Search

Electrostatic elds in the toner image transfer nip of laser printers were calculated by exact solution of the Poisson equations for a two-dimensional (2D) model and by applying for the paper the approximation of dielectric thickness. Both the distribution and location of the electric eld strength component parallel to the paper surface were investigated and eld values were calculated for different paper and toner parameters. The conditions of the occurrence of Paschen discharge in the toner image transfer nip were analysed.

Interdiffusion in carboxylated styrene/buyl acrylate latex films studied by topographic and thermal analysis

A robust method is used for analyzing roughness at a wide range of lateral length scales. The method is based on two-point correlation where both the amplitude and lateral spacing of surface heights are considered when determining the roughness. Atomic force microcopy and confocal optical microscopy images were captured for a set of pigment-coated samples. The effects of sampling interval, image size and filtering on surface roughness were studied. Isotropy and periodicity of roughness were determined by analyzing the angular distribution of the correlation length (T) and the autocorrelation function (ACF). A clear dependence of root mean square (RMS) roughness (σ) on T was established for randomly distributed surfaces. By taking into account the σ–T dependence it was possible to obtain σ for various length scales for each sample and thus attaining the most relevant σ for a certain surface function, which in this study was specular reflection of light (gloss). The roughness analysis showed that a small amount of DPP coating was sufficient to completely cover and change the surface of the substrate, while kaolin coatings gave a different response.

The thermal properties of two conventional polyester-based toners and a chemically prepared styrene/acrylate toner with different thermal histories were studied by scanning probe microscopy (SPM) and differential scanning calorimetry (DSC). The thermal transition temperatures detected by SPM agreed with the results of the DSC measurements. The validity of SPM for detecting thermal transitions was further confirmed by studying two amorphous reference polymers with different glass transition points ( T g ) and three crystalline reference polymers with different melting points ( T m ). When the toner sample was heated by the SPM probe above the glass transition temperature of the toner powder ( T probe > T g ), changes occurred in the surface topography and roughness causing different levels of local sintering of the particles. A set of roughness parameters calculated from the SPM image data were used to quantify the most essential features of toner surfaces. Environmental scanning electron microscopy (ESEM) was used to study the penetration depth of heat dissipated by the SPM probe. The probe-annealing was compared with oven-annealing in order to establish the effect of thermal history on the thermal properties of the materials.

Scanning probe microscopy (SPM) was used to study the thermal characteristics of latex films consisting of blends of two different styrene-butadiene copolymers with different glass transition temperatures (Tg). The resonance frequency (ω) and the quality factor (Qp) of an SPM probe oscillating above the sample surface were determined at different probe temperatures (Tp). Thermal transitions associated with a change in heat capacity were observed in the Δω-Tp curves. The results were compared with differential scanning calorimetry measurements. The very slow heating rate used in the SPM method effectively eliminated the contribution of volumetric changes of the films around Tg. Annealing of the samples in an oven did not influence the thermal transitions observed in the Δω-Tp curves. The SPM method also enabled a novel approach for determining transition-induced dimensional changes (vertical contraction, expansion) of the films. Annealing was found to increase the dimensional stability of the blend films. The latex blends were also annealed by the SPM probe and the film progressed from particulate phase morphology to a continuous phase. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008

The glass transition temperature ( T g ) for two latices with different styrene/butadiene compositions was determined by the thermal SPM probe resonance frequency method. The results were compared with the T g values obtained by differential scanning calorimetry (DSC), dynamical mechanical analysis (DMA), process rheometer (PR) and thermo-mechanical analyzer (TMA) measurements. The T g values detected by the thermal SPM method agreed well with the T g values obtained by DSC and calculated by the Fox–Flory equation. DMA, on the other hand, showed a significantly higher T g value for both latices than those obtained from theoretical calculations, the thermal SPM method and DSC. The T g obtained from the PR curve was slightly higher for the latex with a low styrene content, whereas good agreement was obtained with the thermal SPM data for the latex with a high styrene content. The glass transition temperature determined by TMA agreed fairly well with the thermal SPM data for the latex with the low styrene content, whilst the value of T g for the second latex was much less than those obtained by the other methods. The thermal SPM method detects changes in thermal behavior (thermal diffusivity, heat capacity) during heating of the latex films rather than changes in the mechanical properties. Information about the sample history could be seen in the thermal SPM curves, which was further associated with the degree of latex film formation, especially when the roughness of the films was taken into consideration.

