Thermoplastic coating powders

Table 3.4 summarizes the consumption of thermosetting binders used in various regions. The epoxy-polyester systems predominate over polyester-trisglycidyl iso-cyanurate and epoxy systems. The consumption of thermoplastic coating powders, particularly those used in the fluidized-bed and flocking processes, is substantially lower than that of thermosetting powders (Table 3.5). Their production does not show a comparably significant growth rate.

Table 3.5. Estimated production (in 10 t) of thermoplastic coating powders in 1991 classified according to binder types...

Thermoplastic Coating Powders. Polyethylene is mainly used for the exterior coating of pipes. It is also employed for coating wire goods, especially in the domestic appliances sector. 

Thermoplastic polyesters achieved some commercial success during the mid-1980s however, these were eventually replaced by nylon coating powders in functional coatings and thermosetting polyester powders in decorative appHcations because of lack of any unique characteristics or price advantages (see Polyesters, thermoplastic). 

Linear polyesters Polyesters may be obtained in a wide variety of forms including rubbers, fibres, films, laminating resins, surface coatings and thermoplastic moulding powders. The last named are somewhat similar to the nylons but are more rigid. Chemical applications, would appear to be limited because of their sensitivity to alkaline solutions and hot water. 

An integrally monlded composite article comprised of (I) a nonfoam layer formed from a thermoplastic elastomer powder composition (A) and (II) a foam layer formed from a foamable composition comprised of (i) (B) a thermoplastic synthetic resin powder, and (C) a heat decomposable foaming agent and (D) a liquid coating agent, wherein the thermoplastic elastomer powder (A) is comprised of a composition of an ethylene-alpha-olefm copolymer mbber and a polyolefin resin or thermoplastic elastomer powder comprised of a partially crosslinked composition of an ethylene-alpha-olefm copolymer mbber and a polyolefin resin, the thermoplastic elastomer powder having a complex dynamic viscosity at 250 deg C and a freqnency of 1 radian/sec of not more than 1.5x1,000,000 poise and having a Newtonian viscosity index n, calculated by a specific formula. 

Leong,K. C., Lu, G. Q., and Rudolph, V. (1999), A comparative study of the fluidized-bed coating of cylindrical metal surfaces with various thermoplastic polymer powders, /. Mater. Proc. Technol., 89/90,354—360. 

Thermoplastic coatings are often fabricated from powders. To coat a metallic object it is either dipped into a fluidized bed from which the powder deposits or one uses a spray gun to project the powder onto the metal surface. In electrostatic powder coating the polymer powder is projected in the presence of an electric field. This permits coating of recesses and hidden faces that are not in line of sight with the spray gun. After application of the powder, the object is annealed, and the powder transforms into a compact polymer coating. 

The vast majority of thermosetting coating powders are prepared by melt muting. Some thermoplastic powders are also produced by this method but most are manufactured by the dry-blend process as shown in Figure 1. Production methods based on spray drying from solution (86) and precipitation from solution (87) have been evaluated but never achieved commercial success because of difficulties in solvent and/or water removal from the powders. Many types of coating powders are still manufactured in small batches, eg, 50-1500 kg, due to differences in color or chemistry, where chemical processes are not economical. 

Nonreactive thermoplastic pultrusion utilizes completely polymerized plastics in various preprocessed states such as powder, granulates, filaments, or solutions. The use of preimpregnated fibers is advised due to short flow paths. These preimpregnated fibers can be fed into the pultruder as commingled yarns, thermoplastically coated yarns or tapes. Since impregnation is already done, no impregnation device is needed. Instead, due to the low thermal conductivity of the matrix material and its limited deterioration temperature. 

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