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Tham khảo tài liệu 'coatings of polymers and plastics part 12', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | 264 Ryntz than that of a black basecoat which contains carbon black with excellent opacity. Poor hiding colors such as red yellow and white straight shades require higher film build to achieve hiding than metallics and darker shade colors. Newer special-effect pigments such as coated micas and sputtered or dielectrically deposited pigment-layered composite pigments have allowed color stylists to develop more innovative colors that are richer afford high chromaticity and display sharper hues. Solvent-based basecoats are generally applied and allowed to flash off synonymous with solvent evaporation at room temperature or at a slightly elevated temperature for three to five minutes before the clearcoat is applied. This process of applying one coating over another where the first coating is not in a crosslinked or cured state is referred to as the wet-on-wet process. Optionally a water-based basecoat can be utilized to achieve better aluminum orientation in metallic films. Several researchers 33 34 have ascribed better parallel alignment of the metallic flakes within the basecoat to better metallic orientation. This orientation is believed to occur as a result of the greater degree of shrinkage in water-based coatings due to the lower solids content typically on the order of 30 by weight of water-based coatings than comparable high-solids basecoats solids levels typically on the order of 40 to 50 by weight . The water-based basecoat consists of a urethane or an acrylic dispersion that may or may not be crosslinked. Crosslinkers generally consist of blocked isocyanates or MF resins. The basecoat is spray applied and prebaked with infrared microwave or thermal convection ovens in what is generally referred to as a heated flash to remove a majority of the water 90 prior to clearcoat application. 3.3.3 Clearcoats The solventborne clearcoat is spray applied over the basecoat at a dry film thickness of 1.8 to 2.0 mils. The clearcoat responsible for UV protection chemical .
