Troubleshooting guide

Screen Printing Inks

Solvent and UV screen inks across eight substrate series: the faults that stop jobs, what causes them, and what to change first.

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.

Work to the Safety Data Sheet before you work to this guide. Two-pack hardeners and uncured UV inks are sensitisers, and sensitisation does not reverse; MEK, thinners and screen wash are flammable. Nitrile gloves, eye protection, local exhaust and a clear rule for solvent-soaked rags are part of every method here, not an extra.
Diagnose the screen before the ink. Mesh count, tension, stencil thickness and squeegee edge decide the deposit, and the deposit decides colour, opacity, levelling and edge quality.
Treat squeegee pressure as a diagnostic, not a control. If the job needs more pressure than it did yesterday, something else has changed and pressure is hiding it.
Measure the deposit, do not judge it. Film thickness, density and dyne level are numbers; 'looks thin' is not.
Separate cure from adhesion before acting. Rub the film first, then tape it: they have different causes and often opposite fixes.
Read adhesion 24 h after the print at 23 C and 50 % RH, on the customer's own material, because solvent and two-pack films keep building after the press.
Choose the test for the substrate, not for the habit. A cross-cut belongs on rigid material. On rubber, latex, foam, leather and wax it measures the substrate, not the ink, and it will report a pass the article does not deserve.
Change one variable at a time and write it on the job ticket. A screen press has enough interacting settings that two changes at once teach you nothing.

Screen 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

Screen Printing InksThe process

Where this range runs

The work these products do

Screen Printing InksApplications

Control variables

What to hold, and how to measure it

Variable	Target	How it is measured	How it drifts
Ink viscosity	The figure on the grade's Technical Data Sheet, held within about 10 % of it, measured at 25 C	Rotational viscometer at a defined shear rate, ISO 3219, at 25 C. Use a flow cup, ISO 2431, only where the TDS quotes a cup figure: screen inks are thixotropic and a cup reading is an approximation of one point on the curve	Rises through the shift as solvent leaves the open tray and the mesh, fastest on a warm press with drying fans running. It shows as screen blocking first, then sawtooth edges, then a thinner deposit
Mesh tension	The band the mesh manufacturer gives for that thread count and diameter, broadly 20 to 28 N/cm up to about 90 threads per centimetre, 18 to 24 N/cm from 100 to 140, and lower again above that, matched within about 2 N/cm across a frame and across a colour set	Mesh tension meter read in five positions per frame, centre and four quadrants, before the job and again after 1 000 impressions. Stretch above the working band and let the mesh relax into it before the job	A newly stretched screen relaxes quickly in the first hours and then slowly. As tension falls the deposit thins, the image grows towards the edges and register opens up colour to colour. A fine mesh tensioned to a coarse mesh figure tears instead
Off-contact	1.5 to 3 mm on a flat bed, set so the screen snaps behind the blade and does not lift ahead of it	Steel rule or feeler gauge at the centre and the four corners with the screen at print position	Rises when the bed or the frame moves, and is often increased deliberately to cure blocking. Every increase grows the image and makes orange peel worse
Squeegee durometer and edge	70 to 75 Shore A polyurethane with a sharp square edge for general graphics; 60 to 65 for a heavy deposit, 80 for fine detail	Durometer to ASTM D2240 at several points along the blade, taken on the flat at least 12 mm back from the printing edge with at least 6 mm of rubber under the foot, and compared against a new blade of the same type read in the same place. Readings closer to the edge are not valid D2240 readings and read low for geometric reasons alone. Inspect the edge separately under a loupe and against a steel straight edge	Solvent swells and softens the blade through a shift and abrasion rounds the edge. The deposit thickens, the edge definition goes, and a nick prints as a streak in the same place on every sheet
Squeegee pressure	The lowest setting that sweeps the mesh clean in one pass, then locked and recorded	The press scale, plus a printed test sheet at that setting kept with the job ticket	Creeps up through the shift as operators chase other faults. Higher pressure thins the deposit, grows the image and wears the stencil, so it makes three faults while curing none
Stencil thickness over the mesh	About 15 to 25 % of the mesh thickness for line and halftone work, higher where a heavy deposit is wanted	Stencil thickness gauge over the thread knuckle in several positions, recorded at coating and again after the run	Abrades through the run and loses thickness at every reclaim. Edge definition goes first and the deposit follows
Ink and press room temperature	Ink 20 to 25 C in the tray, press room 20 to 25 C at 45 to 55 % RH	Probe thermometer in the tray, hygrometer at the press, both read at the start and the middle of the shift	The tray warms near dryers and lamps. Roughly, every 10 C rise halves the working life of a two-pack. Drying-in accelerates with temperature too but less steeply, since solvent vapour pressure roughly doubles over 15 to 20 C, and in practice it is air movement over the mesh rather than tray temperature that decides how fast the screen dries in

Screen Printing InksControl variables

Control variables

What to hold, and how to measure it

Variable	Target	How it is measured	How it drifts
Catalyst ratio and pot life	The ratio and the pot life on the grade's Technical Data Sheet, by weight. Broadly 6 to 12 h across our two-pack screen systems, and at the short end, 6 to 8 h, for the silane bonding glass grades. The TDS figure is quoted at 20 C and shortens sharply above it	Balance for both components, weighed in nitrile gloves and eye protection under local exhaust ventilation to the hardener's Safety Data Sheet, with the time of catalysis written on the tin and on the job ticket	The cross-linking reaction runs whether or not the press does. Viscosity climbs slowly and then quickly; the last hour before gelation prints rough and blocks the screen
UV dose and peak irradiance at the substrate	The grade's stated minimum, measured at the substrate. A screen film of 8 to 30 micron needs more than an offset or flexo film of the same chemistry	Band-calibrated radiometer passed through the machine at running speed, backed by 30 MEK double rubs to the house condition, which is a hammer weighted to 1 kg with a defined cloth and stroke, following the general practice of ASTM D5402	Lamp output falls with hours and the quartz devitrifies. Short-wave output goes first, so the surface turns tacky before the body of the film softens. LED arrays drift instead: output falls, diodes die and cooling degrades, with no visible change to look at
Oven schedule, part temperature and dwell	The grade's TDS decides, and it is the part temperature that counts, not the panel setting. For our two-pack screen systems on heat-tolerant substrates expect a force-dry of the order of 15 to 30 min at 80 to 120 C, with full chemical resistance developing over a further 24 to 72 h at 23 C. On heat-sensitive substrates, foam, leather, vinyl, PET-G, thin styrene and wax, the schedule is limited by the substrate and not by the ink, so air-dry or low-temperature jet-dry times apply instead	Trailing thermocouple through the tunnel recording air and substrate temperature against time, never the panel setting	The panel reading and the real air temperature separate as filters load and the conveyor fills. A short dwell at a high temperature skins the film and traps solvent under it, and on a heat-sensitive substrate it distorts the part before it dries the ink
Substrate surface energy	40 mN/m or above after treatment as the house target, with the grade's TDS giving the figure it needs; 38 to 42 mN/m covers most screen work on plastics	Dyne pens or ISO 8296 test inks on the parts about to be run, or ASTM D2578 wetting tension on film where the material allows the test. Measure at the edges and wherever the part is handled, not only in the middle	Treatment decays in store as polar groups reorient into the bulk, faster when the stock is warm. Untreated PE and PP sit at roughly 18 to 31 mN/m and never reach the target without treatment or a grade built for untreated polyolefin

Screen Printing InksControl variables

The mechanism

How a screen actually lays ink down

Ink is not pushed through the mesh. The blade shears it into the open stencil and brings the mesh into line contact with the substrate; the transfer itself happens behind the blade as the screen peels away and the ink chooses the substrate over the thread. The deposit is therefore set by the open volume of the mesh and the thickness of the stencil, not by squeegee pressure. Pressure only has to be enough to close that line of contact, and everything above that amount grows the image, thins the film and wears the stencil. This is why almost every fault on the press floor gets worse when the answer is more pressure.

Screen Printing InksThe mechanism

02 | 20 faults

Faults

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

Fault 1 of 20

Ink dries in the screen, the image blocks up

WHAT YOU SEE

The first prints of the run are clean, then fine detail and halftone dots close in and solids lose density. The operator ends up washing the screen every few sheets, and the worst areas are the ones the squeegee reaches last.

WHAT IT LOOKS LIKE

CAUSES, MOST LIKELY FIRST

Cycle time too long, or the press stopping between partsOpen time is consumed by the clock, not by the number of impressions, so a slow load and unload dries the mesh at the same rate as a stoppage.
Drying fans or warm air blowing across the screenForced air strips the solvent boundary layer above the mesh and dries the ink in the stencil while the tray still looks fine. This is the single strongest variable and it is usually the one that changed.
Tray temperature raised by the dryer or the lampsInk that is already warm starts every stroke closer to the viscosity at which it will not release, and it loses solvent faster in the open aperture.
Thinner added earlier in the shift for another faultThinner leaves the blend faster than the solvents it replaced, so the ink dries in sooner than it did before the addition, and the operator reads that as the fault getting worse on its own.
Mesh finer than the artwork actually needsA small aperture holds a small volume with a high surface to volume ratio, so it skins before a coarser one.

Screen Printing InksInk dries in the screen, the image blocks up

Fault 1 of 20 · continued

Ink dries in the screen, the image blocks up

CHECK, IN THIS ORDER

Time one complete press cycle including the flood dwell, and compare it with the open time on the grade's Technical Data Sheet.
Measure ink temperature in the tray with a probe thermometer, and press room temperature and RH with a hygrometer.
Measure viscosity at the start and again after 30 min on press by the method the TDS names, ISO 3219 rotational or ISO 2431 cup; a rise of more than about 10 % in 30 min is solvent loss.
Read the mixing record for every addition made earlier in the shift, and for the time of catalysis against the pot life on the grade's TDS, broadly 6 to 12 h across our two-pack screen systems and 6 to 8 h for the silane bonding glass grades.
With the press stopped and the guards closed, trace the airflow around the screen with a smoke pencil or a light tissue taped to a rod. If it has to be checked running, hold the tell-tale outside the guarding and never reach into the print carriage.

