Speciality Coatings for Packaging

Supplied with a separate hardener and mixed before application, this gloss varnish cross-links rather than simply drying, and it is specified where the finished pack meets solvents, cleaning agents, fragrances or aggressive fillings that would soften a single-component film. It suits printed paper, board and film converted on flexo or gravure lines with adequate drying capacity, and it is a finishing layer rather than a lamination surface, because the cured film gives a laminating adhesive little to key to. Where the starting point is resistance to a named product formulation rather than a particular finish, the chemical-resistant coating in the product and service resistance range is the grade to begin from instead. The converter holds the mix ratio, works within the pot life, cleans anilox rolls, chambers and pans before mixed varnish sets in them, and lets the cure run before the pack is stacked tightly or filled, since resistance continues to build well after the film is touch dry.

The matt grade uses the same two-component chemistry with a matting package that scatters reflected light, so cross-linked resistance to solvents, cleaning agents and aggressive contents comes with a low-sheen surface. Matting agents sit in the film, so at the same film build the matt grade will not match the gloss grade for rub and chemical resistance, and marking shows more readily on a flat surface. Matting level and film build are therefore set against the handling the pack will actually see, and rub resistance is checked on the intended substrate before a full run. Stirring after mixing and circulation through the run keep sheen even across the job, and mix ratio, pot life and cure are controlled as on the gloss grade.

Applied in line over print, this single-component gloss varnish lifts the finish and protects the ink from rub during converting, filling and transport. No hardener and no mixing means there is no pot life to manage, which makes it the working choice wherever the pack does not face solvents or aggressive contents. It runs at a flexo or gravure coating station on printed paper, board and selected films, and on cartons it is kept clear of the glue lap so the adhesive still keys to the board. Gloss depends on how much varnish the stock absorbs, so a smooth coated board returns more gloss than an uncoated one from the same product, and gloss is assessed on the intended substrate, read at 60 degrees as is standard practice.

The single-component matt varnish reduces surface sheen and gives print a flat finish with light rub protection. Like the gloss grade it is ready to use, and it is chosen for appearance and handling rather than for resistance, so packs that will meet solvents or aggressive fillings take the two-pack matt system instead. Matting agents settle, so the varnish is stirred before the run and circulated during it to hold sheen even. Scuffing shows more on a matt surface, and where handling is heavy the answer is a matt grade formulated with anti-scuff additives, not a scuff-resistant or anti-scratch topcoat applied over it, which would raise the sheen and lose the flat finish.

Soft-touch coating gives a printed surface a dry, velvety drag under the fingertip and a deep matt appearance, and is used on cartons, laminated pouches and sleeves that are picked up and handled at the point of sale. Diffuse reflection from a matt film raises the apparent lightness of solids, so blacks and dark colours read greyer and less saturated than they do on the printed sheet, and colour is approved over the coating rather than from the sheet alone. Feel depends on how evenly the film is laid down and how completely it is cured, which puts anilox or cylinder specification, coat weight consistency and cure setting at the centre of press control, whether that is lamp dose on UV grades or dryer temperature and air volume on water-based grades. Even fully cured, a matt tactile film marks and scuffs more readily than a gloss overprint varnish, and an undercured film can also block in the stack or on the reel, so the coating is usually run with an anti-scratch layer or in an anti-scratch modified grade, with glue tabs and heat-seal areas left uncoated.

Silk-touch coating sits between a full soft-touch film and a plain matt overprint varnish, giving a smooth satin hand with less fingertip drag and a low sheen rather than a dead matt. It is the grade to specify when a pack needs a considered feel but still has to travel through cartoning, sleeving and packing equipment, where the higher surface friction of a soft-touch film can slow transport or mark against machine guides. Carrying less surface texture, it shows scuffing and finger marking less readily than soft-touch, though it lifts the apparent lightness of dark solids in the same way and is commonly paired with an anti-scratch layer on packs that see long transit or repeated handling. Coat weight and cure need the same attention as any tactile finish, stock is fully cured before stacking or rewinding so the coated face does not block, and glue and heat-seal areas are left uncoated.

