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Unipress 30 LED
A dual-cure UV letterpress ink series for lamitubes and narrow-web labels, formulated to cure both under medium-pressure mercury lamps and under LED at 385–405 nm.
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UV Letterpress Inks
One ink, either lamp, on tube and label
Unipress 30 LED is a letterpress ink series for lamitube decoration and narrow-web label work. It is almost 100 % solids: no solvent, no water and no drying tunnel, so weight loss on cure is small — there is nothing to evaporate but the volatile fragments photoinitiator cleavage leaves behind — and the film that leaves the plate is very nearly the film that stays on the substrate. The series is formulated to cure under medium-pressure mercury lamps and under LED sources emitting at 385–405 nm. It is a dual-cure ink rather than an LED-only ink, and that is deliberate; the name marks the LED window the initiator package is built to reach. The cure window for each lamp type — peak irradiance and dose, with the mercury lamp rating stated — is to be confirmed, and it should be established on your own press and lamp rather than carried across from another site.
The reason for dual cure is commercial more than it is chemical. Most tube plants and label houses convert to LED gradually, a head at a time or a press at a time, over several years, and for that whole period they run a mixed lamp fleet. An ink that cures under only one source splits the ink room in two: two stock codes per shade, two shade standards, two shelf-life clocks, two sets of documents, and a repeat job that can only go back on the press it was first printed on. One dual-cure series removes that. Lamps are retrofitted on the schedule that suits the business, and the job goes on whichever press is free. The honest trade-off is that a package tuned for two lamp types is never identical to one tuned for a single lamp, which is exactly why each window is established rather than assumed.
On press the ink is short and stiff, pigmented high so that density comes from concentration rather than thickness. That is what a hard photopolymer relief plate needs: an ink that releases cleanly from the relief surface and then stays where it is put instead of spreading at the shoulder under impression. Film weight is indicatively 1.0–1.5 g/m² at solid, about one to one and a half microns, which is thin enough for 385–405 nm light to reach the substrate without difficulty and thin enough to hold small type, fine reversed text and a sharp highlight dot. The series is formulated for the treated polyethylene outer skin of ABL and PBL tube laminate, for coated label stock and for treated PP, PE and PET film — but adhesion is a property of the interface, not of the ink alone, and adhesion is qualified on your own laminate before a specification is fixed — typically cross-cut classification 0 to ISO 2409 on laminate treated to ≥ 38 mN/m, printed at 1.0–1.5 g/m² and cured to the stated dose. Check surface energy before changing ink, since treated laminate is normally wanted at 38 mN/m or better, and aged sleeve stock with slip additive bloomed to the surface needs re-treatment or a primer. Qualify on your own substrate.
After the press the print has to survive the rest of the line and then the product’s life: the seaming or heading step, where the sleeve end is heated and the shoulder is formed onto it; the cap, torqued down and taken off repeatedly, its skirt rubbing the shoulder; handling in the filler, in the carton and in the customer’s hand; and the filled product itself, where emollients, essential oils, menthol, peroxides and surfactants are the usual aggressors. The ink carries colour and adhesion. It is the overprint coating that carries the surface — a matching UniCure UV overprint coating sets the final gloss or matt finish and provides the rub and scuff resistance — so the two should be specified together. A low-migration variant is available for tubes and labels in personal-care and food-adjacent use, on raw materials selected to the EuPIA Charter, with TPO excluded across the whole series and ITX and benzophenone excluded from the low-migration grade. A migration assessment on the finished pack is carried out on request; the formulation is what we control, the assessment is what establishes conformity.
The series
Six parts of one system: the same binder and photoinitiator platform across process, bases, white, the low-migration grade and the auxiliaries, finished with a matched overprint coating.
