In the engraving technology of anilox rollers, Nd:Yag laser engraving technology is one of the hot topics in recent years. Even in some cases, people have already blown the Nd:Yag laser engraving technology too magically. Nd: The ink pattern formed by Yag laser engraving is different from the ink pattern produced by the conventional CO2 gas laser engraving technique. However, we can conclude that the ink pattern produced by the Nd:YAG laser engraving technique Is performance even better? Is it necessarily better and more printable? This can not be generalized, and in some cases it may be true, but in some cases it is not. The constant-wavelength CO2 laser engraving technique is still outstanding, and it is suitable for many flexographic printing applications. The YAG laser has a slower engraving speed than the CO2 laser. In order to increase the YAG laser engraving speed and catch up with the CO2 laser engraving speed, the YAG laser has been improved, but at the same time it has brought some unforeseen negative effects.
This article aims to discuss the actual application of these two laser engraving techniques, and summarizes the advantages and disadvantages of the two laser technologies, and introduces the differences between the two laser engraving techniques, but more importantly, the introduction of engraving The formation of the ink hole operation performance. However, unfortunately, due to the lack of long-term experimental research on YAG lasers, many problems have not yet been solved.
One, CO2 laser technology There are two kinds of C02 laser engraving methods: one is a pulse type, and the other is a constant wavelength type. The pulsed CO2 laser can control whether the laser is emitting or not (YAG laser is also the case), but the constant wavelength is different. We can know by its name, it will always keep the laser beam constant, so we can create a Stable laser environment.
During the engraving process, the laser beam is focused on the polished ceramic surface, and its constant light wave is divided into several segments by a shutter-type mechanical component. In this way, the generated laser light is very intense and is emitted in a spaced manner. At the same time, it can maintain excellent anti-interference, better consistency and higher stability. The laser beam can only ablate and evaporate part of the ceramic, while the rest of the ceramic is in a molten state. These molten state ceramics (also known as re-sprayed ceramics) form a web wall. This led to a new debate: Is the second time that the ceramic coating can be as hard and strong as the original ceramic layer?
During the engraving of the anilox roller, the laser beam actually ablated part of the ceramic and formed a round hole. If the 600-angle engraving is used, the ink-carving holes after carving should of course be hexagonal pyramid shapes. So, how can we change these holes from circular to hexagonal? The laser ablates the surrounding ceramic coating and forms the final desired hexagonal pyramid shape. Laser engrave an ink hole, need to ablate seven times to form the final shape, not only ablate its own ink hole, but also include six ink holes around it. During this process, the surrounding molten ceramic layer that has not been ablated forms a mesh wall. Of course, the size of the anilox roller has also increased and it has reached a predetermined size standard.
Will the molten ceramic layer (secondary spray coating) produced during the engraving process affect the ceramic composition? Will the wall be damaged more easily? In fact, the molten ceramic layer may make the resulting mesh wall more compact or more stable. Frankly speaking, no one knows the exact answer, but it is verified by time in production. Unfortunately, the word “coating” seems to have a less objective negative meaning.
During the engraving process, if the CO2 laser is not properly controlled, the surface of the anilox roll will have some undesirable effects, such as very rough, too wide, too thin, or cracked network walls. However, as long as the operation principle of the coating flow is controlled, high-quality ink holes can be obtained. The new YAG laser seems to be able to solve these problems in the CO2 laser engraving. However, then again, if the use of CO2 lasers is correct and reasonable, these problems will not occur and occur at all.
Second, Nd: YAG laser technology Nd: YAG laser is: ytterbium: yttrium aluminum garnet abbreviation, it is a solid-state laser. This bizarre/magical/exciting technology has a truly positive/advantageous effect on the anilox roll engraving - in a particular parameter and application. For YAG lasers, since this is a new application, it will take some time before it can be widely accepted and adopted by people. However, we have discovered some of its specific characteristics from the current research of YAG laser-engraving anilox rollers. Moreover, we have obtained some relevant conclusions through continuous “research-improvement” experiments.
Different from the CO2 laser engraving technology, the YAG laser engraving technology does not form a network wall by the second spraying of the ceramic layer. On the contrary, when the YAG laser contacts the surface of the ceramic layer, the laser beam energy is higher and stronger. As a result, most ceramics are ablated and evaporated, leaving little ceramic coating. Therefore, the previously polished ceramic surface constitutes most of the network walls. However, when the ink hole is observed with an electron microscope, a small amount of the second-sprayed ceramic layer can still be seen. As we said earlier, the ink hole formed by the CO2 laser engraving is a hexagonal pyramid, and the ink hole produced by the YAG laser engraving is circular, but can be adjusted if the engraving angles of several surrounding ink holes are changed to 600, you will get a hexagonal pyramid shape of the ink hole.
Third, the comparison of ink hole shape
Due to the different types of lasers and the different engraving methods, the shape of the resulting ink hole is different. CO2 laser engraving forms a bowl-shaped ink hole, while YAG laser engraving forms a cylindrical ink hole, and more vertical wall. The CO2 laser ensures uniform, predictable, high-quality ink placement by controlling the ratio between ink hole width and depth. In general, the ratio of depth to width is between 23% and 33%. The smaller the ink hole (anilox roller above 1000 lpi), the less CO2 laser energy is needed to engrave the ceramic layer; the smaller the ink hole width, the smaller the depth of the ink hole. Therefore, the texture The higher the number of roller screens, the smaller the amount of ink transferred.
If YAG laser engraving technology is used, the intensity of the laser beam will not be reduced even when a small ink hole is engraved. When engraving small ink holes, the YAG laser is just the opposite of the CO2 laser. The depth of the YAG laser ablated ceramic layer is very deep. The 1400 lpi anilox roller is carved out by the ink and the 800 lpi laser engraved by the CO2 laser. The roller transfer ink is comparable. However, since the YAG laser engraved ink hole is cylindrical, the ink at the bottom of the ink hole cannot be completely released and transferred to the plate. In addition, since the mesh wall of the ink-receiving hole after the YAG laser engraving is in the vertical direction, the ink below a certain depth in the ink-performing hole cannot be released/released.
Although the YAG laser engraved ink hole is cylindrical, it can still keep the wall thickness very thin. However, when the CO2 laser engraving is used, the cylinder-shaped ink hole can be formed after a large number of ceramic layers are baked and melted. This is actually a result of the deep engraving. A large number of ceramic layers are ablated, which can also result in the walls being too rough, too wide and of poor quality, and this may affect the printability of the anilox roll.
YAG laser-engraved 1400lpi, 2.0BCM anilox roller and CO2 laser-engraved 800lpi, 2.0 BCM anilox roller, tested the ink density between the two, there is another problem: the ratio of ink hole width to depth It is not suitable for YAG laser engraving because the effect on the thickness of the wall is not obvious.