Digital Printing and Screen Printing (I)

Digital printing technology has revolutionized the process of printing plate making and printing. It has taken away part of the screen printing market, but digital printing cannot replace screen printing because the screen printing materials are very extensive and there is “universal printing”. It is said that it has the advantage that other printing cannot be replaced, especially in the electronics industry.

At present, screen printing is a very common printing process. It is a method that can be printed on various shapes and materials, and it has been developed globally due to its wide range of applications. Due to the rapid development and development of screen printing printing materials and extensive and printing machinery, inks and other consumables, screen printing has played an advantage in competition with plain printing, gravure printing, and embossing (flexo printing).

Digital printing is pressureless printing, it can not copy all the screen printing products, it can not meet the needs of all users, digital printing will promote the development of screen printing is no doubt. Taken together, it is particularly evident in the following areas:

First, direct digital imaging and screen printing

Although the use of projection exposure for photopolymer emulsion screens has become a new technology currently in use, an updated screen printing plate technology, direct digital imaging, will bring a major breakthrough to screen plate making.

Direct digital imaging uses existing precision computer technology to control the wax injection system and scan the screen version with a modulated scan head.

Direct scanning of the original, computer-aided design, or information already stored on disk can be made using computer input. Unlike the projection method, the template is a full-size scan, the number of dots does not decrease, and the resolution depends on the laser beam focusing. The diameter of the laser beam can be large or small, usually 20μ, and a screen dot with a dot size of 5μ can be used to print a 120μ line screen printing plate.

Traditional color screen printing color separation screen production, can not be separated from film (photosensitive bottom plate), especially in the face of super-large screen printing, is nothing more than the use of film imposition, enlarge film or casting screen version. Either way, it must be based on the premise that high-precision, high-line film film production. Splicing a film is not only expensive, but it is difficult to ensure that it does not reveal stitching marks. Zooming in on the film and the screen printing net, due to the constraints of image factors, lens spheres, and other objective factors, caused a lot of trouble for the actual production, making it difficult to control the quality of the screen. Tongli Wire Mesh Production Technology Development Co., Ltd. introduced the Luscher JetScreen screen printer from Switzerland on the basis of the original computer color separation and platemaking system. The image was directly drawn on the photosensitive screen, which was combined into a set of fully functional color. Screen printing color separation template production system. The system makes screen printing color screens as easy to operate as computer inkjets. In the process of screen printing, the system does not require film film, saves time and money, eliminates the need for vacuum adsorption, saves equipment, eliminates sand holes formed by scratches or dust on the glass, and completely avoids the collision of mesh points with yarns. The moiré produced by the net has a print resolution of 630 dpi and resolution of the screen (repetition accuracy) of 0.02 mm.

Jetscreen bottomless plate making system will make the screen printing technology of color screen printing enter a new era, which will make it possible to solve the design of large-format screen printing that was difficult to achieve in the past. The newest shortcut jet wax printer can spray 3 x 8 (m) patterns.

Process flow: The system is free to read in the customer's own or design the desired pattern by various means; or after completing the plate making, any kind of media can be used to store the image data. The screening angles of yellow, blue, green, and black are different when screened. The number of screen lines and the number of screen meshes are also different. There are matching storages in the computer, such as 22.5°, 85.5°, and 112.5°.

Regarding the computer-to-silk screen image transfer time, if a 65-line/inch prismatic dot screen is used, the resolution is 633 × 633 dpi, the printing area is 1 square meter, and the transfer time is 20 minutes. For lower line counts, for example, 38 lines/inch or 50 lines/inch screen resolution, the resolution is reduced, and the image conversion time is much faster. The printing area of ​​1 square meter is only 15 minutes. A slight decrease in resolution does not affect the image quality because the viewing distance must be at least 1 meter. In general, the resolution of digital printing is not higher than 600 dpi.

The imaging speed is 1000mm × 1000mm (ie, 1 square meter). If the printing area is 1230mm × 820mm, although it is rectangular, the actual area is still 1m 2 , so the imaging speed does not change. The imaging speed of the portrait part is higher than that of the landscape because the head moves up and down faster than the lateral speed.

Digital screening printing technology includes the latest random screening, FM screening technology. Imaging is much faster than using a traditional screen. When selecting the imaging speed, the operator can adjust the image fineness, color value, viewing distance, and print size. Obviously, the lower the number of screen lines, the faster the nozzle moves on the template.

During the operation of the system, a hot melt wax is sprayed onto the stencil by the spray head. The optical density of the hot melt wax is higher than 3.0. It contains a special UV blocking agent to prevent the UV light from being emitted when exposed. When the nozzle sprays the image onto the stencil, the image immediately hardens, dries, and adheres tightly to the stencil to prevent sidewall corrosion during exposure. Hot melt waxes do not exhibit seepage, nor do they affect the fineness of the image. The imaged template can also be stored for a period of time before exposure, without affecting the image quality.

Water or solvent resistant emulsions and sensitizers in stencil emulsions can be used. Smooth surface energy can be achieved for direct stencils, capillary sensitized films, and film/emulsion systems. The lower the Rz value, the finer the image.

The plate making process of the computer-to-plate system is not only to make the image uniformly sprayed, rich in subtle layers, clear edges, and long service life of its own. At the same time, all printing inks, especially water-based UV inks, can be used. It is worth mentioning that the computer-to-plate system has a more realistic and natural effect on the reproduction of skin tones.

Compared with projection platemaking, direct digital imaging platemaking has many advantages. It is technically more advanced. A printing plate can be made in one step, completely eliminating the use of silver salt film, thus eliminating the environment brought by washing chemicals. Pollution. Computer-aided design data can be sent directly to the template without an intermediate photographic step. The digitized image scanner can directly input the original image to drive the laser imaging of the screen plate. The resolution of the image depends on the focusing of the laser beam, 5-20μ laser Beams are relatively easy to reach.

At present, the screen direct digital imaging system equipment has been sold in Beijing Tongli Company, including: microcomputers; high-quality digital image scanners; software programs that generate digital data; and lasers whose spectral output is close to the ultraviolet range.

Screen-printing digital plate-making technology is the latest plate-making method for photosensitive screen printing plates and has been put into commercial use. This plate-making method uses less energy to expose and harden the photosensitive layer of the screen plate. Its emergence and application have brought about fundamental changes to the traditional screen printing plate making process, marking that the screen plate making technology has begun to enter a new stage of digitization.

(to be continued)