JPH0632275B2 - Heating element - Google Patents

Description

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

2. Description of the Related Art A conventional heating element having a positive temperature coefficient of resistance (hereinafter referred to as PTC) has a structure as shown in FIG. 4, for example, as disclosed in Japanese Patent Publication No. 57-43995.

That is, a pair of strip-shaped electrodes 2 facing each other is provided on an insulating substrate 1, and a PTC resistor 3 is provided on the strip-shaped electrodes 2. The PTC resistor 3 self-controls the temperature to an appropriate temperature. It was something.

However, in the case of such a configuration, the temperature distribution becomes abnormally non-uniform, especially when the PTC heating element has a high calorific value.
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, if a voltage is applied to this heating element to energize it, theoretically, as shown by the solid line a in FIG. 5, the heating resistor 3 portion has a substantially uniform heating temperature, for example, as shown in FIG. It is self-controlled to a certain temperature by the PTC characteristic of the resistor. However, due to the non-uniformity of the resistance distribution of the PTC resistor 3, the partial difference in the adiabatic state from the outside, the local heating from the outside, etc., the resistance distribution in the direction between the pair of electrodes 2 becomes slightly non-uniform, When a portion having a relatively large resistance value (FIG. 5A) occurs, the voltage applied to the A portion becomes large, and the A portion generates a larger amount of heat than the other portions, as shown by the broken line b in FIG. A temperature distribution is generated. Along with this, the resistance value of the A section becomes higher due to the PTC characteristic, the voltage applied to the A section further increases, and the A section further increases in temperature. In this way, finally, as shown in FIG. 7, a high-temperature heat generating portion A is exhibited. The heat generation amount distribution in the direction between the pair of electrodes 2 at this time is shown in FIG. In this way, once a slight temperature distribution occurs, the temperature difference is promoted and increased by the PTC characteristics of the resistor. 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 limits the amount of heat generation or uses an insulating substrate having a very good thermal conductivity, so that this voltage concentration phenomenon occurs. Had to deal with.

By the way, when a resistor having excellent thermal conductivity, that is, a ceramic resistor 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, in terms of workability, there is no choice but to restrict the size and shape considerably, and in the case of heating with a large area, it is unavoidable to dispose a large number of these small elements, and the connection for power supply becomes complicated. In addition, it is not practically practical in the industrial application field of the present invention, which is not flexible and is easily cracked and is difficult to be thermally coupled to a radiator or the like.

Therefore, the present invention solves the above-mentioned conventional problems, and provides a safe, highly reliable, and high-performance heating element configuration without abnormal heat distribution, smoke, ignition, etc. even at high heat values. The purpose is to provide.

Means for Solving the Problems Achieving the above-mentioned object The technical means of the present invention has a different idea from the conventional art. That is, it has a pair of electrodes facing each other and a positive temperature coefficient of resistance whose main component is a composition in which conductive fine particles are dispersed in a crystalline polymer, and a thickness of 1 mm provided between the pair of electrodes. The following thin-walled plate-like resistor is provided, and the thermal conductivity at a temperature of 20 ° C in the direction of current conduction between the pair of electrodes is λ ₂₀ [Kcal / mh ° C], and the thermal conductivity at an operating temperature is λυ [Kcal. / mh ° C], and the volume resistivity of the PTC resistor at a temperature of 20 ° C is ρ ₂₀ [Ω
m], volume resistivity at operating temperature ρυ [Ωm],
When the working voltage is expressed by E [V], ρυ / ρ ₂₀ > 1.5 ρ ₂₀ λ ₂₀ > 0.005E ² ρυλυ <30ρ ₂₀ λ ₂₀ so that the resistance of the resistor between the pair of electrodes is satisfied. A heat dissipation plate having a high thermal conductivity is formed on the outer peripheral surface of the current conducting portion.

