According Wikipedia, the oldest known surviving document dates back to the 26th century BC, as the ancient Egyptians used their form of ink on papyrus. With Gutenberg’s invention of what would become a printing press, a new type of ink was needed. In Gutenberg’s case, it was a combination of lampblack and varnish.
Today, there are many types of printing presses, all of which have their own advantages and markets. Letterpress, which was a staple of printing until the 1940s, is very rarely seen today. As such, there are also several types of inks.
Here are the main types of inks used by printers today:
Offset inks (paste)
Letterpress inks have been phased out by offset inks. While a letterpress ink was printed in individual sheets, offset presses could produce pages either by roll-to-roll or sheet-fed presses. The three main types of offset inks are sheet-fed, heatset, and freeze-set inks. The inks are usually oil-based and are dried after printing. However, there is a growing emphasis on using renewable resources such as soy products.
Offset printing became the dominant printing process for about seven decades, until the 2010s. They were ideal for publications; cooler inks (or news inks) are the main inks for newspapers, telephone directories, etc. They consist of carbon black and binders, except where color pigments are required.
Magazines would typically be on heatset presses (or publication burning, which will be discussed later). They are roll-to-roll presses, capable of operating up to 2,500 feet per minute. Again, the composition of heatset inks is similar to that of coldset inks.
However, newspaper and magazine markets have suffered from the widespread use of the Internet. Sales of new and heatset inks suffered accordingly.
This brings us to leaf inks. Leaf inks are found in magazines and annual reports, which have declined in recent years. However, as the sheets are fed into the press, they can also be thicker substrates, allowing the production of folding boxes. These presses now run up to 20,000 sheets per hour.
Packaging has proven to be a growth market for sheetfed printers. Sheetfed inks are often UV cured. According to a recent study by Smithers, offset printing is facing change as technology redefines the industry.
Liquid inks for packaging
Liquid inks, mainly flexo and gravure inks, are the dominant technology for packaging, with flexo being the main process. Both flexo and gravure presses are roll-to-roll presses. Inks cover the full range of water-based, solvent-based and UV-based technologies, depending on the substrate and application.
For example, since solvent-based inks are dried to remove the solvent, they are usually found on plastic substrates, and appear more often on flexible packaging. Water-based inks, on the other hand, are the main inks for corrugated board because they can dry in corrugated or kraft boards. Digital is advancing in these markets, but we’ll get to that shortly.
As for the composition of liquid inks, the main difference between paste inks and liquid inks is the type of resin as well as the additives. Paste inks use hydrocarbon resins, while liquid inks will use acrylic, nitrocellulose, polyamide, and other types of resins.
Digital printing is the fastest growing area of printing. It has conquered markets that were previously dominated by screen (billboards, ceramic tiles) and offset (direct mail). It is also developing in markets such as textiles and folding cardboard. Digital inks have also developed in the corrugated printing market.
The key to the growth of digital printing lies in the advantages of technology; the ability to profitably produce short runs, whether personalized mailings, prototypes or personalized items, or regional or targeted campaigns, can only be achieved on digital presses. There are hybrid presses that combine digital technology with flexo or sheet feed, allowing the printer to personalize items or add unique track and trace codes.
In terms of composition of digital inks, there is a range of colorants that can be used. Dyes were initially used for most applications, but pigments have become much more common than before due to their lightfastness. The key is that the pigments must be properly dispersed, as the viscosity needed to eject the ink without clogging the print head is crucial. For this reason, traditional resins are not commonly used. In terms of traditional additives, surfactants, defoamers and rheology modifiers are commonly used for inkjet inks.
Energy drying inks
Over the past two decades, energy curing inks have made tremendous inroads into packaging as well as digital printing. These are broken down into ultraviolet (UV), electron beam (EB) and, more recently, UV LED, the use of which is growing rapidly because it does not require the mercury-based lamps used in traditional UV.
The benefits of energy hardening are found in the hardening process. When exposed to UV, UV LED or EB light, the inks dry instantly. This allows for a smaller footprint, as there is no need for ovens to heat up inks, solvent capture equipment, or huge spaces to allow inventory to dry. UV inks tend to be more expensive than water-based or solvent-based inks. Because there are no solvents or volatile organic compounds (VOCs), UV and EB are considered more environmentally friendly technologies.
The binders used in energy curing inks are different from conventional inks. In the case of UV and UV LED, photoinitiators are essential to cross-link the inks to the substrate. EB uses acrylic monomers for its hardening.
Conductive inks have become an important niche market for ink suppliers. Traditional photovoltaics is the biggest market for conductive inks because the backplane is screen printed. Sensors are a booming field.
Screen printing is the main process, followed by inkjet. It depends on the application. For example, screen printing allows the manufacturer to deposit a thick layer of conductive ink or paste, which improves conductivity. In contrast, a printer can use inkjet if the idea is to use small amounts of ink in targeted areas, such as conductive traces.
The most interesting compositional difference is the type of conductive material used for these inks and pastes. Silver is by far the most common, as its conductivity is excellent. In terms of cost, copper oxide would be ideal, but the downside is that copper oxidizes quickly. Carbon-based inks are making progress in this area.