In high-temperature exhaust dyeing of polyester warp knits, the processing window for C.I. Disperse Violet 57 is controlled by dispersion stability and fibre accessibility above the glass transition. A production-scale jet dyeing machine operated at a liquor ratio of 1:8 to 1:15 shows levelling failure and specking when the dye dispersion contains aggregates larger than 1 μm, measured by laser diffraction per ISO 13320; such aggregates collect in stagnant boundary layers at the folded edges of warp-knit beams and overflow compartments. Predispersed liquid brands are therefore used, or powder dye is pre-pasted with naphthalene sulfonate condensate or lignosulfonate dispersant at 0.5–2.0 g/L before injection through 25 μm wedge-wire screens. The dyebath is buffered with acetic acid/sodium acetate to pH 4.5–5.5; excursions above pH 6.0 reduce exhaustion and dull the violet shade. The temperature is raised at 1–2 °C/min to 130 °C and held for 30–45 min, with the shorter hold reserved for pale depths below 0.5% o.w.f. After dyeing, the knitted fabric is reduction cleared with sodium dithionite at 2–3 g/L and sodium hydroxide at 2–3 g/L at 70–80 °C for 20 min, neutralized, and hot-rinsed to remove surface dye and dispersant residues that depress rub fastness. Automotive seat covers and technical sportswear dyed with this route are assessed against ISO 105-C06:2010, ISO 105-B02:2014, ISO 105-X12:2016, and ISO 105-E04:2013. In service water above 100 ppm CaCO₃, a sequestering agent is added prior to the dispersant to prevent calcium-induced flocculation. A recurrent production failure on hydrophobic warp knits is pressure differential increase across the filter bundle after three to four batches due to residual cationic softener; an anionic pre-scour with sodium carbonate is specified before dyeing.

What Limits Package Density and Flow-Reversal Efficiency in Polyester Yarn Dyeing?

Package dyeing machines equipped with reversible axial flow pumps impose a different constraint on C.I. Disperse Violet 57: the wound density of polyester filament yarn on perforated cones or tubes must be maintained between 0.36 g/cm³ and 0.42 g/cm³. Outside this range, differential pressure across the package rises above 1.0 bar at normal pump speed, and flow reversal produces core-to-edge shade variation even when the dyebath is fully exhausted. The machine is filled with water at 50–60 °C, and the dye is added as a 15–20% w/w liquid or as a pre-pasted powder dispersion through the dosing tank; direct powder addition to the main vessel has been observed to form lumps on the package face that remain until reduction clearing. Alternating inside-out and outside-in flow cycles of 3–5 min each are maintained through the heating phase, with a circulation rate of 30–50 L/kg fibre/min on high-density yarn packages. The dyebath is held at pH 5.0–5.5 with acetic acid, and excess dispersant is limited to 1 g/L because higher concentrations lower final exhaustion and increase reduction-clear loading. Exhaustion is completed at 130 °C for 30–60 min, followed by cooling to 80 °C and reduction clearing without unloading, using 2 g/L sodium dithionite and 2 g/L sodium hydroxide at 70–80 °C for 20 min. A final acid rinse with 0.5 mL/L acetic acid prevents alkaline residues that reduce needle heat resistance of sewing thread. Package-dyed polyester yarns for automotive embroidery and outdoor upholstery stitching are tested to ISO 105-B02:2014, ISO 105-C06:2010, and ISO 105-X12:2016.

When Thermosol Fixation Is Selected for Polyester/Cellulose Woven Blends

When a woven polyester/cotton fabric is dyed continuously, C.I. Disperse Violet 57 is applied from a pad bath containing an anti-migrant such as polyacrylate or alginate at 5–15 g/L and a wetting agent at 0.5–1.0 g/L. The pad liquor is buffered to pH 4.5–5.5; combined pad baths containing urea must be checked for scorch tendency at thermofixation temperatures because urea decomposition can generate acidic by-products that shift the violet shade. A horizontal pad mangle with compensating rubber rollers runs at 60–70% pick-up; lower pick-up on tightly woven poplins causes dye migration during drying and produces listing or side-to-side shade variation. The fabric is pre-dried with infrared or cylinder dryers at 100–120 °C, then thermofixed on a pin stenter at 195–210 °C for 45–90 s. Residence time above 210 °C is avoided because thermal decomposition or sublimation of the dye reduces depth and fastness. After thermofixation, the cotton component is dyed with reactive or vat dyes in a second stage when the blend ratio requires a solid shade; the polyester component is otherwise left as the only coloured phase. The combined fabric is then reduction cleared, soaped, and tested to ISO 105-C06:2010 and ISO 105-X12:2016. European workwear programs often add ISO 15797:2018 industrial laundering fastness for polyester/cotton blends dyed with disperse dyes. The output is typically poly/cotton workwear or shirting.

