JPH07307495A - Peltier element - Google Patents

Abstract

PURPOSE:To obtain a Peltier element which is low-cost, which prevents a thermoelectric material or a metal material constituting the element from being corroded when moisture is interposed and whose durability can be improved sharply by a method wherein a water-repelling treatment is conducted to a current- carrying part and to at least a part on the surface of an electric insulation material surrounding and supporting the current-carrying part. CONSTITUTION:Thermoelectric materials 1, 2, are electrified with DC, and they are heated by heat generated in the inflow part and the outflow part of the current or by absorbing the heat. In such a Peltier element, a water- repelling treatment is conducted to current-carrying parts 1 to 4 and to at least a part on the surface of electric insulation materials 5 surrounding and supporting them. For example, a water-repelling treatment 6 is conducted to the side face of N-type thermoelectric materials 1 and of P-type thermoelectric materials 2, to copper electrodes 3 and to the whole outer surface of solder parts 4 bonding them. A 2% solution of octadecyl trichlorosilane by using chloroform and carbon tetrachloride as solvents is used, it is coated and dried, the Peltier element is cleaned, and it is finally cleaned by running water.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a Peltier device which is excellent in corrosion resistance, practical, and highly reliable.

[0002]

2. Description of the Related Art Peltier elements are used in cooling parts of sensors, refrigerators, dehumidifiers, etc., because of the property that a temperature difference occurs at both ends when a direct current is applied to a thermoelectric material. The conventional general Peltier device will be described below with reference to FIG. In FIG. 2, 1 and 2 are N-type and P-type bulk thermoelectric materials, respectively, and a Bi-Te-Sb-based alloy is used as a Peltier element used near room temperature. The N-type thermoelectric material 1 and the P-type thermoelectric material 2 are electrically connected in series alternately via the metal electrode 3. These are bonded to two ceramic substrates 5. Generally, an alumina substrate is used for the ceramic substrate 5, and a copper plate electrode is used for the metal electrode 3. Further, solder 4 is usually used at the joint between the metal electrode 3 and the ceramic substrate 5 and at the joint between the metal electrode 3 and the thermoelectric materials 1 and 2.

When a direct current is passed between the metal electrodes 3 at both ends of this Peltier element, the Peltier effect causes the thermoelectric material 1,
A temperature difference occurs at both ends of 2. When the thermoelectric material is P-type, the inflow part of the current is cooled and the outflow part is heated. Also,
Conversely, in the case of the N type, the inflow part of the current is heated and the outflow part is cooled. As a result, heat is pumped from the lower surface to the upper surface, and it is possible to cool objects and air through the ceramic substrate 5 on the lower surface. At that time, the temperature of the cooling side end of the thermoelectric material and the temperature of the cooling side copper electrode become lower than that of the lower ceramic substrate. When the Peltier element is used in a normal indoor atmosphere, the temperature on the cooling side thereof becomes lower than the dew point depending on the operating conditions, and the moisture in the air is condensed on the surfaces of the thermoelectric material and the copper electrode. As a result, when the operation is continued for a long time, the metal material such as the thermoelectric material is corroded, the element resistance increases, the heat absorption amount decreases, and the performance as the Peltier element deteriorates. Therefore, a method to prevent dew condensation by sealing the side surface of the Peltier element with silicon resin or placing the whole Peltier element in a box that prevents moisture from entering from the outside by using rubber packing etc. was also devised. There is.

[0004]

However, in such a moisture-proof method, heating is performed through the wall surface of the box, that is, heat is circulated from the heat radiating side to the cooling side, resulting in a decrease in cooling efficiency. In addition, the cost of the Peltier device itself was increased.

[0005]

According to the present invention, in a Peltier element in which a direct current is applied to a thermoelectric material and is heated or cooled by heat generation or heat absorption generated in an inflow part and an outflow part of the current, the energized part and the surrounding part are surrounded. It is preferable that at least a part of the surface of the supporting electrical insulating material is treated to be water repellent, and the surface including the current inflow portion and the surface including the current outflow portion are separated by the water repellent surface. Further, the surfaces of the thermoelectric material and the metal material that come into contact with the outside air are coated with a coating that is electrically insulating and has low moisture permeability.

