Analysis of the characteristics of water-based printing inks
During printing, check the viscosity, pH value and drying performance of the ink at any time. For the control of flexographic printing inks, there are mainly these three aspects. In the production process, due to the volatilization of water and solvents, the performance of the ink becomes unstable, the viscosity increases, the pH value decreases, and the printability is affected. Therefore, during the printing process, an appropriate amount of pH stabilizer or a corresponding solvent should be added at regular intervals (to combine the specific printing speed and ink drying conditions) to adjust the pH and viscosity of the ink. At the same time, because the flexographic plate is a short-station printing, the stroke between color and color is relatively short. If the solvent in the ink is not completely dried, it will cause poor stacking or blocking.
Water-based inks are widely used in flexographic printing, especially in the printing of corrugated boxes. Surface tension can cause beads to form on the surface of water-based inks and cause small dots to be lost. Good ink overprinting can ensure smooth four-color printing. Since the surface tension of water is higher than that of alcohol, in order to obtain a good dry overlay effect, the relative pressure between the two drying cylinders must be reduced, so that the hot air flow between the cylinders can be more quickly and the drying speed can be accelerated. The drying of water-based ink is divided into three steps: water evaporates from the ink; amine must also be separated from the ink to make the ink water-resistant; polymer particles must be connected to form a film on the surface of the dried ink layer. In a humid environment, water-based inks are more stable and will not change viscosity due to solvent volatilization, unlike solvent-based inks. To ensure the quality of water-based ink printing, it is necessary to prevent excessive mechanical agitation and maintain a stable pH value.
The development of squeegee technology has improved the quality of flexo printing and effectively controlled the contamination of printed products when ink was transferred from the ink fountain to the surface of the substrate. Common two-roller ink supply systems with ink tanks and box-type squeegee systems are available. The tank of the box-type squeegee system is completely closed and there is no leakage of ink. When the anilox roller is turned to the proper position, the scraper scrapes off the excess ink and returns it to the fuel tank. In addition, there is a plastic or metal scraper inside the fuel tank. Anilox roller technology has been adapted to this squeegee system. When cleaning the anilox roller, an automatic system with ultrasonic or high pressure is used. Liquid cleaning (not mechanical cleaning) reduces the damage to the anilox roller and dots.
Problems and Solutions Frequently Occuring in Printing
Overprinting is not allowed
Uneven tension on corrugated paper
Tissue paper absorbs too much water, and multi-color printing deforms the paper
Paper with bent leaves or bent cardboard
Inadequate printing plate adhesion makes plate positioning inaccurate
Problem with printing press positioning system
Too much pressure during previous color printing distorts the image
Adjust the tension control of the retracted paper
Control the sizing degree of the double tile machine or detect the viscosity of the ink
Replace flatter paper
Rebond plates
Adjust the positioning system of the printing press, or replace parts
Reduce printing pressure appropriately
Substrate adhesion, dirt
Ink is not dry
Stored prints are too hot
Increase drying temperature
Printed products in a cool place
Paste plate
The printing plate is too shallow
Printing pressure is too high
Too much ink supply
Ink viscosity is too high
Ink drying speed is too fast
Deepen the printing plate
Adjust printing pressure
Reduce ink supply
Reduce the viscosity of ink
Reduce drying temperature
Poor overprint
In the multi-color printing, the previous ink has not dried yet.
The color of the post-print causes the ink of the previous color to peel off.
Post-printed color cannot be overprinted
Increase the drying speed of the first color
Reduce the viscosity of the next color or reduce the printing pressure
Reduce the viscosity or increase the adhesion of the latter color
Printed pinhole
Ink dries too fast on the roller
Uneven ink transfer
Slow down the drying speed of ink
Control of ink fraction
In the carton printing workshop, fractional ink has always been a big problem, and often there are three or four and a half barrels of ink in a variety. The reasons are nothing more than two: first, the ink pickers like to use the original barrel of ink, which can reduce the troubles such as hue deviation; second, the remaining half of the barrel of ink cannot be returned in time. The solution is actually very simple. On the one hand, the reservoir management must strengthen supervision, and half of the barrel of ink must receive half of the barrel. As for the residual ink caused by flushing water, the hue deviation can be solved by properly adding the original ink; The remaining ink can be used to adjust the ink, which requires sufficient experience of the ink adjuster.
