Lithol Rubine 404B is a barium-containing monoazo lake pigment classified under C.I. Pigment Red 57:1 with CAS Registry Number 5281-04-9. The product is used in solvent-borne and waterborne printing inks, polyolefin masterbatch, rubber compounds, and low-warpage industrial coatings where a magenta-shade red with moderate transparency and controlled oversize content is specified. The pigment is synthesised by diazotisation of 2-amino-5-methylbenzenesulfonic acid, coupling with 3-hydroxy-2-naphthoic acid, and subsequent lake formation on a barium-containing substrate. Lithol Rubine 404B is supplied as a free-flowing powder; the supplier-specific surface treatment reduces dusting and improves feed uniformity on twin-screw compounding lines compared with conventional uncoated PR57:1 powders. The “404B” designation is supplier-specific and does not denote a generic Colour Index modifier. Typical bulk density is 0.25–0.35 g/cm³, and specific gravity is 1.45–1.65 g/cm³ according to manufacturer technical data. The pigment is practically insoluble in water, ethyl acetate, ethanol, and aliphatic hydrocarbon solvents, a behaviour common to the lake class and relevant to low solvent bleeding in packaging gravure inks.

What Differentiates Lithol Rubine 404B from Other PR57:1 Lakes in Solvent-Based Ink?

In solvent-based nitrocellulose and polyvinyl butyral packaging gravure inks, Lithol Rubine 404B is dispersed at pigment loadings of 12–18 wt% with a high-speed dissolver using a Cowles blade tip speed of 18–20 m/s. The dispersed grind is subsequently milled on a three-roll mill at 25–30 °C until a Hegman grind gauge reading of ≤15 µm is obtained under ASTM D1210. Compared with uncoated PR57:1 grades, the lower 45 µm sieve residue of ≤0.5% reduces the number of milling passes required for full development of colour strength. Shade strength and tinting strength are evaluated against a supplier-approved batch using ISO 787-24 for relative tinting strength of white reductions. In publication gravure inks, the pigment exhibits a magenta-red mass tone and does not produce a measured colour shift exceeding 1.0 CIELAB unit after 24 h of solvent contact at 25 °C in toluene, ethyl acetate, or isopropanol. The non-bronzing behaviour of the grade is controlled by particle geometry and barium lake stoichiometry; bronzing is not eliminated by composition alone and can reappear if dispersion is over-attenuated below a critical particle size.

For waterless offset inks, tack stability is measured on an Inkometer at 32 °C and 400 rpm. Lithol Rubine 404B at 14–16 wt% in a quickset varnish typically produces tack values between 10 g·m and 14 g·m during the initial 10 min, with a decrement of ≤2 g·m after 10 min of roller distribution. Oil absorption of 40–50 g/100 g directly influences vehicle demand; exceeding 18 wt% pigment loading without additional solvent or diluent can raise tack above acceptable lithographic limits in high-speed sheetfed presses. Lithol Rubine 404B is not recommended for free-radical UV offset inks unless cationic cure is used, because residual ionic species from the lake process may induce viscosity drift in acrylate formulations.

Thermal Endurance and Compounding Behaviour in Polyolefins

In LDPE and LLDPE masterbatch production, Lithol Rubine 404B is processed on co-rotating twin-screw extruders with L/D ratios of 40:1–44:1 and barrel temperatures from 130 °C to 160 °C. The product is pre-dried for 2 h at 80 °C when storage relative humidity exceeds 60%; residual moisture above 1.5% in the pigment causes surface voids and accelerated filter pressure rise in the strand die. At a 20 wt% pigment loading in LDPE with a melt index of 20 g/10 min at 190 °C and 2.16 kg under ISO 1133-1, the melt temperature at the die is typically 165–175 °C. Pressure rise across a 200 µm woven screen pack stabilises below 5 bar/h; a faster pressure rise indicates pigment agglomeration or insufficient dispersive mixing. Batch-to-batch variation on production-scale lines is monitored by extruder torque at 60–70% of motor rating and by melt-pressure measurements upstream of the screen changer. The supplier-specific surface treatment of the 404B grade improves feed intake into the main hopper and reduces dusting relative to uncoated PR57:1 powders.

Injection moulding of the pigmented LDPE compound is performed with melt temperatures between 180 °C and 200 °C and mould temperatures of 20–40 °C. Because PR57:1 is a barium-containing monoazo lake, the pigment is not suitable for polyamide or polycarbonate at processing temperatures above 250 °C; thermal degradation of the azo chromophore can produce yellowing and odour. Heat resistance is evaluated by pressing a 0.5 mm coloured LDPE sheet for 10 min at 180 °C and measuring colour change against an unexposed sheet. A total colour difference of ≤2.0 CIELAB units after this dwell is typically reported in supplier technical data.

