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Inkjet printing is a type of computer printing that recreates a digital image by propelling droplets of ink onto paper or plastic substrates. Inkjet printers were the most commonly used type of printer in 2008, and range from small inexpensive consumer models to expensive professional machines. By 2019, laser printing outsold inkjet printers by nearly a 2:1 ratio, 9.6% vs 5.1% of all computer peripherals.
The concept of inkjet printing originated in the 20th century, and the technology was first extensively developed in the early 1950s. While working at Canon in Japan, Ichiro Endo suggested the idea for a "bubble jet" printer, while around the same time Jon Vaught at Hewlett-Packard (HP) was developing a similar idea. In the late 1970s, inkjet printers that could Digital printing generated by computers were developed, mainly by Epson, HP and Canon. In the worldwide consumer market, four manufacturers account for the majority of inkjet printer sales: Canon, HP, Epson and Brother.
In 1982, Robert Howard came up with the idea to produce a small color printing system that used piezos to spit drops of ink. He formed the company, R.H. (Robert Howard) Research (named Howtek, Inc. in Feb 1984), and developed the revolutionary technology that led to the Pixelmaster color printer with solid ink using Thermojet technology. This technology consists of a tubular single nozzle acoustical wave drop generator invented originally by Steven Zoltan in 1972 with a glass nozzle and improved by the Howtek inkjet engineer in 1984 with a Tefzel molded nozzle to remove unwanted fluid frequencies.
The emerging ink jet material deposition market also uses inkjet technologies, typically printheads using piezoelectric crystals, to deposit materials directly on substrates.
The technology has been extended and the 'ink' can now also comprise solder paste in PCB assembly, or living cells, for creating biosensors and for tissue engineering.
Images produced on inkjet printers are sometimes sold under such as Digigraph, Iris printer, giclée, and Cromalin. Inkjet-printed fine art reproductions are commonly sold under such trade names to imply a higher-quality product and avoid association with everyday printing.
In CIJ technology, a high-pressure pump directs liquid ink from a reservoir through a gunbody and a microscopic nozzle (usually .003 inch diameter), creating a continuous stream of ink droplets via the Plateau-Rayleigh instability. A piezoelectric crystal may be used to create an acoustic wave as it vibrates within the gunbody and causes the stream of liquid to break into droplets at regular intervals: 64,000 to 165,000 irregular-sized ink droplets per second may be achieved. The ink droplets are subjected to an electrostatic field created by a charging electrode or by a magnetic flux field as they form; the field varies according to the degree of drop deflection desired. This results in a controlled deflection by electrostatic charge on each droplet. Charged droplets may be separated by one or more uncharged "guard droplets" to minimize electrostatic repulsion between neighboring droplets.
The droplets pass through another electrostatic or magnetic field and are directed (deflected) by electrostatic deflection plates or flux field to print on the receptor material (substrate), or allowed to continue on deflected to a collection gutter for re-use. The more highly charged droplets are deflected to a greater degree. Only a small fraction of the droplets is used to print, the majority being recycled.
CIJ is one of the oldest (1951) ink jet technologies in use and is fairly mature. Drop-on-demand was not invented until later. The major advantages of CIJ are the very high velocity (≈20 m/s) of the ink droplets, which allows for a relatively long distance between print head and substrate, and the very high drop ejection frequency, allowing for very high speed printing. Another advantage is freedom from nozzle clogging as the jet is always in use, therefore allowing volatile solvents such as ketones and alcohols to be employed, giving the ink the ability to "bite" into the substrate and dry quickly. The ink system requires active solvent regulation to counter solvent evaporation during the time of flight (time between nozzle ejection and gutter recycling), and from the venting process whereby air that is drawn into the gutter along with the unused drops is vented from the reservoir. Viscosity is monitored and a solvent (or solvent blend) is added to counteract solvent loss.
In the later 1950s, heated wax inks became popular with CIJ technologies. In 1971, Johannes F. Gottwald patent US3596285A, Liquid Metal Recorder used molten metal ink with a magnetic flux field to fabricate formed symbols for signage. This may have been the first 3D metal object printed using magnetic core memory as data to produce each symbol.
The basic problem with inkjet inks is the conflicting requirements for a coloring agent that will stay on the surface versus rapid bleed through the carrier fluid.
