3) Computer Direct Sleeve Plate Technology
1 defects of flat photosensitive resin flexo
Although the use of flat photosensitive resin flexo can achieve good image information transfer and maintain the integrity of the image, the printed image is always different from the original. The reason for this phenomenon is that: It is flat, but it is printed in a circular manner. The flat printing plate made by standard exposure technology must ultimately be rolled onto the cylinder for printing. Since the plate is stretched in the circumferential direction, although the prepress process can be pre-calculated and compensated, even if the most advanced prepress workflow is used, the flexographic plate twisting and stretching phenomenon occurs even when the plate is mounted. The new type of photosensitive resin plate has excellent shape-preserving properties, and the plate is easily deformed and changed in size.
With the development of computer-to-plate technology, sleeve plates are pre-installed on rollers and exposed or engraved in a "circumferential" manner. The final printed image is exactly the same as it was when it was designed.
2 sleeve printing plate production technology
The technique of making a plate directly on a sleeve plate by a computer is simply referred to as a sleeve plate making technique. There are currently two main types:
a. Slit-sleeve plate: The unexposed photopolymer flexographic plate is placed on a sleeve and exposed to laser light. Finally, a plate cylinder that can be printed on the machine is made. This type of printing plate is mounted on the sleeve during the entire process and it is not necessary to mount the plate before printing on the machine. Greatly improved the printing plate quality and work efficiency. Such as Helio Flex F2000 laser flexographic platesetter, the machine is an external drum exposure machine, both on the surface plate material imaging, but also on the sleeve plate imaging. Digital imaging exposures for photopolymer, photosensitive flexographic plates. The machine uses 8 laser heads and 60W fiber laser to achieve the best image quality. The Helio FlexF2000 predicts which part of the plate or sleeve the pixel to be exposed will be before imaging is started, so that the part without the image is skipped over, and the average can be saved because it can be quickly fed over the unexposed surface. 20% of the time.
Advantages of slotted sleeve plate cylinder technology: To avoid turning up the printing plate during printing (especially when the plate cylinder diameter is small), so that the accuracy of overprinting of the printed matter is higher; the printing operator can according to the type and thickness of the printing plate, The bottom pad of the flexographic plate is optimally selected; the familiar photosensitive resin flexographic printing plate can be continuously used, and the imposition is omitted, and the production efficiency is improved; the user still has a wide range of options for the plate material, for example, according to According to the transfer performance of the printing plate to the ink, or according to different printing materials, or according to the UV ink corrosion resistance and other factors, the type of plate is selected and replaced.
b. Seamless Sleeve Plate Making Technology: Laser exposure on a photopolymer-coated seamless plate sleeve requires a special platesetter.
Advantages of seamless sleeve printing plate technology: Continuous pattern printing can be carried out; multiple-patch imprints can be arranged in discrete or other special ways; printed screens do not break during printing. The ills of the line or seam.
3 Comparison between Traditional Flexo Platemaking Process and Computer Direct Flexo Printing Process
1) Insufficiency of traditional flexo platemaking process
The traditional flexographic plate production process is: film preparation -> back exposure -> main exposure -> wash plate -> drying -> detacking -> post exposure. Compared with the digital platemaking process, the traditional flexo platemaking process has defects in many aspects:
1 High-light part outlets are easy to lose, and shadow assignments are easy to merge. When the flexographic printing master copy was drafted, in the high light part, the outlets were markedly polarized, and either the small outlets (less than 5% of the outlets) had been lost during the printing and became an absolute net; or the dot enlargement rate was too great. Already near the middle of the network. In the dark tone, the network will be in the ground state at around 85%.
2 Since smaller dots are easily lost during printing, in order to reproduce the gradation of the original, the coarser screen lines are often used for plate making and printing. Therefore, the traditional flexographic positioning can only be limited to the printing of low-end products.
3 When the main exposure film and the plate contact, easy to invade the dust, resulting in poor polymerization of the plate to form a depression, vacuum leakage occurs when the vacuum occurs, making the film and the plate is not closely attached, resulting in the image edge is not true.
4 The prepress system is more complex and depends too much on the skill of the operator. The exposure time is determined by the text and is not easy to control.
5 The highlights will have higher mesh points than the actual field. When printing, the highlights will be subject to greater printing pressure, which will cause larger dot gains.
2) Advantages of Computer Direct Flex System
In the workflow of CTP, the production process of negative film has been directly replaced by the imaging process on the printing plate. The cancellation of the film minimizes the loss of quality. In production practice, it has been proved that the computer-based flexo version has the following advantages:
1Comparison the appearance of the flexo CTP plate with that of the traditional plate. The former surface is smoother, and the various parts of the plate (from separate dots, solid dots to fine dots in the high-light area) are almost on one plane. With traditional flexographic printing plates, the fine dots of highlights are usually more prominent than others. Even after the revision, the tops of these dots are several microns higher than the solid parts of the same plate. This means that in the printing process, the dots on the field that were completely printed on the field before the highlights are compressed, resulting in more serious dot gains. In contrast, CTP plates provide more consistent printing characteristics, effectively reducing dot gains. Reproduction of 5% dots during printing is difficult in traditional flexo printing processes.
The size of all image areas on the 2CTP plate was reduced during imaging. This indicates that each line, each field area, especially the dot, is reduced by a few microns, effectively compensating for the dot gain during the printing process. . Since this size reduction process has been automatically integrated into the actual production, there is no negative impact on prepress workflow and image quality. In the traditional platemaking mode, the two are unavoidably affected because the size reduction operation in the traditional platemaking mode is applied as an intermediate process to the film manually.
3 Improve the speed of plate making, reduce plate making costs, and reduce environmental pollution. For example, DuPont developed the Celie rapid system and used thermal development instead of solvent development. The entire process was in a completely dry state, avoiding the slight expansion and deformation of the plate caused by the solvent immersed in the plate during the solvent wash process; The influence of platewashing and drying factors on dot gaining; meanwhile, the speed of plate making was increased. The Cyrel Rapid System is a hot-working version.
4 Compared with traditional flexographic printing plates, digital photosensitive resin printing plates always contact the printing materials at the center of the dot first, so it is easy to use 10% hollow dots.
5 After the flexo CTP is applied, the data from different places can be transmitted to the attached laser device without loss and high-efficiency plate-making can be performed.
6 After the flexo CTP is used, the printing press is faster and easier to prepare. Even with the sleeve technology press, printing a batch of six-color prints takes at least half an hour to change the plate in the traditional plate-making mode. However, with the flexo CTP, printing press preparation time can be greatly reduced.
In addition, the quality of flexo-printed CTP plates has improved significantly. Can expand the flexographic product range.
