understanding evolution in the color electrophotographic printing

understanding evolution in the color electrophotographic printing
Imaging & printing
first half 2002
understanding evolution in the color electrophotographic
printing process
Since the mid-1980s Color Electrophotographic (EP) Printing commonly known as
laser printing technology, has been a popular choice with businesses and personal
users who demand high quality, professional looking printed communications. With
EP currently in its third generation of significant improvements, segment leaders are
making key advancements in system design and supplies refinement and improvement. Hewlett-Packard continues to be a leader in the integrated system approach
to the color EP design, particularly in the area of printing supplies. This article
explores one area of advancement that is new to many consumers: chemically
grown polymer toners and their relationship to quality in color EP printing.
basics of ep technology
In the color laser printing process, four individual color toners–Cyan (C), Magenta
(M), Yellow (Y), and Black (K)–are precisely layered to create thousands of other
colors. Each color toner cartridge has a hopper containing one toner color and a
developer roller that distributes toner from the cartridge hopper in a uniform layer.
After the laser-optics system produces the latent image on the Organic
Photoconductor (OPC) or imaging drum, a calibrated electrostatic charge applies a
single color onto the transfer assembly. This same process is repeated for the
remaining colors until all four layers of toner are stacked on the transfer assembly.
As each succeeding color reaches the transfer assembly, the printer’s
on-board computer perfectly aligns the next individual color with the previous color
layers for optimal registration.
Next, a single sheet of paper or other media is passed into the transfer assembly
where the transfer roller provides the exact charge to attract toner away from the
transfer assembly surface and onto the paper. The paper then passes through a
heated fuser where the toner is melted onto the page and a finished document
emerges from the printer. Any residual toner is automatically cleaned from the
various components and placed in a collection receptacle.
hp color LaserJet 4500/4550 ep process
hp color LaserJet 8500/8550 ep process
So how do four basic toner colors create millions of other colors? In the case of
HP Color LaserJet printers, a technology called ImageREt precisely places tiny dots
of toner in adjacent or overlapping positions while varying the size of nearby color
dots. This combination of the four toner colors in these extremely tiny patterns and
sizes represents consistent color images to the human eye. It also presents a more
realistic true-to-life appearance of images and colors than earlier blending
technologies associated with first and second generation EP technology.
The color EP process has become a standard technology for business reports,
presentation graphics, and other important professional documents. Some reviewers
have even claimed that today’s high-quality laser printing devices rival more
expensive offset color printing for image quality and general appearance. Businesses
and organizations ranging from realtors to manufacturers use color EP printing to
create product sales and marketing information, promotional materials, and a host of
other internal and external communication vehicles. With continued advancements in
self-monitoring “smart” supplies, additional cost and time-savings are expected to be
realized, making additional applications highly likely.
benefiting from a systems approach in electrostatic printing
system components
Choosing manufacturer recommended replacement parts for automobiles ensures we
get the performance we expect and depend on every day. After all, the engineers
approached the design as a system, with each part relying on the other parts to do
their job based on the characteristics of other parts of the system. Change key
properties of, say, the control modules or the engine sensors and the entire vehicle’s
performance is affected. The same premise applies to today’s laser printing systems,
where the quality of what you see on a printed page begins with things you can’t
see. This is because color laser printing is inherently more complex than monochrome
laser printing. As a system, components that were designed together to work together
compliment one another to deliver results that meet our expectations of quality.
In the EP process, this reliance on each system component means the toner becomes
as important as the various mechanical parts of both printer and print cartridge.
Because approximately 70 percent of a laser printer’s imaging system comes from
the print supplies themselves, this makes the print cartridge, and the toner contained
inside, a highly critical part of the EP process described above. For example, HP
print cartridges designed for chemically grown toner should be used where specified
to ensure optimal performance from the printer. Again, this is because the engineers
counted on the precise performance characteristics of the toner in relation to the rest
of the system to ensure the quality of the output.
chemically grown toners: a new generation of improvement
One of the critical components HP has leveraged in distinguishing its leading line of
color laser printers is chemically grown polymer toners. HP first introduced the use of
chemically grown toners for its color printers in 1998 and has been a leading force
in the advocacy of advanced polymer toners for color printing ever since. Today
each HP LaserJet color toner particle is chemically grown to exacting standards with
multiple layers designed to interact with the printing system under precise conditions.
