DefoamerIntroduction:
Defoamers in water-based inks can quickly remove bubbles from the system and also have an anti foaming effect. Water based defoamers are not only environmentally friendly with low usage, but also do not affect the performance of water-based inks, while improving the surface properties of water-based inks. Therefore, using water-based ink defoamers is a very good choice.
Defoamers used for water-based inks:
The reason why water-based ink is prone to producing bubbles actually depends on its composition: water-based ink is generally composed of insoluble pigments, water-soluble or water dispersible resins, surfactants, water, a small amount of ethanol, and other additives. It belongs to the alkaline system, also known as the saponification system, similar to soap water or detergents, and is prone to producing bubbles when frequently flipped.
The phenomenon of bubbles generated by water-based ink is particularly prone to occur when printing large areas with open ink supply. When using a closed-loop ink supply system, this drawback can be described as negligible.
How to improve foam suppression performance:
Adding defoamers is a direct and effective method, but it is worth noting that most domestic manufacturers use silicone based defoamers. Excessive addition can cause ink particles to thicken, resulting in pinholes in printed patterns and small dents, cracks, and other defects in flexible plates. Therefore, it is important to control the amount of defoamers added, preferably at around 0.5% to 1.5%. As for other aspects of defoamers, they have been described earlier.
As for the mechanical aspect, a front ink blocking plate can be used to increase the printing speed appropriately, making it difficult for bubbles to transfer to the mesh roller. Make full use of the circulation pump to supply ink, the lower layer of ink in the ink hopper is relatively stable, and the bubbles are relatively light, generally floating on the surface of the ink and not entering the ink chamber with the ink delivery tube. Adding a front ink blocking plate can create a relatively stable semi closed ink area near the inner web roller in the open ink hopper, and block the continuously generated bubbles outside this area, reducing the probability of bubbles approaching the web roller. Appropriately increasing the vehicle speed increases the pressure in this semi enclosed area, effectively limiting the duration of air bubbles. These two effects coincide with the advantages of a closed ink supply system, making it a very scientific and effective method.
Controlling viscosity and pH value is because ink is prone to producing bubbles when it is too thick or excessively diluted. The reason why ink thickens is also due to the large contact area between the ink hopper and the air in the open ink supply system. Ammonia or amines, which are easily volatile components in the ink, evaporate and escape, causing a slight imbalance in the alkaline system. The most obvious manifestation at this time is an increase in ink viscosity and a decrease in pH value. The method used is to add a stabilizer with a pH value of 11 every 30 to 40 minutes to supplement the alkaline components.
Many printing factories also use manual ink skimming methods. When the machine is stopped, the ink in the ink hopper stops flipping, and the bubbles that were originally wrapped in the ink float to the surface of the ink. At this time, tools such as cardboard can be used to skim off the bubbles, reducing the number of times defoamers are added, which also helps to maintain the printing adaptability of the ink and reduce the occurrence of dents in the flexible plate.
How to improve the anti foaming performance, in addition to using ink defoamers, there is actually a simpler way. After adding two self-made ink blocking plates, insert two pieces of waste cardboard into the ink flowing along both sides of the front baffle. At this time, the cardboard must be perpendicular to the direction of the flowing ink. The key is to insert the side ink blocking plate at a depth that is neither too deep nor too shallow, controlled at the boundary between the bubble layer and the ink layer.
