JPH0217608A - Positive resistance temperature coefficient heating element - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a positive resistance temperature coefficient heating element useful as a warming appliance and a general heating device.

2. Description of the Related 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. The temperature was self-controlled to an appropriate level due to positive resistance temperature characteristics.

However, especially when high power density or high temperature is required, it is essential to always maintain a good temperature distribution in the direction between the pair of electrodes in order to make the temperature distribution of the heating element itself uniform. As a solution, the Special Public Interest Publication (1982-5) 515
As shown in the above publication and FIG. 3, a method was adopted in which the distance between a pair of electrodes was made close to each other. In Fig. 3, 1°2 is 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. The possibility of developing a high-power positive resistance temperature coefficient heating element has been discovered.

Problems to be Solved by the Invention However, although the conventional positive resistance temperature coefficient heating element described above had an excellent structure for producing high output, relatively low-resistance conductive materials such as carbon black Considering the withstand voltage breakdown characteristics of positive resistance temperature coefficient resistors constructed by mixing and dispersing fine powders, and the volume resistivity range where extremely high resistance is required, there are many problems that must be solved. had the following issues. In order to construct a positive resistance temperature coefficient heating element with very close electrode spacing,
It is essential not only to select conductive fine powder with excellent withstand voltage breakdown characteristics, but also to obtain sufficiently large positive resistance temperature characteristics to ensure that the resistance does not run out of control beyond the peak resistance value. there were. In addition, the volume resistivity value is 103 to 105 Ωam, compared to the conventional 10° to 102 Ωam.
A semiconductor region of Ωom was required, and the composition ratio of the conductive fine powder had to be significantly reduced. the result,
The number of contact points between conductive fine powders has been drastically reduced, and the resistance-temperature characteristics are not only controlled by the melting point of the crystalline polymer, but also by the thermal stress of various constituent materials due to thermal expansion, thermal contraction, etc. at lower temperatures. The unstable components assumed to have increased dramatically, resulting in extremely unstable characteristics. Furthermore, over time, significant changes in resistance value and temperature coefficient of resistance occur due to crystal growth of the crystalline polymer, thermal stress in various parts of the heating element, or aggregation of conductive fine powder. They lacked stability, had extremely short heat-generating lifetimes, and were at risk of abnormal heating, smoke, and ignition, and were far outside the acceptable range for practical use. As described above, it has not been possible to create a useful positive resistance temperature coefficient heating element having a volume resistivity of 103 Ωam or more simply by adjusting the composition ratio of the conductive fine powder.

The present invention solves this problem and provides a positive resistance temperature coefficient heating element that can realize excellent resistance stability that can withstand practical use.

Means for Solving the Problems In order to solve the above problems, the positive resistance temperature coefficient heating element of the present invention is obtained by crosslinking and finely dividing a conductive composition formed by mixing and dispersing conductive fine powder in a crystalline polymer. A thin positive resistance temperature coefficient resistor is formed by mixing and dispersing a conductive filler formed by a crystalline polymer and a dimensional stability imparting agent into a crystalline polymer, and a pair of resistors are provided to apply a voltage in the direction of the thickness of the resistor. It is equipped with an electrode body.

For production The effect of this technical means is as follows.

In other words, the material composition of the positive resistance temperature coefficient resistor is divided into a part in which conductive fine powder is dispersed in a high proportion in a crystalline polymer and a part in which it is hardly dispersed, and both parts are arranged in a seabird shape. The conductive filler, which is made by crosslinking and subdividing a conductive composition made by mixing and dispersing conductive fine powder in a crystalline polymer, is the former part, and has a volume resistivity. The conductive fine powder can be at the 10°Ωam level and is extremely stable, and because it is cross-linked by electron beams or organic peroxides, the conductive fine powder is reliably fixed in the conductive filler and remains stable over time. It is also possible to exhibit stable resistance characteristics. However, especially in the latter part, stress relaxation due to processing, heat, crystal growth, etc. in the crystalline polymer causes the conductive filler to repeatedly move extremely minutely to a stable position over time, resulting in agglomeration of the conductive filler during annealing. Changes such as relaxation of the structure occur, reducing conductive paths and increasing resistance, but the dimensional stability imparting agent mixed and dispersed in the crystalline polymer alleviates this change, making it extremely It becomes possible to maintain stable resistance stability. In this way, it is possible to achieve excellent stability of a resistor having a high resistance of 11030a or more, and to realize a high output positive resistance temperature coefficient heating element.

