JPS63158809A - Method of hardening resistance element for variable resistor - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed description of the invention]

[Industrial Application Field 1] The present invention relates to a method for heating a resistance element of a variable resistor to harden its resistor layer.

[Prior art 1] A resistance element in a variable resistor is made by forming a resistor layer on the surface of a substrate made of, for example, a phenol resin laminate, and this resistor layer is made of carbon powder such as carbon black or graphite. and a binder resin such as phenol resin or epoxy resin are dispersed in a solvent to form a resistive ink by patterning by printing or other means. The substrate is heated to cure the body layer. In order to harden this resistor layer, a conveyor is provided to convey the workpiece, a tunnel-shaped furnace is provided in the middle of the conveyance path of the conveyor, and the interior of the furnace is heated, for example, by a heater, etc. Conventionally, it has been known to heat the resistor layer using a heating means such as a near-infrared lamp, pass the substrate through the furnace, and heat the work to harden the resistor layer. There is. [Problem to be Solved by the Invention 1] In the prior art system described above, the conveyor is inserted into the furnace, so both ends of the furnace are connected to the inlet and outlet of the workpieces transported by the conveyor. In order to become
Must be left open. Therefore, the heat from these openings at both ends is released to the outside, and the cold conveyor enters the entrance, so the temperature distribution inside the furnace is not uniform, with the center being high and the temperature being high at both ends. part is in a low state. Furthermore, even in the central part of the furnace, there may be a temperature difference between a place close to the heat source and a place far from the heat source, making it difficult to strictly control the temperature inside the furnace. If the temperature distribution in the furnace cannot be maintained uniformly, the degree of hardening of the resistor layer will be uneven, resulting in variations in the resistance value after hardening, making it difficult to maintain a constant quality resistor element. This may cause inconveniences such as not being able to obtain the required information. For this purpose, some furnaces are known in which a blower or the like is installed inside the furnace to agitate the air inside, but even if such a configuration is adopted, it is not always possible to strictly control the temperature distribution inside the furnace. It was not possible to maintain it in a uniform state. In addition, the temperature distribution in the direction of movement of the belt conveyor is not uniform, and the temperature at both ends of the furnace is low in the shape of a mountain, so the heating time to sufficiently harden the resistance element is long, at about 20 minutes. Therefore, the overall length of the furnace becomes correspondingly longer, and there is also the problem that the installation area of the furnace is required to be large. The present invention has been made in view of the above points, and it is an object of the present invention to provide a method for curing a resistance element for a variable resistance base, which allows a workpiece to be heat-cured under uniform temperature conditions. [Means for Solving the Problems] In order to achieve the above-mentioned object, the present invention provides a method for curing a resistor layer by heating a workpiece consisting of a substrate on which the resistor layer is formed. The workpiece is first passed through a vapor phase heating tank maintained at a low temperature below the curing temperature of the resistor layer, and then transferred to a vapor phase heating tank at a high temperature at least as high as the curing temperature of the resistor layer. ,
The feature is that the resistance layer is cured by heating.

