Insulated electrical conductors

Polymeric compositions which contain a thermoplastic aromatic polyester, preferably polybutylene terephthalate, and a polyester block copolymer having a recrystallization temperature greater than 150.degree. 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. To prevent cracking of such insulation when it is contacted by a varnish used to provide hermetic sealing, it can be covered by a thin layer of a fluoropolymer.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
This invention relates to novel polyester compositions and to 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"). 
2. Introduction to the Invention 
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 are of course very important, and a great variety 
of polyester compositions have, therefore, been used or proposed for use, 
particularly as insulating coatings on wires. Reference may be made for 
example to U.S. Pat. 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 to copending, commonly 
assigned U.S. patent application Ser. Nos. 08/275,174 filed Jul. 14, 1994 
(MP1467-US2), 08/429,384 filed Apr. 26, 1995 (Docket No. MP1517-US1) and 
08/435,339 filed May 4, 1995 (Docket No. MP1566-US1). The entire 
disclosure of each of said patents and patent applications is incorporated 
by reference herein for all purposes. 
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. Pat. No. 5,225,635 (Wake et al.), 
the disclosure of which is incorporated herein by reference, 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. 
SUMMARY OF THE INVENTION 
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.degree. C. and 
is a polyester block copolymer. These compositions are referred to herein 
as "modified PBT compositions", although the polyester can contain other 
units in addition to butylene terephthalate units. 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. 
However, it has been found, when testing such insulated wires as hermetic 
lead wires, that under some circumstances, the insulation ceases to be 
fully effective, because cracks develop in it. We have discovered that 
this cracking problem is caused by contact between the insulation and 
certain sealing compositions (often referred to as "varnishes") which are 
used to provide hermetic seals around the compressor motors which are used 
in refrigeration systems and to which the lead wires carry power. The 
varnish may be for example a dispersion of acrylic polymers in water (for 
example the products sold by duPont under the trade names LACTON and 
CAVALITE), or a dispersion of a phenolic epoxy polymers in water (for 
example the product sold by Schenectady under the trade name Isopoxy 800). 
After the hermetic lead wires have been attached to the compressor motor, 
the housing containing the compressor motor is dipped into a bath of the 
varnish. Even if the lead wires do not enter the bath, the varnish drips 
onto, or is splashed onto, the lead wires. When the varnish is cured, it 
forms a brittle coating which adheres tenaciously to the modified 
polyester insulation. If the wire is flexed, the varnish cracks, forming a 
notch from which cracking of the modified polyester layer can propagate. 
We have further discovered, in accordance with the present invention, that 
this problem can be mitigated by coating the insulation of the hermetic 
lead wire, at least in the area which may be contacted by the varnish, 
with a layer of a protective material, preferably a fluoropolymer, which 
prevents the cured varnish from adhering to the modified polyester 
insulation. Preferably the protective material is in the form of an outer 
coating of a polymeric composition which covers the modified PBT layer 
over the whole length of the insulated wire. In the latter case, the 
protective material may also reduce the amount of extractables when the 
insulation is contacted by a chlorofluorocarbon (CFC) refrigerant or other 
refrigerant. We believe that the use of such protective materials will 
also reduce cracking of other insulating compositions, particularly 
compositions which are based on PBT or the like, especially when they may 
be contacted by varnishes and like compositions, and/or reduce 
extractables from such insulating compositions when contacted by 
refrigerants. Disclosures of PBT insulating compositions are to be found 
in, for example U.S. Pat. Nos. 4,332,855 (MP0267), 4,767,688 (RK255), 
5,248,713 (MP1360) and copending commonly assigned U.S. patent application 
Ser. Nos. 08/004,749 (MP1467-US1), 08/275,174 (MP1467-US2) and 07/435,395 
(RK334) as well as Ser. Nos. 08/275,174, 08/429,384 and 08/435,339 already 
referred to. The disclosure of each of these U.S. Patents and applications 
is incorporated herein by reference. 
In a first preferred aspect, this invention provides a polymeric 
composition which can be melt-extruded or which has been melt-extruded, 
and which comprises a polymeric component which comprises a blend of 
(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.degree. 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. The term "polymeric component" is used in 
this specification to denote that part of the composition which is made up 
of polymeric material. The composition can consist of the polymeric 
component or it can also contain a non-polymeric component. 
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, this invention provides an insulated 
electrical device which comprises a metal conductor, preferably a wire, 
and an insulating jacket which surrounds the conductor, the insulation 
comprising 
(A) an inner layer composed of a first melt-extruded polymeric composition 
which comprises a polymeric component which comprises a blend of 
(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.degree. 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; and 
(B) an outer layer composed of a second melt-extruded polymeric composition 
which comprises a polymeric component which consists essentially of one or 
more fluoropolymers. 
In a fourth 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 or third preferred aspect of the invention. 
