Grauel Problem solver

Problem solving auxiliaries for possible printing problems at dry-offset (Letterset) - machines

Area where problems may occur

Causes scope

ink

ink dosing

curing

ink intensity variations

adhesion

ink curing

ductor blade

ink adhesion

ductor

dirty ink, haze

tipping roller

23 Verreiberwalze

ink transfer roller

gear mrks, stripes, ghosting

inking roller

wavy edges, double print

25 Gummizwischenwalze

rubber inter roller (optional according to printing unit type)

porous, faint image

cliché

ink and lacquer flow out

rubber blanket (transfer roller)

drive

product

possible reason for problem

Problem- bereich

Problem description

We recommend/assume

Insufficient or uneven ink transfer in the roller train. Faint image.

Machine too cold, let it warm-up to production temperature; wrong set pressure of the rollers; dirty ink; products dirty.

Faint image.

Ink too cold, let machine warm-up; wrong set pressure of the rollers; dirty ink; products dirty; bad pre-treatment; dirty rollers or clichés.

Ink shade and ink quantity change.

After approx. 1 hour of production check for swollen (heat deformation) or shrunk (solvents, wash-up liquid) rubber rollers; ink temperature fluctutation.

Ink misting.

Ink is too warm, coour shade is fading out.

Ink misting.

Too much ink, adjust ink flow, redress rubber rollers.

Ink misting.

Discuss ink composition with ink producer.

Ink contamination due to heavy return flow of ink back into the ink fountain.

Reduce the ink flow; too much ink is fed to the roller train.

Ink contamination due to heavy return flow of foreign ink back into the ink fountain .

Adjust the ink tack after changing the normal ink sequence (light to dark).

Positive impression too large for negative cut-out.

Have the clichés redone, avoid overlapping ink layers ( better: separate inks).

Return flow of ink into the fountain due to heavy ink flow; frequent back and forth flow of ink overstresses the ink and prevents curing.

Reduce the ink flow, too much ink is fed - ink which has been left in the ink fountain for too long must be removed. In case the tipping roller cycle is adjustable, it is better to transfer less ink more frequently than visa-versa.

Fainting image.

The machine temperature is up, the ink viscosity in the ink fountain is lowered. The hydraulic pressure above the ductor blade is reduced and less ink is drawn through the ductor gap. Increase tipping time at ductorroller and/or increase ink profile.

Ink does not "dry" in the overlap area (especially dark ink shades).

Overlap area to be screened in order to avoid 200 % ink lay-down. If 2 clichés are used for 1 full-tone colour, one of the clichés should be recessed in the overlap area to avoid heavy ink lay-down.

The ink "pearls", uneven full-shades.

Increase pre-treatment as surface tension is still to low. Increase pressure between printing blanket and product. Smoothen the ink with additives (Attention: ink shade may change).

Fainted image, printed wet ink is getting darker when whiped with bare finger.

Increase pressure between printing blanket and product. Use 2 clichés for full tone background colours.

Uneven ink transfer due to high temperature in the roller train.

Check and reduce the nip pressures between the rubber rollers. 0,1 mm more rubber roller adjustment increases the ink layer temperature by more than 10°C.

pearls shaped (droplets) ink dots do not flow.

Check surface condition of rubber rollers for pores; increase the surface tension for better wetting and improved adhesion; add a slip additive to the printing inks to lower the surface tension of the ink; reduce viscosity and tack - better ink flow.

Insufficient flow-out of the over-varnish - "piston rings" - rough or dull surface finish, no gloss .

Change relative speed (+/-) between the applicator roller and the product surface; the product should run at the same or slightly higher speed than the applicator roller; this avoids a lift-off bulge. Heated lacquers have better flow-out; to obtain better flow-out and gloss with onmandrel curing apply thinner layers.

Uneven ink flow - ink stays in the ink fountain.

Ink and ink unit too cold, normal is 25 - 30 ºC - increase the oscillation strokes - use ink stirrer for ink fountain, use ink agitators or add print varnish for better ink flow.

Overheated zones in the ink train; too much heat increases the reactivity of the ink and stray UV-light may prematurely polymerise the ink. Dull ink lay-down and no adhesion to the underground.

Too much heat due to friction between ductor blade and fountain sidewalls and the fountain roller or too much pressure between rubber rollers, especially at the oscillating rollers. Adjust accordingly, if applicable use ductor and oscillation rollers which may be cooled down.

"Pearly" ink lay down on product surface.

Ink temperature too high or too low, adjust to approx. 28 º C. Product surface temperature is too low (condensation). Antistatic additives have migrated to the surface, to be burnt-off. Apply more pressure between the rubber blanket and the product.

