Troubleshooting guide

Water Based Gravure Inks

Fault finding for water-based gravure on paper and paper-based packaging: pH, cells, doctor blade, drying and resolubility.

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.

  • Before any work at the cylinder, the blade or the impression nip, isolate and lock off the drive, or move the press only by the guarded inching control with all guards in place and no hand in or near a nip. Where the cylinder must turn while the press stands, use the machine's slow-turn function with the guards closed, never by hand.
  • Treat the two additives an operator handles most as the hazards they are. The amine or ammonia pH stabiliser is corrosive and gives off vapour at an open tray: gloves, goggles, extraction at the mixing point, and never mixed with an acid or a hypochlorite cleaner. Cross-linkers are handled as sensitisers, the aziridine types in particular: nitrile gloves, goggles, local extraction, nothing decanted into an unlabelled container. Read the safety data sheet for both before the first addition of a shift.
  • Measure pH before viscosity, every time; on a water-based gravure unit the viscometer is usually reporting a pH problem.
  • Change one variable at a time and give the ink loop five minutes to circulate before you read anything back.
  • Take every reading in the tray at press temperature, and write the temperature next to the number on the log.
  • Before you blame the ink, prove the cylinder and the blade: measure cell depth on the cylinder in front of you and look at the blade edge under a loupe.
  • Separate what is drying from what is formulation: give the print 24 h at 23 C and 50 % RH before you judge rub, water resistance, odour or bond.
  • Adhesion, lamination bond, seal performance and odour in the pack belong to the pack and not to the ink alone, so qualify them on the customer's own material, construction and conditions.
  • Do the cheap checks first. A density read across the web, a pH reading and a flow cup take minutes; a cell depth measurement stops the press and a re-engraving is a fortnight and a five-figure decision.
Water Based Gravure InksHow to use this guide

01

The process

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

The process

What is controlled at each step

1Ink make-upand pH setStir, strain andset pH beforeviscosity; recordboth against thebatch number.HOLDpH 8.7 to 9.32Pump, trayandReturn line underthe ink surface,lowest pump speedthat keeps thetray full.HOLDFoam3Cell filland doctorCells fill, theblade wipes theland clean; theblade edge decidesthe tone.HOLDBlade pressure4Transfer attheRubber coveredroller presses theweb onto thecylinder; wherethe unit is set upfor it, ESA raisesthe attractionHOLDImpression5ImpingementdryingHigh velocity airremoves water;volume andextraction beforetemperature, andthe substrate setsthe temperatureHOLDAir volume6Chill andrewindWeb cooled beforethe reel;properties developas the lastcarrier leaves.HOLDWeb temperature
Water Based Gravure InksThe process

Control variables

What to hold, and how to measure it

VariableTargetHow it is measuredHow it drifts
pH9.0 plus or minus 0.3, that is 8.7 to 9.3, for amine-stabilised paper gravure grades, and the same window for film grades unless the grade sheet says otherwise. Dose stabiliser when the reading reaches 8.7. Treat 8.5 as the point at which the ink is already out of control, because that is where the alkali-soluble resin begins to come out of solution.Calibrated glass electrode standing in the running ink in the tray, at press temperature. Buffer at pH 7 and pH 10 at the start of every shift, at the temperature of the ink, and record the slope where the meter reports it. Paper strips are not a measurement.Falls steadily through the run as amine evaporates from the open tray and the dryer draught, typically 0.1 to 0.3 per hour on an uncovered tray in a warm pressroom. Nothing on the viscometer announces it; the first sign is a longer flow cup time.
Working viscosity15 to 20 s on a DIN 4 mm cup (DIN 53211) at 25 C, typical for this class; the grade sheet number for the job always winsDIN 4 mm cup to DIN 53211, with a thermometer in the tray and the temperature written next to the reading. Name the cup on the log. The ISO 2431 4 mm flow cup is a different geometry with a different orifice and body, its reference temperature is 23 C rather than 25 C, and it gives a different efflux time for the same ink, so the two readings are not interchangeable and a target quoted for one cup does not apply to the other.Rises with amine loss and with water loss from an open tray, and falls as pump work and dryer heat warm the ink. A 5 C rise takes roughly 2 s off the cup, about 0.4 s per degree, which is enough to hide a real thickening for most of a shift.
Ink temperature22 to 28 C, and within 2 C of the temperature at which the cup reading was set. Outside that, re-read the cup at the new temperature rather than correcting the ink.Digital thermometer in the tray, not in the drum standing on the floor. Write the temperature next to every cup reading so the correction is arithmetic and not a guess.Climbs through the shift from pump work and radiated dryer heat, then drops overnight. A press that sets viscosity cold in the morning and never re-reads it hot will thin the ink twice over. At roughly 0.4 s per degree, a 2 C tolerance is already most of the 1 s tolerance held on the cup.
Engraving geometryEngrave for release and resolubility, not by a fixed percentage taken off a solvent cylinder. Widen the cell opening with a larger stylus angle, typically 130 to 140 degrees against 120 degrees for solvent work, and reduce depth to suit, then prove the volume on a print trial against measured solid density on the paper the job will run. Higher ink solids allows some of the volume reduction, but it is not the governing reason: a deep, narrow cell is the one that skins in and the one a water-based ink will not empty.Cell depth gauge or calibrated microscope on the cylinder land, taken at a solid, a mid-tone and a highlight step, with the stylus angle and screen taken from the cylinder record. The final depth comes from the proof, not from an arithmetic rule.Cells lose volume over the life of the cylinder as the chrome and the land wear, and highlights lose volume further as dried ink plugs them. Both show as a weak print at correct viscosity and correct pH, so measure cell depth on a high-mileage cylinder before changing anything in the ink.
Doctor blade pressure and angleThe lowest pressure that wipes the land clean, blade set at 55 to 65 degrees to the tangent, oscillation runningThe pressure gauge on the blade holder where one is fitted; otherwise the count of hairlines on the print is the instrument. Isolate and lock off the drive before any work at the blade.Operators raise it to chase a line. Water is a poor boundary lubricant compared with solvent, so the extra load goes straight into the edge: it wears a flat within the hour, the wipe degrades, and the lines multiply rather than clear.
Substrate surface energy, film work40 to 44 mN/m at the moment of printing on the reel about to run, wetting and holding for 2 s. Treat 38 mN/m as the reject limit rather than as the bottom of the window; water-based inks need more treatment than solvent inks for the same wet-out.Test inks to ISO 8296 or dyne pens on the reel you are about to run, wetting tension to ASTM D2578. Not the supplier's certificate from the day it was made.Decays on the reel with time, heat and warehouse storage, and slip additive blooms to the surface as the reel ages. A reel that measured 42 mN/m three months ago can be at 34 mN/m today.
Dryer air velocity and extractionAir temperature is set by the heat tolerance of the substrate, not by the ink: typically 60 to 90 C on paper, and 50 to 75 C on PE and BOPP film with the web temperature held below the film's distortion limit. Set air volume and extraction first and use temperature last, and control to the measured web temperature at the dryer exit rather than to the panel setting. Nozzle velocity to the machine's own commissioning figure, recorded at commissioning and re-measured quarterly; impingement tunnels commonly sit in the region of 20 to 40 m/s at the nozzle face, but the commissioning number for the machine is the target, not the class figure. Exhaust air held well clear of saturation, with the extraction damper position logged.Hot wire anemometer at the nozzle face, compared against the commissioning record. Hygrometer or wet bulb in the exhaust duct. Infra-red thermometer on the web at the dryer exit.Filters load and nozzles block over weeks. Velocity falls while the temperature display stays exactly where it was set, so the panel says nothing has changed while the drying capacity has halved. Falling velocity at an unchanged temperature reading is the fault to look for.
Water Based Gravure InksControl variables

Control variables

What to hold, and how to measure it

VariableTargetHow it is measuredHow it drifts
Web temperature at dryer exit40 to 55 C on paper, measured before the chill roll; on film, below the distortion limit of the film in useInfra-red thermometer aimed at the printed side at the last dryer exit, at the speed the job actually runs.Falls as speed rises and as coverage increases. It is the earliest honest sign that the tunnel is out of capacity, well before the rub test fails.
Non-volatile matter and film weightTypically 35 to 45 % non-volatile by weight for this class; the grade sheet figure for the specific product always wins. Dry film typically 1.5 to 3.0 g/m2 on paper.Non-volatile matter to ASTM D2369 or an equivalent written in-house method: 1 to 2 g spread evenly in a tared dish, 60 min at 110 C, cooled in a desiccator and weighed, run in duplicate, with the method written down so every reading is comparable. Thirty minutes at 105 C does not take a water-based acrylic to constant weight and the figure reads differently depending on how the sample was spread. For printed samples, weigh, dry 60 min at 105 C, cool in a desiccator and re-weigh, and quote residual carrier as a percentage of the dry ink film rather than as a bare weight. Reel weight difference or print-and-weigh for film weight.Non-volatile matter rises in an open tray as water leaves, and falls a step with every water addition. Two shifts of both, and the ink in the tray is no longer the ink on the data sheet. The comparison that matters on press is the tray sample against the unopened drum of the same batch.
Foam in the trayNo standing foam on the tray surface, and no air in the return stream50 ml shaken 30 s in a graduated cylinder; the foam head should collapse within about 30 s.Builds through the shift as the ink level drops, the return line breaks the surface and the surfactant balance shifts. It starves the cells before it is visible as a print fault.
Make-up water and microbial controlDeionised or softened water only, from a clean dedicated line; biocide dosed to the supplied instruction and recorded; no ink left standing in the loop between jobs or over a shutdown; drums stored below 25 C and not below 5 CConductivity meter and a hardness test on the water line that actually feeds the press. Smell check on the tray and on the drum headspace at the start of every shift, and a dated biocide addition record. Handle biocide to its safety data sheet: gloves, goggles and extraction at the mixing point.Hardness climbs when a softener regenerates late or a hose is taken off the treated line. Biocide is consumed over time and by every contamination event, so an ink that has been open and topped up for weeks has none left and will go sour over the first long shutdown.
Water Based Gravure InksControl variables

The mechanism

The pH loop that dries ink in the cell

1. The amine leaves,hour by hourOpen tray, long returnline and dryer draughtstrip the amine.pH falls from 9.3 towards8.5 with nothing added orchanged.Typically 0.1 to 0.3 pHper hour on an uncoveredtray.Nothing on the viscometersays this is happeningyet.2. The resin comes outof solutionThe alkali-soluble resinis soluble only while pHholds it up.Below about 8.5 it startsto separate and the inkthickens.A part-dried film in thecell no longer re-wets infresh ink.Resolubility is lostbefore water resistance isgained.3. What the press floorseesFlow cup time climbs;transfer and solid densityfall away.Highlights speckle, solidsmottle, cells screen inafter a stop.Hairlines multiply asdried fines return underthe blade.All four get read as fourseparate faults.4. The two correctionsWater: cup time drops forten minutes, pH fallsanother step.Stabiliser: pH back to 8.7to 9.3, viscosity followsit down.Circulate five minutes,then re-measure beforejudging.Correct with water onlyafter pH is right, in 1 to2 % steps.

