Troubleshooting guide

Water Based Flexo Inks

Press-floor fault finding for UniWet Hydra, UniFine HD, UniCold, UniHot, UniWet Glacier and UniCraft: pH first, then viscosity.

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.

Measure pH before you measure viscosity, and measure both in the tray at running temperature, because in an amine-solubilised ink almost every viscosity symptom is a pH symptom wearing a disguise.
Correct pH with the supplied stabiliser and correct viscosity with water, in that order and never the other way round; water added to a low-pH ink fixes the reading for ten minutes and deepens the fault.
Every check in this guide is made with the guards closed and your hands outside them. Nothing here is worth a hand near a running nip, a solvent rag near a dryer, or bare skin on an uncured UV coating. If a reading cannot be taken from outside the guards, stop the press, isolate it and inch it.
Before you change the ink, prove the three things that are not the ink: anilox volume and screen measured not assumed, substrate wetting tension measured on the reel you are about to run, and dryer air volume and extraction rather than dryer temperature.
Resolubility and water resistance are traded against each other in every water-based grade, so decide which failure you cannot afford on this job and pick the grade for it, rather than asking one ink to do both.
Judge resistance on conditioned print, not at the rewind: rub, water and block resistance develop as the last of the carrier leaves and the emulsion coalesces, so test 24 h after the run at 23 C and 50 % RH.
Adhesion, slip, seal and migration belong to the pack, not to the ink, so qualify them on the customer's own liner, cup stock or metallised paper and on the customer's own forming and filling line.

Water Based Flexo 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

Water Based Flexo InksThe process

Control variables

What to hold, and how to measure it

Variable	Target	How it is measured	How it drifts
pH of the running ink	8.2 to 9.0 for amine-stabilised grades; 8.5 to 9.2 on corrugated post-print with UniCraft. Above 9.5 the ink is over-stabilised and carries its own set of faults, so 9.5 is an upper action limit and not just a comfortable margin.	Calibrated glass electrode with automatic temperature compensation, two-point calibration at pH 7.00 and 10.01 that day, electrode cleaned of dried ink and stored in KCl, read in the tray at running temperature. Paper strips are not adequate for this control.	Falls steadily as amine evaporates, typically 0.1 to 0.2 pH units per hour from a covered, circulating system and 0.3 to 0.5 units per hour from a wide open tray at speed on a corrugated press, faster still with a large ink surface, a hot tray or an ammonia-based stabiliser. Establish the rate for your own press by logging pH against time on a long run rather than assuming a figure. Viscosity begins to rise as the reading passes about 8.2 and the plate begins to fill below about 8.0.
Viscosity	18 to 25 s for flexo, 15 to 20 s for gravure; UniFine HD narrow-web label inks run at the low end of that band, typically 17 to 21 s, because the fine, low-volume engravings used for HD work release poorly at higher viscosity. Take density from pigment strength, not from body.	4 mm flow cup, either ISO 2431 or DIN 53211, named on every reading together with the temperature. The ISO 2431 4 mm cup and the DIN 53211 4 mm cup are not the same geometry and do not give the same number, and a Zahn 2 reading is a third number again. This house uses the 4 mm cup at 25 C as a works method; readings are not converted to kinematic viscosity, because ISO 2431 declares flow cups valid only between about 20 s and 100 s and our working bands sit at or below that limit. Where a number below 20 s has to be controlled, use a 3 mm cup so the reading falls inside the valid window.	Rises through a run from water loss and from falling pH together. A 5 C rise in ink temperature drops the reading by roughly 1 to 3 s on a 4 mm cup without anything having changed in the ink, so an ink brought back to the target number on a hot afternoon is in fact too thick: it prints heavy and fills in once the tray cools. Correct every reading back to 25 C, or log the temperature beside the number and compare like with like.
Ink temperature in the tray	25 C nominal, held within plus or minus 2 C across a run, which is about 1 s on the cup. The old 8 C band was wider than the effect it was meant to control.	Stem or infra-red thermometer in the tray, taken at the same point in the circuit every time and logged next to the viscosity reading. Where the tray cannot be held to plus or minus 2 C, correct every reading back to 25 C with a measured temperature coefficient for the grade so the correction is auditable.	Climbs through a shift from pump work and dryer set-back, most of it in the first two hours. Note which way that cuts: a hotter ink reads thin on the cup, so an uncompensated automatic viscosity controller stops adding water and lets the real viscosity climb behind a display that looks correct. The commonest reason a controller genuinely keeps adding water is falling pH thickening the ink; a cooling tray, or a controller whose target was set at a different temperature from the one it is now measuring, does the same thing. Log the ink temperature next to every controller set point.
Substrate wetting tension	38 mN/m is the bare working minimum for PE-coated cup stock with UniCold; 40 to 44 mN/m is where water-based inks actually wet PE without edge and start-of-reel breakup. Do not chase treatment above about 44 mN/m: over-treatment builds a weakly bound oxidised layer on the polyethylene, so adhesion falls while the dyne reading rises.	Wetting-tension test inks to ASTM D2578, or ISO 8296 test inks, applied to the reel you are about to run, not to a retained sample, and read at both edges and the centre. Dyne pens are acceptable for a go or no-go check if they are in date.	Treatment decays in storage, faster in heat, and the outer wraps of a reel decay differently from the core. A reel that measured 40 mN/m at the extruder can be at 34 mN/m three months later.
Anilox volume and screen	Screen and volume are not independent, so specify the pair. Process and line on coated stock: 3.5 to 4.5 BCM at 300 to 360 lpi, or 2.0 to 3.0 BCM at 440 to 500 lpi. Solids on kraft and liner: 6 to 9 BCM at 140 to 200 lpi, falling to 4 to 5 BCM by 300 lpi. UniFine HD: 1.0 to 2.5 BCM at 800 to 1200 lpi for process and highlight work, 2.5 to 4 BCM at 500 to 700 lpi for line, solids or opaque white. UniCraft on corrugated: 6 to 9 BCM at 140 to 200 lpi for solids and heavy coverage, 3 to 5 BCM at 200 to 300 lpi for combined solid-and-line plates, 2 to 4 BCM at 300 to 360 lpi for a station carrying bar codes, fine reverses or small type. Keep the anilox screen at four to five times the finest halftone ruling on the plate.	Measured volume from the roll supplier or an in-house 3D interferometric or volumetric check, plus a cell-condition inspection at 100x with a handheld scope, which takes two minutes and needs no roll removal. The engraving figure on the end cap is a history, not a measurement.	Cells wear and plug. A roll 30 % down on volume prints as a weak ink at perfect pH and viscosity, and the loss is gradual enough that nobody notices the day it happened. Where solids and a bar code share one plate, meter for the code and recover solid density with pigment strength, not with volume.
Dryer air volume, extraction and web temperature	Air 50 to 70 C on PE-coated stock and film, up to 90 to 110 C on uncoated paper and corrugated liner. Nozzle velocity nominally 15 to 30 m/s, with extraction volume 10 to 20 % above supply so the print station sits under slight negative pressure. Web temperature is the governing limit: below about 60 C on PE-coated cup stock, and below the softening point of the coating on any extrusion-coated grade.	Anemometer at the nozzle and at the extraction duct, probe on an extension and hands outside the guarding, with the dryer at its production setting and the press at speed. Web temperature with an infra-red thermometer aimed at the web after the last dryer. Record the three readings, not the temperature set point.	Falls as filters load and ducting gathers deposit. A dryer that is on temperature but has lost half its extraction has an almost saturated air layer over the web and dries worse than a cooler dryer with clean air turnover.
Film weight	0.8 to 1.5 g/m2 dry for process and line colours on coated stock at 3 to 4.5 BCM; 2 to 4 g/m2 dry for solids on absorbent liner at 6 to 9 BCM. The old 1.5 to 3.0 g/m2 figure for process colours was roughly double what that metering can deliver, and it quietly sanctioned the over-inking the rest of this guide is fighting.	Weigh a cut area of printed and unprinted substrate on a four-place balance after conditioning. Cross-check against the anilox: dry g/m2 is approximately BCM x 1.55 x transfer efficiency x solids content x 1.05, so 4 BCM at 45 % transfer and 40 % solids is about 1.2 g/m2. A measured film weight well above that means ink is being gained from impression and viscosity rather than from metering.	Creeps up as operators chase density with impression and viscosity instead of anilox. Every extra gram of wet film is carrier that has to be removed, so speed falls roughly in proportion.

Water Based Flexo InksControl variables

Control variables

What to hold, and how to measure it

Variable	Target	How it is measured	How it drifts
Foam and free board in the tray	No standing foam head; return line discharging below the ink surface	Look at the tray and at the return. For a comparable number, pour 100 ml of tray ink into a 250 ml stoppered graduated cylinder, shake by hand for 30 s at about two strokes per second, stand it down, and record the foam volume immediately and the time for the head to collapse to 10 ml. Run fresh drum ink alongside it the same way as the reference, and record the operator, because the shake is the variable.	Grows through a shift as the tray level falls and the return starts to fall through air. Foam starves the anilox before it is visible as pinholes, so density falls first and pinholes arrive later.
Defoamer dosage	To the supplied instruction, typically a small fraction of a percent, added once and circulated	Dose by weight from a graduated container, logged. Never top up by eye from the drum.	Over-dosing is cumulative across a shift and does not undo. The result is silicone repellence that prints as craters and reads on the floor as an adhesion or treatment fault, and the ink has to be replaced rather than corrected.
Pressroom relative humidity	45 to 65 % RH at 20 to 30 C where the building allows it	Thermohygrometer at web height near the dryers, logged hourly, not a reading from the office wall.	Rises through a Greater Noida monsoon to 80 % RH and above. Nothing changes in the ink; the drying curve simply lengthens, paper and board take up moisture and move dimensionally, and coated stock and film lose real speed.

Water Based Flexo InksControl variables

The mechanism

The pH spiral: why adding water makes it worse

In an amine-solubilised water-based ink, the rising viscosity an operator sees on the cup is a symptom of falling pH, not of thickening. Correcting it with water dilutes the amine that was already short, so pH falls further and the same symptom returns sooner and larger. The loop is broken at one point only: restore pH with the supplied stabiliser first, and correct viscosity with water afterwards. The one thing the loop does not excuse is dosing by reflex: above about 9.5 the stabiliser becomes the fault.

