Illumination – Light modifier – Refractor
Reexamination Certificate
1999-02-09
2001-11-27
Cariaso, Alan (Department: 2875)
Illumination
Light modifier
Refractor
C362S019000, C362S330000, C362S331000, C385S901000
Reexamination Certificate
active
06322236
ABSTRACT:
BACKGROUND
The present invention is directed generally to a light transmissive film, and particularly to a film that reduces the incidence of defects in a display.
The use of films for displays is well known. For example, in backlit displays, brightness enhancement films use a prismatic structure to direct light along the viewing axis, thus enhancing the brightness of the light perceived by the viewer. As another example, a backlit computer display screen may use a number of different films in order to produce a screen with high contrast and high overall brightness, while simultaneously maintaining high, uniform brightness in certain selected directions and lower brightness in other directions. Such screens may use several types of films, such as diffusing films, in combination with a prismatic film or a lenticular film.
One problem with using films in a display is that the cosmetic requirements for a display intended for close viewing, such as a computer display, are very high. This is because such displays are viewed closely for long periods of time, and so even very small defects may be detected by the naked eye, and cause distraction to the viewer. The elimination of such defects can be costly in both inspection time and in materials.
Defects are manifested in several different ways. There are physical defects such as specks, lint, scratches, inclusions etc., and also defects that are optical phenomena. Among the most common optical phenomena are “wet-out” and Newton's rings. “Wet-out” occurs when two surfaces optically contact each other, thus effectively removing the change in refractive index for light propagating from one film to the next. This is particularly problematic for films that use a structured surface for their optical effect, since the refractive properties of the structured surface are nullified. The effect of “wet-out” is to create a mottled and varying appearance to the screen. Newton's rings are the result of a slowly varying air gap between two films, as may be created by a particle of dust between two films. Newton's rings may be formed in transmission or in reflection. The result of Newton's rings is that the viewer perceives a contour pattern on the screen that may be distracting.
Several approaches have been followed to overcome the problem of defects in multiple-film display assemblies. One is simply to accept a low yield of acceptable display assemblies produced by the conventional manufacturing process. This is obviously unacceptable in a competitive market. A second approach is to adopt very clean and careful manufacturing procedures, and impose rigid quality control standards. While this may improve the yield, the cost of production is increased to cover the cost of clean facilities and inspection.
Another approach to reducing defects is to introduce a diffuser to the display, either a surface diffuser or a bulk diffuser. Such diffusers may mask many defects, and increase the manufacturing yield at low additional cost. However, the diffuser scatters light and decreases the on-axis brightness of light perceived by the viewer, thus reducing the performance.
There continues to be a need to reduce the occurrence of defects in displays, so that the manufacturing yield may be improved with little additional cost while, at the same time, maintaining performance.
SUMMARY OF THE INVENTION
Generally, the present invention relates to a surface on a film that may be used to reduce the occurrence of optical defects in a display that uses the film. In particular, the surface has randomized characteristics that reduce such defects as wet-out, Newton's rings, and Moiré effects. The invention also relates to a method for making the film, a tool used for making the film, and a method of making the tool.
In one embodiment the film has a first surface free of regular structure, the first surface having a plurality of local height maxima, a characteristic measure of the first surface having a random value within a predetermined range. The film also has a second surface opposing the first surface. A method of making an optical film includes embossing a pattern lacking regular structure onto a first surface of a film wherein the first surface has a plurality of local height maxima, a characteristic measure of the first surface having a random value within a predetermined range. The characteristic measure may be a difference between the actual heights and a nominal height of the film surface, average separation between the local height maxima on the surface, or slope angle of the first surface proximate a local height maximum.
In another embodiment, the invention includes a film having an anti-wet-out surface on a first surface having no regularly refractive structure, and a second surface opposing the first surface. In another embodiment, the film includes a first surface, and wet-out reducing means disposed on the first surface for reducing wet-out between the first surface and another optical surface.
In another embodiment of the invention, an optical device includes a light source, and a film having an anti-wet-out surface on a first surface having no regularly refractive structure. A second optical component has a second surface opposing the first surface, and light from the light source passes through the film and the second optical component.
In another embodiment of the invention, a method of making an optical film includes forming an anti-wet-out surface on a first surface of the optical film.
In another embodiment of the invention, a method of making a drum for embossing a surface on a film includes rotating a drum around a rotation axis relative to a cutting tool, cutting the surface of the drum with the cutting tool, and randomly varying a cutting characteristic of the cutting tool to produce characteristic variations lying randomly within a predetermined range. A drum for embossing a surface on a film includes a surface free of regular structure and having a plurality of local height minima, a characteristic measure of the surface having a random value within a predetermined range.
The above summary of the present invention is not intended to describe each illustrated embodiment or every implementation of the present invention. The figures and the detailed description which follow more particularly exemplify these embodiments.
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Campbell Alan B.
Cobb, Jr. Sanford
Kretman Wade D.
McKee Andrew
3M Innovative Properties Company
Cariaso Alan
Miller William D.
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