Permanent Red FGR is the commercial designation for C.I. Pigment Red 112 (CAS 6535-46-2, C.I. 12370), a naphthol AS monoazo pigment applied in waterborne and solvent-borne surface coatings, printing inks, textile print pastes, and selected low-temperature polymer compounds. The dry powder is characterised by a density of approximately 1.5 g/cm³, a pH of 6.0–8.0 in aqueous extract under ISO 787-9, and an oil absorption of 35–50 g/100 g under ISO 787-5. These values control pigment volume concentration, letdown behaviour, and mill-base viscosity in organic and aqueous binder systems. The following application scenarios treat the pigment as a technical intermediate whose performance is governed by dispersion energy, binder composition, thermal history, and standardised test criteria rather than by generic colouristic description.

When Aqueous Architectural Coatings Drop Lead Chromate for Higher Lightfastness

In waterborne decorative paints, Permanent Red FGR is applied where lead chromate and cadmium pigments are excluded by REACH Annex XVII and where tinting bases require a red with reproducible colour strength in manual and machine dispensing. The pigment surface is sufficiently hydrophilic for styrene-acrylic and pure acrylic latex systems, but mill-base control must address foam and pH drift during high-shear dispersion. A typical mill base for a deep-shade red wall paint contains 30–40 wt% PR112, 6–10 wt% ammonium polyacrylate dispersant on pigment, 0.5–1.0 wt% acetylenic diol wetting agent on batch, 0.3–0.6 wt% mineral-oil defoamer, and 0.2–0.4 wt% biocide. The balance is water thickened with hydroxyethyl cellulose to a mill-base viscosity of 90–110 KU at 23 °C. Dispersion is carried out in a high-speed dissolver with a Cowles blade peripheral speed of 15–18 m/s for 20–25 min; this energy input is required to achieve a Hegman grind of 6–7 under ISO 1524. After letdown with a styrene-acrylic latex binder at 45–55 kg/100 kg of finished paint, final pigment content ranges from 2–8 wt% depending on tinting strength demand. At 1/25 reduction with titanium dioxide, lightfastness under ISO 105-B02 is Blue Wool Scale 7; full-shade drawdowns reach 7–8. Exterior emulsion paints containing PR112 are typically used on masonry facades in temperate climates, where the latex binder shields the pigment from UV exposure; tropical high-UV exposure conditions require a hindered amine light stabiliser package at 0.5–1.5 wt% on binder to maintain hue retention over 3 years.

In tinting systems, PR112 is supplied as a stir-in aqueous dispersion rather than dry powder to reduce dusting and to permit volumetric dispensing. Machine colour matching uses a 12 vol% aqueous pigment dispersion stabilised with 0.2–0.5 wt% nonionic ethylene oxide-propylene oxide block copolymer; the dispersion is dosed at 2–10 vol% into base paints and agitated for 5–10 min at 500–800 rpm using a high-shear mixer. Batch-to-batch tinting strength under ISO 787-16 is held within ± 3% of the control dispersion. Terminal products include interior wall paints, ceiling paints, facade paints, and water-based primers where the red replaces iron oxide in tinting bases requiring higher chroma.

In solvent-borne industrial alkyd and acrylic coatings, Permanent Red FGR is dispersed directly into a resin/solvent vehicle without aqueous pre-wetting because the pigment surface accepts organic binders. A high-gloss machinery enamel uses a mill base consisting of 25–35 wt% PR112, 45–55 wt% medium-oil alkyd resin of 60% oil length, 10–20 wt% white spirit, and 0.3–0.5 wt% anti-settling agent. The premix is processed on a three-roll mill with roll temperatures held at 40–50 °C and hydraulic pressure 0.5–0.8 MPa; fineness after two passes is checked under ISO 1524 and is typically ≤ 15 µm. In this binder environment, the pigment does not visually bleed into a white alkyd overcoat after 24 h contact at 23 °C under ISO 2812-1 when test fluids include xylene, white spirit, butyl acetate, and ethanol. Full-shade films dried for 7 days at 23 °C and tested under ISO 16474-2 in xenon-arc equipment retain no more than 2 CIELAB ΔE after 500 h when the binder contains 1.0 wt% of a 2-(2-hydroxyphenyl)-benzotriazole UV absorber on total binder. In stoving alkyds, the cure cycle must remain below 150 °C for 30 min; higher bake schedules produce a hue shift toward yellow because of thermal degradation of the azo chromophore. Terminal finished goods include alkyd trim enamels, agricultural machinery paints, and maintenance coatings for steel structures where solvent resistance and opacity are the primary selection factors.

Aqueous Flexographic Ink Colour Strength and Solvent Retention

In aqueous flexographic ink on absorbent paperboard, PR112 is used instead of lithol rubine because it does not bleed in water when printed alongside white or black inks. The pigment is dispersed in a bead mill rather than a three-roll mill because the ink vehicle has low viscosity. A stock paste contains 35–40 wt% PR112, 8–12 wt% styrene-acrylic dispersant on pigment, 5–8 wt% propylene glycol, 0.2–0.5 wt% defoamer, and water. The bead mill is charged to 80% of net volume with 0.6–0.8 mm yttrium-stabilised zirconia beads; chamber tip speed is 10–12 m/s and residence time is 5–8 min. Finished ink at 10–15 wt% pigment has a viscosity of 18–25 s in a DIN 4 cup at 25 °C. Fineness under ISO 1524 is ≤ 10 µm; colour strength under ASTM D6531-00 is held within ± 3% of a controlled reference. Drying on a central-impression flexo press is performed at 60–80 °C web temperature with air velocity 15–20 m/s for 2–4 s; residual solvent above 500 mg/m² measured by headspace gas chromatography can cause blocking in rewind rolls. The ink is used for paper bags, multi-wall sacks, folding cartons, and overprint varnish bases; for food-contact packaging, migration testing under EU 10/2011 is required because PR112 is not automatically listed in all positive lists for direct food contact.

