Stock material or miscellaneous articles – Liquid crystal optical display having layer of specified... – With bonding or intermediate layer of specified composition
Reexamination Certificate
1998-11-18
2002-04-30
Copenheaver, Blaine (Department: 1772)
Stock material or miscellaneous articles
Liquid crystal optical display having layer of specified...
With bonding or intermediate layer of specified composition
C428S001100, C428S001500, C428S001520, C349S153000, C349S190000
Reexamination Certificate
active
06379759
ABSTRACT:
BACKGROUND OF THE INVENTION
1 Field of the Invention
The present invention relates to a sealing agent useful for liquid crystal displays using a plastic film or sheet as a substrate, and to a liquid crystal display using the sealing agent.
2 Discussion of the Background
Liquid crystal displays are widely used as display devices for personal computers, word processors and the like because they are thin and light weight, and consume low power. Among these liquid crystal displays, displays in which glass is used as the substrate of their liquid crystal cells have been typically used (hereinafter referred to as glass type LCDs). Currently, as so-called “mobile devices” are developed and liquid crystal displays are used in the mobile devices, liquid crystal display cells in which a plastic film or sheet is used as the substrate (hereinafter referred to as film type LCDs) have been increasingly used because of their light weight, good flexibility, and resistance to being easily crushed.
Liquid crystal displays are used while liquid crystal is sealed with a sealing agent in a substrate of the liquid crystal displays. The sealing agent preferably has good adhesive strength so as not to be destroyed by a stress applied to the liquid crystal displays using the sealing agent. In addition, the sealing agent is required not to adversely affect molecules of the liquid crystal contacting the sealing agent. Further, the sealing agent which is used for liquid crystal displays having a plastic film substrate preferably has flexibility because the displays are used while they are bent. Furthermore, the sealing agent which is used for liquid crystal displays useful for mobile devices is required to have maximum heat resistance. Thermosetting epoxy resins have been typically used as a sealing agent for liquid crystal displays. In film type LCDs, the crosslinking temperature of the sealing agent cannot be set to be as high as for glass type LCDs because the film or sheet substrate has relatively poor heat resistance compared to the glass substrate. Therefore the sealing agent for the film type LCDs has a drawback of poor heat resistance.
In addition, film type LCDs are required to have flexibility, which glass type LCDs are not required to have. Therefore sealing agents which are different in kind from those used for glass type LCDs have been used for film type LCDs, or sealing agents which are the same kind as those used for glass type LCDs have been used while being crosslinked at a relatively low temperature compared to that for the glass type LCDs. When such film type LCDs are preserved at a high temperature, which is a requisite for the sealing agent, liquid crystal tends to impregnate into the sealing agent, and thereby the sealing agent swells, resulting in decrease of the adhesive strength of the sealing agent layer (a problem hereinafter termed “poor resistance to liquid crystals”). In addition, in this case, the switching current of the liquid crystal tends to increase because of the mixing of the sealing agent in the liquid crystal, resulting in malfunction of the film type LCDs (a problem hereinafter termed “a liquid crystal contamination problem”). Therefore a need exists for a sealing agent having good reliability, without causing these problems.
In attempting to solve these problems, Japanese Laid-Open Patent Publication No. 62-18523 discloses polyol type epoxy resins serving as a sealing agent for film type LCDs. The sealing agent has good flexibility and adhesive strength; however, the sealing agent swells and the switching current of the liquid crystal gradually increases when the film type LCD using the sealing agent is preserved at about 80° C. Thus, this sealing agent cannot entirely address the problem of poor heat resistance.
Japanese Laid-Open Patent Application No. 9-12679 discloses a sealing agent for film type LCDs which includes as the essential components 10 to 50 parts by weight of a silicone-modified epoxy resin which is liquid at room temperature, 90 to 50 parts by weight of a bisphenol type epoxy resin which is also liquid at room temperature, 20 to 80 parts by weight of a trifunctional thiol type crosslinking agent which is also liquid at room temperature, 0.5 to 5.0 parts by weight of a silane coupling agent, 1 to 10 parts by weight of amorphous silica having an average particle diameter not greater than 1 &mgr;m, and 5 to 50 parts by weight of an inorganic filler other than amorphous silica, which has an average particle diameter not greater than 2 &mgr;m. However, the sealing agent also does not entirely improve the heat resistance because the switching current of the liquid crystal gradually increases when the film type LCD using the sealing agent is preserved at about 80° C.
Because of these reasons, a need exists for a sealing agent for film type LCDs which has good flexibility and good heat resistance as well as good resistance to liquid crystals. In addition, a need exists for a film type LCD which successfully addresses the problems mentioned above.
SUMMARY OF THE INVENTION
Accordingly, an object of the present invention is to provide a sealing agent useful for film type LCDs which has good flexibility and good heat resistance as well as good resistance to liquid crystals even when the cells of the film type LCDs are manufactured by an assembling method including heat treatment at a conventional heating temperature.
Another object of the present invention is to provide a film type LCD which uses the above-mentioned sealing agent and which has good heat resistance and good resistance to liquid crystals, and successfully addresses a liquid crystal contamination problem.
Briefly these objects and other objects of the present invention as hereinafter will become more readily apparent can be attained by a sealing agent which includes at least epoxy ingredients of a bisphenol type epoxy resin and a non-bisphenol type epoxy resin, and crosslinking agent ingredients of an aromatic amine compound and/or an alicyclic amine compound.
The non-bisphenol type epoxy resin preferably includes an alcohol type epoxy resin, a polysulfide modified epoxy resin or a silicone oil modified epoxy resin.
The sealing agent preferably includes a crosslinking catalyst including an acid.
In another aspect of the present invention, a film type LCD which includes a plastic film substrate in which a liquid crystal is sealed with the sealing agent mentioned above is also provided.
DETAILED DESCRIPTION OF THE INVENTION
Other features of the invention will become apparent in the course of the following descriptions of preferred embodiments, which are given for the purpose of illustration only and are not intended to be limiting.
The present inventors discovered that the above-described problems can be solved by a sealing agent which includes epoxy ingredients including specified epoxy resins, and a crosslinking agent including a specified amine compound.
In detail description, it was discovered that the resistance to liquid crystals and the liquid crystal contamination problem can be successfully addressed by a sealing agent including a bisphenol type epoxy resin, and an aromatic amine type crosslinking agent and/or an alicyclic amine type crosslinking agent. The reason is considered to be that the bisphenol type epoxy resin has a high cohesive force due to having aromatic rings therein and is inactive because of having a high glass transition temperature; thereby the epoxy resins tend to be hardly impregnated with molecules of liquid crystal, resulting in improvement of the resistance to liquid crystals and the liquid crystal contamination problem. By using an aromatic amine and/or alicyclic amine as a crosslinking agent, this effect can be enhanced.
The combination of the bisphenol type epoxy resin and the crosslinking agents of the aromatic amine and/or the alicyclic amine, however, has a drawback in that the resultant sealing agent becomes too hard after crosslinking and tends to be peeled from a substrate when the substrate is stressed.
It was also discovered that this peeling problem
Kamoi Sumio
Mochizuki Yumi
Yoshikawa Masao
Chevalier Alicia
Copenheaver Blaine
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
Ricoh & Company, Ltd.
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