Abstract: Disclosed are a protective coating layer, and a preparation method and use thereof. The present application provides a protective coating layer, including: 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, where 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. The present application effectively solves the technical problem that the existing protective coating layer with nanoparticles exhibits poor adhesion to a substrate and cannot provide a protective effect for a long time.

Abstract: The present invention discloses a waterproof structure of a card tray hole of a metallic-shell mobile phone. The waterproof structure includes: an SIM card seat; a card tray arranged in the SIM card seat; a card tray push rod which is arranged at one side of the SIM card seat and is used for pushing the card tray so as to eject the card tray out of the shell; and a waterproof sealing needle, which is arranged in a card tray push rod hole formed on the shell of the mobile phone and corresponding to the card tray push rod. The waterproof structure of the card tray hole of the metallic-shell mobile phone can prevent water from entering a shell inside from a shell outside, thereby achieving the waterproof effect.