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Taking Control of Screen Coating

(May 2009) posted on Wed May 20, 2009

The stencils you use for printing are only as good as the coating procedures you follow to produce them. Here you


By KIWO Technical Support Department

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Another common cause of residue on the screen that can show up in the emulsion coating is water and other chemicals that hide in the profile of retensionable frames. Generally this problem is at its worst when the screen is dried in the upright position. Water and contaminants trapped in the profile run down the screen after degreasing. The contamination dries on the screen and later interferes with a good bond between the fabric and the emulsion. For this reason, always give retensionable frames a good wipe after degreasing and store them parallel to the floor when drying.

 

Don’t abrade

Abrading mesh scratches the surface of the threads, which aids in stencil adhesion but is usually only required when using indirect stencils. One reason not to abrade mesh is that you may decrease the ink-transfer efficiency of the final printing screen. Because the surface area of the thread is effectively larger, the ink clings to the threads for the same reasons capillary film clings better. This may result in less ink from the mesh transferring to the substrate. Another reason to avoid abrading the mesh is that it will likely cause more ghost haze and stains to remain in the mesh after reclaiming, also due to the increased surface area.

 

Stencil parameters

The stencil’s main function is to allow for accurate reproduction of the image from the film positive (or from the image rendered by a computer-to-screen imaging system). The quality of the stencil pertains to how effectively it bridges the mesh and the amount of resolution and edge definition it provides after exposure. These abilities vary dramatically for any given emulsion because of several factors related to coating and exposure, as well as the chemical characteristics of the emulsion.

One of the main functions of the stencil is to create a gasket with the material being printed. Among the reasons why capillary stencil films are popular is because their uniform surface leads to a good gasket right off the roll. With proper control during coating, direct emulsions also can be used to create similarly smooth stencils.


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