JP2005217207A - Variable resistor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a variable resistor for improving linearity characteristics by reducing a contact resistance to be generated in a boundary part between an electrode pattern surface and a slider. <P>SOLUTION: This variable resistor is configured by containing nickel powder in an overcoat film 9 coating a conductive coating film 8 configuring electrode patterns 3a and 3c. Thus, the resistivity of the nickel coating film containing nickel powder can be made lower than the resistivity of a carbon coating film containing carbon. As a result, the contact resistance can be made lower than the case that the overcoat film 9 of the electrode patterns 3a and 3c is formed by carbon coating film in a conventional manner, and linearity characteristics can be improved. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a rotary variable resistor used for a position sensor or the like, and more particularly, a variable resistor having improved linearity characteristics by reducing contact resistance generated at a boundary portion between an electrode pattern surface and a slider. About.

  As shown in Patent Document 1 below, the rotary variable resistor that rotates on the substrate side has an inner electrode pattern and an outer electrode pattern formed by printing on the inner peripheral side and outer peripheral side of the substrate in a ring shape or an arc shape. A resistance pattern is printed in an arc shape between the inner electrode pattern and the outer electrode pattern. One end of the resistance pattern is connected to the inner electrode pattern, and the other end is connected to the outer electrode pattern.

  On the other hand, three sliders are provided on the fixed portion side, and each slider can slide on the surface of the inner electrode pattern, the resistance pattern, and the outer electrode pattern. Then, when the substrate is rotated in a state where a predetermined voltage is applied between the inner electrode pattern and the outer electrode pattern via the slider, the resistance changes in proportion to the moving distance (rotation angle). The value can be extracted as a voltage from the remaining slider.

  Although the following Patent Document 1 does not describe specific materials for the electrode pattern and the resistance pattern, the resistance pattern and the electrode pattern are usually made of a conductive paste such as carbon paste or silver paste as a baking plate or a glass epoxy plate. It is formed by applying it on an insulating substrate such as a screen printing method and baking it to remove the organic solvent in the paste.

  In the electrode pattern (conductive film) formed using the silver paste, the resistance value due to the entry of sulfide gas such as hydrogen sulfide or sulfurous acid gas into the gaps such as pinholes and holes formed in the electrode pattern Increase or disconnection may occur.

Conventionally, as a measure for preventing such sulfidation, generally, means such as coating (overcoating) the entire surface of the electrode pattern with a thin carbon layer has been taken.
JP-A-62-143403

However, the specific resistance of a carbon coating film formed by applying a carbon paste by a printing method and baking is much higher than that of a silver coating film formed by applying a silver paste by a printing method and baking. Specifically, the specific resistance of the silver coating film is about 5 × 10 ^{−5 to} 3 × 10 ⁻⁴ (Ω · cm), whereas the specific resistance of the carbon coating film is 1 × 10 ⁰ (= 1). ) To about 1 × 10 ³ (Ω · cm). For this reason, there exists a problem that the contact resistance produced between the said slider and an electrode pattern becomes high.

  The carbon coating usually contains conductive particles in which carbon black and graphite are mixed. In such a case, when the slider comes into contact with the carbon coating film on which the carbon black is deposited, the value of the contact resistance increases rapidly, while on the other hand, there is a slider on the carbon coating film on which the graphite is deposited. When contacted, the contact resistance value is likely to vary abruptly depending on the rotational position, and this variation is also caused by carbon powder scraped by sliding entering between the electrode pattern surface and the slider. Arise.

  As described above, in the conventional variable resistor, the contact resistance is high, and the variation due to the rotational position is large. Therefore, the linearity characteristic as the variable resistor (the characteristic of the output voltage with respect to the sliding distance (rotation angle) on the resistance pattern) ) Will decrease. Specifically, the linearity characteristic is about ± 2%.

