JP3175171B2 - Manufacturing method of positive resistance temperature coefficient heating element - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a heating element having a positive temperature coefficient of resistance (hereinafter, referred to as "heating element") used for heating appliances and general heating appliances.
(Hereinafter simply referred to as a heating element).

[0002]

2. Description of the Related Art FIG.
After kneading the crystalline polymer and carbon black as shown in the figure, forming a pair of electrodes, covering with an exterior material, measuring the properties such as temperature coefficient of positive resistance, pressure resistance test, and heat generation characteristics, and as a finished product Was. FIG. 4 shows a partial perspective view of the finished product. In the figure, 1 is a positive resistance temperature coefficient resistor (hereinafter simply referred to as a resistor), 2 and 3 are electrodes provided in contact with the resistor 1, 4 and 5 are provided in contact with the electrodes 2 and 3 Lead terminals 6 and 7 are a resistor 1, electrodes 2 and 3, and a lead terminal 4.
And 5 for covering.

[0003]

However, in the above-described manufacturing method, the state of the carbon black mixed and dispersed in the resistor 1 is uniformly controlled down to the microscopic portion to ensure the quality characteristics of 100% of non-defective products. It was extremely difficult to do.

An object of the present invention is to solve such a problem and to provide a method for manufacturing a heating element having excellent quality characteristics.

[0005]

In order to achieve the above-mentioned object, a method of manufacturing a heating element according to the present invention comprises a method of manufacturing a heating element, wherein a positive resistance temperature coefficient comprising a crystalline polymer and carbon black as main components is provided between a pair of electrodes. A resistor is provided, and an impact voltage equal to or lower than a dielectric breakdown voltage is applied between the pair of electrodes.

[0006]

According to the present invention, a defect such as an incompletely mixed carbon black in the resistor or a conductive foreign substance can be detected by the above construction.

[0007]

Embodiments of the present invention will be described below with reference to the accompanying drawings.

The structure of the heating element of this embodiment is the same as that of FIG. 4, and a metal foil electrode 2 is provided on the upper and lower surfaces of a resistor 1 having a thickness of 1.0 mm.
And lead terminals 4 and 5 are connected to the metal foil electrodes 2 and 3 by soldering. The entire body including the resistor 1, the metal foil electrodes 2 and 3, and the lead terminals 4 and 5 is packaged with package members 6 and 7.

In this embodiment, a heating element was manufactured by the method shown in FIG. First, a mixture of 45 parts of low-density polyethylene and 55 parts of furnace black was kneaded with 145 ° C. hot mixnole while dicumyl parl as a crosslinking agent.
3.5 parts of oxide was added to 100 parts of the above mixture and sufficiently dispersed.

After the above mixture is processed into a sheet,
The crosslinking reaction was completed by performing a heat treatment at 160 ° C. for 1 hour. Next, the sheet was processed into a fine powder having an average particle diameter of 70 μm by freeze pulverization. Next, the fine powder 6
Seven parts and 33 parts of high-density polyethylene were kneaded with 160 ° C. heated mixin mul to prepare a resistor.

Next, a laminated structure element of copper foil / resistor 1.0 mm / copper foil was prepared by extruding the resistor and using a laminating machine. Next, after cutting the laminated structural element at intervals of 200 mm, a nickel-plated lead terminal is soldered to the above-mentioned copper foil, and then heat-sealed with a polyester film / ionomer-resin laminated film to form an exterior and generate heat. Body manufactured.

Next, a needle-shaped connection terminal is connected to the lead terminals 4 and 5 of the heating element through the outer package 7, and an output terminal of an impact voltage generator is connected to the terminal. By applying the voltage, defects inside the heating element were inspected to remove defective products. As shown in FIG. 2, the configuration of the shock voltage generator is as follows: a capacitor 11 for charging a high voltage; a charging circuit 12 for charging the capacitor 11; an opening / closing mechanism 13 for starting discharge; Reactance 14,
Discharge protection resistor 15 connected in series with heating element, discharge time limiting resistor 16 connected in parallel with heating element, voltage monitor terminal 1
7, consisting of a current monitor terminal 18 and a shock voltage of 19, 2
0 is generated between output terminals. The capacitor 11 was set at 1 μF, the reactance 14 was set at 50 μH, the discharge protection resistor 15 was set at 5Ω, and the discharge time limiting resistor 16 was set at 1 kΩ.

