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screen printing => Screen Making => Topic started by: jvanick on November 17, 2014, 02:00:54 PM
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we had a set of screens break down today, and it looks like chatter marks on either side of the screen, like the squeegee was 'skipping' and then breaking down the emulsion. The screens have roughly 6000 or so prints on them, so maybe it's just overuse for SP1400?
never have really seen this before, and wondering what's causing it.
Emulsion if it matters: SP1400
Approx squeegee pressure: 45-50 psi
20 degree angle
70/90/70 duro squeegee (relatively sharp)
Plastisol ink.
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If it's just on the edges of the squeegees that you see the chatter marks, it's an easy fix- round your squeegee corners. Also, top tape your squeegee drop/finish areas as well as the very edge where the sq corner hit the emulsion.
If the chatter marks are inside the image area it's just a matter of your blade/pressure/substrate/# of impressions/off contact, etc. being too much for the emulsion. SP1400 is tough chit from what I hear but 6k impressions will start to get at most any emulsion, just a matter of friction over time. You can combat break down inside the image area by face coating the ink side of the screen, putting a little more emulsion on there to resist the wear/tear.
But really, rounding the corners and top taping will solve most of this. Good luck!
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If it's just on the edges of the squeegees that you see the chatter marks, it's an easy fix- round your squeegee corners. Also, top tape your squeegee drop/finish areas as well as the very edge where the sq corner hit the emulsion.
If the chatter marks are inside the image area it's just a matter of your blade/pressure/substrate/# of impressions/off contact, etc. being too much for the emulsion. SP1400 is tough chit from what I hear but 6k impressions will start to get at most any emulsion, just a matter of friction over time. You can combat break down inside the image area by face coating the ink side of the screen, putting a little more emulsion on there to resist the wear/tear.
But really, rounding the corners and top taping will solve most of this. Good luck!
we already round the squeegee ends, and tape where the squeegee drops are... plus tape the ink side where the edges of the squeegees ride.
This is actually IN the image area, not edges.
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Are the chatter marks parallel or are the marks from stencil openings outward in any direction?
Al
Murakami
What was the ambient shop temp over weekend?
Alan
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They were parallel AND starting from the open area out in some cases, other cases, it was in the middle of the screen itself.
ambient temperature doesn't go below 60. It *is* very dry in here... in the screen room it's about 22% RH right now, in the shop, around 30%. (if that makes a difference)
Pic of one of the screens attached. The "line" you're seeing at about on the 1/3rd of the image is where the the tape is on the back side of the screen.
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We see this with emulsions when it's dry sometimes. Particularly with HVP. I would try the face coat on the ink side or just plan on swapping out screens every 5k impressions.
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I have had this happen with any emulsion that is "Harder" than other emulsions. I.E. non diazo Water Resistant.... This happens all the time with Murakami's HV, Saati's PHU, and other emulsion like this that are designed to be water/discharge resistant without needing a hardener. The reason for the cracking is the mesh is "Flexing" or moving with each print stroke and causing the emulsion to actually delaminate/crack since the emulsion does not have the ability to flex with the movement of the mesh. High pressure and hard squeegee's exacerbate this effect.
Now, is the above what happened to the SP1400? I have no idea. But the description is almost identical to what I and others have experienced on multiple occasions.
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And now I see some pictures!
That is identical to what happens here. Its related to the flexibility of the emulsion.
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We run the PHU and have had the "cracking" in the past. At least for us when it gets cold and dry (winter) I cut my exposure time down about 10 ltu across the board, it seams to help and I have not had any screens break down.
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Alan Buffington and I troubleshot this issue awhile back and yep, the verdict was pretty much too dry. There is a Murakami dual cure, I want to say SP7500?, that he suggested as it's more flexible.
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I have this problem often in winter. I expose screens one day and print later in the week. Would misting the screens with water to "rehydrate " them before printing work?
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We run the PHU and have had the "cracking" in the past. At least for us when it gets cold and dry (winter) I cut my exposure time down about 10 ltu across the board, it seams to help and I have not had any screens break down.
so you're saying to try deliberately underexposing the screen?
hmm... and here I originally thought that it was because we were under-exposing... interestingly enough, it doesn't seem to be happening at least as much on our 200 and 230 mesh screens.