The single mechanism behind most water-based gravure faults. Amine loss, not solids gain, is usually what moves the flow cup, and the correction that reads well at the cup is the one that makes it worse. Measure pH in the running ink with a calibrated electrode at press temperature, and cross-check the electrode before you act on the number.

Water Based Gravure InksThe mechanism

02  |  20 faults

Faults

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

Fault 1 of 20

Viscosity climbs through the run

WHAT YOU SEE

The flow cup reads longer every hour on the same ink, transfer falls off and density drifts down. The operator adds water, the cup comes back for a while, and by the second shift the ink is thin in the cup but printing weak and dirty.

WHAT IT LOOKS LIKE

IN SPECIFICATION5 mmWEAK DIRTY TRANSFER5 mmCompare the solid with the approved reel; the weak panel prints pale and dirty at the same cup.

    CAUSES, MOST LIKELY FIRST

  1. Amine loss, pH falling towards and below about 8.5The alkali-soluble acrylic resin is only in solution while the amine holds the pH up; as pH falls towards 8.5 the resin begins to come out of solution and the ink thickens, which the viscometer reports as a viscosity fault.
  2. Water evaporating from an open tray and a long recirculation loopNon-volatile matter rises, and at 40 % solids a one point gain moves viscosity much further than the same gain would at 30 %.
  3. Dried skin and fines returning to the tray from the blade, the chamber and the doctor tray endsPartly dried ink redissolves incompletely and carries gel particles that raise the working viscosity and block filters.
  4. Returned ink from an earlier job tipped in without checking itReturns are usually low in pH and high in solids, so they push the whole batch down the same curve faster.
  5. A batch that has gone microbially sour, or a heavy defoamer over-doseBoth are uncommon causes of a steady climb and both are ruled in or out by other evidence. A sour batch usually takes pH and viscosity down together with a smell, not up. A heavy defoamer over-dose shows first as craters, pinholes and foam that no longer breaks; only where it has flocculated the dispersion will the cup time move, and a flow cup measures efflux at low, uncontrolled shear and does not report shear thickening in any useful way. Check pH, non-volatile matter and filter residue first, and read the dosing log only to rule it in or out.
Water Based Gravure InksViscosity climbs through the run

Fault 1 of 20  ·  continued

Viscosity climbs through the run

CHECK, IN THIS ORDER

  • Measure pH with a calibrated glass electrode standing in the running ink in the tray, at press temperature, buffered at 7 and 10 that shift, and cross-check with a second electrode before the batch is condemned.
  • Measure the flow cup, DIN 4 mm cup to DIN 53211 at 25 C, with a thermometer in the tray, and write the temperature and the cup type beside the reading.
  • Determine non-volatile matter to ASTM D2369, 1 to 2 g for 60 min at 110 C, cooled in a desiccator, and compare against the unopened drum from the same batch.
  • Filter 500 ml through a 100 um mesh and look at what the mesh holds on a white tile.
  • Read back the addition log: water, stabiliser, defoamer, biocide and returns, with quantities and times.

THEN CHANGE

  • Dose the supplied pH stabiliser, circulate for five minutes, then re-measure pH before touching anything else. Handle the stabiliser as corrosive: gloves, goggles and extraction at the mixing point, never mixed with an acid or a hypochlorite cleaner.
  • Correct viscosity with clean deionised water only after pH is back in window, in steps of 1 to 2 % by volume with a five minute circulation between steps.
  • Fit a tray cover and drop the free surface area; take the return line below the ink surface to stop splash and evaporation.
  • Strain the tray through 100 um and fit an in-line filter if one is not already there.
  • Set the automatic viscosity controller to be interlocked with a pH reading every 30 min, rather than running on viscosity alone.

CONFIRM IT IS FIXED

pH holds 8.7 to 9.3 over two hours of running and the DIN 4 mm cup time at 25 C stays within 1 s of the set point, with solid density on the scanning densitometer within 0.05 of the approved reel.

THE TRAP

Adding water to bring the cup time down. It corrects the reading for about ten minutes, dilutes the amine further and takes the pH down another step, so the next thickening arrives sooner and deeper than the last. By the fourth correction the ink is both dilute and out of solution.
Water Based Gravure InksViscosity climbs through the run (continued)

Fault 2 of 20

Cells screen in after a stop

WHAT YOU SEE

The press stands for ten minutes for a splice or a reel change. On restart the image comes back starved, mid-tones mottled and solids patchy, and it clears slowly over several hundred metres or does not clear at all.

WHAT IT LOOKS LIKE

CLEAN OPEN CELLS5 mmCELLS SCREENED IN5 mmLook at the mid-tones after a stop; screened cells print starved and patchy, not an even tone.

    CAUSES, MOST LIKELY FIRST

  1. pH has fallen, so the resin no longer resolubilisesResolubility is the ability of a part-dried film in the cell to be re-wetted by fresh ink; it depends on the alkali-soluble fraction staying soluble, which depends on pH. Below about 8.5 it is already lost.
  2. Cylinder stopped clear of the ink in the panCells left in air skin in minutes; cells left wetted do not. It costs nothing to check and it is corrected in seconds, which is why it is looked at before anything that needs an engraver.
  3. Dryer set-back blowing hot air over the cylinder while the press standsAn over-pressured tunnel pushes air back down the web path and dries ink in exactly the place it must never dry.
  4. A water-resistant, emulsion-rich grade used where a resoluble grade is neededEmulsion polymer gives water resistance once dry and by design does not redissolve, so the grade that survives a wet pack is the grade that punishes a stop.
  5. Cells engraved too deep or too narrow for a water-based inkA deep, narrow cell holds a larger reservoir behind a smaller opening, so the skin that forms is thicker than fresh ink can re-dissolve on the first revolutions. This is listed last because it is the only cause here that cannot be fixed on the shift.
Water Based Gravure InksCells screen in after a stop

Fault 2 of 20  ·  continued

Cells screen in after a stop

CHECK, IN THIS ORDER

  • Measure pH first, in the tray, with a calibrated electrode.
  • Check that the ink level in the pan covers the cells when the press is standing.
  • With the press stopped and the drive locked off, check from outside the guarding whether air is moving over the cylinder from the dryer, using a light tell-tale taped to a rod rather than a hand held at the nip.
  • Read the grade off the tin and confirm whether it is a resoluble or a water-resistant grade for this job.
  • Measure cell depth and stylus angle at the tones that fail, with a cell depth gauge or calibrated microscope, once the cheap checks have cleared.

THEN CHANGE

  • Restore pH to 8.7 to 9.3 with the supplied stabiliser before anything else.
  • Keep the cylinder wetted whenever the press stands: use the machine's slow-turn function with the guards closed, never by hand, and never with the drive live and a hand at the pan.
  • Close the dryer damper on a stop and stop the set-back.
  • Wash the cylinder with warm water or the supplied cleaner, then blow the cells out with clean, oil-free air at a reduced pressure, not more than about 2 bar (30 psi) at the nozzle, through a regulated blow gun, with goggles and gloves on, the extraction running, and the air directed away from yourself and from anyone else on the deck. Never direct compressed air at skin.
  • Move to a grade with a higher alkali-soluble resin fraction if the job allows the water resistance to come from an overprint varnish instead.

CONFIRM IT IS FIXED

After a deliberate ten minute stop with the dryer at running settings, the print returns to full density and clean mid-tones within 50 m, repeated three times on the same job.

THE TRAP

Winding on impression to force the tone back. Impression does not empty a dried cell; it flattens the covering, broadens the dot everywhere else, scores the blade and marks the paper, and the mottle is still there when you back it off.
Water Based Gravure InksCells screen in after a stop (continued)

Fault 3 of 20

Hairlines down the reel, and blade life that collapses to an hour

WHAT YOU SEE

Sharp fine lines running in the web direction through solids and mid-tones, one or two at first and more as the run goes on, shifting slightly across the web when blade oscillation is running. Blade life falls from a shift to an hour, the wipe degrades quickly after each change, and grazing light shows fine scoring on the cylinder land.

WHAT IT LOOKS LIKE

CLEAN EVEN WIPE5 mmBLADE HAIRLINES5 mmLook for sharp fine lines running with the web through solids and mid-tones.

    CAUSES, MOST LIKELY FIRST

  1. Grit under the blade: dried ink skin, a corrosion particle, a pigment agglomerate or paper dust, with no in-line filtration to take it outA single particle lodges at the blade edge and holds a channel open, so that strip of the cylinder land is never wiped. Unfiltered ink puts the same particle back under the blade every revolution, and each pass cuts the edge further.
  2. Blade pressure set far higher than the wipe needsWater is a poor boundary lubricant compared with solvent, so excess pressure at the edge goes straight into wear, and it drives any particle harder into the edge. The pressure that was added to clear one line creates the next three.
  3. Blade edge nicked, or worn to a flatA flat edge rides on the land instead of wiping it and leaves a ridge of ink that prints as a line.
  4. Abrasive pigments at high loading, particularly opaque whitesTitanium dioxide at white loadings is genuinely abrasive against a steel edge, so white decks wear blades faster than colour decks by design and should be judged against their own standard.
  5. Scoring in the cylinder chrome, or chrome hardness and surface finish out of specificationA damaged land cannot be wiped by any blade and the line does not move when the blade is changed. A soft or rough chrome surface abrades the blade and then takes the damage itself.
Water Based Gravure InksHairlines down the reel, and blade life that collapses to an hour

Fault 3 of 20  ·  continued

Hairlines down the reel, and blade life that collapses to an hour

CHECK, IN THIS ORDER

  • Filter a litre of the running ink through a 100 um mesh and look at the residue on a white tile under a loupe.
  • With the drive isolated and locked off, take the blade out and inspect the edge under a loupe or a bench microscope for nicks and flats, and record what the wear looks like at every change.
  • Read the blade holder pressure and the set angle against the machine standard, and confirm oscillation is running at the full stroke setting.
  • Light the cylinder at a grazing angle and look for scoring on the land.
  • Check whether the line stays in the same place across a blade change; if it does, the cylinder is at fault, not the blade.

