American Offset Printing Ink
American Offset Printing Ink

pH & Conductivity

INTERACTIONS

Equipment                                              Blankets

Press                                                          Speeds

Dampening Systems                            Substrates

Press Conditions                                      Washes

Fountain Solution                            Maintenance

Chemistry                                                Training

Blending                                          Pressmanship

Incoming Water                                          Plates

Inks

 

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

  • To reduce pH, keep plate image area ink receptive and keep plate background water receptive.
  • To lower water surface tension to maintain wetting characteristics of plate non-image area.
  • To minimize corrosive action of acid on plates, extending plate life and improving print quality.
  • To protect non-image area from accepting ink.

 

COMPOSITION OF FOUNTAIN SOLUTIONS

Water                                         Solvents

Gum                                      Surfactants

Acids                              Wetting Agents

Salts                                          Biocides

Buffers                                   Defoamers

 

  • Gums desensitize the non-image area of a plate
  • Acids aid gum to bond to a plate
  • Salts protect and renew a plate surface
  • Buffers provide a constant pH
  • Solvents help hold surfactants in solution
  • Surfactants lower surface tension
  • Wetting agents lower surface tension
  • Biocides prevent algae and fungus growth
  • Defoamers  prevent and minimize foaming

 

 


 

pH INFORMATION

  • pH is the measure of acidity or alkalinity of a solution.
  • Maintenance of fountain solution at optimum pH is vital to high-grade, trouble free offset printing.
  • 7 is neutral, below 7 is acid, above 7 is alkaline.
  • Acid allows the highest quality printing - 3.5 to 4.5 pH is typically a good range for sheetfed printing.
  • The acid side of the table allows gum to adhere to the plate better.
  • A whole number change on the pH scale represents a tenfold change in pH.  A pH of 5.0 indicates ten times the acidity of a pH of 6.0.
  • Examples of pH:

Stomach acid 1 to 3

Lemon juice 2.3

Coke 2.5

Ocean water 8.2

Hand soap 9.5

 

 CONDUCTIVITY

  • Conductivity is the ability of a material to conduct electricity.  It rises basically in a straight line, meaning if 1 ounce per gallon gives a conductivity of 300, it will rise 300 for each additional ounce.
  • As conductivity rises in the tanks, do not water fountain solution down to lower it.  If you are running 4 ounces per gallon and you water it down, then the ratio of water to solution will go from 4 ounces solution and 128 ounces of water to 4 ounces solution and 160 ounces or more of water.  This dilution factor could greatly cause problems on press.
  • Alcohol, when added to a fountain solution, acts as a diluent, reduces the solutions overall conductivity reading.  Alcohol has a conductivity reading of 0.

 

 

ALKALINITY

Acid vs. Alkaline Substrates

Calcium Carbonate

Reasons for Change

Saturation Point

Deposits in Rollers and Plates

pH Rise

Solutions to Problem

 

  • Paper companies have changed paper stocks form acid to alkaline. Alkaline stocks use calcium carbonate as an ingredient.
  • Calcium carbonate has an alkaline pH which cause buffers, in some fountain solutions, to no longer hold.
  • Alkaline stocks are more environmentally friendly plus they are whiter, brighter and lower in cost.
  • With the Addition of alkaline stocks the fountain solution could become saturated.
  • When saturation occurs, calcium carbonate can deposit on rollers and plates which will show stripping and blinding.
  • Fountain solution pH will rise so it is very important to monitor pH.  As calcium carbonate works into the water, from paper stocks, it can break down the buffers and lose their ability to operate.
  • One prevention method is to treat your water, clean tanks often and use a calcium rinse to remove paper deposits.  If pH rises above 4.5 its time to dump and re-mix.

 

 

DAMPENING SYSTEM MAINTENANCE

Conductivity Rise

pH Rise

Flush the System

Chrome Roller

Metering Roller

Filtration

 

  • Monitor conductivity.  If conductivity rises 50% above starting point, dump and re-mix.
  • Monitor pH.  This will help avoid scumming, tinting and color variation.
  • Drain and flush dampening system.  Flushing the system, tanks, lines and pans, all help and are good house keeping practices.
  • Keep the chrome roller desensitized.  This will prevent feed back and allows the chrome roller   to carry more water.
  • Do not use oil based solvents to clean metering rollers.  MRC is designed to evaporate and leave no oil residue.
  • Filtration will provide a more effective means of contamination removal and keep presses running clean.

 


AN IMPORTANT REMINDER

Mix

Monitor

Maintain

 

  • Mix - once you have determined the correct dosage for your press, mix the same way day in and day out.
  • Monitor - Read pH and conductivity on a regular basis.  It is a quality control procedure.

          This will greatly prevent problems.

  • Maintain - Regular maintenance of your dampening system is critical to allowing the solution to preform its job at optimum performance.
  • Measure all fountain solution components, including water, accurately.

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. 

 

Any Questions, Need Help?

American Offset Printing Ink

3847 Corporation Cir

Charlotte, NC 28216

Just call us at:

Toll Free: 800-338-4122

Phone: 704-392-6412

Fax: 704-392-6542

E: info@americanoffset.com

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