Evaluation of Electric Insulation Properties of Lacquer Films for the Use to Electronic Circuits

Lacquer, which is called Urushi in Japanese, is natural coating material having various merits such as resistance to water and chemicals, and has been used in traditional Japanese crafts. We investigated electric insulation properties of lacquer films for using them as board and coating material of electronic circuits. The results of our experiments showed that the lacquer films have humidity dependence on the insulation resistivity in the 25-75% range of relative humidity, because they have hygroscopicity. The lacquer films have an insulation resistivity of approximately 1015Ω･at room temperature. However, the insulation resistance decreased by 4-5 orders of magnitude at higher than a certain voltage. It was clarified that the insulation performance at lower than 5 V in the electronic circuits could be maintained by using the lacquer film, which was more than 5µm of thickness.