Printer systns using toners and ink jet inks are catipared and contrasted with particular reference to the materials and their potential for colour printing processes. Sate conclusions are drawn that highlight where particular systems may be nxst suited to certain market segments such as colour desktop publishing and high speed colour printing.

The problems to develop colored single component toners are well known. Because of the unattractive colors of ordinary magnetic pigments it is possible to produce only dull, pastellic color toners, which were not very successful in the market. It will be shown, that this problem can be overcome by using a special iron-powder. named Sicopur FF 4068. which is made by decomposition of iron pentacarbonyl, as a magnetic pigment in colored s ingle component toners

Metal salts of B-diketones such as aluminum acetylacetonate (Al(acac)3) have been found to be potent negative charging additives for liquid electrostatic toners when used in conjunction with surfactant "charge directors". This paper describes the use of these additives and efforts to uncover the mechanism of charging for toners when these salts are used in conjunction with acidic resins. Although pigment interactions were not studied, when pigments were included in the toners the charging results were comparable. Charging of particles in liquid electrostatic toners is not yet fully understood. Fowkes and coworkers have demonstrated that proton exchange is the operative mechanism in charging of carbon black particles in hydrocarbon 1 Results are presented here for a system which does not appear to be charging by an acid/base mechanism. Charging in this system was found to be dependent on the presence of surface ionic species. The chemical nature of these species suggests that charging may be taking place by partitioning of surface ions into surfactant inverse micelles.

AB diblock copolymer additives offer many process and product improvements in liquid electrostatic toners. One area where AB diblocks are superior is as hydrocarbon-soluble charge directors. Unlike conventional charging agents for liquid toners, which are typically natural occurring substances or by-products of the oil industry, these polymers are synthetic, thus can be made reproducibly and pure. Also, their high molecular weights result in very low toxicity vs. nonpolymeric charge directors. In the past, polymeric charge directors for liquid toners have been random copolymers, made from at least two monomers: a polar one to impart charge, and a non-polar one for hydrocarbon solublity. AB diblock copoiymer charge directors have been found to be superior to conventional and random diblock copolymers.1 In random copolymers, the mixing of the polar and nonpolar components dilute the desired charging, resin compatibility, and hydrocarbon solubility of the additives. With AB diblocks, the non-polar and polar segments of the polymer are completely separated, resulting in a sufactant-type structure, which can form inverse micelles with toner particles in hydrocarbon dispersants. Also, since these polymers are grown stepwise, the length and composition of each block can be precisely controlled to optimize for a specific toner. In this work, syntheses of hydrocarbon-soluble AB diblock quaternary ammonium salts and their behavior as negative charge directors in toners are discussed.

Dyed or pigmented synthetic microcapsules are employed in a variety of printing, electronic imaging, and non-silver imaging processes. At the Xerox Research Centre of Canada, we have studied the preparation of synthetic microcapsules, with high pigment content. Various options, useful for the microencapsulation process will be discussed with focus on a new hybrid interfacial polycondensation/free radical polymerization process to produce uniform thin polymeric shells surrounding discrete pigmented core particles. The factors which control the formation and the particle size ofcapsules in this process will be outlined. The influence ofpigment loading on the bulk density and flow properties of the microcapsules will be discussed. The effect ofvarious reaction parameters on the molecular and rheological properties ofthe core and shell polymer will be presented.

Mono-dispersed stable polymer particles of styrene-acrylic copolymer were prepared in a hydrocarbon medium. Those particles were stabilized through acid-base interactions between polymer particles and polymeric stabilizer. Poly(dodecyl methacrylatemethacrylic acid) copolymer was used as stabilizer for the particle formation. In order to interact with acid groups in the stabilizer, basic monomer, DMAEMA (N,N-dimethylaminoethyl methacrylate) was also copolymerized in the particle polymer. The size of polymer particle was controllable through appropriate choices of concentrations of both stabilizer and DMAEMA. Adsorption behavior of charge control agent on those polymer particles were quite dependent on the chemical nature of surface structure. "Core-shell" type polymer particles were quite effective to enhance the adsorption of charge control agent and thus to increase charge to mass ratio of the particles. Mechanism of particle charging was also discussed.

