Although the process of gravure printing is simple, the printed images have rich gradation, vivid colors, good definition and high quality. The only challenge is the difficulty of making gravure cylinders. With the development of science and technology, gravure platemaking technology has become more and more advanced and increasingly complex. People who have experienced erosion in the gravure platemaking era know that the etching plate making process is quite complicated. In the etching platemaking, a large amount of materials and equipment are required, and many processes are manually operated. Compared with the etching platemaking process, the electronic engraving plate making process is much simpler, the digital control of the process is realized, the operation is simple, and the quality is reliable. At present, no film engraving has been realized, the original information is no longer scanned, and the data information can directly drive and control the electricity. The engraving needle controls the engraving process through software.
The electronic engraving platemaking process greatly simplifies the production process of the gravure cylinder, improves the production efficiency, the quality of the plate cylinder and the reliability of the plate making process. To improve the working environment is more conducive to the health of operators.
Electronic engraving plate making technology
At the end of the 19th century, with the development of photographic technology, people put forward higher requirements for the printing of continuous tone images. The first proposed is the mesh tuning theory for continuous tone screening. The gray value of the image is represented by different area mesh points. This method has been used so far, but the manuscript screening method has changed greatly. Originally used non-contact screening, and later replaced by contact screening, now completed by the RIP (raster image processor), usually using a value between 0 and 255 to represent the gray value of the image, converted by RIP Dots of different shapes, sizes, and positions.
The electronic engraving gravure process is much simpler than the plate imaging of letterpress, offset and flexo. The value corresponding to the gray value of the original image can be directly transmitted to the electronic engraving machine, and the diamond engraving needle can be controlled to sculpt on the surface of the copper layer, and the area and depth of the engraving hole can be changed. Electronic engraving High-quality gravure plate cylinders suitable for specific printing conditions including printing presses, ink, paper, etc. can be obtained by simple adjustment of the tone curve.
Using the gray value data to control the electric engraving needle can achieve the exact matching with the gravure mesh image, which greatly improves the reliability of the process and the quality of the plate cylinder.
Unlike offset printing, in the reproduction of text and lines, electronic engraving cannot achieve finer reproduction than the selection of engraving lines, and the reproduction quality of text and lines is limited. HELL has improved the dynamic control of electric engraving needles and developed HQH software that effectively eliminates the "sawtooth edge" of the tiny yin and yang lines. Gravure text is softer than offset printing.
Traditional gravure platemaking technology
Traditional photogravure, also known as "shadow edition," relies on changes in the depth of the cell site to express the tone level. It is necessary to separately treat the carbon paper drying mesh and solar sunning pattern with a screen and continuously adjusting the positive images, and obtain the mesh holes with the same area size and different depth according to the permeability of the carbon paper to the etching solution.
The process is complex. There are 11 steps from preparation of carbon paper to corrosion. The predictability and reproducibility of the process are poor, and the depth of corrosion of the net hole and the control of the net wall are quite difficult. What is even more difficult is the control of the highlighted part. The bright tone requires that the depth of corrosion of the cell is very shallow, not to exceed 1 μm, but it is too difficult to achieve.
Photographic direct screen plate making technology
The basic principle is: After the plate cylinder has been plated with copper and polished, it is coated with a photosensitive layer, exposed and then imaged to corrode the copper layer.
The photosensitive layer was first coated on the copper layer of the platen roller and exposed with a high-pressure mercury lamp. Later laser etching technology emerged. Instead of film, the image data directly controls the fine laser beam imaging on the photosensitive layer. Regardless of whether the imaging process is a digital method or a conventional screen film, a dot structure with an area change is only created on the coating, and depth information cannot be reflected. With this type of plate, lines and text can be reproduced very well, but the image is less effective.
Compared with the electronic engraving process, all the photogravure direct-gravure gravure platemaking processes (even with digital imaging technology are no exception) have three fundamental problems: the imaging method is not suitable for high-quality printing, the disadvantages of the corrosion process itself, and complexity The process steps.
Engraving the zinc layer directly with a laser beam
Using short-wavelength laser pulse engraving, the resulting tone is very steep, soft and delicate. Engraving directly on the metal layer also involves the sensitivity of the metal layer to the laser. The small changes in the sensitivity of the metal to the laser beam all affect the energy threshold. Since only the pulse energy above the threshold can generate a network, the energy threshold changes. It affects the size of the cell. If the laser beam's focused energy density fluctuates, it will also cause a change in the size of the cells. Both of these static changes will lead to dimensional deviations of the cells. If this change occurs at the same time, it will inevitably lead to greater deviations. Since the laser beam is focused through the glass lens, only a fixed imaging area can be set. This gives the laser beam only one fixed diameter. One way to increase the engraving stability and increase the resolution of the zinc layer is to use a few small cells to form a grid, the resulting hexagonal grid can accommodate 7 relatively small independent cells, but this method greatly reduces the engraving speed .
Future carving method
Electronic engraving is widely used due to its simple process, high reliability, low cost, good quality, and particularly good image reproducibility. Compared with etching plates, the only disadvantage of electronic engraving is that the profile is poor. In the field of packaging and printing, in addition to electronic engraving gravure, the application of corrosion version is also more common. Even when using laser etched digital imaging instead of traditional film imaging, the depth of the cyberspace cannot be controlled when imaging, which limits the reproduction of halftone products to a certain degree.
In response to this situation, HELL has targeted the solution to the fundamental shortcomings of electronic sculpting - the sharp definition of text and lines. This goal was achieved through two different methods: the development of electronic engraving gravure technology and the development of laser direct engraving copper layer technology.
XT ultra-fine electronic engraving technology
Similar to the laser photocopying technology, XT super-fine electronic engraving technology can use different resolutions for text and image engraving. The text uses 1000 lines/cm, and the image uses 60 lines/cm. Improved text and image resolution, and the depth of the cell can also be changed as required. XT technology means that basic parameters such as resolving power, maximum cell volume, and cell depth can be individually adjusted.
XT technology is widely used and can be used in electronic fields such as printing circuits on aluminum foil. In the field of packaging and printing, XT technology can be applied to graphics that are very delicate. It also plays an important role in security printing. In prints such as magazines and catalogues, XT technology is used for text and line engraving.
Laser engraving directly on the copper layer
According to the principle of XT technology, HELL has developed a prototype of a laser engraving machine that directly sculpts cells on the surface of copper or chromium. The laser beam writing resolution can be individually adjusted. The XT technology also requires a screen controller to be placed in the XT engraving head, while engraving the side of the screen to complete any shape of the cell sculpture. For the first time, this technology will complete the screening process in the engraving head, not only engraving amplitude modulation network points, but also carving FM tuning network points.
HELL's XT technology was first developed for the packaging industry and, under the right conditions, will be extended to large-format catalogs and magazine printing.