After a certain batch of cardboard boxes with a beer packing box in a packing factory, there were wrinkle and streaks on the surface after calendering. According to the quality requirements, the appearance of the paper product after calendering should be clean, smooth, no scratches, and no wrinkles. What to do, what caused it? After careful observation of the product, we advise the customer to press the light with a different batch of packaging box paperboard under the same calendering process parameters (such as calendering temperature, pressure, speed, etc.). No wrinkles and streaks after calendering. Through comparative analysis, it is believed that the reason is due to the difference in the quality of the two kinds of cardboard. The paperboards with wrinkles and stripes after calendering are relatively poor in paper quality. However, the lot of paperboard has been finished. If it is scrapped because of the wrinkles and streaks after calendering, it will not be able to meet the quality requirements. Therefore, it will cause untimely delivery and a large amount of waste. And if it can be processed through appropriate remedial measures, so that the quality of calendering requirements, one can be delivered on time, and the other can reduce losses.
For this reason, under our guidance, the user has selected one of the effective measures to solve the problem through the handling and testing of several different methods. The method is: glazing the non-calendered surface board after glazing, and then heat drying once on the calender. The temperature of the hot bake is the same as the temperature of the calender, and can be not heated when the calender is baked. Under pressure, in the case of the calender belt drive, this side of the board is placed on the strip surface at the discharge end, and the strip is brought into the drying tunnel by the steel strip and returned to the calender. This is the head of the material. After such heat baking and then calendering (ie, adding a coating and a hot bake) in accordance with the normal calendering process, the wrinkles and stripes on the surface of the batch of cardboards have disappeared.
Incidentally, under normal circumstances, the calendered temperature is generally controlled at 115 °C ~ 120 °C, the pressure is controlled at 150 ~ 180kg/m2, speed 6 ~ 10m/min is appropriate. Of course, in the on-site operation, it is also necessary to adjust and grasp the thickness of the paperboard properly. It is worth noting that, for the paper products to be calendered, there must be some choice in paper quality, otherwise the calender quality requirements cannot be achieved.
Post-press processing: Common problems and treatment methods for varnishing process
In the post-press processing process, the glazing process can not only increase the surface appearance of the finished product, but also can play a protective role. The following is a brief analysis of some of the problems that arise during the glazing process.
First, the film surface appears streaks or wrinkles
Varnish of high viscosity, too late, leveling, prone to streaks, according to the different printability, selection of leveling, good wettability of glazing oil; or add an appropriate amount of thinner to reduce the viscosity of glazing oil . If the amount of coating is too large, the amount of coating can be reduced by adjusting; sometimes, the wettability of the coating on the surface of the printed matter is not good, and the smoothness of the dried film is affected, or the leveling property of the coating oil is poor. The process conditions do not match the coating oil suitability. Other types of coating varnish may be used or the process conditions may be changed to match that of the varnish. The solvent in the varnish has poor volatility, and the drying performance of the coating is poor. Consider using a solvent with a high volatilization rate or changing the type of varnish; it may also make the coating layer too thick, and the solvent inside the coating is not complete. Volatile, high residue, can reduce the amount of coating, reduce the thickness of the film layer; or coating the coating or calendering in the low temperature, drying time is short and the coating drying is bad, can improve the coating production and pressure coating The operating temperature in the light, reduce the speed, and completely dry the coating.
Second, the film coating film poor gloss If it is the quality of coating oil, you should consider more according to the process and economic requirements to use better quality of the coating oil; if the coating is too thin, insufficient coating or coating If the oil concentration is small, and the surface of the print with high roughness and strong absorption is not easy to fill and fill, then the coating amount should be increased to increase the coating concentration, or a layer of light primer should be applied on the surface before processing, and then the coating can be applied. Coating, it may also be coating coating drying and calendering when the temperature is low, the calendering pressure is small, the operation should adjust the process parameters, increase the temperature, increase the pressure; also estimated to be the device itself, if Because of the wear of the calendered steel belt, the smoothness of the gloss is reduced, and it is necessary to repair and improve the surface condition of the calendered steel strip.
Third, after calendering, the blank part of the printed product is a light-colored part, and the light-colored part of the printed product has a certain dissolving effect on the ink layer. This is to change the type of the varnishes or change the solvent composition; if the ink is poorly dried, the ink layer will not dissolve. The performance is not good, we must improve the ink drying conditions, such as ink drying and then coating, reduce the solvent in the coating solvent for the amount of solvent; the layer is not completely dry, the film residual solvent is high, then To improve the coating drying temperature or reduce the speed, extend the drying time, reduce the coating residual solvent.
