JPS6245673B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention has a so-called positive temperature coefficient of resistance (hereinafter referred to as "positive temperature coefficient of resistance"), which generates heat when energized and whose resistance value increases as the temperature rises.
The present invention relates to improvements in self-temperature-controlled heating elements that have PTC characteristics (referred to as PTC characteristics).

Conventionally, as this type of heating element, a single-layer type heating element is known in which a uniform mixture of polyethylene, polypropylene, or rubber and carbon powder is formed into a sheet shape, and electrodes are attached to both ends of the sheet.

By the way, in this single-layer self-temperature-controlled heating element, localized abnormal heat generation is likely to occur, and once such abnormal heat generation occurs, it not only rapidly expands, but also causes the temperature to rise further. Accidents have frequently occurred in which the temperature of the thermoplastic resin or rubber, which is the constituent material of the device, reaches or exceeds the melting point, eventually leading to burnout and rendering the device unusable.

It is known that the frequency of occurrence of burnout accidents in self-temperature-controlled heating elements increases as the distance between the electrodes increases.

Therefore, in order to reduce the distance between the electrodes, PTC
A multilayer heating element has been proposed in which metal foil electrodes of the same size as the heating element are closely attached to both sides of a heating element having a characteristic.

According to this multi-layer heating element, the thickness of the heating element corresponds to the distance between the electrodes, so the distance is much shorter than that of the single-layer heating element, and it is seen as a promising means for preventing burnout. There is.

However, in this multilayer heating element, since metal foil electrodes of the same size as the heating element are closely attached to both sides of the heating element, the flexibility of the element is reduced. Therefore, when this heating element is used in a curved shape, there are problems in that wrinkles occur in the metal foil electrode on the inside of the curve, and cracks occur in the metal foil electrode on the outside of the curve.

The present invention relates to a self-temperature-controlled heating element that solves the problems of conventional products.
or a sheet made of a mixture of rubber and a conductor, or a sheet made by impregnating and coating a cloth-like substrate with the mixture, wherein both sides of the high-resistance sheet having a positive temperature coefficient are coated with thermoplastic resin and/or rubber. A sheet made of a mixture of conductors or a sheet made by impregnating and coating a cloth-like base material with the mixture, and when the electrical resistance of the high-resistance sheet is XΩ-cm, the electrical resistance is not more than X×10 ^-3 Ω-cm. A low resistance sheet exhibiting an electrical resistance of

Both the high-resistance sheet and the low-resistance sheet used in the present invention are made of thermoplastic resin such as polyethylene, polypropylene, ethylene-vinyl acetate copolymer, ethylene-ethyl acrylate copolymer, polyethylene terephthalate, polyvinylidene fluoride, etc. Carbon powder on rubber
Fine conductors such as carbon beans, metal powder, carbon short fibers, etc. are mixed uniformly to a thickness of 0.05 to 5.
It is formed into a sheet shape of about mm, or it is made by coating and impregnating a woven fabric, nonwoven fabric, or mesh base fabric with a dispersion of the mixture of the thermoplastic resin and/or rubber and a conductor, and it becomes flexible. It is rich.

The amount of conductor mixed with the thermoplastic resin and/or rubber is approximately 15 to 60 parts by weight per 100 parts by weight of resin and/or rubber in the case of high resistance sheets, and about 15 to 60 parts by weight in the case of low resistance sheets. So that the electrical resistance is lower than that of the resistance sheet, that is, when the electrical resistance (volume resistance) of the high resistance sheet is X Ω-cm, that of the low resistance sheet is less than X × 10 ^-3 Ω-cm. Therefore, it is mixed in a larger amount than in the former case, usually about 30 to 100 parts by weight.

In the present invention, when the electrical resistance of the low resistance sheet is XΩ-cm, the electrical resistance of the high resistance sheet is
The reason for setting it below 10 ^-3 Ω-cm is to ensure that only the high-resistance sheet generates heat uniformly over its entire surface when energized.If the difference in electrical resistance between the two sheets is too small and deviates from the above relationship, the This is not preferable because only the vicinity of the electrode generates heat, and the desired self-temperature-controlled heating element cannot be obtained.

In the present invention, when the electrical resistance of the high-resistance sheet and the low-resistance sheet is set as described above, only the high-resistance sheet generates heat uniformly over its entire surface when current is applied, while the low-resistance sheet spreads the current through the thickness of the element. Although it functions to flow in the horizontal direction, it does not generate any heat itself. The reason for this is not necessarily clear, but when the electrical resistance of the high-resistance sheet and the low-resistance sheet are set as described above, the potential distribution on the surface of the low-resistance sheet almost disappears, and the electric potential inside the low-resistance sheet is It is inferred that virtually no consumption occurs and therefore no heat generation occurs.

Hereinafter, examples of the present invention will be explained with reference to the drawings. In Figures 1 and 2, 1 is usually 10 ⁴ to 10 ¹⁰
It is a high-resistance sheet with an electrical resistance of about Ω-cm, and low-resistance sheets 2 and 2' are adhered to both sides of the sheet by means such as heat fusion or conductive adhesive. 2 and 2' are provided with electrodes 3 and 3', respectively. Although not shown, one end of a lead wire is connected to each electrode 3, 3'. In the present invention, two or more electrodes can also be attached to the low resistance sheet.

