JPH0812791B2 - Positive resistance temperature coefficient heating element - Google Patents

Description

TECHNICAL FIELD The present invention relates to a heat collecting tool and a structure of a heating element useful as a general heating device.

2. Description of the Related Art A conventional heating element having a positive temperature coefficient of resistance (hereinafter referred to as PTC) is disclosed, for example, in Japanese Patent Publication No. 57-43995 and Japanese Patent Publication No. 55-401.
The structure is as shown in Japanese Patent Laid-Open No. 61, and it was self-controlled to an appropriate temperature by the PTC characteristics of the PTC resistor between a pair of electrodes.

However, especially when a high power density is required, it is essential to improve the temperature distribution in the direction between the pair of electrodes in order to make the temperature distribution of the heating element itself uniform. As shown in Japanese Laid-Open Patent Publication No. 60-28195 and FIG. 3, a method has been taken in which a distance between a pair of electrodes is close to each other. In FIG. 3, 1 and 2 are a pair of parallel plate electrodes provided close to each other, and by arranging a PTC resistor 3 between them, it becomes possible to expose a high-output PTC heating element. It was

Problems to be Solved by the Invention However, in order to realize such a thin-walled PTC heating element, there are many problems in the constituent materials and processing methods. Above all, it is very difficult to secure the processing stability or the heat resistance stability of the resistance temperature characteristic because the PTC resistor has a high resistance. In such a thin-walled structure, the volume resistivity of the PTC resistor is required to be in a very high resistance region of 10 ³ to 10 ⁵ Ωcm level. Since carbon black has a considerably low volume resistivity of the material itself, a small addition amount is required to obtain a value of 10 ³ to 10 ⁵ Ωcm, and it is not only necessary to finely adjust the carbon black composition ratio. In order to keep the arrangement of the carbon black, an extremely high precision processing method is indispensable. Furthermore, even if it is used for a long period of time, it must maintain a stable function as a heating element, which is extremely difficult in practice. there were.

Means for Solving Problems The technical means of the present invention for solving the above problems is a melting point T ₁
Mainly containing a conductive filler obtained by dispersing conductive fine particles in a first crystalline polymer having a temperature difference of ₁ and a second crystalline polymer having a melting point T ₂ higher than the melting point T _1. comprising a thin positive resistance temperature coefficient resistor whose components, and a pair of electrode bodies provided in order to apply a voltage in the thickness direction, T ₂
The positive resistance temperature coefficient heating element is formed by performing the first annealing at a higher temperature and then performing the second annealing at a temperature lower than T _{2 and} higher than T ₁ .

Action The action of this technical means is as follows. That is, a thin-walled positive resistance temperature coefficient resistor composition in a very high resistance region having a room temperature volume resistivity of 10 ³ Ωcm or more, which is obtained by dispersing conductive fine particles in a crystalline polymer, has a crystalline property. Not only does it show a significant positive resistance temperature coefficient near the melting point of the polymer, but it is also affected by the linear expansion coefficient in the lower temperature range, and the composition becomes fine due to crystal growth of the crystalline polymer or aggregation of conductive fine powder. It becomes strongly affected by the structure, lacks stability, and cannot be put to practical use as a single item.

However, the volume resistivity of the dielectric filler in which the conductive fine particles are dispersed in the crystalline polymer having the melting point T ₁ is 10
A stable resistor can be realized by forming a stable resistance region of less than ³ Ωcm and dispersing this conductive filler in the second crystalline polymer having a melting point T ₂ higher than T ₁ . However, in such a composite material, during processing, processing strains are caused by differences in melting points T ₁ and T ₂ , differences in melt index (M1) value indicating melt viscosity, heat and pressure accompanying various processes, and the like. It will become big. Processing strain is reduced by actual use and the structure becomes stable, but as a result, the resistance temperature characteristics change significantly over time, which is not satisfactory in actual use. . Then, the first annealing is performed at a temperature higher than T ₂ to melt the first and second crystalline polymers, and the working strain is removed. Next, by performing a second annealing at a temperature lower than the melting point T _{2 and} higher than T ₁ , the second crystalline polymer having the melting point T ₂ is melted while the first crystalline polymer having the melting point T ₁ is in a molten state. The crystalline polymer is stably crystallized. After that, the first crystalline polymer is stably crystallized while being cooled to room temperature.

