DE2409009A1 - PRESSURE SENSITIVE RESISTOR ELEMENTS AND METHOD OF MANUFACTURING THEM - Google Patents

Description

Me invention "relates to pressure-sensitive resistors and a process for their manufacture.

Pressure sensitive resistance devices are known. They comprise, generally speaking, a matrix of insulating, elastomeric or compliant material in which a plurality of relatively fine electrically conductive powders is distributed more or less uniformly. The prior art materials that exhibited the highest resistance fluctuations consist of Dispersions in which conductivity is generated by the dielectric medium between the lights broken open under pressure and thus the most insulating

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ORIGINAL INSPECTED

and the austerity-resistant matrix is destroyed. The following The conductive particles were designed to be embedded in the non-conductive Matrix suggested, but not always for a pressure-sensitive product: iron, copper, Chromium, titanium, tungsten, platinum, boron, stainless steel, silicon, silver, gold, nickel, cobalt, aluminum, Zinc, "nichrome", carbon (in the form of e.g. kiss or Graphite) etc. The metals or the carbon can be in the form of fibers, flakes, spheres or irregularly shaped Particles are present and their size, insofar as they are found to be suitable, may vary about 0.03 microns to about 2 ^ 00 microns, however There is agreement that the smaller particles are preferred.

The invention consists, inter alia, in the provision of a pressure sensitive element in which small conductive Particles are embedded in a flexible or elastomeric base and have a very low electrical pressure under pressure Has resistance.

The object of the invention is achieved by apart from the conductive particles and the resin mixture forming the matrix, a potentially semiconducting material is provided, which is absorbed on the conductive particles. The conductive particles are preferably pretreated with a solution, which the potentially semiconducting material before they are added to the resin mixture forming the matrix. The potentially semiconducting material can be of such a nature that it prevents polymerization of the resin mixture, which can be advantageous in this respect, than the polymerisation of the resin only on the contact surfaces between the individual conductive particles (or their coating) and the matrix is prevented. The usual

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Process for making such products, therefore, confesses in that the cleaned conductive particles and a polymerization catalyst or a vulcanizing agent of the monomeric (or partially polymerized) elastomer mixture, that is to form the matrix "is added, whereupon the mixture is poured or deformed and then added to the polymerize "or hardened vulcanized product. According to the invention, this mixture also contains a substance which is absorbed on the particles and has potential semiconductor properties and optionally the curing of the Matrix prevents.

The conductive particles can be selected from the above-mentioned known substances. It has been found, however, that the best results are obtained with particles with a large specific surface area. The hand product known under the name "Raney-Nickel" has a relatively high specific surface area and gives particularly good results, just like those commercially available as "Carbonylnickel" (precipitated from nickel carbonyl ) / hxds. ice places. If it is intended that a circuit will stop working after a certain time (e.g. after 10 to 45 days), bullets coated with mercury can be used. Carbon particles can in particular be used in combination with other conductive particles, but these carbon particles absorb the polymerization (peroxide) catalyst and slow down the curing. The size of the conductive particles is preferably between about 0.1 and 44 microns.

The ratio of elastomer resin to conductive particles can be between about 100: 75 and 100: 110. A special one appropriate product has a ratio of resin to conductive particles as mentioned above and the size of the metallic

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ropes conductive particles is below 3 microns and their Surface area is about 0.5 m / g or more.

Silicone elastomers are preferred as the material for the matrix, as these products are good insulating and other electrical products Have properties, their basic physical properties over a wide temperature range are maintained, inert and resistant to oxidation, resistant to corrosion and most chemicals are inert and have good resistance to water and weathering influences. Under the Silicone-elastomer mixtures are the so-called "RTV" compounds (which vulcanize at barely any temperature) are particularly suitable and preferred because they are particularly easy to vulcanize or be subjected to polymerization or crosslinking can. At least two types of such ETV silicone resin mixtures are available, one of which is essentially one is a thermosetting silicone in which curing is accelerated by adding a peroxide curing agent, while the other accelerates hardening by adding metal soaps (especially tin and Eobalt soaps) will. Both types lead to polymerisation or vulcanized elastomers of practically the same chemical structure (i.e. a long-chain structure the general formula:

