The biggest feature of water-based ink is to reduce the emission of VOC (organic volatiles) into the atmosphere, thus preventing air pollution, improving the printing operation environment, and greatly reducing the potential for fire hazards. It can completely eliminate the harmful effects of certain toxic substances in solvent-based inks on the human body and the pollution of packaged goods, and improve the overall environmental quality. It is particularly suitable for packaging and printing products that require strict sanitary conditions such as foods and medicines.

Water-based inks are made from water-soluble resins, advanced pigments, solvents, and auxiliaries that have been scientifically compounded and ground. The water-soluble resin mainly acts as a binder in the ink, which is to uniformly disperse the pigment particles, so that the ink has a certain fluidity, and provides adhesion with the substrate material, so that the ink can form a uniform film layer after printing. . The hue in the ink is mainly determined by the pigment. The pigment is evenly distributed in the binder in the state of particles. The pigment particles can absorb, reflect, refract, and transmit light, and thus can exhibit a certain color. It is generally required that the pigment has a vivid color, a proper coloring power and hiding power, and a high degree of dispersion. In addition, depending on the purpose of use, it is also possible to have different wear resistance. The role of the solvent is to dissolve the resin, so that the ink has a certain degree of fluidity, can be successfully transferred during the printing process, and adjust the viscosity and drying properties of the ink. Water-based ink solvents are mainly water and a small amount of ethanol.

Flexographic water-based inks are generally used without dilution. Their viscosity can range from 30′′ to 45′′/25° C. (coated with 4# cups). The viscosity of the flexo-based water-based ink used in the carton can be lower, as long as the water stabilizer is added regularly. The viscosity change can be basically controlled. The gravure water-based ink is generally diluted with a diluent of ethanol and water 1:1 according to the conventional practice, and the viscosity is generally controlled at 15′′-25′′/25°C.

Drying of ink and wash is mainly volatile drying and infiltration drying. The drying performance of ink refers to the time required for the ink to dry after being transferred to the substrate. This is one of the important indicators for measuring the quality and performance of the ink. Therefore, controlling the drying performance of the ink is an important step to obtain good printing results. means.

The drying speed of a flexographic water-based ink depends on the printing speed of the printing press, the drying capacity of the drying equipment and the properties of the substrate material, and the ink's own composition. The general principle for selecting the ink drying speed is that under the existing conditions of the printing machine, the ink should be sufficiently dry before the next printing group and before rewinding or stacking, but it cannot be dried on the printing plate. If the ink dries too quickly, it will dry and build up on the plate and anilox roller, and it may clog the anilox roller, resulting in the loss or destruction of the halftone dots, and the leak in the solid part; if the ink has dried faster Slow, there will be print odor phenomenon, or in the case of multi-color overprint will cause the back of the dirty.

In fact, the ink viscosity and PH value will also have a certain influence on the drying performance of the ink. For example, if the viscosity is too high, the drying speed of the ink will be reduced. If the PH value is too low, the ink will be dried too quickly. Therefore, in the printing process, the viscosity and pH of the water-based ink should be adjusted and controlled first, and then an appropriate amount of quick-drying agent or slow-drying agent should be added to the ink according to the actual printing speed to adjust the drying speed of the water-based ink.

The fineness of water-based ink refers to the size of the pigment particles in the ink and its uniformity of dispersion in the binder. It is also a very important quality indicator. The fineness of the ink will not only have a certain influence on the coloring power and the color equal performance of the ink, but also affect the rheology of the ink. Ink particles are too thick, it is easy to cause the edge of the network hair, paste, and other ills; However, if the ink particles are too thin, the ink flow is too large, it will cause the network to expand, will inevitably affect the quality of printed matter.

Commonly used additives in water-based inks are: pH stabilizers, slow-drying agents, defoamers, dilutants, and the like.

(1) PH stabilizer. PH stabilizer is mainly used to adjust and control the pH value of water-based ink, making it stable within the range of 8.0-9.5. At the same time, it can also adjust the viscosity of water-based ink and dilute the ink. In general, appropriate amount of pH stabilizer should be added at regular intervals during the printing process to keep the water-based ink in a good printing state.

(2) Slow drying agent. The slow drying agent can suppress and slow the drying speed of the water-based ink, prevent the ink from drying on the plate or the anilox roller, and reduce the occurrence of printing failures such as blocking and stencil printing. Control the amount of slow drying agent, generally should be controlled in the 1%-2% of the total amount of ink, if you add too much, the ink is not completely dry, the print will be dirty or produce odor.

(3) Defoamer. Defoamers function to suppress and eliminate the generation of bubbles. In general, when the viscosity of the water-based ink is too high, the PH value is too low, or when the printing press operates at a high speed, air bubbles are likely to be generated. If the amount of air bubbles generated is large, there will be a leakage of white ink and uneven ink. It will affect the quality of prints.

Water-based ink complies with environmental requirements. The product has non-toxic, non-corrosive, non-irritating odor, non-flammable, non-explosive, good safety, convenient transportation, high concentration, low dosage, low viscosity, good printing adaptability, and performance. Stable, good adhesion fastness, fast drying, excellent water resistance, alkali resistance and anti-wear performance after drying; easy to adjust operation before printing, after printing and printing process, the printed matter appears full of prints, bright colors, high gloss, Rich and rich, printed complex patterns can also reach rich levels, can print bright and high-gloss colors and other characteristics.

Reprinted from: 21st Century Fine Chemicals Network