The viscosity of the solvent-based gravure printing machine ink is too high, causing scratches, biting, paste, and printing problems such as “orange peel”.
In summary, when designing and manufacturing solvent-based gravure printing machine inks, it is necessary to select suitable pigments, resins, and solvents to match, so that the inks reach a suitable initial viscosity. The printing plant should use the appropriate mixed solvent, preferably the thinner provided by the original ink manufacturer, to adjust the original ink to the appropriate “working viscosity” before printing on the machine, in order to get high quality prints.
In addition, the viscosity of the ink during printing is also related to the printing speed. In general, the faster the printing speed, the lower the viscosity of the ink is required, otherwise the ink transfer effect is not ideal.
The solvent-based gravure printing machine ink is a volatile drying type ink, that is, when the solvent overflows from the wet ink film, the ink film changes from a liquid state to a solid state. Therefore, the speed of solvent evaporation has a direct effect on the drying properties of the ink.
In the design and production of solvent-based gravure printing press inks, solvent mixing of medium boiling point, low boiling point and high boiling point is generally selected to meet the drying requirements of the ink. If the resin is improperly selected, the softening point of the resin is low, the resin is not good for solvent removal, the release of the solvent to the solvent is not good, and the excessive high-boiling solvent will soften the ink film, etc., which will affect the evaporation rate of the solvent, resulting in solidification and drying. Excess solvent remains in the latter ink film.
When preparing a solvent-based gravure press ink, the resin is generally selected first, followed by the solvent. The dissolution parameter of the mixed solvent is similar to the dissolution parameter of the dissolved substance, so that it is easy to dissolve and the volatilization speed is also faster. Since the pigment is added to the prepared ink, the volatilization rate of the mixed solvent is greatly lowered, and the larger the pigment particles, the slower the volatilization rate of the solvent, and the worse the drying property of the ink. At the same time, the greater the amount of pigment, the slower the volatilization rate of the mixed solvent, which is due to the mutual traction between the solvent and the pigment surface, which resists the removal rate of the solvent.
In addition, the higher the room temperature, the lower the relative temperature of the air, the faster the air circulates, and the volatilization rate of the mixed solvent is accelerated, and vice versa.
Printing failures due to improper drying of the ink are mainly:
(1) At a certain printing speed, the initial drying of the ink will cause problems such as paste, scratches, whitening of the ink, poor gloss, and poor leveling.
(2) In the continuous color printing, since the ink is too dry, the sticking roller will occur at the next station printing, and the printing product will be retracted. The volatilization rate of the solvent in the ink depends not only on the boiling point of the solvent, vapor pressure, latent heat of vaporization, but also on the temperature of the printing environment, relative humidity, air volume and thickness of the ink layer. Therefore, it should be adjusted at any time according to changes in conditions. The rate of evaporation of the solvent in the ink.
Under normal production conditions, if the ink is dried too fast, an appropriate amount of slow-drying diluent should be added; if the ink is dried too slowly, a quick-drying diluent should be added. If conditions permit, the temperature of the printing environment should be controlled between 18~25°C, and the relative humidity should be controlled below 65%, which is conducive to the stability of ink performance.
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