JPS63318702A - Formation of protective coating layer of thermistor unit - Google Patents

Abstract

PURPOSE:To improve the heat resistance, corrosion resistance and electrolytic corrosion resistance of a thermistor unit by spray-coating the outer periphery of a thermistor element with a primer containing a fluorine compound, electrostatically coating the outer periphery with a powdered tetrafluoroethylene perfluoroalkoxyethylene copolymer resin and baking the thermistor element at a specific temperature. CONSTITUTION:A protective coating layer 9 is formed onto the outer periphery of a thermistor element 5 in which a heat sensitive element 1 is sealed with a pair of electrode bodies 2, 3 and a heat-resistant insulating package 4. In such a thermistor unit, a primer containing a fluorine compound is spray-coated to shape a foundation layer 10, the outer periphery of the foundation layer 10 is electrostatically coated with a powdered tetrafluoroethylene perfluoroalkoxyethylene copolymer resin to form an overcoating layer 11, and the foundation layer 10 and the overcoating layer 11 are baked at a temperature of 350-400 deg.C, thus shaping the protective coating layer 9. Accordingly, the foundation layer 10 is fast stuck to the surface of the thermistor element 5 and attached closely to the overcoating layer 11 in a melting manner, thus forming the protective coating layer 9 having reliability for a prolonged term.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a method for forming a protective coating layer on a thermistor unit used in electric ovens, microwave ovens, and the like.

2. Description of the Related Art In general, thermistor units used in electric ovens, microwave ovens, etc. are installed in the oven compartment or in the hood at the exhaust port to detect air temperatures from room temperature to about 300°C. The structure of the thermistor unit is 2. For example, a heat-sensitive element is made by baking a transition metal oxide, turning it into a thin pellet, applying conductive paste to both sides of the pellet, and providing electrodes thereon. A heat-sensitive element is sandwiched between a pair of electrode bodies made of Dumet wire. In order to easily fit the thermistor element, which is formed by sealing this heat-sensitive element with a pair of electrode bodies and an envelope made of glass, and the pair of electrode bodies of this thermistor element, on an oven wall, etc. It is fixed by spot welding to a pair of metal supports made of stainless steel, copal, etc., which are placed upright in parallel at a predetermined interval on a base made of heat-resistant insulating material such as alumina or steatite. The thermistor element has the characteristic that the resistance value of the heat-sensitive element changes depending on the temperature.Using this property, a full electric field is applied to both ends of the thermistor element, and the change in voltage is captured by the control circuit to open the This is a temperature detection means to control the amount of power of the heating element that heats the inside of the refrigerator. The open compartment and exhaust hood are 30cm long.
The environment is extremely harsh, not only because of the high-temperature atmosphere near 0°C, but also because moisture generated from the two foods condenses, and dirt such as oil and salt scattered from the two foods tends to adhere.

Conventionally, thermistor units used in this type of harsh environment have been designed to prevent malfunctions, corrosion, and high-temperature oxidation caused by deterioration of insulation caused by adhesion of moisture and salt, and to prevent electrolytic corrosion caused by moisture and the application of a DC electric field. In order to prevent the electrode body from corroding and disconnecting due to this phenomenon, heat-resistant enamel paint containing a solvent made of polyimide, polyamideimide, silicone, etc. is applied to the surface of the thermistor unit by dipping or spraying, and then dried. A protective coating layer was formed by baking.

Problems to be Solved by the Invention However, in the conventional method for forming a protective coating layer of a thermistor unit, an interface is formed due to defects in the protective coating layer or poor adhesion between the protective coating layer and the thermistor element due to the following reasons. Due to storage, insulation may deteriorate and malfunction may occur.

Disadvantages include poor high-temperature oxidation resistance and the electrode body easily breaking due to electrolytic corrosion, resulting in poor durability during long-term use, poor coating workability of the protective coating layer, and complicated quality control. 0 (1) When a protective coating layer is formed on the surface of the thermistor unit by dipping, it is easy to form lumps in areas that differ in one dimension, and when those areas dry and bake, they sometimes blister and form pinholes. Moisture and salt can penetrate into the thermistor element.