Water Based Flexo InksThe mechanism

02 | 20 faults

Faults

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

Fault 1 of 20

Viscosity keeps climbing through the run

WHAT YOU SEE

The cup reading creeps up every check, the operator adds water, and an hour later it is back up again with the print looking dirtier and weaker each time. By the end of the shift the ink in the tray no longer looks like the ink in the drum.

WHAT IT LOOKS LIKE

CAUSES, MOST LIKELY FIRST

pH has fallen below about 8.2 and the alkali-soluble resin is coming out of solutionThe amine that holds the acrylic solution resin dissolved is volatile and leaves with the water, so the resin begins to precipitate and the dispersion thickens; the viscometer reports a chemistry failure as a thickening.
Water has been added repeatedly instead of stabiliserEach water addition dilutes the amine as well as the ink, so pH falls further and the next rise arrives sooner and larger.
Ink temperature has risen and the viscosity was over-corrected earlierA hot tray reads thin, the operator thickens by adding fresh ink or lets water evaporate, and when the press stops and the ink cools the true viscosity is far above target.
Ammonia used as the correction instead of a slow-evaporating amineAmmonia leaves as fast as it is added, so pH is restored for minutes and the cycle repeats faster than before.
Skin and partly dried ink from the tray edges being stirred back inPrecipitated resin and dried particles raise the measured viscosity and will not redissolve at working pH.

Water Based Flexo InksViscosity keeps climbing through the run

Fault 1 of 20 · continued

Viscosity keeps climbing through the run

CHECK, IN THIS ORDER

Confirm first that the pH meter was two-point calibrated at 7.00 and 10.01 that day and that the electrode has been cleaned of dried ink and stored in KCl. A fouled or drifting electrode invents this fault, and every correction made on its reading makes the ink worse.
Measure pH in the tray with the calibrated electrode at running temperature before touching the viscosity, and compare with the reading logged at make-ready.
Measure viscosity on a 4 mm cup, named as ISO 2431 or DIN 53211, and take the ink temperature at the same moment with a stem thermometer.
Read back the shift log: count water additions against stabiliser additions since make-ready.
Look at the tray edges and the doctor chamber ends for skin, and filter a sample through a 150 micron mesh to see what is in it.

THEN CHANGE

Restore pH with the supplied stabiliser. These stabilisers are ammonia or alkanolamine solutions, corrosive to skin and eyes with a vapour that irritates the airway, and the vapour release is highest at the moment they meet a warm open tray. Decant by weight into a closed graduated container, never into an unlabelled one; wear nitrile gloves and goggles, and a face shield when decanting from a drum; work with local extraction or in the ventilated ink-preparation area; dose into the return line or the circulating stream rather than pouring across an open tray, and never while an operator is leaning over it; keep the eyewash station accessible. Refer to the SDS for the supplied grade. Circulate for several minutes before re-measuring.
Re-measure viscosity only after pH is back in the 8.2 to 9.0 band, and correct with water in small additions with a re-measurement between each.
Cool or stabilise the tray temperature to 25 C plus or minus 2 C and re-baseline the viscosity target there.
Filter the ink and scrape the tray rather than stirring skin back in.
Move the check interval to every 30 minutes for the rest of the run and log pH, viscosity, cup type and temperature together on one line.

CONFIRM IT IS FIXED

pH holds in the 8.2 to 9.0 band across three consecutive 30 minute checks with no water addition, and viscosity holds within 2 s on the named 4 mm cup at 25 C over the same period. Density on the solid holds within the agreed tolerance on the densitometer.

THE TRAP

Adding water because the cup reading is high. It corrects the number for ten minutes, dilutes the amine that was already short, and moves the ink faster towards the plate filling and dry-in that follow. Water is the last correction in this category, not the first.

Water Based Flexo InksViscosity keeps climbing through the run (continued)

Fault 2 of 20

pH over-corrected, ink over-stabilised above about 9.5

WHAT YOU SEE

The mirror image of the fault above, and it arrives on presses where the operators have been taught only that pH falls. Drying slows for no reason anyone can name, foam will not go away, rub and water resistance come out short on a print that looks fully dry, there is a sharp ammoniacal smell at the tray and later in the stack, and photopolymer plates start swelling and losing relief inside a shift.

WHAT IT LOOKS LIKE

CAUSES, MOST LIKELY FIRST

Stabiliser added on a schedule rather than on a readingAn operator dosing every hour regardless of the meter walks the ink up past 9.5 on a covered circulating system that was only losing 0.1 to 0.2 units per hour.
Stabiliser added to correct a viscosity rise that was not a pH faultThickening from water loss, from a cooling tray or from returned skin reads as a high cup number, and dosing stabiliser at it adds alkali the ink did not need.
A drifting or uncalibrated electrode reading lowAn electrode fouled with dried ink can read half a unit low, so the operator doses to a true 9.6 while the meter shows 9.1.
Excess amine holding the resin in solution when it should be coming outThe film only develops water and rub resistance as the amine leaves and the emulsion coalesces. An over-alkaline film stays redispersible for longer, so resistance is late and, at production speed, never arrives.
Amine and ammonia attacking press materialsHigh pH swells photopolymer plates and attacks some elastomer rollers and seals, and it accelerates corrosion of aluminium, brass and copper fittings in the circuit.

Water Based Flexo InkspH over-corrected, ink over-stabilised above about 9.5

Fault 2 of 20 · continued

pH over-corrected, ink over-stabilised above about 9.5

CHECK, IN THIS ORDER

Measure pH in the tray with a freshly calibrated electrode and, if the reading is near the limit, confirm it with a second meter before dosing anything.
Read the shift log for stabiliser additions: dose, time and the pH reading each one was made against. Additions with no reading beside them are the fault.
Smell the tray and then smell a conditioned printed sample in a closed jar at room temperature. A sharp ammoniacal note in the sample, not just at the tray, is the one that reaches the filler.
Run the rub and water resistance tests on conditioned print at 24 h and compare with a retained sample from a run that was accepted.
Inspect the plates for swelling, softening and loss of relief, and check roller, seal and fitting condition in the circuit.

THEN CHANGE

Stop dosing and let the ink come back down on its own. Amine leaves with the water, so a covered system that is left alone will fall back into band; there is no safe acid correction on a press ink and adding acid will shock the dispersion out.
Where the ink must be brought back on this run, blend with fresh drum ink of known pH rather than trying to neutralise, and re-measure after circulating.
Replace the plates that have swollen. A swollen photopolymer plate does not recover its relief and will print soft for the rest of its life.
Change the dosing rule: stabiliser is added against a reading, by weight, logged with the reading, and never on a timer.
Where odour has reached the print, extend drying dwell or reduce speed, let the reels stand loose and cool, and do not release stock to a food filler until the odour check on conditioned samples is clear.

CONFIRM IT IS FIXED

pH back inside 8.2 to 9.0 and holding, rub and water resistance on conditioned print at 24 h back at the level of the retained accepted sample, no ammoniacal note on a conditioned sample held in a closed jar, and plate relief measured back at specification on the replacement plates.

THE TRAP

Treating pH as a one-way variable. Everything about a water-based press teaches that pH falls, so an operator with a high viscosity reading reaches for stabiliser by reflex. Above about 9.5 the same chemical that fixes the commonest fault on the press becomes the cause of slow drying, permanent foam, failed resistance, odour in the pack and a set of scrapped plates.

Water Based Flexo InkspH over-corrected, ink over-stabilised above about 9.5 (continued)

Fault 3 of 20

Plate fills in, print goes dirty

WHAT YOU SEE

Fine type and shadow dots bridge and go solid, the plate shoulders carry a ring of dried ink, and the print picks up a general haze that cleaning fixes for one reel and no longer.

WHAT IT LOOKS LIKE

CAUSES, MOST LIKELY FIRST

Low pH has destroyed resolubility, so ink dries where it sits on the plate and in the cellsBelow about 8.0 the resin is no longer re-wetted by fresh ink, and the partly dried film on the plate land and in the cell wall builds instead of being carried away.
Dryer set-back blowing hot air over the plateAn over-pressured or badly balanced dryer pushes air back onto the printing nip and dries ink at the one place it must stay open.
Anilox cells partly plugged, so the released film is thin and dries faster on the plateA plugged cell gives up a thin, quickly drying film that skins on the plate rather than transferring cleanly.
Impression set too heavyOver-impression spreads ink onto the plate shoulder where there is no transfer path, and it dries there.
A high-water-resistance grade being run on a stop-start jobThe emulsion-rich grades that give condensation resistance are deliberately less resoluble, and a press that stops every twenty minutes punishes that choice.

Water Based Flexo InksPlate fills in, print goes dirty

Fault 3 of 20 · continued

Plate fills in, print goes dirty

CHECK, IN THIS ORDER

Measure pH first and compare against make-ready, then measure viscosity on the named 4 mm cup at 25 C.
Stop and inspect the plate under a loupe: look for dried ink on the shoulder and in the fine reverses rather than for ink in the dot.
Inspect the anilox at 100x with a cell microscope and measure volume, or run a proofing check against a known-good roll.
Find dryer set-back without reaching into the machine: tape a light paper streamer or a length of thread to a fixed guard upstream of the print station and watch which way it blows, or take an anemometer reading with the probe on an extension and your hands outside the guarding. Never place a hand near a running nip or inside a dryer housing. If the airflow cannot be judged from outside the guards, stop the press and inch it.
Check the impression setting back to the lightest kiss that gives full solids.

THEN CHANGE

Correct pH with stabiliser, handled as set out in the viscosity fault, and let it circulate before judging anything else.
Deep-clean the anilox and the plate, and change to a clean roll if cell volume is down.
Rebalance the dryer so extraction runs 10 to 20 % above supply at the print station and the set-back stops.
Back the impression off to kiss and re-establish density through anilox volume, not pressure.
If the job genuinely stops often, move to a higher-resolubility grade and put the water resistance into an overprint coating instead.

CONFIRM IT IS FIXED

Run 2000 metres or the agreed length without a plate clean, then inspect the plate shoulder and the 2 % to 5 % tone under a loupe and find them open. pH held in band over the same run.

THE TRAP

Washing the plate and carrying on. The clean plate proves the press can run for twenty minutes, hides the pH failure that caused it, and lets the anilox continue to dry in while everyone is looking at the plate.

