Detailed explanation of the water free offset prin

Detailed explanation of anhydrous offset printing technology of optical disc (middle)

(2) plate making steps: the key to anhydrous offset plate making and development is to cut and remove the silica gel layer equivalent to the image and text part. The shear force is stronger than the adhesion between the silicone layer and the photosensitive adhesive layer of the image and text part, and the silicone layer of the image and text part can be removed by applying it to the interface of the two layers

a) make up: the film for anhydrous printing can be negative or positive. The so-called patchwork is the process of pasting and fixing the film on the printing plate according to certain requirements and operating specifications. Whether to use light barrier film shall be determined according to the type of film and lithography

b) exposure: the traditional UV light source plate exposure device and light source are used to expose the Toray waterless printing plate. The proportion of exports to emerging countries will also be greatly increased, and the light time is about 60 seconds. When the negative type waterless printing plate is exposed, the UV light of the film penetrates the silicone rubber layer and reaches the photosensitive resin layer. The photosensitive resin in the graphic part absorbs UV light, reacts, and falls off at the connection between the photosensitive resin and the silicone rubber layer. This reaction is very fine, and the printing plate is easy to obtain a high resolution. When the number of lines is 175 lines/inch, it can reproduce points between 0.5% and 99.5%

c) in addition to the protective film: the Toray waterless printing plate needs to be processed after exposure. Before processing the printing plate, the protective film on the silicone layer must be removed

d) swelling: the development processing equipment is unique to the system, which uses special chemical and mechanical methods to process the printing plate. Use appropriate p.p.g (polypropylene glycol) and p.e.g (polyethylene glycol), namely Toray pa-l pretreatment solution, to make the photosensitive layer of the graphic part swell, and the silica gel layer float, so that the adhesion between the two layers is greatly weakened. There is no chemical change in the blank part

e) mechanical stripping: if a negative picture is used, the photosensitive part will peel off, and the non photosensitive part (i.e. the blank part) will retain the silicone layer; If a positive picture is used, the photosensitive part hardens and the non photosensitive part falls off to form a graphic part. The expanded anhydrous printing plate is evenly applied with shear force on the interface of the expanded silica gel layer through the nylon brush, so that the silicone layer of the image part is peeled off and separated. So far, the development process of the anhydrous printing plate has been completed, and the anhydrous printing plate is thus made

f) dyeing: the developed waterless version can be printed without dyeing. The function of dyeing is mainly used to identify and check the quality of the printing plate

the point to be emphasized here is: after the anhydrous offset printing plate making, you get a flat intaglio plate, and the non graphic part of the plate is an ink repellent silicone rubber layer; In the graphic part, the silicone rubber layer is removed, leaving an ink absorbing resin layer, forming a "ink absorbing hole" structure. These "ink absorption holes" provide a supporting wall when the ink is transferred from the printing plate to the rubber drum. In this way, in the process of completing the ink transfer, the dot expansion formed under the printing pressure is very small, and the faithful reproduction of graphics and texts is basically realized

(3) waterless offset printing ink

waterless offset printing uses a specific ink. It requires high viscosity to ensure good repellency to the silicone rubber layer of non graphic parts, that is, the high viscosity ink can ensure that the silicone rubber layer is not stained with ink, and there is no dirty version (the blank part is not inked). At the same time, it has good affinity to the graphic part of the printing plate, and can match the type and material of the rubber blanket, so as to ensure the smooth transmission and transfer of the yield point of some metal materials of the ink. It also requires that the ink does not contain rough particles, so as to prevent scratching the protective film on the surface of the printing plate, and at the same time, avoid the heat generated by particle friction and reduce the viscosity of the ink

(4) temperature control system

for high viscosity waterless offset ink, the important factor affecting the viscosity of ink is temperature. Small changes in temperature will cause great changes in ink viscosity. For example, the viscosity of ink at 25 ℃ is 100-150 poise, However, at 40 ℃, the viscosity drops sharply to 30-40 poises. "Today's Lilians. In the continuous printing process, due to mechanical friction (friction between ink rollers, between ink rollers and printing plates, between printing plates and blanket) And other factors will cause the temperature of the printing plate to rise, because the viscosity of the anhydrous ink is large, and the friction between the anhydrous ink and the ink roller will also increase the temperature, resulting in the decrease of the viscosity of the printing ink

because of the high requirements for ink viscosity, we have to use a temperature control system on the printing machine to accurately control the ink temperature. Air cooling and water cooling methods are usually used in CD offset press without horizontal version. No matter what method is adopted, it is to control the temperature at a constant value, so as to maintain the viscosity of anhydrous ink

air cooling method: that is, blowing constant temperature cold air to the surface of the ink roller and the printing plate cylinder to reduce the temperature of the plate, maintain the ink temperature and maintain the viscosity of the ink. Such as German kammann offset press

water cooling method: mainly in offset press lithography, sufficient cooling water is introduced to control the temperature. For example, Taiwan produces offset press

although various brands of waterless offset printing inks are suitable "At present, these service capabilities are provided by partners. The appropriate temperature varies, but it is necessary to control the temperature difference between the layout and the ink roller to keep it within the range of ± 15 ℃. Some inks only have a temperature tolerance of ± 0.8 ℃, while others have a temperature tolerance of ± 1.5 ℃. Too high temperature will make the silicone resin in the non graphic part stained with ink, resulting in dirty version, too low temperature, poor ink transfer, and false white spots on the full version. Therefore, there is no horizontal offset ink temperature The balance control technology of levelless offset press is a key technology

in the actual printing production operation, the operator should adjust the temperature according to the selected ink and the printing speed

3.2 pressek system

pressek pearl dry waterless printing plate system is composed of two parts: waterless printing plate and waterless ink similar to Toray company

pressek claims that the temperature control system on the printing press is an optional option. The maximum printing capacity of Pearl dry waterless printing plate is 50000. If the printing volume is less than 10000, it has no effect on the temperature on the printing machine. Temperature control system is only required for long version activities. Pearl dry waterless printing plate is also renewable, and the maximum format size is four Kai

pearl dry waterless version is composed of four layers: ink repellent silicone rubber layer, light absorbing imaging layer, ink absorbing layer, aluminum base or polyester base. Pearl dry waterless printing plate imaging, no film, no exposure, no processing. Its imaging mainly uses an ablation technology. Using an infrared laser diode, ablate the silicone rubber coating on the printing plate to expose the ink absorbing layer below. In the imaging process, the laser quickly heats the imaging layer to record pictures and texts. The imaging layer is evaporated, and the silicone rubber coating on it is stripped from the printing plate to form graphics and texts. After the plate is imaged, it can be installed on the plate cylinder for printing and production after simple cleaning

the system can use the direct plate making machine of pressek company for imaging. (to be continued)