JPS62188B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for producing Ni-coated mica powder suitable for conductive pigments and conductive fillers used in the production of conductive paints, conductive plastics, etc. In this specification, both the conductive pigment and the conductive filler are collectively referred to as conductivity-imparting powder. Metal powders such as Ag, Cu, Al, and Ni have long been known as conductive powders used as conductive pigments, but since Ag is expensive and Al and Cu are easily oxidized, Ni is the most popular. Used as a practical conductive pigment. As the conductive pigment, Ni powder made from nickel carbonyl (referred to as carbonyl nickel) is generally used. This is a fine particle with a particle diameter of several microns or less, and is spherical. The conductivity of a paint coating is caused by contact between pigment powders, but spherical particles are not advantageous in this sense; for example, in order to obtain a conductive coating that has an electromagnetic shielding effect, Ni powder and a resin binder must be combined. Conductive powder in proportion of 60% or more, usually
It is necessary to contain 70 to 80%. As a result, the proportion of the resin binder decreases, resulting in poor strength of the coating film and the disadvantage that it is easily peeled off. Furthermore, fine carbonyl nickel powder has poor dispersibility, requiring strong dispersion treatment in paint production, and the surface smoothness of the coating film is also poor. Furthermore, Ni powder is black and has little aesthetic effect. In addition, since the Ni powder settles during storage of the paint, it is necessary to redisperse it before use, but the agglomeration of the sediment is strong and redispersion is not easy. This is because the Ni powder has a large specific gravity (8.9), is fine, and is spherical. The conductive pigment is preferably a powder with a low specific gravity and a particle size of 5 to 60 microns, and is preferably flake-like or fibrous rather than spherical. Conductive fillers include carbon powder and fibers, Al flakes, Ni powder, Ni-coated carbon powder, Cu or brass fibers, but carbon materials lack conductivity, and Al lacks oxidation resistance.
Ni-coated carbon fibers are expensive, and what has been practically used is Ni powder or brass fibers. However, these fillers have a specific gravity of 8 or more, and when mixed with resin, for example, in order to achieve conductivity with an electromagnetic shielding effect, they must account for 60% by weight, preferably 70% or more of the total resin composition. must also be included. Therefore, the specific gravity of the resin containing the conductive filler becomes 2 or more, which impairs the lightness of the resin. That is, it is desirable that the conductive filler mixed with the resin has a specific gravity as low as possible. Conductivity depends on the volume % of conductive filler (typically 20 volume %
Therefore, the small specific gravity of the conductive filler has the advantage that the required amount (weight) of the conductive filler to be included is small. In this sense, it has been known that nickel-coated mica powder is advantageous as a conductivity-imparting powder. 1. The specific gravity of mica is approximately 2.8, and even if the powder is coated with Ni, its specific gravity is smaller than Ni. For example, even if it is coated with 40% Ni, its specific gravity is approximately
3.9, and can exhibit conductivity with a small weight. 2. Mica particles have a flake shape, and even when coated with Ni, they generally maintain this shape, and the particles can easily come into contact with each other in a coating or plastic, and can exhibit electrical conductivity at a small weight percent. Additionally, mica powder inherently has good dispersibility;
Ni-coated powder also has good dispersibility and is easy to disperse and form into a paint. 3. Mica is cheaper than Ni, and even Ni-coated mica powder is cheaper than Ni. Generally, Ni is coated on the powder surface by electroless plating, which usually requires the following steps. (1) If oil or fat is attached to the powder surface, degrease it. (2) Pre-treat with stannous chloride solution, etc. (3) Apply treatment to attach palladium chloride to the powder surface (activation). (4) Apply Ni plating. In the electroless plating of mica powder, the present inventors have found that by strictly selecting the activation conditions in (3), it is possible to omit the step (2) and to apply a uniform Ni coating. It has been found that a Ni-coated mica powder with excellent gloss can be obtained. That is, according to the present invention, when coating mica powder with nickel by electroless plating, the mica powder is suspended in an aqueous palladium chloride solution with a pH of 2 or less, or the mica powder is suspended in an aqueous palladium chloride solution with a pH of 2 or less. The activated mica thus obtained A method of producing a nickel-coated mica powder is provided which comprises electroless plating the powder. The mica powder used in the method of the present invention has a major axis of 5 to
500μ is preferable. Mica powder usually has less dirt on its surface and can be used as is without degreasing. This was suspended in a predetermined amount of water, and palladium chloride was added as Pd to 0.05
Concentration of ~0.20g/, preferably 0.06-0.10g/
After adding Ni to a concentration of It becomes uniform. Palladium chloride is usually used dissolved in water or an aqueous hydrochloric acid solution, and when an aqueous hydrochloric acid solution is used, the pH can be reduced to 2 or less by adding it to the mica suspension. If the pH is 2 or higher, add hydrochloric acid to 2
Do the following. In this state, palladium chloride is considered to exist as a solution. Next, add water to this solution to bring the pH to 4 or higher. As water is added, the volume of the solution increases and the pH rises. When the pH reaches 4 or higher, the palladium chloride begins to hydrolyze, and palladium begins to precipitate on the mica surface. In this case, if the time to raise the pH from 2 to 4 or higher is too short, non-uniform precipitation will occur, so it is usually
It is important to do this for at least 1 minute and up to 1 hour. Other methods of increasing the pH, such as adding alkali, result in uneven palladium precipitation and subsequent
Ni plating does not occur uniformly, resulting in a coated powder with poor gloss. If the amount of Ni coated is 10% of the weight of the coated powder, the entire surface of the powder can be covered and conductivity close to that of Ni alone can be achieved. On the other hand, there is no profit worth exceeding 50%. The present invention will be specifically explained below using Examples. Example 270g of mica powder with a specific surface area of about 3m ² /g was mixed with 3g of water.
900% palladium chloride aqueous solution
cc (0.3 g/containing as Pd) was added. Add water over 10 minutes to 1 hour while stirring well.
The total amount was adjusted to about 30-60 so that the final pH was 3-8. The dispersed mica powder was filtered and dried. 240 g of mica powder subjected to the above palladium activation treatment was suspended in 1 water, and an aqueous solution 1 in which 590 g of nickel sulfate (NiSO ₄ .6H ₂ O) was dissolved was added, heated, and kept at 70°C. Here, a solution of 390 g of hydrazine sulfate ((NH ₂ ) ₂ H ₂ SO ₄ ) dissolved in 620 c.c. of 29% NH ₄ OH aqueous solution was added, stirred for 30 minutes to precipitate Ni, filtered and washed. , dried and Ni
A coated mica powder was obtained. The coverage was approximately 35%. This powder was made into a paint using an acrylic paint base (Kansai Paint Co., Ltd. No. 2026) and applied to a thickness of 50μ, and the surface gloss and surface resistance of the paint film were examined. The conditions and results of treatment with palladium chloride aqueous solution are summarized in the following table.

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Claims (1)

[Claims] 1. When coating mica powder with nickel by electroless plating, either suspend the mica powder in an aqueous palladium chloride solution with a pH of 2 or less, or suspend the mica powder in an aqueous palladium chloride solution and then adjust the PH to 2 or less, Thereafter, an activation treatment is carried out by raising the pH of the treatment medium to 4-7 over time so that a uniform coating of palladium occurs, and the thus obtained activated mica powder is electrolessly plated. A method for producing nickel-coated mica powder comprising: