JPH07243805A - Resistance ink for strain gage and strain gage - Google Patents

Abstract

PURPOSE:To improve a gage factor by a method wherein at least one out of graphite and a metal powder is diffused, as a main conductive material, to a thermosetting resin so as to form a resistance ink. CONSTITUTION:When graphite or a metal powder is used as a main conductive component, a gage factor is lowered when the mixture amount of the metal powder is too much, but a resistance becomes too high and unstable when the mixture amount is small. As a result, e.g. in the case of graphite and a pehnolic-resin binder, the content of graphite is set at 8 to 25vol.%. In addition, since the metal powder alone is stable and a high resistance is hard to obtain, graphite is mixed. In addition, when a thermoplastic resin is used as a binder, its hysteresis is large and it is unsuitable for a sensor. As a result, a thermosetting resin is used. An ink which is composed in this manner is printed on an insulation-treated phosphor bronze plate, it is heated and hardened, and a resistor is formed. Thereby, it is possible to obtain the printed resistor which is suitable for a strain gage.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a composition of a resistance ink for printing (resistive ink for strain gauge) used for a sensor for detecting the strain amount of a strain generating element, and a strain gauge using this ink.

[0002]

2. Description of the Related Art Foil gauges and semiconductor type sensors are well known as resistive strain sensor elements. However, there is a problem in terms of cost when used for general purposes such as for general household appliances.

On the other hand, an organic printing resistor is widely known as one capable of forming a resistor at low cost, but when it is used as a strain sensor, its gauge factor is small (the change in resistance value due to strain is small. ) On the other hand, there is a problem in using it as a strain gauge because the resistance value changes greatly with temperature and humidity.

In order to use the printed resistor as a strain gauge, the following two directions can be considered: a) improving the gauge factor, b) improving the environmental stability, but using the environmental stability as the strain gauge. Since it is actually very difficult to improve it to the extent possible, it is considered to improve the gauge factor.

[0005]

The relationship between the strain amount of the resistor and the change in resistance value is generally expressed by the following equation.

ΔR / R = ε · (1 + 2ν) + Δρ / ρ [ΔR / R: change in resistance, ε: strain, ν: Poisson's ratio, Δ
ρ / ρ: change in resistivity], so that the gauge factor [(ΔR /
In order to improve R) / ε], it is effective to use a material having a large Poisson's ratio ν or to significantly change the specific resistance due to strain. However, since it is impossible to change the Poisson's ratio ν drastically, the latter can only be increased by increasing Δρ / ρ.

The present invention has been made based on such a background, and by variously examining the composition, an ink for a strain gauge having an improved gauge ratio, and a strain gauge made by using this ink are provided. The purpose is to do.

[0008]

The above object can be achieved by a first means prepared by dispersing at least one of graphite and metal powder as a main conductive material in a thermosetting resin.

Further, it is achieved by the second means using a resistance ink prepared by dispersing at least one of graphite and metal powder as a main conductive material in a thermosetting resin.

[0010]

In the present invention, the thermosetting resin is composed by dispersing at least one of graphite and metal powder as the main conductive material to improve the gauge factor and make the printed resistor suitable for strain gauges. .

[0011]

[Example] In the case of a distributed type resistor such as a printed resistor,
The specific resistance is determined by the ratio of the conductive component to the binder resin and the dispersion state thereof. Printed resistors, which are widely used for variable resistors, exhibit their conductivity mainly in carbon black.

This is because carbon black is chemically stable and inexpensive, and as shown in FIG.
The main reason for this is that the slope of the curve showing the relationship between the blending amount and the specific resistance is relatively gentle with respect to other conductive powders, and it is easy to obtain a desired resistance value. However, this seems to be disadvantageous for a strain gauge in which it is desired to change the resistance value as much as possible with respect to a slight volume change.

On the other hand, as shown in FIG. 1, conductive powder such as graphite or metal powder, which has excellent conductivity as compared with carbon black and whose structure is not well developed, shows a change in the conductive component state in the resistance film. , A large change in resistance occurs.