(2) When a protective coating layer is formed on the surface of the thermistor unit by a spraying method, the thickness of the film tends to become thinner in the areas of scratches and shadows, making it difficult to obtain a film that is water resistant and resistant to high temperature oxidation.

Means for Solving the Problems In order to solve these drawbacks, the present invention uses a secondary forming method and binding method. In other words, in the thermistor unit according to the present invention, a heat-sensitive element is sealed with a pair of electrode bodies and a heat-resistant insulating envelope, and a primer containing a fluorine compound is sprayed on the outer periphery of the thermistor element to form a base layer. The operation of the method for forming the protective coating layer of the thermistor unit of the present invention will be described below.

(1) A primer containing a fluorine compound is spray applied to form a base layer, and then a tetrafluoroethylene perfluoroalkoxyethylene copolymer resin is applied on top of the primer, which is hard to cure even under a high temperature strainer at 300°C and does not cause cracks or peeling. Therefore, long-term reliability can be ensured. (2) The function of the underlayer containing a fluorine compound is to ensure adhesion between the thermistor element and the overlayer.

It has a thin film thickness of 5 to 20μ that does not easily cause blisters.
Even if some scratches occur, there will be no variation in adhesion. The upper layer is coated with powdered resin using electrostatic coating, and the film thickness is precisely controlled using electrostatic voltage.

Example Hereinafter, two embodiments of the present invention will be described in detail with reference to the drawings.

FIG. 1 shows an embodiment of a thermistor unit according to the present invention. 5 shows the structure of a diode type thermistor element. That is, i is a heat-sensitive element which has negative resistance-temperature characteristics mainly composed of oxides of transition metals such as iron, nickel, manganese, and cobalt, and has conductive electrodes coated on both sides, and 2 and 3 are heat-sensitive elements. A pair of electrode bodies made of Dumet wire sandwiched between both sides of the element 1.

Reference numeral 4 denotes an envelope made of glass for sealing the heat-sensitive element 1 with the pair of electrode bodies 2 and 3. Further, 6 and 7 are made of heat-resistant and corrosion-resistant metal such as stainless steel, copper, etc.
Nuteatite is a heat-resistant insulating material.

A pair of metal supports 9 are provided upright and parallel to a base 8 made of alumina or the like at predetermined intervals. Reference numeral 9 denotes a thermistor element 5, a pair of metal supports 6 and 7, and heat-resistant, water-resistant, corrosion-resistant and It is a protective coating layer with insulating properties.
For example, a base layer 10 made of polyimide, polyamideimide, polyphenylene sulfide, etc. and a fluorine compound.

The base layer 10 is composed of a top layer 11 of tetrafluoroethylene perfluoroalkoxyethylene copolymer resin provided around the outer periphery of the base layer 10.

FIG. 2 shows the thermistor element 5 and the protective coating layer 9 in detail. That is, a primer containing a liquid fluorine compound is applied to the outer periphery of the thermistor element 5 to a thickness of 5 to 20 μm by a spray method, and then left to stand naturally or dried at a temperature of 50 to 180° C. to form the base layer 10.
Next, a 20 to 40 μ-sized polytetrafluoroethylene perfluoroalkoxyethylene copolymer resin is applied to the outer periphery of the base layer 10 to a thickness of 30 to 80 μ by electrostatic coating, and then heated at a temperature of 350 to 400°C. By baking for 20 to 40 minutes, the base layer 10 comes into close contact with the surface of the thermistor element 5 and melts and comes into close contact with the top layer 11, so that a reliable protective coating layer 9 is formed.

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

The protective coating layer 9 of this embodiment consists of two layers, a base layer 10 and a top layer 11.
Since it is provided to bring the upper layer 11 into close contact with the thermistor element 5., its function is that of the thermistor element 5. It is sufficient that the film is in close contact with the metal struts 6 and 7 and the base 8 and in close contact with the upper layer 11 by melting, and does not necessarily have to be a completely pinhole-free film. The base layer 10 must be completely spray coated with a primer containing a fluorine compound to form a film of 5 to 20 μm, be melted and adhered to the tetrafluoroethylene perfluoroalkoxyethylene copolymer resin that is the material of the top layer 11, and be stable in heat resistance. Even if pinholes are generated in the upper layer 11, moisture and salt do not easily enter the thermistor element 5.

