Laser printer

Laser printer

Overview

A laser printer is a common type of computer printer
Computer printer
In computing, a printer is a peripheral which produces a text or graphics of documents stored in electronic form, usually on physical print media such as paper or transparencies. Many printers are primarily used as local peripherals, and are attached by a printer cable or, in most new printers, a...

 that rapidly produces high quality text and graphics on plain paper
Special fine paper
Special fine paper is a classification of paper used for copying and digital printing.- Copy paper :Copy paper is used for copying and laser printers. The basis weight is 70-90 g/m² and ISO brightness 80-96%. It is made of 90–100% virgin chemical pulp or 100% deinked pulp with total pigment content...

. As with digital photocopier
Photocopier
A photocopier is a machine that makes paper copies of documents and other visual images quickly and cheaply. Most current photocopiers use a technology called xerography, a dry process using heat...

s and multifunction printer
Multifunction printer
An MFP , multifunctional, all-in-one , or Multifunction Device , is an office machine which incorporates the functionality of multiple devices in one, so as to have a smaller footprint in a home or small business setting , or to provide centralized document...

s (MFPs), laser printers employ a xerographic
Xerography
Xerography is a dry photocopying technique invented by Chester Carlson in 1938, for which he was awarded on October 6, 1942. Carlson originally called his invention electrophotography...

 printing process, but differ from analog photocopiers in that the image is produced by the direct scanning of a laser
Laser
A laser is a device that emits light through a process of optical amplification based on the stimulated emission of photons. The term "laser" originated as an acronym for Light Amplification by Stimulated Emission of Radiation...

 beam across the printer's photoreceptor.

A laser beam projects an image of the page to be printed onto an electrically charged rotating drum coated with selenium
Selenium
Selenium is a chemical element with atomic number 34, chemical symbol Se, and an atomic mass of 78.96. It is a nonmetal, whose properties are intermediate between those of adjacent chalcogen elements sulfur and tellurium...

 or, more common in modern printers, organic photoconductors.
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Encyclopedia

A laser printer is a common type of computer printer
Computer printer
In computing, a printer is a peripheral which produces a text or graphics of documents stored in electronic form, usually on physical print media such as paper or transparencies. Many printers are primarily used as local peripherals, and are attached by a printer cable or, in most new printers, a...

 that rapidly produces high quality text and graphics on plain paper
Special fine paper
Special fine paper is a classification of paper used for copying and digital printing.- Copy paper :Copy paper is used for copying and laser printers. The basis weight is 70-90 g/m² and ISO brightness 80-96%. It is made of 90–100% virgin chemical pulp or 100% deinked pulp with total pigment content...

. As with digital photocopier
Photocopier
A photocopier is a machine that makes paper copies of documents and other visual images quickly and cheaply. Most current photocopiers use a technology called xerography, a dry process using heat...

s and multifunction printer
Multifunction printer
An MFP , multifunctional, all-in-one , or Multifunction Device , is an office machine which incorporates the functionality of multiple devices in one, so as to have a smaller footprint in a home or small business setting , or to provide centralized document...

s (MFPs), laser printers employ a xerographic
Xerography
Xerography is a dry photocopying technique invented by Chester Carlson in 1938, for which he was awarded on October 6, 1942. Carlson originally called his invention electrophotography...

 printing process, but differ from analog photocopiers in that the image is produced by the direct scanning of a laser
Laser
A laser is a device that emits light through a process of optical amplification based on the stimulated emission of photons. The term "laser" originated as an acronym for Light Amplification by Stimulated Emission of Radiation...

 beam across the printer's photoreceptor.

Overview


A laser beam projects an image of the page to be printed onto an electrically charged rotating drum coated with selenium
Selenium
Selenium is a chemical element with atomic number 34, chemical symbol Se, and an atomic mass of 78.96. It is a nonmetal, whose properties are intermediate between those of adjacent chalcogen elements sulfur and tellurium...

 or, more common in modern printers, organic photoconductors. Photoconductivity
Photoconductivity
Photoconductivity is an optical and electrical phenomenon in which a material becomes more electrically conductive due to the absorption of electromagnetic radiation such as visible light, ultraviolet light, infrared light, or gamma radiation....

 allows charge to leak away from the areas exposed to light. Dry ink (toner
Toner
Toner is a powder used in laser printers and photocopiers to form the printed text and images on the paper. In its early form it was simply carbon powder. Then, to improve the quality of the printout, the carbon was melt-mixed with a polymer...

