Common problems and solutions in nine flexographic printing processes
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First, the color is too deep
1. Phenomenon: The color of the printed product is different from the original one, and it is deeper than the original.
2. Reason: (1) The viscosity of the ink is high. (2) The number of anilox rolls is low and the amount of ink stored is large. (3) High color content and high ink color saturation. (4) Plate making (networking point) problem. (5) The choice of substrate is not suitable. (6) The printing workshop is not constant temperature and humidity, which affects the use of ink.
3. Solution: (1) Reasonably add thinner to reduce viscosity. The amount of diluent added not only affects the viscosity of the ink, but also affects the color density of the print. (2) Reasonably replace or increase the number of anilox roller lines. (3) Add a thinner. (4) According to different substrates, the calibration value of the dots is generally increased or decreased. (5) The substrate is not the same as when it is actually produced. The surface of the substrate is smooth, there are no pits, the ink cannot be absorbed, and the ink layer remaining on the surface is thick. The relative reflection density is large, and the printed matter is darker in color. (6) Maintain constant temperature and humidity to ensure viscosity.
Second, stripes or spots
1. Phenomenon: Undesirable spots of light or dark color are present on the roll.
2. Reason: (1) The reticulated roller has no ink on the part. (2) The printing plate is not flat and the ink is uneven. (3) Bubbles are formed during the printing process; the ink splashes onto the material to be printed. (4) The ink is too thin. (5) Ink viscosity is poor. (6) The thickness of the substrate is uneven. (7) The embossing roller is damaged or stuck with dirt.
3. Solution: (1) Clean the anilox roller or check the ink volume. If it is insufficient, please add enough. (2) Check the printing plate, and check the unevenness from the ink to the ink supply. (3) Add an antifoaming agent to the ink. (4) Check the ink fountain cover, ink tube connector, ink tank to prevent excessive flow and leakage of ink. (5) Add new ink. (6) Increase the viscosity and replace the thin and uniform substrate. (7) Check the impression cylinder, replace it, and remove dirt.
Third, the ink is too weak or too thin and too shallow
1. Phenomenon: The ink color intensity is too low and too shallow. Ink saturation is insufficient and color density is insufficient.
2. Reasons: (1) too much solvent or too low viscosity, affecting the ability to drive pigments. (2) The anilox roller is worn or not cleaned and has a hole blocking phenomenon. (3) The ink is unevenly stirred and settled, the coloring power is insufficient, and the pigment is dispersed. (4) The hardness of the printing plate is not suitable, the number of the anilox roller lines is too high, and the amount of ink is not enough. (5) The ink roller is not properly adjusted, and the printing pressure is too small. (6) In the transfer process of the ink, the use of the ink transfer roller is improper. (7) In the aqueous ink, the volatile compound exceeds the standard and the ink layer is thin. (8) The printability of the substrate is poor. (9) There are too many ink thinners. (10) The viscosity of the ink is too high, resulting in poor transfer.
3. Solution: (1) Add new ink and adjust to the proper viscosity. (2) Replace the old roller with a new or re-engraved anilox roller. (3) The ink taken out of the tub is sufficiently stirred before being added to the fountain. (4) Replace the appropriate one. (5) Reduce the number of netting lines, adjust the ink roller, and attach too much ink to the net roller to increase the printing pressure. (6) Replace the ink transfer roller (using low hardness) that matches the material to be printed. (7) Volatile compounds exceed 3%. (8) Select the substrate according to the requirements of the printed product. The paper with strong ink absorption is selected, and the ink layer remaining on the surface of the paper during printing is thin, so the reflection density is low and the printed product is light in color. It is generally considered that the thickness of the lithographic ink layer is 1-2 μm, the thickness of the flexographic ink layer is 2-5 μm, and the thickness of the concave ink layer is 10 μm, which satisfies the printing requirements. (9) Re-adjust the ink. (10) Reasonably adjust the viscosity of the ink.
Fourth, the outline is not clear during the printing process
1. Phenomenon: The edges of the pattern are blurred.
2. Reason; (1) printing pressure is too large. (2) The viscosity of the ink is too low. (3) The quality of the printing plate is poor. (4) The main color ink contains other color inks. (5) The printing ink is dried too fast. (6) The machine speed is too low and the room temperature is high.
3. Solution: (1) Use proper pressure and the correct double-sided tape. (2) Increase the viscosity of the ink. (3) Re-plate. (4) Replace with new ink. (5) Reasonable adjustment. (6) Maintain constant temperature and humidity and increase machine speed.
Fifth, small words are not clear
1. Phenomenon: Small prints and fine dots are not clear (fuzzy).
2. Reasons: (1) The plate is too hard, and the clarity or flatness is not good. (2) The ink is poor and the fineness is not enough. (3) The solvent formulation is improper, the volatilization is too fast, the ink transfer is unstable, and the machine speed is slow. (4) Printing operation problems (insufficient or inconsistent pressure). (5) The picture is too thick and blurred. (6) The surface of the substrate is rough and the ink absorption is strong. (7) The accuracy of the overprinting of the machine is not enough, so that the overprinting accuracy of the female type is poor. (8) The paste is inaccurate, the thickness of the double-sided adhesive is not uniform, or there are bubbles when the plate is applied. (9) The ink is not cleaned and dried in the groove of the anilox roll. (10) The viscosity of the ink is large and the transfer is uneven (at a constant temperature).
