Polyester Jersey Print Durability
A print studio has an order for 300 polyester sports jerseys. The design is a white logo printed on a dark navy background using water-based pigment ink with a white underbase. The screens are 43 T (approximately 110 mesh) for the underbase and 62 T (approximately 160 mesh) for the colour. Prints are cured in a tunnel dryer at 150°C for 90 seconds. After five domestic washes at 40°C, the white underbase has cracked along the seams and the navy background has greyed where the print overlaps; crock testing shows grade 2–3. The studio has a sample of the same fabric and one week before delivery. The customer requires a wash fastness of at least grade 4 and no visible cracking after 10 washes.
1. Identify the likely causes of the cracking, greying and low crock result. Distinguish between ink, screen and curing factors.
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Cracking along seams Cracking is likely caused by a combination of a thick, brittle ink film and insufficient flexibility. The 43 T underbase screen deposits a relatively thick white layer; thick pigment films crack when the garment stretches at seams. The binder may also be under-cured, leaving a weak film, or over-cured, making it brittle. Water-based pigment inks need adequate binder and, on polyester, often a crosslinker to survive stretch and washing.
Greying where the print overlaps This is probably dye migration (sublimation) from the navy polyester disperse dye into the white underbase during curing. At 150°C, disperse dyes can vaporise and migrate into the print film. A standard white underbase does not block them. The grey appearance is not necessarily dirt; it is dye that has moved into the print.
Low crock grade (2–3) Poor crock resistance can come from under-curing, insufficient binder, too much pigment relative to binder, or a rough, thick ink surface that rubs off. It may also be worsened by dye migration, because migrated dye can transfer. The 62 T colour screen may be depositing a film that is not fully fused to the fabric.
Curing factor 150°C for 90 seconds may be below the effective cure window for this ink system, especially through a thick underbase. The actual fabric surface temperature, not the dryer display, must reach the ink manufacturer’s specification. Overloading the tunnel or uneven dwell time can leave some prints under-cured.
2. Recommend specific changes to the print and curing process, and justify each change against the customer’s requirements.
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1. Use a dye-blocking underbase Replace the standard white underbase with a bleed-resistant/blocking white or a grey blocker designed for polyester. This interferes with disperse-dye migration and should reduce greying. Justification: the fault appears where the print overlaps the navy, which points to dye sublimation rather than simple ink opacity.
2. Reduce ink film thickness and improve flexibility A 43 T underbase is very open and deposits a thick film. Consider a higher mesh count for the underbase, or print a thinner white through a finer screen and double-stroke only if opacity demands it. Use a flexible, low-crock binder and add crosslinker according to the ink supplier’s instructions. Justification: thinner, more flexible films crack less at seams while still meeting opacity.
3. Correct the cure Measure the actual temperature at the fabric surface with a thermolabel or temperature probe. Increase cure to the ink manufacturer’s recommended window, typically around 160°C for 2–3 minutes for water-based pigments, while staying below the temperature that would damage the polyester. Do not rely on 150°C for 90 seconds unless the ink data sheet confirms it. Justification: proper cure improves wash fastness and crock resistance.
4. Control the fabric and wash test Pre-test the navy fabric for dye migration by curing a white print sample without washing. Wash the revised sample for 10 cycles at 40°C and assess cracking, greying and crock. Justification: the customer’s requirement is 10 washes, not five; five washes already failed, so the revised process must be tested beyond the failure point.
5. Consider a low-crock top or silicone additive If crock remains below grade 4, a suitable low-crock additive or protective top layer may help, but it must not stiffen the print or change the handle. Test before production.
3. Outline a test plan to prove the revised print meets the customer’s specification before the full 300-piece run.
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Sample preparation Print at least six test pieces on the same navy polyester jersey, using the revised underbase, ink and curing conditions. Include a control printed with the original process so the improvement can be demonstrated.
Tests
- Wash fastness: wash to ISO 105-C06 at 40°C for 10 cycles, or the customer’s stated domestic procedure. Assess colour change of the print and staining of adjacent fabric against grey scales. Pass: grade ≥4.
- Crock resistance: ISO 105-X12 dry and wet rub, before and after washing. Pass: grade ≥4, or the customer’s stated requirement.
- Crack and stretch test: visually assess the print at seams after washing; stretch the print manually or on a tensile tester to check elongation. Pass: no visible cracking after 10 washes.
- Dye migration: cure a white print on navy without washing and inspect for greying; compare with a print on white fabric.
- Adhesion/feel: check that the print is not excessively stiff and that it remains bonded after washing.
Interpretation and decision If the revised sample passes all tests, record the cure temperature, dwell time, mesh count, ink batch and binder ratio as the production standard. If crock or greying still fails, do not start the 300-piece run; switch to a proven dye-blocking system or discuss a design change with the customer. Because only one week remains, run the tests in parallel and keep the customer informed of the risk.