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The Federation of Societies for Paint Technology authorised Levinson to do a study on powder coating, electrocoating and radiation. In an article [Journal of Paint Technology, July (1972) p. 37] Levinson describes the advantages and disadvantages of powder coating, the technology involved, the economics of the various systems, the relationship to ecology, the manufacture of powders, the resins which are useful, and future trends.

POWDER coating technology has provided a means of applying resin coatings to substrates via processing techniques which have two distinct advantages over conventional coating procedures. The first and probably most significant advantage from an ecological standpoint is the elimination of solvent carriers. The absence of solvents eliminates the emission of fumes and vapours thereby providing an environment that is virtually free of pollutants. Safety standards are also improved because the hazard of fire is substantially reduced.

Over the last few years, the share of powder coatings used for the protection of aluminium extrusions and claddings for architectural uses in competition with conventional liquid paints and as an alternative to anodising has sharply increased. In 1987, about 47 million m2 or 135 thousand tons of aluminium used in outdoor architecture have been powder coated in France, Germany, Italy and United Kingdom. This paper gives a thorough description of the latest developments of the polyester powder coating systems used for aluminium extrusions and claddings in Europe, underlining the criteria of the choice of the weathering resistant powders, the importance of metal pretreatment and of the coating process itself as well as of the quality control in this industry. A comparison with competitive coating technologies is also given.

In recent years aluminium has become a very widely used material in the construction industry. Light weight, good corrosion resistance and ease of fabrication lends itself to a whole variety of end uses. Although the tendency for aluminium to oxidise in the atmosphere is itself a form of chemical “protection”, improvements in weather and chemical resistance can be gained from the use of a variety of surface coatings. These coating technologies are typically of the following types: polyvinylidine difluoride, water‐borne electro‐paint, conventional solvent‐based paints, powder coatings and anodising. The two most popular technologies in use today are: TGIC (Triglycidyl isocyanurate)/polyester powder coatings and polyvinylidine difluoride (PVDF) solvent‐based coatings. Coated aluminium has the added competition in the window frame and door frame market from uPVC. Only coated aluminium will be discussed in this paper.

More articles have been published about powder coating in the last two years than about any other phase of the protective coatings industry. From this almost overwhelming flurry of print, certain factors emerge. The first is that powder coating technology is certainly a valid and useful one. It has established itself as an integral contributor to the achievements of the protective coatings industry and, without doubt, it will be with us for many years to come. Its success is due to its many advantageous factors which have been reviewed many times in the past. Great strides have been made in that a highly versatile group of powders are now available with both thermoset and thermoplastic properties; it is possible to achieve thin coatings; and the savings in terms of effective powder usage have been well‐documented. Where there is overspray, equipment has been evolved for recycling. Stressed most often has been powder coating's contribution to a non‐polluting painting operation. Powder coating, on the other hand, does not solve the energy shortage problem since the coatings must be fused and baked. However, less energy is required than for solvent based coatings simply because the energy requirements associated with solvent removal are eliminated.

More than two decades after their frist start the thermosetting powder coatings became in 1985 a technically viable product and a commercial success. Powder coatings are 100% dry paints that contain no solvents. They are generally applied to metal substrates by means of electrostatic spray equipment that provides each powder particle with a small electric charge, which in turn makes it stick to the substrate. The coated objects then go into a high temperature oven (usualy 150 to 200°C), where the powder coating melts and reacts chemically while sintering together to a continuous smooth finish of a thermoset film.

Modern powder coatings were introduced in 1952. They created great interest and much was written about them and much predicted for them. They did indeed find a niche, but they did not deliver quite as had been anticipated and by the early 1960's their star was waning. But one must never discount the impact of advancing technology — particularly when economy, convenience and performance are involved. Novel methods of application, primarily electrostatic spraying to complement the original fluidised bed approach, new formulations, faster curing epoxies and a better understanding of both the virtues and the defects of this method for industrial coating, has brought powder coatings back into their own.

A variety of thermoplastic and thermosetting polymers may be employed as binders in powder coating formulations. Some typical applications of various powder coatings are shown in Table 1.

A disadvantage found when conventional weather resistant powder coatings are compared to liquid coatings is their relatively poor flow properties. The flow of thermoset powder coatings depends on a number of factors, including the selection of suitable pigments and fillers, pigment concentration, additives such as flow agents, bake schedule, reactivity and structure of the resinous components, melt viscosity, and the viscosity profile during crosslinking. This paper reports about recently developed carboxyl terminated triglycidyl isocyanurate (TGIC) cured polyesters which result in powder coatings with remarkably improved flow properties due to the polyester's molecular structure and functionality and the viscosity profile during the curing process. These improvements have been reached without any prolongation of the gel time and without compromising the weathering resistance of the film. Such new powder coatings completely crosslink at 160°C within 15 minutes yielding films with excellent mechanical properties.