THEN CHANGE

  • Fit a new blade and clean the holder out completely, including the backing blade and the end seals, with the drive isolated and locked off.
  • Fit or replace the in-line filter at 100 to 150 um and strain the tray, and fix the source of the grit, whether that is corrosion, skinning or dust.
  • Reduce blade pressure to the minimum that wipes the land clean, and re-set the angle to 55 to 65 degrees.
  • Wet the blade and the cylinder before every start rather than running the blade dry onto the land.
  • Fit lamella blades where the machine is set up for them and keep the oscillation running.

CONFIRM IT IS FIXED

Line-free print over 2000 m with a fresh blade, the filter in place and pressure at the reduced setting, checked on the solid patch of the control strip, with blade life back to the press standard for that deck and no new scoring on the land under grazing light after a full shift.

THE TRAP

Increasing blade pressure to wipe the line away, or fitting a harder blade to make it last. Pressure works for a minute, then the particle scores the edge into a flat and the flat leaves its own line. A harder edge that is still loaded too heavily transfers the wear to the chrome, so a blade problem becomes a re-chrome.
Water Based Gravure InksHairlines down the reel, and blade life that collapses to an hour (continued)

Fault 4 of 20

Comets, specks and grit, and filters that block early

WHAT YOU SEE

Tear-shaped drags trailing out of dense areas in the web direction, sharp at the head and fading at the tail, coming and going and worse as speed rises. Dark specks and grit in solids and light tints. Filters that used to run a shift block in an hour, and the residue on the mesh is dark and hard rather than soft ink.

WHAT IT LOOKS LIKE

CLEAN SOLID5 mmCOMETS AND DRAGS5 mmLook for tear shaped drags trailing out of solids in the web direction, sharp at the head.

    CAUSES, MOST LIKELY FIRST

  1. Dried ink skin from the tray, the pipe walls and the pump bodyWater-based ink skins wherever it stands still, and the skin breaks up into exactly the particle size that holds ink out of the wipe as a comet and prints as a speck.
  2. Corrosion in mild steel pans, pipework and fittingsAn alkaline water-based ink attacks unlined steel, and the rust it lifts prints as brown and black specks, cuts the blade edge and blocks filters fast.
  3. Hard make-up waterCalcium and magnesium salts shock the dispersion locally and precipitate, giving grit that was not in the ink when it was delivered.
  4. Contamination of the loop from a previous job: solvent ink, an incompatible binder system, a cationic additive or wash-up residue left in the pump and pipeworkIncompatible systems flocculate on contact, and the flocculate behaves as grit. It presents as specks, a shade shift and a sudden viscosity change that no pH correction will cure.
  5. A batch that has been through a freeze-thaw cycle in winter storage or transportWater-based dispersions coagulate irreversibly once frozen. The drum arrives as a gritty, filter-blocking material that looks like a manufacturing fault and cannot be stirred or strained back into service.
Water Based Gravure InksComets, specks and grit, and filters that block early

Fault 4 of 20  ·  continued

Comets, specks and grit, and filters that block early

CHECK, IN THIS ORDER

  • Filter a litre of running ink through 100 um and inspect the residue on a white tile under a loupe: dark hard grit means corrosion, soft lumps mean skin, stringy or slimy residue means the batch has gone sour.
  • Test the make-up water for hardness and conductivity; deionised or softened water should be the standard.
  • Inspect the pan, pipework, fittings and pump internals for rust and for material that is not stainless or plastic, with the drive isolated and locked off.
  • Check the delivery record on any drum that has travelled in frost, and check the storage temperature history; a load that has been below 5 C is a receiving check, not a press problem.
  • Check the wash-up routine, what ran in the loop before this job, and whether ink has been left standing between jobs.

THEN CHANGE

  • Run an in-line filter at 100 to 150 um and change it on a schedule rather than when it blocks.
  • Use deionised or softened water for all make-up and thinning.
  • Replace mild steel parts of the ink path with stainless steel or plastic, and clean and passivate what is left.
  • Wash the loop out at the end of every job, including the pump body and the dead legs, and never run a water-based ink into a loop that has not been cleared of the previous system.
  • Set a minimum storage and transport temperature of 5 C, and quarantine and check any load that has travelled in frost before it goes to the press; a frozen batch is scrapped, not reworked.

CONFIRM IT IS FIXED

A filter that runs a full shift without blocking, no comets on the solid patch over 1000 m at full running speed, and print free of specks over 2000 m on a light tint, which is where specks show first.

THE TRAP

Taking the filter out because it keeps blocking, or raising viscosity to weigh a comet tail down. Without the filter the grit goes under the blade instead of into the mesh, and a filter problem becomes hairlines, a worn blade and a scored cylinder. A thicker ink wipes worse, holds the particle longer and makes the tail longer, and it costs transfer in the highlights at the same time.
Water Based Gravure InksComets, specks and grit, and filters that block early (continued)

Fault 5 of 20

Missing dots and snowflaking in highlights

WHAT YOU SEE

Fine highlight tones break up into white specks, vignettes go grainy where they should fade smoothly, and the effect is worst on the smoothest coated stock and at the top of the speed range.

WHAT IT LOOKS LIKE

FULL HIGHLIGHT DOTS5 mmSNOWFLAKING HIGHLIGHTS5 mmLook into the highlights with a loupe; dots go missing and the tone breaks into white specks.

    CAUSES, MOST LIKELY FIRST

  1. Ink too high in viscosity, so it will not release from a small cellRelease from a fine cell depends on the ink splitting; a thick ink stays in the cell and the dot is simply missing.
  2. Highlight cells partly dried in, or engraved too narrowA skin in a small cell removes most of its volume, and highlights are where the loss shows first. A narrow cell opening makes both the skinning and the release worse.
  3. Impression roller hardened with ageA covering that has gone hard does not conform to the cylinder and the paper, so the contact that pulls the dot out is never made.
  4. Electrostatic assist off, set wrong, or not effective on this inkESA does not pull ink out of the cell. It raises the electrostatic attraction between the ink in the cell and the substrate so that contact is made and the ink bridges at the nip, and highlights benefit most. Its effectiveness depends on the resistivity of the ink, and water-based inks are far more conductive than solvent inks, so settings do not transfer from a solvent job and some units cannot use ESA effectively with water-based ink at all.
  5. Substrate too smooth and too low in absorbencyA hard, closed coated surface gives the ink nothing to key to at the moment of split.
Water Based Gravure InksMissing dots and snowflaking in highlights

Fault 5 of 20  ·  continued

Missing dots and snowflaking in highlights

CHECK, IN THIS ORDER

  • Flow cup, DIN 4 mm cup to DIN 53211, at press temperature with a thermometer in the tray, after pH has been read.
  • Print the step wedge and read from 3 % up with a densitometer rather than judging by eye.
  • Measure the impression roller with a Shore A durometer and compare against the specification for the covering.
  • Inspect highlight cells for skin using the guarded inching control, with the guards in place and no hand in or near the nip.
  • Confirm with the press builder what the ESA unit is set up for with water-based ink, and check the set voltage or current against the machine standard for this ink type, not against the solvent standard.

THEN CHANGE

  • Correct pH first, then bring viscosity down in 1 s steps and re-run the wedge after each step.
  • Wash and blow out the cylinder to clear any skinned highlight cells, using oil-free air at not more than about 2 bar (30 psi) through a regulated blow gun, goggles and gloves on, extraction running, air directed away from people.
  • Replace a hardened impression roller with a covering at the specified durometer.
  • Set the electrostatic assist to the machine standard for water-based ink where the unit supports it, and do not treat switching ESA on as the cure until the press builder has confirmed the unit works with a conductive ink. Before any work on the ESA roller or its covering, switch off and lock out the ESA supply, wait the manufacturer's discharge time and earth the roller with the supplied earthing stick before touching it; only trained personnel reset ESA voltage.
  • If the design will carry it, re-engrave the highlight range with a wider cell opening, 130 to 140 degree stylus, for the same tone value.

CONFIRM IT IS FIXED

The step wedge prints continuously from 3 % upward at full running speed with no white specks, on three consecutive reels.

THE TRAP

Winding on impression to fill the highlights. It never cures a release problem; it flattens the covering, causes dot gain and haloing in the mid-tones, and marks the paper, so a highlight fault becomes a full tone-curve fault.
Water Based Gravure InksMissing dots and snowflaking in highlights (continued)

Fault 6 of 20

Solids weak and mottled on paper

WHAT YOU SEE

Density below the approved reel on large solids, with a cloudy uneven look across the web. Worst on uncoated and recycled papers, and the mottle moves with the paper reel rather than with the press setting.

WHAT IT LOOKS LIKE

EVEN SOLID5 mmWEAK MOTTLED SOLID5 mmLook across a large solid for cloudy uneven laydown; density should match the approved reel.

    CAUSES, MOST LIKELY FIRST

  1. Substrate absorbency and sizing varying across and along the reelThis is the cause that moves with the reel, which is what the symptom describes. Uneven sizing pulls carrier and pigment in at different rates, which reads as cloud in a flat solid, and on absorbent paper part of the carrier goes into the sheet and takes pigment below the surface with it.
  2. Viscosity run too low after repeated water additionsDilution takes pigment out of every cell, so the tone falls everywhere and shows first on solids.
  3. pH low, so transfer from the cell is poorAn ink whose resin is coming out of solution splits badly at the nip and leaves ink behind in the cell.
  4. Ink strength wrong for the coverage and the stockA grade built for coated stock does not hold out on a rough absorbent liner and the pigment sinks below the surface.
  5. Cell volume insufficient for the ink and the stock, or lost to wearOn absorbent paper the ink needs volume in the cell to leave enough pigment at the surface. This is listed last because cell depth cannot change from reel to reel, and measuring it means stopping the press and getting a gauge on a cylinder.
Water Based Gravure InksSolids weak and mottled on paper

Fault 6 of 20  ·  continued

Solids weak and mottled on paper

CHECK, IN THIS ORDER

  • Read solid density with a densitometer at five points across the web, not one.
  • Flow cup at press temperature, and pH with a calibrated electrode.
  • Compare a hand drawdown of fresh ink from the drum against a drawdown of tray ink on the same paper.
  • Compare the failing paper reel against the reel that ran well: grammage, smoothness and water absorbency by the Cobb test.
  • Measure cell depth on the cylinder at the failing solid only when the checks above have cleared the ink and the paper.

