| Part of a series on the |
| History of printing |
|---|
| Woodblock printing (200) |
| Movable type (1040) |
| Printing press (1454) |
| Etching (ca. 1500) |
| Mezzotint (1642) |
| Aquatint (1768) |
| Lithography (1796) |
| Chromolithography (1837) |
| Rotary press (1843) |
| Offset printing (1875) |
| Hectograph (19th century) |
| Hot metal typesetting (1886) |
| Mimeograph (1890) |
| Screen printing (1907) |
| Spirit duplicator (1923) |
| Dye-sublimation (1957) |
| Phototypesetting (1960s) |
| Dot matrix printer (1964) |
| Laser printing (1969) |
| Thermal printing (ca. 1972) |
| Inkjet printing (1976) |
| Stereolithography (1986) |
| Digital press (1993) |
| 3D printing (ca. 2003) |
An inkjet printer is a type of computer printer that creates a digital image by propelling droplets of ink onto paper. Inkjet printers are the most commonly used type of printer[1] and range from small inexpensive consumer models to very large professional machines that can cost up to thousands of dollars.[2]
The concept of inkjet printing originated in the 19th century, and the technology was first extensively developed in the early 1950s. Starting in the late 1970s inkjet printers that could reproduce digital images generated by computers were developed, mainly by Epson, Hewlett-Packard (HP), and Canon. In the worldwide consumer market, four manufacturers account for the majority of inkjet printer sales: Canon, HP, Epson, and Lexmark, a 1991 spin-off from IBM.[3]
The emerging ink jet material deposition market also uses inkjet technologies, typically printheads using piezoelectric crystals, to deposit materials directly on substrates.
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There are two main technologies in use in contemporary inkjet printers: continuous (CIJ) and Drop-on-Demand (DOD). Drop-on-demand is further divided into thermal DOD and piezoelectric DOD
The continuous inkjet method is used commercially for marking and coding of products and packages. The idea was first patented in 1867 by Lord Kelvin, and the first commercial devices (medical strip chart recorders) were introduced in 1951 by Siemens.[4]
In continuous inkjet technology, a high-pressure pump directs liquid ink from a reservoir through a gunbody and a microscopic nozzle, creating a continuous stream of ink droplets via the Plateau-Rayleigh instability. A piezoelectric crystal creates 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 droplets per second may be achieved. The ink droplets are subjected to an electrostatic field created by a charging electrode as they form; the field varies according to the degree of drop deflection desired. This results in a controlled, variable electrostatic charge on each droplet. Charged droplets are separated by one or more uncharged “guard droplets” to minimize electrostatic repulsion between neighbouring droplets.
The charged droplets pass through an electrostatic field and are directed (deflected) by electrostatic deflection plates to print on the receptor material (substrate), or allowed to continue on undeflected 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.
Continuous ink jet is one of the oldest ink jet technologies in use and is fairly mature. The major advantages are the very high velocity (~50 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.
Most consumer inkjet printers, from companies including Canon, Hewlett-Packard, and Lexmark (but not Epson), use print cartridges with a series of tiny chambers each containing a heater, all of which are constructed by photolithography. To eject a droplet from each chamber, a pulse of current is passed through the heating element causing a rapid vaporisation of the ink in the chamber to form a bubble, which causes a large pressure increase, propelling a droplet of ink onto the paper (hence Canon's tradename of Bubble Jet). The ink's surface tension, as well as the condensation and thus contraction of the vapor bubble, pulls a further charge of ink into the chamber through a narrow channel attached to an ink reservoir.
The inks used are usually water-based (aqueous) and use either pigments or dyes as the colorant. The inks used must have a volatile component to form the vapor bubble, otherwise droplet ejection cannot occur. As no special materials are required, the print head is generally cheaper to produce than in other inkjet technologies. The thermal inkjet principle was discovered by Canon engineer Ichiro Endo in August 1977.
Thermal inkjet printers are not the same as thermal printers, which produce images by heating thermal paper, as seen on older fax machines, cash registers, ATM receipt printers, and lottery ticket printers.
Most commercial and industrial inkjet printers and some consumer printers (those produced by Epson and Brother Industries) use a piezoelectric material in an ink-filled chamber behind each nozzle instead of a heating element. When a voltage is applied, the piezoelectric material changes shape, which generates a pressure pulse in the fluid forcing a droplet of ink from the nozzle. Piezoelectric (also called Piezo) inkjet allows a wider variety of inks than thermal inkjet as there is no requirement for a volatile component, and no issue with kogation (buildup of ink residue), but the print heads are more expensive to manufacture due to the use of piezoelectric material (usually PZT, lead zirconium titanate). A drop-on-demand process uses software that directs the heads to apply between zero to eight droplets of ink per dot, only where needed.
