TERNARY BLENDS AS WIRE INSULATIONS

Abstract: Blends of poly(arylene ether ketone) together with polyetherimide and silicone-polyimide copolymer exhibit excellent stress craze resistance, flexibility and flame retardance and are particularly well suited for use as single layer insulation or as the inner and/or outer layer of double layer insulation for electrical wiring applications.

Description: This invention relates to blends of a poly(arylene ether ketone) such as a polyether ether ketone (PEEK), a polyether ketone (PEK) or a polyether ketone ketone (PEKK) with a polyetherimide (PEI) and a silicone-polyimide copolymer (S-PI). Such blends form flexible flame retardant materials which may be used for the manufacture of moulded articles such as a thin-wall wire insulation or jacket. Polyether ether ketones are currently used over irradiated polyphenylene oxide (for example, "Noryl") to form a dual wall wire insulation. This combination of materials passes required specification tests (for example, U.K. Ministry of Defence, Defence Standard 61-12, Part 18/2) but enhanced fire retardancy and stress crazing properties would be beneficial for some applications. Also, PEEK materials are relatively inflexible and quite expensive. Silicon-polyimide materials, such as "Siltem", are not only more flexible and less costly than PEEK but also more flame retardant and it would be expected that a blend of PEEK and S-PI would yield improved properties over PEEK alone. However, this is not so; it would seem that the two materials are insufficiently mutually compatible so that two phases remain after thorough blending resulting in separation and inhomogeneity upon extrusion and fibrillation and poor flexibility of the extruded product. Polyetherimides are known to blend quite well with PEEK materials but suffer from the disadvantage of being subject to stress crazing. For this reason alone, such blends are totally unsuitable as wire insulation. In a similar manner, PEI and S-PI form homogeneous blends. EP-A-0 266 595 for example describes flame resistant polymer blends containing a polyetherimide and an impact strength - enhancing amount of a siloxane - polyetherimide copolymer which are said to have high impact strengths, good blow moldability and injection moldability, amenability to thermoforming and very low flammability and to be particularly suited to the manufacture of aircraft cabin interior components. However, as illustrated below, such blends also suffer from stress crazing and so, too, are unsuitable as wire insulation. Surprisingly, it has now been found that PEEK or PEK together with PEI and S-PI form homogeneous blends having good solvent resistance (i.e. resistance to stress crazing) and excellent flame retardancy properties. According to the invention, there is provided a blend of a poly (arylene ether ketone), for example a polyether ketone, a polyether ether ketone or a polyether ketone ketone, together with a polyetherimide and a silicone-polyimide copolymer. The poly(arylene ether ketone) will contain units of the general formulae which may carry one or more substitutents on the arylene rings. The polyether ketone is suitably one containing repeating units of the general formula the polyether ether ketone suitably contains repeating units of the general formula and the polyether ketone ketone suitably contains repeating units of the general formula in which in all cases (III) to (V) the phenylene groups may carry one or more substituents. The polyetherimide will generally contain repeating units of the general formula in which Z and R are organic groups, for example in which R is Z is or a group of the formula in which X is C y H 2y , -O- or -S-, q is 0 or 1 and y is an integer from 1 to 5 and the bonds of the -O-Z-O- group are in the 3,3′; 3,4′; 4,3′ or the 4,4′ position. However, the polyetherimide may also contain units of the formula and/or units of the formula in which Z and R have the meanings given above, R′ is an alkyl, alkenyl, alkoxyalkyl, ketyl, ketenyl, fluoroalkyl or fluoroalkenyl group having at least 4 and preferably from 8 to 18 carbon atoms, or is a phenyl or substituted phenyl groups (for example, phenyl substituted by fluoro or even amino), R″ is hydrogen or together with R′ and the nitrogen forms an alicyclic group, R‴CO is an acyl or fluoroacyl group having at least 4 and preferably from 8 to 18 carbon atoms and X′ is a halogen, preferably chlorine, obtained by reacting a polyetherimide of the formula (III) above with an amine of the general formula R′-NH-R″ or an acyl or fluoroacyl halide of the general formula R‴CO-X′ (for example, perfluorobutanoyl chloride), respectively. The silicone-polyimide copolymer is suitably one containing groups of the formula R₁ and R₂ are organic groups. Of the amines of the formula R′-NH-R'', there are preferred long chain primary amines and fluorinated amines (for example heptafluorobutylamine and pentafluoroaniline). The reaction between the polyetherimide and the amine is suitably carried out at an elevated temperature and under atmospheric or slightly elevated pressure, for example in a screw mixer at a temperature from 300 to 400°C, especially about 310°C. By grafting on the amine (for example octadecylamine) or acyl group, reactive sites are provided for subsequent crosslinking for example by irradiation. Crosslinking between the side chains can be achieved (as is the case with polyethylenes) after the addition of a sensitiser, for example triallyl isocyanurate (TAIC) and N,N-metaphenylene dimaleimide (such as that available as HVA-2 from Du Pont), by irradiation. The blends according to the invention have excellent resistance to environmental stress crazing in halogenated solvents and aviation fuel, and exhibit improved flexibility and flame retardance compared to PEEK alone. These properties, in conjunction with good abrasion resistance, low toxic fume emission and smoke evolution, little or no halogen content and a wide temperature range of operation enable the use of the blends in high performance electronic and electrical wiring applications such as aircraft, ship and vehicle electrical systems, mass transit systems and high temperature equipment, as a single layer insulation or as the inner and/or outer layer of a double layer insulation. Blending may be carried out at an elevated temperature for example from 300 to 400°C, for example in a twin screw mixer. A range of useful blends may be obtained in this manner containing from 5 to 95% by weight PEEK or PEK, from 5 to 95% by weight PEI and up to 80% by weight S-PI, based on the blend. However, when the blend is to be used as a single layer insulation, then the PEEK content of the blend is preferably at least 45% by weight. As described below in greater detail, blends according to the invention have been tested according to Defence Standard 61-12 (Part 18) Issue 2 and it has been found that blends containing from 45 to 95% by weight PEEK and up to 54% by weight PEI/S-PI comply with that standard. A preferred composition in this respect contains, by weight, 60% PEEK, 5% PEI and 35% S-PI. Suitable materials for use in the blends of the invention include the PEEK material available from ICI under the trade name "Victrex", the PEK material available from Hoechst Plastics under the trade name "Hostatec" and the PEI and S-PI materials available from General Electric Plastics and General Electric Silicones under the trade names "Ultem" and "Siltem", respectively. By way of illustration of the invention, a number of PEEK/PEI/S-PI blends were prepared and each was coated onto a tinned copper conductor by extrusion. The resulting wires were tested and found to comply with Defence Standard 61-12 (Part 18) Issue 2, as follows: Critical Oxygen Index (clause 8.2.7) composition (weight %) oxygen index, % PEEK PEI S-PI Specification limit, 29% 15 15 70 50 20 20 60 51 25 25 50 48 50 25 25 53 70 15 15 41 Each blend was found to have less than 2.0% change in diameter (specification limit ± < 5.0%). In addition, the abrasion resistance (clause 8.2.12) was found to be about 6,000 (specification limit 500) although the abrasion resistance is capable of significant improvement by optimising extrusion conditions to provide a glossy surface. In a further test, additional blends of PEEK, Ultem and Siltem were prepared and coated onto tinned copper conductors by extrusion, and then tested for compliance with Defence Standard 61-12 (Part 18) Issue 2. The results obtained are set out in Table 3. By way of comparison, blends of PEEK and Ultem only and of Ultem and Siltem only were coated onto tinned copper conductors by extrusion and tested for solvent resistance in the same way. The results obtained are set out in Tables 4 and 5.

