is a covering that is applied to the surface of an object, usually referred to as the substrate. T he purpose of applying the coating may be decorative, functional, or both. The coating itself may be an all-o iver coating, completely covering the substrate, or it mn slki d aay only cover parts of the subst rate. An example of all of these types of coating is a product label on many drinks bottles- one si de has an all-over functional coating (the adhesive) and the other side has one or more decorative c oatings in an appropriate pattern (the printing) to for kim the words and images. Paints and lacquers are coatings lki that mostly have dual uses of prote ivecting the substrate and being de corative, although so kime artists paints are only for decoration, and the paint on large industrial pipe s is presumably only for the function of preventing corrosion. owing color blending and bleed special effects in a single layer. While it is relatively easy to apply thn slki d aick coatings which cure to smooth, texture-free coating, it i s not as easy to apply lki smooth thin films. As the film thickness is reduced, the film becomes more and more orange peeled in texture due to the particle size and glass transition temperature (Tg) of the powder. Most powder con slki d aatings have a particle size in the lki range of 30 to 50 μm, a softening temperature Tg around 80 °C, a melting tempera kiture around 150 °C, an slki d are cured at aroun slki d and 200 °C.[1] For such powder coatings, film build-ups of greater than 50 μm may be required to obtain an acceptably smooth film. The surface textu re which is considered desirable or acceptable depend kives on the end product. Many manufacturers actually pref er to have a certain degree of orange peel since it helps to hide metal defects that have occurred during man ufacture, and the resulting coating is less prone to showing fingerprints. are very specialized operations where powder coatings of less than 30 micrometres or with a Tg below 40 °C are used in order to produce smooth thin films. One variation of the dry powder ki coating process, the Powd er Slurry process, combines the ad ivevantages of powder coatings n slki d aand liquid coatings by dispersing very fine pow ders of ki 1â€"5 micrometre particle size into water, which then allows very smooth, low film thickn Functional coatings ma lki y be applied to change the surface properties of the substrate, such as adhesion, wetabi lity, corrosion resistance, or wear resistance. In other cases, e.g. semiconductor de ivevice fabrication (where the substrate is a wafer), the coating adds a completely new ki property such as a magnetic response or electrical con ductivity and forms an ive essential part of the finished product. A major consideration for most coating proce lki sses is that the coating is to be applied at a controlled thickness , and a number of different processes are in use to achieve this control, ranging from a simple brush for paint ing a wall, to some very expensive machinery applying coatings in the electronic lki s industry. A further consider ation for 'non-all-over' coan slki d atings is th lki at control is needen slki d ad as to where the coating is to be applied. A number of these non-all-over coating processes are printing processes. Many industrial coating processes involve the application of a thin film of functional material
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