Section
| HS Code | 657051 |
| Productname | Acid Red A |
| Chemicalname | Sodium 4-[(2-hydroxy-1-naphthalenyl)azo]-1-naphthalenesulfonate |
| Synonym | C.I. Acid Red 88; Fast Red A; Solid Red A |
| Casnumber | 3734-67-6 |
| Einecscode | 216-760-3 |
| Cinumber | 15620 |
| Dyeclass | Acid dye |
| Molecularformula | C20H13N2NaO4S |
| Molecularweight | 400.38 g/mol |
| Appearance | Red to dark red powder |
| Color | Red |
| Solubility | Soluble in water and ethanol |
| Primaryuse | Dyeing wool, silk, nylon, leather, and paper |
| Storageconditions | Store in a cool, dry, well-ventilated area away from light |
As an accredited Acid Red A factory, we enforce strict quality protocols—every batch undergoes rigorous testing to ensure consistent efficacy and safety standards.
| Packing | Acid Red A is supplied in a 25 kg moisture-proof woven bag with an inner polyethylene liner, sealed for safe transport and storage. |
| Container Loading (20′ FCL) | Acid Red A is packed and secured in a 20′ FCL container for safe, compliant ocean shipment. |
| Shipping | Acid Red A is typically not listed as a dangerous good; ship as non-hazardous general cargo per the SDS. Use sealed, labeled containers in a dry, ventilated area; avoid moisture, heat, and contamination. Verify carrier and local transport regulations, and confirm classification with the manufacturer before shipment. |
| Storage | Store Acid Red A in a cool, dry, well-ventilated area away from direct sunlight, heat, and ignition sources. Keep containers tightly closed and properly labeled. Protect from moisture and dust. Separate from strong oxidizers and incompatible chemicals. Use appropriate secondary containment to prevent spills. Observe local regulations and SDS requirements for safe storage and handling. |
| Shelf Life | Acid Red A typically has a shelf life of about two years when kept dry, tightly sealed, and protected from light and heat. |
Pre-scoured merino top and wool yarn are dyed with C.I. Acid Red A (C.I. 15620; sodium 4-[(2-hydroxy-1-naphthyl)azo]naphthalene-1-sulphonate) through an exhaust process in package or hank dyeing machinery. The monoazo colorant contains a single sulphonate substituent and behaves as a levelling acid dye on protein fibre. In a Thies TRD package dyeing machine operating at a liquor ratio of 10:1 to 20:1 and a pump capacity of 30 L/kg/min with inside-out flow reversal of 3 min forward and 3 min reverse, the dyebath is set at 40°C and raised to 98°C at a ramp rate of 1.0°C/min. Glacial acetic acid at 2-3% owf and sodium sulphate at 5-10% owf hold the bath at pH 4.0-4.5. Below pH 3.5 the strike rate becomes rapid enough to create package cross-section shading; above pH 5.0 exhaustion falls to levels that make shade reproducibility difficult in pale depths. The dye is predissolved at 70°C in a 1:20 water ratio before addition to the circulating bath. Because the molecule has a single sulphonate group, it migrates at the boil more readily than disulphonated acid dyes, which supports level migration but also lowers wet fastness. Dyestuff powder stored in opened containers above 60% relative humidity tends to cake and requires pre-drying at 40°C before weighing. Batch-to-batch variance increases when process water hardness exceeds 150 mg/L CaCO3; calcium-induced dye aggregation can deposit on yarn package surfaces and reduce flow. A sequestering agent at 1 g/L is added to the bath before dye introduction. If pump pressure fluctuates by more than 0.2 bar during the hold phase, unlevel package cores have been observed on production runs. After dyeing, the exhausted bath is cooled to 60°C before rinsing to prevent thermal shock damage to wool. Wash fastness is assessed under ISO 105-C10; light fastness is assessed under ISO 105-B02. Published fastness data for C.I. Acid Red A on wool indicates lower wet fastness than milling acid dyes, so depths above 2.0% owf are typically aftertreated with a formaldehyde-free syntan at 2% owf for 20 min at 60°C. Outdoor wool articles are outside the recommended end-use unless the fibre is additionally protected with a UV absorber.
