Updated: 2026

Types of Paint Pigments and Their Role in Coating Performance

What pigments contribute to a coating

A pigment changes how a coating interacts with light and, in some formulations, how it conducts heat or electricity or protects a substrate. Unlike a soluble dye, a pigment remains a dispersed particulate phase. The binder surrounds those particles and forms the continuous film that holds them in place.

This distinction matters when a white coating hides poorly, a dark coating loses gloss or a heavily filled film becomes weak. The cause may sit in pigment selection, dispersion, film thickness or binder balance. A resin and binder selection guide helps explain the film-forming side of that balance; the pigment supplies a different part of the formulation.

Four useful ways to describe paint pigments

Inorganic pigments

Inorganic pigments include titanium dioxide, iron oxides and carbon black. Titanium dioxide is widely used for white pigmentation and hiding power; iron oxides provide red, yellow, brown and black shades; carbon black provides black coloration. Their behavior depends on the particular grade, particle characteristics and surface treatment, rather than the family name alone.

For example, selecting a titanium dioxide grade is only the start of obtaining opacity. Dispersion, particle distribution in the film and dry film thickness also affect hiding. Similarly, a carbon black that produces a strong black shade may impose a demanding dispersion task. A pigment label cannot establish the gloss or durability of the finished coating.

Organic pigments

Organic pigments include azo, phthalocyanine and quinacridone families. They offer a wide range of colors, but tint strength, transparency, solvent resistance, heat stability and weathering behavior vary by chemistry and grade. "Organic" does not mean biodegradable, and it does not establish suitability for exterior service.

A formulator should assess the supplied pigment in the actual resin, carrier and cure process. A color that looks correct in a pigment paste may shift after letdown, hardener addition or baking. Migration or bleeding concerns also need a system-specific assessment rather than a broad organic-versus-inorganic rule.

Extender and filler pigments

Calcium carbonate, talc, kaolin and barium sulfate are common examples. These materials can adjust the solids balance, rheology, texture and film structure. Their contribution depends on particle shape, size, surface chemistry and the refractive-index relationship with the binder.

An extender is therefore more than a cheaper replacement for a color pigment. Substituting equal weights of two fillers can change their volume in the dry film because their densities differ. That change may alter binder demand and film properties even when the batch weight stays constant.

Functional pigments

Functional pigments are selected for an additional task, such as corrosion inhibition, electrical conductivity or infrared reflection. Zinc phosphate is an example used in anticorrosive formulations. Conductive and reflective systems require suitable pigment chemistry and a film structure that supports the intended function.

This is a functional description, not a separate chemical family: a functional pigment may also be inorganic. Its presence does not by itself prove corrosion protection, conductivity or thermal performance. Those outcomes belong to the tested coating system.

Dispersion comes before a crosslinker diagnosis

Dispersing a pigment involves wetting the particles, breaking down agglomerates and stabilizing the resulting dispersion against reaggregation. Resin, dispersant and carrier must work together. Increasing mixing time cannot compensate for every wetting or stabilization problem.

Compare the pigment grind before and after letdown. Then compare the mixture before and after hardener addition, where applicable. A change at one of these stages helps locate the problem: poor initial dispersion needs a different investigation from a stable grind that flocculates when the hardener is introduced.

A fineness-of-grind gauge can reveal coarse particles or agglomerates, but it does not describe the full particle-size distribution. Color development, gloss, viscosity drift and storage behavior provide additional evidence. Pigment oil absorption, measured by a method such as ASTM D281, characterizes pigment vehicle demand in a paste under that method; it is not a polyisocyanate compatibility test.

Pigment loading: weight percentage is not volume balance

Pigment volume concentration (PVC) expresses the volume of pigments and extenders as a proportion of the total nonvolatile pigment-plus-binder volume. It differs from pigment weight percentage. Carrier liquids that evaporate are excluded; the nonvolatile binder contribution must be counted consistently for the cured system.

PVC (%) = pigment and extender volume ÷ (pigment and extender volume + nonvolatile binder volume) × 100.

As loading increases, more particle surface must be wetted and the binder has less volume available between particles. Critical pigment volume concentration (CPVC) marks the point where the binder just fills the voids between the packed pigment particles. Film porosity and related properties can change substantially around that point. There is no universal CPVC value for all pigment blends or resins; published research on pigment volume concentration provides the technical background.

The useful question is how a loading change behaves in this formulation. When increasing filler reduces gloss or film cohesion, compare volume balance, dispersion and cure together. Adding more hardener is not a direct substitute for missing binder volume.

