Abstract

Streaks in offset printing are color density fluctuations or contrast variations, usually perpendicular to the print direction. These are visually disturbing, especially when printing even surfaces. In offset printing, a slight streaking cannot be eliminated 100% due to the nature of the system. The causes of streaks can be very versatile. All process parameters, from substrates to inks, machine settings and condition, can be considered as causes. Often several components in combination lead to streaking. The elimination of the malfunction requires a structured procedure in the exclusion process.

Below you will find a list of the most common causes and remedies. This list is not complete because the possible number of causes for streaking in printing is so extensive.

Possible causes

 

Cause 1 – Underpacking:

The blanket packing must be set exactly to the manufacturer’s specifications. In addition, for some press types the actual total packing height must be measured manually and entered in the press console for each printing unit. This is the only way to correctly control the printing pressure.

Remedy:

  1. Check the blanket packing and renew if necessary
  2. Measuring the packing height

 

Cause 2 – Blanket

Blankets may be responsible for streaks in the printout. This is typically indicated by uneven stripes with smooth edges across the sheet width.

Remedy:

  1. Installing new blankets
  2. Use different blankets
  3. Mount the blankets correctly

 

Cause 3 – Rollers

Printing rollers and their correct adjustment are important for even printing and constant ink transport. Roller streaks are typically contrast-rich and appear at short intervals. Depending on which rollers or roller pairs are affected, different strip patterns appear in the print.

Remedy:

For standard inking units:

  1. Adjustment of all printing rollers according to manufacturer’s specifications. Usually all rollers are first adjusted to the distributors. Then to the printing plate.

For anilox inking units:

  1. Replace doctor blades
  2. Adjust doctor blades according to manufacturers recommendation

 

 

Cause 4 – Damage to the bearings of the printing rollers

Remedy:

  1. Remove affected rollers and replace bearings. Check bearing shells/receivables, replace if necessary.

Cause 5 – Rollers calcinated

Over time, printing rollers accept particles from the dampening solution and become hydrophilic. This disrupts ink transport and results in uneven ink transfer. Typical indication: Print streaks that occur at irregular intervals across the print run.

Remedy 1

  1. Cleaning of the rollers. Decalcifying the rollers with a deglacer. Ensure that all rollers are in contact during the application. For some machine types, the roller bridge must be deactivated when idling.

Remedy 2

  1. Change osmosis water hardener
    In most cases, the osmosis water is hardened with calcium prior to dampening solution conditioning. Over time, calcium settles on the rollers and makes them hydrophilic.
    Alternatively, a magnesium-based hardener can be used to delay the water accepting effect.

 

Cause 6 – Substrate

Some substrates tend to cause visible streaks in the print due to their absorbance.
In particular, uncoated papers or laminated cardboard are more prone to this than other substrates.
Typical indication: Aprubated ink density changes perpendicular to the printing direction with the length of half or full circumference of the ink form rollers.

Possible remedies: 

  1. Changing the substrate
  2. Reduction of ink application (reduction of ink density)
  3. Priming of the substrate
  4. Pre-moistening of the substrate in the upstream pressure unit

 

Cause 7 – Dampening units

The constant and uniform dampening of the printing plate is essential for correct ink transfer and for preventing overemulsion of the printing ink. Normally, only one dampening form roller is used for film dampening units. The dampening unit must therefore be set very accurately to the manufacturer’s specifications.

Remedy:

For film dampening units:

  1. Adjusting the dampening rollers according to the manufacturer’s specifications
  2. Checking, if necessary renewing the metering rollers and dampening form rollers

For spray dampening systems:

  1. Reducing the dampening solution quantity
  2. Optimizing the pulse frequency

 

Cause 8 – too fine screens

If the selected screen ruling is too fine for the substrate, this increases the system-related tendency to form streaks.
Typical indication: Only certain area coverages are affected by stripe formation.

Remedy:

  1. Choosing a coarser screen

 

Cause 8 – Excessive printing pressure

If the printing pressure between the blanket cylinder and the substrate is set too high, printing streaks are produced by wringing and driving out the blanket surface or substrate. Typical indication: streaking from the sheets half length and especially towards the format edges.

