Screen Printing Computer Direct Plate (CTS) System Overview
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With the wide application of offset CTP technology, computer direct plate making will gradually become popular and become the mainstream plate making method. Similarly, screen printing has been developing computer-to-plate technology. CTS-computer to screen has been developed abroad for many years, but it is still in its infancy in China. This article will briefly introduce the relevant technologies and information.
First, the development history of CTS
As early as the end of the 1980s, the United States took the lead in launching the CTS system. The early CTS systems were each positioned in different silk screen markets, some targeting the silk screen market for clothing, and some targeting the silk screen market for decorative materials. A part of the CTS system uses the principle of laser exposure to combine the two methods of imaging and exposure of the screen plate into one. The CTS system converts the text image of the typesetting file into a bitmap image by RIP, and then sends the bitmap image data to the system modem to control the laser exposure to form an image on the screen. By the 1990s, the CTS system of the inkjet principle appeared. It is by spraying opaque ink on the common silk screen photosensitive layer, replacing the dots on the positive film with ink dots, and then exposing the whole plate to develop a screen printing plate.
Second, the basic composition and workflow of the CTS system
The most important device in the CTS system is the screen imaging output device, so the general system name is determined according to the name of the output device.
(1) The composition of the CTS system is basically the same as that of the DTP system, but the output devices are quite different. Usually the CTS system consists of the following parts:
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1. Graphic input section: This section digitizes the original and inputs various digitized files.
2. Graphic processing and typesetting part: CTS and DTP are also using traditional image processing software, graphics processing software and typesetting software, such as Photoshop, Freehand, Coredraw, Illustrator and Pagemaker and other software to process images, color separation, typesetting.
3. RIP: Like offset printing, CTS RIP is to interpret various graphic files and PostScript files, so that the screen output device can understand and control the screen output device work. CTS can also accept a variety of design software files and EPS and PS files, and can convert these file information into a color-coded version of the network.
4. Proofing equipment: Like the offset printing, the CTS process also needs to be proofed for layout before the official output. The proofing device can be either an inkjet printer or a dedicated proofing device.
5. Output equipment: screen output equipment is the focus of CTS is also difficult, one of the main reasons for the lack of domestic CTS is that the price of the screen output equipment is too high and there is no corresponding production technology in China. The working principle of the output device is basically two major categories: one is a laser exposure device, which is exposed and hardened by a laser spot on the coated screen, and then developed to allow the mesh of the unvisited portion to penetrate. The output resolution of such an output device is high. The other type is an inkjet output device. The ink with high light-blocking ability ejected by the output device is coated on the screen of the photosensitive adhesive, and then the whole plate is fully exposed, and the photo-sensitive adhesive covered by the light-blocking point is not visible. It is washed away to expose the mesh. Its output resolution is relatively low, at 300dpi-600 dpi.
(B) CTS system simple workflow
1. Digital device: a scanner or digital camera used to generate digital images;
2. Perform image processing, color correction and color separation in the image processing software to generate CMYK four-color images or spot color images;
3. Perform graphic production, graphic and text mixing in the graphics software or the group software, and generate the final input large version file;
4. RIP accepts the typesetting file to interpret each element, generates a page dot matrix image and controls the screen image of the output device output screen;
5. Exposure and development to form a silk screen.
Third, CTS system type
According to the specific working mode, the screen output devices can be divided into three types: thermal inkjet system, inkjet state transition system, and laser exposure system.
1. Thermal inkjet system: Its working principle is the same as that of inkjet printer. The screen output device applies an image of the ink to the photosensitive layer, and then the screen is fully exposed and developed to form a screen. The ink is extruded by heating the heating element in the nozzle to produce a bubble, so it is called a thermal inkjet system. The heating element is turned on or off by computer control. When a "pip" is required, the heating element heats up to create a bubble which, in its volume, extrudes the ink and ejects it onto the screen. To use a row or a matrix of nozzles on the nozzle, it is generally necessary to rely on the movement of the nozzle to complete the output of the screen.
2. Inkjet state transition system: This system uses a piezoelectric nozzle to continuously inkjet, the ink begins as a solid waxy ball, then is heated to a semi-solid state, sprayed onto the screen, the ink is dried immediately after contact with the screen, and then Exposure development and other processes. The inks that are continuously ejected do not all reach the screen. They pass through a device called a charging plate, that is, a piezoelectric plate. Under the control of the computer, the piezoelectric plate can cause the ink beads to be charged with static electricity. The charged and uncharged ink beads must pass through a continuous electrostatic field, and the uncharged unobstructed passage through the electrostatic field can reach the printing. On the screen, the charged ink beads are deflected in the electrostatic field and are collected again.
The advantage of the above two inkjet systems is that no vacuum pumping device is required. In the conventional silk screen printing method, a vacuum device is required to ensure the adhesion of the film and the screen photosensitive layer to reduce image loss, and more importantly, during plate making. You can fully expose the screen without worrying about losing details. The key issue for both systems is that the ink must be of sufficient density to block UV light from subsequent exposures; in addition, both inkjet systems can use conventional silkscreen-coated photoresists and exposure equipment, as well as nozzle cleaning, ink cartridges. Complement automation. However, the thermal inkjet liquid ink is prone to splashing, and the ink of the inkjet state transition mode is quickly cured without causing splashing.
3. Laser exposure system: the output device of this system is actually the laser head to produce a light column for exposure, directly using the screen as a film. The difference between a laser exposure system and an inkjet system is that the laser system uses a laser instead of ink, so it does not require a full full exposure step. The key issue of this system is to have a photoresist suitable for laser sensing, and it is not possible to use conventionally made photoresist. Most of these systems are used in indirect silkscreening processes.
In addition, there is also a method of directly spraying the photosensitive adhesive, that is, spraying the photosensitive adhesive on the non-image portion and then curing. This eliminates the need for development processing. However, considering the viscosity and fluidity of the photosensitive adhesive, the mesh size of the mesh of different meshes, etc., this method is too difficult, so few people study this method.