The successful design of a color-imaging system requires knowledge of the factors used to produce and control color. This knowledge can be derived, in part, from measurements of the physical properties of the imaging system. Color itself, however, is a perceptual response and cannot be directly measured. Though the visual process begins with physics, as radiant energy reaching the eyes, it is in the mind of the observer that the stimuli produced from this radiant energy are interpreted and organized to form meaningful perceptions, including the perception of color. A comprehensive understanding of color reproduction, therefore, requires not only a knowledge of the physical properties of color-imaging systems but also an understanding of the physics, psychophysics, and psychology of the human observer. The human visual process is quite complex; in many ways the physical properties of color-imaging systems are easier to understand.
The rapid emergence of color in the next five years will necessitate significant growth in the present technologies to generate quality output. An overview is given of the existing color technologies and some of the major technical advances required for future growth. The emphasis here is on the marking engine technologies, specifically on the leading ones, i.e., thermal, ink jet, and electrophotography.
This paper is a summary of some of the current trends and major issues in color reprographics and printing. Most such systems are, or will be, digital and, therefore, have much in common. A systems view is taken, examining how various elements must be handled to accomplish the goal of making the output print match the user's desires, a process often called WYSIWYG (what you see is what you get). The wide variety of color printer technologies forces one of two approaches; either the system is locked to a given printer or color must be described in device-independent (colorimetric) terms, with the latter approach becoming more common. A desire for device-independence creates a new set of problems; real scanners are not colorimetric, visual adaption makes comparison of displays to prints difficult, users lose the freedom to adjust their creations for a specific printer's idiosyncrasies, etc. The various digital printer technologies also bring new questions to be treated. Simple emulation of non-digital procedures can require very high sample densities, often not available or affordable. Thus, for example, new approaches to halftones are springing up. Examples are used to illustrate how some of these problems are being approached and where issues remain.
My paper will cover the market-related issues and estimated potential of the color hard copy market.
The color hard copy market has been evolving over the past eight to ten years with steady progress in technology and application development.
The color hard copy market is very applications-specific, with some color hard copy technologies better suited to the requirements of an application area than others. Color hard copy market segmentation including major application areas and technologies best suited for the requirements of those applications will be discussed.
A number of factors are driving the evolution of the color hard copy market. Factors such as the use and availability of color monitors, color copiers, and software will be put into perspective. As the color hard copy market continues its development into the 1990's, it's important to understand the business potential today and over the next five years. I will discuss the growth dynamics of the color hard copy market and the estimated potential of each of the major technology areas.
Color hardcopy printing systems are required to be digital and capable of full color expression. In addition, it is desirable that they are completely dry, safe, noiseless, fast, compact, and almost maintenance-free. Accurate tome reproduction, as well as color reproduction, is necessary to produce pictorial images like photographs. On the other hand, such precision is unnecessary for most business uses, where a short through-put time is a more important factor. Therefore, the most suitable printing method for each purpose should be selected. Various printing methods for color hardcopies have been studied recently. The technologies of thermal dye diffusion transfer, thermal ink transfer, and electrophotographic laser printing have been developed extensively in Japan. A lot of research on these printing technologies has been published, and many new products came onto the market last year. This paper deals with the current status of color hardcopy technologies in Japan. The salient features of the specifications of various printing methods are compared, and recent trends are discussed.
This paper addresses trends in the publishing and printing industry from a large commercial printer's perspective, how these changes affect the suppliers to the graphic arts industry, and the impact they have on the quality of the printed output. The article starts with a brief background about R.R. Donnelley & Sons, Co., the largest commercial printers in North America, and its involvement in research and development. Following this, the major trends seen in the graphic arts industry are presented. These include a trend from analog to digital processing which leads to a filmless environment and digital proofing, the increased use and capabilities of electronic printing machines primarily for quick turn around, demand printing applications, and the widespread use of color that must be easy to use yet provide the expected printed results. To conclude, the author provides some comments on the concept of quality as it pertains to a printed color image and what the quality implications may be for some of the trends discussed earlier.