Water Based Flexo InksPlate fills in, print goes dirty (continued)

Fault 4 of 20

Colour is weak at correct viscosity

WHAT YOU SEE

Density is short of the target on the densitometer, the operator has already put viscosity and impression up to compensate, and the ink is suspected of being under strength.

WHAT IT LOOKS LIKE

CAUSES, MOST LIKELY FIRST

Anilox volume lost to wear or pluggingCell volume sets laydown. A roll 30 % down delivers 30 % less ink regardless of ink strength, and the press reads that as a weak ink.
Low pH degrading transferAn ink below about 8.0 wets the plate poorly and splits badly at the nip, so less of the metered film reaches the substrate.
Foam in the supply starving the chamberAir in the chamber means cells are filled with a foam and ink mixture and give up less pigment per revolution.
Poor hold-out on absorbent stockOn unsized kraft and test liner the vehicle carries pigment down into the fibre, so the colour layer left at the surface is thinner than the film laid on.
Ink over-extended at a previous make-readyTransparent white or extender added to reduce a shade earlier in the week is still in the drum, and nobody logged it.

Water Based Flexo InksColour is weak at correct viscosity

Fault 4 of 20 · continued

Colour is weak at correct viscosity

CHECK, IN THIS ORDER

Measure pH in the tray with a calibrated electrode at running temperature first. It takes thirty seconds and low pH alone will produce this symptom.
Draw down the tray ink and a fresh drum sample side by side on the job substrate with the same bar, and read both on the densitometer. Five minutes, and it separates an ink problem from a press problem.
Look into the chamber or tray for a foam head and check where the return line discharges.
Look at the cells at 100x with a handheld scope: two minutes, no roll removal, and a plugged or scored roll is visible.
Only when those are clear, measure the anilox volume properly and compare it against the specified volume and screen for the station. Do not trust the end-cap engraving figure.

THEN CHANGE

Restore pH with stabiliser and re-measure density before making any ink change.
Kill the foam: drop pump speed, put the return below the ink line, and only then consider defoamer at the supplied dose.
Change to a clean anilox of the correct volume and screen, or deep-clean the existing roll and re-measure.
On absorbent liner, improve hold-out with the grade intended for it rather than with more film; UniCraft is built to hold pigment at the liner surface at 6 to 9 BCM at 140 to 200 lpi for solids.
Replace over-extended tray ink with fresh drum ink rather than trying to strengthen it.

CONFIRM IT IS FIXED

Solid density meets the agreed target on the densitometer at the specified anilox volume and screen, nominal impression and viscosity in the 18 to 25 s band on the named 4 mm cup at 25 C, and a drawdown of tray ink now matches the drum standard.

THE TRAP

Reaching for a stronger ink or more impression. More impression gains dot gain and plate filling rather than density, and a stronger ink hides a dying anilox until the roll is beyond cleaning.

Water Based Flexo InksColour is weak at correct viscosity (continued)

Fault 5 of 20

Foam in the tray, pinholes in solids

WHAT YOU SEE

A head of froth in the tray or chamber, density falling away without any viscosity change, and small round voids scattered through the solids that get worse as the ink level drops.

WHAT IT LOOKS LIKE

CAUSES, MOST LIKELY FIRST

Return line falling through air into the trayFree fall entrains air faster than the ink can release it, and each pass through the pump makes the bubbles smaller and harder to break.
Pump running faster than the job needsExcess circulation shears air into the ink and holds it there; the ink is being whipped, not moved.
Low ink level in the tray or chamberA shallow tray gives the air no residence time to escape, so the foam that arrives goes straight back to the anilox.
Defoamer over-dosed in a previous correctionExcess silicone creates surface repellence, which prints as craters with a raised rim rather than the clean-edged voids of true foam, and it cannot be dosed back out.
Static, dust, fibre pick or hickeys, which are not foam at allA fibre lifted from the liner, a board dust speck or a dried ink hickey on the plate prints a void of the same size as a foam pinhole, and on a dry winter web static pulls dust onto the substrate faster than the press can print over it.

Water Based Flexo InksFoam in the tray, pinholes in solids

Fault 5 of 20 · continued

Foam in the tray, pinholes in solids

CHECK, IN THIS ORDER

Watch the return line at running speed and confirm it discharges below the ink surface.
Shake 100 ml of tray ink in a 250 ml stoppered cylinder for 30 s, stand it down and time the collapse of the head to 10 ml, comparing with fresh drum ink treated the same way.
Look at the defects under a loupe and sort them by what is in the middle: a clean-edged round void with nothing in it is foam; a void with a raised rim and a bare centre is silicone repellence; a void with a fibre, a dust speck or a shadow at its centre, or a raised speck on the reverse, is pick, dust or a hickey and has nothing to do with the ink.
Check the shift log for defoamer additions and their dose.
Measure the ink level in the tray or chamber against the normal running level, and check the static bars and the web cleaner are working if the voids carry specks.

THEN CHANGE

Drop the pump to the lowest speed that keeps the chamber full, and extend the return line below the ink surface.
Raise the tray or chamber level back to normal so the air has residence time.
Only then dose defoamer by weight at the supplied rate, once, and circulate before judging it.
Where the defects are silicone craters, discard the tray ink, clean the circuit through, and restart on fresh ink.
Where the defects carry fibre or dust, bring the static bars and web cleaning brushes back into service and take the pick up with the substrate supplier; no ink change will cure it.

CONFIRM IT IS FIXED

No standing foam head after 15 minutes at running speed, solid areas free of voids at 10x over a 500 metre check, and density back on target without any viscosity change.

THE TRAP

Adding more defoamer because the first dose did not work. The first dose usually failed because the mechanical cause was still running, or because the voids were never foam. The second dose turns a foam problem into a silicone repellence problem, which is not correctable and costs the tray of ink.

Water Based Flexo InksFoam in the tray, pinholes in solids (continued)

Fault 6 of 20

Streaks, score lines and bands down the web

WHAT YOU SEE

Fine lines running in the direction of web travel, sometimes one, sometimes a group; or a band of light density that repeats at the plate cylinder circumference, usually a short distance below a heavy solid on the same plate. Neither moves when pH and viscosity are corrected, which is why they get chased for whole shifts.

WHAT IT LOOKS LIKE

CAUSES, MOST LIKELY FIRST

Doctor blade worn, chipped or bedded in unevenlyA blade with a flat or a nick leaves a ribbon of ink standing proud out of the cells, and that ribbon prints as a continuous line in the running direction for as long as the blade is in that position.
Blade angle or pressure wrong, giving chatterToo much pressure makes the blade stand up, flutter and wipe unevenly, and it wears the blade and the roll together. The correct setting is the lightest pressure that wipes clean, not the pressure that feels safe.
Dried ink trapped under the blade or in the chamberA fragment of dried ink lodged at the blade edge holds it off the roll locally, and in a water-based ink that fragment appears within minutes of a stop if circulation has stopped too.
Anilox scoredA hard particle, board dust or dried ink, carried under the blade will score the ceramic. The score is permanent, it prints a line in the same place on every job, and no blade change will remove it.
Chamber end seals leaking, worn or dried outA failed seal leaks ink at the web edge and lets air into the chamber, so the edge of the print carries both streaking and foam-starved density.

Water Based Flexo InksStreaks, score lines and bands down the web

Fault 6 of 20 · continued

Streaks, score lines and bands down the web

CHECK, IN THIS ORDER

Map the defect before touching anything: measure how far across the web it sits and whether it repeats at the plate cylinder circumference. A line at a fixed cross-web position is blade or roll; a band repeating at the cylinder repeat is ghosting.
With the press stopped and isolated, run a fingernail or a plastic scraper along the blade edge to find flats, nicks and trapped debris, and read the blade hours against the change interval.
Check blade angle and pressure against the chamber specification, and reset to the lightest pressure that wipes clean.
Inspect the anilox at 100x along the line position, and run a straight edge or a light across the roll to find a score.
Inspect the chamber end seals for wear, hardening and leakage, and look for ink tracking at the web edge.

THEN CHANGE

Change the blade, and change it as a scheduled item rather than when a line appears. Reset to the lightest wiping pressure afterwards.
Clean the chamber out fully, not just the blade edge, and keep circulation running through every stop so no ink dries in it.
Replace worn end seals as a pair and fit them wet.
A scored anilox has to come out. It can sometimes be re-engraved; it cannot be cleaned better.
For ghosting, meter the station for the lightest element rather than the heaviest: come down in volume, raise the screen, and recover solid density with pigment strength. Where the design allows, separate the heavy solid onto its own plate or move it around the cylinder so it does not sit one repeat above a critical tone.

CONFIRM IT IS FIXED

A 1000 metre check run with the line gone at 10x across the full web width, or, for ghosting, the light band no longer measurable on the densitometer at three positions around the cylinder repeat. Blade hours and filter changes logged against the job.

THE TRAP

Adding blade pressure to make a streak go away. It hides the line for a few hundred metres, then wears a flat into the new blade and starts scoring the ceramic, which turns a consumable fault into a roll replacement.

Water Based Flexo InksStreaks, score lines and bands down the web (continued)

Fault 7 of 20

Ink dries in the anilox and in the circuit at every stoppage

WHAT YOU SEE

After a stop of a few minutes the print comes back weak and mottled, and the anilox has to be washed before the job will run again. On UniWet Glacier the same thing happens faster and the deposit is harder to remove. After an overnight or weekend stop the damage is not in the roll at all but in the pumps, hoses, filters and chamber body.

WHAT IT LOOKS LIKE

CAUSES, MOST LIKELY FIRST

The anilox was left standing in contact with air with no circulationA thin film in the cell has a very high surface-to-volume ratio, so the water goes quickly and the resin is left in the cell.
pH already low when the press stoppedA low-pH ink has lost its resolubility, so the dried film in the cell cannot be re-wetted by the fresh ink when the press restarts.
A self-cross-linking grade left standingUniWet Glacier is formulated with a self-cross-linkable resin system, and once that network has formed in a cell or a hose it does not come out with water.
The circuit not cleaned at shutdownPumps, hoses, filter housings, chamber bodies and the tray hold far more ink than the roll does, and they dry from every air interface inward. Dried resin in a hose sheds into the next run as grit and blinds filters; dried ink in a diaphragm pump costs the pump.
Dryer set-back drying the roll from outsideHot air reaching the anilox during a stop dries the cells from the surface down.

