Coil and Extrusion Coatings

Coil coating is a continuous process, and the line is built so that the process section never stops. Metallic coated steel, either galvanised or zinc-aluminium alloy coated, or aluminium strip, is uncoiled and stitched to the tail of the coil ahead of it, with an entry accumulator feeding the line while the join is made. The strip is cleaned, rinsed, chemically pretreated and dried, then roll coated. Most lines coat in two stages: the prime coater applies primer to both faces, the strip runs through the first oven and is quenched, then the finish coater applies the topcoat to the front face and the backing coat to the reverse, and the strip runs through the second oven. Cure is set by peak metal temperature, not by oven air temperature, and the strip is in each oven for seconds rather than minutes. Line speed, oven length and oven temperature together fix that window, so the coating has to reach full cure inside it, and it has to hold its viscosity, its wetting and its colour across a run that may last hours. After the final oven the strip is quenched, dried and recoiled. Cutting to length, profiling and roll forming happen afterwards, normally on separate lines.

Order of operations is what separates this range from Powder Coatings and General Metal Finishing. Those ranges coat a finished part: the component is fabricated first, then cleaned, coated and cured, and the film is never asked to bend afterwards. Coil reverses that sequence. Paint is cured on flat strip, and every bend, roll form, profile, lock seam and punched edge that follows happens in a film that is already hard. Route a fabricated component to powder or to general metal finishing, and route flat strip that will be formed after painting to this range. Flexibility here is measured rather than assumed. T-bend to ASTM D4145 and EN 13523-7 records the tightest bend the film will take without cracking, and a tape pull across the bend shows whether adhesion survives the deformation. Reverse impact to ASTM D2794 and EN 13523-5, pencil hardness to ASTM D3363, solvent rub resistance to ASTM D5402, cross-cut adhesion to ISO 2409 and specular gloss to ISO 2813 fix the remaining film and mechanical properties. Durability is taken separately, by neutral salt spray to ASTM B117, humidity to ISO 6270-2, accelerated ultraviolet to ASTM G154 and natural weathering to ISO 2810. Accelerated exposure ranks systems against each other, it does not convert into years in service, so a long-life claim has to rest on outdoor data rather than on cabinet hours.

Chemistry is chosen against service life, forming severity and the climate the sheet will sit in. Polyester covers general building sheet, shutters and appliance stock. Silicone-modified polyester raises gloss and colour retention on exposed roofing and hardens the film against the abrasion it picks up in transit and on site, and the same hardness makes it less forgiving to form, so its bend limits are tighter. Polyvinylidene fluoride, normally a 70:30 blend of PVDF and acrylic, holds colour and resists chalking on architectural cladding over long exposure, and it is the chemistry architectural specifications are usually written around. Plastisol gives a thick, embossed film with the impact and abrasion resistance that industrial roofing and deep profiles need, and of the four it is the most sensitive to heat and ultraviolet, which limits it in fully exposed service in hot locations. The reverse face carries its own coat, either for blocking resistance in the recoiled state or for adhesion to the polyurethane foam core of a sandwich panel.

These are applicator products, and the infrastructure they need is specific. A coil coating cannot be applied on site or in a general paint shop: it goes to a coil coating line with a stitcher, an accumulator, roll coaters, ovens able to hold the peak metal temperature the chemistry needs at the running line speed, and a quench. Liquid coatings for architectural aluminium extrusions need a spray line and an oven of the same order, and powder is the more common route for extrusions in this market, so a liquid system suits an applicator already set up to spray and bake. Coil-applied stock for can making sits outside this range and is covered by Metal Packaging Coatings, where the film is specified against the pack contents and the process cycle rather than against outdoor exposure. Colour continuity between coil coated sheet and spray coated profile has to be agreed on approved panels before production, because the two routes lay down different films. Where a project specification names a third-party approval scheme, that requirement sits with the specified system and the applicator and has to be settled before the order is placed. Arctic formulates and colour matches these systems at its technical centre and laboratory in Greater Noida, Uttar Pradesh, and manufactures them on a production line built for batch-to-batch consistency.