This paper describes a new type lith system, which while providing infectious development, does so with a relatively much slower kinetics of the continuation stage. Furthermore, the sensitivity of the induction period to exposure is relatively smaller across the exposure spectrum. Theoretical considerations indicate that the above unusual characteristics should produce a normal contract halftone; i.e., a distribution of equal density black dots, whose shape and position are determined by the corresponding image points of the original, and whose size, by their corresponding density. A sytem has been developed that does meet the above kinetics. The system produces a screenless halftone which can be used with ordinary plates, inks, and presses, to provide printed results that are capable of resolving in excess of 600 lines/ins.
In recent years there has been great interest and growth in the ability to create images electronically. This trend has been driven by the lower cost of computing and storing data, and the speed in which this can be accomplished. The ability to scan, create, and transmit color images is possible even with the enormous amount of data needed to create color images with gray scale and high resolution. In the past, there has not been a great demand for color copiers because few color images were in existence. The above-mentioned trend is changing this, and in addition scanners can quickly translate color graphics into electronic forms at affordable costs. The replacement of black and white televisions and monitors with color was rapid and nearly 100% once the technology was available at a reasonable cost. It is felt by some equipment manufacturers that soft copy will replace hard copy and there will be a diminishing need for imaging media. The author believes, however, that the need for hard copy will continue, and in fact may increase, but with new technology. To create black and white or color hard copy from electronically generated data, some essential characteristics are needed. They are: (1) total dryness, (2) rapid access, (3) gray scale, (4) high resolution, (5) good image quality, and (6) easy to use, low-cost, reliable equipment. Some of the leading technologies for this are electrostatic, thermal dye transfer, ink jet, instant silver photography, and 3M's Dry Silver. This paper gives a general overview of these technologies, but its main emphasis is 3M's Dry Silver approach.
A high-speed nonsilver lithographic system has been demonstrated for direct laser imaging. The system is negative working and is based on a photoinsolubilization of a polymer coating by redox amplification. The essential components consist of a cobalt(III)amine (Coen), a redox transfer ligand (PAN), a light-sensitive quinone (Q), and a polysulfonamide binder (A6). On exposure, the quinone photogenerates a hydroquinone reducing agent. On heating, the hydroquinone reduces Coen to produce Co(II). PAN then complexes this Co(II) to form CO(II) PAN which, in turn, reduces more Coen. This resulting reaction produces Co(III)PAN and more Co(II) centers, which in the presence of excess PAN and Coen continues the cycle, giving photographically useful amplification.
Polysulfonamide (A6) is an excellent medium with optimal acidity and thermomechanical properties to promote this chemistry. It provides toughness required for a dry-film photoresist, ink receptivity for lithographic plate, and aqueous development for both applications.
Exposure to an Argon ion laser (4881514nm) at dose O.5-lmj/cm2 followed by heating (5 sec/120 C hot plate) produced high-density images that were insolubilized in an aqueous alkaline developer to give final nonswell images of excellent quality.
The silver halide film imaging industry traditionally has not been considered a major polluter. Still, today we face increasing sewer discharge controls for used processing solutions. The environmental community recognizes an emerging hierarchy of waste management. In decreasing level of desirability, this hierarchy includes: make no waste (Green products), recycle, minimize generation of waste, and disposal. Efforts to manage black and white silver halide films processing effluents within the hierarchy are discussed.
While silver halide photosensitive materials offer superiority in image quality -- both in color and black-and-white -- they require chemical solutions for processing, and this can be a drawback. To overcome this, researchers turned to the thermal development of silver halide photographic materials, and met their first success with black-and-white images. Later, with the development of the Konica Dry Color System, color images were finally obtained from a completely dry thermal development system, without the use of water or chemical solutions. The dry color system is characterized by a novel chromogenic color image-forming technology and comprises four processes. (1) With the application of heat, a color developer precursor (CDP) decomposes to generate a p-phenylenediamine color developer (CD). (2) The CD then develops silver salts. (3) Oxidized CD then reacts with couplers to generate color image dyes. (4) Finally, the dyes diffuse from the system's photosensitive sheet to its image-receiving sheet. The authors have analyzed the kinetics of each of the system's four processes. In this paper, they report the kinetics of the system's first process, color developer (CD) generation.
