2.8 Orange peel and crust:
A, failure phenomenon:
When the ink is packaged and printed and the varnish is being painted, it does not produce a smooth surface, but forms an uneven film of orange peel or an oil film failure phenomenon. It is easy to print with a solvent or water type ink with fast solvent evaporation. Orange peel and crust occur.
B. Reasons:
The phenomenon of orange peel appeared after the ink film or full version of the packaging and printing products appeared, and the root cause of the ink film or oil film was not very smooth. During the drying process of ink film or oil film, due to the evaporation of the solvent in the system, the surface layer and the inside of the film are not the same from the microscopic analysis. It may be that the concentration of the binder (resin) in the surface layer is higher than that of the ink layer and the oil layer. A gradient of surface tension and a gradient of viscosity are produced. This will begin to flow and this (orange peel) defect will occur when the flow stops. It may also be due to the increase in the concentration of ink or coating oil, the slower evaporation rate of the solvent, and the gradual diffusion of the solvent resulting in the gradual elimination of the difference in concentration and the difference in surface tension. It can eventually form a smooth ink film or flat oil film - leveling. After the viscosity of the ink or coating oil rises to a certain extent, the flow stops. The third reason is that the concentration of ink or varnish rises above the yield value and stops flowing. Some flow to a certain scale value at the beginning, and some flow to a certain scale value at the last moment. What we need is to complete the flow gradually and within a certain period of time.
We all know that in the first two cases, it may cause poor leveling and produce bumpy results. When we use inkjet printing or glazing, it may also be due to improper solvent selection (such as excessive volatilization rate). Fast solvents or dilution solvents, plus excessively high ambient temperature or excessive ventilation of the printing or finishing (air blow), plus spray, too long distances (including too low gravure blades), printing inks or coating High oil viscosity is highly likely to cause the production of orange peel.
C. Countermeasures:
In order to prevent the occurrence of ink film or oil film orange peel, one important factor is to improve the surface tension state of ink printing and varnish coating. Adding a small amount of dimethyl silicone oil and other additives can achieve significant results. Dimethicone is accumulated on the surface of the ink film, and the adjustment solvent can evaporate, volatilize, and oxidize evenly. The appropriate high-boiling solvents and diluents are formulated, leveling agents are added to improve the leveling of the ink film, and a certain printing pressure is controlled to ensure that the thickness of the ink film is uniform and smooth.
Source: "Ink Industry"