JPH0687426B2 - Heating element - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a heat collecting tool and a heating element useful as a general heating device.

2. Description of the Related Art A conventional heating element having a positive temperature coefficient of resistance (hereinafter referred to as PTC) is disclosed in, for example, Japanese Patent Publication No. 57-43995 and Japanese Patent Publication No. 55-40161.
As shown in the publication, the structure is as shown in FIG.

That is, a pair of opposed strip electrodes 2 are provided on an insulating substrate 1, and a PTC resistor 3 is provided on the strip electrodes 2. The PTC resistor 3 is self-controlled to an appropriate temperature. .

Problems to be Solved by the Invention However, in the case of such a configuration, especially the PTC heating element 3
When the heat generation is high, the temperature distribution becomes abnormally uneven,
There is a problem that not only an abnormally high temperature portion and a portion that hardly generates heat are generated, but also the abnormally high temperature portion has a risk of exhibiting smoke and ignition phenomena.

This is due to the following phenomenon.

Now, when a voltage is applied to the PTC heating element 3 to energize it, theoretically, as shown by the solid line a in FIG.
The heat generation temperature is substantially uniform in the resistor 3 part, and is self-controlled to a certain temperature by the PTC characteristic as shown in FIG. 7, for example. However, the non-uniformity of the resistance distribution of this PTC resistor 3,
In the case where the resistance distribution in the direction between the pair of electrodes 2 becomes slightly nonuniform due to a partial difference in the adiabatic state from the outside, local heating from the outside, etc. The voltage applied to the portion becomes large, the amount of heat generated in the portion A becomes larger than that in the other portions, and the temperature distribution as shown by the broken line b in FIG. 6 occurs. Along with this, the resistance of part A is PT
Due to the C characteristic, the resistance becomes even higher, the voltage applied to the A portion becomes larger, and the A portion becomes even hotter. In this way, finally, as shown in FIG. 8, the high-temperature heat generating portion A is exhibited. FIG. 9 shows the heat generation distribution in the direction between the pair of electrodes 2 at this time. In this way, once a slight temperature distribution occurs, the PTC characteristic of the PTC resistor 3 promotes and increases the temperature difference. This phenomenon will be called a voltage concentration phenomenon in the following description.

This voltage concentration phenomenon is more likely to occur as the amount of heat generation increases, and the conventional PTC heating element 3 limits the amount of heat generation or uses the insulating substrate 1 having very good thermal conductivity. I had to deal with the voltage concentration phenomenon.

By the way, when a resistor having excellent thermal conductivity, that is, a ceramic resistance element using barium titanate or the like is used, the limit of the amount of heat generated for suppressing this voltage concentration phenomenon can be considerably increased. Then, the size and shape can be considerably increased in terms of workability, but this resistor has no choice but to limit the size and shape in terms of workability, so that it is suitable for heating elements with a large area. Has to arrange a large number of these small elements, which complicates the connection for power supply and the like, is not flexible and is easily broken, and is difficult to be thermally coupled to a radiator or the like. In the above-mentioned field of use, there was a big problem that it was not practically practical.

Therefore, the present invention eliminates such conventional problems,
The purpose is to provide a safe and highly reliable heating element.

Means for Solving the Problems A means for solving the above problems is a composition in which conductive fine particles are dispersed in a pair of electrodes and electrically conductive between the electrodes and in a crystalline polymer. A resistor having a positive temperature coefficient of resistance containing as a main component, the resistor material itself between the pair of electrodes, or on the joint surface with the pair of electrodes to configure the resistor thinly, It is configured to form a voltage-dependent characteristic region having a negative resistance.

Action The action of this technical means is as follows.

That is, the resistance distribution of the PTC resistor is non-uniform,
The temperature distribution of the PTC resistor occurs when the adiabatic state is different, etc., and the PTC characteristic increases the resistance value of the part with relatively high temperature, and the action of increasing the voltage applied to this part. Along with this, the resistance value of this portion will become smaller due to the voltage-dependent characteristic of the resistance, and these two will cancel each other well, preventing abnormal heat distribution, smoke, ignition, etc. due to the voltage concentration phenomenon. It is possible to realize a safe and highly reliable heating element capable of generating a large amount of heat.

Embodiment An embodiment of the present invention will be described below with reference to the accompanying drawings.

Generally, a PTC heating element has a structure in which a PTC resistor is arranged between a pair of electrodes, and the resistor is, for example, 30% by weight of carbon black having a particle size of 50 mm and polyethylene.
It can be obtained by annealing a material sufficiently kneaded with 70% by weight and well dispersed and setting it to have a high specific resistance of 5 × 10 ⁴ Ωcm at room temperature.

FIG. 1 is a perspective view of an embodiment of the present invention, in which a PTC resistor having a high specific resistance obtained as described above is provided on the electrode plates 7 and 8 that closely face and face each other in the shape of a copper material. 9 is arranged. The resistance temperature characteristic diagram and the resistance voltage characteristic diagram between the pair of electrodes are as shown in FIG. 2 and FIG. 3, respectively. As can be seen from these figures, this heating element is different from the conventional one. While it has the PTC characteristic like the PTC resistor, it has the characteristic of becoming smaller as the resistance value voltage increases. This is because the voltage barrier layer is formed between the electrode plates 7 and 8 and the PTC resistor having a very high specific resistance, and the negative voltage dependence characteristic of the resistance appears between the barrier layers. To do.

