FM dot printing suitability
There are many processes to transform the dots from the negative film to the printing to the substrate, and the changes in each conversion directly affect the color reproduction of the image. This is true of any screening technology. However, FM screening has different structures, finer dots, and a different change pattern than traditional screening. The control conditions may be stricter. According to the actual conditions, it is assumed that the recording accuracy is 1200dpi, that is, the ink dot is 20μm. Let's discuss the requirements of FM dot printing suitability.
1. Image density of output film
Generally, the laser dots of FM screening are often round dots with jagged edges. The thinner the dots, the less halogen silver particles are deposited on the negative film, and the lower the density. According to the requirements of standardized operation of printing, its density must be greater than 2.30. At the same time, there should not be more than two bright spots with a diameter of 6μm inside the dot, otherwise it will not meet the requirements.
Therefore, the film output from the laser recording device is preferably a special hard film matching the device. The output dots are required to be strong, dense, and transparent and clean. Because the dots are small, it is not allowed to use the etching method to eliminate spots or modify the dots in the film processing process, and to avoid repeated and multiple copies. Therefore, in addition to the strict specification and standard operation of the film processing conditions, it is best to have a clean environmental condition suitable for FM screening and supporting processing chemicals and dust.
2. Requirements for printing
The basis of the printed dots is the sand mesh on the surface of the printed spot. The finer the sand mesh, the more sand meshes supporting the mesh dot, the stronger the adsorption force, and the smoother the edge of the mesh dot. In order to keep its proper printing durability from being worn out, try to use a fine-grained, high-resolution plate. According to international standards, the ideal average thickness of sands is 2.5μm and the depth is 3μm. Assuming that each sand is regarded as a cone, each 20μm FM point has a total of 64 sands support, the total contact area is about 817μm × μm. However, the average thickness of the current PS version in China is greater than 5μm. Obviously, there is only 16 sand mesh support at a frequency modulation point, and the total contact area is 490μm × μm. Both the number of supported sand mesh particles and the total contact area are relatively small, so the adsorption The force is greatly weakened, which is also one of the reasons for the outlets to be out of version. At the same time, the larger the particles, the more the amount of photosensitive resin liquid applied, and the thicker the film layer, and the dots tend to increase due to the light penetration effect. Of course, it is not as fine as possible, otherwise it will affect the hydrophilicity of the printing plate. From this point, the printing plate of the FM dot is best at a certain particle size, increase the area of ​​the particle side or change the nature of the plate to obtain the best Hydrophilic.
The key of 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 exposure is used to reduce the deformation of the dots caused by the light penetration effect, and the developer concentration, temperature, and printing are strictly controlled Environmental conditions, any dust or stains and scratches on the glass of the printing machine can affect the quality of the printing.
c. Blanket. The blanket is an intermediate carrier in offset printing, which plays the role of ink transmission. Therefore, the blanket should not only have good ink adhesion and water resistance, but also have a good ability to transfer ink. In the printing of FM dots, the smoothness and flatness of the blanket should be emphasized in order to keep the dots intact and clear. It is best to use a smaller air cushion blanket with printed dots.
4. Suitability of printing operations
The correct transfer of dots during printing is one of the key elements for evaluating the quality of printing, but the original concept of controlling percentage and tone in traditional screen printing is no longer applicable. FM dot printing can only check whether the ideas are complete and not lost. The increase of outlets is inevitable.
We know that if the pressure is too large during printing, or the amount of grinding is too large, the idea will definitely increase. If according to the theoretical law of the area around the dot, the dot increase is calculated by the perimeter of all printed dots, then the FM dots are small and almost isolated, and the sum of the dots is much larger than the traditional dots, but all dots are normal The increase in the situation is uniform. At the same time, due to the high accuracy of the FM dot recording, the idea is thin, and the tone can be copied is almost unlimited. Therefore, the image is still soft and high definition, but it does not mean that the pressure or ink volume can be increased. Since the FM dots are isolated and unevenly distributed, the force of each dot in the unit area is not uniform, especially the highlights are few and rare, the dots in the unit area are the most stressed, the wear is serious, and the risk of dot loss is the greatest . Therefore, the use of hard liners is more suitable for printing FM dots.
In addition, because all the isolated ink spots on the printing are surrounded by the wetting liquid, it is easy to be wetted by the chemical liquid. Excessive water consumption or inappropriate pH value will also cause the dot loss. Therefore, the key to printing is to master the printing pressure and water-ink balance.
At the same time, the original printing quality control strips used in printing are not suitable for FM dot printing, and it is necessary to develop new tools for measuring and controlling printing quality.
FM outlets are good for printing
In summary, in the entire printing process of FM dot printing, all aspects of the operation must be standardized, and environmental requirements are extremely high, especially in the plate-making stage. But in the printing operation, it is obviously much easier than traditional dot printing.
a. Not sensitive to accurate requirements for overprinting. Because the FM points on each color version are irregularly distributed, even if the distribution of dots of different colors in the same part is also different, a slight error can not reflect the major change of color, and it is easy to obtain gray balance, so it can save the cost of adjusting the overprint error A lot of time.
b. The key in printing is to pay attention to the fact that the FM dots cannot be lost. Even if the dots increase, they are even and consistent, and will not affect too much change in the tuning value. At the same time, there is no need to worry about the occurrence of white spots and moire.
c. Because the frequency modulation dots are fine, dark tone is not easy to produce paste, so the ink and ink balance is not very sensitive.
d. Since the FM dots are randomly distributed and isolated, it is not easy to cause paper fluffing during printing, and the phenomenon of increased scumming on the back is also greatly reduced, so the viscosity of the printing ink can be slightly larger.
According to the test, FM screen printing using a laser spot of 1200dpi as an inking point can not only improve the printing quality, but also reduce the labor level of the operator, which is a new technology worth promoting.
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