Acid Light Yellow 2G is the commercial grade designation for the sulfonated monoazo pyrazolone colorant listed as C.I. Acid Yellow 17, C.I. 18965, CAS 6359-98-4, and molecular formula C16H10Cl2N4Na2O7S2 with relative molecular mass 551.29 g mol⁻¹. The material is supplied as a free-flowing yellow powder, standardised against a reference lot to 100%, 150%, or 200% dye strength by visible spectrophotometry at the aqueous λmax, which falls in the 400–430 nm region depending on buffer pH and ionic strength. Typical solution preparation uses demineralised water at 80–90 °C under mechanical agitation; stock concentrations of 10–50 g L⁻¹ are common in dyehouse practice. The molecule carries two sulfonate groups and a dichloro-substituted phenyl ring, giving high anionic solubility and migration behaviour characteristic of levelling acid dyes. Powder moisture uptake increases under relative humidity above 60%; storage below 30 °C in sealed drums is specified to prevent caking and strength drift. Typical bulk density is 0.45–0.65 g cm⁻³, and dust generation during manual weighing requires local exhaust ventilation. Commercial pack sizes are usually 25 kg or 50 kg fibre drums with an internal polyethylene liner; the product is not classified as dangerous goods for surface transport under current UN criteria.

What Process Variables Govern Reproducible Exhaustion on Wool and Polyamide?

Exhaustion of Acid Light Yellow 2G on nylon and wool is controlled primarily by dyebath pH, electrolyte concentration, temperature ramp, and liquor ratio. In package dyeing machines with out-to-in flow reversal and capacity of 200–500 kg, the dye is applied to polyamide 6 or 66 at 0.5–2.0% owf in a liquor ratio of 1:8 to 1:15. The bath is set at 30–40 °C with 10–20 g L⁻¹ calcined sodium sulfate and pH buffered to 5.0–6.0 using acetic acid and ammonium acetate or monosodium phosphate. Temperature is raised at 1.0–1.5 °C min⁻¹ to 98–105 °C and held for 30–60 min. Under these conditions, the dye diffuses into nylon in a temperature-dependent manner; exhaustion rates below 70 °C are moderate, and the levelling phase is dominated by migration rather than rapid ionic adsorption. Wool dyeing is carried out at pH 4.5–5.5 with formic or acetic acid; the use of ammonium sulfate releases ammonia during heating and retards pH drop, improving levelness in hank and top dyeing. Insufficient bath circulation, package density above approximately 400 kg m⁻³, or differential pressure below 0.5 bar can produce radial shade variation. The dye is sensitive to free copper and iron cations: sequestering agent addition is required where chelatable metal content exceeds 0.5 mg L⁻¹ in the process water. Flow reversal cycles are typically set at 2–3 min inward and 2–3 min outward; production bottlenecks arising from excessive package density are usually corrected by winding density reduction rather than by increasing pump speed.

On continuous nylon 66 automotive interior fabric ranges, Acid Light Yellow 2G is padded in combination with a migration inhibitor and a wetting agent at a wet pickup of 60–80%, followed by horizontal steamer fixation at 102–105 °C for 20–40 min. Published data for this specific configuration is limited; production records from multi-bowl pad mangles indicate that shade stability depends more on pad bath pH drift than on dye concentration. The liquor pH should be held between 5.5 and 6.5; steam injection can alter the apparent fixation yield by diluting the pad bath at the nip. Batch-to-batch shade variance is minimised when the fabric is pre-scoured to remove spin finish and when the pad bath is prepared with softened water. Laboratory evaluation on the same substrate using the same auxiliaries is required before bulk transfer to this method. The final fastness profile is assessed by ISO 105-C06 A2S for wash, ISO 105-B02 for light, and ISO 105-X12 for rubbing; automotive interior specifications commonly require light fastness of at least ISO 105-B02 grade 5 at a defined depth.

Dye Strength Standardisation, Moisture Uptake, and Spectrophotometric Release Testing

Commercial dye strength is normally controlled by visible spectrophotometry against a working reference; the instrument is calibrated with a certified neutral-density glass filter and the sample solution is measured in 1 cm quartz cells. Absorbance at λmax is converted to dye strength using the ratio of absorbance to reference after correction for moisture and insolubles. Lot releases typically require strength between 95% and 105% of the reference, water-insoluble matter not exceeding 0.2% by ISO 787-3, volatile matter not exceeding 5.0% by ISO 787-2, and pH of a 1% aqueous solution in the range 7.0–9.0 by ISO 787-9. Because the dye is a disodium sulfonate salt, it is hygroscopic; opened drums exposed to high-humidity air above 60% relative humidity can absorb moisture, lowering effective tinctorial strength and interfering with gravimetric dispensing. Dyehouse dispensing systems should be calibrated against the lot certificate of analysis; where dust-free granules are specified, particle size distribution is determined by dry sieve analysis to ensure at least 95% passes through a 250 µm mesh. The product is incompatible with concentrated cationic fixing agents in the same bath because anionic dye-cationic agent precipitation occurs; cationic fixatives should be applied in a separate exhaust bath after rinsing. Stability of stock solutions at 10–50 g L⁻¹ is generally limited to 24–48 h at ambient temperature; prolonged storage may require refrigeration at 4 °C or the addition of 0.1% sodium benzoate as a preservative.

