Method for improving conductivity of electroconductive rubber

A method of improving the conductive properties of the conductive rubber

[0001]

TECHNICAL FIELD

[0002] The present invention belongs to the field of electrically conductive material, in particular to a porous conductive rubber by electroless plating and electroplating, the porous rubber is formed in the metal coating, and even a metal formed networks to enhance the conductivity of the conductive rubber method.

Background technique

[0003] The carbon-based conductive material (e.g. conductive carbon black, carbon fibers, graphite, carbon nanotubes, and graphene) or metallic materials (such as metal powders, metal fibers, etc.) is filled into a rubber material, a conductive rubber prepared mainly method. However, due to the added conductive filler is dispersed, such a conductive rubber, the volume resistivity and the surface resistivity than the usual metallic conductive material is large, the ability to carry a large amount of current conduction in some cases does not seem sufficient. Such as a conductive rubber switch contact material can only be used in current is small (for example, less than 200 mA) circuit in order to ensure that the switch contacts with a suitable life. Moreover, a conductive powder or conductive rubber conductive fiber filled, there may be a conductive powder or conductive fibers detached from the conductive rubber problem in use.

[0004] Patent Application No. 201310620701.0 literature "conductive rubber" discloses a rubber simultaneous addition of electrically conductive graphite and conductive particles prepared both good conductivity, but also has a greater tensile strength method of conductive rubber, said the conductive particles are copper, aluminum, a mixture of magnesium powder, copper powder, aluminum powder, magnesium powder parts by weight ratio of 2: 3: 1. Patent Application No. 201410417394.0 literature, "an improved conductive rubber" discloses a styrene-butadiene rubber added simultaneously conductive filler, carbon black, graphite, copper and other materials prepared by a conductive rubber, it has good electrical conductivity, and heat and oil resistant features. European Patent Application EP1090959 "Conductive Silicone Rubber Composit1n", disclosed by the addition of nickel or gold layer is coated in silicone rubber particles of organic resin or inorganic material to obtain a low volume resistivity of conductive silicone rubber method. These are patents on ideas by adding a conductive filler dispersed to prepare conductive rubber.

[0005]

SUMMARY

[0006] The object of the invention: Hand filled conductive rubber volume resistivity and surface resistivity greater than the conductive metal material. The object of the present invention, is to reduce the contact resistance of the surface of the conductive rubber filled into a metallic conductive material level, i.e., the contact resistance with the filled conductive rubber contacts PCB coating is less than I Ω, thereby expanding the conductive rubber applications.

[0007] The present invention discloses a method for improving the filled conducting rubber: Through the porous conductive rubber existing hole inner walls, or in the preparation of solid conductive rubber by mechanical or physical means and the hole in the inner wall of the hole the electroless plating or electroplating, or electroless plating and then to electroplating, the hole in the wall to form a conductive rubber attached to the inner wall surface of the metal plating holes. Hole in the inner wall surface of the porous rubber chemical plating or electroplating may be copper, an alloy of nickel, tin, lead, cobalt, iron, silver, or combinations of these elements, or the first copper, nickel, tin, lead, cobalt, iron, mom, silver or alloys of these elements, and further silver, gold, ruthenium, rhodium, palladium, platinum and other precious metals, such that the inner walls of pores of porous conductive rubber forming a metal plating layer.

[0008] When electroless plating and electroplating implementation, allowing the bath flowing constantly from the porous conductive rubber holes too, so bath metal deposition process flow occurs in the pores of porous conductive rubber in; can be the first low-cost metal plating such as nickel, then coated with the high price of metals such as gold, which saves precious metal and almost reached the same good conductive properties.

[0009] The porous conductive rubber type is one or more conductive fillers in the rubber is obtained. Said conductive powder filler is electrically conductive or conductive fibers, such as conductive carbon black, carbon fibers, graphite, carbon nanotubes, graphene, metal powders, metal staple fibers, metal coated powders, beads or short fibers, having a conductivity oxide powder.

[0010] wherein the porous conductive rubber is open celled foam conductive foam rubber or mixing hole conductive rubber having open and closed cells; conductive rubber holes is fully or partially in communication and some holes in the exposed conductive rubber surface. As optimized using communication hole completely porous conductive rubber as a base material by electroless plating and electroplating, the hole in the substrate inside the inner wall surface of the metal coating, and ultimately form a continuous network in a complete metal porous conductive rubber.

