Section
| HS Code | 729133 |
| Productname | Lithol Rubine WF188 |
| Pigmenttype | Organic monoazo pigment |
| Colorindexname | Pigment Red 57:1 |
| Colorindexnumber | 15850:1 |
| Casnumber | 5281-04-9 |
| Chemicalclass | Monoazo calcium salt |
| Chemicalformula | C18H12CaN2O6S |
| Molecularweight | 424.44 g/mol |
| Colorshade | Bluish red |
| Physicalform | Powder |
| Density | 1.6-1.8 g/cm³ |
| Bulkdensity | 0.4-0.6 g/cm³ |
| Particlesize | 0.1-1.0 µm |
| Oilabsorption | 40-50 g/100 g |
| Ph | 6.0-8.0 |
| Moisturecontent | ≤1.0% |
| Watersolublematter | ≤1.0% |
| Solubilityinwater | Insoluble |
| Lightfastness | 4-5 |
| Heatresistance | 180-200 °C |
| Acidresistance | 4-5 |
| Alkaliresistance | 3-4 |
| Soapresistance | 4 |
| Waterresistance | 4 |
| Migrationresistance | Low |
| Dispersibility | Good |
| Primaryapplication | Water-based flexographic inks |
As an accredited Lithol Rubine WF188 factory, we enforce strict quality protocols—every batch undergoes rigorous testing to ensure consistent efficacy and safety standards.
| Packing | Lithol Rubine WF188 is supplied in 25 kg moisture-resistant paper bags with inner polyethylene liners, palletized for industrial handling. |
| Container Loading (20′ FCL) | Lithol Rubine WF188 is packed in 25 kg bags on pallets and loaded into a 20′ FCL container for export. |
| Shipping | Lithol Rubine WF188 is generally a non-hazardous organic pigment preparation and is not regulated as dangerous goods for transport, unless the SDS states otherwise. Ship in original sealed, labeled containers; protect from moisture, heat, and direct sunlight; avoid dust generation and follow SDS handling requirements. |
| Storage | Store Lithol Rubine WF188 in a cool, dry, well-ventilated area away from direct sunlight, heat, sparks, and strong oxidizers. Keep containers tightly closed to prevent moisture and dust ingress. Avoid dust generation and store separately from food, feed, and incompatible materials. Follow the SDS and local regulations. |
| Shelf Life | Lithol Rubine WF188 shelf life is typically 24 months from manufacture when stored sealed in original packaging under cool, dry conditions. |
In sheetfed offset ink manufacturing, Lithol Rubine WF188 is introduced into a rosin-modified phenolic varnish after the vehicle has been adjusted to a viscosity suitable for high-speed predispersion. The pigment belongs to C.I. Pigment Red 57:1 and consists of a calcium salt of 4-[(4-methyl-2-sulfophenyl)azo]-3-hydroxy-2-naphthoic acid. Dispersion on a three-roll mill is normally run at a premix viscosity of 40–80 Pa·s at 25 °C; the mill charge is adjusted with additional varnish or presscake until a Hegman gauge reading of 0–15 µm is obtained by ISO 1524. The millbase is then let down with a high-boiling aliphatic distillate or a rapeseed oil ester, keeping tack within the range required by the press configuration. On a sheetfed press, Lithol Rubine WF188 is used as a spot red or as a component in a matched brand color rather than as the process magenta specified in ISO 2846-1. The pigment is formulated as a spot color so that the ink technician can balance trapping against dampening solution uptake; water pick-up on a lithographic emulsions test may rise when tack exceeds 12–16 tack units at 1,200 s⁻¹. On multi-unit presses, ink film thickness is set between 1.0 µm and 1.8 µm on uncoated paper, while coated board may require a lower film weight to avoid set-off. The pigment exhibits low solubility in mineral oil and in common offset distillates, which can reduce roller staining during long runs. However, a fountain solution concentrate above 2.5–3.5 % by volume can destabilize the ink-water balance and lower density in solid areas. Production batch records should include tinting strength against a retained control standard and a printed drawdown on a Prufbau or IGT printability tester to document shade stability under standard illuminant D65. For packaging applications, the final print is screened for soluble heavy metals according to EN 71-3 and for primary aromatic amines under REACH Annex XVII Entry 43. Published data for migration limits in direct food contact lithographic overprint lacquers is limited, so the pigment is generally positioned for indirect contact and non-food packaging unless a functional barrier is demonstrated under EC 1935/2004.
