Waterless offset printing features and technical environment

Waterless offset printing technology refers to an offset printing technology that does not require aqueous solution dampening, but uses an ink-repellent silicone rubber layer as a blank part of the printing plate, and uses an ink roller temperature control device and a special special ink to complete the printing.

Waterless offset printing before printing, printing process is basically the same with a water offset printing, but because waterless offset printing system was canceled, the printing plate, ink, printing equipment need to use a cooling system, which is different from the water offset printing.

The waterless offset printing technology has a low dot gain rate and has good dot reproducibility, especially the details of the dark tone can be reproduced well; without fountain solution, the ink color of the printing product is uniform, thick and colorful. Bright, high quality prints. Therefore, waterless offset printing is particularly suitable for printing high-end fine prints.

Waterless offset printing technology is overprinted accurately, and the printing plate is printed quickly, which can save paper for test printing; it will not cause paper stretching and deformation and improve the accuracy of overprinting; there is no adjustment of the ink-water balance process, and adjustment of the water supply system can be omitted in mechanical adjustment and Maintenance; After a dozen or more trials, you can officially start printing, thus shortening the preparation time and saving paper consumption.

Waterless offset printing technology reduces the volatilization of harmful gases such as VOCs and HAPs and is therefore of great significance for environmental protection.

Gradation replication features:

1. Good reproducibility

Water is generally the main reason for the dot gain. Because the blank part of the waterless offset printing plate has the property of water repellency, there is no water participation in the printing, the dot gain is low, the minimum dot size and the maximum dot size can remain the same, and there is good Dot reproducibility. Tests conducted by the Printing Technology Foundation of the United States on waterless offset technology show that waterless offsets have a much smaller increase in the overall number of sites than water offsets. Offset watermarks usually produce 15% to 17% of the intermediate tone dot gain, while waterless offset marks only produce 8% to 10% dot gain.

2. Large contrast of printed products, good transferability of tone

Waterless offset printing products are rich in dark tone and intermediate tone levels, and their dot reproducibility is good. From 200 to 500 lines/inch, 2% of high-light parts and 98% of dark parts can reproduce very well, especially dark. The fine level of tune. The reproducibility of waterless offset printing plates is 96% from 2% to 98%, and the reproduction rate of PS plates from 5% to 95% is only 90%.

Since printing does not use water, higher ink layer densities can be printed. Table 1 records the average field density values ​​for water and waterless offset samples, and the black ink solid density for waterless offset prints can reach 2.1, which increases the contrast and allows the dark details to be reproduced well.

3. Waterless offset printing is suitable for FM network technology

The network size of the FM network is the same, and the reproduction of the tone is represented by the number of outlets. Due to the good reproducibility of the waterless offset printing dots and the small increase in dots, the FM frequency modulation technology is suitable for waterless offset printing. The image using the FM network is more consistent and more vivid, the colors and layers are more fully embodied, and high-fidelity printing is conditionally achieved.

Color reproduction features:

Waterless offset printing can be performed with high screen printing. Without water and fewer dot gains, a high number of lines greater than 200 lines per inch can be reproduced without the occurrence of stencil or jamming as with ordinary plates.

Waterless offset printing does not have the phenomenon of ink unevenness due to fluctuations in ink balance. Due to no water, the ink is not emulsified, the dots are full, the ink layer is thick, the ink is uniform, the color is bright, and the gloss is good. At the same time, the problem of reduced density after drying is also avoided, thereby increasing the color rendering range of the ink.

Waterless offset technology environment:

Waterless offset printing is a new printing method with its own prerequisites. It needs a special plate, a special special ink, a printer ink roller temperature control (cooling) device, good equipment performance and a relatively perfect digital working environment.

Waterless offset printing plate

An offset printing plate is a multilayer structure. The substrate is an aluminum plate, a layer of diazo photosensitive material is coated on the aluminum plate, and the uppermost layer is an ink-repelling silicone rubber layer of about 2 mm thick as a blank portion of the printing plate. In order to bond the layers well, a gluing layer made of a photosensitive diazonium compound was also coated.

2. Waterless offset ink

The special ink used in waterless offset printing has the characteristics of low viscosity, high viscosity, high thixotropy, and stable performance. Waterless offset printing uses a special ink. Its basic composition is similar to ordinary offset printing inks. However, waterless offset printing inks require the addition of special binders to achieve specific viscosity and rheology, and have higher viscosity than commonly used offset printing 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 realizing waterless offset printing.

3. Temperature control (cooling) system of printing machine ink roller

The temperature control device of the ink roller adopts cooling water to reduce the temperature of the ink roller or the rubber roller, and the water is input into the roller core of the ink roller or the rubber roller through the cooling device, the roller is cooled, and then the water flows back to the cooling device. Internally, cycled over and over again to control the temperature of the ink and maintain the required ink viscosity and rheology.

4. Good mechanical properties

Waterless offset eliminates the ink balance and the quality of the product depends on the ink. Therefore, besides the quality factor of the ink, the mechanical performance requirements of the printing equipment are also higher, especially the ink supply system. In addition to the pressure between the ink roller is easy to cause the ink bar, but also easy to cause the layout from the dirty; too little pressure can lead to poor transmission of ink, affect the quality of printed products.

5. Paper

Waterless offset printing also has certain requirements for printing paper. For the same paper, traditional printing can be produced smoothly with a certain viscosity of ink, and waterless offset printing can cause paper lint and powder dropping when using the same viscosity ink. At the same time, the electrostatic phenomenon is also very easy to occur. Therefore, the humidity requirement for the printing environment is relatively strict. Generally, the humidity is required to be 50% to 60%.

6. The effect of digital work environment and computer-to-plate technology on waterless offset printing

Waterless offset ink volume control has special significance for the quality control of printed products. Only accurate control of ink volume can give full play to the technical advantages of waterless offset printing. The establishment of the digital workflow helps to obtain the ink volume adjustment data of each ink zone, and at the same time, it can use the obtained ink volume adjustment data to adjust the ink volume of each ink zone of the printing machine without having to repeat the test printing to ensure the printing quality. Saves preparation time for printing.

The computer-to-plate technology has reduced the number of copies and minimized the loss of color and gradation. The complete digital process has enabled the copying process to be fully controlled. Advanced color management technology and precise dots have minimized the color difference between print and digital proofing. The application of computer-to-plate technology can give full play to the advantages of waterless offset printing, and is particularly suitable for the printing of high-fidelity printing products.

With the development and maturation of computer-to-platemaking technology, watermarkless printing and printing will become the linkage technology for this type of new technology.

Author: Lu Xinguang

Reprinted from: Printing Technology