Silk screen CTS system (on)

In recent years, offset CTP has become a hot topic in the printing industry. In fact, in the field of silk screen printing, there are also computer-to-plate technologies. That is, there is no need for film printing. Images are output directly from the computer to the silk screen, and the plate is processed to form a printing plate. .
In foreign countries, the direct-printing of silk screens is called CTS, meaning Computer To Screen. The study of silk screen and direct platemaking was started very early in foreign countries. It was only after computer image processing technology was applied to the field of printing that the digital controlled CTS system was implemented. A leap from CTF (Computer To Film) to CTS has been achieved.
The type and working principle of the CTS system 1 Laser ablation system When the personal computer did not appear in 1969, Monsanto Research applied for a patent for screen printing and direct plate making. This is a patent for laser ablation screen printing direct plate making technology. The principle of laser ablation technology is to coat and dry the screen sensitive adhesive on the wire mesh, then cover the screen with a metal image mask, and burn the photosensitive layer with a CO2 laser or an argon laser to make the screen The graphic part of the screen is transparent.
With the advent of PCs, image processing has entered the era of digitization. Soon, digital technology was applied to the laser ablation process to form a laser ablation system. That is, through a computer to control where the ablation, without the need to cover the metal image cover, as shown in Figure 1: Laser ablation system is mainly used in the silk screen printing industry. We know that printing in the printing and dyeing industry uses a screen printing method. The screen printing plate is in the shape of a metal roller. Therefore, a laser ablation system is very suitable. The laser ablation system is used for printing in the printing and dyeing industry, which not only saves a large number of films, but also avoids deformation caused by the film bending on the rollers.
The laser ablation system can only be used for metal mesh, and can not be used in nylon mesh and polyester mesh, because these two meshes cannot resist the high energy of ablation laser.
2 laser exposure system
In 1990 Mografo of Denmark developed a digitally controlled laser exposure CTS system that uses imaging instead of ablation. The working principle of the laser exposure system is as follows: firstly apply a screen sensitive adhesive on the screen and dry it, then use a computer to control the laser exposer to image on the screen, and develop it into a screen version, as shown in FIG. 2 . The photosensitive adhesive used in this system is different from the ordinary screen-printing photosensitive adhesive and requires special photosensitive adhesive. This is because the sensitivity range of the traditional photosensitive adhesive is between 360-420mm, while the laser has only a narrow range of a few nanometers, the exposure range is small, and only a special photosensitive adhesive can adapt. In addition, the laser exposure system is expensive, and each set is up to millions of dollars, so the market application of laser exposure system is not very good.
3 Inkjet imaging systems Because of the limitations of laser exposure system materials and the limitations of market applications, companies are actively developing new technologies to manufacture affordable systems with excellent performance. New technologies are mainly focused on inkjet imaging systems. The basic system is to transplant the technology of ink jet printers to silk screens. The inkjet systems on the market include Gerber's Screen Jet, Luscher's JetScreen, KIWO's Image Jet, Berg Engineering's Stencil Writer, and Sevcia's Stencil Master.
The working principle of the ink-jet imaging system is as follows: first, the screen-sensitive adhesive is coated on the screen and dried, and the light-blocking ink is printed on the photosensitive layer through the ink-jet system, and the ink is dried and then the network is irradiated with ultraviolet light. The version was fully exposed. At this time, the light-hardening was observed in the place where the ink was not sprayed, and the place where the ink was sprayed could be washed away. The next step of development is to use water as the developer, which is to rinse off the sprayed ink with water to form the graphic part of the screen plate. Figure 3 shows the working principle of the inkjet imaging system. Inkjet imaging systems have been widely used due to their ability to directly use traditional screen-printing sensitized films and various screen-printing sensitized films and are inexpensive.
The advantage of the inkjet system is that it can fully expose the screen without worrying about the details of the image loss. However, the key issue is that the ink must have enough density to block the full-exposure UV light and the density of the ink layer should be greater than 3.0.
Inkjet imaging system can be divided into two types according to the principle of spray point formation: one is a heated inkjet system; the Other is a piezoelectric inkjet system.
