The glazing process is a supporting production process for packaging and decoration printing. Trademarks, product advertisements, invitations and book covers are printed. By glazing, the gloss and artistic effect of the printed surface can be increased, and the role and function of the printed product can be beautified. The colors are more vivid and eye-catching, giving people a beautiful visual effect, which doubles the value of the product. Glazing is also an important method to improve the appearance, performance and protection of printed products, and it is also an effective method to improve the quality and grade of printing. Correctly recognizing certain situations related to the glazing quality of printed products, and then taking corresponding technological measures to carry out effective control, is of great significance for improving the quality of color printing products.
1. The relationship between paper characteristics and the glazing quality of printed products
The process practice shows that the quality of the glazing of the printed matter is directly related to the performance of the paper. The paper with a good surface smoothness has weak absorption, and the oil layer will float on the surface after the varnish (coating) is coated. To form a high-brightness film. The paper with poor smoothness, because of its rough surface, will be quickly absorbed by the rough fiber after the glazing coating is applied to the paper surface, and the paper surface will not form a bright coating, and the gloss effect is 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 gloss effect of the printed product, a layer of casein primer can be coated on the paper surface before polishing The function of the primer makes the varnish layer float on the paper surface after the glazing of the printed product, forming a high brightness film layer. It can be seen that the absorbency of the paper surface affects the leveling of the glazing paint from the beginning of the coating to the drying. This is because the paper surface absorbs the solvent in the glazing paint, which makes the glazing paint for a period of time. As the viscosity increases, the internal resistance of the paint layer flowing on the paper increases, so its leveling is poor. That is, when the varnish is not applied smoothly, a continuous and uniform film layer cannot be formed, resulting in poor gloss on the paper. This is an inevitable manifestation of excessive absorption on paper. Therefore, in the actual production process, according to the actual production conditions and the absorption and smoothness of the paper surface, the glazing process and the glazing paint should be adjusted accordingly. If the absorption of paper on the printed matter is too strong, 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. If the coated paper has a smooth surface, the gloss effect will be significantly improved after glazing. The surface gloss of whiteboard paper or white cardboard is correspondingly poor, and the brightness of the printed product is not significant enough after glazing. 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 paper's easy oil absorption and the lack of gloss on the printed product, the proportion of the coating can be increased appropriately, and the method of applying two coats of varnish can be used to increase the brightness of the printed product.
2. The relationship between the production temperature and the glazing quality of the printed products
The production process shows that the temperature also has a certain relationship with the glazing quality. Because, temperature will affect the concentration and fluidity of varnish. Generally, the temperature of the glazing of the printed matter should be controlled at about 20 ° C, which can achieve relatively good results. However, if the temperature is low in winter, the glazing oil is relatively easy to solidify and thicken due to the low temperature, and the fluidity of the glazing oil is poor. The oil film on the surface of the printed product after glazing is easy to be uneven. The quality of product coating is also poor. In order to overcome the problems caused by environmental changes, the varnish should be placed in a room with a relatively stable temperature. Generally, the varnish should be placed in a room with a temperature of 20 ° C to 25 ° C to keep the varnish relatively stable.
3. The relationship between printing inks and glazing quality of printed products
The characteristics of printing inks are also an important factor affecting the quality of glazing. The affinity of the printed 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 product cannot be compatible with the glazing paint, it is difficult for the varnish to form a smooth and uniform film on the paper surface when glazing. If the printing ink particles are large and the pigment dispersion is small, the leveling of the varnish on the paper is poor, which makes it difficult to form a high-quality continuous film. When the printing ink layer is poorly dried, the glaze coating is also difficult to obtain a good gloss effect, and it is even easy to produce chain quality problems such as trachoma and air bubbles. In addition, the printing ink must have solvent resistance and heat resistance, otherwise the printed matter will be discolored or wrinkled skin and other undesirable phenomena. Therefore, the printing ink of glazing products should be resistant to alcohols, ester solvents and acid and alkali, and should have the characteristics of long-term discoloration and good gloss, and have a strong adhesion printing effect on paper. In order to prevent the ink color of the printed product from mutating and affecting the quality of the product.
4. The relationship between the crystallization of the ink layer of the printed product and the glazing quality of the printed product
When the printing area of ​​the background ink is large, the printing semi-finished product is left for too long, and the excessive drying oil is added to the background ink, the printing ink layer will form 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. In this case, as long as 5% lactic acid is added to the glazing oil, mix it evenly and then apply the glazing coating. By adopting this modified glazing oil, the vitrified crystal film on the surface of the printed matter can be damaged, so as to achieve the requirement of evenly absorbing the glazing oil, and a bright film can be formed on the ink layer.
5. The relationship between the properties of glazing paint and the glazing quality of printed products
The viscosity of the glazing paint has a great influence on the leveling and wettability of the paint. When the surface gloss and absorbency of the printed product are different, the viscosity of the paint used should also be different in order to obtain 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 the glazing. Because the absorption rate of the glazing paint on paper and paperboard with the same absorption performance is inversely proportional to the viscosity of the paint, that is, the smaller the viscosity value of the paint, the stronger the absorption. Therefore, for high-gloss paper and cardboard, the viscosity of the varnish can be lowered appropriately. The surface tension of the glazing coating is also an important factor affecting the coating quality. The glazing coating with a small surface tension can be easily and better wetted and attached to the surface of the printed matter, that is to say, the surface tension promotes the glazing coating The reduced surface area makes its leveling a smooth and uniform continuous coating. The glazing paint with large surface tension has certain limitations on the wetting of the printed 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 contraction, and even trachoma. In addition, the volatilization rate of the solvent in the glazing paint has a great influence on the quality of the glazing coating. When the volatilization of the solvent is too fast, the viscosity of the glazing coating will change too much within a certain period of time, and its leveling property will also change suddenly, making it difficult to achieve leveling of the coating in time, and it cannot form a continuous and uniform coating layer It is easy to produce streaks, trachoma, and may also induce moisture condensation, which makes the dried coating crack and white.
6. The relationship between the machine and the glazing quality of the printed products
The precision and operation technology of the glazing machine also have a great relationship with the glazing quality of the printed products. When the coating roller, coating amount control roller and pressure roller of the machine have bending deformation, poor center of circle, and the wear gap of the shaft head or bush portion of the roller, it will cause the instability of the glazing coating and Unevenness. In addition, if the gloss of the paper surface is not good and the absorbency is high, when the glazing speed of the machine is opened too fast, it is easy to cause insufficient brightness of the glazing of the printed product. In order to ensure the glazing quality of printed products, we should usually pay attention to the lubrication and maintenance of the machine to reduce the wear and looseness of the roller shaft. If the related parts of the machine coating device already have bad phenomena such as wear and deformation, timely measures should be taken to repair and correct. In addition, in the glazing process, attention should be paid to the characteristics of the surface of the printed matter, and the glazing speed should be reasonably controlled to ensure the quality of the glazing coating.
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