  Accordingly, the present invention is to solve the above-described conventional problems, and provides a variable resistor capable of improving the linearity characteristics by reducing the contact resistance generated at the boundary portion between the electrode pattern surface and the slider. The purpose is to do.

The present invention provides a variable resistor provided with a substrate provided with a resistance pattern and an electrode pattern, and a fixed part provided with a slider that slides each of the resistance pattern and the electrode pattern.
The electrode pattern is composed of a conductive coating film containing silver powder formed on the substrate, and an overcoat coating film formed so as to cover an upper surface and a side surface of the conductive coating film,
The overcoat coating film comprises nickel powder and a binder resin.

  As described above, in the present invention, nickel powder is contained in the overcoat film covering the conductive coating film constituting the electrode pattern. The nickel coating containing nickel powder was found to be capable of lowering the specific resistance compared to the carbon coating containing carbon. As a result, the contact resistance can be reduced and the linearity characteristics can be improved as compared with the conventional case where the overcoat coating film of the electrode pattern is formed by the carbon coating film.

  Moreover, in this invention, it is preferable that the content rate of the said nickel powder in the said overcoat coating film is 22 vol% or more and 38 vol% or less. Thereby, the said contact resistance can be reduced more appropriately over a long period of time.

  In the present invention, the nickel powder preferably contains at least scaly nickel powder. By using an overcoat coating film containing scaly nickel powder, the sliding property of the slider on the overcoat coating film can be improved, and a long-life variable resistor is manufactured. I can do it.

  In the present invention, a dehydration condensation type thermosetting resin is preferably used for the binder resin, and a phenol resin is preferably used for the dehydration condensation type thermosetting resin. As a result, a nickel film having high conductivity (low specific resistance) can be obtained.

  Moreover, in this invention, it is preferable that the said electrode pattern is hot-pressed. Thereby, even if there is a pinhole or the like in the nickel coating film, the pinhole or the like can be appropriately blocked, and the sulfidation of the silver coating film constituting the conductive coating film can be suppressed.

  In the present invention, nickel powder is contained in the overcoat coating film covering the conductive coating film constituting the electrode pattern. The nickel coating film containing the nickel powder can have a lower specific resistance than the carbon coating film containing carbon. As a result, the contact resistance can be reduced and the linearity characteristics can be improved as compared with the conventional case where the overcoat coating film of the electrode pattern is formed by the carbon coating film.

  1 is an exploded perspective view showing a variable resistor of the present invention, FIG. 2 is a plan view showing a substrate as an embodiment of the present invention, and FIG. 3 is a sectional view of the substrate shown in FIG. FIG. 4 is a circuit configuration diagram when the variable resistor is used as a position sensor, and FIG. 5 is a diagram showing linearity characteristics of the variable resistor of FIG.

  A variable resistor 1 shown in FIG. 1 is used as a position sensor or the like, and includes a rotating body 2, a substrate 3, a support base 4, and a rotating shaft 5.

  The rotary body 2 has a circular base 2A and a knob 2B protruding from the base 2A in the Z2 direction shown in the figure. By rotating the knob 2B, the rotary body 2 can be rotated in the α1 direction and α2 shown in the figure. It has become.

  The substrate 3 is an insulating substrate made of a polyester resin or a polyamide resin. For example, an extruded substrate obtained by adding glass fiber and mineral (mineral) to polyethylene terephthalate (PET) can be used. The glass fiber is preferable in that it has a function of improving the strength of the substrate 3, and mineral is a preferable additive in that it has a function of reducing the difference in heat resistance between the extrusion direction and the width direction of the substrate 3. Further, the mineral is inexpensive and contributes to raising the deflection temperature under load, although not as much as glass fiber.

