A plastic substrate is processed by a functional water obtained by electrolysis
of water or functional water containing active oxygen or active hydrogen for a
predetermined time period to selectively remove an alkali and/or halogen component
in a surface layer of the plastic substrate to stabilize or remove oligomer in
a resin matrix, whereby deterioration of resin and deterioration of properties
of a recording medium caused by a remaining unreacted catalyst used for processing
the plastic substrate surface or the like can be prevented and the adhesion strength
and the durability of a recoding coating to be formed on the substrate are improved.
