DE2526600A1 - PRESSURE SENSITIVE RESISTANCE - Google Patents

Description

Patent attorney

sw a graft

June 13, 1975

Inoue-Japax Research Incorporated

5289 Aza Michimasa, Nagatsudamachi, Midoriku

Yokohamashi, Kanagawaken (Japan)

Pressure sensitive resistance

The present invention relates to a pressure sensitive resistor or an elastic conductor, i.e. an electrical one conductive, elastically deformable body, its electrical resistance or its electrical conductivity as the puncture of the applied pressure vary.

Heretofore, pressure-sensitive resistors useful as converters or transducers and switching elements in various devices have been made from fine particles of a metal such as gold, platinum, palladium, silver, aluminum, copper or nickel, supported by an electrically non-conductive binder are bound, which forms an elastically deformable substrate. Alternatively, the metal particles are mixed with a rubber material and then vulcanized therewith with the aid of a vulcanizing agent. In the case of the metal particles used, the size of which is 0.5 to 50 microns, in general ^; generally a few microns or less, they are usually those made by mechanical pulverization followed by classifying or sieving,

58I- (A 478) -Bo-HÖ

509851/0459

252660Q

so that the particle size is adjusted to the desired size. The surface energy of the mechanically produced Metal particles, which are generally spherical, columnar, or flaky, are characteristically large enough to to adversely affect the elastic non-conductive substrate, thereby losing its properties over time go while the particles themselves are rapidly oxidized. Accordingly, the service life of an ordinary pressure sensitive Resistance elements undesirably short.

Further, the conductive particles which have heretofore been used in the manufacture of pressure-sensitive resistors are as above spherical, columnar or scaly, and they have a uniform particle size on, so that de not packed tightly in the non-conductive elastic Substrate. Accordingly, it has the conductivity of an ordinary pressure-sensitive resistance element an unsatisfactorily limited value which cannot be improved by increasing the proportion of metal particles can.

Attempts have been made to avoid the deterioration in the pressure sensitive and electrical properties of the element which occurs over time by coating particles of such a metal. Noble metals, however, have the disadvantage that they adversely affect the rubber substrate over time due to their high surface energy, apart from the fact that they make the product expensive.

The object of the present invention is to provide an improved pressure-sensitive resistor with an excellent pressure sensitivity, excellent electrical properties, little deterioration over time and great durability that can be produced economically.

509851/0469

A pressure-sensitive resistance element according to the invention comprises an electrically non-conductive, elastically deformable one Body and electrically conductive metal particles distributed in the body, each particle having many protrusions and having depressions on its surface and wherein a protrusion of a particle having a protrusion or a depression of a neighboring particle can engage when pressure is applied to the element.

The metal particles have a particle size in the range of 0.5 to 200 microns, preferably 1 to 50 microns, and make an amount of 10 to 80 volume * out.

The non-conductive elastic body in which the metal particles are distributed can be made of natural rubber, synthetic rubber, Nylon, neoprene, vinyl chloride, tetrafluoroethylene, urea, polyethylene, polyisobutylene, or polyacrylonitrile any other resinous or flexible dielectric material that is common.

The metal particles used in the present invention are made by any of the methods described below so that they each have a plurality of protrusions and have depressions on their surface as described above. The particles can be dendritic or tree-shaped, petal-shaped, burr-shaped or cactus-shaped in contrast to spherical, columnar and flaky, mechanically pulverized finely divided materials be with smooth surface that have been used so far.

The metal particles with irregular surface for mixtures with the non-conductive elastic material to produce a desired pressure-sensitive conductive element according to the invention advantageously have an increased surface area / volume ratio (cm ² / cm · ^) and therefore a decreased surface energy, so that the Metal particles less

5098B1 / 0A59

are susceptible to oxidation and have less of an effect on the elastic properties of the element. Be accordingly the service life and durability of the element are improved. Furthermore, it is not necessary to use a noble metal for the particles so that cheaper metals such as iron, nickel or chromium can advantageously be used. Manganese, copper, aluminum and magnesium can be used in the same way.

The use of the above-mentioned particles according to the invention brings the further advantage of closer packing of the conductive particles in the non-conductive, elastically deformable body with it. Accordingly, the minimum Resistance value of the element can be reduced considerably as compared with conventional elements. Furthermore, a gradual change in resistance with respect to the pressure applied due to the fact that a contact between projections or between a projection and a recess of adjacent metal particles before a complete Particle contact occurs, which area can increase as the pressure increases. The possibility of a denser Providing packing can also lead to a reduction in the metal content in the element.

