Waterborne ink viscosity analysis

Water-based ink is a mixture of organic pigments, binders, solvents, and related additives. The main difference is that the solvents used in water-based inks are not organic solvents but water, that is, water-based inks. The binder is mainly composed of resin and water. In order to print the desired effect, ink-and-wash inks must have appropriate operating suitability for printing. There are many factors affecting the printability of water-based inks. The following analysis will mainly focus on the effects of ink viscosity, thixotropy, adhesiveness, pH value, and paper ink absorbability on printability.

Viscosity is the size of ink cohesion and is the most important control indicator in ink applications. In the printing process, the ink has a certain viscosity is a necessary condition to maintain its normal transmission, transfer: the viscosity of the ink is too low, it will cause the color light, dot large amount of expansion, high light spot deformation, uneven ink transfer and other defects; ink viscosity High, it will affect the transfer performance of the anilox roller, uneven ink, sometimes the color is not printed deep, and easy to cause dirty version, paste version, blistering, quit and other ills. The factory viscosity of the ink is different depending on the manufacturer or the product. Generally, it is controlled within the range of 30 to 60s/25°C (with 4* cups). It is better to adjust the viscosity to 40~50s when using.

For offset printing inks, the ink can be evenly coated on the printing plate by the ink roller reconciliation. However, the flexographic printing ink is filled in the anilox roller hole and transmitted only by its own fluidity and adhesiveness. The ink is on the plate, and the ink must fill the cells in a very short period of time. Only the lower viscosity, that is, the thinner ink, has such properties. If the viscosity is too large, it will cause the following defects:

Ink transfer and transfer are difficult. Because the speed of the flexo printing machine is very fast, the first color is printed to the second color printing, and the interval is only a few seconds to a few tenths of a second. It requires the ink to have small viscosity, easy separation, fast transfer, and fast drying;

Can easily cause the paper to pull hair, remove powder phenomenon, and even cause paper peeling;

It is difficult for the ink to fill in the net room, and it is also difficult for the scraper to scrape off the ink of the net wall portion smoothly. Practice has proved that, under the same conditions, the state of the ink layer with small viscosity is more advantageous to the transfer of the ink than the viscosity.

Therefore, the flexographic ink generally has a relatively small viscosity, and the range thereof is 0.15 to 0.3 Pa·s. However, the viscosity of the ink should not be too small, otherwise it is easy to imprint and cause the ink in the dot to be easily deformed, which will deteriorate the reproducibility of the graphic and text. In severe cases, it will cause emulsification of the ink, or it will not be able to transfer and transfer normally, and gradually accumulate pigment on the anilox roller and printing plate. When the accumulation reaches a certain degree, it will cause a paste plate.

Generally for relatively smooth substrates, when the ink supply is sufficient, the transfer rate is higher, so the viscosity of the ink is required to be slightly higher; the viscosity of the ink used for the soft structure of the paper should be slightly lower.

In actual production, when a printer with a squeegee is used, the amount of ink transferred when the temperature is too low is not as stable as when the temperature is slightly higher. An increase in the temperature of the ink causes the viscosity to decrease, resulting in a decrease in the density of the print and a dilution of the ink layer. To maintain the consistency of print quality, we must maintain the consistency of ink viscosity. The printer must attach great importance to the effect of the ink temperature, and the temperature of the used ink should be stabilized at the temperature of the printing shop before printing. This measure is very important, otherwise the ink density in the printing process will be greatly changed.