Process for applying a layered structure on a lens
View Patent ↗The invention relates to an improvement for applying a layered structure ( 1 ) onto a convex surface of a lens ( 10 ). After thermoforming the layered structure, a curvature direction of the layered structure is inverted. The structure is then applied on the lens surface by continuously pushing the structure ( 1 ) against the lens surface, starting from a contact point between a convex surface of the structure and the convex surface of the lens. The curvature direction of the layered structure is then inverted again, so that it recovers the curvature direction that resulted from thermoforming. Stresses within the layered structure are then reduced, and the structure can be assembled with the lens without defects.
1. Process for applying a layered structure on a convex surface of a lens, comprising the following steps:
/a/ providing the layered structure with a planar shape;
/b/ thermoforming the layered structure so that it becomes curved with a first surface being concave and a second surface being convex;
/c/ inverting the curvature of the layered structure so that said first surface turns convex and said second surface turns concave;
/d/ bringing the first surface of the layered structure in contact with the lens surface at an initial contact point; and
/e/ starting from the initial contact point, applying the first surface of the layered structure against the lens surface via pressure applied on the second surface of the layered structure, the first and second surfaces of the layered structure turning back to concave shape and convex shape, respectively, at a peripheral border of an increasing contact zone.
2. Process according to claim 1 , wherein step /e/ is carried out so that substantially no pressure is applied on the second surface of the layered structure out of the increasing contact zone.
3. Process according to claim 1 , wherein step /e/ is carried out with the layered structure heated.
4. Process according to claim 3 , wherein a temperature of the layered structure is equal or at least 75° C. during step /e/.
5. Process according to claim 1 , wherein the surface lens has a curvature radius below 305 millimeters, preferentially below 100 millimeters, and particularly less than 75 millimeters.
6. Process according to claim 1 , wherein steps /d/ and /e/ are carried out with an adhesive layer provided between the lens surface and the first surface of the layered structure.
7. Process according to claim 6 , wherein the adhesive layer is applied on the lens surface and/or on the first surface of the layered structure.
8. Process according to claim 6 , wherein the adhesive layer comprises a material of pressure-sensitive adhesive type.
9. Process according to claim 1 , wherein pressure is applied on the second surface of the layered structure during step /e/ via a resilient membrane being inflated and pressing on the second surface of the layered structure within the increasing contact zone.
10. Process according to claim 1 , wherein step /b/ is carried out so that, between steps /b/ and /c/, a curvature of the layered structure at least one point in the first surface of said layered structure is greater than or equal to a curvature of the lens surface at a point in said lens surface which corresponds to said at least one point in the first surface of the layered structure after step /e/.
11. Process according to claim 10 , wherein the lens surface has a constant curvature, and wherein step /b/ is carried out so that, between steps /b/ and /c/, the layered structure has a curvature greater than or equal to the curvature of the lens surface at any point in the first surface of the layered structure.
12. Process according to claim 10 , wherein the lens is of progressive addition type and the surface lens has curvature at a near vision point higher than a curvature of said lens surface at a far vision point, and wherein step /b/ is carried out so that, between steps /b/ and /c/, the layered structure has a curvature greater than the curvature of the lens surface at the far vision point.
13. Process according to claim 1 , wherein the layered structure comprises polarizing film.
14. Process according to claim 13 , wherein the polarizing film is polyvinyl alcohol-or polyethylene terephthalate-based.
15. Process according to claim 13 , wherein the layered structure further comprises a protecting film disposed on one side of the polarizing film.
16. Process according to claim 15 , wherein the protecting film is cellulose triacetate-or cellulose acetate butyrate-based.
17. Process according to claim 15 , wherein the layered structure comprises two protecting films disposed on either side of the polarizing film.
18. Process according to claim 1 , wherein the layered structure further comprises at least one functional coating on said second surface of the layered structure.
19. Process according to claim 1 , wherein the lens is an ophthalmic lens.