WO2016011909A1 - 一种耐电弧烧蚀的开关触点及其制备方法 - Google Patents

一种耐电弧烧蚀的开关触点及其制备方法 Download PDF

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WO2016011909A1
WO2016011909A1 PCT/CN2015/084165 CN2015084165W WO2016011909A1 WO 2016011909 A1 WO2016011909 A1 WO 2016011909A1 CN 2015084165 W CN2015084165 W CN 2015084165W WO 2016011909 A1 WO2016011909 A1 WO 2016011909A1
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layer
tungsten
metal
tungsten alloy
nickel
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PCT/CN2015/084165
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English (en)
French (fr)
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韩辉升
王振兴
丁阳
张红梅
管建华
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南通万德科技有限公司
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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01H—ELECTRIC SWITCHES; RELAYS; SELECTORS; EMERGENCY PROTECTIVE DEVICES
    • H01H1/00—Contacts
    • H01H1/02—Contacts characterised by the material thereof
    • H01H1/021—Composite material

Definitions

  • the present invention relates to a component (i.e., an electrical contact or contact) between two conductors in a switch or circuit in an electrical or electronic product that is electrically contactable by mutual contact and a method of making the same.
  • a component i.e., an electrical contact or contact
  • An electrical contact or contact is an important component of a switch or two conductors that are in contact with each other to allow current to pass through, and functions to connect, carry and disconnect normal current and fault current, and its quality and service life are directly Determines the quality and service life of the entire switch or circuit. Electrical contacts or contacts are mainly used in relays, contactors, air switches, current limiting switches, motor protectors, micro switches, instrumentation, computer keyboards, handhelds, household appliances, automotive appliances (window switches, rearview mirrors). Switch, light switch, starter motor and other load switches), leakage protection switch, etc.
  • the switching components are often a combination of a printed circuit board (PCB) with contacts and rubber buttons with contacts.
  • the circular contacts on the PCB are divided into two non-conducting halves by a straight line or curve (such as an S-curve).
  • the contacts on the buttons are circular without splitting.
  • a circuit on the PCB can be turned on by making a face-to-face contact with a circular contact on the PCB with a circular contact of the same diameter on the button.
  • the contact material on the button is conductive rubber or metal.
  • the contact resistance is large, and the conductive rubber contact is not suitable for the PCB circuit with a large on-current (for example, a current greater than 50 mA).
  • the metal contacts are in contact with the PCB contacts, the contact resistance is small, and the metal contacts can be used for both the PCB circuit with a small current and the PCB circuit with a large current.
  • metal contacts have problems such as chemical corrosion resistance, arc erosion resistance, and high manufacturing cost, which limits their application.
  • switching elements In the atmosphere, switching elements often generate sparks or arcs when switching on or breaking circuits.
  • the presence of the switching arc phenomenon will cause the contacts to be oxidized and ablated, and may carbonize the organic matter in the air to generate carbon deposits, causing the contact resistance of the switch to gradually increase or even break.
  • Patent Document No. 201220499100.X discloses "a three-layer composite electrical contact" which is coated with a layer of silver on the contact surface of the copper-based contact body to make the contact have better electrical conductivity. And it is more economical than using silver completely.
  • silver has poor atmospheric corrosion resistance and poor salt spray resistance.
  • Silver easily reacts with hydrogen sulfide (H 2 S) in the atmosphere to form black silver sulfide. Silver is used as a point contact, and although the initial surface resistance is small, its service life in the atmosphere is also limited. Although the cost of silver plating is relatively low, silver is also one of the precious metals.
  • Patent Document No. 200580045811.2 discloses a "flat primary battery with gold-plated end contacts" which can be used, for example, in a digital camera.
  • the battery can have an anode comprising lithium and a low resistance contact.
  • the anode and cathode may be in the form of a spirally crimped sheet with a separator therebetween.
  • the external positive and negative contacts are plated with gold to improve contact resistance.
  • the electrical resistance of the invention is small, but since the melting point of gold is less than that of refractory metals such as tungsten and molybdenum, the spark resistance of the voltage withstand voltage is not good. In addition, the high price of gold also limits the range of applications of the electrical contacts.
  • the patent document with the patent number 201020143455.6 discloses a "nickel-plated tungsten contact", which belongs to the technical field of basic electrical components, and aims to solve the problem that the existing tungsten contact is easily oxidized and affects the electrical conductivity.
  • the existing tungsten contacts are mainly made of rivet type studs and tungsten sheets which are welded by pure copper.
  • the outer surface of the tungsten contact welded with the seat pin and the tungsten piece is covered with a nickel-plated layer to form a nickel-plated tungsten contact.
  • the utility model has the advantages of simple and practical structure, stable electrical conductivity and durability, and is suitable for electric appliances such as automobiles, motorcycles and electric horns.
  • the patent's contacts use a tungsten sheet with a nickel-plated layer, but nickel has low arc-ablative resistance and is not suitable for harsher applications where the operating current or voltage is large.
  • nickel is used as a switch contact to contact and disconnect (switch on and off) the gold-plated contacts of the PCB.
  • the contact resistance of the switch is about 4,000 times. Significantly elevated, even making the circuit completely open.
  • U.S. Patent 4,019,910 discloses the preparation of an electroless plating bath of a multi-metal nickel alloy.
  • the nickel alloy contains, in addition to boron or phosphorus, one or more metals such as tin, tungsten, molybdenum or copper.
  • the electroless plating solution contains an ester complex obtained by reacting a mineral acid with a polybasic acid or a polyhydric alcohol, such as a diboron ester of glucoheptonic acid, a tungstate or a molybdate.
  • the nickel alloy is mainly composed of nickel, and the nickel content is usually in the range of about 60% to about 95% by weight.
  • the alloy has excellent mechanical properties and corrosion resistance, some of which are non-magnetic or non-ferromagnetic, such as phosphorus-containing nickel alloys, particularly nickel-phosphorus-tin-copper alloys.
  • the multi-metal nickel alloy disclosed in the invention contains a relatively large amount of boron or phosphorus, as used as a contact material, and the presence of a relatively large amount of boron or phosphorus will affect the initial resistance of the contact.
  • nickel alloys with a high nickel content, nickel content (such as nickel-copper alloy or monel, nickel-chromium alloy, etc.), nickel-containing stainless steel, or nickel obtained by electroless plating are the main constituents of nickel alloys. As the contacts of the switch, they have poor arc resistance and low switching life.
  • U.S. Patent Application No. 20090088511 discloses an electroless plating solution for selectively forming a cobalt-based alloy protective film on a bare copper wire.
  • the electroless plating bath contains cobalt ions and another metal ion (tungsten and/or molybdenum), a chelating agent, a reducing agent, a specific surfactant, and a tetraalkylammonium hydroxide.
  • tungsten and/or molybdenum tungsten and/or molybdenum
  • a chelating agent e.g., tungsten and/or molybdenum
  • a reducing agent e.g., a reducing agent
  • a specific surfactant etraalkylammonium hydroxide
  • this protective film is relatively hard and brittle due to the high cobalt content, and the surface resistance increases due to the cobalt oxide-based alloy easily generating cobalt oxide under the action of an electric arc.
  • This protective film is not resistant to arc ablation and should not be used to make electrical contacts or contacts.
  • U.S. Patent No. 6,821,324 describes an aqueous plating bath for cobalt tungsten phosphorous chemical deposition containing cobalt hexahydrate, from tungsten trioxide (WO 3 ) or phosphotungstic acid [H 3 P (W 3 O 10) 4 ]
  • tungsten trioxide WO 3
  • phosphotungstic acid H 3 P (W 3 O 10) 4
  • a soluble tungsten ion source, and a phosphorus-containing reducing agent which does not contain an alkali metal ion and an alkaline earth metal ion, and the resulting deposited film contains no oxygen and has a low electrical resistivity.
  • This deposited film can be used in capping or barrier layers in semiconductor chips, VLSI products, jewelry, nuts and screws, magnetic materials, wings, advanced materials and automotive parts to prevent inter-layer metal diffusion and migrate.
  • the plating solution described in the invention has a small selection of raw materials, and since the plating solution does not contain alkali metal ions and alkaline earth metal ions, the concentration of tungsten ions in the plating solution is low (especially when tungsten trioxide is used as a raw material).
  • the tungsten content in the formed cobalt-tungsten-phosphorus deposited film is difficult to adjust, and it is difficult to obtain a deposited film having a high tungsten content.
  • the bath described in the present invention can be deposited on substrates such as silicon, silicon dioxide, jewelry, magnetic materials, and metals, and deposition is not selective to the substrate.
  • the temperature of the switching arc can be 6000 ° C, and in the presence of oxygen, when heated to above 300 ° C, cobalt is oxidized to form CoO or Co 3 O 4 , the alloy with cobalt as the main component, the arc ablation resistance is not Good, not suitable as a contact material, so there are no cobalt alloy electrical contacts or contacts in the industry.
  • U.S. Patent No. 6,679,132 describes the formation of a cobalt-tungsten alloy from a bath containing no alkali metal, in which no tetramethylammonium hydroxide is used, and no catalyst is used before depositing the cobalt-tungsten metal alloy onto the substrate.
  • a substrate such as a palladium catalyst pretreats a deposited layer of a cobalt-tungsten alloy using the plating solution.
  • the cobalt-tungsten alloy contains a large amount of cobalt and is not resistant to switching arc ablation. The alloy also does not relate to how to perform selective chemical deposition.
  • the invention of the patent application No. 201110193369.5 provides a "ply-faced metal-rubber composite conductive particle" which is formed by bonding a metal surface layer to a rubber substrate or by cutting after bonding.
  • the metal surface layer is a pockmark having pits, bumps or both; the pits or bumps are on the outer surface, the inner surface or both surfaces of the metal surface layer.
  • the depth of the pit is smaller than the thickness of the metal surface layer, and the height of the bump is not less than one tenth of the thickness of the metal surface layer.
  • the metal surface layer is made of metal or alloy, the outer surface can be plated with gold, silver, copper or nickel; the rubber substrate is silicone rubber or urethane rubber; the metal surface layer and the rubber substrate can have a bonding layer, and the bonding layer is The heat vulcanized adhesive, primer or the same material as the rubber matrix.
  • the inner surface of the metal surface layer may be coated with an auxiliary agent such as a coupling agent.
  • the metal surface layer of the present invention has high strength, stable electrical conductivity, high strength of the adhesive layer, and sufficient rubber base.
  • the invention does not propose a solution to solve the problem of arc erosion resistance of conductive particles.
  • the invention also does not teach a specific method of how to obtain one or more layers on the outer surface of the metal facing.
