Inkjet printing
Ink jet printers are the most common type of computer printer; and industry and commerce also use them extensively for special-purpose applications. For example, many ATMs, stock control systems, and cash registers use an inkjet printer.
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, 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.
Technology
Most current inkjets (Epson being a notable exception) 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). When the bubble condenses, surplus ink is sucked back up from the printing surface. The ink's surface tension pumps another charge of ink into the chamber through a narrow channel attached to an ink reservoir. Epson's Micro Piezo technology uses a piezoelectric crystal in each nozzle instead of a heating element. When current is applied, the crystal bends, forcing a droplet of ink from the nozzle.
Older ink jet printers directed ink streams electrostatically or piezoelectrically; ultrasound was used to induce waves in the ink, which then broke into little droplets that would fall on the right place on the page.
The continuous ink jet method is used commercially for marking and coding of products and packages. Richard Sweet, a scientist at Stanford University, invented the technology in the 1960’s. In continuous ink jet technology, a high-pressure pump directs liquid ink from a reservoir through a microscopic nozzle, creating a continuous stream of ink droplets. A piezoelectric crystal causes the stream of liquid to break into droplets at regular intervals. 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 are then directed (deflected) to the receptor material to be printed by electrostatic deflection plates, or are allowed to continue on undeflected to a collection gutter for reuse. 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 ~75 to 125 kHz; only a few percent of the droplets are used to print; the rest are recycled.
Inkjet Inks
The basic problem with inkjet inks is the conflicting requirement for a colorizing agent that will stay on the surface and rapid dispersement of the carrier.
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 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. In fact, disposable heads have proven to be equally good. At present, fixed heads are more likely to be found on industrial high-end printers and large format plotters. Because development of a fixed (or piezo) inkjet head requires a large investment in R&D, there are only very few companies offering them: Xaar, Spectra, Hitachi, Scitex Vision (recently acquired by Hewlett-Packard), Brother, Konica and ToshibaTec (the latter 2 being licensees of Xaar).
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 within reasonable cost limits, 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 sixth 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. Hewlett-Packard is now also experimenting with fixed print heads on many of their upcoming low-volume models.
Advantages
Compared to earlier consumer-oriented printers, ink jets 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 ink jets with photorealistic-quality color printing are widely available.
In comparison to more expensive technologies like thermal wax, dye sublimations, and laser printers, ink jets have the advantage of practically no warm-up time and lower cost per page (except when compared to laser-printer).
Disadvantages
The disadvantages of inkjets include flimsy print heads (prone to clogging) and expensive ink cartridges (sometimes costing US$30 – $40 or more). This typically leads value-minded consumers to consider laser printers for medium-to-high volume printer applications. Alternatively, consumers can save money by using compatible generic cartridges or re-filling kits.
Other disadvantages include ink bleeding, where ink is carried sideways away from the desired location by the capillary effect; the result is a muddy appearance on some types of paper. Most ink jet printer manufacturers also sell special clay-treated paper designed to reduce bleeding, but such paper is expensive and sometimes has a peculiar texture.
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." Also, highlighter markers cannot be used with such documents.
Underlying business model
A common business model for inkjet printers involves selling the actual printer at or even 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 division with the profits made by their consumables division, and have a little left over.
Alternatives for consumers are cheaper copies of cartridges, produced by other companies, and refilling cartridges themselves, for which special refill sets are for sale. As a result of the large differences in pricing due to OEM markups, there are many companies specializing in these types of alternative off-brand 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 tying using microchips in the cartridges to prevent the use of third-party or refilled ink cartridges. In Lexmark v. Static Control, the Supreme Court of the United States 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 there.
Professional inkjet printers
Besides the well known small inkjet printers for home and office, there is a whole market for professional inkjet printers; most of them being for wide format printing. "Wide format" means that there are printers ranging in print width from 24" inch up to 5 meters. The application of most of these printers is for printing advertising graphics; a minor application is printing of designs by architects or engineers.
In terms of units, the major supplier is Hewlett-Packard. They own over 90% 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 new Designjet 4000/4500. Besides this they also have the Designjet 5500, a 6 color printer that is used especially for printing graphics.
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 €. Major applications that these printers are used for, are billboards, point-of-sales displays, truck curtains, exhibition graphics and banners. The major suppliers are: Inca, Durst, Océ, Nur, Wolfenstien,Vutek, Zünd, Scitex Vision, Gandinnovations and Colorspan.
Inkjet inks
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 require often 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 are being used. All these inks require piezo inkjet heads:
In solvent inks, VOC's 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 a high dose of UV-light. Advantage of UV-curable inks is that they dry instantly, can print on a wide range of uncoated substrates and make a very robust image. Disadvantage is that they are more expensive and require expensive curing modules in the printer.
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 a very durable image with a strong color and good durability.
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.
External links
- Ask Jack - ink replacement. - The Guardian.
- Readers report their experience of using ink refills and generic cartridges in an effort to cut printing costs.