In jet overflow dyeing of 100% cotton interlock and single jersey, Longsheng Chemical textile dye is introduced after substrate wetting and residual peroxide control. The dye is pre-dissolved separately at 30°C and strained through 80–150 mesh to remove undissolved particles, which in jet dyeing deposit on folded fabric edges and cause crease marks. When the target shade exceeds 3.0% on weight of fabric, the liquor ratio is held at 1:5 to 1:8 to suppress hydrolysis losses; lower liquor ratios increase hydrolysis when carbonate dosing is not staged. Sodium sulfate or sodium chloride is added in three increments after the dye has circulated for 10–15 min, reaching 40–80 g/L depending on shade depth, with the higher range used for dye concentrations above 4.0% owf. Only after electrolyte addition is the bath heated at 1–2°C/min to the fixation temperature. For cold-dyeing reactive types, fixation proceeds at 60°C; for hot-dyeing types, 80°C is maintained. Sodium carbonate is dosed in three portions: 5 g/L at the start of the fixation hold, another 5 g/L after 10 min, and the remaining 5–10 g/L after 20 min. This staged alkali profile keeps pH below 11.0 in the first stage and reduces unlevel dye uptake on compact-spun yarns with high twist. Fixation is held for 45–60 min. After drain, the fabric is rinsed at 40°C, neutralized with acetic acid, then soaped with a low-foam nonionic detergent at 95°C for 15 min. Soaping below 90°C leaves hydrolysed dye on the fibre surface and lowers wet rubbing fastness. Residual peroxide from bleaching must be below 5 mg/L before dyeing; catalase treatment is used when residual H₂O₂ exceeds this threshold. The dyebath is not combined with amine-containing softeners because amine residues accelerate reactive dye hydrolysis and reduce fixation yield. Compliance for dyed cotton knit apparel sold in the EU requires REACH Annex XVII entry 43 restricted aromatic amine release below 30 mg/kg after reductive cleavage, and OEKO-TEX Standard 100 limit conformity for chlorinated phenols and heavy metals. End products include tubular jersey for T-shirts, interlock for infant wear, and French terry for hooded sweatshirts.

Compliance verification for dyed cotton knit exports requires minimum fastness values shown in the table.

High-temperature polyester exhaust dyeing with disperse dye

Longsheng Chemical disperse textile dye is dispersed in cold water before being added to a dyebath adjusted to pH 4.5–5.0 with acetic acid/sodium acetate buffer. The pH range is critical because alkaline hydrolysis of the disperse dye at pH above 6.0 causes shade dulling and filter deposition on circulating pump seals. A low-foam anionic dispersing agent is added at 0.5–1.0 g/L; this concentration is reduced for high-energy dyes with fine particle size because overdosing can inhibit dye uptake. The prepared bath is raised at 1.5–2.0°C/min to 130–135°C in fully flooded jet machines, with liquor ratio 1:8 to 1:12. The holding time at maximum temperature is 30–45 min for regular 75 denier woven polyester, but is extended to 60 min for high-tenacity low-pill fibre and microfibre constructions. Above 135°C the dispersion can become unstable, leading to agglomeration on cooler machine surfaces such as lint screens and heat exchanger tubes. Below 125°C, dye penetration into the amorphous regions of the fibre is insufficient, and sublimation fastness drops. Reduction clearing after dyeing uses sodium hydrosulfite at 2–3 g/L and sodium hydroxide at 2 g/L at 70–80°C for 20 min. This step removes surface disperse dye and is not eliminated for black and navy shades. The cleared fabric is neutralized and rinsed until conductivity of the final rinse falls below 200 µS/cm to avoid alkali residues that impair downstream heat setting. End products include polyester taffeta, twill for fashion outerwear, and microfibre linings. Compliance requires ISO 105-P01 dry heat fastness at 180°C for 30 s for downstream heat setting, and ISO 105-X12 crocking control for deep shades.

