Section
| HS Code | 698626 |
| Product Name | Direct Brown RN |
| Product Type | Direct dye |
| Colour Index Name | C.I. Direct Brown 2 |
| Colour Index Number | 22311 |
| Cas Registry Number | 1325-37-7 |
| Chemical Class | Azo direct dye |
| Appearance | Brown powder |
| Colour Shade | Brown |
| Solubility | Soluble in water |
| Ionic Character | Anionic |
| Primary Substrates | Cellulose fibers such as cotton, viscose, and linen; also used on silk and nylon |
| Dyeing Method | Exhaust dyeing with electrolyte addition |
| Typical Dyeing Ph | Neutral to weakly alkaline |
| Light Fastness | Moderate |
| Washing Fastness | Moderate |
| Storage Conditions | Cool, dry, and sealed container |
As an accredited Direct Brown RN factory, we enforce strict quality protocols—every batch undergoes rigorous testing to ensure consistent efficacy and safety standards.
| Packing | Direct Brown RN is supplied in 25 kg net multi-ply paper sacks with polyethylene liners, palletized and shrink-wrapped for transport. |
| Container Loading (20′ FCL) | Direct Brown RN is packed and loaded into a clean, dry 20-foot FCL container for secure ocean transport. |
| Shipping | Direct Brown RN is typically shipped as a non-hazardous chemical in sealed, labeled containers, protected from moisture and direct sunlight. Transport under ambient conditions in compliance with local regulations. Use appropriate personal protective equipment and follow the supplier’s safety data sheet. |
| Storage | Store Direct Brown RN in a cool, dry, well-ventilated area away from direct sunlight, heat, moisture, and ignition sources. Keep containers tightly closed, clearly labeled, and upright. Segregate from strong oxidizers, acids, and bases. Prevent dust generation and avoid inhalation or skin contact. Use appropriate personal protective equipment and follow local regulations. Store separately from food, drink, and animal feed. |
| Shelf Life | When stored unopened in a cool, dry, well-ventilated area, Direct Brown RN has a shelf life of approximately 24 months. |
Direct Brown RN, commonly indexed as C.I. Direct Brown 1, is applied as an anionic disazo colorant for cellulosic substrates. In open-width jet treatment of cotton poplin and viscose twill, the dyestuff is exhausted from a neutral bath at liquor ratios between 1:8 and 1:15. The pre-dissolved dye is charged at 50–60°C, and electrostatically screened sodium chloride is then metered in increments of 5–10 g/L over 30–45 min, reaching 15–30 g/L for medium depths and 30–45 g/L for heavy brown shades on mercerized cotton. The heating gradient is restricted to 1.0–1.5°C/min up to 85–95°C, followed by a migration plateau of 30–45 min before controlled cooling to 60°C for overflow rinsing. Because the sulphonate groups confer strong substantivity, rapid salt addition without a migration phase produces shadowing at padded seams and edge-marking on rope-scoured knit goods. On production-scale winch machines, lightweight regenerated cellulose requires reel speeds below 250 m/min to limit crease formation. Batch-to-batch variation in cotton maturity alters accessible primary hydroxyl site density; fabric absorbency outside the 2–5 s range by AATCC 79 frequently forces re-standardization of the master dosing curve. Hard-water cations exceeding 150 mg/L as CaCO₃ are sequestered with polyphosphate or EDTA at 0.5–1.0 g/L to prevent calcium sulphonate precipitation on the yarn surface. After exhaustion, a cationic fixing agent based on polydicyandiamide or quaternary polyamine is applied in a fresh bath at 40–50°C and pH 5.5–6.5 for 20 min; this step raises wet fastness relative to the unfixed dye when evaluated according to ISO 105-C06:2010 and ISO 105-X12:2016. High-salt exhaustion elevates effluent conductivity to 40–80 mS/cm before dilution, which constrains direct discharge under integrated pollution prevention and control permits. Terminal articles for this route include cotton toweling, viscose blouse weights, and cross-dyed upholstery where wet fastness after fixation is acceptable for the intended care cycle.