  As shown in FIG. 2, a hole 3 </ b> A is formed in the center of the substrate 3. On the inner peripheral side of the sliding surface (Z1 side surface in FIG. 1) 3B of the substrate 3, a first electrode pattern 3a having a substantially ring shape is formed around the hole 3A. A substantially ring-shaped second electrode pattern 3c is formed on the outer peripheral side of the sliding surface 3B. A resistance pattern 3b having a substantially arc shape (a shape lacking a part of the ring shape) is formed between the first electrode pattern 3a and the second electrode pattern 3c. One end of the resistance pattern 3b is connected to the first electrode pattern 3a, and the other end of the resistance pattern 3b is connected to the second electrode pattern 3c. That is, the first electrode pattern 3a and the second electrode pattern 3c are respectively connected to both ends of the resistance pattern 3b.

  Here, the first and second electrode patterns 3a and 3c are composed of a conductive coating film 8 using silver powder as a conductive filler, and an overcoat coating film 9 covering the upper surface and side surfaces of the conductive coating film 8. Yes. In the substrate 3 shown in FIG. 2, for example, the center angle between one end and the other end of the resistance pattern 3b is set to 270 °.

  The support base 4 shown in FIG. 1 is formed of a synthetic resin or the like. A concave portion 4A is provided on the Z2 side surface of the support base 4, and a central hole 4B is formed at the center of the concave portion 4A. Also, a rectangular hole 4C is formed inside the recess 4A, and three sliders 6a, 6b, 6c appear from the hole 4C. The sliders 6a, 6b, and 6c are insert-molded inside the support base 4 so as to appear from the hole 4C.

  The sliders 6a, 6b, and 6c are obtained by nickel-plating phosphor bronze and silver-plating the surface, and then bending the tip into a substantially circular shape. The sliders 6a, 6b, and 6c have elasticity in the Z1-Z2 direction shown in the drawing, and can respectively press the surfaces of the first electrode pattern 3a, the resistance pattern 3b, and the second electrode pattern 3c. is there.

  Terminals 7 a, 7 b, 7 c extending in the Y 2 direction are provided at the end of the support base 4, and the terminals 7 a, 7 b, 7 c are inside the support base 4 and the sliders 6 a, 6 b, 6 c. Are connected to each. Accordingly, a voltage can be applied between the sliders 6a and 6c that are electrically connected to both ends of the resistance pattern 3b through the terminals 7a and 7c, respectively, and an output can be taken out from the terminal 7b through the slider 6b. ing.

  As shown in FIG. 1, the variable resistor 1 is assembled by inserting the rotating shaft 5 through the center hole 4B of the support base 4 and the hole 3A of the substrate 3, and further on the surface of the rotating body 2 on the Z1 side in the figure. This is done by inserting into a hole (not shown) provided. The surface of the substrate 3 on the Z2 side is fixed to the rotating body 2, and is integrally supported with the rotating body 2 so as to be rotatable in the α1 and α2 directions.

  As shown in FIG. 3, the electrode patterns 3 a and 3 c are configured by a two-layer structure of a conductive coating film 8 and an overcoat coating film 9 covering the conductive coating film 8, while the resistance pattern 3 b is It is a single layer structure of the resistance coating film 10. In the present invention, the “coating film” refers to the film itself constituting the electrode patterns 3a and 3c and the resistance pattern 3b which are final products, and does not mean a state during the manufacturing process. The state during the manufacturing process is called “paste”.

  First, the resistance pattern 3b will be described. The resistance coating film 10 constituting the resistance pattern 3b has a configuration in which carbon powder is mixed in a binder resin. As the carbon powder contained in the resistance coating film 10, the same powder shape may be used, or two or more types having different shapes may be used. For example, carbon black and graphite are selected as the different shapes. As the binder resin, a phenol resin which is a dehydration condensation type thermosetting resin is selected.

  Next, the conductive coating film 8 constituting the electrode patterns 3a and 3b has a configuration in which silver powder is mixed in a binder resin. For example, a phenol resin which is a dehydration condensation type thermosetting resin is used as the binder resin. The conductive coating 8 containing silver powder has a very low specific resistance.

