TOKAI’s ophthalmic lens factories are in operation 24 hours a day, 365 days a year, and everything from the receiving of orders to inventory management, production, and delivery is managed uniformly by computer. We utilize the most sophisticated machinery and skills of our specialized technicians to produce high-performance lenses. This is an introduction to our flow of lens production explained process by process.
Process schedule chart
The combined monomer (liquid plastic raw material) is prepared and injected into a cast called the mold. It is then heated in an electric furnace and hardened in a uniform molecular structure. The lateral surfaces of the lenses that have been molded are ground and cleaned so they become smooth.
Surfacing and polishing
(1) Rough grinding
Lenses that undergo blocking (at the axes and center marking) are cut by a machine called the generator and curved at their reverse sides in accordance with their specified powers. Thick lenses can be designed with the desired thicknesses and curves in a short period of time because the use of generators involves much cutting. However, the cutting surface is still rough in this stage and curve accuracy is not sufficient especially when the user has astigmatism. Fine curve adjustments are made in the next smoothing operation.
(2) Precision grinding
The surface that has undergone processing with the generator is cut again with a machine that uses diamond blades to make a precise curve with less than 0.1 millimeters in difference.
The surface that has been precisely cut is polished with an abrading agent that is mixed with abrasive powder to give it a shine.
Some lenses are automatically cleaned after polishing to remove tainting and foreign substances.
Inspections on external precision
Surface accuracy, optical precision, and external precision of the lenses are inspected in accordance with the work instructions. Only products that pass the standards set by TOKAI go through the next processes.
Tint processing being done
Lenses that require coloring undergo tint processing. Lenses offered by TOKAI come in over two thousand colors. Color tones and concentration of colorants are finely adjusted in accordance with the specifications of the lenses or the kind of coating processing that they undergo after tinting. The colors of the finished lenses are inspected through comparisons with sample colors by using luminous transmittance meters and colorimeters, but it is our experienced and skilled special technicians that make the final evaluations.
(1) Hard coating
Coating work is done in a clean room where temperature and humidity are controlled. First, the surfaces of the lenses where tainting and dust have been removed with ultrasonic cleaning are coated with silicone hard coating liquid and hardened with thermal treatment.
Tainting and dust is removed again with ultrasonic cleaning.
(3) Multi coating
Antireflection coating is vacuum-deposited on both sides of the lenses with vacuum deposition equipment. Multi coating not only decreases refractions on the surfaces of the lenses, but can also be done in various ways to meet your needs such as that for increasing refractions so that your lenses act as mirrors and for preventing tainting and water marks.
We can also edge the lens (a service where lenses are scraped to fit the shapes of the frames) by request from eyeglass shops. After gathering information on the frames by computer, jigs are attached to the centers of the lenses so that they can be scraped accurately.
Lenses that have gone through each process and inspection undergo final optical, exterior, and color tone inspections with our technicians and testing equipment.
After the lenses are given total inspections with automatic inspection and packaging machines, they are separately packed by type and power. The entire staff strictly complies with detailed work rules that involve the numbers of lenses they carry after packing as well as the amount of spaces when boxing so that they do not become damaged such as through scraping during the final packing process of lens production.
Finished lenses are sorted by numbers in accordance with their destinations and delivered promptly and accurately. Special order (RX) lenses are sent together with quality cards, which are proof of quality assurance. Information on lenses such as that on power for each and every customer is readily available at all times.