JP4279285B2 - Silver-coated stainless steel strip for movable contact and method for producing the same - Google Patents

Description

  The present invention relates to a silver-coated stainless steel strip and a method for producing the same, in which a long-life movable contact can be obtained with a high yield.

  A disc spring contact, a brush contact, a clip contact, or the like is used for electrical contact portions such as a connector, a switch, and a terminal. These contacts are relatively inexpensive and have a nickel base coating on a base material such as copper alloy or stainless steel, which is excellent in corrosion resistance and mechanical properties, and coated with silver that is excellent in conductivity and solderability. Composite contact materials are frequently used (Patent Document 1).

  Composite contact materials using stainless steel substrates are superior to those using copper alloy substrates in terms of mechanical properties, fatigue life, etc., which is advantageous for miniaturization of contacts and can be increased in number of operations. It is used for movable contacts such as tactile push switches and detection switches with a long life.

  However, the composite contact material using a stainless steel substrate has a problem that the silver coating layer of the contact portion is easily peeled off because the contact pressure of the switch is large. The peeling is particularly likely to occur at a small-diameter dome-shaped movable contact, and is an important issue to be solved for downsizing the switch.

Various proposals have been made for improving the life of composite contact materials using a stainless steel substrate, but all have problems.
That is, (1) In the case where a nickel layer, a palladium layer, and a gold layer are formed in this order on a stainless steel substrate (Patent Document 2), the electrical resistance of the contact increases because the palladium layer is inferior in conductivity. (2) A nickel layer, a copper layer, a nickel layer, and a gold layer formed in this order on a stainless steel substrate (Patent Document 3) is cracked in the gold layer during bending because the nickel layer is hard, and the lower layer is Exposed and corrosion resistance decreases. (3) A nickel layer, a copper layer, and a silver layer electroplated in this order on a stainless steel substrate (Patent Documents 4 to 6) have a hard nickel base layer and a thickness of 0.2 to 0.5 μm, so that they are contact points. The high level of workability required for downsizing of the product cannot be obtained.

In addition, the silver-coated composite contact material has a problem that the silver coating layer is peeled off when the small movable contact is press-molded at a high speed, resulting in a decrease in manufacturing yield.
As a countermeasure, a method of preventing hydrogen embrittlement, which is considered to be a cause of peeling, was devised by using stainless steel or iron-nickel alloy for the anode when nickel is plated on a stainless steel substrate ( In this method, however, the nickel plating solution is contaminated with iron ions, and iron is excessively deposited on the plating layer, so that the adhesion of the plating layer is lowered.
JP 59-219945 A Japanese Patent Laid-Open No. 11-232950 JP-A-63-137193 JP 2004-263274 A JP 2005-002400 A JP 2005-133169 A JP 61-23788 A

The present inventors have conducted intensive research in view of such a situation, and that the peeling of the silver coating layer occurs between the stainless steel substrate and the nickel underlayer, and when the predetermined activation treatment is applied to the underlayer. It has been found that the adhesion of the resin is improved, and further research has been made to complete the present invention.
An object of the present invention is to provide a silver-coated stainless steel strip and a method for producing the same, in which a silver-coated layer does not peel off during high-speed press molding or during use, and a long-life movable contact can be obtained with a high yield.

  According to the first aspect of the present invention, a nickel underlayer having a thickness of 0.01 to 0.1 μm is formed on at least a part of the surface of a stainless steel substrate, and the nickel underlayer is held at a temperature of 40 to 90 ° C. for 3 seconds or more. And an intermediate layer having a thickness of 0.05 to 0.2 μm made of at least one of nickel, nickel alloy, copper, and copper alloy on the nickel underlayer after the activation treatment. A silver-coated stainless steel strip for a movable contact, wherein the outermost layer of silver or a silver alloy is formed on the intermediate layer.

  According to a second aspect of the present invention, a nickel underlayer having a thickness of 0.01 to 0.1 μm is electroplated on at least a part of the surface of a stainless steel substrate, and then the nickel underlayer is heated for 3 seconds at a temperature of 40 to 90 ° C. The activation treatment is held as described above, and the activation treatment temperature is applied by the heat used in the plating pretreatment including the formation of the nickel underlayer and the electric resistance of the stainless steel material, and then the activation treatment is performed. An intermediate layer made of at least one of nickel, nickel alloy, copper, and copper alloy and having a thickness of 0.05 to 0.2 μm is formed on the nickel underlayer, and then a silver or silver alloy outermost layer is formed on the intermediate layer. It is a manufacturing method of the silver covering stainless steel strip for movable contacts characterized by forming a surface layer.

