What should be paid attention to when corrugated board adopts flexographic printing (on)
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The following issues should be noted when using flexographic printing on corrugated board.
First, problem that should be paid attention to before printing
1 When using flexographic printing on corrugated board, the flexible plate should be made of a thicker photosensitive resin plate with a thickness of about 4 to 7 mm. When flexo printing, the amount of compression of the printing plate is used to reduce the pressure on the corrugated cardboard. The resulting deformation.
2 When corrugated board is flexographically printed, it is best to use R/bak air-cushion lining technology. Although the photosensitive resin plate has flexibility and compressibility, it has the effect of compensating for printing defects of a thick substrate having a low plasticity. However, if the pressure is too large, the printing plate is deformed, the plate fatigue is increased, and the life of the printing plate is shortened.
3 When corrugated board is used for flexographic printing, the use of water-based ink should determine the viscosity of the ink according to the design of the printing plate and the set printing speed, and pay attention to the change of viscosity during printing. Since the surface of the corrugated cardboard is yellowed and the flatness is poor, the ink permeates quickly, the tinting strength of the ink should be strong, and the proper permeation drying property is maintained.
4 When corrugated board is flexographically printed, the processing of the original image should take into account the characteristics of the printing equipment and materials. At present, the number of screen lines for corrugated board printing and color painting in China is generally about 60 lines/in, the number of colors is 3-4 colors, and a few use 5 to 6 colors. Flexographic printing can only print up to 2% of the dots, and the dot gain is larger, and the color of the corrugated paper is yellowed. Therefore, in the image processing, attention should be paid to correctly setting the gray balance of the plate-making dot correction curve and outputting the negative film.
5 When the corrugated board is flexographically printed, the paper-type photosensitive resin plate is thicker than the printing plate, and the light transmittance is different from the thin plate. Pay attention to the back exposure, main exposure, rinsing and post-exposure treatment. process.
6 After the corrugated board is flexographically printed, the corresponding die-cutting method and box making equipment can be used for die-cutting, and various corrugated products such as corrugated boxes and corrugated boxes can be made.
Second, corrugated cardboard is treated by flexographic printing
1 When the corrugated board is flexographically printed, the overprinting is not caused by a variety of reasons. We will explain the inaccurate overprinting and the corresponding solutions for different reasons as follows:
(1) Overprinting is not allowed due to uneven tension in unwinding or winding. The solution is to adjust the unwinding and winding tension balance.
(2) Overprinting is not allowed due to uneven thickness of the plate. The solution is: pad or replace the plate.
(3) Overprinting is not allowed due to uneven thickness of the printing material and inconsistent tensile deformation. The solution is to use a thick and consistent substrate as much as possible.
(4) Overprinting is not allowed due to unstable printing speed. The solution is to control the speed and keep the voltage stable.
2 In the flexographic printing process, the edge contour is obvious (image crush)
In the printing process, there is a phenomenon that the edge of the printed graphic image has a dark color and a shallow middle. The reason for this phenomenon is that the viscosity of the ink is too high, the ink is poorly stirred; the amount of ink on the surface of the printing plate is too large, the flatness of the printing plate is poor, and the printing pressure is too large.
The solution is to adjust the viscosity of the ink, properly mix the ink, control the amount of ink transferred, the stencil, adjust the height of the layout, and adjust the printing pressure.
3 During the flexographic printing process, the edges of the lines appear hairy
In the printing process, the printed images are unclear, some are halo and feathery, and the edges are burr. The reason for this phenomenon is: the ink is drying too fast; the pressure between the anilox roller and the printing plate is too large or uneven, the viscosity of the ink is too large to cause the hair on the plate; the printing plate is worn, the static electricity; the printing speed is too slow, the pigment in the ink Too much ingredients or poor dispersion.
The solution is: slowing down the drying agent to reduce the drying speed of the printing ink; adjusting the printing pressure, reducing the viscosity of the ink and cleaning the printing plate, checking the wear of the printing plate, using the static eliminator to increase the printing speed, and adding the solvent to the ink and fully Stir well.
4 poor transfer of printing ink during flexographic printing
In the printing process, printing inks have difficulty in transferring ink and uneven color of ink during transfer and transfer. The reason for this phenomenon is: insufficient or uneven printing pressure, poor printing plate hardness, ink roller, anilox roller wear and aging, ink is incompatible with the substrate, the surface of the substrate is not flat; the drying speed of the ink is greater than the printing speed. .
The solution is to adjust the printing pressure, check the hardness of the printing plate, replace the ink roller, the anilox roller, check the ink formulation and the substrate, change the substrate, adjust the drying speed of the ink and the printing speed to match.
5 When the corrugated board is printed with flexographic printing, the dots or lines are unclear.
When the corrugated board is flexographically printed, the dot or line marking is unclear due to various reasons. We will make the dot or line imprint unclear for different reasons and the corresponding solutions are as follows:
(1) The dots or lines are unclear due to uneven thickness of the plate defects. The solution is to check the plate accuracy and printing pressure.
(2) The dot or line is unclear due to the low embossing force. The solution is: re-regulate.
(3) The dot or line is unclear due to poor adjustment of the printing mechanism. The solution is to adjust the printing mechanism and make it run smoothly.
(4) The dot or line is unclear due to the plate roller jump. The solution is to check the ovality of the plate cylinder and gear.
(5) The dot or line is unclear due to improper adjustment of the ink adjustment screw. The solution is to loosen the screws.
(6) The dot or line is unclear due to improper pressure between the anilox roller and the plate. The solution is to adjust the pressure between the anilox roller and the plate.
6 Plate wear occurs during flexographic printing
During the printing process, the printing plate is subject to friction damage or corrosion, and the printing quality cannot be guaranteed. The reason for this phenomenon is that the printing pressure is too large, the contact is too strong; the quality of the printing plate is poor; the ink solvent is improperly selected, and the printing plate is corroded; the ink particles are too thick.
The solution is to reduce the printing pressure and make a reasonable contact; to fully replace the plate or replace the plate, and replace the solvent; replace the ink with a large fineness.
7 Pinholes appear during flexographic printing
During the printing process, the printed matter exhibits many round holes like pinholes. The reason for this phenomenon is: improper adjustment of the printing force of the printing machine, slight corrosion of the printing plate, uneven surface of the printing plate, granular protrusion, drying of the ink on the anilox roll; abrasion of the anilox roll, poor ink transfer; ink Too thin, low viscosity; printing ink layer is too thin; mechanical impurities adhere to the plate, ink wettability is poor; ink viscosity is too low or drying is too slow; ambient temperature is too low, humidity is too large.
The solution is: increase the printing pressure, improve the quality of the printing plate; exchange the substrate; use the slow drying solvent, cover the ink fountain, replace the anilox roller, adjust the ink, increase the viscosity; adjust the thickness of the ink layer; remove the impurity of the layout; Additives improve ink wettability; increase ink viscosity and dryness; increase temperature and reduce humidity.