Composite sheet and substrate for display device comprising the same

PURPOSE: A substrate for a display device is provided to reduce flatness and moisture permeability and to improve flex resistance, flexibility, and durability. CONSTITUTION: A substrate for a display device comprises a matrix(2), a reinforcing agent(1) impregnated in a matrix, a coating layer formed on at least one side of the matrix, and a barrier layer(4) formed on one side of the coating layer. If the elastic modulus of the matrix is E2 at 25°C and the elastic modulus of the coating layer is E3 at 25°C, E3/E2 is 5 x 10^4 or less. The coating layer has a gradient elastic modulus structure. The elastic modulus of the matrix at 25°C is 0.1GPa or less. The elastic modulus of the coating layer is 0.1GP-10GPa. The elastic modulus of the barrier layer is 10GPa or more. The coating layer comprises one or more selected from an acrylic-based resin, epoxy-based resin, silicon-based resin, urethane-based resin, and unsaturated polyester-based resin.