Fabric preparation and ink selection
By Jim Hingst
Fabric preparation -- abrading and degreasing the fabric -- is critical to creating a high-quality stencil. Improper mesh preparation can cause pinholes and stencil-durability problems.
Abrading the surface improves stencil adhesion, whether it's a direct emulsion or a capillary film. Historically, screenprinters used household cleaners to abrade fabric. However, such cleaners can damage the mesh threads and leave residual particles. Thus, suitable commercial products are better.
Degreasing is the final fabric-preparation step. After the abrasion process, oily residue can still remain in the fabric, and thus decrease adhesion.
Before coating the screen, remove any grease, dust or dirt from the fabric using such products as sodium hypochlorite or bleach. Afterwards, rinse the screen with cold water to remove the residual solution. If cleaned correctly, the fabric surface should have an even film of water.
After degreasing the mesh, dry the screen vertically to prevent dust from settling. Furthermore, coat it after degreasing. Mesh static can also attract dirt.
Screen-stencil creation can involve various products. Coating the screen with a liquid-direct emulsion remains common. Different types of capillary films are also used. One capillary film is cut, reverse-weeded and then adhered to the screen, while another type is applied to the fabric, then exposed. A final type is first exposed, then adhered to the mesh.
Direct-emulsion method
For the photographic, or direct, method, coat the screen with a light-sensitive emulsion. After the emulsion dries, position the film positive over the coated screen. When the screen is exposed to ultraviolet light, emulsion that isn't covered by the film positive's image hardens. After exposure, the formerly covered emulsion is washed away with water.
Today, emulsions comprise a two-part system: the base and sensitizer. With countless characteristics, emulsions are manufactured to cover various applications.
Unused emulsion sensitizers and bases should be kept in non-metallic containers stored in a refrigerator. Never store such chemicals near heat or bright light, in freezing temperatures, or beyond their maximum shelf life, as they tend to deteriorate and produce poor stencil quality.
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