JPH053072A - Positive resistance temperature coefficient heating element and its manufacture - Google Patents

Abstract

PURPOSE:To provide a positive resistance temperature coefficient heater element without generating an abnormal overheating, smoking, firing, and the like, and with a safety, a long service life, and a high output. CONSTITUTION:This positive resistance temperature coefficient heater unit is composed of a sheet form positive resistance temperature coefficient resistor 4 which consists of a conductive minute powder and a crystalline polymer, a pair of electrode units 5 and 6 furnished to apply a voltage in the thickness direction of the positive resistance temperature coefficient resistor 4, and armoring materials 7, 8, 9, and 10 to armor the resistor 4 and the electrode units 5 and 6. And by composing to diffuse an oxidation preventive agent which consists of pentaerythritil-tetraxyth [3-(3 and 5 di-t-butil-4-hydroxyphenul) propionate] on the projection plane in the thickness direction of the positive resistance temperature coefficient resistor 4 at the position A where the pair of electrode units 5 and 6 are not superposed, a positive resistance temperature coefficient heater element of a safety, a long service life, and a high output can be obtained.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a positive resistance temperature coefficient heating element useful as a heating tool and a general heating device, and a method for producing the same.

[0002]

2. Description of the Related Art A conventional positive resistance temperature coefficient heating element is disclosed in, for example, Japanese Patent Publication No. 57-43995 and Japanese Patent Publication No. 55-4016.
The configuration is as shown in Japanese Patent Publication No. 1 and is self-controlled at a constant temperature by the positive resistance temperature characteristic of the resistor between the pair of electrodes. However, especially when a high power density or high temperature is required, it is essential to make the temperature distribution in the direction between the pair of electrodes always good in order to make the temperature distribution of the heating element itself uniform. As a solution, as shown in Japanese Examined Patent Publication No. 62-59515 and FIG. 4, a method is adopted in which the distance between a pair of electrodes is close to each other. In FIG. 4, reference numerals 1 and 2 denote a pair of parallel plate electrodes provided close to each other, and a resistor 3 formed by mixing and dispersing conductive fine powder in a crystalline polymer is disposed between the parallel plate electrodes to increase the height. It has been found that a positive temperature coefficient of resistance heating element may emerge.

[0003]

However, the conventional positive resistance temperature coefficient heating element as described above is very excellent as a structure for producing a high output, but the portion where resistance heating is generated from both sides is an electrode. Since the structure is covered with, the contact area between the electrode and the resistor is large, and thermal stress concentrates at the interface between the electrode and the resistor and the end of the electrode, creating a hot zone due to voltage concentration. There was a case that the life of the product deteriorated due to the damage of the product. Further, because the electrode interval is very close, especially in the end portion of the heteropolar electrode, deterioration of the crystalline polymer, further, microcracks and the like due to the deterioration of the crystalline polymer, moisture, atmospheric pressure, Furthermore, depending on the burr on the electrode end surface, air discharge, breakdown of withstand voltage, smoking,
There was also a risk of ignition. As a heating element, the highest priority is to ensure safety up to the end of its life, but the mechanism of such safety has not been clarified, and there is no danger of abnormal overheating, smoking, ignition, etc. ,
It was not possible to produce a high output positive resistance temperature coefficient heating element that is safe and has a long life.

SUMMARY OF THE INVENTION It is an object of the present invention to solve the above conventional problems and provide a positive resistance temperature coefficient heating element having a long life and high safety, and a method for manufacturing the same.

[0005]

In order to achieve the above object, a positive resistance temperature coefficient heating element of the present invention is a sheet-shaped positive resistance temperature coefficient resistor comprising conductive fine powder and a crystalline polymer, Consisting of a pair of electrode bodies provided for applying a voltage in the thickness direction of the positive resistance temperature coefficient resistor, and an exterior material that covers the positive resistance temperature coefficient resistor and the pair of electrode bodies, Positive temperature coefficient of resistance Pentaerythrityl-tetrakis [3- (3,5-di-t-butyl-
4-hydroxyphenyl) propionate].

