Optical plastic molding technology is current advanced technology for manufacturing plastic aspheric optical parts, which includes injection molding, casting molding and compression molding. Optical plastic injection molding technology is mainly used for mass production of aspheric lens optical parts with a diameter of less than 100 mm, and can also manufacture micro lens arrays. Casting and press molding techniques are mainly used to manufacture aspherical lens optical parts with a diameter of more than 100 mm.

 

Plastic aspheric optical parts are widely used in military, photography, medicine, industry and other fields due to their light weight and low cost, optical parts and mounting parts can be injection molded into a whole to save assembly workload, have advantages of good impact resistance, etc. For example, 9 aspherical plastic lenses are used in American AN/AVS-6 pilot low-light night vision glasses.
In addition, aspherical plastic lenses are also used in AN/PVS-7 infantry low-light night vision goggles, HOT night vision goggles, "Copperhead" laser-guided projectile seeker and other optoelectronic-guided seekers, laser rangefinders, military telescopes, and viewfinders of various cameras. American TBE company has done economic analysis and comparison of several optical plastic lens molding technologies when manufacturing some aspherical optical parts for terminal-guided automatic seekers, and believes that use of injection molding technology to manufacture aspherical plastic optical lenses cost-effective optimal.

Injection molding method is an aspherical optical plastic lens processing technology that inject quantitative optical plastic that has been heated into a fluid into a stainless steel mold, molds it under heating and pressure conditions, then cool and solidify, open mold to obtain required optical plastic parts. Key link of this technology is mold. Due to low working temperature requirements for optical plastic molding, requirements for mold are relatively lower than those for glass molding.
Ultra-precision machining of aspherical molds is quite difficult. Usually, surface of mold base is ground into an approximate aspherical surface on a numerically controlled (NC) machine tool, then surface accuracy and surface of aspherical surface are gradually improved by fine grinding method. Roughness is finally processed into required surface shape accuracy and surface roughness by polishing. However, due to low machining accuracy of CNC machine tools, it is necessary to repeatedly inspect and modify mold during mold processing process to gradually improve accuracy of mold, thus increasing cost of mold.

 

In order to change this situation, mold processing is now carried out by computer numerical control (CNC) ultra-precision aspheric surface processing machine tools and aspheric surface uniform polishing machines with good rigidity and high resolution. First, use a computer numerical control ultra-precision aspherical surface machining machine to process die base into an aspherical surface with a surface shape accuracy of ±0.1 microns, then use a polishing machine to uniformly lightly polish aspherical surface shape while maintaining same accuracy. Throwing off a thickness of 0.01 microns improves roughness of mold surface.
Following introduces a high-precision plastic optical lens injection molding technology developed by Japanese research and development of gate seal molding method.

Gate seal molding method is a method of injecting molten resin into a metal mold heated to a temperature above resin conversion temperature (injection amount should be: pressure of resin when mold is opened after cooling is just equal to pressure of atmosphere) and then quickly sealing gate. After temperature and pressure are uniform, under condition of constant relative volume and uniform temperature-pressure, slowly cool to below thermal deformation temperature of resin, then open mold and take out molding method of finished product.
First, high temperature molten resin is injected into mold at a high pressure of about 130 MPa, gate is sealed under high temperature (T1) conditions. Pressure of resin sealed in mold is reduced to 30 MPa during homogenization process (temperature at this time is a certain temperature T2 which is slightly higher than resin conversion temperature). At this time, as long as mold monomer can maintain its clamping force, do not open mold cavity. After a certain period of time from resin injection, single mold can be removed from mold clamping device of press. After single mold is slowly cooled, mold can be opened to take out finished product.