Lithol Rubine 4BE is a blue-shade red monoazo pigment supplied as a dry powder, presscake, or pigment preparation and identified generically as C.I. Pigment Red 57:1, Constitution No. 15850:1. The pigment is the calcium salt of 4-[(4-methyl-2-sulfophenyl)azo]-3-hydroxy-2-naphthalenecarboxylic acid; CAS Registry Number 5281-04-9. In printing ink and coatings applications, the grade is specified where high color strength, clean rubine mass tone, and adequate solvent resistance are required in a cost-sensitive red pigment. Typical physical data reported on certificates of analysis include an oil absorption of 45–55 g/100 g under ISO 787-5:1980, an aqueous extract pH of 7.0–8.5 under ISO 787-9:2019, and a density near 1.50 g/cm³. The product is not a high-performance pigment; its technical position is defined by the balance between coloristic brightness and thermal and lightfastness limitations.

Commercial production typically involves diazotization of a substituted aromatic amine, coupling onto 3-hydroxy-2-naphthoic acid, and precipitation as the calcium salt on a natural or synthetic substrate. The laking step influences crystal size, surface polarity, and aggregate hardness, which in turn affect dispersion energy demand and rheological behaviour in ink vehicles. The sulfonic acid group is present as the calcium salt, which reduces water solubility and improves compatibility with non-polar ink vehicles; however, strongly alkaline fountain solution can ionize the pigment surface and promote emulsification. Because the 4BE suffix is a commercial grade designation rather than a discrete chemical species, particle size distribution and surface treatment differ among suppliers. Aqueous extract conductivity, water-soluble matter, and residue on sieve at 45 µm are therefore batch-specific; the certificate of analysis should be treated as the controlling specification.

How Does the 4BE Grade Differ from Other Pigment Red 57:1 Toners?

Published data for this specific configuration is limited because the 4BE suffix is a commercial grade designation rather than a discrete chemical species. In practice, the 4BE grade is typically distinguished from standard C.I. Pigment Red 57:1 toners by surface treatment level, particle size distribution, and rheological behaviour in lithographic vehicles. Compared with non-surface-treated PR57:1, the 4BE grade generally produces lower yield stress in paste inks at equal pigment volume concentration, which can allow higher pigment loading before the mill base becomes too stiff for pumping. Compared with C.I. Pigment Red 48:3, Lithol Rubine 4BE is usually bluer and more coloristically intense in lithographic prints, but has lower heat resistance and lower lightfastness in pale reductions. The table below summarises the generic class differences relevant to product substitution.

Dispersion Viscosity, Transfer, and Film Performance in Lithographic Inks

In sheetfed and coldset offset ink manufacturing, the pigment is introduced into a resin-oil vehicle at 18–25 wt% pigment loading. Dispersion is generally performed on a three-roll mill with roll temperatures maintained between 35 °C and 45 °C and nip pressures adjusted to avoid overgrinding. Overgrinding can reduce tinctorial strength by breaking primary aggregates and increasing surface area; the resulting increase in vehicle demand raises tack and can disturb ink-water balance. Finished ink tack is measured on an inkometer; typical sheetfed offset values are 8–12 g-m, depending on varnish composition and pigment concentration. Mill base temperature should not exceed 45 °C during extended passes because heat build-up can reduce varnish viscosity and alter pigment wetting, producing batch-to-batch variance in tack and shade. Filtration through a 10 µm screen is used to remove undispersed agglomerates before let-down; frequent screen blockage indicates either excessive moisture or overstable aggregates. In high-speed dispersion, the pigment is wetted at tip speeds of 18–25 m/s; bead milling with 0.6–1.0 mm yttria-stabilized zirconia beads is preferred for gravure inks. Flow curves generated on a controlled-stress rheometer at 25 °C should be checked for yield stress and thixotropic recovery; high thixotropy in the mill base can lead to poor transfer from roller train to blanket. Proofing should follow ISO 2834-1 for paste inks and ISO 2834-2 for liquid inks, with evaluation of color strength, gloss, and rub resistance on the target substrate.

