Stock material or miscellaneous articles – Composite – Of inorganic material
Reexamination Certificate
2000-01-27
2002-08-20
Dixon, Merrick (Department: 1774)
Stock material or miscellaneous articles
Composite
Of inorganic material
C428S378000, C428S379000, C428S457000, C428S688000
Reexamination Certificate
active
06436557
ABSTRACT:
TECHNICAL FIELD
The present invention relates to flame retardant resin compositions that do not produce harmful gases such as hydrogen halide when burned and have excellent mechanical strength and relates to products made by using the same, including insulated wire, tube. heat-shrinkable tube, flat cable, and high voltage DC electric wire.
BACKGROUND
The insulation of insulated wires used in the field of electronic appliances and vehicles, insulators for tubes, heat-shrinkable lubes, and flat cables, and the insulation and sheath of high voltage DC electric wires for television sets, electromagnetic cooking ranges, copying machines, and the like are generally required to have a mechanical strength of 1.0 kg/mm
2
or more in terms of tensile strength. For example, referring to the UL Standards widely adopted in the field of electronic appliances, in the case of insulated wires, tubes, heat-shrinkable tubes, and flat cables using such plastics as polyethylene as the insulator, the insulator is required to have a tensile strength of 1.06 kg/mm
2
or more.
Further, flame retardance is also required of the insulated wires, tubes, heat-shrinkable tubes, flat cables, and the high voltage DC electric wires used in the above fields. Generally, horizontal flame retardance of the same is required in the field of vehicles and vertical flame retardance in the field of electronic appliances.
As a method for testing the vertical flame retardance, the vertical test (VW-1 test) provided in Subject 758 of the UL Standards as shown, for example, in
FIG. 1
, is well known. This is a combustion test performed on a specimen
5
of an insulated wire, a tube, a heat-shrinkable tube, a flat cable, or a high voltage DC electric wire vertically held by a fastener
3
. In the test, the flame of a burner
2
is applied to the same specimen five times from under the specimen for a duration of 15 seconds each time with 15 seconds intervals between the respective applications thereof In the test, it is required that the insulation cease to flame within 60 seconds, absorbent cotton
4
placed thereunder should not ignite from burning droppings from the specimen, and kraft paper
1
fixed above the specimen should not burn or scorch.
In the case of a tube, an all-tubing flame test is sometimes performed to assess the flame retardance of the specimen, namely, a metallic bar with the same diameter as the inner diameter of the tube is inserted through the tube and the specimen is subjected to the same test as the VW-1 test. Sometimes, a heat-shrinkable tube is also subjected to an all-tubing flame test to assess its flame retardance, namely, the heat-shrinkable tube is put on a metallic bar having the same diameter as the inner diameter of the heat-shrinkable tube when it becomes shrunken and the same test as the VW-1 test is performed on the specimen.
As materials for the above-described insulators of insulated wires, tubes, heat-shrinkable tubes, and insulators of flat cables satisfying the requirements for both mechanical strength and flame retardance, resin compositions comprising polyvinyl chloride such as flexible polyvinyl chloride compositions have long been known. Since such materials are excellent in both mechanical strength and flame retardance and, economical as well, they are widely used as the materials for forming insulated wires and flat cables applicable to the fields of electronic appliances and vehicles.
However, the resin compositions produced by using polyvinyl chloride generate combustion gases harmful to the human body, such as hydrogen chloride, once burned, and also many of the resin compositions are mixed with heavy metal substances such as lead-based compounds for stabilizing their processing. Hence, they have an undesirable aspect against protection of the environment.
In view of these problems, there have been known and put to practical use flame retardant resin compositions obtained by mixing ethylene polymer such as polyethylene with a phosphorus-containing flame retardant agent, or by mixing the same with a flame-retardant agent such as aluminum hydroxide or magnesium hydroxide, i.e., the so-called non-halogen flame retardant resin compositions. However, there have been problems with some of the phosphorus-containing flame-retardant agents in that they exhibit acute toxicity when taken by mouth and, further, they corrode the conductors when mixed in resin compositions used in insulated wires and flat cables.
On the other hand, flame-retardant agents made of metal hydroxide have only a moderate flame-retardant effect on such plastics as ethylene polymer. Therefore, in order to obtain flame retardance equivalent to that of the polyvinyl chloride resin composition, it is required, for example, to have 100 parts or more by weight of metal hydroxide compounded with 100 parts by weight of ethylene polymer such as polyethylene, though this is not always true because it depends on the shape and size of the product. The drawback of compounding such a large quantity of metal hydroxide with the base resin, however, is that it markedly lowers the mechanical strength of the resin composition.
Insulated wires based on the UL Standards to be used for wiring work within electronic appliances are normally prescribed to have a minimum thickness of 0.15 mm at 30 V rating, 0.4 mm at 300 V rating, and 0.8 mm at 600 V rating. Further, it is preferred that the insulated wire to be used for wiring work within electronic appliances have as small an outer diameter of as possible to allow easy handling of the wire, and for the conductor, a diameter of about 1.0 mm or less is used except in special cases (refer to page 13 of “Handbook of Electronic Wire Products”, published by Sumitomo Electric Industries, Ltd.).
Halogen-free polyolefin insulated wires having a conductor of 1.0 mm or less in outer diameter and an insulation of 0.1 mm to 1.0 mm thickness which pass the VW-1 test and satisfy the requirements for mechanical strength such as initial tensile strength have been unknown. Recently, however, a thin-wall high-strength non-halogen insulated wire satisfying the UL Standards was developed (Japanese Patent Nos. 2525982 and 2525968).
Although the above-mentioned insulated wire satisfies the requirement to cease to flame within 60 seconds as provided in the Standards for the VW-1 test, it occasionally continues burning over 20 seconds. Therefore, the development of a non-halogen flame retardant insulated wire with greater flame retardance has been desired.
On the other hand, in the case of high voltage DC electric wire, ethylene-&agr;-olefin copolymer such as polyethylene is used to cover the conductor to improve the anti-tracking property of the wire. However, to offset the drawback of inflammability of polyethylene, it has been the practice to cover the high voltage DC electric wire with a flame retardant resin composition having, as the main ingredients, a halogen-containing polymer such as polyvinyl chloride, thereby securing the flame retardance of the high voltage DC electric wire. However, since the resin composition using polyvinyl chloride generates combustion gases harmful to the human body such as hydrogen chloride, once burned, and many of the resin compositions contain heavy metal substances such as a lead-base compound for the purpose of stability in the fabrication, it has an undesirable aspect from the viewpoint of environmental preservation. Therefore, the development of a non-halogen high voltage DC electric wire has been desired.
DISCLOSURE OF INVENTION
Through various investigations on the above enumerated problems, the inventors have learned that a flame retardant resin composition obtained by having 100 parts by weight of thermoplastic resin compounded with 100 to 250 parts by weight of metal hydroxide and either 5 to 50 parts by weight of acetate or 5 to 80 parts by weight of calcium carbonate does not generate harmful gases such as hydrogen halide, e.g., hydrogen chloride when burned, exhibits flame retardance of the same level or higher than that of PVC in the VW-1 test according t
Hayami Hiroshi
Moriuchi Kiyoaki
Shukushima Satoshi
Dixon Merrick
Smith , Gambrell & Russell, LLP
Sumitomo Electric Industries Ltd.
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