When Printing Inks on Food-Packaging Substrates Require Article 7 Barrier Demonstration

Lithol Rubine 404B is not listed in Annex I of Commission Regulation (EU) No 10/2011; consequently, the pigment cannot be assumed compliant for direct food-contact plastic layers. Printing inks and coatings intended for food-packaging substrates fall outside direct food-contact requirements only if the printed layer is on the non-food-contact side of a functional barrier, or if compliance is demonstrated under Article 7 and Article 8 of the regulation. Heavy-metal content in the supplied pigment is controlled below the threshold limits specified by RoHS Directive 2011/65/EU: lead ≤1000 ppm, cadmium ≤100 ppm, mercury ≤1000 ppm, and hexavalent chromium ≤1000 ppm. The product also conforms to CONEG model legislation limits for total lead, cadmium, mercury, and chromium VI in packaging components. Under REACH, the substance is subject to registration requirements; users must obtain an up-to-date safety data sheet from the supplier for SVHC status and occupational exposure limits.

Non-Bronzing Behaviour Is Not Automatic in PR57:1 Lakes.

Bronzing is a surface-reflection phenomenon dependent on the migration of the lake counterion and the orientation of pigment platelets during drying. Lithol Rubine 404B is controlled to a medium oil absorption of 40–50 g/100 g and a specialised barium-lake composition, which lowers the tendency for unwetted pigment to migrate to the film surface during solvent evaporation in gravure inks. Non-bronzing behaviour cannot be assumed under all letdown conditions. If the pigment concentration is below 4 wt% in a very fast-drying solvent blend, or if excessive dispersant is used, surface orientation can still occur. Published data for this specific configuration is limited; laboratory drawdowns on corona-treated polyethylene film with ethyl acetate/ethanol at 80:20 are required for new formulations. The product’s performance is best when dispersed in the vehicle before addition of wax dispersions and slip additives, because post-additive correction can change particle wetting and flocculation characteristics.

Aqueous flexographic and inkjet ink dispersions containing Lithol Rubine 404B require careful control of amine concentration. The pigment is milled as a dry powder or high-solids press cake into a waterborne acrylic resin solution with pH held between 8.5 and 9.5 using dimethylamine or ammonium hydroxide. At pH values above 10, the barium lake can undergo partial dissociation, causing shade drift toward the yellow edge and an increase in water-soluble matter. The aqueous extract pH of the raw pigment is 6.5–8.0, but the dispersed ink pH is determined by the resin neutralisation system. Foaming during high-speed stirring on a Cowles dissolver at 12–15 m/s is controlled with a silicone-free defoamer at 0.1–0.3 wt% of the formulation. The product is not recommended for use with amine-based additives that remain in the dried film in high concentration, as this can increase water sensitivity and migration of ionic species.

In solvent-borne industrial alkyd enamels, Lithol Rubine 404B is dispersed at 5–8 wt% in a high-speed dissolver with a saw-tooth disc at 15 m/s, followed by bead milling in a horizontal mill charged with 1.0–1.2 mm yttria-stabilised zirconia beads. The resulting paste is drawn down at 75 µm wet film thickness to evaluate gloss and haze. At full shade, the pigment exhibits a light fastness of 4–5 Blue Wool under ISO 105-B02, which is lower than that of perylene reds and quinacridone magenta grades; therefore, Lithol Rubine 404B is specified primarily for indoor applications and short-life decorative coatings. In two-component polyurethane systems, the barium lake is stable in the absence of strong acid catalysts and amine accelerators. Accelerated storage at 50 °C for 7 days in xylene/butyl acetate shows no hard settling when the mill base is formulated with a wetting and dispersing additive at 3–5 wt% based on pigment.

In rubber compounding, Lithol Rubine 404B is added at 0.5–1.5 phr in natural rubber and SBR formulations. It does not interfere with sulfur-accelerated vulcanisation kinetics at cure temperatures below 180 °C; above this temperature the azo bridge begins to decompose, and the resulting degradation products can stain adjacent surfaces. The pigment disperses on a two-roll mill at 50–70 °C when added with a process oil premix. Water-soluble matter of ≤1.0% limits bloom migration in soft rubber seals. For peroxide-cured elastomers with cure temperatures exceeding 200 °C, the product is not recommended.