We studied the optical image density of nonfused toner images on paper as a function of toner mass, focusing on the influence of toner particle size on image density, which we studied both theoretically and experimentally. Four different sizes from the same bulk were used to form the solid image. The toner mass required to obtain sufficient image density decreases with particle size. We defined the normalized number oftoner layers, which determines image density regardless ofparticle size. Using mean toner sizes calculated from a cross section ofparticles, we found that theoretical and experimental results agreed well. These results will be useful in developing high-quality electrophotographic printers.

Printed materials are affecting people's lives in a variety of ways and to a constantly increasing extent, both in the private and in the business spheres. In particular, the predicted reduction of printed materials resulting from electronic data processing - the so-called "paperless electronic office" - has not occured, indeed quite the reverse. In recent years electrophotographic reprography has established itself successfully as a competitor to conventional printing processes. In the office a photocopier is now a part of the standard equipment. Because of BASF's traditional intensive involvement with pigments and colored printing inks its interest in new technologies in these areas is especially great. BASF has therefore been engaged in research on carriers for some years now.

I propose to review some of the scientific basis for pigment technology as it is applied to printing inks and the newer printing systems. In this I interpret pigments as referring to solid particulate colouring material in inks, be they Litho ink, electrostatic toner or ink jet systems. The science of pigments for inks can be broken into a number of subdivisions each of which have specific and overlapping influences on performance.

The purpose of this paper is to describe recent advances in liquid toner technology and their applications, both present and potential. As a preface, it is important to keep in mind that liquid toners represent only a segment of an overall imaging system that also incorporates hardware, media and quite possibly, pertinent software. Recent advances in toner design has occurred as a direct outcome of simultaneous advances in the design of the overall imaging system.

When Chester Carison invented xerography, he employed sulfur and anthracene as photoconductors. Although the initial commercialization of his idea relied on inorganic photoconductors, the current trend is towards use of organic photoconductors because of their material variety, economy and flexibility. High speed copying and printing machines use belts coated with organic photoreceptors, while personal copiers and printers use aluminum drums dip-coated with organic photoreceptors. Multilayered, organic photoreceptors are now routinely mass produced by the millions with both visible sensitivity for copiers and infrared sensitivity for printers. This paper presents a brief overview of key photoreceptor properties and follow with a survey of electronic organic materials of current interest. The photodischarge characteristic is determined mainly by three factors: the photogeneration, the injection, and the transport of charge carriers. These functions can be accomplished by separate electronic material layers; photogeneration by organic pigments and charge transport by aromatic-amine electron-donor molecules. The photogeneration layers are usually fabricated by solvent coating a dispersion of a pigment in a polymeric binder while the charge transport layers are solvent coated to form a solid solution of the aromatic amine in a polymeric binder. Examples and characteristics of organic pigments and charge transport molecules of current interest are discussed.

This paper describes light-induced changes in xerographic characteristics of multilayer organic photoreceptors composed of a carrier generation layer (CCL) and a carrier transport layer (CTL) . It has been found that the light-induced changes were caused by resistivity change in the CTL and depend on the optical bandgap of the CTL. It has been aLso found that a stable photorecepthr is obtained by controlling compositions of carrier transport material and binder matrix. The lightinduced changes in the CCL were not found.

Hole transport has been investigated in films of solid solutions of N,N'-diphenyl-N,N'- bis(3-methylphenyl)-[1, 1 '-biphenylj-4,4'-diamine (TPD), ETPD, a structural variant of TPD and a hydrazone molecule in two different polymer binders. Rather than being 'inert' as generally assumed, the binder plays a major role in influencing the rate of charge exchange between molecules. It is found that the absolute values of the drift mobilities, their electric field dependence and the activation energies are strong functions of the binder polymer employed to cast the film. At equivalent molecular concentrations but with two different binder polymers, the mobilities can vary by as much as two orders of magnitude. In some instances mobility decreases as the electric field is increased. The increased mobility of dispersions in polystyrene is directly related to the reduction in the activation energies. The role that binder plays may be related to the dispersibility of the diamine molecules in the polymeric binders.