EXAMPLE Hereinafter, an example of the present invention will be described based on the accompanying drawings. In the positive resistance temperature coefficient heating element of this embodiment, for example, as shown in FIG. A sheathing material 7.8 is sheathed on top. The positive resistance temperature coefficient resistor 4 is formed as follows. That is, as a conductive fine powder, a thermal blank and a furnace black are uniformly dispersed in a ratio of 1:1 to make a fine powder, and while 55 wt% of this fine powder and 45 wt% of low density polyethylene are kneaded, organic peroxide is mixed. 3 wt% of dicumyl peroxide is added to low density polyethylene,
After completing the crosslinking reaction by applying heat treatment,
A pulverized product having an average particle size of 70 μm, that is, a conductive filler, was obtained by freeze pulverization.

Next, the conductive filler and the dimensional stability imparting agent were kneaded so as to be uniformly dispersed in high-density polyethylene (organic acid modified specification) so that the carbon black composition ratio was 29 wt% of the total amount. , a positive resistance temperature coefficient resistor 4 was obtained. Furthermore, this resistor 4 was processed into a heating element as described above, and then annealed to obtain predetermined resistance characteristics. In order to examine the effectiveness of the present invention, samples of the dimensional stability imparting agent were obtained by processing six types of compositions shown in the table below as described above.

(Left below) Here, the ratio of the additive to the high-density polyethylene (
ph"), and dimensional stability refers to the effect of suppressing the rate of thermal deformation caused by stress such as processing, heat, and crystal growth in crystalline polymers. The thermal deformation rate produced by
It was shown that the rate was reduced compared to the sample without addition of lJll16.

In fact, a comparison experiment was conducted by conducting an energization test on samples of 11k11-6. Regarding the energization mode, the evaluation was conducted by intermittent energization every 10 minutes in order to perform an accelerated evaluation using a thermal cycle. The results are shown in Figure 2. As is clear from Figure 2, the maximum temperature during intermittent energization cycles is higher in samples with higher dimensional stability effects.The energization life is longer, and the magnetic 4 sample with the highest dimensional stability effects maintains the initial temperature even after 7000 hours. It was found that the heat generation characteristics were very stable, and the resistance temperature characteristics were also very stable. On the other hand, in the sample without the addition of N16, the temperature started to decrease after 2000 hours, and at 300 hours
After 0 hours, the resistance becomes so high that it almost no longer generates heat.
It turned out that it had an extremely short lifespan. In other samples, a slight temperature drop phenomenon began to appear between 6,000 and 70,001 t of energization life, and it can be estimated that the intermittent energization life was on the order of 10,000 h. Although the lifespan differs depending on the mode in which it is actually used, the more dimensional stability imparting agent is added, the longer the energized lifespan will be, contributing to the excellent performance of maintaining stable heat generation characteristics over time. be. A composition that suppresses thermal deformation rate due to stress such as processing, heat, and crystal growth in a crystalline polymer.
A composition in which the thermal deformation rate produced by heating a single resistor to the annealing temperature is preferably 10% or more lower than that of a composition without additives will not only ensure long-term resistance stability but also be suitable for various applications. Dimensional stability imparting agents can be added as appropriate to ensure a heat-generating life that is compatible with the practical period of use and the heat resistance properties of the constituent materials, etc., making it possible to establish safety even at the end of the product's life. This has excellent effects.

This is thought to be due to the following mechanism.

In other words, the agglomerated structure of the conductive filler during annealing is relaxed by repeating extremely small displacements of the conductive filler to a stable position over time due to stress relaxation due to processing, heat, crystal growth, etc. in the crystalline polymer. As a result, the conductive path decreases and the resistance increases, but the dimensional stability imparting agent mixed and dispersed in the crystalline polymer alleviates this change, resulting in extremely stable resistance stability. will be able to hold. In this way, 103Ωam
The excellent stability of the high-resistance resistor described above can be achieved, and a high-output positive resistance temperature coefficient heating element can be realized.

The dimensional stability imparting agent is not limited to those described here, but any dimensional stabilizer may be used, and the thermal deformation rate is preferably 10% compared to the additive-free composition. % or more, and there are few that also have an effect as a crystal nucleating agent, and some that have a reducing action and also have the effect of stabilizing the material.