) particles are then electrostatically picked up by the drum's charged areas, which have not been exposed to light. The drum then prints the image onto paper by direct contact and heat, which fuses the ink to the paper.

Unlike impact printers, 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 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
Lithography is a method for printing using a stone or a metal plate with a completely smooth surface...

 in some commercial applications.

The cost of this technology depends on a combination of factors, including the cost of paper, toner, and infrequent drum replacement, as well as the replacement of other consumables 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.

A duplexing printer
Duplex printing
Duplex printing is a feature of computer printers and multifunction printers that allows the automatic printing of a sheet of paper on both sides...

 (one that prints on both sides of the paper) can halve paper costs and reduce filing volumes. 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. Duplexing can also give a slower page-printing speed, because of the longer paper path.

In comparison with the laser printer, most inkjet printer
Inkjet printer
An inkjet printer is a type of computer printer that creates a digital image by propelling droplets of ink onto paper. Inkjet printers are the most commonly used type of printer and range from small inexpensive consumer models to very large professional machines that can cost up to thousands of...

s and dot-matrix printers simply take an incoming stream of data and directly imprint it in a slow lurching process that may include pauses as the printer waits for more data. A laser printer is unable to work this way because such a large amount of data needs to output to the printing device in a rapid, continuous process. The printer cannot stop the mechanism precisely enough to wait until more data arrives, without creating a visible gap or misalignment of the dots on the printed page.

History



The laser printer was invented at Xerox
Xerox
Xerox Corporation is an American multinational document management corporation that produced and sells a range of color and black-and-white printers, multifunction systems, photo copiers, digital production printing presses, and related consulting services and supplies...

 in 1969 by researcher Gary Starkweather
Gary Starkweather
Gary K. Starkweather is an American engineer and inventor most notable for the invention of the laser printer and color management.In 1969, Starkweather invented the laser printer at Xerox's Webster research center...

, who had an improved printer working by 1971 and incorporated into a fully functional networked printer system by about a year later. The prototype was built by modifying an existing xerographic copier
Xerography
Xerography is a dry photocopying technique invented by Chester Carlson in 1938, for which he was awarded on October 6, 1942. Carlson originally called his invention electrophotography...

. Starkweather disabled the imaging system and created a spinning drum with 8 mirrored sides, with a laser focused on the drum. Light from the laser would bounce off the spinning drum, sweeping across the page as it traveled through the copier. The hardware was completed in just a week or two, but the computer interface and software took almost 3 months to complete.

The first commercial implementation of a laser printer was the IBM
IBM
International Business Machines Corporation or IBM is an American multinational technology and consulting corporation headquartered in Armonk, New York, United States. IBM manufactures and sells computer hardware and software, and it offers infrastructure, hosting and consulting services in areas...

 model 3800 in 1975, used for high-volume printing of documents such as invoices and mailing labels. It is often cited as "taking up a whole room," implying that it was a primitive version of the later familiar device used with a personal computer
Personal computer
A personal computer is any general-purpose computer whose size, capabilities, and original sales price make it useful for individuals, and which is intended to be operated directly by an end-user with no intervening computer operator...

. While large, it was designed for an entirely different purpose. Many 3800s are still in use.
The first laser printer designed for use in an office setting was released with the Xerox Star
Xerox Star
The Star workstation, officially known as the Xerox 8010 Information System, was introduced by Xerox Corporation in 1981. It was the first commercial system to incorporate various technologies that today have become commonplace in personal computers, including a bitmapped display, a window-based...

 8010 in 1981. Although it was innovative, the Star was an expensive ($17,000) system that was purchased by only a relatively small number of businesses and institutions. After personal computer
Personal computer
A personal computer is any general-purpose computer whose size, capabilities, and original sales price make it useful for individuals, and which is intended to be operated directly by an end-user with no intervening computer operator...

s became more widespread, the first laser printer intended for a mass market was the HP
Hewlett-Packard
Hewlett-Packard Company or HP is an American multinational information technology corporation headquartered in Palo Alto, California, USA that provides products, technologies, softwares, solutions and services to consumers, small- and medium-sized businesses and large enterprises, including...

 LaserJet
LaserJet
LaserJet as a brand name identifies the line of dry electrophotographic laser printers marketed by the American computer-company Hewlett-Packard . The HP LaserJet was the world's first desktop laser printer.-Technology:...