In this self-temperature-controlled heating element, the thickness of the high-resistance sheet 1 corresponds to the distance between the electrodes, so the distance is very short and the element can be prevented from burning out.

The high-resistance sheet 1 and both low-resistance sheets 2 and 2' are both sheets made of a mixture of a thermoplastic resin and/or rubber and a conductor, or a sheet-like material in which a base fabric is impregnated and coated with a dispersion of the mixture. Since the high resistance sheet 1 and both low resistance sheets 2, 2' are closely attached together, the element is also highly flexible, and even when used in a curved shape, the low resistance sheets 2, 2' No wrinkles or cracks will occur.

The electrical resistance of the low-resistance sheet in the present invention is X×10 ^-3 when that of the high-resistance sheet is XΩ-cm.
It is set so that it is less than Ω-cm,
By increasing the amount of conductor mixed with the thermoplastic resin and/or rubber, the electrical resistance can be obtained up to about 10 ^Ω -cm.

However, since an increase in the amount of conductor mixed causes difficulty in sheet forming, if it is desired to further reduce the electrical resistance of a low-resistance sheet, for example, a third
As shown in the figure, this objective can be achieved by providing metal vapor deposited layers 4, 4' on the electrode attachment surfaces of both low resistance sheets 2, 2'. Alternatively, a conductor similar to that used to obtain the resistance sheet may be densely scattered and fixed on the electrode attachment surfaces of both low resistance sheets.

In addition, in order to achieve the same purpose as shown in FIG. 3, as shown in FIG.
A large number of thin metal wires 5, 5' each having a diameter of about 0.01 to 2 mm can be embedded at predetermined intervals so as to be substantially orthogonal to 3'. In this case, it is also possible to embed a large number of metal strips with a width of 30 mm or less and a thickness of about 5 to 100 μm so as to be almost perpendicular to the electrodes, and further, a metal strip with a thickness of 10 to 100 μm and a mesh size of 0.5 μm. ~Ten
A metal mesh of about mm can be embedded.

In addition, when the self-temperature-controlled heating element of the present invention is used, its outer surface is usually covered with an insulating coating, and the sheets can be stacked together if the coating ensures close contact between the sheets and electrical contact. It's fine just by itself.

The present invention is constructed as described above, and since the distance between the electrodes is short, it is possible to prevent burnout of the heating element, and since it is highly flexible, it does not cause wrinkles or cracks even when curved. It has the characteristics that it can be used safely without any problems.

Hereinafter, the present invention will be explained in more detail with reference to Examples. In addition, all "parts" in the examples mean "parts by weight."

Example 1 100 parts of ethylene-ethyl acrylate copolymer (manufactured by Nippon Unicar Co., Ltd., trade name DPDJ-6169),
A mixture consisting of 20 parts of carbon powder with an average particle size of 0.03 μm (manufactured by Kabot Co., Ltd., trade name Vulcan . This high-resistance sheet has PTC characteristics, and the measurement results of its resistance-temperature curve (applied voltage AC 100 V) are shown as curve A in FIG.

Separately, a mixture of 100 parts of the copolymer and 60 parts of carbon powder was formed into a sheet having the same dimensions as the high-resistance sheet to obtain two low-resistance sheets. Attach a copper foil electrode with a thickness of 35μ and a width of 10mm. The resistance-warm curve of this low-resistance sheet was measured in the same manner as above.
It is indicated by B in the figure.

Next, a low resistance sheet was placed on both sides of the high resistance sheet, and the temperature was 150℃ and the pressure was 10Kg/ ^cm2 .
The sheets were heated and pressurized for 10 minutes to adhere the sheets to each other by heat fusion, thereby obtaining a self-temperature-controlled heating element having the same structure as shown in FIG. 2.

As can be seen from curves A and B in Fig. 5, in this heating element, when the electrical resistance of the high-resistance sheet is X Ω-cm in the operating temperature range, that of the low-resistance sheet is X × 10 ^-3 Ω-cm. It is set as below.

When one end of the lead wire is connected to each electrode of this heating element and a voltage of 100 VAC is applied from the other end of the lead wire, the surface temperature of the element rises over time, and after 2 minutes it reaches 85 ℃, and the current was continued for 4 hours, but the surface temperature was maintained at 85±2℃ and no burnout occurred.

Furthermore, this heating element was curved to have a radius of curvature of 5 mm and energized for the same period of time as above, but the surface temperature of the element was maintained at 85 ± 2°C, and the temperature was the same as when heating in a flat shape. It showed a uniform heat generation state. Further, no wrinkles or cracks were caused in the element.

Example 2 100 parts of ethylene-vinyl acetate copolymer (manufactured by Nippon Unicar Co., Ltd., trade name DQDJ-1830) and Example 1
A mixture consisting of 20 parts of the same carbon powder as used in was molded into a sheet with a thickness of 0.2 mm and a length and width of 10 cm each, and the initial resistance value (20°C AC 100 V) was 2 ×
A high resistance sheet having a resistance of 10 ⁶ Ω-cm and PTC characteristics is obtained.

