Some problems we encounter in sublimation printing

Problems encountered in sublimation are usually rooted in the process described in Figure 1. These include abnormally shaped parts, color matching, paper sticking and dishwasher/ultraviolet (UV) resistance.
Abnormally Shaped Parts. The uneven surfaces of ceramic parts can cause problems with sublimation. An uneven surface prevents even application of pressure, which is necessary to direct the gas to the part. Absence of pressure and direction causes blurring and light/blank spots. Creative methods of applying pressure—such as wrapping an elastic band around the part—or increasing the heat can compensate for these irregularities. Regular part measurements, however, can identify problem parts before they are decorated.
Color Matching. Color is a result of dye penetration into the coating. The amount of penetration can vary with the coating characteristics. A coating with a lower glass transition temperature would be softer at a 220~230℃ sublimation temperature, allowing greater dye penetration and showing darker colors, but some sharpness would also be compromised. Heat and pressure also affect dye penetration, and can be adjusted for the coating. A quality program with color testing is critical to isolating the cause of a color matching problem.

Sublimation paper Sticking. Referring back to Figure 1, the coating becomes soft when heated. If the coating becomes too soft, either because of excessive heat or a lower glass transition temperature of the coating, the pressure may force the ink, and the paper, into the coating. Upon cooling, the transfer paper will be frozen into the coating and hard to remove. Removal of the transfer paper while the part is still hot is one way to prevent the sticking, as is reducing the pressure. However, if this problem is experienced as part of a standard testing procedure, where heat, pressure and paper are constant, it could be an indication of coating or equipment problems.
UV Resistance. Resistance to sunlight radiation is a function of the coating chemistry. Coating suppliers have developed chemistries that resist UV degradation in other industries, such as outdoor paints and automotive applications. But for sublimation, each coating must be custom-formulated to meet the sublimation decorator’s needs. In some cases, there may be a trade-off—imparting high UV resistance may compromise the coating strength, for example, or may affect another coating property. Developing a UV resistant sublimation coating requires a joint effort from both the sublimation decorator and the supplier.
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