Front-loading sodium sulphate at ambient temperature creates a solubility and aggregation conflict in exhaust baths. Direct Brown RN is supplied as a water-soluble sulphonated powder; its aqueous solubility declines rapidly when ionic strength rises before the bath reaches 70°C. If the full electrolyte charge is added at 35–40°C, the dye forms colloidal aggregates that are no longer redistributed through the substrate by circulation. Cheese-dyeing apparatus operating at differential pressure below 0.5 bar exhibits retained aggregates on the inner package layers. The defect cannot be removed by extending the top-temperature plateau because thermal disaggregation is too slow relative to the 20–30 min migration window. Package densities above 350 g/L intensify the effect by reducing interstitial flow velocity. The corrective procedure uses a split salt profile: 40% of the sodium chloride dose is added at 60°C after 15 min of dye distribution, and the remaining 60% is metered over 30 min after the bath reaches 80–85°C. In-line conductivity feedback is set to a maximum slope of 0.5 mS/cm per minute; exceeding this slope stops the dosing pump and triggers an operator alarm. The constraint is critical when dye input exceeds 2.0% on weight of fibre for heavy brown shades, because the dyebath exhaustion curve moves above 80% before the final salt fraction, leaving insufficient free dye for migration. Instrument-based release criteria use ISO 105-A05:1996 with a tolerance of 0.8 DE CMC(2:1) against the approved standard swatch. Viscose warp yarns present additional risk because pre-swelling reduces the effective diffusion path and can create streak-like colour differences if the salt front is non-uniform.
In chrome-tanned bovine leather drum dyeing, Direct Brown RN is applied at 1.0–3.0% of shaved wet-blue weight from a float of 80–150% at 55–60°C. The anionic sulphonate groups compete with retanning syntans for cationic chromium sites, so the standard sequence is neutralization, anionic syntax addition, dye addition, then formic acid fixation at pH 3.8–4.0. For full-grain footwear leather, surface build-up is limited by running the drum for 30–40 min before acidification. Through-penetration on split suede requires 60–90 min at higher float and the addition of an anionic leveling agent before the dye is introduced. The terminal colour fastness of Direct Brown RN on leather is tested after fatliquoring and finishing by ISO 11640:2018 for rub fastness and ISO 105-B02:2014 for light fastness. Residual dye in the spent float is monitored spectrophotometrically; if residual absorbance exceeds 15% of the initial bath, the concentration is reduced for the next lot to limit chemical oxygen demand in tannery effluent. For European leather goods, azo chromophore compliance is verified by reductive cleavage testing according to EN 14362-1:2012 and EN 14362-3:2012, with restricted primary aromatic amines controlled below 30 mg/kg.
Substitution of sulphur dyeing with Direct Brown RN in package equipment shifts the critical process control point from reduction-oxidation balance to electrolyte-migration control. For cotton yarn on perforated stainless steel cones at a package density of 340–380 g/L, the bath is run at 1:5 to 1:7 liquor ratio, which is narrower than piece dyeing and requires a more precise salt ramp. Sodium sulphide and the oxidation air step are omitted, eliminating hydrogen sulphide odour and reducing the sulphide oxidation load on effluent treatment. However, the wet fastness boundary moves downward relative to sulphur-dyed shades. Dark package lots therefore require 3–5 g/L of a low-formaldehyde quaternary amine fixing agent at pH 5.5–6.0 and 45°C for 20 min. Package pressure differential must remain below 0.8 bar during aftertreatment to avoid channelling and inner-to-outer shade variation. Fixed yarn is tested for washing fastness according to ISO 105-C06:2010 and for perspiration fastness according to ISO 105-E04:2013. The substitution does not reduce total dissolved solids discharge because sodium chloride at 20–35 g/L remains necessary for dark brown shades. This trade-off makes the replacement viable mainly for medium-depth workwear knitting yarns where finished goods are not marketed as high-stability articles requiring repeated industrial laundering.
