Analysis of several conditions related to the quality of printed products
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The glazing process is a supporting production process for packaging and decoration printing, trademark labels, product advertisements, invitations and book covers, etc., through glazing, it can increase the gloss and artistic effect of the printed surface, beautify the function and function of the printed matter, and make the surface of the product The color is more vivid and dazzling, giving people a beautiful visual effect, so that the product value doubles. Glazing is also an important method to improve the appearance, performance and protection of printed matter, and is also an effective way to improve the quality and grade of printed matter. It is of great significance to improve the quality of color printing products by correctly understanding certain conditions related to the quality of printed products and taking corresponding technical measures to effectively control them.
First, the relationship between paper quality and print quality
The process practice shows that the quality of the glazing of the printed product is directly related to the performance of the paper. The paper with good surface smoothness is weak in absorption, and the oil layer will float on the surface after the coating of the varnish (paint). Forming a high-brightness film layer. The paper with poor smoothness, because of its rough surface, will be quickly absorbed by the rough fiber after it is applied to the paper surface, and the paper surface will not form a bright coating, and the gloss effect will be poor. Therefore, the higher the smoothness of the paper, the better its glazing effect. In the actual production process, if the smoothness of the paper surface is poor, in order to improve the glazing effect of the printed product, a layer of casein base material may be applied on the paper surface before glazing. The role of the bottoming is to make the varnish layer of the printed product float on the paper surface to form a high-brightness film layer. It can be seen that the absorbency of the paper surface affects the leveling property of the glazing paint from the start of coating to the drying time, which is because the paper surface absorbs the solvent in the glazing paint, so that the glazing paint is in a period of time. When the viscosity is increased, the internal resistance of the coating layer flowing on the paper surface is increased, so that the leveling property is poor, that is, the coating is not smooth when coated, and a continuous and uniform film layer cannot be formed, resulting in poor gloss on the paper surface. This is an inevitable performance of the paper's absorption is too good. Therefore, in the actual production process, the glazing process and the glazing coating should be adjusted accordingly according to the actual production conditions and the absorbency and smoothness of the paper surface. If the paper surface of the printed product is too strong, the viscosity of the glazing coating should be increased appropriately, that is, the amount of the diluent should be appropriately reduced. Process practice shows that the quality and characteristics of paper and paperboard directly affect the quality of glazing products. For example, because of the smooth surface of the coated paper, the gloss effect will be significantly improved after glazing. The surface gloss of white paper or white cardboard is correspondingly poor, and the brightness of the printed product after glazing is not significant enough. This is because the glazing oil is easily absorbed by the cardboard fiber and does not float on the paper surface. In order to make up for the paper's easy oil absorption and the lack of brightness of the printed product, the proportion of the paint can be appropriately increased, and the varnish of the last two passes can be adopted to increase the brightness of the printed product.
Second, the relationship between production temperature and print quality
The production process shows that the temperature also has a certain relationship with the quality of the glazing. Because the temperature will affect the concentration and fluidity of the varnish. Generally, the temperature of the glazing of the printed product is controlled at about 20 ° C, and a relatively good effect can be obtained. However, if the temperature is low in winter, the glazing oil is more likely to solidify and thicken due to lower temperature, and the fluidity of the glazing oil is poor. The oil film on the surface of the printed product after glazing is easily uneven. The quality of the product coating is also poor. In order to overcome the problems caused by environmental changes, the glazing oil should preferably be placed in a relatively stable temperature room. The glazing oil should generally be placed in a room at room temperature of 20-25 ° C to maintain a relatively stable fluidity of the glazing oil.
