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Laser printing is an
electrostatic Electrostatics is a branch of physics that studies electric charges at rest ( static electricity). Since classical times, it has been known that some materials, such as amber, attract lightweight particles after rubbing. The Greek word for ...
digital printing process. It produces high-quality text and graphics (and moderate-quality photographs) by repeatedly passing a laser beam back and forth over a negatively-charged cylinder called a "drum" to define a differentially-charged image. The drum then selectively collects electrically-charged powdered ink (
toner Toner is a powder mixture used in laser printers and photocopiers to form the printed text and images on paper, in general through a toner cartridge. Mostly granulated plastic, early mixtures only added carbon powder and iron oxide, however, ...
), and transfers the image to paper, which is then heated to permanently fuse the text, imagery, or both, to the paper. As with digital
photocopier A photocopier (also called copier or copy machine, and formerly Xerox machine, the generic trademark) is a machine that makes copies of documents and other visual images onto paper or plastic film quickly and cheaply. Most modern photocopier ...
s, laser printers employ a xerographic printing process. Laser printing differs from traditional xerography as implemented in analog photocopiers in that in the latter, the image is formed by reflecting light off an existing document onto the exposed drum. Invented at
Xerox Xerox Holdings Corporation (; also known simply as Xerox) is an American corporation that sells print and digital document products and services in more than 160 countries. Xerox is headquartered in Norwalk, Connecticut (having moved from St ...
PARC in the 1970s, laser printers were introduced for the office and then home markets in subsequent years by IBM, Canon, Xerox,
Apple An apple is an edible fruit produced by an apple tree (''Malus domestica''). Apple trees are cultivated worldwide and are the most widely grown species in the genus '' Malus''. The tree originated in Central Asia, where its wild ancest ...
,
Hewlett-Packard The Hewlett-Packard Company, commonly shortened to Hewlett-Packard ( ) or HP, was an American multinational information technology company headquartered in Palo Alto, California. HP developed and provided a wide variety of hardware components ...
and many others. Over the decades, quality and speed have increased as prices have decreased, and the once cutting-edge printing devices are now ubiquitous.


