PROCESS FOR THE PRODUCTION OF POLYAMIDE CASTINGS

摘要

1284923 Polyamide mouldings containing cavities or metal shafts VYZKUMNY USTAV SYNTHETICKYCH PRYSKYRIC A LAKU 9 Sept 1969 [11 Sept 1968 (2) 12 Aug 1969] 44456/69 Heading B5A Polyamide castings containing cavities or fitted with a metal shaft are made by casting a lactam melt comprising an alkaline catalyst, promoter and optionally pigments, fillers and other additives around a core or metal shaft provided with a deformable jacket of elastic macromolecular material in a preheated mould. The lactam is polymerized at a temperature below the melting point of the polyamide formed. The core and jacket may then be removed. For forming cavities in the moulding the jacket preferably comprises a hollow inflatable jacket of a thermostable macromolecular material such as silicone rubber. This may be formed by winding the elastomer around the shaft and sealing the ends of the jacket formed with cold curable silicone rubber. The jacket is inflated during polymerization by a gas at a pressure of 1-20 atm. and the gas pressure is maintained during polymerization and is released during or after cooling. When the shaft is to remain in the moulding, the jacket may be inflatable or of a foamed elastomer, and the gas pressure inflating the jacket is lowered during polymerization to allow the casting to shrink on to the shaft. The lactam used is preferably 6- caprolactam or its mixture with laurolactam containing 0À1-2 mole per cent of the sodium salt of 6-caprolactam as a catalyst and 0À05- 5 mole per cent of N-acetyl-6-caprolactam, hexamethylene-1,6-diisocyanate or triphenylmethane-4,41,411-triisocyanate as promoter. The mould is preferably preheated to 120-200‹ C. and the lactam melt to 80-180‹ C.