JPS6056744B2 - Styrenic resin composition - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a styrenic resin composition that exhibits good mold release properties during molding.

When molding resin by injection molding, injection blow molding, extrusion molding, compression molding, or other molding methods, the molded product may stick to the mold or become difficult to separate from the mold, resulting in decreased productivity and damage to the molded product. Various problems may occur, including deformation or destruction of the material.

Problems caused by mold defects like this are particularly likely to occur when molding products that require high dimensional accuracy or have complex shapes, and can sometimes be caused by selecting appropriate molding conditions. Although it may be possible to solve the problem, it is usually difficult to solve the problem simply by changing the molding conditions, and even if the problem can be solved, the time required for the molding cycle becomes longer and productivity decreases. Therefore, as a means to solve this problem of female mold defects, generally, a mold release agent is applied to the mold, etc., or a mold release agent is added to the resin in advance to improve the mold releasability of the resin. As mold release agents used for this purpose, higher fatty acids, metal salts of higher fatty acids, polyoxypropylene glycols, silicone oil, etc. are known.

However, when blending such a mold release agent into a resin to improve the mold release agent of the resin, it is preferable to blend a large amount of the mold release agent from the perspective of improving mold release properties, but on the other hand, Adding a large amount of mold release agent is economically disadvantageous, and it also deteriorates the thermal stability of the resin composition, resulting in poor appearance such as coloring of the surface of the molded product, and even lowering the heat distortion temperature of the molded product. Another problem arises, such as a decrease in

Styrenic resins are no exception to this, and they have excellent moldability that is suitable for molding products with particularly high dimensional accuracy and complex shapes.
There has been a demand for the development of a styrenic resin composition that does not have the above-mentioned problems.

In view of this point of view, the present inventors have conducted extensive research on styrene resin compositions with good mold release properties, and have found (2
) higher fatty acid and/or its metal salt 0.02-2, moderate %; and (B) low molecular weight polyethylene 0.02-2. By using a seed amount% (however, the sum of (4) and (B) is 0.1 to [mass]%), not only is the mold release property good, but also the main styrene resin The present invention was achieved based on the discovery that the thermal stability and other physical properties such as mechanical strength are not impaired. Higher fatty acids and/or metal salts thereof are known per se as excellent mold release agents, but one or more of these higher fatty acids and/or metal salts thereof and one or more low molecular weight polyethylenes are used. It is not known to use more than one species in combination, and the object of the present invention can be achieved by using both in combination.

In the present invention, styrenic resins include polymers obtained by individually polymerizing styrene monomers such as styrene, methylstyrene, and chlorostyrene, such as polystyrene, polymethylstyrene, and polychlorostyrene. In addition to coalescence, copolymers of these styrenic monomers and other monomers, elastomers, etc. that can be copolymerized with these styrenic monomers are included.

Other monomers that can be copolymerized with styrenic monomers include:
For example, acrylonitriles such as acrylonitrile and methacrinitrile, unsaturated carboxylic acids such as acrylic acid and methacrylic acid, unsaturated carboxylic acid esters such as methyl acrylate and methyl methacrylate, dienes such as chloroprene, butadiene, and isoprene, 1- Examples include olefins such as butene and 1-pentene, and α,β monounsaturated carboxylic acids such as maleic anhydride and their anhydrides. Elastomers that can be copolymerized with styrene monomers include polydiene rubbers such as butadiene rubber, chloroprene rubber, and isoprene rubber, styrene-diene elastomers such as styrene-butadiene rubber, and molecules such as styrene-butadiene-styrene rubber. Examples include block copolymer elastomers having polydiene blocks in their structure. Furthermore, the styrenic resin also includes a resin mixture formed mainly of the above-mentioned various styrene 7 resins and blended with other resins. These styrenic resins can be produced by various polymerization methods such as bulk polymerization, solution polymerization, emulsion polymerization, suspension polymerization, or bulk-suspension polymerization. , antioxidants, ultraviolet absorbers, heat stabilizers, colorants, and other commonly used additives may be appropriately contained.

Further, the higher fatty acids used in the present invention are linear saturated monocarboxylic acids having about 12 to n carbon atoms, such as lauric acid, myristic acid, palmitic acid, margaric acid, stearic acid, arachidic acid, and behenin. Examples include acids.

