Before a flexographic job is printed, a number of factors need to be checked to ensure accuracy. Make ready on a flexographic press includes installation of the required plate cylinders and inks, setting levels for impression and ink pressure, register adjustment, and any setup for inline finishing, such as cutting, folding, or gluing. Pressure levels are particularly critical for accurate printing. Finally, after press adjustments are complete, the press operator checks colors for the job, running a sample at (or near) production speeds. Designers should also make sure to perform a press check for the first actual print run. Here is a list of flexo prepress check you should do .
These are some of the elements that should be verified prior to printing.
|Is the point size and font correct? Is the typography what was expected? Has plate elongation affected leading, letter spacing, or word spacing?|
|Have all of the images elongated and reproduced accurately?|
|Internal (color to color) and external (images to die-cut, sealing areas, perforations, etc.) If all colors have been accurately distorted, and the plates accurately mounted, the job should be in register.|
|Have plate mounting and plate elongation maintained accurate trap areas?|
|Have the bar codes been positioned to allow proper open area surrounding the code for scanning? Has the bar code been positioned with the bars parallel or perpendicular to the web direction? When mounted perpendicular to the web direction, bar codes will be affected by plate elongation.|
|Has the job been set-up to print in the right direction on press? Will the print direction match the packaging or labeling operation?|
What to Look For During a Flexo Press Check ?
Is the type sharp? Has the weight of the type changed? With a loupe, look for outline halos.
Are the colors in register? Make sure colors line up and check areas where inconsistent elongation may have caused misregistration. For a four-color process with traditional screening, color-to-color register should not vary by more than a single row of halftone dots.
Is the density of the color appropriate, especially in situations where screens and solids are printing from the same cylinder? Is the color strength consistent from side to side?
Do spot colors match? Each color should be verified under 5000° Kelvin lighting conditions. When appropriate, use color measurement instruments to verify acceptable match.
Is the ink laydown consistent, without mottle? Are there pinholes or voids? Under a loupe, halftone dots should appear sharp, not slurred.
Is the width, caliper, and type of substrate as specified? If the substrate is an opaque film, is the opacity appropriate?
External Register :
Does the print line-up with the specified finishing operation, such as diecuts, sideseals, slots, scores, and glue areas? Request a mock-up container to check accuracy of external register.
Ink and Impression Levels:
Look at the edges of solids for an outline halo, which is the result of excess ink or impression pressure. The press operator may be able to relieve some pressure; some plates may have spot color inaccuracies that require a plate remake or remount.
Dot Gain :
Dot gain levels should be comparable to those achieved
during fingerprint trial.
UPC and Bar Coding:
Over-impression can change the width of bars and spaces, potentially making the bar code unreadable
Has the job been installed in the right direction on press? If the press is running roll-to-roll, is the print rewind in the proper direction?