Troubleshooting guide

UV Curable Adhesives

Press-floor fault finding for UV laminating, cold-foil and pressure-sensitive adhesives: cure through the substrate or through the foil carrier, oxygen inhibition at a free surface, bond development, open time and shrinkage stress.

Uniform Industries · Greater Noida, India · ufindustries.com
Figures are typical for the class and carry their test method. The values that govern a supply are those on the Technical Data Sheet for the grade.

Before you start

How to use this guide

Work down the page. Cheap checks before expensive ones, and measure before you change anything.

Nothing in this category is judged at the rewind. UV adhesive bond climbs for hours after cure, so a peel taken at the machine tells you the job is running, not that the job is good. The 24 h peel is the release number for the reel; the qualification number is the 7 day peel and, where the pack is filled or heated, the aged and filled peel.
Before you change the adhesive, measure what the adhesive is actually receiving: delivered dose under the production film or the production foil carrier, with the radiometer band stated, not the lamp setting, and film transmission at the cure wavelength on the reel about to run.
Establish which machine you are standing at before you diagnose anything. On most cold-foil units the adhesive is printed, the foil is nipped onto it wet, and the lamp cures through the clear PET carrier before the carrier is stripped. Pre-nip cure to a controlled tacky state is a minority configuration and has different controls.
Read the failure mode, not just the peel figure. Adhesive left on both faces is cure or cohesive strength; a clean face is an interface problem, and the two have opposite fixes.
Anywhere the adhesive cures with nothing over it, oxygen inhibition leaves a soft surface however much dose you put in. That is an irradiance and atmosphere problem, not a dose problem, and it is the cause behind most reel blocking and edge tack in this category.
Bond, foil transfer and seal strength belong to the whole construction, not to the adhesive. Qualify adhesive, print, film or foil, liner and any overprint as a set, and re-qualify when any one of them changes supplier or lot.
Rule the other components out before you change the adhesive. The first check on any of these faults is the job docket against the last good run: film lot, foil lot, liner lot, adhesive lot, ink and varnish, press speed, any lamp or setting change. It costs nothing and it finds more of these faults than any instrument.
Acrylate shrinks on cure, so every gram of adhesive you add to buy bond also adds stress that shows later as tunnels, curl or edge lift; take coat weight down before you take it up.
Separate cure faults from tension faults by when they appear: cure faults are there at 24 h and stay, tension and shrinkage faults arrive after the reel has stood and are worst near the core.
Treat the safety conditions as running conditions. Uncured acrylates are skin sensitisers and eye irritants, so nitrile gloves and eye protection for every handling task and never clean adhesive off skin with solvent. Guards and interlocks stay on at every UV station, extraction runs on medium-pressure mercury because it makes ozone, and nobody looks for a UV leak with their eyes.

UV Curable AdhesivesHow to use this guide

The process

What happens, in order, and the one variable held at each step.

The process

What is controlled at each step

UV Curable AdhesivesThe process

Control variables

What to hold, and how to measure it

Variable	Target	How it is measured	How it drifts
Adhesive coat weight	1.5 to 3.0 g/m2 for cold foil, 2.0 to 5.0 g/m2 for film lamination, typical for this class. Agreed per construction and written on the job ticket, not carried across from another job.	Cut at least five coated and uncoated pairs adjacent on the same web at the same cross-web position, weigh on a four-place balance, average them and quote the spread. The substrate swamps the signal on a single pair: 100 cm2 of 20 micron BOPP weighs about 180 mg against roughly 20 mg of adhesive at 2 g/m2, and film basis weight varies by several per cent. On board it is worse, 100 cm2 of 250 g/m2 board weighs about 2.5 g. For a definitive figure take a coated specimen from before the lamp, weigh it, wash the uncured adhesive off that same specimen with acetone, dry and reweigh. Cross-check against anilox volume and expected transfer.	Falls through the run as anilox cells plug or the screen blinds. It shows as foil pinholing and a slow loss of bond rather than a step change, which is why it is usually found late. A 10 per cent start-to-end tolerance is only meaningful once the figure is an average of several pairs or a wash-off result.
Delivered UV dose at the adhesive	Grade and construction specific, always stated with the radiometer band and head. As an indicative order of magnitude, film lamination cured through clear film commonly needs of the order of 100 to 300 mJ/cm2 at the adhesive; cold foil cured through the carrier commonly sits lower. Take the window from the adhesive supplier for that grade, verify it on the construction, and log it with the band. A dose figure without a band is not a specification.	Band-matched radiometer run through the cure station at production speed with the production film, or the production foil carrier, taped over the sensor window. A standard radiometer puck is 10 to 12 mm thick and rigid and will not pass a closed laminating or foil nip, so run it with the nip open, carry the sensor on the web past the lamp, or use a thin strip-type radiometer where the geometry will not clear a puck. A reading on the open web with nothing over the sensor is not this number.	Falls with lamp hours, window or quartz contamination and reflector condition, and halves when speed doubles. Mercury loses short wave first while a broadband meter still reads acceptably.
Peak irradiance at the web	Peak irradiance is W/cm2 in the band the head covers. A 385 to 405 nm LED array rated 8 to 16 W/cm2 at its emitting window will read lower at the working distance; record what the meter reads at the web and treat the window figure as a specification, not a measurement. A medium-pressure mercury lamp rated 120 to 200 W/cm of arc length typically gives of the order of 1 to 4 W/cm2 at the web, depending on reflector, focus and band. Never quote W/cm as an irradiance at the web: it is arc power per unit arc length and no radiometer reads it.	Radiometer peak reading taken at the actual working distance, not at the emitting window, with the band declared.	Falls sharply with lamp-to-web distance and with any web flutter or lift at the cure station; a loose web reads lower at the edges than at the centre. Irradiance, not dose, is what beats oxygen inhibition at a free surface.
Film and foil carrier UV transmission at the cure wavelength	Stated per film lot and per foil lot. Clear BOPP and clear PET are typically 70 to 90 per cent at 395 nm; a UV-blocked PET can be under 10 per cent at 365 nm. A cold foil carrier is normally clear PET of 12 to 23 micron, but its transmission is still a lot property and is measured, not assumed.	UV-Vis transmission scan from 300 to 420 nm on the reel about to be run, and the supplier spectrum for the lot. Read it in the band the radiometer reads.	Changes between lots and suppliers without notice, usually when a UV blocker, a slip package or a filler level is changed. A change of film or foil lot is one of the most frequent and most easily missed causes of a lost bond, because nothing on the press changes when it happens.
Adhesive temperature and viscosity	Held within 2 C of the agreed running temperature, typically 22 to 30 C at the tray or chamber.	Rotational viscometer at the stated running temperature and a stated shear rate, with spindle and speed recorded so the reading is reproducible. Do not use a flow cup on these grades: ISO 2431 is a flow cup method for Newtonian and near-Newtonian liquids, and UV laminating and cold-foil adhesives are shear thinning, so a cup time does not convert to a viscosity and does not track what the anilox sees.	Rises overnight as the tray cools and falls as press heat builds through a shift. Transfer, coat weight and foil pinholing follow it directly.
Substrate surface energy	38 mN/m minimum on polyolefin, 42 mN/m preferred where the pack will be handled or filled hot.	ASTM D2578 wetting tension, dyne pens or ISO 8296 test inks, on the reel as it is at the press. Handle the inks with gloves and in extraction; the standard formulations contain formamide and 2-ethoxyethanol, both reproductive toxins.	Corona treatment decays over weeks in store, and slip and antiblock additives bloom to the surface of PE and PP. Reels treated to 42 mN/m at the film plant frequently read 34 mN/m at the press.
Web tension at the nip	Set each web on its own cross-section, not by feel or by rank. A working range of roughly 2 to 8 N per 100 mm of width on 12 micron PET, and proportionally more on a thicker or heavier base; the underlying rule of thumb is about 0.25 to 1.0 lb per inch of width per mil of caliper. Run each web at the lower end of its own range, match the two webs on that basis rather than on absolute newtons, and record both figures on the job ticket.	Load cell reading on the running web, confirmed with a hand tension meter at the unwind and at the nip, with caliper and width recorded alongside so the figure can be compared between jobs.	Rises as the unwind reel gets small if taper is not set, so the last third of a reel laminates under different conditions from the first third.

UV Curable AdhesivesControl variables

Control variables

What to hold, and how to measure it

Variable	Target	How it is measured	How it drifts
Nip pressure and evenness	Even across the full width, set to the construction. Uneven nip is a wet-out fault long before it is a bond fault.	Full-width nip impression strip, or pressure-sensitive film across the web.	Loses evenness as the rubber roller wears at the edges or grows at the centre with heat; edge bubbles and centre squeeze-out are the visible result.
Rewind tension and taper	Taper of 20 to 40 per cent from core to full reel is typical for a laminate that is still developing bond.	Build the hardness profile during winding: take reel hardness readings at several diameters as the reel grows, and across the width at each diameter, then plot hardness against diameter. That curve is the taper. On a finished reel only the outer surface is accessible, so readings there confirm the width profile, not the taper.	Wound-in pressure builds through the reel, so tunnels and curl appear near the core first and are absent from the sample cut at the end of the run.
Anilox or screen specification for the target coat weight	Chosen for the coat weight, not inherited from the last job. The cell volume must deliver the specified g/m2 at the transfer efficiency of that press, plate and adhesive. A ruling too coarse for the coat weight lays a ribbed film and shows screen mark in the foil; one too fine will not release a viscous adhesive.	Cell volume measurement on the anilox, and a coat weight trial at the running temperature on the production substrate before the anilox is accepted for the job.	Effective volume falls as cells plug or as the land wears. Record the anilox specification and the date of its last chemical clean on the job ticket.
Incoming adhesive lot check	Every lot checked on receipt against the retained reference before it goes on the press: viscosity at a stated temperature and shear rate, colour, and cure response on a draw-down at a stated dose.	Rotational viscometer at the stated temperature and shear rate; a draw-down at the specified coat weight cured at a logged dose and assessed by solvent rub and by tack against the reference.	Lot to lot variation is small but it is not zero, and material stored warm or held past its date behaves differently. Without this check every fault in this document gets blamed on the press.
Static on the web	Low enough that the foil or the film does not flutter at the applicator or at the strip point and does not pull dust into the adhesive film. Treat static as a control, not as weather.	Static field meter reading at the unwind, at the applicator and at the strip bar with the press at speed, with pressroom relative humidity recorded at the same time.	Rises as humidity falls, so a job that ran in summer is a different job in a dry winter pressroom. Ionising bars lose output as the emitter pins foul, and nobody notices until the foil starts to speck.
Guarding, extraction and personal protection at the UV stations	Every UV station fully guarded with interlocks working, extraction running on medium-pressure mercury, no unshielded light path onto an operator position, and nitrile gloves and eye protection worn for every adhesive handling task.	Interlock function check and guard inspection on the shift check sheet; extraction flow verified; UV-sensitive indicator paper or photochromic strips used to find light leaks rather than looking for them by eye.	Guards come off for a make-ready and do not go back, interlocks get defeated and extraction gets throttled. Medium-pressure mercury makes ozone and puts out enough UV to cause photokeratitis and skin erythema in seconds at press distance; uncured acrylates are skin sensitisers, and sensitisation does not reverse.

