| abstract |
A protective ink mixture used for an insulating protective layer of a printed wiring board such as a membrane switch has a high adhesive strength to a base film, does not have a decrease in sliding resistance and insulating properties, and is non-halogen. An object of the present invention is to obtain a flame-retardant protective ink mixture having sufficient flame retardancy. A conductive circuit is formed on a base film, and a protective insulating layer covering at least the conductive circuit is provided. For the protective insulating layer 3, a protective ink mixture containing 100 parts by weight of a polyester resin and 60 to 150 parts by weight of melamine cyanurate having an average particle diameter of 5 μm or less is used. As the polyester resin, 100 parts by weight thereof contains 60 to 80 parts by weight of a polyester resin having a glass transition temperature of −15 ° C. to −18 ° C., and 20 to 40 parts by weight of a polyester resin having a glass transition temperature of 15 ° C. to 20 ° C. The use improves the bending resistance of the protective insulating film. [Selection diagram] Fig. 1 |