Analysis on the direct plate making system of laser engraving in flexographic printing
Abstract of this paper: The traditional flexographic plate making method is complicated, with low automation and difficult quality control. In 1980s, flexible CTP technology based on laser technology appeared. Laser direct engraving technology has simple plate making process and easy control of plate making quality. It is simpler and more efficient to form laser engraving sleeve directly by combining with computer printing plate sleeve directly. With the continuous progress of modern science and technology, flexographic laser direct plate making technology is gaining market attention.
Key words: flexographic printing, laser engraving plate making, computer-to-plate, computer direct sleeve making 1 comparison of plate-making methods 1.1 the traditional flexographic plate making process Traditional flexographic plate-making process is very cumbersome, which involves a series of steps, such as making negative pictures, preparing plates, back exposure, front exposure, developing, drying, debinding, post exposure, plate inspection, etc., which costs a lot of cost and time. Moreover, the process is cumbersome and the degree of automation is low, and some plate-making failures are easy to occur due to human negligence.
1.2 Flexo computer-to-plate technology Flexographic computer-to-plate technology is mainly divided into direct engraving and indirect engraving.
1.2.1 indirect plate making by laser engraving The representative of indirect engraving technology is CDI(Cyrel Digital Imager) computer laser direct plate making technology jointly developed by Esco and DuPont. This technology is to use laser engraving machine to ablate the black film compounded on the photosensitive resin plate, and then use traditional equipment such as exposure machine and plate washing machine to complete plate making. In fact, the indirect plate-making technology only turns the film into a black coating on the surface of the printing plate. Other plate-making technologies are not much different from the traditional plate-making technology, which is a compromise method under the technical conditions. However, it has greatly simplified the plate-making technology and saved time and cost.
1.2.2 direct plate making by laser engraving Direct engraving means that the engraving machine uses high-energy laser to directly ablate the plate with a certain thickness on the non-graphic part of the printing plate, and form the raised graphic part dot. This eliminates the need for exposure, plate washing and drying. In the past, limited by the output speed, the price of high-energy laser equipment, the life of laser, the output resolution, the compatibility between printing quality and traditional equipment, etc., indirect engraving has been the mainstream technology of flexographic plate making in the world, and its market share has exceeded 90%. With the rapid development of science and technology, the emergence of laser technology, new materials and new processes, and the progress of laser engraving technology in recent years, especially the improvement of pixel size, engraving speed and plate material, the quality and level of laser direct engraving plate making have been significantly improved. The world’s advanced laser engraving and plate making machine manufacturers have also invested huge research and development and promotion work. Coupled with the continuous development of the sleeve printing plate system made directly by computer, it is believed that in the near future, laser engraving technology will become the mainstream plate-making technology of flexographic printing.
2. The main process of direct plate making by laser engraving 2.1 plate making principle There are two different mechanisms for engraving flexographic plates with low thermal conductivity: instantaneous vaporization and combustion. Its principle is to shoot the focused laser beam to the printing plate, melt or vaporize the specified range of the printing plate, remove the unnecessary part of the printing plate by suction and cleaning and wiping, and make a convex-concave image.
2.2 plate making process Firstly, the computer is used to make the figures, images and characters to be carved. Then, the special computer image software will convert the image and text information of the manuscript into executable depth, size, shape and other relevant parameter data of the modulated laser beam. Then the control system controls the movement of the laser beam according to the command. Laser acts on the surface of the material, and the image and text information can be ablated into dot residues after ablation by a special device 3 main components of laser engraving direct plate making system Like most CTP systems, flexo printing is mainly composed of three parts: computer system, imaging system and plate supply system Cheng.
3.1 computer system The role of computer system is in the first place among the three components, because it affects the whole workflow to And the quality of the final printing plate. Computer system is usually composed of image digitization system, image page description language, raster image processing system, data storage system and control system, which can complete the editing and typesetting of images, and save the arranged layout in the format of page description language for the output of imaging system.
