JPH05266974A - Self-control type heating element - Google Patents

Abstract

PURPOSE:To provide a self-control type heating element having excellent flexibility, durability against repeated bending, and a long lifetime. CONSTITUTION:A self-control type heating element is made of a composition including at least a conductive filler into a thermoplastic elastomer, and is provided with a heating element portion 2 crosslinked by electron beam irradiation and two parallel conductors 1 embedded in the heating element portion 2.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a self-controlled heating element which is wound around a pipe or steam pipe for transporting a viscous fluid or the like and used as a heater for keeping heat.

[0002]

2. Description of the Related Art Conventionally, PTC (Positive Temperature)
PTC materials that exhibit Coefficient behavior, that is, self-regulating properties, are well known.

As a known example of the PTC substance, a composition containing polyvinylidene fluoride resin and conductive carbon black dispersed in the resin (Japanese Patent Publication No. 62-5050).
5), and a composition containing a polyethylene resin and conductive carbon black dispersed in the resin (see JP-A-49-68296).

Compositions containing such thermoplastic crystalline polymers have been widely used in self-regulating heaters and the like because they exhibit a sharp increase in resistance starting at a temperature several degrees below their crystalline melting point.

FIG. 2 is a perspective view showing the structure of a conventional typical self-controlled heater. As shown in the figure, two conductors 1 are arranged in parallel at a predetermined interval. A core portion 5 made of a composition is formed so as to embed the two conductors 1 near the side ends.

After the core portion 5 is formed, the composition is crosslinked by irradiation with an electron beam such as high energy electrons. Further, a polymer jacket 3 made of an organic polymer is formed by extrusion so as to cover the surface of the core portion 5. The polymer jacket 3 is provided to impart desired chemical or physical properties to the surface of the article. The electron beam irradiation may be performed after the core portion 3 and the polymer jacket 3 are formed.

In the self-controlled heater 10 as described above, when a commercial voltage is applied between the two parallel conductors 1, a current flows between the conductors 1 via the core portion 5. Along with this, the core portion 5 generates heat, and the composition forming the core portion 5 begins to expand. As a result, the distance between the conductive particles such as carbon black dispersed in the composition increases, and the resistance between the conductors 1 increases.

In particular, in the vicinity of the crystal melting point of the composition, the resistance sharply rises, so that no current flows between the conductors 1,
Heat generation from the core portion 2 is suppressed. In this way, the self-control heating heater 10 operates in the self-control function.

[0009]

Among the conventionally known PTC substances, compositions comprising polyvinylidene fluoride resin have excellent thermal, chemical and mechanical stability, and therefore, self-controlled heating. It has been widely used in heaters. However, this composition was more likely to undergo disintegration than crosslinking due to electron beam irradiation, and the resin itself was likely to decompose. Therefore, the chemical and / or physical properties of the composition are deteriorated, causing defective products. In particular, when this composition is used in a self-controlled heating heater, the flexibility of the composition is likely to be impaired even if a cross-linking aid and the like are used in combination, and the conductor 1 and the composition are formed by repeated bending of the self-controlled heating heater. Voids were sometimes formed in the bonding interface 4 with the core portion 5 made of a material.

When a void is formed at the joint interface 4, the contact resistance between the conductor 1 and the core portion 5 increases, and even if a commercial voltage is applied between the conductors 1, the resistance between the conductors 1 increases, so that the current flows. It stops flowing. Therefore, there is a problem that the self-control heating heater 10 does not function as a heater and the product life is short.

Also, when a composition made of polyethylene resin is used for a self-controlled heater, the resin itself is not decomposed by electron beam irradiation, but it is flexible like the composition made of polyvinylidene fluoride resin. Because of poor sex
There are problems that it is difficult to handle, the range of use is limited, and the product life is shortened.

The present invention has been made to solve the above problems, and an object of the present invention is to provide a self-controlled heating element having excellent flexibility and long product life.

[0013]

A self-regulating heating element according to the present invention comprises a composition in which at least a conductive filler is added to a thermoplastic elastomer, and a heating element portion crosslinked by electron beam irradiation and a heating element. And a pair of conductors embedded in the section and spaced apart from each other.

