JPH01304684A - 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 having higher heat resistance than the resin, and a surface- graphitized carbon black. 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 e.g., a chlorinated polyethylene-type thermally plastic elastomer in a prescribed amount respectively are mixed each other and pre-kneaded by a hot roll, a surface-graphitized inert carbon black in a prescribed amount is added to the mixture, and the resulting mixture is kneaded. By this work, the crystalline resin is retained in the three dimensional molecular chain of the elastomer while the resin is resolved in the elastomer and further the inert carbon black is retained in the solid solution of the resin and the elastomer. Due to the surface property of the carbon black, the carbon black is prevented from cohering when electricity is conducted between electrodes, and cross-linking effect as same as a costly cross-linking by a radioactive ray is attained. High flexibility of the composition can also be attained by addition of the elastomer.

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 electric carpets.

2. Prior Art The conventional self-temperature control heating element composition of this rice plant is composed of a crystalline resin such as low density polyethylene and Mogul L (CABO).
Made by T, particle size 24m! , DBP oil absorption 60 ao/
It was formed by kneading active carbon black having a functional group on the surface, such as 100 g, P H3,0), and then crosslinking with radiation. A heating element composition that is simply kneaded with crystalline resin and activated carbon black has a major problem in that when a voltage is applied continuously or repeatedly, the resistance value gradually increases and eventually no heat is generated at all. Was.

The cause of this is that the activated carbon black is uniformly dispersed in the crystalline resin, resulting in a conductive path between the activated carbon black and the crystalline resin, which is induced by continuous and repeated application of voltage. This was thought to be due to partial aggregation of black (decreased dispersibility).

This agglomeration of carbon black is caused by its own activity (that is, active carbon black with a large number of polar functional groups on its surface has a large cohesive force) and a larger factor of carbon black. This seems to be due to the low heat resistance of the crystalline resin that is the dispersion medium.

Furthermore, the heat generation saturation temperature of the self-temperature-controlled heating element is set to be about 2O-jo'c lower than the melting point of the crystalline resin. This is because the self-temperature controllability (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 portion forming the conductive path is
If the temperature exceeds that level, the melting point may be reached in some cases. 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 activated carbon black and then crosslinking the mixture with radiation.

The effect of radiation crosslinking is to change the molecular matrix of the crystalline resin from a two-dimensional structure to a three-dimensional structure, thereby improving heat resistance (preventing rapid deterioration of physical properties near the melting point), as well as improving the structure of the crystalline resin and activated carbon. (For this purpose, it is necessary to use activated carbon black that has a polar functional group on its surface, and the crystalline resin and the surface polar functional group of the activated carbon black are excited by radiation and react.) This was thought to prevent activated carbon black from agglomerating.

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 these conventional problems, and aims to provide a self-temperature-controlling heating element composition that is low in 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, an elastomer having higher heat resistance than the crystalline resin, and a graphitized surface. and inert carbon black.

Effect With the above-described structure, the crystalline resin is held by a highly heat-resistant elastomer having a three-dimensional molecular structure, thereby preventing a sudden drop in viscosity near or above the melting point of the crystalline resin. The heat resistance of the crystalline resin can be improved in appearance.

In addition to the fact that inert carbon black with low agglomeration is used, aggregation of the inert carbon black added to the resin/elastomer system 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 the crystalline resin, for example, Sumikasen E-104 (manufactured by Sumitomo Chemical ■, low density polyethylene, melting point 110 ° C.),
As an elastomer having higher heat resistance than at least the crystalline resin, for example, Elasthren (manufactured by Showa Yuka),
14010B (manufactured by Mitsubishi Kasei ■, particle size 8
4mu, DBP oil absorption 73 o a / 100 g,
A predetermined amount of PH10.5) was added thereto, and the mixture was further kneaded 20 times to obtain a mixed wire material. For characteristic evaluation, this was taken out in sheet form from a hot roll, a pair of copper wires were placed between the sheets as electrodes at 1 mm intervals, and the heating element for measurement was obtained by pressure molding at 170°C for 2 hours. I used it.

In the above configuration, within the heating element composition, crystalline resin molecules are incorporated into the three-dimensional molecular chains of the elastomer in a compatible manner, and inert carbon black is further captured in this compatible body. and uniformly distributed. In this way, while the crystalline resin alone rapidly softens and melts near and above its melting point, in the above-mentioned compatible composition, the crystalline resin is held by the molecular chains of the highly heat-resistant elastomer. , high viscosity can be maintained even in the above temperature range.

In addition, although the details of why carbon black agglomerates are unknown, we have investigated extensively and found that active carbon black, which has a large number of polar functional groups on its surface, has a high aggregation property. I found something strong. for that,
As shown in this example, inert carbon black whose surface was graphitized by high-temperature treatment and had no polar functional groups on its surface was used.

In this way, it has the effect of preventing the agglomeration of carbon black that tends to occur when electricity is applied between the electrodes, similar to radiation crosslinking, and imparting rubber elasticity by adding an elastomer, without using expensive radiation irradiation equipment. This has the effect of providing a self-temperature-controlling heating element composition that is inexpensive and highly flexible. The above heating element composition comprises 1
Currently, in AC100V current test in 00℃ atmosphere,
The fever has continued stably for over 2000 hours. In addition, in the above example, the case where the crystalline resin and the elastomer are compatible is shown, but the same effect can be obtained even if they are incompatible, but if they are incompatible, phase separation occurs at high temperature. In this respect, a compatible system is preferable.

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 inert carbon black whose surface is graphitized.