THEN CHANGE

Add the retarder named for that grade in 2 to 3 % steps, mixing at least 2 min before judging the result.
Reduce drying fan power to the minimum that still clears the delivery once the machine is set, and screen the frame from stray air.
Keep the flood stroke close behind the print stroke and flood immediately whenever the press stops.
Keep the tray out of the radiant heat of the dryer and the lamps, and work from a smaller quantity refreshed more often.
Where the mesh is finer than the artwork needs, coarsen it. A lower thread count per centimetre holds more volume and stays open longer.

CONFIRM IT IS FIXED

Run 500 impressions without a screen wash, then measure the finest line or dot at the start, the middle and the end on a print microscope: less than 10 % closure, with solid density inside the tolerance agreed with the customer, read on one instrument at a stated density status and geometry, ISO 5-3 for the spectral condition and ISO 5-4 for the geometry, or as dE00 to ISO 13655 with M1 illumination where a spectrophotometer is available.

THE TRAP

Adding thinner. It drops viscosity for about ten minutes, then leaves faster than the original solvent blend and puts the ink back where it started, with a thinner film, weaker colour and worse adhesion. The fault is evaporation rate, so the answer is retarder, not thinner.

Screen Printing InksInk dries in the screen, the image blocks up (continued)

Fault 2 of 20

Sawtooth edges, moire and dot gain in halftone work

WHAT YOU SEE

Straight edges look serrated under a loupe, small text fills in at the corners and fine reverses close up. In halftone and process work a coarse interference pattern appears across the tint and the printed tone reads heavier than the film. The edge fault is usually worse on edges running one particular way across the sheet.

WHAT IT LOOKS LIKE

CAUSES, MOST LIKELY FIRST

Stencil too thin over the meshThe threads protrude into the underside of a thin stencil, so the ink edge is defined by the weave rather than by the stencil, and it prints the weave.
Mesh at 0 and 90 degrees to the artworkAn edge parallel to a thread lands exactly along it and serrates the whole length. At an angle the error averages out.
Mesh count too close to the screen ruling, or the mesh angle too close to the screen angleTwo regular grids set at a small angle to each other beat against one another and the print carries the beat pattern. It is worst when the thread count and the ruling are close, and no amount of exposure or pressure removes it.
Mesh tension lowA slack mesh distorts under the blade, so the aperture moves under the ink during the stroke and the ink lands where the stencil is not.
Deposit heavier than the halftone needsA screen dot carries a thick film that spreads on release, so tone value increase rises with the deposit. A tint that holds at 8 micron closes up at 20 micron.

Screen Printing InksSawtooth edges, moire and dot gain in halftone work

Fault 2 of 20 · continued

Sawtooth edges, moire and dot gain in halftone work

CHECK, IN THIS ORDER

Measure stencil thickness over the thread knuckle with a stencil thickness gauge and compare it with the mesh thickness; aim at roughly 15 to 25 % for line and halftone work.
Check the mesh angle on the frame against the artwork; 22.5 degrees to the squeegee direction is the usual setting for line work, and the mesh angle has to be offset from the screen angle as well.
Compare the mesh count with the screen ruling. A working rule is a thread count of at least 3.5 to 4 times the ruling in the same units; closer than that and moire is a design fault, not a press fault.
Read mesh tension in five positions with a tension meter against the band the mesh manufacturer gives for that count, with no more than about 2 N/cm spread across the frame.
Read tone value increase from a printed control strip against the film, with a densitometer at a stated density status or on a print microscope, and compare it with the value the separation was made for.

THEN CHANGE

Build the stencil up with extra face coats on the print side, dried flat and print side down.
Re-stretch or replace slack frames. Do not compensate for a slack mesh with pressure.
Re-make the stencil at the correct mesh angle for the artwork, offset from the screen angle as well as from the squeegee direction.
Where the mesh count is too close to the ruling, move to a finer mesh or coarsen the ruling. Moire is decided when the job is planned, not on the press.
Reduce the deposit for halftone work with a finer mesh or a thinner stencil, and re-linearise the separation to the measured tone value increase rather than printing heavier.

CONFIRM IT IS FIXED

Print a resolution target and a tint ladder and read them at 30x on a print microscope: no visible serration on the held lines, the finest reverse the job needs still open, no interference pattern visible in the tints at 300 mm, tone value increase repeatable between screens and inside the tolerance agreed with the customer, and the same result on five consecutive sheets.

THE TRAP

Winding squeegee pressure up to sharpen the edge. More pressure bends the mesh forward under the blade and drives ink under the stencil, so the edge gets worse while the image also grows and the register opens up.

Screen Printing InksSawtooth edges, moire and dot gain in halftone work (continued)

Fault 3 of 20

Orange peel, the solid will not level

WHAT YOU SEE

The solid carries an even dimpled texture visible in reflection, and gloss reads low and patchy. Most obvious on dark solids and on gloss UV work.

WHAT IT LOOKS LIKE

CAUSES, MOST LIKELY FIRST

Viscosity too high for the mesh in useInk that has not flowed out before its viscosity climbs keeps the mesh pattern it was given at release.
Off-contact, stroke speed and pressure out of balanceToo much off-contact snaps the screen away before the film has flowed together, and a fast stroke gives the ink less shear time.
Solvent too fast, or the UV lamp too close behind the strokeThe film's viscosity climbs, or the network is fixed, before levelling is complete. On UV the lamp freezes the mesh pattern in place.
Mesh too fine, or thread diameter too heavy for the inkA heavy thread leaves a deeper impression in the deposit for the same open area.
Poor wetting of the substrateA film that is not wetting evenly will not flow out evenly either.

Screen Printing InksOrange peel, the solid will not level

Fault 3 of 20 · continued

Orange peel, the solid will not level

CHECK, IN THIS ORDER

Measure viscosity by the method on the TDS at the tray's actual temperature, not at the temperature it was mixed.
Measure off-contact at the centre and the corners; 1.5 to 3 mm on a flat bed is usual and the screen should snap behind the blade.
Measure gloss at 60 degrees, ISO 2813, on the affected area and on the approved sample.
Time the interval from print stroke to lamp or oven entry on the machine as it runs.
Check surface energy on the actual part with dyne pens or ISO 8296 test inks.

THEN CHANGE

Adjust viscosity in 2 to 3 % steps, reactive thinner on UV grades and the named thinner and retarder on solvent grades, mixing to full homogeneity before judging.
Reduce off-contact to the smallest value that still gives a clean snap, then bring pressure down to match.
Slow the print stroke. Ink needs shear time to flow out.
Increase the distance or the time between the print stroke and the first lamp so the film can level before it is fixed.
Move to a thinner thread at the same count where the required deposit allows it.

CONFIRM IT IS FIXED

Gloss at 60 degrees, ISO 2813, inside 5 gloss units of the approved sample at three positions across the sheet, and no mesh pattern visible under raking light at 300 mm.

THE TRAP

Raising squeegee pressure to press the texture flat. Levelling happens after release, so pressure cannot touch it; what pressure does do is distort the image and force ink under the stencil edge.

Screen Printing InksOrange peel, the solid will not level (continued)

Fault 4 of 20

Pinholes and fish eyes in the printed film

WHAT YOU SEE

Small round holes with a raised rim in the solid. In the same place on sheet after sheet when the cause is in the screen, scattered at random when it is in the substrate or the ink.

WHAT IT LOOKS LIKE

CAUSES, MOST LIKELY FIRST

Silicone or oil on the substrate, from mould release, slip additive, aerosol lubricant or handsA local low-energy spot has a lower surface tension than the wet ink, so the film retracts away from it and leaves a crater with a raised rim.
Air entrained in the inkBubbles from vigorous stirring or a long drop into the tray are carried into the aperture, burst at the film surface and leave a hole that cannot flow shut once viscosity rises.
Air release failure in a heavy depositBubbles carried up from the body of a thick film as the surface skins open craters that the ink is already too viscous to close. It is the heaviest deposits, whites and floods, that show it, and the count follows the film weight rather than the sheet.
Dust, fibre or dried ink skin blocking an apertureNo ink transfers at that point, and the defect repeats in the same position every impression.
Static pulling dust onto plastics just before printThe charge is generated at separation from the stack and the dust arrives after the last clean.

Screen Printing InksPinholes and fish eyes in the printed film

Fault 4 of 20 · continued

Pinholes and fish eyes in the printed film

CHECK, IN THIS ORDER

Hold two consecutive prints to raking light and mark the defects: repeating positions mean the screen, random positions mean the substrate or the ink.
Wipe an unprinted patch with a clean solvent swab, print over it and compare; if it prints clean the cause is surface contamination.
Measure surface energy across the sheet with dyne pens or ISO 8296 test inks, including the edges and wherever the part is handled.
Stand a sample of the tray ink in a clear jar for 10 min and look for a rising bubble population.
Compare the pinhole count in the heaviest solid against a lighter tint printed from the same tray. A fault that follows the film weight is air release, not contamination.

THEN CHANGE

Clean the substrate with the cleaner recommended for that material and put the operators in clean cotton gloves. Deal with the source of the silicone in the room, not only with the sheet in front of you.
Stir with a slow blade kept submerged, and let catalysed ink stand for the de-aeration time on the TDS before it goes into the tray.
Filter the ink through the mesh size the grade's TDS specifies.
Where the deposit is heavy, reduce the film weight or slow the snap so the film has time to release its air before the surface skins.
Earth the press and fit a static bar or an ioniser where plastics are being run.

CONFIRM IT IS FIXED

Fifty consecutive prints inspected under raking light with no pinhole larger than 0.2 mm in a solid, checked again at 24 h in case slow retraction continues after the press.

