JPH0215580B2 - - 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. 179241-1983).
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, the present inventors have developed a method for producing a polyolefin foam that exhibits little volume change after extrusion molding of the foam by blending a higher fatty acid ester of a polyhydric alcohol or a higher fatty acid triglyceride with a polyolefin resin. Developed (Special Publication No. 58-30896, Publication No. 58-30898). [Problems to be Solved by the Invention] In order to reduce the electrical insulation and improve the conductivity of plastic foam, the present inventors blended carbon black into the raw material plastic and extruded it. I tried foam molding, but
To obtain conductivity that does not charge static electricity (surface resistivity at 10 mm intervals: 10 ¹⁰ ohms),
At least 30% (by weight) of carbon black must be blended, but if this amount of carbon black is blended into the raw material plastic and extruded and foam molded, the expansion ratio of the plastic foam will decrease, Furthermore, it is encountered that the mechanical strength of the plastic foam is reduced, thereby making it difficult to use the plastic foam as a packaging material or as a spacer;
After repeated research with the aim of improving this point, we found that when a mixture of fatty acid esters of higher alcohols and higher fatty acid triglycerides was added to the raw material formulation for plastic foam, the plastic foam contained a considerable amount of carbon black. The expansion ratio of the plastic foam can be improved, the mechanical strength of the plastic foam can be maintained, the conductive performance of the plastic foam can be improved, and even the occurrence of bleed can be improved. It was discovered that no whitening phenomenon occurred, and based on this finding, the present invention was achieved. The object of the present invention is to provide a conductive plastic foam that does not reduce its expansion ratio and maintains its mechanical strength even though it contains carbon black, and has improved conductive performance and reduced static electricity charging. The purpose of the invention is to provide a method for manufacturing the same. [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 extrusion foaming the mixture. % (by weight) of polyolefin resin and 10 to 30% (by weight) of carbon black to a raw material mixture containing these in a ratio of 0.5 to 15 parts by weight of fatty acid ester of a higher alcohol per 100 parts by weight of the raw material mixture. This is a method for producing a conductive plastic foam, which is characterized by mixing a mixture of a higher fatty acid triglyceride and a higher fatty acid triglyceride, and foam-molding the mixture. According to the present invention, a mixture of polyolefin resin, carbon black, fatty acid ester of higher alcohol, and higher fatty acid triglyceride,
A raw material mixture is prepared by mixing 90 to 70 parts by weight of polyolefin resin, 10 to 30 parts by weight of carbon black, and 0.5 to 15 parts by weight of a mixture of fatty acid ester of higher alcohol and higher fatty acid triglyceride. If so, additives such as a nucleating agent, a lubricant, a plasticizer, a dispersing agent or a blowing agent can be further mixed in the preparation of the raw material formulation. The raw material mixture thus obtained is foam-molded by a conventional method.
