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Uniforce-250 — Conventional UV Offset Inks
A conventional UV offset series for sheet-fed litho on coated paper, board and UV-suitable plastics, cured by medium-pressure mercury lamp.
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UV Offset Inks
What the series is, and where it fits
Uniforce-250 is our conventional UV offset series: six grades on one oligomer and photoinitiator platform, formulated for the broad spectrum of a medium-pressure mercury lamp. How UV offset behaves in general — ink and water, the rubber in the press, dose and depth — is explained on the UV offset inks page. This page is about what this series does. It is intended for coated paper and board — commercial sheet work, folding cartons, label sheets — and for UV-suitable plastics with the right surface preparation, with a plastics grade for treated film and sheet, a metallics grade, an opaque white for metallised and clear stock, and a low-migration grade for food packaging. Solids are almost 100 %, so what is laid on the sheet is very nearly what stays there, and the stack can be turned, coated, foiled and die-cut in the same shift.
On press a paste ink is judged by its rheology and its tack. A UV paste ink for litho is built short: a short body is what lets the film split cleanly at each nip and transfer at speed rather than mist or fly, and enough body is what keeps it feeding evenly from the duct without flooding back to the fountain roller. Wet-on-wet trapping needs tack to descend through the units, and the sequence for a job is set with the press. The process set is supplied graduated from 16 ± 1 first down to 12 ± 1 last down against a bench tack of 13 ± 2 for a single mid-sequence ink, IGT at 400 rpm, 30 °C, 1.3 cm³ charge, read at 60 s; body is 45 ± 15 Pa·s on the Laray at 25 °C with a yield value of 150 ± 50 Pa. A UV ink has no oxidative drying mechanism, so it does not dry in the duct and there is no skin to break in the morning — what does start a duct gelling is stray UV and daylight, so cover it and keep scattered lamp light off the train. Water balance needs more attention than with an oil-based ink, because an acrylate vehicle emulsifies less water: run the lowest dampening that keeps the plate clean, and watch the fount with a meter rather than the sheet. Typical film weight for process colours on coated stock is 1.0 to 1.5 g/m².
What the cured film is asked to give is gloss, because it stays on the surface of a coated stock instead of penetrating into it; rub and scuff resistance from the moment the sheet leaves the lamp; chemical resistance that continues to build for around 24 hours as the dark reaction completes; and colour strength from a thin film, using high-strength, heavy-metal-free pigments. All four depend on one thing: the dose actually delivered at the substrate. An under-cured film looks printed and fails everywhere else.
Uniforce-250 LM is the low-migration grade for food packaging, and what that means is a way of formulating. TPO is excluded from the whole series, not only from the food grades — it has been reclassified as reprotoxic category 1B under CLP by the 19th ATP, applying from September 2025, and it sits on the EuPIA exclusion list. In the LM grade ITX and benzophenone are excluded as well; photoinitiation is by high-molecular-weight and multifunctional acylphosphine oxides with polymeric amine synergists in place of free amines; and monomer selection is weighted towards higher-functionality acrylates, so that less of what remains after cure is small enough to move. What it is not is a conformity statement for a finished pack. That comes from a migration assessment on the pack itself, which we will carry out on request, and it depends on cure, ink load, substrate and set-off as much as on the ink — see low-migration technology. A matching UV coating from the UniCure range, applied in the coater or from the offset duct, finishes the job in gloss or matt within the same cure window. Figures on this page are typical values for this class of ink, each quoted with the method that produced it. The values that govern a supply are the ones on the Technical Data Sheet for the grade you buy.
The Uniforce-250 series
Six variants on one oligomer and photoinitiator platform, so colour, gloss and cure window stay consistent across the set. The variant names match the range list on the UV offset inks page.
