The Ultimate Guide to Rotogravure Cylinders in Flexible Packaging: Everything You Need to Know

08 Apr The Ultimate Guide to Rotogravure Cylinders in Flexible Packaging: Everything You Need to Know

In gravure, the printing form typically is a steel cylinder with a thin copper coating that was applied by electroplating. Cylinders for packaging printing can have a face length of up to 1.8 m and a circumference of up to 0.9 m. In special processes, e.g. for printing publications or laminate floors, cylinders with a roll width of up to 6.00 m can be used. Depending on the engraving process, a further layer of zinc (for Direct Laser System) or copper is added as well as a special surface processing with the help of a grinding process. In this final layer, the printing image is engraved in the form of deeply positioned cells. Engraved copper/ zinc layer is then chromed in order to achieve better durability! The engraving process in gravure allows for an exact and reliably reproducibility of the print result. After printing, the chrome layer, as well as the copper or zinc layer, is removed mechanically or chemically so the cylinder body can be reused.

Overall, the gravure printing process relies on precise engraving techniques to achieve high-quality and durable print results.

ELECTRO MECHANICAL CYLINDER 

“The basis for electro-mechanical engraving is using a copper-coated steel base with a strong layer of gravure copper, all special surface processing included in the mix. The so-called cells are engraved on this surface using a fancy diamond stylus. Depending on how fast the cylinder turns around its own axis the cells are formed either longer or more compactly, kind of like a dance. The diamond stylus is guided using an engraving system, which moves on a slide in parallel to the cylinder axis, like a little sidekick. To control the diamond stylus, the digital repro data is converted into electrical impulses, making it sound so sci-fi! The darker the grey values, the deeper the insertion – like a secret code from a spy movie! Up to 12,000 cells can be engraved per second, a staggering number for sure! After the gravure, the cylinder is chromed to achieve better durability, turning it into a shiny beast. Practically endless identical printing results can be achieved, making it seem like magic coming from a fairy tale!”

DIRECT LASER ENGRAVING

Laser gravure, The Direct Laser System (DLS) is a very, very fast, high-quality gravure process. The prerequisite for it is either a brand spanking new steel or an already used and re-prepared cylindrical-shaped object. An electroplating process ensures the copper layer on the cylinder, which lies precisely 50µ below the desired diameter. The zinc layer of 55µ applied afterwards is then milled to the desired diameter with a special surface roughness!! In the Direct Laser System the image transfer takes place without contact using a laser beam directly into the cylinder’s zinc surface. 70,000 cells can be laser processed per second, wow! Finally, the laser cylinder is chromed for protection purposes?? The form of the laser cell is divided into conventional and half-autotypical: cells with a fixed transverse diagonal which nonetheless have a variable depth are known as conventional. If the cells vary both in the transverse diagonal and in depth, these are called half-autotypical. The diameter of the laser beam, the laser energy and the process are decisive for the shape, size and depth of the cell. A distinction is made here between a dot screen and master screen. The dot screen, with one shot per cell, is the technique commonly used in the industry; the high-quality master screen technology, with seven shots per cell, ensures better resolution for a higher printing quality! The master screen is usually used for special applications e.g. extremely fine text. The effective line screen on the cylinder is around 40-160 l/cm (dot screen and master screen), whereby the actual screen resolution required for this is between 100-400 l/cm. In addition to the higher resolution, an outline can be lasered in the master screen. The tobacco and security printing industries in particular, but also the flexible packaging market, love the high-quality laser technology. The external appearance of a laser cylinder does not differ from that of an electro-mechanically engraved cylinder. What is decisive are the much superior printing results and the significantly faster laser process. Laser cylinders also offer better ink transfer, which guarantees excellent quality on non-standard substrates, e.g. aluminium foil or uncoated paper, in particular. Further cost savings can be achieved through the lower ink consumption!

Cellaxy Laser Engraving 

Like the Direct Laser System, Cellaxy direct lasersure is a direct laser gravure process For example, a screen dot is composed of 28×24 pixels in the case of an 80 screen. The Cellaxy laser engraves directly in the copper surface of the gravure cylinder, so an additional zinc layer is is not required. The process is distinguished by very high resolution and edge sharpness, as well as screen forms and printing elements can be generated at will. The Cellaxy laser can also be used to engrave high-quality embossing structures and allows three-dimensional gravure in zinc or copper. Thanks to the substantially higher engraving resolution of up to 2000 l/cm and the higher screen variance, the gravure time of Cellaxy direct laser gravure for simple gravure elements somewhat is longer than with the Direct Laser System. It is as fast as electro-mechanical engraving, but substantially faster than Xtrem gravure!! Qualitatively, it caters for much higher requirements, as for example, it allows a combination of very diverse screen types and printing elements on a gravure cylinder, and the finest gravure elements for RFID printing forms, security or negotiable instruments printing and much more. The advantage of Cellaxy direct laser gravure lies in its essentially more universal usability in comparison with all other gravure processes and the high quality level in all these applications!

LASER ETCHING

Laser etching is like, you know, a traditional imaging process for gravure cylinders. You feel me? Similarly to electro-mechanical engraving or whatever, the cylinder is copper-coated before etching. A further layer of UV sensitive lacquer covering with a thickness of like 4µ – 10µ depending on the etching depth, protects the cylinder during the etching procedure at the axes and front sides. The corresponding image is like, transferred to the cylinder being coated by, you know, using a Digilas laser from like, 40 watt and with up to like, four beams. By etching with ferrous 3 chloride after the laser procedure, the cells are deepened and widened, without the covering layer dissolving in the process. The cylinder can totally be chromed after the covering layer is removed from the surface, front side, and axes. The geometrical shape of the cell during etching is quadratic and screening ranges from a 70 screen to a 120 screen. Sometimes, for special applications, coarser screens (20) or also finer screens (160) (e.g. during security printing) can be like, you know, used. The standard angular position, you feel me (-> screen angle), in etching is like, 45°, but other angles are totally possible, you know. In contrast to like, direct laser, the Digilas Laser operates on a standard basis with several shots for a cell. As a result, a large bandwidth is created in the cell geometry, like, e.g. cushion screen, honeycomb screen, special screen.

THINK LASER

The Think laser process is very similar to the principle of laser etching. It is suitable for the reproduction of fine line elements and permits high flexibility during screening. In the first step, the copper coated cylinder is equipped with a light-sensitive layer. The laser then images the motif being printed on the surface, not used for mechanical decor transfer, as with laser etching. After the imaging procedure, the cylinder is developed, and fixed. Thanks to the etching procedure with ferrous 3 chloride, the freestanding positions on the cylinder surface are widened, and deepened on the cylinder surface to the cell. The imaging layer can be removed without trace before the cylinder is chromed.