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screen printing => Waterbase and Discharge => Topic started by: Cole on November 30, 2018, 09:43:29 AM
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To be more specific, the discharge is creating a line where the edge of the tape is. The weird thing is that the line isn't even discharging the same color as the ink. For example, I was printing white and blue, but the line by the edge of the tape is off white. Looks like pure base, unpigmented. I've attached a picture below. I was asking another printer about this and he said that he thinks it's a chemical reaction happening between the tape and the ink. Normally, I would just tape over the line on the shirt size of the screen and continue, but my tape has a hard time sticking once the screen is moist with ink. Even if I get the tape to stick, the line appears again where the edge of the tape is.
Sorry if I'm not explaining this well. It's a weird thing that I only experience on longer runs. I'm using LXP emulsion, post exposing in the LED unit for 1 minute, and using medium pressure on the auto. If anyone has non chemically reacting tape suggestions, please let me know. Or if there is another solution to this problem, please help me before I lose my mind!
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your screens are breaking down where the edge of the tape is. post expose the screens and it will help.
You also need to use the tape with rubber glue on the back. It will stick better to the moist screens (just in case you are using the acrylic glue).
pierre
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I had this exact same issue last week when running a 2 color print. My print was light pink flash light blue and the tape ended up getting basically damp and not holding all too well.
I think the issue was that I was pulling over the registration mark that was taped, a little bit of ink or even outgassed ink vapor made it through the tape and since the tape was kind of damp it left a very faint impression. My solution while printing was to not print over the registration mark and that seemed to work. In the future I'm going to move the registration marks further away or try out a different tape.
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I had this exact same issue last week when running a 2 color print. My print was light pink flash light blue and the tape ended up getting basically damp and not holding all too well.
I think the issue was that I was pulling over the registration mark that was taped, a little bit of ink or even outgassed ink vapor made it through the tape and since the tape was kind of damp it left a very faint impression. My solution while printing was to not print over the registration mark and that seemed to work. In the future I'm going to move the registration marks further away or try out a different tape.
are you using rubber based tape?
pierre
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No I'm using the cheapy white tape. I have some blue R-Tape I'll probably use for reg marks going forward.
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It's as if the water breathes through to the edge of the tape since it can't where the tape is.
We either don't use reg marks or put them out of the area of the print completely along with screen info, then we don't need to use any tape on the screen where the squeegee prints.
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If one must use those pesky reggie marks, we always found the blue painters tape to work well for taping off discharge screens.
The leaking on the tape edge could be an issue with the emulsion itself.
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we call this screen sweats. This is typically from a screen that's breakdown, where the tape is trapping the pigment, but letting the discharge base seep out. So you'll get lines you'll be chasing non stop.
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All above is correct. Many printers can be daunted by no reg marks but in some cases is necessary. I would love to give the perfect recipie for screen prep, however I have found it varies from shop to shop. Post exposing and using a hardener are excellent considerations. In a perfect world, no tape on the underside of the screen is best. No matter what tape is used, yes it is trapping water vapor contaminated with DC activator.
The daunting/exasperating aspect is...…..although the lines are off white, they might be coming from a screen with DC color. And most often not visible until the substrate exits the dryer. Not trying to scare anyone off
because all these issues can be addressed. Not without a little effort, however, once you find the sweet spot it's a breeze
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we call this screen sweats. This is typically from a screen that's breakdown, where the tape is trapping the pigment, but letting the discharge base seep out. So you'll get lines you'll be chasing non stop.
I use the LXP emulsion from CCI, which is supposed to be good for discharge. I also post expose it to try and prevent breakdown. Is there anything else I should try to harden the screen more without sacrificing the ability to reclaim it? I know you print a ton of discharge, so is there a certain tape that you've found that doesn't allow the discharge base to seep out?
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Someone might have already say this because I didn't read all the post, I've had that happen also, so now when I do a discharge print I tape both sides of the screen mostly on the back side I tape where the squeegee edges will be, better safe than sorry, I've double taped the back when I know I've got a long run.
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I had this exact same issue last week when running a 2 color print. My print was light pink flash light blue and the tape ended up getting basically damp and not holding all too well.
I think the issue was that I was pulling over the registration mark that was taped, a little bit of ink or even outgassed ink vapor made it through the tape and since the tape was kind of damp it left a very faint impression. My solution while printing was to not print over the registration mark and that seemed to work. In the future I'm going to move the registration marks further away or try out a different tape.
I had that same issue. I thought it was the registration marks too. So on the next job I didn't even use registration marks. I taped them off on the inside of the screen with clear tape, put the screen on press, laid out the film on the pallet, and registered the screens to the film rather than printing my key screen and registering all the other colors to it. The issue still happened. I thought maybe it was too much squeegee pressure, so I backed it off A LOT and it still didn't solve the issue. I think Eric is spot on about what's happening. The way he describes the tape trapping the pigments, but allowing the discharge through sounds right to me. This was happening on a longer run than what I normally do, so this was new territory for me. I was in the middle of a 240 piece order when the line started showing up. Maybe my screen wasn't post hardened enough.
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I had this exact same issue last week when running a 2 color print. My print was light pink flash light blue and the tape ended up getting basically damp and not holding all too well.