Desktop inkjet printers, as used in offices and homes, tend to use aqueous ink based on a mixture of water, glycol and or pigments. These inks are inexpensive to manufacture but difficult to control on the surface of media, often requiring specially coated media. HP inks contain sulfonated polyazo black dye (commonly used for dyeing leather), nitrates and other compounds. Aqueous inks are mainly used in printers with thermal inkjet heads, as these heads require water to perform the ink-expelling function.
While aqueous inks often provide the broadest color gamut and most vivid color, most are not waterproof without specialized coating or lamination after printing. Most dye-based inks, while usually the least expensive, are subject to rapid fading when exposed to light or ozone. Pigment-based aqueous inks are typically more costly but provide much better long-term durability and ultraviolet resistance. Inks marketed as "Archival" are usually pigment-based.
Some professional wide format printers use aqueous inks, but the majority in professional use today employ a much wider range of inks, most of which require piezo inkjet heads and extensive maintenance.
Fixed head designs are available in consumer products, but are more likely to be found on industrial high-end printers and large format printers. In the consumer space, fixed-head printers are manufactured primarily by Epson and Canon; however, many more recent Hewlett-Packard models use a fixed head, such as the Officejet Pro 8620 and HP's Pagewide series.
An intermediate method does exist: a disposable ink tank connected to a disposable head, which is replaced infrequently (perhaps every tenth ink tank or so). Most high-volume Hewlett-Packard inkjet printers use this setup, with the disposable print heads used on lower volume models. A similar approach is used by Kodak, where the printhead intended for permanent use is nevertheless inexpensive and can be replaced by the user. Canon now uses (in most models) replaceable print heads which are designed to last the life of the printer, but can be replaced by the user should they become clogged.
To combat this drying, nearly all inkjet printers include a mechanism to reapply moisture to the printhead. Typically there is no separate supply of pure ink-free solvent available to do this job, and so instead the ink itself is used to remoisten the printhead. The printer attempts to fire all nozzles at once, and as the ink sprays out, some of it wicks across the printhead to the dry channels and partially softens the hardened ink. After spraying, a rubber wiper blade is swept across the printhead to spread the moisture evenly across the printhead, and all jets are again fired to dislodge any ink clumps blocking the channels.
Some printers use a supplemental air-suction pump, using the rubber capping station to suck ink through a severely clogged cartridge. The suction pump mechanism is frequently driven by the page feed stepper motor: it is connected to the end of the shaft. The pump only engages when the shaft turns backwards, hence the rollers reversing while head cleaning. Due to the built-in head design, the suction pump is also needed to prime the ink channels inside a new printer, and to reprime the channels between ink tank changes.
Professional solvent- and UV-curable ink wide-format inkjet printers generally include a "manual clean" mode that allows the operator to manually clean the print heads and capping mechanism and to replace the wiper blades and other parts used in the automated cleaning processes. The volume of ink used in these printers often leads to "overspray" and therefore buildup of dried ink in many places that automated processes are not capable of cleaning. The ink consumed in the cleaning process needs to be collected to prevent ink from leaking in the printer. The collection area is called the inkjet spittoon, and in Hewlett-Packard printers this is an open plastic tray underneath the cleaning/wiping station. In Epson printers, there is typically a large absorption pad in a pan underneath the paper feed platen. For printers that are several years old, it is common for the dried ink in the spittoon to form a pile that can stack up and touch the printheads, jamming the printer. Some larger professional printers using solvent inks may employ a replaceable plastic receptacle to contain waste ink and solvent, which must be emptied or replaced when full.
There is a second type of ink drying that most printers are unable to prevent. For ink to spray from the cartridge, air must enter to displace the removed ink. The air enters via an extremely long, thin labyrinth tube, up to long, wrapping back and forth across the ink tank. The channel is long and narrow to reduce moisture evaporation through the vent tube, but some evaporation still occurs and eventually the ink cartridge dries up from the inside out. To combat this problem, which is especially acute with professional fast-drying solvent inks, many wide-format printer cartridge designs contain the ink in an airtight, collapsible bag that requires no vent. The bag merely shrinks until the cartridge is empty.
The frequent cleaning conducted by some printers can consume quite a bit of ink and has a great impact on cost-per-page determinations.
Clogged nozzles can be detected by printing a standard test pattern on the page. Some software workaround methods are known for rerouting printing information from a clogged nozzle to a working nozzle.
In comparison to technologies like thermal wax, dye sublimation, and laser printing, inkjets have the advantage of practically no warm up time, and often lower cost per page. However, low-cost laser printers can have lower per-page costs, at least for black-and-white printing, and possibly for color.
