Laser gravure engraving technology
The use of lasers as a high-performance means for plate making is a long-term goal of pre-press processing and platemaking. As a high-energy, high-performance recording tool, laser engraving machines have played an increasingly important role in offset printing and gravure printing since the 1970s. On the basis of computer graphic information processing, the use of laser to image and output the film and offset printing plate is the most common and most promising offset printing method. The so-called "CTFilm", "CTPlate" naturally includes laser plate recording.
It is well known that the mechanical electromagnetic gravure electronic engraving machine was invented in 1962 by the German company HellGmbH. This is very close to the invention of the laser. In fact, the company's technicians tried to use lasers to engrave copper-plated cylinders at the time. However, due to the high reflectivity of copper to light, they turned to high-energy electron beam engraving and succeeded.
The gravure printing of the gravure plate began in 1977, when Crosfield Electronics of the United Kingdom used a laser to engrave a cell in a gravure cylinder with a polymer resin layer to make a gravure cylinder. Although the system has not really been put into practical use due to reasons such as quality stability, etc., as a useful technology research and exploration, it has pointed out that the laser gravure printing plate can continue to develop.
At the Drupa2000, a printing event held in Düsseldorf, Germany in May 2000, it was observed that the laser plate recording technology has entered a practical stage. In addition to the technology for printing CTPlate, many manufacturers have launched The gravure printing plate and the flexographic version of the laser plate making equipment have become a highlight of CTC (Computer To Cylinder).
As far as the types of gravure cells are concerned, there are generally four types, namely: variable area cells, concave depth variable cells, variable area and concave depth, and variable frequency cells. At the current state of the art, laser engraving of these four cells has been achieved.
1. Variable area cell
As the name implies, this type of cell reproduces the gradation level change of the image only by changing its open area. The area of the cell in the deep color is large, while the area of the cell in the shallow color is small, and the depth of the cell is unchanged. In this regard, it is similar to the principle of image reproduction of offset dots. Therefore, this type of intaglio is also called "dot gravure".
It should be noted that although the basic principle of image tone reproduction is similar to offset printing, the structure of the cell can not be separated from the basic technical requirements of the gravure plate. This is: the wall must be formed and retained, not on the plate. There is a large area of no-net wall. Therefore, from the microscopic structure of the cell, it is not equivalent to the plain dot.
2. Concave depth variable mesh
This is the most typical gravure cell, often referred to as "classic gravure" or "traditional gravure." This type of cell only reproduces the gradation level change of the image by changing the depth of the cell recess. The color of the cells is deeper in the depth of the color, while the cells in the shallow color are shallower and the area of the cells is unchanged. Since the cell area is the same, the thickness of the mesh wall is equivalent.
3. Variable mesh area for both area and concave depth
Such a cell is often found on a cylinder engraved by a mechanical electromagnetic gravure engraving machine, which is the most commonly used cell type for non-laser electroglossogravure. The characteristics of the cells are: the opening area of the cell in the depth of the color and the depth of the recess are large, and the opening area of the cell and the depth of the recess are small in the shallow color of the face, and it is obvious that the thickness of the mesh wall is not equal.
4. FM network
Applying the principle of FM screening to the gravure, you can generate an FM groove gravure.
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