Specify this grade against a single hard point dragged across the surface, a guide rail, a knife edge, a staple or grit in a carton, cutting through ink and lacquer and leaving a visible line. The coating combines a harder, more cross-linked surface with enough lubricity that the point glides over the film rather than digging into it, and it is applied over solvent and water-based inks on film, metallised substrates and paperboard. Hardness on its own is not the answer, so surface hardness is balanced against the flexibility needed to survive creasing, folding and converting without micro-cracking. Cure is the control point for the converter, because an undercured film scratches far more readily than a fully cured one, and the cure window is confirmed against the press and the ink system before the coating is specified.

Scuffing is repeated low-pressure rubbing, pack against pack in a case or web against roller, and it shows as dulling, greying or ink transfer rather than the clean cut line the anti-scratch grade answers. Resistance comes from a binder with enough cohesive strength and ink adhesion to resist being rubbed away, working with slip and wax-type additives that let surfaces glide past each other instead of gripping. Friction is set to a window rather than pushed as low as it will go, because a surface that is too slippery lets stacks slide, cases shift and reels telescope, and coefficient of friction is normally checked to ASTM D1894 on both the coated face and the reverse. Arctic Materials supplies the coating for printed film and board facing long transit, repeated handling or high-speed case packing, and matches it to heat sealing, over-printing and lamination before it is specified.

Blocking is the reel or the stack sticking to itself, so sheets tear or the web picks on unwind, typically after a job has been wound warm, stacked under load or stored in a hot warehouse. The defence is a binder that stays hard and non-tacky at storage temperature, supported by fine matting and anti-block particulates that hold adjacent layers slightly apart and stop intimate contact forming. That surface texture lowers gloss and changes how the surface takes over-print and seal, so the finish is agreed with the converter rather than assumed. Where the requirement is a controlled parting force against a named adhesive rather than the prevention of unintended adhesion, the release coating is the correct product, and in either case winding tension, residual solvent and stack temperature stay with the converter, since no coating compensates for a reel wound hot and tight.

Slip coating is the standard grade of the range, and it holds the surface friction of a printed or overprinted web in the middle window, so the web feeds, forms and seals cleanly without the finished pack losing stability in stacking and transport. It runs in line on flexo and gravure presses over inks and varnishes on films such as BOPP, PET and PE and on paper-based substrates, and it is kept clear of glue flaps, seal panels and any area to be laminated or overprinted, because a surface formulated to resist sliding contact also resists bonding. Static and kinetic coefficient of friction are read to ASTM D1894 on film and to TAPPI T 549 or ASTM D4918 on paper and board, on conditioned samples and on the couple the machine actually presents, which is how converters fix a working window for their own line and pack format. Coat weight consistency, drying, reel tension and storage conditions stay with the converter, because under-dried coating, blocking in the reel and migration of slip additives with time and temperature all move the friction of the delivered web away from the level seen at the press.

Where the standard slip level does not suit the machine or the pack, these grades take friction deliberately to one end or the other of the same formulating approach. High-slip is chosen where the web must run and release readily over formers, collars, plough folders and chutes, or where a case packer needs cartons to slide into collation without stalling, and it is not a substitute for a release or heat-resistant coating where the web contacts hot sealing jaws. Low-slip raises friction instead, so filled bags hold position on a pallet and stacked packs do not creep in transit, and it suits friction-fed magazines and hoppers that must pick single blanks or sheets. Both are matched to the substrate, the ink and varnish system and the line speed, and both are verified by the converter to ASTM D1894, or the equivalent paper and board method, on the finished print or laminate rather than on the coating in isolation, since over-slipping brings its own penalties in winding and reel stability.

Where the web passes under a sealing jaw, through a shrink tunnel or over a hot roller, this coating stops the ink softening, picking off or transferring to hot metal. It gives the jaw a harder and more thermally stable surface to run against, so the print stays intact and the tooling stays clean through a long run. Performance depends on the ink system, the substrate and the dwell time and pressure at the jaw, so the grade is matched to the seal conditions the converter actually runs. The film must be fully dried, and on cross-linking grades fully cured, before the web meets heat, since retained solvent and incomplete cure are the usual causes of pick-off.