THE TRAP

Adding a flow additive or more thinner to close the holes. It lowers the ink's surface tension slightly, which hides a light case and makes a heavy one worse by thinning the film, and it does nothing about the silicone, which will still be in the room on the next job. A screen-side pinhole is a different fault altogether: an uncoated speck in the stencil prints an unwanted ink dot in a clear area, and that belongs with stencil breakdown and the degreasing record.

Screen Printing InksPinholes and fish eyes in the printed film (continued)

Fault 5 of 20

Streaks and lines running with the stroke

WHAT YOU SEE

Fine continuous lines of heavier or lighter ink in the squeegee direction, in the same position on every sheet, often only noticed on a large solid.

WHAT IT LOOKS LIKE

CAUSES, MOST LIKELY FIRST

Nick or scratch on the squeegee edgeThe notch carries a channel of ink past the point where the blade should have cleaned the mesh.
Dried ink, emulsion residue or a ghost image in the meshA partly blocked line of apertures transfers less ink along its whole length.
Screen wash, haze remover or reclaim chemistry left in the weaveResidue releases into the first prints of the next run, so the streak carries a local adhesion loss and a haze as well as a density difference, and it clears after a few dozen sheets, which is what makes it hard to find later.
Blade swollen or softened by the ink's solventA polyurethane attacked by ester or ketone solvent loses hardness and a straight edge, which is a dimensional change and not simply wear.
Flood bar damaged or set low enough to scrape the stencilIt lays an uneven charge of ink for the print stroke to shear.

Screen Printing InksStreaks and lines running with the stroke

Fault 5 of 20 · continued

Streaks and lines running with the stroke

CHECK, IN THIS ORDER

Inspect the squeegee edge under a loupe at the position that corresponds to the streak on the sheet.
Check the blade against a steel straight edge and read durometer along its length to ASTM D2240, back from the printing edge, comparing with a new blade of the same type.
Hold the screen to the light and look for residue or haze in the mesh at the streak position.
Take the first sheets of the run onto the production substrate and tape them at 24 h. A streak that also fails adhesion is chemical carry-over from the reclaim, not a blade fault.
Measure blade projection from the holder at both ends and the centre, and check bed to screen parallelism with a feeler gauge at four corners with the screen at print position.

THEN CHANGE

Dress the blade on a squeegee sharpener, or replace it.
Change to a blade material rated for the solvents in that ink and its thinner.
Reclaim the screen properly. A ghost image or a haze left in the mesh is a printing defect, not a cosmetic one.
Rinse and dry the screen fully after reclaim so no wash or haze remover is left in the weave, and print waste sheets before the first good one.
Set the flood bar to carry ink over the image without touching the stencil, and level the bed and re-check parallelism.

CONFIRM IT IS FIXED

Twenty sheets after the change inspected at raking light with no line visible at 500 mm, density variation across the stroke direction inside the tolerance agreed with the customer at a stated density status, and the first sheets taping to the same classification as the rest of the run.

THE TRAP

Increasing pressure so the blade cleans the mesh over a nick. It bends the blade onto its face, widens the contact, thickens the whole deposit and wears the nick into a groove.

Screen Printing InksStreaks and lines running with the stroke (continued)

Fault 6 of 20

Ink lifts on tape or scratches off

WHAT YOU SEE

The print looks right and the film is hard, but a cross-cut and tape pull takes it off, or a thumbnail scratches through to the substrate. It often passes at the press and fails the next day.

WHAT IT LOOKS LIKE

CAUSES, MOST LIKELY FIRST

Substrate surface energy too low, untreated polyolefin or treatment decayed in storeA liquid ink that did not wet the surface has nothing to hold to. Untreated PE and PP sit at roughly 18 to 31 mN/m, far below the surface tension of the ink. The house target after treatment is 40 mN/m or above, with the grade's TDS giving the figure it needs. Where the part cannot be treated, the answer is a grade formulated for untreated polyolefin, such as UniCure PP-900, and not a higher dyne reading.
Mould release, plasticiser or slip additive at the surfaceA weak boundary layer. The ink is well bonded to a layer that is not bonded to the part.
Bloom out of a rubber or latex substrateVulcanisation accelerators, sulphur, talc and moulding release powder migrate to the surface and form a release layer, so the print sits on something that is not attached to the part. It is the dominant adhesion failure on balloon and rubber work, and it comes back after every wipe while the compound is still blooming.
Wrong series for the substrateGlass needs silane coupling, metal needs a two-pack or a UV grade built for it, wood needs its primer. A plastics grade cannot do a glass grade's job.
Catalyst omitted or the ratio wrong, or the cure schedule not achievedAn uncross-linked film has the cohesive strength of a lacquer and none of the interfacial chemistry the system relies on.

Screen Printing InksInk lifts on tape or scratches off

Fault 6 of 20 · continued

Ink lifts on tape or scratches off

CHECK, IN THIS ORDER

Rub the film first, because it is the cheapest test on the list and it splits the fault in two: 30 MEK double rubs at the house condition, in nitrile gloves under local exhaust and away from ignition sources. A film that rubs through is under-cured, and that is a cure fault with a different fix, so go to the oven profile or the UV dose and not to the treater.
Measure surface energy with dyne pens or ISO 8296 test inks on the parts you are about to run, not on a retained sample from the last delivery.
Cross-cut on rigid material to ISO 2409 with the blade spacing set by film thickness, tape and classify, then repeat at 24 h after conditioning at 23 C and 50 % RH. On rubber, latex, foam, leather and wax the cross-cut reads the substrate rather than the ink, so use a single scribe line with tape and an agreed dry and wet rub count instead.
Confirm the catalyst by weight from the mixing record, with the ratio and the time written down.
Profile the oven with a trailing thermocouple for air and part temperature against time, rather than reading the panel.

THEN CHANGE

Flame or corona treat immediately before print, and print inside the window the treatment holds.
Clean the part with the recommended cleaner. Where the release is coming out of the tool, it has to be fixed at moulding.
On rubber and latex, wash the bloom off immediately before print and re-qualify whenever the compound or the cure changes. A compound that blooms heavily has to be changed at the moulder, because no ink holds to a surface that keeps renewing itself.
Move to the series built for that material: UniScreen-35 or UniGlazier 833SB on glass, Unital-SS or the SCure UV series on metal, UniScreen-7Wood over its primer on wood, UniScreen-04 Leather on leather, UniScreen-05FM on foam, the UniTex series on rubber and latex, UniCure PP-900 on polyolefin.
Where a primer is specified, use it. UniScreen-7Wood is a primer-required system, so a missed primer is a process omission and not an ink fault.

CONFIRM IT IS FIXED

On rigid material, ISO 2409 cross-cut with the 1 mm cutter at classification 0 or 1 at 24 h. On rubber, latex, foam, leather and wax, a scribe and tape with no lift plus the agreed dry and wet rub count, since the cross-cut is not valid there. In both cases at least 30 MEK double rubs at the house condition with no breakthrough where solvent resistance is specified, and the end-use resistance the article is actually specified on, all on the customer's own material.

THE TRAP

Increasing the film weight to get more adhesion. A heavier film stores more shrinkage stress and takes longer to release solvent, so it usually adheres worse. Adhesion is a property of the ink and the substrate together, qualified on the customer's own material, and it is never a property of the ink alone.

Screen Printing InksInk lifts on tape or scratches off (continued)

Fault 7 of 20

Deposit and opacity drift through the run

WHAT YOU SEE

The first hundred prints hide the substrate and the last hundred do not, or a white looks thin after the screen has been washed and re-hung. Measured film thickness has fallen.

WHAT IT LOOKS LIKE

CAUSES, MOST LIKELY FIRST

Mesh tension falling through the runA slacker mesh deflects further under the blade, so the operator adds pressure to keep it sweeping, and more pressure means a thinner deposit.
Squeegee pressure creeping up while other faults are chasedThe blade bends over, the contact widens and more ink is sheared back into the flood instead of into the aperture.
Blade edge rounding as the run proceedsA rounded edge does not clean the mesh at the same pressure, so the operator compensates and the deposit changes again.
Viscosity rising from solvent lossThicker ink releases less completely from the aperture, particularly on fine mesh.
Stencil abrading and losing thicknessStencil thickness is part of the volume that defines the deposit, so losing it loses ink.

Screen Printing InksDeposit and opacity drift through the run

Fault 7 of 20 · continued

Deposit and opacity drift through the run

CHECK, IN THIS ORDER

Read mesh tension before the job and again after 1 000 impressions with a tension meter, and log both on the job ticket.
Measure cured film thickness by the method the substrate allows: an eddy-current or magnetic gauge on metal only; on glass and rigid plastics a micrometer or dial gauge reading printed against unprinted at the same point, or a cross-section under a microscope; on absorbent stock a wet-film comb converted by the solids figure on the TDS. Typical cured screen deposits are 8 to 30 micron for graphics. Record the method with the number, because a coating thickness gauge reads nothing at all on plastics, glass, wood, leather, foam or wax.
Read density or opacity with a spectrophotometer against the approved sample at fixed intervals, not by eye.
Record the squeegee pressure setting at the start and after every intervention.
Measure stencil thickness before the job and again at the end.

THEN CHANGE

Use pre-stretched or retensionable frames stabilised in the band the mesh manufacturer gives for that count, and keep frames in matched sets for a job.
Set squeegee pressure to the lowest value that sweeps clean, lock it, and treat any increase as a fault to be diagnosed.
Change to a fresh blade of the same durometer at fixed intervals rather than when the fault appears.
Hold viscosity to a measured figure on a schedule, using the retarder rather than the thinner.
Where more opacity is genuinely needed, change the mesh. A lower thread count per centimetre deposits more ink.

CONFIRM IT IS FIXED

Density, or L* on a white, read at the start, at every 250 impressions and at the end, all inside the tolerance agreed with the customer, with cured film thickness at the end matching the start inside the repeatability of the method actually used, and the method recorded alongside the number.