UV Curable AdhesivesControl variables

The mechanism

Where the dose actually goes in a UV laminate

A UV laminating adhesive is cured through the incoming film, and a cold foil adhesive is usually cured through the foil carrier. Either way the number that matters is not what the lamp is set to but what survives the film and reaches the interface against the substrate. That interface cures last, and it is where the bond is made.

UV Curable AdhesivesThe mechanism

02 | 20 faults

Faults

Symptom, cause, check, change, confirm. The trap is the move to avoid.

Fault 1 of 20

Laminate peels apart a day after the run

WHAT YOU SEE

The reel laminates cleanly, looks right at the rewind and passes a hand pull at the machine. Next morning the two webs strip apart by hand, often with adhesive left on both faces, and the whole run is in question.

WHAT IT LOOKS LIKE

CAUSES, MOST LIKELY FIRST

Delivered dose at the adhesive is below the window because the film is absorbing itThe adhesive cures through the incoming film, so every micron of film and every UV absorber in it removes dose before the initiator ever sees it.
Speed raised without a lamp changeDose is inversely proportional to speed, so a 20 per cent speed increase leaves about 83 per cent of the dose and a 25 per cent increase leaves 80 per cent; doubling the speed halves it. This is the cheapest cause to confirm because it is already on the press log.
The film carries a UV blocker, a high filler load or a metallised layerA blocked PET or a TiO2-filled white film can transmit under 10 per cent at 365 nm, so a lamp setting proven on clear film delivers almost nothing to the adhesive.
Lamp or array output has fallenMercury loses short wavelength first and an LED array loses peak irradiance with hours and with window contamination, while a broadband meter still reads acceptably.
Coat weight above the top of the range for the dose availableThe interface against the substrate is the last part of the film to cure, and a heavier film screens it further.

UV Curable AdhesivesLaminate peels apart a day after the run

Fault 1 of 20 · continued

Laminate peels apart a day after the run

CHECK, IN THIS ORDER

Compare the job docket against the last good run: film lot and supplier, foil lot, adhesive lot, press speed and any lamp or setting change. This costs nothing and finds the most common cause.
Log lamp or array hours and inspect the LED window or the quartz sleeve for haze and deposit.
Peel 15 mm strips at 24 h and record the failure mode: adhesive on both faces is cure or cohesive strength, a clean face is an interface problem.
Measure delivered dose with a band-matched radiometer at production speed with the production film taped over the sensor, nip open or sensor carried on the web, and state the band with the reading.
Run a UV-Vis transmission scan from 300 to 420 nm on the film reel about to be used, and ask the supplier for the lot spectrum.

THEN CHANGE

Raise irradiance at the web before anything else: lamp-to-web distance, reflector condition, focus and web flutter at the cure station.
Move to a wavelength the film actually transmits, a 395 or 405 nm array or an iron- or gallium-doped mercury lamp, rather than more of a wavelength the film blocks.
Bring coat weight down to the bottom of the specified range and re-test at 24 h.
Reverse the construction where the press allows it, so cure happens through the more transparent web.
Change to a grade whose initiator package is matched to the transmission window of that film.

CONFIRM IT IS FIXED

15 mm peel at 24 h and again at 7 days on the production film, meeting the agreed value for that construction with a consistent failure mode. Bond still climbing at 24 h is normal; bond that falls between 24 h and 7 days is not. Under-cure with residual mobile monomer is the most likely cause of a falling bond, but slip and antiblock migrating to the interface, residual cure stress and plasticising from the fill all do the same thing, so read the failure mode and check both dose and the film additive package before concluding.

THE TRAP

Slowing the press and calling it solved. Slowing does raise dose, but it does not raise peak irradiance and it will not push a wavelength through a film that blocks it, so the job now runs slowly and still fails. Measure film transmission before touching the speed setting.

UV Curable AdhesivesLaminate peels apart a day after the run (continued)

Fault 2 of 20

Bond fails only over the heavy ink solids

WHAT YOU SEE

The laminate holds across open areas but lifts with a fingernail over dense black, opaque white or heavy solids. The map of the failure is the map of the print.

WHAT IT LOOKS LIKE

CAUSES, MOST LIKELY FIRST

The ink beneath is under-curedA soft ink surface gives the adhesive a weak layer to key into, and the failure is inside the ink film rather than at the adhesive.
Slip or wax at the ink surfaceWax and silicone added at the press migrate to the surface within minutes and act as a release layer under the adhesive.
The ink film screens the cure where the unit cures from the print sidePigment absorbs the same UV the adhesive needs, and opaque white and dense black are the worst two, for different reasons.
Uncured monomer and photoinitiator migrating out of the ink into the adhesiveMobile species plasticise the interface, so bond that was acceptable at 24 h keeps falling.
Step height at the edge of a heavy solidThe adhesive bridges the step instead of wetting into it, so local coat weight is well below the measured average.

UV Curable AdhesivesBond fails only over the heavy ink solids

Fault 2 of 20 · continued

Bond fails only over the heavy ink solids

CHECK, IN THIS ORDER

30 MEK double rubs to ASTM D5402 on the print before the laminating station; a print that fails the rub will not hold a laminate. MEK is highly flammable and has an occupational exposure limit, so do the rub in extraction, with gloves, away from any UV station.
Peel 15 mm strips over the heaviest solid and over an unprinted area on the same reel, and record both figures.
Tape pull the print alone over the failing colour with a stated tape and a stated pull geometry. On a 12 to 20 micron film do not use a cross-cut: ISO 2409 assumes a substrate the blade can score without cutting through, and on thin film the blade goes straight through the print and the substrate, so the result reports substrate damage.
Ask the press crew what was added to the duct or tray for that colour, and check the ink data sheet for its slip package.
Section a sample and look at where the split runs: ink to substrate, ink to adhesive, or inside the adhesive.

THEN CHANGE

Fix the ink cure first: dose at the ink station, not at the adhesive station.
Remove press-added slip and wax from any colour that will be laminated, and control slip on the outer surface instead.
Move to a laminating grade or a primer intended for heavy ink coverage.
Reduce the ink film weight over areas that must be laminated where the design and the colour standard allow it.
Move opaque white to a gallium-doped lamp or a 395 to 405 nm array, because TiO2 transmits far better above its absorption edge near 400 nm. Dense black will not respond the same way, since carbon black absorbs strongly across the whole UV and visible range; for black, cut the ink film weight over areas that will be laminated and raise peak irradiance rather than changing wavelength.

CONFIRM IT IS FIXED

24 h peel over the heaviest solid within 20 per cent of the peel over the unprinted area on the same reel, with the same failure mode in both.

THE TRAP

Raising adhesive coat weight to bridge the weak area. A thicker layer on a release surface still releases, and the extra adhesive volume adds shrinkage stress that starts tunnelling two days later.

UV Curable AdhesivesBond fails only over the heavy ink solids (continued)

Fault 3 of 20

Tunnels and channels appear in the reel

WHAT YOU SEE

Straight or wandering air channels running in the machine direction, absent at the rewind and obvious the next morning. Worst near the core, and the reel looks perfect at the outside where the sample was cut.

WHAT IT LOOKS LIKE

CAUSES, MOST LIKELY FIRST

Tension mismatch between the two webs at the nipOne web is laminated stretched and relaxes afterwards, and the bond is not yet strong enough to hold the two lengths together.
The reel was wound before the bond had developedWound-in pressure acts on a young bond, and the weaker web slides rather than holds.
Shrinkage on cureAcrylate loses volume as it polymerises, so the adhesive layer pulls the webs relative to each other; heavier coat weight means more shrinkage.
Rewind tension too high, or no taper setWound-in pressure climbs through the reel, which is why the core is always the worst part.
A thin film laminated to a heavy base at a common tension12 micron PET at the tension a 60 micron base tolerates is running at several times the strain, which is why each web is set on its own cross-section and not by rank.

UV Curable AdhesivesTunnels and channels appear in the reel

Fault 3 of 20 · continued

Tunnels and channels appear in the reel

CHECK, IN THIS ORDER

Read both unwind tensions and the rewind tension from the press controls, verify them on the running web with a hand tension meter, and convert each to N per 100 mm of width so the two webs can be compared on cross-section.
Measure peel at the nip, at 1 h and at 24 h to establish how fast the bond is actually developing.
Cut a cross-section through a channel and see which web is the longer one.
Take reel hardness readings at several diameters as the next reel is wound, and across the width at each diameter, and plot hardness against diameter. On a reel that is already finished only the outside can be read, which gives the width profile and not the taper.
Check whether the channel pattern follows the print, which would point to the heavy ink solids fault rather than to tension.