3.2 imaging system The function of the imaging system is to receive the page description information transmitted by the computer system, interpret it by RIP, generate instructions to control the imaging head (laser), expose the printing plate, and complete the printing plate production. There are two ways: inner roller exposure and outer roller exposure. In the internal cylinder digital flexo direct plate making phase l, the plate is always kept inside the cylinder during exposure; In the external cylinder digital flexo direct plate making machine, the plate is always kept in the cylinder during the exposure process 3.3 version supply system The function of the plate supply system is mainly used to store flexographic plates, and complete the conveying, positioning and cutting of flexographic plates during plate making. Digital flexo printing direct plate making machine in exposure mode 4 equipment and material selection 4.1 Selection of Laser Laser engraving system mainly uses high-power laser to remove rubber or materials in non-graphic areas of printing plates. The laser power required by this type of flexible CTP system is far greater than that required by CDI system, and CO2 gas laser with power of 250W is generally used. Laser engraving flexible CTP system. Under the control of the computer system, the laser beam directly acts on the rubber flexographic plate, and the high-energy CO2 laser beam can directly remove the rubber on the non-inked blank part of the flexographic plate like a carving knife, thus completing the production of the flexographic plate 5 advantages of laser direct engraving flexo printing plate  (1) it is unnecessary to dry and wash, which saves a lot of expenses and reduces the cost.
(2) Save plate making time (3) The engraving quality is stable and easy to control, and the printing plate will not expand without washing.
(4) A large number of auxiliary equipments are saved and the investment is reduced (5) Carved mesh points are sharper and steeper than traditional mesh points, and the mesh points are round. High contrast and small dot gain rate.
(6) The whole workflow is fully digitized, and the industrial process is greatly simplified. Quality control is also easier to achieve 6 Laser engraving direct sleeve making technology 6.1 Introduction of sleeve printing plate system CTS(Computer to Skeeve) technology, also known as ITR(In The Round) flexographic plate-making technology, can directly fix the plate on the printing machine without pasting, so it can effectively improve overprinting accuracy, save downtime and improve production efficiency.
6.2 Classification of sleeve printing plate system 6.2.1 Slotted sleeve technology PTS That is, the photosensitive resin flexographic plate is pasted on the sleeve, and then the laser ablation molding process is carried out. That is to say, the plate is mounted on the sleeve first and then the plate is made.
6.2.2. Seamless sleeve technology CTS Seamless sleeve printing plate for laser engraving is mainly composed of inner layer, middle layer and surface layer. The inner layer is usually made of multilayer glass fiber as the main body and supporting structure of sleeve. The middle layer is made of special polyurethane rubber, which has strong elasticity and compressibility, thus reducing vibration and making the packaging sleeve run stably. The surface layer is mainly rubber and hard polymeric material, which protects the inner material and provides ablation.
6.3 Laser engraving sleeve technology The laser sleeve technology combines the advantages of laser technology and sleeve technology, and the plate-making process is completely digitized and automated. The engraved sleeve can be printed directly on the machine only by simple post-processing, thus eliminating a series of steps such as exposure, washing and printing, and greatly improving the working efficiency. At the same time, because there is no need to calibrate repeatedly, the error is reduced as much as possible. The debugging time from receiving the original manuscript to starting up is greatly shortened, the waste products are reduced, and the benefit is improved.
7 New technology of flexographic laser direct engraving and plate making With the further progress of this laser technology, laser engraving technology not only allows us to make printing plates with fine dots on the plane, but also can accurately control the shapes of printing plate dots in three-dimensional space, so as to further improve the printing quality. The following applications are represented:
7.1 control dot shoulder angle Through laser direct engraving technology, dot shoulder angles of various specifications can be made as required. Today’s traditional printing plates or CDI printing plates are mostly close to 45 ~ 50, and laser direct engraving technology can realize engraving of arbitrary dot shoulder angle. Generally speaking, the average dot shoulder angle of laser direct engraving printing plates is 75 ~ 80 in high light part and 90 in dark tone part, and its shoulder angle is steep, while sharp dot can bring clear printing.
