HP ORANGE 3548 — PO34 Diarylide Orange for Solvent-Based Printing Inks

Technical Information

What Is PO34

Pigment Orange 34 (CAS 15793-73-4, C.I. 21115) is a diarylide pyrazolone organic pigment with molecular formula C₃₄H₂₈Cl₂N₈O₂ and molecular weight 651.55 g/mol. Structurally derived from 3,3′-dichlorobenzidine coupled to two tolyl-methyl-pyrazolone units, it produces a vibrant yellowish-orange color through its extended conjugated bisazo system. As a diarylide pigment, PO34 inherently offers stronger solvent resistance and higher tinting strength than comparable monoazo oranges such as Pigment Orange 13. The HP ORANGE 3548 grade delivers this chemistry in a form optimized for industrial ink and coating applications where reliable color development in aggressive solvent systems is essential.

Why Choose HP ORANGE 3548

HP ORANGE 3548 sits at the performance sweet spot of the PO34 family — a balanced yellowish-orange shade designed for solvent-based gravure and flexographic printing inks where dispersion stability and color reproducibility matter most. Compared to HP ORANGE 3136, the economy workhorse grade that dominates shipment volumes, HP ORANGE 3548 offers tighter shade control and more consistent batch-to-batch tinting strength, making it the preferred choice when press operators cannot tolerate ΔE drift above 1.5. Against HP ORANGE 3631, which trades some chroma for improved outdoor weatherability, HP ORANGE 3548 delivers higher color saturation — critical for packaging prints where visual impact drives shelf appeal. The diarylide backbone gives HP ORANGE 3548 natural resistance to solvent attack in toluene- and MEK-based ink formulations, eliminating the re-dissolution issues that plague monoazo alternatives. For formulators targeting the mid-range price-performance window between budget generic PO34 and premium benzimidazolone oranges (PO64, PO73), this grade provides the most cost-effective route to production-grade solvent ink color.

Key Features

• Bisazo diarylide structure — the dual azo-linkage architecture means the pigment resists breakdown in aggressive solvent systems where monoazo oranges dissolve or shift shade on-press.
• Tight batch-to-batch shade control — HP ORANGE 3548 is manufactured with consistent particle size distribution, which translates to predictable tinting strength across production runs without reformulation adjustments.
• High tinting efficiency in thin-film applications — this grade develops full color strength at low pigment loading, reducing raw material consumption in gravure and flexo ink formulations.
• Broad system compatibility — performs reliably across solvent-based, water-based, and offset ink vehicles, giving formulators a single-grade solution for multiple product lines.
• Cost-effective alternative to premium oranges — delivers 90%+ of the performance of benzimidazolone-class oranges at 40-60% of the cost, making it the pragmatic choice for high-volume packaging and publication printing.

Recommended Applications

Primary: Solvent-based gravure printing inks (packaging, publication), flexographic inks for films and foils, offset lithographic inks for commercial printing.

Secondary: Water-based flexo inks, industrial coatings, textile printing pastes, flexible PVC coloration.

Shade Selection Guide: For economy-grade general-purpose orange, consider HP ORANGE 3136. For outdoor-durable coatings requiring superior lightfastness, evaluate HP ORANGE 3631. For high-end automotive or industrial finishes where maximum weatherability is mandatory, explore benzimidazolone alternatives such as Pigment Orange 64 (HP ORANGE 3364) or Pigment Orange 73 (HP ORANGE 3642).

Frequently Asked Questions About PO34

Pigment Orange 34 vs Pigment Orange 13: which performs better in solvent inks?

Both share the diarylide pyrazolone backbone, but PO34 (CAS 15793-73-4, C.I. 21115) carries tolyl groups on the pyrazolone ring while PO13 uses unsubstituted phenyl groups. This structural difference gives PO34 slightly higher tinting strength and better solvent resistance — in toluene-based gravure inks, HP ORANGE 3548 maintains stable dispersion where PO13 may show flocculation after extended milling. For offset and water-based systems where solvent attack is minimal, PO13 remains a cost-effective alternative, but for high-speed gravure runs on film substrates, HP ORANGE 3548 consistently outperforms.

Can C.I. 21115 be used in food-contact packaging applications?

Pigment Orange 34 is an insoluble organic pigment, which means it does not migrate in the same way as soluble dyes. However, food-contact compliance depends on the specific regulatory framework: EU Regulation 10/2011 for plastics, FDA 21 CFR for US applications, and Swiss Ordinance 817.023.21 for printing inks on food packaging. HP ORANGE 3548 can be formulated into compliant systems when the ink manufacturer verifies migration limits through extraction testing. Always request the specific compliance documentation package — including heavy metal test reports per EN71-3 and migration simulation data — before specifying any pigment for food-contact ink applications.

How does the lightfastness of diarylide orange PO34 compare to benzimidazolone grades?

Diarylide pigments like PO34 (C.I. 21115) typically achieve Blue Wool scale ratings of 5-6 in full shade, which is adequate for indoor packaging, publication printing, and most industrial coating applications. Benzimidazolone oranges such as PO64 or PO73 reach ratings of 7-8, making them necessary for outdoor signage, automotive coatings, and architectural paints exposed to direct UV. HP ORANGE 3548 occupies the practical middle ground — sufficient weatherability for indoor commercial use at a fraction of the cost of high-performance alternatives. For any application where the printed surface will face prolonged outdoor UV exposure, upgrade to HP ORANGE 3631 within the same CI family for improved durability.

What ink systems work best with HP ORANGE 3548?

HP ORANGE 3548 was engineered for solvent-based gravure and flexographic inks, where its diarylide structure provides natural resistance to toluene, MEK, and ethyl acetate — the most aggressive solvents in high-speed printing. It disperses well in polyamide- and polyurethane-based binder systems commonly used for film and foil substrates. The grade also performs reliably in offset ink formulations and water-based flexo inks when properly predispersed. For NC (nitrocellulose) and acrylic binder systems, HP ORANGE 3548 shows excellent compatibility without the compatibility issues that affect some monoazo oranges. Formulators targeting multiple ink types from a single pigment inventory find this versatility reduces SKU complexity.

Why do batch color variations occur with Pigment Orange 34, and how is HP ORANGE 3548 different?

Color inconsistency in diarylide pigments typically stems from variations in coupling reaction conditions — temperature, pH, and diazo component ratios during synthesis affect crystal size distribution and therefore shade. Most generic PO34 suppliers produce batches with ΔE tolerances of 2-3 units, which causes visible press drift and forces ink manufacturers to reformulate each batch. HP ORANGE 3548 is produced with controlled coupling parameters and post-synthesis conditioning that narrows the ΔE window to under 1.5 between batches. Each production lot ships with a QC report documenting shade coordinates (L*a*b*), tinting strength ratio, and dispersion fineness — giving formulators the data to predict press behavior without trial-and-error adjustments.