Coatings clearcoats

General Electric Xenoy PC/PBT with clearcoat polyurethane (PUR) is used to mold body panels for the European Smart Car. The clearcoat offers the UV and scratch-and-mar protection. Smart Car colors are offered in red, yellow, black, and white straight shades. This process stiU uses a coating, clearcoat. However, it eliminates the primer and basecoat. 

Basecoat is the layer which contains the color pigments. This layer is covered by the transparent coating (clearcoat). 

Intuitively, it seems likely that a decrease in crosslink density on exposure would promote coating erosion. In clearcoats, on the other hand, the most serious appearance problem is crack formation. 

A unique two-coat, topcoat system is used in the automobile industry. A basccoat is applied to a primed surface to provide opacity, color, and a metallic appearance, while the clearcoat provides gloss mid a miiioilike finish (referred to as distinctness of image). 

Figure 10 shows this effect. At the left side the topography and a line scan of the uncoated fiber reinforced material is shown. At the right side of Fig. 10 the roughness of the clearcoat, coated directly on the substrate and dried under varying conditions is represented. The higher drying temperature causes a more distinct surface structure. 

Fig. 10 Structure development of clearcoat at varying drying temperature left 3-D substrate, bottom roughness profile- riehr profile clearcoat coated directly on substrate at RT, 80 °C and 140 °C (scan length 15 mm, y-scale 2 pm left 1 pm right) ...

In this paper the recently developed techniques to characterize the mar resistance of coating systems were presented. The techniques base on methods that create a single scratch onto a surface. Characteristic values like the critical load as a measure for the transition from plastic behaviour to brittle fracture can be determined and used to rank different clearcoat systems and to compare these results with other physical properties. In the field of mar resistance the cross-linking density of the... 

The data obtained clearly demonstrate that the scratch resistance of polyacrylate coating materials can be strongly enhanced by incorporation of methacryloyloxymethylsilanes (the reasons for the low value of gloss retention observed for 3c are not yet fully understood). As an additional benefit, the cured clearcoats revealed an extremely high chemical resistance no change in the films were observed after a 500 h exposure to 30% aq. H2SO4 test or after 100 cycles in the MEK rub test [4]. 

Much development work has produced powder coatings for decorative niche markets. They are now available in a wide range of gloss levels, colors, and specialized surface effects such as metallics, pearles-cent, fluorescent, antique, hammertone, textured, wrinkled, and clearcoats. Metallic powder coatings have presented an application challenge, because some types of metallics are dry blended. Application equipment manufacturers have learnt how to apply these challenging materials. ° ... 

Automotive Finishes. Important industrial automotive topcoats are produced from alkyd resins. Two-coat metallic finishes consist of an acrylic clearcoat and a metallic basecoat. Solventborne basecoats are generally composed of cellulose acetobutyrate and a low molecular mass, branched polyester resin which exhibits high reactivity with precondensed melamine cross-linking resins. 

Generally, the binders have a low content of organic solvents (ca. 10%) and can be applied over a wide temperature and humidity range. Water and organic cosolvents used in clearcoats applied by wet-on-wet coating evaporate rapidly after predrying with convection or IR radiation. 

The basecoat-clearcoat system is presently the most commonly used type of topcoat for cars because it is the standard application system for metallic colors. Today, about 70 % of all cars have metallic topcoats. The basecoat-clearcoat system consists of a colored layer (basecoat) which is overcoated after a short flash-oflf time with a protective layer of clearcoat. Both coats are cured together at 120-140 "C. The basecoat contains pigments which provide two types of finish solid (straight) colors or metallic. 

The laminate sheet is a flexible decorative sheet for use in surfacing an automobile body panel. The laminate revealed in this invention contains several layers, including clearcoat, tie coat, color coat, and adhesive layer. Clearcoat is formulated from polyvinylidene fluoride (to assure excellent weather resistance), tie coat is formulated from acrylic (good adhesion to both clear coat and color coat and weather resistance), color coat was formulated from PVC (see formulation in the above table) and adhesive was pressure sensitive acrylic formulation. 

This relates, for example, to coatings, in which stabilizer molecules may migrate from the clearcoat to the basecoat or plastic substrate. These problems may be alleviated by the use of physically persistent stabilizers. High molar mass stabilizers (M >500gmor ), including oligomers with appropriate molecular structures (M=3500-5000 g mol ), are sufficiently physically persistent and do not evaporate at the elevated temperatures of curing [87]. 

Electrical conductor wire, printed circuit board coatings, optical fibers, magnetic media, coatings, computer disc clearcoats, coatings for metallized substrates... 

Uses Matting agent, mar resist, aid, scratch resist, aid for solvent-borne and waterborne coatings, esp. wood coatings, varnishes, plastic coatings, and stoving enamels based on acrylics, acid-catalyzed systems, polyesters, two-pack PU, acrylic and PU disps., NC and blends Features Smooth, soft surf, feel esp. rec. in clearcoats where minimal haze is required... 

Topcoat consisting of basecoat/clearcoat, two-coat one-bake method... 

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]. 

If the pigment is omitted, the material is usually called a varnish. The term clearcoat is used for unpigmented coatings applied over metallic paints. The pigmented varnish - the paint - is sometimes called an enamel, lacquer, finish or topcoat, meaning that it is the last coat to be applied and the one seen when the coated object is examined. Lacquers are normally thermoplastic solution paints or varnishes, but the term is sometimes (confusingly) used to describe all clear woodfinishes. Enamels are normally thermosetting paints, hard, with a superficial resemblance to vitreous enamels. 

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