Application guide

The application process decides the product far more than the market does. A varnish for a sheet-fed coating unit and a varnish for a rotary screen unit share a name and almost nothing else: they are metered differently, they build a different film, they dry by a different mechanism and they fail in different ways. This guide is organised by process for that reason. Each section covers what the process is good at, what actually sets the film weight, the three faults that come up most often, and the information Arctic’s technical centre in Greater Noida needs from you before a product can be specified.

Process figures given below are industry-typical ranges, offered to frame the conversation. They are not Arctic measurements, not recommendations for your line and not a guarantee of any result on it. Your own metering, drying and substrate decide the numbers that matter.

1. Gravure, wide web

Gravure prints from an engraved chrome-plated cylinder. Cells cut into the surface carry the ink, a doctor blade wipes the land clean, and the impression roller presses the web against the cylinder so the cells release. Arcova is Arctic’s wide-web gravure range. Because the engraving does not change through a run, gravure is the most repeatable of the processes here: it holds long runs, high solids, dense solids and fine vignettes on film and on metallised substrates, and it is the usual choice where the same job returns month after month and has to match the last delivery.

Film weight is set by the engraving, not by pressure and not by ink strength. Cell volume comes from screen ruling, stylus angle and cell depth together. Coarser rulings with deeper cells carry more ink and are used for solids and whites; finer rulings carry less and are used for process work and highlights. Wide-web rulings typically fall somewhere between about 60 and 200 lines per cm across that spread, with the coarse end reserved for opaque laydown. Ink strength changes the colour you get from a given cell volume. It does not change how much ink the cell holds.

Viscosity is the one variable that drifts on its own through a run. Solvent evaporates from the tray and the duct, viscosity climbs, transfer from the cells falls and density drops with it. Control it against a flow cup reference measured to ISO 2431 rather than by eye, and correct with the solvent blend the ink was built for rather than with whatever is nearest. Solvent gravure inks are commonly run in a window of roughly 14 to 22 seconds in a 4 mm cup, water-based systems higher, but the working figure belongs to the job and the engraving, not to a general table. Record the figure that gives you the agreed density and hold it.

Line speed is limited by drying capacity, not by the mechanical speed of the press. Every deck has to deliver a dry film to the next nip and a dry reel at the rewind. When coverage goes up, when a heavy white is added, or when the substrate is a heat-sensitive film that limits the air temperature you can use, the ceiling comes down. Running past it does not show up immediately: it shows up as retained solvent in the reel, as blocking, or as odour and bond failure after lamination.

• Missing dots and screening in highlights. Fine cells stop releasing when viscosity is too high, when the blade is set too hard, or when static holds the ink in the cell. It appears first in the lightest tones and in the direction of travel.
• Doctor blade lines and hazing. A worn or chipped blade, a hard particle trapped under it, or a blade angle and pressure that have been increased to cure hazing rather than to cure its cause. Hazing is usually a wiping problem or a contamination problem, and raising blade pressure hides it for an hour and wears the cylinder.
• Retained solvent and blocking in the reel. Drying set for the press speed rather than for the coverage actually being laid down, made worse by a tight wind and a warm reel going straight into storage.

To specify an Arcova product, Arctic needs the substrate and its treatment level, the print structure (surface print, or reverse print followed by lamination), the engraving detail for each deck including ruling and intended coverage, the solvent blend you can use and whether you have recovery, dryer zone lengths and available air temperatures, working and maximum line speed, the laminating adhesive if the job is laminated, and the resistance the finished job has to survive with the test method that defines pass and fail.

2. Flexographic, wide web and narrow web

Flexo transfers ink from an engraved ceramic anilox roll to a relief plate, and from the plate to the substrate. A doctor chamber with two blades meters the anilox and keeps the ink enclosed, which matters for solvent retention and for colour stability through a shift. Arcoflex is the wide-web range for solvent and water-based work, and Arcray is the narrow-web UV and LED-UV range for labels and sleeves. Arcfibre covers paper, board and corrugated post-print; Arcweb covers label and shrink sleeve stocks. Flexo suits mid and long runs with fast changeover, it handles plate-mounted sleeves and repeat changes cheaply, and it is the default on narrow web where a job may run once and never return.

