Screen Printing Emulsions
Last night I screen printed the Non-Gelatin Emulsion that I have been talking about. I screened it onto cleaned glass plates 5x7. Overall, screen printing,for me, is easier and cleaner than draw down with a coating rod. However, using a 110 monofilament polyester screen, wet coating thickness was only 1.0-1.5 mils. The atached image shows the thinness. Also a pattern,not mesh marks, is evident. This pattern is not evident on draw-downs. The only surfactant in this emulsion is TRX-200 at 1 drop,undiluted, per 0.1 M of Ag.
I will have to order a screen with far fewer threads/inch. I recall that they go down to 24 threads/inch, or even less.
They go way farther than that. I used to use a 300 mesh count polyester at the metal fabricators I used to work at long ago. You can control the thickness by changing the softness of the squeegee, blade angle, and sharpness of the edge. A rounded edge will put more ink through the screen for instance as well as a steeper squeegee angle. Experiment.
Also you are not limited to a single coat. Multiple layers build up well.
I remember those SS mesh screens from "back in the day". They can deposit way more ink than even the coursest polyester screens. The problem is that they are not sold by any of the "screen printing supplies' sites that I have found. Do you remember a source? I found sources for stainless steel mesh. But I would have to strech my own screens.
If possible, I wish to avouid having to screen more than one layer.
Actually these were polyester mesh. We did use the stainless mesh for some items. It was tricky to stretch in a frame.
The 300 was our standard mesh and we used a 350 or 400 for printing images that had reverse type in them to reduce the bleed into the type, we did some very small items.
Heres one place that carries that mesh.
Looking at that glass plate you coated it's evident you have a contamination issue with the ripples and holes. How did you clean the glass prior to coating, anything that would leave a residue?
I suspect you're barking up the wrong tree. I've seen Bill clean glass plates (in my own kitchen!) and he certainly knows how to clean glass.
Originally Posted by glbeas
(By the way - I tried to get Bill to wash the windows on my home. I told him what a great honor it was to wash the windows on my fine, old house, and that he could have the pleasure of washing them for a small fee. I guess Bill had already read Tom Sawer as he turned me down...)
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There are fingerprints and 2 big holes where I poked the plate while in the Fix. For my cleaning method see my article in thelightfarm.com.
I will order a screen with 24/25 monofilament polyester and go from there. I know that I will need to alter rheology to print with such a course mesh..
I will need to slow down on this for a while. I am out of a crucial chemical and need to prepare negatives for a workshop I will be taking next month. Believe me, its hard to stop. Perhaps I need to find "Rehab for Emulsion Makers". If its anywhere, So Cal is the place.
Great work, my friend. You really are a testament to obsession. I approve!
Certainly a good start. What are you using as a stencil emulsion? and are you coating it both sides of the mesh?
If I were doing this I would try to increase the stencil emulsion thickness rather than go for a coarser mesh which may leave marks.
EDIT: Thinking about this, you are probably not using anything as a stencil emulsion as you are just printing a rectangle. In which case, I would experiment with masking off the area with increasing thickness of tape.
Steve and Gary,
I am realy,realy grateful for your input. It has been a long time since I pushed a squeegee (and then I only did it in the lab, with experemental formula. I would have been fired on my first day as a Production screen printer.)
Steve, I had completely overlooked the importance of the block-out emulsion/stencil thickness. Duhh!. I was using only 1 layer of tape for block-out. I also will need to get a softer squueegee. I bought only a 70 durometer.
But I had an idea while contemplating squeegee hardness vs. screen tension and off-contact: What if I were to use a screen,say 110 for intance. With an emulsion with low viscosity and little thixotropy, have very little off - contasct between screen and glass plate, use a glass coating rod instead of a squeegee.
In this case the screen mesh would serve only to contrle coating thickness and eveness.
You probably ask: Why have a screen at all? For better thickness and eveness controle. It is an Idea that I will try once I have more emulsion to test with. Probably next week sometime.
Well, for thicker deposits we don't use a screen. We use laser etched stainless steel sheets about 0.004" thick. They are bonded to a mesh to hold them in the frame but the mesh is cut away from the printing areas.
Originally Posted by wildbillbugman
These are typically used for PCB solder paste (we use them to print conductive epoxy onto polyester). The coating thickness is generally equal to the stencil thickness and a sharp edged stainless steel squeegee is used.
We get ours from here: http://www.tecan.co.uk/core/about/overview.php
Not sure how the rod will work - possibly a bit like a rounded off squeegee and deposit a little bit more onto the substrate. You could also try zero snap off distance as they do with textile printing.
Originally Posted by wildbillbugman