Photochromic polyurethane laminate
A photochromic polyurethane laminate that is constructed to solve certain manufacturing difficulties involved in the production of plastic photochromic lenses is disclosed. The photochromic laminate includes at least two layers of a resinous material and a photochromic polyurethane layer that is interspersed between the two resinous layers and which contains photochromic compounds. The polyurethane layer is formed by curing a mixture of a solid thermoplastic polyurethane, at least one isocyanate prepolymer, at least one photochromic compound, and a stabilizing system.
1. A process for producing a transparent photochromic polyurethane laminate, comprising:
a) preparing a solvent casting solution by dissolving a solid thermoplastic polyurethane, at least one isocyanate polyurethane prepolymer, and at least one photochromic compound, in a solvent;
b) casting the solution on a release liner film to form a cast film;
c) evaporating the solvent from the cast film to a substantially dry state to form a photochromic polyurethane film;
d) transfer-laminating the photochromic polyurethane film between two transparent resin sheets;
e) curing the photochromic polyurethane film, thereby forming a photochromic polyurethane laminate.
2. The process according to claim 1 , wherein step d) comprises transfer-laminating the photochromic polyurethane film between two transparent resin sheets through a sequential process.
3. The process according to claim 1 , wherein step d) comprises transfer-laminating the photochromic polyurethane film between two transparent resin sheets through an in-line process.
4. The process according to claim 1 wherein step a) comprises forming the solid thermoplastic polyurethane by reacting:
a) a polyol selected from a group consisting of polyester polyols and polyether polyols, having a molecular weight in the range of about 500 to 6,000 g/mol, and a functionality of 2;
b) with a diisocyanate in an equivalent ratio of diisocyanate to polyol in the range of about 1.2:1.0 to 8.0:1.0; and
c) with a diol as a chain extender having a molecular weight in the range of about 62 to 499 g/mol;
wherein the theoretical NCO index of the thermoplastic polyurethane is in a range of 90 to 105.
5. The process according to claim 4 wherein the step of forming the solid thermoplastic polyurethane comprises selecting a polyester polyol from a group consisting of polycaprolactone polyol and poly(butylene adipate) polyol.
6. The process according to claim 4 wherein the step of forming the solid thermoplastic polyurethane comprises selecting a polyether polyol from a group consisting of polypropylene glycol and polytetramethylene glycol.
7. The process according to claim 4 wherein the step of forming the solid thermoplastic polyurethane comprises selecting a diisocyanate from a group consisting of hexamethylene diisocyanate, isophorone diisocyanate, cyclohexane diisocyanate, methylcyclohexane diisocyanate, and dicyclohexylmethane diisocyanate.
8. The process according to claim 4 wherein the step of forming the solid thermoplastic polyurethane comprises selecting a diol from a group consisting of propane diol, butane diol, pentane diol, hexane diol, diethylene glycol, dipropylene glycol, and cyclohexane diol.
9. The process according to claim 1 wherein step a) comprises employing an isocyanate polyurethane prepolymer having a molecular weight in the range of about 1,000 to 6,000 grams per mole.
10. The process according to claim 1 wherein step a) comprises forming the isocyanate polyurethane prepolymer by reacting:
a) a polyol selected from a group consisting of polyester polyols and polyether polyols, having a molecular weight in a range of about 500 to 3000 g/mol and a functionality of 2;
b) with an aliphatic diisocyanate, a cycloaliphatic diisocyanate, or both, in an equivalent ratio of diisocyanate to polyol in a range of about 1.2:1.0 to 8.0:1.0.
11. The process according to claim 10 wherein the step of forming the isocyanate polyurethane prepolymer comprises selecting a polyester polyol from a group consisting of polycaprolactone polyol and poly(butylene adipate) polyol.
12. The process according to claim 10 wherein the step of forming the isocyanate polyurethane prepolymer comprises selecting a polyether polyol from a group consisting of polypropylene glycol and polytetramethylene glycol.
13. The process according to claim 10 wherein the step of forming the isocyanate polyurethane prepolymer comprises selecting a diisocyanate from a group consisting of hexamethylene diisocyanate, isophorone diisocyanate, cyclohexane diisocyanate, methylcyclohexane diisocyanate, and dicyclohexylmethane diisocyanate.
14. The process according to claim 1 wherein the step of preparing a solvent casting solution comprises selecting a photochromic compound from the group consisting essentially of naphtho[2,1b]pyrans and naphtho[1,2b]pyrans.
15. The process according to claim 1 wherein the step of preparing a solvent casting solution comprises combining said solid thermoplastic polyurethane with said isocyanate-terminated polyurethane prepolymer at a ratio in a range of about 9:1 to 1:9, by weight.
16. The process according to claim 1 wherein step c) comprises forming a photochromic polyurethane film having a thickness in a range of about 10 μm to about 100 μm.