'Inkjet printers' are a type of
computer printer that operates by propelling tiny droplets of liquid
ink onto paper. They are the most common type of
computer printer for the general consumer due to their low cost, high quality of output, capability of printing in vivid color, and ease of use.
The emerging
Ink jet material deposition market uses ink jet technologies, typically piezoelectric ink jet, to deposit materials on substrates.
In general
In the personal and
small business computer market, inkjet printers currently predominate. Inkjets are seen as inexpensive, quiet, and reasonably fast; and many models can produce high-quality output.
Like most modern technologies, the present-day inkjet has built on the progress made by many earlier versions. Among many contributors,
Epson,
Hewlett-Packard and
Canon can claim a substantial share of credit for the development of the modern inkjet. In the worldwide consumer market, four manufacturers account for the majority of inkjet printer sales: Canon, Hewlett-Packard, Epson, and
Lexmark.
Ink jet printers use one of three main technologies: thermal, piezoelectric, and continuous.
Thermal Ink Jet
Most cheap consumer inkjet printers (
Lexmark,
Hewlett-Packard,
Canon) work by having a print cartridge with a series of tiny electrically heated chambers constructed by
photolithography. To produce an image, the printer runs a pulse of current through the heating elements causing a steam explosion in the chamber to form a bubble, which propels a droplet of ink onto the paper (hence Canon's tradename of ''Bubblejet'' for its inkjets). The ink's
surface tension as well as the condensation and thus contraction of the vapour bubble, pulls a further charge of ink into the chamber through a narrow channel attached to an ink reservoir.
The ink used is usually water-soluble pigment or dye-based and the print head is generally produced more cheaply than other ink jet technologies. The principle was discovered by Canon engineer
Ichiro Endo in August 1977.
Note that this has no relation to
thermal printers, which produce images by heating thermal paper, as seen on older fax machines, cash register and ATM receipts and lottery ticket printers.
A new development in thermal inkjet printing is the full-page thermal technology announced by Memjet in March 2007. Unlike traditional scanning inkjet printheads, the Memjet printhead does not move, reducing vibration, noise and mechanical complexity, while increasing performance. This design and other innovations enable breakthrough speed. The technology can print full-color, photo-quality images (4x6” or A6) at 30 ppm, full-color and black-and-white business communication (8.5x11” or A4) at 60 ppm, and draft mode at 90 ppm. The technology is based on research from Silverbrook Research of Australia, and is based on more than 1,600 U.S. patents. The first OEM printers using the Memjet technology are expected to be available in 2008 or 2009.
Piezoelectric Ink Jet
Most commercial and industrial ink jet printers use a
piezoelectric material in an ink-filled chamber behind each nozzle instead of a heating element. When a voltage is applied, the crystal changes shape or size, which generates a pressure pulse in the fluid forcing a droplet of ink from the nozzle. This is essentially the same mechanism as the thermal inkjet but generates the pressure pulse using a different physical principle. Piezoelectric ink jet allows a wider variety of inks than thermal or continuous ink jet but is more expensive.
Continuous Ink Jet
The continuous ink jet 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 model was introduced in
1951 by
Siemens.
In continuous ink jet 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. 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 drops per second may be achieved. The ink droplets are subjected to an electrostatic field created by a charging electrode as they form, the field varied 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 neighboring 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 few percent of the droplets are actually used to print, the majority being recycled.
Continuous ink jet is one of the oldest ink jet technologies in use and is fairly mature. One of its advantages is the very high velocity (~50 m/s) of the ink droplets, which allows for a relatively long distance between print head and substrate. 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 "bite" into the substrate and dry quickly.
The ink system requires active solvent regulation in order to accommodate for 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 in order to counteract the described solvent loss.
Inkjet Inks
black ink refill kit for inkjet printer
color ink refill kit for inkjet printer
refilling a
Canon ink tank
The basic problem with inkjet inks is the conflicting requirement for a colouring agent that will stay on the surface and rapid dispersement of the carrier.
Desktop inkjet printers, as used in offices or at home, all 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 and therefore often require specially coated media. Aqueous inks are mainly used in printers with disposable, so-called thermal inkjet heads, as these heads require water in order to perform.
In professional wide format printers, a much wider range of inks is used, most of which require piezo inkjet heads:
★ 'Solvent inks:' the main ingredient of these inks are
VOCs. The main advantage of these inks is that they are very inexpensive and also enable printing on uncoated
vinyl substrates, which are used to produce vehicle graphics, billboards and banners.