 8ppm, released in 1984, using a Canon engine controlled by HP software. The HP LaserJet printer was quickly followed by laser printers from Brother Industries
Brother Industries
is a diversified Japanese company that produces or imports a wide variety of products including printers, sewing machines, large machine tools, label printers, and typewriters, fax machines, and other computer-related electronics. It markets its multifunction printers as Multi-Function Centers...

, IBM
IBM
International Business Machines Corporation or IBM is an American multinational technology and consulting corporation headquartered in Armonk, New York, United States. IBM manufactures and sells computer hardware and software, and it offers infrastructure, hosting and consulting services in areas...

, Apple
LaserWriter
The LaserWriter was a laser printer with built-in PostScript interpreter introduced by Apple in 1985. It was one of the first laser printers available to the mass market...

 and others. First-generation machines had large photosensitive drums, of circumference greater than the paper length. Once faster-recovery coatings were developed, the drums could touch the paper multiple times in a pass, and could therefore be smaller in diameter.

Laser printers brought fast, high quality text printing with multiple fonts on a page to the business and consumer markets. No other commonly available printer could offer this combination of features.

As with most electronic devices, the cost of laser printers has fallen markedly over the years. In 1984, the HP LaserJet sold for $3500, had trouble with even small, low resolution graphics, and weighed 71 pounds (32 kg). Low end monochrome laser printers often sell for less than $75 as of 2008. These printers tend to lack onboard processing and rely on the host computer to generate a raster image
Raster graphics
In computer graphics, a raster graphics image, or bitmap, is a data structure representing a generally rectangular grid of pixels, or points of color, viewable via a monitor, paper, or other display medium...

 (see Winprinter), but still will outperform the LaserJet Classic in nearly all situations.

How it works


There are typically seven steps involved in the laser printing process:

Raster image processing


Each horizontal strip of dots across the page is known as a raster
Raster scan
A raster scan, or raster scanning, is the rectangular pattern of image capture and reconstruction in television. By analogy, the term is used for raster graphics, the pattern of image storage and transmission used in most computer bitmap image systems...

 line or scan line
Scan line
A scan line or scanline is one line, or row, in a raster scanning pattern, such as a line of video on a cathode ray tube display of a television set or computer monitor....

. Creating the image to be printed is done by a Raster Image Processor
Raster image processor
A raster image processor is a component used in a printing system which produces a raster image also known as a bitmap. The bitmap is then sent to a printing device for output. The input may be a page description in a high-level page description language such as PostScript, Portable Document...

 (RIP), typically built into the laser printer. The source material may be encoded in any number of special page description languages such as Adobe PostScript (PS, BR-Script
BR-Script
BR-Script is the PostScript implementation of Brother Industries.- PostScript 3 compatible printers :DCP-8060 BR-Script 3 HP PCL6DCP-8065DN BR-Script 3 HP PCL6DCP-8080DN BR-Script 3 HP PCL6 IBM PPR Epson FX...

), HP Printer Command Language
Printer Command Language
Printer Command Language, more commonly referred to as PCL, is a page description language developed by Hewlett-Packard as a printer protocol and has become a de facto industry standard. Originally developed for early inkjet printers in 1984, PCL has been released in varying levels for thermal,...

 (PCL), or Microsoft XML Page Specification
XPS
XPS may refer to:* X-ray photoelectron spectroscopy XPS, also known as ESCA* Exopolysaccharide, or extracellular polymeric substance, a sliming substance secreted by bacteria and responsible for cells adhesion onto surfaces and in biofilms...

 (XPS), as well as unformatted text-only data. The RIP uses the page description language to generate a bitmap of the final page in the raster memory.

For fully graphical output using a page description language, a minimum of 1 megabyte of memory is needed to store an entire monochrome letter/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 0.25 inches (6.4 mm) margins, reducing the printable area to 8.0 × 10.5 inches (266.7 mm), or 84 square inches. 84 sq/in × 90,000 dots per sq/in = 7,560,000 dots. Meanwhile 1 megabyte = 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 CYMK 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 page at 300 dpi.

Memory requirements increase with the square of the dpi, so 600 dpi requires a minimum of 4 megabytes for monochrome, and 16 megabytes for color at 600 dpi.
Printers capable of tabloid and larger size may include memory expansion slots.