History

In the 1960s, the
Xerox Corporation Xerox Holdings Corporation (; also known simply as Xerox) is an American corporation that sells print and digital document products and services in more than 160 countries. Xerox is headquartered in Norwalk, Connecticut (having moved from St ...
held a dominant position in the
photocopier A photocopier (also called copier or copy machine, and formerly Xerox machine, the generic trademark) is a machine that makes copies of documents and other visual images onto paper or plastic film quickly and cheaply. Most modern photocopier ...
market. In 1969,
Gary Starkweather Gary Keith Starkweather (January 9, 1938 – December 26, 2019) was an American engineer and inventor most notable for the invention of the laser printer and color management. Starkweather received a B.S. in physics from Michigan State Universit ...
, who worked in Xerox's product development department, had the idea of using a laser beam to "draw" an image of what was to be copied directly onto the copier drum. After transferring to the recently formed
Palo Alto Research Center PARC (Palo Alto Research Center; formerly Xerox PARC) is a research and development company in Palo Alto, California. Founded in 1969 by Jacob E. "Jack" Goldman, chief scientist of Xerox Corporation, the company was originally a division of Xero ...
(Xerox PARC) in 1971, Starkweather adapted a Xerox 7000 copier to make SLOT (Scanned Laser Output Terminal). In 1972, Starkweather worked with Butler Lampson and Ronald Rider to add a control system and character generator, resulting in a printer called EARS (Ethernet, Alto Research character generator, Scanned laser output terminal)—which later became the
Xerox 9700 The Xerox 9700 was a high-end laser printer manufactured by Xerox Corporation beginning in 1977. Based on the Xerox 9200 copier, the 9700 printed at 300 dots-per-inch on cut-sheet paper at up to two pages per second (pps), one- or two-sided, that ...
laser printer. * 1976: The first commercial implementation of a laser printer, the IBM 3800, was released. It was designed for
data center A data center (American English) or data centre (British English)See spelling differences. is a building, a dedicated space within a building, or a group of buildings used to house computer systems and associated components, such as telecommun ...
s, where it replaced line printers attached to
mainframe computers A mainframe computer, informally called a mainframe or big iron, is a computer used primarily by large organizations for critical applications like bulk data processing for tasks such as censuses, industry and consumer statistics, enterprise ...
. The IBM 3800 was used for high-volume printing on continuous stationery, and achieved speeds of 215 pages per minute (ppm), at a resolution of 240 dots per inch (dpi). Over 8,000 of these printers were sold. * 1977: The
Xerox 9700 The Xerox 9700 was a high-end laser printer manufactured by Xerox Corporation beginning in 1977. Based on the Xerox 9200 copier, the 9700 printed at 300 dots-per-inch on cut-sheet paper at up to two pages per second (pps), one- or two-sided, that ...
was brought to market. Unlike the IBM 3800, the Xerox 9700 was not targeted to replace any particular existing printers; however, it did have limited support for the loading of fonts. The Xerox 9700 excelled at printing high-value documents on cut-sheet paper with varying content (e.g. insurance policies). * 1979: Inspired by the Xerox 9700's commercial success, Japanese camera and optics company Canon developed the Canon LBP-10, a low-cost desktop laser printer. Canon then began work on a much-improved print engine, the Canon CX, resulting in the LBP-CX printer. Having no experience in selling to computer users, Canon sought partnerships with three
Silicon Valley Silicon Valley is a region in Northern California that serves as a global center for high technology and innovation. Located in the southern part of the San Francisco Bay Area, it corresponds roughly to the geographical areas San Mateo Cou ...
companies: Diablo Data Systems (who rejected the offer),
Hewlett-Packard The Hewlett-Packard Company, commonly shortened to Hewlett-Packard ( ) or HP, was an American multinational information technology company headquartered in Palo Alto, California. HP developed and provided a wide variety of hardware components ...
(HP), and
Apple Computer Apple Inc. is an American multinational technology company headquartered in Cupertino, California, United States. Apple is the largest technology company by revenue (totaling in 2021) and, as of June 2022, is the world's biggest company ...
. * 1981: The first small personal computer designed for office use, the Xerox Star 8010, reached market. The system used a desktop metaphor that was unsurpassed in commercial sales, until the
Apple Macintosh The Mac (known as Macintosh until 1999) is a family of personal computers designed and marketed by Apple Inc. Macs are known for their ease of use and minimalist designs, and are popular among students, creative professionals, and software ...
. Although it was innovative, the Star workstation was a prohibitively-expensive () system, affordable only to a fraction of the businesses and institutions at which it was targeted. * 1984: The first laser printer intended for mass-market sales, the
HP LaserJet LaserJet as a brand name identifies the line of laser printers marketed by the American computer company Hewlett-Packard (HP). The HP LaserJet was the first popular desktop laser printer. Canon supplies both mechanisms and cartridges for most HP ...
, was released; it used the Canon CX engine, controlled by HP software. The LaserJet was quickly followed by printers from Brother Industries, IBM, and others. First-generation machines had large photosensitive drums, of circumference greater than the loaded paper's length. Once faster-recovery coatings were developed, the drums could touch the paper multiple times in a pass, and therefore be smaller in diameter. * 1985: Apple introduced the LaserWriter (also based on the Canon CX engine), but used the newly released
PostScript PostScript (PS) is a page description language in the electronic publishing and desktop publishing realm. It is a dynamically typed, concatenative programming language. It was created at Adobe Systems by John Warnock, Charles Geschke, Do ...
page-description language (up until this point, each manufacturer used its own proprietary page-description language, making the supporting software complex and expensive). PostScript allowed the use of text, fonts, graphics, images, and color largely independent of the printer's brand or resolution. : PageMaker, developed by Aldus for the Macintosh and LaserWriter, was also released in 1985 and the combination became very popular for
desktop publishing Desktop publishing (DTP) is the creation of documents using page layout software on a personal ("desktop") computer. It was first used almost exclusively for print publications, but now it also assists in the creation of various forms of online ...
. Laser printers brought exceptionally fast and high-quality text printing in multiple fonts on a page, to the business and home markets. No other commonly-available printer during this era could also offer this combination of features.


Printing process

A laser beam (typically, an aluminium gallium arsenide (AlGaAs)
semiconductor laser The laser diode chip removed and placed on the eye of a needle for scale A laser diode (LD, also injection laser diode or ILD, or diode laser) is a semiconductor device similar to a light-emitting diode in which a diode pumped directly with ...
) that can emit red or infrared light) projects an image of the page to be printed onto an electrically-charged, selenium-coated, rotating, cylindrical drum (or, more commonly in subsequent versions, a drum called an
organic Organic may refer to: * Organic, of or relating to an organism, a living entity * Organic, of or relating to an anatomical organ Chemistry * Organic matter, matter that has come from a once-living organism, is capable of decay or is the product ...
photoconductor made of N-vinylcarbazole, an organic
monomer In chemistry, a monomer ( ; '' mono-'', "one" + '' -mer'', "part") is a molecule that can react together with other monomer molecules to form a larger polymer chain or three-dimensional network in a process called polymerization. Classification ...
). Photoconductivity allows the charged electrons to fall away from the areas exposed to light. Powdered ink (
toner Toner is a powder mixture used in laser printers and photocopiers to form the printed text and images on paper, in general through a toner cartridge. Mostly granulated plastic, early mixtures only added carbon powder and iron oxide, however, ...
) particles are then electrostatically attracted to the charged areas of the drum that have not been laser-beamed. The drum then transfers the image onto paper which is passed through the machine by direct contact. Finally, the paper is passed onto a finisher, which uses heat to instantly fuse the toner that represents the image onto the paper. There are typically seven steps involved in the process, detailed in the sections below.


