Background of the Invention

The invention relates to a dual wall wire insulation in which the inner layer of insulation comprises a blend of polyalkylene terephthalate and a polylactone and the outer layer of insulation comprises a blend of polybutylene terephthalate and a segmented polyester.

Polyesters, such as poly(alkylene terephthalates), for example, polyethylene terephthalate) (PET) and poly(butylene terephthalate) (PBT), are subject to thermal degradation, especially at elevated temperatures. In copending commonly assigned U.S. application Serial No. 07/537,558 filed June 13, 1990 (the '558 application), thermally stabilized polyester compositions comprising a poly(al ylene terephthalate), a polylactone, a carbodiimide and an aliphatic phosphite are disclosed. It has been found that wires insulated with these stabilized polyester compositions have excellent thermal stability, but exhibit inadequate fluid and abrasion resistance for certain uses.

Summary of the Invention

It has now been discovered that the fluid and abrasion resistance of a conductor coated with a thermally stabilized polyester composition as described in the '558 application can be improved by applying an outer layer of insulation comprising a blend of a polytetramethylene terephthalate (also known as polybutylene terephthalate) and a polymer having certain flex and solubility characteristics. The resulting dual wall coating on the conductor exhibits excellent thermal stability as well as fluid and abrasion resistance.

The use of a blend of a polytetramethylene terephthalate (PTMT) and a polyester having a flex modulus of 500 to 100,000 psi and a solubility parameter of ± 1.5 of the solubility parameter of the

PTMT for coating electrical conductors is disclosed in U.S. Patents Nos. 4,332,855 and 4,767,668, the entire disclosures of which are incorporated herein by reference. However, the use of such blends as insulation on wire or cable is limited because of the relatively poor heat aging properties of the blends. It is surprising that the use of these compositions as an outer layer of insulation over the stabilized polyesters of the '588 application provide a dual wall insulation which exhibits acceptable heat aging performance in addition to improved fluid and abrasion resistance.

One aspect of this invention comprises a conductor provided with

(a) a first polymeric layer surrounding the conductor and comprising a stabilized composition comprising a poly(alkylene terephthalate) and a polylactone; and

(b) a second polymeric layer surrounding the first polymeric layer and comprising a composition comprising:

(i) a polyester in which at least 70 mole % of the repeating units are tetramethylene terephthalate units and which has a solubility parameter S; (ii) 10 to 100% by weight, based on the weight of the polyester (i), of a second polymer which (a) has a flex modulus of 500 to 100,000 psi, and (b) has solubility parameter of (S+1.5) to (S-1.5).

Detailed Description of the Invention

FIRST POLYMERIC LATER

The first polymeric layer comprises a poly(alkylene terephthalate), such as poly(ethylene terephthalate) and poly(butylene terephthalate), in an amount of at least about 30% by weight (all percents given herein are by weight based on the weight of the composition unless otherwise stated). Preferably, the polyfalkylene terephthalate) is present in the amount from about 30% to about 90%, more preferably from about 40% to about 65%.

Poly(alkylene terephthalates) are known polymers, some of which are commercially available. The polymers are prepared by polymerizing terephthalic acid or an ester thereof, which may be substituted, for example by halogen, such as bromine, with a glycol, for example ethylene or butylene glycol. The glycol may also be substituted, for example, by halogen, such as bromine. The use of a polyalkylene terephthalate containing at least 70% poly(butylene terephthalate) repeating units is particularly preferred. These polymers typically have a molecular weight greater than about 10, 000 weight average molecular weight.

The composition of the first polymeric layer also contains at least about 3% polylactone. Preferably, the composition contains about 3 to about 40%, more preferably from about 5 to about 30% polylactone. Preferred polylactones have repeating units of the general formula:

-4-0— R— CO-→- wherein R is divalent alkylene of, e.g., from 2 to 30 carbon atoms, straight chain and branched, and the number of repeating units is such that the average molecular weight is up to about 100, 000.

More particularly, the polylactone has the general formula:

-4-0— <-C -RlR ² — ⁾ π— CO-→5-

wherein R ¹ and R ² are hydrogen or alkyl, e.g., methyl or ethyl, m is, for example, 2-5 and n is from about 25 to about 1500. Especially preferred compounds within this family will comprise those in which R ¹ and R ² are each hydrogen, or are methyl or ethyl on the carbon adjacent to the linking oxygen atom. The most preferred such polylactones are poly(beta-propiolactone), poly(gamma- butyrolactone) , poly(delta-valerolactone) , poly(epsilon-caprolactone) or mixtures of at least two of them. The use of polycaprolactone is especially preferred.