Charging



In older printers, a corona wire
Corona discharge
In electricity, a corona discharge is an electrical discharge brought on by the ionization of a fluid surrounding a conductor that is electrically energized...

 positioned parallel to the drum, or in more recent printers, a primary charge roller, projects an electrostatic charge onto the photoreceptor (otherwise named the photo conductor 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
Alternating current
In alternating current the movement of electric charge periodically reverses direction. In direct current , the flow of electric charge is only in one direction....

 bias is applied to the primary charge roller to remove any residual charges left by previous images. The roller will also apply a DC
Direct current
Direct current is the unidirectional flow of electric charge. Direct current is produced by such sources as batteries, thermocouples, solar cells, and commutator-type electric machines of the dynamo type. Direct current may flow in a conductor such as a wire, but can also flow through...

 bias on the drum surface to ensure a uniform negative potential.

Numerous patents describe the photosensitive drum coating as a silicon
Silicon
Silicon is a chemical element with the symbol Si and atomic number 14. A tetravalent metalloid, it is less reactive than its chemical analog carbon, the nonmetal directly above it in the periodic table, but more reactive than germanium, the metalloid directly below it in the table...

 sandwich
Sandwich
A sandwich is a food item, typically consisting of two or more slices of :bread with one or more fillings between them, or one slice of bread with a topping or toppings, commonly called an open sandwich. Sandwiches are a widely popular type of lunch food, typically taken to work or school, or...

 with a photocharging layer, a charge leakage barrier layer, as well as a surface layer. One version uses amorphous silicon containing hydrogen as the light receiving layer, Boron nitride
Boron nitride
Boron nitride is a chemical compound with chemical formula BN, consisting of equal numbers of boron and nitrogen atoms. BN is isoelectronic to a similarly structured carbon lattice and thus exists in various crystalline forms...

 as a charge leakage barrier layer, as well as a surface layer of doped silicon
Doping (semiconductor)
In semiconductor production, doping intentionally introduces impurities into an extremely pure semiconductor for the purpose of modulating its electrical properties. The impurities are dependent upon the type of semiconductor. Lightly and moderately doped semiconductors are referred to as extrinsic...

, notably silicon with oxygen or nitrogen which at sufficient concentration resembles machining silicon nitride
Silicon nitride
Silicon nitride is a chemical compound of silicon and nitrogen. If powdered silicon is heated between 1300° and 1400°C in an atmosphere of nitrogen, trisilicon tetranitride, Si3N4, is formed. The silicon sample weight increases progressively due to the chemical combination of silicon and nitrogen...


Exposing



The laser is aimed at a rotating polygonal mirror, which directs the laser beam through a system of lenses and mirrors onto the photoreceptor. The cylinder continues to rotate during the sweep and the angle of sweep compensates for this motion. The stream of rasterized data held in memory turns the laser on and off to form the dots on the cylinder. Lasers are used because they generate a narrow beam over great distances. The laser beam neutralizes (or reverses) the charge on the black parts of the image, leaving a static electric
Static electricity
Static electricity refers to the build-up of electric charge on the surface of objects. The static charges remain on an object until they either bleed off to ground or are quickly neutralized by a discharge. Static electricity can be contrasted with current electricity, which can be delivered...

 negative image on the photoreceptor surface to lift the toner
Toner
Toner is a powder used in laser printers and photocopiers to form the printed text and images on the paper. In its early form it was simply carbon powder. Then, to improve the quality of the printout, the carbon was melt-mixed with a polymer...

 particles.

Some non-laser printers expose by an array of light emitting diodes spanning the width of the page, rather than by a laser ("exposing" is also known as "writing" in some documentation).

Developing


The surface with the latent image is exposed to toner
Toner
Toner is a powder used in laser printers and photocopiers to form the printed text and images on the paper. In its early form it was simply carbon powder. Then, to improve the quality of the printout, the carbon was melt-mixed with a polymer...

, fine particles of dry plastic powder mixed with carbon black
Carbon black
Carbon black is a material produced by the incomplete combustion of heavy petroleum products such as FCC tar, coal tar, ethylene cracking tar, and a small amount from vegetable oil. Carbon black is a form of amorphous carbon that has a high surface-area-to-volume ratio, although its...

 or coloring agents. The charged toner particles are given a negative charge, and are electrostatically attracted to the photoreceptor's latent image, the areas touched by the laser. Because like charges repel, the negatively charged toner will not touch the drum where the negative charge remains.