[0006]

The function of this technical means is as follows.
That is, pentaerythrityl-tetrakis [3-
(3,5-di-t-butyl-4-hydroxyphenyl)
Propionate] is an antioxidant that can diffuse into positive temperature coefficient resistors to prevent oxidative deterioration of crystalline polymers, etc., and eliminate the risk of smoke, ignition, etc., caused by defects such as microcracks. However, due to factors such as the compatibility and low melting point of this antioxidant, it is necessary to form a non-conducting part in the chain of conductive fine powder in this positive temperature coefficient resistor to increase the electrical resistance. become. In the case of the present invention, the portion where the pair of electrode bodies are superposed on the projection surface in the thickness direction of the positive resistance temperature coefficient resistor is an effective heat generating portion,
It is hard to deteriorate because it is covered with an electrode body made of a metal material or the like. On the other hand, a site that does not polymerize hardly contributes to heat generation and is a site that easily deteriorates, and pentaerythrityl-tetrakis [3- (3,5-di-t-butyl-4-hydroxyphenyl) propionate] is present in this site. Introducing an antioxidant consisting of can suppress the deterioration of the positive temperature coefficient resistor and prevent the risk of smoking, ignition, and the like. Further, the volume resistivity of the positive resistance temperature coefficient resistor in this portion which is not covered with the electrode is increased, and the hot zone due to the voltage concentration which is likely to occur in this portion is prevented.

[0007]

Embodiments of the present invention will be described below with reference to the accompanying drawings. For example, as shown in the perspective view of FIG. 1 and the sectional view of FIG. 2, the positive resistance temperature coefficient heating element of the present embodiment has an electrode body 5 on the upper and lower surfaces of a positive resistance temperature coefficient resistor 4 having a thickness of 0.5 mm. ，
6 is adhered, and a hot melt layer 7,
8 and an outer covering material composed of electric insulating layers 9 and 10 thereon. The positive resistance temperature coefficient resistor 4 is formed as follows. That is, as conductive fine powder, while kneading 60 wt% of furnace black and 40 wt% of high-density polyethylene, 3 wt% of dicumyl peroxide, which is an organic peroxide, was added to high-density polyethylene,
After completing the crosslinking reaction by applying a heat treatment,
A pulverized product having an average particle size of 50 μm, that is, a conductive filler was obtained by freeze pulverization. Next, this conductive filler was kneaded so that the composition ratio of carbon black was 45.0 wt% of the total amount so as to be uniformly dispersed in maleic acid-modified high-density polyethylene, to obtain a positive resistance temperature coefficient resistor 4. It was Further, the positive resistance temperature coefficient resistor 4 was bonded to the electrode body as described above, and then pentaerythrityl-tetrakis [3-
(3,5-di-t-butyl-4-hydroxyphenyl)
Propionate] antioxidant (Ciba Geigy:
IRGANOX 1010) is added to the hot melt layers 7 and 8 and the electric insulating layers 9 and 10 in that order, and then annealed to obtain a desired positive resistance temperature coefficient characteristic.
The antioxidant contained in the hot melt layers 7 and 8 was diffused by annealing the portion A of the positive resistance temperature coefficient resistor shown in FIG. In the case of the present embodiment, the antioxidant can be effectively diffused by using a material having compatibility with the material of the positive resistance temperature coefficient resistor 4 for the hot melt layer. Due to this diffusion, the resistance A of the positive temperature coefficient resistor increases in resistance. Therefore, the hot zone, which tends to occur in this area, is suppressed and the life is extended. It also improves In order to investigate the effectiveness of the present invention, the samples with and without addition of the antioxidant were processed and the following comparative experiments were actually carried out.

This comparative experiment was carried out by a method of evaluating energization after promoting heat resistance at 150 ° C., and resistance stabilization treatment was carried out by energization aging before energization measurement. The result is shown in FIG. As is clear from FIG. 3, the sample to which this antioxidant was added was subjected to a heat resistance treatment of 3000 at 150 ° C.
The exothermic temperature hardly changed up to the h level, and the exothermic temperature gradually decreased thereafter, and the number of test samples n
The variation of 10 was also small. On the other hand, in the sample without addition of this antioxidant, n = 10
Of the test samples of n = 3 are 300 to 40
The exothermic temperature had dropped from 0 h, and the other samples had no exothermic abnormalities up to the 4000 h level, but n = 2 at about 4500 h and n = 1 at about 5000 h. The actual life of the heating element is determined by heat, current flow, humidity, etc., but if this current life is estimated by simulation etc., the sample with the antioxidant added will gradually generate heat after 30,000 to 40,000 h. The temperature drops and it safely reaches the end of life. In addition, in the composition without antioxidant, 3000 to 4000 h
Some have a short heat generation life, or generate heat over the level of 20000h, but there are also some that have a very high risk of sparking at the end of the life, and further smoking / ignition. is assumed. Although the life varies depending on the mode actually used, the addition of this antioxidant showed excellent performance of ensuring high safety up to the life end. Further, an antioxidant can be appropriately added so that not only long-term safety can be achieved but also a heat generation life suitable for a practical period in various applications and heat resistance characteristics of constituent materials. Thus, pentaerythrityl-tetrakis [3- (3,5-di-t-butyl-4]
-Hydroxyphenyl) propionate] is added to clarify the safety mechanism up to the end of the life, and there is no risk of abnormal overheating, smoking, ignition, etc. It is possible to provide a positive resistance temperature coefficient heating element for output, which is extremely useful in practice.

