Diffuse reflective articles

• US 20030118805A1
• Filed: 10/17/2002
• Published: 06/26/2003
• Est. Priority Date: 10/24/1997
• Status: Active Grant

• Current Assignee: Minnesota Mining and Manufacturing Co (3M Company)
• Original Assignee: Minnesota Mining and Manufacturing Co (3M Company)
• Inventors: Kaytor, Scott R., Kretman, Wade D.
• Granted Patent: US 6,780,355 B2
• Time in Patent Office: Days
• US Class Current: 428/304.4
• CPC Class Codes: C08J 2323/02 not modified by chemical after treatment
• CPC Class Codes: C08J 5/18 Manufacture of films or sheets
• CPC Class Codes: F21S 41/37 characterised by their material, surface treatment or coatings
• CPC Class Codes: F21V 7/24 characterised by the material
• CPC Class Codes: F21V 7/28 characterised by coatings
• CPC Class Codes: G02B 5/021 the diffusion taking place at the element's surface, e.g. by means of surface roughening or microprismatic structures
• CPC Class Codes: G02B 5/0247 by means of voids or pores
• CPC Class Codes: G02B 5/0284 used in reflection
• CPC Class Codes: G02B 6/0031 Reflecting element, sheet or layer
• CPC Class Codes: G02B 6/0046 Tapered light guide, e.g. wedge-shaped light guide
• CPC Class Codes: G02B 6/0051 Diffusing sheet or layer
• CPC Class Codes: G02B 6/0065 Manufacturing aspects; Material aspects
• CPC Class Codes: G02B 6/0096 the lights guides being of the hollow type
• CPC Class Codes: Y10T 428/24355 Continuous and nonuniform or irregular surface on layer or component [e.g., roofing, etc.]
• CPC Class Codes: Y10T 428/249953 Composite having voids in a component [e.g., porous, cellular, etc.]
• CPC Class Codes: Y10T 428/249954 With chemically effective material or specified gas other than air, N, or carbon dioxide in void-containing component
• CPC Class Codes: Y10T 428/249958 Void-containing component is synthetic resin or natural rubbers
• CPC Class Codes: Y10T 428/249978 Voids specified as micro
• CPC Class Codes: Y10T 428/249986 Void-containing component contains also a solid fiber or solid particle
• CPC Class Codes: Y10T 428/24999 Inorganic
• CPC Class Codes: Y10T 428/249995 : Constituent is in liquid form
• CPC Class Codes: Y10T 428/249997 : Encapsulated liquid

Abstract

Diffuse reflective materials proximate to a structure formed by thermally induced phase separation of a thermoplastic polymer and a diluent providing enhanced flexibility and reflectivity especially in the visible wavelengths of 380-730 nanometers are described. Such materials find a wide variety of application among combinations with other reflective layers. The diffuse reflective articles are useful in backlight units of liquid crystal displays, lights, copy machines, projection system displays, facsimile apparatus, electronic blackboards, diffuse white standards, photographic lights and the like.

Claims

1. A diffuse reflective article comprising a diffuse reflective material proximate to a structure wherein said diffuse reflective material is made of a porous polyolefin sheet comprising a network of polymer domains and fibrils interconnecting the domains, the porous polyolefin sheet comprising a first surface having a surface element configured to reduce optical coupling with the structure.

2. A diffuse reflective article comprising a diffuse reflective material proximate to a structure wherein said diffuse reflective material is made of a porous polymeric sheet comprising a network of polymeric material having voids therein which material comprises:

(a) a polymer component, and

(b) a diluent component, said diluent component being miscible with the polymer component at a temperature above the melting point of the polymer component or a liquid-liquid phase separation temperature of a total solution of polymer and diluent;

wherein the porous polymeric sheet comprises a first surface having a surface element configured to reduce optical coupling with the structure.

3. The diffuse reflective article of claim 2 wherein the porous polymeric sheet has a reflectivity greater than 92% at a wavelength of 550 nm according to ASTM E 1164-94 using a spectrophotometer with an integrating sphere.

