JPH05325647A - Silicone gel porous conductor and its manufacture - Google Patents

Abstract

PURPOSE:To attain a large volume change, make linear the correlation between the distortion and resistance value, and expand the applicable range as a pressure-sensitive conducting element by forming many holes in the silicone gel containing a conducting filler. CONSTITUTION:For manufacturing a silicone gel porous conductor by applying the stripping method, a conducting filler 2a, soluble grains 7, and the stock solution of silicone gel are mixed into an A-component SA and a B-component SB at the preset wt.%, a catalyst is mixed, and the mixture is hardened. The components SA, SB are reacted to obtain a hardened object nearly closely stacked with the filler 2a and the grains 7, and hardened silicone gel is formed with the filler 2a and the grains 7 dispersed. It is sliced to the proper thickness, holes 4 are formed when it is boiled in a tub B and dried, and a disk-like sheet 1 made of the porous conducting silicone gel having continuous bubbles is obtained. A large volume change is attained, and the applicable range can be expanded.

Description

Detailed Description of the Invention

[0001]

[Object of the Invention]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention enables a large volume change, and makes the correlation between strain and resistance more linear, not only as an ON / OFF contact element, but also as a pressure-sensitive conductive material. The present invention relates to a silicone gel porous conductor with an expanded application range as an element.

[0002]

BACKGROUND OF THE INVENTION Conventionally, a conductive rubber containing a conductive filler in natural rubber, SBR, NBR, butyl rubber, etc.
As a contact element for calculators and keyboards of personal computers, and as a pressure-sensitive conductive element for electronic musical instrument keyboards, variable-speed electric zoom switches for video cameras, etc., by utilizing the relationship between the strain and the continuous change in resistance. Widely used. Under these circumstances, the present applicant has paid attention to the cushioning property and the vibration damping property in recent years, and has been focusing on the silicone gel which is being widely used as a shoe pad, a cushioning pad for various exercise equipment, an insulator for OA equipment and the like. A conductive silicone gel containing a conductive filler is disclosed in Japanese Patent Application No. 183746/1985.
(Japanese Patent Laid-Open No. 62-44902).

However, even conductive silicone rubber, which is highly evaluated among the conductive rubbers, requires a large scale of equipment due to the kneading and vulcanization of the rubber itself, making it difficult to process in general, and at the time of processing. Since a large amount of force or high heat is applied, the electrical performance is not stable due to the destruction of the conductive filler, etc. Furthermore, since the viscosity of the polymer itself is high, the amount and type of conductive filler that can be added is limited, resulting in There are various problems such as the inability to freely control the characteristics of the conductive rubber.

On the other hand, the conductive silicone gel proposed by the applicant of the present invention solves these problems, but it is also applied to an element requiring a larger volume change. In the case of, and when the correlation between the strain and the resistance value needs to be more linear, further improvement is required.

[0005]

[Technical Items Attempted to Develop] The present invention has been made in view of such a situation as described above, and enables the conductive silicone gel to undergo a further large volume change, and at the same time, correlates the strain and the resistance value. As the relationship is more linear, simply O
It is an object of the present invention to provide a silicone gel porous conductor and a method for producing the same, which has an expanded application range not only as an N / OFF contact element but also as a pressure-sensitive conductive element.

[0006]

[Constitution of Invention]

[Means for Achieving the Object] That is, the silicone gel porous conductor according to the first invention of the present application is characterized in that a large number of holes are formed in a silicone gel containing a conductive filler.

The second invention of the present application, which is a method for producing a silicone gel porous conductor, includes a step of mixing a conductive filler into a stock solution of the silicone gel before curing, and a step of dissolving or contracting the silicone gel. Alternatively, a step of mixing particles that are heat-dissipative and that does not oxidize and corrode the conductive filler, a step of curing the stock solution, and then eluting the particles with a solvent, or shrinking by drying, or heating. And a step of forming vacancies at the site where the particles were present and the particles were present.

