Examples of such a dimensionally-stable plate-like material include paper, paper laminated with a plastic film such as polyethylene, polypropylene or polystyrene film, such a metallic plate as aluminum plate (inclusive of aluminum alloy plates), a zinc plate or a copper plate, such a plastic film as cellulose diacetate, cellulose triacetate, cellulose propionate, cellulose butyrate, cellulose acet