Epoxy-based thermosetting powder coatings: Surface appearance, scratch adhesion and wear resistance (original) (raw)
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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.
Surface and Coatings Technology, 2015
The knowledge of the coating properties in terms of scratch and wear resistance is extremely important to prevent severe damage. This paper focused on the study of a comparative evaluation of the scratch and wear performance of two thermosetting powder coatings filled with different weight fractions of molybdenum disulfide (MoS 2 ) solid lubricant. Indeed, the thermoset polyester and epoxy organic powder were deposited onto aluminum substrates by an electrostatic spray coating process. The effect of MoS 2 solid lubricant on the friction and wear behavior of both polyester and epoxy composite powder coatings were assessed via reciprocating tribometer under dry friction conditions. The micro-mechanical performance of the scratch resistance of the composite coatings was conducted using progressive load scratch tests. The experimental findings of the tribological analysis have proven a significant reduction of the friction coefficient and a higher anti-wear ability of the polyester composite coatings compared with the epoxy matrix to which the addition of MoS 2 particles has a little effect on the friction-reducing mechanism. Finally, the investigation of the scratch resistance of the polyester or epoxy composite powder coatings filled with MoS 2 confirms that the incorporation of MoS 2 particles to either polyester or epoxy matrices leads to a significant decrease of the critical loads characterizing the coating damage. From the residual depth trends and contact pressure analyses, the epoxy composite coatings reinforced by 5 wt.% of MoS 2 are found to have a great scratch resistance response compared to the polyester composite reinforced by the same wt.% of MoS 2 .
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.
Industrial & Engineering Chemistry Research, 2018
Epoxy-based powder coatings are an attractive alternative to solvent-borne coatings. Here, inhouse synthesized low glass transition temperature (T g) particles containing epoxy resin and polymethyl methacrylate formed coatings at room temperature upon impact with a surface. Suspension polymerization was used to prepare particles as a function of diglycidyl ether of bisphenol A (DGEBA) and methyl methacrylate ratios. Higher incorporation of DGEBA decreased the T g to below ~20°C and eliminated the need to heat the particles and/or aluminum substrates to form coatings. Using an electrostatic powder coating apparatus, a ~70% particle deposition efficiency was achieved on aluminum substrates heated to 200°C. Whereas, at room temperature, high-speed single particle impact experiments proved that particle bonding occurred at a critical velocity of 438 m/s, comparable to commercial cold spray technologies. The in-house synthesized particles used in this study hold potential in traditional and emerging additive manufacturing applications.
Effects of thermal treatment on the tribological characteristics of thermoplastic polymer film
Thin Solid Films, 2011
Friction tests were carried out using a microtribometer to investigate the effect of thermal treatment on microscale friction and wear between poly(methyl methacrylate) (PMMA) film and a fused silica lens. Two films were examined: one that was baked at 413 K for 2 min and one that was baked at 433 K for 24 h. The friction forces on the PMMA films were measured under atmospheric conditions as the temperature of the films was increased from 300 K to 443 K. The contact area between the films and the lens was also examined. As the temperature increased, the friction force increased for both films. The slope of the friction force with temperature and the contact area varied, depending on the state of the film surface; glassy, rubbery, and viscous flow states. The baking conditions also affected the slope, contact area, and wear generation. For temperatures at which the samples were in a glassy state, wear particles were not generated on the sample baked for 24 h. The results demonstrate that the tribological characteristics can be altered by the thermal treatment of the PMMA film as well as the temperature. When the film contains some residual solvent, the residual solvent in the PMMA film can diffuse to the PMMA surface due to heating and thus decrease the friction force under room-temperature conditions.
