Troubleshooting guide

UV Offset Inks

Press-floor fault finding for Uniforce-250 mercury UV and Unimax 400 UV LED offset on sheet-fed and combination presses.

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.

Separate cure from adhesion before you change anything: confirm the film is cured with MEK double rubs to ASTM D5402 first, because a soft film and a poorly bonded film look identical at the delivery and have nothing in common.
Measure the dose at the sheet with a band-calibrated radiometer passed through the press at running speed; the lamp percentage at the console and the hours counter tell you nothing about what reached the ink.
Fix roller and fount temperature before you touch the water setting or the ink duct, because almost every ink and water complaint on a UV offset press is a temperature complaint wearing a different name.
Change one variable at a time and give it five hundred sheets: UV offset has no drying lag, so the sheet at the delivery is the sheet the press is making now, but the roller train and the fount take a few hundred sheets to settle after any change. Five hundred is the figure used throughout this guide, and it is the figure to use everywhere.
Judge adhesion, crease, scuff and gloss 24 hours after the run, not at the delivery, because the dark reaction is still going and the sheet you condemn at midnight often passes in the morning.
Handle every test in this guide as work with uncured acrylate and solvent. Nitrile gloves for any contact with wet or freshly printed ink, eye protection and extraction for solvent rubs, and no hands, probes, rags or strips in a moving roller train. Any measurement inside the machine, nip strips, roller diameters, packing and duct probes, is taken with the press stopped, isolated and locked off, and no guard is opened or interlock defeated to look at a running lamp.
Write down the incoming water conductivity, the fount reading, the roller temperature, the lamp rating and the dose at the start of every job, because a fault diagnosed against a baseline takes minutes and one diagnosed against memory takes a shift.

UV Offset InksHow 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 Offset InksThe process

Control variables

What to hold, and how to measure it

Variable	Target	How it is measured	How it drifts
Fount conductivity	Make-up specification for a fresh tank: base water + 900 to 1300 uS/cm at 25 C. Running tolerance once the job has started: +/- 200 uS/cm on the figure that job actually started at, logged beside the incoming water reading	Calibrated conductivity meter at the fount tank, incoming mains water read on the same meter at the start of the shift	Climbs steadily through a run as calcium carbonate and coating binder come off the board into the circulation. A climb of 300 uS/cm above the start-of-job reading is a refresh, even when the absolute figure still sits inside the make-up window, which is exactly why the start-of-job figure is logged. The absolute number means nothing unless the incoming water was logged.
Fount pH	4.8 to 5.5	pH meter calibrated on 4.0 and 7.0 buffers at 25 C, read at the tank, not on paper strips	Rises as alkaline coating dissolves into the tank. The desensitising film on the plate fails while the meter still reads inside the window, so read pH and conductivity together and treat a climbing pair as one signal.
Fount temperature	10 to 14 C at the tank	Thermometer at the tank outlet, not the chiller set point	Creeps up through a long run as the chiller falls behind the heat the lamps put back into the press. Every 2 C of rise behaves like a step of extra alcohol taken out, and the operator sees it as scumming.
Roller train temperature	28 to 32 C surface	Non-contact IR thermometer on the roller face at three positions across the width after 500 sheets at speed. Never bring a contact probe, a hand, a rag or a strip into a moving roller train. If a contact reading is needed, stop the press, isolate and lock it off, and read within a few seconds of stopping	Rises in the first twenty minutes and again after every stop and restart. Above about 35 C the ink body drops, the ink takes water it should not take, and density falls without anyone moving a key.
Ink duct temperature	22 to 28 C	Probe in the ink body in the duct, away from the duct blade, with the press stopped and isolated	Tracks the room and the lamp housings. A duct sitting at 32 C on a summer afternoon runs a different ink from the one specified, and the tack ladder built at the house temperature no longer describes it.
Dose at the substrate	80 to 150 mJ/cm2 process colours, 120 to 200 mJ/cm2 dense black, 150 to 250 mJ/cm2 opaque white and metallics	Band-calibrated radiometer, UV-A 320 to 390 nm for Uniforce-250 or 385 to 405 nm for Unimax 400, passed through the press on a carrier sheet at running speed, per unit. Record the lamp rating in W/cm, or the array wavelength and rating, beside every reading	Falls with lamp age, reflector fouling, quartz devitrification and ink mist on the LED window. The loss is gradual and invisible until a job with a narrow window fails, so trend it against the commissioning figure rather than waiting for a complaint.
Peak irradiance at the sheet	Mercury, Uniforce-250: 1 to 3 W/cm2 UV-A at the sheet, quoted with the lamp rating, typically 1 to 1.5 W/cm2 from a 120 W/cm system and 2 to 3 W/cm2 from a 200 W/cm system, both on a clean reflector at the correct focus. LED, Unimax 400: 8 to 12 W/cm2 process, 12 to 16 W/cm2 under opaque white and dense black	Same radiometer pass, reading peak rather than integrated dose, with the lamp rating in W/cm or the array rating recorded alongside	Changes with lamp-to-sheet distance, reflector condition and focus. It is the number that beats oxygen inhibition, and it is the one operators never look at because the console only offers them a percentage. It is set by the source and its geometry and does not change with press speed, so trend each press against its own commissioning reading rather than against the published range.

UV Offset InksControl variables

Control variables

What to hold, and how to measure it

Variable	Target	How it is measured	How it drifts
LED array working distance	5 to 15 mm sheet-fed, 2 to 8 mm interdeck, to the array maker's figure	Feeler gauge or shim at three positions across the array, cold, with the press stopped, isolated and locked off	Opens up when packing is changed, when a transfer cylinder jacket is replaced, or when someone lifts the array for cleaning and does not return it. Five millimetres of extra gap typically costs 15 to 30 % of peak irradiance.
Tack ladder across the sequence	16 +/- 1 first down descending to 12 +/- 1 last down, 1 to 2 points per unit, on the inkometer scale	Inkometer to ASTM D4361, 1200 rpm, 32 C, 1.32 cm3 charge, read at 60 s, the house method across the whole range. These are inkometer-scale numbers. An IGT Tack-o-scope or any other instrument reads on its own scale and its figures cannot be compared with these; print the instrument, speed, temperature, charge and read time beside any tack figure you quote back to us	Does not drift in the tin, but drifts on press as duct and roller temperature move. A ladder measured at a different charge, speed, temperature or instrument is not comparable with the published figure and must not be used to argue with it.
Emulsification, water pick-up	15 to 25 % w/w on Uniforce-250 at the house conditions, typical for a sheet-fed UV offset ink and far below an oil-based ink	Duke-type incremental water addition on the inkometer at 1200 rpm and 32 C, the same conditions as the house tack method, water added in weighed increments to the end point, pick-up reported as % w/w with the conditions attached	Water uptake is strongly temperature dependent, so a figure quoted without its temperature and its water-addition schedule cannot be argued with. A duct sample taken at the end of a run and compared against a fresh tin on the same conditions is the only useful comparison.
Film weight on a solid	1.0 to 1.5 g/m2 process on coated stock, 1.8 to 2.5 g/m2 opaque white, 1.5 to 2.5 g/m2 metallics	Gravimetric, but taken so that board variation does not swallow the answer: cut a known area of at least 100 cm2 of solid and an equal area of unprinted stock from the same sheet, side by side and at the same position across the sheet, weigh both on a four-place balance and take the difference. Average at least three pairs. Do not weigh a printed sample against unprinted stock from a different sheet or a different pallet: board basis weight varies by several g/m2 within a pallet, which is more than the whole ink film being weighed. Cross-check against ink consumption per thousand sheets, which is what catches a systematic error in the weighing	Climbs when an operator chases density on a tired blanket or on absorbent stock. It is the single variable that most changes cure at depth, set-off, crease performance and, on the LM grade, migration risk.

UV Offset InksControl variables

The mechanism

Why the top and the bottom of a UV film fail for opposite reasons

A cross-section through a printed UV film, top to bottom. The same film can be tacky at the surface and liquid at the board while being perfectly hard in the middle, and the two failures have opposite cures. Oxygen starves the top and is beaten by peak irradiance, the light per unit time, which the lamp and its geometry set and press speed does not. Pigment starves the bottom and is beaten by wavelength and by a thinner film. Neither is beaten by running slower, which is the first thing every operator reaches for.

UV Offset InksThe mechanism

02 | 20 faults

Faults

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

Fault 1 of 20

Scumming and tinting in the open areas

WHAT YOU SEE

The clear areas of the sheet pick up a wash of colour that deepens through the run, worst in the middle of the sheet and worst after a stop. The operator opens the water, the tint clears for a few hundred sheets, then the solids go flat and the fault comes back.

WHAT IT LOOKS LIKE

CAUSES, MOST LIKELY FIRST

Fount conductivity has climbed with calcium and coating binder picked up from the boardDissolved salts stop the fount laying down a continuous desensitising film on the non-image area, so the open metal accepts ink.
Roller train running above 32 CThe ink softens, its body drops, and a softer ink transfers into a thinner water film and onto the plate shoulder.
Dampening feed set below what the ink load on that form needsA heavy solid form carries more ink to the plate, which needs more water to hold the open areas, and the setting that worked on the last job is now short.
Fount temperature has drifted above 14 CA warmer fount evaporates faster off the plate and loses the alcohol or surfactant that was doing the wetting, so the effective feed falls without the setting changing.
Plate not fully desensitised in processing, or gum washed off during a long stopThe oleophobic layer in the non-image area is incomplete, so ink wets bare aluminium regardless of what the dampening is doing.

