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.

Digitalization 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.

Nano and laser technology in the manufacture of anilox rollers

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.

High-quality ceramic anilox rolls require a strong resistance to abrasion and breakage (ie, the hardness and toughness of ceramics), but ordinary ceramics are not ideal in both cases. Today, a high-tech ceramic, nano-ceramic, is also beginning to be applied to anilox rollers. The characteristics of nano-ceramics are mainly in the mechanical properties, including the hardness of nano-ceramic materials, fracture toughness and low temperature ductility. Due to the nano-ceramics in the microstructure, the grain size, grain boundary width, second phase distribution, and defect size are all on the nanometer level. Thus, the strength, toughness, and superplasticity of the material are greatly improved, which greatly overcomes many shortcomings such as large brittleness (cracks), poor uniformity, low reliability, poor toughness, and poor strength of the engineering ceramic, so that the ceramic has a metal-like strength. , flexibility and ease of processing. For example, polycrystalline ceramics consist of grains of a few nanometers in size, which can become ductile at low temperatures and can undergo 100% plastic deformation. The nano-titania ceramic material has excellent toughness at room temperature, undergoes bending at 180° C. without cracks, and opens up new fields for replacing conventional ceramic applications. In addition, the mechanical properties of nano-scale ceramic composites, especially at high temperatures, make the hardness and strength higher. Compared with ordinary ceramic materials, nano-composite ceramics have greatly improved mechanical properties, surface finish, wear resistance, and high temperature performance. Studies have shown that the introduction of nano-dispersed phases in the micron-sized matrix for compounding can increase the fracture strength and fracture toughness of the material by 2 to 4 times. It can also increase the hardness and elastic modulus of the material and improve the creep resistance and fatigue resistance. Destructive performance. From the perspective of flexo development, people's demand for high-quality flexographic printing will continue to increase, but high-quality flexo printing requires an anilox roller with a high number of lines, and laser engraving of an anilox roller with a high number of lines, Roller ceramic hardness, toughness, etc. must have very good characteristics, in order to make the laser engraving of the cell contour clear, smooth wall, to ensure accurate ink transfer, so that the ink release performance is good, so as to print a good product. However, due to the brittleness of the texture of the general ceramic materials, the poor toughness and strength, together with the pre-processing technology and other issues, the processing accuracy of the ceramic anilox roll does not meet the requirements, and thus its application has been greatly limited. The application of nano-ceramics, due to the characteristics of nano-, nano-ceramics will overcome some of the defects of traditional ceramics, so that the ceramic hardness, toughness, wear resistance and other characteristics have greatly improved, which laid a good foundation for engraved anilox roller lay the foundation. Therefore, it was predicted that with the wide application of nanotechnology in ceramic manufacturing, ceramic anilox rollers may eventually eliminate all metal anilox rollers.

Many experts believe that if it can solve the technical problem of inhibiting grain growth in the sintering process of single-phase nanoceramics, and thus control ceramic nanocrystals with a ceramic grain size below 50 nanometers, it will have high hardness, high toughness, and low temperature. The unparalleled advantages of traditional ceramics such as superplasticity and easy processing. Cahn, a well-known British material expert, pointed out that nano-ceramics are a strategic way to solve ceramic brittleness. For the flexographic printing anilox roller, when the anilox roller is processed by the plasma thermal spraying process, a high-quality ceramic coating is required to be sprayed on the surface of the substrate, and the coating hardness range is HV 300 to 1300, and the general porosity is required. The rate must be less than 1%. For anilox rollers above 1200 lines, the porosity must be less than 0.5%, and the coating structure must be uniform, without cracks, high hardness, and high density, so as to ensure that the texture The roller has very good precision in engraving high number of lines, improves the abrasion resistance of the anilox roller and resistance to acid, alkali and corrosion, etc., and improves the service life of the product and the quality of flexographic prints.

In the manufacture of anilox rollers, apart from nanotechnology and laser high-tech, a graphite carbon fiber material has been newly developed in the aerospace industry in recent years. Due to its light weight and hard characteristics, it is welcomed in the manufacturing industry. Invented in 1994, the carbon fiber core was quickly applied to the flexo-printed anilox roller core, which became a new generation of highly advantageous anilox rollers. Although steel rolls have long been the most preferred material for anilox rolls due to their physical properties such as strength, mechanical processing properties and durability, they are replaced by such carbon fiber roll cores instead of the conventional steel roll cores. Its strength is 2 times that of steel rollers and its weight is 1/10 that of steel rollers. The anilox roller of this carbon fiber core has been found out through trial and has the following advantages: (1) Since the carbon fiber anilox roller is particularly light, it is easy to handle in the roll change and labor is reduced. (2) Carbon fiber anilox rolls are not easily damaged during roll change, which saves a large amount of money for re-engraving new rolls. (3) In the driving part of the printer, the total weight of the carbon fiber anilox roller is 1/10 of the weight of the steel roller, which is beneficial to reduce the friction between the rollers and the service life of the anilox roller is accordingly increased, thereby reducing downtime. Time, increased productivity. When the speed of the printing press reaches 3000 sheets per hour, the difference between the steel roll and the carbon fiber anilox roll is even more obvious. The steel core anilox roll beats very much at its center.