A recently described scanning stylus instrument1 has been used to investigate the electrical properties of individual microscopic electrical defects in organic xerographic photoreceptors. Using a shielded scanning stylus with an effective diameter of 85 pm we have mapped the shape of individual microscopic electrical defects with 5 im resolution and measu red thei r cu rrent-voltage characteristics. H ig h resolution ma ps reprod uced the shape of the stylus indicating that the underlying defect is much smaller than the stylus size. The observed current-voltage characteristics were approximately quadratic in the applied voltage and the currents were basically constant on the time scale of tens of seconds. This observation is an indication of charge injection from the substrate and space charge limited (SCL) currentflow. The magnitude ofthe current enables an estimate of the upper limit of the size of the injecting spot of about 4 pm. This conclusion is derived on the basis of one dimensional SCL current flow and the argument is presented which indicates thatthe defects may be much smaller, possibly point-like in nature.

The series of N,N'-disubstituted diimides of perylene-3,4,9,10-tetracarboxylic acid, represented by the general structure shown below, is of interest for two reasons: a) the color of the solid pigment is markedly dependant on the nature of the substituent, R, and can vary from red to brown or black and, b) they are generally well known as effective organic photoconductors. We have synthesized and characterized a series of compounds with a selection of alkyl groups having different degrees of chain branching (R=C5H11, 6 isomers) and chain length. Thin layers of pure material were vacuum deposited onto transparent conductive su bstrates a nd spectroscopically cha racterized. Xerographic photo receptors were prepa red by overcoating these with a charge transport layer and the spectral photosensitivity between 400 and 800 nm was measured. The effect of chain length and chain branching upon solid state absorption spectrum and xerographic spectral photosensitivity will be presented and compared with the properties of previously described perylene bisimide photocond uctors.

A study has been made of a family of six substituted arninobenzaldehyde-hydrazories in which molecular properties are related to electrophotographic function. The transport molecules are characterized by optical absorption, oxidation potential and strength of charge transfer complexation with the polymer binder. The evaluation of electrophotographic function includes charge transport mobility, charge injection efficiency from the generation layer and residual voltage. I lole mohilities in these materials differ by several orders of magnitude. The mobility is not (simply) correlated with any molecular electronic property such as oxidation potential or absorption wavelength. The most relevant molecular parameter appears to be number of phenyl substituents on the amine and hydrazine nitrogen atoms. The polymer binder also afTects the mobility. A solid solution in of DElI in polyarylate, which is a weak electron acceptor and forms a weak charge transfer complex with the donor transport molecule, has a lower activation energy for transport than l)El I in polycarhonate which forms no such complex. The charge injection efficiency has been related, in the past, to the oxidation potential (E0) ol the transport molecule. It is shown here that E0 correlates better with the residual voltage, and a simple model is developed to explain the relationship.

There has been much interest recently in hydrogenated amorphous silicon-based photoreceptors. The conventional configuration has become a diode-like semiconductor structure with an insulator overcoat layer operated in reverse bias. We have investigated the electric field and temperature dependence of the xerographic dark discharge of a corona or capacitively charged a-Si :H photoreceptor of configuration Al/a-Si:H(p)/a-Si:H(i)/a-5i1 _xCx:H . The band gap mismatch at the semicondutor/insulator interface appears as an energy barrier in the conduction band only. The role of this energy barrier in the dark discharge mechanism has been investigated by us. With a high initial field charging regime thermal generation within the intrinsic region was identified as the rate-limiting process. The zero-field energy barrier for thermal emission is measured to be 0.94 eV. These observations are in agreement with other workers, but previously reported anomalous temperature-dependent high-field behaviour was not observed. An apparent bulk controlled negative differential resistance (NDR) was found by us to control the discharge in the low-initial field regime. A NDR has been observed previously in the d.c characteristic of these devices where an increasing bias was applied step-wise. The observation of a similar NDR in the xerographic discharge mode is somewhat surprising.

