Troubleshooting guide

Pad Printing Inks

Press-floor fault finding for the UniPad series: cliche, cup, pad, solvent balance and adhesion on three-dimensional parts.

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.

Change one thing at a time and log it; pad printing has four interacting variables (ink, cliche, pad, cycle rate) and a double change tells you nothing.
Before touching the ink, confirm the cliche and the pad, because most faults blamed on ink are a worn etch, a solid without a support screen, a scored doctor ring or a pad past its life.
Read solvent balance as two numbers, not one: thinner sets flow time, retarder sets open time, and the fault tells you which one is wrong.
Judge adhesion and resistance only on fully cured print: 72 h to 5 days at 20 to 25 C, or a forced cure of typically 15 to 30 min at 60 to 80 C where the part allows it. Confirm any bake against the substrate's heat distortion temperature first, because soft PVC softens from about 65 to 70 C and PS and PE from about 80 C, and qualify the oven schedule with a thermocouple on the customer's own part.
Measure surface energy on the actual part from the actual moulding lot, not on a sample printed last month, because treatment decays and mould release migrates.
When a two-component grade is in the cup, the clock runs whether the press does or not; pot life is elapsed time from mixing at a stated temperature, not running time, and it roughly halves for each 10 C the press room rises.
State the machine condition before any hand goes near it. The pad down-stroke onto plate and part is a crush point, the ceramic doctor ring edge cuts, and the cup carries spring or magnet force. Tack and pad-face checks are made with the pad stopped at the top of its stroke in guarded jog or single-shot with the cycle start released; ring, cup and plate work is done with the machine isolated and locked off; pad path is watched on the machine's own guarded single-cycle function, never a hand-turned or defeated cycle.
Work to the safety data sheet for the grade, thinner, retarder and cleaner in use before any procedure in this guide. Local exhaust ventilation at the machine, and never an open inkwell without extraction; nitrile gloves and eye protection for all ink, thinner, retarder, cleaner and rub testing; no ignition sources, containers bonded and earthed, lids closed, solvent-damp rags in a closed metal bin emptied each shift. Polyisocyanate hardeners are skin and respiratory sensitisers: handle under extraction with gloves and eye protection, hold the required diisocyanate handling training where it applies, and leave mixed waste in a vented container to react out rather than sealing it, because it continues to react and generates gas with moisture.

Pad Printing InksHow to use this guide

The process

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

The process

What is controlled at each step

Pad Printing InksThe process

Control variables

What to hold, and how to measure it

Variable	Target	How it is measured	How it drifts
Ink flow time, as run	Typical for this class, 18 to 25 s as run; set the working figure for your cliche and cycle rate and hold it to +/- 2 s	Flow cup to ISO 2431, 4 mm cup, ink and cup conditioned to 23 C +/- 0.5 C, sampled from the cup not the tin. Name the cup on every record, ISO 2431 No. 4 or DIN 53211 4 mm, because their times are not interchangeable, and keep the same cup and the same temperature for the life of the job	Rises through the shift as solvent leaves. Steep in an open inkwell, slow but never zero in a sealed cup. Shows first as loss of fine detail, then as patchy pick-up.
Solvent balance, thinner against retarder	Typically 15 to 25 % total addition by weight on a fresh mix, with retarder substituted for part of the thinner as the room warms	Weighed on a balance and logged per mix; open time confirmed by a gloved fingertip touch on the pad at the flash point, with the pad stopped at the top of its stroke and the cycle start released	Fast solvent leaves first, so the mix grows relatively slower and richer in retarder as the day goes on, then goes fast again at the next top-up. Print that dried well at 09:00 stays soft at 14:00.
Press room temperature	20 to 25 C, held to +/- 2 C across a shift	Calibrated thermometer at machine height within 1 m of the cup, not the plant gauge on the far wall	Climbs through the day and with every machine started nearby. Temperature, not humidity, is what drives evaporation from the open cell in a solvent ink. A 5 C rise shortens open time noticeably and roughly halves the pot life of a mixed two-component ink for each 10 C.
Relative humidity	45 to 60 % RH	Calibrated hygrometer at the machine, logged at start-up, mid-shift and end of shift	Falls in winter and under air conditioning. Relative humidity has little direct effect on the evaporation of organic solvents; what it does is raise static on moulded parts below about 40 % RH and pull dust into the wet film, and at high RH shorten the pot life of a two-component mix through the isocyanate and water reaction and cause blushing with fast blends.
Cliche etch depth and solid support screen	About 25 micron for steel, 18 to 25 micron for thin photopolymer, held to +/- 3 micron across the image; about 28 to 30 micron on steel where opacity is critical and no deeper. Solid areas above about 8 to 10 mm across carry a fine support screen etched into the cell to the platemaker's standard, so the doctor ring rides on the screen lands instead of dipping into open cell	Calibrated dial depth gauge or optical profilometer at three points: a solid, a fine line and the image edge, with the machine isolated and the plate off where it has to come off. Record the screen ruling on the plate record with the depth measurements	Wears shallow under the doctor ring, fastest at the leading edge and around isolated fine detail. Opacity and detail go together as it wears. A solid with no support screen scoops and mottles from the first thousand cycles, whatever the depth reads.
Pad durometer	Harder pads, about Shore A 10 to 20, for fine detail on flat and gently curved faces, where less pad deformation means less image growth and cleaner release; softer pads, about Shore A 2 to 8, where the pad must conform into curvature, a recess or texture, accepting more image growth and a narrower release window	Hardness by durometer to ASTM D2240, scale stated on the record: Type OO below about Shore A 20, Type A above it, read at the stated dwell (1 s or 15 s, the same each time) on a flat area at least 6 mm thick and at least 12 mm from any edge, away from the printing face. Where the pad geometry cannot meet the specimen requirement, record the pad supplier's own stated hardness at fitting and track change by print growth and detail loss instead	Rises with age and solvent exposure as the silicone loses plasticiser. A small rise is inside the noise of a durometer reading on a curved pad, so the usable signal is image growth measured against the artwork and fine detail dropping out.
Doctor ring, cup seal and cup pressure	No wipe line, no ink haze on the land, no weep from under the ring, ring replaced on a counted cycle schedule rather than on complaint	x30 loupe on the ring edge and on the doctored plate with the machine isolated and locked off, using a cotton bud rather than a bare fingertip on the ceramic edge; a light box behind the plate shows any residual film. Spring or magnet pressure checked against the machine specification	The ceramic ring develops a flat and then a nick. Streaks appear at one repeatable position in the image and stay there through every ink change. Separately, the cup seal swells and nips with solvent and the spring or magnet pressure falls, and the cup starts to weep ink onto the land.

Pad Printing InksControl variables

Control variables

What to hold, and how to measure it

Variable	Target	How it is measured	How it drifts
Hardener addition and pot life	By weight to the ratio on the grade's Technical Data Sheet. Pot life is quoted at a stated temperature, for example about 8 h at 20 C for UNIPAD-20HR, and roughly halves for each 10 C the room rises, so the same mix is worth about 4 h in a 30 C press room. UNIPAD-12PP is supplied as a one-component polyolefin build; where a hardener option is offered for chemical resistance, take the ratio and the pot life from that grade's Technical Data Sheet, and qualify the mixed build on the customer's part, because the added crosslink density can cost adhesion on polypropylene	Weighed on a balance, mix time and press room temperature written on the cup in marker, elapsed time read off the clock	Flow time climbs slowly, then sharply in the last hour. Pot life is elapsed time from mixing and it runs through breaks and stoppages.
Substrate surface energy	Pad inks sit at about 28 to 32 mN/m and need the substrate to exceed them by roughly 8 to 10 mN/m. Treat polyolefin to at least 38 mN/m and aim for 42 mN/m or higher at the moment of printing, to leave margin for decay between treatment and press. Untreated engineering and styrenic plastics typically read about 34 to 46 mN/m: ABS 35 to 42, PS about 38, PVC about 39, PMMA about 41, PET 41 to 44, PC about 46. These are indicative only	Wetting tension by test liquids, in the manner of ASTM D2578: liquid drawn across the surface with a swab and the film judged at 2 s, on the actual part from the actual moulding lot, within the shift of printing. D2578 is written for polyethylene and polypropylene film, so on mouldings and other polymers the reading is indicative and is used for trend and pass or fail against your own treated reference, not as a conformity statement. Pens are a convenience version of the same test and drift as they age: date them and check against fresh liquids	Corona and flame treatment decay over hours to days as low molecular weight species migrate back. Recycled-content polyolefin falls faster. Mould release and slip additive bloom on standing parts, and a filled or recycled moulding can read well below the book value.
Cycle rate and pad open time	Set so the film is tacky, not wet and not skinned, at the moment the pad meets the part	Cycle timer on the machine plus a fingertip touch on a test transfer with the pad stopped at the top of its stroke; count the seconds between pick-up and transfer	Operators speed up for output and slow down for a fiddly load. Both move the tack window, and both are usually done without telling anyone.

Pad Printing InksControl variables

The mechanism

The tack window: why ink leaves the pad

Transfer is not adhesion, it is a race. The silicone pad is deliberately low-energy so ink barely wets it, and the pad-side surface of the film loses solvent while the pad travels. That drying makes the pad side tacky and leaves the part side open, so the film prefers the part and comes away whole. Too little open time and the film is still wet on both sides, so it splits and half stays on the pad. Too much and the pad-side skin sets, so the film tears at the edges and the detail closes. Retarder and cycle rate are the two levers on that window; pad pressure is not.

