JPH03192607A - Manufacture of composite material for high foam polyethylene for insulation and high foam body coated insulation cable - Google Patents

Abstract

PURPOSE:To improve the adhesion property of a foam body with a conductor core wire and reduce the blateness of the core by mixing ethylene-based copolymer of specified characteristics with ethylene-based resin composite material for high foam body insulation cable. CONSTITUTION:Low density polyethylene by 100wt.%, chemical foaming agent 1-5wt.%, and high foam insulation polyethylene composite material consisting of 1-8wt.% ethylene-based copolymer selected among ethylene-vinyl acetate copolymer or ethylene-ethyl acrylate copolymer including 15-30wt.% comonomer are sued. The low density polyethylene is obtained by polymerizing normal ethylene using radical polymerization catalyst under a high pressure, and the high pressure low density polyethylene having long chain branching has a high fusion density at the time of foaming work. The adhesion property is thus improved, and the blateness can be small.

Description

Detailed Description of the Invention [Field of Industrial Application] The present invention relates to a highly foamed insulating polyethylene composition suitable for insulation coating of insulated wires such as coaxial cables, and a highly foamed insulation coating using the composition. Concerning the manufacturing method of insulated wires.

[Prior Art] In recent years, insulated wires, especially coaxial cables used for high-frequency signal transmission, have been designed to reduce the dielectric constant and tan δ by increasing the foaming rate of the insulator. The aim is to reduce the number of repeaters, make images and sounds clearer, and reduce the number of repeaters.

Chemical foaming methods and gas foaming methods are generally known for producing such high foaming rate insulated wires.

In the chemical foaming method, a chemical foaming agent is blended with the resin component at a temperature below its decomposition temperature, the mixture is fed to an extruder, and the conductor is extruded and coated at a temperature above its decomposition temperature, and then this is foamed in air. After that, it is cooled and solidified. This method requires lower equipment costs than the gas foaming method and is easier to operate, so it has gained a certain share of the market despite the foaming rate being lower than the gas foaming method.

In order to improve the characteristics of foam-covered insulated wires using the chemical foaming method, it is sufficient to increase the degree of foaming in order to lower the capacitance. A method for manufacturing electric wires is disclosed (Special Publication No. 11412/1983), but
In highly foam-covered insulated wires with a high degree of foaming of 60% or more, the adhesion between the foam and the conductor core wire is low, resulting in the following problems. That is, when the wire ends are processed, the core shrinks at the cut end of the wire, causing the core wire to protrude outward, making the wire unusable.

In addition, to prevent moisture from entering from outside after installation, communication cables are maintained by constantly filling the cable with an inert gas such as nitrogen gas, or by filling the cable with waterproof compound. However, if the foam insulation is not evenly adhered around the conductor, maintenance gas may leak through the gap between the conductor and the insulator, and cables filled with waterproof compound may have poor insulation between the conductor and the insulation. There is a risk that external moisture may enter through the gap between the product and the body.

In addition, the gas generated within the highly foamed layer immediately after extrusion tends to escape outside the highly foamed layer, and especially if it escapes between the conductor and the highly foamed layer, there is no exit to the outside, so the conductor and the highly foamed layer A gap is formed between the two, which is unfavorable in terms of electrical characteristics.

Various methods have been proposed to improve these methods.

For example, a method in which a plastic thin film layer is provided between the conductor and the highly foamed layer and the highly foamed layer is fused to the thin film layer (Japanese Patent Application
No. 7-55154, Japanese Patent Publication No. 55-6969) are known. This method prevents the generation of voids between the conductor and the highly foamed layer, and is good. However, in practice, it is necessary to fuse the thin film layer to the highly foamed layer, so it is necessary to modify the crosshead or use a tandem method. In addition, one more extruder is required,
This is a problem in terms of equipment. Furthermore, as another method, there is a method of heating the conductor in advance with flammable gas, inert gas, non-flammable gas, energized acid, induction type electric heating means, etc., but moisture generated by combustion of gas may adhere to the conductor and have a negative effect on the foaming effect, the conductor may not be heated evenly, and the heating equipment may become complicated and expensive.
There are problems such as the extreme eccentricity of the core, making it extremely difficult to form a perfect circle required for so-called coaxial cables.