Further, the method for producing a silicone gel porous conductor according to the third invention of the present application is the step of mixing a conductive filler into the stock solution before curing of the silicone gel, and the dielectric loss coefficient is higher than that of the stock solution. A step of adding a volatile liquid that is large and does not dissolve in the stock solution, and that does not oxidize and corrode the conductive filler to make it turbid, and vaporize particles of the volatile liquid by dielectrically heating the turbid stock solution. The method is characterized by including a step of performing expansion and cross-linking and hardening of the stock solution. These inventions are intended to achieve the above object.

[0009]

The present invention will be described in detail below. First, the substances applied to the present invention will be described. First silicone gel is made of a dimethyl siloxane component units, (hereinafter referred to as component A) stock solution serving diorganopolysiloxane silicone gel used in the following formula _{^{[1]: RR 1 2 SiO-}} (R 2 2 SiO) ^{_{n SiR 1 2 R ... [1}} ] [ wherein, R is an alkenyl group, ^{R 1} is a monovalent hydrocarbon group having no aliphatic unsaturated bond, ^{R 2} is a monovalent aliphatic hydrocarbon group (At least 50 mol% of R ²
Is a methyl group, and when it has an alkenyl group, its content is 10 mol% or less), and n is the viscosity of this component at 25 ° C. is 100 to 100,000 cSt.
The viscosity at 25 ° C is 50
00cSt or less, and at least 3 S in one molecule
Organohydrogenpolysiloxane (B) which is a stock solution of a silicone gel having a hydrogen atom directly bonded to an i atom
Component) and the ratio (molar ratio) of the total amount of alkenyl groups contained in the component A to the total amount of hydrogen atoms directly bonded to the Si atoms in the component B is 0.1 to 0.1.
It is an addition reaction type silicone polymer obtained by curing a mixture adjusted to 2.0.

To explain this silicone gel in more detail, the above-mentioned component A has a linear molecular structure, and the alkenyl groups R at both ends of the molecule are added to hydrogen atoms directly bonded to the Si atom in component B. And a compound capable of forming a crosslinked structure. The alkenyl group present at the terminal of the molecule is preferably a lower alkenyl group, and a vinyl group is particularly preferable in view of reactivity. R ^{1 at the} terminal of the molecule is a monovalent hydrocarbon group having no aliphatic unsaturated bond, and specific examples of such a group include an alkyl group such as a methyl group, a propyl group and a hexyl group. , A phenyl group and a fluoroalkyl group. In the above formula [1], R ² is a monovalent aliphatic hydrocarbon, and specific examples of such a group include an alkyl group such as a methyl group, a propyl group and a hexyl group, and a vinyl group. And lower alkenyl groups. However, at least 50 of R ²
When it is a mol% methyl group and R ² is an alkenyl group, the amount of the alkenyl group is preferably 10 mol% or less. If the amount of alkenyl groups exceeds 10 mol%, the crosslink density tends to be too high and the viscosity tends to be high. Also n
The viscosity of this A component at 25 ° C. is usually 100 to
100,000 cSt, preferably 200-20000
It is set to fall within the range of cSt.

The above-mentioned component B is a cross-linking agent for component A and is S
The hydrogen atom directly bonded to the i atom adds to the alkenyl group in the A component to cure the A component. The component B has only to have the above-described action, and as the component B, those having various molecular structures such as linear, branched, cyclic, or network can be used. In addition, a hydrogen atom and an organic group are bonded to the Si atom in the component B, and this organic group is usually a lower alkyl group such as a methyl group. further,
The viscosity of component B at 25 ° C. is usually 5000 cSt or less, preferably 500 cSt or less. B like this
Examples of the component include organohydrogensiloxane whose both ends are blocked with triorganosiloxane groups, a copolymer of diorganosiloxane and organohydrogensiloxane, tetraorganotetrahydrogencyclotetrasiloxane, HR ¹ ₂ SiO 1 Copolymer siloxane composed of 1/2 units and SiO 4/2 units,
And HR ¹ ₂ SiO 1/2 unit and R ¹ ₃ SiO 1 /
Mention may be made of copolymer siloxanes composed of 2 units and SiO 4/2 units. However, in the above formula, R ¹
Has the same meaning as above. And Si in the above B component
The ratio of the total molar amount of hydrogen atoms directly bonded to the total molar amount of alkenyl groups in the component A is usually 0.
It is produced by mixing the component A and the component B and curing the mixture so as to be in the range of 1 to 2.0, preferably 0.1 to 1.0.