Pad Printing InksThe mechanism

02 | 20 faults

Faults

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

Fault 1 of 20

Image fills in, fine detail and reverses close up

WHAT YOU SEE

The first prints of the shift are clean, and within an hour serifs bridge and small reverse text closes. Wiping the plate by hand recovers it for two or three cycles, then it comes back.

WHAT IT LOOKS LIKE

CAUSES, MOST LIKELY FIRST

Solvent blend too fast for the cycle rateInk in the open etch skins over between the doctor stroke and pick-up, so the pad lifts a rubbery crust that spreads instead of a clean film.
Press room too warmEvaporation from the open cell rises steeply with temperature, so the same mix that worked at 21 C skins at 27 C. Relative humidity does not drive this in a solvent ink; a mix that has started to skin has changed by temperature, not by humidity.
Etch too shallow for the detail being asked of itA shallow cell holds little ink and skins through its whole depth at once, so fine detail closes before solids do.
Flow time corrected with more fast thinnerEach top-up of fast solvent lowers flow time briefly and then evaporates faster than the previous mix, so the skinning gets worse with every correction.
Cup parked clear of the image during stoppagesParking off the image leaves the etched cells open to air, so the ink in them skins before the run restarts. A one-component ink thickens by solvent loss; only a mixed two-component charge carries on reacting.

Pad Printing InksImage fills in, fine detail and reverses close up

Fault 1 of 20 · continued

Image fills in, fine detail and reverses close up

CHECK, IN THIS ORDER

Measure press room temperature with a calibrated thermometer at machine height and compare with the figure logged at start-up; log relative humidity as well, but read it as a static and dust indicator, not as a cause of skinning.
Measure flow time to ISO 2431 at 23 C +/- 0.5 C from the cup itself, with the cup named on the record, and compare with the ratio logged at mixing.
Measure etch depth at a solid, a fine line and the image edge with a dial depth gauge or optical profilometer against the plate specification, typically about 25 micron for steel, and confirm large solids carry their support screen.
With the machine isolated and locked off, inspect the cells under a x30 loupe for a dried skin or pigment build, and note whether the filling is confined to fine detail or spread across the image.

THEN CHANGE

Substitute matched retarder for part of the thinner in steps of 2 to 3 % by weight, mixing and re-measuring flow time after each addition.
Bring the room back to 20 to 25 C, or move the machine away from the heat source that changed.
Run at a steady cycle rate without long idle periods, and with a sealed cup park it over the image at every short stop so the cells stay flooded, discarding the first few prints on restart. For a stop longer than the ink's open time, and at end of shift, strip and clean the plate, cup and ring rather than leaving ink standing anywhere on the machine.
Re-etch or replace the cliche if depth is below specification, and open the fine detail slightly in the artwork if the part genuinely needs it.

CONFIRM IT IS FIXED

Run 200 consecutive cycles with no hand wiping, then measure the smallest positive line and smallest reverse on prints 1, 100 and 200 with a x30 measuring loupe. All three sit within the agreed tolerance with no trend across the three, and the reverse detail stays open. Set the tolerance from the first approved run of the job, typically of the order of +/- 0.05 mm on line width, and record it on the job sheet; a pad print gains at the edges by design and will not measure identical to the artwork.

THE TRAP

Adding more fast thinner. Flow time drops and the press feels better for ten minutes, then the mix evaporates faster than before and closes the detail harder. The correction is retarder, not thinner.

Pad Printing InksImage fills in, fine detail and reverses close up (continued)

Fault 2 of 20

Patchy pick-up, part of the image missing

WHAT YOU SEE

The print is complete in some areas and absent or broken in others, usually the same areas each cycle. Larger solids suffer before fine lines do.

WHAT IT LOOKS LIKE

CAUSES, MOST LIKELY FIRST

Pad face contaminated with silicone oil, dust or dried inkA contaminated face has lower surface energy than clean silicone in those spots, so the ink refuses to wet it and is left in the cell.
New pad not preparedA pad as moulded carries a residual release and silicone oil film, so it picks up ink unevenly for the first cycles until the face is wiped off and run in.
Ink flow time too highThick ink will not flow out of the cell against the pad's short contact time, so the pad lifts only the top of the film.
Pad too soft or wrong shape for the imageA soft or flat-faced pad lands rather than rolls and traps air between pad and cell, so the trapped area comes away empty.
Etch too deep in that area, or a large solid with no support screenDeep cells hold more ink than the pad can lift in one compression, and an unscreened solid lets the doctor ring dip and scoop, so both leave a residue and a mottled print.

Pad Printing InksPatchy pick-up, part of the image missing

Fault 2 of 20 · continued

Patchy pick-up, part of the image missing

CHECK, IN THIS ORDER

With the machine stopped at the top of the stroke and the cycle start released, examine the pad face and the cells under a x30 loupe after a pick-up, and note whether ink is left in the cell or missing from the pad.
Check the pad condition and its hardness record from fitting, reading to ASTM D2240 with the scale stated where the pad geometry allows a valid reading.
Measure flow time to ISO 2431 at 23 C +/- 0.5 C and compare with the working figure for this cliche.
Map the failing areas against the etch depth measured with a dial depth gauge, against the support screen in the solids, and against the pad's contact geometry.

THEN CHANGE

Wipe the pad face with the recommended cleaner and a lint-free cloth, or change to a fresh pad if the face has gone glazed.
Prepare a new pad before production: wipe the face with adhesive tape or the recommended cleaner and run twenty to thirty cycles onto scrap.
Thin to the working flow time with the matched thinner, in 2 % steps by weight.
Fit a pad with a steeper, more pointed profile so contact rolls out from a line instead of landing flat.
Increase pad compression on the plate in small increments until the whole image lifts, then stop; excess compression deforms the image.

CONFIRM IT IS FIXED

Twenty consecutive prints show the complete image with no missing area, and inspection of the cliche under a x30 loupe after pick-up, machine isolated, shows the cells emptied evenly across the whole image.

THE TRAP

Winding pad pressure up to force the pick-up. It usually works for a few cycles, then the pad begins to spread on the plate, the image grows and the edges go ragged, and now there are two faults instead of one.

Pad Printing InksPatchy pick-up, part of the image missing (continued)

Fault 3 of 20

Ink stays on the pad, incomplete release

WHAT YOU SEE

The print on the part is thin or partial and a mirror of the missing area is visibly still sitting on the pad face at the top of the stroke.

WHAT IT LOOKS LIKE

CAUSES, MOST LIKELY FIRST

Open time too short, the film is still wet at transferRelease depends on the pad-side surface drying faster than the part-side; a wet film wets the silicone as readily as the part and splits rather than transfers.
Substrate surface energy too lowThe part cannot out-compete the pad for the ink, so the film stays where it already wets. Classic on untreated PP, PE and silicone-contaminated mouldings.
Pad face swollen or glazed by the wrong cleanerAggressive general solvent swells the silicone and leaves a tacky, matt face that holds the film instead of letting it go.
Too much retarder in the mixThe pad-side surface never reaches the tacky stage inside the cycle, so there is no release differential to drive transfer.
Part temperature well below room temperatureA cold part slows the interfacial wetting on the part side and favours the pad, particularly on metal and on parts brought in from outside.

Pad Printing InksInk stays on the pad, incomplete release

Fault 3 of 20 · continued

Ink stays on the pad, incomplete release

CHECK, IN THIS ORDER

Stop the cycle with the pad at the top of its stroke in guarded jog or single-shot, cycle start released, then touch the film with a gloved fingertip at the point transfer would occur; a correct film is tacky and marks the glove without stringing.
Measure wetting tension on the part with test liquids in the manner of ASTM D2578, on a part from the lot about to be run, not on a retained sample.
Check the retarder proportion against the mix log, and measure flow time to ISO 2431 at 23 C +/- 0.5 C.
Measure part temperature with a contact probe or surface thermocouple and compare with press room temperature; on bright metal and glossy dark mouldings do not rely on an infrared reading, which is emissivity-dependent and can be wrong by tens of degrees.
After any pad clean or a pad change, run twenty to thirty conditioning cycles onto scrap and see whether pick-up and release settle.

THEN CHANGE

Increase the delay between pick-up and transfer, or reduce the retarder in favour of matched thinner in 2 % steps.
Flame, corona or plasma treat the part to at least 38 mN/m, aiming at 42 mN/m or higher, and print within 24 h of treatment. Where the polypropylene is clean, trial UNIPAD-12PP, which is formulated for polyolefin adhesion with reduced dependence on pretreatment, and qualify it on the customer's own moulding lot before committing.
Return to the recommended pad cleaner and a lint-free cloth, and replace a face that has gone matt or tacky.
Allow cold parts to reach press room temperature before printing.

CONFIRM IT IS FIXED

Fifty consecutive transfers leave the pad face clean, and the print on the part carries the full image, assessed spectrophotometrically against the approved standard where the geometry allows a reading, reporting delta E 00 with the measurement conditions stated (ISO 13655, M1), or visually against the approved retained sample under standardised D50 viewing to ISO 3664 where it does not.

THE TRAP

Reaching for tack-reducing additive or for a softer pad. Neither addresses the release differential, and a softer pad deforms more, grows the image and releases less cleanly, so the symptom deepens.