UV Offset InksScumming and tinting in the open areas

Fault 1 of 20 · continued

Scumming and tinting in the open areas

CHECK, IN THIS ORDER

Read fount conductivity and pH at the tank with a calibrated meter, then read the incoming mains water on the same meter and work with the increment, not the absolute figure
Compare the tank reading against the start-of-job figure for this job, not only against the make-up window: a climb of 300 uS/cm is a refresh even if the absolute number still looks in specification
Read fount temperature at the tank outlet, not the chiller set point, and confirm 10 to 14 C
Read roller surface temperature with a non-contact IR thermometer at three positions across the width after 500 sheets at speed
Clean the plate with UV-approved plate cleaner and re-gum: if the tint returns in the same place it is the plate, if it returns everywhere it is the fount chemistry

THEN CHANGE

Dump the fount, flush the circulation and remake at 3 to 5 % v/v concentrate on water at 8 to 12 dH; do not top up a loaded tank
Bring roller temperature back into 28 to 32 C and fount temperature back into 10 to 14 C, then wait 500 sheets before judging
Reset dampening to the minimum that keeps the plate clean, then re-read solid density and reset the keys from there
If the tint is local and repeatable, re-image the plate
Fit a paper-band or bag filter of about 25 to 50 micron on the fount return, change it every shift on heavily coated board and clean the tank out at the same interval. A magnetic separator only catches ferrous debris from the press and does nothing for calcium carbonate or coating binder, which are what load the fount on coated board

CONFIRM IT IS FIXED

The open areas stay clean at a dampening setting at or below the one that held density at the start of the run, with conductivity inside +/- 200 uS/cm of the start-of-job figure and pH 4.8 to 5.5, and solid density back in spec on Status E to ISO 5-3.

THE TRAP

Opening the water. It clears the tint for a hundred sheets and then over-emulsifies the ink. Uniforce-250 carries only 15 to 25 % w/w water at the house conditions, far less than an oil-based ink, so the operator arrives at a flat, greasy, poorly trapping ink and now has two faults to unpick instead of one.

UV Offset InksScumming and tinting in the open areas (continued)

Fault 2 of 20

Surface stays tacky, the film under it is hard

WHAT YOU SEE

Scratch the solid with a gloved thumbnail and the film is solid, but a firm gloved thumb twist marks it and the gloss mattes where you touched it. Highlights and light tints feel tackier than the solids. The pile blocks by the morning.

WHAT IT LOOKS LIKE

CAUSES, MOST LIKELY FIRST

Oxygen inhibition at the top micron of the filmAtmospheric oxygen quenches the growing radical chain at the surface faster than the initiator can generate radicals there, leaving unpolymerised monomer on top of a fully cured body.
Peak irradiance at the sheet has fallen, on mercury through lamp age and reflector fouling, on LED through working distance and a fouled windowIt is radical flux per unit time, not total dose, that outruns oxygen diffusion into the surface, and peak irradiance is what sets the flux.
Short-wave output lost on a mercury lamp with a devitrified or solarised quartz envelopeThe short-wave lines below about 280 nm cure the top micron and are the first output an ageing or clouded lamp loses, while a UV-A reading still looks acceptable.
Wrong grade for the array on an LED pressA package tuned to 395 nm sees a small fraction of the photons from a 405 nm array, so surface cure fails first even when the body looks acceptable. An LED array has no short-wave output at all, so surface cure on LED rests wholly on peak irradiance and the initiator package.
Amine synergist depleted by an over-thinned or heavily extended inkDiluting with a varnish or an unextended base cuts the synergist concentration that manages oxygen at the surface without cutting the film weight.

UV Offset InksSurface stays tacky, the film under it is hard

Fault 2 of 20 · continued

Surface stays tacky, the film under it is hard

CHECK, IN THIS ORDER

Wearing a nitrile glove, twist a gloved thumb under firm pressure on the heaviest solid within one minute of the final lamp: no marking, no smearing, no matting. Anything that marks is uncured acrylate. Never test with bare skin, change the glove as soon as ink is on it, and wash any skin contact with soap and water, not with solvent
Twenty IPA double rubs with a cotton pad under about 1 kg hand load within five minutes, no colour on the pad, run in nitrile gloves with eye protection, under extraction and well away from lamps and hot housings
Measure peak irradiance, not just dose, with the band-calibrated radiometer at running speed, and record the lamp rating in W/cm beside it
Read the short-wave band rather than only looking at the glass: on mercury, take the radiometer pass with a four-band head and compare UVB, 280 to 320 nm, and UVC, 250 to 260 nm, against that press's commissioning figures, because that is where an ageing or devitrified envelope loses output first while the UV-A total still reads acceptable. Then inspect the envelope for clouding and the reflector for varnish haze, cold, with the press isolated
On LED there is no short-wave output to lose, so inspect the emitting window for ink mist and measure the peak

THEN CHANGE

Raise peak irradiance first: close the LED working distance, clean the window or reflector, replace a lamp that has passed its rated hours
On mercury, change the lamp on short-wave performance rather than on the hours counter
Cut film weight on the affected unit if the design allows, since a thinner film has less surface to protect and less monomer to leave behind
Stop extending the ink with clear varnish and take the colour to a mixing base instead
If the array geometry is fixed and irradiance cannot be raised, tell us the array wavelength, the film weight and the measured peak, and the synergist package is matched to it

CONFIRM IT IS FIXED

Gloved thumb twist clean at one minute, at least 20 IPA double rubs clean at five minutes, and at 24 hours at least 50 MEK double rubs on process solids and at least 30 on opaque white to ASTM D5402.

THE TRAP

Slowing the press. Peak irradiance at the sheet is fixed by the lamp or the array and its geometry, not by press speed, so slowing raises total dose while leaving the radical generation rate at the surface exactly where it was, and it gives oxygen longer to diffuse into the film during exposure. The tacky surface gets no better and often gets worse, and the speed is lost as well. The one exception is a press that tracks lamp power to running speed: those lamps do drop power as the press slows, which lowers irradiance as well.

UV Offset InksSurface stays tacky, the film under it is hard (continued)

Fault 3 of 20

Cure fails at depth under opaque white

WHAT YOU SEE

The process colours are hard and the white on the same sheet is hard on top but lifts in a sheet when you pick at an edge, or shows a soft, cheesy layer against the board. Odour in the pile. On a reverse-printed job, everything printed over the white fails with it.

WHAT IT LOOKS LIKE

CAUSES, MOST LIKELY FIRST

White film weight above 2.5 g/m2, run heavy to hold opacityEvery extra micron of pigmented film is another layer of scattering and absorption between the lamp and the board interface, and the loss is not linear. It is the cheapest thing to check and the one the printer controls directly.
Dose on the white unit below its own 150 to 250 mJ/cm2 window, or never read on that unit as distinct from the press averageThe white unit is usually the first or the last in the sequence and often the one with the oldest lamp; a press average tells you nothing about it.
Wrong lamp doping on a mercury press, or a 395 nm array where 405 nm is needed on the white unitThe rutile absorption edge sits close to 400 nm, so ten nanometres of array wavelength, or the difference between one doping and another, changes how much light reaches the bottom of the film more than any change in exposure time will.
Dense black run at the process doseCarbon black absorbs across the whole band and screens the same way, so a dense black needs 120 to 200 mJ/cm2 rather than the 80 to 150 mJ/cm2 the colours are set at.
The mechanism under all four: rutile titanium dioxide screens the light before it reaches the bottom of the filmRutile absorbs and scatters hard below about 400 nm, so the top of the white takes the photons the bottom needed. This is a constant of every opaque white ever printed rather than something that changed today, but it is why film weight, dose and wavelength all bite far harder under a white than under a process colour.

UV Offset InksCure fails at depth under opaque white

Fault 3 of 20 · continued

Cure fails at depth under opaque white

CHECK, IN THIS ORDER

Print the white alone on board, cure it, then lift a corner of the film and rub the underside with MEK to ASTM D5402, gloved and under extraction: a soft, smeary underside beneath a hard top face is under-cure at the interface. Use a tape pull only to show the film is not attached; on its own it cannot separate under-cure from an adhesion failure in the board coating, which is the confusion this guide sets out to avoid
Measure the white film weight gravimetrically on printed and unprinted areas cut from the same sheet, against the 1.8 to 2.5 g/m2 specification
Read the dose on the white unit specifically with the band-calibrated radiometer, not the dose the press averages
Confirm which lamps are doped and with what, or which array wavelength sits on the white unit, from the press log and not from memory
Odour check on the pile: waft the air above the sheets towards you from a short distance, in the normal press-room extraction, rather than putting your face into the stack or inhaling directly. Residual acrylate odour in a sheet whose surface is hard is cure at depth, every time

THEN CHANGE

Reduce white film weight toward 1.8 g/m2 and hold opacity with two lighter hits rather than one heavy one where the press allows
Read and correct the dose on the white unit against its own 150 to 250 mJ/cm2 window before touching anything else on the press
On Uniforce-250, move the white unit to a gallium-doped, or indium-doped, lamp, which puts useful output into 400 to 450 nm, above the rutile absorption edge. An iron-doped lamp peaks nearer 350 to 400 nm, still inside the region rutile takes out, and helps far less under a heavy white; do not treat the two dopings as interchangeable
On Unimax 400, move the white unit to a 405 nm array and run it at 12 to 16 W/cm2 peak with 150 to 250 mJ/cm2 in band
Raise dense black to 120 to 200 mJ/cm2 on its own unit rather than lifting the whole press

CONFIRM IT IS FIXED

The white cannot be lifted from the board with tape 24 hours after the run, a tape pull across a scored area takes no ink, at least 30 MEK double rubs on the white to ASTM D5402, and no residual acrylate odour in a closed sample bag opened under extraction at 24 hours. Keep the ISO 2409 cross-cut classification for plastic and metallised substrates: on coated carton board the blade cuts through into the board coating and what lifts is coating and fibre, so the classification does not describe the ink film and cannot be used as an acceptance.

THE TRAP

Adding dose at the same wavelength. More exposure time at 365 or 395 nm sends more photons to a layer that has already absorbed them, so the top gets harder and more brittle while the interface stays wet. The fix is film weight, dose on the right unit and wavelength, not time.

UV Offset InksCure fails at depth under opaque white (continued)

Fault 4 of 20

Under-cured sheets in the first hundred after every stop and restart

WHAT YOU SEE

The job passes at the press and the converter finds soft, set-off or scuffed sheets scattered through the middle of a pallet rather than at the top or the bottom. The sheets either side of them are perfect. On a job that stopped often, the bad sheets are spread through every pallet.

