During the job evaluation phase you should have identified the screen or screens that will work best for your job. Before you begin preparing your screen it is a good idea to ensure that no changes have been made and that your screen is still appropriate for the job.
Degreasing and Drying
Degreasing a screen is one of the most important and easy steps that you can take in preparing your screen for printing. Simply scrub your screens using a quality screen degreasing agent and a scrub brush and you are done. Remember to let your screens dry in a clean environment where dust and other particles will not be able to gather upon it. DO NOT use compressed air to dry your screens. Compressed air is very tempting because it will dry your screen in a hurry but it will also introduce any oils or moisture in your airlines onto the screen and could cause issues in the coating process.
As with your screen choice, your emulsion choice should have been made during the evaluation process. Again, in this step you are simply verifying that nothing has changed and that your emulsion choice is still appropriate for the print your doing.
Coating and Drying
Once your screen has been degreased and dried you will be ready to coat it with emulsion. There are two types of emulsion, liquid emulsion and capillary film.
Liquid emulsion is spread onto the screen mesh with a tool called a scoop coater. Scoop coaters come in a variety of sizes and have two coating edges, one for thick coats and one for thin. The decision to use one edge or the other will be based upon the thickness of the stencil you will need for your print.
Capillary film on the other hand, is applied to the screen mesh by placing the film onto the moistened screen mesh and using a squeegee to smooth it against the surface of the mesh. As with liquid emulsion you will want to let the screen and emulsion dry before use.
The type of ink you are using and the need to apply more or less ink with each print stroke will usually determine stencil thickness. For example, light colored inks that 35 are being printed onto dark garments, such as white ink on a black garment, will require a thicker stencil. This thick stencil will allow more ink to be deposited with each print stroke, thus allowing for better coverage. Conversely, inks that absorb rather than cover (as in the case of water-based ink), require a very thin stencil to achieve a quality print. Specialty additives and inks may also require some adjustment to stencil thickness. It is a good idea to obtain the manufacturer’s specifications for stencil thickness if you want to ensure that your stencil is correct for your ink type.
Handling a Coated Screen
Once you have coated a screen it is important that it be placed in a proper environment to dry. Screens coated with liquid emulsion should be placed print-side down and no portion of the wet emulsion should be in contact with any surface. Because you are still dealing with unexposed emulsion your drying rack will need to be in a UV safe environment. You will also want to ensure that the humidity in the room is conducive to the drying process. If the moisture content in the air is greater than that in the screen, there is little to no hope of evaporation and you will thus be left with a terminally wet screen. Finally, you will want to make certain that dust and other particulates are not able to fall into the wet emulsion as these could cause a defect in the print clarity when you go to press.