In viscosity measurement, it is hoped that dispersed particles can fully exhibit uniform and complete spherical dispersion characteristics and form a good flow. For all thin inks, most of them require it to conform to the law of motion of the following formula.
In the formula, u is the plastic viscosity of the ink; n 0 is the viscosity of the medium; K is the combination constant (also known as the wetting value), which represents the affinity between the pigment and the medium. The value of K depends on the wet adjustment or affinity of the pigment and the medium. The high affinity of the linking material can make the surface of the pigment particle fully and evenly surrounded by the medium molecules, that is, fully plain and wet, and the K value is large.
Non-polar pigments such as carbon black have a large K value for weakly polar and non-polar linking materials such as mineral oil and linoleum; while for polar linking materials, the K value is small; chrome yellow and other highly polar pigments, The K value of the polar linking material is large, and vice versa, the K value is small.
The affinity between the pigment and the binder is not sufficient, and the flow is not good.
All in all, fluidity is the reflection of the sum of factors such as relative density, viscosity, coagulation, yield value, touch resistance, and ink filament length of the ink. In order to handle these complex relationships well, in the design formula, the quick-setting material must have an appropriate viscosity, the frequency material must have an appropriate temperature range, the content of the frequency material should not be too high, and the liquid-solid interface must be well handled. relation.
In order to obtain good fluidity, the ink should minimize thixotropy and property value. The reason why the ink has thixotropy and yield value is that the ink must have a certain color concentration, and the pigment content cannot be too low. After the pigment content in the ink reaches a certain level, the system becomes a plastic fluid.
At the same time, the better the medium can infiltrate the pigment, the more effective the thixotropy will be.
Thixotropy, for gravure printing ink, first of all, it shows poor leveling, which makes the viscosity of the ink difficult to control, and the transportation in the ink supply device on the printing machine is not smooth, so that the quality of the printed product is not good, and it may cause plastic plate, Poor delivery and poor coating, resulting in "orange peel" phenomenon in printed products. Therefore, when braking gravure ink, it is necessary to make the ink flow freely, fine and uniform, and have a certain cohesion.
To test the ink flow, in addition to using the No. 4 cup to test the seconds, it also depends on the amount of ink on the arm of the retention cup and the ratio of the number of milliliters that flow out. Under a certain viscosity, the less the retention and the greater the outflow, the better the fluidity, and vice versa.
