Polyester compositions

Novel polyester compositions, particularly suitable for the insulation of wires, contain an aromatic polyester, especially polybutylene terephthalate. The presence of certain tin (II) compounds, for example tin (II) oxide, oxalate, phthalate, pyromellitate, or phosphite, reduces the flammability and smoke generation of such compositions. The presence of an aliphatic polyester, and optionally a thermoplastic elastomer, can also improve the properties of such compositions.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
This invention relates to polyester compositions. 
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, for many uses, 
include flammability and smoke generation when burned. 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, and 
4,332,855 and the United States Patents cited as references on page 1 
thereof; copending, commonly assigned U.S. patent application Ser. No. 
07/537,558, filed Jun. 13, 1990 (MP1360); European Patent Publication No. 
0057415; and Japanese Patent Document Nos. 099256 (December/1971), 7199256 
(February/1985), 7199257 (February/1985) and 210446 (May/1986). The entire 
disclosure of each of said patents, application and patent documents is 
incorporated by reference herein for all purposes. 
SUMMARY OF THE INVENTION 
We have discovered, in accordance with the present invention, that the 
presence of one or more compounds containing a metal atom linked to an 
oxygen atom, in particular a tin (II) atom linked to an oxygen atom, for 
example a tin (II) salt of a carboxylic acid, a tin (II) salt of an 
oxoacid of phosphorus, tin (II) oxide (SnO), or zinc oxide (ZnO), can have 
a very beneficial effect upon certain polyester compositions. In 
particular, such a compound can reduce the flammability of the composition 
and/or reduce the smoke generated by it when burned. This is especially 
useful when the composition is in the form of an electrically insulating 
coating around a wire. 
In one aspect, this invention provides a shaped article which is composed 
of a composition which comprises: 
(a) 50 to 85% by weight of a polymeric component which comprises 
(i) 60 to 94%, based on the weight of the polymeric component, of an 
aromatic polyester, preferably polybutylene terephthalate, 
(ii) 3 to 20%, based on the weight of the polymeric component, of at least 
one aliphatic polyester, preferably polycaprolactone, and 
(iii) 3 to 20%, based on the weight of the polymeric component, of at least 
one thermoplastic elastomer, preferably a thermoplastic elastomer 
containing polyester blocks; 
the ingredients (i), (ii) and (iii) constituting 80 to 100% by weight of 
the polymeric component; and 
(b) 15 to 45% by weight of at least one additive compound which contains a 
divalent tin atom and an oxygen atom linked to the divalent tin atom, 
preferably SnO.

DETAILED DESCRIPTION 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. The term "coating" is used herein to 
denote a coating which is the sole insulating coating around the 
conductor; 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. 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 polyester compositions contain a polymeric component which comprises at 
least one aromatic polyester, preferably poly (1,4-butylene 
terephthalate), which is often referred to herein as PBT. Suitable 
aromatic polyesters include those disclosed in the documents referred to 
above and incorporated herein by reference and those disclosed in U.S. 
Pat. No. 5,081,176, the disclosure of which is incorporated herein by 
reference. The aromatic polyester is preferably free from halogen. The 
aromatic polyester can alternatively or additionally be present as a block 
in a block copolymer, e.g. a thermoplastic elastomer. Examples of such 
copolymers include copolyester esters and copolyether esters, e.g. the 
polymers sold under the trade names Hytrel (du Pont) and Arnitel (Akzo), 
and graft copolymers comprising an aromatic polyester backbone, e.g. a 
polyalkylene terephthalate backbone, and polymeric side chains which are 
grafted to the backbone and which comprise units derived from addition 
polymerization of a monomer containing ethylenic unsaturation, as 
disclosed in PCT (International) Application No. WO 93/08234. The 
polymeric component also contains other polymers, including aliphatic 
polyesters, (preferably polycaprolactone) and thermoplastic elastomers, 
and optionally polyolefins, said other polymers preferably being 
compatible with the aromatic polyester and preferably having a solubility 
parameter which differs by at most 1.5 from the solubility parameter of 
the aromatic polyester (the Solubility Parameters being measured by the 
procedure described in Polymer Handbook, edited by Brandrup and Immergut, 
2nd Edition, pages IV 339 to 339). Such other polymers, preferably are 
present in amounts less than 50%, particularly less than 30%, especially 
less than 20%, based on the weight of the polymeric component; and are 
preferably free from halogen. Other polymers which can be present are 
disclosed in the documents incorporated herein by reference, in particular 
U.S. Pat. No. 4,332,855. 