THEN CHANGE

  • Restore pH and then set viscosity to the grade sheet rather than to habit.
  • Take the failing paper reel out of the run and qualify it separately with the supplier.
  • Move to a higher pigment strength grade built to hold out on absorbent stock.
  • Print a primer or a sealing coat on very absorbent liners so the colour stays at the surface.
  • Re-engrave deeper for the solids, or move the solid to a deeper cell channel on the cylinder, once the ink and the paper have been cleared.

CONFIRM IT IS FIXED

Solid density within 0.05 of the approved reel at five points across the web and holding over 2000 m, on the paper lot the job will actually run.

THE TRAP

Thinning the ink and running faster to get the solid to level out. More water means less pigment per cell, and higher speed means less dwell in the dryer, so the solid goes weaker and the rub resistance goes with it.
Water Based Gravure InksSolids weak and mottled on paper (continued)

Fault 7 of 20

Colour drifts weaker through the run

WHAT YOU SEE

The first reels match the approved print and the tenth does not. Density has crept down, the shade has moved slightly, and nothing obvious has been changed on the press.

WHAT IT LOOKS LIKE

ON STANDARD5 mmSTRENGTH AND SHADE DRIFT5 mmCompare the tenth reel with the approved print; shade and strength should stay inside tolerance.

    CAUSES, MOST LIKELY FIRST

  1. Cumulative water additions through the shiftEvery correction of a pH-driven viscosity rise removes pigment from the ink, and the losses add up quietly.
  2. Pigment settling in an unstirred drum or a dead leg in the trayThe ink feeding the cylinder becomes progressively leaner than the ink that was approved.
  3. Make-up ink drawn from a different manufacturing batchBatch to batch strength tolerance is real, and topping up a running tray with a second batch shifts the mixture.
  4. Cylinder cells losing volume over a long runThe chrome and the land wear and the cells lose volume, which reads as a weaker ink at correct viscosity and correct pH.
  5. Substrate change at a reel spliceWhiteness, shade and absorbency of the paper move the printed colour without the ink changing at all.
Water Based Gravure InksColour drifts weaker through the run

Fault 7 of 20  ·  continued

Colour drifts weaker through the run

CHECK, IN THIS ORDER

  • Trend solid density reel by reel on the densitometer instead of judging reel against reel by eye.
  • Read the print with a spectrophotometer against the retained target and record dE.
  • Check the drum stirrer is running and draw a sample from the bottom of the drum as well as the top.
  • Read back the ink addition log and the batch numbers used since the approved reel.
  • Measure cell depth on a cylinder that has high mileage.

THEN CHANGE

  • Stop correcting with water: fix pH, then let viscosity settle, then judge strength.
  • Keep drums stirred and blend a new batch into the tray gradually rather than in one addition.
  • Hold one batch for the whole job where the run length allows it.
  • Return to the approved standard by adding fresh unthinned ink rather than by adding tint on press.
  • Re-engrave or change the cylinder when measured volume loss explains the density loss.

CONFIRM IT IS FIXED

Density and dE against the retained target hold reel to reel for the rest of the job, with the addition log showing no water added other than after a pH correction.

THE TRAP

Correcting shade on press with additions of a strong base colour. It moves the shade back for one reel and leaves the job with an ink that no longer matches any batch on the shelf, so the next repeat starts from nowhere.
Water Based Gravure InksColour drifts weaker through the run (continued)

Fault 8 of 20

Print rubs off the finished reel

WHAT YOU SEE

Colour comes off on a thumb at the rewind, reels mark each other in transit, printed bags scuff when they are filled. Often it looks fine at the machine and fails at the customer.

WHAT IT LOOKS LIKE

PASSES RUB TEST5 mmCOLOUR RUBS OFF5 mmTwist a thumb on the print and look for colour on the skin; the bad panel marks and lifts.

    CAUSES, MOST LIKELY FIRST

  1. Drying incomplete: the film is touch-dry but still holds carrierWater-based films harden as the last of the water and amine leave, so rub resistance develops after the reel is wound, not at the dryer exit.
  2. Air volume and extraction below what the coverage needsSaturated tunnel air will not accept more water however hot it is, so the temperature display looks correct while drying has stopped.
  3. Film weight too heavy for the tunnel at that speedWater has a latent heat of vaporisation of about 2260 kJ/kg, roughly six times that of ethyl acetate at about 366 kJ/kg, so the same wet film weight costs several times the drying energy it would on a solvent press and a heavier film costs capacity in direct proportion.
  4. A resoluble, resin-rich grade being asked for handling resistanceThe resin fraction that keeps the cylinder open is the fraction that stays soft; the emulsion fraction is what resists rub.
  5. The print was tested too soonA rub test at the machine on a reel wound ten minutes ago is testing the dryer, not the ink.
Water Based Gravure InksPrint rubs off the finished reel

Fault 8 of 20  ·  continued

Print rubs off the finished reel

CHECK, IN THIS ORDER

  • Sutherland rub tester, 4 lb (1.8 kg) weight, 50 strokes, printed face against the specified receptor stock, sample and receptor conditioned 24 h at 23 C and 50 % RH to ISO 187, inspected for visible transfer. Run the same test with a damp receptor for wet rub.
  • Infra-red thermometer on the web at the last dryer exit, at the speed the fault appears.
  • Hot wire anemometer at the dryer nozzles against the commissioning figure, and a hygrometer or wet bulb in the exhaust duct.
  • Weigh a cut sample, dry 60 min at 105 C, cool in a desiccator and re-weigh, and quote residual carrier as a percentage of the dry ink film.
  • Check the grade on the tin against the end use the customer described.

THEN CHANGE

  • Raise air volume and extraction before you raise air temperature, and clean the dryer filters.
  • Reduce film weight by re-engraving shallower with a wider cell opening, or reduce speed until the web temperature at the exit is back in window.
  • Move to a grade with a higher emulsion polymer fraction, accepting that it will be less forgiving of a stop.
  • Apply an aqueous overprint varnish over heavy coverage rather than trying to get everything from the ink.
  • Give the reel dwell and retest at 24 h before judging the ink.

CONFIRM IT IS FIXED

50 dry Sutherland rubs at 1.8 kg with no visible transfer to the receptor, tested 24 h after printing and conditioned at 23 C and 50 % RH, on the reel that will go to the customer, with the acceptance agreed with the customer for the end use rather than fixed at 50 rubs for every job.

THE TRAP

Turning the dryer temperature up and leaving the extraction where it was. Air that is already near saturation cannot take more water; the paper gets hotter, cockles and goes brittle, and the print is no drier than it was.
Water Based Gravure InksPrint rubs off the finished reel (continued)

Fault 9 of 20

Reel blocks and picks in the rewind

WHAT YOU SEE

Print transfers to the reverse of the web, layers stick or tear when the reel is unwound at the converter, and it is worst near the core and in hot weather.

WHAT IT LOOKS LIKE

CLEAN REVERSE5 mmREEL BLOCKING AND PICKING5 mmUnwind the reel and look at the reverse for transferred image; layers should part without picking.

    CAUSES, MOST LIKELY FIRST

  1. The reel is wound hotA film that is still above about 40 C at the core continues to soften under nip pressure for hours, and nip pressure in a reel is continuous.
  2. Residual carrier in the filmWater and amine still leaving the film keep it thermoplastic and tacky, and the reel is the worst possible place for that to happen.
  3. Winding tension too high or taper set wrongInterlayer pressure at the core can be several times the pressure at the outside, which is why the core blocks first.
  4. A soft, resin-rich grade on heavy solidsThe alkali-soluble fraction that gives gloss and resolubility also gives a lower blocking resistance.
  5. No chill roll, or the chill roll not in serviceWithout it the reel stores the dryer's heat instead of losing it.
Water Based Gravure InksReel blocks and picks in the rewind

Fault 9 of 20  ·  continued

Reel blocks and picks in the rewind

CHECK, IN THIS ORDER

  • Measure reel core temperature with a probe or infra-red thermometer within a minute of the reel coming off.
  • Read the winding tension and the taper profile from the machine and compare against the standard for this grammage.
  • Run a block test: 10 cm squares, printed face to web reverse, under about 100 kPa (1 kg/cm2) for 24 h at 40 C as the routine condition, and at 50 C where the pack ships or stores warm, then peel and inspect.
  • Check that the chill roll is running and that chilled water is actually flowing through it.
  • Check ink film weight on the heavy solids.

THEN CHANGE

  • Bring the chill roll into service and get the web down below about 35 C before the rewind.
  • Reduce winding tension and set a proper taper so the core is not the tightest part of the reel.
  • Reduce film weight on solids, or reduce speed until drying is complete.
  • Move to an emulsion-rich grade, or protect heavy coverage with an overprint varnish carrying slip.
  • Let reels stand upright and cool before stacking or shipping.

CONFIRM IT IS FIXED

No picking or face transfer after 24 h at about 100 kPa (1 kg/cm2) at the condition agreed for the supply chain, 40 C as routine and 50 C where the pack ships warm, and no blocking on reels unwound at the converter a week later.

THE TRAP

Winding tighter because the reel is telescoping. Tighter winding raises interlayer pressure exactly where the blocking starts, so a handling problem at the rewind becomes a scrapped reel at the customer.
Water Based Gravure InksReel blocks and picks in the rewind (continued)

Fault 10 of 20

Print bleeds when the pack gets wet

WHAT YOU SEE

Colour transfers or smears under a damp cloth, on a bag carried in the rain, or on a wrap that has been in a chilled cabinet and picked up condensation.

WHAT IT LOOKS LIKE

WATER RESISTANT5 mmWET RUB BLEED5 mmRub the print with a damp cloth; the bad panel smears and bleeds colour onto the cloth.

    CAUSES, MOST LIKELY FIRST

  1. A high resolubility grade in a job that needs water resistanceResolubility and water resistance are traded against one another by design; an alkali-soluble resin that redissolves in fresh ink will also respond to water on the pack.
  2. Amine not fully out of the filmWater resistance develops only as the amine leaves and the resin loses its alkali solubility, so an under-dried film is water sensitive even if it is touch dry.
  3. No cross-linker where the specification needs oneWithout a deliberate cross-link the film is thermoplastic and re-wettable, because nothing reacts during drying.
  4. No overprint varnish over heavy coverageThe ink is being asked to be the surface of the pack as well as the colour of it.
  5. Film weight too heavy for the drying availableThe lower part of a thick film dries last and stays sensitive longest.
Water Based Gravure InksPrint bleeds when the pack gets wet

Fault 10 of 20  ·  continued

Print bleeds when the pack gets wet

CHECK, IN THIS ORDER

  • Wet rub: 20 double rubs with a damp cotton pad under light thumb pressure, 24 h after printing, and look at the pad.
  • Sutherland rub tester with a damp receptor, 4 lb (1.8 kg) and a stated stroke count, for a repeatable number.
  • Check drying completeness by weight loss: weigh, dry 60 min at 105 C, cool in a desiccator, re-weigh.
  • Read the grade off the tin and check it against the end use, not against what was ordered last time.
  • Check whether a cross-linker was specified for this grade and whether it was actually dosed and within its pot life.