Raster image processing

The document to be printed is encoded in a page description language such as PostScript, Printer Command Language (PCL), or
Open XML Paper Specification Open XML Paper Specification (also referred to as OpenXPS) is an open specification for a page description language and a fixed-document format. Microsoft developed it as the XML Paper Specification (XPS). In June 2009, Ecma International adopt ...
(OpenXPS). The
raster image processor A raster image processor (RIP) is a component used in a printing system which produces a raster image also known as a bitmap. Such a bitmap is used by a later stage of the printing system to produce the printed output. The input may be a page d ...
(RIP) converts the page description into a bitmap which is stored in the printer's raster memory. Each horizontal strip of dots across the page is known as a raster line or scan line. Laser printing differs from other printing technologies in that each page is always rendered in a single continuous process without any pausing in the middle, while other technologies like
inkjet Inkjet printing is a type of computer printing that recreates a digital image by propelling droplets of ink onto paper and plastic substrates. Inkjet printers were the most commonly used type of printer in 2008, and range from small inexpens ...
can pause every few lines. To avoid a
buffer underrun In computing, buffer underrun or buffer underflow is a state occurring when a buffer used for communicating between two devices or processes is fed with data at a lower speed than the data is being read from it. The term is distinct from buf ...
(where the laser reaches a point on the page before it has the dots to draw there), a laser printer typically needs enough raster memory to hold the bitmap image of an entire page. Memory requirements increase with the square of the dots per inch, so 600 dpi requires a minimum of 4 megabytes for monochrome, and 16 megabytes for color (still at 600 dpi). For fully graphical output using a page description language, a minimum of 1 megabyte of memory is needed to store an entire monochrome letter- or A4-sized page of dots at 300 dpi. At 300 dpi, there are 90,000 dots per square inch (300 dots per linear inch). A typical 8.5 × 11 sheet of paper has margins, reducing the printable area to , or 84 square inches. 84 sq/in × 90,000 dots per sq/in = 7,560,000 dots. 1
megabyte The megabyte is a multiple of the unit byte for digital information. Its recommended unit symbol is MB. The unit prefix ''mega'' is a multiplier of (106) in the International System of Units (SI). Therefore, one megabyte is one million bytes o ...
= 1,048,576 bytes, or 8,388,608 bits, which is just large enough to hold the entire page at 300 dpi, leaving about 100 kilobytes to spare for use by the raster image processor. In a color printer, each of the four
CMYK The CMYK color model (also known as process color, or four color) is a subtractive color model, based on the CMY color model, used in color printing, and is also used to describe the printing process itself. The abbreviation ''CMYK'' refers ...
toner layers is stored as a separate bitmap, and all four layers are typically preprocessed before printing begins, so a minimum of 4 megabytes is needed for a full-color letter-size or A4-size page at 300 dpi. During the 1980s, memory chips were still very expensive, which is why entry-level laser printers in that era always came with four-digit suggested retail prices in US dollars. Memory prices later decreased significantly, while rapid improvements in the performance of personal computers and peripheral cables enabled the development of low-end laser printers which offload rasterization to the sending PC. For such printers, the operating system's print spooler renders the raw bitmap of each page into the PC's system memory at the target resolution, then sends that bitmap directly to the laser (at the expense of slowing down all other programs on the sending PC). The appearance of so-called "dumb" or "host-based" laser printers from
NEC is a Japanese multinational information technology and electronics corporation, headquartered in Minato, Tokyo. The company was known as the Nippon Electric Company, Limited, before rebranding in 1983 as NEC. It provides IT and network soluti ...
made it possible for the retail cost of low-end 600-dpi laser printers to decrease to as low as US$700 by early 1994 and US$600 by early 1995. 1200 dpi printers have been widely available in the home market since 2008. 2400 dpi electrophotographic printing plate makers, essentially laser printers that print on plastic sheets, are also available.


Charging

In older printers, a corona wire positioned parallel to the drum or, in more recent printers, a primary charge roller, projects an
electrostatic Electrostatics is a branch of physics that studies electric charges at rest ( static electricity). Since classical times, it has been known that some materials, such as amber, attract lightweight particles after rubbing. The Greek word for ...
charge onto the photoreceptor (otherwise named the photoconductor unit), a revolving photosensitive drum or belt, which is capable of holding an electrostatic charge on its surface while it is in the dark. An AC bias voltage is applied to the primary charge roller to remove any residual charges left by previous images. The roller will also apply a DC bias on the drum surface to ensure a uniform negative potential. Numerous patents describe the photosensitive drum coating as a
silicon Silicon is a chemical element with the symbol Si and atomic number 14. It is a hard, brittle crystalline solid with a blue-grey metallic luster, and is a tetravalent metalloid and semiconductor. It is a member of group 14 in the periodic ...
"sandwich" with a photocharging layer, a charge leakage barrier layer, as well as a surface layer. One version uses
amorphous silicon Amorphous silicon (a-Si) is the non-crystalline form of silicon used for solar cells and thin-film transistors in LCDs. Used as semiconductor material for a-Si solar cells, or thin-film silicon solar cells, it is deposited in thin films ont ...
containing
hydrogen Hydrogen is the chemical element with the symbol H and atomic number 1. Hydrogen is the lightest element. At standard conditions hydrogen is a gas of diatomic molecules having the formula . It is colorless, odorless, tasteless, non-to ...
as the light-receiving layer, boron nitride as a charge leakage barrier layer, as well as a surface layer of doped silicon, notably silicon with
oxygen Oxygen is the chemical element with the symbol O and atomic number 8. It is a member of the chalcogen group in the periodic table, a highly reactive nonmetal, and an oxidizing agent that readily forms oxides with most elements ...
or
nitrogen Nitrogen is the chemical element with the symbol N and atomic number 7. Nitrogen is a nonmetal and the lightest member of group 15 of the periodic table, often called the pnictogens. It is a common element in the universe, estimated at se ...
which at sufficient concentration resembles machining silicon nitride.


