JPS6024916A - Manufacture of molded product made of silane cross linked polyolefine - Google Patents

Abstract

PURPOSE:To obtain the molded product without foaming, preventing the deterioration of the properties of the molded product by cooling under pressure the molded product immediately after it has been extruded. CONSTITUTION:The cross head of an extruding machine connected to the cylindrical cooling tank 3, is caused to be a closed system, and said closed system is pressurized by feeding air or nitrogen gas. The molded product made of silane cross linked polyolefine extruded from the extruding machine, is cooled by such pressurized atmosphere. Consequently, the molded product without foaming in a coated portion is molded. Thus, the foaming of silane cross linked polyolefine resin at extruding process may be suppressed, omitting the control for the set temperature of the extruding machine, the revolution number of a screw and the blended amount, etc.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing a silane-crosslinked polyolefin molded article that can significantly suppress foaming of the molded article.

Further, in the present invention, when extrusion molding a silane crosslinked polyolefin resin composition into the shape of an electric wire, there are no restrictions on the setting conditions of the extruder or the amount of filler, etc. to be blended.

The present invention relates to a method for producing a silane-crosslinked polyolefin molded article in which foaming inside the molded article is significantly suppressed by cooling the molded article under pressure immediately after extrusion.

Conventionally, as a method for producing crosslinked polyolefin molded bodies, the process of adding a silane crosslinking agent to an insulating material such as a polyolefin resin and directly extruding it onto a conductor, etc., is advantageous in terms of cost compared to other crosslinking methods. Although it is a method,
When using this method, there was a major problem in that foaming occurred in the molded product during extrusion molding of the composition. The causes of this foaming include (4) direct foaming factor, (B
) There are indirect foaming factors, (AJ direct factors include (a)
Increase in material temperature due to shear heat generation in the extruder, (b) Generation of bubbles due to water and low volatile matter contained in the material silane crosslinking agent, (/1 Hydrates contained in fissies such as flame retardants) (B) Indirect factors include: (B) Indirect factors include: (B) Increase in material viscosity due to a rise in material temperature due to a crosslinking reaction occurring in the extruder during the crosslinking process, and reaction formation. In the silane crosslinking process, the following factors are unavoidable: generation of bubbles due to low volatile content in the silane crosslinking process. Therefore, as means for suppressing these foaming, there are several ways to control the extrusion conditions such as the extrusion setting temperature of the extruder and the screw rotation speed, limit the amount of filler and the amount of silane crosslinking agent, etc. Although similar drying treatments have been considered, conventional methods have lacked a decisive factor. Furthermore, removal of water and low volatile matter contained in the silane crosslinking agent requires advanced technology and installation of equipment.

Therefore, in the silane crosslinking process, extrusion at high temperature is advantageous in order to cause a craft reaction within the extruder, but foaming due to crosslinking within the extruder becomes a problem. However, the set temperature of the extruder to suppress foaming,
If the screw rotation speed is suppressed, the properties such as the degree of crosslinking and tensile strength required for wire insulating materials will decrease. or,
As the amount of fillers such as flame retardants added increases, the degree of foaming increases and the appearance deteriorates, but reducing the amount of fillers added affects properties such as flame retardancy. Furthermore, the preliminary drying treatment of fillers for the purpose of removing moisture takes time and effort, and requires drying equipment and the like.

The present invention has been made in the face of the above-mentioned various problems, and as a result of intensive investigation into ways to improve the problems, the present invention has been developed to produce a silane-crosslinked polyolefin molded product that does not deteriorate the layer properties of the molded product and can obtain a molded product that is free from shrinkage and foaming. This method has been established, and is characterized in that when a polyolefin resin composition containing a silane crosslinking agent is extruded, the molded product immediately after extrusion is cooled under pressure.

In addition, in the present invention, the polyolefin resin composition containing a silane crosslinking agent includes, in addition to a crosslinking accelerator, a flame retardant,
It also includes those containing fillers such as heat stabilizers as necessary.

That is, in one embodiment of the method of the present invention, for example, the crosshead of an extruder is connected to a cylindrical cooling tank, the system is made into a closed system, and the inside of the system is pressurized by supplying °C air or nitrogen gas. By cooling the silane-crosslinked polyolefin molded product that has come out of the molded product in a pressurized atmosphere, it is possible to produce a molded product with no foaming in the covered portion. Further, as the source of pressurization in the present invention, it is possible to use air from a compressor or inert gas such as nitrogen gas from a cylinder. The pressurizing quantity is 1. The degree of foaming generated in the molded product varies depending on the total pressure, but if there are several foams with a diameter of 1rrrrrL or less per radial cross section, it is considered a small number (both O',
At a pressure of 5 kJ, g, even if there are several dozen foams with a diameter of 1 to g trtm, at least 1.5 kVC!
Foaming can be eliminated by applying a pressure of rLg.

