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screen printing => Newbie => Topic started by: Appstro on May 02, 2014, 11:03:54 AM
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I have tried adjusting my offset, angle and pressure of sqeegee, thinning the ink ever so much and I am using a new screen...
Note: is mostly in the center of the screen. The outside images and letters seem to be OK. This is hit, flash hit.
Thanks for your advice as always! ;D
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Is your flood bar digging in too deep? Sometimes that can happen and push ink through the stencil just like that. Or if you have your squeegee chopping just outside of your pallet, causing your screen to slightly pull. Just a couple things to check on. Sometimes if you have an un-level pallet or two, and you stroke more than once in the up position, the flood bar can dig in too deep pressing into the shirt and the pallet and cause this to happen too.
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Its a manual silver press. Maybe the pallet is warped...? I will take a look.
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^The squeegee chop thing has caught me before. Glad to have a front and rear carriage stop. ;)
I'd ask what your screen tension is, if it's only bad in the middle.
Could certainly be a bowed platen too--not enough OC has done this to me, but it's always the whole image, and usually on fleece...
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You know what? I think it is squeegee chop! I was pushing the squeegee past the end of the pallet. I could feel it drop off the end. Was that it then??? The image placement on the screen was centered but I guess it was close to the end of the pallet.
I am having a challenging time trying to figure out what the correct placement should be on my screens. They are either too high or too low. :(
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I gottchya, manual printing. ok, well almost same issues can occur, if you flood too hard, you may be pushing ink through the mesh and opposite direction of your print direction, so when you actually push/pull your squeegee, how ever you print, it can do that. Or if you flood your screen hard with the screen down already on the shirt, I've had that happen before, or even bringing your squeegee beyond your pallet, doing the same, "stretching" of the mesh/image can develop that. If you are thinning your ink, and still using a low mesh count, you may just be pushing your ink through too hard on your flood. Keep lots of test shirts around to find your happy medium before going into production. That's what we do. I'd rather everything dialed in and sacrifice that little bit of time, rather than wrecking good product.
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You know what? I thin it is squeegee chop. I was pushing the squeegee past the end of the pallet. I could feel it drop off the end. Was that it then??? The image placement on the screen was centered but I guess it was close to the end of the pallet.
I am having a challenging time trying to figure out what the correct placement should be on my screens. They are either too high or too low. :(
That can totally cause it, Adjust your pallets out, draw a line where you want your shirt to stop, giving yourself some play so that you can rock them puppies out and not worry about falling off the pallet. Think of it, if you fall off the pallet, you will stretch that mesh down, which will pull on your image, pulling it across the wet imprint you just did, and ghosting it out like that. It's totally a possibility.
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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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How tight is your screen? Ill bet its a little loose. Plus Ill bet that you are pushing down too hard on your pallet, which is causing deflection of your pallet. Lower your off contact a little, push a little slower and dont try to drive the ink into the garment but try to place it on top of the garment surface. Then when the job is done look at your screen to see how tight it is.
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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? ;)
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I used to run into this as well. It is from hard flooding the stencil and then printing with too much pressure and at too low of an angle and too slow. I fixed it by soft flooding ALWAYS which allows me to keep using lots of pressure and i can still do a push stroke with the lower angle. I also upped my speed.
The middle is doing this because the pressure in the middle of the squeegee is great than on the edges, so you are flooding more and printing more in the middle.
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Sounds like the screen might be around 10 newtons and the blade interference is increasing the tension on the outsides giving a decent opportunity for the mesh to get up and out of the way but the middle of the screen is sitting in the ink deposit after the squeegee passes.
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After looking at the pic instead of just reading, the tension is probably the problem and the mesh is shifting in the print stroke direction. Classic sign of low tension screens. The blade moves the mesh down to the shirt then the print stroke happens and the mesh shifts along with the squeegee stroke making the edge definition in the north/south direction really bad.
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Easy fix is the soft flood. I have some statics from like 4 years ago that have horrid tension and prevent this with my flood. Even if there is shift, there isnt ink filling the well of the stencil.
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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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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.
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Well.....where do I get "good" screens??? This screen is new so it must be no good?? Mclogan???
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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.
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^^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..
Sent using Tapatalk
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
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^^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..
Sent using Tapatalk
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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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.
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" 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...
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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.