  • the noble metal such as gold-plated silver on the surface of the invention has a large surface area, a large amount of precious metal, and a high cost.
  • tungsten has the highest melting point of various pure metals, which is 3410 ° C.
  • the vapor pressure of tungsten is very low and the evaporation rate is also small.
  • the chemical properties of tungsten are very stable. They do not react with air and water at normal temperature. When not heated, any concentration of hydrochloric acid, sulfuric acid, nitric acid, hydrofluoric acid and aqua regia do not work for tungsten.
  • the alkaline solution does not work for tungsten.
  • Tungsten is also a material with relatively low electrical resistivity and good electrical conductivity.
  • tungsten has a higher resistivity than silver, copper, gold, aluminum, and molybdenum, but is smaller than zinc, nickel, cadmium, palladium, iron, platinum, tin, lead, antimony, titanium, and mercury. Point material helps to reduce the contact resistance of the contacts. However, the hardness of tungsten or tungsten alloy is very high.
  • a tungsten alloy contact with strong bonding between the plating layers, good arc erosion resistance and low cost, and a preparation method thereof will be disclosed, and the contact may be heated with rubber because it contains a rubber layer.
  • Vulcanization bonding and thermal vulcanization molding to prepare rubber buttons comprising arc-resistant ablation contacts will be disclosed, and the contact may be heated with rubber because it contains a rubber layer.
  • the first object of the invention is to overcome the drawbacks of conventional gold-plated or silver-plated switch contacts with high cost and low arc resistance, or Overcoming the disadvantages of low-cost but poor arc resistance, copper-based, tin-based, nickel-based or stainless steel contacts provide a switch contact with low manufacturing cost, good electrical conductivity, and arc ablation resistance.
  • the arc-ablative switch contact provided by the invention is a composite body having a five-layer layer structure, the first layer is a hydrophobic rubber layer of 0.1-10.0 mm thick, and the second layer is 0.01. - 1.0mm thick metal foil layer, the third layer is a 0.1-10 micron thick transition metal iron, cobalt, nickel or copper alloy coating; the outermost layer is 0.01-10 micron thick tungsten alloy coating, the weight ratio is 50-99% tungsten; there is a 0.01-10 micron thick low tungsten alloy coating between the third layer and the outermost layer, and the low tungsten alloy coating contains 5-75% by weight of tungsten; transition metal The alloy plating layer, the tungsten alloy plating layer, and the low tungsten alloy plating layer are formed by an electroless plating method.
  • the low-tungsten alloy plating layer contains a metal tungsten element in a weight ratio of 10 to 75%, and the above-mentioned transition metal element iron, cobalt, nickel or copper in a weight ratio of 25 to 90%.
  • the presence of a transition metal element of iron, cobalt, nickel or copper in the low-tungsten coating can match the properties between the low-tungsten coating and the transition metal alloy coating to bond more closely.
  • the transition metal element of the third layer is preferably nickel, which is inexpensive and corrosion resistant, and has good compatibility with the tungsten-containing alloy plating layer and strong bonding force.
  • the electroless plating technology of nickel is very mature, and the raw materials are easy to obtain and easy to apply.
  • the tungsten alloy or the low tungsten alloy is preferably a tungsten-molybdenum alloy in which the content of the tungsten element is higher than the content of the molybdenum element.
  • Metal tungsten and metal molybdenum are refractory metals, especially tungsten, which have the highest melting point of all pure metals.
  • the vapor pressure of tungsten and molybdenum is also small, the evaporation rate is small, the conductivity is relatively high, and it is stable in the atmosphere.
  • the raw materials of tungsten electroless plating and molybdenum electroless plating are more readily available than other refractory metals, and the price is lower. Therefore, we use a tungsten alloy coating or a tungsten-molybdenum alloy coating as the outermost layer of the contact to obtain a switch contact with good electrical conductivity and arc ablation resistance. In the alloy coating containing tungsten, the weight percentage of tungsten is greater than the weight percentage of molybdenum to ensure better arc ablation resistance of the resulting switch contacts.
  • the hydrophobic rubber layer is caused by a low content of a carboxyl group, a hydroxyl group, a carbonyl group, an amino group, an amide group, a nitrile group, a nitro group, a halogen group, a thiol group, a sulfonate group and a benzenesulfonate group in the rubber molecular chain, thereby making the rubber
  • the surface of the rubber material having a water contact angle greater than 65°; or the hydrophobic rubber layer is due to the rubber containing no or a small amount of hydrophilic filler or additive, so that the water contact angle of the rubber surface is greater than 65 ° rubber material composition; EPDM rubber, methyl vinyl silicone rubber or methyl vinyl phenyl silicone rubber is preferred.
  • the more hydrophobic the rubber material used the more advantageous it is for the metal plating to be deposited on the metal surface of the rubber metal layered composite used in the present invention without depositing on the surface of the rubber material.
  • a hydrophilic rubber, a rubber material containing a surfactant or an antistatic agent, and a rubber material containing a large amount of hydrophilic or water-absorbent filler are not suitable as the rubber layer of the contact. If these rubber materials are used, metal plating will also be deposited on these rubber materials during electroless plating.
  • the hydrophobic rubber layer is prepared from ethylene propylene diene monomer, methyl vinyl silicone rubber or methyl vinyl phenyl silicone rubber Made.
  • EPDM rubber, methyl vinyl silicone rubber and methyl vinyl phenyl silicone rubber are non-polar rubbers, which are highly hydrophobic, and they have good weather resistance and can maintain good elasticity in the atmosphere for a long time. Therefore, they It is a preferred material for the hydrophobic rubber layer.
  • the hydrophobic rubber in the hydrophobic rubber layer has a repulsive ability to water, and water cannot be spread on the surface of the hydrophobic rubber.
  • the higher the hydrophobicity of the rubber material in the composite of the first layer of the hydrophobic rubber layer and the second layer of the metal foil the better.
  • the water contact angle of the rubber substrate needs to be greater than 65°.
  • the carboxyl group, hydroxyl group, carbonyl group, amino group, amide group, nitrile group, nitro group, halo group, sulfhydryl group, sulfonate group and benzenesulfonate on the rubber molecular chain will increase the polarity and hydrophilicity of the rubber.
  • carboxyl, hydroxyl, sulfonate and benzenesulfonate will greatly increase the polarity and hydrophilicity of the rubber.
  • the rubber material has a deposited layer of transition metal and a deposited layer of tungsten alloy, not only the electroless plating solution is wasted, but also the thermal vulcanization bonding or thermoplastic bonding of the rubber material with other rubber materials, and the thermal vulcanization is not favored. Adhesion or thermoplastic bonding is necessary in subsequent processing.
  • the first layer of hydrophobic rubber layer is present for the first layer of hydrophobic rubber layer and other rubbers for thermal vulcanization bonding and thermal vulcanization molding to prepare rubber buttons containing contacts.
  • the rubber substrate it is necessary to limit the content of these polar groups in the rubber substrate to obtain a highly selective tungsten alloy chemical deposition. In order to obtain the most selective chemical deposition, these groups cannot be contained in the rubber substrate.
  • the rubber body or surface contains no or a small amount of hydrophilic fillers, additives or surfactants, which is also beneficial for selective chemical deposition.
  • EPDM rubber, methyl vinyl silicone rubber, and methyl vinyl silicon phenyl rubber are weaker and more hydrophobic rubber materials, which are suitable for compounding with metal foil to prepare layered composites.
  • electroless plating is performed using the aforementioned electroless plating solution, chemical deposition does not occur on the rubber layer.
  • the second metal foil layer is a metal sheet having bumps or pits, a metal sheet having convex or concave lines, a metal sheet having a convex or concave surface, and a small area of less than 1 mm 2
  • Metal sheet of metal, metal mesh, metal foam or metal fiber sintered felt metal material is magnesium, aluminum, titanium, chromium, manganese, iron, cobalt, nickel, copper, zinc, tin or an alloy containing these elements
  • the metal foil is laminated in a single metal or a different metal; it is preferred to use a flat sheet of stainless steel, copper or copper alloy, nickel or nickel alloy, or with bumps or pits.
  • the third layer transition metal alloy plating layer is nickel or a nickel alloy, cobalt or a cobalt alloy.
  • the tungsten alloy coating or the low-tungsten alloy coating is a tungsten-molybdenum alloy, and the weight percentage of tungsten is more than the weight percentage of molybdenum; the content of tungsten in the tungsten alloy coating is higher than that in the low-tungsten alloy coating.
  • a second object of the invention is to provide a method of preparing the above-described arc-resistant ablation switch contacts.
  • a second technical solution a method for preparing an arc-resistant ablation switch contact, the preparation of the switch contact comprising the following steps:
  • the metal foil is a stainless steel, copper or copper alloy, nickel or nickel alloy sheet of 0.01 mm to 1.0 mm thick; the metal foil is degreased and cleaned with a cleaning agent and an organic solvent; or by sandblasting Grinding the surface of the metal sheet by mechanical roughening; or chemical etching to treat pits or bumps having a diameter of less than 1 mm; or plating one or both sides of the metal sheet by plating or electroless plating to 0.1 ⁇ m To a pure nickel layer or a nickel alloy layer of 10 micrometers; then, the obtained metal foil is degreased and washed with a cleaning agent and an organic solvent;
  • Hydrophobic rubber is formed by thermal vulcanization bonding and thermal vulcanization, and bonded to a metal foil coated with a primer or an adhesion promoter to form a layered composite.
  • transition metal alloy coating low-tungsten alloy coating and tungsten alloy coating: immersing the above-mentioned cylinder or object in an electroless plating solution containing soluble transition metal iron, cobalt, nickel or copper, low tungsten alloy In the plating solution and the tungsten alloy plating solution for more than 30 minutes, stirring, forming a transition metal alloy plating layer, a low tungsten alloy plating layer and a tungsten alloy plating layer on the metal surface of the cylinder or the object by electroless plating; or, the above-mentioned cylinder Put it in an electroless plating solution containing soluble transition metal iron, cobalt, nickel or copper, in a low-tungsten alloy plating solution and in a tungsten alloy plating bath, and let the drum rotate for more than 30 minutes each time, by electroless plating.
  • the metal surface of the cylinder sequentially forms a metal alloy plating layer, a low tungsten alloy plating layer and a tungsten alloy plating layer;
  • the soluble tungsten compound is one or more selected from the group consisting of potassium tungstate, sodium tungstate, ammonium tungstate, ammonium dithanoate, ammonium tetratitanate, ammonium heptoxide, and ammonium octatitanate.
  • Tungsten trioxide or tungstic acid can also be used. Although tungsten trioxide or tungstic acid is insoluble in neutral water, it is soluble in alkaline water.