The interactions between paper coating lubricants and a carboxylated styrene/butadiene latex emulsion and their effect on latex film morphology have been studied. Calcium stearate, non-ionic polyethylene emulsion and organic triglyceride lubricants showed different interaction characteristics with the latex emulsion according to viscosity, zeta potential and isothermal calorimetric measurements. Calcium stearate lowered the viscosity of the dilute latex emulsion at low concentration suggesting a strong interaction with the latex particles due to a change in the hydrodynamic dimensions of the latex particles. The exothermic enthalpy change supported the assumption of a dissociative interaction. In contrast, both non-ionic polyethylene and organic triglyceride emulsion showed less pronounced enthalpy changes, indicating lower affinity for the latex particles. The reduction in viscosity showed, however, that at low lubricant concentrations there is an interaction between the latex particles and particularly the organic triglyceride emulsion. This suggests a selective adsorption of stabilizing agents and species from the lubricant emulsion which alters the hydrodynamic radius of the latex particles. The effects of the colloidal interactions on the morphology of the latex films monitored by Atomic Force Microscopy (AFM) indicated that specific surface interaction occurring in aqueous media influenced the topography and the surface chemical heterogeneity of the latex films. Especially in the case of calcium stearate, it seems that the dissolved species arrange themselves around the latex particles inhibiting film formation. The organic triglyceride, on the other hand, showed a lower interaction potential in the aqueous phase and it had a different impact on the film formation.

This paper concerns the combined influences of high impaction rates and surface geometries on the spreading–absorption behaviour of Newtonian fluid droplets under non-equilibrium conditions. A volume of fluid method is used to simulate the motion of up to 50 μ m diameter droplets onto surfaces comprising protuberances below 12 μ m in width. On both flat and systematically arranged pyramidal surfaces, spreading is an exponential function of the maximum depth of absorption. Surface spreading is furthermore a linear function of the droplet Reynolds number and a simple method of predicting spreading from the Reynolds number has been identified herein. At high impact velocities, kinetic energy driven spreading dominates over wetting driven flow; though, its relativity to absorption is a function of the droplet pressure pulse. Lateral (plan view) spreading on irregular surfaces is found to be inversely proportional to surface roughness. In this paper, surface geometry is shown to be a critical determinant of both spreading and absorption and thereby, the research herein provides details that could be useful in functionalising surfaces. Finally, new surface roughness equations derived herein make the comparison of surface spreading to surface roughness more realistic than commonly used roughness factors such as the Wenzel and R a roughness.

Association between a sodium salt of a linear dodecylbenzene sulphonate and a non-ionic fatty alcohol ethoxylate surfactant during film formation of styrene/butadiene latex

Changes in the surface chemical properties of kaolin minerals may significantly affect the amounts of poly(vinyl alcohol) (PVOH) and its more hydrophobic analogue, partly hydrolysed polyvinyl acetate (PVOH/Ac), which are adsorbed. It is shown that pre-adsorbed anionic sodium polyacrylate (NaPA) and sodium hexametaphosphate (SHMP) dispersants increase the adsorbed amounts of both PVOH and PVOH/Ac. The mineralogical characteristics of the minerals were found to be even more important for the adsorption process, which is attributed to the larger amounts of PVOH/Ac adsorbed onto kaolin minerals with higher concentrations of montmorillonite contaminants (>1%). Very low affinity was found between the polymers and those kaolin minerals substantially free from montmorillonite. The low affinity of PVOH and PVOH/Ac for a silica surface strongly suggests that the silanol groups located on the basal plane of kaolin particles may not act as main anchor sites for the polymer. This strongly indicates that the non-ionic polymers have a great affinity for the ancillary montmorillonite mineral on the kaolin.

The influence of the latex surface chemistry on the association of latices with different cellulose derivatives has been investigated by means of isothermal calorimetry and electrophoresis. The chemistries of three grades of coating latices differed with regard to the type and amount of vinylic monomer and the level of carboxylation. In addition, a styrene/butadiene latex substantially free from surfactant was used to establish the influence of physically pre-adsorbed surfactants on the association with the cellulose derivatives sodium carboxymethylcellulose (NaCMC), hydroxyethylcellulose (HEC) and ethyl(hydroxyethyl)cellulose (EHEC). The results show that the latex chemistry, in terms of hydrophilic character originating from carboxylic acid groups, significantly affects the adsorption of the non-ionic HEC and EHEC. A higher degree of carboxylation or a more polar latex, such as vinyl acetate/acrylate, reduces the association with non-ionic cellulose derivatives. The addition of anionic sodium dodecylbenzene sulphonate or non-ionic fatty alcohol ethoxylate surfactants to the surfactant-free styrene/butadiene latex emulsion did not significantly change the association behaviour with EHEC, although it was evident that, for example, a sodium dodecyl sulphonate type of surfactant participated significantly in the adsorption process. Even if the surface polarity of the latex governs the association characteristics at the interface, the solubility properties of the cellulose derivatives must be considered, meaning that the hydrophobic character plays an important role in the associative interaction between the latex and cellulose derivatives in aqueous media.