★ 'UV-curable inks:' these inks consist mainly of acrylic monomers with an initiator package. After printing, the ink is cured by exposure to strong UV-light. The advantage of UV-curable inks is that they "dry" as soon as they are cured, they can be applied to a wide range of uncoated substrates and produce a very robust image. Disadvantages are that they are more expensive, require expensive curing modules in the printer and the cured ink has a significant volume and so gives a slight relief on the surface.
★ 'Dye sublimation inks:' these inks contain special
sublimation dyes and are used to print directly or indirectly on to fabrics which consist of a high percentage of polyester fibres. A heating step causes the dyes to sublimate into the fibers and create an image with strong color and good durability.
Inkjet head design
Two main design philosophies operate in inkjet head design. Each has strengths and weaknesses.
The 'fixed-head' philosophy provides an inbuilt print head (often referred to as a ''Gaither Head'') that is designed to last for the whole 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. On the other hand, if the head is damaged, it is usually necessary to replace the entire printer.
Epson have traditionally used fixed print heads featuring micropiezo technology. These print heads are available in consumer products and are typically more accurate in dot placement than comparable thermal printers.
Other fixed head designs are more likely to be found on industrial high-end printers and large format plotters and use piezo inkjet heads. Because development of these heads requires a large investment in research and development, there are only a few companies offering them:
Kodak VersamarkTrident,
Xaar,
Spectra (Dimatix),
Hitachi / Ricoh,
HP Scitex,
Brother,
Konica Minolta,
Seiko Epson, and ToshibaTec (a licensee of Xaar).
Hewlett-Packard has introduced a fixed-head thermal inkjet printer with its newer printer models such as the HP Photosmart 3310.
The 'disposable head' philosophy uses a print head which is a part of the 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 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.
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.
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 models with "Think Tank" technology, the ink tanks are separate for each ink color.
Cleaning mechanisms
The primary cause of inkjet printing problems is due to moisture evaporating from the nozzles on the printhead, 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. However this seal is not perfect, and over a period of several weeks the moisture can still seep out, causing the ink to dry and harden.
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 will wick 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.
Most Epson printers also use a supplemental air-suction pump, utilizing the rubber capping station to suck ink through a severely clogged cartridge. Due to the built-in head design, the suction pump is also needed to prime the ink channels inside a new Epson printer, and to reprime the channels between ink tank changes.
The ink consumed in the cleaning process needs to be collected somewhere to prevent ink from leaking all over the surface under the printer. The collection area is known as the spittoon, and in Hewlett Packard printers this is an open plastic tray underneath the cartridge storage and cleaning/wiping station. In Epson printers, there is typically a large fibrous 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. Some larger professional printers using solvent inks may employ a replaceable plastic receptacle to contain waste ink and solvent.
The type of ink used in the printer can affect how quickly the printhead nozzles become clogged. While the official brand of ink is highly engineered to match the printer mechanism, generic inks cannot exactly match the composition of the official brand since the actual ink composition is a trade secret. Generic ink brands may alternately be too volatile to keep the printhead moist during storage, or may be too thick and jellied leading to frequent printhead channel clogging.
There is a second type of ink drying that most printers are unable to prevent. In order for ink to spray out of the cartridge, air needs to enter somewhere 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 slow down moisture from evaporating out through the vent tube, but some evaporation still occurs and eventually the ink cartridge dries up from the inside out.
Advantages
Compared to earlier consumer-oriented 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 inkjets with photorealistic-quality color printing are widely available.
In comparison to more expensive technologies like
thermal wax,
dye sublimations, and
laser printers, inkjets have the advantage of practically no warm up time and lower cost per page (except when compared to laser printers).
Present-day inkjet printers use
stochastic or FM screening, which gives better-quality results than low-cost laser printers when printing photographic images. Some inkjet printers print dots of more than one size, so that the screening is not purely "FM".
For some inkjet printers, monochrome ink sets are available either from the printer manufacturer or 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 special 'cleaning cartridge'.
As opposed to most other types of printers, inkjet cartridges can be refilled. Most cartridges can be easily refilled by drilling a hole in and filling the tank portion of the cartridge. This method is more cost effective as opposed to buying a new cartridge each time one runs dry.
