JPS59113037A - Method for crosslinking polyethylene under heating - Google Patents

Abstract

PURPOSE:To obtain effectively crosslinked polyethylene usable for insulating layers of electric wires and cables, etc. without causing expansion nor hexagonal patterns, by crosslinking polyethylene with far infrared rays. CONSTITUTION:A polyethylene composition containing an organic peroxide, e.g. di-alpha-cumyl peroxide, is molded into a given shape and then irradiated with radiation of far infrared rays under heating to decompose the organic peroxide in the polyethylene composition under heating and crosslink the polyethylene.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to improvements in methods for chemically crosslinking polyethylene.

Although polyethylene is a chain polymer and has excellent electrical insulation properties, it has poor thermal properties, so this drawback is overcome by crosslinking, and it is widely used, for example, as an insulating layer for electric wires and cables.

By the way, there are various methods for this crosslinking method, but a common method is to mold a polyethylene composition containing an organic peroxide into a predetermined shape and then crosslink it by thermal decomposition of the organic peroxide.

For this thermal decomposition, most foils are heated with steam, but this method has the risk of reducing the commercial value due to the formation of a tortoise-shell pattern on the surface of cross-linked polyethylene due to steam heating, and it also increases the cross-linking speed. In this case, the pressure-resistant structure of the manufacturing equipment must be made even more robust because crosslinking must be carried out at higher temperatures using steam at even higher pressures, but in reality, raising the temperature to over 200°C increases the vapor pressure. This is practically impossible because of the excessive increase in crosslinking rate, and this has the disadvantage that the crosslinking rate is also limited by itself.

In addition, from the viewpoint of preventing foaming from crosslinking the polyethylene mixture, the atmospheric pressure is 2°F or higher, preferably 5 to 5°C.
q/cj, and it is said that crosslinking treatment under an atmosphere of higher pressure than necessary to prevent foaming involves waste of EE manufacturing equipment.

Instead of steam heating, a method has been developed to crosslink polyethylene with a crosslinking agent by radiant heating in an inert gas atmosphere, such as nitrogen gas or carbon dioxide gas, with the necessary gas pressure applied to prevent foaming. , Gas King is 8kfA at 200-350℃
It was considered that an infrared heater could be used for radiant heating, as described below.

However, in the above method using an infrared heater as a heat source, most of the infrared rays radiate over the entire wavelength range of 0.76 to 2.5 μm, and far infrared rays (2.5 to 10 μm), which are more efficient for radiant heating,
00 μTrL) is not effectively radiated, the method involves a large amount of energy loss and requires a large number of heat sources in order to accelerate the crosslinking rate of polyethylene.

The present invention was made in view of the above-mentioned circumstances, and relates to a method for effectively crosslinking polyethylene using far infrared rays.

Next, an embodiment of the present invention (in the case of a cable) will be described as follows.

Example 1 On a 22*A conductor, di. α, cumyl peroxide 0
．． The coating was carefully coated with high-density polyethylene containing 3.5% by weight, and while pressurized with nitrogen gas, an infrared lamp was used as a heat source and titanium oxide sprayed stainless steel was used as a radiant plate to radiate far infrared rays, and the heating temperature was 200℃ nitrogen. A crosslinked polyethylene electric wire without foaming or hexagonal pattern was obtained at a gas pressure of 5 to -.

Example 2 Diameter 1. The conductor is coated with low-temperature polyethylene containing Shiro α and Kumirnoguichi Oyaside to a thickness of 07 mm, and radiant stainless steel is thermally sprayed with zirconium oxide using a 7-Z heater as a heat source in nitrogen with a gauge of 1 El Kicrl. The crosslinking was carried out by heating at 210° C. using a plate.

The obtained crosslinked polyethylene electric wire did not have foaming or a hexagonal pattern.

In order to manufacture cross-linked polyethylene electric wires similar to those described above, the method of the present invention, which uses far-infrared rays from the same heat source as the conventional infrared beam radiation, has less energy loss, so the cross-linking speed is faster, and , the effect is that the crosslinking equipment needs to be smaller in order to achieve the same crosslinking speed.

In addition, although the above-mentioned example described the production of a crosslinked polyethylene electric wire, it can be carried out in the same way for a crosslinked polyethylene sample or a crosslinked polyethylene sample.

Next, to explain the present invention with reference to the drawings, Fig. 1 shows an example of an experimental apparatus, in which a semicircular reflector plate 3 is provided on the back side of the heater 1, and a large amount of infrared rays is emitted on the opposite side of the heater 1. A radiating stainless steel plate and a radiating plate 2 made of a far-infrared radiating ceramic made of metal oxides such as chromium, zirconium, and titanium are coated on the stainless steel plate by thermal spraying, etc., and cross-linked polyethylene is placed on the outside. It is designed to be heated and crosslinked.

Note that a thermocouple wire 5 was attached to the polyethylene sample 4 to measure the temperature.

Figure 2 shows the relationship between the radiation heating time of polyethylene and the temperature of polyethylene based on the above actual test. C and remains the same after that, but in the radiant plate coated with the metal oxide ceramic described above, far-infrared radiation increases, rising to 90°C in 17 minutes and reaching 100°C in 40 minutes. It can be said that this method is an extremely effective heating means.

Incidentally, the surface temperature of the radiation plate according to the present invention is 180~
The temperature was 202°C, but for stainless steel it was 180-193°C.

Note that chromium oxide, zirconium oxide, titanium oxide, etc. may be formed not only by thermal spraying onto a stainless steel plate, but also as a ceramic sintered body, for example.

It goes without saying that it is more effective to use a heat source that can irradiate more far infrared rays when implementing the present invention.

[Brief explanation of the drawing]

Figure 1 shows a cross-sectional view (a) and a partially longitudinal side view (b) of an example of the experimental equipment, and Figure 2 shows a relationship curve between polyethylene temperature and heating time for an experimental example using this equipment. Ru. 1 heater, 2 radiant plates, 3 reflectors. Representative Patent Attorney Mamoru Takeuchi Figure 1

Claims (1)

[Claims] A feature of this method is that after a polyethylene composition containing an organic peroxide is molded into a predetermined shape, radiant heating is performed using far infrared rays to thermally decompose the organic peroxide pentoxide in the polyethylene composition and crosslink the polyethylene. A method for thermally crosslinking polyethylene.