THEN CHANGE

Take the thinner web down to the lowest tension in its own range that tracks, and leave the heavier web alone.
Set a rewind taper of 20 to 40 per cent from core to full reel.
Let the reel stand 24 h before slitting or die cutting, supported on its core on a shaft or in cradles so the reel edges carry no weight. Stand a reel on end only where it is narrow and light enough that the bottom edge will not dish or crush.
Reduce adhesive coat weight; shrinkage stress scales with the volume of adhesive present.
Move to a lower-shrinkage grade where the construction is inherently tight.

CONFIRM IT IS FIXED

A full production reel, not a sample roll, free of channels at 24 h and again at 72 h, inspected at the core as well as the outside.

THE TRAP

Winding harder to pull the tunnels flat. It stores more stress in the reel and the channels come back larger when the reel is relaxed or unwound at the converter.

UV Curable AdhesivesTunnels and channels appear in the reel (continued)

Fault 4 of 20

The laminate or the label curls

WHAT YOU SEE

Sheets or die-cut labels bow towards one face, or the slit reel will not lie flat. Usually worse on thin, unbalanced constructions and worse again in a dry store.

WHAT IT LOOKS LIKE

CAUSES, MOST LIKELY FIRST

Cure shrinkage pulling the construction towards the adhesive sideThe adhesive contracts as it cures and the webs are already bonded, so the stress has nowhere to go except into curvature.
Coat weight above what the construction needsShrinkage force is proportional to the amount of adhesive, so curl tracks coat weight almost linearly.
An unbalanced constructionA thin film on a thick base, or a one-sided coating, has no opposing layer to hold it flat.
Moisture loss from a paper or board componentPaper shrinks as it dries under the lamps and in store, and the cured adhesive layer will not follow it.
Heat at the cure stationThe web is laminated hot and cools restrained, which locks a bow into it. A medium-pressure mercury lamp puts a large infra-red load on the web; an LED array of the same useful output puts much less, which is why the same construction can curl on one press and not on another.

UV Curable AdhesivesThe laminate or the label curls

Fault 4 of 20 · continued

The laminate or the label curls

CHECK, IN THIS ORDER

Measure curl as the rise of the corners of a 100 mm square cut sample on a flat surface, at 1 h and at 24 h, stating the conditioning.
Measure coat weight by cut-area weighing over several pairs and compare to the specified range.
Cut samples at three coat weights in one trial and plot curl against coat weight.
Check web temperature after the cure station with a contact or infra-red thermometer.
Condition samples at 50 per cent RH for 24 h and re-measure before blaming the adhesive, particularly on paper constructions.

THEN CHANGE

Reduce coat weight to the bottom of the range; this is the change with the largest effect on curl.
Add or increase cooling after the cure station so the web is not restrained while it contracts.
Balance the construction at design stage, with a matching coating or film on the other face.
Move to a lower-shrinkage grade with a higher oligomer to monomer ratio.
Condition and store the finished reel at controlled humidity where a paper component is involved.

CONFIRM IT IS FIXED

Corner rise under the agreed limit on a 100 mm square at 24 h after conditioning, measured on material from the core and the outside of the reel.

THE TRAP

Reverse-bending or back-rolling the reel to take the curl out. It relaxes for a few hours and returns, and it can start delamination at the same time.

UV Curable AdhesivesThe laminate or the label curls (continued)

Fault 5 of 20

Cold foil transfers patchy or pinholed

WHAT YOU SEE

The foil image shows small unfoiled specks, broken fine line and type, or whole areas that never transfer. Solids look grey or mottled rather than bright.

WHAT IT LOOKS LIKE

CAUSES, MOST LIKELY FIRST

Adhesive coat weight too low or transfer falling through the runCold foil needs a continuous adhesive layer at 1.5 to 3.0 g/m2; below that the foil has discrete islands to key to and the gaps read as pinholes.
Anilox or screen partially blockedCured adhesive in the cells is not removable by normal washing, and cell volume falls silently over a shift.
Substrate too rough or too absorbentUncoated board and rough paper take the adhesive into the surface, so there is nothing left at the plane where the foil must key.
Adhesive too cold or too viscous to lay a level filmTransfer from anilox to plate to substrate falls as viscosity rises, and the film is laid ribbed rather than flat.
Nip pressure low or uneven across the widthFoil transfer is a nip event, and a soft or worn nip roller loses the edges or the centre first.

UV Curable AdhesivesCold foil transfers patchy or pinholed

Fault 5 of 20 · continued

Cold foil transfers patchy or pinholed

CHECK, IN THIS ORDER

Determine adhesive coat weight by cut-area weighing over several pairs at the start, middle and end of the run.
Inspect the anilox under a microscope or with a cell-volume measurement, not by eye, and check the ruling is right for 1.5 to 3.0 g/m2.
Measure adhesive temperature in the chamber or tray and viscosity at that temperature on a rotational viscometer.
Take a full-width nip impression strip and read it across the whole width.
Read the static field at the unwind and at the nip with the press at speed, and check the ionising bar emitters for fouling.

THEN CHANGE

Bring coat weight back into 1.5 to 3.0 g/m2 by anilox change rather than by pressure.
Clean or replace the anilox; chemically clean if adhesive has cured in the cells.
Bring adhesive temperature up to the agreed running temperature and hold it there.
Reset nip pressure evenly across the width and check the roller for wear or crown loss.
Fit or service ionising bars at the unwind and the nip, and control pressroom humidity.

CONFIRM IT IS FIXED

A foiled solid with no visible pinholing at 10x magnification, and reproducible gloss readings to ISO 2813 at a stated angle, or L star by spectrophotometer, across the width at the start, middle and end of the run. Do not use a densitometer on a metallised surface: it assumes a diffusely reflecting print and a specular metal returns a figure that depends on geometry rather than on foil coverage. If a density figure is contractually required, state the method and status used and treat it as a relative check only.

THE TRAP

Winding the nip pressure up to force transfer. It squeezes the adhesive out at the edges of the image, gives ragged foil edges and halo, and wears the roller so the next job starts worse.

UV Curable AdhesivesCold foil transfers patchy or pinholed (continued)

Fault 6 of 20

Cold foil lifts at the edges and flags

WHAT YOU SEE

The foil is down across the image but lifts at the edges, at die cuts and at creases, sometimes only after the job has been converted or handled.

WHAT IT LOOKS LIKE

CAUSES, MOST LIKELY FIRST

Mismatch between the adhesive and the foil release layerThe release coat is tuned to a particular adhesive; too easy a release and the foil lifts back off, too tight and it will not transfer at all.
Adhesive cure state wrong where the carrier is strippedOn the common cure-through-carrier unit the adhesive is cured through the clear PET carrier and the carrier is then peeled, so the dose reaching the adhesive, and the distance from the lamp to the strip point, set whether the foil stays down. On a pre-nip tack-cure unit it is the pre-nip lamp setting that does this instead. Establish which machine you have before changing anything.
Adhesive squeezed out beyond the imageAdhesive outside the foil edge picks up nothing, cures in air, stays proud and tacky, and gives the edge somewhere to start lifting.
Shrinkage stress at the foil edgeA heavy adhesive film contracts on cure and the stress concentrates at the boundary of the image.
Mechanical stress in convertingDie cutting, creasing and matrix stripping put a peel force exactly at the image edge, which is the weakest point.

UV Curable AdhesivesCold foil lifts at the edges and flags

Fault 6 of 20 · continued

Cold foil lifts at the edges and flags

CHECK, IN THIS ORDER

Confirm the adhesive is at the intended cure state where the carrier is stripped, and log the lamp setting, the carrier lot and the lamp-to-strip distance that produced it.
Run the same adhesive with an alternative foil, changing one variable only.
Tape pull the foil image with a stated tape applied with a defined roller and pulled at 180 degrees, at 1 h and at 24 h, including across the image edge. Do not cross-cut a foil image: the blade cuts through a metal layer tens of nanometres thick and through the adhesive into the substrate, so an ISO 2409 classification would report substrate damage rather than foil adhesion.
Inspect the image edge under magnification for adhesive squeeze-out beyond the foil.
Check coat weight and reduce it as a trial in the same run.

THEN CHANGE

Qualify adhesive, foil and any overprint coating together as a set, and treat a change of foil supplier as a change of the whole system.
Set the lamp and the lamp-to-strip distance to the specified figures for that adhesive and hold them; log them as job parameters.
Bring coat weight to the lower end of 1.5 to 3.0 g/m2 to reduce squeeze-out and shrinkage stress.
Trim the adhesive image slightly inside the foil area at plate stage where the design allows.
Move creases and die cuts off the foil edge at artwork stage rather than compensating at the press.

CONFIRM IT IS FIXED

No lift at the image edge after a tape pull at 24 h, and no lift on a creased and folded sample of the production board, tested along and across the grain.

THE TRAP

Adding adhesive coat weight when the foil flags. The cause is nearly always the release and cure relationship, and more adhesive adds squeeze-out and shrinkage at the exact edge that is already lifting.

UV Curable AdhesivesCold foil lifts at the edges and flags (continued)

Fault 7 of 20

Craters and fisheyes in the adhesive film

WHAT YOU SEE

Small round voids in the adhesive, visible as unfoiled dots or as clear spots and weak patches in a laminate, sometimes with a raised rim. Often they repeat in the same place on the web.

