Flexographic direct plate making technology
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Like the lithographic printing, the flexo platemaking now uses computer-to-plate technology. Such as DuPont The company introduced the Sally digital imaging system and the Cyrel digital flexo plate.
We know that the traditional flexographic plate making process is: prepress plate making, negative film, printing plate and so on. In the plate making process, a special printing machine is used to make the negative film and the plate close together, and the back exposure and main exposure, development, post exposure and other processes are also carried out, the operation is very complicated, and the quality is difficult to grasp. In particular, the tone level of the image may also be lost. Direct printing with flexo printing can also greatly improve work efficiency, save film consumption, save materials, and greatly improve plate quality, and increase the reproduction range of images.
First, the structure of flexographic direct plate making plate
The flexographic plate-making plate structure is composed of a resin film base, a photosensitive resin layer, and a black laser absorbing layer on the photosensitive layer as shown in FIG. The photosensitive resin layer is the same as the photosensitive resin layer of the ordinary photosensitive resin plate, and the black laser absorbing layer can be ablated by laser.
Second, the principle of plate making of flexographic direct plate making
As shown in Fig. 2, at the time of plate making, the infrared ray emitted from the image generator of the direct plate-making machine first ablates the black absorbing layer of the image portion to expose the underlying photosensitive resin layer. Since the photopolymerizable photosensitive layer is insensitive to infrared rays, the emulsion layer which is ablated by the laser is not affected by the infrared laser.
After laser ablation, the plate can be fully exposed. The black coating left in the blank of the printing plate blocks the light, so that the photosensitive layer in the blank is not sensitive; and the photosensitive layer in the image is photopolymerized due to the loss of the black coating protection, which forms the final Graphic part. After exposure, general digital flexo plates can be developed in the usual way, namely: solvent washing, drying and finishing. However, some digital flexo plates require a black coating to be rinsed off with water before rinsing with solvent.
Third, the difference between digital flexo printing and ordinary flexo printing
1. During the exposure process, the scattering and diffuse reflection of light are different. When the ordinary flexographic printing plate is exposed, the ultraviolet rays pass through the vacuum layer, the film base, the emulsion layer and the antihalation layer, and the total thickness thereof is large, and there is a serious scattering and Diffuse problem. When the digital flexo plate is exposed, the light passes through only a layer of black coating of less than 0.001 in., and there is only weak scattering and diffuse reflection.
2. The exposure environment is different, the ordinary plate is exposed under vacuum, and the digital plate is exposed in the air. The photopolymerization photosensitive resin has a different photopolymerization mechanism in air and in a vacuum, and thus the dot-point dot shape, the exposure latitude, and other properties of the printing plate are also different.
3. The dot shape is different, the dot reproduction range is large, the convex dot on the ordinary flexo plate has a circular cross section, the longitudinal section is trapezoidal, and the top of the dot is flat, and the raised dot on the digital flexo plate is small and inclined. The degree is small, the tip of the point is round, but not flat. The edge of the dot of the digital flexo is sleek. The outline of the dot on the ordinary flexo plate is clear. Clearly defined dots are easy to break when printed, and dots on digital flexo plates, especially highlights, are less likely to occur, so print quality is good.
4. The exposure latitude is different, and the black coating on the digital flexo plate greatly improves the latitude of the UV main exposure. Experiments show that the digital flexo printing master exposure time is increased by 5 to 10 minutes, which has no effect on the convex height of the image portion on the printing plate, while the ordinary flexographic printing plate is different. As long as the exposure time is slightly increased, the image will be convex. The height of the rise is significantly reduced. Exposure latitude is great for the perfect shape of the dot. Since the digital flexo plate has a certain degree of exposure latitude, it is not necessary to pay special attention to highlights and dark points during exposure, and it can also ensure that the highlight points are not lost, and the dark spots are not sticky. It is recommended to set the main exposure time of the digital flexo plate to 10 min, which is enough to ensure that the highlight point is not lost. In the preparation of the ordinary flexo printing plate, the exposure time must be strictly controlled, not only the highlight point is not lost, but also the dark tone point is not confused.
