Section
| HS Code | 389435 |
| Product Name | Lithol Rubine WF |
| Chemical Class | Organic monoazo pigment; calcium salt |
| Color Index Name | Pigment Red 57:1 |
| Color Index Number | 15850:1 |
| Cas Registry Number | 5281-04-9 |
| Ec Number | 226-109-5 |
| Appearance | Red pigment preparation |
| Color Shade | Bluish red |
| Form | Water-based pigment dispersion |
| Solubility In Water | Insoluble as pigment; dispersible in aqueous systems |
| Specific Gravity | Approximately 1.8 g/cm3 |
| Light Fastness | Good |
| Heat Stability | Up to approximately 180 °C |
| Acid Resistance | Good |
| Alkali Resistance | Good |
| Water Resistance | Good |
| Solvent Resistance | Moderate |
| Primary Applications | Water-based printing inks and coatings |
As an accredited Lithol Rubine WF factory, we enforce strict quality protocols—every batch undergoes rigorous testing to ensure consistent efficacy and safety standards.
| Packing | Lithol Rubine WF is packaged in 25 kg multi-wall paper bags with polyethylene liners, supplied palletized for safe storage and transport. |
| Container Loading (20′ FCL) | Lithol Rubine WF is packed in bags/pallets, loaded into a 20′ FCL container, evenly distributed, and secured for ocean shipment. |
| Shipping | Lithol Rubine WF is shipped as a non-hazardous solid pigment powder in sealed fiber drums or bags. Store in a cool, dry, well-ventilated area away from moisture and ignition sources. Avoid dust generation. It is generally not regulated for transport under DOT, IMDG, or IATA unless local rules specify otherwise. |
| Storage | Store Lithol Rubine WF in a cool, dry, well-ventilated area away from direct sunlight, heat, ignition sources, and incompatible oxidizers. Keep containers tightly closed, properly labeled, and in original or compatible packaging. Avoid moisture, dust generation, and contact with food or feed. Use appropriate PPE, segregate incompatible materials, follow the SDS and local regulations. Prevent environmental release and store securely. |
| Shelf Life | Lithol Rubine WF is stable for about five years when stored cool, dry, and in its original unopened packaging. |
In sheetfed offset lithographic ink production, Lithol Rubine WF (C.I. Pigment Red 57:1, CAS 5281-04-9) is introduced at 18–22 wt% into a pre-dissolved varnish composed of a rosin-modified phenolic resin, a 30–35 wt% linseed oil/soybean alkyd vehicle, and a high-boiling mineral oil fraction. Dispersion is carried out on a three-roll mill with hydraulic roll pressures of 15–25 MPa and roll temperatures held below 50°C, followed by a single pass on a bead mill with 1.0 mm zirconia media when a Hegman gauge reading below 12.5 µm is required under ASTM D1210. The predispersion step is not only a particle size reduction operation; excessive shear and thermal input break down the calcium lake crystals and increase pigment surface area beyond the level that the resin-oil vehicle can wet, leading to a measurable drop in tack from 10–12 g-m to 7–9 g-m on an inkometer at 1200 rpm and 32°C, accompanied by ink misting on press. At the specified loading, the ink yields a print film thickness of 1.2–1.6 µm on coated cartonboard and optical density above 1.6 on a reflection densitometer for spot-colour work, while lower loadings below 12 wt% are generally unable to cover substrate mottling in solid red areas. The end products are commodity folding cartons, book covers, and promotional posters where indoor lightfastness is acceptable and direct food contact is excluded under EU Regulation 1935/2004 unless migration testing demonstrates compliance. The ink is not formulated for exterior exposure because the pigment has only moderate lightfastness and will fade on outdoor signage within a season.
