Cyan Mottling when printing before magenta help

[kwikford]

Hello, we are running TKS 6000's and have run into a problem of potential mottling. Our color sequence is C-M-Y-K and lately the cyan looks washed out and grainy when we are running a screened two color overlay consisting of cyan and magenta. We are thinking it might be back trap mottling and will be doing a test here soon but I had one question. With back trap mottling would you have your cyan ink train looking contaminated with fine dust? We have set the rollers, changed blankets and nothing has changed, checked conductivity,etc. Any help is appreciated.

thank you

 

[Kaoticor]

I am probably not understanding your question right... You say when the cyan is printed over a Magenta image, it looks washed out and grainy. But didn't you say that you are printing cyan first?

 

[kwikford]

I rewrote my original post but when we run a screened overlay of cyan and magenta, the cyan looks terrible. The cyan plates have a fine dust like appearance and the cyan ink train looks grainy. Sorry about the confusion, wrote the post before I had my coffee.

 

[gordo]

I rewrote my original post but when we run a screened overlay of cyan and magenta, the cyan looks terrible. The cyan plates have a fine dust like appearance and the cyan ink train looks grainy. Sorry about the confusion, wrote the post before I had my coffee.

It's still not clear. Your ink sequence is CMYK yes?
So magenta prints on top of cyan.
Is the cyan by itself looking terrible?
What does magenta have to do with the cyan problem? Is the magenta printing on top of cyan making the cyan look terrible?

best, gordo

 

[kwikford]

It's still not clear. Your ink sequence is CMYK yes?
So magenta prints on top of cyan.
Is the cyan by itself looking terrible?
What does magenta have to do with the cyan problem? Is the magenta printing on top of cyan making the cyan look terrible?

best, gordo

The best way I can describe this is when we run a deep purple ad, the cyan looks like it is washed out. Turning down the water helps a little but not enough. The cyan ink train looks dusty. thanks, John

 

[J]

Originally Posted by gordo
It's still not clear. Your ink sequence is CMYK yes?
So magenta prints on top of cyan.
Is the cyan by itself looking terrible?
What does magenta have to do with the cyan problem? Is the magenta printing on top of cyan making the cyan look terrible?

best, gordo

The best way I can describe this is when we run a deep purple ad, the cyan looks like it is washed out. Turning down the water helps a little but not enough. The cyan ink train looks dusty. thanks, John

If you're hoping for some help, why don't you simply start by answering the questions you've been asked?

J

 

[kwikford]

Originally Posted by gordo
It's still not clear. Your ink sequence is CMYK yes?
So magenta prints on top of cyan.
Is the cyan by itself looking terrible?
What does magenta have to do with the cyan problem? Is the magenta printing on top of cyan making the cyan look terrible?



J - good point. here we go:

Our sequence is CMYK so yes the magenta prints on top of the cyan. The cyan by itself looks good but looks bad when the magenta is printed on top of the cyan. Any help is appreciated. thank you

 

[Cornishpastythighs]

Here's a link for you Kwik
http://www.fpc.fi/uploads/files/Mottling_printing_at_sheet_fed_offset.pdf

 

[kbarz]

kwikford,, this must be a wet trap problem,,are your inks uni tack, or progressive, if progressive you can try to reduce tack in magenta,,or if you are trying to put a magenta solid on top of cyan screen this my not trap well, so try changing your rotation to m,c,y,k.. and back trap mottle dosent leave dust in rollors.. also you may want to tell your manager that it may be best to test first then put money job on press.. please let us know what you find kbarz

 

[kwikford]

Here's a link for you Kwik
http://www.fpc.fi/uploads/files/Mottling_printing_at_sheet_fed_offset.pdf

cornish, thanks for the link. I have read up on different web pages regarding mottling and we are going to run a test with just the cyan running to see if it looks better than with running the magenta with it. I'll let you know what we find. thanks for the input

 

[kwikford]

kwikford,, this must be a wet trap problem,,are your inks uni tack, or progressive, if progressive you can try to reduce tack in magenta,,or if you are trying to put a magenta solid on top of cyan screen this my not trap well, so try changing your rotation to m,c,y,k.. and back trap mottle dosent leave dust in rollors.. also you may want to tell your manager that it may be best to test first then put money job on press.. please let us know what you find kbarz

kbarz, I'll mention changing the color rotation as an option. I don't know if we are running a uni tack or progressive but I will definately ask. Any idea what would cause the dust in the cyan ink train? Other plants of ours run the same fount, ink, but I believe the paper may be different. Thank you for everyones patience and help.

