Inkjet printer
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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.
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[edit] In general
In the personal and small business computer market, inkjet printers currently predominate. Inkjets are usually inexpensive, quiet, 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.
[edit] Thermal Ink Jet
Most consumer ink jet 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. A steam explosion in the chamber forms a bubble, which propels a droplet of ink onto the paper (hence Canon's tradename for its inkjets, Bubblejet). The ink's surface tension as well as the condensing and thus contraction of the vapour-bubble, pulls another 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 but the print head is produced usually at less cost than other ink jet technologies. The technology principle was discovered by Canon engineer Ichiro Endo in August 1977.
Note that this is not the same thing as a thermal printer, which produce images by heating thermal paper, as seen on some fax machines, cash register and ATM receipts, and lottery ticket printers.
[edit] Piezoelectric Ink Jet
All Epson printers and 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.
InkJet with Piezoelectric is very fast and cost effective. When the Piezo crystal has an applied voltage, the crystal will shake the ink stream causing it to break off in very small, fine droplets as the ink leaves the orifice plate hole. This droplet of ink can then be either charged or not charged depending on if the droplet of ink is to be printed or not.
If the droplet is to be printed onto the paper, the ink droplet is not charged. However, if the droplet is not required to be printed to the paper, it is charged with a positive bias, this way the ink droplet is then attracted to the negatively biased charge plate, the ink will hit the plate and will be vacuumed away by an ink recycle system. (This is used during the printer's automatic head cleaning procedure, albeit consuming usable ink in the process.)
The emerging Ink jet material deposition market uses ink jet technologies, typically piezoelectric ink jet, to deposit materials on substrates.
[edit] Continuous Ink Jet
The continuous ink jet method is used commercially for marking and coding of products and packages. The first patent on the idea is from 1867, by William Thomson. 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 effects an acoustic wave as it vibrates within the gunbody and causes the stream of liquid to break into droplets at regular intervals - 64000 to 165000 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 is 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) to the receptor material (substrate) to be printed by electrostatic deflection plates, or are allowed to continue on undeflected to a collection gutter for re-use. The more highly charged droplets are deflected to a greater degree.
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 the ink drops to be thrown a long distance to the target. Another advantage is freedom from nozzle clogging as the jet is always in use. Volatile solvents (ketones and alcohols) can therefore be used, giving the ability of the ink to "bite" into the substrate and dry quickly. The fluid handling systems can be quite complex. Droplets are generated at ~ 64 to 165 kHz; only a few percent of the droplets are used to print; the rest are recycled.
[edit] Inkjet Inks
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.
Small inkjet printers as being used in offices or at home, all use aqueous inks based on a mixture of water, glycol and some 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 being 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 in use currently. Most of these inks require piezo inkjet heads:
In solvent inks, VOCs are the main ingredient. Advantage of these inks is that they are very inexpensive and enable printing on uncoated vinyl substrates, which are used a lot in advertising for billboards and fleet graphics.
UV-curable inks consist mainly of acrylic monomers with an initiator package. After printing, the ink has to be 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 printed on a wide range of uncoated substrates and make a very robust image. Disadvantages is 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 contain special sublimation dyes and are used to print directly or indirectly on fabrics that consist of a high percentage of polyester fibres. In a heating step the dyes sublimate into the fibers and create an image with strong color and good durability.
[edit] 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 are typically 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 traditionally 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.
Fixed-head designs normally 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 come up with fixed-head printer based on Thermal Inkjet with its newer printer model such as HP Photosmart 3310.
The disposable head philosophy uses a print head which is part of the replaceable ink cartridge. Every time the printer runs out of ink, the entire cartridge is 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.
[edit] 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.
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.
[edit] 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.
[edit] Disadvantages
Inkjet printers show a number of disadvantages:
- Clogging of the print head, as a result of the printer not being used for a period
- High cost of the ink, sometimes equivalent (in cost/volume terms) to that of first-growth claret
- "Intelligent" ink cartridges, containing a microchip that tells the printer the cartridge is empty even when the user can see that ink remains
- Limited color gamut
- Limited capacity of ink cartridges, requiring frequent replacement
- Limited lifetime of the print, i.e. until visible fading or change in color balance
- Multiple-ink cartridges, e.g. holding the C, M and Y inks, which must be replaced as a whole even when only one color is exhausted.
- More expensive paper required for inkjet printers than for laser printers: see Inkjet paper. Double-sided printing is not usually practical with inkjet printers.
Item 1 appears to be inherent in the design of print heads, because of their very fine ink channels.
Items 2 and 3 have been addressed by third-party ink suppliers, although printer manufacturers do not encourage the use of third-party inks. Some cartridges can be refilled as shown above. Third-party ink cartridges have chips that always read "full", but may contain less ink than the manufacturer's own cartridges and therefore yield no cost saving.[1] Independent testing[2] shows that with these inks the lifetime of the print may be considerably shorter. (See also #Underlying business model.)
Item 4 is also addressed by some third-party ink suppliers. The color gamut for CMYK inkjet printers is broadly similar to that of CMYK offset litho printing, and it is not possible to improve much on the printer manufacturer's ink set. Printers using six or more ink colors can give a substantially improved color gamut, approximating to the Adobe RGB color space. Six-color printers are based on the CcMmYK color model. If more than six colors are used, the additional inks may be a light black, a second full black (allowing the ink to be chosen to match the type of paper, and addressing metamerism issues), and additional colors such as red, green and blue.
Item 5 is an inherent problem when the ink cartridge is inside the printer, usually directly attached to the print head.
Item 6 is a function of the basic type of ink. The earliest inkjet printers intended for home and small office applications used dye-based inks. Even the best of such ink systems cannot compete with the pigment-based inks that are now available on printers designed for demanding users. Lifetime depends on the specific combination of inks and paper.
Items 2–7 are addressed by continuous ink systems (not to be confused with continuous ink jet printers, described above), from third-party suppliers. In these, the ink containers are outside the printer: they can therefore be much larger and can be replaced or topped up individually. Continuous ink systems typically contain pigment inks, and some have been produced for printers that originally only had dye-based inks. The suppliers often provide color profiles for their ink systems when used with specific papers.
Even with the all the cost-reduction options, inkjet printing remains expensive. Unless photo-realistic reproduction is necessary, value-minded consumers may therefore prefer laser printers for medium-to-high volume printing applications.
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.
[edit] Underlying business model
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. Hewlett-Packard, for example were recently able to cover the entire 12-month losses accumulated by their other Printer divisions with the profits made by their consumables division, and have a little left over[citation needed].
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.
[edit] USB cable markup
Another common business model for selling newer inkjet printers involves selling them without the USB 2.0 cable necessary to connect the printer to the computer. Large electronics retailers such as Best Buy and Circuit City carry these cables, but only carry very expensive marked-up models, for example this USB cable for $28 [2]. These vendors advertise such features as "24K gold-plated connectors" for the cables they sell, but equally functional USB cables can be purchased for as little as $2-$3 from lesser-known web-based sellers.
[edit] 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.
[edit] 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.
[edit] Notes
- ^ [1]
- ^ 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.
[edit] See also
- Daisy wheel printer
- Dot matrix printer
- Dye-sublimation printer
- 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
