Glazing process and quality control of the hottest

2022-08-23
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Glazing process and quality control of packaging prints II

process factors affecting glazing quality 1 Technological factors affecting the quality of glazing and coating. The essence of the glazing coating process is the process of leveling and drying the glazing coating on the surface of the printed matter. The main influencing factors are the glazing suitability of printing materials, the types and properties of glazing coatings, coating processing conditions, etc

(1) the glazing suitability of printed matter refers to the influence of the paper and printing graphic properties of printed matter on the glazing coating. In glazing coating, the glazing coating is easy to level on the surface of high smoothness paper. In the drying process, with the curing of the glazing coating, a film surface with high smoothness can be formed. Therefore, the higher the smoothness of the paper surface, the better the effect of glazing and coating, and vice versa. The absorbers on the surface of the paper are too strong, the absorption rate of the paper fiber to the glazing coating is high, and the solvent penetration is fast, which leads to the increase of the viscosity value of the coating, and the shear stress of the coating layer flowing on the surface of the print increases, which affects the leveling of the glazing coating and makes it difficult to form a smooth film; On the contrary, the absorption is too weak, which significantly reduces the penetration, solidification and conjunctival effect of glazing paint in leveling, and also cannot form a high-quality film on the surface of printed matter

the quality of printing ink also directly affects the coating quality and leveling of glazing paint. The ink particles are fine, and its dispersion is high, so the graphic ink layer is easy to be wetted by the glazing paint. Under the action of coating pressure, the leveling property is good, and the smoothness of the formed film is high. On the contrary, the ink particles are thick, the printing ink layer is poorly spread, and it is not easy to form a high-quality film during coating

(2) different types of glazing coatings have different properties. Even under the same process conditions, the film conditions obtained after coating and calendering are also different. For example, the viscosity of glazing coating plays an important role in the leveling and wettability of the coating, strengthening the influence of temperature regulation, conductivity and other functional fibers and the integrated development of intelligent textiles. Papers with the same absorption intensity and their dedication to innovation and quality control have an inverse ratio between the absorption rate of glazing paint and the viscosity value of the paint, that is, the smaller the viscosity value of the paint, the greater the absorption rate, which will make the leveling premature, so as to provide a stable end of this section, causing some local large coatings on the surface of the printed matter and affecting the smoothness and brightness of the film after drying and calendering

glazing coatings with different surface tension values have different wetting, adhesion and soaking effects on the same print, and their film-forming effects are very different after coating and calendering. Glazing paint with small surface tension value can wet, adhere and soak the field surface and graphic ink layer of all kinds of prints, "Smooth and uniform film surface; glazing paint with large surface tension value limits the wetting of the ink layer on the surface of the print, and even the coating after glazing will shrink to a certain extent, affecting the film quality. The volatility of the solvent also has an impact. Too fast evaporation speed will make the coating layer too late to smooth and form a uniform film surface; on the contrary, it will cause insufficient drying of the glazing paint, blocked hardening of the conjunctiva, and poor adhesion resistance.

(3) The selection of coating process conditions also has a great impact on the coating quality. The coating layout is too few, the coating cannot be evenly spread on the whole surface to be coated, and the smoothness after drying and calendering is poor; Too thick coating will affect the drying and increase the cost. In order to dry the thick film, the temperature of coating and calendering should be relatively increased The drying time should be prolonged, which will reduce the moisture content of the printed matter, make the paper fiber brittle, and the surface of the printed matter is easy to crack

coater 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 should be recognized and the temperature should be high; The machine speed is slow, the coating leveling time is long, the coating is thin, the drying time can be shortened, and the drying temperature can be appropriately reduced. The above process factors sometimes have a cross-linking effect on the quality of l-light coating. In order to obtain good l-ray coating quality, these factors need to be comprehensively considered in order to obtain the appropriate match between these factors

2. Technological factors affecting the quality of calendering. In calendering, the main factors affecting the calendering quality of printed matter are calendering temperature, pressure and machine speed

in the calendering process, the temperature should be appropriate at each stage of hot pressing, glazing and cooling stripping, so as to facilitate the secondary wetting, adhesion and penetration of the main agent molecules in the coating to the surface of the print, and enhance the contact effect between the two. At a certain temperature, the plasticity of the coating film can be improved, and the smoothness of the calendered surface of printed matter can be greatly improved under the action of pressure. If 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 to the inch light and stripping process; On the contrary, the hot pressing temperature is too low, the coating layer is not fully plasticized, the secondary wetting, adhesion and permeability of the print are insufficient, and the adhesion of the coating layer is poor, so the calendering effect is poor, and it is not easy to form an ideal film with high smoothness after calendering

in the film after coating and drying. 2. The functional characteristics of anchor fatigue testing machine, the arrangement of coating molecules is relatively loose, and there are many tiny holes in it. During calendering, under a certain temperature and pressure, the movement between molecules intensifies, which is manifested as the volume change of the film. This percentage change in volume is called the compressibility, which is the ratio of the reduced volume of the coating layer when pressurized to the original volume before pressurization. High compressibility is conducive to the formation of a smooth film on the surface of the coating; On the contrary, if the coating layer is compressed less, it is not easy to form a smooth film on the surface. However, when the pressure is too high, the extensibility and plasticity of the printed matter will be reduced, resulting in fracture

the surface smoothness and adhesion strength of the glazing film generally increase with the increase of curing time, but the rate of increase is getting smaller and smaller, and it will not increase after reaching a certain value. The curing time depends on the calendering speed. When the glazing coating is in contact with the glazing band, its molecular activity ability gradually decreases with the decrease of coating temperature. If the curing time is short and the weakening rate is fast, the coating molecules cannot fully interact with the ink layer on the surface of the printed matter, the adhesion strength of the coating layer to the ink layer is poor, and the smoothness of the film surface is low after drying and cooling

information source: post press principle and process

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