Optical: systems and elements – Polarization without modulation – Glare prevention by discriminating against polarized light
Reexamination Certificate
2000-02-04
2001-07-31
Spyrou, Cassandra (Department: 2872)
Optical: systems and elements
Polarization without modulation
Glare prevention by discriminating against polarized light
C359S487030, C359S494010, C359S490020, C359S506000, C359S599000, C359S900000, C349S084000, C349S096000
Reexamination Certificate
active
06268961
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to optical films, devices containing the optical films, and methods of using and making the optical films. The invention also relates to optical films having at least one particle-containing layer, devices containing the optical films, and methods of using and making the optical films.
BACKGROUND OF THE INVENTION
Polymeric films are used in a wide variety of applications. One particular use of polymeric films is in reflective polarizers which reflect light of one polarization for a given wavelength range and substantially pass light of the orthogonal polarization. Such reflective polarizers are used, for example, in conjunction with backlights in liquid crystal displays to enhance brightness of the display. For example, a reflective polarizer can be placed between a backlight and a liquid crystal display panel. This arrangement permits light of one polarization to pass through to the display panel and light of the other polarization to recycle through the backlight or to reflect off a reflective surface positioned behind the backlight, giving the light an opportunity to depolarize and pass through the reflective polarizer.
One example of a polarizer includes a stack of polymer layers of differing composition. One configuration of this stack of layers includes a first set of birefringent layers and a second set of layers with an isotropic index of refraction. The second set of layers alternates with the birefringent layers to form a series of interfaces for reflecting light. Another type of reflective polarizer includes continuous/disperse phase reflective polarizers that have a first material dispersed within a continuous second material that has an index of refraction for one polarization of light that is different than the corresponding index of the first material. Other types of reflective polarizer include wire grid polarizers and polarizers formed using birefringent cholesteric materials.
SUMMARY OF THE INVENTION
Generally, the present invention relates to optical films, devices containing the optical films, and methods of using and making the optical films. The invention also relates to optical films having at least one particle-containing layer, devices containing the optical films, and methods of using and making the optical films.
One embodiment is an optical film including a reflective polarizing element and a surface layer. The reflective polarizing element substantially reflects light having a first polarization state and substantially transmits a second polarization state. The surface layer is disposed on the reflective polarizing element and in a same optical path as the reflective polarizing element. The surface layer is configured and arranged to transmit light and includes a plurality of particles that roughen an exterior surface of the surface layer. Preferably, using the optical film in an optical device does not substantially reduce the gain advantage of the optical device when compared with an optical device utilizing the same optical film without particles in the surface layer.
The surface layer can be disposed on the reflective polarizing element by a variety of methods including, for example, coating or otherwise depositing the surface layer after forming the reflective polarizing element. Alternatively, the reflective polarizing element and surface layer can be formed together (e.g., coextruded). Substantially all or only a portion of the particles in the surface layer can be exposed or projecting from the surface layer. In at least some instances, substantially all of the particles can be embedded within the surface layer while still roughening an exterior surface of the surface layer.
Another embodiment is an optical device containing the optical film. The optical device also includes at least a light source or display medium (e.g., a liquid crystal display medium). In at least some optical devices, the reflective polarizing element and surface layer are disposed between a light source and a display medium and, in at least some of these devices, the surface layer is positioned between the reflective polarizing element and the display medium.
Yet another embodiment is a method of making the optical film described above. The reflective polarizing element is formed to substantially reflect light having a first polarization state and substantially transmit light having a second polarization state. The surface layer is formed on a first major surface of the reflective polarizing element. The surface layer includes particles that roughen an exterior surface of the surface layer.
A further embodiment of the invention is an optical film including a reflective polarizing element and a particle containing layer disposed on the reflective polarizing element. The reflective polarizing element substantially reflects light having a first polarization state and substantially transmits light having a second polarization state. The particle containing layer is disposed in the same optical path as the reflective polarizing element and is configured and arranged to transmit light. The particle-containing layer includes a plurality of particles that roughen an exterior surface of the optical film. The particle-containing layer can be a surface layer of the optical film or a cover layer can be disposed over the particle-containing layer with the particle-containing layer roughening the exterior surface of the cover layer.
The above summary of the present invention is not intended to describe each disclosed 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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Cross Elisa M.
Hebrink Timothy J.
Horn Robert W.
Kallman Guy M.
Kausch William L.
3M Innovative Properties Company
Burtis John A.
Jr. John Juba
Spyrou Cassandra
LandOfFree
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