Anilox volume sets laydown. This is the single point most often misunderstood on the shop floor: when a solid looks weak, the instinct is to ask for a stronger ink, but the anilox is what decides how much ink crosses the nip. A stronger ink at the same volume gives a different colour in the same film thickness, which may be what you want or may give you a film too thin to carry the rub and seal performance you also need. Typical published volumes run in a wide spread, roughly 2.5 to 6 cm³/m² for narrow-web process work, roughly 6 to 14 cm³/m² for solids and opaque white, and higher again for varnish and coating stations. Cell count, cell angle and cell geometry change release as much as nominal volume does, and a worn or partly plugged anilox delivers less than its engraving says. Plate durometer, mounting tape and impression pressure change dot shape and transfer quality. They do not increase film weight; they only spread it.

• Anilox cell plugging. Dried water-based ink or cured UV ink in the cell bottoms, showing as density that falls slowly over a shift and never fully returns after a wash. It is a cleaning regime problem and it is usually discovered too late, once the roll has lost a measurable share of its volume.
• Impression set too heavy. Squeeze produces gain, haloed edges, bounce and gear marking, and it gets worse as the operator adds pressure to chase a solid that a low anilox volume cannot give. Set impression by kiss and fix the laydown at the anilox.
• Under-cure under an opaque film on UV and LED-UV. Pigment absorbs the energy that should reach the base of the film, so the surface cures, the base stays soft and the job passes a rub test on the press and fails adhesion the next day. Heavy whites and deep colours need the dose and the photoinitiator matched to them, and LED at a single wavelength is not interchangeable with a mercury lamp on dose alone.

For an Arcoflex or Arcray specification Arctic needs the anilox volumes and line counts at each station and their approximate age and condition, plate type, thickness and tape durometer, the ink system in use (solvent, water-based, UV or LED-UV, and for LED the emission wavelength), lamp or LED unit count and power, web width and running speed, the substrate and its treatment, the colour standard you sign off against and the measurement geometry used, and the end-use resistance required with its method.

3. Sheet-fed offset coating unit

A coating unit on a sheet-fed press applies an aqueous overprint over freshly printed ink, in line, at press speed. Application is either a chambered doctor blade onto an anilox roll, which meters accurately and repeats, or a two-roll arrangement metered by a nip gap and a speed differential, which is more variable and more operator-dependent. Transfer to the sheet is by a blanket for full coverage or by a photopolymer coating plate for spot work, free zones and registered effects. Arclear covers overprint varnishes; Arcguard, Arcglide, Arctouch and Arcvista cover mechanical resistance, slip, tactile finish and decorative effect on the same unit; Arcfibre covers the paper and board side.

Film weight follows the anilox volume in a chambered unit and the nip and speed ratio in a two-roll unit. Aqueous overprints are generally applied in a modest wet film, commonly quoted in the region of 1 to 4 g/m² wet depending on the unit and the board, with the useful figure being the one that gives you the gloss and the rub result on your own stock.

Holdout on fibre governs the result more than the varnish formulation does. Gloss comes from a continuous film sitting on the surface. On a well-coated board the varnish stays up and reflects; on an uncoated or absorbent grade, part of it goes into the sheet, the film that remains is thinner and broken, and gloss collapses no matter what is applied. The same board property explains why gloss differs between the coated face and a reverse side, why it changes between mill lots, and why a matt finish is easier to hold than a high gloss. Describe the surface by measurement where you can: water absorptiveness to ISO 535 and roughness to ISO 8791 say more than a grade name, and gloss should be agreed to ISO 2813 at a stated angle.

• Gloss variation across the sheet and between piles. Almost always holdout, ink film thickness underneath, or moisture in the stock, and only rarely the varnish itself.
• Blocking and set-off in the pile. Sheets stacked high and warm before the film has hardened, particularly with heavy ink coverage underneath and an oxidative ink set that is still working.
• Craters and pinholes from contamination. Silicone from press-room sprays and release agents is the common cause, at levels far below anything visible. Anti-set-off powder, its grade and its dose also change both gloss and the finish you feel.

Arctic needs the board grade and whether it is coated on one or both sides, the ink set and whether the varnish runs wet on wet in line or off line, the application unit type with anilox volume or nip settings, pile height and how warm the pile runs, the finish required with its method and value, and above all the downstream operations: gluing needs varnish-free zones and a stated adhesive type, foil stamping and lamination both need a surface the applied film will accept, and none of that can be retrofitted after the varnish has been chosen.

4. Roll coating and die coating on a web, including aluminium foil

Here the coating is the product rather than a finish on top of one. Roll coating (gravure roll, reverse roll, smooth roll) and slot die coating apply a uniform full-coverage film at a controlled weight, then an oven drives off solvent or water and completes cure. Arcfoil covers aluminium foil lacquers, Arcbar barrier coatings, Arcseal sealing layers, Arcresist resistance coatings and Arclear clear finishes. The process is the right one wherever a functional layer has to be laid down evenly at a specified weight across the full width, rather than in an image.

