Waterless printing of lithography

Working principle of waterless printing: Dongli waterless printing system consists of three parts: waterless printing plate, specially configured waterless ink and printing equipment with temperature control system.

The structure of Toray Watermark-free Edition is multi-layered, the bottom layer is an aluminum-based edition, and the top layer is a silicone rubber layer with a thickness of 2 microns. According to the different types of Toray watermark-free edition, its printing resistance ranges from150,000 to 600,000 copies, based on ordinary coated paper. If the paper surface is rough, the printing resistance will decrease to some extent. Toray watermark-free version is recyclable, just like the traditional recyclable PS version. Dongli printing plate is very suitable for all kinds of sheet-fed and rotary offset presses.

The exposure of this printing plate can also use the traditional vacuum printer and light source, and the exposure time is similar to that of the traditional printing plate. During the exposure process, the amount of UV light is controlled by the density on the film, so that the light penetrates the silicone resin layer and shines on the intermediate photopolymer layer. The light reaction on the photopolymer layer is very accurate, the resolution of the printing plate is very high, which can reach 175 lines/inch, and the range of dot output is 0.5%-99.5%. The following figure shows the imaging mechanism of traditional wet printing plate and watermark-free plate.

After exposure, the printing plate is developed, and the development process is very simple. The equipment for developing watermark-free plates is different from the traditional developing equipment, which uses special chemical reagents and treats the mechanical structure of plates. The treated printing plate is an ink-repellent silicone layer in the non-graphic area, and the silicone layer in the graphic area has been removed, leaving the photopolymer material with ink attached. When designed, the printing plate can be designed to selectively absorb and repel ink without using any water or alcohol.

The main difference between waterless ink and traditional ink lies in the difference of resin and binder used. The binder of waterless printing ink is selected according to its rheology, which is higher than that of traditional ink. The principle of waterless printing is that the silicone layer in the non-graphic area of the printing plate has low surface energy. If the viscosity of ink is high, the mutual attraction between its own molecules is higher than the affinity with silicone, so the material here has strong ink repellency.

The main factor affecting viscosity is temperature. Because there is no water in the waterless printing process, a substance that cools the surface temperature of the printing plate is lost. Due to friction, the surface temperature of the plate cylinder will continue to rise. At the same time, due to the high viscosity of anhydrous ink, the temperature of the roller surface will also rise during the process of grinding ink in the roller.

This is why it is necessary to accurately control the temperature on waterless printing equipment. The most popular system uses vibration refrigeration technology. In the process of refrigeration, the hollow vibrating cooling roller in the ink wheel pumps out coolant. This structure has been used in high-speed rotary offset press for many years. After improvement, it is also applied to sheet-fed printing equipment. Almost all sheet-fed printing machine manufacturers provide hollow ink vibrating rollers to control the temperature. The following figure shows the temperature control system of a typical waterless printer. The effect of temperature control varies with the number of ink vibrating rollers.

The function of the temperature control system is to circulate the coolant through the running track of the roller and remove the heat generated by the mechanical movement of the printing unit.

It is worth noting that this type of system is not designed to cool (or refrigerate) the ink roller, but only to maintain the inherent normal temperature during the normal operation of the printing machine. Only by keeping a fixed temperature can the viscosity of ink be kept in the best state. The following figure shows the optimal temperature task window in the waterless printing temperature control system.

The proofing of waterless printing can be done directly with film. Please note that not all simulation systems can reproduce the low dot gain of waterless printing.

Some experienced waterless printing enterprises provide high-precision proofs, and some waterless printing enterprises use calibrated digital proofing systems to make proofs, which have also achieved good results. PresstekPEARLdry printing system consists of printing plate and specially formulated anhydrous ink, and their inks are very similar to those used by Toray Company.

According to Presstek, whether to install temperature control system is the choice of printing enterprises. However, in order to obtain higher printing tolerance, it is recommended to install a temperature control system. The maximum printing tolerance of pearl plate is 50,000. PEARLdry printing plate is also recyclable, and the largest printing plate size is 23.75×29.4 (quarto). The following picture shows PEARLdryABL negative plate used in waterless printing.

Like Toray printing plate, the top layer of pearlescent printing plate is also a silicon reporting layer that repels ink. There is a photosensitive layer in the middle, which can absorb ink and maintain the stability of printing plate size.