Solvent-based flexographic and gravure inks based on 1/4-second nitrocellulose resin dissolved in an ethyl acetate/ethanol blend incorporate Lithol Rubine WF at 8–12 wt% of total liquid ink. The grind is performed in a horizontal bead mill with 1.0–1.2 mm zirconia beads at a tip speed of 10–12 m/s, and the discharged ink is adjusted to 18–25 s on a DIN 4 cup at 25°C according to DIN 53211. Because the pigment exhibits measurable solubility in alcohol and ketone solvent mixtures, increasing the pigment loading above 12 wt% produces a viscosity rise over 48 h and red staining of polyurethane gravure doctor blades and cylinder chrome surfaces. For surface-printed low-cost PE bread bags, PP snack wrappers, and paper carrier bags, the pigment is milled to a grind gauge reading below 15 µm; for gravure cylinder applications, a 5 µm grind is preferred to prevent doctor blade streaks. The end product is generally limited to surface-print packaging where lamination and retort conditions are not specified, because the pigment can bleed into adhesive tie layers and shift colour after lamination. Food-contact compliance is not presumed by the use of a nitrocellulose vehicle; formulators must apply the CEPE/EuPIA good manufacturing practice and verify that the final printed article meets the overall migration limit of 10 mg/dm² under Commission Regulation (EU) No 10/2011 if food contact is intended. For non-food packaging, REACH Annex XVII entry 43 requires that the pigment not release listed aromatic amines above 30 mg/kg when tested according to EN 14362-1:2017.
Water-based flexographic inks formulated with styrene-acrylic emulsions and neutralised with ammonia or 2-amino-2-methyl-1-propanol to pH 8.5–9.5 place Lithol Rubine WF in an alkaline environment that can destabilize both the pigment dispersion and the emulsion polymer. The calcium sulfonate lake structure shows partial alkali sensitivity; at pH values above 9.0, the pigment surface becomes increasingly ionic, which raises the soluble electrolyte concentration in the liquid ink and produces viscosity drift in 24–48 h after mixing. Published data for this specific configuration is limited, but production-scale batches on central impression flexo presses indicate that when the ink is held above pH 9.0, the risk of pinholing on treated polyethylene film increases and anilox cell bridging becomes visible after 2–3 h of continuous run. The safe operating window for this pigment in water-based systems is therefore pH 7.8–8.7, with a volatile amine buffer rather than a fixed alkali such as sodium hydroxide. Pigment loading is generally 10–14 wt% in the concentrated dispersion, and the final press-ready ink is diluted to 20–40 s on a DIN 4 cup at 25°C. The end products are low-cost paper bags, corrugated preprint overprints, and non-food flexible packaging where water-based inks are required by local VOC regulations. The pigment should not be used in water-based systems that must remain stable at pH 10 or higher, such as aqueous can lining primers, because the colour strength falls and the ink reddens the plate and anilox rolls.
Calendered plasticised PVC film and sheet use Lithol Rubine WF at final pigment concentrations of 0.5–2.0 phr, typically introduced as a pre-dispersed chip containing 40–50 wt% pigment in DOP or DINP. The chip is produced by three-roll milling or a twin-roll plastisol process at controlled temperatures below 80°C, then added to the dryblend or plastisol before a two-roll mill operating at 160–170°C and a four-roll inverted-L calender running at 170–185°C. The critical processing constraint is not initial colour development but heat history: static oven tests at 200°C for 30 min show progressive darkening, and plate-out on calender bowls increases when the compound contains more than 50 phr plasticiser. In flexible PVC formulations containing DOP at 60–80 phr, contact bleeding onto white PVC or ABS under 7-day, 60°C compression is a known operational boundary, limiting the pigment to non-critical decorative films, stationery covers, and low-cost table cloths. For toy applications, the final PVC article must be tested to EN 71-3:2019+A2:2024 for soluble barium, lead, and other restricted elements; technical-grade Lithol Rubine WF often requires batch release documentation because residual metal levels vary by manufacturing route. For food-contact PVC, the pigment is not suitable without specific migration testing under EU 10/2011, and the general compliance posture is to avoid direct food contact or fatty food contact use.
Lithol Rubine WF is compounded into LDPE, HDPE, and PP masterbatches at 20–40 wt% pigment loading on a co-rotating twin-screw extruder with an L/D ratio of 32:1–44:1. The temperature profile is 140–180°C for LDPE and 190–220°C for PP; the melt temperature of PP should not exceed 220°C for residence times above 2–3 min, because the calcium lake pigment begins to darken red-shade and generates filter pressure rise due to agglomeration. The masterbatch is let down at 25:1–50:1 in blown film, extrusion coating, or injection moulding; final pigment concentration is normally 0.5–1.5 wt%. In polypropylene, the pigment can act as a nucleating agent, increasing the crystallization temperature and raising film haze measured under ASTM D1003; this effect is more pronounced in flat-die cast film than in blown film. Melt flow rate testing per ASTM D1238-20 is used as a QC guard: a shift of more than 15% from the natural carrier resin often indicates poor pigment dispersion or moisture-related hydrolysis, requiring a pre-drying step at 80°C for 2 h when ambient relative humidity exceeds 60%. The end products are red PP strapping tape, LDPE refuse sacks, HDPE bottle caps, and non-food PP housewares. Food-contact polyolefin packaging is not automatically permitted; the pigment grade must be demonstrated to meet 21 CFR 178.3297 purity and processing limits before use, and migration testing under EU 10/2011 is required for any direct food-contact application.