1 Heated inkjet system Figure 4 is a working schematic of a heated inkjet system. There is a heating element in the nozzle of the heating type ink jet system. It is turned on or off by computer control. When the heating element is heated, it causes the temperature in the ink chamber to rise and generates a bubble, which generates a pressure under the pressure of the bubble. Drops of ink, and the ink droplets are pressed out of the nozzle, the ink droplets fly to the substrate, and new ink is added to the ink chamber. The nozzles of the system can be arranged in a row, or form a matrix. Each nozzle can emit ink droplets. Generally, it depends on the movement of the nozzle to complete a screen printing.
The disadvantage of the heated ink jet system is that many tiny ink droplets are generated during the jetting process, resulting in ink splashing and affecting the sharpness of the image. The heated ink jet system requires stricter ink viscosity and can only use water. Base ink.
2 Piezo Inkjet System Figure 5 is a schematic diagram of a piezo inkjet system. There is a block of piezoelectric crystal on the showerhead. Under the action of the current, the piezoelectric crystal deforms and bends, so that the volume of the ink cavity is reduced, and the ink cavity is pressed, and the ink droplet is pressed out through the nozzle to reach the substrate. When the current is generated, the piezoelectric crystal is bent and controlled by the computer. Piezoelectric inkjet systems do not produce droplet spatter and can use both water-based and solvent-based inks. The piezoelectric ink jet system generally uses a wax-like ink, and the ink is sprayed onto the screen in a state of heating to a semi-solid state, and the ink is dried immediately after contacting the screen plate.
Critical issues of the CTS system RIP
Since halftone dots are used for silk screen plates, ink dots ejected on the screen should also be dots. In this way, unlike a general color printer, a raster image processor (RIP) is required to interpret the page and generate a dot matrix image, and then the RIP controls the print head to print dots, in effect, the RIP and laser image of the CTS system. The working principle and completed work of the RIP of the machine is almost the same, and all of them use software RIP.
Proofing In order to check the effect of image separation and check the contents of the page for errors, digital proofing should be performed before outputting. If you wait for plate-making later, you will find that the problem has been greatly reduced.
Resolution of the laser exposure CTS system is relatively high, up to 2540dpi, while the resolution of the inkjet CTS system is relatively low, generally only 600-720dpi, if the maximum resolution of the system is 720dpi, then the final output of the maximum resolution is 75L/Inch. The actual can only be about 55L/Inch, for the inkjet CTS system, too high resolution means a smaller idea, but the idea is too small may cause the ability to block the UV light, exposure can not be blocked Sufficient light causes flushing during development. In addition, the imaging speed is much faster if the resolution is low.
Blocking ink dust, sand particles, and residual ink around the nozzle may seal the nozzle and cause the ink to fail. To prevent ink blocking, the ink head should be cleaned frequently and the environment should be kept clean.
The print head is a complicated device. It needs to generate ink droplets at a frequency of 8-20 kHz, and at the same time, it should move at a predetermined speed and direction on the screen. At this time, any influence from the outside world may cause missing prints or The idea deviates from its normal position. For example, due to the influence of dust, air current, and static electricity, the direction of the flight of the point may be offset. The result is a bit of sub-overprinting, which is somewhat sub-printed. Another example is the influence of the electron impact on the adjacent nozzles and the sound of the ink jet on the adjacent nozzles. The influence will also affect the nozzles that can not spray the ink dots, and the heating elements of the nozzles may malfunction, or the electric corrosion of the nozzles will also affect some nozzles to spray no ink dots.
In order to solve the problem of missing printing, the CTS system adopts the following technologies to solve the microwave technology. The method of printing continuous pixel dots is to subdivide the dots. This method uses multiple nozzles to print multiple times to complete the continuous area of ​​the printing, each nozzle to complete a single print. If some of the nozzles on the front face fail to print, the subsequent printing will make up for it. Even if there is no printing on some places, it is difficult to find among the dots that have already been printed. This method uses 1 pass, 2 passes, 3 passes, 4 passes, etc. However, the imaging speed is greatly slowed down.
The idea of ​​this method of spray coverage technology is so dense that the idea cannot be seen at all. This method is slow in imaging and consumes a large amount of ink.
Turn off some nozzle technology Some CTS system's driver software allows the operator to select the number of nozzles or specify the nozzle array to work, so that some nozzles are not "excited" during ink ejection. Operators can use this command to remove those that cannot be printed. nozzle. In operation, the CTS system can use the remaining nozzles to re-image the area where the nozzle was turned off. (Liu Wuhui) ("Printing Arts")