Abstract: A disc molding die includes a stationary-side mirror block disposed on a stationary die, a movable-side mirror block disposed on a movable die and facing the stationary-side mirror block so as to define a cavity in combination with the stationary-side mirror block, and a cavity ring disposed on the radially outer side of one of the stationary-side mirror block and the movable-side mirror block so as to define the outer circumferential edge of each disc substrate. The portion of the cavity ring facing the cavity is roughened. When resin is charged into a cavity, very small spaces are formed between the resin and the inner circumferential surface of the cavity ring, due to the roughened portion of the cavity ring facing the cavity. Therefore, the release resistance during die opening or releasing can be decreased.

Abstract: In an injection mold having a cavity formed between opposing faces of a fixed mold and a movable mold for defining a shape of a product, and cooling channels formed in the fixed mold and the movable mold, respectively, for cooling resins injected into the cavity, cooling channels of the movable mold are formed at positions at least opposite to those where cooling channels of the fixed mold are not formed, thereby obtaining an injection mold capable of securing uniformity of optical properties of the obtained molded article, such as birefringence and causing no deterioration of mechanical properties of the molded article such as a deflection even when a cooling time is shortened in order to increase cycle of the injection molding.

Abstract: An injection compression molding method for compact discs or the like, includes the step of changing the clamping pressure or compression pressure, after the internal cavity pressure in the mold after injection has reached its peak, stepwise or continuously as the cooling proceeds, thereby making the applied pressure per unit area with respect to the effective pressure range constant. In a compact disc formed by this method, the residual stress after cooling is uniform, so that its optical properties are improved substantially.

Abstract: A process for the preparation of substrate for optical disk characterized in that pellets of 4-methyl-1-pentene polymer or copolymer having a melt flow rate (MFR), as measured according to ASTM D1238 under a load of 5 kg and at a temperature of 260.degree. C., of 240-1200 g/10 min, and a melting point as measured by means of DSC of 234.degree.-240.degree. C., are injection molded into the substrate under the conditions where a temperature of at least part of a cylinder is 320.degree.-370.degree. C. and a mold temperature is not more than 55.degree. C.

Abstract: An injection mold of the type in which a film gate of a resin is formed and in which shearing of the film gate is conducted by a movement of a gate cutter alone. The gate cutter has a stepped cylindrical form with a main cylindrical portion of a greater diameter and a coaxial end cylindrical portion of a smaller diameter. When the mold is closed, the end cylindrical portion being received in the bore of a confronting die leaving therebetween an annular gap of a radial size which determines a gate thickness. The outer peripheral surface of the portion of the gate cutter received in the bore of the die presenting a gate land.

Abstract: An injection molding die apparatus for use in the production of an optical disk substrate has a stationary die part having a mirror-finished surface, a movable die part carrying a stamper, an outer peripheral ring slidably fitting on the outer periphery of the movable die part and contactable with the stationary die part when the movable die part has been moved close to the stationary die part, such that a die cavity to be charged with injected molten plastic is formed by the mirror surface of the stationary die part, the stamper and the outer peripheral ring.

Abstract: A mold for forming an optical disk base provided with a movable specular plate, a stationary specular plate, and an annular stamper having inner and outer peripheral edges. The reverse surface of the stamper is in contact with one of the specular plates, and the stamper is supported at its inner end portion by an inner stamper retainer and at its outer end portion by an outer stamper retainer. A cavity is formed between the stamper and the other one of the specular plates when the mold is closed.

Abstract: A process and an apparatus for producing an aromatic dicarboxylic acid by oxidizing a benzene derivative with molecular oxygen in the liquid phase in a lower aliphatic carboxylic acid as a solvent in the presence of an oxidation catalyst, wherein a starting material liquid e.g., a benzene derivative or a solution thereof in the lower aliphatic carboxylic acid, is fed into the liquid-phase reaction system in a uniformly dispersed state by being passed through a porous material causing the pressure of the starting material liquid just after passing through said porous material to drop more than about 1 kg/m.sup.2 in relation to the pressure of the starting material liquid just before passing through said porous material. The resultant aromatic dicarboxylic acid has high purity and has good color.

Abstract: A process for producing terephthalic acid of high quality suitable for use in direct polymerization comprising oxidizing a para-dialkylbenzene and/or an oxidized intermediate thereof in the liquid phase with molecular oxygen or a molecular oxygen-containing gas in the presence of an oxidation catalyst containing a heavy metal in a lower aliphatic carboxylic acid solvent, the reaction being carried out in the presence of a specified amount of a phenol. Polyesters prepared from the resulting terephthalic acid have good color.

Abstract: An apparatus for producing an aromatic dicarboxylic acid by oxidizing a benzene derivative with molecular oxygen in the liquid phase in a lower aliphatic carboxylic acid as a solvent in the presence of an oxidation catalyst, wherein a starting material liquid e.g., a benzene derivative or a solution thereof in the lower aliphatic carboxylic acid, is fed into the liquid-phase reaction system in a uniformly dispersed state by being passed through a porous material causing the pressure of the starting material liquid just after passing through said porous material to drop more than about 1 kg/m.sup.2 in relation to the pressure of the starting material liquid just before passing through said porous material. The resultant aromatic dicarboxylic acid has high purity and has good color.

Abstract: A reaction vessel for continuously producing an aromatic carboxylic acid sparingly soluble in a solvent by liquid-phase oxidizing a corresponding alkyl aromatic compound with a molecular oxygen-containing gas in the presence of a lower aliphatic carboxylic acid solvent and an oxidation catalyst. The adhesion of the aromatic carboxylic acid on the inside wall of the reaction vessel at the interface between the vapor-phase portion and the liquid-phase portion is prevented by locating in the reaction vessel a means such as a porous annular pipe for spraying onto the inside wall of the reaction vessel above the level of the reaction liquid a part of a solvent-catalyst mixture supplied continuously to the reaction vessel.