Light directing film having variable height structured surface and light directing article constructed therefrom

• US 5,771,328 A
• Filed: 04/03/1997
• Issued: 06/23/1998
• Est. Priority Date: 03/03/1995
• Status: Expired due to Term

• Current Assignee: Minnesota Mining and Manufacturing Co (3M Company)
• Original Assignee: Minnesota Mining and Manufacturing Co (3M Company)
• Inventors: Cobb, Sanford Jr., Gardiner, Mark E., Wortman, David L.
• Primary Examiner(s): Bovernick, Rodney B.
• Assistant Examiner(s): Sanghavi, Hemang
• Application Number:
  US08/832,132
• Time in Patent Office: 446 Days
• Field of Search: 385/146, 385/147, 385/901, 385/36, 359/831, 359/833, 359/834-836, 359/528, 359/837, 362/309, 362/327, 362/339, 362/32, 428/30, 349/57, 349/62, 349/64, 349/65
• US Class Current: 385/146
• CPC Class Codes: B29D 11/00788 Producing optical films
• CPC Class Codes: F21V 5/02 of prismatic shape F21V5/04 takes precedence
• CPC Class Codes: G02B 5/0221 the surface having an irregular structure G02B5/0226 takes precedence
• CPC Class Codes: G02B 5/0231 the surface having microprismatic or micropyramidal shape macroscopic prism arrays G02B5/045
• CPC Class Codes: G02B 5/0278 used in transmission
• CPC Class Codes: G02B 5/045 Prism arrays
• CPC Class Codes: G02B 6/0053 Prismatic sheet or layer; Brightness enhancement element, sheet or layer
• CPC Class Codes: G02B 6/0055 Reflecting element, sheet or layer
• CPC Class Codes: Y10S 385/901 Illuminating or display apparatus

Abstract

A light directing film including a first surface and a second structured surface. The structured surface includes a repeating pattern of prism zones including at least a first zone having a plurality of prism elements with peaks disposed at a first distance from a reference plane and a second zone having a plurality of prism elements with peaks disposed less than the first distance from a reference plane. The width of the first zone preferably measures less than about 300 microns.

Claims

1. A light directing film comprising a first surface;

a structured surface opposite said first surface and having an array of prism elements, each prism element having opposing facets which intersect at a peak, said array including a repeating pattern of prism zones, the pattern including at least;

a first zone that measures less than about 300 microns in width and comprising a first prism element having a peak defining a first dihedral angle and disposed at a first distance from a reference plane disposed between the structured surface and the first surface; and

a second zone that measures between 200 and 4000 microns in width adjacent said first zone and comprising a second prism element having a peak defining a second dihedral angle substantially equal to the first dihedral angle and disposed at a second distance from the reference plane, said second distance being less than said first distance, whereby, when the structured surface of said light directing film is placed adjacent a planar surface, optical coupling occurs primarily in said first zone.

2. The light directing film of claim 1, wherein:

said first distance measures between 1 micron and 175 microns.

3. The light directing film of claim 1, wherein:

said second distance measures between 0.5 microns and 174.5 microns.

4. The light directing film of claim 1, wherein:

said second distance is at least about 0.5 microns less than said first distance.

5. The light directing film of claim 1, wherein:

said second distance is less than said first distance by at least about 1.0 wavelength of light.

6. The light directing film of claim 1, wherein:

said second distance is less than said first distance by at least about 2.0 wavelengths of light.

7. The light directing film of claim 1, wherein:

said second distance is between about 33 and 95 percent of said first distance.

8. The light directing film of claim 1, wherein:

said second zone includes a plurality of prisms having peaks disposed at different heights above the reference plane.

9. A light directing article comprising:

a first sheet of light directing film having a first surface and a structured surface opposite said first surface, said structured surface including a linear array of prism elements oriented along a first major axis, said array including a repeating pattern of prism zones, the pattern including at least a first zone that measures less than about 300 microns in width comprising a first prism element having a peak defining a first dihedral angle and disposed at a first distance from a reference plane and a second zone that measures between 200 and 4000 microns in width adjacent said first zone and comprising a second prism element having a peak defining a second dihedral angle substantially equal to the first dihedral angle and disposed at a second distance from the reference plane which is less than said first distance, the reference plane being disposed between the structured surface and the first surface;

a second sheet of light directing film having a substantially planar surface disposed adjacent said first sheet of light directing film and having a structured surface opposite said substantially planar surface having a linear array of prism elements oriented along a second major axis;

said first major axis intersecting said second major axis within a predetermined angular range, whereby, optical coupling between said first sheet and said second sheet occurs primarily in said first zone.

10. An optical display, comprising:

a light source;

a viewing screen;

light transfer means for directing light from said light source to said viewing screen, said light transfer means including at least a first sheet of light directing film, said film including a first surface and a structured surface opposite said first surface and having an array of prism elements, each prism element having opposing facets which intersect at a peak, said array including a repeating pattern of prism zones, said pattern including at least;

a first zone that measures less than about 300 microns in width and comprising at least a first prism element having a peak defining a first dihedral angle and disposed at a first distance from a reference plane located between the structured surface and the first surface; and

a second zone that measures between 200 and 4000 microns in width adjacent said first zone and comprising at least a second prism element having a peak defining a second dihedral angle substantially equal to the first dihedral angle and disposed at a second distance from the reference plane, said second distance being less than said first distance, whereby, when the structured surface of said light directing film is placed adjacent a planar surface, optical coupling occurs primarily in said first zone.