07.03.2016
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In order to achieve a good printing result, it is important to pay particular attention to the most important influencing factors in rotary screen printing. The decisive influencing factors are the screen type, the ink, the squeegee, and the travel distance. These factors and their influence on screen printing will be discussed in this article. The travel distance is a variable that the printer can influence by adjusting the machine speed, the length of the travel distance, and the rheology of the screen printing ink.
-2.jpg)
The optimal flow of the printing ink is crucial in screen printing, as screen printing is still the printing process that achieves by far the highest ink layer thicknesses. The more ink there is on the substrate, the more important it is that the ink flow corresponds optimally to the desired print image. Otherwise, any discrepancies can be detected visually by the end user and impair the quality of the overprint with other printing processes. In label printing, the term "flow time" refers to the time required for the ink to flow on the self-adhesive material before it is cured by drying.
The printing press manufacturer refers to the "travel distance" because the length of the distance (from the printing unit to the dryer) can be designed and modified in terms of mechanical engineering. The label printer himself probably refers to the flow time, because the printing ink has too little or too much time to flow before drying. Regardless of which perspective you choose, flow distance or flow time, the printing ink should ultimately have an optimal color flow in accordance with the print image. A distinction is made here as follows:
-2.jpg)
-2.jpg)
The machine speed and the length of the travel distance are two parameters that are directly related to each other and simultaneously influence the flow behavior of the screen printing ink. As a rule, the printer changes the machine speed, but the travel distance is specified by the machine design.
At high machine speeds, the ink hardly has time to run – drying ensures that a sharp ink edge remains. At low machine speeds, however, the ink has the necessary time to run – the ink edge is flat when it dries. This physical property is the main difference between screen printing and other printing processes such as flexo or offset printing, which allow for higher printing speeds.
-2.jpg)
-2.jpg)
With a short run length, the printing ink hardly has time to run – drying causes a color edge to remain. In contrast, with a long run length, the ink has the necessary time to run – the color edge is flat when dry.
The printer now has the option of influencing the ink's flow behavior using the following variables: machine speed, length of the flow path, doctor blade position and hardness (see Gallus In Touch 32), and the rheological properties of the printing ink.
With the "machine speed" setting, the printer simply runs the machine faster or slower. This gives the ink more or less time to spread.
To change the "Travel distance" parameter, the web path must be changed. The distance between the printing unit and the dryer must be increased or decreased, causing the printed web to travel a different distance and take more or less time to reach the dryer.
The rheological properties of screen printing ink can be modified using either an ink thinner or a flow agent. It is important to note that these additives must be used in moderation. If too many additives are added to the printing ink, the color tone may change, the ink may smear, or printing failures may occur in combination printing. Leveling agents can also cause problems with overprinting or foil embossing. For this reason, thinners should be used primarily.
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Silicone-free inks separate from the substrate if the flow distance is too long, which can lead to irregular crater formation. This is because silicones reduce the surface tension in the printing ink. If a printing ink is silicone-free, it has a higher surface tension. However, if this is higher than the surface tension of the substrate, the ink will "bead" off the substrate unless it dries quickly enough. The beaded ink leads to irregular cratering. To remedy this printing problem, either the machine speed must be increased or the run length must be shortened.
If the travel distance is too short, regular pinholes may appear across the entire surface when using silicone-based inks. The ink is pressed through the mesh openings of the screen, but the ink droplets do not run quickly enough before drying. This means that the areas of the print image where the mesh is physically in contact remain without ink. To remedy this printing problem, either reduce the machine speed, increase the travel distance, or dilute the printing ink with a flow agent or thinner.
Thanks to its many years of experience in screen and combination printing, Gallus is the right partner to contact if you have any questions about the run length. The service and support team at Gallus Rotascreen will be happy to advise customers on the subject of run length.
07.03.2016
In order to achieve a good printing result, it is important to pay particular attention to the most important influencing factors in rotary screen printing. The decisive influencing factors are the screen type, the ink, the squeegee, and the travel distance. These factors and their influence on screen printing will be discussed in this article. The travel distance is a variable that the printer can influence by adjusting the machine speed, the length of the travel distance, and the rheology of the screen printing ink.
The optimal flow of the printing ink is crucial in screen printing, as screen printing is still the printing process that achieves by far the highest ink layer thicknesses. The more ink there is on the substrate, the more important it is that the ink flow corresponds optimally to the desired print image. Otherwise, any discrepancies can be detected visually by the end user and impair the quality of the overprint with other printing processes. In label printing, the term "flow time" refers to the time required for the ink to flow on the self-adhesive material before it is cured by drying.
The printing press manufacturer refers to the "travel distance" because the length of the distance (from the printing unit to the dryer) can be designed and modified in terms of mechanical engineering. The label printer himself probably refers to the flow time, because the printing ink has too little or too much time to flow before drying. Regardless of which perspective you choose, flow distance or flow time, the printing ink should ultimately have an optimal color flow in accordance with the print image. A distinction is made here as follows:
The machine speed and the length of the travel distance are two parameters that are directly related to each other and simultaneously influence the flow behavior of the screen printing ink. As a rule, the printer changes the machine speed, but the travel distance is specified by the machine design.
At high machine speeds, the ink hardly has time to run – drying ensures that a sharp ink edge remains. At low machine speeds, however, the ink has the necessary time to run – the ink edge is flat when it dries. This physical property is the main difference between screen printing and other printing processes such as flexo or offset printing, which allow for higher printing speeds.
With a short run length, the printing ink hardly has time to run – drying causes a color edge to remain. In contrast, with a long run length, the ink has the necessary time to run – the color edge is flat when dry.
The printer now has the option of influencing the ink's flow behavior using the following variables: machine speed, length of the flow path, doctor blade position and hardness (see Gallus In Touch 32), and the rheological properties of the printing ink.
With the "machine speed" setting, the printer simply runs the machine faster or slower. This gives the ink more or less time to spread.
To change the "Travel distance" parameter, the web path must be changed. The distance between the printing unit and the dryer must be increased or decreased, causing the printed web to travel a different distance and take more or less time to reach the dryer.
The rheological properties of screen printing ink can be modified using either an ink thinner or a flow agent. It is important to note that these additives must be used in moderation. If too many additives are added to the printing ink, the color tone may change, the ink may smear, or printing failures may occur in combination printing. Leveling agents can also cause problems with overprinting or foil embossing. For this reason, thinners should be used primarily.
Silicone-free inks separate from the substrate if the flow distance is too long, which can lead to irregular crater formation. This is because silicones reduce the surface tension in the printing ink. If a printing ink is silicone-free, it has a higher surface tension. However, if this is higher than the surface tension of the substrate, the ink will "bead" off the substrate unless it dries quickly enough. The beaded ink leads to irregular cratering. To remedy this printing problem, either the machine speed must be increased or the run length must be shortened.
If the travel distance is too short, regular pinholes may appear across the entire surface when using silicone-based inks. The ink is pressed through the mesh openings of the screen, but the ink droplets do not run quickly enough before drying. This means that the areas of the print image where the mesh is physically in contact remain without ink. To remedy this printing problem, either reduce the machine speed, increase the travel distance, or dilute the printing ink with a flow agent or thinner.
Thanks to its many years of experience in screen and combination printing, Gallus is the right partner to contact if you have any questions about the run length. The service and support team at Gallus Rotascreen will be happy to advise customers on the subject of run length.