WHAT IT LOOKS LIKE

CAUSES, MOST LIKELY FIRST

Silicone contaminationSilicone lowers surface tension locally by a large margin, so the adhesive pulls away from the spot; a few parts per million is enough.
Slip additive blooming out of the substrateErucamide and similar slip agents migrate to the surface of PE and PP over weeks and act like a contaminant applied from below.
Compressed air line carrying oil or waterAn air knife or web cleaner without a coalescing filter sprays a fine mist of oil on the web before the applicator.
Adhesive surface tension too high for the substrateThe adhesive will not spread on a low-energy surface, and the film breaks into islands wherever there is a nucleation point.
Foam and entrained air in the adhesiveBubbles that break at the film surface leave a crater with a rim.

UV Curable AdhesivesCraters and fisheyes in the adhesive film

Fault 7 of 20 · continued

Craters and fisheyes in the adhesive film

CHECK, IN THIS ORDER

Measure surface energy on the reel at the press with dyne pens or ISO 8296 test inks; below 38 mN/m expect craters on polyolefin.
Look for the repeat distance of the defect and match it against roller circumferences to find the contaminating roll.
Check the compressed air line for a coalescing filter and blow onto a clean gloss card to look for mist.
Separate craters from static specks: a crater is a round void with a rim and repeats on a roller pitch, a static speck is a dust particle with adhesive drawn around it and tracks pressroom humidity.
Audit the pressroom for silicone sprays, aerosol release agents, hand creams and silicone anti-set-off spray.

THEN CHANGE

Find and remove the silicone source, then clean the whole adhesive path; it will not dilute out.
Corona treat in line immediately before the applicator so the surface is fresh at the point of coating.
Fit or service the coalescing filter on the air supply and any web cleaner.
Reduce foam by lowering pump speed or chamber recirculation, and let the adhesive stand before use. Do this by managing flow and standing time, not by sealing or purging the container: the stabiliser in an acrylate needs dissolved oxygen to work.
Ban silicone anti-set-off spray and silicone-containing cleaners from any press running this work.

CONFIRM IT IS FIXED

A 300 mm foiled or laminated solid free of craters at 10x, with the substrate reading at or above 38 mN/m at the point of coating.

THE TRAP

Raising coat weight to fill the craters. The contaminant is still there and the crater simply becomes a larger, deeper one; it also hides the source so it returns on the next job.

UV Curable AdhesivesCraters and fisheyes in the adhesive film (continued)

Fault 8 of 20

Adhesive gels in the chamber or on the roller

WHAT YOU SEE

The adhesive thickens, strings, or sets solid in the chamber, tray, pump lines or anilox cells, sometimes warm to the touch. The press can lose a station in minutes and the anilox may not recover.

WHAT IT LOOKS LIKE

CAUSES, MOST LIKELY FIRST

Stray UV reaching the adhesiveReflected or leaked UV from the lamp housing starts polymerisation in the bulk, and once started it does not stop.
Heat in the adhesive pathEvery 10 C rise roughly doubles the rate of the dark reaction; a hot pump, a hot press frame or a tray beside a lamp housing is enough.
Stagnant adhesive in a dead leg of the circulationMaterial that is not moving heats locally and has no fresh stabilised material supplied to it.
Contamination from another chemistryAmines and certain catalysts left in a shared pump or line will initiate the adhesive.
Long standing time at temperature, or a circulation that has been sealed or inertedThe stabiliser used in acrylates, the hydroquinone and MEHQ type, needs dissolved oxygen to function. Time at elevated temperature and stray light consume it, and removing air disables it, so never blanket, seal or nitrogen-purge an adhesive circulation or storage vessel. Keep an air headspace. Nitrogen at a cure station is a different thing entirely and is dealt with under oxygen inhibition.

UV Curable AdhesivesAdhesive gels in the chamber or on the roller

Fault 8 of 20 · continued

Adhesive gels in the chamber or on the roller

CHECK, IN THIS ORDER

Shield-test the station: shut the lamp down and see whether thickening stops.
Measure temperature at the tray, chamber, pump body and return line with a contact thermometer.
Find light leaks without looking at the lamp: run UV-sensitive indicator paper or photochromic strips along the web path and around the housing with the guards closed and the press in a safe state, or take a radiometer reading at the tray. Never look towards an open mercury arc.
Check the anilox cells under a microscope for cured deposit.
Confirm the line was purged and identify what ran through it previously.

THEN CHANGE

Shield the applicator and the tray from the lamp housing and from daylight; fit blackout covers rather than relying on distance.
Cool the adhesive path and keep the running temperature to the agreed figure.
Remove dead legs from the circulation and keep a genuine flow through the chamber, with an air headspace maintained in the container.
Dedicate pumps, lines and chambers to UV adhesive and do not share them with other chemistries.
Discard gelled material into an open, vented container kept away from heat and combustibles and remove it from the pressroom. Gelling acrylate is a runaway exothermic polymerisation, so never seal warm or actively gelling adhesive into a closed drum or bin and never try to stop it by dilution. Clean the anilox with the manufacturer specified cleaner, wearing gloves and eye protection, with extraction running, and dispose of the washings as chemical waste.

CONFIRM IT IS FIXED

Viscosity at the running temperature unchanged over a four-hour run, measured at start and end on the same instrument at the same shear rate, and a clean anilox cell count after wash-up.

THE TRAP

Thinning gelled adhesive with monomer or solvent to keep running. The reaction is not reversible; the material is scrap, and running it puts partly polymerised gel through the anilox and ruins it. Sealing it into a drum to deal with later is worse again.

UV Curable AdhesivesAdhesive gels in the chamber or on the roller (continued)

Fault 9 of 20

Bond falls off as the press speeds up

WHAT YOU SEE

The laminate is sound at set-up speed and steadily worse at running speed. Nothing else changed, and slowing down cures it, so the crew runs the job slowly.

WHAT IT LOOKS LIKE

CAUSES, MOST LIKELY FIRST

Dose falls in proportion to speedThe same lamp delivers half the dose at twice the speed, and the interface against the substrate is the first thing to be starved.
Less time at the nipWet-out is a time and pressure event; at speed the adhesive has less time to flow into the surface before the web leaves the nip.
Adhesive temperature falling as the web carries heat awayA colder adhesive transfers less and lays a poorer film, and coat weight drops with it.
Web flutter at the cure station at speedThe web lifts and the distance to the lamp increases, which reduces irradiance far faster than it reduces exposure time.

UV Curable AdhesivesBond falls off as the press speeds up

Fault 9 of 20 · continued

Bond falls off as the press speeds up

CHECK, IN THIS ORDER

Measure delivered dose with a band-matched radiometer at set-up speed and at running speed and record both figures with the band.
Measure coat weight by cut-area weighing at both speeds.
Watch the web at the cure station at speed, with a strobe if available, for flutter and lift. Observe through the machine UV-filtered viewing window with the guards in place.
Measure adhesive temperature in the chamber at both speeds.
Peel samples from both speeds at 24 h side by side.

THEN CHANGE

Add lamp power or a second lamp at the cure station rather than accepting the slower speed.
Raise irradiance by bringing the lamp closer, servicing the reflector and cleaning the window.
Fit or tighten web support at the cure station to stop flutter.
Hold adhesive temperature with a tempered tray or chamber.
Agree a maximum speed for that construction and put it on the job ticket rather than leaving it to the shift.

CONFIRM IT IS FIXED

24 h peel at full production speed equal to the peel at set-up speed within 15 per cent, with delivered dose logged at that speed with the band stated.

THE TRAP

Running the job slowly and treating it as solved. The dose window has not been established, the next shift will speed up, and the same reel will come back from the converter.

UV Curable AdhesivesBond falls off as the press speeds up (continued)

Fault 10 of 20

Bubbles and silvering in the laminate

WHAT YOU SEE

Fine silvery speckle or visible bubbles between the webs, often stronger at one edge or in a band. The laminate is optically poor even where the bond is acceptable.

WHAT IT LOOKS LIKE

CAUSES, MOST LIKELY FIRST

Air entrapped at the nipAir brought in on the web is not being expelled, usually because the nip geometry or the wrap angle lets it ride through.
Coat weight too low to fill the substrate roughnessThe adhesive bridges the peaks and leaves air in the valleys, which reads as silvering.
Foam in the adhesiveAir entrained by pumping and recirculation is carried onto the web and trapped by the second web.
Uneven nip pressureThe low-pressure region across the width never expels its air, so the defect appears as a band.
Adhesive too viscous to flow out at the nipWet-out is limited by viscosity at the nip temperature and by the time available.

UV Curable AdhesivesBubbles and silvering in the laminate

Fault 10 of 20 · continued

Bubbles and silvering in the laminate

CHECK, IN THIS ORDER

Take a full-width nip impression and read pressure across the whole width.
Determine coat weight by cut-area weighing and compare against the surface roughness of the substrate.
Let a sample of adhesive stand in a clear container and look for persistent foam.
Measure adhesive viscosity on a rotational viscometer at the actual running temperature and a stated shear rate.
Check the wrap angle and the approach of both webs into the nip.

THEN CHANGE

Correct roller wear or crown first, then even up nip pressure across the width.
Raise coat weight to the top of the specified range for a rough or matt substrate.
Reduce pump speed and recirculation, and de-aerate by standing the adhesive before the run.
Raise adhesive temperature in the chamber or tray only within the agreed window, and only after nip evenness and coat weight have been corrected; heat applied at the nip itself is the trap below, not a fix. Hold the new temperature and re-check viscosity at the start and the end of the run.
Change the web approach so air is wiped out ahead of the nip rather than carried into it.

CONFIRM IT IS FIXED

No visible silvering in a 500 mm length viewed against a light box, and, where the laminate is clear, transmission haze to ASTM D1003 or ISO 14782 within the agreed range across the full width. Silvering is an internal haze, so haze is the number that tracks it; gloss to ISO 2813 is a surface measurement and will not see it.

THE TRAP

Adding heat at the nip to chase the bubbles out. It brings the adhesive nearer its gel point before cure, shortens the working window and can start gelling in the chamber.

