Permanent Red 2BL is supplied as a calcium lake monoazo pigment classified under C.I. Pigment Red 48:2, CAS 7023-61-2. The trade designation identifies a yellow-shade red grade within the 2B acid lake family. The pigment is obtained by diazotization of 2-amino-4-chloro-5-methylbenzenesulfonic acid, coupling with 3-hydroxy-2-naphthoic acid, and precipitation with calcium chloride. The dried pigment is milled so that ≥99.0% passes a 45 µm sieve under ISO 787-7. Compactor bulk density is typically 0.25 g/cm³ to 0.45 g/cm³; specific gravity of the pigment particle is reported between 1.60 and 1.70 by ISO 787-10. Oil absorption under ISO 787-5 is commonly 40 g/100 g to 55 g/100 g, and the aqueous suspension pH under ISO 787-9 is maintained at 6.5 to 8.5. Moisture content after conditioning at 105 °C is specified at ≤0.5%.

Colour release is controlled spectrophotometrically. A standard letdown at 1:10 TiO₂ in plasticised PVC is measured with a sphere spectrophotometer in CIELAB under D65 and 10° observer; release tolerances are typically ΔE ≤ 0.8, tinting strength 95% to 105%, and chroma difference ΔC ≤ 0.5. Batches outside the tinting-strength window require letdown adjustment or rework on a production-scale pigment mill. The particle-size distribution measured by laser diffraction under ISO 13320 typically reports D50 0.18 µm to 0.25 µm and D90 0.35 µm to 0.45 µm after recirculation milling. Over-milling can increase viscosity in plastisol and reduce lightfastness by increasing surface area.

For food-contact polymers, a compliant lot must be selected. In the United States, 21 CFR 178.3297 covers colourants for polymers; in the European Union, compliance under Regulation EU 10/2011 is based on overall migration and any specific migration limits for colourant impurities. Standard PR48:2 does not contain lead, mercury, cadmium or hexavalent chromium above 0.1% by weight in a homogeneous material, consistent with RoHS Directive 2011/65/EU. Toy use requires additional assessment under EN 71-7; migration limits are product-specific and are not automatically met by a standard pigment lot.

What Distinguishes the Calcium Lake PR48:2 from Barium and Strontium Analogues?

The metal cation in the lake controls shade, tint strength and thermal stability. Relative to the barium analogue C.I. Pigment Red 48:1, Permanent Red 2BL shifts CIELAB hue angle 2° to 4° toward the yellow region and generally provides lower tinting strength at equal pigmentation, but it offers lower specific gravity and lower raw-material cost per kilogram. Compared with the strontium analogue C.I. Pigment Red 48:3, the strontium lake tends to survive 5 °C to 10 °C higher melt temperature in high-density polyethylene, while PR48:2 usually has faster wetting in low-energy polyolefin compounds. The following ranges are typical industrial values; lot-specific certificates of analysis should govern because milling intensity and surface treatment shift the results.

Because the specific gravity difference is approximately 0.10 to 0.15 units, a formulator replacing PR48:1 with PR48:2 at equal weight percent reduces volumetric pigment concentration by 5% to 8%. This changes rheology and opacity in a 1:10 TiO₂ reduction. Substitution therefore requires re-optimisation of the letdown ratio rather than direct drop-in replacement.

In polyolefin masterbatch production on a co-rotating twin-screw extruder with a 44:1 L/D ratio and 250 kg/h throughput, the pigment is preblended with LDPE at 40% loading. Melt temperatures in the first two-thirds of the screw are held at 170 °C to 200 °C, and final zones are capped at 220 °C. Screw speed is set at 600 rpm to 900 rpm, with specific mechanical energy input 0.20 kWh/kg to 0.30 kWh/kg. Screen-pack pressure is kept below 35 bar through a 200 µm filter; dispersibility assessed by a 14 µm screen test under DIN EN 13900-5 should remain below 2.0 bar/g for a 0.1% LDPE reduction. In injection moulding of polypropylene at clamp force 1200 kN and melt temperature 220 °C, masterbatch letdown at 2% in a 1.5 mm plaque should show no visible agglomerates at 50× microscopy; agglomerate counts above 10 per 100 cm² require raising the shear zone intensity or reducing output by 15%.

At bulk density 0.25 g/cm³ to 0.45 g/cm³, hopper bridging occurs when the pigment is stored above 60% relative humidity. A vibratory feeder with screw diameter 40 mm and hopper angle ≥60° is specified for continuous masterbatch lines. Loss-in-weight feeding accuracy should be maintained at ±0.5% to avoid tint shifts in 1:10 reductions.