In beater addition to bleached softwood kraft pulp, Direct Brown RN is added as a 1% stock solution at 0.05–0.5% on dry fibre before alum addition. The anionic dye is retained on cellulose by direct substantivity and subsequent aluminium polycation complexation at pH 5.0–6.5. Alum dosing above 2.0% on fibre can reduce stock pH below 4.5 and depress dye exhaustion; backwater residual dye is monitored by UV-Vis photometry. If first-pass retention falls below 80%, cationic polyacrylamide is added at 0.02–0.05% on dry fibre. Handsheets formed according to TAPPI T 205 sp-18 are used to standardize shade before mill-scale furnish changeover. For surface size press application on uncoated kraft liner, Direct Brown RN is combined with oxidized starch at 40–60°C, and the viscosity is held between 20–50 mPa·s at 60°C. One-pass pickup limits colour strength relative to beater addition, and published comparative fastness data for this configuration is limited. Terminal papers include recycled napkin stock, unbleached packaging liner, and decorative tissue where contact with food is excluded.
Direct-style printing with Direct Brown RN is used for low-cost cellulosic goods where high wet fastness is not a requirement. The print paste contains 8–15% dye, 5% urea, 0.1% sodium hexametaphosphate, and 40–60% of a low-viscosity sodium alginate or guar gum thickener. The paste is applied to mercerized cotton sheeting through flat-screen mesh at 60–80 threads/cm. After drying at 100°C, the fabric is steamed at 102°C for 5–7 min to swell the cellulose and allow dye diffusion from the print film. Cold rinsing removes thickener residues, and a cationic fixative is applied at 2–4 g/L to reduce crocking. Finished prints are evaluated for rubbing fastness according to ISO 105-X12:2016 and washing fastness according to ISO 105-C06:2010. The process omits the reduction and oxidation stages required for vat and reactive printing, which lowers energy input, but the terminal articles are restricted to decorative bunting, disposable garments, and short-life home textiles where light fastness and repeated washing performance are not market barriers.
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Direct Brown RN is a water-soluble anionic disazo dyestuff assigned in conventional Colour Index listings to C.I. Direct Brown 1 (30045). The commercial model designation RN denotes a neutral-to-red brown shade on cellulosic substrates, distinguishing it from brighter yellow-brown direct browns in the same application class. It is supplied as a dark brown free-flowing powder standardised to 100% or 150% tinctorial strength with sodium sulfate diluent; the active chromophore contains sulfonated aromatic rings and is free of complexed chromium or cobalt. Because dye-fiber attachment on cotton and viscose occurs through hydrogen bonding and van der Waals forces rather than covalent fixation, the product does not require alkali for fixation. This attachment mode reduces processing temperature and alkali consumption relative to reactive brown dyes, but it also restricts wet fastness under ISO 105-C10 to a lower grey-scale range unless a cationic aftertreatment is used. The anionic nature of the dissolved dye makes it incompatible with quaternary ammonium softeners in the same bath; precipitation occurs if a cation-active finishing chemical is added without an intermediate rinse. Direct Brown RN is used mainly in exhaust dyeing of cotton, viscose, modal, jute, and regenerated cellulose, with smaller-volume use in paper and leather. The exact batch-specific chromophore composition and aromatic amine profile should be verified against the supplier certificate because commercial nomenclature alone does not define the regulatory status of the lot.
Bulk-supply acceptance is based on tinctorial strength against a retained reference, not on absolute dye content, because the commercial powder contains inorganic diluents and moisture. The following acceptance matrix is compiled from standard direct-dye quality control parameters; a terminal user should require a lot certificate that reports the actual values against these or equivalent limits.
