The reason why the PS version of the developer foams more
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The PS version users in the southeastern coastal areas of China often encounter a very headache when using the Huaguang PD type developing machine for PS plate development - a large amount of foam is generated, which affects the normal development processing of the PS plate. This phenomenon is rarely encountered in the north. Why is it easy to generate bubbles on the southeast coast, how to solve this headache problem in actual work?
In the classification of water chemical areas, the southeast coastal areas of China are humid areas with abundant precipitation and small evaporation, so the runoff is large; therefore, the soil layer is thin, and there are many hard granite rocks. The soil has been leached for many years, and most of the soluble salts have been lost. Therefore, the water has less salt content, low salinity and low hardness, and is extremely soft water (water hardness <1 meq/liter). Moreover, the tap water supplied in the southeastern coastal areas is mostly surface water. Generally speaking, surface water is softer than ground water. The tap water supplied in northern and inland areas of China is mostly groundwater with high hardness (hardness of deep well water in the north area is >300 meq/liter).
Surfactants are included in both the PS coating and the developer. The coating generally contains macromolecular and nonionic surfactants, and the main function is to solubilize and disperse in the preparation of the coating liquid. An anionic surfactant is added to the developer to facilitate developer penetration. At the same time, they also reduce the surface tension of the developer.
When the liquid forms a foam, its surface area increases. Generally, the surface tension is small and foaming is more likely, but the stability of the bubble is independent of the surface size of the liquid. The formed bubbles, due to the action of gravity, the liquid in the gas-liquid liquid film automatically flows downward, and the fluid molecules flowing in the liquid film discharge process have a larger free energy than the liquid molecules at the bottom, so the bubbles are continuously discharged. The liquid thins the membrane wall and ruptures, causing the foam to disappear. When a surface epimerizing agent molecule is adsorbed on the surface of the liquid film, the foam is stabilized because the surfactant molecular film hinders the flow of the liquid. In addition, the surfactant molecules attached to the foam film act as a "repair" to the liquid film, giving the foam good stability. Anionic surfactants are much more stable to foam than nonionic surfactants. Therefore, the foaming material at the time of development processing is mainly an anionic surfactant in the developing solution.
The type of surfactant is the main factor determining the foaming power, but the environmental conditions, such as humidity, water hardness, developer pH and additives, have a certain influence on the foaming power.
Since the hard water softener contained in the development softens the water, although the water is softened, the ion content in the water is not reduced by the softening of the water. When the Huaguang PD developer is diluted 1:4 by water, it is calculated according to the ideal state. The concentration of anionic surfactant in the working fluid is within its critical micelle concentration. In the eastern coastal areas, when the Huaguang PD developer is diluted by tap water with low salinity and low salt content, the water has little effect on the critical micelle concentration of the anionic surfactant in the developer, or has no effect at all. Therefore, the anionic surfactant in the working fluid is in the range of its critical micelle concentration, the surface tension of the working fluid is the smallest, and the foaming force is the largest, so that a large amount of bubbles are generated during use to affect the normal progress of the development process.
However, the northern part of China and the inland areas use much groundwater, with high salinity and high metal ion content. Although the softener is added to soften the water, the total number of ions does not change. With this water, the metal ions ionize the double layer of the micelle, causing the anionic surface-active ionic groups to repel each other, and more of the surfactant's ionic groups enter the micelles to cause aggregation of the micelles. The number increases. At the same time, since the counter ion is immobilized on the surfactant complex, so that the repulsive force between the ions of the same charge is reduced, the micelle is easily formed. The critical micelle concentration of the anionic surfactant is thus reduced. In general, divalent metal salt ions such as (Cu, Zn, Mg, etc.) have a greater effect on the reduction of the critical micelle concentration than monovalent metal salt ions such as (K, Na). Just because the critical micelle concentration decreases, the concentration of anionic surfactant in the working fluid is greater than the critical micelle concentration. When the surface tension of the working fluid becomes large, the foaming power becomes small. Therefore, excessive bubbles are not generated and the development is normally performed.
Since foaming is mostly related to the critical micelle concentration, it is also started by the critical gelatinization concentration for defoaming. Theoretically, the objective is to reduce the critical micelle concentration of the anionic surfactant in the working fluid.
So how do you avoid creating too many bubbles in the development? The easiest and most practical method is to add high-priced metal salts. Still another method is to add another anionic surfactant solution such as soapy water or the like to reduce the critical micelle concentration of the surfactant in the working fluid to prevent the generation of bubbles. The most practical method is to add alcohol. Because the alcohol molecules can penetrate into the micelles to reduce the repulsive force between the surfactant ions, and because the addition of the alcohol molecules is easy to form and increase, the critical micelle concentration is lowered to avoid the generation of bubbles to achieve defoaming. The role. The amount of alcohol used is: 50 ml of a mixture of ethanol: butanol = 1:1 (volume ratio) is added to 25 L: Huaguang PD developing working solution (various water quality may be increased or decreased according to the defoaming effect). In this way, a good defoaming effect can be achieved, and the problem that the developing solution is prone to foaming when used is solved.