van der R Rob Linde

Organic-inorganic hybrid coatings for coil coating application based on polyesters and tetraethoxysilane

Abstract Organic–inorganic hybrid coating systems based on polyesters and tetraethoxysilane (TEOS) are synthesized and evaluated to develop protective coatings with improved performance for prefinish construction steel and aluminium. The coatings have to combine flexibility, necessary for enduring deformation of the metal substrate after coating, and hardness for improved mechanical properties. Two systems have been studied: a polyester–TEOS system and a polyester–epoxide–TEOS system. The polyester–TEOS system contains polyester oligomers which are crosslinked with silica clusters, formed via the sol-gel process. The polyester–epoxide–TEOS system consists of an organic network of polyester and epoxide with silicon compounds, formed by the sol-gel process. Both systems form transparent hybrid organic–inorganic coatings. The influence of the inorganic compound on the Konig hardness of the coatings is determined. The polyester–TEOS system shows an increase in hardness with increasing silica content. It appeared difficult to incorporate in situ formed silica in the organically crosslinked polyester–epoxide–TEOS system.

Oxidation of model compound emulsions for alkyd paints under the influence of cobalt drier

A systematic investigation on the oxidation of different model compounds (including methyl oleate (MO), ethyl linoleate (EL), and methyl linolenate (MLn)) in emulsions under the influence of an emulsifiable cobalt drier was performed. Raman spectroscopy, attenuated total reflectance (ATR)-FTIR, and NMR were used. Raman spectroscopy proved to be a powerful technique at following the oxidation of these model compounds in emulsions not only after but also during the water evaporation. Raman and ATR-FTIR (D2O was used instead of H2O) investigations clearly demonstrated that there was essentially no observable chemical change during the water evaporation. The oxidation of model compounds in emulsions, after the water evaporation, was found to be similar to the oxidation of bulk/solvent-borne model compounds. The presence of an emulsifier (sodium dodecyl sulfate) and water did not show any significant effects on the oxidation of the model compounds. An increase in the intensity of conjugated double bonds and isolated trans-double bonds was first observed, and followed by a decrease. More than 90% of double bonds disappeared for EL and MLn after 13 days of oxidation as examined by NMR, which may be attributed to the addition of radicals to double bonds (propagation-like reaction) and the β-scission of double-bond-containing radicals into by-products. The number of double allylic group in the model compounds also showed a significant influence on the rate of oxidation for emulsions after water evaporation.

The pigmentation of powder coatings with the use of block copolymer dispersants

The dispersing of pigments in powder coatings is a difficult and complicated process. The incomplete dispersion under standard extrusion conditions can be attributed to a combination of poor pigment wetting and insufficient disruption of the pigment agglomerates, as a result of the rheological properties of the powder coating resin. The use of block copolymer dispersants for improving the pigment dispersion in powder coatings is studied in this project. Novel block copolymer dispersants from 2-vinylpyridine and ϵ-caprolactone have been synthesized and tested. These block copolymers show a high affinity for TiO2 pigments and are capable of improving the stability of a TiO2 dispersion in a polyester powder coating resin.

Morphology of hybrid coatings based on polyester, melamine resin, and silica and the relation with hardness and scratch resistance

The morphology of hybrid coatings based on polyester, melamine resin, and various amounts of silica has been investigated, and the hardness and scratch resistance were determined. By increasing silica content, an increase of silica particles in size and number was observed. Small silica particles were preferentially present at the surface. The influence of the silica content on the König hardness, indentation hardness, and elastic modulus was minor. The improved scratch resistance determined for a hybrid coating with 11.4 wt% silica, compared to a similar organic coating without silica, was attributed to small silica particles preferentially present at the surface.