Troubleshooting guide

UV Letterpress Inks

Unipress 30 LED dual-cure letterpress and dry offset: the faults that actually stop ABL, PBL and narrow-web label jobs.

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.

Decide first whether the fault is in the ink film, at the interface or in the light, because the three have different cures and the wrong one wastes a shift; a tape pull separates interface from film, and a radiometer reading at press speed separates light from both.
Measure the lamp before you touch the ink: delivered dose and peak irradiance, with a band-matched radiometer carried through at running speed on the heaviest solid, not a set-up crawl and not a broadband head under an LED array.
A number without its instrument is not a measurement. Dose, irradiance, tack, colour and density all read differently on different heads and instruments, so record make, model, band, speed, temperature or status beside every figure, and compare only like with like.
Measure the substrate on the reel or sleeve you are about to run, not on the last one, because surface energy on treated polyethylene falls with age and slip additive comes back to the surface without changing how the web looks.
Treat body, tack and roller temperature as one measurement, since a train at 24 C and a train at 34 C give different tack and different transfer from the same tin, and a tack ladder read at the wrong temperature is a wrong ladder.
Change one variable, print, measure, record the addition on the job ticket; every reducing or stiffening paste addition dilutes the photoinitiator package in proportion, so an ink corrected three times is a different ink under the lamp.
Handle uncured ink as a skin sensitiser and the deck as a UV hazard. Fresh nitrile gloves and eye protection for ink, skins, wash rags and duct scrapings; never clean skin with press wash; solvent-wetted and ink-wetted rags into a closed metal bin and off the deck at the end of the shift; no lamp or emitter inspection with a lamp struck, a guard open or an interlock defeated.
Nothing on a tube is finished at the delivery; test adhesion, rub and cap torque at 24 hours after cure at 23 C and 50 % RH, and qualify filled-product resistance on the customer's own filled pack rather than on a coupon.

UV Letterpress 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 Letterpress InksThe process

Control variables

What to hold, and how to measure it

Variable	Target	How it is measured	How it drifts
Delivered cure dose	Quoted for a named radiometer and a named band, and not transferable between instruments: on a UVA 320 to 390 nm head at mercury stations, 80 to 140 mJ/cm2 on process shades and 150 to 250 mJ/cm2 on the white; on an LED-band head, 250 to 450 mJ/cm2 on process shades and 400 to 700 mJ/cm2 on the white. The figure that matters most is the one logged when the job last ran correctly; hold within about 20 % of it on the same instrument.	Band-matched radiometer, UVA 320 to 390 nm head at mercury stations and an LED-band head at LED stations, carried through at substrate plane and at the top press speed of the job. Record make, model and band on every reading; different makes and band definitions disagree by twenty to thirty percent on the same lamp.	Falls quietly with lamp hours, fouled quartz or LED window, tarnished reflector and drifting head gap; the print looks the same long after the reading has dropped a third.
Peak irradiance	Typically 1 to 3 W/cm2 UVA at the substrate plane on a focused 120 to 200 W/cm mercury lamp, and 8 to 16 W/cm2 at the LED window; a mercury station reading much under 1 W/cm2 is usually aged, defocused or running at part power	Same radiometer, peak channel, read at the working distance rather than at the lamp face, on the same instrument each time	Falls as the head gap opens, but by no simple law: an LED array at 2 to 5 mm is an extended source in its near field, so fall-off over this range is closer to linear than to square, and a mercury station's fall-off is set by the reflector focus. Re-read after any packing, web path or mandrel change that moves the substrate plane. It is what beats oxygen at the surface, and it falls faster than dose does.
Roller train temperature	28 to 32 C, chilled oscillators	Contact probe or infra-red thermometer on the vibrator drum, read after fifteen minutes at running speed, not from a cold start	Climbs 3 to 6 C in the first half hour from mechanical work; body collapses above 35 C and tack rises sharply below 26 C.
Ink body	40 +/- 10 Pa.s, yield value 150 to 300 Pa; opaque white 55 +/- 10 Pa.s, yield value 250 to 450 Pa	Falling-rod (Laray) viscometer at 25 C, ISO 12644, on a sample drawn from the duct	Reads longer as the train warms and shorter with every reducing-paste addition; corrections accumulate through a shift and nobody records them.
Tack	Inkometer to ASTM D4361: 11 +/- 2 as supplied, graduated about 12 down to 8 through a wet-on-wet set. The ladder is only valid on the instrument it was measured on; a Tack-o-scope reads on its own scale at its own speed and its numbers do not belong in the same ladder.	One named instrument only, at one stated condition, for the whole set. Inkometer: ASTM D4361, 1.32 mL charge, 1200 rpm, 32 C, read at 60 s. Tack-o-scope: the maker's stated speed, temperature and charge, quoted in its own units. Record instrument, speed, temperature and charge beside every number.	Moves with roller train temperature, which is the dominant variable: nothing evaporates from a 100 % solids ink, so as the train climbs 3 to 6 C in the first half hour tack falls and the whole ladder falls with it. A ladder measured at set-up on a cold train does not describe the run.
Substrate surface energy	38 mN/m minimum at the print station, typically 40 to 44 mN/m on a freshly treated polyethylene skin; treat 38 as the floor, not the middle of a band. Above roughly 48 mN/m is its own risk, because very heavy treatment leaves low-molecular-weight oxidised material as a weak boundary layer.	Test-ink solutions to ASTM D2578, applied with a clean swab and read on whether the film holds unbroken for two seconds, on the reel or sleeve about to run and within the shift of printing. Dyne pens are a quick indicator only, are not the D2578 method and drift once contaminated.	Falls with reel age and with storage heat as slip and antiblock additives bloom back to the surface; nothing about the web looks different when it happens.
Film weight at solid	1.0 to 1.5 g/m2 on process shades, 2.0 to 2.5 g/m2 per pass on the opaque white, 1.5 to 3.0 g/m2 on the overprint coating	Gravimetric on a balance readable to 0.1 mg, but never on single cuts: a 1.0 g/m2 film over 100 cm2 is only 10 mg, while the laminate itself weighs 2.5 to 3.5 g per 100 cm2 and half a percent of basis-weight variation is more than the whole ink film. Take at least five printed cuts of 200 to 400 cm2 and five unprinted cuts from the same cross-web position and the same metre of web, and compare the means. Resolution on a lamitube laminate is about +/- 0.2 g/m2 at best.	Creeps up when density is chased at the duct keys, and the extra film is the first thing that stops light reaching the bottom of a white.

UV Letterpress InksControl variables

Control variables

What to hold, and how to measure it

Variable	Target	How it is measured	How it drifts
Impression	Kiss, set to the first clean transfer and stopped there	Packing gauge to the plate data sheet, confirmed by looking for a halo at the relief shoulder on a magnifier	Creeps up all shift, because pressure is the fastest looking cure for weak density and the slowest to be blamed for halo and plate wear.
Form roller stripe	Stripe width 3.0 +/- 0.5 mm against the plate, even across the full width, or the press builder's own figure for the roller diameter fitted; UV-compatible EPDM at 25 to 35 Shore A	Set by the ink stripe left on the plate surface and read the band width across the band with a rule or a stripe gauge. Where the press is set by nip interference instead, that is a separate figure, typically of the order of 0.1 mm, and the two must never be confused.	Widens as rollers swell, narrows as they harden and glaze; a wrong press wash moves it within one wash-up.
LED head gap	2 to 5 mm from the window to the substrate plane	Feeler gauge or shim at the station, checked with the web in its running path	Opens after web path changes, mandrel swaps and window cleaning, and every millimetre of it is peak irradiance the surface never sees.
Web tension	To the laminate supplier's figure for the gauge and width; a starting point on a 250 to 350 micron ABL or PBL web is of the order of 0.5 N per 10 mm of width, with 10 to 20 % taper into the rewind	Tension transducer on an idler where the machine has one, or a calibrated tension meter, read at running speed and again through acceleration, not from the drive display alone	Rises through a reel where taper is not set, and rises again in effect wherever a mercury station heats the web; necking, wrinkle, register loss towards the shoulder, post-cure curl and a reel that blocks all follow from it.
Coating anilox volume	Typically 4 to 8 cm3/m2 to deliver 1.5 to 3.0 g/m2 of UNIPRESS-30OG or 30OM, but take the figure from the coating data sheet for the cell geometry and doctoring in use and confirm the delivered weight on the balance rather than from the cell volume	Cell volume from the anilox maker's certificate, cell condition by microscope or cell-count loupe at three points across the width, and delivered coat weight gravimetrically across the same three lanes	Falls as cells plug with cured coating and as the roll wears; plugging is lane by lane, so the first sign is a band of the reel that blocks or scuffs while the rest is sound.

UV Letterpress InksControl variables

The mechanism

Where the cure runs short, and why the surface stays tacky

A mercury lamp's short wavelengths are strongly absorbed, so the top of the film gels first and the interface finishes last. An LED at 385 to 405 nm is weakly absorbed and reaches the whole 1.0 to 1.4 micron depth at once, so cure is far more even through the film and the limit is at the air face. Under both lamps the surface is the oxygen-inhibited face, and oxygen quenches radicals in the top few tens of nanometres faster than light makes them; that race is won by peak irradiance, not by total dose. Under both lamps a pigmented white scatters and absorbs the light before it reaches its own base, which is why a white needs 395 or 405 nm and its own dose rather than the one set for the process shades.

