Screen Printing Computer Direct System (CTS) System Overview

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, and 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.

I. History of the development of CTS

As early as the late 1980s, the United States took the lead in introducing the CTS system. The early CTS systems were positioned in different silk screen markets, some in the silk screen market for garments, and some in the silk screen market for decorative materials. A part of the CTS system uses the laser exposure principle to combine the screen printing and exposure. The CTS system converts the text image of the layout file into a bitmap image via 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 through the injection of opaque ink in the ordinary silk screen photosensitive layer, with ink dots instead of the dots on the positive film, and then full-page exposure, developed into a silk screen.

Second, the basic composition of the CTS system and workflow

The most important device of the CTS system is the screen image output device, so the general system name is based on 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 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 layout part: CTS and DTP are the same as the use of traditional image processing software, graphics processing software and layout software, such as Photoshop, Freehand, Coreldraw, Illustrator, and Pagemaker and other software to process images, color separation, typesetting.

3, RIP: Like offset printing, CTS RIP is to explain various graphic files and Postscript files, so that the screen output device can understand, and control the output device of the screen version. CTS can also accept a variety of design software files and EPS and PS files, and can convert these file information into color-coded outlets.

4. Proofing equipment: Like offset printing, the CTS process also requires proofing before official output. Proofing equipment can use inkjet printers, or you can use a dedicated proofing device.

5. Output Devices: Screen output devices are the key and difficult point of CTS. One of the main reasons for the low domestic CTS is that the output prices of screen output devices are 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 light spot on a coated screen plate, and then developed so that the mesh portion of the unseen light portion penetrates. The output resolution of this output device is high. The other type is the ink-jet output device. The ink with high light-blocking ability that is ejected by the output device is coated on the screen of the photosensitive resin, and then the full-page full-exposure is performed. The photosensitive resist covered by the light-blocking dots is not visible. It is rinsed off to expose the mesh. Its output resolution is relatively low at 300 dpi-600 dpi.

(II) Simple workflow of CTS system

1. Digital devices: scanners or digital cameras 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, in the graphics software or groupware for graphics production, graphics and text and produce the final input large version of the file;
4. The RIP accepts the typesetting file to explain each element, generates a page dot matrix image, and controls the output device to output the screen image of the screen.
5, exposure, development, forming a silk screen.

Third, CTS system type

According to the specific working methods screen output devices can be divided into three types: thermal inkjet system, inkjet state transition system, laser exposure system.

1. Thermal inkjet system: Its working principle is the same as that of inkjet printer. The screen output device applies the image on the photosensitive layer with ink, and then the screen is fully exposed and developed to form a screen. The ink is heated by the heating element in the nozzle to generate bubbles and extruded. It is called a thermal inkjet system. The heating element is controlled by a computer to open or close. When a "pip" is required, the heating element heats to generate a bubble that extrudes the ink in its volume and ejects it onto the screen. A nozzle or a matrix of nozzles is used on the nozzle, and generally the output of the screen is to be completed by the movement of the nozzle.

2. Inkjet State Transition System: This system uses a piezo-electric jet to continuously eject ink. The ink starts as a solid wax-like ball, which is then heated to a semi-solid state and ejected onto the screen. The ink immediately contacts the screen plate and is dried, and then processed. Exposure and other processes. The inks that are continuously ejected do not all reach the screen. They pass a device called a charge plate, that is, a piezoelectric plate. The piezoelectric plate can cause the charged ink beads to be charged with static electricity under the control of the computer. The charged and uncharged ink beads must pass through a continuous electrostatic field, and the uncharged can reach the printing plate through the electrostatic field without hindrance. On the screen, the charged ink beads deflect in the electrostatic field and are collected again.

The advantage of the above two inkjet systems is that no vacuum pumping device is needed. The vacuum device is required in the traditional silk screen platemaking method to ensure the close contact between the film and the photosensitive layer of the screen to reduce the image loss, and more importantly, when the plate is made. You can fully expose the screen without worrying about losing details. The key problem of the two systems is that the ink must have enough density to block the UV light from the back exposure; in addition, both ink jet systems can use traditional silk-screened photosensitive adhesives and exposure equipment, and nozzle cleaning can be achieved. Supplementary automation. However, thermal inkjet liquid inks are prone to splatter, while inks in the inkjet state transition mode cure quickly without splashing.

3, laser exposure system: This system's output device is actually a laser head to produce a light column for exposure, directly to the screen as a film. The difference between the laser exposure system and the inkjet system is that the laser system uses laser instead of ink, so it does not require the subsequent full exposure step. The key problem of this system is to have a photosensitive adhesive suitable for laser sensing, and it is not possible to use traditional photosensitive adhesives. Most of these systems are used in indirect screen printing processes.

In addition, there are also people highlighting the use of direct-emulsion adhesive method, that is, in the non-graphic part of the photosensitive emulsion spray, and then curing. This eliminates the need for development. However, taking into account factors such as the viscosity and fluidity of the sensitized adhesive, and the size of the screen meshes in different meshes, this method is too difficult, so few people have studied this method.