Liquid crystal cells – elements and systems – Particular structure – Having significant detail of cell structure only
Reexamination Certificate
1999-08-31
2002-07-09
Sikes, William L. (Department: 2871)
Liquid crystal cells, elements and systems
Particular structure
Having significant detail of cell structure only
C349S123000, C349S117000
Reexamination Certificate
active
06417899
ABSTRACT:
This invention relates to a liquid crystal display including at least-one polarizer. More particularly, this invention relates to a liquid crystal display (LCD) including at least one polarizer located between opposing substrates of the display.
BACKGROUND OF THE INVENTION
In conventional liquid crystal displays (LCDs), polarizers are typically positioned exterior or outside of opposing substrates of the display. For example, see certain illustrations in U.S. Pat. No. 5,499,126 (i.e. the '126 patent), the disclosure of which is incorporated herein by reference. As shown in the '126 patent, conventional LCDs include a liquid crystal (LC) layer sandwiched between first and second opposing glass substrates. In turn, the combination of the glass substrates and liquid crystal layer is disposed between first and second polarizers. Thus, typical LCD polarizing layers are positioned on the outside or exterior of the glass substrates, while color filters are positioned interior of the substrates.
In conventional LCDs, color filters are often located on the passive or viewer-side glass substrate and positioned between the polarizers and also between the opposing substrates. For example, as shown in
FIGS. 20 and 21
of the '126 patent, red, green, and blue color filters are located on the interior of one of the glass substrates. Thus, the color filters are positioned both (a) between the opposing glass substrates, and (b) between the opposing polarizers.
Because color filters have a de-polarizing effect on light passing through a display due to pigment light scattering, light proceeding through conventional displays is at least partially de-polarized by the color filter(s) before reaching the analyzer (or viewer side polarizer). Unfortunately, de-polarizing of light prior to the light reaching the analyzing or viewer side polarizer can reduce contrast ratio of a display. Even though such de-polarizing effects are small, they do have a significant effect on a display's contrast ratio. This is especially true for advanced LCD compensation displays (i.e. displays having retarders for improving viewing characterisitics) which have increased contrast ratio over viewing angle (e.g. as disclosed in U.S. Pat. No. 5,739,881). In sum, de-polarizing effects caused by color filter(s) which occur prior to the viewer side polarization are undesirable because of the potential for significantly reducing contrast ratio of the display and the display's overall viewing characteristics.
A conventional approach to reducing adverse effects of color filter de-polarizing is the dispensement of smaller dye pigments in color filter material. Unfortunately, this requires a significant effort in chemical formulation, and cannot completely eliminate adverse effects of color filter de-polarizing.
Another problem of conventional LCDs is that the provision of polarizing layers on the outside or exterior of a display's substrates renders the polarizer(s) susceptible to degrading environmental conditions such as humidity and salt. It would be desirable if polarizers were not exposed to such environmental conditions.
Prior art or conventional polarizers are often mass-produced in roll form. For example, a roll of polymeric material, e.g. polyvinyl alcohol, may be dyed with dichroic material. Orientation of the polymer and dichroic molecules may be achieved by heating the dyed polymer and stretching it in the lengthwise or long direction of the roll. The result is a conventional stretched anisotropic light absorbing film with an absorption or optical axis (for polarizing) parallel to the stretching direction. A disadvantage of such a stretching manufacturing method of making polarizers is that the absorption or optical axis of the resulting polarizer(s) is typically parallel to the long direction of the roll. This orientation of the axis typically creates at least a 30% material yield loss for twisted nematic LCD applications. Such material waste results from cutting display-sized polarizer sheets from a polarizer roll at, for example, a 45° angle relative to the roll edge so that the polarizer absorption axis is not parallel to a side or edge of the polarizer. For example, in certain twisted nematic LCD applications, the polarizer absorption axis is typically positioned or aligned at a 45° angle relative to an edge of the display in order to achieve symmetric horizontal gray scale linearity (e.g. see the front page of the '126 patent). Thus, prior art stretching methods of manufacturing polarizers are undesirable.
Polarizer International LLC has disclosed an internal polarizer of liquid crystalline material. The polarizer may be positioned interior of an LCD's substrates. Unfortunately, shearing is typically required in order to define some type of axis in such polarizers. The use of shearing is impractical and inefficient in LCD fabrication processes, and furthermore cannot be used to pattern or pixelate polarizers.
It will be apparent from the above that there exists a need in the art for an improved liquid crystal display (LCD) including at least one (and potentially more than one) polarizer located between substrates of the display. This will reduce environmental hazards to polarizing material, improve contrast ratios exhibited by the display(s), result in an easier to make polarizer, etc. Still further, there exists a need in the art for an LCD including a polarizer positioned internal of color filter(s) so that the polarizer on the viewer side of the display may be positioned between the color filter(s) and the liquid crystal material in order to prevent adverse color filter de-polarizing effects from occurring prior to viewer side polarization. There also exists a need in the art for a non-stretching method for making polarizers for use in LCDs.
The term “interior” or “internal” as used herein means on the side or surface closest to the nematic liquid crystal material to which voltage is selectively applied via pixel electrodes. For example, if something is said to be positioned or located on the “interior” or “internal” side of a substrate, then it is positioned or located on the side of the substrate closest to the liquid crystal (LC) layer. Also, for example, the phrase “on the substrate” does not mean that it is located directly on the substrate, but only that it is ultimately supported by the substrate at some point during the manufacturing process.
This invention will now be described with respect to certain embodiments thereof, accompanied by certain illustrations.
SUMMARY OF THE INVENTION
Generally speaking, this invention fulfills the above described needs in the art by providing a liquid crystal display comprising:
a liquid crystal layer sandwiched between first and second substrates;
a plurality of color filters disposed between said liquid crystal layer and said first substrate;
an internal polarizer disposed between (i) said liquid crystal layer, and (ii) said color filters, in order to reduce adverse effects of depolarization caused by said color filters.
This invention further fulfills the above described needs in the art by providing a polarizer structure for use in a liquid crystal display, the polarizer structure comprising:
a substantially transparent substrate;
an alignment layer provided on said substrate, said alignment layer defining a polarizer alignment direction; and
a polarizer layer on said substrate so as to be in direct contact with said alignment layer so that an optical axis of said polarizer layer is oriented in a direction dictated by said alignment direction defined by said alignment layer.
This invention further fulfills the above described needs in the art by providing a liquid crystal display comprising:
first and second substrates;
a liquid crystal layer positioned between said first and second substrates;
at least one electrode for selectively applying a voltage to said liquid crystal layer;
first and second polarizers positioned in a manner such that said first and second substrates are located in between said first and second polari
Jones Michael R.
Zhong John Z. Z.
Chowdhury Tarifur R.
Guardian Industries Corp.
Michael Best & Friedrich LLC
Saret Larry L.
Sikes William L.
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