Here is a simple guide to solve commonly experienced problems in printing. If you don't find your answers here please email us at info@convertechblades.com
How Recognised:
Cylinder Wear. Doctor blade wear.
CAUSE
REMEDY
1.Poor dispersion
1.Mix the ink. Consult ink maker.
2.Specific pigment
2.Better pigment selection. Consult ink maker.
3.Foreign matter
3.Filter ink
4.Soft chrome &/or copper
4.Remake cylinder
5.Excessive blade pressure
5.Reduce blade pressure
6.Corrosive ink
6.Consult ink maker
How recognised:
Ink or varnish does not bind to each other or to the substrate.
CAUSE
REMEDY
1.Improper thinner used
1.Consult ink maker for proper thinner
2.Ink film not cured
2.Increase oven temperature
3.Improper ink used
3.Consult ink maker
How recognised:
Ink adheres to back of web in rewind.
CAUSE
REMEDY
1.Oven temperature too low
1.Check oven temperature
2.Thinner too slow for press speed
2.Use faster thinner
3.Trapped solvent
3.Use proper solvent balance. Check for surface drying
4.Web too hot when rewound
4.Reduce web temperature, use chill rolls
5.Excessive rewind pressure
5.Adjust web tension
6.Ink too soft
6.Consult ink maker
How recognised:
Printed ink has milky white looks
CAUSE
REMEDY
1.Improperly balanced thinner
1.Use balanced thinner
2.Humidity too high
2.Add slow prime solvent to thinner
3.Ink contaminated with water etc.
3.Discard ink - consult ink maker
How recognised:
Spider web-like build up on blade, impression roll cylinder & in oven
CAUSE
REMEDY
1.Ink starvation
1.Check pipes for ink blockage
2.Oven imbalance
2.Adjust air flow for a slight negative pressure
3.Oven air velocity too high
3.Reduce air flow in oven
4.Ink drying too fast
4.Slow reducer
5.Ink viscosity too high
5.Reduce viscosity
How recognised:
Weak print. Colour intensity varies light to dark
CAUSE
REMEDY
1.Ink drying too fast
1.Scrub cylinder. Retard ink with slower reducer
2.Ink viscosity too high
2.Reduce viscosity
3.Ink not flowing out
3.Add clear extender
4.Air blowing on cylinder
4.Balance oven to achieve negative pressure
5.Poor wipe
5.Adjust doctor blade
6.Too much impression pressure
6.Adjust impression pressure
7.Ink contaminated
7.Replace with fresh ink
How recognised:
Air bubbles on surface of ink
CAUSE
REMEDY
1.Air entrapped in ink
1.Increase level of ink sump to prevent starvation
2.Slow pump and application flow
3.Use recommended defoamer
How recognised:
Very light and uneven transfer of ink in non-image area
CAUSE
REMEDY
1.Blade pressure too light-blade angle too flat
1.Increase blade pressure & increase blade angle
2.Poor edge on doctor blade
2.Replace blade
3.Ink dried on bottom of blade
3.Clean blade thoroughly or replace
4.Ink in non-image area not drying between blade and impression
4.Move blade away from nip. Put air on cylinder
5.Rough cylinder
5.Hand polish or rechrome
How recognised:
Solid areas show random areas in which ink is not transferring - Dots missing in process printing
CAUSE
REMEDY
1.Rough substrate
1.Increase impression pressure
2.Partially plugged cylinder
2.Scrub cylinder with solvent & brass brush
3.Impression too light
3.Increase impression pressure
4.Ink starvation
4.Increase applicator flow
5.Damaged or pitted impression roll
5.Regrind or replace impression roll
6.Particles in ink
6.Filter ink through fine ink filter
7.Excessive foam
7.See remedies for foam
How recognised:
Solid areas have variation in colour - grainy pattern
CAUSE
REMEDY
1.Viscosity too low
1.Increase viscosity with fresh ink
2.Pigment selection
2.Better pigment combination for colour match
3.Ink solids too low-ink not flowing
3.Add pigmented extender
4.Cylinder too deep or cylinder worn out
4.No immediate solution-replace cylinder
5.Poor wipe
5.Adjust doctor blade
How recognised:
Printed image transferring to idle roll
CAUSE
REMEDY
1.Ink drying too slowly
1.Use faster thinner blend
2.Ink viscosity too high
2.Reduce viscosity
3.Oven temperature too low
3.Increase oven temperature and air velocity
4.Web temperature too high
4.Decrease oven temperature
5.Ink too soft
5.Consult ink maker for proper non-stick additives
6.Improper ink for substrate
6.Consult ink maker
How recognised:
Over printing ink not transferring over underlying inks pick back.
