JPS6355539B2 - - Google Patents

Description

[Detailed description of the invention]

(Industrial Application Field) The present invention relates to a thermoplastic resin composition having electromagnetic shielding properties. (Prior art) With the rapid development of electronic devices, digital electronic devices such as microcomputers and word processors have become widespread and are being used in these devices.
There is a problem of electromagnetic interference caused by electromagnetic waves generated from ICs, LSIs, etc. that affect peripheral devices. Furthermore, as equipment becomes smaller and more mass-produced, plastic molded products are being used as housings for various electronic devices, so there is a need for effective electromagnetic shielding technology for plastics. A conventional method for shielding plastic molded products is to form a conductive layer on the surface of the molded product. These are methods that give shielding properties to plastic by applying, for example, zinc spraying, sputtering, plating, vacuum deposition, conductive paint coating, etc. to the surface of plastic molded products ("Industrial Materials" Vol. 30, No. 10). pp. 17-24, published by Nikkan Kogyo Shimbun, 1982). (Problems to be Solved by the Invention) In all of these methods, after the molded product is molded, various surface treatments are performed and then secondary processing is performed, resulting in poor productivity and secondary processing. There are drawbacks such as the need for equipment for subsequent processing. Also,
When used for a long period of time, the electrically conductive layer on the surface may peel off, resulting in poor durability and reliability. On the other hand, as another method for imparting shielding properties to plastic molded articles, a method of mixing conductive additives into the molded articles is also used. but,
If a large amount of conductive additive is not mixed, a sufficient shielding effect cannot be obtained. Furthermore, when a large amount of conductive additives are mixed in, the mechanical properties tend to deteriorate significantly. The present invention solves these problems. (Means for Solving the Problems) The present invention provides: (A) 15 to 60% by weight of a rubbery polymer, which is an acrylic acid alkyl ester polymer, and at least an aromatic vinyl compound, a vinyl cyanide compound, and a methacrylic acid ester. Contains a thermoplastic resin obtained by graft polymerizing 85 to 40% by weight of a type of monomer and (B) brass fiber, and the (A) component and (B) component are 95/95/(B). 5
It relates to a thermoplastic resin composition that is blended so that the ratio is ~50/50 (volume ratio). Component (A) of the present invention is obtained by graft polymerizing an aromatic vinyl compound, a vinyl cyanide compound, or a methacrylic acid ester to a rubbery polymer that is an acrylic acid alkyl ester polymer. The monomer used in the production of the acrylic acid alkyl ester polymer that becomes the rubber component is acrylic acid-
Ethyl acrylate, propyl acrylate, hexyl acrylate, although n-butyl is particularly suitable.
1 or more carbon atoms such as 2-ethylhexyl acrylate
All those having 13 alkyl groups can be used alone or in combination. Further, this acrylic acid alkyl ester polymer must be a cross-linked polymer; if a non-cross-linked one is used, only a molded product with low impact resistance will be obtained. To introduce crosslinking into this acrylic acid alkyl ester polymer, there are a method of crosslinking with an organic peroxide and a method of copolymerizing a polyfunctional monomer. The polyfunctional monomer is a monomer having two or more functional groups that can be copolymerized with an acrylic acid alkyl ester, and by copolymerizing this, an acrylic rubber with excellent rubber elasticity can be obtained. As this polyfunctional monomer, polyvalent vinyl compounds and polyvalent acrylic compounds such as triallyl isocyanurate, triallyl cyanurate, divinylbenzene, triacryl formal, and ethylene glycol dimethacrylate are effective, but among these, in particular, Triallyl isocyanurate and triallyl cyanurate are the best. The amount of this polyfunctional monomer added is suitably 0.1 to 10% by weight, particularly preferably 0.5 to 5% by weight, based on the total monomers. If it is less than 0.1% by weight, a sufficient degree of crosslinking cannot be obtained, and if it exceeds 10% by weight, the degree of crosslinking is excessive, and in either case, sufficient impact resistance cannot be imparted. Further, the acrylic acid alkyl ester polymer may contain other components such as styrene and acrylonitrile, as long as the acrylic acid alkyl ester component is contained in an amount of 50% by weight or more. The monomer to be graft-polymerized to the above rubbery polymer includes styrene as an aromatic vinyl compound;