I'll give that a shot for tomorrow's print run and see what happens.
now, I wonder what 10 LTU is on a LED unit... maybe 1 or 2 seconds when I typically expose for 22 seconds?
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They are not underexposed as far as I can tell. Still getting a solid 7 on the stofer strip, non of the other tell tail signs. I believe it has to do with moisture content when exposing. I started this season two weeks ago, no signs on press but when scrapping the ink out of the screen I could hear the emulsion cracking. Reduced my exposure time and it went away.
As a reference a 156 yellow coated 2/1 with PHU is 75l ltu in the summer, 65 winter on our 3140.
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Hmm. Using Saati PHU our 3140 has us exposing at 150 ltu for plastisol and 180 ltu for waterbase. Yellow 150/54 sure lock panels. Gets us a solid step 7 @ 150 ltu.
But we coat 2/2 sharp side.
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I'm proberly doing it wrong. I have not had any issues with those times of screens breaking down. Biggest run that we have done with this emulsion was 3k plastisol and a 600 straight discharge double stroked. I keep the exposure time the same for both but post expose twice the exposure time or set in the sun for a bit when doing WB or discharge.
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Just wanted to post a quick update on this...
my rep at our supply company told me that there's a specially forumulated SP1400 called SP1400-W for winter/dry conditions.
We received a 5er of it today, and it's currently sensitizing... we'll be coating screens with it tomorrow so I should have a report by monday or tuesday on how well they hold up :)
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Whoa, that sounds great. Do they have a version for HVP as well?
This thread jinxed us, we had to pull a screen in under 100 impressions yesterday due to this issue. It's dry in here now, around 20% humidity in the shop. Going to try adding just a touch of distilled water to the HVP and see if it solves it.
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Yes we do a sell a more flexible version for winter. Overnight temps in the shops can get quite low, and with cold blowing wind, no storm, the air is quite dry. We offer SP-1400W which we sell in the midwest predominantly for this reason. HVP does not have a winter version. In some cases I have had companies install vaporizers to bring humidity up to 35%-50% in the screen rooms, but screens left set up overnight on press can be affected by cold dry air. It's the cold/dry conditions that cause it. We are not seeing it here in Socal where the humidity can get down to single digits.
Zoo City is correct, we do offer 1400W for winter printing and SP-7500 which was Engineered to be more flexible for long runs and has the same resolution and print qualities as SP-1400. It is a dual cure that was designed for sim process type of work.
Al
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We're at around 20-30% humidity, 60˚F in our screen room. Conditions on the shop floor are about the same on humidity, more toward the 20% (maybe the humidistats we have only go down to around 20% and it's actually lower?) but the temp on the floor probably drops to around 50˚F overnight. We can humidify the screen cab but humidifying the whole shop would not be practical.
Any solution at all for users of stencils with HVP or similar?
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We have not had many reports of HVP cracking. I have often wondered if washing the screen with warm water on press and drying with scrap t-shirts in the morning would help.
We do have two new emulsions we are testing for textiles. Murakami T3 for wb and discharge, no hardeners needed. This requires a 5K+ Metal Halide or Starlight exposure. (Again we haven't tested on the Vastex, Douthitt, Lightspeed, or other LED models at this point yet so I can't speak for them yet.) Long exposure time on a 5k metal halide, 5-6 minutes. Starlight would be a little over half of that from our initial test results. For short run discharge and wb under 5k I'd stick with HVP or SP-1400. But if you library screens or have long runs it works great, with incredible resolution (better than SP-1400) and reclaim that is very easy.
The other emulsion is TSR which is for High Solid Acrylic Inks. Again designed for long run HSA inks and requires a hardener. 4 minutes on a 4k metal halide, 2'30" maybe on the Starlight. While the long exposure seems time consuming, reshooting screens is more time consuming. HSA is not waterbase or solvent, its a combination of both typically. HSA will one continue to move into plastisol sales for large companies printing for major sports brands or companies. It's soft hand and no PVC or Pthalates appeals to major retail brands. It requires learning a new ink system and a matching emulsion like Murakami TSR that can withstand these new inks.
