JPS61261329A - Production of electroconductive crosslinked polyolefin foam - Google Patents

Abstract

PURPOSE:To perform easily the continuous production of the titled foam excellent in electroconductivity and moldability, by kneading a specified resin mixture with an electroconductive furnace black, a crosslinking agent and a blowing agent, molding the kneading and heating the molding. CONSTITUTION:100pts.wt. resin mixture is obtained by mixing 60-90pts.wt. at least one member (A) selected from among a low-density PE (a) of a density of 0.915-0.930g/cm<3> and a MI of 1-10g/10min, an ethylene/vinyl acetate copolymer (b) of a vinyl acetate content of 5-20wt% and a MI of 1-10g/10min and an ethylene/ethyl acrylate copolymer (c) of an ethyl acrylate content of 5-20wt% and a Mi of 1-10g/10min with at least 10pts.wt. ethylene/propylene copolymer (B) of a density <0.910g/cm<3> and a propylene content of 5-25wt%. This resin material is kneaded with 5-20pts.wt. electroconductive furnace black having a hollow shell structure, 0.3-2pts.wt. crosslinking agent and 1-50pts.wt. blowing agent and molded, and the obtained molding is heated.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to a method for producing an electrically conductive crosslinked polyolefin foam.

[Conventional technology]

Conventionally, conductive crosslinked polyolefin foams have been produced by crosslinking and foaming a composition in which conductive carbon black is added to a polyolefin thermoplastic resin. In this case, crosslinking is mainly performed by electron beam crosslinking. In addition, many of the products using chemical crosslinking are produced in a batch process under pressure.

[Problem that the invention seeks to solve]

For products manufactured by electron beam crosslinking, moldability deteriorates when the expansion ratio is increased, and moldability deteriorates because the carbon concentration is increased in order to improve conductivity. In addition, methods using chemical crosslinking have the disadvantage of very poor productivity because they are batch-type.

The present invention has been made in view of these points, and has developed a method for producing conductive crosslinked polyolefin foam that can continuously produce high-magnification foams with excellent conductivity and formability. It is something.

[Means for solving problems]

The present invention has a density of 0.915 to 0,930 Q/α3. Melt index 1~10Q/10g/10min
low-density polyethylene alone, or a mixture of ethylene-vinyl acetate copolymer with a vinyl acetate content of 5 to 20 wt%, or ethylene-ethyl acrylate copolymer with an ethyl acrylate content of 5 to 20 wt%60 to
A resin mixture of 100 parts by weight is prepared by mixing 90 parts by weight of an ethylene-propylene copolymer, and 5 to 20 parts by weight of conductive furnace black having a hollow shell structure is contained in this resin mixture, and Production of a conductive crosslinked polyolefin resin foam characterized by containing a crosslinking agent and a foaming agent, and heating the same to perform crosslinking and continuous foaming to obtain a high foam with an expansion ratio of 10 times or more. It's a method.

The low density polyethylene used in the present invention has a density of 0.9
15-0,930 Q/α3, preferably 0.918-
0.925 Q/α3, melt index 1-10g
/10g/10min, preferably 2-7g/1
It is low density polyethylene of 0g/10min.

Also, ethylene-vinyl acetate copolymer contains vinyl acetate! It is an ethylene vinyl acetate copolymer with a content of 15 to 20 wt%, preferably a melt index of 1 to 10 G/10 g/10 min. Furthermore, the ethylene-ethyl acrylate copolymer has an ethyl acrylate content of 5 to 20 wt%, preferably a melt index of 1 to 20 wt%.
10G/10a+in ethylene-ethyl acrylate copolymer.

Also, as an ethylene-propylene copolymer, the density is 0.
．． Less than 910g/a113 and propylene content 5-25
wt% is desirable.

The conductive furnace black used in the present invention is different from other conductive carbon blacks in that it has a hollow shell-like particle structure and has an extremely large specific surface area. Therefore, this type of furnace black exhibits a conductive mechanism that utilizes the tunnel effect due to its characteristic particle structure.
Compared to other conductive carbon blacks, it exhibits conductivity when mixed with a small amount of resin and can achieve the desired purpose. Kerachan Black EC (trade name of Akzo Corporation) is a well-known example of furnace black.

