Stock material or miscellaneous articles – Composite – Of silicon containing
Reexamination Certificate
2001-01-29
2002-11-05
Dawson, Robert (Department: 1712)
Stock material or miscellaneous articles
Composite
Of silicon containing
C174S11000P, C174S1100SR, C174S1100SY, C428S450000, C524S430000, C524S436000, C524S437000, C525S191000, C525S222000, C525S240000, C525S241000
Reexamination Certificate
active
06475628
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of Invention
This invention relates to a halogen-free resin composition containing metal hydroxide, to a method of making the composition and to electrical wire having this resin composition as a covering on an electrical conductor core. Such an electrical wire is useful, for example, in a motor vehicle.
2. Description of Related Art
Polyvinyl chloride has been widely used as the covering material of electrical wire for an automobile, because it is superior in properties such as mechanical strength, extrusion processability, flexibility and coloring property. However, with recent concern for the global environment, halogen-free resin material has come to be used for the production of automobile parts including the covering of electrical wires in an automobile in place of polyvinyl chloride, because polyvinyl chloride discharges a harmful halogen gas on combustion.
A halogen-free resin composition in which a metal hydroxide is blended with a polyolefin-base polymer as a flame-retardant is known as a wear resistant resin composition having the merit of no generation of a poisonous gas such as a halogen gas on combustion (see JP-A-7-176219, JP-A-7-78518 and the like). In order that such a flame-retarding resin composition has a self-extinction property, a large quantity of a metal hydroxide is required to be added; however, this causes problems that mechanical strength such as the:wear resistance, tensile strength and the like of the composition are much reduced. In order to prevent the deterioration of mechanical strength, it may be considered that amounts of a polypropylene having a comparatively high hardness and a high density polyethylene are increased, but the flexibility of the covered electrical wire is reduced thereby and the processability becomes poor.
Various specific prior art proposals in this field will now be mentioned.
JP-A-6-290638 discloses resin compositions containing metal hydroxide for electrical wire insulation, in which the resin composition is based on polypropylene (>80%). Additional components are polyethylene modified with acid anhydride and styrene copolymer.
U.S. Pat. No. 5,561,185 describes resin composition for electrical wires containing metal hydroxide, in which the resin components are (a) 40-88.5% by weight of propylene which is 50% by weight or more of a ethylene/propylene random copolymer, (b) 1.5 to 30% by weight of a polyethylene modified with carboxylic acid derivative, e.g. maleic anhydride and (c) 10 to 48% by weight of an ethylene-series copolymer, typically ethylene/vinyl acetate copolymer.
U.S. Pat. No. 5,180,889 also describes a resin composition containing metal hydroxide as a covering of conductors in a crush resistant cable assembly. The resin components are (a) a low density copolymer of ethylene and alpha-olefin, (b) an elastomeric styrene-ethylene-butylene-styrene tri-block copolymer, preferably modified with maleic anhydride and (c) optionally an impact propylene and copolymer or polypropylene. Component (a) in the examples is 50% by weight or more of the total resin components.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a halogen-free olefin-based resin composition comprising a mixture of components providing a good balance of properties, for example wear resistance, flame resistance, tensile property, flexibility and the like which are required for the covering material of an electrical wire, e.g. for an automobile.
The present invention provides a resin composition containing the following resin components:
(a) 30-80 parts by weight of a polyolefin thermoplastic elastomer having a melting point of 130° C. or more and a Shore hardness of 90 or less,
(b) 1-20 parts by weight of a polypropylene modified with 0.1-10% by weight of an acid anhydride,
(c) 5-50 parts by weight of a styrene-based polymeric elastomer, and
(d) 10-30 parts by weight of a propylene polymer having a melt flow rate of 0.1 to 5 g/10 min and selected from propylene homopolymers and propylene-ethylene copolymers having a propylene content of at least 50% by weight,
wherein the total amount of the components (a), (b), (c) and (d) is 100 parts by weight and substantially no other resin component is present in the composition,
and further containing
(e) 30-200 parts by weight of a metal hydroxide, based on 100 parts by weight of the resin components.
The invention also provides an electrical wire having this composition as a covering or a conductor.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
The respective components contained in the composition of the: present invention are carefully selected to provide the desired properties and are illustrated as follows.
The polyolefin thermoplastic elastomer (a) is preferably based on propylene and ethylene. A block copolymer of polypropylene with a propylene-ethylene rubber (for example, PER T310 and the like, which are commercially available from Tokuyama Co., Ltd.) is preferable. This type of polymer has hard segments of polypropylene and soft segments of ethylene-propylene copolymer in the molecule. The hard segment content is preferably 5-50% by weight, more preferably 15-45% by weight. An alternative preference for component (a) is an elastomeric propylene-ethylene random or block copolymer. When the melting point is less than 130° C., the heat resistance of the whole composition is inferior, and when the Shore A hardness exceeds 90, the whole composition is too hard.
The amount of component (a) is 30-80 parts by weight relative to the total polymer amount (a), (b), (c) and (d), and preferably is in the range 40-60 parts by weight. When the proportion of the polyolefin thermoplastic elastomer (a) exceeds 80 parts by weight, the wear resistance of the composition is lowered. On the other hand, when this proportion is less than 30 parts by weight, the composition becomes hard and the processability is reduced.
The component (b) is a polypropylene modified with 0.1-10% by weight of a carboxylic acid anhydride typically an unsaturated acid anhydride, for example maleic anhydride.
The amount of component (b), per 100 parts by weight of total polymer (a), (b), (c) and (d), is 1-20 parts by weight, preferably 5-20 parts by weight. When the proportion of component (b) exceeds this upper limit, it reacts intensively with the metal hydroxide, so that the tensile elongation of the composition is lowered and the flexibility of the composition is reduced. On the other hand, when its proportion is less than 1 part by weight the wear resistance of the resin composition is not improved.
The polypropylene component (b) gives the composition heat resistance, both during extrusion and if over-heating occurs in use, e.g. in an automobile.
The styrene-based polymeric elastomer, component (c), is an elastomer polymer containing styrene monomer units. Preferably the styrene-based polymer has the structure of a block copolymer of styrene monomers and olefin monomers. This polymeric elastomer may be modified with 0.1-10% by weight of carboxylic acid anhydride, typically unsaturated acid anhydride, e.g. maleic anhydride. A preferred example of the styrene-based elastomer (not modified with acid anhydride or so modified) is a polymer obtained by block-copolymerizing styrene with butadiene, and saturating double bonds of the resulting block-copolymer by hydrogenation (known as SEBS). Typically the ratio of the styrene/butadiene is in the range 3/7 to 2/8 by weight. Alternatively there is used, for example, a styrene-based elastomer obtained by block polymerizing styrene and isoprene and hydrogenating the double bonds of the block copolymer (this product can be regarded as polystyrene-poly(ethylene-propylene)-polystyrene, and is known as SEPS).
The amount of component (c) per 100 parts by weight of total polymer (a), (b), (c) and (d) in the composition is 5-50 parts by weight, preferably 10-30 parts by weight. When the proportion of component (c) exceeds 50 parts by weight, the wear resistance of the composition is not improved. On the other hand, when its proportion is
Fujimoto Hiroshi
Hase Tatsuya
Sato Masashi
Dawson Robert
Oliff & Berridg,e PLC
Sumitomo Wiring Systems Ltd.
Zimmer Marc S
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