The influence of aluminium and titanium dopants on the structure and properties of MCM-41 silica has been evaluated and compared with previously published results. The acidity and basicity of the surface states (adsorption sites) were of special interest. The total acidity was studied by using temperature-programmed ammonia desorption (NH3-TPD). Additionally, organic probe molecules with known Lewis and/or Brϕnsted acid or base functional groups were adsorbed on the powder samples in dry cyclohexane. Both UV–vis spectroscopy and microcalorimety were used to quantify the adsorption. The adsorption data of the monofunctional probes were fitted with Langmuir-, Freundlich- and Henry-corrected Langmuir isotherms providing both the number of the surface sites and strength of probe molecule adsorption. The surface charge densities, relating to Brϕnsted acidity and basicity, were determined for the doped samples in water using potentiometric titration. DRIFT spectroscopy was used to identify the type of the surface sites. The hexagonal pore structure of the doped MCM-41 samples was observed to remain roughly unaltered for all samples. The NH3-TPD analysis indicates that the acidity increases as a result of modification. The probe adsorption showed that the number of sites increases and the strength of adsorption enhances with surface modification. It seems that the simple Langmuir-isotherm is sufficient for the surface state analysis in most cases. In a few cases, the Freundlich- or the Henry-corrected Langmuir isotherm gave, however, a superior fit to the experimental surface excess data. The DRIFT-analysis confirmed the existence of Lewis sites and the formation of Brϕnsted type acid sites with enhanced Al- or Ti-doping, which was supported by the other methods used.

The interactions between highly cationic starch and likewise cationic calcite were investigated by determining the adsorption isotherms and the flocculation of the calcite dispersions at different concentrations of starch. Starch of varying degree of substitution (DS), 0.2, 0.35, and 0.5, and molecular weight (MW), ∼3800 and ∼2×106 g mol−1, were used. The experiments were in addition made at three different temperatures; 25, 35, and 45 °C. It was found that the interactions in most cases were of fairly low character. Consequently, the entropy and low solubility of the starch are expected to be the dominant driving forces for adsorption. The cationic character of both the untreated calcite and the starch generate an electrostatic repulsion that counteracts a possible adsorption. There is also repulsion between the cationic substituents in the starch, which among others factors controls the solubility of the starch in the aqueous phase. The repulsion can be affected by adding electrolytes. NaCl was used for this purpose in this investigation. As a result of the changes in the electrostatic repulsions the adsorbed amount of starch onto calcite did also change. The adsorption did increase with increasing NaCl concentrations, as did the degree of flocculation. The high MW starches did in all the conditions examined adsorb to a higher degree than did the low molecular ones. Increasing the temperature from 25 to 45 °C causes changes in the adsorption and flocculation behavior of the dispersions, especially in systems where starch with DS of 0.2 is present. The starches of higher charge are less affected by the temperature due to stronger internal repulsion. The low MW starches did not flocculate the calcite dispersions, while the starches of high MW initially flocculated the dispersions and restabilized them at higher concentrations. The high MW starch with DS 0.2 induced the strongest flocculation.

Electrospinning is an efficient process for producing polymeric and hybrid nanofibers. There is, however, a lack of understanding concerning scalability of the process and in particular the production rate optimization. The electrospinning mass transfer intensity depends predominately on solution parameters, process parameters and the design of the equipment. These parameters influence the deposition intensity of the spinning process differently, but it is not known which factors dominate. The e-spinning deposition intensity of polyethylene oxide, polyvinyl alcohol and their mixtures was investigated using a bubble foamed polymer solution surface to promote high mass deposition. Based on the measured properties of the solutions, a mathematical criterion was developed which made it possible to predict the electrospinning intensity of a given polymer solution. The proposed formula agrees with the experimental data and confirms that spinning intensity can be predicted from pre-determined solution parameters. Using computer modeling, the weighting coefficients of the solution parameters have been determined, showing which parameter is the most important for the process intensity. The criterion and the same weighting coefficients were applied to the analysis of published data and it was found that they can be applied not only for electrospinning from the foamed surface but also from the free surface. A physical explanation of the criterion is proposed. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015, 132, 42034.

