Evolution of Powder Coatings
An Introduction to Powder Coatings and Vecor Technologies Opacifiers
Everyone knows (at least in general) what paint is. Travel to your local paint dealer or big box retailer, get your paint and supplies and go home to slap paint on your walls, decks, or ceilings.
If you’re careful you’ll paint what you need painted and nothing more. If you’re like me you hire a professional painter to avoid disaster.
Fewer people know about powder coatings although many may have heard of PC. That’s because it is an inherently industrial process involving electrostatic spraying of fine powder on a conductive surface which is then typically heated to 400 ℉ (204 ℃) for up to 20 minutes to melt the powder into a solid coating-not exactly a DIY project for redecorating your kitchen.
But you have lots of powder coated products around your house, both indoor and outdoor. Virtually all metal appliances-large and small- are powder coated. Whether the end use is an indoor or outdoor location there is a suitable powder coating.
Liquid coatings have been used by man for 30,000 years (think cave drawings) while powder coatings were introduced just about 60 years ago. How has this relatively recent technology grown into an industry that will produce 4.4 million metric tonnes in 2025?
Powder Coating Pros (Partial List)
· Automation. Powder coating can be applied using automated conveyor lines, which can process hundreds of parts in a single shift
Time efficiency. Powder coating typically only requires one coat for a high-quality surface, while liquid coatings may require multiple coatings
Waste Reduction. Powder coating typically uses electrostatic spraying and dust recovery systems which can reduce waste by up to 95%/
Environmental Benefits. Powder coatings are 100% solid and release little to no Volatile Organic Compounds (VOC’s) This is a huge concern for a manufacturer as well as for the public.
Durability. Powder coatings are more durable than liquid coatings and can withstand UV degradation and chemical exposure depending on the formulation.
Substrate Flexibility. Powder coatings can be used on a wider range of substrates. Although initially limited to electrically conductive substrates, advances have been made with lower temperature cure formulation suitable even for wood based materials.
Powder Coating Cons (Partial List)
UV Exposure. Depending on the formulation, UV light can degrade powder coatings. This can be alleviated by proper selection of powder coatings with UV resistant resins.
Difficult to do Thin Coats. The minimum coating thickness is 40µ-60µ without suffering quality issues. This is in part due to the particle size of the powder ranging from a d10 of approximately 12.5µ to a d90 of approximately 55µ.
Powders Can’t be Mixed to make different colors. Simply put, you can’t tint powders with other powders the way liquid coatings can be tinted to produce a wide range of colors from a single base. Therefore, powder coatings are available in a wide range of colors.
Capital Start-Up Costs Are High. Specialized equipment is needed for high volume production including ovens, fluid bed coaters and electrostatic spray systems as well as conveying equipment.
Basic Types & Formulations for Powder Coatings
Powder Coatings are available in three basic variations
Thermoplastic. This powder coating forms a film by melting with no cross-linking of polymers and can therefore be re-melted and cooled almost infinitely. This type of powder coating is most commonly used on items such as household appliances where there is little chance of re-melting It is often applied in a fluid bed and produces a thick coating.
Thermoset. This type of powder coating contains a polymer that cross-links upon heating and cannot be remelted. A wise man I once worked for described it in terms of an egg. “You can fry an egg, but when you cool it down it doesn’t go back to a liquid.” That’s thermoset. Thermoset powder coatings are ideal for use in high heat uses like appliances, electronics, and electrical equipment coatings.
Ultraviolet Cured. Developed in the 1990’s these coatings are particularly useful for substrates that are temperature sensitive, such as fiberboard.
Resin type determines the setting and binding properties of any powder coatings whether thermoplastic or thermoset. Commonly used resins are
Epoxy
Polyester
Acrylic
Fluoropolymer
Epoxy Polyester
Hybrid Polyester
Polyurethane
Resin content can be as high as 60% by weight in a powder coating formula.
Pigments provide the color needed in powder coatings just as they do in liquid paint.
Fillers are generally lower cost materials that can influence physical properties, such as viscosity, hardness, and corrosions resistance. A common extender, for example, is barium sulfate which increases corrosion resistance and weathering resistance. Common powder coating extenders include
Metakaolin
Barium sulfate (very high density)
Talc
Calcium carbonate
Wollastonite
Metakaolin and talc generally comprise approximately 20% of a formula.
Among the most important of powder coatings formulas are Opacifiers. Not only do they add opacity, but they can also increase brightness and hiding power. The most common opacifiers used in powder coatings include
Titanium dioxide. This is a preferred opacifier in both the powder coatings and liquid coatings industries. It is expensive and very fine TiO2 can be prone to clumping in the limited mixing process used in powder coating manufacture. Although very fine TiO2 can increase opacity by higher light scattering abilities, small particles may tend to clump. TiO2 is often coated to help prevent clumping. TiO2 content in powder coatings most often ranges from 15% to 30%.
The Vecor manufacturing process helps avoid the clumping properties of TiO2 and is delivered in a very fine particle size.
Zinc oxide
Zinc sulfide
Antimony
Opacifiers work by not dissolving into the melt, which causes the suspended particles to scatter and reflect light. In general, the lighter the coating color, the more important the selection of opacifier.
Vecor offers a range of aluminosilicate based opacifiers that can partially replace expensive opacifiers such as TiO2. All Vecor materials are manufactured in an environmentally friendly manner offering not only a cost advantage but also a lowered carbon footprint.
In the same manner that powder coatings are environmentally more friendly than solvent based liquid coatings, so is the range of Vecor pigments.
