Glazing process and quality control of packaging printing

The glazing process is a technique and method for applying a layer of a coating without a transparent coating on the surface of a printed product, forming a thin and uniform transparent bright layer on the surface of the printed product after being leveled, dried, and calendered.

Polishing process and classification

The glazing process of printed products generally includes coating and calendering of the glazing coating. The application of glazing coatings, in a certain way, applies a layer of lacquer coating evenly over the surface of the prints. Commonly used coating methods include spray coating, printing coating, and glazing coating machine coating.

Spray coating is manual operation. Its working speed is slow and coating quality is poor. However, it is easy to operate and flexible. It is suitable for the coating of prints with small batches and rough surface.

Printing coating is generally a coating device that has been modified for use as a gloss coating. Compared with manual spray painting, this method has better quality and higher production efficiency. It can use existing printing equipment and can be used in one machine for two purposes. It is easy to use and is suitable for general medium and small-sized printing factories. However, solvent-type glazing coatings should be used. During the operation, care should be taken to ensure that the viscosity of the coating is relatively stable and a certain amount of coating must be controlled.

Special coating coater coating can realize accurate control of coating amount. The coating quality is stable and reliable, and it is suitable for coating coating of various grades of printed matter. It is currently the most common coating method.

The coating quality requirements for coating are: coating on the coating surface should be uniform, suitable coating amount, good leveling, and a certain degree of adhesion with the print surface. After applying the gloss coating on the surface of the print, it is usually required to be calendered by the calender. Calender calendering can change the surface state of a dried glazing coating to form an ideal mirror surface.

The glazing process can be comprehensively classified according to different ways: according to the glazing method, it can be divided into an offline glazing process and an on-line glazing process; the glazing coating can be divided into an oxidative polymerization coating glazing, a solvent evaporation coating glazing, and light Curing paint coating and heat-curing coating coating; according to the product can be divided into full-cap glazing, local glazing, extinction and artistic glazing; according to the print input method can be divided into manual feeding and automatic feeding.

Glazing coating

At present, all types of coating coatings developed have their own technological advantages; oxidative polymerization coatings mainly rely on the oxygen in the air to form a dry film; the requirements for drying sources are not high, and equipment investment is low; Volatile coating coatings rely on the evaporation of solvent in the coating to form a film. They have good leveling during coating, drying, and film formation. Their processing performance and application range are wide. They are applicable to various grades and large-volume prints. Glazing processing; thermosetting glazing coating relies on the active functional groups contained in the polymer structure of the film-forming resin and the catalyst in the coating. When heat is generated, cross-linking reaction takes place and the film is formed. The curing is rapid and the production efficiency is high. It is suitable for automation. Polishing; Light-curing coating coating is absorbed by the radiation, the coating structure of the internal molecular polymerization and dry film, the gloss of the coating coating is high, the wear resistance of the film, folding resistance , Heat resistance is relatively good, suitable for high-grade printed products of the glazing processing.

The basic composition of all kinds of coating coatings is roughly the same, that is, it consists of three parts: the main agent (film forming tree), additives and solvents. The main agent is the film-forming substance of the varnish coating. After the prints are glazing, the quality and physiochemical properties of the film, such as glossiness, folding resistance, post processing suitability, etc., are all related to the selected main agent. The main agent is a natural resin glazing coating. The transparency of the film is poor, yellowing is easy, and sticking is also easy to occur. The glazing coating with synthetic resin as the main agent has good film forming property, high gloss and transparency, and high resistance. Grinding, water resistance, aging resistance, and strong applicability.

Additives are auxiliary substances that need to be added in order to improve the physicochemical properties and process characteristics of glazing coatings. For example, a curing agent added to improve the film forming property of the main agent resin and increasing the cohesive strength of the film; a surface activating agent added for improving the leveling property of the coating agent and lowering the surface tension thereof; Antifoaming agents added by synthesis and coating operations; plasticizers added to improve the elasticity of the film and enhance water resistance and flex resistance.

The role of the solvent is to disperse, dissolve, and dilute the main agent and auxiliary agent. Commonly used solvents are aromatics, esters, alcohols and so on. The physicochemical properties such as toxicity, odor, drying and leveling of the coating coating are directly related to the selection of the solvent. Aromatic solvents have low evaporation heat, high volatilization rate, and high solubility, but these solvents are more toxic. Ester solvents have good solubility, high volatilization rate, and low cost, but the odor is relatively large; alcohol solvents in the dissolution performance, The volatilization rate is not the same as above, but it is non-toxic, odorless, and free from pollution. If water can be used as a coating solvent, the cost is the lowest and the source is the widest. It does no harm to the human body and does not pollute the environment. Therefore, the development of water-based glazing coatings in recent years is attracting great attention at home and abroad. (to be continued)