WHAT IT LOOKS LIKE

CAUSES, MOST LIKELY FIRST

Mercury lamps idling at standby power when the drive restartsA medium-pressure lamp dropped to standby takes tens of seconds to return to full output, and on many presses the shutter is interlocked to the drive rather than to lamp output, so the first sheets pass under a lamp that is not yet at running power.
A press that tracks lamp or array power to running speed, with the tracking curve wrongPower is tied to speed so that dose per sheet stays constant. If the curve is set wrong, or the press accelerates faster than the lamp responds, the sheets printed through the acceleration ramp see a dose below the window.
A slow, sticking or partly open shutterThe shutter is the only thing between a running lamp and the sheet on many presses, and one that opens late or only part way puts a real but unmeasured reduction on those sheets alone.
Ink film weight higher on the first sheets after a stopThe roller train equalises during a stop, so the first sheets carry more ink than the running condition. The heaviest film of the whole job meets the lowest dose of the whole job on the same sheets.
Restart waste put back on the pileSheets pulled at a restart are often laid back on the pile rather than binned, which buries an under-cured sheet where nobody looks and where the converter finds it weeks later.

UV Offset InksUnder-cured sheets in the first hundred after every stop and restart

Fault 4 of 20 · continued

Under-cured sheets in the first hundred after every stop and restart

CHECK, IN THIS ORDER

Mark the first hundred sheets after a deliberate stop, take them off the pile and run the gloved thumb twist and 20 IPA double rubs on every tenth sheet
Pass the radiometer through immediately after a restart as well as at steady running speed, and compare the two readings on the same unit
Ask the press maker what the standby power is, how long the lamps take to return to full output, and whether the shutter is interlocked to lamp output or only to the drive
Where the press tracks power to speed, have the tracking verified with the radiometer at 30, 60 and 100 % of running speed rather than trusting the console
Watch what the operator does with the sheets pulled at a restart

THEN CHANGE

Pull and bin a fixed number of sheets after every stop, a hundred as a starting figure, and set the final number from the rub test rather than by feel
Have the shutter interlock and the standby-to-full timing checked, and correct a shutter that opens ahead of the lamp
Correct the power-to-speed tracking curve against measured dose, per unit
Reduce the number of stops: a job that stops every 500 sheets for a blanket wash makes the same fault every time it restarts
Never return restart waste to the pile, and make that a written rule rather than an instruction given once

CONFIRM IT IS FIXED

Sheets taken at 10, 30 and 100 sheets after a restart give at least 20 IPA double rubs clean at five minutes and at least 50 MEK double rubs to ASTM D5402 at 24 hours, matching sheets taken from the middle of the run.

THE TRAP

Judging the restart sheets by eye. An under-cured sheet at the delivery looks exactly like a cured one, the fault is found at the converter weeks later, and by then it sits in the middle of every pallet on the job and the whole run is suspect rather than a hundred sheets of it.

UV Offset InksUnder-cured sheets in the first hundred after every stop and restart (continued)

Fault 5 of 20

Second and third down will not trap

WHAT YOU SEE

The second colour looks weak and mottled over the first, greys and neutrals go dirty, and a reversed sequence proof from the same inks looks correct. Wiping the sheet shows the second colour sitting loose on the first rather than keyed into it.

WHAT IT LOOKS LIKE

CAUSES, MOST LIKELY FIRST

The tack ladder is inverted or flat because inks were reordered on the pressWet-on-wet trapping needs each down colour to be lower in tack than the one under it; a later ink of equal or higher tack pulls the first film back off the sheet instead of laying on it.
Roller and duct temperature differences between units have moved the effective tackTack falls as the ink warms, so a unit running at 34 C and a unit running at 28 C are no longer a ladder even though the tins were correct.
Over-emulsification of the first-down inkWater carried in the first film sits at the interface and stops the second ink wetting it.
Interdeck pinning set too hardA first colour pinned to near full cure presents a crosslinked, low-energy surface that the next ink cannot key into, which is chemical trapping failure dressed as mechanical.
First-down film weight too heavyA thick wet film has less cohesive strength against the next blanket and splits rather than accepting the next colour.

UV Offset InksSecond and third down will not trap

Fault 5 of 20 · continued

Second and third down will not trap

CHECK, IN THIS ORDER

Pull a sample from each duct and run the house tack method, inkometer to ASTM D4361 at 1200 rpm, 32 C, 1.32 cm3 charge, read at 60 s, and write the four figures in sequence order with the instrument and conditions beside them
Read roller surface temperature on every unit in the sequence with the IR thermometer, not just the one that looks wrong
Print each colour alone on the same stock and overprint by hand to separate an ink problem from a press problem
Measure the interdeck pinning dose on its own with the radiometer and compare it with the full cure dose
Check first-down film weight gravimetrically against 1.0 to 1.5 g/m2, printed and unprinted areas cut from the same sheet

THEN CHANGE

Restore the published ladder: Uniforce-250 is supplied graduated 16 +/- 1 first down to 12 +/- 1 last down on the inkometer scale, Unimax 400 typically 14 to 16 first down to 10 to 12 last down on the same scale; put the grades back in their intended units
Bring all units into 28 to 32 C before adjusting any ink
Cut the interdeck pinning dose to the minimum that stops back trap, which is far less than a cure
Reduce first-down film weight and hold density by cleaning the blanket rather than by adding ink
If the sequence cannot be changed for commercial reasons, tell us the sequence and we will supply the set graduated to it rather than reduce tack on press with varnish

CONFIRM IT IS FIXED

Measured tack descends by 1 to 2 points per unit in running sequence on the house inkometer method, the overprint solid reads to the agreed density on Status E, and a hand overprint of the same inks on the same stock matches the press sheet.

THE TRAP

Reducing the tack of the offending ink on press with reducing varnish or a thin oil. It lowers tack and film strength together, so the ink traps a little better and then piles, mists and loses density and gloss, and the ladder is no longer the one anybody has a record of.

UV Offset InksSecond and third down will not trap (continued)

Fault 6 of 20

Ink goes short and greasy, density falls away

WHAT YOU SEE

Two hours into the run the solids drop half a point with nobody touching a key, the ink in the duct looks curdled or buttery rather than glossy, and the operator opens keys to hold density, which makes it worse.

WHAT IT LOOKS LIKE

CAUSES, MOST LIKELY FIRST

Over-emulsification from too much dampeningUniforce-250 takes only 15 to 25 % w/w water on the Duke-type test at the house conditions, far less than an oil-based ink, so it saturates and the excess breaks the ink body rather than being carried.
Roller train above 32 CA softer ink emulsifies more water at the same dampening setting, which is why the fault appears an hour in rather than at start-up.
Fount conductivity and pH climbing on coated boardA loaded fount wets the ink film more aggressively and pushes the emulsion past the point it returns from.
Too much alcohol or the wrong surfactant substitute after a changeSurfactant substitutes change the water film thickness at the same conductivity, and the setting was not re-established after the swap.
Fount tank contaminated with wash solvent or coatingCarried-over wash or coater flush changes the surface tension of the fount, so the water sheets differently on the plate and into the ink.

UV Offset InksInk goes short and greasy, density falls away

Fault 6 of 20 · continued

Ink goes short and greasy, density falls away

CHECK, IN THIS ORDER

Take a duct sample and a fresh tin sample and run both on the Duke-type incremental water addition method at the house conditions, inkometer at 1200 rpm and 32 C, and compare water pick-up against the 15 to 25 % w/w figure. Quote the conditions with the result or the number cannot be argued with
Read conductivity, pH and temperature at the tank, with the incoming water reading and the start-of-job figure beside them
Read roller surface temperature with the IR thermometer at three positions across the width
Look at the ink on the duct roller: a UV ink that has taken too much water goes short and loses its gloss in the duct, which is visible before the densitometer catches it
Check the fount return for wash solvent smell and for coating, wafting rather than inhaling

THEN CHANGE

Dump the duct ink, wash the train, dump and remake the fount, and start again from a clean baseline rather than trying to recover the emulsion
Restore roller temperature to 28 to 32 C and fount to 10 to 14 C first, then reset the water
Bring dampening back to the minimum that holds the plate clean and reset the keys from there
Re-establish the alcohol or surfactant setting and re-check conductivity after the change, since a surfactant substitute at 1 to 3 % is not a drop-in for 5 % isopropanol
Keep ducts covered and keep press ink out of the original container

CONFIRM IT IS FIXED

Solid density holds inside +/- 0.05 on Status E over 2000 sheets at constant key settings, duct ink water pick-up back inside 15 to 25 % w/w at the house conditions, and the ink regains its gloss in the duct.

THE TRAP

Opening the keys to chase the falling density. It puts more ink into an emulsion that is already saturated, so the film gets thicker, cure at depth suffers, set-off starts in the pile, and the density still does not come back.

UV Offset InksInk goes short and greasy, density falls away (continued)

Fault 7 of 20

Set-off and blocking in the delivery pile

WHAT YOU SEE

The back of each sheet carries a ghost of the sheet below, worst in the heavy solids and worst in the centre of the pile. On a bad pile the sheets stick and tear apart at the guillotine.

WHAT IT LOOKS LIKE

CAUSES, MOST LIKELY FIRST

Under-cure on the heaviest solid, usually the opaque white or the dense blackAn uncured or partly cured film is still liquid at the surface and transfers to the back of the next sheet under pile pressure.
Film weight above specification on the solidsMore uncured monomer per unit area means more to transfer, and a heavy film also cures less well at depth, so the two faults compound.
Pile too high and too hotUV inks leave the delivery warm from lamp infra-red, and pressure plus residual heat in the centre of a tall pile keeps a marginal film mobile long enough to transfer.
Spray powder removed or reduced because the job is UVThe assumption that a UV job needs no powder is right only when cure is right; on a marginal job the powder was the only thing holding the sheets apart.
Set-off from a standard overprint varnish rather than from the inkA coater varnish cured at the ink dose will set off in the pile and be blamed on the ink underneath it.