I think the issue was that I was pulling over the registration mark that was taped, a little bit of ink or even outgassed ink vapor made it through the tape and since the tape was kind of damp it left a very faint impression. My solution while printing was to not print over the registration mark and that seemed to work. In the future I'm going to move the registration marks further away or try out a different tape.
I had that same issue. I thought it was the registration marks too. So on the next job I didn't even use registration marks. I taped them off on the inside of the screen with clear tape, put the screen on press, laid out the film on the pallet, and registered the screens to the film rather than printing my key screen and registering all the other colors to it. The issue still happened. I thought maybe it was too much squeegee pressure, so I backed it off A LOT and it still didn't solve the issue. I think Eric is spot on about what's happening. The way he describes the tape trapping the pigments, but allowing the discharge through sounds right to me. This was happening on a longer run than what I normally do, so this was new territory for me. I was in the middle of a 240 piece order when the line started showing up. Maybe my screen wasn't post hardened enough.
no doubt you need to expose better. If it's photopolymer, you can post expose. If it's diazo, you'll have to expose longer.
pierre
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I use the LXP emulsion from CCI, which is supposed to be good for discharge. I also post expose it to try and prevent breakdown. Is there anything else I should try to harden the screen more without sacrificing the ability to reclaim it? I know you print a ton of discharge, so is there a certain tape that you've found that doesn't allow the discharge base to seep out?
Emulsion manufacturers make permanent and reclaimable hardeners, just insurance, but proper initial full exposure is your best bet.
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We print discharge and wb all day every day and no tape on the shirt side of the screen. That is a recipe for disaster. The screen needs to breath or pay the consequences. If you do not have a reg system and are using reg marks to film take the extra step and block out the reg marks with emulsion. Then expose again. You can still see the reg marks through the emulsion and most importantly you now have no tape on the back side of your screen. No tape is your friend.
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And tape is expensive. Like replacing shirts and setting up a job twice
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Perhaps a bandaid but also a safeguard for us, in addition to post exposing, is Mod Podge on the bottom of the screen.
Sent from my iPhone using Tapatalk
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We print discharge and wb all day every day and no tape on the shirt side of the screen. That is a recipe for disaster. The screen needs to breath or pay the consequences. If you do not have a reg system and are using reg marks to film take the extra step and block out the reg marks with emulsion. Then expose again. You can still see the reg marks through the emulsion and most importantly you now have no tape on the back side of your screen. No tape is your friend.
This is what I've been trying to do. There are so many variables mentioned already, buy we've struggled with the tape line breaking down on runs over 100pieces and I'm trying to keep tape off the shirt side of the screen if possibe and only taping the squeegee side. We have an Alan802 style pre reg system and so we block out the reg marks with CCI Aqua Block, then tape over that on the squeegee side.
We are on WR-14 diazo emulsion right now and I've also been overexposing our screens to a solid 10 on the 21 step calculator. Sometime i feel LED exposure units need more juice, but that's a whole other conversation......
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Edit - sorry that may not have made sense above, we use aqua block all over the shirt side of the screen before it goes up on press, just as an extra layer of protection. It covers all the tape areas including the reg marks and we also put tape on the squeegee side
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We print discharge and wb all day every day and no tape on the shirt side of the screen. That is a recipe for disaster. The screen needs to breath or pay the consequences. If you do not have a reg system and are using reg marks to film take the extra step and block out the reg marks with emulsion. Then expose again. You can still see the reg marks through the emulsion and most importantly you now have no tape on the back side of your screen. No tape is your friend.
That pretty much sums it up. Assuming you get your exposure times nailed down as mentioned. Hardner may help some but will not eliminate the nightmare as long as you continue to tape the shirt side of the screen. Using Natural rubber tape will not help in anyway either We use tape that so when pulling it for reclaim it doesnt leave much residue .
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We print discharge and wb all day every day and no tape on the shirt side of the screen. That is a recipe for disaster. The screen needs to breath or pay the consequences. If you do not have a reg system and are using reg marks to film take the extra step and block out the reg marks with emulsion. Then expose again. You can still see the reg marks through the emulsion and most importantly you now have no tape on the back side of your screen. No tape is your friend.
Thanks for the info Brandon! Do you still tape the inside of your screen to stop the edges of the squeegee from breaking down the emulsion? Or is that something that should be solved with pressure adjustment?
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Hey, yup we tape the inside of the screen. You can do the permanent block out inside your screens but we prefer tape for various reasons.
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And yes you can put tape where the squeegee is. Still round off the edges of the blade but yes you can do this as an insurance method.
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Hey, yup we tape the inside of the screen. You can do the permanent block out inside your screens but we prefer tape for various reasons.
When you tape the inside, is there a specific tape that you use as far as adhesive goes? Rubber vs Acrylic.
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Hey, yup we tape the inside of the screen. You can do the permanent block out inside your screens but we prefer tape for various reasons.
When you tape the inside, is there a specific tape that you use as far as adhesive goes? Rubber vs Acrylic.
Always natural rubber back tape
https://www.uline.com/BL_3073/Natural-Rubber-Adhesive-Tape-Polypropylene (https://www.uline.com/BL_3073/Natural-Rubber-Adhesive-Tape-Polypropylene)
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For reg marks or small breakdown, use UPS thermal shipping labels(the ones they give you for free) those things are indestructible!