Furthermore, in the present invention, there are no restrictions on the conditions such as the extruder's set temperature, screw rotation speed, linear speed, etc., and there is no restriction on the amount of substances added such as flame retardants, heat stabilizers, crosslinking accelerators, etc. .

This K makes it easier to impart properties such as degree of crosslinking and tensile strength.

Note that the polyolefin resin used in the present invention is not particularly limited, and may include polyethylene, polypropylene, ethylene-vinyl acetate copolymer, ethylene-tetrahylene copolymer, ethylene-ethyl acrylate copolymer, and even chlorine-based resin. It can also be applied to resins such as chlorinated polyethylene, and systems in which fillers such as various flame retardants, heat stabilizers, and pigments are added to these resins.

The present invention will be further explained below with reference to Examples and comparison with Comparative Examples.

Examples 1-6. Comparative Example 1~1゜The extruder used in the Examples and Comparative Examples was 55mmφ, %
-28 The outline of the pressurized cooling device is as shown in the schematic diagram of FIG.

The cooling tank 8 is a 400 mmφ x 4000 g iron cylinder, and the sliding head portion 2 is connected to the crosshead 1 of the extruder. Also, a rubber backing 4 is placed at the terminal to prevent pressure loss. Reference numeral 6 indicates cooling water, 8 indicates waste water, 6 indicates a compressor as an air supply source, and 7 indicates a nitrogen cylinder as a nitrogen gas supply source.

Further, Table 1 summarizes the compositions, extrusion conditions, and the presence or absence of foaming of the obtained molded products in Examples 1 to 5 and Comparative Examples 1 to 10.

The names and patterns of each component in each composition were as follows.

(1) Product name F-184 manufactured by Showo Denko Co., Ltd. (2) Product name Evaflex EV2 manufactured by Mitsui Polychemical Co., Ltd.
60, (8) Product name EP-02, manufactured by Japan Synthetic Rubber Co., Ltd.
4.) Product name MB 780 manufactured by Nippon Unicar Co., Ltd.
(5) Hisilite H-4 manufactured by Showa Light Metal Co., Ltd.
2-M% (6) Dibutyltin silaurylate, silane crosslinking catalyst, trade name mark BT- manufactured by Adeka Argus Chemical Co., Ltd.
11゜(7) Vinyltrimethoxysilane, silane crosslinking agent, manufactured by Tone Silicone Co., Ltd., trade name 5Z-6800, (8) Dicumyl peroxide, peroxide, manufactured by Mitsui Petrochemical Industries, Ltd., clear from the table For example, in Comparative Example 1, when the composition shown in the table was extruded onto a copper wire using an extruder with a set temperature of 200° C. and a screw rotation speed of 6 Orpm, a small amount of foaming occurred.

In addition, in Example 1, extrusion molding was carried out using the same composition and the same extrusion conditions as in Comparative Example 1, and at that time, air was applied to L2 pressure at 0.5 kV and cooling was performed, and the foaming disappeared. The degree of crosslinking, Ts and El at this time showed the values shown in the table.

As described above, according to the method of the present invention, foaming during extrusion molding of polyolefin resin due to silane crosslinking can be suppressed without controlling the set temperature of the extruder, screw rotation speed, blending amount, etc. can. In this way, since there are no limitations on the setting conditions and compounding conditions, the practical value is extremely great, as conditions can be selected according to the required characteristics.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram illustrating a pressurized cooling device of a manufacturing apparatus according to an embodiment of the present invention. 1... Extruder crosshead 2... Head part 8... Cooling tank 4... Rubber backing 5... Cooling water 6... Compressor
7°...Nitrogen cylinder 8...Drainage. Patent applicant Furukawa Electric Co., Ltd.

Claims (1)

[Scope of Claims] L A method for producing a silane/crosslinked polyolefin molded article, which comprises cooling the molded article under pressure immediately after extrusion when extruding a polyolefin resin composition containing a silane crosslinking agent. The method for producing a silane crosslinked polyolefin molded article according to claim 1, wherein the polyolefin resin composition blended with the λ silane crosslinker contains fillers such as a flame retardant and a heat stabilizer.