Transferring


The photoreceptor is pressed or rolled over paper, transferring the image. Higher-end machines use a positively charged transfer roller on the back side of the paper to pull the toner from the photoreceptor to the paper.

Fusing



The paper passes through rollers in the fuser assembly where heat (up to 200 Celsius) and pressure bond the plastic powder to the paper.

One roller is usually a hollow tube (heat roller) and the other is a rubber backing roller (pressure roller). A radiant heat lamp is suspended in the center of the hollow tube, and its infrared 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 fuser roller, so there is less mass to be heated and the fuser can more quickly reach operating temperature.
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 a very short contact time

Cleaning



When the print is complete, an electrically neutral soft plastic blade cleans any excess toner from the photoreceptor and deposits it into a waste reservoir, and a discharge lamp removes the remaining charge from the photoreceptor.

Toner may occasionally be left on the photoreceptor when unexpected events such as a paper jam occur. The toner is on the photoconductor ready to apply, but the operation failed before it could be applied. The toner must be wiped off and the process restarted.

Multiple steps occurring at once


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. Some "laser
Laser
A laser is a device that emits light through a process of optical amplification based on the stimulated emission of photons. The term "laser" originated as an acronym for Light Amplification by Stimulated Emission of Radiation...

" printers actually use a linear array of light-emitting diode
Light-emitting diode
A light-emitting diode is a semiconductor light source. LEDs are used as indicator lamps in many devices and are increasingly used for other lighting...

s to "write" the light on the drum (see LED printer
LED printer
An LED printer is a type of computer printer. LED technology uses a light-emitting diode array as a light source in the printhead. The LED bar pulse-flashes across the entire page width and creates the image on the print drum or belt as it moves past....

). The toner is based on either wax
Wax
thumb|right|[[Cetyl palmitate]], a typical wax ester.Wax refers to a class of chemical compounds that are plastic near ambient temperatures. Characteristically, they melt above 45 °C to give a low viscosity liquid. Waxes are insoluble in water but soluble in organic, nonpolar solvents...

 or plastic
Plastic
A plastic material is any of a wide range of synthetic or semi-synthetic organic solids used in the manufacture of industrial products. Plastics are typically polymers of high molecular mass, and may contain other substances to improve performance and/or reduce production costs...

, 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. The Warm Up process that a laser printer goes through when power is initially applied to the printer consists mainly of heating the fuser element.

Color laser printers



Color laser printers use colored toner
Toner
Toner is a powder used in laser printers and photocopiers to form the printed text and images on the paper. In its early form it was simply carbon powder. Then, to improve the quality of the printout, the carbon was melt-mixed with a polymer...

 (dry ink), typically cyan
Cyan
Cyan from , transliterated: kýanos, meaning "dark blue substance") may be used as the name of any of a number of colors in the blue/green range of the spectrum. In reference to the visible spectrum cyan is used to refer to the color obtained by mixing equal amounts of green and blue light or the...

, magenta
Magenta
Magenta is a color evoked by light stronger in blue and red wavelengths than in yellowish-green wavelengths . In light experiments, magenta can be produced by removing the lime-green wavelengths from white light...

, yellow
Yellow
Yellow is the color evoked by light that stimulates both the L and M cone cells of the retina about equally, with no significant stimulation of the S cone cells. Light with a wavelength of 570–590 nm is yellow, as is light with a suitable mixture of red and green...

, and black
Black
Black is the color of objects that do not emit or reflect light in any part of the visible spectrum; they absorb all such frequencies of light...

 (CMYK).

While monochrome printers only use one laser scanner assembly, color printers often have two or more scanner assemblies.

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 production cost than monochrome printers.

DPI Resolution

  • 1200 DPI
    Dots per inch
    Dots per inch is a measure of spatial printing or video dot density, in particular the number of individual dots that can be placed in a line within the span of 1 inch . The DPI value tends to correlate with image resolution, but is related only indirectly.- DPI measurement in monitor...

     printers were commonly available during 2008.
  • 2400 DPI electrophotographic printing plate makers, essentially laser printers that print on plastic sheets, are also available.

Laser printer maintenance


Most consumer and small business laser printers use a toner cartridge that combines the photoreceptor (sometimes called "photo conductor unit" or "imaging drum") with the toner supply bin, the waste toner hopper, and various wiper blades. When the toner supply is consumed, replacing the toner cartridge automatically replaces the imaging drum, waste toner hopper, and wiper blades.

