Ink transfer changes with aging blankets

[Tarun Chopra]

Hi,

Just wanted comments on changes in ink-transfer capabilities of blanket with aging, categorising three phases of blanket life - New Blanket, Mid-life Blanket, End-life Blanket.

Thanks

 

[D Ink Man]

Tarun,

It can be generally be stated that ink transfer wil diminish as a blanket gets impressions and age on them. This would be particularly true with the more compressible blanket types versus a generally harder conventional one. The give and take or release will become lessened that will reduce the blankets ability to transfer a given ink. it is usually not a significant loss of transferrance, but the longer you run a over impressioned blanket the more significant it will become. Think of it as a tire on your car. They are rated for a certain number of expected miles. This in actuality can be much more or less than what you will experience based on many factors in motoring. Look at blanket life and the result you are getting on the end of your press for printability. That should be the tell
tale. And like a tire, you do not want to run it bald and end up in a ditch for possible even worse ramifications. Hope this helps. D

 

[Tarun Chopra]

Hello D Ink Man,

Can it be rightly said that the ink film thickness transfered to the substrate is reduced? Indicating the fact that the density would drop as the blanket ages?

So, for understanding, we can say that if for any reason we are not getting the desired density on substrate - blanket (could be end of life) can be a culprit.

Are there any indicators pointing that the blanket is end of life?

Thanks

 

[Deleted member 16349]

Hello D Ink Man,

Can it be rightly said that the ink film thickness transfered to the substrate is reduced? Indicating the fact that the density would drop as the blanket ages?

So, for understanding, we can say that if for any reason we are not getting the desired density on substrate - blanket (could be end of life) can be a culprit.

Are there any indicators pointing that the blanket is end of life?

Thanks

Tarun,

Blanket life may affect quality of the transferred ink but not necessarily the amount of ink being transferred. If you have a smashed blanket and lose squeeze then sure that will affect transfer locally.

If you suspect that the blanket life is causing problems with transfer, increase the ink feed and see what happens. If the density goes up, then how can the blanket limit the ink transfer if it is set to the proper squeeze. It transfers what ink is supplied.

Ultimately it is the ink feed that controls the average ink transfer to the substrate. If you draw lines through a roller train, plate, blanket substrate diagram, the amount of ink that crosses those lines is the same. It has to be, because of Conservation of Mass. You can not create or destroy the amount of ink between any one of those lines.

An old blanket might affect the ink split ratio between the blanket and the paper and that will affect the ink distribution (ink film thickness) in the roller train and in turn that can affect the ink feed on conventional presses. On a press with positive ink feed, the changes in ink distribution on the roller train will have no affect on the average ink transfer rate to the substrate.

That is one of the benefits of postive ink feed. It makes the process much more consistent and independent of changes in ink split ratio, roller squeeze, etc.

 

[Tarun Chopra]

Hello Erik,

Could you please explain:

Blanket life may affect quality of the transferred ink but not necessarily the amount of ink being transferred

If you can maintain the ink transfer capability of an old blanket by increasing the ink supply then why change the blanket? Is there a better (more consistent) indicator that the blanket has worn out and cannot be used further.

As ink splitting behavior changes with aging blanket, is it possible that the state of equilibrium might be difficult to maintain with previously established ink release values from CIP data (presuming all other factors are constant)?

Basic idea is to understand the point of time when the press operator says that the blankets cannot be used any further and they need a new replacement blanket based on observations of print quality (ignoring smashes etc)? And are the ink release values (CIP Inking Data) effected because of old blanket (whose ink transfer capabilities has changed because of age)?

Thanks

 

[Deleted member 16349]

Hello Erik,

Could you please explain:



If you can maintain the ink transfer capability of an old blanket by increasing the ink supply then why change the blanket? Is there a better (more consistent) indicator that the blanket has worn out and cannot be used further.

As ink splitting behavior changes with aging blanket, is it possible that the state of equilibrium might be difficult to maintain with previously established ink release values from CIP data (presuming all other factors are constant)?