Particle size distribution of the dispersed dye is a further processing variable. Longsheng Chemical disperse dye grades for exhaust dyeing are milled to submicron particle size; if the dispersion is exposed to freezing temperatures, particle aggregation can occur and is not reversible by simple stirring. Before adding to the bath, the dye is therefore dispersed through a high-shear mixing valve at 40°C and filtered through 100 mesh. In black shades, oligomer deposits from polyester can co-deposit with dye agglomerates on the pump impeller and heat exchanger plates. A reduction clearing step with hydrosulfite removes surface dye but not oligomer, so an alkaline oligomer extraction with 2–3 g/L sodium hydroxide at 130°C for 30 min may be required after deep-shade runs. Amine-based levelling agents are avoided in the dyebath because they can react with disperse dye and reduce build-up on high-energy shades.

Continuous pad-dry-thermofix processing of polyester/cotton shirting and workwear fabrics uses Longsheng Chemical disperse dye for the polyester component before the cotton is processed with a reactive type. The pad liquor contains 20–40 g/L disperse dye, 5–10 g/L anti-migrant such as polyacrylamide-based or alginate derivative, and 1–2 g/L wetting agent. Pad pickup is set at 60–70% by adjusting roller pressure; higher pickup carries more liquor into the fabric and increases migration during pre-drying. Pre-drying is performed at 100–120°C in a hot flue or IR zone to reduce moisture to below 10%, followed by thermofixation at 200–220°C for 45–90 s. The specific thermofixation temperature is selected according to the dye's sublimation fastness and the fabric weight; heavier twill needs the upper dwell time. After thermofixation, the cotton portion is dyed by pad-steam with Longsheng Chemical reactive dye at 20–40 g/L, after which the fabric is soaped and dried. The main processing conflict in this route is migration during pre-drying: uneven hot-air flow across the stenter chain causes side-to-side shade variation exceeding ΔE 0.8 on automated spectrophotometer readings. Production lines therefore verify air balance and padder deflection weekly. End products include twill workwear, poplin shirting, and pocketing fabric. Compliance uses ISO 105-C06 for wash fastness and ISO 105-X12 for crocking.

What Adjusts Fixation Yield in Rotary Screen Printing with Reactive Dyes?

Print paste composition for rotary screen printing on mercerized cotton sheeting with Longsheng Chemical reactive dye is governed by the required rheological profile at shear rates generated by a magnetic rod bed. The paste is prepared with medium-viscosity sodium alginate thickener at 400–600 g/kg of a 6% stock paste, urea at 100–200 g/kg, sodium bicarbonate at 15–25 g/kg, and dye at 10–40 g/kg. Water is added to bring the paste to 1 kg. Urea is not merely a humectant; it raises dye solubility inside the gum film during steaming and lowers the viscosity of the thickened paste, so its level must be increased as dye concentration approaches 40 g/kg or the dye will crystallize during the intermediate drying step. Rotary screens of 80–125 mesh are used for blotch grounds, while 155–195 mesh screens are used for fine outlines; coarser meshes deposit more paste and require higher drying capacity. After printing, the fabric is dried at 100–120°C and steamed with saturated steam at 102–105°C for 8–12 min. Steaming below 8 min leaves unfixed dye that bleeds during wash-off; steaming above 12 min can cause reduction of some vinyl sulfone reactive groups if the steam contains reducing contaminants. Wash-off begins with cold rinse, then hot soaping at 95°C with nonionic detergent, then final rinse. Printed cotton apparel and bed linen are checked for residual unfixed dye using ISO 105-C06 wash testing and ISO 105-E04 perspiration testing.

Rotary screen printing lines require control of the paste's apparent viscosity at low shear and high shear. A typical print paste measured on a Brookfield viscometer at 20 rpm falls within 5000–15000 mPa·s; at the shear rate generated by the magnetic rod, the viscosity drops to permit penetration into the fabric, but the paste must recover quickly to maintain the print line edge. If the paste viscosity is above the upper limit, the screen mesh will clog and the printed fabric will show pinholing in the ground areas. If it is below the lower limit, the paste will flow beyond the pattern edges, producing haloing or flushing. Thickener selection therefore depends on the fabric construction; woven poplin with a tight surface requires a lower-viscosity alginate than terry fabric with high absorbency. During wash-off, the printed fabric is passed through open-width washers with counterflow water at 40°C, 60°C, and 95°C in sequential compartments; the 95°C soaping stage is designed to remove hydrolysed dye before the final cold rinse. The printed fabric is then dried at 120°C and framed to width.