| Parameter | Acceptance range | Reference method |
|---|---|---|
| Appearance | Dark brown powder | Visual |
| Colour strength vs reference | 100 ± 3 % | ISO 11664-4 spectrophotometry |
| pH of 10 g/L aqueous solution | 7.0–9.0 | ISO 787-9 |
| Moisture mass fraction | ≤ 5.0 % | ISO 787-2 |
| Solubility in softened water at 80 °C | ≥ 40 g/L | ISO 7579 |
| Dispersion stability after 30 min at 80 °C | No specking or residue on 10 μm filter | Calibrated filtration test |
| Restricted aromatic amines in dyed textile | ≤ 30 mg/kg per listed amine | EN 14362-1:2012 |
When a lot is supplied at 150% strength, the moisture and diluent specifications apply to the formulated powder rather than to the isolated chromophore. Lot-to-lot variation in moisture and filler content means that equal powder weights do not produce equal shade depth unless the strength certificate is used to correct the weighing. Storage in sealed containers below 60% RH is recommended; exposure to humid air increases moisture mass fraction and alters tinctorial strength.
In overflow and soft-flow machines operating at 1:8 to 1:12 liquor ratio, the solubility reserve of Direct Brown RN is reduced by high electrolyte concentrations and by shear forces at the circulation pump. If the dye solution is injected into a bath already containing ≥ 30 g/L sodium chloride at 80 °C, the dissolved dye can aggregate before it reaches the fabric. Field observations on production-scale equipment include specky dyeing along fabric creases, brown deposits on heat-exchanger surfaces, and filter blockage in the circulation loop. The corrective procedure is to predissolve the powder in a separate vessel with softened water at 80 °C and to meter the solution into an electrolyte-free bath over 10–15 min. Sodium chloride or sodium sulfate is then added in three equal portions at 5–10 g/L increments, allowing 10 min between additions. The processing window for maximum colour yield is 80–90 °C; temperatures above 95 °C do not improve fixation and may shift the dyeing equilibrium toward the bath, while temperatures below 70 °C reduce migration and produce unlevel dyeing on jiggers and beam dyeing machines. Foam generation in jet machines at circulation pump pressures above 2.0 bar requires a nonionic defoamer; overdosing above 0.5 g/L reduces solubility and can redeposit on fabric.
For exhaust dyeing on cotton and viscose, the dye is applied at 0.5–3.0 % on weight of fibre. The bath is set at 40 °C with a polyphosphate or polycarboxylate sequestrant when raw water hardness exceeds 150 ppm CaCO₃. After the dye solution is metered into the bath, the temperature is raised to 80–90 °C at 2 °C/min. Sodium chloride or sodium sulfate is dosed in three stages to a final concentration of 10–40 g/L, adjusted by shade depth and liquor ratio. The bath is then held for 30–45 min. After the dyeing period, the fabric is cooled to 60 °C before draining and rinsed in cold water. Direct Brown RN does not require oxidation, reduction, or alkali fixation; this distinguishes it from vat and sulphur brown products on the same cellulosic substrate. In paddle dyeing machines and jiggers, the same dyeing cycle is used, but salt addition must be slower because the mechanical agitation is less uniform than in overflow machines.
In pad-dyeing ranges, Direct Brown RN can be applied at 10–30 g/L with 20 g/L urea and 5 g/L sodium chloride at wet pick-up of 60–80 %. Nip pressure is set at 1.5–2.5 bar; lower pressure increases pick-up and can cause migration during drying. After padding, the fabric is dried at 100–120 °C and finished without steam fixation because the dye does not require chemical fixation. The pad method is less selective than exhaust dyeing and should be reserved for uniform cellulosic fabrics where high production throughput is required. Selvedge-to-centre shade variation in pad-dry applications is controlled by pad trough circulation and by maintaining a constant liquor level; a drop in trough volume below 20 % alters concentration and produces dark selvedges.
