Chap. 3. Colorants for Reprographics
Dyes & Pigments
- Electrophotography
Hi-Tech Use
Traditional Use
- Thermography
- Ink-Jet Printing
Electronics
Reprographics
- Electrography, Ionography, and Magnetography
Magnetography
Electrography
Electrophotography
Continuous
Thermography Photocopying
Ink-Jet Printing
Laser Printing
Polymer Coloration Technology
Chap3- 1
Electrophotography
Direct thermal printing
Dye diffusion thermal transfer
DOD
Chap3- 2
Electrophotography
An impact printer has mechanisms resembling those of a
Dot Matrix Printing : Impact Printing
Dot Matrix Printing : Impact Printing
- A dot matrix printer's print
head contains a cluster of
pins. The printer can push
the pins out to form
patterns in rapid
sequence.
- The pins press an inked
ribbon against the paper,
creating an image
Chap3- 3
- In a 9-pin print head, the
pins are aligned in a
single row
- In a 24-pin print head, the
pins are “staggered” in two
rows. This enables it to
print overlapping dots,
creating finer characters
and lines
Chap3- 4
Electrophotography
Electrophotography
Ink Jet Printing : Non-Impact Printing
Non Impact Printing
- The printer sprays tiny
droplets of ink onto the
paper.
- cf. Laser printing produce
higher-quality print than
ink jet printing, but are
more expensive
- Electrography was invented 1938 by Chester Carlson
- It was later renamed to Xerography (dry writing) from “xeros”
(dry) and “graphia” (writing)
- Georg Christoph Lichtenberg invented a dry electrostatic
printing process in 1778, but Carlson combined electrostatic
printing with photography.
Chap3- 5
Electrophotography
Electrophotography
-
“photography using electric rather than chemical processes to
transfer an image onto paper, as in xerography”.
-
Xerography is then identified as “an electrostatic printing process
for copying text or graphics whereby areas on a sheet of paper
corresponding to the image areas of the original are sensitized with
a charge of static electricity so that, when powdered with a toner
carrying an opposite charge, only the charged areas retain the
toner, which is then fused to the paper to make it permanent”.
-
Chap3- 6
So how is this accomplished?
the text of the first
xerographic image
- Carlson was proved right only
after a discouraging ten-year
search for a company that
would develop his invention
into a useful product.
- It was the Haloid Company, a small photo-paper maker in Rochester, N.Y,
which took on the challenge and the promise of xerography and thus
became, in a breathtakingly short time, the giant multinational company now
known to the world as Xerox Corporation.
Chap3- 7
Chap3- 8
Electrophotography
Electrophotography
-
electrophotography comprises the two very familiar and
ubiquitous technologies of photocopying and Laser/LED
(light emitting diode) printing.
-
Xero-graphy = Dry-writing (Greek)
-
Creation of a visible image using surface charge pattern on
a “photoconductor”
-
Visible images consist of fine
charged
particles
called
toners”
Magnetic
material
Resin
Colorant
Chap3- 9
Electrophotography
Electrophotography
Photocopying Process : using inorganic photoconductor
(2) Exposure
(3) Development
toner
1) The
photoconductive
surface, usually a drum
Original document
or a belt, is given a
uniform
electrostatic
charge. (positive
for
carrier
most
inorganic
photoconductor)
toner
(4) Transfer
Plain paper
(5) Fusing
Fuse to paper
Doctor blade
(6) Cleaning
Photocopying Process : using inorganic photoconductor
Photoconductive
surface(photoreceptor)
(1) Charging
Chap3- 10
2) The charged drum or belt
is exposed to the subject
using white light to
produce
a
latent
electrostatic image on the
photoconductor.
Photoconductive
surface(photoreceptor)
(1) Charging
(2) Exposure
Original document
(3) Development
toner
(4) Transfer
Plain paper
(5) Fusing
Fuse to paper
(6) Cleaning
Chap3- 11
The latent electrostatic
image is developed by
oppositely
charged
toner particles.
4) The developed image is
transferred
to
a
substrate usually paper.
toner
Doctor blade
Light neutralizes charge by
making entire photoreceptor
conductive
carrier
3)
Light neutralizes charge by
making entire photoreceptor
conductive
5) The image is fixed by
heat, usually by hot
roller.
6) Finally the photo conductor
undergoes a cleaning step
to make it ready for the
next copy.
Chap3- 12
Electrophotography
Electrophotography
Photocopying Process : using inorganic photoconductor
Photocopying Process : using inorganic photoconductor
(1) Charging
Photoconductive surface (ex. Se on Al)
(photo-receptor or photoconductor)
Charging wire at high
voltage emit +ve ions
Chap3- 13
Electrophotography
The exposure lamp
illuminates the original
document
Thus the drum acquires
+ve charge
Chap3- 14
Photocopying Process : using inorganic photoconductor
Original document
Original document
Se drum conducts charge
only when exposed to light.
