JPH0249391B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to silver-plated articles, more specifically, to silver-plated articles in which an electroless silver plating film is further formed on an electroless nickel-plated film on an inorganic or organic base material, and an industrially advantageous manufacturing method thereof. Generally, in electroless silver plating, unlike nickel plating, it is technically impossible to directly form an electroless silver plating film on the plated object. Therefore, conventionally, a method has generally been adopted in which, following electroless copper plating or electroless nickel plating, gold strike plating is further applied, and then electroless silver plating is formed. However, in the former case, after silver plating, as time passes, the original physical properties of the silver plating deteriorate due to mutual diffusion between the underlying copper film and the surface silver, so it is not possible to obtain a very good silver plating product. . In the latter case, electroless nickel plating followed by gold plating on the lower layer is not economical because the plating process is not only long but also expensive. On the other hand, it has recently been discovered that electroless silver plating can be grown directly on electroless nickel plating using an amine borane reducing agent. This method is cheaper than gold plating and does not cause deterioration of physical properties like copper plating, but since amine borane reducing agents are very expensive, it was hoped that an economically cheaper lower layer treatment method would emerge. By the way, in view of the above-mentioned problems, the inventor of the present invention has been conducting intensive research on silver plating methods and has decided to adopt a method of adding a silver plating liquid to small base materials such as organic or inorganic powder particles. As a result, we succeeded in forming a silver plating film directly on a nickel plating film containing phosphorus or boron, and have already filed an application [Japanese Unexamined Patent Publication No. 162779/1983 (Japanese Patent Application No. 18475/1983). However, this method is difficult to apply when the base material is a molded article, and as described above, no silver plating is formed when the object to be plated is immersed in a silver plating solution. Therefore, the present inventor further determined the size of the molded product of the base material,
Or, whether it is a method of adding plating liquid to the base material,
Moreover, as a result of repeated research on whether it is possible to directly apply a silver plating film to a nickel-based plating film using the dipping method, the present invention was completed. That is, the gist of the present invention is a silver-plated article characterized in that a silver plating film is formed on a base layer of a copper-containing nickel alloy plating film on a base material, and yet another aspect of the invention is The gist is that the base material of the copper-containing nickel alloy plating film is coated with a copper-containing electroless nickel plating solution using alkali hypophosphite as a reducing agent, and then the silver plating film is coated with an electroless silver plating solution. The present invention relates to a method for manufacturing a silver-plated article, which comprises forming a silver-plated article. The silver-plated article and its manufacturing method according to the present invention will be explained in detail below. In the present invention, the size or shape of the base material that can be subjected to electroless plating is not particularly limited, and can range from colloidal fine particles to particles of several centimeters in size, from base materials that are powdery or granular in appearance to large molded materials. Any item is fine. The shape of the molded product may be determined by microscopic observation to be spherical, plate-like, rod-like, needle-like, hollow, or fibrous. In short, the object of plating is the base material to be plated, which is treated as granular or powdery in appearance, from the core material to the molded product. Furthermore, the material of the base material includes all materials that can be electrolessly plated, regardless of whether they are organic or inorganic. Furthermore, the base material need not have a chemically uniform composition, but may be either crystalline or amorphous. What is important is that the surface of the substrate is capable of forming a nickel film coating. Examples of such base materials include metals, metal or non-metal oxides (including hydrated materials), metal silicates including aluminosilicates,
Metal carbides, metal nitrides, metal carbonates, metal sulfates, metal phosphates, metal sulfides, metal salts, metal halides, or carbon, and organic base materials include natural fiber wood, natural resin, polyethylene, polypropylene, polyvinyl chloride, polystyrene,