The calcium lake structure of Lithol Rubine WF188 is sensitive to the neutralization level of the amine-solubilized acrylic resin. In a typical water-based flexographic ink, the letdown vehicle is a styrene-acrylic emulsion or an acrylic solution neutralized with ammonia or a tertiary alkanolamine to a pH of 8.0–9.2. When the pigment presscake or dry powder is added under high shear, free calcium species can exchange with the ammonium cation and reduce the effective resin solubility. The resulting viscosity increase is measured on a Brookfield viscometer at 60 rpm and is often accompanied by a drop in pH to 7.5–7.8. The correction is made by incremental addition of an amine-neutralized resin solution, not by direct caustic, because local pH overshoot above 9.5 can promote hydrolysis of the ester groups in the acrylic polymer. On a production disperser, the premix is processed for 15–20 min at a tip speed of 18–22 m/s, then milled in a horizontal bead mill charged with 0.5–1.0 mm zirconia beads. The finished ink is passed through a 25 µm filter bag; frequent filter blocking indicates incomplete dispersion or resin shock. The ink is then adjusted to a flow time of 25–35 s in a 4 mm flow cup according to ISO 2431. Lithol Rubine WF188 can be used in corrugated preprint, paper bags, and wrappers where the printed surface is not in direct contact with moist or fatty food. For food-safe printed napkins or paper cups, the formulation must be tested for soluble metals and aromatic amines, but published data for PR 57:1 in direct food-contact flexo prints is limited. Foaming in water-based systems can be controlled with a silicone-free defoamer if the dosage does not exceed 0.2–0.5 % by weight; excess defoamer can cause craters in the print film.
During single-screw extrusion of plasticized PVC, Lithol Rubine WF188 is typically pre-dispersed as a pigment paste in a plasticizer such as DINP or as a compounded color masterbatch. Dry-blend preparation in a high-speed mixer reaches a drop temperature of 105–115 °C, after which the blend is cooled to 40–50 °C before extrusion. The pigment is added at 0.5–2.0 phr in full-shade applications, while tint shades with titanium dioxide may require 0.05–0.3 phr pigment and 2–5 phr TiO₂. Extruder barrel temperatures are normally set between 150 °C and 185 °C along the feed-to-die profile. At melt temperatures above 200 °C, the blue-shade red can shift toward a yellower hue and the tinting strength can drop; this threshold is more critical in rigid PVC profile extrusion than in flexible tubing or calendered sheet. A two-roll mill is used for short-run color development, with a front roll temperature of 165–175 °C and a nip gap of 0.5–1.0 mm. The pigment is evaluated for heat stability by a static oven test at 180 °C for 10 min against a standard control, and for bleed resistance by contact with white PVC under 60 °C for 24 h. In calendered soft PVC, the pigment remains transparent and clean in mass tone, but outdoor weathering of tints is limited by moderate lightfastness; red shades with high TiO₂ content can fade more rapidly than full-shade components. Published data for Lithol Rubine WF188 in rigid PVC pipe extrusion is limited, and its application there is generally restricted to low-temperature foam core or decorative layers. For EU plastic materials, the grade must comply with REACH Annex XVII and applicable limits for cadmium, lead, and soluble chromium. In US food-contact PVC, use of the pigment must be confirmed under 21 CFR 178.3297 or a suitable food additive regulation; without a specific clearance, the compound is restricted to non-food articles.
