A colorant is a concentrated dispersion of colour pigment that can add colour to a base paint. An immense variety of colours can be obtained when colorants, each containing one specific colour pigment, are combined. A line of foolproof colorants should comply with several requirements to assure that a certain mixing always gives the same colour.
First, each batch of colorant must have the same colour tone and colour strength. Secondly, the colour tone and colour strength of each of the individual colorants must remain constant, even when the materials are stored for a long time. A clever choice of raw materials assures a robust line of colorants.
Waterbased colorant composition
A colorant used for waterbased paints is most often a liquid, waterbased, concentrated dispersion of one specific colour pigment. Waterbased colorant developers strive to create products that are compatible with as many different waterbased paint systems as possible. These systems can be based on, for example, acrylic dispersion, polyurethane dispersion or alkyd emulsion. Colorants should contain the least possible different components to assure a broad compatibility.
Resin in a colorant might create compatibility problems with the binder system of the base paint, and therefore should be excluded. The desired colorants are often referred to as Resin-Free Pigment Concentrates (RFPC) or Binder-Free Pigment Concentrates (BFPC).
|Core Additives||Dispersant||Prevent flocculation|
|Rheology additive||Prevent sedimentation of high density pigments|
|Other additives||Wetting agent||Lower surface tension to assure wetting of hydrophobic pigments|
|Humectant||Slow down evaporation of water|
General composition of a waterbased colorant.
A modern waterbased colorant is zero-VOC, implying that the product is free of organic solvents. A rheology additive is needed to prevent sedimentation of the pigment particles during storage. Use of a suitable rheology additive is especially important for colorants based on inorganic pigments, which have a high density.
Aerosil® 200 is a fumed silica that is often used in waterbased colorants to prevent sedimentation. As colorants become more and more environmentally friendly, they are more interesting for micro-organisms like bacteria, fungi and algae. Waterbased colorants must contain an effective preservative for that reason.
Preferably wetting agents are excluded from colorants as wetting agents can give problems like foam sensitivity. No wetting agent is needed when hydrophilic pigments are used. Many waterbased colorants contain a humectant to prevent drying-in, caused by the evaporation of water.
A key raw material in colorants is the dispersant, assuring stabilisation of the separated solid particles against flocculation. In a foolproof colorant, the pigment particles repel each other by both electrostatic repulsion1 and steric stabilisation2. It is said that such a dispersant gives electrosteric stabilisation.
This dual-stabilisation mechanism is needed to assure that the colorants are miscible with as many different waterbased paint systems as possible.
Preferably, a system developer uses the least possible different dispersants for the whole range of colour pigments in a colorant line. This implies that the dispersant molecules must adsorb strongly at the surface of a wide variety of different colour pigments.
A good dispersant for waterbased colorants complies with a few key criteria. First, the product should be solvent-free. Secondly, to assure strong adsorption of the polymeric molecules at the surface of as many different pigments as possible, the molecules must have a multi-anchor structure. This implies that each dispersant molecule has a variety of chemical groups that have a strong affinity for specific solid surfaces. These chemical groups, called anchoring groups, achieve this criterion.
Disperbyk®-199 is a polymeric solvent-free dispersant designed to stabilise a broad range of colour pigments against flocculation in waterbased systems. The compatibility of colorants based on these types of dispersants is broad because these additives do not contain resin and they give both electrostatic and steric stabilisation.
To develop or not develop colorants
The exact choice of raw materials and the amounts to use in a line of colorants depends on several factors like the pigment selection and the types of paints to be coloured. The development of foolproof waterbased colorants that have constant colour tone and colour strength is a time-consuming and expensive task. Many paint manufacturers therefore choose to incorporate ready-to-use colorants from colorant specialists, like Chromaflo Technologies.
- Dispersants for Electrostatic Stabilisation, Jochum Beetsma, 7 October 2016
- Dispersants for Steric Stabilisation, Jochum Beetsma, 28 October 2016
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