Registered in England No. 1725990 © Pomeroy Pressroom Products Ltd 2010 Website design by: AH Designs Q & A / Advice - Conductivity: Manufacturers of fountain solutions, such as Vegra, spend considerable time and resources on developing products that are safe, effective and which produce consistent results. Ultimately, however, the success with which a particular fountain solution functions depends on the skill and experience of the printer, who is generally responsible for diluting the concentrate and then monitoring the results once it is on the press. Measuring fountain solutions: A press-ready fountain or dampening solution contains concentrate, usually added at a strength of around 2.0% to 2.5%, water drawn direct from the mains or a holding tank, plus isopropanol alcohol. Although the use of alcohol is slowly decreasing, due to concerns over health and safety and VOC emissions, the balance between the various elements must be maintained if the fountain solution is to produce the best possible results, in terms of both print quality and press performance. Conductivity is a simple, accurate and easily repeatable method of measuring the concentration of fountain solution additive in dampening water. In particular, the strength of the fountain solution concentrate must be controlled carefully if it is to achieve its primary task, of holding the pH of the dampening solution at a predetermined level. Typically, pH is maintained at 4.5 to 5.5 for web offset, 5.0 to 5.5 for sheetfed and 5.5 to 7.0 for newspaper printing; the exact level, however, will vary from area to area, depending on the water supply and the paper and inks used. The simplest method of monitoring the strength of a fountain solution would appear to be measurement of the pH level. Unfortunately, this is both unsatisfactory and, in many instances, misleading, as pH can be affected by a number of factors, such as the acidity of paper, inks and natural buffers including the calcium carbonate present in hard water. Modern fountain solution concentrates contain chemical buffers, which are designed to maintain the pH level within a tightly defined band, once they have been diluted to the manufacturer’s specification, almost regardless of dosage. As a result, adjusting the strength of the fountain solution, solely on the basis of a change in pH, will have little measurable impact on the operation of the buffers but will adversely affect the function of other important components in the fountain solution concentrate. Typically, pH is maintained at 4.5 - 5.5 for web offset, 5.0 - 5.5 for sheetfed and 5.5 - 7.0 for newspaper printing. These components include surfactants, to control surface tension and viscosity: wetting agents, to enhance the interfacial tension between ink and water and to reduce the volume of alcohol: antibacterial agents; plus corrosion inhibitors, for use with newspaper presses. The various components will have been selected by the manufacturer to address specific requirements and to help the printer achieve the best possible results, at a price the end user is prepared to pay. For example, a higher than recommended dosage and an excessive concentration of surfactants can cause ink to emulsify. Too high a level of wetting agent will inhibit the ability of the dampening water to form an even film around cylinders and across rollers. Conversely, too low a concentration will cause bacterial contamination, leading to the growth of algae and fungi. Why use conductivity? As has already been highlighted, pH has only limited relevant when monitoring the concentration of additives in the fountain system. By comparison, conductivity produces a simple and accurate indication of the concentration of fountain solution, by measuring the volume of salts introduced by the addition of the fountain solution concentrate and held in solution in the dampening water. The salts held in the solution will be directly proportional to the quantity of concentrate added. Measuring the conductivity enables the correct concentration of fountain solution concentrate to be added repeatedly, without error. The conductivity can be measured simply by placing two electrodes or probes, connected to a suitable meter, into the diluted fountain solution. Any salts dissolved in the liquid will affect its ability to conduct electricity; the more salts present the greater the conductivity and the lower the resistance to the flow of an electrical current. Provided that the raw water used has previously been analysed, to determine its natural salt content, it is then possible to determine accurately the level of fountain solution concentrate present when compared with a mix of concentrate and water when using the same raw water. Different concentrates will each give a unique reading in a known type of water, which will vary depending on the water type. One point to be noted is that alcohol is non-conductive and its addition to the dampening solution will reduce the level of conductivity. This makes it important to monitor its dosage accurately; better still is to eliminate the alcohol, using a Vegra Alcodamp fountain solution. Monitoring conductivity ensures that accurate mixing of the fountain solution can be repeated time after time without error, providing known conditions for printing and helping to improve quality and reduce waste. What is pH? pH is a measure of the acidity of alkaline of a solution. This is calculated as ‘the logarithm of the reciprocal of the hydrogen ion concentration in moles per cubic decimetre of solution’. In simples terms, pH increases as alkalinity rises and decreases as the solution becomes more acid. The pH scale runs from 0 to 14, with a neutral solution being rated as 7.0. Conductivity meters: Modern hand held conductivity meters (and combination meters), incorporate accurate and reliable solid state electronics and easy to read LCD displays, making the measurement of both conductivity and pH quick and simple. Combination Meters