The curing reaction in this case is usually carried out using a catalyst. The catalyst used here is preferably a platinum-based catalyst, and examples of this catalyst include finely pulverized elemental platinum,
Examples thereof include chloroplatinic acid, platinum oxide, platinum-olefin complex salts, platinum alcoholates, and chloroplatinic acid-vinylsiloxy acid complex salts. Such complex salts are composed of A component and B
It is usually used in an amount of 0.1 ppm (platinum equivalent, the same applies below) or more, preferably 0.5 ppm or more based on the total weight of the components. The upper limit of the amount of such a catalyst is not particularly limited, but, for example, when the catalyst is liquid or when it can be used as a solution, 200 p
An amount of pm or less is sufficient.

Here, compounds such as sulfur, phosphorus, tin compounds and amines easily react with the above platinum catalyst, so that crosslinking,
These are so-called catalyst poisons that inhibit curing, and specifically, these include potassium sulfate, ammonium sulfate, as sulfur compounds.
Sulfates such as ammonium persulfate, sodium persulfate, sodium sulfite, hydrosulfide, sulfur hydroxyamine,
Sulfur, carbon disulfide, sodium sulfoxylate (Rongalit), thioglycolic acid and its derivatives such as butyl thioglycolate, mercaptan compounds such as β-mercaptopropionic acid, thioacetic acid, thiourea, sulfonate,
Examples thereof include surfactants such as sulfate ester salts. Examples of the phosphorus compound include phosphoric acid, ammonium phosphorous phosphite, phosphorous acid such as hypophosphorous acid sodium pyrophosphate, sodium acid metaphosphate and sodium tripolyphosphate, and salts thereof, trimethyl phosphate, dialkyldithiophosphoric acid, phosphite ester and the like. Be done. Further, tin compounds include various tin chlorides and tin oxides, and other examples include rhodan salts and stannous sulfate. Amine compounds include iminobispropylamine, triethylamine, 3-diaminopropylamine, tetramethylethylenediamine. , 3-methoxypropylamine and the like.

Then, the above-mentioned components A, B and the catalyst are mixed and left to stand at room temperature or heated to cure to form the silicone gel used in the present invention. When curing by heating, the heating temperature is usually 50.
~ 160 ° C. The silicone gel thus obtained has a penetration of usually 5 to 250 as measured by JIS (K-2207-1980 50 g load). Such hardness of the silicone gel allows the amount of the above-mentioned component A to form a crosslinked structure with the hydrogen atom directly bonded to Si in the component B. As another method, it can be adjusted by previously adding a silicone oil having methyl groups at both ends in an amount within a range of 5 to 75% by weight with respect to the obtained silicone gel. The silicone gel can be prepared as described above, or a commercially available one can be used. Examples of commercially available products that can be used in the present invention include CF502
7, TOUGH-3, TOUGH-4, TOUGH-
5, TOUGH-6, TOUGH-7 (made by Toray Dow Corning Silicone Co., Ltd.) and X32-902 / cat1
300, KE1308 / cat1300-L4 (manufactured by Shin-Etsu Chemical Co., Ltd.), F250-121 (manufactured by Nippon Unica Co., Ltd.) and the like.

In addition to the components A and B and the catalyst described above, pigments, curing retardants, flame retardants, fillers and the like may be added within a range that does not impair the properties of the silicone gel.
In addition, in some cases, in order to enhance other functions such as anti-vibration and cushioning properties, a silicone gel mixed with a filler of fine hollow spheres may be used, and such a material may be Philite manufactured by Nippon Philite Co., Ltd. (Registered trademark), Expancel (registered trademark) sold by the same company, Matsumoto Microsphere (manufactured and sold by Matsumoto Yushi-Seiyaku Co., Ltd.), and the like.