In overflow jet equipment, polyamide 6.6 microfibre knits are processed with C.I. Acid Red A at a rope speed of 250-350 m/min and nozzle pressure of 0.5-1.0 bar. The liquor ratio is held at 8:1 to 12:1, and the bath is ramped from 40°C to 98°C at 1.0°C/min. Citric acid or monosodium phosphate is used to maintain pH 4.5-5.5; this range moderates the strike rate on polyamide 6.6, which retains the dye through ammonium end-group interaction. Anionic leveling agent is restricted to 1 g/L or replaced with a nonionic leveling agent because excess anionic auxiliary competes for dye sites and reduces yield. Nozzle pressure above 1.0 bar has produced rope entanglement and surface crack marks on lightweight microfibre in production-scale jets. The low molecular mass of C.I. Acid Red A gives adequate migration on polyamide, but the same property produces bleed in wet contact and limits wash fastness. Aftertreatment with a formaldehyde-free syntan at 2-4% owf for 20 min at 60°C is applied after rinsing; free formaldehyde release from syntan is controlled under ISO 14184-1. Cationic fixing agents are not introduced into an anionic dyebath because precipitation in circulation lines and on fabric surfaces has been observed in production-scale jet machines. Microfibre knits can exhibit lower visual depth than regular-denier polyamide at equal dye uptake because of high fibre surface area; published data for this specific configuration is limited, and shade sorting should be validated against a physical standard under ISO 105-A01.
| Process step / substrate | Parameter | Method | Use in batch release |
|---|---|---|---|
| Wool yarn exhaust dyeing | Wash fastness | ISO 105-C10 | Grey scale rating recorded; aftertreatment triggered above specified staining threshold |
| Wool yarn exhaust dyeing | Light fastness | ISO 105-B02 | Rating reported against blue wool reference; no generic pass/fail assigned |
| Polyamide 6.6 microfibre knit | Wash fastness | ISO 105-C06 | Aftertreated and non-aftertreated panels compared |
| Polyamide aftertreatment | Free formaldehyde | ISO 14184-1 | Quantitative release reported in mg/kg |
| Chrome-tanned leather | Colour fastness to water | ISO 11642 | Wet migration check for lining and suede |
| Chrome-tanned leather | Colour fastness to rubbing | ISO 11640 | Dry and wet cycles recorded after fatliquoring |
When C.I. Acid Red A is applied to chrome-tanned crust, leachable chromium and residual tanning acid in the hide must be neutralized before dye addition. In a stainless steel drum of 3.0 m diameter rotating at 12-16 rpm, the wet-blue weight is used as the reference mass, and the float is set at 150-200% at 40°C. Neutralization is carried out with 1% sodium formate and 0.3% sodium bicarbonate for 30 min, bringing the internal float to pH 4.0-4.5. The dye is predissolved at 60°C in a 1:10 water ratio and added over 20 min. The drum continues for 60 min, followed by fixation with 0.5% of 85% formic acid over 15 min. Surface strike is a known failure mode when the float pH falls below 3.8; grain surface dye precipitation appears as bronzing on finished leather. At pH above 4.8, exhaustion is incomplete and the spent float remains visibly coloured. Drum speed above 16 rpm can cause excessive mechanical action on suede splits; below 12 rpm dye distribution may be uneven. If cationic retanning agents are required, they are applied only after dye fixation and an intermediate rinse because direct addition can precipitate the anionic colorant in the drum. The anionic dye competes with fatliquors during subsequent processing, so fatliquoring is performed as a separate step after fixation. Wet migration on suede is assessed under ISO 11642, and dry wet rub fastness is assessed under ISO 11640. Published data for C.I. Acid Red A on suede specifically is limited; control samples should be drum-milled with each batch to compensate for hide-to-hide variation in tannage uniformity.
On a high-speed tissue machine, C.I. Acid Red A is metered into the size press as a 1-5 g/L solution for surface colouring of non-food decorative grades. The dye has negligible direct affinity for bleached kraft fibre, so retention depends on a cationic mordant; poly-DADMAC or alum is dosed at 0.5-2.0 kg per dry tonne of fibre. The size press is maintained at pH 5.0-6.5 to balance dye solubility and cationic fixative stability. At machine speeds of 800-1500 m/min, contact time in the nip is short, and dye retention can fall below 60% without fixative; excess cationic polymer can cause precipitation in the metering line and reel surface specks. The low viscosity of the dye solution has a negligible effect on size press pickup, but shade variation is influenced by base-sheet ash content and residual peroxide from bleaching. Residual oxidant in the furnish should be checked before dye addition because monoazo colorants are sensitive to oxidative loss. Low light fastness restricts the end-use to short-life decorative tissue, inner plies, and non-archival paper; food-contact and skin-contact wet applications are outside the normal operating envelope unless a positive migration assessment is completed for the specific grade.