The thermoplastic elastomer used in the present invention preferably contains olefin type, polyester type, polyamide type, styrene type, urethane type and vinyl chloride type elastomers. Especially, from the viewpoint of sensitivity of self-controllability,
Olefin-based, polyester-based and polyamide-based elastomers containing crystal components are preferred.

The conductive filler used in the present invention preferably contains acetylene carbon black, furnace carbon black, Ketjen black, graphite, metal powder and the like. In particular, acetylene black is preferable in terms of processability and purity. However, the conductive filler is basically for imparting conductivity, and is not limited at all.

Although the amount of the conductive filler added is not specified here, those skilled in the art can easily determine the amount added.

Further, the composition used in the present invention is
If necessary, a crosslinking aid, a vulcanizing agent, a stabilizer, a filler, a pigment, a processing aid, and another polymer may be contained as needed.

[0018]

In the self-regulating heating element according to the present invention, the heating element portion is made of a composition which contains a thermoplastic elastomer and is crosslinked by electron beam irradiation. The composition containing the thermoplastic elastomer does not decompose even when irradiated with an electron beam due to cross-linking, and has excellent flexibility having rubber elasticity and conformability. For this reason, even when repeatedly bent and used, the degree of adhesion at the joint interface between the heating element and the conductor is kept high, and voids are unlikely to occur at the joint interface between the heating element and the conductor. As a result, the contact resistance does not suddenly increase between the heating element and the conductor, and a normal heater function is ensured for a long period of time.

Further, during bending such as winding, the heating element portion flexibly follows the conductor operation. Therefore, the workable range is expanded and the workability is greatly improved, such as facilitating winding on a small diameter pipe.

[0020]

Embodiments Embodiments will be described below with reference to the drawings.

FIG. 1 is a sectional view of a self-controlled heater according to an embodiment of the present invention. After the materials were mixed in the composition shown by weight ratio in Table 1, they were melt-kneaded and pelletized by a 50 mmφ extruder.

As shown in FIG. 1, the pellets obtained by this melt-kneading were twisted with seven copper wires having a diameter of 1.45 mmφ to have a conductor cross-sectional area of 1.25 mm ² and arranged in parallel at 10 mm intervals. The core portion 2 is covered by covering the two conductors 1
Formed. The thickness of the core portion 2 on the conductor 1 is about 1.5 mm
Made thick This was cross-linked by electron beam irradiation of 24 mega rat, and the polymer jacket 3 was coated on it to prepare a trial sample of a self-controlled heater.

In Table 1, compositions according to the present invention are examples 1 to 6 of the present invention, and compositions according to the prior art are conventional examples 1.
~ 3.

[0024]

[Table 1]

The trade name and manufacturer of each component are shown in the margins of Table 1. The following test was conducted to investigate the change in resistance between the conductors after bending.

A heater sample having a length of about 1 meter was wound around a metal pipe having an outer diameter of 30 mm five times, and this operation was repeated 5 times, and the resistance between the conductors before and after the winding was measured by a digital multimeter. . The results are also shown in Table 1.

As is clear from Table 1, in the conventional self-controlled heaters (conventional examples 1 to 3), the resistance value between the conductors increased after bending. On the other hand, in the self-controlled heaters according to the present invention (Examples 1 to 6 of the present invention), almost no difference was observed in the resistance value between the conductors before and after bending. Thus, it can be seen that the self-controlled heater according to the present invention can be used as a long-life heat-retaining heater.

[0028]

According to the self-controlled heating element of the present invention,
Since the heating element follows the conductor operation excellently, the contact resistance between the conductor and heating element does not increase due to repeated bending and other uses, and the product life as a heater for heat insulation is secured for a long time. . In addition, the self-regulating heating element according to the present invention has excellent flexibility and can be wound around a small diameter pipe, and thus has a wide range of use without difficulty in working.

[Brief description of drawings]

FIG. 1 is a sectional view of a self-regulating heater according to an embodiment of the present invention.

FIG. 2 is a perspective view showing a structure of a conventional typical self-controlled heater.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 conductor 2 core part 3 polymer jacket 100 self-control heating heater In addition, in each figure, the same code | symbol shows the same or corresponding part.

Claims (1)

[Claims] 1. A heating element part made of a composition in which at least a conductive filler is added to a thermoplastic elastomer, crosslinked by electron beam irradiation, and embedded in the heating element part and arranged at a distance from each other. A self-regulating heating element comprising a pair of conductors.