Coating methods?

[3Deep]

Ok I just need to ask this and get some science behind from you experts, I know what I get when I coat a screen 1/1, now when I coat 2/1 what am I really getting, in my lame thinking I think alls I,m doing is pushing emulsion to the other side of the screen then remove the thickness of it when I coat the other side with one coat.   I,m I really building up the print side of the screen or scraping it back to where I started in the first place 1/1, I know I get a good thick screen with the roll edge of the coater I can just about see it being thick, just a question I'd like to have an answer to in real world not data sheets.

Darryl

[Frog]

Unless you are not applying any emulsion to the inside (either with a dry coater, or angled so as not to pour out any more, you are putting down a little more as well as pushing the first two coats back to the substrate side where it does its jobs of providing an ink well, eliminating the effect of the mesh pattern on image edges, and forming a gasket.

With the visual reference of coating the substrate side until the squeegee side shines or glistens (emulsion past the mesh), you almost can't go wrong. This glistening could be in 1, 2 or even more coats depending on mesh, coater edge, and technique.

[alan802]

I personally think there is only one right way to coat a screen for 95% of what we do and that's the way Frog mentioned.  Here is an article from Murakami explaining the coating process (not entirely) and has some good points in it but it lacks the explanation of the most important part of coating a screen.  Great article other than that.

http://murakamiscreen.com/wp-content/uploads/2012/06/Emulsion-Coating.pdf

I always teach my guys to coat about 5-6" per second with a few pounds of pressure and to make sure the two sides of the coating trough along with the round edge of the coater are in contact with the mesh at all times.  The two sides aren't as important as the edge but they need to be extremely close at a minimum to keep from getting the thick beads of emulsion that take forever to reclaim.

[Frog]

Alan, it's a band-aid at best, but when your guys do get those thick edge trails (or beginning or end points as well), just have'em scrape off the ugly excess with a small piece of cardboard or credit card.
It would be nice to not have to, but why compound the problem with the crappy reclaim later rather than take a few seconds to clean up each boo-boo bead while wet.

Heck, I've seen blobs that create their own off-contact spacers!

[alan802]

We do exactly that Frog, the stir sticks that come with the emulsion is used for that purpose if it happens, but we usually only have excess around the softened corners of screens that I just stretched and haven't retensioned yet.  Once I retention I then get rid of any excessive corner softening I did when originally tensioning.  It's an old habit that I could easily fix by not softening so much but I'm much more careful stretching thin thread mesh and haven't lost a mesh in a long time.

And, with mention to EOM and the glisten method, if you do the coating procedure correctly then you will be right in the 15-20% sweet spot in EOMR.  I've measured hundreds/maybe a thousand screens and not one single screen that was done with the glisten method was under 10% EOMR with the vast majority of them being 15-20%.  The low EOMR screens were coated too fast, mainly the final coat on the squeegee side was too quick.  We've adjusted our lower EOMR screens to coat a tad bit slower and those mesh counts start at about 175 and go up.  The lower mesh counts are able to get a good EOM with a faster coat speed where the less open % mesh counts do not.  Just like with getting ink through the mesh, mesh count is extremely important to how the emulsion flows through and what kind of coats you'll have to do to get a proper EOM.  305's at our shop require 3-4 coats on the shirt side with our current emulsion, Murakami HVP.

Check your screens tomorrow and rub your finger across the stencil edges and let us know what you feel, if anything.  You should feel a definite "step" on all of your screens 200 and under but your higher mesh screens might not be so easy to feel, especially if you have very little to no feeling left in your finger tips like me.  I like our workhorse mesh counts, 150/48 and 180/48 to have 20% EOMR which the glisten method nails it right on the money.  You really don't need a thickness gauge as long as you commit to the glisten method and do it correctly.

[brandon]

While they can cost anywhere between a few hundred to a couple of thousand a micrometer is a nifty tool to have. Especially if you have different people coating your screens. It can help you find your desired EOM with different people's speed and pressure applied. Just my two cents. Not every shop needs one, they are just good to have

[3Deep]

Good points! Yep I get those thick edges when I 'm in a hurry, but like you guys I take old cards and scrape those edges down they are a pain like Allen said to reclaim.  One of my reasons for asking this question is because I have some screens print like a charm and others that make me want to rip the mesh out, but I know it's all in how I coat each screen...sometimes it's a grab what's dry and go, not a good habit to do. Oh and I have mesh mess's like crazy all types of brands some not as good as others..

