Damping Solution

The damping solution must work well with every printing element: the press, damping unit, printing plate, stock, and offset ink. Very early on in the history of offset printing, it was realized that untreated tap water is seldom suitable as a damping solution.

To meet demands on modern damping solutions, damping solution additives which have been adapted to the water are added to the water. They serve the following general purposes:

Corrosion protection of printing plates.
Adjustment of surface tension.
Stable adjustment of ink/damping solution balance.
Corrosion protection of certain machine parts.
Good anti-microbial effect.

In addition, it is possible to incorporate special agents (e.g. to prevent roller stripping, to accelerate ink drying, or to substitute alcohol) into the damping solution additive.

The PH

The pH indicates the acidity of a medium. Within its dimensionless numerical series, the pH range from 0 to 7 is defined as acid, and the range from 7 to 14 as alkaline, whilst pH 7 re-presents the neutral point.

As the offset printing process has developed, the range between 4.8 and 5.3 has proven to be the most favorable for printing purposes. New developments in newspaper printing also include the use of damping solution additives buffered in the neutral range. Two methods can be used for determining the pH:

pH-indicator strips are available in a wide range of calibrations and types. However, the ob-served measurement error in buffered systems is often 0.5 pH units, and this method is therefore not recommended.
In contrast, electrical pH-meters with glass electrodes permit very accurate measurements of pH, even if the solution is buffered. The only prerequisite is that the device is serviced and calibrated as prescribed.

Electrical conductivity

Electrical conductivity is often referred to in practice as a second criterion. However, it has no relevancy to the technical printing performance and can therefore only be used to test if the correct amount of damping solution additive has been intermixed. Certain borderline conditions need to be observed, however, in this connection for which please consult our folder “Electrical conductivity” (MB 8).

Surface tension

The measurable variable for judging the wetting capacity of liquid is its surface tension. Water has approximately the same surface tension of 72 mN/m whether it is classified as soft or very hard. A damping solution with such a high surface tension cannot adequately wet the printing plate surface. This is why substances (tensides) are added to the damping solution additives which specifically reduce surface tension.

Isopropanol

Since isopropanol, too, has the effect of reducing surface tension, a suitable combination of tensides and alcohol substitutes in the damping solution may permit to considerably reduce the isopropanol content required in the damping solution. It may even be possible to eliminate isopropanol entirely if the damping units are suitably equipped, e.g. with ceramic or hydrophilic rubber roller.

Corrosion protection

To protect printing machines against corrosion, it is strongly recommended to use corrosion-inhibited damping solution additives which have been authorised for use, as demanded by the machine manufacturers. In this connection we emphasize again the possible promotion of corrosive effects by substances contained in water, for which specific limits have been set.

Germicidal effect

Damping solution additives must be capable of effectively suppressing the growth of microorganisms in the damping solution circuit. The only way to keep the damping system in good condition is to use damping solution additives with suitably designed preservatives that retain long-term effectiveness. The anti-microbial agents used currently are free from formaldehyde or formaldehyde repository compounds. However, if the system should sludge up, e.g. by germs that have developed a resistance, thorough cleaning by means of cleaners with strong cleaning and germicidal effects (SYSTEM CLEANER 8080 09) becomes inevitable.

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