  On the other hand, the overcoat coating film 9 has a configuration in which nickel powder is mixed in a binder resin. A nickel coating film containing nickel powder (hereinafter, nickel coating means a coating film having a binder resin and nickel powder) is a carbon coating film containing carbon powder ( Hereinafter, it is known from experiments described later that the specific resistance can be significantly reduced as compared with a carbon coating film (which means a coating film having a binder resin and carbon powder).

Moreover, the resistance value increase due to oxidation of the nickel coating stops midway. By leaving the nickel coating film in a humidity atmosphere (in the experiment described later, the temperature is set to 60 ° C. and the humidity is 90 to 95% RH), the surface of the nickel coating film is oxidized and has a specific resistance. Although the value rises by an order of magnitude from the original specific resistance, since the original specific resistance is 1 × 10 ⁻¹ to 1 × 10 ⁻² (Ω · cm) level, it is 1 × 10 in an originally unoxidized state. Compared with a carbon coating film having a specific resistance of about ⁰ to 1 × 10 ³ (Ω · cm), it can still maintain a low specific resistance even when oxidized.

  As shown in FIG. 4, a contact resistance r1 is provided between the first electrode pattern 3a and the slider 6a, and a contact resistance r2 is provided between the second electrode pattern 3c and the slider 6c. Each occurs.

  However, if a nickel coating having a specific resistance lower than that of the carbon coating is used as the overcoat coating 9 as in the present invention, the sliders 6a and 6c slide on the conductive patterns 3a and 3c. The contact resistances r1 and r2 generated at the time can be reduced as compared with the conventional case. In addition, since the contact resistances r1 and r2 can be greatly reduced as compared with the prior art, variations in contact resistance due to the rotational position can be relatively reduced. As a result, as shown in FIG. 5, the sliding distance (rotation angle θ) of the slider 6b and the output voltage Vo can be kept in a favorable proportional relationship, and the linearity characteristic (linearity) is improved as compared with the conventional case. be able to. In the present invention, the linearity characteristic can be improved to about ± 1%.

In this invention, it is preferable that the content rate of the nickel powder in the said overcoat coating film 9 exists in the range of 22 vol%-38 vol%. According to the experimental results to be described later, by setting the content of nickel powder in the nickel coating within the range of 22 vol% to 38 vol%, even when left in a humidity atmosphere for 500 hours, 1 × 10 ⁰ (Ω · cm) or less, that is, a specific resistance lower than that of the carbon coating film can be obtained. Moreover, the specific resistance in an initial state can be made into 2 * 10 ^<-2 > (ohm * cm) or less by making the content rate of the said nickel powder into the range of 25 vol%-35 vol%, and it is preferable.

  The powder shape of the nickel powder includes a flat sugar shape (hereinafter referred to as spike shape), a scale shape, a spherical shape, and a filament shape having a large number of protrusions on a spherical surface. It is preferable to contain nickel powder. Since the scaly nickel powder has a flat shape, the flat surface portion having the largest area of the scaly nickel powder is likely to be arranged along the direction parallel to the surface of the overcoat coating film 9. As a result, the slidability of the sliders 6a and 6c on the overcoat coating film 9 is improved, and it is appropriate even if the load on the electrode patterns 3a and 3c of the sliders 6a and 6c is small. Further, the sliders 6a and 6c can be appropriately slid on the electrode patterns 3a and 3c. In addition, if grease (lubricant) is applied on the overcoat film 9, the wear resistance can be improved, and a long-life variable resistor can be manufactured.

  The nickel coating film may contain a small amount of silver powder or carbon powder in addition to the nickel powder. Silver powder is useful for preventing oxidation, but if it is added too much, a problem of sulfidation occurs. On the other hand, when carbon powder is contained, the slidability of the sliders 6a and 6c on the overcoat coating film 9 can be improved, but if it is excessively added, a problem of increased contact resistance occurs. For this reason, it is preferable to suppress the content of the silver powder and the carbon powder to about several vol% in the overcoat coating film 9 (when both silver powder and carbon powder are contained, both are several vol%).