UV Letterpress InksThe mechanism

02 | 20 faults

Faults

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

Fault 1 of 20

Tacky surface, thumbnail marks the solid

WHAT YOU SEE

The print feels hard when you press it flat but a thumbnail drags a mark across a solid, and the wad picks up colour well before 30 MEK double rubs. It is almost always an LED station and almost always a heavy black, a dense spot or the white. The cured face is the air face: oxygen quenches radicals in the top few tens of nanometres as fast as the light makes them.

WHAT IT LOOKS LIKE

CAUSES, MOST LIKELY FIRST

LED window or quartz sleeve fouled, or head gap openedInk mist and dust on the window, and every extra millimetre of gap, take irradiance off the web before they take dose off it, and surface cure lives on irradiance.
Emitter or lamp output down on hours, or reflector tarnishedEmitter and mercury lamp output both fall with service life, and a station can be a third down while the print gives no warning until the rub test fails.
Wavelength wrong for the shade385 nm is scattered and absorbed more than 395 or 405 nm in a white or a dense black, so radical flux at the surface is short even when the reading looks normal.
Film weight above the top of the windowA heavier film absorbs more light on the way down and presents the same oxygen-exposed surface, so the same dose arrives at a thicker job.
Press wash residue left in the nipSolvent carried in from wash-up dilutes the incoming film and the photoinitiator in it, so the film behaves under-initiated at a normal radiometer reading.

UV Letterpress InksTacky surface, thumbnail marks the solid

Fault 1 of 20 · continued

Tacky surface, thumbnail marks the solid

CHECK, IN THIS ORDER

Look at the LED window, or the quartz sleeve and reflector, clean them, and see whether the print changes before any instrument comes out; this is the cheapest check on the list and the commonest cause.
Measure the head gap with a feeler gauge at the substrate plane, with the web in its running path.
Read delivered dose and peak irradiance with a band-matched radiometer, LED-band head at LED stations, carried through at the top speed of the job on the heaviest solid, and re-read after the clean to see what the cleaning was worth. Record the instrument make, model and band.
Weigh film weight gravimetrically against the window, on five printed and five unprinted cuts rather than one of each.
Check lamp or emitter cooling: water flow and inlet temperature on an LED array, blower and extraction on a mercury station.

THEN CHANGE

Clean the window and close the head gap to 2 to 5 mm, then re-measure before changing anything else.
Raise peak irradiance, by moving the head closer or stepping the emitter power up, in preference to adding dose at the same irradiance.
Move any job carrying white or dense black to 395 or 405 nm emitters rather than giving it more 385 nm.
Bring film weight back to 1.0 to 1.5 g/m2 and take the density back with pigment, not thickness.
Fix the cure first and re-measure until the ink alone passes the rub. Only then apply UNIPRESS-30OG or 30OM in line at 1.5 to 3.0 g/m2, at its own cure window, for rub, scuff and cap-torque duty. Never coat over a film that is still tacky: the coating hides the under-cure, it does not cure it, it seals mobile monomer and photoinitiator fragments into the pack, and it will let go at the intercoat later.

CONFIRM IT IS FIXED

At least 30 MEK double rubs (ASTM D5402, 1 kg) with no breakthrough to substrate on the ink alone, before any coating, plus no mark from a firm thumb twist on the solid, one hour after cure, with the radiometer reading and its instrument logged at press speed.

THE TRAP

Slowing the press. It raises exposure time and total dose but leaves peak irradiance where it was, and peak irradiance is what beats oxygen diffusion at the surface, so the tack survives at half the output while the job takes twice as long.

UV Letterpress InksTacky surface, thumbnail marks the solid (continued)

Fault 2 of 20

Print lifts on tape pull from the laminate

WHAT YOU SEE

The cross-cut lattice loses squares, or the tape takes the print off cleanly in a sheet with the laminate underneath untouched. It is usually one reel, or the tail of a reel, rather than the whole job.

WHAT IT LOOKS LIKE

CAUSES, MOST LIKELY FIRST

Surface energy below 38 mN/m on the polyethylene skinCorona treatment decays with reel age and storage heat, and a poorly wetted surface gives the film no polar sites to anchor to.
Slip and antiblock additive bloomed back to the surfaceMigratory amide slip additives in the polyethylene skin travel to the interface over weeks, leaving a weak boundary layer that the ink bonds to instead of to the polymer.
Contamination on the webSilicone from a roller, mould release from a moulded body or oil mist from the line sits under the film and the failure plane goes there.
Undercure through the filmAn under-crosslinked film has no cohesive strength to resist the tape and comes away looking like an adhesion failure.
Over-treatment on a very heavily treated reelAbove roughly 48 mN/m the treated skin carries low-molecular-weight oxidised material, which is itself a weak boundary layer; the reading looks excellent and the bond is not.

UV Letterpress InksPrint lifts on tape pull from the laminate

Fault 2 of 20 · continued

Print lifts on tape pull from the laminate

CHECK, IN THIS ORDER

Test surface energy with test-ink solutions to ASTM D2578, applied with a clean swab, on the reel you are about to run and within the shift of printing, at the edge and at the centre; use dyne pens only as a quick indicator.
Cross-cut tape adhesion on a 2 mm lattice, which is the ISO 2409 spacing for a soft substrate such as a polyethylene skin, or ASTM D3359 Method B where that is the house method, 24 hours after cure at 23 C and 50 % RH. Record the tape type and batch, the dwell before peel and the peel angle, because on a 1.5 micron ink film these decide the result more than the lattice does.
Run the MEK double rub first to separate an undercure from an interface failure; a film that fails the rub is a cure problem, not an adhesion problem.
Check in-line corona or flame treatment is running and measure again immediately after the treater.
Wipe a clean solvent swab over the unprinted web, wearing gloves, and look for pickup that would indicate silicone or release contamination.

THEN CHANGE

Re-treat in line and confirm at least 38 mN/m at the print station, not at the unwind.
Move to fresh stock or reverse the reel order so the oldest laminate is not the one carrying the job.
Prime where treatment will not hold, and qualify the primer on the customer's own laminate before it goes on a production job.
Fix any undercure found by the MEK rub before touching treatment, since the two look identical on a tape pull.
Return the failed construction to the laboratory rather than compensating on press if it fails with surface energy at or above 38 mN/m and cure confirmed.

CONFIRM IT IS FIXED

Cross-cut classification 0 with no removal, 2 mm lattice on the polyethylene skin, 24 hours after cure at 23 C and 50 % RH, on the reel actually running, with surface energy logged at or above 38 mN/m and the tape, dwell and peel angle recorded.

THE TRAP

Adding cure energy. More dose on a film that is already crosslinked tightens the film and can make the lift worse, because the failure is at an interface the light never reaches; it also burns lamp hours and heat into a thin laminate while the real cause, a decayed treatment, sits untouched.

UV Letterpress InksPrint lifts on tape pull from the laminate (continued)

Fault 3 of 20

Halo round the dot, solids spread at the shoulder

WHAT YOU SEE

Under a magnifier every dot carries a fine ring and solid edges look furred; type gains weight and the job reads darker than the proof although density on a solid is normal.

WHAT IT LOOKS LIKE

CAUSES, MOST LIKELY FIRST

Over-impressionPast kiss, the relief shoulder is pressed into the web and ink squeezes out sideways from under the printing face, laying a ring beyond the image.
Ink run long with repeated reducing-paste additionsYield value below about 150 Pa lets the film flow at the shoulder after transfer instead of standing where it was put.
Roller train above 35 CBody collapses with temperature, which does the same thing to the film as over-reduction without anyone having added anything.
Film weight above the windowMore ink than the relief can carry cleanly has to go somewhere at the nip, and it goes sideways.
Relief shoulder rounded on a worn or solvent-attacked plateA rounded shoulder presents a widening printing face as impression increases, so the tolerance to pressure disappears.

UV Letterpress InksHalo round the dot, solids spread at the shoulder

Fault 3 of 20 · continued

Halo round the dot, solids spread at the shoulder

CHECK, IN THIS ORDER

Look at a solid edge and a 50 % tint at 30x magnification and confirm the ring is outside the image rather than a bleed in it.
Check plate packing and bearer pressure against the plate data sheet with a packing gauge, and back off to first clean transfer.
Draw a duct sample and read body and yield value on the falling-rod viscometer at 25 C, ISO 12644.
Read roller train temperature at running speed with a probe on the vibrator drum.
Weigh film weight gravimetrically on five printed and five unprinted cuts.

THEN CHANGE

Return to kiss impression, set to the first clean transfer and stop there, then re-check packing.
Bring the roller train back to 28 to 32 C with the chillers before judging body.
Stiffen with UNIPRESS-30SP in 1 % steps to a maximum of 5 % w/w, recording each addition on the job ticket.
Replace an over-reduced charge with fresh ink rather than stiffening it back; the photoinitiator has been diluted along with the body.
Change the plate if the shoulder is rounded, and review the plate cleaner against what the plate maker recommends.

CONFIRM IT IS FIXED

Clean dot edge at 30x with no ring, solid edges sharp, at kiss impression, with body back inside 40 +/- 10 Pa.s and yield value 150 to 300 Pa on the Laray at 25 C.

THE TRAP

Reducing the ink to make it transfer at the higher pressure. It lowers yield value further, which is exactly what lets the film spread at the shoulder, and each addition dilutes the photoinitiator so the job then also fails the rub test at the dose that worked yesterday.

UV Letterpress InksHalo round the dot, solids spread at the shoulder (continued)

Fault 4 of 20

Later colours will not trap, dry offset

WHAT YOU SEE

On a wet-on-wet dry offset tube line the second or third down colour transfers patchily onto the first, or lifts the first colour back off the blanket. The solid looks mottled and the overprint shade is wrong.