Therefore, as described above, an attempt was made to improve the gauge factor by using such graphite or metal powder as the main conductive component.

First, the conductive powder was examined.

FIG. 2 is an explanatory view showing the contents of each example and comparative example of the material and the compounding ratio of the conductive powder.

As Examples 1 to 4 and Comparative Example 1, the conductive materials and the compounding ratios shown in the figures were used. It should be noted that if the blending amount of the conductive powder is too large, the gauge factor becomes low, and if it is too small, the resistance becomes too high and becomes unstable, so that it has an appropriate range. This range depends on the combination of the conductive powder and the bander resin, but in the case of the graphite and the phenol resin used in this Example 1, the graphite content is 8 to 25.
It was Vol%. In addition, in Examples 3 and 4,
The reason why graphite is mixed is that it is difficult to stably obtain high resistance with the metal powder alone.

The ink shown in FIG. 1 is printed on an insulating phosphor bronze plate and heat-cured to form a resistor, and then the phosphor bronze plate is bent to cause distortion in the resistor. The change was observed. The result is shown in FIG.

As can be seen from the results of Examples 1 to 4, the resistors having the conductive component of carbon black, which are used in ordinary printed resistors, show only the characteristics which are not so different from those of the metal foil gauges, and In addition, the resistance of the resistor, which is mainly composed of conductive powder having a poorly developed structure, is as large as 2 to 10 times that of the metal foil gauge.

Next, the binder was examined.

FIG. 4 is an explanatory view showing the contents of the examples and comparative examples of the binder material and blending ratio. Note that FIG.
In addition to the components shown in (1), an appropriate amount of solvent for viscosity adjustment is included.

The binder affects the hysteresis as well as the gauge factor. The binder is required to have flexibility that responds quickly to stress and elastic limit value that is as large as possible in order to surely return to the original state when the stress is removed. From such a viewpoint, some binder resins were selected, resistance inks were prepared, and the correlation of strain-resistance change was investigated.

The results are shown in FIGS.

Examples 1, 5 and 6 use a thermosetting resin, and Comparative Examples 2 and 3 use a thermoplastic resin. Comparing the two, the former has a smaller hysteresis, while the latter has a larger hysteresis and is not suitable as a sensor. This is because in the case of the thermosetting resin, the three-dimensional network structure is developed and the plastic change is small.

From these results, it can be said that a thermosetting resin having a three-dimensionally developed structure is suitable as the binder of the resistance ink for the strain gauge.

[0026]

According to the first aspect of the present invention, the thermosetting resin is composed of at least one of graphite and metal powder dispersed as the main conductive material to improve the gauge factor of the printing resistor. It can be made suitable for strain gauges.

According to the second aspect of the present invention, by using the above resistance ink, the manufacturing process is simple, and a metal plate (surface-insulated) or plastic (film is used as a base material). It is possible to provide a strain gauge having advantages such as the use of inexpensive materials such as (including).

[Brief description of drawings]

FIG. 1 is a characteristic diagram showing a correlation between volume content of conductive powder and resistance.

FIG. 2 is an explanatory diagram showing the contents of each example and comparative example of the material and blending ratio of the conductive powder.

FIG. 3 is a characteristic diagram showing a relationship between strain and change in resistance value.

FIG. 4 is an explanatory diagram showing the contents of the examples and comparative examples of the binder material and blending ratio.

FIG. 5 is a characteristic diagram showing a relationship between strain and change in resistance value.

FIG. 6 is a characteristic diagram showing a relationship between strain and change in resistance value.

Claims (2)

[Claims] 1. A resistance ink for a strain gauge, characterized in that at least one of graphite and metal powder as a main conductive material is dispersed in a thermosetting resin. 2. A strain gauge comprising a resistance ink composed of a thermosetting resin in which at least one of graphite and metal powder is dispersed as a main conductive material.