Waterless printing, info search...

[Disappointed]

In connection with my other topics here..
http://printplanet.com/forums/sheetfed-web-offset-discussion/30330-presstek-52di-info-sought
And here...
http://printplanet.com/forums/sheetfed-web-offset-discussion/30424-presstek-52di-users-please

I am looking for assistance from other waterless offset users, specifically with plate cylinder temperatures.

We have an issue presently that is badly affecting the start of each run by serious toning in the cyan followed by yellow and magenta. This ONLY affects the start of a new set of plates, never during a run so its not the usual toning effect. I have ruled out the ink now as the manufacturer has assured me that the formulation has not changed in several years and this issue has only started in the last six months or so. We have used the same inks and roller temperatures for over two years.

Recently I have been monitoring all aspects of the system in order to get a hand on what is going on here. One area i have found slightly concerning is plate cylinder temperature, this can go from room temp of 16c in the morning to over 34c by about 2pm, this seems a serious rise to me and is well above toning temps as far as I know. Toning starts at around 25c or mid-morning.

The press has cooled rollers and duct and these are set at 18c. Rollers surfaces run at 19-20c when moving. Blanket surface was 36c when the plate was at 34c.

Roller pressures are meticulously set (especially so lately) at 3mm stripe, blankets are never over-packed so where does the heat come from?? There is no sideways movement on the forme rollers and we have fitted two units with new ones but no change.

Any thoughts?

 

[Alois Senefelder]

Heat

Heat

Hello Disappointed,

The compression of the Blankets as they rotate through the - Forces of Pressure generate the heat.


Regards, Alois

 

[Deleted member 16349]

Hello Disappointed,

The compression of the Blankets as they rotate through the - Forces of Pressure generate the heat.


Regards, Alois

That is one of the positive reasons for the use of water. It helps to cool and lubricate surfaces.

 

[Disappointed]

Hello Disappointed,

The compression of the Blankets as they rotate through the - Forces of Pressure generate the heat.


Regards, Alois

Thanks for that, makes sense.

I had also been told that the shearing forces in the ink creat heat but is there enough there to cause temperature rise?

 

[Disappointed]

That is one of the positive reasons for the use of water. It helps to cool and lubricate surfaces.

Yes, we know that, but we have never had water on this press but only started having a problem in the last six months or so. This is why I am searching for areas to concentrate on.

 

[Deleted member 16349]

Yes, we know that, but we have never had water on this press but only started having a problem in the last six months or so. This is why I am searching for areas to concentrate on.

Sorry, I was just trying to be a bit funny. Maybe its not so funny for you since you have a problem.

I have wondered that if waterless was invented first, would people think that lithography correctly done, was an advancement to the offset process. I am a strong believer that in the end, lithography will out perform waterless.

Back to your temperature problem. Heat, which is energy can be created due to friction or the repeated compression and relaxing of the rollers. Energy is force x distance. So if you have a frictional force over a distance or you have the rollers or blanket compressed repeatedly, this will generate heat which will result in a temperature rise if there is no way to get rid of it.

So if this is a temperature rise problem, of course you need to look for the sources of heat generating actions and the ability of the system to get rid of heat.

On the other hand, I am not sure it is a temperature issue. From you description you say the problem is at the start and clears up later. Later when the plate is hotter? Have I understood that correctly?

Could it be that you actually have to preheat the plate above some temperature? Probably not.

Also if it is only at the start, maybe there is some surface contamination of the plate that eventually gets cleared up as you run. Maybe related to your batch of plates. Maybe the rolled up plates are causing some oils or substances on the back of the plate material to transfer to the image side. Maybe you are blowing contaminated air onto the plate when it is being exposed.

A suggestion. If after you are running clean and the plate cylinder is at the higher temperature, maybe stop and let it cool down. Then restart and see if the toning comes back at the lower temperature. If it does, then maybe for some reason you would need preheating. I hope not. But if the toning does not come back at the lower plate cylinder temperature, then I would suspect some kind of contamination of the plate that eventually gets cleaned off.

Just some ideas.

 

[Disappointed]

Thanks Erik, exactly the sort of reply i was seeking.

My personal gut feeling is that there has been an unannounced change made to the make-up of the plate surface and this change allied with temperatures at their limits and our chosen ink has made the system sensitive to toning on new plates. The "normal" ink as used by many other users is not susceptible (yet) as no other users are reported to be suffering, our main issue is that we cannot change inks as the normal set are not ISO certified colours and are very 'cold' in appearance when printed. The fact that we have been very happy for two years previous also negates me wanting to change.

One more "stir-it-up" fact - These machines have what is known as a plate-saver feature, using this allows me to re-use the unused portion of the plate at the rear of the image, the plate is only advanced enough to remove the previous image. This saves a vast amount of money on plates when doing small format runs. Now for the kicker - this area has been run against the rollers and blankets for the length of the previous run - it NEVER tones! When the fault occurs it will now start on the fresh plate area only, never on the saved plate area.

