Indicating Technical Control Indicators for Ink and Wash Applications

Flexo printing has developed rapidly in recent years. It has broken the traditional offset printing pattern of "dominant world" and can be used with offset printing and gravure printing. It has been recognized as a "best and most effective" in foreign countries. The future of development is printed. It is no exaggeration to say that these are mainly the contributions of flexo ink. Because it replaces traditional solvent-based inks, in addition to its uniqueness in the choice of binders and solvents, it also has a wide range of printing adaptability and economical properties in terms of performance. What is more important is the excellent environmental protection of ink. Performance, in full compliance with the development trend of modern printing, will inevitably become an important part of China's packaging products into the international market.

In China, since flexo printing has only emerged in recent years, printers are accustomed to the control of traditional solvent inks, and when they control ink, they either use inertial thinking or simply do not know where to start. It is often a waste of large amounts of manpower, material resources, and financial resources, resulting in heavy losses. Therefore, for those who are engaged in flexo printing, it is particularly important to properly understand the technical control indicators of ink and wash.

Due to limited space, this article only discusses the main technical indicators of flexographic ink viscosity, PH value, thickness, dryness.

1. Viscosity

Viscosity is a property that impedes the flow of fluids and is a measure of the ability of fluid molecules to interact with each other and hinder their ability to move relative to each other, that is, the resistance to fluid flow.

Viscosity is the most important control indicator in ink applications because it directly affects the ink transfer transfer performance and flexographic print quality. Viscosity is 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 the printing, the low viscosity of the ink transfer is fast, resulting in the disadvantages of light color, large dots, high light dot distortion, uneven ink transfer, etc.; high viscosity, slow ink transfer, will affect the transfer performance of the anilox roller, resulting in ink color Inconsistent colors, sometimes dark prints, and dirty, dirty version, and other ills.

Low viscosity can be adjusted by mixing with new ink; high viscosity can be diluted with water, water and ethanol (50% each), and can also be adjusted with ink stabilizer. In addition, in the printing process, the temperature has a greater influence on the viscosity of the ink, usually the viscosity increases when the temperature rises, and vice versa, the viscosity increases. Therefore, in the printing process, in order to maintain the consistency of the print density, the temperature of the printing shop should be kept constant.

2. PH value

Since the binder used in the ink is mainly an alkali-soluble acidic resin, the control of the pH value is very important. Usually the PH value should be controlled at 8.5 to 9.5. At this time, the printing performance of the ink is the best and the quality of the printing product is the most stable.

Since amines are constantly evaporating during the printing process, operators are also required to add new inks and various additives from time to time, so the pH of the ink is changing at any time. When the PH value of the ink is higher than 9.5, the alkali is too strong, the viscosity of the ink will decrease, resulting in slower drying speed and poorer water resistance; when the PH value is lower than 8.5, the alkali is too weak, and the viscosity of the ink will increase. High, resulting in faster drying speed, easy to jam the printing plate and anilox roller, causing the plate surface to be dirty, and it will produce bubbles.

Since the influence of PH value and viscosity are directly related, it is recommended that the two be linked together in actual printing. Especially in case of color printing, this problem should be paid more attention. Usually, in addition to the viscosity cup, a simple pH indicator should also be prepared for testing at any time. When the PH value of the ink is relatively low, a pH stabilizer or a small amount of an alkaline substance may be added. When the pH is high, a solvent or diluent may be added for dilution.

3. Thickness

The thickness of the ink is the degree to which solid powdery substances such as pigments and fillers mixed in the linking section are dispersed.

The thickness of the ink is also an important quality indicator because it is not only related to the application properties of the ink (including tinting power, hue, stability, etc.), but also related to the rheological properties and economic benefits of the ink. Ink is too thick to cause defects such as heaping ink, stencil, etc., and the coloring power and hue of the ink will also be deteriorated. If the ink is too thin, the liquidity will be large, and it will flow after printing. This flow will cause the dot expansion, affecting Print quality. In addition, the thickness of the ink also affects its dispersibility. When the dispersibility of the ink is not satisfactory, its printing performance is not satisfactory, and the print surface is not smooth, smooth, and soft, and it will produce a "block"-like feeling, thus greatly reducing the printing effect.

In the actual printing, inks with different thicknesses and fineness can be selected according to specific requirements. In the case of prints with relatively fine mesh and high precision, the fineness of the ink must be relatively high. When the print is not very precise or the actual print, the thickness of the ink may be appropriately reduced. This is also for the sake of Reduce costs and increase economic efficiency.

4. Dryness

Dryness of ink is a very important technical indicator. In addition to the performance of the ink itself, the drying speed of the ink is related to the printing speed, the drying capacity of the drying equipment, and the performance of the substrate. This article only considers the ink's own factors.

The principle for selecting the ink drying property is usually: the ink should be able to be fully dried before the next printing and before rewinding or stacking under the existing conditions of the printing machine, but cannot be dried on the printing plate.

Ink adopts water as a solvent and uses alkali-soluble acidic resin as a linking material. It is mostly used for the printing of corrugated boxes and paper bags. Therefore, the drying form is mainly osmotic drying and a small amount of volatile drying. Since water is used as a solvent, its volatilization rate is lower than other solvents, and thus the ink drying is slower than the solvent ink. Therefore, a small amount of alcohol is generally added to the solvent to increase the drying speed of the ink. In addition, the selection of different types of resins under solvent-specific conditions also affects the drying properties of the ink. Because different resins have different curing speeds on the substrate and different solvent release characteristics, the ink drying performance is also different.

In practical applications, the drying property of ink is also related to its viscosity and PH value. The ink is dry but may be too viscous, and can be solved by further dilution; the ink dries quickly, it may be PH value below 8.5, and stabilizers may be added for adjustment. In addition, a quick-drying agent or a slow-drying agent may be added to the ink according to the actual printing speed, and the drying speed of the ink may be appropriately changed to obtain a stable printing effect. The amount of quick-drying agent or slow-drying agent is generally 1% to 2% of the total amount of ink.

5. Conclusion

There are still many quality indicators that need to be controlled in the application of ink and ink. In addition to the main indicators mentioned in this article, they also include: color, gloss, adhesion, and stability. In actual printing, in order to comprehensively improve printing quality, comprehensive consideration should be given to index.

Reprinted from: 21st Century Fine Chemicals Network