Protective coating layer, and preparation method and use thereof

A protective coating layer, comprising:

• a rusty-surface liquid layer, a nano-zinc yellow epoxy primer layer, a nano-epoxy micaceous iron oxide (MIO) intermediate coating layer, and a nano-fluorocarbon top coating layer, wherein the rusty-surface liquid layer is applied on a metal substrate;
• the nano-zinc yellow epoxy primer layer is applied on a surface of the rusty-surface liquid layer;
• the nano-epoxy MIO intermediate coating layer is applied on a surface of the nano-zinc yellow epoxy primer layer;
• and the nano-fluorocarbon top coating layer is applied on a surface of the nano-epoxy MIO intermediate coating layer;
• a slurry of the rusty-surface liquid layer comprises:
• tannic acid 5 g/L to 20 g/L;
• phosphoric acid 0 g/L to 200 g/L;
• sodium molybdate 1 g/L to 4 g/L;
• citric acid 1 g/L to 4 g/L;
• mixed alcohol 5 g/L to 20 g/L, wherein the mixed alcohol comprises isopropyl alcohol (IPA) and tertiary butyl alcohol (TBA), and a mass ratio of the IPA to the TBA is 1:1;
• and
• sodium dodecylbenzenesulfonate (SDBS) 0.5 g/L to 5 g/L;
• a slurry of the nano-zinc yellow epoxy primer layer comprises an epoxy resin, a dispersing agent, zinc phosphate, iron oxide yellow, talc powder, a filler, a mixed solvent, and a curing agent, wherein the filler is one or more selected from the group consisting of nano-aluminum powder (NAP), nano-zirconium powder (NZP), and nano-silicon dioxide;
• a slurry of the nano-epoxy MIO intermediate coating layer comprises an epoxy resin, a dispersing agent, talc powder, MIO, a filler, a mixed solvent, and a curing agent, wherein the filler is one or more selected from the group consisting of NAP, NZP, and nano-silicon dioxide;
• and
• a slurry of the nano-fluorocarbon top coating layer comprises a fluorocarbon resin, a defoaming agent, a polyamide (PA) wax, a mixed solvent, a filler, a solvent, and a curing agent, wherein the filler is one or more selected from the group consisting of NAP, NZP, and nano-silicon dioxide.