Coatings application method selection

A matter of considerable importance in the selection of an application method is its efficiency. Spray techniques are usually inefficient, since many droplets drift past the target and are lost. Even electrostatic spraying can waste as much as 35% of the paint. There is some loss of paint in most methods, but roller coating, curtain coating and electrodeposition are very efficient. Electrodeposition is also a very useful technique where corrosion resistance is important, since it applies a uniform coating over nearly all surfaces of even the most complex-shaped article. 

Coatings for flexible substrates are most often reactive systems that contain no solvents. Because they are usually highly viscous, they tend to produce a rough surface. Therefore, the selection of the proper application method and additives is crucial. The selection is determined by the following factors 7... 

We devote a significant part of this chapter to the method of chemical vapour deposition, the development of which has been closely tied to the need to deposit thin films of a range of metals and inorganic materials for use in semiconducting devices, ceramic coatings and electrochromic materials. Table 27.3 lists some applications of selected thin film materials. Part of the challenge of the successful production of thin films is to find suitable molecular precursors, and there is much research interest in this area. 

Another commonly used application-specific method is discrete particle encapsulation (DPE). In this method, selected chemicals are used to form a thin polymeric shell around each nanoparticle providing the characteristics a user needs. Then a second thin-shell coating is added, so the nanoparticle will disperse in the best needed format. This shell contains spacer molecules that prevent the nanoparticles from coming into contact with each other. The result is steric stabilisation for nanoparticles in non liquid solvents and polymers, and electrosteric stabilisation for those needing to disperse in a fluid. 

There are a large number of standard test methods available for paints to ensure that specific performance criteria are met. The most widely used standards originate from the American Society for Testing and Materials (ASTM), British Standards Institution (BSI), Deutsche Institut fiir Normung (DIN), and the International Organization for Standardization (ISO). The methods used will depend on the paint type and intended application. A selection of methods is described below that are likely to be used for water-based coatings. 

The purpose of this chapter is to aid readers in selecting surface preparation methods, coating materials, and application methods. It also acquaints them with curing methods and helps them to comply with environmental regulations. 

A coating of a corrosion resistant metal on a corrosion prone substrate can be formed by various methods. The choice of coating material and selection of an application method are determined by the end use. 

Spraying assures excellent application where selective or spot coating is required and may be easily automated. Spraying can be accomplished by several methods (conventional air assisted, airless spray or electrostatic spray). Sprayed films usually give the best aesthetic appearance to a coated part (no runs, sags or tears). Dry film thickness is easier to control with spraying because adjustments can be made in adhesive dilution, fluid flow. 

Conformal cxiating materials are available in five basic chemistries, each with multiple application methods and several drying/curing options. As such, no one material will fit every application, but the wide variety will allow the designer to select a material that meets most technical, budgetary, and manufacturing needs. The various coatings and their characteristics are summarized in Table 41.1. 

In the selection of a coating method and equipment, the product s size, configuration, intended market, and appearance must be considered. To aid in the selection of the most efficient application method, each will be discussed in greater detail. 

Protection by separation of surface from environment by protective coating should be evaluated together with relevant parts of compatibility, mechanics, and surface. Further the problems and limitations of the applicator, climatic and working conditions, properties of materials in relation to procedures and schedules should be reviewed application methods to suit the geometry chosen systems that permit maximum application of money-saving practices, use of the minimum number of different materials and least number of colors selected maintenance practice anticipated. 

---