JPS61235473A - Paint for resistor - Google Patents

Abstract

PURPOSE:To obtain the title paint for resistors, which does not cause rise in resistance due to anodic oxidation, produces a less sliding noise and has good resistance to moisture and heat, by blending an electrically conductive powder composed of tungsten dioxide powder and carbon black and a synthetic resin. CONSTITUTION:In a paint for resistance obtd. by blending an electrically conductive powder and a synthetic resin, the paint is characterized in that part of the electrically conductive powder is tungsten dioxide (WO2) powder and the remainder thereof is carbon black in a weight ratio of the WO2 powder to the carbon black of pref. 95:5-10:90. The paint allows the quantity of the electrically conductive powder to be increased as compared with the case where carbon black alone is used. Accordingly, the paint has good workability, because it has proper thixotropic properties required of a paint in screen printing, etc.

Description

[Detailed Description of the Invention] Industrial Fields of Use The present invention is applicable to printed wiring boards of various electronic devices, fixed resistors,
The present invention relates to resistance paints used for resistance elements such as variable resistors, electromagnetic wave shielding plates, radio wave absorption plates, antistatic plates, etc.

BACKGROUND OF THE INVENTION Conventionally, as a resistive paint, one in which conductive powder such as carbon black such as acetylene black or graphite powder is dispersed in a synthetic resin such as an epoxy resin or a phenol resin is known. In addition, for the purpose of improving workability such as printability and environmental stability such as under high load conditions, we use Sin, powder, and Ti.
Resistance paints are known in which insulating powder such as e2 powder is dispersed together with carbon black in a synthetic resin.

Problems to be Solved by the Invention In the case of the conventional example, the proportion of carbon black in the resistance composition is extremely small in the high resistance region.

When a current is passed in a high humidity atmosphere, anodic oxidation occurs, and the carbon black vaporizes as carbon dioxide gas, which causes the resistance value to increase at an accelerated rate, reaching infinity (insulating material). Furthermore, resistance paints containing insulating powders such as S10□ powder, Tie powder, etc. have the disadvantage of high sliding noise when used as sliding contacts, such as resistance elements for variable resistors. Furthermore, since the current conduction path is due to carbon black and their mutual contact, there is a drawback that in a high resistance region where the proportion of carbon black is small, the resistance value changes greatly when humidity or temperature fluctuates.

The present invention solves these problems and eliminates the increase in resistance caused by anodic oxidation as in the conventional method.

The object of the present invention is to provide a resistance coating material that has low sliding noise and good moisture resistance and heat resistance properties when used as a sliding contact.

Means for Solving the Problem In order to solve this problem, the present invention provides a resistive paint made of at least conductive powder and a synthetic resin, in which part of the conductive powder is tungsten dioxide (WO) powder. The other part is carbon black.

Function: With this structure, there is no increase in resistance due to anodization even when current is passed in a high humidity atmosphere, the moisture resistance and heat resistance are good, and when used as a sliding contact, the sliding noise is low.

Embodiments Hereinafter, embodiments of the present invention will be described based on the drawings.

That is, the present invention provides a resistive paint comprising at least conductive powder and synthetic resin, in which a portion of the conductive powder is tungsten dioxide (WO2) powder and the other portion is carbon black.

The weight ratio of WO2 powder and carbon black is 95 = 5 ~
The time was set at 10:90.

WO3 has been known for a long time, but when it is dispersed as a powder alone in a synthetic resin such as phenol resin and used as a resistance paint, the resistance value decreases in an atmosphere of high humidity and temperature, as shown in Figure 1. By combining WO powder, which has extremely large fluctuations, and carbon black, the fluctuations in resistance value can be extremely reduced in high humidity and high temperature environments, as shown in Figure 2, which shows the film structure of the resistance paint. It can be inferred that this is caused by the structure of WO2 powder 1 and carbon black 2. That is, while the WO8 powder 1 is granular, the carbon black 2 is a chain-like 1. When using a conductive powder with a zero-grain structure or a chain structure alone, the powder particles may absorb moisture and expand/contract due to heat and the synthetic resin that binds the powder particles together. The state of mutual contact can be either dense or rough depending on the state of the atmosphere. On the other hand, since the resistance value is expressed as the sum of the resistance of the conductive powder itself and the contact resistance between the powders, in the case of the granular powder or chain powder alone,
It is thought that the resistance value fluctuates greatly due to fluctuations in temperature and humidity atmosphere. As shown in Figure 2, when Woi powder 1 and carbon black 2 are mixed and dispersed in synthetic resin 3, even if the synthetic resin absorbs and desorbs moisture due to changes in the atmosphere and expands and contracts due to heat. As shown in the conceptual diagram of FIG. 3, it is presumed that the change in resistance value is small because the conductive bus 4 is easily obtained. Furthermore, since both carbon black and WO2 are good conductive materials, when used as sliding contacts, the level of sliding noise is lower than when using carbon black alone. Furthermore, even in the high resistance range, WO2 is stable with respect to temperature and humidity and can lower the synthetic resin ratio in the resistance film compared to conventional ones, so moisture absorption can be reduced and anodic oxidation can be virtually prevented. . Furthermore, since the resistive paint according to the present invention can contain a larger amount of conductive powder than conventional carbon alone, it has appropriate thixotropic properties and is easy to work with, such as screen printing. It's good.

