POLYESTER COMPOSITIONS

Abstract: Polymeric compositions which contain a thermoplastic aromatic polyester, preferably polybutylene terephthalate, and a polyester block copolymer having a recrystallization temperature greater than 150 DEG C, preferably a thermoplastic elastomer containing aromatic polyester blocks and aliphatic polyester blocks. The ratio of the block copolymer to the aromatic polyester is 0.05:1 to 0.35:1, preferably 0.15:1 to 0.30:1. These compositions are particularly useful as the insulation on hermetic lead wires for use in refrigerant systems.

Description: POLYBSTER COMPOSITIONS This invention relates to novel polyester compositions and insulated electrical conductors, especially insulated wires for use as lead wires in refrigeration systems and other hermetically sealed electrical apparatus (often called "hermetic lead 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. 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, 4,767,668, 4,483,970 and 5,248,713, and International Publication Nos. 94/16014 and 96/02591. The disclosure of each of said publications is incorporated herein by reference. In conventional hermetic lead wires, the insulation is a wrapped polyester tape sandwiched between two polyester fiber braids. Such insulation is expensive and difficult to apply. U.S. Patent No. 5,225,635 (Wake et al. ) discloses a hermetic lead wire in which the insulation comprises an insulating layer made by melt-extruding a composition containing chlorosulfonated polyethylene, an acid acceptor, a filler, and a peroxide crosslinking agent. We have discovered, in accordance with the present invention, that very useful compositions can be made by modifying polytetramethylene terephthalate (also referred to as PTMT, polybutylene terephthalate, and PBT) or a like aromatic polyester by addition thereto of a second polymer which has a recrystallization temperature greater than 150°C and is a polyester block copolymer. Such compositions have an excellent combination of resistance to deterioration by refrigerants and retention of physical properties when subjected to heat aging, and are particularly suitable for use as insulation on hermetic lead wires. In a first preferred aspect, this invention provides a polymeric composition which comprises (1) a thermoplastic aromatic polyester which consists essentially of 70 to 100% by weight of tetramethylene terephthalate units and 0 to 30% of other units which are randomly copolymerized with the tetramethylene terephthalate units, and (2) a second polymer which has a recrystallization temperature greater than 150°C and is a polyester block copolymer; the ratio by weight of the second polymer (2) to the aromatic polyester (1) being from 0.05:1 to 0.35:1. In a second preferred aspect, the invention provides an insulated electrical device which comprises a metal conductor, preferably a wire, and an insulating jacket comprising a melt-shaped layer of a composition according to the first preferred aspect of the invention. In a third preferred aspect, the invention provides an electrical assembly which comprises a hermetically sealed enclosure containing a refrigerant liquid and an insulated electrical conductor within the enclosure and contacted by the refrigerant, wherein said conductor is as defined in the second preferred aspect of the invention. The invention is chiefly described herein by reference to thermoplastic polyester compositions which can be melt shaped, preferably melt extruded around a conductor, e.g. a solid or stranded wire, to provide an insulating coating around the wire. Generally the wire size is 4 to 38 AWG, preferably 10 to 30 AWG. When the wire is to be used as a hermetic lead wire, it is preferably a stranded wire. The term "coating" is used herein to denote a coating which is the sole insulating coating around the conductor; or a coating which is one of several insulating coatings around the conductor (the polyester composition being the innermost coating, or the outermost coating, or an intermediate coating or two or more of these coatings) ; or an insulating jacket around two or more conductors each having an individual insulating coating around it. The thickness of the coating is generally 0.05 to 0.8 mm (0.002 to 0.030 inch), preferably 0.08 to 0.4 mm (0.003 to 0.015 inch). However, it is to be understood that the invention is also applicable to other melt-shaped configurations, e.g. tubing and molded parts, and to compositions which can be shaped in other ways, and to compositions whose prime function is not to provide electrical insulation. Parts and percentages given in this specification are by weight unless otherwise noted. The Aromatic Polyester Component (1) of the composition is an aromatic polyester which contains 70 to 100%, preferably 95 to 100%, particularly 100%, by weight of tetramethylene terephthalate units, and in which any other units are randomly copolymerized with the tetramethylene terephthalate units. Such other units can be, for example, other alkylene terephthalate units, e.g. ethylene terephthalate units, or aliphatic polyester units. The Polyester Block Copolymer The polyester block copolymer used in this invention is preferably a thermoplastic elastomer (TPE) comprising aromatic polyester blocks and aliphatic polyester blocks. The melting point of the TPE is preferably greater than 170°C, particularly greater than 180°C, especially greater than 200°C. The percentage by weight of aromatic polyester blocks is generally 10 to 90%, preferably 37 to 90%, particularly 70 to 90%. The aromatic and aliphatic polyester blocks can be linked together, for example, through ester groups and/or urethane groups, for example through a urethane group of the formula -0- (CH 2 ) n -OOC.NH.Ar.CH 2 .Ar.NH.CO- where n is 2 to 6 , preferably 4, and Ar is an aromatic radical, preferably 1,4-phenylene. The repeating units in the aromatic polyester blocks have the formula -O- (CH 2 ) p -O.CO.Ar.CO- where p is at least 2, preferably 2 to 6, particularly 4, and Ar is an arylene group, preferably a 1,4-phenylene group. Preferably all the repeating units are the same, especially tetramethylene terephthalate units. The repeating units in the aliphatic polyester blocks have the formula -0- (CH 2 ) q -O.CO- (CH 2 ) r -C0 wherein each of q and r, which may be the same or different, is at least 2, preferably 2 to 6, particularly 4. Preferably all the repeating units are the same. Suitable block polyesters are available from DSM Engineering Plastics under the trade name "Arnitel", e.g. Arnitel UM550, UM551, and UX4854, and are described in U.S. Patent No. 4,483,970 (Huntjens et al. , assigned to Akzo N.V.), the disclosure of which is incorporated herein by reference. Relative Amounts nf TPK and Aromatic Polyester The ratio by weight of the polyester block copolymer to the aromatic polyester is preferably 0.05:1 to 0.35:1, particularly 0.15:1 to 0.30:1, especially 0.22:1 to 0.27:1. Other Polymeric Ingredients The polymeric component of the compositions preferably consists essentially of the polyester block copolymer and the aromatic polyester, but can also contain one or more other polymers (e.g. other polyesters, including homopolymers and random and block copolymers, such as polyethylene terephthalate) , preferably in amount less than 20%, particularly less than 10%, based on the weight of the TPE. Non-Poly eric Ingredients The compositions can contain non-polymeric ingredients, generally in amount less than 20%, preferably less than 10%, particularly less than 4%, by weight based on the weight of the composition. Such additives can be inorganic or organic, and include antioxidants, stabilizers, processing aids, coloring agents, fillers and flame retardants, including antimony trioxide, e.g. in amount 3-15%, and brominated flame retardants, e.g. in amount 5 to 15%. For further details of suitable additives, reference may be made to the documents incorporated herein by reference. For use on hermetic lead wires, the composition preferably has less than 0.8%, particularly less than 0.6%, especially less than 0.35% extractables when subjected to the Freon extraction test described below. Such compositions can for example be obtained by blending an aromatic polyester which has less than 0.3% extractables with a polyester block copolymer which has more than 1.2% extractables in the Freon extraction test. When the hermetic lead wire is to be used with a refrigerant which is not Freon 22, the composition preferably has a similarly low level of extractables in a test which is the same as the Freon extraction test except that the Freon 22 is replaced by the refrigerant actually used. The melt-extruded insulating jacket preferably has an initial elongation of at least 200%, particularly at least 300%, especially at least 360%, and an elongation of at least 200%, particularly at least 300%, especially at least 360%, after aging for 168 hours at 156°C. EXAMPLES The invention is illustrated by the following Examples, which are summarized in the Table below. In the Table, the following abbreviations are employed. TPE 1 is the TPE sold by DSM Engineering Plastics under the trade name Arnitel UX4854. TPE 2 is the TPE sold by DSM Engineering Plastics under the tradename Arnitel UM551V. Arnitel UX4854 and UM551V are believed to be TPE's as defined above in which Ar is a phenylene group, each of p, q and r is 4, and the aromatic and aliphatic polyester blocks are linked together through a urethane group of the formula -0-(CH 2 ) 4 -00C.NH.Ar.CH 2 .Ar.NH C0- where Ar is 1,4-phenylene. PBT is the polybutylene terephthalate sold by Hoechst Celanese under the trade name Celanex 1600A. WT10, BK10, RD10, RD11, and OR10 are the color concentrates sold by Wilson Color Inc. under the tradenames Wilson-89-WT-10, Wilson-89-BK-10, Wilson-89-RD-10, Wilson-89-RD-ll, and Wilson-89-OR-10, respectively. In each of the Examples, the ingredients and amounts thereof shown in Table 