Lithol Scarlet LB198 is a monoazo lake pigment identified as C.I. Pigment Red 49:1 with CAS Registry Number 1103-38-4. The pigment is prepared from the parent dye acid 2-[(2-hydroxy-1-naphthyl)azo]naphthalene-1-sulfonic acid, isolated as the barium salt at a 2:1 dye-to-metal stoichiometry. The nominal molecular formula is C₄₀H₂₆BaN₄O₈S₂, corresponding to a molecular mass of approximately 891.9 g/mol. The commercial suffix “LB198” is a supplier-specific grade designation rather than a separate Colour Index identity. In dry powder form, the product is a yellow-shade red powder with relatively high tinting strength and a specific gravity slightly above 1.6 g/cm³. Its pigment class imposes a comparatively low thermal stability ceiling and a defined sensitivity to strongly acidic or strongly alkaline aqueous media. The product is normally evaluated using the pigment test methods of ISO 787, ASTM D281, and ISO 1524, with compliance obligations depending on the end-use regulations.

Particle Size and Oil Absorption Data for PR 49:1 Lakes

Typical screening data for PR 49:1 grade literature are summarized in Table 1. Oil absorption is the principal formulation variable because it determines dispersant demand and mill-base rheology. A batch at the upper end of the oil absorption range may require 10–15 % more vehicle to reach the same flow in a high-pigment offset ink. The presence of residual water-soluble barium or sodium salts from synthesis is controlled by washing and is reported as water-soluble matter; elevated water-soluble matter shifts the conductivity of water-based ink systems and can destabilise some synthetic thickeners. The primary particle size is not directly measured on dry pigment for routine release; instead, dispersion fineness after milling is assessed by a grind gauge per ISO 1524. Product-specific certificates of analysis for LB198 should be used for release decisions.

Predispersion of LB198 in solvent-borne packaging inks begins with wetting the pigment into the low-acid portion of the vehicle at a dissolver tip speed of 20 m/s. A jacketed horizontal bead mill with 0.6–0.8 mm yttria-stabilised zirconia media is then used to reduce the grind to 5 µm or below. During milling, the batch temperature should remain below 45 °C; higher temperatures can partially solubilise the monoazo dye and deposit a bronze film on the printed ink surface. Ketone-rich solvent systems extract the soluble dye fraction, so the finished solvent balance should keep total ketones below 5 % by mass unless a bleeding test confirms acceptable overprint behaviour. On a three-roll mill, paste yield stress increases sharply when pigment loading exceeds 25 wt% in a high-viscosity offset vehicle, and the first roller temperature is held below 35 °C to prevent surface sintering before complete dispersion. Plant-scale flexographic inks made with LB198 typically require final in-line filtration through a 30 µm cartridge to remove undispersed agglomerates.

Within the PR 49:1 family, LB198 may differ from other grades in specific surface treatment. Rosin-treated grades have lower oil absorption and softer agglomerates, which aid dispersion in offset inks but can reduce heat resistance further. Resinated PR 49:1 grades may also show a slight yellow-shade shift and reduced water-soluble matter due to encapsulated dye. LB198, depending on the surface treatment, is normally selected for solvent ink and polyolefin masterbatch applications where processability and low agglomerate content are more important than maximum heat stability. A practical consequence of surface treatment is that different PR 49:1 products with identical Colour Index and CAS numbers can show different viscosity responses in the same bead mill formulation; substitution must be accompanied by a mill-base rheology comparison and a short press trial.

What Limits Processability Above 160°C in Tinted Polyolefin Compounds?

PR 49:1 is not a high-heat pigment. The barium lake structure begins to exhibit visible shade drift when melt temperatures approach 160 °C, shifting from a clean yellow-shade red toward a duller red-brown. The drift is generally attributed to partial dissociation of the lake and recrystallisation of the monoazo dye in the polymer matrix. In polyolefin masterbatch production, a corotating twin-screw extruder with L/D ≥ 40:1 should be operated with barrel temperatures between 130 °C and 150 °C from the first kneading block onward. A downstream side feed after the melt seal limits residence time above 150 °C. At 40 wt% pigment loading in LLDPE, a 100 µm screen pack can show pressure rise above 0.5 MPa over a 4-hour run when agglomeration is not eliminated. Pre-drying at 80 °C for 4 h is specified by some compounders when storage relative humidity exceeds 60 % or when the matter volatile at 105 °C exceeds 2.0 % by ISO 787-2. The product is incompatible with highly alkaline amine additives above pH 9.0, which accelerate lake hydrolysis; acid-functional dispersants that lower the mill-base pH below 5.0 are similarly undesirable.