WHAT IT LOOKS LIKE

CAUSES, MOST LIKELY FIRST

Tack sequence not descendingA later colour tackier than the one under it pulls the earlier film back off the blanket instead of laying on top of it.
Tack read on the wrong instrument or at the wrong temperatureTack is strongly temperature dependent and strongly instrument dependent, so a ladder built on a cold bench, or half on an inkometer and half on a Tack-o-scope, does not describe what happens on a train at 30 C.
First-down colour too soft or too heavyAn over-reduced or over-fed first colour gives a mobile surface the next film cannot grip.
One unit off temperatureA failed or fouled chiller leaves that unit running hot, so its body and tack fall and it drops out of the ladder; a unit left over-chilled, or set up cold and never brought to temperature, sits above the ladder instead. Either way the ink is unchanged and the ladder is broken by temperature.
Blanket glazed or wrong specificationA glazed or swollen blanket releases unevenly, which reads as a trapping fault although the tack ladder is correct.

UV Letterpress InksLater colours will not trap, dry offset

Fault 4 of 20 · continued

Later colours will not trap, dry offset

CHECK, IN THIS ORDER

Measure tack on every shade in the set on one named instrument at one stated condition, inkometer to ASTM D4361 at 1.32 mL, 1200 rpm and 32 C read at 60 s, and write the ladder down with the instrument beside it.
Read roller temperature unit by unit at running speed; do not assume the chillers are all doing the same thing.
Weigh film weight on the first-down colour gravimetrically.
Check the blanket is a UV-compatible specification and is compatible with the wash in use, and look for glaze under a light.
Pull a print with the later units off to see whether the first colour on its own is laying correctly.

THEN CHANGE

Re-sequence the set to a descending ladder, typically 12 down to 8 on the inkometer, before changing any ink.
Bring every unit to 28 to 32 C and re-measure the ladder rather than correcting an ink to cover a chiller fault.
Adjust individual shades with UNIPRESS-30RP in small recorded steps to close a gap in the ladder.
Bring the first-down film weight back into the window if it has been fed heavy for density.
Change a glazed blanket and clean the rest with a wash the blanket maker accepts.

CONFIRM IT IS FIXED

Full, even trap on the overprint solid at running speed, with a measured descending tack ladder of about 12 down to 8 on one inkometer at ASTM D4361 conditions, and overprint density matching the approved proof.

THE TRAP

Re-ordering the colours on press to make the trap work. It hides a broken tack ladder, and the job then has a colour order that does not match the plate set, the proof or the next repeat, so the same fault returns on the reprint with the operator who fixed it on a different shift.

UV Letterpress InksLater colours will not trap, dry offset (continued)

Fault 5 of 20

Weak density although impression is already heavy

WHAT YOU SEE

The solid reads short of target on the densitometer, the operator has taken impression up to try to recover it, and the job now has halo as well as weak density.

WHAT IT LOOKS LIKE

CAUSES, MOST LIKELY FIRST

Film weight at the bottom of the windowDensity in this class comes from pigment concentration in a 1.0 to 1.5 g/m2 film, so a thin lay cannot be recovered with anything else.
Ink starved at the ductA skinned or bridged charge over the keys, a duct blade set wrong, or a duct roller ratchet or drive fault, all starve the train while the keys are open; it is the cheapest cause to find and the one most often looked at last.
Cold roller train holding tack high and transfer poorBelow 26 C tack rises sharply and the film will not split cleanly from roller to plate to web.
Form roller stripe wrongA narrow or uneven stripe starves the plate regardless of what the duct keys are set to.
Rollers glazed or swollenA glazed surface will not carry a full film and a swollen roller has lost its nip geometry, both of which starve the image.

UV Letterpress InksWeak density although impression is already heavy

Fault 5 of 20 · continued

Weak density although impression is already heavy

CHECK, IN THIS ORDER

Look in the duct before anything else: skin over the keys, a bridged charge, a blade hard on the roller or a ratchet that is not indexing.
Weigh film weight gravimetrically on five printed and five unprinted cuts before adjusting anything.
Read roller train temperature at running speed with a probe on the vibrator drum.
Run a stripe test against the plate and confirm 3.0 +/- 0.5 mm, even across the width.
Check the ink record on the job ticket for accumulated reducing-paste additions.

THEN CHANGE

Clear and re-charge the duct, skim any skin rather than stirring it in, and confirm the blade and ratchet are working before touching the keys.
Raise ink feed towards 1.5 g/m2 and confirm it on the balance rather than by eye.
Bring the roller train to 28 to 32 C and let it settle before re-judging.
Reset the form roller stripe to 3.0 +/- 0.5 mm and check it across the full width.
Replace a charge that has been reduced more than about 5 % w/w with fresh ink.

CONFIRM IT IS FIXED

Target density held across the web at kiss impression, read at a stated status and geometry on the same instrument as the proof, with film weight measured at 1.0 to 1.5 g/m2 gravimetrically and the roller train logged at 28 to 32 C.

THE TRAP

Chasing density with impression. Pressure adds a little apparent density and a great deal of halo, dot gain and plate wear, and once the shoulder is printing the operator is looking at a second fault that hides the first; density is set with ink film, not with pressure.

UV Letterpress InksWeak density although impression is already heavy (continued)

Fault 6 of 20

Opaque white will not hide, ground reads grey

WHAT YOU SEE

The white ground on an aluminium or metallised laminate looks grey or blue-grey and the colours printed over it read dirty. The laboratory drawdown of the same tin looked fine.

WHAT IT LOOKS LIKE

CAUSES, MOST LIKELY FIRST

One pass at this film weight is not a full hideAt 2.0 to 2.5 g/m2, about 1.4 to 1.7 micron, the white gives a contrast ratio of 0.70 to 0.80, which is a ground and not a full hide; a 12 micron wet laboratory drawdown gives 0.95 or better and is not what the press lays.
White fed at the bottom of the windowOpacity rises steeply with film thickness in this range, so a small shortfall in lay is a large and visible shortfall in hide.
White stirred insufficientlyRutile settles, and the top of an unstirred pail is short of the titanium dioxide the opacity depends on.
White reduced to make it runReducing paste dilutes the pigment that is doing the hiding as well as the body that was inconvenient.

UV Letterpress InksOpaque white will not hide, ground reads grey

Fault 6 of 20 · continued

Opaque white will not hide, ground reads grey

CHECK, IN THIS ORDER

Measure the press lay gravimetrically first, since the hide argument is really a film weight argument.
Then measure hide one of two ways and say which: reproduce the measured film weight on a black-and-white chart with a calibrated proofer or K-bar and read contrast ratio to ISO 2814, or judge it on the job by printing the white over a black bar and over bare laminate in the same pass and comparing Y or L* over the two grounds. A chart figure and a press figure are not interchangeable, and an opacity chart cannot be run through a tube decorator.
Read the white's body on the falling-rod viscometer at 25 C against 55 +/- 10 Pa.s and yield value 250 to 450 Pa.
Check the job ticket for reductions and the container for a stirred or unstirred pail.
Look at the job specification and decide whether it was ever a one-pass job.

THEN CHANGE

Take the white to the top of its window at 2.0 to 2.5 g/m2 per pass and confirm on the balance.
Specify a double hit at 4.0 to 5.0 g/m2 where the pack needs it, which gives 0.85 to 0.92 contrast ratio at the same measurement condition.
Move to UNIPRESS-30OWH where the design needs the higher hide within the same pass count.
Stir the pail through before use and use opened containers first.
Take the white to a screen station where the construction genuinely needs a full hide.

CONFIRM IT IS FIXED

Contrast ratio of 0.70 to 0.80 for a single pass at 2.0 to 2.5 g/m2, or 0.85 to 0.92 for a double hit at 4.0 to 5.0 g/m2, measured at the press film weight and reported with the method it came from, chart or press, with the overprinted colours matching the approved proof.

THE TRAP

Driving the white lay up past the window to force the hide. Beyond about 2.5 g/m2 per pass the film stops light reaching its own base, so the extra white cures badly at the interface and the job trades a grey ground for a white that scratches off; the honest answer is a second hit or a screen station.

UV Letterpress InksOpaque white will not hide, ground reads grey (continued)

Fault 7 of 20

White scratches through to the laminate

WHAT YOU SEE

The white surface is hard and passes a thumbnail, but a coin or a fingernail edge takes the whole film off down to the laminate in a flake. It shows up at heading and capping rather than at the press.

WHAT IT LOOKS LIKE

CAUSES, MOST LIKELY FIRST

Light not reaching the bottom of the white filmRutile titanium dioxide scatters and absorbs strongly in the near UV, so the interface is the last place served and the first to be starved, under mercury and under LED alike.
Wavelength too short for a white385 nm is absorbed and scattered more than 395 or 405 nm in a pigmented white, so it never reaches the interface at useful intensity.
Dose below the white's own windowThe white needs 150 to 250 mJ/cm2 on a UVA head under mercury and 400 to 700 mJ/cm2 on an LED-band head, well above the process shades, and lamps are often set for the process set.
White laid too heavyEvery extra micron is more scattering between the lamp and the interface, so over-feeding for opacity starves through-cure.
Treatment marginal under the whiteA film that is also poorly anchored gives a clean flake that looks like undercure and is partly an interface failure.

UV Letterpress InksWhite scratches through to the laminate

Fault 7 of 20 · continued

White scratches through to the laminate

CHECK, IN THIS ORDER

Tape pull the white solid as well as running the MEK rub; a hard surface with a clean lift is a through-cure failure.
Read dose in the correct band at press speed and compare against the white's window, not the process window, on the same instrument each time.
Confirm which emitter wavelength the white is running under at each station.
Weigh the white film weight gravimetrically.
Measure surface energy on the laminate with test-ink solutions to ASTM D2578.

