Symptoms of static electricity in screen printing
1. After screen printing, the ink on the printed surface is pulled up along with the screen, forming a fuzzy mess. The "flying" ink strands only break apart after the workpiece is removed.
2. During overprinting, the edges of the ink and pattern of the preceding and succeeding colors repel each other, preventing them from properly matching, resulting in no ink being printed between the two colors.
3. During screen printing, the workpiece sticks to the screen, especially at the end of the squeegee.
4. The printed material sticks together and cannot be separated.
5. During the squeegee printing process, the ink has difficulty spreading evenly on the screen, clumping and sticking together.
6. The printed material attracts dust, resulting in ink defects, pitting, and a rough, uneven surface after screen printing.
The above problems are primarily caused by static electricity, but sometimes the presence of static electricity can also be linked to substandard printing processes. For example, in low-humidity environments and when the ink contains insufficient solvent, static electricity cannot be transferred through the air due to low humidity. Furthermore, inks with low solvent content and high viscosity naturally produce stringing. Another example is the increased speed during screen printing, where intense friction between the squeegee and the screen generates static electricity. This is especially true when using high-tension screens, where the polyurethane squeegee exerts high pressure and speed on the screen, which is particularly conducive to static electricity generation. This is the principle behind the term "triboelectric charging."
Static electricity in screen printing can cause numerous quality issues and even prevent printing from continuing. So how can static electricity be avoided and eliminated?
Using a suitable anti-static ion blower can effectively suppress static electricity.
First, control the screen's own process conditions. When the screen is under high tension, minimize the screen pitch. Lowering the screen pitch reduces squeegee pressure, which reduces friction on the screen and reduces the likelihood of static electricity generation. In screen printing on optical discs, to ensure image accuracy, minimize moiré patterns and overprint accuracy, and avoid static electricity, the tension is as high as 26 N/cm, while the screen pitch is as small as approximately 1.0 mm. If static electricity still occurs under these conditions, adjusting the squeegee speed can alleviate this issue.
The screen printing environment should be optimized for screen printing. The optimal temperature is 23°C ± 2°C, with a relative humidity of 60%-70%. This helps control the evaporation rate of solvent-based inks and the viscosity of UV-cured inks. This stabilizes the ink's viscosity, ensuring optimal printability. Excellent printability prevents stringing due to the ink itself.