Next, the conductive filler added to impart conductivity to the silicone gel will be described.
The conductive filler is a conductive substance such as carbon black, carbon fiber, graphite, metal powder, metal oxide, metal flake, and metal fiber, and includes fine particles of any shape such as spherical, fibrous, and flake. Furthermore, there are fine particles obtained by plating or coating conductive organic or inorganic fine particles with a conductive substance such as nickel, cobalt, gold or silver. The conductive filler used in the silicone gel porous conductor of the present invention may be any of these conductive fillers whose surface does not oxidize and erode when mixed in the silicone gel stock solution.

Further, it is generally desirable that the conductive filler is uniformly distributed in the silicone gel, and it is necessary to take care so as not to cause precipitation as much as possible. For this purpose, it is preferable to use glass-based or resin-based minute hollow spheres coated with a conductive metal such as nickel. In addition,
For example, if fine particles of a magnetic material such as nickel are used, not only conductivity can be imparted, but magnetism can also be imparted, so that a magnetically sensitive silicone gel porous conductor can be made, and magnetic shielding, magnetic detection, etc. It can be used for.

Next, a method for producing the silicone gel porous conductor will be described. To make the conductive silicone gel porous, a drying shrinkage method, an elution method, a microwave heating method,
A heating extinction method can be applied.

First, a method for producing a silicone gel porous conductor by applying the dry shrinkage method will be described. The dry shrinkage method is a method in which the swollen granules mixed in the silicone gel are dried and shrunk, and this is removed from the traces of the swollen granules. This method will be specifically described with reference to FIGS. 1 and 2. As an example of swollen granules, sodium alginate binds to calcium ions to form water-insoluble calcium alginate on the surface or inside the surface. Spherical particles in a hydrogel state were used.

The sodium alginate used here is a typical substance of alginate, which is kelp, cabbage,
It is a substance that forms cell membranes of brown algae such as arame, and is used as an emulsion stabilizer, a viscous agent, and a mold release agent. This substance is an extremely highly viscous colloidal substance with strong hydrophilicity,
It has the property that it dissolves well in both cold water and warm water to form a very viscous and homogeneous solution. When a metal salt of aluminum, barium, calcium, copper, iron, lead, zinc, nickel or the like is added to this solution, a water-insoluble alginate is formed. Since this water-insoluble alginate is in a hydrogel state immediately after being taken out from the aqueous solution, it has a property that when it is dried, the water evaporates to largely contract. The dry shrinkage method utilizes such shrinkage of sodium alginate.

That is, in FIG. 1, first, a 1% sodium alginate aqueous solution A and 1
% Calcium chloride aqueous solution C is prepared, sodium alginate A is sucked into the tube using the microtube pump P, and this is dropped into the calcium chloride aqueous solution C. By doing so, the dropped particles settle down while being spherically shaped by hydraulic pressure, and at the same time, become insolubilized from the surface and gradually insolubilize to the inside to become swollen granules 2 of hydrous calcium alginate gel. Depending on the concentration of sodium alginate, the diameter of the tube, etc., the average of 3 m
Since m-diameter particles were obtained, the particles were taken out of the aqueous solution, washed with water, drained appropriately, and then the swollen particles 2, the conductive filler 2a, and the silicone gel stock solution were mixed. .. In the examples, the weight ratio of the conductive filler 2a, the swollen granules 2 and the stock solution of the silicone gel was 1:
A component S _A and B component S _B were distributed and mixed so that the ratio became 1: 2.

Next, the A component S _A and the B component S _B are mixed, and as shown in FIG. 2, the mixture is poured onto a glass plate 3 provided with spacers having a thickness of 5 mm on the four sides, and also from above. By stacking glass plates and leaving them in a heating furnace kept at 80 ° C. for 50 minutes, the A component S _A and the B component S _B react with each other to cure the whole, and the conductive filler 2a and the swollen granules. A silicone gel sheet 1 in which 2 and 2 are dispersed is obtained. Subsequently, the upper and lower glass plates were removed, and the heating furnace was heated to 100 ° C. and left for 3 hours, and the swollen granules of calcium alginate were dried and shrunk as shown in FIG. Voids 4 as removal marks are formed at the site where the swollen granules were present in the sheet 1, and dry and shrunk particles of calcium alginate having a diameter of 0.4 mm or less are formed in the pores 4. It adheres as fine particles 5. By washing away the dried and shrunk calcium alginate fine particles 5 with water, the silicone gel is made porous, and the added conductive filler imparts conductivity to the silicone gel. The body sheet 1 will be obtained.

