JPH02304892A - Exothermal body with positive temperature coefficient of resistance - Google Patents

Abstract

PURPOSE:To obtain an exothermal body having positive temperature coefficient of resistance, a long life, and high output by using a fine powder prepared by pulverizing a conductive composition consisting of mainly a crystalline polymer and carbon black after crosslinking the composition and a binder resin to which a proper amount of carbon black is added. CONSTITUTION:A composition consisting of a fine powder which is prepared by pulverizing a conductive composition of mainly a crystalline polymer and carbon black after crosslinking the composition by electron beam or an organic peroxide and a binder resin to which a proper amount of carbon black is used. The carbon black added to the binder resin is not enough to form primary conductive pass but effective to remarkably decrease contact resistance in contact interfaces between conductive fillers and to stabilize the contact resistance and thus propagation of micro breakdown phenomena due to concentration of electric voltage is prevented. Consequently, a resistant composition with positive temperature coefficient of resistance with controllability of the resistance and guaranteed characteristic of long life and high reliability is obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION FIELD OF INDUSTRIAL APPLICATION The present invention relates to a heating element having a positive temperature coefficient of resistance and having an organic material as a base material, which is used in heating appliances and heating appliances.

2. Prior Art A conventional heating element having a positive temperature coefficient of resistance has a structure as shown in, for example, Japanese Patent Publication No. 57-43995 and Japanese Patent Publication No. 55-40161, in which a resistor is connected between a pair of electrodes. The temperature was self-controlled to an appropriate temperature due to the positive resistance temperature characteristics of

However, especially when high power density is required, heating elements based on organic materials have insufficient thermal conductivity, so not only are they unable to extract heat, but they also concentrate heat locally. This caused a phenomenon in which the heating element itself was destroyed, and the path to higher output was closed. As a solution to this problem, as shown in Japanese Patent Publication No. 62-59515 and Figure 3,
A structure has been devised in which the distance between a pair of electric bridges is made extremely close to each other to significantly reduce thermal resistance. In Fig. 3, reference numerals 1.2 are a pair of parallel plate electrodes placed close to each other, and a resistor 3 formed by mixing and dispersing conductive fine powder in a crystalline polymer is placed between them. This is an attempt to develop a high output positive resistance temperature coefficient heating element.

Problems to be Solved by the Invention However, although the conventional positive resistance temperature coefficient heating element as described above had an extremely excellent structure for producing high output, it More challenges were imposed on resistor materials.

To summarize them, (1) In order to support a voltage of 100V for general household use with a close electrode structure, it is necessary to form a resistor with a volume resistivity of the semiconductor region of 10' to 10'ΩC1. In this resistance value region, the dependence of the resistance value on the amount of the conductive fine powder added is extremely large, and it is difficult to control the resistance value using general processing methods.

(2) In order to support the voltage of 100V for general household use with a close electrode structure, it is necessary to withstand the voltage gradient of the lever from IKV to 5KV/cm, and a resistor connected in parallel between different electrodes must be used. Voltage breakdown due to abnormal resistance characteristics must be prevented between any different poles in the body. In this case, it is also impossible to uniformly control the resistance characteristics down to the minute parts using general processing methods.

(3) Considering the volume resistivity value of the semiconductor region of to3 to 10 SΩcm, it is necessary to significantly reduce the composition ratio of the conductive fine powder. As a result, the number of contact points between conductive fine powders has been drastically reduced, and the resistance-temperature characteristics are not only controlled by rapid volumetric expansion near the melting point of crystalline polymerizability, but also by thermal expansion at lower temperatures.

The influence of internal stress, thermal stress, etc. becomes more significant, and there is a strong tendency for undesirable fluctuations to occur in the positive resistance temperature characteristics.

(4) Similarly, over time, significant changes in resistance and temperature coefficient of resistance occur due to crystal growth of crystalline polymers, thermal stress in various parts of the heating element, agglomeration of conductive fine powder, etc. They lack stability in temperature and power, have a very short heat generation life, and are at risk of abnormal overheating, smoke, and fire.

In this way, simply adjusting the composition ratio of the conductive fine powder is far from fulfilling the function of a resistor formed between a pair of closely spaced electrodes, especially when used with a 100V power supply. Therefore, it was not possible to create a high output and highly reliable positive resistance temperature coefficient heating element using a resistor having a volume resistivity of 10"0 cm or more.

