How to use this guide · finding and fixing defects quickly
This guide is organised by printing process, offset, flexo, gravure, digital, and then by finishing defects that appear after printing. Each defect entry follows the same structure: what it looks like (identification), what causes it (primary causes in order of likelihood), and how to fix it (correction). A defect that appears in multiple processes is listed under the process where it most commonly occurs, with cross-references where relevant.
For a defect already on press, check the identification description first, many defects look similar but have different root causes. The identification description distinguishes between visually similar defects (e.g., hickeys vs pinholes, ghosting mechanical vs chemical ghosting) so the correct correction is applied.
Offset printing defects · the complete reference
| Defect | Identification | Primary causes | Correction |
|---|---|---|---|
| Hickeys (halo spots) | Small circular or irregular spots, a dark ink centre surrounded by a white halo ring. Appear as scattered spots in solid ink areas and tints. Each hickey is a foreign particle (paper fibre, dust, dried ink skin) picked up by the blanket, transferring ink around but not over itself. | Paper fibres shedding from the sheet edges or surface, most common with uncoated paper and coated paper with poor pick resistance. Dried ink skins forming in the ink train from long periods of press standing. Dust accumulation in the press room. Blanket surface contamination. | Clean the blanket and ink rollers. Increase fountain solution flow slightly to improve pick resistance at the sheet surface. Switch to a higher pick-resistance paper grade. Install press room air filtration. For recurring hickeys from a specific paper, test ink tack, reduce tack by 1–2 units if it is pulling fibres from the surface. |
| Scumming / tinting | A faint even tint appears in areas that should be clean white, non-image areas carry a very slight ink film. Scumming is localised (in specific non-image zones); tinting is a uniform pale wash across the entire sheet in one colour. | Insufficient fountain solution, non-image areas of the plate are not fully desensitised. Fountain solution pH too high (above 5.5). Ink tack too high, ink is stripping the plate surface. Plate under-exposed or incorrectly processed, non-image areas retaining ink-receptive coating. Ink emulsification, too much water in the ink body. | Increase fountain solution flow. Check and adjust pH to 4.5–5.2. Reduce ink duct setting slightly, less ink on rollers. Increase press speed to improve ink-water balance. If persistent, inspect plate under magnification for coating residue in non-image areas, replace plate if surface is contaminated. |
| Mechanical ghosting | A faint "ghost" image of a previously printed element appears in a clean area of the same sheet, typically offset by one or more roller circumferences from the original image. The ghost is lighter than the main image. Appears most visibly in large solid areas adjacent to image-heavy areas. | Ink starvation, the ink train cannot replenish fast enough after a heavy coverage area, leaving depleted rollers that print a ghost impression on the next roller revolution. Most common with long ink trains at high press speeds when large solid areas follow high-density image areas in the direction of press travel. | Reduce press speed to allow ink train replenishment. Increase ink duct opening in the affected zones to feed more ink. Redesign the job layout to avoid placing large solids immediately after high-coverage image areas in the print direction. In some cases, a full press restart with fresh ink train is required to eliminate ghosting already established in the rollers. |
| Chemical ghosting | Similar to mechanical ghosting but appears on the reverse side of the sheet, a shadow image of a previously printed side visible from the unprinted reverse. Appears hours or days after printing as ink dries. Unlike mechanical ghosting, chemical ghosting cannot be seen until after delivery. | Ink oxidation products (volatile compounds released during drying) react with the ink on the unprinted side of the sheet above it in the delivery pile, altering the gloss and colour of the ink below. Particularly common with heavy ink coverage and heavy anti-setoff powder, the powder traps the volatile oxidation products between sheets. | Reduce delivery pile height, fewer sheets means less time for volatile accumulation. Increase anti-setoff powder to create more air gap between sheets. Interleave with tissue paper for very sensitive jobs. Allow longer drying time before stacking. Difficult to prevent completely on heavy-ink jobs with tight schedules, warn the client if it is a known risk. |
