Production and Resolution of Flexo Printing Inks

First, the phenomenon of ink bars <br> In the printing of a large area of ​​the ground or flat screen, the printed products (the direction of the horizontal and the paper have 90 °) showed a deep trace of ink. Seriously affected the image color reproduction. Divided into regular and irregular.
1. Arrange fine lines along the axial direction of the plate cylinder (regularly, gear bars).
2. There is a regular ink bar or multiple ink bars when printing.
3, no regular movement when printing.

Second, the reasons for the production of ink bars

1. As the gears are worn for a long time, the gap is enlarged, and there are various errors such as tooth shape, tooth direction and tooth surface smoothness. After the pressure is combined, there are gaps between the gears, and chattering and collision will occur during operation, causing mechanical vibration; The meshing clearance is too large, the speed is low, and a serious collision occurs during the transmission, causing the plate cylinder to rotate suddenly. Loss of continuity does not work smoothly. In this way, the surface of the printing plate and the substrate is abraded so that the dot is enlarged and elongated into an ellipse to produce an isometric ink bar. A standard new gear has a roughness that does not meet the standard. Unacceptable gears must be vibrated during meshing to affect the equilibrium of the image transfer process. The radial runout influences the correct meshing of the gears on the pitch circle, which affects the smoothness and uniformity of the transmission. If the tooth shape tolerances are not qualified, the machine will vibrate during the gearing process and the drive balance between the rollers will be damaged. There is a problem with gear assembly. The tooth-to-tooth contact area is not up to standard, and the load distribution is not uniform. The use of double-sided adhesive is improper. There are problems with the plate design: First, there is no balance line. The second is that the printing roller has a wide and long bar in the horizontal direction and it is easy to cause machine vibration; the pressure is too heavy, and the gear produces a greater impact shock during printing, resulting in an ink bar, the heavier the pressure, the greater the friction. The easier it is to spread the imprints, expand the outlets, and create an ink bar. As time goes by, the elasticity of the plate disappears; when designing the printed gear, the choice of the gear module is wrong. Among the various parameters of the gear, the module mainly relates to the tooth profile strength of the gear, and also relates to the smoothness of the transmission. The smoothness of the gear transmission is reflected in the degree of transmission overlap. During transmission, the greater the degree of coincidence, the greater the number of teeth involved in engagement and the more balanced the drive. For the printing press, the actual load is not large, and it should mainly take care of the balance of the transmission; the pressure angle of the design is wrong, and the size of the pressure angle affects the tooth profile of the gear. When the pressure angle is large, the radius of curvature of the tooth profile is large; when the pressure angle is small, the overall profile of the tooth profile is relatively flat. The radius of curvature is small and the meshing part is enlarged; the diameter of the plate cylinder is selected too small, and the degree of coincidence of the gear meshing area is small.

2. If the cutting edge is too high, the whole machine will vibrate when rotating; the high part of the printing plate butt joint (fixed position) or the plate butt gap is too large. Sticky tape joints overlap; foreign objects or gear vibrations on the surface of the anilox roll will cause the squeegee to pulsate during operation, creating a thick ink area on the roller and printing plate; improper pressure adjustment, whether positive pressure or If the side pressure is too large, it will make the gap of the printing plate mouth collide with the anilox roller or the embossing roller to collide with it to generate ink bars; the engraving of the web roller is mistaken and the ink arrangement is wrong; the surface of the plate cylinder or the embossing roller is beating Large, causing pressure suddenly large and small. The amount of ink transferred to the substrate increases; there is a foreign matter between the gears, which causes the two rollers to jump when they mesh, and the imprint force suddenly produces small ink bars; the printing plate is pressed before printing, and the local deformation may have a large amount of ink. Ink roller and plate did not come off after shutting down. The ink roller rotates, damages the printing plate, causes the ink volume to be non-uniform; The balance line breaks cause the vibration; The quality of the plate-making film or the rinsing exposure is uneven; The plate roller balance precision is not up to standard; The gear (public line) processing has the error adjacent node The distance between them will make the plate roller surface line speed and paper movement speed uneven, resulting in relative slip between the printing plate and paper, the dot is elongated along the paper moving direction (ellipse) and the distal hair The doctor blade vibrates when the anilox roller causes blistering to cause rotation. Chromium oxide ceramics are inactive and do not react with chemical agents. Corrosion foaming is therefore usually the result of a chemical reaction with the base material. If the new ink roller or the reprocessed ink roller shows partial blistering within several weeks, it can be considered that the long-term use of the ink or paint causes the base roll steel of the roll to be incompatible with the base layer of the sprayed layer. Caused. In general, the pH of the substance causing the corrosion reaction is either very large or very small (more than 12 to 14 and less than 3 to 5).

3, the adhesive glue bubbles are not eliminated, so that the printing plate is uneven and higher than the pressure; the pressure is normal (fluctuation, deflation) plate roller working jitter; machine running is not uniform, high speed plate roller centrifugal force increased , Rotational meshing is not good, gears, squeegee dither with uneven ink; the accuracy of the embossing cylinder (including gear common line, round runout, hardness, bearing) is lost or damaged; imprinting roller is not clean, with some dirt ,Thickening of the substrate, the accumulation of errors in the operation; plate roller reciprocating motion and the stability of the work is poor; three roller bearing wear, affected by sudden pressure vibration.