Third, the relationship between printing ink and print quality
The characteristics of printing inks are also an important factor affecting the quality of glazing. The affinity of the printing ink layer and the particle size of the ink will directly affect the coating quality and leveling properties of the coating. If the ink layer on the print cannot be compatible with the glazing coating, it is difficult for the glazing oil to form a smooth, uniform film on the paper surface during glazing. If the particles of the printing ink are large and the dispersion of the pigment is small, the leveling property of the varnish on the paper surface is poor, which makes it difficult to form a high-quality continuous film layer. When the printing ink layer is poorly dried, the glazing coating is also difficult to obtain a good gloss effect, and even a chain quality failure problem such as blisters and bubbles is easily generated. In addition, the printing ink must have solvent resistance and heat resistance, otherwise the printed image will be discolored or wrinkled. Therefore, the printing ink of glazing products should be resistant to alcohols, ester solvents and acid and alkali resistant. At the same time, it should have the characteristics of long-term non-discoloration and good gloss, and have strong adhesion printing effect on paper. In order to prevent the varnish of the printed product after glazing, the quality of the product is affected.
Fourth, the relationship between the crystallization of printed ink layers and the quality of printed products
When the printed base ink has a large coating area, the printing semi-finished product is placed for too long, and the excess ink is added to the ground ink, the ink layer is crystallized on the surface of the paper, so that the glazing is performed. When the coating is not easy to adhere to the ink layer, it is easy to cause fading and unevenness in the oil layer. If this is the case, simply add 5% lactic acid to the varnish and mix well before applying glazing. By adopting the modified varnish, the vitrified crystal film on the surface of the printed product can be destroyed, thereby achieving the requirement of uniformly adsorbing the varnish, and forming a bright film on the ink layer.
Fifth, the relationship between the characteristics of glazing coatings and the quality of printed products
The viscosity of the glazing coating has a great influence on the leveling and wettability of the coating. When the surface gloss and absorption of the printing are different, the viscosity of the coating used should be different to achieve better results. . This requires that when determining the viscosity of the glazing coating, it should be fully considered according to the characteristics of the material, in order to better ensure the quality of glazing. Since the absorption rate of the glazing coating of paper and paperboard with the same absorption performance is inversely proportional to the viscosity of the coating, the smaller the viscosity value of the coating, the stronger the absorption. Therefore, the gloss of paper, paperboard and varnish with high gloss can be suitably lower. The surface tension of the glazing coating is also an important factor affecting the coating quality. The glazing coating with low surface tension can easily and well wet and adhere to the surface of the printed product, that is, the surface tension promotes the glazing coating. The surface area is reduced, allowing it to level into a smooth and uniform continuous coating. The glazing coating with a large surface tension has certain limitations on the wetting of the surface of the printed product. When the surface tension value of the glazing coating is greater than the surface tension value of the ink layer on the surface of the printing product, the glazing coating after coating is applied. The layer is prone to some shrinkage and even blisters. In addition, the volatilization rate of the solvent in the glazing coating also has a large influence on the quality of the glazing coating. When the solvent volatilizes too quickly, the viscosity of the glazing coating changes excessively within a certain period of time, and the leveling property thereof changes abruptly, making it difficult to achieve leveling in time, and a continuous and uniform coating layer cannot be formed. It is easy to produce streaks, blisters, and may also induce moisture condensation, causing cracks and whitening of the coating after drying.
Six. The relationship between the quality of the machine and the quality of the printed product
The precision and operation process of the glazing machine also has a great relationship with the glazing quality of the printed product. When the coating roller, the coating amount control roller and the pressure roller of the machine have bending deformation, a difference in the center of the circle, and a wear gap occurs in the shaft head or the bearing pad portion of the roller, the glazing coating is unstable and Uneven situation. In addition, if the gloss of the paper surface is not good and the absorbency is high, when the speed of the glazing of the machine is too fast, the brightness of the printed product is likely to be insufficient. In order to ensure the glazing quality of the printed products, we should pay attention to the lubrication and maintenance of the machine, and reduce the wear and looseness of the roller shaft. If the associated components of the machine coating device already have any defects such as wear and deformation, measures should be taken to repair and correct them in time. In addition, during the glazing process, it should be noted that the speed of the glazing is reasonably controlled according to the characteristics of the surface of the printed product to ensure the quality of the glazing coating.