The present invention solves these problems and provides a more reliable positive resistance temperature coefficient heating element that can withstand mechanical deformation.

Means for Solving the Problems In order to solve the above-mentioned problems, the positive resistance temperature coefficient heating element of the present invention consists of a conductive composition mainly composed of a crystalline polymer and carbon blank, which is heated by an electron beam or an organic film. A positive resistance temperature coefficient resistor made of a composite composition of a fine conductive composition powder having a positive temperature coefficient of resistance, which is formed by crosslinking with an oxide, etc. and then finely dividing it, and a binding resin made by adding an appropriate amount of carbon black. , a pair of electrode bodies formed integrally with the resistor, and a wA edge exterior body covering the entirety of these electrode bodies.

action The effect of this technical means is as follows.

That is, a crystalline polymer in which carbon black is dispersed at a high pressure rate is crosslinked with an electron beam or an organic peroxide, and then finely divided to once form a conductive composition fine powder. This conductive composition fine powder has positive resistance-temperature characteristics and also exhibits a volume resistivity several orders of magnitude higher than carbon black, making it a material that can be called a conductive filler with positive resistance-temperature characteristics. A composition in which this conductive filler is dispersed in a binding resin constitutes a resistance network of series and stranded combinations of four-electric fillers, resulting in a positive resistance temperature characteristic resistor composition with a higher volume resistivity value. . Since the connection point of this resistance network is a contact connection at the conductive filler interface via the bonding resin, it is not necessarily stable against displacement due to thermal stress or bending, and voltage concentration is applied to the unstable point. The conductive bus is easily destroyed by

The appropriate amount of carbon black added to the binding resin is not sufficient to form a main conductive path by itself, but it significantly reduces and stabilizes the contact resistance at the contact interface between conductive fillers, and increases the voltage. It is possible to prevent the progression of microscopic destructive phenomena due to concentrated application.

As a result, the initial resistance value can be controlled by the conductive filler formation method, especially in applications where a positive resistance temperature characteristic resistor with a high volume resistivity value is placed between a pair of adjacent electrodes to generate high output. On the other hand, on the other hand, the micro-destruction phenomenon of the conductive network, which is considered to be a drawback, is significantly delayed, making it possible to guarantee a long usable time. Due to this effect, it is possible to construct a positive resistance temperature coefficient heating element that can guarantee reliability even in harsh usage environments such as mechanical deformation while having high output.

Embodiment Hereinafter, one embodiment of the present invention will be described based on the accompanying drawings. For example, as shown in Fig. 1, metal foil electrodes 5 and 6 are attached to the upper and lower surfaces of a positive resistance temperature coefficient resistor 4 with a thickness of 0.6 mm, and both are further covered with an outer covering material 7°8. There is. In order to apply 100 V to the heating element configured as shown in Figure 1 and generate heat, the resistance value of the solid must be 104Ωc.
A positive resistance temperature coefficient resistor in the high resistance range exceeding the m level is essential.

Conductive fine powder is added to the crystalline polymer composition at 10'ΩcIII.
It is not possible to make a stable material by simply adding it while adjusting it so that the resistivity value is . Therefore, the positive resistance temperature coefficient resistor 4 was manufactured by the following procedure.

Example (1) While kneading 45 parts of low density polyethylene and 55 parts of a furnace blank using a heated mixing roll at 145°C, 3.5 parts of dicumyl peroxide was added as a crosslinking agent to 100 parts of the kneaded material, well dispersed. After the kneaded material was taken out in the form of a sheet, it was heat-treated at 160°C for 1 hour to complete the crosslinking reaction. Furthermore, a conductive composition fine powder having an average particle size of 10 pm was obtained by cryo-pulverization. On the other hand, apart from this, high density polyethylene 80
and 20 parts of the furnace blank were kneaded using a heating mixing roll at 160°C to produce low-conductivity high-density polyethylene.

Then, 40 parts of this low-conductivity high-density polyethylene and 60 parts of the conductive composition fine powder were kneaded using a heating mixing roll at 160°C to obtain a positive resistance temperature-dependent resistor composition. This sheet was heat pressed at 200°C with w4 foil/resistor 0.
6! A laminated structure element of II/copper foil was produced.

