Drum screen printing ink in different environments (3)

8. Lightfastness of ink
The light resistance of the drum screen printing ink is the strength of the ink resistant to light. Ink fading is caused by the absorption of light energy by pigment molecules. The lightfastness of inks depends mainly on the lightfastness of the pigments or dyes. The lightfastness of the graphics printed on the drum surface depends on the lightfastness of the pigments, the material of the drum, the thickness of the ink layer, the degree of adhesion of the binder and the ink. 
9. Chemical resistance of ink
The ability of steel drum screen printing inks to resist water, acids, alkalis and solvents is collectively referred to as chemical resistance. The measurement standards and methods are based on the actual application. At present, there are commonly used soaking methods and wet rubbing methods. The soaking method is to immerse the dried steel drums in the selected water, acid, alkali and solvent, and remove them after a certain period of time, and compare the degree of change before and after soaking in the steel drum printing graphics; the wet wiping method is a cloth. After soaking in the selected solution, wet and dry several times on the dried steel drum after printing, and then compare the difference between the wet and the rubbing of the steel drum after printing. 
Second, steel drum screen printing ink adhesion 
Drum screen printing requires the ink to have good adhesion, and the problem of adhesion of the screen printing ink is also the most prominent problem of the ink after the drum screen printing. If there is no adhesion of the ink on the steel drum after the printing of the steel drum, it means that there is no printing, and it also causes great waste. The problem of ink adhesion involves the adhesion mechanism of ink and steel drums. At present, it is generally believed that the following factors affect ink adhesion:
1. Influence of resin
Resin constitutes the main component of the ink binder. The adhesion of the ink is closely related to the resin properties. 
1 molecular weight. If the molecular weight of the resin is too close to the molecular weight of the drum coating, the ink solvent is not easy to choose. If the molecular weight of the resin is too large, in order for the ink to reach the required viscosity for screen printing, the solid (resin) content in the ink is too little, resulting in a waste of solvent. It has a high molecular weight, a high melting point, and is difficult to dissolve in solvents, which is detrimental to the adhesion effect. If the molecular weight of the resin is too small, the cohesive force is poorly compatible and the adhesion effect is poor. The choice of the molecular weight of the ink distribution resin is very important and must be appropriate. 
2 glass transition temperature. The polymer segment movement only has a significant diffusion rate above the glass transition temperature. The whole chain movement can only be carried out at high temperatures. For room-temperature curing inks, the glass transition temperature of the resin should be very low, which is obviously beneficial for adhesion. 
3 resin components. The functional groups and branching structures in the resin molecules directly affect the adhesion of the ink on the steel drum. Therefore, the printing inks used for the steel drums with different coatings in the steel drum screen printing are also different. For example, the coating on the surface of steel drums is coated with amino baking varnish and galvanized coating, chrome-plated coating and tin-plated coating. 
4 resin monomer content. Changes in the content of a certain element of the synthetic resin monomer, so that the performance of the resin will also change. Therefore, when designing a drum screen printing ink formula, synthesizing some special resins will greatly improve the ink performance. Changes in the content of a certain element of the resin monomer will lead to a prominent change in a certain characteristic of the resin. 
5 The polarity and crystallinity of the resin. The presence of polarity facilitates the adhesion of the ink, but the highly polar linear polymer also has high crystallinity, and copolymerization and grafting can be used to modify the resin to destroy the crystallinity and maintain polarity. (To be continued)