Úvod:
Elektrofotografii objevil roku 1938 Chester Carlson, ale počátky v používání této metody nebyly jednoduché,
neboť byl odmítnut mnoha významnými firmami, které v tento vynález projevily nedůvěru. Až za několik let od
objevu tato metoda začala slavit úspěchypo celém světě.
Elektrofotografie je proces stojící za laserovými tiskárnami, kopírovacími systémy a faxovými přístroji.
Podstatou těchto systémů je fotocitlivá jednotka složená z kovového válce, potažená fotocitlivým filmem
(fotovodičem).
Po nabití fotovodiče a zobrazovací expozici vzniká latentní (neviditelný obraz), který je pomocí toneru vyvolán
a přenesen na papír., kde je teplotou či tlakem fixován do struktury papíru.
Jako fotovodiče se používají amorfní křemík ( patřil mezi první fotovodiče), amorfní Se, sulfidy Cd ajn.
Současným trendem mezi fotovodiči jsou organické fotovodiče: elektron- donorové polymery, elektronakceptorové polymery, vhodné z ekonomických důvodů.
I tonery neobsahují jen tiskový prášek, ale používají se i kapalné náplně a novinkou jsou polymery (f. Avecia).
Rozlišujeme elekrofotografii kontaktní, kapalnou a zajímavostí je Kirlianova elektrofotografie (o ní více viz
prezentace).
Osnova:
1.
2.
3.
4.
5.
6.
Historie elektrofotografie
Princip a proces
Fotovodiče (amorfní, organické)
Oblasti použití (laserový tisk)
Zajímavosti (Kirlianova elektrofotografie)
Literatura ( skripta, internetové adresy)
Some Interesting Milestones in Laser Printing Technology
The Invention of Electrophotography (1938)
In 1938, Chester Carlson, a patent attorney and a graduate of Caltech, discovered a dry printing
process called electrophotography. Electrophotography later on became the basic technology for laser
printing.
For nine years, Carlson tried to sell his idea to more than twenty companies including RCA,
Remington Rand, General Electric, Eastman Kodak, and IBM. They all turned him down, wondering
why anyone would need a machine to do something you could do with carbon paper.
Commercial Development of Electrophotography (1949)
In 1949, Haloid Co. located in upstate New York agreed to fund the applied research of
electrophotography. The intent was to develop this new technology into a dry copying process. The
term "xerography", Greek for "dry writing", was coined. Later the small Haloid Company renamed
itself as the Xerox Corporation.
"914", the First Automatic Xerographic Machine (1959)
In 1959, the Xerox 914 copier was introduced into the U.S. market. The 914 changed the course of
history for graphic communications and Xerox Corporation. Since then, the predominant technology
used in copying machines has been the xerographic process.
The First Laser Printer for Computer Output (1978)
Having many unique advantages over other processes, xerography was adopted for computer output
printing. Xerox was the forerunner in this endeavor. In 1978, Xerox introduced the 9700 laser
printer*. This was the first laser printer commercially available in the U.S. and in the world. It could
output 120 pages per minute. It is still the fastest commercial laser printer. However, the 9700 was
physically too large and carried a large price tag as well.
* The founder of American Calco was part of the Xerox team introducing the 9700.
Then Came Desktop Laser Printing (1984)
In the early eighties, personal computers became popular for business and home use. Better quality
text and graphics was a must for desktop publishing. Impact printers were unable to meet the needs.
In 1984, Hewlett Packard marketed the "LaserJet" printer (8 pages per minute). The remarkable
feature of this printer was its use of an operator replaceable "all-in-one" toner cartridge. The entire
development subsystem was built into this toner cartridge.
Electrophotography
Process used by laser printers, fax machines and copying machines where an electrical charge is placed onto
paper. When exposed to an optical image through light such as a laser or LEDs forming from the static charge.
Toner is then spread over the paper attracting to the static charge portions of the paper where finally the toner is
fused to the paper by heat and pressure making the final print.
Technology of Electrophotography
Electrophotography is the image-producing technology behind plain-paper fax machines, printers and copying
machines. In the electrophotographic process, a photosensitive surface (light exposure reduces the surface's
resistance) is uniformly charged with static electricity. When the surface is exposed to an optical image through
light, a latent or invisible image is formed from the electrostatic charge. Toner, a fine powder, is spread over the
surface. The toner adheres only to the charged areas, thereby making the latent image visible. Fusing the toner to
the paper makes the image semi-permanent.
