JPH04167390A - Positive characteristic thermistor heating element - Google Patents

Abstract

PURPOSE:To prevent characteristics of a thermistor heating element from being deteriorated by some external factor by using a protecting layer of fluororubber to protect the surface of the thermistor heating element which is not covered with any electrode plate. CONSTITUTION:Electrode layers 2 are formed by baking of silver paste on both end faces of a cylindrical positive characteristic thermistor PTC heating element 1. Disc-shaped electrode plates 3 each made of stainless are stuck on both sides of each electrode layer 2 by a silicon type conductive adhesive 4. Each of the electrode plates 3 consists of a disc portion 3a stuck to electrode layer 2 and a connection terminal 3b extended into the shape of L from one part of its peripheral edge. Fluororubber is packed in a recessed portion formed by the peipheral portion 5 of each electrode plate 3 and the outer peripheral face of the element 1 which is not covered with electrode plate 3, so that a protecting layer 6 is formed. The element 1 is completely sealed from outside by the electrode plates 3 and the protecting layer 6.

Description

Detailed Description of the Invention (Field of Industrial Application) The present invention relates to a positive temperature coefficient thermistor (rPTc
(referred to as J).

(Prior art) A mat-type electronic mosquito repellent that exterminates mosquitoes by heating a mat impregnated with an insecticidal ingredient such as flamethrin or allethrin or a chemical solution containing the insecticidal ingredient to volatilize the insecticidal ingredient, and a liquid-type electronic mosquito repellent. Traps and the like are becoming widely used.

A PTC heating element is used as a heating element for the chemical liquid in this electronic mosquito repellent.

The PTC heating element has a specific resistance value at low temperatures and acts as a heating element, and has a self-temperature control function that rapidly increases the resistance value and cuts off electricity when the temperature exceeds a predetermined temperature (Curie temperature). This is because it has extremely high safety.

(Problem to be solved by the invention) FIG. 3 shows the structure of this type of conventional PTC heating element.

A PTC heating element 11, which has electrode layers 12 formed on both sides by aluminum spraying or silver paste baking, is sandwiched between stainless steel electrode plates 13, at least one of which has spring elasticity, and is housed in a recess of an insulating case 17. The opening of the insulating case 17 is covered with an insulating plate 18, and a metal heat sink 19 is placed and fixed on top of the insulating plate 18. Electrode plate 1
The drawer portion 3 is taken out to the outside through a gap 20 provided on the bottom surface of the insulating case 17.

In the above-mentioned PTC heating element, there is a gap between the bottom of the insulating case and the take-out part of the electrode plate, and when a chemical containing an insecticidal component is evaporated, the vapor etc. enters through the gap.
The PTC heating element will be directly exposed to these. As a result, resistance-temperature characteristics and voltage-current characteristics deteriorate, and long-term energization can even lead to destruction.

Figure 4 (al and (b)
The structure of the PTC heating element shown in 1 is considered.

This PTC heating element has a disk-shaped PTC heating element 11 whose periphery is sealed with an electrode plate and an adhesive, and electrode layers 12 are provided on both sides by aluminum spraying or silver paste baking, etc. It is sandwiched between stainless steel disk-shaped electrode plates 13, and the space between the peripheral edge 15 of the electrode plate 13 and the side surface of the PTC heating element 11 is sealed with a silicone-based insulating adhesive 16,
It is integrated.

This PTC heating element is made of PTC by electrode plate and adhesive.
Since the area around the heating element C is sealed, it is possible to prevent the intrusion of chemicals, but since it is a silicone-based adhesive, some of the chemical vapor passes through the silicone-based adhesive, gradually causing PTC.
It deteriorates the resistance-temperature characteristics and voltage-current characteristics of the heating element, and may lead to destruction if it is energized for a long time.

Additionally, if petroleum-based chemicals containing insecticidal ingredients are accidentally applied, the silicone adhesive will swell and the PT
The disadvantage is that the contact resistance between the PTC heating element and the electrode plate increases over time due to the force that separates the C heating element from the electrode plate, and the contact resistance reaches infinity in about a few tens of hours. be.

The purpose of the present invention is to eliminate the above-mentioned drawbacks,
It is an object of the present invention to provide a highly reliable PTC heating element that exhibits stable characteristics without being affected by the vapor or liquid of a chemical containing an insecticidal component.

(Means for Solving the Problems) In order to achieve the above object, a PTC heating element according to the present invention is a positive temperature coefficient thermistor heating element consisting of a positive temperature coefficient thermistor heating element and an electrode plate. A characteristic thermistor heating element is sandwiched between electrode plates, and
The surface of the positive temperature coefficient thermistor heating element that is not covered with the electrode plate is sealed with a protective layer made of fluororubber.

(Function) According to this configuration, the PTC heating element is completely sealed and isolated from the outside air by the protective layer made of fluororubber, so that resistance-temperature characteristics and voltage-current characteristics due to the influence of chemical vapor, etc. It becomes possible to prevent deterioration of characteristics. In addition, fluororubber has extremely good oil resistance, so even if it is accidentally sprayed with petroleum-based chemicals, it will not swell and will not cause P.
It becomes possible to prevent an increase in contact resistance between the TC heating element and the electrode plate.