For compound shades, Acid Light Yellow 2G is typically paired with other levelling acid dyes such as C.I. Acid Blue 25 and C.I. Acid Red 337 in nylon apparel. Compatibility should be verified by draw-off testing using 1.0% total dye owf, pH 5.5, and 10 g L⁻¹ sodium sulfate; differences in apparent exhaustion rate cause hue shift during the heating cycle. Dyehouse records from overflow jet machines document that Acid Light Yellow 2G exhausts more rapidly than C.I. Acid Blue 25 above 90 °C, so the yellow component is often added after the blue component has been circulated for 15 min when hue stability is critical. The use of 0.5–1.0% of a levelling agent with affinity for nylon reduces the rate difference but may depress final exhaustion by 2–5%.

When Acid Light Yellow 2G Replaces Acid Yellow 36 in Jet Dyeing of Polyamide Sportswear

Acid Light Yellow 2G differs from C.I. Acid Yellow 36 and C.I. Acid Yellow 23 in chemical constitution, shade direction, and fastness behaviour. In jet dyeing of polyamide tricot used in sportswear, Acid Light Yellow 2G produces a greenish yellow, whereas Acid Yellow 36 is redder and Acid Yellow 23 is brighter with a narrower visible absorption. The dichloro pyrazolone structure of Acid Light Yellow 2G provides better light fastness and lower staining on adjacent white nylon than many aminoazobenzene-based acid yellows; however, its wet fastness remains in the levelling-dye class and is not equivalent to acid milling or metal-complex dyes. When replacing Acid Yellow 36, the existing recipe should be re-optimised: dyebath pH should be shifted from 6.5–7.0 to 5.0–6.0 because the target dye has different uptake kinetics, and the sodium sulfate addition may be reduced from 20 g L⁻¹ to 10–15 g L⁻¹ to avoid over-exhaustion. Fabric rope speed and jet nozzle pressure can be maintained, but the hold time at 100 °C should be verified by draw-off testing every 15 min; batch-to-batch shade variation of ΔE CMC(2:1) greater than 0.8 against the standard is considered unacceptable in typical apparel programmes.

Differential Fastness and Migration Behaviour in Wool-Polyamide Blends

On wool-polyamide union fabrics, Acid Light Yellow 2G builds more strongly on nylon than on wool at pH 5.0–6.0, producing tone-in-tone or heavier nylon component depth; this is typical of levelling acid dyes with high migration. When uniform solidity is required, the dyebath pH can be shifted toward 4.5 with acetic acid, but precipitation risk with residual amphoteric auxiliaries increases. Migration kinetics in the polyamide phase are diffusion-controlled; at temperatures above 90 °C, the dye migrates from nylon to wool in surface-contact areas, causing cross-staining during prolonged high-temperature finishing. Cross-staining is assessed by ISO 105-E04 for perspiration and ISO 105-E01 for water; reported grades for Acid Light Yellow 2G are usually 3–4 or 4 at medium depths, lower than acid milling dyes but acceptable for dry-clean-only outerwear. The dye is not recommended for machine-washable wool where ISO 105-C06 A2S grades above 4 are specified; in such applications, a 1:2 metal-complex acid yellow should be evaluated instead.

Compared with 1:2 metal-complex acid yellow dyes, Acid Light Yellow 2G has a brighter shade and much higher migration, but it lacks the high wet fastness associated with the octahedral metallised complex. In applications requiring repeated domestic laundering at 60 °C, the substitution of Acid Light Yellow 2G for a metal-complex yellow should be validated by ISO 105-C06 C2S on the final article. The levelling acid dye also exhibits greater sensitivity to retarding agents; over-addition of cationic levelling agents can reduce final exhaustion by 5–10% and cause unstable bath turbidity. Where dyehouse effluent limits for colour are imposed, the sulfonated structure remains soluble in dilute alkaline wash-off and is best removed by ozonation or coagulation with polyaluminium chloride; direct biological treatment alone may leave visible residual colour.

In leather finishing, Acid Light Yellow 2G is added to aqueous base coats at 0.5–2.0% by weight of finish solids. The dye is pre-dissolved at 40–50 °C and screened before addition to avoid undissolved particles that cause pitting in roller coating. Finishes containing the dye should not be overdried above 80 °C surface temperature, as shade migration can occur in the final pressing operation. Colour fastness of the finished leather is evaluated according to ISO 11640 for rubbing and ISO 11642 for water spotting; typical results for pale pastel shades are moderate, and the dye is therefore restricted to interior leather articles or to applications where a protective clear topcoat reduces direct surface contact. In aqueous paper surfacing, published data for this specific configuration is limited, and mill-scale trials are required before adoption.