TECHNOLOGY FOCUS - INORGANIC CHEMISTRY - Preferred Composition: The inorganic nanoparticles are titanium dioxide, or zirconium dioxide. The content of inorganic nanoparticles with respect to total mass of ultraviolet-resistant layer is 10-30 %mass. The inorganic material of waterproof layer is sheet-shaped inorganic material including mica or clay. The content of inorganic material in waterproof layer is 5-35 %mass, preferably 15-30 %mass. Preferred Properties: The thickness of sheet-shaped inorganic material is 1 nm. The particle diameter of inorganic particles is 100-1000 nm. The particle size of sheet-shaped inorganic material is 300-600 nm. The water-proof layer has thickness of 10-40 mu m.    TECHNOLOGY FOCUS - ORGANIC CHEMISTRY - Preferred Composition: The ultraviolet-resistant layer further comprises hardening agent. The hardening agent is organic titanate, isocyanate, silane and melamine. The ultraviolet-resistant layer and/or promoting layer comprises ultraviolet absorbent chosen from 2-hydroxy-4-methoxy benzophenone, and 2-(2'-hydroxy-3',5'-di-t-butylphenyl)-5-chlorobenzotriazole.    TECHNOLOGY FOCUS - POLYMERS - Preferred Composition: The polymer film comprises polyethylene terephthalate, polypropylene, polyethylene, cellulose triacetate, polycarbonate, polymethyl methacrylate, poly-2,6- naphthalene dicarboxylate, and polycyclo olefin ester. The promoting layer comprises organic polymer and inorganic particles. The backboard further comprises waterproof layer provided between substrate layer and ultraviolet-resistant layer. The waterproof layer comprises polymer material, inorganic material and ultraviolet absorbent. The polymer contained in promoting layer is copolymer of ethylene-vinyl acetate. The content of vinyl acetate in ethylene-vinyl acetate copolymer is 3-10 mol%. Preferred Property: The substrate layer has thickness of 60-400 mu m. The ultraviolet-resistant layer has thickness of 5-50 mu m. The promoting layer has thickness of 50-200 mu m. Preferred Process: The ultraviolet-resistant layer and promoting layer are formed by wet-coating process.