Gravure printing is mainly used in a wide range of fields such as food packaging, human leather, cigarette packaging, building and home decoration materials, floor materials, fabrics and so on. Gravure printing ink has high gloss, strong coloring power, bright colors, good transfer and overprinting performance, high printing density, high contrast, dot tone expansion and balance, high printing plate durability, fast printing speed and other advantages.
Many domestic gravure manufacturers use many 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.
According to the actual situation in China, there are three ways to make gravure digital plates:
â‘ Electronic engraving machine mode;
â‘¡Laser engraving and post-etching treatment methods;
â‘¢ Laser ablation plate-making method of electroplating alloy.
1. Electronic engraving machine
Electronic engraving machine is a precision machine with high quality stability that uses modern technology such as integrated automation control. Taking the German Hell machine as an example, the engraving frequency is 4000Hz-8000Hz. The range of the network cable is 40-140 lines / cm. After the original is processed by color separation, it is transmitted to the workstation of the electric engraving machine in the form of 1-BitTiff graphics or bill unit after passing through RIP. The signal drives the diamond engraving needle to vibrate on the surface of the printing plate copper cylinder to engrave pits. The diamond engraving head is shaped like a pyramid. The v-shaped pits made by the electric carving head not only have a change in depth, but also a change in the size of the area, thus completing the halftone reproduction of the graphic.
All production data of electric carving are collected in digital form, which can be used in subsequent jobs, with high reliability. The manuscript becomes a digital signal after being scanned and sent to the software for color separation and then transmitted to the electric engraving machine or color proofing machine. This is very beneficial to the standardization and standardization of the production process, thereby ensuring the quality of the printed matter. Moreover, the electric engraving workstation uses TIFF graphic data for transmission. After the HelioLight group version of the workstation, it is easy to integrate and set the working parameter configuration. The engraving software generates the electric engraving curve, records the electric engraving parameters and displays the engraving status, until the disc is burned to save the file (Convenient for multiple use and revision).
The electric carving process is relatively mature, the control is simple, and the level reduction 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; due to the mechanical wall partition between the mesh and the mesh, the edge of the line composed of the mesh is inevitable , Small text is not clear and easy to break or paste when printing. However, Haier, Germany recently introduced Xtreme engraving technology, which can reproduce the finest parts very finely at a network line number of up to 400 lines / cm. Fine text can independently select the recording resolution without relying on the number of engraving network lines, through optimization The ink flow smoothes the outline and produces outlines. It can realize both conventional outlets and FM plus network replication.
In addition to the relatively mature products of American Ohio, German Haier, Japan Screen and Swiss mdc, there are also domestic manufacturers who have developed products with similar performance.
2. Laser engraving and post-etching process
Laser engraving and post-etching process is another advanced digital plate making method after electro-engraving. It accepts color-processed image files through the interface like electro-engraving, and sends the screened graphic 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 pits of different sizes on the drum after corrosion at different times.
Taking the German SCHEPERS laser machine from Sibas, Ohio as an example, it uses a neodymium-doped yttrium aluminum garnet (Nd3 +: YAG) solid-state laser, the laser power is not higher than 50W, and is focused into a 20μ spot by the lens.
The laser crushes the black glue on the surface of the drum, and the residue is discharged into the collection bag by the suction pipe. The remaining black glue forms an anti-corrosion protective layer on the surface of the drum. Finally, the concentration and spray time of the FeCL3 solution are controlled in the corrosion tank. The layer or the surface of the iron roll generates dots with uniform depth and different sizes.
The laser engraving process overcomes the weaknesses of electric engraving text and thin lines hairiness and imagination, highlighting the characteristics of high ink content, thick color, clear writing, and long-lasting durability. Compared with traditional photogravure plate making, it has high screen accuracy , Arbitrarily edit the mesh shape, without seams and other advantages. Applicable to cigarette plates, anti-counterfeiting printing and other particularly small but high-definition printing plates. It is widely used in currency, securities, ticketing and other high-precision anti-counterfeiting printing and high-end tobacco and alcohol packaging. More advantages in the process.
There is also a sensitizer laser method, which uses a purple laser to expose and then rinse the photosensitive layer of the graphic part. Other processes are basically the same as the laser engraving method.
3. Laser direct ablation plate-making method of electroplating alloy
At present, DÅwyler's DLS (Direct-Laser-System) system is used in the market. The high-power YAG pulse laser vaporizes the zinc layer on the surface of the galvanized roller to form a dot by non-contact irradiation, and then finish hard chrome plating After the whole process, zinc was chosen because its physical characteristics (melting point, boiling point, hardness) and reflection characteristics are more suitable for laser ablation than copper. The DLS system supports common PS, PDF, TIFF data formats. By adjusting the energy of each laser pulse point and the diameter of the focal point to generate dots of different sizes and different depths, the current maximum dots are 140μ and depth 35μ, which are mainly suitable for cigarette packets and anti-counterfeiting print. The extensive application of laser ablation technology in gravure will rapidly spread with the development of laser technology. It does not require mechanical adjustment, the fine lines and text are clearer, and it is easier to control the level than corrosion.
At present, the German HELL company has launched a new laser engraving machine, Cu-Diretlaser system. It uses high-resolution laser to engrave directly on the surface of the copper drum. The contour, dot distribution and depth of the engraved information can be arbitrarily changed, so as to achieve the output effect that only the laser phototyper can reach before.
Advantages of digital platemaking technology
Digital plate making is that the color information is transmitted in the form of digital signals during the process of copying the original to the printing plate. Its main advantages are:
â‘ Simplified the plate-making process, the produced graphic files can be obtained by computer control;
â‘¡ Reduce the direct cost of plate-making and eliminate the use fee of film;
â‘¢Reduce the signal loss in the process of color restoration, which is more conducive to color management;
â‘£ Solve the continuous seamless stitching of graphics on the drum, which greatly enhances the practicality in the fields of decoration and textile;
⑤ The format size can be changed more freely. At present, 2800mm × 2000mm format printing plates can be made in China, and there is no need to be restricted by the output of the phototypesetting machine;
â‘¥It can provide accurate positioning for the implementation of multiple processes on the same drum, and there can be dots with different line numbers and different screen angles on the same version.
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