Stock material or miscellaneous articles – Coated or structually defined flake – particle – cell – strand,... – Rod – strand – filament or fiber
Reexamination Certificate
1999-10-05
2001-03-13
Krynski, William (Department: 1774)
Stock material or miscellaneous articles
Coated or structually defined flake, particle, cell, strand,...
Rod, strand, filament or fiber
C428S372000, C428S375000, C174S1100PM, C174S1100SR, C174S1210AR, C525S240000
Reexamination Certificate
active
06200679
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to flame-resistant flexible resin compositions used for coatings, which do not generate halogen-type noxious gases even when accidentally burned. The resin compositions of the invention are in particular suitable for use as coatings for electrical cables, especially as substantially thick coatings for electrical cables. The invention also relates to electrical cables that use such resin compositions as fire-proof coatings.
2. Description of the Background Information
Poly(vinyl chloride), also known as PVC is commonly used as an insulating coating material for electrical cables. The reason for this preferential use is that PVC satisfies the prerequisites for coating materials, such as high electrical insulation, flame resistance, oil-proofing, water-proofing and ozone resistance. Further, by blending with appropriate additives such as a plasticizer or a filler, PVC can easily provide a wide spectrum of products, depending on the purpose, ranging from heat-proof to cold-proof, or from hard products to soft products.
However, PVC suffers from the fact that it is a halogen-containing polymer. When PVC is burned accidentally, it generates noxious gases such as hydrogen chloride. Accordingly, when an electrical cable containing PVC is set on fire, hydrogen chloride gas is generated from the PVC and may cause secondary damages such as corrosion of the metals used for wiring.
Moreover, in our environmentally conscious age, it has become necessary to reduce or recycle industrial wastes such as plastic materials. As is well known, PVC is already used for coating automobile wiring-harness cables. However, the hydrogen chloride gas generated from PVC when incinerated has recently caused serious damage. As a result, it is now required to use halogen-free-type, flame-resistant coating materials that do not generate toxic gases such as hydrogen halide gas.
Typical halogen-free-type flame-resistant materials include a mixture consisting of a polyolefin resin, and a metal hydroxide as a halogen-free flame-resistant agent. However, electrical cables obtained by coating with known halogen-free type flame-resistant materials are less flexible and less resilient, in comparison with PVC-based products. Moreover, in order to guarantee flame resistance, a considerable amount of metal hydroxide has to be added to the flame-resistant materials. Now, an increase in the amount of added flame-resistant agents (flame retardants), is to the detriment of mechanical strength of the product, such as wear resistance or tensile strength.
In order to confer wear resistance to such halogen-free materials, the latter may be hardened, or coatings with these materials may be made thicker. For instance, an electrical cable can be given a thick coating with a layer thickness of 0.5 to 0.8 mm, so that, even if wear resistance is decreased by addition of a metal hydroxide, the risk of wearing away the coating remains small. The conductive portion of the electrical cable may thus be protected from possible exposure.
However, when a coating containing such a hard material is thickened, the coated electrical cable becomes too hard, and makes the wiring process more difficult. It thus appears that to solve these problems, an electrical cable should first be coated thickly with a flexible material. Examples of appropriate materials include ethylene-vinyl acetate copolymer (EVA), ethylene-ethylacrylate copolymer, and the like. They can be used alone or in a mixture.
However, such flexible materials usually have a very low melting point, poor heat resistance and poor oil proofing capacity. They are thus unsuitable as a coating material for electrical cables used in oily environments such as in automobiles. To remedy these shortcomings, such materials may be cross-linked by electron beams, or through chemical treatments such as vulcanization.
However, to cross-link the coatings of an elongate electrical cable, large scale equipment is required, both for electron beam irradiation and for vulcanization treatment. This means that the productivity of electrical cable manufacture is lowered and the production has to be entrusted to a specialized manufacturer. Accordingly, there exists a strong need for non-cross-linked coating materials which are oil- and heat-proof, and highly flexible.
In order to ensure high heat resistance without proceeding to cross-linking, polypropylene having a relatively high melting point may be blended with high-density polyethylene. However, the blending of these two polymers impairs flexibility. Further, electrical cables have to be subjected to end portion conditioning in later stages. As illustrated in
FIG. 1
, when an end of a cable is peeled off or stripped of the insulating coatings made of such polymers in such a conditioning process, there forms a cut-out face after the coating
1
that is partially chipped away. Such a cut-out face leaves behind whisker-like trails
2
of insulating coating
1
(hereafter referred to as whiskers) along a conductive portion
3
. This gives rise to the so-called “necking” phenomenon. When the conductive portion
3
with such whiskers
2
is forcibly connected to a terminal, the whiskers get caught between the conductive portion
3
and the terminal. As a result, contact resistance increases and conductivity deteriorates. Accordingly, when the above-mentioned polymer mixture is used, its whisker-trailing effect due to low formability creates problems.
SUMMARY OF THE INVENTION
The present invention has therefore a primary object to remedy these shortcomings of the prior art, and to provide a non cross-linked resin composition containing no halogen, which has a good formability, flexibility, heat resistance and oil-proofing, as well as to provide an electrical cable coated with such a resin composition.
To this end, there is provided a flame-resistant flexible resin composition at least comprising 100 parts by weight of polymeric material comprising about 50 to 90 parts by weight of thermoplastic elastomer copolymer comprising polyolefin and rubber, about 5 to 25 parts by weight of a second copolymer comprising ethylene and vinyl-based compound containing at least one carbonyl group, and up to about 25 parts by weight of polyolefin having a crystallinity of at least about 55%, and about 30 to 200 parts by weight of at least one metal hydroxide a surface of which has not been treated with stearic acid.
Preferably, the thermoplastic elastomer comprising polyolefin and rubber has a melting point of at least about 130° C. and a JIS-A hardness of up to about 90.
Preferably also, the copolymer comprising ethylene and vinyl-based compound containing at least one carbonyl group is at least one compound selected from the group consisting of ethylene-vinyl acetate copolymer, ethylene-acrylate copolymer and ethylene-methacrylate copolymer.
The polyolefin having a crystallinity of at least about 55% is preferably high density polyethylene or polypropylene.
The electrical cable according to the present invention utilizes the above-mentioned flame-resistant resin composition as a coating material. Preferably, the coating is about 0.5 to 0.8 mm thick.
REFERENCES:
patent: 3758643 (1973-09-01), Fischer
patent: 3821333 (1974-06-01), Goodwin et al.
patent: 3835201 (1974-09-01), Fischer
patent: 3862106 (1975-01-01), Fischer
patent: 3941859 (1976-03-01), Batiuk et al.
patent: 4412938 (1983-11-01), Kakizaki et al.
patent: 5470902 (1995-11-01), Kubo et al.
patent: 6034162 (2000-03-01), Miautani et al.
patent: 2-195603 (1990-08-01), None
patent: 10199201 (1998-07-01), None
patent: 10340627 (1998-12-01), None
English language abstract of JP 2-195603. Undated.
Hase Tatsuya
Matsumoto Shin-ichi
Senoo Ryou
Yamano Yoshiaki
Gray J. M.
Greenblum & Bernstein P.L.C.
Krynski William
Sumitomo Wiring Systems Ltd.
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