JP2006063249A - Electrically conductive crosslinked polyolefin foam and method for producing the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for producing an electrically conductive crosslinked polyolefin foam good in electrical conductivity and flexibility. <P>SOLUTION: The method for producing the electrically conductive crosslinked polyolefin foam comprises incorporating and kneading a polyolefin resin with an electrically conductive zinc oxide, an electrically conductive plasticizer, a foaming agent and a crosslinking agent followed by heating to effect expansion. Specifically, in this method, 100 pts. wt. of the polyolefin resin is kneaded with 50-200 pts. wt. of the electrically conductive zinc oxide with 1×10<SP>4</SP>Ω cm or less in volume resistivity, 20-70 m<SP>2</SP>/g in specific surface area and 500-1,200 mL/100g in bulk specific volume and 10-50 pts. wt. of the electrically conductive plasticizer. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

    The present invention relates to a conductive cross-linked polyolefin-based foam and a method for producing the same.

In recent years, the use of conductive foams such as packaging, transportation, storage materials and antistatic mats for various devices using electronic components has been widely expanded.
Conventionally, urethane foam has been known as a conductive plastic foam (Japanese Patent Publication No. 52-36902), but there are problems such as carbon loss and color fading, and weather resistance because the base material is urethane. There were problems such as very bad nature.

    The present applicant has added and kneaded carbon black, a foaming agent and a crosslinking agent to polyolefin, crosslinked in a mold under pressure, and then heated and foamed under normal pressure, and then a method for producing a conductive crosslinked polyolefin foam (Japanese Patent Application No. 2-229095) was developed.

Further, the applicant of the present invention is a method for producing a conductive cross-linked polyolefin foam in which a conductive powder in which the periphery of conductive zinc white and titanium oxide particles is coated with a metal oxide composed of tin oxide and antimony oxide is kneaded into polyolefin. (Japanese Patent Publication No. 3-20419) was developed.
Japanese Patent Publication No. 52-36902 Japanese Patent Publication No. 2-29095 Japanese Patent Publication No. 3-20419

    However, the carbon black kneaded conductive cross-linked polyolefin foam of the above prior art can only obtain a black foam, and the conductive cross-linked polyolefin foam kneaded with conductive zinc white is foamed in various colors such as white. Although the body was obtained, since the added number of conductive zinc white was as large as 50 to 300 parts, it was inferior in flexibility. Accordingly, an object of the present invention is to provide a conductive cross-linked polyolefin-based foam having sufficient conductivity but having a color other than black and rich in flexibility, and a method for producing the same.

The present invention focuses on the fact that a combination of a specific conductive zinc oxide and a conductive plasticizer can provide high conductivity with a small number of added parts, and the conductive cross-linked polyolefin foam of the present invention is A conductive cross-linked polyolefin foam obtained by adding and kneading conductive zinc oxide, a conductive plasticizer, a foaming agent and a cross-linking agent to polyolefin resin and heating and foaming.

In the present invention, it is preferable that the conductive zinc oxide has a volume resistance of 1 × 10 ⁴ Ω · cm or less, a specific surface area of 20 to 70 m ² / g, and a bulk specific volume of 500 to 1,200 ml / 100 g.

    In the method for producing a conductive cross-linked polyolefin foam of the present invention, 50 to 200 parts by weight of conductive zinc oxide, 10 to 50 parts by weight of a conductive plasticizer, a foaming agent and a cross-linking agent are added to 100 parts by weight of a polyolefin resin. The resulting crosslinkable foamable composition is heated under pressure and then decompressed to produce a foam.

In the production method of the present invention, the volume resistance value of the conductive zinc oxide is 1 × 10 ⁴ Ω · cm or less, the specific surface area is 20 to 70 m ² / g, and the bulk specific volume is 500 to 1,200 ml / 100 g. preferable.

In the production method of the present invention, when the conductive zinc oxide and the conductive plasticizer are less than the above ranges, sufficient conductivity and flexibility cannot be obtained, and when added exceeding the above ranges, foam molding is hindered. , Satisfactory foam cannot be obtained.

