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Topic: probs with peeling emulsion  (Read 2309 times)
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aliengrace
« on: September 30, 2006 03:52:21 AM »

Hi there,

So i've started using photoemulsion. Could anyone please give me pointers on what the following problem might be caused by?

I've got this issue where the design doesn't want to wash out even though it looks pale and pulpy, and if I blast enough (a few minutes with coldish water, hardish spray), the whole damn emulsion starts peeling off in big plasticky bits. Am using speedball emulsion.  That problem or the design washes off easily and the emulsion follows right after which I assume is underexposure.

Is this overexposure even if the exposed emulsion comes out when rinsed?  Is it that cos I'm trying so long to get the design out that the exposed emulsion follows after?  My setup is 500W halogen, 2ft away, 43T white mono mesh @ 17-22min - I think is overexposure from what others say.

I'm having (newbie I hope) problems getting an even coating on the mesh with the scoop coater, when I hold the screen up to the light I can see the thickness varies.  Could my diazo emulsion be too thick?  Not drying properly? (damn I've tried to give it hours and hours with a warm fan in the vicinity) but I read some comment saying oh diazo it takes a couple of *days*.  Humidity ~60%, temp ~20C.  Also, I find most of the emulsion, sometimes about all of it, ends up on the bottom print side.  I coat the bottom, then the top, then dry it bottom side down (like people say to do), and it ends up through to the bottom side most of the time.

Could it be um, undercutting going on?  Or inadequately opaque stencils?  Glass bigger than the screen, and I've had to layer and staple two transparencies together to get more opacity.

I use sugar soap to degrease, and then I scrub and rinse it heaps, but could this be the wrong thing to use?

I want to step test (only done it with yellow mesh so far and underexposed even the max), but I want to work out why this is happening before I waste more emulsion and time in case it's something other than overexposure going on.

Thanks!!  Cheesy
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free_loader
« Reply #1 on: September 30, 2006 11:13:18 AM »

sounds like your screen was properly prepped before you loaded it up with emulsion, and that some of your images may have been under exposed ...

to prep the screen you want to use a strong degreaser and scrub it really well .. then don't let it touch anything until you loaded it up with emulsion

as for loadin the emulsion evening ... i go the hi-tech route ... a plastic spoon and an old credit card ... spoon on a blob .. and spread it as thinly as possible with the credit card ... i usually only spoon the emulsion onto one side of the screen .. but it spread it on both sides with the card .. (the winner is the thinner .. don't have to take her skinny a$$ out to a fancy dinner, like sizzler) ..ok .. sorry 'bout the bloodhound gang outbusrt .. but that song always pops in my head when i'm spreading emulsion ..

once you get it spread .. look thru the screen at some dim light source ,, i use the TV.. to make sure you don't have any gaps

now it should dry a bright green color

when you expose the screen .. it should turn a dark aqua blue .. and when you lift off your stencil .. you should see your image clearly on the screen (the image will still be the same bright green)
( i use the sun to expose .. it's free and takes 1  minute or less)

for washing out the screen a massaging showerhead works fantastic .. and don't be afraid to use your fingers to rub the design as you spray it ..

follow those directions and you can't go wrong

« Last Edit: September 30, 2006 11:43:52 AM by free_loader » THIS ROCKS   Logged
entriq
« Reply #2 on: September 30, 2006 11:40:35 AM »

It is possible that your film positive is not opaque enough, and is letting enougth light through to start exposting the image area.

There are numerous factors that need to be considered.
Sometimes the easiest thing is to find someone who is nearby who is successfully doing screen printing and have them take you through the paces.
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entriq
aliengrace
« Reply #3 on: October 01, 2006 02:29:54 AM »

Thanks for your replies.  I doubt the screens were underexposed as I kind of got an okay bit on a step test at the max on a yellow screen (20 min), that was less time than the white screens were exposed for.  It could be opacity - damn - I've spent so much money on transparency double-ups!  I'm going to put some strips of duct tape of different thicknesses on some acetate for my next step test to see if that makes a difference.  I am assuming from your replies that it wasn't that I was rinsing the screen too much that made the exposed parts peel off.  Also, I've acquired a glass cutter so that the glass will rest on the mesh and not the frame.  It's maybe possible that the screens weren't dry enough as the coatings were quite thick.  As for degreasers, don't have any of the american brands here (for a wonder), so I don't know what's a guarantee to use - assume you meant I might *not* be degreasing it enough.  Maybe one of the evil cleaners you need gloves for like Domestos, rather than sugar soap??  As for finding someone locally who knows screenprinting and is willing to share, I wouldn't know where to start to look, but thanks for the suggestion.  The industrial printing suppliers I've found (Jones Brothers, Craigieburn Vic Aust) are a bit useful for some questions.

