Pigment Wetting & Dispersion

An Introduction to Pigments

Pigments are solid, insoluble powders that are used to provide color to various materials including paints, coatings, and inks.  They are available commercially in a wide range of colors and chemistries.  While the options for pigments can seem endless, all of them have something in common.  They must be properly dispersed in order to provide optimal performance and appearance in inks, paints, and coatings.

What is Pigment Dispersion?

Pigment dispersion is the process of suspending insoluble pigments in a liquid medium, typically water or organic solvent, so that they can be used in inks paints and coatings.  Traditionally, pigment dispersion is comprised of three main steps; wetting, deagglomeration, and stabilization.  These three steps are outlined in further detail below.

Pigment Wetting

When solid pigments are first added to the liquid medium they are agglomerated and air is entrapped in the surface of the pigment agglomeration.  In order for proper wetting to occur the air entrapped in the pigment needs to be replaced with the liquid medium.  The use of a wetting aid speeds up the process and ensures complete wetting of the pigment.

Deagglomeration

Once complete wetting of the pigment particles is achieved, the large agglomerations of pigment must be broken up into smaller particles.  This is commonly achieved through mechanical shear via the grinding mill.  Reduction of the surface tension in the liquid medium allows for easier and faster deagglomeration.

Stabilization

The deagglomerated pigment particles now must be stabilized or else they will agglomerate and fall out of suspension.  In this step, dispersing agents adsorb onto the pigment particles and keep them separated.  Stabilization of pigments in suspension can be classiified as either electrostatic or steric.

Electrostatic Dispersants

Electrostatic dispersants carry an  ionic charge.  They interact with the surface of the pigment particles to produce like charged surfaces, typically cationic.  These like charges on the surface of the pigment particles repel each other and keep the pigment in stable suspension.  Changes in pH and addition of ionic material can destabilize particles suspended with electrostatic dispersants. 

Steric Dispersants

Steric dispersants consist of molecules with an anchoring head group that is attracted to the pigment particles and tails that are attracted to the liquid phase of the dispersion.  The head groups adsorb onto the surface of the pigments and the tails orient themselves outward from the surface.  The protruding tails keep the pigment particles separated and suspended.  Steric stabilization is incredibly stable at high salt concentrations and over a wide pH range.

Why are Pigment Wetting & Dispersion Aids Important?

In many cases, the pigment is the most expensive ingredient in a ink, paint, or coating formulation.  Optimization of the wetting and dispersion of pigments ensures optimal appearance and physical properties if the formulation while using the least amount of pigment possible.  Selecting the right wetting and dispersing aid for your formulation is critical for producing high quality inks, paints, and coatings while keeping production costs down.

Surfactants as Wetting and Dispersing Aids

Surfactants, or surface active agents, are molecules that reduce the surface tension at the interface between two substances.  In the case of wetting and dispersing pigments, a reduction of surface tension between the solid pigment particles and the liquid carrier allows for faster and more efficient wetting and deagglomeration.  Additionally, surfactants can adsorb onto the surface of pigment particles and provide steric stabilization of the dispersion.  Commercially, there are many types of surfactants that are used today as wetting aids and dispersing agents in inks, paints, and coatings.  These surfactants are compared below based on performance characteristics.
Selection of the appropriate surfactant for pigment wetting and dispersion should be based on the liquid carrier (water or organic solvent), the pigment, and the end use application.  While there is no "one size fits all" solution, alcohol ethoxylates are generally accepted as one of the best all around choices for pigment wetting and dispersion.

NOVELUTION - Alcohol Ethoxylate Wetting Aids

For far too long there have been gaps for wetting aids and dispersants between performance, sustainability, and economy.  NOVELUTION is the solution to that problem.  NOVELUTION Nonionic Surfactants are a family of branched alcohol ethoxylates designed by Sasol to meet the growing needs of  ink, paint, and coating manufacturers.  These surfactants are excellent wetting aids and stabilizers that are alkyl phenol free.  When used as a wetting aid, NOVELUTION Nonionic Surfactants provide faster more complete wetting in turn provides inks, paints, and coatings with improved color strength, reduced pigment flooding, and increased freeze thaw stability.

Commercially Available NOVELUTION Grades

The NOVELUTION 3 series ethoxylates listed below are based on 100% branched tridecanol and are available in a wide range of grades varying in physical form, HLB, and cloud point.  This line of ethoxylates is designed to provide optimal pigment wetting for inks, paints, and coatings while producing minimal foam.
Contact us today to speak with one of our product specialists to find the NOVELUTION grade that is right for your next ink, paint, or coating application.

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