UV Curable AdhesivesBubbles and silvering in the laminate (continued)

Fault 11 of 20

Coat weight drifts and the adhesive mottles

WHAT YOU SEE

The film looks patchy, ribbed or screen-marked, foil brightness and laminate appearance vary across the width, and the coat weight measured at the end of the run is below the figure measured at the start. The press and the web downstream get progressively dirtier.

WHAT IT LOOKS LIKE

CAUSES, MOST LIKELY FIRST

Anilox cells plugging with cured adhesiveStray UV or dried-in material cures in the cells and cell volume falls progressively through a shift.
Doctor blade wear or wrong blade pressureA worn or rolled blade edge lets material ride over the land and the coat weight climbs unevenly. Excess blade pressure does not empty the cells, because a blade rides on the land and meters the surface; it deflects and wears the blade, wears and scores the anilox land, and shows as streaking. A falling coat weight is plugged cells or a worn-down land, so measure cell volume before touching the blade setting.
Adhesive viscosity changing with temperatureTransfer efficiency from anilox to plate to web is viscosity dependent, so an unheated tray gives a different coat weight at hour one and at hour six.
Anilox ruling wrong for the target coat weightA ruling too coarse for the coat weight lays a ribbed film that shows as screen mark in the foil and as orange peel in a laminate; one too fine will not release a viscous adhesive at all.
Adhesive misting at the applicator at speedFine mist thrown off the roller nip lands on the press and on the web downstream, so measured coat weight falls while contamination rises through the run.

UV Curable AdhesivesCoat weight drifts and the adhesive mottles

Fault 11 of 20 · continued

Coat weight drifts and the adhesive mottles

CHECK, IN THIS ORDER

Weigh several adjacent coated and uncoated pairs at the start, middle and end of the run and plot the trend of the averages, not of single pairs.
Measure anilox cell volume, or inspect cells under a microscope for deposit, and confirm the ruling is right for the target coat weight.
Measure adhesive temperature and viscosity at the same times as the coat weight samples.
Check the defect repeat distance against anilox and plate circumferences.
Wipe a clean black card held near the applicator at speed and look for mist deposit.

THEN CHANGE

Clean the anilox properly, chemically where adhesive has cured in the cells, and put a cleaning interval on the job ticket.
Replace the doctor blade and set blade angle and pressure to the press specification; do not use blade pressure to chase coat weight.
Fit a tempered tray or chamber and hold the running temperature within 2 C.
Change to an anilox whose volume delivers the specified g/m2 at the transfer efficiency of that press.
Reduce misting by lowering roller speed differential and adhesive temperature where the process allows, and shield the web downstream of the applicator.

CONFIRM IT IS FIXED

Coat weight at the end of the run within 10 per cent of the figure at the start, each figure being the average of at least five coated and uncoated pairs, with the same value measured at both edges and at the centre.

THE TRAP

Correcting a falling coat weight with more impression or more blade pressure. It masks the anilox problem for an hour, damages the plate, the blade and the anilox land, and the real coat weight keeps falling underneath.

UV Curable AdhesivesCoat weight drifts and the adhesive mottles (continued)

Fault 12 of 20

Overprint will not key to the cold foil

WHAT YOU SEE

Ink or varnish printed over the foil scratches off, rubs at the fold or tapes off cleanly, while the same ink is sound on the unfoiled board alongside.

WHAT IT LOOKS LIKE

CAUSES, MOST LIKELY FIRST

The exposed foil surface is a release surfaceAfter transfer the face you print on was the side against the release coat, and release chemistry can remain on it.
The foil has no receptive top coat for that ink classMetallised surfaces are low energy and non-absorbent, so an ink formulated for board has nothing to key into.
The adhesive under the foil is not fully curedMobile monomer migrates up through the very thin metal layer and softens the boundary the overprint is sitting on.
Overprint over-cured because the metal reflects UV back into itA metallised surface reflects UV back into the coating, so the overprint over foil receives more effective dose than the same coating on absorbent board. The risk is over-cure: a brittle, heavily shrunk film that keys poorly. The correction on foil is usually less dose than the board setting, not more.

UV Curable AdhesivesOverprint will not key to the cold foil

Fault 12 of 20 · continued

Overprint will not key to the cold foil

CHECK, IN THIS ORDER

Tape pull the overprint over the foil and over the adjacent unfoiled board with the same tape and pull geometry, and compare. If a cross-cut is used, note that the blade passes through the foil and the adhesive into the board, so the result includes foil adhesion and not only overprint adhesion.
Measure surface energy on the transferred foil with dyne pens; expect a low reading if release is present.
30 MEK double rubs to ASTM D5402 on the overprint over the foil and on the board alongside, in extraction and with gloves.
Ask the foil supplier for the specification of the printable face and whether a receptive top coat is present.
Measure the overprint dose on the foil and on the board separately, and test the same overprint on an alternative foil, changing one variable only.

THEN CHANGE

Specify a cold foil with a printable receptive top coat; this is a foil specification, not an ink fault.
Change to an ink or varnish formulated for metallised and low-energy surfaces.
Corona or flame treat the foil surface in line before the overprint station where the press allows it.
Confirm the adhesive under the foil is fully cured before any overprint is applied, and log the dose that achieves it.
Re-establish the overprint cure window on the foil surface, usually at a lower dose than the board setting, rather than carrying the board setting across.

CONFIRM IT IS FIXED

No removal on a tape pull over the foil at 24 h, compared directly against the same tape pull on the adjacent unfoiled board, with 30 MEK double rubs passed on the same area.

THE TRAP

Blaming the overprint ink and trying three more inks. The usual causes are the foil printable face and the dose on a reflective surface, and until those are settled every ink will give the same result.

UV Curable AdhesivesOverprint will not key to the cold foil (continued)

Fault 13 of 20

UV PSA oozes, the matrix will not strip

WHAT YOU SEE

Adhesive squeezes at the die cut, the matrix breaks or webs, the die and the cutting cylinder build up, and labels block on the reel at the slit edge.

WHAT IT LOOKS LIKE

CAUSES, MOST LIKELY FIRST

Adhesive under-cured, so cohesive strength is lowA UV pressure-sensitive layer needs cure to build the internal strength that lets it cut cleanly; soft adhesive flows under the die rather than cutting.
Coat weight above the specificationA thicker layer takes more dose and gives the die more material to displace at the edge.
Die cutting too soon after cureCohesive strength is still developing, and the reel is being converted before the adhesive has reached its final state.
Cutting pressure too highExcess pressure presses adhesive sideways out of the cut line instead of parting it.
Liner caliper or release value wrong for the die settingA thinner or softer liner than the die was set for lets the blade go deeper, and a liner whose release is too light lets the matrix lift early and break.

UV Curable AdhesivesUV PSA oozes, the matrix will not strip

Fault 13 of 20 · continued

UV PSA oozes, the matrix will not strip

CHECK, IN THIS ORDER

Measure delivered dose at the adhesive with a band-matched radiometer at production speed, band stated.
Determine coat weight by cut-area weighing over several pairs.
Check the die cut under magnification for a clean parted edge against a smeared one.
Measure liner caliper and check the release force against the retained reference by the FINAT low-speed release method.
Measure web and adhesive temperature at the die station.

THEN CHANGE

Raise delivered dose to the specified window and verify with the radiometer, not with the lamp dial.
Bring coat weight back to specification.
Let the reel stand 24 h before converting and make that part of the job specification.
Re-set die pressure to the minimum that cuts through the face and not into the liner.
Hold liner caliper and release value to specification, and re-set the die when the liner changes.

CONFIRM IT IS FIXED

Full matrix strip at production speed on a reel converted at 24 h, with a clean cut edge at 10x and no adhesive build-up on the die or the anvil after a full reel, or at minimum 10 000 impressions at production speed, with the die inspected under magnification at the end.

THE TRAP

Increasing die pressure when the matrix breaks. It cuts into the liner, extrudes more adhesive at the edge and turns a cure problem into a liner problem as well.

UV Curable AdhesivesUV PSA oozes, the matrix will not strip (continued)

Fault 14 of 20

UV PSA tack and peel are too low

WHAT YOU SEE

Labels sit down but lift at the edge on a curved pack, or come away from a textured or low-energy surface within a day. Loop tack feels dead compared with the approved sample.

WHAT IT LOOKS LIKE

CAUSES, MOST LIKELY FIRST

Over-cureBeyond the optimum dose the network keeps crosslinking, which raises cohesive strength and takes the tack away. This is the mirror image of the matrix-stripping fault, and it is why dose has a window and not a minimum.
Coat weight below the specificationPressure-sensitive performance depends on having enough adhesive to flow into the roughness of the surface being stuck to.
Surface energy of the application surfaceA low-energy or contaminated pack surface limits wet-out, and this is a property of the customer pack, not of the adhesive.
Silicone from the liner transferring to the adhesive or the faceA liner whose cure or coat weight is off releases free silicone, which migrates into the adhesive surface and kills tack; it shows as a whole-lot fault, not a press fault.
Application temperature and dwellPeel builds over hours after application; a figure taken at 20 minutes is not the final figure.

UV Curable AdhesivesUV PSA tack and peel are too low

Fault 14 of 20 · continued

UV PSA tack and peel are too low

CHECK, IN THIS ORDER

Loop tack by FINAT FTM 9 and 180 degree peel by FINAT FTM 1 on the customer own face material and application surface.
Measure delivered dose and compare against the specified window, checking both ends of it.
Determine coat weight by cut-area weighing.
Measure the surface energy of the application surface with dyne pens.
Check the liner release force by the FINAT low-speed release method against the retained reference, and test the same adhesive on a reference liner lot.

THEN CHANGE

Bring dose down into the window; on this fault less dose is the correction, not more.
Raise coat weight to specification for the roughness of the application surface.
Move to a grade with a softer set for low-energy or textured surfaces.
Reject or re-qualify a liner lot whose release force is off the reference.
Reduce face stiffness or increase the label radius at design stage.