  The silver-coated stainless steel strip for the movable contact of the present invention has an activation treatment on the nickel base layer, so that the adhesion between the stainless steel substrate and the nickel base layer is improved, and the silver coating layer is used during high-speed press molding or as a movable contact. Is prevented from being peeled off, thereby improving the productivity, miniaturization and life of the movable contact. The silver-coated stainless steel strip is excellent in productivity because it can be produced by a conventional method except that the nickel underlayer is subjected to an activation treatment for holding at a temperature of 40 to 90 ° C. for 3 seconds or more. Moreover, the activation treatment temperature is low in cost because it can be applied by the heat used in the plating pretreatment including the formation of the nickel underlayer and the electric resistance of the stainless steel material.

  In the present invention, the nickel underlayer reacts with iron contained in the stainless steel substrate by the activation treatment, and changes to a nickel iron alloy whose component change in the thickness direction is gentle. Therefore, during press molding or during use as a movable contact, the strain concentrated on the interface between the stainless steel substrate and the nickel underlayer is dispersed in the thickness direction of the nickel underlayer, preventing peeling between the stainless steel substrate and the nickel underlayer. The

  In the present invention, a rolled tempered material such as SUS301, SUS304, or SUS316 or a tension annealing material that is excellent in stress relaxation characteristics and fatigue fracture resistance is suitable for the stainless steel base material that bears the mechanical strength of the movable contact.

  In the present invention, the nickel underlayer formed on the stainless steel substrate is activated by the subsequent activation treatment, and the adhesion with the stainless steel substrate is improved. Therefore, peeling of the silver coating layer composed of the intermediate layer and the uppermost layer formed on the nickel underlayer is prevented.

  The nickel underlayer after the activation treatment (hereinafter referred to as the “activation layer” as appropriate) is nickel formed by the reaction of iron of a stainless steel base material with the nickel underlayer, and the component gradually changes in the thickness direction. Made of iron alloy. Stainless steel contains chromium, cobalt, molybdenum and the like in addition to iron, but these components may be mixed into the activated layer.

  The activation layer is formed by an activation treatment in which a stainless steel substrate is held at 40 to 90 ° C. for 3 seconds or longer after the nickel underlayer is formed.

  When electroplating a nickel underlayer on a stainless steel substrate, the feeding roll is usually installed near the plating tank to lower the feeding voltage, but in the present invention, the feeding roll is placed at a position away from the plating tank. It installs and the resistance calorific value of a stainless steel base material is enlarged, and a nickel plating layer is heated to 40-90 degreeC using this heat.

  In the present invention, the reason why the activation treatment is performed at a temperature of 40 to 90 ° C. for 3 seconds or more is that the iron nickel alloy layer is not sufficiently formed on the nickel underlayer even if it is less than 40 ° C. or less than 3 seconds. If it exceeds, the surface of the activated layer is oxidized and the adhesion between the intermediate layer is lowered. Particularly desirable activation treatment conditions are 60 to 80 ° C. and 4 to 6 seconds.

In the present invention, the reason for prescribing the thickness of the nickel underlayer to 0.01 to 0.1 μm is that if it is less than 0.01 μm, the adhesion to the stainless steel substrate is not sufficiently improved and exceeds 0.1 μm. In addition, the adhesion improving effect is saturated, and brittle precipitates are generated in the activated layer, which causes cracking of the silver coating layer during press molding or use as a contact.
A particularly desirable thickness of the nickel underlayer is 0.02 to 0.1 μm.

  In the present invention, the reason for forming an intermediate layer (nickel, nickel alloy, copper, copper alloy, etc.) on the nickel underlayer after the activation treatment is that oxygen passing through the uppermost layer (silver or silver alloy) This is to prevent the activation layer from being oxidized by trapping and reducing its adhesion improving effect.

  In the present invention, the reason for defining the thickness of the intermediate layer to 0.05 to 0.2 μm is that the effect is not sufficiently obtained when the thickness is less than 0.05 μm, and the effect is saturated when the thickness exceeds 0.2 μm. It is. In particular, since the nickel layer is hard, if it becomes thick, it will crack during bending and cause the silver coating layer to peel off.