CAUSE
REMEDY
1.First down ink not drying
1.Increase oven temperature and air velocity
2.Over printing ink redisolving 1st down ink picking back
2.Consult ink maker for lean reducer blend. Sandwich dissimilar inks
3.No pick back but ink not transferring to 1st down ink or not flowing
3.Use slower reducer mix reduce oven temperature of 1st down ink
How recognised:
Small uncoloured holes in printed area
CAUSE
REMEDY
1.Rough or contaminated substrate
1.Increase impression pressure
2.Ink fails to flow out
2.Reduce viscosity - retard ink drying
3.Wrong ink for substrate
3.Consult ink maker for reformulation
4.Contaminated ink
4.Discard ink
How recognised:
Dried ink rubs off printed product
CAUSE
REMEDY
1.Ink improperly dried
1.Increase oven temperature, air velocity
2.Ink too soft
2.Use additives as recommended by ink maker
3.Insufficient wax or slip compound
3.Consult ink maker for wax additive
How recognised:
Definite pattern of cell walls. Ink not flowing out
CAUSE
REMEDY
1.Ink viscosity too high
1.Reduce viscosity with recommended reducer
2.Ink drying in cells
2.Set oven for negative pressure to prevent air from blowing on cylinder
3.Improper ink for substrate
3.Consult ink maker for proper ink
4.Ink contaminated by foreign matter
4.Thoroughly flush system and start with fresh ink
5.Cylinder worn or cell walls too wide
5.Remake cylinder
6.Ink starvation
6.Increase ink flow, raise inner pan
How recognised:
Small random spots of unprinted area showing through a deposited ink missing dots in process
CAUSE
REMEDY
1.Ink drying too fast
1.Retard with slow reducer
2.Ink viscosity too high
2.Reduce viscosity
3.Rough stock
3.Increase impression pressure
4.Cylinder plugged
4.Scrub cylinder thoroughly
5.Cylinder worn
5.Replace cylinder
How recognised:
Hair lines of ink starting from printed area occurring in random directions
CAUSE
REMEDY
1.Ink viscosity too low
1.Raise viscosity with fresh ink
2.Static in web
2.Use tinsel or static bar
3.Low moisture contact
3.Use steam generator to add moisture
How recognised:
Distinct solid lines that occur in non-image area. This condition may be continious or intermittent. Lines move as blade oscillates
CAUSE
REMEDY
1.Abrasion or mars in surface of cylinder
1.Repolish cylinder
2.Worn or nicked doctor blade
2.Replace doctor blade
3.Insoluble particles
3.Filter or replace with fresh ink
How recognised:
Relatively wide streaks that show up in non- image area. Usually in non - systematic pattern
CAUSE
REMEDY
1.Soft particles behind doctor blade caused by contamination of ink
1.Clean blade well filter or replace ink. Thoroughly flush system
2.Excessive ink
2.See remedy for foam
3.Damaged doctor blade
3.Replace doctor blade
4.Worn cell walls on trailing edge design
4.Replace cylinder
How recognised:
Wavy print pattern in direction of web travel
CAUSE
REMEDY
1.Ink viscosity too low
1.Raise viscosity
2.Vehicle solid too low
2.Add high solids extender
3.Ink contaminated
3.Replace ink
4.Too much impression
4.Reduce impression pressure
5.Worn cylinder, incorrect engraving
5.Replace cylinder
6.Ink not wetting substrate
6.Consult ink maker
CAUSE
REMEDY
1.Foreign Particle under blade
- Reduce blade pressure under blade
- Install ink filters in ink system
- Install magnets in ink system
- Change the doctor blade
2.Cut in doctor blade
- Install ink filters
- Change doctor the blade
- Check roughness of anilox roller
- Check new blade tip for damage
3.Abrasive ink and/or solvents
- Use STAINLESS STEEL doctor blade
- Use different pigments
CAUSE
REMEDY
1.Blades is wavy
- Clean the doctor blade holder and remount blades
- Check blade holder for damage
- Tighten bolts from center out alternating sides
- Replace missing bolts if any
- Provide even tensioning of bolts on holder by using a torque wrench
- Make sure blade is not too long for holder
- Check end seal placement
2.Alignment
- Ensure centerline of chamber is parallel to center line of anilox roller
- Make sure both the blades in the chamber contact the anilox roller at the same time
- Ensure uniform extension from holder
3.Vibration
- Blade chatter- blade angle too steep
- Gear vibration from press
- Bounce from printing plate, fix the plate uniformly
CAUSE
REMEDY
1.Extra pressure on doctor blade
- Look for the reasons why excessive pressure is needed and correct
- Install mechanical units to ensure the chamber does not contact anilox roller
- Metal filings (slivers) from the blade tip. (Excessive pressure causes wiping by back of blade rather than the tip. The blade tip becomes thin and wears through, releasing slivers in inking system. This can damage the anilox.)
2.. Contact area too large
- Use correct width doctor blade (check with holder manufacturer for correct size)
- Use reduced thickness blade tip
- Check blade angles
3.Poor steel quality
- Try alternative blade materials (check with CONVERTECH to correctly match blade to application)
CAUSE
REMEDY
1.Contact area too large for cell count
- Use pre-ground lamella blade to reduce contact area
- Incorrect blade angle
- Use thinner blades
2.Cell volume or cell count of anilox not matched to line screen count of plate
- Guideline: Cell count should be 4-5 times that of plate
CAUSE
REMEDY
1.Incorrect chamber alignment
- Ensure chamber is parallel to anilox roller and both top and bottom blades are contacting anilox roller at the same time
2.Incorrect end seals or incorrect setting
- Check with holder manufacturer for correct material and dimensions
- Check blade settings (ensure blade extension is correct to match cut on end seal)
3.Blade is wavy
- Improper seating of blade in holder allows ink to escape holder
- Poor condition of holder
- Missing or worn bolts in holder assembly
4.Re-doctoring of ink from containment blade
- Reduce excessive blade pressure
- Correct ink viscosity
- Incorrect containment blade for press holder or anilox