The atoms of Se presented on
the Al drum emit electrons
→ neutralize the +ve ions
Electrophotography
Photocopying Process : using inorganic photoconductor
(2) Exposure
The photoconductive surface,
usually a drum or a belt, is given a
uniform
electrostatic
charge.
(positive
for most
inorganic
photoconductor)
The charged drum or belt is exposed to
the subject using white light to produce a
latent electrostatic image on the
photoconductor.
Printed matter
absorbs light
Blank areas
reflect light
Chap3- 15
(2) Exposure
The charged drum or belt is exposed to
the subject using white light to produce
a latent electrostatic image on the
photoconductor.
Se drum conducts charge
only when exposed to light.
-
The light reflected from the document is
projected through the optical system.
-
The optical system focuses the light on
the exposure slit which is present near
the Se drum.
-
The revolving drum loses its +ve charge
when the reflected light falls on it.
-
Due to the exposure an invisible
electrostatic image called latent image
is formed on the Se drum.
Chap3- 16
Electrophotography
Electrophotography
Photocopying Process : using inorganic photoconductor
Photocopying Process : using inorganic photoconductor
Original document
(2) Exposure
Se drum conducts charge
only when exposed to light.
The charged drum or belt is exposed
to the subject using white light to
produce a latent electrostatic image on
the photoconductor.
(3) Development
Latent image
carrier
Printed matter
absorbs light
The latent electrostatic image is
developed by oppositely charged
toner particles.
toner
Blank areas
reflect light
When the reflected light from the blank areas is
incident on the +vely charged drum, the exposed
regions lose their +ve charges
-
When the brush roller comes and contact
with a Al drum, the –vely charged toner
particles are transferred to the latent image
that is positive in charge, hence latent image
become switchable.
Chap3- 18
Electrophotography
Photocopying Process : using inorganic photoconductor
(4) Transfer
The quenching lamp illuminate the
drum and dissipate the +ve charge
on the drum, thereby loosening the
toner particle
Magnetic brush roller fix up the developer
particles.
The rest of the positive charges
produce a latent electrostatic image
on the photoconductor Chap3- 17
Electrophotography
+vely charged
paper
-
The developed image is transferred
to a substrate usually paper.
When the +vely charged paper comes
and contact with the drum, the –vely
charge tonner particle get attached to
the paper
Chap3- 19
Photocopying Process : using inorganic photoconductor
(5) Fusing
Fuse to paper
The image is fixed by
heat, usually by hot roller.
-
The transferred paper passes through
the heating chamber consists of two
rollers (upper roller & lower roller)
-
The halogen lamp is mounted on the
axis of the upper roller.
-
This lamp heats the roller and particles
of toner melt into the fibers of the paper.
-
The lower roller presses the melted
tonner into paper fibers and thus we get
photocopy of the documents
Chap3- 20
Electrophotography
Electrophotography
Photocopying Process : using inorganic photoconductor
(6) Cleaning
Doctor blade
Photocopying Process : using inorganic photoconductor
Finally the photo conductor undergoes a cleaning
step to make it ready for the next copy.
Cleaning is normally done by exposing it to
light to remove any residual electrical
charge and by removing any excess toner
with a doctor blade
Light neutralizes charge
by making entire
photoreceptor conductive
Chap3- 21
Electrophotography
(1) Charging
Photoconductor
(2) Exposure
Original document
-
carrier
toner
toner
(4) Transfer
Plain paper
(5) Fusing
Fuse to paper
(6) Cleaning
& (7) Erasure
Chap3- 22
Electrophotography
Photocopying Process : using organic photoconductor(OPC)
(3) Develop
https://www.youtube.com/watch?v=PgkYN8V4CcA
Light neutralizes charge by
making entire photoreceptor
conductive
-
-
Laser Printing Process : seven steps for Canon-based systems
The process for
photocopiers based
on OPCs comprises
the same steps as
in
photocopying
process
using
inorganic
photoconductor.
The only difference
is that the OPC has
a negative rather
than positive charge
The toner particles
need
to
be
positively charged
Chap3- 23
(1) Charging
(2) Writing
Photoconductive
surface(photoreceptor)
a laser is used to
write on the
charged PC
carrier
(3) Development
(4) Transfer
Plain paper
(5) Fusing
Fuse to paper
(6) Cleaning
& (7) Erasure
Light neutralizes charge by
making entire photoreceptor
conductive
1) the first step involves
giving the photoconductor
drum or belt a uniform
electrostatic charge shown
as negative.