Injection moulding trials with translucent polypropylene at let-down ratios of 2–4 % are sensitive to undispersed agglomerates larger than 45 µm, which appear as visible specks in transmitted light. A two-stage screw with a mixing section length of 5 D and a back pressure of 50–80 bar reduces the defect frequency compared with a general-purpose screw. Published data for this specific configuration is limited; therefore process settings should be validated with a colour difference measurement per BS EN 12877-2 against the approved packaging standard.

In water-based flexo inks, LB198 is dispersed with an anionic polymeric dispersant at 15–25 % on pigment mass. The system is neutralised to pH 8.0–8.5 with a volatile amine; this pH is an operational boundary because the lake structure is increasingly hydrolysed above pH 9.0. The pigment is then let down with an acrylic or polyurethane dispersion and cured at 120–150 °C. Crockfastness of printed textiles is evaluated per ISO 105-X12 and depends mainly on binder film formation. Ammonia should be avoided when the pigment has a low water-soluble salt content because a rapid pH excursion above 9.0 during let-down can release the parent dye and stain the unprinted substrate.

If Lithol Scarlet LB198 Is Evaluated Against PR 57:1, Different Failure Modes Emerge

Comparison with other red lakes is not a direct reformulation exercise because the tinctorial strength, oil absorption, shade, and thermal stability of each pigment differ. A start-point comparison is shown in Table 2. In solvent ink formulations, PR 49:1 provides a yellower red than PR 57:1 and a lower raw-material cost per unit of chroma, but it is more sensitive to over-milling and bronzing in high-ketone systems. PR 48:2 is a bluer red with better heat stability and solvent resistance; its higher density and different oil absorption require adjustment of the solids content when it replaces LB198. PR 53:1 is an orange-red barium lake used in rubber and low-cost polyolefin compounds; it may tolerate slightly higher processing temperatures but can show lower chroma in certain solvent ink formulations. None of these lakes should be considered a direct drop-in replacement without complete reformulation and passage of the relevant lightfastness, heat stability, and migration protocols.

When LB198 is used in pigmented nitrocellulose/polyurethane flexo inks, over-lacquering with a high-ester or high-ketone overprint varnish can dissolve part of the pigment and produce bleeding. A standard overprint varnish resistance test is conducted by drawdown and topcoat application, followed by 24 h contact and visual assessment of bleed against a white substrate. The pigment is better suited to surface printing than to lamination inks because it can migrate into adhesive layers when monomeric plasticisers or high-solvating adhesives are present. For lamination applications, a higher-molecular-weight disazo red or DPP red is generally specified unless short-term shelf-life and low cost are the dominant criteria.

PR 49:1 is generally limited to rigid or semi-rigid PVC because plasticiser diffusion above 20 phr of dioctyl phthalate can transport the low-molecular-weight dye component to the surface. In a typical soft PVC cable compound, migration testing per EN 12877-2 is used to evaluate heat stability and migration; if visible spew occurs after ageing at 80 °C for 24 h, the grade is rejected for that formulation. The barium lake structure does not prevent migration if the dye component is partially dissolved by the plasticiser; only a high-molecular-weight pigment or a crosslinked matrix can provide resistance under those conditions.

Regulatory status is application-specific. Barium lake pigments are not automatically cleared for direct food contact; indirect food-contact polymers must be checked against 21 CFR 178.3297, EU Regulation 10/2011, and any applicable national positive lists for the specific polymer and service temperature. Migration testing per EN 1186 or ASTM F1306 is required for the final article under the intended time-temperature conditions. In toy and child-use articles sold in the EU, soluble barium extraction is controlled under EN 71-3 using the appropriate acid extraction protocol for the specific material. Under REACH, the Safety Data Sheet should be checked for any restriction or exposure scenario applicable to the barium salt and its decomposition products. RoHS compliance under Directive 2011/65/EU requires that lead, cadmium, mercury, and hexavalent chromium remain below the maximum concentration values in homogeneous materials; certificates of analysis typically report these metals by IEC 62321-5. If the grade is supplied as a surface-treated or barium sulfate-extended product, the regulatory statement and tinting strength can differ from the neat C.I. Pigment Red 49:1, and the exact designation must be confirmed on the lot-specific certificate of analysis.