NOVELTY - A resin composition comprises 100 parts mass silane-grafted polyethylene resin, 10-100 parts mass pretreated filler, 0-1.5 parts mass additive, 0.05-0.5 part mass catalyst. The resin is prepared using 100 parts mass polyethylene homopolymer, polyethylene copolymer, and/or metallocene polyethylene, 0.2-5 parts mass silane, and 0.05-5 parts mass initiator. The polyethylene has a melting point of 120-135 degrees C as measured by differential scanning calorimeter, a melt flow rate of 1-2 g/10 minutes, and a density of 0.9-0.959 g/cm3.    USE - Resin composition is used for forming core layers in preparation of solar-cell module backplates (all claimed).    ADVANTAGE - The resin composition fully meets the requirements of solar-cell module backplates. The resin composition enables preparation of solar-cell module back plates having excellent adhesiveness, interlaminar peeling strength, high-temperature heat-aging resistance, low-temperature impact resistance, and electrical insulation property, and low water absorption saturation and low water-vapor permeability.    DETAILED DESCRIPTION - A resin composition comprises 100 parts mass silane-grafted polyethylene resin, 10-100 parts mass pretreated filler, 0-1.5 parts mass additive, 0.05-0.5 part mass catalyst. The resin is prepared using 100 parts mass polyethylene homopolymer, polyethylene copolymer, and/or metallocene polyethylene, 0.2-5 parts mass silane, and 0.05-5 parts mass initiator. The polyethylene has a melting point of 120-135 degrees C as measured by differential scanning calorimeter, a melt flow rate of 1-2 g/10 minutes, and a density of 0.9-0.959 g/cm3. The filler is pretreated with a silane coupling agent. The additive is antioxidant, UV absorber, and/or light stabilizer. INDEPENDENT CLAIMS are included for the following:    (1) solar-cell module backplate consisting of an upper surface layer, a core layer, and a lower surface layer in a mass ratio of 10-20:20-40:40-60. The upper surface layer is a layer formed using polyethylene resin composition containing 100 parts mass polyethylene resin or ethylene-vinyl acetate copolymer resin, 10-50 parts mass pretreated filler, and 0-1.5 parts mass additive. The core layer is formed using the resin composition. The lower surface layer is a layer formed using polypropylene resin composition containing 100 parts mass polypropylene resin, 10-50 parts mass pretreated filler, and 0-1.5 parts mass additive; and    (2) preparation of solar-cell module backplate, which involves co-extruding polyethylene resin composition, the resin composition, and polypropylene resin composition into a three-layer co-extruded sheet by melt-extrusion using a screw extruder, casting, cooling, drawing, and winding.