Digital plate making technology for gravure printing
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Gravure printing is mainly used in food packaging, human leather, cigarette packaging, construction and home decoration materials, flooring materials, fabrics and other fields. Gravure printing ink has high gloss, strong tinting strength, bright color, good transfer and overprinting performance, high printing density, large contrast, balanced dot-tone adjustment, high printing durability, and fast printing speed.
Many domestic gravure manufacturers use a lot of plate-making methods, but with the rapid improvement of printing plate-making technology in recent years, digital plate-making has gradually occupied the mainstream of the market. Digital plate making is the process in which color information is transmitted as digital signals in the process of being copied onto a printing plate. Its main advantages are:
1 Simplified the plate making process, and the good graphic documents can be printed by computer control; 2 reduce the direct cost of plate making, and eliminate the use fee of film;
3 reduce the loss of signal during the color reproduction process, which is more conducive to color management;
4 solved the continuous seamless splicing of the graphics on the drum, and greatly enhanced the practicality in the fields of decoration and textile;
The size change of the 5-format is more free. At present, the printing plate of 2800mm×2000mm format can be made in China, which is completely free of the limitation of the output film of the photo-aligning machine; 6 can provide precise positioning for multiple processes on the same roller, which can be different on the same plate. The number of lines and the points of different network lines.
According to the actual situation in China, there are three ways to digitally print gravure:
1 electronic engraving machine mode;
2 laser engraving and post-corrosion treatment;
3 laser direct ablation plate making method.
First, the electronic engraving machine
The electronic engraving machine is a precision machine with high quality stability, such as application integrated automation control. Take the German Hell machine as an example. The engraving frequency is 4000Hz-8000Hz. The network cable range is 40-140 lines/cm. After the original is separated, it can be transferred to the electro-engraving machine workstation through RIP and then transmitted in 1-bit Tiff format or ticket unit. The digital signal drives the diamond engraving needle to vibrate on the surface of the plate copper cylinder to engrave the pit. The diamond engraving head has a quadrangular pyramid shape. The v-shaped pits produced by the electric carving head not only have a slight change, but also a change in the size of the area, thereby completing the halftone reproduction of the graphic.
All production data of electric carvings are collected in digital form and can be used in subsequent jobs with high reliability. From the beginning of scanning, the original becomes a digital signal and is sent to the software for color separation and transmission to the electric engraving machine or color proofing machine. This is very advantageous for the standardization and standardization of the production process, so that the quality of the printed matter is more guaranteed. Moreover, the electro-engraving workstation uses TIFF graphic data to transmit, and the HelioLight group workstation performs convenient integration and sets the working parameter configuration. The engraving software generates the electro-engraving curve, records the electro-engraving parameters and displays the engraving state, and burns the disc to save the file. (convenient to use and redesign multiple times).
The electric carving process is relatively mature, the control is simple, and the level is realistic. The disadvantage is that the amount of ink on the ground is limited, and the ink layer has insufficient hiding power for some rough substrates; since the mechanically engraved cells and the cells are separated by a mesh wall, the edge of the line composed of the cells is inevitably jagged. Small text is not clear and easy to break or paste when printing. However, Haier has recently introduced the Xtreme engraving technology, which can reproduce the most subtle parts in a very fine line up to 400 lines/cm. The fine text can be independently selected without depending on the number of engraved lines. The ink stream smoothes the outline and creates outlines. Both regular outlets and FM screening replication can be implemented.
In addition to the mature products of American Ohio, Germany Haier, Japan Screen and Switzerland mdc, some manufacturers in China have developed similar products.
Second, laser engraving and post-corrosion process
The laser engraving and post-corrosion process is an advanced digital plate-making method after electric engraving. It accepts the color-processed image file through the interface like the electric engraving, and sends the screened image signal to the laser modulator. The laser acts on the protective layer pre-coated on the surface of the drum to expose the copper or iron bottom, and then forms different sizes of dot pits on the drum after different time of corrosion.
Take the Westbass Ohio SCHEPERS laser machine in Germany as an example. It uses a yttrium aluminum garnet (Nd3+:YAG) solid-state laser with a laser power of no more than 50W and is focused by a lens into a 20μ spot. The laser crushes the black rubber on the surface of the roller, and the residue is discharged into the collection bag by the suction pipe. The retained black rubber forms a corrosion-resistant protective layer on the surface of the roller, and finally controls the concentration of FeCL3 liquid and the spray time in the corrosion tank. The surface of the layer or the iron roll produces dots of uniform depth and different sizes.
The laser engraving process overcomes the weakness of the electro-engraving text and fine lines, and highlights the characteristics of high ink content, thick color, clear writing, and durability. Compared with the traditional gravure plate making, it has high screening precision. , free to edit the mesh shape, no seams and so on. It is suitable for printing plates such as cigarette printing and anti-counterfeiting printing, which are particularly small but require high definition. It is widely used in high-precision anti-counterfeiting printing such as currency, securities and ticketing, as well as high-grade tobacco and alcohol packaging. It is made in fine embossing roller and rubber roller. More advantages in the process.
There is also a sensitizer laser method in which the photosensitive layer of the image portion is exposed and washed by a violet laser. Other processes are basically the same as laser engraving.
Third, the laser direct ablation plate-making method of electroplating alloy
At present, Dōwyler's DLS (Direct-Laser-System) system is used in the market. The high-power YAG pulsed laser vaporizes the zinc layer on the surface of the galvanizing roller by contactless illumination to form dots, and then hard chrome plating is completed. Throughout the process, zinc was chosen because of its physical properties (melting point, boiling point, hardness) and reflective properties that are more suitable for laser ablation than copper. The DLS system supports the common PS, PDF, and TIFF data formats. By adjusting the energy of each laser pulse point and the diameter of the focus point, the dots of different sizes and depths are generated. At present, the maximum mesh point is 140μ and the depth is 35μ, which is mainly applicable to cigarette packets and anti-counterfeiting. print. The wide application of laser ablation technology in gravure is rapidly spreading with the development of laser technology. It does not require mechanical adjustment, fine lines and text, and easier control than corrosion.
At present, HELL in Germany has launched a new laser engraving machine, Cu-Diretlaser system. It uses a high-resolution laser to perform fine engraving directly on the surface of the copper drum. The contour of the engraved information, the distribution of the dots, and the depth can be arbitrarily changed, thereby achieving an output that was previously only possible with a laser imagesetter.