[nickpayne]

Hi,

Been have some issues with washing out design. First my process currently consists of;

- Coating both sides (with a 2 part diazo emulsion), and resting screens upside down
- Exposing for 4 mins 45 seconds in a homemade UV lightbox (4 x 18w blacklights)
- Washing out with regular garden hose spray attachment

The clarity of the design is perfect on one side and the inkwell side ALWAYS ends up slimy (I have tested with increasing exposure time, going all the way up to 18 minutes; very hard to washout but still slimy on inkwell side), I have tried coating only one side.

The designs come out okay but inevitably the runny emulsion leaves a soapy residue in the design and I have to rinse out.

If anybody has any suggestions they would be highly appreciated.

Thanks

 

[splathead]

Sounds like you may not be letting your emulsion dry long enough before exposing.

How long are you waiting? Overnight is best.

 

[bpfohler]

Bad or old emulsion that's not sticking to your screens or contaminated screens?
How old is you emulsion? Did you degrease your screens?

 

[TLK]

Hi Nick,

Do you coat squeegee side last so the emulsion is pushed through to the substrate side of the mesh?

I was going suggest longer exposure but you said you've tried that. Maybe the light is not strong enough to penetrate the emulsion and harden all the way through. If it's not happening after 18 mins then it's unlikely to happen. Get yourself an exposure calculator or download one to print out.

In the meantime, washout the screens as usual, use a sponge to remove the slimy residue and wash off again.

Dry your screens upright or in a vertical position to help any left over residue run away.

 

[sben763]

Hi,

Been have some issues with washing out design. First my process currently consists of;

- Coating both sides (with a 2 part diazo emulsion), and resting screens upside down
- Exposing for 4 mins 45 seconds in a homemade UV lightbox (4 x 18w blacklights)
- Washing out with regular garden hose spray attachment

The clarity of the design is perfect on one side and the inkwell side ALWAYS ends up slimy (I have tested with increasing exposure time, going all the way up to 18 minutes; very hard to washout but still slimy on inkwell side), I have tried coating only one side.

The designs come out okay but inevitably the runny emulsion leaves a soapy residue in the design and I have to rinse out.

If anybody has any suggestions they would be highly appreciated.

Thanks

Are these stardard black lights or unfiltered black lights. If standard black lights it will take much longer to fully expose. If unfiltered what is the output spectrum. Not all lights are created equal. Also in winter you need to prewarm fluorescent bulbs if cold.

Since it’s exposing don’t think it’s bad emulsion just sounds like under exposure. This can simply be not long enough exposure or emulsion not being totally dry. If humid without a dehumidifier or heat it can’t fully dry

 

[NoXid]

Diazo is sloooooow. Use a poly type emulsion instead. It will work better with your weak light source.

My first exposure unit had 4 x 40 watt unfiltered UV tubes. I used Diazo, put the emulsion on too thick, and got the slime! I also exposed for about twice as long as you.

See the link in my sig for info on testing for proper exposure time. If it is slimy, time is too short, UV is too weak, emulsion is too thick, emulsion is too slow, emulsion is not dry enough, or most likely a combination of all of the above.

 

[nickpayne]

Thanks for all the feedback and suggestions.

These are the lights I am using they are 18W T8 lights; https://www.amazon.co.uk/gp/product/B003GSVGBA/ref=oh_aui_detailpage_o00_s00?ie=UTF8&psc=1

Ultraviolet output of 80µW/cm², is that too low? It doesnt state anything about them being unfiltered but the strange thing is they do (at least partially) expose the screen.

In terms of screen drying I use a fan in a pitch black room directed at the screens in a rack (upside down) so I am not sure this is the issue.

Again thanks for all the suggestions!!

 

[NoXid]

Thanks for all the feedback and suggestions.

These are the lights I am using they are 18W T8 lights; https://www.amazon.co.uk/gp/product/B003GSVGBA/ref=oh_aui_detailpage_o00_s00?ie=UTF8&psc=1

Ultraviolet output of 80µW/cm², is that too low? It doesnt state anything about them being unfiltered but the strange thing is they do (at least partially) expose the screen.

In terms of screen drying I use a fan in a pitch black room directed at the screens in a rack (upside down) so I am not sure this is the issue.

Again thanks for all the suggestions!!

4 x 18 watts of UV tubes is not a lot of UV. I had over twice that, and still considered my unit underpowered. Which is not to say that it won't work, but you need to help it a bit by doing everything else right. The unfiltered tubes look sort of whiteish, the filtered ones look black/violet (when off). Either will work, one just works a little faster. Having the wrong tubes isn't your problem. Having more would help. Commercial tube units seem to have 7 or 8 tubes, and would have low iron glass.

How thick is your glass and is it low iron? Regular glass filters out UV, the thicker the glass and the higher the iron content the more UV is filtered out. I used regular thickness regular glass for my first DIY unit. It worked, just not fast.

How humid is the air where you are? If the air is over 50% humidity, you need to help the drying process with some heat or a dehumidifier. You can get a cheap (under $10) humidistat from Home Depot, or the like.

The biggest gift you can give yourself in this endeavor is to ditch the Diazo emulsion and get some photo-polymer emulsion, like Saati PHU. It is a lot faster, so your limited UV will have a lot less work to do.


I eventually built a 1000 watt metal halide unit with vacuum top and low-iron glass. 25 second exposures with PHU. Slime be gone!

