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 user 2005-05-11 at 10:30:00 am Views: 42
  • #9363
    Hidden science
    May 05

    It’s easy to take printing for granted.For
    most people, it’s as simple as clicking ‘print’, waiting a few seconds and
    picking up their document from the printer’s output tray.

    But behind
    that apparent simplicity, there’s actually some remarkable science and
    technology in today’s printing systems, responsible for everything from output
    quality to fade resistance to reliability. And contrary to common perception,
    print supplies – laser and inkjet cartridges
    and paper – can have as much to do with getting consistently great results as
    the printer itself.

    By understanding the often-overlooked factors that
    go into choosing the right supplies, resellers can help customers make more
    informed purchase decisions and deliver a value-added service to differentiate
    their business in an increasingly competitive marketplace.

    educating customers, understanding the technology responsible for great printing
    can also help resellers better recognise the long-term value of original
    supplies, which are designed and tested to perform as part of an integrated
    printing system to deliver optimum results. Original supplies ensure that
    customers get the consistent print quality and reliability they’re looking for,
    lowering reseller support costs and increasing user satisfaction that drives
    repeat business.

    How monochrome laser printing works

    a workhorse in business settings, monochrome laser printers have continually
    delivered better print quality, increased reliability and faster speeds since
    they were introduced more than 20 years ago. Many of the scientific advances and
    technological breakthroughs responsible for these improvements are associated
    with the print cartridge.

    “Since introducing the first Hewlett-Packard
    (HP) LaserJet printer in 1984, HP has invested hundreds of millions of dollars
    in R&D to improve laser printing,” says John Solomon, VP of printing and
    imaging supplies at HP. “Most people are surprised to learn that a good deal of
    the innovation is actually in the print cartridges. They’re amazingly complex
    products, representing some truly pioneering technology.”

    Laser printers
    rely on what’s known as an electrophotographic (EP) process, which uses a laser
    beam to prepare a photoreceptive drum to receive toner. The laser beam
    temporarily exposes the drum (like creating a film negative), which attracts
    toner particles in the pattern of the image to be printed. Using static
    electricity, the toner particles ‘jump’ from the drum to a sheet of paper that
    has been positively charged by the cartridge. The toner is then fused to the
    paper with heat and pressure. In a matter of seconds, the paper emerges from the
    printer with a printed replica of the image on the computer screen.

    of the most important components of the EP process, such as the primary charging
    roller, developer roller and drum, are found inside the print cartridge. Because
    of the precision needed to produce thousands of flawless pages, a cartridge’s
    components are designed and calibrated to perform as an integrated unit that
    matches the technical requirements of a specific model of printer. Disrupting
    how these components work together – either by prying open the cartridge in the
    remanufacturing process or by selectively replacing parts with aftermarket
    alternatives – can impair performance.

    Plus, a cartridge’s components
    have a specific usable life. The thin, organic photo-conducting layer on the
    printing drum, for example, can wear down over time and reduce its ability to
    transfer toner particles accurately. Common print quality issues associated with
    worn or damaged cartridge components that have been pushed past their usable
    life include banding, spotting, ghosting and mystery dots.

    Then there’s
    the toner, which might be the most critical component in laser printing. Much
    more than fluffy black dust, monochrome toner is actually a marvel of
    microengineering, precisely developed as part of an integrated printing system.

    Toner particles are extremely small, each many times smaller than the
    width of a single human hair. For example, the toner particles in HP’s newest
    LaserJet print cartridges average just seven microns in size. How small is a
    micron? So small that a single cartridge includes more than 5,000 billion
    individual particles. That’s enough toner particles to circle the moon.

    These remarkably tiny toner particles also serve a very important
    purpose: delivering excellent print quality. The smaller the toner particles,
    the greater a printer’s accuracy in producing crisp, sharp lines and images.

    It’s essential that the toner particles are very similar in size, which
    requires tight controls over the development and manufacturing process. Toner
    that’s inconsistent from particle to particle, such as the generic toners used
    in many remanufactured cartridges, can make it more difficult for the
    cartridge’s imaging system to predictably control its placement on the page.

