Pigment Red 170 — commonly abbreviated as PR170 — is one of the most widely used naphthol AS pigments in the red color space, prized for its clean, bright shade and its versatility across coatings, plastics, printing inks, and textiles. But PR170 isn't a single, uniform product: it's sold in a range of crystal grades and particle forms, each tuned for a different balance of shade, lightfastness, heat resistance, and cost. Choosing the right grade for a given application is what separates a pigment that performs from one that fades, bleeds, or shifts shade in production. This guide walks through what PR170 is, how its key properties vary by grade, and how to match it to your application.
What Is Pigment Red 170?
PR170 (Colour Index Pigment Red 170, C.I. 12475) is a monoazo pigment from the naphthol AS family, identified by CAS number 2786-76-7 and the molecular formula C26H22N4O4. It's produced through a diazotization-coupling reaction, in which a diazonium salt is coupled with a naphthol AS derivative to form the final pigment molecule, which is then isolated, washed, and conditioned into the crystal form used in the finished product.
Chemically, PR170 sits between the classic, lower-cost monoazo reds (like Toluidine Red, PR3) and the high-performance, higher-cost pigment families (like quinacridones and DPP reds) — it offers a meaningfully better performance profile than the entry-level azo reds, at a fraction of the cost of the premium classes, which is why it remains a workhorse pigment across so many industries.
Key Properties
Color Shade and Crystal Grades
PR170 is not sold as a single shade — manufacturers offer a family of grades built on the same chemistry but different crystal structures and particle sizes, which shift both hue and performance. Common designations include F2RK (yellowish-shade red), F3RK (medium shade), and F5RK (bluer shade), along with transparent and opaque versions of each. Transparent grades have finer particles and are used where color needs to layer or show through — ink and coatings applications where undertone matters. Opaque grades have larger particles, offer better hiding power, and are typically chosen for solid-shade coatings and plastics where coverage matters more than transparency.
Lightfastness
PR170's lightfastness depends heavily on the grade and the form it's used in. Transparent grades typically rate around level 6 on the Blue Wool Scale, while opaque grades can reach level 7 — good enough for most outdoor architectural and automotive refinish applications, though not in the same class as premium pigments like quinacridones or DPP reds, which can reach level 7–8 even in transparent form. For applications with genuine long-term outdoor exposure, always confirm the lightfastness rating of the specific grade you're sourcing rather than assuming all PR170 performs the same.
Heat Resistance
Standard PR170 grades typically hold up to around 15 minutes at 160–165°C without significant color shift, which covers most coil coating, powder coating, and plastics processing conditions. High-performance grades with improved crystal stability push that ceiling higher and also offer better dispersibility, which matters for processes like PVC calendering or polyolefin extrusion that run pigment through repeated heat cycles. If your process involves prolonged exposure above 180°C, it's worth requesting heat-resistance data for the specific grade rather than relying on the generic PR170 datasheet.
Chemical and Solvent Resistance
PR170 offers good resistance to acids, alkalis, and soap, making it suitable for products that will see cleaning agents or outdoor weathering with rain exposure. Its resistance to organic solvents is good but not exceptional — strong solvent systems can cause some bleeding, so it's worth testing compatibility if you're formulating a solvent-heavy coating or ink system rather than assuming full resistance.
Migration and Bleed Resistance
In plastics and packaging inks, PR170 has a reasonably good reputation for resisting migration and bleeding into adjacent materials — an important property for food-contact packaging, soft PVC articles, and multi-layer laminates where pigment migration into another substrate is a real risk. That said, migration resistance is influenced by the plastic matrix, plasticizer content, and pigment loading, so it's still worth running a migration test on the actual production formulation rather than assuming compliance.
Applications by Industry
Automotive and Industrial Coatings
PR170 is a long-standing choice for automotive refinish, agricultural and construction equipment coatings, and general industrial coatings, where its medium-to-bluish red shade and reasonable weatherability deliver dependable performance at a lower cost than premium red pigments. Opaque, high-performance grades are generally preferred here for their combination of hiding power and improved heat and light stability.
Architectural and Decorative Paints
In architectural coatings, PR170 provides a bright, clean red shade for both interior and exterior latex and solvent-based paints. Exterior use calls for the higher-lightfastness opaque grades; interior applications, where UV exposure is minimal, can generally use more economical standard grades.
Plastics and Masterbatches
PR170 colors polyolefins, PVC, and various engineering plastics, and is commonly used in masterbatch production. Its good migration resistance makes it a reasonable fit for soft PVC and packaging applications, though — as with heat resistance — it's worth checking the specific grade's performance against your processing temperature and dwell time, particularly for extrusion or injection molding processes that run hotter or longer.
Printing Inks
In both solvent-based and water-based printing inks, PR170 delivers high tinting strength and a clean shade, and its migration resistance makes it a popular choice for flexible packaging. For water-based systems, look for grades that have been surface-treated or optimized for aqueous dispersion, since standard grades developed for solvent or coatings systems don't always disperse as readily in water.
Textile Printing
PR170 is also used in textile printing pastes and pigment dyeing of cotton, wool, and silk, where its combination of wash fastness and lightfastness holds up well for most apparel and home textile applications.
Common Mistakes to Avoid
- Treating all PR170 grades as interchangeable. Shade, lightfastness, heat resistance, and dispersibility all vary meaningfully between F2RK, F3RK, F5RK, and their transparent/opaque versions — specify the grade, not just the pigment name.
- Assuming solvent resistance without testing. PR170's solvent resistance is good but not top-tier; aggressive solvent systems should be tested for bleeding before committing to a formulation.
- Overlooking heat resistance limits in plastics processing. Standard grades are rated for moderate heat exposure; high-temperature processes like PVC calendering or engineering plastics need a high-performance grade or a different pigment family altogether.
- Skipping migration testing in food-contact or soft PVC applications. General good migration resistance is not the same as compliance — always test the actual production formulation.
- Choosing on price per kilogram instead of cost per unit of color strength. A lower-cost grade with weaker tinting strength can require a higher loading to hit the same shade, erasing any savings.
PR170 remains one of the most cost-effective, versatile red pigments available, but getting the most out of it means matching the grade — not just the pigment — to your application's shade, heat, light, and chemical resistance requirements.
TRESAI Chemical supplies the full range of Pigment Red 170 grades, from standard transparent and opaque forms to high-performance heat- and light-stable variants, along with technical data sheets and free samples for qualification testing. Contact our technical team to find the right PR170 grade for your formulation.