The only appropriate printing technology for a page printer which corresponds in size and performance to a high-end laptop computer is thermal transfer with a line head (printing simultaneously over the paper width). The printer 'MT735 COMPACT' uses such a thermal transfer line head engine. For high speed printing (4 to 8 ppm) this printing technique results in a high power consumption. To reach small outline dimensions and also print without line connection the authors used rechargeable batteries as a power supply. A battery has no problem supplying a large current, but at the same time it shows voltage drops and homogeneous print quality is not self-evident. The authors investigated these effects and developed a realtime process-control of the thermal line head to compensate for these problems. Simultaneously, printing pattern inhomogeneities of the line head are equalized (internal wire resistance).
All thermal transfer serial printers currently use one-directional printing. A new bidirectional printing method for a thermal transfer printer is proposed. The new method features an electro-thermal ink transfer printing system and one-directional ink ribbon feeding at a constant speed. The image quality problems which were found in a preliminary experiment have been solved by using a newly developed ribbon and controlling the drive current pulse.
Thermal dye transfer printing has become accepted as a source of high-quality color hardcopy output. In this process, heat is used to transfer dye from a dye donor ribbon to a receiver sheet. The amount of dye transferred to the receiver sheet is proportional to the amount of thermal energy supplied to the dye donor ribbon. With this technology, it is straight forward to print a 2-to-8-bit tone scale which is necessary for a photographiclike appearance. With is technology, printing of digital images from a variety of applications--which include video, medical, and high-end computer graphics--is possible. Although this technology is capable of generating color hardcopy output with a photographiclike appearance, it is often the case that such output will not have the same image stability characteristics as conventional AgX photographs. Photographic prints are exposed to light, heat, oxygen, water, and fingerprints in normal handling. In this paper, techniques are described to characterize the image stability of thermal dye transfer prints. The results of these studies show that there are both similarities and differences in the image stability of thermal dye transfer prints and conventional photographs.
The authors have investigated the light-fastness of thermal transferred dye images in relation to the concentration of dye that is transferred to the image-receiving sheet from the dye donor materials. It has been found that light-fastness is influenced by the dye concentration on the surface of the image-receiving sheet and also by the concentration below the surface.
A major advance in the field of thermal printing was the introduction of the QuietwriterR marketed by IBM which is based on resistive ribbon and utilizes the most advanced thermal printing technology. This printing technology is also termed Resistive Ribbon Thermal Transfer (R2T2) printing (1), because it is based on an electrically conductive ribbon. A recent detailed review of resistive ribbon printing is provided in ref. 2. In conventional thermal printing processes (3), the gating factor for the speed is the time it takes for the print head to cool down between cycles. Due to this limitation, the printing cycle for each successive printing element is about 2m seconds. A further drawback of this thermal printing technology, is the dependence of print quality on the type of paper used requiring very smooth paper for reasonable quality printing. This is probably due to inadequate heating of the ink resulting in high melt viscosity and consequently poor ink flow from ribbon to paper. This problem is alleviated in resistive printing where ink transfer temperatures are much higher than in the case of thermal head printing (4). In this technology the ink reaches temperatures far above the melting point of the ink. This is achieved by pumping enough energy into the ribbon to reach the necessary threshold temperature. however, there is a practical limit to the energy that the ribbon can withstand in a certain pulse without undergoing decomposition. Therefore, a need was recognized for approaches to improve thermal printing efficiency while minimizing the input energy requirement.
The paper presents a method for automatic adaptation of the color spaces of a scanner and a printer. A colorimetry-based color processing model is set up. Parameters for color correction are determined from the scan values of a color test chart printed with the output device by an optimization process. Finally, advantages of using CIE colorimetry in the reproduction process are discussed.
