Polyurethane based adhesive for polarizing structure and polarized lens

1. A polyurethane based adhesive obtained by reacting at least one polyisocyanate compound with at least one polyol compound derived from caprolactone monomer, wherein the at least one polyol compound has a number average molecular weight more than 200 and less than 297 and a functionality in a range between 2.3 and 2.5, inclusive of the endpoints wherein the at least one polyisocyanate compound is a hexamethylene diisocyanate and the at least one polyol compound derived from caprolactone monomer is a polycaprolactone polyol, wherein NCO:OH ratio of the at least one polyisocyanate compound and the at least one polyol compound is 3:1.

2. A polarizing structure comprising:

a polarizing film;

a protective film provided on at least one face of the polarizing film with an adhesive layer,

wherein said adhesive layer is a layer of the polyurethane based adhesive of claim 1 .

3. The polarizing structure according to claim 2 , wherein two protective films are placed on each side of the polarizing film.

4. The polarizing structure according to claim 3 , wherein the polarizing film is a light-polarizing polyvinyl alcohol-based layer (PVA), and each of said protective films are independently selected from the group consisting of polycellulosics, polycarbonates, polyesters, poly(meth)acrylics, polycyclic olefin copolymers, polyolefin, thermoplastic polyurethanes, polythiourethanes, polyvinyls, polystyrenes, polyamides, polyimides, polysulfones, polyether sulfones, poly ether ether ketones, polyphenylene sulfides, polyoxymethylenes, polyurethanes, epoxys or blend thereof.

5. The polarizing structure according to claim 4 , wherein the polarizing film is a light-polarizing polyvinyl alcohol-based layer (PVA).

6. A method for manufacturing a polarizing structure comprising the following steps:

providing a polarizing film;

providing a protective film on at least one face of the polarizing film;

deposing a layer of polyurethane based adhesive of claim 1 between said polarizing film and said protective film;

pressing the protective film against the polarizing film to form a polarizing structure; and

curing the polarizing structure at a temperature between 40° C.-90° C. for about 16 hours.

7. The method of claim 6 , wherein prior to said deposing a layer of polyurethane based adhesive, the method further includes a step of surface treating of the protective film with at least a caustic treatment.

8. The method of claim 6 , wherein said deposing a layer of polyurethane based adhesive comprises spin coating or roll coating the adhesive either onto one face of the polarizing film or one face of the protective film, or one face of the polarizing film and one face of the protective film.

9. A polarized optical element comprising:

an optical base element;

a polarizing structure; and

an adhesive layer placed between one surface of the optical base element and the polarizing structure so as to permanently retain said polarizing structure on the surface of the optical base element,

wherein the polarizing structure comprises a polarizing film and a protective layer provided on at least one face of the polarizing film with a polyurethane based adhesive of claim 1 .

10. The element according to claim 9 , wherein said adhesive layer includes a tri-layer adhesive which comprises a layer of hot melt adhesive layer sandwiched between two latex layers.

11. The element according to claim 9 , wherein said adhesive includes a pressure sensitive adhesive.

12. The element according to claim 9 , which further includes at least one functional coating placed on the protective film on the opposite side of said protective film from the polarizing film, said coating selected from the group consisting of hard coating, anti-reflective coating, photochromic coating, tinted coating, anti-fog coating and anti-smudge coating.