Registration or doopid pressmen?

[Green Printer]

Ink drying is a chemical reaction and one of many that happens in the offset process. Ink absorption type of drying is not a chemical reaction. Ink drying by oxidation is a chemical reaction. Ink drying by energy input of UV or EB is a chemical reaction. Cobalt and mag dryers are used as a catalyst for drying.
Tung oil is a dryer additive catalyst for drying. Some inks won't dry for weeks because of glycols present prevent the ink from oxidizing and forming a chain.
This is just a small part of what happens in the offset process because of chemical reactions

 

[Deleted member 16349]

Ink drying is a chemical reaction and one of many that happens in the offset process. Ink absorption type of drying is not a chemical reaction. Ink drying by oxidation is a chemical reaction. Ink drying by energy input of UV or EB is a chemical reaction. Cobalt and mag dryers are used as a catalyst for drying.
Tung oil is a dryer additive catalyst for drying. Some inks won't dry for weeks because of glycols present prevent the ink from oxidizing and forming a chain.
This is just a small part of what happens in the offset process because of chemical reactions

Good examples and yes there are some chemical reactions. I stand corrected. But the primary aim of my comment is that chemistry has not been able to explain why the process is inconsistent and unpredictable when everything is working properly on press. The lack of consistency and predictability is a result of problems with the mechanical design of the press and the unaccurate algorithms used to preset the press.

If you still want to believe that chemistry is the dominating factor in the process, then one will still continue not to have success in solving the fundamental problems that are still in the process and that are not that difficult to correct.

Over the last hundred years, the narrow chemical approach to solving the problems of offset printing has helped a lot with the quality of the materials but has not at all explained the problem that is now critical for the economical operation of offset printing as a manufacturing process.

 

[Green Printer]

Good examples and yes there are some chemical reactions. I stand corrected. But the primary aim of my comment is that chemistry has not been able to explain why the process is inconsistent and unpredictable when everything is working properly on press. The lack of consistency and predictability is a result of problems with the mechanical design of the press and the unaccurate algorithms used to preset the press.

If you still want to believe that chemistry is the dominating factor in the process, then one will still continue not to have success in solving the fundamental problems that are still in the process and that are not that difficult to correct.

Over the last hundred years, the narrow chemical approach to solving the problems of offset printing has helped a lot with the quality of the materials but has not at all explained the problem that is now critical for the economical operation of offset printing as a manufacturing process.

A very common problem that can occur is roller striping, is it chemical or mechanical?

 

[Deleted member 16349]

A very common problem that can occur is roller striping, is it chemical or mechanical?

I would clasify it as physical in the sense that I don't think there are any chemical reactions but there is probably a deposit on the rollers that has formed that prevents the ink from wetting the roller. I can see why someone would call this a chemical problem since it might be caused by some precipitation of compounds from solution and go to the layer of the roller. Is precipitation a chemical process or a physical process? I tend to think of it as a physical process.

Physical chemistry is important in the process. Please don't get the idea that I think it is not important. But trying to solve every problem with a "chemical" solution to the problem, will not move the process forward. One has to try to find out what the root cause is and then take steps to correct it. Many of those root causes are mechanical and knowledge based.

My particular interest is in moving the process to the next level. I am not interested in the status quo. I am talking about having a press starting up and going directly to its density targets and running consistently for the whole run, without the operator having to adjust any ink settings and doing that with technology that cost less than a conventional offset press. If you have particular knowledge in how the "chemistry" approach can move the process to that next level, I would be happy to hear about it. I am sure everyone would be happy to hear about it.

 

[Green Printer]

I would clasify it as physical in the sense that I don't think there are any chemical reactions but there is probably a deposit on the rollers that has formed that prevents the ink from wetting the roller. I can see why someone would call this a chemical problem since it might be caused by some precipitation of compounds from solution and go to the layer of the roller. Is precipitation a chemical process or a physical process? I tend to think of it as a physical process.

Physical chemistry is important in the process. Please don't get the idea that I think it is not important. But trying to solve every problem with a "chemical" solution to the problem, will not move the process forward. One has to try to find out what the root cause is and then take steps to correct it. Many of those root causes are mechanical and knowledge based.

My particular interest is in moving the process to the next level. I am not interested in the status quo. I am talking about having a press starting up and going directly to its density targets and running consistently for the whole run, without the operator having to adjust any ink settings and doing that with technology that cost less than a conventional offset press. If you have particular knowledge in how the "chemistry" approach can move the process to that next level, I would be happy to hear about it. I am sure everyone would be happy to hear about it.

