JPS6111272B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to an inexpensive and high-performance conductive paint. Conductive silver paint has traditionally been widely used as electrodes or wiring materials for various electronic components and printed wiring boards, and with the recent expansion of computerization in various industries, the demand for conductive silver paint has continued to increase. There is. The reason why silver is often used as a main conductive material is because it has the highest electrical conductivity among metals and has high chemical stability. However, in the case of silver paint, since the conductive material is silver, the material cost is very high. Furthermore, in the case of silver paint, there are many accidents due to silver migration, and when high reliability is required, even more expensive gold paint has to be used. In addition, the above-mentioned silver migration phenomenon imposes many restrictions on product design, which is one of the factors that hinders the recent demand for smaller sizes and higher densities. There are materials using carbon black and graphite as inexpensive conductive materials, but compared to silver's specific resistance of 1.62×10 ^-6 Ωcm, graphite has a specific resistance of 0.2 to 1×10 ^-3 Ωcm. However, since carbon black has an even higher resistivity, it is completely impossible to obtain conductivity equivalent to that of silver paint, and although it can be used as a resistive paint, it is unsuitable as a conductive paint. In addition, when copper powder is used as a conductive material, the inherent resistance of copper itself is not much different from that of silver, but the surface of the copper powder oxidizes when it is powdered or baked as a paint.
The contact resistance between each copper powder in the coating state increases extremely, resulting in a resistivity close to ∞.
As a countermeasure to this problem, attempts have been made to mix silver powder and copper powder to form a paint, but in order to obtain a resistivity of about 10 ^-3 Ωcm, it is necessary to contain at least 70 to 80% by weight of silver powder. First, the goal of producing an inexpensive conductive paint could not be achieved. It has also been proposed to use silver-copper composite powder, which is made by plating or mechanically forcibly bonding silver to copper powder, as a conductive material, but in this case as well.
In order to obtain a specific resistance of about 10 ^-3 Ωcm, the silver content must be at least 70 to 80% by weight, which is not advantageous compared to silver paints. Moreover, even when silver powder and copper powder are mixed or when silver-copper composite powder is used, if the silver content is less than 70% by weight, oxidation of the copper powder surface will proceed in a short period of time due to the effects of humidity and temperature, resulting in resistance. The value has increased by hundreds to tens of thousands of times. Furthermore, when nickel powder is used as a conductive material, it has the same drawbacks as copper powder. As mentioned above, many attempts have been made to create inexpensive conductive paints, but they have the same performance as silver paints.
Moreover, an inexpensive conductive paint has not yet been developed. The present invention is capable of solving all of the above-mentioned drawbacks, and aims to provide an inexpensive conductive paint that can completely eliminate accidents caused by silver migration, which are unavoidable in the case of silver paint, and restrictions on product design. It is something to do. In detail, by using the conductive paint of the present invention, the cost is 1/10 to 1/2 compared to silver paint, and the conductivity is almost the same as that of silver paint.
Environmental stability, such as moisture resistance, heat resistance, sulfur gas resistance, and salt spray resistance, is equivalent to or better than that of silver paint, so it can be used for printed wiring board wiring and electronic components that currently use silver paint or gold paint. It can be used as a substitute for electrode paints, etc. In the present invention, carbon black of at least 80 mμ or more is added to nickel (Ni) powder, its alloy powder, powder containing silver as a component thereof, or a mixture of silver powder with any of the above three types of powder. For example, silver-Ni (70% by weight)
When composite powder was used as a conductive material, the resistivity of the one without the addition of carbon black was ¹⁰¹ Ωcm, and it was unstable, changing 100 to 300 times after environmental resistance tests such as moisture resistance. It has been found that by adding it, the specific resistance becomes 10 ^-3 to ^{10 -4} Ωcm, and the moisture resistance and environmental resistance properties can be equal to or even improved as those of silver paint. Generally, carbon black has a particle size of 10mμ to 30m.
Most of the carbon blacks are μ, and there are few types of carbon black with a diameter of 80 mμ or more. Carbon black with a diameter of less than 80 mμ does not have the effect of the present invention, and is preferably
The effect of the present invention was greatest for FT grade carbon black with a diameter of 90 mμ to 200 mμ. In addition, the particle size is 10 mμ
The effect of the present invention can be obtained even if a combination of carbon black of approximately 30 mμ and carbon black of 80 mμ or more is added. Carbon black with a large particle size generally has a small structure and therefore an extremely small amount of oil absorption. The effect of the present invention is that the carbon black with the large particle size described above penetrates closely between the metal powders, and has the effect of preventing the oxidation of the metal powders during baking and environmental resistance such as moisture resistance, and even reducing them. it is conceivable that. In addition, in the present invention, at least 80 m