Pad Printing InksInk stays on the pad, incomplete release (continued)

Fault 4 of 20

Adhesion fails cross-cut or tape on polyolefin

WHAT YOU SEE

The print looks perfect and can be lifted whole with adhesive tape, or a thumbnail takes it off in a sheet. Usually on polypropylene or polyethylene, sometimes on acetal or PBT.

WHAT IT LOOKS LIKE

CAUSES, MOST LIKELY FIRST

Surface energy below the wetting thresholdPad inks sit at about 28 to 32 mN/m and need the substrate to exceed them by roughly 8 to 10 mN/m, so untreated PP and PE at 29 to 31 mN/m cannot anchor the film. Surface energy is a wetting precondition, not a prediction of adhesion.
Treatment has decayed since the part was treatedLow molecular weight species migrate back to the surface within hours to days, and recycled-content polyolefin does it faster, so a part treated last week is not a treated part. A reading of 38 mN/m sits at the bottom of the wetting condition and routinely fails a cross-cut once decay is added.
Mould release or internal slip additive on the surfaceA monolayer of silicone or fatty amide keeps the ink from ever touching the polymer, which is why some polypropylene mouldings print well and the next lot does not.
Wrong grade for the substrateA one-component ink that works by solvent bite has nothing to bite into on a crystalline polyolefin or a solvent-resistant engineering plastic.
Hardener omitted, under-dosed or the ink used past pot lifeWithout full crosslinking there is no chemical anchoring to the oxidised groups that treatment created.

Pad Printing InksAdhesion fails cross-cut or tape on polyolefin

Fault 4 of 20 · continued

Adhesion fails cross-cut or tape on polyolefin

CHECK, IN THIS ORDER

Test wetting tension with test liquids in the manner of ASTM D2578 on the part about to be printed, and repeat on a freshly treated part to see how far it has decayed.
Run a cross-cut to ISO 2409 on fully cured print, 72 h to 5 days at 20 to 25 C or after a qualified forced cure: lattice of six cuts each way at 1 mm spacing for films up to 60 micron on a hard substrate and 2 mm on a soft one, cut with a sharp blade through to the substrate without gouging, brushed, then a 25 mm tape of 10 +/- 1 N/25 mm peel adhesion applied and removed at the specified angle.
Wipe a part with isopropanol, dry it, print it and re-test; recovery points to surface contamination rather than to the ink. Do not use this on stress-sensitive plastics such as PC, PMMA, PS and ABS, where the solvent itself can craze the part.
Check the hardener weight and mixing time against the log, and confirm the grade against the substrate on the Technical Data Sheet.
Ask the moulder for the release agent and masterbatch in use, and whether the lot contains recycled content.

THEN CHANGE

Flame, corona or plasma treat to at least 38 mN/m, aiming at 42 mN/m or higher at the moment of printing, and print within 24 h.
Where the polypropylene is clean, trial UNIPAD-12PP, which is formulated for polyolefin adhesion with reduced dependence on pretreatment; qualify it by cross-cut on fully cured print on the customer's own moulding lot before committing, and treat the part where the trial fails.
Where chemical resistance is also required, take the hardener ratio and the pot life from the grade's Technical Data Sheet, add the hardener by weight, mark the mixing time and press room temperature on the cup, and discard at pot life.
Have the moulder change to a non-silicone release, or degrease the parts in line before printing.
Where treatment is not available on the shape, qualify a primer on the customer's own part before committing the job.

CONFIRM IT IS FIXED

Cross-cut to ISO 2409 on fully cured print gives classification 0 or 1 on five parts taken across the moulding lot, repeated after the pack's own condition where one applies. On plastics the classification is comparative, so it is valid only against the customer's own part and an agreed retained reference. Adhesion belongs to the part and the ink together and cannot be guaranteed from the ink alone.

THE TRAP

Repeating the tape test an hour after printing and passing it. Solvent still in the film makes a soft print grip the tape. The honest test is after full cure, and it is the one the customer will do.

Pad Printing InksAdhesion fails cross-cut or tape on polyolefin (continued)

Fault 5 of 20

Pinholes, fisheyes and craters in the printed film

WHAT YOU SEE

Small round voids in solids, with a visible rim, sometimes showing the substrate. Often clustered in one area of the part or on one cavity's output.

WHAT IT LOOKS LIKE

CAUSES, MOST LIKELY FIRST

Silicone contamination on the partA low surface energy spot repels the wet film outward from the centre, opening a crater with a raised rim. Mould release and aerosol lubricants are the usual sources.
Silicone or oil contamination in the ink or cupOnce in the ink the defect follows the job from part to part and no amount of part cleaning fixes it.
Air entrained in the inkVigorous stirring, topping up onto a low charge, or a ring that is not seating entrains air, and the bubble bursts in the film after transfer, often as chains of small voids that follow the ink rather than the part.
Dust and airborne fibre settling on the wet filmParticulate landing after transfer is wetted by the film, which draws back around it and leaves a void when the particle falls off.
Part surface too cold or wet with condensationCondensed moisture breaks the film locally and leaves a circular void.

Pad Printing InksPinholes, fisheyes and craters in the printed film

Fault 5 of 20 · continued

Pinholes, fisheyes and craters in the printed film

CHECK, IN THIS ORDER

Look at the void under a x30 loupe: a smooth raised rim points to silicone, a broken edge points to a burst bubble, a fibre in the centre points to dust.
Print a known clean control part with the same cup and ink; defects that persist are in the ink, defects that vanish are on the part.
Check whether the fault tracks one mould cavity by printing parts marked by cavity number.
Measure part temperature with a contact probe or surface thermocouple against room dew point on cold mornings, rather than with an infrared thermometer, whose reading on bright or glossy parts is emissivity-dependent.
With the machine isolated and locked off, inspect the cup seal and ring seat for a slow leak or a nipped seal, and check the stirrer for aeration.

THEN CHANGE

Isolate the machine from silicone sprays and mould release aerosols, and stop any nearby use of them; silicone travels on air.
Discard the contaminated ink, strip and clean the cup, pad and plate, and make a fresh mix.
Degrease the parts with isopropanol and a lint-free cloth where the polymer tolerates it, or have the moulder change to a non-silicone release.
Stir at low shear, top up onto a working charge rather than a nearly empty cup, and re-seat the ring so it seals to the plate.
Extract and filter the air at the machine, and enclose the load and transfer zone.

CONFIRM IT IS FIXED

Fifty consecutive parts across at least two mould cavities show no void greater than 50 micron in any solid area, measured with a graticule loupe or a measuring microscope, with that limit and the measuring method stated in the job specification.

THE TRAP

Adding flow additive or levelling aid to make the craters heal. It masks light contamination, then changes the release balance on the pad and the wetting on the part, and the job starts failing adhesion instead.

Pad Printing InksPinholes, fisheyes and craters in the printed film (continued)

Fault 6 of 20

Ragged, sawtooth or feathered image edges

WHAT YOU SEE

Edges that should be sharp look serrated or furred under a loupe, sometimes only on the trailing edge of the image, sometimes all round.

WHAT IT LOOKS LIKE

CAUSES, MOST LIKELY FIRST

Ink surface skinning on the pad before transferA partly set film tears rather than splits cleanly, and the tear follows a jagged line.
Too much compression on the part, or a pad too soft for the jobAn over-compressed or over-soft pad slips at the edge of contact rather than rolling, and drags the film sideways as it lands.
Poor doctoring leaving a thin film on the landInk outside the etch transfers as a fringe and reads as a feathered edge.
Static on the partCharge on a moulded plastic part pulls ink filaments outward from the edge as the pad lifts away.
Etch walls worn or raggedA worn cell edge prints a worn edge; no ink or press adjustment recovers it.

Pad Printing InksRagged, sawtooth or feathered image edges

Fault 6 of 20 · continued

Ragged, sawtooth or feathered image edges

CHECK, IN THIS ORDER

Inspect the edge under a x30 loupe and decide whether it is torn (dry film), smeared in one direction (pad slip), or fringed all round (doctoring or static).
With the machine isolated, hold the cliche to a light box after doctoring and look for residual ink film on the land.
Check the pad against its hardness record at fitting, reading to ASTM D2240 with the scale stated where the geometry allows a valid reading, and measure the printed image against the artwork for growth.
Check for static with a field meter or by observing whether dust jumps to the part, particularly below 40 % RH.
Measure etch depth and examine cell walls with a dial depth gauge and a loupe.

THEN CHANGE

Add matched retarder in 2 to 3 % steps to hold the film open through the stroke.
Reduce pad compression on the part to the minimum that gives full transfer, and fit a more pointed profile so contact rolls out from a line. Change hardness only in the direction the part geometry requires, and expect a softer pad to grow the image and release less cleanly rather than to sharpen the edge.
Replace or re-seat the doctor ring, and confirm the cup seals flat to the plate.
Fit an ionising bar at the load position, and raise room humidity to 45 to 60 % RH.
Re-etch or replace the cliche where the cell walls have gone.

CONFIRM IT IS FIXED

Twenty consecutive prints inspected at x30 show a continuous edge with no serration visible, and a 0.2 mm positive line reproduces within the agreed tolerance with parallel sides.

THE TRAP

Increasing pad pressure to crush the edge flat. The image gains size, the edge gains a halo, and the pad wears out early.

Pad Printing InksRagged, sawtooth or feathered image edges (continued)

Fault 7 of 20

Doctor streaks in the same place every cycle

WHAT YOU SEE

One or more fine lines running in the doctoring direction, in the same position on every print, unchanged by ink or pad changes.

WHAT IT LOOKS LIKE

CAUSES, MOST LIKELY FIRST

Nick or flat on the ceramic doctor ringA damaged ring edge leaves an unwiped ribbon of ink on the land at that point, which transfers as a line.
Hard particle trapped between ring and plateDried ink, pigment agglomerate or swarf rides under the ring and scores both the ring and the plate.
Cliche surface scoredA scratch in the land holds ink below the ring edge, so the fault is now permanent in the plate.
Cup not seating flat, or spring and magnet pressure fallenUneven seating leaves a gap at one edge of the ring, wiping cleanly at one side and poorly at the other, and a weak cup weeps ink onto the land as it travels.
Ink too coarse or poorly dispersedOversized particles will not pass under the ring and drag, which is why an incompletely stirred or contaminated mix streaks.

Pad Printing InksDoctor streaks in the same place every cycle

Fault 7 of 20 · continued

Doctor streaks in the same place every cycle

CHECK, IN THIS ORDER

With the machine isolated and locked off, run the ring edge under a x30 loupe using a cotton bud, never a bare fingertip, and find the nick.
With the machine isolated, rotate the cup by a few degrees and restart: a streak that moves with the cup is the ring, a streak that stays put is the plate.
Inspect the cliche land under raking light for a score line.
Determine fineness of grind on a grind gauge to ISO 1524, recording the scale and the reading, and compare with a fresh sample from a sealed tin of the same grade; also filter a sample through the mesh specified for the grade.
Check the cup mounting for flat seating and even spring or magnet pressure against the machine specification.

THEN CHANGE

Replace the doctor ring; a nicked ring is consumable, not repairable.
Strip and clean the cup, plate and ring, and filter the ink back through a mesh before returning it.
Re-lap or replace the cliche where the land is scored.
Re-seat the cup, renew a swollen or nipped seal, and reset the spring or magnet pressure to the machine specification.
Work from freshly stirred ink and keep the cup lid closed between runs.

CONFIRM IT IS FIXED

Fifty consecutive prints show no line in the doctoring direction, and the doctored plate viewed against a light box carries no residual film on the land.

THE TRAP

Increasing doctor ring pressure to wipe the streak away. It cuts the ring and the plate faster, so the single line becomes several within a shift.

Pad Printing InksDoctor streaks in the same place every cycle (continued)

Fault 8 of 20

Print too thin, opacity below standard

WHAT YOU SEE

The colour reads weak against the approved sample, particularly white and yellow on a dark part, and two hits are needed where one used to do.

WHAT IT LOOKS LIKE

CAUSES, MOST LIKELY FIRST

Pigment settled in the cupHeavier pigments, particularly titanium dioxide whites, settle if the ink stands, and the top layer that reaches the cell is weak.
Ink over-thinnedThinner adds no pigment; every 5 % addition dilutes the film that reaches the part.
Etch depth worn shallowInk film on the part is set by the volume in the cell, so a plate that has lost 5 micron has lost about a fifth of its laydown.
Poor cell emptying on pick-upIf the pad lifts only part of the cell contents the print is thin even though the plate is right.
Wrong build for an opacity-critical jobHigh opacity needs a high pigment load in a dry film of only about 2 to 5 micron; a general build asked to cover a dark moulding will not get there in one hit.

Pad Printing InksPrint too thin, opacity below standard

Fault 8 of 20 · continued

Print too thin, opacity below standard

CHECK, IN THIS ORDER

Stir the cup thoroughly, make ten prints and see whether the colour recovers.
Check the thinner addition against the mix log, and measure flow time to ISO 2431 at 23 C +/- 0.5 C.
Read the print against the approved standard: spectrophotometrically where the geometry allows, reporting delta E 00 with the measurement conditions stated (ISO 13655, M1), or visually against the retained sample under standardised D50 viewing to ISO 3664.
With the machine stopped and the cycle start released, inspect the cliche after pick-up under a x30 loupe for ink left in the cells.
Only then take the plate out and measure etch depth in a solid with a dial depth gauge or optical profilometer against the plate specification.

THEN CHANGE

Keep the ink stirred and do not run from a cup that has stood overnight without remixing.
Return the flow time to the working figure with a slower blend rather than more thinner, and rebuild the mix if it has been over-thinned.
Re-etch the cliche to the plate specification, and where opacity is critical specify a deeper solid, typically 28 to 30 micron on steel. Do not go beyond about 30 micron: deeper cells do not empty in one pad compression and the gain in opacity is lost to mottle and residue.
Specify an opaque or high-pigment build within the grade family already correct for the substrate and the exposure. Grade follows substrate and resistance; opacity follows pigment loading and cell volume. Where one hit cannot cover, lay an opaque white first and the colour second.

CONFIRM IT IS FIXED

Ten consecutive prints match the approved standard within the agreed tolerance, recorded as delta E 00 to ISO 13655 M1 where a reading is possible and as a visual match to ISO 3664 D50 where it is not, with the figure written down so it can be repeated at the next run.

THE TRAP

Increasing the printing pressure to push more ink out. The film on the part is set by the cell volume, not by pressure; all that comes back is a spread image and a shorter pad life.

Pad Printing InksPrint too thin, opacity below standard (continued)

Fault 9 of 20

Image distorted or stretched on a curved part

WHAT YOU SEE

Text and logos that are correct on the cliche come out elongated, compressed or bowed on the part, worst on strongly domed or recessed surfaces.

WHAT IT LOOKS LIKE

CAUSES, MOST LIKELY FIRST

Pad shape wrong for the part geometryThe pad face stretches as it rolls; a shape that rolls out unevenly across a curve applies uneven stretch to the image.
Excessive compression on the partOver-compression flattens the pad beyond its designed roll and spreads the image outward at the contact edges.
Part not seated squarely in the jigAn offset part meets the pad off its axis, so one side of the image is stretched and the other is compressed.
Cliche artwork not distortion-compensatedPad printing onto a curve needs pre-distorted artwork; without it, the geometry error is in the plate and no press setting removes it.
Pad too soft for the workA soft pad deforms more as it rolls and wraps into a recess, so it drags the film and grows the image; hardness is chosen for the depth of curvature, and only as much softness as the geometry demands.

Pad Printing InksImage distorted or stretched on a curved part

Fault 9 of 20 · continued

Image distorted or stretched on a curved part

CHECK, IN THIS ORDER

Print onto a flat reference part with the same pad and plate; a correct flat print puts the fault in the geometry, not in the artwork.
Measure the printed image on the part against the artwork dimension with a measuring loupe or a shadowgraph.
Check the jig with a dial gauge or a feeler for consistent seating across ten parts, machine isolated.
Reduce pad compression in small increments and re-measure the printed dimension at each setting.

THEN CHANGE

Fit a pad shape matched to the part, generally a steeper cone or a bar pad running across the curve rather than along it, and no softer than the curvature requires.
Set pad compression to the minimum that gives complete transfer.
Re-machine or re-set the jig so the part presents squarely and repeatably.
Pre-distort the artwork and re-make the cliche where the curvature is significant.

CONFIRM IT IS FIXED

The printed image measures within the agreed dimensional tolerance on ten parts taken across a production run, checked with a measuring loupe or shadowgraph against the artwork.

THE TRAP

Redrawing the artwork to chase the distortion before checking the jig and the pad. If the part seating is inconsistent, the compensation is different on every part and the redraw makes it worse on half of them.

Pad Printing InksImage distorted or stretched on a curved part (continued)

Fault 10 of 20

Two-component ink gels in the cup before the shift ends

WHAT YOU SEE

Flow time climbs slowly, then sharply. Thinner no longer brings it back, the ink strings on the plate, and there is a rubbery skin in the cup.

WHAT IT LOOKS LIKE

CAUSES, MOST LIKELY FIRST

Pot life exceededThe isocyanate and polyol carry on reacting whether the press runs or not. Pot life is quoted at a stated temperature, for example about 8 h at 20 C for UNIPAD-20HR; read the figure and the temperature from the grade's Technical Data Sheet.
Press room too warmCrosslinking rate roughly doubles for each 10 C rise, so a 30 C afternoon halves the working window against the 20 C figure.
Hardener over-dosedExcess hardener accelerates the build and consumes the pot life early, without improving final resistance.
Moisture in the mixIsocyanate reacts with water, from a damp thinner, a wet cup or high humidity, and the reaction is faster than the one wanted.
Fresh ink topped into a partly reacted mixThe old reacted material seeds the new, so the fresh addition sets faster than a clean mix would.

Pad Printing InksTwo-component ink gels in the cup before the shift ends

Fault 10 of 20 · continued

Two-component ink gels in the cup before the shift ends

CHECK, IN THIS ORDER

Read the mixing time and press room temperature written on the cup and compare with the clock, counting breaks and stoppages.
Measure flow time to ISO 2431 at 23 C +/- 0.5 C every hour and plot it; a sharp upward turn marks the end of usable life.
Check the hardener weight against the ratio on the Technical Data Sheet, and check that a balance was used rather than a graduated jug.
Measure room temperature and relative humidity, and check the thinner container for water contamination.

