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Technical Bulletin 1/84

1. Poor registration ­ from clogged suckers.
2. Hickies ­ donut-shaped voids in images.
3. Plate wear ­ most prevalent with preprinted sheets with spray powder.
4. Gear wear ­ spray deposits buildup in the gears.
5. Background spots ­ mostly from preprinted sheet with spray powder.
6. Slurry images ­ plate looks good.
7. Pinholes ­ cannot be seen on plates.
8. Weak image density ­ plate image good.

Cause:
Excessive spray powder on preprinted sheets and/or the use of excessive spray powder when printing can cause any one or a combination of the above-mentioned problems.

Corrections:
When using offset spray powders, if you can see the spray, you are using too much. Remember, the spray does not dry the ink. It prevents ink set-off from the printed side of a sheet to the back of the sheet on top. With preprinted sheets which already have been sprayed, attach a tinsel static eliminator across the feed board. The strands of the tinsel should brush each sheet before it reaches the blanket and impression cylinder. With an A.B. Dick or Ryobi Press without feed board, attach the tinsel eliminator to the breaker bar on the feed pile or across the feed pile side guides. In either case, this tinsel will prewipe each sheet and minimize the amount of powder reaching the blanket and plate.

Once a problem is evident, try the following remedies:

1. Clean the sucker feet, feed board, and the upper and lower feed rollers.
2. Clean the press and use fresh ink.
3. Clean the blanket with press wipe and hot water and/or de-tack the blanket. To de-tack, clean with slow-drying blanket wash and light machine oil mixed. Rub blanket vigorously several times, and dry with fresh press wipe. The application of a commercial rubber rejuvenater, such as velvee, according to product directions, is helpful in preventing this problem.

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