Both would print plastisol with ease.
Alan
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We'll try a little rehydration on the HVP screens.
Excited to check these out Alan, we're still down as always to beta for you and Murakami.
An emulsion for HSA is long overdue. You are correct in it's special requirements; it has all of the needs of a WB/DC stencil combined with much higher EOM requirements for opacity without printing this ink on a 28 station oval. On top of all that it gets scrubbed down rigorously on press. Tall order to fill for an emulsion.
5-6 minutes. Starlight would be a little over half of that from our initial test results.
And here is where I had such a hard time explaining that we could really, seriously, use a 2up setup for LED exposure. "Nah, it's super fast, you won't even need to shoot 2up" is absolutely true for plasti screens, not even close for HSA screens. Still, 2.5min is way better than the 5-6min. that we currently are dealing with. Our Olec bulb has even scorched the back of the reflector at this point.
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Ok Chris looking for some beta testers for TSR for HSA inks and T3 for discharge and wb with no hardener needed.
Message me and I'll get you all some samples to test, expecially in winter weather. I can also sample others who are interested.
Al
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Got something that works well on a Nuarc 3140?
Currently exposure times with the Saati PHU are 170 ltu for plastisol screens and 200 for waterbase screens for the Sure Loc 150/54 Murakami panels coated 2/2 sharp side with the PHU. If you have something comparable I would love to try it out!
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PM sent Alan. We currently have an Olec 5kw setup, shooting 2up at 63" from glass. Our Starlight arrived last week but was damaged in shipment so it will be another week or two before that gets installed. If we hit the window we could trial on both potentially.
Would the TSR work equally will across HSA/DC/WB/plasti? Is the TSR a diazo added emulsion? I'm presuming the TSR has a higher build to eom per coat. We harden all screens, have made that a very fast, efficient part of the process at this point, so non-permanent hardener is no problem and we do use Murakami A+B on the real long runs. We do not post expose screens however.
Sorry to the original poster for the thread jack!
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so after a few days now with the SP1400W, here's our findings...
1. it's runnier than standard 1400... and with the same coating technique seems to build a slightly thicker stencil... I forgot to bring our thickness meter to the shop, so I'm not 100% sure how much more it might be building.
2. it takes longer to expose... much longer. 26 seconds for standard SP1400, 40 seconds-ish for SP1400W on a 156 mesh.
3. when using it on the manual press it seems like it's a 'slicker' surface...
4. most importantly, NO BREAKDOWNS! Even at 3500-4000 shirts, the screen looks great.
if the SP7500 is like this and is a year-round emulsion, I might look to switching to it, unless there's a significant cost difference.
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Another Winter approaches and we're having the chatter breakdown/stencil cracking issues worse than ever. It's very low humidity here, reading 14% on our basic digital hygrometer in the screen cabinet. Xenon Nova, the emulsion we use nearly exclusively, held up ok last year to the dry climate but is struggling this. We're upping the amount of water that we add to the dry diazo powder to see if it helps but I hate messing with the emulsion's viscosity too much.
Has anyone successfully tried to wet the screens down and then dry them before going on press or a similar fix?
How about Murakami TSR? I see it's on the website now but no TDS. Anyone out there using it during the Winter?
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We've since switched to Saati PHU-2 for faster exposure and better reclaim...
initially we were having some edge breakdown issues, but we narrowed the issues to the fact that we were coating screens at nearly 50% EOM. once we got our screens into 20-25% EOM, the issues went away.
*the edge breakdown issues were JUST at the corners of the squeegees, the breakdown never continued into the middle of the stencil like it did with the SP1400.
Based on this, I'd check your emulsion thickness and see what it is...
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Do you round your corners?
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Do you round your corners?
yup... rounded...
just changing the EOM% seems to have fixed the issue...
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It definitely happens on the higher eom screens. Not exclusively but close to it. I'd like to experiment with lowering eom but nows not the time. We also need to start measuring consistently.