Exposing

A laser printer uses a laser because lasers are able to form highly-focused, precise, and intense beams of light, especially over the short distances inside of a printer. The laser is aimed at a rotating
polygon In geometry, a polygon () is a plane figure that is described by a finite number of straight line segments connected to form a closed '' polygonal chain'' (or ''polygonal circuit''). The bounded plane region, the bounding circuit, or the two ...
al mirror which directs the light beam through a system of lenses and mirrors onto the photoreceptor drum, writing
pixel In digital imaging, a pixel (abbreviated px), pel, or picture element is the smallest addressable element in a raster image, or the smallest point in an all points addressable display device. In most digital display devices, pixels are the ...
s at rates up to sixty-five million times per second. The drum continues to rotate during the sweep, and the angle of sweep is canted very slightly to compensate for this motion. The stream of rasterized data held in the printer's memory rapidly turns the laser on and off as it sweeps. The laser beam neutralizes (or reverses) the charge on the surface of the drum, leaving a static electric negative image on the drum's surface which will repel the negatively-charged toner particles. The areas on the drum which were struck by the laser, however, momentarily have no charge, and the toner being pressed against the drum by the toner-coated developer roll in the next step moves from the roll's rubber surface to the charged portions of the surface of the drum. Some non-laser printers (
LED printer An LED printer is a type of computer printer similar to a laser printer. Such a printer uses a light-emitting diode (LED) array as a light source in the printhead instead of the laser used in laser printers and, more generally, in the xerograp ...
s) use an array of
light-emitting diode A light-emitting diode (LED) is a semiconductor Electronics, device that Light#Light sources, emits light when Electric current, current flows through it. Electrons in the semiconductor recombine with electron holes, releasing energy i ...
s spanning the width of the page to generate an image, rather than using a laser. "Exposing" is also known as "writing" in some documentation.


Developing

As the drums rotate,
toner Toner is a powder mixture used in laser printers and photocopiers to form the printed text and images on paper, in general through a toner cartridge. Mostly granulated plastic, early mixtures only added carbon powder and iron oxide, however, ...
is continuously applied in a 15-
micron The micrometre ( international spelling as used by the International Bureau of Weights and Measures; SI symbol: μm) or micrometer (American spelling), also commonly known as a micron, is a unit of length in the International System of Un ...
-thick layer to the ''developer roll''. The surface of the photoreceptor with the latent image is exposed to the toner-covered developer roll. Toner consists of fine particles of dry plastic powder mixed with carbon black or coloring agents. The toner particles are given a negative charge inside the toner cartridge, and as they emerge onto the developer drum they are electrostatically attracted to the photoreceptor's latent image (the areas on the surface of the drum which had been struck by the laser). Because negative charges repel each other, the negatively-charged toner particles will not adhere to the drum where the negative charge (imparted previously by the charge roller) remains.


Transferring

A sheet of paper is then rolled under the photoreceptor drum, which has been coated with a pattern of toner particles in the exact places where the laser struck it moments before. The toner particles have a very weak attraction to both the drum and the paper, but the bond to the drum is weaker and the particles transfer once again, this time from the drum's surface to the paper's surface. Some machines also use a positively-charged "transfer roller" on the backside of the paper to help pull the negatively charged toner from the photoreceptor drum to the paper.


Fusing

The paper passes through rollers in the fuser assembly, where temperatures up to and pressure are used to permanently bond the toner to the paper. One roller is usually a hollow tube (heat roller) and the other is a rubber-backed roller (pressure roller). A radiant heat lamp is suspended in the center of the hollow tube, and its
infrared Infrared (IR), sometimes called infrared light, is electromagnetic radiation (EMR) with wavelengths longer than those of Light, visible light. It is therefore invisible to the human eye. IR is generally understood to encompass wavelengths from ...
energy uniformly heats the roller from the inside. For proper bonding of the toner, the fuser roller must be uniformly hot. Some printers use a very thin flexible metal foil roller, so there is less thermal mass to be heated and the fuser can more quickly reach
operating temperature An operating temperature is the allowable temperature range of the local ambient environment at which an electrical or mechanical device operates. The device will operate effectively within a specified temperature range which varies based on the de ...
. If paper moves through the fuser more slowly, there is more roller contact time for the toner to melt, and the fuser can operate at a lower temperature. Smaller, inexpensive laser printers typically print slowly, due to this energy-saving design, compared to large high-speed printers where paper moves more rapidly through a high-temperature fuser with very short contact time.


