The commercial product Yellow 5GN corresponds to Colour Index Acid Yellow 110, CAS 12220-74-5, an anionic metal-free monoazo dye supplied as a water-soluble yellow-brown powder. The product is standardised to a defined dye strength against a manufacturer reference lot by visible-region spectrophotometric measurement after dissolution in demineralised water; commercial strength tolerances are typically stated as ±3% on the certificate of analysis. The dye’s anionic sulphonate groups confer exhaustion onto protonated amino end-groups of polyamide and on the amide groups of wool under weakly acidic dyebath conditions. It is therefore assigned to the milling acid dye class rather than to disperse or reactive categories. The material’s solubility in demineralised water at 80°C is sufficient for 60 g/L stock dissolution under mechanical stirring, but undissolved particulate can pass through 100 µm filter screens if stock water is discharged rapidly into cold dyebaths. The powder has a bulk density in the range 0.40–0.60 g/cm³ and should be weighed with an accuracy of ±0.5% for production colour kitchens. The colour strength is measured after cooling the solution to 25°C and reading the absorbance ratio at the visible absorption maximum against a working standard; the standard itself is qualified under ISO 105-A05 for grey scale assessment of adjacent staining.

What Controls Exhaustion and Levelness in Nylon 6.6 Automotive Fabrics?

Under weakly acidic conditions, Yellow 5GN exhausts onto nylon 6 and nylon 6.6 with a strike rate controlled primarily by pH and temperature. At pH 3.5, the initial exhaustion is rapid and shade unlevelness can become fixed within the first 15 min of the ramp; at pH 5.0–5.5, the exhaustion curve is sufficiently retarded for migration during the 95–98°C hold to correct 10–15% initial depth variation on a 300 kg beam dyeing machine. Production-scale beam dyeing of nylon 6 warp-knit tricot has shown that selvedge levelness failures are most often associated with liquor ratio below 8:1, low bath circulation, or pH drift caused by hydrolysis products from elastane blends. The addition of 1–2 g/L of an anionic levelling agent increases the apparent dye solubility and retards uptake; excessive addition above 3 g/L reduces final exhaustion below 95% and shifts shade reproducibility. The original equipment requirement is therefore a buffered acid dosing loop rather than single-shot acetic acid addition. For dyeing of nylon 6.6, the final hold is extended by 10 min because the amino end-group density of nylon 6.6 is lower than that of nylon 6, which reduces the saturation uptake of Acid Yellow 110 at equal depth.

Pre-dissolution in demineralised water at 80°C is required before addition to the mother liquor. Water hardness above 150 mg/L CaCO₃ can cause precipitation of the sulphonated dye as an insoluble calcium salt, which appears as filtration pressure increase in package dyeing and as specking on fabric. A polyphosphate or polyacrylate sequestrant is therefore added to the stock tank at 0.5–1.0 g/L before dye introduction when the supply water exceeds this hardness. The dye solution should be strained through a 100-mesh stainless steel screen and introduced to the bath through the dosing line over 10–15 min, not by direct gravity discharge. Simultaneous addition of cationic fixing agents before full exhaustion is incompatible because a dye–cationic complex precipitates at the liquor surface and on machine walls. The product is also sensitive to residual chlorine in municipal water; if free chlorine exceeds 0.3 mg/L, sodium thiosulphate at 0.1 g/L is required. In blended fabrics containing nylon 6 and cellulose, Acid Yellow 110 has no substantivity for the cellulosic portion; the cotton or viscose component must be dyed with a separate reactive or direct dye class and the acid dye bath must be cleared from the cellulosic portion with an anionic washing-off agent to avoid staining of adjacent white fibres under ISO 105-C06.

Package Dyeing Rheology, Pressure Drop and Colour Consistency

In package dyeing of nylon 6 yarn, Yellow 5GN builds depth evenly when the package density is kept below 0.38 g/cm³ and the main pump delivers a specific flow of 30–40 L/kg/min. Pressure drop across the package should not exceed 0.6 bar during the heating ramp; values above 0.8 bar indicate fibre swelling, package collapse, or precipitated dye and must be corrected before the hold period. Pump reversal every 3–4 min distributes the dyebath through inner and outer package layers; without reversal, radial depth variation can reach 0.5–1.0 ΔE CIELAB units. Batch-to-batch shade variance on a 250 kg package machine is reduced when the dye is weighed to ±0.5% and the final pH is controlled to 5.2 ± 0.2. Colour measurement after rinsing and drying against a spectrophotometer with D65 illuminant and 10° observer is used to release lots; tolerances of 0.8 ΔE CIELAB are typical for automotive interior programs. In beam dyeing of nylon 6.6 automotive headliner fabric, the dye’s moderate strike rate permits the use of a single contact thermosiphon dyeing vessel without flow reversal, provided the beam winding density is maintained at 0.32–0.36 g/cm³ and acetic acid is metered over 20 min after reaching 70°C.