THE TRAP

Chasing opacity with more pressure and a slower stroke. Both of them reduce the deposit. Opacity is set by the open volume of the mesh and the stencil, which means it is a decision made before the job starts, not a knob on the press.

Screen Printing InksDeposit and opacity drift through the run (continued)

Fault 8 of 20

UV print tacky on top, hard underneath

WHAT YOU SEE

The film has body and will not scratch off, but it feels tacky or greasy, marks in the stack, and a dense black or a heavy white is worse than a process colour.

WHAT IT LOOKS LIKE

CAUSES, MOST LIKELY FIRST

Oxygen inhibition at low peak irradianceOxygen quenches the radicals in the top few micron of the film. The depth of that inhibited layer is set by the ratio of radical generation rate to oxygen diffusion rate, which means it is decided by irradiance rather than by total dose.
Lamp output fallen, or the quartz sleeve devitrifiedShort-wave output is lost first and that is the surface-cure band, while a broadband reading can still look acceptable.
Heavy screen film screening its own depth, or a pigment absorbing in the initiator bandAn opaque white scatters and a dense black absorbs the same wavelengths the photoinitiator needs, so the film competes with its own cure.
Conveyor speed raised without re-measuring doseDose is inversely proportional to speed, so doubling the speed halves the dose at the same lamp setting. That costs through-cure first and surface cure second.
The grade and the lamp do not matchThe photoinitiator package is chosen for the emission band. A mercury-sensitised ink under an LED unit will not cure.

Screen Printing InksUV print tacky on top, hard underneath

Fault 8 of 20 · continued

UV print tacky on top, hard underneath

CHECK, IN THIS ORDER

Measure dose and peak irradiance at the substrate with a band-calibrated radiometer passed through the machine at running speed.
Do 30 MEK double rubs at the house condition, in nitrile gloves under local exhaust: a film that fails the rubs is under-cured through, a film that passes but stays tacky is surface inhibited.
Check lamp hours against the rated life for the source: about 1 000 to 2 000 h for a medium-pressure mercury arc, typically 20 000 h or more for an LED array. On mercury, inspect the quartz for devitrification and the reflector for coating loss. On LED the failure modes are output drift, dead diodes and inadequate cooling, so read the measured irradiance and check the array's water or air temperature rather than the hour counter.
Measure the cured film thickness, because the dose a 25 micron screen film needs is not the dose a 2 micron offset film needs.
Confirm the grade suits the lamp and the mix: SCure-41UVLED and SCure-72UVLED are LED grades, SCure-39UV, SCure-40UV and SCure-66UV are mercury grades. SCure-40UV, SCure-41UVLED and SCure-72UVLED are two-pack UV systems, so check the time of catalysis against their pot life as well as checking the lamp; only SCure-39UV and SCure-66UV are single-pack.

THEN CHANGE

Raise peak irradiance before anything else: lamp to substrate distance, reflector condition, focus.
Replace lamps at their rated hours, or earlier when the measured irradiance at the commissioning setting has fallen about 25 %.
Where the deposit is heavy, use a doped lamp for cure at depth, or print a lighter film twice through a finer mesh.
Reduce film weight. On a UV screen ink the quickest route to full cure is usually less ink.
Use nitrogen inerting only where the line is built for it: oxygen depletion monitoring on the inerted zone, alarms and interlocks, a purge before any entry and a confined space procedure for work inside the tunnel. Nitrogen is an asphyxiant and there is no smell or sensation to warn of it.

CONFIRM IT IS FIXED

Thirty MEK double rubs at the house condition with no breakthrough, no thumb-twist mark at the delivery with the twist made in a nitrile glove, and no set-off in a stack built 30 min after cure and left overnight under its own weight. Never test a tacky UV film with bare skin: an inhibited surface holds unreacted acrylate monomer and acrylate sensitisation is permanent.

THE TRAP

Reaching for conveyor speed first. Slowing the press raises dose but leaves peak irradiance unchanged, and it is irradiance, not dose, that beats oxygen at the surface, so it is a weak and expensive answer to a tacky face. It does help through-cure in a heavy deposit, which is why it sometimes appears to work. Raise irradiance first, through lamp to substrate distance, reflector, focus and lamp age, and treat speed as the last adjustment.

Screen Printing InksUV print tacky on top, hard underneath (continued)

Fault 9 of 20

Prints block or set off in the stack

WHAT YOU SEE

Sheets or parts stick together, the back of one carries a ghost of the print below, or the print marks under its own weight after a few hours in a pile.

WHAT IT LOOKS LIKE

CAUSES, MOST LIKELY FIRST

Solvent retained in the filmScreen lays 8 to 30 micron, so the solvent has to leave through a film several times thicker than an offset or flexo film, and the surface skins before the base is dry.
Stacked too soon or too highThe film keeps building for hours after the oven, and weight applied inside that window embeds a mark that never recovers.
Oven dwell short of the scheduleDwell at part temperature is what removes solvent from a thick film; a high temperature on a short dwell only skins it.
Heat applied too fast at the oven entryA heavy film driven straight into high heat boils solvent out through a surface that has already skinned. That leaves pinpoint craters, solvent pop, and the solvent that does not escape stays in the film to block the stack.
Too much retarder added to keep the screen openRetarder solves a screen problem and creates a drying problem. It is a deliberate trade and it has to be recorded.

Screen Printing InksPrints block or set off in the stack

Fault 9 of 20 · continued

Prints block or set off in the stack

CHECK, IN THIS ORDER

Profile the tunnel with a trailing thermocouple and compare against the grade's schedule. For our two-pack screen systems on heat-tolerant substrates that is of the order of 15 to 30 min at 80 to 120 C part temperature, with resistance building over a further 24 to 72 h at 23 C.
Press a clean sheet against the print under a known weight for 30 min and look for transfer.
Measure retained solvent rather than smelling for it: weigh a cut sample, re-bake it to constant weight and record the loss as a percentage of the dry film, or send a sealed sample for headspace GC. A solvent smell at the delivery is a prompt to measure, not a measurement, and the nose is not an instrument on solvent work.
Read the mixing record for the retarder percentage actually added.
Record the stack height and the time from delivery to stacking.

THEN CHANGE

Restore the schedule, dwell first. A higher temperature on a short dwell makes retention worse, not better.
Bring the film up to temperature in stages rather than straight into the hottest zone, so the solvent leaves before the surface skins.
Cut the retarder back and deal with screen drying through cycle time and fan control instead.
Interleave, or rack rather than stack, for the first few hours.
Reduce the film weight through a finer mesh where the design allows it, and on barrier substrates allow a longer airing and cooling period before the parts are packed.

CONFIRM IT IS FIXED

A blocking test, print face against unprinted back, 24 h at 40 C under a defined load, with no transfer and no gloss change on separation, gloss read to ISO 2813. On heat-sensitive substrates run the same test at the highest temperature the article will actually see.

THE TRAP

Turning the oven up. A hotter surface skins faster and locks the solvent underneath, so blocking gets worse while the panel says the oven is hotter. Dwell at part temperature, not panel temperature, is what takes solvent out of a thick screen film.

Screen Printing InksPrints block or set off in the stack (continued)

Fault 10 of 20

Image grows and register drifts at the edges

WHAT YOU SEE

The second and third colours will not fit the first. The error is small at the centre and grows towards the edges of the image, and it gets worse as the run goes on.

WHAT IT LOOKS LIKE

CAUSES, MOST LIKELY FIRST

Mesh tension low or uneven across the frameThe mesh stretches under the blade and the image prints wherever the stretched mesh happens to be at that moment.
Off-contact too highThe mesh must elongate further to reach the substrate, so every point of the image is displaced outward in proportion to the local elongation. The displacement is near zero at the centre and largest at the edges, and it grows with off-contact and with falling tension. It is a fraction of the off-contact distance and not equal to it, so it has to be measured on a register target rather than calculated.
Squeegee pressure too highIt pushes the mesh forward in the stroke direction, which is why the error is directional rather than symmetrical.
Frames not from a matched setDifferent tensions colour to colour produce different amounts of growth on the same artwork.
Substrate changing dimension between coloursBoard and thin plastics move with temperature and moisture. Thin styrene, PVC, PET, foam and coated board shrink, curl or stretch through the dryer, so the sheet that comes back for the second colour is not the size it was for the first.

Screen Printing InksImage grows and register drifts at the edges

Fault 10 of 20 · continued

Image grows and register drifts at the edges

CHECK, IN THIS ORDER

Measure tension in five positions on every frame in the set against the band the mesh manufacturer gives for that count, matched within about 2 N/cm.
Measure off-contact at the centre and the four corners with the screen at print position.
Print a register target and measure centre and edge error with a measuring magnifier; a growing error towards the edge is tension or off-contact, a uniform shift is the bed or the stops.
Measure a long dimension on the substrate before and after the dryer with a steel rule or a comparator, and count how many dryer passes each colour has had.
Check the vacuum bed: read hold-down across the sheet, look for blocked holes and hole marks printing through thin stock, and watch whether the sheet lifts at snap-off.

THEN CHANGE

Re-tension or replace frames, and let newly stretched screens stabilise before they are used.
Reduce off-contact to the minimum that still gives a clean snap, and reduce squeegee pressure to the minimum that sweeps clean.
Clear and balance the vacuum bed, and mask the open area outside the sheet so the hold-down is even.
Hold dryer temperature as low as the ink allows, give the sheets the same number of dryer passes, and let them cool and stabilise in the press room before the next colour.
Compensate the artwork for measured growth only after tension, off-contact and substrate movement are right, never before.

CONFIRM IT IS FIXED

A register target measured on ten sheets spread through the run, with edge to centre error inside the job tolerance and no drift between the first sheet and the last.

THE TRAP

Rescaling the film or the artwork to make the job fit. It corrects one screen at one tension on one day and has to be redone every time the frame relaxes. It also buries the tension problem, which is simultaneously causing the sawtooth edges and the deposit drift on the same job.