  The intermediate layer is made of nickel, nickel alloy, copper, or copper alloy. However, if a contact material with a longer life is required, copper or copper alloy has better oxygen trapping and workability than nickel. Recommended. The nickel alloy is an alloy containing 1 to 10% by mass of one or more selected from cobalt, chromium and copper in nickel, and the copper alloy is one or two selected from tin, zinc and nickel in copper. An alloy containing 1 to 10% by mass can be used.

  In the present invention, the reason why the thickness of the outermost layer (silver or silver alloy) is specified to be 0.5 to 2.0 μm is that when it is less than 0.5 μm, the effect of excellent contact stability of silver or silver alloy is sufficiently obtained. If the thickness exceeds 2.0 μm, the effect is saturated. As a silver alloy, an alloy containing 0.1 to 2.0% by mass of antimony in silver is recommended because of its excellent wear resistance.

  In the present invention, when the intermediate layer is a copper layer or a copper alloy layer, the metal elements (silver and copper, copper and nickel) of the layers in contact with each other are solid-solved with each other. It's hard to get up.

  In particular, when the intermediate layer is a copper layer or a copper alloy layer, a silver and copper alloy layer is formed thick between the intermediate layer and the outermost layer by heat treatment in a non-oxidizing atmosphere after the outermost layer is formed. Stress is improved. If the temperature of the heat treatment is too high or the time is too long, the outermost silver is all alloyed and the contact stability and conductivity are lowered. The thickness of the alloy layer of silver and copper is preferably 0.1 μm or less, and the heating conditions are preferably 200 to 400 ° C. × 1 minute to 5 hours. As the non-oxidizing atmosphere at the time of heat treatment, a reducing atmosphere or inert gas atmosphere such as hydrogen gas, helium gas, argon gas, and nitrogen gas can be used, and an argon gas atmosphere is particularly preferable.

  In the present invention, the nickel underlayer, intermediate layer (nickel, nickel alloy, copper, copper alloy), outermost layer (silver, silver alloy) are electroplating, electroless plating, physical / chemical vapor deposition, etc. Although it can be formed by any method, the electroplating method is advantageous in terms of productivity and cost. The respective layers may be formed on the entire surface of the stainless steel substrate, but it is economical to form the layers only on the contact portions.

  Hereinafter, the present invention will be described in more detail based on examples, but the present invention is not limited to these examples.

  Using a plating line that continuously winds the metal strip, it is applied to SUS301 strip of thickness 0.06mm and width 100mm, electrolytic degreasing, water washing, nickel base plating, activation treatment, water washing, intermediate layer (nickel , Nickel alloy, copper, copper alloy) plating, water washing, silver strike plating, outermost layer (silver) plating, water washing, and drying were performed in this order to produce a silver-coated stainless steel strip. Ni-2 mass% Co alloy was used for the nickel alloy of the intermediate layer, and Cu-1 mass% Sn alloy and Cu-5 mass% Zn alloy were used for the copper alloy. A part of the silver-coated stainless steel strip using copper as the intermediate layer was heat-treated in an argon atmosphere at 250 ° C. for 2 hours.

The conditions of each process are as follows.
(1) Electrolytic degreasing: SUS301 was applied by cathodic electrolysis using an aqueous solution of sodium orthosilicate 100 g / l. (2) Nickel base plating: Using a plating solution of nickel chloride 5 g / l and 30% free hydrochloric acid, it was applied under conditions of a cathode current density of 2 A / dm ² . (3) Activation treatment: SUS301 strip after nickel base plating was applied in hot water to hot water at 40 to 90 ° C. for 3 seconds or more. The temperature of the SUS301 strip from the electrolytic degreasing to the activation treatment was controlled by immersing the SUS301 strip in a washing tank whose temperature was adjusted by a cooler. (4) Intermediate layer (nickel-based) plating: Using a plating solution containing 250 g / l of nickel chloride and 50 g / l of free hydrochloric acid, the plating was performed under conditions of a total cathode current density of 5 A / dm ² . (5) Intermediate layer (copper-based) plating: A plating solution containing 150 g / l of copper sulfate and 100 g / l of free sulfuric acid was used under the condition of a cathode current density of 5 A / dm ² . (6) Silver strike plating: Using a plating solution containing 5 g / l of silver cyanide and 50 g / l of potassium cyanide, it was applied under conditions of a cathode current density of 2 A / dm ² . (7) Silver plating: Using a plating solution containing 50 g / l of silver cyanide, 50 g / l of potassium cyanide, and 30 g / l of potassium carbonate, it was applied under conditions of a cathode current density of 5 A / dm ² .