UV Offset InksSet-off and blocking in the delivery pile

Fault 7 of 20 · continued

Set-off and blocking in the delivery pile

CHECK, IN THIS ORDER

Start at the delivery, because that is the state the pile is being built in: within a minute of the last lamp, glove up, thumb-twist the heaviest solid and run the 20 IPA double rub screen, on the ink and separately on the varnish if one is applied
Measure dose on the unit carrying the heaviest solid, not the press average
Weigh the solid gravimetrically against 1.0 to 1.5 g/m2 process and 1.8 to 2.5 g/m2 white, printed and unprinted areas from the same sheet
Put a thermometer into the centre of the pile ten minutes after the delivery; anything much above 35 C is holding the fault open
Print the ink without the coating for 200 sheets and pile it separately to decide which layer is transferring

THEN CHANGE

Raise the dose on the offending unit to its own specification: 150 to 250 mJ/cm2 under opaque white and metallics, 120 to 200 mJ/cm2 on dense black
Cut film weight on the solid and recover density by cleaning the blanket and correcting packing
Take smaller piles and let them stand before the next operation
Restore a light spray powder setting until cure is confirmed
Match the coating to the ink: specify the low-migration UniCure coating with the LM grade, since a standard overprint varnish brings back the conventional photoinitiators and monomers the LM grade is formulated to avoid. Whether the finished pack meets a migration specification is assessed on the pack itself, at the stated dose and film weight, and is not established by the choice of ink and coating

CONFIRM IT IS FIXED

A pile of 500 sheets stood overnight under its own weight shows no image transfer on the reverse, and the solid gives at least 50 MEK double rubs on process colours and at least 30 on opaque white at 24 hours.

THE TRAP

Turning the powder up and carrying on. It masks the fault for one job and then takes the powder into the coater and the foiling unit, where it shows as pinholing and poor foil pick, and the uncured film is still uncured when the pack reaches the customer.

UV Offset InksSet-off and blocking in the delivery pile (continued)

Fault 8 of 20

Piling on the blanket and the plate

WHAT YOU SEE

Solid density drops away over a few thousand sheets and the operator finds a dry, crusty build-up on the blanket in the solid areas, or a white deposit on the plate in the image. Wash up and it runs clean for another few thousand.

WHAT IT LOOKS LIKE

CAUSES, MOST LIKELY FIRST

Coating or fibre picked off the stock and carried into the ink filmA weak coating or a dusty edge trim releases particles that the tacky ink collects and deposits where the film is thickest.
Ink tack too high for the stockA high first-down tack tears the coating rather than transferring to it, and the torn coating becomes the pile.
Over-emulsified ink losing its transferA short, water-loaded film splits badly and leaves pigment on the blanket instead of carrying it to the sheet.
Opaque white and metallics piling on their own accountHeavily pigmented inks with a coarser grind, 12.5 micron or below on the ISO 1524 grindometer against 7.5 micron for process, have less vehicle holding more solid and separate more readily.
Fount conductivity high enough to precipitate salts into the filmDissolved calcium comes out of solution at the ink and water interface and builds on the plate as a hard white deposit.

UV Offset InksPiling on the blanket and the plate

Fault 8 of 20 · continued

Piling on the blanket and the plate

CHECK, IN THIS ORDER

Look at where the pile sits: blanket only points at the stock or the ink, plate and blanket together points at the fount
Run a tape lift on the unprinted stock to judge coating pick and surface dust
Take the duct ink to the house tack method, inkometer to ASTM D4361 at 1200 rpm, 32 C, 1.32 cm3, 60 s, and compare against the ladder figure for that unit
Read fount conductivity and pH, and read the hardness of the incoming water
Check the grindometer reading of the duct ink to ISO 1524 for a coarse contaminant or a dried skin ground back in

THEN CHANGE

Reduce the first-down tack by putting the correct graduated grade in that unit rather than by adding reducer
Change to a stock with a better bound coating, or reverse the sequence so that the heaviest tack is not first onto the weakest coating
Dump and remake the fount, and fit a paper-band or bag filter on the return on chalky board
Correct the emulsion before anything else if the ink has gone short, since a water-loaded ink will pile whatever the stock is
Clean the blanket with a UV-approved low-aromatic wash and let it dry fully before restarting, since residual wash softens the next film

CONFIRM IT IS FIXED

Solid density holds inside +/- 0.05 on Status E for a full pile with no wash-up, and the blanket is clean in the solid areas at the end of it.

THE TRAP

Adding reducing varnish to drop the tack. It reduces the tack and the cohesive strength together, so the ink piles less on the blanket and more in the roller train, then mists at speed and loses gloss and density, and the tack ladder is no longer a known quantity.

UV Offset InksPiling on the blanket and the plate (continued)

Fault 9 of 20

Rollers strip and the blanket has swollen

WHAT YOU SEE

Ink refuses to stay on one or two rollers and leaves bare rubber stripes, or the blanket has grown so that the impression has changed and the packing no longer measures what it did. Rubber feels soft and slightly sticky.

WHAT IT LOOKS LIKE

CAUSES, MOST LIKELY FIRST

Nitrile rollers or a conventional blanket left on a UV pressAcrylate monomer swells and plasticises nitrile, so the rubber grows, softens and loses its ink-carrying surface; EPDM is required throughout.
Water glaze on the roller surface from a loaded fountCalcium and gum build a hydrophilic glaze that the ink will not wet, which looks exactly like swell but measures as no change in diameter.
Aromatic wash used on a UV pressHigh-aromatic washes swell EPDM as well, and a single wash-up with the wrong drum can cost a set of rollers.
Roller settings made cold and never checked hotThe stripes appear only once the train reaches 30 C and the nips close up, so a cold setting reads correct and a hot press does not.
Coating or varnish carried back into the ink train from a coater flushAcrylate coating chemistry is more aggressive than the ink and finds the weakest roller first.

UV Offset InksRollers strip and the blanket has swollen

Fault 9 of 20 · continued

Rollers strip and the blanket has swollen

CHECK, IN THIS ORDER

Measure roller diameters with a caliper against the original specification to separate swell from glaze, with the press stopped, isolated and locked off
Read the roller specification off the roller ends or the maintenance record and confirm EPDM throughout, including the form rollers and the riders
Take nip readings hot, after 500 sheets at speed: stop the press and isolate it, place the strips with no part of the machine able to move, inch the rollers under the machine's own inching control with no hands in the train, then stop and isolate again to read the strips. Do not take a nip reading on a running press
Check the wash in use against the UV-approved low-aromatic specification on the safety data sheet
Rub a stripped area with roller deglaze, gloved, and see whether ink wets it afterwards

THEN CHANGE

Replace nitrile with EPDM rollers and fit UV-compatible EPDM-faced blankets before anything else; nothing else on this list matters until that is done
Deglaze the roller train and reset the nips hot, to the method above
Withdraw non-approved washes from the press room rather than relying on operators to pick the right drum
Dump and remake the fount and fit a return filter to stop the glaze rebuilding
Re-measure packing after a blanket change and record it, since a swollen blanket has already moved the impression and the dot gain with it

CONFIRM IT IS FIXED

Roller diameters back to specification, hot nip readings even across the width, ink carrying evenly with no bare stripes, and the blanket measuring its nominal thickness under a dial gauge.

THE TRAP

Increasing the nip pressure to force ink onto a stripping roller. It compresses a roller that is already swollen, heats the train further, accelerates the swell and adds slur and dot gain on the sheet, so the stripe disappears and three new faults arrive.

UV Offset InksRollers strip and the blanket has swollen (continued)

Fault 10 of 20

Scuffing and scratching after the delivery

WHAT YOU SEE

The job passes at the press and comes back from the die-cutter, the folder-gluer or the carton line with scuffed solids and grey marks along the running direction. Dark solids and heavy blacks show it first.

WHAT IT LOOKS LIKE

CAUSES, MOST LIKELY FIRST

Marginal surface cure that passed a thumb test but not a rub testA soft top micron has no scratch resistance even when the body of the film is hard, and conveyor rails find it before the customer does.
Scuff and slip not specified for the conversion routeScuff resistance on a cured acrylate film is an abrasion property of the surface, measured on the construction, not a property that can be inferred from cure alone.
Matt or silk finish with a high pigment surfaceA matt surface is rougher at the micron scale, so the contact points carry all the load and mark first.
Set-off powder taken out of the jobPowder acts as a spacer in the pile and in the feed, and removing it on a UV job removes the spacer as well.
Heavy metallic ink on a high-traffic panelLeafing aluminium in UF250MT-S30 orients at the surface and marks readily, so it needs a coating over it on any panel that is handled.

UV Offset InksScuffing and scratching after the delivery

Fault 10 of 20 · continued

Scuffing and scratching after the delivery

CHECK, IN THIS ORDER

MEK double rubs to ASTM D5402 at 24 hours, and separately the 20 IPA double rub check within five minutes of the press, both gloved and under extraction
Measure scuff and abrasion resistance on the finished construction with a Sutherland-type rub tester to ASTM D5264, at an agreed load, stroke count and receptor surface, since abrasion is the property being complained about. Use coefficient of friction to ASTM D1894 separately, and only to diagnose feeding, stacking and conveyor behaviour
Run a sample through the conversion line unprinted to see whether the rails are marking the board itself
Check the dose on the unit carrying the solid that is marking
Look at where the marks are: running-direction lines are rails and guides, random marks are pile handling

THEN CHANGE

Fix the cure first if the rub test is marginal, since no coating will save a soft film underneath it
Apply a matching UniCure UV coating over the affected panels, specifying the low-migration coating where the LM ink is used
Dress or tape the conveyor rails and reduce line pressure on the affected panel
Restore a light spray powder setting
Where a metallic or a heavy matt black is on a handled panel, take the scuff requirement into the design review rather than into the press run

CONFIRM IT IS FIXED

The converted pack passes the customer's own line trial without marking, with scuff and abrasion measured to ASTM D5264 on that construction at an agreed load, stroke count and receptor, and agreed as the acceptance; quote coefficient of friction to ASTM D1894 alongside it where the complaint is marking on rails. At least 50 MEK double rubs at 24 hours on the marking solid.

