Patent GB-1137492-A (GB)
Title: Polycarbonate filaments
Inventor: RELLENSMANN WOLFGANG
IPC: D01F6/64
Filed: 1965-12-09
Abstract: 1,137,492. Polycarbonate filaments. FARBENFABBIKEN BAYER A.G. 9 Dec., 1965 [10 Dec., 1964 (2)], No. 52368/65. Heading B5B. [Also in Division C3] Filaments of linear polycarbonates having a molecular weight of from 50,000 to 95,000, show when stretched an X-ray interference width of not more than 1.5 degrees and a crystallite melting-point not below 260 C. Such polycarbonate filaments may be made from a solution of a linear, high molecular weight polycarbonate in an organic solvent, by adding to the solution of the polycarbonate at least one non-solvent or weak solvent in which the solubility of the polycarbonate is not higher than 5% by weight, non-solvent or weak solvent having an average cohesion energy value V mo1 e of 8 to 10 and a boiling-point of between 60 and 180 C., and being added in such a proportion as to form a gelled polycarbonate solution containing from 14 to 35% by weight of the polycarbonate; heating the gelled solution to a temperature of between 70 and 150 C.; spinning the solution into filaments; and stretching the filaments obtained in a ratio of from 1 : 2 to 1 : 8. Specified weak solvents are dichloropropane and chlorobenzene, and in general chlorinated aliphatic and aromatic hydrocarbons. In examples, the solvents used other than those specified above, include methylene chloride, and a mixture of glycol monomethylether monoacetate and methylene chloride. Preferred polycarbonates are those which are based on di-(monohydroxyaryl)- alkanes, -sulphones, -sulphoxides, -sulphides or -ethers, or mixtures of these dihydroxy compounds with one another. In a preferred method the polycarbonate is dissolved in methylene chloride to form a 15-25% solution, advantageously a 20-24% solution, is then filtered and, immediately before spinning, the weak solvents used according to the invention are added to the solution in such a quantity that the resulting spinning concentration is 14- 24% by weight, advantageously 17.5-19.5%. The solvent exchange may be so effected that a polycarbonate solution of relatively low concentration is concentrated up to almost the point of concentration gelling by evaporation of solvent at normal or slightly reduced pressure and raised temperature and this concentrated solution can be admixed with a weak solvent of higher boiling-point, which is an excellent solvent at high temperature, and then the solution is immediately thereafter heated to the spinning temperature. Solvent exchange may also be effected by concentrating a dilute solution of a polycarbonate in a mixture of low boiling-point good solvent (such as methylene chloride) and a poor solvent of higher boiling-point (which acts as a good solvent at a higher temperature), at high temperature with removal of the more volatile solvent and by keeping this solution at high temperature. The weak solvent or a mixture thereof with the good solvent may be continuously admixed with the solution immediately prior to the heating. Both wet-spinning and dry-spinning methods may be used, the latter being preferred. In this latter case the filaments are spun into an inert atmosphere at 200-250 C. and the filaments drawn at 100-500 m. per min. Filaments so made show an improved crystallinity, enhanced resistance to solvents, excellent uniformity after stretching and improved resistance to temperature, with a higher crystallite melting-point.