Rubber batches containing Lithol Rubine WF188 are mixed on a two-roll mill or in an internal mixer with a fill factor of 0.70–0.80. The pigment is added at 1–3 phr in gum rubber stock. In an internal mixer, the masterbatch is dropped at 120–140 °C to avoid premature scorch, then the curatives are added on a cooled mill at 50–60 °C. The vulcanization kinetics of a sulfur-cured SBR or natural rubber system are evaluated on a moving die rheometer at 160 °C and 0.5° arc. Lithol Rubine WF188 can interact with the zinc oxide/stearic acid complex, and the degree of interaction depends on the free calcium content of the pigment. If the pigment carries high residual calcium chloride, the cure rate can be retarded and reversion resistance may fall. Contact staining and migration are tested according to ASTM D925-14; the pigment is generally selected for non-contact rubber goods such as shoe soles, mats, and gaskets when a blue-shade red is required. In white rubber tile compounds or two-color co-cured parts, migration of the red pigment into the white adjacent phase is checked at 70 °C for 72 h under a load of 5 kg. The pigment has limited lightfastness in rubber, so full-shade articles are preferred over pale tint shades. For peroxide-cured EPDM or nitrile rubber, published data on pigment–peroxide interaction is limited, and a screening cure study at 170 °C with a rheometer and tensile set analysis is required before production release.
Indoor alkyd enamels and decorative solvent-borne coatings can be tinted with Lithol Rubine WF188 when the expected service environment excludes prolonged UV exposure. The pigment is dispersed in a long-oil alkyd resin with a high-speed dissolver and then ground in a bead mill to a Hegman value of 5–7 according to ISO 1524. The millbase may contain 15–25 % pigment, 40–50 % alkyd resin, and the balance as a low-aromatic mineral spirit. Drier levels are kept at the minimum required for through-dry; excess cobalt and calcium naphthenate can accelerate yellowing of the clear binder and shift the red hue. The final coating is applied by air spray or brush at a wet film thickness of 50–75 µm. Dry film opacity and rub resistance are evaluated after 24 h at 23 °C and 50 % relative humidity. The pigment's solvent resistance is sufficient for interior trim, furniture, and toy finishes, but the grade is not intended for exterior house paints or automotive topcoats because the calcium lake chromophore has moderate lightfastness and can fade in full-shade and tinted coatings under long-term xenon-arc exposure. For toy finishes, overcoat systems must satisfy EN 71-3 extraction limits for soluble heavy metals and ASTM F963-23 toy safety requirements. Published data for Lithol Rubine WF188 in two-component polyurethane or acid-catalyzed wood coatings is limited; in these systems, compatibility must be checked by drawdown clarity and gloss retention after oven aging at 50 °C for 7 days.
Water-based art material tinting bases, including poster paints, finger paints, and wax crayons, are a secondary application for Lithol Rubine WF188. The pigment is dispersed into a gum arabic or dextrin solution with a nonionic wetting agent at 0.2–1.0 % by weight of the total formulation. The mix is stirred in a vacuum planetary mixer to prevent air entrainment, then milled on a small three-roll mill or a bead mill until the particle size distribution yields a uniform drawdown without visible agglomerates. The final product is tested for shelf stability at 40 °C for 30 days and for microbial resistance with a suitable preservative system; Lithol Rubine WF188 does not act as a biocide and can support mold growth in insufficiently preserved gum-based formulations. For toys and educational materials sold in the EU, the pigment and finished article must comply with EN 71-3 and EN 71-7 for finger paints. Extractable barium, cadmium, lead, and chromium limits are verified with inductively coupled plasma optical emission spectrometry after the specified acid extraction. In the US, art materials intended for children are labeled under ASTM D4236 if chronic hazard evaluation is required. The pigment is not recommended for dry pastel or powder paint applications where inhalable dust may be generated without engineering controls; a dust-free granular form or predispersed paste is preferred. Because PR 57:1 is an azo pigment, the end-use buyer should request a certificate of analysis showing that primary aromatic amine content is below the limit specified by the applicable regulation. Published data for the pigment in cosmetic face paints and theatrical makeup is limited, and those applications require separate regulatory review under the relevant cosmetic ingredient lists.
