“Good rheological modification may help reduce the overall cost”
Do you see developments in the additive sector that could lead to complexity reduction for formulators of coatings?
Yannick Nabil-Moreau: Complexity is part of our daily life in the coating world. Selecting the right additive is as critical as the other ingredients of the formulation! Thus, additives remain a tool to control multiple and complex requirements. High build anti-corrosion coatings are the mainstay of the marine and protective coatings industry that require long lasting protection in hostile environments’ with high corrosivity.
Coatings manufacturers are faced with ever more challenging demands: increasing performance requirements, formulation cost pressures, complex regulatory affairs, product stewardship, reduction of VOC content, eliminating hazards, sustainability targets, processing reproducibility, aesthetics’ challenges and so on.
Yannick Nabil-Moreau is a Global Technical Manager at Arkema and responsible for the Crayvallac Additives.
Additives are used as problem solvers within a coating formulation. The amount usually introduced in a system tends to be very small, often less than 1 %, but their impact on properties and their benefits is huge. High solids and solvent free coatings can be modified to control flow and sag properties by the addition of viscosity thickeners, the thickeners induce rheological properties in the coating. To obtain satisfactory sag control without loss of flow and levelling, it is necessary to choose rheological modifiers which exhibit some time dependant recovery – thixotropy. The degree of true thixotropy is dependent on the type of rheology modifier.
What trends do you think will influence the additive market in the near future?
Nabil-Moreau: Today, many formulators are faced with a strong pressure to further reduce VOC’s for all industrial coatings including marine and protective coatings. This trend is typically shifting formulations to very higher solid and or solvent free systems. Some countries like China and Korea are strongly following these new regulations, which influences the worldwide market and drives to the development of high-solid formulations with VOC competing with standard waterborne coatings.
In addition to reducing VOC content, the economics of actual coating processes are such that significant cost savings can be achieved through the fewer coats that may be required to give a specified system film thickness. Higher solids coatings can reduce the number of coats required. Therefore, good rheological modification may even help reduce the overall cost of the system.
However as everyone knows there is a lot more to the application of a high build coating than simply putting on more paint; high film builds, and high solids paints exacerbate such key film appearance issues as sagging, slumping, good edge cover and excellent flow – all being critical properties to an effective anti-corrosion coating.
High solids solvent based and/or solvent-free coatings generally mean that the proportion of volatile (VOC) materials that can evaporate to the atmosphere after application is relatively low, minimising the difference in film thickness between the wet film and subsequent dry film.
In regular solids coatings, the evaporation of the volatile solvent immediately produces an increase in the coating viscosity, which allows the build-up of a coating with easily controlled flow and hence sag control.
With higher solids coatings however, the effects of the loss of solvent on viscosity increase are likely to be relatively low (due to higher solids and lower solvent levels). Higher solids coatings will exist as a low viscosity easily flowing material immediately after application. The development of crosslinking is steady rather than rapid (due to the low molecular weight components) and therefore the opportunity for flow control will be poor unless rheologically modified using a suitable additive.
Our latest generation of Thixotropic amide rheological additives are capable of meeting the most demand needs of the coatings manufacturer when formulating a high build and or solvent free system.
The interview was conducted by Jan Gesthuizen