RRR

Ii \

Si-O-Si-O-Si-O

I I t

RRR

where R is usually a lower alkyl radical, which effects the crosslinking between the chains), but the poly-

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biu / c-i -oaisuhe νοα ovarian type usually incompatible with those of the peroxide type and the catalyst useful for the soap type mixtures (i.e. a metal soap) usually acts as a polymerization inhibitor in the peroxide-type mixtures. The potential semiconductor material, which according to the invention is added to the mixture or preferably to the conductive particles in a pretreatment, can also be an inhibitor for the polymerization of the resin. Silicone mixtures containing fillers such as silica, Containing asbestos, mica, etc., which increase the viscosity of the unpolymerized mixture, are in accordance with the invention also useful.

In addition to the silicone mixtures preferred for forming the matrix Other flexible or elastomer-forming, monomeric or flowable intermediate polymer mixtures can be used as matrix-forming Substances are used. Such mixtures include the natural and synthetic rubber types, polymerizable Urethanes, polyalkylenes, ethyl vinyl acetate, etc. In the case of natural or synthetic rubber types, however, sulfur should be excluded as a vulcanizing agent be.

Suitable catalysts for the peroxide type of silicones include: tert-butyl peroxypentalate, 2,4-dichloro-benzoyl peroxide, Gaproyl peroxide, lauryl peroxide, p-chlorobenzoyl peroxide, tert-butylperoxyisobutyril, acetyl peroxide, benzoyl peroxide, di-tert-butyl diperphthalate, tert-butyl peracetate, tert-butyl perbenzoate, dicumyl peroxide, 2,5-dimethyl-2, cdi- (tert-butyl peroxy) hexane, di-tert-butyl peroxide, Methyl ethyl ketone peroxide, p-methane hydroperoxide, cumene hydroperoxide, tert-butyl hydroperoxide, etc. Such catalysts can be used alone or in combination or in solution in a corresponding

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speaking solvents are used. It looks like, that a trace of aluminum powder or contact of the metal particles with an aluminum surface causes the formation the resistance materials according to the invention improved.

The material representing a potential semiconductor can be a substance that already has semiconductor properties or a substance that reacts with other substances in the mixture (e.g. the peroxide catalysts) Semiconductor material results. In many of the following examples, the semiconductor material is the reaction product of a Tin or lead soap with a peroxide, since the effect is first observed in this way. Suitable metal soaps for this type are among others tin laurate, bibutyltin dilaurate,> Stannous octoate, cobalt octoate, lead octoate and lead naphthenate. The reaction of such soaps with the above-mentioned peroxides results in a very useful semiconductor material; it is preferably carried out in the presence of an aryl compound, if the peroxide is not itself Aryl is. The conductivity of a bond between stannous oxide and aromatics has already been described by H. Inokuchi et al. (in "Symposium on Electrical Conductivity in Organic Solids"; Office of Ordinance Research, Duke Univ., Durham, N.C. April 20-22, 1960 (see chapter "The Photovoltic Behavoirs of Aromatic Hydrocarbons "). Zum Many metal complexes which have good semiconductor properties can also be used for the purposes of the invention; see "Organic Semi-Conductors "by Okamota and Walter Brenner, ITew Xork University, (1964), pp. 66-68. May also be used also the non-metallic complex semiconductors, such as the semi-quinone-type molecular complexes, as shown on the pages 69 to 71 of the above publication. In In this connection it should be noted that in US Pat. No. 3,469 a polymer of the quinone type is described, which as a pressure

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- ι -

sensitive resistance works. According to the invention, the amount of semiconductor material added to the powder can vary from about 95% (based on the weight of the powder) to proportions as low as 1 or 2 % .

As already mentioned, semiconductor materials, which prevent the hardening of the resin, or constituents or contain reaction products that prevent hardening are used; they evidently increase that desired effect. For example, metal soaps know how peroxide-curable silicone resins cure on the contact surface between the metal particles and the Har 2,31a tr ix prevent. In certain cases, water, a polymer, can also be used.! - cation inhibitor, can be added to make the metal powder prior to mixing with the resin-forming matrix material a To form slurry.

