Powder coating
Unlike conventional liquid paint, which is delivered via an evaporating solvent, powder coating is typically applied electrostatically and then cured under heat or with ultraviolet light.
[4] This process coats an object electrostatically and then cures it with heat, creating a finish harder and tougher than conventional paint.
Originally used on metal manufactures, such as household appliances, aluminium extrusions, drum hardware, automobile parts, and bicycle frames, the practice of powder coating has been expanded to allow finishing of other materials.
Many manufacturers prefer to have a certain degree of orange peel since it helps to hide metal defects that have occurred during manufacture, and the resulting coating is less prone to showing fingerprints.There are very specialized operations that apply powder coatings of less than 30 μm or with a Tg below 40 °C in order to produce smooth thin films.
The chemical cross-linking for hybrids and TGIC powders—representing the major part of the global powder coating market—is based on the reaction of organic acid groups with an epoxy functionality; this carboxy–epoxy reaction is thoroughly investigated and well understood, by addition of catalysts the conversion can be accelerated and curing schedule can be triggered in time and/or temperature.
In the powder coating industry it is common to use catalyst masterbatches where 10–15% of the active ingredient is introduced into a polyester carrier resin as matrix.
In general all thermosetting powder formulations contain next to the binder resin and cross-linker additives to support flow out and levelling and for degassing.
Common is the use of flow promoter where the active ingredient—a polyacrylate—is absorbed on silica as carrier or as masterbatch dispersed in a polyester resin as matrix.
UV-curable powder coatings are photopolymerisable materials containing a chemical photoinitiator that instantly responds to UV light energy by initiating the reaction that leads to crosslinking or cure.
The selection of the method depends on the size and the material of the part to be powder coated, the type of impurities to be removed and the performance requirement of the finished product.
These often occur in multiple stages and consist of degreasing, etching, de-smutting, various rinses and the final phosphating or chromating of the substrate and new nanotechnology chemical bonding.
Silicon carbide grit blast medium is brittle, sharp, and suitable for grinding metals and low-tensile strength, non-metallic materials.
This method of preparation is highly efficient on steel parts such as I-beams, angles, pipes, tubes and large fabricated pieces.
These materials typically have low-energy surfaces, are hydrophobic, and have a low degree of wetability which all negatively impact coating adhesion.
Plasma treatment physically cleans, etches, and provides chemically active bonding sites for coatings to anchor to.
In this case, the powder picks up a positive charge while rubbing along the wall of a Teflon tube inside the barrel of the gun.
A coating method for flat materials that applies powder with a roller, enabling relatively high speeds and accurate layer thickness between 5 and 100 micrometres.
When a thermosetting powder is exposed to elevated temperature, it begins to melt, flows out, and then chemically reacts to form a higher-molecular-weight polymer in a network-like structure.
Advanced hybrid systems for indoor applications are established to cure at a temperature level of 125–130 °C (257–266 °F) preferably for applications on medium-density fiberboards (MDF); outdoor durable powders with triglycidyl isocyanurate (TGIC) as hardener can operate at a similar temperature level, whereas TGIC-free systems with β-hydroxy alkylamides as curing agents are limited to approx.
[15] A major challenge for all low-temperature cures is to optimize simultaneously reactivity, flow-out (aspect of the powder film) and storage stability.
Low-temperature-cure powders tend to have less color stability than their standard bake counterparts because they contain catalysts to augment accelerated cure.
Ultraviolet (UV)-cured powder coatings have been in commercial use since the 1990s and were initially developed to finish heat-sensitive medium density fiberboard (MDF) furniture components.
[citation needed] Certain low grade powder coats can be removed with steel wool, though this might be a more labor-intensive process than desired.
According to a market report prepared in August 2016 by Grand View Research, Inc., the powder coating industry includes Teflon, anodizing and electro-plating.
Increasing use of powder coatings for aluminum extrusion used in windows, door frames, building facades, kitchen, bathroom and electrical fixtures will fuel industry expansion.
Rising construction spending in various countries including China, the U.S., Mexico, Qatar, UAE, India, Vietnam, and Singapore will fuel growth over the forecast period.
[17] Increasing demand for tractors in the U.S., Brazil, Japan, India, and China is expected to augment the use of powder coatings on account of its corrosion protection, excellent outdoor durability, and high-temperature performance.
