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  1. #1
    SplitEar's Avatar

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    Default Emulsion peeling on complex images, but over exposed.

    Hi, i've been screen printing for over a year now and havent had many issues, i primarily use Kiwo chemicals and Permaset Aqua water based inks for my garment printing.

    I recently decided to up my mesh count and take on some more complex designs to print, my inks work perfect with the new (yellow) mesh (around 56 - 71, depending) but when exposing i am having issues with getting fine detail out of my screens.

    I use Kiwo Azocol Z-1 emulsion, it is a diazo based emulsion which i mix myself.

    For exposing i have SIX 400 watt (2400 watts) halogen lights pointing directly at my screen which i sandwich between glass and a raised block of wood. After the maths this left me with a 10minute exposure time, but the emulsion i use is not incredibly light sensitive, so a minute either side doesn't effect the image massively.

    The problem i am currently facing with fine detailed designs is that when i expose for 10 minutes the detail won't wash out, and to complicate matters: as i apply water to the screen to wash these details out, it peels the emulsion away at the edges where the image has successfully washed out, leaving me with a jagged reproduction of what i was hoping to achieve.

    To me this seems like problems of BOTH under-exposing and over-exposing, but with such an insensitive emulsion, i can't see why this is happening.

    I am currently trying to expose with 2 acetates taped together to give me more of an opaque stencil, but i don't see how that would help. Maybe another emulsion? I have previously achieved very high detail, but recently, it just won't cut it at all.

    I use Pregan NT9 to degrease my screens thoroughly before i coat.

    Thanks, any help is massively appreciated.
    -Alex

  2. #2
    squeegeethree's Avatar

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    1. Halogen are less than ideal for exposing emulsion. The wavelength of light best for exposing is down on the blue, violet and ultraviolet side of the spectrum (373 nm being peak). Halogen, like most incandescent lights, typically are warmer then you want for exposing ideally.

    2. Degreasing helps only so much with new screens. Abrading them slightly helps even more. We do a sacrificial coat with all our new screens. We coat them, expose them without an image (usually we just stick them outside in the sun) and then reclaim them. This eliminates the new screen blues for us.

    3. You coating method may suck. Try a nice, thin 1 over 1 coat. Press hard when coating don't be shy. If you can scrap off excess emulsion (by tipping the scoop back and skimming over the coated screen) then you may have too much emulsion on your screen. If your coat looks blotchy are streaky and not perfectly even in coloration then you are doing it wrong.

    4. Improve you films output.

  3. #3
    SplitEar's Avatar

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    I think maybe point 1 is definitely a winner.
    I have achieved damn good detail previously with a 7minute exposure with EIGHT 400watt halogen lights (3200watts) surrounding the screen, and im wondering if i elevate the lights more than 12inches off the screen so they point more 'down' rather than across the image it might stop light undercutting the acetate.

    I unfortunately don't have enough money to upgrade my exposure system currently!

    I always do a 1 and 1 thin coat at all times, and always scrape excess emulsion to avoid it dripping down the screen as i coat the 2nd side.

    I'm currently trying out with 2 acetates taped together to achieve more of an opaque stencil.

    What happens is as i'm trying to wash out the detail, the emulsion bulges and bubbles under the water pressure.
    Is this a symptom of under exposure or over exposure?

    Im going to try an 8min exposure with a doubled up acetate next.

    Thanks for the help, incredibly useful.
    -Alex

  4. #4
    Aaron Gein's Avatar

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    Sounds to me like light is getting through your films and partially exposing your stencil. Wasn't a problem at 7min, but that extra 3min now is giving just enough time for it to harden up on you. We had this same problem at my day job when I started working there. I switched them over to a pure-photopolymer (we only print plastisol there) and it cut the exposure time from 10min to 5min....the problem disappeared. Obviously the better answer is to get better/denser films....but the owner is cheap and wont invest in an epson so we're stuck using laser film through an ancient HP5000 laser printer and spraying toner aide on it to darken it. It sucks. But yeah, your problem sounds like the same problem we were having....light getting through the film and slightly exposing underneath due to the long exposure and crappy film...then when you wash out you have to use higher water pressure to clear the stencil out causing your edges to get all ragged.