  The binder resin in the overcoat coating 9 is preferably a dehydration condensation type thermosetting resin, and specifically, the dehydration condensation type thermosetting resin is preferably a phenol resin. preferable. By using a dehydration-condensation type thermosetting resin as the binder resin, the curing shrinkage can be increased, and the overcoat coating film 9 having high conductivity (low specific resistance) can be produced.

  The electrode patterns 3a and 3c described above are formed by printing and baking a conductive paste by a screen printing method or the like. The conductive coating film 8 is formed by printing and baking a silver paste on the substrate 3 by a screen printing method or the like. The overcoat coating film 9 is formed by applying nickel paste on the upper surface and side surfaces of the conductive coating film 8. It is printed and printed by a printing method or the like.

  The material constituting the nickel paste will be mainly described. The nickel paste is composed of nickel powder, a binder resin, a solvent, and other additives.

  The nickel powder preferably has an average particle size of 10 μm or less. When the average particle diameter exceeds 10 μm, a large powder is partially included, which is not suitable for screen printing. More preferably, the average particle diameter is 5 μm or less. The nickel powder may be spiked, scaly, spherical, or filament-shaped. In the paste, only one of these shapes may be used, or two or more may be used. May be.

  When two or more kinds of nickel powders having different shapes are mixed, it is preferable to use scaly nickel powder and nickel powder of other shapes. The scale-like nickel powder is obtained by flattening, for example, spherical nickel powder.

  As the binder resin, in order to obtain a highly conductive overcoat coating film 9, a curable resin having a large curing shrinkage is desired. Specifically, it is preferable to use a dehydration condensation type thermosetting resin. As the dehydration condensation type thermosetting resin, a resol type phenol resin, a resol type cresol resin, a xylene modified phenol resin, a furan resin, a phenol modified furan resin, a melamine resin or the like is used. Among these, it is preferable to use a phenol resin.

  The solvent is one that dissolves the binder resin and does not dry on the substrate 3. Specific examples include butyl carbitol acetate, carbitol, methyl triglyme, triglyme, isophorone, and anone. As the additive, a urethane-based dispersant for assisting the dispersion of the nickel powder, a silicone-based antifoaming agent for suppressing the generation of bubbles in the paste, and the like are used.

  When the nickel paste composed of the above materials is screen-printed and baked so as to cover the conductive coating film 8, the solvent constituting the paste evaporates and does not remain in the coating film, and the additive remains. Even a trace amount of 0.1 vol% or less. For this reason, the overcoat coating film 9 after printing and baking is almost composed of a binder resin and nickel powder.

The conductive coating 8 and the resistance coating 10 are also formed by the same method as the overcoat coating 9.
In the present invention, it is preferable that the electrode patterns 3a and 3c composed of the conductive coating film 8 and the overcoat coating film 9 are hot-pressed after drying and then heat-cured. By performing hot pressing, even if there is a pinhole or the like in the overcoat coating 9, the pinhole or the like is blocked by the hot pressing, and the conductive coating 8 containing silver powder is sulfided through the pinhole. Can be prevented.

  The hot pressing is preferably performed not only on the electrode patterns 3a and 3c but also on the resistance pattern 3b.

  The hot press is performed with a mold configured such that a pair of mirror surfaces are opposed to each other. In the hot press step, the substrate 3 is placed between the mirror surfaces of the hot press mold, and the substrate 3 is pressed while being heated between the mirror surfaces of the mold.

  When sliding, a contact resistance is also generated between the resistance pattern 3b and the slider 6b, but an input of a detection circuit such as an A / D converter of a microprocessor (not shown) connected to the terminal 7b shown in FIG. Since the impedance is as large as several MΩ, the influence of the contact resistance can be ignored when the output voltage Vo is detected by the detection circuit.

