Electrostatic spray deposition (ESD) of polymeric powders on thermoplastic (PA66) substrate (original) (raw)
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Surface and Coatings Technology, 2006
This paper deals with an electrostatic spray deposition (ESD) process of 'self organizing' TiO 2 -epoxy powder paints on metal substrates. The first part of the paper focuses on analyzing the influence of both electrical and aerodynamic operational parameters on ESD process. Design of experiments (DOE) was used to plan experimental trials. ANOVA tables were calculated and used as support instruments to interpret the experimental findings and to understand physical phenomena involved in the deposition process as well as the role of TiO 2 . As a result, several process maps were produced which report consistent trends in coating thickness versus operational parameters. Best deposition conditions could therefore be deduced. Initial attempts to produce 'self-organizing' TiO 2 -based gradient coatings are also discussed.
Surface and Coatings Technology, 2011
The scratch performance of powder-coated substrates depends on many factors, including the coating material and thickness, the deposition techniques, and the characteristics of the baking processes. In the present investigation, two thermoplastic (PPA571, an alloy of acid-modified polyolefins) and thermoset (TGIC-free, transparent, bronze-pigmented polyester) organic powders were deposited onto flat aluminium substrates by the 'hot dipping' fluidised bed and electrostatic spray coating technologies. In the former technology, the metal substrates were pre-heated to 300°C before being dipped in the fluidised bed and powder coated. In the latter technology, after electrostatic painting, the coated substrates were submitted to a curing process for 20 min at 170°C to allow the formation of continuous films. The resulting coatings differed in morphology, thickness and adhesion strength. The scratch responses of the coatings were evaluated by progressive-mode scratch tests. Different contact conditions between the scratching geometry and the coating surface were analysed using three conical (Rockwell C) diamond indenters with tip radii of 100, 200 and 800 m. Electrostatically sprayed thermoset coatings showed a better overall scratch resistance with minor deformation events and damage of a lesser extent compared to the thermoplastic coatings. On the contrary, the thermoplastic coatings displayed very singular scratch properties regardless of the deposition process, having the largest deformation events and most massive interfacial rupture.
High‐density polyethylene coating on carbon steel by an electrostatic powder spray system
Journal of Applied Polymer Science, 1998
Plain carbon steel specimens were surface-treated mechanically and then chemically before applying high-density polyethylene (HDPE) coating. Pretreated specimens were coated with HDPE powder, both with and without a heat stabilizer (Irganox 1010), using a spray electrostatic technique. Effects of various variables, such as surface roughness, prephosphating treatment, addition of stabilizer, and the role of curing time and temperature were investigated. Mechanical and immersion tests were conducted to measure adhesion, ductility, and corrosion resistance of the coated specimens. Scanning electron microscopy and infrared spectroscopy were used to study the microstructure of produced coating and its interface with the substrate, as well as the possible chemical changes that occurred. The results obtained revealed that, pure HDPE can be coated on plain carbon steel with a good performance. It was further observed that an addition of 0.5 wt % of heat stabilizer to HDPE powder increases the performance of produced coating significantly. This was evidenced by the measurements of adhesion, ductility, and corrosion resistance in sulfuric acid, sodium hydroxide, ferric chloride, water, and salt spray, as well as scanning electron microscopic examinations and infrared spectra.
Progress in Organic Coatings, 2013
A comparative evaluation of electrostatic spray and 'hot dipping' fluidized bed to deposit two different organic paints belonging to the class of thermoplastic (PPA571, an alloy of acid modified polyolefins) and thermoset (TGIC-free transparent pigmented bronze polyester) powders was performed. Visual appearance of the investigated coatings was evaluated by color, gloss and coating thickness measurements as well as by the determination of the surface morphologies. Micro-mechanical performance of the coatings was assessed by progressive load scratch tests. 'Hot dipping' fluidized bed is found a fast deposition technique as, after substrate pre-heating, it takes just few seconds to have the part completely powder coated. On the other hand, electrostatic spray deposition is a potentially selective coating technique, but it lasts longer (generally, 6 to 15 s) and, moreover, the coated parts must be post-cured for long time (at least, 15 min) and at high temperature (150-200°C) to give rise to the formation of continuous films. Indeed, whilst 'hot dipping' fluidized bed is found particularly suitable for the deposition of thick and smooth thermoplastic coatings, electrostatic spray deposition is found the most viable technique to deposit thinner and highly scratch and wear resistant thermoset coatings.