Uniforce-250 Process
UF250-Y10 / M10 / C10 / K10
Uniforce-250 Dense Black
UF250-K11
Uniforce-250 Mixing Bases
UF250-B01 to UF250-B12
Uniforce-250 Transparent White
UF250-T00
Uniforce-250 Opaque White
UF250-W20
Uniforce-250 LM — Low Migration
UF250LM-Y10 / M10 / C10 / K10, W20, B01–B12
Uniforce-250 PL — Plastics
UF250PL-Y10 / M10 / C10 / K10, W20
Uniforce-250 MT — Metallics
UF250MT-S30 Silver, UF250MT-G30 Gold
Product data
| Process | Sheet-fed offset lithography, UV-configured. Also the offset decks of combination narrow-web presses. |
|---|---|
| Cure | Medium-pressure mercury lamp rated 120–200 W/cm (300–500 W/inch), broadband. Iron-doped lamps for cure at depth in heavy films; gallium-doped lamps at 400–420 nm, above the rutile absorption edge, under heavy opaque white. Typical dose at the substrate: 80–150 mJ/cm² process colours, 120–200 mJ/cm² dense black, 150–250 mJ/cm² opaque white and metallics, and 150–250 mJ/cm² for the LM process set. Peak irradiance 0.5–1.5 W/cm² UV-A at the substrate. Measured with a band-calibrated UV-A (320–390 nm) radiometer passed through the press at running speed — not read off the lamp percentage at the console. Not an LED ink: it will not cure under a 385–405 nm array. |
| Substrates | Gloss, silk and matt coated paper, folding carton board (FBB, SBS), cast-coated and metallised board, self-adhesive label stock, and UV-suitable plastics with the PL grade — corona-treated PP and PE, PET, rigid PVC and styrene sheet at ≥ 40 mN/m surface energy, checked with dyne pens or ISO 8296 test inks at the press. Uncoated stock absorbs ink into the fibre and needs a heavier film for the same density, at lower gloss. Adhesion on plastics is judged 24 h after the run, not at the delivery. |
| Film weight | 1.0–1.5 g/m² for process colours on coated stock; 1.8–2.5 g/m² opaque white; 1.5–2.5 g/m² metallics; 1.0–1.3 g/m² for the LM grade, where ink load is one of the few migration variables the printer controls directly. Gravimetric, on a printed solid. |
| Tack and viscosity | Bench tack 13 ± 2 for a single mid-sequence ink, IGT tack meter at 400 rpm, 30 °C, 1.3 cm³ ink charge, read at 60 s — the house charge, because a tack figure taken at a different charge is not comparable with it. The ladder is published as a separate specification: the process set is supplied graduated from 16 ± 1 first down to 12 ± 1 last down for wet-on-wet trapping, the first-down grade carrying its own 16 ± 1 rather than the bench value. Viscosity 45 ± 15 Pa·s, Laray falling-rod viscometer at 25 °C, reported at 2 500 s⁻¹, with a yield value of 150 ± 50 Pa. Fineness of grind ≤ 7.5 µm for process colours and bases and ≤ 12.5 µm for opaque white and metallics, ISO 1524 grindometer at 25 °C. Water pick-up 15–25 % w/w, Duke-type emulsification tester at 1 200 rpm, 20 min, 25 °C — lower than an oil-based ink, which is why water faults show late on the sheet. |
| Density | Specific gravity 1.05–1.20 g/cm³ for process colours, 1.45–1.60 g/cm³ for opaque white, 1.10–1.25 g/cm³ for the leafing aluminium silver UF250MT-S30 and 1.35–1.65 g/cm³ for the gold UF250MT-G30, which is built on brass (gold bronze) flake of about 8.5 g/cm³ and is therefore a heavier ink than the silver; ISO 2811-1 pyknometer at 25 °C. Solid ink density on gloss coated (PS1 class) stock at 1.2 g/m², Status E response to ISO 5-3 with ISO 5-4 measurement geometry, no polarising filter: black 1.75–1.90, cyan 1.40–1.50, magenta 1.40–1.50, yellow 1.20–1.30. Quote the status with the number: the same yellow reads about 0.95–1.10 on a Status T instrument. Wet and dry readings sit close together, because nothing evaporates and little penetrates. |
| Gloss | 55 ± 10 GU at 20° and 80 ± 8 GU at 60°, ISO 2813, on a printed solid on gloss coated board, read 24 h after cure. 20° is the discriminating geometry on a high-gloss UV film; 60° is the mid-gloss angle and separates high-gloss films poorly. The LM grade typically runs a little lower, at 50 ± 10 GU at 20°, because its initiator and monomer selection is made for low mobility rather than for surface finish. |
| Colour range | Process set UF250-Y10 / M10 / C10 / K10, dense black UF250-K11, twelve mixing bases UF250-B01 to B12 (Yellow, Orange, Warm Red, Rubine, Rhodamine, Purple, Violet, Reflex Blue, Process Blue, Green, Black, Transparent White), transparent white UF250-T00, opaque white UF250-W20, plastics set UF250PL, metallics UF250MT-S30 Silver and UF250MT-G30 Gold, low migration UF250LM. Shades matched to a customer’s own standard or to a published colour reference agreed at order. Light fastness on the full-tone unvarnished film, ISO 12040 filtered xenon arc against ISO 105-B02 blue wool references: yellow 4–5, magenta 4–5, cyan 8, black 8 — tints and process builds lose one to two steps. |
