The history of ink goes way back, with the earliest known surviving document dating back to the 26th century BC, according to Wikipedia.

　　Today, there are many types of printing presses, each with its own advantages and markets. Letterpress printing was a printing staple until the 1940s and is rarely seen today. The following are the main ink types used in today’s printing presses:

　　Offset (paste) ink

　　Letterpress inks were eliminated by offset inks. While letterpress inks are printed from sheets, offset presses can print pages in large quantities via roll-to-roll or sheet-fed presses. The three main types of offset inks are sheet-fed, thermoset, and coldset inks. The ink is usually oil-based and dries after printing. However, there is an increasing emphasis on the use of renewable resources, such as soy products.

　　Offset printing was the dominant printing process for about seventy years until the 2010s. They are ideal for publications; Coolest (or news ink) is the primary ink for newspapers, phone books, etc. They consist of carbon black and a binder unless colored pigments are required.

　　Magazines can usually be printed on a heatset press (or publication gravure). These are roll-to-roll presses capable of operating at speeds of 2,500 feet per minute. Likewise, thermoset inks are similar in composition to coldset inks.

　　However, with the widespread use of the Internet, the newspaper and magazine market has been affected. News and thermoset ink sales were affected accordingly.

　　Which brings us to sheet-fed inks. Sheetfed ink appears in magazines and annual reports and has declined in recent years. However, as the sheets are fed into the printing press, they can also be thicker substrates, allowing the production of folding cartons. The presses can now run up to 20,000 sheets per hour.

　　Packaging has proven to be a growing market for sheet-fed printers. Sheetfed inks are usually UV cured. Offset printing is facing change as technology redefines the industry, according to a recent study by Smithers.

　　Liquid ink for packaging

　　Liquid inks, mainly flexo and gravure inks, are the dominant technology for packaging, with flexo being the dominant process. Flexo and gravure printing machines are roll-to-roll printing machines. Depending on the substrate and application, inks cover the entire spectrum of water-based, solvent-based and UV technologies.

　　For example, because solvent-based inks are dried to remove the solvent, they are often found on plastic substrates and more often on flexible packaging. In contrast, water-based inks are the primary inks for corrugated paper because they can dry into corrugated board or kraft paper. Digitalization is making progress in these markets, but we’ll get to that shortly.

　　As for the composition of liquid ink, the main difference between paste ink and liquid ink is the type of resin and additives. Paste inks use hydrocarbon resins, while liquid inks will use acrylic, nitrocellulose, polyamide, and other types of resins.

　　digital ink

　　Digital printing is the fastest growing area in printing. It has captured markets previously dominated by screens (billboards, tiles) and offset printing (direct mail). It is also growing in markets such as textiles and folding cartons. Digital ink has also expanded into the corrugated printing market.

　　Key to the development of digital printing is technological advantage; only on digital presses can small batches be produced cost-effectively, whether it is personalized mailings, prototypes or custom projects, or regional or targeted events. There are hybrid presses that combine digital technology with flexo or sheetfed printing, allowing printers to personalize projects or add unique tracking codes.

　　When it comes to the composition of digital ink, a variety of colorants can be used. Dyes were originally used for most applications, but due to their lightfastness, pigments have become more common than before. The key is that the pigments must be properly dispersed, as the viscosity required to eject the ink without clogging the print head is critical. For this reason, traditional resins are not commonly used. In terms of traditional additives, surfactants, defoaming agents and rheology modifiers are commonly used in inkjet inks.

　　Energy curable ink

　　Over the past two decades, energy-curable inks have made considerable progress in packaging and digital printing. These are broken down into ultraviolet (UV), electron beam (EB) and most recently UV LED, the use of which is growing rapidly as it does not require the mercury-based lamps used in traditional UV.

　　The advantages of energy curing are reflected in the curing process. The ink cures instantly when exposed to UV, UV LED or EB light. This reduces the floor space as there is no need for an oven to heat the ink, solvent capture equipment or a huge space for the 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 binder used in energy-curable inks is different from traditional inks. For UV and UV LEDs, photoinitiators are essential to cross-link the ink to the substrate. EB is cured using acrylic monomer.

　　Conductive ink

　　Conductive inks have grown into a sizable niche market for ink suppliers. Traditional photovoltaics is the largest market for conductive inks because the backsheet is screen printed. Sensors are an evolving field.

　　Screen printing is the main process, followed by inkjet. It depends on the application. For example, screen printing allows manufacturers to apply a thick layer of conductive ink or paste, thereby increasing conductivity. In contrast, a printer might use inkjet if the idea is to use a small amount of ink on a targeted area, such as a conductive trace.

　　The most interesting difference in composition is the type of conductive material used in these inks and pastes. Silver is by far the most common because it conducts electricity very well. In terms of cost, copper oxide would be ideal, but the disadvantage is that copper oxidizes very quickly. Carbon-based inks are making progress in this area.