It is important to have a good quality flexo Plate in order to get a high quality print. To achieve this, the technician should be familiar with enough knowledge of the technical problems of the flexographic printing plates and how to solve them.
Here we list some of the common flexographic plates problems, its causes and their technical solutions.
- Problem: Undesired pattern when printing multiple colours
- Causes: Wrong screen angle of the separations; wrong ratio of anilox and printed line count; problems with cylinder rolling conditions
- Solutions: Confirm and correct screen angles. Ratio of anilox to printed line count should be minimum 5:1; optimise register; confirm cylinder rolling conditions
- Problem: Unoptimised ablation of the black mask (stripes, etc)
- Causes: Laser intensity too low; drum rotation not optimised; incorrect focus setting; beam issue in a multi-beam imaging system
- Solutions: Exact calibration of laser energy as well as drum rotation; confirmation and correction of focus setting
Missing or unstable highlight dots
- Problem: Missing or unstable highlight dots
- Causes: Insufficient bump up curve
- Solutions: Determination of the correct bump up values according to the line count, plate type and imaging system. All plate making parameters should remain constant
Missing highlight dots
- Problem: Missing highlight dots and dots tips
- Causes: Plate swelling as a result of aggressive ink or cleaners; unsuitable plate cleaning devices; insufficient polymer cross linking in combination with long washout times
- Solutions: Use suitable, lint-free and soft plate cleaning devices
Insufficient relief depth
- Problem: Insufficient relief depth; floor starts to print
- Causes: Too long back exposure in combination with too short plate processing
- Solutions: Confirmation and adjustment of plate processing parameters
- Problem: “Star shaped“ deep cracking in plate surface
- Causes: High ozone content during light finishing as a result of long UVC exposure, possibly in combination with mechanical stress on the polymer; high temperature in light finishing unit; plate was light finished while still too warm
- Solutions: Testing of UVA and UVC light finishing; confirm if ozone producing sources are present; confirmation if ventilation inside the light finisher is working properly; plate should be cooled down to room temperature prior to light finishing
This is the part one for this Flexographic plate troubleshooting – problems causes and solutions. Read our part two of this article to know all the remaining problems causes and solutions of flexographic plates.