Claims: A blend comprising a poly(arylene ether ketone) together with a polyetherimide and a silicone-polyimide copolymer. A blend according to claim 1, wherein the poly(arylene ether ketone) contains unit of the general formulae which may carry one or more substituents on the arylene rings. A blend according to claim 1 or claim 2, wherein the poly(arylene ether ketone) is a polyether ketone, a polyether ether ketone or a polyether ketone ketone. A blend according to claim 3, wherein the polyether ketone contains repeating units of the general formula in which the phenylene groups may carry one or more substituents. A blend according to claim 3, wherein the polyether ether ketone contains repeating units of the general formula in which the phenylene groups may carry one or more substituents. A blend according to claim 3, wherein the polyether ketone ketone contains repeating units of the general formula in which the phenylene groups may carry one or more substituents. A blend according to any one of claims 1 to 6, wherein the polyetherimide contains repeating units of the general formula in which Z and R are organic groups. A blend according to any one of claims 1 to 7, wherein the polyetherimide contains units of the formula in which Z and R are organic groups, R' is an alkyl, alkenyl, alkoxyalkyl, ketyl, ketenyl, fluoroalkyl or fluoroalkenyl group having at least 4 carbon atoms, or is a phenyl or substituted phenyl group, and R'' is hydrogen or together with R' and the nitrogen forms an alicyclic group, obtainable by reacting a polyetherimide as specified in claim 7 with an amine of the formula R'-NH-R''. A blend according to any one of claims 1 to 8, wherein the polyetherimide contains units of the formula in which Z and R are organic groups, R'''CO is an acyl or fluoroacyl group having at least 4 carbon atoms and X' is a halogen, obtained by reacting a polyetherimide as specified in claim 7 with an acyl or fluoroacyl halide of the formula R'''CO-X'. A blend according to any one of claims 7 to 9, wherein Z is or a group of the formula in which X is C y H 2y , -O- or -S-, q is 0 or 1 and y is an integer from 1 to 5 and the bonds of the -O-Z-O- group are in the 3,3′; 3,4′; 4,3′ or the 4,4′ position. A blend according to any one of claims 7 to 10, wherein R is A blend according to any one of claims 1 to 11, wherein the silicone-polyimide copolymer contains groups of the formula in which R₁ and R₂ are organic groups. A moulded article comprising a blend according to any one of claims 1 to 12. A moulded article according to claim 13, in the form of a single layer insulation or as the inner and/or outer layer of a double layer insulation applied to an electrical conductor.

Inventors: ALESBURY, COLIN KEVIN, MURPHY, RICHARD JOHN, DR.
Applicants: PIRELLI GENERAL PLC
Application year: 1988
Main classification: C08L71
IPC codes: C08L79, H01B3, C08L71, C08L83