| Picking and plucking | Rough or pitted appearance in solid ink areas, fibre or coating particles visibly lifted from the paper surface. The surface appears torn in small patches. Found on the printed sheet; the corresponding areas on the blanket show paper contamination. | Ink tack too high for the paper's pick resistance. The ink film is strong enough to pull fibres or coating from the paper surface faster than the paper can release. More common with coated papers at high press speeds, with high-tack inks, and with recycled or poorly manufactured paper grades. | Reduce ink tack by adding a small amount of tack reducer or reducing the pigment concentration. Reduce press speed. Switch to a higher pick-resistance paper grade. Check ink temperature, warm inks are less tacky and less likely to pick. If picking is severe, the paper grade is incorrect for the ink specification, change paper. |
| Slur and doubling | Slur: fine details appear smeared or soft in the direction of press travel, dots have a tail in the printing direction. Doubling: a faint secondary impression appears offset from the main image, as if the dot printed twice, slightly displaced. Both are visible under 10× magnification in halftone areas. | Slur: relative movement between the blanket and sheet during impression, caused by incorrect packing height, worn blanket, or sheet skidding. Doubling: sheet bounce back after impression, sheet fails to lie flat against the impression cylinder, creating a secondary contact impression. Also caused by loose sheet grippers, incorrect gripper pressure, or blanket surface inconsistency. | Check and correct packing heights (plate cylinder and impression cylinder). Replace worn blanket. Verify gripper pressure and gripper timing on all gripper bars. Reduce press speed slightly to reduce sheet dynamics. Inspect impression cylinder surface for contamination or wear. |
| Misregister, colour-to-colour | Coloured fringes around fine detail or text, cyan, magenta, or yellow fringe visible around black elements or at colour boundaries. Under 10× magnification, halftone dots from different separations are visibly misaligned. Visible without magnification on fine text below 6pt. | Mechanical register variation between press units. Sheet stretch from impression pressure, particularly on flexible or poorly sized papers. Temperature and humidity variation affecting paper dimensions between press passes. Feeder register not set correctly, sheets not consistently positioned at the gripper. | Check and adjust register at all press units. Verify feeder side guide and gripper timing. Check paper moisture content, condition paper to press room humidity before running. For very fine text or tight register requirements, verify that the paper grade has adequate dimensional stability. On multi-pass jobs, ensure minimum time between passes to avoid paper dimension change. |
| Ink setoff | Ghost image of the printed face visible on the back of the next sheet in the delivery pile, the wet ink transferred to the sheet above it. Appears as a faint reversed-image contamination on the unprinted back. More visible after the pile is opened than immediately in delivery. | Ink not dried before stacking, delivery pile too deep, drying time too short, insufficient anti-setoff powder. Very heavy ink coverage on one side. Low absorption paper preventing ink from penetrating and setting quickly. High humidity in press room slowing oxidative drying. | Increase anti-setoff powder quantity and verify even distribution. Reduce delivery pile depth. Allow sheets to dry longer before jogging or handling. For critical jobs, consider UV offset, UV inks cure instantly and eliminate setoff risk. Check fountain solution pH, incorrect pH can slow ink drying significantly. |
Ink and drying defects · slow drying, chalking, blocking
| Defect | Identification | Primary causes | Correction |
|---|---|---|---|
| Slow or incomplete drying | Ink remains tacky hours or days after printing, smears when touched, transfers ink when handled. Can lead to setoff, blocking in the pile, and lamination or varnish adhesion failure. | Ink-paper combination wrong, ink vehicle not compatible with paper coating. Fountain solution contamination in the ink slowing oxidative drying. pH too high (above 5.5) from excessive fountain solution. Very high ambient humidity (above 70% RH) slowing oxidation. Ink film too thick, excess coverage from over-inking. Very cold press room temperature (below 18°C). | Check fountain solution pH, correct to 4.5–5.2. Reduce fountain solution feed. Increase press room temperature to above 20°C. Add drier (cobalt or manganese based) to the ink, maximum 2–3% by weight to avoid over-drying problems. Switch to an ink formulated for the specific paper coating type. For urgent situations, UV curing equipment as a post-printing pass can save already-printed sheets. |