Package dyeing of polyester-wrapped core-spun sewing thread with Longsheng Chemical disperse dye is run in high-pressure vertical or horizontal spindle machines. The packages are wound at a density of 0.38–0.42 g/cm³; densities above 0.42 g/cm³ create pressure differentials across the package and cause inside-to-outside shade variation, while densities below 0.36 g/cm³ cause channeling. The dye bath is set at pH 4.5–5.0 and raised to 130°C at 1°C/min or less. Flow reversal is cycled between inside-out and outside-in every 3–5 min because the polyester fibres in core-spun thread have a highly oriented surface that resists dye adsorption under low flow. The addition of 0.5 g/L low-foam dispersing agent and 1.0 g/L carrier is restricted to pale shades; carrier use in deep shades can reduce colour fastness to rubbing. After dyeing, reduction clearing uses sodium hydrosulfite and sodium hydroxide at 70°C for 20 min. End products are polyester sewing thread for automotive upholstery and industrial garment assembly, where shade consistency under D65 and TL84 light booths is controlled to ΔE CMC 1.0 or less. Compliance includes ISO 105-B02 light fastness and ISO 105-X12 crocking.

Production-scale failure modes in package dyeing of sewing thread include inside-to-outside shade variation and winding density-induced flow channelling. A 5% variation in package winding density between packages on the same spindle causes measurable shade difference because the flow through the lower-density package is greater and the dye uptake is faster. Package dyeing machines therefore require differential pressure sensors to monitor flow across the package column. If the differential pressure exceeds 1.0 bar at the beginning of dyeing, the lot is rewound or rejected before dye addition. The dyeing control system ramps the main circulation pump from low to high flow after the temperature reaches 80°C to avoid yarn hair displacement. Published data for this specific configuration of polyester-wrapped core-spun thread is limited, and pilot-scale calibration is required before bulk shade matching.

When Finished Cotton Garments Are Dyed in Rotary Drum Machines

When finished cotton garments are dyed in rotary drum machines, Longsheng Chemical reactive dye is used at liquor ratios above 1:15 because low-liquor garment dyeing produces abrasion marks on seams and rib trim. The garments are loaded at 50–70% of drum capacity and pre-scoured at 60°C with a nonionic wetting agent. Dye is added after the drum speed is reduced to 6–12 rpm to limit mechanical stress. Electrolyte is added in two stages: half at 30°C, the remainder after 10 min of circulation; for a 2% owf shade, total sodium chloride is 30–40 g/L. Alkali is then dosed as soda ash in three equal additions over 30 min to reach 10 g/L, and fixation proceeds at 60°C for 45 min. High-electrolyte concentrations in garment dyeing can cause localized dye precipitation on cotton rib cuffs, so the salt is dissolved separately and added through the drum’s dosing line. After dyeing, the garments are drained, rinsed, and fixed with a cationic fixative only when the target wet fastness requires it, because excess fixative reduces handle. End products are ring-spun cotton T-shirts, hooded sweatshirts, and soft-structured knitted outerwear. Compliance for these garments uses ISO 105-C06 wash fastness and ISO 105-E04 perspiration fastness. Shade approval on garment-dyed lots is performed under D65 and TL84 illuminants; metamerism is minimized by using the same dye combination that was used in the laboratory garment drum, not a piece-goods jet.

In garment dyeing, the abrasion of seams and rib trim is the primary process limit. Drum speed above 12 rpm causes mechanical fibrillation on cotton rib cuffs and shoulder seams, which appears as lighter dye uptake on the abraded fibres. The garments are therefore loaded with buffer garments or reduced drum speed. The dyeing programme also includes a pre-treatment with 0.5–1.0 g/L nonionic surfactant and 0.5 g/L soda ash at 50°C to remove knitting oils and improve absorbency. Shade matching in garment dyeing differs from piece dyeing because the garment seams and multilayer areas restrict liquor exchange. This means the level dyeing period at 30°C is extended to 20 min before salt addition, and fixation at 60°C is held for 60 min rather than 45 min to allow dye to penetrate the seam allowances. After dyeing, the garments are centrifuged at low speed and tumble dried at 60°C to avoid migrating dye. The finished garments are checked for dimensional stability and seam performance. Compliance is verified by ISO 105-C06 and ISO 105-E04.