07.03.2016
To achieve a good print result, it is important to pay particular attention to the most important factors influencing rotary screen printing. The decisive factors are the screen type, the ink, the squeegee, and the travel distance. Today's article will focus on ink and its influence on screen printing. The ink is a variable factor that the printer can influence to a certain extent by adding additives.
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UV screen printing ink consists of approx. 17% pigments, 28% monomers, 45% oligomers, 8% photoinitiators, and 2% additives. The pigments are mainly responsible for the color, the monomers for the rheology (flow behavior, fluidity, and viscosity) of the ink, the oligomers for binding the color pigments, the photoinitiators activate the polymerization, and the additives give the ink its stability. The formulation and composition of these individual color components vary between color suppliers and are the proprietary knowledge of the respective manufacturer.
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The subject of color is extremely complex, as individual color components influence not just one but usually several properties of the color. Pigments, which are responsible for the color of a paint, are characterized not only by their color, but also by their transparency and their resistance properties, such as lightfastness, chemical resistance, and heat resistance. In UV-curing paints, they therefore influence the ability of UV rays to penetrate the paint film and thus the drying process itself. Pigments also play a role in the storage stability of paints and their rheology.
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The printer itself has the ability to influence the color with various additives. Thinners, flow agents, defoamers, antistatic agents, and hardeners are the most common additives used by printers. They are added to the ink to change its properties. This allows the printer to change the rheological properties and, to a certain extent, the drying properties of the ink. The other ink properties can only be influenced to a limited extent.
Practical experience shows that color problems in the print shop often have nothing to do with the ink itself, but rather with how it is handled. For example, even the smallest residues of silicone-containing UV ink in the ink fountain will inevitably lead to rejection when silicone-free UV ink is filled into the same ink fountain. If this is the case, there is often no other option than to empty the entire ink fountain and clean it thoroughly. The same problem can occur in the print image if the first ink contains silicone and the second ink does not. In this case, it is necessary to match the first and second printing inks. It therefore makes sense to have one or more specialists in the company who have been intensively trained in the proper handling of printing inks and can pass on this knowledge internally.
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Needle holes appear across the entire surface if the ink is not liquid enough. After the ink has been pressed through the mesh openings of the screen, the ink droplets cannot spread quickly enough before drying. This leaves areas of the print image without ink where the mesh fabric is physically in contact with the substrate. To remedy this printing problem, the ink must be liquefied with a flow agent or thinner.
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If a missing color spot appears in combination printing, the second printing ink does not completely cover the first. One possible cause for this is that the first printing ink has too high a layer thickness. In this case, it is recommended to reduce the ink application of the first color if possible, or to add a thinner to the second color.
Thanks to its many years of experience in screen and combination printing, Gallus is also the right partner for questions about screen printing inks. The Gallus Rotascreen service and support team will be happy to advise customers on this topic.
07.03.2016
To achieve a good print result, it is important to pay particular attention to the most important factors influencing rotary screen printing. The decisive factors are the screen type, the ink, the squeegee, and the travel distance. Today's article will focus on ink and its influence on screen printing. The ink is a variable factor that the printer can influence to a certain extent by adding additives.
UV screen printing ink consists of approx. 17% pigments, 28% monomers, 45% oligomers, 8% photoinitiators, and 2% additives. The pigments are mainly responsible for the color, the monomers for the rheology (flow behavior, fluidity, and viscosity) of the ink, the oligomers for binding the color pigments, the photoinitiators activate the polymerization, and the additives give the ink its stability. The formulation and composition of these individual color components vary between color suppliers and are the proprietary knowledge of the respective manufacturer.
The subject of color is extremely complex, as individual color components influence not just one but usually several properties of the color. Pigments, which are responsible for the color of a paint, are characterized not only by their color, but also by their transparency and their resistance properties, such as lightfastness, chemical resistance, and heat resistance. In UV-curing paints, they therefore influence the ability of UV rays to penetrate the paint film and thus the drying process itself. Pigments also play a role in the storage stability of paints and their rheology.
The printer itself has the ability to influence the color with various additives. Thinners, flow agents, defoamers, antistatic agents, and hardeners are the most common additives used by printers. They are added to the ink to change its properties. This allows the printer to change the rheological properties and, to a certain extent, the drying properties of the ink. The other ink properties can only be influenced to a limited extent.
Practical experience shows that color problems in the print shop often have nothing to do with the ink itself, but rather with how it is handled. For example, even the smallest residues of silicone-containing UV ink in the ink fountain will inevitably lead to rejection when silicone-free UV ink is filled into the same ink fountain. If this is the case, there is often no other option than to empty the entire ink fountain and clean it thoroughly. The same problem can occur in the print image if the first ink contains silicone and the second ink does not. In this case, it is necessary to match the first and second printing inks. It therefore makes sense to have one or more specialists in the company who have been intensively trained in the proper handling of printing inks and can pass on this knowledge internally.
Needle holes appear across the entire surface if the ink is not liquid enough. After the ink has been pressed through the mesh openings of the screen, the ink droplets cannot spread quickly enough before drying. This leaves areas of the print image without ink where the mesh fabric is physically in contact with the substrate. To remedy this printing problem, the ink must be liquefied with a flow agent or thinner.
If a missing color spot appears in combination printing, the second printing ink does not completely cover the first. One possible cause for this is that the first printing ink has too high a layer thickness. In this case, it is recommended to reduce the ink application of the first color if possible, or to add a thinner to the second color.
Thanks to its many years of experience in screen and combination printing, Gallus is also the right partner for questions about screen printing inks. The Gallus Rotascreen service and support team will be happy to advise customers on this topic.