[0006]

In general, the corrosion of the metal part is caused by the supply of the moisture adhering to the surface due to the dew condensation and the oxygen in the air.
Furthermore, when the Peltier element is energized when moisture due to dew condensation covers the surface of the thermoelectric material, the copper electrode, or the ceramic substrate, an electrochemical reaction occurs on the same thermoelectric material surface or between adjacent copper electrodes or thermoelectric materials. Accelerated by heavy corrosion. As described above, when the current-carrying part of the Peltier element and at least a part of the surface of the electrically insulating material surrounding and supporting it are treated to be water-repellent, the condensed water does not become a liquid film covering the surface due to the water-repellency of the surface. Continue to maintain the state of isolated water drops. As a result, the corrosion is not subject to electrochemical acceleration.

Further, normal corrosion which tends to occur at the three-phase interface of water, air and metal is also suppressed. In addition, if the surface of the thermoelectric material or metal material in contact with the outside air is covered with a film with low moisture permeability,
Since the water is blocked, the progress of corrosion can be suppressed, and the performance of the Peltier element is not impaired because it is electrically insulating. Furthermore, since all the means of the present invention are surface treatment and coating treatment with an extremely thin film-like substance, the cooling performance is not significantly deteriorated by heat conduction. Also, since a large amount of surface treatment and coating treatment can be performed at one time, cost reduction is possible compared to the method of sealing the side surface of the Peltier element with silicone resin or the like, and moisture-proofing the entire Peltier element using rubber packing or the like. It is possible.

[0008]

EXAMPLES As an example of the present invention, Bi-Te-S will be described below.
A Peltier device using a b-based alloy as a thermoelectric material will be described with reference to the drawings. [Embodiment 1] FIG. 1 shows a Peltier device according to the present invention, in which a water-repellent portion is designated by 6. That is, water repellent treatment was performed on the side surfaces of the N-type thermoelectric material 1 and the P-type thermoelectric material 2, all the outer surfaces of the copper electrodes 3 and the solder 4 for joining them, and the inside of the ceramic substrate 5. As the water repellent agent, a 2% solution of octadecyltrichlorosilane was used with chloroform-carbon tetrachloride as a solvent.
After drying, it was washed with chloroform and finally washed with running water.
In order to investigate the effect of the water repellent treatment, the contact angle of water in air was measured and a value of about 145 ° C. was obtained. An attempt was made to measure the thickness and amount of the treated film, but it could not be detected. Although the mechanism of octadecyltrichlorosilane surface treatment is not well understood, water molecules and OH adsorbed on the surface of thermoelectric materials and ceramics.
The group and chlorine of octadecyltrichlorosilane are bound by the dehydrochlorination reaction, and the chlorine of the adjacent octadecyltrichlorosilane reacts with water molecules to cause the dehydrochlorination reaction, resulting in the formation of the Si-O-Si-O-bonded film. Thought to form.

In order to verify the corrosion durability of the Peltier element subjected to the water-repellent treatment, electricity was repeatedly applied for 20 minutes at 4 amps alternately in the forward and reverse directions. The test atmosphere at this time was 40 ° C. and 90% relative humidity. A temperature difference of about 50 ° C. was observed between the upper and lower ceramic substrates when a current of 4 amps was applied. Therefore, it is considered that there is a larger temperature difference between both ends of the thermoelectric element. The test was continued for 1 week, and the electrical resistance value of the device was measured every 24 hours and 4
The change of the endotherm when the ampere was energized was traced. The resistance value of the Peltier device that had not been subjected to the water repellent treatment was observed to gradually increase from the 4th day, and one week later, the resistance value was 40 times, which was 1.3 times the initial value. On the other hand, in the element that has been subjected to water repellent treatment,
There was no change in the observed electric resistance value. In addition, the heat absorption amount of the element not subjected to the water repellent treatment decreased to one third or less after one week, but the value of the element subjected to the water repellent treatment decreased to about 5%. As a result of performing the same corrosion durability test on several Peltier devices having different sizes, almost the same effect was confirmed although there was some variation in the effect. By carefully observing the element in which the phenomenon of increase in electric resistance and the amount of heat absorption was observed, it was confirmed that white powder was blown from the vicinity of the thermoelectric material, the solder, and the copper electrode and was corroded.

