The selection of screen printing ink should be adaptable to the printing equipment and environment, with both good printability and excellent performance.
1. Dryness. The requirement for drying performance of screen printing is that the ink on the screen plate can stay dry for a long time without forming a film, and after printing, it is required to dry as dry as possible on the substrate. When using multi-color continuous overprinting, there is a higher requirement for the drying performance of screen printing ink.
2. Wire drawing properties. Due to the high molecular weight and strong viscosity of the connecting material in the ink, when the printing plate is lifted, there are many ink filaments on the back of the screen, which is called drawing. This is a taboo phenomenon in silk screen printing, as it not only easily causes printing and screen printing to become dirty, but also makes silk screen printing impossible. Therefore, silk screen printing ink is required to have the basic performance of avoiding wire drawing during the printing process.
3. Fineness. Fineness represents the size of pigments and other solid material particles in the ink, and also indicates the uniformity of their distribution in the connecting material. The fineness of screen printing ink is generally between 15-45um. If the fineness is too large, there will be a paste in the printing process, and the pattern cannot be printed. If the screen is thicker, the fineness can also be correspondingly increased. Generally, coarser particles should be less than one-fourth of the mesh area.
4. Plasticity. Plasticity refers to the property of being able to completely or partially maintain its deformation after being subjected to external forces. Screen printing ink is a thick suspended colloid between fluid and semi solid, which has both fluidity and plasticity. When the content of pigments and other solid materials is low, the ink becomes thin and the plasticity is small. Printing ink requires a certain degree of plasticity to ensure the accuracy of printing, otherwise the printed lines may easily expand.
5. thixotropy. Thixotropy refers to the property that changes the flow performance of a fluid under the action of an external force. For example, in the process of silk screen printing, the reversible phenomenon that the ink thickens after being stationary for a certain time and thins again after being stirred can be explained by the concept of thixotropy. The smaller the thixotropy of screen printing ink, the better. To eliminate this adverse factor, the ink should be fully stirred before printing.
6. Viscosity. Viscosity is the resistance of fluid flow, also known as internal friction coefficient or viscosity coefficient. If the ink viscosity is too high, it is difficult to transfer to the substrate through the screen plate, causing printing difficulties and incomplete imprints; If the viscosity is too low, it can cause the print to expand, affect the printing quality, and even cause waste.