Post-printing fining problems and solutions

In the post-printing process, various problems often occur during the coating process. These failures mainly reflect poor film quality and sometimes inconvenient operation. The same, but can always find the reasons from the different applicability of printed paper, ink and coating coatings, poor processing of glazing and equipment conditions or their mutual influence. As long as careful observation and careful analysis are made, correct conclusions can be drawn and effective measures can be taken to address them.

The common faults in glazing are the following nine points:

One, film marks or wrinkles

Cause: The coating has a high viscosity value, the paint is too late, and it is prone to streaks. According to the printability of different prints, choose a good leveling, wettability good glazing coating; or add an appropriate amount of thinner to reduce the viscosity of the paint. If the coating amount is too large, the coating amount can be reduced by adjusting; sometimes, the coating property of the coating coating on the surface of the printed matter is not good, the smoothness of the dried coating is affected, or the leveling property of the coating is poor, and the processing conditions are Unlike the suitability of the coating, other types of coating or other process conditions may be used to match the properties of the coating.

Second, prints stick to each other

Reason: The solvent in coating coating has good volatility, and the drying performance of the coating is bad. Consider changing the solvent with high volatilization rate or changing the type of coating coating; or the coating film layer may be too thick, and the solvent inside the coating is not Completely volatilize, high residue, reduce the thickness of the film layer; or the working temperature is low in the coating or calendering, the drying time is short and the coating is not dry, and the working temperature in coating and calendering can be increased. Reduce the speed and dry the coating thoroughly.

Third, film formation film gloss difference

If it is the quality of the top coating, you should consider changing the quality of the 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, the roughness is high and the absorption is strong The surface of the printed matter is not easy to fill and fill, then the coating amount should be increased to increase the concentration of the coating, or a layer of light primer must be applied before the processing, and then the coating of the coating; or it may be coating and drying. The temperature at the time of calendering is lower than the pressure of low pressure light, then the process parameters should be adjusted during the operation to increase the temperature and increase the pressure; it is also estimated that the reason is the equipment itself, such as the wear of the calendered steel strip, the smoothness of the gloss is reduced, It is necessary to repair and improve the surface condition of the calendered steel strip.

Fourth, the blank part of the printed product is light-colored after calendering, and the light-colored part is discolored

Cause: The coating solvent of the coating has a certain function of dissolving the ink layer. It is necessary to change the type of coating or change the composition of the solvent. If the ink is poorly dried and the solvent resistance of the ink layer is not good, the ink drying condition must be improved. After the ink is dried, the ink is dried. Photocoating, reducing the amount of solvent used for dissolving the ink in the coating with less light; the coating layer is not completely dried, and the residual solvent in the film layer is high, the drying temperature during coating or the speed of the coating must be reduced. Extend the drying time and reduce the residual solvent inside the coating.

Fifth, uneven coating, bubbles, pits, etc.

Cause: The surface tension value of the coating material is large, and the wetting effect on the ink layer on the surface of the printed matter is not good, the surface tension value should be reduced, and the wetting performance of the coating on the ink layer should be improved; the solvent in the coating is poorly volatilized, and the solvent in the coating layer Residue is high, you can use a high volatilization rate of the solvent or the coating is completely dry and then calendered; may also be coating speed in the coating is too fast, drying temperature is low, so that the coating is not completely dry, solvent evaporation does not Completely, it is necessary to adjust the coating process conditions; the ink layer on the surface of the printed matter will also produce crystallization phenomenon, which should take effective measures, such as removing the oil on the crystallographic surface of the ink layer or hair treatment to improve the coating The wetting effect of the ink layer reduces or eliminates the adverse effects of the crystallization of the ink layer on coating.

Sixth, film surface foaming

Reason: During the process of calendering, the pressure is too high, the temperature of the calendered strip is too high, so that the coating film layer is partially softened, which requires appropriate reduction of the pressure and temperature of the calendering; it may also be the conditions of the glazing coating and calendering process Wood matching, after the paint layer on the surface of the print is cooled, the peeling force is the same as that of the top tape, and the process conditions need to be changed to match the glazing coating to reduce the speed of the calender and improve the peeling between the coating layer and the top tape. force.

VII. Adhesion between printed matter and glazing tape during calendering

Reason: The coating is too thin, the coating amount should be increased; the viscosity of the coating is too low to increase the viscosity value of the coating; then the pressure of the light is too small, the temperature of the light is insufficient, the temperature of the light is increased, and the calendering is increased pressure.

Eight, the printed calendered, the surface easily cracked

Cause: The high temperature causes the printed product to be dehydrated excessively in calendering and the moisture content is reduced. As a result, the paper fibers become brittle, the working temperature in calendering should be reduced, and effective measures must be taken to maintain a certain moisture content in the printed matter; Too much pressure in the light will make the printability and plasticity of the printed matter decrease and the toughness worsen. This will reduce the pressure in the calendering. If the post-processing suitability of the glazing coating is poor, you should re-select the post-processing suitability. Gloss coating; post-processing process conditions are not suitable to choose, you can adjust the post-processing conditions to match the suitability of the printed calender after printing.

Nine, after the light is not uniform on both sides of the film surface brightness

Causes: During the calendering, the pressure on both sides of the glazing band is not equal, or the wear on both sides of the glazing band is inconsistent. The pressure on both sides of the glazing band should be adjusted to make them equal, and the parallelism between the hot roller and the transfer roller is adjusted so that Both ends of the strip of light are even and uniform, and wear may be uniform. It may also be uneven on both sides of the glazing coating. This requires adjusting the glazing unit to check the parallelism and gap between the metering roller and the applicator roller. The thickness of the side coating is as uniform as possible.