JPH0443587A - Heating element with positive temperature coefficient of resistance - Google Patents

Abstract

PURPOSE:To prevent deterioration of a resistance body and realize a heater of a very long life by composing it of conductive grains in the form of fine grains so as to form conductive passes and produce fewer interface cracks between the conductive grains and binder by the cause of a differential thermal expansion. CONSTITUTION:A PTC resistance body 1 is composed of metal electrode lines 2, 3 disposed parallel to each other at a constant interval along the length, and the whole body is coated with an insulating body 4 (of polyvinyl chloride or the like). For the composition of the PTC resistance body, it comprises binder of crystalline high polymeric composite matter and conductive fine grains of a grain size of 0.5 - 100mum.

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 warming appliance and a general heating device.

2. Description of the Related Art A conventional string-shaped heating element with a positive temperature coefficient of resistance (hereinafter referred to as PTC) is a PTC resistor provided between a pair of electrode wires.
The temperature is self-controlled to an appropriate level by the TC characteristics. However, especially in cases where large power densities are required,
In order to make the temperature distribution of the heating element uniform, it is essential to improve the temperature distribution in the direction between the pair of electrode wires, and as a solution, the distance between the pair of electrode wires is made close to each other. methods have been taken.

In FIG. 2, electrode wires 7 and 8 are parallel linear metal electrodes that are placed close to each other at a constant interval, and a PTC resistor 9 is arranged to surround these electrode wires 7.8. As a result, a high-output PTC heating element is realized.

Problems to be Solved by the Invention In general, such PTC heating elements have the disadvantage that, with long-term use, the resistance of the entire heater increases and the heat generation temperature decreases. In particular, the type of PTC resistor in which a polymer composition is mixed with a conductive powder made of a finely divided crosslinked material has a sea-island structure between the conductive powder and the polymer as a binder, which improves safety and processing. Although it has excellent stability, it is difficult to obtain uniform heat generation distribution, so the above-mentioned tendency was noticeable. This is mainly because interfacial cracks occur due to the difference in thermal expansion between the crosslinked conductive powder and the uncrosslinked polymer as a binder, and the conductive bus is severed. This tendency is noticeable in the vicinity.

An object of the present invention is to improve the above-mentioned problems and 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 string-like positive electrode whose main component is a conductive composition obtained by dispersing conductive fine powder in a crystalline polymer composition. a resistor with a temperature coefficient of resistance,
A heating element having a positive temperature coefficient of resistance, comprising a pair of metal electrode wires surrounded by the resistor and facing each other in parallel with a constant interval, and an electrical insulator sheathing the metal electrode wires, and a conductive composition. After cross-linking with an electron beam or a cross-linking agent such as an organic peroxide, this is ultra-fine to form a fine particulate conductive composition, which is then mixed and dispersed in a crystalline polymer composition to form a conductive composition. A heating element with a positive temperature coefficient was made using a thermoplastic composition.

Effects FIG. 3 shows the results of examining the influence of the particle size of the conductive powder in the polymer composition on the rate of change in resistance value during intermittent energization of 100 V in the above configuration. As is clear from FIG. 3, there is a close relationship between the maximum particle size of the conductive powder and the rate of change in resistance value. In particular, when the maximum particle size is 100 μm or less, the change in resistance value is extremely stabilized. This is because there is a difference in thermal expansion between the conductive powder and the polymeric material as the binder, and repeated heat-generating energization causes interface cracks, especially in large powders.However, in the present invention, fine particles with a maximum particle size of 100 μm or less By equalizing the formation of conductive paths and stress unevenness, a mechanism is formed to minimize the occurrence of interface cracks, which can improve the high resistance caused by energization of the heating element and extend its life. It becomes possible.

EXAMPLE Hereinafter, a PTC heating element shown as an example of the present invention will be explained based on the drawings.

In FIG. 1, a PTC resistor 1 and this PTC resistor 1 are shown.
A metal electrode wire 2 (16 twisted copper wires with an outer diameter of 0.1 mm) and a metal electrode wire 3 (the metal electrode wire 2 and (same configuration). Further, the entire body is covered with an insulator 4 (polyvinyl chloride, etc.) to form a PTC heating element.

In addition, in the said Example, the PTC resistor 1 consists of the following composition. Using polyethylene as a crystalline polymer composition, 3.5 parts by weight of dicumyl peroxide as a crosslinking agent was blended with 100 parts by weight of a kneaded low-density polyethylene containing 40% by weight of furnace black as a conductive fine powder. A particulate conductive composition having a particle size of 0.5 to 35 μm and an average particle size of 15 μm was prepared by freeze-pulverizing the crosslinked product obtained by heat-treating at 180° C. for 1 hour.

Thereafter, this particulate conductive composition was used as a crystalline polymer composition in which carbon black as a conductive fine powder was mixed in low density polyethylene at a composition ratio of 28% by weight. Note that the resistor with this positive temperature coefficient of resistance is 3.2X
The volume resistivity value of 10'Ω-mouth is shown. Furthermore, ACl
When current was applied at ooV, a saturation temperature of about 62°C was exhibited.

To compare the above example of the present invention using conductive particles with a particle size of 0.5 to 35 μm and the sample using conductive particles with a particle size of 0.5 to 300 μm, the ambient temperature was 100 μm.
A continuous current durability test was conducted at ℃ and an applied voltage of 200V. The latter is 200% as the time for the resistance value change rate to reach 50%.
However, in the above-mentioned example, even after 7,500 hours, this has not yet been reached, indicating excellent current-carrying durability.

In the above examples, low density polyethylene was shown as the base crystalline polymer composition, but polyamide,
It may also be an ethylene-vinyl acetate copolymer, a graft polymer of acrylic acid or maleic acid, polypropylene, or the like.

Effects of the Invention As described above, according to the heating element having a positive temperature coefficient of resistance of the present invention, since it is composed of extremely fine conductive particles, it is difficult to form a conductive path when electricity is applied and to thermal expansion due to heat generation. Since interfacial cracks that occur frequently between the conductive particles and the binder due to the difference in maximum particle size are less likely to occur, deterioration of the resistor can be prevented and a heating element with an extremely long life can be realized. Also,
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 reliable and safe self-temperature control function.

[Brief explanation of drawings]

Fig. 1 is a sectional view of a PTC heating element showing an embodiment of the present invention, Fig. 2 is a sectional view of a conventional PTC heating element, and Fig. 3 is the resistance during intermittent energization when the maximum particle size of the conductive powder is AClooV. It is a graph showing the influence on the value change rate. 1... PTC resistor, 2, 3... metal electrode wire, 4... insulator. Agent's name Patent attorney Shigetaka Awano Haka 18 Figure PTC Camellia Chain Return Tane 1%1 wI Connection Salary Figure 2

Claims (1)

[Claims] After dispersing conductive fine powder in a crystalline polymer composition and crosslinking it with an electron beam or a crosslinking agent such as an organic peroxide,
This is finely powdered to form a particulate conductive composition having a particle size of 0.5 to 100 μm, and this is mixed and dispersed in a crystalline polymer composition to form a conductive composition as a main component. A resistor having a positive temperature coefficient of resistance in the form of a long string, a pair of metal electrode wires surrounded by the resistor and facing in parallel with a constant interval, and an electrical insulator sheathing the metal electrode wires. A heating element with a positive temperature coefficient of resistance.