Incidentally, in this embodiment, since the adjacent pores 4 are in a continuous state with each other, a method of washing with water can be adopted, but when the mixing ratio of the swollen granules 2 is low, the respective pores are small. Since the particles 4 are not continuous and the fine particles 5 cannot be washed with water, it is necessary to take additional steps such as immersing the particles in ammonia water or reducing the concentration of sodium alginate. Needless to say, it is also possible to deal with this by forming adjacent pores continuously by using a highly water-absorbent resin or a water-swellable granule of a water-soluble granule to be described later having a high volume contraction rate.

In the above dry shrinkage method, the swollen granules are mixed in the silicone gel stock solution together with the conductive filler, so that the conductive filler and the swollen granules have a chance to come into direct contact with each other. It is necessary to use a body that does not oxidize and erode the conductive filler used and lose its conductivity. Since the silicone gel porous conductor obtained by such a dry shrinkage method has relatively large pores, it can be applied to a bulky impact sensor or the like.

Next, a method for producing a silicone gel porous conductor by applying the elution method will be described. The elution method is
This is a method in which soluble particles are mixed in silicone gel and cured, and then the particles are eluted in a solvent to form a trace. This method will be specifically described with reference to FIG. 3. Here, sucrose is used as the soluble granule and water is selected as the solvent for eluting it.

The sucrose used is generally commercially available, and there are two kinds of conductive fillers, specifically, Metallite CG manufactured by Metallic Engineering Co., which is a spherical ceramic coated with silver. Of 1
To 9 parts, 3 parts of DONACARBO S-241, a pitch-based carbon fiber manufactured by Dainippon Ink and Chemicals, Inc., was mixed and used.
As the silicone gel, KE1308 manufactured by Shin-Etsu Chemical Co., Ltd. and 1300-L4 as its catalyst were used. This one has a penetration of 10 when cured normally.
It has been adjusted to zero.

Further, the conductive filler 2a, the soluble granules 7 and the stock solution of the silicone gel are in a weight ratio of 2:
3: 3 become as component A S _A, mixed by distributing the component B S _B, further by mixing the component A S _A and the B component S _B and the catalyst, poured into a cylindrical mold K, which Was cured in a standing state. In addition, in order to remove air taken in during mixing, it is desirable to perform vacuum degassing before curing. Here, if the amount of the undiluted solution of the silicone gel is a little larger than the conductive filler 2a and the soluble granules 7, the conductive filler 2a and the soluble granules 7 will naturally fall during curing, and sequentially. It deposits from the bottom of the silicone gel stock solution and cures in a state where the silicone gel stock solution fills the surrounding area. Alternatively, if pressed from above and below during this period, the excess silicone gel stock solution squeezes out between the conductive filler 2a and the soluble granules 7 as if it was squeezed out, and it is suitable between the conductive filler 2a and the soluble granules 2a. Cures in the presence of an amount of undiluted silicone gel.

Therefore, for example, when left at 80 ° C. for 1 hour, the A component S _A and the B component S _B react with each other to form a cured product in which the conductive filler 2a and the soluble particles 7 are deposited almost densely inside. can get. Next, the cured silicone gel in which the conductive filler 2a and the soluble granules 7 are dispersed is taken out from the molding die K and sliced into an appropriate thickness, for example, every 10 mm, and this is stirred in hot water. Put in B. Then, after repeating boiling while exchanging hot water several times, if hot and cold water is cut off and dried, sucrose will be dissolved in water at the site where sucrose, which is the soluble granules 7 in the silicone gel, was present. Then, the pores 4 which are the traces of the removal are formed, and the disc-shaped sheet 1 of the conductive silicone gel which has been made porous in the form of open cells is obtained.