4. The article of claim 2, wherein the polymeric material comprises:

(a) at least 20 parts by weight of the polymer component; and

(b) less than about 80 parts by weight of the diluent component.

5. The article of claim 2, wherein the polymer component is substantially non-absorbing to light at a wavelength between 380 and 730 nanometers.

6. The article of claim 2, wherein the polymer component is selected from the group consisting of polypropylene and polyethylene.

7. The article of claim 2, wherein the diluent component is substantially non-absorbing to light at a wavelength between 380 and 730 nanometers.

8. The article of claim 2, wherein the diluent component is mineral oil.

9. The article of claim 2, further comprising a specular reflective layer in combination with the porous polymeric layer.

10. The article of claim 2, wherein the structure is an optical cavity with the diffuse reflective material lining a portion of the cavity facing a light source.

11. The article of claim 10, wherein the optical cavity is in combination with a partially transparent image in which said image is a liquid crystal display.

12. The article of claim 2, wherein:

the structure comprises an optical cavity and light source positioned proximate the optical cavity; and

the diffuse reflective article is configured to line a portion of the cavity and partially wrap around the light source so as to direct light from the light source into the optical cavity.

13. The article of claim 12, wherein the optical cavity includes a light guide.

14. The article of claim 2, wherein the article is incorporated into a liquid crystal display.

15. The article according to claim 12, wherein the diffuse reflective article partially enclosing the light source reflects light into the light guide.

16. The article of claim 12 wherein the optical cavity is in combination with a brightness enhancement film.

17. The article of claim 12, wherein the optical cavity is in combination with a reflective polarizer film.

18. The article of claim 2, wherein the structure is a sign cabinet comprising walls and a light source, wherein at least one of the walls is lined with the diffuse reflective material.

19. The article of claim 2, wherein the structure is a light conduit comprising an optical lighting film, at least one of a back reflector and an extractor, wherein the back reflector, the extractor or both comprise the diffuse reflective material.

20. The article of claim 2, wherein the diffuse reflective article comprises a fluorescent compound.

21. A method of improving diffuse reflectivity of light comprising using a diffuse reflective material to cause light energy to reflect off of it, wherein the material comprises a porous polymeric sheet containing at least one surface element positioned to reduce optical coupling with a substrate, the sheet comprising a network of polymeric material having voids therein which material comprises:

(a) a polymer component, and

(b) a diluent component, said diluent component being miscible with the polymer component at a temperature above the melting point of the polymer component or a liquid-liquid phase separation temperature of a total solution of polymer and diluent.

22. The method of claim 21, wherein the polymer component is selected from the group consisting of polypropylene and polyethylene.

23. The method of claim 21, wherein the diluent component is mineral oil.

24. A method of making an article comprising a diffuse reflective material configured for positioning proximate to a structure, the method comprising:

providing a polymer component;

providing a diluent component, said diluent component being miscible with the polymer component at a temperature above the melting point of the polymer component or liquid-liquid phase separation temperature of the total solution of polymer and diluent;

combining the polymer component and diluent component to form a porous polymeric sheet having a first thickness; and

applying a force to the porous polymeric sheet to form a sheet having a second thickness.

25. The method of making an article according to claim 24, wherein the step of applying a force to the porous polymeric sheet comprises applying a mechanical force.

26. The method of making an article according to claim 24, wherein the step of applying a force to the porous polymeric sheet comprises calendering the porous polymeric sheet.

27. The method of making an article according to claim 24, wherein the article has a second thickness that 70 to 85 percent of the first thickness.

28. The method of making an article according to claim 24, wherein the article has a second thickness of from 150 to 300 μ

m.

29. The method of making an article according to claim 24, wherein the article has one or more elements configured to reduce optical coupling with a substrate.

30. A reflective article comprising a reflective material proximate to a structure, wherein the reflective article comprises a first surface having a surface element configured to reduce optical coupling with the structure.

31. The reflective article of claim 30, wherein the reflective article is a specular reflector.

32. The reflective article of claim 30, wherein the reflective article is a diffuse reflector.