random black splotches on sheet fed press

[bcg1]

Hi I am in the graphics department and trying to help the pressman solve a major problem.

He is getting random pepper spray type splotches on the sheets.

He is running a Hamada B452A Sheet fed Press. Using Mitsubishi plates. Sheet size is 12.5" x 19"

The problem happens when he is starting a job and stops to check color 5-20 minutes, then starts back up again, it starts on the black plate, which is the first unit? (not sure on the correct terminology, I'm just the designer)

He has tried cleaning the water unit, changing the solution, and changing the ink used. He ordered different plate material and is trying that next.

Any suggestions?

 

[Ret Heidelberg Instructor]

It could be several things causing the blotching on re-start. You might have emulsified ink that is flying around. Depending on the plate, if it is a polyster type it might require a lot more wetting on re-start. I used to see this a lot with polyester plates. They want a lot of water because they have litltle or no grain.Try letting the press idle with the dampening system on between stoppages. The only problem with doing this is it might lead to the first problem I mentioned. If you try another plate and the problem goes away then you need to get a rep from your supplier to assist you with the problem

 

[kbarz]

blk splotches

blk splotches

not sure why a pressman would want to stop press to check color, i prefer to keep feeding sheets,, but back to the spots this could be caused by form rollers not set to the plate, check the settings to the plate. then make sure the #4 ink from roller is not set to tight to the ossiclater, this can cause alot of grief if not set right,, to tight will cause very light scum,or the spots like you are describing.. hope this helps (pressman with 35 yrs in trade kbarz)

 

[RGPW17100]

Another thing is depending on how good a job he does cleaning the press. Too much press wash can start causing ink growing like stalactites in the roller train. When the forms go up when being shut off they may be contacting this stuff and it is sticking to the form rollers. Too much press wash when cleaning can do this. Also using the ink ductor roller to clean the ink pan roller will cause press wash and ink slop to sling in the press. I would check the roller hangers and see if anything needs cleaning.

 

[nhprinter]

I'm not sure why, but when a question like this is asked on this forum everyone automatically assumes that the pressman is a dumbass. I'm going to go the other way and assume that he's just stumped by a problem he's never seen.

I think the correct route is to look at the plate material. Many (30+) years ago we had a similar problem with a photodirect plastic plate made by 3m. Some things never change.

 

[Cornishpastythighs]

It does sound like the dampener has loaded up with ink.

 

[D Ink Man]

Ink Avenue Correction Very Possible

Ink Avenue Correction Very Possible

Offset paper or Coated, 1st question? You may need a combination oil base, rubber base ink if you want to try to solve with the easiest change, ink. Certainly make sure that your ink is HEAVY BODIED #1. If you may be interested in a black like described, please reply and I will get you an ink that can overcome this condition. Dealt with this type of issue many a time. D

 

[bcg1]

Thanks so much for all the replies, I will pass this onto the press room and reply with there answers.
Thanks!

 

[alic57]

Emulsification or ink tack. Is the pressroom hot and the press running high speed?

 

[kbarz]

nhprinter,, sorry if i made you upset by posting my view on his or her press related problem. was not assuming that any one was ( as you worded it dumbass ) sorry if my posting upset you. and i assume this because i do fall into the everyone that replied to this posting. kbarz

 

[nhprinter]

nhprinter,, sorry if i made you upset by posting my view on his or her press related problem. was not assuming that any one was ( as you worded it dumbass ) sorry if my posting upset you. and i assume this because i do fall into the everyone that replied to this posting. kbarz

kbarz...don't take it personally. It's just my general feeling after 2 years of seeing responses on this board.

This forum can be a great tool, but for the most part it is very often a quick assumption that the pressman doesn't know what he's doing which might deter someone from posting a question. That would be too bad.

 

[RGPW17100]

A lot of times obvious things are sometimes overlooked. It is better to have a list of 10 things to look for then 2 or 3 less obvious things. Our presses are run to the point where we have little time to do needed maintenance like cleaning roller ends, striping rollers etc. This will tend to lead to problems that arent obvious. Better to have too much information then not enough

 

[otherthoughts]

For what it's worth?

For what it's worth?

Hi I am in the graphics department and trying to help the pressman solve a major problem.

He is getting random pepper spray type splotches on the sheets.

He is running a Hamada B452A Sheet fed Press. Using Mitsubishi plates. Sheet size is 12.5" x 19"

The problem happens when he is starting a job and stops to check color 5-20 minutes, then starts back up again, it starts on the black plate, which is the first unit? (not sure on the correct terminology, I'm just the designer)

He has tried cleaning the water unit, changing the solution, and changing the ink used. He ordered different plate material and is trying that next.

Any suggestions?

Another possibility to consider, is that the printing plates may be oxidizing whenever the press is stopped for prolonged periods of time. A very quick and simple way to determine whether or not plate oxidation may be the culprit or not, is to look more closely at just how random these pepper spray type splotches are.

If your pepper spray pattern and location on consecutively printed sheets, change from one sheet to the next? Then oxidizing plates are not your problem.

On the other hand, if the pepper spray pattern and location on consecutively printed sheets, are identical from one sheet to the next? Then plate oxidation may be your problem, a yes answer to this question simply means that the plate likely plays some role in your problem and that the pepper spray type splotches, are not random from sheet to sheet.

In my days as a pressman, (many years ago now), peppery spots appearing after a prolonged press stop, often indicated to me that I needed to add more Gum Arabic to my Fountain Solution which would help to protect my plates from oxidation during the press stop.

Article
Gum Arabic and Fountain Solutions

Best Regards
OtherThoughts

 

[Ultra007]

Without seeing the sheets, this one could be any one of a hundred issues. But I will tell you something I had run into half a lifetime ago. Running on large format machines (64") we would start seeing little "specks" that seemed to be etched into the plate. Re-made plates , same thing. Washed blankets and plates, same thing. Washed up the rollers, same thing. It was most visible in the black but upon inspection it may be in all colors. Once the specks were visible, they would be in the same spot on every sheet and maybe new ones showing up after running long periods of time.
What we found was that due to the fountain solution we were running (alco subs), the rolers were experiencing a build up of surfactant or something from the solution. A normal wash up didn't take it off but hot water with a mild soap/ vinegar did. It was this invisible film of material breaking off and etching the plate thus picking up ink. Give it a try.