In a fifth preferred aspect, the invention provides an electrical assembly 
which comprises an electrical motor, an insulated hermetic lead wire for 
delivering electrical power to the motor, a housing which surrounds the 
motor, and a layer of a cured epoxy polymer varnish which hermetically 
seals the housing and which extends over at least part of the insulated 
lead wire, the lead wire (i), when subjected to the CFC extraction test, 
having less than 0.8% by weight extractables, and (ii) comprising a wire 
and polymeric insulation surrounding the wire, the insulation comprising 
(A) an inner layer composed of a first melt-extruded polymeric composition 
which comprises a blend of 
(1) a thermoplastic aromatic polyester, and 
(2) a second polymer which has a recrystallization temperature greater than 
150.degree. C. and is a polyester block copolymer; and 
(B) an outer layer which is composed of a second melt-extruded polymeric 
composition comprising a fluoropolymer and which, when the varnish on the 
surface of the insulated wire cracks, prevents the cracking of the varnish 
from causing cracking of the inner layer of insulation.

DETAILED DESCRIPTION OF THE INVENTION 
Parts and percentages given in this specification are by weight unless 
otherwise noted. 
Modified PBT Insulation 
The modified PBT compositions which are used in this invention can be melt 
shaped, preferably melt extruded around a conductor, e.g. a solid or 
stranded wire, to provide an insulating layer which surrounds 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 "layer" is used herein to denote a layer which is the sole 
insulating layer around the conductor; a layer which is one of several 
insulating layers around the conductor (the modified PBT composition being 
the innermost layer, or an intermediate layer or the outermost layer, 
except in the third preferred aspect of the invention, when the protective 
layer covers the modified PBT layer); or an insulating jacket around two 
or more conductors each having an individual insulating coating around it. 
The thickness of the layer is generally 0.002 to 0.030 inch, preferably 
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. 
The Aromatic Polyester 
Component (1) of the modified PBT compositions 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 to modify the aromatic 
polyester 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.degree. C., particularly 
greater than 180.degree. C., especially greater than 200.degree. 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 formul 
a 
EQU --O--(CH.sub.2).sub.n --OOC.NH.Ar.CH.sub.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 
EQU --O--(CH.sub.2).sub.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 
EQU --O--(CH.sub.2).sub.q --O.CO--(CH.sub.2).sub.r --CO 
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. Pat. No. 4,483,970 (Huntjens et al., assigned to Akzo 
N.V.), the disclosure of which is incorporated herein by reference. 
Relative Amounts of Block Copolymer 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 modified PBT 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 aromatic polyester. 
Non-Polymeric Ingredients 
The modified PBT 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 modified PBT composition preferably has 
less than 0.8%, particularly less than 0.6%, especially less than 0.35% 
extractables when subjected to the CFC 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 CFC extraction 
test. When the hermetic lead wire is to be used with a refrigerant which 
is not the CFC specified in the CFC extraction test 
(chlorodifluoromethane, often referred to by a trade name, Freon 22), the 
modified PBT composition preferably has a similarly low level of 
extractables in a test which is the same as the CFC extraction test except 
that the Freon 22 is replaced by the refrigerant actually used. 
The melt-extruded insulating modified PBT 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%. 
Protective Materials 
When the modified PBT insulation is used in a system which causes it to be 
contacted by a varnish, as discussed above, it is preferably protected by 
means of a protective material which is applied over the modified PBT 
insulation before it is contacted by the varnish. 
The polymeric component in the protection material is preferably a 
fluoropolymer. The term "fluoropolymer" is used herein to denote a polymer 
or mixture of polymers which can be melt-extruded and which contains more 
than 10%, preferably more than 25%, by weight of fluorine. Thus the 
fluorocarbon polymer may be a single fluorine-containing polymer, a 
mixture of two or more fluorine-containing polymers, or a mixture of one 
or more fluorine-containing polymers with one or more polymers which do 
not contain fluorine. Preferably the fluoropolymer comprises at least 50%, 
particularly at least 75%, especially at least 85%, by weight of one or 
more thermoplastic crystalline polymers each containing at least 25% by 
weight of fluorine, a single such crystalline polymer being preferred. 
Such a fluoropolymer may (but preferably does not) contain, for example, a 
fluorine-containing elastomer and/or a polyolefin, preferably a 
crystalline polyolefin, in addition to the crystalline fluorine-containing 
polymer or polymers. The fluorine-containing polymers are generally homo- 
or co-polymers of one or more fluorine-containing olefinically unsaturated 
monomers, or copolymers of one or more such monomers with one or more 
olefins. The fluoropolymer may have a melting point of at least 
200.degree. C., e.g. up to 300.degree. C. Preferably the polymeric 
composition has a flex modulus similar to the flex modulus of the modified 
PBT layer, so that it does not wrinkle when the insulated wire is bent. A 
preferred copolymer is a ethylene/chlorotrifluoro-ethylene copolymer, this 
term being ued to denote a copolymer of ethylene and 
chlorotrifluoroethylene, and optionally one or more other comonomers, 
which contains at least 80% by weight of units derived from ethylene and 
chlorotrifluoroethylene and in which the molar ratio of ethylene units to 
chlorotrifluoro-ethylene units is from 0.5:1 to 1.5:1, preferably 0.85:1 
to 1.15:1, e.g. about 1:1. Another preferred fluoropolymer is a copolymer 
of ethylene and tetrafluoroethylene, this term being used to denote a 
copolymer of ethylene and tetrafluoroethylene and optionally one or more 
other comonomers, which contains at least 80% by weight of units desired 
from ethylene and tetrafluoroethylene, and in which the molar ratio of 
ethylene units to tetrafluoroethylene units is from 0.5:1 to 1.5:1, 
preferably 0.85:1 to 1.15:1, e.g. about 1:1. Other fluoropolymers are 
copolymers of vinylidene fluoride with one or more of hexafluoropropylene, 
tetrafluoroethylene, and hexafluoroisobutylene; and copolymers of 
tetrafluoroethylene and hexafluoropropylene. 