Basic idea is to understand the point of time when the press operator says that the blankets cannot be used any further and they need a new replacement blanket based on observations of print quality (ignoring smashes etc)? And are the ink release values (CIP Inking Data) effected because of old blanket (whose ink transfer capabilities has changed because of age)?

Thanks

I don't think you completely understood what I was trying to explain. The blanket itself does not control ink transfer.

But I think you want to know what is the practical point for changing a blanket. I suspect it will be quality of the print and maybe registration issues.

You say that the operator claims a blanket needs to be changed. Have they shown you why they believe this or are you also looking for some other way to determine if you should believe your operator?

Also as a side issue, CIP values for keys can not be counted on as being highly accurate. If you are thinking that old blankets are affecting the accuracy of getting to density with the CIP values, I would say that blankets are not a big issue.

 

[Tarun Chopra]

Erik,

Yes, I actually want to know a point where blankets needs replacement along with a quanifiable and verifiable aspects influencing print quality. There should be some visible phenominon indicating that blanket has reached end of life and need replacement.

Most of the press operators have their own reasons for changing blankets but none of them appear to be based on any scientific basis!!!

Thanks

 

[Deleted member 16349]

Erik,

Yes, I actually want to know a point where blankets needs replacement along with a quanifiable and verifiable aspects influencing print quality. There should be some visible phenominon indicating that blanket has reached end of life and need replacement.

Most of the press operators have their own reasons for changing blankets but none of them appear to be based on any scientific basis!!!

Thanks

Now this is a good question but unfortunately I don't have a good answer for it.

 

[D Ink Man]

When to Change the Blanket('s)

When to Change the Blanket('s)

Replace a blanket if you are starting to suffer quality in print, especially dot gain. If we assume that you are printing at the same density as say when the blanket was newer, the inks rheology is the same, the files are the same coming out of pre press, the fountain solution is consistently the same; well I could go on and on here, because the lithographic process is the most variable driven entity that can be imagined, then change the blanket. Also if you start to notice piling, picking or linting type problems with the same type paper stocks that you normally run, again, change the blanket. These blankets will become harder, higher durometer and lose their ability to properly accept ink form the plate to their surface and adequately transfer to provide suitable printing on paper. Not a pressman, but using a micrometer, carefully check your packing and see where it is when the blanket is new, and then also check after 100,000 impressions or at least once a week. Keep the blanket properly taunted down and locked to press specifications for best life and of course, best printability. Also as a blanket ages, remove it from the cylinder and spot check it in random impression areas and also in the outside normal non print area to check the thousandths of thickness. Knowing all this should tell you when it is time to get new rubber on your road. Hope this helps. D

 

[Tarun Chopra]

Hello D Ink Man,

Would the dot gain increase or decrease, to my understanding keeping everthing else constant because of reduced ink transfer capabilities the density and dot gain would be reduced, am I correct?

Thanks

 

[D Ink Man]

Dot gain would actually increase. Reduction of transfer and trying to push ink films to previous established target densities would create this, and also should mention, you will be more liable to create an over emulsification situation between the fount and ink in this situation. For the sake of Christ, please change the blanket for your operator. I'll send you a few bills to help if you are afraid of sacrificing the cabbage. You should slurraintly understand this by now. Let me know, good luck. D

 

[Tarun Chopra]

Thanks for all the info.

The idea is to understand why and when to take 'necessary' corrective steps based on certain established parameters which have a logical and scientific reasoning and not being tossed about with info which is based on presumptions of individuals.

I was surprised when I asked press operators this question - everyone had a unique reason and all the reasons were based on their individual experiences however correct or incorrect those might be.

Thanks

 

[nhprinter]

"I was surprised when I asked press operators this question - everyone had a unique reason and all the reasons were based on their individual experiences however correct or incorrect those might be."

The key word there is "experiences". Sometimes you can't over analyze what a pressman feels.

