Pigments for Inks
Copper phthalocyanine pigments form the foundation of blue and green colour space across the entire printing ink industry, from conventional offset and flexographic processes to modern digital and UV-curable systems. Their outstanding tinctorial strength, transparency, and compatibility with virtually all ink vehicle chemistries — including mineral-oil, vegetable-oil, water-based, solvent-based, and radiation-curable binders — make them the default choice for process cyan and a wide range of spot colours. CPC blues deliver the clean, bright masstone and excellent rheological behaviour that pressrooms demand at commercial print speeds, while PG 7 provides the only single-pigment green that combines full gamut saturation with the heat and solvent resistance needed for laminated packaging. Formulators can fine-tune shade, flocculation resistance, and flow properties by selecting the appropriate crystal modification and surface treatment for each ink platform.
Key Performance Requirements
Dispersibility
Rapid and complete wetting-out in the ink vehicle is critical to achieving target colour strength in a single mill pass and avoiding costly regrinding. The pigment must break down to primary particle size quickly under the shear conditions of a three-roll mill, bead mill, or high-speed disperser, and must not re-agglomerate during storage or on press.
Transparency / opacity control
Process CMYK printing relies on the subtractive colour model where cyan ink must be highly transparent to allow accurate overprint trapping with magenta and yellow. For spot-colour and metallic ink applications, however, controlled opacity may be desired. Crystal form, particle size distribution, and surface treatment all influence the transparency–opacity balance of the final ink film.
Rheological stability
Ink viscosity, yield value, and thixotropic recovery must remain within specification from the mill base through the press run, even under the thermal and mechanical stress of high-speed printing. Pigment flocculation in the ink causes viscosity drift, loss of gloss, and shift in colour strength. Non-flocculating grades with engineered surface chemistry are essential for demanding sheetfed and UV applications.
Lightfastness
Printed materials such as packaging, labels, and point-of-sale displays may be exposed to prolonged natural or artificial light. CPC blues inherently offer blue-wool scale ratings of 7–8 in full shade, but lightfastness can decrease significantly in tints with TiO₂ or extender pigments. Grade selection and pigment loading must be matched to the end-use exposure requirement.
Recommended Grades
| Grade | Shade | Rationale |
|---|---|---|
| PB 15:3 | Greenish blue | The industry workhorse for process cyan in heatset, coldset, and sheetfed offset inks. Its beta crystal form delivers a clean greenish-blue shade with excellent transparency, high tinctorial strength, and reliable rheological behaviour across a broad range of oil- and resin-based vehicles. |
| PB 15:4 | Greenish blue | Engineered non-flocculating beta form for high-end sheetfed, UV-curable, and packaging gravure inks where maximum gloss retention, colour consistency, and resistance to viscosity drift are paramount. The stabilised surface treatment prevents reagglomeration even in aggressive solvent systems. |
| PB 15:0 | Reddish blue | Untreated alpha crystal form providing a reddish blue shade that is well suited to water-based flexographic and gravure inks. Its natural wetting behaviour in aqueous systems simplifies dispersion, and the warmer hue is preferred for certain spot-colour and corrugated-board applications. |
| PB 15:1 | Reddish blue | Stabilised alpha form with improved solvent resistance, designed for solvent-based flexographic and publication gravure inks. The aluminium-chloride stabilisation prevents undesirable crystal phase change during ink manufacture and storage, ensuring consistent shade and strength throughout the product's shelf life. |
| PG 7 | Bluish green | The standard chlorinated copper phthalocyanine green pigment used across all ink platforms. Its fully chlorinated ring structure delivers a bright, yellowish-green hue with outstanding fastness to light, heat, and solvents, making it the first choice for both process colour and spot-green formulations. |
Technical Considerations
- Process CMYK cyan is typically formulated with PB 15:3 at pigment concentrations of 12–18 % in the finished ink, tuned to hit ISO 2846 / ISO 12647 spectral targets. Shade adjustments are made by blending with small amounts of PB 15:0 (warmer) or PG 7 (cleaner), and printers expect batch-to-batch delta E of less than 1.0.
- Water-based flexographic inks require pigments that wet out readily in alkaline resin solutions without excessive foam or viscosity build. PB 15:0 and specially treated PB 15:3 grades with hydrophilic surface chemistry are preferred because they disperse quickly at the moderate shear available in Cowles-type dissolvers common in flexo plants.
- UV and EB curable inks use photoinitiators that absorb in the 200–400 nm range; the pigment must not screen the initiator from the UV source or cure will be incomplete. PB 15:3 and PB 15:4 have relatively low UV absorption in the curing window, but at high pigment loadings or in thick film applications the cure energy must be increased or the ink chemistry adjusted.
- For food-contact packaging inks, the pigment must comply with Swiss Ordinance SR 817.023.21, Nestlé Guidance, and EuPIA exclusion-list requirements. CPC pigments are generally positive-listed, but each grade must be supported by a statement of composition confirming the absence of PCBs, soluble heavy metals above threshold, and specified aromatic amines.
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