This indicates to me that this can only be a plate fault- something is being rubbed off the coating by the rollers or blanket which prevents the toning occurring. Trouble is, i can get no response on the plate material and we do not know who makes them.

This is an intriguing fault to be sure.

Oh, and by the way, i feel that waterless is one way forwards, it prints sharper, starts up quicker and discounting the trouble i am in at present, runs with less fuss that ink-water printing. Although having said that, i feel the ultimate system will be one with full-width ink-jet heads, instant dry ink, and sheet or reel feeder. That would give zero make-ready, instant colour match and run lengths from 1 to many - no plates to wear out, no blankets to dent, just direct imaging straight to the paper surface, probably eight heads per side. Of course you cant do metallics or specials but......

The effect...


Dave

 

[Disappointed]

More info,

This problem can be fought by adding silicon oil to the inks. All waterless inks contain silicon oil, the ones I am using have 0.5% content. This oil rides on the surface of the ink film on the rollers and coats the non-image areas of the plate thereby helping them reject the ink itself, pretty similar to the action of water in standard offset. The image areas have a much lower surface tension than the non-image silicon coated area and readily accept ink even with the added oil content.

Troubles arise though if you want to apply post-press finishes like hot-foil, varnish, laminates etc. The maximum content seems to be 1% so we have an addition range of 0-0.5% oil. My tests have proved that by adding 0.5% to the cyan and 0.3% to the yellow and magenta cures the problem but we are now running at the limits of addition and we all know that is never a good idea.

I have now returned to the standard ink mix until we can find the root cause of this issue as we can't afford to have jobs that will not hot-foil as we do a lot of this. This also indicates that the area of used plate created by the plate-saver feature has also been pre-coated with silicon oil by the rollers on the previous run.

Everything is still leaning on this being a plate fault I feel.

 

[erictoray]

Dissapointed,

You may want to look at what if anything has changed within the press (or components) itself. New blankets, roller settings, plate to blanket settings, etc.
As pointed out in previous posts, friction will cause heat which will cause toning. Waterless inks have a Critical Toning Index (CTI) which the manufacturers can provide to you. In theory, if you stay within this range your press should not tone. However, if the parameters are out of spec, all bets are off.

PRST DI presses are only temperature controlled at the ink vibrators and possibly the ducts. Have you had anyone check the actual temperature control unit or thermostat for proper function? It is possible that the setting that you are seeing on the console is not really the temperature at all. Another area to check is the actual pressroom conditions for heat and even humidity. You do not want an extreme in either heat or cold in the room and of course humidity should be at 40% or better.

Please feel free to contact me offline if you like @ [email protected] should you desire.

 

[Disappointed]

Nothing has changed really, I am running the same blankets as I was before the problem arose, the rollers are checked meticulously (especially so recently), the machine had a full service in December, the chiller indicates 18c and the rollers measure 19c when running, the room is at a capped 21c so it can be lower in the morning but never goes over 21c any time of year, i have no control over humidity but as its air conditioned its low at around 20-40%rh

Yes the ducts are chilled as are three vibrator rollers in each unit. Everything is within the same parameters I have maintained for the last five years, although inks were changed 2-1/2 years ago. The problem has only started in the last six months. It seems very few manufacturers know the CTT for their inks either that or its a trade secret

there is a known issue that occurred with the plates which affected the first five on each roll, this was admitted by the manufacturers and replaced, this fault is different to the current fault and affected many users, my trouble only affects me

 

[Deleted member 16349]

One more "stir-it-up" fact - These machines have what is known as a plate-saver feature,

Now for the kicker - this area has been run against the rollers and blankets for the length of the previous run - it NEVER tones! When the fault occurs it will now start on the fresh plate area only, never on the saved plate area.


View attachment 3253

Dave

I think you are on your way to finding out what the problem is.

It does not seem to be temperature related but plate related. Good observation regarding the plate saver feature.

I was surprised to read about the use of silicon oil in your other post. It seems that this process is almost back to lithography. or Oilography or Soilography. ;-)

Good luck in convincing the plate supplier that they have a problem.

 

[Disappointed]

Yes - that one point alone regarding the plate-saver area has thrown everything and everyone into a frenzy of "well I'm baffled, never seen that before" It really does contradict everything else and points a finger directly at the plates, but it seems only if using these inks (just to make things more complex).

Yes, waterless goes way back to the days of rotogravure etc, it works by holding the ink within recessed areas of the plate and not on the surface as in conventional offset. It's a very simple process really, the only important factor is temperature - waterless is always dependant upon temperatures to maintain the two different surface tensions between ink / background and ink / image areas.

This time it seems something has changed that makes my ink / plate combination susceptible to toning unless there is a raised level of silicon oil present.

