Fault analysis and treatment of polishing 0

Fault analysis and treatment of glazing

common faults in glazing are:

first, there are streaks or wrinkles on the film surface

the possible reasons are: the viscosity value of glazing coating is high, and the coating is too late to level, so streaks are easy to appear. According to the different suitability of printing materials, glazing coatings with good leveling and wettability can be selected; These materials can meet the requirements of high strength, high wear resistance, boiling resistance and high temperature resistance, or add an appropriate amount of diluent to reduce the viscosity of the coating. If the coating amount is too large, the coating amount can be reduced by adjustment; Sometimes, the polishing coating has poor wettability to the ink layer on the surface of the print, which affects the smoothness of drying film formation, or the leveling of the coating is poor, and the process conditions do not match the suitability of the coating. Other types of polishing coatings may be used or the process conditions may be changed to match the performance of the coating

II. Printing materials adhere to each other

the reason is that the solvent in the glazing coating is volatile and the drying performance of the coating is poor. We can consider changing the solvent with high volatilization rate or changing the type of glazing coating; It may also be that the coating film is too thick, the solvent inside the coating is not completely volatilized, the residue is high, and the thickness of the film layer is reduced; Or the working temperature in glazing coating or calendering is low and the drying time is short, which makes the coating dry poorly. It can improve the working temperature in glazing coating and calendering, reduce the machine speed and make the coating dry completely

III. poor gloss of film-forming film

if it is the quality problem of coating, it should be considered to use high-quality polishing coating according to the process and economic requirements; If the coating is too thin, the coating amount is insufficient or the coating concentration is small, and it is difficult to fill the surface of printed matter with high roughness and strong absorption, the coating amount shall be increased to increase the coating concentration, or a layer of polishing primer shall be applied before processing, and then polishing and coating shall be carried out; It may also be that the temperature of glazing coating drying and calendering is low, and the calendering pressure is small, then the process parameters should be adjusted to increase the temperature and pressure during operation; It should also be estimated that it is due to the equipment itself. If the calendered steel strip is worn and the gloss smoothness decreases, it is necessary to repair and improve the surface condition of the calendered steel strip

IV. after calendering, the blank part of the printed matter is light colored, and the light colored part changes color

the reason may be that the glazing coating solvent has a certain dissolution effect on the ink layer, which requires changing the coating type or changing the solvent composition; If the ink is not dry well and the solvent resistance of the ink layer is not good, it is necessary to improve the ink drying, and then polish and apply after the ink is dry, so as to reduce the amount of solvent that dissolves the ink in the glazing materials; If the coating layer is not dried thoroughly and the solvent residue in the film layer is high, it is necessary to increase the drying temperature or reduce the machine speed during glazing and coating, prolong the drying time and reduce the solvent residue in the coating

v. uneven coating, bubbles, pitting and other

reasons: the surface tension value of glazing coating is large and the wetting effect on the ink layer on the surface of printing is not good. We should reduce its surface tension value and improve the wetting performance of coating on the ink layer; The solvent in the coating volatilizes poorly and the solvent residue in the coating is high. The solvent with high volatilization rate can be used or the coating can be pressed and polished after being completely dried; It may also be that the machine speed in glazing and coating is too fast and the drying temperature is low, which makes the coating drying incomplete and the solvent volatilization incomplete, so the process conditions of glazing and coating should be adjusted; The ink layer on the surface of printed matter will also produce crystallization, which requires effective measures, such as removing the oil quality of the crystallization surface of the ink layer or roughening treatment, and improving the wetting effect of the coating on the ink layer, so as to weaken or eliminate the adverse effect of the crystallization of the ink layer on the polishing coating

VI. blistering on the film surface

the reason is that in the calendering process, the pressure is too high and the temperature of the calendering steel strip is too high, which makes the coating film soften locally, which needs to reduce the calendering pressure and temperature appropriately; It may also be that the glazing coating is matched with the calendering process conditions, so that after the coating layer on the surface of the print is cooled, the stripping force of the same light band is poor, and the column spacing is 540mm;, It is necessary to change the process conditions to match with the glazing coating, reduce the speed of the calender and improve the peeling force between the coating layer and the light band

VII. In calendering, the adhesion between printed matter and glazing tape is poor

the reason is that the coating is too thin and the coating amount should be increased; If the viscosity of the coating is too low, increase the viscosity of the coating; Then, the pressure of calendering is too small and the calendering temperature is insufficient. It is necessary to increase the calendering temperature and pressure

VIII. The surface of printed matter is easy to break after calendering

the reason is that the high temperature makes the printed matter dehydrate too much and the water content decreases, so the paper fiber becomes brittle. The working temperature in calendering should be reduced and effective measures should be taken to maintain a certain water content in the printed matter; After the hardness tester is in the state of normal operation mechanism, conduct formal test on the sample. If the pressure is too high in calendering, the elongation and plasticity of printed matter will be reduced, and the toughness will be deteriorated, which can reduce the pressure in calendering; If the post-processing suitability of glazing coating is poor, the glazing coating with good post-processing suitability shall be re selected; If the selection of post-processing process conditions is inappropriate, the post-processing process conditions can be adjusted to match the suitability of printed matter after calendering

IX. the film surface brightness on both sides is inconsistent after calendering

the reason is: during calendering, the pressure on both sides of the calendering belt is not equal, or the wear on both sides of the calendering belt is not consistent. Adjust the pressure on both sides of the calendering belt to make it equal, and adjust the parallelism of the hot pressing roller and the transmission roller to make the tension on both sides of the calendering belt consistent and wear evenly; It may also be that the thickness of the glazing coating is uneven on both sides, so it is necessary to adjust the glazing coating mechanism and check the parallelism and gap between the metering roller and the coating roller to make the coating thickness on both sides as consistent as possible

Niu Yifan

reprinted from: Printed today