I. Quality Status of Color Newspaper Printing
With the development of economy, readers are increasingly demanding the quality of newspapers, especially color newspapers. The main economic income of newspapers comes from advertising, and advertisers are increasingly critical about the print quality of newspapers. Therefore, constantly improving the printing quality of newspapers and improving their visual effects have always been the target of newspaper printing companies. For this reason, the newspapers continue to invest huge sums of money to buy high-end printing presses, and some newspapers also purchased CTPs. With the adoption of new equipment, the quality of newspaper making and printing has indeed improved to some extent. However, because of the particularity of newspaper printing, such as: newsprint is rough, ultra-high-speed newspaper printing is more difficult to print delicate layers and other reasons, newspapers can usually only use 100-120lpi network cable printing, its image visual quality is far worse than the magazine Etc. How to break this quality bottleneck has become a technological problem that printers must face.
Second, the existing network technology and its application analysis
1. The Limits of Copying of Printing Machines and Paper Constrain the Improvement of Print Quality
From the visual effects of prints to improve the quality of prints, the development of prepress technology has played a very important role. The continuous innovation of the equipment: From the photographic color separation, electronic color separation to DTP, which is now called CTF, until now the most advanced CTP, the visual effect of printed matter has indeed been improved. But people tend to ignore the role of dot technology in it.
CTP is a hot topic at present. After adopting CTP, the printing quality has actually improved compared with CTF, but there is no substantial breakthrough, because the factors that restrict the quality of printed matter are not only the copy quality of the printing plate, but also the limit of the copying of the printing press and paper. It is also a very important factor. CIP can reproduce 10μ lines on the plate, but when printing, it is difficult to take into account the 10μ lines of yin and yang.
Therefore, to further improve the printing quality of color newspapers, we must find ways to break through the printing limit. Using new types of outlets is a very effective way, and CTP has laid a good foundation for the application of new types of outlets.
2. The classification and characteristics of outlets
Currently, there are three types of network point technologies: amplitude modulation network, frequency modulation network, and hybrid network. Their application effects vary.
AM outlets
AM network is currently the most widely used network. Its characteristic is that the location and number of outlets are fixed, and the level is expressed in terms of the size of outlets.
The advantage is that midtones perform well. Oversmoothness and naturalness, printing condition defects will only affect the highlights and shadows, and will not affect the reproduction of the entire image.
The disadvantage is: when using high-line printing on newsprint paper, such as: more than 1331pi, highlights can easily lose the dark tone easily paste version, serious image layout quality. The result of using low-net printing is that the net is thick, the image is not delicate, the level is not rich, and sometimes the real moire, especially clothing advertising, seriously restricts the printing quality of newspapers. Therefore, newspaper printing generally can only use 100-120lpi.
FM network point
The FM network has many advantages over the AM sites. Its characteristic is that the network size is fixed, the level is expressed by the change of the distribution density, the location of the nodes is random, there is no concept of network lines and screen angles, and the diameter of common screen dots is used to distinguish.
The commonly used dot diameters are: 31μ (equivalent to 1% of the AM network 1OOlpi), 20μ (equivalent to 1% of the amplitude modulation network 150lpi), 14μ (equivalent to 1% of the amplitude modulation network 200lpi) and 10μ (equivalent to 300lpi of the AM network) 1%).
Its advantages are: no net flower, delicate image, no moire, can well copy the bright tone and dark tone. The disadvantages are: the dot gain during printing is very large, usually more than 30%, while the AM point expansion is generally 15%.
So why is the expansion of the FM network outlets larger? Let's do the following analysis. Suppose: δ = the expansion value of the dots at the time of printing, and R = the radius of the dots, as shown in Fig. 5, then: the dot expansion area ≈δx2πR, the dot expansion per unit area ≈ 2 π R/ n RR = 2 /R.
Visible network expansion is inversely proportional to the radius of the network, and the FM network is much smaller than the amplitude of the network. Therefore, the network of the FM network will have serious network expansion from dark tone to high tone.
The larger the dot expansion value per unit area, the more sensitive to changes in the printing pressure, the amount of ink, the printing speed, etc., thus making it difficult to control the level and color of the color newspaper. In addition, due to the different characteristics of each press, resulting in different network expansion values, each printer usually requires a set of calibration data, so that each set of FM screen printing plate can only fit a specific printing press, and increased production. The difficulty.
Poor printing process is the fatal weakness of FM network, high quality is accompanied by high cost. Therefore, although the FM network has been popularized for many years, it has rarely been actually used, even in regions where CTP is widely used.
(to be continued)