Synthetic thermoplastic resins such as polybutene, polyamide, polyacrylic acid ester, polyacrylonitrile, polyacetal, ionomer, polyester, synthetic thermoplastic resin such as alkyd resin, phenolic resin, urea resin, melamine resin, xylene resin, silicone resin or diallyl phthalate resin. Examples include curable resins. They may be one type or a mixture of two or more types. The term "mixture" includes anything from chemically heterogeneous compositions to mixtures used as base materials. It goes without saying that when applying nickel alloy plating to such a base material, pretreatment appropriate to the material of the base material is performed, and these pretreatments are well known in the field of electroless plating. That is, cleaning, etching, sensitization and activation treatments are included. For example, the cleaning treatment may be performed with water or an alkaline agent, the sensitization treatment may be performed with a soluble tin salt aqueous solution, and the activation treatment may be pretreated by contacting the base material with a soluble palladium salt aqueous solution. These are already known, and there is no need for special pretreatment in the present invention. In addition, in these preliminary treatments, if the surface of the base material is unstable, it is preferable to perform a desired stabilization treatment. For example, in the case of a base material having a backing surface made of aluminum or an aluminum alloy, the surface is modified and stabilized by zincate treatment. In the present invention, the pretreated base material is coated with a base layer using a copper-containing nickel plating solution. This plating treatment is the same as the next silver plating treatment, but two modes can be considered depending on the physical properties of the base material, mainly whether it is a powdered product or a molded product. One method is to form a plating film by adding or immersing the base material in a prepared plating solution, i.e., a plating bath, to cause a plating reaction, and this is a method that has been commonly used in the past. This is a plating process. The other method is to perform plating by adding a plating liquid to a dispersion of a base material using a desired dispersion medium such as water, an alkaline agent, or other plating composition liquid that does not cause a plating reaction, and causing a plating reaction. This is a method of forming a film, and this method was previously developed by the present inventor, and can be said to be particularly excellent for plating core materials or base materials of powder or granular materials or small molded objects. The present invention is characterized in that it can be carried out without any problem, and this is why the size of the base material is not limited. Therefore, when considering the combinations of the above two aspects in each plating process, there are dipping-immersion method, dipping-addition method, and addition-
There are immersion methods and addition-addition methods, but these are not particularly limited and depend on the physical properties, shape, and
A desired plating method may be appropriately designed depending on the use of the plated product. First, the formation of a copper-containing nickel alloy plating film, which is the coating treatment for the base layer, is performed using a plating solution that further contains copper (Cu ⁺⁺ ) in addition to the conventional nickel plating solution that uses alkali hypophosphite as a reducing agent. It is characterized by In most cases, the plating solution is prepared in a bath and the substrate is immersed in it, and the ratio is as follows: Table 1 Electroless nickel-copper-phosphorus alloy plating bath nickel salt
0.02-0.2 mol/(preferably 0.05-0.2 mol/) Cupric salt 0.001-0.05 mol/Complexing agent 0.05-0.6 mol/Hypophosphite
0.03-0.4 mol/(0.10-0.3 mol/) Accelerator 0-0.5 mol/PH 3.5-14 (preferably 8-11) Bath temperature 50-98°C Nickel salt dissolves in water and becomes nickel ion For example, nickel sulfate, nickel chloride, and nickel acetate can be used. If it is less than 0.02 mol/mol, the reaction rate will be slow and it is not practical. In addition, if the amount exceeds 0.2 mol/min, it is likely to combine with phosphite produced by oxidation of hypophosphite and cause precipitation.
In order to prevent this, the concentration of the complexing agent must be increased, which is not economical. Practically 0.05~
0.2 mol/ is preferred. The cupric salt may be one such as copper sulfate, copper chloride, copper nitrate, acetic acid, etc., as long as it can dissolve in water and supply cupric ions. 0.001 mol/
If it is less than that, the subsequent silver plating will not grow. Also
If it exceeds 0.05 mol/l, interdiffusion between the subsequent silver plating film and the underlying copper will occur, which will affect the physical properties of the silver film, which is not preferable. The concentration is preferably 0.001 to 0.05 mol/mole, which is the minimum eutectoid amount of copper necessary to grow a silver plating film without affecting the silver film. As the complexing agent, those commonly used in electroless nickel plating, such as citric acid, tartaric acid, gluconic acid, malic acid, pyriphosphoric acid, and ethylenediamine, are used. The concentration of the complexing agent may be an amount sufficient to complex the metal ions in the solution. Hypophosphite as a reducing agent is used in the form of sodium or potassium salt. If it is less than 0.03 mol/mol, the reaction rate is too slow to be practical; on the other hand, if it is less than 0.5 mol/
If it exceeds this, the liquid becomes unstable and tends to self-decompose.
Practically speaking, it is preferably 0.10 to 0.4 mol/. Increasing plating speed by adding commonly known accelerators such as acetic acid, formic acid, propionic acid, malonic acid, succinic acid, adipic acid, boric acid or its alkali metal salt (sodium tetraborate). is the same as general electroless nickel plating, and the appropriate amount of addition is 0 to 0.5 mol/.
The pH of the solution is not particularly limited, but is practically 8-8.