 

[turbotom1052]

this is the very time when you want to run the magenta before the cyan. As far as the dust in the rollers ill ask if your using an abrasive roller paste such as putz pomade or any other abrasive paste? Perhaps your not getting all of it out. If so id suggest you tap on some binding varnish or water repellant varnish and let it run in for a bit. The tack of this will grab ahold of any powdery substance you may have in there and lift it out with a thorough washup. Just be sure that your rollers are in decent shape before you run in the water repellant varnish as its got enough tack to tear apart rollers that are overdue to be changed!!!

 

[Alois Senefelder]

Linting

Linting

Hello kwkford,

You are printing on a Newsprint substrate that is prone to Linting this Lint is then getting into the roller trains.


Regards, Alois

 

[kbarz]

kwikford, if yuo are running a 5,6,7 color press, if you have any open units in front of the 4cp use them to help remove paper dust. and if you just installed a new grain roller in your cyan unit this can cause the cyan to look grainey or mottley, and i have seen the grain rollor lose its fibers if not installed correct..needs very small stripe to plate 2-3 mm lets us know what you find.. kbarz

 

[kwikford]

this is the very time when you want to run the magenta before the cyan. As far as the dust in the rollers ill ask if your using an abrasive roller paste such as putz pomade or any other abrasive paste? Perhaps your not getting all of it out. If so id suggest you tap on some binding varnish or water repellant varnish and let it run in for a bit. The tack of this will grab ahold of any powdery substance you may have in there and lift it out with a thorough washup. Just be sure that your rollers are in decent shape before you run in the water repellant varnish as its got enough tack to tear apart rollers that are overdue to be changed!!!

Hi turbotom, we don't use any roller paste or any kind of paste. Our rollers are newer and we have tried a thorough wash up and the cyan ink train returns to its dusty self again. Thanks for the input and keep it coming.

 

[kwikford]

kwikford, if yuo are running a 5,6,7 color press, if you have any open units in front of the 4cp use them to help remove paper dust. and if you just installed a new grain roller in your cyan unit this can cause the cyan to look grainey or mottley, and i have seen the grain rollor lose its fibers if not installed correct..needs very small stripe to plate 2-3 mm lets us know what you find.. kbarz

Hey Kbarz, we only run 4 over 4 towers for color so its a bummer we can't try that out. I've haven't heard of a grain roller and we run a inker which gets fed from the rail which transfers ink to a knurled copper roller with a 6mm gap in between. After that the ink is transferred to the first transfer roller with a 8mm stripe. Thanks for the input

 

[Kaoticor]

Here is a little bit of information about backtrap mottling (not saying that is the problem, just giving some information since you feel that may be the cause, since it is hard to identify your problem without samples).

You mentioned that cyan by itself looks fine. (Just make sure it is the cyan that looks bad and not actually the Magenta!! I know, it sounds basic). When Switching off the printing units following the ‘problem’ unit (where theaffected image is being produced), it should clearly show whether backtrap mottling is the cause. If good printing results are seen in that color by itself, backtrap mottling is very probably the cause.

1. A big influence in mottling and absorbtion is the paper.

2. Ensure that you dont have excessive or weak squeeze. You might not notice a print problem in other types of jobs, but these settings could be apparent only when you run certain kinds of overlays.

3. If you have to do something drastic, you can move the affected ink as far back as possible to reduce the back-splitting process to an absolute minimum.

 

[Alois Senefelder]

Clarification !

Clarification !

Hello kwikford,


Are we "talking" about print problems on a Cold-set Web Offset Press ???

Such as shown in the PDF - Cromoman Press ? because you are getting lots of information related to Sheet- fed Press problems !!


Regards, Alois

 

[Ajax]

Sounds like you got a sheet wrapped around a form roller.

 

[kwikford]

test run tonight

test run tonight

oh crap, am I in the wrong forum. Yes we are running a cold set offset press like the diagram in the attachment. Let me know if there is another forum I should be in but I thought I would share the results of our test tonight. We only printed on the cyan with the other couples disengaged and at the end of the test we turned the water off. The mottling was definately in the cyan and when we shut down, the cyan plates on one side of the unit were caked and the other cyan side looked great. We also tested a unit that had the moddling problem all night and after shutting down, you could see speckles of blue on the cyan plate where the moddling wasn't letting the blue print. We are leaning towards impression settings too tight as of now and any more help is appreciated. thanks