  • tungsten trioxide or tungstic acid When tungsten trioxide or tungstic acid is used, it is first dissolved with sodium hydroxide alkali solution or ammonia water having a pH greater than 12, and then the electroless plating solution is disposed with dissolved tungstic acid or tungsten trioxide. It is preferred to prepare an electroless plating solution by using sodium tungstate which is easy to dissolve and has a low price.
  • the soluble transition metal nickel, cobalt, copper compound is nickel sulfate, nickel chloride, nickel nitrate, nickel ammonium sulfate, basic nickel carbonate, nickel sulfamate, nickel acetate, nickel hypophosphite, nickel hypophosphite, Nickel hydroxide, cobalt sulfate, cobalt chloride, cobalt nitrate, cobalt ammonium sulfate, basic cobalt carbonate, cobalt sulfamate, cobalt acetate, cobalt oxalate, copper sulfate, copper chloride, copper nitrate, hydrated basic copper carbonate, One or more of copper acetate.
  • nickel hydroxide When using nickel hydroxide, it is first dissolved with ammonia water. We found in the tungsten plating alloy, but the nickel precursor in the electroless plating solution is compounded with nickel sulfate and basic nickel carbonate, so that the plated tungsten alloy layer has a bright silver white color, and the surface resistance of the obtained tungsten alloy plating layer. Lower.
  • a compound of a soluble transition metal element other than nickel, cobalt or copper, and a soluble main group element may be added to the plating solution.
  • Compounds such as tin compounds, antimony compounds, antimony compounds and lead compounds, but attention should be paid to the effect of these compounds on the selectivity of electroless plating on the deposited substrate. In addition, attention should be paid to the physiological toxicity, environmental toxicity and hazardous properties of these compounds. For example, soluble lead compounds that are harmful to humans and the environment should be used sparingly or not.
  • silver is a commonly used element in electrical contacts or contacts, it is not recommended to add a soluble silver compound such as silver nitrate to the tungsten alloy plating solution.
  • the layered composite of the first layer of the hydrophobic rubber layer and the second layer of the metal foil layer is carried out.
  • the chemical deposition that occurs will occur not only on the metal foil layer of the second layer but also on the hydrophobic rubber layer of the first layer, so that chemical deposition is not selective to the substrate.
  • the deposition time is long enough, it is clearly visible to the naked eye that there are grayish black or silvery white deposits on the hydrophobic rubber layer and on the metal foil layer.
  • the surface of the metal foil layer and the surface of the hydrophobic rubber layer contained a large amount of silver. After the addition of silver nitrate is eliminated using the same formulation, the chemical deposition layer is formed only on the metal surface of the metal foil layer during the electroless plating.
  • the tungsten alloy plating layer is electrolessly plated with a soluble tungsten compound of 55-150 g/L, a soluble nickel compound of 10-50 g/L, a soluble cobalt compound of 0-30 g/L, 20- 150 g/L of reducing agent, 30-150 g/L of complexing agent, 20-100 g/L of pH adjusting agent, 0.1-1 g/L of stabilizer;
  • sodium hypophosphite is a reducing agent in the plating solution.
  • the obtained tungsten alloy plating layer is subjected to electroless plating at a temperature of 65 to 75 ° C for 30 to 300 minutes, and the pH of the plating solution is 8.0 to 9.5.
  • the low-tungsten alloy plating layer uses an electroless plating bath containing 10-45 g/L of soluble tungsten compound, 10-150 g/L of soluble nickel compound, 0-60 g/L of soluble cobalt compound, 20 - 120 g / L of reducing agent, 30-150 g / L of complexing agent, 20-100 g / L of pH adjuster, 0.1-1 g / L of stabilizer;
  • sodium hypophosphite is a reducing agent in the plating solution.
  • the electroless plating temperature of the obtained low-tungsten alloy plating layer is 75-90 ° C for 50-300 minutes, and the pH of the plating solution is 8.5-10.5. In this way, a low-tungsten alloy plating layer having a stronger bonding force, a high bonding force on both sides of the plating layer, and a thicker plating layer can be obtained. If the temperature of the electroless plating solution is too low, the chemical deposition reaction rate is very slow; if the temperature is too high, the reaction is too fast and the plating layer appears black.
  • the plating solution used for the electroless plating contains 5-60 g/L of soluble molybdenum compound, and contains 5-40 g/L of soluble tin, antimony, lead or antimony compound or any combination of these compounds.
  • Molybdenum is also a high melting point metal, but the price of the molybdenum compound is lower than the corresponding tungsten compound.
  • the pH adjusting agent is one or more of sodium hydroxide, potassium hydroxide, sodium carbonate, ammonia water, and sodium pyrophosphate. The pH of the bath is preferably adjusted with ammonia or sodium hydroxide solution.
  • the pH should not be greater than 12 because the excessively high pH causes the deposition rate to be accelerated, but the adhesion between the plating layer or the deposited layer and the metal substrate is deteriorated, so that the plating or deposition The color of the layer becomes darker and even becomes black.
  • a strong acid weak base salt or a strong base weak acid salt may be added to the plating solution as a pH buffer for the plating solution.
  • the stabilizers are potassium iodide, potassium iodate, benzotriazole, 4,5-dithiooctane-1,8-disulfonate, 3-mercapto-1. a mixture of one or more of propane sulfonate, sodium thiosulfate, thiourea.
  • the stabilizer is preferably sodium thiosulfate, thiourea or a mixture of the two, so that the tungsten alloy coating has a good metallic luster at the same time.
  • the role of the stabilizer is to inhibit the autocatalytic reaction occurring during the electroless plating process to stabilize the plating solution, prevent the intense autocatalytic reaction, and prevent the formation of a large amount of phosphorus-containing ferrous metal powder.
  • the stabilizer is a poisoning agent for electroless plating, that is, a countercatalytic reaction, so it cannot be excessively used, and it is necessary to control its amount in the plating solution so as not to affect the electroless plating efficiency.
  • the plating solution used for the electroless plating further contains 0.1-1 g/L of a surfactant; the surfactant is: dodecylbenzenesulfonate, lauryl sulfate, n-octyl
  • a surfactant is: dodecylbenzenesulfonate, lauryl sulfate, n-octyl
  • One or more surfactants in sodium sulfate preferably: sodium lauryl sulfate or sodium dodecylbenzene sulfonate.
  • the addition of some surfactants helps the gas on the surface of the plated material to overflow, reduces the porosity of the coating, and densifies the coating, thereby increasing the arc resistance of the coating.
  • the reducing agent is one or more of sodium hypophosphite, sodium borohydride, alkylamine borane, and hydrazine. If borohydride or aminoborane is used as the reducing agent, the tungsten alloy coating will contain a small amount of boron (mass fraction up to 7%). With ruthenium as a reducing agent, the content of non-metal (phosphorus or boron) in the obtained coating layer is almost zero, and the metal content can reach 99% or more.
  • Sodium hypophosphite as a reducing agent has a good cost performance. When sodium hypophosphite is used as the reducing agent, phosphorus and metal are co-deposited due to phosphorus precipitation.
  • the coating contains a small amount of phosphorus (mass fraction up to 15%) in addition to metal tungsten, cobalt and nickel. Phosphorus is detrimental to the electrical conductivity of the contacts and can damage the corrosion resistance of the tungsten alloy. Therefore, it is necessary to control the phosphorus content in the tungsten alloy.
  • the phosphorus content in the coating can be controlled by controlling the concentration of sodium hypophosphite, the concentration of the complexing agent, and the pH. Controlling the phosphorus content provides a dense, non-porous tungsten alloy coating.
  • the contact resistance between the tungsten alloy coating and the tungsten alloy coating obtained by us is higher than the contact resistance between pure nickel and nickel content of 99.5% or more pure nickel with a nickel content of 99.5% or more. Small, the resulting coating can significantly improve the resistance to switching arc of metal substrates.
  • the complexing agent is one or more of sodium citrate, ammonium citrate, sodium tartrate, sodium potassium tartrate, disodium edetate, and tetrasodium ethylenediaminetetraacetate.
  • the function of the complexing agent is to control the concentration of free metal ions available for reaction, improve the stability of the plating solution, prolong the life of the plating solution, and improve the quality of the plating layer.
  • Complexing agents have an effect on deposition rate, phosphorus content and corrosion resistance.
  • the plating solution used for the electroless plating contains 0.05-50 g/L of an electroless plating brightener;
  • the electroless brightening agent is butyne diol, propynyl alcohol, 1-diethylaminopropyl 2-yne, ethoxylated propynyl alcohol, sodium sulphonyl phenylimide (sodium saccharin), sodium vinyl sulfonate, sodium propyne sulfonate, pyridine-2-hydroxypropane sulfonate inner salt, alkyl phenol A polyoxyethylene ether (for example, an alkylphenol ethoxylate having a trade name of OP-10) or a commercially available chemical plating brightener.
  • the electroless brightening agent is butyne diol, propynyl alcohol, 1-diethylaminopropyl 2-yne, ethoxylated propynyl alcohol, sodium sulphonyl phenylimide
  • the tungsten-containing plating layer of the present invention is divided into two layers of a tungsten alloy plating layer and a low tungsten alloy plating layer, and the content of tungsten increases from the inner layer to the outer layer.
  • Three or more kinds of plating solutions containing soluble tungsten compounds are used, so that the plated tungsten alloy layer can be divided into three or more layers according to the tungsten content, and the content of tungsten increases from the inner layer to the outer layer.
  • Such improvements are also considered to be the scope of protection of the present invention.
  • This kind of switch contact with tungsten alloy or molybdenum alloy is in contact with the conductive switch (such as gold finger) of printed circuit board (PCB).
  • the contact resistance of the contact is smaller than that made directly from stainless steel.
  • the contact resistance between the piece and the gold finger is low, and the conduction stability is better: the small disc made of stainless steel and the PCB gold finger pass the 500 mA DC, after about 5,000 times of switching, due to the presence of the switch Arc ablation, the contact resistance between the small wafer and the PCB gold finger is significantly increased (from about 1 ohm to more than 100 ohms, or even non-conducting); and under the same circuit conditions, this plating
  • the tungsten wafer's small wafer (switch contact) and the PCB gold finger pass 500 mA DC, and after about 30,000 switching, the contact resistance between the small wafer and the PCB gold finger is still below 1 ohm.
  • This tungsten-plated switch contact has a thick tungsten alloy coating, and the bond between the coating and the foil is strong. Compared with the switch contacts coated with gold, platinum or silver, it can withstand greater Current and higher voltage for better ablation resistance. In addition, since the price of tungsten is not higher than gold or platinum, the cost of the plating is low.
  • the resulting contacts can have an appearance similar to that of gold, silver, silver, steel or some titanium nitride.
