JP2643398B2 - Positive resistance temperature coefficient heating element and method of manufacturing the same - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a positive resistance temperature coefficient heating element useful as a warming device and a general heating device, and a method for producing the same.

2. Description of the Related Art A conventional heating element having a positive temperature coefficient of resistance has a configuration as disclosed in Japanese Patent Publication No. 57-43995 and Japanese Patent Publication No. 55-40161, for example. It was self-controlled to an appropriate temperature by the positive resistance temperature characteristic. However, especially when a large power density or high temperature is required, it is essential to always make the temperature distribution between the pair of electrodes good in order to make the temperature distribution of the heating element itself uniform. As a solution, Japanese Patent Publication No. 62-51515
As shown in FIG. 12 and FIG. 12, a method has been taken in which the distance between a pair of electrodes is made closer to each other. In FIG. 12, reference numerals 1 and 2 denote a pair of parallel plate electrodes provided close to each other, between which a resistor 3 formed by mixing and dispersing conductive fine powder in a crystalline polymer is arranged. It has been found that a high power positive temperature coefficient of resistance heating element can be developed.

Problems to be Solved by the Invention However, the conventional positive temperature coefficient heating element as described above is very excellent as a structure for producing high output, but has a relatively low resistance conductive material such as carbon black. Considering the withstand voltage breakdown characteristics of the positive resistance temperature coefficient resistor composed by mixing and dispersing the conductive fine powder, and the region of the volume resistivity where extremely high resistance is required, many problems must be solved. Had the problem of. In order to construct a heating element with a positive resistance temperature coefficient in which the electrode spacing is very close, not only must a conductive fine powder with excellent withstand voltage breakdown characteristics be selected, but also by obtaining a sufficiently large positive resistance temperature characteristic Therefore, it was essential to take care not to runaway beyond the peak resistance value. Further, a pair of electrodes are very close to each other at the end face of the positive resistance temperature coefficient heating element, which is a very problematic problem in view of the ionization voltage of air. Depending on the situation, there is a possibility that air discharge may occur and smoke or fire may occur, which has a very dangerous surface. To deal with such danger, as shown in Japanese Patent Application Laid-Open No. 61-284,082, etc., the positive resistance temperature coefficient resistor itself is required to make the creepage distance along the outer surface of the resistor larger than the thickness of the resistor. Periodic improvement measures were taken and safety was improved. However, the portion where the creepage distance is secured by the resistor material itself has an extremely high resistance at the beginning and hardly contributes to heat generation like an electric insulator. Due to crystal growth, thermal stress of each part of the heating element, or agglomeration of the conductive fine powder, a large change in the resistance value and the temperature coefficient of resistance will occur, especially in the case of a heating element with a higher positive temperature coefficient of resistance. This creepage also generates a small amount of heat, but heat is generated, and voltage concentrates on the minute part of this part, and the resistance increases and the heating life is very short, or abnormal overheating, smoke, or ignition And the like, which greatly deviates from a practically acceptable range. Thus, by simply adjusting the composition ratio of the conductive fine powder, the volume resistivity value is 103Ωcm.
The above-mentioned useful positive temperature coefficient of resistance heating element could not be created.

The present invention has been made to solve the above problems and to provide a structure of a high-output positive temperature coefficient of resistance heating element capable of realizing excellent performance and safety for practical use, and a method of manufacturing the same.

Means for Solving the Problems In order to solve the above problems, a positive resistance temperature coefficient heating element of the present invention is a thin positive resistance temperature coefficient resistor made of a conductive fine powder and a crystalline polymer; A pair of electrode bodies provided to apply a voltage in a direction perpendicular to the substrate, and a boundary portion between a part where the pair of electrode bodies overlaps in the thickness direction of the resistor and a part where the resistors do not overlap, or an electrode which overlaps The resistance element in the vicinity of the body end has a portion protruding in the thickness direction.

Operation The operation of this technical means is as follows. That is, a pair of electrodes of the positive resistance temperature coefficient heating element can be brought close to each other so that a high output can be obtained. Depending on the situation, there is a possibility that air discharge occurs and smoke or fire may occur, which is extremely dangerous. In addition, by interposing this resistor material here, the safety can be considerably improved, but due to the temporal change of the resistor material in this portion, the voltage is concentrated on a minute portion and the resistance increases, There is a danger of smoke or ignition due to deterioration of the resistor material. The resistor of the part with such danger,
In other words, by protruding the resistor in the thickness direction of the resistor in the vicinity of the boundary between the portion where the pair of electrode bodies overlap in the thickness direction of the resistor and the portion where the pair does not overlap, or the end portion of the electrode body where the overlap occurs. The distance between the electrodes to which a voltage is applied in this portion can be lengthened, and high performance and safety can be maintained even if there is a change over time. In this manner, a high-output positive temperature coefficient of resistance heating element can be realized with a high-resistance resistor having a volume resistivity of 10 3 Ωcm or more.

