JPS6252691B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a novel method for vulcanizing a molded article made of a composition containing a conductivity-imparting agent by high-frequency heating.

When heating and vulcanizing a molded article made of a composition containing a conductivity-imparting agent such as carbon black by high-frequency heating, if there is temperature unevenness in the molded article before high-frequency heating, the temperature will change when high frequency is applied. There are many cases where unevenness becomes even larger and uniform vulcanization cannot be achieved.

The present invention proposes a novel vulcanizability described in the claims that does not have the above problems.

According to the research conducted by the present inventors, non-uniform vulcanization occurs for the following reasons.

In high frequency heating, the frequency is usually 10MHz~
A high frequency of about 3000 MHz is used, and the composition containing the conductivity imparting agent exhibits dielectric loss-temperature characteristics such that the dielectric loss is minimized at a specific temperature in the above frequency range. The temperature at which the above minimum value is reached (hereinafter referred to as T _MIN ) varies depending on the type and amount of the conductivity imparting agent, the type of organic polymer that is the base of the composition, etc., but let's heat and vulcanize it now. If high-frequency heating is applied to a molded product in which there are parts with a temperature lower than T _MIN and parts with a temperature higher than T _MIN , the low-temperature parts will change as the temperature increases due to the heating. For example, as T _MIN approaches, the dielectric loss of the composition in that part decreases, making it gradually difficult to heat.On the other hand, in the high temperature part, conversely, the dielectric loss increases due to the temperature increase due to high frequency heating. increases, making it easier to heat up.

Since a composition containing a conductivity-imparting agent exhibits the above-mentioned unique behavior, in the present invention, the molded article is previously maintained at a temperature of T _MIN or higher before high-frequency heating is performed. In this way, even if high-frequency heating is applied, all parts of the molded product are maintained at a temperature above T _MIN in advance, so even if the temperature rises due to heating,
Since there is no part where the dielectric loss decreases and the dielectric loss only increases as the temperature rises, substantially uniform heating and therefore uniform vulcanization can be performed.

In the present invention, carbon black, particularly conductive carbon such as furnace black, acetylene black, or ketene black, or a natural or synthetic organic polymer composition rendered conductive by incorporating a conductivity imparting agent such as metal powder, etc. Vulcanization can be performed on short or long molded products such as pipes, tubes, tapes, rods, profiles, etc.
The present invention has a more significant effect when applied to a molded article made of a composition having an electrical conductivity of at least about 10 ⁰ to ^{10 3} Ω·cm as measured by ASTM D991-68 at room temperature.

Examples of such compositions include semiconductive rubber and plastic compositions used for conductor shielding layers and insulation shielding layers of power cables having solid insulator layers such as cross-linked polyethylene insulated power cables. . Therefore, the present invention is also effective when applied to the case of vulcanizing a conductor shielding layer and/or an insulating shielding layer of a power cable having a solid type insulating layer.

The T _MIN of the composition constituting the molded article to be heated and vulcanized according to the present invention is determined by a method of determining the dielectric loss by a perturbation method using a cylindrical cavity resonator while increasing the temperature stepwise in an air circulation oven. It can be measured by

The molded article to be heated and vulcanized is heated with high frequency while being maintained at a temperature of T _MIN or higher in advance. When the molding temperature of the composition is T _MIN or higher, after molding,
It is best to perform high-frequency heating while each part of the molded product maintains a temperature above T _MIN .

The attached figure is a partial sectional view of an example of an apparatus for carrying out the method of the present invention, in which a conductor 1 having a crosslinked polyethylene insulating layer is connected to a crosshead 3 of an extruder 2, a vulcanized tube 4 with a coaxial cavity, Then, it passes successively through a cooling pipe 5 filled with high-pressure cooling water. A semiconductive compound is extruded from the extruder 2, and an insulating shielding layer 8 is formed on the insulating layer 7. A high frequency wave from a high frequency oscillator (not shown) passes through a waveguide 9 and is supplied to a coaxial cavity vulcanized tube 4 made of a metal with good conductivity such as copper or aluminum, thereby heating the insulating shielding layer 8. be done.

10 is a ceramic window provided at the opening of the waveguide 9. Reference numeral 11 denotes a cylindrical heating jacket provided on the inner wall of the inlet of the vulcanization tube, and the conductor shielding layer 8 is heated to a temperature higher than T _MIN of the composition forming the layer 8 prior to high-frequency heating by the jacket. It should be noted that if the extrusion temperature of the conductor shielding layer 8 is above T _MIN and the layer still maintains a temperature above T _MIN when high-frequency heating is applied, no heating is necessary compared to the jacket 11 . In order to prevent the generation of voids during vulcanization and cooling, it is preferable to create a pressurized atmosphere of about 2 to 30 kg/cm ² in the vulcanization tube. Further, the vulcanized tube 4 may have a diameter approximately equal to the outer diameter of the insulating shielding layer 8, and lubricating oil may be supplied to the inner wall of the vulcanized tube for smooth advancement of the cable.

Hereinafter, the present invention will be explained in more detail with reference to comparative examples and examples.

Comparative example 1 On a copper conductor with an outer diameter of 13.0 mmφ (19 pieces/2.6 mm),
An insulating layer made of low density polyethylene (density: 0.920, melt index 1.1) containing a chemical crosslinking agent etc. with a thickness of 12.0 mm, and an ethylene layer containing acetylene black and dicumyl peroxide with a thickness of 0.5 mm.
Vinyl acetate semiconductive composition (volume resistivity 1.5×10 ²
Ω・cm, T _MIN : 95℃) The upper half of the insulation shielding layer of the cable core is output at 100℃ and the lower half at 90℃.
When applying a high frequency of 25kW frequency 2.450MHz, 30
After seconds, the upper half-circle reached about 250°C, while the lower half-circle was about 120°C.

Example 1 The insulating shielding layer of the cable core, which had the same structure as Comparative Example 1 and was formed of an insulating layer and an insulating shielding layer made of the same composition as Comparative Example 1, was uniformly maintained at 100°C over the entire circumference in advance. When high frequency waves were applied under the same conditions as in Comparative Example 1, the temperature required for vulcanization was reached uniformly over the entire circumference, and vulcanization was carried out to the desired degree of crosslinking over the entire circumference of the insulating layer. Ta.

[Brief explanation of the drawing]

The accompanying drawings are explanatory diagrams of the present invention, in which 8 is an insulating shielding layer made of a composition containing carbon black as a conductivity imparting agent, 11 is a preheating device, 4 is a high frequency vulcanization device, and 9 is a high frequency waveguide.

Claims (1)

[Claims] 1. When heating and vulcanizing a molded article made of a composition containing a conductivity imparting agent by high-frequency heating, the dielectric loss of the composition at the frequency of the high frequency applied during high-frequency heating of the molded article must be minimized in advance. A vulcanization method characterized by bringing the vulcanization to a temperature equal to or higher than .