Styrene-butadiene rubber compounds coloured with Lithol Rubine WF are mixed in an internal mixer with a discharge temperature below 65°C, using 1–3 phr pigment addition, 5 phr zinc oxide, 1 phr stearic acid, 1.75 phr sulphur, and 1.2 phr TBBS accelerator per ASTM D3182-21. The pigment is not inert in this matrix: the calcium sulfonate azo lake can interact with zinc ions released during in-situ formation of zinc stearate and during sulfur cure at 160°C, producing a slight hue shift toward a more yellow red when cure time is extended beyond the rheometer T90. Published mechanistic data for this specific configuration is limited, but batch records from production-scale rubber sheeting lines show that the shift is reduced by using stearic acid at the lower end of the range and by adding the pigment in the second mixing stage rather than with the initial filler. Vulcanizates are typically cured at 150–170°C for T90 + 3 min, with tensile properties checked per ISO 37:2017; the pigment contributes no reinforcement and should not exceed 3 phr because higher loadings increase Mooney viscosity and scorch risk. End products are red rubber mats, footwear soles, and automotive floor mats where low-cost shade and indoor colour stability are acceptable. Outdoor use and contact with oils or solvents are operational limitations because the pigment has limited migration fastness in hydrocarbon elastomers; product compliance for toy rubber requires EN 71-3:2019+A2:2024 and REACH Annex XVII 43 certification.
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Lithol Rubine WF is a calcium lake of Colour Index Pigment Red 57:1, CAS 5281-04-9, produced by coupling diazotized 4-aminotoluene-3-sulfonic acid with 3-hydroxy-2-naphthoic acid and insolubilizing the resulting monoazo dye as a calcium salt. The WF suffix denotes a water-fine finishing route that reduces coarse agglomerates and dusting tendency without altering the Colour Index classification. The product is supplied as a low-dusting red powder intended primarily for oil-based sheet-fed offset inks, water-based flexographic and gravure inks, polyolefin masterbatch, rubber, and selected industrial coatings. The spectral position is a blue-shade red to magenta mass tone, with undertone controlled by particle size distribution, free calcium content, and residual sulfonate chemistry. Because the pigment is a metal salt of a sulfonated azo colorant, its processing window is narrower than that of quinacridone or DPP red pigments, and formulation latitude depends heavily on dispersion equipment and vehicle pH.
In sheet-fed offset ink production, Lithol Rubine WF is typically incorporated at 18–22 mass % into a quickset varnish by high-speed predispersion at a Cowles blade tip speed of 10–15 m/s, followed by three-roll milling at 40–50 °C roll temperature with hydraulic pressures of 0.3–0.5 MPa. The resulting fineness of grind measured according to ISO 1524:2013 is generally achievable at 5–10 µm on a Hegman gauge. The calcium lake wets rapidly in alkyd and linseed-oil ester vehicles, but over-dispersion can fracture primary particles and shift the masstone toward a yellower red. On production-scale three-roll mills with roll diameters of 400 mm and above, the practical bottleneck is not initial wetting but post-milling rheological adjustment: the standard PR 57:1 lake requires additional varnish reduction at higher loadings, whereas the WF grade has a narrower particle-size cut and typically reaches an equivalent tack at 1–3 % lower vehicle demand. Inkometer tack values for sheet-fed formulations usually land between 8 and 12 at 800 rpm and 32 °C, but the exact setting depends on the gelled varnish and solvent balance rather than on pigment loading alone.
