Optical bodies made with a birefringent polymer

• US 6,574,045 B2
• Filed: 01/31/2002
• Issued: 06/03/2003
• Est. Priority Date: 10/12/1999
• Status: Expired due to Term

• Current Assignee: 3M Innovative Properties Company (3M Company)
• Original Assignee: 3M Innovative Properties Company (3M Company)
• Inventors: Hebrink, Timothy J., Condo, Peter D., Merrill, William W.
• Primary Examiner(s): Chang, Audrey
• Assistant Examiner(s): Curtis, Craig
• Application Number:
  US10/062,327
• Publication Number:
  US 20020122252A1
• Time in Patent Office: 488 Days
• Field of Search: 359/498, 359/497, 359/494, 359/500, 156/102, 428/212
• US Class Current: 359/361
• CPC Class Codes: B32B 2307/42 Polarizing, birefringent, filtering
• CPC Class Codes: B32B 2367/00 Polyesters, e.g. PET, i.e. polyethylene terephthalate
• CPC Class Codes: B32B 2551/00 Optical elements
• CPC Class Codes: B32B 27/08 of synthetic resin
• CPC Class Codes: B32B 27/36 comprising polyesters
• CPC Class Codes: G02B 5/0841 comprising organic materials, e.g. polymers
• CPC Class Codes: G02B 5/0866 incorporating one or more organic, e.g. polymeric layers
• CPC Class Codes: G02B 5/305 including organic materials, e.g. polymeric layers
• CPC Class Codes: G02B 5/3083 Birefringent or phase retarding elements G02B5/3008, G02B5/3016 take precedence; systems for polarisation control G02B27/286; manufacturing phase modulating patterns by lithographic processes G03F7/001
• CPC Class Codes: Y10T 428/24942 including components having same physical characteristic in differing degree
• CPC Class Codes: Y10T 428/2495 Thickness [relative or absolute]

Abstract

A optical body has at least two polymeric materials forming a reflective interface for at least one polarization of light. One optical body is a multilayer optical film that includes birefringent first optical layers and second optical layers interleaved with the first optical layers. Each first optical layer is formed using a polymer, such as a copolymer of polyethylene naphthalate. The second optical layers are formed so that they have a lower in-plane birefringence than the first optical layers for 632.8 nm light. Optical bodies can be used as, for example, polarizers and mirrors. The optical bodies can be formed using polymers that provide better index matching and are more easily protected from UV light without coloring the optical body.

Claims

1. A method of making a multilayer optical body, the method comprising steps of:

forming a stack of polymeric optical layers, the stack of optical layers comprising

a plurality of first optical layers, each first optical layer comprising a polymer with no more than about 20% crystallinity, as determined using differential scanning calorimetry, and

a plurality of second optical layers forming a plurality of optical interfaces with the first optical layers; and

orienting the first optical layers at a temperature that is about the glass transition temperature of the polymer of the first optical layers or lower to give the first optical layers an in-plane birefringence of at least about 0.16.

2. The method of claim 1, wherein forming a stack of layer comprises forming a stack of layers comprising a plurality of first optical layers comprising a copolymer of polyethylene naphthalate.

3. The method of claim 1, wherein the step of orienting the first optical layers comprises orienting the first optical layers at a temperature that is about the glass transition temperature of the polymer of the first optical layers or lower to give the first optical layers an in-plane birefringence of at least about 0.19.

4. The method of claim 2, wherein the step of forming a stack of optical layers comprises forming the plurality of first optical layers using a copolymer of polyethylene naphthalate with less than 70 mol % and at least about 20 mol % of the carboxylate subunits being naphthalate subunits.

5. The method of claim 2, wherein the step of forming a stack of optical layers comprises forming the plurality of first optical layers using a copolymer of polyethylene naphthalate with about 25 to 65 mol % of the carboxylate subunits being naphthalate subunits.

6. A method of making a multilayer optical body, the method comprising steps of:

forming a first polymer comprising a copolymer of ethylene naphthalate with less than 70 mol % of the carboxylate subunits of the copolymer being naphthalate subunits; and

forming a stack of polymeric optical layers, the stack of optical layers comprising

a plurality of first optical layers, each first optical layer comprising the first polymer, and

a plurality of second optical layers interleaved with the plurality of first optical layers to form a plurality of optical interfaces with the first optical layers, wherein the second optical layers have a lower in-plane birefringence than the first optical layers for 632.8 nm light.

7. The method of claim 6, further comprising orienting the first optical layers.

8. The method of claim 6, wherein the step of forming a first polymer comprises forming the first polymer comprising a copolymer of polyethylene naphthalate with less than 70 mol % and at least about 20 mol % of the carboxylate subunits being naphthalate subunits.

9. The method of claim 6, wherein the step of forming a first polymer comprises forming the first polymer comprising the copolymer of polyethylene naphthalate, wherein the copolymer has about 25 to 65 mol % of the carboxylate subunits being naphthalate subunits.

10. The method of claim 6, wherein the step of forming a first polymer comprises forming the first polymer comprising the copolymer of polyethylene naphthalate, wherein the copolymer has with no more than about 20% crystallinity, as determined using differential scanning calorimetry.

11. The method of claim 7, wherein the step of orienting the first optical layers comprises orienting the first optical layers at a temperature that is about the glass transition temperature of the polymer of the first optical layers or lower to give the first optical layers an in-plane birefringence of at least about 0.16.

12. A method of making a multilayer optical body, the method comprising steps of:

forming a first polymer comprising a copolymer of ethylene naphthalate;

forming a stack of polymeric optical layers, the stack of optical layers comprising

a plurality of first optical layers, each first optical layer comprising the first polymer, and

a plurality of second optical layers interleaved with the first optical layers to form a plurality of optical interfaces with the first optical layers; and

cooling the stack to room temperature, wherein, upon cooling, the copolymer of first optical layers has no more than about 20% crystallinity as determined using differential scanning calorimetry.

13. The method of claim 12, further comprising orienting the first optical layers prior to cooling the stack to room temperature.

14. The method of claim 12, wherein the step of forming a first polymer comprises forming the first polymer comprising the copolymer of polyethylene naphthalate, wherein the copolymer has less than 70 mol % of the carboxylate subunits being naphthalate subunits.

15. The method of claim 12, wherein the step of forming a first polymer comprises forming the first polymer comprising the copolymer of polyethylene naphthalate, wherein the copolymer has about 25 to 65 mol % of the carboxylate subunits being naphthalate subunits.

16. The method of claim 13, wherein the step of orienting the first optical layers comprises orienting the first optical layers at a temperature that is about the glass transition temperature of the polymer of the first optical layers or lower to give the first optical layers an in-plane birefringence of at least about 0.16.