The reason why powdered tetrafluoroethylene perfluoroalkoxyethylene copolymer resin is applied to the upper layer 11 by electrostatic coating is as follows. Since the tetrafluoroethylene perfluoroalkoxyethylene copolymer resin has a melting point of 302 to 310°C, it is easy to melt at a temperature of 350 to 400°C and form a pinhole-free film.

It is clear from the principle of electrostatic painting that heat aging is difficult at temperatures below 300℃, and the amount of powder deposited depends on the electrostatic voltage set, so it will adhere to thin areas, but it will remain at a certain thickness and will reach the desired area. Since it has the property of not adhering any further, a reliable and uniform film can be obtained without causing blisters or scales, and the formed film is hydrophobic and water repellent, so it is difficult to cause insulation deterioration. etc.

The base layer 10 and the top layer 11 have a coating density of 350 to 40% after coating.
By firing at a temperature of 0°C, the layers melt and adhere to each other and do not form an interface, so moisture and salt do not enter, and the polytetrafluoroethylene perfluoroalkoxyethylene copolymer resin of the upper layer 11 It is possible to ensure insulation resistance on the surface of the thermistor element 5 for permanent use. If the firing temperature is lower than 350° C., it is not preferable because the base layer 10 becomes difficult to adhere to the thermistor element 5 and the upper layer 11, and the film of the upper layer 11 tends to form dipin holes due to insufficient melting. In addition, the firing temperature is 400℃
Exceeding this is not preferable because the resins of the base layer 10 and the top layer 11 may undergo thermal deterioration or foam to form pinholes. Therefore, the firing temperature is preferably 350 to 400°C, and the time is preferably 20 to 60 minutes, more preferably 30 to 40 minutes.

The base layer 10 is formed by spray coating to a thickness of 5 to 20 μm, and the top layer 11 is coated with a powder electrostatic coating voltage of 30 μm.
It may be formed to have a thickness of ~100μ.

If the thickness of the base layer 10 is less than 5 μm, the adhesion strength between the upper layer 11 and the thermistor element 5 will be reduced, and if the thickness is greater than 20 μm, the film will foam and wrinkle, causing close contact with the base material and pinholes. It causes Therefore, the thickness of the base layer 10 is preferably 8 to 12 microns rather than 5 to 20 microns. On the other hand, if the thickness of the upper layer 11 is less than 20 μm, pinholes are likely to occur, and if it is more than 100 μm, the temperature detection sensitivity of the thermistor element 5 will be reduced. Therefore,
The thickness of the upper layer 11 is 30 to 100 μm, preferably 40 μm.
It is preferable to set the thickness to be at least twice that of the base layer 10.

In this way, the base layer 10 can be provided with a thickness of 10μ as a guide by spray coating, and the top layer 11 can be coated with tetrafluoroethylene perfluoroalkoxyethylene copolymer resin to a certain thickness using an electrostatic coating method. Since a pinhole-free protective coating layer 9 can be obtained by firing at 400° C., it is possible to improve workability and stabilize quality.

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

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

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

(3) The coating has excellent workability and does not easily cause defects such as pinholes, blisters, and scratches, making quality control easy.

[Brief explanation of drawings]

FIG. 1 is a partially cutaway front view of a thermistor unit according to an embodiment of the present invention, and FIG. 2 is an enlarged sectional view of the main part of FIG. 1. 1... Heat-sensitive element, 2, 3... Electrode body. 4... Enclosure, 5... Thermistor element. 9...Protective coating layer, 10... Base layer. 11... Upper layer.

Claims (1)

[Claims] A thermistor element (5) in which a heat-sensitive element (1) is sealed with a pair of electrode bodies (2), (3) and a heat-resistant insulating envelope (4).
In a thermistor unit comprising a protective coating layer (9) provided around the outer periphery of the thermistor unit, a primer containing a fluorine compound is spray applied to form a base layer (10), and the base layer (10)
Electrostatically coat powdered tetrafluoroethylene perfluoroalkoxyethylene copolymer resin around the outer periphery of the upper layer (11).
Base layer (10) at a temperature of 350-400℃
A method for forming a protective coating layer for a thermistor unit, characterized in that a protective coating layer (9) is formed by firing a top layer (11) and a top layer (11).