The time evolution of the surface potential of xerographic photoreceptors charged in the dark can yield valuable information conerning, the underlying thermal generation processes and the energetic distribution of emission centres. Xerographic dark discharge of a-Se :Te films proceeds according to the xerographic depletion discharge (XDD) model. According to this model the depletion time td should be singly activated. We find that for a-Se :Te alloys in the alloying regime 5-1 2wt% Arrhenius plots of td are non-linear and yield characteristic attempt-to-escape frequencies typically 1 8 times greater than phonon frequencies in these materials. This result can be only partially accounted for by the recent fourth-order approximation of the demarcation energy concept. The presence of exponential distributions of emission centres in this material system is shown by the application of the field-enhanced XDD model at constant temperture. A theoretical fit of temperature-dependent data is then achieved by consideration of the occupation function of emission centres close to EF and the temperature dependence of the mobility gap. For the materials studied, the best fit to the experimental data was achieved with EF located at an energy corresponding to half the optical gap from the mobility edges. The thermal generation mechanism is identified as the process C3 -* C30+h followed by C3° C1 + h.

The photoferroelectric barium titanate (BaTiO3)/polyvinylidene fluoride (PVDF) composite films in the ratio 70:30 are found to possess good photosensitivity in the visible region of the spectrum. Results on the investigations of charge generation, trapping, recombination, discharge, and retention properties of the composite film are presented in this paper. The dark polarization and dark depolarization characteristics of the film show that it can accept and retain very high charge for a very long time. The charge decay properties of the dark polarized and photo depolarized electrosensitized sample indicate that it can be used successfully in electro-photographic applications as the dark decay is found to be slow while the light decay is very fast. In addition to this, the photo polarization and photo depolarization studies of the polarized films show that the film has very good remnant polarization,which persists for several hours to days. The persistence of polarization, its magnitude, and the decay characteristics depend on the charging conditions. The resultant dark and photo depolarization current values are found to increase linearly with increase of the poling field, illumination intensity, and poling time. The polarization properties of the film are comparable to that of the BaTiO3 single crystal. The results of the studies show that BaTiO3IPVDF composite films may find many interesting applications as a photoreceptor in the fields of electrophotography, holography, and optical memory. It may also be useful as a photorefractive nonlinear optical material.

No Abstract Available

A model of the imaging process involving both the checkerboar& process and the analog process of imaging has been developed to describe both the granularity and the grey scale characteristics of the microencapsulated imaging process. The model is shown to provide a quantitative rationale of sensitometric and microdensitometric behavior of the system. The results of the analysis demonstrate that while the analog process governs the grey scale character of capsule images, there is a significant contribution from the digital process. This digital process manifests itself primarily in the granularity characteristics of the image and, except in special cases, contributes relatively little to the grey scale of the image.

We propose a new image- recording system employing light and heat energies. This transfer recording medium comprises a substrate and a recording layer on which plural kinds of colored microcapsules are arranged to form an image. Each microcapsule contains a colorant, a monomer and a photo-initiator. Only when the light with a proper wavelength and the heat energy are simultaneously applied to the microcapsules, the monomer is polymerized and hardens the microcapsules, so that the hardened microcapsules can not be transferred to paper any longer. This photo thermal microcapsule transfer technology through a single transferring step will realize to make high-quality full-color image by a compact apparatus, and can be applicable for digital color printers or copying machines.

Benzalphthalide and a number of its analogues significantly enhance the sensitivity of thermal coatings. These sensitizers are effective in coatings developed by benzyl-p-hydroxybenzoate (benzylparaben) , 2 , 2 -bis (p-hydroxyphenyl) propane (bisphenol A) and bis-(3-allyl-4-hydroxyphenyl)sulfone in combination with a variety of leuco dyes. The background stability of the coatings depends upon the specific benzalphthalide employed.

