Talking about Frequency Modulation Technology

Dots are the most basic units of a graphic on a printing plate, and they are responsible for reproducing the tones, levels, and contours of the original. According to the principle of the network, it can be divided into two types of amplitude modulation network and frequency modulation network. The former can be widely used due to its advantages such as simple, fast, and good imaging effect. At the same time, people also clearly recognized its deficiencies, such as the absolute elimination of moire, etc., so with the development of printing technology, people began to turn their attention to another type of network--FM network.
The theory of FM screening has been around for some time. In early 1993, Agfa Corporation and Linotype-Hell Corporation officially launched FM screening technology. In August 1993, China Founder Founder Corporation also developed its own FM screening technology.
FM screening technology is the image scanned by the input, processing, through the output device when the same size points randomly distributed in different spaces, the number of points and the degree of density that is the frequency of network appearance, to show the image density and level The technical method. Therefore, the fineness of the image it represents is no longer explained by the number of black-and-white lines per cm. It is defined by the size of the dots. The smaller the dot size, the higher the accuracy of the displayed image. The better the degree.
The technology produces images that are closer to photographic effects. Due to the different exposure levels in the photographic process, there is a difference in the amount of photosensitive silver salt particles in the same area. After the development, there are few silver salt particles at the low density on the image, and there are many silver salt particles at the high density, and the density change is determined by the number of silver salt particles in different regions. The amplitude of the network is different. It is represented by the dot size (in number), so it cannot approach the effect of photography.
At present, the structure of the launch of each company's outlets is different, and the names of the outlets are also different. For example, Agfa Corp. calls it "Crystal Network", Linotype-Hell Inc. calls "Diamond Network", Dainippon Screen Inc. calls "RANDOT", etc. Different, so the number and location of printing dots within each unit image area are different, but all belong to FM screening.
The mesh size of the FM screening depends on the output resolution and screening parameters. For example, if the output resolution is 2400 dpi and the screening parameter is 2x2 laser dots as a dot, the dot diameter of the screen dot is 21μm; the screening parameter is 3x3 dots. With the laser spot as a dot, the diameter of the dot is 32 μm.
In the whole process, the most critical factor is the conversion and adjustment of the FM network. The core is to select the appropriate randomness (random dots) and the laser beam diameter to match the newly generated FM network point is smooth and solid, uniform size, very few isolated light spots This is the key to quality control. The new typesetting machine is meeting this requirement. The diameter of the laser beam can be adjusted according to the dot size. In addition, in order to cooperate with the next process, dot gain should be selected, and the value can generally be controlled within 5%. In addition to this, the photographs of the film should be paid attention to temperature, speed, pH and other values, with high-speed rapid film, in order to ensure the quality of the idea. In terms of printing, due to the fact that there is no limit to the screen angle in frequency modulation, the accuracy of equipment overprinting is rather low, and the color inks that are usually used are also acceptable.
Shaiban is an easily overlooked part, but it is also a link that has a greater impact on product quality. First, because the diameter of the FM network is small, no secondary exposure is required. Otherwise, the loss of the network will be a lot, which will sacrifice the cost of some or even all of the 2% outlets. Therefore, only one exposure is needed, and the time and light must be controlled.
In general, FM networks have the following advantages over AM networks:
1) Because the dots are randomly distributed, there will be no moiré after overprinting;
2) Due to the large size of the outlets, the intermediate adjustment will not cause the step change due to the large dot gain value during printing.
3) The details are good, some fine lines of the image will not be refracted or burrs due to screening;
4) Can display delicate levels, suitable for high-precision printing needs;
5) The printing point of the printing plate is finely pinpointed, so the fountain solution is also finely dispersed, making the printing operation easy to stabilize;
6) The full dispersion of extremely small points makes it easy to separate the printed sheets and blankets, and reduces the back-scratching of printed sheets.
Everything has its advantages and disadvantages. There are still some problems with FM screening:
1) No revision can be performed after image output;
2) There are certain difficulties when copying;
3) Do not use a dot with a very low resolution, otherwise aliasing will occur.
4) Overprinting is very difficult when images have no fit lines, so the edges of the image are sometimes not clear;
5) Low print rate.
In response to these problems, a multi-screen image copying technique using both FM screening and AM screening has been proposed. This kind of multiple screening is to solve the contradiction between traditional modulation and screening printing, which is easy to adapt to, but easy to appear, and the contradiction between emerging FM screening and the absence of “rhizome” but poor printability. This kind of screening method uses computer processing to use different screening methods in different areas of the same image. For example, in the middle tone, the "rhizome" area is screened by FM screening. In the highlight and dark tone areas, the amplitude modulation screening is used. Its long, each avoiding its short.
At present, in the field of flexographic printing, FM screening technology is widely used, such as printing some high-precision product packaging boxes, cigarette packets, etc., I believe that with the deep application of computer technology in the field of printing, FM screening technology will also Will continue to promote in other areas of printing.