Electrostatic coating process

The organic cellulose ester plastics are versatile materials and can be processed by almost any hot-processing technique used for thermoplastics. The principal techniques for all three plastics are injection molding and extrusion. Blow molding is also possible. Butyrate and propionate powder are used in tluidized-bed and electrostatic coating processes, as well as in the rotational molding process. 

The powder can be applied directly to the substrate surface by electrostatic coating processes or dusting onto a warmed surface. It can also be formed into shapes or preforms by the application of pressure in a die mold. This process is similar to how pharmaceutical tablets are made. In this way shaped preforms can be made that will conform to a specific joint geometry. There are a wide variety of applications to which epoxy preforms can be adapted. They can be used to... 

Halar . [Ausimont] Ethylene chlorotri-fluoroeAylene copolymer, melt pro-cessable fluoropolymer for extrusion, itg. mtdding, blow molding, rotomold-ing, fluidized bed or electrostatic coating processes. 

The use of nylon-11 for powder coatings or dry coatings (qv) has been developed in response to a growing concern for the environment (44) (see Coating PROCESSES, powder technology). Electrostatic deposition allows thin films to be appHed to metal substrates. Once the powder is appHed, it must be melted and coalesced into a continuous plastic film. Eorced draft or irradiant ovens are used for fusion, and because no polymerization or cross-linkage are required for curing, coated objects can be processed quickly and air-cooled (45). 

The volume of thermosetting powders sold exceeds that of thermoplastics by a wide margin. Thermoplastic resins are almost synonymous with fluidized-bed appHed thick-film functional coatings whereas thermosetting powders are used almost exclusively in electrostatic spray processes and appHed as thin-film decorative coatings. 

Almost all PVC powder coatings are appHed by the fluidized-bed coating process. Although some electrostatic spray-grade formulations are available, they are very erratic in their appHcation characteristics. The resistivity of plasticized PVC powders is low compared to other powder coating materials and the appHed powder quickly loses its electrostatic charge. For the same reason, PVC powders show poor appHcation characteristics in an electrostatic fluidized bed and are seldom used in this process. 

Figure 19 Schematic diagram of a continuous electrostatic powder coating process.

Considering the processing fundamentals of this dry process, almost all of the issues associated with the scale-up of more traditional film-coating processes are eliminated, and the key objective is to feed tablets directly from the tablet press into the electrostatic coating operation, and thence in to packaging. Thus, once the process is defined in terms of coating one tablet, it is replicated an appropriate number of times in order to coat all of the tablets in the batch. 

Sn, Sb)02/Mica Sn(0,F)2/Mica electrically conductive conductive flooring, antistatic packaging materials, light colored primed plastic surfaces which can be electrostatically painted in further coating process, light colored conducting surfaces in clean room conditions for dust reduction [5.235]... 

In dry coating processes the frit is ground dry with or without additives to the required fineness. For powder coating no further additives are necessary. Powders for electrostatic coating have to be hydrophobized to adjust the specific resistivity of the powder surface to lO to 10 Clem. This is achieved by adding charging agents to the mill. Special silicones are especially suitable therefor. 

In sheet steel enameling (particularly for flat-ware), the powder electrostatic coating has become the preferred process. The electric voltage difference between the pistol and the object is with 60 to 90 kV slightly weaker than that... 

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