Table 1 shows the test results of the heating element according to the manufacturing method of this embodiment. The numerical values in the table are the number of heating elements that have undergone dielectric breakdown when an impact voltage is applied at 20 ° C.

However, the number of tests is 10.

[0015]

[Table 1]

As is clear from Table 1, the heating element of this embodiment is at the limit that can withstand an impact voltage of 2500 V. Therefore, when the heating element having the configuration as in the present embodiment is manufactured by applying an impact voltage of 2500 V, a heating element having excellent quality characteristics can be obtained.

Practically, by applying an impact voltage 10% to 20% lower than the upper limit, it is possible to detect only a defective product having actual harm without damaging a good product.

In order to confirm the above-mentioned effects, a heating element having an abnormal portion in a resistor was prepared and its quality characteristics were measured.

A heating element A for comparison has 650 to 7 in the resistor.
Heating element B contains 1% by weight of a copper powder of 750-800 μm.

An impact voltage was applied to the heating elements A and B in the same manner as in the example. Table 2 shows the inspection results.

[0021]

[Table 2]

As is clear from Table 2, the heating element A was 15
The upper limit of the impact voltage is 00 V and the heating element B is 500 V.
Therefore, if the inspection is performed at 2000 V, the heating element A can be detected with a high probability and the heating element B can be detected with a probability of almost 100%.

From these results, it can be seen that when an abnormal portion is formed by mixing a conductive foreign substance into a resistor, the impact voltage is lowered. There is an effect that can be obtained.

Next, each of the heating element and the heating element A of this embodiment is 15
The results shown in Table 3 were obtained when the dielectric breakdown characteristics were measured by repeatedly applying an impact voltage to the individual pieces.

The numerical values in the table are the total number of destructions.

[0026]

[Table 3]

From the results shown in Table 3, it can be understood that the quality is gradually reduced by repeated application of the impact voltage, and eventually the dielectric breakdown occurs. Therefore, a method of repeatedly applying a low voltage is effective for performing an inspection without damaging a normal heating element.

Further, the dielectric breakdown characteristics were measured by changing the temperature of the heating element. Table 4 shows the results. The numerical values in the table are the number of heating elements that have undergone dielectric breakdown at various temperatures.

However, the number of tests is 10.

[0030]

[Table 4]

As is evident from Table 4, the lower the temperature, the higher the detection sensitivity. When the temperature was higher than 60 ° C., the detection sensitivity was greatly reduced. This is presumably because, due to the temperature characteristics of the heating element, as the temperature increases, the number of conductive paths decreases, and the voltage applied to defects in the resistor decreases. In general, the breakdown voltage of low-density polyethylene tends to decrease as the temperature increases, but in the case of the heating element of the present invention, the effect of increasing the resistance value due to the temperature coefficient of positive resistance is better, and the breakdown voltage is higher. Become. Heating elements designed with 20 ° C. as a standard condition improve detection sensitivity when an impact voltage is applied at 20 ° C. or less.

