Process for injection molding information recording disks

Abstract

An injection molding process wherein the times of heating to melt a resin are reduced to minimize the thermal hysteresis and to decrease the deterioration of physical properties caused by the thermal hysteresis, so that high quality information recording disks may be produced. A molding process wherein the plasticating and the injection and filling of a material resin are carried out in separate cylinders, allows constant molding for a long period of time. A material resin such as polycarbonate is supplied without predrying to an injection apparatus for a first time molding. Resin is kneaded by the apparatus while volatile components are heated to be vaporized and exhausted through a vent port. An inert gas atmosphere is provided within the cylinder to prevent the material resin from being oxidized. Since predrying can be dispensed with, the thermal hysteresis will be extremely small and the deterioration of the resin caused by such heating may be suppressed. Also, there is less chance of generation of carbonized black spots caused by foreign matter, molding failures caused by hydrolysis may be eliminated, and residual monomers can be vaporized and exhausted concomitantly.