Remedy:

  1. Reduce printing pressure (Kissprint to determine optimum printing pressure)
  2. Checking, if necessary correcting the blanket cylinder underpacking

 

Cause 9 – bearer ring pressure too high

If the pressure between the bearers is set too high, this can lead to vibrations and bearing damage.
Typical indication: Regular, sawtooth-shaped stripes across the entire print format.

Remedy:

  1. Adjust the bearer ring compression according to the manufacturer’s recommendations (perform a Kissprint between the printing plate and the blanket to determine the optimum pressure level)

 

Cause 10 – Drive

The drive of the printing press must be constant and with a consistent torque. Variations in the drive power produce uncontrollable streaks in the printed image.
Typical indication: Strong uneven streaking, especially in the printing unit closest to the drive. The stripe effect decreases in the following printing units.

Remedy:

  1. Check and adjust the belt tension between the main motor and the drive wheel of the printing press.
  2. Contact Manufacturer Service

 

Cause 11 – Broken Rollers or bearers

Broken rollers, bearers or damaged shafts may cause serious vibration and/or serious ink-transfer disruption.

Remedy:

  1. Check ink-train and dampening system drive components
  2. Replace worn-out parts
  3. Adust settings accordingly to manufacturers recommendation

This listing is incomplete and will be extended in the future

More images showing:

Streaking (Offset)

Need support for your individual case?
Contact us now!

More Press Troubleshooting Tips:

Streaking (Offset)

Streaks in print are color density fluctuations or contrast variations, usually perpendicular to the print direction.

Piling

  Abstract Piling is an unwanted effect, where the pigments of the ink build-up negatively on the blankets. Serious...

Offset Ink Drying Issues

Abstract: While drying, conventional offset inks dry by evaporating volatile components (solvents) into the...

Ink Misting

Ink misting. Dirty printing presses caused by Ink-Aerosoles.

Framing

Picture Framing. An printing issue were ink is getting transferred over non-printing area

Coating Chamber Leaking

How to address leaking/slinging coating units in industrial printing machinery.

Pile Blocking

How to address blocking piles after press delivery (Offset)

Pile Blocking

How to address blocking piles after press delivery (Offset)

Offset Ink Drying Issues

Abstract: While drying, conventional offset inks dry by evaporating volatile components (solvents) into the...

Ink Misting

Ink misting. Dirty printing presses caused by Ink-Aerosoles.

Streaking (Offset)

Streaks in print are color density fluctuations or contrast variations, usually perpendicular to the print direction.

Framing

Picture Framing. An printing issue were ink is getting transferred over non-printing area

Coating Chamber Leaking

How to address leaking/slinging coating units in industrial printing machinery.

Piling

  Abstract Piling is an unwanted effect, where the pigments of the ink build-up negatively on the blankets. Serious...

Coating Chamber Leaking

How to address leaking/slinging coating units in industrial printing machinery.

Pile Blocking

How to address blocking piles after press delivery (Offset)

Framing

Picture Framing. An printing issue were ink is getting transferred over non-printing area

Piling

  Abstract Piling is an unwanted effect, where the pigments of the ink build-up negatively on the blankets. Serious...

Streaking (Offset)

Streaks in print are color density fluctuations or contrast variations, usually perpendicular to the print direction.

Offset Ink Drying Issues

Abstract: While drying, conventional offset inks dry by evaporating volatile components (solvents) into the...

Ink Misting

Ink misting. Dirty printing presses caused by Ink-Aerosoles.

Pile Blocking

How to address blocking piles after press delivery (Offset)

Coating Chamber Leaking

How to address leaking/slinging coating units in industrial printing machinery.

Ink Misting

Ink misting. Dirty printing presses caused by Ink-Aerosoles.

Offset Ink Drying Issues

Abstract: While drying, conventional offset inks dry by evaporating volatile components (solvents) into the...

Framing

Picture Framing. An printing issue were ink is getting transferred over non-printing area

Piling

  Abstract Piling is an unwanted effect, where the pigments of the ink build-up negatively on the blankets. Serious...

Streaking (Offset)

Streaks in print are color density fluctuations or contrast variations, usually perpendicular to the print direction.