Post By glenncolorguy
Low dot gain on Komori Lithrone SX-29 6 color press
I completed a G7 calibration in early August, 2012 on our newly installed Komori Lithrone SX-29. The G7 calibration and subsequent verification runs were textbook to say the least. Now, in the last two weeks our dot gains on this press have dropped 5-6%, and of course there are color matching issues. Plate curve and desired dot on the plates has been confirmed, no change there. What do I need to test/check to alleviate this issue? Thank you.
Plate Sharpening and Wear
Have you check the plate for Image Wear ? at the end of the print run.
What do the 10/45/50 and 80% halftone areas on the Print Control Strip look like (KCMY) tones
I also recommend that you use GATF Star Targets
Last edited by Alois Senefelder; 10-01-2012 at 01:36 PM.
Originally Posted by Alois Senefelder
Plate wear is ok. I measured plates after the run and the readings are ok. Control strips look good. Other than the GATF Test Form we don't normally run the GATF Star Targets. Thank you.
Different paper? Ink tack? I see about that much difference between our medium and low tack inks. Makes for lots of head scratching when different raw materials get used and people expect the same results. Especially when three or four of them get changed at a time like happens here sometimes.
If your native press TVI has changed and you press team can't get it back to where it was then you have no choice but to adjust curves.
You may be able to skip a dedicated press run to fix this. Since your G7 verification run was good two months ago you should be able to use recent pull sheets to get back into G7 compliance using TVI adjustments. If you go this route keep in mind the TVI calculations in Curve may not match the readings from your console or handheld.
Simple ink transfer problem. Are you using UV or conventional inks? When you did the G7 certification did you measure any roller ink films?
Last edited by Green Printer; 10-01-2012 at 04:27 PM.
Check list: Did the ink change? Blankets, fountain solution, paper, rollers hardness. Did anything that was documented on your G7 run change? Sometimes vendors change raw materials without alerting the customer.
Try reading the plate screen before printing and make sure it matches your G7 run. Put it on press and measure screen values. Try changing one blanket and measure again. Sometimes there is invisible calcium build up on blankets that can change the dot. Make sure the blankets are cleaned with water every time.
Also check with prepress to make sure they are keeping up with their chemistry, sometimes the dot size may be correct but if the chemistry is in a different state than when you did your G7 run, you may have an issue.
If all of these things check out, it may be possible that you had something go astray in your G7 run. Blankets need to be torqued to the same ft. lbs every time, roller settings, roller temp, dirty grippers, stuck grippers, oscillating rollers on or off, chrome rollers cleaned properly. G7 test runs need to be documented thoroughly and your press has to be in good condition so you can achieve the same product every time. If you do this properly it makes trouble shooting much easier. If any of these items mentioned are changed from your original test run, you need to recalibrate. Something as simple as changing the blanket torque may change your dot size. Make sure you use a torque wrench every time and retorque blankets after a few thousand sheets.
Dot Gains Dropping on Press
<<in the last two weeks our dot gains on this press have dropped 5-6%, and of course there are color matching issues. Plate curve and desired dot on the plates has been confirmed, no change there. What do I need to test/check to alleviate this issue?>>
The problem with G7 runs and "Fingerprint" runs in general is that they are rarely typical and very commonly we find that real day-to-day press performance is quite different. Your press may have simply gone back to its normal performance profile. THe important thig is to provide the press with appropriate plate curves to keep it printing optimum results at all time. The only way to do this is to continually monitor dot gain and gray balance on press, and create plate curves that are appropriate for typical average press performance over time.