daisywheel printer

Inkjet printer

[ingk-jet]

Inkjet printers operate by propelling variably-sized droplets of liquid or molten material (ink) onto almost any sized page. 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.

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 the 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.

The emerging ink jet material deposition market also uses ink jet technologies, typically piezoelectric jets, to deposit materials directly on substrates. 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 the head is damaged, it is usually necessary to replace the entire printer.

Technologies

There are three main technologies in use in contemporary inkjet printers: thermal, piezoelectric, and continuous.

Thermal inkjets

Most consumer inkjet printers (Lexmark, Hewlett-Packard, and Canon) use print cartridges 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 known as aqueous (i.e. water-based inks using pigments or dyes) and the print head is generally cheaper to produce than other inkjet technologies. The principle was discovered by Canon engineer Ichiro Endo in August 1977.

Note that thermal inkjets have no relation to thermal printers, which produce images by heating thermal paper, as seen on older fax machines, cash register, ATM receipt, and lottery ticket printers.

Certain Epson printers use special Durabrite Ultra ink which is a type of thermal ink.

Piezoelectric inkjets

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 piezoelectric material 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 the print heads are 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 devices (medical strip chart recorders) were 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 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 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 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. 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 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 in order to counteract the solvent loss.

Inkjet inks

The basic problem with inkjet inks are the conflicting requirements for a colouring agent that will stay on the surface and rapid dispersement of the carrier fluid.

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, often requiring 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.

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:

  • Solvent inks: the main ingredient of these inks are VOCs. The chief advantage of solvent inks is that they are comparatively inexpensive and enable printing on uncoated vinyl substrates, which are used to produce vehicle graphics, billboards and banners. Disadvantages include the vapour produced by the solvent and the need to dispose of used solvent.
  • 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 they produce a very robust image. Disadvantages are that they are 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

There are two main design philosophies in inkjet head design: fixed-head and disposable head. Each has its own strengths and weaknesses. Most inkjets are used for photo printing.

Fixed head

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, typically requiring no calibration. On the other hand, if the head is damaged, it is usually necessary to replace the entire printer. 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 Versamark, Trident, 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.

Disposable head

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 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 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. Further even when capped 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. Once ink begins to collect and harden drop volume can be affected, drop trajectory can change, or the nozzle can fail to jet ink completely.

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.

Some use a supplemental air-suction pump, utilizing the rubber capping station to suck ink through a severely clogged cartridge. The suction pump mechanism is 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.

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, jamming the printer with sticky slime. Some larger professional printers using solvent inks may employ a replaceable plastic receptacle to contain waste ink and solvent which needs to be emptied and/or replaced when full.

The type of ink used in the printer can also 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.

The frequent cleaning conducted by 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 pattern on the page. Methods are known for re-routing printing information from a clogged nozzle to a working nozzle.

Inkjet advantages

Compared to earlier consumer-oriented colour 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 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).

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.

Inkjet disadvantages

Inkjet printers may have a number of disadvantages:

  1. 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--or $8000 per gallon.) According to the BBC (2003), "The cost of ink has been the subject of an Office of Fair Trading investigation. [Which? magazine] has accused manufacturers of a lack of transparency about the price of ink and called for an industry standard for measuring ink cartridge performance" .
  2. 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 some inkjet printers will refuse to print with a cartridge that declares itself empty, in order to prevent consumers from refilling cartridges. Thus, Epson embeds a chip which prevents from printing when the chip claims the cartridge is empty, although a Which? researcher who over-rode the system found that in one case he could print up to 38% more good quality pages, even though the chip stated that the cartridge was empty .
  3. The lifetime of inkjet prints produced by inkjets using aqueous inks is limited; they will eventually fade and the color balance may change. On the other hand, prints produced from solvent-based inkjets may last several years before fading, even in direct sunlight, and so-called "archival inks" have been produced for use in aqueous-based machines which offer extended life.
  4. Because the ink used in most consumer 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.
  5. The very narrow inkjet nozzles are prone to clogging with dried ink. The ink consumed 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 total ink installed in the machine.

These disadvantages have been addressed in a variety of ways:

  1. 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.
  2. 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.
  3. 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 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 manufacturers' inks, cause leaks, and produce inferior-quality output (e.g. of incorrect color gamut). Consumer Reports has noted that 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 3rd party inks’ material compatibility is likely to be significantly less.

Some inkjet anufacturers 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.

Overall expense

Even with many available options for cost-reduction, inkjet printing using desktop printers is costly over time due to expensive replacement ink cartridges with much lower capacity than laser-printer cartridges. Unless photo-realistic reproduction is necessary, value-minded consumers often prefer laser printers for medium- to high-volume printing applications.

Continuous ink system

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. Some inkjet printers enforce this product tying using microchips in the cartridges to prevent the use of third-party or refilled ink cartridges. The microchips can function by storing an amount of ink remaining in the cartridge, which is updated as printing is conducted. Expiration dates for the ink may also be used. Even if the cartridge is refilled, the microchip will indicate to the printer that the cartridge is depleted. For some printers, special circuit flashers are available that reset the quantity of remaining ink to the maximum. Some manufacturers have been accused of indicating that a cartridge is depleted while a substantial amount of ink remains in the cartridge.

Alternatives for consumers are cheaper copies of cartridges, produced by third parties, and refilling cartridges, using refill kits. Due to the large differences in price caused by OEM markups, there are many companies specializing in alternative ink cartridges. Most printer manufacturers discourage refilling disposable cartridges or using aftermarket copy cartridges because of the loss in revenue. Using incorrect inks may also 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 even cause damage to the printhead.

In Lexmark Int’l, Inc. v. Static Control Components, Inc., 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. 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.

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.

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, but 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 new T-series (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.

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 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.

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 m. 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: Gandinnovations, LexJet, Inca, Durst, Océ, NUR (now part of Hewlett-Packard), Lüscher, VUTEk, Zünd, Scitex Vision (now part of Hewlett-Packard), Mutoh, Mimaki, Roland DGA, Seiko I Infotech, Leggett and Platt, Agfa, Raster Printers, DGI and MacDermid ColorSpan (now part of Hewlett-Packard).

Inkjet printing of functional materials

  • Three-dimensional printing constructs a prototype by printing cross-sections on top of one another.
  • U.S. Patent 6,319,530 describes a "Method of photocopying an image onto an edible web for decorating iced baked goods". In other words, this invention enables one to inkjet print a food-grade color photograph on a birthday cake's surface. Many bakeries now carry Print-Ons brand decorations, which are printable using edible inks MEMS.
  • Inkjet printers are used to form conductive traces for circuits, and color filters in LCD and plasma displays.

Inkjet trade names

Images produced on Inkjet printers are sometime sold under other names since the inkjet's connection with "digital", "computers", and everyday printing have negative connotations. These trade names or coined names are usually used in the fine arts reproduction field. They include:

References

See also

External links

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