Basecoats waterborne

Optionally, a waterborne basecoat can be utilized to achieve better aluminum orientation in metallic films. Several papers910 have described metallic orientation and the advantages of waterborne basecoats, so this concept will not be thoroughly discussed here. 

The waterborne basecoat consists of a urethane or an acrylic dispersion with passivated aluminum for metallic glamour. The aluminum must be passivated to prevent reaction with water and the evolution of hydrogen gas. Passivating agents can include polymers, hexavalent chromium (now mandated for removal), or phosphate esters. The basecoat is pre-baked (with infrared or thermal ovens) to release the majority of the water prior to clear-coat application. 

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. 

Amino resins are also employed in waterborne systems used in industrial coatings (e.g., automotive spray primers and basecoats, can and coil coatings). Stable coatings can be formulated with hexakis(methoxymethyl)melamine or partially methylated melamine resins. 

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]. 

Solventborne metallic basecoats contain 15 to 30% solids and 85 to 70% volatile organic solvents. These solvents are not released into the atmosphere, but are converted to combustion gases in afterburners. To reduce emission of organic solvents from this source, waterborne basecoats have been developed. 

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. 

Uses Abrasion resist, aid, toughener, flexibilizer, hardener, gloss aid in water-based coatings (automotive OEM, refinish, primers, basecoats, topcoats), adhesives for wood/plastic/metal substrates, inks binder in waterborne inks, bonding and laminating applies. 

Uses Acrylic for waterborne OEM basecoats or baked coatings Features No or very low VOC... 

Chem. Descrip. Tliermosetting acrylic copolymer (60%) in butyl glycol Uses Binder for waterborne automotive solid color basecoats Properties Water-dilutable dens. = 1.02 g/cm (20 C) dynamic vise. 11,000-18,000 mPa s (23 C) acid no. 30-50 flash pt. (PM) = 65 C 58-62% NV... 

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]. 

BASF plans to offer this eco-efficient product as the first part of a complete automobile refinishing coating system, followed by their globally available waterborne basecoat (sold under the Glasurit brand as line 90), and finished with the application of their one-component, UV-A-curable clearcoat. 

New Jersey. A minimum of 65 percent TE is required for all industries except wood. Shops using waterborne coatings are automatically compliant regardless of TE. VOC limits (Ib/gal) for all others are automotive— primers, 2.8, topcoats, 2.8, specialty coats, 5.0, and repair, 4.8 automotive refinishing— basecoats, 6.0, clearcoats, 4.4, and all others, 5.0 coil coating, 2.6 miscellaneous metals— color, 4.3, performance coatings, 3.5, and all others, 3.0 leather, 5.8 urethane users, 3.8. 

One of the main applications for these aqueous microgels produced by IC3 is in waterborne basecoats (Aquabase) for use as clearcoat/basecoat finishes in the automotive industry. 

Waterborne basecoats are predominantly IK in nature and will not be discussed here as they are extensively dealt with elsewhere (see Chapter 10). The 2K waterborne basecoat technologies (76,77) are now available for use when needed and offer many of the advantages of 2K coatings, with the environmental friendliness of water. 

Although not discussed in this chapter, changes in solvent composition will shift to be more ecologically friendly. Conversion to fully compliant hazardous air pollutant solvents (HAPS) will require complete reformulation of most coating resins. Free solvent replacement to HAPS compliant can occur immediately and substitution in all manufactured resins should be fully implemented within the next few years. Greater use of waterborne materials (primers, basecoats, and clears) is expected within the next five to ten years as long as application properties, performance, and durability can be attained. 

Due to the ecological and low bake requirements for plastics being coated in Europe, both solventbome and waterborne basecoats are used in conjunction with a low-bake, 80°C, 2K isocyanate clearcoat. Descriptions of these technologies will be discussed in relation to the influential European drivers. 

Very often, it is requested to use the exact waterborne basecoat on the plastic part that is used on the car body. One reason for this is the belief that a superior color match will be evident. However, there are two issues to consider with respect to this. Firstly, OEM waterbased basecoats are formulated using melamine resins that crosslink when curing the clearcoat at 130°C. In the case of plastic coatings, 2K clearcoats are used with lower oven temperatures of only 80°C. At this reduced temperature, chemical reaction cannot take place and some colors exhibit weakness humidity testing. Secondly, in many cases OEM basecoats don t match the master panel when applied on plastic parts due to dramatically different application conditions. Therefore a separate version of each color for plastic components is advisable. This then can be formulated differently (e.g., avoiding the extensive melamine cure needed) using more flexible resins and other formulation techniques. However, as to the need to use special plastic part basecoats or to use OEM basecoats, there are no general rules. Therefore, different routes are followed by many of the automotive companies and their suppliers. 

In order to achieve maximum paint utilization, special electrostatic, high-rotation (HR) sprays are increasingly being examined for their specific apphcation potential, which in combination with the (highly conductive) waterborne paint systems also has a particular effect on the design of the entire paint supply system. The use of HR sprays for jpplying the basecoat is also being advanced... 

Waterborne basecoats are non-Newtonian in their viscosity behavior. Figure 6 illustrates the rheological characteristics of metallic waterborne basecoats. Owing to the relationship between viscosity and shear gradient with intrinsically viscous paints, the dynamic viscosity of waterborne basecoats at rest is considerably higher than that of solvent-containing basecoats. As the customary flow cup for determining the viscosity of paints only provides reUable data for Newtonian liquids, other processes such as rotation viscometers are recommended. 

Viscosity flow of waterborne basecoat --- Viscosity flow of solventtxjme basecoat... 

Fig. 6 Rheologic characteristics of waterbased basecoats. Comparison of conventional and waterborne systems.

The effect of the humidity (see processing range) is more crucial with waterborne basecoats than with conventional systems. Even after a 10-minute flash-off period there is still too much residual solvent in the paint film under... 

Brochure Herherts (now DuPont Performance Coatings), Waterborne Basecoat Technology, 1996. 

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