Patent GB-561052-A (GB)
Title: Improvements in and relating to the manufacture of moulded polyamide articles
IPC: C08L77/00
Filed: 1942-07-22
Abstract: The stiffness of a moulded polyamide article is increased by rapidly cooling the article in the mould in which it has been formed and then heating it above 120 DEG  C. but below the melting point of the polyamide.  The heating temperature may be 185-190 DEG  C. for polyhexamethylene sebacamide and 230-240 DEG  C. for polyhexamethylene adipamide.  The heating may be effected in an oil bath, and its duration may be 2-10 minutes.  The heating lowers the impact strength, and should preferably be stopped before the latter has been decreased to less than half its original value.  The moulding may be by the injection method, in which case the rapid cooling is effected by cold water forced through conduits in the mould; filaments of higher melting-point polyamides may be placed in the mould before injection of lower melting-point polyamides, for reinforcing purposes. Alternatively, the moulding may be effected by compressing finely divided polyamide at pressures above 10,000 lbs/sq. inch and at temperatures just below melting point.  Before moulding, the polyamide should be dried, e.g. to 0.4 per cent moisture content; this drying reduces dripping of the molten polymer from the nozzle during injection, ensures good surface and uniform toughness, and raises the impact strength.  In one example, polyhexamethylene sebacamide is mixed with a non-heat hardening phenol formaldehyde resin, and the mixture is then moulded.  Reeds for woodwind instruments, bobbins, heads for spools, clubs, tooth-brush handles, dentures, teeth fillings, golf-club heads and inserts therefor, ferrules for gold clubs and knives, handles, e.g. for surgical instruments, lenses, e.g. for black-out lamps, knobs, automobile horns and accessories and lamp housings may be made according to the invention.  Specifications 461,236, 533,306 and 536,130 and U.S.A. Specifications 2,071,250 and 2,130,948 are referred to.  As open to inspection under Sect. 91, the Specification states also that the invention increases the hardness of articles made according thereto, and that sliding-clasp fasteners may be made thereby.  This subject-matter does not appear in the Specification as accepted.ALSO:The stiffness of a moulded polyamide article is increased by rapidly cooling the article in the mould in which it has been formed, and then heating it above 120 DEG  C. but below the melting point of the polyamide.  The heating temperature may be 185-190 DEG  C. for polyhexamethylene sebacamide and 230-240 DEG  C. for polyhexamethylene adipamide.  The heating may be effected in an oil bath, and its duration may be 2-10 minutes.  The heating lowers the impact strength, and should preferably be stopped before the latter has been decreased to less than half its original value.  The moulding may be by the injection method, in which case the rapid cooling is effected by cold water forced through conduits in the mould; filaments of higher melting-point polyamides may be placed in the mould before injection of lower melting-point polyamides, for reinforcing purposes. Alternatively, the moulding may be effected by compressing finely divided polyamide at pressures above 10,000 lbs./sq. inch and at temperatures just below melting point.  Before moulding, the polyamide should be dried, e.g. to 0.4 per cent moisture content; this drying reduces dripping of the molten polymer from the nozzle during injection, ensures good surface and uniform toughness, and raises the impact strength.  In one example, polyhexamethylene sebacamide is mixed with a non-heat hardening phenol-formaldehyde resin, and the mixture is then moulded.  Reeds for woodwind instruments, bobbins, heads for spools, clubs, tooth-brush handles, dentures, teeth fillings, golf-club heads and inserts therefor, ferrules for golf clubs, and knives, handles, e.g. for surgical instruments, lenses, e.g. for blackout lamps, knobs, automobile horns and accessories and lamp housings may be made according to the invention.  Specifications 461,236, [Group IV], 533,306 and 536,130, and U.S.A.  Specifications 2,071,250 and 2,130,948 are referred to.  As open to inspection under Sect. 91, the Specification states also that the invention increases the hardness of articles made according thereto, and that sliding-clasp fasteners may be made thereby.  This subject-matter does not appear in the Specification as accepted.