Section
| HS Code | 443760 |
| Product Name | Direct Fast Red F3B |
| Synonyms | C.I. Direct Red 80; Sirius Red F3B; Direct Red 80 |
| Color Index Name | C.I. Direct Red 80 |
| Color Index Number | 35780 |
| Cas Number | 2610-10-8 |
| Einecs Number | 220-027-3 |
| Molecular Formula | C45H26N10Na6O21S6 |
| Molecular Weight | 1373.08 g/mol |
| Dye Class | Direct dye |
| Appearance | Dark red to brown-red powder |
| Water Solubility | Soluble in water |
| Application | Dyeing of cotton, viscose, paper, and leather; biological collagen stain |
As an accredited Direct Fast Red F3B factory, we enforce strict quality protocols—every batch undergoes rigorous testing to ensure consistent efficacy and safety standards.
| Packing | Packaging: Direct Fast Red F3B supplied in 25 kg polyethylene-lined paper bags, securely sealed for industrial transport and storage. |
| Container Loading (20′ FCL) | Direct Fast Red F3B loaded in a 20-foot FCL container, properly packaged and secured for ocean transport. |
| Shipping | Direct Fast Red F3B is generally shipped as a non-hazardous dye/chemical under normal transport regulations, with no typical UN hazard class. Use sealed, labeled, moisture-resistant containers; prevent spills. Store and transport in a cool, dry, ventilated area away from oxidizers, following the SDS and local rules. |
| Storage | Store Direct Fast Red F3B in a cool, dry, well-ventilated area away from direct sunlight, heat, moisture, and ignition sources. Keep containers tightly closed and labeled. Separate from oxidizing agents and strong acids. Avoid dust generation and store near spill containment. Use appropriate PPE when handling. Do not store with food, feed, or beverages. |
| Shelf Life | Direct Fast Red F3B should be stored cool, dry, and well-ventilated; unopened containers typically retain shelf life for about 24–36 months. |
In jet and softflow processing of cotton/viscose single jersey, rib, and interlock fabrics, Direct Fast Red F3B (C.I. Direct Red 80) is introduced only after complete predissolution in demineralized water at 60–80°C and passage through a 100 µm wedge-wire filter; the working bath is held at 30–40°C during dye addition, then ramped to 95–98°C at 1.0–1.5°C/min to avoid knotting and shade tailing on high-speed softflow jets operating at fabric speeds of 200–350 m/min. Exhaustion on cellulosic substrates depends on electrolyte dosage rather than alkali, so Glauber's salt is introduced in three equal portions at 5–30 g/L only after the bath reaches 80–90°C; adding salt too early or too quickly produces filter-blocking aggregates on circulation pump screens and unlevel red streaks on selvedges. The addition rate for pale-to-medium shades falls between 0.10% and 2.50% on weight of fabric, while deep burgundy shades may require up to 4.00% owf with extended circulation and a final 20–30 min exhaustion check at 95°C. Because wet fastness of this polyazo direct dye without aftertreatment is limited, dyehouse operations apply a formaldehyde-free cationic fixer at 1.0–4.0% owf in a fresh bath at 40–50°C for 20–30 min, followed by warm rinsing and hydroextraction; the finished goods are then submitted for wash fastness testing under ISO 105-C06 A1S:2010, light fastness screening under ISO 105-B02:2014, and crocking assessment under ISO 105-X12:2016, with additional reduction-cleavage verification per EN ISO 14362-1:2017 when buyer RSL compliance is required. Terminal product categories in this segment include cotton jersey T-shirts, viscose and modal undergarments, interlock nightwear, and terry towels, with OEKO-TEX Standard 100 Annex 4 limits checked on the final article rather than the raw dye.
