JPH0797717B2 - Cu powder coated with Ag and Ni - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION <Technical Field> In recent years, computer equipment has been widely used.
It has been pointed out that external electromagnetic waves affect the computer device and cause malfunction. This is because an organic resin is used for the housing of the computer, and radio waves pass through the organic resin. As a countermeasure against this, it has been practiced to make the organic resin conductive so as to exert the effect of electromagnetic wave shielding.

The present invention relates to Cu powder coated with Ni and Ag, which is particularly suitable for being mixed with an organic resin to make the resin conductive.

<Prior art and its problems> As a method of making an organic resin conductive, a conductive filler is contained in the organic resin.

The surface of the organic resin material is metallized by thermal spraying of metallic zinc.

Conductive paint is applied to the surface of the organic resin material.

Etc. are known, but the most widely used method is.

Conductive paint is one in which conductive powder is contained in the paint, but for the purpose of electromagnetic wave shielding, it is necessary to make it highly conductive rather than antistatic, so conductive powders for filling are Ni, Cu. , Ag, etc. are used. In this
Ag has the highest conductivity, has oxidation resistance, and does not deteriorate even if left for a long time, but is expensive. Although Cu is inexpensive and has excellent conductivity, it is easily oxidized and lacks long-term durability. Ni is durable, but less conductive than Cu and Ag.

The present invention relates to a conductive powder used for an electromagnetic wave shield coating and a conductive paste, and its object is to improve the oxidation resistance and conductivity of Cu.

Attempts have been made to include an antioxidant in the paint for the purpose of improving the oxidation resistance of Cu, but organic substances are the main ones, and there is nothing satisfactory. It is also known to coat Cu with Ag, but if Ag is coated so as to cause oxidation resistance, the amount of Ag coated becomes large and it becomes expensive.

The present inventors studied to improve the oxidation resistance by coating the surface of Cu powder with Ni. However, when Ni was coated, the oxidation resistance was equivalent to that of Ni, but the conductivity was lower than that of Cu.

For this reason, the present inventors were able to enhance the conductivity to the same level as Ag and Cu by further coating a small amount of Ag on this Ni-coated Cu powder. That is, an epoch-making powder having an oxidation resistance of Ni and an electrical conductivity of Ag, Cu was found.

<Structure of the Invention> According to the present invention, on the surface of the core of the Cu particles, from the bottom, 0.01 to 0.2% of Pd first coating layer with respect to Cu weight, 1 to 10.0
%, A second coating layer of Ni, a third coating layer of 0.2 to 5.0% Ag, and a conductive powder for an electromagnetic shield and a conductive paste made of Ag, Ni-coated Cu powder.

The particle size of the Cu powder used in the Ag, Ni-coated particles of the present invention is not particularly limited, but is preferably 0.5 to 500 µ, more preferably 1 to 100 µ. The purity is also not particularly limited.

The first layer of Pd is inevitably formed as an underlayer due to Ni plating, and has no positive meaning in the present invention.

The Cu powder can be coated with Ni by a conventional chemical plating method. That is, after Pd is deposited on Cu powder, it is suspended in a Ni aqueous solution, and a reducing agent such as hydrazine is added to this, so that Ni becomes Cu.
Precipitates on the powder surface. Further, Ag coating can be performed by chemical plating. That is, the target powder can be obtained by suspending Ni-coated Cu powder in an aqueous solution of ammoniacal Ag and adding a reducing agent such as formalin and tartaric acid.

The coating amount of Ni is 1 to 10 wt% with respect to the weight of Cu. 1w
If it is less than t%, the Ni coating is not perfect and the oxidation resistance cannot be maintained. On the other hand, if it exceeds 10 wt%, the conductivity is lowered and a large amount of Ag coating is required.

0.2 to 5.0 wt% is suitable for the Ag coating. If it is less than 0.2 wt%, the conductivity does not appear, and if it exceeds 5.0 wt%, the effect of conductivity is almost unchanged.

It goes without saying that the powder according to the present invention can be used not only as a conductive filler for a conductive paint used for electromagnetic wave shielding but also as a filler for a conductive paste.

<Detailed Description of the Invention> Example After immersing 10 g of Cu powder (manufactured by Fukuda Metal Haku Co., Ltd., particle size: 30 μm) in 20 ml of an aqueous palladium chloride solution (0.3 g / concentration as Pd: 0.3 g / concentration), and depositing all Pd on the surface (Pd deposition amount 0.06wt
%), Suspended in an aqueous nickel sulfate solution, added hydrazine (0.5 to 4 g) while maintaining the temperature at 60 ° C, and reacted for about 1 hour to give N.
i was deposited on the surface of the particles. The amount of Ni deposited was varied from 0.5 to 10 wt%. Next, this powder was collected and suspended in an aqueous ammoniacal silver nitrate solution, and hydrazine was added to this to collect Ag-precipitated powder, which was washed with water and dried. Ag precipitation amount is 0.2-
It was changed to 5.0 wt%. This powder was added to acrylic paint (Kansai Paint Co., Ltd. Aclick 200 resin 35 wt%, acetone, MEK, toluene mixed solvent 65 wt%) and dispersed using a homomixer at 2000 rpm for 15 minutes to give a conductive acrylic paint. Preparation, this was applied on an acrylic plate in a thickness of 50 μm, and tested for electrical resistance and oxidation resistance. The results are shown in the table below.

Here, the electric resistance is shown as a “resistance ratio” where the resistance of Cu is 1. That is, the resistance ratio of 1 means that the conductivity is the same as that of Cu, and the larger the value of the resistance ratio is, the lower the conductivity is as compared with Cu. When the resistance ratio of the coating film is 3 or more, the electromagnetic wave shielding property is reduced by one digit, the electromagnetic wave shielding effect is substantially lost, and the conductive paste is not suitable for circuit formation. Therefore, the resistance ratio is preferably 2 or less.

Oxidation resistance is measured by measuring the sheet resistance after leaving the coating film in saturated steam at 80 ° C for 1 hour and increasing the resistance by one digit or more compared to the sheet resistance before leaving × less than one digit. Those with an increase in resistance were marked with Δ, and those with no change in resistance were marked with ◯.

As can be seen from these results, when the Ni coating amount was less than 1 wt%, the oxidation resistance was insufficient, and when it was more than 10 wt%, the conductivity was remarkably reduced. If Ag coating is not performed, the conductivity will drop significantly, and even if the amount of Ag exceeds 5 wt%, the conductivity will not improve,
It will only be economically disadvantageous. The powder of the present invention shows sufficiently high oxidation resistance by Ni coating, and shows high conductivity comparable to copper powder by Ag coating, and is sufficiently used for electromagnetic wave shield and conductive paste in view of conductivity level. It is possible.

Therefore, like the copper powder, the conductive powder of the present invention can be used as an electromagnetic wave shield by being made into a paint or mixed with a resin, and can also be used as a conductive powder in a conductive paste.

Claims (1)

[Claims] 1. A first coating layer of 0.01 to 0.2% Pd and 1 to 10.0% N based on the weight of Cu in order from the surface of the core of Cu particles.
Conductive powder for electromagnetic wave shield and conductive paste, comprising Ag, Ni-coated Cu powder, having a second coating layer of i and a third coating layer of Ag of 0.2 to 5.0%.