Yellow ink gets very dirty

We normally run KCMY (yellow last). Our yellow INK has been getting very dirty lately...migration on our Komori L526?
I was wondering if anyone runs YKCM, or YCMK or some other order that lays down the yellow 1st and therefore it stays clean.

 

i dont run a komori, but i do every now and then clean all rollers with roller paste, clean all damper covers, or replace them, and then run opaque white on the press a couple of times, and clean that off until it stays white. This seems to work for a good few 1000 impressions

 

I am not familiar with Komori but there are two reasons I can think of for dirty yellow. If its the first one down, it has to be in the ink rollers, either there are some rollers not correctly set, or you need a better wash up procedure. We use a three step, seems to do pretty good, when we run white ink, it takes a bit more to get the tower cleaner but for the most part, it does good. A sneaky middle form roller is usually the culprit when we have problems. To sum it up, settings or rollers themselves, especially if Y is the first one down.

 

Thanks for the response, but I totally screwed up. We do NOT lay down the yellow 1st. We lay down KCMY (yellow last). I'm wondering if anyone has a solution for keeping the yellow clean when it's laid down last, or if your having luck running the Yellow 1st. Thanks.

 

Try running CMYK, this is how i have always done it, ive always been told that the cyan and magenta are the two critical colours. i also dont use a process black anymore and use a dense black. I once ran out of process so just used dense and i prefered it.

 

I run a Komori L640 and usually run KMCY. I've also had problems with yellow going dirty but it can be avoided by adding reducer to the yellow ink and running with slightly more damp on the yellow unit. If this doesn't help I've also found that using a different blanket can make a difference. I use mainly UV ink and prefer to use a quick release blanket but some blankets I've tried release the ink a bit too well and allow the darker colours to transfer onto the yellow plate and then back into the yellow rollers.

 

We don't run a lot of process color here and I don't know the reasons one would want to lay yellow down last, but if its a have to all the time, I'd get in contact with the ink manufacturer and talk to them about your tack level on the black. As a previous post stated, they use reducer, which forces yellow to lay down on the sheet, no tack to pull off other inks. This is what you want to do. If you have never had your inks formulated for running yellow last, your tack levels are wrong as the ink manufacturer may be setting em up for CMYK.

 

The only thing that will cause back trapping is wrong tack sequence as HPC has stated,sad how some people want to reinvent the wheel here.

 

Platgraph
Chances are your issue is the tac of the ink, I run KCMY, when other operators start getting dirty yellow it because they don't pick up the densitometer, and read the hardest colour to see with the human eye, the yellow. Only to find that the density is in the .70 -.80 range (on a coated sheet). That is too light, pick up the density to .95 - 1.05 and it makes all the difference.
Now are your inks a unitac or a sequence tac? Unitac any order, sequence tac you will have to contact your supplier to what colour sequence you should be running.
FSA

 

since ink tack is directly related to ink film thickness, with a thicker film of ink being less tacky, id suggest that your yellow ink is too strong!!! Try reducing the strength of the yellow ink with app. 15 to 20% of transparent white then bring job up to color and watch your yellow ink getting dirty problem go away. If it works then you need to either get a different ink set or have your ink supplier send in a yellow thats not as heavily pigmented so that you have to push a bit more. Also be sure that you have a little yellow ink flowing into your rollers in areas where there is no images inline with the fountain zones. You should always print color bars up to full density even if there is no image inline with them. This applies to ALL colors.

 

why not just try running C M Y K?

 

steve,
very often you will encounter jobs that can not be printed with black down last without going back to prepress and dropping out other colors. as an example.... a bold black typeface that runs through a solid yellow onto white paper. Even with the correct tack it will look much different when the typeface transitions from the solid yellow to the blank stock. Just one example

 

Solution!

Hi, I have probably the solution for you problem.
We are using UV color only in our webpress witch is a single tower press - 9 towers in total (One tower/unit for each color). When the press was new in 95` we startet with the most commond setup CMYK, but since we print wet in wet (drying at the end) we experienced that the yellow unit was poluted from the CM color unit after just some few productions. The yellow color went orange or green and infected the print of course. The highlights disaperd and the midtones awfull. Because of this we changed the setup to YCMK. Remark that our yellow color is specially made for this and is marked with "first unit". With this setup we clean our rollers only once a year, just for control. After our change in the setup we never experince troble with polution.

 

Tack can be an issue, but the release properties of the blanket have a huge impact on this. What kind of blankets are you using? A slow releasing blanket will cause all kinds of problems you wouldn't expect to see. If your blanket does not release quick enough, it will pull back the other colors and dirty up your yellow. If you can't use a better blanket due to cost reasons, try this- Take a rag and wipe regular household bleach on it. Then take a water rag and clean the bleach off. Bleach will seal the rubber surface and give it quicker release properties. I have done this in the past and found it works every time. Most ink made today is unitack or the tack is so close that you run into these problems because of the high speed of newer presses. The only way to get rid of dirtying yellow with tack spread is a 2-3 point tack spread between colors. Most ink companies will accommodate this, for a higher price per set. That I why I suggest the blankets.

 

In my experience, this is one of two things. 1. Your ink tack sequence is out of wack. Ask your ink manufacturer for the tack values of each color. 2. You are running your ink film thickness too heavy on the yellow. Reduce your density on the yellow if possible. If this is not possible, you need to go to your manufacturer. Start with investigating these two things and you should be headed in the right direction.

 

I'm not familiar with komori too. I think you should go in this progression CMYK. Good luck

 

agree with that I add trans white to yellow When running heavy black coverage also use a quicker relaese blanket helps

 

Hi,if you want to be sure you can check first rollers are they set up correctly and also you can try cleaning rollers with white ink or some cleaning paste for rollers.But sometimes dark colors can be transferred from blanket and over printing plate in the succeeding ink system and can contaminate light colors usually yellow (i have that kind of problem.) So you can raise dampening on light colors or increase yellow and use quality blanket.Also try different ink.

 

From all the advice I've seen Tack is very important. Strongest tack first unit, lightest tack last unit. You can lay jelly on peanut butter, not peanut butter on jelly. Pressures between rollers are also critical for thourgh wash ups. We run YMCK. We use GRACOL standards.