how do you check for undercutting with a microscope?

[jvanick]

I just picked up one of those little 200x usb microscopes and put one of my 300tpi screens under it.

halftones were exposed at 50lpi.

here's the pics:

[Frog]

How about viewing the film (perhaps a cut section) right next to your exposed screen dots, and compare size?

[Dottonedan]

Good call Frog.  (Hows the show?)   That would be one of the things I'd be looking at.


2nd,  What are we looking at?  Is the the squeegee side or the shirt side of the stencil? I can't tell.


Either way, Dang, looks very thin. THAT is another reason for undercutting. You seem to have (little to no wall) to trap ink.


In fact, from the looks of these pics it's as if the stencil does not continue past the top layer, thru the threads and (have much of any) thickness onto the back side. Now, I know you coat the other side as well, but you may not be putting (enough) thickness down on either side. The (shirt side) should be close to a smooth surface and will form a good seal. Like a gasket on a motor so that no oils (ink) leaks out.


People prefer to only coat one time on each side for high mesh and fine detail like 50-60 lpi, That to me IMO is too thin even for high detail...but no matter how you do it, you somehow need to make sure you have a good flat surface on the other side. To do that, you probably need to coat 1 time....slower, or maybe two times thin....and then let that dry, and come back and apply a face cost. This fills in those knuckles and makes for a smooth surface.


These two images seem to leave hills and valleys for ink to travel under.


I was a good idea to post these pics. This helps you identify some big trouble areas for you.

[Inkworks]

My first thought was dang, I hope that's squeegee side or you're gonna have trouble holding detail.

[jvanick]

that is the squeegee side.  however, it was a stencil that was previously used and cleaned.  I'm waiting for a fresh one to dry right now.  after it's dry enough, I'll take some more shots.

it is a 1/1 (glisten method tho, so 2 wet coats on the substrate side, + 1 on the squeege side) - fine edge of the scoop coater.

so I think what I'm understanding is that the emulsion should be 'smooth' on top of the mesh.

[Inkworks]

Check this out:

http://www.theshirtboard.com/index.php/topic,2621.0.html

Depending on how the shirt side looks, you may want to use the round edge of your coater, and remember 2/1 may not work on all screen mesh counts, some may take 3 on the shirt side.

[Frog]

that is the squeegee side.  however, it was a stencil that was previously used and cleaned.  I'm waiting for a fresh one to dry right now.  after it's dry enough, I'll take some more shots.

it is a 1/1 (glisten method tho, so 2 wet coats on the substrate side, + 1 on the squeege side) - fine edge of the scoop coater.

so I think what I'm understanding is that the emulsion should be 'smooth' on top of the mesh.

The way I got it was that minimum EOM (emulsion over mesh) is enough to completely negate any affect of the mesh itself on edges of your stencil.
The extreme at the other end, would be the saw-toothing, especially on diagonal lines that we have all seen at some time.

[Screened Gear]

If your looking at your emulsion that close you want to check for good bridging of the emulsion from thread to thread. If your edges are washed away to the mesh then you have underexposed emulsion. You should have nice sharp, not rounded off edges. Rounded edges also means you washed off emulsion that should have stayed to give you a tight gasket to the shirt during printing.

From looking at your screen you are under exposed.

First thing to look into is how dark your film is. This plays a big part in fully exposing your emulsion. If your film is not dark enough you will never be able to expose your film fully. If you wash out your screen and the emulsion comes off in sheets or even clumps then your film is not dark enough (or you over exposed, not likely for most shops) What happens is film is letting to much light though, lightly exposing the design. This makes alot of other issues. Washouts will take longer. Your edges of the stencil will not come out clean. you will also have to use more force to get the screen to wash out that could hurt or wash out fine detail.

Hope this helps

Jon

[alan802]

I always advise using the round edge of the coater.  In my opinion there is no real need for the sharp edge when coating screens for the regular textile printing that most of us do.  You can still get a thin stencil with the round edge if that's your goal, and you can get a thick stencil with the sharp edge (takes a lot more effort), but if you want to reach the proper EOM with the least amount of work then the round edge wins every time.  I even do face coating with the round edge, and that was the only application that I could see using the sharp side but it's also my opinion that we really don't need to be doing face coats unless we're trying to win a golden squeegee award or something similar.  The round versus sharp coating is summed up like this:  The round edge can do everything the sharp edge can do, but the sharp edge can't do what the round edge does (without doing extra work).

