JPH0471417B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Field of Application] The present invention relates to a conductive crosslinked polyethylene foam with excellent heat shrinkage resistance, and more particularly to a conductive crosslinked polyethylene foam that is particularly suitable as a material for preventing electrostatic breakdown during heat aging of ICs. [Conventional technology] Conventionally, as polyethylene conductive foam,
A product containing crystalline or linear 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). In recent years, the guaranteed operating temperature of integrated circuits has been increasing year by year, and as a result, temperatures of 100° C. or higher are being applied even during aging before shipment. However, the above-mentioned conventional polyethylene conductive foam has a practical temperature of up to about 100°C, and if used at 100°C or higher for more than 24 hours, the shrinkage rate of the foam will exceed 5%, making it unusable. There is a drawback. [Problems to be Solved by the Invention] Therefore, an object of the present invention is to provide a conductive crosslinked polyethylene foam having excellent heat shrinkage resistance that cannot be achieved with the conventional polyethylene conductive foam described above. There is a particular thing. [Means for solving the problems] The conductive polyethylene foam according to the present invention is made of low-density polyethylene 30 having a melting point of 106 to 112°C, a density of 0.918 to 0.925 g/cm ³ , and a melt flow rate of 0.1 to 0.5 g/10 min. ~70 parts by weight (hereinafter simply referred to as "parts"), melting point 131~137℃, density 0.945~0.964g/
^cm3 , a composition containing 70 to 30 parts of high-density polyethylene with a melt flow rate of 4.5 to 9.0 g/min, and 7 to 15 parts of conductive carbon black. Since the composition is a conductive crosslinked polyethylene foam, it has extremely excellent heat shrinkage resistance. [Aspects and effects of the invention] The low density polyethylene of the present invention has a melting point of 106
~112℃, preferably 108~110℃, density 0.918~
It is low density polyethylene with a melt flow rate of 0.925 g/cm ³ , preferably 0.918 to 0.922 g/cm ³ and a melt flow rate of 0.1 to 0.5 g/10 min, preferably 0.25 to 0.40 g/10 min. The high density polyethylene used in the present invention has a melting point of 131 to 137°C, preferably 132 to 135°C.
℃, density 0.945~0.964g/ ^cm3 , preferably 0.950~
0.956g/cm ³ , melt flow rate 4.5-9.0g/
10 min, preferably 5.0 to 5.5 g/10 min of high density polyethylene. The composition ratio of the above two types of polyethylene is 30 to 70 parts of low density polyethylene, particularly preferably 40 to 60 parts.
parts, 70 to 30 parts of high density polyethylene, particularly preferably 60 to 40 parts. When the composition ratio of high-density polyethylene exceeds 70 parts, the flexibility of the resin is insufficient, making it difficult for IC lead pins to penetrate, and when the composition ratio of the resin is less than 30 parts, heat shrinkage resistance is insufficient. 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 to 15 copies per 100 copies. The above melting point refers to the differential scanning calorimeter (DSC)
is the melting end temperature of Density and melt flow rate are measured by the method specified in JISK6760-1971. 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 well-known foaming agent, foaming aid, and crosslinking agent are added and kneaded to the above-described mixture of low density polyethylene, high density polyethylene, and conductive carbon black, and the resulting foamable crosslinkable composition is pressed. Fill it into a closed mold and heat it under pressure to a temperature of 120~
Heat shaping or crosslinking is performed at 140°C for 20 to 45 minutes. As a result, a foamable crosslinked composition having a gel fraction of 0 to 15% and an expansion ratio of 1 to 2.2 times is obtained. Next, the foamable crosslinked composition thus obtained is placed in a mold of a desired shape, such as a non-closed rectangular parallelepiped type, under normal pressure, and placed in a metal bath, oil bath, etc. using Rose alloy, Wood alloy, etc. In a salt bath using one or more molten salts such as sodium nitrate, potassium nitrate, potassium nitrite, etc., in a nitrogen stream, or in a rectangular parallelepiped shape with a heating heat medium conduit (heat medium: steam, etc.) on its outer wall. ), and after heating for a predetermined period of time inside the foam or covered with an extensible iron plate or the like, the foam is cooled to obtain a foam. Heating temperature is 145-175℃ depending on the type of polyolefin used, preferably 160-170℃
℃, heating time is 20-40 minutes, preferably 25-40 minutes