Action The inventors have found that in the PTC heating element in which the volume resistivity between the pair of electrodes is set by the thermal conductivity and the working voltage,
It has been found that the voltage concentration phenomenon does not occur even when the amount of heat generated is high. A pair of electrodes and a resistor are configured to satisfy this phenomenon, and heat dissipation is large in the outer peripheral surface of the current conducting part of the resistor between the pair of electrodes where abnormalities such as voltage concentration phenomenon easily occur. By configuring the plate, it becomes possible to prevent an abnormal heat generation distribution due to a voltage concentration phenomenon including a pair of electrode end regions, as well as a risk of smoke and ignition. Further, with such a structure, the heat dissipating member made of metal or the like is also covered on the end portions of the pair of electrodes where thermal deterioration of the polymer material or the like in the resistor easily progresses. Furthermore, since this PTC resistor is made of a polymer material, it has flexibility, good workability, and good thermal bondability to the heat load body.

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

The thermal conductivity at a temperature of 20 ° C. in the direction of current conduction between the pair of electrodes is λ ₂₀ [Kcal / mh ° C.], the thermal conductivity at an operating temperature is λ _u [Kcal / mh ° C.], and the PTC resistor has a temperature of 20 ° C. Volume resistivity at the temperature of ρ ₂₀ [Ωm], volume resistivity at the operating temperature ρ _u [Ωm], and operating voltage E
When expressed by [V], if it is constructed so as to satisfy the relation ρυ / ρ ₂₀ > 1.5 ρ ₂₀ λ ₂₀ > 0.005E ² (A) ρυλυ <30 ρ ₂₀ λ ₂₀ (B) It has been experimentally revealed that the voltage concentration phenomenon does not occur. This relational expression is derived by analyzing that the voltage concentration phenomenon occurs when the amount of heat generation is high or the thermal conductivity between the pair of electrodes is small. As an example of a structure capable of high heat generation that satisfies this relationship, there is a structure as shown in FIG. As shown in FIG.
A pair of strip-shaped electrodes 4 and 5 are arranged on both sides of a thin-walled strip-shaped PTC resistor 6, and the strip-shaped electrode 4 is provided with an insulating film 7 and a heat radiating plate 8 as a heat load. Also, 9,
Reference numeral 10 is a lead wire for power feeding. According to this structure, even if the amount of heat generation is high, the volume resistivity ρ ₂₀ can be calculated by the formula (A) by decreasing the distance 1 between the pair of electrodes 4 and 5 or increasing the area of the electrodes 4 and 5. It is possible to easily use a sufficiently large value that satisfies the relationship of. Also,
Equation (B) sets the rate of change of the product of the volume resistivity and the thermal conductivity at the time of inrush and at the time of stability, but if this rate of change is too large, the voltage concentration phenomenon will occur, This limit is set, and by changing the creeping surface of the end portion between the pair of electrodes 4 and 5 in FIG. The magnification can be further reduced. Further, not only that, the thermal uniformity of the creeping portion of the end portion between the electrodes 4 and 5 is improved, and the voltage concentration phenomenon can be surely suppressed to the end portion.

Here, the PTC resistor 6 is a polymer composition containing a particulate conductive agent centered on carbon black. For example, the resin used therefor is a polyethylene-vinyl acetate copolymer or a polyethylene-ethyl acrylate copolymer. ,
There are polyolefins such as polyethylene and polypropylene, and crystalline resins such as polyamide, polyvinylidene halide, and polyester, which have a sharp positive temperature coefficient near their crystal transformation points. The distance between the pair of electrodes 4 and 5 is 0.
It is about 3 to 3 mm, and the PTC resistor 6 may be a composition having a high specific resistance.
The characteristics that satisfy the relationships of Eqs. (A) and (B) are easily obtained.
In order to realize a PTC heating element having a further high calorific value, it is effective to further reduce the distance between the electrodes 4 and 5, and preferably 1 mm or less.

Here, the PTC characteristic for self-controlling property has a positive temperature coefficient of resistance as described above, and as shown in the literature and experimental data described later, ρυ / ρ ₂₀ > 1.5 1.0 <λ ₂₀ The relationship of /λυ<1.5 is satisfied. In addition, the resistor 6 made of such a material
By using, the flexibility of the PTC heating element in which an electrode is formed on this resistor can be easily realized.

Actually, various experiments were conducted in this configuration.
Those satisfying the setting conditions of the expressions (A) and (B) had no voltage concentration phenomenon. An example of this is shown below. Here, the heat generation density is the heat generation amount per area of each PTC heating element.

