BYK additives for high- and 100% solids systems

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BYK additives for high- and 100% solids systems

Wednesday, 13 March, 2024

When formulating more environmentally friendly paints, reducing volatile components is a vital aim. Traditional systems have naturally developed towards high- or 100% solids systems. In these systems, the formulator faces a number of challenges: firstly, scant to zero solvent presence, meaning higher viscosity and lower compatibility; secondly, increased chemical drying and, as a result, higher polarity and higher surface tension.

For suitable viscosity reduction in bases and finishes, the use of wetting and dispersing additives of a high molecular weight with a large number of pigment affinic groups is essential. Hyperbranched polymers (such as polyurethane or polyamine) make it possible to design additives with a high solids content whilst also offering easy handling properties. These structures include: DISPERBYK-2150TF, DISPERBYK-2155TF, DISPERBYK-2205, DISPERBYK-2152TF and BYK-9076. The controlled polymerisation additive (polyaddition) DISPERBYK-2013 is based on a linear structure and significantly reduces the viscosity of milling, which is one of the goals we need to achieve. The addition of these wetting and dispersing additives enables the achievement of Newtonian profiles in milling, the removal of foam, and a high level of gloss and colour strength.



Figure 1: hyperbranched polyamine

Surface and antifoaming additives will enable the formulator to achieve the best appearance. The choice of antifoaming additive will be made primarily based on the resin (polarity) and the application method (spray, roller, brush, etc.). If the milling has been done correctly and good pigment stabilisation has been achieved, no antifoaming additive will need to be added. The antifoaming additive is normally added in the completion stage and which one to choose depends on the application. Until now, on account of their optimal efficacy, the most common practice was to use antifoaming additives based on PFAS (perfluoroalkyl substances) chemistry. Nowadays, as these additives are not environmentally friendly and since some of them are associated with negative impacts on human health, it is necessary to replace them with safer alternatives in all formulations. To this end, BYK has launched a new range of PFAS-free silicone antifoams:

BYK-1810 (for PU 2K, epoxies and alkyds), BYK-1815 (for general use) and BYK-1816 (for PU single coats) are the most suitable products in these systems. For specific instances, such as with airless applications – where air incorporation is very pronounced – it is advisable to use specific, silicone-based antifoaming additives (like BYK-1880) which spontaneously remove air after application. When it comes to high viscosity systems, such as 100% epoxies, a polymeric antifoaming additive with a 100% solids content, such as the highly efficient and broadly compatible BYK-1765, would be the most appropriate choice.



Figure 2: Results with BYK-1815 in a high-solids PU 2K (dosage as supplied)

The appropriate choice of surface additives is another vital step in improving appearance. To control the surface tension of paint, the chemistry of modified polydimethylsiloxanes is used. If possible, these should be free of tin, aromatics and D4, D5 and D6 cycles. The final choice will depend on their surface activity and their ability to impede foam stabilisation. It should be noted that 100% and high-solids systems have high surface tensions owing to the large number of functional groups in the resins (chemical drying). For this reason, the use of active silicones may sometimes be necessary to improve wetting on difficult substrates. A common combination is the use of an active silicone, such as BYK-3760, to eradicate Bénard cells (generated by differences in surface tension between the paint-air interface and the paint near the substrate), along with another silicone which exhibits low surface activity but is more incompatible (such as BYK-320, apolar or its cumene-free version BYK-LP G 26292) in order to prevent foam stabilization and assist in levelling. As with antifoaming agents, if we are dealing with specific applications, for example HVLP (high volume, low pressure) spray or automotive refinishing systems, we will also require specific additives. BYK-3558 is an additive with a branched acrylic structure with silicone polyethers that endow these systems with excellent levelling and a slight reduction in surface tension. It is a single additive that blends the advantages of silicone and acrylate chemistry.



Figura 3: Results with BYK-3760+BYK 320 and BYK-3558 in a high-solids PU 2K
(dosage as supplied on Component A)

Rheological properties also perform an important role in the functioning of any paint. Whether it is to prevent sagging, to avoid particle sedimentation or to control the immobilisation (viscoelasticity) of the paint, it is vital to choose suitable rheological additives. The use of bentonites is commonplace in these systems, but they are known for the complexity involved in separating their layers due to the low solvent presence (even with pre-gels). Consequently, it is advisable to use mixtures of minerals (the GARAMITE range whose additives cover the entire polarity spectrum) which, owing to their disordered structure, leave open spaces that allow the paint system to seep between the gaps. It is thus simpler to achieve the three-dimensional structure responsible for delivering the appropriate rheological profile.

Lastly, some abrasion and scratch resistance is needed in any industrial, maintenance or refinish paint. For this, the use of waxes based on blends of Teflon and polyethylene is common. The properties offered by PTFE are highly specific: it is chemically inert, temperature resistant, has a high density and does not impair the gloss of the coating. However, PTFE is a PFAS and, as a result, must also be replaced in all formulations. Consequently, PFAS-free waxes have been introduced to the market to improve abrasion and scratch resistance on the paint surface. CERAFLOUR-1050, 1051 and 1052 (based on polyethylene and polyethylene alloys) provide efficiency on a par with waxes based on polyethylene/Teflon by offering a narrow particle size distribution, being suitable for food contact, not impairing levelling and enabling even distribution across the whole paint film.



Figure 4: Results with CERAFLOUR-1050, CERAFLOUR-1051 and CERAFLOUR-1052 E in a BPA-free PE/melamine system (1% wax by formula weight)

Accordingly, BYK offers a comprehensive range of dispersing, antifoaming, surface, rheological and wax agents for high- and 100% solids systems.

Authors: Pilar Casas (pilar.casas@altana.com; +34 699 659 491) and Juan José Andrés Bello (juanjose.andresbello@altana.com; +34 622 304 229), both from BYK-Chemie GmbH – BYK Marketing & Technical Service.

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