Measure the main index of flexo ink

What are the main indicators of flexographic ink? Here we come to detail and we introduce:

1, fineness

Fineness is a physical index that measures the size of pigments, fillers, and other particles in the ink and is directly controlled by the ink manufacturer. The user generally understands it and cannot change its size during use. The fineness of flexographic water-based ink is generally less than 20μm. The instrument for measuring fineness is a fineness scraper.

2, viscosity

Viscosity is one of the main indicators of water-based inks. Viscosity values ​​will directly affect the quality of prints. Therefore, the viscosity of water-based inks must be strictly controlled during flexographic printing. The viscosity of the water-based ink is generally controlled in the range of 30-60 seconds/25°C (with a No. 4 cup of paint), and the viscosity is generally controlled to be between 40-50 seconds. If the viscosity is too high and the leveling property is poor, the printability of the water-based ink may be affected, and the phenomenon of a dirty plate, a paste plate, etc. may easily occur. If the viscosity is too low, the ability of the carrier to drive the color material may be affected.

If aqueous inks are left for a long time, some poorly stabilized inks tend to precipitate and delaminate, and some may experience false thickening. At this time, sufficient stirring can be performed and the above problems can disappear naturally. When using fresh water-based ink, be sure to mix evenly beforehand and then make dilution adjustments. In normal printing, the ink fountain must be stirred regularly.

Water-based ink freezes easily below 0°C. If the water-based ink freezes, it can be placed in a room with high temperature, let it dissolve naturally, and after mixing, it can be used continuously. In the large temperature difference between winter and summer, the performance of viscosity is the most sensitive. When the temperature is high, the water evaporates quickly and the drying is fast. During the operation, it is necessary to pay attention to reducing the drying time or increasing the speed of the machine. When the temperature is low, the water evaporates slowly and the water-based ink will dry slowly. In the operation, the water-based ink may be dried faster. Speed ​​or add drying device. When using in winter, it is better to place the water-based ink stored in the warehouse into the workshop in advance to balance the viscosity.

3, drying

Drying is one of the most important indicators in water-based inks, because the speed of drying is the same as the viscosity and can be directly expressed in the quality of prints. The operator must understand the principle of drying in detail in order to properly set the drying time of the water-based ink according to the product or substrate. To ensure that the water-based ink dries well, it must also be considered that the viscosity is moderate or the pH is stable.

The drying of water-based ink includes three ways of volatilization, absorption and reactive solidification. After the water-based ink print is completely dried, it has a strong water resistance and rubbing resistance. Drying is too fast, the surface of the ink layer is easy to crust, the water-based ink is easy to dry onto the printing plate, causing the surrounding of the dirty plate and the pattern to be unclear, and the internal water cannot be excluded, resulting in inaccurate overprinting, which can be adjusted with a retarder. This can be solved by increasing printer speed or shutting down the drying system. When shutting down, it is best to clean the anilox roller or ink fountain. When it is stopped for a short time, it is necessary to stir the ink fountain frequently to prevent surface crusting. Drying is too slow, the paper is stretched, and the luster is reduced. This can affect the overlapping printing and may cause blocking. This brings a lot of trouble to the operator of the machine. At this time, it should first check the pH value is correct, according to the level of pH, add appropriate amount of stabilizer or ethanol adjustment, so that water-based ink drying faster.

4, pH

Water-based ink contains a certain amount of ammonium solution, which is used to increase its stability or enhance the water resistance after printing. Therefore, pH is one of the important indicators.

The pH value of the water-based ink at the factory is generally controlled at about 9. The pH value of the machine table can be adjusted or controlled between 7.8 and 9.3. It should be flexible according to the different substrates and temperature. At the same time, it is necessary to take into account the relationship between the drying and the viscosity, and add appropriate amounts of various additives to adjust. The pH of golden ink should not be too high to be controlled between 8 and 8.5, making it slightly alkaline. Usually 2 to 3 hours to test once, with the follow-up adjustment, try to control the pH value in the best printability range.

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