JPS6034793B2 - heating element - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a heating element that exhibits positive resistance-temperature characteristics and is made of a kneaded product of a crystalline resin, conductive powder, and electrically insulating inorganic powder.

U.S. Pat. , 591,526, U.S. Patent No. 3
．． It is known from the specification of No. 673,121.

Generally, when current is passed through a heating element with a positive temperature coefficient of resistance, a large amount of power is obtained at first due to the low resistance value, but as the temperature rises, the resistance value increases and the power gradually decreases. , the temperature is ultimately maintained at a balance between heat generation and heat radiation.

Figure 1 shows the PTC curves of PTC heating elements A, B, and C (A has excellent switching characteristics, B has a fairly large temperature coefficient of resistance, and C has a small temperature coefficient of resistance).
and heat dissipation curves D and E under certain conditions (D indicates a heat dissipation curve in a low temperature atmosphere or low voltage application, and E indicates a heat dissipation curve in a high temperature atmosphere or high voltage application), and the intersection point of these is the equilibrium temperature.

Now, when the condition changes from D to E, the constant temperature Tc at A
However, it varies from T to L in B, and from T3 to T4 in C.

Therefore, it is desirable that the fluctuation range of the equilibrium temperature is such that the temperature coefficient of resistance is large and the change in resistance value until the rise temperature is reached is very small. However, in general, as shown by B in FIG. 1, the resistance value tends to increase gradually up to the rise temperature Tc.

In particular, a kneaded composition of a crystalline polymer and a conductive material exhibits a positive temperature coefficient of resistance due to an increase in the contact resistance of the filled conductor due to the melting of the crystals. Since the temperature range in which the crystal melts is wide, the increase in resistance value up to the rise temperature Tc is large. Furthermore, when a composition with positive resistance-temperature characteristics is used as a heating element, if there is a part with a high resistance value, the voltage will concentrate there and the temperature will rise, resulting in a decrease in the resistance value. Due to the characteristic of increasing voltage, heat is generated where voltage concentration occurs locally, and as a result, the overall equilibrium temperature decreases. Figure 2 shows the situation. With conventional compositions of crystalline resin and conductive powder, non-uniform distribution of heat generation is unlikely to occur, and a heating element with low resistance, large temperature coefficient of resistance, and small increase in resistance up to rising temperature can be created. Things were difficult.

Furthermore, once the crystalline resin and conductive powder are determined, the PTC characteristics of the composition are determined, and it has been impossible to obtain arbitrary PTC characteristics. The present invention provides a composition that solves the above-mentioned conventional drawbacks, and is a composition in which a crystalline resin, a conductive powder, and an electrically insulating inorganic powder are kneaded together.

Crystalline polymers include polyethylene, polypropylene,
Polymethylbentene, polyacetal, nylon 6, nylon 11, polyvinylidene fluoride, polytetrafluoroethylene and copolymers thereof are most suitable. Furthermore, as the electrically insulating inorganic powder, oxides and nitrides of groups 0 and m of the periodic table of elements are optimal, such as magnesium oxide (Mg0), silicon oxide (Si02), beryum oxide (
Be○), and shelbalic acid nitride (BN). The optimum content, expressed as weight/g cent, is 20 to 80% of the crystalline resin, 1 to 70% of the conductive powder, and 5 to 50% of the electrically insulating inorganic powder.

This is because if the amount of crystalline resin is less than 20%, it does not exhibit PTC characteristics, and if it is more than 80%, the resistance value becomes too high, and if the amount of conductive powder is less than 1% to 70%, the resistance value becomes too low. Or, it is too expensive to be put to practical use. Hereinafter, the features of the present invention will be explained based on Examples in comparison with conventional heating elements.

First, the heating element according to the present invention uses polyvinyl fluoride IJ-dene as a crystalline resin, carbon black (Diablack G manufactured by Mitsubishi Kasei) as a conductive powder, and magnesium oxide (Mg0) powder as an electrically insulating inorganic powder. The mixture is then kneaded using a heated roller or kneader at the following ratio, and then pulverized to produce a paste in which isophorone is dispersed. Polyvinylidene fluoride: 4% by weight Carbon black: 4% by weight Magnesium oxide 2% by weight On the other hand, as a comparative sample, polyvinylidene fluoride: 5% by weight Carbon black: 5% by weight A paste with a composition of % is prepared.

The above two types of samples were coated on an alumina substrate, and after drying, the resistance value (the amount of coating was changed to have the same resistance value) and Q value (Q value = ln (RL'RT,) were lowered, Table 1 shows the voltage at which the heat generation peak occurs.
Shown below.

As can be seen from Table 1, Comparison of characteristic values with Sample 1 (product of the present invention) and Sample 2 (conventional product), the heating element according to the present invention (Sample 1
) has a high Q value, and the threshold voltage for generation of heat generation distribution is much higher than that of sample 2.

This is because by adding M and powder, the Mg○ powder acts as a kind of filler, and the expansion is suppressed to the temperature at which the resin crystals melt, and then expands rapidly when melting starts, resulting in resistance. It is thought that the temperature coefficient has increased. Furthermore, since the Mg◯ powder has high thermal conductivity, it is thought that the heat diffusion of the resistor is improved and the critical voltage at which the heat generation distribution occurs is increased. When the composition according to the present invention is used as a heating element in this manner, the fluctuation range of the controlled temperature is reduced, and the composition has the effect of being less susceptible to room temperature fluctuations and voltage fluctuations.

In addition, since the threshold voltage for generating heat distribution has increased, there is an advantageous effect in terms of destruction of the heating element due to abnormal voltage and long life. Furthermore, when the product of the present invention is used as a temperature sensor or a safety element, it has the effect that the response is longer and reliability is increased. As is clear from the above description, the heating element according to the present invention is an epoch-making device that has dramatically improved performance compared to similar heating elements of similar types.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing the resistance temperature curve and heat dissipation curve of the PTC heating element, and FIG. 2 is a diagram showing the state of heat generation distribution of the PTC heating element when voltage concentration occurs locally. Figure 1 Figure 2

Claims (1)

[Scope of Claims] 1. A heating element having positive resistance temperature characteristics made of a kneaded product of a crystalline resin, conductive powder, and electrically insulating inorganic powder. 2. The heating element according to claim 1, wherein the electrically insulating inorganic powder is an oxide or nitride of Group II or Group III of the periodic table of elements having high thermal conductivity. . 3. The heating element according to claim 1, wherein the heating element composition is pulverized and dispersed in a solvent to form a paste, which is applied to a substrate provided with electrodes and dried.