For some inkjet printers, monochrome ink sets are available either from the printer manufacturer or from third-party suppliers. These allow the inkjet printer to compete with the silver-based photographic papers traditionally used in black-and-white photography, and provide the same range of tones: neutral, "warm" or "cold". When switching between full-color and monochrome ink sets, it is necessary to flush out the old ink from the print head with a cleaning cartridge. Special software or at least a modified device driver are usually required, to deal with the different color mapping.
Some types of industrial inkjet printers are now capable of printing at very high speeds, in wide formats, or for a variety of industrial applications ranging from signage, textiles, optical media, ceramics and 3-D printing into biomedical applications and conductive circuitry. Leading companies and innovators in hardware include HP, Epson, Canon, Konica Minolta, Fujifilm, EFi, Durst, Brother, Roland DG, Mimaki, Mutoh and many others worldwide.
The very narrow inkjet nozzles are prone to clogging. The ink consumed in cleaning them—either during cleaning invoked by the user, or in many cases, performed automatically by the printer on a routine schedule—can account for a significant proportion of the ink used in the machine. Inkjet printing head nozzles can be cleaned using specialized solvents, or by soaking in warm distilled water for short periods of time (for water-soluble inks.)
The high cost of OEM ink cartridges and the intentional obstacles to refilling them have been addressed by the growth of third-party ink suppliers. Many printer manufacturers discourage customers from using third-party inks, stating that they can damage the print heads due to not being the same formulation as the OEM inks, cause leaks, and produce inferior-quality output (e.g., of incorrect color gamut). Consumer Reports has noted that some third-party cartridges may contain less ink than OEM cartridges, and thus yield no cost savings, while Wilhelm Imaging Research claims that with third-party inks the lifetime of prints may be considerably reduced. However, an April 2007 review showed that, in a double-blind test, reviewers generally preferred the output produced using third-party ink over OEM ink. In general, OEM inks have undergone significant system reliability testing with the cartridge and print-head materials, whereas R&D efforts on third-party ink material compatibility are likely to be significantly less. Some inkjet manufacturers have tried to prevent cartridges being refilled using various schemes including fitting chips to the cartridges that log how much the cartridge has printed and prevent the operation of a refilled cartridge.
The warranty on a printer may not apply if the printer is damaged by the use of non-approved supplies. In the US the Magnuson–Moss Warranty Act is a federal law which states that warrantors cannot require that only brand name parts and supplies be used with their products, as some printer manufacturers imply. However, this would not apply if non-approved items cause damage.
Because the ink used in many low-cost consumer inkjets is water-soluble, care must be taken with inkjet-printed documents to avoid even the smallest drop of moisture, which can cause severe "blurring" or "running". In extreme cases, even sweaty fingertips during hot humid weather could cause low-quality inks to smear. Similarly, water-based highlighter markers can blur inkjet-printed documents and discolor the highlighter's tip. The lifetime of inkjet prints produced using aqueous inks is generally shorter (although UV-resistant inks are available) than those produced with solvent-based inkjets; however, so-called "archival inks" have been produced for use in aqueous-based machines which offer extended life.
In addition to smearing, gradual fading of many inks can be a problem over time. Print lifetime is highly dependent on the quality and formulation of the ink. The earliest inkjet printers, intended for home and small office applications, used dye-based inks. Even the best dye-based inks are not as durable as pigment-based inks, which are now available for many inkjet printers. Many inkjet printers now utilize pigment based inks which are highly water resistant: at least the black ink is often pigment-based. Resin or silicone protected photopaper is widely available at low cost, introducing complete water and mechanical rub resistance for dye and pigment inks. The photopaper itself must be designed for pigment or for dye inks, as pigment particles are too large to be able to penetrate through dye-only photopaper protection layer.
The highest-quality inkjet prints are often called "giclée" prints, to distinguish them from less-durable and lower-cost prints. However, the use of the term is no guarantee of quality, and the inks and inkjet paper used must be carefully investigated before an archivist can rely on their long-term durability.
To increase the durability of inkjet printer prints, more attention is needed for the inkjet ink cartridge. One way to treat ink cartridges on an inkjet printer is to maintain the temperature of the printer itself. Excessive variation in space temperature is very bad for printer ink cartridges. The user should prevent the printer becoming too hot or too chilly as the cartridges can dry up. For lasting printer efficiency, the user should ensure the area has a regular and steady temperature level.