THE TRAP

Adding wax compound to the ink on press. It raises slip on the sheet, drops gloss and, on any panel that will be coated or foiled later, causes the coating to crawl and the foil to refuse. The scuff answer belongs in the coating, not in the ink duct.

UV Offset InksScuffing and scratching after the delivery (continued)

Fault 11 of 20

Coating, foil or glue will not key over the cured ink

WHAT YOU SEE

The ink is hard and passes its rub test, and the layer on top of it fails: an aqueous or UV coating crawls, pinholes or pulls back off the solid, cold or hot foil refuses to pick in the printed areas, or a glue flap peels apart clean at the ink surface on the folder-gluer. It follows the heavy solids and the panels that cured hardest.

WHAT IT LOOKS LIKE

CAUSES, MOST LIKELY FIRST

Interdeck pinning set too hardA heavily pinned film is already crosslinked and low in surface energy, so there is little left at the surface for the next layer to wet or react with.
Over-cure on the last unitThe same mechanism plus cure shrinkage, which is why the panel that cured hardest is often the one the coating rejects.
Wax or silicone from an additive, or heavy spray powder, sitting on the ink surfaceBoth raise slip and lower surface energy, and a coating crawls on them while foil finds nothing to key to.
A cold glue asked to bond to a coated or heavily inked lapA cured UV coating is a low-energy surface that a water-based adhesive was never intended to wet, so the joint fails at the coating rather than in the board.
Coating chemistry mismatched to the inkAn aqueous coating over a fully cured, low-energy acrylate behaves differently from the same coating over an oil-based ink, and the coater settings carried over from conventional work do not transfer.

UV Offset InksCoating, foil or glue will not key over the cured ink

Fault 11 of 20 · continued

Coating, foil or glue will not key over the cured ink

CHECK, IN THIS ORDER

Measure surface energy of the cured ink film itself with dyne pens or ISO 8296 test inks, on the printed solid at the delivery and again at 24 hours, since it falls as the dark reaction completes
Coat half a sheet with the pinning lamp at the running setting and half with it backed off, and compare the two halves
Check whether the failure follows a colour or the whole panel: failure only over the heavy black or the white points at cure and surface energy, failure everywhere points at the coating or the coater
Check the duct for wax compound or silicone, and check the spray powder setting and grade
Where a glued or sealed joint is the complaint, measure it on the customer's own construction: ASTM D3330 peel for a laminated or taped joint, ASTM F88 seal strength for a sealed one

THEN CHANGE

Cut the interdeck pinning to the minimum that stops back trap
Bring the final dose back inside the specified window rather than running above it for comfort
Take wax and silicone out of the ink and reduce spray powder to the minimum that holds the pile
Keep the glue lap free of coating, and take the lap out of the heavy ink at the design stage rather than at the folder-gluer
Trial the actual coating, foil and adhesive on the actual printed construction before the job is scheduled, not after the first pallet has been converted

CONFIRM IT IS FIXED

The coating lays flat with no crawling or pinholing over every solid on the sheet, the foil picks cleanly at production speed, and the glued joint tears board fibre rather than peeling clean at the ink surface, on the customer's own board and adhesive. Bond strength and seal performance are properties of the construction and the interface and are qualified on that construction, not by the ink specification.

THE TRAP

Adding dose because the coating is lifting. It is the same reflex as the adhesion fault and the same mistake: a harder, more crosslinked, lower-energy surface is exactly what the second layer cannot key into, so every step in that direction makes the coating, the foil and the glue worse while the ink rub test keeps passing.

UV Offset InksCoating, foil or glue will not key over the cured ink (continued)

Fault 12 of 20

Ink lifts off plastic or metallised board

WHAT YOU SEE

Cross-hatch and tape pull takes the ink cleanly off the sheet in squares. The film is hard and glossy and MEK rubs pass, so the ink is cured; it simply is not attached. Often worse at the reel or pallet edges and worse on stock that has been in the warehouse.

WHAT IT LOOKS LIKE

CAUSES, MOST LIKELY FIRST

Surface energy below 40 mN/m at the pressCorona treatment decays in storage, so a substrate that was treated to 44 mN/m at the converter may be at 34 mN/m by the time it runs.
Slip additive bloomed to the surface of PE and PPErucamide and similar additives migrate to the surface over weeks and present a low-energy, weakly bound layer that the ink keys into instead of the polymer.
Standard grade run on plastic instead of the PL gradeThe plastics grade is built with the adhesion package for non-absorbent, low-energy surfaces; the coated-board grade is not.
Dose run above the window for the plastics gradeExcess dose drives crosslink density and cure shrinkage, which builds stress at the interface and can pull a well-wetted film off a smooth substrate.
Lacquer or release layer on metallised boardMetallised board is a coated construction and the ink is bonding to a lacquer whose surface chemistry varies between suppliers and batches.

UV Offset InksInk lifts off plastic or metallised board

Fault 12 of 20 · continued

Ink lifts off plastic or metallised board

CHECK, IN THIS ORDER

Measure surface energy with dyne pens or ISO 8296 test inks, or to ASTM D2578, on the actual reel or pallet you are about to run, not on the certificate that came with it
Confirm cure first with MEK double rubs to ASTM D5402, so that adhesion and cure are not confused
Cross-hatch to ISO 2409 with a tape pull at 24 hours, not at the delivery
Check the grade code in the duct against the PL specification for that substrate
Wipe a test area with IPA, gloved, let it dry, and print over it: if adhesion returns, the problem is bloom, not treatment level

THEN CHANGE

Re-treat in line to 40 to 44 mN/m, or prime, where treatment has decayed below 40 mN/m
Move to the UF250PL plastics set for PP, PE, PET, rigid PVC and styrene sheet
Bring the dose back into the specified window for the plastics grade rather than running the plastics unit at the board setting. Excess dose raises crosslink density and cure shrinkage and can worsen adhesion at the interface, but that is a reason to stay inside the window and not a reason to run under it: confirm cure with MEK double rubs at the corrected setting before the job is accepted, because an under-cured film fails cross-hatch too, for the opposite reason
Rotate substrate stock and run treated material inside the treater's stated shelf life
Where a metallised or lacquered board is involved, ask the board supplier for the lacquer identity and trial before the job is scheduled

CONFIRM IT IS FIXED

Cross-hatch classification 0 to 1 to ISO 2409 with a tape pull at 24 hours, on the customer's own substrate from the same batch that will run. Adhesion is a property of the interface and the construction, and it is qualified by trial on that material rather than guaranteed by the ink specification.

THE TRAP

Adding dose because the ink is coming off. Adhesion failure and cure failure look the same to an operator and the reflex is the lamp. On film, dose above the window raises cure shrinkage and interfacial stress, so the cross-hatch result goes from bad to worse while the MEK rubs keep passing. The answer is the window, the treatment and the grade, not more lamp.

UV Offset InksInk lifts off plastic or metallised board (continued)

Fault 13 of 20

Slur, doubling and heavy dot gain

WHAT YOU SEE

Midtones go dark and muddy, the 50 % patch reads well over the curve, and a loupe shows the dot smeared in the running direction or printed twice slightly offset. Solids look acceptable, which is why it is missed until the proof comparison.

WHAT IT LOOKS LIKE

CAUSES, MOST LIKELY FIRST

Blanket packing wrong after a blanket changePacking height sets the surface speed difference between plate, blanket and sheet, and a few hundredths of a millimetre is enough to smear the dot.
Swollen blanket from monomer attack or the wrong washA blanket that has grown is running over-packed even though the packing sheets have not been touched.
Excess water in the inkAn emulsified film spreads more on impression, so a dampening fault reads on the densitometer as dot gain.
Ink film weight above specificationA thicker wet film squeezes further under impression, and a UV ink does not lose volume by absorption or evaporation the way an oil ink partly does.
Gripper or transfer cylinder timing on a combination pressDoubling, as distinct from slur, is a mechanical register fault at handover and shows as a second, sharp, offset dot rather than a smear.

UV Offset InksSlur, doubling and heavy dot gain

Fault 13 of 20 · continued

Slur, doubling and heavy dot gain

CHECK, IN THIS ORDER

Measure packing with a dial gauge on the plate and blanket cylinders and compare against the press build figure, with the press stopped, isolated and locked off
Measure the blanket thickness itself, since a swollen blanket reads as packing that was never added
Read the 50 % patch and the solid on the same strip with a densitometer to ISO 5-3, Status E, and calculate gain rather than judging it by eye
Look at the dot under a loupe: smeared in one direction is slur, two sharp offset images is doubling
Check emulsification and dampening before blaming the press, because water is the cheaper thing to rule out

THEN CHANGE

Reset packing to the press build and record it
Replace a swollen blanket with a UV-compatible EPDM-faced blanket
Correct dampening and roller temperature and re-read the gain before making any mechanical change
Bring film weight back to 1.0 to 1.5 g/m2 and hold density by correcting the blanket and packing
Refer doubling to press maintenance for gripper and transfer timing; it is not an ink fault and no ink change will hide it

CONFIRM IT IS FIXED

Tone value increase on the 50 % patch back inside the agreed curve for that stock and screen, measured to ISO 5-3 Status E, with a clean single dot under the loupe.

THE TRAP

Pulling density out of the solids to compensate for the dark midtones. The curve is wrong, not the level, so the job ends up with weak solids and midtones that are still heavy, and the plate curve gets changed to hide a mechanical fault that then follows the press onto the next job.

UV Offset InksSlur, doubling and heavy dot gain (continued)

Fault 14 of 20

Mottle and patchy gloss in the solids

WHAT YOU SEE

A large solid or a heavy tint shows a cloudy, orange-peel or blotchy appearance that does not move with the sheet, and gloss varies across the same panel. Usually worst on silk and matt coated board and on recycled grades.