| Process | Substrate | Typical addition level | Equipment and stage | Control standard |
|---|---|---|---|---|
| Jet exhaust dyeing | Cotton/viscose knits | 0.10–2.50% owf | Softflow jet, after salt addition | ISO 105-C06 A1S:2010 |
| Pad-dry-fix | Woven cotton/viscose | 8–25 g/L | Padder, 70–80% pickup | ISO 105-X12:2016 |
| Stock dyeing | Bleached chemical pulp | 0.005–0.300% on OD pulp | Thick stock line before fan pump | EN 646:2019 |
| Leather drum dyeing | Chrome-tanned shaved leather | 0.5–3.0% on shaved weight | Drum, 40–50°C | ISO 11640:2012 |
| Water-based ink | Absorbent paper | 0.5–5.0% wt | High-speed disperser, 1 µm filtration | EN 71-3:2019+A1:2021 |
The pad liquor is prepared with 8–25 g/L Direct Fast Red F3B for medium red shades on mercerized cotton, together with 5–15 g/L of a low-viscosity acrylic migration inhibitor and 0.5–1.0 g/L of a non-foaming wetting agent; hard water above 5°dH must be corrected by sequestration because calcium and magnesium ions precipitate the anionic dye and produce uneven crusting on the pad trough. The fabric is padded at 25–30°C with a padder nip pressure of 2–3 bar and a pickup of 70–80%, then passed over a 100–130°C hotflue or multi-cylinder dryer; pad-liquor viscosity is maintained below 50 mPa·s to avoid foam and skip at line speeds above 60 m/min. Drying is a critical boundary because over-drying above 130°C drives dye migration toward fabric faces and creates back-to-face shade differences, while under-drying leaves residual moisture that destabilizes the subsequent fixer bath. After drying, the goods are padded with a cationic fixing agent at 10–30 g/L and re-dried at 110–120°C, which improves wet rubbing resistance but may reduce light fastness by 0.5–1.0 grade; this trade-off requires batch-specific evaluation against ISO 105-B02:2014 and ISO 105-X12:2016. Reduction-cleavage testing under EN ISO 14362-1:2017 and screening against REACH Annex XVII entry 43 form the compliance basis for azo dye split products, while final textile articles for European apparel import are checked against OEKO-TEX Standard 100 Annex 4 and buyer RSL lists. Finished product types include woven cotton shirting, bed sheeting, workwear uniforms, pocketing, and lining fabrics where the direct dye is selected for its relatively simple application and medium red shade reproducibility across mercerized and non-mercerized cellulose.
When bleached chemical pulp is processed into tissue and folding boxboard, Direct Fast Red F3B is added continuously into the thick stock line or machine chest at 0.005–0.300% on oven-dry pulp for tinted tissue grades and 0.02–0.50% for saturated red packaging board; the dye is first dissolved as a 1–2% aqueous solution at 60–70°C and filtered through 50 µm before the fan pump to avoid visible speck contamination on the wire. Retention is controlled by alum addition at 0.5–1.5% on dry pulp and pH adjustment to 4.8–6.5; when pH falls below 4.5, the anionic dye loses substantivity and increases colour in the white water, while pH above 6.8 produces weak retention and shade drift. On single-felt tissue machines running at 1200–1800 m/min, the dye is preferentially metered after the refiners and before the headbox to minimize thermal degradation in steam-heated pulpers; production workers record red shade stability against a closed-loop spectrophotometer because batch pulp variation in kappa number and carboxylic charge shifts final shade by up to 0.5 CIELAB ΔE units. For paper and board intended for food contact, Direct Fast Red F3B is not automatically cleared for direct contact with aqueous or fatty foods, and suitability must be established under EN 646:2019 for colour fastness and FDA 21 CFR 176.170 or EU 1935/2004 migration testing; where compliance data is absent, the dye is restricted to non-food-contact packaging layers or decorative outer plies. Terminal products include colored tissue, napkins, party decoration paper, folding boxboard, and laminated board surfaces.
The neutralization stage before drum dyeing controls the distribution of the anionic dye within the leather cross-section; chrome-tanned shaved hides are neutralized with sodium bicarbonate or sodium formate at 0.5–1.5% on shaved weight to a cut pH of 5.0–5.5, because residual cationic chrome complex at lower pH precipitates Direct Fast Red F3B on the grain and produces bronzing. The dye is added at 0.5–3.0% on shaved weight in a 40–50°C aqueous bath at 200–400% float, followed by 30–60 min of drum rotation; retanning syntans should be introduced only after the direct dye has penetrated, and cationic fatliquors or chrome syntans are avoided in the same bath because they form dye-fatty complexes that reduce colour strength and create uneven grain shading. Fixation is completed by dilute formic acid added in two portions to a final bath pH of 3.8–4.2, which reduces liquor colour and improves wet rubbing behaviour; after washing and sammying, retanned leather is assessed for rub fastness under ISO 11640:2012 and perspiration fastness under ISO 11641:2012. Compliance screening includes REACH Annex XVII entry 43 for restricted aromatic amines, ZDHC MRSL v3.1 verification for leather chemical inputs, and brand RSL limits on the finished hide. Produced article types include full-grain shoe upper leather, corrected-grain leather goods, lining leather, and split leather for work gloves.
