Silver plating film and method for producing silver plating film

Abstract

To provide a silver plating film with a lower surface friction coefficient.SOLUTION: A silver plating film containing silver atoms, carbon atoms, and nitrogen atoms has a carbon atom content of 0.30 mass% or more based on the total mass of the silver plating film, and a nitrogen atom content of 1.00 mass% or more based on the total mass of the silver plating film.SELECTED DRAWING: None

Description

[Technical field]

[0001] The present invention relates to a silver plating film. The present invention also relates to a method for producing the silver plating film. [Background technology]

[0002] In recent years, with the advancement of electronic equipment in automobiles, the current flowing through cables connecting electronic components in automobiles has become larger, and high voltages have been applied. Furthermore, electric automobiles, which have been increasing in number in recent years, are driven by electricity, so large currents flow through cables. Electronic components and power sources are often connected by cables and connectors. The connector passes current between the electronic components and the cable through the connector contact material, and as a connector contact material for automobiles, which are becoming increasingly equipped with electrical equipment, a highly conductive silver plating film is preferably used.

[0003] While silver plating films have high conductivity, they generally have low surface hardness, and adhesion is likely to occur when silver plating films slide against each other. When this happens, the connector contact material (silver plating film) is likely to wear out when the connector is repeatedly inserted and removed and slides against it. One method for reducing the wear of the silver plating film is to increase the hardness of the silver plating film, and such a silver plating film is also called hard silver plating. For example, Patent Document 1 describes the formation of a silver plating film containing antimony and having a high Vickers hardness. Another method for reducing the wear of the silver plating film is to place a solid lubricant such as carbon particles on the surface of the silver plating film. For example, Patent Document 2 discloses a technique for forming a silver plating film made of a composite material containing carbon particles by electroplating using a silver plating solution containing added carbon particles. The document describes that the silver plating film containing the carbon particles has excellent wear resistance. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2009-079250 A [Patent Document 2] Patent Publication No. 2021-025133 Summary of the Invention [Problem to be solved by the invention]

[0005] However, the present inventors have studied the method described in the above Patent Document 1 and found that the wear resistance does not reach the level currently required. When the present inventors have studied the cause of this, they have found that the friction coefficient of the silver plating film surface is related to the wear resistance and that there is room for improvement in the friction coefficient of the silver plating film surface.

[0006] Furthermore, in the method described in Patent Document 2, it is necessary to disperse carbon particles in the plating solution, and when plating, it is necessary to perform a dispersion process of the carbon particles and sufficient stirring of the plating solution. In addition, various impurities accumulate in such a plating solution with use, and a filtration process may be performed to remove the impurities. If a plating solution in which the above-mentioned carbon particles are dispersed is filtered, the carbon particles are removed together with the impurities, so it is difficult to subject such a plating solution to a filtration process. Furthermore, the silver plating film formed by the above method needs to be cleaned to remove excess carbon particles adhering to the surface of the silver plating film. For these reasons, the method described in Patent Document 2 is complicated and tends to increase production costs, and there has been a demand for a method for producing a silver plating film that is highly productive and has a low friction coefficient.

[0007] The present invention has been made in view of the above problems, and an object of the present invention is to provide a silver plating film having a low surface friction coefficient. Another object of the present invention is to provide a method for producing a silver plating film, which can produce a silver plating film having a low surface friction coefficient with good productivity. [Means for solving the problem]

[0008] The present inventors have conducted extensive research to solve the above problems, and have completed the present invention. That is, they have found that the above problems can be solved by the following configuration. [1] A silver plating film containing silver atoms, carbon atoms, and nitrogen atoms, the carbon atom content is 0.30 mass% or more based on the total mass of the silver plating film, The content of the nitrogen atoms is 1.00 mass % or more based on the total mass of the silver plating film. [2] The silver plating film according to [1], wherein the content of the silver atoms is 90.00 mass% or more based on the total mass of the silver plating film. [3] The silver plating film according to [1] or [2], further comprising oxygen atoms, the content of the oxygen atoms being 0.10 mass% or more based on the total mass of the silver plating film. [4] The silver plating film according to [1] or [2], wherein the content of sulfur atoms is 2.0 mass% or less based on the total mass of the silver plating film. [5] The silver plating film according to [1] or [2], wherein the content of the carbon atoms is 0.35 mass% or more based on the total mass of the silver plating film. [6] The silver plating film according to [1] or [2], wherein the content of the nitrogen atoms is 1.30 mass% or more based on the total mass of the silver plating film. [7] A method for producing a silver plating film by passing an electric current through a plating solution containing a silver ion source, comprising the steps of: The plating solution contains a nitrogen-containing polymer compound that contains carbon atoms and nitrogen atoms, The nitrogen-containing polymer compound has a number average molecular weight of 1000 or more, A method for producing a silver plating film, wherein the content of the nitrogen-containing polymer compound in the plating solution is 0.5 g / L or more. [8] The method for producing a silver plating film according to [7], wherein the nitrogen-containing polymer compound contains a nitrogen atom having a lone pair of electrons. [9] The method for producing a silver plating film according to [7] or [8], wherein the silver ion source contains a silver atom and a cyano group coordinated to the silver atom. Effect of the Invention

[0009] According to the present invention, a silver plating film having a low surface friction coefficient can be provided. Furthermore, according to the present invention, a method for producing a silver plating film can be provided that can produce a silver plating film having a low surface friction coefficient with good productivity. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] The present invention will be described in detail below. The following description of the configuration may be based on a representative embodiment of the present invention, but the present invention is not limited to such an embodiment.

[0011] The following describes the meaning of each description in this specification. In this specification, a numerical range expressed using "to" means a range that includes the numerical values ​​before and after "to" as the lower and upper limits.

[0012] <Silver plating film> The silver plating film of the present invention contains silver atoms, carbon atoms, and nitrogen atoms, and the carbon atom content is 0.30 mass% or more, based on the total mass of the silver plating film, and the nitrogen atom content is 1.00 mass% or more, based on the total mass of the silver plating film. The silver plating film of the present invention has a low coefficient of friction on its surface. Although the reason for this is not entirely clear, the present inventors speculate as follows. The silver plating film of the present invention has a carbon atom and nitrogen atom content of a predetermined value or more relative to the total mass of the silver plating film. In this case, a certain amount of carbon atoms and nitrogen atoms are present on the surface of the silver plating film, and it is considered that, for example, a nitrogen-containing polymer compound described below plays the role of a lubricant. As a result, it is considered that the silver plating film of the present invention has a low coefficient of friction on its surface.

