Powder Coatings

Powder coating is an application technology rather than a market, and it runs across most of the work Arctic already publishes: general metal finishing batches, appliance panels, off-highway machines, architectural aluminium, pipe, and, in low temperature cure chemistry, wood-based board. The coating is supplied as a dry ground solid and laid onto the part in one of three ways. It is electrostatically charged at the gun and sprayed at an earthed part, where the charge holds it in place until it is fused. A preheated part is dipped into an air fluidised bed of it, and the powder melts on contact with the hot surface. On large fabrications and site work it is fed through a flame spray gun and melts on the way to the surface. Sprayed powder then goes into an oven, where it melts, flows out and, if it is a thermoset, cures. A part coated from a fluidised bed already carries the heat that fused the film, so it needs at most a short post heat to flow the surface out, not a cure pass. Two families behave differently once the powder is molten. A thermosetting powder crosslinks and cannot be melted again, which is where its hardness and its solvent resistance come from. A thermoplastic powder does not crosslink, it melts and resolidifies, so it can be laid down far thicker and stays tough and flexible rather than hard. Either family can in principle be sprayed or dipped, but in practice thermosets are sprayed and thermoplastics are dipped or flame sprayed, because that is where the film build each one is bought for sits.

Heat is the constraint that governs the category. The whole part has to reach cure temperature and hold it, and thermosetting powder conventionally cures at around 180 °C metal temperature for a stated dwell. That is general industry practice rather than a figure for any particular grade, and it is what rules out assemblies carrying heat sensitive components, most plastics and, in standard chemistry, wood-based board. Low temperature cure chemistry exists to move that window down far enough to bring those substrates back in. Geometry is the second constraint. A charged spray wraps some way around an edge and onto the back of a thin section, but a deep recess or a box section acts as a Faraday cage and charged powder will not enter it. Tribostatic guns, which charge the powder by friction rather than in a corona field, reach into that geometry better than corona guns without removing the limit. Electrocoat does throw into recessed geometry, which is why complex weldments are commonly e-coated first and powder coated over the top. Chemistry then settles where the finished part can live. Of the common powder chemistries, epoxy leads on adhesion, chemical resistance and corrosion protection, but it chalks and loses gloss outdoors under ultraviolet. Polyester holds colour and gloss in exterior service. Epoxy polyester hybrid is the economical interior finish. Polyurethane flows to a smoother, thinner film and is exterior durable in its own right. Superdurable polyester is the grade architectural specifications call for where weathering has to hold over a long service life.

What the plant needs is the first question a buyer asks, so it is worth stating plainly. Thermosetting powder needs pretreatment, a spray booth with electrostatic guns, a clean dry compressed air supply, powder recovery if the material is to be reclaimed, a reliable earth path to every part on the conveyor, and a cure oven large enough to bring the whole part to temperature and hold it there. Powder is a combustible dust, so the booth, the recovery unit and that earthing are safety equipment and not only process equipment. Thermoplastic powder needs a fluidised bed tank and a preheat oven, or flame spray equipment for large fabrications and site work, and in most cases a blast-cleaned surface with a primer or adhesion promoter under it. Against that capital there is no mixing, no thinning, no solvent to store or handle and nothing to flash off. Powder is near zero VOC, so there is no solvent abatement plant to run, although dust extraction still applies and polyurethane grades need oven extraction for the by-product released as the blocked isocyanate cures. Where the powder is reclaimable, overspray that misses the part is collected in the booth and sprayed again, so material use is high, with the qualification that frequent colour changes and bonded metallic powders are usually sprayed to waste. Film build in a single pass is high, which often removes the second coat a liquid system would need. Powder is a new capability area for Arctic Materials. Grades are supplied to an agreed chemistry and cure window, with colour, gloss level and cure schedule settled per grade against the oven and the substrate in question, and each is issued with a Technical Data Sheet and a Safety Data Sheet. Pipeline grades are described here as powder chemistry; the asset specification that governs a coated pipeline sits with the pipe and tube work under Industrial and Infrastructure Coatings.

Thermosetting epoxy for interior steel and for functional service where adhesion, chemical resistance and corrosion protection decide the specification. Epoxy chalks and loses gloss under ultraviolet, so these grades sit indoors, under a weatherable topcoat, or in service where appearance is not the point.

The interior workhorse. Hybrid chemistry keeps most of the mechanical and chemical performance of epoxy, adds overbake and yellowing resistance, and costs less than a full polyester. It is the default for appliance housings, enclosures, shelving, racking and indoor fabrications, and it is not an exterior finish.

The exterior standard, crosslinked with a TGIC-free hardener of the HAA type. These grades hold colour and gloss in outdoor service on architectural aluminium, galvanised steel and general fabrication, and they are specified where weathering matters but a long architectural warranty period is not being asked for. HAA crosslinking gives off water as it reacts, so film build is controlled more tightly than with other chemistries.

Built on higher durability polyester resin for architectural work where gloss and colour have to hold over a long service life. Facade sections, window and door profiles, louvres, curtain walling and railings, including high ultraviolet and coastal exposure.

Cured through a blocked isocyanate, flowing out to a smoother and thinner film than a standard polyester and exterior durable in its own right. For parts where the finish itself is on show. The line needs oven extraction, because the blocking agent leaves the film as vapour when the isocyanate de-blocks.

Thermoset chemistry reformulated to crosslink well below a conventional powder schedule, around 130 to 150 degrees C object temperature on metal and lower again on board, so the substrate no longer has to survive full cure heat. This brings in medium density fibreboard and other wood-based board, assemblies carrying heat-sensitive components, and heavy castings and thick sections that are slow to bring to temperature.