  In the above embodiment, a rotary variable resistor is shown and described, but the present invention is not limited to this, and conductive patterns and resistance patterns are provided on the substrate in parallel straight lines. It may be a variable resistor in which the slider moves linearly along the pattern.

The nickel pastes of Examples 1 to 7 and Comparative Examples 1 to 3 shown in Table 1 below were produced.

  The used nickel powder had a spike shape, and the average particle size was 5 μm. Further, a resol type phenol resin was used as the binder resin, butyl carbitol acetate was used as the solvent, and a small amount of additives such as an antifoaming agent were added.

  Five nickel pastes of each of Examples 1 to 7 and Comparative Examples 1 to 3 were applied onto a substrate by screen printing and cured by heating at 200 ° C. for 20 minutes to obtain a nickel coating film. Table 2 shows the volume content of the nickel powder contained in the nickel coating film in each example and comparative example.

  And the specific resistance in each nickel coating film is measured, and FIG. 6 shows the relationship between the volume content of nickel powder in the nickel coating film and the specific resistance.

As described above, since five nickel coatings of each of the examples and comparative examples were manufactured, a plurality of specific resistance values are plotted against the volume content of the same nickel powder in the graph. For example, when the content of nickel powder is 15 vol%, there are only two specific resistance values plotted, but this is because the other three samples have high specific resistance values of 1 × 10 ⁵ (Ω · cm) or more. In some cases, the plot cannot be plotted on the graph, or the plots overlap because the volume resistivity of other nickel powders shows the same specific resistance value for a plurality of samples.

As shown in FIG. 6, if the nickel powder in the nickel coating is set within the range of 25 vol% to 35 vol%, the coating specific resistance value can be reliably reduced to 2 × 10 ⁻² (Ω · cm) or less. I understood.

  The specific resistance value is increased when the content of the nickel powder is less than 22 vol%, for example, because the conductive path (conductive path) in the coating film is small due to the decrease in the amount of nickel powder. On the other hand, when the content of the nickel powder is increased, for example, more than 38 vol%, the specific resistance value increases. Conversely, the binder resin contained in the coating film becomes too small, and the shrinkage of curing is weak, so that the space between the nickel powders is appropriate. This is probably because the contact resistance between the nickel powders cannot be effectively reduced because they cannot be brought into contact with each other.

  The nickel coating films of Examples 1 to 7 and Comparative Examples 1 to 3 were allowed to stand in a humidity atmosphere of 90 to 95% RH at a temperature of 60 ° C. for a maximum of 500 hours. FIG. 7 shows whether the value changes.

As shown in FIG. 7, in all the samples, it was found that the coating resistivity value increased as the standing time in the humidity atmosphere increased. This is considered to be because the nickel coating was oxidized, but in Examples 1 to 7 (all nickel contents are in the range of 22 vol% to 38 vol%), even if left in the above humidity atmosphere for 500 hours. The specific resistance could be kept at 1 × 10 ⁰ (= 1) Ω · cm or less, and a specific resistance sufficiently smaller than that of the carbon coating film containing carbon powder could be obtained.

Therefore, in the present invention, good moisture resistance can be obtained by setting the content of the nickel powder contained in the nickel coating film within the range of 22 vol% to 38 vol%. Further, preferably, if it is set within the range of 25 vol% to 35 vol%, the specific resistance value of the nickel coating film in the initial state can be 2 × 10 ⁻² (Ω · cm) or less, and even after being left in a humidity atmosphere. It was found that the specific resistance value can be set to a sufficiently small value.

  Next, four nickel pastes of Examples 8 to 11 made of the following materials were manufactured, and these nickel pastes were screen-printed and applied onto a substrate, followed by heat curing at 200 ° C. for 20 minutes to form a nickel coating film. Got.