3. Solution: (1) Re-plate, so that the ink is even. (2) Replace the ink and measure with a 50mm fineness scraper. (3) Adjust the solvent formulation. (4) Pay attention to correct operation. (5) Adjust the amount of ink. (6) Replace the substrate to minimize the diffusion of ink and improve the surface roughness. (7) Check and adjust so that the circle jump is less than 0.015mm, the parallel level is less than 0.03mm, and the overprinting accuracy is within 0.1mm, so that the diffusion plate forming version is qualified. (8) Check and correct. Replace the adhesive tape and carefully stick the plate according to the operating procedures. (9) Clean and clean. (10) Reasonable adjustment to promote transfer. [FS:PAGE]
Sixth, overprinting on the spot color gold and silver ink is not true
1. Phenomenon: After the gold and silver ink is printed, the spot color ink can still be seen.
2. Reasons: (1) The gold ink layer is thick, the amount of ink stored is large, it is not easy to dry, and the viscosity is large. (2) The printing pressure is large and the ink is formed. (3) The amount of ink transferred is small, and the ink layer is not thick enough. (4) The fineness of the gold ink is not enough, the quality of the connecting material is not good, and the quality of the ink is problematic. (5) The surface of the paper is rough. (6) The time interval between the printed base color and the printed gold and silver ink is too long. (7) The surface tensions of the two inks differ greatly, and the above ink (gold ink) pigment cannot uniformly cover the underlying ink layer.
3. Solution: (1) Add a quick-drying solvent to the gold ink, and use a slow-drying agent for the spot color. If the printing effect is not affected, the viscosity of the ink should be as moderate as possible. Large area printing of gold should reduce the speed of the machine and increase the drying time of the ink. (2) The adjustment is reasonable. (3) In order to enhance the metallic sense, the gold and silver ink is printed with full and thick light, and the viscosity of the printed real-time gold and silver ink should be slightly larger, but the dot or fine line should be similar to the ordinary ink. (4) Exchange other supplier inks. (5) Process or exchange. (6) The time cannot be separated too long and is printed without the bottom ink being dry. (7) Corona treatment can be added, the surface tension value can be changed, the adhesion can be improved, and the viscosity of the second color can be lowered. The spot color ink can be hollowed out to enhance metal adhesion.
Seventh, graphic distortion or incomplete
1. Phenomenon: The dots and texts are not printed.
2. Reason: (1) The roundness of the roller is not enough. (2) The surface of the roller is dirty and not smooth. (3) The pressure at both ends is not balanced. (4) The substrate is wrinkled or the tension is not suitable, the smoothness is poor, and the fibers are unevenly arranged. (5) The ink roller in the ink fountain does not rotate. (6) The ink viscosity is too high and the fluidity is poor. (7) The ink volatilizes too fast, the ink transfer roller absorbs less ink, the ink supply is insufficient, and the printing transfer is incomplete. (8) The quality of the printing plate is poor (the ozone concentration is too high, and the local unevenness). (9) The unevenness of the printing plate makes the graphic deformation after the embossing, the printing plate is repeatedly peeled off, the printing plate itself is deformed, and the printed graphic is deformed. (10) The plate diameter is selected incorrectly, causing the plate to deform greatly. The flexographic plate is a highly flexible plate that, when mounted on a plate roll, necessarily affects the image, graphics and text on the surface of the plate. The printed product does not correctly reproduce the original and may even be severely deformed.
3. Solution: (1) Replace the qualified roller. (2) Cleaning. (3) Adjust the pressure. When the printing pressure is too small, the transfer of printed graphics is not complete. The outlets are unreal, the color is gray, and the original defects of the printing plates and papers are more exposed. When the printing pressure is too large, the graphic lines will be distorted and the print will be enlarged. Compared with the normal pressure friction condition, the printing plate wear is increased, the printing durability is reduced, the machine load is increased, the power consumption is also increased, and the printing portion is more resistant, which affects the working life of the parts. . (4) Replace the printing material. (5) Adjust to make it flexible. (6) Adjust the viscosity in an appropriate amount. (7) Adjust the ink. (8) Reasonable ink transmission. (9) Strictly check the flatness and the integrity of the graphic. Image-based products should be checked or considered from the original, from image to tone, level, color, sharpness and stereoscopic effect. The text is mainly based on the text, the layout rules, and the uniformity of the ink. an examination. The plate maker recalculated the deformation rate and re-applied. (10) When the plate standard is correct, try to choose the standard, correct double-sided adhesive tape, plate roller diameter.
Eighth, water pattern
1. Phenomenon: In the direction of the paper, there is obvious ink transfer pattern and uneven printing.
2. Reasons: (1) The surface of the substrate is not flat and has a paper grain. (2) The ink has low viscosity, thinness and poor hiding power. (3) Poor ink fluidity. (4) There is a problem in the production of mesh on the surface of the net roll. (5) The amount of ink is too large, and the paper cannot be transferred, absorbed, and deposited on the surface of the substrate. (6) The problem of making the plate. (7) The mesh roller is too dirty.
3. Solution: (1) calendering, improve smoothness or change paper. (2) Add the original ink to increase the viscosity and color density. (3) Use a good fluidity ink. (4) Replacement of the manufacturer. (5) Change (reduce) the amount of ink or switch to two passes. (6) The replacement plate (7) must be cleaned.
Ninth, dry version
1. Phenomenon: During the process of printing ink, the pattern is blurred, the small characters are incomplete, the printed land is uneven, and the ink is dried on the printing plate.
2. Reason: (1) The machine speed is too low. (2) There is no cleaning plate after the machine is stopped or the printing plate is not regularly and irregularly printed during the printing process. (3) The ink is dried too fast. (4) The evaporation of ink exceeds the standard and the pH value decreases.
3. Solution: (1) Increase the speed of the machine appropriately. (2) Clean the printing plate or clean the printing plate at regular intervals and irregularly after the machine is stopped. (3) Add appropriate amount of slow-drying agent to adjust. (4) Add an appropriate amount of stabilizer to adjust the pH.