Screen Printing Forum

I am trying to burn a screen that has 1 coat each side, using ulano qtx emulsion. I am using 4 - 48" floresent sunlight bulbs that are about 20" above the screen.

I have been burning the screens for 3.5 - 4.5 min and pretty much getting the same result, washes out really hard and the screen gets messed up because the emulsion breaks down around the design.

does anyone use floresent lights with qtx? if so how long do you burn your screens for?


thanks


Lew

I use rlx but I do use flourescent for exposure on vector art jobs. I use a single point for high res work. Sounds like you need to do a step wedge test for proper exposure time and maybe get the light source closer to the screen. My unit has the bulbs about 4 or 5 inches off the screen.

I have used Vlano QTX for over a year now and like it best. Using a homeade light box, with 6 bulbs about 4 ft long, I put the screen directly on the light box, about 4 in from the light. I shoot all screens at 20 sec, even high mesh and the come out perfect. I also use film instead of velm when printing art. Hope this helps.

I use QTX (1/1 coats) and expose 110-220 mesh (using clear film) at 2 1/2 - 3 minutes under Flo bulbs. Your distance from the glass seems pretty far. Best bet is to get an exposure calculator from Ulano and test a few shots. If you are burning vellum, exposure times can be 2x that of clear film for proper exposures.

When you say your screen is washing out hard, I assume you mean the image area(?), if so either your positive is not dense enough to keep the UV light rays from penetrating into the emulsion, or you are somehow fogging the image area with UV light. Make sure that no UV light can reflect from the back side on to the screen during exposure, and try to ensure that no UV light is exposed to the screen until you are ready for your exposure.

Difficult washout in the image area means that the emulsion has been crosslinked by UV light in those areas. High heat can also cause crosslinking in the emulsion, so try to keep your coated screens (and the pot of emulsion itself) cool. The tip on the exposure step from d flemming is excellent advise. Your screen supply dealer can provide you with either an Exposure Calculator (made by autotype, kiwo, and other mfgs.), or provide you with the procedures to preform a manual step test of your light source.

Knowing the proper exposure level in your light source is the most important factor in screen making. Your light source is unique. Nobody but you can determine the exact exposure time on your light source but you, as each exposure unit, even exact same manufactured units put out different levels of UV light. Without an exposure test, you are just guessing, and will have hit and miss results. Over time, as the UV output diminishes from your lamps, you will need to adjust your exposure time accordingly. The exposure calculator is the best tool to keep on top of the performance of your light source, whichever type you are using. They're worth the expense if you plan to be serious about making screens. The exposure "calculator" is also a valuable tool to use to eliminate the variables of exposure when troubleshooting stencil problems. Everybody knows the value of controling the variables in the screen printing business.

Good Luck!

One trick that I picked up on is if you are using a laserwriter for your outputs is run the velum through your dryer before shooting your screens.

It seems like the fuser in the laserwriter doesnt heat up the velum enough.

You will see a huge difference in the opacity of your toner after doing this.

Using the same emulsion as you guys, we were really having the same problems shooting out screens until we tryed this.

dont know if this will help or not, but it worked for us!

Good luck,