Polishing process adaptability and selection in printing

The glazing process is a process in which a colorless, transparent coating is applied (or sprayed or printed) on the surface of a printed product, and after the leveling, drying, and calendering, a thin and uniform transparent bright layer is formed on the surface of the printed matter. method. The glazing process is an important means for enhancing the practical value and quality of products such as packaging and decorating products, labels, and book covers. Glossing can increase the gloss of prints, make the colors more colorful, give people a beautiful visual effect, and at the same time make the product worth more.

The good results of the glazing process are obvious, but if you do not understand the factors that affect the quality of glazing, it will be difficult to guarantee the quality of glazing. Therefore, it is very necessary to improve the quality of printed materials by correctly understanding the factors that affect the quality of glazing and then adopting corresponding measures to overcome them.
The essence of the coating process is the process of smoothing and drying the coating on the surface of the printed matter. The main factors affecting the coating quality are:

Glazing suitability

1. Surface smoothness of the substrate

In the coating process, the gloss coating is easily leveled on the surface of a high-smooth paper. In the drying process, after the varnish is cured, a smoother film surface can be formed, so the higher the surface smoothness of the paper, the better the varnish coating effect and vice versa. Such as coated paper, due to its smooth surface, gloss after the gloss effect has improved significantly. The white paper or offset paper has a rough surface, and the polishing oil is almost completely absorbed by the rough paper fibers, so the coating effect is relatively poor, and the brightness is not significant enough.

2. Absorption of substrates

Absorption of the surface of the paper is too strong, the absorption rate of the paper fiber to the glazing coating is high, the solvent penetration is fast, the viscosity value of the coating is increased, the shear stress of the coating layer flowing on the surface of the print increases, and the leveling of the glazing coating is affected However, it is difficult to form a relatively smooth film layer; on the contrary, the absorption is too weak, so that the penetration, solidification, and conjunctival action of the glazing coating in the leveling are significantly reduced, and a high-quality film layer cannot be formed on the print surface as well.

3. Ink properties

The ink on the surface of the printed matter has a great influence on the gloss, such as the solvent resistance, heat resistance and alcohol resistance of the ink, so that the printed artwork is easily discolored or wrinkle-skinned. When the coating is applied, the coating oil is not applied or generated. "Face," deinking, and "dotted" problems. Therefore, the need for polishing products printing ink should be resistant to alcohols, ester solvents and acid and alkali. In addition, it is also required that the color of the ink be durable and good in gloss, and has strong adhesion to the paper so as to prevent the ink from being changed due to coating and thus affecting the gloss of the product.

In addition, the particle size of the ink also has a certain influence on the glazing. The ink has a fine particle size and a high degree of dispersion, and the ink layer is easily wetted by the coating material. Under the effect of the coating pressure, the leveling property is good, and the resulting film has a high degree of smoothness. On the contrary, the ink particles are coarse and the printing ink layer is spread poorly, and it is difficult to form a high-quality film layer after coating.

Varnish type and performance

Varying the type of coating, its adhesion, viscosity, surface tension and volatile properties are different, resulting in the quality of the coating is not the same.

1. Varnish coating viscosity

The viscosity of the coating coating has an important influence on the leveling and wetting of the coating. Absorption rate of glazing paint on paper with the same absorption strength is inversely proportional to coating viscosity value, that is, the smaller the coating viscosity value is, the greater the absorption rate will be, and the leveling will end prematurely, causing some local paint on the surface of the printed material to be excessive. Affects the smoothness and brightness of the film after drying and calendering.

2. Varnish surface tension

Gloss coating with different surface tension has different effects on wetting, adhesion, and impregnation of the same print, and the coating effect after coating and calendering varies greatly. The glazing coating with small surface tension value can wet, adhere to and saturate the solid surface and graphic ink layer of all kinds of printed products, and level and smooth the film surface; the glazing coating with large surface tension value and the ink layer on the printed matter The wetting will be limited and the coating after glazing may produce a certain amount of shrinkage and affect the film formation quality.

3. Solvent Volatility in Coating Coatings

This point only for solvent evaporation coating coating, if the evaporation rate is too fast, it will make the coating layer too late to even into the film surface; the contrary, it will cause the coating coating to dry, hardened conjunctiva obstructed, poor stain resistance.

Selection of coating process conditions

Coating amount, drying method, drying temperature, coating speed, etc. all belong to the coating process conditions. The improper selection of these process conditions may affect the quality of coating.

1. Coating amount selection

When the coating amount is too low, the coating cannot uniformly spread the entire surface to be coated, and the smoothness after drying and calendering is poor; if the coating amount is too large, the drying speed will be affected, the production cost will be increased, and in order to dry the thicker film layer, Increasing the temperature at the time of coating and calendering requires a longer drying time, which can lead to a decrease in the content of prints, a brittleness of paper fibers, and a crack in the printed surface.

2. Coating machine speed and temperature selection

The coating machine speed, drying time, drying temperature and other process conditions also affect each other. When the machine speed is fast, the coating leveling time is short, and the coating is thick. In order to obtain the same drying effect, the drying time is longer and the temperature is higher; the machine speed is slow, the coating leveling time is long, and the coating is thin. The drying time can be shortened and the drying temperature can be appropriately reduced. Under normal circumstances, the temperature of the coating oil is controlled at about 20 degrees.

When the ambient temperature is too low, the varnish is easily solidified, which is not good for the normal flow of the varnish, so that the oil film on the surface of the varnished product is not uniform, so its brightness is also necessarily poor. In order to overcome the disadvantages caused by environmental conditions defects, the varnish should be placed in a relatively warm place, so that the varnish to maintain the liquidity required for polishing. (Text / Xu Hongping)