JPH0447912A - Injection mold for plastic lens and manufacture thereof - Google Patents

Abstract

PURPOSE:To make it possible to efficiently manufacture axisymmetrical plastic lens by a method wherein a mold having a gate, through which resin is introduced, is provided on the optical axis or near the axis, which is the axisymmetrical center line, is used. CONSTITUTION:In the mold concerned, a second sprue 8 is provided so as to provide a gate 7 on the optical axis of optical surfaces. By employing the above- mentioned constitution so as to fill resin through the axisymmetrical center of an axisymmetrical lens, axisymmetrically filling state can be realized, resulting in preventing the unaxisymmetry of a shape due to filling from occurring. And, at manufacturing, after the removing process, annealing process of a lens, the vapor depositing process of antireflection film, Indian ink is painted 13 in the region, in which the surface shape distorts near a gate mark. By applying the above-mentioned method, no lowering of optical performance due to the distortion of the surface shape occurs. Further, since the shaded area is negligibly small to the effective area of the lens, the lowering of the amount of transmitted light is also negligibly small.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to an injection molding facility for plastic lenses used in projection television receivers, video cameras, etc., and a conventional method for manufacturing plastic lenses using this mold. Technological advances Projection type television receivers Video cameras, CD players As devices with optical systems become more widespread, mass production methods meet the rapid increase in demand for optical systems. Cost advantages, lightweight, constant aspheric surface, high aberration correction ability. Injection molding is commonly used in the production of plastic lenses.The following is a process for conventional injection molding of plastic lenses and the production of plastic lenses using the same. The method will be explained with reference to the drawings. Figure 3 is a cross-sectional view showing the structure of the main parts of a conventional plastic lens mold. In Figure 3, la and lb are called nests, and their opposite sides are Optical surfaces 2a and 2b for forming the functional surfaces of the lenses are formed on the respective sides of the lens, and 3a and 3b hold the nests 1a and 1b and form the side surfaces of the lenses to form closed spaces (cavities). Die set for construction, 4 a.

4b is a plate that serves as a support for installing the die sets 3a and 3b in the mold clamping mechanism; a sprue 5 and a runner 6 are formed as a passage for introducing the molten resin into the cavity; Even if gate 7 is formed as an entrance to the mold, in such a configuration, molten resin is injected from an injection mechanism (not shown) into the cavity, cooled and solidified, and then the resin block is taken out from the mold and transferred to the product section. Problems that the invention aims to solve are problems that the invention attempts to solve, such as: resin blockage that occurs when filling resin into a cavity, differences in filling times for each part, etc. If a deviation occurs between the obtained molded lens and the mold shape, L if it is rotationally symmetric, the lens shape that should originally be rotationally symmetric becomes rotationally asymmetric. The ability to obtain the desired shape by modifying the mold shape (normally, a processing method that assumes a rotationally symmetrical shape is used for machining the lens surface of the mold, so corrections are required for rotationally asymmetrical deviations) This problem is extremely serious, and - in boat fishing, optical performance deteriorates extremely sensitively to rotationally asymmetric deviations. In order to solve the problem! ζ Plastic lens mold mold C according to the present invention A method for manufacturing a plastic lens according to the present invention, which has a gate for introducing resin on or near the optical axis, which is the center of rotational symmetry. A lens is molded using the above-mentioned mold.By providing a light-shielding area near the gate marks that occur in the resist molding process, light rays do not pass through this area. If used, the rotational asymmetry of the lens shape caused by the rotational asymmetry of the filling state can be prevented. Also, if the manufacturing method described above is used, optical defects near the gate marks that occur when using the mold as described above can be prevented. It is possible to realize a plastic lens with high rotational symmetry and high optical performance without causing deterioration of optical performance due to surface shape disturbance. An embodiment of the manufacturing method will be explained with reference to the drawings. Fig. 1 is a sectional view showing the main parts of an embodiment of the mold for molding a plastic lens of the present invention. Components numbered ~7 correspond to the same numbers of components 1 to 7 in FIG. 3 used to explain the conventional technology, and their basic operations are almost the same as those explained in the conventional technology. Similarly, a.Here, what differs from the conventional structure in terms of structure is that the second sprue 8 is provided and the gate 7 is placed on the optical axis of the optical surface.A With this configuration, it is rotationally symmetrical. By filling the resin from the rotationally symmetrical center of the lens, a rotationally symmetrical filling state can be achieved and rotational asymmetry in the shape due to filling can be prevented. When molding a concave lens with a thin center and a tight center as shown in FIG. Although good filling can be easily achieved using this method, there is concern that such a method will leave gate marks on the optical surface, and that the optical performance will be significantly impaired due to the disturbance of the shape in this area. (According to the method for manufacturing a plastic lens of the present invention, such inconveniences will not occur.) Below, an example of the method for manufacturing a plastic lens of the present invention will be described. After the annealing process of vapor deposition of the anti-reflection coating, ink is applied to the areas near the gate marks where the surface shape is disordered.

Figure 2 is a cross-sectional view showing the lens after this blacking process has been completed. In other words, there is no deterioration in optical performance due to surface shape disturbance, and since the light shielding area is negligibly small compared to the effective area, the decrease in the amount of transmitted light due to this is negligible. In one embodiment of the method for manufacturing a plastic lens, a force using a black amount to provide a light-shielding area (the present invention is of course not limited to this,
Other methods such as pasting a black sticker may also be used (~Also, the step of providing the light-shielding area is done after the annealing/bi-evaporation step. This step can be inserted anywhere as long as there is no problem with reliability etc. None Effects of the Invention As is clear from the detailed explanation above, according to the plastic lens injection mold and manufacturing method of the present invention, it is possible to efficiently manufacture a plastic lens with excellent rotational symmetry. It is now possible to create a lens system with high optical performance.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional view of the main parts of an embodiment of the plastic lens injection molding mold of the present invention. FIG. 2 is a cross-sectional view of a lens obtained by an embodiment of the plastic lens manufacturing method of the present invention. The figure is a main sectional view showing a conventional plastic lens injection mold. Plate 5...Sprue 6...Lunch 7...Gate 8...Second sprue 11...Plastic lens 12...Gate trace 13...Name of light-shielding layer agent Patent attorney Shigetaka Awano et al. 1 person/L, fb-2L, zb-optical surface 8L

Claims (2)

[Claims] (1) A mold for injection molding a plastic lens, characterized in that a gate is provided on or near the optical axis of an optical surface. (2) A process of injection molding using a mold with a gate on or near the optical axis of the optical surface, a process of separating the product part from the sprue and runner part by the gate part, and a gate of the product produced by the process. A method for manufacturing a plastic lens, comprising the step of providing a light-blocking area so that no light passes through the trace.