Helio-Klischograph
A Helio-Klischograph is a system for the electromechanical engraving of gravure cylinders . In contrast to the Klischograph , the machine developed by Rudolf Hell in 1961 can engrave pressure cylinders , i.e. cylindrical objects.
technology
Two cylinders, called the master cylinder and the impression cylinder, are driven synchronously and rotate at the same speed. The master copies, usually halftone or opal films, are located on the master cylinder . The printing cylinder consists of a steel core with a thin copper layer into which the print image is engraved using an electromagnetic engraving system with a diamond stylus.
The scanning unit consists of a light source and two photo multipliers , which are located in the optical head together with the recording optics and the electronics connected to them. The optical head moves slowly along the rotating cylinder, the photo multipliers receive the light reflected from the original image and pass it on as electrical signals. The signals are amplified and sent to an engraving stylus that is driven by an electromagnetic system. The copper surface of the printing cylinder moves evenly under the stylus. The graver cuts a chip out of the copper around 4,000 times per second. It cuts into small cells, the cell size results from the respective recorded brightness / scanning signal. The further the stylus penetrates into the copper layer, the larger the cell volume and the darker the printed color will later be. The fine copper shavings produced during the engraving are sucked off through a channel.
The engraved cells form a pyramid that opens downwards. In the dark parts of the picture they almost collide with one another, except for a narrow bridge. This bridge is important for the squeegee , with which the excess paint is wiped off the cylinder. In the lighter areas of the image, the bridge becomes wider and wider and in the very light tones there are only tiny depressions.
The opal films are engraved on a 1: 1 scale and can be positive or negative, as well as reversed or corrected. The grid is done electronically in the engraving machine. With four-color printing , a different screen angle occurs for each color by changing the ratio of feed and peripheral speed. The engraving resolution in illustration, packaging and decorative gravure printing is in the 60 to 80 grid.
History and today's situation
After the successful use of the Klischograph in the relief printing area, those responsible from the gravure printing department commissioned Hell to develop a corresponding solution for this process as well. In 1961 the first Helio-Klischograph was presented to the professional world. After half-tone slides were scanned, opal film was soon used as a more suitable scanning template.
In the 1980s, for economic reasons, the adoption of offset films as printing templates prevailed. This process was called offset-gravure conversion or OT conversion . The scanning head was set so that the screened offset films were scanned integrally and converted into corresponding halftone values. The most important prerequisite for the OT conversion was the descreening of the originals, as otherwise a moiré would occur on the engraved gravure cylinder .
From 1995 onwards, the gravure cylinders were mainly engraved directly from the digital database to describe the printing form. Today, data is transferred from a digital workflow that usually starts with PDF pages and can be automated as required. The engraving systems read 8-bit and 1-bit Tiff files . The gray levels of the Tiff files are converted into an engraving signal and passed on to the engraving system and the stylus.
Electromechanical engraving has evolved over the past few years. There are engraving systems for the helioclischograph that can engrave around 8,000 cells or up to 12,000 cells per second. A further improvement was achieved through the introduction of high-resolution engraving for text and linework elements using the "XTreme" process from Hell Gravure Systems and "TranScribe" from Daetwyler. Cups are also engraved here, but they are cut into the copper layer in several cylinder revolutions and are produced by a higher lateral resolution with overlap and without the usual stylus frequency.
A new development is engraving with the laser beam , which enables higher engraving speeds. Depending on the process, a zinc surface or a thicker chrome layer is engraved instead of the copper. Basically, with laser engraving, cells are burned into the cylinder surface, which have a correspondingly larger or smaller volume depending on the strength of the electronic signal. The high writing resolution of up to 2,540 dpi enables very high contour definition. This is why direct laser engraving is particularly suitable for printing labels and packaging, such as cigarette packaging. The well-known suppliers Daetwyler and Hell-Gravure are working on both laser technology and the further development of electromechanical engraving. The manufacture of a laser engraving machine is much more complex than that of an electromechanical machine. In addition, a laser engraving machine requires around ten times the energy per cylinder.
The more than 4,000 electromechanical engraving machines that image more than eight million cylinders worldwide are now compared to an estimated 50 laser machines with a capacity of around 150,000 cylinders. It is currently unclear which system will prevail on the market.
Individual evidence
- ↑ a b c Helio-Klischograph ( Memento of the original from January 10, 2015 in the Internet Archive ) Info: The archive link was inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice.
- ↑ a b c Helmut Kipphan (Hrsg.): Handbuch der Printmedien. Verlag Springer, 2000, ISBN 3-540-66941-8 , p. 49ff.
literature
- Helmut Kipphan (Hrsg.): Handbuch der Printmedien. Springer-Verlag, 2000, ISBN 3-540-66941-8 .
- Michael Limburg: The digital Gutenberg. Springer-Verlag, 1996, ISBN 3-540-61204-1 .