Screen Printing InksImage grows and register drifts at the edges (continued)

Fault 11 of 20

Stencil breaks down in the middle of the run

WHAT YOU SEE

The image loses its edge, ink appears where it should not, or the emulsion lifts from the mesh in patches, usually starting in the squeegee contact area or at the edges of the image.

WHAT IT LOOKS LIKE

CAUSES, MOST LIKELY FIRST

Emulsion not compatible with the ink's solventA diazo or low-solids emulsion intended for water-based work swells and softens in ester and ketone solvents.
Under-exposed stencilThe emulsion nearest the mesh never fully cross-linked, so it washes and wears away from the mesh side while the print face still looks sound.
Mesh not degreased or not abraded before coatingThe emulsion holds to the thread mechanically, and a greasy or glassy thread gives it nothing to hold to. The same omission leaves uncoated specks that print as unwanted ink dots in clear areas.
Aggressive screen wash between runsRepeated solvent attack and scrubbing thin the stencil a little at a time until a run finds the limit.
Excessive squeegee pressure, or a blade that is too hardThis is abrasion, and in that contact the stencil is the softest thing present.

Screen Printing InksStencil breaks down in the middle of the run

Fault 11 of 20 · continued

Stencil breaks down in the middle of the run

CHECK, IN THIS ORDER

Check the emulsion system against the ink class: solvent-resistant dual-cure or capillary film for solvent screen inks, and a system rated for UV inks where UV is being run.
Run an exposure calculator and read the step that holds. Under-exposure is the most common stencil fault in a busy press room.
Look at where the emulsion has gone: lost from the mesh side means exposure or degreasing, worn from the print side means abrasion or solvent.
Read the degreasing and mesh preparation record for that screen, and water-break test a freshly degreased screen: a correctly degreased mesh holds an unbroken water film with no beading.
Measure squeegee durometer to ASTM D2240, back from the printing edge, and note the pressure setting.

THEN CHANGE

Move to the correct emulsion system for the ink class and post-expose the stencil after washout.
Increase exposure to the calculator result, and re-run the calculator with every new emulsion batch and after any exposure lamp change.
Degrease with Uniclear-105 to its data sheet and abrade new mesh where the emulsion supplier calls for it, in gloves and eye protection.
Use the mildest wash that clears the ink and keep screen wash off the stencil edges.
Drop the pressure and use the softest blade that still sweeps the mesh clean.

CONFIRM IT IS FIXED

The stencil completes the full run length with no loss of edge at 30x under a loupe, and the exposure calculator step is written on the job ticket so the repeat order starts from the same place.

THE TRAP

Touching a failing stencil in with blockout on press. It bridges the hole for a few hundred impressions, and the emulsion around it shares the same exposure and wear history, so the next failure is already on its way.

Screen Printing InksStencil breaks down in the middle of the run (continued)

Fault 12 of 20

Two-pack ink thickens and gels in the tray

WHAT YOU SEE

The ink works for the first few hours, then goes short and rubbery. It will not thin properly, the print looks rough and the screen starts blocking within minutes.

WHAT IT LOOKS LIKE

CAUSES, MOST LIKELY FIRST

Pot life exceededCross-linking runs whether or not the press does. Once the pot life on the grade's TDS has passed, broadly 6 to 12 h across our two-pack screen systems and 6 to 8 h for the silane bonding glass grades, the ink has lost its working properties.
Too much catalystExcess hardener accelerates the reaction and can leave unreacted material in the cured film as well.
Warm press room or a warm trayThe reaction rate roughly doubles for every 10 C rise, and the TDS pot life is quoted at 20 C, so a tray near a dryer has a much shorter life than the printed figure.
Fresh catalysed ink added to an old trayThe whole tray then behaves like the oldest ink in it.
Moisture in the ink or on the toolsOn a moisture-sensitive system it consumes hardener and generates gas, which shows as body and as small bubbles.

Screen Printing InksTwo-pack ink thickens and gels in the tray

Fault 12 of 20 · continued

Two-pack ink thickens and gels in the tray

CHECK, IN THIS ORDER

Read the mixing record: time of catalysis, ratio, and how the ratio was measured.
Measure ink temperature in the tray and press room temperature.
Weigh a check sample of the mix on a balance to confirm the ratio against the TDS.
Measure viscosity at catalysis and hourly afterwards by the TDS method, at the tray's actual temperature.
Confirm the tools and the tray were clean and dry before use.

THEN CHANGE

Catalyse only what the next few hours will use and write the time on the tin.
Weigh both components on a balance under local exhaust ventilation, in nitrile gloves and eye protection, to the hardener's Safety Data Sheet. Isocyanate hardeners are respiratory sensitisers, sensitisation is permanent and there is no safe exposure level afterwards. Volume by eye is the usual source of a 10 % error.
Cool the press room or the ink store and keep catalysed ink away from the dryer and out of direct sun.
Discard gelled ink to the waste route on its Safety Data Sheet. A gelled two-pack cannot be recovered with solvent and printing it costs more than replacing it.
Keep a dedicated clean, dry set of tools for catalysed material.

CONFIRM IT IS FIXED

Two separate numbers, and they are not the same number. Working viscosity held within about 10 % of the TDS figure throughout the window, by the TDS method at the tray's actual temperature, because that is what the press needs; and the unadjusted climb of the catalysed tray read hourly, where a rise of the order of 20 % across the working window is normal for a cross-linking system and a sharp rise after it is the signal to discard rather than to thin. The tray is emptied at the end of the pot life window, not at the end of the shift.

THE TRAP

Thinning a ropy two-pack to keep it running. Solvent lowers the viscosity but does nothing to the network that has already formed, so the film prints with less body, less adhesion and less chemical resistance. The customer finds that on the finished part rather than at the press.

Screen Printing InksTwo-pack ink thickens and gels in the tray (continued)

Fault 13 of 20

Ink crawls or mottles on plastics

WHAT YOU SEE

The solid breaks up into islands or shows an uneven mottled texture. Worst on polyolefins and on parts that came straight out of the mould or out of a store bag.

WHAT IT LOOKS LIKE

CAUSES, MOST LIKELY FIRST

Surface energy below what the ink needsThe ink's surface tension exceeds the substrate's critical surface tension, so the wet film minimises its area and pulls into islands.
Mould release or slip additive bloomed to the surfaceIt is a very low energy layer, and where it is migrating out of the part it re-forms after every wipe.
Corona treatment decayed in storeTreatment is not permanent. Polar groups reorient into the bulk over weeks, and faster when the stock is warm.
Antistatic or cleaning spray used on the partsMost of them leave a surfactant film, which is precisely the contamination that causes the fault.
Wrong series for the polymerA grade formulated for rigid PVC or for polycarbonate has no adhesion promotion built in for a polyolefin.

Screen Printing InksInk crawls or mottles on plastics

Fault 13 of 20 · continued

Ink crawls or mottles on plastics

CHECK, IN THIS ORDER

Dyne pens or ISO 8296 test inks on the actual parts. For screen work on plastics expect to need 38 to 42 mN/m, with 40 mN/m or above as the house target after treatment and the grade's TDS giving the figure it needs.
Compare a freshly treated part with a stored one to separate treatment decay from a treatment fault.
ASTM D2578 wetting tension on film substrates where the material allows the test.
Clean a patch, print it and compare it against the untouched area.
Confirm the polymer with the moulder. A PP part and a PE part need different answers.

THEN CHANGE

Flame or corona treat immediately before print and print within hours, not weeks.
Move to the series for that material, for example UniSwitch 40FP for membrane switches and front panels, UniPET-67 for PET-G and polycarbonate, the VL-99 series for vinyls, UniLite for in-mould decoration, UniCure PP-900 where the part is polyolefin, or UniCure Ultra 5000 across a broad range of other plastics. Neither UV grade is a substitute for treatment on an untreated polyolefin, and every substrate is qualified individually on the customer's own parts.
Take the mould release out of the moulding process for parts that are to be printed.
Use a primer or adhesion promoter where the polymer calls for one.
Store treated parts covered and off the floor, and run treated stock first in, first out.

CONFIRM IT IS FIXED

Wetting tension at or above the grade's stated requirement across the whole part, an even solid under raking light at 300 mm, and ISO 2409 class 0 or 1 at 24 h on the customer's own parts where the part is rigid enough for the cross-cut to mean anything.

THE TRAP

Adding thinner so the ink wets better. Thinner reduces viscosity, not surface tension in any useful degree, and the thinner film that results retracts more easily. Treat the surface instead.

Screen Printing InksInk crawls or mottles on plastics (continued)

Fault 14 of 20

Print cracks when the part is flexed

WHAT YOU SEE

On rubber, latex, foam, leather and flexible vinyl the print looks correct flat, then crazes or flakes when the part is stretched, folded or compressed. Balloons and foam sheets show it first.

WHAT IT LOOKS LIKE

CAUSES, MOST LIKELY FIRST

A rigid grade on a flexible substrateElongation at break of the film is below the strain the part sees, and a chemically resistant, highly cross-linked film is brittle by the same chemistry that makes it resistant.
Film too heavyFor a given strain a thicker film carries more stress at the surface and cracks first.
Over-catalysed or over-bakedExtra cross-linking buys resistance and spends flexibility, and the trade is not reversible.
Plasticiser moving between substrate and filmFlexible PVC loses plasticiser into the ink, which hardens the interface over days rather than hours.
Substrate stretched at print and relaxed afterwardsThe film is laid on a surface that is about to change dimension, so it is in compression as soon as it is fixed.

Screen Printing InksPrint cracks when the part is flexed

Fault 14 of 20 · continued

Print cracks when the part is flexed

CHECK, IN THIS ORDER

Flex the actual part through the strain it sees in use, at least ten cycles, and inspect under a loupe. Do this on the customer's own material.
On coated metal, conical or cylindrical mandrel bend to ASTM D522 or ISO 1519. On the flexible substrates where this fault actually occurs there is no mandrel test that means anything, because the substrate yields long before the mandrel puts useful strain into the ink film: stretch, fold or compress the printed part through the strain it sees in service instead, or compare the elongation at break of the printed part against the elongation figure on the ink's TDS.
Measure cured film thickness by a method the substrate allows, and record the method.
Check the catalyst ratio by weight and the cure schedule against the TDS.
Age a sample seven days at 40 C and repeat the flex, because plasticiser migration takes time to show.

