Mirror surface decorative sheet having crack elongation and specified surface roughness, and mirror surface decorative plate using same

A mirror surface decorative sheet comprising at least a base sheet and a surface-protecting layer, and having a crack elongation as measured by the following method of 10 to 20%,

• the base sheet being formed of a polypropylene resin, the base sheet having a thickness of 150 to 500 μm, the base sheet having a ten-point mean roughness (Rzjis) of a surface that is on the surface-protecting layer side as measured according to JIS B 0601:
• 2001 of 5 μm or less,
• the surface-protecting layer being a cured product of an ionizing radiation-curable resin composition, the surface-protecting layer having a thickness of 7 to 17 μm:
• Measurement of crack elongation:
• a rectangular test sample is prepared according to JIS K 7127 using a decorative sheet, placed in a temperature environment of 70° C., and pulled at an arbitrary elongation using a tensile tester at a tensile rate of 20 mm/min, an 80-mm distance between chucks, and a width of 25 mm;
• thereafter, the test sample between the chucks is colored with a whiteboard marker, the colored portion is wiped off with cloth, and the degree of elongation at which the color cannot be wiped off due to the occurrence of cracking is determined as a crack elongation.