In the present invention, in preparing the resin mixture, the low-density polyethylene, ethylene-vinyl acetate copolymer, and ethylene-ethyl acrylate copolymer may be used alone or blended at any desired ratio.
~90 parts by weight, and blended with at least 10 parts by weight of ethylene-propylene copolymer to make a total of 100 parts by weight. In this case, the preferred amount of ethylene-propylene copolymer is 15 to 30 parts by weight. If the ethylene-propylene copolymer is less than 10 parts by weight, it will be difficult to achieve high foaming. If the amount exceeds 40 parts by weight, the moldability of the resulting foam will be extremely poor, and thermoforming will be particularly difficult.

In addition, the usage ratio of furnace black is 1 part resin mixture.
The ratio is 5 to 20 parts by weight to 00 parts by weight. If this amount is less than 5 parts by weight, sufficient conductivity cannot be obtained;
If it exceeds 0 parts by weight, it will not be possible to mold a highly foamed product having a closed cell structure, and the elongation rate at high temperatures will be extremely low, resulting in very poor moldability.

The crosslinking agent in the present invention includes dicumyl peroxide,
Ditertiary butyl peroxide, 1,3-bis(tertiary butylperoxy)isopropyl bunzene, etc. are used, and 0.3 to 2 parts by weight are used per 100 parts by weight of the polymer component, but dicumyl peroxide is preferably used. The amount is 0.5-1.2 parts by weight. Furthermore, crosslinking aids such as triallyl isocyanurate, trimethylpropane trimethacrylate, triallyl cyanurate, etc.
．． 3 to 2 parts by weight may be used.

Foaming agents in the present invention include azodicarbonamide, pp--oxyhisbenzenesulfonyl hydrazide,
Examples include dinitrosopentamethylenetetramine, but since crosslinking and foaming are performed at the same time, the decomposition temperature is 200°C.
C. or higher is preferred. These foaming agents are used in an amount of 1 to 50 parts by weight based on 100 parts by weight of the resin.

The resin composition of the present invention may contain a small amount of an inorganic compound or a cell nucleating agent such as calcium stearate or fatty acid amine.

[Action of the invention: Effect]

The method of the present invention involves kneading a resin composition having the above-mentioned composition using a mixing roll, a pressure kneader, a Banbury mixer extruder, etc., and then forming the resin composition into a plate or sheet by extrusion molding or press molding. This is heat-treated on a support, for example, a wire mesh, in a hot-air constant temperature bath to cause cross-linking and foaming to produce a conductive cross-linked polyolefin foam.According to the present invention, it has excellent conductivity and moldability. This allows for easy continuous production of high-strength crosslinked polyolefin foams with excellent properties.

[Example: Comparative example]

Next, examples of the present invention and comparative examples thereof will be described. Note that the effects of Examples and Comparative Examples were evaluated based on the following criteria.

Apparent density of foam: Based on JISK6767.

Volume resistivity: Japan Rubber Association standard (SRI8230
1) Formability: Vacuum forming machine “Buravac F” manufactured by Sanwa Kogyo Co., Ltd.
E-36 type" was used to measure and compare the forming drawing ratio.

(Forming drawing ratio: This is the maximum drawing ratio that allows molding. The larger this value is, the deeper drawing is possible, and the molding of complex molded products is also possible.) Example 1 Low-density polyethylene (density 0. 920 Q/α3. Melt index 2. Og/10g/10min > g
o parts by weight and EP (ethylene propylene) rubber (density 0.
88a/α3. Melt index 1. Og/10g/
10min) 20 parts by weight and Ketjen Black EC
10 parts by weight and 0.6 parts by weight of dicumyl peroxide,
After sufficiently kneading 15 parts by weight of azodicarbonamide in a processing kneader, it is formed into a sheet with a thickness of 2.0a+ using an extruder, and then heated by continuously passing through a hot air oven at 230°C to cross-link it. A foamed sheet having a thickness of about 6IIR was obtained by foaming. The resulting foam had an apparent density of 9, volume resistivity, and moldability, which were measured and shown in Table 1 below.

Example 2 ffi density 1t HolJ ethylene (density 0.920 Q/
cm3. Melt index 2. OQ/10iin
) 20 parts by weight and ethylene-vinyl acetate copolymer (vinyl acetate content 15 wt%.

