Illumination – Light modifier – Refractor
Reexamination Certificate
1997-05-09
2001-08-28
Cariaso, Alan (Department: 2875)
Illumination
Light modifier
Refractor
C362S330000, C362S339000, C359S456000, C359S599000, C349S064000, C349S112000
Reexamination Certificate
active
06280063
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to enhancing the on-axis luminance (referred to here as “brightness”) of a diffuse lighting device.
Displays used in devices such as computers feature a material such as a liquid crystal composition and a light source for back-lighting the material. Films disposed between the back light and the display have been used to enhance the brightness of the display by controlling the exit angles of light.
SUMMARY OF THE INVENTION
In general, the invention features a brightness enhancement article that includes: (a) a transparent, flexible substrate; (b) a first major surface that includes an array of linear prisms having blunted or rounded peaks; and (c) a second major surface characterized by a plurality of light scattering protrusions. These protrusions imbue the surface with a matte appearance. The peaks are characterized by a chord width, cross-sectional pitch width, and radius of curvature in which the chord width is equal to about 20-40% of the cross-sectional pitch width and the radius of curvature is equal to about 20-50% of the cross-sectional pitch width. The article has a haze value between about 20-60% and a transmission value no greater than about 94% when measured under conditions in which the first surface has a substantially planar topography.
The prisms are preferably characterized by a root angle ranging from about 70° to about 110°, more preferably from about 85° to about 95°. Root angles of about 90° are particularly preferred.
In one preferred embodiment, the second major surface is integral with the substrate (e.g., the protrusions may be in the form of “bumps” made of the substrate material). In another preferred embodiment, the second major surface is defined by a layer that includes a resin provided on the substrate. Where the second major surface is defined by a separate resin layer, the protrusions may be in the form of particles dispersed in the resin layer, or may be integral with the resin layer itself (e.g., they may be in the form of “bumps” made of the resin).
In one preferred embodiment, the first major surface of the article is integral with the substrate. In such embodiments, the haze and transmission values are measured by applying a material such as an index-matching oil to the first major surface to fill in the “valleys” between the blunted or rounded peaks to render the surface substantially planar.
In another preferred embodiment, the first major surface is defined by a separate layer that includes a resin provided with the above-described prisms. In such embodiments, the haze and transmission values are measured on the article prior to application of this resin layer.
The invention also features a method of enhancing the brightness of a uniform, diffusely-emitting, lighting device that includes placing the above-described brightness enhancement article substantially parallel to a light-emitting surface of the device. The invention further features a uniform, diffusely-emitting, lighting device that includes the above-described brightness enhancement article. Examples of preferred devices include back-lit displays such as back-lit liquid crystal displays.
The invention provides a brightness enhancement article having a matte appearance that exhibits good gain, wide viewing angles in both horizontal and vertical planes, soft cut-off, and good abrasion resistance. The matte appearance also helps mask cosmetic imperfections in the article, as well as the device with which the article is used, such as scratches, white spots, and stains which may arise during manufacture or installation.
Other features and advantages of the invention will be apparent from the following description of the preferred embodiments thereof, and from the claims.
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Cobb, Jr. Sanford
Fong Bettie C.
Kotchick Keith M.
Kretman Wade D.
Miller Richard A.
3M Innovative Properties Company
Buckingham Stephen W.
Cariaso Alan
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