The products according to the invention show a remarkable drop in their electrical resistance when they are below Tension is set as well as compressed.

The invention is explained in more detail by means of the examples.

The strips manufactured according to the examples were tested between electrodes or search electrodes (probes) an ohmmeter "on" opposite sides of the strip round probes of 4.2 mm. were arranged $ the testing was carried out first without pressure and then under manual pressure.

example Λ

80 g nickel powder (moon 255 »a carboxyl nickel powder with a specific surface of about 0.5 m / g) were dry mixed with 2 g of very finely divided silver powder

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BATH

(y_9 from JDuPont), whereupon the powder mixture was added to a liquid mixture of 10 g benzene, 10 g tetrachlorethylene, 8 drops dibutyltin laurate and 10 drops tert-butyl perbenzoate, so that a slurry was formed. 90 g of silicone resin mixture (tin-catalyzed type) were mixed with this and the mixture was _{poured into a flat mold with a thickness of 1.6 "to 3 5} 2 mm. The resin cast in this way was kept at 90 ^° C. for 4 hours and then overnight at Cured 135 C. The resulting strip exhibited switching properties with a resistance between the two sides varying from 1 megaohm without pressure to down to 1000 ohms under pressure. This could be improved by aging for two months, after which the resistance was between 1 and 1.5 megohms and (under pressure) only 3 olim could be varied.

Example 2_

90 g kickel powder (moon 255) were introduced into a solution of 1 g tin octoate in 20 g tetrachlorethylene, whereupon the Let the mixture stand for a few hours at room temperature. In a separate vessel, 90 g of silicone resin (Dow ET7 3120, a tin soap-catalyzed silicone resin of pasty consistency, which contains an iron oxide filler) mixed with a solution containing 9 drops of tert-butyl perbenzoate contained in 20 g of ethyl alcohol, whereupon the mixture was degassed, for example by applying a vacuum. The excess liquid was on the metal slurry poured off and the rest mixed with the resin and poured the mixture into a shallow bowl. The shell was slowly heated to 95 ° C and held at this temperature for one hour, resulting in partial curing low steam generation. After the sticky mixture has been left to stand at room temperature for a further 24 hours

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curing was completed at 150 ° C. Stripes from about 0.8 to 3 »2 mm in thickness showed a resistance of 100,000 ohms without the application of pressure over the entire thickness down to 1 ohm under pressure.

B is ρ ie 1 3

100 g of nickel powder (Mond 255) were mixed with a solution of 2 g of tin octoate in 20 g of butanol and left to stand for a few hours. In a separate vessel, 100 g of silicone resin mixture (GE RTV 550, a tin-catalyzed polymerizable resin) were mixed with a solution of 0.5 g of tin laurate and 9 drops of tert-butyl perbenzoate in 20 g of butanol; The resin solution was mixed with the metal slurry and the mixture was degassed and poured into z \ re ± shallow bowls, one of which was left uncovered, the other was covered. The curing of the mixture in the covered bowl was delayed. Both bowls were cured according to Example 4. The resulting cured strips gave a product with switching action which had a resistance between 10,000 ohms without application of pressure down to about 0.2 ohms under application of pressure, the pressure sensitivity being different for the differently treated strips, namely for the one below Delay cured strips was better.

Example 4

In a mixture of 1 g of stannous octoate, 40 g of perchlorethylene and 10 drops of t-butyl peroxybenzoate were dispersed 97 g of carbonyl nickel powder and the mixture heated in a loosely closed container gradually within one hour to 110 ⁰ C. In a separate vessel 102 g of silicone resin mixture (GE ETV 21, a polymeric with metal soap

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sated mixture.) and 0.5 S dibutyltin laurate mixed and degassed. After cooling, the nickel powder and the remaining perchlorethylene were mixed with the resin and cast into a strip which was cured for two hours at 80 ° C. The cured strip was approximately 1.6 mm thick and worked extraordinarily, well as a resistor from the Switching action type; he pointed between Below the electrodes of the ohmmeter a resistance of 1 megohm without the application of pressure down to 10 ohms manual printing application.

