If high rates of seconds are increasing your costs and creating unwanted downtime, have a look at the quality control remedies Davis discusses for each stage of the garment-printing process.
By Rick Davis
The key to consistently producing screens that deliver the quality and durability you need is to set the proper screenmaking procedures in stone and ensure that they’re always adhered to. This applies to procedures for tensioning, cleaning, reclaiming, degreasing, coating, drying, exposing, and developing your screens.
In the statistical process-control audits I’ve conducted in the past, I found that a large percentage of the seconds that were produced resulted from a defect of one kind or another in the screens. Although a great number of these defects were actually pinholes that could be repaired, the fact remained that seconds were generated and production time was lost.
Pinholes are most often generated by one of two causes: poorly degreased and rinsed screens or lint contamination. In the first case, the emulsion’s ability to adhere properly to the mesh is impaired, resulting in breakdowns on the press. In the second scenario, lint settles on the screen, which results in pinholes that are invisible during the screenmaking process but open up under the stress of printing. Again, both situations are controllable.
Bubble entrapment generated by improper coating procedures is another contributor to pinhole formation. Most bubbles that are caught within an emulsion coating result from coating the screen too fast, which allows air to be trapped between the emulsion coatings on the coat and print side of the screens. Once a bubble is trapped within the emulsion coating, it is a matter of time before the wear and tear of the squeegee on the screen’s surface will pop the bubble and produce the pinhole. This is simply resolved by slowing the speed at which you pass your coater over the screen during the coating process.
Finally, improper screen tension can really boost your seconds rates. Although most large garment screen-printing facilities use retensionable frames, some are too quick to neglect the retensioning process. The result is an expensive retensionable frame that holds a screen tension just higher than that of a wooden frame. Improper screen tension also leads to slower production speeds, excessive ink consumption, and poor registration. Some facilities simply do not realize the value of screen tension and chalk up their high seconds counts as part of the process. The issue is simply resolved by routinely following the appropriate retensioning procedures.
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