THEN CHANGE

  • Change to an emulsion-rich, water-resistant grade and accept the shorter tolerance for stops.
  • Dose the supplied cross-linker to instruction and observe the pot life. Handle it as a sensitiser, the aziridine types in particular: nitrile gloves, goggles and local extraction at the mixing point, nothing decanted into an unlabelled container, and part-used cross-linked ink disposed of as waste rather than returned to stock. Do not carry cross-linked ink over to the next shift.
  • Apply a water-resistant aqueous overprint varnish over the print.
  • Complete the drying: air volume and extraction first, then speed and film weight.
  • Give the reel 24 h before testing so the property has developed.

CONFIRM IT IS FIXED

20 damp double rubs at 24 h with no colour on the pad, and no bleed after the pack has stood in a chill cabinet for 24 h on the customer's own board or film.

THE TRAP

Asking for maximum resolubility and maximum water resistance from one ink. The press gets an ink that stops on the cylinder or a pack that runs in the rain; the honest answer is to say which failure cannot be afforded and put the other property in an overprint varnish.
Water Based Gravure InksPrint bleeds when the pack gets wet (continued)

Fault 11 of 20

Foam in the tray, pinholes in solids

WHAT YOU SEE

A head of foam sits on the tray, the pump note changes, and solids come out with small round holes and crater rims. Often it starts an hour into the run rather than at the start.

WHAT IT LOOKS LIKE

FOAM FREE TRAY5 mmFOAM AND PINHOLING5 mmLook at the tray for a head of foam and at the solid for small round holes with raised rims.

    CAUSES, MOST LIKELY FIRST

  1. Return line breaking the ink surface and splashingEvery splash entrains air, and a recirculating loop passes the same ink through it hundreds of times a shift.
  2. Pump speed higher than the unit needsExcess flow goes back down the return and beats air into the ink rather than feeding the cells.
  3. Ink level in the tray too lowA low level shortens the time available for entrained air to break out before the ink reaches the cylinder.
  4. Defoamer over-dosedExcess silicone stops being a defoamer and becomes a surface contaminant; the round craters that follow are repellence, not foam, and heavy over-dose can also re-stabilise the foam it was meant to kill.
  5. Silicone or wash water contamination in the loopA trace of silicone from a spray or a cleaner is enough to crater a solid, and it will not filter out.
Water Based Gravure InksFoam in the tray, pinholes in solids

Fault 11 of 20  ·  continued

Foam in the tray, pinholes in solids

CHECK, IN THIS ORDER

  • Shake 50 ml in a graduated cylinder for 30 s and time how long the foam takes to collapse; more than about 30 s is a problem.
  • Look at the return line with the press running and confirm the outlet is below the ink surface.
  • Read the defoamer dosing record against the supplied instruction.
  • Look at the craters under a loupe: a foam pinhole has a clean round hole, a silicone crater has a raised rim and a dry centre.
  • Check what has been sprayed or wiped anywhere near the ink loop.

THEN CHANGE

  • Take the return line below the ink surface and stop it splashing.
  • Reduce pump speed to the lowest that keeps the tray full and stable.
  • Raise the working level in the tray so entrained air has time to break out.
  • Dose defoamer strictly to the supplied instruction and record every addition.
  • If defoamer has been over-dosed or silicone has got in, replace the ink and clean the loop; it cannot be corrected in the tray.

CONFIRM IT IS FIXED

Foam collapses within 30 s in the cylinder test and solids print free of pinholes and craters over 1000 m at full speed.

THE TRAP

Adding more defoamer because the foam is still there. Past the correct dose it stops working and starts creating repellence, and the craters that follow get read as an adhesion or substrate fault, so the ink gets changed for no reason.
Water Based Gravure InksFoam in the tray, pinholes in solids (continued)

Fault 12 of 20

Ink beads and crawls on treated film

WHAT YOU SEE

On BOPP or PE the ink pulls back into islands, solids show fisheyes, and fine type breaks up. The same ink runs perfectly on paper on the deck next door.

WHAT IT LOOKS LIKE

WETS OUT EVENLY5 mmINK BEADING BACK5 mmLook for ink pulling back into islands on the film, with round bare spots in the solid.

    CAUSES, MOST LIKELY FIRST

  1. Treatment at or below about 38 mN/m at the moment of printingWater-based inks are far less forgiving of marginal treatment than solvent inks, because water simply does not wet a low energy surface. 38 mN/m is the reject limit, not a working level.
  2. Treatment decayed on the reelCorona treatment falls off with time, warehouse heat and reel pressure; the certificate from the film mill describes the day it was made, not today.
  3. Slip additive bloomed to the surfaceErucamide and similar additives migrate to the film surface over weeks and give a low energy layer that measures and prints badly.
  4. Wrong side of the film being printedOnly one face is treated, and the two look identical on the reel.
  5. Ink surface tension too high for the filmEven a treated film needs an ink brought down towards 30 to 32 mN/m by surfactant and co-solvent before it will lay flat.
Water Based Gravure InksInk beads and crawls on treated film

Fault 12 of 20  ·  continued

Ink beads and crawls on treated film

CHECK, IN THIS ORDER

  • Test inks to ISO 8296 or dyne pens on the reel you are about to run, on both faces, reading the wetting tension to ASTM D2578 and watching for 2 s.
  • Check the reel's manufacture date and how long it has been in the warehouse.
  • Check whether in-line corona is fitted, switched on and set, and measure after it as well as before.
  • Measure the ink surface tension, or take it from the grade sheet, and compare against the film reading.
  • Print a small test patch after the in-line corona at full power to see whether wetting recovers.

THEN CHANGE

  • Bring the film up to 40 to 44 mN/m with in-line corona immediately before the first print deck.
  • Apply a water-based primer where corona alone will not hold the surface.
  • Reject and return film that will not take treatment because of additive bloom, and qualify slip-containing films individually before they are bought.
  • Adjust the ink with the supplied wetting additive only, and only to the stated dose.
  • Confirm which face is treated before the reel goes on the machine, not after the first 200 m.

CONFIRM IT IS FIXED

Test inks at 40 mN/m and above wet the reel and hold without drawing back for 2 s, and the printed solid runs free of fisheyes over a full reel.

THE TRAP

Turning the dryer up or the impression on to force the ink to lie down. Neither makes a low energy surface wettable; the beads simply dry harder in place, and the heat starts to distort the film as well.
Water Based Gravure InksInk beads and crawls on treated film (continued)

Fault 13 of 20

Lamination bond falls away after ageing

WHAT YOU SEE

Peel is acceptable at 24 h, then drops after a week in the warehouse or after a hot fill. Tunnelling appears in the printed areas and the laminate delaminates cleanly at the ink.

WHAT IT LOOKS LIKE

BOND HOLDSbond holds5 mmDELAMINATES AT INKbond holdsbond opens5 mmPeel the laminate after ageing; it should not open cleanly along the printed ink layer.

    CAUSES, MOST LIKELY FIRST

  1. Ink film not fully dry when it reached the laminatorResidual water and amine are trapped at the ink and adhesive interface and continue to weaken it for days after the laminate is made.
  2. Ink film weight too heavy in the printed areasThe adhesive has to key through a thicker, softer layer, and the failure is always in the printed areas rather than the clear ones.
  3. Binder not chosen for laminationSurface print binders are built for rub and gloss; lamination needs a binder, typically a polyurethane dispersion, that the adhesive can key to.
  4. Slip and wax additives in the ink or blooming from the filmA low energy species at the interface is exactly what a bond cannot tolerate.
  5. Adhesive coat weight too low for the coverageThe adhesive must wet the print as well as the film, and heavy coverage raises the demand.
Water Based Gravure InksLamination bond falls away after ageing

Fault 13 of 20  ·  continued

Lamination bond falls away after ageing

CHECK, IN THIS ORDER

  • Ply-bond peel to ASTM F904, or a described T-peel at 15 mm width and 100 mm/min, on the customer's own construction, measured at 24 h, at 7 days and after ageing at 50 C. Report the width, the rate, the peel angle and the locus of failure, whether ink to film, ink to adhesive or adhesive to film.
  • Weigh a cut sample, dry 60 min at 105 C, cool in a desiccator and re-weigh to see what carrier was still in the print at lamination.
  • Measure ink film weight on the failing colours.
  • Ask the laminator for the adhesive coat weight in g/m2 and the cure schedule actually used.
  • Check the grade in use is a lamination grade and not the surface print grade of the same colour.

THEN CHANGE

  • Complete drying before the reel reaches the laminator: air volume, extraction and dwell, then speed.
  • Reduce film weight by shallower engraving in the areas that are to be laminated.
  • Change to a lamination grade with a polyurethane dispersion binder, or print a primer under the ink.
  • Raise the adhesive coat weight for heavy coverage, agreed with the laminator, and give the laminate the full cure time.
  • Qualify slip-containing films and inks separately before the job rather than after.

CONFIRM IT IS FIXED

Ply-bond peel holds at or above the value agreed with the customer after 7 days at 50 C, measured on the customer's own film, adhesive and construction, with the locus of failure recorded. Bond is a property of the pack and of the lamination, so it is qualified there and not claimed from the ink alone.

THE TRAP

Raising adhesive coat weight to cover for a wet ink film. It buries the water instead of removing it, the laminate passes the 24 h test, and the failure surfaces after despatch when the whole order has been converted.
Water Based Gravure InksLamination bond falls away after ageing (continued)

Fault 14 of 20

Seal strength falls where the print runs through the seal

WHAT YOU SEE

Seals through the printed area peel open, channel, or fail at a lower force than the unprinted control from the same reel. It shows on the filling line rather than at the press, and it is worst on heavy solids that run to the edge, on heat-seal papers and on paper-based lidding.

WHAT IT LOOKS LIKE

SEAL HOLDSbond holds5 mmSEAL OPENS ON PRINTbond holdsbond opens5 mmPeel a seal through the printed area against an unprinted control from the same reel.