Fourth, uneven coating, there are bubbles, pits, etc. Varnish lacquer surface tension value, the printing surface of the ink layer is not good wetting effect, should reduce the surface tension value, improve the wetting properties of the ink coating layer; The solvent in the paint is poorly volatilized, and the residual solvent in the coating is high. The solvent with high volatilization rate may be used or the coating may be completely dried and then calendered; the speed may be too fast in the coating and the drying temperature may be low. If the coating is completely dried and the solvent evaporates incompletely, the process conditions for glazing should be adjusted; the ink layer on the surface of the printed matter will also undergo crystallization. This requires effective measures, such as removing the crystallographic surface of the ink layer. The oil is subjected to a roughening treatment to improve the wetting effect of the coating oil on the ink, so as to weaken or eliminate the adverse effect of the crystallization of the ink layer on the coating of the coating.
Fifth, the membrane surface blistering in the calendering process, the pressure is too high, the temperature of the calendered strip is too high, so that the glazed layer partially softened, which requires appropriate reduction in the pressure and temperature of the calendering; may also be varnish and The calendering process conditions do not match, so that after the glazing layer on the surface of the printed product is cooled, the peeling force is the same as that of the upper strip, the process conditions need to be changed to match the glazing oil, the calender speed is reduced, and the glazing layer is improved. The peel force between the bands.
Sixth, after the printing calendering, the surface is easy to crack the temperature is too high, so that the printing process in the calendering process is too dehydrated, the water content is reduced, so the paper fiber becomes brittle, the operating temperature of calendering should be reduced, and take effective measures to maintain A certain amount of water content in the printed matter; Excessive pressure in the calendering can reduce the extensibility and plasticity of the printed matter, and the ductile denaturation can reduce the pressure in the calendering. If the post-processing of the varnish is poor, it should be reselected. Better processing suitability of the varnishes; the selection of post-processing conditions is not appropriate, and the post-processing conditions can be adjusted to match the suitability of calendered presses.
7. The brightness of the film surface on both sides is not uniform After calendering, the pressure on both sides of the glazing band is not equal, and 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. Adjust the hot roller and The parallelism of the transfer roller makes the sides of the glazing tape uniform and evenly worn; it may also be uneven on both sides of the glazing oil, which is to adjust the glazing unit to check the gap between the metering roller and the coating roller. The degree of parallelism and the gap make the coating thickness on both sides as uniform as possible.
For this reason, under our guidance, the user has selected one of the effective measures to solve the problem through the handling and testing of several different methods. The method is: glazing the non-calendered surface board after glazing, and then heat drying once on the calender. The temperature of the hot bake is the same as the temperature of the calender, and can be not heated when the calender is baked. Under pressure, in the case of the calender belt drive, this side of the board is placed on the strip surface at the discharge end, and the strip is brought into the drying tunnel by the steel strip and returned to the calender. This is the head of the material. After such heat baking and then calendering (ie, adding a coating and a hot bake) in accordance with the normal calendering process, the wrinkles and stripes on the surface of the batch of cardboards have disappeared.
Incidentally, under normal circumstances, the calendered temperature is generally controlled at 115 °C ~ 120 °C, the pressure is controlled at 150 ~ 180kg/m2, speed 6 ~ 10m/min is appropriate. Of course, in the on-site operation, it is also necessary to adjust and grasp the thickness of the paperboard properly. It is worth noting that, for the paper products to be calendered, there must be some choice in paper quality, otherwise the calender quality requirements cannot be achieved.
Post-press processing: Common problems and treatment methods for varnishing process
In the post-press processing process, the glazing process can not only increase the surface appearance of the finished product, but also can play a protective role. The following is a brief analysis of some of the problems that arise during the glazing process.
