Lithol Rubine 5BPC is a trade designation for a calcium-salt azo pigment based on 3-hydroxy-4-[(4-methyl-2-sulfophenyl)azo]-2-naphthalenecarboxylic acid, assigned C.I. Pigment Red 57:1 and CAS 5281-04-9. The model code 5BPC denotes a manufacturer-specific surface treatment and particle size control; it does not alter the C.I. classification. The product is supplied as a fine, free-flowing magenta powder with a masstone that appears as a cool, blue-shifted red when dispersed in lithographic varnish or alkyd. The 5BPC grade is differentiated from conventional PR57:1 grades primarily by controlled particle size distribution and surface pH adjustment for high-speed ink and masterbatch wetting. Representative analytical values include a specific gravity of 1.50–1.60 g/cm³ measured following ISO 787-10, oil absorption of 40–55 g/100 g following ISO 787-5, and pH of aqueous extract in the range 6.5–8.0 following ISO 787-9. The molecular structure places the product in the β-naphthol-derived BONA pigment class, and the calcium lake form is widely used as a process red in sheetfed offset and water-based packaging inks. As a synthetic organic pigment, it is insoluble in the usual printing ink solvents and in common plasticizers; it is not classified as a dye. The product's tinctorial strength and rheological behaviour depend on surface treatment, particle aggregation, and the dispersion regime applied by the end user. Published data for this specific 5BPC configuration is limited; therefore, the following operational guidance is derived from the industrial behaviour of C.I. Pigment Red 57:1 grades with similar analytical profiles and from supplier technical bulletins for Lithol Rubine calcium salt products.

How Does Lithol Rubine 5BPC Differ From Barium and Manganese 2B Lake Red Pigments?

The principal comparative set in the red monoazo lake class includes C.I. Pigment Red 57:1 (calcium salt), C.I. Pigment Red 57 (barium salt), C.I. Pigment Red 48:2 (calcium salt of 2B acid), and C.I. Pigment Red 48:4 (manganese salt of 2B acid). Lithol Rubine 5BPC belongs to the first group and shows a bluer masstone than the barium analogue; the barium salt appears yellower and denser because of the higher atomic mass of barium. In ink formulations, the calcium salt provides higher colour strength per unit weight and lower rheological viscosity at equivalent pigment loading, which permits higher paste solids in sheetfed oleoresinous systems but reduces bleed resistance in some solvent-based gravure formulations. The 2B acid calcium salt, C.I. Pigment Red 48:2, is even yellower and offers greater heat resistance, making it more suitable for polyolefin concentrates processed above 200 °C. The manganese salt, C.I. Pigment Red 48:4, is selected where enhanced solvent fastness is required; published data for direct comparison with 5BPC in oleoresinous inks is limited. Lithol Rubine 5BPC is not a direct replacement for PR48:2 in applications requiring continuous processing above 220 °C. In contrast, PR57:1 grades typically maintain acceptable shade and no visible darkening through 5 min oven ageing at 180–200 °C when evaluated in high-density polyethylene using EN 12877-1. The calcium salt also exhibits higher tinctorial strength and higher oil absorption than the barium salt, so formulators should expect an increase in binder demand when moving from PR57 to PR57:1. In solvent-based publication gravure inks, the barium salt may be preferred where low viscosity at high colour strength is decisive; PR57:1 is more commonly selected for sheetfed offset, water-based flexo, and plastisol. These differences are systematic and are attributed to metal cation influence on crystal lattice, refractive index, and dispersion wetting rather than to differences in the chromophore itself.

Dispersion Variables in Three-Roll Mill and Bead Mill Processing

On production-scale three-roll mills, Lithol Rubine 5BPC is typically supplied as a flushed or predispersed paste; dry powder grades are incorporated at 15–25 wt% into lithographic varnish in a high-speed disperser before roll milling. The high oil absorption of the pigment requires that the first pass be run with the feed roll and centre roll separated by 30–50 µm; subsequent passes are tightened to 10–20 µm to reduce agglomerates. Hegman grind values measured according to ISO 1524 commonly fall below 15 µm after two passes, while the final letdown is adjusted to target print density. In bead mills operating with aqueous polyurethane or acrylic letdown, a premix with a pigment volume concentration of 8–12% is milled at a tip speed of 10–14 m/s. Published data for this specific grade in bead mill applications is limited; however, the pigment's narrow particle size distribution reduces the energy input required to achieve a 5 µm maximum particle size relative to coarser PR57:1 grades. Overheating during dispersion should be avoided because local temperature excursions above 80 °C can initiate crystal ripening and shade shift in high-boiling ink solvents. The pH of the aqueous millbase should be maintained between 7.0 and 8.5; acidic conditions below pH 6.0 can reduce pigment wettability and may increase viscosity. In solvent-based systems, the use of high-acid-value resins should be evaluated because free carboxylic acid groups can interact with the pigment surface and alter flow.