[Example 8]
Resol type cresol resin 64 parts by mass Spike-like nickel powder (average particle size 5 μm) 170 parts by mass Scale-like nickel powder (thickness 1 μm, width 15-20 μm) 30 parts by mass Filamentous nickel powder (average particle size 3 μm) 18 parts by mass Calvi Toll 82 parts by weight Additive 4 parts by weight

[Example 9]
Resol type phenol resin 64 parts by mass Spike-like nickel powder (average particle size 5 μm) 140 parts by mass Filamentous nickel powder (average particle size 3 μm) 78 parts by mass Carbitol 88 parts by mass Additive 4 parts by mass

[Example 10]
Xylene-modified phenolic resin 64 parts by weight Scale-like nickel powder (thickness 1 μm, width 15-20 μm) 50 parts by weight Filamentous nickel powder (average particle size 3 μm) 168 parts by weight Carbitol 80 parts by weight Additive 4 parts by weight

[Example 11]
Resol type phenol resin 64 parts by weight Spherical nickel powder (average particle size 5 μm) 80 parts by weight Filamentous nickel powder (average particle size 3 μm) 138 parts by weight Carbitol 75 parts by weight Additive 4 parts by weight

  In addition, all content of the nickel powder in the nickel coating film of the said Examples 8-11 is 30 vol%, and is the same as content of the nickel powder in the nickel coating film in Example 4.

  The nickel coating films of Example 4 and Examples 8 to 11 were left in a humidity atmosphere of 90 to 95% RH at a temperature of 60 ° C. for a maximum of 500 hours. FIG. 8 shows the measurement.

In each Example from which the shape of the nickel powder contained in a nickel coating film differs from FIG. 8, even if it leaves to the said humidity atmosphere for 500 hours, a coating-film specific resistance value is 1 * 10 < ⁰ > (= 1) ((omega | ohm) It was found that it can be suppressed to cm) or less.

An exploded perspective view showing the variable resistor of the present invention, The top view which shows the board | substrate as embodiment, Sectional drawing in the AA line of FIG. Circuit configuration diagram when using a variable resistor as a position sensor, The figure which shows the linearity characteristic of the variable resistor of FIG. A graph showing the relationship between the volume content of nickel powder in the nickel coating and the specific resistance of the coating, A graph showing the relationship between the humidity test standing time and the coating specific resistance value of each Example and Comparative Example in which the volume content of nickel powder is different, A graph showing the relationship between the humidity test standing time and the specific resistance value of each example in which the shape of the nickel powder is different,

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Variable resistor 2 Rotating body 3 Board | substrate 3a 1st electrode pattern 3b Resistance pattern 3c 2nd electrode pattern 4 Support base 5 Rotating shaft 6a, 6b, 6c Slider 7a, 7b, 7c Terminal 8 Conductive coating film 9 Overcoat coating film 10 Resistance coating film r1 Contact resistance between the first electrode pattern and the slider r2 Contact resistance between the second electrode pattern and the slider

Claims (6)

In a variable resistor provided with a substrate provided with a resistance pattern and an electrode pattern, and a fixed portion provided with a slider that slides each of the resistance pattern and the electrode pattern,
The electrode pattern is composed of a conductive coating film containing silver powder printed and formed on the substrate, and an overcoat coating film formed by printing so as to cover the upper surface and side surfaces of the conductive coating film,
The overcoat coating film has a nickel resistor and a binder resin and is configured to have a variable resistor.   2. The variable resistor according to claim 1, wherein a content of the nickel powder in the overcoat coating film is 22 vol% or more and 38 vol% or less.   The variable resistor according to claim 1, wherein the nickel powder includes at least scaly nickel powder.   4. The variable resistor according to claim 1, wherein a dehydration condensation type thermosetting resin is used as the binder resin.   The variable resistor according to claim 4, wherein a phenol resin is used for the dehydration condensation type thermosetting resin.   The variable resistor according to claim 1, wherein the electrode pattern is hot-pressed.

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