Unipress 30 LED Process
UNIPRESS-30PY / 30PM / 30PC / 30PK
Unipress 30 LED Bases
UNIPRESS-30MB01 to 30MB12
Unipress 30 LED Opaque White
UNIPRESS-30OW (high hide: 30OWH)
Unipress 30 LED LM
Suffix -LM, e.g. UNIPRESS-30PC-LM, 30OW-LM
Unipress 30 LED Auxiliaries
UNIPRESS-30SP, 30RP, 30EX, 30MW
Unipress 30 LED Overprint Coatings (matched)
UNIPRESS-30OG gloss, 30OM matt
Product data
| Process | UV letterpress on a hard photopolymer relief, and dry offset (letterset) for tubes and cylindrical bodies; narrow-web self-adhesive labels and lamitube decoration |
|---|---|
| Chemistry | Almost 100 % solids free-radical acrylate; no solvent, no water, no drying tunnel. Weight loss on cure 1–3 %, from photoinitiator fragments rather than from evaporation |
| Cure, mercury | Medium-pressure mercury lamps rated 120–200 W/cm; peak UVA irradiance 0.6–1.2 W/cm²; 80–140 mJ/cm² UVA on process shades and 150–250 mJ/cm² on the opaque white. Band radiometer, UVA 320–390 nm, run at substrate plane and press speed |
| Cure, LED | 385–405 nm, peak irradiance 8–16 W/cm² measured at the substrate plane and not at the emitting window, head gap 2–5 mm; 250–450 mJ/cm² on process shades and 400–700 mJ/cm² on the opaque white, measured in the LED band at the substrate plane and press speed. 395 or 405 nm heads preferred on any job carrying white. Dose is peak irradiance multiplied by the time under the emitting window, so the achievable dose at a given speed is fixed by the total emitting length: at 16 W/cm², 700 mJ/cm² needs about 44 ms, which is about 90 mm of emitting length at 120 m/min and about 30 mm at 40 m/min. Quote the number of heads and the emitting length with the line speed — on a single head the white, not the line, sets the maximum speed. |
| Film weight | 1.0–1.5 g/m² at solid, about 1.0–1.4 µm; opaque white 2.0–2.5 g/m² per pass and 4.0–5.0 g/m² as a double hit. Gravimetric, 100 cm² cut from the printed web |
| Plate | Hard photopolymer relief, Shore D 62–72 (ISO 868); narrow-web label plates 0.73–0.95 mm, dry offset tube plates 0.95–1.14 mm. No dampening system |
| Relief depth and ruling | 0.40–0.55 mm relief on a 0.73–0.95 mm plate, 0.55–0.70 mm on a 0.95–1.14 mm plate; 133–175 lpi narrow web, 120–150 lpi dry offset, minimum holdable dot 2–3 % at 150 lpi |
| Tack | Bench tack 11 ± 2 as supplied for a single ink; tackmeter at 400 rpm, 30 °C, 1.3 cm³ ink charge, read at 60 s — the house charge across every sheet in the range, since tack read at another charge is not comparable. The ladder is a separate specification: graduated 12 → 8 through a wet-on-wet set, with the opaque white first down at 12 ± 1. |
| Viscosity | 40 ± 10 Pa·s with a yield value of 150–300 Pa; falling-rod (Laray) viscometer at 25 °C, ISO 12644. Opaque white 55 ± 10 Pa·s, yield value 250–450 Pa |
| Substrates | ABL and PBL tube laminate (treated PE outer skin), coated label stock, treated PP, PE and PET film. Treat and verify at 38–42 mN/m with test inks (ASTM D2578) within the shift of printing |
| Adhesion | Typically cross-cut classification 0 with no removal on ABL and PBL laminate treated to ≥ 38 mN/m and printed at 1.0–1.5 g/m² and the stated dose; fibre tear on coated label stock. ISO 2409, 1 mm lattice with tape pull, 24 h after cure at 23 °C / 50 % RH. Adhesion is a property of an interface rather than of an ink: treatment level, ageing, slip additive and the metallising or top-coat lacquer differ between laminate suppliers and between reels, so the result is qualified on the customer’s own laminate before a specification is fixed. |
| Resistance | Cure check ≥ 30 MEK double rubs (ASTM D5402, 1 kg) with no breakthrough. Typical results for the ink-and-coating system on a coupon of the stated construction — ABL laminate, ink at 1.0–1.5 g/m², matched overprint coating at 1.5–3.0 g/m², both cured to the stated dose: 100 dry rub cycles at 1.8 kg (4 lb Sutherland block, 23 °C / 50 % RH) with no transfer, and 50 cap open-and-close cycles at 0.8–1.5 N·m with no print removal. These belong to that construction and that cap-and-shoulder geometry rather than to the ink: cap torque, heading, filled-product and migration performance are qualified on the pack, on request. |
| Opacity of the white | Contrast ratio 0.70–0.80 at 2.0–2.5 g/m² single pass, 0.85–0.92 as a double hit at 4.0–5.0 g/m², and ≥ 0.95 at a 12 µm wet laboratory drawdown. ISO 2814 over a black-and-white chart |
| Pack sizes | 1 kg and 2.5 kg tubs and 5 kg pails; opaque white and mixing bases also in 10 kg pails; auxiliaries in 1 kg tubs |
| Shelf life and storage | 12 months from the date of manufacture in the unopened original container at 15–25 °C, away from daylight and any UV source; opaque white 9 months and stirred through before use |
| Documentation | Technical Data Sheet, Safety Data Sheet and Regulatory Summary with every delivery |
Compliance and standards
- Raw materials selected to the EuPIA Charter
- TPO-free
- ITX- and benzophenone-free in the LM grade
- Heavy-metal-free pigments
- Low-migration grade available
- Migration assessment on request
- REACH-registered raw materials
White paper
Dual cure: what mercury and LED each do to the film
A medium-pressure mercury lamp emits across a broad band with a large share of its energy at short wavelengths. Short wavelengths are absorbed strongly, so they are spent in the top few microns of the film. A mercury lamp therefore cures from the surface down, and the surface gels first. An LED source at 385–405 nm is narrow-band and long-wavelength. It is absorbed far less strongly, passes through the film and cures from the substrate up, which leaves the surface to cure last — and the surface is the part exposed to atmospheric oxygen, which quenches growing radical chains. Under-cure on an LED line shows as a print that is hard underneath but marks under a thumbnail or fails a rub test.
