Analysis on the plate-making technology of electronic engraving gravure printing
Gravure printing plates can be divided into two categories in terms of manufacturing methods, one is engraved gravure, the other is gravure, and the engraved gravure includes manual or mechanical engraving gravure and electronic engraving gravure.
Hand-carved intaglio is carved on the copperplate with various carving knives, which can directly engrave concave lines, or coat a layer of anti-corrosion film on the copperplate first, scratch the anti-corrosion film to expose the copperplate surface, and then carry out chemical corrosion. Mechanical engraving intaglio is directly carved by machines such as color engraving machine, floating engraving machine, parallel line engraving machine and scaling engraving machine, or the etching resistant layer on copper surface is etched to make intaglio.
Gravure carved by hand or machine has delicate lines and exquisite patterns, which are mainly used to print banknotes and bonds with anti-counterfeiting value.
Electronic engraving gravure, using an electronic engraving machine, according to the photoelectric principle, controls the engraving knife, and engraves a net hole on the surface of the roller, whose area and depth change simultaneously.
The manufacturing process of electronic engraving intaglio is as follows:
Making scanning film → installing printing plate cylinder → testing → engraving → chrome plating 1. make scanning film In the past, the scanning negative film used continuously adjusted milky white film, which was expensive and difficult to control the negative film quality. In the 1980s, the electronic engraving machine added electronic conversion components, and carried out rubber-concave conversion according to the designed procedures, that is, engraved intaglio plates with screened negatives for offset printing. Therefore, most of the negatives with color separation and screening are now used for plate making.
2. Install the plate cylinder Install the printing plate on the electronic engraving machine by crane, and remove the grease, dust and oxide from the layout before engraving. Paste the scanned negative flat on the original roller.
3. Testing According to the requirements of the original manuscript (scanned film) and the hue of ink, the trial engraving value is formulated in combination with the printed products. For example, the paper for decorative printing is rough and has strong ink absorption, and the engraving depth must be between 45 μ m and 50 μ m to meet the printing requirements. The current and voltage on the engraving amplifier must be adjusted.
4. Carving The scanning head scans the manuscript, the engraving head and the scanning head operate synchronously, and the surface of the printing plate cylinder is engraved into different meshes.
The new electronic engraving machine has three shapes of dot angles, which can be arbitrarily selected during operation, so as to avoid turtle writing caused by inaccurate overprinting. See figure 4-26 for three mesh point angles.
When carving characters, the fine lines can’t be lost, and fine screen lines must be used for carving. If 100 lines /cm are used, the carving of characters can achieve very ideal results.
At present, electronic engraving intaglio is made by split electronic engraving system, that is, the scanner is separated from the electronic engraving machine and connected with the input and output interfaces of the image workstation respectively. Scanners can scan positive and negative negatives, and can scan milky white films and carry out glue-concave conversion. Workstation has a variety of image processing functions, which can carry out overall and local color correction, cutting, combination and scaling, and color gradient on images. Make yellow, magenta, cyan images and line images into one. The net wire of the electronic engraving machine ranges from 31.5 to 200 lines /cm.