CONFIRM IT IS FIXED

180 degree peel by FINAT FTM 1 and loop tack by FINAT FTM 9 at 24 h on the customer own face material and application surface, meeting the agreed values, together with shear or holding power by FINAT FTM 8 still within specification, and the dose logged at the figure that produced all three. Tack and shear move in opposite directions with dose, so confirm both ends or you will trade this fault for the matrix-stripping fault on the same reel.

THE TRAP

Adding dose because the label is failing. Under-cure and over-cure both give poor labels, and adding dose to an over-cured adhesive removes the last of the tack.

UV Curable AdhesivesUV PSA tack and peel are too low (continued)

Fault 15 of 20

Odour or taint in the pack after lamination

WHAT YOU SEE

The finished reel or the filled pack smells of acrylate, and the complaint often arrives from the filler rather than from the converter. Nothing was wrong at the press.

WHAT IT LOOKS LIKE

CAUSES, MOST LIKELY FIRST

Under-cure, so unreacted monomer and initiator fragments remainOdour in this class is almost always residual mobile species, which means dose, and dose through a film is easy to get wrong.
Cure starved at the substrate interfaceThe bottom of the adhesive layer is the last to cure and sits against the structure that faces the pack contents.
A film that blocks the cure wavelengthThe same cause as the delamination fault, showing as odour before it shows as bond loss.
Set-off in the reelIn a wound reel the adhesive or print face is in contact with the face that becomes the inside of the pack, so mobile species transfer with no barrier in the path. This is the route behind the historic photoinitiator contamination cases, and it is why the reel, not just the structure, has to be considered.
Coat weight above what the dose supportsMore adhesive means more material to cure and more residual if the dose does not scale with it.

UV Curable AdhesivesOdour or taint in the pack after lamination

Fault 15 of 20 · continued

Odour or taint in the pack after lamination

CHECK, IN THIS ORDER

Measure delivered dose through the production film at production speed with a band-matched radiometer, band stated.
Run sensory testing to DIN 10955, or the equivalent Robinson taint transfer test, stating sample area, headspace volume, jar type, conditioning temperature and time, panel size and scoring scale, run blind against an unprinted reference and against a known-good reel. Two people with a jar and no method will not settle a customer complaint.
Send samples for residual monomer and photoinitiator determination by gas chromatography.
Check film transmission at the cure wavelength on the lot in use.
Test the components separately, adhesive on its own substrate, print on its own, film on its own, so the adhesive is not changed for someone else fault.

THEN CHANGE

Raise delivered dose into the specified window and log it per job with the band.
Move to a wavelength the film transmits, a doped mercury lamp or a 395 to 405 nm array.
Reduce coat weight to the bottom of the range.
Move to a grade formulated with a lower-mobility initiator and oligomer package, raw materials selected to the EuPIA Charter and exclusion policy, for constructions intended for food packaging. This is a formulation statement about the product; it is not a claim of conformity for the pack.
Where a pack is food contact, run the assessment on the finished structure with the fill, the contact time and the storage conditions stated, against the framework that applies to it: the general safety requirement of EU 1935/2004 Article 3, the simulants and conditions of EU 10/2011 for the plastic layers, the Swiss Ordinance lists where the brand owner requires them, and EuPIA good manufacturing practice. There is no harmonised specific measure for printing inks or adhesives, so the assessment is made on the finished pack and not on the adhesive.

CONFIRM IT IS FIXED

Sensory result at 24 h at or below the agreed reference level by the stated method and panel, supported by residual monomer and photoinitiator figures, and, where the pack is food contact, by a migration assessment on the finished structure under the stated contact conditions. No conformity statement is made for the adhesive on its own.

THE TRAP

Airing the reels off in a warm store. Warming a wound reel drives mobile species from one face onto the other, so the odour redistributes into the food-contact face instead of leaving.

UV Curable AdhesivesOdour or taint in the pack after lamination (continued)

Fault 16 of 20

Adhesive skins before the nip

WHAT YOU SEE

Transfer is good at the applicator and poor at the nip, the film looks dull or set on the web, and the fault gets worse whenever the press slows or stops.

WHAT IT LOOKS LIKE

CAUSES, MOST LIKELY FIRST

Stray UV between the applicator and the nipAny leaked light starts polymerisation on the web before the second web arrives, and a partly gelled surface will not wet out.
Web path too long for the gradeOpen time is a property of the adhesive; a path designed for a different chemistry can exceed it.
Dryer or press heat on the open webHeat accelerates the dark reaction and raises viscosity on the web before the nip.
Adhesive at the end of its pot or shelf lifeStabiliser depletion shortens the working window, and material that has been recirculated for days behaves differently from fresh.
Press stops with the web under a lamp or a hot dryerThe stationary web takes a large local dose and, under medium-pressure mercury, a large local infra-red load. On thin PE and PP that shows as distortion, shrinkage, wrinkling or a burnt hole as well as a skinned adhesive.

UV Curable AdhesivesAdhesive skins before the nip

Fault 16 of 20 · continued

Adhesive skins before the nip

CHECK, IN THIS ORDER

Find stray light without looking at the lamp: lay UV-sensitive indicator paper or photochromic strips along the open web path between applicator and nip with the guards closed and the press in a safe state, then read them. If any visual inspection of a lit station is unavoidable, do it with the guards in place, through the machine UV-filtered viewing window, wearing a UV-rated face shield and with extraction running. Never look towards an open mercury arc.
Time the web path from applicator to nip at production speed and compare it with the stated open time for the grade.
Measure web temperature between the applicator and the nip with an infra-red thermometer.
Record how long the material has been in the circulation and check it against the pot life and the incoming lot check.
Correlate the fault with press stops by marking the reel at each stop, and inspect the web at those marks for heat distortion as well as for skinning.

THEN CHANGE

Shield the open web path from every light source, including the lamp housings and daylight through roof lights.
Shorten the web path to the nip where the press allows it, or move the applicator.
Remove heat from the open web between the applicator and the nip.
Replace circulated material that is past its working life, and do not top it up.
Set the press to shutter or lift the lamps and open the dryers automatically on a stop, and check that the shutter actually closes.

CONFIRM IT IS FIXED

Full wet-out and specified 24 h peel on material laminated immediately after a two-minute press stop, matched against material laminated in steady running, with no heat distortion at the stop mark.

THE TRAP

Raising coat weight so there is more wet adhesive at the nip. It buys a few metres, deepens the skin, and adds shrinkage stress to a laminate that is already poorly wetted.

UV Curable AdhesivesAdhesive skins before the nip (continued)

Fault 17 of 20

Bond falls after ageing, hot fill or at the seal jaw

WHAT YOU SEE

The laminate passes at 24 h and fails weeks later, or delaminates at the seal jaw on the filling line, or fails after the pack is filled with an oily or surfactant product.

WHAT IT LOOKS LIKE

CAUSES, MOST LIKELY FIRST

The bond was marginal at the start and the ageing only revealed itA peel figure at the lower end of the range has no margin for the plasticising effect of time, heat or fill.
Migration from the fill through the inner web into the interfaceOils, essential oils and surfactants swell the adhesive and lower the interfacial bond; the barrier of the structure may not sit between the fill and the adhesive.
Slip and antiblock additives migrating out of the film over weeksThey accumulate at the interface and act as a release layer built up after the fact.
Temperature and pressure at the seal jawAt the jaw the adhesive sees the highest temperature in the whole process while under pressure, so a laminate that is sound in the pack can split at the seal. Cohesive strength falls with temperature, and a bond adequate at 23 C may not be adequate at 60 C or at jaw temperature.
Residual cure stress relaxingShrinkage stress stored at cure keeps working at the interface for weeks.

UV Curable AdhesivesBond falls after ageing, hot fill or at the seal jaw

Fault 17 of 20 · continued

Bond falls after ageing, hot fill or at the seal jaw

CHECK, IN THIS ORDER

Peel at 24 h, 7 days and after accelerated ageing at 50 C for 7 days on the actual construction, stating the acceleration assumption used. On the conventional Q10 equals 2 basis, 7 days at 50 C is of the order of six weeks at 23 C, so it is a screen and not a shelf-life demonstration.
Peel at the fill temperature, not only at ambient, using a heated chamber on the tensile tester.
Run a seal initiation ladder on the finished structure, jaw temperature against seal strength to ASTM F88, and note the temperature at which the failure mode changes from seal to delamination.
Fill a made-up pack with the actual product and hold it at the storage condition, then peel.
Rule the other components out before changing the adhesive: ask the film supplier for the slip and antiblock package and its migration behaviour, and check the ink and varnish on the same ageing.

THEN CHANGE

Establish a peel target with margin over the failure mode rather than accepting the minimum passing figure.
Move to a grade with the chemical and heat resistance the fill and the sealing process require, and re-qualify.
Change the inner web or add a barrier layer so the fill is not in contact with the adhesive interface.
Widen the seal window at the filler, or move to a face or sealant layer whose seal initiation temperature sits below the temperature at which the adhesive interface gives way.
Reduce coat weight and cure stress, and confirm dose is in the window at every speed run.

CONFIRM IT IS FIXED

Peel on the finished construction at 24 h, 7 days and after 7 days at 50 C, all meeting the agreed value, plus a peel and a seal strength to ASTM F88 on a pack filled with the actual product and held at the real storage condition. Where a shelf life is being claimed, run real-time ageing on the finished construction in parallel; an accelerated result is a screen.

THE TRAP

Signing the job off on the 24 h peel alone. This category most expensive failures all pass at 24 h, which is exactly why the ageing point exists.

UV Curable AdhesivesBond falls after ageing, hot fill or at the seal jaw (continued)

Fault 18 of 20

Adhesive stays tacky wherever it cured in air

WHAT YOU SEE

The adhesive is hard under the film or under the foil but soft, tacky or smeary wherever it was exposed to air at cure: outside the foil image, at bleed and squeeze-out, at the web edge beyond the second film, and on any station that cures the adhesive with nothing over it. The reel blocks, the slit edge glues, and rollers downstream pick up adhesive.