2) The second step, a laser
is used to write on the
charged
photoconductor
drum the information stored
in the printers memory. At
the points where the laser
radiation hits the charged
photoconductor, the charge
is dissipated:
→ the image to be printed
has a zero electrostatic
charge but the background
area remains negatively
charged.
Chap3- 24
Electrophotography
Electrophotography
Laser Printing Process : seven steps for Canon-based systems
Photoconductive
surface(photoreceptor)
(1) Charging
(2) Writing
a laser is used to
write on the
charged PC
carrier
(3) Development
(4) Transfer
Plain paper
(5) Fusing
Fuse to paper
(6) Cleaning
& (7) Erasure
Light neutralizes charge by
making entire photoreceptor
conductive
Laser Printing Process : seven steps for Canon-based systems
3) The third step is the
development
step:
the
developer uses a toner
which
has
the
same
electrical charge as the
photoconductor, in this case
negative, so that it is
repelled from the negatively
charged background into the
uncharged image areas
(reverse development).
4) The fourth, fifth and sixth
steps of transferring the
developed image from the
photoconductor to the final
paper substrate, fixing it by
heat and cleaning/erasing
the photoconductor are the
same as in photocopying.
Chap3- 25
Electrophotography
Chap3- 26
Electrophotography
Laser Printing Process
Laser Printing Process : seven steps for Canon-based systems
2. Exposure
-
Once the laser printer or copier has been turned on and gone
through a short warming-up period,
This allows time for the upper fuser roller to heat to the proper
fusing temperature
-
The laser passes through an
opening in the cartridge and
focuses on the evenly charged
drum surface.
-
As the drum rotates the focused
beam of the laser scans across the
drum, emitting light and discharging
the drum in the pattern of the image
and/or characters to be printed.
1. Charging
-
The process begins with the charging
of the organic photo conductor
(OPC drum) by the primary charge
roller (PCR).
-
A constant flow of electrical current
from the PCR produces an even
negative charge on the surface of the
rotating drum.
Chap3- 27
This “writing to the drum” leaves a zero electrostatic latent image on
the drum surface (it’s there, but you can’t see it yet).
Chap3- 28
Electrophotography
Electrophotography
Laser Printing Process
Laser Printing Process
3. Development
3. Development
- As toner is magnetically attracted to the
mag roller it bunches up behind the doctor
blade, trying to get through this gap.
- There is a small gap between the doctor blade, or “leveling blade”, and
the magnetic developer roller (mag roller).
- The friction created by these bunched
particles rubbing against one another
results in a negative charge build-up on
the individual toner particles. (“triboelectric
charge”).
- Since both the toner and mag roller are
charged negatively the toner is repelled
(pushed) toward the zero electrostatic
areas of the drum (the latent image).
- The negatively charged areas of the drum (blank areas) also repel toner,
leaving only the image on the drum dusted with toner particles. This occurs in
an area of the cartridge called the development zone or development station.
Chap3- 29
Chap3- 30
Electrophotography
Laser Printing Process
-
Electrophotography
Laser Printing Process
4. Transferring
5. Fusing
-
The transfer roller, which carries a
positive charge, is located inside
the printer and is not a part of the
cartridge.
-
The paper travels on a path
between the OPC drum and this
roller.
-
The toner-covered image on the
surface of the drum is moved down
toward the paper by the rotation of
the drum.
The positive charge of the transfer roller attracts the negatively
charged toner, pulling it off the drum and down onto the paper.
Chap3- 31
-
-
The paper, along with the transferred
toner image, then travels beyond the
transfer roller, and outside of the
cartridge.
-
Here it becomes sandwiched between
the fuser assembly, composed of an
upper fuser roller and a lower
pressure roller.
-
Heat is applied by the upper roller, fusing
the toner into the paper, while the lower
roller applies pressure, imbedding the
toner into the paper fibers.
The paper cools as it exits the printer with the clean image fixed to the page.
If the paper is removed before it has passed between these two rollers, as when
a paper jam occurs, the image can be easily wiped or blown off the paper.
Chap3- 32
Electrophotography
Electrophotography
Laser Printing Process
Laser Printing Process : cold vs hot offset
Chap3- 33
Electrophotography
Chap3- 34
Electrophotography
Laser Printing Process : cold vs hot offset
Laser Printing Process
Fixing ratio as a function of media thickness at 130˚C and different speeds
Fixing quality as a function of fusing roller temp.
Chap3- 35
Chap3- 36
Electrophotography
Electrophotography
Laser Printing Process
Laser Printing Process
6. Cleaning
-
-
-
7. Erasure
As the drum continues to rotate it
passes under the wiper blade, which
removes debris (excess toner, paper
fibers, etc.) from the drum.