How pigments, resins and PU crosslinkers interact

In a conventional two-component polyurethane coating, isocyanate groups react with hydroxyl groups in the binder to form a polyurethane network. The chemistry of the isocyanate–hydroxyl reaction explains the crosslinker's role. Pigment mass does not replace the binder's hydroxyl content when calculating the reactive balance.

However, the pigment package is not chemically invisible. Paste resins, dispersants, pigment surface treatments and moisture can change mixing behavior or introduce reactive components. In solventborne systems, unintended water can react with isocyanate and produce carbon dioxide, contributing to film defects. Waterborne polyisocyanate systems deliberately contain water and require an appropriate dispersible crosslinker and controlled mixing; they cannot be treated as solventborne formulations with accidental moisture.

Review the complete binder package, including any resin carried by a pigment paste. Choose the mixing sequence and point of hardener addition for the formulation and supplier instructions. Do not assume a reactive hardener belongs in the initial pigment-grinding stage. Pot life, application viscosity and cured-film properties must be checked after the intended mixing process.

Where Dongsen product families enter the evaluation

Dongsen manufactures and supplies polyisocyanate hardeners and crosslinkers for professional formulators. The starting point is the binder chemistry, medium and cure process. Pigment type adds constraints to that choice; it does not identify a universally suitable hardener.

Aromatic polyisocyanates are a family to assess in compatible PU systems where the intended appearance and exposure permit aromatic chemistry. Yellowing-sensitive light shades require particular care. A pigment's own stability cannot establish the binder's light stability.

Aliphatic polyisocyanates are a family direction when light stability is an important binder requirement. This does not guarantee the weathering, color retention or gloss retention of the full pigmented coating. Those depend on the complete formulation and exposure test.

Solvent-based blocked polyisocyanates belong in a review of suitable bake-cured systems. Evaluate resin reactivity, actual coating temperature and dwell time. A deblocking range alone is not proof that the film has reached full cure.

Waterbased polyisocyanates provide a category to investigate for compatible waterborne binder systems. Confirm dispersion stability, mixing, usable time and film formation with the actual pigment package. "Waterbased" describes the formulation medium, not a guarantee of color stability or compatibility.

No individual grade is designated here as a best fit. A grade-specific recommendation needs the current TDS, formulation details and relevant sample evidence. Dongsen does not supply standalone pigments or finished paints.

For a product-family review, share your resin, pigment package and cure conditions.

What formulators should compare on test panels

A panel comparison is most useful when the pigment package, binder, dry film thickness, substrate and cure conditions are recorded. If the hardener is the variable under review, keep other factors as consistent as practicable and calculate each candidate's addition from the relevant reactive data. Equal hardener weights do not necessarily give equal reactive ratios.

Separate application behavior from cured-film performance. Record mixing stability and usable time first, then assess hiding, color, gloss, adhesion, hardness or flexibility and the resistance properties relevant to the intended service. Agree on conditioning and methods before comparing results. For example, ASTM D523 covers specular gloss; a gloss measurement does not establish adhesion or cure completeness.

If pigment chemistry, paste composition or cure conditions are unknown, that is a reason to gather information before selecting a grade. A useful technical inquiry identifies the observed problem and the comparison already made, rather than requesting the "best hardener for pigments" without a defined coating system.

Frequently asked questions

Are extender pigments the same as color pigments?

They serve different primary roles, although classifications can overlap. Extenders usually adjust formulation balance or film structure. They do not automatically replace the hiding or tinting contribution of a color pigment.

Can more PU hardener improve pigment dispersion?

Not as a general remedy. Hardener addition can change a mixture's behavior, but dispersion requires a suitable wetting and stabilization package. Locate when the defect appears and check both dispersion and reactive balance.

Does a light-stable pigment make the complete coating non-yellowing?

No. The binder, crosslinker, additives, cure and exposure also contribute to color change. Evaluate the complete coating under the intended conditions.

How should a pigment paste be included in PU formulation calculations?

Count its pigment and nonvolatile binder contributions consistently. Where the paste contains a reactive resin or other reactive component, use its relevant data in the binder and crosslinking calculation. Do not calculate hardener addition from pigment weight alone.

Does Dongsen supply paint pigments?

No. Dongsen's role is upstream polyisocyanate hardener and crosslinker supply. For a pigmented coating inquiry, provide the resin, pigment package and cure conditions so a suitable crosslinker direction can be reviewed.

Key takeaways

• Pigment chemistry and pigment function describe different, overlapping aspects of a material.
• Dispersion, volume loading and binder balance should be checked before attributing a film defect to the hardener.
• Crosslinker selection belongs to a defined resin and cure system; a controlled panel comparison determines whether a candidate suits the actual pigmented formulation.