What sets the film weight depends on the head. In roll coating it is the metering element plus the speed ratio between applicator roll and web, so viscosity and nip pressure both feed into the result and the coating’s rheology is part of the metering. In slot die coating the weight is volumetric: pump rate divided by coated width and line speed. Within the operating window that makes weight largely independent of viscosity, which is why die coating is chosen where weight tolerance is tight. In both cases the number that matters is dry weight, so the solids content of the supplied product converts your wet setting into the dry film. Foil lacquers commonly sit in the region of 0.8 to 4 g/m² dry, with sealing layers substantially heavier, but the target belongs to the specification and not to a general range.

Cure is set by the temperature the substrate reaches, not by the oven air temperature. This is the most expensive misunderstanding on a coating line. An oven set to 200 degrees does not put the web at 200 degrees. Aluminium foil in particular is a heat sink with high conductivity and low mass: at speed, through short zones, it can leave the last zone well below the air setting, and the lacquer is then under-cured while every gauge on the panel reads correctly. Peak metal temperature, or peak web temperature on film, is the control variable. Measure it with a travelling profiler or a thermocouple attached to the web, establish the relationship between line speed, air setting and peak temperature for your own oven, and control against that. Under-cure shows as retained solvent and odour, poor solvent rub resistance, blocking in the reel, and adhesion that fails after forming rather than at the coater.

• Under-cure from controlling on air temperature. Compounded by a speed increase that nobody re-profiled, and confirmed only after the coated reel has gone downstream.
• Ribbing, streaks and orange peel. Speed ratio, nip pressure, worn rolls or viscosity drift in an open pan, all of which change the applied film across the width as well as along it.
• Dewetting and craters on foil. Residual rolling oil that was not fully removed in annealing, or handling contamination. It shows as small circular voids and as adhesion that varies between the bright and the matt face.

Arctic needs the substrate, meaning foil gauge and temper or film type and thickness, the coater type and metering geometry, working line speed, oven zone count, zone lengths and available air temperatures, whether you can measure peak web or metal temperature, the target dry coat weight and the tolerance on it, every downstream operation including embossing, forming, seaming, slitting and lamination, and the resistance requirement stated as a property with a method.

5. Rotary and flat-bed screen

Screen printing pushes ink through an open mesh with a squeegee, and it is the process of choice when the film has to be thick. Nothing else in this list builds height in one pass. Arctouch covers tactile finishes, Arcvista decorative and structural effects, Arcveil scratch-off and security layers, and Arcguard the harder wearing surfaces. Typical work is opaque white on transparent film, relief you can feel, structure and grain effects, heavy-build spot varnish, and scratch-off panels where the layer has to be both opaque and removable by design.

Film weight is set by the screen, not by the ink. Mesh count and thread diameter give the open volume, the emulsion or stencil build adds to it, and squeegee angle, pressure and speed determine how completely that volume transfers. Deposits across the process span a very wide band, from roughly 8 µm at fine mesh up to well over 100 µm where a coarse mesh is combined with a built stencil, which is an industry-typical spread rather than a menu. The ink is formulated to sit rather than to flow: it must shear thin under the squeegee and recover fast enough not to spread once it is down, which is the opposite of what a gravure or flexo ink is asked to do.

• Mesh marking and poor flow-out. The weave prints through because the rheology does not match the mesh, or the squeegee is too fast for the ink to level before it sets.
• Pinholes and progressive screen blocking. Ink drying in the mesh during stoppages, dust or fibre on the substrate, or contamination on the stencil. It starts as isolated voids and becomes a systematic pattern.
• Cure that does not reach the base of the film. A thick opaque layer absorbs its own curing energy. The surface hardens, the layer underneath stays soft, adhesion fails later and solvent resistance never arrives. Heavy builds need a photoinitiator package matched to the film thickness, and for LED matched to the emission wavelength, at a dose far above what a thin varnish needs.

Arctic needs the mesh specification and stencil build, whether the unit is rotary or flat bed, squeegee type, angle and speed, running speed, the curing system with lamp type and power or LED wavelength and unit count, the substrate and its treatment, the relief height or tactile effect you are aiming at and how you intend to judge it, and whether anything is printed or varnished over the screen layer afterwards.