 

[rathishvm1]

Hi friends,
Maintaining consistency is what matters in printing quality maintenance. When printing quality suffers variation because of quicker deterioration of the solid image or dot on a printing plate due to carcass soaking in solvent and water emulsion etc it needs replacement. Also similar to ink train rollers reducing efficiency of ink transfer due to glazing etc, blankets too tend to reduce ink transfer from what is supplied upto plate onto the substratum say newsprint. That point when a 100% solid is not printed with consistent ink film thickness determines the blanket needing to be changed. Please correct me if I am wrong, Mr.Tarun / Mr.Erik.

 

[Deleted member 16349]

Hi friends,
Maintaining consistency is what matters in printing quality maintenance. When printing quality suffers variation because of quicker deterioration of the solid image or dot on a printing plate due to carcass soaking in solvent and water emulsion etc it needs replacement. Also similar to ink train rollers reducing efficiency of ink transfer due to glazing etc, blankets too tend to reduce ink transfer from what is supplied upto plate onto the substratum say newsprint. That point when a 100% solid is not printed with consistent ink film thickness determines the blanket needing to be changed. Please correct me if I am wrong, Mr.Tarun / Mr.Erik.

I think that it is difficult to have a specific rule when a blanket should be changed since printers do a lot of different kind of printing. Some may have a lot of solid work and others won't. Some will print screens that can be affected by dot gain and other printers don't print screens so much. If a printer is printing mostly text for books, then maybe they can get away with not having to change the blankets often, since there are no solids or screens. On the other hand, if a printer is printing high quality images, than maybe even small defects can be a problem.

I don't think there is a wrong or right answer. It depends on what your customers think is important and can see in the print. If you change a blanket too early, then you lose money but if you change the blanket too late, you might lose a customer. I don't think it is so easy to know just when it is the right point to change.

 

[DanB]

Back in the days when I ran a press, one thing my supervisor had me do is rotate blankets, one week on the press and one week off the press. I don't know if that did anything to prolong the life of the blankets or not but it made sense to me.

 

[CD102]

Back in the days when I ran a press, one thing my supervisor had me do is rotate blankets, one week on the press and one week off the press. I don't know if that did anything to prolong the life of the blankets or not but it made sense to me.

Is the blanket somehow rejuvenated by being off the press for a week? I never liked putting a used blanket back on the press because it might have mash that wasn't visible in the last job but will show up in the new job. And when that happens, I wasn't changing the blanket once, but twice. But I worked in a carton shop and blankets got mashed often.

 

[DanB]

Is the blanket somehow rejuvenated by being off the press for a week?

I don't know if the blanket got rejuvenated or not. I was just doing what the boss told me to do.

I knew my blankets and if I smashed one to the point of giving me trouble, it was replaced. We were doing simple 8-up b/w forms and really had very few smashes. There was an occasional sheet that had a splice from the web when it was sheeted that did not get detected and fed through the press but these didn't do too much damage.

 

[GazKL440]

There is no particular rule regarding blanket changing, i mean you dont simply say "ok its done a million impressions, time to file it". When a blanket is affecting print quality, swap it out... We often get weeks out of blankets which can equate to millions of impressions, and only change them if required, as they aren't cheap and no one can afford to waste money hey? Our biggest issue with our blankets is impression marking from running similar jobs for days on end that eventually leave a sort of impression image on the surface, and when higher quality jobs are required often the screens will show a ghosting type image from the previous campaign run, and perhaps dot gain from patching... So we change them all but keep the best of the recently removed for the next long run job..

 

[HecTiK]

Our biggest issue with our blankets is impression marking from running similar jobs for days on end that eventually leave a sort of impression image on the surface, and when higher quality jobs are required often the screens will show a ghosting type image from the previous campaign run, and perhaps dot gain from patching... So we change them all but keep the best of the recently removed for the next long run job..

We've had that problem a few times. We use a blanket rejuvinator that helps out a lot. The image is stained on the blanket, but doesn't show up in print after we use the rejuvinator.