What causes this???

[alan802]

This is the type of stuff I used to see often back when we first started.  I still don't know how we made it through because most of the issues we really couldn't fix for the most part.  I think I'd add off contact and change blades and angles along with a dozen other bandaids until it went away.  Then as we started incorporating good screens into production the issues simply went away.

[Appstro]

Well.....where do I get "good" screens??? This screen is new so it must be no good?? Mclogan???

[alan802]

I've gotten so many supposedly good statics and honestly I only know of two places that have screens with better than crap tension and the first place is Xenon and the second is Murakami.  My local supplier carries the Murakami smartmesh statics with S (thin) thread.  He has 135/48, 150/48, 180/48, 225/40 and I think the 310 or 305's.  The Xenon screens will come in at 25 newtons or so and end up in the high teens once you use them a few times and the Murakami will come in around 22-23 newtons and settle around 19-20 newtons.  I wish Xenon would have sold me some thin thread statics a while back so I could have tested them but the only place to get thin thread statics is Murakami direct or my local guy, River City Graphic Supply in Austin.  In my humble opinion, the best mesh for printing plastisol on dark garments is the Murakami Smartmesh S thread.  I will never go back to standard mesh counts because EVERYTHING (except durability) is better with thin thread.  And if you don't have a bunch of gorillas handling the screens then the thin thread stuff will last years and tens of thousands of imprints.  You can print white ink through the 225 with 22-25 psi (auto) or equivalent on a manual press and that is impossible with regular 230's where you have to force the ink through the stencil.

[ScreenFoo]

^^This is great, just the suppliers he mentioned could save you a lot of time and aggravation...

The stencil holds the shape.. What side of the coater are you using to coat with? If the knuckles of the mesh is pertruding then it will cause the ink to get pass the stencil edges.. The print side of the stencil needs to create a gasket with the shirt and that means a layer only just thick enough to go pass the knuckles of the mesh and create a smooth even surface, not too thick otherwise you will be giving your ink unnecessary work to do. In your case a high solids photopolymer emulsion is recommended or even better ulano ez film 30 or 50 microns, that way your only concern is getting the exposure right. The film will cost you about 1.60 per screen or 3cents a shirt for a 1color, 50 shirt run..
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If the problem is just in the middle, how did he make just the center of the stencil too thin?  ;)

Well in his case, he's buying pre stretched screens and do not have a meter to check it's tension, then he goes about coating the screen as usual using the maximum width coater that screen can accommodate (I'm betting on him only having one width coater).. And this is where his problem begins.. We know (he doesn't) that tension increases rapidly nearest the frame's edge so the emulsion will be applied thicker at the outside than in the middle of the mesh. At wash out what little solids remaining in those thin areas takes a beating..

If he still prefers to use the all of the above scenario in his operation then he can go with a smaller coater which will mean smaller images (not happening), higher solids emulsion or cap film which I think will give a higher percentage of success in his case..

If it were image stretch alone then how are both sides of the letters stroke, being blurred and better ink coverage away from the blurred areas? Also he played with different on press config and nothing changed it, that's because the problem is in the stencil.

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So you imply there is no knowledge of tension, emulsion, or coating technique, but full knowledge of every applicable press parameter? 
I have to admit, this seems rather unlikely to me--but it is certainly possible.

If you look closely at what Alan mentions in the pic, the vertical strokes have about one percent of the blurring *on both sides* that the horizontal strokes do, which I agree would point to tension/no band-aid OC being the major culprit--I would also think that there would be significant blurring in the direction of the stroke, and/or in every direction if the stencil edge was really THAT poor, but why would there be significant blurring in only two directions but not the other two because of a low percentage of solids in the emulsion or not using cap film? 

Oh yeah, and how do you put more emulsion on the edges of a low tension screen then the center?   I can do the opposite, no prob, but after reading this I want to learn a new parlor trick.    ;D

[starchild]

^^This is great, just the suppliers he mentioned could save you a lot of time and aggravation...

The stencil holds the shape.. What side of the coater are you using to coat with? If the knuckles of the mesh is pertruding then it will cause the ink to get pass the stencil edges.. The print side of the stencil needs to create a gasket with the shirt and that means a layer only just thick enough to go pass the knuckles of the mesh and create a smooth even surface, not too thick otherwise you will be giving your ink unnecessary work to do. In your case a high solids photopolymer emulsion is recommended or even better ulano ez film 30 or 50 microns, that way your only concern is getting the exposure right. The film will cost you about 1.60 per screen or 3cents a shirt for a 1color, 50 shirt run..
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If the problem is just in the middle, how did he make just the center of the stencil too thin?  ;)

Well in his case, he's buying pre stretched screens and do not have a meter to check it's tension, then he goes about coating the screen as usual using the maximum width coater that screen can accommodate (I'm betting on him only having one width coater).. And this is where his problem begins.. We know (he doesn't) that tension increases rapidly nearest the frame's edge so the emulsion will be applied thicker at the outside than in the middle of the mesh. At wash out what little solids remaining in those thin areas takes a beating..

Oh yeah, and how do you put more emulsion on the edges of a low tension screen then the center?   I can do the opposite, no prob, but after reading this I want to learn a new parlor trick.    ;D

Set your uv exposure unit for a 8% eom burn, coat an under tensioned screen (the softer part of the screen would "pool" to maybe 24% eom the perimeter of the screen would "hold" say 13% eom)  let dry, expose for the 8% eom and washout (the center of the screen will not be fully exposed) then check the eom of the screen.

A high solids emulsion would help retain edge sharpness and cap film will ensure even exposure and edge regardless of the screen tension.

Oh he did say he changed his off contact distances and it did not have any effect. Maybe the sceen was so loose that he needed a 2 inch off contact..

6 yrs of parlor tricks and counting..

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[alan802]

I never thought about how much underexposed emulsion would wash out during development but makes perfect sense, and would be more extreme the more underexposed the emulsion is and how hard the person spraying works it with the pressure washer.  I saw the vertical blemishes and would have looked at the mesh shifting along with the print stroke causing one side and the mesh shifting back to it's original position causing the other side imperfection.  I thought nothing of the ink deposit inconsistencies from different locations on the screen and only of the blemishes above and below the text.

[ScreenFoo]

" tension increases rapidly nearest the frame's edge so the emulsion will be applied thicker at the outside than in the middle of the mesh"

to

" coat an under tensioned screen (the softer part of the screen would "pool" to maybe 24% eom the perimeter of the screen would "hold" say 13% eom) "

Sounds exactly opposite to me.  As I said, I have no problem coating and undertensioned screen thicker in the middle.
Just trying to make sure the "newbies" don't get confused by even more conflicting information...

[jason-23]

This happens to me when my mesh is weak and I'm pushing too hard, wipe screen down and move on, or make a fresh screen with tighter mesh.