Offset Powder Buildup...

[kdw75]

When printing jobs on our 4-color press, I generally can get by with very little offset powder, since it has an infrared dryer, but in some cases I have to turn it up a little. The problem comes when I flip it over to run the back side. About every 200-400 sheets, I will have to shut down and wipe the blankets, as they get a spots with lots of powder buildup, on the first couple units. It is enough to cause image problems, especially when there isn't much ink flow. I am using Varn offset powder, compressible blankets, and TOYO medium tack inks. Surely, there is some fix for this, or at least a way to minimize it.

 

[dabob]

we rack our high pile in 5 - 6 inch lifts, use a dryer additive if necessary and we in the worst case have to stop every 500 - 600 to wash the blankets . . . but that is worst case . . . very heavy coverage on both sides of the sheet . . .

 

[QualityPrint]

Few things for this...
-Doyle has a sheet cleaner that they can retrofit for your press that acts as a vacuum for every sheet. You will have to look into it for the cost.
-An aerator/jogger helps immensely for this. We prefer the Toppy brand. This forces air between each sheet and the vibrations shake out the spray powder.
-You can always run it through the press with the blankets on impression one time then send it through again to print. Of course we all know the downfalls to this but if you are stopping that frequently it might actually save you time. Especially on longer runs.
-Outfit the press with UV dryers (HUV and LED) to rid the need for spray at all.
-Change the sequence of the ink to CMYK or CKMY to move the tackiest of the inks (Black) further down the line. We used to run CKMY all the time for this.
-there are softwares out there geared towards limiting the total coverage on your images. Alwan Colorhub is one. This reduces CMY and replaces it with K while maintaining a gray balance. Works pretty well and helps with drying and color stability.

Hope this helps

 

[kdw75]

What micron powder are you using? Do the problem areas show up randomly on the sheet, or are they in the same spot(s) everytime? If there is a consistent pattern, what is it?

I am not certain of the micron size of the powder. The powder shows up across the blanket, but there seems to be a couple areas that have the heaviest amount, almost in line with the sheet guides on the feeder.

 

[Alois Senefelder]

Spray Powder.


Check 1) Micron size 2) Spray Powder Grade 3) Check spray pattern of the Powder Sprayer

Regards, Alois

 

[aqazi81]

As Alois and alibryan said,
1. Check your micron size and if you have no idea about it, contact your supplier to give you appropriate size powder for your jobs. Ask for the coated spray powder.
2. Check you spray powder unit that it is spraying smoothly, place a black sheet or any dark colored sheet under your spray nozzles and push the test button on your spraying unit and regulate each nozzle according to your job. Always go for minimum sufficient powder to prevent set-off.
3. You can run the sheets with impression on and dampening on to dust off the sheets.

I hope this helps.

 

[9162]

Make sure your not using a "coated" spray powder you want a uncoated style that will disperse with moisture and not build up