If an inkjet head becomes clogged, third-party ink solvents/head cleaners and replacement heads are available in some cases. The cost of such items may be less expensive compared to a transfer unit for a laser printer, but the laser printer unit has a much longer lifetime between required maintenance. Many inkjet printer models now have permanently installed heads, which cannot be economically replaced if they become irreversibly clogged, resulting in scrapping of the entire printer. On the other hand, inkjet printer designs which use a disposable printhead usually cost significantly more per page than printers using permanent heads. By contrast, laser printers do not have printheads to clog or replace frequently, and usually can produce many more pages between maintenance intervals.
Inkjet printers have traditionally produced better quality output than color laser printers when printing photographic material. Both technologies have improved dramatically over time, although the highest-quality giclée prints favored by artists use what is essentially a high-quality specialized type of inkjet printer.
Some manufacturers, most notably Epson and Hewlett-Packard, have been accused of indicating that a cartridge is depleted while a substantial amount of ink remains. A 2007 study found that most printers waste a significant quantity of ink when they declare a cartridge to be empty. Single-ink cartridges were found to have on average 20% of their ink remaining, though actual figures range from 9% to 64% of the cartridge's total ink capacity, depending on the brand and model of printer. This problem is further compounded with the use of one-piece multi-ink cartridges, which are declared empty as soon as one color runs low. Of great annoyance to many users are those printers that will refuse to print documents requiring only black ink, just because one or more of the color ink cartridges is depleted.
In recent years, many consumers have begun to challenge the business practices of printer manufacturers, such as charging up to US$8,000 per gallon (US$2,100 per liter) for printer ink. Alternatives for consumers are cheaper copies of cartridges, produced by third parties, and the refilling of cartridges, using refill kits. Due to the large differences in price caused by OEM markups, there are many companies selling third-party ink cartridges. Most printer manufacturers discourage refilling disposable cartridges or using aftermarket copy cartridges, and say that use of incorrect inks may cause poor image quality due to differences in viscosity, which can affect the amount of ink ejected in a drop, and color consistency, and can damage the printhead. Nonetheless, the use of alternative cartridges and inks has been gaining in popularity, threatening the business model of printer manufacturers. Printer companies such as Hewlett-Packard, Lexmark, and Epson have used patents and the DMCA to launch lawsuits against third-party vendors. An anti-trust class-action lawsuit was launched in the US against HP and office supply chain Staples, alleging that HP paid Staples $100 million to keep inexpensive third-party ink cartridges off the shelves.
In Lexmark Int'l v. Static Control Components, the United States Court of Appeals for the Sixth Circuit ruled that circumvention of this technique does not violate the Digital Millennium Copyright Act. The European Commission also ruled this practice anticompetitive: it will disappear in newer models sold in the European Union. Patents protecting the structure of their cartridges prevent the sale of cheaper copies of the cartridges. For some printer models (notably those from Canon), the manufacturer's own microchip can be removed and fitted to a compatible cartridge thereby avoiding the need to replicate the microchip (and risk prosecution). Other manufacturers embed their microchips deep within the cartridge in an effort to prevent this approach.
In 2007, Eastman Kodak entered the inkjet market with its own line of All-In-One printers based on a marketing model that differed from the prevailing practice of selling the printer at a loss while making large profits on replacement ink cartridges. Kodak claimed that consumers could save up to 50 percent on printing by using its lower-cost cartridges filled with the company's proprietary pigmented colorants while avoiding the potential problems associated with off-brand inks. This strategy proved unsuccessful, and Kodak exited the consumer inkjet printer business in 2012.
A more recent development is the supertank printer, which uses an integrated continuous ink system. Supertank printers are defined by their large, permanently installed ink tanks which are filled from ink bottles. The printer itself is typically sold at a substantial premium, but ink bottles are inexpensive and contain enough ink to print thousands of pages. Supertank printers generally ship with full bottles of ink in the box, allowing up to two years of printing before the tanks needs to be refilled. Epson pioneered this technology by launching the EcoTank range, first in Indonesia in 2010, with a North American launch in 2015. The supertank concept proved commercially successful, and Canon and HP launched their own lines of supertank printers, under the names MegaTank (Canon) and Smart Tank (HP).