Embodiments Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings.

As shown in FIG. 1, for example, as shown in FIG. 1, electrodes 5 and 6 are adhered to the upper and lower surfaces of a long positive resistance temperature coefficient resistor 4, Materials 7 and 8 are exterior. FIG. 2 shows a sectional view of the structure of the electrodes 5 and 6 and the resistor 4 of the heating element. The resistor 4 has a thickness of 0.4 mm at the center in the width direction, and both ends have protrusions. 4
−a and 4-b are present, and the electrode 5 follows this shape and closely adheres to this portion. Therefore, the distance L1 between the electrodes 5 and 6 at both ends is the distance between the electrodes, that is, the distance obtained by adding the protruding distance L2 in the thickness direction of the protruding portion of the resistor to 0.4 mm. By appropriately setting L2, the distance L1 between the electrodes 5 and 6 at the end of the heating element can be sufficiently ensured, so that air discharge caused by burrs on the electrode end faces can be prevented, and there is also a danger of smoking and ignition. It is extremely secure. Even if the resistance value of the resistor material at the end of the heating element decreases with time, or the shape changes due to crystal growth, thermal shrinkage, etc., the resistor in such a risky part is formed with this thickness. By protruding in the vertical direction, the distance between electrodes to which a voltage is applied in this portion can be lengthened, and there is also an effect that high security can be maintained even if there is a change over time. Here, the protruding distance in the thickness direction of the protruding portion of the resistor may be an appropriate distance for ensuring such safety, but is preferably 10% or more of the distance between the pair of electrodes. It is effective.

By the way, if only the creepage distance at the ends of the pair of electrode bodies is to be ensured, a structure as shown in FIG. 11 can be considered. Electrodes 1a and 2a having different sizes are bonded to both surfaces of a positive resistance temperature coefficient resistor 3a having a uniform thickness of 0.4 mm,
A sufficient creepage distance X is secured. Although the volume resistivity of the resistor material is large and the A1 and A2 portions of the resistor 3a hardly generate heat, a voltage is applied.
Due to the aging, the crystal growth of the crystalline polymer, the thermal stress of each part of the heating element, or the aggregation of the conductive fine powder, etc.
Significant changes in resistance value and temperature coefficient of resistance will occur, especially in the case of higher output positive temperature coefficient heaters.
The surface portions A1 and A2 also generate a small amount of heat, but generate heat.Voltage concentrates on minute portions of this portion, and the resistance increases, resulting in a very short heating life or abnormal overheating. , Smoke and ignition.

Actually, a positive resistance temperature coefficient heating element having the structure shown in FIGS. 2 and 11 was prototyped so as to have the same resistance temperature characteristic, and a comparative experiment was performed. AC20 twice the normal voltage of AC100V for acceleration evaluation
Continuous energization was performed at 0V. As shown in FIG. 3, the temperature of the heating element having the structure of FIG.
Although heat generation hardly occurred at 500 hours, the heating element having the structure shown in FIG. 2 of the present invention maintained the initial temperature even after 2000 hours, and was found to be very effective. This mechanism is considered to be due to the above-mentioned voltage concentration phenomenon being prevented by the structure of the present invention. The structure of the present invention has a protruding portion in the thickness direction of the antibody,
Since the projecting portion has almost no heat generation function, the projecting portion also has the effect of preventing the heating portion from being exposed to mechanical stress in the thickness direction of the resistor.

Next, FIG. 4 shows an embodiment in which the copper electrode 9 completely covers the protruding portion in the thickness direction of the resistor 10, but the heat concentration effect of the copper electrode 9 causes the voltage concentration phenomenon at the electrode end. Second prevention effect
It is higher than the heating element having the structure shown in the figure. Where the electrodes
If a heat load such as an iron plate is attached to the 11 side, the voltage concentration phenomenon at the electrode end will not only be a safe and long-life heating element that will not occur even if the output is further increased, but also the oxygen, humidity, etc. An object of the present invention is to provide a heating element which does not transmit through a resistor and has excellent heat and moisture resistance. In FIG. 5, a pair of electrodes 13 and 14 are arranged on both surfaces of a dumbbell-shaped positive temperature coefficient resistor 12, which is effective in reducing stresses caused by processing, heat and the like.

