understanding evolution in the color electrophotographic printing
Imaging & printing technology backgrounders first half 2002 understanding evolution in the color electrophotographic printing process history 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. applications 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 Feature Benefits Chemically grown manufacturing process Allows smaller and very uniform particle size Allows very smooth, spherical shape Allows different properties for exterior and interior of particles 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 pigment spherical polymerized toner particle formulation 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 toner. 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. Conclusions 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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