JPH0586813B2 - - Google Patents

Description

[Detailed description of the invention]

(Industrial Application Field) The present invention relates to a pressure-sensitive conductive rubber sheet, and more specifically, it is made of a vulcanized rubber composition in which whiskers, which are specific inorganic fillers, are mixed into rubber.
This invention relates to a pressure-sensitive conductive rubber sheet that is a thin film of 200 μm or less and whose resistance value changes significantly when subjected to pressing force. (Prior art) Conventionally, it has been reported in Japanese Patent Publication, for example, that a rubber sheet made of a rubber elastic body mixed and filled with highly conductive carbon black, metal particles, etc. undergoes deformation under pressure, resulting in a significant decrease in electrical resistance. Publication No. 55-5804,
JP-A-55-147549 and JP-A-56-5840
This has already been disclosed in publications such as No. In addition, in order to improve the sensitivity of conductive rubber sheets, there are rubber sheets in which cellular structure voids are formed in the surface layer of the sheet, and a conductive material such as metal powder is highly loaded, for example, in JP-A-58. -Disclosed in Publication No. 209810. Further, various rubber sheets have been proposed in which metal fibers are filled in the thickness direction (for example, Japanese Patent Laid-Open No. 58-220307). (Problems to be Solved by the Invention) As described above, as a mechanism in which a conventional conductive rubber sheet has pressure-sensitive conductivity, when the sheet is first distorted by a pressing force, at this time, the sheet body is The degree of contact between the dispersed conductive particles increases and the resistance value between the electrodes decreases.On the other hand, when the conductive rubber sheet receives pressure from both electrode plates, it The contact area with the conductive rubber sheet gradually increases, and as a result, the electrical resistance value decreases. However, with the former mechanism, the probability of contact between conductive particles tends to change due to changes in the temperature of the matrix, etc., and the conductive particles and matrix separate due to compressive deformation of the sheet, resulting in a stable resistance value. It is said that there are some drawbacks that cannot be avoided. In addition, when the latter mechanism is repeatedly used over a long period of time, the surface of the rubber matrix becomes fatigued and hardened when subjected to large strains, and it also lacks creep resistance, resulting in the electrode plate being located on the surface of the rubber matrix. As the electrical resistance value starts to come into contact with the conductive material being applied, the electrical resistance value when no pressure is applied decreases, making it impossible to increase the change in electrical resistance value when pressure is applied, and ultimately maintaining good sensitivity over a long period of time. It is said that there is a drawback that it cannot be done. The present invention improves a pressure-sensitive conductive rubber sheet that changes the resistance value between electrodes by changing the degree of contact between conductive particles, and uses fillers with excellent conductivity such as carbon black or metal particles. By using whiskers, which are inorganic fillers with inferior conductivity compared to whiskers, the mechanical bond with the rubber matrix is improved, and by reducing the thickness of the sheet, the electrical resistance value due to pressure is reduced. The purpose of the present invention is to provide a novel pressure-sensitive conductive rubber sheet that significantly reduces the pressure-sensitive conductive rubber sheet. (Means for solving the problem) Add 100 parts by weight of electrically insulating rubber to
A rubber paste made of a rubber composition containing 2 to 400 parts by weight of an inorganic filler, which is a needle-shaped single crystal whisker having a diameter of 0.05 to 3 μm and a length of 5 to 500 μm, is applied and solidified by vulcanization. In particular, the obtained pressure-sensitive conductive rubber sheet is made into a sheet with a thickness of 20 to 160 μm. Examples of the matrix rubber having electrical insulation properties in the present invention include natural rubber, polybutadiene rubber, polyisoprene rubber, styrene-butadiene copolymer rubber, nitrile rubber, butyl rubber, chloroprene rubber, acrylonitrile-butadiene copolymer rubber, and ethylene rubber. - There are propylene copolymer rubber, chlorosulfonated polyethylene 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 crosslinked with sulfur, a sulfur compound, or a peroxide, or is used after being crosslinked. Furthermore, whiskers which are inorganic fillers include α-silicon carbide (α-SiC), β-silicon carbide (β-SiC), silicon nitride (Si ₃ N ₄ ), α-alumina (Al ₂ O ₃ ), They are titanium oxide, zinc oxide, tin oxide, graphite, Fe, Cu, Ni, etc., and are needle-like single crystal bodies with a diameter of 0.05 to 3 μm and a length of about 5 to 500 μm. When adding the above inorganic filler to rubber, it is necessary to treat it with a silane coupling agent, titanium coupling agent, etc. beforehand, or to add a silane coupling agent or titanium coupling agent when mixing with the rubber. is also possible. This results in better dispersibility in rubber. The amount of whiskers added is 2 to 400 parts by weight, preferably 5 to 200 parts by weight, per 100 parts by weight of rubber. If the amount of whiskers added is less than 2 parts by weight, the pressure-sensitive conductivity effect will be reduced. becomes smaller. on the other hand,
If it exceeds 400 parts by weight, it will be difficult to mix and disperse it into the rubber, and the obtained rubber sheet will become a conductor, making it impossible to achieve the object of the present invention. In particular, the whiskers used in the present invention are
Because it is a needle-like crystal, it protrudes toward the surface of the sheet-like composite due to its unique morphology, while whiskers are randomly dispersed inside the sheet. Therefore, when the sheet-like composite is pressurized by both electrode plates, the chance that the whiskers protruding from the sheet surface and the whiskers dispersed inside the sheet come into contact increases, resulting in pressure-sensitive conductivity. considered to be a thing. However, the sheet-like composite of the present invention has a thickness of 200 μm.
If the thickness exceeds 100 µm, it becomes insulated even when pressed and does not exhibit any pressure-sensitive conductivity, so it is necessary to maintain the thickness of the sheet-like composite at about 20 to 160 μm. The above-mentioned pressure-sensitive conductive rubber sheet includes a rubber having electrical insulation properties and an inorganic filler other than whiskers.
Then, if necessary, softeners, anti-aging agents, vulcanization aids, crosslinking agents, etc. commonly used in rubber are added.
These components are kneaded using a Banbury mixer, kneader roll, etc. to make a sheet, or the thus kneaded product is dissolved in a solvent to make a rubber paste, which is applied onto the substrate. It can be manufactured by molding a thin film and vulcanizing it. (Example) Next, the present invention will be explained in more detail using specific examples. Examples 1 to 4, Comparative Examples 1 to 3 Based on the formulation shown in Table 1, the rubber compound was kneaded using a Banbury mixer, and the kneaded rubber was dissolved in a solvent to make rubber paste, which was spread on a flat aluminum plate. After applying and forming a coating film, it was placed in the open and vulcanized at 150°C for 20 minutes. Furthermore, the first
The whisker SiC shown in the table has a diameter of approximately 1 μm and a length of approximately
100 μm, and powder SiC has a particle size of about 0.7 μm. The thickness thus obtained is 80 μm.
A thin film of ~160 μm was cut into a 30×33 mm test piece, and its electrical resistance value was measured when no pressure was applied (however, a 12 g electrode plate was placed on the test piece) or when the test piece was pressed. The result is the second
Shown in the table. To measure the electrical resistance value, first, the test piece is held between approximately 100 g of Teflon plates. At this time, a copper plate of approximately 0.3 mm in thickness is installed between the test piece and the Teflon plate, and this pair of copper plates is used as an electrode plate. The resistance value was determined using a digital multimeter. Pressurization was performed by placing a weight on the Teflon plate located on the upper side. According to the results, even though the materials are the same, the rubber sheet mixed with whiskers has better pressure-sensitive conductivity than the powdered rubber sheet.