Simple Cartridge Replacement Makes High Image Quality Available All the Time
The Canon all-in-one cartridge contains such core elements of the electrophotographic process as the
photosensitive unit, electrostatic charger and cleaner, all of which wear out rapidly and require periodic
maintenance. However, simply replacing our cartridge introduces brand-new elements, and even the toner is
replenished. Quality is restored immediately.
Copying machines and laser beam printers form electrostatic charged latent images on the photosensitive unit
surface by exposing the image areas of the original to light. A developing unit turns this into a visible image, and
the transfer roller prints the image on paper. The paper leaves the photosensitive unit, and the image is fixed
when the fusing process applies toner to the paper. A rubber blade then removes residual toner from surface of
the photosensitive unit in preparation for further output. This entire process takes place within our all-in-one
cartridge, which generated hundreds of new Canon patents.
The Theory Behind the Canon All-in-One Cartridge
Polymerised toner
Polymerised toners or Chemically Produced Toners (CPT) offer exciting possibilities to the laser
printing and digital copying industry, and are especially suitable for new colour applications.
The toner is manufactured using our proprietary aggregation process which avoids the melt-extrusion,
grinding and classification steps involved in conventional toner manufacture.
Papiere pre laserovú tlač, takýto papier sa musí vyznačovať potrebnou štruktúrou a orientáciou jednotlivých
vlákien, nesmie v žiadnom prípade prášiť či už sa jedná o povrch, alebo okrajový orez. Totiž prípadný prach
môže zapríčiniť problémy pri prenose tonera. Na fixáciu tonera vplýva i porozita papiera. I napriek tomu, že v
niektorých prípadoch je priechodnosť papiera v laserovej tlačiarni veľmi vysoká, ak papier obsahuje vlhkostné
pásy – taktiež to vedie k zlému prenosu tonera. Dôležitý je i obsah plnidla, nakoľko plnidlá sú látky menej
hygroskopické ako vlákna celulózy.
Z uvedeného dôvodu sa doporučuje konečné formuláre papiere pre laserovú tlač skladovať
minimálne jeden týždeň v klimatických podmienkach . Pritom i tlačová farba ktorá sa pri
spracovaní použije by nemala obsahovať prchavé komponenty a tlačené plochy by mali byť tlačené rastrom nie
plnou plochou.
Cleaner-less process
Magnetic Brush Injection Charging with Cleaner Mechanism
Magnetic brush injection-charging technology lies behind Canon's creation of the cleaner-less process.
Conventional copying machines fix the toner to the photosensitive drum using the corona discharge method
(noncontact method) and an electrostatically charged roller (contact method). However, these methods also fix
discharge products on the drum, causing damage and deteriorating the image.
Magnetic brush injection charging, on the other hand, applies a low-voltage charge directly and highly efficiently
to the drum with a magnetic brush, alleviating any damage to the drum. This technology creates no ozonedepleting substances, one of the reasons it is environmentally conscious. The brush consists of magnetically
charged particles attached to the surface of the roller, which has an internal magnet. When the roller is rotated,
the particles stand up like the bristles of a brush and come into contact with the drum, at which time the electric
charge passes through them to the drum surface. The magnetic brush-charging device also incorporates a
cleaner-substituting mechanism that collects the residue toner and then recycles it.
Variations in the transfer toner particle charge prior to collection were overcome by the careful positioning of an
auxiliary brush. Hence, Canon has stabilized the residue collection process.
Magnetic Material Technology Contributes to Practical Applications
The critical elements of the injection charge are the charge component (the brush), the surface of the
photosensitive drum and the contact of the two. If a part of the brush is prevented from coming into contact with
the drum's surface, the area won't be sufficiently charged. The brush and the drum must be in consistent contact
across the whole surface area. By optimizing this contact, Canon has succeeded in developing a practical
application for the injection-charged method.
The conventional corona discharge method charges the photosensitive drum by covering it with ions. But in the
magnetic brush injection-charging method, the charge is emitted directly onto the surface of the drum, causing
the electroconductive microparticles to disperse along the surface.
The creation of a cleaner-less process requires an in-depth knowledge of the qualities of magnetic materials.
Canon has expertly utilized the magnetic material technology it has accumulated through its development of
electrophotographic technologies.
Fotoconductors
The Photosensitive Unit is the Heart of the Copying Machine
The photosensitive unit is at the core of copying machines, laser beam printers and all other electrophotographic
imaging systems. It is composed of a metal cylinder coated with thin photoconductive film. Using differences in
electrical resistance to produce light and dark shades on this film, images corresponding to the exposed original
image can be rendered on paper.