  • the product of the invention is suitable for various high-grade places, and is particularly suitable for making electrical and electronic equipment such as automobiles, electric tools, game machines, etc., and requires a large current (current greater than 50 mA) to pass the switch contacts under the button.
  • the tungsten alloy contact of the present invention contains a hydrophobic rubber layer and has characteristics of being easily vulcanized and bonded with rubber to form a rubber button product containing a contact.
  • Figure 1 is a schematic cross-sectional view of the present invention
  • Nickel plating bath nickel hexahydrate 20g / L, sodium hypophosphite 23g / L, succinic acid 8g / L, sodium acetate 15g / L, citric acid 8g / L, sodium lactate 16g / L, sodium saccharin 2 g / L, thiourea 0.0005 g / L, potassium sulfate 0.001 g / L, ethylene glycol 0.002 g / L.
  • the pH is controlled at 4.5-5.3 and the temperature is controlled at 85-90 °C.
  • Tungsten alloy plating solution sodium tungstate dihydrate 75g / L, nickel sulfate hexahydrate 25g / L, sodium hypophosphite sodium 80g / L, sodium acetate 20g / L, sodium citrate 30g / L, saccharin Sodium 20g / L, ammonium sulfate 15g / L, thiourea 0.2g / L, sodium lauryl sulfate 0.5g / L, potassium iodate 0.1g / L, ammonia water amount.
  • the pH is controlled at 8.0-8.5 and the temperature is controlled at around 75 °C.
  • Low-tungsten alloy plating solution sodium dihydrate sodium dihydrate 25/L, nickel sulfate hexahydrate 70g/L, tetrahydrate basic nickel carbonate 10g/L, sodium hypophosphite sodium 100g/L, sodium acetate 20g /L, sodium citrate 70g / L, sodium saccharin 10g / L, ammonium sulfate 15g / L, thiourea 0.2g / L, sodium lauryl sulfate 0.5g / L, potassium iodate 0.1g / L, ammonia water .
  • the pH is controlled at 8.5-9.0 and the temperature is controlled at around 80 °C.
  • a stainless steel sheet is used as the metal foil layer 2 in this patent, and the methyl vinyl silicone rubber is the hydrophobic rubber layer 1.
  • a stainless steel sheet of 0.075 mm thick material of SUS304 was degreased with an alkaline cleaning agent, washed with tap water, soaked in 5% diluted hydrochloric acid for 30 seconds, and washed with deionized water. The cold wind blows dry.
  • a methyl vinyl silicone rubber and a stainless steel sheet containing 1% vinyl tributyl butyl peroxysilane (VTPS) and 0.5% dicumyl peroxide (DCP) were placed on the surface of the cavity and coated with Teflon.
  • VTPS vinyl tributyl butyl peroxysilane
  • DCP dicumyl peroxide
  • one side of the stainless steel sheet was thermally vulcanized and bonded to the silicone rubber at 175 ° C, and the vulcanization time was 8 minutes to form a 1.0 mm thick layered composite sheet of stainless steel and silicone rubber.
  • Methyl vinyl silicone rubber is commercially available from SE 4706U manufactured by Dow Corning Toray or KE 961U or other grades of methyl vinyl silicone rubber manufactured by Shin-Etsu.
  • VTPS is a coupling agent containing a peroxy group which crosslinks vinyl-containing silicone rubber and also promotes adhesion between vinyl-containing silicone rubber and metal.
  • the composite sheet was die cut into small discs having a diameter of 2 to 10 mm.
  • the pellet was washed with an alkaline cleaning solution for several minutes, washed with water, then activated with 5% hydrochloric acid for 1 minute, then washed with deionized water and dried.
  • the 500 small wafers were placed in 300 ml of the newly plated nickel plating solution, stirred, taken out after 60 minutes, washed with deionized water, and then placed in the newly prepared low-tungsten alloy plating solution. After stirring, the transition metal plating layer 3 and the low tungsten alloy plating layer 4 are deposited on the metal surface, taken out after 120 minutes, filtered, and placed in the newly prepared tungsten alloy plating solution, and stirred, and the tungsten alloy plating layer 5 continues to be formed.
  • the metal foil layer is deposited on the surface of the metal foil layer, taken out after 90 minutes, washed with deionized water, drained, blown cold air or dried in a constant temperature oven at 70 ° C to obtain a layered composite having a five-layer structure.
  • a layered composite is a switch contact.
  • the silicone rubber surface of the tungsten alloy-coated small wafer containing the silicone rubber layer is thermally vulcanized and thermally vulcanized with other silicone rubber to form a rubber button containing a contact.
  • the contact is in contact with the gold-plated contacts of the printed circuit board (PCB), has a stable and low contact resistance, and the tungsten-plated contacts have better conduction stability and good arc erosion resistance. As the switch contacts have a long service life.