In this way, since the various constituent materials are in a stable state, the change with time of the resistance-temperature characteristic becomes very small during actual use, and a stable positive resistance temperature coefficient heating element can be realized.

Embodiment An embodiment of the present invention will be described below with reference to the accompanying drawings.

In FIG. 1, reference numeral 4 is an antibody having a low positive temperature coefficient of resistance of 0.5 mm, and a pair of electrodes 5 and 6 are mounted on the upper and lower surfaces of the low antibody 4. Positive resistance temperature coefficient Low melting point for antibody 4 130
A composition obtained by subdividing a kneaded material obtained by kneading high temperature polyethylene with high temperature polyethylene into thermal black and dispersing it into a polyester elastomer having a melting point of 160 ° C. was used. Specifically, it was manufactured by the following procedure.

First, high-density polyethylene and thermal black are kneaded at a ratio of 1: 1 and then frozen and ground to obtain an average particle size of 10
A ground product of 0 μm was obtained. Then, this pulverized product was kneaded in a polyester elastomer at a carbon black composition ratio of 35 wt% to obtain a composition of a resistor 4.

The composition was processed into the structure shown in FIG. 1 and then annealed at 170 ° C. for 1 h and then at 140 ° C. for 1 h to obtain a PTC heating element of the present invention. As a comparative example, a PTC heating element that was only annealed at 170 ° C. for 1 hour was manufactured and a comparative experiment was conducted. As a comparative experiment, an energization test was conducted at AC 100 V for 3000 hours. Surprisingly, as shown in FIG. 2, the PTC heating element of the comparative example was 3000 h at 14.5 ° C. as shown in FIG. 2 (a).
Despite the temperature rise, the PTC heating element of the embodiment of the present invention shows 7.5% even after 3000 hours as shown in FIG. 2 (b).
It had an excellent effect of reaching a temperature rise of ℃ and stabilizing. This is because after annealing at 170 ° C, both the high-density polyethylene and the polyester-based elastomer are melted, and processing strain, thermal stress, etc. are gradually eliminated, and then at 140 ° C, only the polyester-based elastomer is high-density polyethylene. In the molten state, it crystallizes in a stable position in a stable state, and while it is cooled to room temperature, the high-density polyethylene is partially compatible with the polyester elastomer and is stable in a structure in which both are appropriately phase-separated. This is due to the fact that the carbon black is crystallized, the thermal strain and thermal stress due to annealing are almost eliminated, a stable sea-island structure is realized, and the position of the carbon black is stabilized. Further, as a second comparative example, a resistor composition containing only carbon black and high-density polyethylene was processed in the same manner and annealed at 170 ° C. for 1 hour only. As shown in Fig. 2 (c) at 3000h 1
It was found that the temperature rises by 8.6 ° C., and the effect of the present invention is very remarkable for resistance stabilization.

The material forming the positive temperature coefficient resistor is not limited to the combination of high density polyethylene, thermal black, and polyester elastomer, and may be medium density polyethylene, low density polyethylene, linear polyethylene, or ethylene acetate. Crystalline resins such as vinyl copolymers, ethylene acrylic acid copolymers, ionomers, polyamides, polyvinylidene fluoride, polyesters, various thermoplastic elastomers, and functional groups such as acrylic acid and maleic acid in the above crystalline polymers. It may be any crystalline polymer such as a modified polymer to which is added, as long as two or more crystalline polymers having different melting points are appropriately combined.

The carbon black may be channel black, acetylene black, furnace black, or the like, or may be a composition in which two or more kinds of carbon black are combined.

Further, it is naturally possible to improve the resistance stability of three or more compositions of the above-mentioned crystalline polymer by annealing between the melting points of these polymers.

