Light reflector with variable diffuse light reflection

Abstract

Disclosed is a diffuse reflector polymeric film comprising a macro reflection efficiency variation. The invention provides improved light reflection for a back lit display while simultaneously diffusely reflecting specular light sources.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS [0001] This application is a continuation-in-part or U.S. Ser. No. 10 / 147,775 filed May 16, 2002, which parent application was co-filed with Ser. Nos. 10 / 147,703; 10 / 147,776; 10 / 147,777; and 10 / 147,659; the contents of all of which are incorporated herein by reference.FIELD OF THE INVENTION [0002] The invention relates to a diffuse reflector comprising a macro reflection efficiency variation which serves to diffuse specular light. In a preferred form, the invention relates to a variable back light diffuse reflector for transmission, transflection, and reflection type rear projection liquid crystal display devices. BACKGROUND OF THE INVENTION [0003] Reflectors are often used in optical displays, such as liquid crystal displays, to even out illumination across the display and to diffusely reflect the light from the backlight or light coming in the display from the environment. Prior art reflectors include planar specular reflectors and planar di...

AI Technical Summary

Benefits of technology

[0023] The invention provides a diffuse reflector polymeric film comprising a macro reflection efficiency variation visible to the naked eye, including a reflective layer that has a reflectivity at 500 nanometers of greater than 50%. The invention also provides a diffuse reflector for rear projection displays, back-li

Problems solved by technology

The backlight consumes a relatively large amount of power.

This display does not use a backlight reducing the amount of required power but the ambient light reflection cannot produce satisfactory brightness for vivid color images and is used on calculator and other text displays.

One problem with currently available transflective displays is that they have good performance in either reflective or transmissive mode, but not both.

This stems from the fact that the backlight assembly is not as efficient a diffuser / reflector as the back reflector and diffuser traditionally used in a purely reflective display, and the display thus appears less bright when viewed under ambient light.

These reflectors tend to need high levels of reflection efficiency causing light to be scattered at a wide angle across the entire film, where the light is scattered around the edges of the film and lost.

In this prior art method of evening illumination, printing is a very costly and time consuming because each light guide is screen printed individually.

The primary disadvantages of the above methods of roughening a reflective surface is that they either do not make the surface rough enough or they do not make the roughness random enough to enable the surface to function as an isotropic diffuse reflector.

EDM is cost and time prohibitive to make diffuse reflectors on a large scale.

The TIPS diffuse reflector can not deliver as high a reflectivity as a metallized surface.

The light scattering regions of the TIPS diffuse reflector are on the order of the wavelength of light and could add color to the light diffused thus imparting a non-desirable coloration to the display.

Voided films with TiO2 typically have diffuse reflectance measurements of 85 to 88% at 500 nm making them inferior to the variable diffuse reflectors without inorganics that have more efficient diffuse reflectances.

Also, voided films tend to be thicker and therefore add weight to the display device.

The fine control of a shape such as an inclined angle of the convex-concave is difficult, with the result that a sufficient light scattering cannot be obtained.

These methods described are labor and time intensive, use hazardous materials, and must be made in a sheet as instead of rolls making them prohibitively expensive.

The engraving process has many limitations including misalignment causing tool lines in the surface, high price, and lengthy processing.

This method is difficult to apply to create a master chill roll to manufacture complex random three-dimensional structures and is also cost prohibitive.

This procedure to form a master to create three-dimensional features into a plastic film is time consuming and cost prohibitive.

While the materials and methods disclosed in this patent are suitable for reflective photographic products, the % light energy transmission (less than 40%) is not suitable for liquid crystal display as % light transmission less than 40% would unacceptable reduce the brightness of the LC device.

These micro-structures can be non-uniform across the lens to minimize certain lens aberrations.

These non-uniform micro-structures reduce lens aberrations, but are not able to significantly alter the macro-optical characteristics of the optical body.

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