Types of Coatings

There are hundreds of different types of coatings, many being complex formulations with numerous components. Indeed, to be successful a coatings chemist and company must be able to change a formulation to fit 

Exterior house paints Interior house paints Undercoats, primers, and sealers Varnishes Stains 

Swimming pool Arts and crafts Metallic Multicolored 

Wood furniture and fixtures Automotive metal containers Machinery and equipment Factory-finished wood Metal furniture and fixtures Sheet, strip, and coil Transportation (nonautomotive) Appliances Electrical insulation Marine 

Paint A coating with a colored pigment included. It is always opaque. 

According to the U.S. Department of Commerce Census Bureau, the total amount of organic coating material sold in the United States in 1997 was 5.56 x 10 L, at a value of 16.56 billion. The total sales can be broken down into architectural coatings, product original equipment manufacturers (OEM) coatings, special-purpose coatings, and miscellaneous paint products, with approximately one third of the total sales for the main purpose of corrosion protection [1]. 

Inorganic coatings include enamels, glass linings, and conversion coatings. Porcelain enamel coatings are inert in water and resistant to 

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Therefore, this type of coating is not sensitive to defects, pinlroles or mechanical damage during service. A typical example is galvanized steel (Zn layer on steel). 

Paper may be coated either on equipment that is an integral part of the paper machine, ie, on-machine coating, or on separate converting equipment. Many plants include both types of coating equipment and utilize each to its maximum advantage for paper and paperboard. The combination of techniques is of particular value where more than one coating must be appHed to the sheet in order to obtain a product of desired quaUty. 

In the late 1800s, when the demand for coated paper for the halftone printing process increased, casein rapidly replaced glue. Casein forms a hard, tough film when dry, and can be waterproofed easily with formaldehyde (qv). The properties of soy protein are similar to those of casein, and soy protein has been substituted for it in many types of coated papers requiring a casein-type binder (see Soybeans and other oilseeds). Casein, a valuable food product, is seldom used as a paper adhesive, in spite of its excellent adhesive properties. 

In addition, all of the process raw materials must be clean and not iatroduce contaminants. The raw materials and temporary coatings must also be defect-free, and these have to be manufactured under similar conditions so that no contaminants are iatroduced. The solvents used to clean the substrate and develop the resists must be filtered and pure. Care must also be taken to ensure that no trace compounds or elements are present that may affect the electronic properties. The specific type of coating aid, the type of functional coating, and the process used to apply the functional coating are all widely varied ia actual practice. 

The requirements (a) to (c) are obligatory for all types of coating and all objects to be protected for example, they are well known in the protection of steel structures. The objects discussed in this handbook are continuously in contact with electrolytes. For this reason in addition, requirement (d) is of great importance and is discussed in detail below. 

In order to choose the type of coating and determine the necessary coating thickness, many practice-oriented tests would have to be carried out in which the evaluation of damage areas and choice of service conditions are not always comparable [42-44]. However, information on the various thickness ranges of the PE coating in Ref. 4 was deduced from such experiments. 

There are three basic types of coatings, thermai barrier coatings, diffusion coatings, and piasma sprayed coatings. The advancements in coating have aiso been essentiai in ensuring that the biade base metai is protected at these... 

Figure 11-11. Comparative resistance in various types of coatings.

A wide range of polyurethane-type products has become available in recent years for coating applications. These include simple solutions of linear polyurethanes, two-pot alkyd-isocyanate and polyether-isocyanate systems and a variety of prepolymer and adduct systems. The coatings can vary considerably in hardness and flexibility and find use mainly because of their toughness, abrasion resistance and flexibility. Uses include metal finishes in chemical plant, wood finishes for boats and sports equipment, finishes for rubber goods and rain-erosion-resistant coatings for aircraft. One type of coating is potentially competitive with PVC leathercloth. Both alkyd-di-isocyanate and adduct-diisocyanate compositions may be coated on to fabrics from solutions of controlled viscosity and solids content. Such coated fabrics are soft, flexible and, unlike PVC leathercloth, free from plasticisers. 

Another major type of coating process is wire covering. The tremendous demand for insulated cables in the electrical industry means that large tonnages of plastic are used in this application. Basically a bare wire, which may be heated or have its surface primed, is drawn through a special die attached... 

New types of coating are regularly developed and marketed. Before selecting such coatings the specifiers should be satisfied that the test results and practical experience is sound. 

Sometimes the type of coating is determined by special requirements such as abrasion or heat resistance. The coating may have to withstand specific chemicals or solvents. All coatings have to be a compromise of properties. A gain in one may be a loss in another. 

The choice of voltage for use with a holiday detector depends on the thickness and type of coating applied to the structure. As a guide, in the case of pipelines, a voltage equivalent to approximately 5 kV/mm thickness is used in testing a coal-tar coating. 

This brief summary illustrates the fact that a wide range of coating properties can be obtained by applying the same type of processing treatment to different materials. Table 12.4 shows the types of coating obtainable on ferrous materials. 

Properties of the deposits Almost any material which can be melted is suitable for plasma spraying, giving a vast range of possible coatings of single or mixed metallic or non-metallic substances. It is often possible to produce types of coatings which are not obtainable in any other way. Typical of the materials which are plasma sprayed are copper, nickel, tantalum, molybdenum. Stellites, alumina, zirconia, tungsten and boron carbides, and stainless steels. 

The application of any coating process may affect the physical or mechanical properties of the substrate material and any such effects should be considered when choosing the type of coating to be used and its method of application. 

This type of coating is applied to both individual items and on continuous-coil plant. The process is in use in North America, Great Britain and other European countries. 

Vacuum deposited coatings This type of coating can be deposited from... 

In pipelining, the trend is towards all-welded steel for long lines, and since the wall thickness is less than that of cast iron, protection is the more important. Many types of coating are used, from thick concrete to thin paint films, and each has its own particular suitability, but the majority of pipelines throughout the world today are coated with hot-applied coal tar or petroleum asphalt-base-filled pipeline enamels, into which reinforcing wraps, such as glass fibre are applied. 

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