    CAUSES, MOST LIKELY FIRST

  1. The ink film in the seal area is an interlayerThe seal has to form through it, so the heat-seal coating is no longer sealing to itself. Every square metre of print in a seal area is material the jaw has to melt through.
  2. Film weight too heavy at the sealThe thicker the interlayer, the less of the seal layer meets itself at the jaw, and the narrower the seal window becomes.
  3. Ink not fully dry at the seal areaResidual water and amine flash at the jaw temperature and blow voids and channels into the seal.
  4. Slip and wax at the surface of the printA low energy species in the seal area is exactly what a seal cannot tolerate, for the same reason a bond cannot.
  5. Seal conditions set for the unprinted constructionThe print changes the heat transfer through the web, so the jaw temperature, dwell and pressure that work on the plain material are not the right ones through the print.
Water Based Gravure InksSeal strength falls where the print runs through the seal

Fault 14 of 20  ·  continued

Seal strength falls where the print runs through the seal

CHECK, IN THIS ORDER

  • Seal strength to ASTM F88, printed seal against unprinted control cut from the same reel, on the customer's own construction and sealing conditions.
  • Record the jaw temperature, dwell and pressure actually used, and the failure mode: peel, tear, or delamination at the ink.
  • Measure ink film weight in the seal area.
  • Weigh, dry 60 min at 105 C, cool in a desiccator and re-weigh a cut sample from the seal area to confirm the print was dry when it was sealed.
  • Check the grade for wax and slip content against the end use.

THEN CHANGE

  • Keep the print out of the seal area at the design stage wherever the pack allows it. This is the only reliable fix.
  • Reduce film weight in any area that has to be sealed.
  • Complete the drying before the reel leaves the press.
  • Use a grade without wax or slip where the seal area must be printed, and put any slip into an overprint varnish that stays outside the seal.
  • Agree jaw temperature, dwell and pressure with the converter on the printed construction, not on the plain material.

CONFIRM IT IS FIXED

Seal strength to ASTM F88 on the printed seal within the tolerance agreed with the customer against the unprinted control, on the customer's own material and sealing conditions, with the failure mode recorded. Seal performance is a property of the construction and the sealing conditions, so it is qualified there and not claimed from the ink.

THE TRAP

Turning the jaw temperature up to force the printed seal to hold. It seals for the trial, and it distorts or embrittles the substrate and narrows the seal window, so a seal that needed a design change becomes a pack that fails somewhere else on the line.
Water Based Gravure InksSeal strength falls where the print runs through the seal (continued)

Fault 15 of 20

Paper cockles and register wanders

WHAT YOU SEE

The web goes wavy at the edges, register creeps between decks through the reel, and it is worst on lightweight uncoated paper with heavy coverage on one or two colours.

WHAT IT LOOKS LIKE

FLAT STABLE WEB5 mmCOCKLED WANDERING WEB5 mmLook along the web edge for waves and cockle where heavy coverage sits on light paper.

    CAUSES, MOST LIKELY FIRST

  1. Water uptake into the paper from heavy ink coverageThe sheet takes up water, swells locally under the printed areas and does not come back to the same dimension when it dries.
  2. Film weight higher than the job needsMore carrier per square metre means more water into the sheet, and register loss is proportional to it.
  3. Over-drying in the tunnelDriving the paper below its equilibrium moisture makes it shrink and curl, so the cure for cockle becomes the cause of curl. Paper tolerates a higher air temperature than film, but its own limit is moisture, not distortion.
  4. Uneven coverage across the decksA heavy solid on one colour and light coverage on the rest puts the moisture in unevenly across the web.
  5. Web tension profile not set for the grammageA stretched web registers at the deck and relaxes at the rewind.
Water Based Gravure InksPaper cockles and register wanders

Fault 15 of 20  ·  continued

Paper cockles and register wanders

CHECK, IN THIS ORDER

  • Measure paper moisture with a paper moisture meter at the infeed and at the rewind.
  • Infra-red thermometer on the web at each dryer exit.
  • Measure ink film weight on the heavy colours.
  • Read the tension profile deck by deck from the machine and compare against the standard for that grammage.
  • Measure register at the start, middle and end of a reel rather than judging from one sample.

THEN CHANGE

  • Reduce film weight by re-engraving shallower where the design allows.
  • Raise air volume and extraction and reduce air temperature, rather than drying harder.
  • Set dryer temperatures deck by deck so the web leaves the last dryer at 40 to 55 C and not hotter.
  • Balance heavy coverage across decks where the separation allows it.
  • Move to a heavier grammage or a better sized paper if the job keeps failing on the same stock.

CONFIRM IT IS FIXED

Paper moisture at the rewind within 1 % of the infeed reading, and register holding within the agreed tolerance from the start of the reel to the end, over three consecutive reels.

THE TRAP

Drying harder to get the cockle out. It drives the sheet below its equilibrium moisture, so the wave becomes a curl, the fold cracks at the converter and the register error gets larger instead of smaller.
Water Based Gravure InksPaper cockles and register wanders (continued)

Fault 16 of 20

Press cannot hold speed, print wet at the last deck

WHAT YOU SEE

The press ran 300 m/min in February and will only hold 180 m/min now, on the same job and the same ink. Print is still wet at the last deck and rub tests fail at full speed.

WHAT IT LOOKS LIKE

DRY AT THE DECK5 mmWET AT LAST DECK5 mmTwist a thumb on the last deck print at full speed; a wet film marks and picks up.

    CAUSES, MOST LIKELY FIRST

  1. High ambient humidityThe dryer can only remove water into air that has room for it, so a humid intake lengthens the drying curve with nothing changed in the ink.
  2. Dryer filters loaded and nozzles partly blockedVelocity falls while the temperature reading stays where it was set, so the panel shows a dryer that is working and the tunnel is not.
  3. Extraction closed down or shared with another machineSaturated air recirculating in the tunnel removes nothing, however hot it is.
  4. Coverage and film weight higher than the job was costed atWater at about 2260 kJ/kg of latent heat, against about 366 kJ/kg for ethyl acetate, sets a hard limit on how much carrier a given tunnel can take away per minute.
  5. Ink solids reduced by repeated water additionsEvery point of non-volatile matter lost is more water per square metre to remove at the same colour.
Water Based Gravure InksPress cannot hold speed, print wet at the last deck

Fault 16 of 20  ·  continued

Press cannot hold speed, print wet at the last deck

CHECK, IN THIS ORDER

  • Measure pressroom temperature and relative humidity, and the exhaust duct humidity or wet bulb.
  • Hot wire anemometer at the dryer nozzles, compared against the machine's commissioning figures rather than against a class number.
  • Inspect and weigh the dryer filters.
  • Infra-red thermometer on the web at the last dryer exit at the speed the fault appears.
  • Measure non-volatile matter to ASTM D2369, 60 min at 110 C, cooled in a desiccator.

THEN CHANGE

  • Clean or replace dryer filters and clear the nozzles before anything else.
  • Open the extraction and check it is not being shared beyond its capacity.
  • Raise air volume before raising temperature, and set the temperature by the heat tolerance of the substrate, not by the ink.
  • Dehumidify or temper the dryer make-up air where the plant allows it.
  • Reduce film weight, stagger the heavy colours across decks, and accept a genuine speed reduction during high humidity months rather than shipping wet reels.

CONFIRM IT IS FIXED

Web temperature at the last dryer exit back in the 40 to 55 C window at the target speed on paper, with the 24 h Sutherland rub passing at that speed.

THE TRAP

Closing the extraction to keep the heat in. It raises the tunnel temperature and the tunnel humidity together, so the air reaches the web hotter and already loaded with water, the drying gets worse and the paper gets hotter and cockles.
Water Based Gravure InksPress cannot hold speed, print wet at the last deck (continued)

Fault 17 of 20

Ink in the tray or the drum has gone sour

WHAT YOU SEE

A sour or sulphurous smell off the tray or off a returned drum, lids bulging on closed containers, pH and viscosity both falling over a weekend with nothing added, and gloss and rub resistance down on print from that batch. Worst after a shutdown, in warm weather, and on a loop that is left full between jobs.

WHAT IT LOOKS LIKE

EVEN GLOSS5 mmDULL SOURED BATCH5 mmCompare the sheen on print from the suspect batch; soured ink prints patchy and dull.

    CAUSES, MOST LIKELY FIRST

  1. Ink left standing in the tray, the pump and the pipework between jobsA water-based ink is a nutrient medium. Organisms grow in the dead legs and the pump body and consume the surfactant and the thickener, so pH and viscosity fall together before anything shows on the print.
  2. Biocide consumed, or never dosedThe in-can preservative is used up over time and by every contamination event. An ink that has been open and topped up for weeks has none left.
  3. Contaminated make-up water or a dirty hoseA hose end left on the floor puts the organism straight into the tray, and the loop then distributes it.
  4. Returned ink put back into stock without a checkOne spoiled drum will seed a clean batch, and the batch that is seeded is usually the one blended into the next job.
  5. Warm storageGrowth rate rises steeply with temperature, so a drum stood next to a dryer or a radiator spoils in a fraction of the time one in a cool store would.
Water Based Gravure InksInk in the tray or the drum has gone sour

Fault 17 of 20  ·  continued

Ink in the tray or the drum has gone sour

CHECK, IN THIS ORDER

  • Smell the tray and the drum headspace before anything else; a sour or sulphide smell is the diagnosis.
  • Measure pH and the flow cup: a fall in both, with no water added and a clean addition log, is microbial and not amine loss, which raises viscosity as pH falls.
  • Look for gas: open a closed container slowly with the lid pointed away from the face and away from other people, and look for a bulged lid or a hiss.
  • Filter a litre through 100 um and look for stringy or slimy residue rather than hard grit.
  • Check how long ink has stood in the loop, when the loop was last washed out, and the dated biocide addition record.

THEN CHANGE

  • Take a spoiled batch out of service. Do not try to correct it with pH stabiliser; it will not recover, and the odour goes into the packed product.
  • Wash the loop out at the end of every job and before every shutdown, including the pump body, the dead legs and the return line. Do not leave ink standing over a weekend.
  • Dose the supplied biocide strictly to instruction and record every addition. Handle it to its safety data sheet: gloves, goggles and extraction at the mixing point.
  • Use deionised or softened water from a clean, dedicated line, and keep hose ends off the floor.
  • Strain and smell returns before they go back into stock, and discard anything sour rather than blending it away.

CONFIRM IT IS FIXED

pH and flow cup hold across a weekend shutdown with the loop washed out, no sour smell off the tray or off the returned drums at the start of the next job, and no odour complaint on the packed product from that batch.