Well, here I come!  Boy, am I aching to get my sexy images onto fabric!!  Roll Eyes Grin  Thanks again!  Will post with more results!! x

*edit* I like my welded scoop coater, but I'm going to try to press harder and angle the scoop coater back to get a thinner coating, at least on the outside, on the inside I'll go easier so I don't push it all back through.  At least if it's too thin, I'll know, and arrive eventually at an average.
« Last Edit: October 01, 2006 02:34:59 AM by aliengrace » THIS ROCKS   Logged

_chittybangbang
« Reply #4 on: October 07, 2006 09:08:37 PM »

It could be that the emulsion wasn't fully dry before you exposed it to light... I had that trouble before. If that is the case, then just make sure you leave the emulsion to dry long enough Wink
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aliengrace
« Reply #5 on: October 08, 2006 02:51:39 AM »

Cheers Smiley One of the screens that I let really really dry still did peel somewhat but not as badly.  I used a stronger degreaser and scrubbed the screen with an abrasive (bicarb) as well to help prime the new screen, and the new couple of exposures peel much less on rinsing.   Still not 100% happy however, so I'll try again.. and again..

A question: within reason, can you wash a screen too much just after exposure?  Like, could the exposed parts, properly hardened, reasonably start peeling if you were still clearing the emulsion out with a cold non-electrically-powered but hard jet of water?  I'd like to eliminate the possibility that I'm not being efficient in my rinsing out of the screen in time.
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_chittybangbang
« Reply #6 on: October 08, 2006 06:29:55 AM »

I find (for me) if you scrub REALLLY hard continuously on one certain area of the screen, then yes it does come off. How long are you letting it dry for? Are you using a fan to dry it off or anything?
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aliengrace
« Reply #7 on: October 08, 2006 07:58:02 AM »

hmm, in terms of drying, i'm letting it dry for at least a day (it's the speedball diazo stuff) at about 18-22 degrees celcius (room temp), at about 60% humidity which is not really low (ideally 40 - 50% apparently) but not too bad.  i've had a fan in there on at least some of those hours.  the emulsion stuff really isn't laid on thick, it's quite transparent when held up to a safe light.  oh yeah, and i put the emulsion on once i've pointed a heater at the freshly degreased screen and all the monofilament mesh holes with water stretched across them shrink to nothing - could the screen *still* be holding a significant amount of water do you reckon??  if it's the emulsion not drying after 24 hours, well, that's going to drive me nuts.  maybe i should get a quicker drying non-diazo emulsion if that's the case.

hmm, i was just blasting the whole screen really.  not for more than a few minutes.  also the emulsion seems to invariably end up only on the print side, which dries face down, no matter whether i coat the top side only or not.  is this normal?  i've been wondering if a bottom-side-only coat means that it adheres less to the screen.  i don't completely trust my emulsion to act normally as it was sitting on my shelf unopened for several months before i used it.

well, i've been too busy to really go full-bore at solving the problem.  my step tests are still rather inconclusive.  i'm just going to have to juggle a whole lot of variables, waste the rest of my big emulsion jar, and keep notes on everything, as the solution *is* out there for me.  (ya know, sometimes i'm tempted to think the universe is playing tricks, just on me, and then i remind myself that physics and hence chemistry don't make exceptions.)  thanks for the suggestions, hopefully i too can dispense advice once i've worked it all out! x
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aliengrace
« Reply #8 on: October 16, 2006 05:37:55 AM »

okay... so for the record for anyone who's curious, i've got a decent screen or two.  not getting the peels anymore, the universe is not playing tricks on me anymore   Grin

*increased exposure time - it was a bit underexposed!

*made the emulsion much thinner, just coated the print side of the screen.  maybe it should be thicker for durability, but it seems okay for now, it's pretty viscous stuff and i don't press really hard with the coater, and it gets pushed partly through to the non-print side anyway.  the emulsion being thinner -->  drying all the way through, and light definitely penetrating all the way through in order to harden.

*using a stronger degreaser on the screen, and used bicarb to scrub my new site as a bit of an abrasive for better adhesion, like the stuff they sell in profesh printing supply places for new screens. 
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free_loader
« Reply #9 on: October 16, 2006 05:55:38 PM »

w00t!!! congratz :-)
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