Water Based Flexo InksInk dries in the anilox and in the circuit at every stoppage

Fault 7 of 20 · continued

Ink dries in the anilox and in the circuit at every stoppage

CHECK, IN THIS ORDER

Inspect the cells at 100x immediately after a stop and again after washing, and record which cells are still carrying deposit.
Measure pH at the moment of the stop, not after the restart.
Check whether the ink is a self-cross-linking grade before choosing the stop procedure; the grade sheet says so.
Check that the dryer cuts back or diverts when the press stops.
Time the actual stops on the job and see whether they are two minutes or twenty.

THEN CHANGE

Write a stop rule into the job: on a self-cross-linking grade such as UniWet Glacier, either idle the anilox in ink with circulation running or clean it immediately, with no third option.
Keep circulation running through every short stop so the cells, the chamber and the hoses stay wet.
Write a shutdown rule for anything longer than a meal break: return the ink to a closed container, flush the circuit through with water while the ink in it is still wet, run the flush until it comes out clean, and leave filters out and hoses drained rather than full.
Restore pH before restarting rather than after the first weak reel.
Interlock the dryer so hot air cuts back at press stop.

CONFIRM IT IS FIXED

Stop the press for the longest interval the job actually sees, restart, and reach full density within the agreed number of metres with no anilox wash and no visible cell deposit at 100x. After a shutdown, the first filter of the next run is clean at the first change.

THE TRAP

Deciding to deal with it at the end of the run. On a self-cross-linking grade, ink left in the cells over a lunch break is a chemical-clean job and can cost the roll, and ink left in the circuit over a weekend costs the pump and the hoses as well. The cheap fix is a two minute idle or a flush at the moment of the stop.

Water Based Flexo InksInk dries in the anilox and in the circuit at every stoppage (continued)

Fault 8 of 20

Dry rub and scuff fail after the run

WHAT YOU SEE

Print looks fine at the rewind, then marks and burnishes in the stack, on the strapping line or through cup forming. The customer's incoming test fails and the ink is blamed.

WHAT IT LOOKS LIKE

CAUSES, MOST LIKELY FIRST

Drying incomplete, with carrier still in the filmRub resistance develops as the last water and co-solvent leave and the emulsion polymer coalesces; a touch-dry film at the rewind can still be days short of its final hardness.
Tested too earlyA rub test at the rewind measures an immature film, not the product, and will fail prints that are perfectly acceptable a day later.
Film weight too high for the dryer capacityDensity chased with viscosity and impression leaves more carrier to remove than the dryer can take out at speed.
Resin-rich, high-resolubility grade chosen for a job that needs rubResolubility and rub resistance sit at opposite ends of the same binder balance.
pH run high, so the film never finished coalescingAn over-alkaline film stays redispersible for longer, and at production speed the resistance simply does not arrive.

Water Based Flexo InksDry rub and scuff fail after the run

Fault 8 of 20 · continued

Dry rub and scuff fail after the run

CHECK, IN THIS ORDER

Condition the print to ISO 187 standard atmosphere, 23 C plus or minus 1 C and 50 % plus or minus 2 % RH, and test 24 h after the run on a Sutherland rub tester to ASTM D5264, recording load, stroke count, stroke rate and receptor, and whether the test is a dry rub or a wet rub.
Measure dryer air velocity at the nozzle and at the extraction duct at production speed, probe on an extension and hands outside the guarding, and measure web temperature at the last dryer with an infra-red thermometer. Do not report the temperature set point.
Weigh the dry film on a cut area against unprinted stock on a four-place balance and compare with the 0.8 to 1.5 g/m2 band for process work on coated stock.
Measure pH and check it has been in band, not above 9.5, through the run.
Check the grade against the job requirement: high-resolubility or high-rub, and which one the order actually asked for.

THEN CHANGE

Give the print its conditioning time and retest before making any change.
Raise dryer air volume and extraction before raising dryer temperature, keeping the web below about 60 C on PE-coated stock, and reduce speed if the numbers say the capacity is not there.
Bring film weight down by returning to the specified anilox volume and screen and a kiss impression.
Move to a higher-emulsion or wax-modified grade where the pack is palletised and strapped.
Add or increase the overprint coating; on coated board with UniHot, UniCoat OPV 301 is the intended route.

CONFIRM IT IS FIXED

Sutherland rub test to ASTM D5264 at 24 h after printing, conditioned to ISO 187, at the agreed load, stroke rate and stroke count, with transfer to the receptor at or below the level agreed with the customer on their own board. Report both the transfer to the receptor and the damage to the print, and state the parameters on the report, because the acceptance limit lives in those parameters rather than in the standard number.

THE TRAP

Rubbing the print with a thumb at the rewind and condemning the ink. The film is not finished at the rewind; that test rejects good work and sends the press chasing an ink change that will not help.

Water Based Flexo InksDry rub and scuff fail after the run (continued)

Fault 9 of 20

Print washes off the cold cup

WHAT YOU SEE

The printed cold-drink cup marks or lifts where condensation runs down it, where a hand holds it, or where a condiment is wiped across it. It passed every test dry.

WHAT IT LOOKS LIKE

CAUSES, MOST LIKELY FIRST

Treatment on the PE below 38 mN/mUniCold needs polyethylene treated to at least 38 mN/m, and realistically 40 to 44 mN/m, before the film is properly held. Below that the whole film is weakly keyed and water gets under it. Measure it on the reel that ran, not on a retained sample.
Incomplete drying, so the emulsion has not coalescedWater resistance is the last property to develop; an under-dried film is still substantially redispersible.
No overprint coating where the construction needs oneCondiment and beverage resistance is often a coating property on a cup, not an ink property.
Ink over-extended or over-thinned on pressExtender and water both dilute the binder that carries the resistance.
Wrong grade for the dutyA resin-rich, high-resolubility ink is designed to be re-wetted by water, and on a cup that sweats that property is the failure. It is the most expensive move on this list and the least often the answer, which is why it comes last.

Water Based Flexo InksPrint washes off the cold cup

Fault 9 of 20 · continued

Print washes off the cold cup

CHECK, IN THIS ORDER

Measure the wetting tension on the cup stock with ASTM D2578 test inks on the reel about to run, at both edges and the centre, and again on the retained reel if there is a dispute.
Run a wet rub test after 24 h conditioning to ISO 187 at 23 C and 50 % RH, and a controlled soak or condensation test agreed with the customer.
Check the dryer air volume and dwell at the running speed, and the web temperature at the last dryer.
Check the shift log for extender and water additions.
Confirm the grade on the drum is the UniCold grade specified for PE-coated cups and not a general paper grade.

THEN CHANGE

Restore treatment: run a reel that measures 38 mN/m or above, preferably 40 to 44 mN/m, or bring the corona treater back into specification before printing again. Do not push treatment above about 44 mN/m.
Increase drying dwell or reduce speed until the film is genuinely finished at the rewind.
Apply the specified overprint coating at the specified coating weight.
Stop extending on press; change the shade in the ink room against a drawdown standard.
Move to the UniCold grade intended for PE-coated cups and board tableware where the four checks above are clear and the duty genuinely needs it.

CONFIRM IT IS FIXED

Conditioned 24 h, the print survives the agreed wet rub and condensation test on the customer's own cup stock with no transfer above the agreed level, and a defined tape pull on the printed PE-coated area removes no more than the agreed percentage of ink.

THE TRAP

Treating this as an ink strength or adhesion fault and adding a stronger ink or a promoter. The usual real causes are treatment below 38 mN/m and a film that never finished drying, and neither is corrected by anything in the ink can.

Water Based Flexo InksPrint washes off the cold cup (continued)

Fault 10 of 20

Ink beads or fisheyes on PE-coated cup stock

WHAT YOU SEE

The ink pulls away from the substrate into islands and threads, solids look reticulated, and reverses break up. It is worse at the reel edges or at the start of a reel.

WHAT IT LOOKS LIKE

CAUSES, MOST LIKELY FIRST

Surface energy below the ink's wetting requirementA formulated water-based flexo ink has a surface tension of about 28 to 35 mN/m and needs the substrate to sit roughly 7 to 10 mN/m above it to spread reliably. Untreated polyethylene is about 30 to 31 mN/m, which is why 38 mN/m is the bare working minimum and 40 to 44 mN/m is where water-based inks actually wet PE without edge and start-of-reel breakup. Solvent inks at 22 to 26 mN/m tolerate marginal treatment; water-based inks do not.
Treatment decayed in storage or applied unevenly across the webCorona treatment falls back over weeks and does so unevenly, so the edges or the outer wraps read differently from the middle.
Over-treatment above about 44 mN/mTreating far above that builds a low-molecular-weight oxidised layer on the polyethylene that is itself weakly bound to the bulk. Adhesion falls while the dyne reading rises, so an operator fighting a beading fault by raising treatment can make the pack worse while every measurement says it is getting better.
Silicone or slip additive migrating to the surface of the PESlip agent blooming from the extrusion coating gives a low-energy, contaminated surface that repels the ink locally.
Defoamer over-dosed in the inkExcess silicone in the ink itself repels the next ink down and reads as a substrate problem.

Water Based Flexo InksInk beads or fisheyes on PE-coated cup stock

Fault 10 of 20 · continued

Ink beads or fisheyes on PE-coated cup stock

CHECK, IN THIS ORDER

Measure wetting tension with ASTM D2578 test inks across the web, at both edges and the centre, on the reel about to run, and record the figure rather than a pass or fail.
Compare the reel's treatment date and storage time against the supplier's stated retention.
Cut a sample from the reel and take it away from the press. With the press stopped, away from dryers and any ignition source, in ventilated air and wearing nitrile gloves and eye protection, wipe the sample with isopropanol on a lint-free cloth, let it flash off fully, then draw down or print the sample and compare. If the defect goes, the surface was contaminated. Isopropanol has a flash point around 12 C: never apply it to a moving web or inside a dryer zone, and put solvent-wetted cloths in a closed metal bin.
Check the ink's own defoamer history in the shift log.
Trace air blowers and dryer air back to the compressor and check the filters and traps for oil carry-over.

THEN CHANGE

Re-treat in line into the 40 to 44 mN/m band, or reject the reel and run one that measures. Set an upper limit on the treater as well as a lower one; more is not better past about 44 mN/m.
Where slip bloom is the cause, take it up with the substrate supplier; it is a material issue, not an ink issue.
Replace ink that has been over-dosed with defoamer rather than trying to correct it.
Fix the air system: service filters and traps so no oil reaches the web.
Where treatment cannot be raised inside that band, a water-based primer keyed to the film is the route, applied in line.