  • the contact resistance between the stainless steel contact and the gold-plated contact of the PCB is significantly increased by the contact of stainless steel without tungsten alloy plating after passing through 300 mA of DC for about 3000 times.
  • Example 1 the plating solution of Example 1 was still used, and a stainless steel sheet of SUS304 having a thickness of 0.075 mm was still used as the metal foil in the contact.
  • the stainless steel flat sheet was degreased with an alkaline cleaning agent, washed with tap water, soaked in 5% diluted hydrochloric acid for 30 seconds, and washed with deionized water. The cold wind blows dry.
  • the stainless steel piece was placed in the above nickel plating bath, stirred, and the nickel alloy was deposited on both sides of the stainless steel sheet, taken out after 60 minutes, washed with deionized water, and dried. Then, a methyl vinyl silicone rubber containing 1% vinyl tributyl butyl hydroperoxide (VTPS) and 0.5% dicumyl peroxide (DCP) and a stainless steel plate coated with a nickel alloy were placed on the surface of the cavity. Teflon In the mold, one side of the stainless steel sheet was thermally vulcanized and bonded to the silicone rubber at 175 ° C for a curing time of 8 minutes to form a 1.0 mm thick layered composite sheet of stainless steel sheet and silicone rubber. In this test, SE4706U methyl vinyl silicone rubber produced by Dow Corning Toray Co., Ltd. was mixed with VTPS and DCP.
  • the composite sheet was die cut into small discs having a diameter of 2 to 10 mm.
  • the pellet was washed with an alkaline cleaning solution at 70 ° C for 10 minutes, washed with water, then activated with 5% hydrochloric acid for 1 minute, then washed with deionized water and dried.
  • Example 1 a low-tungsten alloy plating layer 4 and a tungsten alloy plating layer 5 were plated on the above-mentioned small wafers using a low-tungsten alloy plating solution and a tungsten alloy plating solution, respectively.
  • the contacts thus produced have been tested and their service life (number of switching times) is more than doubled compared to corresponding stainless steel contacts without electroless plating.
  • the stainless steel sheet of the first embodiment was replaced by a 400 mesh stainless steel plain mesh (stainless steel model 304), and the contact and the electroless plating solution of the first embodiment were used to obtain a contact having a lower contact resistance and better. Resistance to arc ablation.
  • the 400 mesh stainless steel mesh has a small mesh opening, and the silicone rubber does not penetrate the mesh of the stainless steel mesh when molded with the silicone rubber. If a stainless steel mesh with a small mesh size, such as a stainless steel mesh of 80 mesh or less, is used, a process problem in which the silicone rubber penetrates the stainless steel mesh is generated during molding. Therefore, a larger mesh stainless steel mesh is required to prepare a plated switch contact.

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Abstract

本发明公开了一种耐电弧烧蚀的开关触点，具有五层的层状结构：第一层为疏水性橡胶层，第二层为金属薄片层，第三层为过渡金属铁、钴、镍或铜合金的镀层，第五层为钨合金镀层，在第三层与第五层之间可以有第四层低钨合金镀层，镀层为化学镀形成的。第五层钨合金镀层中含有重量比为50-99％的钨元素，第四层低钨合金镀层中含有重量比为5-75％的金属钨元素。本发明公开的开关触点，具有很好的耐电弧烧蚀性能，成本较低，并具有良好的金属色泽，且适于与橡胶复合从而制成含有耐电弧烧蚀的开关触点的橡胶按键。

Description

一种耐电弧烧蚀的开关触点及其制备方法 技术领域
本发明具体涉及一种电力或电子产品中的开关或电路中两个导体之间可通过相互接触从而可供电流通过的零部件(也就是电触头或触点)及其制备方法。
背景技术
电触头或触点是开关或电路中两个导体之间通过相互接触从而可供电流通过的重要零部件，承担接通、承载和分断正常电流和故障电流的功能，其质量和使用寿命直接决定着整个开关或电路的质量和使用寿命。电触头或触点主要应用于继电器、接触器、空气开关、限流开关、电机保护器、微型开关、仪器仪表、电脑键盘、手持机、家用电器、汽车电器(车窗开关、后视镜开关、灯开关、起动电机等负荷开关)、漏电保护开关等。电触点或触点的制备材料很多，主要有银、银镍、银氧化铜、银氧化镉、银氧化锡、银氧化锡氧化铟、银氧化锌、紫铜、黄铜、磷铜、青铜、锡铜、铍铜、铜镍、锌白铜、不锈钢等。
在汽车电器、家用电器、电脑键盘和手持机等设备中，其开关部件常常是设有触点的印刷电路板(PCB)和设有触点的橡胶按键的组合。PCB上的圆形触点，被一条直线或曲线(如S型曲线)分割成不导通的两半。按键上的触点是不用分割的圆形。用按键上的一个相同直径的圆形触点，与PCB上的一个圆形触点作面对面的接触，就可以接通PCB上的一个电路。按键上的触点材料，是导电橡胶或金属。导电橡胶触点与PCB触点相接触时的接触电阻较大，导电橡胶触点不适用于接通电流较大(例如电流大于50毫安)的PCB电路。金属触点与PCB触点相接触时的接触电阻较小，金属触点既可以用于接通电流较小的PCB电路，也可以用于接通电流较大的PCB电路。但目前金属触点存在耐化学品腐蚀、耐电弧烧蚀性能不理想、制作成本高从而使其应用受到限制等问题。
在大气中，开关元件在接通电路或分断电路时常产生电火花或电弧。开关电弧现象的存在，将使触点受到氧化和烧蚀，并且可能使空气中的有机质碳化从而产生积碳，使开关的接触电阻逐渐增大甚至断路。
申请专利号为201220499100.X的专利文件公开了“一种三层复合电触点”，该触点是在铜基触点本体的接触面上镀一层银，使得触点的导电性能更好，且比完全采用银制成要节省生产成本。虽然银的导电性和传热性在所有的金属中都是最高的，但银的耐大气腐蚀性能较差、耐盐雾性能较差。银易与大气中的硫化氢(H2S)反应生成黑色的硫化银。银作为点触点使用，虽然初始表面电阻小，但其在大气中的使用寿命也受到限制。虽然镀银的成本比较低，但银也是贵金属之一。另外，在这样的电触点中，没有橡胶层，因此，这种电触点不适于与橡胶进行热硫化粘合和热硫化成型从而制成含有电触点的橡胶按键。只有含有橡胶层的触点，或者全部由导电橡胶构成的触点，才可能顺利与其它橡胶进行热硫化粘合和热硫化成型从而制成含有触点的橡胶按键，而不会在热硫化粘合和热硫化成型过程中产生溢胶、粘合不良等质量问题。
申请专利号为200580045811.2的专利文件公开了一种“具有镀金端触点的扁平一次电池”，该电池可用于例如数字照相机。该电池可具有包含锂的阳极和低电阻的触点。阳极和阴极可呈其间带有隔板的螺旋形卷曲的薄片形式。外部正负触点用金镀覆以改善接触电阻。该发明电触点的电阻虽小，但是由于黄金的熔点不及钨、钼等难熔金属，所以其耐电压产生的火花性能欠佳。另外，黄金高昂的价格也限制了该电触点的应用范围。