In general, a skin layer is apt to be formed on a portion which is hardened by contact with a molding die, which inhibits elution of soluble granules, so that the skin layer is peeled off.
If the soluble granules are eluted after the surface layer is perforated or crushed, the elution is promoted. Further, an absorbent sheet is placed on a substantial boundary surface of the silicone gel such as a mold or a glass plate when the silicone gel is cured, and the absorbent sheet is brought into contact with the stock solution of the silicone gel, and then the absorbent sheet is removed. If the absorbent particles are peeled off and the soluble granules are eluted, the absorbent sheet removes the excess silicone gel stock solution from the surface layer and the skin layer is not formed during gel hardening, facilitating the dissolution of the soluble granules. It There are cases where the absorbent sheet is peeled off after the silicone gel is cured, and cases where it is peeled after contact and before curing.The absorbent sheet is made of paper, cloth, non-woven fabric or the like which has the ability to absorb the gel stock solution. A combination of can be applied. Further, in order to accelerate the elution rate of the soluble granules, a method of mixing a soluble granule such as sucrose with an easily water-soluble substance having a higher solubility than this granule can be adopted.

Further, since the conductive filler and the soluble granules are mixed in too small amounts, a layer made of only silicone gel is formed on a part of the surface layer. When an electrode is provided on the surface layer, the electrode is made of this silicone gel only. It is necessary to avoid the layer and cut off the layer containing the conductive filler or the layer consisting of the silicone gel. Further, in the above embodiment, the silicone gel is cured in the molding die, but it is of course possible to directly mold it on a flat plate such as a glass plate into a sheet shape.

Further, in the above-mentioned examples, sucrose was used as the soluble granules and water was used as the solvent thereof, but various soluble granules and their solvents can be selected in addition to this in the elution method. However, the solubility constant (Solubility Para
If the solvent is more than 9.9, it cannot be applied because it causes the silicone gel to swell or corrode significantly. Therefore, water is the most suitable solvent to be selected. And, when the solvent is water, it is necessary to select water-soluble granules, and the water-soluble granules include sodium polyacrylate, carboxymethyl cellulose, polyethylene oxide, polyvinylpyrrolidone, amide acrylate, glue, gelatin. , Casein, polypeptide, fungus, agar, sodium alginate, glucose,
There are sucrose, pullulan which is a natural polysaccharide, xanthan gum, starch, sodium ascorbate and the like, and among them, those which do not oxidize and corrode the conductive filler when they are dissolved in water are selected. When the soluble granules are starch, an enzyme solution can be used in water as a solvent, and examples of the enzyme include amylase, maltase, pepsin, trypsin, elepsin, glucose and fructose. On the other hand, the solubility constant is 9.9 except water.
Examples of the above solvent include acetone, ethanol, methanol, and the like, and polyvinyl alcohol, methyl cellulose, ethyl cellulose, water-soluble nylon, shellac, styrene, and the like as those which can be dissolved therein, but a conductive filler and these. Select a material that does not oxidize and corrode the conductive filler due to contact with soluble granules or solvent penetration.

Here, the fact that the conductive filler is not oxidatively corroded can be said also in the above-mentioned examples and the examples described later. For example, in the case of observing the influence of the silicone gel stock solution, in the silicone gel stock solution. It can be determined by observing the surface and confirming the resistance value change after soaking in the same manner, and similarly, contacting with swollen granules or soluble granules or a solvent thereof, and observing the change thereafter, Whether or not it can be used can be confirmed, and it is determined and selected based on the compatibility with the conductive filler used.

Since the pores of the silicone gel porous conductor obtained by the elution method can be made considerably fine, it is suitable as a pressure-sensitive conductive element that requires the sensing of fairly minute changes.

Next, a method for producing a silicone gel porous conductor by applying a microwave heating method will be described.
In this microwave heating method, an easily volatile liquid having a large dielectric loss coefficient is dispersed in a silicone gel, and after the gel is hardened, the liquid is heated in a high frequency electric field by dielectric heating to raise the temperature of the liquid and evaporate and expand it. In addition to this, the silicone gel stock solution is also cross-linked and cured.