[0011] electroless plating and electroplating on ABS and other plastic substrate is a mature technology, when the porous conductive rubber plating and electroplating can learn from. However, chemical crosslinking of rubbers, including porous conductive rubber, there is swelling characteristics in solvent. Therefore, in the porous conductive rubber plating and electroplating pretreatment, we've added a step swelling. Our plating pretreatment steps include cleaning, swollen, roughened, and, sensitization, activation, reduction or peptization step in the use of colloidal palladium activation, sensitization and activation processes and the two were together. Optimization of electroless plating of the entire process including cleaning, swelling, roughening and activation, glue and electroless plating steps:

a caustic wash: the composition of the alkaline solution used is sodium hydroxide 5 -20g / L, sodium phosphate dodecahydrate 30-40g / L, sodium carbonate 20-30g / L, an appropriate amount of a surfactant, The cleaning time is 10_30min, caustic temperature 65_75 ° C

. B swell: the organic solvent to swell the silicone rubber foam or water; swell at ambient temperature, time is not less than

0.5min;

. C roughening: containing chromic anhydride 300-500g / L, chromium sulfate solution 100-300mVL roughened, the roughening temperature of 60-90 ° C, time l-5min;

. D and: neutralizing solution consisting of: ammonia 5-15g / L, sodium hydroxide 10-20g / L, sodium sulfite 10_50g / L;

. E Activation: Use A bath: Pd chloride 0.5-1.5g / L, concentrated hydrochloric acid 100_300ml / L, stannous chloride 2_4g / L; and solution B: concentrated hydrochloric 50-150ml / L, stannous chloride 50- 100g / L, stannate 2-10g / L formulation was activated, the activation temperature is room temperature, time l_3min;

. F glue: The glue solution containing dilute hydrochloric acid 100ml / L, the glue temperature is 40-45 ° C, time 30s; g Plating: containing a nickel salt: 25-35g / L; hypophosphite : 25-40g / L; triethanolamine: 20_50ml / L; citrate: 15-40g / L; sodium: 0-10g / L of electroless plating baths; electroless plating process, with ammonia or sodium hydroxide solution controlling the pH between 9.0-9.5;

After plating, can be nickel-plated, nickel-plated in order to improve efficiency and save the cost of raw materials. Further, after the electroless nickel plating or nickel plating or electroplating may also be silver, gold, platinum, palladium and other precious metals.

[0012] swollen solvent is used for processing rubber and have a swelling action on the swelling ratio of the rubber or the mixture is greater than 5 percent more organic solvents of a single organic solvent; This step is carried out before the step of roughening; alternatively used for the organic solvent swell treated are: by volume mixture of methanol, ethanol, ethyl acetate, ethyl acetate and xylene, ethyl acetate, isopropanol and the like. Our tests found that the swelling process is conducive to chemical plating, help to increase the adhesion between the coating and the rubber. This may be because the swelling treatment of porous conductive rubber on the one hand the inner wall of the hole a cleaning solvent, the residue can be removed crosslinker porous rubber inner wall surface pores decomposed, plasticizers, fats, fatty acids, and paraffin low molecular weight substances, on the other hand, since the rubber swelling solvent, the process of the morphology of the porous rubber wall cavities also affect the resulting impact on the chemical plating.

[0013] After the porous conductive rubber plating and electroplating, allow a gap exists. That is, after the electroless plating and electroplating the resulting porous composite of rubber and metal, the porosity of between 0-90%.

[0014] porous conductive rubber rubber material may be natural or synthetic rubber; synthetic rubber material of the silicon rubber, fluoro rubber, fluoro silicone rubber, ethylene propylene rubber, EPDM, SBR, butadiene rubber, isoprene rubber, nitrile rubber, chloroprene rubber, chlorinated polyethylene, chlorosulfonated polyethylene, acrylic rubber, polysulfide rubber, polyurethane rubber, or blends of these modified products and rubber. Preferably silicone rubber and EPDM rubber.

