In today's fiercely competitive environment, businesses are under tremendous pressure and must constantly improve the imaging quality of digital or traditional photosensitive resin plates. Recently, the development of screening technology can push the plate making quality of the flexible version to a new stage.
A major limitation of flexographic printing is that all the dots on the highlights of the printing plate or printed product cannot be formed well. Due to the limitation of amplitude modulation screening, when applying small dots or thin lines to digital files, it often results in obvious boundaries between the ink layer and the blank area. In the past, people accepted it as usual, or had to increase the color of the highlight area to avoid the feeling of segmentation in the image, as shown in the following figure.
Target image Typical flexo effect
One solution to these challenges is to use HybridAM hybrid amplitude modulation screening technology, which increases the dot size of highlight areas by adding or supplementing colors without sacrificing the authenticity of the image. The effect it obtains is that it can reduce or eliminate the obvious transition from the ink area to the blank area.
The Hybrid AM algorithm uses FM screening technology to limit the size of the smallest dots, so as to avoid the use of tiny dots, that is, by changing the number of dots to control the tone (FM), instead of changing the size of the dot To control (AM).
The image below shows the concept of Hybrid AM. In Figure 1, the image shows a typical flexo result. The range of tones is compressed, and there is a very obvious transition from the ink area to the non-ink area in the highlight.
In Figure 2, by using Hybrid AM mixed amplitude screening, you can add the smallest dots on the printing plate, while randomly removing some dots in the highlight area to avoid any extra colors.
Figure 1: Target / Flexo Printing Figure 2: Target / Hybrid AM Screening
Hybrid AM screening is not a new concept. However, in the past, it was not as omnipotent as one would hope, because the smoothness of the screen lacks realism, resulting in visible grainy and striped highlights. The lack of realism and consistency of the network cable is due to the limitation of the dots of the amplitude modulation screening in the highlight area, and as a result, the smooth structure as the frequency modulation screening technology cannot be produced. There are several Hybrid AM screening equipment on the market, but they are completely different. Although the basic principles are the same, the smoothness of the screen depends on how the screen equipment establishes the network cable in the highlight area.
So after studying the relative advantages and disadvantages of different Hybrid AM algorithms, Creo believes that the use of mixed dot size can obtain a more realistic copy, effectively eliminating the inconsistency between the highlight area and the transition area. In addition, the same screening principle can also be used for dark tones to help minimize the obvious transition from halftone to solid areas. The traditional Hybrid AM screening uses fixed-size dots in the FM screening part of the highlight area; this leaves a small hole in the AM screening grid, resulting in inconsistent replication and mottling.
The application of Hybrid AM screening in the CTP workflow of flexo printing effectively removes the need for jump curves. At the same time, the sharpness of the dots minimizes the expansion of the dots, which is an inherent feature of digital printing plates.
By using element-based allocation tools, further improvements in quality can be obtained. It allows you to choose Hybrid AM screening at the appropriate location without forcing you to use it for the entire design.
Another new technology is HyperFlex (tm) screening, which is complementary to Hybrid AM screening.
When amplitude modulation screening is used to expose the photosensitive resin plate, regularly arranged dots support each other during the formation of the printing plate, creating an effect, commonly referred to as "bridging". However, when other alternative screening technologies such as Hybrid AM screening are used, the number of dots in the highlight area is reduced, thus reducing overall support. This increases the pressure on each dot and affects the reproduction of dots during development and printing.
HyperFlex screen helps the photosensitive resin plate to form small dots or image elements. As can be seen from the image below, the use of HyperFlex screening helps improve the plate-making process.
In Figure 3, we try to break the limitations of the plate-making process, and generate a 25-micron idea with 120 lpi at a 1% tone. As you can see, the dots on the printing plate are not well formed, so there is a great risk that the printing effect is far less than expected.
In Figure 4, the HyperFlex screening technology is only used in highlight areas, helping to reduce the depth of unevenness between the dots and expanding the shoulder base, so that the dots can be formed well, and small dots can not be obtained with the existing technology. Another benefit is that the surface area of ​​the dots is unchanged, so the HyperFlex screening process will not cause unwanted dots to increase on the printed matter.
Figure 5 below shows that applying Hybrid AM screening on the entire printing plate will have a cross section. Note that in the highlights, all ideas are the same size, but some are isolated and unsupported. These isolated dots cannot be well formed on the printed matter.
Figure 5: Plate surface Figure 6: Plate surface
In contrast, Figure 6 shows the same printing plate with HyperFlex screening. As a result, in high-gloss areas, the slope is shorter, giving more support to isolated dots, resulting in excellent printing results.
In short, new digital technology continuously enhances the plate-making performance of photosensitive resin plates. Improving Hybrid AM screening and combining Hybrid AM screening with HyperFlex screening are examples of how to apply scientific technology to flexo printing to continue to enhance its competitive strength.
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