This method will be specifically described below with reference to FIG. First, the easily volatile liquid is a substance that does not contain a substance that is a catalyst poison, has a dielectric loss factor larger than that of the gel stock solution, and can be mixed and stirred to form an emulsion using the stock solution before curing as a dispersion medium. A liquid which is easily volatilized and which does not oxidize and corrode the conductive filler is selected as described above. Examples of such liquid include water, ethyl alcohol, methyl alcohol and the like. The reason for selecting a substance having a dielectric loss coefficient larger than that of the undiluted gel solution is that the dielectric constant ε and the dielectric tangent ta of the dielectric heating by applying a high frequency.
There is a selective heating property that the product with n δ, that is, the faster the dielectric loss coefficient is, the faster it is heated. This is because heat is transferred to the stock solution therein, and the volatile liquid itself is essential for vaporizing and expanding to secure and form pores in the crosslinked and hardened tissue. In addition, in order that the easily volatile liquid can be turned into an emulsion when mixed and stirred, it is desired that the easily volatile liquid does not dissolve in the stock solution before curing and the specific gravity is close to this.

In this embodiment, water is applied as such an easily volatile liquid, and the components _{A A} and B A as the silicone gel stock solution are applied.
Water W is mixed into a mixture of the component S _B and the catalyst in an emulsified liquid. In this case, water is mixed into each of the A component S _A and the B component S _B , and then the whole is mixed again. Is desirable.
Also at this time, the conductive filler 2a is mixed into each of the A component and the B component. In addition, in this example, when the silicone gel was adjusted to have a penetration of 40 when it was normally cured, the conductive filler 2a was added to 30 parts of each of A component S _A and B component S _B. 20 parts and 3 parts of water are mixed and well stirred to disperse so that the whole becomes a cloudy liquid, and then A component S _A and B component _B are mixed and poured into a dish-shaped mold H. Then, dielectric heating is performed by the high frequency M of 2450 MHz in the microwave region. This gives a volume of about 20
After 0% expansion, crosslinking and hardening proceed, and after 10 minutes, the whole gels.

By the above operation, each particle of water dispersed as an emulsion in the raw material before curing rises in temperature faster than the stock solution before curing, and this heat is the surrounding dispersion medium before curing. It is transferred to the undiluted solution and assists the inductive heating of the undiluted solution, which has inferior dielectric heating properties to water, and accelerates its crosslinking and curing. At the same time, the water itself vaporizes and expands at each occupied position, expanding the space occupied by the water in the pre-curing stock solution. At this point, the cross-linking and hardening of the undiluted solution is also progressing, and the cross-linking and hardening is further progressing in the state where the space is expanded, and pores 4 are formed in the part where water was present, and the whole becomes porous and fixed To be done. In order to ensure the cross-linking, after that, for example, 1 to
Leave it for two hours.

In order to carry out this work continuously, although not shown, the raw material before curing is poured out onto a belt conveyor or the like, passed through a tunnel for irradiating microwaves, and when further heating is required. May pass through a tunnel that irradiates far infrared rays or the like. Further, after the conductive filler and water are mixed and dispersed to form a turbid liquid, if dielectric heating is performed for a while, a slight difference in specific gravity between the three causes the conductive filler and the upper layer and the lower layer of the sheet to become conductive. The size and distribution of water particles are biased, so that a silicone gel porous conductor having characteristics is obtained.

In this embodiment, water is used as a representative of those having a large dielectric loss coefficient and being easily vaporized and expanded. However, when water alone is used, the pores formed tend to be independent. It is also possible to add a compound or a hydrolyzable agent that hydrolyzes to generate a gas. Such agents include sodium bicarbonate,
There are ammonium carbonate, urea, etc., and those that do not oxidize and corrode the conductive filler are selected.

Further, expandable micro hollow spheres can be applied as a foaming aid in the presence of water. EXPANCEL (registered trademark) sold by Nippon Philite Co., Ltd. is a micro hollow sphere having an average particle size of 40 μ, and is composed of vinylidene chloride and acrylonitrile copolymer as a shell wall and liquid isobutane encapsulated therein. 80 ℃
By heating above, the thermoplastic shell wall softens,
At the same time, the isobutane inside expands by gasification and expands the shell wall, but the shell wall is ruptured and the gas contained therein is released to contribute to the expansion of pores. Is. In this case, when a hollow sphere coated with a conductive substance is used as the conductive filler, it is necessary to make sure that the conductive filler is not destroyed.

