1. Field of the Invention
The present invention relates to an input device and an input device manufacturing method and, more particularly, to an input device in which an electrode layer is disposed on a substrate having a two-dimensional or three-dimensional curved surface and a method for manufacturing such an input device.
2. Description of the Related Art
In various information processing apparatuses, light-transmissive input devices are disposed in front of display panels, such as color liquid crystal panels. These input devices are referred to as touch panels. In touch panels, capacitance is formed between electrodes. Coordinates of a position to which a person's finger is brought close are determined from a change in a movement of electric charges that occurs when the finger approaches. A capacitive sensor is used to detect this change in a movement of electric charges.
In recent years, display devices that display information on two-dimensional or three-dimensional curved surfaces have appeared. Touch panels are also required to be mounted in a shape matching such curved display surfaces.
Japanese Unexamined Patent Application Publication No. 2012-242871 and U.S. Patent Application Publication No. 2010/0103138 disclose curved touch panels and methods for manufacturing such curved touch panels. A curved touch panel described in Japanese Unexamined Patent Application Publication No. 2012-242871 is manufactured in the following manner. An electrode layer including a plurality of electrode regions is formed on a thermoplastic resin plate by using an electrically conductive ink containing an electrically conductive substance and a binder to create a patterned plate. The patterned plate is heated, and the softened patterned plate is shaped into a soft curved product. The soft curved product is cooled or is allowed to cool. Consequently, a touch panel is produced as a curved product.
U.S. Patent Application Publication No. 2010/0103138 discloses that a curved touch panel is manufactured by bending a flat flexible printed circuit board having a touch sensor function and then bonding this curved flexible printed circuit board and a curved substrate to each other.
However, in the case where touch panels have curved surfaces, an optical issue (so-called iridescence) occurs because of optical anisotropy of a panel material. To deal with such an optical issue, a material having optical isotropy can be used as the panel material. However, materials having optical isotropy are fragile and are unsuitable for a layer desired to be thin. For example, the sensitivity is desirably increased by decreasing a distance between a sensor electrode and a touched surface as much as possible in capacitive touch sensors. Thus, a surface-side layer is desirably made as thin as possible. However, the use of a material having optical isotropy for this layer causes an issue that the layer easily cracks. On the other hand, it is conceivable to make the thickness of the surface-side layer relatively thin by increasing a distance between sensor electrodes while maintaining the thickness of the surface-side layer. However, this configuration increases the thickness of the entire input device.