JP4342270B2 - Resistance pattern for electric circuit - Google Patents

Description

The present invention relates to a resistance pattern for an electric circuit on which a metal slider slides .

  Conventionally, a resistance pattern is formed on a circuit board by printing a resistance paste for an electric circuit formed by kneading carbon powder, an organic binder and a solvent on the circuit board by screen printing or the like, and firing the circuit board. Was going by.

  By the way, among the resistance patterns, the resistance pattern for the variable resistor has a lubricity on its surface so that the sliding movement of the sliding element can be performed smoothly because the metal sliding element slides on the resistance pattern. It is necessary to be. For this reason, as shown in Patent Document 1, for example, there is conventionally a mixture of fluororesin powder in a resistance paste for electric circuits.

  Conventionally, graphite powder has been used as a carbon powder of a resistance pattern for a variable resistor having lubricity on the surface. There are two theories, namely, the surface slip theory that the lubricity of graphite is caused by an extremely thin adsorbed layer that adsorbs water vapor molecules, and the internal slip theory due to the change in bonding force due to water vapor (adsorbed gas) between the graphite molecules. is there. In any case, in graphite, the water vapor and the frictional force are closely related, and the amount of water vapor depends on the temperature (atmospheric pressure). Therefore, it is known that the coefficient of friction of the resistance paste changes depending on the temperature.

  Here, the line graph shown by two dotted lines in FIG. 1A shows the state of change of the friction coefficient with respect to the temperature of the conventional resistance pattern. Explaining the experimental method, as shown in FIG. 1 (b), the resistor paste (carbon powder made of graphite powder, organic binder made of phenol resin, ethylene glycol monobutyl ether made on the substrate on the heater 100, as shown in FIG. Sample 110 and a small amount of additive (antifoaming agent etc. kneaded) are printed and fired to fix sample 110 on which a resistance pattern is formed, and an elastic metal plate (beryllium copper plate) on the resistance pattern of sample 110 ) The sliding contact 121 of the manufactured slider 120 is pressed at a predetermined pressure (30 gF), and in this state, the heater 100 and the sample 110 fixed thereto are moved in the horizontal direction (arrow A direction). By detecting the horizontal force applied to the moving element 120 by the load cell, the friction coefficient is measured. The measurement was performed when the ambient temperature was 23 ° C., 41 ° C., 59 ° C., 78 ° C., 98 ° C., and 115 ° C., and for the first and fifth reciprocations of the heater 100 and the sample 110. The resistance pattern has a specific resistance of 400 (Ω / □) [length × width = (1 cm × 1 cm), thickness = 10 μm, resistance value is 400Ω], and organic binder and carbon powder. A kneaded mixture was used.

  As indicated by the dotted line in FIG. 1A, it was confirmed that the friction coefficient increases as the temperature increases. In other words, the higher the temperature, the greater the resistance when sliding the slider and the smoother sliding becomes.

  On the other hand, as a method of reducing the frictional resistance of the slider sliding on the resistance pattern, there is a conventional method of overcoating grease on the printed resistance pattern. The one-dot chain line in FIG. 1A shows the state of change in the friction coefficient with respect to the temperature of the resistance pattern overcoated with grease. The experimental method is the same as that described above. As shown by the alternate long and short dash line in FIG. 1A, in the case of a resistance pattern coated with grease, the coefficient of friction becomes small at room temperature.

However, in the case of a resistance pattern overcoated with grease, after forming the resistance pattern, it is necessary to apply grease again and then wipe off excess grease, resulting in a problem that the manufacturing process becomes complicated. As described above, the frictional resistance decreases, but the coefficient of friction increases as the temperature rises. This is the same as in the case of the resistance pattern in which the grease is not applied. The feeling of sliding becomes worse.
JP-A-2-263877

The present invention has been made in view of the above points, and an object of the present invention is to provide a resistance pattern for an electric circuit that can keep the frictional resistance of the resistance pattern small from a low temperature to a high temperature and at the same time easily form the resistance pattern. It is in.