According to this microwave heating method, the obtained silicone gel porous conductor has relatively large pores and it is difficult to obtain a highly accurate one, but it is possible to mass-produce relatively quickly. Become.

Next, in the heat extinction method, heat extinction particles are mixed in the silicone gel, and further an appropriate conductive filler is mixed and cured, and then this is heated to extinguish the heat extinction substance. This is a method of forming pores in the portion where the heat-extinguishing substance was present. This includes
For example, a sublimable substance such as naphthalene or dry ice is mixed with a conductive filler in a silicone gel stock solution and cured, and then heat is applied to sublime the sublimable material, or added when the silicone gel stock solution is cured. The sublimable substance is sublimated by heat, and in this case as well, the heat-dissipating particles such as the sublimable substance are selected from those that do not oxidize and corrode the conductive filler.

Since the silicone gel porous conductor thus obtained has a large number of pores formed in the conductive silicone gel, the pores ensure bulkiness and allow a larger volume change. Because of this large volume change, the contact and separation of each conductive filler becomes clear, and the correlation between strain and resistance becomes more linear, of course, swollen granules,
By examining soluble granules and their solvents, easily volatile liquids, sublimable granules, etc. in advance, mechanical pores will be formed by these, and the risk of oxidative erosion of the conductive filler Is avoided in advance, and it becomes possible to design a desired silicone gel porous conductor with considerable freedom and obtain various properties.

[0044]

As described above, according to the present invention, the conductive silicone gel is allowed to undergo a larger volume change.
By making the correlation between strain and resistance more linear, not only simple ON / OFF contact elements but also a pressure-sensitive conductive element can be applied to expand the range of application, pressure sensors on the palm of robots, and Braille reading for the blind. Sensor, three-dimensional acceleration sensor, electromagnetic shield packing, impact force measuring machine,
It enables the development of completely new applications as an excellent pressure-sensitive sensor, such as vibration detection pickup.

[Brief description of drawings]

FIG. 1 is an explanatory diagram showing stepwise a pre-stage of a method for producing a silicone gel porous conductor by a dry shrinkage method.

FIG. 2 is an explanatory diagram showing a stepwise subsequent step of a method for producing a silicone gel porous conductor by a dry shrinkage method.

FIG. 3 is an explanatory view showing stepwise a method for producing a silicone gel porous conductor by an elution method.

FIG. 4 is an explanatory view showing stepwise a method for producing a silicone gel porous conductor by a microwave heating method.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 sheet 2 swollen granules 2a conductive filler 3 glass plate 4 pores 5 fine particles 7 soluble granules A sodium alginate B bath C C calcium chloride aqueous solution H dish shaped mold K cylindrical shaped mold M high frequency P micro tube pump S _A A component S _B B component W Water

Claims (3)

[Claims] 1. A silicone gel porous conductor having a large number of pores formed in a silicone gel containing a conductive filler. 2. A step of mixing a conductive filler into a stock solution before curing of a silicone gel, and a granule which is more soluble or shrinkable than the silicone gel or which can be extinguished by heating and which does not oxidize and corrode the conductive filler. A step of mixing, a step of curing the stock solution, and a step of eluting the granules with a solvent afterwards, or shrinking by drying, or disappearing by heating to form pores at the site where the granules were present. A method for producing a silicone gel porous conductor, comprising: 3. A step of mixing an electrically conductive filler into an undiluted solution before curing of silicone gel, and a process of easily volatilizing the electrically conductive filler so as not to dissolve into the undiluted solution because the dielectric loss coefficient is larger than that of the undiluted solution. A volatile liquid is added to make the liquid turbid, and the turbid liquid is dielectrically heated to vaporize and expand particles of the volatile liquid and to crosslink and harden the liquid. A method for producing a silicone gel porous conductor.