JPS6166729A - Production of electrically-conductive plastic foam - Google Patents

Abstract

PURPOSE:To obtain the titled foam without lowering expansion magnification, by blending a compound of carbon black and a polyolefinic resin with a mixture of a higher alcohol fatty acid ester and a higher fatty acid triglyceride. CONSTITUTION:(A) 100pts.wt. raw material compound comprising 10-30wt% carbon black (preferably KETCHEN black, etc.) and 90-70wt% polyolefinic resin (polyethylene, polypropylene, etc., especially ethylene-vinyl acetate copolymer) is blended with (B) 0.5-15pts., preferably 2-10pts. mixture of a higher alcohol fatty acid ester (stearyl sterate, acetyl palmitate, lauryl myristate, etc.) and a higher fatty acid triglyceride etc.) to give raw material pellets, and the these pellets are (e.g., stearyl triglyceride, etc.) to give raw material pellets, and these pellets are expansion molded.

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 used in precision machinery, electrical parts, or electronic parts without being charged with static electricity. The present invention relates to a method for producing plastic foam suitable for packaging items such as those that must be protected from dust.

[Technical background and explanation of conventional technology]

Plastic foam has a suitable elasticity and is highly flexible, making it suitable for packaging fragile, expensive or essential items, or for use as a spacer between these items. Although it is widely used to prevent packaged items from touching each other or being crushed, plastic foam has a very high electrical resistance and is rarely used as an insulator. +51 to be a body
1 [ is easily charged with electricity. For this reason, plastic foam tends to attract dust, making it unsuitable as a packaging material. For example, it is often practically impossible to use watches, cameras, etc. as packaging materials for audio equipment, etc.

To date, plastic foams have been coated with IB additives to reduce their electrical insulating properties and make them conductive, preventing static electricity build-up and thereby preventing dust build-up. Attempts have been made to coat plastic foams with carbon black or to incorporate carbon black into plastic foams (Japanese Unexamined Patent Publications No. 40326/1982, No. 179241/1983, and 1985/1985).
37, JP-A-58-198538). In addition, polyolefin M containing a large amount of carbon black
Since N is electrically conductive to maintain the gas pressure necessary for foaming, we also attempted to reduce the specific volume resistivity of the conductive foam by blending carbon black and an amide compound into the polyolefin M finger. (Japanese Unexamined Patent Publication No. 58-8032).

On the one hand, we have discovered that polyolefin-based II!
By blending higher fatty acid esters of polyhydric alcohols or higher fatty acid triglycerides with fat, we have developed a method for producing polyolefin foams with little volume change after extrusion molding of the foam (Japanese Patent Publication No. 58-30896, Japanese Patent Publication No. 30896/1989, 58-30898).

[Problems to be solved by the invention]

The present inventors attempted to mix carbon black into raw material plastics and perform extrusion foam molding in order to reduce the electrical insulation properties and improve the conductivity of plastic foams. , to the extent that it does not charge static electricity (l
In order to obtain the conductivity of the surface resistor (OI0 ohm) at the on+ interval, at least 30% (by weight) of carbon black must be blended. When the blended product is extruded and foam molded, the expansion ratio of the plastic foam decreases, and furthermore, the mechanical strength of the plastic foam decreases, which makes it difficult to use the plastic foam as a packaging material or a spacer. In order to improve this point, we repeatedly conducted research and added fatty acid esters of higher alcohols and I%IRIIII to the raw material composition of plastic foam.
When three mixtures of fatty acid triglycerides are added, the expansion ratio of the plastic foam increases, even though the plastic foam contains a considerable amount of carbon black.
It was discovered that the mechanical strength of the plastic foam can be maintained, the conductive performance of the plastic foam can be improved, and the whitening phenomenon that occurs as bleed does not occur, and based on this knowledge, the present invention has been developed. reached.

The purpose of the present invention is to provide a conductive plastic foam that does not have a lower expansion ratio and maintains mechanical strength even though it contains carbon black, and has improved conductive performance and reduced static electricity charging. The purpose is to provide a method that can produce convex.

Means for Solving Problem C] The present invention provides a method for producing J4 electrically conductive plastic foam, which consists of blending carbon black into a foamable raw material mixture for plastics and extrusion foam molding.
90-70% (superposition) of jellyolefin m fat and 1
To the raw BIE3 compound containing these at a ratio of 0 to 30% (111 parts by weight) of carbon black, 0.5 to 15 parts by weight of fatty acid ester of higher alcohol and higher fatty acid triglyceride based on 100 parts by weight of the raw material mixture. This is a !Ji! production method for conductive plastics foam, which is characterized by mixing a mixture of 1 and 2 and foam-molding the mixture.