Further, when the volume resistance value of the conductive zinc oxide is out of the range of 1 × 10 ³ to 1 × 10 ⁴ Ω · cm, the surface resistance value is large, and a conductive foam cannot be obtained. When the specific surface area is out of the range of 30 to 50 m ² / g and the bulk specific volume is out of the range of 700 to 1,000 ml / 100 g, foam molding is inhibited and a satisfactory foam cannot be obtained.

    According to the method of the present invention, a conductive foam having sufficient conductivity and having a color other than black and rich in flexibility can be obtained.

    In the present invention, polyolefin is, for example, polyethylene, ethylene-vinyl acetate copolymer, polypropylene, polytetrafluoroethylene, ethylene-propylene copolymer, poly-4-methyl-1-pentene, polyvinyl chloride, polyvinylidene chloride, Examples thereof include polyvinylidene fluoride, tetrafluoroethylene, and an ethylene copolymer.

The conductive zinc oxide referred to in the present invention has a volume resistivity of 1 × 10 ³ to 1 × 10 ⁴ Ω · cm, a specific surface area of 30 to 50 m ² / g, and a bulk specific volume of 700 to 1,000 ml / 100 g. Zinc oxide.

The conductive plasticizer referred to in the present invention is a conductive plasticizer mainly composed of an aliphatic dibasic acid ester.

    The cross-linking agent as used in the present invention has a decomposition temperature at least equal to or higher than the flow start temperature of the polyethylene resin in the polyethylene-based resin, and is decomposed by heating to generate free radicals between or within the molecules. Organic peroxides that are radical generators that cause crosslinking, such as dicumyl peroxide, 1,1-ditertiary butyl peroxide, 1,1-ditertiary butyl peroxy-3,3,5-trimethylcyclohexane 2,5-dimethyl-2,5-ditertiary butyl peroxyhexane, 2,5-dimethyl-2,5-ditertiary butyl peroxyhexyne, α, α-ditertiary butyl peroxyisopropylbenzene, tertiary butyl per Oxyketone, tertiary butyl peroxy There are benzoates, etc., and the optimum organic peroxide must be selected according to the resin used at that time.

The foaming agent referred to in the present invention is a chemical foaming agent having a decomposition temperature equal to or higher than the melting temperature of the polyethylene resin, such as an azo compound azodicarbonamide, barium azodicarboxylate, etc .; a nitroso compound dinitrosopenta. Methylenetetramine, trinitrotrimethyltriamine, etc .; p, p′-oxybisbenzenesulfonyl hydrazide, etc. of hydrazide compounds; p, p′-oxybisbenzenesulfonyl semicarbazide, toluenesulfonyl semicarbazide of sulfonyl semicarbazide compounds, etc. There are Jid etc.

In the present invention, a foaming aid can be added depending on the type of foaming agent. Examples of the foaming aid include compounds mainly composed of urea, metal oxides such as zinc oxide and lead oxide, compounds mainly composed of salicylic acid and stearic acid, that is, higher fatty acids or higher fatty acid metal compounds.

In the present invention, for the purpose of improving the physical properties of the composition to be used or reducing the price, a compounding agent (filler) that does not significantly adversely affect the cross-linking, such as zinc oxide, titanium oxide, calcium oxide, magnesium oxide, oxidation Metal oxides such as silicon, carbonates such as magnesium carbonate and calcium carbonate, fiber materials such as pulp, various dyes, pigments and fluorescent materials, and other conventional rubber compounding agents can be added as necessary. .

Next, the manufacturing method of the electroconductive crosslinked polyolefin-type foam of this invention is demonstrated.

A well-known foaming agent, foaming aid and crosslinking agent are added to a mixture comprising 100 parts by weight of the polyolefin resin, 50 to 200 parts by weight of conductive zinc oxide, and 10 to 50 parts by weight of a conductive plasticizer. The mixture is kneaded with a heated mixing roll, a pressure kneader, an extruder or the like. The resulting foamable composition is charged into a mold during pressing, heated under pressure, then depressurized to produce a foamed product, which is a method for producing a conductive cross-linked polyolefin foam.

    The conductive cross-linked polyolefin foam obtained by the production method of the present invention is a foam having sufficient conductivity and having a color other than black and rich in flexibility. It can be applied to antistatic materials and buffer materials.

