Silk screen CTS system (1)
We are a big printing company in Shenzhen China . We offer all book publications, hardcover book printing, papercover book printing, hardcover notebook, sprial book printing, saddle stiching book printing, booklet printing,packaging box, calendars, all kinds of PVC, product brochures, notes, Children's book, stickers, all kinds of special paper color printing products, game cardand so on.
For more information please visit
http://www.joyful-printing.com. ENG only
http://www.joyful-printing.net
http://www.joyful-printing.org
email: info@joyful-printing.net
In recent years, offset CTP has become a hot topic in the printing industry. In fact, in the field of silk screen printing, there is also the technology of computer direct plate making, that is, there is no need for film printing, and the image is directly output by the computer to the silk screen plate, and the plate is formed after development.
Direct printing in foreign countries is called CTS, which means Computer To Screen. Foreign countries have started research on silk-screen direct plate-making very early, but only after computer image processing technology was applied to the printing field, the digitally controlled CTS system was realized. A leap from CTF (Computer To Film) to CTS has been realized.
Type and working principle of CTS system
1 laser ablation system
When the personal computer did not appear in 1969, Monsanto Research applied for a patent for silk screen direct plate making. This is the patent for laser ablation silk screen direct plate making technology. The principle of laser ablation technology is to first coat the wire mesh photoresist on the wire mesh and dry it, then cover the screen with a metal image cover, and burn the photosensitive layer with CO2 laser or argon laser to make the wire mesh The mesh part of the version is transparent.
The emergence of PCs has brought image processing into the era of digitization. Soon digital technology has been applied to laser ablation platemaking methods to form laser ablation systems. That is, through the computer to control where to ablate, without covering the metal image cover, as shown in Figure 1: laser ablation system is mainly used in the printing and dyeing industry silk screen. We know that the printing of the printing and dyeing industry uses a silk screen method. The screen version is in the shape of a metal drum, so it is very suitable to use a laser ablation system. The laser ablation system is used in printing and printing industry, which not only saves a lot of film, but also avoids the deformation caused by the bending of the film on the drum.
The laser ablation system can only be used on wire mesh and cannot be used on nylon mesh and polyester mesh because these two screens are not resistant to the high energy of ablation lasers.
2 laser exposure system
In 1990, Mografo of Denmark developed a digitally controlled laser exposure CTS system that uses exposure rather than ablation to image. The working principle of the laser exposure system is: firstly apply the screen photoresist on the screen and dry it, then image it on the screen through a computer controlled laser exposer, and then make a screen version after development, as shown in Fig. 2. The photographic adhesive used in this system is different from ordinary silkscreen photographic adhesives and requires a special photographic adhesive. This is because the traditional photosensitive adhesive has a sensitization range of 360-420 mm, and the laser has only a narrow band of several nanometers, and the exposure range is small, and only a special photosensitive adhesive can be adapted. In addition, the price of laser exposure systems is relatively high, each set up to millions of dollars, so the market application of laser exposure systems is not very good.
3 inkjet imaging system
Due to the limitations of the materials of the laser exposure system and the limitations of market applications, companies are actively developing new technologies to manufacture systems with moderately good performance. The new technologies are mainly focused on inkjet imaging systems. These systems are basically The technology of inkjet printers has been transplanted to screen printing. Inkjet systems on the market include Screen Jet from Gerber, JetScreen from Luscher, Image Jet from KIWO, Stencil Writer from Berg Engineering, and Stencil Master from Sevcia.
The working principle of the inkjet imaging system is: firstly apply the screen photoresist on the screen and dry it, and spray the light-blocking ink on the photosensitive layer through the inkjet system, and then dry the ink and then use the ultraviolet light to carry out the mesh. The version is fully exposed, where the place where the ink is not sprayed is light hardened, and the place where the ink is sprayed can be washed away. The next step is to develop, generally using water as a developing solution, that is, water is used to rinse off the place where the ink is sprayed to form a graphic portion of the screen plate. Figure 3 is a schematic diagram of the working principle of the inkjet imaging system. The inkjet imaging system has been widely used because it can directly use conventional silk-screening photosensitive glue and various silk-screen printing photosensitive films, and is inexpensive.
The advantage of an inkjet system is that it can be fully exposed to the screen without worrying about image loss details, but the key issue is that the ink must have sufficient density to block the UV light during full exposure, requiring a density of the ink layer greater than 3.0.