| Property | Standard method | Lithol Rubine WF | General PR 57:1 |
|---|---|---|---|
| Density at 25 °C | ISO 787-10 | 1.45–1.58 g/cm³ | 1.42–1.55 g/cm³ |
| Oil absorption | ISO 787-5 | 35–48 g/100 g | 38–55 g/100 g |
| Matter volatile at 105 °C | ISO 787-2 | ≤ 2.0 % | ≤ 2.5 % |
| Residue on sieve 45 µm | ISO 787-7 | ≤ 0.10 % | ≤ 0.30 % |
| pH of aqueous extract | ISO 787-9 | 6.0–8.5 | 6.0–9.0 |
| Specific surface area by BET | ISO 9277 | 25–45 m²/g | 20–50 m²/g |
| Light fastness, deep shade | ISO 105-B02 | 4–5 | 3–4 |
| Heat stability in HDPE | supplier method | 180 °C | 170–180 °C |
Values represent typical industrial supplier envelopes. The certificate of analysis for the exact batch prevails, and published data for this specific WF configuration is limited outside ink-grade documentation.
Water-based flexographic and gravure inks expose the calcium lake to a different set of dispersion conditions from oil-based inks. The pigment is normally introduced into an aqueous solution containing anionic or nonionic wetting agents and a pH-control buffer. The recommended operating pH window for Lithol Rubine WF is 8.0–9.0; sustained pH above 9.5 can partially hydrolyze the calcium lake structure and increase the concentration of soluble sulfonated colorant species, producing viscosity drift, bleeding, and shade change. On a production-scale flexographic dispersion line using a bead mill with 0.8–1.2 mm zirconia beads and a residence time of 15–25 min, the WF grade reaches a particle-size endpoint of ≤ 5 µm more rapidly than standard powder grades because fewer coarse aggregates survive the final pulverization step. Acrylic and styrene-acrylic emulsions are generally compatible at neutral to slightly alkaline pH, but polyurethane dispersions with strong cosolvent packages should be checked for solvent entrapment and colloidal instability when the millbase is let down. Ink manufacturers using water-based gravure presses at drying temperatures of 60–80 °C report that pH-controlled batches maintain redraw consistency; the main batch-to-batch variable is not the pigment hue but the residual calcium ion released during alkaline dispersion.
During twin-screw compounding of LLDPE masterbatch, Lithol Rubine WF is pre-blended at 40–45 wt% pigment loading with a low-melt-index carrier resin and processed on a co-rotating twin-screw extruder with L/D 25:1 to L/D 32:1 and barrel temperatures of 160–190 °C. Melt temperature must remain below 200 °C for short residence times because deeper thermal exposure causes the calcium lake to darken and lose blue undertone. Screw speeds of 300–500 min⁻¹ are typical, but the controlling parameter on the production floor is filter pressure rise through a 100 µm pack screen; an abrupt pressure increase above 0.8 bar/h often indicates that predrying was insufficient or that the WF grade contains residual sulfonic acid salts that agglomerate under melt shear. Pre-drying is required when the volatile content measured by ISO 787-2 exceeds 2.0 %, and open storage at relative humidity above 60 % should be avoided. Injection molding of pigmented polypropylene with a clamp force of 1000–1500 kN and a barrel temperature of 190–210 °C is feasible only when the screw backpressure is kept low; high backpressure increases work heat and can move the melt beyond the thermal stability boundary of the lake.
When Lithol Rubine WF replaces quinacridone magenta PR 122 in short-run packaging ink, the formulation must be corrected for three fundamental differences. First, the light fastness of PR 57:1 is substantially lower; under ISO 105-B02:2014 deep-shade testing, PR 57:1 is commonly positioned at Blue Wool Scale 4–5, whereas PR 122 typically falls at 7–8. This makes the calcium lake unsuitable for exterior graphics and long-life packaging exposed to direct sunlight. Second, the heat stability of PR 57:1 is inferior; PR 122 tolerates melt processing in polyolefins above 260 °C, while PR 57:1 is generally limited to 180–200 °C depending on residence time. Third, the oil absorption of PR 57:1 is higher than that of PR 122, so a direct weight-for-weight replacement may increase ink tack and reduce flow. In offset ink, the practical replacement sequence is to lower the pigment loading by 2–4 %, add a small amount of an acid-functional dispersant, and adjust tack with a low-viscosity alkyd diluent. The substitution is cost-driven and acceptable only when the application tolerance for light exposure and thermal stress is narrow.