CONFIRM IT IS FIXED

Wetting tension measures 38 mN/m or above, and no higher than about 44 mN/m, across the full web width on the reel in the press, and a 500 metre run gives continuous, unbroken solids and clean reverses at 10x.

THE TRAP

Thinning the ink with water to make it flow out. It lowers the ink's viscosity but not the substrate's surface energy, so the ink beads just as badly on a weaker, wetter film, and now the density is short as well.

Water Based Flexo InksInk beads or fisheyes on PE-coated cup stock (continued)

Fault 11 of 20

Mottle, poor hold-out and flute marking on kraft liner

WHAT YOU SEE

Solids on brown kraft or test liner look cloudy and uneven, colour looks weak and dead rather than light, and the pattern follows the fibre and the sizing rather than the print. On corrugated post-print there may also be print voids over the flute tips at speed, a striped pattern following the flutes, or a smear at the trailing edge of the plate.

WHAT IT LOOKS LIKE

CAUSES, MOST LIKELY FIRST

Uneven absorbency across the linerBasis weight, sizing and moisture vary within and between liner reels, so the vehicle penetrates at different rates and leaves different amounts of pigment at the surface.
Poor hold-out from the grade or from over-thinningA thin, low-solids ink sinks. Pigment carried into the fibre does not contribute colour.
Too much film weight from too high an aniloxA heavier wet film penetrates deeper on absorbent liner, so more ink can give less colour.
Board moisture out of balance after corrugatingWarm, dry board straight off the corrugator drinks ink; board conditioned overnight does not, so the first boxes of a shift look different from the last.
Washboarding, skip-out over the flute tips and flute crushThe liner is only supported at the flute tips, so contact pressure varies tip to valley. Too little impression skips the valleys; too much crushes the flutes, which prints a striped mottle and takes measurable box compression strength out of the finished case. The crush is permanent and is a structural failure, not a print failure.

Water Based Flexo InksMottle, poor hold-out and flute marking on kraft liner

Fault 11 of 20 · continued

Mottle, poor hold-out and flute marking on kraft liner

CHECK, IN THIS ORDER

Take a wetting or absorbency check on the liner, and compare reels or bundles across the job.
Draw down the same ink on the job liner and on a coated stock; if the coated stock is clean, the fault is substrate absorbency, not ink.
Measure the anilox volume and screen for the station and compare against 6 to 9 BCM at 140 to 200 lpi for UniCraft solids on corrugated.
Measure board temperature and moisture coming to the printer, and check how long it has been off the corrugator.
Look across the sheet at a low angle for washboarding, measure caliper before and after the print station to find crush, and inspect the trailing edge of the image for drag.

THEN CHANGE

Run the grade built for the substrate: UniCraft is formulated to hold pigment at the liner surface rather than to flood it.
Come down in anilox volume and recover density through pigment strength rather than film.
Stop thinning: hold viscosity at the top of the 18 to 25 s band for absorbent liner.
Let the board condition before printing, and keep board from one corrugator run together through the job.
Set impression to the lightest setting that gives full solids across the flute valleys, and measure caliper loss to prove the flutes are not being crushed to get it.

CONFIRM IT IS FIXED

Solids on the job liner read within the agreed density tolerance at three positions across the web and hold across the reels, with no visible mottle at normal viewing distance on the pack as it will be seen, no skip-out over the flute valleys at 10x, and caliper loss at the print station inside the agreed limit.

THE TRAP

Opening up the anilox to fix mottle. The heavier film sinks further into the fibre, so mottle stays, density does not move, and the drying load and washboarding both get worse. The same reflex applied to impression crushes the flutes and takes strength out of a box that has to survive a stack.

Water Based Flexo InksMottle, poor hold-out and flute marking on kraft liner (continued)

Fault 12 of 20

Second colour rejects the first, wet trap fails

WHAT YOU SEE

The down-web colour crawls, breaks up or refuses to lie over the colour printed before it, worst where the first colour is a heavy solid and best in the light tones.

WHAT IT LOOKS LIKE

CAUSES, MOST LIKELY FIRST

First-down colour not dry enough at the next stationA wet, mobile film is not a surface the next ink can wet, so the second colour slides on it instead of laying on it.
First-down colour over-dried into a closed, water-resistant filmThe opposite error: a fully coalesced emulsion film has a low surface energy and the next water-based ink will not wet it.
Too much film weight on the first stationA heavy first-down solid cannot be dried between stations at speed, so every trap problem gets worse as the solid gets heavier.
Second colour heavier in body than the firstIn water-based flexo, trap is governed mainly by the dry state and surface energy of the first-down film at the second station, with a secondary contribution from ink body: a second colour with more body than the first is more likely to disturb it at the nip. Decreasing viscosity down the press is a sound working convention, but it is the inter-station dryer and the first-down film weight that will actually move this fault, not the viscosity ladder.
Silicone contamination from over-dosed defoamer in the first colourA repellent surface will not accept the next ink anywhere.

Water Based Flexo InksSecond colour rejects the first, wet trap fails

Fault 12 of 20 · continued

Second colour rejects the first, wet trap fails

CHECK, IN THIS ORDER

Judge the state of the first-down colour without touching the running web: read its temperature with an infra-red thermometer aimed from outside the guards. Then stop the press, isolate it and inch the web clear of the nips before making any touch or tape check on the stationary web between the two stations. Record the press speed at which it was running, because the answer is speed-dependent. Never touch a moving web and never apply tape to one.
Measure the viscosity of all stations on the same named 4 mm cup at 25 C and write them down in press order.
Measure between-colour dryer air volume and temperature at each station.
Measure the film weight of the first-down colour on a cut area.
Check the defoamer history of the first-down colour.

THEN CHANGE

Adjust the between-colour dryer on the first station towards enough dry, not maximum dry, and use air volume rather than temperature to tune it.
Reduce the first-down film weight by coming down an anilox step.
Set viscosity in decreasing order down the press and re-measure with one cup, as a working convention rather than as the cure.
Reorder the colours where the design allows, putting the heavy solid later.
Replace any station's ink that has been over-dosed with defoamer.

CONFIRM IT IS FIXED

A 500 metre run shows continuous second-down colour over the heaviest first-down solid at 10x, with density of both colours on target and no lift visible on a tape check of the trapped area taken from a cut sample.

THE TRAP

Turning the between-colour dryer up. Past a point it closes the first film into a water-resistant surface that the next ink rejects harder, so the fault gets worse in exactly the direction the operator believes is right.

Water Based Flexo InksSecond colour rejects the first, wet trap fails (continued)

Fault 13 of 20

Blocking in the reel or set-off in the stack

WHAT YOU SEE

Reels that stick face to back when unwound, printed board that lifts ink onto the reverse of the sheet above it, or cup blanks that pick when separated at the forming machine.

WHAT IT LOOKS LIKE

CAUSES, MOST LIKELY FIRST

Carrier still in the film at the rewindAn immature water-based film softens under pressure and heat, and a tight reel supplies both.
Web or stack wound warmHeat from the dryers is stored in the reel and keeps the film soft for hours after the run.
Winding tension too highPressure is the second half of blocking; the same film that survives a loose reel blocks in a tight one.
Film weight above what the dryer can finishMore carrier to remove in the same dwell means less of it has left by the rewind.
On cup stock, the reverse of the web is the food-contact faceSet-off in a rewound cup-stock reel does not transfer ink onto a printed back, it transfers ink onto the PE surface that will hold the drink. That is a contamination event on the food-contact side and a potential migration route, not a print defect, and it is treated as a stop rather than as a quality deviation.

Water Based Flexo InksBlocking in the reel or set-off in the stack

Fault 13 of 20 · continued

Blocking in the reel or set-off in the stack

CHECK, IN THIS ORDER

Measure web temperature at the rewind with an infra-red thermometer and record it against the reel that blocked, and again on the outside of the made reel before it is wrapped.
On cup stock, unwind a metre from a suspect reel and inspect the unprinted food-contact face under a loupe and at a low angle for any ink transfer at all. There is no acceptable level; any transfer quarantines the reel.
Run a block resistance test on conditioned samples: printed face to reverse under a known load at a known temperature and time, agreed with the customer.
Check winding tension and taper against the standard for the substrate.
Weigh the dry film on a cut area, and record pressroom and warehouse temperature and RH over the period the reels stood.

THEN CHANGE

Add chill capacity, or a chill roll, before the rewind and get the web temperature down.
Reduce winding tension and taper it off through the reel.
Reduce film weight to the specified anilox and take density from pigment strength.
Let reels or stacks stand loose and cool before palletising and wrapping.
Where any transfer is found on a food-contact face, stop, quarantine the affected reels, notify the customer, and do not release on the basis that the mark is faint. Establish the drying and winding conditions before restarting.

CONFIRM IT IS FIXED

Web temperature at the rewind at or below 35 C, and at or below 30 C on PE-coated or heat-sealable stock, measured with an infra-red thermometer on the web just before the reel and again on the outside of the made reel before wrapping. No ink transfer of any kind on the food-contact face of a cup-stock reel. The agreed block test on conditioned samples passes at the load, temperature and dwell the customer's distribution actually imposes.

THE TRAP

Winding tighter to keep the reel stable, or wrapping and palletising a warm reel to clear the floor. Both add the pressure and the retained heat that turn an almost-dry film into a blocked one, and on cup stock they put ink on the face the drink will touch.

Water Based Flexo InksBlocking in the reel or set-off in the stack (continued)

Fault 14 of 20

Cups will not form, blanks slip in the mandrel

WHAT YOU SEE

Cup blanks slide at the forming station, seams are misplaced or fail, and the forming machine loses rate. The print looks perfect.

WHAT IT LOOKS LIKE

CAUSES, MOST LIKELY FIRST

Coefficient of friction too low on the printed surfaceCup forming pulls on the printed face; UniHot is formulated to give a high coefficient of friction so the blank is held, and anything that lowers it costs the seam.
Slip additive or wax raised to fix a rub complaintSlip and rub resistance are traded; an addition made last week for scuffing shows up this week as a forming failure.
An overprint coating chosen for gloss and slipA slippery OPV over a high-friction ink hands the forming machine a surface it cannot grip.
Substrate change, coated for uncoated or a different PE weightCoefficient of friction is a property of the printed surface as a whole, and it depends as much on the board and coating as on the ink.
Ink film still soft and transferring to the mandrelAn under-dried film behaves unpredictably at the forming station and builds up on tooling.

