Dear Mr.Cheng:
We should discuss the ECCO jobs on two aspects:
(A) Color measurement Readings:
The readings on L*a*b* and Delta E are good control of colors when a JOB is REPEATED on the same ink on the same printing process,e.g. OFFSET printing. In this case the color measurement can be manageable.The paper boards and OPV may make some difference,but adjustable.
When you change the process from OFFSET to Water-Based FLEXO ,the changes are to big: Firstly the ink pigments for Water-Based will behave very differently from that of OFFSET ink;
Secondly the thickness of ink-film are very different;
Thirdly the boards used for OFFSET are quite different with that of water-based as well.
On the fourth place, Grey color is a compound color comprises of many types of pigments ,absorb and reflect different wavelengths of light source.
No matter what sort of printing processes,all the colors will appear differently under different light sources.This behaviour make the comparisons of colors using different printing processes some more difficult to align-in to each other.
In conclusion,
With different printing processes,the color measurement of L*a*b* will be quite different ,especially on compound colors such as grey ,brown,dark blue etc.That is why you need to reset new values of L*a*b*. After this you can use these new values to control the FLEXO process.
We suggest for setting of FLEXO standard on this color,first thing you need to approve the color under a specific LIGHT source.And after that you can make new color measurement and record for future control.
(B) The slip of the carton:
We have instructed our In-Plant technician to lower the slip of OPV when you test the ECCO color again.
Hope the above explanation will be assistful to you.
Best regards,
C H Tan.