In addition, a resistor having a central portion protruded as shown in FIG.
The electrodes 16 and 17 may be formed on both sides of the 15,
In this case, it is also effective in adjusting the calorific value and distribution. Also,
As shown in FIG. 7, electrodes 19 and 20 may be formed on both sides of a resistor 18 protruding only on one side, and as shown in FIG. Alternatively, the electrode 23 may be formed.

As described above, the structure of the heating element of the present invention is not limited as long as a pair of electrode bodies is formed on both surfaces of a thin positive temperature coefficient resistor having a portion protruding in the thickness direction. More preferably, the resistor in the vicinity of the boundary between the effective heat generating portion and the non-effective heat generating portion in which the distance between the pair of electrodes is not more than a predetermined distance is protruded in the thickness direction. However, it is effective in preventing the voltage concentration phenomenon. In addition, such a structure also has the advantage that the concentration of an electric field at a sharp portion such as an edge of an electrode or a burr can be suppressed, and further provides higher safety. FIG. 9 shows that the electrodes 25 and 26 are formed on both surfaces of the resistor 24, but the electrode 25 does not exist on the protruding portion of the resistor 24, but after extrapolating the insulating materials 27 and 28 thereon, The same effect can be obtained by further attaching aluminum foil 29 to prevent the voltage concentration phenomenon.

By the way, as a material constituting the positive resistance temperature coefficient resistor, low density polyethylene, medium density polyethylene, high density polyethylene, linear polyethylene, ethylene vinyl acetate copolymer, ethylene acrylic acid copolymer, ionomer, polypropylene, polyamide, Remarkable positive resistance temperature characteristics among crystalline polymers such as polyvinylidene fluoride, polyester, and organic acid-modified polyethylene such as acrylic acid and maleic acid, and carbon blacks such as thermal black, furnace black, channel black, and acetylene black. And any other material may be added. However, in the case of a resistor material which is unstable with time, the above-mentioned effect may be reduced by lowering the volume resistivity of the protruding portion of the structure of the present invention, but the conductive fine powder is contained in the crystalline polymer. Cross-linking after mixing and dispersing, and further dispersing the finely divided conductive fine particles into other resin materials, thereby making the conductive fine powder difficult to move and increasing the resistance stability, thereby further improving the safety and performance. Can be increased. In addition, by providing the crystalline polymer with a functional group modified with an organic acid, it is possible to increase the adhesiveness to a metal electrode such as copper or a copper alloy, thereby improving the adhesiveness between the electrode and the resistor. In addition, since the soaking effect is also increased, the safety against the voltage concentration described above can be further improved.

Next, FIG. 10 is a view showing an embodiment relating to a method for manufacturing a heating element of the present invention. The positive resistance temperature coefficient resistor 30 is processed to have a large area or a long shape so as to have projections in the thickness direction at regular intervals, and at the same time or after this, electrodes 31 and 32 are formed on the resistor 30. Adhesive processing follows the shape. Thereafter, by cutting the protrusions indicated by arrows V1 and V2 perpendicularly to the directions of the arrows, it is possible to simultaneously process a plurality of heating elements very similar to the heating elements illustrated in FIGS. 1 and 2. Since the cut end face has a sufficient distance between the electrodes, it is extremely safe without sparks even if there is a burr, etc. Is possible. The cutting direction is not limited to the thickness direction of the resistor 30, but may be cut horizontally in the direction of arrow H, and then cut vertically in the directions of V1 and V2. Since the direction is not between the pair of electrodes, the safety is further improved. Further, when the electrode is cut in a direction perpendicular to the H direction and in a horizontal plane direction, a plurality of upper electrodes are formed. However, a sufficient distance can be secured between the plurality of electrodes. The present invention also provides a new method of manufacturing a high-performance and safe heating element in which a plurality of electrodes are formed on at least one surface of a resistor because the burr does not coincide with the direction between a pair of electrodes.

