The Printing Process, When it “Piles” up

A portion of the ink roller train

A portion of the ink roller train

Chemicals and paper pulp build up on the blanket cylinder to cause piling:

1. Ink and paper material building on the blankets surface.

2. A portion of the ink roller train of a magenta printing unit.

3. A sample of fountain solution being removed from the circulation tank of a press.Piling is a build-up of ink and/or paper material on the blanket during printing. (Figure 1)

There are 3 common types of piling:Image Area Paper Piling Image Area Ink Piling Non-Image Area Piling In both sheet-fed and web offset printing, the ink film can lose its volatile materials as it passes through the printing units on the press. If the ink film reaches a “critical state’ while the paper is still in the press, the ink may lift oft (image area ink piling) from the sheet, or the tack of the ink can pull the fibers and/or coating from the sheet (image area paper piling). An ink can lose these volatile, thin oils in the following ways:

  • In the Ink Train (Figure 2) a very thin film of ink can have prolonged exposure to the air. This can occur during a long makeready, or when running a light coverage form.
  • When Fountain Solution (Figure 3) is added, the ink’s ability to retain its thin oils may change.
  • On the Plate, an even thinner ink film is again exposed to the air while being mixed with the fountain solution.
  • The surface of the Blanket can absorb these thin oils from the ink film. Blankets vary in their oil absorbency characteristics.
  • When the ink film is printed onto the Paper, and then passes through multiple printing units, the surface of the sheet absorbs these thin oils from the ink film, and the printed film again contacts additional blanket surfaces.
Ink loses its oil properties causing piling

Ink loses its oil properties causing piling

4. The first down ink builds tack as it proceeds through the press, and causes coating pick on the last unit.

5. An ink which has lost its lubrication will split back to the blanket’s surface.

Image Area Paper Piling If the tack of the ink film has increased as it lost its volatile material, its “printing tack” may be considerably greater than its “can” tack. Therefore it now has the ability to pull up the paper’s surface and result in ink and paper building up on the blanket’s surface. This type of piling can occur more severely in the last units on the press and at times may occur exclusively on the last printing unit. For example, the first down ink could be printed at a tack of 12 (at 800 rpms, 900 F).
As the ink film builds tack on the paper and reaches the fourth printing unit, its printing tack may now be 18, which is high enough to pick the paper. This type of piling has been commonly called Carry-Over Piling. (Figure 4) Possible corrective measures would be: Reduce the tack of the ink. Add transparent white to the ink to reduce its color strength. (Running a thicker film should lower the printing tack, but a caution to watch dot gain.) Replace the paper. Replace the ink with a slower setting formulation.
Non-Image Area Piling Occasionally ink, paper and fountain solution material will build up on the blanket in the non-image areas. This defect, seen most often in web offset printing, is not fully understood and can be removed by frequent washups. It was not documented for this publication.
Image Area Ink Piling
If the ink film has lost a quantity of its thin oil and has become a “soft” and “doughy” material, and lost its lubrication properties it will not transfer to the paper properly and will build up on the blanket. (Figure 5) Corrective measures would be: to add petroleum/mineral oil to the ink (1/2.1 oz. per pound) to improve its lubrication, check the fountain solution to assure that minimum etch is present,* or try a new batch of ink.
Piling is a "soft" and "doughy" material

Piling is a "soft" and "doughy" material

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