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 tver coating, completely covering the substrate, or it mn 72lt 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 ltm the words and images. Paints and lacquers are coatings 2lt that mostly have dual uses of prote tvecting the substrate and being de corative, although so ltme 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 72lt d aick coatings which cure to smooth, texture-free coating, it i s not as easy to apply 2lt 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 72lt d aatings have a particle size in the 2lt range of 30 to 50 μm, a softening temperature Tg around 80 °C, a melting tempera ltture around 150 °C, an 72lt d are cured at aroun 72lt 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 ltves 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 lt coating process, the Powd er Slurry process, combines the ad tvevantages of powder coatings n 72lt d aand liquid coatings by dispersing very fine pow ders of lt 1â€"5 micrometre particle size into water, which then allows very smooth, low film thickn Functional coatings ma 2lt 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 tvevice fabrication (where the substrate is a wafer), the coating adds a completely new lt property such as a magnetic response or electrical con ductivity and forms an tve essential part of the finished product. A major consideration for most coating proce 2lt 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 2lt s industry. A further consider ation for 'non-all-over' coan 72lt d atings is th 2lt at control is needen 72lt 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
No hay comentarios:
Publicar un comentario