WHAT IT LOOKS LIKE

CAUSES, MOST LIKELY FIRST

Uneven absorbency across the coated surfaceA coating with variable holdout takes the ink film differently from point to point, and a 100 % solids ink shows it because nothing evaporates to level the film.
Water in the ink film breaking the levellingEmulsified droplets disturb the wet film surface, and the cure freezes that surface in place within a fraction of a second.
Film weight too low for the stockA thin film on an absorbent or uneven stock cannot bridge the surface and reads as mottle; uncoated and recycled board need 1.5 to 2.0 g/m2 rather than 1.0 to 1.5 g/m2.
Blanket surface worn or smashedA blanket that no longer releases evenly lays an uneven film, and the pattern repeats at blanket circumference if you look for it.
The film gelling before it has levelled, on a short press or under a close interdeck lampA wet offset film needs a moment to level after the nip. Where the pinning lamp or the final array sits very close behind the nip, the surface is frozen with the nip pattern still in it.

UV Offset InksMottle and patchy gloss in the solids

Fault 14 of 20 · continued

Mottle and patchy gloss in the solids

CHECK, IN THIS ORDER

Look for a repeat: a pattern that repeats at the blanket or cylinder circumference is mechanical, an unrepeating cloud is the stock or the emulsion
Weigh the solid gravimetrically and compare against the specification for that stock class
Measure gloss to ISO 2813 at 20 degrees and at 60 degrees in the good and bad areas of the same panel, since 20 degrees is the discriminating geometry on a high-gloss UV film
Print the same solid on a known gloss coated board to isolate the stock
Run a test with the interdeck pinning on that unit switched off and compare the same solid, which separates a levelling fault from a stock fault

THEN CHANGE

Raise film weight toward the upper end of the specification for that stock and accept the extra ink
Correct the emulsion and roller temperature before touching the ink
Where the pinning lamp or the array sits very close behind the nip, back the pinning off to the minimum that stops back trap, move the array back within the maker's working-distance range, or reduce peak on that unit alone, so the wet film has time to level before it gels
Change the blanket if the pattern repeats at its circumference
Apply a UniCure UV coating over the panel where the stock will not give an even finish on ink alone

CONFIRM IT IS FIXED

Gloss within +/- 5 GU at 20 degrees across the panel to ISO 2813 at 24 hours, and a visual match to the approved press sheet under the agreed viewing conditions.

THE TRAP

Reaching for a gloss or levelling additive. On a 100 % solids ink these move the surface tension of a film that is already on the sheet, so they redistribute the mottle rather than remove it, and they carry into the next job on the same rollers.

UV Offset InksMottle and patchy gloss in the solids (continued)

Fault 15 of 20

Print cracks on the crease and the score

WHAT YOU SEE

A fine white line along the fold in a heavy solid or a heavy white, visible on the folder-gluer or in the carton on the customer's line. Runs along the score, worst across the board grain.

WHAT IT LOOKS LIKE

CAUSES, MOST LIKELY FIRST

Film weight too heavy at the creaseThe cured film has to stretch over the outside of the fold and the strain at the surface goes up with film thickness, so the heaviest film cracks first.
Dose run above the windowExcess dose keeps building crosslink density past the point that gave chemical resistance and takes elongation out of the network; chemical resistance and brittleness are traded deliberately.
Board dried out below about 6 % moistureDry fibre has lost most of its ability to hinge, so the bead forms badly and the board itself cracks under the film. A pallet that has stood unwrapped in a dry heated press room or converting hall cracks on the crease whatever the ink is doing, and this is the first thing to check because it is nothing to do with the press.
Scoring and creasing rule set for unprinted boardA shallow or badly matched crease forces the fold radius smaller than the film can take, and the board is doing the cracking as much as the ink.
Board grain running the wrong way to the foldFolding across the grain puts the fibres perpendicular to the fold, so the board hinges badly and the crease bead forms unevenly, and the strain the cured film has to take at the outside of the fold goes up. It is fibre orientation and the quality of the bead, not a tighter radius.

UV Offset InksPrint cracks on the crease and the score

Fault 15 of 20 · continued

Print cracks on the crease and the score

CHECK, IN THIS ORDER

Crease and fold a sheet of the unprinted board on the same rule and look for cracking in the board coating alone, before blaming the ink
Check the board moisture and the storage history: how long the pallet stood unwrapped, and the humidity in the press room and the converting hall
Measure the film weight gravimetrically at the panel that cracks
Measure the dose on the units carrying that panel and compare against the specified window, checking for over-dose as carefully as for under-dose
Fold with and across the grain on the same board and compare

THEN CHANGE

Reduce film weight first, since it is the fastest and most reliable lever
Re-wrap and condition the board, and hold the converting hall humidity, before any change is made on the press
Bring dose back inside 80 to 150 mJ/cm2 for process and 150 to 250 mJ/cm2 for white rather than running above it for comfort
Correct the creasing rule and matrix for the calliper being run, and check the fold direction against the board grain
Change to a more flexible coating, or leave the crease uncoated where the design allows

CONFIRM IT IS FIXED

A 180 degree fold on the finished board shows no white line under a loupe at 24 hours, on board creased with the production rule, folded in the production direction, and conditioned as it will be at the converter.

THE TRAP

Adding dose because a cracked crease looks like a weak film. It is the opposite fault. More dose makes a harder, more brittle network and the crease gets worse with every step the operator takes to fix it.

UV Offset InksPrint cracks on the crease and the score (continued)

Fault 16 of 20

Ghost images of heavy solids down the sheet

WHAT YOU SEE

A faint positive or negative image of a heavy solid repeats further down the sheet in a tint or a lighter solid, at a fixed distance that matches a roller circumference.

WHAT IT LOOKS LIKE

CAUSES, MOST LIKELY FIRST

Roller ghosting from ink starvationA heavy solid strips ink off a form roller and the roller has not been refilled by the time that part of its surface comes round to the next image area, so it lays a thinner film there.
Ink film weight too high on the offending unitThe heavier the demand of the solid, the deeper the depletion on the roller and the more visible the ghost.
Roller settings or oscillation not distributing across the widthA worn oscillator or a badly set vibrator does not spread the depletion, so it survives a full revolution as a distinct image.
Form layout placing a heavy solid directly up-sheet of a flat tintIt is a geometry problem first, and no ink adjustment removes a ghost that the imposition created.
Ink body too short after over-emulsificationA short ink transfers and refills less readily, so depletion recovers more slowly.

UV Offset InksGhost images of heavy solids down the sheet

Fault 16 of 20 · continued

Ghost images of heavy solids down the sheet

CHECK, IN THIS ORDER

Measure the repeat distance on the sheet and match it against roller and cylinder circumferences to identify which roller is doing it
Check whether the ghost is positive or negative, since a negative ghost is starvation and a positive ghost is usually mechanical
Check roller settings hot, with the press stopped and isolated and the strips read within a few seconds of stopping, and confirm the oscillators are stroking their full travel
Check film weight and emulsion state on the offending unit
Turn the form 180 degrees on a test plate if the press allows, to confirm it is layout driven

THEN CHANGE

Reduce film weight on the offending unit and recover density by cleaning the blanket and correcting packing
Reset roller nips hot and correct the oscillator stroke
Move the colour to a different unit where the sequence allows, so that the demanding solid and the vulnerable tint are not on the same roller train
Re-impose the form so the heavy solid does not sit directly up-sheet of a flat tint, on the next job if not on this one
Correct any emulsification fault first, since a short ink makes every ghost worse

CONFIRM IT IS FIXED

No visible ghost under the agreed viewing conditions on a pull from the middle of the run, with density on the affected tint even within +/- 0.03 along the sheet on Status E.

THE TRAP

Opening the keys in the ghost band. It flattens the ghost at one running speed and then over-inks the band at every other speed, and it leaves the depleted roller untouched, so the fault returns the moment the press changes pace.

UV Offset InksGhost images of heavy solids down the sheet (continued)

Fault 17 of 20

Ink gelled in the duct or on the rollers

WHAT YOU SEE

Lumps or a rubbery skin in the duct, or a hard film building on the ink train near the lamp end. The lumps will not disperse and print as hard specks. Often found at the start of a shift after the press stood with the lamps running.

WHAT IT LOOKS LIKE

CAUSES, MOST LIKELY FIRST

Stray UV reaching the duct or the roller trainA leaking lamp housing, an unshielded interdeck lamp or an open reflector sends photons where the ink is standing, and the polymerisation cannot be reversed.
Daylight on the duct, particularly with Unimax 400The long-wave initiator package absorbs in a band that daylight contains, so light exclusion is a storage and duct condition, not a precaution.
Duct temperature too highThermal initiation is slow but real, and a duct sitting at 35 C under a lamp housing over a weekend will gel.
Press ink returned to the original containerInk that has been on the press carries stray radicals, water and contamination back into a fresh tin and gels the lot.
Roller train not washed before a long stopA thin film on a warm roller near a lamp end is the most exposed ink on the press.

UV Offset InksInk gelled in the duct or on the rollers

Fault 17 of 20 · continued

Ink gelled in the duct or on the rollers

CHECK, IN THIS ORDER

Never look at running UV lamps, and never open a guard or defeat an interlock to do it. With the guards closed and the press in its normal running state, tape UV-sensitive indicator strips or photochromic dose cards along the duct ends and the roller train, run the lamps for a few minutes, then stop the press, isolate and lock it off, and read the strips
Inspect lamp housings, shutters, end seals and reflectors cold, with the press isolated. If a visual check of a live housing is unavoidable it is a maintenance task done behind a UV-rated face shield and UV-blocking eyewear, not a press-floor check
Check for daylight falling on open ducts, particularly on presses near a roller shutter door
Put a thermometer into the ink body in the duct, away from the blade, with the press stopped, and confirm 22 to 28 C
Check whether ink covers are being used, and used during long stops as well as overnight

THEN CHANGE

Discard gelled ink; the reaction cannot be reversed and it must not be thinned, strained or blended back in. Handle it in nitrile gloves, do not seal a warm, still-reacting mass into a closed container, keep it away from heat and lamp housings, and dispose of it as chemical waste to the safety data sheet, never into general waste or a drain
Shield the duct and the train from the lamp housings and from daylight, and close any reflector leaking back along the press
Bring duct temperature into 22 to 28 C and keep ducts covered during stops as well as overnight
Wash the train before any stop long enough for the press to stand with lamps live
Stop returning press ink to original containers, and store low-migration grades separately and labelled apart from standard inks

CONFIRM IT IS FIXED

A fresh duct charge runs a full shift with no lumps, no skin on the train, and a grindometer reading to ISO 1524 at or below 7.5 micron for process and 12.5 micron for white and metallics at the end of it.

