Blanket scumming

Hi all, has anyone ever seen this happen. About one quarter of the blanket gets this heavy glaze and streaks. Rest of blanket is clean. Shows up as a dry up on sheet. The plate is clean and has a nice scum line. Thanks for any suggestions. Hopefully the pics show up ok

 

Hi sir, please change the blanket!

 

We have done that already many times. Tried different blankets, just keep happening. I cant figure out why it only happens on the Near side.

 

Have you checked roller stripes? -ink and dampening-
Roller bearings?
Ink form rollers oscillate or not?

 

yes we have checked stripes. clean bearers once a week, we just integrated the bridge roller. That might have helped. I'll give it another day to make sure

 

Check for a build up of dry ink between the water pan and matte chrome on water unit

 

Hi sir
With my experience it cn be one of those causes
Too high ink tack
Ink is absorbed too quickly
Too much wetting (over-emulsification)
Unfavorable wetting values
Poor substrate quality (paper coating)

 

I suggest you to Reduce ink tack
Slower ink absorption
Reduce wetting
Improve wetting values (pH, IPA, hardness)
Better media quality (paper coating)
Good luck and let me know

 

Tell me if you have a thermoregulation system on the printing unit ??

 

What machine is it? How many units? If more than one, is this happening on all units , or just this one? What plates do you use? Process/processless?

 

Hello there,
For any scumming problem on any printing machine, the basic phenominon is same. The application of dampening solution on the PLATE is to Repelling Ink from Non-Image Areas. The dampening solution forms a thin layer of water on the non-image (blank) areas of the printing plate. Since the printing plate is designed to be hydrophilic (water-attracting) in non-image areas and oleophilic (ink-attracting) in image areas, the water layer prevents ink from adhering to these non-image areas.

• If the (chemistry) foutain solution (Isopropyl Alcohol (IPA) or Alcohol Substitutes) is Good, its temperature is Good, the PH value is Good, and the circulation is also good - Check the machine rollers and its speed
  
• Then check the marked rollers which apply solution to the Prining Plate. if the dampening solution transfered to the plate is too less, scum appears.
• IF the roller adjustment is bad - Scum appears
• IF the Roller diameter is changed (it has a life), the the water transer is improper - Scum appears
• If the Dampening Roller (motor) Speed is not synchronized with machine- Scum apperas
• Look at the below picture to see, how a thin layer of water is applied on the plate.

 

Thank you everyone. I will try to check all suggestions and give a response. appreciate you all.