For water-based flexographic inks, C.I. Acid Red A is dissolved in a water/propylene glycol mixture at 10-20% dye weight before letdown into a styrene-acrylic resin solution. The finished ink is adjusted to pH 8.5-9.5; below 8.0 the anionic dye solubility decreases, and above 10.0 alkali pick-up can destabilize the resin emulsion. Viscosity is controlled at 18-25 s Zahn cup #2, and the ink is printed with an anilox roll of 200-250 lpi and cell volume 3.0-4.0 BCM. Drying in forced-air ovens at 60-80°C with 1-2 s dwell produces a water-resistant film only after complete coalescence; rewetting causes dye bleed because the sulfonated colorant remains water-soluble. Flocculation is observed when the ink contacts cationic primers or polyethylenimine-treated films, which can block anilox cells and cause print mottle. The dye is therefore used in non-food outer packaging, tags, and decorative prints where low light fastness and wet bleed are acceptable. For toy packaging, heavy metal migration may require assessment under EN 71-3. For food-contact printed matter, a migration assessment is mandatory before use; a thin flexographic ink film is not automatically a functional barrier.
Digital textile printing of pre-treated polyamide and silk fabrics with C.I. Acid Red A requires low-salt purified dye and filtration through a 0.45 µm absolute filter before the ink is loaded into a piezoelectric drop-on-demand printhead. The ink is formulated to a viscosity of 4-8 mPa·s at 25°C and a surface tension of 28-32 mN/m; these parameters protect jetting performance in printheads operating at 5-20 kHz. If salt content exceeds 100 mg/kg, nozzle dehydration and crystallisation at the meniscus may occur, causing missing nozzles and banding. The substrate is pre-padded with an acid-dye print paste containing urea at 10-15% and steamed at 101-103°C for 20-30 min. Washoff after steaming removes unfixed dye and thickener; fixation is lower on silk than on polyamide because fewer protonated amine sites are available at the fibre surface. An ink aged at 60°C for 7 days should not show viscosity change above 0.5 mPa·s or a measurable filter pressure rise. Published data for C.I. Acid Red A in specific printhead models is limited, so jetting trials with continuous printhead cleaning cycles are required before full production.
Competitive Acid Red A prices that fit your budget—flexible terms and customized quotes for every order.
For samples, pricing, or more information, please contact us at +8615365186327 or mail to sales3@liwei-chem.com.
We will respond to you as soon as possible.
Tel: +8615365186327
Email: sales3@liwei-chem.com
Flexible payment, competitive price, premium service - Inquire now!
Acid Red A is the commercial designation for the sodium salt of a sulfonated monoazo colorant assigned to C.I. Acid Red 88, C.I. 15620, CAS 1658-56-6. The product is supplied as a red-brown powder or low-dusting granular solid and is used primarily in exhaust dyeing of protein and polyamide substrates such as wool, silk, and nylon. As an anionic dye, it is retained by protonated amino groups under acidic conditions. Its aqueous spectral curve exhibits a principal absorbance band near 505 nm. Commercial model designations include standardized powder grades, low-dusting granular grades, and predissolved liquid formulations carrying the same dye strength relative to a manufacturer reference.
The nominal molecular formula of the sodium salt is C20H13N2NaO4S; the free acid corresponds to C20H14N2O4S. The diazo component is 1-aminonaphthalene-4-sulfonic acid, and the coupler is 2-naphthol. Technical grades may contain sodium chloride or sodium sulfate as standardizing diluents. Representative certificate-of-analysis acceptance limits for the powder grade are given in Table 1.
| Quality parameter | Test condition or method | Typical acceptance limit |
|---|---|---|
| Dye strength | UV-Vis at 505 nm versus manufacturer reference | 100 ± 3 % |
| Water solubility | Dissolution at 90 °C, visual after cooling to 25 °C | ≥ 50 g/L |
| Water-insoluble matter | Filtration through 40 µm sintered glass | ≤ 0.2 % by mass |
| Moisture | Oven drying at 105 °C | ≤ 5.0 % by mass |
| pH of 1 % solution | Electrometric at 25 °C | 7.0–9.0 |
| Iron | ICP-OES after acid digestion | ≤ 50 mg/kg |
| Aromatic amine release | EN ISO 17234-1 | Not detected for listed amines |
For powder grades, pre-dissolution in demineralized water at 80–90 °C with mechanical stirring at 300–500 rpm is required before addition to the dye bath. Water hardness above 150 mg/L CaCO3 equivalent should be sequestered; calcium interaction with sulfonate groups can reduce apparent solubility and produce surface deposition on fabric.
