Hello Everyone,
Switching emulsions is not the answer. The issue is the light and exposure time. HVP should be prepared as follows. While I had my shop I ran 290,000 units on one set of screens using basically the same emulsion Aquasol TS, HVP is just a higher viscosity.
So here is the way to prepare a bullet proof screen:
1. Add 8 grams of diazo to HVP. This aids in water resistance. Without it you need a 5k or higher metal halide with an excellent histogram, or spectral output in UV wavelengths, not the white light portion.
2. Dry it overnight, if it is raining you may want a dehumidifier in the room, or put back in a hot box at 100 degrees for 15 minutes prior to exposure. If you have a hot box an hour or more is necessary to dry the screen, if wet 3-4 hours depending on humidity. Here in Socal, 1 hour at 30% humidity. The lower the mesh count the more time needed.
3. Can you over expose on your unit? If your DIY Metal Halide cannot overexpose a 110T screen it may not have enough UV in it. Just because you get an image does not mean you achieved a durable exposure. It's not how fast you can expose, its' how well you can expose. Images break down, Good exposures do not. So push the time as far as you can before overexposing. You must have your exposure time just below overexposure for discharge, plastisol can get away with underexposure on short runs.
4. During development try to rub off the details while the screen is wet. If you can rub off the details the emulsion is underexposed, or you aren't using a good degreaser. Go back and do a step test with your film. Stouffer guides are density strips with good density, but they are not your films. You need to find out how much light you can use, not how little you can use. 90-95% of the strength comes from the initial exposure, everything else is a band aid. Take an unexposed screen out into the sun for the same amount of time as your exposure unit. The inside will be squeaky clean exposed. No slime at all. More on the sun in a minute.
Here is the URL to perform a step test.
http://murakamiscreen.com/wp-content/uploads/2012/07/Step-Test-Instructions.pdf5. Once you find a step test time you like, then throw on the stouffer density strip after the step test with the new time to see what it reads so you can hit that hardness level again and again. Remember, if you can rub off details during development the exposure is inadequate, or the lamp does not have good spectral output in the 350, 380, and 420 nanometer wavelengths, these are the key wavelengths. White light doesn't count too much. Its the UV at the nanometers listed that need to be bright and have the most strength.
6. Develop the screen as always. Any slime? It will breakdown.
7. IF there is no slime, squeegee off the excess water and then you can apply MS hardener. The risk you take applying hardener when wet is you can wipe soft emulsion back in the image and it will block the open areas. That is the main reason to dry the screen first. However if you wipe the inside of the screen and don't see emulsion color you can apply MS hardener to a wet screen. If you do see emulsion color put it out in the sun and post expose. SBQ remains sensitive to post exposure and the sun will aid DIY exposure units to achieve a better exposure. The strongest screens will come from an 8k metal halide with a fresh bulb. Tons of UV, all the molecules line up and cross link completely, much stonger molecular bonds are formed.. (This never happens on 1k or DIY units FYI.) So dry in sun, squeegee side towards the sun, then apply MS hardener, or if you want to cut out the mesh and emulsion use Murakami Hardener A&B to create a semi-permanent screen, you still need great exposure, hardeners put a skin on the surface of the emulsion. A weak exposure inside the hardened surface is still a weak exposure.
9. So how does a DIY shop get really strong discharge screens if none of the above tips still won't prevent breakdown? Use a sun exposure unit between 10 am and 2pm in full sunlight. This is a spring, summer, early, fall exposure since we need sunlight that would give you a sunburn. Winter, only in the deep south.
Email me at
abuffington@murakamiscreen.com for a PDF drawing of a sun exposure unit that is an enclosed box rather than the description below.
Here is how to do it without the drawing. Get a window frame that fits over your screen. Get a piece of 4 inch upholstery foam from an old cushion that fits within your screen and will be flat against the inside of the screen with the window frame resting on it with the frame outside the screen frame so that only glass is resting on the screen frame. Cover foam in black t-shirt fabric, cut to size and spray adhesive to adhere. Place foam on top of flat small cart with wheels. Place screen with art film in position over the foam. Place window frame on top of screen. Place some weight on the frame, or if it presses the art flat against the emulsion you don't need more weight. If you do, quart containers w water work. Roll cart out in the sun at noon. As soon as it hits the sun start a timer and expose HVP for 60-90 seconds, it can be as low as 30! depending on UV in your area. If you have added diazo you will see the emulsion turn dark pink with HVP. You may need to experiment with time. SP-1400 would provide more latitude and a greater emulsion color change and exposure would be in the 2 minute range.
Roll cart back into safe light area and remove and develop. This screen will outdo any DIY. I printed for Disney for 3 years using a large table with 4 of these setups and shot screens like mad from 11-2 before buying a 7500 watt lamp. The sun can create one strong screen. Clouds don't help, clear uninterrupted sun.
The sun is a 23k exposure unit minimally. I had to pull my light meter out of the sun as it was still going up at this level!
Thanks to all my competitors who feel selling a different emulsion is the answer, obviously not the answer to his issues.
Al
