Effect of Surfactant on the Surface Tension of Fountain Solution

The smaller the surface tension of the fountain solution, the better its spreading performance. Under normal circumstances, pure water has a high surface tension of up to 72.75 x 10-5 N/cm. Therefore, it is necessary to reduce its surface tension in order to apply it to wetting plates. The best way at present is to add surfactants in pure water, such as adding ethanol, isopropanol, and some other lower alcohols, lower carboxylic acids, etc. The surface tension of the solution decreases rapidly as the concentration of the substance increases. If the concentration of the substance continues to increase, the surface tension hardly changes. Therefore, the amount of the surfactant added to the solution should be appropriate, and should not be excessive.
Surfactants are "biparental" molecules that consist of a non-polar lipophilic hydrocarbon chain portion and a polar, hydrophilic group. Its properties depend on the structure of the hydrophilic group. Therefore, the surfactant can be classified into cationic surfactant, anionic surfactant, and amphoteric surface depending on whether the hydrophilic group is ionized in water and ionized ion type. Active agent, non-ionic surfactant 4 major categories.
Cationic surfactants, which are easily adsorbed on solid surfaces in media, are often used as flotation agents.
Anionic surfactants can be ionized in water and the surface active base is negatively charged.
The molecular structure of the amphoteric surfactant is similar to the amino acid in the protein, and there are both an acidic group and a basic group. When ionized in acidic solution, the surface active baseband is positively charged; when ionized in alkaline solution, the surface active baseband is negatively charged; in neutral solution it is neither ionized nor charged, and has the function of preventing metal corrosion and surface static electricity due to its surface The activity is not affected by the acidity and alkalinity of the solution, so it can be considered for use in fountain solutions.
Non-ionic surfactants do not ionize in aqueous solution. Hydrophilic groups mainly consist of a certain number of oxygen-containing groups. They are not affected by strong electrolytes, inorganic salts, acids and alkalis and have high stability. The non-ionic surfactant is added to the fountain solution and does not react chemically with the other electrolytes in the fountain solution. Therefore, the use of non-ionic surfactants to reduce the surface tension of fountain solution is most appropriate.
The blank part of the offset printing plate is affixed with a fountain solution, and the graphic part is attached with ink. If the surface tension of the ink is less than the surface tension of the fountain solution, under the effect of the diffusion pressure, the ink will infiltrate into the direction of the fountain solution to form dots of the printing product. Expand, dirty in the blank part. Conversely, if the surface tension of the fountain solution is less than the surface tension of the ink, the fountain solution soaks in the direction of the ink under the influence of the diffusion pressure, so that the dots of the printed product disappear. Only when the surface tension of the fountain solution is equal to the surface tension of the ink, the diffusion pressure at the interface is zero, the fountain solution and the ink remain relatively balanced at the interface and do not wet each other, and the printing effect is ideal. In general, the surface tension of offset ink is about 30~36*10-5N/cm, and the ink balance of offset printing is achieved under dynamic conditions, so the surface tension of fountain solution should be slightly higher, preferably at 35~ 42×10-5N/cm. Therefore, the concentration of the surfactant in the fountain solution should be such that the surface tension of the fountain solution reaches a concentration corresponding to 35 to 42×10 -5 N/cm. If this concentration is exactly the critical micelle concentration of the surfactant, then More ideally, a stable surface tension solution can be obtained.