JPH0746631B2 - Positive resistance temperature coefficient heating element - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a heating element having a positive resistance temperature coefficient used for heating appliances and general heating appliances.

(Prior Art) A composition in which a conductive fine powder such as carbon black is dispersed in a crystalline polymer such as polyethylene, ethylene-vinyl acetate copolymer, ionomer, polypropylene and polyvinylidene fluoride has a temperature near its melting point. It is known that the resistance value rapidly increases due to a rapid change in physical properties when the crystal part becomes amorphous. For this reason, applying its characteristics, when the temperature reaches a predetermined temperature, the power suddenly drops, and the heat generator itself prevents temperature runaway, while keeping the temperature constant according to the fluctuation of the heat load. A so-called self-regulating heating element in which electric power is automatically controlled has been studied.

A conventional positive resistance temperature coefficient heating element will be described with reference to FIGS. 3 to 5 are perspective views of a conventional positive resistance temperature coefficient heating element. In FIG. 3, 7 is a ceramic substrate having excellent electrical insulation and thermal conductivity, 8a and 8b are electrodes, and 9 is an electrode.
Is a positive temperature coefficient resistor having a crystalline polymer and carbon black as main components, 10 is an electrically insulating film, and 11 is a metal soaking plate.

FIG. 3 shows an example of a typical positive resistance temperature coefficient heating element based on the prior art disclosed in Japanese Examined Patent Publication No. 55-40161. The ceramic substrate used here is a ceramic-based material. Generally, a ceramic-based sintered body, which is made of a bonded body, exhibits extremely good heat conduction characteristics even though it is an electrical insulator, and therefore maintains a uniform temperature distribution over almost the entire surface of the positive resistance temperature coefficient resistor. It has a high ability and can maintain a stable heat generation state due to the normal resistance value distribution and the potential distribution, and it was very effective in constructing a high output positive resistance temperature coefficient heating element. As an example, when an alumina sintered body having an extremely excellent thermal conductivity of 29 Kcal / mh ° C. was used, a power density exceeding 1 W / cm ² was possible.

However, such a ceramic-based material such as an alumina sintered body cannot be put to practical use in terms of manufacturing technology and strength when forming a large area heating element or a long heating element. There wasn't.

Therefore, as an alternative to this ceramic-based substrate material, for example, the fourth disclosed in Japanese Patent Publication No. 57-43995 is disclosed.
A composite material substrate consisting of an electric insulating film 10 and a metal heat equalizing plate 11 as shown in the figure has been used, but the resin, which is the material of the electric insulating film 10, has a thermal conductivity of about two orders of magnitude compared to ceramics. The low thermal conductivity of the composite material did not exceed that of the ceramic. Therefore, the upper limit of the power density of these heating elements was 0.3 W / cm ² . As a result, in many applications, the output of the heating element is insufficient, or the mounting area of the heating element becomes unnecessarily large, and the leakage current due to induction reaches a dangerous level. It had been.

Therefore, paying attention to the structure of the positive resistance temperature coefficient heating element, for example, as shown in JP-A-60-28195 or FIG. 5, the distance between the pair of electrodes 8a and 8b should be close to each other. As a result, a method of significantly increasing the heat diffusion capacity of the positive resistance temperature coefficient resistor 9 itself without depending on the soaking effect of the substrate has been studied. The way to realize the body has been opened.

(Problems to be Solved by the Invention) However, the conventional positive resistance temperature coefficient heating element as shown in FIG. 5 is very excellent as a structure for generating a high output, but has a large bending rigidity. Due to its structure, if it is attached to a part with a small curvature or is used for applications requiring flexibility, stress exceeding the allowable limit will be applied to either the electrode body or the resistor, resulting in disconnection or resistance of the electrode body. It was unavoidable to cause a large change in the resistance of the body.

The present invention aims to increase the output of a positive resistance temperature coefficient resistor having a high specific resistance value by reducing the distance between a pair of electrodes, and to make the structure a thin tape to have a flexible positive resistance temperature coefficient. A coefficient heating element is provided.

(Means for Solving Problems) In order to solve the above problems, the present invention provides a thin flat plate core, a pair of electrodes spirally wound around the core without contacting each other, and the pair of electrodes. A positive resistance temperature coefficient heating element constituted by a heating element composed of a positive resistance temperature coefficient resistor disposed between the heating element and an outer cover that covers the entire heating element, and at a side end portion of the thin flat plate core. It is characterized in that the pair of electrodes are fitted into the notched grooves provided at a predetermined interval, and the winding pitch of each of the pair of electrodes is fixed.