Because solvent-based flexographic and gravure systems use alcohol/ester solvent blends, the pigment is often predispersed as a nitrocellulose or polyvinyl butyral chip or as a high-solids presscake. Solvent bleed resistance in alcohol/ester blends is generally good when evaluated by a 24 h spot test at 25 °C, but the pigment should be screened for bleed in the specific solvent blend because the calcium salt can exhibit partial solubility in highly polar ketone-rich systems. Typical gravure formulations use 8–15 wt% pigment on total ink; reduction with toluene-free alcohol/acetate blends at 1:10 to 1:20 may shift hue toward the bluer side. In polyvinyl butyral-based gravure inks, dispersion is often adjusted to a Zahn No. 2 cup value of 18–22 s at 25 °C. Print density and gloss on coated paper are evaluated according to ISO 2834-2 after proofing on a laboratory printability tester; rub resistance is checked with a Sutherland rub tester under ASTM D5264. Pigment predispersion through a horizontal bead mill is usually completed in two passes; single-pass processing can leave undispersed agglomerates that raise gravure cylinder wear. Published data for this specific configuration is limited, and pilot-scale press trials are required to confirm dot gain and gloss on high-speed central impression presses.

When Substituted into Melt-Processed Polyolefin Compounds

When Lithol Rubine 4BE is used as a replacement for higher-heat-stable red pigments in injection-moulded polypropylene or polyethylene, the processing window must be kept below 200 °C melt temperature. On a 40:1 L/D twin-screw extruder running at 250–350 rpm, melt residence times above 180 °C for more than 45–60 s can cause shade drift, strength loss, and plate-out on die lips. A 5 °C overshoot above the 190 °C nozzle setpoint can produce measurable shade drift in thin sections. On injection moulding lines with clamp forces in the 800–1,200 kN range, nozzle temperature should be held below 190 °C for thin-wall parts because local shear heating can raise melt temperature above the pigment’s degradation threshold. The pigment should be pre-dried at 60–70 °C for 4–6 h when bag storage relative humidity exceeds 60 % RH, because residual moisture can cause screw slippage and feeding irregularities. In polyolefin compounds, the pigment is typically added as a single-pigment masterbatch at 40–50 wt% pigment loading to limit dust and improve dispersion. Use of amine-based processing stabilizers should be evaluated for possible interaction; azo pigments can undergo reductive cleavage under aggressive processing conditions, resulting in color loss and potential plate-out. Migration kinetics in polymer matrices are significant because the low-molecular-weight calcium salt can migrate in plasticized PVC at elevated temperature; contact bleeding tests under DIN 53775 are recommended. For applications requiring continuous service above 200 °C, C.I. Pigment Red 48:3 or quinacridone pigments are preferred. The lower heat threshold of PR57:1 is a consequence of the calcium salt lattice and the polar sulfonic acid group; published data for this specific configuration is limited when the pigment is used in polyolefin formulations above 200 °C.

Compliance Testing Under 21 CFR, REACH, and Heavy-Metal Specifications

The pigment’s regulatory profile is product-specific and must be confirmed against the supplier’s certificate of analysis. For packaging inks and plastics, heavy metal migration limits are typically assessed under EU 94/62/EC, with a combined lead, cadmium, mercury and hexavalent chromium limit of 100 mg/kg of packaging. Extractable metal testing may be performed according to EN 71-3:2019 for toy safety, though the pigment is not universally cleared for all toy matrices. In the European Union, use in food-contact materials requires verification under Regulation (EU) No 10/2011 and applicable national measures; the calcium salt of a sulfonated monoazo pigment may be subject to migration limits and purity criteria. For United States food-contact polymer applications, compliance with 21 CFR 178.3297 is relevant only when the pigment is listed in the applicable section and used within limitations. REACH compliance in the European Union requires confirmation of registration status for the tonnage band; the pigment is not classified as a substance of very high concern under the existing candidate list. RoHS Directive 2011/65/EU applies to electrical and electronic equipment, not to inks, but pigmented plastic enclosures may require verification. Users should obtain a heavy metals certificate including lead ≤100 mg/kg, arsenic ≤50 mg/kg, and mercury ≤25 mg/kg unless regional limits differ. The table below provides a typical compliance checklist used for industrial applications.