Third, the solution to the "melancholia" phenomenon

1, to ensure the accuracy and position of the various components of the machine drive system, do not make it excessive wear, especially pay attention to the plate roller and the embossing roller gear; precise adjustment of the printing pressure, as far as possible to make two gears in the pitch circle or Engaging work in the vicinity of it, the pressure in the printing area can be large (reducing the backlash), and the pressure of the printing dots can be small. At the same time, balance lines are adopted on both sides of the layout to ensure smooth pressure for good operation. Strictly speaking, a refined gear When meshing on the pitch circle, if the printing plate is selected, the selection of the paper thickness is extremely limited in order to make the printing pressure appropriate. Appropriately increase the speed of the machine because the gears operate more smoothly due to centrifugal force at high speeds. Many prints have ink bars at low speeds, but they tend to turn better or disappear at high speeds. The smoothness of different speeds is different; all the red Dan powder is applied to the tooth surface, and the roller is inspected (liquid state, large viscosity). The gear must be in high-precision meshing state during movement. With white corundum grinding paste with a uniform load of grinding and polishing, to improve the tooth surface finish, so that friction resistance is small, to eliminate chatter. (Rough grinding with 280#4h, fine grinding with W40-W7, depending on the time). The use of ultra-high viscosity gear lubricants can reduce the (vibration) friction between the plate cylinder and the impression cylinder gears; replace the gears. Reassembly, contact spots, tooth height not less than 45%, tooth length not less than 65%. Make the gear load distribution evenly; Adopt the low density double-sided glue, will play the role of buffering the vibration; Add the balance line. Re-typed design originals, the ideal pattern should be slashes, curves, wavy lines and so on. At the same time to avoid large areas of the field and the small print, dot on a plate; reasonable adjustment of pressure; on the premise of ensuring gear strength and wear resistance, the appropriate design of a small module gear, select the appropriate tooth width and helix angle, you can get the actual The required overlap factor. On the basis of proper selection of the modulus, the appropriate degree of coincidence is designed to reduce the contact stress of the gears, improve the wear resistance of the gears, and avoid the tooth shape error caused by the gear wear, and thus the associated influence. The smoothness and accuracy of the drive during printing result in unstable print quality. Selecting a smaller pressure angle increases the degree of meshing engagement, increases the number of engaged teeth, and improves the smoothness of the drive. At the same time, the slight selection of the pressure angle is appropriate, and the change in the backlash caused by the change in the center distance is smaller, so the impact on the smoothness of the drive will be smaller. A reasonable increase in the diameter of the roller will increase the meshing area of ​​the gear.

2, carefully adjust the adhesive re-adhesion, carefully adjust the pressure. When a plate is attached to a stencil, the surface of the plate becomes longer due to circumferential stretching. Different types of plates will have their own fixed extension values ​​due to their different thicknesses. When the flexographic printing film is used for color separation, according to the size of the web, it has already been subjected to different ratios of one-direction reduction in the direction of paper feeding. Therefore, it is necessary to cut according to the reduced size when loading the printing plate before printing so that the plate can be attached to the printing plate. On the platen, the butt joints are seamless and smooth and do not overlap or leave large gaps at the joints. Therefore, when cutting, the cutting length should be accurately calculated. Such as: 1.7mm version, fixed extension coefficient of 9.9, film shrinkage rate = (9.9/printing roller circumference)%, plate version ratio = (1-9.9/printing roller circumference)%, plate length = version Roller circumference × printing plate miniature rate, actual cut more than 0.5mm when cutting; timely cleaning inspection; reasonably adjust the pressure and tighten; replace the anilox roller. Engraving reworked ceramic anilox roller to make it have the ideal characteristics The ink hole wall thickness is small, stable and flat, the ink hole shape and size is consistent and has a smooth bowl-shaped ink hole, so that it can ensure that the ink film thickness is stable when the ink is transmitted. No change; find manufacturers or machine maintenance workers to detect, replace the qualified; remove the root residue; check the movement parts to qualified or replace the printing plate; the balance line is filled; negotiated with the plate maker; balance test roller surface weight ≤ 30g; check the common normal variation of gear ≤ 0.025mm; check the cause and replace the manufacturer. If it is not possible to remove or replace substances that are likely to cause corrosion reactions, the base material can also be replaced. Stainless steel is the most common anti-corrosion material used on the texture roller.

3, re-post or needle exhaust; use to the standard, maintain the correct pneumatic pressure, work can not fluctuate or have a leak; adjust the speed, maintain uniformity; can stop the machine to check the accuracy of the imprint roller gear; clean; check , tightening, increase stability; check the imprinting roller, plate roller, such as mesh roller bearings will be replaced.

(Author/Li Xinsheng)

Guangdong packaging