Fourth, flexo direct plate making machine
The principle and structure of the digital flexo platesetter and the film output laser imagesetter are somewhat similar. The digital flexo plate-making machine has two modes of inner roller exposure and outer roller exposure in the exposure mode. In the inner drum digital flexo direct plate-making machine, the plate material is kept inside the drum during the exposure process; in the outer drum digital flexo-printing plate-making machine, the plate material is kept outside the drum during the exposure process. When the drum rotates at a high speed, the exposure head is laterally moved relative to the drum for exposure. At present, flexographic platesetters are basically external drum type, and only small or medium (30in, 40in) platesetters have internal drums.
The digital flexo platesetter is controlled by a raster image processor (RIP). A raster image processor (RIP) is hardware or software that interprets data from the front end of a computer and sends it to a laser imagesetter. The internal interpretation of the RIP of the digital flexo plate-making machine is PostScript. Language. Its work tasks and principles with PostScript The laser imagesetter is the same. It describes and interprets the content of the page sent by the application, forms a bitmap image mode, and controls the digital flexo plate-making machine to perform laser ablation, and records the page information on the plate.
The raster image processor consists of two parts: an interpretation part and a control part. The interpretation part accepts the page information from the computer and encodes it for use by the control part; the control part is used to control the operation of the imaging system.
Fifth, the application of digital flexo printing
At the time of plate loading, since the plate is stretched, the height of the small dots which are originally equal to the solid area is lowered, so this factor must be taken into consideration before the plate making to improve the balance between the highlight area and the printing pressure in the field.
The primary problem facing flexographic direct plate making is the price issue. Whether it is a plate making device, a proofing system or a digital flexo plate, the price is higher than ordinary flexo printing. However, digital plate printing eliminates the process of developing and fixing film and film, eliminating the need for various chemicals, places where film is stored, and vacuum operation procedures for film and plates during printing, which saves a certain cost. And the plate making efficiency and printing quality are unmatched by ordinary printing plates.
One of the main reasons why digital flexography can survive is that it can be used for high quality flexo printing. With the improvement of the quality of digital printing plates, the economic advantages of flexographic printing will also create favorable conditions for the development of new markets. At the same time, it will provide more choices for printing and printing customers, so that customers can get the lowest price. , the best quality to get the required prints.
Sixth, sleeve flexographic direct plate making technology
The flexo plate mentioned above should be applied to the plate cylinder after plate making before printing. There is now a more advanced flexographic direct plate-making technology in foreign countries, which can be directly plated on the sleeve, and then the sleeve plate can be printed on the plate cylinder, which is more efficient. This technology is the direct plate making technology of the sleeve. The sleeve direct plate making method can be divided into two methods of laser engraving and laser ablation.
1. Laser engraving sleeve technology has been used abroad to directly engrave a flexographic plate on a sleeve. In this way, the sleeve can function both as a normal sleeve and as a printing plate. The page made by the prepress system can be directly output to the sleeve by the computer, eliminating the need for exposure, rinsing, curing, and printing, and the working efficiency is greatly improved. For example, the laser engraving sleeve technology of PLOYWEST in Germany can produce a plate with a combination of solid and hierarchical dots to obtain super-fine graphics.
2. The laser ablation sleeve technology, in the packaged printed matter, often encounters a number of patterns designed to repeat the same version, and can be cut at will. The joints at both ends do not show seams. Although it can be done on a reel press, if you print on a single sheet of paper, it is very difficult to see the seams. The sleeve technology can solve this problem well, because on the sleeve plate, the CTP technology can be used to directly make plates, and the problem can be easily solved. The steps of its making are as follows:
2.1 Apply a layer of hot melt adhesive to the nickel or other metal roll of the hollow core. After drying, the cut photosensitive resin is wrapped on the metal roll and the two ends are assembled. Vacuum is drawn from the core of the metal roll (the surface of the roll has a lot of small air holes) so that the photosensitive plate is in close contact with the surface of the metal roll. Then, it was placed in an oven to be heated, and the plate was fused with the adhesive layer on the surface of the metal roll, and then taken out and cooled.
2.2 Put the sleeved version of the first step after cooling on the peripheral grinding machine, and grind the outer circumference of the sleeve plate to a certain diameter according to the size requirements of the printing (detected by laser), and the layout is naturally smooth and flawless. After rubbing it, apply a black coating to the surface of the sleeve. Dry and spare. 3 The second step of the prepared sleeve plate is subjected to digital laser scanning, so that the black coating on the sleeve plate is subjected to laser thermal erosion, and then UV exposure is performed as usual. 4 Put the exposed sleeve plate into the corrosion chamber for rinsing and corrosion, then take it out and blow dry.