Davis examines the most influential parameters and considers the steps needed to reduce or prevent the occurrence of these unwanted marks.
By Rick Davis
Residual platen impressions have hampered production since the introduction of the flash-curing unit. Residual platen impressions refer to the impression of the platen that is "pressed" into the garment during the printing process. The problem is most apparent on printing dark youth garments.
The factors that contribute to residual platen impressions are numerous. In this installment, we will examine the most influential parameters and consider the steps needed to reduce or prevent the occurrence of these unwanted marks.
Causes and effects
Although platen impressions plague printers on garments of all colors and sizes, the problem is most prevalent on dark youth garments. Residual platen impressions are more visible on dark fabrics than on light ones. And garment size is a factor because of the interaction between a youth-sized platen and an adult-sized squeegee; the combination of the heat from flashing applications along with the pressure of the squeegee depressing the fabric over the side of the platen creates a visible impression of the platen edge.
The platen edge marks appear as lines of lighter color in the fabric. What causes them is that the fibers on the fabric's surface have been compressed and matted down into the fabric itself. The same effect can be seen when applying a heat transfer to a garment. The difference with the transfer application is that the platen edges are not so well defined since it is a platen-to-platen process, as opposed to a squeegee-to-platen process.
In most applications involving dark youth garments, the platen leaves a residual impression of some form, but it might be very faint. The degree to which the latent image becomes visible depends on a number of variables, including flash-curing temperature, squeegee durometer, squeegee speed and pressure, squeegee length in relation to platen width, and the nature of the fabric itself. The greater the surface nap on the garment fabric, the more apparent the effect can be.
You can take several steps to reduce the occurrence of residual platen impressions. The primary printing elements on which to focus include the screen, the squeegee, and the flash-curing unit.
The screen As you probably expected, screen tension and off-contact distance play crucial roles in controlling residual platen impressions. The tension and off-contact of the screen determine the squeegee pressure required to transfer the image, and as with so many other aspects of textile screen printing, less is better.
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