Disadvantages
Inkjet printers may have a number of disadvantages:
# The ink is often very expensive (for a typical
OEM cartridge priced at $15, containing 5
ml of ink, the ink effectively costs $3000 per liter)
# Many "intelligent" ink cartridges contain a
microchip that communicates the estimated ink level to the printer; this may cause the printer to display an error message, or incorrectly inform the user that the ink cartridge is empty. In some cases, these messages can be ignored, but many inkjet printers will refuse to print with a cartridge that declares itself empty, in order to prevent consumers from refilling cartridges.
# The lifetime of inkjet prints is limited; they may eventually fade and the color balance may change.
# Because the ink used in most inkjets is water-soluble, care must be taken with inkjet-printed documents to avoid even the smallest drop of water, which can cause severe "blurring" or "running." Similarly, water-based
highlighter markers can blur inkjet-printed documents.
These disadvantages have been addressed in a variety of ways:
# Third-party ink suppliers sell ink cartridges at significantly reduced costs (often 10%-30% of OEM cartridge prices) and also sell kits to refill cartridges, and bulk ink, at even lower prices.
# Many vendors' "intelligent" ink cartridges have been
reverse-engineered. It is now possible to buy inexpensive devices to reliably reset such cartridges to report themselves as full, so that they may be refilled many times.
# Print lifetime is highly dependent on the quality and formulation of the ink, as well as the paper chosen. 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.
Third-party ink and cartridges
The high cost of OEM ink cartridges, and the intentional obstacles to refilling them have been addressed by third-party ink suppliers.
Many printer manufacturers discourage customers from using third-party inks, claiming that they may damage the print heads, leak, and produce inferior-quality output. However, some OEM cartridges can be refilled, and the "intelligent" cartridge microchips may be circumvented as explained above. Some cartridges lose ink capacity upon refilling due to air growth in the internal foam.
The quality of third-party ink and cartridges is widely debated.
Consumer Reports has noted that third-party cartridges may contain less ink than OEM cartridges, and thus yield no cost savings.
[1] Wilhelm Imaging Research[2] claims that with third-party inks the lifetime of prints may be considerably reduced. However, an April 2007 review
[3] showed that, in a
double-blind test, reviewers generally ''preferred'' the output produced using third-party ink over OEM ink. They plan next to compare the longevity of prints using OEM and third-party ink.
OEM inks generally have undergone significant system reliability testing with the cartridge and print-head materials, whereas R&D efforts on 3rd party inks material compatibility is likely to be significantly less.
The third party refill industry is a relatively new business having been around for only six years. As the industry matured into three or four major refillers, a sub industry has emerged to service the refill industry. Higher volumes justified the cost of developing new inks and more effective refill and cleaning equipment to match the new processes that the major chains of refillers have developed. As a result, the process has moved from a simple topping up with a syring to flushing old ink out and replacing it with cartridge specific new ink using modern vacuum filling equipment. This has significantly improved the refill process.
Continuous ink system
Main articles: Continuous ink system
Many of the disadvantages of inkjet printers are addressed by third-party '
continuous ink systems' (not to be confused with
continuous ink jet printers, described above). These conversion kits connect the ink cartridges to reservoirs outside the printer: they can therefore hold much more ink, and may be replaced or filled individually. Continuous ink systems typically hold pigment inks, and some have been produced for printers that were only designed to use dye-based inks. The suppliers often provide
color profiles for their ink systems when used with specific
papers.
Overall expense
Even with many available options for cost-reduction, inkjet printing remains expensive. Unless photo-realistic reproduction is necessary, value-minded consumers often prefer
laser printers for medium- to high-volume printing applications.
Underlying business model
Microchips from Epson ink cartriges. These are small
printed circuit boards, the black dome contains the chip itself.
A common
business model for inkjet printers involves selling the actual printer at or below production cost, while dramatically marking up the price of the (proprietary) ink cartridges.
Alternatives for consumers are cheaper copies of cartridges, produced by other companies, and refilling cartridges, for which refill kits are available. Owing to the large differences in pricing due to OEM markups, there are many companies specializing in these alternative ink cartridges. Most printer manufacturers discourage refilling disposable cartridges. Aside from the obvious economic reasons, the heating elements in thermal cartridges often burn out when the ink supply is depleted, permanently damaging the print head.
Some inkjet printers enforce this
product tying using
microchips in the cartridges to prevent the use of third-party or refilled ink cartridges. 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. In fact, the
European Commission ruled this practice anticompetitive: it will disappear in newer models sold in the European Union.
