With the rapid development of the flexographic printing industry in China, the quality of flexographic products, especially in the printing process, the reproduction effect and plate making process at the tone level have also received more and more attention.
From continuous color manuscripts to prints, it is necessary to convert the continuous tone image information of the manuscript into a mesh tone. The tone level of the color manuscript and all the color changes (tone, lightness, and saturation of the color) are represented by dots, that is, all the tone levels of the color manuscript are compressed to a dot of 0-100% to express (actually The scope is even smaller.)
As with other printing methods, the level of performance in flexo platemaking is still achieved using dots. And the flexographic printouts are larger than offset prints. Therefore, the quality of printed products depends to a large extent on the accuracy of the control of outlets. In order to accurately control the outlets and ensure that the level of the original image can be correctly restored, the changes in the outlets should be fed back to the pre-mastering process. Before the release of the film, the factors of the processing, printing, and printing processes should be taken into consideration.
When a color document is scanned into a computer and becomes a digital image, the image is subjected to gradation compression processing. Generally speaking, high-contrast color manuscripts whose gradation density contrast is mostly larger than the gradation density range of printed matter can not be linearly and evenly averagely compressed in order to adjust the compression of gradation adjustments. The level should be less compressed, and the dark level should be more compressed. In this way, the difference in the density level of the high-order end can be opened, and the level of the main tone of the middle tone is somewhat deeper, while the density of the dark tone end is flatter.
There are two main attributes of outlets: dot shape and dot size. There are circular dots, square dots, diamonds (chains), etc. from the shape. What are the dot enlargement ratios of these dots? How do we in flexo plate? What is the optimal configuration choice?
In fact, in the process of filming, printing, and printing, the outlets are always changing, and the changes in the outlets will cause changes in the hue of the entire screen, and its main features will be expanded. According to the geometric dot enlargement theory, the increase of the wind point is that the edge portion spreads evenly outward. The percentage increase of the edges of the dots is consistent. That is, assuming that 10% of the dot gain is increased by 10 microns, then 90% of dot edges also increase by 10 microns. Therefore, under the condition that the pressure is constant under the conditions of the same area and different shapes of the outlets, the larger the perimeter, the larger the outlet expansion rate.
Here we analyze common circular and square dots as an example.
Generally, under the condition that the number of meshes is the same and the network adjustment value is the same, the expansion rate of circular outlets is smaller than that of square outlets because the perimeter of the circular outlets is smaller than the perimeter of the square outlets. However, this argument does not seem to be completely accurate.
From the curves of Fig. 1 and Fig. 2, we can see that when the square dot is around 50%, the dot gain rate is the largest. Because the perimeter of the square is the longest, and the circular dot is around 60%-70%, the dot gain rate is the largest, because the perimeter of the circular dot is the longest.
Comparing Fig. 1 and Fig. 2, the increase rate of the square dots at the dots of 10% to 50% and 80% to 90% is larger than that of the circles; the dots at the dots of 60% to 70% are the increase ratios of the square dots to the square dots. Bigger.
In addition, the network expansion rate is also related to the thickness of the network cable. In general, the finer the network cable, the larger the network expansion rate.
Because of the difference in the thickness of the network cable, the number of outlets in the same area is also different. If the network cable is thick, the number of outlets is small; if the network cable is thin, the number of outlets is large. Dot enlargement is that the edges spread out evenly, and the percentage increase of the edge of the dot is consistent. Therefore, the larger the number and the greater the perimeter, the larger the area expansion.
From Fig. 3, it can be seen that in the printing and printing process, the fine mesh line reacts much more sensitively than the thick mesh line under pressure.
In flexo platemaking, the shape should mainly consider two major factors.
First, is the beginning of the outlet symmetrical? Since flexo is a letterpress, a certain degree of height is required for the point of view, and the flexographic plate is softer. When the pressure acts on the dot during the printing process, the dot will be deformed. If the shape of the dot is asymmetrical, Then, in the cross-section, the narrower part of the area will be larger, while the wider part will be smaller. In this way, this kind of network point will have different dot gain rate under different net angles, and its stability is relatively poor compared to symmetrical ones. In addition, during the printing process, the narrower cross-section of the dot is also easier...
Second, the ratio of perimeter to area of ​​outlets is relatively small. As mentioned earlier, the smaller the perimeter and area ratio of outlets, the smaller the outlet expansion rate, and the easier the outlets are controlled. Therefore, we should choose outlets with smaller dot gain rates.
The dot size changes with different inks, different papers, and different pressures, but the general trend is similar. In the high-light part, the outlets showed obvious bipolar changes, either the dots had been lost during the printing, and they had become net-free, or the dot-out rates were too large to become outlets that were already close to the middle tone. About 40% of the intermediate tone will form a more obvious polarization, which is very different from offset printing. The reason for this is that when the dots are 50% in size, the dots are in a theoretical angle. At this time, there was a sudden change in the area ratio between the area before and after the angle, resulting in a large change in the size of the network. In the flexographic printing, due to the influence of the printing and the effect of the printing pressure, the dots will be deformed to an angle when the dots are about 40%. Therefore, the middle dot of the flexo will be at about 40%. Too steady state. In the dark tone, flexo's outlets will be on the ground around 85%.
In summary, during the actual plate-making printing process, how to select an appropriate dot shape for a specific situation, or to be precise, how to select a different dot in a different dot value interval, so that the dot enlargement rate is controlled At the smallest degree, improving the printing effect becomes a very important issue. At present, we have developed a complete set of software. The actual use of the software, the effect is also good, with this set of software design of the 1998-1999 sprite drink and Guoshi full nutrient packaging received by everyone.
