JPH0475316B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Application Field] The present invention is a nickel plating method in which a dense and highly conductive nickel plating film is formed on the particle surface of a water-dispersible core material, particularly a powder or granule, by an electroless nickel plating method. Concerning the manufacturing method of materials. More specifically, the present invention relates to a method for industrially providing a nickel plating material suitable for electroconductive materials, conductive pigments, etc. as electromagnetic shielding materials. [Prior Art] In general, due to advances in technology and development of applications, electroless plating is now applied regardless of the material, organic or inorganic, and regardless of its shape or size. However, in many cases, the base material is plate-shaped or molded, and the development of applications for fine plating base materials such as powder or granules is recent, and there are no established manufacturing methods. At present, it is only processed according to conventional general methods. That is, in the case of electroless plating, the method used is usually to immerse the plating base material in a pre-prepared plating solution, allow it to react for a predetermined time, and then stop the reaction. . However, if the plating reaction is repeated in this method, the plating reaction will not substantially occur even if the chemical is replenished, and the operation must be discontinued industrially. A large amount of aging fluid (described as "aging fluid") is generated. Conventionally, proposals have been made to regenerate such aged liquids by removing reaction products such as alkali phosphites, but due to the complex composition of the liquids, industrial reuse or separation and recovery of nickel salts are difficult. In many cases, the reality is that it has no choice but to undergo detoxification treatment and be disposed of. [Problems to be Solved by the Invention] When the aging liquid is used in the same immersion method as described above when the plated substrate is a powder or a powdered material, the specific surface area becomes smaller than that of a large plated substrate such as a molded body. However, in this case, there are problems common to conventional bath preparation methods as described below: (1) The liquid nature of the plating bath is such that precipitation is not formed. Because it is easy, PH
It cannot be higher than 4.5. Therefore, the phosphorus content of the formed nickel film increases and the conductivity of the film deteriorates; (2) If the nickel and hypophosphite concentrations are high in the early stage of the reaction, a rough nickel plating film is likely to occur; Self-decomposition of the bath is also likely to occur; (3) The effective utilization rate of sodium hypophosphite is low; therefore, in order to reduce and precipitate all the nickel ions in the aging solution, Acid soda is insufficient and must be replenished; (4) Hydrogen is generated rapidly in the early stages of the plating reaction, so safety measures must be taken to prevent explosions. Furthermore, even if the powder is quickly added to the bath, the specific surface area is large, making it difficult to control the plating reaction. On the other hand, if the powder and granules can be added to the plating bath all at once, the above problems can be suppressed to some extent, but if the powder is added over time, there will be a difference in the thickness of the plating film between the beginning and the end, resulting in non-uniformity. It is inevitable that it will happen. Particularly, when plating powder or granules, a problem arises when a plating film is applied to aggregated secondary particles, and upon use, the secondary particles are broken and defects in the coating occur due to exposure of the uncoated surface. Therefore, when plating powder or granules, it is most important to apply a plating film to a well-dispersed material with as few secondary particles as possible. There was no hope that it could be reused. In view of the above-mentioned facts when plating such fine particles of powder or granule material, the present inventor first proposed a method for electroless plating of the powder core material by making the core material into an aqueous suspension. developed a method for applying a plating film by adding an electroless plating solution to this (Japanese Patent Application Laid-Open No. 60-59070). [Means for Solving the Problems] The present invention is a further development of the invention disclosed in the above-mentioned Japanese Patent Application Laid-Open Publication No. 1999-19103, and after further intensive research into a plating method using a method of adding a plating liquid, Surprisingly, it was discovered that a high-quality nickel plating film can be formed using a method of adding an aging liquid to an aqueous suspension, and the present invention was completed based on this finding. Therefore, the present invention provides a method for producing a nickel plating material, which comprises contacting a water-dispersible plating base material with an electroless nickel plating solution.
10, an aqueous suspension of plating base material is prepared, and then at least an electroless nickel plating aging solution is added to the suspension, and a nickel plating film is formed on the surface of the base material while maintaining the pH range. The object of the present invention is to provide a method for producing a nickel-plated material, which is characterized by forming a nickel-plated material. [Function] First, to explain the plating base material (hereinafter simply referred to as "core material") in nickel plating materials, one of its characteristics is that the core material is limited to base materials that can be dispersed in water. It is. A water-dispersible core material is one that can form a suspension substantially dispersed in water to the extent that a nickel film can be formed on the core material by ordinary dispersion means such as stirring. Since it can be suspended in water, it must be substantially insoluble in water, preferably stable enough to not dissolve or deteriorate even in acids or alkalis. Therefore, the shape and size of the core material basically does not matter as long as it is substantially insoluble in water and can be dispersed, but in many cases, the core material is in the form of powder or granules. shall be. These may be powdery or granular in appearance, ranging from colloidal fine particles to particles on the order of several mm. Further, when its shape is observed under a microscope or with the naked eye, it may be spherical, plate-like, rod-like, needle-like, hollow, or fibrous. In addition, plate-like, needle-like, or fibrous core materials with large aspect ratios are
Since it can be dispersed even if it has a size of cm, it can be used as a core material. In short, any dispersible material that can be treated as a granular, powdery or fibrous material can be used as the core material. Further, the material of the core material includes all materials capable of electroless plating, regardless of whether they are organic or inorganic. These may be either natural or synthetic. Furthermore, it goes without saying that the core material does not need to have a chemically uniform structure, but it may be either crystalline or amorphous (including glass). What is important is that the surface of the core has the ability to chemically react with the plating solution to form a film, and that it is a dispersible material. Examples of such core materials include metal powders (including alloys), metal or non-metal oxides (including hydrated materials), metal silicates including aluminosilicates, and metals. These include carbides, metal nitrides, metal carbonates, metal sulfates, metal phosphates, metal sulfides, metal salts, metal halides, or carbon, and organic core materials include natural fibers, natural resins,
Polyethylene, polypropylene, polyvinyl chloride, polystyrene, polybutene, polyamide, polyacrylic acid ester, polyacrylonitrile,
Thermoplastic resins such as polyacetal, ionomer, polyester, alkyd resins, phenolic resins, urea resins, melamine resins, xylene resins,
Examples include thermosetting resins such as silicone resins and diallyl phthalate resins. these are,
It 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 performing electroless nickel plating on the surface of such a core material, a second feature of the present invention is to prepare an aqueous suspension of the core material in such a state that the plating reaction occurs. The fact that the core material is in a state where a plating reaction occurs means that before plating the core material, pretreatment operations such as cleaning, etching, sensitization, and activation are performed in accordance with the physical properties of the core material. This refers to a state in which a plating reaction can occur, and all known methods can be applied to such pretreatment. For example, the cleaning treatment is performed by immersing and degreasing the core material in an alkaline degreasing solution and then immersing it in hydrochloric acid, sulfuric acid, or phosphoric acid. Subsequent catalytic treatment is carried out with a soluble stannous salt and then with a soluble palladium salt solution, or with a mixed colloidal solution of a stannous salt and a palladium salt, then with an acid or alkaline aqueous solution, or with a silane coupling agent and palladium. Pretreatment may be performed by contacting each core material with a mixed aqueous solution. These are already known, and there is no need for special pretreatment in the present invention. Next, an aqueous suspension of a core material refers to a suspension of a core material in water or an aqueous solution to which at least one kind of a plating agent has been added; These are agents that can constitute the plating solution, such as nickel salts, hypophosphites, complexing agents, reaction accelerators, and PH regulators, and they may be one type or two or more types. However, when the plating liquid itself is used as a suspending medium, it is necessary to use it in a thin enough state that no plating reaction occurs when preparing a suspension of the core material. Usually, an aqueous suspension with a simple pH adjustment is sufficient, but depending on the core material, an aqueous suspension with a complexing agent added is often suitable. Complexing agents are compounds that have a complexing effect on nickel ions, such as carboxylic acids (salts) such as citric acid, tartaric acid, malic acid, lactic acid, gluconic acid or their alkali metal salts and ammonium salts, glycine, etc. amino acids, amines such as ethylenediamine and alkyl amines, other ammoniums, EDTA, pyrophosphoric acid (salt), etc., and they may be used alone or in combination of two or more. The content of the complexing agent in the suspension is 1 to 100 g/
, preferably in the range of 5 to 50 g/. In addition, the pH of the suspension is 4-10, preferably 4.5-10.
It was adjusted to a range of 8 and uniformly dispersed. The dispersibility of the core material in an aqueous suspension differs depending on its physical properties, so the dispersion method for the core material is determined by appropriate means, such as normal stirring, high-speed stirring, or a dispersion device such as a colloid mill or homogenizer. It is desirable to prepare a suspension in a state of dispersion close to that of primary particles, with as much of the agglomerates as possible removed. In addition, when dispersing the core material, for example, a dispersant such as a surfactant can be used as necessary, as described above. The concentration of the suspension is
There is no particular reason to limit it, but if the slurry concentration is low, the processing capacity will be large, which is not economical, and
On the other hand, if the concentration becomes high, the dispersibility of the core material deteriorates, so the slurry concentration may be appropriately set to a desired value depending on the physical properties of the core material. Often 50g/~700
g/, preferably in the range from 100 g/ to 500 g/. Furthermore, when 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. A third feature of the present invention is to form a nickel plating film on the surface of the plating substrate by adding at least an electroless nickel plating aging solution to the aqueous suspension of the core material thus prepared. Electroless nickel plating aging solution (aging solution) is a well-known concept in this field, and is generally a solution that has already been used in plating reaction operations.
This refers to the liquid after the plating reaction that is no longer able to maintain an efficient plating reaction. That is, an electroless nickel plating solution is basically composed of a nickel solution, a reducing agent (sodium hypophosphite), a complexing agent, and a PH adjuster (acid or alkaline agent) in desired proportions. It is an aqueous solution that
Normally, the plating process is carried out by immersing the object to be plated in this solution prepared as described above, and the desired agent is replenished as needed according to changes in the solution composition as the plating reaction progresses. , the final result is an aged liquid containing a large amount of reaction products (sodium phosphite). In the present invention, the aged liquid means the aged liquid as described above, and does not mean the separated liquid used in the nickel plating process according to the present invention. It is completely unexpected that such an aged solution can still be added as an effective plating solution in the method of the present invention, and although the detailed mechanism of action is not clear, it is probably due to the following reasons. It will be done. Even though the aging solution contains more nickel salt and sodium hypophosphite, which is a reducing agent, compared to the plating solution used during bath preparation, the so-called aging phenomenon occurs due to the reaction product phosphorous acid. Due to the presence of large amounts of soda. In other words, as the production of sodium phosphite increases due to the plating reaction, a self-decomposition reaction to nickel phosphite occurs simultaneously, but when the pH is increased to increase the reducing power, this reaction becomes inevitable and Not only does precipitation become more likely to occur, but increasing the complexing agent to suppress this also slows down the plating reaction rate. However, in the method according to the present invention, since the plating liquid is added to the aqueous suspension of the core material, the plating liquid is always diluted into the suspension, and the range is sufficient to allow for pH changes. This is thought to be due to the fact that the influence of the reaction product, sodium phosphite, is significantly smaller in the reaction system than in the method of immersing the plated object in a plating bath with a normal concentration.
The plating reaction can proceed gently even at a low plating drug concentration. Therefore, even if the aging solution is used, as long as the basic chemicals of the nickel plating solution, such as reducing agents such as nickel salt and sodium hypophosphite, are sufficiently present, the present invention can be used directly without using the aging solution. This means that it can be used as a plating solution. Of course, it goes without saying that a new licking agent can be added thereto. That is, in the present invention, adding at least the nickel plating aging solution means that the above-mentioned aging solution can of course be used as it is, but it can be diluted or concentrated as necessary, or this aging solution can be used as a base material. This also means that other drugs can be added and used. In the present invention, nickel salt means a mixed salt of a single nickel salt such as nickel sulfate and the other soluble metal salts mentioned above, and in this case, a nickel alloy plating film can be formed. The most typical reducing agent is alkali hypophosphite, but there are other reducing agents such as alkali hydrogen borate. In addition, a PH regulator is a drug that adjusts the PH of the reaction system in advance or in response to changes in the PH of the reaction system in order to form a stable plating film due to the plating reaction. ,Sodium hydroxide,
Refers to alkaline agents such as potassium hydroxide, or acidifying agents such as sulfuric acid, hydrochloric acid, etc. The complexing agent is a complexing agent that has a chelating effect on nickel ions in order to suppress the formation of nickel hydroxide, which is generated depending on the pH, and is as described above. When adding the aging liquid to the aqueous suspension containing the complexing agent prepared in this manner, the suspension is subjected to stirring, ultrasonic dispersion treatment, etc. as necessary to maintain a sufficiently dispersed state. It is desirable that the temperature be set so as to be controllable. In the present invention, the plating reaction occurs quickly with the addition of the aging solution, but at this time, the addition rate as well as the solution concentration directly affect the plating reaction, and these factors also affect the physical properties of the core material, especially the surface properties. After fully considering these factors, the addition rate of the plating solution should be set and controlled in order to form a uniform and strong plating film without causing unevenness of the plating film. addition is necessary, and in many cases it is better to add gradually and quantitatively. In this way, by controlling and adding the aging liquid to the aqueous suspension, a rapid plating reaction occurs with the generation of hydrogen gas, and a uniform and strong plating film is formed 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. Note that the plating reaction temperature is preferably in the range of 50 to 90°C. After the addition of the aging liquid is completed, after confirming the end of hydrogen gas generation, after applying a dispersion method for a while, the plating process is completed, and then the mother liquor is separated by a conventional method, and the plating material is washed with water and separated. and dry and collect. [Example] The present invention will be further explained with reference to Examples (hereinafter simply referred to as "examples" unless otherwise specified). Examples 1 to 4 100g of progopitite mica with an average particle size of 250μm
2.5g/silane coupling agent [Chitsuso Co., Ltd.]
APS-E] and 0.2 g/palladium chloride in a mixed solution 1, treated for about 60 minutes with thorough stirring, filtered, and thoroughly dried at 110°C. Next, 10 g of this pretreated mica was adjusted to the pH shown in Table 1, added to an aqueous solution heated to 75 to 80°C, and stirred and dispersed to sufficiently deagglomerate, to prepare an aqueous suspension for each sample. Prepared. Next, an electroless nickel plating aging solution [manufactured by Nippon Kanzen, nickel glittering solution: Blue Schumer aging solution (nickel concentration 5.6 g/, sodium hypophosphite concentration 30.3) was added to the aqueous suspension under stirring.
g/)]1.2 was added little by little, and plating treatment was performed. In addition, the pH of the reaction solution was initially set.
In order to maintain a constant pH value, an aqueous sodium hydroxide solution was added dropwise as appropriate. After adding the entire amount of aged liquid and stopping the generation of hydrogen, it was filtered, repulped and washed, and dried to obtain nickel-plated mica in suspension at different pH levels. Examples 5 to 8 The pH of the aqueous suspension in which mica is dispersed is 6.5,
As shown in Table 1, the pretreatment and plating treatment were carried out under the same conditions as in Example 1 except that the electroless nickel plating aging solution was changed to obtain nickel-plated mica. Examples 9 to 13 Plating was performed using various powders shown in Table 1 as core materials instead of mica. That is, these core materials were pretreated under the same conditions as in Example 1, and then the aging solution was added to each aqueous suspension prepared under the same conditions as in Example 1, except that the pH of the aqueous suspension was kept constant at 6.5. The powder was added and subjected to plating treatment to obtain nickel plating powder for various core materials. As mentioned above, the overseparated mother liquor after plating treatment according to Examples 1 to 13 is colorless and transparent, which means that the Ni ⁺⁺ in the aged liquor has been substantially consumed, and it is possible to perform plating very rationally. This indicates that a reaction was occurring. Comparative Examples 1 to 5 Five batches of the same aging liquid used in Example 1 were prepared,
Each bath was adjusted to a pH as shown in Table 1. Next, mica was subjected to the same pretreatment as in Example 1.
Plating treatment was carried out by adding 10 g of each to each plating bath under stirring. During the plating process, sodium hydroxide was appropriately added dropwise to adjust the pH of the reaction solution in order to keep it at the originally set pH. In each batch, when mica was first added, hydrogen was generated vigorously and the reduction reaction progressed, and the reaction was more intense in batches with a pH closer to neutrality, but eventually the hydrogen generation stopped, so sodium hypophosphite was added. A total amount of 18 g was added to each bath in small amounts to regenerate the reaction. However, batches with a pH of 5.5 or higher eventually undergo a self-decomposition reaction and form a precipitate, so the so-called nickel plating treatment was not applied. After the reaction was completed, the mother liquors separated by filtration had a pale blue color in all batches. This is still
This means that no plating reaction occurred despite the presence of Ni ⁺⁺ . Physical Properties of Nickel Plated Materials The physical properties of each of the samples obtained in Examples 1 to 13 and Comparative Examples 1 to 5 were determined by the following measurements or procedures, and the results shown in Table 1 were obtained. <Nickel content in plating film> A predetermined amount of the sample was dissolved in nitric acid, the Ni content was measured by ICP analysis, and the Ni content in the sample was expressed in weight%. <Phosphorus content in the plating film> Regarding the sample dissolved in nitric acid, the same
P was determined by ICP analysis and expressed as weight % of P/Ni+P. <Resistance value of plating material> After filling a glass container (1.59 cmφ x 20 cm) with a sample at a predetermined filling rate, the resistance was measured by the 4-probe method and expressed as volume resistivity (Ωcm). <Electron micrograph observation of plating film> Scanning electron micrograph of the plated surfaces of the samples obtained in Examples 2 and 4 and Comparative Examples 3 and 5 (approximately 10,000x magnification)
Observe at. Figure 1 shows the electron micrograph of Example 2.
