With ever-changing regulations and environmental requirements comes a continuous need for advanced water-borne (WB), low VOC or VOC-free coating formulations that deliver similar qualities as solvent-borne (SB) systems. Even with all the progress in WB coatings since their introduction several decades ago, there is still room for improvement. This is particularly challenging when it comes to dispersing pigments and matching performance of SB formulations. To address these challenges, new WB dispersant technologies must allow formulators to develop coatings with improved properties and potentially lower cost.
The Challenges of WB Dispersants
Dispersants have two parts: pigment/colorant-affinic anchoring groups and stabilizing chains. In order to achieve desired properties, a dispersant must have a suitable architectural design with a well-controlled molecular weight distribution and a right ratio of anchoring groups to stabilizing chains.
There are two types of stabilizing mechanism in WB systems - steric and electrostatic. Steric chains are the dominant stabilizing groups in SB dispersions. Having limited options in choosing stabilizer chains in WB dispersants adds to the complexity of WB systems. In addition, factors such as electrolytes, pH, and other coatings/formulation components in the WB system impact dispersions and their performance properties. Consequently, it can be difficult to observe much differentiation when it comes to performance in WB systems compared to those in solvent. With WB formulations, the chemistry has to be exceptional to see a jump in performance, where there is less sedimentation and a good, stable dispersion in a can of paint with acceptable tinctorial properties.
Water-borne systems may require other complex coatings and formulation components to work effectively such as binders, water-miscible cosolvents, surfactants, defoamers, and rheology modifiers. This makes formulating more difficult, as multiple components introduce more charges and also bring compatibility and pigment-affinity competition challenges into the system, which increase instability. Basically, an aqueous coating formulation must be stable despite presence of pH, electrolyte, water miscible components, soluble polymers, and colloidal phases.
Once formulated, the coating needs to be manufactured. Proper dispersant choice can impact milling time, rheology behavior, in-process stability, particle size, which all relate to the time and cost to produce a batch of paint. Water-borne coatings tend to require longer milling times and greater control of rheological and dispersing properties.
Further formulation such as adding binders, cosolvents, additives (e.g. corrosion inhibitors, adhesion promotors, rheology controller agents) may be needed to achieve desired properties. These obviously increase the complexity of the system and introduce more challenges in manufacturing of the coatings.
In-Can Stability Challenges
As paint sits on the shelf, a good dispersant allows for fewer agglomerates and keeps the dispersion stable for some reasonable period in environmental and storage conditions. The more agglomerates there are, the more material is wasted, which equates to more time and money.
Impact on Tinctorial and Film Properties
Dispersants have a critical role in achieving superior tinctorial properties such as color strength, gloss, and haze. Even small agglomerates can affect aesthetic properties of the paints/coatings. Additionally, since WB dispersants contain hydrophilic groups, they could have negative impact on the water and cession resistance of the coatings. Therefore, it is important to ensure the dispersant is designed in a way to minimize this negative impact while maintaining the tinctorial properties.
Creating Technical Differentiation and Addressing Cost
By identifying unmet needs in the market and listening to the voice of our customers, Lubrizol has developed a new line of Solsperse™ Hyperdispersant technology to help overcome these various challenges. The Solsperse W-Series also provides a very high level of appearance and performance, manufacturing efficiencies and quality, as well as the ability to effectively work with difficult-to-disperse pigments in both resin-containing and resin-free systems.
Solsperse™ W100 is is designed with multiple anchoring that works with a wide range of pigments: organic, inorganic or carbon black. It can be used in resin-containing or resin-free formulations to reduce the complexity chemists face: one dispersant works for a wide range of pigments, binders and applications. It also helps control costs through performance efficiencies, as significantly less dispersant is needed when compared to competitive dispersants to achieve the same performance. The product is also more hydrophobic than other dispersants available, so it promotes better water and corrosion-resistance in coatings.
Solsperse™ W200 is designed by development of a novel anchoring group that has been targeted at carbon black and organic pigments, enabling improved coloristic performance for water-borne coatings. This patented product provides rapid wetting, shorter milling time, faster dispersing and stabilization. This means less energy is used during the milling process resulting in saving money. Less of the product is needed in carbon blacks than other dispersants; therefore, it also reduces costs.
Contact your Lubrizol account manager or visit www.lubrizol.com/solsperse to learn more about optimizing pigment dispersing in water-borne coatings.
By Lubrizol Performance Coatings Team