Production method for a membrane switch member

A method for manufacturing a membrane switch member, the method comprising the steps of:

• preparing a membrane switch sheet including a base film and an adhesive layer, the base film including a flat portion and a semi-spherical or dome shaped protruding portion, the protruding portion being protruded on a front face side of the base film having a uniform thickness, the adhesive layer being formed on a back face of the flat portion of the base film;
• closing a pair of molds
• in a state where the membrane switch sheet is disposed such that the protruding portion contacts a convex portion cavity forming face of a first mold of the pair of molds to invert the protruding portion to a concave portion, and
• in a state where a face on a base film side of the membrane switch sheet is retained on a mold inner face of the first mold, and
• a second mold of the pair of molds defines a cavity between a face of an adhesive layer side of the membrane switch sheet and a mold inner face of the second mold;
• injection-molding by injecting a material including a supercritical fluid gas and a resin material in a mixed state into the cavity of the closed pair of molds;
• and
• after the injection-molding, releasing mold-clamping and removing the first mold from the second mold for opening the pair of molds and after the removing, causing gas produced from the injection-molded resin to grow on a back face side of the concave portion, thereby causing the protruding portion of the membrane switch sheet to re-invert from a state inverted to the concave portion to a protruded protruding state, and then resulting in manufacturing a membrane switch member in which a void is formed between the protruding portion and an injection molded and cooled-solidified resin layer and the flat portions is adhered to the resin layer by the adhesion layer.