Impressions - August/September 2012 - (Page 56)

tS Screen Printing Production Today’s newest performancewear styles can contain an increased content of Lycra spandex, as shown on this garment label. The increased stretchability and heat sensitivity of these fabrics can cause challenges during the screen printing process. The most difﬁcult problem affecting many screen printers when working with performance fabrics is polyester dye migration, and it often is the most bafﬂing. Here, you can see the comparison of using a low-bleed ink vs. a regular ink printed on red polyester fabric. DEFEATING DYE MIGRATION By far, the most difﬁcult — and often most bafﬂing — problem affecting many screen printers is polyester dye migration. How many times have printers thought they did everything correctly, yet the white ink on a red polyester shirt still turned pink? The critical issue as far as dye migration goes is heat, and this is a very important point to remember. Polyester dyes are synthetic, so they don’t absorb dyes like a natural ﬁber, such as cotton, would. They need help to do this. The polyester dye pigment molecules are sublimated at temperatures in the 260°F-270°F range, then chemically sealed onto the ﬁber. Plastisol inks, on the other hand, need higher temperatures to cure — typically in the 300°F-320°F range. Put properly, the ink needs to become fused instead of cured. The two main components of plastisol are resin and plasticizer. When mixed, they stay wet for a long time. Once heat is applied, the resin begins to absorb the plasticizer. For textile plastisol inks, once the 300°F-320°F range is attained, the two elements become fully fused, or 100% solid. When printing on polyester, the problem begins once the garment is exposed to temperatures beyond the 260°F-270°F range, which causes the dye to be set. At this stage of the ink-fusing process, there is the danger that the polyester dye will be sublimated again. If this happens, the 56 Impressions | August/September 2012 plasticizer in the ink will try to “pull” the polyester dye molecules up into itself. This can happen either immediately, days or even weeks later. Once the dye molecules have become gaseous, the proverbial genie is out of the bottle. There are two main ways to combat dye migration. First, you can use low-bleed inks. when combined with low-bleed characteristics, are proving to be very effective at combating polyester dye migration. COMPOUNDING PROBLEMS When we turn our attention to printing on performance fabrics, the aforementioned compounding problems come to the forefront. Many newer synthetic fabrics have a higher percentage of stretchable material in them — upwards of 20% in some cases. The standard approach when printing onto stretchable fabrics is to either add a stretch additive to the ink or to use ink that already contains the additive. The problem here is that as far as low-bleed inks are concerned, any addition — be it a stretch additive, extender or ink reducer — is not good. All of these additives can diminish the inks’ low-bleed characteristics and impinge on their ability to block dye migration. When we use additives with low-bleed inks, we basically dilute their ﬁghting ability. The challenge for ink companies and printers alike has been ﬁnding that balance between needing more stretch — because we’re now using a 80%/20% poly elasticine blend (instead of 95%/5%) — and needing the bleed-blocking capabilities of the ink. Printing on heat-sensitive materials provides another set of challenges. If the material can withstand temperatures of Use Info•Action #29 for SGIA at impressionsmag.com/infoaction The importance of testing cannot be overstressed. These are plastisol inks — typically white — that have a bleed-blocking additive or additives in them. The better ones often are more expensive and are worth paying for. A blocker gray also can be used but, while effective, it can be problematic when it comes to achieving a bright white overprint. The second way to combat dye migration is to use a low-fusing plastisol. This ink cures at a lower temperature than is typical of plastisol. The newer low-fusing plastisol inks now can be fused at temperatures as low as 275°F. The idea here is to keep the genie in the bottle. Get the temperature low enough so that the ink still will fuse, but the polyester dye will not sublimate; rather, it will stay sealed onto its ﬁber. Some low-fusing plastisol inks on the market today show great promise and, impressionsmag.com http://www.impressionsmag.com/infoaction http://www.impressionsmag.com

Table of Contents for the Digital Edition of Impressions - August/September 2012

Impressions - August/September 2012
Table of Contents
First Impressions
From the Show Director
FYI
Product Gallery
ISS Conference
Warming Trends
Redefining Fleece
Jackets of All Trades
How to Handle the Unhappy Customer
Shop Spotlight
Embroidery Technique
Embroidery Production
Screen Printing Production
Screen Printing Graphics & Design
Online Directory
Digital Decorating
Business to Business
Classifieds
Ad Index

Impressions - August/September 2012