Conventionally, selenium or cadmium sulfide was the main material for this photoconductive film, but Canon
developed a photosensitive unit that uses an organic photoconductive film. Furthermore, Canon succeeded in
commercializing a photosensitive unit using amorphous silicon (A-Si) in 1984. At that time, A-Si was attracting
attention worldwide as the first amorphous material to possess semiconductive properties. Expectations soared
for A-Si application in photosensitive units in copying machines, solar batteries, sensors and numerous other
products in diverse industrial fields. However, A-Si has a comparatively low resistance, making it difficult to
charge. Consequently, many laboratories and office equipment manufacturers concluded early on that A-Si was
not appropriate for photosensitive units in copying machines. The necessity to develop this film-forming
technology posed another challenge that few manufacturers were willing to undertake.
Canon persevered in developing an A-Si film-forming technology by capitalizing on the materials
semiconductive properties and concentrating on compensation for low resistance. Unrelenting determination-and
countless trial and error-resulted in the successful release of the world's first A-Si photosensitive unit. Even
today, mass production of A-Si photosensitive units continues to present technological challenges.
Amorphous Structure of A-Si Film (Conceptual Illustration)
The illustration shows the amorphous structure of A-Si film. Silicon atoms are configured at random
and hydrogen atoms bond to fill the structural defects
Three-Layer Structure of the A-Si Photosensitive Unit Section
The layered structure of the A-Si photosensitive unit consists of a blocking layer to stop the charge
injection from the substrate, a photosensitive layer (A-Si) that produces charges by light and a
protective surface layer.
Electrophotography
Commercial Application of Organic Materials
in Electrooptic Devices
Manfred Lutz
AEG Elektrofotografie GmbH, D 59581 Warstein, Germany
Phone: +49 2902 861212, Fax: +49 2902 861 1260, E-mail: efo@aeg.do.eunet.de
The essential steps of electrophotographic imaging are
- charging a high resistivity photoconductor in the dark
- imagewise exposure of the charged photoconductor resulting in a charge pattern, the
latent image, on the surface
- developing that latent image by bringing charged toner particles into contact with
the charge patterns
- transferring the toner image on to paper or other media
- fusing the toner on to the media
- cleaning and conditioning the photoconductor for the next imaging cycle
To be useful in electrophotographic imaging, a photoreceptor should meet the following
criteria:
- high resistivity in the dark to hold the charge
- high light sensitivity in the visible and near infra red part of the spectrum
- carrier traverse through the photoconductor in times shorter than the image
development time
- charged, partially discharged, and residual voltages must remain stable with repetitive
cycling during a multiple copy or printing run
- capability to be fabricated into large - area, defect - free films
The current trend is toward the use of organic photoreceptors because of their material
variety,
economy, and flexibility. The first organic photoreptor consisted of a single - layer charge transfer
complex of an electron-donor polymer (polyvinylcarbazole) with an electron-acceptor (2,4,7trinitrofluorenone). This charge-transfer complex absorbs visible Iight und enables charge
transport
of both electrons und holes. The photogeneration efficiency of this photoreceptor is relatively
low
and highly field dependent.
To enhance photosensitivity of organic photoreceptors dual-layer structures are employed.
Hole transporting polyvinylcarbazoIe is replaced by other electron-donor molecules in solid
solutions of mechanically durable polymers such as bisphenol A or Z polycarbonate. Typical
electron-donor molecules include triphenylamines and diamines, pyrazolines, hydrazones,
oxadiazoles, and stilbenes. Transport layers generally consist of a 40-50 wt % solution of the
electron-donor compound, 10-25 µm thick, and have hole mobilities of 10-6-10-5 cm2V-1s-1.
Because
these organic charge transport layers are transparent, the photogeneration ]ayer is overcoated
with
the transport Iayer and the photoreceptor is charged negatively. The photogeneration layers
consist
of pigments such as phthalocyanines, bisazocompounds, thiapyrylium salts, perylenes, and
many
other pigments.