Linear low density polyethylene (trade name: affinity EG8200, density 0.920 g / cm ³ , melt flow rate 5.0 g / 10 min, manufactured by Dow Chemical Japan), 50 parts by weight, olefin elastomer (trade name: L- 601, density 0.99
g / cm ³ , melt flow rate 2.6 g / 10 min, manufactured by Asahi Kasei Co., Ltd., 50 parts by weight, conductive zinc oxide (trade name: passette CK, volume resistivity 1 × 10 ³ to 1 × 10 ⁴ Ω · cm, Specific surface area 30 to 50 m ² / g, bulk specific volume 700 to 1,000 ml / 100 g, manufactured by Hux Itec Corp.) 110 parts by weight, conductive plasticizer (trade name: US-600, main component aliphatic dibasic acid ester, (Compared with Taoka Chemical Co., Ltd.) A composition comprising 30 parts by weight, 3 parts by weight of azodicarbonamide, and 1.4 parts by weight of dicumyl peroxide was kneaded with a 100 ° C. kneader and heated in a press at 155 ° C. The mold (160 × 160 × 20) was filled with the kneaded product, heated at a pressure of 100 kg / cm ² for 40 minutes, decomposed the foaming agent and the crosslinking agent, and then depressurized to obtain a foam.

The apparent density of the obtained foam was 250 kg / m ³ , and when the surface resistance value was measured, it was 8 × 10 ⁷ Ω and had conductivity.

    Foam was obtained by foaming under the same composition and conditions as in Example 1 except that the amount of conductive zinc oxide added was changed to 70 parts by weight and the amount of conductive plasticizer added was changed to 20 parts by weight.

The apparent density of the obtained foam was 230 kg / m ³ , and when the surface resistance value was measured, it was 9 × 10 ⁷ Ω and had conductivity.

    Foam was obtained by foaming under the same composition and conditions as in Example 1 except that the amount of conductive zinc oxide added was changed to 180 parts by weight and the amount of conductive plasticizer added was changed to 40 parts by weight.

The apparent density of the obtained foam was 280 kg / m ³ , and when the surface resistance value was measured, it was 6 × 10 ⁷ Ω and had conductivity.
Comparative Example 1

    Foam was obtained by foaming under the same composition and conditions as in Example 1 except that the amount of conductive zinc oxide added was changed to 30 parts by weight and the amount of conductive plasticizer added was changed to 5 parts by weight.

The apparent density of the obtained foam was 210 kg / m ³ , and when the surface resistance value was measured, it was 6 × 10 ⁹ Ω, which was inferior in conductivity.
Comparative Example 2

    The conductive zinc oxide and conductive plasticizer were foamed under the same composition and conditions as in Example 1 except that the amount of conductive zinc oxide added was changed to 250 parts by weight and the amount of conductive plasticizer added was changed to 80 parts by weight. It was not possible to obtain a satisfactory foam because the number of added parts was too large.

As described above, according to the method of the present invention, a conductive cross-linked polyolefin-based foam excellent in conductivity and flexibility can be produced. The conductive cross-linked polyolefin-based foam produced by the method of the present invention can be applied to an antistatic material or a buffer material for electric and electronic equipment.

Claims (4)

A conductive cross-linked polyolefin foam obtained by adding conductive zinc oxide, a conductive plasticizer, a foaming agent, and a cross-linking agent to a polyolefin resin, heating and foaming. 2. The conductive crosslinked polyolefin according to claim 1, wherein the conductive zinc oxide has a volume resistance of 1 × 10 ⁴ Ω · cm or less, a specific surface area of 20 to 70 m ² / g, and a bulk specific volume of 500 to 1,200 ml / 100 g. Foam. To 100 parts by weight of polyolefin resin, 50 to 200 parts by weight of conductive zinc oxide, 10 to 50 parts by weight of conductive plasticizer, a foaming agent and a crosslinking agent are added and kneaded, and the resulting crosslinkable foamable composition is subjected to pressure. A method for producing a conductive cross-linked polyolefin-based foam, characterized in that after heating, the pressure is released to form a foam. ^4. The production method according to claim 3, wherein the conductive zinc oxide has a volume resistance value of 1 × 10 ⁴ Ω · cm or less, a specific surface area of 20 to 70 m ² / g, and a bulk specific volume of 500 to 1,200 ml / 100 g.