Choose this grade when the deciding factor is the chemistry the pack will meet rather than the finish it has to carry: solvents, surfactants, household cleaners, agrochemicals and cosmetic bases, whether from a spill at the filling head or from slow contact in storage. It resists staining, softening and ink lift where the contents wet the printed surface, and the more resistant grades are two-component systems in which resin and cross-linker react on the web, so the converter mixes to the stated ratio, works within the pot life and allows the cure to develop before the pack is filled. Where a specific gloss or matt appearance is the starting point and resistance follows from it, the two-pack varnishes in the overprint range carry the same cross-linking chemistry with the finish already set. Resistance is specific to the chemistry involved, so the grade is selected against the actual product formulation and qualified by solvent rub testing and by spot or immersion contact with the filled product, and it protects the external printed face only and is not offered for direct food contact.

Fried snacks, nuts, bakery and ready meals put oil onto the outside of the pack through filling spillage, handling and case transit, and the printed face then darkens, the ink lifts and paper-based structures stain translucent where the oil sits. The coating lies over the print and gives a surface that oil does not readily wet or penetrate, on BOPP, PET and paper-based structures, though on paper the specification depends heavily on the base sheet, since an open or poorly formed sheet will wick oil whatever sits on top. It is an external coating and does not control oil migrating from the product side, which remains the job of the sealant, the barrier layer or a grease-resistant base sheet. On paper and board, converters normally qualify the coated sheet by kit testing to TAPPI T559 and by hot oil hold tests on the finished structure.

Condensation in chilled distribution, wet hands at retail, rain on a transit pack and washdown in the filling hall all attack an unprotected printed surface. The coating keeps print from blushing, softening or rubbing away when the pack is wet and holds the printed surface together through repeated wet and dry cycles, which is wet rub resistance rather than water repellency alone. On paper and board it slows surface wetting, so the fibre is less likely to raise under a brief spill, although it does not stop absorption through cut edges or prevent the loss of stiffness that comes with bulk moisture uptake. It is surface protection and not a moisture barrier through the structure, which remains the job of the film, the laminate or the moisture-barrier coating now in development.

Arctic Materials is developing a moisture-barrier coating for paper, board and mono-material film, intended to slow the passage of water vapour into or out of a pack, since ingress softens board and cakes hygroscopic contents while loss dries out contents that need to hold their moisture. Unlike the water-resistant coating, which protects the printed surface itself, this layer is aimed at transmission through the structure. Performance rests on the polymer and on the continuity of the dried film together, so formulation and coat weight are being resolved as one problem, and the layer then has to survive creasing, scoring and cut edges without opening a path through itself. Blocking in the reel is the other constraint, because the soft, hydrophobic film formers that give a useful vapour barrier are also the ones most likely to tack under winding pressure and warehouse heat, and the work is at formulation and trial stage rather than in commercial supply.

Under development for paper, board and film structures, this coating is intended to restrict oxygen transmission in place of a metallised or foil ply. Oxygen drives rancidity in fats, fading in pigments and dyes and loss of active content, so the sensitivity of what is inside dictates how tight the barrier has to be. Humidity is the hard part, because the polar polymers that give a useful oxygen barrier take up water and lose performance as relative humidity rises, so a structure that behaves well in a dry laboratory can behave differently in a monsoon warehouse. Oxygen transmission rate is conventionally measured by coulometric sensor to ASTM D3985, which is run under dry conditions, with humidity-controlled work following ASTM F1927, and Arctic Materials will report against both once the development programme concludes.

An aroma-barrier coating for paper, board and film is in development, to hold volatile flavour and fragrance compounds inside a pack and to keep external odours from migrating in. Both directions matter, since coffee, spice and fragrance packs lose their character when volatiles escape, and recycled fibre, retained solvent and print odour can taint the contents from the other side. Aroma compounds vary widely in molecular size and polarity, so no single transmission test settles the question, screening has to be run against the specific volatiles a given product releases, and the converter’s drying and residual solvent control weigh as heavily on the result as the coating does. The grade is at development stage and is not offered for commercial supply.

