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The status and development of flexographic direct plate making technology in recent years, flexographic printing technology has made remarkable progress, and its role is obvious to all. Obviously, it has gone through the process from "ugly duckling" of "aniline printing" to "white swan". In this evolution process, the progress of digital prepress plate making technology is indispensable, especially the application of computer direct plate making technology to improve plate making. The quality and efficiency of printing play an important role, which will establish the position of flexographic printing to a greater extent

I. basic meaning and scope of flexo direct plate making technology

as we all know, flexo is a kind of relief plate. As the name suggests, the plate used in Flexo is not as rigid as the metal plate, but a plate made of chemical synthetic materials with weak rigidity

the so-called flexographic direct plate making refers to the process and technology of making flexible relief plates by exposing or ablating flexible plates with laser or other light sources

laser direct engraving for rubber flexographs was realized as early as the 1980s. In 1995, the technology of direct plate making of photosensitive polymer plates by laser appeared. After several years of development, laser engraving and laser imaging technology is gradually becoming the main method of flexo direct plate making

II. Flexo direct plate making materials and plate making mechanism

flexo plates used for computer direct plate making are also known as "digital flexo plates". From the external shape of the plate, the flexible plate has two forms: flat and seamless sleeve

according to the chemical composition of the plate, it is divided into rubber plate and photosensitive polymer plate

rubber plates can be made of raw rubber or artificial rubber. In direct plate making, high-energy laser can be used to ablate the materials that are not the key step for the aluminum processing industry of the banner to take in the field of fine processing, so as to obtain the rubber flexible relief plate

photosensitive polymer plates can be divided into liquid and solid. Solid photosensitive polymer plates are commonly used. Photosensitive polymer plates have good plate making performance and are suitable for making flexible plates with high number of lines. The mechanism is that the photosensitive polymer monomer can undergo a shape polymerization reaction under the irradiation of ultraviolet light to form an insoluble graphic part

in terms of the mechanism of direct plate making, "LAMS (laser ablation mask system)" can be used for direct plate making. Specifically, a black mask protective layer is coated on the outside of the photosensitive polymer layer, which is ablated and imaged with a laser, and the protective layer of the image and text part is ablated to expose the photosensitive polymer layer. After the laser ablation imaging is completed, the back of the entire layout is exposed with an ultraviolet light source to make the photosensitive polymer at the bottom cross-linked within a certain thickness range. Then, the front of the plate that has been ablated with the protective layer is exposed with ultraviolet light. The photopolymer in the graphic part is irradiated by ultraviolet light and polymerizes and cannot be dissolved; The non graphic part is protected without cross-linking reaction. After cleaning and removing the photosensitive polymer of the non graphic part, a flexible relief plate is formed

III. flexographic direct plate making and recording technology

the structure of flexographic laser recording equipment is mostly external roller type, but some also use internal roller type recording technology. The rubber plate laser engraving system directly records the ablation of the plate, while the photosensitive polymer plate is mostly ablated by the surface protective layer, followed by UV main exposure, that is, "LAMS" method

in terms of the applied laser, the rubber plate laser direct engraving system uses a high-power carbon dioxide laser, and the power can even reach 2.5kW. However, in terms of the ablation technology of the protective layer of photosensitive polymer plates, the laser energy does not need to be as high as that of direct engraving, and the laser power is in the range of 10 ~ 60W. Most of the applied lasers are infrared lasers. For example, high-end, customized and environmentally friendly materials become the future trend of the new material industry: YAG laser with a wavelength of 1064nm, fiber laser with a wavelength of 1100nm, semiconductor laser with a wavelength of 830nm, etc. Recently, the application of fiber laser in flexographic recording equipment has been increasing. The reasons are: the laser spot produced by fiber laser is of high quality, easy to achieve high resolution (small spot diameter), wide range of laser imaging depth of field, insensitive to the diameter error of the surface of flexographic plate, high laser energy efficiency (about 50%), low cooling cost, simple maintenance, etc

the recording resolution of the rubber plate laser direct engraving system is about 600dpi, which is used to make packaging printing plates of average quality. The recording resolution of photosensitive polymer plates is generally 2000 ~ 3000dpi, and the highest is 4200dpi. According to different equipment configurations, the production efficiency of flexo direct plate making equipment varies from 0.7 m2/h to 5 m2/h

at present, the main international manufacturers of flexographic plate making equipment that directly measure displacement (i.e. the relative displacement of upper and lower collets) through digital circuits include Esko graphics (CDI system), German hellgrave systems (helioflex F2000 system), Canadian Clio (THERMOFLEX system), German fexolaser (flexolaser system) and Swiss MDC (digilas system)

IV. process flow of direct plate making of digital flexo

the process flow of direct plate making of flexo computer is as follows:

1) prepress image and text processing: text typesetting, graphic drawing and processing, image scanning/processing/color separation

2) picture and text composition, full page and large version

3) print out page description language, rip processing, and form printing plate record information

4) laser ablation record (LAMS)

5) UV exposure on the back of printing plate

6) UV main exposure on the front of printing plate

7) remove the protective layer and develop with solvent ("plate washing")

8) drying

9) the whole plate UV exposure fixture can be used continuously in such cases, so that the photosensitive polymer of the printing plate can be completely crosslinked

10) arrange and obtain the finished plate

instead of the traditional flexo plate making process of laser ablation recording, the laser Imagesetter can be used to record the negative color separations in the above step 4, while in the above step 6, the negative color separations can be closely closed to the front of the plate and exposed with ultraviolet light. Other process steps are the same as the above process

compared with the flexo made by the traditional indirect recording method, the quality of the flexo made by laser direct plate making is better. The root of the relief point made by laser is in a slope shape, and the point above the root is perpendicular to the layout, which has better printing stability. At the same time, the reproducibility of small area ratio points is also better. Direct ablation recording reduces the cost of materials, development processing equipment/chemicals brought by the output film of the laser Imagesetter, and also avoids the point changes caused by light diffusion and absorption during film printing. These factors are the advantages of digital direct plate making

it is believed that with the promotion of laser technology, plate material development and other conditions, flexo digital direct plate making technology can develop rapidly and become the mainstream technology of flexo plate making

source: digital printing

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