[0013] The silver plating film of the present invention will now be described.

[0014] [composition] The composition of the silver plating film of the present invention will be described. As described above, the silver plating film of the present invention contains silver atoms, carbon atoms, and nitrogen atoms, and the carbon atom content is 0.30 mass% or more, based on the total mass of the silver plating film, and the nitrogen atom content is 1.00 mass% or more, based on the total mass of the silver plating film. In the present invention, the composition of the silver plating film is determined by analysis using glow discharge optical emission spectrometry. The specific measurement method is as described in the Examples section below.

[0015] In the silver plating film of the present invention, the content of silver atoms is preferably 50% by mass or more, more preferably 70% by mass or more, and even more preferably 90% by mass or more, based on the total mass of the silver plating film, in terms of the electrical conductivity of the silver plating film. The content of silver atoms is often 98.5% by mass or less, based on the total mass of the silver plating film. The silver plating film of the present invention may contain elements other than silver, carbon, nitrogen, and oxygen and sulfur, which will be described later. Examples of metal elements other than silver include gold, bismuth, cadmium, cobalt, chromium, copper, iron, indium, iridium, molybdenum, nickel, lead, palladium, platinum, rhodium, rhenium, ruthenium, tin, titanium, thallium, tungsten, and zinc. Examples of metalloid elements other than silver include selenium, arsenic, germanium, and antimony. Examples of non-metallic elements other than silver, carbon, and nitrogen include bromine and iodine. It is also preferable that the silver plating film does not contain any metal elements other than silver.

[0016] The carbon atom content is 0.30% by mass or more, preferably 0.35% by mass or more, and more preferably 0.40% by mass or more, based on the total mass of the silver plating film. The carbon atom content is often 1.40% by mass or less, based on the total mass of the silver plating film, and is preferably 1.00% by mass or less, more preferably 0.70% by mass or less, and even more preferably 0.60% by mass or less, based on the superior wear resistance of the silver plating film.

[0017] The nitrogen atom content is 1.00 mass% or more, preferably 1.15 mass% or more, more preferably 1.20 mass% or more, and even more preferably 1.30 mass% or more, based on the total mass of the silver plating film. The nitrogen atom content is often 4.00 mass% or less, based on the total mass of the silver plating film, and is preferably 3.00 mass% or less, more preferably 2.50 mass% or less, and even more preferably 2.00 mass% or less, based on the viewpoint of superior wear resistance of the silver plating film.

[0018] Carbon atoms and nitrogen atoms are preferably contained in the silver plating film of the present invention as a nitrogen-containing polymer compound contained in the plating solution described below, or as a component derived from the nitrogen-containing polymer compound.

[0019] The silver plating film may contain atoms other than those mentioned above. Examples of the atoms other than those mentioned above include oxygen atoms and sulfur atoms. In particular, it is preferable that the silver plating film contains oxygen atoms.

[0020] When the silver plating film contains oxygen atoms, the content of oxygen atoms is preferably 0.05 mass% or more, more preferably 0.10 mass% or more, and even more preferably 0.20 mass% or more, based on the total mass of the silver plating film. The content of oxygen atoms is often 2.00 mass% or less, preferably 1.00 mass% or less, and more preferably 0.60 mass% or less, based on the total mass of the silver plating film.

[0021] The silver plating film may also contain sulfur atoms. When the silver plating film contains sulfur atoms, the content of sulfur atoms is preferably 0.10 mass% or more based on the total mass of the silver plating film, and from the viewpoint of the electrical conductivity of the silver plating film, the content of sulfur atoms is preferably 4.00 mass% or less, more preferably 1.00 mass% or less, based on the total mass of the silver plating film. It is also preferable that the silver plating film does not contain sulfur atoms.

[0022] [Atom distribution] It is preferred that carbon atoms and nitrogen atoms are uniformly dispersed on the surface of the silver plating film of the present invention. Specifically, when the surface of the silver plating film is observed with a scanning electron microscope, a region in which at least one of carbon atoms and nitrogen atoms is present is observed, and the average equivalent circle diameter of the region is preferably 100 nm or less. The average equivalent circle diameter is more preferably 50 nm or less, and even more preferably 30 nm or less, in terms of superior wear resistance. The average equivalent circle diameter is often 1 nm or more. The above-mentioned circle equivalent diameter is determined by the following procedure. First, the surface of the silver plating film is observed with a scanning electron microscope, and a backscattered electron image is obtained at a magnification of 100,000 times. Regions in which at least one of carbon atoms and nitrogen atoms is observed are observed as low brightness (black) regions in the backscattered electron image. Next, the average brightness of each pixel in the reflected electron image is obtained, and the reflected electron image is binarized using the average brightness as a threshold to obtain a processed observation image. In the processed observation image, the circular equivalent diameters of the grain sizes of the black regions are measured, and the arithmetic mean value of the circular equivalent diameters of 100 black regions is taken as the average circular equivalent diameter. Here, if there are fewer than 100 black regions in the processed observation image, the above analysis is performed based on a backscattered electron image acquired in a different field of view, and the circle equivalent diameters are measured until there are 100 black regions.

[0023] It is also preferable that carbon atoms and nitrogen atoms are uniformly dispersed in the thickness direction of the silver plating film of the present invention. Specifically, the carbon atom content is preferably 1.0 to 1.8 in the thickness direction as calculated by the following procedure. That is, when the composition of the silver plating film is analyzed by the method described below, the carbon atom content (%) is calculated at the 25% thickness position, the 50% thickness position, and the 75% thickness position when the entire thickness of the silver plating film is taken as 100%, and the ratio of the maximum content value to the minimum content value among the above content values ​​is taken as the carbon atom content ratio in the thickness direction. Moreover, with regard to the content ratio of nitrogen atoms in the thickness direction, when the content ratio is calculated in the same manner as the content ratio of carbon atoms in the thickness direction, the value is preferably 1.0 to 1.8.

