Liquid crystal cells – elements and systems – Nominal manufacturing methods or post manufacturing... – Sealing of liquid crystal
Reexamination Certificate
1999-10-29
2003-11-04
Parker, Kenneth (Department: 2871)
Liquid crystal cells, elements and systems
Nominal manufacturing methods or post manufacturing...
Sealing of liquid crystal
C349S153000, C349S189000
Reexamination Certificate
active
06642991
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to the field of substrates, and more particularly, to the field of using absorbing materials in substrates, the substrates being coupled together by a means for cohering or like means for cohesively laminating so as to significantly decrease or eliminate water or like liquid buildup or condensation between the coupled substrates.
BACKGROUND OF THE INVENTION
Liquid crystal display (LCD) devices are well known in the art and are useful for many applications in numerous industries (such as, for example, the avionics, consumer goods and the computer industries). Several types of LCD substrates are in production. The manufacture of LCD substrates typically require capturing a thin layer of liquid crystal between two pieces of transparent substrates, such as glass or plastic, forming a liquid crystal cell. When an electric field is applied, the field alters the molecular alignment of the liquid crystal, thus affecting the light that is passed through the crystal. This phenomena turns small windows of light known as pixels (picture elements) “on” and “off.” LCD displays are usually light-weight, require low power and provide precise viewing resolution. Further, LCD displays are now manufactured as rigid substrates or flexible substrates.
The liquid crystal must be in a particular orientation, or oriented in the correct direction, to operate properly. The orientation of the liquid crystal is achieved in the manufacturing process by rubbing the two plates with a polymer, creating parallel furrows. The most common type of LCD on the market today is a passive form in which all the pixels in each row are tied together, thus reducing the need to control each pixel independently. But, that means the pixels remain in a state between on and off, resulting in a loss of contrast. It also produces annoying ghost images, especially of moving objects, in either the rigid substrate or the flexible substrate form.
Researchers have been struggling for years to develop cost-efficient active displays in which each pixel is controlled by its own transistor. Active matrix displays are now available on laptops, but they are expensive to manufacture, partly because the transistors can be so easily damaged during the fabrication of the display screen. Some technologies not currently on the market could potentially reduce the cost, including ferroelectric liquid crystal cells (in which a thin film transistors would be used to control the pixels individually). In a ferroelectric screen, each pixel would be either on or off, thus producing an image that is light and dark, like the numbers on a digital watch.
Fabrication of LCD displays has proven extremely difficult, often resulting in low yields and thus, higher costs. When the polymer is rubbed across the film of transistors to provide alignment for the liquid crystal, it may cause mechanical damage and electrostatic charges that can potentially damage the transistors. The yield of the transistors then decreases drastically, which affects the price of the finished LCD display substrate. And, because of the sensitivity of such screens, the screens must be protected, usually by adhering another substrate (such as a glass cover of equivalent dimensions) to the LCD substrate. Moreover, another advantage of employing another substrate is that it increases optical performance. An optical coating (such as an anti-reflective coating) may also optionally be coated on to the substrate which is coupled or otherwise adhered to the LCD display.
One method of adhering a protective substrate to the LCD cell (active and passive plate combination) is known as the “gravity pour” method. In this method, a clean LCD cell is placed immediately adjacent to a clean protective substrate at a 90 degree vertical angle so that the LCD substrate and the protective substrate are parallel to each other and in close proximity to each other. Bond tape (such as VHB high bond tape manufactured by Minnesota Mining and Manufacturing), similar to double-sided tape, is then applied to the periphery edges of the LCD substrate (typically within 0.060 inches from the outer periphery). The LCD substrate with cover glass attached is preferably oriented at approximately 90 degrees from horizontal. Then, the two substrates are precisely brought together so that the bond tape provides a seal between the periphery edges of the two substrates. In this construct, an air gap or air cell is created between the two substrates of known width (usually 0.025 inches to 0.045 inches apart, which are the typical commercial widths available for bond tape). Then, silicone or another like optical coupling material is poured between the two substrates along an opening in the top edge of the tape-bonded substrates and allowed to slowly permeate between the substrates by gravitational forces. Another opening (usually also located at the top edge) is also required to allow the air volume to escape from the air gap as the pour process continues. This gravitational pour process usually takes more than an hour and may or may not be successful in completely filling the entire air gap between the bonded substrates. The viscous fluid typically employed has a characteristic viscosity of about 150 cps, but can go as high as 4500 cps.
The problems associated with using the pour prior art adhesion process, however, are numerous. First, adhesive optical materials bond the substrates together to form an almost permanent, rigid planar beam. And, for example, filling all the air cell space between the two substrates is difficult due to the viscosity of the adhesion fluid which often leads to visible air volume space or air bubble formation between the substrates. Further, this process is slow, which means that unless the timing is precise for the complete permeation of the air gap with fluid, those optical fluids which undergo a chemical cure will do so before the substrate adhesion process is complete (since most viscous fluid pot life is in the range of 15 minutes to 1 hour). Thus, if the fluid cures too quickly before the gravity pour process is complete, it may require repeated pour processes, unusable substrates, partially bonded substrates or damaged substrates. The position of the substrates at 90 degrees also introduces substantial friction between the two substrates, which reduces the even flow of viscous fluid between the substrates during the injection process. And, because the gravity pour method results in inconsistent permeation, the final substrate does not always possess uniformity of throughout the substrate. Moreover, other manufacturers in the art have used fluids or UV cured adhesives or optical epoxies to optically couple substrates, however the gap between the substrates is very small as to transmit the axial deflection directly to the LCD substrate, which causes optical distortions which can persist. Finally, if the gravity pour process is not executed precisely under careful conditions, the two substrates, after bonding, sometimes exhibit a bowl shape in the middle of the substrates due to increased hydrostatic pressure, leading to an unusable LCD substrate.
U.S. patent application Ser. No. 09/410,888 commonly-owned by the assignee of the present invention, discloses a novel method for optically coupling substrates together. The two substrates are then sealed adjacent to each other by a means for sealing. A means for optically coupling (such as an optically clear fluid) is then de-gassed to remove any dissolved or remaining gas within the means. Then, a pressurized means for injecting (such as a pressurized syringe) is filled with the de-gassed means for optically coupling, while a means for exhausting the means for optically coupling is provided through the means for bonding along a top edge of the bonded substrates. The method requires providing two clean substrates and positioning each at approximately a 20 degree angle (or an incline of various ranges) parallel to each other and in close proximity to each other. The pressurized means for injecting then in
Hogue Robert B.
Krum David D.
Panuska Brian R.
Chung David Y.
Honeywell International , Inc.
Parker Kenneth
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