THEN CHANGE

Use the flexible series for the material: UniTex-88 BL on balloons, UniTex-84 RR and UniTex-85 R2 on rubber, UniTex-89 UL on unlacquered foil balloons and UniTex-87 LQ on lacquered and coloured ones, UniScreen-04 Leather on leather, UniScreen-05FM on foam.
Reduce film weight with a finer mesh or a thinner stencil.
Weigh the catalyst. A 10 % over-addition is easy to make by eye and impossible to undo.
Hold the cure schedule rather than exceeding it. More heat and more time are not free.
On plasticised PVC, qualify the grade on the customer's own compound and repeat the test after ageing.

CONFIRM IT IS FIXED

The part passes the customer's own flex, stretch or compression test with no crazing, tested at 24 h and again after seven days at 40 C.

THE TRAP

Adding a flexibiliser or a soft extender to a rigid grade at the press. The addition is uncontrolled, it lowers cross-link density everywhere, and the same film then fails the chemical and scratch resistance the job was specified on. Change the series instead.

Screen Printing InksPrint cracks when the part is flexed (continued)

Fault 15 of 20

Shade drifts between screens and between shifts

WHAT YOU SEE

The same colour prints heavier or lighter on the second screen, or the afternoon run does not match the morning. The difference is usually in strength rather than in hue.

WHAT IT LOOKS LIKE

CAUSES, MOST LIKELY FIRST

Settling in the tin, or a batch difference nobody checked before the runScreen ink pigments settle hard in storage, so the first ink out of an unstirred tin is weak and the last is strong. It is the commonest reason a colour is wrong on the very first print, before any press variable has had time to move. A new batch shifts strength and viscosity as well.
The deposit changedScreen prints by volume, so the strength of the colour is the thickness of the film, and every deposit variable is a colour variable.
Thinner or retarder added during the runIt dilutes the pigment and lays a thinner dry film, which reads as a weaker colour.
Different mesh between the proof and the production screenA proof pulled on a coarser mesh carries more ink and can never be matched on a finer one by adjusting the formulation.
Dye or plasticiser bleeding out of the substrateFlexible PVC, coloured vinyls and printed rubber feed colourant into the film from below, so light shades warm or discolour over days rather than hours, and the print may soften with it. Nothing at the press corrects it; the substrate and the grade are qualified together.

Screen Printing InksShade drifts between screens and between shifts

Fault 15 of 20 · continued

Shade drifts between screens and between shifts

CHECK, IN THIS ORDER

Stir the tin to the bottom with a paddle or a mechanical stirrer, pull a drawdown onto the production substrate and compare it against the retained standard for that batch before the run starts.
Measure with a spectrophotometer to ISO 13655 with M1 illumination, D50 illuminant and 2 degree observer, against the approved standard, and report dE00. Do not accept an eye match across shifts.
Compare mesh count, thread diameter, tension and stencil thickness between the two screens.
Read the mixing record for every addition made during the run and its percentage.
Check the viewing booth lamps and their hours.

THEN CHANGE

Stir every tin to the bottom before use and approve the batch against the retained standard before the run, not after the first thousand.
Fix the deposit before touching the formulation: same mesh, same tension band, same stencil thickness, same blade.
Record the mesh specification on the job ticket and use it on every repeat order.
Limit press-side additions to a stated percentage and record them.
Match in a booth with D50 lamps inside their rated hours.

CONFIRM IT IS FIXED

dE00 inside the tolerance agreed with the customer, 2.0 being a workable figure for general repeat work, measured to ISO 13655 with M1 illumination, D50 and the 2 degree observer, on the production substrate at the start, the middle and the end of the run. State on the job ticket which dE formula the tolerance refers to, because dE*ab and dE00 are not interchangeable and differ by roughly a factor of two on the saturated solids screen printing produces.

THE TRAP

Correcting a strength difference by adding toner at the press. It moves the whole run away from the standard and cannot be reproduced on the next order. Put the deposit back to specification first, and most strength differences disappear on their own.

Screen Printing InksShade drifts between screens and between shifts (continued)

Fault 16 of 20

Static: dust pick-up and spatter on plastics

WHAT YOU SEE

Sheets cling or repel each other, dust and fibre land on the substrate in the last second before printing, and fine detail shows a halo of spattered ink around it.

WHAT IT LOOKS LIKE

CAUSES, MOST LIKELY FIRST

Press room too dryBelow about 40 % RH the charge cannot leak away through the air, so it accumulates on every insulating surface.
Insulating substrate separated at speedPET, PC, PP and PVC generate and hold charge when pulled from a stack or off a release film.
Screen release generating chargeThe mesh peeling from the substrate separates two insulators, and the field pulls fine droplets sideways as the ink splits.
Press not earthedThe bed, the frame and the squeegee holder are all charge collectors if they have no path to earth.
Air blast from the feeder or the dryerMoving air carries the dust that the charge then holds.

Screen Printing InksStatic: dust pick-up and spatter on plastics

Fault 16 of 20 · continued

Static: dust pick-up and spatter on plastics

CHECK, IN THIS ORDER

Measure surface charge with a static field meter at the feeder, at the print station and at the delivery.
Measure press room RH with a hygrometer at the press, not at the office wall.
Check earthing continuity from the bed and the frame to the earth point with a multimeter.
Look at the defect: a spatter halo that follows the image edge is charge at release, random dust is ambient.
Check whether the fault appears only after the dryer.

THEN CHANGE

Raise press room RH to 45 to 55 % where the substrate allows it.
Fit static bars or an ioniser at the feeder and the delivery, and one over the bed for release spatter.
Earth the bed, the frame, the squeegee holder and the delivery.
Slow the separation by reducing off-contact and peel speed.
Use a tack cloth or an ionised air knife immediately before print.

CONFIRM IT IS FIXED

Field meter readings back below the level at which the fault started, and 50 consecutive prints with no dust inclusion and no spatter halo under a loupe.

THE TRAP

Wiping the parts with an antistatic spray. Most of them leave a surfactant film, which is exactly the low energy contamination that then produces pinholes and adhesion failure on the same job, a day later and on a different shift.

Screen Printing InksStatic: dust pick-up and spatter on plastics (continued)

Fault 17 of 20

Glass print passes on day one, fails in a week

WHAT YOU SEE

The tape test passes at the press and the same print fails after humid storage, a wash cycle or a few days in a warehouse. The ink comes away cleanly and leaves bare glass.

WHAT IT LOOKS LIKE

CAUSES, MOST LIKELY FIRST

Water reaching the interfaceGlass carries silanol groups and an adsorbed water layer. A binder holding only by physical adhesion is displaced as water diffuses through the film and hydrates that layer.
No silane coupling, or the coupling agent cannot reach the glassThe bond that survives water is a covalent Si-O-Si chain from the glass through the coupling agent into the binder, and a contaminated surface prevents it forming.
Glass not clean or not dryFingerprints, lehr release and cutting oil all sit between the coupling agent and the surface it has to condense with.
Cure schedule for the glass system not achievedThe silane condensation and the binder cure both need their time at temperature, and a short dwell leaves both incomplete.
Cure shrinkage stress in a rigid filmGlass does not move and the film shrinks, so the stored stress is released as flaking on the first thermal cycle or impact.

Screen Printing InksGlass print passes on day one, fails in a week

Fault 17 of 20 · continued

Glass print passes on day one, fails in a week

CHECK, IN THIS ORDER

Cross-cut to ISO 2409 with the 1 mm cutter at 24 h and again after an exposure agreed with the customer, for example 48 h at 40 C and 95 % RH, and after the number of wash cycles the article will actually see.
Water-break test the cleaned glass: a clean surface holds an unbroken water film.
Confirm the grade in use. UniScreen-35 is the two-component silane bonding system and UniGlazier 833SB the two-pack solvent system for flat glass; SCure-66UV and SCure-72UVLED are the UV and UV LED routes.
Profile the achieved cure with a trailing thermocouple rather than reading the panel.
Measure the film thickness, since a heavy rigid film stores more shrinkage stress.

THEN CHANGE

Print on clean, dry glass, and print soon after cleaning rather than after a night on a rack.
Use the silane bonding system where the article sees water.
Hold the cure schedule, dwell first.
Reduce film weight to the minimum the hiding requirement allows.
Keep the print inside the decoration area the article allows. On drinking glass the lip and rim exclusion zone is a customer and article requirement, so agree it in writing before the first order and put it on the job ticket with the artwork.

CONFIRM IT IS FIXED

ISO 2409 cross-cut at class 0 after the agreed humidity or wash exposure on the customer's own glass, with the result recorded as the qualification for that article, that decoration area and that wash schedule.

THE TRAP

Accepting the day-one tape test as the answer. It tells you nothing about the bond that matters, because the failure mechanism needs water and time. A glass job is qualified after ageing, or it is not qualified.

Screen Printing InksGlass print passes on day one, fails in a week (continued)

Fault 18 of 20

Print flakes off the candle, or marks the flame

WHAT YOU SEE

On wax the print rubs or flakes at the edges during handling, or the customer reports that the print discolours the flame or leaves residue as the candle burns down.

WHAT IT LOOKS LIKE

CAUSES, MOST LIKELY FIRST

Wrong ink class for the applicationUniScreen-02WAX dries by solvent evaporation and is formulated so that the printed film congeals and separates from the melt pool rather than being drawn into the wick. A plastics or UV grade is not.
Wax surface is low energy and softNothing wets it well, and the layer directly under the ink can move, so the film is anchored to something that deforms.
Bloom on the wax surfaceAdditives and low melting fractions migrate to the surface and form a release layer between the ink and the wax.
Printed on a warm castingThe surface softens, the ink sinks or moves, and the edge definition and the anchorage both suffer.
Film too heavy for a soft substrateA thick film cannot follow the surface and peels from the edges first.

