Analysis of Ink Frequent Failure in Printing Process--Ink Emulsification

Ink emulsification

In the offset printing process, the emulsification of the ink is an inevitable phenomenon, and offset printing relies on moderate ink emulsification to achieve ink transfer. However, if the ink is over-emulsified, a thick layer of meshed, burr-like floc-like ink can accumulate on the surface of the roller when it is stopped.

Over-emulsification of ink (sometimes the surface of the ink core roller is not inked, and some of the water is collected at the contact of the ink groove and the ink core roller) will cause the newspaper image to have a light color, a dull appearance, and a serious distortion of the dot. The drying speed of the ink is slow, and the back of the print is seriously dirty.

Factors that lead to severe emulsification of the ink are the characteristics of the ink, the properties of the printing paper, the concentration of the fountain solution, the temperature and humidity of the workshop, and the printing speed.

Ink characteristics

Inverse relationship between ink viscosity and emulsification, flowability and emulsification are proportional to each other. The ink has high viscosity, strong water resistance, and low emulsification value. On the contrary, the ink has small viscosity, strong fluidity, reduced cohesion between molecules, and is easy to emulsify. The acid value of the ink should not be too large. The free fatty acid in the ink is a typical surfactant. The higher the content, the stronger the polarity of the ink and the more serious the emulsification. At the same time, the high ink acid value requires a thicker fountain solution. Will exacerbate ink emulsification. In addition, the amount of auxiliary materials having emulsification factors such as resins, diluting agents, and driers are controlled in ink manufacturing.

2. Paper performance

The surface of the newsprint contains certain surface active substances and fillers. During the printing process, due to dampening of the fountain solution and peeling of the blanket, these substances are transferred to the ink roller through the printing plate, and then transferred back to the ink fountain by the ink roller. Mixing with the ink reduces the viscosity of the ink and destroys the ink's water resistance, resulting in increased emulsification of the ink. Therefore, it is necessary to select newsprint with tight paper, good water resistance, less powder on the surface, and less hair loss.

3. Fountain solution concentration

Common dampening fluids include common fountain solutions, non-ionic surfactant fountain solutions, and alcohol fountain solutions. Alcohol fountain solution is an electrolyte-free solution, alcohol volatilizes quickly, greatly reducing the emulsification value of the ink. The ordinary fountain solution in the use of the process must control the concentration, the conductivity of the dampening solution in the tank should be controlled between 900 ~ 1400μs, the pH value is controlled between 4.8 ~ 5.5, if the fountain solution concentration is too high Will increase ink emulsification.

4. Workshop temperature and humidity and printing speed

The temperature and humidity of the workshop and the printing speed can also cause ink emulsification. The higher the workshop temperature, the greater the ink flowability, the smaller the viscosity, the weakened water resistance, combined with the high printing speed, the increase of the peeling force, the increase of the surface temperature of the ink roller, and the extreme emulsification of the ink. In addition, when the humidity in the workshop is high, especially in the rainy season in the south, the phenomenon of “cold sweat” often occurs on the surface of the machine. The dripping of condensed water along the surface of the machine into the fountain will inevitably lead to ink emulsification. Therefore, the temperature and humidity of the workshop and the printing speed must be controlled during the production process.