Dampening Systems Substrates
Press Conditions Washes
Fountain Solution Maintenance
Incoming Water Plates
All of the above interactions must be considered in order that the offset printing process run as smoothly as possible. These interactions must maintain consistency or the process can suffer adverse effects. Each interaction plays a key role in the whole of the process.
In a nut shell, this process is a chemical and mechanical reaction, in which ink and water form together on a plate, with water in the non-image area and mix with ink in the image area. Then it is transferred to the blanket and onto the substrate to form an image.
FOUNTAIN SOLUTION FUNCTIONS
COMPOSITION OF FOUNTAIN SOLUTIONS
Acids Wetting Agents
Stomach acid 1 to 3
Lemon juice 2.3
Ocean water 8.2
Hand soap 9.5
Acid vs. Alkaline Substrates
Reasons for Change
Deposits in Rollers and Plates
Solutions to Problem
DAMPENING SYSTEM MAINTENANCE
Flush the System
AN IMPORTANT REMINDER
This will greatly prevent problems.
Too much concentrate can cause - ink emulsification, background tinting, poor ink receptivity ( mottling ), premature plate wear, slow drying of inks and stripping.
Too little concentrate can cause - reverse fill in, scumming, tinting, inadequate gum will leave plate non-image areas unprotected and premature plate wear.
EFFECTS OF PAPER ON FOUNTAIN SOLUTION
The paper on the press can affect the pH and conductivity of the fountain solution. This occurs when paper dust finds its way into the dampening system usually shortly after the press starts up and could show up in a change in fountain solution pH and conductivity.
It is best to buy paper with as neutral a pH as possible and with minimum dust and high resistance to picking. The pH of most paper coatings fall in the 6.0 to 8.5 range. While some coatings at 8.5 may cause scumming, others with a pH as high as 10.0 cause no problems.
pH / CONDUCTIVITY CHANGES DURING THE RUN
In the process with as many variables as offset printing, occasionally press problems are pH/conductivity related. Experience shows that a change in fountain pH/conductivity during the run frequently can be the reason behind common problems. When problems arise, pH/conductivity determination is the logical first troubleshooting step - easy procedures which may save time wasted seeking elsewhere for the cause. While some press problems, like ink drying, can be either pH related or have other causes. This discussion is confined to adverse pH/conductivity as a cause and correctable factor.
Why does pH/conductivity change in the course of a run or shift?
In both theory and practice the conductivity of a solution will tend to rise as the press runs. This is because of a pick-up of contaminants from inks, dust from paper coatings, metal particles from press/dampening system and atmospheric gases. The pH of the solution also can vary, although with buffered solutions, changes in pH are minimal. Fountain acid may weaken ( pH rise ) by reacting with metal offset plate, or by reacting with materials in the paper, ink or plate coating.
Today most fountain solutions are designed with wide operating latitude that protects against most pH/conductivity shifts that occur during a press run. Most printing problems attributable to fountain solutions are due to either too much or too little fountain solution being used. Frequently it is too much.
American Offset Printing Ink
3847 Corporation Cir
Charlotte, NC 28216
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Toll Free: 800-338-4122