GB1090241A - Polyester insulating layers - Google Patents

Abstract

An electrical conductor is coated with an insulating layer of a thermoplastic polyester wherein at least 10 mole per cent of the glycol residues are derived from a 2,2,4,4-tetra-alkyl-cyclobutane -1,3-diol. Such a polyester is describe and claimed in Specification 962,913. Preferably at least 75 mole per cent of the glycol residues derive from a 2,2,4,4-tetraalkylcyclobutane-1,3-diol, and at least 60 mole per cent of the dicarboxylic acid residues derive from an aromatic or hydrogenated aromatic acid, e.g. terephthalic, isophthalic, 2,6-naphthalene dicarboxylic, stilbene dicarboxylic or 1,4-cyclohexane dicarboxylic acids, or are carbonate groups. The alkyl groups or the cyclobutane diol preferably contain 1-4 C atoms, and are more preferably methyl groups. Between the conductor and the above polyester, there may be a thermoset polymer cured in situ, e.g. a cross-linked polyester, preferably comprising not more than 75% of the total thickness of the coating. The thermoplastic polyester may be applied by melt extrusion, or from solution or suspension. Suitable solvents are cresol, phenol, tetrachlorethane, ethylene carbonate, g -butyrolactone, dimethylacetamide, and dichlorbenzene, and suitable suspension media are kerosine, xylene and water. Isocyanate or epoxy compounds or polymers may be added to improve adhesion or cross-linking in the coating. In examples, polyesters are prepared from various mixtures of the cis and trans isomers of tetramethyl cyclobutane-1:3-diol (or the 2:4-dibutyl-2:4-diethyl compound, in Example 2. 8, or a mixture of the tetramethyl compound with the 2:4-dimethyl-2:4-dipropyl compound, in Example 2. 9, or with trimethylolpropane, in Example 7) and esters of terephthalic acid, or isophthalic acid, or a mixture of these, or of carbonic acid, or a carbonic/terephthalic mixture, or stilbene dicarboxylic acid, or naphthalene-2:6-dicarboxylic acid, or a naphthalene-2:6-dicarboxylic/isophthalic acid mixture. The products are dissolved in cresol or chloroform and used as insulating varnishes to coat copper wire, which may have been primed with a thermoset coating of a phthalic acid/maleic acid/glycerol/soya oil alkyd, or an alkylated UF resin, or an epoxy resin/tall oil/glycerol/phthalic acid condensate, or an adipic acid/isophthalic acid/trimethylolethane/masked diisocyanate polyurethane.ALSO:An electric conductor is coated with an insulating layer of a thermoplastic polyester in which at least 10 mole % of the polyol residues are derived from a 2:2:4:4-tetraalkylcyclobutane-1:3-diol. Such polyesters are described in Specification 962,913 (see Div. C3). A thermoset polymer primer may previously have been applied to the conductor and cured in situ. In Examples polyesters are prepared from tetraalkylcyclobutane diols and terephthalic and/or isophthalic and/or carbonic and/or stilbene dicarboxylic and/or naphthalene-2:6-dicarboxylic acids. They are dissolved in cresol or chloroform and used to coat copper wire which may be bare or primed with a thermoset coating of a phthalic acid/maleic acid/glycerol/soya oil alkyd or an alkylated urea formaldehyde resin or an epoxy resin/tall oil/glycerol/phthalic acid condensate or an adipic acid/isophthalic acid/trimethylolethane/masked diisocyanate polyurethane.