THEN CHANGE

Mix in quantities that match the shift, and discard at pot life rather than reviving with thinner.
Bring the press room back to 20 to 25 C, and store mixed ink in the shade of the machine, not under a lamp.
Weigh the hardener on a balance to the stated ratio, and mark the mixing time and the room temperature on the cup.
Use fresh, sealed thinner and dry cups, and keep containers closed in humid weather.
Start each new charge in a clean cup rather than topping up a mix that is hours old.

CONFIRM IT IS FIXED

Flow time measured hourly to ISO 2431 at 23 C +/- 0.5 C stays inside the working band up to the declared pot life, with matched thinner the only permitted correction, and shows no sharp upward turn before it; the mix is discarded at the declared time whatever the reading. Record the curve, because the shape and not a single figure is what triggers the discard, and the last print of the mix passes the same cross-cut to ISO 2409 as the first.

THE TRAP

Thinning a gelling mix to keep it running. The crosslinking has already happened, so thinner only carries the partly reacted resin onto the part, and the print looks acceptable while failing resistance at the customer.

Pad Printing InksTwo-component ink gels in the cup before the shift ends (continued)

Fault 11 of 20

Shade drifts through the shift

WHAT YOU SEE

The first hour matches the approved sample and by mid-shift the colour has moved, usually lighter and duller, and the operator is comparing prints an hour apart without noticing.

WHAT IT LOOKS LIKE

CAUSES, MOST LIKELY FIRST

Flow time rising as solvent leavesThicker ink empties the cell less completely, so film weight on the part falls and the colour weakens.
Irregular thinner additionsAdding by eye rather than by weight changes pigment concentration from one top-up to the next.
Pigment settling in the cup or reservoirHeavier pigments drop out on standing, so shade moves in whichever direction the dominant pigment settles.
Cliche etch wearing during a long runA gradual loss of cell volume reads as a gradual loss of strength that no ink adjustment recovers.
Part colour or gloss varying between moulding lotsA dry film of only about 2 to 5 micron is semi-transparent in many shades, so the substrate shows through and the apparent colour follows the part.

Pad Printing InksShade drifts through the shift

Fault 11 of 20 · continued

Shade drifts through the shift

CHECK, IN THIS ORDER

Measure flow time to ISO 2431 at 23 C +/- 0.5 C hourly and log it against the time of every top-up.
Compare prints against the approved standard every hour, not against the previous hour's print: spectrophotometrically as delta E 00 to ISO 13655 M1 where the geometry allows, otherwise visually under D50 to ISO 3664, with a second illuminant such as A or the customer's store lighting checked for metamerism.
Read the substrate itself against the retained part sample; lot to lot substrate variation is often the whole of the drift.
Measure etch depth at the start and end of a long run with a dial depth gauge.
Where the geometry allows a flat reading, measure gloss to ISO 2813 at 60 degrees as a second indicator of film weight.

THEN CHANGE

Fix a top-up procedure: weighed additions, logged, with flow time measured after each one.
Stir the reservoir on a schedule, and remix any ink that has stood.
Replace or re-etch the cliche when depth falls out of specification.
Retain a signed colour standard and check against it hourly, keeping a boxed sample from each hour for the run record.
Where the substrate varies, print an opaque white first or move to a higher opacity build within the same grade family.

CONFIRM IT IS FIXED

Prints boxed hourly across a full shift all match the approved standard within the agreed tolerance, recorded as delta E 00 to ISO 13655 M1 or as a visual match under D50 to ISO 3664, with the flow time log showing no more than 2 s of movement.

THE TRAP

Correcting the shade by adding a touch of another colour to the cup. It buries the real cause, makes the mix unrepeatable and leaves the next shift with an ink that matches nothing on the shelf.

Pad Printing InksShade drifts through the shift (continued)

Fault 12 of 20

Ink filaments, hairs and spray around the image

WHAT YOU SEE

Fine whiskers of ink radiating from the image edge, loose fibres and dust stuck into the print, worse in dry weather and on freshly moulded parts.

WHAT IT LOOKS LIKE

CAUSES, MOST LIKELY FIRST

Static charge on the plastic partCharge on an insulating moulding pulls ink filaments off the pad as it separates, and attracts airborne dust onto the wet film.
Low relative humidityBelow about 40 % RH charge cannot dissipate through the surface, so every handling step adds to it. This, and not evaporation rate, is what humidity does to a solvent pad ink.
Ink too stringy, thinner too slow or too much retarderA long, wet film separates in threads rather than splitting cleanly.
Airborne fibre and ink mist in the press roomCardboard, clothing and air handling carry fibre that a charged part collects, and at high cycle rates the machine throws its own fine ink mist onto adjacent stations and printed colours.
Pad separation too fastA rapid lift stretches the film beyond its clean break point and leaves filaments standing.

Pad Printing InksInk filaments, hairs and spray around the image

Fault 12 of 20 · continued

Ink filaments, hairs and spray around the image

CHECK, IN THIS ORDER

Measure relative humidity with a calibrated hygrometer at the machine.
Test for charge with a field meter, or watch whether shredded paper jumps to the part.
Inspect the whiskers under a x30 loupe: ink filaments point to static or stringing, fibres with ink around them point to airborne contamination, an even fine speckle away from the image points to ink mist.
Check the retarder proportion against the mix log and measure flow time to ISO 2431 at 23 C +/- 0.5 C.

THEN CHANGE

Fit ionising bars at the load station and at the print station, and earth the jig.
Raise room humidity to 45 to 60 % RH.
Reduce the retarder and return to the matched thinner blend at the working flow time.
Slow the pad lift at separation if the machine allows it.
Enclose the print zone, extract at the machine and keep cardboard out of the immediate area.

CONFIRM IT IS FIXED

Fifty consecutive parts inspected under a x30 loupe show no ink filament outside the image boundary and no embedded fibre, with room humidity logged at 45 to 60 % RH.

THE TRAP

Blowing the parts off with compressed air. The air stream charges the plastic further, so the parts come back dirtier than they went, and the oil and water in an unfiltered line adds a contamination fault.

Pad Printing InksInk filaments, hairs and spray around the image (continued)

Fault 13 of 20

Pad swells, softens or loses its shape

WHAT YOU SEE

The pad face looks matt and swollen, the print grows in size over a few hundred cycles, detail drops out, and the pad no longer returns to its original profile.

WHAT IT LOOKS LIKE

CAUSES, MOST LIKELY FIRST

Solvent attack from an over-retarded or aggressive mixSilicone absorbs slow, strong solvents, swells and loses definition; the effect builds over hours and is only partly reversible.
Wrong cleaning solventGeneral purpose thinners and aggressive degreasers swell silicone far faster than the recommended pad cleaner.
Pad simply at end of lifeSilicone loses plasticiser with cycles and heat, so hardness rises, then the surface cracks and the profile collapses.
Excess compression on plate or partOver-compression works the silicone mechanically and accelerates both swelling and fatigue.
Pad stored in contact with solvent or in direct sunA pad left face down in a solvent-damp tray or on a sunny bench degrades before it is ever fitted.

Pad Printing InksPad swells, softens or loses its shape

Fault 13 of 20 · continued

Pad swells, softens or loses its shape

CHECK, IN THIS ORDER

Measure the printed image dimension against the artwork with a measuring loupe and track how it has grown over the run; image growth and lost detail are the reliable signal, because a durometer reading on a curved pad face carries more noise than the change you are looking for.
Where the pad has a flat area at least 6 mm thick and 12 mm from an edge, read hardness to ASTM D2240 with the scale stated, Type OO below about Shore A 20, and compare with the figure recorded at fitting.
Check which cleaner is actually in use at the machine, against the recommended one.
Count cycles on the pad against the life recorded for the same pad on previous runs.
Inspect the face under a x30 loupe for a matt, crazed or tacky surface.

THEN CHANGE

Return to the recommended pad cleaner and a lint-free cloth only.
Reduce retarder and return to the matched thinner blend at the working flow time.
Replace the pad, and record cycles so replacement becomes scheduled rather than reactive.
Reduce compression on both plate and part to the minimum that transfers the full image.
Store pads face up, dry, out of sunlight, and away from solvent vapour.

CONFIRM IT IS FIXED

A fresh pad printed at the same settings reproduces the artwork dimension within the agreed tolerance, with the hardness figure and scale, or the supplier's stated hardness, recorded at fitting as the reference for the next comparison.

THE TRAP

Wiping a swollen pad with more solvent to clean it up. The swelling is caused by solvent absorption, so the cleaning drives the fault harder and the pad is scrap by the end of the shift.

Pad Printing InksPad swells, softens or loses its shape (continued)

Fault 14 of 20

Second colour will not trap on the first

WHAT YOU SEE

The second-down colour beads, transfers partially, or lifts the first colour back onto the pad. Worst where the second colour overlaps a heavy solid.

WHAT IT LOOKS LIKE

CAUSES, MOST LIKELY FIRST

First colour still wet at the second stationThe second pad wets the soft film better than the part does and picks it off, taking both colours away.
First colour over-dried or already crosslinkedA fully cured two-component film has low surface energy and no solvent for the second ink to bite into, so the second colour beads.
Cycle rate changed without changing the solvent balanceSpeeding up shortens the inter-station time and leaves the first colour wet; slowing down over-dries it.
Mismatched grades between stationsTwo different builds can have incompatible solvent and resin systems, so one refuses to wet the other.
First colour film too heavyA thick film holds solvent longer and stays soft at the second station.

