Since contact screen printing, screen printing plate making process and film are inseparable. In short, the process is to put the film that has been made according to the requirements of screen printing on the screen that has been coated with photosensitive resin and dried, and then expose it to ultraviolet light using a printing plate. The unhardened areas can be washed away with water. After the exposure is completed, the plate is washed with water, that is, the graphic to be printed is displayed, and a screen is ready.

This set of procedures has been used for many years, and suddenly broke into several English letters. What CTP, CTS, is a bit unattractive for a while, and can be analyzed a little. The principle is not difficult to understand.

Basic principles of CTS

In recent years, CTP in the field of offset printing can be described as infinite. The new technology of direct plate making without film has brought a digital revolution to the printing industry. In fact, in the world of screen printing. In foreign countries, the direct plate-making technology in screen printing is called CTS, or Computer To Screen.

The production of this new technology depends on the development of inkjet printers. The inkjet imaging system is formed by transplanting the technology of inkjet printing to the screen printing plate. Its working principle is as follows: coat the screen with photosensitive glue and dry it, spray the light-blocking ink on the photosensitive layer through the inkjet system, and after the ink is dried, use ultraviolet light to fully expose the screen. Light hardened, landlords that are resistant to ink spray can be washed away. After the exposure is completed, the landlord sprayed with ink is washed away with a developing solution (usually water) to form the graphic part of the screen. Compared with the plate-making process described in the opening article, it is easy to see what the role of the film is and the inkjet method replaces it.

Inkjet system classification

According to the principle of inkjet, inkjet imaging systems are divided into heated thermal ink systems and piezoelectric inkjet systems.

The former has a heating device in the nozzle. When heated, the temperature in the nozzle rises and forms a gas. Under the pressure of the bubble, ink droplets are formed, and the ink droplets are ejected from the nozzle. At the same time, new ink droplets will be added. As for the switch of the heating device, it is controlled by the computer according to the desired pattern. The nozzles are arranged in a row or in a distance array, and the entire screen is produced by moving.

As for the latter, the heating device in the nozzle is replaced by a piezoelectric crystal. When a current passes, the crystal is deformed, and a pressure is generated to push the ink droplet out. When the current passes through is also controlled by the computer according to the desired pattern.

Comparing the two, the heated inkjet system will produce ink splashes when printing, resulting in small ink droplets on the edge of the image, affecting the quality of the screen. And this device has requirements for the viscosity of the ink, only water-based ink can be used. The piezoelectric inkjet system will not produce ink splashing, and does not require the viscosity of the ink. Generally, waxy ink is used, which is ejected from the nozzle in a semi-cured state and dried immediately on the screen, which is what some people call a wax spray system.

Precautions

1. Just like we would pay attention to the light blocking property of the film before, in the CTS system, we must pay attention to the light blocking property of the printing ink. Usually we require ink layer density greater than 3.0.

2. The resolution of the inkjet imaging system is not too high, generally only 600 ~ 720dpi. This is because the higher resolution causes the idea to be too small, thereby reducing the shielding power to ultraviolet rays.

3. The nozzle may be clogged and no ink can be ejected. Pay attention to the cleaning of the nozzle. At present, there are some CTS systems, which can be set to turn off the print head that cannot be ink jetted.

4. The computer directly makes a plate, and once it is made, it finds errors and remakes the plate, and the loss can be greater than in the past. Therefore, proofing is not only indispensable, but must be precise and detailed.

Features of CTS direct plate making

1. Reduce the plate-making process and save time.

2. Get rid of the film, print information is easy to save and easy to modify. It avoids the creases caused by improper placement of the film, as well as its traces and size changes.

3. Digital screen positioning during multi-print overprinting reduces human error.

4. There is no requirement for the mesh size of the screen, no special requirements for the screen frame, and no special photosensitive adhesive is required for the photosensitive adhesive. There are no special darkroom requirements.

5. You can exchange printed information with customers through the Internet, saving time and effort.

6. The dot shape and dot size can be set.

In view of the CTS system and various advantages, it is bound to open up a broader market for screen printing. Especially in large-format screen printing, the digitization of the CTS system minimizes many human errors, and its effect is self-evident.

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