Glazing process and analysis of quality factors
The glazing process is a technique and method for applying a layer of uncoated transparent coating on the surface of the printed product, after leveling, drying, calendering, and forming a thin and uniform transparent bright layer on the surface of the printed matter.
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(2) The types of glazing coatings are different, and their properties are also different. Even under the same process conditions, the film layers obtained after coating and calendering are not the same. The viscosity of the above light coating has an important influence on the leveling and wettability of the coating. The absorption rate of the same absorption strength paper on the glazing coating is inversely proportional to the viscosity value of the coating. That is, the smaller the viscosity value of the coating, the larger the absorption rate will cause the leveling to end prematurely, causing some local large coatings on the printed surface to be affected. The smoothness and brightness of the film after drying and calendering.
The glazing coatings with different surface tension values have different effects on the wetting, adhesion and impregnation of the same printed matter, and the film forming effects after coating and calendering are very different. A glazing coating with a small surface tension value can wet, adhere, and saturate the solid surface of various types of printed matter and the ink layer of the image, "flattening into a smooth and uniform film surface; glazing paint with a large surface tension value, The wetting of the ink layer on the surface of the printed matter is limited, and even the coating after glazing will have a certain shrinkage which will affect the film quality. The volatility of the solvent also has an effect. The volatilization rate is too fast, and the coating layer will not be able to level into a uniform film. On the contrary, it will cause insufficient drying of the glazing coating, the hardened conjunctiva is blocked, and the anti-sticking property is poor.
(3) The selection of the coating process conditions also has a great influence on the coating quality. If the coating arrangement is too small, the coating cannot spread the entire surface to be coated evenly, and the smoothness after drying and calendering is poor; if the coating amount is too thick, the drying will be affected and the cost will be increased. In order to dry the thicker film layer, the temperature at the time of coating and calendering is relatively increased. The drying time is lengthened, which causes the water content of the printed matter to decrease, the paper fiber becomes brittle, and the surface of the printed matter is easily broken.
Process conditions such as coater speed, drying time, and drying temperature also affect each other. When the machine speed is fast, the coating has a short leveling time and the coating is thick. In order to obtain the same drying effect, the drying time should be recognized and the temperature should be high; 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 lowered. The above process factors sometimes have an effect on the quality of the L-light coating. In order to obtain good L-light coating quality, these factors should be considered comprehensively in order to obtain an appropriate match between the factors.
2. Process factors affecting calendering quality. In calendering, the main factors affecting the calendering quality of printed matter are calendering temperature, pressure and machine speed.
During the calendering process, the appropriate temperature should be set at each stage of hot pressing, glazing and cooling stripping to facilitate the secondary wetting, adhesion and penetration of the main agent molecules on the surface of the printed matter in the coating, and enhance the contact effect between the two. Under certain temperature conditions, the plasticity of the coating film layer can be improved, and the smoothness of the calendering surface of the printing material is greatly improved under the action of pressure. The temperature is too high, the adhesion strength of the coating layer decreases, the deformation value increases, and the water content of the printed matter decreases sharply, which is unfavorable for the inch light and the peeling process; on the contrary, the hot pressing temperature is too low, and the coating layer is not completely plasticized, The second print: the sub-wetting, adhesion and penetration ability is insufficient, the adhesion of the coating layer is poor, so the calendering effect is poor, and it is difficult to form an ideal film layer with high smoothness after calendering.
In the film layer after coating and drying, the arrangement of the coating molecules is relatively loose, and there are many minute pores in between. When calendering, under certain temperature and pressure, the movement between molecules is intensified, which is manifested by the volume change of the film layer. The percentage change in this volume is called the compression ratio, which is the ratio of the volume that is reduced when the coating layer is pressurized to the original volume before pressurization. The large compression ratio is favorable for forming a smooth film layer on the surface of the coating; on the contrary, the coating layer is compressed to a small amount, and the surface is not easy to form a smooth film layer. However, when the pressure is too large, the elongation and plasticity of the printed matter are lowered to cause breakage.
The surface smoothness and adhesion strength of the glazing film generally increase with the increase of curing time, but the rate of increase is smaller and smaller, and does not increase after reaching a certain value. The length of curing time depends on the calendering speed. When the glazing coating is in contact with the glazing strip, its molecular mobility decreases as the coating temperature decreases. If the curing time is short and the rate of decay is fast, the coating molecules can not fully function with the ink layer on the surface of the printed matter, and the adhesion strength of the coating layer to the ink layer is poor, and the surface smoothness of the film layer after drying and cooling is low.