Non-crosslinking powder applied by dipping a preheated part into a fluidised bed. One dip lays down a thick, tough, flexible film in a single pass, and the part melts and fuses the powder on its own retained heat. There is no crosslinking cure, only a short post-heat to flow the surface out.

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.

Every Arcdura grade is supplied ready to use as a dry ground solid. Nothing is mixed, thinned or catalysed at the line, so the variables that decide the finished film are the pretreatment under it, how the powder is laid on, how thick it goes and how much heat the part itself receives. Those four are where the work sits.

Pretreatment decides corrosion performance far more than the choice of powder. Steel needs degreasing and a conversion coating or a blast-cleaned profile, aluminium needs a chromate-free conversion or an anodic pretreatment for architectural work, and hot-dip galvanised work needs its own sequence with a preheat and degassing hold before the powder goes on, while the surface is still bare. Degas after the powder is applied and the zinc outgasses through the melting film, which is the pinholing the hold is meant to prevent. A salt spray figure quoted against a powder is a figure for the whole system and moves with the pretreatment, not with the grade code.

Sprayed grades are charged either in a corona field at the gun or by friction in a tribostatic gun. Corona lays powder down faster on open panel work. Tribostatic charging reaches further into channels, recesses and box sections, because there is no free ion stream and no strong field concentrating at the mouth of the recess to hold charged powder off it. That reduces the Faraday cage effect, it does not remove it, so complex weldments are commonly electrocoated first and powder coated over the top. Every part on the conveyor needs a clean, continuous earth path through the hook: hooks that have been coated over are the usual cause of thin film, poor wrap and rejects that look like a powder fault. Compressed air must be clean and dry, because oil or moisture in the fluidising and atomising air will show as craters.

Cure is specified by object temperature and time at that temperature, never by oven air temperature. The whole part, including the heaviest section and the thickest weld, has to reach the stated temperature and hold it for the stated dwell, so a mixed load of light sheet and heavy fabrication needs the schedule set by the slowest mass. Ovens should be profiled with a through-oven data logger when the load pattern changes. Undercure shows as poor solvent resistance, checked by solvent double rub to ASTM D5402, and as soft film, long before it shows as a visible defect. Overbake shows as yellowing and embrittlement, and hybrid grades tolerate it better than epoxy. Low-cure grades have the narrowest gap between full cure and overbake of anything in the range, which is the price of a 130 to 150 degrees C schedule, so they need the tightest oven control and cool, dated storage.

Two grades run outside the spray-and-oven route. Arcdura EP 160 is sprayed onto a part that has already been heated, so the film gels and cures on the retained heat of the part with no separate oven pass. Arcdura TP 720 is dipped: the part is preheated, lowered into an air-fluidised bed where the powder melts on contact, withdrawn and given a short post-heat to flow the surface out. Film build there is set by part temperature and dwell in the bed rather than by gun settings, so the preheat schedule is the process control. Arcdura LC 660 runs on wood-based board, where the panel is warmed so its own residual moisture makes the surface conductive enough to hold charge, and board moisture content and density have to be held consistent or the coating will show the variation.

Overspray that misses the part is collected and sprayed again, so material use is high, with two qualifications: frequent colour changes cost reclaim time, and metallic and bonded metallic shades are normally sprayed to waste, because flake separates from the resin particles in the recovery system and is damaged passing through it, so reclaim comes back at a different flake to resin ratio and the shade drifts as it is blended in. Powder is near zero VOC and there is no solvent abatement plant to run, but polyurethane grades release the blocking agent during cure and need the oven extracted. Powder is also a combustible dust. The booth, the recovery unit, the extraction and the earthing are safety equipment as much as process equipment, and should be specified and maintained on that basis.

Powder is specified against the part, the line and the service life together. Arctic can settle chemistry, gloss, film build and cure schedule once the following are known.

• Where does the finished part live? Interior, sheltered exterior, full exposure, coastal or high ultraviolet. This is the first cut: it separates epoxy and hybrid from polyester, and standard polyester from superdurable.
• What is the substrate, and what pretreatment is already installed? Mild steel, hot-dip galvanised, electrogalvanised, aluminium extrusion or sheet, casting, wire, or wood-based board. Name the conversion coating or the blast preparation grade in use, because the corrosion figure belongs to the system.
• What is the heaviest section, and what is the maximum object temperature the part will tolerate? This decides whether a conventional grade or an Arcdura LC grade is needed, and it governs the dwell.
• What can the oven actually deliver? Peak object temperature, time at temperature, conveyor speed, load pattern, and whether the oven has been profiled with a logger.
• How is the powder applied? Corona spray, tribostatic spray, fluidised bed, or spray onto a preheated part. State whether powder is reclaimed or sprayed to waste.
• What is the part geometry? Deep recesses, box sections, internal corners and blind channels change the gun choice and may need an electrocoat primer underneath.
• What film build is specified, and by whom? A minimum build called out in an architectural or asset specification changes the grade as well as the gun settings, and it decides whether adhesion is reported by cross-cut or by pull-off.
• What colour, gloss level and texture? Give the colour reference and the acceptable tolerance, the gloss band, and whether smooth, fine structure or texture is wanted. Metallic and bonded metallic shades carry reclaim restrictions.
• What does the part have to resist in service? Cleaning chemicals, fuels and oils, condensation, abrasion, impact, flexing after coating, or electrical insulation duty.
• What service life and what evidence is required? State the exposure period expected and which test methods the buyer wants reported, so the grade is matched to the property that will actually be measured.
• What plant services are available? Clean dry compressed air, powder recovery, reliable earthing, oven extraction for polyurethane, preheat and fluidised bed capacity, and cool storage for low-cure stock.
• What documentation is needed with the order? Technical Data Sheet, Safety Data Sheet, batch records, and any compliance dossier or declaration required, which is issued on request.

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.