Other methods include polymers having polar groups, such as ethylene-vinyl acetate copolymers, ethylene-ethyl acrylate copolymers, ethylene-acrylic acid copolymers, ethylene-acrylic acid ionomers, and ethylene-methacrylic acid ionomers. , ethylene-vinyl acetate-glycidyl methacrylate terpolymer etc. to polyethylene 100
0.1 to 20 parts by weight, preferably 0.5 parts by weight
-10 parts by weight, and 1.0 to 1.5 parts by weight of a blowing agent (Japanese Patent Application Laid-open No. 1983-1999)
No. 148314). However, although this method improves adhesion to some extent, heating the core wire during processing (this is necessary to increase the degree of foaming of the foam by heating) will cause the core (conductor core wire and foam to (meaning the integrated foam-covered conductor core wire) is flattened, resulting in a product that cannot be used for practical purposes.

[Problems to be Solved by the Invention] The present invention provides a method for manufacturing an insulated wire with a high foam coating of 60% or more, which maintains the perfect circle of the core even when the conductor is preheated, and maintains the adhesion between the foam and the core wire. An object of the present invention is to provide a highly foam-coated insulated wire with excellent properties.

[Means for Solving the Problems] The present inventors have solved the problems (preheating When the conductor core wire was covered with foam, it did not become a perfect circle), and the conductor diameter, degree of foaming, and foaming thickness of the insulating layer were 0, 5 mm, 47%, and 0.3 mm, respectively. The target is a low foaming rate of 47%, and the conductor core wire is not preheated, so there is no need to pay technical consideration to the flatness of the core, and the adhesion between the conductor core wire and the foam is Therefore, in order to solve this problem, an adhesive ethylene copolymer resin with a high melt index that has good adhesion at low temperatures and good processability has been selected. However, with this selection, it has been found that it is difficult to obtain a foam with a foam density of 60% or more, and the problem to be solved by the present invention is to obtain a foam with a foam density of 60% or more without flattening the fur. hypothesized that flattening of the foam would not occur if the melt tension of the foam resin was increased during foaming, and in order to prove this, they conducted tests on many resins and developed the present invention. Completed.

That is, the present invention includes: (1) 100 parts by weight of low-density polyethylene, 1 part of a chemical blowing agent;
~5 parts by weight, and MI of 0.1 to 1.0 g/10 min
Highly foamed insulating polyethylene consisting of 1 to 8 parts by weight of an ethylene copolymer selected from ethylene-vinyl acetate copolymer or ethylene-ethyl acrylate copolymer having a comonomer content of 15 to 30% by weight Composition; (2) A method for producing a highly foam-covered insulated wire with good adhesion and no flatness by extruding the polyethylene composition described in (1) above onto a preheated conductor core wire from an extruder and foaming it. It is.

The low density polyethylene used in the present invention may be any commonly used low density polyethylene, but is usually obtained by polymerizing ethylene at high pressure using a radical polymerization catalyst,
High-pressure low-density polyethylene with long chain branches has a high melt viscosity during foam processing, and in order to obtain a foam with a high foaming rate of 60% or more, and because it has excellent electrical properties,
suitable. In order to improve mechanical strength and processability, high density polyethylene, linear low density polyethylene, etc. may be blended.

The chemical blowing agent used in the present invention has a decomposition temperature of 150 to 24
0°C, p,p-oxy-bis(benzenesulfonylhydrazide) (150-160°C), dinitrosopentamethylenetetramine (190-205°C)
, azodicarbonamide (195-210'C), and the like.

Note that the value in parentheses is the decomposition temperature. This decomposition temperature is 150
At the temperature end of 0.degree. C., foaming occurs during crosstalk with the resin, which is undesirable. Furthermore, if the temperature exceeds 240°C, it is difficult to obtain a perfectly circular core with a center wire during foam molding.