The polylactone can be made by various methods. For example, by polymerizing the corresponding lactone. Further details

on preparative procedures for polylactones may be obtained by reference to The Encyclopedia of Polymer Science and Technology, Vol. 11, John Wiley and Sons, Inc, New York, 1969, p 98-101; H. Cherdron et al., Makromol Chem. 56, 179-186 and 187-194 (1962); U. S. 2, 933, 477 and U. S. 2, 933, 478.

The composition of the first polymeric layer preferably also contains about 0.05% to about 10% of a carbodiimide. Preferably the composition contains about 0.1% to about 5% carbodiimide. The carbodiimide is represented by the formula:

X _x — R ₁ -4N=C=N-^l ₂ -VN=C=N- R ₃ -X ₂

where Ri, R2 and R3 are C1-C12 aliphatic, C6-C13 cycloaliphatic, or C6-C13 aromatic divalent hydrocarbon radicals, and combinations thereof, Xi and X2 are H,

N- C- N-R ₄ H O

I II

A o or

— N- C- O-R,

where R4, R5 and R6 are C1-C12 aliphatic, C6-C13 cycloaliphatic and C6-C13 aromatic monovalent hydrocarbon radicals and combinations thereof and additionally R or R5 can be hydrogen; and n is 0 to 100. The useful carbodiimides have an average of at least one carbodiimide groups (i. e., one -N=C=N-group) per molecule and an average molecular weight of less than about 500 carbodiimide groups. These carbodiimides can be aliphatic, cycloaliphatic or aromatic carbodiimides. The terms aliphatic, cycloaliphatic and aromatic as used herein indicate that the carbodiimide group is attached directly to an aliphatic group, a cycloaliphatic group or an aromatic nucleus respectively. For example, these carbodiimides can be illustrated by formula (I): wherein Ri, R2 and R3 are independently aliphatic, cycloaliphatic or aromatic divalent hydrocarbon radicals and n is at least 0 and preferably 0 to 100_ Xi and X2 are defined as hereinbefore. Carbodiimides useful for the compositions of this invention have one or more carbodiimide groups and thus one or more of the three divalent hydrocarbon groups (i.e., Ri, R2 and R3) and each of these hydrocarbon groups

can be the same or different from the others so that the diimides can have aliphatic, cycloaliphatic and aromatic hydrocarbon groups in one carbodiimide molecule. The use of a polycarbodiimide is preferred.

Carbodiimides can be prepared to use in this invention by well known procedures. Typical procedures are described in U. S. Patent Nos. 3, 450, 562 to Hoeschele; 2, 941, 983 to Smeltz; 3, 193, 522 to Neumann et al, and 2, 941, 966 to Campbell.

The composition of the first polymeric layer preferably also contains about 0.05% to about 10% of an aliphatic phosphite. The phosphite compound preferably is present in an amount of about 0.1% to about 5%.

The term "aliphatic phosphite" is used herein to include hydrogen phosphites, monophosphites, diphosphites, triphosphites, polyphosphites and the like, having at least one aliphatic carbon atom bonded to at least one of the oxygen atoms of the phosphite moiety. The phosphites may be mono- di or tri- esters of phosphorous acid or phosphonic acid. The aliphatic carbon may be part of a straight or branched chain aliphatic group, such as an alkyl group, and may be saturated or unsaturated and may be substituted by one or more substituents, such as chlorine or hydroxyl or carboxyl groups, which do not interfere with its action in enhancing the thermal stability of the composition. The aliphatic group may be substituted by aromatic moieties as long as the carbon atom bonded to the oxygen atom of the phosphite moiety is an aliphatic carbon atom. The aliphatic group is preferably an alkyl group containing at least 1 carbon atom, more preferably the aliphatic group is an alkyl group containing about 6 to about 30 carbon atoms. Other aliphatic groups are also suitable and are exemplified in the following list of aliphatic phosphites.