  5. #5
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    weaponsofmassdesign's Avatar


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    Just curious, but if they are halogen shop lights, have you removed the uv coated glass fronts? There is no mention of it, so I'm not sure if that means yours didn't have them or you are using something different. Just a thought.

  6. #6
    SplitEar's Avatar

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    Yeah, i have a shoddy Inkjet Business 2800 i think it is, not a great printer, but for simple geometric designs, the screens expose perfect. Thanks for the idea though, it makes me a bit more comfortable with my decision to double the acetate up. (I use Folex A3 Inkjet acetates, from what i've been told they're the best?)

    Funny you should mention it, i had no idea the glass in front of Halogen lights was UV coated?
    You suggest i remove the glass entirely from the front?
    I assume this will also lower my exposure time dramatically?

    I use 3 of these:

    Defender Twin Halogen Worklight - Worklights - Lighting -Decorating & Interiors - Wickes

    Thanks again, much appreciated.

  7. #7
    Aaron Gein's Avatar

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    Doh. Yeah, UV is bad for you so halogen work lights always have UV blocking glass.....but UV light is what exposes the emulsion. Remove that glass and your exposure time should drop like crazy.

  8. #8
    SplitEar's Avatar

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    Damnit! Seems like such a rookie mistake, i did the maths with the emulsion with 2400 watts pointing at it, it had an exposure time ranging from 9 - 10.30 minutes, so lord knows where i've gone wrong there.

    Thanks, will take it off ASAP, double up my acetates, and let you know of the results, should be promising.
    -Alex

  9. #9
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    Andymac's Avatar

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    if the emulsion is coming off, it is usually underexposed. doubled up acetate (the frosted kind?) stuff is shit to begin with, blocks light (underexposed) and two, well....just that much harder to solidly expose the emulsion.

    Question - is the stencil solid where there is no film? if it is, then it's the film material. If it gets solid when you up the time, but your detail/image is filled in, then your black is not dense enough, or the light is undercutting. Doubling up shitty transparencies in order to to make the black denser is like drinking two non-alcohol beers to try and get drunk. just switch to tequila and quit fucking around....

    there's no math that will tell you correct exposure. And wattage does not measure the UV dose. Removing the glass is a good idea...

    Good luck
    Andymac

    services www.squeegeeville.com
    equipment www.tmiscreenprinting.com

    Todo es empezar.

  10. #10
    SplitEar's Avatar

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    Quote Originally Posted by Andymac View Post
    if the emulsion is coming off, it is usually underexposed. doubled up acetate (the frosted kind?) stuff is shit to begin with, blocks light (underexposed) and two, well....just that much harder to solidly expose the emulsion.

    Question - is the stencil solid where there is no film? if it is, then it's the film material. If it gets solid when you up the time, but your detail/image is filled in, then your black is not dense enough, or the light is undercutting. Doubling up shitty transparencies in order to to make the black denser is like drinking two non-alcohol beers to try and get drunk. just switch to tequila and quit fucking around....

    there's no math that will tell you correct exposure. And wattage does not measure the UV dose. Removing the glass is a good idea...

    Good luck
    The acetates i use aren't the frosted kind, they're Folex inkjet acetates, completely transparent, rough one side (inkjet side) smooth on the other.

    The stencil is completely solid where there is no acetate, the issue is, like mentioned above, to attempt to wash the detail out, i have to use much more severe water pressure. This then makes the emulsion jagged at the edges because the water pressure is ragging and ripping it at the edges. I do think the light is undercutting the stencil however, as my inkjet printer is completely shitty and not laying down a thick enough ink coat onto the acetate.

    Tequila? I haven't heard of that brand before, not sure if you can get it in the UK?
    Thanks.

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