PDA

View Full Version : Screen Printing Silver/Gelatin Emulsions?



wildbillbugman
03-05-2010, 04:20 PM
Pe and All,
I don`t know why I never thought to ask this befor now. I used to formulate screen printable, photoimageable masks for various industrial aplications. I know that, with the right rheology and surfactants, liquids can be very nicely screen printed onto just about anything. Thickness can be controled by screen mesh. I do not see why virtualy any of the emulsions discussed here or on The Light Farm could not be very nicely coated using this very old technolog. It would be less messy and more conservative of emulsion than blade or rod coating. What say you,PE?
Bill:o

tim_bessell
03-05-2010, 04:36 PM
... and small or large areas would be just as easy to handle. I like that idea!

I wonder if if bubbles would be a deal breaker though.

wildbillbugman
03-05-2010, 05:14 PM
Tim,
There are literaly hundreds of surfactants for getting rid of bubbles in screen printable liquids. I would try Photoflow first.
Bill

glbeas
03-05-2010, 10:08 PM
I've never had a problem with bubbles when I was silkscreening. The squeegee tends to pop any bubbles as they go through the mesh.

Jan Pietrzak
03-05-2010, 11:23 PM
Bill the bug man,

This sounds very interesting, the first thought that came to me was. If you mask the the screen you can coat any size you want. Now I just have to remember what we used for masking the screens. The folks at the home are calling me back to my room.

Jan Pietrzak

wildbillbugman
03-06-2010, 12:48 AM
While I am waiting for more chemicals to make another batch of emulsion I will look into screen printing supplies.
As far as temporary masking of a screen,ordinary tape works..
I have not pushed a squeegee since 1988.
Bill

Steve Smith
03-06-2010, 04:39 AM
I suggested this a while ago (I work for a company who precision screen print electronic circuits and medical sensors). I think it would work well for paper emulsion but any marks left by the mesh would not be good for a film emulsion due to the enlargement involved unless there was some way of re-flowing it after printing. Not sure if there would be drying in problems either. Definitely worth a go though.


Steve.

wildbillbugman
03-07-2010, 01:00 PM
Hi Steve,
I do remember that you sugested this a long time ago. It just went into some dark corner of my mind until a few days ago. Since your experience with screen printing is more recent thane mine, I wonder, could you recommend a couple of mesh counts to start with? PE reccomends a wet thickness of 7 mils. I have been coating close to 9 mils.
My % solids is around 35%, typical of many published emulsion formula.
I have been looking into supplies I'll need to get started. Streched screens in wooden frames are surprisingly cheep. I remember that I was a complete putz at streching mesh using those aluminum frames. So I will buy a couple of pre-stretched wooden framed screens, a 70 durometer squeegee, and some tape. And give it a try.
What you have said about mesh marks is worth being careful about. My interest in silver emulsions is entirely about glass negatives and prints. Someone else can worry about paper and film.
Thanks,
Bill
Regards,
Bill

Photo Engineer
03-07-2010, 01:49 PM
Bill;

I suggest 5 - 7 mils in most cases using 7 - 10% gelatin. At this level, on flexible support, the emulsion will tend to crack with time so you will have to add some polymer to it to prevent cracking. Poly acryl amide or poly vinyl alcohol come to mind, but in a pinch Sorbitol will help to some extent.

PE

Steve Smith
03-08-2010, 02:55 AM
I do remember that you sugested this a long time ago. It just went into some dark corner of my mind until a few days ago. Since your experience with screen printing is more recent thane mine, I wonder, could you recommend a couple of mesh counts to start with? PE reccomends a wet thickness of 7 mils. I have been coating close to 9 mils.

We tend to use a 120 or 140 mesh when we print our conductive silver ink. The printed surface is very smooth and actually has a texture very similar to emulsion on film. We use a machine coater to coat the stencil emulsion onto both sides of the mesh (although we sometimes use Capillex from Autotype). We usually end up with a printed thickness of around 8-10 microns. Perhaps two or more coats would be needed for an emulsion as 1 mil (or 1/1000") is a lot more than a micron. For a thicker print (of dielectric materials) we would go to a 79 or more course mesh and a thicker stencil. Unfortunately the course mesh will leave an impression in the ink/emulsion.


What you have said about mesh marks is worth being careful about. My interest in silver emulsions is entirely about glass negatives and prints. Someone else can worry about paper and film.

I was thinking that texture on a paper could be a feature to work with artistically whereas it would be un-anted in a film.


Steve.

wildbillbugman
03-08-2010, 01:23 PM
Thank you Steve,
I remember those double sided vertical screen presses, from my days of photo-imageable solder mask. Looks like the smallest pre-stretched wooden screens I can buy are 20"x 24". Realy bulky for printing 5"x7" glass plates. But I will try it out.
For mesh marks, I am thinking about a horizontal rack for holding the wet printed panels. This could be placed in an oven at 35C for levaling..
Still, it is a lot of spce for some small plates
Bill

Steve Smith
03-08-2010, 02:50 PM
Looks like the smallest pre-stretched wooden screens I can buy are 20"x 24". Realy bulky for printing 5"x7" glass plates. But I will try it out.

If all I could get pre-stretched was a 20" x 24" frame then I would buy just one then make or have made some hard wood (or metal) frames about 9" x 11" on the outside. I would glue them to the mesh of the large frame then when the glue had set, cut them out individually.

It would be a waste of a large frame but you would end up with some more manageable screens.

I'm not sure what glue to suggest for home use. We us a UV cure glue in our stretching room. Just shine some UV light at it for a few minutes and it's cured.