GB1278307A - Production of polyamide moldings - Google Patents

Abstract

1278307 Injection moulding polyamides BADISCHE ANILIN & SODA FABRIK AG 3 Nov 1969 [4 Nov 1968] 53744/69 Heading B5A A process for the production of a moulding by activated anionic polymerization of lactams having at least six ring carbon atoms comprises mixing at least two lactam melts containing catalyst and activator separately and heated to polymerization temperature in an antichamber whose temperature is from 80‹ to 200‹ C., allowing the resultant mixture to polymerize therein until it is at least dimensionally stable enough not to flow under its own weight, forcing the polymer into a mould through a nozzle-like means at a pressure from 100 to 5000 atmospheres gauge and removing the finished moulding from the mould. The shrinkage is small and pressure need not be maintained while the polymer is in the mould as polymerization is substantially completed before the polymer enters the mould. The temperature of the antechamber is preferably between 125‹ and 180‹ C. The mixture remains in the antechamber for 5 to 90 seconds until it has attained a viscosity between 10<SP>2</SP> and 10<SP>6</SP> centipoises and a modulus of elasticity of at least 0À1 km/mm.<SP>2</SP> and is forced through the nozzle-like means, which is at a temperature at least 25‹ C. above that of the antechamber, in not more than 10 seconds at a rate between 0À1 and 5 kg./sec. The moulding is preferably removed from the mould at a temperature of not less than 125‹ C. In the embodiment shown in Fig. 2, caprolactam containing catalyst and caprolactam containing activator are stored at 75‹ C. in separate reservoirs 1a, 1b respectively. The required quantity of each mixture is passed through heaters 2a, 2b and mixed in antechamber 4 which is closed at its base by piston 5. A cover is placed after the assembly of antechamber 4 and moulds 6 and the assembly is placed between the platens of a press. After a predetermined period of time, the press platens are forced together, forcing piston 5 into antechamber 4 and the polymer through nozzles 8 into mould cavities 6. In an alternative embodiment (Fig. 3) the caprolactam melts are mixed in an antechamber 4 which comprises the barrel of an injection piston, the nozzle 8 being closed by a thin polyamide film arranged between sections 8 and 8a of the nozzle. After injection, excess material solidifies about gripping means 5a on the piston and can be easily removed.