JPH0455619B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to an electrically conductive crosslinked polyethylene foam.

[Conventional technology]

Conventionally, as polyethylene conductive foam,
Products containing crystalline or chain-like low density polyethylene, which is a copolymerization of low density polyethylene and C ₄ to C ₂₀ α-olefin, and conductive carbon (Japanese Patent Application Laid-open No.
59-182822), or one containing low-density polyethylene, an ethylene-1-butene copolymer, and conductive carbon (Japanese Patent Laid-Open No. 179241/1982).

However, the above-mentioned conventional polyethylene conductive foam is intended for vacuum forming, and is designed to have a certain degree of rigidity, but lacks the flexibility of urethane foam.

[Problem that the invention seeks to solve]

Therefore, an object of the present invention is to provide an electrically conductive crosslinked polyethylene foam having flexibility that cannot be achieved with the conventional polyethylene electrically conductive foams described above.

[Means for solving problems]

The conductive polyethylene foam according to the present invention has a density of 0.910 to 0.935 g/cm ³ and a melt flow rate of 0.5 to
10 to 40 parts by weight of 5.0g/10min low-density polyethylene (hereinafter simply referred to as "parts") and a density of 0.920 to
0.945g/ ^cm3 , melt flow rate 0.5~4.0g/
10 minutes, mechanically pressing a crosslinked foam of a composition containing 90 to 60 parts of ethylene-vinyl acetate copolymer with a vinyl acetate content of 10 to 20% by weight and 7 to 15 parts of conductive carbon. Since it is a conductive crosslinked polyethylene foam with a composition within the above specified range, it has extremely excellent flexibility.

[Aspects and effects of the invention]

The low density polyethylene of the present invention has a density of 0.910
~0.935g/ ^cm3 , preferably 0.915~0.930g/ ^cm3 , melt flow rate 0.5~5.0g/10min, preferably
It is low density polyethylene of 2.5-4.0g/10min.

The ethylene-vinyl acetate copolymer used in the present invention has a density of 0.920 to 0.945 g/cm ³ , preferably 0.925 to 0.940 g/cm ³ , and a melt flow rate of
0.5~4.0g/10min, preferably 1.0~3.5g/
10 min, an ethylene-vinyl acetate copolymer with a vinyl acetate content of 10 to 20% by weight, preferably 14 to 16% by weight.

The composition ratio of the above two types of resins is 10 to 40 parts of low density polyethylene, particularly preferably 15 to 35 parts, and 90 to 60 parts of ethylene-vinyl acetate copolymer, particularly preferably 85 to 65 parts.

When the composition ratio of low density polyethylene exceeds 40 parts, the rigidity of the resin increases and a flexible foam cannot be obtained. If the composition ratio of the resin is less than 10 parts, moldability during foaming will be poor.

The conductive carbon black used in the present invention includes furnace carbon black, acetylene carbon black, channel carbon black, etc., and these may be used alone or in combination of two or more. Among carbon blacks, furnace blacks having a surface area (nitrogen adsorption method) of 900 m ² /g or more are particularly preferred conductive carbon blacks.

Conductive carbon black is made of the resin component described above.
Add 7-15 parts per 100 parts.

The above density and melt flow rate are
Measured using the method specified in JISK6760.

In the present invention, for the purpose of improving the physical properties of the composition used or reducing the cost, we use compounding agents (fillers) that do not have a significant adverse effect on crosslinking, such as zinc oxide, titanium oxide, calcium oxide, magnesium oxide, Metal oxides such as silicon, carbonates such as magnesium carbonate and calcium carbonate, fiber materials such as pulp, various dyes, pigments, fluorescent substances, and other commonly used rubber compounding agents may be added as necessary. can.

Next, a method for manufacturing the conductive crosslinked polyethylene foam of the present invention will be explained.

A foamable crosslinkable composition obtained by adding and kneading a well-known blowing agent, a blowing aid, and a crosslinking agent to the above-described mixture of low density polyethylene, ethylene-vinyl acetate copolymer, and conductive carbon black. The product is filled into a closed mold under pressure, and heated and shaped under pressure at a heating temperature of 120 to 160°C and a heating time of 20 to 70 minutes. As a result, a foamable crosslinked composition having a gel fraction of 0 to 15% and an expansion ratio of 1 to 3 times can be obtained.

Next, the foamable crosslinked composition thus shaped is placed in a mold of a desired shape such as a non-closed rectangular parallelepiped type under normal pressure, and heated in a metal bath using a rose alloy, a wood alloy, etc., an oil bath, or a nitric acid bath. In a salt bath using one or more molten salts such as sodium, potassium nitrate, and potassium nitrite, in a nitrogen stream, or in a rectangular parallelepiped with a heating medium conduit (heat medium: steam, etc.) on its outer wall. After heating for a predetermined period of time in a device provided with the foam or covered with an extensible iron plate or the like, the foam is cooled to obtain a foam. The heating temperature is 145-210℃, preferably 160-210℃ depending on the type of polyethylene used.
190℃, heating time is 10-90 minutes, preferably
15-40 minutes.

Furthermore, in the present invention, the foaming/crosslinking process can be carried out in two stages, thereby slowing down the foaming/crosslinking conditions.