Thin-film primers applied to both faces of the cleaned and pretreated strip at the prime coater, and reverse-face backing coats that control blocking in the recoiled state and, where specified, adhesion to a polyurethane foam core. Chromate-free inhibitor packages are the default for new work. The primer sets the corrosion performance of the system and the adhesion base the topcoat forms over, so it is selected against the topcoat chemistry and the substrate together.

The general-purpose topcoat band for building sheet, shutters, profiled decking and appliance stock. Polyester takes tighter bends than either silicone-modified grade at ordinary coil film builds, and it is specified where the project does not call for extended gloss and colour retention. Two grades separate interior and sheltered exterior work from exposed exterior work.

Polyester backbones modified with silicone resin for higher gloss retention, colour retention and film hardness in high ultraviolet and high ambient heat. The harder film resists the abrasion sheet picks up in transit and on site. The trade-off is forming latitude: a silicone-modified polyester needs more generous bend radii than a polyester, typically one T step higher, and the limit has to be agreed with the roll former before the coil is booked.

Topcoats built on a 70:30 polyvinylidene fluoride and acrylic binder with ceramic and other inorganic complex pigments, for cladding, rainscreen and curtain wall where long-term colour, gloss and chalk resistance govern the specification. The film is flexible and soft rather than hard, so it forms well and marks more easily than a silicone-modified polyester. The fluoropolymer needs a higher peak metal temperature to coalesce, which sets a lower maximum line speed than a polyester, and gloss is limited by the chemistry to low and medium levels.

PVC plastisol applied at high film build, gelled and fused in the oven and embossed in line. It gives the impact and abrasion resistance industrial roofing and deep profiles need, in a film that is plasticised rather than crosslinked and that is the most forgiving in the range to form. Heat and ultraviolet resistance sit below silicone-modified polyester and PVDF, cut edges need protecting, and fully exposed service in hot, high ultraviolet locations should be specified against outdoor data.

Spray-applied liquid systems for window, door, shopfront and curtain wall profiles, cured in an oven to the metal temperature the binder needs. Powder is widely used for extrusions in this market, so these liquid systems suit an applicator already set up to spray and bake. Colour is matched to the coil coated sheet on the same building as closely as two different application routes allow.

The figures below are the typical operating window for this range, not a measured result for any one batch. Confirmed values are issued with the Technical Data Sheet and Certificate of Analysis by our laboratory.

These are applicator products for a continuous coil coating line or, in the case of Arccoil EX 710, for a liquid spray line with an oven. They cannot be applied on site or in a general paint shop. The coil line must have a stitcher and an entry accumulator, a clean, rinse, chemical pretreatment and dry section, roll coaters, ovens able to hold the peak metal temperature the chemistry needs at the running line speed, and a quench.

A two-coat system runs in a single pass down a line with two coater and oven sections. The prime coater applies Arccoil PR 210 or PR 250 to both faces, the strip runs through the first oven and is quenched. The finish coater then applies the topcoat to the front face and the backing coat to the reverse, and the strip runs through the second oven, is quenched, dried and recoiled. Arccoil PV 550 is a three-coat system, so on a two-coater line the coil runs twice, primer and basecoat in the first pass and the clear coat in the second, which roughly halves effective output. Arccoil PL 610 is gelled and fused rather than crosslinked, and is embossed in line while the film is hot and before quenching. Cutting to length, profiling and roll forming happen afterwards, normally on separate lines.

Cure is set by peak metal temperature, not by oven air temperature, and the strip is in each oven for seconds rather than minutes. Line speed, oven length and oven temperature together fix that window. Verify peak metal temperature with a strip-attached thermocouple at the start of a run and after any change of line speed, gauge or width, and confirm cure with a solvent rub check to EN 13523-11 rather than by appearance. Under-cure shows first as a low rub count and as adhesion loss after forming, not as a defect on the flat panel. On Arccoil PL 610 the same check does not apply, because the film is plasticised: judge fusion by the specified hardness, impact and abrasion checks instead.