 

[nickpayne]

Ah yes I think I might upgrade to 8 then. This is what my current setup looks like (https://imgur.com/a/QEW3q)

In terms of humidity, after research it says London is most humid in December (around 80%) so I will invest in a dehumidifier and see if that rectifies the issue and will definitely be switching to a photo poly emulsion when I run out of my current batch of diazo.

Thanks!

 

[sben763]

Ah yes I think I might upgrade to 8 then. This is what my current setup looks like (https://imgur.com/a/QEW3q)

In terms of humidity, after research it says London is most humid in December (around 80%) so I will invest in a dehumidifier and see if that rectifies the issue and will definitely be switching to a photo poly emulsion when I run out of my current batch of diazo.

Thanks!

The bulbs you have are filtered. The black appearance when their off is a dead give away. Unfiltered blacklights will be white like a regular fluorescent. They when lite will have a blueish purple instead of the deep purple color of the filtered bulbs. The filtered bulbs are made to make posters, clothing and other materials glow while not being damaging to eyes and skin. You can find some 24” (600mm) t8 unfiltered blacklights and just change them out. From your link I’m guessing your in the UK. I know somethings are harder to find there. You would be better off with daylight bulbs or a grow bulb then thos filtered blacklights although best with the unfiltered blacklights with a UV output of 365nm-425nm range if possible.

With diazo a fan with be just fine and some heat. But photopolymer emulsion is much more sensitive to humidity and as mentioned much quicker. With a 8 bulb unit, humidity 40% and most photopolymer emulsion you should be about 45 sec. with your diazo and light source I’m guessing 5-7 min is your exposure time.

 

[sben763]

REPTILE FLOURESCENT GLO TUBE LAMP UV BULB VIVARIUM REPTILE REPTI PET LIGHT | eBay

Here is some unfiltered in the uk. You would want the dessert version as those are the highest UVB output bulbs. For 8 bulbs about 108 plus shipping. You need to change these every 1-2 years and will loose about 50% of the output depending on use within that 1-2 year period.

You can get a led 240 https://www.ebay.co.uk/itm/High-Pow...948549?hash=item3d4c1c9c85:g:UHQAAOSwGPxZ6Ed~. Take off the glass and mount 10”-15” below the glass depending on screen size. Will loose less then 10% in 5 years if ran 12hrs a day!!!!

 

[nickpayne]

Okay thanks very much, getting this equipment seems in the UK seems to be a lot harder than the US. So it sounds like the unfiltered setup I currently have is not providing enough UV, will an additional 4 of the current unfiltered lights provide enough or is it better to just send the 4 back and get 8 from the ebay link?

 

[sben763]

Okay thanks very much, getting this equipment seems in the UK seems to be a lot harder than the US. So it sounds like the unfiltered setup I currently have is not providing enough UV, will an additional 4 of the current unfiltered lights provide enough or is it better to just send the 4 back and get 8 from the ebay link?

You currently have a filtered bulb setup. You need unfiltered bulbs. The ebay link is just for the bulbs. No fixture.

If you can swing the expensive the LED is the way to go. You would need to extend your frame of your unit as that bulb needs to be further away then the fluorescents. If you go with that LED make sure to remove the glass. Those contain a filter that will cut 75% of the UVB available. Otherwise yes get the unfiltered dessert bulbs. The provide the most UVB of those bulbs and I’d say 10-15x more then you current bulbs.

I have LED I expose screens 10 sec or less. Perfect. With the fluorescent you will still get good results just small details and halftones will be undercut some.

 

[nickpayne]

JESUS! 10 seconds! I thought those kind of times were only possible with metal halide lights. What do you use instead of glass to ensure the positive and screen are flush?

Thanks again

 

[sben763]

JESUS! 10 seconds! I thought those kind of times were only possible with metal halide lights. What do you use instead of glass to ensure the positive and screen are flush?

Thanks again

Sorry you still use your glass but take the glass off the LED light. My metal halide would take 30-45 sec. LED 6.5-10 sec.

Since starting I was at 6.5 min dual (diazo)cure. With photopolymer was 4 min with blacklights unit. 10 sec or less.

 

[nickpayne]

Amazing, they do have a 50W version available too for a lot cheaper, obviously this will increase exposure time but do you think it is a viable option?

All the best

 

[sben763]

Amazing, they do have a 50W version available too for a lot cheaper, obviously this will increase exposure time but do you think it is a viable option?

All the best

You can get away with 100w. Not sure about your import fees and such but I don’t have to deal with duties so I order directly from China although hard to find a 200w like shown in link. I wouldn’t go anything less then 100w. Look up sben7633 on YouTube there should be a video of a 20-25sec exposure with a 100w LED. 200w just seems to fully expose much better with my setup. You can get much cheaper if you buy a heatsink, led die and a driver. Then just assemble your self and fashion a reflector buy a 100w UV LED in the same housing is $100-$150 usd.

 

[TLK]

I still think you need an exposure calculator. Not everything exposes the same and depends on your coating technique, the number of coats you put on the screens, which side of the scoop coater you're using, the mesh count, the mesh colour, the type of artwork you're exposing...

 

[sben763]

You can get a calculator or do a step wedge test. IMO a step wedge test is much more accurate as your using your films, inks and printer. With a calculator it’s pre printed with a image setter. Both will work but some have had to adjust after getting times with calculator as maybe film not as clear.