Transformation of cellulose into monosaccharides can be achieved in a chemical process performed by a special group of enzymes known as cellulases. We have used atomistic molecular dynamics simulations to study endoglucanase II (Cel5A) that is one of the proteins in this group. Based on the atomistic simulation results, we discuss how the Cel5A enzyme interacts with cellulose fibrils comprised of both crystalline and amorphous regions. We show that the enzyme’s carbohydrate-binding domain prefers to interact with crystalline regions of cellulose, while the catalytic domain has a high affinity to the amorphous regions of fibrils. In particular, through electrostatic interactions the catalytic domain attracts loose glucose chains to its catalytic cleft. The atomistic details of the enzyme–cellulose interaction are presented and the implications for practical applications are briefly discussed.

The role of stabilizing agents in the interaction between styrene/butadiene latex and calcium carbonate particles has been studied using isothermal titration calorimetry (ITC) and an electrokinetic sonic amplitude (ESA) technique. It is demonstrated that the polyacrylate sodium salt (dispersing agent, referred to as NaPA) used as stabilizing agent for the calcium carbonate suspensions principally affects the interfacial properties of the calcite surface. An electrostatic barrier is created and this decreases the attractive interactions between the latex and the negatively charged mineral surface. The total enthalpy change observed when an emulsion of styrene/butadiene particles substantially free from surfactant was added to the dispersed calcium carbonate could be described via a relatively complex path. The process included (i) an exothermic response from the association of the latex particles (adsorption process) with the dispersed calcium carbonate surface and (ii) an endothermic bulk phase effect due to the adsorption on the latex particles of dissolved species originating from the calcium carbonate. Stabilization of the latex particles with sodium dodecyl benzene sulfonate (SDBS) or a non-ionic fatty alcohol ethoxylate surfactant did not significantly change the enthalpy of interaction. It was further demonstrated that SDBS had a very weak affinity for the dispersed calcium carbonate particles and that dissolution of species, such as calcium ions, from the calcium carbonate surface, allows further adsorption of SDBS onto the latex particles.

The interfacial properties of styrene/butadiene latex were found to play a substantial role in its interaction with partially hydrolysed polyvinyl acetate (PVOH/Ac) in aqueous solutions. In particular, the level of carboxylation of the latex particles governs the adsorption process. A slightly hydrophobic PVOH/Ac is weakly adsorbed onto medium carboxylated latex at low equilibrium concentrations, whereas a multilayer adsorption occurs at high polymer concentrations, closely resembling the incipient phase separation already observed in the case of PVOH/Ac–polystyrene latex systems. The adsorption mechanism for the monolayer formation is suggested to be of entropic origin, driven by the hydrophobic interactions between the latex surface and especially the acetate groups of the PVOH/Ac chain. Increasing the hydrophilic character of the latex surface through pre-adsorbed sodium dodecylbenzene sulphonate or non-ionic fatty alcohol ethoxylate surfactants did not significantly affect the association behavior between PVOH/Ac and the latex surface. In addition to the importance of the interfacial properties of the latex particles, it has been shown that an increased degree of hydrolysis of the PVOH/Ac macromolecule also leads to an appreciable reduction in its affinity for the styrene/butadiene latex interface.

Mechanisms of inkjet ink spreading and absorption on a coated paper have been studied using a polyelectrolyte multilayering technique. By applying alternating sequences of cationic and anionic polyelectrolyte layers on a mineral coated paper, the role of the interfacial chemistry was evaluated. The polyelectrolyte multilayer was created to imitate a thin resin-like liquid-absorptive layer and to clarify the role of the charge of the protruding polyelectrolyte layer on ink spreading and colorant fixation. The formation of a thin polyelectrolyte layer and coating coverage was confirmed by X-ray photoelectron spectroscopy (XPS). A submolecular mechanical imaging of the polyelectrolyte complexes with an atomic force microscope (AFM) revealed differences in modulus and different nanosize agglomerates were identified which were ascribed to polyion complexes. The polyelectrolyte coatings significantly affect the solid–liquid interaction and particularly the ink spreading revealed as intercolor bleeding and wicking. The interfacial interaction between the ink and the applied polyelectrolyte layers showed differences between dye- and pigment-based colorants, which could be emphasized by the polyelectrolyte chemistry.