According to the present invention, a mixture of polyolefin am, carbon black, fatty acid ester of higher alcohol, and higher fatty acid triglyceride is mixed with 90 to 70 parts by weight of polyolefin am, carbon black, 10 to 30 parts by weight, and fatty acid ester of higher alcohol. A mixture of high 1 & fatty acid triglycerides is mixed in the ratio of 0.5 to 1 part of +531 il to prepare the raw material, but if necessary, cedar agent, lubricant, plasticizer, etc. Additives such as , dispersants or blowing agents can be further mixed. The raw material mixture obtained in this way is foam-molded by a conventional method, but when a single foaming agent such as butane or chlorofluorocarbon is used as the foaming agent, in the molding machine for foam molding, It can also be press-fitted into a raw material mixture, thoroughly stirred and mixed, 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.

In addition, as a blowing agent, azodicarbonamide, N, N-
Any decomposable blowing agent can be used, such as dinitropentamethylenetetramine or 4,4-oxybisbenzenesulfonyl hydrazide.

When producing a 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, and the mixture of the raw material mixture may be foam-molded. It can also be press-fitted through an injection port provided halfway into the cylinder of an extrusion molding machine. The mixture of fatty acid esters of -alcohols and higher fatty acid triglycerides is prepared by combining polyolefin resins and It is used in an amount ranging from 0.5 to 159 parts based on the raw material formulation containing carbon black + ooWffi parts. The blending amount of the mixture of fatty acid ester of higher alcohol and upper fatty acid triglyceride is o, 511ff.
If the amount is less than i part, it may not be possible to impart sufficient electrical conductivity (low inherent surface loss of approximately 10 ohms) to the plastic foam product, and the foam may shrink significantly. Also more mf than 15 mff1 part
! In case of I, during extrusion foaming, the additive bumps and is discharged as a liquid layer, which not only makes the extrusion operation unstable, but also makes it difficult to obtain a beautiful molded product due to poor slippage of the foam molded product during the extrusion operation. Furthermore, a whitening phenomenon called bleed may occur on the conductive plastic foam of the product. usually,? & grade alcohol I
] The mixture of W fatty acid ester and higher fatty acid triglyceride is 0.0% per 100ffi parts of the raw material mixture containing the polyolefin IMI11 and carbon black.
Preferably, it is used in an amount of 5 to +5 (particularly preferably 2 to +0) li parts.

The foamable raw material formulation for extrusion foam molding may contain ingredients added to the foamable raw material formulation used in general plastic foam WFI, such as inorganic powders such as talc or silica, azo Dicarbonamide or other decomposable organic blowing agent, 9 N or CO
When using a foaming nucleating agent such as a gas or a mixture thereof, a spreading agent such as polybutene or polyethylene glycol, a quantitative foaming agent such as butane, chlorofluorocarbon, methyl chloride or a mixture thereof, or crosslinking foam molding, A crosslinking agent such as peroxide can be added to the raw material mixture as necessary.

In some cases, the plastic foam of the P frame 1 made by foam molding may be crosslinked by irradiating it with radiation or the like.

As the polyolefin-based 81 resin in the raw material blend of the present invention, any resin can be used as long as it can produce plastic foam, but usually polyethylene, polypropylene, polybutene, etc. -1, these olefins and pigeon vinyl system Rff1
For example, copolymers with 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 composition of the present invention, any ordinary carbon black can be used since it has tetraelectricity, but
It is preferable to use carbon black having a large specific surface area and high conductivity, such as Ketjen black (manufactured by Lion Akzo).

The primary alcohol component of the fatty acid ester of a higher alcohol in the raw material composition of the present invention may be any monohydric alcohol having 10 or more carbon atoms, such as lauryl alcohol, cetyl alcohol, or stearyl alcohol. Preferably it is alcohol. Also, the above-mentioned l
The fatty acid component of the fatty acid ester of class IIi alcohol is
Any fatty acid having 12 or more carbon atoms may be used, but valmitic acid, stearic acid, behenic acid, montanic acid, or oleic acid is preferred. Furthermore, beef tallow fatty acid, whale oil fatty acid, and yang oil fatty acid containing 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 carnapara 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 with a carbon number of 11 to 20 are used, but animal fats and oils such as beef tallow, pig intestine, or whale oil, soybean oil, olive oil, cacao butter, Cottonseed oil, castor oil, greens! 11i+11.

