JPH04144089A - Heat emitting element having positive resistance temperature coefficient - Google Patents

Abstract

PURPOSE:To suppress the trend of a heat emitting element turning into higher resistance and prolong the lifetime by adding a specific amount of silica to electroconductive particles, leaving to bridging reaction, turning into fine powder, mixing with crystalline highpolymer compound dispersedly, and accomplishing a resistance element consisting chiefly of this obtained substance as major component assuming the form of a long stretching tube, and also providing a pair of electrode wires spirally formed. CONSTITUTION:A (PTC) heat emitting element having positive resistance temp. coefficient is formed from a PTC resistance element 1 in the form of long stretching tube and a pair of electrode wires 2, 3 wound spirally, wherein the resistance element and electrode wires are covered with electric insulation 4. The resistance element 1 is fabricated through such procedures as dispersing 5-35wt.% electroconductive fine powder in crystalline highpolymer compound, bridging using an electron beam or a bridging agent for ex. organic peroxides, turning into finer particles, accomplish granular electroconductive compound, and mixing it with crystalline highpolymer compound dispersedly. The resultant object is not likely with crack initiation in the electroconductive powder due to thermal expansion, and degradation of the resistance value is prevented, and thus a heat emitting element of long life is obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION FIELD OF INDUSTRIAL APPLICATION The present invention relates to a heating element with a positive temperature coefficient of resistance that is used as a heating appliance and a general heating device.

Conventional technology Conventional tube-shaped positive resistance temperature coefficient (hereinafter referred to as PTC)
The heating element is self-controlled to an appropriate temperature by the PTC characteristics of a PTC resistor provided between a pair of electrode wires. However, when particularly high power density is required, it is essential to improve the temperature distribution in the direction between the pair of electrode wires in order to make the temperature distribution of the heating element uniform.
As a solution to this problem, measures have been taken in which the distance between a pair of electrode wires is made closer to each other.

In FIG. 2, the electrode wire 7 and the electrode wire 9 are parallel linear metal electrodes provided close to each other, and between them, the PT
By arranging the C resistor 8, a high output PTC heating element appears.

Problems to be Solved by the Invention In general, such PTC heating elements have a disadvantage that, with long-term use, the resistance of the entire heater increases and the heat generation temperature decreases. In particular, PTC resistors of the type in which a polymer composition is mixed with a conductive powder made by finely powdering a crosslinked material have a seabird structure between the conductive powder and the polymer as a binder, so there are safety concerns and processing problems. Although it has excellent stability, it is difficult to obtain uniform heat generation distribution, so the above-mentioned tendency was noticeable.

The purpose of the present invention is the above! Ill! The purpose is to provide a PTC heating element that is safe and durable for long-term use.

Means for Solving the Problems In order to achieve the above object, the present invention provides a long tube-shaped positive electrode whose bead component is a conductive composition prepared by dispersing conductive fine powder in a crystalline polymer composition. A positive electrode comprising a resistor having a temperature coefficient of resistance, a pair of electrode wires facing each other at equal intervals wound spirally along the longitudinal direction of the resistor, and an electrical insulator sheathing the electrode wires. A heating element with a temperature coefficient of resistance and a conductive composition are cross-linked with an electron beam or a cross-linking agent such as an organic peroxide, and then finely powdered to form a particulate conductive composition. A heating element with a positive temperature coefficient was created using a conductive composition formed by mixing and dispersing it in a molecular composition.

Effect In the above configuration, the amount of hydrophobic glue force (average secondary particle diameter 1.5 μm) added to the particulate conductive composition is 100V.
Figure 3 shows the results of examining the effect on resistance value changes during intermittent energization.As is clear from Figure 3,
It can be seen that there is a close relationship between the amount of silica added in the conductive particles and the rate of change in resistance value. Changes in resistance are particularly stable between 5 and 35% by weight. This is because the conductive powder is reinforced by the first cam, which further reduces thermal expansion.Secondly, a mechanism is formed that prevents thermal deterioration inside the conductive powder, which is extremely difficult to prevent due to energization of the heating element. High resistance can be improved, resulting in longer life or IU performance.