Pad Printing InksSecond colour will not trap on the first

Fault 14 of 20 · continued

Second colour will not trap on the first

CHECK, IN THIS ORDER

With the machine stopped in guarded single-shot and the cycle start released, touch the first colour at the second station position with a gloved fingertip; it should be set to touch and not transfer.
Count the seconds between stations at the running cycle rate and compare with the rate at which the job last ran well.
Confirm both stations are running the same grade family, and check the hardener status of each.
Measure the first colour's film weight indirectly by etch depth on its cliche with a dial depth gauge.
Run a cross-cut to ISO 2409 through both layers on fully cured print to see which interface is failing.

THEN CHANGE

Increase the inter-station distance, add an intermediate station, or fit warm air between stations to set the first colour.
Adjust the first colour's solvent balance with matched retarder or thinner so it is set to touch but not cured when the second arrives.
Bring both stations onto the same grade family, and keep trapping sequences light colour over dark where the job allows.
Reduce the first colour's etch depth where opacity permits, so it empties and sets faster.

CONFIRM IT IS FIXED

Twenty consecutive two-colour prints show full second colour coverage with no lift of the first, and a cross-cut to ISO 2409 on fully cured prints gives classification 0 or 1 through both layers on the customer's own part.

THE TRAP

Slowing the press to give the first colour more time. It usually crosses the window the wrong way, the first film goes past the point where the second can bite into it, and the beading gets worse while output falls.

Pad Printing InksSecond colour will not trap on the first (continued)

Fault 15 of 20

Print cracks or lifts when the part flexes

WHAT YOU SEE

On rubber, soft-touch, soft PVC and textile items the print is sound flat, then crazes, splits or peels along the fold as soon as the part is squeezed, stretched or laundered.

WHAT IT LOOKS LIKE

CAUSES, MOST LIKELY FIRST

Rigid grade on a flexible substrateA hard, highly crosslinked film cannot follow the elongation of the substrate and fails in tension. UNIPAD-15LX is the flexible build for this work.
Over-dosed hardenerExcess crosslinking raises chemical resistance and cuts elongation, so the film becomes brittle exactly where flexibility was needed.
Plasticiser migrating out of soft PVCPlasticiser moves into the ink film over days to weeks, softening and eventually weakening the bond; the fault appears after the goods have been in stock, not at the press.
Surface contamination on rubber and soft-touch partsMould release, bloom and textile finishes sit between ink and substrate, so the bond fails at the first flex.
Film too heavyA thick film strains more at its surface for a given bend radius, so a heavy laydown cracks where a thin one survives.

Pad Printing InksPrint cracks or lifts when the part flexes

Fault 15 of 20 · continued

Print cracks or lifts when the part flexes

CHECK, IN THIS ORDER

Flex or stretch a fully cured printed part by hand and inspect the fold at x30; then repeat after seven days in stock to catch plasticiser migration.
Where the item is laundered, run domestic washing colour fastness to ISO 105-C06 at the temperature and cycle the customer specifies, and assess rub fastness by crockmeter to ISO 105-X12 dry and wet, recording the method, the cycle count and the assessment scale alongside the customer's own acceptance criterion.
Check the hardener weight against the ratio on the Technical Data Sheet.
Test wetting tension on the rubber or soft-touch part with test liquids in the manner of ASTM D2578, and wipe-test with isopropanol to see whether adhesion recovers.
Measure etch depth to confirm the film weight is not heavier than the job needs.

THEN CHANGE

Move to UNIPAD-15LX for rubberised, soft-touch and textile items, using the one-component build where flexibility matters more than chemical resistance.
Reduce the hardener to the stated ratio, weighed, and no higher.
Qualify the ink on the customer's own soft PVC compound over time rather than on day one, because plasticiser behaviour belongs to the compound.
Degrease the part before printing, or have the moulder change the release system.
Reduce etch depth so the film is at the light end of the useful range for that image.

CONFIRM IT IS FIXED

Fully cured prints survive the customer's own flex, stretch or wash cycle with no cracking visible at x30, repeated on parts held seven days and again at the agreed shelf point, with the wash and rub methods and ratings recorded. Flexibility and wash performance belong to the printed article, so they are qualified on the customer's own material.

THE TRAP

Adding hardener to make a cracking print tougher. It raises hardness and cuts elongation, so the film cracks sooner. On flexible substrates the answer is a more flexible build, not a harder one.

Pad Printing InksPrint cracks or lifts when the part flexes (continued)

Fault 16 of 20

Resistance fails at the customer though it passed at the press

WHAT YOU SEE

Adhesion and rub were signed off on the line, then the parts fail alcohol wipe, hand sanitiser, sun cream, fuel or cleaning agent at the customer, sometimes weeks later.

WHAT IT LOOKS LIKE

CAUSES, MOST LIKELY FIRST

Testing before full cureCrosslinking and chemical resistance develop over 72 h to 5 days at 20 to 25 C, or after a qualified forced cure. A press-side test measures a film that is not finished.
Hardener omitted or under-dosed on one mixA one-component film has the adhesion but not the chemical resistance, and nothing on the print shows the difference.
Ink used past pot lifePartly reacted binder transfers as a weak film that looks the same and resists far less.
Wrong grade for the exposureGeneral work belongs to UNIPAD-10GP; sustained contact with chemicals, fuel or hand perspiration is the job UNIPAD-20HR is built for, and alcohol, acid and alkali on metals and hard plastics is the job UNIPAD-11MD is built for.
Bake omitted, or run at a temperature the part cannot takeWhere the cycle specifies a forced cure, air drying alone leaves the resistance short even after days; and a bake set at 80 to 100 C on soft PVC, PS, PE or a flexible moulding distorts the part, so the schedule gets quietly abandoned instead of corrected.

Pad Printing InksResistance fails at the customer though it passed at the press

Fault 16 of 20 · continued

Resistance fails at the customer though it passed at the press

CHECK, IN THIS ORDER

Run the customer's own exposure first: the actual sanitiser, sun cream, fuel or cleaner, for the actual contact time, on the actual part, on fully cured print.
Where the substrate is a metal or a polyolefin, run MEK double rubs to ASTM D5402 as a crosslink check and record the count at which the substrate first shows. Do not use MEK on PS, ABS, PC or PMMA, where the solvent attacks the substrate and the result is meaningless.
Audit the mix log for hardener weight, mixing time, room temperature and pot life on the batch that failed.
Cross-cut to ISO 2409 after the chemical exposure as well as before it, because resistance failures often show as adhesion loss.
Check bake temperature and dwell with a thermocouple or a temperature-indicating strip on the part, not on the oven dial, and check the figure against the substrate's heat distortion temperature.

THEN CHANGE

Move resistance testing to a fully cured sample, retained and tested at 72 h and again at 5 days, and make that the release criterion.
Weigh the hardener to the ratio on the Technical Data Sheet, mark the mixing time and room temperature on the cup, and discard at pot life.
Specify the correct grade against the actual exposure before the job is quoted, not after it fails.
Introduce or correct the forced cure, typically 15 to 30 min at 60 to 80 C where the part allows it, qualify the schedule on the customer's own part with a thermocouple on the part, and verify the part reaches temperature rather than the oven.
Agree a written resistance specification with the customer, naming the reagent, the contact time and the pass criterion.

CONFIRM IT IS FIXED

Fully cured print passes the customer's own named reagent exposure for the stated contact time with cross-cut to ISO 2409 still at classification 0 or 1 afterwards, and, on metals and polyolefins, reaches the agreed MEK double rub count to ASTM D5402 with no substrate showing. Acceptance is agreed per job, because a 2 to 5 micron dry pad film reaches far fewer rubs than a screen film of the same chemistry.

THE TRAP

Signing the job off on a press-side rub test with a thumb and a solvent rag an hour after printing. It passes, the parts ship, and the failure arrives as a claim three weeks later.

Pad Printing InksResistance fails at the customer though it passed at the press (continued)

Fault 17 of 20

Ghosting or a shadow of the previous image

WHAT YOU SEE

A faint second image, offset from the printed one, or a residue of the previous job's artwork appearing on the part.

WHAT IT LOOKS LIKE

CAUSES, MOST LIKELY FIRST

Ink residue left on the pad from the previous cycleIncomplete release leaves a partial film that transfers on the next stroke, printing a ghost of the last image.
Pad not lifting fully clear before indexingA pad that brushes the part or the plate during travel deposits a smear that reads as a shadow.
Plate not fully cleaned between jobsDried ink in the old etch on a re-used plate transfers faintly alongside the new image.
Cup travel overrunning the imageInk dragged past the image edge sits on the land and prints as a shadow at the same offset every cycle.
Static holding a mist of ink on the partCharged parts collect airborne ink from the machine and hold it in the shape of the field, not the image.

Pad Printing InksGhosting or a shadow of the previous image

Fault 17 of 20 · continued

Ghosting or a shadow of the previous image

CHECK, IN THIS ORDER

With the machine stopped at the top of the stroke and the cycle start released, inspect the pad face under a x30 loupe immediately after transfer for residual film.
Watch the pad path on the machine's own guarded single-cycle function, with both hands clear; never turn the machine by hand and never defeat a guard.
With the machine isolated, examine the cliche under raking light for old etched detail or dried ink outside the current image.
Check the offset: a ghost at a constant offset is mechanical, a diffuse haze is static or airborne mist.