In this embodiment, a test was conducted in which an impact voltage was applied before annealing, but the resistor before annealing was placed in a state before the arrangement of the carbon black formed the conductive network. Yes, the resistance is several times to several orders of magnitude higher. Therefore, the impedance of the load is larger than the output impedance of the shock voltage generation circuit, which is advantageous in terms of detection accuracy.
In particular, it is possible to remove inspection constraints such as the ability to inspect a long heating element or a plurality of heating elements simultaneously. In the heating element of this embodiment, the heating element is about 1
The resistance was about 20 times higher, and the voltage loss due to the protection resistor 15 was negligible. On the other hand, when it is necessary to inspect a heating element after annealing or a heating element having a low resistance value for a low voltage, the inspection accuracy can be maintained by setting the protection resistor 15 lower. In some cases, it is desirable to increase the capacity of the capacitor 11 and charge energy sufficient for dielectric breakdown. If the energy may damage a normal heating element, the discharge time limiting resistor 16 connected in parallel with the heating element is set to a lower resistance,
The time constant determined by the capacitor 11 and the discharge time limiting resistor 16 can be made smaller, and the energy can be limited. Further, when it is necessary to detect a finer defect, the detection sensitivity to the capacitance component can be increased by reducing the reactance 14 and making the voltage rise steep. Further, in order to detect the presence / absence of dielectric breakdown with higher accuracy, it is possible to determine a phenomenon peculiar to dielectric breakdown by processing the output of the voltage monitor terminal 17 or the current monitor terminal 18.

The heating element is not limited to those described here, and many combinations of crystalline polymers and carbon black can be used. Particularly useful crystalline polymers include ethylene vinyl acetate copolymer, ethylene ethyl acrylate copolymer, linear low density polyethylene, high density polyethylene, polypropylene, polyvinylidene fluoride and their unsaturated carboxylic acids. And the like.

As the carbon black, among black, channel black, thermal black, acetylene black, lamp black, graphite, graphitized carbon black, and graft carbon black, those exhibiting remarkable positive resistance temperature characteristics. Can be selected. Among them, those particularly useful are those mainly composed of furnace carbon black having a large average particle diameter. More specifically, the average particle diameter is 50 nm or more, and the DBP oil absorption is 90 ± 10 ml.
/ 100 g is preferable.

Also, the structure of the heating element is not limited to the embodiment, and if the heating element is formed between electrodes arranged relatively close to each other, a planar structure, a coaxial structure, It is highly useful, including special structures such as a dumbbell cross-section structure, a laminated structure, and a parallel electrode structure. In particular, when the electrode interval is 1 mm or less, a defect of several hundred μm is fatal, and it is extremely difficult to remove the defect by a visual inspection or a filter. Therefore, according to the manufacturing method of the present invention, it is possible to manufacture a heating element having an electrode interval of 500 μm to 100 μm.

Further, the manufacturing method of the present invention can detect not only structural defects such as foreign matter, but also processing defects of the heating element such as electrode misalignment. Is also applicable.

[0037]

As described above, according to the method for producing a positive resistance temperature coefficient heating element of the present invention, defects such as incomplete mixing of carbon black and conductive foreign matter in the resistor can be detected with high sensitivity. Since it can be detected, there is an effect that a heating element having excellent quality characteristics can be manufactured.

[Brief description of the drawings]

FIG. 1 is a process diagram of a method for manufacturing a positive resistance temperature coefficient heating element according to one embodiment of the present invention.

FIG. 2 is a configuration diagram of an impact voltage generator according to one embodiment of the present invention.

FIG. 3 is a process chart of a conventional method for manufacturing a positive resistance temperature coefficient heating element.

FIG. 4 is a partial perspective view of a conventional completed product.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Temperature coefficient heating element of positive resistance 2, 3 electrodes 11 Capacitor 14 Reactance 15 Discharge protection resistance

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-2-306567 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) H05B 3/14 H05B 3/18

Claims (2)

(57) [Claims] 1. A positive temperature coefficient coefficient resistor comprising a crystalline polymer and carbon black as main components is provided between a pair of electrodes,
A method of manufacturing a heating element having a positive temperature coefficient of resistance, in which an impact voltage lower than a dielectric breakdown voltage and lower sequentially is applied a plurality of times between the pair of electrodes. 2. A positive temperature coefficient coefficient resistor having a crystalline polymer and carbon black as main components is provided between a pair of electrodes,
A positive resistance temperature coefficient heat generation in which an impact voltage is applied by an impact voltage generator in which a rise speed of an impact voltage is less than a dielectric breakdown voltage between the pair of electrodes, and a discharge energy is limited by a capacitor capacity and a discharge protection resistor. How to make the body.