JPH0247549B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to silver plating powder, more specifically, to a silver plating powder in which an electroless silver plating film is further formed on an electroless nickel plating film on an inorganic or organic core material, and an industrially advantageous manufacturing method thereof. . In general, electroless silver plating, like nickel plating, involves sensitizing the plated object with a stannous salt.
Then, after activation treatment with palladium salt,
It is technically impossible to directly form an electroless silver plating film. Therefore, conventionally, a method has been adopted in which electroless copper plating or electroless nickel plating is followed by gold plating, and then electroless silver plating is formed. However, in the former case, as time passes after silver plating, the original physical properties of the silver plating deteriorate due to interdiffusion between the underlying copper film and the surface silver, making it impossible to obtain a very good silver plated 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 grow directly on electroless nickel plating using an amine borane-based ring 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, the present inventors have previously developed and filed a patent application for an improved method for effectively applying electroless nickel plating to organic or inorganic core materials (Japanese Patent Application No. 1982-
No. 166674). The present invention relates to the advanced application of this method, and has succeeded in solving the above problems and forming an excellent silver plating film. That is, the present invention has a nickel plating film using an alkali hypophosphite or an alkali boron hydride reducing agent on an inorganic or organic core material, that is, a nickel film containing phosphorus or boron, and furthermore a silver plating film on the film. It is a silver plating powder characterized by being coated with silver cyanide alkali and a slurry of the nickel plated core material with an electroless nickel solution containing alkali hypophosphite or alkali boron hydride as a reducing agent. , relates to a method for producing silver plating powder, characterized in that a silver plating film is formed by adding an electroless silver plating solution composed of at least an aqueous solution of a reducing agent and a caustic alkali. The silver plating powder and the method for producing the same according to the present invention will be explained in detail below. In the present invention, the particle size of the core material as a base material that can be subjected to electroless plating is not particularly limited, and may be either powdery or granular in appearance, ranging from colloidal fine particles to particles of several centimeters in size. But that's fine. Moreover, the shape may be spherical, plate-like, rod-like, needle-like, hollow, or fibrous according to microscopic observation. In short, the core material is a base material to be plated that is granular or powdery in appearance. Moreover, the material of the core material includes all materials that can be electrolessly plated, regardless of whether they are organic or inorganic. Of course, the core material must be substantially water-insoluble or sparingly water-soluble. Furthermore, it goes without saying that the core material does not need to have a chemically uniform composition, but it may be either crystalline or amorphous. What is important is that the surface of the core has the ability to form a plating film, and that it has a powdery or granular appearance. Examples of such core materials include metal powders, metal or nonmetal oxides (including hydrated materials), metal silicates including aluminosilicates, metal carbides, and metal nitrides. , metal carbonate, metal sulfate, metal phosphate, metal sulfide, metal acid salt, metal halide, or carbon, and organic core materials include natural fiber, 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. This mixture includes anything from chemically heterogeneous compositions to mixtures used as core materials. In applying electroless nickel plating to such a core material, all conventional and well-known methods can be employed without particular limitation, but the following method is preferably recommended. That is, before electroless nickel plating is performed on the surface of the core material, a well-dispersed aqueous suspension is first prepared. Here, the aqueous suspension is not limited to water as a medium, but it is suitable to use any electroless plating solution having a low concentration that does not substantially cause electroless plating. The dispersibility of an aqueous suspension differs depending on the physical properties of the core material, so the dispersion method can be determined by any desired means, such as ordinary stirring, high-speed stirring, or a shear dispersion device such as a colloid mill or homogenizer. It is desirable to prepare an aqueous suspension in a state of dispersion close to that of primary particles by removing as much of the agglomerate of the core material as possible by using diaphragm dispersion or other ultrasonic dispersion. In addition, when dispersing the core material, for example, a dispersant such as a caustic alkali, an alkali such as sodium silicate, an alkali polyphosphate, or a surfactant can be used as necessary. There is no particular reason to limit the concentration of the aqueous suspension, but if the slurry concentration is low, the plating concentration will decrease and the processing capacity will be large, making it uneconomical. Since the dispersibility of the slurry becomes poor, the slurry concentration may be appropriately set to a desired value depending on the physical properties of the core material, but in most cases it is in the range of 50 g/~700 g/preferably 100 g/~500 g/. Further, when nickel plating the core material in this suspension, it is desirable to adjust the temperature of the suspension in advance to a temperature that allows plating so that plating can be carried out effectively. It goes without saying that before nickel plating these core materials, pretreatments such as cleaning, etching, sensitization, and activation treatments are performed in accordance with the physical properties of the core materials. Although this pretreatment is preferably carried out in the form of an aqueous suspension as described above, other methods may also be used. For example, the cleaning treatment may be performed with 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 core material with a soluble palladium salt aqueous solution. , these are already known, and there is no need for special pretreatment in the present invention. Therefore, when an aqueous suspension is prepared in the course of a part or all of a pretreatment operation, the aqueous suspension is prepared after being pretreated by some means in advance, or the aqueous suspension is prepared as an aqueous suspension. There are several ways to balance the pretreatment and preparation of the suspension, such as when a pretreatment operation is performed and then the suspension is transferred to plating treatment.