In sheetfed offset, the 5BPC grade is typically used in the magenta unit at a pigment loading of 18–22 wt% of the finished ink. Tack, measured on a Tackoscope at 30 °C, is commonly adjusted to 8–12, and the ink is formulated to accept 20–35% fountain solution without excessive emulsification. The calcium lake tolerates fount solution pH from 4.0 to 5.5; high-conductivity fount concentrates above 2500 µS/cm can destabilise ink transfer and increase dot gain. In multi-colour sheetfed printing, the grade serves as the process magenta; exact spectral reflectance data for this specific pigment configuration is limited, so visual and spectrophotometric matching under D65 and D50 should be performed on the final print.

In water-based flexographic inks for polyethylene-coated board and pet food packaging, Lithol Rubine 5BPC is generally supplied as a predispersed pigment dispersion or as a stir-in pigment for use with acrylic copolymer letdown. The typical final ink viscosity at 25 °C is 30–60 s on a Shell cup 4, with pH buffered between 8.0 and 9.5 using monoethanolamine or ammonia. Foam control and surface wetting are adjusted with non-ionic surfactants; the pigment's surface pH is close enough to the letdown target that excessive amine addition is not required. Print trials on flexographic presses with anilox rolls of 180–360 lines/cm and cell volumes of 3.5–8.0 cm³/m² indicate that the grade develops adequate colour strength at pigment loadings of 12–18 wt% of the finished ink. The blueness of the ink is sensitive to the resin coalescence rate; fast-drying acrylic resins can trap the pigment in a more aggregated state and shift the printed film to a yellower red. Therefore, the resin selection and drying profile are more critical than grind time when matching a printed standard. The product is not recommended for retortable packaging because steam sterilisation at 121 °C can cause blushing and migration into the adhesive or food simulant under long dwell times.

When Melt-Compounding Polyolefin Masterbatch Requires a Controlled Temperature Window

In polyolefin masterbatch production on a twin-screw extruder with an L/D ratio of 32:1 to 44:1, Lithol Rubine 5BPC is normally added at 0.5–2.0 wt% in the final moulded article or at 20–40 wt% in a single-pigment masterbatch. The recommended barrel temperature profile for high-density polyethylene is 160–200 °C, with the die temperature capped at 200 °C. At 220 °C or above, the pigment may darken and release traces of decomposition products; this limits its use in polycarbonate, polyamide, and other engineering resins processed above 220 °C. Injection moulding parameters for polypropylene closures and caps typically employ a melt temperature of 180–210 °C and a mould cooling time sufficient to prevent heat history from shifting the shade. The pigment is not considered lightfast enough for exterior automotive or outdoor furniture applications; accelerated weathering under ISO 105-B02 generally places the masstone lightfastness in the blue wool range 3–4, with tint lightfastness often one to two steps lower. Migration resistance in plasticized PVC depends on plasticizer type and service temperature; the product is usually limited to indirect food-contact applications where local regulation and migration testing under EU 10/2011 or FDA 21 CFR 176.170 are applied. In rigid PVC pipe and profile formulations, the pigment can be used at conventional loadings with tin stabilizers; combinations with lead stabilizers require colour stability testing because slight shade drift may occur under extended dry heat.

Plastisol formulations based on diisononyl phthalate or di(2-ethylhexyl) phthalate are processed at gelation temperatures of 160–180 °C; at these temperatures, Lithol Rubine 5BPC retains adequate shade stability but can exhibit slight migration into white vinyl adjacent layers after prolonged ageing at 60 °C. Ball and ring viscosity measurements at 25 °C typically show an increase of 15–25 % relative to an unpigmented plastisol at 5 wt% loading. In cast polychloroprene or natural rubber, the pigment can be added before sulphur vulcanisation; scorch time is not significantly affected at loadings below 2 phr. Use with zinc oxide and stearic acid is conventional, but the batch temperature during open-mill mixing should not exceed 110 °C to avoid premature colour development of the azo lake. For polyurethane coatings, published data for this specific grade is limited; no recommendation is made for aliphatic two-pack systems exposed to humid outdoor conditions.

Regulatory and Migration Boundaries Constrain Packaging Use

Because the 5BPC grade is based on calcium rather than barium, it avoids the barium content of C.I. Pigment Red 57; this distinction is relevant under packaging migration requirements. Compliance with EU 10/2011 is generally established through overall migration testing in the intended food simulant, not by pigment classification alone; the resin system and film thickness dominate the migration result. For paper and board coatings, FDA 21 CFR 176.170 applies to components of the coating formed under intended conditions of use; supplier extraction data should be reviewed for chloroform-soluble content and heavy metal release. Heavy metal screening by X-ray fluorescence followed by wet chemical confirmation according to IEC 62321-5 is used to demonstrate that lead, cadmium, mercury, and hexavalent chromium are below the homogeneous-material threshold of 0.1 wt% where RoHS compliance is required. The pigment is not intended for direct food-contact use unless it is listed on the national positive list of the target market and the final article passes the specified migration test battery. Under REACH, the product must be accompanied by a safety data sheet and pre-registration or registration number where applicable; no statement is made here regarding specific SVHC content because published data for this specific 5BPC configuration is limited.