Preparation method for double-layer PET protective film for lithium battery pack

The invention provides a preparation method for a double-layer PET protective film for a lithium battery pack. The preparation method comprises the following steps: firstly, uniformly stirring and mixing acrylic pressure sensitive adhesive, ethyl acetate and butanone, then adding blue paste, white paste, yellow paste, a retarder and an assistant into the mixture in sequence, finally, adding hexamethylene diisocyanate and lithium tetrafluoroborate, and stirring uniformly to obtain an adhesive liquid; secondly, coating a single surface of a PET substrate with the adhesive liquid, performing heating treatment through 6 to 8 sections of baking channels in sequence until the residual solvent amount of the adhesive liquid does not exceed 0.5 parts; adhering the PET substrate which is coated with the adhesive liquid and a PET which is not coated with the adhesive liquid to obtain a double-layer PET composite film; coating the single surface of the PET composite film with the adhesive liquid, heating until the residu