[0015] the vast majority of commercial production of rubber is hydrophobic. Inorganic particulate fillers or fibrous fillers are generally better than hydrophilic rubber. In the coarsening process before plating pretreatment, these fillers may be partially etched by the etching solution and dissolved away to form a micro-rough surface, thereby improving the adhesion between the coating and rubber. Thus, in the preparation of porous conductive rubber, to which a powdered inorganic filler calcium carbonate (or limestone, calcite), calcium sulfate, or gypsum, zinc oxide, zinc sulfide, zinc borate, magnesium oxide, clay, talc, zeolite , feldspar, asbestos, mica, kaolin, bentonite, wollastonite, attapulgite, silica, carbon black, fly ash, meerschaum, titania, glass, quartz, silica, barium sulfate, one or several, or fillers comprising inorganic fibers glass fibers, silica glass fibers, brucite fiber, gypsum fiber, sepiolite fibers, asbestos fibers, fibrous wollastonite, boron fibers, ceramic fibers and metal fibers in one or several species.

[0016] The porous structure of porous conductive rubber, there can be a variety of methods. For example, by using a physical blowing agents or chemical foaming agent foaming during heat conductive rubber obtained by vulcanization molding of porous conductive rubber, may also be obtained by mechanical means porous conductive rubber. The mechanical method, using a high speed drilling machine for drilling machining methods; or porous conductive rubber is obtained by the following method:

(1) when the heat conductive rubber vulcanization molding, the diameter of the surface of a number of metal strands 0.08_2mm smooth and straight buried heat vulcanization mold cavity, parallel or interleaved between the metal wire; conductive rubber in the mold cavity hot vulcanization molding, the wire aside, namely to obtain a porous conductive rubber; or

(2) the number of diameter 0.25-2_ metal pillars fixed to the mold cavity; between the metal posts are parallel, non-parallel, with the wrong or intersecting; after thermal curing, when stripping rubber, metal pillars remain fixed in the model, which is off by metal pillars and holes formed in the rubber; or

(3) when the heat conductive rubber vulcanization molding, and vulcanization molding using a hot wire can be removed and a metal post, pass made much more conductive rubber;

The wire and metal column preferably steel or stainless steel.

[0017] The porous conductive rubber may also be prepared by the method of laser engraving:

The solid rubber block of a crosslinked open-celled or closed-cell or hybrid grooved rubber blocks with a laser carved out a number of 0.l-2mm in diameter straight holes between the holes are parallel, non-parallel or intersecting; holes in whole or in part through the rubber block.

[0018] In summary, there are methods of making the porous conductive rubber variety. These methods may be used alone or in combination. Various methods obtained porous conductive rubber holes pore size of not greater than 5mm. Pore ​​diameter not so small that water and other liquids can not be observed from the speed through the porous conductive rubber, i.e., pores in the porous conductive rubber must be greater than the pore size of 0.005mm, so that it makes the porous conductive rubber hole plating pre-treatment, chemical plating and electroplating possible.

[0019] Advantageous Effects: The present invention, through hole inner walls porous conductive rubber electroless plating and electroplating so as to form a metal plating layer on the porous conductive rubber hole wall, in porous conductive rubber hole at least partially communicating in forming a metal network, will further enhance the porous conductive rubber conductive properties in all directions, so that the porous conductive rubber volume resistivity and surface resistivity greatly reduced. PCB gold plated contacts and the contact resistance is 100 Ω 10 Ω or more conductive carbon black-filled porous conductive rubber, through the use of the method of the present invention, after chemical nickel plating, a conductive rubber is improved, with gold plated PCB contact resistance between the contacts of 0.3-0.5 Ω, such as improved conductive rubber can be used as a conductive material and a high-performance electrical contact materials, in particular, can be turned on and breaking more than 10mA current switch contact material.

detailed description

[0020] the following with reference to specific embodiments of the present invention will be further described.

[0021] Example 1

The present embodiment was prepared by mechanical porous conductive rubber. The side length of 0.5mm square glossy 304 stainless steel wire, straightened and clouds in heat curing the rubber mold. Stainless steel wire arrangement is: the X-axis, Y-axis and Z-direction are arranged in parallel, parallel distance between the axis of stainless steel wire is of 0.75mm. Stainless steel wire three-dimensional direction are in contact with each other. In the Y-axis direction (height direction) can be a square side length of 0.5mm stainless steel wire in place of the metal column, the column height of the metal mold cavity height.