The metal particles that are used according to the invention can be obtained by electrochemical reduction, chemical reduction, Steam condensation or thermal decomposition can be produced.

Electrochemical reduction involves the electrochemical deposition of a metal on a cathode that is rotated may contain the ions of the metal from an aqueous electrolyte solution or a molten salt electrolyte. By regulating the temperature, concentration and flow rate of the liquid electrolyte and the electrolytic voltage and the electrolysis current in a known manner, it is possible to produce a powdery metal deposit or a precipitate of particles with tree-shaped, whisker-like and

509851/0459

252660Q

to obtain spherical crystal growth formations in a desired manner. E.g. electrolysis leads to the formation of hydrogen for the deposition of particles with tree-shaped projections. When the generation of hydrogen is controlled, particles with whisker-like protrusions result. With total avoidance the formation of hydrogen, particles with spherical projections are obtained.

Chemical reduction involves the chemical or electroless precipitation of metal particles from a solution at which it is either an aqueous solution or a molten salt containing a metal compound which thermal reduction or decomposition of a metal compound for the production of metal particles, chemical etching and the cryogenic decomposition. According to these procedures, all of which are also common procedures, you can by controlling the temperature, concentration, pressure and flow rate of the reducing agent and other process parameters in a known manner metal particles with tree-shaped and other crystalline protrusions in the desired manner Way to be made.

509851/0459

252660Q

In a preferred embodiment, the surface each particle (with a "multitude of cracks and pits") coated with a tin film (Sn). The * film thickness is of the order of magnitude of Sngströß units or microns. Conventional spray, vapor deposition, melt spray plating or plating techniques can be used use. Tin has excellent anti-corrosion and protective properties, so that metal objects, which are coated with it, and a non-conductive elastic substrate little changes in the course of the Time subject. Furthermore, tin is a soft and viscous metal and tin coatings are believed to be intimate Allow contact between particles when pressure is applied.

example 1

Nickel particles with petal-like crystalline protrusions on their faces were produced by electrodeposition. In the deposition solution it was an aqueous solution having a pH of 3 and a temperature of 25 ⁰ C, 200 g / l nickel sulfate (NiSO _4), 5 g / l Nickel chloride _(NiCl?) And 25 g / l Boric acid (Η, ΒΟ,), the deposition current having a current density of 4.5 A / cm. The solution was allowed to flow onto a cathode on which the particles were deposited.

After classifying the nickel particles by size, a mixed nickel powder containing 20 % particles was prepared

509851/0459

-7- 252660Q

30 micron particles, 50% 25 micron particles, and 15 % 10 micron particles with the remainder being 5 micron particles. The mixed nickel powder was in a ratio of 80 wt.? mixed with a butyl rubber material containing a vulcanizing agent; the mixture was vulcanized to produce the desired pressure-sensitive conductive member.

An operation of the obtained element is shown in Fig. 1, in which the electrical resistance (ohm cm) as the ordinate and the applied pressure (kg / cm) are plotted as the abscissa. Es it can be seen that the element has a resistance of 3 x 10 ^ Ohm cm when no pressure is applied and that the resistance drops to 1 χ 10 0hm cm. If you can take the pressure takes away, the element has a resistance of 2 χ 10 · ^ Ohm cm, the resistance then gradually returning to the initial value.

The metal particles with the desired surface structure, which are in the elastically deformable, non-conductive body incorporated can also be produced by steam condensation will. In the known steam condensation technique, a metal with a high vapor pressure is used, the in particles in a vacuum or in an inert gas medium or by contact with a cooled metal surface or a . is transferred to another cooled surface. By regulating the heating temperature and the pressure of the medium carrying the steam it is possible to obtain metal particles with desired crystalline protrusions.

Example 2

Magnesium particles with a particle size of about 1 micron were obtained by condensation of magnesium vapor with a vapor pressure made of 2 torr. If different heating temperatures

509851/0459

were applied temperatures of 1000, 1200 and l400 ⁰ C, the resulting particles had tree-shaped, whisker-like or spherical crystalline projections.