A dual-cure ink has to satisfy both geometries with one photoinitiator package. It needs strong absorption in the 385–405 nm window, which is acylphosphine oxide territory; TPO is excluded, having been reclassified as reprotoxic category 1B under CLP by the 19th ATP, applying from September 2025, and listed on the EuPIA exclusion list, so the long-wavelength absorption is carried by other acylphosphine oxides and, in the low-migration grade, by higher-molecular-weight and multifunctional versions of the same chemistry. It also needs enough short-wavelength response to make real use of a mercury lamp without over-initiating the surface and leaving the base of the film soft. Oxygen inhibition at the LED-cured surface is answered mostly in the resin rather than the initiator: higher acrylate functionality, faster gelation, and amine synergy where the grade allows it.
Pigment competes with the initiator for the same photons, and in a narrow band it competes hardest. Under LED the cure-limiting shades are normally the deep ones — black, reflex blue — and opaque white. Titanium dioxide has a refractive index far above the binder’s, so it scatters light strongly rather than letting it through, and rutile grades also absorb below their band edge at around 405–410 nm, so at the short end of the LED range the pigment takes a share of the output as well. Yellow is usually the easiest. The practical consequence is that an LED line runs to the slowest colour in the set: the dose is set on the worst case, not on the average, and a shade change in one unit can change the dose the whole job needs. For white work, longer-wavelength emitters at 395 or 405 nm and more peak irradiance do more than a shorter wavelength the pigment absorbs.
Across a mixed fleet the payoff is one ink code per shade, one shade standard, one shelf-life clock and one set of technical documents, with jobs free to move between mercury and LED presses. The cure window for each lamp type is to be confirmed and should be established on your own press and lamp, against a defined cure test — rub, solvent double rub and tape — and not carried across from another site’s settings.
White paper
Thin film on a hard relief plate: holding the dot and holding the tube
Letterpress prints from a raised image, and the only thing holding a clean dot edge is the ink’s resistance to spreading under impression. A long, soft, flowing ink squashes out at the relief shoulder and prints a dot with a halo and a filled centre; on small type, fine serifs and reversed text the same behaviour thickens strokes and closes counters. A short, stiff, highly pigmented body resists that. It also transfers and releases cleanly from a hard photopolymer plate, where there is no compressible surface to even out an uneven nip.
Film weight is the other half of the same problem. Tube and label letterpress runs thin — indicatively 1.0–1.5 g/m² at solid, about one to one and a half microns — so colour has to come from pigment concentration. The common failure is chasing density with impression: pressure is added, the dot spreads, the highlight plugs and the text thickens, and density gains very little. Density belongs to the ink and the roller train. Impression belongs to the plate, and on a hard plate it should stay at a kiss.
Tack sequence depends on how the press cures. Many tube lines print every station wet-on-wet on the mandrel wheel and cure once at the end, so tack must descend through the set for the later colours to trap. Narrow-web label presses more often pin-cure or fully cure between units, which changes the trapping problem into a surface-energy problem: an over-cured, fully crosslinked surface can reject the next down colour. The sequence that works on one press configuration is not automatically the one that works on the other.
What follows the press decides the specification as much as the press does. On a tube, the seaming or heading step takes the sleeve end to elevated temperature while the shoulder is formed onto it, and an under-cured film near that zone can soften, discolour or pick up on tooling. The cap is torqued on and off repeatedly and its skirt rubs the shoulder. The tube flexes every time it is squeezed, so the cured film has to flex with the laminate and not craze. The filled product reaches the print from outside during filling and wiping, and from inside by permeation where the barrier is polymeric rather than foil; emollients such as isopropyl myristate, essential oils, menthol, surfactants and peroxides are the usual aggressors. None of this is settled by the ink alone. The matching UniCure overprint coating provides the working surface, and the whole system should be qualified on your own laminate, with your own filled product, conditioned — commonly at around 40 °C for a set period — and then tested for adhesion, rub and cap-torque resistance before a specification is fixed.
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