Colorants in Polymer System

While color is ubiquitous in our world, the science behind color is still largely incomprehensible even amongst the industrial practitioners. Today we will delve deeper into the applications of colorants in two major system in polymer processing industries, liquid printing ink and masterbatch.

We look at it from three general factors, colorants (mostly pigments) selection, loading and dispersion in their respective systems.

First, The Pigment Type Selection

Masterbatch Selection is driven by:

• Heat stability — must survive high processing temperatures (e.g., 260–300°C for nylon or engineering plastics).

• Resin compatibility — pigment must not plasticize, degrade, or react with the host polymer.

• Migration/bleed resistance — especially critical for food contact and film applications.

• Light and weather fastness — especially for outdoor applications (agricultural film, construction pipe, automotive).

• FDA/food compliance — subset of pigments approved depending on contact type.

Liquid printing ink selection is driven by:

• Solubility vs. dispersion type — some colorants in gravure are actually dyes (fully soluble), not pigments. Dyes give better transparency and very low viscosity impact but have lower lightfastness. Pigments give better durability but require proper dispersion.

• Transparency vs. opacity — gravure on flexible packaging often requires transparent inks for process color (CMYK) printing, meaning small particle size and low scattering coefficient pigments are preferred.

• Solvent resistance — ink must not bleed or re-dissolve during lamination solvent exposure or overprint varnish application.

• Particle size — gravure cell depth is 15–40 microns; any pigment aggregate larger than ~5 microns risks scratching the doctor blade or clogging cells.

• Chemical resistance — for packaging of food, chemical, or detergent products, pigment must resist contact with the contents.

Masterbatch prioritizes thermal and long-term durability in the plastic matrix; liquid ink prioritizes particle fineness, transparency, and solvent system compatibility for thin-film liquid application.

The second is the pigment loading:

Masterbatch Loading is intentionally high — typically 20–50% pigment by weight (sometimes up to 70% for Titanium Oxide). The whole point of a masterbatch is to be a concentrated intermediate that gets let-down into natural resin at a ratio of 1–5%. This high loading is achievable because the carrier resin is chosen to be compatible and processable under heat and shear in an extruder.

Liquid Ink Loading is much lower — typically 5–20% pigment by weight in the final ink. The constraints here are ink viscosity (must flow and transfer from engraved cells), drying speed, and film thickness on substrate (typically 1–4 microns dry). If you load too much pigment, the ink viscosity spikes and you get cell blocking, streaking, and uneven transfer. So the system is solvent-dominated, not pigment-dominated.

Masterbatch is a concentrated solid designed for dilution; gravure ink is a dilute liquid designed for direct application.

and lastly, the pigment dispersion in the polymer system:

Masterbatch Dispersion is achieved through melt compounding — extrusion under heat (150–280°C depending on resin) and intense mechanical shear. The goal is to break agglomerates down to primary particle size and encapsulate them in carrier resin. Wetting agents and dispersants are used to lower pigment surface energy and aid encapsulation. Dispersion quality is assessed by filter pressure test, specks under microscopy, or tinctorial strength comparison.

Liquid ink Dispersion is achieved through liquid phase milling — ball mills, bead mills, or three-roll mills in a solvent + binder system. The mechanism is wet grinding, where pigment agglomerates are broken by media collision in a low-viscosity liquid. Dispersion agents adsorb onto pigment surfaces to prevent re-flocculation. Fineness of grind is assessed by Hegman gauge (target typically 3–5 for gravure). The dispersion must also remain stable during ink storage without settling or flocculation.

Masterbatch uses thermal-mechanical dispersion; gravure uses wet mechanical dispersion. The failure modes are completely different — masterbatch fails through agglomerate survival causing specks and filter blockage; gravure fails through flocculation causing color drift, gloss reduction, and cell blocking.

Have a specific challenge in your production process?

All technical consultations and inquiries are treated as strictly confidential. Production details, formulation data, and business information you share are used only to serve your specific needs — never disclosed to third parties or supply chain partners without your consent. Reach out at contact@mdm-technology.com