Clearing Screens Versus Dot Gain

[andyandtobie]

Hi everyone, as usual, if this has been covered elsewhere, don't hesitate to glare at me and please point me to the right thread.  I rarely post here, to be honest, because almost everything I've ever needed to know is already here.  But I haven't noticed any threads that particularly discuss this problem.

Anyway, here's my silly question.  I'm having a hard time figuring out how to keep my screens clear without getting massive dot gain.  Is this an ink shear problem?  My first guess is that this is a matter of squeegee speed/pressure/angle and I just haven't figured out the sweet spot yet, but it's getting frustrating.  I end up printing a few shirts and then printing off on paper to clear the mesh again, which adds up to a lot of wasted time.  I'm manually printing plastisol though 225S or 300 statics with Murakami mesh, triple-duro squeegee rubber in the fancy-pants aluminum handles, and QCM ink.  Thanks!

[Frog]

I print manually, and changing from a pull to push stroke helped me clear better.
In what direction do you print?

[andyandtobie]

Thanks, Frog!  Actually, I've always been pushing since we started.  Pull strokes always looked to me like they'd be inefficient and hard on the arms.  But that does make me wonder if the angle is part of the problem.  I'm usually at about a 45 degree angle or flatter, but I know that I'm not real consistent.

[jsheridan]

when you push, do you stand there and push with your arms or do you lock in and lean with your body.

Think like an auto.. how do you use your arms and are you creating different pressure points in the way that you are pushing.

A good hint that your pressure is uneven is image ghosting on the board but only on the top half.

I manual pull  23" long jumbo discharge all day every day and have this weird looking stance that I use as I lock my arms and use my body to pull back the squeegee.

[andyandtobie]

Thanks, jsheridan.  I do lean in a little as I push, but I'm definitely using my arms and shoulders, as well.  Sounds like this may indeed be an issue of squeegee technique, rather than some other variable, huh?  Dang, if only I had the cash for an auto and somewhere to put it...

[jsheridan]

yep, manual is all technique

An auto squeegee just runs along a metal rail set at a precise angle and uses the same pressure over and over and over.. you just load shirts.. sounds kinds boring 

[andyandtobie]

Yeah, I have to admit, I'd go for some of that boredom.  I'm an artist first and a printer second, and the time I spend wrestling with the press seems to suck a lot of the profit out of the jobs that I run.  I'm pretty convinced that the wrestling comes from inconsistencies in technique.  I wish I could just knock out a job chop-chop and get back into my studio as fast as possible, but as it is, a run of just 20 shirts with three to six colors will pretty much kill my day.  A used Javelin came up near me last summer for $9000.  I tried to refinance my house to build a small shop in front and buy the Javelin, but no dice because the banks won't refinance for cash on a manufactured home.  Oh, well.

[Frog]

A lot of talk about technique, but issues with your press can exacerbate the situation as well. Is the problem consistent from board to board and squeegee to squeegee?  And,how about your off contact?

[andyandtobie]

Yeah, I can see what you're saying there Frog, but I really don't think that's a problem in this case.  Seems like it's pretty consistent, I just gradually start getting more and more ink hanging in the mesh, a tiny bit here and there, regardless of color.  If I use more pressure, or stroke it two or three times to clear it, I blow out the image with dot gain.  For off-contact, I usually have about 3/16" between the empty pallet and the screen.  I turn all six heads over all four pallets when I'm setting up, just to make sure.  There is often a little variation, say a 1/16" or so.  I'll print about three or four shirts and I'm clearing it on paper again.  I often just leave one pallet empty just for that purpose, and you know that's not right.  Someday someone will want a big order for something and I'll be in trouble!

[blue moon]

are you printing wet on wet and which ink are you using?
also the squeegee should be almost parallel to the screen when pushing. Lower you can get it the better.
maybe post a quick video, it would be easier to tell.

to clear properly without pushing too hard, you'll need ink that prints well, sharp blade, good screens, proper off contact, correct screen size (the smaller the area of the screen used, the better you are off as screens have a sweet spot) and good mesh. It sounds like you have most of these, so maybe it's time to re-evaluate them!

pierre

[abchung]

I push it here.
I fill the screen with a pull.
Then push at a certain angle.
If it does not clear completely, I push again without flooding. The squeegee holder is at a lower angle so the bottom edge of the squeegee is more vertical. This is to help shear the remaining inks off the mesh.

