Method of Preparing Alignment Layer for Use in Liquid Crystal Devices Using In-Situ Ultraviolet Exposure
KSU.177 – Method of Preparing Alignment Layer for Use in Liquid Crystal
Devices Using In-Situ Ultraviolet Light Exposure
In displays and other electro-optical devices based on liquid crystals (LC), previous common methods for alignment of the LC on substrates used by industry have various shortcomings: (1) in the rubbing method static charge and mechanical stress often lead to damage and particulate impurities and are detrimental to performance; (2) in conventional photo-alignment the anchoring energy and thermal stability are often poor; and (3) vacuum deposition methods can be cumbersome. This invention provides a method of preparing a LC alignment layer while using the conventional polyimides. Instead of first subjecting the alignment layer to prebake and bake cycle to cause imidization and then expose to UV light, this combines two steps into one. Exposure to polarized light is conducted during the bake cycle. Since the polymer chains are not frozen in their orientation at baking temperatures, they are free to reorient and adopt the lowest energy conformation and orientation. The resultant films have much higher anchoring energies than the conventional photo-alignment layers. Another major advantage is that they are thermally more stable. Since the method combines two steps, its use will save time necessary to produce a device.
Applications: Any device requiring alignment of liquid crystal on a substrate.
• Single step process: higher productivity, low cost
• Non-contact method: no damage to active devices, no dust to affect performance
• Strong anchoring and higher thermal stability compared to the conventional photoalignment methods
• Easily adoptable for alignment in multi-domain devices
• Easily implementable on existing manufacturing lines
Inventors: Jae-Hoon Kim and Satyendra Kumar
Patent Status: U.S. Patent 5,936,691
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