Next, it was heat-sealed and packaged with a polyester film/ionomer resin laminated film, and annealed at 170° C. for 3 hours to obtain a positive resistance temperature coefficient heating element having predetermined resistance characteristics. As a comparative example based on the conventional technology, a positive resistance temperature coefficient resistor composition was prepared using 33 parts of high-density polyethylene to which no carbon black was added and 67 parts of conductive composition fine powder, and a positive resistance temperature coefficient heating element was prepared in the same manner. was created. Further, 20 parts of Firzu Black's low S-conductivity high-density polyethylene was processed in the same manner to obtain a heating element shape sample.

These samples were bent to a curvature of 200 to generate stress, and a continuous current test was conducted. The test results are shown in Figure 2 and Table (1). In FIG. 2, the temperature of the conventional sample drops significantly after about 1250 h, indicating that it is at the end of its life. However, the sample according to the present invention shows no tendency for temperature to decrease even after 4000 hours. Although this result was obtained from an accelerated test in the presence of stress, it is thought that similar or even greater differences would occur under practical conditions. It is thus clear that the addition of carbon black to the bonding resin portion further extends the life of the heating element. Furthermore, as is clear from Table (1), the volume resistivity value of low conductivity high density polyethylene is extremely high, at a level of 107Ω, and it is clear that it does not dominate the resistance characteristics of the heating element. It is.

Table (1) (Sample width = 10 mm, length: 200 mm, thickness: 0.6
-) Example (2) While kneading 45 parts of low density polyethylene and 55 parts of furnace black using a heating mixing roll at 145°C, 3.5 parts of dicumyl peroxide was added as a crosslinking agent to 100 parts of the kneaded material. and sufficiently dispersed. After taking out the kneaded material in the form of a sheet, it was heat-treated at 160"C for 1 hour to complete the crosslinking reaction.Furthermore,
A conductive composition fine powder with an average particle size of 70 μm was obtained by freeze-pulverization. 60 parts of this conductive composition fine powder and 32 parts of high-density polyethylene were kneaded using a heating mixing roll at 160°C to obtain a high resistance positive resistance temperature coefficient resistor composition.Next, 8 parts of furnace black was added. The mixture was added to complete the kneading. In the same manner, one to which 4 parts of furnace black was added and another to which 15 parts of furnace black was added were prepared.

The composition of the positive resistance temperature coefficient resistor 3 obtained in this way is 200
A laminated structure element of copper foil/resistor 0.6 ms/copper foil was produced using a 'C hot press. Next, polyester film/
Heat fused exterior with ionomer resin laminated film, 170
Annealing was performed at °C for 3 hours to obtain a positive resistance temperature coefficient heating element having three levels of resistance characteristics.

These samples were bent to a curvature of 200 m to generate stress, and a continuous current test was conducted. The test results are shown in Figure 3 and Table (2). In FIG. 3, the composition ratio of the furnace black to which 8 parts was added is the same as that of Example (1), and 4000 h
There was no tendency for the temperature to decrease significantly over time,
It can be said that the influence of the kneading procedure is relatively small. In contrast,
The product to which 4 parts of furnace blank was additionally added did not have a significant effect on extending the life, and it is clear that the amount of carbon black added was not sufficient to contribute to stabilizing the conductive path. On the other hand, the material to which 15 parts of furnace black was additionally added had a low resistance as is clear from Table (2), and is considered to form a conductive path almost comparable to that of the conductive composition fine powder. It is clear that with this composition, various advantages of the conductive composition fine powder are lost. In this way, by adding an appropriate amount of carbon black to the binding resin part, the conductive composition vl! It can be said that the characteristics of powder are utilized.

The volume resistivity value of the bonded resin portion is desirably at least twice that of the conductive composition fine powder portion, and preferably one or more digits or more.

Table (2) (Sample width: lom, length: 200M, thickness: 0.6
am) The crystalline polymers are not limited to those listed here, but include medium density polyethylene, high density polyethylene, polybdenum, polypropylene, polymethylpentene, polyamide, polyester, polyvinylidene fluoride, and even , organic acid-grafted crystalline polymers such as acrylic acid and maleic acid, copolymers such as ethylene/ethyl acrylate, and derivatives such as ionomers can all be used. As the conductive fine powder, among carbon blacks such as channel black, thermal black, acetylene black, and lamp blank, carbon blacks that exhibit remarkable positive resistance temperature characteristics can be used.