申请专利号为201020143455.6的专利文件公开了一种“镀镍钨触点”，属于基本电器元件技术领域，旨在解决现有的钨触点易氧化，影响导电性能的问题。在公知技术中，现有的钨触点主要是铆钉型座钉和钨片以纯铜为焊料熔焊制作成。本专利中采用在座钉和钨片焊连的钨触点外表面包罩连接镀镍层所组成为镀镍的钨触点。其结构简单实用，导电性能稳定，经久耐用，适用于汽车、摩托车、电喇叭等电器。该专利的触点采用钨片外加镀镍层，但镍的耐电弧烧蚀性能低，不宜用于工作电流或电压较大的较苛刻的场合。我们的测试表明，镍作为开关触点与PCB的镀金触点接触和分断(开和关)，在室温下，但工作电流为300毫安时，开关次数4000次左右之后，开关的接触电阻就显著升高，甚至使电路完全断路。
美国专利4019910公开了制备一种多金属的镍合金的化学镀液。该镍合金中除了含有硼或磷，还含有一种或一种以上的金属如锡、钨、钼或铜。该化学镀液中含有无机酸和多元酸或多元醇反应所得的酯复合物，如葡庚糖酸的二硼酯、钨酸酯或钼酸酯。该镍合金主要由镍组成，镍含量通常在大约60％至大约95％(重量比)的范围内。该合金有优良的机械性能和耐腐蚀性能，其中某些合金如含磷的镍合金，特别是镍-磷-锡-铜合金，具有非磁性或非铁磁性。该发明所公开的多金属的镍合金含有较大含量的硼或磷，如作为触点材料使用，较大含量的硼或磷的存在，将影响触点的初始电阻。我们的测试表明，纯镍、镍含量大的镍合金(如镍铜合金或蒙乃尔合金、镍铬合金等)、含镍的不锈钢、或用化学镀得到的镍为主要组成的镍合金，如果作为开关的触点，都具有较差的耐电弧性能和较低的开关使用寿命。
美国专利申请20090088511公开了在裸露的铜线上选择性地形成一种钴基合金保护膜的化学镀液。化学镀液中包含了钴离子和另一种金属离子(钨和/或钼)、螯合剂、还原剂、特定的表面活性剂和四烷基氢氧化铵。使用该发明所公开的镀液，不需要在化学镀之前使用一种子层(如钯层)。该保护膜具有防扩散、防电迁移的能力。但这种保护膜由于钴含量高，比较硬而脆，由于在电弧作用下钴基合金很容易产生氧化钴而导致表面电阻上升。这种保护膜耐电弧烧蚀性能不好，不宜用来制作电触头或触点。
美国专利号为US 6821324的发明，描述了用于钴钨磷化学沉积的水性镀液含有六水氯化钴、来自三氧化钨(WO3)或磷钨酸[H3P(W3O10)4]的可溶性钨离子源，以及一种含磷的还原剂，不含碱金属离子和碱土金属离子，所得到的沉积薄膜不含氧，具有低的电阻率。这种沉积薄膜可用于半导体芯片、超大规模集成电路产品、珠宝、螺母和螺钉、磁性材料、机翼、先进材料和汽车部件等产品中的封盖层或阻挡层，以防止层间金属扩散和迁移。该发明所描述的镀液，原材料选择的种类少，由于镀液中不含碱金属离子和碱土金属离子，镀液中的钨离子 的浓度较低(特别是当三氧化钨用作原料时)，所形成的钴钨磷沉积薄膜中的钨含量难以调节，难以得到高钨含量的沉积薄膜。该发明所描述的镀液，可在硅、二氧化硅、珠宝、磁性材料和金属等基材上沉积，沉积对基材没有选择性。此外，开关电弧的温度可6000℃，而在氧气存在的情况下，加热至300℃以上时，钴被氧化生成CoO或Co3O4，以钴作为主要成分的合金，耐电弧烧蚀性能不佳，不宜作为触点材料，所以工业上没有钴合金电触头或触点。
美国专利号为6797312的发明，描述了用不含碱金属的镀液形成钴钨合金，在镀液中可不使用四甲基氢氧化铵，在沉积钴钨金属合金到基材上之前，不用催化剂如钯催化剂预处理基材，使用该镀液就可得到钴钨合金的沉积层。该钴钨合金中含有大量的钴元素，不耐开关电弧烧蚀。该合金该发明也没有涉及到如何进行选择性的化学沉积。
本专利权人的申请专利号为201110193369.5的发明提供了一种“麻面金属与橡胶复合导电粒”，由金属面层与橡胶基体粘合而成，或者粘合后分切而成。金属面层为麻面，具有凹坑、凸点或者两者均有；凹坑或凸点在金属面层的外表面、内表面或者两个表面均有。凹坑的深度小于金属面层厚度，凸点的高度不小于金属面层厚度的十分之一。金属面层的材质为金属或合金，外表面可镀金、银、铜或镍等；橡胶基体为硅橡胶或聚氨酯橡胶等；金属面层与橡胶基体之间可有粘接层，粘接层为热硫化胶粘剂、底涂剂或为与橡胶基体相同的材质。金属面层内表面可涂有偶联剂等助剂。本发明的金属面层强度高、导电性稳定，粘接层强度高，橡胶基体弹性足。该发明没有为解决导电粒的耐电弧烧蚀问题提出解决方案。该发明也没有提出如何在金属面层的外表面上获得一层或多层镀层的具体方法。该发明的麻面上镀金银等贵金属，由于表面积大，贵金属用量多，成本高。
众所周知，各种纯金属中以钨的熔点最高，为3410℃。钨的蒸气压很低，蒸发速度也较小。钨的化学性质很稳定，常温时不跟空气和水反应，不加热时，任何浓度的盐酸、硫酸、硝酸、氢氟酸以及王水对钨都不起作用。碱溶液对钨也不起作用。钨还是一种电阻率比较小、导电性比较好的材料。在各种纯金属中，钨的电阻率比银、铜、金、铝、钼大，但比锌、镍、镉、钯、铁、铂、锡、铅、锑、钛、汞小，作为触点材料时有利于降低触点的接触电阻。但钨或钨合金的硬度很高，以机械压制法或粉末冶金法，难以得厚度较小的钨或钨合金合金的薄片(特别是厚度小于0.05mm的钨合金薄片)，如果将较厚的钨合金的薄片，直接用于生产金属触点，不仅将增大金属触点的原材料成本，而且由于钨或钨合金合金的硬度大，进行分割或冲切加工困难。钨和钨化合物的价格也比较昂贵。如何节约用钨也是值得考虑的。由于钨与其它金属性质的显著差异，在电子产品中未有成熟的和广泛使用的应用技术。
本发明中，将公开一种镀层之间结合牢固、耐电弧烧蚀性能好、成本又比较低的钨合金触点及其制备方法，这种触点由于包含橡胶层，因而可与橡胶进行热硫化粘合和热硫化成型从而制备包含耐电弧烧蚀的触点的橡胶按键。
发明内容
第一发明目的：克服传统镀金或镀银的开关触点成本较高、耐电弧性不太高的缺陷，或 者克服铜基、锡基、镍基或不锈钢触点虽然成本较低但耐电弧性较差的缺点，提供一种制造成本低、电导通性能好、耐电弧烧蚀的开关触点。
第一技术方案：本发明提供的耐电弧烧蚀的开关触点，是具有五层的层状结构的复合体，第一层为0.1-10.0mm厚的疏水性橡胶层，第二层为0.01-1.0mm厚的金属薄片层，第三层为0.1-10微米厚的过渡金属铁、钴、镍或铜的合金镀层；最外层为0.01-10微米厚的钨合金镀层，含有重量比为50-99％的钨元素；在第三层与最外层之间还有0.01-10微米厚的低钨合金镀层，低钨合金镀层中含有重量比为5-75％的钨元素；过渡金属合金镀层、钨合金镀层和低钨合金镀层是通过化学镀方法形成的。
在第三层与最外层之间有低钨合金镀层，以便使钨含量高的钨合金镀层与过渡金属镀层性能更加匹配、结合得更加牢固，同时，在保证触点表面性能和耐电弧烧蚀性能基本不变的情况下，使整个镀层中的钨含量下降，达到节约钨从而降低原材料成本的目的。低钨合金镀层中含有重量比为10-75％的金属钨元素、含有重量比为25-90％的上述的过渡金属元素铁、钴、镍或铜。低钨镀层中过渡金属元素铁、钴、镍或铜的存在，可以使低钨镀层和过渡金属合金镀层之间性质匹配，从而粘合得更紧密。
第三层的过渡金属元素优选为镍，镍价格低廉，又耐腐蚀，同时与含钨的合金镀层相容性好，结合力强。此外，镍的化学镀技术很成熟，原材料易得，便于应用。
所述的钨合金或者低钨合金均优选为钨钼合金，其中钨元素的含量高于钼元素的含量。
金属钨和金属钼是难熔金属，特别是钨，在所有的纯金属中具有最高的熔点。钨和钼的蒸气压也很小，蒸发速度小，电导率比较高，在大气中也很稳定，而且，钨化学镀和钼化学镀的原材料比其它难熔金属更易得到，价格较低。因此，我们选用钨合金镀层或钨钼合金镀层作为触点的最外层，以得到导电性能好、耐电弧烧蚀的开关触点。在含钨的合金镀层中，钨的重量百分比含量大于钼的重量百分比含量，以确保所得的开关触点的耐电弧烧蚀性能更好。
作为优化：所述的疏水性橡胶层是由于橡胶分子链上羧基、羟基、羰基、氨基、酰胺基、腈基、硝基、卤基、巯基、磺酸根和苯磺酸根含量低，从而使橡胶表面的水接触角大于65°的橡胶材料构成；或者，所述的疏水性橡胶层是由于橡胶中不含或含有少量的亲水性的填料或添加剂，从而使橡胶表面的水接触角大于65°的橡胶材料构成；优先选用三元乙丙橡胶、甲基乙烯基硅橡胶或甲基乙烯基苯基硅橡胶。
一般来说，所用橡胶材料的疏水性越强，越有利于金属镀层在本发明中所使用橡胶金属层状复合物中的金属面上沉积，而不在橡胶材料的表面上沉积。亲水性橡胶、含有表面活性剂或抗静电剂的橡胶材料、含有大量亲水性或吸水性填料的橡胶材料，不宜用作所述的触点的橡胶层。如果使用这些橡胶材料，在进行化学镀时，将使金属镀层也沉积在这些橡胶材料上。
所述的疏水性橡胶层由三元乙丙橡胶、甲基乙烯基硅橡胶或甲基乙烯基苯基硅橡胶制备 而成。三元乙丙橡胶、甲基乙烯基硅橡胶和甲基乙烯基苯基硅橡胶是非极性橡胶，疏水性强，同时它们的耐候性好，在大气中能长期保持良好的弹性，因此，它们是所述的疏水性橡胶层的优先使用的材料。高腈基含量的丁腈橡胶和氢化丁腈橡胶、端羧基液体丁腈橡胶、氯磺化聚乙烯橡胶、氯醚橡胶、丙烯酸酯橡胶、聚氨酯橡胶等极性比较大的橡胶，以及亲水化的橡胶(如亲水性硅橡胶)和水膨胀橡胶等材料的极性大或含有大量亲水性物质，这些材料表面疏水性不强。这些材料在化学镀液中，含钨的合金镀层就会沉积在这些材料的表面。
疏水性橡胶层中的疏水性橡胶对水具有排斥能力，水不能在疏水性橡胶表面铺展开来。为了获得钨合金在金属材质上的选择性化学沉积，在由第一层疏水性橡胶层和第二层金属薄片的复合体中的橡胶材质的疏水性越高越好。在用镀液进行化学沉积时，为了使沉积在第一层疏水性橡胶层上的合金少得可以忽略不计，橡胶基材的水接触角需大于65°。橡胶分子链上羧基、羟基、羰基、氨基、酰胺基、腈基、硝基、卤基、巯基、磺酸根和苯磺酸根，将增大橡胶的极性和亲水性。特别是羧基、羟基、磺酸根和苯磺酸根，将极大的增大橡胶的极性和亲水性。如果橡胶材质上有过渡金属的沉积层和钨合金的沉积层，将不仅浪费化学镀的镀液，而且不利于橡胶材质与其它橡胶材质的热硫化粘合或热塑性粘合，而这种热硫化粘合或热塑性粘合是后续加工中所必需的。第一层疏水性橡胶层的存在，就是为了第一层疏水性橡胶层和其它橡胶进行热硫化粘合和热硫化成型，从而制备包含触点的橡胶按键。
因此，必需限制这些极性基团在橡胶基材中的含量，以获得选择性良好的钨合金化学沉积。为了获得选择性最佳的化学沉积，橡胶基材中不能含有这些基团。同样的道理，橡胶材质本体或表面不含或少量含有亲水性强的填料、添加剂或表面活性剂，也有利于获得选择性的化学沉积。
三元乙丙橡胶、甲基乙烯基硅橡胶、甲基乙烯基硅苯基橡胶是极性比较弱的、疏水性比较强的橡胶材料，适宜于和金属薄片进行复合制备层状复合体。在使用前述的化学镀液进行化学镀时，化学沉积不发生在橡胶层上。
作为优化：所述的第二层金属薄片层为具有凸点或凹点的金属片材、具有凸线条或凹线条的金属片材、具有凸面或凹面的金属片材、具有面积小于1mm2的小孔的金属片材、金属网、金属泡沫或者金属纤维烧结毡；金属材质为镁、铝、钛、铬、锰、铁、钴、镍、铜、锌、锡或含有这些元素的合金；所述的金属薄片是单一金属材质的或不同金属材质层状复合的；优先选用价格较低的材质为不锈钢、铜或铜合金、镍或镍合金的平整的片材、或带有凸点或凹点的片材或100目以上的金属网。使用带有凸点或凹点的片材或金属网制作触点，可使触点与其它触点的接触压强更大、电导通性更可靠。