Influence of powder properties on the performance of electrostatic coating process
Journal of Electrostatics, 1997
Properties of powder, e.g. particle size distribution, chemical composition, triboand corona charging characteristics, electrical resistivity, hygroscopicity, fluidity and shape distribution play significant roles on the performance of powder coating such as transfer efficiency, film thickness, adhesion and appearance. Our focus in this paper is on particle size distribution, fluidity, charging characteristics and their effects on the first pass transfer efficiency. Even a minor difference in powder properties showed differences in the applications process illustrating the importance of characterizing physical parameters and control techniques to achieve desirable performance.
Assessment of factors influencing the transfer efficiency in electrostatic spray coating process
The electrostatic spray is one of the advanced coating methods that provide uniform and effective coating on the surfaces of the components. This method can reduce the limitations observed in conventional spray painting. The uniform layer of paint depends on various input parameters such as paint flow rate, disc air pressure, paint viscosity, and applied voltage. The design of experiment (DOE) tool optimizes the process parameters to achieve the expected or best coating combinations. The transfer efficiency is an essential factor that determines the quality of the surface coating. In this work, the DOE tool was used to increase the transfer efficiency and reduce the time taken for the coating process with optimized process parameters. The experimental test found that the combined effect of input responses has increased the efficiency of the coating up to 70 %. The determined Transfer efficiency is higher than the conventional method.
Electrostatic fluidized bed deposition of a high performance polymeric powder on metallic substrates
Surface & Coatings Technology, 2006
The electrostatic fluidized bed deposition of a single-layer PPA 571 coating onto low carbon steel rods is reported. A full factorial experimental design was developed in order to study the influence of several operative variables on the effectiveness of the coating process and on the coating thickness and uniformity. The operative variables included exposure time, air flow, the applied voltage, attitude, and the radial and vertical location of the work-piece in the fluid bed. After the experimentation, several process maps were developed as a support to identify the best way to lead the coating process. Finally, by using a statistical approach, the reliability and repeatability of the coating process was also established.
Electrochemical impedance study of thermally sprayable polyethylene coatings
Corrosion Science, 2009
In the present work low density poly ethylene (LDPE) and maleic acid grafted LDPE (LDPE-g-MAc) were pigmented with red iron oxide at three different concentrations (i.e., 20, 30 and 40 wt%). The pigmented compositions were prepared in extruder and then cryogenically grounded to bring them in powder form. These compositions were applied on grit blasted mild steel specimen by flame spray technique. Corrosion resistance of red iron oxide based compositions was studied by electrochemical impedance spectroscopy (EIS). The grafted LDPE containing 30 wt% red iron oxide showed maximum resistance to corrosion compared to 20 and 40 wt% red iron oxide based compositions.
Fluidized bed coating of metal substrates by using high performance thermoplastic powders
This paper deals with fluidized bed coating of metal substrates with high performance thermoplastic powders (polyftalamide, PPA). Two different experimental scenarios were investigated: the conventional hot dipping fluidized bed (CHDFB) process and the electrostatic fluidized bed (EFB) coating process. The preliminary experimental plan was scheduled employing design of experiment (DOE) technique. Three experimental factors and operative ranges large enough for practical purposes were considered in both of the examined scenarios. In particular, coating time and airflow rate were chosen as experimental factors in both CHDFB and EFB. The third factor was the preheating temperature of metal substrates in CHDFB and the applied voltage in EFB.