How to Prep Your Screens

Add to your company's bottom line by improving your production process with properly prepared screens.
Jan 1, 2008

By Charlie Taublieb

Working as a technical consultant to screen printers, I'm amazed at how many screen printers don't know how to properly prepare a screen. Stretching and taping a screen is just the beginning; the prep process involves several steps to ready the screen for exposure and printing.

A properly prepared screen will eliminate potential problems in the production process, saving you time and, ultimately, money. For example, poorly prepared screens can result in fisheyes and pinholes. A fisheye is a small, circular imperfection on a screen that has been coated with emulsion. This imperfection can be caused by a spot on the screen that was not degreased properly. The oil or ink residue on the mesh surface causes the wet emulsion to resist this area, resulting in what looks like a fish's eye. The center of the "eye" is actually a thin film of emulsion that could be prone to stencil breakdown and cause a pinhole during a long production run.

Pinholes are those tiny, open areas in the stencil that can be seen when holding the screen up to a light. The causes of pinholes include underexposure, using too much water pressure when the screen is underexposed, dirty glass or film, or applying an insufficient amount of emulsion. If not fixed with tape or block-out, these pinholes show up as small dots of ink outside the design area on finished garments. The worst-case scenario is that sloppy screen prep can result in screens that will easily break down and cannot be reused.

To avoid these problems, closely follow each step of the screen prep process.

Step 1
Once a screen is stretched and taped, it must be prepped for the emulsion-coating (or capillary film application) process. Shown here with a newly prepared screen is Derrick Block, head of production at AOV Inc., Boulder, Colo. (All images courtesy of AOV.)

Step 2
Place the screen in the sink and wet it thoroughly on both sides. This gets the mesh ready to accept the abrader, which is used to roughen the screen. The abrader is a silicate crystal and is available as a powder or paste, or can be included as a roughener and degreaser combination, which was used for this example. (The screen fabric must be degreased to eliminate any impurities such as dust or oil so the stencil adheres to it properly.) New screens always should be abraded and used screens should be abraded after about every six reclaimings.

Step 3
Work in the abrader/degreaser with a brush or scrubbing pad. If you are using capillary film instead of liquid emulsion, it’s only necessary to abrade the side of the screen that will receive the film. Screens using wet emulsion should have both sides abraded. If you are using a degreaser and roughener independently, rinse the screen after roughening and then apply the degreaser by working it in with a brush.

Step 4
Thoroughly rinse off the degreaser or roughener/degreaser, vacuum off the remaining water and place the screen into a drying cabinet. If the screen rack is in a heated room, the room can act as a drying cabinet. It’s important to work quickly here; the faster the screen dries, the less vulnerable it is to attracting dust or dirt that can stick because the fabric is still damp.

Step 5
Next, prepare the emulsion. In this case, we are using a dual-exposing emulsion, which requires adding a diazo sensitizer. Fill the bottle of sensitizer halfway with warm water. Shake the bottle to dissolve the diazo and then fill the bottle to the shoulder. Empty the entire diazo bottle into the emulsion and stir until the two are completely mixed. Let it stand until all of the bubbles have burst. This could take an hour or longer.

Step 6
Once the screen is dry and the emulsion has no bubbles, the screen can be coated. Pour emulsion into the scoop coater and start by coating the outside of the screen (this is the side that will touch the garment). Next, coat the inside of the screen (the side that will have the squeegee printing on it). When finished, place the screen in the drying rack so the outside faces down and the inside faces up. The temperature should be about 105˚F for diazo and dual-exposing emulsions, and about 95˚F if you are using SBQ polymers. Once the screen is dry, it is ready to be exposed.

Step 7
To begin the exposure process, place the artwork on the screen. If you are using a registration device such as this Tri-loc system, correctly secure the artwork in it. Next, place the screen on your exposure unit.

Step 8
By covering the screen with a piece of cloth, the blanket will not get dirty and the screen will not stick to the blanket. This will extend the life of your blanket and help to avoid getting holes in it. The screen also will draw down better and faster if you use fabric over it. After the screen is exposed, remove it from the exposure unit.

Step 9
Bring the screen to the sink and wet either side. First, apply water to the inside of the screen and then wet the outside. If you use capillary film and SBQ polymer emulsion, wet both sides of the screen, but only wash from the outside. Use a 1,000 psi pressure washer to thoroughly wash the screen.

Step 10
When you are finished washing, use a window squeegee to help get rid of any excess water. Follow that with a wet/dry vacuum to help dry the screen quickly and open up the image area. Compressed air also can eliminate extra water and dry the screen quickly. Now, place the screen in the drying rack. It will be dry in a few minutes and will be ready to tape and block out if necessary.
Next month: Screen reclaiming.

Charlie Taublieb is a screen printing consultant with more than 25 years of industry experience, and a popular speaker at The Imprinted Sportswear Shows. For more information or to comment on Charlie’s article, e-mail him at drprint@aol.com.

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