Daito Communication Apparatus Co., Ltd.

Shoichi Sugaya

Toshiaki Abe

Akira Ueno

Kumakazu Ohkita

A PTC element displaying low volume resistivity and excellent PTC characteristics contains conductive carbonaceous particles having a large particle size, small specific surface area and being essentially unstructured such particles being, for example, thermal black or mesocarbon microparticles. The conductive particles are heat treated in an inactive atmosphere, blended with a crystalline polymer and then cross-linked by gamma radiation. In a variant form, the polymer can be chemically grafted onto the particles. The very low resistivity and excellent PTC characteristics of this PTC device make it suitable for miniaturization.

PTC device

A process for producing PTC (positive temperature coefficient) self-resetting overcurrent protection elements using two different crystalline polymers with an organic peroxide and carbon black. The mixture is kneaded at an elevated temperature. The two crystalline polymers include different proportions of tertiary hydrogen atoms to carbon atoms, so that the desired PTC characteristics of a highly crystallized polymer can obtain the benefit of greater proportions of tertiary hydrogen in a less highly crystallized polymer. A high degree of grafting to carbon black that increases the number of polymer having unpaired electrons in the crystalline polymer mixture through the decomposition of organic peroxide. The resulting mixture tends to disperse the carbon black uniformly throughout the resulting mixture, and to position the carbon black in a three-dimensional matrix in which it is fixed by cross-linking. The uniform distribution of the carbon black reduces localized heating and thus minimizes resistance changes following repeated overcurrent conditions. The first crystalline polymer is selected from high density polyethylene, polyesters, fluorine-containing polymers and mixtures thereof. The second crystalline polymer is either low density polyethylene or medium density polyethylene.

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Tokyo, Japan

Shoichi Sugaya