These 12 problems are common in film flexo printing
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In the long run, the development of flexographic technology in the future is very large. This article summarizes twelve common problems and solutions for film flexo printing. for reference.
1. The adhesion on the film is poor, and it is not resistant to rubbing and rubbing.
Causes and treatment comments:
(1) The PE or PP film has no surface treatment or surface treatment effect, and the surface tension of the film is lower than (3.6 to 3.8) × 10-2 N/m. The surface tension of the film is measured by a surface tension measuring liquid, and if it is not required, it should be resurfaced.
(2) The ink is excessively diluted, the binder is destroyed, or the diluent is misused. The diluent should be selected correctly, and the viscosity of the ink should be controlled at 25 to 35 seconds.
(3) The adhesion of the ink itself to the film is not good. Replace the ink type or negotiate with the ink manufacturer.
2. Heap version
Causes and treatment comments:
(1) There are impurities in the ink, and the ink should be filtered or replaced with a new one.
(2) The ink is thicker, and a certain amount of diluent can be added to adjust the viscosity of the ink to a suitable value of 25 to 35 seconds.
(3) The ink is dried too fast. Add an appropriate amount of slow drying diluent to reduce the drying speed of the ink.
3. The pattern color changes
Causes and treatment comments:
(1) The viscosity of the ink changes. When diluting the ink, stir it while stirring, so that the ink is fully dissolved in the solvent and controlled to the desired viscosity. If there are conditions, mechanical circulation pump can be added, the effect is better.
(2) After the ink is used for a period of time, a diluent is added to lower the ink concentration. The diluent should be added every 30 minutes or so. After adding 2 to 3 times of thinner, add some of the original ink and stir evenly to avoid the concentration of the ink.
4. Color mixing
The color mixture is the color of the ink of the previous color, or the color is diffused and migrated.
Causes and treatment comments:
(1) The previous color ink dries too slowly, or the latter color ink dries too quickly. Use a suitable solvent (the previous color of the ink must be thoroughly dried) or adjust the temperature of the heating system at each location.
(2) The ink viscosity is high. Appropriately reduce the viscosity of the ink.
(3) Influenced by plasticizer in the film of the substrate. Understand the variety of plasticizers, precautions, etc., if it is not suitable, replace the film.
(4) Improper pigments and dyes used in the ink cause migration. Ink that is produced from dyes should be avoided as much as possible.
5. The rewinding of the printed matter
Causes and treatment comments:
(1) The drying speed of the ink is slow, and there are many residual solvents in the printed matter. To adjust the drying speed of the ink, a quick-drying diluent may be added as appropriate or the drying temperature may be appropriately increased to minimize the residual amount of the solvent.
(2) If the tension of the rewinding is too large, the rewinding tension should be appropriately reduced.
(3) The temperature and humidity of the air are high when rewinding.
(4) If the drying temperature is too high, the surface temperature of the film is too high, the accumulated heat cannot be diffused in time during rewinding, or the cooling process is short, and the film cooling is insufficient. The drying temperature should not be set too high, or the cooling time should be lengthened.
6. The edge of the pattern hairs, irregular flash around the print
Causes and treatment comments:
(1) The pressure between the transfer roller and the printing plate is not suitable, and the pressure is generally too large. The pressure between the two should be properly adjusted.
(2) The ink has dried on the plate or anilox roll. A slow drying diluent is added to the ink or the ink tank is capped to reduce evaporation of the solvent in the ink.
(3) The ink is thick. Adjust the ink viscosity to 25 to 35 seconds, or flexibly control the ink viscosity according to the printing conditions.
(4) There are burrs and flash edges on the edges of the print due to the influence of static electricity. Install a static elimination device or add an appropriate amount of antistatic agent to the ink.
7. Sticky
Sticky ink is transferred to the reverse side of the print.
Causes and treatment comments:
(1) The ink is poor in drying property. Change the ink type with faster drying, or use a thinner with faster evaporation to reduce the viscosity of the ink to a suitable level, and check whether the dryer temperature and air circulation between the inks of each color are appropriate.
(2) Residual solvent in the blot. Adjust the drying temperature of the ink, or switch to a thinner with a faster evaporation rate to minimize the amount of residual solvent in the print.
(3) The rewinding tension is too large. Appropriately reduce the rewinding tension.
(4) The film material which has been surface-treated on both sides is used, and the back side has good adsorption to the ink. A single-sided film can be used for single-sided printing to avoid unnecessary waste and cause printing failure.
(5) If the sticky phenomenon occurs after taking the above measures, anti-mite powder can be used.
8. Moiré
There are dots, patterns, or wavy or small hole patterns in the printed pattern.
Causes and treatment comments:
(1) The ink is thin and loses its viscosity. Adjust and control ink viscosity according to print requirements.
(2) The anilox roller is worn or the angle of the cable is not suitable. The anilox roller should be replaced.
(3) The ratio of the number of lines of the anilox roller to the number of screen-added screens is not appropriate, and the anilox roller suitable for the number of screen lines is replaced.
9. There are pinholes or intermittent spots on the pattern
Causes and treatment comments:
(1) The surface of the film is not flat or the filler of the film is not fine. Replace the film or contact your supplier.
(2) The ink does not form a continuous ink film. Increase the thickness of the ink film, or increase the printing pressure. If it still cannot be solved, it should be negotiated with the ink supplier.
(3) The impression cylinder is dirty or the anilox roller is worn. Clean the impression cylinder, check the anilox roller and plate cylinder, and replace it if it is severely worn.
(4) The ink dries too quickly. Use a slow drying diluent to dilute the ink to the proper viscosity or increase the printing speed.
10. Printing ink is too light
Causes and treatment comments:
(1) The ink is too thin and the viscosity is too small. Add appropriate amount of raw ink or binder to adjust the viscosity and tinting strength of the ink.
(2) The ink has dried on the anilox roll or plate and is not transferred to the substrate. Add an appropriate amount of slow drying diluent to reduce the drying speed of the ink.
(3) The ink is mixed with water or other immiscible substances, which destroys the performance of the ink. Replace the ink, or add some of the original ink or a small amount of ester solvent to restore the performance of the ink before continuing printing.
(4) The surface of the film has poor adsorption to the ink. Check that the ink type matches the film or if the film surface tension meets the printing requirements.
(5) The pressure between the anilox roller, the plate cylinder, and the impression cylinder is not suitable.
(6) The number of anilox rolls is too high and the amount of ink transferred is low.
11. The plate expansion, deformation
After printing for a period of time, the printing plate is deformed and softened, and the thickness of the printed pattern is inconsistent.
Causes and treatment suggestions: The diluent used is not compatible with the ink, or the ink with a higher aromatic content is used. Alcohol-soluble or water-soluble inks compatible with flexographic printing and corresponding diluents should be used to avoid the use of aromatic solvents. If necessary, the dosage should be controlled at 3% to 5%.
12. The ink loses mobility
Causes and treatment comments:
(1) The temperature of the storage room where the ink is stored is low (less than 0 ° C), and the ink is frozen. The ink stored under low temperature conditions should be placed in an environment of about 20 ° C for a day and night before use.
(2) The indoor temperature and humidity are high, the solvent in the ink absorbs excess water, and the thixotropic property increases. Control the temperature and humidity in the room, and add some original ink or ester solvent to restore the ink performance.
(3) The type of diluent used is incorrect, the solvent evaporates, and the ink loses balance, causing the resin to precipitate or decompose. Choose a suitable diluent according to the type of ink, or add a small amount of ester solvent. If the problem is still not solved, replace it with a new one.