The compound methods of flexible packaging materials mainly include dry compound method, wet compound method, extrusion compound method, coating compound method, solvent-free compound method, etc. However, no matter which composite method is used, it shall be completed by special equipment. The coating method is to coat a layer of material on the surface of film or paper. The difference between the coating method and the coating method is that the coating layer is used as a layer structure of composite materials while the coating layer method is only used as adhesive. Because the coating thickness is thinner than the thinnest film with similar functions, the coating method is more economical than the lamination method. The composite flexible packaging materials commonly used for coating are as follows: (1) Waterproof wax coating wax is the oldest and most widely used coating material. At present, it has been replaced by polyolefin in some occasions, especially when greater flexibility and stronger sealing strength are required Generally, the mixture of wax and polyethylene is used as the coating layer. For example, the waterproof coating on the outside of paper cups for cold drinks and hot drinks is the mixture coating of wax and polyethylene. (2) Barrier polyvinylidene chloride (PVDC) coating PVDC coating, also known as “K” coating, has excellent comprehensive barrier properties, such as excellent grease resistance. But its price is more expensive than other coatings. However, for opp composite films, the cost of coating is not high because of the thin coating. (3) There are mainly two kinds of varnish coating varnish for printing layer protection, one is volatile varnish containing solvent, and the other is printing varnish, which does not contain solvent and is dried by oxidation curing rather than solvent volatilization. These two types of varnishes are often used for protective coating in the printing process to prevent ink pollution and provide a shiny surface.