Water Based Flexo InksCups will not form, blanks slip in the mandrel

Fault 14 of 20 · continued

Cups will not form, blanks slip in the mandrel

CHECK, IN THIS ORDER

Measure coefficient of friction on conditioned printed samples with a method written for paper and board: TAPPI T 815 inclined plane for static CoF, or a horizontal-plane sled method for static and kinetic together. ASTM D1894 is written for plastic film and sheeting, so use it only where the mating face is a plastic film and record it as adapted from a plastics method.
Whichever method is used, state the sled mass, the sled facing, the test speed, the mating surface (print to reverse, print to PE, print to mandrel steel) and the conditioning. A CoF number without those is not comparable to anything.
Compare against a retained sample of board that ran well, measured the same way.
Check the shift and formulation log for slip or wax additions, and check whether the OPV and its coating weight changed.
Confirm drying is complete and the board and its coating are the specified ones for this job.

THEN CHANGE

Return to the UniHot grade and coating combination that was qualified for the forming line.
Remove the slip addition made for the rub complaint and solve rub with an overprint coating instead.
Change the OPV for one with the friction the forming machine needs, or reduce its coating weight.
Confirm drying is complete so the film is not transferring to tooling.
Requalify CoF on the customer's own board whenever the board or coating changes.

CONFIRM IT IS FIXED

Static and kinetic CoF on conditioned print, measured by the stated method with the sled mass, facing, speed and mating surface recorded, fall in the band agreed with the cup maker, and the forming line runs at rate for an agreed number of blanks with no seam rejects.

THE TRAP

Asking for a higher-slip ink because the blanks are marking in transit. Slip and forming grip are the same property read in opposite directions, and raising slip to cure scuffing is how a good-running cup job is lost.

Water Based Flexo InksCups will not form, blanks slip in the mandrel (continued)

Fault 15 of 20

Bar codes and fine reverses fill in

WHAT YOU SEE

Bar widths grow, the scanner grade falls, fine reverse type closes up, and the problem is worse on the solid-heavy side of the design and worse as the run goes on.

WHAT IT LOOKS LIKE

CAUSES, MOST LIKELY FIRST

Plate filling from falling pHInk drying in the reverses and on the plate land bridges the gap; the same mechanism that makes the print dirty closes the code.
Impression set too heavyOver-impression spreads the bar at the nip, and on corrugated it also crushes the flute and widens the contact area.
Anilox volume too high for the code areaToo much film has nowhere to go but sideways, and bar gain is the result. A code metered at the solids volume is a code printed at a handicap.
Ink spreading into an absorbent linerWicking along the fibre grows the bar after the nip, which is why codes print better on coated liner at the same settings.
Symbol printed in picket-fence orientation, with the bars across the direction of web travelImpression spread and plate distortion act along the web. Bars set across that direction are widened by it; bars set along it are merely lengthened, which costs nothing.

Water Based Flexo InksBar codes and fine reverses fill in

Fault 15 of 20 · continued

Bar codes and fine reverses fill in

CHECK, IN THIS ORDER

Verify the code with a verifier and record the grade and the bar width deviation, not just pass or fail.
Measure pH and check the plate under a loupe for dried ink in the reverses.
Check impression back to kiss and reprint the code area.
Measure the anilox volume and screen serving that station and compare against 2 to 4 BCM at 300 to 360 lpi for code and fine line work on corrugated, not against the solids band.
Check the symbol orientation on the plate against the direction of web travel.

THEN CHANGE

Correct pH and clean the plate so the reverses are open before judging anything else.
Orient the symbol in ladder orientation, with the bars running parallel to the direction of web travel, so that impression spread and plate distortion lengthen the bars instead of widening them. It is free at origination and it is the first thing to change on a repeat.
Back off to kiss impression and re-verify.
Drop to a finer, lower-volume anilox for the station carrying the code, and recover solid density elsewhere with pigment strength.
Move the code to the coated or white-top liner face where the design allows, and set the bar width reduction at origination for the gain measured on this substrate and this anilox rather than to a house default.

CONFIRM IT IS FIXED

The code verifies at the grade the customer specifies, on the job substrate, at running speed, at the start, middle and end of a reel or a pallet.

THE TRAP

Reducing viscosity so the ink prints thinner in the code area. It lightens the whole job, costs density on the solids, and leaves the bar gain where it was, because the gain is orientation, impression, pH and anilox, not ink body.

Water Based Flexo InksBar codes and fine reverses fill in (continued)

Fault 16 of 20

Shade drifts through the run and between batches

WHAT YOU SEE

The first pallet matches the standard, the last one does not, and a repeat order three months later needs a different correction again to reach the same target.

WHAT IT LOOKS LIKE

CAUSES, MOST LIKELY FIRST

pH and viscosity drifting through the runBoth change transfer and film weight, and colour follows film weight; most within-run drift is process, not pigment.
Ink temperature rising through the shiftA hotter tray reads thinner on the cup, so the operator corrects to a number that no longer means the same film weight.
Anilox wear across the life of a jobCell volume falls slowly and continuously, so a job printed on a new roll and repeated on a worn one will not match.
Substrate colour and absorbency changed between deliveriesKraft and test liner shade varies reel to reel, and the brown subtracts from every colour printed on it; on a white-top or coated liner the same ink reads differently again.
On-press extending and shade correction that never reaches the ink roomUntracked additions make a run repeatable only for the operator who made them.

Water Based Flexo InksShade drifts through the run and between batches

Fault 16 of 20 · continued

Shade drifts through the run and between batches

CHECK, IN THIS ORDER

Read the solid with a spectrophotometer against the agreed standard in the agreed illuminant and geometry, and record delta E rather than judging by eye.
Log pH, viscosity with the cup named, and ink temperature on one line at each check and plot them against the colour readings.
Measure the anilox volume and screen at the start of the job and record both in the job record.
Read the unprinted substrate on the spectrophotometer as well as the print, and keep the reading with the job.
Pull the ink room record for the batch and compare the drawdown standard with the retained one.

THEN CHANGE

Hold the process: pH in band, viscosity read at 25 C, temperature stable within plus or minus 2 C, and most of the drift disappears.
Do all shade correction in the ink room against a drawdown on the job substrate, and record every addition.
Fix the anilox volume and screen as part of the job specification, so a repeat runs on the same figures.
Record the substrate reading with the job so that a substrate change is identified before the press is blamed.
For label work, use the supported PMS matching route on UniFine HD rather than correcting by eye at the press.

CONFIRM IT IS FIXED

Delta E against the agreed standard within the agreed tolerance, measured on the job substrate at start, middle and end of the run, with pH, viscosity, temperature and anilox volume all logged inside their bands over the same period.

THE TRAP

Correcting the shade at the press by adding a touch of another colour. It moves the target, is never fully recorded, and guarantees that the repeat order starts from a standard nobody can reproduce.

Water Based Flexo InksShade drifts through the run and between batches (continued)

Fault 17 of 20

Runs well in winter, will not dry in the monsoon

WHAT YOU SEE

The same job, the same ink and the same settings that ran at full speed in January now set off, block and fail rub, the register will not hold across the sheet on light papers, and the only thing anybody has changed is the calendar.

WHAT IT LOOKS LIKE

CAUSES, MOST LIKELY FIRST

High ambient humidity lengthening the drying curveWater leaves the film into air that is already close to saturated, so the same dryer removes less carrier in the same dwell; nothing in the ink has changed.
Dryer extraction not sized for the seasonAir volume matters more than air temperature, and a dryer working against humid, poorly extracted air is working against itself.
Film weight that was marginal in the dry seasonA job that had no drying margin in winter has none to give when the curve lengthens.
Paper and board responding dimensionally to the water in the inkCellulose swells across the fibre when it takes up water and shrinks again as it dries, so a heavy water laydown on a light paper such as UniWet Hydra gives cockle, curl and fan-out, and colour-to-colour register drifts across the web and through the run. On corrugated post-print the same water goes onto one face only, so the board warps and bows towards the printed side. Register drift on paper is a water-laydown fault before it is a tension fault, and it gets worse as the pressroom RH rises.
Loaded dryer filters and fouled ductingExtraction capacity has usually fallen over months, and the wet season is when the loss finally shows.

Water Based Flexo InksRuns well in winter, will not dry in the monsoon

Fault 17 of 20 · continued

Runs well in winter, will not dry in the monsoon

CHECK, IN THIS ORDER

Log pressroom temperature and RH at web height hourly with a thermohygrometer and compare with the dry-season record for the same job.
Measure nozzle air velocity and extraction duct velocity with an anemometer at production speed, probe extended and hands outside the guarding.
Measure web temperature at the last dryer with an infra-red thermometer.
Weigh the dry film on a cut area and compare with the dry-season record.
Measure register drift across the web and through the run, and check it against the total water laydown rather than reaching for tension first. On corrugated, measure warp on a flat table at the stacker.

THEN CHANGE

Raise air volume and extraction before raising dryer temperature.
Service filters and ducting so extraction is back at its design figure.
Reduce film weight where the design allows and take density from the anilox and pigment strength; on light papers this is the register fix as well as the drying fix.
Condition paper and board to the pressroom before printing, and keep reels wrapped until they are wanted.
Accept and plan a genuine speed reduction on coated stock and film for the high-RH months rather than running and reworking.

CONFIRM IT IS FIXED

At the reduced or restored speed, the agreed rub and block tests pass on conditioned samples, register holds inside tolerance across the web at start, middle and end, and web temperature and film weight are back at their dry-season figures.

THE TRAP

Turning the dryer temperature up. Hotter saturated air with no extraction does not remove more water, it skins the surface, traps carrier underneath and produces a print that is touch-dry and blocks in the reel.

Water Based Flexo InksRuns well in winter, will not dry in the monsoon (continued)

Fault 18 of 20

Ink is gritty or seeded out of the drum

WHAT YOU SEE

Fine grit on a drawdown bar, specks in solids, filters blinding quickly, and a drum that will not stir back to a smooth ink. Sometimes the specks are hard and dark rather than resinous.

