Peter Harberts – UNIQCHEM GMBH
Manuel Scolari – EUROSYN
Fundamentals of pigment stabilization
Pigments have been always incorporated into formulations to provide color, opacity, and weather resistance properties that the binder alone cannot provide, their effectiveness depends on a three-step process: wetting, grinding, and stabilization.
During wetting, During the wetting step, air and moisture occurring on the pigment surface are driven off and then replaced by the liquid of the grinding medium; this is followed by grinding, which, thanks to high shear forces, the pigment agglomerates reduced in size, preferable primairy particles.
The stabilization process accours thanks to a dispersing agent. Since these pigment particles naturally tend to flocculate to achieve a favorable energy state, the usage of a dispersing agent is crucial.
Selecting the correct additive can be quite challenging; the choice depends on many things, such as nature of the pigment: inorganic pigments have ionic charges, while organic pigments consist of covalent aromatic structure.
A key parameter is the specific surface area of the pigment, used to determine the quantity of dispersing agent needed. Another thing to consider is that stabilization can be electrostatic (repulsion between charges in aqueous systems) or steric (through adsorbed polymers that create a physical barrier), in this case, it is mandatory to have a total surface coverage and compatibility with the binder. And finally you need to consider if you are working with a solvent-based, waterbased system or solvent-free system. All these parameters must be taken in consideration to achieve optimal stabilization, creating max steric hindrance, preventing sedimentation, loss of gloss, and rub-out while improving optical properties and viscosity.
Chemistry and properties of dispersin agent
Dispersing agents are represented by various chemical natures such as: polyurethanes, polyacrylates, polyesters (amine salts), copolymers (PAS/MSA) and acrylic acid based dispersing agents. Besides the different chemical natures we can find, there 2 main type of dispersing agent based on the molecular weight: LMWD (Low Molecular Weight Dispersants) and HMWD (High Molecular Weight Dispersants). LMWD have an average molecular weight of 500-2.000 g/mol and they are more suited for inorganic pigments. They typically cover a small surface area and they facilitate the wetting of the pigments.
On the other hand HMWD are more versatile; they are generally suited for all kinds of pigments, thanks to their molecular weight ranging from 3.000 g/mol up to 30.000, they have a strong and improved pigment absorption resulting in better stability, thanks to a larger surface area coverage. These kind of pigments feature a better viscosity stability, preventing viscosity build up and flocculation.
Dispersin gent focus: 680U, FA625 e 690W
UniqSperse 680 U is a high molecular weight wetting and dispersing agent for water-based, solvent-based and solvent-free applications, is an excellent additive for the grinding of carbon black to give optimal jetness development but it is also suited for inorganic or organic pigments and resin free pigment concentrates, giving excellent transparency and color development for HPP pigment, while featuring a strong viscosity reduction and showing good compatibility with common resins, plasticizers and UV systems.
UniqSperse FA 625 is an emulsifier and compatibilizer dispersant for universal colorants. It is suitable for waterbased, solvent-based and solvent-free applications. FA 625 shows excellent for the grinding of all pigment types and it’s well suited for inorganic or organic pigments and resin free pigment concentrates.
An important aspect of this product is that it can be post added to give color acceptance in water and solvent based applications. The main couses of flooding and floatings are cause by differences in pigment mobility (e.g. particle size), different charges of the pigments and solvent evaporations & convection. This additive will search for the equilibrium until the system is stabilized.
UniqSperse 690 W is a wetting and dispersing agent additive for water-based application only, most suited for industrial coatings and water-based colorants.
Shows excellent for the grinding of all pigment types, suited for inorganic or organic pigments and resin free pigment concentrates, excellent viscosity reduction and color development, it is an excellent choice for all pigment types, showing exceptional performances on white systems.
