JPH03176981A - Heating element with positive resistance temperature coefficient - Google Patents

Abstract

PURPOSE:To obtain a heating element with a long life by providing conducting composition materials with rubber elasticity between metal electrode wires of the heating element with a positive resistance temperature coefficient and a PTC resistor for electric connection. CONSTITUTION:Long cord-shaped electrode wires 5, 6 coated with conducting rubber composition materials 9, 10 around a pair of long metal electrode wires 7, 8 arranged in parallel at a fixed interval are coated with a resistor 11 with a positive resistance temperature coefficient mainly made of a conducting composition material re-mixed with crystalline polymer and conducting grains obtained by bridge-treating a mixture made of crystalline polymer and conducting fine powder and crushing it, and the resistor 11 is covered with an electric insulator 12 to obtain a PTC heating element. The conducting composition materials 9, 10 with rubber elasticity made of maleic acid anhydride denatured hydrogenated styrene thermoplastic elastomer with the volume specific resistance value 2.1X10<3>OMEGA-cm containing carbon black 35wt.%, for example, are provided between the metal electrode wires 7, 8 and the PTC resistor 11 for electric connection, thus the deterioration of the boundary surface between the metal electrode wires 7, 8 and the PTC resistor 11 caused by the thermal expansion difference due to the heating at the time of excitation can be prevented.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a heating element having a positive temperature coefficient of resistance that is used as a warming appliance and a general heating device.

2. Description of the Related Art The cross section of a conventional heating element having a positive temperature coefficient of resistance (hereinafter referred to as PTC) is as shown in FIG. It has a structure in which a body 3 is covered with an electrical insulator 4, and a metal electrode wire 1.
When a voltage is applied to PTC resistor 3, a current flows through PTC resistor 3 and the resistor temperature rises.When it reaches a certain temperature, the resistance value suddenly increases, and the current is lowered to keep the resistor temperature constant. It had become.

Problems to be Solved by the Invention However, with the above configuration, when used for a long period of time at high power density, the entire heater becomes highly resistant due to interfacial cracks formed mainly at the interface between the PTC resistor and the electrode wire, causing heat generation. It had the disadvantage of lowering the temperature. In particular, a type of PTC resistor in which a cross-linked polymer composition and a conductive powder made into fine powder after pulverization are combined has a sea-island structure between the conductive powder and the binder polymer composition. Although it has excellent safety and processing stability because of its high temperature, it is difficult to obtain uniformity in heat generation distribution, so the above-mentioned tendency was noticeable.

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 solve the above problems, the present invention provides a pair of long metal electrode wires that face each other in parallel at a constant interval, each of which is coated with a conductive rubber composition on its outer periphery. The main material is a conductive composition made by crosslinking and pulverizing a mixture of a string-like electrode wire, a crystalline polymer, and a conductive fine powder to form conductive particles, and then remixing the conductive particles and crystalline polymer. a long resistor having a positive temperature coefficient of resistance and covering the string-like electrode wire as a component;
A heating element having a positive temperature coefficient of resistance is constructed from the electrical insulator covering the resistor.

Function: In the present invention, as described above, by interposing a conductive rubber assembly having rubber elasticity between the PTC resistor and the metal electrode wire, the metal electrode wire is removed by the expansion of the PTC resistor when it is heated by electricity. Absorbs the mechanical load on the metal electrode wire and PT
It becomes possible to prevent interface cracking due to the difference in thermal expansion of the C resistor.

In particular, in the type of PTC resistor made by mixing a crosslinked polymer composition and finely divided conductive powder, there is a difference in thermal expansion between the conductive powder and the polymer material as a binder, and the metal electrode when energized generates heat. Since it is possible to absorb the stress unevenness caused by the expansion of the wire, it is possible to improve the high resistance caused by energization of the heating element.