For water-based flexographic inks printed on uncoated paper sacks, the dye is prepared as a 10–20% aqueous stock solution and then let down to a final working ink concentration of 0.5–5.0% by weight; the dye must be completely solubilized before combining with pH modifiers or polymeric binders because undissolved dye particles clog doctor-blade chambers and produce streak defects on anilox rolls. Ink viscosity is adjusted to 2–20 mPa·s and pH to 7.5–9.2 with an amino alcohol or weak alkali, while 5–15% humectant such as glycerol or polyethylene glycol is included when the ink is used for felt-tip markers and stamp pads; filtration through 1 µm absolute-rated media is standard before filling. Published formulation data for this specific dye in water-based ink bases is limited, so the above ranges represent common processing windows for anionic direct dyes rather than vendor-validated formulations; each lot should be checked for solubility, conductivity, and surface tension stability. Heavy metal migration is assessed under EN 71-3:2019+A1:2021 for toy and stationery applications, while labelling follows ASTM D4236 for art materials; for food-contact printed packaging, the printed side must be separated by a barrier or used only on the outer ply unless migration testing under EU 1935/2004 demonstrates compliance. Terminal product categories include printed paper carrier bags, corrugated cases, napkin bands, drawing inks, and stamp-pad inks for interior-use paper goods; the dye is not recommended for exterior signage because accelerated xenon exposure under ASTM D3424 generally produces lower ratings than pigmented inks.
The picrosirius red protocol depends on the formation of aligned dye-collagen interactions at low pH, and Direct Fast Red F3B—supplied as C.I. Direct Red 80—is prepared at 0.1% weight per volume in saturated aqueous picric acid to produce the staining reagent; the solution must be prepared in a glass or stainless-steel vessel, filtered through 0.45 µm membrane after 24 h of stabilization, and stored in the dark because light exposure shortens the effective staining window. Because saturated picric acid is shock-sensitive when dry, stock containers are kept water-wet and handled in a fume hood. In formalin-fixed paraffin-embedded sections, staining proceeds for 60 min at room temperature, followed by two changes of acidified water to remove unbound dye and to preserve collagen birefringence under polarized light; incomplete rinsing leaves amorphous dye aggregates that obscure the red-to-orange birefringence shift characteristic of fibrillar collagen. The ionic strength and picric acid concentration are critical because the dye is not covalently bound to collagen and excess salt or neutral pH dissociates the complex; the working solution must be monitored for precipitate and discarded if turbidity exceeds 0.5 NTU. Compliance for this reagent-grade use includes ISO 15189:2022 quality management in the staining laboratory, REACH registration for the dye supply, and a certificate of analysis covering dye content, insoluble matter, and absorption maxima; the product is designated for research use and non-clinical histochemistry unless local IVDR notification is completed. Terminal outputs are stained tissue sections for collagen architecture analysis in pathology and biomedical research, not consumer goods.
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Direct Fast Red F3B is the commercial designation for a sulphonated direct azo dye whose Colour Index assignment is C.I. Direct Red 80, C.I. 35780. The CAS registry number 2610-10-8 and the molecular formula C45H26N10Na6O21S6 correspond to the hexasodium salt of a tetrakisazo chromophore; the relative molecular mass is 1373.07 g/mol. The product is supplied as a dark red to brownish-red powder or granulate, standardised with sodium chloride or sodium sulphate to a supplier reference strength. Because the standardising diluent is part of the commercial article, the neat dye content is not a fixed specification and must be read from each lot certificate of analysis before weighing at the dyehouse. The molecule carries six sulphonate groups per formula unit, giving high anionic charge density and controlling both cellulosic substantivity and sensitivity to hard-water cations and cationic aftertreatment agents.
Commercial acceptance is normally based on the Colour Index generic name rather than on the trade name alone, because the same dye is sold under several synonyms, including Sirius Red F3B and Chloramine Fast Red F3B. The inventory parameters in Table 1 are used to confirm that the tendered product matches the required colourant chemistry.