Some laser printers maintain a page count of the number of pages printed since last maintenance. On these models, a reminder message will appear informing the user it is nearing time to replace standard maintenance parts. On other models, no page count is kept or no reminder is displayed, so the user must keep track of pages printed manually or watch for warning signs like paper feed problems and print defects.

Some color laser printers, notably some Lexmark models run "calibration" cycles even when no printing has occurred for weeks. These are widely reported to waste a significant amount of toner from each reservoir, in addition to consuming electricity. This has a significant impact on printing economy, especially in low-volume applications. On some models these calibration cycles can be disabled via a menu choice, for others the printer must be unplugged to avoid this waste. Printers that have this issue have a replaceable "waste toner bin", which is another periodic operating expense.

Manufacturers usually provide life expectancy charts for common printer parts and consumables. Manufacturers rate life expectancy for their printer parts in terms of "expected page-production life" rather than in units of time.

Consumables and maintenance parts for business-class printers will generally be rated for a higher page-production expectancy than parts for personal printers. In particular, toner cartridges and fusers usually have a higher page production expectancy in business-class printers than personal-class printers. Color laser printers can require more maintenance and parts replacement than monochrome laser printers since they contain more imaging components.

For rollers and assemblies involved in the paper pickup path and paper feed path, typical maintenance is to vacuum toner and dust from the mechanisms, and replace, clean, or restore the rubber paper-handling rollers. Most pickup, feed, and separation rollers have a rubber coating which eventually suffers wear and becomes covered with slippery paper dust. In cases where replacement rollers are discontinued or unavailable, rubber rollers can be cleaned safely with a damp lint-free rag. Commercial chemical solutions are also available which may help temporarily restore the traction of the rubber.

The fusing assembly (also called a "fuser") is generally considered a replaceable consumable part on laser printers. The fusing assembly is responsible for melting and bonding the toner to the paper. There are many possible defects for fusing assemblies: defects include worn plastic drive gears, electronic failure of heating components, torn fixing film sleeves, worn pressure rollers, toner buildup on heating rollers and pressure rollers, worn or scratched pressure rollers, and damaged paper sensors.

Some manufacturers offer preventative maintenance kits specific to each printer model; such kits generally include a fuser and may also include pickup rollers, feed rollers, transfer rollers, charge rollers, and separation pads.

Steganographic anti-counterfeiting ("secret") marks




Many modern color laser printers mark printouts by a nearly invisible dot raster
Raster graphics
In computer graphics, a raster graphics image, or bitmap, is a data structure representing a generally rectangular grid of pixels, or points of color, viewable via a monitor, paper, or other display medium...

, for the purpose of identification.

The dots are yellow and about 0.1 mm in size, with a raster of about 1 mm. This is purportedly the result of a deal between the U.S. government
Federal government of the United States
The federal government of the United States is the national government of the constitutional republic of fifty states that is the United States of America. The federal government comprises three distinct branches of government: a legislative, an executive and a judiciary. These branches and...

 and printer manufacturers to help track counterfeiters.

The dots encode data such as printing date, time, and printer serial number in binary-coded decimal
Binary-coded decimal
In computing and electronic systems, binary-coded decimal is a digital encoding method for numbers using decimal notation, with each decimal digit represented by its own binary sequence. In BCD, a numeral is usually represented by four bits which, in general, represent the decimal range 0 through 9...

 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
Electronic Frontier Foundation
The Electronic Frontier Foundation is an international non-profit digital rights advocacy and legal organization based in the United States...

 are concerned about this erosion of the privacy and anonymity of those who print.

Air transport ban


After the October 2010 cargo planes bomb plot, in which shipments of laser printers with explosive-filled toner cartridges were discovered on separate cargo airplanes, the US prohibited pass-through passengers from carrying certain printer cartridges on flights. The US Transportation Security Administration
Transportation Security Administration
The Transportation Security Administration is an agency of the U.S. Department of Homeland Security that exercises authority over the safety and security of the traveling public in the United States....

 said it would ban toner and ink cartridges weighing over 16 ounces (453 grams) from all passenger flights. U.S. Homeland Security Secretary Janet Napolitano
Janet Napolitano
Janet Napolitano is the third and current United States Secretary of Homeland Security, serving in the administration of President Barack Obama. She is the fourth person to hold the position, which was created after the 9/11 terrorist attacks. A member of the Democratic Party, she was the 21st...

 said the ban would apply to both carry-on bags and checked bags on domestic and international flights in-bound to the U.S. PC Magazine
PC Magazine
PC Magazine is a computer magazine published by Ziff Davis Publishing Holdings Inc. A print edition was published from 1982 to January 2009...

opined that the ban would not affect average travelers, whose ink cartridges are generally lighter, but would affect the importing of laser printer supplies, as many laser toner cartridges weigh well in excess of a pound.

