Control index of the hottest ink painting applicat

Ink application technology control index

flexographic printing has developed rapidly in recent years. It breaks the traditional offset printing pattern of "unifying the world", can be "divided into three parts" with offset printing and gravure printing, and has been recognized as a "best and most promising" printing method abroad. It is no exaggeration to say that these are mainly due to flexo ink. Because it replaces the traditional solvent based ink, in addition to the unique choice of binder and solvent, it also has a wide range of printing adaptability and economic characteristics in performance, and more importantly, the excellent green environmental protection performance of ink, which fully conforms to the development trend of modern printing, and will become an important part of China's packaging products entering the international market in the future

in China, due to the rise of flexographic printing in recent years, printing workers are used to the control of traditional solvent based inks. When controlling ink, they either use inertial thinking or don't know where to start. The result is often a waste of a lot of human, material and financial resources and heavy losses. Therefore, for those engaged in flexo printing, it is particularly important to correctly understand the technical control indicators of ink

due to limited space, this paper only discusses the main technical indicators of flexo ink, such as viscosity, pH value, thickness, dryness and so on

1. Viscosity

viscosity is a property that prevents fluid flow. It is a measure of the ability of fluid molecules to interact and hinder their relative motion, that is, the resistance of fluid flow

viscosity is the most important control index in the application of ink, because it directly affects the transfer performance of ink and the quality of flexographic printing. The viscosity is not only related to the viscosity and density of the resin in the binder, but also related to the type and particle size of the pigment. In printing, low viscosity and fast ink transfer will cause the disadvantages of light color, large dot expansion, high gloss dot deformation, uneven ink transfer and so on; High viscosity and slow ink transfer will affect the transfer performance of the corrugated roller, resulting in uneven ink color, sometimes not deep color printing, dirty version, paste version and other disadvantages

low viscosity, which can be adjusted by mixing with new ink; If the viscosity is high, it can be diluted with water or water and ethanol (50% each) or adjusted with ink stabilizer. In addition, in the printing process, temperature also has a great impact on the viscosity of the ink. Usually, the viscosity decreases with the increase of temperature, and vice versa. Therefore, in the printing process, in order to maintain the same density of prints, the temperature of the printing workshop should be kept constant

2.ph value

the binder used in ink painting is mainly alkali soluble acid resin, so the control of pH value is very important. Generally, the pH value should be controlled between 8.5 and 9.5. At this time, the printing performance of ink is the best and the printing quality is the most stable

due to the continuous volatilization of amine in the printing process, the operator has to add new ink and various additives from time to time, so the pH value of the ink is changing at any time. When the pH value of ink is higher than 9.5, the alkalinity is too strong, and the viscosity of ink will decrease, resulting in slower drying speed and poor water resistance; When the pH value is lower than 8.5, the alkalinity is too weak, and the viscosity of the ink will increase, resulting in faster drying speed, which is easy to block the printing plate and the roller, causing dirt on the plate and bubbles

since the influence of pH value is directly related to viscosity, it is suggested to control the two in actual printing, especially in chromatic printing. Generally, in addition to the viscosity cup, a simple pH 77 asphalt waterproof coiled material indicator should be prepared for testing at any time. When the pH value of ink is low, a pH stabilizer or a small amount of alkaline substances can be added. When the pH value is high, solvents or diluents can be added for dilution

3. Thickness

the thickness of ink refers to the degree to which solid powder substances such as pigments and fillers mixed in the linking section are dispersed

the thickness of ink is also a very important quality index, because it is not only related to the application performance of ink (including coloring power, hue, stability, etc.), but also related to the rheological performance and economic benefits of ink. Too thick ink will cause ink pile, paste and other ills, and the coloring power and hue of the ink will also deteriorate; If the ink is too thin, it will flow greatly and will flow after printing. This flow will lead to dot expansion and affect the quality of printing. In addition, the thickness of the ink will also affect its dispersion. When the dispersity of the ink is not ideal, its printing performance will not be satisfactory, which shows that the surface of the printed matter is not smooth, smooth, soft, and will produce a "block" feeling, which greatly reduces the printing effect

in actual printing, ink with different thickness can be selected according to specific requirements. When the printing line is relatively thin and the precision is relatively high, the fineness of ink should be relatively high; When printing prints or field prints that do not require high accuracy, the thickness of ink can be appropriately reduced, which is also to reduce costs and improve economic benefits

4. Dryness

the dryness of ink is a very important technical index. In addition to the performance of the ink itself, the drying speed of the ink is also related to the printing speed, the drying capacity of the drying equipment and the performance of the printing materials. This paper only considers the factors of the ink itself

the principle of selecting ink dryness is usually that the ink should be able to be fully dried under the existing conditions of the printing machine before the next printing and before rewinding or stacking, but not on the printing plate

1 generally, with the increase of frequency, ink uses water as the solvent and alkali soluble acid resin as the binder. It is mostly used for the printing of corrugated boxes and paper bags, so the drying forms are mainly osmotic drying and a small amount of volatile drying. Because water is used as solvent, its evaporation speed is not as fast as other solvents, so the drying of ink is slower than that of solvent based ink. Therefore, it is usually necessary to add a small amount of alcohol to the solvent to improve the drying speed of ink. In addition, under the conditions of solvent determination, choosing different kinds of resins also has an impact on the dryness of the ink. Because different resins have different curing speed on the substrate and different solvent release characteristics, the dryness of the ink is also different

in practical application, solve the technical difficulties of industry pollution sources that some institutional people think, and the dryness of ink is also related to its viscosity and pH value. The ink is dry, but the viscosity may be too high, which can be solved by further dilution; The ink dries quickly, and the pH value may be lower than 8.5, which can be adjusted by adding stabilizer. In addition, quick drying agent or slow drying agent can be added to the ink according to the actual printing speed, and the drying speed of the ink can be appropriately changed to obtain a stable printing effect. The dosage of quick drying agent or slow drying agent is generally 1-2% of the total ink volume

5. Conclusion

there are many quality indicators that need to be controlled in the application of ink painting. In addition to the main indicators mentioned in this paper, they also include: color, gloss, adhesion, stability. In actual printing, in order to comprehensively improve the printing quality, we should comprehensively consider all indicators

reprinted from: Hebei packaging and printing