How Plastic Lenses Are Molded: A Guide to Injection Molding Techniques

Plastic glasses: glasses include myopia glasses, reading glasses, sunglasses, etc. They are injection molding methods using vertical horizontal injection molding machines, which mold a certain number of spectacle lenses at one time, with simple coloring and low cost. Generally, PMMA materials are used, and fiber, transparent nylon or PC plastics are used for higher requirements.

Disc vertical horizontal injection molding machine is generally selected for processing glasses, small screws are selected, and the mold cavity is generally designed to be 1×5 or 1 ×6 circumferential symmetrical arrangement. Reading lenses and myopia lenses require high sizes, requiring a long holding time to reduce shrinkage and bring the product to the designed size. Sunglasses belong to flat mirror light lenses, and the requirements are not very high, but they are generally dyed, which are divided into one-step dyeing and two-step dyeing.

Plastic optical lenses: optical lenses other than spectacle lenses such as index code camera lenses and mobile phone lenses. The material is generally PMMA plastic.

Generally, 50T to 120T vertical horizontal injection molding machines are used. The optical lens is generally thick, the product appearance is rich, the product shrinkage is controlled, and the product does not yellow at the same time, which requires good overall cleanliness and light transmittance. 

The main technical characteristics of optical lenses are as follows:

1) The locking force of the injection molding machine should be sufficient. Optical lens processing does not require the injection molding machine to have a fast injection molding speed, but only requires the machine to provide a stable slow injection speed, which can provide a high enough injection pressure and a stable continuous pressure holding pressure.

2) Long processing cycle is one of its characteristics. Therefore, a standby variable displacement pump or a servo system is used.

3) The mold should be set up with an exhaust groove with a depth of no more than 0.03mm to discharge the air in the mold cavity and the volatile gas of the melt to prevent the product from affecting the transparency.