[0024] It is believed that the silver plating film of the present invention has better wear resistance if the carbon and nitrogen atoms are uniformly dispersed on the surface and also in the thickness direction. This is because, even if the surface of the silver plating film is scraped off by wear, if the carbon and nitrogen atoms are uniformly dispersed in the thickness direction, the carbon and nitrogen atoms are still present on the surface after scraping off, and therefore the friction coefficient is lowered according to the above-mentioned principle.

[0025] Thickness The thickness of the silver plating film of the present invention is often 0.5 μm or more, preferably 1.0 μm or more and more preferably 3.0 μm or more in terms of wear resistance of the silver plating film, and is often 50 μm or less, preferably 15 μm or less in terms of economy. In this specification, the thickness of the silver plating film is a value calculated from the amount of deposition, the area of ​​deposition, and the density of silver of the silver plating film. The thickness of the silver plating film may be obtained using a scanning electron microscope. Specifically, a cross section perpendicular to the surface of the silver plating film is prepared, the cross section is observed using a scanning electron microscope, and the thickness of the silver plating film is measured at 10 points, and the arithmetic average value is taken as the thickness of the silver plating film.

[0026] [Physical Properties] The preferred physical properties exhibited by the silver plating film of the present invention will now be described.

[0027] The surface roughness of the silver plating film of the present invention is preferably 0.5 μm or less, more preferably 0.3 μm or less, and even more preferably 0.2 μm or less, and in many cases the surface roughness is 0.01 μm or more. In this specification, the surface roughness refers to the arithmetic mean height Sa defined in ISO 25178, and is measured using a laser microscope (VK-X1100, manufactured by Keyence Corporation). The measurement conditions are in accordance with ISO 25178.

[0028] The Vickers hardness of the silver plating film of the present invention is preferably 50 HV or more, more preferably 60 HV or more, and in most cases, the Vickers hardness is 200 HV or less. In this specification, the Vickers hardness refers to the one measured in accordance with JIS Z 2244:2020, and specifically, is measured using a micro Vickers hardness tester (HM-221, manufactured by Mitutoyo Corporation).

[0029] The friction coefficient of the surface of the silver plating film of the present invention is preferably 0.5 or less, more preferably 0.4 or less, and in many cases is 0.1 or more. In this specification, the coefficient of friction refers to the dynamic coefficient of friction, which is obtained by measuring using the method described in the Examples section below.

[0030] The surface contact resistance of the silver plating film of the present invention is preferably 1.0 mΩ or less, more preferably 0.5 mΩ or less, and in many cases the contact resistance is 0.1 mΩ or more. In this specification, the contact resistance is a value obtained by a four-terminal method, specifically, the value of the contact resistance during a sliding test performed by a sliding tester. The measurement device used is a contact electrical resistance simultaneous measurement type friction and wear tester FPR-2300 (Rhesca), the measurement conditions are as follows, and the contact resistance is the arithmetic average value of three measurements. Load: 6N Measurement current: 10mA Open circuit voltage: 20mV Sliding distance: 10mm -Sliding speed: 10mm / sec

[0031] <Contact parts> The use of the silver plating film of the present invention is not particularly limited, but it is preferably used, for example, as a contact member. The contact member preferably has a metal substrate and the above-mentioned silver plating film of the present invention disposed on at least a part of the metal substrate. The preferred aspects of the silver plating film of the present invention in the contact member are as described above.

[0032] The material of the metal substrate is not particularly limited, but is preferably a material with a low electrical resistance. Examples of the material of the metal substrate include copper, silver, and gold, and copper is preferred. The metal substrate may have a single layer structure or a multilayer structure. When the metal substrate has a laminated structure, it is preferable that the metal substrate has a base material (metal support) and a plating layer disposed on the surface thereof. The plating layer is not particularly limited, and examples thereof include a copper plating layer, a silver plating layer, a gold plating layer, a tin plating layer, a nickel plating layer, a platinum plating layer, a rhodium plating layer, and an alloy plating layer obtained by adding other metals to the above metals. When the plating layer in the metal substrate having a laminated structure is a silver plating layer, the silver plating layer is a layer different from the silver plating film of the present invention.

[0033] The surface of the metal substrate may be subjected to various treatments, for example, a discoloration prevention treatment. Examples of the discoloration prevention treatment include a treatment for forming a film selected from the group consisting of alkanethiols on the surface of the metal substrate (on the surface of the plating layer when the metal substrate has a plating layer).

[0034] The maximum height (Sz) on the surface of the metal substrate is not particularly limited, and is often 0.1 to 5.0 μm, preferably 0.5 to 1.7 μm. The maximum height on the surface of the metal substrate can be controlled by a known method, for example, in the case of a metal substrate not having a plating layer, it can be controlled by processing conditions such as the cutting depth and feed pitch of the cutting process, or by surface treatments such as blasting and chemical etching after the cutting process. In the case of a metal substrate having a plating layer, it can also be controlled by conditions such as the deposition rate and temperature of the plating.

[0035] Since the contact member has the silver plating film of the present invention, it has a low coefficient of friction and excellent wear resistance, and can be used in a variety of applications. The contact member can be applied to electronic components such as switches and relays used to turn current on and off, and to electrical devices. In other words, the contact member having the silver plating film of the present invention also relates to a connector having the contact member. When the above-mentioned contact members are used, the contact members may be used so as to slide against each other with their silver plating films facing each other. The shape of the connector having the above-mentioned contact member is not particularly limited, and it can be applied to connectors of known shapes.

[0036] <Method of manufacturing silver plating film> The method for producing a silver plating film of the present invention comprises passing an electric current through a plating solution containing a silver ion source to produce a silver plating film. The plating solution contains a nitrogen-containing polymeric compound that contains carbon atoms and nitrogen atoms, the number average molecular weight of the nitrogen-containing polymeric compound is 1000 or more, and the content of the nitrogen-containing polymeric compound in the plating solution is 0.5 g / L or more. According to the method for producing a silver plating film of the present invention, the above-mentioned silver plating film of the present invention can be produced. Moreover, the method for producing a silver plating film of the present invention is excellent in productivity because it is sufficient to use a plating solution containing a predetermined amount of a predetermined nitrogen-containing polymer compound and to pass an electric current, so that existing facilities can be utilized and there is no need to apply special equipment for filtering the plating solution or the like.

[0037] The method for producing a silver plating film of the present invention will be described below. In the following, the method for producing a silver plating film of the present invention will also be referred to simply as the "production method of the present invention."