7.2 relief height Different from the back exposure of photosensitive resin plate, the designed engraving depth is input into the laser engraving system, which can realize accurate engraving depth. Thereby being well matched with the printing pressure. Better control of dot deformation, and get high-quality printed products.
7.3 images below the layout This is the biggest feature of laser direct engraving technology. The laser engraving system controls the image height according to the printing pressure and image gradation. With this technology, we can make high-gloss dots which are difficult to expand in traditional flexographic printing by reducing the height of printing plate dots in high-gloss areas.
8 supplier status The suppliers of flexographic laser engraving plates mainly include BASF of Germany and Fuji Company of the United States.
8.1 BASF, Germany In 2004, BASF reached an agreement with Schablonentechnik Kufstein, a subsidiary of Stork, to jointly develop a laser direct engraving system for flexographic plates. BASF is one of the main plate suppliers in flexographic plate market. Under this agreement, Schablonentechnik Kufstein will develop high-performance laser system, including necessary control parts and software parts. BASF will develop the required plates and bring the system to market. Both sides have realized that laser engraving flexographic printing has a bright future. Moreover, products with more consistent quality can be obtained in a very short time because direct engraving does not need washing and other steps. The prototype BDE 4131 of this engraving system was exhibited at drupa Exhibition. NyloprintWS provided by BASF has better replication performance, and it can replicate less than 5% of outlets; Therefore, the reproduction of the bright tone of the image is ideal, the printing quality is greatly improved compared with the previous one, and fine gradation can be printed ideally. BASF also provides another printing plate nyloflex LD. This printing plate is made of a new polyester material with Shore hardness of 65A. It overcomes the shortcomings of sticky rubber printing plate and easy melting of printing plate edge, so it has great competitiveness in the current flexographic consumables market. In order to give full play to the advantages of sleeve, BASF has introduced a new photosensitive printing plate nyloflex SL330. Scitex Flex-40/45 laser is a new technology in cooperation with Scitex.
8.2 Fuji Company of America At Labelsexpo Americas 2012, fujifilm exhibited its newly developed B2 format direct laser engraving (DLE) flexographic CTP plate making machine. The new DLE flexographic plate developed by fujifilm and the multi-channel CTP plate making machine together constitute a brand-new flexographic plate making system, which provides ultra-high quality image restoration for label and packaging flexographic application. According to fujifilm company, compared with the general Laser Ablation Mask (LAM) system, the DLE flexo printing CTP system has faster plate making speed and better environmental protection performance. The DLE flexo CTP system no longer needs to use multi-step processing technology (UV exposure, solvent or thermal processing, drying) like LAM technology. It uses a well-cured plate, which is produced by using a unique polymerization technology, and at the same time, it uses a digitally controlled engraving technology for plate making, which means that the shape of the dot is more accurate, so the image restoration is sharper and the details are more vivid. Fujifilm’s DLE flexographic plate making system is more environmentally friendly, because it no longer uses a lot of processing equipment like LAM technology, at the same time, its VOC emission is basically zero, and it no longer needs high-temperature plate drying equipment, thus further reducing plate making energy consumption.
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 Laser engraving flexographic dot quality control, Wang Qiang, Printing Today, 2007/03  Flexographic printing technology, Chen Wenge, Printing Industry Press,  flexographic CDI plate making process and its quality control, Gao Jianli, printing technology, 2010/04  Development Trends of Flexible CTP, Yang Lianrong, Printing Today, 2006/0  Development and application of flexographic plate making technology, Zhao Song; Qin Chaohua, Printing Technology, 2010/18  Breakthrough and Development of Flexo Plate Making Technology, Li Yushan, Printing Technology, 2011/18  flexographic plate making system, Liu Chunlin; Zhang Yixin, Guangdong Printing, 2008/03  Brief introduction of flexographic plate making technology, Wang Maosheng, printing industry, 2009/09  New Technology of Laser Direct Engraving Plate Making in Flexo Printing, Zhou Haiyan, Printing Magazine, 2010/08