An object is to provide a surface treatment liquid which can firmly bond, while coating the surface of a treatment target with an extremely thin film, a coating whose hydrophilicity is unlikely to be lowered even when the coating is brought into contact with fats and the like to the surface of the treatment target and a surface treatment method using the surface treatment liquid described above. In a surface treatment liquid containing a resin (A) and a solvent (S), as the resin (A), a resin is used which includes a constituent unit (a1) that includes an organic group including a quaternary ammonium cation group and having a sulfonic acid anion group at a terminal and that is derived from an N-substituted (meth) acrylamide, and includes a reactive silyl group in at least one of molecular chain terminals, the concentration of the resin (A) in the surface treatment liquid is less than 2 mass % and the pH of the surface treatment liquid is 4 or less.
目的是提供一种表面处理液,该表面处理液可以在处理对象表面涂覆极薄的薄膜的同时,牢固地粘合处理对象表面的涂层,即使该涂层与脂肪等接触也不会降低亲
水性,并提供一种使用上述表面处理液的表面处理方法。在含有
树脂 (A) 和溶剂 (S) 的表面处理液中,作为
树脂 (A),使用了一种
树脂,其组成单元 (a1) 包括一个有机基团,该有机基团包括一个季
铵阳离子基团,其末端具有一个
磺酸阴离子基团,该有机基团由 N-取代的(甲基)
丙烯酰胺衍生而来、表面处理液中
树脂 (A) 的浓度低于 2 质量%,表面处理液的 pH 值为 4 或更低。