Basecoats

The CYPHER stent employs two nonerodible polymers polyethylene-co-vinyl acetate (PEVA) and poly-n-butyl methacrylate (PBMA), The combination of sirolimus and these two polymers constitutes the basecoat formulation that is applied to a stent treated with paryleneC. In addition, a drug-free topcoat of PBMA polymer is applied to control the release kinetics of sirolimus (59), making this a diffusion-controlled reservoir device. The chemical structure of the polymers used in the CYPHER stent is shown in Figure 4,... 

A basecoat is applied to the panel after the filling operation. This is normally a pigmented lacquer or vinyl based material whose function is to hide the surface and provide a uniform color on which the grain will be printed. The basecoat is commonly applied by a curtain coater or more commonly with a roller coater. Obviously, skips in the basecoat, whether the result of deformed application rolls or panel unevenness, cannot be tolerated. Surface depressions not completely filled during the filling operation will not be basecoated and will appear as small white dots on the panel. 

Basecoats are normally cured in heated ovens with high air velocity or with infrared heaters excessive panel temperatures should be avoided to prevent drying of the particleboard. A light scuff sanding of the basecoat is used to remove high spots, followed by a brush cleaning to remove the dust and debris. 

The grain pattern is then printed on the panel with one to three printers in tandem each printer has a different color which allows better grain pattern simulation. Lines equipped with three printers can produce a four-tone pattern since the basecoat is normally a different color than the printers. 

Ideal properties as primers and basecoats for other adhesives and coatings... 

The total automotive coating composite, however, consists of more than just the basecoat/clear-coat. The metal sheet stock that is formed into the automotive car body is treated with a corrosion-resistant primer applied by cathodic electrophoresis. This coating, often referred to as ECOAT or uni-prime is a hydroxy functional epoxy/ blocked isocyanate dispersion that deposits onto the cathode of an electrolytic cell at a voltage of between 250 and 425 V. Film thickness, which is dependent upon the residence time, temperature, and coating voltage of the electro-coat bath (electrolytic cell), varies between 0.8 and 1.2 mils (1 mil = 25 xm). The curing temperature required to deblock the isocyanate and yield a cross-... 

The solvent-borne basecoat, consisting of polyester or acrylic binder to be cross-lined with melamine or isocyanate, is applied at a dry film thickness of between 0.6 and 1.5 mils, depending upon the color. Poorer-hiding colors, such as red and white straight shades, require the higher film builds, whereas metal lies and darker colors are applied at the lower film builds. The solvent-borne basecoat is allowed to flash-ofif solvent for approximately 3-5 min at ambient conditions prior to application or the solvent-borne clear-coat. This process is referred to as a wet-on-wet application because the basecoat is not in its cured or cross-linked state. 

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. 

The solvent-borne clear-coat is spray-applied over the basecoat at a dry film thickness of 1.8-2.0 mils. The clear-coat, responsible for UV protection, chemical resistance, chip resistance, and so on, is most often composed... 

Organosol PVC dispersed in an appropriate varnish and conventionally stabilised with a low molecular weight epoxy, resin or epoxidised bean/seed oils Very good Very good Drawn cans Easy-open ends Closures Often used over epoxy-phenolic basecoat... 

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. 

Hazel, N.J., Walker, P. and Bray, R. (1995) LCA based environmental evaluation of automotive OEM basecoat alternatives. Presented at International Body Engineering Conference, 2nd November, Detroit, USA. 

Printed - (35%) surfaces are decorative pattern or simulated wood grain effects created by the application of liquid applied basecoats, inks and protective topcoats to lauan or other tropical hardwoods. 

Figure 2.1. The function of CAB in automotive clear-on-base finishes A) Viscosity of CAB permits application of heavy basecoat B) Solvent evaporates, film shrinks, and fiake orientation begins C) The CAB prevents solvents in the clear topcoat from redissolving the basecoat...

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. 

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. 

High-speed rotating atomizers and electrostatic spraying Metallic basecoat 13 670 75 8.93... 

Clearcoat, acrylic-melamine basecoat, polyester-cellulose, acetobutyrate-melamine, silver metallic bake 130"C, 30 min exposure Florida, 5 South, black box unheated percentage of light stabilizer relative to binder solids benzotriazole I, 2-(2//-benzotriazole-2-yl)-4,6-bis(l-methyl-1-phenylethyOphenol [70321-86-7], Cracking after 2.25 years. Cracking after 5.5 years. 

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