The polymeric component comprises (A) 60-94%, preferably 70-90%, especially 
75-85%, of a thermoplastic aromatic polyester component, especially PBT, 
(B), 3-20%, preferably 5-15%, particularly 6-10%, of at least one 
aliphatic polyester, especially polycaprolactone; and (C) 3-20%, 
preferably 5-15%, particularly 6-10%, of a thermoplastic elastomer, 
preferably an aromatic polyester thermoplastic elastomer, e.g. Arnitel.TM. 
or Hytrel.TM., these percentages being by weight based on the combined 
weights of (A), (B) and (C). The ingredients (A), (B) and (C) constitute 
80-100%, particularly 90-100%, by weight of the polymeric component. In 
this specification, parts and percentages are by weight unless otherwise 
noted. Ingredient (A) preferably contains 70 to 100%, particularly 85 to 
100%, of PBT. Other polymers which may be present as (A), or part of (A), 
include polyethylene terephthalate. Compositions comprising a polymeric 
component as defined above show remarkably good insulation resistance, 
particularly at elevated temperatures, e.g. at 60.degree. C., and/or 
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.degree. C. These compositions, in the form of a 
coating on a wire, retain 50% of their elongation and 80% of their tensile 
strength (at room temperature) after aging for 168 hours at 150.degree. 
and preferably at 180.degree. C. These improved properties apparently 
result from the addition to ingredient (A) of both ingredient (B) and 
ingredient (C), and make it possible for compositions containing the novel 
polymeric component to include relatively large quantities of additives 
which improve flame retardance and/or smoke suppression without 
unacceptable loss of insulation resistance and/or elongation and tensile 
strength. This is especially important for the insulation of wires to be 
used in automobiles, trains, trams and other transit vehicles, and in 
other uses where insulated wires are subject to high ambient temperatures. 
The additive compounds used in accordance with this invention are divalent 
tin compounds which are linked to an oxygen atom. The linkage can be 
covalent or ionic or both; thus the compounds of tin with carboxylic acids 
and oxoacids of phosphorus are referred to herein as salts, but those 
skilled in the art will recognize that such compounds can alternatively be 
regarded as complexes or chelates. 
Tin (II) oxide provides excellent results. The average particle size of the 
tin (II) oxide is preferably less than 10 microns, particularly less than 
5 microns. However, tin (II) oxide suffers from the disadvantage that it 
is dark in color, making shaped articles of compositions containing tin 
(II) oxide difficult to pigment and/or to mark (and, to many, unattractive 
in appearance). The same is true of mixed tin oxides containing 
substantial amount of SnO, e.g. Sn.sub.3 O.sub.4. This disadvantage can be 
mitigated by means of an outer polymeric jacket which is white in color, 
but this is an expense preferably avoided. In many cases, therefore, it is 
preferred to use a tin (II) compound which, either alone or in combination 
with other conventional pigments, e.g. TiO.sub.2, result in a polymeric 
coating having a light, e.g. white, color. 
The divalent tin can be present, for example, as the cation in a salt 
formed with an organic carboxylic acid or with an oxoacid of phosphorus. 
Suitable carboxylic acids include oxalic acid, alkyl carboxylic acids 
(including substituted alkyl, e.g. aralkyl, carboxylic acids) and aryl 
carboxylic acids (including substituted aryl, e.g. alkaryl, carboxylic 
acids). Preferably the tin atom forms part of a ring structure with two 
carboxylate groups which are adjacent to each other in a dicarboxylic 
acid, for example oxalic acid, or an aryl carboxylic acid containing (i) 
two carboxyl groups attached to adjacent carbon atoms of an aromatic ring 
(for example phthalic acid or pyromellitic acid) or (ii) two carboxyl 
groups attached to carbon atoms which form part of adjacent aromatic rings 
in a fused ring system and which are separated by a single carbon atom 
forming a part of both rings. However, the tin (II) compound can also be 
part of a polymer comprising repeating units of the formula 
EQU --O.CO.R.CO.O.Sn-- 
where R is an organic radical. 
The divalent tin can be present as part of a compound which is capable of 
further oxidation, e.g. as the cation in a salt formed with an oxoacid of 
phosphorus which is capable of further oxidation (often referred to as a 
lower oxoacid), e.g. an oxoacid containing at least one hydrogen atom 
linked directly to the phosphorus atom. Tin (II) phosphite, SnHPO.sub.3, 
is an example of such an additive compound. 