Another suitable method for producing metal particles with the desired surface structure is the thermal decomposition of metal compounds in the gas phase or in the form of vapor. Certain metal compounds, such as metal carbonyls, are in the liquid phase at room temperature and are decomposable at elevated temperature, whereby the metal is reduced and forms particles. Iron carbonyl Fe (CO) ₅ and nickel carbonyl Ni (CO) I ₁ decompose below 103 and 43 ⁰ C, respectively, with iron and nickel being deposited in the form of particles with 0.5 to 50 microns. The shape and size of the particles can be adjusted by controlling the heating temperature at the time of decomposition, and particles with desired projections are easily obtained in this way.

Example 3

Nickel carbonyl Ni (CO) ₁ J was ^{heated at 80 °} C .; the decomposed nickel particles were 1 to 5 microns in size and had a plurality of whisker-like protrusions on their faces, the protrusions protruding by 40% of the diameter of the center of the particle.

Like other carbonyls like Fe (CO) ₁₁ , W (CO) g, Mo (CO) ₆ and (PtCl ₂ ) ₂ (CO) ₃ , metal chlorides like CuCl ₃ , BeCl ₃ , TiCl ₁ , ZrCl _{4 are} , AlCl ₂ , SnCl ₄ , TaCl ₅ , SbCl ₃ , NbCl ₅ , BCl ₃ , TaCl ^ NbCl ₅ , and metal iodides, such as GeJ ₃ , CrJ ₂ and SiJ ₁ J, thermally decomposable; they can be used to produce desired metal particles.

509851 / CH59

Example 4

Nickel particles prepared as in Example 3 were mixed with silicone rubber in a proportion by weight of 70%; the mixture was vulcanized to make a pressure-sensitive conductive member. The resulting element had a resistance of 5 x ICr ohm cm when depressurized. When a pressure of 6 kg / cm was applied, the resistance dropped to 2 χ 10 ohm cm; an electric current having a current density of 5 A / cm could flow through the element. This means a more than 30 % improvement in operation over conventional elements with spherical particles. The resistance elements according to the invention exhibited stable pressure-sensitive characteristics in repeated use and little change in operation with the lapse of time.

In Fig. 2 is a device for the production of Metal particles of the desired design for use according to the invention shown, this device for electrochemical or chemical "manufacture is used for purposes of the present invention. The device comprises a container 1, which contains a liquid electrolyte 2, from which a desired metal is electrochemically or chemically finely divided Shape is reduced to a drum 3. When an electrochemical reduction is carried out, the Drum 3 has a cathode, while an anodic counter electrode

4 is provided adjacent in the electrolyte 2, with an electrolysis current via the counter electrode from a current source

5 flows, the two poles of which are connected to the cathode 3 and the anode 4 with the polarity shown. When a chemical reduction is performed, the anode 4 and the power source 5 are omitted.

The drum 3 can rotate in the direction of the arrow, whereby they a finely divided metal deposit with tree-shaped or

509851/0459

carries other crystalline protrusions formed electrochemically or chemically. A scraper 6 is above des. Mirror of the electrolyte 2 for removing and collecting deposited metal particles from the rotating surface the drum 3 is provided.

In the electrolyte and in the vicinity of the zone in which the deposition takes place, a vibrator 7 is provided, which is of a Converter device 8 operated by a conventional alternating current source 9 with an output frequency of, for example, 50 Hz is to set the electrolyte 2 in a vibration of the same frequency. When an electrochemical reduction is carried out such a vibration can alternatively be provided on the anode 4.

In Fig. 3, which schematically shows another device for implementation of the electrochemical particle production shows, a cathode 10 is adjacent to an anode 11 with a central one Bore 11a arranged through which a liquid electrolyte of a given composition in the gap G between the Areas of the cathode 10 and the anode 11 flows. A power source 12 is such with the anode 11 and the cathode 10 connected that an electrochemical deposition current flows between them through the electrolyte passing through the gap G, and a finely divided metal deposit with tree-shaped crystalline projections is produced on the surface of the cathode 10 will. The particle preparation of Example 1 was carried out using a system based on this type.

As in the system of FIG. 2, the electrolyte can be made to vibrate sonically; this becomes as in Fig. 3 is caused by reciprocating the anode 11 in the longitudinal direction at a frequency of 50 Hz, for example.

Even if it is not essential for the purposes of the invention is to set the electrolyte in a sonic vibration,

509851/0459

so this auxiliary measure leads to the advantage that the formation of the desired crystal particles is facilitated and the Effectiveness of particle formation is increased.

