Wash-outs

[elguapo]

I run an SM52-6 with a coating unit and have been having lots of issues with colors, mostly Cyan and Magenta suddenly washing out, sometimes on one side and sometimes across the entire sheet. A minor correction leads to the densities spiking on that unit. Could anyone help me out with an explanation as to why this happens and how to prevent it? I'd really appreciate it! Thanks.

[rbailleu]

let me guess no isopropyl.ipa subs can have this effect. its like walking a tight rope. pretty easy to fall off either side. how old are the damp rollers

[elguapo]

The rollers are about a year old. We do run alcohol, but the dosers on our Technotrans aren't working so
we measure and mix manually. This leads to another question. Due to evaporation, how quickly would the fountain solution mixture get out of balance, and what would be some of the telltale signs?

Thanks!

elguapo

[rbailleu]

if you have checked all the roller setting and the rollers look good. the only other things I could see is mechanical issues. or a balance issue. with alcohol we usually see a toning or scumming if the alcohol evaporates. we currently flush our system weekly on the 52. when using alcohol we only flushed every 2 to 3 weeks. currently we are using heidelberg 201 and 301.

[Dan Roll]

Have you checked your alcohol? Almost nobody does but you should every time you open a new container. There are three checks to perform, one requires a hydrometer centered on a specific gravity reading of 0.8. The specific gravity of IPA is .790; if you measure the gravity of your alcohol and it is higher than this, the alcohol is diluted with water. Some suppliers dilute the product as much as twenty percent because they are sure you will not test it. The other two tests are based on mixing some alcohol with water at a ratio of about half and half. This mixture should immediately form a clear solution, it should not be the least bit cloudy or hazy. If it is cloudy or hazy, it is likely contaminated with petroleum distillate which will seriously interfere with your printing. The last test is to shake this mixture vigorously. You should not be able to form any bubbles. If you can generate any foam at all, the alcohol is contaminated with some form of surfactant. If your alcohol fails any of these three tests, do not use it and it should be returned to whomever sold it to you.

[Ozkan Hangisi]

Thanks Dan. Very usefull infos.

[elguapo]

Thanks guys! You've been a huge help. As you could probably tell, I'm new to process printing (about a year now).

elguapo

[first XL]

Normally when wash out occurs, its all about roller settings. If the image is strong at start and starts to drop, this means the ink is not flowing smooth down the rollers. Set the rollers with the proper stipes, check the water form and rubber pan roller diameter, bring down the water setting and try again. I have seen this many times and that ought to do ya.

[Kaoticor]

Good work on looking for more information to learn! As the other commentors said, check your dampening system roller settings if you havn't already, and if that doesn't do the trick, post again.

[bpel123]

I run an SM52-6 with a coating unit and have been having lots of issues with colors, mostly Cyan and Magenta suddenly washing out, sometimes on one side and sometimes across the entire sheet. A minor correction leads to the densities spiking on that unit. Could anyone help me out with an explanation as to why this happens and how to prevent it? I'd really appreciate it! Thanks.

I had the same problem, in two cases, the FIRST was that a bearing was going out on a transfer roller. even though I set the stripes right, when I went to run, the roller would back off and not transfer the ink to the lower rollers. this caused and surge in density when the ink would build up enough to transfer. the SECOND case was simply roller contamination, use febo often!!! Are your rollers stripping? (like a 1,2,3, inch strip of ink on your rollers missing) if so, its definetly contaminated, or too much fountain solution. some pressman think that more solution is better, for some reason. The minumum 2-3-4 ounces per gallon (instead of 6-7 like the bottle says) is the best. when I started at my company they were using 17 ounces solution, 17 ounces of alc sub and 12 iso. alc.(Per 5 gallons of water) I was toning so bad, I have cut down to 15 oz. solution, 12 alc. sub and 12 iso. alc. Im not done cutting back either. if you use r.o. water, you should use even less, the better the water, the less you will need. THIRD, How cold is it there? warm your press up by running it for a while in the morning with no ink on the rollers.
Hope this helps