The printing plate is imaged and exposed without film and film development. The imaging technology it uses is called ablation technology. A set of IR (infrared) laser diode arrays is used to remove the silicone image layer and expose the aluminum or polyester layer under it so that it can absorb ink. In the imaging process, the laser processes the image area by rapidly heating the image layer. The expansion of the generated gas causes the image and the upper silicone layer to separate from the printing plate. After the printing plate is imaged, the printing plate is peeled off and installed on the printing machine. The system can directly image printing plates (GTP-DI or QuickmasterDI in 8 aperture A3 format) on a printing press, or can be imaged off-line by PEARLsetter of Presstek Company. Off-line imaging includes 8-hole A3 frame (15.75x20) and 4-hole A2 frame (23.75x29.4). The width is 40 inches (102cm), and the printing plate imaging can be completed on the thermal direct printing machine. With the appearance of other PostScript systems, various types of digital proofing systems can be used for proofing waterless printing, such as Iris inkjet printer and 3M Rainbow. Environmental protection: no fountain solution is very beneficial to environmental protection.

Color consistency: In the absence of wetting system, the color of printed matter changes little during printing.

Good color saturation: the density of four-color printing is about 20% higher than that of SWOP standard (web offset printing specification, ink set commonly used in the United States).

Small dot gain: good detail reproduction, small dot gain in waterless printing, high screening number and good detail reproduction. Even with the number of screening lines of 175 lines/inch, the effect of waterless printing is quite good.

Wide printing range: waterless printing, printing on paper that cannot be used by traditional printing. Such as offset paper. Without wetting system, many paper problems in traditional printing will disappear.

Short printing preparation time: about 40% shorter than traditional printing preparation time. (1) environmental protection breakthrough.

Fresh air, abundant water, dense forests and safe working conditions are the environments that all countries in the world pursue. However, in some places, printers have caused serious damage to the environment. Waterless printing will make great contribution to environmental protection.

(2) There are no more volatile organic compounds.

Waterless printing no longer uses volatile organic compounds in fountain solution. Some volatile organic compounds will destroy the ozone layer on the earth and produce global greenhouse effect. Use water-based ink to bid farewell to volatile organic compounds.

With the revolution of ink technology, there is no need for organic solvent to clean blanket, which greatly reduces the emission of volatile organic compounds. Car wash water is a water-based cleaning agent, which consists of 93% water and 7% harmless surfactant (such as soap).

(3) Water resources protection.

1995, 92% of the world's population got enough water. If water resources continue to be consumed at this consumption rate, by 2050, only 58% people in the world will have sufficient water resources. In the future, some countries will even compete for water resources.

Waterless printing can protect water resources. For example, a printing company in Switzerland launched the world's first generation of waterless web printing machine, which can save 250,000 liters of water every year. Most of this water needs to come from a nearby lake, which is the drinking water source for nearly 1 10,000 people.

(4) Protecting forest resources.

To produce a ton of paper, you need 17 trees, which can just provide 20 people with paper for a year.

Although destroying forests provides raw materials for papermaking, it also destroys the natural habitats of countless animals and plants and seriously damages the ecological balance.

Because in the process of waterless printing, the color can come up quickly and register immediately to maintain the consistency of color in the printing process. Compared with traditional printing, this book saves 30% ~ 40% of paper. In addition to protecting the forest, it also greatly reduces the production cost.

(5) A cleaner environment and healthier people.

Printing workers breathe gases containing toxic organic substances all day, which greatly damages workers' health, greatly affects the functions of kidneys and lungs, causes dry skin, and even causes dermatitis and damages the nervous system.

When workers use highly volatile solvents to explore blankets, the damage to health is the most serious.

Obviously, waterless printing does not use a dampening system, which eliminates the toxic substances in the carpet washing solvent, not only protecting air, soil and water, but also protecting human beings themselves. (1) Brighter and brighter colors. As shown in the figure, waterless printing is compared with traditional printed matter.

The prints printed without water have a great contrast. That is to say, the dark parts are darker and the highlights are brighter. It can print out the printing quality that traditional printing can't achieve.

(2) Color reproduction is more realistic. As shown in the figure:

The ink printed by waterless printing house has high density. Therefore, under the same number of screening lines, waterless printing products are richer and more realistic than traditional printing products.

(3) Good resolution. In contrast, it is obvious that waterless printed matter looks sharper and richer. Waterless printing uses a screen number of 300 lines/inch, while traditional printing uses 175 lines/inch.

Waterless prin can provide higher color saturation and great printing contrast, and reproduce more details. In addition, the number of screening lines of 300 lines/inch can eliminate moire fringes that usually appear under the conditions of 175 lines/inch or 150 lines/inch.

(4) More color gamut space. Waterless printing is better. Because its dot gain is small, the details of darkening and dimmer can be clearly expressed. In particular, the ink density on waterless printed matter is high, which can expand the color gamut space and print more saturated colors.

The following figure shows the color gamut space of three kinds of printing measured by SPM 100 for densitometer. The color space of traditional printing is obviously smaller than that of waterless printing.

Due to the high ink density, the color gamut space perimeter of waterless sheet-fed printing is 265,438 0.3% longer than that of traditional web printing and 65,438 0.3% longer than that of traditional sheet-fed printing.