When the resistance has a negative voltage-dependent characteristic, the temperature becomes relatively high when the resistance distribution between the pair of electrodes is non-uniform or the adiabatic state is locally different. The resistance value of the part increases due to this PTC characteristic, but with this, the voltage applied to this part also increases, and the resistance value decreases due to the voltage-dependent characteristic of the resistance. As a result, a uniform heat generation state can be revealed, and the abnormality due to the voltage concentration phenomenon is heat generation distribution.
It is safe because it does not emit smoke or fire. For example, when the temperature on the electrode 7 side becomes high, the resistance value increases on the electrode 7 side and the voltage applied to the region including the barrier layer on the electrode 7 side close to the electrode 7 also increases. Since the resistance value in this region becomes smaller, a safe and highly reliable heating element can be obtained.

Next, FIG. 4 shows an embodiment in which the PTC resistor material itself is provided with a negative voltage dependence characteristic without using the above-mentioned bonding surface with the electrode plate, which is realized by processing as follows. I was able to.

First, 50 weight percent of carbon black having a particle size of 20 millimicrons and 50 weight percent of polyethylene are sufficiently kneaded at a high temperature 100 ° C. higher than the melting point of polyethylene,
A composition in which carbon was sufficiently and uniformly dispersed was obtained. Next, 60% by weight of this composition, 25% by weight of polypropylene and 15% by weight of polyamide were thoroughly kneaded at a temperature of 220 ° C. to obtain this composition. Next, as shown in FIG. 4, the composition 12 was formed at a temperature of 220 ° C. so as to establish electrical conduction between the pair of electrodes 10 and 11, and then annealed at a temperature of 180 ° C., and then at 5 megarads. Irradiation with an electron beam gave a heating element. When the resistance temperature characteristics and the voltage dependence characteristics of the resistance of this heating element were measured, the same characteristic curves were obtained as in Fig. 2 and Fig. 3, respectively.
Although heat was generated at a high power density of / cm ^2, a safe heating element without abnormal heat distribution, smoke, or ignition was revealed. This is due to exactly the same phenomenon as described above, but the negative voltage-dependent characteristic of this resistance is that the virtual barrier layer is formed by the carbon which is very well dispersed and the polyamide which is incompatible with polyethylene. This is because it is formed at various places in the chain.

The PTC resistor is a resin such as carbon black and polyethylene in the above examples, but if the resistor is mainly composed of a polymer composition containing a particulate conductive agent centered on carbon black, Any material may be used. For example, as the resin used for this, there are crystalline resins such as polyethylene-vinyl acetate copolymers, polyethylene-ethyl acrylate copolymers, polyolefins such as polyethylene and polypropylene, polyamides, polyvinylidene halides, polyesters, etc. It shows a sharp positive temperature coefficient near the point.

Effects of the Invention As described above, according to the heating element of the present invention, the following effects are obtained.

(1) Since a voltage-dependent characteristic region having a negative resistance is formed on the resistor material itself between the pair of electrodes or on the joint surface between the thin-walled resistor and the pair of electrodes, the voltage concentration phenomenon occurs even at a high heat generation amount. It is safe because it can generate uniform heat without abnormal overheating, smoking, or ignition.

(2) Since the pair of electrodes and the heat generating portion of the resistor can provide the function of preventing the voltage concentration phenomenon, the responsiveness is good,
It is extremely safe and highly reliable.

(3) Not only can the above-mentioned high safety and high reliability be realized with a simple structure without using a substrate having excellent thermal conductivity, but also it is easy to have flexibility, and various forms can be obtained. It is applicable to PTC heating elements and is a very useful invention.

[Brief description of drawings]

FIG. 1 is a perspective view of a heating element according to an embodiment of the present invention, FIG. 2 is a resistance temperature characteristic diagram of a heating element according to an embodiment of the present invention, and FIG.
FIG. 4 is a resistance voltage characteristic diagram, FIG. 4 is a perspective view of a heating element of another embodiment of the present invention, FIG. 5 is a plan view of a conventional heating element, and FIG. 6 is a heating temperature of the heating element. FIG. 7 is a distribution diagram, FIG. 7 is a PTC characteristic diagram of the same heating element, FIG. 8 is a schematic diagram of occurrence of voltage concentration phenomenon of the same heating element, and FIG. 9 is a heat generation amount distribution chart when the same voltage concentration phenomenon occurs. 7,8,10,11 …… Electrode 9,12 …… PTC resistor.

Claims (1)

[Claims] 1. A positive temperature coefficient of resistance comprising a pair of electrodes and a composition in which conductive fine particles are dispersed in a crystalline polymer, which are arranged so as to be electrically conductive between the electrodes, as a main component. And a resistor having a resistance, and the resistor material itself between the pair of electrodes, or the resistor is formed into a thin wall, and a resistance-negative voltage-dependent characteristic region is formed on a joint surface with the pair of electrodes. A heating element.