Electricity: conductors and insulators – Conduits – cables or conductors – Insulated
Reexamination Certificate
1999-10-15
2001-10-16
Reichard, Dean A. (Department: 2831)
Electricity: conductors and insulators
Conduits, cables or conductors
Insulated
C174S1100SR, C174S11300R
Reexamination Certificate
active
06303866
ABSTRACT:
This continuation application of international application PCT/FR98/02657, filed Dec. 8, 1998.
FIELD OF THE INVENTION
The invention relates to self-adjusting cables of any structure wherein the material having PTC behaviour, that is, having a positive temperature coefficient, is an alloy of compatible polymers. The invention also relates to the process for the production of self-adjusting cables wherein the alloy having PTC behaviour is employed by extrusion without an additional cross-linking or heat treatment step around electrically conductive strands.
BACKGROUND OF THE INVENTION
The self-adjusting cables currently on the market are of two types: either the polyethylene type or the fluorinated polymer type as described in patent EP 40 537.
However, self-adjusting cables of the polyethylene type must be cross-linked or, as described in the U.S. Pat. No. 3,861,029, they must undergo a supplementary heat treatment of the post-cure type, which increases their cost. For their part, self-adjusting cables of the fluorinated polymer type have the disadvantage of being brittle and expensive.
There is, therefore, a real need for extrudable, economical, self-adjusting cables having an excellent ratio of starting current intensity to maximum current intensity, and an excellent linear power and good stability towards aging.
BRIEF SUMMARY OF THE INVENTION
Much to their credit, the Applicants, after considerable research, found a self-adjusting cable having all these characteristics. Said self-adjusting cable is characterised in that the material having PTC behaviour is an alloy of compatible polymers comprising, the percentages being expressed by weight with respect to the weight of said polymers:
from 20% to 50% of at least one polar polyolefin,
from 50% to 80% of at least one “matrix” polymer chosen from the group comprising poly(C
1
-C
4
-alkylene) terephthalates, polyamides, polypropylenes, polycarbonates, polyester and polyether copolymers, polyketones and methyl polymethacrylates,
from 5% to 15%, preferably from 5% to 10% of conductive fillers such as carbon black,
and optionally non-conductive fillers.
In the present invention, the term “alloy of compatible polymers” means a mixture of at least two polymers which are immiscible but which are compatible, or a mixture of at least two immiscible and incompatible polymers but which are rendered compatible by the addition of a compatibilizer. The use of such an alloy of compatible polymers by extrusion makes it possible to obtain a composite structure.
According to the invention, the polar polyolefin contained in the composition of the alloy having PTC behaviour is not very crystalline. Preferably, it is an elastomer and it is chosen from the copolymers of ethylene/vinyl acetate, ethylene/C
1
-C
4
-alkyl acrylate, or mixtures thereof. More preferably, a copolymer of ethylene/ethyl acrylate or ethylene/methyl acrylate is used.
The matrix polymer of the alloy having PTC behaviour is chosen from polypropylenes, polyesters, and aliphatic polyketones, polyamides, polycarbonates, copolymers of polyester and polyether, or mixtures thereof. If this polymer is a polyester, it is preferable to use poly(C
1
-C
4
-alkylene) terephthalates, such as polybutylene terephthalate or polyethylene terephthalate. Polybutylene terephthalate is preferred. The aliphatic polyketone sold by SHELL under the brand name CARILLON® and by BP under the brand name KETONEX® may be mentioned by way of example.
Said matrix polymer has a high melting point, this melting point determining the maximum use temperature of the cable according to the invention.
The polymer is generally crystalline with the exception of polyethylene terephthalate, which may be used in the present invention in the crystalline or amorphous form.
The alloy having PTC behavior may incorporate various additives, for example, antioxidants and non-conductive fillers.
The choice of additives will, of course, depend on the final use envisaged for the self-adjusting cable according to the invention.
For cost reasons, the conductive filler is preferably carbon black. Of course, any other conductive filler may be used alone or in mixture, particularly with carbon black.
The self-adjusting cable according to the invention has an excellent ratio of starting current intensity to rated current intensity and an excellent linear power and entirely satisfactory ageing characteristics.
The self-adjusting cables according to the invention preferably have the following characteristics:
ratio of starting current intensity to rated current intensity at 10° C., less than 3, preferably less than 2, and more preferably less than 1.5; and
linear power at 10° C. between 5 W/m and 130 W/m measured according to the standard DIN VDE 0254.
The present invention also relates to a process characterized in that it comprises the following steps wherein:
the various constituents of the alloy having PTC behavior described above are mixed,
the mixture thus obtained is extruded in the form of granular products,
said granular products are then extruded around electrically conductive strands without the use of either a cross-linking step or a heat treatment step,
the strip thus formed is covered with an electrically insulating material,
then the whole assembly is inserted in a protective metal sleeve,
and finally the sleeve is surrounded by an insulating sheath.
These cables are thus produced without cross-linking or heat treatment, by extruding the alloy having PTC behaviour around conductive cables.
REFERENCES:
patent: 3861029 (1975-01-01), Johannsen et al.
patent: 4242573 (1980-12-01), Batiwalla
patent: 4315237 (1982-02-01), Middleman et al.
patent: 4388607 (1983-06-01), Toy et al.
patent: 4588855 (1986-05-01), Kutsuwa et al.
patent: 4866253 (1989-09-01), Kamath et al.
patent: 4876440 (1989-10-01), Kamath et al.
patent: 5296522 (1994-03-01), Vogt et al.
patent: 5321079 (1994-06-01), Torre et al.
patent: 5321119 (1994-06-01), Torre et al.
patent: 5741842 (1998-04-01), Huggins et al.
patent: 5798418 (1998-08-01), Ouirk
patent: 0 040 537 (1981-11-01), None
patent: 0 283 237a (1988-09-01), None
patent: 0 307 205 (1989-03-01), None
patent: 93/08234 (1993-04-01), None
patent: 93/19127 (1993-09-01), None
Patent abstracts of JP 02296861 Jul. 12, 1990.
Properties of Poly(butylene Terephthalate) Functionalized Polyolefin Blends from Kang and Kim Polymer Engineering and Science, Mar. 1997, vol. 37, No. 3, pp. 603-614.
Brault Alain
Lagreve Christian
Lucas Laurent
Acome Societe Cooperative Detravailleurs
Mayo III William H.
Piper Marbury Rudnick & Wolfe
Reichard Dean A.
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