The invention according to claim 1 of the present application is formed by heating and baking a material obtained by applying a resistive paste for an electric circuit formed by kneading carbon powder, an organic binder, and a solvent on a substrate. In the electric circuit resistance pattern in which the metal slider slides, the electric circuit resistance paste further includes a polyethylene resin that melts at a temperature lower than the firing temperature of the electric circuit resistance paste, and the organic binder and polyethylene. It is an electric circuit resistance pattern characterized by being mixed at a mixing ratio of 2% by weight or less with respect to the entire resin. The carbon powder may be, for example, only graphite powder, a mixed powder of graphite powder and carbon black powder, or only carbon black powder.

According to the first aspect of the present invention, even if the polyethylene resin is dispersed in the form of particles in the electric circuit resistance paste, it is liquefied when the electric circuit resistance pattern is formed by baking, and is near the surface by convection. The surface of the resistance pattern for the electric circuit is thinly covered so that the sliding motion of the slider sliding on the surface can be given lubricity. Can be reduced. Even if the ambient temperature rises, the frictional resistance does not rise, and the frictional resistance of the electrical circuit resistance pattern can be kept small from a low temperature to a high temperature.

  In addition, using the same method as the conventional method of forming a resistance pattern for electric circuits, that is, printing and baking a resistance paste for electric circuits on a substrate, no additional work such as application of grease is required, and friction resistance is reduced. A low resistance pattern can be formed.

In particular, the mixing ratio of the polyethylene resin is set to 2% by weight or less based on the total amount of the organic binder and the polyethylene resin, so that the resistance value of the electrical circuit resistance pattern formed using this electrical circuit resistance paste is almost increased It is suitable for keeping the frictional resistance small.

Hereinafter, embodiments of the present invention will be described in detail.
That is, the electrical circuit resistive paste of the present invention is an electrical circuit resistive paste obtained by kneading carbon powder, an organic binder, and a solvent, and the electrical circuit resistive paste is fired into the electrical circuit resistive paste. It is configured by mixing a thermoplastic resin that melts at a temperature lower than the temperature.

  Here, the carbon powder may be only graphite powder, may be powder obtained by mixing graphite powder and carbon black powder, or may be only carbon black powder. Carbon powders other than these may be used.

  A thermosetting resin is used as the organic binder. Specific examples of the thermosetting resin include a phenol resin and an epoxy resin.

  As the solvent, for example, ethylene glycol monobutyl ether, diethylene glycol monoethyl ether acetate or the like is used.

Thermoplastic resin, for example, the firing temperature of the electric circuit resistor paste is to be 165 ° C., using the material of the thermoplastic resin that melts at a temperature lower than that, the polyethylene resins, for example, polyolefin-based resin. The melting temperature (melting point) of the polyethylene resin is 90 to 130 ° C.

  The mixing ratio of the thermoplastic resin to the organic binder is such that the ratio of the thermoplastic resin is 2% by weight or less with respect to the total weight of the organic binder and the thermoplastic resin. This is because as the blending ratio of the thermoplastic resin increases, the specific resistance increases more than necessary as described below.

  In order to form an electric circuit resistance pattern using the electric circuit resistance paste according to the present invention, the electric circuit resistance paste is screened in a predetermined pattern shape on a substrate (whether a flexible substrate or a hard substrate). It is applied by printing or the like, and then the substrate is heated and baked to volatilize the solvent and simultaneously cure the organic binder.