作为优化：所述的第三层过渡金属合金镀层为镍或镍合金、钴或钴合金。
作为优化：所述的钨合金镀层或低钨合金镀层，是钨钼合金的，钨的重量百分比含量比钼的重量百分比含量多；钨合金镀层中钨的含量比低钨合金镀层中钨的含量多。
第二发明目的：提供上述耐电弧烧蚀的开关触点的一种制备方法。
第二技术方案：一种耐电弧烧蚀的开关触点的制备方法，开关触点的制备包括如下步骤：
(1)金属薄片的处理：金属薄片为0.01mm至1.0mm厚的不锈钢、铜或铜合金、镍或镍合金薄片；用清洗剂和有机溶剂对金属薄片进行除油、清洗；或通过喷砂、打磨将金属薄片进行表面机械粗化处理；或通过化学蚀刻处理以处理出直径小于1mm的凹坑或凸点；或在金属薄片的一面或两面，用电镀或化学镀的方法镀有0.1微米至10微米的纯镍层或镍合金层；然后用清洗剂和有机溶剂对所得到的金属薄片进行除油、清洗；
(2)疏水性橡胶与金属薄片的粘合处理：疏水性橡胶通过热硫化粘合和热硫化成型，粘合在涂有底涂剂或粘合促进剂的金属薄片上，形成层状的复合片材；或者将具有自粘性的疏水性橡胶，通过热硫化成型，粘合在涂有底涂剂或没有底涂剂的金属薄片上，形成层状的复合片材；
(3)切割处理：将上述步骤中的复合片材分割或冲切成包含有疏水性橡胶层和金属薄片层的直径为2-10mm的圆柱体，或者将上述步骤中的复合片材分割或冲切成横截面为椭圆形、多边形、十字形、星形、新月形或它们的任意组合的物体；用碱性清洗液清洗约5分钟，水洗后用5％的盐酸清洗3分钟，然后用去离子水清洗干净，滤干；
(4)过渡金属合金镀层、低钨合金镀层和钨合金镀层的制备：将上述圆柱体或物体，分别浸渍在含有可溶性的过渡金属铁、钴、镍或铜的化学镀液中、低钨合金镀液中和钨合金镀液中各30分钟以上，搅拌，用化学镀的方法在圆柱体或物体的金属表面形成过渡金属合金镀层、低钨合金镀层和钨合金镀层；或者，将上述圆柱体放入在含有可溶性的过渡金属铁、钴、镍或铜的化学镀液中、低钨合金镀液中和钨合金镀液中滚筒中，让滚筒转动各30分钟以上，用化学镀的方法在圆柱体的金属表面依次形成渡金属合金镀层、低钨合金镀层和钨合金镀层；
(5)清洗、干燥：取出后用蒸馏水或去离子水漂洗、沥干、冷风吹干或用70℃的恒温烘箱烘干，即得到金属面层上镀有钨合金的开关触点。
本发明中，所述的可溶性钨化合物是钨酸钾、钨酸钠、钨酸铵、二钨酸铵、四钨酸铵、七钨酸铵、八钨酸铵中的一种或多种。也可选用三氧化钨或钨酸。虽然三氧化钨或钨酸不溶于中性的水，但它溶于碱性水。选用三氧化钨或钨酸时，需先用氢氧化钠碱溶液或pH大于12的氨水使之先溶解，然后用溶解了的钨酸或三氧化钨配置化学镀液。优先选用易于溶解且价格价较低的钨酸钠配制化学镀液。
所述的可溶性过渡金属镍、钴、铜的化合物是硫酸镍、氯化镍、硝酸镍、硫酸镍铵、碱式碳酸镍、氨基磺酸镍、乙酸镍、次磷酸镍、次亚磷酸镍、氢氧化镍、硫酸钴、氯化钴、硝酸钴、硫酸钴铵、碱式碳酸钴、氨基磺酸钴、乙酸钴、草酸钴、硫酸铜、氯化铜、硝酸铜、水合碱式碳酸铜、乙酸铜中的一种或多种。使用氢氧化镍时，先用氨水使之溶解。我们在镀钨合金时发现，但化学镀液中镍的前体使用硫酸镍和碱式碳酸镍复配，可使镀得的钨合金层具有较明亮的银白色，所得钨合金镀层的表面电阻较低。
镀液中可加入镍、钴、铜以外的其它可溶性过渡金属元素的化合物，以及可溶性主族元 素的化合物如锡化合物、锑化合物、铋化合物和铅化合物，但应注意这些化合物对化学镀对所沉积的基材的选择性的影响。此外，也要注意这些化合物的生理毒性、环境毒性和危险特性。比如，应尽量少用或不用对人体和环境有害的可溶性铅化合物。虽然银是电触头或触点中常用的元素，但不建议在钨合金镀液中加入硝酸银等可溶性银化合物。因为我们在实验中发现，在钨合金镀液中加入一定量的硝酸银(如5g/L)后，对第一层的疏水性橡胶层和第二层的金属薄片层的层状复合体进行化学镀时，所发生的化学沉积，将不仅发生在第二层为的金属薄片层上，也发生在第一层的疏水性橡胶层上，这样化学沉积对基材就没有选择性了。当沉积时间足够长时，用肉眼就可清楚地看到疏水性橡胶层上和金属薄片层上都有灰黑色或银白色的沉积层。用X射线荧光光谱分析，发现金属薄片层的表面和疏水性橡胶层的表面都含有大量的银。使用同样的配方取消硝酸银的加入后，则在化学镀的过程中，化学沉积层只生成在金属薄片层的金属面上。
作为优化：所述的钨合金镀层采用化学镀的镀液中，含有55-150g/L的可溶性钨化合物、10-50g/L的可溶性镍化合物、0-30g/L的可溶性钴化合物、20-150g/L的还原剂、30-150g/L的络合剂、20-100g/L的pH值调节剂、0.1-1g/L的稳定剂；
优选次亚磷酸钠为镀液中的还原剂。采用次亚磷酸钠为还原剂时，所得钨合金镀层所采用化学镀的温度为65-75℃，时间为30-300分钟，镀液的PH值为8.0-9.5。
作为优化：所述的低钨合金镀层采用化学镀的镀液中，含有10-45g/L的可溶性钨化合物、10-150g/L的可溶性镍化合物、0-60g/L的可溶性钴化合物、20-120g/L的还原剂、30-150g/L的络合剂、20-100g/L的pH值调节剂、0.1-1g/L的稳定剂；
优选次亚磷酸钠为镀液中的还原剂。采用次亚磷酸钠为还原剂时，所得低钨合金镀层所采用化学镀的温度为75-90℃，时间为50-300分钟，镀液的pH值为8.5-10.5。这样能够获得结合力更强、镀层两面的结合力均高，镀层更厚的低钨合金镀层。如果化学镀液的温度过低，则化学沉积反应速度很慢；温度过高，则反应过快，镀层呈现黑色。
作为优化：所述的化学镀采用的镀液中，含有5-60g/L的可溶性钼化合物，含有5-40g/L的可溶性的锡、锑、铅或铋化合物或这些化合物的任意组合。钼也是高熔点金属，但钼类化合物的价格比相对应的钨类化合物低。
化学镀的时间越长，沉积在金属基材上的钨合金镀层就会越厚。较厚的钨合金镀层有利于触点的耐开关电弧性能。但化学镀的时间并不是越长越好。化学镀的时间过长，不仅生产效率低，而且带碱性的化学镀液，可能会伤害第一层的疏水性橡胶层和第二层的金属薄片层之间的粘合强度，甚至造成脱层现象。所述的pH调节剂为氢氧化钠、氢氧化钾、碳酸钠、氨水、焦磷酸钠中的一种或多种。优先使用氨水或氢氧化钠溶液调节镀液的pH值。当采用次亚磷酸钠作为还原剂时，pH值不可大于12，因为过高的pH虽然使沉积速度加快，但使得镀层或沉积层和金属基材之间的附着力变差，使镀层或沉积层的颜色变深，甚至变成黑色。在镀液中可加入强酸弱碱盐或强碱弱酸盐，作为镀液的pH缓冲剂。
在不考虑颜色、光泽时，所述的稳定剂为碘化钾、碘酸钾、苯骈三氮唑、4,5-二硫代辛烷-1,8-二磺酸盐、3-巯基-1-丙磺酸盐、硫代硫酸钠、硫脲中的一种或多种的混合物。在考虑颜色、光泽时，所述的稳定剂优选为硫代硫酸钠、硫脲或者两者的混合物，使得钨合金镀层同时具有良好的金属光泽。稳定剂的作用是抑制化学镀过程中所发生的自催化反应从而稳定镀液，防止激烈的自催化反应、防止生成大量含磷的黑色金属粉末。但稳定剂是化学镀的毒化剂，即反催化反应，所以不能过度使用，需控制其在镀液中的用量，以免影响化学镀效率。
所述的化学镀采用的镀液中，还含有0.1-1g/L的表面活性剂；所述的表面活性剂为：十二烷基苯磺酸盐、十二烷基硫酸盐、正辛基硫酸钠中的一种或多种的表面活性剂；作优先为：十二烷基硫酸钠或十二烷基苯磺酸钠。加入些表面活性剂有助于镀件表面气体的溢出，降低镀层的孔隙率，使镀层致密，从而增加镀层的耐电弧性能。
所述的还原剂为次亚磷酸钠、硼氢化钠、烷基胺硼烷、肼中的一种或多种。如果以硼氢化物或氨基硼烷为还原剂时，钨合金镀层中将含有少量的硼(质量分数可达7％)。以肼作还原剂，所得到的镀层中非金属(磷或硼)的含量几乎为零，金属含量可达到99％以上。次亚磷酸钠作为还原剂有很好的性价比。选用次亚磷酸钠为还原剂时，由于有磷析出，发生磷与金属的共沉积，镀层中除有金属钨、钴、镍外还含有少部分的磷(质量分数可达l5％)。磷对触点的导电性是有害的，并且可能伤害钨合金的耐腐蚀性能，因此，必需控制钨合金中的磷含量。通过控制次亚磷酸钠的浓度、络合剂的浓度、pH值等措施，可以控制镀层中的磷含量。控制磷含量可得到致密、无孔的钨合金镀层。选用次亚磷酸钠作为还原剂，我们所得到的钨合金镀层和钨合金镀层之间的接触电阻，比镍含量为99.5％以上的纯镍和镍含量为99.5％以上纯镍之间的接触电阻小，所得到的镀层能显著提高金属基材的耐开关电弧性能。
所述的络合剂为柠檬酸钠、柠檬酸铵、酒石酸钠、酒石酸钾钠、乙二胺四乙酸二钠盐、乙二胺四乙酸四钠盐中的一种或多种。络合剂的作用是控制可供反应的游离金属离子的浓度，提高镀液稳定性，延长镀液寿命，提高镀层质量。络合剂对沉积速率、磷含量和耐腐蚀性等均有影响。
作为优化：所述的化学镀采用的镀液中，含有0.05-50g/L的化学镀光亮剂；所述的化学镀光亮剂为丁炔二醇、丙炔醇、1-二乙胺基丙-2-炔、乙氧化丙炔醇、邻磺酰苯酰亚胺钠(糖精钠)、乙烯基磺酸钠、丙炔磺酸钠、吡啶-2-羟基丙磺酸内盐、烷基酚聚氧乙烯醚(例如商品名为OP-10的烷基酚聚氧乙烯醚)或市售等商品化的化学镀光亮剂。
对于本技术领域的普通技术人员来说，在不脱离本发明原理的前提下，还可以做出若干改进和润饰，这些改进和润饰也应视为本发明的保护范围。比如，本发明中的含钨镀层分为钨合金镀层和低钨合金镀层两层，由里层到外层，钨的含量上升。采用三种或三种以上含可溶性钨化合物的镀液，使镀得的钨合金层按钨含量的不同，可分成三层或三层以上，由里层到外层，钨的含量上升。这样的改进，也应视为本发明的保护范围。
有益效果：这种镀有钨合金或钼合金的开关触点，与印刷电路板(PCB)的导通开关(如金手指)接触，触点的接触电阻比直接由不锈钢片制得的小圆片与金手指之间的接触电阻低，有更好的导通稳定性：由不锈钢制得的小圆片与PCB金手指通过500毫安的直流电，开关约5000次后，由于存在开关时的电弧烧蚀，小圆片和PCB金手指之间的接触电阻就明显升高(由约1欧姆升高至100欧姆以上，甚至不导通)；而在同样的电路条件下，这种镀有钨合金的小圆片(开关触点)与PCB金手指通过500毫安的直流电，开关约30000次后，这种小圆片和PCB金手指之间的接触电阻，仍在1欧姆以下。
这种镀有钨合金的开关触点，含钨的合金镀层较厚，镀层与金属薄片之间粘合牢固，与镀有黄金、白金或白银的开关触点比较，能够通过获承受更大的电流和更高的电压，具有更好的耐烧蚀性能。此外，由于钨的价格不高于黄金或铂金，使得镀层的成本低。
调节镀液的配方组成和化学镀的时间和温度，所得的触点可以有类似于黄金、银、白银、钢或某些氮化钛的颜色、光泽等外观效果。本发明的产品适用于各种高档场所，尤其适合于制作汽车、电动工具、游戏机等电器电子设备中，在按键下需要大电流(电流大于50mA)通过的开关触点。
本发明中的钨合金触点含有疏水性橡胶层，具有易于与橡胶进行热硫化粘合和成型从而制成含触点的橡胶按键产品的特性。
附图说明
图1是本发明的一种剖面结构示意图；
图中：1、输水性橡胶层；2、金属薄片层；3、过渡金属合金镀层；4、低钨合金镀层；5、钨合金镀层。
具体实施方式
下面结合具体实施例对本发明作进一步说明。
