Diffuse reflective articles

• US 5,976,686 A
• Filed: 10/24/1997
• Issued: 11/02/1999
• Est. Priority Date: 10/24/1997
• Status: Expired due to Term

• Current Assignee: 3M Innovative Properties Company (3M Company)
• Original Assignee: 3M Innovative Properties Company (3M Company)
• Inventors: Harvey, John C., Pojar, Stephen J., Gagnon, David R., Epstein, Kenneth A., Waller, Clinton P. Jr., Kaytor, Scott R., Strand, Neal T., Hibbard, William A.
• Primary Examiner(s): ZIRKER, DANIEL R
• Application Number:
  US08/957,558
• Time in Patent Office: 739 Days
• Field of Search: 428/315.5, 428/315.7, 428/316.6, 428/317.9, 428/318.4, 428/319.1, 359/599, 359/515, 362/341
• US Class Current: 428/317.9
• 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: 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 6/0065 Manufacturing aspects; Material aspects
• CPC Class Codes: G02B 6/0096 the lights guides being of the hollow type
• CPC Class Codes: Y10T 428/249978 Voids specified as micro
• CPC Class Codes: Y10T 428/249979 Specified thickness of void-containing component [absolute or relative] or numerical cell dimension
• CPC Class Codes: Y10T 428/249981 Plural void-containing components
• CPC Class Codes: Y10T 428/249986 Void-containing component contains also a solid fiber or solid particle
• CPC Class Codes: Y10T 428/249987 With nonvoid component of specified composition
• CPC Class Codes: Y10T 428/24999 Inorganic

Abstract

Diffuse reflective materials attached 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 attached to a structure capable of holding a diffuse reflective sheet material in place for use as a reflector wherein said diffuse reflective material is made of a porous polymeric sheet characterized by a microstructure comprising a network of polymer domains and fibrils interconnecting the domains, in which network the number of fibrils is not predominant over the number of polymer domains, as shown in FIG. 13.

2. A diffuse reflective article comprising a diffuse reflective material attached to a structure capable of holding a diffuse reflective sheet material in place for use as a reflector wherein said diffuse reflective material is made of a porous polyolefin sheet comprising a network of polymer domains and fibrils interconnecting the domains.

3. A diffuse reflective article comprising a diffuse reflective material attached to a structure capable of holding a diffuse reflective sheet material in place for use as a reflector 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.

4. The diffuse reflective article of claim 3 wherein the porous polymeric sheet has a reflectivity greater than 92% at a wavelength of 550 nm according to ASTME 1164-94.

5. The article of claim 3, 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.

6. The article of claim 3, wherein the polymer component is substantially non-absorbing to light at a wavelength between 380 and 730 nanometers.

7. The article of claim 3, wherein the polymer component is selected from the group consisting of polypropylene and polyethylene.

8. The article of claim 3, wherein the diluent component is substantially non-absorbing to light at a wavelength between 380 and 730 nanometers.

9. The article of claim 3, wherein the diluent component is mineral oil.

10. The article of claim 3, further comprising a specular reflective layer in combination with the porous polymeric layer.

11. The article of claim 3, wherein the structure is an optical cavity with the diffuse reflective material lining a portion of the cavity facing a light source.

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

13. The article of claim 12 further comprising a brightness enhancing film.

14. The article of claim 12, further comprising a reflective polarizer film.

15. A sign cabinet comprising walls and a light source, wherein at least one of the walls is lined with a diffuse reflective material 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 solution of polymer and diluent.

16. A light conduit comprising an optical lighting film, at least one of a back reflector and an extractor, which is a strip of material placed against the interior side of the optical lighting film of the light conduit to cause light to exit the conduit, wherein the back reflect or, the extractor or both comprise a diffuse reflective material 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 solution of polymer and diluent.

17. 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 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.

18. The method of claim 17, wherein the polymer component is selected from the group consisting of polypropylene and polyethylene.

19. The method of claim 17, wherein the diluent component is mineral oil.