6. Digital

On a digital line Arctic’s products sit either side of the image, not in it. Arcprime primers prepare the surface before the ink lands; Arclear, Arcvista and Arcweb varnishes go over the printed image to give the rub, scuff, chemical and handling performance that a bare digital ink film often does not have on its own, and to even out the gloss difference between inked and uninked areas. A primer is there to fix wetting and pinholing on a low-energy or non-absorbent surface and to give the ink something to key into. A varnish is there because the finished job has to survive a supply chain.

Film weight is set by whatever meters the coating: an anilox on an inline flexo station, or the metering element on an offline coater. Primers are thin by design, commonly in the region of 0.5 to 1.5 g/m² dry as an industry-typical figure. More primer is not better. A primer laid on too heavily stays soft underneath, and the whole ink film then moves on a layer that was supposed to anchor it.

A press trial closes the specification, and nothing else does. Digital ink chemistries differ between engine families, between generations of the same engine and between ink versions, and the interaction of primer, ink and varnish cannot be predicted from three datasheets. The only reliable answer is the real job, on the actual engine, on the actual substrate lot, then tested: cross-hatch or tape adhesion to ISO 2409, rub to ASTM D5264, and whatever resistance the end use demands. Test again after several days, not only at the press.

• Mottle and bleed. The primer was not fully dry or fully absorbed when the ink landed, so the drop spreads or crawls.
• Varnish attacking the ink layer. Solvent in the varnish softens a thermoplastic ink film, or cure shrinkage lifts and cracks it, and the damage appears at the varnish station rather than at the print head.
• Adhesion that passes on day one and fails in the week. A primer still coalescing, or substrate treatment that has decayed since the roll was made. The day-one test is the least informative one you can run.

Arctic needs the digital process family (aqueous inkjet, UV inkjet, dry toner or liquid electrophotographic), the substrate named exactly with its lot if possible, whether the primer is applied inline or on a separate pass and by what unit, the time and conditions between priming and printing, typical and maximum ink coverage, the varnish requirement expressed as a test and a pass level, and the run lengths involved.

7. Lining machines for can ends and closure shells

This is a compound application, not a coating application, and treating it as a coating is the fastest route to trouble. Arcseam covers can-end sealants and Arcliner covers closure liners. A metered shot of a high-solids compound is dispensed through a nozzle into a spinning end or shell, so that centrifugal force places a bead in the curl of an end or a ring or disc in a closure channel. The piece then passes through an oven to drive off water or solvent and form the film. The compound is placed, not spread: it never crosses a nip, there is no anilox and no doctor blade, and nothing about it is judged by gloss or by print quality.

Weight is set by the machine and the shot: nozzle size and geometry, the metered volume the pump delivers per piece, spin speed, and the timing of dispense against rotation. The compound’s own rheology is part of the placement, since it must pump under shear and then hold position the instant shear stops. Dry compound weight is quoted per end or per shell in milligrams and varies widely with diameter and specification, with published figures for the industry spanning roughly 30 to 180 mg per piece; your specification governs, and wet-to-dry conversion follows the solids.

It behaves differently downstream too. The compound is a gasket, so it is judged by what happens after forming and seaming, or after capping and torque testing, rather than by any property you can see at the lining machine. Compression set, ageing, and behaviour after the pack has been through a heat process are the properties that decide whether it worked.

• Misplacement. The bead lands outside the curl or the channel, thrown by spin speed that does not match the compound’s viscosity, or by a worn or partly blocked nozzle. A bead a millimetre out of position is a leak path.
• Blistering and skinning in the oven. The surface dries first and traps water or solvent underneath, which then blows. It comes from too much heat too early rather than from too much heat overall.
• Incomplete film formation. An under-dried compound stays tacky, blocks in the stack or the bag, picks up on the next piece and is too soft to take the seaming or capping operation.

Arctic needs the end or closure diameter and profile, the metal type and the coating already on it, the lining machine type and nozzle, spin speed and shot setting, the target dry compound weight per piece with its tolerance, the oven profile and dwell, how the lined pieces are stacked, bagged and stored and for how long, the seam or torque specification and the test that defines a pass, and any heat process the closed pack goes through with its temperature and time. State the regulatory framework that applies to the finished article in your destination market at the start of the conversation, so that the specification is discussed against it rather than around it.

Substrate preparation

More application faults originate in the substrate than in the product applied to it, and most of them are visible before the run starts if anyone looks.

