Reference Book
Water:-The quality of the water used in dampening solution greatly affect the
performance of dampening solution and ink. Distilled water that is colourless,
tasteless and odourless and having a pH of 7 is used for preparing dampening
solution.
Acid:- The acid used in dampening solution varies according to the desired
pH. The pH of a dampening solution is the measure of how acidic or alkaline
the solution is. The pH scale begins at 0 (very strong acid) and ends at 14 (very
strong base). The half point 7 represents a neutral solution. For offset printing
a pH value of 4.5 to 5.5 is found good. Ideal value is 5.5. Change in pH value
of dampening solution can greatly influence ink drying time and cause a variety
of printing problems.
In addition to pH level, dampening solution should be consistant in its
conductivity- the amount of electricity the solution will carry. Conductivity is
a more accurate means for measuring concentration than pH. Dampening
solution’s conductivity is related to maintaining the solution’s pH level.
Gum arabic:- It is a gummy, water-soluable substance obtained from certain
types of trees. Gum arabic serves to protect the plate from scratches and prevents
it from oxidising, while in storage. It desensitises the non image area of printing
plate and prevent them from accepting ink. When a job is over, the plate is
cleaned and gummed evenly to preserve for future use. This solution of gum
arabic is strained through a cotton cloth before using, small particles of dirt
may cause serious troubles on the printing plate.
Wetting agents:- These are substances such as iso propyl alcohol, glycerin and
glycol added to dampening solution to lower its surface tension. It allows
water to spread over non image area of a plate more quickly and maintain the
water’s wetting ability and allow the operator to run less water.
Corrosion inhibitors:- These are compounds used in dampening solution to
prevent or minimise damage to the printing plate through oxidation or other
chemical reaction. They increase print quality and extend the life of plates.
Magnesium nitrate is commonly used for this purpose.
Anti-foaming agents:- These are typically silicone based fluids or emulsions
added to dampening solution to reduce the tendency of the solution to foam or
bubble and it reduces distribution problems on the press.
Fungicides and drying stimulators:- Fungicides help to kill any organic growth
in the fountain or in the dampening system. Drying stimulators enhance the
effectiveness of the drier in the ink.