Separately, a mixture of 100 parts of the copolymer and 60 parts of carbon powder was formed into a sheet having the same dimensions as the high-resistance sheet to obtain two low-resistance sheets. Attach a copper foil electrode of 35μ and width of 10mm.

In addition, when forming a low resistance sheet, the diameter
A large number of copper wires of 0.1 mm and length of 10 cm were buried at 5 mm intervals in a direction perpendicular to the electrodes. The initial resistance value of this low resistance sheet was 10 Ω-cm.

Next, low-resistance sheets were placed on both sides of the high-resistance sheet, and heated and pressed for 3 minutes at a temperature of 160℃ and a pressure of 10Kg/cm ² to adhere the sheets to each other by heat fusion, as shown in Figure 4. A self-temperature-controlled heating element with this structure was obtained.

The resistance-temperature curves of the high-resistance sheet and the low-resistance sheet in this heating element are not shown, but in the operating temperature range, when the electrical resistance of the high-resistance sheet is XΩ-cm, that of the low-resistance sheet is
10 ^-3 Ω-cm or less.

When one end of the lead wire is connected to each electrode of this heating element and a voltage of 100 VAC is applied from the other end of the lead wire, the surface temperature of the element rises over time, and after 3 minutes it reaches 80 V. ℃, and the current was continued for 5 hours, but the surface temperature was maintained at 80±3℃ and no burnout occurred.

Furthermore, this heating element was curved to have a radius of curvature of 7 mm and energized for the same time as above, but the surface temperature of the element was maintained at 80 ± 3°C, and the temperature was the same as when it was heated in a flat shape. It showed a uniform heat generation state. Further, no wrinkles or cracks were caused in the element.

Comparative Example 1 A mixture of 100 parts of the same copolymer and 40 parts of carbon powder used in Example 1 was formed into a sheet with a thickness of 0.2 mm and a length and width of 10 cm, and two low-resistance sheets were formed. 35mm thick at one end of each side
μ, attach a copper foil electrode with a width of 10 mm. The resistance-temperature curve of this low resistance sheet is indicated by curve C in FIG.

Next, the above-mentioned low-resistance sheets were placed on both sides of the high-resistance sheet having PTC characteristics used in Example 1, and were brought into close contact with each other under the same conditions as in Example 1, to obtain an element having the same structure as shown in FIG. 2.

In this element, as can be seen from curves A and C in FIG. 5, the electrical resistances of the high-resistance sheet and the low-resistance sheet are closer than those defined by the present invention,
When the electrical resistance of the high resistance sheet is XΩ-cm,
The resistance of a low resistance sheet is not less than X×10 ^-3 Ω-cm.

To find out the heat generation performance of this element, we applied a voltage in the same way as in Example 1, and found that only the areas near both electrodes generated heat, reaching 85°C, while the rest remained at room temperature (20°C). The temperature remained almost the same.

Comparative Example 2 A sheet with a thickness of 35 μm and a length and width of 10 μm was applied to both sides of the high-resistance sheet having PTC characteristics used in Example 1.
A heating element is obtained in which copper foil electrodes of 1 cm are adhered with a conductive adhesive.

After connecting one end of the lead wire to each electrode of this heating element, a voltage was applied in the same manner as in Example 1, and the surface temperature rose and reached 80° C. after 3 minutes, reaching an equilibrium state.

However, when this heating element was bent to have a radius of curvature of 8 mm, cracks appeared in the copper foil electrode on the outside of the curve, making it impossible to conduct electricity.

[Brief explanation of the drawing]

FIG. 1 is a plan view showing an example of a self-temperature-controlled heating element according to the present invention, FIG. 2 is a sectional view taken along the line of FIG. 1 and viewed from the arrow direction, and FIGS. 3 and 4 are FIG. 5, a sectional view showing another example, is a graph showing a resistance-temperature curve of a resistive sheet. 1...High resistance sheet, 2,2'...Low resistance sheet,
3, 3'...electrode.

Claims (1)

[Scope of Claims] 1. A sheet made of a mixture of thermoplastic resin and/or rubber and a conductor, or a sheet made by impregnating and coating the mixture on a cloth-like base material, which is a high-resistance sheet having a positive temperature coefficient. A sheet made of a mixture of a thermoplastic resin and/or rubber and a conductor, or a sheet formed by impregnating and coating a cloth-like base material with the mixture on both sides of the sheet, and the electrical resistance of the high-resistance sheet is XΩ-cm. A self-temperature-controlled heating element characterized in that a low-resistance sheet exhibiting an ^electrical resistance of less than . 2. The self-temperature-controlled heating element according to claim 1, wherein a large number of thin metal wires, band-shaped metal foils, or metal nets are embedded in at least one of the low-resistance sheets. 3. The self-temperature-controlled heating element according to claim 1, wherein a metal vapor deposition layer is provided on the electrode mounting surface of at least one of the low-resistance sheets. 4. The self-temperature-controlled heating element according to claim 1, wherein a conductor is densely spread and fixed on the electrode mounting surface of at least one of the low-resistance sheets.