Metal clear coats

This metal clear coat would normally be applied by conventional air spray or HVLP (High Volume Low Pressure) air spray. The incoiporation of an additive may be necessary to permit electrostatic spray which offers a higher transfer efficiency on complex shapes. 

Polymerization. Thermal polymerization or curing of an ink film at elevated temperatures can foUow many different chemical paths. Condensation and cross-linking reactions may be accompHshed with or without the use of catalysts. However, this method of drying generally has not been widely used for printing inks, except those used for metal and glass decoration, and some clear coatings. 

Figure 5.2 Micrographs of metal-coated lipid tubules. Top panel shows scanning electron micrograph of copper-plated microtubules (bar = 2.0 (Jim), while bottom panel shows optical micrograph of iron-coated microtubules embedded in acrylic-urethane clear coating (bar = 25 p,m). Reprinted from Ref. 135 with permission of Wiley-VCH.

The paint industry uses P.R.175 primarily to color industrial paints and also automobile repair finishes. High transparency makes the pigment an important product for transparent and metallic effect finishes. The pigment is suited to twocoat metallic automobile (O.E.M.) finishes, also referred to as base coat/clear coat finishes, especially if the clear coat contains UV absorbants. Its lightfastness and weatherfastness are excellent. P.R.175 does not bloom, is completely fast to overpainting, and is heat stable up to 200°C. 

No systematic study of inert electrode materials has taken place to date and nothing is known about the anodic processes taking place in ionic liquids. It is probable that noble metal oxide coatings should be suitable but processes such as chlorine evolution will clearly have to be avoided for eutectic-based ionic liquids. The breakdown products of most cations are unknown but it is conceivable that some of them could be potentially hazardous. 

Texas. In Texas, regulators restrict emissions rather than equipment. Emissions are limited across the board for certain industries. Limits (lb/gal) are specified for particular coatings in other industries. For example large appliances, 2.8 furniture, 3.0 coil coatings, 2.6 automotive OEM—primers, 1.2 if submersed and 2.8 if sprayed, topcoats, 2.8, and repair, 4.8 miscellaneous metal—color, 2.5, top clear-coat, 4.3, and all others, 3.0. 

South Carolina. VOC limits (lb/gal) include metal furniture, 3.0 appliances, 2.8 miscellaneous metal—color, 3.5, clear-coat, 4.3, and all others, 3.0 coil coating, 2.6. 

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. 

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. 

Non-leafing pigments on the other hand are perfectly wetted in the binder and therefore oriented more or less parallel to the substrate on the bottom of the wet film. The cured films are rub-resistant with an excellent adhesion to following clear coats. The pigmented film can easily be tinted with transparent color pigments or dyestuffs, thereby creating the typical polychromatic metallic effect . 

Branched acrylic polymers based upon the copolymerization of acrylates and related monomers with methacrylate macromonomers are particularly useful in waterborne coatings. A macromonomer based upon isobutyl methacrylate, 2-ethylhexyl methacrylate, and 2-hydroxyethyl methacrylate was copolymerized with butyl acrylate, 2-hydroxyethyl acrylate, meth-acrylic acid, methyl methacrylate, and styrene.518 After neutralization with dimethylethanolamine or inorganic bases, the polymer could be cross-linked with melamine resin on a metal surface. These systems may be used for either pigmented layers or clear coats. 

However, the use of PU finishes on automotive metal on assembly lines will not come about unless or until the toxicity problem is overcome. Urethane coating producers are active in the development of new PU systems—some involving proprietary blocking agents—to tackle this problem. Their efforts should show some success by 1985. Positive influences here include the growing use of base coat/clear coat systems clear PU topcoats are under active consideration. In addition, vapor permeation curing (VPC) is under investigation. Here, acrylic/urethane topcoats are cured rapidly under ambient conditions in an amine catalyst atmosphere. 

CN. [Sartomer] Epoxy, polybutadiene, and urethane acrylates and blends for paper clear coatings, wood top coatings, screen inks, l o inks, pdyethyl-ene coatings, metal decorative coatings, adhesive papers, wood fillers, sdder masks and photoresists. 

The following regions are clearly outHned in F. 2.16 (i) immunity, in which the metal is considered to be immune from corrosion attack (ii) corrosion region, in which the metal corrodes and forms soluble species and (iii) passive region, in which the metal is coated with oxide or hydroxide. By decreasing the potential (cathodic protection), the metal can move from the active corrosion region to the immunity region. Zinc, because of its equiHbrium potential, is used as a sacrificial anode to protect the iron from corrosion. 

The paint manufacturer is now faced with the problem of a rough substrate which could have influence on the final appearance of the car finish. The sheet metal substrates are E-coated to protect the material against environmental influences (corrosion/acid rain resistance) and then a primer is applied to cover up unevenness of the sheet metal surface. In the case of SMC or SRIM parts the substrate is only primed to smooth the surface. Now the question is, how much does the roughness influence the appearance of the final finish and how can it be measured Therefore, we have done a case study with varying parameters - roughness, baking position, paint systems and with or without clear coat - and the results on the surface appearance were interpreted with a new, optical device for measuring the surface smoothness. 

We used sheet metal with two different levels of roughness Ra = 0.8 jim and Ra = 1.5 xm. Three different types of paint systems were applied and baked in horizontal as well as vertical position. In addition, we applied a clear coat only on half of the panels. The thickness of each layer was kept constant and the coatings were applied by the same operator. The various combinations per panel are given in Table 1. 

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