Elliptical diffuser

• US 5,473,454 A
• Filed: 04/24/1995
• Issued: 12/05/1995
• Est. Priority Date: 06/02/1993
• Status: Expired due to Fees

• Current Assignee: Palomar Technologies Incorporated
• Original Assignee: Hughes Aircraft Company (Rtx Corporation)
• Inventors: Blanchard, Randall D.
• Primary Examiner(s): Lerner, Martin
• Application Number:
  US08/427,303
• Time in Patent Office: 225 Days
• Field of Search: 359/599, 359/452-456, 359/69
• US Class Current: 349/112
• CPC Class Codes: G02B 5/0226 having particles on the surface
• CPC Class Codes: G02B 5/0242 by means of dispersed particles
• CPC Class Codes: G02B 5/0257 creating an anisotropic diffusion characteristic, i.e. distributing output differently in two perpendicular axes
• CPC Class Codes: G02B 5/0268 characterized by the fabrication or manufacturing method
• CPC Class Codes: G02B 5/0278 used in transmission
• CPC Class Codes: G02F 1/133606 including a specially adapted diffusing, scattering or light controlling members

Abstract

A display screen of a projection system embodying a cathode ray tube, liquid crystal light valve, laser or the like is formed of a plastic sheet (22, 22a) that has embedded therein a number of microsphere diffuser particles (24, 24a) initially having a spherical shape and distributed in a uniformly isotropic density. The plastic sheet and its embedded particles are heated and stretched in a single direction and allowed to cool in their elongated form so that the diffuser particles (24a) then have an elongated elliptical shape and a density that is greater along one axis than it is along an orthogonal axis. The particle elongation and decreased density in the direction of stretch cause the diffusing sheet to have a diffusion cone angle (44), as measured in a plane containing the axis of stretch, that is significantly decreased, but with increased screen gain, whereas the diffusion angle (42) in the orthogonal unstretched direction remains relatively large, and also has an increased screen gain. The decreased diffusion angle is oriented in a vertical direction in a common display because the viewer'"'"'s eye, in looking at a display screen, is most commonly positioned within a relatively small vertical cone angle, although the horizontal angle of view may be considerably larger.

Claims

1. A diffuser comprising:

a transparent acrylic substrate, having first and second mutually angulated axes defining first and second directions, and

a plurality of acrylic diffuser particles of consistent, uniformly spherical configuration and size carried by said substrate, said particles being elongated in said second direction, said substrate further comprising a sheet of transparent polymeric light diffuser material having uniformly spherical microspheres of approximately seven microns in diameter embedded therein, wherein said acrylic substrate'"'"'s thickness and a concentration of the acrylic diffuser particles has an approximately linear relationship, said sheet being stretched in a second direction, said microspheres being elliptically deformed and elongated in said second direction.

2. A diffuser screen made by the steps of:

providing a sheet of acrylic plastic having acrylic diffusing microspheres of at least seven microns in diameter embedded therein and uniformly dispersed through said sheet, wherein said sheet of acrylic plastic'"'"'s thickness and a concentration of the acrylic diffusing microspheres has an approximately linear relationship, and

stretching said sheet in a first direction to increase distances between adjacent microspheres in said one direction without substantially changing distances between said microspheres in a second direction transverse to said first direction, and to elongate said microspheres in said first direction.

3. The diffuser screen of claim 2 wherein said step of stretching comprises clamping said sheet between first and second mutually spaced bars, heating said sheet and microspheres, moving said bars away from each other to stretch said microspheres and sheet while heated, and cooling said microspheres and sheet while they remain stretched to thereby set said microspheres and sheet in stretched condition.

4. The diffuser of claim 3 wherein said step of clamping comprises grasping said sheet at first and second edges to exert tension on said sheet while said bars are moved away from each other and while said sheet is cooling, and grasping said sheet at third and fourth edges while said bars are moved away from each other.

