Water based ink application overview

The so-called water-based inks are mainly scientifically processed using water as the solvent. Compared with other printing inks, water-based inks do not contain harmful toxic organic solvents, so they have no adverse effect on the health of printing press operators during the printing process. , No pollution to the atmosphere, no pollution to the print itself. Because the ink is non-flammable, it can eliminate the hidden dangers of flammability and explosiveness in the printing shop and is conducive to safe production. Of course, the scope of application of ink and ink is not the same. The ink is mainly offset, and the ink is mainly flexo and gravure. In developed countries such as Europe, America and Japan, ink painting has gradually replaced inks and become a special ink for printing methods other than offset printing. In the United States, 95% of flexographic prints use ink and 80% of gravure prints use ink.

In addition to being environmentally friendly, ink inks widely used in foreign countries are also very superior in their performance: stable ink, high brightness, strong coloring power, non-erosion plate, strong post-print adhesion, adjustable drying speed, and strong water resistance. Color overprint and spot color printing can be used and so on. The development and application of ink and wash ink in our country started late, but it has developed rapidly, especially in recent years, it has been developing at a rapid rate. With the increase in the demand for ink and wash, the quality of domestic ink painting has also been improved. In the traditional sense, ink ink has the disadvantages of slow drying, poor gloss, ineffable water, and imprecise printing, which have been significantly improved. Under the condition that the price of imported ink is generally high, cheap domestic ink and wash ink has gradually occupied the market.

Second, the composition and characteristics of water-based ink

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.

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.

Third, the application of water-based ink

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 printing inks, the most important application areas at present are flexographic printing and gravure printing. According to information, 95% of the US narrow-format flexographic paper prints use water-based ink, and 80% of gravure prints use water-based ink. Domestic development in recent years is also relatively fast, but there is still a big gap between the number of applications and foreign countries.

The application of water-based ink is an important factor affecting the printing quality. The control index of water-based ink includes fineness, viscosity, drying speed, and pH.

In the flexographic printing, the transfer of water-based ink and the control of the amount of ink are borne by the anilox roller. Therefore, the fineness of the anilox roller must be selected according to the conditions of the product. In the field printing, an anilox roller of about 300 lines is generally selected. The ink layer is relatively thick, and the fine-grained printing of 150 lines requires the selection of an anilox roller of 600 lines. The number of screen lines of an anilox roller is generally four times the number of printed lines in order to obtain better print definition and resolution.

Viscosity is the most important control indicator in water-based ink applications and is a property that prevents fluid flow. Since the viscosity directly affects the transferability of the ink and the quality of the printed matter, the control of the viscosity of the ink is very important. In the printing process, the viscosity of the water-based ink is too low to cause defects such as light color, dot enlargement, and uneven ink transfer. On the contrary, if the viscosity of the water-based ink is too high, the transfer performance of the ink is relatively poor, and a dirty plate is likely to appear. Paste and other ills.

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.

Water-based inks are generally alkaline (mainly dependent on amines), and the pH of water-based inks is usually controlled between 8.0 and 9.5. If the pH of the water-based ink is too high, it will affect the drying of the ink. Speed; If the PH value is too low, the viscosity of the ink rises, the drying speed becomes faster, and the printing plate and the anilox roller are likely to be clogged, causing the layout to be dirty.

1. The drying of ink 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.

2, withdrawal agent: used to reduce the depth of color, the amount is not limited. The addition of a large amount of a dissolving agent may result in a slight increase in the viscosity of the ink, at which point a small amount of diluent may be added at the same time to adjust.

3, thinner: used to reduce the viscosity of ink. The use of less than 3% will not reduce the color depth of the ink and maintain the pH of the ink. Adding more diluent or diluting with tap water with high hardness will lead to the generation of bubbles, and defoaming agent can be added at the same time. The thinner should be added slowly while stirring to prevent the viscosity from being too low.

4, slow drying agent: used to reduce the drying speed of ink, the amount of 0-10%.

5, fast drying agent: used to speed up the ink drying speed, the amount of 0-3%.

6, defoamer: used to eliminate air bubbles, the amount of 1 ‰-2 ‰.

7, PH stabilizer: used to maintain the PH value of the ink, the amount to maintain the PH value of the ink is preferably 8.5-9.5.

8, thickener: used to increase the viscosity of ink, the amount of 0.5% -1%.

V. Conclusion

In China, with the rapid use of high-strength corrugated cartons in the packaging industry, the printing of corrugated cartons has received increasing attention. People pay considerable attention to the quality of water-based ink, an important material for printing. In the production of cartons, although the proportion of the cost of ink is not large, once the printing quality is affected, it will cause the return and scrap of the entire batch of cartons. Therefore, it is necessary to manufacture an excellent quality water-based ink product, and it has become very important to properly adjust its performance in printing. In recent years, with the continuous improvement of environmental protection requirements, there have been increasing requirements and restrictions on hygiene and environmental protection in packaging printing and commercial printing. Under this general trend, efforts will be made to develop water-based inks for pollution-free “green” printing materials that will yield good economic and social benefits.

Source: Chemical Forum