THEN CHANGE

Correct the release problem first, since a ghost is usually incomplete release wearing a different name.
Reset the pad lift and travel so the pad clears both plate and part with margin.
Strip and clean the cliche properly between jobs and at every colour change, or fit a dedicated plate for the job.
Reset cup travel so it stops clear of the image.
Fit ionising bars and extract at the machine to remove airborne ink mist.

CONFIRM IT IS FIXED

Fifty consecutive prints show a single clean image with no second image or haze visible at x30, and the pad face is clean after each transfer.

THE TRAP

Cleaning the pad every few cycles to keep the ghost away. It hides the release fault, resets the pad's conditioned surface each time, and guarantees the ghost comes back worse within the hour.

Pad Printing InksGhosting or a shadow of the previous image (continued)

Fault 18 of 20

Substrate crazes, cracks or whitens under and around the print

WHAT YOU SEE

Fine cracks in the plastic itself, hours to days after printing, under the print or radiating from it. Worst near gates, bosses, weld lines and snap features, and on parts that were solvent-wiped before printing. Clear PC, PS, ABS and PMMA show it first, and it is regularly reported as an ink or adhesion fault.

WHAT IT LOOKS LIKE

CAUSES, MOST LIKELY FIRST

Solvent blend too aggressive for a stress-sensitive polymerKetones and esters plasticise the surface layer; where the moulding carries frozen-in stress, the softened surface relieves it as crazing.
Solvent wipe before printingIsopropanol, and worse a ketone cleaner flooded onto PC or PMMA, drives solvent into stressed areas before any ink is applied, so the ink is blamed for a crack the cleaning made.
Moulded-in stress from the processShort cooling, high injection pressure, sharp corners and moulded-in inserts leave residual stress, and the same ink prints without a mark on an annealed or unstressed plaque of the same grade.
Too much retarder, or a slow blend sitting on the surfaceA slow solvent stays on the part far longer than a fast one, so total solvent contact time rises even though the volume applied is the same.
Assembly or service stress applied after printingA part printed flat and then clipped, bolted or bent takes residual solvent into a loaded surface, and the cracks appear days later in stock.

Pad Printing InksSubstrate crazes, cracks or whitens under and around the print

Fault 18 of 20 · continued

Substrate crazes, cracks or whitens under and around the print

CHECK, IN THIS ORDER

Print an unstressed plaque of the same polymer grade from the same lot and compare with the moulding at 24 h and again at 7 days.
Wipe a clean part with the cleaner alone, no print, and inspect at x30 after 24 h; cracks without ink put the fault in the cleaning step.
Inspect at x30 with the part flexed slightly, and look for cracks radiating from gates, bosses and weld lines rather than following the image.
Check the retarder proportion against the mix log and measure flow time to ISO 2431 at 23 C +/- 0.5 C.
Ask the moulder for the polymer grade, the moulding cycle and whether the parts are annealed.

THEN CHANGE

Move to the mildest solvent blend that still holds the working flow time, and cut retarder to the minimum the cycle needs.
Stop solvent wiping stress-sensitive parts; use an air knife and an ionising bar, or a cleaner qualified on that polymer.
Have the moulder anneal the parts or relieve the stress in the tool before printing.
Qualify the ink, the thinner and the cleaner together on the customer's own moulding, read at 24 h and again at 7 days, before the job is committed.

CONFIRM IT IS FIXED

Twenty parts from the failing lot, printed and held seven days, show no craze or crack at x30 under a slight flex, and the same holds on parts taken through the customer's own assembly step.

THE TRAP

Reading the crack as an adhesion problem and moving to a stronger, more aggressive grade. The stronger solvent attacks the polymer harder, so the cracking gets worse while the adhesion figure barely moves.

Pad Printing InksSubstrate crazes, cracks or whitens under and around the print (continued)

Fault 19 of 20

Print scuffs, blocks or transfers after packing

WHAT YOU SEE

The print is perfect at the press and arrives at the customer marked, glossed off, or carrying a mirror of itself from the face of the next part. Worst where parts are stacked, bagged, tumbled or boxed straight off the machine.

WHAT IT LOOKS LIKE

CAUSES, MOST LIKELY FIRST

Parts packed before the film has handling strengthSolvent release gives a touch-dry surface within minutes, but handling strength comes later and full cure later still, so stacking presses two soft films together.
Film too heavy for the drying availableA deep etch and a slow blend leave solvent under a dry skin, so the print stays soft where it cannot be felt.
Hardener omitted on a grade that offers itA one-component film stays thermoplastic and blocks under load and warmth, particularly in a warm store or a shipping container.
Bake omitted or cut short where the cycle specifies oneForced cure is often what gives the film its handling strength inside the production cycle, and skipping it moves the failure to the pack.
Warm parts stacked straight off the machine or the ovenLoad and temperature together are what block a print, and a stack cooling inside a box holds both.

Pad Printing InksPrint scuffs, blocks or transfers after packing

Fault 19 of 20 · continued

Print scuffs, blocks or transfers after packing

CHECK, IN THIS ORDER

Stack ten printed parts print to face, load them to the weight the pack will see, hold them 24 h at the highest temperature the store or container reaches, then separate and inspect at x30.
Record the time between printing and packing on the line and compare it with the handling time stated for the grade.
Rub the print with a dry cloth under thumb pressure at 1 h, 4 h and 24 h and record where it stops marking.
Check bake temperature and dwell with a thermocouple on the part, not on the oven dial.
Check the hardener weight and mixing time in the mix log for the batch that marked.

THEN CHANGE

Set and write down a minimum time between printing and packing, and hold the parts on a rack until it has passed.
Introduce or correct the forced cure, within the substrate's heat limit, and verify the part reaches temperature.
Interleave or separate parts in the pack where the print faces another surface.
Reduce etch depth to the lightest film the image allows and return to the matched thinner blend rather than a slow one.
Add the hardener where the grade offers it and the exposure justifies it, weighed to the ratio on the Technical Data Sheet.

CONFIRM IT IS FIXED

A loaded stack test at the store or container temperature, held 24 h on parts packed at the stated handling time, separates cleanly with no print transfer and no gloss change at x30, on parts from at least two boxes.

THE TRAP

Judging handling strength with a thumb at the press. A print that resists a thumb at 1 h will still block under the weight of a full box overnight at 35 C.

Pad Printing InksPrint scuffs, blocks or transfers after packing (continued)

Fault 20 of 20

Print rubs or scratches through in service

WHAT YOU SEE

Adhesion passes cross-cut and the print still wears thin or disappears where the part is handled, wiped or rubs against another part. Reported by the customer as an adhesion failure, though the film is still bonded where it remains.

WHAT IT LOOKS LIKE

CAUSES, MOST LIKELY FIRST

The dry film is thin by the nature of the processA pad print dries at about 2 to 5 micron, so it has far less material to lose than a screen print of the same ink before the substrate shows.
Film not crosslinkedA one-component film, or a two-component film mixed short of hardener or used past pot life, has lower cohesive strength and abrades faster.
Cure incomplete at despatchAbrasion resistance builds with the rest of the cure over 72 h to 5 days at 20 to 25 C, so parts tested or shipped at 24 h are tested short.
Cleaning regime in service harsher than the one quotedAlcohol wipes, abrasive cloths and detergents remove far more than the hand contact the job was qualified for.
Print sited where the part rubsA print on a contact face or a grip area wears whatever the ink, so the answer is the position, a recess or a qualified overprint, not a harder ink.

Pad Printing InksPrint rubs or scratches through in service

Fault 20 of 20 · continued

Print rubs or scratches through in service

CHECK, IN THIS ORDER

Run the customer's own rub on fully cured print: the actual cloth, the actual cleaner, the actual load and stroke count, and record the count at which the substrate first shows.
Where a rating scale is wanted on textile and rubberised goods, assess rub fastness by crockmeter to ISO 105-X12 dry and wet and record the rating.
On metals and polyolefins only, run MEK double rubs to ASTM D5402 as a crosslink check and compare the failing batch with a known good one.
Audit the mix log for hardener weight, mixing time and pot life.
Measure etch depth to see whether the film is at the light end of the useful range.

THEN CHANGE

Specify the two-component build with hardener weighed to the ratio, where the substrate and the exposure allow it.
Release only on fully cured print and state the cure in the job specification.
Increase the film within the etch limits, up to about 28 to 30 micron on steel for a solid, and no further.
Agree the cleaning regime in writing with the customer: the cloth, the reagent, the load and the number of cycles.
Where the print sits on a wear face, move it, recess it, or qualify an overprint varnish on the customer's own part.

CONFIRM IT IS FIXED

Fully cured print reaches the agreed cycle count in the customer's own named rub test with no substrate showing, on five parts from the moulding lot, with the load, the cloth and the method recorded.

THE TRAP

Quoting screen printing rub figures for a pad print. The chemistry may be the same, but the dry film is a fraction of the thickness, so the count will not be met and the argument ends at the customer.

