Pros and cons of ink emulsification

As we all know, in the offset printing process, the emulsification of ink is inevitably present. The so-called emulsification is a phenomenon in which a liquid is dispersed into another liquid that is not in phase with it. The ink that is not emulsified at all is not, but absolutely no emulsification is also impossible. Without proper emulsification, offset printing cannot be performed well. The ink transfer process, but the excessive emulsification of the ink brings great harm to the printing. When the press is stopped, we can see that the surface of the ink roller is covered with a thick layer of ink that is like a reticular rugged burr. This is a very obvious ink over emulsification that we can directly observe with the naked eye. phenomenon. What kind of harm does the emulsified excessive ink bring to printing?

Excessive emulsification will cause the printed surface of the printed product to be lighter in color, less bright in color, dull in printed materials, and the network will be visibly deformed. The dots will have burrs, the surrounding area will be not clean, the imprint will be too weak, and the drying will be slow. The back of the printed product will be dirty and the printing will be serious. , resulting in a large number of printing inks n light shades are inconsistent, with dirty, floral version, 瞎 version, text strokes are not beautiful, printing plate is not inked. There are many factors that cause ink emulsification in the printing process, such as solid powder on the surface of the paper, fillers, electrolytes, paper acidity and alkalinity, etc., which can cause over-emulsification. To reduce the over-emulsification of the ink, it is necessary to fully understand what substances are known to cause over-emulsification of the ink.

(1) Paper

The offset papers and coated papers that are commonly used in our production process will have some surface active substances and fillers, which will be wetted by the Fountain solution and peeled off the blankets during the printing process, and will be rolled over many times. Those surface active substances are transferred to the ink roller and the water tank through the printing plate, which invisibly speeds up the emulsification of the ink. The impact of offset paper is greater, especially those with poor sizing and poor sealing of paper and loose powder. The paper powder is transferred to the ink roller through the printing plate, and is mixed with the ink in the ink fountain to reduce the viscosity of the ink and increase the water absorption of the ink. As a result, the emulsification of the ink is intensified.

(2) Ink

The ink has high viscosity, strong water resistance, and low emulsification value. If the ink has small viscosity, strong fluidity, and reduced intermolecular cohesive force, it is easy to emulsify. Another example is that pigments in inks are hydrophilic and water-resistant, and hydrophilic ones are easily emulsified.

(3) fountain solution

The fountain solution has ordinary fountain solution, non-ionic surfactant fountain solution, alcohol fountain solution and so on. The alcohol fountain solution volatilizes quickly, thereby greatly reducing the degree of emulsification of the ink. The ordinary fountain solution in the course of use must be used to test the pH value of the fountain solution, it is controlled at 3.8 to 4.6 the following, in fact, the value should also be selected according to the paper's PH value, as much as possible to maintain a weak acid Keep the ink properly emulsified. However, no matter what kind of fountain solution is used, the dosage should be controlled. The larger the amount, the easier it is to emulsify the ink.

(4) Auxiliary materials for ink transfer

No. 6 varnish or spreader can reduce the viscosity of the ink, increase the fluidity of the ink, but also reduce the water resistance of the ink, it is very easy to cause the emulsification of the ink, so the printing must control the dosage, try to control 2% -3%, must not be blindly added. In addition, diluting agent, white ink, Weili oil, dispersant, dry oil and other auxiliary materials are all easy to cause the emulsification of the ink, wherein, in particular, the white ink and Wiley oil are most likely to cause the emulsification of the ink.

(5) Workshop temperature and humidity

The temperature and humidity of the workshop, as well as the speed of the machine, all have a considerable effect on ink emulsification. For example, the higher the temperature of the shop, the stronger the fluidity of the ink, the smaller the viscosity, the weakened water resistance, the faster the machine speed, the greater the interaction, and the higher the surface temperature of the ink roller. These factors can easily cause over-emulsification of the ink, so the shop must control the temperature to around 20°C.

Reprinted from: Ink Information