THEN CHANGE

Set the lamp for the white and log the reading; the hardest colour on the job sets the dose for the job. Then check the pale shades have not moved at that dose.
Move the white to 395 or 405 nm emitters rather than giving it more 385 nm.
Bring the white lay back to 2.0 to 2.5 g/m2 and get the hide from a second hit instead.
Move to a doped mercury lamp where a mercury line is limited by white and dense shades, accepting the extra heat into thin laminate and re-approving colour afterwards.
Confirm treatment at or above 38 mN/m so that cure and interface are not being blamed for each other.

CONFIRM IT IS FIXED

Cross-cut classification 0 on a 2 mm lattice with a tape pull at 24 hours, no flake from a coin edge, and at least 30 MEK double rubs, with the white's dose logged at 150 to 250 mJ/cm2 on a UVA head or 400 to 700 mJ/cm2 on an LED-band head.

THE TRAP

Reading the surface and declaring it cured. Under mercury the short wavelengths are strongly absorbed and the top of the film gels first; under LED the light reaches the whole depth at once and the air face lags. In both cases a pigmented white scatters the light before it reaches its own base, so a thumbnail on the surface tells you nothing about what is happening 1.5 micron down.

UV Letterpress InksWhite scratches through to the laminate (continued)

Fault 8 of 20

Highlights plug, fine reversed type closes up

WHAT YOU SEE

The light end of the vignette goes solid, small reversed dosage text fills in and serifs bridge. The shadow end is flat as well, so the whole tone scale has lost its ends.

WHAT IT LOOKS LIKE

CAUSES, MOST LIKELY FIRST

Relief depth too shallow for the rulingA shallow relief lets the non-printing floor come close enough to the web to pick up and transfer ink between the dots.
Ink film above the windowA heavy lay bridges the gap between fine elements before impression has done anything.
Over-impressionPast kiss the shoulder prints, and on a fine element there is more shoulder than printing face.
Plate under-washed or under-exposed at platemakingResidual polymer in the floor, or a shoulder that never formed, gives a relief that cannot hold a fine highlight however the press is set.
Ink body too longLow yield value lets the transferred dot spread into its neighbour before the lamp reaches it.

UV Letterpress InksHighlights plug, fine reversed type closes up

Fault 8 of 20 · continued

Highlights plug, fine reversed type closes up

CHECK, IN THIS ORDER

Measure relief and floor depth on the plate with a depth gauge and compare against the plate maker's data sheet for the gauge in use.
Look at the highlight end at 30x on the plate and on the print, so a platemaking fault is separated from a press fault.
Weigh film weight gravimetrically.
Check packing and impression against the plate data sheet.
Read body and yield value on the falling-rod viscometer at 25 C.

THEN CHANGE

Go to a deeper relief, specified per gauge and never leaving a floor below about 0.30 mm: about 0.35 to 0.45 mm on a 0.73 mm plate, 0.45 to 0.55 mm on a 0.95 mm plate, 0.55 to 0.70 mm on a 1.14 mm plate. Confirm relief and floor against the plate maker's data sheet before ordering a remake.
Drop the ruling, to 133 lpi narrow web or 120 lpi dry offset, where the artwork will carry it.
Bring film weight to the bottom of the window at 1.0 g/m2 and take impression back to kiss.
Remake the plate where the depth measurement is short, and review exposure and wash-out with the platemaker.
Stiffen with UNIPRESS-30SP in 1 % recorded steps if yield value is under 150 Pa.

CONFIRM IT IS FIXED

A 3 to 5 % dot holding open at the ruling actually run, typically 133 lpi narrow web and 120 lpi dry offset, and reversed sans-serif text at or above 5 point legible at 10x on the running job, with relief and floor depth measured against the plate data sheet and film weight at 1.0 to 1.5 g/m2.

THE TRAP

Lightening the artwork in prepress to keep the highlight open. It moves the problem into the file where the next repeat inherits it, leaves the shoulder geometry that caused it untouched, and the job now has a tone curve that does not match the proof or any other press in the plant.

UV Letterpress InksHighlights plug, fine reversed type closes up (continued)

Fault 9 of 20

Print rubs off at the shoulder after capping

WHAT YOU SEE

The tube prints and cures correctly but comes back from the capper, the carton or the customer with the print polished off round the shoulder, or with a witness ring where the cap has been turned.

WHAT IT LOOKS LIKE

CAUSES, MOST LIKELY FIRST

No overprint coating, or coat weight shortThe ink carries colour and adhesion; rub, scuff and cap-torque duty belong to the matched coating at 1.5 to 3.0 g/m2.
Coating anilox plugged, worn or wrongly specifiedCells that have cured coating in them deliver less, and they plug lane by lane, so a short coat weight is usually an anilox condition rather than a setting.
Coating undercuredThe coating is the last film down and the most oxygen-exposed, so it is the first to be short of surface cure and the first to polish away.
Cap torque above what the system was qualified atA cap turned harder than the qualification, or a dry cap-to-shoulder fit, puts more work into the same film.
Shoulder geometry concentrating the contactA sharp shoulder radius puts the whole cap load onto a narrow band of print instead of spreading it.

UV Letterpress InksPrint rubs off at the shoulder after capping

Fault 9 of 20 · continued

Print rubs off at the shoulder after capping

CHECK, IN THIS ORDER

Run a Sutherland rub test, conditions per ASTM D5264 (withdrawn but still the reference practice for this instrument; TAPPI T 830 is the alternative): 4 lb (1.8 kg) weight, 100 dry cycles on the coated print, receptor and sample conditioned at 23 C and 50 % RH. Report cycles to first transfer as well as pass or fail.
Run 50 cap open-and-close cycles at 0.8 to 1.5 N.m on the actual cap and shoulder and inspect the contact band.
Weigh the coating film weight gravimetrically at three lanes across the width and read gloss to ISO 2813 at 60 degrees to confirm it is present and even.
Inspect the coating anilox for plugged or worn cells with a loupe or microscope at three points across the width.
Run the MEK double rub on the coated surface to confirm the coating itself is cured.

THEN CHANGE

Apply UNIPRESS-30OG gloss or 30OM matt in line at 1.5 to 3.0 g/m2 and specify it with the ink rather than after it.
Clean or replace a plugged or worn anilox and confirm the delivered weight on the balance, not from the cell volume.
Raise the coating station's cure to its own window rather than the ink's, and clean the window at that station first.
Bring the capping torque back to what the system was qualified at, and record the qualified figure on the specification.
Return shoulder radius and cap fit to the pack designer if the contact band is narrow and repeatable.

CONFIRM IT IS FIXED

100 Sutherland dry rub cycles at 1.8 kg with no transfer, and 50 cap cycles at 0.8 to 1.5 N.m with no print removal, tested 24 hours after cure at 23 C and 50 % RH on the customer's own cap and shoulder, with coat weight logged across three lanes.

THE TRAP

Blaming the ink and asking for a harder one. Rub at the shoulder is a system property of ink, coating, cap material, torque and shoulder radius, and the usual real cause is a coating that is absent, thin or undercured; a harder ink under no coating still polishes off, and reformulating the colour delays the fix by weeks.

UV Letterpress InksPrint rubs off at the shoulder after capping (continued)

Fault 10 of 20

Density and body drift upward through the run

WHAT YOU SEE

The job runs to standard at start-up, then over the first half hour the solids climb, the dot gains and the operator pulls the keys back; by mid-shift the ink looks soupy in the duct.

WHAT IT LOOKS LIKE

CAUSES, MOST LIKELY FIRST

Roller train heating from mechanical workA stiff paste worked through a roller train puts a lot of shear energy in as heat, and body falls with temperature so more film transfers at the same key setting.
Chiller undersized, fouled or offOscillator chilling is what holds 28 to 32 C, and a fouled heat exchanger loses the fight at running speed rather than at set-up.
Ambient hall temperature highAbove about 28 C the chillers start from a worse baseline and the train settles higher than the window.
Ink charged from a cold tinA tin at 15 C reads long and tacky at set-up, so the operator opens the keys to compensate and is then over-fed when the train warms.
Accumulated reducing pasteCorrections made cold stay in the ink when it is hot, and the two effects add.

UV Letterpress InksDensity and body drift upward through the run

Fault 10 of 20 · continued

Density and body drift upward through the run

CHECK, IN THIS ORDER

Log roller train temperature every fifteen minutes for the first hour with a probe on the vibrator drum, at running speed.
Draw duct samples at start-up and at the hour and read both on the falling-rod viscometer at 25 C.
Read hall temperature and humidity against 20 to 28 C and 45 to 60 % RH.
Check chiller flow and inlet temperature, and look at the heat exchanger for fouling.
Read density on the solid at the same three points across the web at each check, at the same status and geometry.

THEN CHANGE

Bring the containers to 20 to 25 C for 12 to 24 hours before printing so set-up is done on ink at working temperature.
Service the chillers and hold the train at 28 to 32 C rather than correcting the ink to a moving temperature.
Set the job once the train has reached temperature at running speed, not on the first pull.
Reverse any reducing-paste additions made during a cold start-up by replacing the charge rather than stiffening it.
Manage the hall to 20 to 28 C where the press room allows it.

CONFIRM IT IS FIXED

Density held within tolerance from start-up to end of run with no key movement, roller train logged at 28 to 32 C throughout, and duct body at the hour still inside 40 +/- 10 Pa.s on the Laray at 25 C.