Illustrative aliphatic phosphites include, for example, distearyl pentaerythritol diphosphite, diisodecyl pentaeiythritol diphosphite, bis(2, 4-di-t-butylphenyl) pentaerythritol diphosphite, diphenyl isodecyl phosphite, diphenyl isooctyl phosphite, phenyl diisodecyl

phosphite, diisooctyl phosphite, triisooctyl phosphite, dilauryl phosphite, trilauryl phosphite, tristearyl phosphite, di-tridecyl phosphite, ethylhexyl diphenyl phosphite, diisooctyl octylphenyl phosphite, diphenyl didecyl (2, 2, 4-trimethyl-l, 3-pentanediol) diphosphite, tris(2-chloroethyl) phosphite, tris(dipropyleneglycol) phosphite, heptakis(dipropyleneglycol) triphosphite, tetraphenyl dipropyleneglycol diphosphite, poly(dipropyleneglycol) phosphite, trilauryl trithiophosphite, bis(tridecyl) hydrogen phosphite, dioleyl hydrogen phosphite, and the like.

Various additives can be added to the polymeric composition. Such additives include antioxidants such as alkylated phenols, e.g., those commercially available as Goodrite 3125, Irganox 1010, Irganox 1035, Irganox 1076, Irganox 1093, Vulkanox BKF; alkylidene polyphenols, e.g., Ethanox 330; thio-bis alkylated phenol, e.g., Santonox R; dilauryl thio-dipropionate, e. g Carstab DLTDP; dimyristyl thiodipropionate, e.g., Carstab DMTDP; distearyl thiodipropionate, e.g., Cyanox STDP; amines, e.g . Wingstay 29, Nauguard 445, etc; UV stabilizers such as [2, 2'-thio-bis(4-t- octylphenolato)] n-butylamine nickel, Cyasorb UV 1084, 3, 5- ditertiarybutyl-p-hydroxybenzoic acid, UV Chek Am-240; flame retardants such as antimony oxide, decabromodiphenyl ether, perchloropentacyclodecane, 1, 2-bis(tetrabromophthalimido) ethylene; pigments such as titanium dioxide and carbon black, and the like. Mixtures of such additives can be used.

One or more additives may be present in an amount of up to 67% of the composition. It is to be understood that for any specified proportions of the other components, additives are present in amounts to provide 100%.

The composition of the first polymeric layer can be prepared by mixing together the components in any appropriate mixer such as, an internal mixer, for example, a Brabender or Banbury, or a twin screw extruder, for example, a ZSK extruder, or the like.

The composition of the first polymeric layer is melt processable and can be extruded over the conductor. Generally, the

composition is extruded directly onto the conductor, but one or more intervening layers may be present, if desired.

B. SECOND POLYMERIC LATER

The second polymeric layer comprises a composition which comprises an intimate mixture of

(i) a polyester in which at least 70 mole % of the repeating units are tetramethylene terephthalate units and which has a solubility parameter S; (ii) 10 to 100% by weight, based on the weight of the polyester (i), of the second polymer which (a) has a flex modulus of 500 to 100,000 psi, and (b) has a solubility parameter of (S+1.5) to (S-1.5).

The flex modulus values referred to herein are measured by the method of ASTM 6790-71. The Solubility Parameters referred to herein are measured by the procedure described in Polymer Handbook, edited by Brandrup and Immergut, 2nd Edition, Pages IV 337 to 339.

In the polyester (i), at least 70 mole %, preferably at least 80 mole %, particularly at least 90 mole %, especially 100 mole %, of the repeating units are tetramethylene terephthalate units.

Polymer (ii) has a flex modulus of 500 to 100,000 psi, preferably less than 40,000 psi, especially less than 10,000 psi, and a solubility parameter which is from (S-1.5) to (S+1.5), preferably (S- 1) to (S+1), where S is the solubility parameter of the polyester (i). In one embodiment, polymer (ii) is a block copolymer in which one of the blocks is composed of repeating units which have the formula

— (CH2)p - O - CO -Ar— CO—O — _*

wherein p is at least 2 and is preferably 4, and Ar is an aryl group which is preferably free from substituents but may be substituted, e.g. by one or more alkyl groups, and which units are preferably tetramethylene terephthalate units. The other polymer block in the

block copolymer is preferably a polyalkylene ether, e.g. polytetramethylene oxide. Thus we have obtained excellent results using a polymer (ii) a block copolymer of polytetramethylene terephthalate and polytetramethylene oxide, e.g. one of the "Hytrel" polymers sold by E. I. du Pont de Nemours. In another embodiment, polymer (ii) is a copolymer of ethylene and at least one copolymerizable monomer containing a polar group, e.g. a vinyl ester of an alkyl carboxylic acid, preferably vinyl acetate.