【Example】

Embodiments of the present invention will be described in detail below with reference to the drawings. First, FIG. 1 shows the configuration of a vapor phase heating tank for carrying out the method of the present invention. In the figure, reference numeral 1 indicates a heating tank with an open upper end, and a fluorocarbon liquid 2 is stored in the heating tank 1 as a liquid for forming a vapor phase. Here, the fluorocarbon must not react with or dissolve the resistance ink described later, and for this purpose, an inert fluorocarbon liquid is used. In order to heat this fluorocarbon liquid 2, a heater 3 is installed at the bottom of the heating tank l.
A heater 3 is provided to vaporize the fluorocarbon liquid 2, and an upper part of the heating tank 1 is configured to condense the fluorocarbon vapor and collect it into the tank. A cooling coil 4 is installed for this purpose. Accordingly, in the present invention, as shown in FIG. 2, two vapor phase heating tanks 1 having the above-mentioned configuration are installed in series, and the first vapor phase heating tank 1a has a temperature of about 120 to 170°C. A fluorocarbon liquid with a relatively low boiling point is stored in the second vapor phase heating tank 1b, and a fluorocarbon liquid with a high boiling point of 200 to 240°C is stored in the second vapor phase heating tank 1b. Then, the work lO to be heated and hardened is conveyed to the conveyor 11,
In order: 1. ``While being conveyed through the second vapor phase heating tanks 1a and 1b, curing is performed by heating. In each of the heating tanks 1a and lb described above, in order to heat the workpiece 10 at a constant temperature, each heating tank 1 is
A saturated vapor phase is formed in portions a and lb, and the conveyor 11 passes through this saturated vapor phase formation section. The apparatus for carrying out the method of the present invention has the above-mentioned configuration. Next, a method for curing a workpiece IO using this apparatus will be explained. Here, the work 10 has a resistor layer 1 on the surface of the substrate 10a.
The substrate 10a is made of thermosetting resin such as phenol resin or epoxy resin, ceramic, or the like. On the other hand, the resistor layer tob is made of a high dielectric constant binder resin made of phenol resin, cresol resin, melamine resin, thermosetting acrylic resin, thermosetting polyester resin, or a resin modified by combining two or more of these resins, carbon black, It is formed by using a resistance ink made by dissolving conductor powder such as graphite powder or metal powder in a solvent, and patterning this resistance ink into an arc shape or a straight line shape on the substrate 10a by means such as screen printing. . The workpiece 10 with the resistor layer 10b patterned on the substrate 10a as described above is conveyed by the conveyor 11 and undergoes a drying process of drying at a temperature of about 120°C, for example, and then undergoes a curing process. will be transported towards. On the other hand, in each heating tank 1a, lb, a saturated vapor phase is formed inside the fluorocarbon liquid 2 by heating the fluorocarbon liquid 2 with a heater 3 so as to maintain it at its boiling point. By forming a saturated vapor phase in this manner, the interiors of tanks 1a and lb are maintained at a uniform temperature at the boiling point of the fluorocarbon. Therefore, when the work lO is conveyed by the conveyor 11 and guided into the first heating tank la, the work 10 is preheated. In this preheating, if the workpiece 10 is rapidly raised to the curing temperature, the substrate 10a may warp, and the solvent remaining after the resistive ink dries will foam, causing curing to begin before it can be completely removed. It is possible to prevent surface defects such as unevenness on the surface of the resistor layer 10b, and also to prevent stress strain from occurring inside the element due to rapid curing, resulting in product failure over a long period of time. When used in a humid condition, it is possible to prevent the inconvenience that the resistance value changes during the process of relaxing stress and strain. In this way, the first heating tank 1
While being preheated in a, it is necessary to keep the resistor layer 10b from curing slowly. Therefore, in the first heating tank 1a, the temperature should be lower than the curing temperature of the binder resin in the resistance ink. low temperature state, i.e. 12
A fluorocarbon liquid having a boiling point of 0 to 170°C, preferably about 165°C is used. The workpiece IO preheated in the first heating tank 1a as described above is conveyed to the conveyor 11 and then guided to the second heating tank 1b. The carbon liquid has a boiling point higher than that of the first heating tank 1a, that is, 200 to 250°C, preferably 215°C.
Use a material that can be maintained at a high temperature higher than the curing temperature of the binder resin in the resistance ink. As a result, when the workpiece IO is introduced into the second heating tank 1b, the resistor layer 1Ob is sufficiently heated and hardened. Since a saturated vapor phase of fluorocarbon is formed in the second heating tank lb, the area where the workpiece 10 is located is maintained at a constant temperature, and for this reason, the resistor Since the layer 10b is heated uniformly, the entire layer 10b is uniformly cured, and a resistive element of constant and good quality without any disadvantages such as variations in resistance value can be formed. Here, in the first heating tank 1a described above, the entire workpiece 10 is preheated, and the solvent is released as much as possible from the resistance ink printed to form the resistor layer 10b on the workpiece 10. , and to proceed with gradual curing, and for this purpose, the first heating tank la of the workpiece 10 is
The residence time in the heating tank 1b may be shorter than that in the second heating tank 1b, which will be described later. Moreover, in the second heating tank 1b,
The workpiece IO, which has been preheated in the first heating tank 1a, is further heated to a high temperature and left there for a period of time necessary to sufficiently harden the resistor layer 10b. Therefore, in order to form a resistance element for variable resistance heating, the residence time in the first heating tank 1a should be about 3 minutes, and the residence time in the second heating tank 1b should be about 3 to 5 minutes. . Therefore, the overall heating time can be shortened, and the installation area of the device can also be small. The solvent is not completely discharged in the first heating tank 1a, and even if the solvent foams when heated in the second heating tank 1b, the solvent is not completely released in the fluorocarbon atmosphere with low surface tension. Since the foam is heated, the fluorocarbon adheres to the four parts created by this foaming, smoothing the surface, and since fluorocarbon is a lubricating material, it has a low resistance. When used as an element, when the slider is slid on the resistor layer 10b, the slider can smoothly slide. Moreover, the first. Since the insides of the second heating layers 1a and lb are both in a vapor phase, there is no risk of foreign matter such as dust getting into them, so that the curing work can be performed in a dust-free environment. Therefore, there is less dust sticking to the resistive element, and the noise level that occurs during operation of the variable resistor as a product can be significantly reduced. Effects of the Invention 1 As detailed above, the present invention uses two vapor phase heating tanks, the first heating tank preheats the workpiece, and the second heating tank preheats the resistor layer. Since the workpiece is cured by heating under uniform temperature conditions, it is possible to improve the quality of the resistance element and the yield, and the workpiece can be heated gradually. As a result, the resistor layer can be formed smoothly, and the sliding properties of the slider are improved.
In addition, stress distortion and the like are not generated in the substrate, and various effects such as the ability to extend the life of the element are achieved.

[Brief explanation of the drawing]

FIG. 1 is an explanatory diagram of the configuration of a vapor phase heating tank used to carry out the method according to the present invention, and FIG. 2 is an explanatory diagram showing the arrangement of the heating tanks. l: heating tank, 1a: first heating tank, lb: second heating tank, 2: fluorinated carbon liquid, lO: workpiece, lOa: substrate, lOb: resistor tank, ll: conveyor. Figure 1 Figure 2

Claims (2)

[Claims] (1) A method for curing a resistor layer by heating a work consisting of a substrate on which the resistor layer is formed, in which the workpiece is maintained in a low temperature state below the curing temperature of the resistor layer. A resistance element for a variable resistor, characterized in that the resistance layer is heated and cured by passing through a heating tank and then transferring to a vapor phase heating tank at a temperature at least equal to the curing temperature of the resistor layer. curing method. (2) A fluorocarbon liquid is used as the heating medium in the vapor phase heating tank,
2) A method for curing a resistance element for a variable resistor as described in section 2).