Printing ink film floating color and hair flower (2)

3. Effect of Surface Tension Gradient on the Floatation of Colored Float For a long time, people have neglected the cause of surface tension gradient on the formation of ink on the ink film. I wonder if the solvent on the surface of the packaging printing ink ink volatilizes and the upper and lower surfaces of the printing ink film The difference in tension is often caused by the formation of eddy currents in the ink film. The difference in surface tension caused by uneven heating or uneven blowing of the surface of the wet ink film will also cause the ink film to move in parallel (sweep) - the formation of flowers.
Too much solubility of the solvent will cause the viscosity of the packaging printing ink to drop rapidly, which will accelerate the settling velocity of the pigment particles. As a result, the sedimentation difference that occurs due to the difference in the particle diameter of the pigment, that is, the generation of eddy currents, may cause the floating color to appear. Created conditions.
In addition, in the mixed solvent system, if the true solvent volatilizes too quickly, not only the surface tension difference but also the volatility gradient of the solvent will be destroyed. As a result, the resin in the ink system will precipitate with the absorbed pigment due to the reduction of the true solvent, and will also cause the pigment particles to agglomerate and affect the improvement of the surface flatness of the ink film, but the evaporation of the solvent is too slow. , Will cause the printing ink viscosity to rise slowly, thus causes the printing ink film to flow the time to be too long, as a result the ink membrane vortex appearance will inevitably occur - Hair flower, floating color and sag and so on.
4. The effect of resin on the floating color in the ink system The variety and variety of resins, wetting ability is not the same. For multiple pigment combinations, the adsorptive capacity of the various pigments for the resin will not be the same. Unsaturated pigments are prone to condensation, which is also a major cause of floating color. .
In the packaging printing ink system, especially when the distribution of molecular weight and molecular weight of the resin is different, the size and distribution of the polar active groups will not be the same. The difference in these distributions is caused by the difference in the ability to wet the pigment. Secondly, the adsorptive capacity of various pigments on the binder (resin) will not be the same—the pigment that absorbs the thin layer of the ink film will be prone to flocculation—floating. In the case of small-molecular-weight rosin or alkyd resin inks, due to their large polarity and strong adsorptive power, the resulting adsorbed ink layer is thin, and the dispersion stability is poor, and flocculation and floating color are very likely to occur. From the theoretical point of view, when the packaging printing ink flocculates, it is more necessary to control the concentration of the resin in the printing ink grinding process according to the performance of different pigments and binders, and to force the polymer (linker) to adsorb on the pigment. On the surface, its purpose is to prevent flocculation failure caused by a single production of pigment.
Poor solubility of the polymer (resin binder) in the packaging printing ink system can also cause the disadvantages of floating coloration. In general, miscibility is poor when using several resins. Secondly, the solubility of the selected solvent does not reach the critical value. That is, people often say that the resin and the resin are poorly mixed. In addition, the affinity for the pigment is not enough, and after the solution volatilizes, the floating color and hair will appear. flower. Even if the turbidity and floating color are eliminated under the influence of the solvent, it will already begin during the evaporation of the solvent. Because the volatilization of solvents and diluents destroys the balance between the resin binders, it is often said that poorly compatible resin binders will release the adsorbed pigments and cause the floating color of the ink film. Hair flowers and so on. 
5. The effect of packaging and printing conditions on the floating color of flowers The water-dry and dry areas in the north of the Yellow River in China and the wet areas in the south of the Yangtze River are also directly responsible for the formation of floating color flowers after printing. Whether it is a dry environment or a high-humidity workshop (except for temperature and humidity control workshops), we all know that the evaporation of solvents during the printing process, the decrease of the surface temperature of the ink film, the condensation of moisture, etc., can cause turbulence in the ink film of the packaging printing ink. The appearance of hydrophilic pigments that appear on the surface absorbs a certain level, which in turn causes the pigments to separate and separate. Since the moisture is once bound into the ink layer and the hydrophilic pigment particles are bound, they often undergo condensation and sedimentation due to the bridging effect of non-intermolecular liquids. - floating color. The occurrence of such failures is particularly evident in packaging printing inks that have a high rate of evaporation and hydrophilic solvents. (To be continued)