Basecoat paints

Acrylic core-shell polymers have been used as principal pxjlymers for aqueous metallic basecoat paints [37—40]. The anionic shell allows pseudoplastic flow behavior which ensures parallel orientation of the aluminium pigments in the wet paint film. This orientation and the low solids content are responsible for the metallic gloss and high color flop (change in color observed on varying the viewing angle) of the basecoats. 

Circulation studies of water-borne metallic basecoats demonstrate a few reasons why specular reflectance is lost during circulation. The flow induced stress of circulation reduces flake size and produces cycles in liquid surface tension. Surface tension in turn controls amount of picture framing and film thickness. If rust is present in the circulation system, it can react with the paint resins, creating gel lumps which under circulation trap the metal flake hindering flake alignment. Smaller flakes, thicker film thickness and poor aluminium alignment all reduce specular reflectance within the sprayed basecoat paint film [109-115]. 

Today, a large and increasing proportion of the automotive OEM metallic basecoats in Europe and North America are already waterborne and refrnish basecoats are also available in waterborne versions. Other paint applications have followed and the significant growth of waterborne systems can easily be seen in the statistics of the paint associations. Also in printing inks, the use of waterborne inks is steadily growing. 

Car paints are cured with heat in special oven lines. Electrodeposition coatings (used as anticorrosive primers) contain only small amounts of volatile organic compounds (VOC), whereas intermediate and topcoats release considerable amounts of VOCs. Intermediate coats based on waterborne resins have been developed to decrease VOC emission and are already being used in some automotive plants. Basecoats, as part of base-clear topcoat systems, contain very high amounts of volatile organic solvents. Waterborne basecoats were developed more recently to lower this source of solvent emission. Some car manufacturers are operating pilot lines with the aim of introducing waterborne basecoats into their production processes. Many car producers in the United States and Europe have already switched their topcoat lines over to waterborne basecoats [11.3]. 

Waterborne basecoats with higher solids contents are now available metallic basecoats contain about 18wt% solids and solid (straight) color basecoats 25-40 wt%. The solvent in waterborne paints is not pure water about 15% of organic solvents is still needed as a cosolvent for proper film formation. Metallic basecoats are applied at a DFT of 15 pm, solid color basecoats at a DFT of 20-25 pm. 

Basecoats are sprayed in two layers. The first layer is sprayed electrostatically with high-speed rotation bells, the second layer is sprayed with compressed air to achieve proper orientation of the aluminum particles in metallic paints. The basecoat is then dried for 3-5 min in a warm air zone at 40 - 60°C. 

Uses Defoamer for water-reducible emulsion and latex systems, high gloss architectural paints, wood preservative stains, aq. flexographic inks, primers, acid catalyzed systems, automotive basecoats, coating colors (folding boxboard), wastewater treatment Properties Lt. yel. si. vise, translucent liq. sol. in butanol, glycol ethers, ethoxypropanol, hexanol, isobutanol, IPA, methoxypropanol, MEK, min. spirits, xylene partly sol. in acetone, ethanol dens. 1.01 g/ml (20 C) flash pt. > 200 C pH = 7.0 (2% in Dl water) nonionic 100% act. 

Uses Associative thickener for latex flat and semigloss paints, water-reducible paints, adhesives, automotive basecoats, cementitious prods., inks, mastics, plaster Features VOC-free Properties Powd. 100% act. 

Uses Associative thickener for premium quality semigloss and gloss paints, esp. tint base paints, can coatings, automotive basecoats, marine topcoats, anticorrosive primers, household cleaners, inks, metalworking compds., paint strippers, tile adhesives Features VOC-free reduces or eliminates color float exc. alkyd-like flow, color acceptance and stability... 

Uses Rheology control agent for paints/coatings, automotive basecoats, anticorrosive primers... 

Setal 31-6001 alkyd, aluminum paints Resin 4640-X-50 Resin 4653-V-50 Resin 4727-X-50 Resin 4778-X-50 Resin 4812-V-50 alkyd, aq. paints Resydrol VAZ 5542w/40WA alkyd, architectural finishes Resin 4489-M-60 alkyd, auto-refiiish basecoats Setal 11-1390 Setal 11-1395 Setal 11-1397 Setal 11-1399 Setal 11-1490 ... 

Papasavva et al. [36] showed diagrams of auto paint lines that indicated abatement on the solvent-borne primer/surfacer ovens, on the heated flashed zone after waterborne basecoat application, and on the solvent-bome clearcoat oven. The abatement equipment included a carbon concentrator, which is likely a device for solvent vapor adsorption on activated carbon. A collection efficiency of 90% was reported. The abatement equipment also included a system for oxidizing the vapors to form water and carbon dioxide. These units were called reactive thermal oxidizers (RTOs) [36], and their destruction efficiency was reported to be 95%. For the various scenarios discussed in Section 6.7.2, the abatement efficiencies were reported to range from 52.3 to 62.5%. Emissions from powder coatings ovens are expected to be so low that abatement is not needed, and calculations with and without powder coating oven abatement gave the same results for VOC emission [36]. 

Two different types of photostabilizers are typically added to antomotive clearcoats, ultraviolet light absorbers (UVA) and HALS. Clearcoat UVA acts to reduce the intensity of light inside the paint system. That is, it reduces clearcoat PIR and screens light sensitive coating layers underlying the clearcoat (e.g., basecoat) from UV light. As a result, clearcoat UVA also acts to extend HALS longevity. Clearcoat UVA performance is not discussed further in this chapter. Typical HALS types that are used in clearcoats are shown below. " ... 

The sample described herein is a typical steel substrate painted using standard automotive spray equipment. There are four paint layers first the e-coat, then primer, basecoat and finally the top or clear coat. The topcoat is a commercial two component isocyanate (2k-iso) -30 pm thick. 

Automotive paint weathering research is based on measurement of chemical changes by means of FTIR (all coating layers), transmittance UV (clearcoat only) and ESR (determination of active HALS content of clearcoat and basecoat slices from weathered test panels) [826]. Gerlock et al. [827,... 

Carter et al. [402] have addressed the chemical assessment of automotive clearcoats (usually melamine-cross-linked systems), which requires evaluation of the cross-linker type, HALS and UV absorbers. Coating systems require a variety of chemical analytical techniques for their evaluation [403], including UV microspectroscopy [402, 404], /xFTIR [402,405], /xRS [406,407], NMR [408], ESR [409], ToF-SIMS [410,411] and hydroperoxide titration [412]. Ideally, what is needed for industrial evaluation purposes is a set of techniques that can follow chemical changes in individual layers of a full automotive paint system, typically consisting of 45 /xm clearcoat, 25 /xm basecoat, 35 /xm primer, and 35 /xm E-coat on metal. The clearcoat must shield underlayers from UV. Unlike the case for IR radiation, examination of 30 /xm and thinner clearcoat layers with 0.3 to 0.4 /xm radiation lends itself quite well to the use of microscopes and microspectroscopic techniques. UV microspectroscopy of 10 /xm paint system cross-sections is the method of choice cfr. also Chp. 1.1). UV microspectroscopy... 

Basecoat (BC)/Clear A paint system in which the color effect is given by a highly pigmented basecoat. Gloss and durability are given by a subsequent clearcoat. 

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