Build Up

[Noodle]

We are using Agfa N94-VCF plates, Violet CF Gum-NP run thru an Agfa VCF 85 processor. Since we started with the plates we have seen a residue build up in our water pans on the press. This will accumulate and turn to blobbs that plug up the system. Prior to the new plates we never touched our water pans, the system has a chiller with 50 micron filters and never had any issues. Have been back and fourth with Agfa, the fountain solution mfg. We have not changed paper, ink, chemicals, nothing changed but the plates. Just wondering if anyone else has seen this problem with these plates.

 

[Dan Roll]

You do not have to be an analytic chemist to make some meaningful observations of these 'blobbs'. First, determine if one of these blobbs is water soluble; take some hot water and see if you can make this material completely disappear by gently stirring it in. If it is not water soluble your suppliers should have little difficulty determining if their products are introducing it into your system. If the material does dissolve, see if the mixture you have made will cast a film. Dissolve as much of the material as you can in some hot water and pour the water onto a glass surface and let it dry (a hair dryer is useful here). If a film is left on the surface (you might be able to peel this film right off of the glass) I would suspect starch from the plate finisher or some film former from the fountain solution. Put a drop of iodine on it and if it turns blue/purple, it is certainly starch. If the material does not cast a film it will leave some form of residue. Scrape this up with a razor blade and heat it over a flame, using the blade like a pan. If the material melts is is likely wax and you might want to talk with your ink supplier. If it will not melt, turn the blade and expose the material to direct flame and see if it will burn. If it burns, some conclusions might be drawn from the ash formed and/or the smell produced. If a caramel smell results from burning you might be looking at gum or some other saccharide material, then you would want to talk to the fountain solution supplier.
What temperature do you maintain for your fountain solution? Whatever is globbing up on you might be temperature sensitive, many water soluble materials lose solubility quickly as the temperature is lowered.

 

[VladCanada]

AGFA finishing gum; you have more thicker layer on plates than normal.
Check and readjust squeezing pair of roller at gumming section before a dryer.

 

[Dan Roll]

I suspect VladCanada is right, that is why I suggested testing for starch as the finisher uses this as a film former and the solubility of starch in water is temperature sensitive......

 

[Noodle]

I appreciate the responses. I actually have had it tested and now am trying to figure out the source in the printing process. The analysis is that it contains Kaolin clay, cellulose lignin and gum arabic. As far as gum layer goes we had a problem and they put tighter springs on the squeeze rollers that was too tight, didn't get enough gum on the plates. The springs have been removed. Checking with other sources in the industry there only seems to be this issue on a few sites that have water pans. The spray bar systems won't see this problem.

 

[Dan Roll]

Kaolin clay is a common paper ingredient
cellulose lignin indicates carboxymethyl cellulose (CMC) or some similar gum, these gums are expensive nowadays and not likely to be present in your fountain solution in high quantities
gum arabic is gum arabic, a common fountain solution ingredient not likely to be
present in your plate finisher.

From your context I am guessing you are a newspaper or insert printer. If you have brush dampening I would be suspicious of the analysis you received. Otherwise, CMC and gum arabic are often used in combination in fountain solutions (but due to their cost not often, or ever, in newspaper formulations) but I have never seen gum come out of solution and form globs before. Gums are insoluble in solvents and if blanket wash is allowed to get into the fountain solution trays it is likely the gum would precipitate, but I am not sure how it manages to form into 'blobbs'.

 

[Noodle]

I won't mention my test lab for now but trust me it is a very reputable source. You are correct we are a newspaper site. I have been working with our fountain solution company and we have been using their product for over two years with no changes in any of our production other than the plates and the gum used for these plates. I will also add that we are VERY careful to keep blanket wash away from the system. I even did a test with adding blanket wash to the fountain solution and it has been setting for two weeks. It is collected at the top of the jar and has not migrated down at all. I even go and shake it up from time to time with no change.