[0038] [Plating solution] The plating solution used in the manufacturing method of the present invention contains a silver ion source and a nitrogen-containing polymer compound that contains carbon atoms and nitrogen atoms. Components contained in the plating solution and components that may be contained in the plating solution will be described below. The plating solution preferably contains water as a solvent.

[0039] (Silver ion source) The silver ion source contained in the plating solution is not particularly limited as long as it can release silver ions in the plating solution, and any known silver ion source can be used. The silver ion source may be a compound that contains a silver atom and a group that is chemically or coordinately bonded to the silver atom, or an ion that is ionically bonded to the silver atom. Among them, the silver ion source preferably contains a silver atom and a group that is coordinated to the silver atom, and preferably contains a silver atom and a cyano group that is coordinated to the silver atom. That is, the silver ion source preferably contains a cyan-based silver complex. The cyan-based silver complex is stable over a wide range of pH levels, and is therefore preferred.

[0040] Examples of sources of silver ions include various silver salts. The silver salt may be a complex salt, including a complex. Examples of silver salts include silver nitrate, silver sulfate, silver alkylsulfonates (e.g., silver methanesulfonate and silver ethanesulfonate), silver cyanide, and dicyanoargentates (e.g., sodium dicyanoargentate and potassium dicyanoargentate). Among these, silver cyanide or dicyanoargentates are preferred, and dicyanoargentates are more preferred.

[0041] The content of the silver ion source in the plating solution (the amount (g) of the silver ion source contained per 1 L of plating solution) can be appropriately adjusted, but is, for example, 1 to 100 g / L, and preferably 5 to 50 g / L.

[0042] (Nitrogen-containing polymer compound) The nitrogen-containing polymer compound contained in the plating solution contains carbon atoms and nitrogen atoms, and has a number average molecular weight of at least 1000. The content of the nitrogen-containing polymer compound in the plating solution is at least 0.5 g / L. The nitrogen-containing polymer compound is not particularly limited as long as it contains a carbon atom and a nitrogen atom, but it is preferable that the nitrogen-containing polymer compound contains a nitrogen atom having a lone pair of electrons. Since protons can be coordinated to and removed from the nitrogen atom having a lone pair of electrons, it is considered that the silver plating film of the present invention is more easily obtained by the mechanism described below. In the nitrogen-containing polymer compound, the nitrogen atom content is preferably 1 atomic % or more, more preferably 5 atomic % or more, and even more preferably 8 atomic % or more, based on the total atoms in the nitrogen-containing polymer compound. In addition, in the nitrogen-containing polymer compound, the nitrogen atom content is often 40 atomic % or less, and preferably 20 atomic % or less.

[0043] Examples of structures formed by nitrogen atoms in a nitrogen-containing polymeric compound include an amine structure, an imine structure, and a quaternary ammonium salt structure. That is, the nitrogen-containing polymeric compound preferably has a group containing each of the above structures. The above structures refer to structures represented by the following formulas (a) to (c).

[0044] [ka]

[0045] Formula (a) represents an amine structure. In formula (a), * represents a bond. It is preferable that a hydrogen atom or a carbon atom is bonded to each of the three bonds in formula (a) independently. When one of the three bonds in formula (a) is bonded to a carbon atom and the remaining two bonds are bonded to hydrogen atoms, formula (a) represents a primary amino group. When two of the three bonds in formula (a) are bonded to carbon atoms and the remaining bond is bonded to a hydrogen atom, formula (a) represents a secondary amino group. When carbon atoms are bonded to three of the three bonds in formula (a), formula (a) represents a tertiary amino group. When formula (a) represents a secondary amino group or a tertiary amino group, the secondary amino group or the tertiary amino group may be included in a ring structure formed by the carbon atom to which it is bound and other atoms bound to that carbon atom, i.e., the secondary amino group or the tertiary amino group may be a cyclic amino group.

[0046] Formula (b) represents an imine structure. In formula (b), * represents a bond. It is preferable that the two bonds in formula (b) are each independently bonded to a hydrogen atom, a carbon atom, or a nitrogen atom, and it is more preferable that each is bonded to a carbon atom. The carbon atom bonded to the formula (b) may form a cyclic structure via other carbon atoms and other atoms. The cyclic structure having the structure of the formula (b) may be an aromatic imine structure having aromaticity, or an aliphatic cyclic imine structure having no aromaticity. Examples of groups containing an aromatic imine structure include groups obtained by removing one hydrogen atom from pyridine, triazine, pyrrole, imidazole, pyrazole, triazole, oxazole, thiazole, imidazoline, quinoline, benzimidazole, and benzotriazole. Examples of groups containing an aliphatic imine structure include groups obtained by removing one hydrogen atom from amidine, guanidine, and the like.

[0047] Formula (c) represents a quaternary ammonium salt structure. In formula (c), * represents a bond. Carbon atoms are bonded to the four bonds in formula (c). In formula (c), A represents an anion. The anion is not particularly limited, and may be an inorganic anion or an organic anion. Examples of inorganic anions include halide ions, nitrate ions, and sulfate ions. Examples of organic anions include ions obtained by removing one hydrogen atom from carboxylic acid compounds, sulfonic acid compounds, and phosphoric acid compounds.

[0048] The nitrogen-containing polymer compound may have only one of the above structures, or may have two or more of the above structures. The nitrogen-containing polymer compound may have the above structures in its main chain or in its side chain. The main chain refers to the longest chain structure in the nitrogen-containing polymer compound, and the side chain refers to the portion bonded to the main chain.

[0049] Among these, the nitrogen-containing polymer compound preferably has an amine structure or a quaternary ammonium salt structure, and more preferably has an amine structure. That is, the nitrogen-containing polymer compound more preferably contains an amino group (one or more groups selected from the group consisting of a primary amino group, a secondary amino group, and a tertiary amino group). When the nitrogen-containing polymer compound has an amino group, the amino group may form a salt with an acid.

[0050] Examples of the nitrogen-containing polymeric compound include polyallylamine, dimethylallylamine, polyetheramine, polyethyleneimine, polymethylolmelamine, aminoethylpolyacrylic acid, and dimethylaminoethylpolyacrylic acid, as well as copolymers having at least two or more types of repeating units of the above polymeric compounds. Among them, the nitrogen-containing polymer compound is preferably polyethyleneimine. The polyethyleneimine may be linear or branched.

