The factors that affect gas cracking include acid gas, humidity, light, temperature, mixed impurities, film thickness, contact time, and so on.
Reduces and avoids slow migration of gas cracks using high boiling solvents, surfactants, and coupling agents. For example, water-based packaging printing inks and water-based lacquer-added amines are effective methods, and the addition of morpholine is more effective. In addition, it is very beneficial to strictly control the production environment of printing ink, varnish, and coating, and continuously increase the ventilation energy, avoiding the intrusion of foreign materials and dust.
Orange peel, crust:
In the process of packaging printing and varnish coating, the ink does not produce a smooth surface, but forms an ink film or oil film failure phenomenon such as orange peel. When printing with a solvent or water type ink with fast solvent evaporation, it is easy. Orange peel and crust occur.
The phenomenon of orange peel appeared after the ink film or full version of the packaging and printing products appeared. The root cause was that the ink film or oil film could not be well leveled. During the drying process of the 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 as the microscopic analysis. This may be because 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 flat ink film or a smooth oil film. Second, the viscosity of the ink or coating oil rises to a certain extent and stops flowing. The third reason is that the concentration of the ink or coating oil rises above the yield value and the flow stops. Some flow to a certain scale value, while others flow to a certain scale value at the last moment. We need to complete the flow (movement) level gradually and within a certain period of time.
In the first two cases, it may cause the result that the bad flow plane produces unevenness. When we use the code printing or coating glazing, it may also be caused by improper solvent selection (such as excessive solvent with excessive volatilization speed or Dilution solvent), together with excessively high ambient temperature or excessive ventilation of the printing and finishing (air blow), plus spray and coating distances too far (including gravure scraper too low), printing ink or coating oil viscosity is too high. It is easy to produce orange peel.
In order to prevent the occurrence of ink film or oil film orange peel, an important one is to improve the surface tension state of ink printing and varnish coating. Often adding a small amount of dimethyl silicone oil and other additives can achieve significant results. Dimethicone accumulates on the surface of the ink film, and the adjustment solvent evaporates, volatilizes, and oxidizes evenly. Proper high-boiling solvents and diluents are formulated, leveling agents are added to improve the leveling of the ink film, and at the same time, a certain printing pressure is controlled to ensure that the thickness of the ink film is uniform and smooth.
Hunan Packaging Liu Jiaju