Each of the above No. 1 to 7 is a table showing different experimental examples such as operating temperature and adiabatic conditions, but from this table (A)
It can be seen that the voltage concentration phenomenon does not occur in those satisfying the relationships of Eq. And (B). In No. 5, a voltage concentration phenomenon occurred immediately after the start of energization, and smoke was emitted from a part of the PTC resistor. Further, No. 6 seemed to be stable after the start of energization, but the voltage concentration phenomenon occurred after about 1 hour. The setting of the rate of change shown in the equation (B) does not occur in the voltage generation phenomenon even if the amount of heat generation is low even outside this setting range. Generally, this large rate of change is the resistance itself because of the durability characteristics of the PTC resistor. Is prone to damage and is set with this meaning included. Generally, the thermal conductivity of a crystalline polymer material is, for example, “Plastic material course polyethylene resin” (published by Nikkan Kogyo Shimbun, August 1969, page 87).
55), the thermal conductivity (λ ₂₀ ) of polyethylene resin, which is a crystalline polymer material, at 20 ° C.
Depends on the type of polyethylene, λ ₂₀ = 0.3
˜0.5 Kcal / mh ° C., and the thermal conductivity at the use temperature of the present invention of about 100 ° C. is λυ≈0.2 to 0.4 K Cal / mh ° C.
Is. Thus, it has been clarified that the thermal conductivity decreases as the temperature rises. It is also stated that the thermal conductivity of composite materials containing carbon black decreases with increasing temperature (AO319A Acta
Phys PO1 A VOL.50, No.1 PAGE.125-127 1976) The thermal conductivity (20 ° C.) of the composite material in this document is λ ₂₀ = 0.2 to 0.4 Kcal / mh ° C. (Λ) and temperature (T) are shown by the relationship of λ = A-BT (A and B are constants determined by the material, and when the operating temperature is about 100 ° C., generally 1.0 <λ ₂₀ / λυ <1. 5, 1.2 <λ ₂₀ /λυ<1.5 was also obtained in the experiment of the present example. Next, for the electrodes 4 and 5, a copper foil was used in this example, but what if it is a conductor? Any electrode may be used, and this electrode also has the effect of improving the temperature distribution.

Next, in this embodiment, the heat load body is the heat dissipation plate 8 which is thermally coupled to the electrode 4. However, the larger the heat conductivity of the heat dissipation plate 8 is, the more the heat diffusion is increased. The temperature distribution is improved, and the heat generation amount per area of the PTC heating element is efficiently increased so as to maintain the self-control temperature due to the PTC characteristic as the heat diffusion of the heat dissipation plate 8 is increased. It also has an advantage that the heating element having a small mounting area can efficiently generate heat, as compared with the conventional heating element shown in FIG. Further, since the mounting area of the heating element can be made small, not only can it be constructed inexpensively with a small amount of material, but also when the heating element is incorporated in a floor heating panel or the like, the leakage current to the outside can be suppressed to be small. It also has the effect of being safe. The same effect as described above can be obtained with other heat load bodies, and the voltage concentration phenomenon can be prevented as described above even if the heat load is small. Further, since this PTC heating element is made of the material of the PTC resistor 6, it is excellent in workability and can have flexibility, so that it can be easily installed in equipment of various sizes.

Next, a second embodiment of the present invention is shown in FIG. In FIG. 2, reference numeral 11 denotes a core thread made of polyester or the like, on which an electrode 12 spirally wound, a thin-walled PTC resistor layer 13, an electrode 14 spirally wound, and an insulating outer coat 15 are sequentially formed. Has been done. Again 16
Is a heat sink. Also in this embodiment, this electrode 1
By setting the volume resistivity between 3 and 14 by the thermal conductivity and the operating voltage, the same effect as above can be obtained.