【table】

[Table] Modified Examples By varying the thickness of each rubber sheet having the formulations shown in Examples 1, 3, and 4 from about 20 μm to 400 μm, the resulting rubber sheets were different when not pressed or when pressed. The electrical resistance value was measured. The results are shown in Table 3, which shows that when the thickness of the rubber sheet exceeds 170 μm, pressure-sensitive conductive properties no longer appear.

[Table] (Effects of the Invention) As described above, the pressure-sensitive conductive rubber sheet of the present invention has a specific amount of whiskers, which are needle-like crystals having a diameter and length within a predetermined range, mixed and dispersed in the rubber. Since the thickness is 20 to 160 μm and there is no conductive material such as carbon black mixed in as in the conventional case, it maintains an almost perfect insulation state when no pressure is applied, while the electrical resistance value decreases significantly when pressure is applied. It exhibits pressure-sensitive conductivity, and its small thickness makes it possible to form a conductive thin film directly on the electrode plate, making it possible to manufacture switches with small strokes.

Claims (1)

[Claims] 1 Add 100 parts by weight of electrically insulating rubber to
A rubber paste made of a rubber composition containing 2 to 400 parts by weight of an inorganic filler, which is a needle-shaped single crystal whisker having a diameter of 0.05 to 3 μm and a length of 5 to 500 μm, is applied and solidified by vulcanization. A pressure-sensitive conductive rubber sheet comprising a sheet having a thickness of 20 to 160 μm.