FM outlets: Irregular distribution of image shades

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 basis of the printing network is the sand spot on the spot surface. The finer the sand, the more the number of sand spots supporting the network, the stronger the adsorption force, and the smoother the edges of the dots, so for a FM network 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.

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 idea will definitely 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 dot is small and almost isolated, the sum of the dots around the dot is much larger than the traditional dot, but all 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 highlights are few and dilute, the stress on the unit area is the largest, the wear is severe, and the risk of network loss is greatest. . Therefore, the use of rigid pads is more suitable for the printing of FM networks.

In addition, because the entire circumference 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.

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. Insensitive to overprinting accuracy requirements. Because the frequency modulation points on each color version are irregularly distributed, even if the distribution of dots of different colors in the same site is different, slight errors do not reflect major changes in color, and the gray balance is easily obtained, so it is possible to save costs due to adjustment of overlay errors. A lot of time.

b. The key to printing is to pay attention to the fact that FM outlets cannot be lost. Even if the outlets are increased, they are uniform and will not affect the change of the adjustment. At the same time do not have to worry about will produce white spots, moire and other phenomena.

c. Because the FM network is fine, dark tone is not easy to produce paste, so the ink balance is not very sensitive.

d, because the FM network is randomly distributed, and was isolated, the printing is not easy to cause the paper to pull hair, the phenomenon of increase in the back side is also greatly reduced, so the viscosity of the printing ink can be slightly larger. According to the experiment, the use of a 1200 dpi laser spot as an ink point for the FM network printing not only can improve the printing quality, but also can reduce the labor level of the operators. It is a new technology worthy of promotion.

Reprinted from: Printer