JPS5833095B2 - Method for manufacturing crosslinked rubber/plastic molded bodies - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an improvement in a heat crosslinking method for a rubber/plastic molded article made of a heat crosslinkable rubber or plastic composition, such as a rubber/plastic coated electric wire.

In recent years, as a method for thermal crosslinking of rubber/plastic molded bodies made of thermal crosslinking compositions such as rubber/plastic coated electric wires, the long molding process has been carried out in a long catenary or vertical heating tube filled with an inorganic molten salt as a heating medium. A method of crosslinking was developed by passing it through the body and heating it.

However, in this inorganic molten salt heating method, which has excellent features such as excellent thermal efficiency and long heat-resistant life, the inorganic salts used as the heating medium have a low melting point, are stable at heating temperatures of 150°C to 350°C, and have a specific gravity of 2. There is nothing less than .0,
Therefore, even in rubber/plastic pipes and sheets with a small specific gravity, or rubber/plastic insulated cables, the electric conductor is a rubber/plastic with a specific gravity of 1.9 or less, such as an aluminum conductor or a cable with a thick insulation coating compared to the conductor diameter. It has been difficult to completely immerse a long molded article in a molten inorganic salt and thermally crosslink it unless a special device for immersion is provided.

That is, the specific gravity of the molten inorganic salt that satisfies the above conditions is about 1.9 even if it is particularly small, and when immersed, the long molded product rises and is pressed against the heating tube wall, and the heating process that forms the long molded product This is because the crosslinked composition layer is deformed and the desired shape cannot be obtained.

The present invention was created as a result of intensive studies to improve the drawbacks of these conventional inorganic molten salt immersion heat crosslinking methods.

The present invention is directed to hollow spherical fine particles of an inorganic molten salt of 97.5 to 50% weight, so-called microballoons.
The present invention relates to a method for producing a crosslinked rubber/plastic molded article using an inorganic molten salt as a heating medium, which prevents the above-mentioned problems by mixing 5 to 50 parts by weight to form a mixture with a small specific gravity.

The inorganic molten salt used in the present invention is one that is solid at room temperature and has a melting point below the decomposition temperature of rubber, plastic, etc., and preferably one with a melting point of 250° C. or below.

In addition, those having low specific gravity are preferred, such as sodium nitrate, potassium nitrate, lithium nitrate, and the like.

In addition, the inorganic hollow spherical fine particles are mainly made of silica, borosilicate glass, ceramic, etc. and have a specific gravity of 0.2 to 0.6.
It is preferable to use a particle size of about 100 μm, and commercially available products such as Glass Micro Balloon FT I O2 manufactured by Emerson & Cumming (specific gravity 0.2 to 0.6, particle size of about 40 to 150 μm) can be used. I can do it.

In the present invention, the amount of microballoon added to the molten salt is 2
．． The reason for limiting the amount to 5 to 50% by weight is that if the amount added is less than 2.5% by weight, the effect of reducing the specific gravity of the heating medium is small, and if it exceeds 50%, the viscosity of the heating medium increases and the heating medium loses fluidity and is immersed. This is because the properties of the molded product decrease and the heat crosslinking of the molded product becomes difficult.

Furthermore, when using the molten salt mixture of the present invention, a stirring device may be provided in the heating tube or the molten salt may be circulated in order to improve the dispersion of the microballoons in the molten salt.

Next, examples of the present invention will be shown.

Example: An aluminum conductor with a size of 150 mm is extruded with a semiconductive polyethylene composition made of polyethylene mixed with semiconductive carbon and coated with a thickness of 0.5 mm, and the outer periphery is coated with a density of 0.92 mm.
A mixture consisting of 100 parts by weight of low-density polyethylene, 2.0 parts by weight of dicumyl peroxide, and 0.2 parts by weight of 4,4'-thiobis(6-tert-butyl-3-methylphenol) was extruded to a thickness of 3.5X. A polyethylene insulated capeple with a specific gravity of 1.6 was produced by coating.

In order to crosslink the cable by heating, 90 parts by weight of a molten salt with a specific gravity of 1.9, which has a lower melting point by mixing sodium nitrate, potassium nitrate, and lithium nitrate as an inorganic molten salt, is mixed with an average specific gravity of 0.
．． 25 glass micro balloons FT 102 (Em
Manufactured by erson & cu-ming 1.
Thermal crosslinking was carried out in a catenary-type vulcanized tube using a heating medium of No. 1.

Comparative Example A cable similar to Example 1 was heat-crosslinked in a catenary-type vulcanized tube using only a molten salt having a specific gravity of 1.9 as a heating medium without adding a glass microballoon.

Table 1 shows the results obtained by examining the thickness unevenness, degree of crosslinking, electrical characteristics, etc. of each of the crosslinked polyethylene insulated cables obtained in the Examples and Comparative Examples.

As shown in Table 1, the deflection ratio of the cables thermally crosslinked using the heat-melting medium of the present invention was significantly improved.
Along with this, the dielectric breakdown strength is also good.

As described above, the method of the present invention takes advantage of the characteristics of molten salt, which has good crosslinking efficiency and long heat-resistant life, and enables the production of elongated molded bodies with low specific gravity by thermal crosslinking, which was previously impossible with inorganic molten salts. Furthermore, since no water is used during crosslinking, crosslinked PE capacitors can be produced without the risk of water tree formation, and other excellent effects are achieved.

Claims (1)

[Claims] 1. When a crosslinkable rubber/plastic molded body is immersed in a heated medium for thermal crosslinking, a heating medium of 97.5 to 50 weight φ machine salt and 2.5 to 50 weight of hollow spherical inorganic fine particles are used. A method for producing a crosslinked rubber/plastic molded article, characterized by using a heating melting medium consisting of: