JPH0645899B2 - Method for producing metal-coated inorganic powder - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION <Field of Industrial Application> The present invention relates to a method for producing a metal-coated inorganic powder. Furthermore,
More specifically, the present invention relates to a method for producing a metal-coated inorganic powder suitable for an antistatic filler, an electromagnetic wave shielding material, a magnetic material, a catalyst and the like.

<Prior Art> Conventionally, metal powders such as Al, Ni, and Cu have been known as conductive powders used for antistatic fillers, electromagnetic shielding materials, and the like. However, from the viewpoints of lightness, dispersibility, safety, price, etc., recently, metal-coated inorganic powder in which a metal is formed on the surface of the inorganic powder such as mica has come to be used.

As a method for forming a metal coating on the surface of such inorganic powder, electroless plating is widely used. In the electroless plating method, an inorganic powder is treated with a noble metal solution containing Pd or Ag to carry out a catalyzation treatment of supporting noble metal fine particles to be catalytic nuclei on the surface, and then electroless plating containing a desired metal. The plating solution is immersed and processed to form a plating film. Among the above treatments, the catalyzation treatment is a pretreatment step which has an important meaning in order to form a uniform plating film, and the precious metal fine particles are strongly and stably dispersed and supported on the surface of the inorganic powder.

As a method of catalyzing treatment, a method is generally used in which the surface of the inorganic powder is washed and then immersed in a Sn ²⁺ salt solution, and then immersed in a Pd ²⁺ salt solution to uniformly reduce and deposit metallic palladium. . As an improved method of this general method, after suspending the inorganic powder in an aqueous solution of palladium chloride having a pH of 2 or less,
A method is also known in which the pH is gradually raised to 4 to 7 so that metallic palladium is uniformly supported (for example, JP-A-60-13).
No. 3,066). Further, a method is also known in which the surface of the inorganic powder is subjected to a noble metal-capturing surface treatment using an epoxy resin and then treated with a silver ion-containing solution to support metallic silver (for example, JP-A-61-161). 257,479).

<Problems to be Solved by the Invention> However, in the known catalytic treatment method, the cost is high because a noble metal such as palladium or silver is used,
In addition, since the Sn ²⁺ or Pd ²⁺ salt solution is strongly acidic, it cannot be applied to inorganic powder having low acid resistance. Furthermore, in order to make the dispersion and carrying of the catalyst nuclei on the surface of the inorganic powder by physical adsorption such as anchoring effect on the fine irregularities of the surface of the inorganic powder uniform and strong, degreasing and roughening as a pretreatment are required. It is necessary to improve the anchoring effect by surface treatment such as aging and washing, and therefore the entire manufacturing process is complicated.

<Object of the Invention> Therefore, a first object of the present invention is to provide a method for producing a metal-coated inorganic powder at low cost by a simple process.

Another object of the present invention is to provide a method for producing a metal-coated inorganic powder which can be easily applied to an inorganic powder having low acid resistance.

Still another object of the present invention is to provide a method for producing a metal-coated inorganic powder having extremely excellent adhesion and smoothness.

Further objects of the present invention will be apparent from the following description.

<Means for Solving Problems> According to the present invention, an ion-exchange treatment step of treating an inorganic powder having ion-exchange properties with a metal ion-containing solution to fix the metal ions to the inorganic powder. The metal ion-fixed inorganic powder is subjected to a reduction treatment, a reduction step of depositing metal fine particles on the surface of the inorganic powder, and the metal fine particle-deposited inorganic powder is treated with a metal ion-containing electroless plating solution, Provided is a method for producing a metal-coated inorganic powder, which includes a plating treatment step of forming a metal coating on the surface of the inorganic powder, in the order of the steps described above.

<Description of the Invention> Next, the manufacturing method of the present invention will be described in detail.

Examples of the ion-exchangeable inorganic powder that can be used in the ion-exchange treatment step include amorphous hydrous compounds such as silica gel and alumina gel; silicate minerals such as zeolite, montmorillonite, hectorite, and fluoromica;
And a wide range of crystalline compounds such as zirconium phosphate are preferred. Among the above compounds, flaky ones such as montmorillonite, hectorite and fluoromica are particularly preferable for the purpose of imparting conductivity to antistatic fillers, electromagnetic wave shielding materials and the like.

As the metal ion that is ion-exchanged with the ion in the inorganic powder and fixed to the powder, any metal ion can be used as long as it is water-soluble and can be reduced to a metal in the reduction treatment step described later. Ni ²⁺ , Co ²⁺ , Fe ²⁺ , Cu ^{2+ and the} like are preferable in view of ease of reduction, intimacy with a metal to be plated, price, and the like, and particularly, the same kind of metal as the metal to be plated. The use of ions is preferable because the purity and adhesion of the coating are improved. The number of kinds of metal ions to be ion-exchanged may be one or two or more.
Examples of the metal ion-containing soluble metal compound that can be preferably used in the present invention include inorganic salts such as nitrates, sulfates and chlorides, as well as organic salts such as acetates and formates and complex compounds such as ammine complexes. You can

The ion exchange treatment in the present invention can be carried out, for example, by immersing the inorganic powder in the metal ion solution. In the ion exchange treatment, stirring or heating may be carried out to accelerate the treatment, if necessary. The amount of ion exchange can be determined by the ion exchange capacity (CEC) of the inorganic powder used, but in the present invention, it is preferable that the amount of metal ions supported increases because the number of catalyst nuclei also increases. Further, the amount of metal supported may be increased by using a so-called titration method in which an alkaline solution such as sodium hydroxide is gradually added to fix the metal hydroxide in the form of metal hydroxide.

By the above-mentioned ion exchange treatment, desired metal ions are extremely uniformly distributed and fixed at any ion exchange points inside and on the surface of the inorganic powder.

In the present invention, the inorganic powder after the ion exchange treatment can be separated from the mother liquor by a method such as centrifugation or filtration. In the separation, if metal ions remain in the mother liquor, it may be washed with water to remove the metal ions on the surface of the inorganic powder.

Next, the reduction treatment of the above-mentioned metal ion-fixed inorganic powder will be described.

The reduction treatment may be carried out in either the gas phase or the liquid phase,
For example, a method of heating in a reducing gas such as hydrogen or carbon monoxide, a method of immersing in an aqueous solution of a reducing agent such as sodium hypophosphite, or boron hydride, and a method of heating if necessary are preferable. Can be adopted.

By such reduction treatment, some or all of the metal ions fixed inside and on the surface of the inorganic powder are deposited on the surface of the inorganic powder as metal fine particles. Therefore, since the metal ions are extremely uniformly distributed as described above, the catalyst nuclei are also extremely uniformly deposited. Furthermore, unlike the conventionally known method,
Since the catalyst nuclei are precipitated not from the liquid phase but from the inorganic powder itself, the supporting power is strong and the adhesion of the resulting plated coating is extremely large.

In the present invention, the deposition state of the catalyst nuclei can be controlled mainly by adjusting the reduction conditions, and it is preferable to appropriately select the reduction conditions according to the purpose and application.
For example, when the reduction temperature is lowered and / or the reduction time is shortened, the particle size of the catalyst nuclei becomes small and the catalyst nuclei are densely distributed. Therefore, it is possible to obtain a plated film having particularly excellent smoothness by performing the plating treatment. Inorganic powder having such a plated coating is suitable for conductive materials and the like. On the contrary, when the reduction temperature is raised and / or the reduction time is extended, the catalyst nuclei grow into grains, and the grain size becomes large and the grains are coarsely distributed. As a result, the plated film after plating becomes granular and is suitable for a catalyst or the like.

In the present invention, the inorganic powder on which catalyst nuclei have been deposited in the reduction treatment step is then treated with a desired metal ion-containing electroless plating solution to form a metal coating on the surface of the inorganic powder. As a treatment method, it is preferable to immerse the sheet in an electroless plating solution bath.

The electroless plating bath that can be preferably used in the present invention is
Either an acidic bath or an alkaline bath may be used, but an alkaline bath is preferable in that the amount of co-deposition of impurities is small. Further, in the plating treatment, it is desirable that the inorganic powder and the plating liquid are evenly contacted by stirring. As the metal to be plated, not only a single metal,
It may be an alloy. As the single metal that can be plated by the method of the present invention, Ni, Co, Fe, Cu, W and the like are preferably mentioned, and as the alloy of two or more kinds of metals,
Alloys such as Ni-Co, Ni-Fe, Co-Fe, and Cu-W are preferable.

The electroless plating bath can be adjusted by a conventionally known method. That is, for example, a method of adjusting the bath by adding a metal salt, a reducing agent, a complexing agent, a pH adjusting agent, a stabilizer and the like in addition to the desired metal ion can be adopted. In the present invention, as the reducing agent, sodium hypophosphite, sodium borohydride, hydrazine, formalin, aminoborane and the like can be preferably used. Examples of complexing agents that can be preferably used in the present invention include ammonia, citrate, tartrate, succinate, malate, glycine and ethylenediaminetetraacetic acid (EDTA). The components of the plating bath can be arbitrarily selected by those skilled in the art depending on the desired metal coating composition and properties. Also, the amount of metal to be plated changes mainly depending on the temperature and time of the plating process, and if the plating process is performed at a high temperature for a long time, the amount of the metal to be plated will increase. The amount of metal decreases when treated.

By the above plating treatment, a metal coating is formed on the surface of the inorganic powder, and in the present invention, the catalyst nuclei are extremely uniformly and strongly dispersed and carried on the surface of the inorganic powder, so that the smoothness and adhesion of the metal coating are obtained. Is significantly better.

In the present invention, the metal-coated inorganic powder after the plating treatment is filtered, separated from the plating solution by a method such as centrifugation,
It can be washed with water and dried if necessary.

<Examples> Next, the present invention will be described based on Examples to show specific modes of the present invention, but the Examples described below do not limit the technical scope of the present invention.

Example 1 10.0 g of naturally occurring purified Na-montmorillonite powder (Yamagata Prefecture Sazawa Mine, CEC = 115 meq / 100 g)
Was added to 500 ml of a 0.1 M copper sulfate aqueous solution, and the mixture was stirred at room temperature for 3 hours to ion exchange Na ⁺ in the montmorillonite with Cu ²⁺ , then filtered, washed with water, and dried at 110 ° C.

This dried product was subjected to reduction heat treatment in a carbon monoxide gas stream (about 100 ml / min) at 250 ° C. for 30 minutes in an atmosphere firing furnace to deposit Cu fine particles on the surface of montmorillonite. Observation with a transmission electron microscope revealed that the Cu fine particles had a very small particle size of about 200Å.

Next, this montmorillonite is used as an electroless mesh bath 1 having the following composition.
It was added to the inside and stirred for 20 minutes to perform Cu plating.

Copper sulfate 30 g / 1 formalin (37%) 65 ml / 1 EDTA 20 g / 1 8-hydroxy-7-iodo-5-quinolinesulfonic acid 0.34 g / 1 pH (adjusted with NaOH) 13.0 Bath temperature 50 ° C. Cu coating The montmorillonite was shiny and had a Cu coverage of about 35 wt%. Also, when the surface was observed with a scanning electron microscope, it was found that the entire surface was uniformly and uniformly plated, and was excellent in smoothness. After pressure molding (1 ton / cm ² ), the volume resistivity was measured and found to be 1.5
It was × 10 ^-3 Ω · cm, indicating good conductivity.