[0009] In general, when an antioxidant is added to an organic positive temperature coefficient resistor, oxidative deterioration of the resin is improved, but it has a great influence on electrical properties such as resistance and is difficult to use stably. It was The antioxidant consisting of pentaerythrityl-tetrakis [3- (3,5-di-t-butyl-4-hydroxyphenyl) propionate], which is the hindered phenolic antioxidant of the present invention, has the following electrical properties. The resistor has the effect of specifically stabilizing and increasing the resistance, and is susceptible to the deterioration of the resistor, the hot zone, etc., and the above-mentioned effects can be obtained by configuring the pair of electrode bodies in a non-polymerizable portion. Is what makes it possible. The composition of the antioxidant is not limited to diffusion from the exterior material, as long as it can act on the site where the pair of electrode bodies does not polymerize, and for example, even if added to this site before coating the exterior material. Of course, this antioxidant-added resistor may be formed at the site where the electrode body does not polymerize. Furthermore, the conductive fine powder is dispersed in a crystalline polymer, and then a particulate positive temperature coefficient of resistance coefficient resistance composition obtained by crosslinking and subdividing is dispersed in a binder such as a crystalline polymer to enhance resistance safety. In the above composition, since the conductive fine powder forms a clear chain, the above-mentioned action of this antioxidant becomes remarkable, and its reliability is further ensured. Further, as described above, in order to increase the output, it is preferable that the thickness of the positive temperature coefficient resistor is 1 mm or less, and the above effect becomes more remarkable as the electrode interval becomes closer. .

[0010]

As described above, according to the present invention, the following effects can be obtained.

(1) Suppressing deterioration of easily deteriorated parts,
It is possible to obtain a positive temperature coefficient resistor having high safety for a long period of time without danger of abnormal overheating, smoke generation, ignition, etc.

(2) An antioxidant is added to the exterior material, and the antioxidant is diffused by annealing to the site where the positive resistance temperature coefficient resistor is prone to deterioration. Therefore, the positive resistance temperature coefficient resistor having the structure of the present invention can be easily manufactured. Can be manufactured.

[Brief description of drawings]

FIG. 1 is a perspective view of a positive resistance temperature coefficient heating element according to an embodiment of the present invention.

FIG. 2 is a sectional view of the heating element.

[Fig. 3] Heat generation temperature performance diagram of the same heating element

FIG. 4 is a perspective view of a conventional positive resistance temperature coefficient heating element.

[Explanation of symbols]

4 Positive resistance temperature coefficient resistor 5,6 electrode body 7,8 Hot melt layer (exterior material) 9,10 Electric insulation layer (exterior material)

Claims (6)

[Claims] 1. A sheet-like positive resistance temperature coefficient resistor comprising conductive fine powder and a crystalline polymer, and a pair of positive resistance temperature coefficient resistor provided for applying a voltage in the thickness direction of the positive resistance temperature coefficient resistor. A portion composed of an electrode body and an exterior material for exteriorizing the positive resistance temperature coefficient resistor and the pair of electrode bodies, and a portion where the pair of electrode bodies does not overlap with each other in a projection plane in the thickness direction of the positive resistance temperature coefficient resistor. Pentaerythrityl-tetrakis [3-
(3,5-di-t-butyl-4-hydroxyphenyl)
Propionate] antioxidant with a positive temperature coefficient of resistance. 2. The positive resistance temperature coefficient heating element according to claim 1, wherein the positive resistance temperature coefficient resistor is formed by dispersing conductive fine powder in a crystalline polymer and then crosslinking the fine particles. 3. The positive resistance temperature coefficient heating element according to claim 1, wherein the positive resistance temperature coefficient resistor has a thickness of 1 mm or less. 4. A portion in which a pair of electrode bodies are not polymerized on a projection plane in the thickness direction of the positive resistance temperature coefficient resistor by adding an antioxidant to an exterior material having compatibility with the positive resistance temperature coefficient resistor and annealing. The method for producing a positive resistance temperature coefficient heating element according to claim 1, wherein the antioxidant is diffused into the material. 5. The method for producing a positive resistance temperature coefficient heating element according to claim 4, wherein the positive resistance temperature coefficient resistor comprises a conductive polymer powder dispersed in a crystalline polymer and then crosslinked. 6. The method for producing a positive resistance temperature coefficient heating element according to claim 4, wherein the positive resistance temperature coefficient resistor has a thickness of 1 mm or less.