THE TRAP

Correcting the ink at every reading. Stiffening a warm charge in the morning and reducing it again after the break leaves an ink that is neither, with 5 % or more of paste in it and a photoinitiator diluted in proportion, so by the afternoon the same press is failing the rub test at the dose that was fine at breakfast.

UV Letterpress InksDensity and body drift upward through the run (continued)

Fault 11 of 20

Ink skins or gels in the duct or on the train

WHAT YOU SEE

A rubbery skin forms on the duct surface, or gel specks appear in the print as hard undissolved marks. Often found after a break, a meal relief or an overnight stop.

WHAT IT LOOKS LIKE

CAUSES, MOST LIKELY FIRST

Stray UV or daylight on the deckThe ink is a photopolymer; any light in its absorption band starts the reaction in the duct as readily as at the cure station. Light that reaches the duct is also light that reaches the operator, so it is a safety defect before it is an ink defect.
Ink standing on a stopped trainA thin film on a warm roller with an open surface reacts and oxidises long before the tin in the store does.
Roller temperature above 35 CThermal initiation accelerates and the film on the rollers skins.
Contaminated or returned ink put back in a fresh containerGel nuclei and cured fragments seed the whole container.
Container left open in the storeDaylight and stray UV in the store gel the ink in the tin, which is then blamed on the press.

UV Letterpress InksInk skins or gels in the duct or on the train

Fault 11 of 20 · continued

Ink skins or gels in the duct or on the train

CHECK, IN THIS ORDER

Walk the deck with the press stopped, isolated and the lamps de-energised and cooled, and look for direct daylight, reflected sunlight and any unshielded lamp or LED leakage reaching the duct or the train. Never stand at the deck with a lamp struck and a guard open, and never defeat, bypass or prop an interlock or a shutter to see the leak.
Read roller temperature at running speed and at the end of a stop.
Look at the skin, wearing gloves: a rubbery coherent skin is light or heat, hard discrete specks in fresh ink point to the container.
Check the stop log against the thirty-minute rule.
Inspect the store for open, part-used and unlabelled containers and for daylight on the racking.

THEN CHANGE

Shield the deck and cover the duct at every stop. Report leaking curtains, damaged shutters and failed interlocks to engineering as a safety defect, not as an ink defect, because leaked UV is an eye and skin hazard as well as a gelling cause.
Strip the train at any stop longer than about thirty minutes.
Hold the roller train at 28 to 32 C and never let it run above 35 C.
Skim any skin before use, re-close part-used containers immediately and use opened containers first. Handle uncured ink, skins, wash rags and duct scrapings with fresh nitrile gloves and eye protection, never clean skin with press wash, change gloves as soon as they are wetted, and put all solvent-wetted and ink-wetted rags in a closed metal bin removed from the deck at the end of each shift.
Keep returned ink segregated and labelled with the job, and re-use it only on that job; never return it to a fresh container.

CONFIRM IT IS FIXED

A clean duct surface and a clean print after a deliberate thirty-minute stop with the duct covered, with no gel specks visible at 30x on a solid and the train logged at 28 to 32 C.

THE TRAP

Stirring the skin back in to save the ink. It disperses cured gel through the whole charge as hard particles that then print as specks, blind the fine relief and score the plate; a skimmed skin costs a few hundred grams, a stirred one costs the charge and often the plate.

UV Letterpress InksInk skins or gels in the duct or on the train (continued)

Fault 12 of 20

Pinholes and craters in the solid

WHAT YOU SEE

Small round holes or dished craters in an otherwise sound solid, often repeating in the same area of the web or the same part of the tube. The hole shows the substrate cleanly at its centre.

WHAT IT LOOKS LIKE

CAUSES, MOST LIKELY FIRST

Silicone or oil contamination on the webA low surface tension spot pushes the wet film back from it before cure freezes the shape, leaving a crater with a raised rim.
Slip additive bloomed on the polyethylene skinAn additive-rich surface has patchy surface energy, so wetting fails locally rather than everywhere.
Static on the treated polyethylene webA charged web repels the incoming film into hairline voids and pulls dust and fibre onto the print between stations; the same charge is an ignition risk near wash solvent and a handling problem at rewind and die cutting.
Mould release on an extruded body or closureRelease agent transfers to the decoration surface and behaves like deliberate contamination.
Press wash residue on the train or blanketResidual solvent and any silicone in a wrong wash carry into the film and craters follow the roller circumference.

UV Letterpress InksPinholes and craters in the solid

Fault 12 of 20 · continued

Pinholes and craters in the solid

CHECK, IN THIS ORDER

Map whether the defect repeats to a roller circumference, a plate position, a tube position or is random on the web; each points somewhere different.
Measure surface energy with test-ink solutions to ASTM D2578 across the web, including at the defect area.
Check static bars are fitted, powered and clean, measure web charge with a field meter if one is available, and confirm the press and unwind are properly earthed; read hall humidity against 45 to 60 % RH.
Swab the unprinted web with clean solvent, wearing gloves, and look for pickup.
Check the wash in use is a UV-compatible ester and alcohol blend with a flash point above 55 C and contains no silicone.

THEN CHANGE

Find and remove the contamination source: silicone sprays, chain oil, aerosol releases and hand creams have no place near the deck.
Restore static control: clean or replace static bars, confirm earthing of unwind, rollers and rewind, and keep hall humidity in the 45 to 60 % RH band; never let a charged web sit next to open wash solvent.
Re-treat in line and confirm at least 38 mN/m at the print station.
Change to fresh stock where a reel is additive-bloomed, and review storage time and temperature with the laminate supplier.
Wash the train and blanket with the correct wash, wipe dry and let the last traces flash off before re-inking.

CONFIRM IT IS FIXED

A clean solid with no pinholes at 10x over a full reel or a hundred tubes, with surface energy logged at or above 38 mN/m across the web, static bars confirmed working and the contamination source identified and removed.

THE TRAP

Raising the ink film to fill the holes. A thicker film makes the crater deeper rather than closing it, because the defect is a wetting failure and not a coverage failure, and the extra film then costs through-cure on the same job; the hole is cured by finding what is on the web.

UV Letterpress InksPinholes and craters in the solid (continued)

Fault 13 of 20

Down colour crawls over a cured colour

WHAT YOU SEE

On an interstation-cure line the next colour beads, breaks up or fisheyes over a colour that has already been through a lamp, while the same ink lays perfectly on the bare substrate.

WHAT IT LOOKS LIKE

CAUSES, MOST LIKELY FIRST

Earlier unit at full cureA fully crosslinked acrylate surface has low surface energy and little residual unsaturation, so the next film has nothing to wet or bond to.
Pin cure set too highAnything much above about 40 % of full dose closes the surface and produces the same effect as full cure, which is why the working window is 10 to 30 %.
Over-cure by driftA station set at pin cure months ago has been turned up, or a replacement emitter is delivering more than the one it replaced.
Contamination on the pin-cured surfaceInk mist, oil or handling between stations sits on a surface that is already difficult to wet.

UV Letterpress InksDown colour crawls over a cured colour

Fault 13 of 20 · continued

Down colour crawls over a cured colour

CHECK, IN THIS ORDER

Read delivered dose at each interstation lamp with a band-matched radiometer at press speed and express it as a percentage of the final station.
Print the down colour directly onto bare substrate alongside the overprint to prove the ink itself is sound.
Check whether any emitter or lamp at the earlier stations has been changed since the last good run.
Inspect the pin-cured surface for mist or oil under a light.

THEN CHANGE

Drop the earlier units to the lowest dose that holds the image, typically 10 to 30 % of full dose, and keep well clear of 40 %; keep full cure for the last station.
Set interstation lamps against a measured percentage of final dose, and write that percentage on the job ticket so it survives a shift change.
Re-measure after any lamp or emitter change at an interstation position.
Shield the web path between stations from mist and handling.

CONFIRM IT IS FIXED

Even, continuous lay of the down colour over the pin-cured colour at running speed, with interstation dose measured at 10 to 30 % of the final station, and full cure confirmed at the last station by 30 MEK double rubs.

THE TRAP

Treating it as a wetting problem in the ink and asking for an additive or a slip correction. The surface it is failing to wet is one the press made a metre earlier, so the fix is at the lamp, not in the tin; adding surface-active material to the down colour usually buys a patchy lay on this job and a rub failure on the next.

UV Letterpress InksDown colour crawls over a cured colour (continued)

Fault 14 of 20

Poor transfer and roller stripping after wash-up

WHAT YOU SEE

A press that ran correctly before the wash comes back starving, with one or more rollers refusing to take a full film and a soft, dull print. Sometimes the cure fails as well at the same dose as before.

WHAT IT LOOKS LIKE

CAUSES, MOST LIKELY FIRST

Wrong press wash usedConventional oil-based and aromatic washes swell EPDM rollers and attack UV blankets, changing nip geometry within one wash-up.
Wash residue left in the nipSolvent left behind dilutes the incoming ink film and its photoinitiator, which reads as a soft surface at the normal dose and gets blamed on the lamp.
Rollers glazedA glazed surface will not carry a full ink film, and glaze builds up over many wash-ups before it is noticed.
Roller stripe disturbedSwelling and hardening both move the stripe away from 3.0 +/- 0.5 mm.
Plate attacked by a strong cleanerKetones and aromatics swell the relief and round the shoulder permanently, so the plate never prints the same again.

