The shrinkage characteristics of UV-curing inks, especially the diversity of free radicals, are the main reason why these inks are difficult to adhere to hard thermosetting coatings. Depending on the formulation, the UV ink layer containing free radicals may gradually shrink (sometimes more than 50%) as the crosslinking reaction of the ink progresses during curing. The ink film will cure and shrink in a matter of seconds, while the metal substrate and the coating on it will not change (as shown in Figure 1). Due to the rapid shrinkage of the UV ink, a certain pressure is applied to the adhesion point between the ink and the substrate. If the pressure is large enough, the ink film can be easily detached from the metal substrate.
In contrast, after printing on a coated metal using conventional thermosetting solvent inks, the product must be baked at high temperatures for a long time to soften the surface of the metal coating to ensure that the ink adheres better to the coating surface. . After the metal and the coating cool, the ink film also cools down. However, all the slow shrinkage that occurs in this process will not affect the adhesion of the ink.
Cationic UV inks are less likely to shrink than free radical UV inks, and cure speeds are slower. Due to shrinkage of the ink film is not very serious, so that the ink system is usually fixedly attached to the metal material having a thermoset coating. However, cationic inks requires a lot of energy to cure, and after they cure UV lamp, the need to continue to cure or post cure, the ink agglomeration easily occurs. When using this type of ink, care must be taken to be completely cured, to avoid adhesion problems of the ink.
Another issue that needs to be kept in mind is that the coating metals that are currently common on the market are produced by the coil coating company. Their initial market has nothing to do with the printing industry, and it is more of the commercial construction industry or others. Manufacturing area. Therefore, the metals provided by these companies are not suitable for screen printing. These coatings have considerable differences in chemical composition and cross-linking density, with uneven quality, which often limits the adhesion of UV inks.
In order to improve the adhesion of inks to common metals on the market, it is necessary to determine the surface hardness of the substrate before production and test its adhesion (using cross hatching and related tests). In addition to this, tensile testing can also help discover abnormalities on the coating and prevent poor ink adhesion.
The key to guaranteeing an ideal metallic printing effect is a good control of the coating process and the hardness of the coating is maintained at a certain level. Work closely with metal materials and ink suppliers to achieve the desired hardness of the coating, and continuously test the introduced materials to meet your requirements. Many free radical and cationic UV inks are now available for metal substrates. Suppliers of metal materials should also work with printers and ink manufacturers to develop a softer coating that meets printing needs. Products that often need to be printed on metal include: point-of-sale advertising, decorative signage, short-term display boards, and indoor images. In general, thermosetting solvent inks (except epoxy-based ones) printed on metallic materials usually have a durability of 3 to 5 years. If a protective coating is applied to prints, the performance will be even better. Products printed with UV-curable inks have a 2 to 3 year durability and can also extend its durability through a protective coating.
Prepare for metal printing
Although plastic occupies an absolute dominant position in today's image and signage printing market, metal substrates used for screen printing still maintain a strong momentum of development. For those screen printers who want to increase their ability to screen printing, the good news is that in addition to using solvent-based inks, there are more ink types to choose from. Due to the continuous improvement of raw materials, the range of UV-curable inks for metal printing has also been expanded unprecedentedly. They bring many benefits to the metal printing process, such as: high resolution, durability, fast processing and so on. Whether you use UV-curable inks or solvent-based inks, if you can work closely with ink and substrate suppliers to learn more about product performance and use these materials to optimize the printing process, then you will become the top metal Material printer.
In contrast, after printing on a coated metal using conventional thermosetting solvent inks, the product must be baked at high temperatures for a long time to soften the surface of the metal coating to ensure that the ink adheres better to the coating surface. . After the metal and the coating cool, the ink film also cools down. However, all the slow shrinkage that occurs in this process will not affect the adhesion of the ink.
Cationic UV inks are less likely to shrink than free radical UV inks, and cure speeds are slower. Due to shrinkage of the ink film is not very serious, so that the ink system is usually fixedly attached to the metal material having a thermoset coating. However, cationic inks requires a lot of energy to cure, and after they cure UV lamp, the need to continue to cure or post cure, the ink agglomeration easily occurs. When using this type of ink, care must be taken to be completely cured, to avoid adhesion problems of the ink.
Another issue that needs to be kept in mind is that the coating metals that are currently common on the market are produced by the coil coating company. Their initial market has nothing to do with the printing industry, and it is more of the commercial construction industry or others. Manufacturing area. Therefore, the metals provided by these companies are not suitable for screen printing. These coatings have considerable differences in chemical composition and cross-linking density, with uneven quality, which often limits the adhesion of UV inks.
In order to improve the adhesion of inks to common metals on the market, it is necessary to determine the surface hardness of the substrate before production and test its adhesion (using cross hatching and related tests). In addition to this, tensile testing can also help discover abnormalities on the coating and prevent poor ink adhesion.
The key to guaranteeing an ideal metallic printing effect is a good control of the coating process and the hardness of the coating is maintained at a certain level. Work closely with metal materials and ink suppliers to achieve the desired hardness of the coating, and continuously test the introduced materials to meet your requirements. Many free radical and cationic UV inks are now available for metal substrates. Suppliers of metal materials should also work with printers and ink manufacturers to develop a softer coating that meets printing needs. Products that often need to be printed on metal include: point-of-sale advertising, decorative signage, short-term display boards, and indoor images. In general, thermosetting solvent inks (except epoxy-based ones) printed on metallic materials usually have a durability of 3 to 5 years. If a protective coating is applied to prints, the performance will be even better. Products printed with UV-curable inks have a 2 to 3 year durability and can also extend its durability through a protective coating.
Prepare for metal printing
Although plastic occupies an absolute dominant position in today's image and signage printing market, metal substrates used for screen printing still maintain a strong momentum of development. For those screen printers who want to increase their ability to screen printing, the good news is that in addition to using solvent-based inks, there are more ink types to choose from. Due to the continuous improvement of raw materials, the range of UV-curable inks for metal printing has also been expanded unprecedentedly. They bring many benefits to the metal printing process, such as: high resolution, durability, fast processing and so on. Whether you use UV-curable inks or solvent-based inks, if you can work closely with ink and substrate suppliers to learn more about product performance and use these materials to optimize the printing process, then you will become the top metal Material printer.
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