Cleaning and recharging

As the drum completes a revolution, it is exposed to an electrically-neutral soft plastic blade that cleans any remaining toner from the photoreceptor drum and deposits it into a waste reservoir. A charge roller then re-establishes a uniform negative charge on the surface of the now-clean drum, readying it to be struck again by the laser.


Continuous printing

Once the raster image generation is complete, all steps of the printing process can occur one after the other in rapid succession. This permits the use of a very small and compact unit, where the photoreceptor is charged, rotates a few degrees and is scanned, rotates a few more degrees, and is developed, and so forth. The entire process can be completed before the drum completes one revolution. Different printers implement these steps in distinct ways.
LED printer An LED printer is a type of computer printer similar to a laser printer. Such a printer uses a light-emitting diode (LED) array as a light source in the printhead instead of the laser used in laser printers and, more generally, in the xerograp ...
s use a linear array of
light-emitting diode A light-emitting diode (LED) is a semiconductor Electronics, device that Light#Light sources, emits light when Electric current, current flows through it. Electrons in the semiconductor recombine with electron holes, releasing energy i ...
s to "write" the light on the drum. The toner is based on either wax or plastic, so that when the paper passes through the fuser assembly, the particles of toner melt. The paper may or may not be oppositely-charged. The fuser can be an infrared oven, a heated pressure roller, or (on some very fast, expensive printers) a
xenon flash lamp A flashtube (flashlamp) is an electric arc lamp designed to produce extremely intense, incoherent, full-spectrum white light for a very short time. A flashtube is a glass tube with an electrode at each end and is filled with a gas that, when tr ...
. The warmup process that a laser printer goes through when power is initially applied to the printer consists mainly of heating the fuser element.


Malfunctions

The mechanism inside a laser printer is somewhat delicate and, once damaged, often impossible to repair. The drum, in particular, is a critical component: it must not be left exposed to ambient light for more than a few hours, as light is what causes it to lose its charge and will eventually wear it out. Anything that interferes with the operation of the laser such as a scrap of torn paper may prevent the laser from discharging some portion of the drum, causing those areas to appear as white vertical streaks. If the neutral wiper blade fails to remove residual toner from the drum's surface, that toner may circulate on the drum a second time, causing smears on the printed page with each revolution. If the charge roller becomes damaged or does not have enough power, it may fail to adequately negatively charge the surface of the drum, allowing the drum to pick up excessive toner on the next revolution from the developer roll and causing a repeated but fainter image from the previous revolution to appear down the page. If the toner doctor blade does not ensure that a smooth, even layer of toner is applied to the developer roll, the resulting printout may have white streaks from this in places where the blade has scraped off too much toner. Alternatively, if the blade allows too much toner to remain on the developer roll, the toner particles might come loose as the roll turns, precipitate onto the paper below, and become bonded to the paper during the fusing process. This will result in a general darkening of the printed page in broad vertical stripes with very soft edges. If the fuser roller does not reach a high enough temperature or if the ambient humidity is too high, the toner will not fuse well to the paper and may flake off after printing. If the fuser is too hot, the plastic component of the toner may smear, causing the printed text to look like it is wet or smudged, or may cause the melted toner to soak through the paper to the backside. Different manufacturers claim that their toners are specifically developed for their printers and that other toner formulations may not match the original specifications in terms of either tendency to accept a negative charge, to move to the discharged areas of the photoreceptor drum from the developer roll, to fuse appropriately to the paper, or to come off the drum cleanly in each revolution.


Performance

As with most electronic devices, the cost of laser printers has decreased significantly over the years. In 1984, the HP LaserJet sold for $3500, had trouble with even small, low-resolution graphics, and weighed . By the late 1990s, monochrome laser printers had become inexpensive enough for home-office use, having displaced other printing technologies, although color inkjet printers (see below) still had advantages in photo quality reproduction. , low-end monochrome laser printers can sell for less than $75, and while these printers tend to lack onboard processing and rely on the host computer to generate a raster image, they nonetheless outperform the 1984 LaserJet in nearly all situations. Laser printer speed can vary widely, and depends on many factors, including the graphic intensity of the job being processed. The fastest models can print over 200
monochrome A monochrome or monochromatic image, object or palette is composed of one color (or values of one color). Images using only shades of grey are called grayscale (typically digital) or black-and-white (typically analog). In physics, monochr ...
pages per minute (12,000 pages per hour). The fastest color laser printers can print over 100 pages per minute (6000 pages per hour). Very high-speed laser printers are used for mass mailings of personalized documents, such as credit card or utility bills, and are competing with
lithography Lithography () is a planographic method of printing originally based on the immiscibility of oil and water. The printing is from a stone (lithographic limestone) or a metal plate with a smooth surface. It was invented in 1796 by the German a ...
in some commercial applications. The cost of this technology depends on a combination of factors, including the cost of paper, toner, drum replacement, as well as the replacement of other items such as the fuser assembly and transfer assembly. Often printers with soft plastic drums can have a very high cost of ownership that does not become apparent until the drum requires replacement. Duplex printing (printing on both sides of the paper) can halve paper costs and reduce filing volumes, albeit at a slower page-printing speed because of the longer paper path. Formerly only available on high-end printers, duplexers are now common on mid-range office printers, though not all printers can accommodate a duplexing unit. In a commercial environment such as an office, it is becoming increasingly common for businesses to use external
software Software is a set of computer programs and associated documentation and data. This is in contrast to hardware, from which the system is built and which actually performs the work. At the lowest programming level, executable code consist ...
that increases the performance and efficiency of laser printers in the workplace. The software can be used to set rules dictating how employees interact with printers, such as setting limits on how many pages can be printed per day, limiting usage of color ink, and flagging jobs that appear to be wasteful.