The authors designed an electrostatic ink jet printing technique that prints using a voltage lower than conventional techniques. The assembly consists of a closely aligned ink roller, mask screen, paper, and an electrode. A voltage pulse is applied between the ink and electrode, then electrostatic force overcomes the surface tension of the ink, and the ink goes through holes in the screen and sticks to the paper. Major factors affecting the success of this technique are the materials comprising the screen, ink attributes, and electrostatic force.
In this paper, the author explores several key electrophotographic printer (ELP) improvements as well as significant new product offerings. The intent is to include only those printers with major technology and/or market impact potential. In order to provide a reasonable taxonomy of features, the author provides ELP trends in the categories of speed, both higher and lower; image quality; controller and page description language enhancements; integration and system trends; and a brief look at marking system improvements. Lastly, a performance metric has been included to show where ELP technology has gone in the last few years.
The authors have developed an auto focus function for laser beam scanners to maintain the best focusing condition of the laser spot, which contributes favorably to the quality of halftone images. The focus deviation of the laser beam scanner attributable to variations in the ambient temperature, mechanical vibration, etc., is measured by the auto focus detector and is automatically corrected by the focus adjusting mechanism.
Westinghouse has developed a thin film electroluminescent (TFEL) edge emitting imaging station for use in electrophotographic printing. The physical and electrical drive characteristics offer unique opportunities for gray-scale printing and resolution enhancement. The physical dimension of the light-emitting element in the process direction is less than to micrometers . In addition, the light output of the edge-emitting array is not Lambertian but, rather, is highly directed. The majority of light is emitted in a wedge with a 30 deg half angle measured form the plane of the device. The array is activated by an ac waveform. Light emission occurs as the field across the device changes direction. The rise time to peak light emission is a few microsecond(s) and the decay is a few hundred microsecond(s) . This allows an array element to be turned on and off several times during the exposure of a single 300 dot-per-inch pixel in a low-speed printer. This paper provides a detailed description of the physical dimensions, electronic drive system, and light emission characteristics of edge-emitting array. Several print samples are shown illustrating the gray scale and resolution enhancement capabilities.
The deflecting facet of a rotating polygon is used very efficiently to perform multiple deflection of a laser beam in an underfilled mode with the help of a fixed mirror. The resulting larger deflection angle and higher resolution allow the use of a large number of facets on the polygon without compromising on facet width or resolution. By special configuration of the beam, the major part of cross scan facet error, which tends to multiply accordingly, is reduced in a self-correcting mode during the multiple-deflection process. The remaining part of the error is corrected through the anamorphic imaging optics. With the large number of facets allowing low rotational speeds, and with relaxed tolerances and simple optics, practical and cost-effective high-resolution and high-speed laser recorders and printers are made possible. Closed form formulas are developed for ray tracing and design of the system.
Color laser printers are beginning to emerge in various configurations from several vendors. Colorocs offer a 300 DPE, PostScript compatible device. It is a dedicated printer based on the same single pass to paper technology used in its full color copier. The double belt system provides color and black and white bilevel printing up to five and forty pages per minute, respectively. Popular applications packages are moving to support color output devices with the speed and flexibility of laser printers. Color laser printers are finding their way into environments not satisfied by the competing technologies of thermal transfer, dye diffusion and ink jet. Proofing, spot color and business presentations are the leading areas requesting the price performance capabilities of color laser printing. Throughout, plain paper, image quality and cost per page are the critical criteria for the growth of color laser printing.
