JPH01302702A - Formation of protective film or thermistor - Google Patents

Abstract

PURPOSE:To prevent erroneous operation by forming an underlayer between a thermistor unit and an overlayer, drying the underlayer to form the overlayer of a uniform thickness, and melting the overlayer to ensure that the surface of a thermistor element is insulated. CONSTITUTION:An underlayer 6 is formed by spraying a primer containing a fluorochemical around the peripheries of a thermistor element 1, metal pillars 3, 4, and a base body 2. The underlayer 6 is dried in a furnace whose temperature is 100-150 deg.C. On the periphery of the dried underlayer 6, a powder resin whose grain size is 10-15mum, melted at 300-350 deg.C and having a repellent, such as an ethylene tetrafluorideperfluoroalkoxyethylene copolymeric resin is arranged by an electrostatic coating as an overlayer 7. Accordingly, it is ensured that the surface of the thermistor element is insulated, thereby preventing the erroneous operation of the thermistor.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a method for forming a protective coating layer of a thermistor unit having corrosion resistance for use in electrical open circuits, microwave ovens, and the like.

BACKGROUND ART In general, thermistor units used in electric ovens, microwave ovens, etc. are installed in open refrigerators or exhaust hoods, and are used to detect air temperatures from room temperature to about 300°C. In other words, this type of thermistor unit has the characteristic that the resistance value of the thermistor element changes depending on the temperature.Using this characteristic, an electric field is applied to both ends of the thermistor element, and the change in voltage is captured by the control circuit. , is a temperature detection means for controlling the amount of power of the heating element that heats the inside of the open refrigerator. In addition, the open interior of the refrigerator and the exhaust hood not only create a high-temperature atmosphere of nearly 500°C, but also condense from moisture generated from one food item, and easily attract dirt such as oil and salt scattered from the food item. It is under an extremely harsh corrosive environment.

Conventionally, thermistor units used in this kind of harsh environment have one structure: (1) For example, a thermistor element is made by sandwiching a heat-sensitive element between a pair of electrode bodies made of Siemeno wire and sealed with glass, and this thermistor element. The electrode body is fixed by spot cutting to a pair of metal supports that stand upright in parallel at a predetermined distance to a heat-resistant insulating base provided to facilitate installation on an open wall or the like. Furthermore, in order to prevent malfunction, corrosion, or high-temperature oxidation due to a decrease in insulation caused by the adhesion of moisture or salt, and to suppress corrosion and disconnection of the electrode body and the gold maple support due to the electrolytic corrosion phenomenon caused by the application of a DC electric field. A heat-resistant enamel paint containing a solvent such as polyimide, polyamideimide, or olicone was applied to the surface of the thermistor unit or throat by dip or spray methods, and then dried and baked to form a protective coating layer. .

The problem that the invention seeks to solve However, conventional thermistor units.

(,]) When the protective coating layer is formed by the dip method.

Stains tend to form in areas where dimensions change, and when those areas dry and bake, they sometimes cause spray and form pinholes, allowing moisture and salt to penetrate into the thermistor element from these areas.

(l) A protective coating layer is formed by a spray method.

Because the thickness of the film tends to become thinner in areas where there are gaps or shadows,
It is difficult to obtain a film that is water resistant and resistant to high temperature oxidation.

(c) Enamel paints containing solvents will form pinholes when the solvent evaporates from the film during drying, so the coating process, drying process, and baking process will not form a film even if the process is repeated several times. Due to the fact that it is impossible to completely eliminate defects, the insulation on the element surface may deteriorate, causing malfunctions, oxidation at high temperatures, or the electrode body may easily break due to electrolytic corrosion, so durability during long-term use may be affected. In addition to poor performance, the coating workability of the protective coating layer was also poor.

An object of the present invention is to provide a thermistor unit that eliminates the above-mentioned drawbacks of the conventional example.

Means for Solving the Problems The present invention has been made to solve the above problems, and the thermistor element is electrically connected and held to a metal support provided by penetrating the base at a predetermined interval. In the method for forming a protective coating layer of a thermistor unit, the protective coating layer is provided around the outer periphery of the thermistor unit, the protective coating layer consisting of a base layer and a top layer, a first step of forming the protective coating layer into a base layer by spray coating; a second step of drying the base layer;

A third step of forming a top layer on the outer periphery of the base layer by electrostatically coating a powder resin with a particle size of 10 to 50μ that melts at 300 to 350°C and has water repellency;
It is formed from a fourth step of melting at 50° C. to form a film.

