There are many problems in the printing process, such as viscosity, fluidity, thixotropy, plasticity, fineness, drying, etc., which require additives to improve and optimize product performance. How to choose the right wax additive?
1, 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 to the substrate through the screen plate, resulting in printing difficulties, the trace residue; if the viscosity is too low, it will cause the trace to expand, affecting the quality of printing.
2, Flow degree. Flow is a characterization of the fluid flow performance. The flow of ink can be seen as, in the absence of external forces under the action of a certain amount of ink in a certain amount of time in the natural flow of the flat surface. The flow of ink in general control in 30 ~ 50 mm. ink flow is large, the print easy to expand, so that the gap between the small fine lines easy to merge; flow is small, the print lines easy to break the line lack of ink, printing is also difficult.
3, Thixotropy. Thixotropy refers to the nature of the fluid under the action of external forces and cause changes in mobility. Such as in the screen printing process, the ink thickens after a certain period of time at rest, and then become thin after stirring the reversible phenomenon can be explained by the concept of thixotropy. Because the shape of the pigment particles in the ink is irregular, despite the adsorption of a layer of link material, but also an irregular particle, after a certain period of time at rest, the pigment particles will be in contact or close to each other, the attraction enhanced, the ink thickened, become sticky, this temporary stability of the structure under the external stirring is soon destroyed, the attraction between the particles weakened, mobility increased, the ink thinned, viscosity decreased.
4, Plasticity. Plasticity refers to the deformation by external forces can fully or partially maintain its deformation properties. Screen printing ink is between the fluid and semi-solid thick suspended colloid, so there is both liquidity and plasticity. Low content of pigments and other solid materials, ink is thin, plasticity is small.
5, Pulling. Because of the large molecular weight of the linking material in the ink, viscous, 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 the print and screen plate sticky dirty, and even make screen printing can not be carried out, therefore, require screen printing ink has the basic performance in the printing process does not appear to pull the phenomenon.
6, Dryness. Screen printing requirements for drying performance is: the ink in the screen plate can be a longer period of 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 screen printing ink requirements are higher.
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