Exhaust dyeing of wool with Acid Red A follows a levelling acid dye mechanism. At pH 4.0–5.0 the fibre contains sufficient protonated amino groups to attract sulfonate anions, but rapid initial strike can occur below pH 3.8. Dyeing recipes commonly use 1–3 % owf acetic acid 60 % solution plus 5–10 % owf anhydrous sodium sulfate. The electrolyte suppresses fibre surface charge and promotes migration. A temperature ramp from 40 °C to 98 °C at 1.0–1.5 °C/min is typical. Holding at 98 °C for 30–45 min improves penetration through the epicuticle. Exhaustion values above 95 % are attainable on untreated wool at 3 % owf dye, but addition rates above 8 % owf require extended hold times and pH adjustment to 3.8–4.2 to maintain levelness. The practical pH window is narrow: below pH 3.8, strike is rapid and levelness is lost; above pH 5.0, exhaustion falls below 90 % on untreated wool. Batch-to-batch pH control within ± 0.2 units is therefore necessary.
On package dyeing machines with flow reversal and liquor ratios of 1:8 to 1:12, circulation should be adjusted from 20 L/kg/min to 35 L/kg/min during the ramp. Low flow at high temperature produces shade variation between inner and outer package layers. Published production-scale batch records for this dye indicate that unlevel packages are frequently traceable to insufficient flow during the final 20 min of heating rather than to dye strength variance.
Fastness properties of Acid Red A on wool are governed by its monoazo structure and terminal sulfonate group. Washing fastness under ISO 105-C06 A2S at 40 °C is typically grade 3–4 for medium depths. Light fastness under ISO 105-B02 is typically blue wool 3, which limits exterior automotive or outdoor textile end uses. Perspiration fastness under ISO 105-E04 may drop to grade 3 in alkaline perspiration solution because the dye becomes less firmly fixed under high pH. These values are depth-dependent and should be verified on the finished substrate.
Acid Red A differs from C.I. Acid Red 87, a xanthene red, and from C.I. Acid Red 151, an azo red, in affinity and fastness. It builds to a scarlet-to-red shade with moderate to high migration, but its wash fastness on nylon 6 is lower than that of metal-free high-fastness reds containing multiple sulfonated groups. On nylon, Acid Red A can be dyed at pH 4.5–5.5 with anionic levelling agents. It is not recommended for automotive interior or swimwear fabrics where AATCC TM61 2A wash fastness above grade 4 is required. Acid Red A has a lower molecular weight and less complex structure than polyazo or anthraquinone reds, giving lower cost per kilogram but also lower wet fastness. Comparative technical data are summarised in Table 2.
| Property | Acid Red A / C.I. Acid Red 88 | C.I. Acid Red 1 | C.I. Acid Red 151 | C.I. Acid Red 87 |
|---|---|---|---|---|
| Application pH for wool | 4.0–5.0 | 4.0–5.0 | 4.5–6.0 | 3.5–4.5 |
| Water solubility at 90 °C | ≥ 50 g/L | High | Moderate | High |
| Migration on wool | High | High | Moderate | High |
| Light fastness on wool, ISO 105-B02 | Blue wool 3 | Blue wool 4 | Blue wool 4–5 | Blue wool 1–2 |
| Wet fastness on wool | Moderate | Moderate | Good | Poor |
| Copper sensitivity | Shade dulling possible | Low | Low | Moderate |
| Relative cost position | Low | Low | Moderate | Moderate |
For leather drum dyeing, rechromed or vegetable-tanned stock is neutralised to pH 4.0–5.0, and Acid Red A is added at 0.5–3.0 % by shaved weight in a float ratio of 2:1 at 45–60 °C. Penetration through the grain layer requires 30–40 min of mechanical agitation; fixation is completed with formic acid at pH 3.6–3.8. The limited light fastness restricts use to linings, bookbinding leather, and interior articles not exposed to direct sunlight. In paper coating, Acid Red A can be added to size-press solutions at 0.1–1.0 g/L, but retention requires cationic fixatives because the anionic sulfonate group has low affinity to cellulose.
Because Acid Red A is an azo colorant, textile and leather processors should perform reductive cleavage screening according to EN ISO 17234-1 and EN ISO 17234-2 when the final article is destined for the EU. The diazo component is 1-aminonaphthalene-4-sulfonic acid; it is not among the aromatic amines listed in REACH Annex XVII Entry 43, but process impurities and side products must be controlled through the dye manufacturer’s batch release data. The product is not intended for food-contact polymer applications, and no positive listing under FDA 21 CFR 178.3297 is assumed. Storage in original sealed packaging at <30 °C and <65 % relative humidity is recommended. Opened material should be re-sealed to prevent moisture uptake above 5 % by mass, which can impair flowability and dosing accuracy in automatic colour-dispensing systems.
