Halftone screen printing ink flow control (on)

Editor's note: Screen printing is an important branch of all printing methods. People are less concerned about it, whether in large or small academic works or in various online reviews. In order to meet the needs of different people, this original article explaining screen printing separation technology was specially introduced for everyone to discuss. Find a way to combine the smoothness of the traditional halftone dots with the detail reproduction capabilities of the index dots.

Looking at the separations in screen printing is actually looking at their respective ink flows. The ink passes through the screen and lands on the openings of the screen plate created by the emulsion and eventually reaches the outer surface of the substrate. The control of ink flow through screen printing plates is actually the use of special color separation methods to generate screen printing plates. If you need to print a job with a long horizontal line and parallel to the squeegee, then you have to look at how the squeegee hits and suddenly stalls in those areas when the ink flow and squeegee reach the edge of the emulsion layer. . In this way, you will understand that you can easily solve the ink flow problem by adjusting the image, the thickness of the screen plate, or the number of meshes.

Controlling the ink flow of a halftone screen plate is a complicated matter. When you think about how to use mesh to combine inks and images to achieve a perfect copy of the original, there are actually many variables. There is a very interesting phenomenon in the transfer of ink in the mesh, that is, the shape and type of dots can affect the ink flow in their own way. For a traditional halftone, the size of the dot size depends mainly on its coverage, while the dot center still maintains a stable and consistent dot spacing. This will make the excess ink less and less restrictive, especially when the dots are large enough, they can overlap with each other, so that the area of ​​the emulsion layer between the dots becomes extremely small. (This is one of the reasons why 70% to 90% of the hierarchical areas can be quickly filled.)

One alternative to traditional halftones is the so-called density mesh tone. These meshes are composed of equally sized dots, and people can reproduce the tone levels of the image by controlling the distance between them. The most common density mesh is the index network. The index dot is actually one pixel in the image resolution. If the size is used as a standard for comparison, a 180-dpi dot corresponds to 15% of a 55-line/inch halftone dot.

Indexed dots have many advantages in the control of ink flow. Equally sized dots facilitate better control of ink deposits (think salt shakers with equal-sized holes) and will also effectively avoid dot gain during printing, even in areas with high dot coverage. The overprint rate of such outlets is still far lower than other outlets. Another advantage of index dots in screen printing is that all dots are arranged side by side rather than stacked on top of each other as in traditional halftones. The reduction in the number of piled dots means that the lack of ink caused by the pressure at the top of the dots will also be alleviated during the printing process.

The disadvantage of density mesh tones is that they cannot reproduce exquisite shadows or tonal levels. Images with indexed dots appear grainy and the edges of the colors are not clear. Some printers rely heavily on this approach. They use very fine index dots (above 200 dpi) for wet-wet printing to challenge these issues. In theory, wet inks mix together to create a smooth, grain-free surface, but it is difficult to manage traditional halftones, and the ink needs to be controlled so that it does not smear or darken. In the case of turbidity, the desired brightness is achieved. To make the density mesh look textured, you need to use more colors to synthesize the tone levels that can be formed by the traditional mesh tone. People are likely to use six or more colors to print multi-dimensional visual effects on an index print.

A simple solution to this problem is to learn how to combine the traditional mesh and indexing meshes in the same set of color separations. In this way, each type of outlet can have its own place. The author finds that the mixed color separation is very suitable for the printing of images with text and smooth gradations or shadows. If the designs are relatively similar, you may not need to mix the separations.

The pattern designed by the author for a local promotional company needs a combined color separation film because the design of this design is very texture, and the color of the logo and background is very smooth, and the tone level is also very clear. Making a mixed mesh print plate for this pattern helps control the flow of ink on different substrates and achieves the best post-printing results.

Mixed halftone color separations

If you have already created your own layout (except text) in Photoshop, then you are likely to have all the major elements that are limited to each layer. But if you have an original image in your hand, you will use paths or other methods to create selective channels that effectively separate the individual elements of the design. The steps for creating a blended mesh tone are: First, you need to prepare the file, selectively divide the elements that need to perform the traditional color separation, then separate and generate indexed color separation films, and finally combine them to form a complete network. Visual image.

(to be continued)