Inkjet imaging systems can be divided into two categories according to the principle of dot formation: one is a heated inkjet system; the other is a piezoelectric inkjet system.
1 heating inkjet system
Figure 4 is a schematic diagram of the operation of a heated ink jet system. The nozzle of the heated inkjet system has a heating component which is turned on or off by a computer control. When the heating component is heated, it raises the temperature inside the ink chamber and generates a bubble, under the pressure of the bubble, generates a Ink droplets, and the ink droplets are pressed out of the nozzle, the ink droplets fly to the substrate, and new ink is replenished into the ink chamber. The nozzles of the system can be arranged in a row or form a matrix, and each nozzle can emit ink droplets. It is generally necessary to rely on the movement of the nozzle to complete the printing of a screen.
The disadvantage of the heated inkjet system is that a lot of tiny ink beads are generated during the spraying, which forms a phenomenon of splashing, which affects the sharpness of the image, and the heated inkjet system has strict requirements on the viscosity of the ink, and only water can be used. Base ink.
2 piezoelectric inkjet system
Figure 5 is a schematic diagram of a piezoelectric inkjet system. There is a piezoelectric crystal on the nozzle. Under the action of current, the piezoelectric crystal is deformed and bent, so that the volume of the ink chamber is reduced, the ink chamber is pressed, and the ink droplet is pressed out through the nozzle to reach the substrate. When is the current generated to bend the piezoelectric crystal, controlled by a computer. Piezoelectric inkjet systems do not produce ink droplet splatter, and either water-based or solvent-based inks can be used. In general, a piezoelectric inkjet system uses a waxy ink, and the ink is sprayed onto a screen while being heated to a semi-solid state, and the ink is dried immediately after contacting the screen.
Key issues in the CTS system
RIP
Since the screen printing uses halftone dots, the dots ejected on the screen should also be dots. This is different from a general color printer. It is necessary to use a raster image processor (RIP) to interpret the page and generate a bitmap image. Then the RIP controls the printhead to print the dots. In fact, the RIP and laser photoshop for the CTS system. The RIP works and the work done is similar, and also uses 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 output. If you find that the problem is lost after waiting for the plate, it will be big.
Resolution
The resolution of the laser exposure CTS system is higher, 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, the maximum resolution of the final output is 75L/ Inch. Actually only about 55L/Inch can be achieved. For inkjet CTS systems, too high resolution means smaller ideas, but too small a point may cause a decrease in the blocking ability of ultraviolet light, which cannot be blocked when exposed. Sufficient light, causing difficulty in rinsing during development. In addition, if the resolution is low, the imaging speed is much faster.
Blocking ink
Dust, sand, and residual ink around the nozzle may seal the nozzle, causing the ink to come down. To prevent the ink from being blocked, the ink head should be cleaned frequently and the environment should be kept clean.
Missing
The nozzle is a complicated device that generates ink droplets at a frequency of 8-20 kHz and simultaneously moves at a predetermined speed and direction on the screen. At this time, any influence of the outside world may cause a missing print or a point deviation. Normal position. For example, due to the influence of dust, airflow, and static electricity, the flight direction of the point may be shifted. The result is a bit of overprinting, which is a bit of a missed print; and, for example, the influence of the electron rush on the adjacent nozzle, and the sound of the inkjet on the adjacent nozzle. The influence will also affect the nozzles that can not spray the ink dots, and the heating elements of the nozzles fail, or the nozzles are affected by electrical corrosion, and some nozzles can not spray the ink dots.
In order to solve the problem of missing printing, the CTS system uses the following technologies to solve
Microwave technology
The way to print a continuous pixel lattice in this way is to subdivide the dots. This method uses multiple nozzles to print multiple times to complete the printing of the continuous area, and each nozzle completes the printing separately. If some of the previous nozzles fail to print at some point, the subsequent print will fill them up. Even if there is no printing on some places, it is hard to find in the middle of the already printed ideas. This method has a method of printing 1 time, 2 times, 3 times, 4 times, and the like. But this imaging speed is greatly slowed down.
Spray point coverage
The idea of this method is so dense that the idea is not visible at all. This method is very slow in imaging and consumes a large amount of ink.
Turn off part of the nozzle technology
Some CTS system driver software allows the operator to select the number of nozzles or a designated array of nozzles so that some nozzles are not "excited" when ink is ejected, and the operator can use this command to remove those nozzles that cannot be printed. When working, the CTS system can use the remaining nozzles to re-image where the nozzles are turned off.