Understand the role and production process of laser engraved ceramic anilox roller-2

Understand the role and production process of laser engraved ceramic anilox roller-2

 

Importance of porosity

Designers must understand the concept of coating porosity. The lower the porosity, the smoother the coating will be and the more suitable for finer engraving. High quality coatings must have low porosity and proper surface tension to impart a certain water repellency (appropriate release factor). This will make the mesh easier to clean and enhance resistance to various cleaning solvents.

Select engraving parameters

Each engraving consists of three parts: angle, number of lines, depth (or volume). The combination of these three parameters is almost limitless, and the designer's choice depends on the desired pattern effect. The type of engraving also depends on the type of laser used. The basic engraving type is produced by a CO2 laser, and the more complex engraving is produced by a YAG laser. Leaders in the laser engraved anilox industry also offer a variety of terminal technologies for their engraving. Each design has a different effect on the final product.

 

Laser engraving process

Many people are familiar with the application of laser technology, especially in the medical field. However, in recent decades, the application range of laser has been extended to many fields such as welding, automation, drilling, etching, printing and so on. The most common type of laser used is the CO2 laser, which uses pulsed energy from the combination of CO2 molecules with He and N. Each pulse energy leaves an ablation trace on the ceramic layer on the surface of the roll. As the performance of CO2 lasers increases and the pulse frequency increases, manufacturers can produce anilox rolls more stably and at a faster rate.

In recent years, YAG lasers have been printed into the anilox roll industry. Instead of generating laser energy from a gas, it uses YAG ceramic crystals (yttrium aluminum garnet) to generate laser energy. Therefore, it is called a solid-state laser.

The main difference between the two is the laser pulse shape and wavelength. Due to the operating characteristics of the CO2 laser, it produces a so-called "long decay". This causes a decrease in the height of the mesh wall in the direction of rotation, resulting in unnecessary meshing between the meshes. Sometimes this can cause poor printing results. The CO2 laser also has a low rise time, which causes more recasting on the mesh wall, resulting in blade wear and various print quality problems.

Correspondingly, the laser pulses generated by solid-state lasers have very steep rise times and short attenuations, resulting in clean, well-structured, clean mesh walls.

wavelength

 The CO2 laser has a wavelength of 10.6 μm and generates energy in the form of invisible light. The solid laser produces a laser having a wavelength of 1.06 μm. The mathematical relationship between the laser wavelength and the smallest possible spot that can be focused determines the limit of the number of CO2 engraving high lines. The maximum number of lines for CO2 laser engraving is 1000 lpi. Exceeding this number of lines, the quality of engraving deteriorates drastically. The number of lines can easily be reached to 1500 lpi using a solid-state laser. Solid-state lasers also provide good coupling, which is related to the interaction between the laser and the ceramic material. When the laser beam strikes the ceramic material, a portion of the energy is reflected and the remaining energy is absorbed by the material. When the laser reaches the Cr2O3 on the surface of the anilox roll, two processes are produced: melting and vaporization of the ceramic layer. The more complete the vaporization, the better the quality of the ceramic layer. However, usually a part of the coating is melted without vaporization, which causes a so-called recasting phenomenon. The solid laser can keep the recast in a minimum amount while providing the maximum amount of vaporization. The result is a smoother, higher quality engraving that reduces blade wear. In addition, a steeper mesh wall produces a larger mesh volume.

Another benefit is the ability of the laser beam to focus on the ceramic surface. This process is like the focusing of a microscope and a camera. To obtain a consistent engraving effect on the entire roll surface, the focal length is required to be constant. Compared to the CO2 laser, the solid-state laser focal length change is less sensitive, so the engraving effect caused by the taper and the beat of the roller body changes little. It is virtually impossible to machine a roll body without any taper and runout. The use of a CO2 laser may result in different engraving effects at both ends of the roller body.

 

Standard engraving mode

The laser engraved ceramic anilox roll has an initial engraving angle of 45°, in part because it is a typical engraving angle for mechanically engraved anilox rolls. In addition, the customer is familiar with the performance of the 45° engraved roll body. With the development of the industry, more engraving angles have been introduced to the anilox roller users. There are mainly 30° and 60°, and the number of meshes engraved in equal areas is increased by 15% compared to the 45° mode. This makes the ink more uniform and prints better. For electronic or UV drying inks that require higher viscosity, it is recommended to use a 30° engraving mode with slight through grooves between the meshes.

60° engraving has become the most popular engraving mode today, mainly because of the compact mesh arrangement. In addition, this engraving is very suitable for today's squeegee technology, and it is well matched with various types of squeegees, and the running-in period is short. Designers who choose this engraving angle will get a satisfactory print result.

 

Advanced engraving technology

The development of technology has produced a more advanced network engraving mode. For example, spiral and triple helix mesh wall engraving. Although this engraving mode still uses traditional laser technology, it is distinguished from the standard engraving mode by a unique mesh structure. A continuous raised mesh wall between the mesh supports the squeegee, allowing the engraved smooth surface to provide more ink-receiving space. After two years of development, this engraving design can now have a larger amount of ink transfer than conventional engraving. The pinhole problem has also been eliminated due to its superior ink release capability. In addition, it is easier to clean due to the special communication structure between the meshes. The traditional engraving mode makes it easy to deposit ink, glue, varnish, etc. in the lower part of the mesh.

Another new engraving design is a 90° helix, an engraved groove along the circumference of the roll (no separate mesh). The ridge mesh wall supports the squeegee. This engraving provides higher print density, improved ink transfer, easy cleaning, and greater coating weight. Whether engraved with CO2 or YAG laser, the smooth roll surface without mesh improves the squeegee of the squeegee. This smooth surface also reduces blade vibration and improves print quality.