Shock hazards


Although modern printers include many safety interlocks and protection circuits, it is possible for a high voltage or a residual voltage to be present on the various rollers, wires, and metal contacts inside a laser printer. Care should be taken to avoid unnecessary contact with these parts to reduce the potential for painful electrical shock.

Toner clean-up


Toner
Toner
Toner is a powder used in laser printers and photocopiers to form the printed text and images on the paper. In its early form it was simply carbon powder. Then, to improve the quality of the printout, the carbon was melt-mixed with a polymer...

 particles are designed 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. Because of this and its small particle size, toner should not be vacuumed with a conventional home vacuum cleaner. Static discharge from charged toner particles can ignite dust in the vacuum cleaner bag or create a small explosion if sufficient toner is airborne. This may damage the vacuum cleaner or start a fire. In addition, 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.

Toner particles melt (or fuse) when warmed. Small toner spills can be wiped up with a cold, damp cloth.

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 or HEPA is a type of air filter. Filters that are awarded the HEPA accolade are used in various locations, whether in medical facilities, automotive vehicles, airplanes, home filters, or wherever very pure air is sought. The filter must satisfy certain standards of...

) filter may be needed for effective cleaning. These are called ESD-safe (Electrostatic Discharge-safe) or toner vacuums. Similar HEPA-filter equipped vacuums should be used for clean-up of larger toner spills.

Toner is easily cleaned from most water-washable clothing. As toner is a wax or plastic powder with a low melting temperature, it must be kept cold during the cleaning process. Washing a toner stained garment in cold water is often successful. Even warm water is likely to result in permanent staining. The washing machine should be filled with cold water before adding the garment. Washing through two cycles improves the chances of success. The first may use hand wash dish detergent, with the second cycle using regular laundry detergent. Residual toner floating in the rinse water of the first cycle will remain in the garment and may cause a permanent graying. A clothes dryer or iron should not be used until it is certain that all the toner has been removed.

Ozone hazards


As a natural part of the printing process, the high voltages inside the printer can produce a corona discharge
Corona discharge
In electricity, a corona discharge is an electrical discharge brought on by the ionization of a fluid surrounding a conductor that is electrically energized...

 that generates a small amount of ionized oxygen and nitrogen, forming ozone
Ozone
Ozone , or trioxygen, is a triatomic molecule, consisting of three oxygen atoms. It is an allotrope of oxygen that is much less stable than the diatomic allotrope...

 and nitrogen oxides. In larger commercial printers and copiers, a carbon filter in the air exhaust stream breaks down these oxides to prevent pollution of the office environment.

However, some ozone escapes the filtering process in commercial printers, and ozone filters are not used in many smaller consumer 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 for creating a health hazard is theoretically possible in extreme cases.

Respiratory health risks


According to a recent study conducted in Queensland, Australia, some printers emit sub-micrometre
Micrometre
A micrometer , is by definition 1×10-6 of a meter .In plain English, it means one-millionth of a meter . Its unit symbol in the International System of Units is μm...

 particles which some suspect may be associated with respiratory diseases. Of 63 printers evaluated in the Queensland University of Technology
Queensland University of Technology
Queensland University of Technology is an Australian university with an applied emphasis in courses and research. Based in Brisbane, it has 40,000 students, including 6,000 international students, over 4,000 staff members, and an annual budget of more than A$750 million.QUT is marketed as "A...

 study, 17 of the strongest emitters were made by Hewlett-Packard
Hewlett-Packard
Hewlett-Packard Company or HP is an American multinational information technology corporation headquartered in Palo Alto, California, USA that provides products, technologies, softwares, solutions and services to consumers, small- and medium-sized businesses and large enterprises, including...

 and one by Toshiba
Toshiba
is a multinational electronics and electrical equipment corporation headquartered in Tokyo, Japan. It is a diversified manufacturer and marketer of electrical products, spanning information & communications equipment and systems, Internet-based solutions and services, electronic components and...

