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Thermal Label Label sticker Sticker Sticker Paper sticker paper custom Stickers Custom StickersInk Splatter? Anilox Roll Scratches? Have You Paid Attention to These Critical Factors?
With the continuous development of adhesive label printing technology in China, the application of flexographic printing equipment is becoming increasingly widespread. Due to its simple operation, fast speed, and high stability of printing color, it has gradually become one of the mainstream printing methods. However, many label printing companies encounter a variety of problems during the production process, such as ink splatter and anilox roll scratches in flexographic printing, which lead to a decrease in production efficiency. In this article, the author will discuss the key causes of ink splatter in flexographic printing. Ink splatter generally refers to the uncontrolled transfer of UV ink through the doctor blade and ultimately onto the printed material. It is usually manifested as lines or other irregular shapes on the printed material, with the number ranging from a few to many. So, what are the specific causes of UV ink splatter?
PART.01 UV Ink Characteristics
Firstly, the viscosity of UV ink is much higher than that of water-based ink, and it can be five times or even more higher. The high viscosity exerts greater pressure on the doctor blade, which may cause the doctor blade to flutter or deviate. If the parameters or installation of the doctor blade are not standardized, it may even lead to ink directly bypassing the doctor blade and losing its intended function.
Secondly, the thixotropy of UV ink is another important factor causing ink splatter. Thixotropy refers to the change in the fluidity of the ink, which becomes thinner or thicker under the influence of external forces or environmental factors. The stress applied to UV ink is the shear force generated when the ink encounters the doctor blade. When the viscosity of the ink on the surface of the doctor blade or anilox roll decreases, some of the ink will flow under the doctor blade, reducing the shear force as the ink passes through the doctor blade. As a result, the ink may splash out from the doctor blade or accumulate on the back of the doctor blade. With the gradual accumulation of ink, it will eventually be transferred to the printed material from the back of the doctor blade.
PART.02 Doctor Blade Selection
If we consider the doctor blade selection, the material, blade edge shape, contact angle, and pressure control of the doctor blade are all factors that may cause anilox roll scratches.
01 Doctor Blade Material
Practical experience has shown that most plastic and carbon steel doctor blades are more prone to ink splatter compared to coated doctor blades. As the blade wears, the contact area between the doctor blade and the anilox roll gradually increases, and the possibility of ink passing through the doctor blade also increases. In contrast, steel doctor blades with wear-resistant coatings have better wear resistance and longer service life.
02 Blade Edge Shape
When it comes to the selection of doctor blade edge shapes, the possibility of ink splatter is minimized with a beveled blade. Among them, a 15° beveled blade is the preferred choice. Without considering the ink viscosity, the smaller the angle of the doctor blade edge, the less ink will pass through the printing plate, resulting in clearer prints. However, the smaller the angle, the higher the possibility of wear, and the shorter the service life of the doctor blade. Therefore, when using a doctor blade with a sharp angle, it is necessary to select a blade strip with higher hardness and better wear resistance, which helps to extend the service life of the doctor blade and prevent tip deviation and damage.
03 Doctor Blade Thickness
When selecting the thickness of the doctor blade, it is necessary to use the thinnest possible blade while still ensuring the expected ink wiping quality. Since UV ink is the most widely used in flexographic printing, a thicker blade is usually chosen to withstand the hydraulic action of the high-viscosity ink. The blade thickness is generally between 0.25 and 0.30 mm. Therefore, in order to achieve high-quality printing while reducing losses, even if the bottom material of the blade is thicker, a thinner working edge is still needed to remove the ink, thereby minimizing the uncontrollable printing quality issues caused by ink splatter as much as possible.
04 Contact Angle
Under normal circumstances, the contact angle of the doctor blade in flexographic printing should be set between 25° and 42°, with the most ideal angle being 30°. Experiments have shown that to avoid UV ink splatter, the contact angle should be at least 30°, but not exceed 35°. At this angle, the doctor blade can cut through the ink film and clean the surface of the anilox roll, controlling the uniform transfer of ink. If the contact angle is less than 30°, some ink will remain on the surface of the anilox roll, leading to ink splatter.
05 Pressure Control
In terms of doctor blade pressure control, excessive pressure will gradually flatten the contact angle of the doctor blade. In extreme cases, the angle may become too flat, causing the tip of the doctor blade to lift off the anilox roll, resulting in excessive ink and dot gain on the printed material. During the operation of flexographic printing equipment, it is necessary to always run with the smallest possible pressure. If a matte appearance is observed on the surface of the anilox roll, it indicates that the doctor blade parameters are set to the optimal state, and the ink wiping quality is good.
For the occurrence of problems such as ink splatter and anilox roll scratches, it is often not caused by a single factor, but by the interplay of multiple factors. Following this logic, observing and analyzing from multiple angles such as ink characteristics, doctor blade selection, and ink wiping quality can help identify the key causes of ink splatter and anilox roll scratches.
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