Overcoming ink spitting issues with optimized blades
An appealing product packaging has always played an important role in the buying decision process. With technological advances also comes increasing demand for high-definition print images to catch the eye of the consumer. UV inks are a popular ink type in packaging and label printing, amongst other reasons because they dry quickly, which allows high printing speeds, and because printing results can be reproduced perfectly more easily than with other ink types.
However, there is one phenomenon with UV inks that keeps causing printers trouble: Ink spitting. It not only soils the press but also appears on the web in the form of very fine drops showing on the print image. A lot of research has been undertaken to solve this issue. A variety of parameters in the process can be optimized to tackle ink spitting, e.g. a different anilox engraving, ink temperature control and an improved doctor blade set up.
When it comes to doctor blades, we look at two areas: The blade geometry and the blade material.
Steel blades are commonly perceived as the best choice for high quality graphics, since they have a very fine contact zone with the anilox roller to wipe the ink. Typically, the blade thickness is 0.15 or 0.20 mm. When metering high viscosity UV ink, it can happen that the flexible blade bends too much under the pressure coming from the thick ink. As a result, the blade meters unevenly, allowing small amounts of ink to build up on the back. This excess ink then spits into the press and onto the web due to vibration. The vibration gets worse with higher printing speeds.
The Agergaard steelBLADE CAS blades are specially designed to minimize ink spitting because they combine rigidity with flexibility. The blade has thicker base material, which makes the blade less sensitive to vibration. To make sure that the fine contact zone between blade tip and anilox roller remains for precision doctoring, we grind a special profile at the blade tip.
Another option is to adopt a plastic blade material. Plastic has a different material elasticity than steel, being less sensitive to vibration. While there are admittedly limits as to the line count on the anilox roller that can be metered precisely with a plastic blade, it can be an interesting option for many UV based print applications. The Agergaard polyBLADE P series is a very wear-resistant thermoplastic doctor blade with a beveled blade tip.
Our virtual DRUPA 2020 - back to main page