In rotary screen printing, you often need to cover high-quality requests from brand owners and consumers. Geometric, micro- and halftone designs will be the most challenging to create. But what makes these designs so special?
In a printing process, several elements have to be combined: the fabric, the screen and the design. The matching of these three elements can be hard in rotary screen printing, especially with the aforementioned difficult designs, but there is another way to look at it. All of these elements reflect rasters: a repetition of small elements in a regular grid structure.
The information below is visualized in an animation. Watch it here.
Fabric, screen and design: different rasters and orientations
The first important factor to be mentioned is the fabric. A woven or knitted fabric reflects a raster made of weft and warp or stitched courses. Often they are oriented at a 90-degree angle.
The rotary screen also reflects a raster. However, this raster is different from the fabric and the design: it is hexagonal oriented and the angle between the lines of the holes is 60 degrees and not 90. It consists of three directions, in which the screen holes are lined out, as shown in Figure 1.
Fig 1. Rotary screen featuring a hexagonal raster with three directions
Difficult designs and undesired moiré
Engraving a halftone raster or micro design on a screen and printing it subsequently on fabric causes a great chance of unwanted effects. Engravers are challenged to bring the structure of screen- and design-raster to a match and the printers need to add the textile as a next element to it. These three elements — screen, design, and fabric — can interfere with each other and create undesired moiré effects.
As mentioned before, the raster of the screen has a completely different structure than those of the halftone or micro design and those of the textile substrate. It has three directions of repetition whereas the others only have two.
The figures below show examples of what this means for the design. The design consists of small blocks. Those blocks are covered differently by holes of the screen, indicated in yellow. This means that the blocks are printed in smaller and wider dimensions, depending on how the blocks are placed on the holes of the screen.
When this design is printed, the small and the wider blocks are alternating in a regular pattern. This is causing an undesired, and therefore not acceptable, moiré effect (Figure 3). This is why SPGPrints created the Ortascreens™. Simply put, there are 3 reasons why these orthogonal screens can contribute to difficult designs in your rotary screen printing process.
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- Orthogonal hole raster
- 3D surface structure
- Wider hole-diameter
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1. Orthogonal hole raster
The orthogonal screens use a special technique with an orthogonal hole raster, to make sure moiré effects don’t occur. The hole raster looks like this:
Fig 4. Hole raster of the Ortascreen™
The rasters of the design, screen and fabric are easier to match, which is why this can avoid undesired moiré effects in many cases. The same design as seen before is now printed with the new Orta 195 screen. As you can see, it is clear and free of moiré.
2. 3D-surface Structure
Additionally, the Ortascreens™ feature a three-dimensional surface on its outside. The corner points are higher than the bridges between the holes. This is caused by a higher nickel deposition at those corners.
The effect is that the paste can distribute easier on the substrate and provides a very good and even coverage. This is because the paste of adjacent holes can join by streaming over the bridges. It is also advantageous for the printing of lines and small elements. An engraved line can be covered differently by holes in the screen.
In common high mesh screens, the bridges between the holes are as high as the corner points. They are forming a barrier for the paste to flow to the edges of the engraving. The elevated corner points of the Ortascreens™ allow the paste to always flow out to the edge of the engraving. Because of this, a higher level of print definition is possible.
Fig 7. Printing a small line with a conventional screen.
Fig 8. Printing a small line with the Ortascreen™.
3. Wider hole-diameter
Lastly, the hole-diameter of these screens is wider than the comparable high mesh screens. The paste flow which is created under the same printing conditions is enhanced (10% higher) and less printing pressure is required, which causes less bleeding of paste and results in a rich and sharp print. Not only the flow of paste is enhanced. At the same time, the risk of blockage is minimized.
The following samples are showing a comparison between the Ortascreens™ and a common high mesh screen. Figure 10 shows the effect of improved line filling/printing thanks to the 3D structure.
Fig 10. The printing of lines compared between the Ortascreen™ (left) and a conventional high mesh screen (right).
When to use orthogonal screens?
In conclusion, there are a couple of advantages that this new, innovative orthogonal screen raster offers you as a printing company. However, investments like new technology and screens should only be done if they really fit your printing process. But when does this orthogonal innovation add real value to your company?
If the textiles you print contain a lot of geometric features or halftones — designs notorious for their susceptibility to moiré — it might be a good idea to use orthogonal screens to your rotary screen printing machines. Secondly, these printing results will have the best match to digital printers. Is quality of the utmost importance for your clients? This technology might be able to improve your customer’s happiness. Better runnability and flow behavior are other characteristics that might be worth considering for your printing process.
Not sure which screens are best suited for your printing process and the products you create for your clients? Our specialists are happy to help you improve your way of printing. Contact them here and learn everything there is to know about screens, rotary screen printing and more.
