JPS62281304A - Strain-sensitive conductive rubber material - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed Description of the Invention] 3. Detailed Description of the Invention (Field of Industrial Application) The present invention relates to a strain-sensitive conductive rubber material, and more specifically to a conductive rubber foam obtained by mixing a conductive member into rubber. And,
It has extremely low hysteresis, which changes the resistance value or voltage as the tensile elongation changes and remains on the original elongation-resistance curve even after the load is removed, and is especially sensitive to tensile stress. This invention relates to a strain-sensitive conductive rubber material used as a sensor.

(Prior art) Conventionally, carbon black, which has excellent conductivity, was used as a rubber elastic body.
Regarding the fact that a rubber composition mixed and filled with metal particles etc. undergoes compressive strain, its resistance value decreases greatly and exhibits pressure-sensitive characteristics, for example, in JP-A-55-58504 and JP-A-58- It is disclosed in numerous documents such as No. 152033.

The mechanism by which this type of pressure-sensitive conductive rubber exhibits pressure-sensitive properties is as follows:
First, it is said that when the rubber sheet is distorted by a pressing force, the probability that the conductive particles dispersed in the sheet come into contact with each other to form a link increases and the resistance value decreases.

(Problems to be Solved by the Invention) Although conventional pressure-sensitive conductive rubber has the property of sensing compressive strain, it lacks the function of sensing tensile strain in the -axial direction. In other words, when this type of pressure-sensitive conductive rubber is stretched, its resistance value increases as the degree of elongation increases, but even when the load is removed, it does not follow the original resistance value curve, so it lacks repeatability and cannot sense the stretching stress. It could not be used as a sensor material.

The present invention deals with the above-mentioned actual situation, and in particular converts the amount of change in tensile elongation into an electrical signal such as a resistance value or voltage, and senses the tensile stress using a device that has a characteristic of having small hysteresis with respect to the tensile deformation. The purpose of the present invention is to provide a strain-sensitive conductive rubber material that can be used as a sensor.

(Means for Solving the Problems) That is, the present invention is characterized by foaming a material obtained by adding at least 25 to 130 parts by weight of conductive carbon black to 100 parts by weight of electrically insulating rubber. It is a strain-sensitive conductive rubber material.

In the present invention, examples of rubber having electrical insulation properties include natural rubber, polybutadiene rubber, polyisoprene rubber, styrene-pucdiene copolymer rubber, nitrile rubber,
There are butyl rubber, chloroprene rubber, acrylonitrile-butadiene copolymer rubber, ethylene-propylene copolymer rubber, silicone rubber, etc., and it is also possible to use two types of these rubbers. In order to improve mechanical strength and heat resistance, the above-mentioned rubber is crosslinkable with sulfur, a sulfur compound, or a peroxide, or is used after being crosslinked.

Further, as the conductive carbon black used in the present invention, for example, commonly used ones such as furnace black type, acetylene black type, thermal black type, channel blank light etc. are used, and the amount added is 100% of the above rubber. It is 25 to 130 parts by weight, preferably 40 to 100 parts by weight.

If the amount of carbon black added exceeds 130 parts by weight, the expansion ratio will be small and the hysteresis of the conductive rubber composition will increase, while if it is less than 25 parts by weight, changes in resistance or voltage will become insensitive to changes in elongation. It's coming.

Other conductive members that can be used in the present invention include nonmetallic and inorganic short fibers, powder, whiskers, etc. The short fibers include silicon carbide (SiC).
, glass, silicon nitride (Si3N4), etc., with a length of 1100p to 1011p and a diameter of 0.3 to
30 μm, while the powder has a diameter of 0.05 to 1
00 μm ceramic powder, such as silicon carbide (SiC), titanium carbide (TiC), boron carbide (
84C), carbides such as tungsten carbide (WC), silicon nitride (S i 3N4), aluminum nitride (AIN
), boron nitride (BN), titanium nitride (T i N) and other nitrides, alumina (Al2O2), zirconia (Z
r02), beryllia (Bed), and most preferably silicon carbide or silicon nitride.

Furthermore, as a whisker, α-silicon carbide (α-3iC)
, β-silicon carbide (β-3iC), silicon nitride (S i 3
N4), α-alumina (A1203), titanium oxide,
They are zinc oxide, tin oxide, graphite, Fe, Cu, Ni, etc., and are needle-like crystals with a diameter of about 0.05 to 3 μm and a length of about 5 to 500 μm. When adding the above-mentioned inorganic filler to rubber, it is possible to treat it with a silane coupling agent, a titanium coupling agent, etc. in advance, or to add a silane coupling agent or a titanium coupling agent at the time of mixing with the rubber. This further enhances the reinforcing effect and improves the dispersibility into rubber.

Although it is possible to achieve the object of the present invention without adding the above-mentioned inorganic filler, by adding the filler, it can be used not only as a sensor that senses tensile stress but also as a sensor that senses compressive force. can also be used.

The amount of the inorganic filler added is 1 to 80 parts by weight, preferably 10 to 40 parts by weight, per 100 parts by weight of rubber.

