Emulsion exposure problems

[clockworkpictures]

Hi all: I've already red some of the related topics here, but I wanted to show up my problem, just in case someone can give me a very specific hint.

I'm a newbie, and (surprisingly) everything in my first test run went ok: I use a homemade exposure unit using UV fluorescent tubes and (following a direction from a local screenprinter) I exposed the screen for 7 min and everything went fine in the first place.

now I'm going for my fist gig commercial poster and as murphy's law says, something had to go wrong!

1) first try: emulsion started to peel off, so I guess I underexposed it and maybe I also gave too much coats (usually I gave two coats on print side , one on squegee side, this time I gave more)

2) second try I tried to expose to 8 minutes rather than 7 and gave only 3 coats as usual but still had different problems: various stripes in the upper side , like the emulsion went too thin (see picture, over the "o"), and the smallest details show blurred edges and the smallest ones did close. (see other pictures)

overexposed?
emulsion getting old?
did not dry the emulsion completely?

thanks in advance for any possible hint!

[boatdreams]

My guess is that you're not getting 100% contact between the film and the screen during exposure. Are you using any weight or a vacuum frame on top of your screen when exposing?
It also looks like you're not washing out thoroughly enough.

[clockworkpictures]

yes, I'm usig a weight on top but I guess it may be too small and does not distribute the pressure evenly. wash was done extensively so I guess off-contact may be the point. thanks!

[boatdreams]

One thing that works really well is to get a vacuum bag and put the whole screen in there with the film taped in place to the print side and a foam square or something occupying the squeegee side. Seal the bag, and hook it up to a vacuum to remove all the air. Expose.
Also, phone books work awesomely as weights because they're flexible, and you can tile them to meet the needs of your film size/shape.

You should consider going premium. This site is worth supporting.

Oh, and "off-contact" refers to the height of your screen above your pressbed while printing!

[moe7863]

Hi. Im a beginner at screen printing and my first go went fine. Strangely enough my emulsion is also getting slimy, weak and washing out. I've contacted my suppliers and got reccomendations but even that didn't help. The glass i'm using to vacum the image to the screen is roughly 8mm thick. Maybe this is blocking a lot of light from coming through? I am using a 500W halogen bulb for exposure. @clockworkpictures if you find a solution please let me know. Thanks.

[NeroInferno]

If your emulsion is slimy you probabily are underexposing, and you should raise your exposure time. There are some halogen lamps that have got a glass with UV filter, and UV rays needs to burn your emulsion, so remove the halogen lamp glass.

Fabio

[RONLEWHORN]

What are you washing it out with? I was using a pressure washer in the past but it was too much and made it thin in some areas like in your pic. I looks like you hit it too hard there. I now just use a strong hose attachment that gets the job done without being too strong. Then you can wash longer and not worry about taking too much off.

I've also switched to single-coat, print side only coating. Seems to be plenty and wastes less and burns faster.

If you're having issue with contact on your film, I currently have a system of hard insulation foam that is the inner dimensions of the squeegee side of my screen. So I put that down, screen over it, then film, then glass. Give 100% contact. Solid. & CHEAP & EASY!

[NeroInferno]

What are you washing it out with? I was using a pressure washer in the past but it was too much and made it thin in some areas like in your pic. I looks like you hit it too hard there. I now just use a strong hose attachment that gets the job done without being too strong. Then you can wash longer and not worry about taking too much off.

I've also switched to single-coat, print side only coating. Seems to be plenty and wastes less and burns faster.

If you're having issue with contact on your film, I currently have a system of hard insulation foam that is the inner dimensions of the squeegee side of my screen. So I put that down, screen over it, then film, then glass. Give 100% contact. Solid. & CHEAP & EASY!

The washout must me made using common tap water pressure. If you need pressure to washout the screen means your emulsion is:
option 1) old
option 2) overexposed
option 3) emulsion wasn't dried properly after coating, and the ink (if inkjet) on the film adheres to the emulsion, making the washout harder.

Properly coated/exposed screens are easy to wash out. Just mist gently on both the sides and wait a bit. After this spray stronger and the unexposed emulsion falls off.

About the only coat you're right but you must be sure the emulsion with an only coat makes the print side totally even (if not the inkjet film adheres just to the "higher" parts of the mesh ruining the film, and making the washout harder). In the 99% of the cases this doesn't happens and you must print more than one coat. Another factor is how the emulsion is dense.

Fabio