1. Field of the Invention
The present invention relates to a pressure-sensitive resistor which has a pressure-sensitive conductor, and which detects pressures based on contact-resistance variations in accordance with the applied pressure.
2. Description of the Related Art
Hitherto, pressure-sensitive resistors are widely used in various pressure sensors, keyboard switches, automatic-door switches, and pressure-contact switches.
FIG. 11 is a diagram showing a conventional pressure-sensitive resistor.
In FIG. 11, the numeral 50 indicates an upper film, 51 indicates an lower film, 52 indicates an Ag electrode pattern formed on the lower film 51, 53 indicates an Ag electrode pattern formed on the upper film 50 so as to oppose the Ag electrode pattern 52, and 54 indicates a pressure-sensitive conductor formed on the Ag electrode pattern 53 by application. Here, the lower film 51 and upper film 50 are disposed such that the Ag electrode pattern 52 can come into contact with the pressure-sensitive conductor 54.
The pressure-sensitive conductor 54 is formed with an elastomer comprising an insulating rubber material, and conductive particles mixed therein. Accordingly, when the pressure-sensitive conductor 54 is pressed, the intervals between the conductive particles in the pressure-sensitive conductor 54 are narrowed, and the resistance of the conductor is lowered. In summary, the pressure-sensitive conductor 54 exhibits the pressure-sensitive characteristics in which the resistance decreases relative to an increase in applied pressure.
In such a conventional pressure-sensitive resistor, when the upper film 50 is pressed, the pressure-sensitive conductor 54 situated between a pair of the Ag contacting patterns 52 and 53 is compressed. At this time, the resistance can be detected by a pair of the Ag contacting patterns 52 and 53, and the applied pressure corresponding to the resistance can be read from a graph showing the pressure sensitivity characteristics.
In the meantime, in conventional pressure-sensitive resistors, their pressure-sensitive characteristics are determined depending on the material of the pressure-sensitive conductor. Accordingly, when pressure-sensitive resistors respectively having different pressure-sensitive characteristics (pressure-resistance characteristics) should be produced, the materials for their pressure-sensitive conductors must be altered. Due to this, obtaining various pressure-sensitive resistors of various pressure-sensitive characteristics has been difficult.
Further, although printing is preferred to form a pressure-sensitive conductor in view of cost-saving, desired pressure-resistance characteristics can rarely be achieved by printing since the pressure-resistance characteristics of the pressure-sensitive conductor vary depending on its thickness.