We have a Ryobi 525 press that has begun experiencing a considerable amount of Magenta back trapping into the Yellow unit and the fifth unit used primarily for varnish. We run an ink sequence of KCMY. We have tried many things to correct the problem but are not having much success. We did switch to a sequence of YCMK which works for the Yellow but as soon as we add the varnish back in the problem re-appears. We are being told that the ink tack is the most likely culprit but we have not changed anything on the press and we printed a job six months ago that printed just fine and this week we had issues on an exact reprint of this job with some yellow solid areas on the press sheet.

Could let me know if you have run into this problem and if so what did you find was the best solution? Any suggestions you can offer would be greatly appreciated.

BAck trapping is part of any print job and it is good to have it.
The problem could be the "stikiness" of the ink - any ink is "stiky" to a different level.
option A' - the BCMY is normaly good but you musy use the same ser' of ink to maintain the right connection between the inks. tell me what you use.
option B' - too much poressure - the next blanket takes off too much of the ink on the paper - check your pressure / paper thickness.
option C' - Too much emulsification (ink/water) - your press today is not the press you used 6 months ago ! , no . I am not wrong and I never seen you press...
since you printed that job 6 months ago , your printing rollers changed , you room temp could have changed , the humidity is not as it was (am i wrong?)
every thing has it's part.
you can call me - I will be happy to help you solve..

Hello, I have been running a 28' 6-color Akiyama for 18yrs. The press has 3 impression surfaces between unit 5&6 making transfer very fast. Have you changed the brand of plate you use about that time? Some plates run drier than other. Plates that run wetter will resist picking up ink from the blanket better. But like the person before me said, make sure you are not overpacked under your blanket. We have had some luck cutting the packing in the yello unit barely bigger than the crop marks. this keeps magenta from getting on yello blanket where not desired. Squeeze off meters on ends and turn water down though. Or if possible skip a unit between mag & yello. Good luck!

We overcame the problem we were having by switching inks with different tack ratings. We tried just switching the yellow & magenta in different combinations with no luck. When we switched all our process inks we saw a dramatic improvement.

if your magenta ink is backtrapping into your yellow its usually one of 2 things... either your yellow tack is too high or... your yellow ink film is too thin which would in effect cause your yellow tack to increase. thin ink films tend to be tackier than thicker ink films. a good test would be to add transparent white to your yellow so that you could effectively run more yellow. hope this helps you.

Your problem could be roller contamination.had the same problem with yellow back tracking cyan.probably built up over last 6 months since you did the job last.try decontaminating rollers.it worked for me.