Atmospheric beam dyeing of secondary cellulose acetate filament yarn with C.I. Disperse Violet 57 proceeds at a lower temperature than polyester and imposes a narrower pH window. The dyebath is set at 40 °C, buffered to pH 5.5–6.0 with acetic acid, and raised at 1 °C/min to 85 °C. Above 90 °C, the risk of surface saponification and loss of filament tenacity increases sharply; therefore, pressure dyeing is not used. A dispersing agent is required at 0.5–1.5 g/L, and the liquor ratio on a beam machine is commonly 1:15 to 1:20. Because dye uptake on acetate is slower than on polyester, the hold time at 85 °C is 45–60 min for medium-depth violet. After dyeing, the beam is rinsed warm, and, if the finished lining is specified for machine washing, a mild cationic afterfixing agent is applied; however, aftertreatment can shift the violet shade bluer, so the colour coordinates are verified by reflectance spectrophotometer before the fixation bath is discharged. Acetate linings and soft furnishings dyed with C.I. Disperse Violet 57 are tested to ISO 105-C06:2010, ISO 105-X12:2016, and ISO 105-B02:2014. Because light fastness on acetate is lower than on polyester, the dye is restricted to indoor end uses unless an ultraviolet absorber is co-applied.

Print Paste Rheology, Screen Mesh Selection, and High-Temperature Steaming

For rotary or flat-screen printing of polyester fabrics, C.I. Disperse Violet 57 is dispersed in a stock paste based on a low-viscosity alginate or synthetic thickener. The required print paste viscosity is 3,000–8,000 mPa·s at 25 °C measured with a Brookfield viscometer, spindle 6, at 20 rpm; the exact value is matched to the screen mesh, with higher viscosity for fine lines and lower viscosity for large blotches. Flat-bed screen mesh counts of 90–135 threads/cm and rotary screen mesh counts of 80–125 mesh are typical for disperse printing; meshes below 60 mesh produce heavy paste deposition but reduce definition and may cause flushing of the violet shade after fixation. The print paste contains the dye dispersion at 1–4%, a mild acid donor such as tartaric acid to maintain pH 4.5–5.5, and a reduction inhibitor if residual reducing agents are suspected. After printing, the fabric is dried at 100–120 °C and fixed in a high-temperature steamer at 170–180 °C for 6–8 min for polyester; for blends with cotton, fixation conditions are adjusted only after the cotton print paste is combined. The fixed fabric is washed with sodium dithionite reduction clear at 70–80 °C, soaped, and dried. Printed polyester banners, flags, and outerwear panels are tested to ISO 105-C06:2010, ISO 105-B02:2014, and ISO 105-X12:2016. Outdoor printed goods are typically specified to ISO 105-B02 level 6 or higher.

Polyamide stain-blocking aftertreatments are required after pale-depth application

On nylon 6,6 taffeta, C.I. Disperse Violet 57 can be applied at 0.1–1.0% o.w.f. for pale-to-medium violet shades, but wet fastness is inherently lower than on polyester because the dye remains superficially adsorbed and lacks reactive bonding. The dyebath is set at 40 °C, raised to 98–100 °C over 30–45 min, and held for 30–60 min at pH 5.0–5.5. A nonionic levelling agent at 1–2 g/L is necessary to cover barre on high-filament nylon tricot; anionic dispersants are minimized because they compete with dye uptake. After dyeing, the fabric is rinsed and treated with a formaldehyde-free synthetic tanning agent or stain-blocking agent at 2–4% o.w.f. and pH 4.0–4.5 at 70–80 °C for 20 min. Typically, this aftertreatment is specified to improve wash fastness by one to two grey scale steps, although the actual improvement depends on the syntan solids and application pH. The aftertreatment may reduce light fastness, so only indoor nylon applications such as lingerie trims, hosiery, and lining tapes are specified. Fastness is assessed with ISO 105-C06:2010, ISO 105-X12:2016, and ISO 105-B02:2014; dyeings above 1.0% o.w.f. on nylon are not recommended because washing fastness falls below acceptable values for end-use. Published data for this exact dye/fibre configuration is limited; laboratory trials with the target fabric are therefore required before bulk processing.