All posts by sterryInk

Streaks in Print (non-gear streaks)

Blanket is over-packed causing a bump when striking the plate and jarring the form rollers. This creates a bounce and/or skid producing a streak

Tension blankets to press manufacturer’s specifications

Streaks appear across the sheet one revolution back from the top of the plate. Ink form rollers are set too heavily to the plate or durometers are too high

Check durometer of rollers and replace if necessary. Set rollers to pressures specified by the press manufacturer

Slurring

Inspect pressure between blanket and plate or between the blanket and paper

Pack to press manufacturer’s specifications

Blanket tension low

Tension current blanket (or new) to press manufacturer’s specifications

Grippers out of calibration

Check and reset all grippers to press manufacturer’s specifications

Paper with wavy edges or other distortions

Check on a different stock to see if slurring remains. If not, change stock or consult your paper supplier

Poor Scuff Resistance

Ink film not fully dry

Make sure the ink film is thoroughly dry. An oxidizing ink should take 24 to 48 hours to thoroughly dry. Many variables: substrate, fountain solution, ink coverage, ambient conditions

Ink is over-emulsified

Check pH and conductivity and Brix level of fountain solution. Run less fountain solution to achieve proper ink/water balance

Chalking – ink not binding to substrate

Certain papers can be very absorbent leaching away the ink vehicle and leaving the pigment unbound on the surface

Piling

Verify whether the pilling is defective paper coating or ink

If defective paper coating, try a different batch of paper or lower the tack of the ink slightly if necessary

If the Ink becomes over-emulsified/waterlogged, this changes the physical properties of the ink and results in poor transfer

Check that pH, conductivity, Brix level and tempera-ture are to specification and try to run less water

Ink roller train or ink fountain is too cool

Adjust form rollers to 72°-80°F (22°-26°C) and be sure ink fountain is 70°F (21°C) or above to ensure proper ink flow and transfer

Inadequate or excessive blanket cylinder pressure and/or plate or blanket packing

Check blanket cylinder pressures and/or plate and blanket packing are all to manufacturer’s specifica-tions

Rollers are the wrong durometer or improperly set

Check roller settings, clean and condition / deglaze rollers

Ink film thickness may be too high or too low

Verify densities are in normal range

Ink is poorly ground

Check grind. Consult your ink supplier

ph Conductivity Varies Widely

Water quality or supply is varying

Consider installation of a Reverse Osmosis water treatment system. Consult your fountain solution supplier

Concentration of mix is varying

Check doser for accuracy (perform a “jug test”)

Circulating system is contaminated (pressroom supplies, ink or paper)

Thoroughly rinse and clean system with warm water. Avoid contamination by using the correct application of product

Mottling

Paper has an uneven surface

Check paper for texture and absorbency. Try a different stock

Too much water is being carried; inks are water-logged

Reduce water; adjust ink/water balance, check chemistry

Too much water is present in prior unit; water is left on sheet

Reduce water from prior unit

Stock is weak or paper coating is too soft

Reduce ink tack

Excessive pressure exists between blanket, plate and/or stock

Ensure all pressures and packing are within manufacturer’s specifications

Blanket is too hard or glazed

Change to softer blanket or deglaze

Ink is too strong; insufficient ink is being carried to the plate

Weaken ink strength by adding transparent white

Misting or Slinging

Roller train is too hot

Form roller temperatures should be 72°-80°F (22°-26°C). Higher temperatures will lower the tack and viscosity of the ink, lower temperatures will increase the body of the ink

Ink/water setting is out of balance

Check chemistry for pH, conductivity, Brix level and temperature. Adjust settings to run minimum amounts of ink and water

Too much ink is being carried in an effort to achieve the desired density

If possible, substitute a stronger ink to reduce the ink film thickness on the rollers or run as a double hit

Rollers are worn or improperly set

Check rollers for damage and settings

Ink tack is too low

If possible, increase tack to maximum allowable for substrate being printed. Consult your ink supplier

Metering Roller Build-up

Fountain solution circulation system is contaminated

Drain, clean, flush, replace filters and refill with fresh fountain solution. Desensitize rollers

Fountain solution mix is improper

Check pH, conductivity, Brix level and temperature. Ensure pan temperature is no higher than 65°F (18°C)

Automatic dosing systems are faulty

Check to make sure that doser is dispensing desired levels of chemistry (perform a “jug test”).

Rollers are set improperly

Check settings and the skew of the metering roller and reset to manufacturer specifications

Roller durometer is wrong

Replace rollers with recommended durometer

Pan roller is greasy or contaminated

Clean and desensitize the chrome roller with a good chrome roller cleaner and follow up with a hot water / white vinegar (2:1) wash-up

Inappropriate solvents/washes used to clean metering rollers

Be sure to use metering roller cleaner (MRC)

Linting and Picking

Stock has insufficient lint or pick resistance

Change stock, try a different run of paper

Blanket is improperly packed

Correct packing (underpacking and overpacking causes picking)

Blanket is too tacky

Treat blanket surface to reduce tack. Use blankets with good release properties

Impression is improperly set for the ink/stock combination

Set impression to press manufacturer’s specifications

Ink is too tacky for the stock being run

Reduce tack only enough to eliminate the problem

Ink and water are out of balance

Correct ink/water balance

Ink film thickness is too low

Weaken the ink slightly to improve release from blankets

Hickeys

Foreign particles are adhering to the plate or blanket

  1. Check for contamination in ink and/or fountain solution and rollers for deterioration
  2. Use scotch tape to remove hickey for examination. If pigment or ink skin, remove old ink from fountain and replenish with ink from a freshly opened can
  3. If paper fibers, try a different run of paper or if necessary, gradually reduce the tack of ink