Sent from my SM-G900V using Tapatalk
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Got something that works well on a Nuarc 3140?
Currently exposure times with the Saati PHU are 170 ltu for plastisol screens and 200 for waterbase screens for the Sure Loc 150/54 Murakami panels coated 2/2 sharp side with the PHU. If you have something comparable I would love to try it out!
You have something funny going on I think. We run a 3 k and a 150-S coated 1 shirt side and 2 squeegee side are exposing PHU in 28 LTU. We run a little on the thick side too for a stencil. That is a pretty dead on exposure. Finish off with an hour in the sun after block out and we run10k impressions with no hardener or breakdown.
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Got something that works well on a Nuarc 3140?
Currently exposure times with the Saati PHU are 170 ltu for plastisol screens and 200 for waterbase screens for the Sure Loc 150/54 Murakami panels coated 2/2 sharp side with the PHU. If you have something comparable I would love to try it out!
You have something funny going on I think. We run a 3 k and a 150-S coated 1 shirt side and 2 squeegee side are exposing PHU in 28 LTU. We run a little on the thick side too for a stencil. That is a pretty dead on exposure. Finish off with an hour in the sun after block out and we run10k impressions with no hardener or breakdown.
Actually we did have something funny going on.....
Exposure times are now at about 60 ltu for that same mesh with the same emulsion.
The key was - INSTALL YOUR BULB IN THE CORRECT MANNER...........
The last guy we had in the screen room put a new bulb in UPSIDE DOWN.... yea, its a real thing. We installed a new one, correct side up and exposures dropped by 1/2 to 2/3.....
Frikin nuts man.....
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Walt from Murakami sent us out some SP1400W. So far it's been the solution to our chatter problems! SP1400 seems like a great all around emulsion to boot, we're going to do res tests on it next month.
In case this wasn't mentioned this emulsion is freeze/thaw stable.
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Hmm. Using Saati PHU our 3140 has us exposing at 150 ltu for plastisol and 180 ltu for waterbase. Yellow 150/54 sure lock panels. Gets us a solid step 7 @ 150 ltu.
But we coat 2/2 sharp side.
Thats some pretty crazy times. We expose PHU for 25 LTU on a 3 k light and thats more than enough. PHU loves the sun. 30 minutes in the sun after exposing and we have never had an issue. The only time I have had chatter arks was with SP1400.
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when we switched from SP1400-W back to SP1400 the starlight and that emulsion didn't mix well for us here... we were getting very unpredictable results depending on who the hell knows what... which made us start to look for other emulsions...
We switched to PHU .. it was too fast (160S screens were at 3 seconds! to a solid 7)... so we switched to PHU2... (160S at 12 seconds)... we started getting some weird chatter type breakdown sometimes depending on the shirts, pressure, etc...
we did more research (Ross Balfour from Saati involved)... and found that we were coating screens way too thick.. on S-mesh we found that a single round edge coat on the shirt side was plenty to get us to 18-20% EOM.
After we made that simple change (which has saved us a LOT in emulsion as well), we're now running 1000+ piece discharge runs with PHU-2 (with proper post exposure) with all the easy reclaim of a pure-photopolymer. Honestly couldn't be happier with how it's working out.
JBLUE is right tho on that the Saati PHU emulsions love the sun or post-exposure... after a bunch of testing, I don't even think that the LED units gives the right wavelengths for proper post exposure, as I can put 3 screens on the same long-run job (1 post exposed on the Starlight, 1 post exposed on Saati's 300W lamp, 1 post exposed in the sun) and the best looking screen at the end of the job will be the sun post-exposed one, followed by the Saati 300W one, followed very closely by the starlight....
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On most days, 30 minutes in the sun has to be the equivalent of hours in any exposure unit.
But, perhaps 5 minutes would have had similar effect. There has to be a point at which all molecules are cross-linked, and further exposure is merely recreational sun tanning.
(http://1.bp.blogspot.com/-CIgxF5zcBww/UAWOZdj4XWI/AAAAAAAAB88/2lWJxqyBzNE/s1600/zonker.jpg)
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Sounds like you need to move to the Gulf Coast...problem solved!