Influence of a microcomposite and a nanocomposite on the properties of an epoxy-based powder coating
Materials Science and Engineering: A, 2011
The incorporation of nanoclays into coatings has been considered to be commercially favorable due to the improvements obtained in the barrier, thermal, and anticorrosion properties, among others, leading to the development of a new segment in the area of clean technologies: the application of nanocomposites to powder coatings. In this study, in order to compare the performance of a powder coating with the addition of a conventional load (barium sulfate) and a montmorillonite clay (MMT), two mixtures of commercial epoxy-based powder coating were prepared in the melt state, with the addition of 2 and 4% (w/w) of MMT, or 2 and 4% (w/w) of barium sulfate (BaSO 4). The thermal properties were investigated through thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC). X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM) were used to evaluate the load dispersion and the morphology of the systems formed. The physical and anticorrosion properties of the coatings were also investigated. The interaction of the MMT with the polymeric matrix, associated to the aspect ratio, resulted in better barrier properties, thermal stability, and adhesion to the metal substrate.
Isothermal degradation and thermooxidative degradation of an epoxy powder coating
Journal of Thermal Analysis and Calorimetry, 2005
Thermogravimetry was used to study the kinetics of isothermal degradation of an epoxy thermoset powder coating in a nitrogen atmosphere and in oxidising atmospheres of air and pure oxygen. An integral isoconversional procedure was used to analyse how the activation energy varies depending on the degree of conversion and depending on the atmospheres used. In the case of degradation in a nitrogen atmosphere, in addition to the activation energy, the kinetic triplet was completed using an Avrami reaction model and the pre-exponential factor. With this atmosphere, the conclusion was reached that the isothermal and non-isothermal kinetics are equivalent. It was shown that the thermooxidative degradation process is more complex and consists of a two-stage process. The first stage of degradation is similar whether nitrogen, oxygen or air are present. Chain scission occurs and it seems that there is formation of thermally more stable compounds. The second stage of degradation, involving several phenomena, occurs only in the presence of oxygen or air and leads to the total disappearance of the organic material by thermooxidation. These stages are very similar under non-isothermal or isothermal conditions.
Journal of Coatings Technology and Research, 2015
Epoxy-based nanocomposite coatings were formulated by incorporating various types of inorganic nanoparticles (NPs) (ZrO 2 , ZnO, Fe 2 O 3 , and SiO 2). The effect of the incorporation of various NPs on the mechanical, thermal, and morphological properties of these epoxy coatings has been studied. A facile direct incorporation technique has been utilized for the dispersion of the NPs in the epoxy matrix via highspeed mechanical stirring and ultra-sonication using acetone as a solvent. The incorporation of these NPs augmented the mechanical and thermal properties of the epoxy coatings. The results revealed that the incorporation of small amount of these NPs improved the mechanical properties of the coating in all cases, with the SiO 2-reinforced sample being relatively better in both mechanical and thermal properties. The incorporation of Fe 2 O 3 and ZnO resulted in a decrease in the thermal stability and glass transition temperature (T g) of the coatings, while incorporation of SiO 2 and ZrO 2 increased the thermal stability as well as T g of the coatings. A notable increase of 71% in hardness together with 26% increase in the elastic modulus of the epoxy coating was observed with the incorporation of 2 wt% SiO 2 NPs.
The role of the substrate in micro-scale scratching of epoxy–polyester films
Applied Surface Science, 2011
text: The present investigation analyzes the deformation response of electrostatically sprayed epoxy-polyester powder coatings by 'in-situ' micromechanical tests. The characterization of the performance of the coatings was carried out by microscale scratching, by varying the indenter type, the applied load and the sliding speed. The tests were carried out on polymeric coatings deposited on as-received, micro and macro-corrugated AISI 304 stainless steel substrates and 'rigidlyadhered' to them. Further tests were performed on 'free-standing' coatings, that is, on the as-received metal substrates pre-coated with an intermediate layer of siliconbased heat curable release coating. Experimental data allow us to evaluate the influence of the contact conditions between substrate and indenter and the role of the loading conditions on the scratch and penetration resistance of the epoxy-polyester coatings. The different responses of the polymeric coatings when deposited on untreated or pre-treated substrates as well as on an intermediate layer of release coating, contribute to a better understanding of the intrinsic roles of the polymeric material and substrate as well as the influence of the interfacial adhesion between coating and substrate.