Film flexo printing is not yet very mature for domestic flexible packaging manufacturers. But in the long run, flexo printing technology has a lot of room for future development. This article summarizes twelve common problems and solutions in film flexo printing. for reference.
1. The adhesion of the imprint on the film is poor, and it is not resistant to rubbing and rubbing
Causes and handling opinions:
(1) The PE or PP film has no surface treatment or the surface treatment effect is not ideal, and the surface tension of the film is lower than (3.6 ～ 3.8) × 10-2N / m. Use the surface tension measuring liquid to detect the surface tension of the film. If it fails to meet the requirements, the surface treatment should be performed again.
(2) The ink is over diluted, the adhesive is destroyed, or the thinner is misused. Correctly select the thinner, and the viscosity of the ink should be controlled within 25 to 35 seconds.
(3) The adhesion of the ink itself to the film is not good. Change the ink type, or negotiate with the ink manufacturer to resolve.
2. Heap version
Causes and handling opinions:
(1) If there are impurities in the ink, the ink should be filtered or replaced with new ink.
(2) The ink is thick, and a certain amount of thinner can be added to adjust the viscosity of the ink to an appropriate value of 25 to 35 seconds.
(3) The ink dries too fast. Add an appropriate amount of slow-drying thinner to reduce the ink drying speed.
3. Change of pattern color
Causes and handling opinions:
(1) The viscosity of the ink changes. When diluting the ink, it should be stirred at the same time, so that the ink is fully dissolved in the solvent and controlled to the ideal viscosity. If conditions permit, mechanical circulation pumps can be added for better results.
(2) After using the ink for a period of time, add a thinner to reduce the ink concentration. The thinner should be added every 30 minutes or so. After adding 2 to 3 thinners, part of the original ink should be added and mixed evenly to avoid the decrease of the ink concentration.
4. Color mixing
Color mixing means that the latter color ink is contaminated by the color of the previous color ink, or the color diffuses and migrates.
Causes and handling opinions:
(1) The first color ink dries too slowly, or the second color ink dries too fast. Use the appropriate solvent according to the specific situation (the previous color ink must be dried thoroughly), or adjust the temperature of the heating system of each part.
(2) The viscosity of the ink is too high. Properly reduce ink viscosity.
(3) Influenced by the plasticizer in the film of the substrate. Understand the types and precautions of film plasticizers, and replace the film if not suitable.
(4) Improper pigments and dyes used in inks cause migration. The use of dye-based inks should be avoided as much as possible.
5. Rewinding and adhesion of printed materials
Causes and handling opinions:
(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, the fast-drying thinner can be added appropriately or the drying temperature can be increased appropriately to minimize the residual amount of solvent.
(2) If the rewinding tension is too large, the rewinding tension should be properly reduced.
(3) The temperature and humidity of the air are high during 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 when rewinding, or the cooling process is short, and the film is not sufficiently cooled. The drying temperature should not be set too high, or increase the cooling time.
6. The edges of the pattern are hairy, and irregular flashes appear around the imprint
Causes and handling opinions:
(1) The pressure between the ink transfer roller and the printing plate is not suitable, generally the pressure is too high. The pressure between the two should be adjusted appropriately.
(2) The ink has dried on the printing plate or anilox roller. Add a slow-drying thinner to the ink or cover the ink tank to reduce the evaporation of the solvent in the ink.
(3) The ink is thick. Control the ink viscosity at 25 to 35 seconds, or flexibly control the ink viscosity according to the printing conditions
(4) Due to the influence of static electricity, there are burrs and flash on the imprinted edges. Install a static elimination device, or add an appropriate amount of antistatic agent to the ink.
7. Sticky
Sticky dirt is the transfer of ink to the reverse side of the printed matter.
Causes and handling opinions:
(1) The drying property of the ink is poor. Switch to a faster drying ink type, or use a thinner with a faster evaporation rate to reduce the viscosity of the ink to an appropriate level, and check whether the temperature of the dryer and the air circulation between the inks of various colors are appropriate.
(2) Residual solvent in the blot. Adjust the drying temperature of the ink, or use a thinner with a faster volatilization rate to minimize the amount of residual solvent in the blot.
(3) The rewinding tension is too large. Appropriately reduce the rewinding tension.
(4) The film material with surface treatment on both sides is adopted, and the back side has good ink absorption. In single-sided printing, a single-sided film can be used to avoid unnecessary waste and printing failures.
(5) If sticky dirt still occurs after taking the above measures, anti-rubbing powder can be used.
8. Turtle pattern
Unwanted ideas and patterns appear in the printed pattern, or the solid pattern has wavy or small hole patterns.
Causes and handling opinions:
(1) The ink is thin and loses its viscosity. Adjust and control the viscosity of the ink according to the print requirements.
(2) The anilox roller is worn or the angle of the anilox is inappropriate, and the anilox roller should be replaced.
(3) The ratio of the number of lines of the anilox roller to the number of plates and screen lines is inappropriate. Replace the anilox roller with an appropriate number of lines.
9. There are pinholes or intermittent spots on the pattern
Causes and handling opinions:
(1) The surface of the film is not flat or the filler fineness of the film is not good. Replace the film or contact the 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 in time if it is seriously worn.
(4) The ink dries too quickly. Use a slow-drying thinner to dilute the ink viscosity to a suitable viscosity or increase the printing speed.
10. The printing ink is too light
Causes and handling opinions:
(1) The ink is too thin and the viscosity is too small. Add proper amount of original ink or linking material to adjust the viscosity and coloring power of the ink.
(2) The ink has dried on the anilox roller or the printing plate and cannot be transferred to the substrate. Add an appropriate amount of slow-drying thinner to reduce the ink drying speed.
(3) The ink is mixed with water or other incompatible substances, which destroys the performance of the ink. Change the ink, or add part of the original ink or a small amount of ester solvent to resume the printing after the performance of the ink returns to normal.
(4) The film surface has poor adsorption to ink. Check whether the ink type matches the film, or whether the surface tension of the film meets the printing requirements.
(5) The pressure between the anilox roller, plate cylinder and impression cylinder is inappropriate.
(6) The line number of the anilox roller is too high, and the amount of ink transfer is low.
11. Printing plate expansion and deformation
After printing for a period of time, the printing plate is deformed and softened, and the thickness of the printed pattern lines is not consistent before and after.
Causes and treatment suggestions: The thinner used is not compatible with the ink, or the ink with a high aromatic content is used. Alcohol-soluble or water-soluble inks and corresponding thinners suitable for flexographic printing should be used, and aromatic hydrocarbon solvents should be avoided as much as possible. If necessary, the dosage should be controlled at 3% to 5%.
12. Ink loses fluidity
Causes and handling opinions:
(1) The temperature of the warehouse where the ink is stored is low (below 0 ℃), and the ink freezes. Ink stored under low temperature conditions should be placed in an environment around 20 ° C and returned to temperature for one day and night before use.
(2) The indoor temperature and humidity are high, the solvent in the ink absorbs too much water, and the thixotropy increases. Control the temperature and humidity in the room, and add part of the original ink or ester solvent to restore the ink performance to normal.
(3) The type of thinner used is incorrect, the solvent evaporates, and the ink loses its balance, causing the resin to precipitate or decompose. Choose a suitable thinner according to the type of ink, or add a small amount of ester solvent. If the problem still cannot be solved, a new ink should be replaced.
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