Especially when the additive compound is a metal oxide, it is preferably 
free of water of hydration, (i.e. water which can be removed by heating). 
The amount of the additive compound 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 15 to 45%, especially 15 to 25%, by weight of the 
composition. The additive compound can be the sole ingredient which 
provides flame retardance and/or smoke suppression to the composition. 
Particularly preferred compositions for use in the invention contain 
15-45%, particularly 15-25%, of a tin (II) compound, particularly tin (II) 
oxide and/or tin (II) oxalate, and a polymeric component which consists 
essentially of (a) PBT, (b) a mixture of (i) PBT and (ii) an aliphatic 
polyester, preferably polycaprolactone, the aliphatic polyester preferably 
being present in amount 10-20%, based on the weight of the composition, 
(c) a mixture of (i) PBT and (ii) a thermoplastic elastomer containing 
polyester blocks, e.g. "THytrel" or "Arnitel", the thermoplastic elastomer 
preferably being present in amount 10-20% based on the weight of the 
composition, or (d) a mixture of (i) PBT, (ii) an aliphatic polyester, 
preferably polycaprolactone, preferably present in amount 5-10%, and (iii) 
a thermoplastic elastomer containing polyester blocks, e.g. "Hytrel" or 
"Arnitel", preferably present in amount 5-10%. 
The novel compositions used in this invention can also contain other 
ingredients, for example those disclosed in the documents incorporated by 
reference herein. Such other ingredients can include known flame 
retardants and smoke suppressants; however, the compositions of the 
invention are preferably free from halogen-containing ingredients. The 
presence of the additive compound makes it possible to eliminate, or 
reduce the amount of, such known additives. Preferably, the total weight 
percent of the additive compound and any other additive is less than, 
preferably at least 3% less than, particularly at least 10% less than, the 
weight percent of that other additive which, in a composition which is 
identical except that it does not contain any additive compound according 
to the invention, 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 J1128 MIL-W-81044, or 
ASTM D 3032-84) or Smoke Generation (ASTM E 662). Thus other ingredients 
which can be present include phosphorus-containing flame retardants and/or 
Mg(OH).sub.2. The present invention makes it possible to reduce the amount 
of Mg(OH).sub.2 to a level which avoids the problems which otherwise arise 
when using Mg(OH).sub.2 and phosphorus-containing flame retardants 
together, in particular degradation and foaming of the polyester 
composition. 
For many uses, the polyester compositions are preferably free from 
reinforcing fillers such as glass fibers. When, as is preferred, the 
polyester composition is in the form of a coating around a wire, the 
coating can be of any appropriate thickness, e.g. up to 25 mils, 
preferably 8-18 mils. Coatings as thin as 5 mils may be useful, 
particularly in conjunction with other coatings. 
The invention is illustrated by the following Examples. 
EXAMPLES 
Examples 1-10 
The ingredients and amounts thereof (in percentages by weight based on the 
total weight of the ingredients) set out in Table 1 below 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. 
The polybutylene terephthalate (PBT) ingredient used in Examples 1-10 was 
Celanex 1600A available from Hoechst-Celanese. The Tone P700, Tone P767 
and Tone P787 ingredients are polycaprolactones of different molecular 
weights available from Union Carbide. The Arnitel ingredient is a 
thermoplastic elastomer with polyester blocks available from AKZO. The 
stabilizer used in Examples 1-4 and 6-10 was a mixture of 1.75% 
polycarbodiimide (PCD), 1.75% of a hindered phenolic antioxidant (Irganox 
1010) and 0.88% of an aliphatic phosphite (Weston 619). 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 
(Weston 619). 
The elongation and tensile tests were carried out on 3 inch (7.5 cm) 
samples removed from the wire and then aged at 180.degree. C. 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. 
The Insulation Resistance tests were carried out in accordance with ASTM 
D-3032 at 23.degree. C., at 60.degree. C. after the wire had been 
maintained at 60.degree. C. for one hour, and at 60.degree. C. after the 
wire had been maintained at 60.degree. C. for 4 hours. 
Examples 11-18 
In Examples 11-18, the ingredients and amounts thereof (in percentages by 
weight based on the total weight of the composition) were mixed together 
in a Brabender and then pressed into slabs about 0.075 inch thick. Samples 
cut from the pressed slabs were tested to determine their LOI (Limiting 
Oxygen Index) by ASTM D 2863-74), and the Char Level of the samples which 
had been tested by the LOI was observed and expressed on a scale of 0 to 
10, with 0 indicating that the sample showed no char or expansion and 10 
including an extensively expanded and charred residue. 
