A customer recently complained that when printing a low-bleed white ink onto a dark blue fabric, the ink changed color — but not to the expected blue hue.
Instead, the white ink turned … wait for it … pink. The customer then sent us a sample of the fabric and we got the same results upon printing a white-ink design.
“How is that possible?” you may ask. It’s actually not that uncommon for fabric manufacturers to over-dye a fabric with a different color. In this instance, the fabric originally was red and then was dyed blue at a later date. This practice is common, even with 50/50 blends or 100% polyester T-shirts, where dark or black T-shirts initially started out as red, green or a different color.
Most polyester fabrics are dyed using the sublimation process, where the dyes are transferred to the fabric using heat. At a certain temperature, the dye becomes a gas, thus infiltrating the fibers of the fabric and bonding them.
The problem with many of these multiple-dyed fabrics is that the original dye reacts even more readily to heat, thus turning into gas during the ink-curing process at lower temperatures than before. As with the aforementioned dark blue fabric, the original red dye sublimated at temperatures below those to which the blue dye reacted. Thus, the red dye penetrated the ink and turned it red.
What can a printer do? This is a tough question to answer because it totally depends on how the particular fabric dye behaves. Sometimes, it is sufficient to try a stronger blocking ink or even a blocking gray, but other times, it’s impossible to make a white ink stay white on such a fabric.
“I suppose I can print a white underbase and then a red design over it,” quipped another customer who was didn’t want to discard his cache of red-bleeding black T-shirts. Such would be a creative solution; but if possible, test the fabric before committing to a large purchase so that its characteristics are known before actual production.
Mark Brouillard, International Coatings’ product manager, has considerable experience in formulating and manufacturing industrial compounds. For the past 16 years, his focus has been on the formulation and product development of textile screen printing inks. Brouillard coordinates the company’s product development efforts and deployments. For more information, visit iccink.com and read the company’s blog at internationalcoatingsblog.com.
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