Aug. 24, 2023
The glazing process is a supporting production process for packaging and decoration printing. Printed materials such as trademark labels, product advertisements, invitations, and book covers can be used to increase the surface gloss and artistic effect of the printed matter, beautify the role and function of the printed matter, and make the product surface The colors are more vivid and eye-catching, giving people a beautiful visual effect, which doubles the value of the product. Glazing is an important method to improve the appearance, performance, and protection of printed matter, and it is also an effective method to improve the quality and grade of printed matter. It is of great significance to improve the quality of color printing products to correctly understand some situations related to the quality of glazing of printed products, and then take corresponding technological measures to effectively control them.
1. The relationship between paper quality characteristics and glazing quality of printed matter
The process practice shows that the glazing quality of the printed matter is directly related to the performance of the paper. The paper with a good surface smoothness has weak absorption. After the varnish (paint) is coated, the oil layer will float on the surface. , forming a high-brightness film layer. For paper with poor smoothness, due to its rough surface, after the glazing coating is applied to the paper surface, it will be quickly absorbed by the rough fibers, and the paper surface will not form a bright coating, and the gloss effect will be poor. Therefore, the smoother the paper surface, 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 matter, a layer of casein primer can be coated on the paper surface before glazing to play a role. The function of primer makes the varnish layer float on the paper surface after the printed matter is polished, forming a high-brightness film layer. It can be seen that the absorptivity of the paper surface affects the leveling of the glazing coating from coating to drying. As the viscosity increases, the internal resistance of the paint layer flowing on the paper surface increases, so its leveling property is poor, that is, when the varnish is not smooth, it cannot form a continuous and uniform film layer, resulting in poor gloss on the paper surface. This is an inevitable manifestation of the paper's absorbency is too good. Therefore, in the actual production process, the glazing process and glazing paint 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 absorbent, the viscosity of the glazing coating should be appropriately increased, that is, the amount of thinner should be appropriately reduced. Process practice shows that the quality and characteristics of paper and cardboard directly affect the quality of glazing products to a large extent. For example, due to the smooth surface of coated paper, the gloss effect will be significantly improved after being polished. However, the surface gloss of white board paper or white cardboard is relatively poor, and the brightness of the printed matter after glazing is not obvious enough. This is because the varnish is easily absorbed by the cardboard fiber and does not float on the paper surface. In order to make up for the lack of brightness of the printed matter due to the easy oil absorption of the paper, the proportion of the paint can be increased appropriately, and the method of applying varnish twice can increase the brightness of the printed matter.
2. The relationship between printing ink and glazing quality of printed matter
The characteristics of printing ink 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 of the varnish. If the ink layer on the printed matter cannot be compatible with the glazing paint, it will be difficult for the varnish to form a smooth and uniform film layer on the paper surface during glazing. If the particles of the printing ink are large and the dispersion degree of the pigment is small, the leveling of the varnish on the paper surface will be poor, which makes it difficult to form a high-quality continuous film layer. When the printing ink layer is poorly dried, it is also difficult to obtain a good gloss effect on the glazing coating, and even prone to chain quality failures such as blisters and bubbles. In addition, the printing ink must have solvent resistance and heat resistance, otherwise the graphics and text of the printed matter will change color or produce wrinkled skin and other undesirable phenomena. Therefore, printing inks for glazing products should be resistant to alcohols, ester solvents, and acids and alkalis. At the same time, they should have the characteristics of long-term discoloration and good gloss, and have a strong printing effect on paper. In order to prevent the variation of the ink color of the printed matter after glazing and affect the quality of the product.
3. The relationship between production temperature and glazing quality of printed matter
The production process shows that temperature also has a certain relationship with the quality of glazing. Because the temperature will affect the concentration and fluidity of the varnish. Usually, it is advisable to control the temperature of printing glazing at about 20°C, which can achieve relatively good results. However, if the glazing is applied in winter when the temperature is low, due to the low temperature, the glazing oil will be more likely to solidify and thicken, and the fluidity of the glazing oil will be poor. The quality of product coating is also poor. In order to overcome the problems caused by environmental change factors, the varnish should preferably be placed in a room with a relatively stable temperature. Generally, the glazing oil should be placed in a room with a room temperature of 20-25°C, so that the glazing oil can maintain a relatively stable fluidity.
4. The relationship between the properties of glazing coatings and the glazing quality of printed matter
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 printed matter are different, the viscosity of the coating used should also be different in order to achieve better results. . This requires that when determining the viscosity of the glazing paint, it should be fully considered according to the characteristics of the material, so as to better ensure the quality of glazing. Because the absorption rate of paper and cardboard with the same absorption performance on the glazing coating is inversely proportional to the viscosity of the coating, that is, the smaller the viscosity value of the coating, the stronger the absorption. Therefore, for paper and cardboard with high gloss, the viscosity of the varnish can be appropriately lower. The surface tension of the glazing coating is also an important factor affecting the coating quality. A glazing coating with a small surface tension can easily and better wet and adhere to the surface of the printed matter, that is to say, the surface tension promotes the coating quality of the glazing coating. The reduced surface area allows it to level into a smooth and even continuous coating. The glazing coating with a large surface tension has certain limitations on the wetting of the printed product surface. 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 printed product, the glazing coating after coating The layer is prone to shrinkage to a certain extent, and even trachoma. In addition, the volatilization speed of the solvent in the glazing coating also has a great influence on the quality of the glazing coating. When the solvent volatilizes too fast, the viscosity of the glazing coating will change too much within a certain period of time, and its leveling will also change suddenly, making it difficult for the coating to achieve leveling in time and form a continuous and uniform coating layer. It is easy to produce streaks and sand holes, and may also induce moisture condensation, which will cause cracks and whitening of the dried coating.
5. The relationship between the crystallization of the printed ink layer and the quality of the varnish of the printed matter
When the printing area of the base color ink is large, the printing semi-finished product is placed for too long, and due to the addition of excessive dry oil in the base color ink, the printed ink layer forms a crystallization phenomenon on the surface of the paper. When the paint is not easy to adhere to the ink layer, it is easy to cause the oil layer to bloom and uneven. If this happens, just add 5% lactic acid to the glazing oil, stir evenly and then apply glazing. By using this modified varnish, the vitrified crystal film on the surface of the printed matter can be destroyed, so as to meet the requirement of uniform adsorption of varnish and form a bright film on the ink layer.
6. The relationship between the machine and the glazing quality of printed matter
The precision and operation process of the glazing machine also have a great relationship with the glazing quality of the printed matter. When the coating roller, coating amount control roller and pressure roller of the machine have bending deformation and poor centering, and there is a wear gap on the shaft head or bearing bush of the roller, it will cause the instability of the glazing coating and the Uneven situation. In addition, if the glossiness of the paper surface is poor and the absorbency is high, and the machine's glazing speed is too fast, it is easy to cause insufficient glazing brightness of the printed matter. In order to ensure the glazing quality of printed products, attention should be paid to the lubrication and maintenance of the machine at ordinary times to reduce the wear and loosening of the roller shaft. If the related parts of the machine coating device have been worn, deformed and other adverse phenomena, measures should be taken in time to repair and correct. In addition, during the glazing process, attention should be paid to reasonably controlling the glazing speed according to the characteristics of the printed product surface to ensure the quality of glazing coating.
