The printability of FM outlets

FM screening is a new replication process that has emerged with the development of computing technology in recent years. It is different from the general FM screening. FM network prints have the advantages of soft tones, rich layers, vivid images and no Moiré effect. This article discusses the printing suitability of FM network points, printing materials and printing jobs, and the benefits of using FM outlets in printing, based on the fact that the size of FM outlets is the same, but the arrangement is random. 1 Introduction In the process of image duplication, traditional screening methods are used to represent the shades of images. After more than a century of unremitting efforts, printing technicians have achieved a very high level of success. However, in this screening method, many regular rosette patterns occur during color overprinting, and sometimes even moire may occur. At the same time, due to the decomposition of the dots, with the decrease of the number of lines, the sharpness of the image is drastically reduced and the characteristics of the original are lost. In recent years, with the research of high-fidelity duplication technology, there have been superfine dot printings of more than 120 L/cm, which can accurately reproduce fine-grained and continuous-tone image effects. However, regardless of the degree of fineness, the characteristics of its outlets are the regular distribution of positive or negative dots of different sizes in the image part, and there are always its fatal weaknesses. The structure of the rose pattern, that is, the pattern phenomenon caused by the screen angle It is independent of the number of network lines. At the same time, if the number of screen lines exceeds a certain limit, it will not only bring more difficulties to the copying, but also the tone value, especially the high-light part, will be more serious and the resolution will be limited. This is the biggest drawback of the traditional screening method. 2, the characteristics of FM outlets In the 70s of the 20th century, foreign countries began to study an FM screening method. Unlike traditional screening, printing dots are calculated based on the statistics of the hue and gradation of the adjacent parts of the image, in the image area. Randomly distributed within the random, but the same size (mostly 7-40μm), to show the shade of the image. Due to the limitation of technical conditions at the time, it was not able to satisfy a large number of computational needs. Therefore, it was postponed to the 1980s. With the development of electronic computers, the computational capabilities have greatly improved. This enabled the screening method to be realized. However, FM screening at this stage is only a random random screening of first-order functions. The dot sizes are the same. Dot pitch changes and photo images are formed by different size and distances of halogen particles (0.5-5 μm) to form the tone or color. Still different. Therefore, people continue to study that if the second order function is used for random screening, the distance and area of ​​the point can be randomly changed. Then, the second-order function screening and the original photograph are used to express the mechanism of the tone. Very similar, the replica will be more realistic and completely close to the effect of photo images. Of course, the computational complexity of stochastic screening of second-order functions is even greater and more complex, but it is believed that this will be achieved in the near future. In fact, at the present stage, people have adopted a first-order function FM screening to show unparalleled advantages over the traditional screening methods, in order to show that the use of computer algorithms to control the arrangement of points can actually eliminate unsightly pattern periodicity. The structure is more suitable for image reproduction above the three primary colors. Because of the subtle fine tuning of the FM screen, if a 15 μm diameter dot is used, there is no doubt that a 1% -99% tone value can be reproduced. Therefore, the replica has a high resolution, a soft image tone, a rich gradation, and a realistic image. There is no Moll effect, this is why the FM screening method can get the charm of printing experts. 3, the minimum dot size of engraving In the frequency modulation screening technology, the only key parameter is the size of the network point, which is much less than the traditional art screen printing parameters. It does not have the problems of dot network angle, screen number, and dot shape. The size of the FM spot is only related to the recording accuracy of the exposure device. Theoretically speaking, a 1200-dpi photo-recording spot is a square point with a side length of 1/1200 in. However, actually, the spot of light exposed on a photographic film by laser is a circle with a slightly smaller area than the square. 21μm, which is equivalent to a 1.2% dot of 60L/cm, or a 1.5% square point, see Table 1. From Table 1, it can be seen that as the recording accuracy increases, the light spot becomes smaller. From the point of view of the output precision of the current image-setter, the size of the FM dot network that meets the printing requirements is completely guaranteed. The problem depends on the dot size that can be printed in the printing. Therefore, the FM-screening is not based on computer hardware, but rather it is printing. technology. Therefore, the minimum printable size is a key factor in printing, but its value varies depending on the printing equipment, materials, process, and technical level. According to reports, assume that under a certain resolution, take a light spot as the ink-jet point. Foreign countries can print high-quality on glossy paper. The smallest printing dot can reach 8μm, and it can be printed on rough paper. 40μm. However, in China, it is quite difficult to print less than 20μm dots on the test. Clearly the gap is relatively large. 4, FM network printability The production of dots from the film to print onto the substrate undergoes many process conversions, and changes in each of the conversions directly affect the color reproduction of the image. This is true for any screening technique. However, due to the differences in structure, finer mesh points, and the regularity of change and traditional screening, the control conditions may be more stringent. According to the actual conditions, assuming that the recording accuracy is 1200dpi, that is, the dot is 20μm. To discuss the requirements for the printability of the FM network. 