Effect of the Invention As described above, when realizing a high-output, high-temperature, positive-resistance temperature coefficient heating element or the like, this pair of electrodes needs to be very close to each other. In particular, in the vicinity of the electrode, there is a danger that the air is discharged in the air and smoke or fire is caused depending on humidity, air pressure, burrs or distortion of the electrode end face, and the like. In the present invention, the danger is prevented by protruding the resistor in the portion having such danger in the thickness direction, and the resistor is degraded due to the voltage concentration generated in this portion, and the electric field concentration generated from the electrode end portion. In addition to suppressing mechanical stress, it is also effective in mechanical stress relaxation. Further, many of these effects are realized by a simple structure capable of high production. In this way, a long-term excellent performance and safety are realized, and a high-output, long-life positive resistance temperature coefficient heating element is provided, which is extremely advantageous in practical use.

[Brief description of the drawings]

FIG. 1 is a perspective view of a positive resistance temperature coefficient heating element according to one embodiment of the present invention, FIG. 2 is a cross-sectional view of the heating element, and FIG. 3 is a characteristic diagram showing a change over time of the surface temperature of the heating element. 4 to 9 are cross-sectional views of a positive resistance temperature coefficient heating element according to another embodiment of the present invention;
FIG. 10 is a cross-sectional view showing one embodiment of a method for manufacturing a positive resistance temperature coefficient heating element of the present invention, FIG. 11 is a cross-sectional view of a conventional positive resistance temperature coefficient heating element, and FIG. It is a perspective view of a coefficient heating element. 4,10,12,15,18,21,24,30, ... temperature coefficient positive resistance resistor,
5,6,9,11,13,14,16,17,19,20,22,23,25,26,31,32 …… Electrode, 7,8,27,28 …… Insulation material, 29 …… Aluminum plate.

Continuation of the front page (56) References JP-A-63-307683 (JP, A) JP-A-63-146379 (JP, A) JP-A-63-102193 (JP, A) Jpn. , U)

Claims (11)

(57) [Claims] 1. A thin positive temperature coefficient resistor made of a conductive fine powder and a crystalline polymer, and a pair of electrode bodies provided to apply a voltage in the thickness direction. A positive resistance temperature coefficient in which the resistor protrudes in the thickness direction of the resistor in the boundary portion between the portion where the electrode body overlaps in the thickness direction of the resistor and the portion where the electrode body does not overlap or in the vicinity of the end portion of the electrode body where the electrode body overlaps. Heating element. 2. A resistor is elongated, and at least at one end in the width direction, a resistor material has a portion protruding in the thickness direction, and at least a part of the protruding portion is connected to an electrode body. 2. The heating element according to claim 1, wherein the heating element is covered with a temperature coefficient of positive resistance. 3. The positive resistance temperature according to claim 1, wherein the projecting distance in the thickness direction of the projecting portion of the resistor is at least 10% of the distance between the pair of electrodes. Coefficient heating element. 4. A structure comprising a resistor and a pair of electrode members provided for applying a voltage in the thickness direction is formed of an outer layer of an electrically insulating material, and at least a part of a protruding portion of the resistor is formed of a metal. The positive temperature coefficient heating element according to any one of claims 1 to 3, which is covered with a plate. 5. A positive resistance temperature coefficient heating element according to claim 1, wherein a cross-sectional shape of the resistor is close to a dumbbell shape. 6. The positive conductive powder according to any one of claims 1 to 3, wherein the conductive fine powder is mixed and dispersed in a crystalline polymer, then crosslinked, and further subdivided. Resistance temperature coefficient heating element. 7. The positive resistance temperature coefficient heat generation according to any one of claims 1 to 3, wherein at least a part of the crystalline polymer is a polymer having a functional group modified with an organic acid. body. 8. The volume resistivity of the directly opposed resistance temperature coefficient resistor is
Claims 1 to ⁵ having a resistance value higher than 10 ³ Ωcm.
4. A heating element having a temperature coefficient of positive resistance according to claim 1. 9. The positive resistance temperature coefficient heating element according to claim 1, wherein the thickness of the positive resistance temperature coefficient resistance element is 1 mm or less. 10. A thin-film positive temperature coefficient resistor comprising a conductive fine powder and a crystalline polymer, and a pair of electrodes provided to apply a voltage in the thickness direction. The electrode body has a boundary portion between a portion where the resistor overlaps in the thickness direction of the resistor and a portion where the resistor does not overlap, or a portion where the resistor near the end portion of the electrode body where the resistor overlaps protrudes in the thickness direction. After processing a structure of the resistor and a pair of electrode bodies provided to apply a voltage in the thickness direction to a long or large area, the protrusion of the resistor has an appropriate size. A method for manufacturing a cut positive resistance temperature coefficient heating element. 11. The method according to claim 10, wherein the protruding portion of the resistor is cut in a plane direction of the electrode body.