Heat setting optical films
First Claim
Patent Images
1. A method of making an optical film, the method comprising:
- providing a film comprising a polyester-based polymeric material capable of developing birefringence;
conveying the film along a machine direction while holding opposing edge portions of the film, wherein the film has an intended stretch direction transverse and orthogonal to the machine direction, an in-plane machine direction orthogonal to the stretch direction, and a thickness direction;
substantially uniaxially orienting the film in the stretch direction while allowing contraction of the film in the in-plane and thickness directions thereof, the oriented film having an initial refractive index in each of the stretch, in-plane, and thickness directions which define an initial relative birefringence of the oriented film; and
heat setting the substantially uniaxially oriented film, the heat setting thereby altering each of the initial refractive indices in the stretch, in-plane, and thickness directions to a final refractive index in each of the stretch, in-plane, and thickness directions, respectively, the final refractive indices in the stretch, in-plane, and thickness directions defining a final relative birefringence of the heat set film,wherein the polyester-based material, a draw ratio and temperature for said uniaxially orienting, and a temperature and time for said heat setting are chosen such that the final relative birefringence is less than the initial relative birefringence, with the chosen heat setting temperature being above the glass transition temperature and below the melting temperature of the polyester-based polymer material, andwherein the initial and final relative birefringence are each defined as |ny−
nz|/|nx−
nu|, where nx represents refractive index in the stretch direction, ny represents refractive index in the in-plane direction orthogonal to the stretch direction, nz represents refractive index in the thickness direction, and nu represents the average of ny and nz.
0 Assignments
0 Petitions
Accused Products
Abstract
A method of making an optical film includes providing a film, substantially uniaxially orienting the film, and heat setting the oriented film. The film includes a polymeric material capable of developing birefringence.
-
Citations
26 Claims
-
1. A method of making an optical film, the method comprising:
-
providing a film comprising a polyester-based polymeric material capable of developing birefringence; conveying the film along a machine direction while holding opposing edge portions of the film, wherein the film has an intended stretch direction transverse and orthogonal to the machine direction, an in-plane machine direction orthogonal to the stretch direction, and a thickness direction; substantially uniaxially orienting the film in the stretch direction while allowing contraction of the film in the in-plane and thickness directions thereof, the oriented film having an initial refractive index in each of the stretch, in-plane, and thickness directions which define an initial relative birefringence of the oriented film; and heat setting the substantially uniaxially oriented film, the heat setting thereby altering each of the initial refractive indices in the stretch, in-plane, and thickness directions to a final refractive index in each of the stretch, in-plane, and thickness directions, respectively, the final refractive indices in the stretch, in-plane, and thickness directions defining a final relative birefringence of the heat set film, wherein the polyester-based material, a draw ratio and temperature for said uniaxially orienting, and a temperature and time for said heat setting are chosen such that the final relative birefringence is less than the initial relative birefringence, with the chosen heat setting temperature being above the glass transition temperature and below the melting temperature of the polyester-based polymer material, and wherein the initial and final relative birefringence are each defined as |ny−
nz|/|nx−
nu|, where nx represents refractive index in the stretch direction, ny represents refractive index in the in-plane direction orthogonal to the stretch direction, nz represents refractive index in the thickness direction, and nu represents the average of ny and nz. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26)
-
Specification