WHAT IT LOOKS LIKE

CAUSES, MOST LIKELY FIRST

The ink has been frozenA frozen acrylic emulsion coagulates irreversibly; warming the drum recovers nothing and the ink cannot be used.
Dried skin stirred back in from a part-used drum or an open trayPrecipitated resin and dried ink particles will not redissolve at working pH and go straight through to the print.
Returned ink put back without filteringTray ink collects fibre, board dust and dried ink; all of it goes back into the drum with the return.
Corrosion product from the ink circuitWater-based ink rusts steel trays, chamber bodies, pumps and press frames, and the amine and ammonia in it attack copper, brass and aluminium fittings, anilox end journals and seals. Rust and corrosion salts print as hard dark specks and blind filters, and they are routinely diagnosed as gritty ink from the drum when the drum is perfectly good.
Contamination by an incompatible chemistryUV ink, solvent ink or a different binder in the same container or hose shocks the dispersion out.

Water Based Flexo InksInk is gritty or seeded out of the drum

Fault 18 of 20 · continued

Ink is gritty or seeded out of the drum

CHECK, IN THIS ORDER

Draw down on the job substrate with a bar and look at the film at 10x before putting anything on the press.
Filter a litre through a 150 micron mesh and look at what is retained: resinous lumps point at the ink, hard dark specks that are magnetic or that leave a rust mark point at the circuit.
Run the same drawdown from a sealed drum sample that has never been to the press. If the drum is clean and the tray is not, the fault is downstream of the drum.
Inspect the tray, chamber body, pump internals, filter housing and fittings for rust, pitting and white or green corrosion product.
Check the drum's storage history for frost exposure and its date of manufacture against the 12 month window, and check pH and viscosity against the batch record on the label.

THEN CHANGE

Quarantine anything that has been frozen; it cannot be recovered and must not be blended into good ink.
Filter all returned ink before it goes back into a drum, and check pH and viscosity before re-use.
Never stir skin back in; scrape it out and discard it.
Replace corroded steel trays and fittings with stainless steel or a coated equivalent, and keep copper, brass and bare aluminium out of a water-based circuit. Clean, dry and protect the circuit at shutdown rather than leaving it wet and standing.
Dedicate containers, hoses and pumps to water-based ink and clean them through between chemistries.

CONFIRM IT IS FIXED

A drawdown on the job substrate is clean at 10x, a 150 micron filter passes the ink without blinding over a full shift, and pH and viscosity match the batch record on the label.

THE TRAP

Warming a frosted drum and stirring hard to bring it back. It looks like it has recovered for as long as it is being stirred, and it puts coagulated resin through the anilox, the plate and the job. The second trap is condemning drum after drum when the grit is coming out of a rusting tray.

Water Based Flexo InksInk is gritty or seeded out of the drum (continued)

Fault 19 of 20

Ink has gone sour, drums gassing

WHAT YOU SEE

A sour, cheesy or sharply ammoniacal smell when a drum or a return container is opened, drum ends bulging or a lid that releases pressure when it is cracked, viscosity that has collapsed rather than risen, pH that has moved with it, slime or a stringy deposit in hoses, filters and the return, and colour that has gone dull. Worst in returns that have stood over a hot weekend.

WHAT IT LOOKS LIKE

CAUSES, MOST LIKELY FIRST

Bacterial and fungal growth in the inkA water-based ink is a nutrient system: water, acrylic resin, surfactant and often a small amount of biocide that is consumed over time. Once the population is established, the organisms break down thickener and resin, so viscosity falls away instead of rising, and the metabolic gas bulges the container.
Topping up with unclean waterWater from a yard tap, a standing drum or a hose left lying is the commonest route in. Correction water for a water-based press should be clean and, where the plant allows, deionised.
Long-standing returns and part-used drumsInk that has been to the press carries fibre, dust and organisms from the tray. Returned to a warm store and left for weeks, it is an incubator and it seeds the next drum it is blended into.
Dirty circulation: hoses, pumps, filters and trays not cleaned throughResidue left in a hose or a filter housing is where the growth lives between jobs, so a spotless drum of ink is contaminated within a shift of being put into a dirty circuit.
Warm storageGrowth rate roughly follows temperature, so a store that sits at 35 C or above through a Greater Noida summer turns a marginal drum into a spoiled one in days.

Water Based Flexo InksInk has gone sour, drums gassing

Fault 19 of 20 · continued

Ink has gone sour, drums gassing

CHECK, IN THIS ORDER

Smell it, and do the smell test deliberately: crack the lid away from your face in a ventilated area and waft, never put your face over a drum that may be under pressure. A bulging drum is a pressure hazard and is opened slowly, at arm's length, with eye protection.
Record pH and viscosity together. Spoilage shows as viscosity falling with a pH move, which is the opposite signature to the amine-loss fault that dominates this guide.
Look inside hoses, filter housings and the return line for slime, stringing or a film on the wall.
Check the container history: date of manufacture, how long it has been open, whether it is a return, where it has been stored and at what temperature.
Check what water has been used for correction and top-up, and where the hose that delivers it has been lying.

THEN CHANGE

Quarantine and dispose of spoiled ink. It cannot be corrected, and biocide added after the fact kills the organisms without undoing the resin and thickener they have already broken down or the odour they have left. Do not blend it into good ink to use it up.
Clean the whole circuit, not just the drum: hoses, pump, filter housings, chamber and tray, with a cleaner that is rated for the job, then flush and dry. Dry is the point; growth needs standing water.
Use clean water for correction, deionised where the plant allows, from a dedicated line and a hose that is not left lying on the floor.
Put a rule on returns: filter, label with the date, store cool, and use first. Returns that have stood past the agreed period are disposed of, not blended.
Bring the store inside the stated 5 to 35 C window and keep drums closed. Do not ask for additional biocide as a substitute for a clean circuit; biocide levels are set in the formulation and are a regulated part of it.

CONFIRM IT IS FIXED

Fresh ink in a cleaned circuit holds pH and viscosity over a full shift with no odour change, filters do not blind, and a drum from the same batch opened a week later is at the batch-record pH and viscosity with no pressure behind the lid.

THE TRAP

Trying to rescue a sour drum by adding stabiliser to bring the pH back and biocide to stop the smell. The pH comes back and the viscosity does not, the odour survives into the printed pack where it becomes a taint complaint from the filler, and the drum seeds every container and hose it touches on the way to being used up.

Water Based Flexo InksInk has gone sour, drums gassing (continued)

Fault 20 of 20

Print lifts off metallised and foil paper

WHAT YOU SEE

On ice-cream cone sleeves the print tape-tests clean off the metallised face, or it survives the tape and then scuffs off through wrapping, the freezer and handling.

WHAT IT LOOKS LIKE

CAUSES, MOST LIKELY FIRST

Wrong grade for a metallised or foil faceA general paper ink is built for an absorbent surface; on a closed metallised surface there is nowhere for the carrier to go and nothing for the film to key into. UniWet Glacier is the grade designed for metallised and foil paper.
The self-cross-linking network not developedUniWet Glacier is formulated with a self-cross-linkable resin system intended to develop freeze, fat and oil resistance once the film has fully dried and conditioned. Whether the finished sleeve meets the freeze, fat and oil requirement is a property of the whole construction, so it is qualified on the customer's own metallised paper, with their overprint coating, after their forming and wrapping line, against limits agreed in writing.
Surface contamination or release coating on the metallised faceSlip, lacquer or release from the metallising or laminating step gives a low-energy face that the ink cannot wet.
Film too heavy for a non-absorbent faceAll the carrier must leave through the surface, so a heavy film skins and holds carrier under it, and a film with carrier under it has no adhesion.
Silicone from over-dosed defoamerRepellence on a closed surface reads exactly like an adhesion failure and is often diagnosed as one.

Water Based Flexo InksPrint lifts off metallised and foil paper

Fault 20 of 20 · continued

Print lifts off metallised and foil paper

CHECK, IN THIS ORDER

Confirm the grade is UniWet Glacier and not a general paper grade such as UniWet Hydra.
Run a defined tape pull on conditioned print 24 h after the run, on the customer's own metallised or foil paper: state the tape, the application pressure, the dwell, the peel angle and rate, and report the percentage of ink removed from a marked area. Do not report an ISO 2409 cross-cut classification on a bare one micron ink film over vacuum-metallised paper, because the blade cuts through the ink, through the metallised layer and into the paper, so what gets classified is the failure of the substrate structure and not the adhesion of the ink.
Use ISO 2409 cross-cut, with the cut spacing chosen for the film thickness and substrate hardness as the standard directs, only where the print carries an overprint coating thick enough for the classification to mean something, and record that the cut is testing the whole construction.
Measure the wetting tension of the metallised face with ASTM D2578 test inks.
Test after the real cold chain: condition, freeze, and test freeze, fat and oil resistance as the product demands, on the customer's own construction.

THEN CHANGE

Run the grade intended for the substrate and the duty.
Reduce film weight and lengthen drying dwell so the film is finished before the rewind.
Give the print its conditioning time before judging adhesion, and retest at 24 h.
Take a contaminated or release-coated face back to the substrate supplier; a primer keyed to the face is the alternative where the material cannot change.
Replace any ink over-dosed with defoamer rather than correcting it.

CONFIRM IT IS FIXED

The agreed tape pull on conditioned print at 24 h removes no more than the agreed percentage of ink on the customer's own metallised paper, and the sleeve survives the agreed freeze, fat and oil resistance tests and the forming and wrapping line at rate.

THE TRAP

Raising the film weight to get better coverage and, with it, better adhesion. On a non-absorbent metallised face the heavier film simply traps carrier under a skin, so coverage improves and adhesion gets worse.

Water Based Flexo InksPrint lifts off metallised and foil paper (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
Viscosity rising through the run	pH in the tray, calibrated electrode, at running temperature	Add the supplied pH stabiliser with gloves, goggles and extraction, dosed into the circulating stream, then re-measure. No water yet.
Slow drying, permanent foam, ammonia smell, plates swelling	pH against the 9.5 upper action limit, on a freshly calibrated electrode	Stop dosing stabiliser and let the ink come back down; never acidify a press ink.
Plate filling, print dirty	pH, then the plate shoulder and fine reverses under a loupe	Correct pH and stop dryer set-back onto the print station, judged with a streamer on a guard, not a hand.
Weak colour at correct viscosity	pH, then tray ink against drum ink on a drawdown, then cells at 100x	Change to a clean roll of the specified volume and screen; do not add impression.
Pinholes in solids	Foam head in the tray, where the return discharges, and what is at the centre of the void at 10x	Drop pump speed and put the return below the ink surface.
Lines down the web or a repeating light band	Is it at a fixed cross-web position (blade or roll) or at the cylinder repeat (ghosting)	Change the blade and clean the chamber; for a ghost, meter the station for the lightest element.
Anilox and circuit drying in at every stop	Is this a self-cross-linking grade, and was pH in band at the stop	Idle the anilox in ink or clean it immediately; keep circulation running through every stop.
Rub or scuff failing	Sutherland rub to ASTM D5264 after 24 h at 23 C and 50 % RH, not at the rewind	Raise dryer air volume and extraction before dryer temperature.