In the present invention, an organic peroxide whose 1-minute half-life temperature is 0 to 30° C. lower than the decomposition temperature of the chemical blowing agent may be used in combination.

Examples of such organic peroxides include dicumyl peroxide (171°C), 1,1-bis(t-butylperoxy)3,3,5-1-limethylcyclohexane (148°C),
), t-butylperoxyisopropyl carbonate (
172°C), 2,5-dimethyl-2,5-di(benzoylperoxy)hexane (162°C), 2,5-dimethyl-2,5-di(t-butylperoxy)hexane-3
(193°C). Note that the value in parentheses is the 1-minute half-life temperature. When such an organic peroxide is blended, the melt viscosity of the resin during foaming processing increases,
This has the effect of further increasing the degree of foaming of highly foamed products of 60% or more. If the 1-minute half-life temperature of the organic peroxide is higher than the decomposition temperature of the chemical blowing agent, the crosslinking reaction will not occur sufficiently in the foamed state, making it difficult to obtain a highly foamed product. If the half-life temperature is 30° C. or more lower than the decomposition temperature of the chemical blowing agent, premature crosslinking occurs too much, causing mucus on the die or a gel-like substance, making it impossible to obtain a good foam.

The ethylene copolymer used in the present invention has an MI of 0.1 to 1.
．． The material is selected from ethylene-vinyl acetate copolymer or ethylene-ethyl acrylate copolymer having a rough monomer content of 15 to 30% by weight. MI of ethylene copolymer is 0.1
If it is less than g/10 m f n, kneading properties with low density polyethylene will be poor, processability will also be poor, and a foam with a uniform cell structure will not be obtained. Also, 1.0 g/10
If it exceeds min, the core will become flattened when the heated conductor core wire is covered with the foam, which is not desirable.

Further, if the comonomer content of the ethylene copolymer is less than 15% by weight, the adhesion between the conductor core wire and the foam will deteriorate, which is not desirable. For those exceeding 30% by weight, it is expected that the adhesion between the conductor core wire and the foam, which is a problem of the present invention, and the roundness of the core will be good.
Since it is impossible to produce an ethylene copolymer with a comonomer content of 0.1 to 1 g/10 min and a comonomer content of more than 30% by weight using current technology, and therefore the present invention cannot be carried out, the practical 30% by weight The upper limit was %. The ethylene copolymer is blended in an amount of 1 to 8 parts by weight per 100 parts by weight of low density polyethylene. If it is less than 1 part by weight, the adhesion and roundness of the core, which are the effects of the present invention, will not be achieved, and if it is more than 8 parts by weight, a large amount of polar groups of the comonomer will be present, resulting in a decrease in dielectric constant. , jan δ, etc., the characteristics of the coaxial cable produced are deteriorated, and the processability is also deteriorated, which is undesirable.

In the present invention, in order to produce the highly foamed insulating polyethylene composition, low density polyethylene, a chemical foaming agent and an ethylene copolymer are mixed in a temperature range of 120-140°C using a conventional cross-mixing method, such as a -screw extruder. , twin screw extruder, roll mill,
Knead using a Banbury mixer, Busco kneader, etc.

When using an organic peroxide, it may be blended with the above-mentioned low density polyethylene, chemical blowing agent, and ethylene copolymer at the same time.
The ethylene-based polymer is kneaded by the above method to make a blend, and this is brought into contact with an organic peroxide and soaked as a powder or granule at a temperature of 50 to 80°C for 30 to 180 minutes. , a highly foamed insulating polyethylene composition may be prepared.

In order to make a highly foam-coated insulated wire with good adhesion and not flattened using the highly foamed insulating polyethylene composition of the present invention, an extruder is used to run a conductor preheated to 70 to 130°C. The core wire is coated and foamed with a polyethylene composition heated to 150 to 250°C, and the foam is cooled by running it in hot water.

If the preheating temperature of the conductor core wire is lower than 70'C, the adhesion will be poor, and if it is higher than 130°C, the core will become eccentric.
Undesirable. If the foaming temperature is lower than 150°C, foaming will be insufficient and a highly foamed product will not be obtained, and if it is higher than 250°C, overfoaming will occur and the properties of the coaxial cable will deteriorate, which is not desirable.

