TECHNOLOGY FOCUS - POLYMERS - Preferred Composition: The sealing material layer contains ethylene-vinyl acetate copolymer, or polyvinyl butyral resin, and has stacked structure including sealing material layers (A, B and C) having embossed surface structure. The sealing material layer (A) contains ethylene-vinyl acetate copolymer or polyethylene butyraldehyde resin. The sealing material layer (B) contains polyethylene butyraldehyde resin, vinyl polymer, thermoplastic elastomer e.g. polyolefin-based elastomer, thermoplastic vulcanized rubber, fluororubber and fluorosilicone rubber. The sealing material layer (C) contains ethylene-vinyl acetate copolymer or polyethylene butyraldehyde resin. The electrical insulation layer is a weathering layer, and contains fluoroplastic material, thermoplastic rubber elastomer and material chosen from polyethylene mixture, polyvinylidene fluoride, ethylene-tetrafluoroethylene copolymer, tetrafluoroethylene and hexafluoropropylene copolymer, polypropylene, polycarbonate, polycarbonate-polyester alloy, or mixture of nylon and ethylene-vinyl alcohol copolymer. The thermoplastic rubber elastomer is polyolefin-based elastomer containing ethylene-propylene diene rubber, ethylene-propylene rubber, thermoplastic vulcanized rubber, fluororubber and fluorosilicone rubber. The electrical insulation layer has stacked structure, and includes electrical insulation layer (A1), electrical insulation layer (B1) (resistant layer) containing aluminum, and electrical insulation layer (C1) containing fluoroplastics. The fluoroplastic is chosen from polyethylene mixture, polyvinylidene fluoride, ethylene-tetrafluoroethylene copolymer and copolymer of tetrafluoroethylene and hexafluoropropylene. The electrical insulation layer (A1) contains vinyl polymer, polyethylene glycol terephthalate or polycarbonate, polycarbonate-polyester alloy, and thermoplastic rubber elastomer, polyolefin elastomer or thermoplastic vulcanized rubber. The back plate structure further contains organic or inorganic dye, wet material layer containing ethylene and vinyl alcohol copolymer, polyamide or polyvinyl chloride, and resistant material layer comprising ethylene and vinyl alcohol copolymer, polyamide or polyvinyl chloride. The inorganic dye contains barium sulfate, calcium carbonate, titanium dioxide or carbon black.