エポキシ樹脂の電気的特性におよぼすγ線照射の影響

抄録

The radiation damage to materials insulating electric current presents serious problems affecting the delicate functions of such electric apparatuses and measuring instruments as are constantly exposed to electronic radiation. One of the problems concerns epoxy resin which is appropriate material of wide application for manufacture of electric apparatuses by reason of its insulating capacity. Studies have been made, accordingly, of the effect of γ-ray radiation on epoxy resin with this excellent property. Our experimental studies will best be stated in three respects, first regarding the insulation, secondly regarding the test material, and thirdly regarding the radiation. Regarding electric insulation, the resistance against electric insulation, the strength against dielectric breakdown and the resistance against arc were respectively examined. Regarding the test material three kinds of epoxy resins were used, that of the bisphenol type, that of the novolac type and that of the cycloaliphatic type. Regarding radiation the dose of γ was prescribed between 10⁶∼10⁹.
The results obtained from the experiment are briefly as follows.
(1) With increase of γ-ray radiation in dose there is general decrease in insulation resistance. It is observed, however, at the same time that the maximum value of γ-ray radiation so far produced has been about 4×10⁶∼5×10⁷, and it is found also that there can sometimes be restoration of insulation resistance by virtue of its temperature dependence.
(2) The strength in voltage against dielectric breakdotwn decrease slowly with increase of γ-ray radiation in dose.
(3) Regarding the amout of γ-ray radiation that can have an effect on arc resistance of epoxy resin, as far as such an effect is observable, its arc resistance begins to drop at exposure to radiation of ca. 10⁸-γ and over, though there can sometimes be epoxy resin that is intact in arc resistance despite exposure to radiation even of ca. 10⁹γ.
(4) When aromatic amine and acid anhydride are used as curing agents for epoxy resin there is but little effect γ-ray radiation to be observed on its arc resistance.
(5) The amout of curing agents consumed by epoxy resin when it shows its maximum arc resistance in value, and their amount when epoxy resin shows its minimum in value, both under the influence of γ-ray radiation to which the material is respectively exposed, vary from the amount respectively when the material shows its maximum arc resistance in value, and that when it shows its minimum in value accordingly, both free from such influence. This is attributed to the relative variation in the corresponding quantity of epoxy resin itself owing to the molecular split and cross-linking.