THE TRAP

Dosing extra biocide into a batch that is already sour. The organisms die, but the breakdown products, the smell and the lost thickener stay, so the ink is now both spoiled and over-dosed. Biocide is a preservative for a clean ink, not a cure for a spoiled one.
Water Based Gravure InksInk in the tray or the drum has gone sour (continued)

Fault 18 of 20

Odour or taint in the packed product

WHAT YOU SEE

The reel smells at the converter, or the customer reports a smell, or a taste transfer in the filled pack, usually days after despatch and usually from inside a stacked pallet or a closed carton. The print itself looks correct and passes the rub test.

WHAT IT LOOKS LIKE

NO TAINT5 mmODOUR IN THE PACK5 mmThe print looks correct, so judge this one by smell on the reel and in a closed carton.

    CAUSES, MOST LIKELY FIRST

  1. Residual amine or ammonia in an under-dried filmThe amine leaves last. What has not left at the dryer exit leaves slowly into a closed reel and then into a closed pack, which is where it is smelled.
  2. Residual slow co-solvent left in the filmThe glycol ether type co-solvents are there to help the polymer coalesce, and they are the slowest thing in the ink to go. A film that is touch dry can still hold them.
  3. Film weight too heavy for the drying availableThe bottom of a thick film is the last to dry and the first to be smelled, and it is under the part of the film that tests dry at the surface.
  4. A microbially spoiled batch, or an over-dose of defoamer or biocideA sour batch carries its own odour into the pack and it cannot be dried out. Additives dosed past their instruction bring their own smell with them.
  5. The reel wound hot and stacked straight awayHeat and a closed reel hold the volatile material in and drive it into the reverse of the web, so the unprinted face carries the odour to the product.
Water Based Gravure InksOdour or taint in the packed product

Fault 18 of 20  ·  continued

Odour or taint in the packed product

CHECK, IN THIS ORDER

  • Run a sensory examination on the finished pack, for example the sensory testing of packaging materials described in DIN 10955, on the reel that will ship rather than on a press-side cut.
  • Weigh a cut sample, dry 60 min at 105 C, cool in a desiccator and re-weigh, and quote residual carrier as a percentage of the dry ink film.
  • Infra-red thermometer on the web at the last dryer exit at the speed the job actually runs, and reel core temperature within a minute of the reel coming off.
  • Measure ink film weight on the heavy colours.
  • Smell the tray and the drums, and read the additive dosing record, before the dryer is blamed.

THEN CHANGE

  • Complete the drying: air volume and extraction first, then dwell and speed, and temperature last within the substrate's limit.
  • Reduce film weight by shallower engraving with a wider cell opening where the design allows.
  • Chill the web before the rewind, and let reels stand and air before they are wrapped and stacked.
  • Where the end use is odour sensitive, ask for a low-odour grade built without the slower co-solvents, and say plainly that this costs some drying latitude and some resolubility.
  • Give the reel 24 h and re-test. A sensory result taken at the machine is testing the dryer, not the ink.

CONFIRM IT IS FIXED

Sensory result on the finished pack agreed with the customer, taken 24 h or more after printing on the reel that will ship, with residual carrier in the print at or below the level agreed for the job.

THE TRAP

Wrapping and stacking hot reels to get them out of the way. The pallet holds the amine and the co-solvent in, the reverse of the web picks them up, and a drying fault that would have aired off in the warehouse arrives at the customer as a taint complaint on the filled pack.
Water Based Gravure InksOdour or taint in the packed product (continued)

Fault 19 of 20

The pH reading cannot be trusted

WHAT YOU SEE

The meter reads 9.0 in a tray that is visibly thickening, or 8.2 in an ink that is running perfectly. Two meters on the same tray read 0.4 apart. The reading drifts while the probe is standing in the ink, or it locks on one number and never moves.

WHAT IT LOOKS LIKE

STABLE PH READING5 mmUNTRUSTED PH READING5 mmCompare two meters in the same tray; a probe that drifts or locks cannot be trusted.

    CAUSES, MOST LIKELY FIRST

  1. The reference junction is blocked with dried ink or pigmentThe reference path is throttled, so the reading drifts slowly and settles on a number that has nothing to do with the ink. This is the commonest failure on a press-side probe and it is invisible without a cross-check.
  2. The electrode has been stored dry, or in deionised waterThe glass bulb dehydrates and the response goes slow and flat. Deionised water strips ions out of the bulb and does the same damage as leaving it dry.
  3. Buffers old, contaminated, or used at a different temperature from the inkA calibration is only as good as the buffer. Used buffer poured back into the bottle contaminates the whole bottle.
  4. Probe and ink at different temperatures, with no temperature compensationThe electrode's own response is temperature dependent as well as the ink's pH, so a cold probe in a warm tray reports a number that belongs to neither.
  5. The electrode is worn outThe slope falls off with age and with alkaline service, and an electrode living in an amine ink has a hard life. It reads plausibly long after it has stopped reading correctly.
Water Based Gravure InksThe pH reading cannot be trusted

Fault 19 of 20  ·  continued

The pH reading cannot be trusted

CHECK, IN THIS ORDER

  • Buffer at pH 7 and pH 10 at the start of every shift, at the temperature of the ink, and record the slope where the meter reports it; a slope outside about 95 to 105 % of theoretical is the electrode, not the ink.
  • Check the response time: a healthy electrode settles in under about 30 s, one that crawls for minutes is fouled or dying.
  • Cross-check with a second, independently calibrated electrode before any ink is dosed heavily, diluted, condemned or returned on a pH number.
  • Look at the junction and the bulb under a loupe for dried ink, a film or crystals.
  • Check the storage: the probe should be sitting in the maker's storage solution, not dry and not in deionised water.

THEN CHANGE

  • Clean the electrode to the maker's instruction after every use, rinse with clean water and return it to storage solution; never let it dry out.
  • Replace buffers on a schedule, keep them out of the light and the heat, and never pour used buffer back into the bottle.
  • Keep a second electrode calibrated as the standing cross-check, and keep a date-of-first-use record on every probe.
  • Replace an electrode whose slope or response time has gone rather than working around it; it is cheaper than one wrong batch decision.
  • Take the reading in the running ink in the tray at press temperature, not in a cooled sample in a beaker on the bench.

CONFIRM IT IS FIXED

Two independently calibrated electrodes read within 0.1 of each other on the running ink, both buffer cleanly at 7 and 10 with the slope inside the maker's limit, and the same is true at the start of the following shift.

THE TRAP

Trusting the number because the meter is new. A new electrode stored badly for a month is as wrong as an old one, and every decision in this document hangs on that one reading: ink is dosed, diluted, condemned or returned on the strength of it.
Water Based Gravure InksThe pH reading cannot be trusted (continued)

Fault 20 of 20

Decor print bleeds in melamine impregnation

WHAT YOU SEE

The printed decor paper looks correct at the rewind, then colour haloes into the resin during impregnation and the shade shifts after pressing.

WHAT IT LOOKS LIKE

SHARP DECOR PRINT5 mmBLEED INTO RESIN5 mmLook for colour haloing out of the printed line into the resin after impregnation.

    CAUSES, MOST LIKELY FIRST

  1. Pigments not resistant to the impregnating resinThe resin system extracts anything soluble, so a colourant that is not fully pigmentary bleeds into it.
  2. Wax or slip additive in the inkA low energy surface stops the resin wetting the print, which shows as haloing and as poor impregnation rather than as a clean finish.
  3. A general purpose grade being used instead of the decor gradeDecor grades are built without wax and slip and around resin-fast, heat-fast pigments; a gift wrap grade is built around gloss and resolubility.
  4. Light fastness too low for the end useDecor laminates for furniture and flooring live for years under light, and blue wool 3 pigments will not survive it.
  5. Heat stability insufficient for the press cycleA short-cycle melamine press takes the print to platen temperatures commonly in the range 160 to 200 C, and some pigments shift shade there.
Water Based Gravure InksDecor print bleeds in melamine impregnation

Fault 20 of 20  ·  continued

Decor print bleeds in melamine impregnation

CHECK, IN THIS ORDER

  • Run a laboratory impregnation and press trial on the customer's own resin, paper and cycle before the job is printed.
  • Light fastness of the print by filtered xenon arc exposure, reported on the blue wool scale as defined in ISO 105-B01 and ISO 105-B02; decor work needs blue wool 7 to 8, not 3. State the exposure conditions and whether the print was tested as a solid or a tint.
  • Heat test to the customer's actual cycle: short-cycle melamine pressing is typically 160 to 200 C at the platen for 20 to 60 s at 20 to 40 bar. An oven screen, for example 180 C for 10 min, is a cheap pre-screen only and is not the same condition.
  • Confirm from the tin and the batch record that the decor grade was used on every colour, including any spot colour added on press.
  • Check whether any varnish, wax or anti-set-off has been applied to the reel.

THEN CHANGE

  • Change to the decor grade, formulated without wax or slip so the resin wets the print.
  • Select resin-fast, heat-fast pigments at blue wool 7 to 8 for the whole palette, including the tint bases.
  • Remove any overprint varnish or wax treatment from the specification for decor work.
  • Trial on the customer's own resin, paper and press cycle before committing a run, and read dE on the pressed panel rather than on the printed paper.
  • Where a colour cannot be built from resin-fast pigments, say so and re-specify the shade rather than shipping it.

CONFIRM IT IS FIXED

No bleed or haloing in the customer's own impregnation and press cycle, with shade within the agreed dE measured on the pressed laminate, and blue wool 7 to 8 across the palette used.

