Ghosting---help

[Kramer68]

I have a BAKER PERKINS G16 that loves to ghost when given a chance. The kind of ghosting that I am having problems with is the printed image on one side of a page will appear on the other side. Example=heavy coverage on ink on the bottom side of the web will make the image appear on the top side in a screen area. Both the blanket and plate cylinders are double round and the blanket cylinder on the top is ahead of the bottom(1 oclock position). We normally just kick in the auto washers and it will clear up the problem for a short time to pull samples and office copies and then will come back from 2000-3000 impressions later.....

 

[maynardsayswhat]

Unit to unit or transfer through the sheet?

I'm assuming you have reduced your ink density on the heavy coverage side? If it's transferring through the sheet, I'd start with how much ink is being laid down. I had similar problems on a 5-unit King Press back in the day.

Also check your substrate. Many web papers are thin and porous. (A 18# newsprint will have this issue far more often than a 24# bond, for example). You may have to adjust your regular ink and water settings for the specific substrate.

 

[Kramer68]

I get the ghosting on both unit to unit and transfer through. I get it on 30# gloss #5 and even on 70# gloss #3 webs.....

 

[maynardsayswhat]

Without seeing it in person, it certainly sounds like simply too much ink. See how a test run looks with lower densities? There's definitely something amiss if you're getting through-sheet transfer on a gloss!

 

[BeauchampT]

We had super serious mechanical ghosting like this while running a heavy coverage job. White knockouts on the other side of the sheet created the ugliest ghosting/piling imaginable. We found a few solutions:
1) Run your waters on the side with the ghosting higher and the opposite side with less (it affects the 'lubrication' of your blanket with fount).
2) Run a little higher blanket to blanket pressure (or make sure your blankets aren't old).
3) Get an ink with less body (the higher viscosity and tack aggravates the issue).

These things all helped and now seldom have the problem

 

[tamale]

You may want consider the fact that ghosting is often the result of an insufficient ink train.

When in a situation of heavy coverage, as the ink is transferred to the plate, the ink train does not always have the capacity to refill itself in time.

What you are seeing is the image imprinted on the ink form rollers, after printing an image, being transferred to the rest of the plate.

Make sure your ink rollers are well adjusted. Same goes for the dampening form. Check to see if the oscillator rollers are travelling according to spec.

Hope you find the cause.

Tamale

 

[Alois Senefelder]

Confusion

Confusion

Kramer,

I think you are confusing Ghosting with Substrate - Show- through


Regards, Alois

 

[Alois Senefelder]

Clarification

Clarification

Kramer and fellow Lithographers,

Show Through: Degree of visiablity of the printing on the underside of the press sheet, or that of the sheet underneath. This should not be confused with strike through,
which results from ink penetrating into and through sheet.

1) Use a Paper having greater Opacity
2) ---------------having less Absorbency




Regards, Alois

 

[BeauchampT]

I am unsure if this is what Kramer meant, but to Alois I can say that the mechanical ghosting I am refering to fits the description given. A heavy coverage in say black (1st unit) on bottom surface with several knockouts in it creates a strange pattern on the next unit (in my case cyan) in the screen areas. Hold it up to the light and you see that the pattern matches perfectly the outlines of where the heavy coverage ends and knockouts begin. If this isn't what you are seeing Kramer, disregard my comments. And as always Alois, the articles you post are excellent

 

[geefunkull]

Ghosting

Ghosting

Hi
Have you got a register control system, you can use this to periodically move the register to clean the blankets from build up. This also works with vanishing dots, but be weary when movement has been made as some doubling will occur.
This will hopefully enable you to print the required amount of nice clean office copies.
After this you can look at blanket surface chemistry, roughness and feeding properties.

 

[vik la luna]

Are you talking about mechanical ghosting or gas ghosting?
Mechanical ghosting showS up right away ,gas ghosting develops slowly

 

[Kramer68]

I am going to give the register movement a try. Of coarse, since I posted, I havent had any ghosting.....

 

[maynardsayswhat]

That's the power of the intergoogles!

 

[HKafeman]

Ghosting on G16 - some comments

Ghosting on G16 - some comments

Kramer68

This is outside my skill set, but I do know that a lot of work was done in the original design of the Baker Perkins printing units to minimise possible ghosting. There was mathematical modelling of the ink train and careful selection of the roller sizes, etc.

However, one of my ex-colleagues from my days at Baker Perkins is a troubleshooter, trainer, demonstrator, etc. with the right skill set.

I sent him details of this Thread and he says:

I would not class this problem as ghosting but as show through. This can happen on newsprint, particularly lightweight stock.

So I would try using better quality paper.

I cannot understand how you can get show through on gloss paper. Other measures that will help:

• Run with water levels as low as possible to prevent over inking and reducing emulsification.
• Use ink with less water take-up.
• Air curtains can be added to the ink system (reduces water in ink and increases density) which reduces ink usage.
• Check roller settings, particularly D2.
• Ensure using good quality blankets which are correctly set.

Let me know if you need any more assistance and please post any more information, observations or solutions on the forum.

Regards
Henry Kafeman

 

[SHELBY]

I have a BAKER PERKINS G16 that loves to ghost when given a chance. The kind of ghosting that I am having problems with is the printed image on one side of a page will appear on the other side. Example=heavy coverage on ink on the bottom side of the web will make the image appear on the top side in a screen area. Both the blanket and plate cylinders are double round and the blanket cylinder on the top is ahead of the bottom(1 oclock position). We normally just kick in the auto washers and it will clear up the problem for a short time to pull samples and office copies and then will come back from 2000-3000 impressions later.....

Not sure what ink you are useing , or paper..... but if you wash your blankets and it gos away, then its not chemical ghost.....if your water is low, next , reduce your ink you may have to much tack! Try a gel reducer in your ink for a trial.