Flexible packaging factory ink delivery is difficult, the real murder is here
The pigment particles are uniformly dispersed in the binder, and since the pigment is in polar contact with the binder, a charged surface layer is generated, and when it is stationary for a while, they attract each other to become a flocculated state, the ink becomes thick, and the viscosity becomes large. However, when an external force acts (such as stirring), the flocculation state is quickly destroyed, the ink becomes thinner, and the viscosity becomes smaller. This property is called thixotropy of inks in the industry. Too strong thixotropy makes the ink difficult to rotate in the ink fountain and makes ink delivery difficult.
1 Surface properties of all pigments. The same type of carbon black, after surface oxidation treatment by ozone, produces a thixotropy that is much smaller than untreated.
2 pigment dosage. If the content of the pigment in the ink exceeds a certain level, it becomes a plastic fluid, and the fluidity is poor and the thixotropy is large. If the amount of pigment in the ink is small, the thixotropy is small, but it is possible to fail to achieve the desired color density. Therefore, color concentration and thixotropy are a contradiction, and only a balance can be found between the two.
3 the wettability of the pigment. A pigment with poor wettability and a large thixotropy of the ink.
4 particle shape of the pigment. The pigment particles in the ink are larger in needle-like and plate-like shape than spherical thixotropy.
5 The molecular weight of the resin. The molecular weight is large, but the n-heptane value is small and the thixotropy is large. An ink made of a high molecular polymer has a larger thixotropy than an ink made of vegetable oil.
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