Using the glisten method with the round edge, medium pressure (3-5lbs), 4-6"/sec speed, you will be in the sweet spot for EOM.  I have taught all of the guys who have worked here how to coat and I have been measuring those stencils for a long time and once the guys start to get outside those parameters, our EOM gets too thin or too thick.  The most common mistake I see is coating too fast.

[JBLUE]

The glisten method is not needed for everything. You do not need to do it for waterbase for example. You do not need that kind of build up on a WB screen unless you are just interested in increasing your exposure times and spending more money on your emulsion. There is such a thing as too thick and what you have to narrow down is what works for you in your shop and your style of printing. We use the glisten method here on some stuff. There are also times here that we will even coat 1/1 sharp edge on a 305 or 355. That goes against all the written rules. However it works and it works well at that.

[alan802]

Yeah, glisten is really for plastisol printing and like most other settings for WB/DC we don't have to be near as strict or on point with everything except making sure the stencil is burned clean through and will hold up on press.  All the other stuff that we normally try and control for plastisol is not that important for WB/DC.  Off contact, whatever, print pressure, heavy, print speed, who cares, WB/DC really does have a lot of pros that make it easier in so many ways.  We don't normally coat screens with one or the other ink system in mind but rather pick 180-230 mesh for DC prints that have a target EOMR of 10-15% versus a 20-25% goal for the 83-150 mesh counts most commonly used for our plastisol prints. 

Do you guys normally coat your screens differently based on the ink you plan on using?  A 1/1 on a 305 coated here would yeild a zero EOM but as long as it holds the image then it will work fine.  I have been measuring a lot of stencils lately because my screen guy has gotten severely off course with our stencils and our 280-305's with a 2/1 had very little to no EOM, well under 10%, the 3/1 is a bit too high and on high mesh I'd rather have less EOM than more like I would want for low/mid mesh counts.

[tonypep]

The first paragraph reflects points I've been making for a very, very long time Alan. Used to make the "consultants " batshit crazy, especially my friend Bill from the Hood. It's why we don't need retens, for instance. When you radically change the viscosity and rheology of the ink carrier you can throw that stuff out the window. Its an easier and cheaper process for many.

[Screened Gear]

The glisten method is not needed for everything. You do not need to do it for waterbase for example. You do not need that kind of build up on a WB screen unless you are just interested in increasing your exposure times and spending more money on your emulsion. There is such a thing as too thick and what you have to narrow down is what works for you in your shop and your style of printing. We use the glisten method here on some stuff. There are also times here that we will even coat 1/1 sharp edge on a 305 or 355. That goes against all the written rules. However it works and it works well at that.

I agree with Jason. Printers get so used to talking about white ink that they think what works well for thick white ink works for everything. I started on a manual and when I went to an auto, I had problems. To fix those problems everyone tells you thicker EOM and slow the print down as slow as you can. This works but it is also the slowest way for printing. It also uses the most emulsion (maybe why the emulsion manufactures say use the glisten method). After about a year of experience on my auto I started using much less EOM. now I am also printing much faster and getting sharper cleaner lines and edges. I do think you have to work your way though it.  You have to build a feel for what it right and what can be improved on.

Not exactly sure if Tony is modifying his inks but I modify almost all my inks. Even my whites.

[alan802]

We went to thicker stencils but in relative terms they were thicker compared to what they were, which was virtually zero at the time.  I personally think that when printing white plastisol it's good to have a 20% EOMR and up to 30% will help with opacity and not hinder the ink deposit.  Higher than that and you start to see the ink deposit suffer from the "tunnel" being too deep.  There are tons of things you can do to compensate and get more out of a thick stencil but it's not feasible at most shops.  We try to find that sweet spot that gives us maximum opacity/correct ink deposit but allows us to print fast, and with very little pressure.  A 150 micron stencil can work great, or it can screw everything up, it depends on the tools available to the printer and their ability to work through the problem.

[jvanick]

so I've been playing around with trying to get better EOM on my squeegee side... and I seem to be running into trouble.

1 very slow (2 inch/second or so) coat on each side of the screen with the round edge of the scoop coater, medium pressure, seems to be ending in the same results I was seeing with the sharp edge.

squeegee side:



(Looks like I'm seeing some undercutting?)

substrate/shirt side:




I just read a post about somebody else having trouble with getting good EOM with Xenon Nova...  I'm getting what I feel is great detail for my crappy setup (unfiltered uv blacklight setup here), but would like to get metter EOM

suggestions? 

Would prefer to figure out a coating/eom/etc method that works well for plastisol AND wb/dc as many times jobs just 'come up' and it would be nice to not have to worry about having 2 sets of screens.