There are α-methylstyrene, vinyltoluene, chlorostyrene, t-butylstyrene, etc., vinyl cyanide compounds include acrylonitrile, methacrylonitrile, etc., and methacrylic acid esters include methyl methacrylate, ethyl methacrylate, n-butyl methacrylate. , t-butyl methacrylate, 2-ethylhexyl methacrylate, and the like. In particular, styrene is effective as an aromatic vinyl compound, and acrylonitrile is effective as a vinyl cyanide compound. The composition of the monomers to be grafted is such that the aromatic vinyl compound is 100% by weight or less, preferably 60 to 80% by weight, and the cyanide vinyl compound is 40% by weight or less, preferably 20 to 40% by weight or less.
Weight percent is preferred. Also, methacrylic acid ester
It is preferable that the amount is 100% by weight or less and the total amount is 100% by weight. When producing the thermoplastic resin of component (A), the above rubbery polymer is used in an amount of 15 to 60% by weight. Especially 20
Preferably ~60% by weight is used. If it is less than 15% by weight, sufficient impact resistance will not be obtained, and if it exceeds 60% by weight, rigidity and fluidity will decrease. The polymerization method for producing the above-mentioned acrylic acid alkyl ester polymer and the graft polymerization method for producing the thermoplastic resin of component (A) are not particularly limited and may be produced by known methods. For example, an acrylic acid alkyl ester polymer can be produced by emulsion polymerization, and a thermoplastic resin as component (A) can be produced by emulsion polymerization by adding a graft monomer to a rubbery polymer latex. In this case, as a polymerization catalyst, use a common water-soluble polymerization initiator such as potassium persulfate, ammonium persulfate, or hydrogen peroxide, or a polymerization catalyst that forms a redox system such as a combination of kyumene hydroperoxide and Rongalit. I can do it. As the emulsifier for emulsion polymerization, any of anionic surfactants, cationic surfactants, and nonionic surfactants may be used. As the brass fiber of component (B) used in the present invention, short brass fibers are used, and the length is 1 to 12
The thickness is preferably 2 mm to 4 mm. When the length is less than 1 mm, sufficient shielding properties tend not to be obtained, and when it exceeds 12 mm, it tends to be difficult to uniformly knead the brass fiber and thermoplastic resin.
The thickness of the brass fiber is preferably 10 to 200 microns.
In particular, 20 to 120 microns is preferred. As the brass, ordinary 6-4 brass, 7-3 brass, etc. are used. As the brass fibers, short fibers produced by a chatter vibration cutting method are preferred. In the present invention, the ratio of the thermoplastic resin as the component (A) and the brass fiber as the component (B) is 95/5 to 95/5 in terms of volume ratio (A)/(B).
The range is 50/50, particularly preferably 90/10 to 70/30. If the ratio of component (B) is less than 5% by volume, the shielding effect will be reduced, and if it exceeds 50% by volume, uniform kneading with the thermoplastic resin will be difficult and impact resistance will also be reduced. In the present invention, components (A) and (B) can be mixed by a method in which they are mixed in a commonly used tumbler, Henschel mixer, etc., and then kneaded in an extruder, etc. Alternatively, a method of kneading with a kneader, roll, Banbury mixer, etc. can also be used. The thermoplastic resin composition according to the present invention includes pigments,
Known additives such as plasticizers and various stabilizers can be included. (Function) By containing brass fibers and a specific thermoplastic resin (graft copolymer), the thermoplastic resin composition according to the present invention has an excellent electromagnetic wave shielding effect and also has good impact resistance. The material is suitable for molding materials. (Example) Next, an example of the present invention will be shown. Hereinafter, "part" means "part by weight". Example 1 (1) Ingredients for producing acrylic acid alkyl ester polymer Potassium persulfate 1 part Sodium sulfite 0.2 parts Sodium oleate 20 parts Ion-exchanged water 2000 parts Ingredients Acrylic acid butyl ester 980 parts Triallylisocyanurate 20 parts In the reactor After preparing each uniformly dissolved component and components and purging with nitrogen gas while stirring, the temperature was raised to 60°C and reacted for 4 hours.Then, the temperature was further raised to 80°C and reacted for 3 hours, and acrylic acid Alkyl ester polymer latex (a)