In other words, the purpose of performing the foaming/crosslinking process in two stages is to homogeneously heat the foamable crosslinking composition,
That is, the purpose is to eliminate non-uniformity in heating in the thickness direction of the composition, thereby preventing surface cracks due to the appearance of local uneven foaming, entrainment phenomena,
Alternatively, the foaming ratio of the obtained foam can be adjusted up to about 30 times and the thickness can be adjusted up to about 70 mm without causing any outgassing phenomenon. Therefore, this two-stage foaming/crosslinking process is particularly effective when obtaining a final foam with a large thickness and when obtaining a foam with a high expansion ratio, for example, an expansion ratio of 10 times or more. Specifically, in the two-stage foaming/crosslinking step, the foamable crosslinkable composition shaped by the above-mentioned method is heated to 145 to 180% in the first foaming/crosslinking step.
After heating for 5 to 60 minutes, preferably 10 to 45 minutes using the heating method described above, such as in a metal bath, in a nitrogen stream set at a temperature in the range of Put it in the shape mold,
5 to 50 minutes using the heating method described above, such as in a nitrogen stream set to a temperature in the range of 170 to 210 degrees Celsius, or in a metal bath.
After heating for 15 to 40 minutes, preferably 15 to 40 minutes, it is cooled to obtain a foam with a lower density. In the first foaming/crosslinking step, preferably 5 to 70% of the foaming agent is decomposed. If the decomposition rate of the blowing agent is too high, there is no point in dividing the process into two stages, and the above-mentioned effects cannot be obtained.

The foam obtained as described above is then compressed and deformed using, for example, two constant-velocity rolls, so that the foam membrane is partially destroyed and the bubbles are partially communicated.

The obtained conductive crosslinked polyethylene foam having partially open cells has excellent flexibility and is suitable as a simple package material for preventing electrostatic damage in ICs and the like.

〔Example〕

The present invention will be specifically described below with reference to Examples.

Example 1 Low density polyethylene (product name: Novatech)
L300, density 0.922, melt flow rate 3.5, Mitsubishi Chemical Corporation) 25 parts and ethylene-vinyl acetate copolymer (trade name: Evatate H2011, density
0.93, melt flow rate 3, vinyl acetate content
15% by weight, manufactured by Sumitomo Chemical Co., Ltd.) 75 parts, furnace carbon black (product name: Ketsuien Black EC, surface area (nitrogen adsorption method) 1000 m ² /g,
Lion Akzo Co., Ltd.) 13 parts, azodicarbonamide (product name: Vinihole AC#50S, Eiwa Kasei Co., Ltd.) 14 parts, activated zinc white 0.07
α,α′-bis(t-butylperoxy)diisopropylbenzene (trade name: Perkadox)
14/P40, manufactured by Kayaku Nouri Co., Ltd.) 0.9 parts, dicumyl peroxide (product name: Percmil D, manufactured by NOF Corporation), light calcium carbonate 10 parts,
Ester lubricant (product name: Riquemar S-100,
A composition consisting of 0.1 part (manufactured by Riken Vitamin Co., Ltd.) was kneaded using a mixing roll at 80°C, and the kneaded mixture was filled into a mold (905 x 415 x 18 mm) in a press heated to 135°C. The foamable crosslinked composition was shaped by heating under pressure for 30 minutes.

The gel fraction of the foamable crosslinked composition was 5%, and the expansion ratio was 1.1 times.

Next, the obtained shaped product was heated for 50 minutes in a 165°C salt bath (mixed molten salt of sodium nitrate, potassium nitrate, and sodium nitrite), and the primary intermediate foam in which 30% of the blowing agent had been decomposed was taken out. Furthermore, put it in a non-closed mold (2120 x 1060 x 50 mm) and heat it at 180℃.
The foam was heated in a salt bath for 65 minutes to completely decompose the remaining blowing agent and obtain a foam. After cooling the obtained foam, it was passed 10 times between two constant speed rolls set at a roll spacing of 5 mm to partially destroy the cell membrane.
The air bubbles were made partially open. The resulting electrically conductive cross-linked polyethylene foam after mechanical pressing is thick.
40 mm, apparent density 0.046 g/cm ³ , surface resistance value was 0.5×10 ⁶ Ω, and had flexibility like urethane foam.

Note that the surface resistance value is a value obtained by measuring the insulation resistance in the longitudinal direction of a 1 cm x 5 cm length using an insulation resistance meter TYPE 3213 (500 V / 100 MΩ) manufactured by Yokogawa Electric Corporation.

〔Effect of the invention〕

As described above, the conductive crosslinked polyethylene foam according to the present invention has excellent flexibility. Therefore, the sheet obtained by processing the conductive crosslinked polyethylene foam of the present invention is suitable as a simple package material for preventing electrostatic damage in ICs and the like.

Claims (1)

[Claims] 1 Low density polyethylene 10-40 with density 0.910-0.935g/cm ³ and melt flow rate 0.5-5.0g/10min
Parts by weight, density 0.920-0.945g/cm ³ , melt flow rate 0.5-4.0g/10min, vinyl acetate content 10
~20% by weight ethylene-vinyl acetate copolymer 90~
To 60 parts by weight, 7 to 15 parts by weight of conductive carbon, a foaming agent, a foaming aid, and a crosslinking agent are added and kneaded to obtain a foamable crosslinkable composition, and the composition is filled into a closed mold and processed. Heating under pressure to obtain a foamable crosslinked composition with a gel fraction of 0 to 15% and an expansion ratio of 1 to 3 times, and then
A method for producing a conductive crosslinked polyethylene foam, which comprises heating the composition under normal pressure to form a foam, and then mechanically pressing the foam.