American Printer's mission is to be the most reliable and authoritative source of information on integrating tomorrow's technology with today's management.
Sep 1, 1995 12:00 AM
Ink made with those new environmentally sound vegetable-oil additives dries too slowly. And problems with holding reverses open are caused by quirky designers who use funny fonts, right? Not necessarily. Ink salespeople use test results to defend their products, and the designer points out she's been using the typeface successfully for years. To discover the cause of these problems, we must go back to the basics - the basics of utilizing pH and conductivity measurements to monitor fountain solution performance.
Those basics are important to Steve Mott, a professor in the Graphic Communications Dept. at California Polytechnic San Luis Obispo. This campus, in California's state university system, is known nationwide for its superb printing management program.
In his Sheetfed Lithographic Technology course, Professor Mott introduces the concept of controlling the strength of the fountain solution, including measuring pH and conductivity, in the first week or two of the quarter.
Likewise, at Rochester Institute of Technology's School of Printing Management and Sciences, Professor Cliff Frazier starts on the topic early. As part of his introduction to web offset students, he presents the need to determine dampening solution strength and consistency using pH and conductivity measurements.
While experts agree the newer conductivity measuring techniques are preferable for monitoring fountain solution performance, pH is still an important factor in sensitivity, plate life, ink drying and more.
"Conductivity is a better measure of the strength or concentration of fountain solution," Frazier stresses. "This measurement is vital because it will indicate an error in mixing long before pH will. But, tracking pH still is necessary to determine the solution's chemical composition. You can add table salt to a solution and its conductivity would go up, but its chemical activity wouldn't be altered."
In the language of Total Quality Management, testing the waters with both measurements can prevent an out-of-control process.
"If the strength of the fountain solution is too high or too low, the result is a host of production problems that disrupt the quality on press," explains Professor Mott. "The top three problems caused by excess fountain concentrate are ink emulsification, background or plate tinting, and slow drying of inks. If there's too little concentrate, there may be problems holding the reverses open. Also, the press will have a tendency to scum, and it will be difficult to hold ink and water balance.
"It's important to use both pH and conductivity measurements in production," Mott insists, as does Frazier and Lloyd DeJidas Jr., director of graphic services at the Graphic Arts Technical Foundation (GATF), Pittsburgh.
"Conductivity is a measure of a material's ability to conduct electricity," DeJidas explains. "Pure water is a very poor conductor of electricity. As ionic materials are dissolved or go into solution in water, they form ions and the water becomes more conductive. So, conductivity can be used as an approximate measure of water quality.
"pH is a measure of the hydrogen ion concentration in water," DeJidas continues. "A pH of 7 is neutral; a pH less than 7 indicates an acidic solution, and a higher number indicates a basic or alkaline solution. For quality printing, it is important to maintain the optimum pH for your dampening solution."
Conductivity measurements are expressed in a unit called micromhos (mmhos), while pH is noted as a whole number. It's important to remember that while conductivity is a linear progression, a change of one unit in a pH measurement indicates an increase or decrease in acidity by a factor of 10. For instance, while pH 4 is considered mildly acidic, pH 2 is strongly acidic.
In the right range, acids act as mild detergents and prevent ink buildup on plates. Too much acid, however, can cause ink sensitivity because it will over-etch the plates.
The amount of fountain concentrate to add to a given quantity of water to achieve ideal conductivity and pH levels varies not only with the fountain concentrate manufacturer's instructions but also with the chemical composition of water coming into the plant. According to printers throughout the U.S., water characteristics can change dramatically - in some places several times a day!
"If conductivity of the incoming water varies less than 50 mmhos, consistent dampening solution can be mixed," DeJidas notes. "Day-to-day fluctuations of 200 mmhos is an indication that some type of water treatment equipment may be needed to keep incoming water constant."
In addition, today's dampening solutions are typically more than 98 percent water when mixed. Therefore, measuring the characteristics of the incoming water supply is more significant now than it ever was before.
"Starting levels depend on the composition of your tap water and the manufacturer's instructions," Mott points out. "A general rule of thumb we ascribe to is that conductivity should be approximately 2,000 mmhos above that of the incoming tap water.
"For pH, follow the manufacturers' instructions. For sheet-fed work, a pH of 3.5 to pH 4.0 indicates a good functioning concentration."
"A level 4 pH is where gum arabic is most adhesive to the plate," points out Frazier, "so fresh solution could start with measures of a pH of 3.8 and 1,500 mmhos to 1,700 mmhos conductivity for web offset. Use the fountain concentrate manufacturer's label as a guide. For example, if it suggests starting a mix with 2 oz. to 6 oz., start with the midpoint, read pH and conductivity, record the values and try the mix. If it works, it becomes your standard."