Next, specific examples will be described.

Specific Example 1 255 g of WO8 powder with an average particle size of 0.2 μm, 40 g of acetylene black, and 5 g of artificial graphite were weighed and mixed to make 20 epoxy resin (Yuka Shell, product name: Ebicoat 815).
20 g of a 0-order imidazole curing agent dispersed in 0 g using a triple roll was added, and ethyl carpitol acetate was added to adjust the paint viscosity to 100 voids to obtain a resistance paint.

Comparative Example 60g of acetylene black, 7g of artificial graphite and 200g of epoxy resin (Yuka Shell, product name: Ebicoat 815)
20g of imidazole curing agent was added, and ethyl carpitol acetate was added to make the paint viscosity 100.
Adjustments were made to the voids and a resistance paint was obtained.

Comparative Test Example The resistive paints of Specific Example 1 and Comparative Example were each pattern-printed on a phenol laminate using a screen printing method.
The epoxy resin was cured at 60°C for 30 minutes. The following comparative tests were conducted on the respective resistance elements according to the specific example 1 and comparative example.

Test 1: Leave in a constant temperature bath at 70°C and measure the rate of change in resistance value after 1000 hours. Test 2: Leave in a 60°C 90-95% relative humidity bath and measure the rate of change in resistance value after 1000 hours.
Test 3: Apply a DC voltage of 24 V to both ends of the resistance element in a 60°C 90-95% relative humidity chamber, and measure the rate of change in resistance value after 1000 hours. Test 4: Silver-metsuki beryllium copper on the resistive coating. Press a metal brush of 20 g, 15 mm/
The sliding noise was measured when sliding at a speed of 1.2 seconds (DC voltage 24 V applied across the resistance element). The results of these tests 1 to 3 are shown in Figures 4 (a) to (Q), respectively. Figure 4 (a)
In ~(Q), (A) is the resistance change characteristic of the specific example 1, and (B) is the resistance change characteristic of the comparative example. In addition, the results of Test 4 are shown in the following table.

Specific Example 2 Using the same materials as in Specific Example 1 and varying the ratio of carbon black and WO3 powder, the moisture resistance and heat resistance after 1000 hours were measured in the same manner as in the comparative test example. We investigated the rate of change.

The results are shown in FIG.

Effects of the Invention As described above, according to the present invention, there is no increase in resistance due to anodization even when current is passed in a high humidity atmosphere, the moisture resistance and heat resistance are good, and there is no sliding noise when used as a sliding contact. It also has a lower amount of conductive powder compared to the case of carbon black alone, so it has the appropriate thixotropic properties required as paint properties for screen printing, etc., and is easy to work with. It's good. In addition, since the materials used are all inexpensive, they are extremely useful industrially.

[Brief explanation of drawings]

The drawings show examples of the present invention. Figure 1 is a graph showing the relationship between the ratio of carbon black and WO2 powder and resistance change characteristics, and Figure 2 is a diagram of the coating film structure of the resistance paint according to the present invention. , Figure 3 is a conceptual diagram of the conductive bus in the coating film, Figure 4 (
a) to (c) are graphs showing comparative test examples according to the present invention and comparative examples. 1...WO2 powder, 2...carbon black, 3.
... Synthetic resin, 4... Conductive path agent Yoshihiro Morimoto Figure 1

Claims (1)

[Scope of Claims] 1. A resistive paint made of at least a conductive powder and a synthetic resin, wherein a part of the conductive powder is tungsten dioxide (WO_2) powder and the other part is carbon black. paint. 2. The resistance paint according to claim 1, wherein the weight ratio of tungsten dioxide (WO_2) powder and carbon black is 95:5 to 10:90.