Piezo inkjet technology is often used on production lines to mark products - for instance the "use-before" date is often applied to products with this technique; in this application the head is stationary and the product moves past. Requirements of this application are high speed, a long service life, a relatively large gap between the print head and the substrate, and low operating cost.
Recent developments of piezo inkjet technology are extending the technique from printing into manufacturing processes. The newest of these technologies is to deposit layers of plastic material as digital embossing over the top of printed works.[5]
The basic problem with inkjet inks is the conflicting requirements for a coloring agent that will stay on the surface vs. rapid dispersement of the carrier fluid.
Desktop inkjet printers, as used in offices or at home, tend to use aqueous inks based on a mixture of water, glycol and dyes or pigments. These inks are inexpensive to manufacture, but are difficult to control on the surface of media, often requiring specially coated media. HP inks contain sulfonated polyazo black dye (commonly used for dying leather), nitrates and other compounds. Aqueous inks are mainly used in printers with thermal inkjet heads, as these heads require water to perform.
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. Pigment-based aqueous inks are typically more costly but provide much better long-term durability and ultraviolet resistance. Inks marketed as “Archival Quality” 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:
UV Curable Ink Properties and Functions:
• Photoinitiators: Absorb the UV energy from the light source on the print head. Chemical reaction occurs that converts the liquid ink into a solid film.
• Monomers: Used as solvents because of their ability to reduce viscosity (thickness) and combine with other ink components. 100% percent solids and do not release VOCs (volatile organic compounds). Monomers also add improved film hardness and resistance properties.
• Oligomers: Determine the final properties of the cured ink film, including its elasticity, outdoor performance characteristics and chemical resistance.
• Colorants: Can be dye-based or pigment-based. Usually, pigment-based because of the greater light fastness and durability of pigments compared with dyes. Pigments used in outdoor advertising and display applications have similar requirements to those used in automotive paints. Consequently, there is some crossover of use. While a pigment is selected on the basis of the required application, size control and reduction along with dispersion technique are major components of ink formulation.
UV Ink Printing Process:
There are two main design philosophies in inkjet head design: fixed-head and disposable head. Each has its own strengths and weaknesses.
The fixed-head philosophy provides an inbuilt print head (often referred to as a gaiter- head) that is designed to last for the life of the printer. The idea is that because the head need not be replaced every time the ink runs out, consumable costs can be made lower and the head itself can be more precise than a cheap disposable one, typically requiring no calibration. On the other hand, if a fixed head is damaged, obtaining a replacement head can become expensive, if removing and replacing the head is even possible. If the printer's head cannot be removed, the printer itself will then need to be replaced.
Fixed head designs are available in consumer products, but are more likely to be found on industrial high-end printers and large format plotters. In the consumer space, fixed-head printers are manufactured primarily by Epson and Canon. Hewlett-Packard also offers a few fixed-head models, such as the HP Photosmart 3310. Industrial fixed-head print heads are manufactured by these companies: Kodak Versamark, Trident, Xaar, Spectra (Dimatix), Hitachi / Ricoh, HP Scitex, Brother, Konica Minolta, Seiko Epson, and ToshibaTec (a licensee of Xaar).
The disposable head philosophy uses a print head which is supplied as a part of a replaceable ink cartridge. Every time a cartridge is exhausted, the entire cartridge and print head are replaced with a new one. This adds to the cost of consumables and makes it more difficult to manufacture a high-precision head at a reasonable cost, but also means that a damaged or clogged print head is only a minor problem: the user can simply buy a new cartridge. Hewlett-Packard has traditionally favoured the disposable print head, as did Canon in its early models. This type of construction can also be seen as an effort by printer manufacturers to stem third party ink cartridge assembly replacements, as these would-be suppliers don't have the ability to manufacture specialized print heads.
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 if they should become clogged. For Canon models with "Think Tank" technology, the ink tanks are separate for each ink color.
The primary cause of inkjet printing problems is due to ink drying on the printhead's nozzles, causing the pigments and dyes to dry out and form a solid block of hardened mass that plugs the microscopic ink passageways. Most printers attempt to prevent this drying from occurring by covering the printhead nozzles with a rubber cap when the printer is not in use. Abrupt power losses, or unplugging the printer before it has capped the printhead, can cause the printhead to be left in an uncapped state. Even when the head is capped, this seal is not perfect, and over a period of several weeks the moisture (or other solvent) can still seep out, causing the ink to dry and harden. Once ink begins to collect and harden, the drop volume can be affected, drop trajectory can change, or the nozzle can completely fail to jet ink.
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 the jets are again all fired to dislodge any ink clumps blocking the channels.
Some printers use a supplemental air-suction pump, utilizing 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 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 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 10 cm 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 re-routing printing information from a clogged nozzle to a working nozzle.
Compared to earlier consumer-oriented color printers, inkjets have a number of advantages. They are quieter in operation than impact dot matrix or daisywheel printers. They can print finer, smoother details through higher printhead resolution, and many consumer inkjets with photographic-quality printing are widely available.