11 is preferred. If the solution temperature is below 50°C, the plating speed will be too slow to be practical. At high temperatures, the plating speed increases, but when the temperature approaches the boiling point, water evaporates rapidly and fuel consumption for heat retention increases, so a temperature of up to about 98°C is practically preferable. As with general electroless plating, there is no problem in adding a surfactant to increase the affinity between the object to be plated and the plating solution. As described above, when a substrate is plated with a copper-containing electroless nickel plating solution using alkali hypophosphite as a reducing agent, a base layer of a copper-containing nickel alloy plating film is formed. The copper content in this nickel alloy plating film varies depending on the bath composition and plating conditions, but in most cases, the copper content is in the range of 0.1 to 10% by weight to make the next silver plating effective. . As long as alkali hypophosphite is used as a reducing agent, a small amount of phosphorus is necessarily included in the plating film, as in conventional nickel plating. After performing the above-mentioned undercoat plating treatment, the plating solution is separated from the base material, washed with water, and the next silver plating treatment is performed. In this plating process, in the case of a method in which a plating solution is prepared and the substrate is immersed or added thereto, the following bath composition is suitable, for example. Table-2 Electroless silver plating bath (mol/) Silver cyanide alkali (as silver cyanide)
0.01 to 0.1 Alkali cyanide 0.1 to 0.2 Alkali hydroxide 0.1 to 0.5 Alkali hydrogen bororide 0.01 to 0.15 Bath temperature 50 to 80℃ If the silver cyanide concentration is less than 0.01 mol/, the plating speed will be slow, and if it exceeds 0.1 mol/ and the liquid becomes unstable. The alkali cyanide concentration is not particularly limited as long as it is sufficient to complex silver ions in the solution, and may be about 0.1 to 0.2 mol/concentration. If the concentration of the alkali borohydride is less than 0.01 mol/mol, the plating speed will be too slow to be practical. On the other hand, if the amount exceeds 0.15 mol/mol, the surface of the precipitate will become rough and the appearance will be impaired. The plating rate is fastest when the alkali hydroxide concentration is between 0.1 and 0.5 mol/, and decreases when it is lower or higher than that. If the liquid temperature is below 50℃, the plating speed will be slow and it is not practical. Furthermore, if the temperature exceeds 80°C, the liquid becomes unstable and easily decomposes. The composition of the silver plating solution prepared by preparing the bath as described above is a typical example of a specific molded substrate, and there is no inevitable reason to limit it to this. This is because silver plating is more susceptible to subtle effects than nickel plating, so there can be large changes depending on the type, size, shape, etc. of the base material, as well as the conditions of the base plating treatment and silver plating treatment. This is because it occurs. All of the above are immersion-immersion methods in which the base material is immersed or added to the plating solution that has been prepared, but when using the addition method, that is, adding the plating chemical solution to the aqueous medium of the base material, the bath preparation composition is The way of thinking is fundamentally different. The reason for this is that in the case of pre-prepared baths, it is assumed that the bath will be used repeatedly until it ages, whereas in the method of adding plating liquid, the liquid is effectively used after being added to the base material dispersion. This is because it becomes a very thin aged liquid and is either treated as waste liquid or reused in part or in whole as a dispersion medium if necessary. Therefore, the plating solution used when adding any plating solution is generally higher than the concentration in the prepared bath, and even up to the saturation concentration of the plating solution or the saturation concentration of each drug. There is no problem, and the lower limit value is naturally limited from a practical point of view. Furthermore, for the above-mentioned reasons, there is no necessity for the composition ratio to be the same as that of the prepared bath, so there is no problem in varying it centering on the plating reaction. For example, in silver plating treatment, plating occurs based on the following reaction formula: 8KAg(CN) ₂ +KBH ₄ +8KOH →8Ag+KBO ₂ +16KCN+6H ₂ O, so the composition of the silver plating chemical solution should be based on the above reaction ratio. It is suitable for use as an additive plating solution. Next, what should be considered in the plating process using this addition method is that the plating solution is added to the aqueous suspension of the base material in a controlled manner. In order to maintain uniform diffusion of the additive chemical solution and a good dispersion state of the base material, the suspension should be subjected to agitation, ultrasonic dispersion treatment, etc. as necessary, and the temperature should also be set so as to be controllable. It is desirable to leave it there. The reason why the electroless plating chemical solution is added in a controlled manner is that the addition rate as well as the solution concentration directly affect the plating reaction, and this element is also significantly related to the physical properties, particularly the surface properties, of the base material. After fully considering the factors, the rate of addition of the plating chemical solution is determined in order to form a uniform and strong plating film without causing uneven plating, and in many cases it is better to add it gradually. Further, the addition rate of the chemical solution is desirably fast enough that the chemical solution does not self-decompose and the temperature of the solution is kept constant at a predetermined temperature. Regardless of the method used, after silver plating using the method according to the present invention, molded products are washed and powdered products are subjected to over-separation, washing separation, and drying to remove silver plating. Goods can be obtained. In this way, according to the present invention, after treatment with a nickel metal chemical solution containing copper ions, immersion is performed.
