Nowadays, there are many types of printing machines, each with its own advantages and markets. Letterpress printing was the main product of printing until the 1940s, and is now rarely seen. The following are the main ink types used in printing machines today:
Intaglio (adhesive) ink
Intaglio inks are replaced by offset inks. Although intaglio inks are printed on sheet fed machines, offset machines can print large quantities of pages by means of web to web or sheet fed printing machines. The three main types of offset inks are sheet fed, heat-curing and cold-curing inks. Inks are usually oil-based and dry after printing. However, there is a growing emphasis on the use of renewable resources such as soy-based products.
Until the 1910s, lithography had been the dominant printing process for about seventy years. They are the ideal choice for publications; the most common (or news ink) is the ink of choice for newspapers, phone books, etc. They are made up of carbon black and a binder, unless colored pigments are required.
Magazines are usually printed on heat-curing presses (or web offset printing). These are sheet-to-sheet presses that can run at speeds of 2,500 feet per minute. Similarly, the composition of heat-curing inks is similar to that of cold-curing inks.
However, with the widespread use of the Internet, the newspaper and magazine markets were affected. The sales of news and heat-set inks were affected accordingly.
This brings us to sheet fed inks. Sheet fed inks appeared in magazines and annual reports and have been in decline in recent years. However, since the paper is fed into the printing press, they can also be on a thicker substrate, allowing for the production of folding cartons. These printing presses can now run up to 20,000 sheets per hour.
Packaging has proven to be a growing market for sheet fed printers. Sheet fed ink is typically UV cured. According to a recent study by Smithers, as technology redefines the industry, flexo is facing disruption.
Packaging with liquid ink
Liquid inks, mainly flexographic and intaglio inks, are the dominant technology in packaging, with flexography being the dominant process. Flexographic and intaglio presses are web-to-web printing machines. According to the substrate and application, inks cover all areas of water-based, solvent-based and UV technology.
For example, because solvent-based inks dry by removing the solvent, they typically appear on plastic substrates and more often on flexible packaging. In contrast, water-based inks are the ink of choice for corrugated because they can dry to become corrugated board or containerboard. Digital is making inroads in these markets, but we will talk about that soon.
As for the composition of liquid ink, the main difference between the ink paste and liquid ink is the type of resin and additives. Ink paste uses hydrocarbon resin, while liquid ink will use acrylic, nitrocellulose, polyamide and other types of resin.
Digital ink
Digital printing is the fastest growing sector of printing. It has captured the market previously dominated by screen (billboards, tiles) and offset (direct mail). It is also growing in markets such as textiles and folding cartons. Digital ink has also expanded into the corrugated printing market.
The key to the development of digital printing is technological advantage; only on digital printing machines can small quantities of products be produced in a cost-effective manner, whether it is personalized mail, prototypes or custom projects, or regional or targeted activities. There are hybrid printing machines that combine digital technology with flexography or sheetfed, allowing printers to personalize projects or add unique tracking codes.
In terms of the composition of digital ink, a variety of dyes and pigments can be used. Dyes were originally used in most applications, but pigments have become more common than before because of their light fastness. The key is that the pigments must be properly dispersed, as the viscosity required to spray 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 in inkjet inks.
Energy-curable ink
In the last twenty years, significant progress has been made in energy-curable inks for packaging and digital printing. These are broken down into ultraviolet (UV), electronic beam (EB), and more recently ultraviolet LED, which is rapidly growing in use as it does not require the mercury-based lamps used in traditional UV.
The advantages of energy-curable systems are apparent during the curing process. When exposed to UV, UV LED, or EB light, the ink will immediately solidify. This can reduce footprint, as there is no need for ovens to heat the ink, solvent capture equipment, or large spaces for stock to dry. UV inks can often be more expensive than water-based or solvent-based inks. Since there are no solvents or volatile organic compounds (VOCs), UV and EB are considered to be more environmentally friendly technologies.
The binders used in energy-curing inks are different from those in traditional inks. For UV and UV LED, the photoinitiator is crucial for crosslinking the ink with the substrate. EB uses acrylic monomers for curing.
Conductive ink
Conductive ink has grown into a significant niche for ink suppliers. Traditional photovoltaics is the largest market for conductive ink, as the背板 is screen printed. Sensors is a growing area.
Screen printing is the main process, followed by inkjet. It depends on the application. For example, screen printing allows the manufacturer to apply a thick layer of conductive ink or paste, which improves conductivity. In contrast, if the printer's idea is to use a small amount of ink in the target area (e.g. a conductive trace), then the printer may use inkjet.
The most interesting difference in composition is the type of conductive material used in these inks and pastes. So far, silver has been the most common because it conducts electricity very well. In terms of cost, copper(II) oxide would be ideal, but the problem is that the copper quickly oxidizes. Carbon-based inks are making progress in this area.