The UV-barrier coating carries ultraviolet absorbers and is used on transparent film and on clear window areas where the print or the contents need protection from light. It slows fading of printed inks and dyes and ultraviolet-initiated degradation of light-sensitive contents while remaining clear to visible light, so the pack still shows what is inside, and the absorbers are consumed with cumulative exposure, which means the coating delays photodegradation rather than stopping it. Two things need control on press: coat weight uniformity, because absorbance depends on how much absorber sits in the light path, and layer sequence, because an absorber screens only what lies beneath it. A UV-curable ink or varnish applied over this coating cures normally, while a UV-curable layer left to be cured through it, or absorbers loaded into a UV-curable formulation alongside its own photoinitiator, will be short of cure, and Arctic Materials will advise on placement within the structure for a given film and print sequence.

Heat-seal coatings give a web the ability to bond to itself or to a second surface when heat, pressure and dwell are applied at the jaws, which removes the need for a separate sealant film in many lidding and sachet formats. The grade is matched to the surface being sealed to, so a lacquer intended for PET differs from one intended for polypropylene film or for coated board, and it must also anchor properly to the face it is coated on, including print and lacquered foil. Jaw temperature, dwell and pressure stay with the converter, who also confirms that the coated stock does not block in the reel or the stack and does not pick off onto the sealing jaw. Seal strength is normally qualified on the finished structure to ASTM F88, and hot tack to ASTM F1921 where the pack is filled before the seal has cooled.

Cold-seal coatings bond only to themselves and do so under pressure alone, with no heat applied, so the pack closes as the jaws close. That suits heat-sensitive formats such as confectionery and bar wrapping, and it allows faster lines because there is no heating or cooling stage in the seal. The coating is applied in register to the areas that will form the seal, and the opposite face of the web carries a release lacquer so that the cold seal meets a low-adhesion surface in the wound reel instead of blocking against itself. Reel tension, storage temperature and the time between coating and use all affect how the seal performs, and food-contact suitability is not claimed and must be established separately for the finished structure.

Peelable coatings are formulated so that a seal opens by controlled failure at a chosen point, either at the interface between the coating and the sealing surface or within the coating layer itself, rather than by tearing the web, delaminating the structure or picking fibre from board. They are used on lidding for trays and pots and on flow-wrap that has to be opened by hand. The seal has to stay sound through filling, distribution and storage and still release at a force a consumer can apply, so peel is balanced against seal integrity rather than simply reduced. Behaviour depends on the substrate pairing as much as on the coating, so the grade is qualified against the specific tray or film and against the seal conditions the line will run.

Repositionable coatings hold a low and stable tack, so a label, flap or coupon can be applied, lifted and placed again without leaving residue, picking fibre from uncoated board or lifting ink from a printed panel. They are used on promotional flaps, temporary labels and information panels carried on the outside of a pack. Adhesion tends to build with dwell, so the requirement is that tack stays inside the working window rather than climbing towards a permanent bond during storage. Coat uniformity and ageing behaviour are checked on the actual face and receiving surfaces before a run is committed.

Release coatings present a low-energy surface that lets an adhesive or a cold-seal lacquer be removed at a controlled force, so the two faces part predictably rather than not adhering at all, which is what separates them from the anti-blocking coating and its job of preventing unintended contact adhesion. They are used on liners and backing papers, on the face opposite the cold seal so that the reel unwinds cleanly, and wherever a coated surface would otherwise block against the layer behind it. Release level is set against the adhesive it has to face, since too easy a release lets labels lift off the liner in the reel or in transit before they are dispensed, while too tight a release makes the label hard to strip at the peel plate and can tear the face or the liner. Release force is read by standard peel methods such as FINAT FTM 10 on the actual adhesive and liner pairing, because behaviour measured against one adhesive does not carry over to another.