[0051] The nitrogen-containing polymer has a number average molecular weight of 1,000 or more. The number average molecular weight of the nitrogen-containing polymer compound is preferably 1500 or more, and more preferably 5000 or more, in order to lower the coefficient of friction of the surface of the resulting silver plating film, and is preferably 100000 or less, more preferably 50000 or less, and even more preferably 20000 or less, in order to improve the abrasion resistance of the resulting silver plating film. In this specification, the number average molecular weight of a nitrogen-containing polymeric compound is measured by boiling point elevation (ebullometry) of a solution when the molecular weight is 5000 or less, and is measured by high performance liquid chromatography when the molecular weight is more than 5000. In addition, when a catalog value for the number average molecular weight is available, the catalog value may be used.

[0052] The content of the nitrogen-containing polymer compound in the plating solution (the amount (g) of the nitrogen-containing polymer compound contained per 1 L of the plating solution) is 0.5 g / L or more. The content of the nitrogen-containing polymer compound in the plating solution is preferably 0.8 g / L or more, more preferably 1.0 g / L or more, in order to lower the coefficient of friction of the surface of the resulting silver plating film, and is preferably 15.0 g / L or less, more preferably 10.0 g / L or less, and even more preferably 5.0 g / L or less, in order to improve the wear resistance of the resulting silver plating film.

[0053] The silver plating film of the present invention can be formed by the plating solution containing a predetermined amount of a nitrogen-containing polymer compound that satisfies the above requirements. Although the mechanism by which this occurs is not entirely clear, the present inventors speculate as follows. Since the nitrogen-containing polymer compound is likely to be positively charged in the plating solution, it is considered that the nitrogen-containing polymer compound is often present around the electrode on which the silver plating film is deposited when the plating solution is electrified to form the silver plating film. In addition, the structure formed by the nitrogen atoms in the nitrogen-containing polymer compound is likely to be coordinated to the silver present on the surface of the formed silver plating film, so that the nitrogen-containing polymer compound is likely to be adsorbed on the surface of the silver plating film. The nitrogen-containing polymer adsorbed on the surface can exhibit appropriate adsorptivity and coagulation properties by adjusting its number-average molecular weight and content, and the silver plating film can grow on the silver plating film while the nitrogen-containing polymer is still adsorbed on the silver plating film. As a result, the nitrogen-containing polymer (or a component derived from the nitrogen-containing polymer) is incorporated into the silver plating film, causing the silver plating film to grow, and it is believed that the silver plating film of the present invention can be obtained.

[0054] (pH adjuster) The plating solution may contain a pH adjuster in addition to the above components, but the above-mentioned silver ion source and nitrogen-containing polymer compound are not included in the pH adjuster. The pH adjusters include acidic and basic additives.

[0055] In this specification, the acidic additive refers to an additive whose aqueous solution has a pH of less than 7.0. The acidic additive may be used as a pH adjuster in the form of an aqueous solution. Examples of the acidic additive include inorganic acids and organic acids. Examples of inorganic acids include sulfuric acid, nitric acid, hydrochloric acid, and phosphoric acid, as well as salts thereof. Examples of the organic acid include a carboxylic acid compound, a sulfonic acid compound, a phosphoric acid compound, and salts thereof.

[0056] As used herein, a basic additive refers to an additive whose aqueous solution has a pH greater than 7.0. Basic additives include inorganic bases and organic bases. Inorganic bases include, for example, alkali metal hydroxides (eg, sodium hydroxide and potassium hydroxide), ammonia, ammonium salts, and the like. Examples of the organic base include amine compounds, quaternary ammonium compounds, and salts thereof.

[0057] The pH of the plating solution can be adjusted to a desired pH by a pH adjuster, and the content of the pH adjuster can be appropriately adjusted depending on the desired pH of the plating solution.

[0058] (Other additives) The plating solution may contain components (other additives) other than the above components. Examples of other additives include gloss agents, smoothing agents, electrically conductive salts, pH buffers, and surfactants. As the glossing agent and smoothing agent, any glossing agent or smoothing agent commonly used in this field can be used, and commercially available products can be used. Examples of the electrically conductive salt include sulfuric acid, potassium hydroxide, sodium hydroxide, etc. The electrically conductive salt may be included in the plating solution as the pH adjuster. As the pH buffering agent, any pH buffering agent commonly used in this field can be used, and a preferred example is phosphate. Examples of the surfactant include anionic surfactants and nonionic surfactants. Examples of the anionic surfactant include sodium polyoxyethylene alkyl ether sulfate. Examples of the nonionic surfactant include polyoxyethylene alkyl ether condensates. Other examples of the additives include soluble metal compounds, sulfur compounds, cyclic nitrogen-containing compounds, and amino acids. The above other additives may be used alone or in combination of two or more.

[0059] The plating solution may contain a metal ion source other than the silver ion source, but it is also preferable that the plating solution does not contain a metal ion source other than the silver ion source. The other metal ion source refers to a compound capable of releasing ions of metal elements of Groups 3 to 15. When a plating solution containing such other metal ion sources is used, a silver alloy plating film containing silver and the metal elements may be obtained. Here, when attempting to obtain a silver alloy plating film, many metal ions released from the above-mentioned other metal ion sources have a lower deposition potential than silver, so silver tends to deposit preferentially. For this reason, when attempting to obtain a silver alloy plating film, it is necessary to lower (make less noble) the potential of the electrode on which the silver alloy plating film is to be deposited, which makes silver more likely to deposit. In such a state, the deposition rate of silver increases too much, so a compound (brightener) that is easily adsorbed to the surface of silver may be added to the plating solution. On the other hand, under the above-mentioned conditions, silver deposits further before the brightener is strongly adsorbed to the deposited silver, so that the brightener tends to be difficult to be incorporated into the silver alloy plating film. The silver alloy plating film can be obtained by adjusting the number average molecular weight and content of the nitrogen-containing polymer compound.

[0060] (pH of plating solution) The pH of the plating solution is not particularly limited as long as a silver plating film is formed by the procedure described below. The pH of the plating solution may be, for example, 0.0 to 14.0, and preferably 2.0 to 12.0. It is also preferable to adjust the pH of the plating solution to 9.0 to 12.0. The pH of the plating solution can be adjusted with the above-mentioned pH adjusters. When polyethyleneimine is used as the nitrogen-containing polymeric compound, the pH of the plating solution is preferably 9.0 or higher, and more preferably 11.0 or higher, in order to dissolve the polyethyleneimine uniformly in the plating solution.

