Exposure & washout trouble

Here you can discuss issues related to exposing screens for screen printing. This includes determining the exposure, light sources and washing out the stencil in the washout booth. Emulsion issues may also be addressed here.

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strokers
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Joined: Fri May 27, 2016 5:33 pm

Exposure & washout trouble

Post by strokers »

Alright so I'm new to screen printing and I have started hitting a couple of difficulties. My first few screens exposed and washed out quite nicely (at least I thought quite nicely for my first attempts). But now I'm stuck on a design and cannot seem to get it right, even after over a dozen attempts. My trouble at first was that my positive wasn't dark enough so I worked that out and printed out another positive and stuck the two together. Now I'm having difficulty washing out the image after exposing. The image just doesn't want to wash out :evil: , even when I have the hose on it for over 5 minutes. Then when it finally does wash out all the detail goes with it. I don't think its a problem with my exposure time..... so I'm not really sure what it is. My only idea is that because I cannot wash out in my light safe environment when I go outside to washout the image the sunlight is exposing the screen? But I don't have the screen in the sun for very long at all so I'm not sure if that will do it. Just to give you a bit more detail I'll list the products I'm using and how I'm doing things. I'm using Ulano QX-I Emulsion which is a ready-to-use, fast-exposing SBQ-dual-cure direct emulsion (I'm not sure what SBQ is?) also there shouldn't be any problem with the emulsions age as I've only had it for a couple of months. I'm exposing the screens with a 500W bulb which is about 4 inches away from the screen. Here is the image that I'm trying to print for reference. Any help would be much appreciated.
saharawoodlogopositive.jpg
strokers
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Joined: Fri May 27, 2016 5:33 pm

Re: Exposure & washout trouble

Post by strokers »

Is there any chance that my bulb is to close to the screen and the heat from the bulb is causing the emulsion under the image to semi-cure?
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Catspit Productions
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Re: Exposure & washout trouble

Post by Catspit Productions »

Sometimes it takes me a day or 2 to respond since I'm only one person over here ;) I apologize for the delay.

Yes, it could be the heat from the bulb if you are too close on a longer exposure. It could also be the sun fogging the screen since we should really handle the screen making in safe light conditions. I'm not familiar with that emulsion but sometimes a better emulsion can be easier to use. I often switch people out from a Ulano emulsion to a Saati emulsion and that end the problems.

SBQ is referring specifically to the chemical make up of the emulsion. "Today's emulsions use only two types of photo sensitizers. Diazo, which has been around for some time and Styryl Basolium Quaternary photopolymers called SBQ photopolymers which are relatively newer." You can learn more about it here:

http://www.catspitproductionsllc.com/li ... sions.html

But I would guess that if you adjusted the exposure details and worked in safe light conditions, that might solve the problem. The light should be at least 18 to 24 inches away from the screen. Make sure any glass you are using is resting on the mesh only and not the frame edges. If the glass is resting on the frame edges it cannot sandwich the film positive nicely to the emulsion coated screen. Then light can go around the film positive choking and ruining details or more. Then try washing out the stencil inside with a yellow or red light bulb only.

Let us know if that fixes the issue.
Jonathan Monaco
Catspit Productions, LLC
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http://catspitscreenprintsupply.com/
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strokers
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Joined: Fri May 27, 2016 5:33 pm

Re: Exposure & washout trouble

Post by strokers »

Hi Jonathan thanks for your reply. I made a few changes to my setup. I moved the light back as far as I could so now it's about 14 inches away from the screen. I also set up so that I can wash out my screens in my light safe room. My problem now that I moved the exposure light further away from the screen is that my screens are coming out under exposed. Before I made these changes I was exposing my screens for 7-8 minutes with reasonable success, however now I have upped my exposure time to 10 minutes and 30 seconds and still my screens are coming out under exposed. When I go to wash them out all the detail is washed out and the emulsion that remains is left feeling very slimy. Should I just keep increasing my exposure time till I find a time that suits or do you think something else is the problem?