Example 2 Na-type tetrasilicon fluoromica (manufactured by Toby Industries, Ltd., CEC = 210 meq / 10), which is a type of artificial fluoromica
0 g) of 10% sol (500 ml) was added to 0.1 M nickel nitrate aqueous solution 2, dispersed with a homogenizer, and heated and stirred at 60 ° C. for 5 hours to ion exchange Na ⁺ in the mica with Ni ²⁺ . After filtration and washing with water, it was dried at 110 ° C.

This dried product was heated in an atmosphere firing furnace with a hydrogen flow (about 100 ml /
Min), a reduction heat treatment was performed at 400 ° C. for 1 hour to deposit Ni fine particles on the surface of the mica. The particle size of Ni fine particles observed by a transmission electron microscope was about 80 Å, which was very fine.

Next, this mica powder was added to the electroless plating bath 3 having the following composition, and Ni plating was performed by stirring for 20 minutes.

Nickel sulfate 45 g / 1 sodium hypophosphite 30 g / 1 sodium citrate 100 g / 1 ammonium chloride 50 g / 1 pH 11.0 bath temperature 90 ° C. The Ni coating amount was about 30 wt%, and the surface condition was homogeneous and smooth. In addition, this Ni-coated mica has a volume fraction of 25%.
Acrylic paint base (Kansai Paint Co., Ltd.)
No.2026) made into a paint and put on the ABS substrate.
It was applied in a thickness of 0 μm, and the surface resistance and electromagnetic wave shielding characteristics (4 GHz) were measured. As a result, the surface resistance is 0.5Ω
/ □, the electromagnetic shield property was 50 dB or more (measurement value detection limit), and excellent conductivity and electromagnetic shield property were shown.

Example 3 20.0 g of silica gel for chromatography (manufactured by Wako Pure Chemical Industries, Ltd., Wakogel C-200, 100-200 mesh) was added to 200 ml of 0.1 M nickel chloride aqueous solution, and the mixture was stirred at room temperature for one day to obtain N.
i ²⁺ was ion-exchanged. Then sodium hypophosphite
Ni particles were reduced and deposited on the silica gel surface by adding 10.0 g and refluxing at 95 ° C. for 5 hours. After washing with water, it was added to the electroless plating bath 2 having the following composition and stirred for 1 hour to perform Ni plating.

Nickel sulfate 70 g / 1 Ammonia water (28%) 350 ml / 1 Hydrazine (80%) 60 ml / 1 pH 11.5 Bath temperature 70 ° C. Ni coating amount was about 95 wt%. Further, when observed with a scanning electron microscope, Ni was in the form of powder and its particle size was 400 to 2000 Å.

With respect to the Ni silica gel, the catalytic activity of the hydrogenation reaction of toluene was examined by circulating a hydrogen gas containing toluene vapor using a fixed bed circulation type catalytic reactor.
The reaction conditions are: reaction temperature: 175 ° C, total pressure: 2 kg / c
m ² , GHSV: 1300 / hr, toluene concentration: 121
ppm, the reaction product is a gas chromatograph (column: PEG
-20M 10% Chromosorb WAW 60/80, detector: FID). As a result, both the conversion of toluene and the selectivity of methylcyclohexane were 100%, indicating extremely good catalytic properties.

<Effects of the Invention> As described above, according to the method of the present invention, a metal having excellent adhesion and smoothness can be produced inexpensively by a simple process without using any expensive precious metal or strong acid as in the conventional method. A coated inorganic powder can be produced. Furthermore, the method of the present invention can also be used for metal coating of inorganic powder having low acid resistance, which could not be used by the conventionally known method.

Claims (1)

[Claims] 1. An ion exchange treatment step of treating an inorganic powder having ion exchangeability with a metal ion-containing solution to fix metal ions to the inorganic powder, and a reduction treatment of the metal ion-fixed inorganic powder. Then, a reduction step of depositing metal fine particles on the surface of the inorganic powder, and a plating for treating the inorganic fine particle-deposited inorganic powder with an electroless plating solution containing metal ions to form a metal film on the surface of the inorganic powder. A method for producing a metal-coated inorganic powder, which comprises a treatment step and the order of the above steps.