The recovery blade, located at the
base of the waste bin acts as a toner
dam, catching the debris as it falls from
the drum and wiper blade.
-
The PCR “erases” any remaining
positive charge from the OPC drum
by applying a uniform negative
surface charge to the drum.
-
This removes the image and
cleans, or “blanks” the drum for its
next pass under the laser, where it
will be written with the next image.
Also called a “catcher” or scavenger blade” the recovery blade prevents excess
toner, paper fibers, carrying agents and other foreign materials from falling out
of the waste bin onto the paper.
Chap3- 37
Electrophotography
Chap3- 38
Electrophotography
Photocopying Process
Photocopying Process
Chap3- 39
https://www.youtube.com/watch?v=yMmupCmo-70
Chap3- 40
https://www.youtube.com/watch?v=MDLM5fMFyA4
Electrophotography
Electrophotography
Laser Printing Process
Laser Printing Process
Laser printers vs LED printers :
Laser printers use a laser beam that tracks back and forth across the drum,
while LED printers use an array of LEDs that flash the entire line all at once.
- LED printers are usually less expensive to manufacture due to the
simplicity of the LED array.
- Laser printers, on the other hand, require a precisely focused laser
beam and sensitive optical assembly with many moving parts.
https://www.youtube.com/watch?v=WB0HnXcW8qQ
Chap3- 41
Electrophotography
Chap3- 42
Electrophotography
Color Copying Process
Color Copying Process
- In theory, any color can be obtained
by the use of three primary colors.
- Colored copying can either be monochrome (one color
other than black) or full color.
- For the subtractive color mixing used
in the photocopying process the three
primary colors are yellow, magenta
and cyan.
- With monochrome
copying, the process is almost
identical to that already described for conventional black
copying: the only difference is that the carbon black used
as the pigment for black toner is replaced by a dye or
pigment of the appropriate color for a colored toner.
- Requirements for full-color copying:
→ having yellow, magenta and cyan toners.
→ having photoconductors that are sensitive to red, green and blue light :
achieved by using a single panchromatic photoconductor or three
different photoconductors. Here, OPCs are utilized increasingly
because of the ability to fine tune their properties, including spectral
sensitivity.
- The actual copying process for a full-color copy is much
more complex than that for a monochrome copy and is
described briefly.
Chap3- 43
Chap3- 44
Electrophotography
Electrophotography
Color Copying Process - As in conventional monochrome copying, the first step is to
Color Copying Process
give the photoconductor a uniform electrostatic charge.
Expose
Y
M
C
Develop
Transfer
Expose
B
Y
Y
Blue
Light
Y Y
Y
Y
Y
Y
Y
- The colored document to be copied is exposed to blue light (by using a
blue filter). Blue light is absorbed by the color yellow; therefore the yellow
parts of the document do not reflect any of the blue light on to the
photoconductor and so the charge remains intact in the areas of the
photoconductor corresponding to the yellow areas of the document.
- The same is true for black part of the document, since black absorbs all
visible radiation.
- In contrast, the magenta and cyan areas of the document will reflect the
blue light on to the photoconductor and dissipate the charge.
- The latent electrostatic image on the photoconductor is then developed
with a yellow toner (yellow being the complementary color to blue) and
the developed image is transferred to paper.
M
C
Develop
B
Green
Light
Y
M
M
Chap3- 46
Electrophotography
Red
Light
C
Color Copying Process
Develop
Transfer
B
Y Y M M C C Y
C
C
C C
Y
M M
C C
- The latest generation of color copiers, such as Canon Color Laser copier,
are based on semiconductor lasers. The process is somewhat different
than the conventional color copying process described above.
- In a color laser copier, light scans the original document and is reflected
on to a charge coupled device (CCD) line sensor.
- Finally the document is exposed to red light.
- Here, the cyan and black parts of the document absorb the red light, the
yellow and magenta areas reflect it on to the photoconductors.
- The resultant latent electrostatic image is developed with a cyan toner
(cyan being complementary color to red) and the image is transferred to
paper.
Chap3- 47
Y
M M
- The resulting latent electrostatic image is developed with a magenta
toner (magenta being the complementary color to green) and the
developed image is transferred to paper.
Color Copying Process
M
Y
- In this case the magenta and black portions of the document absorb the
green light and the yellow and cyan portions reflect it.
Electrophotography
Y
M M
Y M M
- The document is then illuminated with green light.
Chap3- 45
Expose
Transfer
- The CCDs which make up the array are grouped into units of red, green
and blue filters.
- Each filter screens out two colors, allowing only light of the filter color to
reach the sensor.
- The CCD converts the light into a digital signal which is sent to the copier
printing unit.
Chap3- 48