JPH01304683A - Temperature self controlling heat radiating composition - Google Patents

Abstract

PURPOSE:To prepare a temperature self controlling heat radiating composition with a good flexibility with low cost by mixing and kneading a crystalline resin, an elastomer soluble with the resin, and a conductive powder. CONSTITUTION:A crystalline resin e.g., a low density polyethylene with melting point about 110 deg.C, an elastomer having higher heat resistance than the resin and soluble with the resin e.g., styrene-type thermally plastic elastomer in a prescribed amount respectively are mixed each other and pre-kneaded by a hot roll, a conductive powder, e.g., carbon black in a prescribed amount is added to the mixture, and the resulting mixtures is kneaded. By this work, the crystalline resin is retained in the elastomer having the three dimensional structure, the heat resistance of the crystalline resin is improved in appearance, the conductive powder is prevented from cohering, and due to the addition of the elastomer, rubber elasticity is added to the composition, and a desired composition is prepared without a costly process such as cross-linking by a radioactive ray.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a self-temperature-controlling heating element composition for use in heating appliances such as drowsy carpets.

BACKGROUND OF THE INVENTION Conventional self-temperature-controlling heating element compositions of this type have been formed by kneading and molding a crystalline resin such as low-density polyethylene and conductive particles such as carbon black, followed by radiation crosslinking.

A major problem with heating element compositions that are simply kneading crystalline resin and conductive particles is that when a voltage is applied continuously or repeatedly, the resistance value gradually increases, and eventually no heat is generated at all. It had

The reason for this is that immediately after the crosstalk, the conductive particles are uniformly dispersed in the crystalline resin, and the resulting conductive path consisting of the conductive particles and the crystalline resin is continuously and repeatedly applied. This is thought to be due to the partial aggregation (decreased dispersibility) of conductive particles induced by this.

It is thought that such aggregation of carbon black is caused by the low heat resistance of the crystalline resin that is a dispersion medium for carbon black. Generally, the heat generation saturation temperature of the self-temperature-controlled heating element is set to be about 20 to 30° C. lower than the melting point of the crystalline resin. This is because the self-temperature control property (PTC characteristic) is caused by a change in specific volume at the melting point of the crystalline resin, and this seems to be an appropriate temperature setting. However, this exothermic saturation temperature is the macroscopic temperature of the entire self-temperature-controlling heating element composition, and the microscopic temperature of the crystalline resin part that forms the conductive path is higher than that, or in some cases near the melting point. seems to have reached. When the crystalline resin exceeds its melting point, its physical properties (particularly viscosity when used as a dispersion medium for carbon black) rapidly decrease. Therefore, it seems that it is essentially difficult to disperse and maintain carbon black using only a crystalline resin.

For this reason, as shown in the conventional examples, heating element compositions that have been put into practical use are formed by kneading a crystalline resin and conductive particles and then crosslinking them with radiation. The effect of radiation crosslinking is to change the molecular chains of the crystalline resin from two-dimensional to three-dimensional structures, improve heat resistance (prevent sudden drop in properties, especially viscosity, near the melting point), and conductive particles. It was thought that the purpose was to prevent the agglomeration of

Problems to be Solved by the Invention However, conventional self-temperature-controlling heating element compositions have problems in that they are expensive due to radiation crosslinking, which requires high equipment costs, and lack flexibility.

The present invention solves the above problems and provides a self-temperature-controlling heating element composition that is low cost and highly flexible.

Means for Solving the Problems In order to solve the above problems, the self-temperature-controlling heating element composition of the present invention comprises a crystalline resin, which has higher heat resistance than at least the crystalline resin, and which has a crystalline resin and a heat resistance higher than that of the crystalline resin. It is made by kneading an elastomer that is compatible with the elastomer and conductive particles.

Function The self-temperature-controlling heating element composition according to the present invention is produced by blending a crystalline resin and an elastomer that is compatible with the crystalline resin. was captured, the so-called
It is an interpenetrating resin composition, and the molecular network of this elastomer prevents the crystalline resin from rapidly decreasing in viscosity near or above the melting point, and allows the heat resistance of the crystalline resin to be evaluated. Hanging can be improved. Therefore, agglomeration of the conductive particles added thereto is prevented. Furthermore, since it contains an elastomer, it has the effect of imparting flexibility (rubber elasticity).

EXAMPLE An example of the self-temperature-controlling heating element composition of the present invention will be described below.

As a crystalline resin, for example, Sumikasen E-104 (manufactured by Sumika Kagaku ■, low density polyethylene, melting point 110°C), and as an elastomer compatible with the crystalline resin, for example, Kraton G1650 (manufactured by Shell Chemical ■, styrenic thermoplastic elastomer) were weighed and pre-kneaded 5 times using a hot roll set at 170°C, and a predetermined amount of conductive particles such as carbon black was added and kneaded 20 times to obtain a self-temperature-controlled heating element composition. . The characteristics of the above heating element composition were evaluated by taking it out in a sheet form from a heated roll, and
A pair of copper wires were placed between the sheets as electrodes at intervals of 1 mm, and a heating element for measurement was obtained by pressure molding at 170° C. for 2 hours.

In the above configuration, in the heating element composition, the crystalline resin is partially compatible with the three-dimensional molecular network of the elastomer and enters therein. For this reason, while a crystalline resin alone rapidly softens (melts) near and above its melting point, in the compatible composition, the crystalline resin is held by the molecular chains of the highly heat-resistant elastomer. Therefore, high viscosity can be maintained even in the above temperature range. Therefore, it is considered that the conductive particles added thereto are trapped in the molecular chains of the compatible solution (uniformly dispersed system).

For this reason, it is possible to prevent the agglomeration of conductive particles that would otherwise occur when they pass between the electrodes, in the same way as radiation crosslinking, and the addition of an elastomer has the effect of imparting rubber elasticity, which is similar to radiation crosslinking. It can be done inexpensively using general-purpose equipment without using large equipment that increases costs, and
This has the effect of providing a highly flexible self-temperature-controlling heating element composition.

In addition, as in the above example, if a thermoplastic elastomer is used as the elastomer, a complicated crosslinking process is unnecessary.
It also has the advantage that a general-purpose resin molding machine can be used.

The above heating element composition currently continues to generate heat stably for more than 2000 hours in an AC 100V current test in a 100°C atmosphere.

In the above examples, low density polyethylene and styrene thermoplastic elastomer were used as the crystalline resin and elastomer, but the invention is not limited to these. ) is fine. For example, examples of elastomers that are compatible with low density polyethylene include crosslinked EPR and chlorinated polyethylene rubber.

Effects of the Invention As described above, the self-temperature-controlling heating element composition of the present invention has the effect of providing a self-temperature-controlling heating element that does not require radiation crosslinking, is low cost, and is highly flexible. have

Claims (1)

[Claims] A self-temperature-controlling heating element composition comprising a crystalline resin, an elastomer having at least higher heat resistance than the crystalline resin and having compatibility with the crystalline resin, and conductive particles.