Fountain solutions

Duplicator and Business Form Inks. Duplicator sheet-fed machines require very press-stable yet quicksetting inks. They must also possess good lithographic properties of wide tolerance for fountain solution and provide good printing properties on a wide variety of uncoated papers. 

The basic requirements for the successful use of iron blue as a toning agent in offset printing inks are resistance to damping or fountain solutions and good dis-... 

An overview of the lithographic process is presented with particular emphasis on the role that surface and colloid chemistry plays. Recent research has shown the importance of these chemistries in fountain solution, ink and plate interactions and the effect of these interactions on the dynamic behavior of the lithographic ink on press. Data on the rheological behavior of preformed fountain solution/ink emulsions is presented along with an evaluation of prints made with the inks on an actual press run. The importance of pre-testing the emulsification behavior of printing inks in predicting their printability is demonstrated. 

A laboratory procedure designed to measure the rate of emulsification of fountain solution into ink rather than merely the amount emulsified is shown to be predictive of press performance. 

In order for a lithographic ink to move smoothly and uniformly through the press to the substrate, it is essential that the ink be able to absorb a reasonable quantity of the fountain solution being used as emulsified droplets. Many authors have observed this fact (Banks, (1), Surland (15,, MacPhee (18)) and... 

Some workers have interpreted the emulsification of fountain solution in an ink from the point of view of surface energetics and colloidal behavior. Surface measurements in the form of contact angles, spreading coefficients, interfacial tensions and surface tensions have been widely used to explain the interactive behavior of inks and fountain solutions. 

Rosted (12) states that the amount of fountain solution emuisTfied in the ink is related to the plastic viscosity and tack and that interfacial tension between ink and fountain solution determines the amount of water adhering to the ink surface. The latter observation was confirmed by Karttunen (8), and he also observes that high interfacial tension is accompanied by low bonding efficiency of the water to the ink thus resulting in thin surface water films on press ink rollers. 

Banks (1) in a paper on litho fountain solutions, observed thaT most abnormal litho behavior such as scumming is accompanied by the spread of an oily film over the fountain solution. He also claims that if the fountain solution is adjusted to a surface tension in the range of 36-30 dynes/cm, the spreading of this sensitizing film from the ink will be inhibited. He feels that the prevention of spreading is not dependent on the particular composition of the fountain solution but only on its surface tension. 

Hansen (6) has observed that the interfacial tension of an offset ink with fountain solution should be neither too high, which would prevent sufficient emulsification, nor too low which would cause scumming. He states that the normal range for a good ink should be between 15-25 dynes/cm. 

Several workers have also commented on the possibility of using dynamic surface tension measurements on the fountain solution as being more realistic in view of the fast printing speeds used. This might also make measurements of dampening solutions containing surface active agents correlate better with actual press performance due to the rate of diffusion of materials to the surfaces of these fluids. 

The ink on the image area of the plate has increased in the polar component. This is likely due to the emulsification of fountain solution in the ink as well as surface fountain water both of which may leave a hydrophilic residue upon evaporation. 

However, the ink as actually printed on a lithographic press is an emulsion which may contain as little as 20% or as much as 50% of fountain solution as a finely dispersed internal phase. It is the rheology of this ink emulsion which determines the configuration of the printed areas and the faithfulness of the reproduction of the plate image. 

In this investigation, a set of six experimental heatset lithographic inks were subjected to a variety of rheological measurements both as a dry ink, as well as after being emulsified with a commercial fountain solution. Determinations of apparent viscosity at 2500 secs l and yield stress at 2.5 secs l were made 25°C from 5 point shear rate/stress curves, and inkometer tacks at 1200 RPM/90°F were also measured. 

The rheology of ink emulsions is clearly of prime importance in theprintability and dot resolution of an ink and is significantly influenced by both ink and fountain solution chemistries. 

In view of the complex interactions which occur in lithography due to the presence of the fountain solution, it is not surprising that considerable research effort has been exerted to eliminate dampening systems from planographic press operations. 

The prevalent explanation for isopropanol s role in this kind of dampening system is that its surface tension, about 29 dynes/cm, sufficiently lowers the aqueous fountain solution surface tension to allow wetting of the inked form-roller by that solution, as illustrated in Figure 1. That is, the fountain solution wets and spreads onto, and is carried by the ink film on the form-roller to the printing plate, as a relatively thin, uniform film. 

The rapid, diffusional displacement of fountain solution into or out of the ink, allows extremely rapid, intimate, ink-to-ink contact necessary for replenishing the ink in the image areas that was used in the printing process. It also allows rapid recovery when ink or water feed rates are changed. There is a place for spurious water to go. 

Lithography is not thwarted by this omni-present, overall thin, aqueous, alcoholic film of fountain solution because it automatically gets out of the way of ink transfer as required, by instantly disappearing into whichever layer, ink or fountain solution, is relatively moisture-starved. 

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