Flexo Printing Solutions (3)

(9) Flexo printing direct plate making technology

Like the printing of the flat printing, the flexographic printing plate making now uses the computer direct plate making technology. For example, DuPont has launched the Cyrel Digital Imaging System and Cyrel Digital Flexographic Plate.

We know that the traditional flexo platemaking process is: prepress, negative image film, and printing plate. In the plate-making process, a special plate-making machine is used to allow the negative-tone film and the plate to be closely adhered. The back-exposure and main exposure, development, and post-exposure processes are also performed. The operation is very complicated and the quality is difficult to grasp. In particular, the tone level of the image may also be lost. The use of flexographic printing to directly make plates can also greatly increase work efficiency, eliminate the consumption of film, save materials, and at the same time greatly improve the quality of plate making, so that the reproduction of images can be expanded.

1, the structure of the flexographic printing direct plate

The flexographic printing direct-working plate material structure consists of a resin film base, a photosensitive resin layer, and a black laser absorbing layer on the photosensitive layer. The photosensitive resin layer and the photosensitive resin plate of the common photosensitive resin plate are the same, and the black laser absorbing layer can be ablated by the laser.

2. Platemaking principle of direct plate making by flexographic printing

At the time of plate making, an infrared laser beam emitted from a plate-making machine image generator was first used to ablate the black absorbing layer of the graphic portion, exposing the underlying photosensitive resin layer. Since the photopolymerizable photosensitive layer is insensitive to infrared rays, the place where the photosensitive emulsion layer is ablated by the laser is not affected by the infrared laser.

After laser ablation, the plate can be fully exposed. The black coating remained in the blank space of the printing plate to block the light, so that the photosensitive layer in the blank space is not sensitive to light; and the photosensitive layer at the graphic place is protected from photopolymerization due to the loss of the protection of the black coating. Graphic part. After exposure, general digital flexographic printing plates can be developed in the usual way, namely: solvent rinsing, drying, and finishing. However, some digital flexo printing plates need to be rinsed off with water before they are rinsed with solvent.

3, the difference between digital flexo printing plate and ordinary flexo printing plate

(1) In the process of exposure, light scattering and diffuse reflectance are different. When an ordinary flexographic printing plate is exposed, ultraviolet rays pass through the vacuum layer, the film base, the emulsion layer, and the anti-halation layer. The total thickness is large and there is a difference. Severe scattering and diffuse reflection problems. However, when the digital flexographic printing plate is exposed, the light passes through only a layer of black coating less than 0.001 in., and there is only a slight scattering and diffuse reflection phenomenon.

(2) Exposure environments are different. Ordinary plates are exposed under vacuum conditions, while digital plates are exposed in the air. The mechanism of photopolymerization of photopolymerized photosensitive resins in air and in vacuum is different, resulting in different dot shapes, exposure latitude, and other properties of the printing plate.

(3) Dots are different, and the reproduction range of the dots is large. The cross-section of the raised dot on the ordinary flexographic printing plate is circular, the trapezoidal shape is vertical, and the top of the dot is flat, while the dots on the digital flexographic printing plate are raised. Smaller and less inclined, the top of the point is round but not flat. Digital flexographic printing plate edges are more sleek. On the other hand, the outline of the dots on the plain flexographic printing plate is clear. Clear-cut dots are easy to break when printing, and dots on digital flexo printing plates, especially high-light spots, are not easy to appear, so the printing quality is good.

(4) With different exposure latitudes, the black coating on the digital flexo printing plate greatly improves the latitude of the UV main exposure. Experiments have shown that the increase in the main exposure time of the digital flexographic printing plate is 5 to 10 minutes, which does not have any effect on the height of the image on the printing plate, while the ordinary flexographic printing plate is different, as long as the exposure time is slightly increased, it will make the figure The height of the bulge is significantly reduced. Large exposure latitude favors perfect dot shape. Since the digital flexo printing plate has a certain degree of exposure latitude, it is not necessary to pay special attention to the highlights and dark spots during the exposure, and it is also ensured that the high light spots are not lost and the dark spots are not smeared. It is recommended to set the main exposure time of the digital flexo printing plate to 10 minutes, which is enough to ensure that the high light spot is not lost. In the preparation of ordinary flexographic printing plates, it is necessary to strictly control the exposure time, not only to pay attention to high light spots are not lost, but also take into account the dark spots do not paste.

4, flexographic printing plate making machine

The principle and structure of the laser image-setter for digital flexographic platesetters and film output are somewhat similar. The digital flexographic printing plate making machine divides the inner drum exposure and the outer drum exposure in two modes of exposure. In the inner drum digital flexographic printing plate making machine, the plate material is kept inside the drum during the exposure process; in the outer drum digital flexographic printing plate making machine, the plate material is kept outside the drum during the exposure process. When the drum rotates at high speed, the exposure head moves laterally with respect to the drum for exposure. At present, the flexographic printing platesetter is basically an outer drum type, and only small or medium (30in, 40in) platemakers have inner drum type.

Digital flexographic platesetters are controlled by a raster image processor (RIP). 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 interpretation language for the RIP of the internal cylinder digital flexo printing platesetter is the Postscript language. Its job tasks and principles are the same as Postscript laser imagesetters. It describes and interprets the content of the page sent by the application, forms a bitmap image, and controls the digital flexographic printing plate-making machine to perform laser ablation and record the page information on the plate.

The raster image processor consists of two parts: the interpretation part and the control part. The interpretation part receives the page information from the computer and encodes it for use by the control part; the control part controls the operation of the imaging system.

5. Application of digital flexo printing plate

At the time of loading, due to the expansion and contraction of the printing plate, the height of small dots that are originally equal to the actual area will be reduced. Therefore, before the plate making, this factor must be taken into account in order to improve the balance between the high light area and the printing pressure in the field.

The primary issue facing the flexo plate direct platemaking is the price issue. Regardless of the plate making equipment, the proofing system or the digital flexographic printing plates, the price is higher than that of ordinary flexographic printing. However, digital platemaking eliminates the processing of developing and fixing films and films, eliminating the need for various types of chemicals, places for storing films, and vacuum operating procedures for films and plates during printing. These save a certain amount of money. , And the plate making efficiency and printing quality are unmatched by the ordinary printing plate.

One of the main reasons why digital flexo can survive is that it can be used for high-quality flexographic printing. With the improvement of the quality of digital 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 printing companies and printing customers with more choices so that customers can use the lowest prices. , the best quality to get the desired print.

6. Sleeve flexo plate making technology

The previously mentioned flexographic printing plate is to be plated on the plate cylinder after it is printed before it can be printed. In foreign countries, there is now a more advanced flexographic printing direct plate making technology, which can be directly plated on the sleeve, and then the sleeve plate can be printed on the platen cylinder, and the work efficiency is higher. This technology is sleeve direct plate making technology. Sleeve direct plate making method can be divided into laser engraving and laser ablation two plate making methods.

(1) Laser engraving sleeve technology has been adopted abroad to directly engrave flexographic plates on sleeves. In this way, the sleeve can function both as a normal sleeve and as a printing plate. The pages produced by the prepress system can be output directly from the computer to the sleeve, eliminating the need for operations such as exposure, rinsing, curing, and printing, and the work efficiency is greatly improved. For example, PLOYWEST's Laser Engraving Sleeve Technology in Germany makes it possible to produce a plate combining the field with a hierarchical mesh, resulting in super-fine graphics.

(2) Laser ablation sleeve technology, often encountered in the packaging of prints, some pattern design full version of the same, but also free to cut down. The joints are not visible at the ends. Although it can be done on a roll printing machine, if you use a sheet of paper for printing, it is difficult to make joints invisible. The sleeve technology can solve this problem very well because on the sleeve type plate, CTP technology can be directly used for plate making and the problem can be solved easily. The plate making procedure is as follows:

1 Apply a layer of hot melt adhesive on an air-cored nickel or other metal roll. After drying, put the cut photosensitive resin on the metal roller and put it together. Vacuum from the core of the metal roll (the surface of the roll has many small pores), so that the photosensitive plate close to the surface of the metal roller. Then placed in an oven and warmed, the plate was fused together with the adhesive layer on the surface of the metal roll and then taken out and cooled.

2 Put the first cooled version of the sleeve into the peripheral grinder. According to the size requirements of the print, grind the outer diameter of the sleeve to a certain diameter (detected with a laser). The layout is naturally smooth. After wiping it clean, apply a black coating to the sleeve plate surface. Let it dry and set aside.

3 Digital laser scanning of the sleeve version prepared in the second step causes the black coating on the sleeve plate to be thermally etched by the laser and then exposed to UV light as usual. 4 Put the exposed stencil plate in the corrosive tank for flushing, then remove and blow dry.