GRAFIMPEX

GRAFIMPEX
Equipment & Solutions for Newspaper and Commercial Printers

Tuesday, May 3, 2011

Printing Blanket Problems and Trouble shooting...!

1.Problem - Area of Weak Print

Cause:
Improper Bearer pressure. Packing Damaged.
Blanket Smash
Insufficient packing or back cylinder pressure
Low spot in cylinder
Plate Blinding

Corrective Action:
Check for smashed area and blanket and/or packing. Also try adjusting back cylinder setting.
Check blanket height, repack or replace.
Press condition…over pack or spot pack.
Check plate to blanket squeeze
Remake plate

2. Problem-Bar Pull Off/Out

Cause:
Over tensioned blanket.
Improperly applied bar.
Incorrect bar used.
Improperly installed into cylinder reel rod.
Out of square blanket.

Corrective Action:
Check means of tensioning and calibration of equipment.
Over/under specified mounted thickness.
Insufficient epoxy width or thickness.
Check press listing and bar dimensional specifications.
Check for bent blanket bar legs.
Check for unequal gap bend marks on back of blanket.
Check for contaminated cylinder reel rod and clean if necessary.
Check squareness of blanket.

3.Problem- Delamination

Cause:
Solvent attack.
Excess blanket squeeze.
Ink build up on edges.
Blanket edges not sealed.

Corrective Action:
Obtain samples of blanket wash and ink with MSDS and send to lab for evaluation.
Check back of blanket for excessive use of wash.
Check surface of blanket for face cuts that would allow solvent to attack cement.
Check packing pressure.
Use mourning bands.
Undercut packing.
Seal edges.

4. Problem- Dot Doubling

Cause:
Loose blanket.
Excessive squeeze.
Excessive ink feed to achieve density.
Film/plate movement during exposure.

Corrective Action:
Retension blanket, incorrect installation.
Reduce plate to blanket packing or blanket to impression cylinder setting.
Decrease ink/water amounts.
Change to more ink receptive blanket.
Check dots on plate.

5. Problem-Dot Grain

Cause:
Ink form rolls set too tight.
Ink form rolls too soft.
Low ink viscosity or tack.
Poor ink/water balance.
Ink has too much water pickup.
Excessive squeeze.
Fountain solution temperature too high.
Incorrect fountain solution pH.
Under/over exposed plate/film.
Improper blanket surface.

Corrective Action:
Replace with high viscosity ink or increase tack.
Adjust press speed.
Reduce amount of ink and water.
Have ink checked by ink supplier.
Reduce plate to blanket squeeze.
Reduce blanket to impression cylinder setting.
Reduce temperature to 55 to 60 degrees F.
Adjust solution pH to read between 3.5 to 5.0.
Check dot size on plate and re-make if necessary.
Change to more compatible blanket.

6.Problem- Embossed Blanket

Cause:
Blanket swollen due to excessive pressure, very high ink tack, or lack of cleaning with proper blanket wash.
Solvents in ink may affect blanket (UV inks for example)

Corrective Action:
Check blanket thickness and packing. Use quality blanket wash and clean blankets on a regular basis.If blanket is old, change to a new blanket, or one that works better with your inks.
UV inks and washes can often swell blankets. Try a UV compatible blanket.

7. Problem-Ghosting

Cause:
Ink form rollers starved for ink
Job layout causing problem
Ink/water balance issue

Corrective Action:
Not a blanket issue. Check roller settings, run a thicker ink film with minimum of water.
Job layout often contributes to the problem…change direction of run or general layout if possible.

8. Problem-Loss of Print at Gap

Cause:
Blanket over-torqued. Packing incorrect.
Packing slipped
Press out of phase (timing issue)

Corrective Action:
Insure proper packing of blanket and use torque wrench to tighten to press manufacturer specs. Check torque wrenches for accuracy.
Some print length problems are due to cylinders being out of phase. Check cylinder timing to print length.

9. Problem-Mottled Print

Cause:
Running too much water.
Blanket surface contamination.
Incompatible blanket style with fountain solution.
Excessive fountain solution temperature.
Excessive water absorption of paper.
Partially blind image on plate.
Using course grain plate.
Improper ink/water balance.
Not enough squeeze.

Corrective Action:
Reduce the amount of water.
Inspect surface of blanket for glaze, shiny steaks or spots, excessive talc, etc., clean with solvent and rinse with water.
Change type of blanket used or type of fountain solution.
Reduce temperature to 55 to 60 degrees F.
Contact paper supplier.
Remake plate
Change to finer grained plate.
Adjust balance.
Adjust packing.

10. Problem-Piling---Ink

Cause:
Most frequently an ink problem (ink too short and not water repellent), fountain solution PH or conductivity wrong, or rollers set wrong & heat building up.
Blanket underpacked

Corrective Action:
The blanket is least likely to be the cause of ink piling even though the ink piles on the blanket. If blanket-related, it is generally due to insufficient packing. Verify proper packing and nip pressures. Check ink feed, roller settings and set to minimum, check fountain solution PH & conductivity.

To be continued....!

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5 comments:

  1. Hey Yogi! Nice post. There's not enough of this stuff online for web or sheetfed printers. Good useful stuff. Thanks.
    The Offset Printing Guru

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