| Chalking | Dried ink rubs off as a powder, the ink appears dry but has no binding to the paper surface. The print surface is powdery and lacks gloss. Scuff resistance is essentially zero. | Ink vehicle absorbed into the paper too rapidly before the binder could film-form, typically on very absorbent uncoated or poorly coated papers. The pigment is left on the surface without adequate binder. Also caused by ink formulated for coated paper run on uncoated paper. | Switch to ink formulated for the specific paper grade. Add a small amount of varnish to increase vehicle content and slow absorption. For uncoated papers, use higher-viscosity inks that resist rapid vehicle absorption. Apply an aqueous overprint varnish to bind the pigment layer, this is the most reliable remedial action for a chalked print if the defect is caught before delivery. |
| Blocking in the pile | Sheets in the delivery pile stick together, either ink-to-ink (face of one sheet sticking to face of the next) or ink-to-back (printed face sticking to unprinted back). Sheets must be physically separated and the surface may be damaged in the process. | Ink not fully dry before piling. Insufficient anti-setoff powder allowing direct ink-to-ink contact. Pile too tall, weight of sheets above creates pressure that bonds tacky ink surfaces. High humidity softening the ink vehicle. UV-cured ink not fully cured, UV lamps insufficient or partially failed. | Increase anti-setoff powder. Reduce pile height (maximum 500–800 sheets for heavy ink coverage). Extend drying time before jogging. For UV press: check UV lamp output and replace ageing lamps. Monitor UV cure with a UV dosimeter. Do not laminate or varnish until print is fully dry, lamination of under-dried ink causes permanent blocking under the film. |
| Ink trapping failure | Secondary colours (reds, greens, blues in overprint areas) appear flat, dull, or incorrect, lacking the expected depth and saturation. The overprinted ink has not fully accepted onto the first ink layer. Under magnification, the overprint layer appears incomplete or patchy in areas that should be solid. | Tack sequence incorrect, second ink has higher tack than first. Ink tack increases with temperature, ink train warming during a long run increases tack, progressively worsening trapping. Excess fountain solution emulsified into the ink reducing tack. Incompatible ink series from different manufacturers. | Verify tack sequence, run inks in decreasing tack order from first to last unit. Check ink temperatures, install press-side ink temperature monitoring and cooling if necessary. Reduce fountain solution feed. Use inks from the same manufacturer series for all colours on a job. If trapping worsens during a long run, increase press speed slightly to reduce heat buildup. |
Colour and density defects · variation, dot gain, grey balance
| Defect | Identification | Primary causes | Correction |
|---|---|---|---|
| Colour variation within run | Colour shifts progressively during the production run, prints from the beginning of the run are noticeably different in colour from prints from the end. Most obvious in critical brand colours and neutrals. | Ink density drift, either increasing (as rollers warm and ink becomes less viscous) or decreasing (as ink is consumed faster in heavy coverage areas than it is replenished). Fountain solution pH drift during the run, typically increasing as isopropanol evaporates and buffer capacity reduces. Paper moisture variation between reams. | Implement continuous density monitoring every 500–1,000 sheets. Measure and adjust fountain solution pH every 2 hours. Install automatic ink duct key control systems (CTP-connected closed-loop colour) if available on the press. For manual presses, increase the frequency of density checks on long-run jobs. Condition paper to press room environment for 24 hours before printing. |
| Banding, horizontal density stripes | Regular light and dark horizontal bands across the printed sheet, bands run across the full width of the press sheet perpendicular to the print direction. Repeat interval corresponds to the circumference of a roller or cylinder. | Roller bounce, a roller that is not perfectly round or concentric creates regular density variation as its high and low points alternately contact the image. Gear train vibration causing regular impression variation. Worn or damaged roller bearings. Impression cylinder or blanket cylinder runout exceeding tolerance. | Measure all roller and cylinder runout with a dial gauge, replace any component exceeding 0.005mm runout. Inspect and replace worn roller bearings. Check gear train for worn teeth or lubrication failure. The band repeat interval can be used to identify the source, measure the band spacing and divide by π to find the circumference of the offending roller. |