 

[Dan Roll]

Well, it isn't very common to see gum arabic or CMC gum in newspaper formulations and even if the solution does contain gum, the combination of cost and dosage makes it unlikely there would be much gum in the working solution. You can test your fountain solution for gum content by mixing the fountain concentrate 50/50 with alcohol. This will cause the gum to separate from the concentrate and you should be able to stir it up into a ball (we call these gumballs) and from this you will get a clear idea of what your fountain solution's gum (if it contains any) looks like. From your test of mixing the fountain solution with your blanket wash I am going to guess your fountain solution does not contain any gum or any other mucilage product, as it would of come out of solution under these circumstances and made its presence visible in the form of a film or residue.
Modern plate finishers usually use starch in the form of a dextrin instead of gum for a variety of reasons. Only one major plate manufacturer (not Agfa) has a gum arabic finisher in their line, but they do not lead with it, is available for those who ask for it.
You did not specify the type of dampening you have, but if you indeed have Kaolin in the pans I would guess it to be the four roller Goss type with a sock on the metering roller. Is this correct?

 

[Noodle]

No this is a DGM press with three ink forms, a water form and two transfers. There are no socks on the water roller. The spirial brush makes direct contact with the metering roller.

 

[Dan Roll]

All of the DGM presses I have seen have a standard spiral brush dampener where the brush flings the solution from the top of the pan roller onto an oscillating roller in contact with the form roller (an excellent dampener by the way, with one of the better speed compensators compared to other similar presses). With this configuration it is unlikely that much Kaolin is getting into the trays unless the paper is flinging clay particles in every direction leaving everything covered with a gritty dust.
Have you had any instances of foam in your trays or circulators?

 

[Noodle]

No foam to speak of. Also we do not have any dust build up anywhere from the web accept at the infeeds and angle bars which is before the towers so I don't think that is where we are getting anything from.

 

[Alois Senefelder]

Clarification

Clarification

Noodle,

In Spiral Brush Dampening Systems, the F.S --- Flicks droplets across a GAP between the brush and the Chrome Vibrator Roller.

So there is NO return of F.S.

See PDF

Regards, Alois

 

[Alois Senefelder]

Oooops

Oooops

The PDF




Regards, Alois

 

[Kaoticor]

Exactly what I was thinking. The brush dampening system doesn't allow for contamination by backtracking of F.S. Problem must be coming from something else if we are understanding you right.

Have you checked / changed filters lately in your circulation?

 

[Noodle]

I agree that there would be no back tracking. There are two 50 micron filters on the return to the mixer tank, they get changed every couple of days. The other thing of interest is that we have an overflow tank on our mixer and all fountain solution goes thru the filters before this tank and yet we are seeing the build up occur in the overflow tank.

 

[Dan Roll]

That looks like a lot of material. Does your press run 24/7? It would take some time and a lot of fountain solution consumption to build up that much material if it is coming from the fountain solution, but it is not impossible. If the fountain solution contains materials that are not water soluble (or non-water soluble ingredients inefficiently coupled) material can collect in the fountain solution, but the materials you identified early in this thread would not float, but would more likely collect at the bottom of the trays and circulators. You could try titrating (adding bit by bit) fountain concentrate into water, at the same temperature you run your fountain solution, in a glass jar (beakers are good for this but not usually available in the pressroom). It may be that at certain ratios of fountain solution to water not all the ingredients will go into solution. Materials that will collect on the surface have to either be light enough to float or have a specific gravity less than that of water. I have seen instances of silicone defoamer collecting on the surface of fountain solution in circulators before, but certain non-piling additives or solvents and surfactants have poor water solubility and might contribute to this.

 

[Green Printer]

We are using Agfa N94-VCF plates, Violet CF Gum-NP run thru an Agfa VCF 85 processor. Since we started with the plates we have seen a residue build up in our water pans on the press. This will accumulate and turn to blobbs that plug up the system. Prior to the new plates we never touched our water pans, the system has a chiller with 50 micron filters and never had any issues. Have been back and fourth with Agfa, the fountain solution mfg. We have not changed paper, ink, chemicals, nothing changed but the plates. Just wondering if anyone else has seen this problem with these plates.

Noodle

Did you get the problem solved?

 

[Noodle]

We are in the process of trying a different mix with our fountain solution. We are flushing the water system today and cleaning both processors so that we have a clean start for the testing. It will take a week or two before we know if this worked.