 

[londonbob]

I have had experience with the old GTo-Di from Heidleberg with non chilled rollers. as the day wore on the rollers retained heat and the ink became more difficult to control. this is why short runs would help to keep the press cool. Longer runs resulted in issues with Ink. Toyo Inks manufacture specialty inks for this type of Press and you also need to maintain a heavily air conditioned press room. Ours had pressmen wearing light jackets as we tried to keep temperatures at 60 degrees. Originally the press was designed to do short run products and the savings was that dtp could eliminate so much, but with the much faster off press imagesetters, all of that savings was eliminated. Now it is all trying to make a clunker compete with a race car by using these old fashioned presses. The cost of capital equipment is horrific today and owners are trying to stretch out the lives of outdated equipment.

 

[Disappointed]

Thanks londonbob but this is hardly an old clunker, its a 4 year old press with only 20m on the clock, not even run-in yet. I would never try waterless without press temperature control, just won't work. Our run lengths are between 500 and 20,000, mostly 2,000 - 8,000 sheets.

Dave

 

[Ret Heidelberg Instructor]

I am puzzled by the statement you made that you do not know who manufactures the plate. Most DI plate material with a slicone layer was made by Presstek. (There were a few others that tried also) Could you elaborate a bit more on what we are seeing in the picture of the printed sheet.I can only relate to issues that sometimes occurred on the Heidelberg DI presses.
For example, when the a new plate was loaded to start a new job the printing units would come on impression (blanket to plate only)and the plate material would be tightened. Any residual blanket wash that was still on the blanket would migrate to the plate surface.If the blanket wash make-up was particularly oily in nature this would cause some toning on start-up or after a blanket wash during the run.It is also possble to create toning by using to much ink-retarder spray on the inks in the fountains if you leave them overnight.
From your previous posts, it sounds like you have covered most of the bases I would have looked at trying to troubleshoot the problem.I have one other question that you may already answered in previous posts. If you leave the plates from your last job of the day and re-start again in the morning, do you get toning?

 

[Disappointed]

I did not know that Presstek made them directly, I was presuming they were made by someone like Kodak etc.

Yes, a full cycle would be - Plate advance, smoothing with blanket, imaging, dry clean, wet clean, inking, printing.

I have negated the blanket wash by doing a hand wash first, and also by hand cleaning the plate directly before imaging. It can be proved also by simply advancing a new plate and dropping the forme rollers whereby it will ink the plate almost completely. Bear in mind that for this to happen, the press must be warm i.e. have run for a couple of hours or 2-3 short jobs and it only ever does it at the start of a new set of plates - I can leave the plates overnight or stop in the middle of a run for any period of time and it will not tone, even when hot.

I do not need to use anti-skin spray as the inks are overnight fresh.

It's a baffling problem that really points its finger at the plates I believe.

 

[Disappointed]

Could you elaborate a bit more on what we are seeing in the picture of the printed sheet.

The picture....


Shows the start of a new job at about 11:00-12:00 in the day so the press is warm and the problem has shown its face. The grip edge is at the bottom and shows a feint cyan tone, this is normal and will clear in 4-5 sheets, the portion from grip to midway is the plate-saver area, this part of the plate has been run against the rollers and blanket on the tail-end of the previous run - it will never tone.

From the midway to rear of the job we have heavy magenta and cyan toning, this will take 150-250 sheets to clear and while doing so will badly contaminate the magenta and yellow ink ducts/rollers as the non-image area is covered outside of the print area - this also results in heavy inking of the impression cylinder surface.

If this job were run on a 100% new plate (no plate-saving) then the whole image would resemble the rear half of the sheet.

If I put four drips of silicon oil directly on the rollers before a new job, the problem does not arise. It is a combination of ink/plates/temperature. The ink has not changed so i can rule that out, as far as I know the temperature has not changed, that just leaves the plates.

 

[Alois Senefelder]

A Step back in History

A Step back in History

Hello fellow Lithographers and Disappointed,


Clairification - Waterless Plates

The first so called Waterless Plates hark back to 3M Driography Plate, the next manufacturer of this

type of plate was Toray from Japan. Finally, these plates have no relationship with Gravure, they

are in fact based on the Deep Etch Lithographic Plate Process.


Well for now I've finished wittering on !


Regards, Alois

 

[Disappointed]

Thanks Alois, education never hurts

Dave

 

[Ret Heidelberg Instructor]

Sounds like you have a really baffling issue. You said that adding silcone oil to the rollers prior start of printing a new job works but it seems to be a bandaid solution. Since you stated that you cannot use a different ink, I would be curious to see what would happen if a diferrrent ink was used. Perhaps you could try one unit (your worst one) and see if there is a difference.I would also suggest before starting a new job after imaging try washing them again with your cleaning cycle. I know this can be costly because of overuse of the cleaning cloths.
I am only familiar with Heidelberg DI presses but the chiller was set at around 22.7 and I must say Toyo inks worked the best.The Heidelberg press had only 3 ink formes to the plate and they were set at 3mm on the first and second ink forme and 2-2.5mm on the 3rd forme roller. On that press the 3rd forme provided 5% of the coverage but could be 85% of a problem of the The other rollers were set at 4mm.Let us know how you make out with your efforts. Good luck.