Plitisor

Hey,

So I've been working with a home built exposure unit that uses three 18inch UV lights of the kind usually used in reptile terrariums. I use Ulano FX88 emulsion and Exo-Terra bulbs (33%UVA and 10% UVB output).

It's been working out perfectly for the longest time, but recently my screens started to develop pock marks and pin holes- lots of them- when I was rinsing out the stencil. I have also noticed a lot of foaming/bubbles when I rinse, and sometimes the bubbles dry into the stencil and make it impossible for the ink to be pushed through (we print by hand on a 4 colour set up).

My emulsion is only 6 months old so it isn't expired, and I haven't changed my standard exposure time (5 minutes) or my emulsion fluid. I switched from using hot water to rinse out the stencils, and now use cold because the hot water was causing the images to just come right out, and I even bought brand new bulbs that were exactly the same kind as I'd been successfully using before, however I keep having unsuccessful exposures and it's becoming expensive in terms of wasted emulsion.

Should I up my exposure times? Lower them? Or does anyone know of an emulsion fluid that is more forgiving with home built units than Ulano FX88?

ANY prompt advice is greatly appreciated!!!

 

Reply With Quote

mattvon

I've never used Ulano emulsion, but I'd wonder if 6 months isn't nearing the end of the shelf life for dual-cure emulsion.

I checked the Ulano site for a data sheet and didn't come up with anything. I'm thinking your issue is related to old emulsion, but I'm sure others will chime in...

 

Reply With Quote

Plitisor

I've spoken to my supplier and they've told me that Ulano doesn't mark expiry dates on their product, just uses serial numbers to identify batch codes.

Unfortunately there doesn't seem to be a way to track the batch code number to find out if its actually expired.

It still stirs nicely and it's smooth and lump free. It coats the screens smoothly and the only issues we've been having are when we're exposing and rinsing stencils, as I said, which leads me to blame the unit =\

 

Reply With Quote

mattvon

Hmmm...well, since your exposure unit and this emulsion worked perfectly in the past, we just need to figure out what's changed.

In my experience, pinholes are caused by lots of things. Do you degrease your screens before scoop coating them? Any small amount of dust on either the screen or the glass can cause pinholes.

Pinholes can also be caused by bubbles in the emulsion. I'm still leaning towards old emulsion. It may appear creamy and smooth, but if the photosensitive chemicals have begun to break down, the result will be as you describe.

A new quart of emulsion is reasonably inexpensive--maybe it's worth trying that just to make sure? You're bound to use the emulsion anyhow, so I'd give it a shot.

 

Reply With Quote

PositiveDave

Pop a screen in the sun and see if that exposes correctly, that should eliminate the exposure unit.

__________________
Positivity Ltd.
UK Specialist in Screenprint imagesetting

 

Reply With Quote

out da box

6 months is too old for fx88, I believe. Also check on humidity levels, if it's too high, screens wont dry properly.

__________________
Ridgely, Operations Mngr. Out Da Box
Custom Screenprinting Service Greensboro

 

Reply With Quote

Plitisor

Sounds like I need to try a fresh emulsion.
Cheers everyone =)

 

Reply With Quote

BoomingVoice

Also, is it possible the potency of the bulbs have degraded since day one, requiring longer exposure time?

Just a thought.

M

 

Reply With Quote

Plitisor

Quote: Originally Posted by BoomingVoice Also, is it possible the potency of the bulbs have degraded since day one, requiring longer exposure time? Just a thought. M

That's what we thought, so we bought brand new ones about a month ago. They typically last 8months to a year.

I'm just going to go ahead and get fresh emulsion =)

 

Reply With Quote