The amount of polymer (ii) preferably employed will depend on a balance needed, for the particular end use in view, between physical properties which are influenced by the presence of polymer (ii). We have found that at least 10% by weight of polymer (ii), based on the weight of polymer (i), should be present, preferably at least 15%. The amount of polymer (ii) is preferably less than 100%, particularly less than 50%, especially less than 40%, by weight based on the weight of the polyester (i).

Polymers (i) and (ii) are preferably the only organic polymers in the composition. If other organic polymers are present, the amount thereof is preferably less than 20%, based on the combined weights of polymers (i) and (ii).

The composition of the second polymeric layer can also contain a flame retardant, especially a bromine-containing organic flame retardant. Bromine-containing flame retardants are well known, arid include, for example, decabromodiphenyl ether, as well as other aromatic and aliphatic compounds. The amount of bromine- containing fire-retardant present will generally be at least 3%, preferably at least 5%, e.g. 5-30% or 5-25%, by weight of the composition. The bromine-containing flame retardants are frequently used in conjunction with inorganic flame retardants, for example, antimony trioxide, which are known to demonstrate a synergistic effect with bromine-containing organic flame retardants. Thus preferred compositions contain 3 to 15% by weight of antimony trioxide. The ratio by weight of polymer (ii) to total flame retardant is preferably at least 0.5:1, especially at least 0.75:1.

The compositions of the second polymeric layer preferably contain at least one antioxidant. Suitable antioxidants include the hindered phenols which are well known in the art, present for example in amount from 0.25 to 1% by weight of the composition.

The compositions can also contain conventional additives such as fillers, processing aids and stabilizers, generally in total amount not more than 10% by weight.

The compositions of the second polymeric layer can be melt- shaped, e.g. by extrusion. They can be continuously melt-extruding through a cross-head die onto the first polymeric layer. Generally, the first and second polymeric layers are in direct contact with one another.

The invention will be better understood by reference to the illustrative examples which follow. Examples 1-21 illustrate compositions suitable for the first polymeric layer. Examples 22-28 illustrate compositions suitable for the second polymeric layer. Example 29 composes a conductor of this invention with a conductor coated with only a composition suitable for the first polymeric layer and a conductor coated with only a composition suitable for the second polymeric layer.

Examples 1 - 10

Formulations for the first polymeric layer of this invention containing about 57% of polyfbutylene terephthalate), about 14% of polycaprolactone, 2.0% polycarbodiimide (PCD) and about 24% of a flame retardant mixture containing 1, 2-bis(terephthalimido) ethylene, antimony trioxide and magnesium hydroxide, 2.0% of a hindered phenolic antioxidant and 1.0% of an aliphatic phosphite, as listed in Table I, are prepared in a twin screw extruder at temperatures between 175-290°C.

Examples 11 - 15

The procedures of Examples 1 - 10 are repeated varying only the amounts of distearyl pentaerythritol diphosphite, as listed in Table IV. The results are shown in Table II.

Examples 16 - 21

The procedures of Examples 1 - 10 are repeated varying the amounts of aliphatic phosphite, polycarbodiimide (PCD) and hindered phenolic antioxidant as listed in Table III.

Table III

Examples 22 - 28

The ingredients and amounts thereof used in the Examples are shown in the Table below. In each Example, the ingredients were thoroughly mixed by conventional methods, e.g. in a Banbury mixer.

Table IV

The various ingredients referred to in Table IV are further identified below.

