High-tech and Operational Points in Flexo Printing (I)

Flexographic printing derived from letterpress printing has been developed and improved for more than 100 years. It constantly absorbs advanced technology and improves the quality of printing. Today, excellent flexo printing products are completely comparable to offset printing, marking the beginning of a new milestone in flexo printing. . In recent years, flexo printing has grown at an alarming rate of 70% per year, and now accounts for more than 20% of the global printing market. According to experts' predictions, by 2005, the flexo printing market is expected to rank second in all printing formats. Looking at the remarkable improvement of the quality of flexo printing, the key is the application of high technology, so that the overall level of technology and material quality continue to increase.

I. Digitization and Laser Technology in Plate Making

The high technology of plate making is the laser technology that emerged from the 1960s when the core technology of computer-to-plate (also called laser direct-to-plate or digital direct-to-plate (CTP)) technology was pushed. After the 1990s, with the development of computer technology and equipment materials, CTP technology has matured and continuously demonstrated its superiority, accelerating the research and development and industrialization of CTP technology. According to statistics, in the United States by 1997, 65% of large-scale printing plants had used CTP technology. From 1995 to 2002, the rate of application of CTP increased at a rate of more than one time per year. Computer direct plate making speeds up the plate making, increases the printing plate quantity and the printing quality, is advantageous to the environmental protection, is advantageous to escapes the darkroom operation and so on merit. Today, CTP technology has shown its superiority in lithography, and its market share is constantly expanding. With the improvement of its technology and CTP plate quality, its market prospect is very broad. It can also be said that it is an important direction for the future development of the printing industry. Using CTP technology, not only can be printed on paper, but also printed on other substrates, such as the use of a variety of plastic film and composite film, metal foil, wood, glass, ceramics, textiles and so on.

Digital direct platemaking was first studied in other printing processes. Flexo platemaking is the last printing method to transition to non-film platemaking in various layouts. This is because the flexographic plate has a certain thickness. It is necessary to use digital high-speed laser to directly obtain three-dimensional dots on the plate material. The difficulty can be achieved. It is much higher than the lithography. However, all the constraints of the traditional platemaking methods, such as the use of multi-channel image processing with film processing, not only have poor stability but also have high costs. In addition, the temperature and humidity all have a certain influence on the film, and sometimes it is necessary to prevent the film from being rubbed. Injuries, etc.; When the film and the plate are exposed, the image quality may be impaired due to light diffusion or poor adhesion, and the subtle parts of the tone may not be reproduced. Since the smaller dots are not easily printed, they can only be rough. The number of screen lines is printed. Therefore, flexographic printing can only be found in the production of low quality products. The introduction of a flexographic platesetter directly exposes the image to the flexographic plate, overcoming the above-mentioned disadvantages caused by the use of the film. The flexographic plate used for direct plate making is different from the ordinary plate, and its surface Re-applied a layer of etched layer - synthetic carbon film, this synthetic carbon film can also avoid dust particles. When the laser scans, the patch at the spot is melted to evaporate without leaving any traces, which is equivalent to leaving an extremely clear picture on the surface, and then the back of the flexo is still exposed as usual. (At this time, the exposure time determines the thickness of the plate). The main exposure (the light source passes through the opening of the synthetic film that has been eroded and direct exposure of the underlying photopolymer, so that there is no scattering or diffuse reflection, so the edges of the dots are sharper and sharper. Moreover, the digital version Even if the material is exposed for a long period of time, it will not cause the dot shape to blur. Finally, the etching process is performed.

The application of CTP technology can well solve some of the problems caused by materials and technical problems in the conventional filmmaking. For example, excessive back-exposure time results in inconsistent relief of lower substrate thickness, lack of back exposure or main exposure time resulting in line distortion and dot loss, over-exposure of main exposure time resulting in lighter shades, and inaccuracy of post-exposure errors resulting in excessive plate hardness. , Insufficient wash time caused by the lower relief thickness of the substrate, wash plate for a long time, the brush pressure caused by line deformation and dot loss, not photosensitive material is not completely dissolved caused by the lighter shade and so on. With the continuous deepening and improvement of the research on CTP technology and related technical materials, its superiority will become more apparent. It not only saves time, manpower, materials and other resources, improves the quality of printed matter, reduces environmental pollution, but also The optimization of the process flow and the ease of forming continuous production lines with a high degree of automation, combined with advanced computer technology, can be confident that CTP technology will bring a new revolution in flexo printing.

Second, nanometer and laser technology in the manufacture of anilox roller

In flexographic printing, the quality of the print depends to a large extent on the quality of the anilox roll and its operating results. The anilox roller is responsible for evenly transferring a certain amount of ink to the printing plate, which is both the ink transfer roller and the ink metering roller, so that the use of the amount of ink is realized with precision. Therefore, the anilox roller is known by the flexographic printing industry as the "heart" of the flexo press. In order to stably supply the low-viscosity ink to the flexographic plate, the anilox roller transfer system is the most ideal printing method. Since the early anilox rolls were all iron rollers, the textures on the rolls were impressed and the production was very rough, which made it difficult to ensure the printing quality and printing costs. The anilox roll was then gradually changed to a copper roll, mechanically engraved, and a harder layer of metal (such as chrome plated on a copper roll) was applied to the surface of the roll to increase wear resistance and fineness and increase ink carrying capacity. , thus improving the quality of prints to some extent. Since 1970, it has also been studied that hard ceramics are used to make anilox rollers. In general, the anilox roll is engraved on the surface of the ceramic and has cube-shaped, tapered-shaped, oblique-lined, etc. shapes depending on the site. According to the shape, the number of lines, the depth, etc., the ink supply amount and the ink holding amount are calculated. In improving the quality of the anilox roller, the application of high-tech lasers and nanometers plays a major role. As one of the four major inventions of the 20th century, laser has a common application in the printing field. In the manufacture of anilox rollers, it is mainly used to process the engraved network points, and has the characteristics of high processing precision and good product quality. However, since it is very difficult to engrave fine carvings on ceramics, it was not until 1984 when the laser technology became mature and widely used in the printing industry that the laser anilox roll was widely used. At present, the laser-engraved anilox rollers mainly include: CO 2 laser engraved ceramic anilox roller; YAG laser engraved ceramic network roller; Ultracell super mesh laser engraved ceramic anilox roller. From its processing point of view, the commonly used methods of laser engraving are conventional carbon dioxide laser engraving and YAG laser engraving with multiple impacts. The YAG laser engraving method with multiple impacts is currently the highest preparation method for mesh engraving. The meshes were struck twice by the laser beam, the first hitting the shape, the second hit increasing the depth of the mesh. Double-clicking a shaped mesh has the advantages of a smooth wall, fast and uniform ink transfer, and so on, thereby ensuring print quality. From the viewpoint of the composition of the anilox roller, there are two methods of the anilox roller inking system. One is to use the roll-to-roll method with a very slow peripheral speed, and the other is to use a doctor blade to scrape ink with a squeegee. The anilox roller blade installation method clockwise and counterclockwise. Recently, the ink slot squeegee method was introduced. The two positive and negative squeegees are not only accurate, but also maintain ink volume. Since the ink tank is used, the scattering and evaporation of the ink can be suppressed, and the ink supply can be stabilized according to the printing speed.