The coating color for the direct thermal paper basically consists of the leuco dye, the cobr developer and the sensitizer. Blacking dyes to be used for thermal papers call for other practicable properties than the tone, such as storage stability, thermal sensitivity and white background. Since no universally accepted theory in choosing proper developer and sensitizer is available, however, selection will have to be conducted on the designer's experience. Such practical considerations as the stability of the recorded image and matching with the particular machine to be used for are important beside the chemical considerations.

We have developed a new type of non-glossy surface of an image receiving sheet for a photothermographic color hardcopy system. There is a basic conflict in realizing uniform dye transfer with use of a receiving sheet having a matted surface, because when the degree of roughness exceeds a certain extent, uneven dye transfer readily takes place. It: has been solved by use of "microscopic" phase separation of a certain water-soluble polymer blend which constitutes the surface layer of the image receiving sheet. One of the preferable polymer blends for our purpose proved to be a ternary system, consisting of sodium salt of polymethacrylic acid (PMAA-Na), ammonium salt of polyacrylic acid (PAA-NH4) and water. Phase separation, which proceeded during the evaporation of water from the coated mixture, turned out to be of a spinodal decomposition type and thus capable of stably providing a desirable non-glossy surface.

Recently direct thermal recording systems have become very popular and are increasingly used in various fields. Consequently, strong demand has arisen for a thermal paper that has good response to heat, the background and images thereon having high stability and a strong resistance to various chemicals and various solvents. Many attempts have been made to overcome the difficulties described above. However such attempts have had a tendency to lower response to heat and further to be insufficent with respect to the stability of solvents. Therefore, we have developed a new method for production of a heat sensitive layer having in itself high resistance to various solvents and also using specific new materials. The most important aspect of our new method consists in the use of specific developers with very low solubility in organic solvents and very strong developing activity. Originally, we intended to use the high developing power of zinc salicylate derivatives, these generally having a high solubility in solvents. But now our efforts have been concentrated on lowering the solubility of salicylate. Finally, we found some very specific salicylate that has a very poor solubility in almost all solvents. We have now succeeded in providing a much more reliable thermal paper which has stronger resistance to various kinds of chemicals.

Direct thermal dyes are members of a class of compounds referred to in the imaging industry as color formers or leuco dyes. The oldest members of that class have simple triarylmethane structures, and have been employed for years in various dyeing applications. More complex triarylmethane compounds, such as phthalides and fluorans, are now used in various imaging systems to produce color. Color is derived from all of these compounds via the same mechanism, on a molecular level. That is, an event of activation produces a highly resonating cationic system whose interaction with incident light produces reflected light of a specific color. The activation event in the case of a direct thermal system is the creation of a melt on the paper involving dye and an acidic developer. The three major performance parameters in a thermal system are background color, image density, and image stability. The three major dye physical parameters affecting thermal performance are chemical constituency, purity, and particle size. Those dyes having the best combination of characteristics which can also be manufactured economically dominate the marketplace. Manufacturing high performance dyes for the thermal market involves multi-step, convergent reaction sequences performed on large scale. Intermediates must be manufactured at the right time, and at the right quality to be useful.

This study shows an approach of dimensionless groups to correlate the physical properties of thermal transfer ink and how to form certain criteria for selecting ink ingredients.

This paper describes the relation between the dynamic properties of thermo-fusible ink and print quality. We have payed attention in particular to tensile strength of ink, which may have relation to separation stage in thermal transfer printing process. When a printer works at low speed, melting ink is expected to have returned to the solid state at the separation stage. When printing is made with high speed, however, the ink does not have enough time to be cooled and solidified. We have found the appearance of image voids on rough-surface paper decreases with increasing elongation of warm and softening ink. In addition, we have found a small dot image can be obtained in a good shape with the ink of relatively low tensile strength at room temperature.