Screen Printing InksPrint flakes off the candle, or marks the flame

Fault 18 of 20 · continued

Print flakes off the candle, or marks the flame

CHECK, IN THIS ORDER

Confirm the grade in use is UniScreen-02WAX, which is the grade built for candle work.
Measure the article surface temperature at print with an infrared thermometer; print only on wax that has cooled and stabilised.
Look for bloom: wipe a small area with a lint-free cloth, print it alongside an unwiped area and compare.
Thumbnail and tape check on the cooled print at 24 h, using a scribe and tape rather than a cross-cut, because a cross-cut on wax measures the wax.
Burn a printed sample the way the customer will use it, in a fume cupboard or under dedicated extraction, on a non-combustible tray, away from the ink store and the press, and never unattended. Record burn time, flame appearance and residue.

THEN CHANGE

Print only on stabilised, cool castings made to the wax formulation the sample was qualified on.
Reduce the film weight and use a finer mesh. A thin film follows the surface and stays on it.
Agree the printed area and its position on the candle before the first order. Coverage and the distance from the wick are conditions of the article, not properties of the ink.
Keep handling to a minimum, let the print harden fully before packing, and re-qualify whenever the wax formulation changes, because the behaviour belongs to the wax and the ink together.
Take the burn test result back to the customer as the acceptance, since behaviour in the flame is a property of the finished candle.

CONFIRM IT IS FIXED

Tape and thumbnail at 24 h with no removal, plus a burn test on the customer's own candle. Burn behaviour belongs to the finished candle, wax, wick, coverage and print position together, so it is assessed on that article, against EN 15493 and EN 15426 where those apply to it, and the recorded result is the acceptance for that article and that wax.

THE TRAP

Treating wax as though it were a plastic and reaching for treatment or a primer. Flame treating a candle is not a process, and a primer sits on the same soft, blooming layer the ink was sitting on. The variables are the ink class, the wax formulation and the printed area.

Screen Printing InksPrint flakes off the candle, or marks the flame (continued)

Fault 19 of 20

The ink crazes or cracks the plastic itself

WHAT YOU SEE

Fine hairline cracks in the substrate under and around the print, silvery in reflection, on polycarbonate, acrylic, ABS and polystyrene. It appears hours to days after printing rather than at the press, is worst at gate marks, weld lines, inserts, machined edges and anywhere the part is held in a fixture, and the part often fails at a load it carried before it was printed.

WHAT IT LOOKS LIKE

CAUSES, MOST LIKELY FIRST

Ester and ketone solvents in the ink, the thinner or the screen washThese solvents swell and plasticise the surface of an amorphous polymer, so the chains can move and open the microvoids that become crazes.
Moulding stress already in the partEnvironmental stress cracking needs stress and a chemical agent together. Neither on its own does it, which is why the same ink is fine on an annealed part and cracks a stressed one from the same tool.
Film too heavy, or solvent trapped under a skinned surfaceThe longer the solvent stays in contact with the polymer the deeper it works, so a heavy deposit or a short dwell extends the exposure at exactly the wrong moment.
Load applied while solvent is still in the partAssembly, clipping, bending or a tight fixture while the surface is still softened converts a stress the part carried safely into a cracking one.
Cleaning or wiping solvent used before printThe wipe is often more aggressive than the ink and it floods the whole surface, so the craze pattern follows the cloth rather than the image.

Screen Printing InksThe ink crazes or cracks the plastic itself

Fault 19 of 20 · continued

The ink crazes or cracks the plastic itself

CHECK, IN THIS ORDER

Print a set of parts and hold them 72 h at 23 C, then inspect under raking light at 10x. This fault does not show at the press, so a pass at the delivery proves nothing.
Print an annealed part alongside an as-moulded one from the same batch. If the annealed part survives, the stress is in the moulding and not in the ink.
Apply the ink, the thinner and the screen wash separately to an unprinted part with a cotton swab, hold and compare. It separates ink solvent from cleaning solvent.
Confirm the polymer with the moulder. Polycarbonate, acrylic, ABS and polystyrene behave differently, and a blended or coated grade differently again.
Map the crazes against the tool: gates, weld lines, inserts, machined and drilled edges, and the fixture points.

THEN CHANGE

Move to the series built for that polymer, for example UniPET-67 for PET-G and polycarbonate, or a UV grade where the chemistry allows it, since a UV screen ink carries no evaporating solvent into the surface.
Take the aggressive solvent out of the thinner and the screen wash for that job, and never wipe a stressed amorphous part with a ketone.
Anneal or re-mould the parts. A part that cracks under its own moulding stress is a moulding problem the ink has revealed, and it will show up again in service.
Reduce the film weight and give the print its full dwell so the solvent leaves quickly rather than working into the surface.
Keep the printed part unstressed for 24 to 72 h at 23 C before assembly, bending or packing under load.

CONFIRM IT IS FIXED

Printed parts from the production batch held 72 h at 23 C with no craze visible at 10x, and the part still passing its own mechanical acceptance, tested on the customer's own mouldings and repeated on any new tool, polymer grade or material batch.

THE TRAP

Changing colour and calling it a formulation fault. Every ink in the same class carries the same solvent family, so the next one crazes the same part. The three variables are the polymer, the moulding stress and the solvent, and only the solvent and the film weight are yours to change at the press.

Screen Printing InksThe ink crazes or cracks the plastic itself (continued)

Fault 20 of 20

The second colour lifts the first, or the varnish lifts the print

WHAT YOU SEE

A tape pull takes a multi-colour print off in layers rather than off the substrate, or removes the whole print under a varnish that passed on its own. Common where the print was left overnight between colours, and where a UV varnish goes over a fully cured solvent ink.

WHAT IT LOOKS LIKE

CAUSES, MOST LIKELY FIRST

The first film cured harder than the second could key toAdhesion between two films is part solvent bite and part chemistry. A fully cross-linked or fully evaporated first film gives the second nothing to soften and nothing to react with.
Too long between coloursThe window in which a solvent film still accepts an overprint closes over hours, and a two-pack film closes it for good once it has cross-linked.
Slip, wax or silicone additive at the surface of the first filmThe additive blooms to the top face, which is exactly the face the second film has to hold to.
Over-cure of a UV base before the next passA base taken well past full cure has little residual unsaturation left at the surface, so the next UV layer cures onto it rather than into it.
Wrong varnish for the ink class, or varnish over a film still holding solventA UV varnish shrinks as it cures. Over a soft or solvent-retaining film the shrinkage stress has nothing solid to pull against and it lifts the pair together.

Screen Printing InksThe second colour lifts the first, or the varnish lifts the print

Fault 20 of 20 · continued

The second colour lifts the first, or the varnish lifts the print

CHECK, IN THIS ORDER

Cross-cut and tape the first colour alone, then the two-colour area, then the varnished area on the same sheet. Only the interface that fails needs changing, and testing the finished stack alone will not tell you which one it is.
Record the time between passes, then repeat the test on a sheet overprinted immediately and one overprinted the next day.
Check the overprint window on both Technical Data Sheets, and confirm the ink and varnish come from a system the supplier has qualified together.
Check the cure of the base on its own: 30 MEK double rubs at the house condition, and the measured dose and peak irradiance where the base is UV.
Print the second colour over a wiped and an unwiped area of the first and compare.

THEN CHANGE

Overprint inside the window on the TDS, and print the full set on the same day where the system asks for it.
Where the set has to be split, use the grade the supplier qualifies for overprinting, or a primer or tie coat between the layers.
Cure the base to the minimum that holds rather than to the maximum the line can deliver. Over-cure is a real cause of intercoat failure on UV, not a safety margin.
Ask for the overprintable version of the grade so the slip and wax level suits a second pass.
Rack the sheets covered between passes and handle them in clean cotton gloves.

CONFIRM IT IS FIXED

Cross-cut and tape at each interface at 24 h on the customer's own material, with the classification recorded interface by interface rather than for the construction as a whole, plus the varnished area passing the resistance the finished article is specified on.

THE TRAP

Reading a pass on the top surface as a pass for the construction. Intercoat bond strength is a property of the build, not of any one ink, so it is qualified on the finished construction and re-qualified whenever a layer, a varnish or the interval between passes changes.