The absence of covalent dye-fiber bonds is the primary technical difference between Direct Brown RN and reactive brown dyes. The following comparative data are typical published ranges for cotton direct and reactive systems, and for wool/nylon acid systems; they are not lot-specific guarantees for end-use performance.
| Test or property | Direct Brown RN | Reactive brown | Acid brown |
|---|---|---|---|
| Fastness to washing (ISO 105-C10) | 2–3 | 4–5 | 3–4 on wool |
| Fastness to light (ISO 105-B02) | 2–3 | 4–6 | 3–5 |
| Fastness to rubbing (ISO 105-X12) dry/wet | 4/2–3 | 4–5/4 | 4/3 |
| Dye-fiber attachment | Hydrogen bonding / van der Waals | Covalent | Ionic / coordination |
| Dyeing temperature | 80–95 °C | 60–80 °C | 90–98 °C |
| Electrolyte or pH requirement | 10–40 g/L salt | 30–80 g/L salt, alkali | pH 4–5 formic acid |
| Metal in chromophore | None | None | Possible Cr/Co in metal-complex types |
When the end use requires ISO 105-B02 light fastness of ≥ 6, as in automotive upholstery or outdoor awnings, Direct Brown RN falls outside the operational window and a vat or reactive brown chromophore is specified instead. Conversely, for low-cost one-use disposable textiles or interior packaging where wet fastness is not the controlling property, the direct dye system avoids alkali and oxidation cycles. Shade difference between direct, reactive, and acid browns must be assessed under D65/10° illumination using ISO 11664-4 CIELAB coordinates because metamerism can occur between the three dye classes.
Cationic aftertreatment is the standard method for reducing the wet-fastness gap between Direct Brown RN and reactive brown dyes. A quaternary polyamine fixative applied at 2–4 g/L and 40–60 °C for 15–20 min raises wash fastness under ISO 105-C10 by 1–2 grey-scale grades. The improvement is not permanent after repeated domestic laundering; dyed garments subjected to more than 20 wash cycles often return to the untreated wet-fastness range. The fixative also reduces dye migration during drying by increasing molecular weight and reducing water solubility, but it can stiffen the hand of knitted cellulosic fabrics. The anionic dye and cationic fixative must be separated by an intermediate rinse because direct contact in the bath produces insoluble lakes that deposit on fibre surfaces. In hard water above 150 ppm CaCO₃, calcium ions compete with the fixative and reduce its efficiency; a polyphosphate or polycarboxylate dispersant is added before the aftertreatment stage. The fixative pH should be maintained at 5.0–6.0; below 4.5 the fibre surface charge can reverse and the anionic dye may redissolve.
Commercial Direct Brown RN lots that are produced from benzidine-derived intermediates are subject to the EU azo-colourant restriction under REACH Annex XVII Entry 43. The restriction applies to finished textile and leather articles that release a listed aromatic amine above 30 mg/kg; analytical verification for textiles is carried out according to EN 14362-1:2012. For leather articles, EN ISO 17234-1 is used. A lot certificate should state the residual benzidine content in the dyed article, not merely in the raw powder, because reductive cleavage of the chromophore during testing is the regulated endpoint. Direct Brown RN is not intended for food-contact applications; no FDA 21 CFR migration data should be assumed. Dust control and local exhaust ventilation are required during weighing and dissolution where powdered dye dust exceeds occupational exposure limits specified in the safety data sheet; engineering controls should be validated according to ISO 12100 risk assessment principles.
On leather, Direct Brown RN is applied in drum dyeing at 60 °C and pH 4.5–5.5 at 2–4 % on shaved weight. The dye penetrates chrome-tanned stock more evenly than vegetable-tanned stock unless the surface charge is adjusted with an anionic re-tanning agent. In paper production, beater addition at 0.2–1.5 % on dry fibre mass yields a warm brown sheet; the subsequent addition of alum fixes the anionic chromophore but may reduce colour strength if dosed above 2 % on dry fibre. Published data for the specific bleed limit of Direct Brown RN under EN 646 for coloured paper and board is limited; therefore paper-contact applications require end-use migration testing. Because the product is not surface-active, wetting of the paper furnish is improved by a nonionic wetting agent at 0.1–0.3 g/L. In leather processing, the alkaline buffering of the float should be measured before dye addition because pH drift above 6.0 reduces dye uptake and can create uneven grain shading.
