Label and Shrink Sleeve Coatings

A label is a small piece of print that has to survive a disproportionate amount of mechanical handling. It is die-cut and matrix-stripped, rewound under tension, fed from a magazine or a reel into a labeller at speed, and then stuck, shrunk or moulded onto a container that may afterwards be filled hot, chilled, condensed on, washed or refilled. The overprint varnish is the layer that meets all of that. Arcweb is the Arctic range written for those conditions: twelve grades across six subfamilies, formulated for narrow and mid-web application and for the four label formats a converter is asked to produce.

The four formats do not share a coating. A pressure-sensitive label is printed on face stock over a release liner, then die-cut and matrix-stripped, so the coating has to sever cleanly at the kiss cut and let the matrix lift away in one piece. A wet-glue label is applied by a labeller with water-based glue onto glass or tinplate, so the coating has to tolerate glue pick-up and moisture from the reverse, and on a returnable bottle it has to survive a hot caustic wash without lifting in sheets or greying. A shrink sleeve is printed reverse or surface on PVC, PETG or OPS film, then shrunk in a steam or hot-air tunnel, so the coating has to move with the film. An in-mould label is placed in the mould and the polymer is injected or blown behind it, so the surface behaviour of the coated face is one of the things that decides whether the label de-nests from the stack and seats correctly in the cavity.

The shrink sleeve subfamily asks the most of the coating. It has to shrink with the film without crazing, which rules out any hard, highly crosslinked film at the shrink ratios PETG and PVC reach. It has to give a controlled slide angle so that sleeves leave the magazine one at a time, neither sticking to the sleeve behind nor avalanching down the stack. It has to resist scratch pick-up where sleeved containers rub on conveyor rails and guide plates. It has to carry enough static control that flattened sleeves separate and open rather than clinging. It also has to handle condensation: a sleeve that absorbs moisture in a chill chain or a wet filling hall goes cloudy and patchy at the surface, the wet-look defect converters report as blotching that clears as the container dries. Arctic’s position on this range is that shrink performance cannot be judged on a drawdown card. It can only be judged in a tunnel, on the customer’s film, at the customer’s line speed and heat profile, and qualification is carried out there.

Where this range sits: Speciality Coatings for Packaging serves the flexible packaging and carton converter, coating the film and board webs that become the pack itself, while Arcweb serves the label converter, coating label stock and sleeve film that is applied to a pack made elsewhere. Web width overlaps at the mid-web end, so the division is by construction and end format, not by press width. Against the proposed Arcray narrow-web UV flexo inks the division is simpler still, in that Arcweb is the coating and Arcray is the ink. Compliance dossiers and declarations for a given grade and end use are issued on request with the Technical Data Sheet.

Water-based and UV overprint varnishes for self-adhesive label stock, formulated to sever cleanly at the kiss cut so the matrix strips in one piece, and to rewind without blocking, from everyday gloss protection through to chemical and abrasion resistant durable grades.

Varnishes for cut-and-stack wet-glue labels applied to glass and tinplate with water-based adhesive, including a caustic-wash resistant grade for returnable bottles that must come back through a hot alkaline wash without the coating lifting in sheets, greying or shedding into the bath.

Coatings for reverse and surface printed sleeves on PVC, PETG and OPS that shrink with the film without crazing, and that set slide angle, static behaviour and scratch resistance so sleeves feed from the magazine and survive the conveyor.

Coatings for in-mould labels on polyolefin face stock, where the coated face has to retain the charge applied at the placement head, or hold against vacuum, while still de-nesting cleanly from the stack.

Receptive coatings that let a printed label take variable data downstream, either from a thermal-transfer ribbon at the packing station or from a laser marking unit on the line.

Low-gloss and tactile finishes for premium label work, where the finish has to hold its matt level and its hand feel through die-cutting, rewinding and dispensing rather than only on the printed sheet.

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.

How the range is applied

Arcweb is a narrow and mid-web range. Water-based grades are applied by chambered doctor blade flexo with an anilox chosen for the target coat weight, typically 4 to 8 cm3/m2 for a protective gloss film and more where the finish has to fill a textured stock, and are dried with hot air and IR between stations. UV grades are applied by flexo for normal film builds and by rotary screen where high build is needed, and are cured with mercury or UV LED lamps. Gravure is used on sleeve film and on longer runs where coat weight has to be held very tightly across the web. Wet-glue varnishes are also run through offset press coater units on cut-and-stack work.

The figures in the table above are the typical operating window for the range, not a measured result for any single grade. Confirmed values are issued with the Technical Data Sheet and Certificate of Analysis by our laboratory.