I got it. (2) Ingredients for manufacturing component (A) (thermoplastic resin) Rongarit 2.8 parts Sodium oleate 14 parts Ion-exchanged water 1600 parts Ingredients Styrene 490 parts Acrylonitrile 210 parts Kyumene hydroperoxide 2.8 parts Tersia lead syl mercaptan 2.8 parts TK homo The uniformly dissolved components were placed in a container equipped with a mixer (manufactured by Tokushu Kika Kogyo), and after nitrogen purging and homomixing for 10 minutes at a stirring speed of 4 m/sec, a latex of acrylic acid alkyl ester polymer ( b) 300 parts (solid content) was added and homomixing was performed for 30 minutes. After that, transfer to a reactor purged with nitrogen and 70°C.
Polymerization was carried out at 90°C for 10 hours and at 90°C for 4 hours to obtain a polymer composition latex (A). This latex (A)
was salted out in hot water in which magnesium sulfate was dissolved, and dehydrated and dried to obtain a resin powder. (3) Manufacture of resin composition (B) component 46.4 parts of brass fibers with a diameter of 60 μm and a length of 3 mm (manufactured by Aisin Seiki) After mixing 53.6 parts of component (A) and component (B) for 5 minutes in a Henschel mixer, 230℃ using twin screw extruder
The mixture was melt-kneaded and pelletized under the following conditions. The capacity ratio of component (A) and component (B) is 90/10. A test piece was prepared using an injection molding machine at 230℃,
Characteristic tests were conducted. The shield effect is
It is expressed as the degree of attenuation in an electric field of 500MHz. Example 2 Ingredient (A) is 42.1 parts, component (B) is 57.9 parts,
Other details were the same as in Example 1. The capacity ratio of component (A) and component (B) is 85/15. Example 3 Component (A) was used as 34 parts, component (B) was used as 66 parts, and the other conditions were as in Example 1. The capacity ratio of component (A) and component (B) is 80/20. Example 4 Component V was 57.9 parts of brass fiber with a diameter of 40 μm and length of 2 mm, component (A) was 42.1 parts, and the rest was Example 1.
According to. Example 5 In the production of component (A), component (A) was produced according to Example 1 except that 175 parts of acrylic acid alkyl ester polymer latex (a) was used. Also, (A)
The ingredients were 38.6 parts, the component V was 61.4 parts, and the other conditions were as in Example 1. The capacity ratio of component (A) and component (B) is 83/17. Comparative Example 1 Component (A) is 80.6 parts, component (B) is 19.4 parts,
Other details were the same as in Example 1. The capacity ratio of component (A) and component (B) is 97/3. Comparative Example 2 Component (A) was used as 9.5 parts, component (B) was used as 90.5 parts, and the other conditions were as in Example 1. The capacity ratio of component (A) and component (B) is 45/55. Comparative Example 3 In the production of component (A), the same procedure as in Example 1 was followed except that 77.8 parts of acrylic acid alkyl ester polymer latex (a) was used. Table 1 shows the characteristic test results of the examples and comparative examples.

[Table] 1) Cannot be molded In the above, the volume resistivity is ASTM-D
-257 and Izod impact value are ASTM-D-256
It was carried out in accordance with. The shielding effect was measured using a TR4172 tracking generator spectrum analyzer manufactured by Takeda Riken Kogyo Co., Ltd., with the following conditions: frequency range 10 to 1000 MHz, reference level 0 dB, display line 0 dB, resolution bandwidth 1 KHz, video bandwidth 300 Hz, and input attenuator 0 dB. It was measured with (Effects of the Invention) The thermoplastic resin composition according to the present invention has excellent electromagnetic shielding properties. It also has good impact resistance.

Claims (1)

[Scope of Claims] 1 (A) 15 to 60% by weight of a rubbery polymer that is an acrylic acid alkyl ester polymer, and 85 to 60% by weight of at least one monomer selected from aromatic vinyl compounds, vinyl cyanide compounds, and methacrylic esters. 40
Contains a thermoplastic resin obtained by graft polymerizing % by weight and (B) brass fiber, and the (A) component and (B) component are 95/5.
A thermoplastic resin composition blended at ~50/50 (volume ratio).