Pad Printing InksPrint rubs or scratches through in service (continued)

At the press

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

Quick reference

One page at the press

Symptom	Check this first	Change this first
Image fills in, detail closing	Press room temperature at machine height; flow time to ISO 2431 at 23 C	Substitute retarder for part of the thinner, 2 to 3 % by weight
Patchy or partial pick-up	Pad face and cells at x30 after a pick-up, machine stopped	Clean or prepare the pad; then thin to the working flow time
Ink stays on the pad	Fingertip tack at the transfer point, pad stopped; wetting tension on the part	Lengthen open time, or treat the part to 42 mN/m or higher
Adhesion fails on PP or PE	Wetting tension on the actual moulding lot	Treat and print within 24 h, or trial UNIPAD-12PP and qualify it
Pinholes and craters	Print a known clean control part with the same cup	Remove the silicone source; degrease the parts where the polymer allows
Ragged or sawtooth edges	Edge under x30; doctored plate against a light box	Add retarder, then reduce pad compression on the part
Streak in the same place every cycle	Isolate the machine, rotate the cup a few degrees and see if the streak moves	Replace the doctor ring if it moves; re-lap the plate if it does not
Weak opacity, thin print	Stir the cup and reprint ten; then the mix log for thinner additions	Stop adding thinner; re-etch the solid to 28 to 30 micron on steel

Pad Printing InksQuick reference

Quick reference

One page at the press

Symptom	Check this first	Change this first
Image stretched on a curved part	Print a flat reference part with the same pad and plate	Fit a steeper pad and reduce compression to the minimum that transfers
Two-component ink gelling	Mixing time and room temperature written on the cup against the clock	Discard at pot life and mix fresh; do not thin it back
Shade drifting through the shift	Compare against the approved standard, not last hour's print	Weighed top-ups with flow time measured after each one
Hairs, filaments and dust in the print	Relative humidity at the machine with a calibrated hygrometer	Fit ionising bars and raise RH to 45 to 60 %
Pad swollen or growing the image	Printed image against the artwork with a measuring loupe	Change the pad; return to the recommended pad cleaner
Second colour will not trap	Fingertip tack on the first colour at the second station, machine stopped	Adjust the first colour to set-to-touch, not cured
Print cracks when the part flexes	Flex a fully cured part and inspect the fold at x30	Move to UNIPAD-15LX and reduce the hardener to the stated ratio
Resistance fails at the customer	Hardener weight and pot life in the mix log; the customer's own reagent on cured print	Test only after 72 h to 5 days cure; correct the hardener ratio

Pad Printing InksQuick reference

Quick reference

One page at the press

Symptom	Check this first	Change this first
Ghosting or a shadow image	Pad face at x30 immediately after transfer	Correct the release fault, not the pad cleaning frequency
Substrate crazing under the print	Wipe a part with the cleaner alone, no print, and read it at 24 h	Stop the solvent wipe; move to the mildest blend that holds flow time
Print marked or blocked after packing	Loaded stack test at store temperature for 24 h	Set a minimum time from printing to packing and rack the parts
Print rubs through in service	The customer's own rub on fully cured print, load and cloth recorded	Release only on cured print; specify the two-component build where allowed

Pad Printing InksQuick reference

Test methods

The measurements this guide relies on

Measurement	Method	What it tells you, and the usual acceptance
Cross-cut adhesion	ISO 2409	Lattice of six cuts each way at 1 mm spacing for films up to 60 micron on a hard substrate, 2 mm on a soft one, cut with a sharp blade through to the substrate without gouging, brushed, then a 25 mm tape of 10 +/- 1 N/25 mm peel adhesion applied and removed at the specified angle. Classification 0 to 5; for pad printing, 0 or 1 on fully cured print, 72 h to 5 days at 20 to 25 C or after a qualified forced cure. On plastics the result is comparative, so it is valid only on the customer's own part against an agreed retained reference.
Solvent resistance, double rubs	ASTM D5402	MEK-soaked cloth under a defined load, counted as double rubs to first substrate show, used to confirm that a two-component film has crosslinked. Use it on solvent-resistant substrates, principally metals and polyolefins. Do not use MEK on PS, ABS, PC or PMMA, where the solvent attacks the substrate and the result is meaningless; on those parts use the customer's own named reagent for the stated contact time. Acceptance is agreed per job, because a 2 to 5 micron dry pad film reaches far fewer rubs than a screen film of the same chemistry.
Flow cup viscosity	ISO 2431	Efflux time through a 4 mm cup with ink and cup conditioned to 23 C +/- 0.5 C, giving the working figure the press is set to. Name the cup on the record, ISO 2431 No. 4 or DIN 53211 4 mm, because their geometries differ and their times are not interchangeable, and hold the same cup and temperature for the life of the job. Typical for this class as run is 18 to 25 s; the number that matters is the one recorded when the job last ran well.
Wetting tension, test liquids	In the manner of ASTM D2578	Test liquid drawn across the surface with a swab and the film judged at 2 s, recorded as an indicative wetting tension in mN/m. D2578 is written for polyethylene and polypropylene film; on mouldings and on other polymers the reading is indicative and is used for trend and for pass or fail against your own treated reference, not as a conformity statement. Pad inks sit at about 28 to 32 mN/m and need the substrate to exceed them by roughly 8 to 10 mN/m, so treat to at least 38 mN/m and aim for 42 mN/m or higher at the moment of printing. Pens are a convenience version of the same test and drift as they age: date them and check against fresh liquids.
Durometer hardness	ASTM D2240	Hardness of the silicone pad, scale stated on the record: Type OO below about Shore A 20, Type A above it, read at the stated dwell (1 s or 15 s, the same each time) on a flat area at least 6 mm thick and at least 12 mm from any edge. Many pad geometries cannot meet that specimen requirement, in which case record the supplier's stated hardness at fitting and track ageing by image growth against the artwork and by loss of fine detail, which are the usable signals.
Fineness of grind	ISO 1524	Grind gauge reading, with the scale and the figure recorded, compared against a fresh sample from a sealed tin of the same grade. Used when a streak or a drag in the doctoring direction points at the ink rather than the ring.
Colour measurement and visual assessment	ISO 13655 (M1) and ISO 3664	Where the geometry allows an instrument reading, report delta E 00 against the approved standard with the measurement conditions stated, and agree the tolerance in writing before the run. Where no flat area exists, compare visually against the approved retained sample under standardised D50 viewing to ISO 3664, and check a second illuminant such as A or the customer's store lighting, because pad ink on a pigmented moulding shifts between illuminants.

Pad Printing InksTest methods

Test methods

The measurements this guide relies on

Measurement	Method	What it tells you, and the usual acceptance
Specular gloss	ISO 2813	60 degree gloss on a flat area of the printed part, used as a secondary indicator of film weight and cure. Many pad-printed parts have no flat area large enough for the instrument, in which case gloss is assessed visually against a retained sample.
Lightfastness, blue wool	ISO 12040	Filtered xenon arc exposure of the print, assessed against the blue wool scale, this being the graphic technology method for prints and printing inks; the blue wool references are those of the ISO 105-B series, which is written for textiles. Relevant to promotional and sporting goods that live outdoors. Quote the rating for the film as printed, because a 2 to 5 micron dry pad film fades sooner than the same pigment in a thicker screen film.
Wash and rub fastness on textile and rubberised goods	ISO 105-C06 and ISO 105-X12	Domestic washing colour fastness at the temperature and cycle the customer specifies, and rub fastness by crockmeter dry and wet. Record the method, the cycle count and the assessment scale alongside the customer's own acceptance criterion. Wash and rub performance belong to the printed article, so they are qualified on the customer's own material.
Etch depth	No standard cited; measured with a calibrated dial depth gauge or optical profilometer	Depth of the etched cell at a solid, a fine line and the image edge. About 25 micron for steel and 18 to 25 micron for thin photopolymer, held to +/- 3 micron across the image, and 28 to 30 micron on steel where opacity is critical. Record the support screen ruling in solids above about 8 to 10 mm across with the depth figures. Cell volume sets the film weight on the part, so it sets opacity.
In-vitro cytotoxicity	ISO 10993-5, within an evaluation planned under ISO 10993-1	Cell-culture assessment of extracts from the finished article. UNIPAD-11MD is formulated without intentionally added heavy metals, with residual levels controlled against the limits of the customer's named specification, and from raw materials selected for articles that undergo biological evaluation. Cytotoxicity is one endpoint within a biological evaluation planned under ISO 10993-1; biological safety is a property of the finished article and is assessed on the customer's own device. Nothing here is a statement of conformity for the printed article.

Pad Printing InksTest methods

When the press-floor fixes have not worked

What to send us

A sample of the actual part, at least twenty pieces, unprinted, from the moulding lot that is failing, in the packaging they normally arrive in, plus the moulder's grade, masterbatch, release agent and whether the parts are annealed.
Printed failing parts, boxed not bagged, with the print date and the time since printing written on the box, and an approved good sample from the same job if one exists.
The mix log for the failing batch: ink grade and batch number, thinner and retarder types and weights, hardener ratio and weight, mixing time, press room temperature at mixing, and every top-up with its time.
The flow time log in seconds to ISO 2431 at 23 C +/- 0.5 C across the shift, with the cup named, and press room temperature and relative humidity recorded at start-up, mid-shift and end of shift.
Cliche details: material, etch depth measured at three points with the instrument named, the support screen ruling in the solids, cycle count since the plate was made, and a photograph of the plate under raking light.
Pad details: shape, hardness at fitting and now with the durometer scale stated, or the supplier's stated hardness where the geometry will not take a valid reading, cycle count, and the cleaner in use at the machine.
The test results you already have, with the method, the age of the print at testing and the cure applied, and the customer's own written specification: the reagent, the contact time, the cleaning regime and the pass criterion.

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Pad Printing InksTechnical service