Thick UV-layer cannot be cured.

Keep the ink layer below 2 my to allow the UV radiation to penetrate and cure the ink layer. Important for overlapping areas and full-tone areas.

To thin UV-layer cannot be cured.

Air oxygen can suppress a polymerisation of the ink when ink layer is too thin (0,5 my and less). Especially have a look at this when fine screen or line printing.

UV ink cannot be cured.

Insufficient UV-power- UV lamp - beyond life expectancy - reduce distance between lamp and product surface (Attention: more heat !) - to be controlled regularly with UV test stripes.

UV ink cannot be cured.

Use additives when have been recommended by the ink supplier.

UV ink cannot be cured.

Non suitable detergent liquid stays in the pores of the rubber rollers and contaminates the UV ink. Thoroughly clean the rollers and soak the rollers with UV-"accelerator". Low ink consumption may cause back and forth transfer and overstressing of the ink.

Too much ink - UV ink cannot be cured because an attempt is made to darken a light colour shade by applying more ink.

Adjust the ink shade and not the ink quantity.

Porous image, after TESA-test white missing dots due to excessive surface treatment of PS. Excessive surface treatment of PS may destroy the surface.

Reduce surface treatment.

Insufficient ink adhesion.

Antistatic additives on the product surface must be burnt off - antistatic additives may be hygroskopical and may react with humidity. Use slip agents for inks to lower the surface tension of the ink.

Insufficient ink adhesion.

Increase surface tension up to 44 dyn/cm. Correctly adjust electrodes - adjust flame correctly.

Corona pre-treatment too low in general.

Re-adjust the electrodes, increase the power level, generator activator time is to short. Product walls to thick (for direct high frequency corona), should not exceed 0,5 mm - contact manufacturer; antistatic additives on the product surface; generator or electrodes are defective; Sparks forwarding to metallic product holders reduces the power discharge onto the substrate surface.

Flame pre-treatment too low in general.

Incorrect air - gas ratio and/or bad adjustment of burner, changed to other type of gas; product to beadusted just outside the inner, blue flame; adjust for oxidizing flame with excess oxygen.

"Piston rings" on the ductor roller due to a damaged ductor blade.

Change ductor blade; stroke of oscillating rollers correct? Increase rubber roller pressure.

Ductor blade profile is too wide, too much ink can be forwarded through the gap.

Adjust ink profile and ink quantity to the needs; be careful: never run ductor roller with totally removed ink layer; this will give temperature increase.

Ink flow cut-off in the ink fountain.

The ink level should not drop below 10 - 15 mm; if necessary use ink additives; use automatic ink dosing .

Too much ink when machine is accellerated to productin speed, especially on older machines.

The speed of the ductor roller increases with the higher machine speeds and so does the hydraulic pressurein the ink fountain; more ink is fed into the roller train. Adjust the ink flow at production speed.

Faint image; the ink profile on the ductor roller is to shallow - not enough ink.

Adjust the ink profile better to the print image and increase the tipping time at the ductor; at a fixed tipping roller frequency the tipping time determines the ink quantity forwarded to the ink fountain.

Wear or dry running tipping and rubber roller surfaces.

The lack of a lubricating ink layer between rubber and steel rollers may damage the rubber surface. The ink should never be completely ductored of the ductor roller !

Insufficient ink transfer due to worn rubber rollers.

Tipping- and inking rollers are subjecto to normal wear. If the rubber cover thickness is too thin, mechanical restrictions may lead to a reduced ink transfer - re-adjust rollers.

Circadian ink intensity variations especially with full panel printing and saturated colours.

Increase the tipping cycle (if possible) and decrease ink quantity; or increase the tipping time at the ductor roller but reduce the ink profile with the ductor blade.

Insufficient or uneven ink transfer from the inking roller to the cliché.

Increase the pressure between inking roller and cliché. Attention: this may cause dot increase ! Are the inking rollers misshaped? Ink roller or cliché dirty? Ink ok?

Ink misting: too much ink at sides of rubber rollers which are wider than the printed image. Excessive ink is thrown of.

If possible cut rubber rollers according to print height..

Faint image, insufficient ink transfer to the cliché, not enough pressure between inking roller and cliché.

Increase pressure of the inking rollers; according to "hardness" of the ink adjust the width of the ink stripe on the supporting side areas of the cliché; for full colour print: 1 - 2 mm width, for full panels up to 4 mm width between the rollers.

Gear marks; too much pressure between cliché and transfer roller, gears bottom out.

Check the cliché thickness, too thin? check adjustment betwenn cliché and transfer roller (axle distance too little). Use "Schmitzring" adjustment where available. regularly control of printing unit by means of adjustment discs. Change worn printing blanket or transfer rollers.

Dot increase due to high pressure of the inking roller or to high pressure between cliché and transfer roller; the flanges of the dots are inked.

Reduce pressure of inking rollers - check if inking roller is barrel shaped; cliché thickness uneven or worn? Printing blanket or transfer roller not circular?

Ghosting

Can occur if the printing diameter is larger than the diameter of th inking roller. Use a non driven inking roller with a "wild" diameter - increase the pressure between the inking and the oscillating rollers a bit.

Ghosting

Concave or wide rubber and inking rollers lead to insufficient ink transfer in teh middle part of the rollers (ink build -up on the sides). "Holes" in the ink layer are not being refilled. Regrind and/or cut rubber rollers to suit the print height. Do not put the print image nearby the sides of the ink tranfer roller, as it could be build-up more ink in the side area through too sharp rising side oscillation.

White dots in the printed image - rupture ink lay-down.

Check the surface quality of the rubber rollers. The surface quality should be (DIN) N4 or better.

Gear marks - too large axle distance betwenn cliché and transfer roller, tooth play is shown within the print image.

Check cliché and printing blanket, possibly too thick - therefore adjusted too big axle distance. Pressure between substrate and transfer roller too high, brake adjusted too little.

Faint print in the middle of the image due to insufficient ink transfer.

Ink build-up on the sides of the rubber rollers forces the rollers apart in the middle of the steel rollers. Less ink is transferred in the middle. Wash the rubber rollers more often - better: cut rubber rollers to size.

Varying ink intensity.

Increase pressure between rubber inter rollers and oscillating rollers to intensify the lateral ink shifting.

Dirty ink between the single colours by multi-colour print.

Uneven ink flow - swollen or shrunk rubber rollers - excessive pressure on rubber rollers .

Too much heat due to excessive rubber deformation; check pressure and parallel adjustment of rubber rollers; regrind rubber rollers if necessary; check ifdetergent liquid reacts with rubber compound.

Full-colour print: dot increase, dots run into each other.

Check cliché and printing blanket thickness.

Squeezed-out or frayed contours.

Too much pressure between inking roller and cliché and/or cliché and rubber blanket.

Warped cliché, wrong cliché layout, incorrect hole punching - when using screen print clichés often the whole set has to be changed. bei gerastertem Klischee muß oft der ganze Satz ausgetauscht werden. Brakes too slack, tooth too slack or damaged.

Double image.

The according cliché is bad or loosely mounted (makes noise); brake too slack, tooth too much play or slack onto the shaft. cliché or transfer roller too much play.

"Cloudy" print.

Can already be caused by a dirty colour separation when producing the film.

Dirty colours by multi-colour print.

Wrong adjusted clichés; too high ink flow - by re-separation of excessive inks, the ink in the ink fountain will become dirty.

Gear marks or double print.

Check the teeth on bull gear (transfer roller), on cliché cylinder and if available on inking rollers. Damaged teeth may be shown in print image, worn teeth result in increased gear play; gear play to little (too high pressure because of exceeded roller tolerances).

Full-colour print: process dots run into each other.

Too much pressure applied between rubber blanket and product to overcome wall thickness differences. Improve product surface or use a coarser screen.

Bad ink transfer to product.

Not enough pressure between rubber blanket and product. Increase the pressure with increasing printing speed.

Varying image transfer to the product.

Do you find a repetitive occurrence? I.e. by transfer or cliché rollers: does the fault occur every 2nd blanket or every 4th product holder? Check for true and correct running. Check thread direction of blankets!

Double image

Main drive variations, check electronic motor control. Main drive vibrations. Check gear and chain.

Full-colour print: process dots run into each other.

Dot increase due to too much pressure between: inking roller and cliché (smeared up screen) - cliché and rubber blanket (squeezed out dots) - rubber blanket and product - printing blanket is deformed too much

Gear marks around the product - insufficient gear lubrication

Lucricate the system according to the manual - change damaged teeth or worn gear parts.

Doubleimage (the whole image)

The product fits to loosely on the product holder and becomes deformed.

Ink adhesion problems

Change of material composition (especially for plastics) in the production or by changing suppliers.

Uneven print.

Variations in the product. Adjust production process.

Uneven print - patchy print - smudges.

Configure in such a way that infeed cannot give any pollution. Eventually wash products before printing. Products have to be free of dust, oil and grease.

Insufficient ink adhesion.

Do not use any silicone spray in the printing machine or in the pre-installed machine.