The uneven surface of the electroconductive substrate may preferably have a center line average surface roughness (Ra of 15 300 nm when scanned in a direction parallel to the linear projections and a center line average surface roughness Ra of 20 600 nm when scanned in {HEAD ~ a direction} perpendicular to {TAIL ~ the linear projections} 
The uneven surface of the electroconductive substrate may preferably have a center line average surface roughness ( Ra of 15 300 nm when scanned in a direction parallel to the linear projections and a center line average surface roughness Ra of 20 600 nm when scanned in { HEAD ~ a direction } perpendicular to { TAIL ~ the linear projections }
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