Bio-based Dual Cure binder for high-quality, solvent-based paints, wood oils and clear coats

Alkyd resins are an important product group that can be used in a wide variety of coating systems. By definition, they are based on high proportions of bio-based raw materials – mostly vegetable oils. However, the growing demands pose some challenges for alkyd resins. For example, the solvent content is to be further reduced and cobalt-containing siccatives and anti-skin agents containing oxime are to be dispensed with.

The silane-functional polyurethane-urea binders of the WorléePur Si series achieve exceptional properties, especially in terms of drying speed, hardness and chemical resistance. Before application, a catalyst has to be added so that the hydrolysis and polycondensation of the silane groups contained in the binder can take place. Depending on the binder and the coating formulation, these coatings allow a processing time of days or sometimes even weeks and months. Nevertheless, this technology has not yet been able to serve as a substitute for a large part of the high-quality alkyd-resin lacquers.

Most of the paint systems to be applied by hand with brush and roller use 1 K systems. The consumer often expects an infinite working time without the addition of a separate hardener or catalyst. On the other hand, these types of paints are often subject to the Decopaint Directive and therefore have to comply with applicable VOC limits.

Both points could not be achieved with the previous WorléePur Si technology, which limited the possible applications. Furthermore, the current WorléePur Si products contain only small proportions of bio-based raw materials.

In the WorléePur Si VP-W 3304/07, the WorléePur Si technology has been significantly further developed to also meet the needs of modern 1 K systems. The basis is a polyol which consists of 100% bio-based raw materials. The tall oil fatty acid used is a by-product of paper and pulp production. No additional arable land is used for its production and it is not suitable for human or animal consumption.

In further production, this bio-polyol is reacted with an aliphatic isocyanate monomer and a suitable silane. The product obtained has a bio-based content of about 78% on solid resin and was dissolved 85% in dearomatised KW 180–220 and dipropylene glycol monomethyl ether.

The product cross-links both oxidatively, like common alkyd resins, via the double bonds of the fatty acid and via the silane groups present (hydrolysis, polycondensation). Only known siccatives are necessary for the catalysis. A specific catalyst for the cross-linking of the silane groups is not required. To improve storage stability, the use of known anti-skinning agents is recommended. The lacquers produced in this way can be regarded as 1 K lacquers and can thus be stored like known alkyd-resin lacquers.

The WorléePur Si VP-W 3304/07 represents the first prototype of this technology. It is primarily suitable for formulating a wide range of VOC-compliant paint systems for craft application, especially for categories A/d and A/e of the Decopaint Directive. The limit values for VOCs here are 300 and 400 g/l respectively.

With WorléePur Si VP-W 3304/07 high gloss, silk gloss and matt clear and topcoats can be formulated. The formulations contain conventional raw materials and can be produced using standard manufacturing processes.

Compared to conventional VOC-compliant paint systems, there are several advantages. For example, coatings based on WorléePur Si VP-W 3304/07 usually achieve better drying properties, significantly higher pendulum hardness and chemically and mechanically resilient films after only a short time. Table 1 shows some of these properties of a VOC-compliant and high-gloss topcoat as an example. In particular, a very high MEK resistance is achieved, which is on the same level as, for example, isocyanate-curing 2K coatings. The drying speed can be further optimised by using suitable siccatives and quantities.

Cobalt-free and VOC compliant alkyd-resin-based topcoats show a lower development of hardness over time. Figure 1 clearly shows the differences to WorléePur Si VP-W 3304/07. The hardness development is on a completely different level.

Due to the higher film shrinkage of the long-oil alkyd resin contained in the lacquer, conventional silk-gloss lacquer systems take a relatively long time to reach their final and desired gloss level. Comparable varnishes based on WorléePur Si VP-W 3304/07 are much easier to matt. Figure 2 shows that the desired gloss level is achieved after a short drying time, which makes the formulation of such varnish systems much easier.

In summary, the WorléePur Si VP-W 3304/07 offers several advantages over conventional VOC-compliant alkyd-resin systems

• Dual Cure binder: oxidative drying and additionally moisture curing.
• The drying and especially the hardness development is clearly better compared to alkyd resins with a high solids content.
• The chemical resistance is at a very high level, similar to that of 2 K systems.
• The formulation of high-gloss and silk-gloss, as well as matt topcoats and clearcoats is possible.
• Due to the lower film shrinkage over time, silk-gloss lacquers achieve the desired gloss level significantly earlier.
• The use of bio-based components is possible.

The product forms the basis for the further development of this product range. The adapted technology allows the development of binders for high-quality and modern coating systems. It combines the advantages of alkyd resins with those of modern moisture-curing binders and does so on the basis of high bio-based proportions.?