When using a volatile foaming agent such as butane or chlorofluorocarbon as the foaming agent, it can be press-fitted into the raw material mixture in a molding machine for foam molding, stirred and mixed well, and then foam molded. Foam molding may be any conventional foam molding means such as extrusion foam molding or press foam molding. As the nucleating agent, inorganic powder such as finely powdered talc can be used. As the blowing agent, any decomposable blowing agent such as azodicarbonamide, N,N-dinitropentamethylenetetramine, or 4,4-oxybisbenzenesulfonylhydrazide can be used. can. In producing the conductive plastic foam according to the present invention, the mixture of fatty acid ester of higher alcohol and higher fatty acid triglyceride may be mixed at any time during the preparation of the raw material mixture. It can also be carried out by press-fitting through an injection port provided halfway into the cylinder of an extrusion molding machine in foam molding. The mixture of fatty acid esters of higher alcohols and higher fatty acid triglycerides is a raw material mixture containing polyolefin resin and carbon black in the proportion of 70 to 90% (by weight) polyolefin resin and 10 to 30% (by weight) carbon black. It is used in amounts ranging from 0.5 to 15 parts by weight per 100 parts by weight. The blending amount of the mixture of fatty acid ester of higher alcohol and higher fatty acid triglyceride is
If it is less than 0.5 parts by weight, it may not be possible to impart sufficient electrical conductivity (surface resistivity of approximately 10 ¹⁰ ohms) to the plastic foam product, and the foam may shrink significantly. In addition, if the amount is more than 15 parts by weight, the additive will bump out as droplets during extrusion foaming and will not only cause the extrusion operation to become unstable, but also cause the foam molded product to become less slippery during the extrusion operation, resulting in a beautiful appearance. In many cases, it is difficult to obtain a molded product with good quality, and furthermore, a phenomenon called bleed, in which the surface becomes white, may occur in the conductive plastic foam product. Usually, the mixture of fatty acid ester of higher alcohol and higher fatty acid triglyceride is used in an amount of 0.5 to 15 (particularly preferably 2 to 10) parts by weight per 100 parts by weight of the raw material mixture containing the polyolefin resin and carbon black. is preferable. The foamable raw material mixture used for extrusion foam molding includes ingredients added to the foamable raw material mixture used in the production of general plastic foams, such as inorganic powders such as talc or silica, and azodicarbonamide. or other decomposable organic blowing agents, foaming nucleating agents such as small amounts of N ₂ or CO ₂ gas or mixtures thereof, spreading agents such as polybutene or polyethylene glycol, butane, chlorofluorocarbons, methyl chloride or mixtures thereof, etc. A volatile foaming agent, or in the case of crosslinking foam molding, a crosslinking agent such as peroxide can be added and mixed into the raw material mixture as necessary. In some cases, a non-crosslinked plastic foam produced by foam molding may be crosslinked by irradiating it with radiation or the like. As the polyolefin resin in the raw material mixture of the present invention, any resin can be used as long as it can produce a plastic foam, but usually polyethylene, polypropylene, polybutene-based resin, etc. can be used. 1. Copolymers of these olefins with other vinyl monomers such as vinyl acetate, vinyl chloride, acrylic acid or methacrylic acid, or mixtures thereof are used. Among these, it is preferable to use ethylene-vinyl acetate copolymer. As the carbon black in the raw material mixture of the present invention, any ordinary carbon black can be used since it has conductivity, but carbon black having a large specific surface area and high conductivity can be used. Preferably, a black is used, such as Ketchen Black (manufactured by Lion Akzo). The higher alcohol component of the fatty acid ester of a higher alcohol in the raw material formulation in the present invention may be any monohydric alcohol having 10 or more carbon atoms, and is lauryl alcohol, cetyl alcohol, or stearyl alcohol. is preferable. The fatty acid component of the fatty acid ester of the higher alcohol may be any fatty acid having 12 or more carbon atoms, but palmitic acid, stearic acid, behenic acid, montanic acid, or oleic acid is preferable. preferable. Furthermore, beef tallow fatty acid, whale oil fatty acid, or coconut oil fatty acid containing a mixture of these fatty acids can also be used. As the fatty acid ester of the higher alcohol, stearyl stearate, cetyl palmitate, and lauryl myristate are generally used, but carnauba wax, montan wax, etc. can also be used. As the higher fatty acid triglyceride in the raw material formulation in