White spots during the printing of adhesive labels are a common issue that many manufacturers face. Mr. Qiang Yongsheng, the Technical Service Manager at Dongguan Ande Label Material Co., Ltd., has gathered insights from years of customer feedback and has identified the main causes of white spots in label printing. He also offers practical solutions to address these issues. Let's take a closer look.
In general, there are four primary causes behind the occurrence of white spots in the printing process: uneven material surfaces, dust particles, static electricity, and environmental contaminants in the workshop. This article will explore each of these causes and provide effective solutions to minimize or eliminate the problem.
1. White Spots Caused by Rough Material Surfaces
Currently, most self-adhesive label printing in China is done using either letterpress or flexographic printing methods. Both of these techniques require a very smooth surface on the label material. For example, when using offset printing on coated paper materials, the surface roughness should be less than 1.4 microns. However, for letterpress and flexographic printing, the required surface roughness is even lower—less than 0.7 microns. This is because these two methods apply much less pressure compared to offset printing. If the material surface isn't smooth enough, some areas may not receive ink, resulting in white spots.
This issue is especially noticeable when printing large-area dot graphics. Under high magnification, you'll see that the white spot area has no ink at all. The reason is that the low points on the material surface don't pick up ink from the printing plate. Another key characteristic of this type of white spot is that it often appears as a large, visible area, making the defect quite obvious.
To resolve this issue, you can try the following approaches:
1. Replace the material with a smoother one. If the material's surface is too rough, it’s a quality issue that needs to be addressed by the supplier. You can request them to provide a more suitable material for printing.
2. However, in many cases, replacing the material may not be feasible due to tight production schedules. Self-adhesive label printing companies often have limited time, and changing materials requires significant preparation. If the new material isn’t compatible, the effort could be wasted, affecting overall efficiency. In such situations, you can consider applying a primer or a diluent to the material's surface before printing. These additives are typically clear and won’t significantly affect the final color. They help fill in the surface irregularities, improving smoothness and reducing the chances of white spots appearing during printing.
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