In flexible PVC calendering, the pigment is dispersed into plastisol at 0.5 phr to 2.0 phr with a high-speed dissolver at 25 m/s tip speed for 20 min. The slurry viscosity measured at 20 rpm on a Brookfield RV spindle at 23 °C is typically 15% to 25% higher than unfilled plastisol. Residual moisture ≤0.5% is necessary to avoid pinholes in 0.10 mm calendered film. In rigid PVC extrusion, the pigment is added at 0.25% to 1.0% by dry-blend; a counter-rotating twin-screw extruder with a 25:1 L/D ratio and melt temperature 195 °C is preferred. Output rate is reduced by 10% if pigment moisture is uncontrolled because volatiles raise die pressure and cause surface roughness.

When Processing Temperatures Exceed 240°C in Polyolefin Thin-Film Extrusion

PR48:2 has a narrow thermal operating window in blown film. At melt temperatures above 240 °C, residence times beyond 20 min produce measurable shade drift of ΔE 1.0 to 1.5 CIELAB units against a standard plaque and can increase melt flow rate by 2% to 5% under ASTM D1238 at 190 °C and 2.16 kg. On a 75 mm blown-film extruder with a 30:1 L/D screw, the recommended flat temperature profile is 220 °C to 230 °C. If the die lip reaches 250 °C, dark decomposition specking can appear within 30 min; published data for prolonged production runs under this condition are limited, so thermal-stability trials are required before extended campaigns. The decomposition pathway involves loss of the calcium lake structure and possible release of acidic species; film line operators should monitor head pressure, and an increase of 5% from baseline over 60 min indicates filter blinding by degradation products.

Mixing scales above 100 kg require twin-screw compounding; simple tumble blending is insufficient for this pigment.

Lightfastness and Weathering Boundaries in Outdoor PVC Profiles

Outdoor retention is acceptable only within limited pigmentation ratios. Full-shade lightfastness class 5–6 falls to 4 in a 1:10 TiO₂ reduction under ISO 105-B02. Xenon-arc testing under ISO 4892-2 at 0.35 W/m² at 340 nm and black-standard temperature 65 °C typically produces ΔE 3.0 after 1000 h in white reduction. Chalking occurs before 2000 h in high-humidity cycles; the grade is therefore not recommended for exterior rigid PVC profiles with a 5-year colour-fastness requirement unless UV stabilisation is increased or a DPP red such as C.I. Pigment Red 254 is used at ≤0.05%. The difference between PR48:2 and PR254 is not incremental; DPP red offers lightfastness class 8 and heat stability above 300 °C, but at approximately 3× to 5× the pigment cost per kilogram.

In quickset offset lithographic ink, PR48:2 is used at 15% to 20% by weight. Tack stability on an inkometer at 32 °C is held within 1.0 unit over 20 min; however, the pigment has low resistance to methyl ethyl ketone and is not suitable for solvent-based lamination inks where extraction resistance below 10% colour transfer is required. In air-drying alkyd enamels, the vehicle acid value should be below 15 mg KOH/g; higher acid values produce viscosity increase and pigment flocculation on storage. In water-based flexographic inks, a nonionic wetting agent at 0.5% on pigment weight and pH 8.0 to 9.0 are required; anionic dispersants can destabilise the calcium lake and raise viscosity above 100 mPa·s at 250 s⁻¹.

Migration Limits Are Not Uniform Across Application Classes

Compliance of PR48:2 depends on the application-specific extraction test and legal framework. A single chemical substance can satisfy one regulation and fail another because tests differ in simulant, contact ratio and contact time. In migration cells operated under EN 1186 at 40 °C for 10 days, calcium extraction from a 2% pigmented LDPE film remains below 0.5 mg/dm² when the food-contact side is separated by a 50 µm virgin polymer barrier. Without the barrier, overall migration can exceed 10 mg/dm² in fatty simulant at 60 °C; the pigment fraction contributes to this through low-molecular-weight lake and dispersing-agent migration. Published data for high-temperature migration of this specific PR48:2 grade are limited.

During sulphur vulcanization of an NBR compound, addition of PR48:2 at 1.0 phr does not alter scorch time by more than 0.5 min at 160 °C in a moving-die rheometer, but incomplete dispersion reduces tensile strength by up to 5%. Two-roll milling at 60 °C with a friction ratio of 1.2:1 is used; undispersed pigment streaks are detectable with a 45 µm grind gauge. At loadings above 2.0 phr, the slightly alkaline pH 6.5 to 8.5 can shorten scorch time by 10% in low-sulphur EV systems.

Storage in sealed paper bags at 10 °C to 35 °C and relative humidity ≤60% is required. At 70% RH and 23 °C, powder moisture can increase by 0.8% within 2 h; pre-drying at 80 °C for 2 h in a desiccant dryer is used before extrusion when exposure has occurred.