实施例1：
镀液组成：
(1).镀镍镀液：六水硫酸镍20g/L、次磷酸钠23g/L、丁二酸8g/L、乙酸钠15g/L、柠檬酸8g/L、乳酸钠16g/L、糖精钠2g/L、硫脲0.0005g/L、硫酸钾0.001g/L、乙二醇0.002g/L。pH控制在4.5-5.3，温度控制在85-90℃。
(2).钨合金镀液：二水钨酸钠75g/L、六水硫酸镍25g/L、一水次亚磷酸钠80g/L、乙酸钠20g/L、柠檬酸钠30g/L、糖精钠20g/L、硫酸铵15g/L、硫脲0.2g/L、十二烷基硫酸钠0.5g/L、碘酸钾0.1g/L、氨水适量。pH控制在8.0-8.5，温度控制在75℃左右。
(3).低钨合金镀液：二水钨酸钠25/L、六水硫酸镍70g/L、四水碱式碳酸镍10g/L、一水次亚磷酸钠100g/L、乙酸钠20g/L、柠檬酸钠70g/L、糖精钠10g/L、硫酸铵15g/L、硫脲0.2g/L、十二烷基硫酸钠0.5g/L、碘酸钾0.1g/L、氨水适量。pH控制在8.5-9.0，温度控制在80℃左右。
工艺路线：
以不锈钢片作为本专利中的金属薄片层2，甲基乙烯基硅橡胶为疏水性橡胶层1。
将0.075mm厚的材质为SUS304的不锈钢片由碱性清洗剂除油，用自来水清洗，用5％的稀盐酸浸泡30秒，用去离子水清洗。冷风吹干。将一种含有1％乙烯基三特丁基过氧硅烷(VTPS)和0.5％过氧化二异丙苯(DCP)的甲基乙烯基硅橡胶和不锈钢片放在模腔表面涂有特氟龙的模具中，在175℃下让不锈钢片的一面与硅橡胶进行热硫化粘合，硫化时间为8分钟，形成1.0mm厚的不锈钢和硅橡胶的层状复合片材。甲基乙烯基硅橡胶采用商品化的道康宁东丽公司生产的SE 4706U或信越公司生产的KE 961U或其它牌号的甲基乙烯基硅橡胶，都是可行的。VTPS是一种含有过氧基的偶联剂，它既可以使含乙烯基的硅橡胶交联，同时也促进含乙烯基的硅橡胶与金属之间的粘合。
将此复合片材冲切成直径为2-10mm的小圆片。把这种小圆片用碱性清洗液清洗分钟，水洗，然后用5％的盐酸活化1分钟，然后用去离子水清洗，干燥。
将这样的500粒小圆片，放入300ml的上述镀新配制的镍镀液中，搅拌，60分钟后取出，用去离子水清洗，然后放入上述新配制的低钨合金镀液中，搅拌，过渡金属镀层3和低钨合金镀层4在金属面上沉积，120分钟后取出，滤干，再放入上述新配制的钨合金镀液中，搅拌，钨合金镀层5继续在所生成的金属薄片层2面上沉积，90分钟后取出，用去离子水清洗干净，沥干、冷风吹干或放在70℃恒温烘箱里烘干，即得到具有五层结构的层状复合物，这种层状复合物即一种开关触点。
这种含有硅橡胶层的镀有钨合金的小圆片中的硅橡胶面，和其它硅橡胶进行热硫化粘合和热硫化成型，制成含有触点的橡胶按键。该触点与印刷电路板(PCB)的镀金触点接触，具有稳定的和较低的接触电阻，而且这种镀有钨合金的触点有更好的导通稳定，耐电弧烧蚀性好，作为开关触点使用寿命长。由没有钨合金镀层的不锈钢的触点，在通过300毫安的直流电，开关约3000次后，由于存在开关时的电弧烧蚀，不锈钢触点和PCB镀金触点之间的接触电阻就明显升高(由约1欧姆升高至100欧姆以上，多次试验时甚至可以出现不导通的情况)；而在同样的电路条件下，这种镀有钨合金的小圆片与PCB镀金触点通过300毫安的直流电，开关约20000次后，这种触点和PCB镀金触点之间的接触电阻，仍在1欧姆以下。
实施例2：
本实施例仍采用实施例1的镀液，仍使用0.075mm厚的材质为SUS304的不锈钢片为触点中的金属薄片。
将不锈钢平片由碱性清洗剂除油，用自来水清洗，用5％的稀盐酸浸泡30秒，用去离子水清洗。冷风吹干。
将不锈钢片放入上述镀镍镀液中，搅拌，让镍合金沉积在不锈钢片的两面，60分钟后取出，用去离子水清洗干净，干燥。然后将含有1％乙烯基三特丁基过氧硅烷(VTPS)和0.5％过氧化二异丙苯(DCP)的甲基乙烯基硅橡胶和镀有镍合金的不锈钢片放在模腔表面涂有特氟龙的 模具中，在175℃下让不锈钢片的一面与硅橡胶进行热硫化粘合，硫化时间为8分钟，形成1.0mm厚的不锈钢片和硅橡胶的层状复合片材。本次试验中选用道康宁东丽公司生产的SE4706U甲基乙烯基硅橡胶与VTPS和DCP混炼。
将此复合片材冲切成直径为2-10mm的小圆片。把这种小圆片用碱性清洗液在70℃下清洗10分钟，水洗，然后用5％的盐酸活化1分钟，然后用去离子水清洗，干燥。
接着，如实施例1，分别采用低钨合金镀液和钨合金镀液，在上述小圆片上镀上低钨合金镀层4和钨合金镀层5。如此制得的触点，经测试，其使用寿命(开关次数)比相应的没有化学镀层的不锈钢触点延长一倍以上。
实施例3：
以400目的不锈钢平纹网(不锈钢型号为304)代替实施例1中的不锈钢片，采用实施1中的工艺和化学镀液，所制得的触点，也具有较低的接触电阻和较好的耐电弧烧蚀性能。
400目的不锈钢网网孔很小，在和硅橡胶模压时，硅橡胶不会穿透不锈钢网的网孔。如果选用目数小的不锈钢网，如80目以下的不锈钢网，在模压时就会产生硅橡胶穿透不锈钢网孔的工艺问题。因此，需采用较大目数的不锈钢网来制备有镀层的开关触点。

Claims (10)

  1. 一种耐电弧烧蚀的开关触点，其特征在于：开关触点是具有五层的层状结构的复合体，第一层为0.1-10.0mm厚的疏水性橡胶层，第二层为0.01-1.0mm厚的金属薄片层，第三层为0.1-10微米厚的过渡金属铁、钴、镍或铜合金镀层；最外层为0.01-10微米厚的钨合金镀层，含有重量比为50-99％的钨元素；在第三层与最外层之间还有0.01-10微米厚的低钨合金镀层，低钨合金镀层中含有重量比为15-75％的钨元素；在同一开关触点中，钨合金镀层中的钨含量高于低钨合金镀层中钨的含量；过渡金属铁、钴、镍或铜合金镀层、钨合金镀层和低钨合金镀层是通过化学镀方法形成的。
  2. 根据权利要求1所述的耐电弧烧蚀的开关触点，其特征在于：所述的疏水性橡胶层是由于橡胶分子链上羧基、羟基、羰基、氨基、酰胺基、腈基、硝基、卤基、巯基、磺酸根和苯磺酸根含量低，从而使橡胶表面的水接触角大于65°的橡胶材料构成；或者，所述的疏水性橡胶层是由于橡胶中不含或含有少量的亲水性的填料或添加剂，从而使橡胶表面的水接触角大于65°的橡胶材料构成；优先选用三元乙丙橡胶、甲基乙烯基硅橡胶或甲基乙烯基苯基硅橡胶。
  3. 根据权利要求1或2所述的耐电弧烧蚀的开关触点，其特征在于：所述的第二层金属薄片层为具有凸点或凹点的金属片材、具有凸线条或凹线条的金属片材、具有凸面或凹面的金属片材、具有面积小于1mm2的小孔的金属片材、金属网、金属泡沫或者金属纤维烧结毡；金属材质为镁、铝、钛、铬、锰、铁、钴、镍、铜、锌、锡或含有这些元素的合金；所述的金属薄片是单一金属材质的或不同金属材质层状复合的；优先选用不锈钢、铜或铜合金、镍或镍合金。
  4. 根据权利要求1或3所述的耐电弧烧蚀的开关触点，其特征在于：所述的第三层过渡金属合金镀层为镍或镍合金、钴或钴合金。
  5. 根据权利要求1所述的耐电弧烧蚀的开关触点，其特征在于：所述的钨合金镀层或低钨合金镀层，是钨钼合金的，钨的重量百分比含量比钼的重量百分比含量多；钨合金镀层中钨的含量比低钨合金镀层中钨的含量多。
  6. 根据权利要求1所述的耐电弧烧蚀的开关触点的制备方法，其特征在于：开关触点的制备包括如下步骤：
    (1)金属薄片的处理：金属薄片为0.01mm至1.0mm厚的不锈钢、铜或铜合金、镍或镍合金薄片；用清洗剂和有机溶剂对金属薄片进行除油、清洗；或通过喷砂、打磨将金属薄片进行表面机械粗化处理；或通过化学蚀刻处理以处理出直径小于1mm的凹坑或凸点；或在金属薄片的一面或两面，用电镀或化学镀的方法镀有0.1微米至10微米的纯镍层或镍合金层；然后用清洗剂和有机溶剂对所得到的金属薄片进行除油、清洗；
    (2)疏水性橡胶与金属薄片的粘合处理：疏水性橡胶通过热硫化粘合和热硫化成型，粘合在涂有底涂剂或粘合促进剂的金属薄片上，形成层状的复合片材；或者将具有自粘性的疏水性橡胶，通过热硫化成型，粘合在涂有底涂剂或没有底涂剂的金属薄片上，形成层状的复 合片材；
    (3)切割处理：将上述步骤中的复合片材分割或冲切成包含有疏水性橡胶层和金属薄片层的直径为2-10mm的圆柱体，或者将上述步骤中的复合片材分割或冲切成横截面为椭圆形、多边形、十字形、星形、新月形或它们的任意组合的物体；用碱性清洗液清洗约5分钟，水洗后用5％的盐酸清洗3分钟，然后用去离子水清洗干净，滤干；
    (4)过渡金属合金镀层、低钨合金镀层和钨合金镀层的制备：将上述圆柱体或物体，分别浸渍在含有可溶性的过渡金属铁、钴、镍或铜的化学镀液中、低钨合金镀液中和钨合金镀液中各30分钟以上，搅拌，用化学镀的方法在圆柱体或物体的金属表面形成过渡金属合金镀层、低钨合金镀层和钨合金镀层；或者，将上述圆柱体放入在含有可溶性的过渡金属铁、钴、镍或铜的化学镀液中、低钨合金镀液中和钨合金镀液中滚筒中，让滚筒转动各30分钟以上，用化学镀的方法在圆柱体的金属表面依次形成渡金属合金镀层、低钨合金镀层和钨合金镀层；
    (5)清洗、冷风吹干或烘干：取出上述被镀物，用蒸馏水或去离子水漂洗、沥干、冷风吹干或在70℃的恒温烘箱中烘干，即得到金属面层上镀有钨合金的开关触点。
  7. 根据权利要求6所述的耐电弧烧蚀的开关触点的制备方法，其特征在于：所述的钨合金镀层采用化学镀的镀液中，含有45-150g/L的可溶性钨化合物、10-50g/L的可溶性镍化合物、0-30g/L的可溶性钴化合物、20-150g/L的还原剂、30-150g/L的络合剂、20-100g/L的pH值调节剂、0.1-1g/L的稳定剂；
    优选次亚磷酸钠为镀液中的还原剂。采用次亚磷酸钠为还原剂时，所得钨合金镀层所采用化学镀的温度为60-85℃，时间为30-300分钟，镀液的pH值为8.0-10.0。
  8. 根据权利要求6所述的耐电弧烧蚀的开关触点的制备方法，其特征在于：所述的低钨合金镀层采用化学镀的镀液中，含有10-45g/L的可溶性钨化合物、10-150g/L的可溶性镍化合物、0-60g/L的可溶性钴化合物、20-120g/L的还原剂、30-150g/L的络合剂、20-100g/L的pH值调节剂、0.1-1g/L的稳定剂；
    优选次亚磷酸钠为镀液中的还原剂；采用次亚磷酸钠为还原剂时，低钨合金镀层所采用化学镀的温度为75-90℃，时间为50-300分钟，镀液的pH值为8.5-10.5。
  9. 根据权利要求6所述的耐电弧烧蚀的开关触点的制备方法，其特征在于：所述的低钨合金层和钨合金层的化学镀采用的镀液中，含有5-60g/L的可溶性钼化合物，含有5-40g/L的可溶性的锡、锑、铅或铋化合物或这些化合物的任意组合。
  10. 根据权利要求6所述的耐电弧烧蚀的开关触点的制备方法，其特征在于：所述的过渡金属合金镀层、低钨合金层和钨合金层化学镀采用的镀液中，含有0.05-50g/L的化学镀光亮剂；所述的化学镀光亮剂为丁炔二醇、丙炔醇、1-二乙胺基丙-2-炔、乙氧化丙炔醇、邻磺酰苯酰亚胺钠、乙烯基磺酸钠、丙炔磺酸钠、吡啶-2-羟基丙磺酸内盐、烷基酚聚氧乙烯醚或市售的商品化的化学镀光亮剂。
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