Alternatively, even if it is added, silver plating treatment can be performed directly following this surface treatment. Along with this addition of the plating solution, it is often desirable to separately and simultaneously add an alkaline agent to adjust the pH of the aqueous suspension, if necessary. The reason for this is that the plating reaction progresses with the addition of the plating liquid, and as the reducing agent such as sodium hypophosphite in the liquid is oxidized, the hydrogen ion concentration increases, and the aqueous suspension gradually increases. Due to a decrease in pH. Therefore, in order to maintain the initially set pH constant, it is preferable to add the plating solution and the pH adjuster simultaneously as described above. The addition method may be one in which the alkali is added while controlling the PH meter, but it is also possible to add the alkali in an amount commensurate with the redox reaction of the reducing agent at a predetermined concentration. In this way, by controlling and adding the electroless plating solution to the aqueous suspension, a rapid plating reaction occurs in the suspension, forming a uniform and strong plating film on the surface of the dispersed substrate. . Therefore, the thickness of the plating film can be adjusted depending on the amount added, and the amount added can be set depending on the application. Although the silver-plated articles according to the present invention vary depending on the physical properties of the base material and the purpose of use, the amount of nickel plating on the lower layer and the silver plating on the upper layer may be at least in an amount that can form a plating film on the base material, and the upper limit is There is no particular reason to limit this, and it is naturally limited depending on usage and economic reasons. In addition, in the silver-plated article according to the present invention, the underlying nickel alloy plating contains copper ions and is formed using alkali hypophosphite as a reducing agent, so it is different from those using other reducing agents. In comparison, the nickel film is a crystalline or amorphous plating film of a nickel-copper alloy containing approximately the proportion of copper described above, while the upper layer of silver plating is essentially pure silver. It is configured. In the silver-plated article according to the present invention, each plating film is uniformly and firmly formed on each base material,
Since the shape can be freely set depending on the form of the base material, its use can be expected to expand as an inexpensive alternative to silver. For example, when powder is used, it can not only be used as a conductive pigment in paints and adhesives, but it can also be added to resins and used in combination with other conductive materials to create more effective conductive resins. Obtainable. In addition, silver-plated products that are used as base materials for various parts that have complex shapes and require high precision in the electronics field can fully meet the demand. On the other hand, in the method according to the present invention, since electroless silver plating is directly grown on the surface coated with electroless nickel-copper alloy plating, there is no need to apply gold plating to the intermediate layer as in the conventional method. Therefore, the process is shortened and costs are also reduced. Nickel again
Since the content of copper in the copper alloy is small and it is fixed in the alloy, there is virtually no interdiffusion with the silver on the surface layer, so there is no deterioration of the physical properties of silver. Furthermore, the deposition rate of electroless silver plating is faster on electroless nickel-copper alloy plating than on copper and copper alloys, so we can be confident that it is an excellent silver plating method from an industrial perspective. Hereinafter, the present invention will be explained in more detail with reference to Examples. Examples 1 to 3 and Comparative Example 1 A clean α-Al ₂ O ₃ ceramic plate (50 mm x 50
mm x 2 mm) in a glass beaker containing 500 ml of 1 g/SnF ₂ aqueous solution at room temperature for 30 minutes, then washed with water.
Pretreatment was performed by immersing the sample in a glass beaker containing 500 ml of 0.1 g/PdCl ₂ aqueous solution and 0.1 ml/35% HCl aqueous solution for 5 minutes at room temperature. Next, add 85% to the electroless plating solution (base plating solution) of each composition shown in Table 3.
℃ for 30 minutes and electroless nickel plating treatment to obtain a base layer of a nickel-copper alloy plating film.

【table】

[Table] After washing each sample with the obtained underlayer with water, it was immersed in a glass beaker containing 500 ml of electroless silver plating solution having the following composition at 80°C for 10 minutes to perform electroless silver plating treatment. Silver plating liquid composition Potassium silver cyanide 0.05 mol / Sodium silver cyanide 0.1 mol / Sodium hydroxide 0.4 mol / Potassium borohydride 0.1 mol / Samples of each silver-plated article obtained above were washed with water,
After drying, the plating film was dissolved in nitric acid, and the amount of silver precipitated in the solution was measured by the Borohard method, and the amount of nickel and copper precipitated by the chelate titration method was measured to examine the physical properties of each composition. The results are shown in Table 4. was gotten.