Next, considering the case where the thermal conductivity between the pair of electrodes is large, the ranges of the equations (A) and (B) for preventing the voltage concentration phenomenon become larger. Utilizing this, PT between these electrodes
A material having a high thermal conductivity may be interposed in the C resistor or the exterior portion. However, as described above, a ceramic resistor having excellent thermal conductivity is difficult to work in practice because the workability is likely to be deteriorated. Therefore, for example, as shown in FIG. 3, a strip-shaped PTC resistor 18 is arranged between a pair of strip-shaped electrodes 17 and 17 ', and a heat sink plate 20 and a heat sink plate 21 are thermally coupled to the outer periphery via an insulating outer skin 19. Consider another example. In this case, the B portion of the heat radiating plate 21 is located in the inter-electrode direction, the thickness of the B portion of the heat radiating plate 21 is d ₁ and d ₂ , the distance in the width direction of the electrode is W, and the PTC resistor 18 is Thermal conductivity is λ
_{When T is} the thermal conductivity of the heat sink 21 and λ _H , λ ₂₀ and λ _u in the equations (A) and (B) are It can also be corrected to. Here, α is a coefficient depending on the thermal coupling state and the like. In the present embodiment, α = 0.8 level, but it may be appropriately set in each state.

As described above, the resistor 18 between the pair of electrodes 17, 17 '
By forming the heat dissipation plate 21 having a large thermal conductivity on the outer peripheral surface of the current conducting portion, especially the part B, the danger due to the voltage concentration is surely suppressed to the surface of the pair of electrode end portions, and the positive output of the high output is positive. This is to realize a resistance temperature coefficient heating element.

EFFECTS OF THE INVENTION As described above, the heating element of the present invention has the following effects and is an extremely useful invention in practice.

(1) A heat dissipation plate with a large conductivity is formed on the outer peripheral surface of the current conducting part of the resistor between a pair of electrodes, and an abnormal heat distribution due to the voltage concentration phenomenon including the pair of electrode end regions The risk of ignition is prevented, and a safe and highly reliable heating element can be easily realized even with a high heating value.

(2) A pair of electrode ends in which a heat dissipating plate having a large thermal conductivity is formed on the outer peripheral surface of the current conducting portion of the resistor between the pair of electrodes, and thermal deterioration of the polymer material in the resistor easily progresses. Since a heat radiator made of metal or the like is also interposed in the part, the heat resistance performance of the resistor is improved and the life of the heat generator is extended,
By using a polymer material for the resistor, there is an effect that it is flexible and has good thermal coupling property to the heat load body and high thermal efficiency.

(3) Since it is possible to realize a high heat generation amount, it is possible to downsize the heat generating element, reduce the mounting area for the heat load element, and reduce the leakage current. The degree of freedom in doing so can be greatly expanded.

[Brief description of drawings]

FIG. 1 is a perspective view of a heating element according to the first embodiment of the present invention, and FIG.
FIG. 4 is a perspective view of a heating element according to a second embodiment of the present invention, FIG. 3 is a sectional view of a heating element according to a third embodiment of the present invention, and FIG. 4 is a plan view of a conventional heating element. Fig. 6 is a heat generation temperature distribution diagram of the same heating element, Fig. 6 is a PTC characteristic diagram of the same heating element, Fig. 7 is a schematic diagram of occurrence of voltage concentration phenomenon of the same heating element, and Fig. 8 is the same when the same voltage concentration phenomenon is generated. It is a calorific value distribution map. 4,5,12,14,17,17 '... Electrodes, 6,1
3,18 ... PTC resistor, 8,16,20,21 ...
Heat sink.

Claims (1)

[Claims] 1. A pair of electrodes facing each other and having a positive temperature coefficient of resistance whose main component is a composition in which conductive fine particles are dispersed in a crystalline polymer, and are provided between the pair of electrodes. A thin plate-shaped resistor having a thickness of 1 mm or less (hereinafter referred to as PTC resistor), and 20 in a current conduction direction between the pair of electrodes.
The thermal conductivity at a temperature of ℃ is λ ₂₀ [Kcal / mh ° C], the thermal conductivity at the operating temperature is λυ [Kcal / mh ° C], the PT
Let ρ be the volume resistivity of the C resistor at a temperature of 20 ° C.
₂₀ [Ωm], volume resistivity at operating temperature ρυ [Ω
m], and when the working voltage is expressed by E [V], ρυ / ρ ₂₀ > 1.5 ρ ₂₀ λ ₂₀ > 0.005 E ² ρυλυ <30ρ ₂₀ λ ₂₀ A heating element comprising a heat dissipation plate having a large thermal conductivity on the outer peripheral surface of the current conducting portion of the resistor.