3. the characteristics of the ink
Ink is a paste adhesive with a certain degree of fluidity. Viscosity, yield value, thixotropy, fluidity, and drying all determine the performance of the ink.
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Viscosity: A property that prevents the flow of fluids. It is a measure of the ability of fluids to interact with each other and create a barrier to their relative mobility between molecules, that is, the resistance to fluid flow. The viscosity of the ink is related to the transfer of the ink in the printing process, the nature and structure of the paper, the viscosity of the ink is too large, the transfer of the ink during the printing process is not easy to uniform, and the phenomenon of pulling on the paper occurs, making the printing on the printing surface; the viscosity is too small. Ink is easy to emulsify, dirty, affect the quality of printed matter. The requirements for the viscosity of the ink in the printing process depend on factors such as the printing speed of the printing press, the degree of public software on the paper structure, and changes in temperature and humidity in the surrounding environment.
Yield value: refers to the minimum movement stress required to start fluid flow. If the ink yield value is too large, the fluidity will deteriorate and it will not be easy to open. If the yield value is too small, the dots at the time of printing will easily start to halo and cause the printed matter to be unclear. The size of the yield value is related to the structure of the ink and has a direct influence on the flow of the ink. It is an important indicator for the quality of offset and gravure inks.
Thixotropy: It refers to the phenomenon that the ink is stirred by the action of stirring when the external force is stirred, and the stirring operation stops and the complex recovers to its original consistency. Due to the thixotropy of the ink, after the ink is rotated by the printing press on the ink roller, the fluidity is increased, the ductility is increased, and the ink is easily transferred; when the ink is transferred to the paper by printing, the external force is lost. The ink thickens from the thin and does not spill around, forming a good print. If the thixotropy of the ink is too large, the ink in the ink fountain is not easily rotated, which affects the ink transfer function of the ink roller.
Fluidity: refers to the ink under its own gravity, will flow like a liquid, by the ink viscosity, yield value and thixotropy decided, but also with the temperature is also closely linked. The fluidity of the ink is related to whether the ink can be poured from the container, transferred from the ink tank to the ink fountain of the printing press, smoothly transferred from the ink fountain, well distributed on the printing press, transferred to the printing plate, and transferred. On the substrate, it also affects the printing effect.
The length of the ink: refers to the extent to which the ink is initially drawn into a filament without breaking. The length of the ink is related to the thixotropy, yield value, and plastic viscosity of the ink. The ink with short silk ink is an ink with excellent printing performance in offset printing and letterpress printing. It will not cause ink flying in the printing process. At the same time, the ink layer on the print is also uniform and thick. The length of ink is a common method when measuring ink performance.