PURPOSE: To reduce a coat failure ratio by dissolving and preparing binder including natural resin in solvent at a temperature of 100°C or lower for binder solution, mixing a binder material with the binder solution, preparing slurry of prescribed viscosity, and forming the slurry into a coat on a substrate

CONSTITUTION: A binder is prepared by dissolution treatment at a mixing temperature of 100°C or lower, preferably 70°C or lower. At the same time, for spin coat viscosity as slurry, resin concentration is raised to 5.2% to raise binder viscosity and apply the slurry at a concentration of 200-300cp at the normal temperature. When the slurry solution becomes 300cp or more in viscosity and drops on a glass plate as a substrate, it forms a coat in stages by its spin rotation and causes roughness to the fluorescent screen to become an uneven and sandy-feeling coat. But when the slurry solution is 200cp or less in viscosity, it is not proper as a spin coat and does not produce a uniform coat.