The authors investigated electrophotographic properties of some substituted thiophenecarboxaldehyde-hydrazones as charge transport materials in layered-type photoreceptors from a viewpoint of molecular design. The values of optical bandgap [Eg(opt)] of the polycarbonate films doped with the hydrazones decrease from 2.9 to 2.4 eV with increasing thiophene rings and, therefore, with increasing (pi) -conjugation length. The Eg(opt) values for the thiophene derivatives are smaller than those for phenyl derivatives. Hole mobilities in the polycarbonate films doped with the hydrazones (50% in weight ratio) fall in the range between 1X10MIN6 and 5X10MIN6 cm(superscript 2/Vsec. Any significant difference was not found between the hole drift mobilities for the thiophene derivatives and those for the phenyl derivatives. Hole mobility and charge injection efficiency of the thiophene derivatives increase with decreasing Eg(opt). The hydrazone derivatives with longer (pi) -conjugation length show higher hole mobility and higher charge injection efficiency. And the thiophene derivative shows higher injection efficiency and larger total carrier quantity than the phenyl derivative. The thiophene derivative is superior to the phenyl derivative as a charge transport dopant.
Photoelectrographic masters based on onium salt acid photogenerators have many desirable attributes. They are planar and bipolar, and they require no preconditioning, such as heat or corona treatment. Upon UV exposure, contrast potentials which are > 80% of Vo in < 100 msec after charging are observed. The persistent conductivity lasts for months without noticeable deterioration under ambient conditions. As many as 5000 high-quality prints from a single exposure have been made at rate of ca. 1 print/sec. In this paper, the performance attributes of masters containing a dairyliodonium sulfonate salt as the acid photogenerating compound are demonstrated and discussed.
The author has developed a novel multilayer OPC for a one-shot, 2-color printer, and called it the 2-color OPC. It consists of 3 main layers: an upper OPC layer, middle thin-hole trapping and solvent-blocking layers, and a lower OPC layer. The upper OPC has high sensitivity to 680 nm and the lower OPC has high sensitivity to 780 nm. The following steps are used for a one-shot, 2-color print using the 2-color OPC: (1) positive charge under red light; (2) negative charge; (3) image exposure by 680 nm and 780 nm laser beams which produce two different (plus and minus) latent images. Development, transfer, cleaning, and fixing are then about the same as in the conventional process. In the first charge step, many photo-induced holes traverse through the upper OPC to the hole-trapping layer where they are firmly trapped throughout the other steps. This hole-trapping capability is the key technology and the feature distinguishing this printer from ordinary OPCs. The hole-trapping layer is newly designed for this purpose. If, however, many holes are trapped in shallow traps in the upper OPC midway to the hole-trapping layer most of them will be released at the second charge step resulting in the production of a low (poor) latent image. The author's studies on where holes are trapped, using three different methods, revealed that almost all are trapped in the hole-trapping layer as intended.
The transfer of protons in contact-charging experiments is an example of an ion transfer mechanism and is suggested by the availability and mobility of the H+ ion. In contact charging experiments using metal beads and a resin containing an acidic additive, the author found that the metal beads develop a positive charge, and analysis of the bead surface with a proton-specific dye indicates an increased proton content. These results provide confirmation for proton transfer in contact charging as is often suggested.
In recent years organic salts such as chromium azo dyes have been used as additive to impart desired surface (tribo) charging properties of electrophotographic toners. 1-4 In this study we have prepared solid blends consisting of a chromium hydroxyazoaryl complex salt (T-37 dye), Cr[-0C10H6-NN-C6H3 (Cl)O-]2 [NH4], in a styrene-hutyl methacrylate copolymer containing carbon black powder. We characterized the blends to determine the bulk and interface concentrations of the salt, and relate it to the contact charge. The salt has limited solubility in the copolymer and in organic solvents. It dissolves up to I .7 pmoles/g at a slow rate in the viscous polymer melt at 190 °C. Solid blends with the chromium complex salt in excess of this amount also contain undissolved aggregates of various sizes depending on the preparation conditions. The chromium complex salt also adsorbs on the surface of carbon black up to a monolayer coverage. The carbon efficiently extracts the salt out of THF, and extracts it slowly out of the viscous polymer melt. The toners (10 pm size powder) develop a negative charge on contact. The charge scales with the amount of chromium complex salt in the blend and further varies depending on the proportion of the salt which is soluhilized, exists as undissoled aggregates or is adsorbed on carbon. The chromium complex salt which is adsorbed on carbon is deactivated for charging by the carbon surface.