Recognize and evaluate waterless offset printing

First of all, waterless offset printing in English is Waterless Offset, and it is absolutely necessary to avoid calling it dry offset printing because the latter is the popular name for letterpress offset printing. There are people who are often misused, and the mistakes they make are misleading.

The origin of waterless offset printing:

Speaking of the origin of waterless offset printing, it dates back to the 1930s. At that time, some people had studied the repulsive nature of using mercury and ink. It was a good idea to treat the film with mercury in the blank part of the printing plate to suppress ink. Idea, but development is interrupted because mercury is expensive and harmful to the human body. Until the early 1970s, Curtin of the United States 3M Company invented the waterless offset printing plate. The trade name used was Driography. It was coated with a diazo photosensitive layer and a vulcanized ink repellent on an aluminum plate. Silicone rubber, the thickness of this plate is about 1mm. In view of this, waterless offset printing should use low-viscosity, fast-drying inks, and should not use high-viscosity inks that are greatly affected by humidity and cannot be kept stable.

The successful development of waterless offset printing plate has attracted the attention of the industry, but its cost is more than 5 times that of the common plate, and it cannot be popularized. In the 1980s, this technology was favored by Japan's Daejeon Printing Corporation and Toray Chemical Corporation. Because Japan is a country where both religions and Buddhism coexist, some publishers are required to publish ancient art paintings and statues of temples. The quality requirements are high, and the number of dot lines is generally 600-700 lines/inch. Even up to 1000 lines/inch, from the product quality considerations should use anhydrous offset printing technology. What is even more crucial is that Japan’s territory is limited and its environmental protection requirements are more stringent. It is more appropriate to consider waterless offset printing from the perspective of environmental protection. This is the same idea as Germany and France.

So Dainippon Printing Co., Ltd. and Toray Chemical Co., Ltd. learned the contents of the U.S. patents, and developed a waterless offset printing plate with a more practical and unique technology, named Waterless Plate. Since its introduction into the market in 1979, it has become the mainstream of the Japanese printing market so far, accounting for 8% of the Japanese offset printing market.

China has also been focusing on waterless offset printing since the 1990s. Shanghai Printing Research Institute and Beijing Institute of Printing Technology have been investing in the development of plates and inks. However, funding and technology cannot be completed on time. At present, there are two or three companies in China that use waterless offset printing technology and have a good operating condition. This is a good start. The plates used are all imported from Toray Industries of Japan, so this article is also mainly used to introduce them. .

Waterless offset works:

The main idea behind the principle of waterless offset printing relies on special plates for waterless offset printing and special inks that maintain a certain viscosity, as well as presses specifically designed for waterless offset printing and temperature control. The technical difference between the Japanese Toray company’s plate and the American 3M company is that the American 3M company makes the silicon rubber itself photosensitive, while the Toray company in Japan uses the photocrosslinking effect of the photosensitive resin to form the image.

The biggest difference between waterless offset printing and water offset printing is that a layer of ink-repellent silicone rubber is applied to the photosensitive layer coated with a water offset printing plate. Under dry conditions, the silicone rubber layer is not ink-repellent. When developing by exposure with a positive image, it is necessary to pay attention to the vacuum drawing machine. In the area where the light is not irradiated (the graphic part on the positive image), the silicone rubber is washed away to form a graphic part; the light-irradiated part is retained by the silicone rubber and forms a non-graphical part.

The graphic part and the non-graphic part are almost in the same plane, because the silicone rubber layer is not more than 2μm, and the image part after being washed off is about 2μm low, forming a plano-gravure version.

The ink roller is rolled on the dried printing plate, and the part of the silicone rubber layer washed away, while the part of the silicone rubber layer remaining, the adhesion of the surface ink is less than the cohesion of the ink itself, so in the dry state, Its surface will not stick to ink, so that printing can be completed without fountain solution.

To use coated paper, for example, the printing force of this type of printing plate can reach 300,000 printing. If the surface of the paper is rough, the resistance will decrease accordingly. According to actual production experience, the quality of 50,000 prints is very stable. After the plate is used up, it can be recycled just like a normal PS plate. At present, the waterless offset printing plate has 175 lines per inch of image lines, and dot reproduction ranges from 0.5% to 99.5%. According to related data, if waterless offset printing and FM screening are combined, high-grade printing of 400 lines/inch can be achieved.

Waterless offset production conditions:

With regard to special plates used for waterless offset printing, the above has been made clearer. However, in order to complete the waterless offset printing operation, necessary special inks that match the plate material are still needed. If the viscosity of the ink is high, if the ink is hard, it will easily cause fluffing of the paper and the ink in the solid part. Moreover, the use of high-viscosity ink on the ink roller raises the temperature, causing troubles for the operation, if it is reduced The viscosity of the ink has become a cause of dirt, so it is difficult to grasp. However, the stability of waterless offset depends primarily on the stability of the ink used. After the joint research of the plate manufacturer and the ink manufacturer, the ink viscosity value currently used is positioned at around 6-8. Because the temperature of the ink itself has a great influence on the performance of the ink, it is required that the temperature of the special ink and the temperature of the closely related plate cylinder surface be controlled reasonably. At present, no fouling occurs when the layout temperature is controlled at about 38°C.

In summary, the development of low viscosity, high flow ink is the key. Due to the low viscosity, the solid part on the printed matter improves the ink repellency, eliminates the density unevenness of the dot part, and because the ink film is smooth, the overprint of the secondary color is also smooth. Also, because of good ink repellency and overprintability, good gloss prints can be obtained. Here are three points of reference for manufacturers wishing to develop inks for waterless offset printing.

(1) Consider the ambient temperature of the waterless offset press as far as possible to keep it working at a constant temperature at a low temperature. Therefore, the design scheme of the ink used should be a low viscosity type. For this reason, it is necessary to fully invest in the manufacture of a low viscosity ink that does not cause dirtiness.

(2) The ink used for waterless offset printing should not be over-constrained and should be prepared in more varieties, such as intermediate special inks, synthetic paper inks, special modulation inks, and inks for film printing. Wait.

(3) Recent information indicates that UV curable waterless offset inks can be developed, and this ink is promising.

The printing presses designed for waterless offset printing are produced by 7 to 8 manufacturers around the world. The most famous are Quickmaster DI 46 from Heidelberg, Dominant 745C from Adast, and Karat 74 from KBA. , And Komori's Lithrone 26 and so on. Most of them are 4-color printing units, but also satellites. The printing speed is mostly 8000-10,000 sheets/hour. The number of waterless offset printing equipment introduced in the United States, Japan, and Europe is shown in Table 1.

It is worth noting here that domestic waterless offset printing started shortly before, and there is a lot of prejudice on the objective understanding of it. Therefore, the amount of printed product is not enthusiastic, but this concept will be quickly adopted when waterless offset printing is used. Initially, there is no need to purchase new ones. Equipment, as long as the old traditional offset press can be slightly modified. However, to find experienced technical personnel to do, the specific approach is to close the water supply device, install the cooling pipe in the ink roller of the ink supply system, pay attention to the pressure of the ink roller is adjusted to within 2mm, after doing so can be The new machine is used. If four-color printing is required, gold and silver spot colors must be added, and an offset printing machine with six colors must be used to reconstruct.

In addition to the three major elements of the plate, ink, and printing press mentioned above, the temperature and humidity of the workshop should be kept constant. The optimum temperature is between 20 and 22°C, and the humidity is around 55%.

Waterless offset printing production benefits:

1. Quality management

Because of the small dot gain, high-precision dots can be reproduced, and high-quality prints with dots and line reproduction that cannot be obtained by water offset printing can be obtained. According to the latest data, the adoption of water-free CTP offset printing can reach a high-definition printing level of 500 lines/inch. If combined with FM screening, the effect is better, and high-quality images can be printed on uneven paper and matte paper. As shown in Figure 1.

If the quality can reach 400-500 lines / inch level, can bring two considerable benefits: First, rely on this process technology, can be in line with international standards; the second is to expand the scope of application, access to high added value.

2. Labor management

Due to the elimination of the water bucket device, the time for cleaning the water bucket and the water roller is saved. In particular, the ink and water balance adjustment operation before starting the machine is saved, which not only saves labor and time, but also easily grasps the offset printing machine. Comparing the print preparation time of the senior four-color four-color printing press, the practice has proved that there is an average of 35 minutes for water offset printing and only 15 minutes for waterless printing. And waterless offset printing technology can be mastered in only 1 to 2 days. A waterless offset press can basically be operated by one person and up to 1.5 people, which can save the labor wages of two workers. Overall printing efficiency can be increased by more than 30%. Adapt to the needs of many varieties, small batches, short lead times, high quality market.

3. Progress management

Since there is no need for ink-ink balance adjustment, it is easy to standardize operations, so it can smoothly enter the next process after printing is completed. Because of the reduction in print preparation time, it is equivalent to an increase in printing time. After starting the machine, it is generally possible to print a dozen or more prints. Therefore, the amount of paper can be saved. Water offset printing not only requires more paper, but also wastes production time. Taking 4,000 batch prints as an example, 1 hour is enough from start-up to printing, including print preparation time. This point is very important for maintaining business reputation and is also the cost of market competition.

4. Environmental management

Environmental protection has become the main theme of the 21st century. Once a water-based offset printing with a serious source of pollution is converted to waterless offset printing, the burden on the environment is greatly reduced. Because there is no need for waste liquid treatment, equipment costs and production sites are saved.

Since the wetting device is eliminated, there are no problems associated with water, and while the production environment is kept clean, energy consumption is also greatly reduced, thereby reducing the total cost of production. The mechanical load is reduced, the energy consumption is reduced, and the noise in the workshop is also reduced accordingly.

Waterless offset printing does not emit harmful solvents and gases and is worth promoting.

5. Business activities

Thanks to the high production efficiency of waterless offset printing, it is possible to obtain better quality than the PS version, expand the scope of business, expand the use of the field, in addition to high-end fine arts, photo collections, according to recent information, the printing of beverage cans has been adopted Water offset printing has excellent results, which also indicates the development trend of waterless offset printing.