Color laser printers

Color laser printers use colored toner (dry ink), typically
cyan Cyan () is the color between green and blue on the visible spectrum of light. It is evoked by light with a predominant wavelength between 490 and 520 nm, between the wavelengths of green and blue. In the subtractive color system, or CMYK col ...
,
magenta Magenta () is a color that is variously defined as pinkish- purplish- red, reddish-purplish-pink or mauvish-crimson. On color wheels of the RGB (additive) and CMY (subtractive) color models, it is located exactly midway between red and blu ...
,
yellow Yellow is the color between green and orange on the spectrum of light. It is evoked by light with a dominant wavelength of roughly 575585 nm. It is a primary color in subtractive color systems, used in painting or color printing. In th ...
, and
black Black is a color which results from the absence or complete absorption of visible light. It is an achromatic color, without hue, like white and grey. It is often used symbolically or figuratively to represent darkness. Black and white ha ...
(
CMYK The CMYK color model (also known as process color, or four color) is a subtractive color model, based on the CMY color model, used in color printing, and is also used to describe the printing process itself. The abbreviation ''CMYK'' refers ...
). While monochrome printers only use one laser scanner assembly, color printers often have two or more, often one for each of the four colors. Color printing adds complexity to the printing process because very slight misalignments known as registration errors can occur between printing each color, causing unintended color fringing, blurring, or light/dark streaking along the edges of colored regions. To permit a high registration accuracy, some color laser printers use a large rotating belt called a "transfer belt". The transfer belt passes in front of all the toner cartridges and each of the toner layers are precisely applied to the belt. The combined layers are then applied to the paper in a uniform single step. Color printers usually have a higher cost per page than monochrome printers, even if printing monochrome-only pages. Liquid electrophotography (LEP) is a similar process used in HP Indigo presses that uses electrostatically-charged ink instead of toner, and using a heated transfer roller instead of a fuser, that melts the charged ink particles before applying them to the paper.


Color laser transfer printers

Color laser transfer printers are designed to produce transfer media which are transfer sheets designed to be applied by means of a heat press. These transfers are typically used to make custom T-shirts or custom logo products with corporate or team logos on them. 2-part Color laser transfers are part of a two-step process whereby the color laser printers use colored toner (dry ink), typically
cyan Cyan () is the color between green and blue on the visible spectrum of light. It is evoked by light with a predominant wavelength between 490 and 520 nm, between the wavelengths of green and blue. In the subtractive color system, or CMYK col ...
,
magenta Magenta () is a color that is variously defined as pinkish- purplish- red, reddish-purplish-pink or mauvish-crimson. On color wheels of the RGB (additive) and CMY (subtractive) color models, it is located exactly midway between red and blu ...
,
yellow Yellow is the color between green and orange on the spectrum of light. It is evoked by light with a dominant wavelength of roughly 575585 nm. It is a primary color in subtractive color systems, used in painting or color printing. In th ...
, and
black Black is a color which results from the absence or complete absorption of visible light. It is an achromatic color, without hue, like white and grey. It is often used symbolically or figuratively to represent darkness. Black and white ha ...
(
CMYK The CMYK color model (also known as process color, or four color) is a subtractive color model, based on the CMY color model, used in color printing, and is also used to describe the printing process itself. The abbreviation ''CMYK'' refers ...
); however, newer printers designed to print on dark T-shirts utilize a special white toner allowing them to make transfers for dark garments or dark business products. The CMYK color printing process allows for millions of colors to be faithfully represented by the unique imaging process.