At StorterChilds, a commercial sheet-fed printer in Gainsville, FL, plant engineer Tom Petersen reports that monitoring pH and conductivity is part of the pressroom routine. Measurements are taken when fountain solution is mixed - prior to and after refrigeration. Levels also are monitored during the run. StorterChilds' operators print multicolor work on three two-color presses, a five-color MAN Roland and six-color Komori.
"Our incoming water is hard. It may be as high as 5 (pH) because of the calcium content of the live rock in our area," Petersen says. "We use a reverse osmosis system to treat the water and then mix up a 25-gal. master batch in a vat to keep a consistent fountain solution."
"We use a GATF color bar to monitor dot gain, slur and neutral density," reports company president John Childs. "If these items shift during the run, particularly the neutral density, we check ink/fountain solution balance.
"If we do have problems," Petersen adds, "chances are the fountain solution may have been contaminated during wash-up. The first thing we do is check pH and conductivity."
Experts also point out that alkalinity increases the pH of a working fountain solution. However, since most solutions are "buffered," adding more of the concentrate to fresh mix will not make much difference in pH level. Starting with a more acidic concentrate is the general recommendation to compensate for incoming alkaline tap water.
It also is one way to counter the effects of "acid-free" or alkaline coated papers. Calcium carbonate, which is commonly used in alkaline papermaking, can cause problems on press. Calcium ions can react with ions of certain fountain solution chemicals, thus changing the nature of the solution itself. Calcium also reacts with other materials, forming compounds that can be deposited onto plates, rollers or blankets. In turn, these deposits precipitate glazing, leading to toning in the non-image areas, plate blinding and other problems.
As Mott says, "The 'well-being' of fountain solution is disturbed by chemical contamination from paper."
Lewis Smith, a press operator at Whitman Communications in Lebanon, NH, certainly would agree, even though he has a water supply many printers would envy.
"We don't have to treat our water," Smith reports, "the conductivity measures 50 mmhos out of the tap all year round. When we mix fountain solution, we add concentrate, check the pH and conductivity and then put in any other additives. Additives can change conditions a lot."
Whitman Communications is a 35-employee general commercial printer running two-color presses. Owner Steve Whitman characterizes the firm as specializing in the educational marketplace, serving colleges and other institutions.
"Most of our paper is acid-free," Smith continues. "If press runs are short, less than 5,000 impressions, we may only have to check the fountain solution weekly. When the runs are more than 5,000 sheets, we start to get buildup from the paper on the blankets and have to check the fountain solution more often. Then, we either add more acid or start with a fresh batch."
It seems that some printers paid attention when their graphic arts teachers introduced the intricacies of fountain solutions. Both professors Mott and Frazier also point out that the instruments used to take measurements merit some consideration.
"The old 'dunk-and-dip' color strip for measuring pH is inaccurate at best and misleading at worst," says Mott. "Today, you can buy accurate electronic instruments that measure both conductivity and pH for about $250.
"Keep in mind that the scale on the paper strips only records pH measurement in half steps but that the measurement indicates a logarithmic progression. A half step means that there is five times more or less acid. Furthermore, a strip's validity also depends on whether the person reading it has normal color perception. Ironically, press operators are known for having color perception problems."
"The strips provide ball-park information," explains Frazier. "You need to use a meter for accuracy." He also points out that it's important to know your instruments and check their calibration.
"Conductivity meters are more consistent from brand to brand, while pH meters vary brand to brand," he says. "No matter what the make, however, pH meters should be calibrated every day.
"As for taking the readings, we recommend that it be done at least once at the beginning of a shift because that's a logical time to do it," Frazier adds. "Whether you have to take more readings depends, for instance, on paper contamination. How you can tell when to change then becomes a question. We've established aim points of 2,200 mmhos conductivity or pH 4.5, whichever comes first."
Logically, then, these procedures are integral tools in any TQM program.
"Our quality program may not be as formal as one set up by a consultant, but we do have what we call the 'skeleton' of TQM," says Jeff Wainscott, president of Weadon Progressive Communication Services (Alexandria, VA), which employs 65 people and runs four two-color presses printing general commercial products. "Conductivity and pH measurements are absolutely a part of the quality program and are taken once a shift."
Alan Lithograph in Inglewood, CA (Los Angeles), a $25 million high-end sheet-fed and heatset web commercial printer, recently embraced a formal TQM program, designated Total Customer Satisfaction (TCS). Plant manager Steve Tomlins says measurements are part of the system for keeping the process in control.
"The procedures are basic," Tomlins explains. "Since our tap water is not really hard and the conductivity doesn't fluctuate a great deal, we are not treating it. The idea is to keep the process consistent. We generally start between 1,800 mmhos to 2,000 mmhos for sheet-fed and web presses and measure both when the fountain solution is mixed and at least once a shift."
"These readings are definitely part of statistical process control," concludes Mott. "They would be part of the internal auditing function, and any good SPC program will have this."