Clearcoats

Chemistry (Continued) polyimide, 287-300 polyurethane, 222-236, 546 transition metal coupling, 483-490 Chiral conjugated polymers, 479-480 Chlorinated solvents, 91 Chlorofluorocarbons (CFCs), 201, 205 Chloroformate endgroups, 87 Chloromethylation, 354 Church, A. Cameron, 431 Circular dichroism, 490 Classical catalysts, 433 Clean Air Act of 1990, 201, 205 Clearcoat, 240... 

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. 

Figure 41. Residual gloss and AE%b values for isocyanate-cross-linked polyacrylate resins that contain 15wt% Vossen Blau 2000 (older pigment type which has been replaced by Manox Blue 460 D) relative to the binder and 15 wt% Ti02 (rutile) relative to the iron blue pigment after 1000 h fast exposure to UV [3.193] a) Without clearcoat b) With clearcoat but without UV protection c) With clearcoat and UV protection...

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). 

With this background several measuring methods are currently being discussed in the automotive and paint industry with the objective to obtain a clear characterization of the scratch resistance of clearcoats. Especially procedures that create a single scratch have recently been developed (micro or nano scratch method) [1-8], These methods are different from more practically oriented procedures that are based on relatively simple methods to fly to test or even come close to reality (e.g. car wash brush method). 

Tests with Progressive Load In this context a method was developed in the DuPont Marshall Lab. (Philadelphia) that generates and evaluates a single scratch on a surface (nanoscratch method). This method is used for tests along with development work for clearcoats and it is constantly being improved. 

Depending on the clearcoat system different values for critical load and scratch profile can be observed - especially in the transition range. Figure 2 shows the transition ranges of three so-called public domain samples (measurements by FPL). 

For certain clearcoat systems a partial healing of scratches can be observed on the time scale. In literature this is known as the reflow effect [21], Thermal relaxation phenomena may be used for a physical explanation of this effect. In connection with scratch resistance the cross-linking density of clearcoats is also a decisive factor. Meanwhile, dynamic mechanical analysis (DMA) has been established as a method to determine cross-linking density [21-23],... 

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... 

Nanoparticles are used for the first time for clearcoat paint finishes (PPG-Ceramiclear )... 

Figure 7. (Left) Total ion chromatogram of a waterborne clearcoat. (Right, Top) summed electrospray mass spectrum (19.68-19.98 min) (right, bottom) summed electrospray mass spectrum (22.48-23.38 min).

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]. 

The photooxidation and photodegradation of polymers continues to attract some interest but is not as widespread as in previous years. Review articles have appeared dealing with poly(2,6-dimethyl-l,4-phenylene oxides) , photocatalyst fibres, polymers with azo links and accelerated weathering specifications. Other articles of interest include the design of an integrating sphere for repeatability in polymer ageing and the use of FTIR for monitoring the photostability of clearcoats . 

A number of reviews on polymer photostabilisation have appeared " as well as the stabilisation of ceramic paints clearcoats, wood finishes and car body paints . Hindered piperidine stabilisers (HALS) have also been reviewed in depth " and the surface stabilisation of polystyrene covered . ... 

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. ° ... 

Photostabilization processes have not received much attention in the last year other than a multitude of review and specialist industrial articles. These include stabilization of polypropylene fibres, new stabilizer developments, sorting of stabilizers for polyethylene, trends in UV absorbers, hindered piperidines (hindered amine stabilizers (HAS)) for polyacrylics and urethanes, new stabilizers for polyolefins, enhanced service life applications, stabilizer mas-terbatches for polyester, stabilizers for UV cured acrylic overcoats for PVC, ° stabilization of clearcoats and various commercial packages. ... 

The two major factors involved in producing labels are first, the material to be used, and second, the production method for printing the stock, including the type of ink and clearcoat. 

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. 

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