Nanoscaled Filled Sol-Gel Hybrid Materials for Powder Coatings
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Abstract The sol-gel process has been applied for the synthesis of inorganic-organic powder materials. For this purpose, low reactivity and, for reasons of comparison, nanoscaled sol-gel precursors and nanoscaled silica filler were used to synthesize a low molecular weight inorganic-organic composite which was meltable between 85°C and 100'C and curable at temperatures of 150°C - 200'C. The powders were used for electrostatic coating of aluminum sheets. The resulting coatings of the unfilled system exhibited excellent mechanical properties, e. g. a high abrasion resistance (weight losses between 6 mg and 10 mg per 1000 cycles by taber abrader test (ASTM D1044)) and high values for hardness (universal hardness (DIN 55676): 150 N/mm 2). The hardness of the materials was increased up to 210 N/mm2 by the addition of silica, while the abrasion resistance remained unaffected.
Introduction and State of The Art Especially for applications where solvent emissions have to be avoided, powder coatings exhibit numerous advantages in comparison to solvent - born paints. Due to effective application processes and recycling of oversprayed powder, superior material efficiencies of nearly 100 % can be achieved for these systems. Generally, powder coating systems are divided into two different groups, thermoplastic powder coatings and thermosetting powder coatings. Because of technological constraints, the processing of the thermoplastic systems results in rather thick coatings (1 80im -
200pim) [I]. Hence, this type of powder coating is used for applications where rather thick coatings are requested. Examples are coatings on consumer goods, such as wires, furniture or refrigerators. Typical thermoplastic powder coatings consist of polymeric materials, e. g. polyethylene, polypropylene and polyvinylchloride [1]. Thermosetting powder coatings are normally applied electrostatically resulting in coatings of a thickness around 50 llm. Typical fields of application are automotive coatings and architectural coatings. Common available thermosetting powder coatings are systems based on epoxy resins, polyester- and polyurethane systems [2]. Since only organic materials are used for thermosetting powder coatings, these materials exhibit mechanical properties not sufficient for many applications. As it was shown elsewhere [3, 4], solvent - born inorganic-organic composites have been developed as scratch resistant coatings for polymers and metals. Very good results were obtained by incorporation of inorganic nanoparticles into the coating systems. Since, up to now, only organic powder coating systems have been available, the aim of this paper is to investigate routes for making remeltable sol-gel powders and the influence of nanoparticles on the mechanical properties of the coating materials. For this reason, precursors based on phenylsilanes are investigated, since they are able to form thermoplastic materials as described elsewhere [5,6].
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Mat. Res. Soc. Symp. Proc. Vol. 576 ©1999 Materials Research Society
Experimental The powder coa
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