PTMT Polvmer: Polytetramethylene terephthalate having a Solubility Parameter of about 9.5, a melt index of 6.0 and a density of about 1.31 (Tenite 6 PRO)

Second Polvmer a: Block copolymer of polytetramethylene terephthalate and polytetramethylene ether having a flex modulus of about 7,000 psi and a solubility parameter of about 9.5 (Hytrel 4056)

Second Polvmer b: Block copolymer of polytetramethylene terephthalate and polytetramethylene ether having a flex modulus of about 30,000 psi and a solubility parameter of 9.5 (Hytrel 5556)

Second Polvmer c: Copolymer of ethylene and vinyl acetate

(25%) having a density of about 0.95, a melt index of about 2, a

solubility parameter of about 9.0 and a flex modulus in the range 5,000 to 10,000 psi (EVA 3190)

Second Polvmer d: As second polymer C, but containing 18% vinyl acetate and having a melt index about 2.5 and a density of about 9.4 (EVA 3170)

Antioxidant: Tetrakis [methylene 3-(3',5'-di tert butyl-4' hydroxyphenyl) propionatejmethane (Irganox 1010)

Decabromodiphenyl ether: The commercial product sold as DE 83.

Example 29

This example compares conductors coated with (A) only with Blend (A) of the first polymeric layer; (B) only with Blend B of the second polymeric layer and (C) a dual wall construction of the first polymeric layer (Blend A) surrounded by the second polymeric layer Blend (B). The conductors were prepared by extruding the first polymeric layer over an 18 gauge wire and then extruding the second polymeric layer over the first.

The composition (Blend A) of the first polymeric layer comprises:

The composition (Blend B) of the second polymeric layer comprises:

Polytetramethylene terephthalate 61.5

Polyester block copolymer 24.7 Flame retardant mixture 8.6

Antioxidant 2.1

Carbodiimide 2.1

Phosphite 1.0

The phosphite used was distearyl pentaerythritol diphosphite The antioxidant used was Irganox 1010. The polyester block copolymer used was Hytrel 5556.

The cables were tested using the following procedures.

Test Method and Results

As shown in Tables V and VI, three tests were used as feasibility criteria for use in automatic transmissions. The first test required immersing the wire insulations in automatic transmission fluid (ATF) at 150C for 24 and 168 hours. The wire insulations were inspected after the immersion for fibrillation effects. After immersion for only 24 hours, the single layer Blend B wire exhibited fibril-like structures upon cold drawing, indicative of changes in insulation properties. By contrast, the single layer Blend A and dual wall Blend A/Blend B wires showed no sign of deterioration or fibrillation after ATF immersion for 168 hours. Also, Blend B suffered significant reduction in elongation (55% retention) with a 24-hour immersion in ATF, as compared to 94% and 80% for the Blend A and dual wall wires, respectively.

The second test adopted was related to the abrasion or skiving resistance of the proposed wire insulation. With conventional PBT wires such as those based on Blend B, small strings or fuzzes of insulation material might be shaved off upon scraping the wire over sharp edges during installation. The shaved-off materials could contaminate the transmission fluid contained and circulated in the automatic transmission housing, adversely affecting its proper

functioning. To set up a skiving performance test, an instrument was used to connect the test wire to a reciprocating mechanism and motor via a damping device. The wire was then attached to a weight of 100-1000 grams and taken over a pulley and test blade. The skiving characteristics of the wire were determined by oscillating the wire over the blade at a frequency of 20 strokes per minute for 15 seconds. It was found that insulation could be skived off from a single wall Blend B wire, whereas the single wall Blend A did not yield any shavings. By combining an outer layer of Blend A with an inner layer of Blend B in the dual wall wire, no shavings were scraped off when subject to the same test, thus allowing proper installation of such dual wall wire in automatic transmissions.

The third test compared the thermal stability of the three wires. At 180C, the single wall Blend B wire displayed excellent aging characteristics after 168 hours with retention of tensile strength (T.S.) and elongation up to 85% and 90%. The single wall Blend A wire, however, suffered from a catastrophic failure of insulation embrittlement after 168 hours at 180C. The same insulation material, when used as the outer layer of the dual wall Blend A/Blend B wire, unexpectedly retained the same tensile strength and elongation properties as the single wall Blend B wire. This phenomenon is not typical since dual wall insulations tend to embrittle at the point where its less superior layer will fail. This improved heat aging performance allowed the dual wall wire to be used in automatic transmissions when both hot fluid resistance and thermal stability were essential.

While the invention has been described herein in accordance with certain preferred embodiments thereof, many modifications and changes will be apparent to those skilled in the art. Accordingly, it is intended by the appended claims to cover all such modifications and changes as fall within the true spirit and scope of the invention.