Water Based Flexo InksQuick reference

Quick reference

One page at the press

Symptom	Check this first	Change this first
Print washes off a cold cup	Wetting tension on the cup stock with ASTM D2578 test inks	Run stock at 38 mN/m or above, preferably 40 to 44, before touching the ink.
Ink beading or fisheyes on film	Wetting tension across the web on the reel about to run	Treat into the 40 to 44 mN/m band or reject the reel. Do not thin the ink and do not treat past 44.
Mottle, skip-out or flute marking on kraft liner	Drawdown of the same ink on coated stock alongside the liner, and caliper across the print station	Come down an anilox step and hold viscosity at the top of the band; do not add impression.
Wet trap failure, second colour crawling	First-down film temperature by infra-red from outside the guards, then station viscosities on one cup	Tune the between-colour dryer down, not up, and reduce the first-down film weight.
Blocking in the reel	Web temperature at the rewind, and the food-contact face of a cup-stock reel under a loupe	Chill the web below 35 C, or 30 C on PE-coated stock, and reduce winding tension.
Cup blanks slipping at forming	CoF on conditioned print by a paper and board method, with sled, speed and mating face recorded	Remove the slip or wax addition and take rub resistance from the OPV.
Bar code grade falling	Verifier grade and bar width deviation, symbol orientation, pH and plate condition	Turn the symbol to ladder orientation, back impression off to kiss, and drop that station to 2 to 4 BCM.
Shade drifting in the run or between repeats	Delta E on the job substrate, with pH, viscosity, temperature and anilox volume logged beside it	Hold the process and move all shade correction into the ink room.

Water Based Flexo InksQuick reference

Quick reference

One page at the press

Symptom	Check this first	Change this first
Will not dry in the monsoon, register wandering on light paper	RH at web height, nozzle and extraction air velocity at speed, and film weight	Raise air volume and extraction, cut film weight, accept a speed reduction.
Grit, specks and blinding filters	150 micron filter residue: resin lumps, or hard dark specks and rust from the circuit	Filter returns and inspect the tray, pump and fittings before condemning the drum.
Sour smell, bulging drum, viscosity collapsed	pH and viscosity together, and the inside of the hoses and filter housing	Quarantine the ink, open bulging containers slowly at arm's length, and clean and dry the whole circuit.
Print lifting off metallised paper	Grade on the drum, then a defined tape pull on conditioned print at 24 h	Reduce film weight and lengthen dwell; do not add film to gain adhesion.

Water Based Flexo InksQuick reference

Test methods

The measurements this guide relies on

Measurement	Method	What it tells you, and the usual acceptance
Flow cup viscosity	4 mm flow cup, ISO 2431 or DIN 53211, named on every reading	The working viscosity of the running ink. The ISO 2431 4 mm cup and the DIN 53211 4 mm cup are different geometries and give different numbers, and a Zahn 2 reading is a third number, so name the cup and the temperature every time. Typical for this class: 18 to 25 s at 25 C for flexo, 15 to 20 s for gravure, with UniFine HD label inks at 17 to 21 s. This house reads the 4 mm cup at 25 C as a works method and does not convert to kinematic viscosity, because ISO 2431 declares flow cups valid only between about 20 s and 100 s; where a number below 20 s has to be controlled, use a 3 mm cup so the reading sits inside the valid window.
pH of the running ink	Calibrated glass electrode with automatic temperature compensation, two-point calibration at pH 7.00 and 10.01	The single most useful number on a water-based press. Read in the tray at running temperature, on an electrode cleaned of dried ink and stored in KCl. Target 8.2 to 9.0 for amine-stabilised grades, 8.5 to 9.2 on corrugated post-print, with 9.5 as an upper action limit. Paper strips do not resolve the 0.3 unit changes that matter.
Wetting tension	ASTM D2578, or ISO 8296 test inks	Whether the substrate will accept a water-based ink at all. Measure on the reel you are about to run, at both edges and the centre. A formulated water-based ink sits at about 28 to 35 mN/m and needs the substrate roughly 7 to 10 mN/m above it, so 38 mN/m is the bare working minimum for UniCold on PE-coated cup stock and 40 to 44 mN/m is where it actually wets. Above about 44 mN/m over-treatment builds a weakly bound oxidised layer, so the reading rises while adhesion falls.
Anilox volume and cell condition	Supplier volumetric measurement or in-house 3D interferometric check, with visual inspection at 100x	How much ink the press can actually lay down. Volume and screen are not independent and are specified as a pair, with the screen at four to five times the finest halftone ruling on the plate. Cell volume, not ink strength, sets laydown, and a roll 30 % down on volume prints as a weak ink at correct pH and viscosity. Record the measured volume and screen in the job record so a repeat runs on the same figures.
Film weight	Gravimetric, printed against unprinted on a four-place balance after conditioning	The carrier load the dryer has to remove and the ink cost of the job. Typical for this class: 0.8 to 1.5 g/m2 dry for process and line on coated stock at 3 to 4.5 BCM, 2 to 4 g/m2 dry for solids on absorbent liner at 6 to 9 BCM. Cross-check against the anilox, since dry g/m2 is approximately BCM x 1.55 x transfer efficiency x solids content x 1.05.
Rub resistance	ASTM D5264, Sutherland rub tester, conditioned to ISO 187	Scuff and marking through stacking, strapping, forming and distribution. Condition and test at 23 C plus or minus 1 C and 50 % plus or minus 2 % RH, 24 h after the run. State load (typically 2 or 4 lb), stroke count, stroke rate and receptor, and whether it is a dry rub or a wet rub, because those are different acceptance limits. Report both the transfer to the receptor and the damage to the print. A test at the rewind measures an immature film and rejects good work.
Adhesion on closed surfaces	Defined tape pull, with ISO 2409 cross-cut only where an overprint coating carries the film	Whether the film is held on a closed surface such as PE-coated cup stock or metallised paper. A flexo ink film of about one micron is too thin for a cross-cut classification to mean what it appears to mean: the blade goes through the ink, through the metallised layer and into the paper, so the classification describes the substrate structure. Use a tape pull with the tape, application pressure, dwell, peel angle and rate stated, and report the percentage of ink removed from a marked area on conditioned print at 24 h. Either way it is an interface property of the customer's own material, agreed on their substrate and not claimed generically for the ink.

Water Based Flexo InksTest methods

Test methods

The measurements this guide relies on

Measurement	Method	What it tells you, and the usual acceptance
Coefficient of friction	TAPPI T 815 inclined plane, or a horizontal-plane sled method, for printed paper and board; ASTM D1894 only where the mating face is plastic film	Static and kinetic friction of the printed surface. It governs cup forming, stacking and dispensing. ASTM D1894 is written for plastic film and sheeting, so using it on printed cup board leaves the sled mass, facing, speed and mating surface undefined for the material that matters, and those are the variables that move the answer: state all four plus the conditioning on every result. UniHot is formulated for a high coefficient of friction to help cup fabrication, and the value depends on the type and quality of the board printed as much as on the ink.
Foam collapse	Works method: 100 ml of ink in a 250 ml stoppered cylinder, shaken by hand for 30 s at about two strokes per second	A comparable number for foam shift to shift. Record the foam volume immediately after shaking and the time for the head to collapse to 10 ml, and run fresh drum ink alongside as the reference. Record the operator, because the shake is the variable.
Gloss	ISO 2813, 60 degrees	Finish on coated stock and on overprint coatings, measured on conditioned print. Useful mainly as a batch-to-batch and reel-to-reel consistency number, because absolute gloss on an absorbent liner tells you more about the liner than about the ink.
Light fastness	ISO 12040, filtered xenon arc for prints and printing inks, reported against the blue wool references of the ISO 105-B02 series	Fade resistance of the pigment in the printed film. ISO 105-B02 is the textile method; the scale it defines is used here, but the test for a print is ISO 12040. Quote the figure per colour rather than per class, because no single number covers a process set. Typical for a standard process set: BWS 7 to 8 on phthalocyanine cyan, BWS 4 to 5 on diarylide yellow and standard magenta. UniWet Hydra is measured at BWS 7 on process cyan and BWS 7 to 8 on the red-shade light-fast yellow, on the stated substrate. Quote the pigment, the scale and the substrate, not the word fast.

Water Based Flexo InksTest methods

When the press-floor fixes have not worked

What to send us

The press log for the failing run: pH, viscosity with the cup named, ink temperature and pressroom RH, on one line per check, with every water, stabiliser, defoamer and extender addition recorded against the time it was made and the reading it was made against.
The anilox specification and, more importantly, its measured volume and screen and a cell photograph at 100x for the station in question. The engraving figure on the end cap is not a measurement.
Substrate identification and a wetting tension reading taken with ASTM D2578 test inks on the actual reel or pallet that failed, plus a metre of the unprinted material from the same reel.
Printed samples from the failure, unwrapped and interleaved, together with a sample from a run that was accepted, so the two can be measured side by side rather than compared by description. For an odour or taint question, send samples sealed in clean glass jars, not in polythene, with an unprinted control from the same reel treated the same way.
The full ink and coating build for the job: every grade code, the batch numbers from the drum labels, the overprint coating and its coating weight and cure dose where it is UV, and the drum storage history including any frost exposure, any return blending and how long containers had been open.
The test that failed, the method behind it, the acceptance limit and who set it: a rub failure at the rewind and a rub failure after 24 h conditioning to ISO 187 are different problems with different answers, and a cross-cut classification on a bare ink film is not the same evidence as a defined tape pull.
What the pack has to survive downstream, stated as conditions rather than adjectives: forming line and rate, fill temperature, cold chain, condensation, fats and condiments, transit and stacking load. Adhesion, slip, seal and migration are properties of the finished pack, and we qualify them on the customer's own material and line.

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Water Based Flexo InksTechnical service