A two layered ink sheet with a super-cooling wax layer under a usual hot melt type ink layer was developed. Super-cooling characte- ristics of various waxes was investigated by a light scattering evaluation method. Difference in light scattering intensity between the ones from the molten wax and from the solidified wax was utilized as the light scattering intensity depends on the crystallinity of the wax. By this screening, several kinds of preferable super-cooling waxes were found. The super-cooling ink layer, once heated under the thermal head, keeps it's molten state even when the sheet reaches the peeling transfer place in printing process, with the ink below the solidifying temperature. There, the non solidified layer is easily peeled off the sheet, resulting in the smooth transfer of the overall ink layer on rougher paper surfaces. The thermal transfer ink sheet employing the optimized wax was fabricated. High quality printing on lusterless plain paper was achieved by this ink sheet.

The electric field transfer of charged toner particles across a gap has been investigated. Distributions in size and charge of spherical particles, as well as random placement, are allowed for in a computer simulation. The approximation of a semiinfinite slab model of toner on a substrate is used to derive some general trends. While a complete model would require consideration of nonspherical toner, polarization, and Van der Waals forces, the approach described here is in semi-quantitative agreement with visual observations and measurements of toner mass transfer as a function of field.

Both electrostatic and toner concentration (TC) electrophotographic process control systems can be constructed with the proper use of bias current measurements of the development subsystem. A TC I developability controller can be made by measuring the development bias current for each print or copy, summing the measurements, subtracting offset currents and dispensing toner proportionally to this developed charge measurement. If certain constraints are fulfilled, the system will operate at a constant developed toner mass. Similarly, a photoconductor electrostatic measurement I control system can be made by utilizing bias currents. This is accomplished by choosing a stable portion on the developed charge vs development voltage relationship of the development subsystem. This setpoint is then used to measure photoconductor test patch voltages by monitoring the bias current. In some cases this provides the same function as an electrostatic voltmeter. These low cost techniques enable the practical process control implementations in low and medium speed electrophotographic machines.

This paper presents a new electrophotographic color process of superposing toner images on a photoconductor. This process is characterized by the methods of electrostatic image forming and developing on the photoconductor. To attain high quality color prints, we have developed (1) the electrostatic image forming condition (2) non-contact developing method by using 2-component developer.

Black and white photographic film images consist of randomly located sdlver grains converted from photo-sensitive silver halide crystals as image recording unit, thus resulting in a granular structure from a microscopic viewpoint. In color photographic films, dye clouds are formed around developed silver halide grains. Such granular structures tend to provoke an impression of graininess and are known to further affect image sharpness' as well as bit capacity 2 ) The effect of the image structure on image sharpness also takes place in electronic still cameras using CCD image sensors though of course there is a clear difference in the regularity of imaging unit arrangement. It is thus of theoretical and practical importance to explicitly separate the two factors i.e., the optical and granular contributions influencing upon the image sharpness. The present paper proposes a new analyzing method of separating granular contribution and further characterizes typical imaging systems in terms of optical and granular contributions to their sharpnesses.

The electrographic marking characteristics of 16-level halftone gray scale images are investigated by calculating the electrostatic latent image density ( i.e. developability ) as a function of the receptor thickness and the pixel size. Both the developability of a solidgray area and the contrast developability between two different gray bar-patterns are considered. The numerical results obtained provide a guideline to determine the ideal receptor thickness for optimum image quality. The image qualities expected from different types ofhalftone patterns are compared.

The contact charge on polymers is influenced by added organic salts, and the charge is higher when the additive is polymer-bound rather than molecular.'7 In our studies, the presence of an ionomer consisting of a polystyrene random copolymer with pendent N-methylpyridinium toluenesulfonate groups in the host resin produces a positive charge, and the charge is higher than with the molecular analog, 4-ethyl-N-methylpyridinium toluenesulfonate.68 These studies were made with powders, and the charge was activated by rolling the powder with larger sized particles. The charging is attributed to ion transfer, where the toluenesulfonate anion (OTs) transfers from one particle surface to the other, and the proposal is supported by the observation of OTs on the second surface by XPS. l'he different charge levels were attributed to the relative mobilities of the cation and the anion, where in the ionomers, the cation is 'anchored' to the polymer and only OTs is mobile. With the molecular salt, both ions can transfer, although in unequal amounts, thus producing a smaller net charge. We now report our results from the analyses of the charged powders with a Simpson charge spectrometer, which allow us to relate the charge distributions with the charge levels in these materials.