(Example) Hereinafter, the present invention will be explained in more detail with reference to the drawings.

FIG. 1 (al is a perspective view showing an embodiment of the PTC heating element according to the present invention, and the numerals in the figure) are A-A in FIG. 1(a).
FIG.

Cylindrical P with a diameter of 12 mm and a thickness of 2.5 mm
Electrode layers 2 are formed on both end faces of the TC heating element 1 by baking silver paste.

A layer with a diameter of 14 mm and a thickness of 0.2 m is placed on both sides of this electrode layer 2.
A stainless steel disc-shaped electrode plate 3 having a diameter of m is fixed with a silicone-based conductive adhesive 4.

The electrode plate 3 includes a disk portion 3a fixed to the electrode layer 2 and a connecting terminal 3b extending in an L-shape from a part of the periphery of the disk portion 3a.

A recess formed by the peripheral edge 5 of the electrode plate 3 and the outer peripheral surface of the PTC heating element 1 not covered by the electrode plate is filled with fluororubber to form a protective layer 6.

The PTC heating element 1 is completely sealed from the outside by the electrode plate 3 and the protective layer 6, and is in an airtight state.

Next, the characteristics of the PTC heating element according to this embodiment and the conventional PTC heating element with respect to chemical vapor, etc. will be compared.

Comparative Example 1 is a PTC heating element according to this example in which the protective layer (fluororubber) is removed, and Comparative Example 2 is a PTC heating element according to this example in which a silicone-based insulating adhesive is used instead of protective N (fluororubber). We prepared one using the agent.

A durability test in chemical vapor was conducted for each of the above samples. The test method was to place the chemical mats used in commercially available cloak-type electronic mosquito repellents tightly above and below a PTC heating element, and conduct one cycle of heating with electricity for 8 hours and cooling without electricity for 8 hours. After repeating 3 cycles, remove the chemical cloak, and after 500 hours of continuous energization, the number of sudden changes in the PTC heating element rPTc = j2og (ρmax/ρ25) ρmax (maximum resistivity): value when resistivity reaches maximum [Ω・cm) ρ25 (temperature specific resistance); resistivity at 25℃ [Ω・c
m] and the withstand voltage characteristics were measured.

The results are shown in Table 1 (listed at the end of the detailed description of the invention).

As can be seen from Table 1, the superiority of this example having a protective layer of fluororubber is clear.

Next, each sample was immersed for 12 hours at room temperature in a petroleum-based chemical solution used in a commercially available liquid-type electronic mosquito repellent, and the change in resistance before and after that was measured.

The results are also listed in Table 1.

The superiority of this embodiment is clear from this.

In this example, an example was explained in which a protective layer of fluororubber was provided on the outer peripheral surface of the PTC heating element where the electrode plate was not covered, but as shown in Fig. 2, a protective layer was also provided on the surface of the electrode plate. The entire PTC heating element may be hermetically sealed.

In addition, in this example, the durability was sufficiently demonstrated by using fluororubber as the protective layer, but the effect can be further ensured by providing a case, retaining plate, etc. to maintain mechanical strength. It is also possible to do so, and the effect will not be lost even if a heat sink made of an aluminum plate or the like is attached.

(Effects of the Invention) As explained above, according to the present invention, the surface of the PTC heating element where the electrode plate is not covered is protected by the protective layer of fluororubber, and the entire PTC heating element is protected by the electrode plate and the protective layer. Since it has a sealed structure, it is possible to provide a highly reliable PTC heating element whose characteristics do not deteriorate due to external factors such as chemical vapor and petroleum-based chemical liquid.

Table 1

[Brief explanation of drawings]

Fig. 1 ta+ is a perspective view showing an embodiment of the PTC heating element according to the present invention, and Fig. 1 To) is A- of Fig. 1 fal.
It is an A sectional view. FIG. 2 (18) is a perspective view showing another embodiment of the PTC heating element according to the present invention, and Tbl in FIG.
-B sectional view. FIG. 3 is a sectional view showing an example of a conventional PTC heating element. Fig. 4 fa) is a perspective view showing one possible example of a PTC heating element, and the same figure (bl is a cross-sectional view taken along line CC in Fig. 4 (a). 1.11... PTC heating element 2.12... Electrode layer 3.13... Electrode plate 3a... Disc part 4... Silicone conductive adhesive 5.15... Peripheral part 6... Protective layer 16... Silicone-based insulating adhesive 17...Insulating case 18...Insulating plate 19...Metal heat sink 20...Gap 36...Connecting terminal Patent applicant Ri Labe Co., Ltd. Agent
Patent Attorney Hisashi Inoro Figure 1 -A Figure 2 (b) Figure 3 Figure 4 (b)

Claims (1)

[Claims] In a PTC thermistor heating element consisting of a PTC thermistor heating element and an electrode plate, a PTC thermistor heating element having electrode layers on both sides is sandwiched between the electrode plates, and the PTC thermistor heating element is covered with the electrode plate of the PTC thermistor heating element. A positive temperature coefficient thermistor heating element characterized by having the exposed surface sealed with a protective layer made of fluororubber.