Pan Pacific Symposium Conference Proceedings


Authors: Kiwako Ohmori, et al.
Company: Fujikura Ltd., Aomori Fujikura Kanaya Ltd., Fujikura Kasei Co., Ltd.
Date Published: 1/24/2008   Conference: Pan Pacific Symposium

Abstract: Pressure sensitive sensors are utilized in a wide electronics industry field. Under such an expectation, the authors have been developed membrane type new pressure sensitive sensor which has an excellent environmental characteristic and a wider dynamic range compared with conventional sensors. This is a kind of membrane switch which is formed by using pressure sensitive paste which has high specific resistance and has a feature that the contact resistance is changed continuously depending on the pressure at the contact. The key elements is that the membrane type sensor has a cost advantages because of the simple manufacturing process which is using screen printing on the plastic film base, by the other hand the weakness is the instability of the characteristics by the temperature and humidity conditions.

In general the pressure sensitive paste is composed with the binder and the conductive filler and the resin filler. The resin filler controls surface resistance by making surface rough. Though the current binder has good adhesion and flexibility, the polymer bonding chains is cut in severe environmental condition. It is thought that the polymer chain maintains the conductive filler’s distribution, accordingly the conductivity become unstable. The authors have developed an excellent compound binder which is proof against humidity and other characteristic also is maintained. Furthermore, appropriate inorganic filler stabilize the distribution of the conductive particles. As a result, the resistivity of the electrode is steady for environment condition.

In order to obtain a wide dynamic range it is effective to control the surface roughness and hardness of the electrode and give an appropriate contact resistance. The particulate filler give the surface roughness and adjust surface hardness.

The pressure and output resistance characteristic (P-R characteristic) were investigated with the electrode that is contained current resin filler and new inorganic filler, both of these sensor were able to obtain the sufficient dynamic range. However, in case of using the resin filler, the P-R characteristic changed greatly in the high and low temperature environment. On the other hand, in the case of using inorganic filler, the output resistance steady regardless of the temperature. To investigate this cause the surface hardness of the electrode was measured, and it turned out the dependence on temperature of the resin filler was affected. The electrode that used inorganic filler was optimized based on the above-mentioned study and the sensor that had an excellent P-R characteristic and environmental stability was able to be developed.

Key words: Pressure sensitive sensor, membrane switch, pressure sensitive electrode, carbon paste

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