A series of branched polyester toners was synthesized by design to exhibit a systematic variation in the level of tetrafunctional branching agent and a nearly matched melt viscosity. The branching agent level was varied in five steps from 0 to 5 mole percent of total diol component in the fmal polymer. The various compositions were polymerized by a one-step toner synthetic process to avoid the molecular weight degradation normally associated with the melt compounding step. These materials were then ground to toners that exhibited a broad range of performance characteristics. The toner hot offset temperature was found to be nearly independent of branch agent concentration, while the image glossing characteristics of these materials were found to vary over a broad frequency (or equivalent temperature) range. These results suggest that the hot offset temperature is mainly a function of the melt viscosity of toners with similar chemical and rheological characteristics and the glossing response is determined primarily by their elastic properties above Tg. The change in glossing timescale tracked quantitatively the change in the terminal zone elastic modulus for these and analogous branched polyester toners.

The electrostatic charging of non-aqueous dispersions involves the interaction of basic dispersants or basic charge-control agents with the acidic surface sites of the particles to provide negative charges, or the interaction of acidic dispersants or acidic charge-control agents with the basic surface sites of the particles to provide positive charges . The mechanism has three steps : 1) , adsorption of the dispersant or charge-control molecules by acid-base interaction with the surface sites; 2), proton-transfer or electron-transfer between some of the adsorbed species and surface sites; and 3), desorption of some charge-carrying adsorbed dispersant or charge-control molecules due to a dynamic adsorption-desorption process. In these studies the importance of the last step is illustrated with comparisons of zeta-potentials and heats of adsorption determined with various pigments interacting with several charge-control agents. It is found that although acid-base interactions are necessary for electrostatic charging, stronger acid-base interactions result in lower zeta-potentials, probably because of less desorption in the last step. Additives used to enhance charging of acidic particles are believed to be effective by diminishing surface acidity, so as to weaken the adsorption of charge-control agents, and favor their easier desorption in the last step of the charging process.

The decade of the eighties has seen a remarkable transformation in the performance and capabilities of shared and personal printers. Dramatic gains have been made in four key areas: cost, throughput, reliability and most significantly, print quality. The improvements in text print quality due to algorithmic fonts and increased resolution have been pivotal in the creation of the desktop publishing market. Electronic pre-press systems now include hardware to receive Postscript files accompanied by color originals for scanning and separation. These systems have application in the commercial printing of a wide variety of material e.g. books, magazines, brochures, newspapers. The vision of the future of hardcopy now embraces the full spectrum from typeset text to full color reproduction of natural images due to the advent of grayscale and color capability in printer technology. This will place increased demands for improvements in print quality, particularly in the use of grayscale and color. This paper gives an overview of the challenges which must be met and discusses data communication standards and print quality measurement techniques as a means of meeting these challenges for both color and black and white output.

SONY's announcement of tlavica system shaked the world in 1981. In the new nonphotographic imaging system, image is acquired with CCD to be converted into electric image-signal, stored in magnetic recording media,displayed on a CR1 and printed on a special sheet. To get a hard copy, Sublimation Transfer technology was developed. That announcement brought about world-wide R&D of competitive color imaging systems: Ink-jet, Wax transfer,. Sublimation Transfer(ST) and Electrophotography. In spite of much effort,most of those were insufficient for getting a good hard copy. Developing sufficient ST recording media, Dai Nippon Printing started ST recording media business in 1986. It was the first manufacturing scale production and sale of ST recording media in the world. Nowadays ST technology is known for its advantages: high image quality, consistency from copy to copy, smooth tone-reproduction from high-light to maximum density, and easiness to use. In the following paper progress of ST recording media and the present situation and future markets of the media will be presented.