It is sufficient to appropriately select a rational mode that is suitable for the actual operation and the relationship with the core material. Electroless Nickelmeck solution is added in a controlled manner to the aqueous suspension thus prepared. The suspension may be stirred or stirred as necessary to maintain its dispersion.
It is desirable to apply ultrasonic dispersion treatment, etc., and it is also desirable to set the temperature so that it can be controlled. Since the electroless nickel plating solution is added to an aqueous suspension and diluted according to the volume, it can be used for plating operations by immersing the substrate to be plated in a bath with a normal plating solution concentration. Differently, it is better to have a higher concentration than the normal nickel metal bath concentration. The reason why the electroless nickel plating 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 factor is also significantly related to the physical properties, particularly the surface properties, of the core material. The addition rate of the plating solution is set after fully considering the factors in order to form a uniform and strong nickel plating film without causing uneven plating.In many cases, it is better to add the plating solution gradually. good. It is also desirable in many cases to add an alkaline agent separately and simultaneously with the addition of the plating solution 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 solution, and as the reducing agent such as sodium hypophosphite in the solution is oxidized, the hydrogen ion concentration increases, and the pH of the aqueous suspension gradually increases. By decreasing. 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 core material. . 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. Thus, according to the method of the present invention, a uniform nickel plating film can be applied to a powder or granular core material in a state substantially similar to that of primary particles, and the film thickness can be freely set with high precision. This makes it possible to effectively prepare the surface for silver plating. As described above, the above method is one of the particularly preferred methods in the present invention for nickel plating as a base plating, but when the core material has relatively good dispersibility and has a small specific surface area, As mentioned above, there is no problem in using the reverse addition method of adding the pretreated core material to the electroless nickel plating bath prepared in advance, as has been generally adopted in the past. Thus, after electroless nickel plating of the base material is applied, it is subjected to over-separation by a conventional method, and then repulped and thoroughly washed, and then an aqueous suspension of the electroless nickel plated core material is prepared for silver plating. This slurry concentration may be the same concentration as in the case of nickel plating for the same reason as described above. In this case, it may be a purely aqueous suspension, but preferably up to 1 mol/alkali cyanide and/or alkali hydroxide, particularly preferably
0.005-0.1 mol/alkali cyanide and/
Alternatively, an aqueous suspension mixed with alkali hydroxide is preferable. In addition, it is better to heat this suspension beforehand so that the chemical reaction of silver plating can take place effectively.
