The manufacturing method of colored contact lenses
The production of colored contact lenses consists of six processes: ① material procurement, ② coloring, ③ lens molding, ④ polymerization, ⑤ swelling, and ⑥ sterilization. However, when choosing safe colored contact lenses, the most important factor is the lens molding method, which affects the quality of the lens.
Colored contact lenses sold in Japan are mainly made using the "cast molding method," the "semi-cast molding method," and the "spin-cast molding method."
"Mold" refers to a mold or casting mold, and "cast" means casting or pouring, so it is a method of pouring the material for contacts into a bowl-shaped mold to create them.
1. The cast molding method
The cast molding method involves pouring the raw material for the lenses into a bowl-shaped mold and pressing it from above to solidify the lens. Colored pigments for the contact lenses are also poured in, resulting in lenses that are thin and lightweight to wear.
Since the color pigment is mixed during the molding process, it's possible to produce colored contact lenses in large quantities relatively inexpensively, as long as the materials are available.
Due to their thinness, these lenses can be prone to damage if mishandled, so they are often used in daily disposable types of colored contact lenses, eliminating the need for rubbing and cleaning.
The coloring is securely enclosed within the lens, contributing to its safety.
2. The semi-cast molding method
In a manufacturing method that has evolved the cast molding technique, the principle remains the same as cast molding, but the method of coloring the pigments of color contact lenses differs. In cast molding, the pigments of color contact lenses are poured together to color them, whereas in semi-cast molding, after coloring the outside of the lens, it is thinly coated with a special polymer material.
This method allows for even thinner lenses compared to cast molding, but the drawback is that the strength of the lens is weaker.
3. The spin-casting molding method
The spin-casting method, like cast molding, uses molds to create lenses, but it utilizes centrifugal force to make the lenses. It's designed to be thinner toward the center, with the colored part designed not to touch the iris. While it's considered safe, there's a risk of trouble if, by any chance, defects cause the pigment of the color contact lenses to leak.
