Among these alkali metal salts, those containing water of crystallization are particularly preferably used.

Next, the present invention will be specifically explained using examples.

Example 1 Styrene-maleic anhydride copolymer resin (maleic anhydride component 990g of 8% by weight) surface-coated with a small amount of oil, and sodium acetate (manufactured by Wako Pure Chemical Industries, Ltd.).
10g of Wako grade 1) was powdered and thoroughly blended. Next, this blend was passed through a 26 mmφ extruder (manufactured by Yamashiro Seiki Co., Ltd., L/D=14, compression ratio 2.2).
Extrusion molded. The extrusion conditions are die temperature:
The temperature was 125°C, C ₁ : 225°C, C ₂ : 180°C, and screw rotation speed: 40 rpm.

The extruded foam had a good skin layer on the surface and had fine cells with a particle size of 0.1 to 0.3 mm inside. Further, the foaming ratio of this foam was 9.8. Note that this expansion ratio was calculated according to the formula: expansion ratio = specific gravity of styrene-maleic anhydride copolymer resin/specific gravity of foam (the same applies to each example below).

Example 2 Styrene-maleic anhydride copolymer resin with MFR of 0.41 g/10 min (maleic anhydride component content
Extrusion molding was carried out in the same manner as in Example 1, except that the amount was changed to 15%).

The extruded foam had a good skin layer on the surface, fine cells with a particle size of 0.1 to 0.3 mm inside, and the expansion ratio of the foam was 14.

Example 3 Same as Example 1 except that 970 g of styrene-maleic anhydride copolymer resin with MFR of 0.41 g/10 minutes and 30 g of sodium oxalate (manufactured by Wako Pure Chemical Industries, Ltd., Wako Grade 1) were used. Extrusion molding was performed.

The extruded foam had a good skin layer on the surface, fine cells with a particle size of 0.2 to 0.5 mm inside, and the expansion ratio of the foam was 9.2.

Example 4 The amount of styrene-maleic anhydride copolymer resin
990g and replaced with sodium oxalate
The same procedure as in Example 3 was carried out except that 10 g of sodium lactate was used.

The extruded foam had a good skin layer on the surface, had fine cells with a particle size of 0.2 to 0.5 mm inside, and the expansion ratio of the foam was 8.5.

Example 5 Extrusion molding was carried out in the same manner as in Example 3, except that the same amount of sodium tartrate (manufactured by Wako Pure Chemical Industries, Ltd., Wako 1st grade) was used instead of sodium oxalate. It has a skin layer of 0.2
A foam with fine cells having a particle size of ~0.5 mm was obtained. The foaming ratio of this foam was 9.0.

Example 6 The same operation as in Example 4 was repeated except that the same amount of sodium benzoate (manufactured by Wako Pure Chemical Industries, Ltd., Wako Grade 1) was used instead of sodium lactate, and a good skin was obtained on the surface. Has a layer, 0.1~
A foam having fine cells with a particle size of 0.4 mm was obtained, and the expansion ratio of this foam was 8.3.

Example 7 The same operation as in Example 4 was repeated except that the same amount of magnesium acetate (Wako Pure Chemical Industries, Wako 1st grade) was used instead of sodium lactate, and a good skin layer was obtained on the surface. A foam with a foaming ratio of 13 times was obtained, which had fine bubbles with a diameter of 0.2 to 0.5 mm.

Example 8 The same operation as in Example 3 was repeated except that the same amount of calcium oxalate was used instead of sodium oxalate, and a good skin layer was formed on the surface and a thickness of 0.2 to 0.5 mm inside. A foam with a foaming ratio of 9.2 times and having bubbles with a fine diameter was obtained.

Comparative Example 1 Extrusion molding was carried out in the same manner as in Example 1, except that lead acetate (manufactured by Wako Pure Chemical Industries, Ltd., Wako Grade 1) was used.

The extruded foam had a good skin layer on the surface, relatively large-diameter cells inside, and the expansion ratio of the foam was 3.2.

Comparative Example 2 "Dick Styrene" with MFR of 1.6g/10min
Extrusion molding was carried out in the same manner as in Example 1, except that the material was changed to "XC-510" (manufactured by Dainippon Ink & Chemicals Co., Ltd., styrene resin).

The extruded foam had a rough surface, irregular internal foaming, and an expansion ratio of 1.5.

Claims (1)

[Claims] 1. When manufacturing a foam by foaming a melt-plasticized styrene-maleic anhydride copolymer resin, a group a metal and/or a carboxylic acid salt of a group a metal of the periodic table is used. and
A method for producing a highly expanded styrene-maleic anhydride copolymer resin foam.