One method to bypass printer-region-coding is to store empty cartridges from the old region and refill them with ink from the new region, but, as mentioned above, many modern ink cartridges have chips and sensors to prevent refilling, which makes the process more difficult. On the Internet, there are refill instructions for different printer models available. Another method is to have ink cartridges from the old region shipped to the new region.
Some manufacturers of region-coded printers also offer region-free printers specially designed for travelers.
Another specialty application for inkjets is producing prepress color proofs for printing jobs created digitally. Such printers are designed to give accurate color rendition of how the final image will look (a "proof") when the job is finally produced on a large volume press such as a four-color offset lithography press. An example is an Iris printer, whose output is what the French term giclée was coined for. The largest-volume supplier is Hewlett-Packard, which supplies over 90 percent of the market for printers for printing technical drawings. The major products in their Designjet series are the Designjet 500/800, the Designjet T Printer series (including the T1100 and T610), the Designjet 1050 and the Designjet 4000/4500. They also have the HP Designjet 5500, a six-color printer that is used especially for printing graphics as well as the new Designjet Z6100 which sits at the top of the HP Designjet range and features an eight color pigment ink system. Epson, Kodak, and Canon also manufacture wide-format printers, sold in much smaller numbers than standard printers. Epson has a group of three Japanese companies around it that predominantly use Epson piezo printheads and inks: Mimaki, Roland, and Mutoh. Scitex Digital Printing developed high-speed, variable-data, inkjet printers for production printing, but sold its profitable assets associated with the technology to Kodak in 2005 who now market the printers as Kodak Versamark VJ1000, VT3000, and VX5000 printing systems. These roll-fed printers can print at up to 305m per minute. Professional high-volume inkjet printers are made by a range of companies. These printers can range in price from US$35,000 to $2 million. Carriage widths on these units can range from 54" to 192" (about 1.4 to 5 m), and ink technologies have tended toward solvent, eco-solvent, and UV-curing with a more recent focus toward water-based (aqueous) ink sets. Major applications where these printers are used are for outdoor settings for billboards, truck sides and truck curtains, building graphics and banners, while indoor displays include point-of-sales displays, backlit displays, exhibition graphics, and museum graphics.
The major suppliers for professional high-volume, wide- and grand-format printers include: EFI, LexJet, Grapo, Inca, Durst, Océ, NUR (now part of Hewlett-Packard), Lüscher, VUTEk, Scitex Vision (now part of Hewlett-Packard), Mutoh, Mimaki, Roland DG, Seiko I Infotech, IQDEMY, Leggett and Platt, Agfa, Raster Printers, DGI and MacDermid ColorSpan (now part of Hewlett-Packard), swissqprint, SPGPrints (formerly Stork Prints), MS Printing Systems and Digital Media Warehouse.
They can print an image of 36 megapixels on A3 borderless photo paper with 444 Pixel density.
The majority of compact photo printers can only print pictures. Given this limitation, they are not meant to replace standard inkjets. Many manufacturers advertise the cost per page of photos printed on their machines; this theoretically convinces people that they can print their own pictures just as cheaply as retail stores or through online printing services. Most compact photo printers share a similar design. They are small units, usually with large in order to allow people to browse and edit their photos, as can be done on a computer. The editing options are usually somewhat advanced, allowing the user to crop photos, remove red eye, adjust color settings as well as other functions. Compact photo printers typically feature a large number of connection options, including USB and most memory card formats.
Compact photo printers are currently manufactured by most of the leading printer manufacturers such as Epson, Canon, Hewlett-Packard, Lexmark and Kodak. While they have increased in popularity in recent years, they still make up a relatively small share of the inkjet printer market. LG Corporation's Pocket Photo uses Zink thermal paper which has chemistries embedded on each inkless photo paper and the image will appear with the heat.
Inkjet printers and similar technologies are used in the production of many microscopic items. See Microelectromechanical systems. Inkjet printers are used to form conductive traces for circuits, and color filters in LCD and plasma displays.
Inkjet printers, especially models produced by Dimatix (now part of Fujifilm), Xennia Technology and Pixdro, are in fairly common use in many labs around the world for developing alternative deposition methods that reduce consumption of expensive, rare, or problematic materials. These printers have been used in the printing of polymer, macromolecular, quantum dot, metallic , and carbon nanotubes. The applications of such printing methods include organic thin-film transistors, organic light emitting diodes, organic solar cells, and sensors.
Inkjet technology is used in the emerging field of bioprinting. They are also used for the production of OLED displays.
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