Polarizer guarded cover sheet with adhesion promoter
The invention generally relates to polymer films used as protective cover sheets for polarizer plates, a method for producing polarizing plates, and a Liquid Crystal Display employing the same. More particularly, the invention relates to a cover sheet composite having a removable, carrier substrate and a cover sheet comprising a low birefringence polymer film and a layer that promotes adhesion to polyvinyl alcohol on the same side of the carrier substrate as the low birefringence polymer film. The guarded cover sheet of the invention is less susceptible to defects due to dirt and abrasion during the manufacture of the cover sheet and polarizer plates. In addition, the cover sheet has excellent adhesion to polyvinyl alcohol-containing dichroic films and eliminates the need to alkali treat the cover sheet prior to lamination to the dichroic films.
1. A method of forming a polarizing plate comprising (a) providing two guarded cover sheet composites each comprising a carrier substrate and a cover sheet comprising a layer promoting adhesion to polyvinyl alcohol and a low birefringence polymer film comprising polymeric material having an in-plane birefringence Δn in of less than about 1×10 −4 and an out-of-plane birefringence Δn th of from 0.005 to −0.005, (b) providing a dichroic film, and (c) simultaneously bringing said cover sheets into contact with said dichroic film such that the layer promoting adhesion to polyvinyl alcohol in each of said two cover sheets is in contact with said dichroic film.
2. The method of claim 1 wherein said carrier substrate that is removed prior to bringing the cover sheet into contact with said dichroic film.
3. The method of claim 1 wherein said carrier substrate is removed after bringing the cover sheet into contact with said dichroic film.
4. The method of claim 1 wherein said guarded cover sheet composite further comprises a protection layer on the side opposite to said carrier substrate and said protection layer is removed after bringing the cover sheet into contact with said dichroic film.
5. The method of claim 1 wherein said guarded cover sheet composite further comprises a protection layer on the side opposite to said carrier substrate and said protection layer is removed prior to bringing the cover sheet into contact with said dichroic film.
6. The method of claim 1 wherein adhesive is applied simultaneously with bringing together said dichroic film and said cover sheet into contact.
7. The method of claim 6 wherein said adhesive comprises a polyvinyl alcohol solution.
8. The method of claim 1 wherein pressure is applied as said dichroic film and cover sheets are brought into contact.
9. The method of claim 1 wherein after said dichroic film and cover sheets are brought into contact the polarizing plate is dried.
10. The method of claim 1 wherein said layer promoting adhesion to polyvinyl alcohol is adjacent to said carrier substrate.
11. The method of claim 1 wherein said layer promoting adhesion to polyvinyl alcohol is on the side of the low bifringence film opposite to the carrier substrate.
12. The method of claim 1 wherein said layer promoting adhesion to polyvinyl alcohol comprises hydrophilic polymer.
13. The method of claim 1 wherein said layer promoting adhesion to polyvinyl alcohol comprises polyvinyl alcohol.
14. The method of claim 1 wherein said layer promoting adhesion to polyvinyl alcohol comprises pressure sensitive adhesive.
15. The method of claim 1 wherein said layer promoting adhesion to polyvinyl alcohol has a thickness of between 0.1 and 5 micrometers.
16. The method of claim 1 wherein said layer promoting adhesion to polyvinyl alcohol has a thickness of between 1 and 3 micrometers.
17. The method of claim 1 wherein water is applied simultaneously with bringing together said dichroic film and said cover sheet into contact.
18. The method of claim 17 wherein said water further comprises a material which will chemically bridge between the polyvinyl alcohol dichroic film and said layer promoting adhesion to polyvinyl alcohol.