In particular, a temperature range of 50 to 85°C is suitable. The processing operation for silver plating is similar to the above-mentioned preferred surface treatment for electroless nickel plating, and in the present invention, it is important to add this silver nickel plating composition to the aqueous suspension. Although the chemical composition of electroless silver plating varies depending on the condition of the underlying nickel plating film, purpose of use, processing conditions, etc., in many cases,
It is preferable to use a solution comprising at least an aqueous solution of 0.05 mol/or more of alkali silver cyanide, 0.01 mol/or more of a reducing agent such as an alkali hydrogen bororide, and 0.05 mol/or more of alkali hydroxide. In other words, since the silver plating chemical solution can be used in an additive manner, it is possible to use high concentrations of each chemical up to the saturation concentration, thereby suppressing self-decomposition as much as possible and effectively producing silver while saving cost and energy. This means that plating can be applied. Note that auxiliary drugs may be used as necessary. The aqueous suspension of the nickel-plated core material is dispersed in a desired dispersion machine so as to be as well dispersed as possible, and the above-mentioned silver plating chemical solution is added thereto. There are several methods for this addition, including a method in which each chemical solution is added individually, or a method in which a part or all of the drug solutions are mixed in advance and added at the same time. In this case, silver plating can be achieved by, for example, the reaction of the following formula:
8KAg(CN) ₂ +KBH ₄ +8KOH→8Ag+KBO ₂ +
Since it is produced based on 16KCN + 6H ₂ O, it is necessary to adjust the ratio of each chemical solution so that the reaction system of the aqueous suspension always maintains the above stoichiometric amount and maintains a stable system state. It is. 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. The amount of the silver plating chemical solution to be added may be appropriately set depending on the intended use of the silver plating powder, since the thickness of the silver plating film is formed in proportion to the amount. Thus, after silver plating treatment, a silver plating powder can be obtained by over-separating by a conventional method, washing and separating, and then drying. However, when a core material coated with nickel plating is added to a silver plating chemical solution and silver plating is performed without using the present invention, surprisingly, almost no silver plating film is formed. Although the details of this reason are unknown, it is probably because the concentration of the chemical in the slurry system is much higher than in the silver plating chemical addition method according to the present invention, and it is easy to change. It seems that the formation area is not formed. As described above, according to the method of the present invention, although the concentration of the plating chemical solution in the core material slurry is extremely low, it is possible to add and use a high concentration of the chemical solution necessary for forming the desired thickness of the plating film.
It can be said that the amount of liquid used can be significantly reduced, and moreover, the effective utilization rate of the metal involved in plating with respect to the chemical liquid used is much higher than in the conventional method. Although the silver plating powder according to the present invention varies depending on the physical properties of the core material and the purpose of use, it is sufficient that the amount of the lower layer nickel plating and the upper layer silver plating is at least enough to form a plating film on the core 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 plating powder according to the present invention, the base nickel plating is formed using either alkali hypophosphite or alkali boron hydride as a reducing agent, so compared to those using other reducing agents. The nickel in the coating is a crystalline or amorphous nickel plating of nickel-phosphorous or nickel-boron alloy containing several percent of phosphorus or boron, while the upper layer of silver plating is essentially pure silver. It is made up of. In the silver plating powder according to the present invention, each plating film is uniformly and firmly formed on each core material,
Moreover, since the shape can be set more freely according to the form of the core material than silver powder, its use can be expected to expand as an inexpensive alternative. For example, it can be used not only as a conductive pigment in paints, adhesives, etc., but also by adding it to resins and using it in combination with other conductive materials, if necessary, to obtain more effective conductive resins. Example 1 100g of α-Al ₂ O ₃ powder with an average particle size of 5μ was added at a concentration of 1g/
of stannous chloride and sensitizer 1 consisting of hydrochloric acid at a concentration of 1 ml, the mixture is dispersed to ensure sufficient deagglomeration, and sensitized for about 5 minutes. Next, after the sensitization treatment, activation treatment was carried out by dispersing in the same manner as in an activating agent consisting of 0.1 g/mole of palladium chloride and 0.1 mol/mole of hydrochloric acid. The α-Al ₂ O ₃ core material pretreated in this way was poured into 200 ml of a 10 g/ethylenediamine solution previously adjusted to pH 7, and dispersed at a temperature of 65°C to ensure that there were virtually no agglomerates. A core material slurry was prepared by heating. Next, 300 ml of the Nickel Metsuki chemical solution adjusted to pH 7, which is composed of 180 g/nickel sulfate, 218 g/sodium hypophosphite, and 30 g/ethylene diamine, was added to the above dispersed slurry under stirring at a rate of 50 ml/min, and the entire amount was added. Stirring was continued and maintained until hydrogen evolution ceased. After the plating reaction was completed, the base treatment was completed by overwashing and separation using a conventional method. Next, the core 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/(0.001 mol/) sodium hydroxide at a temperature of 80 ml.
A slurry was prepared by setting the temperature to ℃. Add 150g/(0.75mol/) of potassium cyanide solution 2 and 5g/(0.09mol/) of this slurry.