Further, the blowing agent used in the rubber composition of the present invention is, for example, a nitroso compound such as N,N'-dinitroso pentamethylene tetramine, NXN''-dimethyl-N,N'-dinitroso terephthalamide, or azodicarbonate. Including azo compounds such as composite blowing agents mainly composed of amides and azodicarbonamide, sulfonyl hydrazides such as benzene sulfonyl hydrazide, P, P'-oxybis (benzenesulfonyl hydrazide), and toluene sulfonyl hydrazide. There are organic blowing agents, or inorganic blowing agents such as sodium bicarbonate, ammonium bicarbonate, ammonium carbonate, etc., and the amount added is 2 to 30 parts by weight per 100 parts by weight of rubber. In some cases, the specified foaming ratio cannot be obtained;
If the amount exceeds 1 part by weight, the expansion ratio will not be increased to that extent, and a foam with a distorted shape and poor foaming state will often be obtained.

In the present invention, the dispersion temperature of the blowing agent can be controlled by adding a blowing aid such as urea and its compounds.

Next, there is no particular restriction on the method of mixing the above-mentioned components, and the mixture may be kneaded and heated and pressurized by appropriately known means and methods using, for example, a Banbury mixer, a kneader, a roll, or the like.

In the present invention, softeners, anti-aging agents, processing aids, vulcanization accelerators, crosslinking agents, etc. that are commonly used in rubber can be added.

(Effects) The rubber material obtained in this way is a foam with a diameter of about 1.5 to 15, and compared to an unfoamed rubber material, the resistance value is lower (in the case of a foamed rubber material of 11, the resistance value increases). It changes depending on the size of the material, but as the elongation increases, it shows a decreasing tendency and decreases linearly.In addition, with unfoamed rubber materials, as the elongation increases, the resistance value also increases, which is completely contrary to the foam material. become a trend.

(2) In the case of foam rubber materials, even when the load is removed, the resistance value is almost the same, so the hysteresis is small. It can be used as a tension detection sensor that can sensitively sense curved surface deformation of a detected object.

Next, the present invention will be explained in more detail using more specific examples.

Example 1 100 parts by weight of natural rubber, 4 parts by weight of Zn0, 1 part by weight of stearic acid, 2 parts by weight of accelerator CM, foaming agent (Celmic A
N Sankyo Kasei Co., Ltd.) 10 parts by weight, 30 parts by weight of process oil, 1 part by weight of sulfur, 50 parts by weight of acetylene black,
A rubber compound consisting of 20 parts by weight of Whisker 5iC was kneaded in a Banbury mixer and then extruded into a sheet with a thickness of 2 mm using a roll. This sheet was sandwiched between molds and cured under vulcanization conditions of 133 x 10 minutes, and the resulting sheet 16
The mixture was left in an oven at 0°C for 10 minutes to foam to a predetermined ratio. The obtained foam was cut into a size of 50 x 2 x 2 mm, and lead wires were connected to both ends to prepare a test piece.

The lead wire of the test piece was fixed to the chuck of a tensile testing machine, and the voltage was measured while the test piece was stretched at a speed of 20 m/sec or the load was removed. For voltage measurement, Ω was connected in series with the test piece and a resistor 200 for voltage detection, and a DC voltage of 9 cm was applied across both ends of the resistor 200, and a change in voltage was detected across the Ω of the resistor 200.

FIG. 1 shows the relationship between elongation and voltage during elongation of the test piece, load removal, and repetition of these steps. According to this, the voltage value of the test piece shows a tendency to increase as the elongation increases, and on the other hand, even when the load is removed, the test piece remains close to the original straight line and exhibits characteristics with small hysteresis. Moreover, even if this process is repeated three times, almost the same tendency is obtained, and the repeatability can be said to be good.

Example 2 (Variable of carbon black) Natural rubber 100
parts by weight, 4 parts by weight of ZnO, 1 part by weight of stearic acid, 2 parts by weight of accelerator CM, 20 parts by weight of a blowing agent (manufactured by Cellmic AN Sankyo Kasei Co., Ltd.), 30 parts by weight of process oil, 1 part by weight of sulfur, and 25 to 25 parts by weight of an acetylene blank. A foam test piece was prepared using a rubber compound containing 100 parts by weight in the same manner as in Example 1, and the voltage was measured in the same manner. The results are shown in FIGS. 2 and 3, and it was found that when the amount of acetylene black was 25 parts by weight, there was no change in voltage even if the elongation increased.

Example 3 (Change in expansion ratio) A test piece was prepared, and the relationship between elongation and voltage was determined. The results are shown in FIG.

Comparative Example In Example 1, a test piece (50 x 2
The elongation and voltage deformation of X1) were determined. The results are shown in FIG. As a result, as the elongation of the unfoamed conductive rubber material increases, the voltage decreases, and when the load is reduced, the voltage change greatly deviates from the original value, resulting in increased hysteresis.

[Brief explanation of drawings]

FIG. 1 is a diagram showing the relationship between elongation and voltage during stretching and load removal of the rubber material according to the present invention, and the repetition thereof; FIGS. 2 and 3 show the addition of carbon black to the rubber material according to the present invention. FIG. 4 is a diagram showing the relationship between elongation and voltage when changing the foaming ratio of the rubber material according to the present invention, and FIG. The figure is a diagram showing the relationship between elongation and voltage in conventional rubber materials. Patent applicant Mitsuko Belt Co., Ltd.9. U) Su・Gisagi Figure 2 bone leakage (・A) Figure 3 Figure 4 Figure 1V Watari (≠) Figure 5 Figure 1 Hayabusa, & (%) Procedural amendment (voluntary) May 20, 1988

Claims (1)

[Claims] 1. A strain-sensitive conductive rubber material, characterized in that it is formed by foam-molding a mixture of 100 parts by weight of electrically insulating rubber and at least 25 to 130 parts by weight of conductive carbon black.