    Manufacturers also fine-tune their toner ‘recipes’ to match the
    characteristics of specific printers, adding ingredients that ensure the toner
    is properly transferred and fused to the paper. Solomon says that the toners
    used by original equipment manufacturers such as HP include cleaning agents that
    many remanufacturers leave out. The cleaning agents help printers operate at
    peak performance by minimising wear and tear on sensitive cartridge components.

    Understanding colour laser printing

    Although colour laser
    printing has been around since the mid-1990s, recent innovations have
    significantly improved print quality, durability and speed. These advances –
    along with lower-priced printers – have raised expectations and placed greater
    emphasis on colour printing in the office.

    The colour EP process is
    similar to the process for mono laser printing, but significantly more complex.
    As a result, the demands on the print cartridges are more intense and require
    sophisticated technical engineering and testing.

    Most colour laser
    printers use either ‘four-pass’ or ‘inline’ technology. With the four-pass
    process, the individual cartridges in the printer carousel rotate past the
    imaging drum four times to create a printed page. The print cartridge is made up
    of multiple components that work in tandem with the printer to build an image
    one colour at a time on the drum before it is transferred to the paper and fed
    through the fuser, where it is permanently bonded to the paper.

    contrast, inline technology – commonly referred to as ‘single-pass’ technology –
    uses an all-in-one print cartridge design to produce the page in a single pass.
    While four-pass technology uses a single laser, inline technology relies on four
    lasers and four all-in-one cartridges, each with its own imaging drum.

    Regardless of the technology used, the science behind toner is essential
    to success. In fact, just as with monochrome laser printing, one of the most
    critical factors affecting print quality in colour laser printing is the toner.
    Conventional colour toner is made by pulverising a solid mass of resin and dyes
    to produce particles that are jagged in shape and variable in size, which can
    adversely affect colour accuracy as well as the sharpness of text and lines.

    In contrast, chemically grown polymer toner represents a superior
    alternative to conventional toner. Introduced by HP in 1998, polymerised toner
    is grown through a chemical reaction that creates round and smooth particles
    that are very similar in size. Chemically grown toner also has consistent
    electrical properties, which allow for greater precision through the EP process.
    As a result, chemically grown toner can deliver more true-to-life colours and
    crisper text.

    “We’re seeing more and more volume in colour laser
    printing, particularly with businesses where making a great first impression is
    essential,” says Solomon. “If you compare two printouts side by side, one
    printed with chemically grown toner and the other with conventional toner, it’s
    immediately clear which document has the edge in terms of colour accuracy and
    overall quality.”

    A look at thermal inkjet printing

    As far as laser printing
    has come, the advances in inkjet printing are
    equally notable. Today’s inkjet printers have
    made it easy to get great colour in the office while virtually bringing the
    photo lab to the desktop. In fact, most inkjet
    printers are capable of creating photos that rival those produced by traditional
    retail photo services. And as with laser printing, much of the credit goes to
    the print cartridges themselves.

    Most major manufacturers offer printers
    that use the thermal inkjet printing process,
    which was invented by HP in 1979. With thermal inkjet printing, nothing moves but the ink itself. A heater in the printhead superheats a
    thin film of ink, creating tiny vapour
    bubbles. The vapour bubbles act like pistons, forcing ink droplets through hundreds of microscopic nozzles
    - each just one-third the width of a human hair – onto the paper at more than 30
    miles per hour.

    Thermal inkjet
    cartridges include an integrated circuit, which is responsible for routing
    instructions to each of the nozzles that control the distribution of ink. For each pass of the printhead over the paper,
    the circuit determines when a nozzle should fire and what colour of ink needs to be laid down. Because millions of
    overlapping ink droplets may be needed to
    represent a print’s colour gamut, the integrated circuit is critical to making
    the necessary adjustments that ensure consistent print quality and colour

    The other half of the thermal inkjet printing equation is the ink. In many respects, it’s the hardest-working
    member of the printing system, expected to work flawlessly with the printhead,
    deliver high-quality results on a variety of media and perform reliably across a
    wide spectrum of environments.