First, the film surface appears streaks or wrinkles
Varnish of high viscosity, too late, leveling, prone to streaks, according to the different printability, selection of leveling, good wettability of glazing oil; or add an appropriate amount of thinner to reduce the viscosity of glazing oil . If the amount of coating is too large, the amount of coating can be reduced by adjusting; sometimes, the wettability of the coating on the surface of the printed matter is not good, and the smoothness of the dried film is affected, or the leveling property of the coating oil is poor. The process conditions do not match the coating oil suitability. Other types of coating varnish may be used or the process conditions may be changed to match that of the varnish. The solvent in the varnish has poor volatility, and the drying performance of the coating is poor. Consider using a solvent with a high volatilization rate or changing the type of varnish; it may also make the coating layer too thick, and the solvent inside the coating is not complete. Volatile, high residue, can reduce the amount of coating, reduce the thickness of the film layer; or coating the coating or calendering in the low temperature, drying time is short and the coating drying is bad, can improve the coating production and pressure coating The operating temperature in the light, reduce the speed, and completely dry the coating.
Second, the film coating film poor gloss If it is the quality of coating oil, you should consider more according to the process and economic requirements to use better quality of the coating oil; if the coating is too thin, insufficient coating or coating If the oil concentration is small, and the surface of the print with high roughness and strong absorption is not easy to fill and fill, then the coating amount should be increased to increase the coating concentration, or a layer of light primer should be applied on the surface before processing, and then the coating can be applied. Coating, it may also be coating coating drying and calendering when the temperature is low, the calendering pressure is small, the operation should adjust the process parameters, increase the temperature, increase the pressure; also estimated to be the device itself, if Because of the wear of the calendered steel belt, the smoothness of the gloss is reduced, and it is necessary to repair and improve the surface condition of the calendered steel strip.
Third, after calendering, the blank part of the printed product is a light-colored part, and the light-colored part of the printed product has a certain dissolving effect on the ink layer. This is to change the type of the varnishes or change the solvent composition; if the ink is poorly dried, the ink layer will not dissolve. The performance is not good, we must improve the ink drying conditions, such as ink drying and then coating, reduce the solvent in the coating solvent for the amount of solvent; the layer is not completely dry, the film residual solvent is high, then To improve the coating drying temperature or reduce the speed, extend the drying time, reduce the coating residual solvent.
Fourth, uneven coating, there are bubbles, pits, etc. Varnish lacquer surface tension value, the printing surface of the ink layer is not good wetting effect, should reduce the surface tension value, improve the wetting properties of the ink coating layer; The solvent in the paint is poorly volatilized, and the residual solvent in the coating is high. The solvent with high volatilization rate may be used or the coating may be completely dried and then calendered; the speed may be too fast in the coating and the drying temperature may be low. If the coating is completely dried and the solvent evaporates incompletely, the process conditions for glazing should be adjusted; the ink layer on the surface of the printed matter will also undergo crystallization. This requires effective measures, such as removing the crystallographic surface of the ink layer. The oil is subjected to a roughening treatment to improve the wetting effect of the coating oil on the ink, so as to weaken or eliminate the adverse effect of the crystallization of the ink layer on the coating of the coating.
Fifth, the membrane surface blistering in the calendering process, the pressure is too high, the temperature of the calendered strip is too high, so that the glazed layer partially softened, which requires appropriate reduction in the pressure and temperature of the calendering; may also be varnish and The calendering process conditions do not match, so that after the glazing layer on the surface of the printed product is cooled, the peeling force is the same as that of the upper strip, the process conditions need to be changed to match the glazing oil, the calender speed is reduced, and the glazing layer is improved. The peel force between the bands.
Sixth, after the printing calendering, the surface is easy to crack the temperature is too high, so that the printing process in the calendering process is too dehydrated, the water content is reduced, so the paper fiber becomes brittle, the operating temperature of calendering should be reduced, and take effective measures to maintain A certain amount of water content in the printed matter; Excessive pressure in the calendering can reduce the extensibility and plasticity of the printed matter, and the ductile denaturation can reduce the pressure in the calendering. If the post-processing of the varnish is poor, it should be reselected. Better processing suitability of the varnishes; the selection of post-processing conditions is not appropriate, and the post-processing conditions can be adjusted to match the suitability of calendered presses.
7. The brightness of the film surface on both sides is not uniform After calendering, the pressure on both sides of the glazing band is not equal, and 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. Adjust the hot roller and The parallelism of the transfer roller makes the sides of the glazing tape uniform and evenly worn; it may also be uneven on both sides of the glazing oil, which is to adjust the glazing unit to check the gap between the metering roller and the coating roller. The degree of parallelism and the gap make the coating thickness on both sides as uniform as possible.
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