[0061] In addition, the solubility of nitrogen-containing polymer compounds often changes depending on the pH. It is believed that by adjusting the pH to the above-mentioned preferred range, the nitrogen-containing polymer compound (or a component derived from the nitrogen-containing polymer compound) is incorporated into the silver plating film, which facilitates the growth of the silver plating film, for the following reasons. Specifically, in the vicinity of the electrode where silver plating is performed, H +It is considered that the above phenomenon occurs, and the pH may decrease locally. The solubility of the nitrogen-containing polymer compound decreases only in the vicinity of the electrode as the pH decreases, and the nitrogen-containing polymer compound may form aggregates in the vicinity of the electrode. Therefore, it is considered that the nitrogen-containing polymer compound is easily incorporated into the silver plating film and grows when a nitrogen-containing polymer compound having a predetermined number average molecular weight is used and a predetermined content is used.

[0062] [Formation of silver plating film] In the method for producing a silver plating film of the present invention, a silver plating film is produced by passing electricity through the plating solution. The procedure for producing the silver plating film is not particularly limited as long as electricity is passed through the plating solution, but an example of the procedure is to electrically connect a conductive substrate (e.g., the metal substrate) and a counter electrode via the plating solution, apply a voltage between the conductive substrate and the counter electrode, pass electricity through the plating solution, and form a silver plating film on the conductive substrate. The above embodiment will be described below as an example of a procedure for producing a silver plating film.

[0063] (Conductive base material) The conductive substrate is not particularly limited, and any known conductive substrate can be used. Among them, the metal substrate described in the above-mentioned contact member is preferable. The preferred embodiment of the conductive substrate is the same as the preferred embodiment of the metal substrate. The conductive substrate may also be formed into a desired shape.

[0064] The conductive substrate may be subjected to various surface treatments before the silver plating film is formed. Examples of the surface treatment include a degreasing treatment, an acid activation treatment, and a strike plating treatment. That is, the method for producing a silver plating film of the present invention may include a step of subjecting the conductive base material to the following treatments. In addition, for the surface treatment described below, conditions generally used in the field to which the present invention pertains can be appropriately adopted, and the conditions can be adjusted depending on the purpose of the surface treatment.

[0065] The method for producing a silver plating film of the present invention may include a step of subjecting the conductive substrate to a degreasing treatment. The degreasing treatment is a treatment for removing oils and fats present on the surface of the conductive base material. Examples of the degreasing treatment include a solvent cleaning treatment, an alkali cleaning treatment, and an alkaline electrolytic degreasing treatment. The solvent cleaning treatment refers to a treatment in which the surface of the conductive substrate is brought into contact with a solvent capable of dissolving oils and fats, etc., to remove the oils and fats, etc., from the surface. The alkaline cleaning treatment refers to a treatment in which an alkaline aqueous solution is brought into contact with the surface of the conductive substrate, and oils and fats on the surface are saponified and removed. The alkaline electrolytic degreasing treatment is a treatment in which a conductive substrate is electrically contacted with a suitable anode through an alkaline aqueous solution, and electricity is passed through the conductive substrate as the cathode to generate hydrogen gas bubbles on the surface of the conductive substrate. In the alkaline electrolytic degreasing treatment, a cleaning effect due to the alkaline aqueous solution and a physical cleaning effect due to the generated hydrogen gas bubbles are obtained.

[0066] The degreasing treatment may be any one of the above treatments alone or may be a combination of two or more of the above treatments.

[0067] The method for producing a silver plating film of the present invention may include a step of subjecting the conductive substrate to an acid activation treatment. The acid activation treatment refers to a treatment in which a part of the surface of the conductive substrate is dissolved by an acid to expose an active surface of the conductive substrate. Examples of the acid activation treatment include an acid immersion treatment and an acid electrolysis treatment. The acid immersion treatment refers to a treatment in which the surface of the conductive substrate is brought into contact with an acidic aqueous solution. The acid electrolysis treatment is a treatment in which the conductive substrate is electrically contacted with a suitable counter electrode via an acidic aqueous solution, and a current is passed through the conductive substrate as the cathode or anode. When passing a current, it is also preferable to switch the polarity of the conductive substrate at a predetermined time. The acid electrolysis treatment may also have the effect of the above-mentioned degreasing treatment.

[0068] The method for producing a silver plating film of the present invention may include a step of performing a strike plating treatment on the conductive substrate. Strike plating refers to a process for forming a thin plating layer on a base material prior to plating. In the method for producing a silver plating film of the present invention, when strike plating is performed, the material of the plating layer to be formed preferably contains silver, i.e., the strike plating is preferably a silver strike plating.

[0069] (opposite) The counter electrode is not particularly limited, and any known counter electrode can be used. Since the counter electrode has a high potential, it is preferable that at least the surface of the counter electrode is made of a material having corrosion resistance. In other words, the counter electrode is preferably an insoluble electrode. For example, the material of the insoluble electrode (counter electrode) preferably contains an element selected from the group consisting of titanium, ruthenium, tin, iridium, platinum, and lead. The insoluble electrode (counter electrode) may be a material containing an alloy containing the above element, or a material containing an oxide of the above element. As a soluble electrode, a material containing silver may be used as the counter electrode.

[0070] (Silver plating film formation process) In one aspect of the method for producing a silver plating film of the present invention, the silver plating film is formed on the conductive substrate by electrically connecting the conductive substrate and the counter electrode via a plating solution and applying a voltage between the conductive substrate and the counter electrode to pass electricity through the plating solution. For example, the above method may involve immersing a conductive substrate and a counter electrode in a plating solution contained in a plating tank, and applying a voltage between the conductive substrate (cathode) and the counter electrode (anode). When the voltage is applied, silver ions released from a silver ion source contained in the plating solution are reduced on the surface of the conductive substrate, and a silver plating layer grows. At this time, the silver plating film grows while the nitrogen-containing polymer compound is incorporated into the layer by the above-mentioned mechanism, and it is believed that the silver plating film of the present invention is obtained.

