Automotive
Appliances
Outdoor Furniture
Building & Construction
Electrical / Electronics
Non-Metallic Products
Automotive Industry and Powder Coatings
The automotive industry is increasing its use of powder coatings for economic, quality, and environmental reasons. The powder is being used in the automotive industry for the several parts as listed below.
- Exterior bond intermediate coat known as a "primer surfacer", as well as for finishing of under-the-hood components
- Exterior body intermediate coat
- Wheel finishing (Clear powder coatings)
Clear coats are also now being used over automotive exterior basecoats by some European manufacturers such as BMW and Volvo.
A special area is powder slurries. Here powder particles are wet ground to 3µm size and stabilized in an aqueous environment. Typically, these compositions are then being wet-spayed. Then flash-dried and fully cured in the second curing step.
Powder coatings for body parts are partially replaced back by liquids. This as wet-on-wet combines the curing of two applied film layers simultaneously.
Grow areas for powder coating in automotive are alloy wheels, breaking parts, plastic/heat-sensitive substrates, and parts that require extra protection as well as a decorative finish. Wheels, hubcaps, door handles, radiators, decorative trim, bumpers, shock absorbers, mirror frames, oil filters, engine blocks, battery trays, and coil springs are some of the many automotive products being powder coated.
Other transportation application areas are (motor) bike frames or ski cabins, bars and handles inside of trams, buses or trains, etc.
Appliances are Increasingly Getting Coated with Powder Coatings
The appliance industry benefits from the use of thermosetting powder coating in applications requiring the combination of appearance and resistance to abrasion & chemicals, temperature cycling, and abusive ware.
The appliance industry makes use of powder coating on several areas as listed below.
- Front and side panels of ranges and refrigerators,
- Washer tops and lids,
- Dryer drums,
- Air-conditioner cabinets,
- Water heaters,
- Dishwasher racks,
- Freezer cabinets, and
- Cavities of microwave ovens
Powder coatings have also replaced porcelain enamel on many washer and dryer parts. However powders are being replaced partially by liquid coil coatings. Thermoplastics powder coatings generally have a higher molecular weight compared to thermosetting powders. Their “softening point”, or glass transition temperature, is generally lower than with the classic amorphous thermosetting.
Being partially crystalline compensates for this. Thermoplastic need only to be molten and can be found on the inside of dishwashers. Polyamide thermoplastics have better chemical resistance than polyester-based. But cost increases too.
Thermoplastic and thermosetting powder coatings for food applications can be found on the inside of three-piece food and aerosol cans. To cover and protect the weld. The full body inside the protection of food canisters has been tried, but with epoxy being phased out, this is still a long way to go. Coating speed is also slow.
Outdoor Furniture, Lawn, and Garden Products
Excellent durability, UV stability, hardness, abrasion resistance and corrosion resistance combined with higher film thicknesses of powder coatings make them ideal for outdoor furniture and equipments which see rough use outdoors.
- The farm segment has powder-coated tractors and agricultural equipment.
- Golf clubs and carts, ski poles and bindings, snowmobiles, bicycles, and exercise equipment represent applications in the recreation market segment.
- Homeowners have powder coatings on lawn mowers, snow blowers, barbecue grill, patio furniture, garden tools, bird feeders, and pet cages.
Thermoplastics are being used also for outdoor public play furniture. The metal frames are pre-heated and a powder coating is tumbled on the substrate and melt-coat.
Indoor Furniture - School furniture such as tables and chairs are easy to powder coat. Doorknobs can be powder coated inside or outside. But also powder coatings for kitchens and bathrooms are very suitable and decorative. Having high film weight, they give good abrasion and chemical resistance, and humidity protection.
Architectural and Building / Construction
The architectural and building market is growing for powder coated products because of the excellent durability and variety of finishes and colors that are available.
The advances in polyester-TGIC and fluoropolymer powders have enabled powder coatings to compete with liquid architectural coatings in durability, weatherability, and resistance to fading.
- These are being used on outdoor stadium seating and other exterior applications that were previously susceptible to degradation from ultraviolet rays
- Aluminum extrusions used on frames for windows and doors are powder coated as are building facades, fixtures, and modular furniture
- Many highway and building projects use powder coating on products such as light poles, guard rails, signs, posts, and fencing
- Light poles, lawn furniture, shopping carts and shelving often benefit from powder with fluorocarbon (polytetrafluoroethylene) additives for increased resistance to abrasion
- Clear coat powders are often used as an external protective layer on many brass products such as door-knobs, hinges, railing, lamps, and plumbing fixtures. Some powders can substitute for chrome and brass plating in certain applications
Electrical/Electronics
Powder coatings are used for exterior housings in the electrical and electronic industries. However, they are also being evaluated for unique, functional applications.
Powder coating of copper and aluminum magnet wire significantly reduces environmental problems in the wire industry. The toughness and durability of powder coatings in applications such as transformer and motor windings provide an added bonus.
Makers of electronic components sometimes use electroconductive and electrodissipative powder coatings.
These coatings provide electrostatic discharge protection of the components - critical during the manufacture, testing, and transport of electronic goods.
These powder coatings are often based upon the Epoxy-Polyester chemistry.
Non-Metal Substrates
Originally powder coatings were applied as metal finishing coatings only. However with the development of powder that can be applied and cured at low temperatures, the market has opened to heat-sensitive substrates such as plastics and wood.
- Radiation curing (UV or electron beam) allows the curing of powder on heat-sensitive substrates by reducing the curing temperature to below 121°C. Reducing the curing temperature is not without risk. Either flow or leveling is reduced which impact the appearance in a negative way
- On the other hand, the “softening point” or glass transition temperature of the powder coating particles is reduced. For special applications only, powders can be stored under lower ambient temperatures to prevent caking
Powder Coating on Wood is Growing Significantly
Wood manufacturers and their customers are now able to powder coat a wide range of wood products by developing:
- Powders with reduced heat requirements, and
- A uniform density wood product
Manufacturers of home and office furniture, kitchen cabinets, children's furniture and outdoor grill tables are discovering that powder coating makes these "hard-use" products retain their new look much longer. MDF is very suitable for powder coating because of its low porosity and homogeneous surface. Curing of powder on MDF can be accomplished by infrared, or UV light in conjunction with infrared or convection ovens.
Powder Coatings for Plastics
Plastics need to have some kind of conductivity to be able to powder coat.
- Special techniques have been developed to make the surface temporarily conductive
- The charged powder particles will then adhere electro-physically to the substrate
- Next step is to melt-cure the powder particles
The advantage! No color difference occurs or aging differs of the coated substrates
Powder coatings for heat-sensitive substrates require a dual-cure treatment.
- First, powder particles must melt to form a homogeneous and pore-free surface. Often the substrate is pre-heated too. This is to reduce any trapped humidity in the substrate (wood!) and to support the leveling later on
- Second step is curing. This can be the already mentioned NIR, which can be optimized to preferential heat the coating and not the substrate. Or by UV
Caution is required to find the correct catalyst for the UV curing in case of pigmented coatings. White powder coatings have only a limited window in their spectrum for UV light penetration. The catalyst must be excited just in this window to start up the polymerization.