| Excessive dot gain | Midtones print much darker and heavier than intended, 50% dot in the file prints as 70%+ on the sheet. Shadows fill in; images look muddy. Highlights appear heavier than intended. Measured TVI at 50% significantly exceeds the ISO 12647-2 target of 18% for coated paper. | Impression pressure too high, over-impression mechanically spreads the dot. Blanket swollen from solvent absorption, increases effective nip pressure. Ink too fluid, low viscosity at elevated temperature. Screen ruling too fine for the paper and press combination. Plate curve not compensating adequately for press gain. | Reduce impression pressure incrementally, 0.05mm at a time, and measure TVI after each adjustment. Replace blanket if it is swollen or has lost compressibility. Reduce ink temperature by adjusting roller cooling. Verify plate curve compensation is correctly applied for this press and paper. If gain is consistently above target, build a new plate curve based on current press characterisation data. |
| Grey balance drift | Neutral grey areas (equal CMY tints) show a visible colour cast, either warm (reddish/yellowish) or cool (bluish/greenish). Skin tones appear wrong. White areas appear tinted. Spectrophotometer measurement shows a* or b* deviation above ±2.0 in the grey balance patch. | One or more ink densities have drifted from target, typically cyan increasing (cool cast) or yellow decreasing (warm cast). Ink tack sequence causing one colour to trap differently than designed. Fountain solution chemistry affecting one ink differently from the others. | Measure all four ink densities against target. Identify which ink(s) are off-target and adjust their duct settings. Check grey balance patch a* and b* after each adjustment, corrections are complete when a* and b* return to within ±1.0 of zero. Do not adjust grey balance subjectively, always use spectrophotometer measurement to confirm the correction is accurate. |
Flexographic printing defects · plates, anilox, and substrate
| Defect | Identification | Primary causes | Correction |
|---|---|---|---|
| Halo or outline effect | Printed elements show a darker or heavier ring at their edges, particularly in solid areas where the edge has a noticeably different density from the centre. The edges appear as darker outlines rather than clean solid fills. | Excess ink at plate edges, the plate relief edge picks up more ink than the central relief area because anilox cell edges transfer more ink. More common on analogue rubber plates than on precision digital polymer plates. Impression pressure slightly too high causing plate to deflect and edge-print more heavily. | Reduce impression pressure, the plate should barely kiss the substrate. Switch from rubber to precision-engraved digital polymer plates. If using rubber plates, reduce plate hardness specification. Reduce anilox cell volume, try a lower BCM anilox roller. |
| Ink bridging in fine type | Fine reversed text fills in, the white space within and between characters fills with ink, making text illegible or reducing legibility significantly. Fine positive text appears thicker than intended (ink spread). The counters of letters (o, e, a, d) partially or fully close. | Anilox cell volume too high, delivering more ink than the image can accommodate. Fine type below approximately 4–5pt cannot hold clean reverses in standard flexo. Impression pressure too high, spreading ink laterally. Ink viscosity too low, ink is too fluid and spreads at impact. | Reduce anilox cell volume (BCM). Increase ink viscosity, check and adjust viscosity to specification. Reduce impression pressure. For fine text below 6pt in reversed form, consider whether flexo is the correct process, offset or gravure will hold this feature more cleanly. Specify minimum text size for flexo in the design brief before artwork is prepared. |
| Anilox streaking | Regular fine lines or streaks in the print direction, parallel to the direction of press travel, appearing in solid and tint areas. The streaks correspond to damaged or clogged cells in the anilox roller. | Anilox roller cells clogged with dried ink, particularly UV inks that cure in cells when press is stopped without cleaning. Physical damage (scratches, gouges) to the anilox surface from improper cleaning tools or substrate contact. Dried ink on the doctor blade scoring the anilox surface. | Clean anilox rollers with the correct cleaning system, ultrasonic cleaning for severe clogging, chemical cleaning with appropriate solvent for routine maintenance. Inspect anilox under 10× magnification and replace if cells are damaged. Establish a regular anilox cleaning schedule, at every job change for UV inks. Never use metal scrapers on anilox surfaces. |