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

In Figure 1, 5 and 6 are 1s facing each other in parallel at regular intervals.
The outer periphery of the pair of long metal electrode wires 7 and 8 is coated with a conductive rubber composition 9. A long string-like electrode wire coated with IO, the string-like electrode wire 5.6 is cross-linked and pulverized with a mixture of crystalline polymer and conductive fine powder to form conductive particles. coated with a resistor 11 having a positive temperature coefficient of resistance, the main component of which is a conductive composition obtained by remixing particles and a crystalline polymer;
The resistor is covered with an electrical insulator 12 to form a PTC heating element.

The PTC resistor 11 is made of the following composition.

A mixture of 100 parts by weight of a kneaded material containing 60% by weight of high-density polyethylene as a crystalline polymer and 40% by weight of carbon black as a conductive fine powder was blended with 3.5 parts by weight of dique rubber oxide as a crosslinking agent at a temperature of 18°. The crosslinked product obtained by heat treatment at °C for 1 hour was freeze-pulverized to produce conductive particles with an average particle diameter of 80 μm. after that,
The conductive particles were remixed with high-density polyethylene to form a resistor containing 25% by weight of carbon black. This PTC resistor exhibited a volume resistivity of 1.3 x 10' ohm-cm.

Furthermore, for conductive compositions having rubber elasticity, 35% by weight
2. Contains carbon blank. A maleic anhydride-modified hydrogenated styrene thermoplastic elastomer having a volume resistivity of 1X10'' Ω-cm was used.

The resistors of the above example and the conventional example were tested at an ambient temperature of 100°.
A current durability test was conducted at a C1 applied voltage of 200 V.

The latter is 10 as the time for the resistance value change rate to reach 50%.
00 hours, but in the above-mentioned example, even after 4,200 hours, the current-carrying durability was not reached, indicating that the current-carrying durability was excellent.

In the above examples, polyethylene was used as the crystalline polymer composition as the haze, but polyethylene, polyamide, ethylene-vinyl acetate copolymer, polypropylene, etc. may also be used. Additionally, for conductive compositions exhibiting rubber elasticity, thermoplastic elastomers such as olefin-based TPE, ester-based TPE, and urethane-based TPE may be used as the hese polymer. Further, polyisoprene, ethylene-propylene copolymer, isoprene-isobutylene copolymer, etc. may be used.

In addition, as the metal electrode wire, 16 copper wires with an outer diameter of 0.1 mm are used.
A real twisted one was used. Furthermore, although polyester is used as the electrical insulator, polyvinyl chloride, polyphenylene sulfide, polyethylene naphthalate, etc. may also be used. Although the high-density polyethylene was cross-linked using dichloromethane, it may also be cross-linked using an electron beam.

Effects of the Invention As described above, according to the heating element having a positive temperature coefficient of resistance of the present invention, an electrical connection is made between the metal electrode wire and the PTC resistor through the conductive composition having rubber elasticity. Therefore, it is possible to prevent deterioration of the interface between the metal electrode wire and the PTC resistor due to the difference in thermal expansion due to heat generation during energization, and it is possible to realize a heating element with an extremely long life. In addition, the rate of change in resistance value is greatly improved compared to the conventional example, and a heating element having an extremely reliable and safe self-temperature control function can be realized, which has great effects.

[Brief explanation of drawings]

FIG. 1 is a sectional view of a PTC heating element, not showing an embodiment of the present invention, and FIG. 2 is a sectional view of a conventional PTC heating element. 5.6... String-shaped electrode wire, 7,8...
Metal electrode wire, 9,10... conductive rubber composition,
11... PTC resistor, 12... Electric insulator.

Claims (1)

[Claims] A pair of long metal electrode wires facing each other in parallel at a constant interval, each of which is coated with a conductive rubber composition on its outer periphery, and is made of a crystalline polymer and a conductive fine powder. The positive resistance temperature of the long length of the electrode wire coated with the conductive composition, which is obtained by crosslinking and pulverizing the mixture to form conductive particles, and remixing the conductive particles and crystalline polymer as a main component. A heating element with a positive temperature coefficient of resistance, consisting of a resistor with a constant temperature coefficient and an electrical insulator covering the resistor.