UV Letterpress InksPoor transfer and roller stripping after wash-up

Fault 14 of 20 · continued

Poor transfer and roller stripping after wash-up

CHECK, IN THIS ORDER

Find out which wash was actually used, from the drum on the floor rather than from the standard.
Run a stripe test against the plate and measure the band width against 3.0 +/- 0.5 mm.
Feel and look at the rollers for glaze, swelling or a soft spongy surface, wearing gloves.
Run the MEK double rub on the first good print after wash-up to see whether cure has moved as well as transfer.
Measure relief depth on the plate if the image has changed character as well as density.

THEN CHANGE

Standardise on a UV-compatible ester and alcohol blend with a flash point above 55 C, and remove every other drum from the deck.
Wash, wipe dry and let the last traces flash off before re-inking; do not re-ink a wet train. Gloves and eye protection for the wash, and wetted rags into a closed metal bin.
Deglaze or replace glazed rollers and reset the stripe to 3.0 +/- 0.5 mm.
Replace any nitrile roller found on the deck; nitrile swells in acrylate and must not be used.
Clean photopolymer plates only with a cleaner the plate maker recommends, and replace a plate whose shoulder has been rounded.

CONFIRM IT IS FIXED

Full even film on every roller and target density at kiss impression on the first job after wash-up, with the stripe measured at 3.0 +/- 0.5 mm and at least 30 MEK double rubs at the normal dose.

THE TRAP

Adding cure energy because the print after wash-up is soft. The softness is diluted photoinitiator from solvent in the nip, so the lamp gets turned up and stays up, and the press then runs every subsequent job over-cured, over-heated and with a lamp life nobody can explain; letting the train flash off costs five minutes.

UV Letterpress InksPoor transfer and roller stripping after wash-up (continued)

Fault 15 of 20

Register wanders round the tube circumference

WHAT YOU SEE

On a dry offset tube line the colours fit at one point of the circumference and drift at another, or the image stretches and the text distorts as it approaches the shoulder. On a narrow-web line the same fault reads as register loss down the web with necking or wrinkle at the edges.

WHAT IT LOOKS LIKE

CAUSES, MOST LIKELY FIRST

Mandrel and tube fitA body that is loose, oval or not fully seated on the mandrel presents a changing surface speed to the blanket through one revolution.
Blanket packing or conditionAn uneven or compressed blanket changes the transfer circumference and takes the image with it.
Plate mountingA plate mounted off its register marks, on a stretched or compressible tape, or lifting at the edge, distorts the image before impression has done anything, and a lifting edge also bounces at speed.
Impression too heavyExcess pressure deforms the tube body and the blanket together, and the distortion is largest where the body is least supported, at the shoulder.
Web tension too high or untapered, on a narrow-web lineA thin ABL or PBL web necks and stretches under tension, and mercury lamp heat softens it further, so the image is printed on a web that is not the width or the length it will be at the rewind.

UV Letterpress InksRegister wanders round the tube circumference

Fault 15 of 20 · continued

Register wanders round the tube circumference

CHECK, IN THIS ORDER

Measure tube outside diameter and ovality on a sample from the running batch with a gauge, at the body and near the shoulder.
Check mandrel condition and seating, and confirm the body is fully home.
Check blanket packing with a gauge and look at the blanket for compression marks.
Verify plate mounting against the register marks, inspect the mounting tape for lift and confirm the tape is specified for UV inks and the wash in use.
Measure web tension at running speed and through acceleration, and read web temperature after the last mercury station with an infra-red thermometer.

THEN CHANGE

Return to kiss impression first, since it is the cheapest change and often the whole fault.
Repack or change the blanket and reset the plate on its register marks with fresh tape of the specified compressibility.
Replace worn mandrels and correct seating at the loader.
Bring web tension to the laminate supplier's figure with taper into the rewind, and chill the web after the last lamp before judging register again.
Return an out-of-tolerance body batch to the moulding or heading operation rather than printing it.

CONFIRM IT IS FIXED

Register held within the job tolerance at four points round the circumference on twenty consecutive tubes, or across a full reel on narrow web, at kiss impression, with body ovality measured inside the moulder's tolerance and web tension logged at the specified figure.

THE TRAP

Distorting the artwork in prepress to cancel the drift. It is fitted to one mandrel, one blanket and one batch of bodies, so the corrected file prints wrong the moment any of the three is changed, and the real mechanical fault stays on the press for the next job that uses a standard file.

UV Letterpress InksRegister wanders round the tube circumference (continued)

Fault 16 of 20

Printed reel blocks, labels stick in the roll

WHAT YOU SEE

The finished reel is difficult to unwind, print picks onto the reverse of the web above it, or die-cut labels lift the matrix and each other. Found at rewind, at die cutting or at the applicator rather than at the press.

WHAT IT LOOKS LIKE

CAUSES, MOST LIKELY FIRST

Surface undercureAn oxygen-inhibited surface stays slightly tacky and will bond to whatever it is wound against under reel pressure.
Reel wound hot and tightHeat from mercury lamps, and real radiant heat from a high-power LED array, plus winding tension, put the film under pressure while it is still building properties.
No overprint coatingThe coating is what sets the release surface; a bare ink film is not specified to be one.
Rewound immediately after cureProperty build continues for hours, and the reel is at its worst in the first hour.
Coat weight uneven across the webA lane that is short of coating blocks while the rest of the reel is fine, which reads as a random fault and usually traces back to plugged anilox cells.

UV Letterpress InksPrinted reel blocks, labels stick in the roll

Fault 16 of 20 · continued

Printed reel blocks, labels stick in the roll

CHECK, IN THIS ORDER

Run the MEK double rub on the print at the rewind position and again at one hour.
Measure web temperature at rewind with an infra-red thermometer and web tension against the specified figure and taper.
Weigh coating film weight across the web at three lanes gravimetrically and inspect the anilox for plugged cells.
Check rewind tension against the machine setting, and look at how tightly the reel is being built.
Run a blocking test on printed coupons face to back as they lie in the reel: 24 hours at 40 C and 50 % RH under a defined pressure of about 7 kPa (1 psi) between flat plates, then separate at a steady peel and inspect for transfer, tack or pick. State load, area, temperature, humidity and time on the record and run an unprinted control from the same laminate alongside.

THEN CHANGE

Fix surface cure first: clean the window, close the head gap and raise peak irradiance.
Apply the matched overprint coating in line at 1.5 to 3.0 g/m2 and confirm the coat weight across the full width.
Chill the web after the last lamp, and reduce rewind tension with taper into the reel.
Hold reels before die cutting rather than converting straight off the press.
Interleave where a construction blocks despite correct cure and coating.

CONFIRM IT IS FIXED

No transfer and a clean unwind after the stated blocking test, 24 hours at 40 C and 50 % RH under about 7 kPa against an unprinted control, with the print passing 30 MEK double rubs at rewind and coating weight measured at 1.5 to 3.0 g/m2 across the web.

THE TRAP

Winding softer to stop the blocking. It masks the undercure, so the reel unwinds at the converter and then blocks in the customer's applicator or the finished pack, by which time the reel has been slit, die cut and delivered; blocking is a cure and coating fault, and reel tension only decides when you find out.

UV Letterpress InksPrinted reel blocks, labels stick in the roll (continued)

Fault 17 of 20

Odour or taint reported on the filled tube

WHAT YOU SEE

The customer reports a smell in the empty tube or a taint in a filled personal-care or oral-care product, usually weeks after the run. The print itself looks and tests sound.

WHAT IT LOOKS LIKE

CAUSES, MOST LIKELY FIRST

Incomplete cure leaving unreacted monomer and photoinitiator fragmentsUncured low-molecular-weight material is mobile and volatile and is the commonest source of both odour and a migration query.
Wrong grade for the packA standard build carries conventional low-molecular-weight initiators; food-adjacent, pharmaceutical and personal-care packs are the reason the -LM build exists.
Cure set for the process shadesThe white or a dense shade is under-cured at a dose that suits the rest of the job, so one colour on the pack carries the residue.
Coating laid over a film that was still tackyA coating does not cure what is under it; it seals unreacted monomer into the pack and takes it out of reach of the rub test.
Stray ink contamination inside the tubeMist, handling or a contaminated mandrel puts uncured material where no lamp reaches it.

UV Letterpress InksOdour or taint reported on the filled tube

Fault 17 of 20 · continued

Odour or taint reported on the filled tube

CHECK, IN THIS ORDER

Measure delivered dose in the correct band at press speed for every colour, especially the white, and compare against each colour's own window.
Run the MEK double rub, ASTM D5402 at 1 kg, on each colour separately rather than on the composite print, and on the ink with the coater off.
Confirm from the job ticket which grade was run, standard or -LM, and what the pack specification asked for.
Inspect the inside of a sample tube for ink transfer or mist.
Hold sample tubes closed for 24 hours and assess odour against an unprinted control from the same laminate.

THEN CHANGE

Set the lamp for the hardest colour on the job, log the reading, and re-run the affected batch if dose was short.
Move the pack to the -LM build, which is formulated with low-migration-potential initiators and monomers for sensitive applications, printed on the non-contact face. Whether the construction provides a barrier adequate to the filled product is for the brand owner's own migration testing and documented assessment on the finished pack; we supply formulation data to support it and make no conformity claim ourselves.
Never coat over a tacky film to make it printable; cure the ink first and coat second.
Eliminate mist and handling transfer to the inside of the body.
Allow tubes to stand before cartoning rather than boxing straight off the line.

CONFIRM IT IS FIXED

Each colour independently passing at least 30 MEK double rubs with the dose logged in its own window, and no odour difference against an unprinted control from the same laminate after 24 hours closed; migration and food-contact conformity remain a matter for assessment on the finished pack, on request.