| Ink spitting | Small irregular ink droplets appear scattered in non-image areas, particularly on the trailing edges of image elements and in adjacent clean areas. Under magnification, each droplet is a complete small ink spot without the halo pattern of a hickey. | Ink viscosity too low, ink misting from the anilox-to-plate or doctor-blade contact at high press speed. Excessive press speed for the ink viscosity. Doctor blade angle too aggressive, causing ink to spray. Static charge on the substrate attracting ink mist. | Increase ink viscosity to the recommended range for the current press speed. Reduce press speed. Adjust doctor blade angle and pressure. Install static elimination bars at the substrate entry point. Check that ink has not been over-diluted, measure viscosity with a Zahn cup or viscometer and correct to specification. |
Gravure printing defects · cells, doctor blade, and cylinder
| Defect | Identification | Primary causes | Correction |
|---|---|---|---|
| Missing dots (skipping) | Individual cells in tint and gradient areas fail to transfer, producing a speckled, pitted appearance. Most visible in highlight areas of 5–30% tone. The pattern is random, not aligned to any regular structure. | Substrate surface too rough for complete cell-to-substrate contact. Impression pressure too low. Ink viscosity too high, ink does not empty from cells completely. Chrome layer worn, exposing rough copper beneath. Substrate corona treatment insufficient for ink adhesion. | Increase impression pressure incrementally. Reduce ink viscosity by controlled solvent addition, measure with Zahn cup. Inspect chrome layer, if worn or pitted, re-chrome the cylinder. Verify substrate surface energy with dyne pens, minimum 38 dynes/cm. Test with a different substrate batch if the problem appears on only one reel. |
| Doctor blade chatter lines | Fine parallel lines running in the print direction across solid and tint areas, the lines may be continuous or intermittent. Not to be confused with banding (which repeats at the cylinder circumference). Chatter lines are continuous in the run direction. | Doctor blade vibrating against the cylinder, caused by blade wear creating an uneven contact edge, incorrect blade angle, contamination (ink particle or substrate fibre) lodged under the blade, or cylinder chrome surface irregularity creating vibration. | Replace the doctor blade, this resolves 70% of chatter cases. Adjust blade angle and contact pressure within specification. Ensure ink is filtered to remove contamination that can lodge under the blade. If chatter persists after blade replacement, inspect cylinder surface for hard spots or chrome irregularities, re-chrome if found. |
| Ink adhesion failure on film | Printed ink can be rubbed off the substrate with finger pressure or removed cleanly with tape. The ink film appears to sit on the surface without bonding. Tape adhesion test removes ink cleanly. | Insufficient corona treatment on the film substrate, surface energy below 38 dynes/cm. Ink formulation not compatible with the substrate chemistry. Contaminated substrate surface from handling or storage. Residual slip agents or release agents on the film surface preventing adhesion. | Measure substrate surface energy with dyne pens before printing, reject if below 38 dynes/cm and re-corona treat. Confirm ink-substrate compatibility with the ink supplier and request a test before production. Check substrate storage conditions, film stored in high heat can lose corona treatment. If contamination is suspected, clean a test area with IPA and test adhesion on the cleaned area vs uncleaned area. |
| Colour variation during run | Ink colour shifts progressively during a long run, prints from the beginning differ noticeably from prints toward the end. Most commonly, prints become progressively darker (ink thickening) or lighter (ink thinning from excessive solvent addition). | Ink viscosity drift, solvents evaporate from the open ink trough during the run, increasing viscosity and delivery per cell. Incorrect automatic solvent addition, solvent added at too high or too low a rate. Ink trough temperature variation. Chrome wear increasing effective cell depth over time. | Install automatic viscosity control, a probe in the ink trough with automatic solvent addition. Monitor viscosity at defined intervals (every 30 minutes) if manual. Monitor ink trough temperature, maintain at ±2°C of target. On very long runs, track cylinder density against the OK sheet, any drift beyond ±0.05 density units requires investigation. |
Digital printing defects · toner, inkjet, and colour management
| Defect | Identification | Primary causes | Correction |
|---|---|---|---|
