PIGMENT RED 57:1/ HP RED 2738
for high-speed offset presses.
Technical Information
Technical Information
What Is Pigment Red 57:1
Pigment Red 57:1 (CAS 5281-04-9, CI Number 15850:1) is a monoazo lake pigment, globally the highest-volume organic red used in printing inks. Chemically, it exists as a keto-hydrazone tautomer with 1.5 moles of water of crystallization, a crystal form achieved by maintaining pH below 7.0 during synthesis. This structure gives it a naturally bluish-red shade that aligns nearly perfectly with the standard magenta position on the CIE 12-66 European Color Scale for 4-color process printing — the key reason for its dominance in the printing ink industry worldwide.
Why Choose HP RED 2738
While all Pigment Red 57:1 grades share the same molecular backbone, HP RED 2738 is specifically engineered for low-viscosity offset ink systems. Its particle size distribution and surface treatment are optimized to deliver high gloss and rapid dispersion in low-viscosity vehicles without sacrificing tinctorial strength. Unlike resinated grades designed for high-transparency packaging inks, HP RED 2738 maintains excellent flow properties and press stability in thin-film offset applications where ink viscosity must stay low for clean dot reproduction. This makes it the preferred choice when printers need the characteristic PR57:1 magenta shade with maximum gloss in heatset or sheetfed offset lines.
Key Features
- Delivers the standard PR57:1 bluish-red shade that prints precisely to the European color scale for process magenta
- Optimized for low-viscosity offset vehicles, enabling fast ink take-up and consistent film thickness on press
- High gloss finish in printed films, critical for premium packaging and commercial print where visual impact matters
- Good heat stability up to 180°C allows use in heatset offset drying ovens without color shift or degradation
- Reversible color change above 100°C (from water-of-crystallization release) means no permanent shade drift after cooling
Recommended Applications
Primary: Low-viscosity offset ink systems — heatset and sheetfed, for process magenta and standard red shades.
Secondary: Publication gravure inks where a bluish-red tone is needed and ink viscosity is tightly controlled.
Shade Selection Guide: For yellower red shades, consider other PR57:1 grades with mixed coupling components or larger particle size. HP RED 2738 sits on the bluish side of the PR57:1 range, ideal for true process magenta. For solvent-based gravure packaging inks, use HP RED 2540. For food packaging requiring warm reds, use HP RED 2539. For plastics, use HP RED 23145.
Technical Data:
| Product Information | ||||
| Chemical Type | monoazo | CAS NO. | 5281-4-9 | |
| C. I. Name | Pigment Red 57:1 | EINECS / ELINCS NO. | 226-109-5 | |
| C. I. Constitution No. | 15850:1 | Chemical Formula | C18H12N2O6SCa | |
| Technical Performance | ||||
| Full Shade | Tint | |||
| Weather Resistance | 3 | 3 | Heat Stability °C | 180°C |
| Light Fastness | 5 | 4 | ||
| Physical Properties | ||||
| Physical Form | Powder | Resistance to Acid | 4 | |
| Specific Density (g/cm3): | 1.50 ± 0.1 | Resistance to Alkali | 3 | |
| Specific Surface(㎡/g): | 50 | |||
| Oil Absorption | 80 | |||
| pH Value | 6.5 -7.5 | |||
| Volatile Matter | 1% max | |||
| Packaging | ||||
| 25kgs/bag 350kgs/Pallet | ||||
| Storage | Shelf Life | 5 years | ||
| Should be stored in cool, dry and ventilate place. | ||||
| TRANSPORTATION | ||||
| Avoid inversion, sunlight, moisture and crash. Avoid damage the package. | ||||
- Light fastness: Light fastness rating is assessed on 1 to 8 Blue Wool scale where 1 = ‘Poor’ and 8 = ‘Excellent’.
- Heat Stability : Heat stability values given indicate the maximum temperature at which the pigment can be stoved for 10 min. on the full shade and in reductions without undergoing any significant change in shade.
- Oil absorption: The oil absorption is determined on the basis of EN ISO 787-5 and given in g linseed oil per 100 gm. pigment.
- Solvent bleeding: The bleeding in solvents is tested using the powder grades and the visual rating given on 1 to 5 Grey scale
where 1 = ‘Heavy bleeding’ and 5 = ‘No bleeding”
Technical Note — The data and recommendations provided are based on HONOR Pigment’s internal testing and manufacturing experience. They are offered in good faith to assist customers in evaluating product suitability for their specific applications. As processing conditions, formulations, and end-use requirements vary widely, customers should conduct their own validation under actual use conditions. HONOR Pigment makes no warranties, express or implied, regarding the accuracy of this information or its fitness for any particular purpose. Nothing herein shall be construed as a license or recommendation to infringe any patent. HONOR Pigment’s standard terms and conditions of sale apply.oduct contains particles < 0.1 μm. Any user of this product is responsible for determining the suitability of Honor Pigments’s products for its particular application & to ensure that any proprietary rights & existing laws & legislation are observed.
Frequently Asked Questions About Pigment Red 57:1
Is PR57:1 suitable for low-viscosity offset inks?
Yes, but not all PR57:1 grades perform equally in low-viscosity systems. HP RED 2738 (CAS 5281-04-9) is specifically designed with a particle size and surface chemistry that disperses easily in low-viscosity offset vehicles, giving high gloss and stable print performance. Standard PR57:1 grades intended for high-viscosity or publication gravure inks may yield lower gloss or poor flow in these systems. Always select a grade matched to your ink viscosity range — HP RED 2738 is the optimized choice for low-viscosity offset.
Does CAS 5281-04-9 change color under heat?
Pigment Red 57:1 (CI 15850:1) undergoes a reversible color shift above 100°C, caused by the loss of its 1.5 moles of water of crystallization. The shade turns slightly yellower during heating, but returns to its original bluish-red tone upon cooling. This is a natural property of the pigment’s crystal structure, not a degradation. In heatset offset processes, HP RED 2738 withstands drying oven temperatures up to 180°C without permanent damage, so color consistency is maintained through the print run.
What makes process magenta in 4-color printing?
Process magenta in European standard 4-color printing is defined by the CIE 12-66 scale, and Pigment Red 57:1 (PR57:1) is the dominant pigment used to achieve it. Its naturally bluish-red shade falls almost exactly at the target magenta position, which is why it accounts for the highest volume of any organic red globally. HP RED 2738 delivers that exact process magenta shade with high gloss in low-viscosity offset systems, making it a reliable choice for commercial and packaging printers following European color standards.
Storage: can alkaline ink cause viscosity issues with PR57:1?
Yes, in alkaline ink systems (such as some water-based or alkaline-containing offset inks), PR57:1 can undergo a calcium-to-sodium ion exchange, leading to a rise in viscosity over time. This is a known behavior of the 15850:1 pigment class. HP RED 2738 is primarily formulated for low-viscosity offset systems that are typically neutral to slightly acidic, minimizing this risk. For alkaline ink applications, consult your ink formulator to verify compatibility before storage.
Difference between resinated and non-resinated PR57:1 grades?
Resinated PR57:1 grades contain calcium resinate, which improves transparency and is preferred for overprint varnishes and high-transparency packaging inks. Non-resinated grades like HP RED 2738 offer higher opacity and better gloss in thin films, making them ideal for low-viscosity offset where opacity and print brilliance are needed. HP RED 2738’s non-resinated surface treatment also ensures faster dispersion and better flow in low-viscosity vehicles, a key advantage for high-speed offset presses.