Method for manufacturing polarised lenses for spectacles and lenses produced using that method
A method of manufacturing a polarizing lens for spectacles in which the lens is obtained by injection co-molding the material of the lens on a polarizing optical filter structure is described. The optical filter structure which already has its curved shape received during the stage of filter manufacture is subjected to a thermoforming stage before being inserted into the injection mold in order that the optical filter should obtain the desired curvature for the subsequent stage of injection co-molding the lens onto the optical filter structure.
1. A method of manufacturing a polarized lens for spectacles, wherein the lens is produced by co-injection moulding of the lens on to a polarizing optical filter structure,
wherein the optical filter structure, which already has a curved shape imparted to it during the production of the filter, is subjected, before insertion into the injection mould, to a step of thermoforming for the purpose of providing the desired curvature in the optical filter for the subsequent step of co-injection moulding of the lens on to the optical filter structure.
2. A method according to claim 1 , wherein in the thermoforming step, the optical filter is positioned in a thermoforming mould with the convex surface of the filter bearing on the mould surface which is made with the desired curvature, the application of a vacuum between these surfaces during the thermoforming step enabling the filter to assume the curvature defined by the mould and to retain the curvature when the filter has been cooled and removed from the thermoforming mould.
3. A method according to claim 1 , wherein after the thermoforming step, provision is made for a step of cleaning the optical filter structure, the cleaning step comprising a step of ultrasonic washing by immersion of the optical filter in an aqueous solution with alkaline soap.
4. A method according to claim 3 , wherein the washing solution is prepared with a pH value of 13.4 and a temperature of about 50° C., and provision is made for the optical filter to be kept immersed for about 5 minutes.
5. A method according to claim 4 , wherein the ultrasonic washing step is made to be followed by a first rinsing of the optical filter in water by oscillation of a filter carrying basket in the aqueous solution for about 30 seconds at ambient temperature.
6. A method according to claim 5 , wherein provision is made for a second ultrasonic wash by immersion of the optical filter in an aqueous solution with slightly acid soap, preferably with a pH value of 5.
7. A method according to claim 6 , wherein the second washing step is made to be followed by a further step of rinsing in water by immersion of the optical filter for about 30 seconds at ambient temperature.
8. A method according to claim 7 , wherein provision is made for a further step of rinsing in demineralized water for about four minutes at a temperature of about 50° C.
9. A method according to claim 8 , wherein the washing and rinsing steps are followed by a step of drying the optical filter in a conventional oven at 55° C. for a period of about 10 minutes.
10. A method according to claim 9 , wherein the drying step is followed by a step of blowing the optical filter with ionized air.
11. A method according to claim 1 , wherein the optical filter is made with a layered structure including a true optical layer and at least one protective polyamide layer for protecting the true optical layer.
12. A method according to claim 1 , wherein the portion of the lens structure co-moulded on to the optical filter is made of polyamide.
13. A polarized lens for spectacles made according to the method of claim 1 .