Each of the obtained silver-plated stainless steel strips was press-molded into a dome-shaped movable contact having a diameter of 4 mm, and the occurrence of cracks was examined using a 20-fold stereo microscope (n = 1000).
The assembly switch with healthy movable contact cracking did not occur, FIG. 2 (b), the keying test by the method shown in (b), the contact pressure 9.8 N / mm ^2, keying speed 5 Hz, keying number 100 The contact resistance of the silver coating layer after the keystroke test was examined (n = 20). In addition, the condition of the silver coating layer after the keystroke test was observed.

  As shown in FIG. 1, the switch has a dome-shaped movable contact 4 disposed across a fixed contact 3 on a pair of fixed contacts 2 in a resin case 1. This switch is shown in FIG. As shown in FIG. 2, when the center surface of the dome-shaped movable contact 4 is pressed (keyed) and the back surface thereof is brought into contact with the fixed contact 3, a current flows between the two-pole fixed contacts 2 and 3 (FIG. B)). For the fixed contacts 2 and 3, brass strips plated with silver to a thickness of 1 μm were used. In FIG. 2, 5 is a resin filler.

[Comparative Example 1]
A silver-coated stainless steel strip was produced in the same manner as in Example 1 except that the thickness of the nickel underlayer or intermediate layer, or the activation treatment temperature or treatment time was outside the values specified in the present invention. Went.

The investigation results of Example 1 and Comparative Example 1 are shown in Table 1.
Table 1 also shows the contact resistance before the keystroke test.

  As is clear from Table 1, the silver-plated stainless steel strip for movable contact of Example 1 (Example of the present invention) exhibited a good shape without the silver coating layer being peeled off by press molding. Further, the contact resistance of the silver coating layer increased very little even after the key was pressed 1 million times. In particular, no. No. 14 was subjected to a heat treatment after silver plating to form a silver-copper alloy layer between the intermediate layer and the outermost layer, so that the adhesion between both layers was improved. Therefore, no increase in contact resistance due to keystrokes was observed.

  On the other hand, No. 1 of Comparative Example 1 was used. No. 15 has a nickel underlayer (activation layer) that is too thin. No. 16 has a nickel base layer that is too thick and tends to become brittle. No. 17 was not provided with a nickel underlayer. No. 18 had a low processing temperature and an activation layer was not sufficiently formed. No. 19 has an activation treatment temperature too high. No. 20 has a thin intermediate layer and the activation layer was oxidized. In No. 21, since the intermediate layer was too thick and cracking was likely to occur, the adhesion between the stainless steel substrate and the nickel base layer was lowered in any case. As a result, in Comparative Example 1, many cracks occurred in the silver coating layer during press molding, and the contact resistance of the silver coating layer increased after keystroke.

It is plane explanatory drawing of the switch used for the keystroke test. FIG. 2 is a cross-sectional explanatory view taken along the line AA of the switch shown in FIG. 1, (a) before the switch operation and (b) after the switch operation.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Resin case 2 Fixed contact 3 Fixed contact 4 Dome-shaped movable contact 5 Resin filler

Claims (2)

  A nickel underlayer having a thickness of 0.01 to 0.1 μm is formed on at least a part of the surface of the stainless steel substrate, and the nickel underlayer is subjected to an activation treatment for holding at a temperature of 40 to 90 ° C. for 3 seconds or more. An intermediate layer having a thickness of 0.05 to 0.2 μm made of at least one of nickel, nickel alloy, copper, and copper alloy is formed on the nickel underlayer after the activation treatment, A silver-coated stainless steel strip for a movable contact, wherein an outermost layer of silver or a silver alloy is formed thereon.   The nickel base layer having a thickness of 0.01 to 0.1 μm is electroplated on at least a part of the surface of the stainless steel substrate, and then the nickel base layer is activated at a temperature of 40 to 90 ° C. for 3 seconds or more. And applying the activation treatment temperature by the heat used in the pre-plating treatment including the formation of the nickel underlayer and the electrical resistance of the stainless steel material, then nickel on the nickel underlayer after the activation treatment, An intermediate layer made of at least one of nickel alloy, copper and copper alloy and having a thickness of 0.05 to 0.2 μm is formed, and then an outermost layer of silver or a silver alloy is formed on the intermediate layer. A method for producing a silver-coated stainless steel strip for a movable contact.

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