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Lithol Rubine WF188 is supplied as a commercial grade of C.I. Pigment Red 57:1, a barium lake of 4-[(4-methyl-2-sulfophenyl)azo]-3-hydroxy-2-naphthalenecarboxylic acid. The WF188 identifier is a manufacturer-specific model designation within that Colour Index class and does not represent a distinct chromophore. Published property data for this exact model are limited; therefore, specification values presented here are expressed as the established property envelope for C.I. Pigment Red 57:1, and vendor certificates should be consulted for lot-level limits. The grade is used primarily in water-based flexographic inks, solvent-based liquid packaging inks, and lithographic inks where a transparent magenta-red with high tinctorial strength is required. Direct food-contact use is not established because the barium lake can release soluble barium under acidic conditions.
The pigment is a monoazo lake, and the barium ion is not a surface additive but a constituent of the precipitated crystal lattice. This structural feature contributes to density, colour strength, acid sensitivity, and migration behaviour. The WF188 designation is consistent with a water-flexo or water-washed process stream, often implying reduced soluble salt content and narrower primary particle distribution. That inference is not a substitute for testing; conductivity, pH, and sieve residue should be verified on the actual batch because manufacturing washes can vary across production lines.
| Property | Typical C.I. Pigment Red 57:1 range | Method |
|---|---|---|
| pH of aqueous extract | 7.0–9.0 | ISO 787-9 |
| Moisture content, dry powder | ≤ 1.0% | ISO 787-2 |
| Oil absorption | 35–50 g/100 g | ISO 787-5 |
| Residue on 45 µm sieve | ≤ 0.2% | ISO 787-7 |
| Specific gravity | 1.5–1.7 | ISO 787-10 |
The barium lake crystal is not a high-temperature inorganic pigment. Melt-compounding operations above 220°C can produce crystal-water loss, partial chromophore degradation, and a shift toward a bluer red with lower tinctorial strength. For polyolefin masterbatch production on a co-rotating twin-screw extruder with an L/D ratio of 36:1–44:1, barrel set-points between 180°C and 230°C are typical for the pigment class. Residence times above 300 s at 240°C should be avoided, and hot-runner dead spots in injection moulding can generate black specks and chroma loss. When the dry powder has been stored at relative humidity above 60%, pre-drying at 65°C–75°C for 2 h–4 h is required before melt blending. Thermal fastness is commonly assessed according to DIN EN 12877-1; for C.I. Pigment Red 57:1, visual heat stability in air is typically reported between 200°C and 220°C, with formulation-specific variance expected in polyamide and rigid PVC.
In water-based flexographic ink production, Lithol Rubine WF188 is normally charged as dry powder or presscake into a high-shear disperser before bead milling. A typical premix contains 18–25 wt% pigment solids, 10–15 wt% styrene-acrylic resin solution at 40% solids, and 0.1–0.3 wt% defoamer. The premix is passed through a horizontal bead mill using 0.3–0.6 mm yttria-stabilized zirconia media. Mill-base temperature is controlled below 55°C; if the jacket fails to hold this limit, viscosity can rise and colour strength may drop. Grind fineness is checked by ISO 1524 with a target of 5–10 µm. Final ink pH is adjusted to 8.5–9.5 with ammonia or a volatile organic amine; pH below 8.0 can destabilise the pigment and produce print mottle. Press-side viscosity is normally adjusted to 18–25 s in a DIN 53211 cup with a 4 mm orifice at 25°C.
In polyurethane-based flexographic and gravure inks for surface and lamination printing, the pigment may be dispersed at 15–20 wt% into a ketone/acetate solvent blend. The monoazo barium lake shows stronger solvent bleed than high-performance red pigments, so it is typically restricted to non-retort and non-boil-in-bag structures. A 24 h immersion test in ethyl acetate at 25°C should show no visible bleed into the laminating adhesive when the ink layer is protected by a barrier film. If the ink layer is directly exposed to the adhesive, reformulation to a higher-molecular-weight pigment or a barrier coating is required. Replacement of methyl ethyl ketone with an isopropanol/ethyl acetate blend can reduce chroma loss during gravure dilution, but drying speed must be rebalanced. Laminating adhesives applied at 2.5–3.5 g/m² dry coat weight should not extract visible colour into the sealant layer. Published comparative data for WF188 specifically in this configuration are limited; side-by-side drawdowns are required for final resin selection.