Thanks for your help thus far :D
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Catspit Productions
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Re: Exposure & washout trouble

Post by Catspit Productions »

Okay sorry for the delay. The forum has been having issues and I have been working on fixing them.

I would suggest maybe getting a different light source otherwise you will simply have to increase the exposure time until it works. A black lamp industrial unit will make your life so much easier:

http://catspitscreenprintsupply.com/ran ... unit-110v/
Jonathan Monaco
Catspit Productions, LLC
Learn how to screen print tee shirts!

http://catspitscreenprintsupply.com/
http://www.youtube.com/user/CatspitProductions
mrieff
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Joined: Fri Jul 15, 2016 5:31 pm

Re: Exposure & washout trouble

Post by mrieff »

i am using a kiwo one coat emulsion for screen printing. I think my film positives exposed with the light unit okay since I can see the detail. However, I was unable to wash out the screen. I tried on three screens. The first one I could wash out the stouffer step transparency guide. On the second one, the guide washed out but not my images. On the third nothing washed out. I tried to wash out the screens with a pressure washer and I was doing this outside in the sunlight. Could the sunlight have caused the emulsion to harden so much that it wouldn't wash out?
Thank you,
Margie
farrokh80
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Re: Exposure & washout trouble

Post by farrokh80 »

hi,
I'm new in screen printing and I start to exposing screen for CMYK print with large size 130*70 cm and home made exposing unit 230 mesh with 47 lpi lithographic film and the light is fluorescent the distance between light and glass 6" I am facing with problem that,
When exposing time is 2.30 min for light halftones part is good but for darker parts is under expose and wash out all and when the time is 4 min for light part is over expose and good for darker parts,But when I use screen size such as 50*50 cm and exposing for 3 min it's good for lighter part and darker part.

Please help me sorry if writing is not good and not English.

thanks,
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Catspit Productions
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Re: Exposure & washout trouble

Post by Catspit Productions »

mrieff wrote:i am using a kiwo one coat emulsion for screen printing. I think my film positives exposed with the light unit okay since I can see the detail. However, I was unable to wash out the screen. I tried on three screens. The first one I could wash out the stouffer step transparency guide. On the second one, the guide washed out but not my images. On the third nothing washed out. I tried to wash out the screens with a pressure washer and I was doing this outside in the sunlight. Could the sunlight have caused the emulsion to harden so much that it wouldn't wash out?
Thank you,
Margie
Yes, that could certainly be the problem. You need to handle emulsion coated screens in safe light conditions until after the stencils washed out and dried. It's also possible that your film positive is not dense or black enough. But if you're really experiencing problems with the emulsion and I would call Kiwo for technical support.
Jonathan Monaco
Catspit Productions, LLC
Learn how to screen print tee shirts!

http://catspitscreenprintsupply.com/
http://www.youtube.com/user/CatspitProductions
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Catspit Productions
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Re: Exposure & washout trouble

Post by Catspit Productions »

farrokh80 wrote:hi,
I'm new in screen printing and I start to exposing screen for CMYK print with large size 130*70 cm and home made exposing unit 230 mesh with 47 lpi lithographic film and the light is fluorescent the distance between light and glass 6" I am facing with problem that,
When exposing time is 2.30 min for light halftones part is good but for darker parts is under expose and wash out all and when the time is 4 min for light part is over expose and good for darker parts,But when I use screen size such as 50*50 cm and exposing for 3 min it's good for lighter part and darker part.

Please help me sorry if writing is not good and not English.

thanks,
It sounds like the spread and falloff of your light source is insufficient to expose the large area you're trying to do. You will need to use a more powerful exposure light source with a bigger spread and less falloff. That's about all I could gas from what you wrote here.
Jonathan Monaco
Catspit Productions, LLC
Learn how to screen print tee shirts!

http://catspitscreenprintsupply.com/
http://www.youtube.com/user/CatspitProductions
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