[Jon78750]

I am new to screen printing and to this forum...forgive me if this is a silly question. When exposing a screen......instead of making a transparency with a large format printer and exposing with a lamp.....why not just press the sensitized screen directly up against a high contrast, high resolution computer monitor for as long as necessary.
Anyone know that it doesn't work... to save me trying?
Thanks.....Jon

 

[NoXid]

Emulsion is exposed by UV light, off toward the end of the spectrum that is dangerous to look at--so I would trust that monitors are not emitting much, if any, of it.

"Large format" is a much muddied term. For purposes of printing typical T-shirts art, 13" wide film is wide enough (even 11x17 might do). That is solidly in the category of "desktop" printers, and not what I would call wide format (which to me starts at 17" or 24" wide and takes roll media rather than cut sheets).

 

[Jon78750]

Emulsion is exposed by UV light, off toward the end of the spectrum that is dangerous to look at--so I would trust that monitors are not emitting much, if any, of it.

"Large format" is a much muddied term. For purposes of printing typical T-shirts art, 13" wide film is wide enough (even 11x17 might do). That is solidly in the category of "desktop" printers, and not what I would call wide format (which to me starts at 17" or 24" wide and takes roll media rather than cut sheets).

Thank you for the helpful reply. I did a little research as well. Diazo sensitizer is sensitive to UV, as you point out (maximum sensitivity at about 370 nm) but it does have a tail into the blue region of visible light otherwise it would be colorless. Diazo sensitivity to blue light at 450nm where WLED back-lit computer screens have an emission peak is about 5% of the peak sensitivity in the UV. So for sure it will take a long time to expose. I did try exposing a diazo emulsion screen in contact with an image on a computer monitor for a series of times. At 5 hours exposure I finally got a good water resistent image after processing. Not very practical I agree...but remotely possible as a poor man's computer to screen for amateurs with time on their hands like me. Thanks again for taking the time to reply.
Jon

 

[NoXid]

Thank you for the helpful reply. I did a little research as well. Diazo sensitizer is sensitive to UV, as you point out (maximum sensitivity at about 370 nm) but it does have a tail into the blue region of visible light otherwise it would be colorless. Diazo sensitivity to blue light at 450nm where WLED back-lit computer screens have an emission peak is about 5% of the peak sensitivity in the UV. So for sure it will take a long time to expose. I did try exposing a diazo emulsion screen in contact with an image on a computer monitor for a series of times. At 5 hours exposure I finally got a good water resistent image after processing. Not very practical I agree...but remotely possible as a poor man's computer to screen for amateurs with time on their hands like me. Thanks again for taking the time to reply.
Jon

Cool. There is no substitute for actually trying stuff . Now just rip open that screen and replace the white LEDs with UV LEDs. And take off the bezel so the screen can make direct contact with the emulsion, else the burnt image won't be sharp. Hmmm, and take out the filter layer/sheet, as don't need no stinkin' R or G, just UV ;-)