Example 5

The procedure was as in Example 4-, but with a different one soap-hardened silicone resin was used, namely GE-HW 560, and wherein the ratio of nickel to resin has been increased to 1: 1. The resistance range of the product obtained, that exhibited a diode effect ranged from less than 10 ohms to 1 megohm.

The above-mentioned diode effect or polarizability under pressure was detected on a 16 mm thick material operating at 0.84 to 1.05 at and 5 volts with a limiting resistor of 1,100 ohms in series was subjected to a load of 10 to 15 cycles per minute. Under these Conditions, the material showed a gradual decrease in conductivity over a period of 5 to 15 minutes, which varies from resistance in the low range of less than 1 kilo ohm to over 100 kilo ohms in the upper Area expressly retained the latter value.

A polarity reversal between the silver electrodes in the Specimen produced an immediate reverse response at the low values below 1 kilo ohm. The mechanical Strength remained constant. The electrical effect continues among the cycles even if the current is interrupted.

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Under "pressure: polishable products, like those in example 5 described, can be used as passive counting materials, flexible electromechanical ^ storage sensors, permanent Display and reading devices that can be deleted by switching the electrical polarity, upstream and downstream switching aids in teaching devices, slow moving switches for statistical distribution and other uses where the properties of durability and Resistance are particularly pronounced, so that the energy supply, the workload and the time, force and stress vectors can be recorded. One can use this way to simplify bio-feedback circuits and instrumentation facilities come that have a memory have within the sensor element.

Using the procedure described in Examples 1 to 5 continued to manufacture products in which the conductive metal was silver, tin, copper, and silver-plated nickel nickel coated with mercury. For nickel with a mercury coating, the product exhibited a range of resistance from 1 ohm up to 1 megaohm, after a period of about 10 to 45 days the resistance under pressure is 1000 ohms fraud. If coal is also used in one of the above cases, this obviously absorbs catalyst from the resin and then a long curing time is necessary.

Example 6

The procedure was as in Example 4, but using a silicone resin of the foam type (GE-RTV 7) as the matrix that has been cured with dibutyltin laurate; the nickel particles had been pretreated according to Example 4. The hardening of the resin was prevented by the nickel coated with peroxide.

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hesitates, but the foaming was normal. After the product had been cured for an additional two weeks at room temperature, a 9j5 now thick, obtained non-sticky tape, its Uraformer effect in a low resistance range of 25 ohms at a Pressure from 4.22 at to 4 ohms was 7.4 at.

A second addition was made by adding 10 g of chloroethylene to 30 g of stannous octoate and then adding 10 g of tert-butyl peroxybenzoate. Heat is generated during the addition. 0.5 g of this second additive was added to 6.3 g of the polyol portion of a two-component polyurethane resin. In such polyurethane mixtures, one component is a polyisocyanate and the other is a polyol in a molar ratio of about 2: 1. The resin components used were Polycrin 879 (made by Baker Oastor Oil Co.), to which 15 g of the nickel mixture were added, and 3? 7 g of polyisocyanate, Varite 689 M-2 (also made by Baker Castor Oil Co.). The mixture was poured onto aluminum foil heated to 90 ° to initiate curing, which was then completed by standing at room temperature for 10 hours. Finally, the mixture was then fully cured for a further 30 minutes at 90 ° C. and resulted in a flexible PiIm 1.6 mm thick. The S ¹ IIm had a resistance between the electrodes in the range of 100 ohms without the application of pressure "down to 6 ohms with manual application of pressure.

Untreated metal with a large surface area or equivalent Carbon can be added up to a ratio of metal to resin of 0.4 to 0.5i1j for linearity and to improve the sensitivity of converters.