EXAMPLES Hereinafter, r) Tc heating elements shown as examples of the present invention will be explained based on the drawings.

In FIG. 1, a long tube-shaped PTC resistor] and a pair of equally spaced electrode wires 2 (copper with outer diameters of 0 and 1- line 1
(6 strands twisted) and an electrode wire 3 (same configuration as the electrode wire 2) are provided.

Further, the entire body is covered with an insulator (polyvinyl chloride) to form a PTC heating element.

In addition, in the said Example, the PTC resistor 1 consists of the following composition. 100 parts by weight of low-density polyethylene kneading Th using polyethylene as a crystalline polymer composition and containing 40% by weight of furnace black and 17% by weight of hydrophobic silica with an average secondary particle size of 1.5 μm as conductive fine powder. A mixture of 4.5 parts by weight of dicumyl peroxide as a crosslinking agent was heat-treated at 180'C for 1 hour to obtain a crosslinked product, which was freeze-pulverized to an average particle size of 60 μm.
A particulate conductive composition was prepared. Thereafter, this particulate conductive composition was prepared by kneading carbon black as a conductive fine powder in a composition ratio of 28% by weight into a low-pressure polyethylene as a crystalline polymer composition. The resistor having this positive temperature coefficient of resistance exhibited a volume resistivity of 4.3 x 10''Ω-1.Furthermore, when energized at AC 100⁻, it exhibited a saturation temperature of about 62°C.

In order to compare the example of the present invention using the above-mentioned conductive composition with a sample using conductive particles without addition of silicon oxide, an electric current durability test was conducted at an ambient temperature of 100'C and an applied voltage of 200cm. . The time required for the rate of change in resistance value to reach 50% was 6,500 hours in the latter case, but in the above-mentioned example, this had not yet been reached even after 10,000 hours had elapsed, indicating excellent current-carrying durability.

In the above examples, low-density polyethylene was shown as the crystalline polymer composition as the base, but polyamide, ethylene-vinyl acetate copolymer, graft polymers such as acrylic acid and maleic acid, polypropylene, etc. Good too.

Effects of the Invention As described above, according to the heating element having a positive temperature coefficient of resistance of the present invention, cracks and cracks in the conductive powder due to the difference in thermal expansion due to heat generation during energization are less likely to occur, so that the resistance value decreases. The deterioration of the heating element can be prevented, and a heating element with an extremely long life can be realized. Further, the rate of change in resistance value is greatly improved compared to the conventional example, and it is possible to realize a heating element having an extremely high degree of reliability and a safe self-temperature control function.

[Brief explanation of the drawing]

Fig. 1 is a side view showing the inside of a PTC heating element by cutting open the insulator showing an embodiment of the present invention, and Fig. 2 is a side view showing the inside of a PTC heating element according to an embodiment of the present invention.
C. Side view showing the inside of the heating element by cutting out the insulator, No. 3
The figure is a characteristic diagram showing the influence of the amount of silicon oxide in the conductive powder on the rate of change in resistance value during intermittent energization of AClooV. l...PTC resistor, 2.3...electrode wire, 4...insulator. Name of agent: Patent attorney Akira Okaji 2 people p. 1 Shin 1 (Cao 1y,)

Claims (1)

[Claims] Conductive fine powder and at least 5 to 35% by weight of silicon oxide are dispersed in a crystalline polymer composition, crosslinked with a crosslinking agent such as a solid beam or an organic peroxide, and then pulverized. a resistor having a positive temperature coefficient of resistance in the form of a long tube, the main component of which is a conductive composition formed by mixing and dispersing the particulate conductive plastic material in a crystalline polymer composition; A heating element with a positive temperature coefficient of resistance, comprising a pair of equally spaced electrode wires facing each other wound spirally along the longitudinal direction of the resistor, and an electrical insulator sheathing the electrode wires.