[Example] Next, the present invention will be explained in more detail with reference to Examples.

51 female 1 Melt index 2.0 g 710 min, density 0.917 high pressure process low density polyethylene 100 parts by weight, chemical blowing agent p,p'-oxy-bis(benzenesulfonyl hydrazide) (decomposition temperature 150 ~160℃)
1.3 parts by weight, antioxidant butylated hydroxytoluene 0.2 parts by weight, and melt index 0.8 g71
0min, 5 parts by weight of ethylene-ethyl acrylate copolymer with ethyl acrylate content of 23% by weight was added to 13
The mixture was kneaded in a Banbury mixer at 0°C to form pellets.

The above pellets were put into a 50φmm extruder (L/D=24), foamed and coated on a 1.2 mmφ copper conductor core wire preheated to 130℃ at 160℃, and the wire winding speed was 20m/
The wire was run through warm water (there were six cooling baths in which the temperature was successively lowered from 90° C. to 30° C.) at a speed of 100° C. to obtain a foamed insulated wire with an outer diameter of 5 mm. The degree of foaming was 63%, and the degree of adhesion was measured by the pull-out strength of the conductor core wire from the foam, and the conductor length was 1300 g/50 mm, and no eccentricity of the core was observed.

2-7, 1-7 The same experiment as in Example 1 was conducted except that the ethylene copolymer shown in Table 1 was used instead of the ethylene-ethyl acrylate copolymer in Example 1. .

*2 *3 *4 *5 *6 SR means the swelling rate of the resin.

EEA means ethylene-ethyl acrylate copolymer and EA means ethyl acrylate.

EVA means ethylene-vinyl acetate copolymer, VA
means vinyl acetate.

Bondine HX-8140 manufactured by Sumitomo Chemical Co., Ltd. Bondine HX-8140 manufactured by Mitsui DuPont Polychemical Co., Ltd. Bond First manufactured by Sumitomo Chemical Co., Ltd.* 8 * 9 Adhesion Degree of circularity 1, 2 mm mφ copper core wire, strength when pulling the core wire from a 50 mm length core. A weight of 1,200 g or more is practical, and a weight of 1,200 g or less is problematic.

The maximum or minimum outside diameter of the foam is Outside within 10% of the outside diameter of the front circle Practical when within the specified range (0), and if the deviation is 10% or more O electrical characteristics l Processability Sometimes it's not practical Ta.

Practical impedance of 75Ω or more and static tolerance of 55 nF/Km or less (○
), and those that deviate from this are marked as not practical (×).

Foam with a smooth surface is allowed. (○) indicates that the item is rough. were marked as not possible (x).

-8 Bi-1 An experiment was conducted in the same manner as in Example 1, except that the preheating temperature of the conductor core wire was changed.

Example (with addition of EEA) Comparative example (without addition of EEA) [Effects of the invention] In the present invention, an ethylene-based co-electrical polymer having specific physical properties is blended into an ethylene-based resin composition for high-foam insulated wires. Therefore, a coaxial cable core with a high foam coating of 60% or more has good adhesion between the foam and the conductor core wire, has a small core oblateness, and has good electrical properties. Therefore, the present invention has solved the conventional problems (adhesion, roundness) in high foam coated electric wires for the first time, and it has become possible to manufacture high quality coaxial cables.

Claims (1)

[Claims] 1) 100 parts by weight of low-density polyethylene, 1 to 100 parts by weight of a chemical blowing agent
5 parts by weight, and ethylene selected from ethylene-vinyl acetate copolymers or ethylene-ethyl acrylate copolymers having an MI of 0.1 to 1.0 g/10 min and a comonomer content of 15 to 30% by weight. System copolymer 1
A highly foamed insulating polyethylene composition comprising ~8 parts by weight. 2) A method for producing a highly foam-covered insulated wire with good adhesion and no flatness by extruding the polyethylene composition according to claim 1 onto a preheated conductor core wire using an extruder and foaming it.