Selection of Ink for Metallic Material Screen Printing

The purpose of this article is to let the reader understand what factors affect the final printing performance of a metal material on screen printing, and why it is prudent to select the ink before printing.


As a kind of decoration method favored by people at present, screen printing, in all its advantages and characteristics, the durability of screen printing ink is a key. Both solvent-based and UV-curable inks give the prints rich colors while also helping the prints to avoid damage and abrasion, discoloration, and other environmental factors during handling. The use of screen printing inks with these functions in combination with durable substrates can bring us beautiful prints.

Metal substrates, such as steel and aluminum, have high quality examples of screen printing applications such as metal signs, nameplates, instrument belts, containers, and many other products that often rely on screen printing inks for printing functional images or imprints. However, such printing is a big challenge for some screen printing manufacturers who have no experience in printing metal substrates.

If you need to print on metal materials, the pre-print preparation work must be sufficient. Understanding the natural properties of the coating on metal materials, the production tolerance of the material, and the best combination of ink and substrate, which play a decisive role in the success of printing. To effectively use these materials, printers must first understand the main attributes of these metal materials.

In addition, screen printing inks suitable for different materials and different image requirements have to be found.

Understanding metal substrates

Usually, when we talk about screen printing on metal, the metal in question is not an unprocessed metal material, most of which are coated or processed metal materials. There are about two kinds of coating on metal: thermoplastic coating and thermosetting resin coating.

The thermoplastic coating does not undergo a chemical reaction during the drying process of the substrate, and its drying is completely achieved by evaporation or heating. During the heating process, the coating material is fused with the metal. In the thermoplastic coating of metallic materials, it must be remembered that such coatings cannot resist the corrosion of high temperature and aggressive solvents, in other words, the coatings on metals encounter high temperatures or erosion in the process of screen printing. The solvent will melt again.

Thermosetting resin coatings are generally "polymerized" or "crosslinked"

Chemical reaction to achieve curing. After the coated metal is heated at a high temperature for a long period of time, the coating can be dried to withstand high temperatures and re-melting, and it also has high resistance to solvent corrosion and wear.

Resin systems that can be used as metal-coated base materials are ethylene (plastisol or solution systems), polyester or acrylic, and the like. The vinyl coating is thermoplastic. Although it is softer than the thermosetting coating and more readily attaches ink, the thermoplastic coating has poor chemical resistance and abrasion properties, making them vulnerable to most screen printing applications. limit. Therefore, screen printers prefer to use metal substrates with thermosetting coatings.

Polyester and acrylic are the most common resins in thermosetting coatings. Thermoset coatings, unlike soft thermoplastic coatings, are insoluble in screen printing inks and have a harder crosslinked protective layer that makes it difficult for ink to adhere to the coating.


When ordering coated metal materials from a supplier, it is necessary to clearly understand the type of coating (acrylic, polyester, etc.) on the metal and to confirm whether the coating material contains a smoothing agent that can cause the ink to adhere. Other surfactants. If surfactants are included, suppliers should recommend to printers cleaners that can safely remove these contaminants before printing.

Inks that meet metal screen printing requirements

Both solvent-based and UV-curable inks can be used to decorate coated metal materials, but the use of solvent-based inks is more common. Although technical advancements have allowed UV-curable inks to be used on a wide range of metallic materials, their chemical composition and cure characteristics still limit the range of applications and appear to be inferior to solvent-based inks.

Solvent-based inks for metal printing typically have 2 dry forms: one is air-dried (by evaporation) and the other is heat-cured (chemically hardened or cross-linked).

Air-dried inks are generally used for vinyl, acrylic, or lacquer-effect products. These inks do not chemically react during drying, so they are easily scratched and abraded and cannot resist the attack of solvents, gasoline, and cleaning solutions. If it is not completely dry, the ink film will appear agglomeration problems. Because metal is a relatively heavy substrate, if the phenomenon of ink agglomeration occurs on the metal, it will bring about certain problems. At present, many air-dried inks give prints good flexibility and excellent outdoor durability.

Solvent-based inks that use thermosetting drying methods usually contain some form of epoxy, enamel, polyester, or acrylic (epoxy components are very suitable for thermosetting inks that require high outdoor durability). All of these inks require long-term drying at higher temperatures. After curing, the ink film is very hard, so they are stronger than air-dried inks. They not only resist the corrosion of solvents, gasoline, and cleaning solutions, but also avoid Scratches and wear. Of course, these inks are inferior to air-dried inks in terms of flexibility, but they are suitable for hot embossing or deformation. If a suitable curing and cooling process is performed prior to stacking, prints produced with thermosetting solvent inks will not exhibit ink agglomeration.

UV curable inks for metal printing are also divided into two types: cationic and free radical (acrylate). The main chemical component of cationic UV-curable inks is epoxy resin. This ink system cures at a slower rate than conventional free radical systems. The main component of the latter is acrylic resin. If properly processed, both ink systems can provide good outdoor durability for prints. Both cationic and radical UV-curable inks are chemically reactive, producing a stiff ink film during curing that not only resists abrasion and chemical attack, but also has the same flexibility as thermoset solvent inks.

Match ink and print product performance requirements

Regardless of the type of ink chosen for metal printing, this ink should be able to meet the specific performance requirements of the print. For example, the ink film formed by the screen printing ink not only has a certain hardness, so as to resist problems such as abrasion, scratches, ink accumulation and solvent erosion, but also has enough flexibility to facilitate people to bend and mold the printed matter. Cut and press the bumps. There will not be an ink and a metal substrate that will satisfy all your production requirements. Instead, you will need to perform different coating treatments on the metal, while also matching the ink system with the different coating materials and the end use of the product. match.

For example, if the product is used indoors, it is very suitable for epoxy type inks, other resin-based heat-curing inks are also available; if the product does not need to have solvent resistance, then the use of air-drying solvent-based ink is sufficient However, if prints need both corrosion resistance and outdoor durability, air-drying and epoxy-based solvent inks are not ideal, but other traditional heat-curable or UV-curable inks can be used in this area. When selecting the type of ink, the first task is to ensure that the ink film adheres to the substrate after drying or curing, and that different types of inks are selected according to different materials.


Why is the choice of ink so important for metal printing? This is closely related to the metal coating process. If the metal coating is thermoplastic, many inks can adhere to it. However, if the coating is thermoset (most thermosetting inks are used in most screen printing), the use of any type of screen printing ink is difficult and requires strict and regular monitoring of the entire production process.
The difficulty in printing on metals with a thermosetting coating is that the hardness of these coatings is high, and the hardness of the thermosetting coating is affected by the resin system, the coating method, and the way the coating is cured. The higher the temperature of the curing process and the longer it lasts, the harder the coating surface is, and the harder the surface, the harder it is for the ink to adhere to the coating. The higher surface hardness is the reason why it is difficult for a screen printing factory to print UV-curing inks on metallic materials.

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. Since the shrinkage of the ink film is not so severe, the ink system can usually be firmly attached to a metal material having a thermosetting coating. However, cationic inks require a large amount of energy for curing, and they need to be cured or post-cured after being cured by an ultraviolet lamp, and ink agglomeration is likely to occur. When using such inks, care must be taken to fully cure them and to avoid problems with ink adhesion.

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

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