1 were mixed together and melt extruded as an insulating jacket of the wall thickness (in mils) shown in the Table over a stranded copper wire of the diameter (in mils) shown in the Table. The resulting insulated wire was tested to determine one or more of its Heat Aging, Extractables, Elongation and Tensile Strength. The procedures used in these tests are described below. The results are shown in the Table. Resistance to Heat Aginσ is measured by the method of ASTM D 3032, Section 14. The results given are the average times to failure (in hours) for ten specimens aged at the indicated temperature. The Table also includes estimated minimum times for aging at 125°C (with 18k etc. meaning 18,000 hours etc). Extractables is measured by the CFC Extraction Test described in NEMA Publication MW1000, paragraph 3.55. Elonσation% and Tensile Strength are measured by the method of ASTM D 3032, Section 14, both initially and after aging for 168 hours at 156°C ("aged" in Table). TABLE

Claims: -9- CLAIMS 1. A polymeric composition which comprises (1) a thermoplastic aromatic polyester which consists essentially of 70 to 100% by weight of tetramethylene terephthalate units and 0 to 30% of other units which are randomly copolymerized with the tetramethylene terephthalate units, and (2) a second polymer which has a recrystallization temperature greater than 150°C and is a polyester block copolymer; the ratio by weight of the second polymer (2) to the aromatic polyester (1) being from 0.05:1 to 0.35:1. 2. A composition according to Claim 1 wherein the second polymer is a thermoplastic elastomer which comprises: (a) aromatic polyester blocks in which the repeating units have the formula (I) -O- (CH 2 ) p -O.CO.Ar.- (I) wherein p is at least 2 and Ar is an arylene group, and (b) aliphatic polyester blocks in which the repeating units have the formula (II) -0- (CH 2 ) q -O.CO.- (CH 2 ) r -C0- (II) wherein each of q and r, which may be the same or different, is at least 2; 3. A composition according to claim 2 wherein the thermoplastic elastomer contains 20 to 90% by weight of aromatic polyester blocks of formula I in which p is 4 and Ar is a 1, -phenylene radical, and 10 to 80% by weight of aliphatic polyester blocks of formula II in which q is 4 and r is 4. 4. A composition according to any of claims 1 to 3 wherein at least 95% by weight of the repeating units in the aromatic polyester (1) are tetramethylene terephthalate units. 5. A composition according to any of claims 1 to 4 which comprises a polymeric component which consists essentially of the polyester (1) , the thermoplastic elastomer (2) , and 0-20% by weight, based on the weight of the aromatic polyester (1), of one or more other polymers. 6. A composition according to claim 5 wherein the polymeric component consists essentially of the aromatic polyester and the thermoplastic elastomer; the aromatic polyester is poly(tetramethylene terephthalate); and in the thermoplastic elastomer, each of p, q and r is 4, Ar is 1,4- phenylene, and the aromatic and aliphatic polyester blocks are linked together through a urethane group of the formula -0-(CH 2 ) 4 -00C.NH.Ar.CH 2 .Ar.NH C0- where Ar is 1,4-phenylene. 7. A composition according to any one of claims 1 to 6 wherein the ratio by weight of the thermoplastic elastomer (2) to the aromatic polyester (1) is 0.15:1 to 0.30:1. 8. A composition according to claim 7 wherein said ratio is 0.22:1 to 0.27:1. 9. A composition according to any one of claims 1 to 8 which contains up to 5% by weight, based on the weight of the composition, of at least one non-polymeric material. 10. An insulated wire which is surrounded by a layer of a melt extruded electrically insulating composition as defined in any of claims 1 to 9. 11. A wire according to claim 10 wherein the layer contacts the wire and is 0.076 to 0.76 mm (0.003 to 0.030 inch) thick. 12. A wire according to claim 10 or 11 which, when subjected to the CFC extraction test, has less than 0.8% extractables. 13. A wire according to any of claims 10 to 12, wherein the layer has an initial elongation of at least 300% and an elongation of at least 200% after aging for 168 hours at 156°C. 14. An electrical assembly which comprises a hermetically sealed enclosure containing a refrigerant liquid and an insulated electrical conductor within the enclosure and contacted by the refrigerant, wherein said insulated conductor is as defined in any one of claims 10 to 13. 15. An assembly according to claim 14 wherein the refrigerant is not Freon 22 and the insulated electrical conductor, when subjected to a test which is the same as the Freon Extraction Test except that the Freon 22 is replaced by the refrigerant present in the assembly, has less than 0.8% of extractables.

Inventors: NGUYEN PHU D, TONDRE STEPHEN L, YEUNG ALAN S, NGUYEN, PHU, D., TONDRE, STEPHEN, L., YEUNG, ALAN, S.
Applicants: RAYCHEM CORP, RAYCHEM CORPORATION
Application year: 1996
Main classification: C08L67
IPC codes: C08L67, H01B3