On production-scale horizontal bead mills with a chamber volume of 50 L and rotor tip speeds of 8–12 m/s, C.I. Pigment Red 57:1 presscake can be reduced to a grind below 10 µm in two passes. The mill base often shows pseudoplastic behaviour; viscosity at a shear rate of 100 s⁻¹ may be 120–250 mPa·s at 25°C. If viscosity exceeds 300 mPa·s, bead movement can stall and motor load rises, which is a known batch-scale failure mode. Batch-to-batch moisture variation of ±5 percentage points in presscake can alter premix viscosity enough to change throughput. Conductivity of the diluted mill base is a useful field indicator; values above 200 µS/cm at 10% pigment solids may signal residual soluble barium salts, which can lead to flocculation or pH drift in letdown. Wetting may be improved with a 2–3 wt% dosage of ammonium polyacrylate or styrene-maleic acid copolymer dispersant based on pigment solids.
For toy and food-contact evaluations, the barium lake chemistry creates a specific analytical requirement. Barium lakes are not the colourant class of first choice for direct food-contact articles, because soluble barium extraction can exceed toy-safety limits if the lake is incompletely precipitated or poorly washed. EN 71-3 extraction using 0.07 M hydrochloric acid at 37°C is the standard screening method for toy paints. WF188 should be subjected to batch-level extraction before use in toy applications; a vendor statement alone does not replace lot testing. For food packaging, the printed layer is normally separated from food by a functional barrier or a laminate structure. The relevant food-contact obligation arises from EC 1935/2004 Article 3 and EC 2023/2006 good manufacturing practice, not directly from ink-specific limits under EU 10/2011. Because the chromophore is azo-based, trace primary aromatic amines should also be assessed by migration testing followed by LC-MS/MS if the print is inside a sealed pouch or displayed lamination.
| Assessment area | Standard or method | Critical parameter |
|---|---|---|
| Toy paint soluble barium | EN 71-3:2019+A1:2021 | 0.07 M HCl extraction at 37°C |
| Food-contact GMP | EC 2023/2006 | Migration risk evaluation, trace metals, primary aromatic amines |
| Plastic article migration | EU 10/2011 | Overall and specific migration into simulants; not an ink-specific authorisation |
| Printing ink light fastness | ISO 2836:2021 | Blue wool scale typically 5–6 for C.I. Pigment Red 57:1 |
Differences between Lithol Rubine WF188 and other red pigments are most visible in solvent resistance and mass tone. Unmodified C.I. Pigment Red 57:1 powders often show higher oil absorption and lower aqueous wetting; a water-flexo grade such as WF188 is expected to reduce dusting and improve filterability in high-speed flexographic lines. Compared with C.I. Pigment Red 48:2, WF188 provides a bluer magenta red but less resistance to ketone extraction in lamination inks. Compared with C.I. Pigment Red 53:1, WF188 typically shows better heat stability but can appear duller in high-alkali water-based systems. Compared with high-performance pigments such as C.I. Pigment Red 122, WF188 has lower cost but lower lightfastness and lower solvent fastness. Published side-by-side data for WF188 specifically are limited; ink testing under the intended press and lamination conditions is required before substitution.
Operational boundaries include storage below 60% relative humidity in closed containers, avoidance of strongly acidic additives that may liberate barium ions, and exclusion of hypochlorite-containing washdown sanitizers in water-based ink lines because oxidative bleach can attack the monoazo chromophore. The grade is not suitable for direct food-contact coatings, mouth-contact toy layers, or prolonged exterior exposure without additional light stabilisation. Dry blending with cationic or amine-based additives should be validated for flocculation potential because the pigment surface charge is pH-dependent and reversal can occur above the isoelectric point of the latex or resin system.
