Views: 1 Author: Site Editor Publish Time: 2023-11-03 Origin: Site
Most of the relatively thin ink can be pumped to transport, in the transport process, there will be a lot of air mixing, bubbles. In addition, in the printing process, because the ink is very thin, it will also produce a large number of bubbles when it is scraped off the plate (such as photogravure) or flowed off the roll (such as flexographic and relief ink).
The appearance of bubbles in the ink not only reduces the quality of the printed product, but also may make the printing unable to proceed normally when a large number of bubbles are produced in the ink fountain.
Aromatics, alcohol-based, water-based inks have this phenomenon, j and water-based inks are the most serious, because the water-based inks are usually alkaline amines or amine-soluble proteins, shellac, acrylic copolymers or mixtures of them. It is like soap (or detergent) in water, so the foam is very strong.
Because water-based inks are non-flammable inks; At the same time, they are cheap and therefore meet environmental protection requirements.
Solving the bubble problem is very important for various printing processes, especially the use of water-based inks.
1. Brief mechanism of foam formation and destruction
A bubble is a mass of gas surrounded by a membrane wall of liquid. The bubble wall itself can form a very consistent geometry, and when three bubble walls (films) meet together, l20 is formed. Horns. At least two or more components can form bubbles, and pure liquids cannot form bubbles, because the volume fraction of the gas in the bubble is generally more than 90%.
When a single molecular film of a surfactant that is soluble in a liquid appears on the surface of the liquid, bubbles are created. The elasticity of the liquid surface can also cause bubbles.
In general, the bubble itself is unstable, and its destruction generally occurs due to the displacement of liquid from the bubble wall into the edge of the wall. When the membrane wall is crowded to a thickness of about 10nm, the molecular movement within the membrane wall is sufficient to destroy the liquid membrane and destroy the bubble structure.
2, the function of defoamer
The function of defoamer is generally to eliminate bubbles through its chemical reaction. A chemical (such as an acid or calcium salt) is added to the bubble so that it reacts chemically with the film-forming substance to eliminate the bubble.
However, the function of most antifoam agents is to spread out on the surface of the foam, so that it replaces the molecules of the bubble film on the liquid surface. Usually a surfactant with a strong ability to reduce surface tension is used as a defoamer, and this surfactant molecule is easily adsorbed on the surface. Most industrial defoaming agents also use spreading solvents or emulsifiers as carriers, which can ensure that the defoaming agent can reach all parts of the surface well and play an effective defoaming role.
Another method is to add two good solvents in the system to disperse the surfactant into the liquid, which can also greatly reduce the formation of bubbles.
Silicone oil defoamer is an effective defoamer for both aqueous and non-aqueous systems. They are formed by a series of chemical reactions between powdered silicon and a number of organic chemicals.
Silicone is one of them, it has some special properties that can not be obtained by other materials, because it retains both inorganic properties and organic properties.
The surface tension of the silicone oil liquid is very low, which is because it contains silicon. The surface tension of t dimethylsilicone oil is only about 2.0 ×10-2N/m, compared to 3.5 ×10-2N/m for hydrocarbon oil and 7.28 ×10-2N/m for water. Therefore, as long as a small amount is used, it can play a defoaming role.
The system has a good defoaming effect on water-based inks: after chain closure of trimethylsilicone oil, adjust the relative density with aliphatic hydrocarbons (such as gasoline) to 1. Add 1 times the water and 5% of the emulsifier (such as tween-80) for high-speed stirring, so that it can be fully emulsified and dispersed.
For flexible relief inks and photogravure inks containing aromatics, silicones, especially polymethyl silicones, are more effective. Silicone doesn't work well with alcohol inks.
In general, adding defoamer when manufacturing ink is better than adding it when printing, which is easy to make spots and other drawbacks of printed products. The amount of defoamer is generally a few percent to a few percent.