JPH0215579B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Application Field] The present invention relates to a method for producing conductive plastic foam, and more specifically, it is free from static electricity and must avoid dust from adhering to precision machinery, electrical parts, or electronic parts. This invention relates to a method for producing plastic foam suitable for packaging non-essential items. [Technical Background and Description of the Prior Art] Plastic foams have suitable elasticity;
Moreover, it is highly flexible, so it can be used to wrap fragile items, expensive items, or various items.
Use it as a spacer between these items,
It is widely practiced to prevent packaged items from coming into contact with each other or being crushed.
Plastic foam has a very high electrical resistance and is almost an insulator, so it is easily charged with static electricity. For this reason, plastic foam tends to attract dust and is not only unsuitable as a packaging material, but also used for ICs, transistors, etc.
It is often practically impossible to use them as packaging materials for capacitors, electronic components using them, and electrical equipment using them, such as watches, cameras, or audio equipment. In the past, antistatic agents have been added to plastic foams to make them less electrically insulating and more conductive, making them free from static charges and thus dust-free. Attempts have also been made to coat plastic foam with carbon black or to incorporate carbon black into plastic foam (Japanese Patent Laid-Open No. 58-40326, Japanese Patent Laid-open No. 179241-1982).
Publication No. 198537, Japanese Patent Publication No. 1985-1985
Publication No. 198538). In addition, it is difficult to maintain the gas pressure necessary for foaming with polyolefin resin containing a large amount of carbon black, so by blending carbon black and an amide compound with polyolefin resin, it is possible to create a conductive foam. Attempts have also been made to reduce the volume resistivity (Japanese Unexamined Patent Publication No. 8032/1983). On the other hand, a foaming agent and a crosslinking agent are added to a styrene-vinyl acetate copolymer and a thermoplastic synthetic resin in which inorganic powder is added, and foam molding is performed, thereby achieving excellent heat resistance and flame retardancy.
A method of manufacturing a plastic foam with high expansion ratio and high inorganic filling is also known (Japanese Patent Application Laid-Open No. 1983-1999).
168632). [Problems to be Solved by the Invention] The present inventors aim to reduce the electrical insulation of plastic foam and improve its conductivity, thereby producing a plastic foam that is free from static electricity. Therefore, we tried extrusion foam molding by adding carbon black to the raw material plastic, but it was not possible to obtain conductivity to the extent that it would not be charged with static electricity (surface resistivity at 10 mm intervals: 10 ^{to 10} ohms or less). must contain at least 30% (by weight) carbon black. However, when this amount of carbon black is blended into raw material plastic and extrusion foam molding is performed, the expansion ratio of the plastic foam decreases, and the mechanical strength of the plastic foam also decreases. As a result, we encountered difficulties in using plastic foam as packaging materials or spacers, and we conducted research to improve these issues, and added styrene to the raw material formulation for plastic foam. - Adding vinyl acetate block copolymer improves the expansion ratio of plastic foam and maintains its mechanical strength even though the plastic foam contains a considerable amount of carbon black. Not only can the expansion ratio of the plastic foam be further improved, but also the mechanical strength of the plastic foam can be improved. The present invention was developed based on this finding. An object of the present invention is to provide a method for producing a conductive plastic foam that does not reduce its expansion ratio and maintains its mechanical strength despite containing carbon black. Specifically, in order to further improve the expansion ratio and mechanical strength of plastic foam, even if the amount of carbon black added is reduced, sufficient conductivity is maintained, thereby reducing static electricity charging. The object of the present invention is to provide a method for producing a plastic foam that does not contain plastics. [Means for Solving the Problems] The present invention provides a method for producing a conductive plastic foam, which comprises blending carbon black into a foamable plastic raw material composition and foam-molding the mixture. % polyolefin resin, 10 to 30 parts by weight of carbon black, and 5 to 30 parts by weight of carbon black.
This is a method for producing a conductive plastic foam, characterized by foam-molding a foamable raw material mixture containing 40 parts by weight of a styrene-vinyl acetate block copolymer resin. According to the present invention, polyolefin resin, carbon black and styrene-vinyl acetate block copolymer resin are mixed into
Parts by weight, 10 to 30 parts by weight of carbon black and 5 to 40 parts by weight of styrene-vinyl acetate block copolymer resin
A raw material mixture is prepared by mixing in proportions of parts by weight, but in the preparation of the raw material mixture, if necessary, additives such as a foaming nucleating agent and a blowing agent may be further added and mixed. can. The raw material mixture thus obtained is foam-molded by a conventional method.
For example, if butane or chlorofluorocarbons are used, they may be press-fitted into the pressurized molten raw material mixture in a foam molding machine, stirred and mixed thoroughly, and then foam molded. can. Foam molding may be any conventional foam molding means such as extrusion foam molding or press foam molding. As the foaming nucleating agent, inorganic powder such as finely powdered talc can be used. Examples of the polyolefin resin in the raw material mixture of the present invention include polyethylene, polypropylene,