An electron micrograph of Example 4 is shown in FIG. 2, an electron micrograph of Comparative Example 3 is shown in FIG. 3, and an electron micrograph of Comparative Example 5 is shown in FIG. Note that 1 cm in the electron micrograph corresponds to approximately 1 μm. <Electromagnetic wave shielding properties of polypropylene resin filled with plating material> The sample and polypropylene resin (manufactured by Mitsubishi Yuka Corporation: MA-4PP homopolymer) were blended at a specified filling rate, and heated in a Brabender at 220°C for 4 minutes. After kneading, the mixture was rolled with rolls and hot pressed to obtain a test piece with a thickness of 2 mm. The electromagnetic shielding properties of the test piece are evaluated by measuring the volume resistivity (Ωcm) using this test piece and measuring the radio wave transmission loss (dB) using 4 GHz radio waves using the in-pipe method. Note that the radio wave transmission loss value (dB) is expressed as >40 because the maximum detection sensitivity of the measuring device is 40 dB.

【table】

[Table] [Effects of the Invention] According to the method of the present invention, it is possible to rationally and effectively utilize the aging nickel plating solution, which has hitherto been difficult to process, and to industrially provide excellent nickel plating materials. be able to. The characteristic advantages of the present invention will be specifically described below. (1) The plating reaction rate can be adjusted by the addition rate of the aging solution, and since the reaction is always in the region where the Ni ⁺⁺ and hypophosphite concentrations are low, the reaction rate is slow and the precipitated plating film is A fine and dense product can be obtained. (2) Since the nickel concentration in the plating solution is always maintained at a low level, no precipitate is formed even when the pH reaches 6 to 7. Therefore, since the plating reaction can proceed at a pH of 6 to 7, self-decomposition of hypophosphite is reduced, and the phosphorus content in the precipitated plating film is also reduced. As a result, the product's conductivity improves and its electromagnetic shielding properties improve. (3) By lowering the concentration of nickel and hypophosphite in the plating solution and reducing the hydrogen ion concentration from pH 4.5 to 6-7, the amount of hypophosphite consumed decreases, and the aging solution The amount of nickel present in the liquid can sufficiently reduce the nickel in the liquid. This will help reduce costs. (4) Due to the reduced consumption of hypophosphite and the mild plating reaction, the generation of hydrogen gas can be significantly reduced compared to before, so the safety equipment for dealing with explosions can be significantly simplified.

[Brief explanation of the drawing]

Fig. 1 is a scanning electron micrograph (approximately ¹⁰⁴ times magnification) showing the structure of the nickel plating film of Example 2, and Fig. 2 is a scanning electron micrograph showing the structure of the nickel plating film of Example 4 ( Figure 3 is a scanning electron micrograph (approximately ¹⁰⁴ times) showing the structure of the nickel plating film ^of Comparative Example 3, and Figure 4 shows the structure of the nickel plating film of Comparative Example 5. This is a scanning electron micrograph (approximately ¹⁰⁴ times magnification) showing the structure of.

Claims (1)

[Scope of Claims] 1. A method for producing a nickel plating material comprising contacting a water-dispersible plating base material with an electroless nickel plating solution, in which an aqueous suspension of the plating base material with a pH of 4 to 10 is brought into contact with an electroless nickel plating solution. and then adding at least an electroless nickel plating aging solution to the suspension and
A method for producing nickel-plated materials characterized by forming a nickel-plated film on the surface of a base material while maintaining the pH range. 2. Nickel plating according to claim 1, wherein the water-dispersible plating base material is an inorganic or organic powder, granule, or fibrous material that can be dispersed by crystalline or amorphous stirring means. Method of manufacturing materials.