Dots are the basis for printing and copying graphic information and play a very important role in printing. The quality of the dots on the printing plate will directly affect the quality of the printed dots, which will in turn affect the reproduction of the entire printing process. Therefore, the first step in controlling dots is to choose a plate with good dot reproducibility. Measuring the dot reproducibility of a plate mainly includes the following aspects.
- Reproduction of AM dots
The traditional CTF process is that the computer directly outputs the film, and then the PS plate is printed through the printing machine based on the film. In this process, due to the bottom diffusion phenomenon when the printing plate is exposed, there will be a certain degree of loss of dots when drying. At the same time, the development tolerance of traditional PS plates is small. If the development time is slightly longer, less than 2% of the dots will be lost. If the development time is short, the development will not be transparent, causing staining. Therefore, during the printing process of the printing plate, the dots are reduced by a certain proportion.
This phenomenon no longer exists after using the CTP process. Therefore, CTP has the ability to replicate 1%-99% of the dots in terms of technology. The remaining question is whether the CTP plate has the ability to support 1%-99% of outlets. This is an important indicator of CTP plate production quality.
Like the traditional PS plate, the dots of the CTP plate are also composed of grit. To be able to support dots of less than 3%, the grit of the plate base needs to be fine enough. Because the finer the grit, the more grit will support the high-gloss dots, making the dots stronger and less likely to fall off during printing. However, the mesh of the dots cannot be too fine. If it is too fine, it will affect the wetting of the plate. A plate with too fine mesh will have a smaller tolerance for ink balance during printing, which is not conducive to the control of printing quality.
The reproduction of dots is also related to the coating thickness of the plate and the number of screen lines. The phenomenon of light bleeding is a common phenomenon, which exists both on the printing plate and on the printed matter. The phenomenon of light bleeding is an important factor in the expansion of dots in printing. The thicker the thickness of the coating, the more obvious the phenomenon of light bleeding will be on the dots on the printing plate. Therefore, the more serious the dot expansion will be, affecting the quality of plate making. Appropriate coating thickness is very important for dot reproduction. helpful. Similarly, the greater the number of screen lines, the larger the side length around the dot, and the more serious the dot expansion will be. Therefore, the reproduction of the screen dots on the printing plate is also related to the number of screen lines.
However, no matter what production technology is used, meeting the printing requirements is the most important for traditional FM screening. The purpose of the technology is also to meet the needs of printing. Therefore, testing CTP plates according to the needs of printing is the most important thing for printing units. It is actually the most convenient.
According to the author's market survey, the CTP plates currently on the market can reproduce 1%-99% of the dots at a screen line count of 2001pi. In comparison, the quality is quite good and can be reproduced at a maximum of 2501pi. And most of the ones that can be achieved are heat-sensitive plates. Therefore, in terms of production capacity, it seems that 200-250lpi is the upper limit.
After considering the capabilities of the plate manufacturer, it is also necessary to consider the needs of printing. First of all, the dot reproduction of the CTP plate must not be lower than the standard of the PS version at least - 1501pi, reproducing 2%-98% of the dots, because if this cannot be achieved Requirements, even the printing quality under traditional process levels may not be achieved. If you have special printing needs, such as high-line-count screening, you should determine your plate material needs based on the actual number of screening lines. Generally speaking, most of the thermal plates that can achieve high line count screening are thermal plates.
Although the dot reproduction capability is marked on each plate manual, it is still necessary to conduct relevant tests based on the actual situation. To complete relevant tests, the printing factory needs to use a ladder ruler and a special density meter for measuring plates. It is an effective method to expose the ladder ruler on the printing plate according to the required number of screen lines, and then use a special density meter to measure the density of the corresponding ladder ruler on the printing plate to see if it can meet the requirements mentioned above. method. It should be noted that the plate-making machine must be linearized during drying to achieve 1:1 output, which is more beneficial for the operation of test plates.
- Reappearance of FM outlets
Different from AM dots, FM dots control the dot area rate by controlling the density of dots in the recording unit. This article uses a 1200dpi direct plate-setter for exposure, and the dot size on the printing plate is 20μm to explore the requirements for the printability of frequency-modulated dots.
The basis of printing dots is the grit on the surface of the printing spot. The finer the grit, the greater the number of grits that support the dots, the stronger the adsorption force, and the smoother the edges of the dots. Therefore, for an FM dot with a size of only 20 μm, In order to maintain its due quality, printing plates with fine grit particles and higher resolution should be used as much as possible. According to international standards, the ideal average size of sand mesh is 2.5 μm and the depth is 3 μm. Assuming that each sand mesh is regarded as a cone, each 20 μm frequency modulation point has a total of 64 sand mesh supports, and the total contact area is approximately 817 μm2. However, dots above 1200 dpi are not covered by international standards, so they need to be tested through actual printing tests.
Due to limited equipment conditions in printing, it is difficult to use the method of measuring grit. The detection of FM dots can be done by the same method as the detection of amplitude modulation. However, in order to detect the ability of the printing plate to support FM dots, the resolution of the computer-to-plate making equipment needs to be adjusted. , see if the FM dots obtained at different resolutions can reproduce 1%-100% of the dots, and find the smallest resolution that can reproduce the dots. At the same time, for FM dots, the shape of the dots and the clarity of the edges are also very important factors. They can be measured by observing with a magnifying glass, or by comparing FM dots with AM dots and using various FM dots with different resolutions. Dot ladder ruler comparison method to measure. If the results obtained between FM, AM, and FM with different resolutions are consistent, it means that the plate supports the FM network very well.
Huida Print-All Technology company is an advanced and professional manufacturer of producing printing plates, mainly selling CTP, CTCP, and PS plates as well as offering ODM/OEMs, especially for the offset. For more information, please click the official website link here: https://www.huidaoffsetplate.com/.