THE TRAP

Straining the lumps out and carrying on. A gelled ink is a partly polymerised ink throughout, not a clean ink with lumps in it, so the strained material has already lost transfer, gloss and tack and will pile and print specks for the rest of the run.

UV Offset InksInk gelled in the duct or on the rollers (continued)

Fault 18 of 20

Misting and flying at speed

WHAT YOU SEE

A fine haze of ink on the press frame, on the guards and on the operator, appearing above a certain speed and worst on the lightest-tack units at the end of the sequence. That haze is airborne uncured acrylate, which is a skin and respiratory sensitiser, so it is an exposure event and not only a housekeeping nuisance.

WHAT IT LOOKS LIKE

CAUSES, MOST LIKELY FIRST

Tack reduced on press with reducer or thin oilFilament break-up at the roller nip is governed by cohesive strength, and thinning drops cohesion and tack together, so the film breaks into droplets instead of filaments.
Roller train above 32 CA warmer, softer ink mists at a lower speed than the same ink at 30 C, which is why misting appears an hour into a run rather than at start-up.
Ink film weight too high on a low-tack last-down unitMore ink in the nip means longer filaments and more of them to break.
Roller nips too tightA compressed nip raises shear rate at the exit and throws finer droplets.
An ink at the bottom of the tack ladder being asked to carry a heavy solidThe last-down 12 +/- 1 grade is formulated for trapping, not for a heavy solid at 18000 sheets/h, so the sequence, not the ink, is the fault.

UV Offset InksMisting and flying at speed

Fault 18 of 20 · continued

Misting and flying at speed

CHECK, IN THIS ORDER

First, treat it as exposure: bring the speed below the misting threshold or stop the run until the cause is corrected rather than printing the job out in that state. Keep extraction running, do not let mist settle on bare skin, change overalls that have been misted rather than wearing them all shift, and clean frames and guards down wet rather than dry
Run the duct sample on the house tack method, inkometer to ASTM D4361 at 1200 rpm, 32 C, 1.32 cm3, 60 s, and compare against the ladder figure that unit should be carrying
Read roller surface temperature across the width with the IR thermometer
Note the speed at which misting starts and whether it is repeatable, since a sharp threshold points at mechanics and a gradual onset points at temperature
Check nip settings hot, with the press stopped and isolated for the reading

THEN CHANGE

Stop adding reducer and put the correctly graduated grade in the unit
Bring roller temperature back into 28 to 32 C and hold it
Reduce film weight on the misting unit
Reset roller nips hot to the press specification
Move the heavy solid up the sequence so it runs on a higher-tack grade, or tell us the sequence and we will supply the set graduated to it

CONFIRM IT IS FIXED

No visible haze on the frame at full running speed over 5000 sheets, with measured tack back on the ladder figure for that unit on the house inkometer method.

THE TRAP

Adding more reducer because the misting ink also looks weak. Every step in that direction lowers cohesion further, so the misting worsens while the operator believes they are fixing a body problem, and the ink ends the run outside every specification it arrived with, with more uncured acrylate in the air the whole time.

UV Offset InksMisting and flying at speed (continued)

Fault 19 of 20

Odour or taint complaint on the finished pack

WHAT YOU SEE

The printer sees nothing wrong. The complaint comes back from the packer or the brand owner: an acrylate smell in a closed carton, or a taint in a dry product filled into the pack. Almost always on a job with a heavy white or a dense black.

WHAT IT LOOKS LIKE

CAUSES, MOST LIKELY FIRST

Under-cure at depth, usually under the opaque white or the dense blackResidual unreacted monomer and initiator cleavage products are volatile and concentrate in a closed carton, and the surface can be perfectly hard while the interface is not.
Film weight above specificationMore monomer per unit area means more to leave unreacted and more to release, and on the LM grade ink load is one of the few migration variables the printer controls directly.
Standard overprint varnish used over a low-migration inkA conventional coating brings back the photoinitiators and monomers the LM grade is formulated to avoid.
Set-off from the printed face to the food-contact face in the pile or the reelTransfer in the stack moves material from the outside of the pack to the inside, which is a converting problem rather than a cure problem.
Amine synergist odour from an over-extended inkFree amines have a characteristic smell; the LM grades use polymeric amine synergists in place of small free amines for this reason among others.

UV Offset InksOdour or taint complaint on the finished pack

Fault 19 of 20 · continued

Odour or taint complaint on the finished pack

CHECK, IN THIS ORDER

Seal a sample of the printed sheet in a clean glass jar for 24 hours at 40 C, then open it under extraction and waft the headspace towards you from a short distance rather than inhaling directly, stopping at the first clear positive. It is a fast press-floor screen and not a laboratory result
Measure dose on the white and black units specifically, with the band-calibrated radiometer at running speed
Weigh the film gravimetrically against the specification, and check the LM grade is at the 1.0 to 1.3 g/m2 end
Confirm from the duct labels and the delivery notes that every ink and the coating on the job are LM grades where the specification called for them
Check the pile and reel for set-off onto the reverse face

THEN CHANGE

Correct cure at depth first: a gallium-doped mercury lamp or a 405 nm array on the white unit, at 150 to 250 mJ/cm2 in band
Bring ink load down to the low end of the window on the LM grade
Change to the low-migration UniCure coating where an LM ink is specified
Control set-off with lower piles, light powder and by letting the dark reaction complete before the next operation
Where a barrier is part of the pack design, confirm with the pack designer that it is present and intact, because it is part of the answer and not an optional extra

CONFIRM IT IS FIXED

No detectable odour in the sealed jar screen at 24 hours, cure confirmed at the specified dose and film weight. Beyond that, conformity is not established at the press: migration, food-contact suitability and any claim about the finished pack are assessed on the pack itself, on request, at the specified dose and film weight, on the actual substrate and with set-off controlled.

THE TRAP

Treating an odour complaint as an ink formulation complaint and asking for a different ink. Odour in a cured UV film is almost always under-cure at depth, and a new ink run at the same dose under the same heavy white gives the same result a month later, with a job lost in between.

UV Offset InksOdour or taint complaint on the finished pack (continued)

Fault 20 of 20

Colour drifts through the run

WHAT YOU SEE

The sheet matches the approved proof at start-up and has walked away from it by the time the first pallet is off, usually toward weaker and greyer. The operator pulls it back with the keys, and it walks again after the next stop.

WHAT IT LOOKS LIKE

CAUSES, MOST LIKELY FIRST

Roller train temperature rising from start-up to running equilibriumThe ink softens as the train warms, the transferred film weight changes, and density moves without a key moving.
Emulsion building through the runWater pick-up accumulates toward the 15 to 25 % w/w ceiling and takes body and density with it once it gets there.
Fount conductivity climbing on coated boardA loaded fount changes the water film on the plate, which changes the ink film on the sheet, and the drift is gradual because the loading is gradual.
Lamp output changing as the press reaches thermal equilibriumGloss and therefore apparent density shift as cure conditions settle, and a measured density difference of 0.03 to 0.05 can be a gloss difference rather than an ink film difference.
Blanket loading and packing settling after a changeA new blanket beds in over the first few thousand sheets and the transferred film changes with it.

UV Offset InksColour drifts through the run

Fault 20 of 20 · continued

Colour drifts through the run

CHECK, IN THIS ORDER

Log solid density on Status E to ISO 5-3 at 500, 2000 and 5000 sheets and plot it rather than judging sheet to sheet
Log roller and fount temperature at the same intervals against the same sheet counts, roller temperature read with the non-contact IR thermometer
Read fount conductivity and pH at the same intervals, with the incoming water figure and the start-of-job figure recorded once at the start
Measure gloss to ISO 2813 at 20 degrees on the same solids, since a gloss shift reads on the densitometer as a density shift
Take a duct sample at the end of the run and compare its water pick-up against a fresh tin on the house emulsification conditions

THEN CHANGE

Let the press reach thermal equilibrium before approving the running sheet, and approve against a sheet pulled at speed rather than at crawl
Hold roller temperature at 28 to 32 C and fount at 10 to 14 C with the circulators sized for the job, not the chiller set point
Refresh the fount on a schedule on heavily coated board rather than waiting for the drift
Correct the emulsion rather than the keys when density falls, and reset the keys only after the emulsion is right
Record the start-of-job baseline of temperature, conductivity, lamp rating, dose and density so that the next drift takes minutes to diagnose

CONFIRM IT IS FIXED

Solid density holds inside +/- 0.05 on Status E to ISO 5-3 from the 500th sheet to the end of the run at constant key settings, with roller and fount temperature and fount conductivity logged inside their windows for the same period.

THE TRAP

Resetting the keys at every deviation. It chases a moving process with the one lever that changes film weight, so the ink load ends up outside specification, cure at depth and set-off follow it, and nobody can tell afterwards what the job actually ran at.