The protective material can contain non-polymeric ingredients as specified 
above for the modified PBT compositions. However, since the protective 
material need only protect the modified PBT composition from the effects 
of the varnish, such non-polymeric ingredients are generally used, if at 
all, only in small quantities. 
When, as is preferred, the protective material is in the form of a layer 
covering the modified PBT insulation, the protective layer is preferably 
less than 0.008 inch thick, particularly 0.0005 to 0.005 inch thick, e.g. 
0.0015 to 0.0025 inch thick. 
EXAMPLES 
The invention is illustrated by the following Examples. 
Examples 1-10 
Examples 1-10 are summarized in the Table below. In the Table, the 
following abbreviations are employed. 
______________________________________ 
TPE 1 The TPE sold by DSM Engineering Plastics under the 
trade name ARNITEL UX4854. 
TPE 2 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 
--O--(CH.sub.2).sub.4 --OOC.NH.Ar.CH.sub.2.Ar.NH CO-- 
where Ar is 1,4-phenylene. 
PBT The polybutylene terephthalate sold by Hoechst 
Celanese under the trade name Celanex 1600A. 
WT10, BK10, The color concentrates sold by WILSON Color 
RD10, RD11, Inc. under the tradenames WILSON-89-WT-10, 
and OR10 WILSON-89-BK-10, WILSON-89-RD-10, WILSON-89- 
RD-11, 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 Aging 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.degree. 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. 
Elongation % and Tensile Strength (psi) are measured by the method of ASTM 
D 3032, Section 14, both initially and after aging for 168 hours at 
156.degree. C. ("aged" in Table). 
TABLE 
__________________________________________________________________________ 
Example No. 
Ingredients 
1 2 3 4 5 6 7 8 9 10 
__________________________________________________________________________ 
PBT 78 78 78 78 78 78 84.5 
84.5 
84.5 
84.5 
TPE 1 20 20 20 20 20 20 -- -- -- -- 
TPE 2 -- -- -- -- -- -- 12.5 12.5 12.5 12.5 
WT10 2 -- -- 2 -- -- 3 -- -- -- 
BK10 -- 2 -- -- 2 -- -- 3 -- -- 
RD10 -- -- -- -- -- 2 -- -- -- 3 
RD11 -- -- 2 -- -- -- -- -- 3 -- 
OR10 -- -- -- -- -- -- -- -- -- 1 
Wire Diam. 49 49 49 49 49 49 49 49 49 49 
Wall 8 8 8 16 16 16 16 16 16 16 
Thickness 
Heat Aging at 
190.degree. C. 139 126 165 132 134 117 
180.degree. C. 266 252 273 285 271 256 
170.degree. C. 534 508 534 516 525 511 
Est. Min. at 
125.degree. C. 18 k 19 k 11 k 18 k 18 k 24 k 
Extractables 
R22 0.28 0.29 0.28 0.4 0.5 0.4 0.5 
R134A 0.3 0.2 0.5 0.1 
Elongation 
Initial 364 374 379 438 452 440 390 398 400 408 
Aged 401 405 411 495 495 487 436 436 415 360 
Tensile 
Strength 
Initial 7098 7240 7258 9680 9891 9519 8176 8515 8685 8911 
Aged 7480 7402 7431 9328 9328 8855 8460 8297 8007 6562 
__________________________________________________________________________ 
Example 11 
An insulated wire was made by coextruding two polymeric compositions over 
an 18 AWG wire (diameter 0.046 inch). The first composition, which was 
melt extruded as an inner layer 0.008 inch thick, adjacent the wire, was a 
blend of PBT (79.59 parts) and TPE 1 (20.41 parts), the PBT and TPE 1 
being as used in Examples 1-10. The second composition, which was 
melt-extruded as an outer layer, 0.002 inch thick, over the inner layer, 
was composed of an ethylene/chlorotrifluoroethylene copolymer sold under 
the trade name Halar 500. 
Samples of the resulting insulated wire were coated with a phenolic epoxy 
varnish which is widely used as a sealant (Isopoxy 800, available from 
Schenectady), and the varnish was then cured at 190C for 1 hour. When the 
resulting wire was flexed, the varnish coating cracked, but the modified 
PBT insulating layer was not damaged. 
Example 12 (Comparative) 
The procedure of Example 11 was followed except that the outer ECTFE layer 
was not applied. When the wire was flexed after the varnish coating had 
been cured, both the varnish layer and the modified PBT insulating layer 
cracked.