With the widespread application of offset CTP technology, computer direct plate making will gradually become popular and become the mainstream plate making method. Similarly, screen printing has also been developing computer-to-plate technology. Screen-to-screen (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 relevant technologies and information.
1. The development history of CTS
As early as the late 1980s, the United States first introduced the CTS system. The early CTS systems were positioned in different screen printing markets, some in the clothing screen printing market, and some in the decorative materials screen printing market. Some CTS systems use the principle of laser exposure to combine the two steps of screen imaging and exposure. The CTS system converts the text image of the typesetting file into a dot matrix image by RIP, and then sends the dot matrix image data to the system modem to control the laser exposure to form an image on the silk screen. By the 1990s, the CTS system of inkjet principle appeared. It is by spraying opaque ink on the ordinary silk screen photosensitive layer, replacing the dots on the positive film with ink dots, and then exposing the whole plate, and developing it to make a silk screen plate.
Second, the basic composition and working process of the CTS system
The most important device of 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 similar to that of the DTP system, but the output devices are very different. Usually the CTS system consists of the following parts:
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1. Graphic input section: This section digitizes the original and enters various digitized files.
2. Graphic processing and typesetting: CTS and DTP also use traditional image processing software, graphic processing software and typesetting software, such as Photoshop, Freehand, Coreldraw, Illustrator and Pagemaker to process images, color separation and 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 work of the screen output device. CTS can also accept various design software files and EPS and PS files, and can convert the information of these files into a color-separated version of the network.
4. Proofing equipment: As with offset printing, the CTS process also requires proofing and layout check before formal output. Proofing equipment can use inkjet printers, you can also use dedicated proofing equipment.
5. Output equipment: Screen output equipment is the focus and difficulty of CTS. One of the main reasons for the lack of domestic CTS is that the price of 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 categories: one is the laser exposure equipment, which is exposed and hardened on the coated screen through the laser spot, and then developed to allow the unseen part of the mesh to penetrate. The output resolution of this output device is higher. The other type is the inkjet output device. The ink with high light-blocking ability ejected through the output device is on the screen coated with photosensitive resin, and then the whole plate is fully exposed. It was washed away, exposing the mesh. Its output resolution is relatively low, at 300dpi-600 dpi.
(2) Simple working process of CTS system
1. Digital equipment: scanner or digital camera, used to generate digital images;
2. Perform image processing, color correction and color separation in image processing software to generate CMYK four-color image or spot color image;
3. Make graphics, mix images and graphics in graphics software or group version software and generate the final input large version file;
4. RIP accepts typesetting files to explain each element, generates page dot matrix images and controls the output device to output screen images of screens;
5. Exposure and development to form a silk screen.
3. Types of CTS system
According to the specific working mode, the screen output device 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 coats the image on the photosensitive layer with ink, and then the screen is fully exposed and developed to form a screen. Ink is squeezed out by heating parts in the nozzle to produce bubbles, so it is called thermal inkjet system. The heating part is turned on or off by computer control. When a "pip" is needed, the heating part heats up to generate a bubble. The bubble squeezes the ink out of its volume and sprays it onto the screen. A row or a matrix of nozzles should be used on the nozzle, and the output of the screen is generally completed by the movement of the nozzle.
2. Inkjet state transition system: This system uses a piezoelectric nozzle to continuously eject ink. The ink starts as a solid wax ball, then heated to a semi-solid state, sprayed onto the screen, and the ink is dried immediately after contacting the screen, and then carried out Exposure and development processes. Not all of the ink ejected continuously reaches the screen, they have to pass through a device called a charging board, namely a piezoelectric board. 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. The uncharged can pass through the electrostatic field to the substrate without hindrance. On the screen, the charged ink beads cause deflection in the electrostatic field and are collected again.
The advantage of the above two inkjet systems is that there is no need for a vacuum suction device. A vacuum device is necessary in the traditional screen printing plate-making method to ensure the close contact of the film and the photosensitive layer of the screen to reduce image loss. More importantly, during platemaking You can fully expose the screen without worrying about losing details. The key problem of the two systems is that the ink must have sufficient density to block the UV light during the subsequent exposure; in addition, both inkjet systems can use the traditional screen printing plate of photoresist and exposure equipment, and can achieve nozzle cleaning, ink cartridge Supplement automation. However, the thermal inkjet liquid ink is easy to splash, and the ink in the inkjet state transition mode is cured quickly without splashing.
3. Laser exposure system: The output device of this system is actually a laser beam produced by the laser head for exposure, and the screen is directly used as a film. The difference between a laser exposure system and an inkjet system is that the laser system uses lasers instead of ink, so it does not require the full exposure step. The key problem of this system is to have a photoresist suitable for laser sensing, and can not use traditional plate-making photoresist. This kind of system is mostly used in the indirect screen printing process.
In addition, some people have highlighted the method of directly spraying the photoresist, that is, spraying the photoresist on the non-graphic part, and then curing. This eliminates the need for development processing. However, considering the factors such as the viscosity and fluidity of the photoresist and the different mesh sizes of different meshes, this method is too difficult, so few people have studied this method.
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