Because sulfonated azo lakes are sensitive to alkaline hydrolysis, solvent and pH boundaries control the printable film in packaging applications. Lithol Rubine WF resists aliphatic hydrocarbon solvents and common glycol ethers but can bleed in ketones, esters, and strongly alkaline aqueous systems. In a laminated pouch ink system using ethyl acetate-based gravure, migration testing of the printed film should be performed before conversion, because the pigment itself is not a deliberate low-migration grade. Published data for this specific configuration is limited, and the absence of a supplier migration certificate for the intended film structure is a barrier to use in fatty-food packaging. The same restriction applies to toy coatings where soluble heavy-metal migration under EN 71-3:2019 must be verified batch-by-batch. For industrial equipment surfaces and non-food labels, these constraints are less critical.
The thermal decomposition of PR 57:1 is a property cliff-edge risk rather than a gradual loss of chroma. Differential scanning calorimetry on dry pigment typically shows an exothermic decomposition event near 220–240 °C, which is below the processing temperature of polyamide and polycarbonate. Below the decomposition onset, the pigment can survive short injection-molding cycles in polyethylene and polypropylene, but residence time becomes the controlling variable at melt temperatures above 180 °C. Light fastness is strongly influenced by titanium dioxide reduction: a deep mass tone may retain Blue Wool 4–5, but a strong white reduction can drop to 2–3 because the high surface area of the lake increases photocatalytic contact with titanium dioxide. This is the principal reason PR 57:1 is rarely used in exterior architectural coatings. Solvent resistance should be specified according to the downstream printing and coating method; the pigment withstands mineral oils and aromatic-free aliphatic systems but not aggressive ester solvents such as ethyl acetate or methoxypropyl acetate. For applications requiring ketone resistance, a quinacridone or DPP red is preferred.
Regulatory acceptance of Lithol Rubine WF rests on the pigment supplier’s ability to document heavy-metal content and aromatic amine status. The diazo component does not appear in the EU REACH Annex XVII list of restricted aromatic amines commonly associated with banned azo dyes, but this does not relieve downstream users of their own Article 33 communication duties when a substance identified on the SVHC candidate list is present above 0.1 %. Heavy-metal verification is performed by IEC 62321 series methods for lead, cadmium, mercury, and hexavalent chromium; typical industrial specifications are <1000 mg/kg for lead, mercury, and hexavalent chromium and <100 mg/kg for cadmium, but the certificate of analysis must be reviewed because ore-derived calcium sources can introduce trace lead. Food-contact use is not universal: PR 57:1 is not automatically listed for all polymers under EU Regulation (EU) No 10/2011, and use in food-contact packaging requires a specific supplier letter for the polymer, temperature, and simulant conditions. Published data for this specific WF configuration is limited; a formulator cannot infer food-contact status from a general REACH or RoHS certificate.
| Parameter | Standard or regulation | Typical requirement | Verification status |
|---|---|---|---|
| Restricted aromatic amines | EN ISO 14362-1:2017 | not detected | supplier certificate required |
| Lead | IEC 62321-5 | <1000 mg/kg | supplier certificate required |
| Cadmium | IEC 62321-5 | <100 mg/kg | supplier certificate required |
| Mercury | IEC 62321-4 | <1000 mg/kg | supplier certificate required |
| Hexavalent chromium | IEC 62321-7-2 | <1000 mg/kg | supplier certificate required |
| Soluble heavy metals in toys | EN 71-3:2019 | category-dependent limits | verify before toy-grade use |
| Food-contact plastic | EU Regulation (EU) No 10/2011 | positive listing only | not universally listed; use only with supplier letter |
Batch-to-batch colour variance in Lithol Rubine WF is controlled principally by the laking step rather than by the final dry grinding. Formation of the calcium salt at different pH or calcium addition rates changes the ratio of free acid to calcium salt and alters the undertone even when the total metal content remains within specification. A colourimetric tolerance of ΔE*ab ≤ 1.0 under ISO 787-1 against a stored reference is typical for ink-grade shipments, while wider limits may apply to plastics masterbatch grades. Storage in sealed polyethylene-lined bags at temperatures below 30 °C and relative humidity below 60 % preserves the WF handling advantage. The pigment is not classified as hazardous according to most supplier safety data sheets for industrial use, but dust extraction and local exhaust ventilation are required during manual weighing because fine particulate azo pigments can form explosive dust clouds when dispersed in air above the lower explosive limit.