Hydrogenated oils obtained by hydrogenating vegetable oils such as coconut 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 obscured by these examples.

Examples 1 to 3 (Preparation of raw material pellets) Ethylene-vinyl acetate copolymer (EVA) (melt index: 2. O1 density: 0.930, total amount of vinyl acetate, 10% f!Itt)), carbon black [
Ketjenblack EC (registered trademark 1111) Mixture of stearyl stearate and cetyl palmitate 7096 (M
MI and stearyl triglyceride 30% (:i
i bond, mixture of 1 [Rikemaru 5900 (registered trademark)
, Riken Vitamin Oil C Co., Ltd. product] and talc in the amounts shown in Table 1 were placed in a super mixer and mixed.The mixture was placed in an extruder and extruded linearly from a circular nozzle with a diameter of 3++ m. The raw material pellets containing carbon black were obtained by cutting at a length of .

(Preparation of foamed sheet) Raw material pellets were fed at 10 K9/hr into the hopper of an extrusion molding machine equipped with an annular extrusion nozzle (diameter 300), heated to 200°C, and liquefied butane was
At 1.5 Kg/hr, after press-fitting and mixing well, extrusion F! A foamed sheet was obtained by blowing into the cooled atmosphere from the annular nozzle of a Type 4 machine.

The density and surface resistivity of the foamed sheet were as shown in Table 1.

Comparative Examples 1 and 2 (Preparation of raw material pellets) The ethylene-vinyl acetate comonomer used in the examples, carbon black, stearic acid monoglyceride [Rikemar 510o (registered trademark) Riken Vitamin @ Co., Ltd. product] and talc were Raw material pellets were obtained by using the amounts shown in Table 1 and treating them in the same manner as in Examples.

(Preparation of foamed sheet 1e Raw material pellets were treated in the same manner as in Examples 1 to 3 to obtain foamed sheets.

The density and surface roughness 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, Enzyme vinyl aging: 10
% (1! Jij 85 weight! parts, carbon black [Ketjenblack EC (registered trademark)) 15 flifa parts,
Cetyl vermitate 50% (superposition) and beef tallow hydrogenated oil 50%
Put 5 parts by weight of the mixture of
The raw material pellets containing carbon black were extruded in a line through a circular nozzle and cut into lengths of 311II.

(Similar to foam sheet) Example of raw material pellets! A foamed sheet was obtained by processing in the same manner as in 3.

The foam sheet had a density of 0.045, a surface fixation resistance of 5.3 x 10 ohms, and was a beautiful sheet with no whitening phenomenon.

(Left below) (Measurement of surface resistivity) On the surface of the foam sheet, connect the terminals to the foam sheet at an interval of 10 gm. The electrical resistance value at that interval was measured.

Example 1 and comparative example! According to a comparison between Example 3 and Comparative Example 2, the surface resistivity of the foamed sheet was reduced by blending the mixture of /pffi stearyl stearate and cetilva I remitate into the raw materials, resulting in a conductivity of 1.
It can be seen that sexual performance improves.

〔Effect of the invention〕

According to the present invention, by blending a mixture of a fatty acid ester of a higher alcohol and a fatty acid triglyceride into a polyolefin system mn', a sufficient amount of foamed plastic sheets can be obtained by blending a small amount of carbon black. It is possible to maintain a high foaming ratio, thereby imparting sufficient foaming efficiency, and furthermore, even if a mixture of fatty acid ester of a higher alcohol and higher fatty acid triglyceride is blended in a multi-fit mixture, a whitening phenomenon called bleed does not occur. do not have.

Claims (2)

[Claims] (1) In a method for producing a conductive plastics foam, which comprises blending carbon black into a plastics raw material blend and extrusion foaming,
% (by weight) of carbon black and 90 to 70% (by weight) of polyolefin resin, 0.5 to 15 parts by weight of fatty acid ester of higher alcohol and higher A method for producing a conductive plastic foam, which comprises mixing a mixture of fatty acid triglycerides and foam-molding the mixture. (2) The conductive material 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. A method for producing plastic foam.