| Photoinitiator system | TPO excluded across the whole series, not only from the food grades: reclassified as reprotoxic category 1B under CLP by the 19th ATP, applying from September 2025, and on the EuPIA exclusion list. The LM grade uses high-molecular-weight and multifunctional acylphosphine oxides with polymeric amine synergists in place of small free amines, and excludes ITX and benzophenone. Pigments are heavy-metal-free; raw materials are selected under the EuPIA Charter. |
| Migration position (LM grade) | Uniforce-250 LM is formulated for the printed outer, non-food-contact surface of food packaging, with a functional barrier where the pack design requires one. It is not for direct food contact. No migration figure is quoted and none should be inferred: migration, food-contact conformity and any claim about a finished pack are assessed on the pack, on request, and depend on cure, ink load, substrate, barrier and set-off as much as on the ink. Raw materials are selected with reference to the EuPIA Suitability List and to the substance lists in Annex 10 of the Swiss Ordinance; Regulation (EU) 10/2011 governs plastic food-contact materials rather than inks and is used as a substance reference only. |
| Press consumables | EPDM rollers and UV-compatible EPDM-faced blankets throughout — acrylate monomer swells and softens nitrile. UV-resistant CTP plates, or conventional plates baked to the plate maker’s schedule. UV-approved low-aromatic washes only. UV-stable fount concentrate at 3–5 % v/v, pH 4.8–5.5, with conductivity specified as an increment over the incoming water rather than as an absolute: base water + 900–1 300 µS/cm at 25 °C, which on the 8–12 °dH water specified here (about 140–215 ppm as CaCO₃, roughly 250–400 µS/cm) gives about 1 200–1 700 µS/cm in total. Log the incoming water reading beside it; the absolute number means nothing without it. Isopropanol 0–5 %, or a surfactant substitute at 1–3 % with conductivity re-checked after the change. Dampening chilled to 10–14 °C at the fount tank and set to the minimum that keeps the plate clean. Rollers held at 28–32 °C, ink in the duct 22–28 °C, with dichroic reflectors and lamp cooling to manage the infra-red the lamp puts back into the unit. |
| Pack sizes | 1 kg and 2.5 kg tins; 2 kg cartridges for automatic ink feed systems; 5 kg pails for opaque white and metallics. The LM grade is supplied in 2.5 kg tins, 2 kg cartridges and 5 kg pails. |
| Shelf life and storage | 12 months from the date of manufacture in unopened original containers at 15–25 °C, stored in the dark, away from direct sunlight, stray UV and heat, and protected from freezing. Opened containers within 30 days. Keep ducts covered on press — the ink has no oxidative drying mechanism and will not skin in the duct, but stray UV and daylight will gel it. Press ink must not be returned to the original container. Low-migration grades are stored and labelled separately from standard inks. |
| Documentation and companion coatings | A Technical Data Sheet, a Safety Data Sheet and a Regulatory Summary for every grade, supplied with delivery. Matching UV coatings from the UniCure range for coater or offset-duct application — specify the low-migration coating with the LM grade, since a standard overprint varnish reintroduces everything the ink excludes. |
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
Wash-up, stray light and heat on a mercury UV line
The general set-up argument — EPDM rollers and UV blankets throughout, a UV-stable fount run at minimum dampening, and why acrylate monomer is not kind to nitrile rubber — is on the UV offset inks page. The numbers for this series are these: a fount made for UV, typical working conditions for the class of pH 4.8 to 5.5 with conductivity held to a fixed band above the base water, and isopropanol reduced or replaced by a surfactant substitute. Too much water dulls gloss, weakens colour and leaves a poorly wetted film that cures unevenly; too little and the plate tints. UV ink shows water trouble later on the sheet than oil-based ink does, which is exactly why the meter is more reliable than the eye. Check the fount at the start of every shift and after every top-up.