| Parameter | Control basis |
|---|---|
| Colour Index generic name | C.I. Direct Red 80; C.I. 35780 |
| CAS registry number | 2610-10-8 |
| Molecular formula | C45H26N10Na6O21S6 |
| Relative molecular mass | 1373.07 g/mol |
| Chromophore composition | tetrakisazo, anionic hexasodium sulphonate |
| Commercial standardisation | sodium chloride or sodium sulphate strength adjustment; neat dye content lot-specific |
| Physical form | powder, granulated powder, or liquid formulation depending on supplier |
| Heavy metal and amine control | supplier CoA against REACH Annex XVII entry 43 and Oeko-Tex Standard 100 when skin-contact textiles are claimed |
The standardising salt is not an inert diluent in all circumstances: it contributes to the initial electrolyte load in the dyebath and can shift the apparent strike if the amount is not corrected for the supplier’s strength adjustment. Dyehouses that switch among suppliers compare equal colour strength, not equal powder weight, and adjust salt addition when the standardisation level changes. The visible absorption maximum of an aqueous solution is typically reported near 540 nm; exact λmax shifts with pH, salt content, and solvent. Colour strength is therefore measured against a reference lot by visible spectrophotometry rather than inferred from powder weight.
Dyehouse handling is similar to other dust-forming direct dyes. Granulated forms are preferred for automated colour kitchens because they reduce dust and improve flow through screw feeders. Storage should avoid moisture uptake because the sulphonated powder is hygroscopic; caked material can block powder dosing lines and change the weighed colour strength.
Direct Red 80 is a high-substantivity direct dye. In exhaust dyeing of cotton, viscose, linen, and their cellulosic blends, the principal processing risk is unlevel strike when sodium chloride or sodium sulphate is added as a single charge. The six sulphonate groups create a strong anionic barrier between the dye and negatively charged cellulose; electrolyte is therefore required to compress the double layer and promote exhaustion. The amount and rate of electrolyte addition must be matched to the machine liquor ratio, substrate form, and shade depth.
Exhaust dyeing is typically carried out at 0.1–4.0% o.w.f. for pale to heavy shades, with the lower end used for pastel colourations and the upper end for full depths. A conservative start point for package dyeing machines with liquor ratios of 1:5 to 1:12 is to set the dyebath at 40 °C with 0–5 g/L sodium chloride or the equivalent ionic strength from sodium sulphate, then raise the shade to 80–95 °C only after the first 15–20 min. Electrolyte is introduced in two or three separated doses during the heating phase. A total salt concentration of 5–30 g/L is common for cellulosic direct dyeings, but the exact split is lot-specific because the standardising salt already present in the commercial powder changes the initial bath conductivity. Inadequate total salt causes incomplete exhaustion and increases effluent load; excessive salt can cause dye aggregation, surface deposition on yarn packages, and poor levelness.
Hard-water cations magnify the aggregation risk. At total hardness above the supplier limit, calcium and magnesium ions form sparingly soluble complexes with the sulphonate groups, reducing apparent solubility and generating filtration residues on package dyeing machines. A polyphosphate or polyacrylate sequestering agent is therefore standard practice when the feed water exceeds 100 mg/L CaCO3 equivalent. The exact threshold is supplier-dependent, but the control point is measured before the dyebath is heated.
In pad-steam processing, high substantivity can produce tailing if the dye removed by the fabric is not replaced at the same rate. The pad trough is set with a lower initial dye concentration than the target shade and with controlled electrolyte addition, and the trough volume is kept small. Pad-steam conditions are validated on the specific machine; a recipe cannot be transferred across a three-bowl padder and a padder with different roll hardness without verification.
For winch dyeing of cotton knitwear, rope circulation must be uniform. Direct Red 80 can exhibit rail marks when the fabric speed is low or the rope folds are tight, because the dye is removed rapidly at the point of contact. Machines with high turbulent interchange and low liquor ratio are preferred for full depths; wovens dyed on jigs may require end-to-end shading control due to the high strike at the first end. Regular reversal and controlled batching tension are used to limit side-to-centre variation.
After rinsing to remove unfixed dye, wet fastness is improved with a cationic fixing agent. The cationic agent must not be applied in the same bath as residual anionic dye because precipitation produces a sticky complex that deposits on the yarn and machine surfaces. Fastness claims are verified by ISO 105-C06:2010/Amd 1:2020 wash testing and ISO 105-B02 light fastness testing on the target substrate. Published data for this specific configuration is limited; a substrate-specific baseline is required before quoting a grey scale rating.
Outside textile processing, the same Colour Index product can be applied to paper pulp and leather under conditions that promote retention or fixation. The retention behaviour on paper is dependent on furnish, charge demand, and drainage; no universal addition rate can be stated. Published data for this specific configuration is limited, and mill-specific retention tests are required. In leather dyeing, the dye is usually added after neutralisation or retanning, where protein charge interactions determine uptake. Direct Red 80 should not be assumed to have the same fastness profile on leather as on cotton; wet rub fastness must be tested under ISO 11640 or equivalent.
