This article addresses the topic of silkscreen inks – inks used in screen printing and their relationship with the surface to be printed, taking into account other variables such as ambient temperature and air humidity. This is an important theme for any printing or painting technique, the correct choice of ink largely interferes with a good result, both in the final product and in its durability.

Silkscreen Ink And Substrate

Substrate is the technical term that refers to the surface that is intended to be printed on, be it paper, plastic, fabric, glass, wood, tile, etc.

To ensure good ink adhesion and avoid clogging the screen holes, the substrates must be very clean and dry when printing. The chemical characteristics (composition) and physical (shape and roughness) of the substrate, as well as the ambient temperature and humidity, define the type of ink to be used and any necessary prior procedures.

For example, in the case of printing on glass, if the air humidity is high, the glass may have to be heated before printing; or for polypropylene or polyethylene substrates, it is natural to have to mix a specific additive into the ink or to opt for a pretreatment based on high-frequency discharges that optimize the surface properties so that it becomes more adherent.

Regarding inks, they can be divided into three main groups, according to the drying mode:

1. Evaporation and oxidation (water-based and solvent-based, or mixed inks)
2. Thermosetting (plastisol inks)
3. UV hardening (Ultra Violet curing inks)

⓵ The first group of silkscreen ink refers to paints that dry in air, either through evaporation or oxidation (reaction to oxygen). Exclusively water-based paints are considered the most environmentally friendly – they do not emit volatile organic compounds into the atmosphere – so there has been special interest in their development, but unfortunately the range of substrates covered by these paints is still limited, making solvent-based inks, such as multipurpose, acrylic, vinyl and enamel inks, the best choice for most substrates (metal, certain plastics, wood, glass, cardboard, aluminum, vinyl, etc.), despite their pollutants.

Water-based inks dry more slowly (about 1 hour) and are used mainly on paper and cardboard, extendable to some textiles and some plastics. Acrylic and vinyl inks dry faster (15 to 30 minutes) than enamel inks (4 to 6 hours), but remain vulnerable to solvents after drying, unlike enamel paints. Either of these inks has the disadvantage of drying out during printing in hot and dry environments, necessitating the use of a retarder to avoid the situation.

⓶ The second group of silkscreen ink includes plastisol inks (based on PVC and liquid plasticizer additive), those that do not air dry, remaining moist as long as they are not subjected to heat – almost exclusively used in textile printing. For this type of ink, the term drying does not apply, but rather the term curing or polymerization (union of identical molecules) of the resin contained.

Epoxy inks (compound formed from an epoxide – oxygen and carbon) can be considered in this group. This type of ink cures via chemical reaction between the base and a separately added catalyst, but the use of heat is also common on various substrates as a way to make the print more resistant and durable – commonly used in printing glass, metal, ceramics and some plastics. Plastisol inks can cure in 2 to 4 minutes, while epoxy inks can take 4 to 7 days to fully cure.

⓷ The third group of silkscreen ink involves curing paint by exposure to a light source that is strongly rich in ultra violet rays. This is a highly environmentally friendly ink – 0% volatile content and 100% pigment – it cures very quickly and has the advantage of not hardening during printing, similar to plastisol ink. Applicable to all substrates, it is considered by many professionals to be the great trend of the future. However, the cost of its application is still quite high, since it requires expensive equipment that is only viable in the industrial environment.

The heat method can also be applied to solvent-based paints with the aim of accelerating drying time. Heat application is usually done through an industrial oven or heat press for some textiles, but an iron, hair dryer, or kitchen oven can be used for home screen printing, depending on the substrate.

For simple practical examples for beginners the Speedball type aqueous ink is usually taken as a reference on silkscreen ink; ecological, water-based, easy to dilute and clean, with no additives needed in mild environments, or special procedures; ideal for paper, cardboard and cardstock. Multipurpose inks or aqueous acrylic textile inks are also a good starting option, more versatile on substrates and easy to dilute and clean.

The following set of tables presents a summary of characteristics of some of the most popular types of paints and brands on the market, among water-based, solvent-based and plastisol options, by way of comparison and illustration of the concepts presented so far. Besides the paints presented, there are countless variants, among colors and special finishes, such as glitter, fluorescent, textured, and metallic, among others.

 

Silkscreen Ink and Substrates

---

Find references and more knowledge in Learning Links