AEG – Historical Steps
Selenium Photoreceptors
Organic Photoreceptors
1970 Start commercial production (pure Selenium)
1974 Start commercial production (As2Se3) for copiers
1975 Start commercial production (SeTe) for TOSHIBA
1977 Start commercial production
NON-IMPACT Printer drums (As2Se3) for SIEMENS
Successive development of whole range of Se-based technologies
as standardized layers resulting in 12 different layer types, more
than 100 different products in commercial production
1989 Foundation of AEG Photoconductor Corporation (APC),
North America
1987 Start of OPC development based on Know-How license agreement
1989 Investment for OPC pilot plant, capacity approx. 200 k p.a.
1990 Start of commercial OPC production
1992 Expansion of OPC production capacity and delivery scope
resulting into more than 40 different products and 8 layer types
in commercial production
1995 Start of commercial OPC production at APC in North America
1996 Expansion of OPC production capabilities for large format drums
Laser Beam Printers Born of Canon's Cutting-Edge Technologies
Canon prides itself on advanced technologies in several fields, including semiconductor laser technology,
electrophotography and ultraprecision optical engineering. Our laser beam printers are the result of these assets.
Today, desktop publishing demands the high-quality, high-speed output of images and text data received from
computers, in a compact machine and at an affordable price. By responding to-and exceeding-these demands,
Canon's line-up of laser beam printers has secured a substantial share of the world's printer market. Canon's laser
optical system is at the heart of these products, and has opened the door to new, cutting-edge laser beam printers.
Laser Beam Printers Born of Canon's Cutting-Edge Technologies
Canon prides itself on advanced technologies in several fields, including semiconductor laser technology,
electrophotography and ultraprecision optical engineering. Our laser beam printers are the result of these assets.
Today, desktop publishing demands the high-quality, high-speed output of images and text data received from
computers, in a compact machine and at an affordable price. By responding to-and exceeding-these demands,
Canon's line-up of laser beam printers has secured a substantial share of the world's printer market. Canon's laser
optical system is at the heart of these products, and has opened the door to new, cutting-edge laser beam printers.
Configuration of Canon Laser Optical System
After being reflected from the fast rotating mirror (see above), the laser beams are converged on an
aspherical plastic lens system and successively scanned onto the photosensitive unit. Using the image
data processed by the controller, this scanning can be performed with extraordinary accuracy.
Záměrem Kirlianovy fotografie - jméno je podle ruského inženýra Semjona Kirliana a jeho manželky
Valentiny - je získat fotografie aury, která odhaluje mentální a tělesné poruchy lidí dřív, než se projeví
nějakými
zjevnými
příznaky.
Podle diagnóz z fotografií mohou léčitelé navrhnout příslušné léčení od AKUPUNKTURY až po JÓGU.
Po mnoho století mystiky, duchovní léčitele a okultisty vzrušovaly aury-světélkující, záhadné kontury -,
které
prý
obklopují
lidi,
zvířata,
rostliny
a
ostatní
živé
i
neživé
předměty.
Aury údajně odrážejí celkové zdraví člověka a jejich barvy a jas se dají lékařsky vysvětlit. Z toho
vychází Kirlianova vysokovoltážní fotografie a elektrofotografie. Taková fotografie prý zachytí
interferenční úkazy, které vznikají při setkání vysokofrekvenčního elektrického okruhu s
elektromagnetickým
polem
člověka
neboli
s
jeho
aurou.
Semjon Kirlian učinil tento objev v roce 1939 při opravě přístrojů v laboratoři. Z jednoho přístroje
vylétla jiskra, silně se zablesklo a dostal elektrickou ránu. Když se vzpamatoval, přemýšlel, co by se
stalo, kdyby mezi elektrický výboj a svou holou ruku vložil fotografický papír a udělal fotografii v
okamžiku,
kdy
dostane
elektrickou
ránu.
Zkusil to a na filmu se objevily prsty lemované zářícími světelnými proužky. Manželé Kirlianovi si pak
zřídili vlastní laboratoř a následujících 40 let se zabývali svými záhadnými fotografiemi.
Začali tím, že mezi fotografické desky a vysokofrekvenční elektrické náboje o vysokém napětí vložili
dva podobné listy, jeden ze zdravé rostliny a jeden z nezdravé. Nepoužili k tomu žádný světelný zdroj,
po vyvolání byla na fotografii kolem listu silná aura, kolem nemocného slabá.
Vyhodnocením barev a vzorů aury se dá prý poznat, jaký je zdravotní stav člověka.
Použité adresy:
http://www.doktorka.cz/run/redsys/r-art.asp?id=30
http://www.qea.com/publications3b.html#5
http://www.kommtech.uniwuppertal.de/lehrgebiete/digitale_drucksys/download/DDS%20Grundpraktikum%20Teil1.pdf
http://www.aeg-photoconductor.de/graphics/efo.pdf
http://www.canon.com
http://www.papirnik.cz/casopis/012000/Kuban_PREDNASKA.htm
http://www.avecia.com
Fotochemické procesy (přednášky;Doc Čeppan)