Metal Packaging Coatings

Metal packaging coatings are applied to tinplate, tin-free steel and aluminium by two routes. Coil and sheet are coated flat and cured before the can is made. Bodies that have already been drawn are coated by spray and cured afterwards. Tin-free steel carries no tin layer, so the organic coating is the whole of its corrosion protection and the substrate is never used bare. Speciality Coatings for Packaging, listed elsewhere on this site, is a separate range covering flexible packaging: films, foils, laminates and printed cartons. Cans, can ends, closures and aerosols are coated here, and film, laminate and carton work is coated there. Substrates, application equipment, cure schedules and failure modes all differ across that line, so metal packaging coatings are developed, tested and supplied as their own category.

An internal lining is in contact with the pack contents for the whole shelf life and has to hold through the retort or pasteurisation step as well. Development is directed at the specific pack rather than at a general resistance claim: acid fruit, brine, tomato, fish in oil, carbonated soft drink, beer. Laboratory work establishes film continuity by electrical test on the finished can, where metal exposure is read as current passed through an electrolyte fill, resistance to liquids to ISO 2812, and adhesion by cross-cut to ISO 2409. None of those methods evidence food-contact suitability on their own. That is settled by overall and specific migration testing to EN 1186 and EN 13130 under the simulants and contact conditions of the pack, and for beverage and beer by sensory and taint assessment to DIN 10955. Bisphenol A is the live regulatory issue. Regulation (EU) 2024/3190 prohibits BPA in food-contact coatings and varnishes with staged transition periods, so a lining offered into that market has to be BPA non-intent (BPA-NI), which in practice means polyester, acrylic or polyolefin dispersion chemistry in place of epoxy-phenolic.

Where the coating is applied flat it is cured before the metal reaches its final shape, and the film then has to survive forming. Draw and redraw, necking, flanging, beading, double seaming, and scoring and rivet forming on easy-open ends all take place on cured film, and none of them may cost adhesion, crack the film or break continuity. A sprayed lining is the other way round: the two-piece body is drawn and wall ironed first and coated after, and the cured film still has to take the necking and flanging that follow. Formability is checked by bend to ISO 1519 and cupping to ISO 1520, and for coil-applied stock by the bend and T-bend test of EN 13523-7. Impact is checked to ISO 6272 and cure state by solvent rub to ASTM D5402. Flat panels and formed parts are both tested, because a film that passes in the flat can still fail at a score line or a neck.

The route to market gates this category as much as the formulation does. An internal lining is qualified by the canmaker on its own line and then listed by the brand owner, and the evidence that decides it is the packing trial: filled and seamed packs, processed, held at temperature for the shelf life and then opened and examined. That trial needs a filling and seaming line and is run with the canmaker and the filler, not in a coatings laboratory. Food-contact compliance is established for the finished pack against the law of the market of sale, Regulation (EC) 1935/2004 and Regulation (EU) 2024/3190 in the European Union and the Food Safety and Standards (Packaging) Regulations, 2018 in India, and it rests on a declaration of compliance supported by migration data. No approval, certification or accreditation is claimed for these products, and no direct food contact approval is claimed. Formulation, colour matching and the laboratory testing described above are carried out at the technical centre and laboratory in Greater Noida, Uttar Pradesh, and manufacture runs on a production line built for batch-to-batch consistency.

Product-side linings for two-piece and three-piece bodies, specified against the pack contents and the retort or pasteurisation cycle the pack will see. The range covers the two application routes that matter on a canmaking line: spray into a body that has already been drawn and wall ironed, and roller coating of flat stock that is formed after cure. Grades rise in film build and chemical severity, and any raw material exclusion the brand owner requires for the market of sale is taken at enquiry and recorded in the documentation issued for the grade.

The external decorative system for can bodies: the pigmented basecoat that carries the print, and the overprint varnish that sets final gloss, slip and abrasion resistance. The basecoat is cured before the decorator runs, and the varnish is applied wet on wet over the inks and cured with them, so the two films share a heat history. Both have to survive necking, flanging, filling, conveying, pasteurisation and case packing without scuffing or blocking.

Coil and sheet coatings for end stock that are cured flat and then converted. The film has to hold adhesion and continuity through stamping, curling, rivet forming, scoring and double seaming, and has to be compatible with the sealing compound lined into the curl after the shell is formed. Grades rise with the severity of the conversion, from plain ends to full-aperture easy-open ends.

Systems for crowns, twist-off lug caps and roll-on pilfer-proof closures, covering both the external decorative build and the internal lacquer that sits beneath the sealing compound. The controlling condition is local deformation of a cured film during capping, followed by the pasteurisation cycle with torque held on the closure.

Internal lacquers for monobloc aluminium and three-piece tinplate aerosol cans, specified for the concentrate and the propellant together under pressure across shelf life. Dimethyl ether is the hardest case because it is miscible with water and allows water to be carried into the pack. External decoration for these bodies is taken from the Arccan EX and Arccan SF ranges.

Size coats, whites and finishing varnishes for sheet-fed metal decorating lines, matched to wicket oven schedules and to the stacking, feeding and slip behaviour the line needs between passes. Blocking resistance in the stack governs how soon a sheet can take the next pass, and intercoat adhesion governs whether the stack of coats survives forming.

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.