) of potassium boron hydride and 30g/(0.75
mol/) of sodium hydroxide were each added to the dispersed slurry under stirring at an addition rate of 20 ml/min. 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 powder of a silver plating composition having α-Al ₂ O ₃ as a core material. When this plating powder was observed under a microscope, it was found that the silver plating was formed as a uniform and strong film. Example 2 100 g of phenolic resin powder (trade name: Bell Pearl R-800 manufactured by Kanebo Co., Ltd.) having an average particle size of 20 μm was subjected to pretreatment and nickel plating undercoating under the same operations and conditions as in Example 1. Then, 5 g/(0.1 mol/) heated to 70°C
The 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/) of sodium hydroxide, and was stirred to sufficiently 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/
(2.24 mol/) of an aqueous solution 1 of sodium hydroxide were each added to the above slurry under stirring at an addition rate of 20 ml/min. After the addition was complete, stirring was continued while maintaining the slurry at 70°C for 60 minutes. Next, the slurry was filtered, washed and dried to obtain silver plating powder. Example 3 80g of tungsten carbide powder with an average particle size of 1μ
Pretreatment and nickel plating surface treatment were carried out using the same operations and conditions as in Example 1. Then 85
0.1 g/(0.0015 mol/) potassium cyanide and 0.56 g/(0.01 mol/) warmed to °C
A dispersion medium for a mixed aqueous solution consisting of potassium hydroxide
A slurry was similarly prepared by adding the nickel-plated sample to 200 ml. Next, a mixed aqueous solution consisting of 100 g/(0.5 mol/) of potassium cyanide aqueous solution 2 and 15 g/(0.28 mol/) of potassium borohydride and 90 g/(1.6 mol/) of potassium hydroxide was added.
660 ml were added simultaneously and separately to the above slurry under stirring at addition rates of 30 ml/min and 10 ml/min, respectively. Stirring was continued while maintaining the slurry at 85° C. for 30 minutes after the addition was complete. Subsequently, it was post-treated by a conventional method to obtain a silver plating powder. Examples 4 to 10 Silver plating was performed using the same operations and conditions as in Example 1, except that the core material to be silver plated was changed to those shown in Table 1. All core materials were coated uniformly and firmly. A silver-plated powder was obtained.

【table】

[Table] Comparative Example 1 100 g of α-Al ₂ O ₃ powder with an average particle size of 5 μm was pretreated and nickel plated under the same operation and conditions as in Example 1. Next, 9.95 g/(0.05 mol/) of potassium silver cyanide heated to 80°C, 4.9 g/(0.1
Sodium cyanide in mol/), 16g/(0.4
mol/) of sodium hydroxide and 5.4 g/
The above nickel-plated sample powder was added all at once to an electroless silver plating bath 30 consisting of (0.1 mol/) potassium hydrogen bororide, and stirring was continued while maintaining the temperature at 80° C. for 3 hours. The powder was then collected by filtering and washing. When this powder was observed with the naked eye and with an electron microscope, no silver plating was formed on the powder. Comparative Example 2 100 g of α-Al ₂ O ₃ powder with an average particle size of 5 μm was pretreated under the same conditions as in Example 1. The pretreated sample was added to 500 ml of a 23 g sodium citrate aqueous solution heated to 70°C and adjusted to pH 8.0, and dispersed by stirring. Next, 200 ml of an electroless nickel sulfate solution adjusted to pH 8.0 consisting of 260 g of nickel sulfate and 46 g of sodium citrate and 20 g of diethylaminoborane was added to the above dispersion under stirring at a rate of 10 ml/min. Stirring was continued while maintaining the temperature at 70°C for the next 1 hour. Then, it was filtered and washed to obtain a nickel-metallic sample. This nickel metal is made of almost pure nickel and is substantially free of alloys with boron. Next, the above sample was subjected to silver plating treatment under the same conditions as in Comparative Example 1 to obtain a silver plating powder. The coated metal of each sample obtained in the above Examples and Comparative Examples was dissolved in nitric acid and the amount of metal deposited on each sample was determined, and the results shown in Table 2 were obtained.

【table】

【table】

Claims (1)

[Scope of Claims] 1. A silver plating powder characterized by having a nickel plating film containing phosphorus or boron on an inorganic or organic core material, and further having a silver plating film on the film. 2. Nickel plating an inorganic or organic core material with an electroless nickel plating solution containing alkali hypophosphite or alkali boron hydride as a reducing agent, and add alkali silver cyanide, a reducing agent, and alkali caustic to the slurry of the obtained core material. A method for producing silver plating powder, which comprises adding an electroless silver plating solution composed of at least each aqueous solution to form a silver plating film.