| Banding in digital output | Regular horizontal bands of slightly different density across the output, particularly visible in large flat tints and gradients. The banding pattern repeats at fixed intervals related to the print head or drum circumference. | Inkjet: clogged or failed nozzles, each missing nozzle creates a light band in the output. Also caused by feed roller wear creating uneven substrate advance. Toner: drum or developer roller contamination or wear producing regular light bands. | Run a nozzle check print and clean the print head if clogged nozzles are identified. Replace severely clogged heads. For toner devices: clean the drum and developer roller. Check feed roller condition, replace worn rollers causing uneven advance. Run the machine's built-in calibration routine after cleaning. |
| Colour shift vs analogue proof | Digital output appears noticeably different in colour from the approved calibrated contract proof, either too warm, too cool, too saturated, or too flat. The client accepts the proof but rejects the digital print. | Digital printer not profiled or calibrated to the target press condition (ISOcoated_v2). Device drift since last calibration. Incorrect ICC profile applied to the job. Paper/media profile not matched to the actual substrate. RIP colour management settings incorrect. | Re-calibrate the digital printer against a target measurement set. Verify and update the ICC profile for the specific media and printer combination. Confirm that the correct output intent profile is applied in the RIP. Measure the output with a spectrophotometer against the contract proof, target ΔE 2000 <2.0 for critical colour matching. If ΔE consistently exceeds 3.0, a full device re-profiling is required. |
| Toner adhesion failure (fusing) | Toner rubs off the substrate surface under handling, the toner has not fused to the substrate. Fold and crease tests cause toner to crack and flake at the crease. The print looks normal but has no adhesion. | Fuser temperature too low for the substrate, thicker or coated substrates require higher fuser temperatures than standard office paper. Substrate not compatible with the toner chemistry. Incorrect media type selected in the printer settings, the printer runs a lower fuser temperature for the selected media type than the actual substrate requires. | Select the correct media type in the printer settings for the actual substrate being used. Increase fuser temperature if the printer allows manual adjustment. For substrates outside the printer's specified media range, test adhesion before production, run a small test print and perform tape adhesion and fold tests. Some substrates require pre-treatment or are incompatible with specific toner systems. |
Post-press and finishing defects · lamination, varnish, cutting
| Defect | Identification | Primary causes | Correction |
|---|---|---|---|
| Lamination delamination | The lamination film separates from the printed surface, either immediately after production, or after storage. Visible as bubbles, lifted edges, or complete film separation. The delaminated area has a milky, opaque appearance where the adhesive has failed. | Ink not fully dry before lamination, residual solvent/vehicle in the ink prevents adhesive bonding. This is the most common cause in Indian production, particularly during monsoon season. Lamination adhesive not compatible with the specific ink set or paper coating. Too-smooth ink surface (certain UV inks) preventing mechanical adhesion. | Enforce minimum drying time: 8–12 hours standard, 18–24 hours during monsoon season. Perform tape adhesion test on a sample before the lamination batch runs. If delamination occurs after lamination: heat the affected area with a heat gun, if the delaminated area re-bonds, the cause is insufficient drying, not adhesive incompatibility. If it does not re-bond, investigate adhesive compatibility. |
| Curl and warp after lamination | Laminated sheets or cartons curl, face-up or face-down, after lamination. Severe curl causes problems in subsequent processing (cutting, creasing, folding) and in the finished product. | Lamination film tension unequal on both sides of the sheet, if lamination is on one side only, the film contracts as it cools and cures, pulling the sheet toward the laminated face. Board weight below 300 GSM cannot resist the lamination tension. | Specify minimum 300 GSM board for one-side laminated cartons. For jobs with severe curl tendency, laminate both sides (even with a thinner film on the non-print side) to balance tension. Store laminated sheets flat under weight for 24–48 hours before cutting. In extreme cases, run sheets through the laminator in the opposite curl direction to counteract the bias. |