[0071] The current density for forming the silver plating film is set to 0.5 A / dm because the silver plating film of the present invention is more easily obtained. 2More than 0.8A / dm is preferable. 2 More than 1.0A / dm is preferable. 2 The current density when forming the silver plating film is preferably 3.0 A / dm because the resulting silver plating film has better abrasion resistance. 2 Less than 2.5A / dm is preferable. 2 Less than 2.0A / dm is more preferable. 2 The following is even more preferred: The current density when forming a silver plating film can be calculated from the contact area between the conductive substrate and the plating solution and the value of the current flowing through the entire plating tank.

[0072] The current density is a parameter related to the growth rate of the silver plating film. When the current density is increased, the particle size of the nitrogen-containing polymer compound incorporated in particulate form tends to increase as the silver plating film grows while the nitrogen-containing polymer compound is being incorporated into the layer.

[0073] The voltage application may be continued until the silver plating film has a predetermined thickness. The current density may be constant or variable during the formation of the silver plating film. The current density may be changed in a pulsed manner.

[0074] The plating solution may be made to flow during the formation of the silver plating film. For example, the plating solution may be stirred with a known stirring device, or the silver plating film may be formed while circulating the plating solution. The conductive substrate may also be rocked to stir the plating solution around the conductive substrate. During the process of forming the silver plating film, the concentration of each component in the plating solution may be monitored, and each component may be added to the plating solution so that the concentration of each component is maintained at a predetermined level.

[0075] After the silver plating film is formed by the above procedure, a treatment may be carried out to clean the surface of the conductive base material on which the silver plating film is formed. EXAMPLES

[0076] The present invention will be described in further detail below with reference to examples. The materials, amounts, ratios, processing contents, processing procedures, etc. shown in the following examples can be changed as appropriate without departing from the spirit of the present invention. Therefore, the scope of the present invention should not be interpreted as being limited by the following examples.

[0077] <Example 1> The conductive substrate with a silver plating film of Example 1 was obtained according to the procedure described below.

[0078] [Conductive base material] Conductive copper substrate (surface area: 0.82 dm 2 ) was prepared. The conductive substrate is first heated to 40°C and 10A / dm 2 The specimen was subjected to alkaline electrolytic degreasing treatment for 30 seconds under the above conditions. After the alkaline electrolytic degreasing treatment, the conductive substrate was immersed in sulfuric acid (10 mass %) at 40° C. for 30 seconds to perform an acid activation treatment. After the acid activation treatment, silver strike plating was performed. The silver strike plating was performed using a silver cyanide plating solution (25°C) at 2A / dm 2 The thickness of the strike plating layer formed by the above treatment was 0.01 μm.

[0079] [Plating solution] Plating solution 1 was prepared containing the following components in the following amounts. Plating solution 1 was an aqueous solution in which the only components remaining were water. Potassium dicyanoargentate: 20g / L Polyethyleneimine (number average molecular weight: 1800): 3g / L The pH of the plating solution was adjusted to 11.0 with sulfuric acid and potassium hydroxide. Polyethyleneimine corresponds to a nitrogen-containing polymer compound.

[0080] [Formation of silver plating film] The plating solution 1 was placed in a plating tank, and the conductive substrate that had been subjected to silver strike plating and the counter electrode (Ti-Pt alloy) were immersed in the plating solution 1. A voltage was applied to both electrodes to pass electricity through the plating solution, forming a silver plating film on the conductive substrate. The voltage applied was a current density of 1.0 A / dm 2 It was adjusted so that The silver plating film was formed while the conductive base material was being moved by a swinging device. A silver plating film was formed on the conductive base material by the above procedure. The thickness of the formed silver plating film was 10 μm.

[0081] [Analysis and Evaluation] (Analysis of the composition of silver plating film) The composition of the obtained silver plating film was analyzed by glow discharge optical emission spectrometry (GD-OES). Specifically, the composition of the silver plating film was analyzed using a high-frequency glow discharge optical emission spectrometer (Horiba, Ltd.'s "GD-Profiler2"). Specifically, the composition of the silver plating film was analyzed under the following conditions. High frequency power: 35W Pulse condition: 1000Hz Gas type: Argon gas Gas pressure: 600Pa Duty cycle: 0.25 seconds Gas replacement time: 300 seconds The content of each atom shown in the table below is the average value in the range of 0.0 to 5.0 μm in the analysis results in the depth direction. When the thickness of the silver plating film is other than 5 μm, the average value in the range from the surface of the silver plating film to the depth of the silver plating film is used. The content of each of the above atoms was calculated in advance using a calibration curve measured with a standard sample, and the relationship between the sputtering rate and the amount of light emission was calculated from the amount of light emission and the density of the standard sample. The sputtering rate and the content of each atom were then calculated from the amount of light emission.

[0082] (Evaluation of friction coefficient and wear resistance) The friction coefficient and wear resistance of the obtained silver plating film were measured and evaluated by the following methods. The measurement was performed using a contact electrical resistance simultaneous measurement type friction and wear tester FPR-2300 (Rhesca Corporation) by pressing and sliding a pin probe against the surface of the silver plating film. The measurement conditions were as follows: Sliding distance: 10mm Sliding speed: 10mm / sec Contact load: 6N The above measuring device can measure the kinetic friction force during the sliding test. Since the kinetic friction force is expressed as the product of the kinetic friction coefficient and the normal force, the kinetic friction coefficient can be calculated from the contact load and the kinetic friction force. In practical terms, the dynamic friction coefficient is preferably 0.5 or less. The measured dynamic friction coefficients are shown in the table below. The dynamic friction coefficient is the arithmetic average value of the dynamic friction coefficients measured up to the end of the wear life, which is obtained by the method described below.

[0083] The abrasion resistance of the resulting silver plating film was evaluated in terms of abrasion life. Specifically, the wear life was evaluated by repeatedly sliding a pin probe back and forth against a conductive substrate on which a silver plating film was formed, using the above-mentioned measuring device, and counting the number of times the pin probe was moved back and forth until the conductive substrate was exposed. The table below lists the number of times the pin probe was moved back and forth against a conductive substrate on which a silver plating film was formed, and counting the number of times the pin probe was moved back and forth until the conductive substrate was exposed. With the above-mentioned device, the condition of the silver plating film surface during sliding can be observed while being measured with a CCD camera.