Wash up with a UV-approved wash. Aromatic and strong ester washes strip plasticiser from the rollers and attack the blanket face and compressible layer. The wash also has to remove the ink completely: anything left in the roller pores is still reactive and will glaze the roller over time, and a glazed roller carries water badly long before anyone connects it to the wash. Wash before a long stop. For an overnight stop there is usually nothing to do but cover the duct, since the ink does not dry in it.
Two more things belong on the set-up sheet. Keep the ink away from stray UV and daylight — a duct or a roller train that sees scattered lamp light will start to gel. And control heat. A medium-pressure lamp radiates a great deal of infra-red back into the unit, and paste-ink viscosity and tack move with temperature, so dichroic reflectors, lamp cooling and roller temperature control (typically held around 28 to 32 °C) are part of running the ink consistently, not optional extras.
White paper
Cure is a dose, not a lamp setting
Uniforce-250 is formulated for the mercury spectrum: the short-wave lines at 254 and 313 nm are absorbed in the top micrometre of the film and overcome the oxygen inhibition that would otherwise leave the surface tacky, so a conventional UV ink under mercury cures from the surface down. It is not an LED ink and will not cure properly under a 385 to 405 nm array, which has no short-wave output at all; that work needs Unimax 400, whose initiator package is built for it.
Dose is irradiance multiplied by exposure time, and it is measured in mJ/cm² at the substrate, not read off the lamp percentage on the console. Run faster and the dose falls unless lamp power rises to match. Lamp output also falls with hours in service, through electrode sputtering, solarisation of the quartz envelope and reflectors that have gone dull or dirty, and the short-wave end degrades first — the part that cures the surface. A lamp near the end of its life looks the same to the eye and can be well below the dose the ink needs. Measure with a radiometer through the press on a fixed schedule, log lamp hours, clean quartz and reflectors, and replace lamps on measurement rather than on habit.
The ink itself competes for that light. Pigment absorbs and scatters UV before it reaches the photoinitiator, so the dose a film needs depends on what is in it. Dense blacks absorb strongly and cure slowest. Opaque white scatters and is the hardest of all, which is why it belongs under an interdeck lamp rather than waiting for the end of the press. Yellow is comparatively transparent. Heavier films need more dose than thin ones. An interdeck lamp after the white, or after the colour that has to be trapped on, solves problems the final lamp cannot reach.
Check cure on press, every job. A solvent double-rub test with isopropanol or MEK on the last sheet, a thumb twist on a solid, and a scuff check once the pile has cooled will find an under-cured film before the customer does. Under-cure shows as poor scuff and chemical resistance, weak adhesion on plastics, and, on food packaging, as unreacted monomer and photoinitiator available to migrate. Remember that resistance is still developing for around 24 hours after the lamp as the dark reaction completes, so test chemical resistance the following day and judge adhesion then too. On the Low Migration grade, cure is not a quality preference but part of the compliance case, and the responsibility for it is shared between ink maker, printer and brand owner.
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