. 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 Queensland University, one printer emitted as many particles as a burning cigarette.
"The health effects from inhaling ultrafine particles
Ultrafine particles
Ultrafine particles are nanoscale, less than 100 nanometres. Regulations do not exist for this size class of ambient air pollution particles, which are far smaller than the regulated PM10 and PM2.5 size classes and are believed to have several more aggressive health implications than those classes...

 depend on particle composition, but the results can range from respiratory irritation to more severe illness such as cardiovascular
Circulatory system
The circulatory system is an organ system that passes nutrients , gases, hormones, blood cells, etc...

 problems or cancer
Cancer
Cancer , known medically as a malignant neoplasm, is a large group of different diseases, all involving unregulated cell growth. In cancer, cells divide and grow uncontrollably, forming malignant tumors, and invade nearby parts of the body. The cancer may also spread to more distant parts of the...

." (Queensland University of Technology).


A 2006 study in Japan found that laser printers increase concentrations of styrene, xylene
Xylene
Xylene encompasses three isomers of dimethylbenzene. The isomers are distinguished by the designations ortho- , meta- , and para- , which specify to which carbon atoms the two methyl groups are attached...

s, and ozone
Ozone
Ozone , or trioxygen, is a triatomic molecule, consisting of three oxygen atoms. It is an allotrope of oxygen that is much less stable than the diatomic allotrope...

, and that ink-jet printers
Inkjet printer
An inkjet printer is a type of computer printer that creates a digital image by propelling droplets of ink onto paper. Inkjet printers are the most commonly used type of printer and range from small inexpensive consumer models to very large professional machines that can cost up to thousands of...

 emitted pentanol.

Muhle et al. (1991) reported that the responses to chronically inhaled copying toner, a plastic dust pigmented with carbon black, titanium dioxide and silica were also similar qualitatively to titanium dioxide and diesel exhaust.

See also


  • Cardboard engineering
    Cardboard engineering
    Cardboard modeling 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...

  • Daisy wheel printer
    Daisy wheel printer
    Daisy wheel printers use an impact printing technology invented in 1969 by David S. Lee at Diablo Data Systems. It uses interchangeable pre-formed type elements, each with typically 96 glyphs, to generate high-quality output comparable to premium typewriters such as the IBM Selectric, but two to...

  • Document automation
    Document automation
    Document automation is the design of systems and workflow that assist in the creation of electronic documents. These include logic based systems that use segments of pre-existing text and/or data to assemble a new document. This process is increasingly used within certain industries to assemble...

  • Dot matrix printer
    Dot matrix printer
    A dot matrix printer or impact matrix printer is a type of computer printer with a print head that runs back and forth, or in an up and down motion, on the page and prints by impact, striking an ink-soaked cloth ribbon against the paper, much like the print mechanism on a typewriter...

  • Dye-sublimation printer
    Dye-sublimation printer
    A dye-sublimation printer is a computer printer which employs a printing process that uses heat to transfer dye onto medium materials such as a plastic card, paper, or fabric. The sublimation name is applied because the dye transitions between the solid and gas states without going through a...

  • Inkjet printer
    Inkjet printer
    An inkjet printer is a type of computer printer that creates a digital image by propelling droplets of ink onto paper. Inkjet printers are the most commonly used type of printer and range from small inexpensive consumer models to very large professional machines that can cost up to thousands of...

  • LED printer
    LED printer
    An LED printer is a type of computer printer. LED technology uses a light-emitting diode array as a light source in the printhead. The LED bar pulse-flashes across the entire page width and creates the image on the print drum or belt as it moves past....

  • Managed Print Services
    Managed Print Services
    Managed Print Services involve managing hardcopy device fleets in a unified fashion...

  • Solid ink
    Solid ink
    Solid ink is a technology used in computer printers and multifunction devices originally created by Tektronix in 1986. After Xerox acquired the Tektronix Color Printing and Imaging Division in 2000, the solid ink technology became part of the Xerox line of office printing and imaging products....

  • Steganography
    Steganography
    Steganography is the art and science of writing hidden messages in such a way that no one, apart from the sender and intended recipient, suspects the existence of the message, a form of security through obscurity...

  • Thermal printer
    Thermal printer
    A thermal printer produces a printed image by selectively heating coated thermochromic paper, or thermal paper as it is commonly known, when the paper passes over the thermal print head. The coating turns black in the areas where it is heated, producing an image...



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