Screen printing is an important branch of all printing methods. Whether it is in large or small academic works or in various online reviews, people pay less attention to it. In order to meet the needs of different people, this original article explaining the color separation technology of screen printing was specially launched for everyone to discuss together. Find a way to combine the smoothness of traditional mesh-adjusted dots with the ability to reproduce the details of index dots.
Checking the color separation effect in screen printing is actually to check their respective ink flow. The ink passes through the screen and falls on the openings of the screen printing plate produced by the emulsion, and finally reaches the outer surface of the substrate. Controlling the flow of ink through the screen printing plate is actually using a special color separation method to generate the screen printing plate. If the job you need to print has a long horizontal line parallel to the doctor blade, then you have to see how the doctor blade impacts and suddenly stalls in those areas when the ink flow and doctor blade reach the edge of the emulsion . In this way, you will understand that you can easily solve the problem of ink flow by adjusting the image, the thickness of the screen printing plate or the number of meshes.
Controlling the ink flow of halftone screen printing plates is a relatively complicated matter. When you are considering how to use mesh tone to combine ink and image to achieve the perfect reproduction of the original, there are actually many variables. There is a very interesting phenomenon in the process of ink transfer in the mesh, that is, the shape and type of the dot can affect the ink flow in its own way. For traditional mesh adjustment, the size of the dots mainly depends on its coverage, while the center of the dots still maintains a stable and consistent dot pitch. This will make the excess ink less and less restrictive, especially when the dots are large enough, they can overlap each other, so that the area of ​​the emulsion layer between the dots becomes extremely small. (This is also one of the reasons why 70% to 90% of the layered area can be quickly filled.)
An alternative to traditional mesh tone is the so-called density mesh tone. These mesh tones are composed of dots of equal size, and people can reproduce the tone level of the image by controlling the distance between them. The most common density mesh tone is the index dot. The index dot is actually a pixel in the image resolution. If you compare the size as a standard, a 180dpi dot is equivalent to 15% of a 55 line / inch mesh tone (dot).
Index dots have many advantages in the control of ink flow. The dots of the same size are helpful for better control of ink deposition (think of a salt bottle with the same size of holes) and will also effectively avoid the expansion of dots during the printing process, because even in areas with high dot coverage The overprint rate of this type of dot is still much lower than other dots. Another advantage of index dots in screen printing is that all dots are arranged next to each other, rather than stacked on top of each other as in traditional mesh tone. The reduction of accumulated dots means that during the printing process, the lack of ink caused by the pressure at the top of the dots will also be alleviated.
The disadvantage of density meshes is that they cannot reproduce beautiful shadows or tone levels. Images using index dots look grainy and the edges of colors are not clear. Some printing houses rely heavily on this method. They use very fine index dots (more than 200dpi) to perform wet-wet printing to challenge these issues. In theory, wet ink can form a smooth surface without graininess, but it is difficult to manage the traditional mesh tone, and the ink needs to be controlled so that it does not smudge or darken. (Turbidity) to achieve the desired brightness. In order to make the density mesh tone look textured, it is necessary to use more colors to synthesize the tone hierarchy that can be formed by the traditional mesh tone. People are likely to use six or more colors to print a multi-dimensional visual effect on an index print.
A simple solution to this problem is to learn how to combine traditional mesh index and index mesh in the same set of color separation films, so that each kind of outlet can have its own place. The author found that the mixed dichroic film is very suitable for the printing of images with text and smooth tones or shadows. If the designed patterns are relatively similar, then it may not be necessary to mix color separations.
The pattern designed by the author for a local promotional company needs a combined dichroic film, because the pattern of this design is very textured, and the colors of the logo and background are very stable, and the tone level is also very clear. Making a mixed mesh adjustment plate for this pattern helps to control the flow of ink on different substrates and achieve the best post-press processing effect.
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