In comparison to more expensive technologies like thermal wax, dye sublimation, and laser printing, inkjets have the advantage of practically no warm up time, and 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.
Inkjet printers may have a number of disadvantages:
These disadvantages have been addressed in a variety of ways:
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,[10] while Wilhelm Imaging Research[11] claims that with third-party inks the lifetime of prints may be considerably reduced. However, an April 2007 review[12] 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 is likely to be significantly less. Some inkjet manufacturers have tried to prevent cartridges being refilled using various schemes including fitting smart chips to the cartridges that can detect when the cartridge has run out of ink 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 can not require that only brand name parts and supplies be used with their product, as some printer manufacturers imply. However, this would not apply if non-approved items cause damage.
Most inkjet printers cost less than laser printers to purchase, but their cost per page printed is usually significantly higher. If the number of prints produced over the life of a printer is not very small, the total cost of ownership—purchase price, consumables, maintenance, and all other costs—may be higher for an inexpensive inkjet than a laser printer.
Particularly for printers not used frequently, there are additional costs due to ink wastage in cleaning required with intermittent use, and possible replacement of cartridges which are clogged due to lack of use although not empty.
Inkjet printers are often preferred, particularly for home use, due to their low purchase price and relatively small size. The best photo-quality inkjet printers may produce better quality output than colour laser printers. Laser printers are usually preferred in an office environment with higher printing volume.
A common business model for inkjet printers involves selling the actual printer at or below production cost,[13] while dramatically marking up the price of the (proprietary) ink cartridges (a profit model called "Freebie marketing"). All current inkjet printers attempt to enforce this product tying using microchips in the cartridges to hinder the use of third-party or refilled ink cartridges. The microchips monitor usage and report the ink remaining to the printer. Some manufacturers also impose "expiration dates". When the chip reports that the cartridge is empty (or out of date) the printer stops printing. Even if the cartridge is refilled, the microchip will indicate to the printer that the cartridge is depleted. For many models (especially from Canon), the 'empty' status can be overridden by entering a 'service code' (or sometimes simply by pressing the 'start' button again). For some printers, special circuit "flashers" are available that reset the quantity of remaining ink to the maximum. 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.[14][15] 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.[16][17] 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 $8,000 per gallon for printer ink.[18] 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 HP, Lexmark, and Epson have used patents and the DMCA to launch lawsuits against third-party vendors.[19][20] An anti-trust class-action lawsuit was launched in the US against HP and office supply chain Staples Inc., alleging that HP paid Staples $100 million to keep inexpensive third-party ink cartridges off the shelves.[21][22]
In Lexmark Int'l v. Static Control Components, Case No. 03-5400 (6th Cir. Oct. 26, 2004) (Sutton, J.) 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. [23] While the DMCA case dealt with copyright protection, companies also rely on patent protection to prevent copying and refilling of cartridges. For example, if a company devises all of the ways in which their microchips can be manipulated and cartridges can be refilled and patents these methods, they can prevent anyone else from refilling their cartridges. 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.[1]
In addition to the widely-used small inkjet printers for home and office, there are professional inkjet printers, some for "page-width" format printing and many for wide format printing. Page-width format means that the print width ranges from about 8.5" to 37" (about 20 cm to 100 cm). "Wide format" means print width ranging from 24" up to 15' (about 75 cm to 5 m). The most common application of page-width printers is in printing high-volume business communications that do not need high-quality layout and color. Particularly with the addition of variable data technologies, the page-width printers are important in billing, tagging, and individualized catalogs and newspapers. The application of most wide format printers is in printing advertising graphics; a lower-volume application is printing of design documents by architects or engineers.
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-colour offset lithography press. An example is an Iris printer, whose output is commonly called "iris proofs" or just "irises".
The largest-volume supplier is Hewlett-Packard, which supply 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 & 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 colour 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 3 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(tm) VJ1000, VT3000, and VX5000 printing systems. These roll-fed printers can print at up to 1000 feet 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 tend toward solvent, eco-solvent and UV-curing as opposed to 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 wide- and grand-format printers include: Agfa Graphics, LexJet, Grapo, Inca, Durst, Océ, NUR (now part of Hewlett-Packard), Lüscher, VUTEk, Zünd, Scitex Vision (now part of Hewlett-Packard), Mutoh, Mimaki, Roland DG], Seiko I Infotech, Sun Innovations, Leggett and Platt, Agfa, Raster Printers, DGI and MacDermid ColorSpan (now part of Hewlett-Packard)
Images produced on inkjet printers are sometime sold under other names since the term is associated with words like "digital", "computers", and "everyday printing", which can have negative connotations in some contexts. [26] These trade names or coined names are usually used in the fine arts reproduction field. They include: