P821: OAKTON® pH and CONDUCTIVITY METERS IN PRINTING

Accurate mixing and monitoring of press fountain solutions are an integral part of quality printing. Changes in technology and raw materials present a constant challenge to today's press operators. Oakton's advanced design in portable, pocket-sized meters makes them a leader in the field of quality control in the lithographic industry.

The micro-processor based instrumentation of the pH meter makes it exceptionally fast, stable, accurate and repeatable. Eliminate the guessing associated with common, paper pH test strips. The economically priced pH Testr series allows them to be used at every press.

Maximum quality control necessitates frequent conductivity readings of the fountain solution. Contamination from paper coatings, ink and spray powder cannot be determined with pH readings. Only conductivity monitoring can pin-point problems before they occur.

How to use Oakton Testrs

  1. Read all instructions relating to the meters before attempting to use them.
  2. Once familiar with the meters, take a pH reading and a conductivity reading of the water that will be used to mix the fountain solution. Record these readings in a log book for reference.
  3. Measure one gallon of water in to a clean container.
  4. Add one ounce of fountain solution concentrate to the water.
  5. Take a second conductivity reading of the water.
  6. Subtract the initial conductivity reading from the second. The difference is the amount of conductivity that is added per ounce of the specific fountain concentrate being used. It will vary from solution to solution. Make note of this value.
  7. Divide 1000 by the value of conductivity added per ounce. The resulting answer represents the starting point for the number of ounces of fountain concentrate to use per gallon of water.
  8. Add the required fountain concentrate. The conductivity of this mixture should be about 1000 mmhos higher than the starting water. This condition is commonly referred to as "one thousand over water". Remember, this is not an absolute number and it can vary as the water varies, or as the fountain concentrate changes.
  9. Record this conductivity. When monitoring the fountain solution, readings that are 500 mmhos or more than the starting point are a warning that problems may occur. Readings of 1000 mmhos or higher than the original are almost always associated with problems, and the fountain should be dumped and re-mixed.
  10. Finally, take a pH reading and record it for reference. During the press run, changes in the pH almost never occur more than ± 0.2 to 0.4 pH units. The actual pH value should be approximately between 3.8 to 5.5.

 

USING OAKTON METERS TO TROUBLESHOOT FOUNTAIN PROBLEMS

Problem

Cause

Correction

1. Toning, Tinting, Scumming

An irregular film of ink printing in the non-image areas of a plate.

1. Incorrect pH or conductivity.

2. Insufficient gum or wetting agents in fountain solution.

3. Plate improperly exposed or under-developed.

1.Check and/or correct pH and conductivity as explained above.

2.Check mixture of fountain solution.

3.Use gray-scale when exposing plates; fully develop per directions.

2. Ink emulsification

Too much water in the ink.

1. Incorrect pH or conductivity.

2. Fountain solution mixed too strongly.

3. Too much wetting agent in fountain solution.

4. Ink tack too low.

1.Check and/or correct pH and conductivity as explained above.

2. Mix fountain solution as explained above.

3. Reduce gum, alcohol or alcohol replacement.

4. Add binding varnish to ink too thin from can or lower amount of reducing compound used on stiff ink.

3. Roller stripping

Ink rollers do not accept ink, usually in bands around the rollers.

1. Fountain solution too acidic.

2. Running too much water.

3. Conductivity of starting water too high.

4. Glazed rollers.

5. Worn rollers.

1. Check pH of fountain solution. Adjust as above.

2. Establish a new ink-water balance.

3. Use distilled, deionized or RO-purified water.

4. Deglaze rollers with hot water and deglazer.

5. Replace worn rollers.

4. Ink not drying

Ink remains wet too long, causing problems with offsetting, smearing, color trapping and perfecting.

1. Fountain solution too acidic.

2. Running too much ink.

 

3. Ink not compatible with printing stock.

4. Ink has emulsified

1. Balance fountain solution as explained above.

2. Reduce ink to almost zero, then build-up in small steps for new ink-water balance.

3. Match ink to stock.

4. See Ink Emulsification above.

5. Plate blinding

Plate is not accepting uniform ink film or not accepting ink at all

1. Fountain solution too acidic.

2. Too much gum in fountain solution.

3. Plate surface contaminated.

4. Too much water.

1. Balance fountain solution with meters as explained above.

2. Mix fountain solution correctly.

3. Clean plate with quality plate cleaner, then rinse well with water.

4. Reduce water; establish new ink-water balance.

6. Plate wear

Image on plate wears or breaks-down prematurely.

1. Fountain solution pH incorrect.

2. Too much pressure on plate from blanket or rollers.

3. Ink tack too high.

4. Running too much ink.

1. Check and/or correct pH and conductivity as explained above.

2. Check and/or adjust packing and roller pressure settings.

3. Add reducing compound to ink.

4. Reduce ink settings and establish new ink-water balance.