Method for post-injection lamination to add a functional film to an optical lens
View Patent ↗A method for laminating a functional film on to a thermoplastic injection molded lens. A thermally curable glue is deposited on the lens while it is still in the mold. A functional film is introduced and the mold is closed again. The heat from the mold and the clamping pressure thermoform the film and cure the glue, in a lamination process. A functionally enhanced lens having a film intimately laminated on to one side.
1. A method for laminating a functional film onto an injection molded thermoplastic lens that resides in an injection molding machine having a horizontally oriented parting line, comprising the steps of injecting molten thermoplastic resin into a lens-forming cavity held closed under a primary clamp force;
opening the mold at a time when the lens is rigid enough to retain its shape and separate from an insert;
depositing an unpressurized full metered charge of curable glue onto the center of the horizontally oriented lens;
introducing a functional film between the glue and the separated insert; and
closing the mold to a secondary clamp force less than or equal to the primary clamp force to thinly spread the glue between the film and lens so that it cures with the heat transferred from the mold and the diminishing residual heat of the lens whereby an optically clear laminated ophthalmic lens is formed that avoids visible interference fringes.
2. The method of claim 1 , wherein the thermoplastic resin is injected at a melt temperature T m that is significantly above its glass transition T g temperature, and the lens forming cavity is at a temperature lower than T g to facilitate solidification.
3. The method of claim 2 , wherein the T m is in the range of 500 degrees F. to 600 degrees F. and the mold temperature is in the range of 200 degrees F. to 295 degrees F. when the lens forming resin is polycarbonate.
4. The method of claim 1 , wherein the curable glue comprises an acrylate-based adhesive which is curable at a temperature between T m and the mold temperature.
5. The method of claim 4 , wherein said depositing step comprises applying a liquid glue in an open-air state; and wherein during the closing step the glue is spread in the absence back pressure.
6. The method of claim 4 , wherein the curable glue is VOC-free, and compatible with the lens resin and film material.
7. The method of claim 6 , wherein the curable glue provides an adhesive layer to optically bond an outer film surface to an outer lens surface at a temperature well below the T m of the injecting thermoplastic resin.
8. The method according to claim 4 , wherein the glue includes one or more (meth)acrylate compounds, an initiator, and a metal salt.
9. The method according to claim 6 , wherein the glue includes a monofunctional (meth)acrylate compound, a multifunctional (meth)acrylate compound, a difunctional (meth)acrylate compound, and an aliphatic urethane diacrylate.
10. The method according to claim 8 , wherein the metal salt is Cobalt naphthenate, and the initiator is tert-butylperoxybenzoate.
11. The method of claim 6 , further comprising an additional material blended into the curable glue, wherein the additional material is selected from the group consisting of a photochromic dye, a thermoplastic polyurethane (TPU) and combinations thereof.
12. The method of claim 1 , wherein said closing step includes thermoforming the film to replicate the shape of the lens and any surface textures on the insert.
13. The method of claim 1 , wherein the functional film is selected from the group consisting of a sandwiched polarizing filter, a photochromic film, and an anti-reflective film.
14. The method of claim 1 , wherein the functional film comprises a polarizing filter of polyvinyl acetate (PVA) sandwiched between a protective layer made from a material selected from the group consisting of polycarbonate, cellulose triacetate (TAC), cellulose acetate butyrate (CAB), and polyethylene terephthalate (PET).
15. The method of claim 14 , wherein the protective layer includes a functional feature.
16. The method of claim 1 , wherein the secondary clamp force is in the range from about 1% to about 100% of the primary clamp force.
17. The method of claim 16 , wherein the secondary clamp force is less than the primary clamp force.
18. The method of claim 1 , wherein following said closing step, the method further including the step of:
ejecting the lens from the mold after the adhesive has cured and the laminated lens is capable of withstanding ejection forces without deforming.
19. The method of claim 1 , wherein the thermoplastic resin is selected from polymethyl(meth)acrylate, polycarbonate, polycarbonate/polyester blends, polyamide, polyester, cyclic olefin copolymers, polyurethane, polysulfone and combinations thereof.
20. The method of claim 19 , wherein the thermoplastic resin is polycarbonate.
21. The method of claim 1 , wherein the lens-forming cavity is selected from an afocal lens forming cavity, a unifocal lens forming cavity, a bifocal lens forming cavity, a trifocal lens forming cavity, and a progressive lens forming cavity.