Business-model comparison with inkjet printers

Manufacturers use a similar
business model A business model describes how an organization creates, delivers, and captures value,''Business Model Generation'', Alexander Osterwalder, Yves Pigneur, Alan Smith, and 470 practitioners from 45 countries, self-published, 2010 in economic, soci ...
for both low-cost color laser printers and
inkjet printers Inkjet printing is a type of computer printing that recreates a digital image by propelling droplets of ink onto paper and plastic substrates. Inkjet printers were the most commonly used type of printer in 2008, and range from small inexpensi ...
: the printers are sold cheaply while replacement toners and inks are relatively expensive. A color laser printer's average running cost per page is usually slightly less, even though both the laser printer and laser toner cartridge have higher upfront prices, as laser toner cartridges print many more sheets relative to their cost than inkjet cartridges. Inkjet printers are better at printing photographs and color records, and keeping in mind that there are color laser printers, they're more costly. The print quality of color lasers is limited by their resolution (typically 600–1200 dpi) and their use of just four color toners. They often have trouble printing large areas of the same or subtle gradations of color. Inkjet printers designed for printing photos can produce much higher quality color images. An in-depth comparison of inkjet and laser printers suggest that laser printers are the ideal choice for a high quality, volume printer, while inkjet printers tend to focus on large-format printers and household units. Laser printers offer more precise edging and in-depth monochromatic color. In addition, color laser printers are much faster than inkjet printers, although being generally larger and bulkier.


Anti-counterfeiting marks

Many modern color laser printers mark printouts by a nearly invisible dot raster, for the purpose of traceability. The dots are yellow and about in size, with a raster of about . This is purportedly the result of a deal between the
US government The federal government of the United States (U.S. federal government or U.S. government) is the national government of the United States, a federal republic located primarily in North America, composed of 50 states, a city within a feder ...
and printer manufacturers to help track
counterfeiter To counterfeit means to imitate something authentic, with the intent to steal, destroy, or replace the original, for use in illegal transactions, or otherwise to deceive individuals into believing that the fake is of equal or greater value tha ...
s. The dots encode data such as printing date, time, and printer serial number in
binary-coded decimal In computing and electronic systems, binary-coded decimal (BCD) is a class of binary encodings of decimal numbers where each digit is represented by a fixed number of bits, usually four or eight. Sometimes, special bit patterns are used ...
on every sheet of paper printed, which allows pieces of paper to be traced by the manufacturer to identify the place of purchase, and sometimes the buyer. Digital-rights advocacy groups such as the
Electronic Frontier Foundation The Electronic Frontier Foundation (EFF) is an international non-profit digital rights group based in San Francisco, California. The foundation was formed on 10 July 1990 by John Gilmore, John Perry Barlow and Mitch Kapor to promote Internet ...
are concerned about this removal of the privacy and anonymity of those who print.


Smart chips in toner cartridges

Similar to
inkjet printers Inkjet printing is a type of computer printing that recreates a digital image by propelling droplets of ink onto paper and plastic substrates. Inkjet printers were the most commonly used type of printer in 2008, and range from small inexpensi ...
, toner cartridges may contain smart chips that reduce the number of pages that can be printed with it (reducing the amount of usable ink or toner in the cartridge to sometimes only 50%), in an effort to increase sales of the toner cartridges. Besides being more expensive for printer users, this technique also increases waste, and thus increases pressure on the environment. For these toner cartridges (as with inkjet cartridges), reset devices can be used to override the limitation set by the smart chip. Also, for some printers, online walk-throughs have been posted to demonstrate how to use up all the ink in the cartridge. These chips offer no benefit to the end-user—some laser printers used an optical mechanism to assess the amount of remaining toner in the cartridge rather than using a chip to electrically count the number of printed pages, and the chip's only function was as an alternate method to decrease the cartridge's usable life.


Safety hazards, health risks, and precautions


Toner clean-up

Toner Toner is a powder mixture used in laser printers and photocopiers to form the printed text and images on paper, in general through a toner cartridge. Mostly granulated plastic, early mixtures only added carbon powder and iron oxide, however, ...
particles are formulated to have electrostatic properties and can develop static electric charges when they rub against other particles, objects, or the interiors of transport systems and vacuum hoses. Static discharge from charged toner particles can ignite combustible particles in a vacuum cleaner bag or cause a small dust explosion if sufficient toner is airborne. Toner particles are so fine that they are poorly filtered by conventional household vacuum cleaner filter bags and blow through the motor or back into the room. If toner spills into the laser printer, a special type of vacuum cleaner with an electrically conductive hose and a high-efficiency (
HEPA HEPA (, high-efficiency particulate air) filter, also known as high-efficiency particulate absorbing filter and high-efficiency particulate arrestance filter, is an efficiency standard of air filters. Filters meeting the HEPA standard must ...
) filter may be needed for effective cleaning. These specialized tools are called "ESD-safe" (Electrostatic Discharge-safe) or "toner vacuums".


Ozone hazards

As a normal part of the printing process, the high voltages inside the printer can produce a
corona discharge A corona discharge is an electrical discharge caused by the ionization of a fluid such as air surrounding a conductor carrying a high voltage. It represents a local region where the air (or other fluid) has undergone electrical breakdown ...
that generates a small amount of ionized oxygen and nitrogen, which react to form
ozone Ozone (), or trioxygen, is an inorganic molecule with the chemical formula . It is a pale blue gas with a distinctively pungent smell. It is an allotrope of oxygen that is much less stable than the diatomic allotrope , breaking down in the l ...
and nitrogen oxides. In larger commercial printers and copiers, an
activated carbon Activated carbon, also called activated charcoal, is a form of carbon commonly used to filter contaminants from water and air, among many other uses. It is processed (activated) to have small, low-volume pores that increase the surface area availa ...
filter in the air exhaust stream breaks down these noxious gases to prevent pollution of the office environment. However, some ozone escapes the filtering process in commercial printers, and ozone filters are not used at all in most smaller home printers. When a laser printer or copier is operated for a long period of time in a small, poorly-ventilated space, these gases can build up to levels at which the odor of ozone or irritation may be noticed. A potential health hazard is theoretically possible in extreme cases.