It is 35 minutes. Furthermore, in the above method, gentle foaming is performed to impart good conductivity, and in particular, in addition to imparting a high foaming ratio of 10 times or more and a uniform fine cell structure, cross-linking foaming property by heating under normal pressure is added. Crosslinking and foaming of the composition, the foaming agent in the above composition is 15-85%
It is particularly preferable to carry out the process in two stages: first heating to decompose, and second heating to decompose the blowing agent and crosslinking agent remaining undecomposed by heating at a temperature higher than the first heating temperature. The foam of the present invention can also be produced by heating under pressure for a certain period of time and then removing the pressure at a high temperature. In addition to chemical crosslinking, the foamable crosslinkable composition is supplied to an extruder, extruded into a sheet, irradiated with ionizing radiation, and after crosslinking is heated in the foaming machine to a temperature higher than the decomposition temperature of the blowing agent. ,
The foam of the present invention can be produced by foaming. The obtained conductive crosslinked polyethylene foam has excellent heat shrinkage resistance and is suitable as a material for preventing electrostatic damage during heat aging of ICs. EXAMPLES The present invention will be specifically described below with reference to Examples. Example 1 Low density polyethylene (product name: Yucalon HE-
30, melting point 109℃, density 0.920, melt flow rate
0.3, manufactured by Mitsubishi Yuka Co., Ltd.), 50 parts of high-density polyethylene (product name: Yucalon Hard JY20-8,
Melting point 134℃, density 0.953, melt flow rate 5.0,
(manufactured by Mitsubishi Yuka Co., Ltd.) 50 copies, furnace carbon black (product name: KETSUCHIEN BLACK EC,
Surface area (nitrogen adsorption method) 1000 m ² /g (manufactured by Lion Akzo Co., Ltd.) 13 parts, azodicarbonamide (trade name: Vinifol AC#50S manufactured by Eiwa Kasei Kogyo Co., Ltd.) 14 parts, activated zinc white 0.15 parts, α, α A composition consisting of 1.0 part of '-bis(t-butylperoxy)diisopropylbenzene (product: Perkadox-14/P40 manufactured by Kayaku Nouri Co., Ltd.) and 10 parts of light calcium carbonate was kneaded with a mixing roll at 120°C. , the mold in a press heated to 130℃ (150
x 150 x 18 mm) was filled with the kneaded material and heated under pressure for 30 minutes to obtain a foamed crosslinked composition. The foamed crosslinked composition had a gel fraction of 5% and a foaming ratio of 1.1 times. Next, the obtained foamed crosslinked composition was heated for 30 minutes in a 165°C salt bath (mixed molten salt of sodium nitrate, potassium nitrate, and sodium nitrite) to form a primary intermediate foam in which 30% of the blowing agent had decomposed. Take out the
Furthermore, it was placed in a non-closed mold (390 x 390 x 50 mm) and heated in a salt bath at 180°C for 40 minutes to completely decompose the remaining blowing agent and obtain a conductive foam. The obtained foam had a thickness of 50 mm, an apparent density of 0.045 g/ ^cm3 , and a measured surface resistance value of 0.007 to 0.08.
The additive dimension change (110℃, 100 hours) at ×10 ⁶ Ω is -2.5
It was -2.1%, and the IC lead pins were easily stuck. The surface resistance value was measured using an insulation resistance meter TYPE3213 (500V/100MΩ) manufactured by Yokogawa Electric Manufacturing Co., Ltd.
This is a value obtained by measuring the insulation resistance in the longitudinal direction of a length of cm x 5 cm, and the heating dimensional measurement was based on JIS-K6767. Examples 2 and 3 In Example 1, except for changing the formulation,
A conductive foam was manufactured under the same conditions as in Example 1.
These formulations and results are shown in Table 1. Comparative Examples 1 and 2 The method of Example 1 was carried out under the same conditions except that the composition and disposal were changed. These formulations and results are shown in Table 1.

【table】

〔Effect of the invention〕

As described above, the conductive crosslinked polyethylene foam according to the present invention has excellent heat shrinkage resistance. Therefore, the sheet obtained by processing the conductive crosslinked polyethylene foam of the present invention is suitable as a material for preventing electrostatic damage during thermal aging of ICs.

Claims (1)

[Claims] 1. Melting point 106-112°C, density 0.918-0.925g/cm ³ ,
30 to 70 parts by weight of low density polyethylene with a melt flow rate of 0.1 to 0.5 g/10 min, and 70 to 70 parts of high density polyethylene with a melting point of 131 to 137°C, a density of 0.945 to 0.964 g/cm ³ and a melt flow rate of 4.5 to 9.0 g/10 min. A conductive crosslinked polyethylene foam obtained by crosslinking and foaming a composition containing 30 parts by weight of conductive carbon black and 7 to 15 parts by weight of conductive carbon black. 2 Conductive carbon black has a surface area of 900 m ² /
The electrically conductive crosslinked polyethylene foam according to claim 1, which is a furnace black having a weight of at least g.