When the surface tension of the printing substrate does not match the surface tension of the ink, the ink cannot be completely spread on the surface of the printing material, forming a dewdrop shape, which causes shrinkage failure. So what is the reason for this phenomenon? This article gives a detailed answer to specific cases.
When the surface tension of the printing substrate does not match the surface tension of the ink, such as the surface tension of the substrate is low or the surface tension of the ink is high, the ink cannot be fully spread on the surface of the printing material, forming a dew-like shape, which causes shrinkage failure. The reasons for shrinkage and related cases are listed below.
the reason
1. The surface tension of the substrate is low.
2. The substrate is not clean and has oil stains. The surface tension of most oil stains is lower than that of the substrate.
3. The substrate may have some foreign objects with low surface tension.
4. The ink formula is unreasonable.
5. The viscosity of the ink is uncomfortable. The ink with low surface tension spreads to the surrounding ink layer with high surface tension, the ink film leveling becomes worse, and it will cause shrinkage in severe cases.
6. The ink thinner dries too fast. The reason is basically the same as above. It can be solved by reducing the drying speed.
7. The solvent volatilizes too fast before the ink layer enters the drying oven due to external reasons, and the surface tension of the ink increases.
Actual case study
A printing factory has one nine-color gravure printing machine and one dry compound machine installed in the same workshop, and the air inlet of the drying box is in the workshop, resulting in a power of about 70kW for the negative pressure fan in the workshop. When working at night, shrinkage holes often appear. After 30 minutes of shutdown, the shrinkage holes disappear again, but after 30 minutes, shrinkage holes occur again. There are two main reasons for this phenomenon.
1. The large negative pressure in the workshop leads to a large air flow, especially in the evening printing where only the workshop door is open. The wind at the color group of the printing machine is very large, and the wind plays a major role in the drying of the ink. The wind generated by the negative pressure blows onto the ink film. The solvent has evaporated a lot before the ink layer enters the drying oven. The temperature of the ink layer drops sharply to increase the surface tension of the ink layer. At this time, the ink layer still has fluidity. It is easy to form shrink holes.
2. Lower temperature at night leads to lower ink temperature and higher surface tension of ink, which can also cause shrinkage failure.
If the two conditions exist at the same time, it is more prone to shrinkage failure.
Why does the shrinkage cavity disappear when the machine is turned on again after shutdown?
Because after a period of shutdown, the airflow in the workshop decreases or disappears, and after restarting, the workshop gradually forms a large negative pressure, and the airflow becomes larger, so the shrinkage holes are generated again. It can be solved by increasing the viscosity of the ink, reducing the drying speed of the ink, and eliminating the airflow in the workshop, but the best method is to eliminate the negative pressure, such as moving the air inlet of the gravure printing machine and the dry-recovery machine to the outdoor, and then installing it in the workshop Active air supply device.
Sling Bag,Sling Bags For Women,Sling Backpack,Crossbody Sling Bag
GUANGZHOU KOBE LEATHER CO.,LTD , https://www.kobebags.com