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.