Equipment:
1.Sharp Squeegee (most important for shearing).
2. Mesh size: 305/inch (thin thread/ Saati) would be easier to learn off, because in the beginning we found 230/inch was leaving too much ink on the fabric for the following screens.
3. Good tension but not as important as sharp squeegee. All mesh tension should be above 22N
4. We use Wilflex, Rutland or Matsui

[andyandtobie]

Pierre, I am printing wet-on-wet, or at least attempting to.  Triangle Phoenix White goes down through a 225S and flashed.  Colors are QCM, specifically the QMX mixing components, printed through 300 Murakami statics.  I often end up doing at least one other flash, if not more, which concerns me since I know that you wouldn't be doing that on an auto.  Interesting thought on the "sweet spot," as I'm using 20" x 24" screens, which are as big as I can go with my press.  I do know that I need to get a tension meter desperately, but the screens we have currently don't have much mileage on them- only a few hundred impressions so far.  Squeegee rubber is also fairly fresh.  I do wonder if I need to get my angle down flatter.  Thanks for the ideas!

Abchung, thanks a lot for your description.  It really sounds like maybe this is a shearing problem from what you guys are saying.  I'll try lowering my angle as much as I can.  I started out with 225S for colors and had the same problem with too much ink.  Sometimes I try to push a second time without flooding, but it seems like either I get dot gain again, or I get ink from the back of the squeegee, left on the blade from the flood stroke.  Hmm...

[alan802]

I'm going in a slightly different direction and even though we print 99% of our work with the auto, I'm on the manual doing samples and testing almost on a daily basis so I feel like I can help a little.  I know those inks you speak of, the mesh counts and the squeegees.  I think a few of the biggest causes of dot gain are using too much pressure and your off contact.  If you're having to lean on top of that squeegee to get it to shear all of the ink then you likely be losing your squeegee edge contact and buckling the blade, then you're rolling excessive ink through the mesh.  I know there will be many who disagree with me here and say they print on 225s and 300s all day long on a manual press but I'll tell you that I'd never do it.  I'm not trying to diminish anyone else's strength that may be reading this but if I struggle to shear ink through a 280 or a 300 mesh then everyone reading this will because I'm not a small guy nor am I a weak guy.  A 225/40 doesn't require a whole lot of pressure to print with but with Phoenix I'd have to question just how much pressure you'll need to get the ink to clear.  It really does depend a lot on the ink but even some inks through a 180/48 you'll need in excess of 30lbs of pressure to clear a long bodied darker color.  You can certainly reduce a lot of pressure by proper technique but it really all boils down to physics.  Ink doesn't pass through tiny mesh openings easily.  It also doesn't pass through long "tunnels" without excessive pressure.

If I were a manual shop I don't know that I'd have too many screens above a 225/40 on the press.  With all of the other variables that can add to the dot gain, like your off contact, mesh tension, print size, squeegee edge sharpness and durometer, I'd make sure to tilt them all in your favor.  The easier the ink will clear a screen, assuming your other variables aren't a mess, you should get minimal dot gain.  If you're putting even a little body weight into your print stroke then you could be using excessive pressure.

[jvanick]

I'll chime in and add that the 'tunnel' effect of excessive EOM can cause troubles as well.

[mimosatexas]

Alan and Jason covered exactly what I was going to say.  Simply put, 300 mesh is probably your main issue, and excessive eom is possibly adding to the problem.

I'm an all manual shop, and I print a lot of 55lpi stuff.  The highest mesh I have in my shop is 280, and those almost exclusively get used for CMYK inks and black (usually based down a bit for shadows).  9 times out of 10 if I am printing any other ink using small halftones I am using my 225S screens.  The major benefit of the 225S is it will hold low and high percentages fine (with the right emulsion and exposure setup), and you can do a fast, low pressure push stroke and get a very clean print, complete clearing your ink without excessive gain.  With a 280 or 300, unless your ink is based down, you will often have to use a lot more pressure, a slower stroke, etc to get a clean, even print.