UV Offset InksColour drifts through the run (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
Tint or scum in the open areas	Fount conductivity, pH and temperature at the tank, against the start-of-job figure and the incoming water reading	Dump and remake the fount; correct roller temperature before touching the water setting
Tacky surface, hard film underneath	Peak irradiance at the sheet with the lamp rating recorded, and the short-wave bands against the commissioning figures	Raise peak irradiance: close the LED gap, clean the window, change the lamp. Do not slow the press
Soft or lifting film under opaque white	White film weight gravimetrically, then dose on the white unit alone	Cut film weight toward 1.8 g/m2 and correct the dose on that unit; then move the white to a gallium-doped lamp or a 405 nm array
Soft sheets scattered through the middle of a pallet	Rub-test the first hundred sheets after a deliberate stop, and read the dose immediately after a restart	Bin a fixed number of sheets after every stop and have the shutter and standby timing checked
Second or third colour will not trap	Tack of each duct in sequence order on the house inkometer method, 1200 rpm, 32 C, 1.32 cm3, 60 s	Put the graduated grades back in their intended units, 16 first down to 12 last down
Density falls, ink short and greasy	Water pick-up on a duct sample against 15 to 25 % w/w at the house conditions, and roller temperature	Dump the duct and the fount, restore 28 to 32 C, reduce dampening. Do not open the keys
Set-off or blocking in the pile	Gloved thumb twist and 20 IPA double rubs at the delivery, and pile centre temperature	Raise dose on the heaviest unit and take smaller piles
Piling on the blanket	Whether the build-up is on the blanket only or on plate and blanket together	Blanket only: drop first-down tack by grade. Both: dump and remake the fount

UV Offset InksQuick reference

Quick reference

One page at the press

Symptom	Check this first	Change this first
Rollers stripping, rubber soft or swollen	Roller diameter against specification and the roller compound from the maintenance record, press isolated	Fit EPDM rollers and UV-compatible blankets. Nothing else works until this is done
Coating crawls, foil will not pick, glue lap peels clean	Surface energy of the cured ink film at the delivery and at 24 h, and the interdeck pinning dose	Cut pinning and bring final dose back inside the window. Do not add dose
Ink comes off plastic at cross-hatch	Surface energy with dyne pens or ISO 8296 test inks on the reel you are about to run	Re-treat or prime below 40 mN/m, and move to the UF250PL grade. Correct the dose to the window, do not add to it
Heavy dot gain, smeared dot	Packing with a dial gauge, and blanket thickness itself, press stopped and isolated	Reset packing to the press build; replace a swollen blanket
Mottle or patchy gloss in a solid	Whether the pattern repeats at a cylinder circumference; film weight gravimetrically	Raise film weight toward the top of the window for that stock, or back off a pinning lamp sitting close behind the nip
Cracking on the crease	Crease unprinted board on the same rule, check board moisture and storage, then check dose for over-cure	Condition the board and cut film weight; bring dose back inside the window. Do not add dose
Ghost repeating down the sheet	Repeat distance against roller circumferences; positive or negative ghost	Reduce film weight on that unit and reset roller nips hot
Odour in the closed carton	Sealed jar at 40 C for 24 h, opened under extraction, then dose on the white and black units	Correct cure at depth and cut ink load. Do not change the ink grade first

UV Offset InksQuick reference

Test methods

The measurements this guide relies on

Measurement	Method	What it tells you, and the usual acceptance
Tack, house method	Inkometer to ASTM D4361, house conditions: 1200 rpm, 32 C, 1.32 cm3 charge, read at 60 s	Gives the tack figure the whole range is published on, and the only figure that can be compared with the tack ladder. These are inkometer-scale numbers: bench tack 13 +/- 2 for a single mid-sequence ink, and the sequence ladder is a separate specification, 16 +/- 1 first down to 12 +/- 1 last down on Uniforce-250. A reading taken at a different charge, speed, temperature or on a different instrument is a different number on a different scale and cannot be used to argue with the specification. An IGT Tack-o-scope in particular reads on its own scale and will not return these figures. Print the instrument, speed, temperature, charge and read time beside any tack figure quoted.
Emulsification, water pick-up	Duke-type incremental water addition on the inkometer, 1200 rpm, 32 C, the same conditions as the house tack method, water added in weighed increments to the end point	Reports water pick-up as % w/w with the conditions attached. 15 to 25 % w/w on Uniforce-250, typical for a sheet-fed UV offset ink and far below an oil-based ink. Water uptake is strongly temperature dependent, so the figure means nothing without its temperature and its addition schedule. The useful comparison is a duct sample against a fresh tin of the same batch on the same conditions.
Viscosity and yield value	ASTM D4040, falling-rod (Laray) viscometer at 25 C, reported at 2500 s-1	The body of the ink as supplied. 45 +/- 15 Pa.s on Uniforce-250 and 45 +/- 10 Pa.s on Unimax 400, with a yield value of 150 +/- 50 Pa. A duct sample well outside this has been reduced, contaminated or over-emulsified on press.
Fineness of grind	ISO 1524 grindometer at 25 C	Checks dispersion and finds contamination or a ground-in skin. At or below 7.5 micron for process colours and bases, at or below 12.5 micron for opaque white and metallics. A duct sample that has coarsened during a run is the first evidence of gelling or dried ink returning to the duct.
Solvent resistance, cure check	ASTM D5402, MEK double rubs, cotton pad under about 1 kg hand load, worked in nitrile gloves with eye protection, under local extraction or in a well ventilated area, and well away from lamps, hot housings, heaters and any other ignition source	The decisive test for whether the film is cured. At 24 hours, after the dark reaction, at least 50 double rubs on process solids and at least 30 on opaque white. The five-minute IPA double rub check, at least 20 clean, is the press-floor screen that tells you whether to keep printing, and it is run under the same conditions. MEK and IPA are both highly flammable and MEK is readily absorbed through skin: keep containers closed, put used pads straight into a closed metal waste container, and read the safety data sheet before the first test.
Cross-cut adhesion	ISO 2409, cross-cut with a tape pull	Classification 0 to 1 typical at 24 hours on a properly treated plastic or metallised substrate, class 1 being detachment of not more than 5 % of the lattice area. Use it on substrates that do not fail before the ink does: on coated carton board the blade cuts through into the board coating and what lifts is coating and fibre, so the classification does not describe the ink film and should not be written into an acceptance. On board, use a tape pull across a scored area together with the MEK rub. It is a check on the job in hand rather than a guaranteed property: adhesion is an interface property of the construction and is qualified by trial on the customer's own substrate.
Scuff and abrasion resistance	Sutherland-type rub tester to ASTM D5264, at an agreed load, stroke count and receptor surface	The test for marking and scuffing, which is what conversion lines and handled panels actually complain about. Agree the load, the number of strokes and the receptor with the customer and run it on the finished construction, printed and coated as it will ship. Coefficient of friction to ASTM D1894 measures slip, which is a different property: use it to diagnose feeding, stacking and conveyor behaviour, not as the acceptance for scuff.

UV Offset InksTest methods

Test methods

The measurements this guide relies on

Measurement	Method	What it tells you, and the usual acceptance
Wetting tension	ASTM D2578, or ISO 8296 test inks, or dyne pens at the press	The number that decides whether an ink can bond to a plastic or a metallised surface at all. 40 to 44 mN/m needed on PP, PE, PET, rigid PVC and styrene. Measure on the reel or pallet about to run, not on the treatment certificate, because corona decays and slip additive blooms in storage. The same pens read the surface energy of a cured ink film, which is what a coating, a foil or a glue has to wet.
Gloss	ISO 2813, 20 degree and 60 degree geometry	55 +/- 10 GU at 20 degrees and 80 +/- 8 GU at 60 degrees on a printed solid on gloss coated board at 24 hours. 20 degrees is the discriminating angle on a high-gloss UV film; 60 degrees separates high-gloss films poorly and should not be used alone to settle a gloss dispute.
Solid ink density	ISO 5-3 Status E response with ISO 5-4 measurement geometry, no polarising filter	Black 1.75 to 1.90, cyan 1.40 to 1.50, magenta 1.40 to 1.50, yellow 1.20 to 1.30 on gloss coated stock at 1.2 g/m2. Always quote the status with the number: the same yellow reads about 0.95 to 1.10 on a Status T instrument. Wet and dry readings sit close together, because nothing evaporates and little penetrates.
UV dose and peak irradiance	Band-calibrated radiometer, UV-A 320 to 390 nm for mercury and 385 to 405 nm for LED, four-band head where short-wave loss is in question, no standard number cited	The only honest measure of what reached the ink. Run it through the press on a carrier sheet at running speed, per unit, and record both integrated dose in mJ/cm2 and peak irradiance in W/cm2, with the lamp rating in W/cm or the array wavelength and rating beside them. Peak irradiance is set by the source and its geometry and does not change with press speed; only the exposure time, and therefore the dose, changes. A mercury-calibrated head over-reads on an LED array and an LED-calibrated head is blind to the mercury short-wave lines, so the head must match the source.

UV Offset InksTest methods

When the press-floor fixes have not worked

What to send us

The measured dose and peak irradiance at the sheet, per unit, taken with a band-calibrated radiometer at running speed, with the date of the reading, the lamp rating in W/cm or the array wavelength and rating, the lamp or array hours, and the commissioning figure to compare against.
Fount records for the job: incoming water conductivity and hardness, tank conductivity, pH and temperature at start, middle and end of the run, the start-of-job conductivity figure, and the concentrate and alcohol or surfactant level in use.
Roller surface temperature and ink duct temperature logged against sheet count, plus the press make, model, running speed and the printing sequence with the grade code in each unit.
Any tack figures you want us to act on, with the instrument, speed, temperature, charge and read time they were measured at, since figures from different instruments sit on different scales and cannot be compared.
Printed samples: at least twenty sheets from the point of failure, twenty good sheets from the same job if any exist, and twenty sheets of the unprinted substrate from the same batch and pallet, all flat and interleaved, not folded or rolled.
A retained sample of the ink from the duct and, if available, an unopened tin from the same batch, both labelled with the grade code and the batch number from the tin, sent as separate samples rather than combined.
The substrate identity in full: supplier, grade, calliper or gauge, coating or lacquer type, treatment level as measured at the press, board moisture and storage history where a crease or a curl is involved, and the batch or reel number, since a fault that follows the substrate will not be solved by changing the ink.
For an odour, taint or migration question, the finished pack construction, the intended contents, the fill and storage conditions, the film weight and measured dose on the printed panels, and whether a functional barrier is present, so that the assessment is made on the pack rather than on the ink.

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UV Offset InksTechnical service