  When the slider is slid on the electric circuit resistance pattern formed as described above, the frictional resistance is small and smooth sliding is possible. The reason is considered as follows. That is, the electrical circuit resistive paste according to the present invention contains a thermoplastic resin that melts at a temperature lower than its firing temperature, so that the electrical circuit resistive paste printed on the substrate 30 as shown in FIG. When the resistance pattern 40 is baked, the thermoplastic resin is liquefied and floats on the surface of the electrical circuit resistance pattern 40 by convection to thinly cover the surface of the electrical circuit resistance pattern 40 (thermoplastic resin layer 45). Then, as shown in FIG. 2B, when the sliding contact 51 of the slider 50 is pressed and slid at a predetermined pressure thereon, the sliding contact 51 on the surface of the thermoplastic resin layer 45 is pressed. The portion a melts by the pressure of the sliding contact 51 and frictional heat and becomes liquid, and exists between the electric circuit resistance pattern 40 and the sliding contact 51 as a lubricating oil. The friction coefficient can be reduced. When the sliding contact 51 passes, the thermoplastic resin layer 45 recrystallizes and covers the surface of the electric circuit resistance pattern 40.

  By the way, as a means for smoothing the sliding of the slider, a method of adding fluororesin powder into the electric circuit resistance paste is conceivable. When the electric circuit resistance paste to which a fluororesin is added is printed and baked on a substrate to form an electric circuit resistance pattern, the fluororesin has no melting point and is thermally decomposed at 300 ° C. or higher. As shown, the fluororesin powder 60 is exposed on the surface of the electric circuit resistance pattern 40 after firing. As shown in FIG. 3B, when the sliding contact 51 of the slider 50 slides on the electric circuit resistance pattern 40, the fluororesin powder 60 exposed on the surface is extended by the sliding contact 51. Thus, it is considered that lubricity can be obtained. However, in this case, since the fluororesin powder 60 which is a non-conductor covers the surface of the electric circuit resistance pattern 40, contact reliability between the slider 50 and the electric circuit resistance pattern 40 cannot be obtained.

  On the other hand, in the case of the electric circuit resistance pattern using the electric circuit resistance paste according to the present invention, as described above, the insulating thermoplastic resin layer 45 covering the surface is once liquefied to directly slide the contact. Since 51 contacts the electric circuit resistance pattern 40 on the lower side of the thermoplastic resin layer 45, contact reliability is obtained. In the present invention, since the thermoplastic resin layer 45 only needs to be thinly and uniformly formed on the surface of the electric circuit resistance pattern 40, the amount of the thermoplastic resin charged may be small. As it remains, the amount of input will increase.

  Next, as the electric circuit resistance paste, carbon powder made of graphite powder, an organic binder made of phenol resin, a thermoplastic resin made of polyethylene resin of 1% by weight with respect to the organic binder and the entire thermoplastic resin, Prepare a kneaded solvent made of ethylene glycol monobutyl ether and a small amount of additives (such as antifoaming agent), and measure the change in friction coefficient with temperature of the resistance pattern formed using the prepared resistance paste. The measurement result is shown by the solid line in FIG. The experimental method is the same as the experimental method of the above-described conventional example, and the sample 110 on which the resistance pattern is formed by printing the resistance paste on the substrate and baking it on the heater 100 shown in FIG. 1B is fixed. Then, the sliding contact 121 of the slider 120 made of an elastic metal plate (beryllium copper plate) is pressed onto the resistance pattern of the sample 110 with a predetermined pressure (30 gF), and in this state, the heater 100 and the sample 110 fixed to the heater 100 are fixed. The friction coefficient was measured by moving in the horizontal direction (arrow A direction) and detecting the horizontal force applied to the slider 120 at that time by the load cell. The measurement was performed when the ambient temperature was 23 ° C., 41 ° C., 59 ° C., 78 ° C., 98 ° C., and 115 ° C., and for the first and fifth reciprocations of the heater 100 and the sample 110. The resistance pattern has a specific resistance of 400 (Ω / □) [length × width = (1 cm × 1 cm), thickness = 10 μm, resistance value is 400Ω], and organic binder and carbon powder. A kneaded mixture was used.

