Analysis of the reasons for the inaccurate inking

2022-08-18
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Analysis of the reasons for the inaccurate inking of paper gravure prints (Part 2)

the surface of the three embossing cylinder is aged, worn or adhered with foreign matters

the surface of the embossing cylinder is made of rubber or polyurethane materials. Due to the large embossing force during printing and the long-term erosion of solvents, it is very easy to age or wear, and cracks or small pits appear on the surface. During printing, the pattern part in contact with the defect position will not be inked, resulting in incomplete graphics and text. This phenomenon is more obvious when printing low quantity paper such as coated paper, but it is not easy to appear when printing high quantity paper such as whiteboard

the inaccurate inking of the printing products caused by the aging or wear of the surface of the imprint cylinder is generally manifested as irregular strips or blocks (large-area field color blocks are easy to observe), its horizontal position is basically unchanged, its longitudinal position is basically unchanged, and it has excellent corrosion resistance and lightweight characteristics, which are variable. At this time, the imprint cylinder needs to be replaced. If there are no spare parts, it can be exchanged with the embossing cylinder of other color decks to avoid the contact between the defect position and the graphic part, or it can be solved by repairing and grinding to solve the urgent problem

the width of the paper is too small, the doctor blade fails to scrape the ink of the layout, or the operation is improper, so that the ink is stuck on both sides of the embossing cylinder, so that it does not form insulation, which will lead to the conduction and leakage of the discharge current generated by the electrostatic electrode, thus affecting the adsorption of the ink, weakening the inking effect of the print, especially for the eye-catching print. In this case, it is necessary to wipe the ink on both sides of the embossing cylinder with solvent, properly adjust the doctor blade, or lengthen the length of the doctor blade (the length of the doctor blade slightly exceeds the length of the printing plate by 5 ~ 6cm), so that it can scrape the ink on the surface of the printing plate. At the same time, the diameter of the excess part on both sides of the embossing cylinder can be appropriately reduced by 2 ~ 4mm according to the long-term actual printing width

when there is ink, paper wool, paper powder or other substances on the surface of the imprinting cylinder, it will also affect the uniform distribution of the imprinting force, so that the ink transfer in some areas of the printing plate is insufficient, resulting in the false image and text imprinting of the print. Stop the machine to remove the foreign matters on the imprinting cylinder before printing

poor viscosity of four inks

viscosity is the main control index of inks, which directly affects the transfer performance of inks and the quality of prints. The application range of blow molding machine is mainly determined according to the different materials. In actual production, the viscosity of ink is determined according to the process requirements of the product. Too low viscosity is easy to cause 10% of the most frequently used hardness test methods to spread the ink, poor covering power, the hue can not meet the requirements, the imprint is weak, the bottom is exposed, and the ink color is unsaturated; If the viscosity is too high, the transfer performance of the ink is poor, and the field part of the print is prone to uneven inking, pinhole like spots, incomplete dot and text printing, which also increases the amount of ink

during the printing process, the ink must maintain a certain viscosity value; To ensure the effective circulation of ink, so that ink to maintain good liquidity; Measure the viscosity of the ink frequently (usually once every 20 ~ 30 minutes), and add solvent in time to maintain the consistency of viscosity

five other factors

1 Effect and influence of static electricity

when gravure printing products with dots is used, the reproducibility of the print level is poor, and usually there are small gag like spots, mainly because the hole depth of the dot part is shallow, the ink transfer performance is poor, and the ink is easy to dry in the hole, which is difficult to truly reflect the order (level) of the pattern. It can be solved by adding or opening the electrostatic printing auxiliary ink absorption system. As shown in Figure 1, since the embossing cylinder uses rubber or polyurethane semiconductor materials to make a conductive surface, the discharge current generated by the electrostatic electrode can be transferred to the surface of the embossing cylinder through the electrostatic brush, so that the potential difference between the ink molecules and the embossing cylinder will form an electric field, which will polarize the ink and move towards the direction of the printing material, which is conducive to the full transfer of the ink and effectively improve the printing effect

static electricity on the surface of the paper is not conducive to printing, which directly affects the quality of the print and makes the print appear spots. At the same time, it also has a certain negative impact on electrostatic assisted printing, because it affects the uniform distribution of electrostatic charge on the surface of the embossing cylinder, and then affects the adsorption effect of ink on the paper surface. Especially in dry seasons, paper is prone to static electricity. Static electricity can be eliminated by installing static electricity elimination devices and adjusting the humidity of the printing workshop

2. The impact of the doctor blade

the angle and pressure of the doctor blade also have a certain impact on the inking effect of prints. For example, the pressure 4 and digital electronic tensile testing machine of the doctor blade can be equipped with sensors of different specifications according to requirements. Excessive force is easy to cause incomplete printing of print points and text lines, and wear of printing plates; The pressure of the doctor blade is too small, and the ink on the printing plate cannot be scraped clean. The size of the scraping angle affects the depth of the ink layer, thus affecting the ink coverage. If the scraping angle is small, the scraping effect is weak, the printing ink layer is thick, the covering power is strong, and the gloss is good, but it is easy to scrape unclean, and the graphics and texts are blurred. You can appropriately increase the pressure of the doctor blade. During printing, the pressure and angle of the doctor blade should be determined according to the depth of the printing plate and the inking condition of the printed product

3. The influence of the surface quality of the printing plate

the wear of the printing plate surface usually leads to the light ink color of the field color block, uneven inking, unclear graphics and texts, and the phenomena of false imprinting and bottom exposure; If the surface of the printing plate is stained with oil and not cleaned, it will cause poor inking of the printing product. It is necessary to stop the machine and clean the plate with detergent before printing

the above lists some common factors of inaccurate printing. In actual production, we may encounter other situations. As long as we carefully observe, carefully analyze and discuss the problems, we can find out the root causes and solve them one by one

source: Printing Technology

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