THE TRAP

Answering the customer with a conformity statement. No certification, migration figure or finished-pack claim can be made from a press-floor test, and offering one turns a curable cure problem into a commercial commitment; the correct answer on the floor is to prove the cure, and to send the pack for assessment.

UV Letterpress InksOdour or taint reported on the filled tube (continued)

Fault 18 of 20

Ghost image repeats down the web or round the tube

WHAT YOU SEE

A faint positive or negative image of a heavy element appears in a solid or a tint further down the image, one form roller circumference away on a repeating web, or ahead of and behind a heavy solid on the same tube. Density is on target everywhere else and the plate is clean.

WHAT IT LOOKS LIKE

CAUSES, MOST LIKELY FIRST

Mechanical ghosting to the form roller circumferenceA short letterpress train has too few rollers to refill the form roller before it comes round again, so the band that gave up ink to a heavy solid arrives at the next image still short.
Starvation ghosting behind a heavy solidA heavy element draws the film off the train across its own width, and whatever follows it in the same key zone prints light for the rest of the revolution.
Oscillation short, stalled or ill-timedOscillating rollers are what smear a depleted band sideways; without full stroke the depletion stays exactly where the image put it.
Rollers glazed or stripe shortA roller that cannot carry a full film cannot refill a depleted band inside one revolution, so a train that ghosts is usually a train that is also starving.
Image layoutTwo heavy elements one form roller circumference apart, or a solid sitting directly above a tint in the same key zone, will ghost on any short train however it is set.

UV Letterpress InksGhost image repeats down the web or round the tube

Fault 18 of 20 · continued

Ghost image repeats down the web or round the tube

CHECK, IN THIS ORDER

Measure the distance between the heavy element and the ghost and compare it with the form roller circumference, the plate cylinder repeat and the mandrel circumference; the one it matches names the cause.
Run a stripe test against the plate and confirm 3.0 +/- 0.5 mm, even across the width.
Confirm every oscillator is running and that stroke and timing are to the press builder's figure.
Weigh film weight gravimetrically and read roller train temperature at running speed.
Print the same forme with the heavy element masked out, to prove the ghost follows the image rather than the plate or the blanket.

THEN CHANGE

Reset the stripe and deglaze or replace glazed rollers before anything else.
Restore oscillation stroke and timing, and add the ink train's full rider set where the press has one that has been left off.
Move film weight to the top of its window only where cure allows it, and re-run the MEK rub afterwards, because a heavier film is also a harder film to cure.
Re-lay the artwork or rotate the image in the repeat so heavy elements do not sit one form roller circumference apart, where the design allows it.
Split a heavy element to a different unit rather than trying to feed a short train out of the fault.

CONFIRM IT IS FIXED

No visible ghost at normal reading distance on the running job with the heavy element in place, stripe measured at 3.0 +/- 0.5 mm, oscillators confirmed running, and solid density held across the key zone at kiss impression.

THE TRAP

Opening the keys in the depleted zone. It masks the ghost at one speed on one image, over-feeds everything else in that zone and puts a heavier film under the lamp, so the job that stopped ghosting at the keys often comes back failing the rub; depletion is a roller train problem and it is fixed on the train or in the layout.

UV Letterpress InksGhost image repeats down the web or round the tube (continued)

Fault 19 of 20

Shade moves when the cure is changed, whites and pale tints yellow

WHAT YOU SEE

A colour approved at the proofing dose no longer matches once the lamp has been set for the white or the dense black, or the shade moves after a lamp or emitter change. Pale tints go warm and the drift is largest where there is least pigment to carry the colour.

WHAT IT LOOKS LIKE

CAUSES, MOST LIKELY FIRST

Residual initiator and its photoproductsInitiator that has not absorbed its light leaves residual colour, and initiators and synergists change colour as they are consumed, so shade moves with dose in both directions.
Lamp type or emitter wavelength changedA doped mercury lamp, or a move between 385, 395 and 405 nm, changes the spectrum the initiator sees and therefore the residual colour of the film.
Lamp set for the hardest colour on the jobSetting the dose for the white or a dense black over-exposes the process shades that share the station, and the pale end is where that shows first.
Substrate, not ink, yellowingTreated polyethylene and the laminate adhesive also yellow with UV and heat, so a pale shade over them can move while the ink film has not.
Colour judged too early, or at no stated conditionColour continues to move for hours after cure, and a shade argued on two instruments at different illuminant, observer or geometry is an argument about instruments.

UV Letterpress InksShade moves when the cure is changed, whites and pale tints yellow

Fault 19 of 20 · continued

Shade moves when the cure is changed, whites and pale tints yellow

CHECK, IN THIS ORDER

Print a step of the shade at the dose it was approved at and at the dose the job now runs, on the same substrate in the same pass, and measure both.
Measure to CIELAB with a spectrophotometer at a stated condition, D50 illuminant and 2 degree observer, M1 where optical brighteners are present, and report dE against the approved standard rather than judging by eye under press-room light.
Record which lamp type and emitter wavelength each station carries and whether either has been changed since the approval.
Measure delivered dose in the correct band at the station carrying the shade, not for the job as a whole.
Measure an unprinted control from the same laminate carried through the same lamps, to separate ink yellowing from substrate yellowing.

THEN CHANGE

Approve colour at the dose the job will actually run, and log that dose on the job ticket beside the approved standard.
Where the white or a dense black needs its own dose, give it its own station rather than exposing the whole set at the white's setting.
Hold one lamp type and one emitter wavelength per position through a repeating job, and re-approve colour after any change.
Return a shade that cannot be held across the dose window to the laboratory for a less dose-sensitive build rather than trimming it at the duct.
Where the substrate is what moved, take the evidence back to the laminate supplier rather than reformulating the ink.

CONFIRM IT IS FIXED

dE within the job tolerance against the approved standard, measured at 24 hours after cure at 23 C and 50 % RH at a stated measurement condition on one instrument, with the station's delivered dose logged at the value the colour was approved at.

THE TRAP

Correcting the shade at the duct to cancel a drift the lamp caused. The correction is only valid at the dose of that day, so the next repeat, run at the correct dose, prints wrong in the opposite direction, and the ink record now carries a trim nobody can explain.

UV Letterpress InksShade moves when the cure is changed, whites and pale tints yellow (continued)

Fault 20 of 20

Overprint coating lifts off the ink

WHAT YOU SEE

The coating is hard and cured, but it lifts from the ink at die cutting, at the matrix strip, at the cap or on a tape pull, coming away cleanly and leaving the ink in place underneath. Bare substrate areas and light tints hold; the heavy solids are where it lets go.

WHAT IT LOOKS LIKE

CAUSES, MOST LIKELY FIRST

Ink fully cured or over-cured before the coating went onA fully crosslinked acrylate surface has low surface energy and little residual unsaturation, so the coating sits on it instead of bonding into it. It is the same mechanism as a down colour crawling on a pin-cured surface, one film later.
Slip, wax or silicone at the ink surfaceA slip additive at the surface, or silicone carried in from a wrong wash or an aerosol, gives the coating a weak boundary layer to bond to.
Coat weight short or unevenA thin or broken film has less to hold with and fails first in a lane the anilox is not filling.
Ink undercured underneathA soft, under-crosslinked ink film has no cohesive strength, so the coating comes away with the top of the ink; it looks like intercoat release and is a cure fault.
Judged too earlyBoth films continue to build for hours, so a coating tape-pulled at the delivery reads worse than the same print at 24 hours.

UV Letterpress InksOverprint coating lifts off the ink

Fault 20 of 20 · continued

Overprint coating lifts off the ink

CHECK, IN THIS ORDER

Tape pull the coated solid and look at which face the failure is on: clean coating off cured ink is intercoat, coating with ink attached is ink cohesion or the substrate interface.
Read delivered dose at the last ink station before the coater and express it as a percentage of the final station; a wet-trap set should be at a 10 to 30 % pin cure, not a full cure.
Run the MEK double rub on the ink alone with the coater off, to separate an under-cured ink from an intercoat failure.
Weigh coating weight at three lanes across the web and inspect the anilox for plugged cells.
Confirm the wash in use carries no silicone and that no slip or antistatic aerosol has been used on the deck.

THEN CHANGE

Bring the last ink station before the coater back to a measured pin cure of 10 to 30 % of final dose, and leave full cure to the station after the coater.
Restore coat weight to 1.5 to 3.0 g/m2 evenly across the width, cleaning or replacing a plugged anilox.
Remove silicone from the deck and wash the train with a UV-compatible ester and alcohol blend that contains none.
Fix an under-cured ink first; the coating cannot hold onto a film that has no strength of its own.
Where the construction genuinely needs the ink fully cured before coating, qualify that ink and coating combination in the laboratory on the customer's own material before it goes on a production job.

CONFIRM IT IS FIXED

Cross-cut classification 0 with no removal on a 2 mm lattice through the coating, 24 hours after cure at 23 C and 50 % RH, and no coating lift at the matrix strip over a full reel, with the last ink station logged at 10 to 30 % of final dose and coat weight at 1.5 to 3.0 g/m2 across the width.

THE TRAP

Curing the ink harder to stop the coating lifting. It is the opposite of the fix: the more completely the ink is cured before the coater, the less the coating has to bond to, so the extra dose buys a tighter ink film and a looser coating. Cure the ink hard after the coating, not before it.