Any polymer or copolymer of olefins can be used, such as polybutene-1, copolymers of these monomers, or copolymers of these monomers with other vinyl monomers. However, it is preferred to use low density polyethylene or ethylene-vinyl acetate copolymer. As the carbon black in the raw material mixture of the present invention, any commercially available carbon black can be used, and any carbon black can be used as long as it has conductivity. This can also be used, but highly conductive carbon black, such as Ketschien Black (registered trademark)
(Lion Akzo product) is preferably used. If the amount of carbon black used is less than 10 parts by weight, the conductivity of the plastic foam is often insufficient, and if it exceeds 30 parts by weight, foaming may not be sufficient, the expansion ratio may be low, or bubbles may be formed. The structure often becomes open-celled, reducing the mechanical strength of the plastic foam. As the styrene-vinyl acetate block copolymer in the raw material formulation of the present invention, any polymer produced by block copolymerizing styrene and vinyl acetate by a conventional method can be used. Index values of 0.1 to 5.0 tend to increase the expansion ratio of the plastic foam and increase its mechanical strength. As the blowing agent in the raw material formulation of the present invention,
liquid propane, liquid butane, methyl chloride,
Alternatively, any volatile blowing agent such as chlorofluorocarbon, azodicarbonamide, or other decomposable blowing agent may be used. As the foaming nucleating agent in the raw material formulation of the present invention, any fine inorganic powder such as talc or silica can be used. Further, a small amount of a decomposable blowing agent such as azodicarbonamide, a small amount of nitrogen gas or carbon dioxide gas, etc. can be used. Other ordinary antistatic agents, lubricants, plasticizers, etc. can be used as appropriate, and antistatic agents can be particularly effectively used to improve conductivity. As other additives in the raw material formulations of the present invention, crosslinking agents can also be used to create crosslinked plastic foams. Any known crosslinking agent may be used, such as t-butylperbenzoate, 1,1-di(t-butylperoxy)
-3,3,5-trimethylcyclohexane, 2,
2-bis-(t-butylperoxy)butane, dicumyl peroxide, 2,5-bis-(t-butylperoxy)-2,5-dimethylhexane,
Peroxides such as 1,4-bis(t-butylperoxy)diisopropylbenzene and 2,5-dimethyl-2,5-di(t-butylperoxy)hexyne-3 can be used. When using a crosslinking agent, it is preferably formed by press foam molding. Foam molding of the raw material mixture in the present invention can be carried out by any known foam molding means such as extrusion foam molding or press foam molding. That is, the raw material mixture is charged into an extrusion molding machine, heated and melted, and if necessary, additive components such as a foaming agent are pressed in and mixed, and then extruded into the atmosphere through a suitable nozzle and molded, or Alternatively, foam molding can be carried out by any means such as placing the raw material mixture in a mold and heating it to perform foam molding. The present invention will be disclosed in further detail below using an example of implementing the present invention and a comparative example to be compared with the present invention, but the present invention is not limited to these examples. Examples 1 to 5 (Preparation of raw material pellets) Low-density polyethylene (LDPE, melt index: 3.0, density: 0.921) powder, carbon black [Ketschen Black EC (registered trademark), a product of Lion Akzo Co., Ltd.], styrene-acetic acid Vinyl block copolymer resin [Modieper SV (registered trademark) manufactured by NOF Corporation] and talc were added to Table 1 and 2.
The amount shown in the table was put into a super mixer, mixed, the mixture was put into an extruder, extruded linearly from a circular nozzle with a diameter of 3 mm, cut into 3 mm length, and raw material pellets containing carbon black were obtained. Obtained. (Preparation of foamed sheet) Raw material pellets were fed at 12.0 Kg/hr into the hopper of an extrusion molding machine equipped with an annular extrusion nozzle (diameter 30 mm), heated to 200°C, and liquefied butane was fed at 1.6 Kg/hr. After press-fitting and mixing thoroughly, the mixture was extruded into the cooled atmosphere from an annular nozzle of an extrusion molding machine to obtain a foamed sheet. The density and surface resistivity of the foamed sheet were as shown in Tables 1 and 2. Comparative Examples 1 to 4 (Preparation of raw material pellets) The low density polyethylene, carbon black, polystyrene and talc used in the examples were
The amounts shown in Table 2 and Table 2 were used and treated in the same manner as in the examples to obtain raw material pellets. (Preparation of foamed sheet) Raw material pellets were treated in the same manner as in the examples to obtain a foamed sheet. The density and surface resistivity of the foamed sheet were as shown in Tables 1 and 2. In the foamed sheet of Comparative Example 4, polystyrene was not sufficiently mixed, and the sheet had a brittle and rough appearance, making it unusable.

【table】

〔Effect of the invention〕

According to the present invention, the plastic foam foams well even though it contains carbon black, and the desired expansion ratio can be maintained, and even if the amount of carbon black blended is reduced, the foamed state can be improved. Even with good maintenance, the desired conductivity can be maintained.

Claims (1)

[Scope of Claims] 1. A method for producing a conductive plastic foam, which comprises blending carbon black into a foamable plastic raw material mixture and foam-molding the mixture, comprising 50 to 85 parts by weight of a polyolefin resin. ,Ten~
1. A method for producing a conductive plastic foam, which comprises foam-molding a foamable raw material mixture containing 30 parts by weight of carbon black and 5 to 40 parts by weight of a styrene-vinyl acetate block copolymer resin. 2. The polyolefin resin according to claim 1, wherein the polyolefin resin is selected from the group consisting of polyethylene, polypropylene, polybutene-1, ethylene-vinyl acetate copolymer, and mixtures thereof. Method of manufacturing conductive plastic foam.