Further, the metal salt of a higher fatty acid is a salt of the above-mentioned higher fatty acid with a metal such as lithium, potassium, sodium, calcium, aluminum, magnesium, barium, or zinc. The higher fatty acid is typically stearic acid, and the higher fatty acid metal salts are typically calcium stearate, magnesium stearate, zinc stearate, and the like. These higher fatty acids and/or metal salts can be used alone or in combination with
It is also possible to use a combination of two or more types, or to use one or more selected higher fatty acids and metal salts thereof in combination.

From the viewpoint of influence on mold releasability and physical properties, magnesium salts, calcium salts, and zinc salts of higher fatty acids are particularly preferred. The low molecular weight polyethylene used in combination with the higher fatty acid and/or its metal salt is one that is linear or branched and has a molecular weight in the range of about 1,000 to 20,0(1). In particular, the branching is small and the density is 0.97~
0.97 and a molecular weight of 5,000 to 10,000 is particularly preferred.

This is because if the molecular weight is less than 1,000, there is a tendency for heat resistance to decrease and bleed out.
This is because when the value exceeds 0,000, the strength tends to decrease. (4) The total amount of higher fatty acid and/or its metal salt and (B) low molecular weight polyethylene blended into the styrene resin is 0.1 to 3. Within the range of slag weight%, preferably 0.25 to 2. The amount of rutting is within the range of %, and the amount of each of higher fatty acid and/or its metal salt and low molecular weight polyethylene is 0.02%.
~2.4% by weight, preferably 0.1-1% by weight
is within the range of

If the total amount used is less than 0.1% by weight, the mold releasability of the styrenic resin composition will be insufficiently improved; If the amount is more than % by weight, it is not preferable because it causes a decrease in the physical properties of the resin, especially impact resistance and heat resistance, and has an adverse effect on the processing of the molded product after molding, such as printing and hot stamping. In addition, the amounts of higher fatty acids and/or their metal salts and low molecular weight polyethylene to be used will vary depending on the type of styrene resin, but if they are outside the range of 0.02 to 2.4% by weight, both will be used. The synergistic effect of using them together will be diminished. The above-mentioned higher fatty acid and/or its metal salt and low molecular weight polyethylene may be separately blended into the styrenic resin, or they may be mixed in advance at a certain ratio and then blended.

These can be blended into the styrene resin by using an ordinary extruder or roll, or by adhering them to the surface of the styrene resin in the form of powder or pellets. . Furthermore, as a blending method, it is possible to mix it into the monomer solution when polymerizing the styrene resin, or to mix it during the polymerization or at the final stage of the polymerization.
Although no absolute method has been established to evaluate the mold releasability of styrenic resin compositions containing higher fatty acids and/or their metal salts and low molecular weight polyethylene, Since mold release characteristics depend on the pressure during injection, it can be evaluated based on the maximum injection pressure at which the molded product can be released from the mold without any problems in practice.

In other words, the higher the injection pressure when injecting the resin into the mold, the better the molded product can be obtained, but on the other hand, the adhesion of the resin to the mold improves, and the mold release property of the molded product increases rapidly. Therefore, it can be judged that the higher the injection pressure can be used for molding, the better the mold releasability of the resin will be. This becomes even clearer if one observes the release of the molded product from the mold during molding. According to the present invention, when a conventionally known higher fatty acid and/or its metal salt is used alone as a mold release agent, when low molecular weight polyethylene is used alone, or when a higher fatty acid and polypropylene glycol are used in combination In addition to significantly improving the mold releasability compared to other molded products, there is no problem of lowering the heat distortion temperature, lowering mechanical strength, or deteriorating the appearance of the molded product.

Hereinafter, the present invention will be specifically explained based on Examples and Comparative Examples.

Examples 1 to 2 and Comparative Examples 1 to 5 The first
A mold release agent was mixed in the proportions (parts by weight) shown in the table, and the mixture was kneaded in an extruder and made into pellets.

Claims (1)

[Scope of Claims] 1 Mainly composed of styrene resin, (A) 0.02 to 2.4% by weight of higher fatty acids and/or metal salts thereof, and (B) 0.02 to 2.4% by weight of low molecular weight polyethylene. (however,(
A styrenic resin composition characterized in that the total content of A) and (B) is 0.1 to 3.0% by weight. 2. The styrenic resin composition according to claim 1, wherein the styrenic resin is a rubber-modified styrenic resin.