Screen Printing Techniques and Tips: Scoop Coater Usage

In order to create the stencil of the image to print, two techniques can be used. One is using capillary film, which is a photosensitive material provided in sheets or rolls. The film is actually two parts, a backing that is discarded after exposure, and the photopolymer that forms the stencil. After exposing this film, it is adhered to the screen. While cap film is able to reproduce intricate details due to its uniformity, it is extremely expensive - several dollars per sheet.

That is why the scoop coater was invented - it is used to apply bulk photopolymer or emulsion directly to the screen. With a bit of practice, you will achieve a uniform coating of emulsion on your screen. After drying, you can expose the screen in much the same way the cap film is exposed, and rinse out the print areas.

Shown at left is a scoop coater and a gallon of emulsion. For what you would pay for three or four sheets of cap film, you can buy this high-quality, dual edge coater, AND the gallon of emulsion - enough to coat at least fifty screens!

Coating screens is an art form - don't be discouraged when the first try doesn't work! Within a few attempts though, you'll have the basic idea and be able to produce good screens. A few more tries and you'll be ready to do halftone work (halftones require a very uniform coating in addition to the correct screen mesh, etc).

To begin, you need a lightfast room - one with very limited light. A safelight (red or yellow) is preferable, but a dim, indirectly lit room will work. Avoid flourescent and sunlight - the UV light in these sources will expose the emulsion very quickly! If you can't get a savelight, use a nightlight and you should be OK.

Follow the directions on the emulsion container for preparing the emulsion for use. There are three main types of emulsion - diazo, dual-cure, and photopolymer. The first two require a diazo activator be mixed in prior to use. When your emulsion is ready, fill the scoop coater (slowly - emulsion is thick and gooey and will pile up in the middle and run out of the coater. Diazo activator creates tattoo-like stains on skin and everything else it touches - even metal!).

The scoop coater has end caps with flat spots to indicate the best angle to hold it at. Take a look at these before you start. You are going to tilt the screen back towards you, tip the coater up so the emulsion will flow and the coater is resting on the lands you just looked at, and pull the coater to you in a smooth, steady motion. Work from bottom to top, and when you reach the top, don't forget to tip the coater back so the remaining emulsion doesn't pour out! (Hey, don't laugh... it happens...)

Make one pass on the 'shirt side', then one pass on the 'squeegie side' of the screen. Let the screen dry in a horizontal position with the shirt side DOWN. It is important that the squeegie move over a smooth surface in order to leave a uniform ink deposit. The coating should not be so heavy that it drips, but if any drips do form, at least the shirt has some give and will compensate somewhat for the uneven surface. Thick spots caused by drips CAN ruin the screen coating requiring you to wash it out and try again, so be careful!

When you are done, pour the remaining emulsion out and wipe out the coater very well. It is imperative that you have a good, clean edge on the coater, and dried emulsion will need to be removed before the coater can be used again. It is always easier to clean your equipment right after using it, than to scrape, pick, or peel something off before you can use it the next time! The scoop coater sold by teeshirtprinters.com includes an opaque cover that is suitable for short-term storage, saving you some time when you are coating a large number of screens in short order.

This is not an all-inclusive tutorial on screen coating - visit our other pages to learn how to prepare a scren for coating!