the present invention, triglycerides of fatty acids having 11 to 20 carbon atoms are used, including animal fats and oils such as beef tallow, lard, or whale oil, and soybean oil, olive oil, cacao butter, and cottonseed oil. Hydrogenated oils obtained by hydrogenating vegetable oils such as , castor oil, rapeseed oil, coconut oil or corn oil can also be used. The fatty acid component of these fatty acid triglycerides is preferably stearic acid, palmitic acid, myristic acid, lauric acid, or a mixed fatty acid thereof. An example of implementation of the present invention and an example of comparison will be described below, but the present invention is not limited to these examples. Examples 1 to 3 (Preparation of raw material pellets) Ethylene-vinyl acetate copolymer (EVA) [melt index: 2.0, density: 0.930, vinyl acetate content: 10% (weight)], carbon black [Kettien Black EC] (registered trademark) mixture of stearyl stearate and cetyl palmitate 70% (by weight)
and a mixture of 30% (by weight) stearyl triglyceride [Rikemaru S900 (registered trademark),
Riken Vitamin Oil Co., Ltd. product] and talc in the amounts shown in Table 1 in a super mixer,
The mixture was mixed, put into an extruder, extruded linearly through a circular nozzle with a diameter of 3 mm, and cut into 3 mm lengths to obtain raw material pellets containing carbon black. (Preparation of foamed sheet) Raw material pellets were fed at 10 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 added at 1.5 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 Table 1. Comparative Examples 1 to 2 (Preparation of raw material pellets) The ethylene-vinyl acetate copolymer, carbon black, stearic acid monoglyceride [Rikemar S100 (registered trademark) product of Riken Vitamin Oil Co., Ltd.] and talc used in the examples were The amounts shown in Table 1 were used and treated in the same manner as in Examples to obtain raw material pellets. (Preparation of foamed sheet) Raw material pellets were treated in the same manner as in Examples 1 to 3 to obtain foamed sheets. The density and surface resistivity of the foamed sheet were as shown in Table 1. Example 4 (Preparation of raw material pellets) Ethylene-vinyl acetate copolymer [melt index: 2.0, density: 0.930, vinyl acetate content: 10
% (by weight) 85 parts by weight, 15 parts by weight of carbon black [Ketsuchen Black EC (registered trademark)], 5 parts by weight of a mixture of 50% cetyl palmitate (by weight) and 50% (by weight) hydrogenated beef tallow oil, and 1 part by weight of talc. Place the parts into a super mixer, mix, and mix the mixture into a diameter 3
It was linearly extruded through a mm circular nozzle and cut into 3 mm lengths to obtain raw material pellets containing carbon black. (Preparation of foamed sheet) Raw material pellets were treated in the same manner as in Examples 1 to 3 to obtain foamed sheets. The foam sheet had a density of 0.045, a surface resistivity of 5.3×10 ⁷ ohms, and was a beautiful sheet with no whitening phenomenon.

[Table] (Measurement of surface resistivity) Terminals were brought into contact with the foam sheet at intervals of 10 mm on the surface of the foam sheet, and the electrical resistance values at the intervals were measured. According to a comparison between Example 1 and Comparative Example 1, and Example 3 and Comparative Example 2, the surface resistivity of the foam sheet was reduced by blending a small amount of a mixture of stearyl stearate and cetyl palmitate into the raw materials. It can be seen that the conductivity is improved. [Effects of the Invention] According to the present invention, by blending a mixture of a fatty acid ester of a higher alcohol and a higher fatty acid triglyceride with a polyolefin resin, a sufficient amount of foamed plastic sheet can be obtained by blending a small amount of carbon black. The foaming ratio can be maintained, thereby providing sufficient electrical conductivity, and even when a large amount of a mixture of fatty acid ester of higher alcohol and higher fatty acid triglyceride is blended, a whitening phenomenon called bleed does not occur.

Claims (1)

[Scope of Claims] 1. A method for producing a conductive plastic foam, which comprises blending carbon black into a plastic raw material mixture and extrusion foam molding, wherein 10 to 30% (by weight) of carbon black is added. and raw material formulations containing 90 to 70% (by weight) of polyolefin resin, per 100 parts by weight of the raw material formulation.
A method for producing a conductive plastic foam, which comprises mixing 0.5 to 15 parts by weight of a mixture of a fatty acid ester of a higher alcohol and a higher fatty acid triglyceride and foam-molding the mixture. 2. The conductive plastic according to claim 1, wherein the polyolefin resin is a plastic selected from the group consisting of polyethylene, polypropylene, ethylene-vinyl acetate copolymer, and mixtures thereof. Method of manufacturing foam.