The annealing between the melting points has a large effect, preferably for 30 minutes or more, in order to stabilize the material structure. More preferably, it is constant or at a rate of 1 ° C./minute or less at an appropriate temperature between the melting points. Gradually cool.
Further, in order to further stabilize the crystal structure and the positional relationship between the conductive filler composed of the first crystalline polymer in which carbon black is dispersed and the second crystalline polymer, the temperature between the melting points is increased. If the temperature is fluctuated up or down by 5 ° C. or more, the resistance is further stabilized and hardly changes due to heat resistance. In fact, the second anneal of the previous embodiment is 14
Samples that fluctuated up and down 2 cycles between 0 and 150 ℃,
In the same test 3000h, it was possible to reach a temperature rise of 3.5 ° C or less as shown in Fig. 2 (d).

Further, when the carbon black in the conductive filler is cross-linked with an organic peroxide, an electron beam or the like, the carbon black is fixed to the first crystalline polymer and a more stable conductive filler is not only realized. However, the partial compatibility with the second crystalline polymer becomes remarkable, and the annealing between the melting points can be shortened. In fact
In the case where the conductive filler of the previous example is cross-linked with peroxide, the same annealing conditions are used: 170 ° C-1h, 140 ° C-
1h, +2 as shown in Fig. 2 (e) even in the same test 3000h
The temperature change was ℃ or less.

The second crystalline polymer of the first crystalline polymer may be made a dispersible partially compatible material having a large difference in the value of the solubility parameter (SP), which is the square root of the cohesive energy density. It is valid.

Finally, the following is a summary of the main experiments described above.

Effect of the Invention As described above, when an attempt is made to achieve high output by, for example, generating a positive resistance temperature coefficient resistor material between very close electrodes, a specific resistance value close to the semiconductor region is obtained. Although it is necessary to have a positive resistance temperature coefficient resistor material, simply adjusting the composition ratio significantly reduces the number of contact points between fine powders, so the positive resistance temperature coefficient abnormally increases, Due to the change over time, only a heating element that is unstable and cannot withstand practical use was obtained, for example, the resistance value and the resistance temperature characteristic fluctuated greatly. However, according to the present invention, this point can be overcome. .

As a result, it has become possible to expand the application of the revolutionary positive resistance temperature coefficient heating element with high output and very small resistance change over time. Furthermore, the long-term stabilization of such a positive temperature coefficient material having a large volume resistivity contributes to a great value in practical use in various industrial fields.

[Brief description of drawings]

FIG. 1 is a perspective view of a positive resistance temperature coefficient heating element of an embodiment of the present invention, FIG. 2 is a performance diagram of temperature change with time of the same embodiment and a comparative example, and FIG. 3 is a conventional positive resistance temperature coefficient. It is a perspective view of a heating element. 4 ... Positive resistance temperature coefficient resistor, 5, 6 ... Electrode.

Claims (7)

[Claims] 1. A conductive filler which is obtained by dispersing conductive fine particles in a first crystalline polymer having a melting point T ₁ and is subdivided, and a _second melting point T ₂ having a temperature higher than the melting point T ₁ . and crystalline polymer and the thin positive resistance temperature coefficient resistor whose main component, and a pair of electrode bodies provided in order to apply a voltage in the thickness direction, first at a temperature higher than T ₂ A positive resistance temperature coefficient heating element obtained by performing a second anneal at a temperature lower than T _{2 and} higher than T ₁ after the annealing. 2. The first or second annealing treatment time is 30
The positive resistance temperature coefficient heating element according to claim 1, wherein the heating coefficient is positive or negative. 3. The method according to claim 1, wherein at least one of the first and second anneals has a slow cooling treatment at a constant rate or at a rate of 1 ° C./minute or less for 20 minutes or more. A positive resistance temperature coefficient heating element according to item 2. 4. The method according to claim 1, wherein at least one of the first and second annealing has a process of raising the temperature by 5 ° C. or more in each temperature region.
The positive resistance temperature coefficient heating element according to any one of items 1 and 3. 5. The conductive filler is crosslinked with an electron beam, an organic peroxide or the like, and the conductive filler is crosslinked.
A positive resistance temperature coefficient heating element according to any one of items. 6. The positive resistance temperature coefficient heating element according to claim 1, wherein the conductive filler and the second polymer are partially compatible with each other. 7. The positive resistance according to any one of claims 1 to 6, wherein the first or second crystalline polymer has a crystallinity of 20% or more by X-ray analysis. Temperature coefficient heating element.