Solvent-free coating formulations

Successful solvent-free chemical syntheses have been reported for a variety of small molecules, both with and without the use of microwave irradiation, and for some polymer preparations (Varma, 2000). Solvent-free coatings formulations have also been developed. 

The coating must also be solidified very rapidly once it is applied to the fiber so that it will offer protection when the capstan is reached. This requirement rules out solvent-containing formulations for all but the thinnest coatings, because solvent removal is a slow process. Solvent-free coating formulations that are rapidly cross-linked by thermal activation or by UV radiation can be used very successfully. Thermoplastic hot-melt systems that solidify quickly upon cooling are also viable. The material systems of choice for this application depend upon both coating-application and coating-performance considerations. 

Amidoamines. Amidoamines have all the properties of polyamides, except for a significantly lower viscosity, which make them useful in high solids and solvent-free coating formulations. They are prepared by the reaction of a mono-functional acid like tail-oil fatty acid with a multifunctional amine such as BETA, resulting in a mixture of amidoamines and imidazolines. 

An epoxy resin formulation completely free of organic solvent was applied to carbon steel coupons using supercritical carbon dioxide (CO2) as the volatile solvent. Sleet coupons coated in this manner were compared to coupons coated with a standard military specification marine primer (MlL-P-24441) during exposure to aerated 0.5 nrl sodium chloride (NaCl). The solvent-free coating protected the steel from corrosion in this environment as well, if not better than, the solvent-based primer (Kendig et al., 1999). 

Water-thinnable polyester coatings have been formulated with low molecular weight oligomeric hydroxy-terminated polyesters (171). Up to about 20% of water dissolves in a polyester-Class I MF resin binder, reducing the viscosity to about half This permits making solvent-free coatings. 

Water can also serve to reduce viscosity of oligomers with hydrogen-bond interactions. It has been shown that up to 20% (depending on the formulation) water can dissolve in solvent-free coatings (171). 

T resins are also an important component of silicone powder coatings. T resins useful in powder coatings are obtained by the hydrolysis of MeSiCla or the cohydrolysis of CHsSiCls and CeHsSiCls. These silicone formulations provide high temperature (service temperatures >800°F) and impact resistance (543,544) in solvent-free coatings. 

In the development of maintenance and marine coatings, the emphasis has been on the development of low-solvent, or solvent-free, coatings to satisfy EPA volatile organic content standards. Thus liquid epoxy systems based on polyamidamines have been developed. Epoxies have also been formulated as powdered coatings, thus completely eliminating solvents. 

Uses Surf, additive for solvent-based and solvent-free coatings Properties Cl, colorless liq, aromatic odor sp.gr. 0.94 dens. 7.82 Ib/gal vapor pressure 7 mm Hg flash pt, (Seta) 23 C ref. index 1.465 49% NV Use Level 0.1-0,3 % on total formulation Toxicology TSCA listed... 

Thermosetting epoxy and polyurethane chemically-cured liquid resins can provide, among other characteristics, superior abrasion resistance coatings. Solvent-free formulation applied by hot spray techniques can achieve film thicknesses of up to 5 mm. 

Traditionally, UV curable polymers have been utilized as coatings for wood and vinyl floors, but their applications have increased dramatically over the last twenty years to encompass many diverse areas, including optical fiber coatings (7), adhesives (2), disc replications (3-5), and microelectronics (6). This widespread use of UV cross-linked systems is attributed to their rapid, energy efficient curing and their solvent free, one piece formulations. Typically, UV curable systems require only a small fraction of the power normally utilized in thermally cured systems and their solvent free nature offers an environmentally safer alternative. 

Coating formulations (lacquers) are clear, transparent, low-viscosity, solvent-free liquids that are stable with a shelf life of several months and are suitable for optical applications ranging from the ophthalmic to the optical fibre market. As an example of the former, Figure 4.15 shows a plate half coated with a layer of ABRASIL coating material only a few micrometres thick with the scratch traces from steel wool being observed on the uncoated half.18... 

The yields of radiation-induced polymerizations can be very high. No additives are required, which makes it possible to synthesize very pure polymers. The initiation step is temperature independent giving rise to an easily controlled process at any desired temperature. These features account for the commercial interest in radiation polymerization. The very high speeds attainable within the layers of monomers subjected to powerful electron beams explain the wide use of this technique in radiation curing of adhesives, inks and coatings. The corresponding formulations are "solvent-free" and involve pre-polymers and monomers as reactive diluents. 

The ultraviolet curing of Inks and coatings has also received new attention. The renewed Interest In curing Inks has been Influenced by ecological and economic considerations.. The Inks can be formulated as solvent free systems which are sensitized to mercury 3650A irradiation. The curing energy is only a fraction of that needed with heat curable systems. 

Solvents and pigments need not always be present in a coating formulation. Solvent-free paints and pigment-free varnishes are also available. 

Depending on their chemical composition, polyurethane paints are formulated as two-component (two-pack) or one-component (one-pack) mixtures. They are applied from the liquid phase, which may be solvent-containing, aqueous, or solvent-free, or from the solid phase as a powder coating. They may be cured under a wide range of conditions drying above to stoving at ca. 200°C. 

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