Stock material or miscellaneous articles – Coated or structually defined flake – particle – cell – strand,... – Rod – strand – filament or fiber
Reexamination Certificate
2001-11-16
2003-10-28
Kelly, Cynthia H. (Department: 1774)
Stock material or miscellaneous articles
Coated or structually defined flake, particle, cell, strand,...
Rod, strand, filament or fiber
C428S375000, C428S379000, C174S1200SR, C174S1210AR
Reexamination Certificate
active
06638617
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a low-smoke, highly flame-retardant, and flexible dual layer insulation system which demonstrates improved cut-through resistance. More specifically, the present invention relates to a dual layer insulation system comprising a cross-linked, highly flame-retardant, and halogen-free first insulating layer and a tough, flexible second insulating layer, and to insulated wires and conductors employing such an insulation system.
BACKGROUND OF THE INVENTION
Insulating materials for electrical wires are required to be not only flame-retardant but also, upon flaming, smoke suppressed and non-hazardous (i.e., productive of no harmful gases). Resins containing either halogen atoms in the molecular structure or a flame-retarding amount of a halogen compound cannot be used for this purpose, where such resins evolve corrosive, harmful hydrogen halide gases upon flaming.
Attempts to impart flame-retardancy to halogen-free resins have relied solely upon relatively high loadings of halogen-free, flame-retarding agents. Hydroxides and carbonates of certain metals, such as aluminum hydroxide, magnesium hydroxide and magnesium carbonate, as well as, zinc borate are well known in the art as suitable halogen-free, flame-retarding agents.
Unfortunately, such high loadings of halogen-free, flame-retarding agents adversely impacts upon the mechanical properties (e.g., toughness, flexibility) and processability of the resulting insulating material. Moreover, room temperature and elevated temperature cut-through resistance demonstrated by such prior art materials is inadequate for certain end-use applications including, but not limited to, electronics applications such as secondary power switching equipment for telephonic exchanges.
Accordingly, there is a need for low-smoke, highly flame-retardant, and flexible insulating materials which employ halogen-free resins and flame-retarding agents and which overcome the drawbacks associated with the prior art.
It is therefore a primary object of the present invention to provide such a low-smoke, highly flame-retardant, and flexible insulating material.
It is a more particular object of the present invention to provide a low-smoke, highly flame-retardant, and flexible dual layer insulation system which employs halogen-free resins and flame-retarding agents and which demonstrates improved cut-through resistance.
It is another more particular object of the present invention to provide insulated wires or conductors, which employ such an insulation system.
It is yet another more particular object to provide a process for preparing such insulated wires or conductors, wherein the insulation system comprises tightly adhered insulating layers.
SUMMARY OF THE INVENTION
The present invention therefore provides a dual layer insulation system, which comprises:
a) a first insulating layer having a thickness and comprising a cross-linked, highly flame-retardant, and halogen-free resin composition, wherein said resin composition comprises: 100 parts by weight of a thermoplastic resin; from about 100 to about 250 parts by weight of at least one flame-retarding agent; and from about 1 to about 10 parts by weight of an organosilicon compound represented by the formula:
wherein R represents an alkyl group containing an acrylic or methacrylic group and wherein Y
1
, Y
2
, and Y
3
each represents a group selected from an alkyl group, an alkoxyl group, and mixtures thereof; and
b) a second insulating layer having a thickness and comprising a thermoplastic material selected from alloys of polyolefins and polyamides, polyamides, polyamide/polyether block copolymers, polyesters, polyethylenes, polyurethanes and mixtures thereof,
wherein the thickness of the second insulating layer is at least 4 percent of the thickness of the first insulating layer.
The present invention further provides an insulated conductor, which comprises:
a) a conductor having an outer surface;
b) a first insulating layer, as described above, provided directly on the outer surface of the conductor; and
c) a second insulating layer, also as described above, provided directly on top of the first insulating layer,
wherein the thickness of the second insulating layer is at least 4 percent of the thickness of the first insulating layer.
In another embodiment, the insulated conductor of the present invention comprises a plurality of bunched, twisted or bundled wires, wherein the wires are coated either directly or indirectly with the dual layer insulation system described hereinabove.
The present invention also provides a process for preparing an insulated conductor comprising a conductor and at least two tightly-adhered, extruded, insulating layers provided thereon, wherein said process comprises:
(a) increasing the force under which molten material used to prepare an outer insulating layer is applied to an inner insulating layer provided on the conductor by impeding or constricting the flow of said molten material; and/or
(b) increasing the period of time in which the extruded, insulating layers are in contact prior to solidification by cooling the layers via ambient air cooling.
The foregoing and other features and advantages of the present invention will become more apparent from the following description.
DETAILED DESCRIPTION OF THE INVENTION
By way of the present invention, it has been discovered that a balance of properties (i.e., sufficient smoke suppression and flame-retardancy, flexibility, and improved cut-through resistance) can be achieved by a dual layer insulation system comprising a cross-linked, highly flame-retardant, and halogen-free first insulating layer and a tough, flexible second insulating layer, if the thickness of the second insulating layer is at least 4 percent of the thickness of the first insulating layer.
It has also been discovered that notably enhanced elevated temperature cut-through resistance is demonstrated by the inventive dual layer insulation system when the thermoplastic material of the second insulating layer is a flame-retarded polyamide 11.
The dual layer insulation system of the present invention offers several key benefits. For example, the flexibility demonstrated by the inventive insulation system facilitates installation and routing of wires and conductors used in various electronic applications. In addition, the first or inner insulating layer provides flame resistance over the useful life of the wire or conductor, while the second or outer layer provides toughness, thereby improving the resistance of the wire/conductor to physical abuse during installation and maintenance. This, in turn, reduces the possibility of electrical shock.
As noted above, the cross-linked and halogen-free resin composition of the first insulating layer of the dual layer insulation system of the present invention is highly flame-retardant. Flame-retardancy is generally measured by the Limiting Oxygen Index (LOI), which is basically the amount of oxygen needed in the atmosphere to support combustion. Insulated wires/conductors with an LOI greater than 28 are said to be flame-retardant, in that, there must be at least 28% oxygen present, for them to burn. The higher the LOI, the more flame-retardant the insulated wire/conductor.
The first insulating layer of the present invention demonstrates an LOI of at least 30, and preferably demonstrates an LOI of at least 40.
The resin composition of the first insulating layer is described in U.S. Pat. No. 5,236,985, which is incorporated herein by reference. More specifically, thermoplastic resins suitable for use in the cross-linked, highly flame-retardant, and halogen-free resin composition include polyethylene, ethylene-&agr;-olefin copolymers, ethylene-propylene thermoplastic elastomers, ethylene-vinylacetate copolymers, ethylene-ethylacrylate copolymers, ethylene-methylmethacrylate copolymers, ethylene-methacrylic acid copolymers, ethylene-methylacrylate copolymers and the like.
The thermoplastic resins may be used alone or as a mixture of two or more resins. In a preferred
Kim Young Joon
Listro Anthony E.
Trivedi Akshay H.
Bonzagni, Esq. Mary R.
Gray J. M.
Holland & Bonzagni, P.C.
Judd Wire, Inc.
Kelly Cynthia H.
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