GRAFIMPEX

GRAFIMPEX
Equipment & Solutions for Newspaper and Commercial Printers

Saturday, June 4, 2011

Printing Blanket Problems and Trouble shooting...... PART 2

11. Problem - Pinholes In Blanket


Cause:
Blanket defect; particles coming out of blanket surface.

Corrective Action:
Make sure hole is in surface rubber rather than a hickey on blanket or plate surface.
Replace blanket and save for evaluation and replacement by manufacturer.

12. Problem - Plate Blinding

Cause:
Excess plate to blanket squeeze
Blanket surface too hard
Improper pH
Improper form roller settings
Bad or improperly made plate

Corrective Action:
Adjust plate to blanket squeeze to a measured .004" to .005".
If blanket old and hard to the touch, try a new blanket.
Compressible blankets will give more packing latitude.
Check pH and conductivity.

13. Problem - Plate Cracking

Cause:
Loose plate.
Poor plate bend.
Packing short or askew.
Incorrect plate gage.
Sharp cylinder edge.

Corrective Action:
Check cylinder clamps and adjust or repair as necessary.
Re-clamp plate.
Check bending jig.
Re-make plate.

14. Problem - Plate Cracking Con’t

Cause:
Plate gap not hitting inside blanket gap.

Corrective Action:
Check packing and replace if necessary.
Verify correct thickness and measure plate.
Smooth down edge.
Retime cylinders to correct settings.

15. Problem - Registration---Circumferential

Cause:
Loose blanket or improper packing from one unit to the next
Stock feed problem
Excessive moisture gain between printing units
Erratic infeed tension
Unstable stock

Corrective Action:
Insure blanket is properly torqued.
Check proper packing of plate and blanket between units where fit is an issue.
Reduce water feed or change stock if absorbing excess water is changing stock dimension.
Check infeed rolls set properly.
Verify plate installed and bent properly.

16. Problem - Registration---Lateral

Cause:
Often relates to excess water absorption by paper
Excess nip pressure causes paper to spread
Paper roll tensioned poorly by mill
Press infeed tension erratic

Corrective Action:
First check nip pressure by verifying blanket packing. Use less packing if overpacked.
Try reducing water to minimize absorption.
Adjust press infeed tension settings.
May require paper change. Discuss with paper supplier.

17. Problem - Scumming

Cause:
Incorrect ink/water balance.
Improper water form roll setting.
Contaminated fountain solution.
Plate sensitized in non-image area.
Incorrect fountain solution mix.
Incorrect printing pressure.
Out of round or hard form rolls.
Running abrasive paper.

Corrective Action:
Increase water or decrease ink.
Check stripe and adjust if necessary.
Clean system and replace solution.
Clean and desensitize plate.
Remake plate.
Check pH and conductivity and correct.
Check plate to blanket squeeze.
Check hardness and run out and replace rolls if necessary.
Change paper.
Add non-piling agent to fountain solution.

18. Problem - Slurred Print

Cause:
Excess nip pressure at plate & blanket or blanket & impression
Loose blanket
Improper form roller settings
Improper ink water balance

Corrective Action:
Check blanket packing and plate packing. On sheetfed or business forms web, check
squeeze to impression cylinder…adjust.
Check torque of blanket lock up.
Many times too much ink or improper ink water balance is the problem. Check ink train
settings.

19. Problem - Streaking

Cause:
Press condition known as gear streaks
Can be made worse by excess bearer pressure or plate to blanket squeeze
Ink form rolls set wrong or too hard

Corrective Action:
Older or worn press ears can cause streaking. Compressible blankets can help minimize this.
Other factors can include blanket or plate overpacked. Insure proper nip pressure between plate and blanket.
Check bearer pressures…adjust.
Adjust form rollers, replace if durometer too hard.

20. Problem - Tinting

Cause:
Ink too low in viscosity.
Too acid fountain solution.
Ink not resistant to alcohol or fountain solution.

Corrective Action:
Increase viscosity, contact ink supplier.
Increase pH to a minimum of 3.5.
Reformulate ink.

21. Problem - Trap/Poor

Cause:
Ink tack out of sequence.
Improperly balanced ink strength.
Poor ink/water balance.
Ink tack cross o ver.
Excessive heat generated.
Paper coating not ink receptive.

Corrective Action:
Revise ink tacks or laydown sequence.
Contact ink supplier.
Adjust as necessary, run as little water as possible.
Contact ink supplier.
Check vibrator temperature and reduce coolant temperature.
Contact paper supplier.