JPS6111271B2 - - 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 had 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. It can be used as a substitute for electrode paints, etc. The present invention is characterized in that carbon black of at least 80 mμ or more is added to a copper powder, an alloy powder thereof, a powder containing silver as a component, or a mixture of silver powder with any of the above three types of powder. For example, when silver-copper (70% by weight) composite powder is used as a conductive material, the resistivity of the material without the addition of carbon black is 10 ^-1 Ωcm, and after environmental resistance tests such as humidity resistance, it is 500 to ∞. Although it was unstable due to double change, it was found that by adding the above carbon black, the specific resistance became 10 ^-4 Ωcm, and the moisture resistance and environmental resistance properties could be equivalent to or even improved as silver paint. It is something. Generally, most carbon blacks have a particle size of 10 to 30 mμ, and there are few types of carbon black with a particle size of 80 mμ or more. The effect of the present invention was not found with carbon blacks having a diameter of less than 80 mμ, and the effects of the present invention were most effective with FT grade carbon blacks preferably having a diameter of 90 mμ to 200 mμ. In addition, particles with a particle size of 10 mμ to 30 mμ and 80
The effects of the present invention can be obtained even if carbon blacks of mμ or more are added in combination. 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 refers to copper and silver alloy powder, copper powder chemically plated with silver, or copper powder and silver powder mechanically plated. It means a material that is forcibly bonded together or a mixture of them.The powder alone can obtain sufficient high conductivity, but because it contains silver as a component, the resistivity is lower than that of a material that does not contain silver. It can be further reduced by 10% to 30%. If the silver component is contained in an amount exceeding 80% by weight, it will not be cost-effective compared to silver paint.
The metal powder and silver powder in the present invention are mixed in a ratio of 100:0 to
The reason for using a mixture at a weight ratio of 10:90 is the same as above. Incidentally, it was confirmed that as the silver component ratio increases, the silver migration phenomenon becomes more likely to occur. Also,
By forming both or one of the metal powder and silver powder of the present invention into scales, 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 an electrode that requires sliding properties such as a variable resistor, graphite, molybdenum disulfide, fluorine resin, carbon fluoride, graphite fluoride, etc. By adding and containing powders of atomite and boron nitride either singly or in combination, the surface friction coefficient can be reduced and the sliding resistance can be maintained. Next, specific examples of the conductive paint according to the present invention will be described below. Example 1 96 g of ring element copper powder with an average particle size of 4.2 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. Further, the above paint was applied with a width of 0.5 m/m between the electrodes, and 50 V DC was applied between the electrodes in a humid atmosphere of 90 to 95% RH at 50°C to observe the migration phenomenon. The results are also shown in the table below. In addition, after leaving the same sample in a _3ppmH2S gas atmosphere for 500 hours, it was heated to 50℃ and 90 to 95%RH.
The specific resistances after being left in a humid 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 copper powder with an average particle size of 3.5 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, butyl cellosolve A test similar to that in Example 1 was conducted by mixing 30 g. The results are also shown in the table below. Example 3 Scale-shaped copper-silver composite powder with an average particle size of 2.3 μm (silver component ratio 4.3%, silver plating method) 83 g, FT grade carbon black (average particle size 90 μm, manufactured by Asahi Carbon Co., Ltd.) 17 g, silver powder 8 g of graphite (manufactured by Nippon Graphite Co., Ltd.), 25 g of phenol as a vehicle, and 39 g of ethyl carbitol were mixed, and the results of the same test as in Example 1 were obtained. The mixture was used as an electrode of a variable resistor and slid 20,000 times. The residual resistance values before and after 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 copper (Cu) powder or an alloy powder thereof, and A conductive paint characterized by containing carbon black with a particle size of at least 80 mμ. 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.