Screen Printing InksThe second colour lifts the first, or the varnish lifts the print (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
Screen blocks up, detail closing	Cycle time against the TDS open time; then air movement over the screen	Fans to minimum, flood on every stop, retarder in 2 to 3 % steps. Not thinner
Sawtooth or ragged edges	Stencil thickness over the mesh, then tension at five points	Extra face coats on the stencil; re-tension to the mesh maker's band
Moire or heavy dot gain in a tint	Mesh count against the ruling, mesh angle against the screen angle	Finer mesh or coarser ruling, and a lighter deposit. Re-plan, do not re-press
Orange peel on the solid	Off-contact at centre and corners; time to the lamp	Lower off-contact, slow the stroke, move the first lamp back
Pinholes with a raised rim	Two consecutive sheets: repeating or random defect positions	Clean the substrate and find the silicone source in the room
Streaks with the stroke	Squeegee edge under a loupe at the streak position	Dress or change the blade; check it suits the solvent
Ink tapes off	MEK rubs first to split cure from adhesion, then dyne level on the parts	Under-cure to the oven or the lamp; wetting to the treater or the series
Opacity falling through the run	Mesh tension and squeegee pressure against the start settings	Pressure back to the locked setting; coarser mesh for opacity

Screen Printing InksQuick reference

Quick reference

One page at the press

Symptom	Check this first	Change this first
UV surface tacky, body hard	Peak irradiance and dose at the substrate with a radiometer	Raise irradiance first: lamp distance, reflector, lamp age. Speed last, and only for through-cure
Blocking or set-off in the stack	Oven dwell at part temperature with a trailing thermocouple; retarder percentage	Extend dwell, cut retarder, rack instead of stacking
Register opens towards the edges	Tension on all frames in the set, then off-contact	Match frames within 2 N/cm; drop off-contact to clean snap
Stencil breaking down mid-run	Exposure calculator step; emulsion type against the ink solvent	Full exposure plus post-exposure; solvent-resistant emulsion
Two-pack going short in the tray	Time of catalysis on the tin against the pot life on that TDS	Discard and mix fresh in shift-sized batches. Do not thin it
Ink crawls into islands on plastics	Dyne pens on the actual parts, edges included	Treat immediately before print; check for mould release
Print cracks when flexed	Film thickness and catalyst ratio by weight	Thinner film, and the flexible series for that substrate
Plastic crazes under the print days later	Annealed part against as-moulded from the same batch; swab test with ink, thinner and wash	Take the aggressive solvent out, cut the film weight, keep the part unstressed 72 h

Screen Printing InksQuick reference

Quick reference

One page at the press

Symptom	Check this first	Change this first
Colour lifts colour, or varnish lifts the print	Tape each interface separately on one sheet; time between passes	Overprint inside the TDS window, or a tie coat between the layers
Shade drifts shift to shift	Tin stirred to the bottom and a drawdown against the retained standard	Put the deposit back to specification before touching the colour
Dust and spatter halo on plastics	Field meter at feeder, print station and delivery; RH at the press	Earth the press, fit bars over the bed, RH to 45 to 55 %
Glass passes day one, fails in a week	Cross-cut after humidity or wash exposure, not at the press	Silane bonding system, clean dry glass, full cure schedule
Print flakes off a candle	Grade in use and the casting temperature at print	UniScreen-02WAX on cool stabilised wax, lighter film, agreed print area

Screen 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	Grid cut through to the substrate, tape pulled, classified 0 to 5. Blade spacing is set by film thickness: 1 mm spacing with six cuts each way for films up to 60 micron on a hard substrate, 2 mm for 61 to 120 micron, 3 mm for 121 to 250 micron, and 2 mm at the thin end only where the substrate is soft. A screen film of 8 to 30 micron therefore takes the 1 mm cutter; a wider cutter cuts fewer edges, lifts fewer squares and reports a better class than the print has earned. Expect class 0 or 1 read at 24 h after conditioning at 23 C and 50 % RH. The test is valid on rigid, smooth material only: on rubber, latex, foam, leather and wax the blade sinks into the substrate and the tape lifts substrate rather than ink, so use a scribe and tape with an agreed rub count there. Adhesion is an interface property, so the result counts only on the customer's own material.
Solvent rub resistance	ASTM D5402, as a practice	MEK double rubs following the general practice of ASTM D5402. The standard describes a cheesecloth-wrapped finger or a weighted hammer with the operator applying pressure; it does not specify a load, so the load, the cloth, the stroke length and the number of rubs are written down and held constant. A hammer weighted to 1 kg is the house condition, not a figure from the standard. Carry the test out under local exhaust or in a fume cupboard, in nitrile gloves and eye protection, away from ignition sources: MEK has a flash point near minus 6 C. At least 30 double rubs with no breakthrough to the substrate is the working acceptance for UV screen grades and fully cured two-pack systems. It reads cure, not adhesion: rub first, then tape.
Wetting tension	ASTM D2578, or ISO 8296 test inks	Test inks or dyne pens on the material as it is at the press. For screen inks on plastics expect to need 38 to 42 mN/m, with 40 mN/m or above as the house target after treatment and the grade's TDS giving the figure. Untreated PE and PP sit at roughly 18 to 31 mN/m and will not reach it without treatment or a grade built for untreated polyolefin. Measure the reel or the parts you are about to run, because treatment decays in store.
Viscosity	ISO 3219 rotational, or ISO 2431 flow cup where the TDS quotes a cup	The working figure for a screen ink is the one on its TDS at 25 C. Screen inks are thixotropic, so a rotational measurement at a defined shear rate is the reliable method and a flow cup reading is an approximation of a single point. Hold within about 10 % of the TDS figure through the shift. On a catalysed two-pack, hold the working figure by the TDS method and record the unadjusted climb separately: the two are different numbers and only the first one is what the press needs.
Mesh tension	No standard number applies; read in N/cm on a calibrated mesh tension meter	Five positions per frame, centre and four quadrants. Work in the band the mesh manufacturer gives for that thread count and diameter, broadly 20 to 28 N/cm up to about 90 threads per centimetre, 18 to 24 N/cm from 100 to 140 and lower again above that, with no more than about 2 N/cm spread across a frame and frames in a colour set matched to the same band. A single tension figure applied to every mesh over-tensions the fine counts and under-tensions the coarse ones. This is still the most useful number in a screen room.
UV dose and peak irradiance	No standard number applies; band-calibrated radiometer at the substrate	Pass the puck through the machine at running speed and record dose in mJ/cm2 and peak irradiance in W/cm2. Irradiance decides surface cure against oxygen inhibition; dose decides cure at depth. A screen film needs more than an offset or flexo film of the same chemistry because it is many times thicker. Each grade's minimum is on its Technical Data Sheet, and the source matters: a medium-pressure mercury arc is rated at about 1 000 to 2 000 h, an LED array typically at 20 000 h or more with output drift rather than devitrification as the failure mode.
Squeegee hardness	ASTM D2240, Shore A	Read along the length of the blade, not at one point, on the flat at least 12 mm back from the printing edge with at least 6 mm of rubber under the foot. A reading taken close to the printing edge is not a valid D2240 reading and comes out several points low for geometric reasons alone, which is easily mistaken for solvent attack. 70 to 75 Shore A is the usual starting point for graphics on a flat bed, 60 to 65 for a heavy deposit and 80 for fine detail. A drop of several points through a shift, read in the same place and compared with a new blade, means the solvent is attacking the blade.

Screen Printing InksTest methods

Test methods

The measurements this guide relies on

Measurement	Method	What it tells you, and the usual acceptance
Film thickness	No single standard applies; the substrate decides the method	An eddy-current or magnetic coating thickness gauge reads on metal only and reads nothing at all on plastics, glass, wood, leather, foam or wax. On glass and rigid plastics use a micrometer or dial gauge reading printed against unprinted at the same point, or a cross-section under a microscope; on absorbent stock use a wet-film comb converted by the solids figure on the TDS. Typical cured screen deposits are 8 to 30 micron for graphics. Record the method with the number, and set the run-to-run tolerance from the repeatability of that method rather than from a flat percentage.
Specular gloss	ISO 2813, 60 degrees	Used to quantify orange peel, mesh marking and post-cure haze against an approved sample. Inside 5 gloss units of the standard is a workable acceptance for a gloss screen solid; the tolerance for a job is the one agreed with the customer.
Colour and density measurement	ISO 13655 for spectral measurement; ISO 5-3 and ISO 5-4 for reflection density	Measure colour with a spectrophotometer to ISO 13655 with M1 illumination, D50 and the 2 degree observer, and report dE00 against the approved standard. State which dE formula a tolerance refers to, because dE*ab and dE00 differ by roughly a factor of two on saturated screen solids. Where density is used instead, state the density status, which is the spectral condition of ISO 5-3, and the geometry of ISO 5-4, and read the whole run on one instrument. A density tolerance quoted without those conditions is not a number anyone can repeat.
Light fastness	Filtered xenon arc exposure, scored against the blue wool references of ISO 105-B01 and ISO 105-B02	Xenon exposure assessed against the blue wool scale. Indoor graphics are usually specified at 5 to 6 and exterior or long-life work at 7 to 8, which restricts the pigment choice and therefore the gamut. The figure for a given shade is on its Technical Data Sheet, and a mixed shade is only as fast as its weakest component. Agree the exposure conditions, the irradiance, the black standard temperature and the end point in the specification rather than relying on a standard number alone, because the graphic technology method for prints and printing inks, ISO 12040, has been withdrawn from the ISO catalogue.
Resistance beyond adhesion	No single standard applies; the article's specification decides	A print that passes the cross-cut can still fail in service. Scratch and scuff, hand cream, sanitiser, fuel, cleaning agent and sterilisation resistance are what cosmetics, medical, automotive and industrial parts are actually specified on, and they are tested to an agreed reagent, contact time, load and stroke count on the customer's own part, after the full cure schedule and after the ageing the article will see. Record the conditions with the result; a resistance claim without the reagent and the contact time means nothing.

Screen Printing InksTest methods

When the press-floor fixes have not worked

What to send us

The job ticket: grade and batch number as printed on the tin, catalyst ratio and time of catalysis, and every addition made at the press with its percentage and the time it was made.
Screen data: mesh count and thread diameter, mesh angle to the artwork and to the screen angle, measured tension in N/cm at five positions on each frame, stencil system, measured stencil thickness and the exposure calculator step used.
Press settings: off-contact at centre and corners, squeegee material, durometer and angle, pressure setting, stroke speed, flood setting and full cycle time.
Cure data: for UV, the radiometer record at running speed with dose and peak irradiance, source type and hours; for oven grades, the trailing thermocouple profile showing the dwell at part temperature, not the panel setting.
Samples: at least ten faulty prints and ten good ones where you have them, racked or interleaved rather than stacked, each marked with its sheet number and the time it was printed.
Substrate: 2 m2 of sheet or twenty parts from the same batch, unprinted, in the packaging it arrives in, with supplier, grade, batch, the treatment level measured at the press and the date it was treated.
The end-use requirement: the flex, scratch, chemical, wash or burn conditions the finished article is specified on, and the customer's own acceptance test, since adhesion, resistance and burn behaviour are properties of the finished article and not of the ink.
Conditions and photographs: press room temperature and RH at the time of the fault, plus photographs of the defect at raking light and through a loupe with a scale in frame.

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Screen Printing InksTechnical service