WHAT IT LOOKS LIKE

CAUSES, MOST LIKELY FIRST

Oxygen inhibition at the free surfaceOxygen quenches the acrylate radical as fast as the initiator makes it, so the top few microns of an adhesive cured in air never build network. The bulk cures and the surface does not, at any dose.
Peak irradiance too low at that stationOxygen inhibition is beaten by generating radicals faster than oxygen can diffuse back in, which is a peak irradiance effect and not a dose effect. More time at low irradiance makes it worse, not better.
Adhesive coated outside the covering web or the foil imageAny adhesive wider than the second web, or outside the foil image, cures in air by definition, however well the station is set.
Very low local coat weight, at an edge or in fine lineA thin film has a larger proportion of its thickness inside the oxygen-affected layer, so hairline foil and fine type go soft first.
Grade not formulated for an open surface cureAn initiator package intended to cure under a film has no surface-cure component and no amine synergist to consume oxygen at the surface.

UV Curable AdhesivesAdhesive stays tacky wherever it cured in air

Fault 18 of 20 · continued

Adhesive stays tacky wherever it cured in air

CHECK, IN THIS ORDER

Compare tack on an area cured under the film against an area cured in the open on the same reel and at the same dose; a difference at equal dose is oxygen inhibition, not under-dose.
Measure peak irradiance in W/cm2 at the web at that station and read it against the dose figure. Adequate dose with low peak irradiance is the signature.
Measure how far the adhesive image runs beyond the covering web or the foil image, at both edges.
Solvent rub to ASTM D5402 on a draw-down cured in air and on one cured under a film, and compare, in extraction and with gloves.
Find where blocking and roller pickup start on the reel and match it to the exposed area.

THEN CHANGE

Raise peak irradiance at that station rather than dose: lamp closer, reflector serviced, window clean, web supported against flutter.
Cure under the covering web or the foil carrier wherever the press allows it; a surface cured under film is not oxygen inhibited.
Inert the cure zone with nitrogen where the press is equipped for it. This is inertion at the lamp only. Never blanket, seal or purge the adhesive circulation or the storage vessel, where the stabiliser needs dissolved oxygen to function.
Trim the adhesive image inside the covering web and inside the foil area at plate stage.
Move to a grade with a surface-cure initiator package where an open cure cannot be avoided.

CONFIRM IT IS FIXED

No tack difference at 24 h between adhesive cured in the open and adhesive cured under the covering web, judged by solvent rub and by thumb tack, and a full reel that unwinds at 24 h with no blocking at the slit edge and no transfer onto a clean roller.

THE TRAP

Slowing the press to beat a tacky surface. Oxygen inhibition is an irradiance and atmosphere problem, so more time at the same low irradiance simply lets more oxygen diffuse in and the surface stays soft.

UV Curable AdhesivesAdhesive stays tacky wherever it cured in air (continued)

Fault 19 of 20

Foil doubles, slivers or misses at the carrier strip point

WHAT YOU SEE

The foil image is doubled or ghosted, fine slivers of foil come away at the strip bar and blow around the press, the carrier web breaks, or foil re-lays onto the web after it has been stripped. Often intermittent and worse at speed.

WHAT IT LOOKS LIKE

CAUSES, MOST LIKELY FIRST

Strip angle wrongThe carrier has to peel away from the transferred image at a controlled angle. Too shallow and the foil is dragged rather than parted; too sharp and the carrier tears at the image edge.
Strip tension wrong or unstableCarrier tension sets the peel force at the strip point. Too low and the foil re-lays onto the web; too high and foil is pulled out of fine line and type, and the carrier runs near a break.
Distance from the lamp to the strip point wrongOn a cure-through-carrier unit the adhesive must have reached the right state by the time the carrier peels. Too close to the lamp and it is still building strength; too far and it has cured hard against the carrier.
Carrier UV transmission low or variable between lotsThe adhesive is cured through the carrier, so a change in the carrier film changes delivered dose at the adhesive exactly as a laminating film does, and nothing on the press looks different.
Static at the strip barThe stripped carrier and the foil both carry charge, so slivers cling and re-lay onto the web instead of leaving with the carrier.

UV Curable AdhesivesFoil doubles, slivers or misses at the carrier strip point

Fault 19 of 20 · continued

Foil doubles, slivers or misses at the carrier strip point

CHECK, IN THIS ORDER

Record strip angle and carrier tension as set, and treat them as job parameters rather than leaving them to the operator.
Measure the distance from the lamp to the strip point and compare it against the setting that ran the last good job.
Run a UV-Vis transmission scan from 300 to 420 nm on the foil carrier lot, as you would on a laminating film, and ask the foil supplier for the lot spectrum.
Read the static field at the strip bar with the press at speed and check the ionising bar emitters for fouling.
Inspect the stripped carrier: a clean negative of the image is right, foil left in the image area is under transfer, foil taken out of the image is over-peel.

THEN CHANGE

Set strip angle and carrier tension to the press specification and log them on the job ticket.
Move the strip point relative to the lamp in small steps and re-read the foil at each one.
Fit or clean the ionising bar at the strip bar and control pressroom humidity.
Treat a change of foil supplier or foil lot as a change of the whole system and re-qualify adhesive, foil and overprint together.
Reduce coat weight to the lower end of 1.5 to 3.0 g/m2 to cut the squeeze-out that slivers at the image edge.

CONFIRM IT IS FIXED

A full reel foiled with a clean stripped carrier, no slivering at the strip bar, no doubling at 10x, and a tape pull at 24 h with no lift at the image edge.

THE TRAP

Raising carrier tension to stop the foil re-laying. It raises the peel force at the strip point, pulls foil out of fine line and type, and puts the carrier nearer a break.

UV Curable AdhesivesFoil doubles, slivers or misses at the carrier strip point (continued)

Fault 20 of 20

The reel blocks, the edges glue and the roll telescopes

WHAT YOU SEE

The finished reel is hard to unwind, layers stick, adhesive shows as a bead at the slit edge, roll edges gum up the converter machine, or the roll telescopes in store. Usually found by the converter and not at the press.

WHAT IT LOOKS LIKE

CAUSES, MOST LIKELY FIRST

Adhesive squeezed beyond the web edge or outside the imageAdhesive outside the covering web cures in air, stays tacky and welds one layer to the next under wound-in pressure.
Coat weight above specificationMore adhesive means more to squeeze out at the nip and at the slitter, and a larger bead at the edge.
Under-cure or oxygen inhibition at the free surfaceA surface that never built cohesive strength flows under wound-in pressure over days, so the reel is worse on the third day than on the first.
Rewind tension too high, or no taper setWound-in pressure both forces cold flow at the edge and locks the layers together, and it is highest near the core.
Reel stored or shipped warmCohesive strength falls with temperature, so a reel that was sound leaving the press blocks in a warm store or a container.

UV Curable AdhesivesThe reel blocks, the edges glue and the roll telescopes

Fault 20 of 20 · continued

The reel blocks, the edges glue and the roll telescopes

CHECK, IN THIS ORDER

Unwind a metre from the finished reel at 24 h and at 7 days and compare release at the core, the middle and the outside.
Inspect the slit edge at 10x for a bead of adhesive, and measure how far the adhesive image runs beyond the covering web.
Determine coat weight by cut-area weighing and compare against the specification.
Read rewind tension and taper, and the hardness against diameter curve built during winding.
Record store and transit temperature, not only pressroom temperature.

THEN CHANGE

Trim the adhesive image inside the covering web and inside the foil area at plate stage.
Bring coat weight back to specification.
Cure the free surface properly: raise peak irradiance, or cover the surface before cure, rather than adding dose.
Reduce rewind tension and set a taper of 20 to 40 per cent from core to full reel.
Store and ship the reel at a controlled temperature and state that condition to the converter on the delivery paperwork.

CONFIRM IT IS FIXED

A full production reel unwinding cleanly at 24 h and again at 7 days, checked at the core and the outside, with no adhesive bead visible at the slit edge at 10x and no transfer onto a clean roller.

THE TRAP

Slitting the glued edge off and re-reeling. It removes the evidence and the bead returns on the next reel, because the adhesive image is still wider than the web that covers it.

UV Curable AdhesivesThe reel blocks, the edges glue and the roll telescopes (continued)

At the press

One page to work from, and the methods behind every number.