Function The method for forming the protective coating layer of the thermistor unit of the present invention is as described above, and the first step of spray coating forms a base layer between the thermistor unit and the upper layer to improve adhesion and corrosion resistance reliability. The second step of drying the base layer completely volatilizes the solvent contained in the base layer, and the third step of electrostatically coating the powder resin forms the top layer of a film with a uniform thickness. The fourth step of melting serves to melt the upper layer without pinholes without overcoming the change in the characteristics of the thermistor element.

Example An embodiment of the present invention will be described below in detail with reference to the drawings.

FIG. 1 shows an embodiment of a method for forming a protective coating layer for a thermistor unit according to the present invention.

1 is a heat-sensitive element having negative resistance-temperature characteristics mainly composed of oxides of transition metals such as iron, nickel, manganese, and cobalt, sandwiched between a pair of electrode bodies 1a and Ib at both ends and sealed with glass. 3゜4 is the electrode body ia of the thermistor element 1, Ibk is a metal support made of stainless steel, Kovar, etc. that maintains electrical connection; 2 is a metal support filter; 4
5 is a thermistor element 1. The thermistor element 1. A base layer 6 made of polyimide, polyamideimide, etc. containing a fluorine compound is spray-coated on the surfaces of a pair of metal support filters 4 and the base 2, and a base layer 6 made of polyimide, polyamideimide, etc. containing a fluorine compound is melted at 300 to 350°C and has water repellency. This is a protective coating layer consisting of a top layer 7 formed around the outer periphery of a base layer B by electrostatic coating of a powdered ethylene perfluoroalkoxyethylene copolymer resin.

Next, the operation of the above configuration will be explained.

The protective coating layer 5 of the present invention can be formed by the following manufacturing method. First, the first step is to attach the thermistor element 1° and the metal supports 6 and 4.
Then, a base layer 6 having a thickness of 5 to 20 μm is formed around the outer periphery of the substrate 2 by spray coating a brimer containing a fluorine compound. Next, in the second step, the base layer 6 applied in the first step is dried in an oven at 100 to 150°C. Furthermore, in the third step, 10, which melts at 300 to 350° C. and has an aqueous property, is added to the outer periphery of the base layer 6 dried in the second step.
The upper layer 7 is provided by electrostatic coating with a powder resin, such as a tetrafluoroethylene perfluoroalkoxyethylene copolymer resin, having a particle size of ~50 μm. In the fourth and final step, the upper layer 7 is melted at 320 to 450°C to form a film.

The base layer 6 provided on the surface of the thermistor unit must contain a fluorine compound in order to improve adhesion to the water-repellent top layer 7, such as a fluororesin-based top layer 7. They may have the same ingredients. In addition, since the base layer 6 is provided to improve adhesion with the top layer 7 and reliability of corrosion resistance, the film does not need to be completely pinhole-free, so spray coating is suitable, and its thickness is The thickness may be 5 to 20 μm, which is 1/2 or less of the upper layer 7.

The second step is to remove 100% of the solvent contained in the applied base layer B.
This is done to ensure complete volatilization in a furnace at ~150° C. and to prevent foaming when the upper layer 7 is formed into a molten film in the fourth step.

In the filtration step, the reason why the tetrafluoroethylene perfluoroalcoquine ethylene copolymer resin of K powder wood DW is provided as the upper layer 7 of the protective coating layer 5 by electrostatic coating is as follows. Since the tetrafluoroethylene perfluoroalcoquine ethylene copolymer resin has a melting point of 602 to 310°C,
As is clear from the principle of electrostatic coating, it is easy to melt and form a pinhole-free film at a temperature of ~450°C, it is difficult to undergo heat aging at temperatures below 300°C, and powder adhesion is reduced by a set electrostatic coating. It adheres to thin areas depending on the electric voltage, but it has the property of not adhering any further to areas that have reached a certain thickness, so a reliable and uniform film can be obtained without spraying or scratching. In particular, since the formed film has hydrophobicity and water repellency, deterioration in insulation is unlikely to occur.

In addition, the upper layer 7 resin of the protective coating layer 5 was heated to 300 to 350°C.
The reason why it is limited to heat-melting materials having a melting point of is as follows. First, hot-melt resins do not contain solvents.

It has a property of melting when heat is applied to form a pinhole-free film, and this property is absolutely essential for the protective coating layer 5. Next is the thermistor unit.

From detecting the temperature inside the microwave oven.

