Computer graphics processing and selective visual display system – Display peripheral interface input device – Touch panel
Reexamination Certificate
2000-05-08
2003-01-14
Chow, Dennis-Doon (Department: 2675)
Computer graphics processing and selective visual display system
Display peripheral interface input device
Touch panel
C345S174000, C178S018050
Reexamination Certificate
active
06507337
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to a touch panel, and particularly relates to a touch panel that has two resistance members facing each other with a certain space in between and that detects a touched position by measuring resistence between each standard point of the two resistance members and a contact point.
BACKGROUND OF THE INVENTION
Recently, personal digital assistants (PDA), sub-notebook personal computers, and the like have been used as portable data terminals. For such data terminals, portability and ease of use are taken into account. In general, as an input device of such a data terminal, a resistence-member touch panel is set on a display device such as a liquid crystal display. Input operations in the data terminal are executed by touching the surface of the resistance-member touch panel by a finger or pen. The touched position is detected as X-Y coordinates.
The resistance-member touch panel has a touch substrate that is used in input operations and a display substrate. The touch substrate is made of polyethylene terephthalate, polycarbonate, or poly methacrylate resin that is transparent. For protection, a light-hardening acrylate resin film is formed on either or both of surfaces of the resin. The display substrate is made of soda-lime glass or tempered glass. The surface of each substrate, that is facing the other substrate, is covered by a thin layer of indium/tin oxide (referred to as “ITO” hereinafter) as a transparent conductive layer.
The touch panel requires high transparency in a visible-light region and, especially the transmittance of light with a wavelength of 550 nm or so needs to be high. To achieve the high transparency for the touch panel, an appropriate metal oxide can be inserted between the conductive substrate (in this case, the touch substrate or display substrate) and the transparent conductive layer, according to an well-known technique. Hereinafter, the inserted metal oxide is referred to as the “undercoat layer.” The technique is specifically explained. A metal oxide layer of silicon dioxide (SiO
2
) or of silicon dioxide/tin oxide base (SnSiO
x
, for example) is formed between each substrate and the corresponding transparent conductive layer. In this case, the conductive layer, the metal oxide layer, and the film are formed so that their refractive indexes becomes high-low-high or low-high-low in this alternate order in the arrangement. By means of this alternation, the transparency of the touch panel is improved. In general, the light reflectivity is high in areas of the touch panel that are in contact with air, and this is the main factor that decreases the light transmittance. On this account, the technique has a profound significance although it is not further explained in detail in this specification.
As stated above, the transparent conductive substrate is composed of: a substrate that is made of polyethylene tetephthalate, polycarbonate, poly methacrylate resin or glass; an undercoat layer that is made of an insulating metal oxide, such as SiO
2
, and is directly formed on the substrate; and a transparent conductive layer formed on the undercoat layer. In this construction, a contact level (or, a degree of adhesion) is low between the substrate and the undercoat layer. As such, after the transparent conductive substrate has been left under high temperature and high humidity for long hours or when it comes in contact with any kind of alcohol or alkaline solution, the transparent conductive layer easily comes off the substrate. In this way, the transparent conductive substrate is poor in environment resistance and solution resistance.
When pressure is given to the touch panel through an input operation, a liquid crystal layer of the liquid crystal display directly receives the pressure. This may cause jitter on the liquid crystal layer and so may impair the display function. To avoid this problem, a bond layer is provided on a non-display area (an outer region) of the liquid crystal display, and the touch panel is fixed to the liquid crystal display via this bond layer. By the medium of the bond layer, there would be a space between the touch panel and the liquid crystal display. As such, it should be obvious that the display substrate definitely requires an appropriate rigidity against the pressure.
The following are mainly required as characteristics of the touch panel that is provided for a portable data terminal.
(1) high transparency
(2) high resistance against mechanical impact and friction caused when the touch panel is touched in an input operation
(3) high suitability for reduction in thickness and weight
(4) high impact-resistance (so that the substrate and the like will not be broken when the data terminal is dropped)
(5) wide operating temperature
(6) appropriate rigidity
The characteristics described in (1) and (2) can be achieved at the practically required level through: improvements to the technique of forming a transparent conductive layer on the touch substrate made of polyethylene terephthalate and on the display substrate made of glass; insertion of appropriate inorganic metal oxide or resin layer between the touch substrate and the transparent conductive layer; and formation of an appropriate resin layer onto the surface of the touch substrate (this resin layer is referred to as the “hard coat layer” hereinafter).
As to the characteristics described in (3) and (4), the reduction in thickness and weight is limited when only conventional techniques are used. As one example, suppose that glass is used for the display substrate. In this case, even if tempered glass instead of typical soda glass is used, a metal frame for impact absorbency or a transparent resin sheet as a reinforcing material needs to be attached to the surface of the tempered glass. As long as glass is used, it may be impossible to keep the glass from being broken when a strong mechanical impact is given.
To address this problem, it has been suggested that the glass should be replaced with a transparent resin film, such as polycarbonate or polymethyl methacrylate, that is relatively thin and has a proper rigidity.
There are roughly two ways to construct the display substrate when the transparent conductive layer such as ITO is formed on the transparent resin film replacing the glass substrate.
One way is to form the transparent conductive layer directly onto one side of the transparent resin film. Note that the transparent resin film in this example serves as a supporting member formed from material, such as polycarbonate or polymethyl methacrylate. This construction is referred to as the “single-piece construction” that includes the transparent conductive layer and the supporting member.
The other way is achieved by the construction that is referred to as the “multilayer construction” hereinafter. As described above, the transparent resin film is made up of polycarbonate or polymethyl methacrylate whose one side is covered by the transparent conductive layer. In this multilayer construction, a transparent resin sheet, such as polycarbonate or. polymethyl methacrylate, covers the non-conductive surface of the transparent conductive resin, with an acrylic base bond layer being set in between. The transparent resin sheet serves as a supporting member to give the rigidity to the display substrate. Thus, the multilayer construction of the display substrate includes, from above, the transparent conductive layer, transparent resin film, bond layer, and supporting member.
In the case of the single-piece construction, an organo-siloxane layer that has a bridging construction is inserted between the supporting member and the transparent conductive layer such as ITO. By doing so, a transparent conductive resin film is realized, which has: durability that is practically required to withstand friction caused from input operations; high adhesion with the transparent conductive layer; transparency; proper rigidity; and heat resistance.
In general, transparent conductive layers are formed according to the vacuum film-thinning technique, such as t
Furukawa Shuji
Noda Kazuhiro
Sato Hirotoshi
Tanimura Kohtaro
Chow Dennis-Doon
Gunze Limited
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