Because of its formulation, uniform size and spherical shape, this toner ensures a
broad range of colors, sharp black text and lines, and outstanding results on many
kinds of paper. HP’s precision printing system monitors and adjusts the charge of the
toner particles and automatically calibrates output properties for great results,
every time.
features and benefits of hp chemical toner
Chemically grown
manufacturing process
Allows smaller and very uniform particle size
Allows very smooth, spherical shape
Allows different properties for exterior and interior of
Holds higher charge than conventional toners
• More controllable, therefore better color print quality
Spherical particles
More consistent charge capabilities over life due to
uniform, regular surface properties
Uniform size of particles
Exterior shell, wax core
Good toner flow—due to roundness and chargeability
• Easy to transfer
Consistent charging and control
Uniform pile height, better color trueness
Uniform pigmentation
Enables oil-less, fast fusing
Since the human eye is very sensitive to color print quality, particularly in regard to
color accuracy factors including hues, shades, and true-to-life representation,
individual toner particles must be very uniform in size and other properties to ensure
color accuracy is true to the eye. The particles must be able to be placed very
accurately on the page. And since most printed areas are a combination of two or
more of the four toner colors, the correct amount and placement of toner as the colors
are combined is also critical to accurate color reproduction. Chemically grown toners
meet each of these challenges and more.
At the particle level, chemically grown HP polymer toners feature a harder outer shell
and softer inner body referred to as an encapsulated structure. This soft inner body
contains wax that enabled HP to produce an oil-free fusing system for cleaner
wax layer
operation. During the fusing process, wax migrates between the heat roller of the
fuser and the toner resin to prevent toner offset and paper curling around the
heat roller.
The smooth, spherical surfaces of all HP chemical toner particles are precisely
engineered to allow for higher and more uniform charge capability. The round,
uniform shape of the particles help the toner flow easily, evenly, and quickly over
the image areas. These uniform particles also provide a very even pile height,
ensuring accurate color trueness across an image area and precise measurement
by computer-controlled supplies monitoring systems within the printers themselves.
Each of these characteristics works together to stabilize the adhesion between
toner particles and drum surface, enabling accurate and efficient transfer of
All HP Color LaserJet printing systems are designed and calibrated to work with
these precise charging and lubrication properties of chemically-grown toner to
ensure optimal results. The result of this integrated system approach employing
chemically grown toner is high quality professional printing, and consistent color
and image representation. Results that are easy to see with the naked eye and
quick to make a positive impact on the company’s bottom line.
When EP print supplies not specifically designed with the printing system are
used concerns arise. This is due to seemingly subtle differences in particle weight,
charging properties and other toner characteristics. This is especially true for
systems designed for chemically grown toners. Chemically grown toner is one
such supply. It is designed to exhibit specific characteristics including uniform
sphericity, particle size, charging properties, lubrication performance, and
chemical makeup. When toners without these precision-engineered properties are
used in a system that specifically relies on them, the toner may not transfer
predictably and smoothly to the paper and a wide variety of print inconsistencies
may be noticed. In limited testing of other available aftermarket toners conducted
by HP, this appears to create a variety of problems including sharp reduction in
the life of other consumables such as the imaging drum and fuser. Print quality
problems seem to increase over the life of the cartridge. Although these internal
tests were limited in scope and preliminary in nature, they raise concerns about
the experience of printer owners who use non-chemically grown toners in systems
designed for chemically grown.
Chemically grown toner has been credited with several advancements in
color image reproduction and it illustrates and reinforces the value of the
systems design approach. Output from this integrated EP printing system
approach can in many instances closely emulate the offset printing
process. Therefore, by using HP specified supplies each and every time,
users can give their printer precision-engineered new imaged components
and ensure optimum print quality every time they print.
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