Narrow-Web UV and LED-UV Flexo Inks

Arcray is Arctic’s range of ultraviolet and LED-UV curing flexographic inks for the narrow-web label press. The inks carry no solvent and no water. They are reactive systems that convert from liquid to solid film by photopolymerisation under a UV source at the print station, in a fraction of a second, with no evaporation and no drying tunnel. That single difference sets everything else: applied film weights are low, the delivered anilox volume needed for a given density is lower than in solvent work because the ink is 100 percent solids and nothing evaporates, colour strength has to be developed inside a very thin layer, and each station is cured before the next, so trapping is dry trapping onto a cured underlayer rather than wet on wet.

The boundary with the neighbouring Arctic range matters when a specification is written. The Printing Inks range, Arcova gravure, Arcoflex flexo, Arcol, Haptone, Arlam and Arcene, is wide-web packaging printing on flexible film, in solvent and water-based chemistry, for laminates and surface print. Arcray is narrow-web UV and LED-UV for self-adhesive labels and sleeves: different press, different cure, different colour model. A wide-web gravure ink is matched in the laboratory and delivered as a finished batch, whereas a narrow-web UV ink is normally bought as a mixing scheme and blended to the brand colour at the printer, against a formula and a spectrophotometer, on the day it is needed.

LED curing is not a cooler version of the same lamp, and it should not be specified as though it were. A mercury-arc lamp emits across a broad band that includes short-wave UV-C, which is absorbed in the top few micrometres of the film and is what overcomes oxygen inhibition at the surface. An LED source emits in a narrow band, typically around 395 nm, so the photoinitiator package has to absorb at that wavelength and the surface cure has to be built into the chemistry rather than borrowed from the lamp. A mercury-arc formulation does not simply work under LED: it will usually undercure, and the symptom shows first as surface tack or poor rub resistance rather than as a soft film. The compensation is that LED puts almost no infrared load into the web, which is why it suits thin filmic facestock, shrink film, direct thermal facestock and any job where the stock distorts or the adhesive softens under arc lamps. Every Arcray grade is declared as arc cure, LED cure or dual cure. The PR, LC, OW, MX and FL grades are dual-cure formulations that carry a photoinitiator package for both sources; the LM grades are formulated for LED at 395 nm. The cure source, its wavelength and its power must be stated at enquiry.

The range is organised into six subfamilies: process and extender, the mixing scheme for line and spot colours, opaque whites, metallics, fluorescent and rainbow effect colours, and low-migration LED-UV grades for indirect food contact work. Grade numbers rise with pigment loading and film build inside each subfamily. The figures in the specification table are the typical operating window for the range, and confirmed values are issued with the Technical Data Sheet and Certificate of Analysis by our laboratory.

Four-colour process cyan, magenta, yellow and black on a common vehicle, with a matching unpigmented extender for strength reduction and tinting.

Line and spot colours built on a matched mixing scheme, blended to a brand standard at the printer, with a higher loaded pre-blended option for colours that must hold density in one hit.

Opaque whites for conventional flexo stations, high-volume anilox and rotary screen, including a last-down high-slip white for shrink sleeves.

Silver and gold metallic inks based on pigment flake, for narrow-web stations set up with coarser anilox and adjusted doctoring.

Daylight fluorescent colours and a rainbow effect set for split-duct and adjacent-station blending, where visual impact is the requirement and light fastness is limited.

LED-UV colours and white formulated with highly reactive, higher-functionality raw materials to reduce extractables, for labels and sleeves on indirect food contact packs.

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.

Arcray is applied on a narrow-web flexographic label press, inline or central impression, with UV curing at each station or at selected stations. The figures quoted for any grade are the typical operating window for the range, and confirmed values are issued with the Technical Data Sheet and Certificate of Analysis by our laboratory. What governs a good result on the line is the interaction between four things: anilox volume, ink rheology, cure energy at the web, and the surface condition of the stock at the moment of printing.

Anilox and film build. A UV ink is 100 percent solids, so everything the anilox delivers stays on the substrate and the volume needed for a given optical density is lower than in solvent work at the same density. Process colours normally run 3.0 to 5.0 cm3/m2, line and spot colours 4.0 to 6.0 cm3/m2, opaque whites 6.0 to 12.0 cm3/m2 or a rotary screen station, and metallics 8.0 to 14.0 cm3/m2 with light doctoring so the flake is not sheared. Increasing anilox volume to chase density also increases the energy needed to cure the film, so the two have to be set together rather than in sequence.