[0084] <Comparative Example 1> Except for not adding polyethyleneimine to the plating solution, a silver plating film was formed on a conductive substrate in the same manner as in Example 1. The formed silver plating film was analyzed and evaluated in the same manner as in Example 1. The analysis and evaluation results are shown in the tables below.

[0085] <Examples 2 and 3, Comparative Example 2> Except for changing the number average molecular weight of polyethyleneimine as shown in the table below, a silver plating film was formed on a conductive substrate in the same manner as in Example 1. The formed silver plating film was analyzed and evaluated in the same manner as in Example 1. The analysis and evaluation results are shown in the tables below.

[0086] <Examples 4 to 6, Comparative Examples 3 and 4> In the above Examples 1 to 3 and Comparative Examples 1 and 2, the current density was 2 A / dm 2 A silver plating film was formed on the conductive substrate in the same manner, except for changing the method to , and the analysis and evaluation were performed. The analysis and evaluation results are shown in the table below.

[0087] <Examples 7 to 9, Comparative Example 5> Except for changing the number average molecular weight of polyethyleneimine to 70,000 and changing the content of polyethyleneimine as shown in the table below, a silver plating film was formed on a conductive substrate and analyzed and evaluated in the same manner as in Example 1. The analysis and evaluation results are shown in the table below.

[0088] <Result> The number average molecular weight of polyethyleneimine (nitrogen-containing polymer compound) and the content of the nitrogen-containing polymer compound contained in the plating solution used to form the silver plating films in Examples 1 to 9 and Comparative Examples 1 to 5 are shown in Table 1, as well as the analysis results and evaluation results. In addition, in Table 1, in the item of abrasion resistance, the entry "6000 or more" means that the conductive base material was not exposed even after 6000 sliding operations. In addition, when the surface of the silver plating film in each of the above examples was observed with a scanning electron microscope, regions in which at least one of carbon atoms and nitrogen atoms was present were observed. The average equivalent circle diameter of the above regions was obtained by analyzing using the above-mentioned method, and was 10 to 30 nm in all of the examples.

[0089] [Table 1]

[0090] From the results shown in Table 1, it was confirmed that each Example in which the carbon atom content was 0.30 mass% or more relative to the total mass of the silver plating film and the nitrogen atom content was 1.00 mass% or more relative to the total mass of the silver plating film had a low friction coefficient. On the other hand, it was confirmed that the friction coefficient was not reduced in each of the comparative examples in which the carbon atom content and the nitrogen atom content did not satisfy the above range. Also, it was confirmed that each of the examples was superior in wear resistance compared to each of the comparative examples. It was also confirmed that a silver plating film having a low friction coefficient can be obtained when the plating solution contains a nitrogen-containing polymer compound containing carbon atoms and nitrogen atoms, the number average molecular weight of the polymer electrolyte is 1000 or more, and the content of the polymer electrolyte is 0.5 g / L or more. Furthermore, the method for producing a silver plating film using this plating solution does not require special operations, etc., and is highly productive. From a comparison between Example 1 and the other Examples, it was confirmed that when the carbon atom content was 0.35 mass % or more relative to the total mass of the silver plating film, the abrasion resistance was superior. From a comparison between Example 1 and the other Examples, it was confirmed that when the nitrogen atom content was 1.20 mass % or more with respect to the total mass of the silver plating film, the abrasion resistance was superior.

[0091] Furthermore, the Vickers hardness, surface roughness (the arithmetic mean height Sa) and contact resistance of the silver plating films of Comparative Example 1, Example 2 and Example 5 were measured by the methods described above. The Vickers hardness of the silver plating film of Comparative Example 1 was 76.4 HV, whereas the Vickers hardness of the silver plating film of Example 2 was 74.6 HV and the Vickers hardness of the silver plating film of Example 5 was 76.2 HV. Thus, the Vickers hardness of the silver plating film of the present invention was approximately the same as that of the conventional silver plating film. The surface roughness of the silver plating film of Comparative Example 1 was 0.498 μm, whereas the surface roughness of the silver plating film of Example 2 was 0.091 μm, and the surface roughness of the silver plating film of Example 5 was 0.118 μm. Thus, the surface roughness of the silver plating film of the present invention was smoother than that of the conventional silver plating film. The surface contact resistance of the silver plating film of Comparative Example 1 was 0.18 mΩ, whereas the surface contact resistance of the silver plating film of Example 2 was 0.28 mΩ, and the surface contact resistance of the silver plating film of Example 5 was 0.26 mΩ. From the above results, it was confirmed that the surface contact resistance of the silver plating film of the present invention is at a level that does not pose a problem in practical use.

Claims

1. A silver plating film containing silver atoms, carbon atoms, and nitrogen atoms, the content of carbon atoms is 0.30% by mass or more based on the total mass of the silver plating film, The content of the nitrogen atoms is 1.00 mass% or more based on the total mass of the silver plating film.

2. The silver plating film according to claim 1 , wherein the content of the silver atoms is 90.00 mass % or more based on the total mass of the silver plating film.

3. 3. The silver plating film according to claim 1, further comprising oxygen atoms, the content of said oxygen atoms being 0.10 mass% or more based on the total mass of said silver plating film.

4. 3. The silver plating film according to claim 1, wherein the content of sulfur atoms is 2.0 mass% or less based on the total mass of the silver plating film.

5. 3. The silver plating film according to claim 1, wherein the content of carbon atoms is 0.35 mass% or more based on the total mass of the silver plating film.

6. 3. The silver plating film according to claim 1, wherein the content of the nitrogen atoms is 1.20 mass% or more based on the total mass of the silver plating film.

7. A method for producing a silver plating film by passing an electric current through a plating solution containing a silver ion source, comprising the steps of: The plating solution contains a nitrogen-containing polymer compound that contains carbon atoms and nitrogen atoms, The number average molecular weight of the nitrogen-containing polymer compound is 1,000 or more, The method for producing a silver plating film, wherein the content of the nitrogen-containing polymer compound in the plating solution is 0.5 g / L or more.

8. The method for producing a silver plating film according to claim 7 , wherein the nitrogen-containing polymer compound contains a nitrogen atom having a lone pair of electrons.

9. 9. The method for producing a silver plating film according to claim 7, wherein the silver ion source contains silver atoms and cyano groups coordinated to the silver atoms.

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