Unique waterless offset printing technology (on)

Waterless offset printing is a lithographic offset printing method that does not require fountain solution. It uses silicone rubber-coated printing plates and special inks to make the non-graphical part of the ink, played a horizontal version of the offset fountain solution, which is an important feature of waterless offset.

The biggest advantage of waterless offset printing is that it completely solves the problem of ink and water balance in horizontal offset printing, and also brings difficulties to printing operators and affects the quality of printed products. In recent years, there has been some development in waterless offset printing, but due to the high cost of consumables, the development speed is not as fast as people expected. However, with the development of science and technology, with the advantages of waterless offset printing, it will have a broader development prospect in the near future.

1, the difference between waterless offset printing and water offset printing

Waterless offset printing, printing, printing process and lithographic offset printing process is basically the same, but because waterless offset printing system was canceled, the printing plate, ink, printing equipment must use cooling system, which is Lithographic offsets differ.

(1) Waterless offset printing plate

Waterless offset printing plates are available in both positive and negative format, which differs from the structure of offset printing plates (PS plates) with water. The waterless offset printing plate is composed of a transparent protective film, a silicone rubber layer, a photosensitive resin layer, a primer layer, and an aluminum base plate. The lowermost layer of the printing plate is an aluminum base plate, and an undercoating layer is applied on the surface of the aluminum base plate. In order to enhance the adhesion of the photosensitive resin layer to the aluminum base plate. The photosensitive resin is applied thereon (the image portion constituting the printing plate upon exposure). Then, the ink-repelling silicone rubber layer is further coated on the photosensitive layer so that the ink cannot be attached and a blank portion of the printing plate is obtained. When exposed, the silicone rubber layer is cross-linked by ultraviolet light. If it is of positive type, the photosensitive portion is hardened, so that the silicone rubber layer and the polymer of the photosensitive resin layer are firmly bonded together, and the silicone rubber layer of the non-photosensitive portion is peeled off from the photosensitive resin layer. In negative contrast, the photosensitive silicone rubber layer is peeled off from the photosensitive resin layer, and the non-photosensitive portion retains the silicone rubber layer. No matter whether it is a positive or negative type offset printing plate, after the photosensitivity, the non-graphical part of the silicone rubber layer is slightly higher than some of the graphic part, so the waterless offset printing plate is a flat intaglio plate.

The protective film on the silicone rubber layer not only protects the plate from scratches, but also allows the film to completely adhere to the plate. It also prevents oxygen molecules from passing through the silicone rubber layer, affecting the photopolymerization reaction and keeping the plate in storage. shorten.

Waterless offset printing process is the same as lithographic offset PS, but the structure and mechanism of the plate are different. The printing plate can still use all kinds of original printing equipment, no need to re-purchase new equipment, and it does not need original drying. Edition equipment is modified.

(2) waterless offset ink

Waterless offset printing uses a special ink. Its basic composition is similar to that of lithographic offset printing inks. However, waterless offset printing inks require the addition of special binders in order to achieve specific viscosity and rheology, and are more viscous than conventional offset inks.

The water-free offset printing ink is in contact with the printing plate silicone rubber layer, and its intermolecular cohesion is less than the interfacial cohesion between the ink and the photosensitive resin layer, so that the ink and the non-graphical part of the silicone rubber layer are repelled, thereby achieving waterless printing.

(3) waterless temperature control auxiliary equipment

Waterless offset printing Since the dampening system was eliminated, the ink leveling system has no dampening fluid and the temperature rises, and the ink is decomposed by heat, causing non-textured portions to be smeared. Therefore, a cooling system must be installed on the press to control the temperature of the ink to ensure good viscosity and rheology of the ink during printing.

The cooling system on the press has a water cooling system and an air cooling system.

Water cooling system: It uses cooling water to reduce the temperature of the tandem roller or rubber roller. The water is fed into the roller core of the ink roller or rubber roller through the cooling device, the roller is cooled, and then the water flows back to the cooling device. Cycle over and over again to control the temperature of the ink and maintain the required viscosity and rheology of the ink. In general, high-speed printing press adopts ink cooling system, while medium-speed printing press or waterless offset printing machine converted from ordinary offset printing press adopts rubber roller cooling system or air cooling system.

Air-cooled system: It is the air-cooling device that blows cool air to the platen roller to cool the plate surface and control the ink temperature. This system is generally suitable for medium speed printers.

2, the advantages of waterless offset

Waterless offset printing has higher quality than offset printing, and it has advantages over water offset printing in terms of improving printing efficiency, ease of operation, and environmental protection.

Small outlets, good reproducibility, and high quality prints. Lithographic offset printing due to the fountain solution causes the dots to increase significantly and their dot gain values ​​are above 10 to 15%. Waterless offset printing has no influence due to fountain solution, and the dot gain value is only 7%. Therefore, the dark tone and intermediate tone levels of printed products are more abundant, and the dot reproducibility is good. 2% dots and dark tone of highlights from 200 lpi to 500 lpi are obtained. Some of the 98% of the dots can be reproduced well, especially the subtle levels of shadowing can be clearly reproduced. The dot reproduction rate of waterless offset printing from 2% to 98% is 96%, while the dot reproduction ratio of PS version from 5% to 95% is only 90%. Waterless offset printing quality is obviously higher, and can now produce high-precision prints of 700 lpi to l000 lpi.

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