What governs a good result on the line:

• Pretreatment. A clean, correctly weighted conversion coating is the foundation of the corrosion result. No primer recovers a contaminated or under-treated strip.
• Coater setup. Roll speed ratio, nip pressure and pick-up roll condition set film build and film build uniformity across the width. Check thickness at both edges and the centre.
• Supply viscosity and temperature. Hold the supply at the agreed viscosity and coater temperature and correct with the supplied thinner only, to the supplied ratio. Solvent added off specification changes wetting, flow and the cure window together.
• Peak metal temperature. Hold it inside the grade window. Over-cure embrittles a polyester and shows as a failed T-bend; under-cure shows as poor solvent resistance and as adhesion loss after forming. Under-fusion of a plastisol shows as a soft, easily marked film.
• Forming validation. Judge flexibility by T-bend to EN 13523-7 or ASTM D4145 with a tape pull across the bend, and judge adhesion after forming rather than on the flat panel. Remember the order: plastisol is the most forgiving film in the range, PVDF and polyester form well, and the silicone-modified grades need the most generous radii. Run a forming trial on the actual roll former before committing a production coil.
• Reverse face and recoiling. Confirm that the backing coat matches the duty, blocking resistance to EN 13523-24 for recoiled stock or foam adhesion to EN 13523-20 for sandwich panel, and that the strip is cool enough at the recoiler for the backing coat specified.
• Colour continuity. Hold colour against the approved panel across the run and record it to ASTM D2244. Colour continuity between coil coated sheet and spray coated extrusion has to be agreed on approved panels before production, because the two routes lay down different films.

Accelerated exposure ranks systems against each other and does not convert into years in service, so a long-life claim has to rest on outdoor data. Where a project specification names a third-party approval scheme, that requirement sits with the specified system and the applicator and has to be settled before the order is placed. A compliance dossier for a specified system is issued on request.

Arctic specifies from the substrate, the forming schedule and the service environment together. The following need to be answered before a grade and a film build can be fixed.

• Substrate and coating mass. Galvanised steel, zinc-aluminium alloy coated steel or aluminium, the zinc or alloy coating mass, the strip gauge and width, and the pretreatment already running on the line.
• Order of operations. Is the strip formed after painting? If the component is fabricated first and coated afterwards, the enquiry belongs in Powder Coatings or General Metal Finishing rather than here.
• Forming severity. The tightest bend radius, the profile depth, whether there are lock seams, reverse bends or punched edges, and the T-bend rating the roll former will accept. This decides between polyester, silicone-modified polyester, PVDF and plastisol as much as the environment does.
• Service environment and expected life. Interior, sheltered exterior or fully exposed; ultraviolet load and ambient peak temperature; coastal, industrial or inland atmosphere; and the design life the specification names.
• Specification driver. Whether the project is written around a fluoropolymer, around a durable polyester, or around a performance class, and whether a named third-party approval scheme applies.
• Colour, gloss and effect. The colour reference, the 60 degree gloss target, the Delta E tolerance, and whether the finish is solid, metallic or pearlescent. Metallic finishes are directional and need the orientation fixed on the drawing.
• Film build. The primer and topcoat thickness the specification calls for, and for plastisol the fused thickness and the emboss pattern.
• Reverse face duty. Blocking resistance for recoiled stock, adhesion to a polyurethane foam core for sandwich panel, or a finished reverse-face colour for exposed soffits and liners.
• Line capability. Target line speed, oven length, the peak metal temperature the ovens can hold at that speed, the number of coater passes available, and coater roll condition. A PVDF or three-coat system will not run at polyester line speed.
• Formulation constraints. Whether chromate-free is mandatory, and any restricted substance list the customer applies to its own supply chain.
• Batch and continuity. Coil tonnage, call-off pattern, and whether repeat orders must match the first production coil rather than the master panel.
• Approval route. Who signs off colour, gloss and texture on production panels, and whether forming trials on the customer roll former are part of that sign-off.

For Arccoil EX 710 the questions change at the application end: alloy and temper, and the bake the temper will tolerate, because a liquid fluoropolymer cures far hotter and longer than a liquid polyester; profile length and section; the conversion coating in use; spray equipment and transfer efficiency; oven capacity and the metal temperature and dwell it can hold; and the coil coated sheet the profile has to be matched to.

The Technical Data Sheet, Safety Data Sheet and regulatory declaration for any grade in this range are issued by our laboratory against the substrate and process you are running. Tell us the job and we will specify against it.