FM outlets: Irregular distribution of image shades (medium)

3. Selection of printed 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 dot 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 dot network, the ink layer cannot be very thick, and the density will be affected. For this reason, the coloring power, color saturation, fine grain 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 requirements of paper whiteness, surface tensile strength, the smoothness of the paper, thickness uniformity is particularly important, according to foreign reports, advanced coating paper can be printed out 8μm size of the network, and The rough surface of the paper is only about 30μm, so it should be chosen as smooth as possible coated paper.

FM network printability
The production of dots from the film to the printing on the substrate undergoes many process conversions, and the 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.

1. Output film image density
Normally, the frequency of the laser dots for the screened screen 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 in the film process, and to avoid repeated copies. Therefore, in addition to the film processing conditions must be strictly standardized, standard operation, it is best to have suitable for the frequency modulation and screen processing liquid and dust-proof clean environmental conditions.
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 frequency modulation point, and the total contact area is about 817 μm. ×μm. However, at present, the average thickness of the PS plate in China is more than 5 μm. Obviously, only 16 sand supports are required for a single FM gauze, and the total contact area is 490 μm×μm. Whether it is the number of sand grains supported or the total contact area is relatively 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, and the thicker the film layer is, the network dots are easily 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 photo-bleeding 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.

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.

(to be continued)

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