UV Letterpress InksOverprint coating lifts off the ink (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
Tacky surface, fails MEK rub	Look at and clean the window, then peak irradiance and dose at press speed	Clean the window, close the head gap to 2 to 5 mm
Print lifts on tape pull	Surface energy with test inks on the reel running now	Re-treat in line to at least 38 mN/m
Halo round the dot	Packing and impression against the plate data sheet	Back off to kiss impression
Later colours will not trap	Tack on every shade, one inkometer at ASTM D4361 conditions	Re-sequence to a descending ladder, 12 down to 8
Weak density, heavy impression	The duct itself, then film weight gravimetrically	Clear the duct, feed to 1.5 g/m2, take impression back to kiss
White will not hide	Film weight, then contrast ratio at that film weight	Take the white to 2.5 g/m2, or specify a double hit
White scratches off to laminate	Which wavelength and what dose the white is getting	Move the white to 395 or 405 nm and set the lamp for it
Highlights plug, type fills	Relief and floor depth on the plate with a depth gauge	Deeper relief to gauge, or a coarser ruling

UV Letterpress InksQuick reference

Quick reference

One page at the press

Symptom	Check this first	Change this first
Rubs off at the shoulder	Coating weight across three lanes and the anilox condition	Coat in line at 1.5 to 3.0 g/m2
Coating lifts off the ink	Dose at the last ink station as a percentage of final	Drop that station to a 10 to 30 % pin cure
Density drifts up through the run	Roller train temperature at running speed	Hold 28 to 32 C before touching the keys
Ink skins or gels in the duct	Daylight, lamp leakage and the stop log, press isolated	Shield the deck, cover the duct, strip at 30 minutes
Pinholes and craters	Whether the defect repeats to a roller or is random	Remove the contamination, restore static control and treatment
Ghost repeats down the web	Repeat distance against the form roller circumference	Reset the stripe, restore oscillation
Down colour crawls on cured colour	Interstation dose as a percentage of final dose	Drop earlier units to a 10 to 30 % pin cure
Shade moves with the cure setting	The same shade printed at both doses, measured to CIELAB	Approve and run at one logged dose per station

UV Letterpress InksQuick reference

Quick reference

One page at the press

Symptom	Check this first	Change this first
Register wanders on the tube	Body ovality and mandrel seating, impression at kiss	Return to kiss impression, then repack the blanket
Reel blocks, labels stick	MEK rub at the rewind position, web temperature and tension	Fix surface cure, then coat in line

UV Letterpress InksQuick reference

Test methods

The measurements this guide relies on

Measurement	Method	What it tells you, and the usual acceptance
Falling-rod (Laray) viscometer	ISO 12644	Body and yield value on a duct sample at 25 C. Process shades 40 +/- 10 Pa.s with a yield value of 150 to 300 Pa; opaque white 55 +/- 10 Pa.s with 250 to 450 Pa. A yield value under 150 Pa is what lets a film spread at the relief shoulder.
Inkometer tack	ASTM D4361	Tack of each shade and the ladder through a wet-on-wet set: 1.32 mL charge, 1200 rpm, 32 C, read at 60 s. 11 +/- 2 as supplied, graduated about 12 down to 8. A Tack-o-scope reads on its own scale at its own speed and charge; quote it in its own units and never put readings from two instruments in one ladder. Record instrument, speed, temperature and charge beside every number.
Band-matched UV radiometer	No standard cited; a UVA 320 to 390 nm head at mercury stations and an LED-band head at 385 to 405 nm stations	Delivered dose and peak irradiance at the substrate plane at running speed. On a UVA head, 80 to 140 mJ/cm2 on process shades and 150 to 250 mJ/cm2 on the white; on an LED-band head, 250 to 450 and 400 to 700 mJ/cm2. Windows belong to the instrument that produced them: makes and band definitions disagree by twenty to thirty percent on the same lamp, so record make, model and band, and hold within about 20 % of the reading logged when the job last ran correctly. A broadband head will not report what an LED array delivers.
Surface energy test inks	ASTM D2578	Wetting tension of the treated polyethylene skin on the reel about to run, using test-ink solutions applied with a clean swab and read on whether the film holds unbroken for two seconds. 38 mN/m is the floor at the print station and 40 to 44 mN/m is typical on a freshly treated skin; above about 48 mN/m over-treatment leaves its own weak boundary layer. Dyne pens are a quick indicator only, are not the D2578 method and drift once contaminated.
Cross-cut tape adhesion	ISO 2409, or ASTM D3359 Method B as a house alternative	Adhesion on a 2 mm lattice, which is the ISO 2409 spacing for a soft substrate such as a polyethylene skin, with a tape pull 24 hours after cure at 23 C and 50 % RH. Record the tape type and batch, the dwell before peel and the peel angle, because on a 1.5 micron ink film these decide the result more than the lattice does. Classification 0 with no removal on laminate at or above 38 mN/m; fibre tear on coated label stock. It is a described test, not proof of conformity to a paint standard.
MEK double rub	ASTM D5402	Degree of cure, 1 kg load on a cotton wad, one hour after cure. At least 30 double rubs with no breakthrough to substrate. Run it on each colour separately and on the ink with the coater off, because the white is normally the one that fails and a coating hides an under-cured ink under it. Gloves, eye protection, extraction or open air, no ignition source, and the wetted wad into a closed metal container.
Gravimetric film weight	No standard cited; balance readable to 0.1 mg, five printed and five unprinted cuts of 200 to 400 cm2	Ink lay at solid. 1.0 to 1.5 g/m2 on process shades, 2.0 to 2.5 g/m2 per pass on the white, 1.5 to 3.0 g/m2 on the overprint coating. Never on single cuts: a 1.0 g/m2 film over 100 cm2 is 10 mg while the laminate itself weighs 2.5 to 3.5 g per 100 cm2, so ordinary basis-weight variation swamps the ink. Take cuts from the same cross-web position and the same metre of web and compare the means; resolution is about +/- 0.2 g/m2 on a lamitube laminate. Where tighter control is needed, keep a deliberately unprinted lane on the same web, or track ink consumption per thousand units, as the cross-check.

UV Letterpress InksTest methods

Test methods

The measurements this guide relies on

Measurement	Method	What it tells you, and the usual acceptance
Contrast ratio	ISO 2814	Hiding power of the white over a black-and-white chart. Because a chart cannot be run through a tube decorator, reproduce the measured press film weight on a chart with a calibrated proofer or K-bar, or judge the job by printing the white over a black bar and over bare laminate in the same pass and comparing Y or L*. Say which of the two the figure came from; they are not interchangeable. 0.70 to 0.80 at a single pass of 2.0 to 2.5 g/m2, 0.85 to 0.92 as a double hit at 4.0 to 5.0 g/m2. A 12 micron laboratory drawdown reads 0.95 or better and is not what the press lays.
Sutherland rub tester	ASTM D5264 (withdrawn but still the reference practice for this instrument; TAPPI T 830 is the alternative)	Rub and scuff of the finished ink and coating system: 4 lb (1.8 kg) weight, 100 dry cycles on the coated print, receptor and sample conditioned at 23 C and 50 % RH, reporting cycles to first transfer as well as pass or fail. Companion test of 50 cap open-and-close cycles at 0.8 to 1.5 N.m on the customer's own cap and shoulder. Tested at 24 hours, not at the delivery.
Reflection density	ISO 5-3 for status, ISO 5-4 for geometry	Solid and tint density on the cured print at three points across the web. State the condition, Status E or Status T and 0/45 geometry, and use the same instrument and condition as the approved proof. A density figure without its status is not a measurement.
Spectrophotometric colour	CIELAB, D50 illuminant and 2 degree observer, M1 where optical brighteners are present	Shade against the approved standard, measured at 24 hours after cure at 23 C and 50 % RH, on one instrument at one stated condition, with the delivered dose for that station logged beside the reading. UV inks move with dose and with lamp type, so a colour without its cure condition cannot be repeated.
Blocking test	No standard cited; 24 hours at 40 C and 50 % RH under about 7 kPa (1 psi) between flat plates	Whether the printed and coated film will bond to what it is wound against. Coupons face to back as they lie in the reel, separated at a steady peel and inspected for transfer, tack or pick, with an unprinted control from the same laminate alongside. State load, area, temperature, humidity and time on the record, because blocking is a pressure, time and temperature result and is not repeatable without them.

UV Letterpress InksTest methods

When the press-floor fixes have not worked

What to send us

The radiometer log: delivered dose and peak irradiance for every station, in the correct band, read at the substrate plane and at the top speed of the job, with the instrument make, model and band, the lamp or emitter hours, and the date of the last window or reflector clean.
A printed sample and an unprinted sample from the same reel or the same body batch, unconverted, with the reel or batch number, plus the substrate supplier's name and the laminate specification.
The job ticket exactly as the operator kept it: film weights measured, every stiffening or reducing paste addition with its percentage and the time, roller train temperature through the run, web tension where the machine records it, and the impression setting.
The ink container label and the remaining material from the running charge, with grade code, batch number and date of manufacture, kept in the container and not decanted.
The measurements you already took: test-ink reading on the running reel, Laray body and yield value on a duct sample, the tack ladder with its instrument and condition, the MEK double rub count per colour, and the coating weight across three lanes.
The plate itself, or its relief and floor depth measurements and the platemaking record, where the fault involves highlights, type, halo or shoulder geometry.
For a pack complaint, the filled pack and an empty of the same construction, the filling and capping conditions including the torque actually applied, and the storage time and temperature between printing and the complaint.

Technical servicesales@ufindustries.com | +91 8750051884 | E105, GNEPIP, Industrial Area Site-5, Greater Noida, Uttar Pradesh 201306, India

UV Letterpress InksTechnical service