Stock material or miscellaneous articles – Composite – Of epoxy ether
Reexamination Certificate
2002-03-20
2003-12-09
Dawson, Robert (Department: 1712)
Stock material or miscellaneous articles
Composite
Of epoxy ether
C428S413000, C428S414000, C428S426000, C428S427000, C428S428000, C428S447000, C428S443000, C523S001000
Reexamination Certificate
active
06660387
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a display device substrate to be used in the production of panels for display devices, particularly liquid crystal display devices and organic EL devices. More particularly, the present invention relates to a display device substrate which is lighter in weight and less liable to break than the conventional one.
The recent rapid development in computer networks and digital communications has involved an even larger number of personal users in the advanced information society having information networks as one of its bases, and it has created the need for diversification and sophistication, of networks and components thereof.
As a result, conventional desktop personal computers are required to have not only an improved information processing capability (including an improved data display performance), but also a new ability to access networks freely and easily through a portable telephone or portable information terminal. Such portable information equipment is expected to function as a platform that provides various applications in which image information is involved in addition to its original functions.
Improvements required of portable information equipment (or terminals) in its fundamental performance include faster transmission speeds for networking, a larger data processing capacity, a better display visibility, lighter weight, and easier handleability and transportability.
Such requirements are applicable also to the flat panel display (such as liquid crystal display device and organic EL device), which is major component of portable information equipment. Improvements sought are reduction in weight and thickness and high-density display (or high definition display).
Attempts have been made to meet such sophisticated and diversified requirements. For example, in the case of a liquid crystal display (LCD), one way to meet requirements for reduction in weight and thickness is to manufacture the LCD panel from a thinner substrate than before. Glass substrates are commonly used in the LCD technology. Therefore, the above-mentioned requirements will be met to some extent by manufacturing the LCD panel from thin glass substrates. Unfortunately, glass suffers the disadvantage of being broken easily by impact due to dropping or external pressure. Therefore, further reduction in thickness would be difficult to achieve from the standpoint of an LCD's impact resistance and breakage prevention.
Glass sheets now available for LCD panels have a thickness of 1.1 mm, 0.7 mm, 0.5 mm, or 0.4 mm (with 0.7 mm being common) according to “Liquid Crystal Device Handbook” (Chapter 4, Section 4.2, page 218, compiled by Japan Society for the Promotion of Science, issued in 1989 by Nikkan Kogyo Shimbunsha). A glass sheet with a thickness of 0.4 mm is difficult to handle in the LCD manufacturing process because of its liability for chipping and breakage, which leads to reduced yields. At present, reduction to about 0.3 mm is considered to be the maximum that can be achieved for display device glass substrates.
Another way under study for improvement in the technical field of an LCD is replacement of glass sheets by plastics sheets, as disclosed in Japanese Patent Laid-open No. 6-175143. Plastics sheets can be made thinner than glass sheets on account of their flexibility (hence providing good crack resistance) and high resistance to dropping impact and external pressure. Plastics sheets have a specific gravity of 1.2-1.4, whereas glass sheets have a specific gravity of 2.3. Therefore, an LCD with a substrate made of a plastic sheet is lighter and thinner than that with a substrate made of a glass sheet.
Unfortunately, plastics sheets usually have a lower transmission for visible light and a higher rate of gas permeability than glass sheets. The latter property poses a problem with foaming in liquid crystal inside the panel.
Plastics sheets with good gas barrier properties should necessarily be thick, and this means that such plastics sheets have a poor light transmission, giving rise to a dark display. Therefore, the resulting LCD based on use of a plastics sheet is inferior in visibility to the conventional LCD based on use of a glass sheet.
In addition, plastics sheets are inferior in heat resistance to glass sheets. At high temperatures, they are subject to discoloration (decrease in light transmission) and deformation (such as bending and warpage). Therefore, production of an LCD with a plastics sheet should be carried out at low temperatures. This makes it necessary to develop new materials usable at low temperatures, such as the sealing agent to bond together paired substrates, with a liquid crystal interposed between them, and an alignment film to align the liquid crystal.
Moreover, a plastics sheet suffers another disadvantage in that it is difficult to form an electrode film thereon from low-resistance ITO (indium-tin oxide) at high temperatures. ITO varies in resistance or conductivity depending on its film-forming temperature. Thus, the disadvantage of an LCD based on use of a plastics sheet is that finely patterned ITO electrodes have a high resistance, which is detrimental to a high definition display.
The conventional plastics sheet does not withstand heat encountered in the process of producing TFTs (thin film transistors) necessary for a high-quality LCD of the active matrix drive type. Thus, it is difficult to form TFTs on a plastics sheet, and hence it is difficult to realize a high-quality display by means of an active matrix drive so long as the LCD is formed with a substrate made of a plastics sheet.
Thus, an LCD formed with a plastics sheet is not comparable to that formed with a glass sheet in producing a high definition display. Thus, it will not be able to display moving pictures.
A third improvement in the technical field of the LCD is to form the display device from a laminate substrate consisting of a pair of glass sheets and a plastics sheet held between them, as disclosed in Japanese Patent Laid-open Nos. 7-43696, 7-49486, and 7-287218. A conventional three-layered laminate substrate used for LCD panels is shown in section in FIG.
1
. It consists of a pair of glass sheets
101
and
102
and a soft plastics sheet
103
held between them.
The advantage of the laminate substrate is that the plastics sheet has improved heat resistance owing to the presence of the outer glass sheets. On the other hand, the plastics sheet is usually made of polyvinyl butyral (which is comparatively soft), as disclosed in Japanese Patent Laid-open No. 7-43696, so that the plastics sheet produces no stress in the glass sheets laminated onto both sides thereof.
If an extremely thin plastics sheet (100 &mgr;m or so) is used to reduce the total thickness of the substrate, it produces the effect of preventing the glass sheet from shattering when the substrate is broken, but it will not produce the effect of improving impact resistance or preventing the glass sheet from being broken.
It is understood from the foregoing that the conventional technology still has problems to be solved and that there is room for improvement before it is applied to the current flat panel display (LCD and organic EL device).
In order to realize a flat panel display (LCD and organic EL device) with improved performance (including light weight, small thickness, and high definition display), which will be necessary for moving pictures in the future, it is necessary to develop a new technology which fully utilizes the features of a glass sheet and a plastics sheet, but eliminates their disadvantages.
More specifically, the flat panel display according to the new technology should have high heat resistance (ascribed to glass) and light weight and small thickness (ascribed to plastics) and better impact resistance than glass.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a new display device substrate which meets the requirements for reduction in weight and thickness and improvement in gas barrier properties, heat resistance, an
Amagi Shigeo
Hanawa Yasuo
Kondou Katsumi
Oaku Hitoshi
Oishi Tomoji
Dawson Robert
Zimmer Marc S
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