Particles that can be used according to the invention can also be produced by chemical or electrochemical etching of particles with a smooth surface, e.g. made of spherical particles. In the case of electrochemical etching, these Particles are held between a pair of electrodes, passing a liquid electrolyte through the spaces between the Allows particles to flow and an electrolyte current flows between the electrodes through the particles and the electrolyte. As a result of electrochemical corrosion, the surface of each particle becomes irregular, with a multitude of Projections and depressions are formed on the surface. With chemical etching, the particles can simply be in Form of a mass are kept in contact with a stream of a corrosive fluid in a treatment chamber.

Example 5

A mass of spherical copper particles with a particle size of 35 microns was held under a pressure of 1.5 kg / cm in a treatment chamber. Air which had been heated to a temperature of 450 ^° C. was passed through the mass, flowing through the spaces between the particles for 25 minutes. The treated particles had irregular surfaces with depressions as deep as 8 to 10 microns, and the surface area per volume (cm ² / cm ⁵ ) of each particle was three times that of untreated particles.

509851/0459

Example 6

The copper particles from Example 5 were further subjected to a reduction treatment, with gaseous hydrogen, which ^{had been heated to a temperature of 450 °} C., being passed through the particle mass for 30 minutes. This made the protrusions made in Example 5 pointed; the surface area per volume of each particle increased 3.3 times that of untreated spherical particles.

Example 7

Nickel particles (5 microns) each having a plurality of protrusions about 0.3 microns in length were placed in a 30 torr vacuum where they were deposited on the facets by vapor deposition with a tin-I film about 100 angstroms thick were coated. These particles were incorporated into a silicone rubber material in a volume fraction of 74%. The electrical resistance of the resulting body, which was ΙΟ- ⁵ ohm cm without pressure, dropped to 0.01 ohm cm when a pressure of 1.5 kg /

ρ
cm was applied.

The metal particles (each having a plurality of projections) can preferably also be combined with an organometallic Compound, e.g. an organotin compound which is methyl tin isooctyl thioglycolate, Dioctyltin mercaptide or dibutyltin mercaptide. Organometallic compounds with semiconductor properties are effective as antioxidants for the metal and are soluble in the rubber materials.

Example 8

There were nickel particles (5 microns), each with a multitude of

509851/0459

number of projections had, incorporated in a volume ratio of 78 % in a mixture of 100 parts of rubber material, 20 parts of methyl tin isooctyl thioglycolate, 5 parts of heat stabilizer and 40 parts of plasticizer. The electrical resistance of the resulting body, the 10 ⁷ ohm cm, excluding any pressure fell to 0.01 cm from 0hm, when a pressure of 1 kg / cm was applied. The body showed no noticeable change over time afterwards

the tests were carried out 2 × 10 times.

The use of an organometallic compound is also advantageous in order to give the product a larger To give linearity to the pressure / resistance relationship.

509851 / CU59

Claims (8)

Claims V 1. J Pressure-sensitive resistor, characterized by an electrically non-conductive, elastically deformable body and electrically conductive metal particles distributed in the body, each particle having a plurality of protrusions and depressions on its surface, and the protrusions of the particles at Attack protrusions or depressions of adjacent particles when pressure is applied to the body. 2. Pressure-sensitive resistor according to claim 1, characterized in that the particles have a particle size in the range of 0.5 to 200 microns and contained in an amount of 10 to 80 volume- #. 3. Pressure-sensitive resistor according to claim 2, characterized in that the particles have a particle size in the range of 1 to 50 microns. 4. Pressure-sensitive resistor according to claim 2, characterized in that the projections of the particles represent dendritic, whisker-shaped or spherical crystalline formations. 5 · Pressure-sensitive resistor according to claim H _3, characterized in that the particles consist of iron, nickel or chromium. 6. Pressure-sensitive resistor according to claim 4, characterized in that the particles consist of manganese, copper, aluminum or magnesium. 509851/0459 7. Pressure-sensitive resistor according to one of the preceding claims, characterized in that the metal particles with are coated with a tin film. 8. Pressure-sensitive resistor according to one of the preceding "claims, characterized in that it additionally has a contains organometallic compound. 9 · Pressure sensitive resistor according to claim 8, characterized in characterized in that it contains an organotin compound. 509851/0459