THE TRAP

Sealing the print with an overprint varnish to hold the colour in. The varnish stops the resin wetting the print, so the bleed becomes a delamination, and a colour problem turns into a structural failure in the finished laminate.
Water Based Gravure InksDecor print bleeds in melamine impregnation (continued)

03

At the press

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

Quick reference

One page at the press

SymptomCheck this firstChange this first
Viscosity climbing through the runpH with a calibrated electrode in the running tray, cross-checked against a second electrodeDose pH stabiliser, circulate five minutes, re-read; water last
Cells screened in after a stoppH, then whether the cylinder was left clear of the ink in the panKeep the cylinder wetted on slow-turn with guards closed; close the dryer damper
Hairlines down the reel, blade life collapsingFilter residue on a white tile and the blade edge under a loupeNew blade, clean holder, 100 um filter, drop blade pressure
Comets, specks and early filter blockingFilter a litre of ink and look at what the mesh holds: hard grit, soft skin or slimeStrain the tray, wash the loop, fix the source of the grit
Speckled highlights, missing dotsFlow cup at press temperature after pH, then the impression covering hardnessCorrect viscosity down after pH; treat ESA as a machine question, not a cure
Weak, mottled solids on paperDensity at five points across the web, then pH and flow cup, then the failing reel against the good reelSet viscosity to the grade sheet and qualify the paper reel; measure cell depth only after that
Colour drifting weaker reel by reelDensity trend and the ink addition log since the OK reelStop water corrections, add fresh unthinned ink of the same batch
Rub failure at the rewindWeb temperature at the last dryer exit with an IR thermometerRaise air volume and extraction before temperature
Water Based Gravure InksQuick reference

Quick reference

One page at the press

SymptomCheck this firstChange this first
Reel blocking and pickingReel core temperature and the winding tension taperChill before rewind and reduce taper tension
Colour bleeding when the pack is wetWhich grade is in the tray, resoluble or water resistantEmulsion-rich grade, supplied cross-linker handled as a sensitiser, or a water-resistant OPV
Pinholes and craters in solidsFoam collapse in a graduated cylinder and the defoamer recordSubmerge the return line and slow the pump; do not add defoamer
Ink beading on filmTest inks to ISO 8296 on the reel you are about to runIn-line corona to 40 to 44 mN/m, or a water-based primer
Lamination bond falling after ageingResidual carrier in the print by weight loss, and the ply-bond peel at 24 h and 7 daysComplete the drying and change to a lamination grade; adhesive coat weight last
Printed seals failing on the filling lineASTM F88 on the printed seal against the unprinted control from the same reelTake the print out of the seal area, or cut film weight there
Print still wet at the last deckNozzle velocity against the commissioning figure and exhaust humidityClean the filters, open the extraction, cut film weight
Cockle, curl and register wanderPaper moisture before and after the dryerReduce film weight and air temperature, raise air volume
Water Based Gravure InksQuick reference

Quick reference

One page at the press

SymptomCheck this firstChange this first
Sour smell, pH and viscosity both fallingSmell the tray and the drum headspace; check when the loop was last washed outTake the batch out of service and wash the loop; do not dose stabiliser or extra biocide
Odour or taint complaint on the packed productResidual carrier in the print by weight loss, and reel core temperature at the rewindComplete the drying and let reels air before wrapping; sensory test at 24 h
A pH number that does not match what the ink is doingBuffer at 7 and 10 at ink temperature and read the slope; cross-check a second electrodeClean or replace the electrode before any ink is dosed, diluted or condemned
Decor bleeding in impregnationWhich grade was used, and a laboratory press trial on the customer's resin and cycleDecor grade without wax or slip, blue wool 7 to 8 across the palette
Water Based Gravure InksQuick reference

Test methods

The measurements this guide relies on

MeasurementMethodWhat it tells you, and the usual acceptance
Flow cup viscosityDIN 53211, 4 mm cup (the DIN 4 cup)Working viscosity as an efflux time. 15 to 20 s at 25 C on the DIN 4 mm cup is typical for water-based gravure, against 18 to 25 s for flexo. The ISO 2431 4 mm flow cup is a different geometry with a different orifice and body and a 23 C reference temperature, and it gives a different time for the same ink, so name the cup on the log and never compare a reading from one against a target set on the other. Take it in the tray at press temperature and record the temperature with the number, because a 5 C rise takes roughly 2 s off the reading.
Press-side pHNo single standard governs it; use a calibrated glass electrode buffered at pH 7 and pH 10 each shift at the temperature of the inkThe control variable for an amine-stabilised system. Acceptance 8.7 to 9.3 in the running ink at press temperature, dosing at 8.7, with 8.5 treated as already out of control because that is where the alkali-soluble resin begins to come out of solution. Record the slope where the meter reports it and keep a second calibrated electrode as a cross-check before any batch decision. Paper strips are not accurate enough to run a press on.
Non-volatile matterASTM D2369, or an equivalent written in-house methodSolids as supplied and solids in the tray. 1 to 2 g spread evenly in a tared dish, 60 min at 110 C, cooled in a desiccator and weighed, run in duplicate. Typically 35 to 45 % by weight for this class; the grade sheet figure for the product wins. The comparison that matters on press is the tray sample against the unopened drum of the same batch. For printed samples, weigh, dry 60 min at 105 C, cool in a desiccator and re-weigh, and quote residual carrier as a percentage of the dry ink film.
Rub resistanceASTM D5264 has been withdrawn by ASTM; retain it as a described in-house method rather than citing it as an active standardHandling resistance of the dried print. Sutherland rub tester, 4 lb (1.8 kg) weight, 50 strokes, printed face against the specified receptor stock, sample and receptor conditioned 24 h at 23 C and 50 % RH to ISO 187, then inspected for visible transfer to the receptor. Run the same test with a damp receptor for wet rub. Acceptance is agreed with the customer for the end use rather than fixed at 50 rubs for every job.
Wetting tension of the substrateASTM D2578, with test inks to ISO 8296Surface energy of the film at the moment of printing. 40 to 44 mN/m, wetting and holding for 2 s, measured on the reel about to run rather than taken from the mill certificate. Treat 38 mN/m as the reject limit, not as the bottom of the window; water-based inks need more treatment than solvent inks for the same wet-out.
Ink adhesion to filmDescribed tape test; ISO 2409 cross-cut only where the standard appliesKey of the dried ink to the surface. On flexible film, apply a defined tape to the print, state the tape type and width, press it down with a standard roller, pull at 180 degrees in one movement, and report the percentage of ink removed and the area tested. Name the tape, because the result is meaningless without it. Use ISO 2409 cross-cut only on rigid or board-backed substrates, since it is written for coatings on dimensionally stable substrates up to 250 um and a cross-cut blade drawn through a 1 to 3 g/m2 ink film on unsupported BOPP or PE cuts the substrate and gives a classification that means nothing. Adhesion is an interface property of the customer's own material, so it is qualified on their reel and not claimed for the ink alone.
Ply-bond peelASTM F904, or a described T-peelLamination bond on a laminated construction. ASTM F904 compares ply adhesion of flexible laminates; where a described method is used instead, state it in full, for example T-peel at 15 mm width and 100 mm/min. Measure at 24 h, at 7 days and after ageing at 50 C, and report the width, the rate, the peel angle and the locus of failure, whether ink to film, ink to adhesive or adhesive to film. ASTM D3330 is the peel test for pressure-sensitive tape and is not the test for laminate ply bond. Bond is a property of the construction, the adhesive and the cure as much as of the ink, so it is agreed and qualified on the customer's own laminate.
Water Based Gravure InksTest methods

Test methods

The measurements this guide relies on

MeasurementMethodWhat it tells you, and the usual acceptance
Seal strengthASTM F88Force to separate a seal, run on the printed seal against an unprinted control cut from the same reel, on the customer's own construction. Record the jaw temperature, dwell and pressure actually used and the failure mode: peel, tear, or delamination at the ink. Seal performance is a property of the construction and the sealing conditions, so it is qualified there and not claimed from the ink.
Light fastnessFiltered xenon arc exposure of the print, reported on the blue wool scale as defined in ISO 105-B01 and ISO 105-B02Expected life under light. The blue wool scale is the right reference scale, but ISO 105-B02 itself is a textile standard and is cited here only for the scale, not as the exposure method for a print. State the exposure conditions and whether the print was tested as a solid or as a tint, since tints fade faster than solids of the same pigment. Blue wool 3 is adequate for short-life promotional wrap; bags and outdoor use need 6 and above; decor laminates for furniture and flooring need 7 to 8 across the whole palette including the tint bases.
Blocking testNo standard cited; described methodWhether the reel will stick. 10 cm squares, printed face to web reverse, under about 100 kPa (1 kg/cm2) for 24 h, at 40 C as the routine condition and at 50 C where the pack ships or stores warm, then peeled and inspected for picking and face transfer. Quote the pressure in kPa with the kg/cm2 equivalent in brackets, agree the condition with the customer for the actual supply chain, and run it on the job before the reels are stacked and shipped.
Sensory testing of the packSensory examination of packaging materials as described in DIN 10955Whether residual amine, ammonia, co-solvent or additive can be smelled or tasted in the packed product. Run it on the finished pack, 24 h or more after printing, on the reel that will ship rather than on a press-side cut, and record the drying condition and the residual carrier figure alongside the result, because odour tracks residual carrier rather than ink chemistry alone.
De-inkabilityINGEDE Method 11, scored against the EPRC De-inkability ScorecardWhether the print releases in the pulper and is removed by flotation. De-inkability is a property of the whole print, that is the ink, the coat weight, the substrate and any varnish, and it is assessed case by case. Water-based acrylic prints can score poorly on flotation de-inking because the ink disperses to fine particles, and filtrate darkening and low ink elimination are the usual failure routes. No de-inkability statement is made to a customer, for any grade or range, until a scorecard result exists on the actual print.
Water Based Gravure InksTest methods

When the press-floor fixes have not worked

What to send us

  • The pH and viscosity log for the run at 30 min intervals, with the ink temperature and the cup type written beside each reading, the electrode calibration and slope record for that shift, and the addition log showing every quantity of water, stabiliser, defoamer, biocide and returned ink that went into the tray, with times.
  • Batch and lot numbers for every ink, varnish, cross-linker and additive in the unit, the date each container was first opened, and the storage and transport history of any drum that has stood warm or travelled in frost.
  • Three metres of the fault, cut at the fault, marked with the web direction, the deck number and the running speed, plus three metres of acceptable print from the same job for comparison.
  • Five metres of the unprinted substrate from the same reel, with its grade, grammage and lot number, and the surface energy reading you took on that reel with test inks, with the date of the reading.
  • Cylinder data for the failing deck: screen, engraving angle, stylus angle, measured cell depth at a solid, a mid-tone and a highlight, chrome hardness, and the date of the last re-chrome.
  • Dryer data at the speed the fault appears: air temperature per deck, nozzle velocity by anemometer against the commissioning figure, exhaust humidity, extraction status, and the web temperature at the last dryer exit measured with an infra-red thermometer.
  • For lamination, seal and decor faults, a sample of the finished construction, the adhesive and coat weight or the impregnating resin and press cycle used, the sealing conditions where a seal is involved, and the peel, seal or impregnation result at 24 h and after ageing, so the interface can be assessed on the real pack.
  • For odour, taint and food-contact questions, a wrapped sample of the finished pack and of the unprinted substrate as a control, the residual carrier figure by weight loss, the drying settings and speed, and the sensory method and panel used. Formulation statements are supplied for the ink; conformity of the finished pack is assessed on the pack by the pack's owner, with a migration and sensory assessment on the finished construction on request.
Technical servicesales@ufindustries.com  |  +91 8750051884  |  E105, GNEPIP, Industrial Area Site-5, Greater Noida, Uttar Pradesh 201306, India
Water Based Gravure InksTechnical service
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