| Cutting edge burr or rough edge | The cut edge of a sheet or carton is not clean and straight, showing a ragged or feathered edge, a visible burr on one face, or delamination of the lamination film at the cut edge. | Guillotine blade worn, a sharp blade cuts cleanly; a worn blade drags and tears. Too many sheets in the cutting lift, excessive pressure causes the lower sheets to be dragged rather than cut. Incorrect blade bevel angle for the material. For laminated stock: blade not sharp enough to cut through the lamination film cleanly. | Replace or sharpen the guillotine blade. Reduce cutting lift to maximum recommended for the stock weight and lamination. Verify blade bevel angle specification for the stock being cut, laminated stock requires a sharper bevel than unlaminated board. Back-trim the stack, make a small trim cut of 1–2mm on each side after the primary cut to produce clean edges. |
| UV varnish orange peel | Large spot UV or flood UV varnish areas show a textured surface, a dimpled, slightly rough appearance visible in raking light. The varnish looks more like an orange skin than a smooth high-gloss surface. | UV varnish viscosity too high, the varnish does not level before curing. Press speed too high, insufficient lamp exposure time for the varnish to cure and level. Insufficient UV lamp output, ageing lamps. The varnish surface area is too large for the ink unit to apply it with sufficient uniformity. | Reduce UV varnish viscosity by reducing dilution. Reduce press speed to increase lamp dwell time. Check UV lamp intensity, replace ageing lamps. For large solid UV panels, increase lamp power or add a second pass through the lamp. Consider switching from spot UV to flood UV for very large varnish areas where coverage uniformity is critical. |
| Crease cracking | When a carton is folded at a crease, the printed or laminated surface cracks or shows white lines at the crease position. Particularly visible on dark-coloured panels and immediately after erection of the carton. | Grain direction wrong, board folded against the grain. Crease rule incorrect depth or width for the board caliper. Lamination film too rigid for the crease (some lamination grades are less flexible than others). Very cold or dry ambient conditions causing board brittleness. UV varnish applied over crease area, standard UV varnish is rigid and cracks at creases. | Verify grain direction before production, grain must parallel the crease. Adjust crease rule depth for the specific board caliper, die-cutting supplier to advise. Use a crease-flexible lamination film grade. Keep UV varnish away from crease lines (minimum 5mm clearance). For UV varnish over crease-adjacent areas, specify a flexible UV varnish formulation. Maintain production humidity above 50% RH during creasing. |
Prevention · the press room disciplines that eliminate most defects
Most print defects are preventable. The same defects appear repeatedly in press rooms that lack systematic prevention disciplines, and rarely in press rooms that have them. The following disciplines eliminate or significantly reduce the incidence of the defects described in this guide.
Measure · do not guess
Every defect in this guide has a measurable root cause. Density drift causes colour variation, measure density. Dot gain causes heavy midtones, measure TVI. pH drift causes scumming, measure pH. A press room that measures consistently catches the cause before the defect appears in the print. A press room that relies on visual judgement only finds defects after the damage is done. The investment in a spectrophotometer, a pH meter, and a viscosity measurement cup is the highest-return quality investment a press room can make.
Clean · consistently, not only when there is a problem
Hickeys from dried ink, anilox clogging in flexo, and doctor blade contamination in gravure are all preventable by routine cleaning schedules. The cleaning that prevents these defects takes 15–30 minutes per shift. The production loss from stopping to chase a hickey problem mid-run takes significantly longer. Establish cleaning schedules and enforce them, at every job change, at every shift start, and at defined intervals during long runs.
Condition materials · paper, ink, and substrates
Paper conditioned to press room humidity for 24 hours before printing has fewer dimensional stability problems, fewer static issues, and fewer moisture-related defects. Ink conditioned to press room temperature flows correctly from the first sheet. Film substrates tested for corona treatment level before printing avoid adhesion failures. Material conditioning is free, it is a discipline, not an investment.
Qualify the process before committing to production
Every new paper, ink, or substrate combination should be qualified on a test run before a production commitment. A 100-sheet qualification run costs almost nothing. A reprint of a 50,000-sheet production run because the ink did not dry on the new paper grade costs enormously more. Never assume that a new material will behave identically to a previously used one, verify before committing.