Emulsion peeling on complex images, but over exposed.

[CrookedCartoon]

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

[Catspit Productions]

Yes, I would first start with a high quality photopolymer or dual cure emulsion if you need something forgiving with poor film positives.

The issue you are experiencing is probably a combination of the emulsion and the light source. It may also have to do with your film positive if it is not crisp and dense with very black graphics.

This is what I would suggest:

Switch to a Saati photopolymer emulsion:

http://www.catspitproductionsllc.com/sa ... icals.html

Use a SINGLE, 500 or 1000 watt light source rather than multiple bulbs. This will reduce scatter and diffusion. The bulb should be directly under or over the screen at a 90 degree angle to it. Make sure the film positive is very opaque. Use a heavy piece of non UV glass with sanded edges to keep the film positive in contact with the screen. The glass may need to fit within the frame edges to do this.

The issue where the emulsion is coming up at the edges during washout is simply due to your taking too much time in the washout booth. At a certain point you just end up soaking the emulsion with water and it will come off the mesh. Also forcing out a stencil in areas where the burn was not good will cause “saw toothing” which may be what you described.

It may not be that you’re under exposed or over exposed. Perhaps the emulsion and exposure source are not capable of pulling this off. That is a probability.

[OffsetnScreen]

I'm having this issue as well....and what kind of exposure time would be common with the single point 1000 watt halogen ? I've seen people writing between 5 and 12 minute exposure times...using the ryonet style startup exposure unit...I was at 90 seconds today..with bad wash out results...the solid type was ok and sharp but the halftone was seemingly underexposed and washed away..i have to recoat screens before I try it again...thinking bout trying to utilize the nuarc 1000k unit, i wouldnt be able to use the vacuum frame portion though....it has the integrator and the exposure can be set digitally...reckon i need to set up test exposures with it soon. I was amazed at how dark my laser haftone and solids on vellum printed after i found the correct adjustment today...she's dumpin nice toner....then I sprayed the sheets with clear Krylon which darkened even further...nice dots in the halftone from Illlustrator...I need to re-test the Rhino-tech paper now that shes dumpin nice toner....Peace

[Catspit Productions]

Yes, you know as I read your post OffsetnScreen I also thought that this could be a sandwiching issue as well.

The film positive needs to be in full and complete contact with the emulsion coated screen during exposure. It needs to make a nice tight seal so the light can barely go around the inkjet ink through the film base.

I think sometimes using a piece of glass to sandwich film positives is maybe not enough. This too could be part of any issues with halftones and basic exposure units without a vacuum top.

I’m not sure what exposure times would be with a 1000 watt. 90 seconds does not seem like enough time for a 500 watt unit which the Ryonet unit most likely is.

Exposure times can really vary depending on the exposure source, film positives and emulsion. Start somewhere and tweak form there. Maybe 5 minutes for a photopolymer and 10 for a dual cure on a 500 watt. Maybe half that on the 1000 watt but you’ll need to tweak the time from that starting point based on how it washes out.

Also water proof inkjet film positives will give you darker more dens blacks and you can print color rich blacks which have red and yellow in them to block UV light.

[OffsetnScreen]

Thanks Jonathan, we ordered your inket film just before new years and I got large sheets of acetate for mounting from DickBlick art supply house, however, the HPinkjet that we have is not Postscript and wont RIP a halftone, so, since i discovered how to really dump toner , which i was not doing in the past tests of the rhino product, I thought I'd give the Rhino Laser method another try. You are absolutely right in your assumption of not having good contact under the glass during exposure, I saw slight wrinkles and thought it wasnt tight...no rings of newton here, this is gonna be an issue. I read one of your posts where you said perhaps that overlay glass needs to be a bit smaller than the insides of the frame and heavy. I replaced the scratched up pane I had been using that came from a light table all scratched up , it might as well have been frosted. I should remember making contact proofs and spreads and chokes, from negatives and positives, the theories havent changed, it just seems like a lifetime ago that I worked in a darkroom and used those skills everyday. I will be purchasing a nice Epson wide type with external tanks and postscript rip just so I can use your inkjet film.

[Catspit Productions]

You're very welcome. Yeah scratched up glass like it's frosted is no good.... LOL.

Good luck!