From continuous color manuscripts to prints, it is necessary to convert the continuous tone image information of the manuscript into a mesh tone. The tone level of the color manuscript and all the color changes (tone, lightness, and saturation of the color) are represented by dots, that is, all the tone levels of the color manuscript are compressed to a dot of 0-100% to express (actually The scope is even smaller.)
As with other printing methods, the level of performance in flexo platemaking is still achieved using dots. And the flexographic printouts are larger than offset prints. Therefore, the quality of printed products depends to a large extent on the accuracy of the control of outlets. In order to accurately control the outlets and ensure that the level of the original image can be correctly restored, the changes in the outlets should be fed back to the pre-mastering process. Before the release of the film, the factors of the processing, printing, and printing processes should be taken into consideration.
When a color document is scanned into a computer and becomes a digital image, the image is subjected to gradation compression processing. Generally speaking, high-contrast color manuscripts whose gradation density contrast is mostly larger than the gradation density range of printed matter can not be linearly and evenly averagely compressed in order to adjust the compression of gradation adjustments. The level should be less compressed, and the dark level should be more compressed. In this way, the difference in the density level of the high-order end can be opened, and the level of the main tone of the middle tone is somewhat deeper, while the density of the dark tone end is flatter.
There are two main attributes of outlets: dot shape and dot size. There are circular dots, square dots, diamonds (chains), etc. from the shape. What are the dot enlargement ratios of these dots? How do we in flexo plate? What is the optimal configuration choice?
In fact, in the process of filming, printing, and printing, the outlets are always changing, and the changes in the outlets will cause changes in the hue of the entire screen, and its main features will be expanded. According to the geometric dot enlargement theory, the increase of the wind point is that the edge portion spreads evenly outward. The percentage increase of the edges of the dots is consistent. That is, assuming that 10% of the dot gain is increased by 10 microns, then 90% of dot edges also increase by 10 microns. Therefore, under the condition that the pressure is constant under the conditions of the same area and different shapes of the outlets, the larger the perimeter, the larger the outlet expansion rate.
Here we analyze common circular and square dots as an example.
Generally, under the condition that the number of meshes is the same and the network adjustment value is the same, the expansion rate of circular outlets is smaller than that of square outlets because the perimeter of the circular outlets is smaller than the perimeter of the square outlets. However, this argument does not seem to be completely accurate.
From the curves of Fig. 1 and Fig. 2, we can see that when the square dot is around 50%, the dot gain rate is the largest. Because the perimeter of the square is the longest, and the circular dot is around 60%-70%, the dot gain rate is the largest, because the perimeter of the circular dot is the longest.
Comparing Fig. 1 and Fig. 2, the increase rate of the square dots at the dots of 10% to 50% and 80% to 90% is larger than that of the circles; the dots at the dots of 60% to 70% are the increase ratios of the square dots to the square dots. Bigger.
In addition, the network expansion rate is also related to the thickness of the network cable. In general, the finer the network cable, the larger the network expansion rate.
Because of the difference in the thickness of the network cable, the number of outlets in the same area is also different. If the network cable is thick, the number of outlets is small; if the network cable is thin, the number of outlets is large. Dot enlargement is that the edges spread out evenly, and the percentage increase of the edge of the dot is consistent. Therefore, the larger the number and the greater the perimeter, the larger the area expansion.
From Fig. 3, it can be seen that in the printing and printing process, the fine mesh line reacts much more sensitively than the thick mesh line under pressure.
In flexo platemaking, the shape should mainly consider two major factors.
First, is the beginning of the outlet symmetrical? Since flexo is a letterpress, a certain degree of height is required for the point of view, and the flexographic plate is softer. When the pressure acts on the dot during the printing process, the dot will be deformed. If the shape of the dot is asymmetrical, Then, in the cross-section, the narrower part of the area will be larger, while the wider part will be smaller. In this way, this kind of network point will have different dot gain rate under different net angles, and its stability is relatively poor compared to symmetrical ones. In addition, during the printing process, the narrower cross-section of the dot is also easier...
Second, the ratio of perimeter to area of ​​outlets is relatively small. As mentioned earlier, the smaller the perimeter and area ratio of outlets, the smaller the outlet expansion rate, and the easier the outlets are controlled. Therefore, we should choose outlets with smaller dot gain rates.
The dot size changes with different inks, different papers, and different pressures, but the general trend is similar. In the high-light part, the outlets showed obvious bipolar changes, either the dots had been lost during the printing, and they had become net-free, or the dot-out rates were too large to become outlets that were already close to the middle tone. About 40% of the intermediate tone will form a more obvious polarization, which is very different from offset printing. The reason for this is that when the dots are 50% in size, the dots are in a theoretical angle. At this time, there was a sudden change in the area ratio between the area before and after the angle, resulting in a large change in the size of the network. In the flexographic printing, due to the influence of the printing and the effect of the printing pressure, the dots will be deformed to an angle when the dots are about 40%. Therefore, the middle dot of the flexo will be at about 40%. Too steady state. In the dark tone, flexo's outlets will be on the ground around 85%.
In summary, during the actual plate-making printing process, how to select an appropriate dot shape for a specific situation, or to be precise, how to select a different dot in a different dot value interval, so that the dot enlargement rate is controlled At the smallest degree, improving the printing effect becomes a very important issue. At present, we have developed a complete set of software. The actual use of the software, the effect is also good, with this set of software design of the 1998-1999 sprite drink and Guoshi full nutrient packaging received by everyone.