As the binding resin, not only the crystalline polymers mentioned above can be used, but also a wide variety of materials such as various elastomers such as nitrile rubber, butyl rubber, and acrylic rubber, various resins such as polyester, and various thermoplastic elastomers. You can choose from among them. It is also possible to select the crystalline polymer and the binding resin from the same material. Particularly useful materials include polyethylene and polypropylene grafted with ionomers containing carboxyl groups, ethylene-vinyl acetate copolymers, ethylene/ethyl acrylate, maleic acid, and the like. These materials not only have excellent affinity with conductive fine powder and reactivity during crosslinking (they are also very advantageous for ensuring adhesion with electrodes. In this case, it is desirable to select a material containing carboxyl groups for the bonding resin.Crosslinking agents are not limited to dicumyl peroxide, but can also be used for crystalline resins. An appropriate material with a half-life of 1 Ill temperature can be selected depending on the melting point.

Effects of the Invention As mentioned above, when trying to achieve high output by generating heat between positive resistance temperature coefficient resistor materials and electrical bridges that are very close together, it is possible to achieve a specific resistance value close to that of a semiconductor region. However, simply adjusting the composition ratio will greatly reduce the number of contact points between the conductive fine powders, so the resistance-temperature characteristics will be similar to that of the crystalline polymer. In addition to being controlled solely by the melting point, unstable components assumed to be due to thermal stress of various constituent materials due to thermal expansion and contraction in lower temperature ranges will increase dramatically, and many improvements will be required. Despite this, it has not been possible to ensure long-term life characteristics that can be said to be semi-permanent.The positive resistance temperature coefficient heating element of the present invention solves these problems. That is, a novel method in which carbon black is fixed in a conductive composition fine powder by crosslinking, and the conductive composition fine powders are electrically and stably bonded to each other using a semiconductive bonding resin containing an appropriate amount of carbon black. By introducing a resistor structure of
Can guarantee controllability of resistance value and long-term life characteristics.
We have achieved a positive resistance temperature coefficient resistor composition with high reliability. Application of this composition provides a positive resistance temperature coefficient heating element with high output and long life. As a result, even when used as a heating element for snow melting or for floor heating, which is built into a house, the product's lifespan will not be significantly inferior to that of a house, eliminating concerns regarding maintenance. It is something that can be done.

[Brief explanation of the drawing]

FIG. 1 is a perspective view of a positive resistance temperature coefficient heating element according to an embodiment of the present invention, FIG. 2 is a diagram showing the life characteristics of the positive resistance temperature coefficient heating element shown in embodiment (1) of the present invention, and FIG. This figure shows the life characteristics of the positive resistance temperature coefficient heating element shown in Example (2) of the present invention, and FIG. 4 shows a perspective view of the positive resistance temperature coefficient heating element based on the prior art. 4... Positive resistance temperature coefficient resistor, 5, 6...
...Metal foil electrode, 7.8...Exterior material. Name of agent: Patent attorney Shigetaka Awano Haka 1 person 4-Sho A7! L, r indicator resistance red s, g-Ichikin A branch' anti-7, 8--Ichimasu Zayori' Sai Figure 1 Figure 12! !轡ま（尤）

Claims (4)

[Claims] (1) Conductive composition fine powder having a positive temperature coefficient of resistance, which is formed by crosslinking a conductive composition mainly composed of a crystalline polymer and carbon black with an electron beam or an organic peroxide, and then dividing the conductive composition into fine particles. , a positive resistance temperature coefficient resistor made of a composite composition of a bonding resin made by adding an appropriate amount of carbon black, a pair of electrode bodies formed integrally with the resistor, and an insulating exterior body covering the entirety of these. A positive resistance temperature coefficient heating element consisting of. (2) The positive resistance temperature coefficient heating element according to claim (1), wherein both the crystalline polymer and the binding resin are crystalline polyolefins. (3) The volume resistivity value of the binding resin alone, which is made by adding an appropriate amount of carbon black, is at least one order of magnitude higher than the volume resistivity value of the binding resin that does not contain carbon black and the conductive composition fine powder. The positive resistance temperature coefficient heating element according to claim (1) or (2). (4) The volume resistivity value of the positive resistance temperature coefficient resistor is 10^
3Ωcm or more, and the distance between a pair of electrodes is 1mm
The positive resistance temperature coefficient heating element according to any one of claims (1) to (3), which is as follows.