On wool piece goods, Yellow 5GN is applied at pH 4.5–5.5 with 5–10% Glauber’s salt and a nonionic wetting agent. The temperature ramp from 40°C to 98°C should be controlled at 1.5°C/min; rapid heating above 2°C/min can cause tip overdyeing on loose stock and crease mark unlevelness on woven fabric. The dye is assessed for washing fastness under ISO 105-C06 and perspiration fastness under ISO 105-E04, but the light fastness on wool is typically one grey scale step lower than on polyamide because of photodegradation of the wool substrate itself. For machine washable wool with shrink-resist treatment, fastness may be reduced by chlorine or resin processes; pre-testing under ISO 105-C06/C2S is required. Acid Yellow 110 is not recommended for high-temperature wool dyeing above 105°C because fibre damage occurs before any substantial exhaustion gain.

Acid Yellow 110 differs from low-molecular-weight levelling acid yellows such as C.I. Acid Yellow 49 in that the former provides higher washing fastness on polyamide under ISO 105-C06/C2S but possesses a lower migration rate at equivalent pH. In shade matching, the colourist must therefore delay acid addition and extend the hold by 10–15 min when replacing a levelling yellow. It also differs from C.I. Acid Yellow 23, which is tartrazine; tartrazine has a smaller molecular structure and lower wet fastness on nylon, making it unsuitable for high-performance apparel where ISO 105-C06 results above grade 4 are specified. Compared with pre-metallised acid yellows, Yellow 5GN is metal-free and avoids cobalt or chromium restrictions under ZDHC MRSL and REACH, although light fastness in pale depths may be lower than that of a 1:2 metal-complex colorant under ISO 105-B02 xenon arc exposure.

Correction of off-shade lots in full-scale production is limited by the dye’s migration characteristics. If the shade is 0.5–1.0 ΔE CIELAB from the reference, an addition of 0.1–0.3% o.w.f. dye is made at the start of a second hold at 90°C with pH adjusted to 5.0. If the shade is more than 1.5 ΔE CIELAB too dark, an alkaline strip at pH 8.5–9.0 with 2–3 g/L nonionic surfactant and 1 g/L ammonia can be performed, but repeated stripping weakens nylon 6 and should be limited to one cycle. The colour kitchen should not add dye powder directly to a hot bath because localised concentration at 80°C produces specks; all additions are made from a prepared stock solution at 10–20 g/L.

When Acid Yellow 110 Is Substituted for Tartrazine-Based Acid Yellows

When Acid Yellow 110 is specified as a replacement for tartrazine-based acid yellow in nylon automotive interior fabric, the required dye quantity at equal visual depth is generally lower because of the higher chroma of the standardised commercial dye; laboratory drawdowns under ISO 105-A05 are required to confirm the corrected recipe. The fastness specification for automotive nylon seat fabric typically includes light fastness under ISO 105-B02 at 1/1 standard depth, wet fastness under ISO 105-C06/C2S, and perspiration fastness under ISO 105-E04. Published data for this specific configuration is limited; therefore, the product should be qualified on the actual fabric lot and processing line before bulk substitution. The absence of metal ions in the colorant reduces the risk of exceeding the ZDHC MRSL limit values for cobalt and chromium, but the finished article must still be tested under EN 14362-1:2012 for prohibited arylamines released by reductive cleavage of the azo group. For full-depth black or dark shading, Acid Yellow 110 is normally combined with C.I. Acid Red and C.I. Acid Blue trichromatic components; the yellow component must be evaluated for catalytic fading effects under ISO 105-B02 when mixed with anthraquinone-based red dyes, because the azo chromophore can exhibit photochromic shifts and visible fading at high ultraviolet exposure in pale depths.

For regulatory documentation, the powder should be accompanied by a safety data sheet that identifies CAS 12220-74-5 and any impurity or residual solvent below the thresholds specified in REACH Annex XVII. The dye is not classified as dangerous goods under the UN Model Regulations for transport. The manufacturer’s certificate of analysis should include strength, pH of a 10 g/L solution, insoluble matter, heavy metal content by ICP-OES, and absence of arylamines listed in EU Regulation 1907/2006 Annex XVII. Textile processors using continuous exhaust equipment should verify that the dyebath pH remains between 4.5 and 5.5 throughout the hold; excursions below 4.0 cause unlevel uptake, while excursions above 6.0 reduce exhaustion on nylon below acceptable levels. Hard water above 150 mg/L CaCO₃ requires sequestration, and contact with copper or iron from corroded pipework should be avoided because transition-metal ions can dull the shade and reduce light fastness. Storage in closed containers at ≤30°C and <65% RH is advised; moisture pickup above 8% can alter the standardised dye strength and cause weighing errors in automated dispensary systems.