In order to investigate the cause of deterioration of the element in which the corrosion gradually progressed due to the water repellent treatment and the heat absorption amount decreased, the contact angle of water was measured. In particular, it was found that the water repellency of the ceramic substrate was impaired. It was suggested that the water repellent film with octadecyltrichlorosilane gradually deteriorates at high temperature (up to 100 ° C.), so it was subjected to water repellent treatment using another silicon water repellent or Teflon water repellent. As a result of manufacturing an element and similarly performing a durability test, no deterioration in performance was observed even after 2 weeks. Further, in a Peltier element assembling process, a corrosion durability test was also performed on an element in which only the thermoelectric element was subjected to water repellent treatment, or conversely, only the ceramic substrate was subjected to water repellent treatment. As a result, the effect was lower than that of the element whose entire surface was subjected to the water repellent treatment, but the corrosion resistance was improved as compared with the element which was not subjected to any treatment.

Example 2 An element was produced in which the thermoelectric material and the metal part of the Peltier element were covered with polyvinyl butyral as a coating having electrical insulation and low water permeability. 0.5 of polyvinyl butyral powder dissolved in methanol
%, And pass the Peltier device shown in FIG.
It was dried in dry Ar at 0 ° C. for 5 hours. The Peltier element coated with polyvinyl butyral was cut to investigate its properties, and the surface of the thermoelectric material, the electrode, and the solder surface were observed with a microscope. As a result, a polyvinyl butyral coating was formed with a thickness of about 20 μm I understood it. In order to verify the corrosion durability of the Peltier element subjected to the coating treatment, as in Example 1, in the air of 40 ° C. and relative humidity of 90%, a forward current and a reverse direction were alternately applied at a current of 4 amperes and 2 times.
The energization was repeated every 0 minutes. The test was continued for one week, and changes in the electric resistance value and the heat absorption amount of the device were traced. In the Peltier device subjected to this coating treatment, as in the case of Example 1, there was no change in the observed electric resistance value. Also,
There was no detectable change in the amount of heat absorption within one week. Furthermore, in the subsequent corrosion durability test, a slight decrease in the heat absorption amount was observed after 3 weeks. A slight amount of corrosion was observed in the solder part where the surface condition of the device was observed.

Further, in order to improve the durability, a corrosion test was conducted on a Peltier device in which butadiene rubber was dissolved in a solvent to form a film on the surface of the device. As a result, the heat absorption amount was slightly lower than at the beginning of the test, but the decrease was not observed even after 4 weeks, indicating that the corrosion resistance was improved. However, it is considered that the heat absorption amount was low because the thickness of the film of butadiene rubber was large, and it is necessary to improve the film forming method. Next, as a coating treatment with an inorganic material, an alumina gelling agent was used to form an alumina coating on the conductive portion of the Peltier device. In the corrosion resistance test, the corrosion resistance was significantly improved as compared with the blank element which was not subjected to the film treatment, but it was not as high as the organic film forming element. However, it is considered that the corrosion resistance can be further improved by selecting the optimum inorganic coating material.

[0013]

As described above, according to the present invention, it is possible to prevent the corrosion of the thermoelectric material and the metal material which compose the Peltier element due to the water content at a low cost, and to greatly improve the durability.

[Brief description of drawings]

FIG. 1 is a vertical cross-sectional view of a Peltier device according to an embodiment of the present invention.

FIG. 2 is a vertical sectional view of a conventional Peltier device.

[Explanation of symbols]

 1 N-type thermoelectric material 2 P-type thermoelectric material 3 Metal electrode 4 Solder 5 Ceramics substrate 6 Water-repellent treated part

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Yoshiaki Yamamoto 1006 Kadoma, Kadoma City, Osaka Prefecture Matsushita Electric Industrial Co., Ltd.

Claims (2)

[Claims] 1. A Peltier element for supplying a direct current to a thermoelectric material and heating or cooling by heat generation or heat absorption generated at an inflow part and an outflow part of the current, the surface of an electrically insulating material surrounding the energized part and supporting it. A Peltier element characterized in that at least a part of the water-repellent treatment is performed. 2. A Peltier element for applying a direct current to a thermoelectric material and heating or cooling by heat generation or heat absorption generated at an inflow part and an outflow part of the current, wherein the surface of the thermoelectric material and the metal material in contact with the outside air is electrically charged. A Peltier element characterized by being covered with a film that is insulating and has low moisture permeability.