Printing Ink Pigments FAQ
Answers to the most common pigment questions from ink formulators
Frequently Asked Questions
What pigment particle size is best for offset printing ink?
Offset inks require D50 0.05-0.5 µm with Hegman grind 6-7 (ASTM D1210). Finer than 0.05µm causes excessive viscosity and poor flow; coarser than 0.5µm reduces gloss, transparency, and color strength. PR57:1 (rubine) and PB15:3 are typically milled to Hegman 7+. PY12/13 are used at Hegman 6-7 for process yellow. Triple-roll milling is the standard for achieving this dispersion quality in paste inks.
Which yellow pigment has the best transparency for process printing?
PY12 and PY13 (diarylide yellows) are the standard process yellows for offset and gravure — they provide excellent transparency (critical for 4-color process), clean greenish-yellow shade, and high color strength at 10-15% loading. Limitation: lightfastness only grade 4-5 (full tone) and 3-4 (tint), unsuitable for long-term outdoor exposure. PY150 (benzimidazolone) offers better lightfastness (grade 7-8) but at 4-6x the cost and with a reddish shade that shifts the process color gamut.
Why does my flexo ink keep foaming during printing?
Foaming in flexo inks is caused by surfactant-stabilized air bubbles from pigment dispersants. Root causes: excess dispersant (above pigment demand), wrong dispersant type (high-foaming anionic types), or mechanical air entrainment from high-speed mixing. Solutions: reduce dispersant to calculated demand (mg dispersant per m² pigment surface area), switch to low-foaming dispersants (non-ionic or polymeric types), add defoamer (0.1-0.3% silicone-free for water-based), de-aerate ink before use (vacuum or slow stirring).
What’s the best blue pigment for all printing processes?
PB15:3 (beta copper phthalocyanine) is the universal blue — it works across offset, flexo, gravure, screen, and inkjet. Key properties: heat stability 300°C, lightfastness grade 8, acid/alkali/solvent resistance grade 5, no migration. It requires bead milling for full dispersion (primary particle 50-100nm), but once dispersed is stable indefinitely. Variations: PB15:1 (alpha, redder shade, less stable), PB15:4 (beta, surface-treated for better dispersion in water-based).
How to prevent pigment settling in low-viscosity gravure inks?
Gravure inks operate at very low viscosity (15-25 seconds Zahn Cup #2, ~20-50 cP), making pigment settling a critical issue. Prevention: use pigments with D50 < 0.1µm and narrow distribution (D90 < 0.3µm), add anti-settling agents (BYK-410 at 0.5-2%, microgel technology), increase pigment concentration in the dispersion paste (40-50% vs typical 30%), use resin-based dispersants that provide steric stabilization, ensure zeta potential > ±35mV for electrostatic repulsion.
Can I use offset ink pigments for UV-curable inks?
Most conventional pigments transfer to UV systems, but verify: photo-initiator compatibility — some pigments (particularly carbon black PBk7) absorb UV wavelengths needed for curing, slowing cure speed; acid resistance for cationic UV systems — PR57:1 and other lake pigments may release metal ions that interfere with cationic polymerization; dispersion stability — UV monomers have lower viscosity than offset vehicles, which may cause pigment re-agglomeration. PB15:3, PR254, PY150, and PG7 perform excellently in UV systems.
Which red pigment gives the brightest rubine shade for offset?
PR57:1 (Lithol Rubine, CI 15850:1) is the standard magenta for 4-color process offset printing — bluish-red shade, high color strength, excellent transparency, and bright clean mass tone. Typical loading: 15-18% in offset ink. Tradeoffs: lightfastness only grade 5 (full tone) and 3-4 (tint) — unsuitable for outdoor posters or packaging, heat stability limited to 180°C (cannot use in heat-set above 150°C), migration risk in food packaging (not FDA-compliant). For higher performance, PR122 (quinacridone magenta) offers lightfastness 7-8 but at 3-5x cost.
How to achieve high color strength with low pigment loading?
Color strength is inversely proportional to particle size — smaller particles (higher surface area) = stronger color per gram. Strategy: optimize dispersion to reach primary particle size (use bead mill not dissolver for hard pigments like PB15:3), select pigments with inherently high specific surface area (PB15:3 SSA 40-80 m²/g, PR254 SSA 30-60 m²/g), use pigment synergists (copper phthalocyanine sulfonic acid derivatives for PB15:3 at 2-5% of pigment weight), avoid over-grinding (amorphization reduces crystallinity and color strength).
Why is my ink scratching off the substrate?
Scratching indicates insufficient adhesion, not necessarily a pigment problem. Causes: wrong binder for substrate (e.g., nitrocellulose on polypropylene without primer), pigment loading too high — pigment acts as a “filler” interrupting binder film continuity (keep PVC below CPVC), under-cured UV or oxidation-dried system (check dwell time and dryer temperature), pigment surface treatment interfering with binder crosslinking. Test: increase binder:pigment ratio from 3:1 to 5:1 and recheck scratch resistance.
Which pigments resist heat-set web offset drying at 150°C?
150°C is a moderate temperature — most organic pigments survive: PY12/13 (diarylide, stable to 180°C), PR57:1 (Lithol Rubine, borderline at 180°C — may darken slightly), PB15:3 (stable to 300°C), PBk7 (carbon black, stable). Best practice: request a heat stability test at 160°C for 10 minutes. Avoid pigments with heat stability below 150°C: some specialty yellows (PY1 stable to 140°C only), some fluorescent pigments (degrade at 120°C).
Quick Reference Table
| Ink Process | Typical CIs | Key Requirement | Common Issue |
|---|---|---|---|
| Offset | PY12, PY13, PR57:1, PB15:3 | Transparency, water balance | Emulsification, tinting |
| Flexo Water-based | PY14, PY83, PR48:2, PB15:3 | Low viscosity, fast drying | Foaming, pH drift |
| Flexo Solvent | PY12, PR57:1, PB15:3 | Solvent release, adhesion | Solvent retention |
| Gravure | PY12, PR57:1, PB15:3, PG7 | Ultra-fine particle <0.1µm | Settling, streaking |
| Screen | PY83, PR170, PB15:3 | High loading, opacity | Mesh clogging |
| UV Inkjet | PR122, PB15:3, PY150, PBk7 | <0.2µm, low viscosity | Nozzle clogging |
Pro Tip
When transitioning from solvent-based to water-based ink systems, remember that the same pigment may require a completely different dispersant package. Solvent-based dispersants are often incompatible with water, causing immediate flocculation.
Need Help Selecting?
Our technical team responds within 24 hours.