Quick reference

One page at the press

Symptom	Check this first	Change this first
Laminate peels apart at 24 h	Job docket against the last good run, then delivered dose under the production film, band stated	Raise irradiance, or move to a wavelength the film transmits
Bond poor only over heavy solids	30 MEK double rubs (ASTM D5402) on the print before lamination	Cure the print, and remove press-added slip from those colours
Tunnels and channels in the reel	Both unwind tensions in N per 100 mm of width, and the rewind taper	Drop the thinner web to the bottom of its own range, set 20 to 40 per cent taper
Laminate or label curls	Coat weight by cut-area weighing against the specified range	Reduce coat weight to the bottom of the range
Foil transfer patchy or pinholed	Coat weight and anilox cell condition under magnification	Restore coat weight to 1.5 to 3.0 g/m2 by anilox, not by pressure
Foil lifts at the edges	Cure state where the carrier strips, then the same adhesive on another foil	Set lamp and lamp-to-strip distance to the logged figures, reduce coat weight
Foil doubles or slivers at the strip bar	Strip angle, carrier tension and lamp-to-strip distance as set	Reset to the press specification and log them on the job ticket
Craters and fisheyes	Surface energy at the point of coating, and the defect repeat distance	Find and remove the silicone source, then corona treat in line

UV Curable AdhesivesQuick reference

Quick reference

One page at the press

Symptom	Check this first	Change this first
Adhesive gelling in the chamber	Light leaks by indicator paper, and temperature at tray, pump and return	Black out the applicator, cool the path, keep an air headspace
Bond falls as speed rises	Dose at set-up speed and at running speed, both logged with the band	Add irradiance or lamp power; stop web flutter at the cure station
Bubbles and silvering	Full-width nip impression strip	Correct roller wear, even up nip pressure, then raise coat weight
Coat weight drifting through the run	Averaged cut-area weighing at start, middle and end; anilox cell volume	Clean the anilox and hold adhesive temperature within 2 C
Overprint lifts off the cold foil	Tape pull on the foil against the same pull on the board alongside	Specify a foil with a printable receptive top coat
PSA oozes, matrix will not strip	Delivered dose, then coat weight, then liner caliper	Raise dose into the window and convert at 24 h, not at the press
PSA tack and peel too low	Loop tack and 180 degree peel on the customer face and surface	Bring dose down into the window; confirm shear has not gone with it
Adhesive tacky outside the image or at the web edge	Peak irradiance in W/cm2 at that station, and how far the image runs out	Raise irradiance or cover the surface; trim the image inside the web

UV Curable AdhesivesQuick reference

Quick reference

One page at the press

Symptom	Check this first	Change this first
Reel blocks or the slit edge glues	Slit edge at 10x for an adhesive bead, and rewind tension and taper	Trim the adhesive image inside the covering web, reduce rewind tension
Adhesive skins before the nip	Indicator paper along the open web path, and time to nip against open time	Shield the open web path and shutter the lamps on a stop
Odour or taint in the finished pack	Delivered dose through the production film, then sensory testing to a stated method	Raise dose into the window, or move to a wavelength the film transmits
Bond falls after ageing, fill or at the seal jaw	Peel at 7 days and after 7 days at 50 C on the real construction	Re-qualify the grade against the fill and the seal condition, with margin

UV Curable AdhesivesQuick reference

Test methods

The measurements this guide relies on

Measurement	Method	What it tells you, and the usual acceptance
Laminate bond peel	Ply adhesion to ASTM F904, or T-peel to ASTM D1876 or ISO 11339, with the geometry fixed for that construction	The release number for a laminating adhesive, taken at 24 h and at 7 days on the production construction. Fix the geometry and do not swap between tests: T-peel and 180 degree peel load the interface differently and their values are not comparable on the same laminate. State strip width, 15 mm or 25 mm, crosshead speed, 300 mm/min unless the standard specifies otherwise, peel angle and conditioning with every result. Acceptance is agreed per construction, and the failure mode matters as much as the value, since adhesive on both faces indicates cure and a clean face indicates the interface.
Peel adhesion, pressure sensitive	FINAT FTM 1, 180 degrees at 300 mm/min	Final peel of a UV pressure-sensitive construction, on the customer own face material and application surface. Reported at 20 min, 24 h and 72 h because peel builds; a 20 min figure is not the specification.
Loop tack	FINAT FTM 9	Immediate grab at the moment of application, which is what decides whether a label sits down on the line. Falls at both ends of the dose window, so it is read alongside the radiometer figure and not on its own.
Shear, holding power	FINAT FTM 8	The other half of the pressure-sensitive balance. Tack and shear move in opposite directions with dose, so a change made to recover tack is only confirmed once shear is shown to be still in specification. Without this figure a tack fault gets traded for a die-cutting fault.
Release force, liner	FINAT low-speed release method, FTM 3	Release of the face and adhesive from the liner, against the retained reference for that liner lot. A liner whose release or silicone cure is off shows as lost tack or as a broken matrix, and both look like adhesive faults until this is measured.
Solvent rub	ASTM D5402, MEK double rubs	Cure state of the print that the adhesive has to key to, and of a draw-down of the adhesive itself where it is accessible. 30 double rubs without softening is the usual pass for print under a laminate. It cannot be run on adhesive already covered by a film. MEK is highly flammable and has an occupational exposure limit, so run it in extraction, with gloves, away from any UV station.
Tape pull adhesion	Stated tape, applied with a defined roller and pulled at 180 degrees, compared against a control area	Adhesion of print on film, of a cold foil image, and of an overprint over foil. The comparison is the diagnosis, so pull on the foil and on the adjacent unfoiled board together. A cross-cut to ISO 2409 is the right method for a coating on a substrate the blade can score without cutting through, which is print or varnish on board; it is not right on a 12 to 20 micron film, nor on a foil image where the blade passes through a metal layer tens of nanometres thick into the substrate and the classification reports substrate damage.

UV Curable AdhesivesTest methods

Test methods

The measurements this guide relies on

Measurement	Method	What it tells you, and the usual acceptance
Wetting tension	ASTM D2578, dyne pens or ISO 8296 test inks	Surface energy of the substrate at the point of coating, and of the surface a pressure-sensitive label will be applied to. 38 mN/m is the practical floor on polyolefin; measure on the reel at the press, not on the certificate. The standard ink formulations contain formamide and 2-ethoxyethanol, both reproductive toxins, so gloves and extraction.
UV radiometry	Band-matched radiometer, wavelength band declared with every reading	Delivered dose in mJ/cm2 and peak irradiance in W/cm2 at the adhesive, taken at production speed with the production film or foil carrier over the sensor. Match the head to the source: a UV-A head, 320 to 390 nm, for a 385 nm array, a UV-V head, 395 to 445 nm, for a 395 or 405 nm array, and a full multi-band head for a mercury lamp. A UV-A head will badly under-read a 405 nm array. The same lamp reads two to three times differently on two different bands, so a dose in mJ/cm2 without a band is not a number. A standard puck will not pass a closed nip, so run with the nip open, carry the sensor on the web, or use a thin strip-type instrument.
UV transmission of the film and the foil carrier	UV-Vis transmission scan from 300 to 420 nm on the reel to be run	The percentage of the cure wavelength that actually reaches the adhesive. Clear BOPP and PET are typically 70 to 90 per cent at 395 nm; a UV-blocked PET can be under 10 per cent at 365 nm. Read it in the same band the radiometer reads. A change of film or foil lot is one of the most frequent and most easily missed causes of a lost bond, because nothing on the press changes when it happens.
Coat weight by weighing	Cut-area weighing on a four-place balance, averaged over at least five adjacent pairs, or acetone wash-off on a single specimen	The applied weight in g/m2. The substrate swamps the coating on a single pair, so average several pairs cut adjacent at the same cross-web position and quote the spread. Where the substrate is board, or where a tolerance tighter than about 10 per cent has to be resolved, weigh a coated specimen taken before the lamp, wash the uncured adhesive off that same specimen with acetone, dry and reweigh.
Haze and gloss	Transmission haze to ASTM D1003 or ISO 14782; specular gloss to ISO 2813 at a stated angle	Silvering and entrapped air are an internal scattering defect, so transmission haze is the number that tracks them on a clear laminate. ISO 2813 is specular gloss at 20, 60 and 85 degrees and measures the surface, not the interior; it is the right instrument for foil brightness and for a varnish, and the wrong one for silvering.
Viscosity	Rotational viscometer at a stated temperature and shear rate, spindle and speed recorded	The number that predicts transfer, coat weight and wet-out. UV laminating and cold-foil adhesives are shear thinning, so the shear rate has to be stated for the reading to mean anything, and a flow cup method such as ISO 2431, which assumes Newtonian or near-Newtonian behaviour, will not track what the anilox sees.
Sensory, odour and taint	DIN 10955, or the equivalent Robinson taint transfer test	Odour and taint transfer from the finished material, run blind against an unprinted reference and a known-good reel. State sample area, headspace volume, jar type, conditioning temperature and time, panel size and scoring scale, or the result will not settle a complaint.

UV Curable AdhesivesTest methods

Test methods

The measurements this guide relies on

Measurement	Method	What it tells you, and the usual acceptance
Seal strength	ASTM F88	Where the laminate is sealed, this tells you whether the adhesive interface or the seal is the weak point. Run a jaw temperature ladder on the finished structure, after ageing and, where relevant, after filling, and note the temperature at which the failure mode changes from seal to delamination. It is a construction property, qualified on the customer own material.

UV Curable AdhesivesTest methods

When the press-floor fixes have not worked

What to send us

The full construction, written out layer by layer from the outside in, with supplier and grade for every film, foil, carrier, liner and face material, and the lot numbers of the ones that ran, together with the adhesive, ink and varnish lot numbers.
Radiometer readings taken at production speed with the production film or foil carrier over the sensor, stating the wavelength band and the head used, plus lamp or array hours and the date the window or quartz sleeve was last cleaned.
Which cold-foil architecture the press is: cure through the carrier before strip, or pre-nip tack cure, with strip angle, carrier tension and lamp-to-strip distance where it applies.
Coat weight measured by averaged cut-area weighing, or by acetone wash-off, at the start, middle and end of the failing run, with the anilox specification, its cell volume and its last chemical cleaning date.
Peel results at 24 h and 7 days with the failure mode described for each, and the standard, strip width, peel geometry, test speed and conditioning used, on samples from the core and the outside of the same reel.
Samples: 2 m of the failing reel taken from the core, 2 m taken from the outside, 2 m of the same construction from a run that was good, and an unrun sample of the incoming film, foil or liner lot.
Press conditions as run: speed, both unwind tensions expressed in N per 100 mm of width with the caliper stated, rewind tension and taper, nip pressure and the method used to set it, adhesive temperature at the tray or chamber, and pressroom temperature and relative humidity.
The incoming lot check on the adhesive drum in use, viscosity at a stated temperature and shear rate against the retained reference, and how long the material had been in circulation.
For a food-contact pack, the fill, the fill and storage temperatures, the contact time, the seal jaw condition and the brand owner specification, so the assessment is run on the finished structure rather than on the adhesive on its own.

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UV Curable AdhesivesTechnical service