The selection of photo emulsion should pay attention to the issues

Select photo emulsion to have adaptability with the printing equipment and environment, both good printability and excellent performance.

Dryness: screen printing requirements for drying performance are: the ink on the screen plate can be a long time without drying film, and after printing, and require it to dry on the substrate as dry as possible. Multi-color continuous overprinting, the drying performance of photo emulsion requirements are higher.

Pulling sex: due to the large molecular weight of the linking material in the ink, viscous strong, when the printing plate is lifted, the back of the screen appears a lot of ink filament phenomenon called pulling. This is a more taboo phenomenon in screen printing, it is not only easy to make prints and screen plates sticky dirty, and even make screen printing can not be carried out, therefore, require photo emulsion with the basic performance of the phenomenon of pulling silk in the printing process.

Fineness: fineness indicates the size of the pigment and other solid material particles in the ink, but also that these particles in the connection material distribution of the uniform degree. The fineness of photo emulsion is generally between 15 to 45um. Fineness is too large, in printing will produce a pasted plate, can not print the pattern. If the screen is coarse, fineness can also be increased accordingly. Generally, coarser particles should be less than a quarter of the mesh

area.

 

Plasticity: plasticity refers to the nature of deformation by external forces that can be fully or partially maintained after the deformation. Photo emulsion is a thick suspension colloid between fluid and semi-solid, so it has both fluidity and plasticity. Low content of pigments and other solid materials, the ink is thin, plasticity is small. Printing ink requires a certain degree of plasticity to ensure the accuracy of printing, otherwise, the printed lines are easy to expand.

Thixotropy: Thixotropy refers to the fluid under the action of external forces and the nature of the fluidity caused by changes in performance. Such as in the screen printing process, the ink at rest for a certain period of time after thickening, stirring, and then become thin reversible phenomenon can be explained by the concept of thixotropy. The thixotropy of photo emulsion, the smaller the better, in order to eliminate this disadvantage, before printing, to fully stir the ink.

Viscosity: viscosity is the resistance to fluid flow, also known as the coefficient of internal friction or coefficient of viscosity. If the ink viscosity is too high, it is not easy to transfer through the screen plate to the substrate, resulting in printing difficulties, the print residue; if the viscosity is too low, it will cause the print to expand, affecting the quality of printing, and can even cause scrap.