Surface-treated steel sheet

A surface-treated steel sheet comprising:

• a galva-annealed steel sheet having a steel sheet serving as a base material and a galva-annealed layer on the steel sheet;
• and
• a surface-treating layer on the galva-annealed layer, wherein:
• the surface-treating layer contains a base resin and SiO2-coated Al flakes which are Al flakes each having a surface coated with a SiO2 layer;
• an average thickness of the SiO2 layers is 10 to 100 nm;
• an average particle size R of the SiO2-coated Al flakes is 1.00 to 30.00 μm, and a ratio (R/t) of the average particle size to an average thickness t of the SiO2-coated Al flakes is 10 or more;
• and
• a coverage by the SiO2-coated Al flakes on a surface of the galva-annealed steel sheet is 20% or more,
• the coverage being a value given by the following equation:
• coverage
• ⁢
• [
• %
• ]
• =
• (
• ∑
• Ln
• /
• L
• 0
• )
• ×
• 100
• ,
• equation
• ⁢
• (
• 1
• )
• where, when a cross section of the surface-treating layer, the galva-annealed layer, and the steel sheet taken along a thickness direction is observed with a scanning electron microscope, L0 is a dimension of a viewing field in a direction orthogonal to the thickness direction, and Σ Ln is a presence length of the SiO2-coated Al flakes present in the viewing field.