Respiratory health risks

According to a 2012 study conducted in Queensland, Australia, some printers emit sub-
micrometer Micrometer can mean: * Micrometer (device), used for accurate measurements by means of a calibrated screw * American spelling of micrometre The micrometre ( international spelling as used by the International Bureau of Weights and Measures; ...
particles which some suspect may be associated with respiratory diseases. Of 63 printers evaluated in the
Queensland University of Technology Queensland University of Technology (QUT) is a public research university located in the urban coastal city of Brisbane, Queensland, Australia. QUT is located on two campuses in the Brisbane area viz. Gardens Point and Kelvin Grove. The unive ...
study, 17 of the strongest emitters were made by HP and one by
Toshiba , commonly known as Toshiba and stylized as TOSHIBA, is a Japanese multinational conglomerate corporation headquartered in Minato, Tokyo, Japan. Its diversified products and services include power, industrial and social infrastructure systems, ...
. The machine population studied, however, was only those machines already in place in the building and was thus biased toward specific manufacturers. The authors noted that particle emissions varied substantially even among the same model of machine. According to Professor Morawska of the Queensland University of Technology, one printer emitted as many particles as a burning cigarette: In December 2011, the Australian government agency Safe Work Australia reviewed existing research and concluded that "no epidemiology studies directly associating laser printer emissions with adverse health outcomes were located" and that several assessments conclude that "risk of direct toxicity and health effects from exposure to laser printer emissions is negligible". The review also observes that, because the emissions have been shown to be volatile or semi-volatile organic compounds, "it would be logical to expect possible health effects to be more related to the chemical nature of the aerosol rather than the physical character of the ‘particulate’ since such emissions are unlikely to be or remain as ‘particulates’ after they come into contact with respiratory tissue". The German Social Accident Insurance has commissioned a human study project to examine the effects on health resulting from exposure to toner dusts and from photocopying and printing cycles. Volunteers (23 control persons, 15 exposed persons and 14 asthmatics) were exposed to laser printer emissions under defined conditions in an exposure chamber. The findings from the study based on a broad spectrum of processes and subjects fail to confirm that exposure to high laser printer emissions initiates a verifiable pathological process resulting in the reported illnesses. A much-discussed proposal for reducing emissions from laser printers is to retrofit them with filters. These are fixed with adhesive tape to the printer's fan vents to reduce particle emissions. However, all printers have a paper output tray, which is an outlet for particle emissions. Paper output trays cannot be provided with filters, so it is impossible to reduce their contribution to overall emissions with retrofit filters.


Air-transport ban

After the 2010 cargo plane bomb plot, in which shipments of laser printers with explosive-filled toner cartridges were discovered on separate cargo airplanes, the US
Transportation Security Administration The Transportation Security Administration (TSA) is an agency of the United States Department of Homeland Security (DHS) that has authority over the security of transportation systems within, and connecting to the United States. It was created ...
prohibited pass-through passengers from carrying toner or ink cartridges weighing over on inbound flights, in both carry-on and checked luggage. ''
PC Magazine ''PC Magazine'' (shortened as ''PCMag'') is an American computer magazine published by Ziff Davis. A print edition was published from 1982 to January 2009. Publication of online editions started in late 1994 and have continued to the presen ...
'' noted that the ban would not impact most travelers, as the majority of cartridges do not exceed the prescribed weight.


See also

*
Cardboard engineering Cardboard modeling or cardboard engineering is a form of modelling with paper, card stock, paperboard, and corrugated fiberboard. The term ''cardboard engineering'' is sometimes used to differentiate from craft of making decorative cards. It is ...
* Daisy wheel printer * Document automation * Dot matrix printer * Dye-sublimation printer * List of printer companies *
Solid ink Solid ink (also referred to as hot melt ink) is a type of ink used in printing. Solid ink is a waxy resin-based polymer that must be melted prior to usage unlike conventional liquid inks. The technology is used most in graphics and large fo ...
*
Thermal printer Thermal printing (or direct thermal printing) is a digital printing process which produces a printed image by passing paper with a thermochromic coating, commonly known as thermal paper, over a print head consisting of tiny electrically heated ...
*
Winprinter The Graphics Device Interface (GDI) is a legacy component of Microsoft Windows responsible for representing graphical objects and transmitting them to output devices such as monitors and printers. Windows apps use Windows API to interact with GD ...


References

{{Lasers Digital press Laser image generation Laser printers Office equipment History of computing hardware American inventions Computer-related introductions in 1975