The polishing process is the technique and method of applying a layer of transparent coating without packaging on the surface of printed materials, leveling, drying, and pressing to form a thin and uniform transparent layer on the surface of printed materials. The polishing process and classification of printed materials generally include two operations: coating and pressing of the polishing coating. The application of glossy coating refers to the process of uniformly applying a layer of glossy coating on the surface of printed materials using a certain method. There are three common coating methods: spray coating, printing coating, and glossy coating machine coating. Spray coating is a manual operation, which has a slow working speed and poor coating quality. However, it is easy to operate and has strong flexibility, making it suitable for coating small batches of printed materials with rough and uneven surfaces. Printing coating is usually a coating that uses printing equipment and has been modified to be used as a glossy coating. This method has better quality and higher production efficiency compared to manual spraying and coating. It can utilize existing printing equipment, with one machine for two purposes, and is simple and easy to operate. It is suitable for polishing and coating processing in general small and medium-sized printing factories. But solvent based glossy coatings should generally be used, and attention should be paid to ensuring the relative stability of the viscosity value of the coating during operation, and a certain amount of coating should be controlled. A dedicated polishing coating machine can achieve accurate control of coating amount. The coating quality is stable and reliable, suitable for polishing and coating processing of various grades of printed materials, and is currently the most commonly used coating method. The quality requirements for glossy coating are: uniform coating on the coating surface, appropriate coating amount, good leveling, and a certain degree of adhesion with the printed surface. After applying glossy coating on the surface of printed materials, it is usually necessary to go through the pressure of a calender. The calendering machine can change the surface state of the dried glossy coating, forming an ideal mirror surface. The polishing process can be comprehensively classified according to different methods: according to the polishing method, it can be divided into offline polishing process and online polishing process; According to the gloss coating, it can be divided into oxidation polymerization type coating gloss, solvent volatile type coating gloss, light curing type coating gloss, and heat curing type coating gloss; According to the product, it can be divided into full cap polishing, partial polishing, extinction, and artistic polishing; According to the input method of printed materials, it can be divided into manual paper feeding and automatic paper feeding. The various types of glossy coatings currently developed have their own technological advantages; Oxidative polymerization type glossy coatings mainly rely on oxygen in the air to undergo polymerization reaction and dry into films, with low requirements for drying sources and low equipment investment; Solvent based glossy coatings rely on the evaporation and drying of solvents in the coating to form a film. They have good leveling properties during the coating, drying, and film forming processes, and their processing performance and applicability are wide, suitable for the glossy processing of various grades and large quantities of printed materials; Heat cured glossy coatings rely on the active functional groups contained in the polymer structure of the film-forming resin and the catalysts in the coating to undergo cross-linking reaction and dry film formation when exposed to heat. They cure quickly, have high production efficiency, and are suitable for automated glossy processing; UV curable glossy coating is a film formed by the polymerization reaction of the internal structure of the coating molecules after absorbing radiation energy. The glossiness of the glossy coating is high, and the wear resistance, folding resistance, and heat resistance of the film layer are relatively good. It is suitable for polishing high-end printed materials