Because of the high sulphonation and water solubility, unfixed Direct Red 80 is poorly removed by conventional activated sludge alone. Textile mills discharging substantive dyeing liquors use adsorption or coagulation stages before biological treatment to meet discharge colour limits. The actual treatment requirement is site-specific and is driven by the permit limits, not by the dye name.
In substitution evaluations, Direct Fast Red F3B is not a drop-in equivalent for lower-molecular-weight direct reds or for acid reds used on polyamide. The largest practical difference is the balance between migration and wet fastness. Because the tetrakisazo molecule is larger and carries more sulphonate groups than many conventional direct reds, it exhausts more aggressively onto cellulose and migrates less once the dye has contacted the fibre. This behaviour is advantageous when wet fastness after fixing is important, but it reduces shade levelness in high-speed machines. Table 2 compares the product class against lower-molecular-weight direct reds and acid red types.
| Attribute | Direct Fast Red F3B / C.I. Direct Red 80 | Lower-molecular-weight direct red | Acid red type for polyamide |
|---|---|---|---|
| Primary substrate | cotton, viscose, linen, paper, collagen staining | cotton, viscose, linen | wool, silk, nylon |
| Anionic group density | six sulphonate groups per molecule | fewer sulphonate groups | varies; dyeing requires acid pH |
| Migration before fixation | moderate to low; high initial strike | higher migration and better leveling | high migration on polyamide under pH control |
| Wet-fastness potential | improved with cationic fixing agent; verify by ISO 105-C06 | needs fixing agent for acceptable wet fastness | usually good on nylon without cationic fixing; poor cellulosic substantivity |
| Collagen staining role | used in picrosirius red protocols for birefringence | not equivalent | not applicable |
| Substitution assessment | requires salt-response and wash-fastness revalidation on target substrate | shade match alone is insufficient | class change is not direct substitution |
The substitution of Direct Fast Red F3B by another substantive red in a production dyeing programme is a technical requalification, not a shade-only adjustment. The incoming dye must be compared on equal depth, on the same substrate preparation, and in the same machine type, because the standardising salt and the high-molecular-weight chromophore change the salt demand and the strike profile. If the substitute is a low-molecular-weight direct red, the dyehouse may observe better migration but lower wet fastness; if the substitute is an acid red, cellulosic exhaustion will be poor. This distinction is the central specification issue for users comparing products.
One application in which Direct Fast Red F3B is not readily replaced is the picrosirius red method for collagen. The working stain is commonly prepared at 0.1% w/v Direct Red 80 in saturated aqueous picric acid. Sections are stained for 60 min, washed in acidified water, dehydrated through graded ethanol, cleared in xylene, and mounted in a synthetic resin. Under bright-field illumination, collagen fibres appear red; under polarised light, thick type I collagen fibres display yellow-to-orange birefringence, while thinner type III fibres display green birefringence. The differentiation depends on the dye–collagen interaction and on the acidic picric acid environment, not on simple cellulosic substantivity.
This staining use imposes higher purity expectations than textile dyeing does. A product sold for histology should be free of insoluble particles that can precipitate on tissue sections. Histology suppliers provide a formulation different from textile-grade powder even when the Colour Index number is identical. Purchasing units should not assume that a textile-grade lot is suitable for staining; the criteria are particulate purity, dye content consistency, and absence of interfering salts, not shade performance on cellulose. The histology-grade product is not automatically food- or cosmetic-compliant.
Because Direct Red 80 is an azo dye, reductive cleavage of the azo linkages generates aromatic amine fragments. Regulatory control of textile articles in the EU is therefore assessed under REACH Annex XVII entry 43, which restricts listed carcinogenic amines at or above 30 mg/kg. The standard analytical route is EN 14362-1:2017 or its current equivalent. Direct Red 80 is not commonly included in the restricted amine list for textile screening, but the dye should be accompanied by a supplier declaration confirming that the commercial lot does not release restricted amines under the specified reduction conditions. Absence of a current declaration creates a compliance gap even if the C.I. number is unchanged.
In addition, metal removal is a practical concern for effluent and for finished articles. Suppliers commonly control extractable heavy metals against the limit values of Oeko-Tex Standard 100 when the substrate is intended for direct skin contact; the specific limit depends on the product class. Textile processors should require a lot-specific CoA rather than relying on class-level statements, because standardising salts and process residues can vary among dye plants.