[Table] Examples 4 to 7 After performing appropriate pretreatment on different substrates, nickel-copper alloy plating and silver were applied under the same conditions as in Example 3 except that the nickel sulfate concentration was 0.1 mol/. I did the treatment for the wood. Table 5 shows the results of measuring the amount of precipitation on the obtained silver-plated article in the same manner as described above.

[Table] Example 8 100 g of α-Al ₂ O ₃ powder with an average particle size of 5 μm was nickel-plated and silver-plated in the following manner to produce a powder-silver-plated article. Pre-treatment operation: 1g of stannous chloride/and 1g of hydrochloric acid
Add the sample powder to 1 ml of aqueous solution and stir for 5 minutes at room temperature. Then, it was overwashed and sensitized. Next, palladium chloride 0.1g/, hydrochloric acid 0.1
The treated product was added to 1 ml/aqueous solution and stirred at room temperature for 5 minutes to activate the base material (core material), followed by pretreatment by over-washing. Next, add 200 ml of demineralized water heated to 65°C to the pretreated sample.
An aqueous suspension was prepared by stirring to achieve sufficient agglomerate dispersion. Next, nickel sulfate 0.65 mol/, copper sulfate 0.05
300ml mixed solution of 0.5 mol/mol/ethylenediamine, 1.95 mol/sodium hypophosphite
and 150 ml of an aqueous solution of 3.9 mol/min of sodium hydroxide as a pH regulator at a rate of 25 ml/min, separately and simultaneously added to the above-mentioned suspension under stirring,
After the addition was completed, the temperature was maintained at 65° C. until the generation of hydrogen ceased, and a copper-containing nickel plating surface treatment was performed. Next, the base material α-Al ₂ O ₃ after the above treatment was uniformly dispersed in 200 ml of a mixed solution consisting of 0.5 g/(0.008 mol/) potassium cyanide and 0.4 g/(0.01 mol/) sodium hydroxide at a temperature of 80°C. ℃
A slurry was prepared using the following settings. Add 150g/(0.75mol/) of potassium cyanide solution 2 and 5g/(0.09mol/) of this slurry.
) of potassium boron hydride and 30g/(0.75
Electroless silver plating solution 2 consisting of sodium hydroxide (mol/) was added to the stirred dispersion slurry at a rate of 20 ml/min, respectively. After the addition was completed, stirring was continued while maintaining the temperature at 80°C for 30 minutes. The powder was then filtered, washed, separated and dried to obtain a silver-plated powder having α-Al ₂ O ₃ as a core material. When this silver-plated article was observed under a microscope, it was found that the silver plating was formed as a uniform and strong film. Example 9 100 g of phenolic resin powder with an average particle size of 20 μm (trade name: Bellbar R-800 manufactured by Kanebo Co., Ltd.) was subjected to pretreatment and copper-containing nickel plating base treatment using the same operations and conditions as in Example 8. Ta. Then, 5 g/(0.1 mol/) heated to 70°C
The copper-containing nickel-plated sample was added to 200 ml of a dispersion medium consisting of an aqueous solution of sodium cyanide and 0.8 g/(0.02 mol/) sodium hydroxide, and was stirred to thoroughly disperse the sample to prepare a slurry. Then, 300 g/(1.5 mol/) of potassium cyanide aqueous solution 1 and 15 g/(0.28 mol/) of potassium borohydride and 90 g/
Electroless silver plating solution 1 consisting of (2.24 mol/) sodium hydroxide was each added to the above slurry under stirring at a rate of 20 ml/min. After the addition was complete, stirring was continued while maintaining the slurry at 70°C for 60 minutes. The slurry was then filtered, washed and dried to obtain a silver plated article.

Claims (1)

[Scope of Claims] 1. A silver-plated article comprising a silver plating film on a base layer of a copper-containing nickel alloy plating film on a base material. 2. The silver-plated article according to claim 1, wherein the base material is a molded product. 3. The plated article according to claim 1, wherein the base material is a granular material. 4. Coat the substrate with a base layer of a copper-containing nickel alloy plating film using a copper-containing electroless nickel plating solution using alkali hypophosphite as a reducing agent, and then forming a silver plating film using an electroless silver plating solution. A method for producing a silver-plated article characterized by: 5. The method for producing a silver-plated article according to claim 4, characterized in that in the electroless plating process, at least one of the electroless plating solutions is added to the object to be treated to cause a plating reaction.