Melt index 2.0 G/10g/10min
) 60 parts by weight and soil tyrene-brobylene copolymer (EP
Rubber, density 0.88g/'α3. melt index 1
．． Og/10main) 20 parts by weight, 0 parts by weight of Ketjen Black ECl, 0.6 parts by weight of dicumyl peroxide
A foam was produced under the same conditions as in Example 1 using 15 parts by weight and 15 parts by weight of azodicarbonamide. The properties of the obtained foam were measured in the same manner as above and are also listed in Table 1.

Example 3 Ethylene-vinyl acetate copolymer, vinyl acetate content 10vt%
, melt index 2. Oa, /10iin) 4
0 parts by weight and ethylene-ethyl acrylate copolymer (
Ethyl acrylate content iowt%, melt index 1.5 o/10g/10min) 40 heavy chain parts and ethylene-propylene copolymer density 0.880
/as3. Melt index 1. OQ/10g/1
0min > 20 parts by weight and Ketjen Black ECl
A foam was produced under the same conditions as in Example 1 using 0 parts by weight of dicumyl peroxide, 0.6 parts by weight of dicumyl peroxide, and 15 parts by weight of azonecarboxamide.

Each characteristic of the obtained foam was measured and listed in Table 1.

Comparative Example 1 Low density polyethylene (density 0.9200/aR3, melt index Q/10g/10min) 1001
1 part by weight, 10 parts by weight of Ketjenblack EC, 0.6 parts by weight of dicumyl peroxide, and 15 parts by weight of azodicarbonamide.
A foam was produced under the same conditions as in Example 1 using parts by weight. Each characteristic of the obtained foam was measured and listed in Table 1.

Comparative Example 2 Low density polyethylene (density 0.920 g/an3.
Melt index 2. OQ/1 (1min)
50 parts by weight and ethylene-propylene copolymer (density 0.
880/c113° Melt index 1.0 g/1
A foam was produced under the same conditions as in Example 1 using 50 parts by weight of Ketjenblack EC, 0.6 parts by weight of dicumyl peroxide, and 15 parts by weight of azodicarbonamide. Each characteristic of the obtained foam was measured and listed in Table 1.

Comparative Example 3 Low density polyethylene (density 0.920 l/α3. Melt index 2.0 CI+ /10g/10min
> 801 parts by weight and ethylene-propylene copolymer (density 0.88g/α3° melt index 1.Og/1
A foam was produced under the same conditions as in Example 1 using 20 parts by weight of 0g/10min), 3 parts by weight of Ketjenblack EC, 0.6 parts by weight of dicumyl peroxide, and 15 parts by weight of azodicarbonamide. Each characteristic of the obtained foam was measured and listed in Table 1.

The following can be seen from the experimental results shown in the table.

Comparative Example 1 is a product in which no ethylene-propylene copolymer was used, and in this case, the apparent density of the foam was 0.
,075 Q/as3, making it impossible to obtain high magnification.

In addition, in Comparative Example 2, 50% of the ethylene-propylene copolymer was used.
In this case, the density is reduced to some extent, but the moldability is poor.

Comparative Example 3 is a case where less than 5 parts by weight of Ketjenblack EC is used, and in this case, moldability is good at high magnification, but conductivity is poor.

As is clear from Table 1 and the Examples, the method of the present invention allows the production of conductive crosslinked polyolefin foams with high magnification and excellent moldability, and its industrial value is extremely large.

Claims (1)

[Claims] Low-density polyethylene alone with a density of 0.915 to 0.930 g/cm^3 and a melt index of 1 to 10 g/10 min, or an ethylene vinyl acetate copolymer with a vinyl acetate content of 5 to 20 wt%, or an ethyl acrylate content A resin mixture of 100 parts by weight is prepared by mixing ethylene-propylene copolymer with 60-90 parts by weight of a mixture of 5-20 wt% ethylene-ethyl acrylate copolymer, and a hollow shell is added to this resin mixture. In addition to containing 5 to 20 parts by weight of conductive furnace black having a structure, a crosslinking agent and a foaming agent are also contained, and this is heated to perform continuous foaming at the same time as crosslinking, so that the foaming ratio is as high as 10 times or more. A method for producing a conductive crosslinked polyolefin foam, the method comprising obtaining a foam.