Two application routes run through this category and they are not interchangeable. Flat stock, whether coil or cut sheet, is coated by roller coater and fully cured before the metal reaches its final shape, so every forming step that follows acts on a cured film. Bodies that have already been drawn and wall ironed are the other way round: the body is formed and washed first, the lining is sprayed into it, and the film is cured afterwards, with only necking and flanging still to come. A grade written for one route will not perform on the other, because the rheology, the solids and the elongation demand are all set by the route.

Film weight is the first control on the line. On a roller coater it is set by roll pressure, roll speed ratio and coating viscosity, and it is verified by gravimetric weight difference on sampled panels rather than by gauge reading alone. On a spray machine it is set by gun output, body index time and gun position, and the deposit is deliberately uneven, with the heavier weight placed on the dome radius and the wall thinning towards the open end where the metal will be necked. Under-deposit at a draw radius or at the dome is the usual origin of a continuity failure, and it will not show on a flat panel.

Cure is specified as peak metal temperature and dwell, not as air temperature. A wicket oven running sheet and a pin oven running bodies deliver very different heat histories for the same nominal set point, and coil lines run hotter for a much shorter dwell. Peak metal temperature is confirmed with a traced thermocouple, and cure state is checked on the line by solvent rub to ASTM D5402 before the next coat is applied. An undercured film will pass gloss and adhesion in the flat and then fail on intercoat adhesion, on blocking in the stack or on chemical resistance after the process cycle.

Forming after cure is where the film is actually tested. Draw and redraw, necking, flanging, beading on three-piece bodies, double seaming, and rivet forming and scoring on easy-open ends all deform a cured film, and none of them may cost adhesion, crack the film or break continuity. Flexibility is assessed by cupping to ISO 1520 and bend to ISO 1519, with T-bend to EN 13523-7 on coil-applied stock, but panel results only screen a grade. The real assessment is on converted parts: ends after scoring and seaming, bodies after necking, closures after capping, each tested again after the process cycle with the sealing compound in place.

Sequence matters as much as the schedule. On an end line the coated stock is blanked and the shell stamped and curled first, the sealing compound is lined into the curl and dried, and only then does the conversion press form the rivet, score the panel and stake the tab. On three-piece welded bodies the internal system is not complete until the side-seam stripe has been applied over the weld and cured by induction or hot air. The weld destroys the coating locally, the stripe restores it, and stripe coverage, alignment and cure are where internal failures concentrate. The same applies to three-piece aerosol bodies, where the seam sits under propellant pressure for the whole shelf life.

The result that decides an internal lining is the packing trial, not a laboratory panel. Filled and seamed packs are processed on the customer line, held at temperature for the declared shelf life and then opened and examined for corrosion, detinning, staining, blistering, seam attack and any change to the contents. That trial is run with the canmaker and the filler. Compliance of the finished pack with the food-contact legislation of the market of sale is assessed by the party placing the pack on that market, against the simulants, contact times and temperatures that legislation sets, with sensory and taint assessment to DIN 10955 where the brand owner requires it. Arctic supplies the formulation description, the laboratory data and a compliance dossier on request, and claims no approval, certification or accreditation for these products.

Specifying a metal packaging coating correctly needs the pack, the line and the market of sale, in that order. The following are the questions Arctic will ask, and the answers should come from the canmaker and the filler together, because neither holds all of them.

The pack and its contents

• What is the fill, in detail: pH, salt content, sulphur-bearing protein, oil phase, added acid, carbonation, alcohol, essential oils or fragrance in an aerosol concentrate.
• What is the process cycle: retort temperature, time and overpressure, or pasteurisation temperature and holding time, and how many cycles the pack sees.
• What is the declared shelf life and the storage climate it must hold through.
• For aerosols, which propellant, at what pressure, and what proportion of the concentrate is water.

The pack construction

• Two-piece drawn and wall ironed, two-piece drawn and redrawn, three-piece welded, monobloc extruded, end stock or closure stock.
• Substrate and specification: tinplate with its tin coating weight, tin-free steel, or aluminium with its alloy and temper, and the gauge.
• Is the coating applied flat and formed afterwards, or sprayed into a formed body.
• Which sealing compound is used, at what stage of conversion it is lined in, and is it solvent based or aqueous.
• For easy-open ends, the score geometry and the target residual thickness, and whether a repair lacquer is applied.

The coating line

• Coil coater, sheet roller coater with a wicket oven, can decorating line with a basecoater, decorator and pin oven, or internal spray machine, and the line speed.
• Available cure schedule as peak metal temperature and dwell, and whether that schedule can be changed.
• Target dry film weight and the number of coats the line can run.
• Stack height, stack temperature and the time before the next pass, which set the blocking requirement.
• Solvent-borne or waterborne, and what the oven and the abatement system are rated for.

Market and compliance

• Which market the finished pack is sold into, and therefore which food-contact legislation the pack must be assessed against.
• Does the brand owner require any raw material to be excluded from the coating, and from what date.
• Which simulants and contact conditions the brand owner has specified for migration testing.
• Is sensory and taint assessment required, and against which reference.
• Which documents the brand owner needs in the dossier, and who signs the declaration of compliance for the finished pack.

Qualification

• Who runs the packing trial, on which line, and how many packs are laid down.
• What the teardown schedule is, and what the acceptance criteria are for corrosion, staining, blistering and seam condition.
• What the continuity acceptance limit is on the finished can, and at what sampling rate the line reads it.
• For external systems, the required gloss level, the slip window for the conveyor and case packer, and the abrasion demand of the distribution route.

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.