It is exposed to an environment that usually reaches 200 to 280°C, and reaches about 600°C for a short time. Therefore, it must have a heat resistance of about 600°C, and the melting point of the resin must be 300°C or higher. On the other hand, if the melting point of the resin is 350°C or higher, such as tetrafluoroethylene, it must be fired at 400°C or higher. However, the thermistor unit is made of metal,
Since it is composed of different materials such as ceramic and glass, when the temperature exceeds about 450°C, the difference in thermal expansion coefficient becomes large and it becomes easily damaged, and when the temperature of the thermistor element 1 exceeds about 450°C, the characteristics change easily. That is, electrode bodies 2 and 3
This is not preferable because it causes problems such as oxidation due to heat. Therefore, the melting point of the resin is preferably about 350°C or lower. For the above reasons, the melting point of the upper layer 7 resin of the protective coating layer 5 is preferably 300 to 350°C, and 602 to 350°C.
Tetrafluoroethylene perfluoroalcoquine ethylene copolymer resin having a total melting point of 10'C is said to be optimal.

Furthermore, the reason for limiting the particle size of the powder resin to 10 to 50 microns is as follows. In other words, when the particle size of the powder is less than 10μ, the cohesive force of the powder increases and it hardens, making it difficult to perform electrostatic coating efficiently.On the other hand, when the particle size of the powder exceeds 50μ, the thermistor unit Because thermistor element 1 and metal support 4 have a thin and complicated structure,
It becomes impossible to form a uniform film with a thickness of 20 to 80 μm around the outer periphery. From this, it is suitable that the particle size of the powder resin is 10 to 50 microns, more preferably 20 to 40 microns.

In the fourth step, the thermistor unit surface (zeta-adhered powder resin, such as tetrafluoroethylene perfluoroalkoxyethylene copolymer m resin, is melted at 162°C to 450°C to form a film, but the film forming temperature is 620° to 450°C.
The reason for limiting the temperature to ℃ is as follows. The temperature to form a film is 32
If the temperature is lower than 0°C, the melting will be insufficient and pinholes will be formed, while if it exceeds 400°C, the characteristics of the thermistor element 1 will change and high-temperature oxidation will occur, which is undesirable. Therefore, the optimum temperature for film formation is 620 to 450°C, more preferably 350 to 400°C, and the time may be 10 to 40 minutes.

The protective coating layer 5 provided on the surface of the thermistor unit is composed of a base layer 6 that does not need to be troubled due to variations in thickness or the presence or absence of pinholes, and a top layer 7 that is formed by uniformly depositing resin and forming a molten film by electrostatic coating. Because it can be formed, film thickness management is easy and workability and quality can be improved.

When a DC voltage of 6 to 6 V is normally applied to the thermistor unit in a corrosive environment where moisture and salt adhere for a long period of time, the parts of the electrode bodies 1a and 1b and the metal support 6.4 located on the positive side of the thermistor element 5 There is a so-called electrolytic corrosion phenomenon in which wires are corroded and disconnected. Therefore, Table 1 is obtained by examining the galvanic corrosion resistance of the thermistor unit of the present invention and the conventional example.

Table 1: Schematic table of ppR tetrafluoroethylene perfluoroalkoxyethylene copolymer resin Table 1 shows that a thermistor unit with a voltage of 6V applied was left in an atmosphere of atomized 10% saline at 40°C. , shows the time in the trench where the electrode bodies 1a and 1b are corroded and disconnected. This result shows that the thermistor unit of the present invention has a pinhole-free protective coating layer 5 and is water repellent.

Electrolytic corrosion resistance is significantly improved.

Effects of the Invention As detailed above, the method for forming a protective coating for a thermistor unit according to the present invention can be expected to have the following effects, and its industrial effects are significant.

(b) Malfunctions can be prevented because insulation on the surface of the thermistor element can be ensured.

←) The heat resistance, corrosion resistance, and electrolytic corrosion resistance of the thermistor element can be significantly improved, so it can withstand long-term use even in harsh environments.

The method for forming the C'l protective coating layer has excellent coating workability and is less likely to cause defects such as pinholes, blisters, and scratches, making quality control easy.

[Brief explanation of the drawing]

FIG. 1 is a fragmentary cross-sectional view showing a method of forming a protective layer for a thermistor unit according to an embodiment of the present invention. 1... Thermistor element, 2... Base. 4... Metal pillar 5... Protective coating layer. 6. Base layer, 7. Upper layer.

Claims (1)

[Claims] The thermistor element (1) is electrically connected to and held by metal supports (3) and (4) provided through the base (2) at a predetermined interval, and a protective coating layer (5 ), a first step of forming the protective coating layer (5) into a base layer (6) by spray coating;
6), and a third step of drying the base layer (6) by electrostatically coating a powder resin with a particle size of 10 to 50 μ, which melts at 300 to 350°C, to form the top layer (7). process and
A method for forming a protective coating layer for a thermistor unit, comprising a fourth step of melting the upper layer (7) at 320 to 450°C to form a film.