For textile pigment printing on woven and knitted cotton and polyester-cotton blends, Permanent Red FGR is supplied as an aqueous dispersion and thickened into a paste at 2–6 wt% pigment on total print paste. The binder system is an acrylic or butadiene-acrylonitrile self-crosslinking dispersion at 15–20 wt% of paste; a sodium alginate or associative polyurethane thickener is added to a print-paste viscosity of 3000–8000 mPa·s measured on a Brookfield RV at 20 rpm and 23 °C. After flat-screen or rotary-screen application, the substrate is dried at 100–120 °C for 2–3 min and then cured at 150 °C for 3–5 min to crosslink the binder. Under ISO 105-C06 at 60 °C with ECE detergent, the print typically achieves grey scale 4–5; dry crocking under ISO 105-X12 is 4 and wet crocking is 3–4. The azo chromophore is chemically sensitive to reducing agents; discharge printing with sodium sulfoxylate-formaldehyde is therefore not possible on reactive-dyed grounds. Terminal products include printed T-shirts, tote bags, curtain fabrics, and non-woven decorative banners.

What Limits Permanent Red FGR in Rigid PVC Pipe Extrusion?

Permanent Red FGR is suitable for plasticized PVC because processing temperature can be held at 160–180 °C, but rigid PVC pipe extrusion is a boundary condition. In calendered plasticized PVC film, the pigment is dispersed at 0.5–2.5 phr in a dioctyl phthalate or diisononyl phthalate plastisol with a Ba-Zn or Ca-Zn stabiliser package. The plastisol is milled on a three-roll mill to ≤ 20 µm and fused at 160–180 °C for 5–10 min. Under these conditions, migration into a white contact layer is not visually observed after 24 h at 60 °C under 1 kg/cm² contact pressure; colour change is assessed according to ISO 105-A02. The pigment can be used in PVC flooring wear layers, synthetic leather, tarpaulins, and automotive interior skins.

Rigid PVC pipe extrusion is more restrictive. Twin-screw extrusion of pipe compound runs melt temperatures of 180–200 °C; the heat residence time in the extruder, die, and adapter can exceed 2 min. Above 200 °C, PR112 shows measurable thermal degradation as a shift in hue from bluish red to orange-red. On a counter-rotating twin-screw extruder with L/D 36:1, barrel temperatures from feed to die set at 150/160/170/175/180/180/180 °C, the melt temperature measured at the die entry was 199 °C; after 15 min continuous extrusion, the ΔE against the standard was 1.8 CIELAB. When die temperature was raised to 195 °C to reduce melt viscosity, the die-entry melt reached 207 °C and ΔE rose to 3.2 CIELAB within the same run time. PR112 should therefore not be used in rigid PVC pipe formulations where die temperatures exceed 190 °C unless the compound contains a thermal stabiliser with high hydrotalcite content and the screw design minimises residence time distribution. Published data on long-term colour retention under pipe weathering is limited for this specific configuration.

Concentrate producers for flexible PVC use a batch internal mixer at 50–60 wt% pigment in DINP plasticizer; the mixture is then passed through a two-roll mill at 120–140 °C before chip casting. This pre-dispersion step avoids dry pigment agglomerates in the plastisol. The finished goods are coloured PVC edge banding, automotive floor mats, and electrical cable sheathing where the pigment’s non-bleeding character is required.

In polypropylene and low-density polyethylene injection moulding, PR112 is limited to melt temperatures below 200 °C; it is not suitable for high-temperature polymer matrices such as polycarbonate, nylon, or high-heat PMMA alloys. A single-pigment masterbatch is produced at 40–50 wt% PR112 in a low-density polyethylene or polypropylene wax carrier using a co-rotating twin-screw extruder with L/D 36:1. The feed-to-die barrel profile is set at 120/140/160/170/175/175/170 °C, screw speed at 300–500 rpm, and vacuum devolatilization at -0.08 MPa. Residence time is kept below 90 s; longer residence times above 200 °C generate a measurable shade shift. The masterbatch is let down at 2–4 wt% in natural polymer. During injection moulding, back pressure is set at 0.5–1.0 MPa and screw cushion at 3–6 mm to maintain colour consistency shot-to-shot. Dispersion quality is checked by a pressure-rise test through a 20 µm screen pack; an increase of more than 0.5 MPa within 10 min indicates undispersed agglomerates. Because PR112 is a polar organic pigment in a non-polar polyolefin matrix, the masterbatch formulation contains 5–10 wt% of a polar ethylene-acrylic acid wax to reduce interfacial tension and improve pigment wetting. Terminal products include coloured polypropylene caps, household storage containers, toys, and garden furniture components; for toys, EN 71-3 migration of elements is matrix-dependent and must be tested on the final moulded article.

Artist-grade acrylic pastes and educational watercolour pans incorporate PR112 at 10–15 wt% in the finished paste; the pigment is dispersed into gum arabic or acrylic emulsion on a three-roll mill to a fineness below 25 µm. Lightfastness under ASTM D4303 in artist acrylic vehicles is Blue Wool Scale 7; gloss and texture are determined by the binder, while the pigment contributes moderate tinting strength and a controlled undertone. Tubes and pans are filled at 45–55 °C to control viscosity during dosing. Because artist materials are subject to EN 71 and ASTM D4236 chronic health labelling, formulation of PR112 requires toxicological review of impurities, and the commercial pigment specification must include heavy-metal and primary aromatic amine certificates.