Further, when a dimensional stability imparting agent is added to the conductive filler, thermal deformation of the crystalline polymer in the conductive filler is also alleviated, so that even more excellent resistance stability can be maintained. Furthermore, by having compatibility with the crystalline polymer, voids in the resistor can be completely eliminated, and risks such as microcracks can be prevented. Also,
A dimensional stability imparting agent may be added to the exterior material and applied to the resistor that comes into contact with the dimensional stability imparting agent. Furthermore, the degree of crosslinking of the conductive filler can be increased by using a crystalline polymer having an organic acid-modified functional group.
Further stabilization is also possible.

The material constituting the conductive filler is not limited to the combination of low-density polyethylene, thermal black, and furnace black, but also includes medium-density polyethylene, high-density polyethylene, linear polyethylene, ethylene-vinyl acetate copolymer, Crystalline polymers such as ethylene acrylic acid copolymer, ionomer, polypropylene, polyamide, polyvinylidene fluoride, polyester, and polyethylene modified with organic acids such as acrylic acid and maleic acid, and carbon such as channel black, acetylene black, etc. Even if black is used in combination with a conductive material that exhibits remarkable positive resistance temperature characteristics, the same effect can be achieved.

Similarly, the crystalline polymer kneaded with the conductive filler is not limited to high-density polyethylene, and may be the same as the crystalline polymer in the conductive filler.

Effects of the Invention As described above, in order to realize a high-output, high-temperature positive resistance temperature coefficient heating element, a resistor having a volume resistivity around the semiconductor region is required. If only the composition ratio of the conductive fine powder is adjusted, the number of contact points between the conductive fine powders will be drastically reduced. Therefore, the resistance temperature characteristics are not only controlled by the melting point of the crystalline polymer, but also in the lower temperature range. The unstable components assumed to be due to the thermal stress of various constituent materials due to thermal expansion, thermal contraction, etc. will increase dramatically, resulting in extremely unstable characteristics and a very short heat generation life However, the positive resistance temperature coefficient heating element of the present invention solves these problems. That is, by fixing the conductive fine powder in the conductive filler by crosslinking, and by suppressing the phenomenon of high resistance due to stress relaxation in crystalline polymers due to processing, heat, crystal growth, etc., by using a dimensional stability imparting agent. This provides a high-output, safe, and long-life positive resistance temperature coefficient heating element that achieves excellent long-term resistance stability. Furthermore, by adjusting the effect of the dimensional stability imparting agent through the temperature order and amount added, it is possible to set a heat generation life that is suitable for various uses and surrounding materials, thereby increasing safety up to the end of its life. becomes.

[Brief explanation of drawings]

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 characteristic diagram showing changes in the surface temperature of the heating element over time, and Fig. 3 is a conventional positive resistance temperature coefficient heating element. FIG. 3 is a perspective view of a heating element. 4...Positive resistance temperature coefficient resistor, 5.6...
・・Electrode, Seinon Aki
...Exterior material.

Claims (6)

[Claims] (1) A particulate conductive composition (hereinafter referred to as a conductive filler) obtained by crosslinking and subdividing a conductive composition obtained by mixing and dispersing conductive fine powder in a crystalline polymer, and its dimensional stability. A positive resistance temperature coefficient comprising a thin positive resistance temperature coefficient resistor formed by mixing and dispersing an imparting agent into a crystalline polymer, and a pair of electrode bodies provided to apply a voltage in the thickness direction of the positive resistance temperature coefficient resistor. heating element. (2) The dimensional stability imparting agent reduces the thermal deformation rate by 10 when a single resistor is heated to the annealing temperature of the heating element.
The positive resistance temperature coefficient heating element according to claim 1, which is made of a material that reduces the temperature coefficient of positive resistance by at least %. (3) Claim 1, wherein the dimensional stability imparting agent is composed of a material made by bonding benzaldehyde to sorbitol.
Or the positive resistance temperature coefficient heating element according to claim 2. (4) The positive resistance temperature coefficient heating element according to any one of claims 1 to 3, wherein the dimensional stability imparting agent has compatibility with the crystalline resin. (5) The positive resistance temperature coefficient heating element according to claim 1 or claim 2, wherein the dimensional stability imparting agent has a structure represented by at least ▲a mathematical formula, a chemical formula, a table, etc.▼. (6) Claims 1 to 5, wherein the dimensional stability imparting agent is contained in the exterior material that is in contact with the positive resistance temperature coefficient resistor.
The positive resistance temperature coefficient heating element according to any one of the above.