Surface energy and treatment on film. Polyolefins are low-energy surfaces and untreated polyethylene and polypropylene sit around the low thirties in mN/m, below the surface tension of most inks and coatings, so the liquid beads rather than wets. Corona or flame treatment oxidises the surface and raises it. Common industry practice is to print on film treated into the high thirties to low forties mN/m, with higher levels usually asked for where the print is reverse-printed and laminated. Measure it rather than assume it: wetting tension by ASTM D2578, or contact angle if you have the instrument.

Treatment decays, and it decays in the roll. Oxidation is a surface effect and the surface reorganises. Low molecular weight material and the slip and antiblock additives in the film migrate back to the surface over time, so a roll treated to a good level at the film plant can arrive at your press well below it. Warm storage accelerates it, additive-rich films lose it faster, and the inside of a tightly wound roll loses it differently from the outside. Measure at the press on the day, not at goods inwards, and treat in line immediately before printing where the film and the line allow it.

Residual rolling oil on aluminium foil. Foil is rolled with a lubricant that is burned off during annealing. What remains determines whether a lacquer wets the surface or pulls away from it, and residual oil is the usual explanation for craters, dewetting and adhesion that varies down the reel. Ask the foil supplier for the residual level, and check incoming reels with a water break test or wetting tension. Remember also that double-rolled foil has a bright side and a matt side with different topography, and they do not behave the same way under the same lacquer at the same weight.

Moisture and conditioning on fibre. Paper and board exchange moisture with the air around them until they reach equilibrium, and they change dimension as they do it. A cold pallet unwrapped in a warm press hall picks up moisture at the edges, giving wavy edges, curl, misregister and variable holdout, and a stack that is too dry gives brittleness, cracking on the fold and static. Condition the stock in its wrapper in the press hall until it reaches room temperature before opening it, which for a full pallet means days rather than hours. Moisture content to ISO 287 and water absorptiveness to ISO 535 describe the stock far better than its trade grade does.

Cleanliness on metal. Drawing and stamping lubricant, fines from the press shop, oil mist, and fingerprints all sit between the metal and the coating. Silicone deserves separate mention across every process in this guide: it migrates through the air, it survives ordinary cleaning, it transfers from one reel or pile to the next, and it produces craters at concentrations no inspection will find. Keep silicone sprays and silicone-bearing release agents out of any area where coating is applied, and keep cloths and gloves from those areas out of it too.

Before you order

These are the questions Arctic asks before quoting or specifying. Answering them in advance shortens the exchange considerably, and an honest “not measured” is more useful than an estimate presented as a fact.

• Process and format. Which process from the sections above, web or sheet, web width or sheet size, and working and maximum line speed.
• Substrate, exactly. Grade and supplier designation, thickness or grammage, coated or uncoated, treated or untreated, metallised or plain, and whether it carries a slip or antiblock package.
• Treatment level measured at the press, with the date and method, not the level stated on the delivery note.
• Structure. Surface print or reverse print, laminated or not, the laminating adhesive type if there is one, and what the sealing layer is.
• Metering detail. Anilox volumes and line counts, cylinder engraving, mesh and stencil build, or nozzle and shot weight, whichever applies, plus the age and condition of those parts.
• Target film weight, stated wet or dry, with its tolerance and the method you will use to check it.
• Drying or curing. Oven zone count, lengths and available air temperatures, and whether peak web or metal temperature can be measured. For UV, lamp type and power or LED wavelength, number of units, and whether dose is measured.
• Ink and solvent system already running on the line, including the solvent blend, and whether there is solvent recovery.
• Everything that happens downstream. Slitting, lamination, forming, embossing, foil stamping, gluing and which adhesive, seaming, sleeving and shrink tunnel temperature.
• Performance requirements as property, method and pass level. Adhesion (ISO 2409 or a stated tape test), rub and scuff (ASTM D5264), coefficient of friction (ISO 8295 or ASTM D1894), gloss (ISO 2813 at a stated angle), seal strength (ASTM F88), and any chemical or product resistance the pack will meet.
• Any heat process the finished pack sees, with temperature and dwell.
• Storage and transport conditions for the converted stock, and the elapsed time between converting steps.
• Commercial frame. Annual volume, batch size, pack size and delivery point.
• Regulatory framework that applies to the finished article in the destination market, named at the outset.
• Who signs the job off, and against what. A physical retain, a printed standard, a colour value with its measurement geometry, or a written specification.

Send substrate with the enquiry wherever you can: unprinted material from the same lot you will run, and a retain of the current job if you are replacing something that already works. Work at Arctic’s technical centre and laboratory in Greater Noida starts from the substrate you actually have, and a product selected from a range of over 550 against real material and a real process description will get you to a press trial faster than any specification written from a datasheet.