What governs a good result on the line

Four variables decide most outcomes on a label line. The first is coat weight. Too little varnish leaves the ink exposed to scuff, and too much stiffens the face stock and raises the load the die has to cut through. The second is cure or dry state at the die. A UV film that is over-cured is brittle and chips at the die edge, and one that is under-cured stays tacky, re-bonds across the cut and blocks in the rewind; both faults look like a varnish problem and are usually a lamp, speed or anilox problem. Matrix break itself is first a die, strip tension and matrix width problem, and the coating contributes by two opposite routes, a heavy or elastic film the kiss cut does not sever cleanly so the matrix stays tied to the label, or an under-cured film that bonds back across the cut behind the die. Checking cut depth and strip tension before changing varnish saves most of these jobs. The third is surface energy. Filmic face stock and sleeve film that is not top-coated should be corona treated in line at the time of coating rather than relied on from film manufacture, because treatment decays, and a low-energy surface shows as fisheyes, pinholes and poor anchorage. The fourth is friction. Slide angle is a static friction property and is set deliberately on sleeve and in-mould grades, and changing a varnish without re-checking both static and kinetic friction is the common cause of magazine feed faults.

Shrink sleeve qualification

Shrink performance cannot be judged on a drawdown card. A coating that looks sound flat will still craze, blush or crack once the film has moved 50 or 60 per cent, and the shoulder and base of a container are where it shows first. Sleeve grades are therefore qualified in the tunnel, on the customer’s film, at the customer’s line speed, with the customer’s steam or hot-air profile, and the assessment covers crazing, gloss loss, ink anchorage after shrink, slide angle from the magazine, scratch pick-up on the conveyor and behaviour under condensation. Arctic supplies coated material for that trial and reviews the results with the converter before a specification is fixed.

Digital and hybrid presses

Label work is increasingly printed by digital process, and Arcweb grades are used over digital print as protective and functional layers. Behaviour differs by process, because a liquid electrophotographic image, a dry toner image, a UV inkjet image and an aqueous inkjet image each present a different surface to the coating. Anchorage over any digital print is confirmed by a press trial on the customer’s press, ink set and substrate before a grade is specified.

Documentation

Every grade is supplied with a Technical Data Sheet and a Safety Data Sheet, and a Certificate of Analysis is issued with the batch. Compliance dossiers and declarations covering the end use a customer has to satisfy are issued on request with the Technical Data Sheet.

What we need to know to specify correctly

Label coatings are specified against the construction and the line, not against a gloss figure. The following answers let Arctic recommend a grade and set the trial.

• Which label format? Pressure-sensitive, wet-glue, shrink sleeve or in-mould. Each one leads to a different subfamily.
• What is the face stock or film? Paper grade, or film type and thickness, whether it is coated or top-coated, and whether it is corona treated at your end.
• What ink set is underneath? Water-based flexo, UV flexo, offset, or digital, and for digital which process: liquid electrophotographic, dry toner, UV inkjet or aqueous inkjet.
• How is the coating applied? Flexo with what anilox volume, gravure with what cylinder, or rotary screen, and what drying or curing is available, including lamp type and installed power.
• What is the line speed and the web width? Both set the dwell time you have for drying or cure.
• For pressure-sensitive work: what is the die, the cut depth setting and the matrix strip speed, and are you seeing matrix break now? What is the rewind tension and the storage temperature of finished reels?
• For wet-glue work: is the container single-trip or returnable, glass or tinplate, and if returnable, what is the caustic concentration, wash temperature and contact time? What adhesive does the labeller run?
• For shrink sleeve work: what film and thickness, what shrink ratio in each direction, steam or hot air, what tunnel profile and line speed, reverse or surface printed, and what magazine and mandrel does the applicator use?
• For in-mould work: injection or blow moulding, what polymer, what is the placement system, is the label held by an electrostatic charging bar, by vacuum or by both, and what de-nesting behaviour does the current label give you?
• What downstream marking is applied? Thermal transfer with which ribbon class, or laser marking at which wavelength and power.
• What end use and exposure? Chilled, wet, frozen, hot fill, outdoor, chemical or cleaning agent contact, the service period the label has to last, and any durability protocol you have to satisfy.
• What finish is required? Gloss level, matt level, tactile effect, and whether a coefficient of friction or slide angle target is already specified on your line.
• What documentation do you need? Technical Data Sheet, Safety Data Sheet, Certificate of Analysis, and any declaration required for the end use you are supplying.

With those answers Arctic issues a recommended grade, a coat weight window and a trial plan. Sleeve and in-mould grades are only released to a specification after the trial on your own film, tunnel or moulding line.

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.