As the main substrate for metal-coated products, the quality of metal substrates directly affects the quality of packaging products. Deformation of metal substrates affects the adhesive properties of film coating. Fedorov et al. subjected PET-composite steel substrates to uniaxial tensile deformation followed by annealing treatment. The results showed that as the strain caused by deformation increased, the adhesion force at the metal-polymer interface decreased, and the bonding strength was restored after heat treatment. The surface morphology of metal substrates also affects the adhesion of the film. Microscopic roughening of the metal surface allows polymer to form mechanical interlocks during bonding and curing, enhancing the adhesion between metal and film and improving the quality of film coating. Ochoa-Putman et al. improved the adhesion performance of polymer PP to metal substrates by plasma treatment of metal steel surfaces. The experiments found that with the increase of steel surface roughness, the friction coefficient between the film and polymer also increased, achieving good mechanical interlocking effects and generating relatively strong mechanical bonding forces. By using laser engraving to create micro-tooth features on aluminum surfaces, solid joints composed of aluminum alloy and polyvinyl chloride (PVC) were produced. Chen Junxiang et al. combined aluminum metal surfaces treated with hydrochloric acid corrosion with polymer PPS. The results showed that the metal surface treated with surface treatment obtained micrometer-sized pores, and with the increase of corrosion time, the interface bonding strength showed a trend of first increasing and then decreasing under the joint influence of pore size and pore density. Beeck et al. found that roller press pretreatment can reduce the damage to the film-iron interface during the production process. By comparing the interface damage after roller press pretreatment with the simulation of surface roughness changes caused by deformation and the simulation without pretreatment, it was found that the interface damage was significantly reduced. Chen Jing et al. used three different methods, mechanical polishing, chemical etching, and annealing, to pretreat the surface of 304 stainless steel, and then hot-pressed with polyamide 6 (PA6). The results of mechanical property tests showed that the bonding strength of the samples after annealing treatment was optimal, and the adhesive interface not only had mechanical interlocks but also possibly formed hydrogen bonds between the polymer PA6 and the stainless steel surface, increasing the adhesion strength. Li Hui et al. found that applying silane coupling agent treatment to metals can enhance the bond strength at the interface with polymers. The reason is that after metal surfaces are treated with silane coupling agents, “molecular bridge” is formed on the surface, connecting the metal-polymer interface mainly in the form of chemical bonds, thus improving the adhesion of the metal-polymer interface.
