Coil coating is an important architectural feature

Finish first, fabricate later with coil coating

Coil coating is an automated and efficient method of coating metal. It is a continuous process which takes a coil of metal through every step of finishing, from cleaning to curing, before being packaged for shipment. The metal arrives entirely finished and ready to be used – the slogan of the industry is “Finish first, fabricate later!”. Coil coating delivers a product of consistently high quality that is durable, corrosion resistant, cost-effective, recyclable, and greener than other alternatives. It is also available in a range of coating chemistries and the resulting painted metal sheet can be formed without loss of performance.

In this article we will look at the coil coating process, the different coating technologies used for coil coating, how coil coating benefits fabricators, and coil coaters operating in New Zealand.

The main steps in the coil coating process

The coil coating process starts with an untreated coil of metal sheet which is unwound, treated, coated, cured, rewound, and packaged for shipment at a rate of 100-200 metres per minute. This process can be for one or both sides of the metal sheet, and can apply and cure up to three layers of paint. The metal sheet is most commonly aluminium, steel or galvanised steel, and coil dimensions vary;  for steel the average coil is 1.6m wide and 0.5mm thick, where aluminium lines are typically larger at 2m wide. The typical line will include decoilers, entry accumulators, brushers, coaters, treatment and quenching tanks, curing ovens, and finally recoilers. The coil coating process looks like this:

  1. Stitching the strip to the previous coil
  2. Cleaning the strip
  3. Power brushing
  4. Pre-treating with chemicals
  5. Drying the strip
  6. Application of primer on one or both sides
  1. First curing oven (15-60 seconds)
  2. Cooling the strip
  3. Top coating on one or both sides
  4. Second curing oven (15-60 seconds)
  5. Cooling to room temperature
  6. Rewinding of the coated coil

As you can see, the process is intensive and thorough. This production line allows for a consistent, accurate, and high performance coating application.

Coil coating’s top 5 benefits

Businesses in the building and construction, HVAC, appliance, automotive, transportation, and furniture industries are increasingly using pre-painted or coil coated materials in their manufacturing and building. The top five reasons for this are:

  1. Environmentally friendly
    The closed loop of the coil coating system eradicates an enormous percentage of waste associated with the painting process. The coating application efficiency is over 90%, excess metals are recyclable, emissions and disposal are low and well-controlled.
  2. Reduced costs
    Coil coating significantly reduces or eliminates paint wastage, material handling costs, energy consumption, hazardous waste disposal, insurance premiums, capacity restraints, and the cost of compliance.
  3. High quality finish
    Coating a smooth flat sheet of metal allows the finish to be smooth and consistent while removing the risk of nooks and crannies causing adhesion problems and hiding imperfections. The uniform layer of coating also allows strict maintenance of colour consistency.
  4. Corrosion resistance
    Studies have shown that coil coated metal consistently offers better corrosion resistance than post-painted surfaces. The consistency and accuracy of the painting process also ensures the best possible protection and finish.
  5. Customisation
    Coil coated metals allow for a wide range of colours, thickness, performance characteristics, and even aesthetics, including printing, stripes, embossing and more.

The different coating chemistries used for coil coating

For a process so finely tuned, there is a remarkable degree of flexibility with regards to coating technologies. The metal sheet can be coated with your specific end use in mind. Available coatings include polyesters, polyurethanes, epoxies, fluoropolymers, and more. These can also be applied with different finishes, from matte to high gloss, and textures like wrinkle.

Polyester coatings

Polyester is an extremely hard and tough coating, used across a wide range of heavy-duty surfaces. Polyester is available in a range of formulations which enhance certain properties. This is usually indicated by cost – the lower the cost, the less durable the coating.  Combine versatility with the lower cost and it is clear why polyester is a common choice for warehouses and industrial or storage buildings. Polyester is also used for appliances due to its superior scratch resistance, great flexibility and formability, and stain and dirt resistance.

Applications: Heating, ventilation, and air conditioning (HVAC) equipment, garage doors, warehouses, appliances such as refrigerators, freezers, water heaters, washers, and dryers.

Polyvinylidene fluoride (PVDF) coatings

Also called 70% PVDF (from the percentage of PVDF in the resin), polyvinylidene fluoride is a high performance fluoropolymer coating which is particularly used for architectural applications. Though known for their non-stick properties, fluoropolymers are also stable, chemical resistant, corrosion resistant, and temperature resistant, as well as having superior colour and gloss retention due to their UV stability. In short, they provide excellent protection against weathering, sun exposure, chemicals,  heat, and other harsh outdoor elements.

Applications: Architectural and residential metal roofing systems, composite and insulated metal wall panel systems, curtain walls, siding, canopies.

Silicone modified polyester (SMP) coatings

Silicone modified polyester is created by adding silicone resin to a polyester resin coating. The resulting coating is somewhere between polyester and PVDF, with the hardness of polyester and a fade and chalk resistance more comparable with that of PVDF. SMPs are more scratch and abrasion resistant that PVDF, meaning they are able to withstand rougher handling conditions. SMPs are durable, and have good weatherability, colour consistency, colour and gloss retention, and resistance to chalking, fading, and scratching. They can be modified to have an expected lifespan of up to 20 years.

Applications: Commercial and residential metal roofing, agricultural and industrial building components, siding, gutters, and downspouts.

Coil coating in New Zealand – manufacturers and applicators

The coil coating companies operating in New Zealand include New Zealand Steel (which produces ColorSteel roofing and cladding) and Pacific Coilcoaters (which produces ColorCote roofing and cladding).The biggest user of coil coated metal is the building and construction industry, accounting for 75% of the global market in 2017. The world’s leading coil coatings producers are AkzoNobel, Axalta, Beckers, Valspar, and PPG Industries.

If you are interested in what coil coating can do for your project, our experts are here to help. Get in touch through the “Request a Quote” button beneath this article and let us know about your coating needs. Then we collaborate with our coating partners to determine the best coating solution for your project.