    As with toner, inks are the product of highly sophisticated science
    and are designed to meet a broad array of applications. In fact, thermal inkjet printers are remarkably versatile, ideal for
    at-home photo printing and business presentations as well as large-format
    banners and backlit displays. According to Solomon, HP invests hundreds of
    millions of dollars and up to four years in developing and manufacturing a new
    ink, fine-tuning its chemical formula to
    optimise such characteristics as colour accuracy, bleed, dry time and fade

    Inks are tremendously
    sophisticated and very difficult to get just right,” says Solomon. “There are so
    many variables to consider when developing a new ink, from the additives that control every aspect of
    its performance, to how it interacts with different media, to how it holds up to
    light and other environmental factors. If I could offer just one piece of advice
    to anyone interested in getting consistently good results from their printer,
    I’d tell them to pay attention to the inks
    they’re using.”

    Solomon also says that refilled inkjet cartridges use generic inks that haven’t been optimised to work with
    specific printers or media, and they often can’t deliver the colour richness and
    accuracy that most users need. Generic inks
    are also more apt to cause reliability issues because they’re not subjected to
    the intense testing required by OEMs to eliminate any microscopic impurities
    that can play havoc with sensitive printheads.

    Paper is more than
    just paper

    More than 5,000 years ago the Egyptians invented paper by
    softening strips of the papyrus plant and weaving them into mats before pounding
    them flat and drying them in the sun. Paper has come a long way since then, and
    today it reflects highly specialised technology, designed and tested in labs
    rather than in the fields.

    Paper, or more broadly speaking, ‘media’ can
    be grouped into two basic categories that cover the most common printing
    applications: fibre-based and photographic-based.

    Fibre-based media
    include papers commonly used in home and business settings. They’re made of
    wood-based cellulose fibres and filler, and include a coating that’s made of
    pigments and binders to control brightness, stiffness and water absorption.

    Photographic-based media are designed with up to six separate micro-thin
    layers, each with an important role in ensuring the best possible results. With
    the rise in popularity of digital cameras and greater emphasis on using imagery
    in professional documents, choosing photo media has become increasingly
    important for consumers and businesses.

    Like fibre-based media, most
    inkjet photo papers are made with a cellulose
    core but are enhanced with a special coating that reacts in specific ways with
    ink. In either case, inkjet photo papers are commonly labelled as either
    ‘swellable’ or ‘porous.’

    Porous paper is made with lots of small
    cavities – picture a cross section of a sponge – that absorb ink to let a print dry quickly. Prints created with
    porous paper are more likely to fade when exposed to light and air, but can
    offer very good water resistance.

    In contrast, swellable paper is
    designed to soak up ink and then swell up. As
    the water in the ink dries, the colourant
    molecules are left behind in a protective layer. When paired with advanced inks, swellable paper is the key to longer fade

    These papers are more than just a sheet of plain paper with
    a special coating, however. They’re actually made of up to six micro-thin layers
    that help improve image quality, water resistance and handleability after

    The first layer locks in the ink exactly where it’s supposed go, so yellows stay
    yellow and blues stay blue, rather than bleeding together to create green. The
    second layer absorbs ink quickly so prints dry
    fast. The middle layers add crease resistance while contributing gloss. The back
    coat controls paper curling, and the final layer includes small plastic beads
    that prevent photos from sticking together after they’re printed.

    Solomon points to improvements in media when describing the growing
    importance of inkjet printing. “For all of the
    advances we’ve made with inks, their impact
    simply wouldn’t be as significant without similar breakthroughs in media,” he
    says. “HP’s approach is to design our papers and inks together along with the printer, so they’re all
    able to take full advantage of each other’s strengths. Remove one component and
    you weaken the entire system, and risk being disappointed with results that just
    don’t meet expectations.”

    Seeing the big picture

    it’s tempting to dismiss all laser and inkjet
    cartridges as being easily interchangeable, the fact is there are notable
    trade-offs -including poorer print quality, lower fade resistance and lesser
    reliability – for substituting remanufactured supplies into a printing system
    designed to work as an integrated whole. The key is recognising those trade-offs
    associated with non-original supplies and deciding whether they’re worth the

    The bottom line on print supplies is you get what you pay for.
    Manufacturers’ significant investment in research and development to make
    improvements and advance innovation in original supplies gives resellers an
    opportunity to help customers get the most from their printers, deepening
    loyalty and driving repeat business.