Cure. Cure is the process step that everything else depends on. Lamp power, lamp-to-web distance, reflector condition and line speed together determine the dose delivered, and dose should be measured with a radiometer at the web rather than inferred from the lamp rating. Under LED at 395 nm the energy arrives in a narrow band with no short-wave UV-C, so surface cure has to come from the ink chemistry: a mercury-arc formulation run under LED will typically show surface tack, poor rub resistance and weak adhesion even when the film feels hard underneath. Whites and dense colours always need more energy than the colours around them, and on a mixed job the white station should be checked separately.

Substrate condition. Filmic facestock and sleeve film need a surface energy of 38 mN/m or above at the point of printing, not at the point of manufacture, because corona treatment decays in storage. In-line treatment is the reliable answer on PP and PE; PET and PETG facestock is normally specified top-coated or primed, because corona alone is often insufficient. Paper facestock, direct thermal top-coated paper and vinyl each have their own behaviour and should be trialled with the exact stock that will be used in production, including the adhesive and the liner. On direct thermal facestock the infrared load from a mercury-arc lamp can darken the thermal coating, so LED is normally the safer specification and any arc work must be proved on the production stock.

White and shrink sleeves. On a surface-printed clear filmic label the white is the opacity carrier and is printed first, under the colours. On a reverse-printed shrink sleeve it is the last-down layer that backs the colours, which is why OW 620 carries slip: the sleeve has to feed through the applicator without blocking or scuffing against itself. Shrink film also has to survive the print process undistorted, which is the main practical argument for LED on this work, since LED puts almost no infrared load into the web. A chill roll is recommended.

Colour management. Line and spot colours are built from the LC 310 mixing scheme at the printer, blended by weight to formula and verified with a spectrophotometer before the run, with measurement to ISO 13655 and process control against ISO 12647-6 aim data where four-colour work is involved. Ink returned from the press should be recorded and re-used within the scheme rather than accumulated, and the mixing station should be kept free of contamination from metallic and fluorescent grades.

Low-migration working. The LM grades only perform as intended if the press discipline supports them. That means full cure verified by radiometer on every run, segregated pumps, buckets, blades and cleaning equipment, control of set-off in the rewound reel, and control of the storage environment. Low-migration inks do not make a pack compliant on their own: the pack construction, the barrier, the filling and the storage conditions all contribute, and compliance for a given pack is established by testing that pack.

Trials. A press trial on the customer’s own press, cure source, anilox set and production stock is required before any Arcray grade is specified for a running job. Cure source, wavelength, lamp power and maximum line speed should be recorded at the trial and repeated in production.

Arctic specifies from the press and the pack, not from a colour name. The following information allows a grade to be proposed and a trial to be set up.

• Cure source. Mercury-arc, LED, or both on the same press. For LED, the wavelength, the lamp power in W/cm2, the lamp-to-web distance and whether every station is lamped or only selected stations.
• Press and speed. Web width, number of stations, inline or central impression, whether interstation cure is fitted at every station, whether a rotary screen station is fitted, the anilox volumes available, and the maximum and typical running speed.
• Substrate. The exact facestock and liner, adhesive type, whether the film is corona treated in line or supplied top-coated, the measured surface energy at printing, whether direct thermal facestock is involved, and for sleeves the film type and the shrink ratio required.
• Colour requirement. Process, spot, or both. Whether colours will be blended from the mixing scheme or bought pre-matched, the colour standard being worked to, the tolerance in delta E and the measurement condition.
• Opacity target. For white, the opacity required, the measurement method, whether it must be achieved in one laydown, and whether the white is first down or last down.
• End use and exposure. Chemical, moisture and abrasion exposure in filling, distribution and use; expected outdoor or retail light exposure and for how long, which decides whether fluorescent grades are viable at all.
• Finishing. Overprint varnish, laminate, cold foil, hot foil, die cutting, and whether the label is applied wet, to a chilled pack or to a hot-filled pack.
• Food contact position. Whether the pack is an indirect food contact application, the pack construction and barrier, the food type and storage conditions, and which regulation the brand owner requires the pack to satisfy. A declaration and compliance dossier is issued on request with the Technical Data Sheet, and migration behaviour for that pack is established by testing that pack.
• Housekeeping. For low-migration work, whether segregated ink handling, dedicated cleaning equipment and radiometer verification are already in place.
• Volumes and supply. Annual volume by colour, pack size preferred, shelf life expectation and whether the mixing scheme will be held at one site or several.

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.