This invention relates to polyester compositions suitable for use as insulation on wires.

Many polyester compositions are known, including compositions which can be melt-shaped, e.g. melt-extruded around a conductor to provide an insulating coating. The physical and electrical properties of such polyester compositions, including flammability and smoke generation when burnt, are very important. A great variety of polyester compositions have been proposed for use as insulating coatings on wires. Reference may be made for example to United States Patent Nos. 2,167,278, 3,671,487, 3,835,089, 4,048,128, 4,332,855, and 5,081,176, PCT Publication No. 91/19760 (MP1360) and European Patent Publication No. 0057 415.

We have discovered certain novel polyester compositions which have excellent heat aging properties. These novel compositions comprise a polymeric component comprising

(A) 60 to 95% of at least one aromatic polyester,

(B) 3 to 20% of at least one aliphatic polyester, and

(C) 3 to 20% of at least one thermoplastic elastomer,

the percentages being by weight based on the weight of the polymeric component.

The invention is chiefly described herein by reference to electrically insulating compositions which can be melt shaped, preferably melt extruded around a conductor, e.g. a solid or stranded wire, to provide an insulating coating thereon. The insulating coating of the novel composition can be the sole insulating coating, or one of several insulating coatings around the conductor. 'If there are several coatings, the polyester composition may be the innermost coating, or the outermost coating, or an intermediate coating. However, the invention is also applicable to other melt-shaped configurations, e.g. tubing and molded parts, to compositions which can be shaped in other ways, and to compositions whose prime function is not to provide electrical insulation.

The aromatic polyester is preferably poly (1, 4-butylene terephthalate); other aromatic polyesters which can be used include polyethylene terephthalate and those

disclosed in the documents referred to above. The aliphatic polyester is preferably polycaprolactone. The thermoplastic elastomer is preferably a polyester thermoplastic elastomer, e.g. one of the polymers sold under the trade names Amitel and Hytrel. The thermoplastic elastomer can for example contain aromatic polyester blocks (e.g. polybutylene terephthalate blocks) and aliphatic polyester blocks (e.g. polybutylene succinate) linked to each other, for example through urethane linkages. Arnitel is an example of such a thermoplastic elastomer. The polymers (A), (B) and (C) preferably constitute 80-100%, particularly 90-100%, by weight of the polymeric component. Other polymers which can be present in the polymeric component include polyolefins and the polymers disclosed in the documents referred to above, in particular U.S. Patent No. 4,332,855. Preferably all the polymers in the composition are compatible with the aromatic polyester and have a solubility parameter which differs by at most 1.5 from the solubility parameter of the aromatic polyester. Preferably all the polymers in the composition are free from halogen.

The novel compositions of the invention show remarkably good heat aging properties, in particular in their retention of elongation and tensile strength when aged at elevated temperatures, e.g. for 168 hours at 150°C. The preferred compositions, in the form of a coating on a wire, retain at least 50% of their elongation and at least 80% of their tensile strength (at room temperature) after aging for 168 hours at 150° and preferably after aging for 168 hours at 180°C. The improved retention of physical properties apparently results from the presence of both ingredient (B) and ingredient (C), and makes it possible to include relatively large quantities of additives which improve flame retardance and/or smoke suppression, without unacceptable loss of elongation and tensile strength. This is especially important in wires to be used in automobiles, trains, trams and other transit vehicles, and in other uses where wires are subject to high ambient temperatures.

We have discovered that the novel compositions show a surprising improvement in flame retardance and/or smoke reduction when they contain SnO or ZnO, particularly when they contain SnO. The amount of SnO or ZnO is selected to provide the desired level of improved flame retardance and/or smoke reduction without unacceptable impairment of other physical and/or electrical properties. The amount is generally 3 to 60%, e.g. 10 to 50%, preferably 15 to 45%, by weight of the composition. The metal oxide can be the sole ingredient which provides flame retardance and/or smoke suppression to the composition, or other such ingredients can be present. Examples of other ingredients are other metal oxides and known additives, for example those disclosed in the documents referred to above. However, the

compositions are preferably free from halogen-containing ingredients. The presence of SnO makes it possible to reduce the amount of such known additives. Preferably, the total weight percent of SnO and other additives is less than (preferably at least 3% less than, particularly at least 10% less than) the weight percent of those additives which, in a composition which is identical except that it does not contain SnO, produces the same level of flame retardance and/or smoke suppression in one of the known tests for such properties, e.g. Limiting Oxygen Index (ASTM D 2863-74), Flammability (SAE Jl 128 MIL-W-81044, or ASTM D 3032-84) or Smoke Generation (ASTM E 662). Other ingredients which can be present include phosphorus-containing flame retardants and/or Mg(OH)2, the amount of Mg(OH)2 being reduced to a level which avoids the problems which otherwise arise when using these together, in particular degradation and foaming of the polyester.

The novel compositions are preferably free from reinforcing fillers such as glass fibers. When, as is preferred, the composition is in the form of a coating around a wire, the coating can be of any appropriate thickness, e.g. 0.025 inch (0.0635 cm), preferably 0.008 to 0.018 inch (0.02 to 0.046 cm). Coatings as thin as 0.005 inch (0.0125 cm) may be useful, particularly in conjunction with other coatings.

In constructions in which SnO is used, the layer is gray in color. It may be desirable to provide an outermost layer constructed of a different polymer for purposes of appearance. However, as discussed above, the layer constructed of the novel composition described herein may be the innermost coating, the outermost coating, or an intermediate coating.

EXAMPLES 1 - 10

The ingredients and amounts thereof set out in the Table were mixed together in a Brabender, and then melt-extruded over a 20 AWG 19/32 tin-coated copper stranded wire as a coating 0.010 inch (0.025 cm) thick. The products were tested and the results are set out in the Table.

Polybutylene terephthalate (PBT) used in Examples 1-10 was Celanex 1600A available from Hoechst-Celanese. Tone P700, Tone P767 and Tone P787 are polycaprolactones of different molecular weights available from Union Carbide. Arnitel used was thermoplastic elastomer with polyester blocks available from AKZO. The formulation for the stabilizer used in Examples 1-4 and 6-10 was 1.75% polycarbodiimide (PCD), 1.75% of a hindered phenolic antioxidant (Irganox 1010) and

0.88% of an aliphatic phosphite (Western 619). The formulation for the stabilizer used in Example 5 was 2.2% polycarbodiimide (PCD), 2.2% of a hindered phenolic antioxidant (Irganox 1010) and 1.2% of an aliphatic phosphite (Western 619).

The elongation and tensile tests were carried out on 3 inch (7.5 cm) samples removed from the wire. The VW-1 tests were carried out in accordance with the UL VW-1 test, and the results are expressed in the form x/y, where y is the number of samples tested and x is the number of samples which passed the test.

TABLE

*Examples 1 and 2 are comparative examples not in accordance with the invention.