Stripping is when the surface tension or dyne of the rollers becomes less than that of the ink water combo. The root cause is usually a chemical problem. Could be polyphosphates, or calcium, or ink semi polymerizing etc.

If you do a good roller paste cleaning and calcium cleaning and the problems does not reoccur it was contaminated or dirty rollers. If the problem continues on just one unit it is ink. If the problem continues on all units it is ink or water. If you dump your water and make a new batch and it is fixed it was a water problem. If it still occurs it is probably an ink problem.

I do think that the chemistry approach is coming. Those out there whom are much more involved could answer such a question. Since being just a user I also would like to know how the chemistry approach is progressing.

 

[Deleted member 16349]

Stripping is when the surface tension or dyne of the rollers becomes less than that of the ink water combo. The root cause is usually a chemical problem. Could be polyphosphates, or calcium, or ink semi polymerizing etc.

If you do a good roller paste cleaning and calcium cleaning and the problems does not reoccur it was contaminated or dirty rollers. If the problem continues on just one unit it is ink. If the problem continues on all units it is ink or water. If you dump your water and make a new batch and it is fixed it was a water problem. If it still occurs it is probably an ink problem.

I do think that the chemistry approach is coming. Those out there whom are much more involved could answer such a question. Since being just a user I also would like to know how the chemistry approach is progressing.

Another point is that I do not tend to describe a process by the failures in the process. I look at the process in terms of its capability when everything is working as it is supposed to work and think of what can be done to improve the performance from that point on. Roller stripping would be a failure. It does not happen all the time. One could say the same thing about ink drying problems.

You can have a car and it can get a flat tire. One would not define the process of driving a car and its performance capabilities while having a flat tire. Of course these problems have to be corrected to get things going again but in themselves these events do not limit the performance during normal operation.

 

[meddington]

I can see why someone would call this a chemical problem since it might be caused by some precipitation of compounds from solution and go to the layer of the roller. Is precipitation a chemical process or a physical process? I tend to think of it as a physical process.

I believe by definition, precipitation of compounds from a solution is indeed a chemical process/reaction. In the case of stripping where by a compound (say, calcium) is drawn out of a solution (fountain solution) by either a reagent or simply a break down of the calcium compound. Though the latter may be due to physical action, it results in a chemical change of the compound itself. There could be (and are) other causes of stripping, possibly involving settling of a substance suspended in the fountain , but if we're talking precipitation, in my opinion this is a chemical reaction.

I don't want to take away from anyone's overlying points, and this is really a discussion of semantics, but perhaps we could all agree that offset lithography is in part facilitated by the careful balance of the chemical properties of all components.

 

[Deleted member 16349]

perhaps we could all agree that offset lithography is in part facilitated by the careful balance of the chemical properties of all components.

I can agree to that.

The components have been designed to have particular physical chemical properties that help the process work.

 

[Print 1 Solutions]

I have to share this. . . a press trainer was on premises for one year. Once the press was up and running for about 5 months the trainer (not our employee) sent the pressman in to tell me that "my magenta plates were not hitting". I asked him what he meant and he said that the register marks on the magenta plates did not match up with the other three - that the trainer said I needed to fix my magenta mark! He thought that each line in the register mark was individually drawn. I showed him how they are made and he still was insistent that it was either me or the platesetter. I went out, pulled the set of plates, got a ruler and measured everything - which was all ok - while the trainer went upstairs to the owner and told him that I could not make a magenta plate that could hit.

I got called into the main office, explained that everything from my department checked out, but that I would call in a tech to confirm it. (Because you know, 20+ years of experience, being a female in this business, I still don't know anything.) Anyway, I called one of my favorite, trusted techs - he told me it had to be the blanket on the press. . . I relayed this to the pressman, who told the trainer, who said, "bullsh#t". The next morning, before the trainer arrived the pressman changed out the blanket, hung a set of plates and the problem was gone. . . I told the trainer that I must have mixed up the unexposed plates in the drawer and used two cyans in a row, and that I would never do that again!

He was so smug, then the pressman told him he changed the blanket. . . stoopid pressroom trainers!

klh

Great post! We had a pressman here that was allways blaming the plates for miss-register. We would have CTP tech in to recalibrate, but the problem would crop up again and again. Long story short - he's gone and we have a new operator for almost 3 years and guess what? No register problems, no uneeded recalibrating. When the new operator started she asked for a torque wrench for the blankets! Smart Presswoman!

 

[Alois Senefelder]

re Roller Stripping

re Roller Stripping

Hello everyone, I hope the following Information is useful.


Regrds, Alois