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Additional investigations were carried out to provide a better understanding of the greater constant fluctuations that can be obtained with this method carried out. The experiments confirmed the assumption that the results are due to the formation of an incompatible dispersed phase and to the Delay or prevent the polymerisation of the resin in the immediate vicinity of the conductive one Particle. According to Example 4, the metal-containing mixture initially produced contains both tin octoate and the peroxide inhibitor and a reaction takes place between the tin octoate and the peroxide. In connection with this Hypothesis should be noted that the instructions for use for the silicone resins of the "A and B platinum type" (GE-RTV-600 series) read that these resins are incompatible are made with RTV resins that are hardened with tin soaps. The instructions for use can also be found that all forms, etc. used for the latter RTV resins are carefully washed with soap and water or with Solvents have to be cleaned, after which they have to be provided with an insulating coating after drying, before they are used in RTV-600 series resins. It is also known that particles of colloidal size, like the conductive particles of the mixture, they are usually charged and, in suspensions, ions of opposite charge attract. As already mentioned, apparently a reaction takes place between the benzoyl peroxide and the. Tin octoate when these are mixed with the metal particles according to Examples 1 to 6. It seems to be here to act a reaction that is much more complex than a simple redox reaction in which only stannous oxide arises, although stannous oxide itself is a well-known semiconductor. The reason why such a reaction is essential seems to be more complex, is that much better results are obtained if the peroxide is an aryl

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is peroxide or if, e.g. as a solvent, aryl groups are.

A very "special advantage of the invention is that that the high conductivity can be obtained under pressure "without the elastomeric resin matrix with metal particles overloads. A product is thus obtained with greater flexibility, higher tensile and compressive strength and better resistance under repeated pressure cycles. In addition, the product has a lower specific weight: so has that according to the invention Product with a dense silicone matrix a spec. Weight of around 2.5ι while a heavily loaded with metal particles Product a spec. Weight from 3.5 to 4.0. 3? For certain A lower specific weight can be important for application purposes.

The products of the invention can be made within a total conductivity range of E.g. 0.01 ohms under pressure up to 100 megohms without application of pressure. In practice, the conductivity depends on pressure on the thickness and hardness of the matrix layer and these two parameters can easily be varied. The generated Conductivity can be directional or anisotropic; for example, several spaced pairs of pressure sensitive conductors act across the Thickness of a web of material are arranged independently, i.e. there is little, if any lateral conduction or interference that might be caused by adjacent pairs of conductive probes.

PATENT CLAIMS:

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Claims (9)

PATENT CLAIMS V 1) 7 Pressure-sensitive electrical resistance element, which has a resistance of 1 "to several megohms in a pressure-free state in a thickness of about 3.2 mm up to about 100 to 0.5 ohms under pressure and that from an essentially discontinuous phase is sufficient conductive particles about 0.1 to 44 microns in size in a matrix of hardened elastomeric resin wherein the ratio of resin to conductive particles is about 100: 75 Ms 100: 110, characterized in that the elastomeric resin is on its contact surface with the conductive particles is ■ incompletely cured. 2) resistance element according to claim 1, characterized in that the elastomeric resin is a Silicone resin is. -3) resistance element according to claim 2, characterized in that the conductive particles Metal particles are coated with a layer of the reaction product, a metal soap and a Peroxy compound. 4) resistance element according to claim 3, characterized in that g. e - 409835/0364 indicates that the metal particles are coated Never give the reaction product of tin octoate and a peroxy compound. 5) resistance element according to one of claims 1 to 4-, characterized in that di.e conductive Particles are separated from the matrix by a layer made of a material with semiconductor properties. 6) A method for producing the electrical resistance elements according to any one of claims 1 to 5> _5, characterized in that one (1) a polymerizable elastomeric resin blend of liquid to pasty consistency, which can be polymerized with the help of a polymerization catalyst and whose polymerization is delayed or prevented by the presence of an inhibitor can be, xvorauf man (2) conductive particles approximately 0.1 to 4 microns in size mixed with the resin mixture in such a way that that the ratio of resin to conductive particles is about 100: 75 to 100: 110 and that in addition introducing a polymerization catalyst and a polymerization inhibitor into the mixture, whereupon man (3) the mixture hardens. 7) Method according to claim 6, characterized that a silicone resin which is hardened by a metal soap is used as the elastomeric resin and wherein the polymerization inhibitor is a peroxy compound. 409835/0 364 8) Method according to claim 7j characterized that the elastomeric resin is a silicone resin which is cured by a peroxy compound and in which the inhibitor is a metallic soap. 9) Method according to claim 7 or 8, characterized in that the conductive particles Metal particles used that are pretreated before admixing with a solution of the polymerization catalyst and the inhibitor. 409835/0364