As a kind of printing process, gravure printing has the advantages of thick ink layer, bright colors, high saturation, high printing durability, stable printing quality, fast printing speed and other advantages in the field of printing, packaging and graphic publishing. Occupy an extremely important position. From the perspective of application, in foreign countries, gravure printing is mainly used for fine publications such as magazines and product catalogs, packaging printing and printing of securities such as banknotes and stamps, but also in special fields such as decorative materials; gravure printing is mainly used In food packaging, human leather, cigarette packaging, building and home decoration materials, floor materials, fabrics and other fields. 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 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 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‘¡The direct cost of plate-making is reduced, and the use fee of film is eliminated;
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 of the field of decoration and textile;
⑤The format size can be changed more freely. At present, the printing plate of 2800mm × 2000mm format can be made in China, which is not subject to the limitation of the output film of the phototypesetting machine; The number of lines and the dots of different network angles.
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 made by color separation, it is transmitted to the workstation of the electric engraving machine in 1-Bit Tiff graphic format or bill unit after passing through RIP The digital 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 image and text data for transmission. After the HelioLight group version workstation for easy integration and setting of 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 mesh wall partition between the mechanically carved mesh and the mesh, the edge of the line formed by 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 mature products of Ohio, Germany, Haier, Japan and 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 breaks 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. 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, the DLS (Direct-Laser-System) system of DÅwyler Company is used in the market. The high-power YAG pulsed laser vaporizes the zinc layer on the surface of the galvanized roller to form dots by non-contact irradiation, and then the hard chromium plating is completed. 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.
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