(Operation) According to the present invention, according to the above configuration, the distance between the pair of electrodes is increased by inserting the pair of electrodes into the notch grooves provided at the side ends of the thin plate-shaped core at predetermined intervals. It is possible to fix them extremely close to each other, and since they are covered so that the positive resistance temperature coefficient resistor is buried, the diffusion efficiency of heat to the positive resistance temperature coefficient resistor is high, High output can be obtained as a heating element. On the other hand, the core is a long thin flat plate core, and the electrode is spirally wound around it, so it is used for devices that have a low bending rigidity structurally and flexibly bend or have a curved surface with a small curvature. However, the stress exceeding the allowable limit is not applied to the electrodes and the resistor, and the electrode is not broken or the resistance value of the resistor is significantly changed. Further, since at least one of the heating element and the outer surface of the outer cover is formed flat, the heat conduction to the object to be heated is very good.

(Embodiment) An embodiment of the present invention will be described with reference to FIGS. 1 and 2.
1 and 2 are perspective views showing the structure of a positive resistance temperature coefficient heating element according to an embodiment of the present invention by cutting out a part thereof, in which 1 is a thin flat plate core, 2a and 2b. Is a copper foil electrode, 3 is a positive resistance temperature coefficient resistor, 4 is a shape-retaining material, 5 is an electric insulating jacket, and 6 is a notched groove.

The thin plate-shaped core 1 is made of polyaramid fiber nonwoven fabric with a thickness of 50 μm. This polyaramid fiber nonwoven fabric has excellent heat resistance and mechanical strength, and since it is fibrous, it has a boundary with the positive resistance temperature coefficient resistor 3. This was selected by paying attention to the fact that the core portion and the resistor portion can be integrated by forming an impregnated structure in each portion. But,
The material of the thin plate-shaped core 1 is not limited to the polyaramid fiber nonwoven fabric, and this component can be selected from many alternative materials. As alternative materials, woven fabrics, non-woven fabrics and films of organic, inorganic and composite materials are considered, and the best form is fibrous or porous. However, in practice, it is considered that most forms of materials can be used by applying adhesion treatment or the like. In terms of electrical characteristics, an insulating material is generally used, but some conductivity is acceptable as long as it does not interfere with the heat generation characteristics of the positive resistance temperature coefficient resistor 3. Rather, the moderately adjusted conductivity has an effect of preventing a micro arc caused by the concentration of the voltage locally when a micro crack is generated inside the positive resistance temperature coefficient resistor 3. In that case, the resistance value is preferably set in a range higher than the positive resistance temperature coefficient resistor 3 by 2 to 3 digits.

The copper foil electrodes 2a and 2b are a pair of copper foil electrodes wound around the polyaramid fiber nonwoven fabric of the thin plate-shaped core 1 and are arranged so that the electrode interval is 1 mm. Also, copper foil electrode 2
In order to prevent the contact resistance value of the positive resistance temperature coefficient resistor 3 from increasing, a and 2b are solder-plated and the winding pitch for the thin flat plate core 1 is accurately and stably maintained. In addition, embedding the electrodes 2a and 2b in the positive resistance temperature coefficient resistor 3 and forming the thin plate core 1 and the positive resistance temperature coefficient resistor 3 into a close contact structure can reduce the electrodes 2a and 2b.
The positive resistance temperature coefficient acts extremely effectively to prevent an increase in the contact resistance value with the resistor 3.

As shown in FIG. 2, a notch groove 6 for winding an electrode is accurately provided at a side end portion of the thin plate-shaped core 1 so that the winding pitch of the electrodes 2a and 2b around the thin plate-shaped core 1 can be adjusted. If it is fixed accurately, the effect of preventing the increase in the contact resistance value of the electrodes 2a and 2b with the positive resistance temperature coefficient resistor 3 can be further ensured.