The inclusion of carbon black with a diameter of μ or more means that even if carbon black with a diameter of less than 80 μm is additionally included as described above, or other graphite, carbon fluoride, etc. are additionally included as will be described later. This is to prevent the effects of the present invention from being significantly impaired. Furthermore, the metal powder in the present invention containing 0 to 80% by weight of silver as a component is an alloy powder of Ni and silver, a chemically silver-plated Ni powder, or a metal powder that is mechanically plated with Ni powder and silver powder. It refers to a material that is forcibly bonded together or a mixture of these.Although powder alone can provide sufficient high conductivity, by containing silver as a component, the resistivity is lower than that of a material that does not contain silver. and an additional 10%
It can be reduced by ~50%. If the silver component is contained in an amount exceeding 80% by weight, it will not be cost-effective compared to silver paint. The reason for using a mixture of metal powder and silver powder in a weight ratio of 100:0 to 10:90 in the present invention is also for the same reason as above. Incidentally, it was confirmed that as the silver component ratio increases, the silver migration phenomenon becomes more likely to occur. Further, by making both or either of the metal powder and silver powder of the present invention into a scale shape, high conductivity can be obtained by reducing the content ratio of the metal component and silver component in the coating state. Preferably, it is advantageous in terms of cost to use scale-like materials for both. When the conductive paint of the present invention is applied to electrodes that require sliding properties such as variable resistors, graphite,
By adding powders of molybdenum disulfide, fluororesin, carbon fluoride, graphite fluoride, and boron nitride, singly or in combination,
Sliding resistance can be maintained by reducing the surface friction coefficient. Next, specific examples of the conductive paint according to the present invention will be described below. Example 1 96 g of cyclic Ni powder with an average particle size of 5.1 μm, 17 g of SRF grade carbon black (average particle size 116 μm, manufactured by Asahi Carbon Co., Ltd.), 23 g of phenol resin as a vehicle, and 32 g of butyl carbitol were mixed and kneaded in a roll mill. and created a conductive paint. The table below shows the specific resistance of this paint applied to a phenol laminate board using a 200 mesh stainless steel screen and baked at 180°C for 20 minutes. Furthermore, the above paint was applied with a width of 0.5 m/m between the electrodes, and 50 VDC was applied between the two electrodes in a humid atmosphere of 90 to 95% RH to observe the migration phenomenon. The results are also shown in the table below. In addition, after leaving the same sample in a 3ppm _H2S gas atmosphere for 500 hours, it was
The specific resistances after being left in a RH humidity atmosphere for 1000 hours and after being left in an 85°C atmosphere for 1000 hours are also shown in the table below. Example 2 83 g of scaly Ni powder with an average particle size of 4.8 μm, 17 g of SRF grade carbon black (average particle size of 84 μm, manufactured by Mitsubishi Chemical Corporation), 22 g of epoxy resin (#1001, manufactured by Ciel Chemical Co., Ltd.) as a vehicle, The same test as in Example 1 was conducted by mixing 30 g of butyl cellosolve. The results are also shown in the table below. Example 3 Scale-shaped Ni-silver composite powder with an average particle size of 3.2 μm (silver component ratio 2.0%, silver plating method) 83 g, FT grade carbon black (average particle size 90 μm, manufactured by Asahi Carbon Co., Ltd.) 17 g, silver powder The same test as in Example 1 was conducted by mixing 8 g of Graphite (manufactured by Nippon Graphite Co., Ltd.), 4.5 g of graphite (manufactured by Nippon Graphite Co., Ltd.), 25 g of phenol as a vehicle, and 39 g of ethyl carbitol. The results and the residual resistance values before and after using it as an electrode of a variable resistor and sliding it 20,000 times are also shown in the table below. Conventional Example 83 g of silver powder with an average particle size of 3.4 μm, 20 g of phenol resin, and 31 g of ethyl carbitol were mixed and tested under the same conditions as Examples 1 to 3. The results are also shown in the table below.

[Table] The present invention is constructed as described above, and can be obtained at 1/10 to 1/2 the cost compared to silver paint, and has almost the same conductivity as silver paint. Moreover, it has environmental stability equivalent to or better than silver paint, so it is a conductive material that can replace the current use of silver paint and gold paint, such as wiring for printed wiring boards and electrode paint for electronic components. The industrial properties of this paint are great.

Claims (1)

[Scope of Claims] 1. A conductive paint made of a metal powder as a main conductive material, an organic binder as a vehicle, and a solvent as necessary, in which the metal powder is nickel (Ni) powder or an alloy powder thereof,
A conductive paint characterized by further containing carbon black having a particle size of at least 80 mμ or more. 2. The conductive paint according to claim 1, which uses a metal powder containing 0 to 80% by weight of silver as a component. 3. The conductive paint according to claim 1, wherein the metal powder is a mixture of metal powder and silver powder at a weight ratio of 100:0 to 10:90. 4. The conductive paint according to claim 3, which uses metal powder and/or silver powder in the form of scales. 5. The conductive paint according to claim 1, which contains graphite, molybdenum disulfide, fluororesin, carbon fluoride, graphite fluoride, and boron nitride powders singly or in combination.