4.1 Output Film Image Density Normally, the frequency of the laser dots for screen-screening is often a jagged circular dot. The finer the dots, the less the halogen silver particles deposited on the negative film and the lower the density. According to the requirements of the printing plate standardization operation, the density must be greater than 2.30. At the same time, there must not be more than two bright spots with a diameter of 6 μm inside the outlet. Otherwise, they do not meet the requirements. Therefore, the film output from the laser recording apparatus preferably uses a special hard film that matches the apparatus. The outlets required are strong, dense, and transparent. Because the dots are small, it is not allowed to use etching methods to eliminate spots or correct dots during film processing, and to avoid repeated copies. Therefore, in addition to the film processing conditions must be strictly standardized, standard operation, it is best to have a suitable for FM screening and the use of liquid handling and dust-proof clean environmental conditions. 4.2 printing requirements The printing dot is based on the sand spot on the surface of the blotch. The finer the sand, the more the number of sand spots supporting the dot, the stronger the adsorption force, and the smoother the edge of the dot, so for a FM dot with a size of only 20 μm, In order to maintain its proper ink resistance so as not to be worn out, it should be possible to use fine grained, high resolution printing plates. According to international standards, the ideal average grain size is 2.5 μm and the depth is 3 μm. Assuming that each grain is considered to be a cone, there are 64 grain supports for each 20 μm of FM. The total contact area is about 817 μm. ×μm. However, at present, the average thickness of the PS plate in the country is more than 5μm. Obviously, there are only 16 sand supports in one FM point, and the total contact area is 490μm×μm. Whether it is the number of sand grains supported or the total contact area is small, so the adsorption The force is greatly reduced, which is one of the reasons for the dot-outs. At the same time, the particles are coarse and the amount of the photosensitive resin to be coated is increased. The thicker the film layer is, the more easily the dot is increased due to the light penetration effect. Of course, it is not the finer the better, otherwise it will affect the hydrophilicity of the printing plate. From this point of view, the printing plate of the FM spot is best to increase the side area of ​​the particles or change the nature of the plate to obtain the best Hydrophilic. The key to the printing operation is to ensure that the dots are not lost or deformed. Therefore, the printing plate is required to be in close contact with the negative film, and the point light source is used for exposure to reduce the distortion of the dot caused by the light penetration effect, and the developer concentration, temperature and the printing plate are strictly controlled. Environmental conditions, any dust or glass stains, scratches can affect the quality of the printing plate. 4.3 Selection of printing materials Due to the finer and different structure of the FM network, printing materials such as ink, paper, and blanket have higher requirements. a. Ink: The FM network is almost completely isolated and randomly distributed in the image area. Even in dark places, calculation methods can be used to make it possible to avoid duplicate dots as much as possible (at most only some of the dots may be close to each other). When the tone of a screen with a conventional screen is more than 50%, the dots start to be connected or networked. different. Under a small 20μm ink point, the ink must exhibit good viscoelasticity on the printing plate, blanket, and transfer to the paper. When the external force is intermittent or completely stopped, the ink-spot can immediately restore the original structure and remain isolated. Features not lodging, so the ink thixotropic, yield value and viscosity are larger. Due to the fine dots, the ink layer cannot be very thick, and the density will be affected. For this reason, the coloring power, color saturation, fine particle size, and strong water resistance of the ink are required. Considering the overall effect, inks that are suitable for printing with FM dot printing should be developed. b, paper. Paper and ink are two inseparable aspects of the printing effect. In order to ensure that the FM network is not lost, in addition to the general requirement for whiteness and surface tensile strength, the smoothness and thickness uniformity of the paper are particularly important. According to foreign reports, the advanced coating paper can print dots of 8μm in size. The rough surface of the paper is only about 30μm, so it should be chosen as smooth as possible coated paper. c. Blanket. The rubber blanket is an intermediate carrier in offset printing and plays a role in the transfer of ink. Therefore, the blanket must not only have good ink adhesion and water resistance, but also have a good ability to transfer ink. In FM network printing, the smoothness and flatness of the blanket must be emphasized in particular to maintain the integrity and clarity of the outlets. It is best to use a smaller air-cushioned blanket with a printed dot. 4.4 Suitability of print jobs The correct transfer of dots at the time of printing is one of the key elements for evaluating the quality of printing. However, the concept of controlling percentages and tonalities in traditional screen printing is no longer applicable. FM network printing can only inspect whether the dots are complete and not lost. The increase in outlets is unavoidable. We know that if the pressure is too high in the printing, or if the amount of grinding is too large, the point must increase. If you press the theoretical rule of the perimeter of the network, the dot gain is calculated by the perimeter of all printing dots, then because the dots are small and almost isolated, the sum of the dots around the dot is much larger than the traditional dots, but all the dots are normal. The increase in the situation is even. At the same time, there is almost no limitation on the high-accuracy recording of the FM network, the fineness of the dots, and the reproducible tone. Therefore, the image is still soft and clear, but it does not mean that the pressure or ink can be increased. Because the FM network is isolated and unevenly distributed, the force on each part of the unit area is also uneven. In particular, the high-light part has a small number of ideas and is thin. The unit area has the largest stress, wear, and the risk of losing the most . Therefore, the use of rigid pads is more suitable for the printing of FM networks. In addition, since the entire surrounding of the inked dot on the print is surrounded by the wetting liquid, it is prone to be wetted by the liquid, and excessive water consumption or inappropriate pH may cause dot loss. Therefore, the key to printing is to master the printing pressure and ink balance. At the same time, the print quality control strips used in the original printing are not suitable for FM network printing. It is necessary to develop new tools for measuring and controlling the printing quality. 5 FM network points are conducive to printing To sum up, the printing of FM network points throughout the printing process must be standardized in all aspects, and the environmental conditions are extremely demanding, especially at the plate making stage. However, in the printing operation, it is obviously easier than traditional dot printing. a