D

[alan802]

I'd also be willing to bet that the screens you have the most trouble with are your lower tension screens.

[3Deep]

Allan you could be right, most times I just grab what's dry and go instead of taking my time and grouping my screens.

D

[Frog]

Darryl, if you are using statics, you often don't need a fancy meter to know when they are past their useful tension.
Don't dick around! Pull 'em, get a pile of six or eight and send 'em off to Xenon for re-stretch at about 1/2 or even 1/3 the price of new (unlike many re-stretch services!)
Good product, good service, good price. You may have other options in your area as I understand that a even some other member/suppliers in your region also offer this service.

*Note to roller fanboys - save your derision for another thread please. Just trying to optimize a situation here within set parameters.

[alan802]

Darryl, if you are using statics, you often don't need a fancy meter to know when they are past their useful tension.
Don't dick around! Pull 'em, get a pile of six or eight and send 'em off to Xenon for re-stretch at about 1/2 or even 1/3 the price of new (unlike many re-stretch services!)
Good product, good service, good price. You may have other options in your area as I understand that a even some other member/suppliers in your region also offer this service.

*Note to roller fanboys - save your derision for another thread please. Just trying to optimize a situation here within set parameters.

I've got some Xenon statics and they are holding steady tension from when they were new.  I got 5 and they are all sitting around 23-25 newtons.

[3Deep]

Frog, I got some of those panel frames way back, don't use them that much mesh on them suck, need to replace the mesh.  I 've got some frames that are low I use them for one or maybe two spots prints on very easy stuff, I'm like a pack rat just can't seem to let them go lol.  I think i'm going to try and buy some S mesh frames, but I do know tight mesh coats a whole lot better than loose mesh. @ Alan, I got some frames from Sonny and they are not tight as I would like them and I let him know this, but for that matter I got frames from them when they were RemaDura.

D

[alan802]

I think low elongation S thread mesh is the best bet for static frame users.  The typical lifespan of a static with average mesh is it is stretched to say 28 newtons, glued, and sent to the customer.  Now this may not be typical of higher quality screen makers so don't come after me with the exceptions to the rules.  Then before it's used one time it's probably down in the low to mid 20's, let's be conservative and say 25 newtons.  Then one time through production it's down to 22, conservative once again since I know most average mesh will lose about 20% after the first run through production, then another 15-20% on the second run so most statics are well below 18 newtons after two runs through the production chain.  Low elongation S threads don't lose as much tension between jobs or after the initial stretching.  The Sefar thin thread that I've used is as good or perhaps even lower elongation than the smartmesh but I've only had 123/55 and 180/48.  Some mesh loses 25% of it's tension after one run, and I've had _______brand mesh go from 60 newtons to 45 before it's ever printed with and then down to 35 after the first print run.  S thread tends to lose much less, around 3-5% according to my notes, and that makes it an ideal candidate for static frames.  And the argument has never been about rollers versus statics, it's really always been about proper tension versus low tension and if a static can have a 150/48 that work hardens in the 23-26 newton range then it will be as good as the newman roller for at least as long as the mesh stays on the frame.  It won't last as long a roller that's properly cared for but they will last a long time.  And since S thread doesn't require the higher tension levels to keep a high mesh opening % you don't have to keep track of your screens as closely because they'll still print great at 18-20 newtons and a regular thread with a much smaller mesh opening will be a lot harder to print through when it's 18-20 newtons.

I've got notes on exactly how much some of our mesh elongates and I can calculate the exact percentages but most of the notes were taken before the first print run and only document how much the mesh relaxes after the first tensioning till I put it into production.

[3Deep]

And since S thread doesn't require the higher tension levels to keep a high mesh opening % you don't have to keep track of your screens as closely because they'll still print great at 18-20 newtons and a regular thread with a much smaller mesh opening will be a lot harder to print through when it's 18-20 newtons.

Allan, I think you just solved my mystery about printing through high mesh counts, I did a check a few mintues ago with my tension meter and my 305's and a few of the 230 are 18  and down to 14 newtons...that won't work, the mesh has closed up making it hard to push ink thru them, no matter how I coat the screens.

Darryl