Flexo printing screen to expand the performance of the photosensitive resin plate making technology

In today's fierce competitive environment, businesses are under tremendous pressure and must continuously improve the image quality of digital or traditional photopolymers. Recently, the development of screening technology can push the plate quality of the flexible version to a new stage.

One of the major limitations of flexo printing is that all dots of the highlights on plates or prints do not form well. Since AM screening has such a limitation, when a small dot or thin line is applied to a digital file, there is often a clear boundary between the transition of the ink layer to 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 image segmentation, as shown below.

Target image Typical flexo effect

One solution to these challenges is to use Hybrid AM hybrid AM screening technology, which increases the size of the highlight area by adding or adding colors without sacrificing the authenticity of the image. It has the effect that it can reduce or eliminate the obvious transition from the ink area to the blank area.

The Hybrid AM algorithm uses the FM screening technology to limit the minimum dot size, avoiding the use of tiny dots, that is, controlling the tone by changing the number of dots, not by changing the dot size. To control (AM).

The following image shows the concept of hybrid AM hybrid AM screening technology. In Figure 1, the image shows a typical flexographic result. The range of gradation is compressed. In the highlight part, there is a very clear transition from the ink area to the non-ink area.

In Figure 2, by using Hybrid AM mixed AM screening, you can add a minimum point on the plate, and randomly remove some points in the highlight area to avoid any extra colors.

Figure 1: Target/flexo 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 expect because of the lack of realism in the smoothness of the screening, which produced visible grainy and streaky highlights. The lack of realism and consistency of the cable is due to the limitation of the screen of the highlighting area of ​​the highlight area, and as a result, the smooth structure of the FM screening technology cannot be produced. There are several Hybrid AM screening devices on the market, but they are completely different. Although the basic principles are the same, the smoothness of the screening depends on how the screening device establishes the network lines in the highlight area.

After studying the advantages and disadvantages of different Hybrid AM algorithms, Creo thinks that using hybrid dot size can achieve more realistic replication, effectively eliminating the inconsistency between highlight areas and transition areas. In addition, the same screening principle can also be used for the darker portion to facilitate minimizing the apparent transition of the halftone portion to the solid portion. The traditional Hybrid AM screening uses a fixed-sized dot in the FM screening part of the highlight area; this leaves a hole in the AM screening grid, resulting in inconsistent replication and variegation.

The application of Hybrid AM Screening in the flexo CTP workflow effectively eliminates the need for jump curves, and at the same time, due to the sharpness of the dots, the dot gain is minimized, which is the inherent characteristic of digital printing plates.

By using element-based allocation tools, further improvements in quality can be achieved. It allows you to choose to use Hybrid AM screening at the right place, without forcing you to use it for your entire design.

Another new technology is HyperFlex(tm) screening, which complements Hybrid AM screening.

When the photosensitive resin plate is exposed by the amplitude modulation screening, the regularly arranged dots support each other during the formation of the printing plate, resulting in an effect that is often referred to as "bridge". However, when other alternative screening technologies such as Hybrid AM screening are used, the number of high-light area sites is reduced, thereby reducing overall support. This increases the pressure on each point and affects the reproduction of dots during development and printing.

HyperFlex screening helps the photosensitive resin to form small dots or image elements. As can be seen from the image below, the use of HyperFlex screening helps to improve the plate making process.

In Figure 3, we try to break the limitations of the platemaking process by generating 25 micron dots at 120 lppi at 1% tone. As you can see, the dots on the plate are not well formed, and there is a great risk that the printing effect will be far less than expected.

In FIG. 4, the HyperFlex screening technology is only applied to the highlight area, which helps to reduce the depth of the bumps between the dots and expands the shoulder base so that the dots can be well formed and small dots that cannot be obtained by the prior art can be obtained. Another benefit is that the surface area of ​​the dot is not changed, so the HyperFlex screening process does not cause unwanted dot gain on the printed matter.

Figure 5 below shows the application of Hybrid AM screening on a block plate. There will be a cross section. Note that in the highlight part, all the ideas are the same size, but some are isolated and unsupported. These isolated outlets cannot be well formed in print.

Figure 5: Plate surface Figure 6: Plate surface

In contrast, Figure 6 shows the same plate with HyperFlex screening. As a result, in the high-light areas, the slope is shorter, giving more support to isolated sites and achieving excellent printing results.

In short, the new digital technology continues to enhance the plate-making performance of the photosensitive resin plate. Improving Hybrid AM screening, combining Hybrid AM screening with HyperFlex screening is an example of how the use of science and technology has enabled Flexo to continue to increase its competitiveness.