USB cable markup
Another common business model for selling newer inkjet printers involves selling them at very low prices—sometimes below cost—but without the
USB 2.0 cable necessary to connect the printer to a computer. Vendors recover the costs by charging very high prices for separate USB cables. This allows retailers to advertise extremely low prices for inkjet printers.
Large electronics retailers that sell inkjet printers, such as
Best Buy and
Circuit City, sell a variety of USB cables, but all have very high
markup.
[4] If a customer buys both a cheap inkjet printer and a USB cable, the high
profit margin on the cable will allow the retailer recover the losses from selling the printer below cost. However, similar USB cables can be purchased for ''much'' lower prices from retailers that do not also sell inkjet printers. Compare these prices on equivalent products:
★
6-foot black USB 2.0 A-B cable for '$31.99' from
Circuit City
★
6-foot black USB 2.0 A-B cable for '$2.49' from Firefold.
Professional inkjet printers
Besides the well known small inkjet printers for home and office, there is a market for professional inkjet printers; some being for page-width format printing, and most being 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 that these are printers ranging in print width from 24" up to 15' (about 75 cm to 5 m). The application of the page-width printers is for printing high-volume business communications that have a lesser need for flashy 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 of the wide format printers is for printing advertising graphics; a minor application is printing of designs by architects or engineers.
Another specialty application for inkjets is producing
prepress color proofs for
printing jobs created in the ''digital realm''. 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 offset lithography press. A well-known example of an inkjet designed for proof work is an
Iris printer, and outputs from them are commonly "''iris proofs''" or just "''irises''".
In terms of units, the major 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 1050 and the DesignJet 4000/4500. Besides this they also have the
HP Designjet 5500, a six-color printer that is used especially for printing graphics. The constantly growing niche of page-format printing has been filled by
Kodak, with the Kodak Versamark(tm) VJ1000, VT3000, and VX5000 printing systems.
Scitex also made a short-lived entry into high-speed, variable-data, inkjet printing, but sold its profitable assets associated with the technology to Kodak in 2005.
A few other suppliers of low volume wide format printers are
Epson,
Kodak and
Canon. Epson has a group of 3 Japanese companies around it that all use predominantly heads and inks coming from Epson:
Mimaki,
Roland and
Mutoh.
More professional high-volume inkjet printers are made by a range of companies. These printers can range in price from 25,000€ to as high as 1.5 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: LexJet, Inca, Durst,
Océ, NUR, Lüscher,
VUTEk, Zünd, Scitex Vision, Gandinnovations,
Mutoh, Mimaki, Roland DGA, Seiko I Infotech, Leggett and Platt, Agfa, Raster Printers and MacDermid ColorSpan.
Inkjet Printing of Functional Materials
Three-dimensional printing constructs a prototype by printing cross-sections on top of one another.
High-end inkjet printers can be used to produce fine-art prints called
giclées.
U.S. Patent 6,319,530 teaches a "Method of photocopying an image onto an edible web for decorating iced baked goods". In plain English, this
invention enables one to inkjet print a food-grade color
photograph on a
birthday cake's surface. Many bakeries now carry
Edible Image brand printers.
Inkjet printers and similar technologies are to be used in the production of many microscopic items. See
MEMS.
Notes
1. [1]
2. Wilhelm Imaging Research offers general information on the factors that limit print life, and test reports on print life with specific printer/ink/paper combinations.
3. TrustedReviews.com - The Inkjet Investigation: compares the quality of prints using OEM and third-party ink cartridges from various manufacturers.
4. These vendors often advertise irrelevant features such as "24K gold-plated connectors" to justify the high prices of their USB cables, insinuating that these properties will improve the reliability or speed of the cable. However, the USB standard was specifically designed to make the connectors and cables as cheap to manufacture as possible. Given the digital nature and fixed timing of the USB protocol, any cable that meets the minimum specifications should perform equally well, making the benefits of expensive cables highly dubious.
See also
★
Daisy wheel printer
★
Digital printing
★
Dot matrix printer
★
Dye-sublimation printer
★
IS&T Society for Imaging Science and Technology
★
Laser printer
★
Photo printer
★
Thermal printer
★
DeskJet (the major line of Inkjet printers by Hewlett-Packard)
★
Inkjet transfer
★
Inkjet paper
★
Ink cartridge
★
Inkjet refill kit
★
Additive_manufacturing
External links
★
IS&T's NIP conference series on digital printing technologies
★
Printing Enters The Jet Age
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