Category Archives: Flexographic

Weak Print Color

Ink viscosity is too low

Increase ink viscosity

Anilox volume is too low

Increase anilox to proper volume

Sticky-back tape is too soft

Use harder tape for line work to achieve good ink transfer

Ink is over-extended

Check formula and add fresh ink

Ink formulation is too weak

Check raw ink formula for proper strength; check to see if ink is re-work and has proper strength

Substrate is not receptive to ink

Check substrate surface; check for proper film treatment

Ink is drying on plates or anilox

Eliminate any excess air blowing on plates and anilox; add slower drying solvents.

Ink is kicking-out or settling

Make sure ink is properly mixed, with no settling on bottom or signs of ink separation

Ink is aged I used – worn out

Refresh ink

Poor Trapping

First down color is not fully dry

Increase drying speed of first down ink by:

  1. Reducing ink viscosity
  2. Reducing ink film thickness by using shallower anilox volume
  3. Adding faster drying solvents
  4. Increasing dryer temperature and air velocity in dryer

Second down ink is drying too fast and not printing

Check and eliminate air blowing on plates; add slower drying solvents

Wax or slip aid in first down ink is excessive

Check formula and remake ink if necessary

Second down ink is not compatible with first down ink

Consult your Sun Chemical representative for proper ink type

Ink Smearing / Bleeding

First down ink is not fully dry

Increase drying speed of ink by:

  1. Reducing ink viscosity
  2. Reducing ink thickness by changing metering conditions
  3. Adding faster drying solvent
  4. Adjusting air balance and heat

Second down ink, top lacquer or adhesive is too rich causing first down ink to dissolve

Check second down material and reformulate for non-aggressive properties. Consult your Sun Chemical representative for a more resistant first down ink

Foreign object is dragging on wet print

Trace web and remove dragging object

Not wiping well, doctor blade issues

Reset doctor blades to correct contact angles. Replace blades. Check chamber balance – side to side – in and out

Pinholes

Substrate is poor or marginally treated

Check and adjust treatment level or change stocks

Surface of substrate has holes

Check substrate and reduce ink viscosity for better wetting. Consult your substrate supplier

Surface tension of ink is not low enough to properly flow out on substrate. (Seen mostly in aqueous inks.)

Reduce surface tension of inks by adding wetting agents

Impression between plate and substrate is too low

Increase plate impression and check print appearance

Sticky-back tape is too soft

Use hard tape for solid print areas when possible

Ink is drying too fast

Add slower drying solvents

Dried ink, dirt or rust is on impression cylinder

Check and clean cylinder/drum

Use of defoamer in water inks is excessive

Add fresh ink or check formula and reformulate ink

Anilox worn

Replace or mechanically clean

Mottled Print

Substrate is poor or marginally treated

Check and adjust treatment level or change stocks

Surface of substrate has holes

Check substrate and reduce ink viscosity for better wetting. Consult your substrate supplier

Surface tension of ink is not low enough to properly flow out on substrate (Seen mostly in aqueous inks.)

Reduce surface tension of inks by adding wetting agents

Impression between plate and substrate is too low

Increase plate impression and check print appearance

Sticky-back tape is too soft

Use hard tape for solid print areas when possible

Ink viscosity is too low

Increase ink viscosity

Ink out of balance / contaminated

Increase resin solids / refresh ink. Strain ink or remake

Dirty Print – Halos

Pressure between plate and substrate is excessive

Reset plate pressure to “kiss” impression

Plate or sticky-back tape is too hard

Use plate with softer durometer; switch to a cushion sticky-back tape

Edges are cupped on plate

Check plate and replace if necessary

Plate cylinder is out of round causing intermittent halos

Check run-out of plate cylinder and anilox roll; replace plate and/or anilox roll

Fill – In

Print impression is excessive

Reset plate pressure to “kiss” impression

Water-based ink pH is too low

Increase water-based ink pH

Ink is drying too fast

Add slower drying solvents to reduce tack. Tacky inks will usually show stringing from type edges

Plates are worn, uneven, cupped or poorly made

Check plates and replace if necessary

Ink viscosity is too high

Reduce ink viscosity

Plate relief height is incorrect

Adjust plate relief to correct height range

Foreign matter appears in ink

Filter or replace ink; eliminate source of contamination

Ink out of balance – pigment to resin, resin to solvent

Add resin I refresh ink, make sure the correct solvent is being used. Make sure ink is well mixed

Dirty Print – Feathering

Impression between plate and substrate is excessive

Reset plate pressure to “kiss” impression

Water-based ink pH is too low

Reduce anilox volume

Ink is drying too fast

Check ink formulation; add slower drying solvents

Air hitting plates or anilox roll is excessive

Block stray air; balance dryers to eliminate “blown-down” on plates

Ink viscosity is too high

Reduce ink viscosity

Dust or lint is picked up from substrate

Check to be sure ink filters are working; filter ink;

Ink formula out-of-balance, affects film splitting I transfer

Check solvent blends for Alcohol I Ester balance. For clean printing, the resin structures must have the correct solvents

Ink viscosities uncontrolled. Wrong viscosity cups (out-of-range) for viscosities run. Cups need cleaning and calibrating

Record and control press-side viscosities. Check cups for accuracy and selection

Dirty Print – Dot Bridging

Anilox volume is too deep for dot size and an excessive amount of ink is metering to the plate

Reduce anilox volume or increase plate dot size

Ink is flooding plate dots due to loose ink metering or worn doctor blades

Check and adjust ink metering; check and replace doctor blade if indicated

Stray air is blowing on plate or anilox

Block stray air; balance dryers to eliminate

Plate impression or plate relief is excessive

Reset plate impression. Eliminate high spots if bridging is localized

Ink is drying too fast

Add slower drying solvents

Ink formula out-of-balance, affects film splitting / transfer

Check solvent blends for Alcohol / Ester balance. For clean printing, the resin structures must have the correct solvents

Ink too tacky

Incorporate harder resin

Blocking / Offset

Ink is not drying properly

Add faster drying solvents and/or increase air delivery

Solvents are trapped

Add faster drying solvents and/or increase air and heat delivery. Also check for ink skinning

Web rewound is too warm

Reduce chill roll temperature

Rewind pressure on web is excessive

Reduce web tension

Ink or varnish are over-plasticized

Remake ink or varnish. Add anti-block agent

Ink or top lacquer is soft or has a low melting point

Remake ink or lacquer

Web temperature is too low

Increase web temperature

Moisture condensation appears on chill roll

Check and reset chill roll temperature above dew point

Ink has lost solubility creating a surface tack. Tacky inks are prone to blocking / offsetting

Add active (true) solvents for resin to remove surface tack

Blocking / Offsetting

Add a wax compound or silicone (if applicable) to formula structure. Wax / Silicones will act as a release in the re-wind