Mobile information terminals equipped with a display and a transparent touch panel as an input device are becoming more common. A resistive transparent touch panel mostly used as the transparent touch panel is configured such that two transparent electrode substrates, each having a transparent electroconductive layer thereon, are disposed so as to have respective transparent electroconductive layers facing to each other with a gap of about 10 to 100 μm therebetween, and thereby the surfaces of transparent electroconductive layers come into contact with each other only at a portion in which external force is applied. This configuration enables the two transparent electrode substrates to work as a switch. In such a touch panel, for example, a menu can be selected and graphics and letters can be written.
Recently, the frame size of a liquid crystal display body or the like is small, and also the frame size of a transparent touch panel small. With this reduction in the frame size, an edge-pressing durability, i.e. writing durability in the edge of the transparent touch panel, has become desirable for a transparent touch panel, in addition to writing durability which is conventionally required.
In order to improve the writing durability which is required for a transparent touch panel, Patent Documents 1 to 3 have proposed a transparent electroconductive laminate fabricated by laminating two transparent polymer films by an adhesive or transparent resin layer having a specific hardness (or Young's modulus). In any of these methods, two transparent polymer films are laminated through an adhesive or a transparent resin layer, and this causes a problem that the production process is complicated and the production efficiency is low, although a writing durability is improved. Moreover, when a large transparent touch panel exceeding 10 inches is produced, the transparent electroconductive laminate is disadvantageously flexed due to structurally low rigidity.
Patent Document 4 has proposed a resistive touch panel capable of mass production and reduction in the production cost, which is a touch panel characterized in that at least one transparent electrode film is formed of a transparent electroconductive polymer material such as thiophene-based electroconductive polymer or polyaniline-based electroconductive polymer. In Patent Document 4, a laminate of an ITO film and a transparent electroconductive polymer film is also proposed. However, for example, a transparent electroconductive laminate using an electroconductive polymer material as the transparent electrode has a problem that contact resistance obtained when transparent electroconductive layers are in contact with each other in the transparent touch panel is large, and therefore the transparent touch panel does not work, or a problem that transmittance and environmental reliability cannot be ensured.
Patent Document 5 has proposed a touch panel wherein an electroconductive fine particle-containing polymer layer is formed on a transparent electrode surface of a transparent substrate, and Patent Document 6 has proposed a technique of forming a metal and/or metal oxide thin film as an electroconductive layer by a vacuum deposition method, an ion plating method or a sputtering method, and then laminating thereon a coating material having electrical conductivity.
In the transparent touch panel using a transparent electroconductive laminate proposed in Patent Documents 4 to 6, a cured resin layer is not provided between the transparent electroconductive layer and the polymer film. Therefore, when a polyethylene terephthalate generally used as a movable electrode substrate of a transparent touch panel is used as the polymer film, oligomer components are disadvantageously mitigated from the polymer film after a heat treatment and the like. Furthermore, since the properties of the transparent electroconductive layer are not specified, there is a problem that when such a transparent electroconductive laminate is used for a transparent touch panel, writing durability necessary for a transparent touch panel cannot be ensured.
Patent Document 1: Japanese Unexamined Patent Publication No. 2-66809
Patent Document 2: Japanese Unexamined Patent Publication No. 2-129808
Patent Document 3: Japanese Unexamined Patent Publication No. 8-192492
Patent Document 4: Japanese Unexamined Patent Publication No. 2005-182737
Patent Document 5: Japanese Unexamined Patent Publication No. 7-219697
Patent Document 6: Japanese Examined Patent Publication No. 3-48605