magenta screen over blue solid?

when printing blue sky We get alot of streaking/ roller lines going across sheet in the center of the sheet. 28X40 in. We are doing art work as of sorts and the sky always shows a quite visable (im guessing water form) line all the way across sheet. The plate seems wet when unit is opened So i feel that the magenta screen isnt sitting on the cyan solid. Tried reversing magenta/cyan but then outher netural tones go south on us? Is it a fountain solution problem...rollers are set very well.

 

Measure the circumfrence of your water form - The distance from the lead of your sheet to the line you are getting, does this equal the circumfrence?

Run the sheet through with only the magenta deck on - If the line is still there then chances are its roller settings.

Normaly if you are getting back trap mottle via printing magenta screen over cyan solid, you will get a mottled effect over that entire coverage area, not just in one thin line. The mottle can be caused by fount / Ink, I know for certain when we ran K+E Novavite ink we had to run KMCY as magenta would never sit over cyan, be it screen or solid.

But our previous ink T+K TOKA best one, you could run either sequence with no problems.

 

First try backing off pressure. We have done this in the past and it worked.

....Also have a look at your form damper setting, reduce the nip line to as little as 3mm, this will reduce the bounce as the form falls into the cylinder gap causing lines on the sheet.

 

my first thought would be to change the units to print magenta then cyan. you may have to adjust color to suit. i print k,m,c,y, as my default sequence for that very reason!!! theres no reason you shouldnt be able to get pleasing color with that rotation.
if its not possible to do that id check for an overpacked blanket on all units. just because the streak winds up visable on 1 color it doesnt always mean that the color with the streak is the culprit. any unit after that color has been laid down can also cause that streak so you may want to verify that by printing the questionable color alone. if its not visable then you add impression to the following units one at a time in order of printing till youve isolated the problem. you could also start running the press at production speed and just stop the press dead with the stop button while still on impression. go down the line and pull the sheets out of the grippers whever you can and look at the unfinished image to isolate it that way.
good luck,
tom

 

Isolating the units would be my first attempt. Although, I've seen a job isolated and no streak in any one unit but you put them all together and wham!! This particular instance happened to be a pre press problem and was cured by changing the angle of the magenta screen. If you are 100% sure that it's not mechanical you might want to look into this. What other people are saying about the cylinder gap or diameter of the water form is always going to show up horizontally, not vertically. What do the streaks look like? And, what condition is your magenta blanket in?

 

does your company /prep dept put the solid sliders at the tail end with the color bar patches? sometimes those solid bars will repeat in the image , but yeah like print 101 said 3mm on the w/f stripe should help also and always check your settings to the vibrator , also like it was mentioned above less presure / less streaking....
steve

 

That problem is a mechanical ghost and is caused solely by the ink forms being plate driven and not roller driven by the oscillators. If you've checked the stripes and I'm mistaken, I would start at an ink and water balance. Is your companie's water R.O.'d

 

Lou is right you just have to try different things and find out what works for you , every press streaks , fact of life...I would also look at the blank stock cause now the paper we get to print on has streaks built into the finish!
also some ipa helps when they just wont go away....youll get it , let us know how you make out
steve