Digital printing may have become the hottest topic in the printing industry. At the same time, it has also caused a lively discussion in the paper industry. “What should the paper industry do for digital printing? What are the requirements for paper quality for this new printing?†According to Pira's 2001 forecast, digital commercial printing There will be greater growth, especially brochures and direct mailings. However, there is only a rough estimate of the size or growth of the digital printing paper market. It is only known that the number of digital printers on the market is increasing, and their production efficiency is expanding. Therefore, the amount of paper used is also growing. As for the calculation of the amount of paper for digital printing, it is difficult because many digital printers still use traditionally printed paper on their digital presses. Although most digital printers have some special performance requirements for paper, However, the familiar offset printing paper is still widely used.
Regardless of the type of printing, the basic requirements for printed materials on paper are nothing more than: weight, thickness, brightness, opacity, and smoothness. In these areas, digital printing is no exception. However, sometimes special digital presses also put some specific requirements on the paper. For example, digital printers, copiers, or desktop printers that use electrostatic printing principles are most common. For such printing equipment, the paper requires good dimensional stability, low flexibility, and low wrinkling in environments with varying temperature and humidity. At the same time, it also requires proper abrasion resistance, surface conductivity, sufficient stiffness, and less paper or dust during the printing process.
In addition, the quality of paper on the print quality must also pay attention. Because the principle of electrostatic printing is used for printing, pigment is used instead of ink, so the electrical properties of the paper, such as resistivity and dielectric constant, should be controlled at appropriate levels. It must also be borne in mind that the moisture content of the paper has a great influence on the properties of the paper, but also its printing performance.
The print quality of prints printed using electrostatic printing principles depends on having the correct machine parameters. However, the uniformity of the paper is also important: the distribution of fibers or fillers in the paper must be uniform, and the smoothness of the surface should be colored. The advantages and disadvantages of material transfer are also crucial, especially for those models whose paper surface is in close contact with the color material. After the color material reaches the paper, it is mostly fixed by hot pressing. Therefore, the smoothness of the surface of the paper, surface chemical properties and heat treatment performance must also be at a suitable level. Stiffness should be required for low gram coated paper to prevent it from curling on the hot roller.
The changes in environmental humidity caused by paper during transportation, handling, and storage have a great influence on the digital printing quality of the electrostatic printing principle. Therefore, the relevant warehouses, printing plants, and other applications use air-conditioning controls.
Digital printing using inkjet technology is very different from digital printing using electrostatic principles. Because ink jets are 50 to 90% solvent-based, pigments are mostly pigmented solid polymer particles. The liquid properties of inks used in ink-jet technology have requirements for the surface absorption and absorption of paper, including: after the ink droplets are sprayed on the paper, the pigment should remain on the paper and does not spread, which requires the control of its solvent. The speed and amount absorbed, and the controlled solvent eventually evaporates from the paper, creating a uniform and consistent print. Therefore, inkjet digital printers have high requirements for surface properties, pore structure, chemical composition, and mechanical properties of paper, and are not the same for all inkjet printers or inkjet materials.
The paper used for inkjet digital printers must also be as wrinkle-free, flexible, and dimensionally stable as possible. Its surface abrasion resistance and electrostatic effects must also be controlled within the desired range to ensure good printing performance.
In short, although most of the digital presses used are ordinary Offset printing papers, some digital printers with special structures or technologies have certain requirements for paper under certain conditions. . It can be said that so far, no one kind of paper can adapt to all digital presses, and this should be noted.
Reprinted from: Graphic Arts