5. A diffuser comprising:

a sheet of stretched transparent material,

a plurality of elliptically deformed microspheres embedded in said sheet, said microspheres being elongated in a first direction and spaced from one another by relatively larger distances in said first direction and by relatively smaller distances in a second direction, said sheet of transparent material comprising first and second sections having adjoining edges that are cut at an angle and bonded to one another to maintain precision of effective thickness of the joined sections for maintaining optical performance of diffusion at the adjoining edges.

6. A diffuser comprising:

a transparent polymeric light diffuser substrate that is stretched in a first one of first and second mutually orthogonal directions and not narrowed in said second direction,

a plurality of acrylic diffuser particles of consistent, uniformly spherical configuration and size embedded in said substrate, wherein said substrate'"'"'s thickness and a concentration of said diffuser particles has an approximately linear relationship, said diffuser particles comprising a plurality of elliptically deformed microspheres of at least seven microns in diameter that are elongated in said first direction, said elliptically deformed microspheres being spaced from one another in said first direction by distances that are substantially greater than the distances between particles in said second direction.

7. A diffuser comprising:

a transparent substrate that is stretched in a first one of first and second mutually orthogonal directions and not narrowed in said second direction wherein said transparent substrate comprises first and second stretched sheets, each stretched in said first direction and each having adjacent slanted edges, said slanted edges being bonded to each other with the slanted edges abutted against each other to form a diagonal point having an effective thickness that maintains optical performance of diffusion over said joint; and

a plurality of diffuser particles embedded in said substrate, said particles comprising a plurality of elliptically deformed microspheres that are elongated in said first direction, said elliptically deformed microspheres being spaced from one another in said first direction by distances that are substantially greater than the distances between particles in said second direction.

8. A diffuser comprising;

a transparent substrate that is stretched in a first one of first and second mutually orthogonal directions and not narrowed in said second direction, wherein said transparent substrate comprises first and second stretched sheets, each stretched in said first direction and each having adjacent slanted edges, said slanted edges being bonded to each other with the slanted edges abutted against each other to form a diagonal point having an effective thickness that maintains optical performance of diffusion over said joint, wherein each of said slanted edges includes first and second slanted portions interconnected by a rebated portion, said slanted and rebated portions of the edges of said first and second sheets being mutually overlapped and bonded together; and

a plurality of diffuser particles embedded in said substrate, said particles comprising a plurality of elliptically deformed microspheres that are elongated in said first direction, said elliptically deformed microspheres being spaced from one another in said first direction by distances that are substantially greater than the distances between particles in said second direction.

9. A rear projection screen, comprising:

a liquid crystal display panel having front and rear surfaces;

at least one layer of transparent acrylic substrate having first and second mutually angulated axes defining first and second directions, and a plurality of acrylic diffuser particles carried by said substrate, wherein said substrate'"'"'s thickness and a concentration of said diffuser particles has an approximately linear relationship, said particles being elongated in said second direction, said substrate further comprising a sheet of transparent polymeric light diffuser material having seven micron microspheres embedded therein, said sheet being stretched in a second direction, said microspheres being elliptically deformed and elongated in said second direction mounted upon the rear surface of the liquid crystal display panel;

said substrate having the concentration of between 20 and 30 percent of said diffuser particles to a material thickness of approximately one half after stretching.

10. A back lighted liquid crystal display panel, comprising:

a liquid crystal display panel having a front and a rear surface;

a transparent acrylic substrate elliptical diffuser sheet having first and second mutually angulated axes defining first and second directions, and a plurality of acrylic diffuser particles carried by said substrate, wherein said substrate'"'"'s thickness and a concentration of said diffuser particles has an approximately linear relationship said particles being elongated in said second direction, said substrate further comprising a sheet of transparent polymeric light diffuser material, having seven micron microspheres embedded therein, said sheet being stretched in a second direction, said microspheres being elliptically deformed and elongated in said second direction mounted upon the rear surface of the liquid crystal display panel, said diffuser sheet layered upon said rear surface of said liquid crystal display panel;

at least one lamp illuminating said diffuser sheet; and

at least one reflector reflecting said lamp.