[0022] The conductive carbon black filled conductive silicone rubber compound (such as KE-3601SB-U, Shin-Etsu Co.) into the mold cavity under pressure at 175 ° C for 10 minutes to cure the silicone rubber vulcanized rubber. The stainless steel wire was removed from the silicone rubber vulcanized rubber, that is to obtain a porous conductive silicon rubber. At 200 ° C under the porous conductive silicone rubber vulcanization Sec 2 hours.

[0023] The porous conductive silicon rubber clean, roughened and, sensitization, activation, restore, and electroless nickel plating. The present invention uses an alkaline cleaning agents and cleaning alcohol solution using sulfuric acid and chromic anhydride-containing high chromium roughening was roughened using a 10% aqueous ammonia solution was neutralized using hydrochloric acid containing titanium trichloride and sensitized liquid sensitization, palladium chloride activation was activated using reducing solution containing sodium hypophosphite reduction, followed by electroless nickel plating. Electroless nickel plating bath formula is: nickel sulfate 25g / L, sodium citrate 12g / L, ammonium chloride 30g / L, sodium hypophosphite 35g / L. In the plating bath temperature is maintained at 50 ° C, with aqueous ammonia to adjust the pH between 9.0 and 9.5. Let electroless plating solution continuously flowing from the hole porous conductive silicon rubber over when plating. When the flow rate is very slow, the porous conductive silicon rubber was removed from the bath, drying and re-placed in the bath. Plating time was 150 minutes. After the completion of plating, washed with deionized water, chemical nickel plating porous conductive silicon rubber, after drying, to obtain an enhanced conductive properties of conductive silicon rubber. This rubber machined to a diameter of 7.5mm, a thickness of Imm small wafer, electrical contacts, and as heat curing silicone rubber molding, made of silicon rubber keys with electrical contacts. When this electrical contacts and gold-plated PCB contacts the contact, the contact resistance between the two is only 0.3 Ω, far less than I Ω, meet some key switch on the electrical contacts of low resistance.

[0024] Example 2

As in Example 1, but the electroless nickel plating time was 30 minutes, followed by five minutes of nickel plating. The resulting product also has a lower contact resistance.

[0025] Example 3

As in Example 1, to prepare a nickel-plated by enhancing the conductivity of conductive silicon rubber, and having a diameter of 7.5_ thickness of Imm mm. This chemical plated small rounds, the average thickness of the gold layer is 0.Ιμπι. Only the gold layer deposited on the surface of the nickel film bun in the silicone rubber surface is not deposited gold layer. The resulting small wafer as an electrical contact material in a current of 200mA to remain in contact resistance I Ω The following switching times than not gilded small round as the switching frequency electrical contact material, at least 20% more.

[0026] Example 4

Porous conductive rubber formulations are: conductive silicone rubber (KE-3601SB-UH00 parts, 5 parts of a foaming agent H (N, N 'twelve-nitroso five tetramine), 7.5 parts brucite fiber, crosslinking agent paste 8? (50%) 1.5 parts. the brucite fiber diameter of water between 1-5μπι, length between 1-20μπι. the main ingredient is the fiber brucite magnesium oxide hydrate It is a safe, no pathogenic natural inorganic mineral material. coarsening process was roughened, porous rubber alkaline brucite fibers will be acidic etching, thereby increasing the porous microscopic holes in the rubber wall roughness to increase the adhesion of the coating rubber.

[0027] at 130 ° C under the above formulation silicone rubber compound made on vulcanizing machine vulcanizing period of 10 minutes, followed by oven post cure at 200 ° C for 2 hours to obtain a side length of 150mm, a thickness of Imm square porous conductive silicon rubber sheet.

[0028] This porous electrically conductive silicone rubber sheet in the thickness direction by laser ablating a plurality of holes having a diameter of 0.25mm, holes evenly distributed in a plane, hole pitch of any adjacent two holes of 1mm, to further increase the porous type conductive silicon rubber porosity.

[0029] This porous silicone rubber as described in Example 1 is shown in plating can be prepared one conductivity performance has been the promotion of conductive rubber, conductive silicon rubber that is porous and nickel complexes.