TABLE 1 
__________________________________________________________________________ 
Example No. 
Ingredients 1* 2* 3 4 5 6 7 8 9 10 
__________________________________________________________________________ 
PBT 61.62 
65.62 
64.62 
65.62 
64.4 
65.62 
65.62 
65.62 
65.62 
65.67 
Tone 14 10 9 5 5 -- -- 5 5 5 
P 700 
Tone -- -- -- -- -- 5 -- -- -- -- 
P 767 
Tone -- -- -- -- -- -- 5 -- -- -- 
P 787 
Arnitel -- -- 5 5 5 5 5 5 5 5 
SnO 20 20 20 20 20 20 20 -- -- 20 
SnO -- -- -- -- -- -- -- 20 -- -- 
(dried) 
SnO -- -- -- -- -- -- -- -- 20 -- 
(ground) 
Stabilizer 4.38 
4.38 
4.38 
4.38 
5.6 4.38 
4.38 
4.38 
4.38 
4.38 
TESTS 0/3 
2/4 
3/4 
3/3 4/5 4/5 2/4 3/3 3/3 3/3 
VW-1 
Elongation 327 
236 
363 
345 361 317 345 371 397 -- 
Orig. % 
% of original elongation retained after 
62 hrs 9 52 52 61 81 101 73 32 49 -- 
121 hrs 10 22 26 33 10 77 44 3 50 -- 
184 hrs 24 26 3 3 3 9 3 0 50 -- 
234 hrs 3 5 0 0 0 0 0 0 53 -- 
Tensile Strength 
% of original tensile strength retained after 
62 hrs 102 
80 100 
88 72 88 88 76 71 -- 
121 hrs 91 79 80 71 69 94 73 53 65 -- 
184 hrs 67 75 81 71 35 90 24 0 65 -- 
234 hrs 76 64 0 0 0 0 0 0 71 -- 
Insulation Resistance 
Mohm-kft (Mohm-km) 
at 23.degree. C. 1200 
2400 
2400 
4050 
4500 
5400 
5400 
5400 
4500 
-- 
(365) 
(731) 
(731) 
(1234) 
(1371) 
(1646) 
(1646) 
(1646) 
(1371) 
at 60.degree. C. 2.5 
6.0 
4.8 
7.8 12.6 
12.0 
10.5 
13.5 
15.9 
-- 
after 1 hr (0.8) 
(1.8) 
(1.5) 
(2.4) 
(3.8) 
(3.6) 
(3.2) 
(4.1) 
(4.8) 
-- 
at 60.degree. C. 2.5 
7.8 
6.0 
9.6 14.1 
12.0 
11.7 
12.6 
15.0 
-- 
after 4 hrs (0.8) 
(2.4) 
(1.8) 
(2.9) 
(4.3) 
(3.6) 
(3.6) 
(3.8) 
(4.6) 
-- 
__________________________________________________________________________ 
TABLE 2 
__________________________________________________________________________ 
Example No. 
Ingredients 
11* 
12 13 14 15 16 17* 18* 
19* 
__________________________________________________________________________ 
PBT 100 
70.0 
70.5 
80.0 
70.0 
70.0 
77.6 
77.6 
70.0 
(Celanex 1600A) 
Tin (II) oxalate 
-- 30 -- -- -- -- -- -- -- 
Tin (II) phosphite 
-- -- 29.5 
-- -- -- -- -- -- 
Tin (II) oxide 
-- -- -- 20.0 
-- -- -- -- -- 
Tin (II) 
-- -- -- -- 30.0 
-- -- -- -- 
pyromellitate 
Tin (II) phthalate 
-- -- -- -- -- 30.0 
-- -- -- 
Tin (II) sulfide 
-- -- -- -- -- -- 22.4 
-- -- 
Tin (IV) oxide 
-- -- -- -- -- -- -- 22.4 
-- 
Tin (II) 
-- -- -- -- -- -- -- -- 30.0 
pyrophosphate 
TESTS 
LOI 20.5 
35.0 
32.5 
29.5 
26.5 
23.5 
21.0 
19.0 
18.5 
Char Level 
&lt;1 10 8 10 10 10 &lt;1 &lt;1 &lt;1 
__________________________________________________________________________ 
*Examples 1, 2, 11, 17, 18 and 19 are comparative examples not in 
accordance with the invention