It is necessary to pay attention to the measurement of ink viscosity in use, neither too high nor too low. Pay attention to changes in pH. Because in the printing process, due to the volatilization of water, it will cause the viscosity of the aqueous ink to increase and the pH value will drop. The pH should be controlled between 8.5 and 9.5. If it exceeds this range, the pH stabilizer can be used to adjust the viscosity. When it is slightly larger, appropriate amount of water can be added for adjustment.
In the course of use, if there is more foam in the ink, a small amount of defoamer may be added, and the added amount is generally controlled within 0.2% of the ink volume. In addition, before use, pay attention to ink adhesion, abrasion resistance, water resistance and drying. The choice of these properties depends on the use of the corrugated paper. For example, for the packaging of frozen products, aquatic products or canned beverages, inks with strong adhesion, quick drying, and water-repellent deinking should be selected.
5. Ensure printing accuracy, control printing pressure
The overlay accuracy depends first of all on the accuracy of the flexographic printer and the parallelism of the paper feeding section to push the paperboard. Furthermore, it is the layout accuracy (here, no gradation compression and reduction problems are involved), the loading and correction. After the printing plate is ready, a 0.5mm thick transparent polypropylene film base can be taken, and a straight line can be drawn at the center of its length to cover the printing plate. The watermark can be drawn along the edges of the printing plate to accurately trace all the edge lines (such as overprinting three lines. The color can be painted again). Finally, press the cover printing color to stick the corresponding printing plate in the painted position. Then use the double-sided adhesive to attach the printing plate to the cylinder of the printing machine. The middle line of the printing plate and the printing machine are installed. The correct alignment of the center of the platen roller ensures accurate overprinting.
In the flexo printing of corrugated board, it is necessary to pursue the exquisiteness of the pattern, but also to consider the difficulty of printing. Such as small text and pattern, if overprinting, due to overprinting accuracy is not ideal, it is bound to cause unsightly printing patterns and increase the scrap rate, generally trapped to solve this problem. The trapping of corrugated cardboard is usually 0.5 to 1mm. Complementary colors are difficult to overprint, and there are obvious black edges at the intersection of two colors, which affects the aesthetics of packaging. Relatively speaking, dark and light-colored overprints will be much better.
6. Note the clarity of printed graphics
The clarity of printed graphics is one of the most intuitive print quality. To ensure the clarity of printed graphics, we must first choose a medium that is wear-resistant, moderately elastic, and of good quality. Whether it is a plate printed with a negative film or a plate with a manual knife, the pattern and line depth on the plate should not be less than 3mm. The arc should be round and the straight line should be straight. When printing, the ink should be properly lightened, the ink layer should not be too thick, and the pressure should be moderately stable (no obvious dent marks on the surface paper). The speed of the printing press should generally be controlled to be higher than 800r/min. It is too low. The ink on the surface paper is uneven and will be exposed. If it is too fast, the ink will be too thick and the layout will be blurred. At the same time, it is also necessary to prevent paper, paper, etc. from entering the printing press and sticking to the printing plate. If any, it should be stopped, wiped and reprinted.
7. Note the impact of full-printing on carton strength
When the corrugated board is printed, the paperboard is formed by passing the paper guide roller and the printing roller on the printing machine to the grooved portion. In the transfer process, the cardboard is deformed to a different degree by the pressure of the roller, which will inevitably affect the strength of the carton in the future, and is particularly prominent in full-printing. Carton of the same material, after printing, compared with before, its strength should be reduced by about 30%. Therefore, in the production process, generally three measures can be taken to alleviate this problem. First, the gaps of the paper guide rollers of the printing press are adjusted appropriately to be slightly smaller than the paperboard thickness of 0.1 to 0.15 mm, so that the paper boards to be printed can pass without deformation. should. Secondly, attention should be paid to adjusting the printing pressure so that the pressure of the printing plate can meet the requirements of clear printing. Thirdly, the speed of the printing press (1000 r/min or more) can be appropriately increased, so that the paper board can pass through the printing press as soon as possible, and the time for pressing the paper board can be reduced.
8. Note the handling of some issues in printing
In the direct printing of corrugated board flexo printing, the problems often encountered include: printing plate graphic expansion, line roughening, incapable of covering the background color in the overlay printing, and the printing product presents many holes such as pinholes. The surface paper is printed in a fuzzy manner, the surface of the paperboard is indented, the surface of the print is powdery and easy to fade, and the surface of the paperboard is fluffed. To solve these problems, either by adjusting the viscosity of the ink, or by controlling the pressure, or adjusting the gap of the paper feed roller, or cleaning, etc., the paperboard can be replaced separately. (Finish)