The positive resistance temperature coefficient resistor 3 is extruded in parallel with the nonwoven fabric of the thin plate core 1 so as to embed the electrodes 2a and 2b, and generates heat by applying a voltage between the electrodes 2a and 2b. It is composed. As a material, it is natural to select a conductive material that is difficult to be oriented by a voltage in consideration of disposing it between electrodes that are close to each other, and to use a resistor material having a specific resistance value close to that of the semiconductor region. Focusing on stabilizing the contact state with the electrodes 2a and 2b, acrylic acid-modified polyethylene having excellent adhesiveness is used as the crystalline polymer. In this case, a copolymer type crystalline polymer having many functional groups is advantageous in terms of adhesiveness, while a purer material is disadvantageous,
It is necessary to select in consideration of this point. As for the shape of the positive resistance temperature coefficient resistor 3 after molding, it is common that even if the electrodes 2a and 2b are completely buried, the appearance thereof appears in the surface shape, but more heat is generated from the heating element. In order to take out, it is important to finish at least one surface of the outer surface to be flat so as to easily form a heat conduction path from the shape-retaining material 4 to the object to be heated through the electrically insulating outer cover 5.

The shape-retaining material 4 is a shape-retaining material that coats the positive resistance temperature coefficient resistor 3 on the exterior. Since the positive resistance temperature coefficient resistor 3 is annealed at a temperature of 160 ° C. or more, the deformation of the resistor 3 at that time is caused. To prevent this, a heat shrinkable polyethylene cross-link is used. However, the material is not limited to the cross-linked polyethylene, but it goes without saying that a material of the same system as the positive resistance temperature coefficient resistor 3 is desirable. Further, when the positive resistance temperature coefficient resistor that does not need to be annealed is used, the shape retaining material 4 is not necessary.

The electric insulation jacket 5 is a heat-resistant vinyl chloride jacket covering the entire heating element with electrical insulation. When using vinyl chloride,
It is necessary to pay attention to the prevention of plasticizer migration.
If the above is not used, it may be necessary to take measures such as winding a separator such as a polyester film around the surface of the positive resistance temperature coefficient resistor 3. Further, when it is desired to conduct more heat to the object to be heated and the outer shape of the shape-retaining material 4 is not formed flat, at least one outer surface of the electrically insulating jacket 5 is formed flat and the object to be heated is heated. It is necessary to maintain good adhesion to the body.

(Effects of the Invention) According to the present invention, a positive resistance temperature coefficient resistor made of a material having a specific resistance value close to that of a semiconductor region is used to generate heat between electrodes that are very close to each other, and high output is achieved. It is possible to form a thin tape-shaped positive resistance temperature coefficient heating element that is extremely excellent in bending resistance and heat transfer to the object to be heated.

As a result, the use of high-output positive resistance temperature coefficient heating element has been limited to rigid structure equipment or equipment with large curvature, but to cloth-like equipment or equipment with many curved surfaces with small curvature, etc. It is also possible to use it for flexible equipment, and it has the original feature that the high output positive resistance temperature coefficient heating element has a small induced leakage current per power, and its application range can be greatly expanded.

[Brief description of drawings]

FIG. 1 and FIG. 2 are perspective views showing the structure of a positive resistance temperature coefficient heating element according to an embodiment of the present invention by cutting out a part thereof, and FIG.
FIG. 5 to FIG. 5 are perspective views of a conventional positive resistance temperature coefficient heating element. 1 ... Thin flat plate core, 2 ... Copper foil electrode, 3 ... Positive resistance temperature coefficient resistor, 4 ... Shape retention material, 5 ... Electrical insulation jacket, 6 ... Notched groove.

Claims (6)

[Claims] 1. A thin plate-shaped core, a pair of electrodes spirally wound around the core without making contact with each other, a heating element composed of a positive temperature coefficient resistor arranged between the pair of electrodes, and the heat generation. A positive resistance temperature coefficient heating element constituted by an outer cover covering the entire element, wherein the pair of electrodes are fitted in notch grooves provided at predetermined intervals at side ends of the thin plate core. A positive resistance temperature coefficient heating element, characterized in that the winding pitch of each of the pair of electrodes is fixed. 2. A thin flat plate core having an electrical insulating property or a volume specific resistance value such that the calorific value is smaller than that of a positive resistance temperature coefficient resistor. Positive resistance temperature coefficient heating element. 3. The positive resistance temperature coefficient heating element according to claim 1, wherein the thin plate-shaped core is made of a fibrous or porous material. 4. A pair of electrodes is embedded in a positive temperature coefficient resistor, which is characterized in that (1).
A positive resistance temperature coefficient heating element as described in the item. 5. The positive resistance temperature coefficient heating element according to claim 1, wherein at least one outer surface of the heating element is formed flat. 6. The positive resistance temperature coefficient heating element according to claim 1, wherein at least one outer surface of the outer cover is formed flat.