  As shown by the solid line in FIG. 1A, the resistance pattern formed using the present invention has a smaller frictional resistance value than the conventional resistance pattern shown by the dotted line in FIG. It was confirmed that the temperature did not increase even when the ambient temperature increased, but rather gradually decreased. From the above, the resistance pattern for an electric circuit formed using the resistance paste for an electric circuit according to the present invention can always keep the frictional resistance of the resistance pattern small from a low temperature to a high temperature, even in a high temperature environment. Even if it exists, it turned out that the sliding feeling of a slider maintains a favorable state.

  FIG. 4 is a diagram showing a measurement result obtained by measuring a change in specific resistance when the content of the thermoplastic resin is changed. The measurement method is as follows. As a resistance paste for an electric circuit for forming a resistance pattern for an electric circuit, carbon powder made of graphite powder, an organic binder made of phenol resin, a thermoplastic resin made of polyethylene resin, and ethylene glycol monobutyl ether And kneading a small amount of additives (such as antifoaming agent), wherein the blending ratio of organic binder and carbon powder [weight of organic binder: weight of carbon powder] is [2: 1]. The blending ratio of the thermoplastic resin is 0.0% by weight with respect to the organic binder and the whole thermoplastic resin, for the one (plotted by a round dot) and the one of [4: 1] (plotted by a square dot). The specific resistance (Ω / □) of the resistance pattern for an electric circuit formed using these various electric circuit resistance pastes was varied between ˜5.0% by weight. Respectively were measured. The electrical circuit resistance pattern for which the specific resistance was measured has a length and width of 1 cm and a thickness of 10 μm.

  As shown in the figure, it can be seen that as the content of the thermoplastic resin in the organic binder increases, the specific resistance of the electric circuit resistance pattern increases rapidly. That is, when the content exceeds 2.0% by weight, the resistance value increases considerably (1.5 times or more) as compared with a resistance pattern for an electric circuit that does not contain any thermoplastic resin. Therefore, in order to make the rate of increase in resistance value as small as 1.5 times or less, the content of the thermoplastic resin in the organic binder is desirably 2.0% by weight or less.

FIG. 1A is a diagram showing temperature-friction coefficient characteristics of an electrical circuit resistance pattern formed using the electrical circuit resistance paste according to the present invention and a conventional electrical circuit resistance pattern, and FIG. These are figures which show the measuring method of a friction coefficient. FIG. 2A is a schematic enlarged cross-sectional view of an essential part of an electric circuit resistance pattern formed by using the electric circuit resistance paste according to the present invention, and FIG. 2B is a slide on the electric circuit resistance pattern. It is a principal part general | schematic expanded sectional view which shows the state at the time of the child | child 50 sliding. FIG. 3A is a schematic enlarged cross-sectional view of a main part of a resistance pattern for an electric circuit formed using a resistance paste for electric circuit formed by kneading fluororesin powder, and FIG. 2B is a resistance pattern for the electric circuit. It is a principal part general | schematic expanded sectional view which shows the state at the time of the slider 50 sliding on the top. It is a figure which shows the relationship between the content rate of the thermoplastic resin, and specific resistance in the resistance pattern for electrical circuits formed using the resistance paste for electrical circuits concerning this invention.

Explanation of symbols

30 Substrate 40 Resistance pattern 45 for electric circuit Thermoplastic resin layer 50 Slider 51 Sliding contact a Pressure contact portion 100 Heater 110 Sample 120 Slider 121 Sliding contact

Claims (1)

Electricity in which a metal slider slides on a substrate formed by heating and firing a resistor paste for an electric circuit formed by kneading carbon powder, an organic binder, and a solvent on a substrate. In the resistance pattern for circuits,
The electrical circuit resistor paste further includes a polyethylene resin that is melted at a temperature lower than the firing temperature of the electrical circuit resistor paste at a mixing ratio of 2% by weight or less with respect to the total of the organic binder and the polyethylene resin. A characteristic resistance pattern for an electric circuit.

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