A titration microcalorimetric study of the interactions between polyvinyl alcohol and coating colour minerals

High alkalinity in peroxide bleaching has traditionally been achieved using sodium hydroxide and sodium silicate. In the present work, partial and total substitution of traditional sodium-based peroxide bleaching auxiliary chemicals with a highly pure magnesium hydroxide-based bleaching additive was studied on two high-brightness mechanical pulp types from Norwegian spruce (Picea abies): pressure groundwood and thermomechanical pulp. Peroxide bleaching with 3.0% charge was carried out on both pulps to a given brightness level. The bleached pulp was studied with respect to electrical conductivity, zeta potential, and water retention value. The bleaching filtrate was measured for total organic carbon content, biological and chemical oxygen demand, cationic demand, extractives content, and turbidity. The main results from this study were that the cationic demand and electrical conductivity of the bleaching filtrate were significantly lowered for both pulps when a magnesium-based bleaching process was used. At the same time, the zeta potential of the dilute pulp suspension was only slightly affected. Magnesium hydroxide-based peroxide bleaching seems to increase the water retention value of the pulp, especially on fines-rich pressure groundwood, predicting a good strength potential of the pulp. The bleaching filtrate from the magnesium hydroxide-based process was significantly cleaner in all categories measured, which indicates that this is an environmentally sound concept.

The surface chemical and physical character of offset paper was studied before and after application of model fountain solutions based on isopropyl alcohol and an alcohol-free surfactant solution. The paper surface features were characterised with atomic force microscopy and the surface energies were determined by contact angle measurements. Changes in the surface chemical properties induced by the fountain solutions were investigated with X-ray photoelectron spectroscopy and time-of-flight secondary ion mass spectroscopy. Coated papers wetted with the surfactant solution revealed a slight increase in the root mean square roughness, but the isopropyl alcohol solution led to no observable changes. The change in sub-micro roughness is ascribed not only to substrate swelling or migration of coating constituents but also to the presence of surfactant on the surface. A change in the surface energy and particularly the polar contribution was observed after application of the surfactant solution. The X-ray photoelectron spectroscopy showed an increase in the oxygen-to-carbon ratio, which confirms the presence of surfactant on the surface. Time-of-flight secondary ion mass spectroscopy showed that the isopropyl alcohol solution did not change the elemental composition of the surface whereas the surfactant solution clearly did so. The distribution of surfactant on the surface was confirmed by mapping the characteristic fragments of the molecule.

A novel method was developed for studying the ink-paper interface and the structural variations of a deposited layer of ink. Combining high-resolution x-ray tomography with laser ablation, the depth profile of ink (toner), i.e., its varying thickness, could be determined in a paper substrate. X-ray tomography was used to produce the 3D structure of paper with about 1 μm spatial resolution. Laser ablation combined with optical imaging was used to produce the 3D structure of the printed layer of ink on top of that paper with about 70 nm depth resolution. Ablation depth was calibrated with an optical profilometer. It can be concluded that a toner layer on a light-weight-coated paper substrate was strongly perturbed by protruding fibers of the base paper. Such fibers together with the surface topography of the base paper seem to be the major factors that control the leveling of toner and its penetration into a thinly coated paper substrate.

The flocculation performance of cationic starches on calcite pretreated with anionic sodium polyacrylate (NaPA) was investigated by measuring the mean particle size and the dynamic mobility of the calcite dispersions. Cationic starches of different molecular weight and degree of substitution were used. By varying the amount of anionic sodium polyacrylate, which has a strong affinity to the calcium carbonate surface, one is able to anionically modify the particles and reverse the charge character of the originally cationic calcium carbonate. By such modification of the charge character of the calcium carbonate dispersion, it is possible to approach the mechanisms of flocculation caused by cationic macromolecules like starch. The importance of different mechanisms of flocculation, such as bridging, charge neutralization, and flocculation induced by polyelectrolyte complexes (PEC), was further investigated in this work. It was found that when the NaPA is completely absorbed at the calcite surfaces the mechanism of the flocculation induced by the starch is mainly bridging flocculation. Excess NaPA in the calcium carbonate dispersion will result in polyelectrolyte complexes formed between the non-absorbed NaPA and the oppositely charged starch polymers. These complexes will in most cases strongly enhance the flocculation due to mainly charge neutralization. Depending on the ratio of non-absorbed NaPA and the starch in the aqueous phase, the calcite dispersion is either re-stabilized or more strongly flocculated due to the formed polyelectrolyte complexes. Both the mobility and the particle size measurements support the mechanisms described. It was further demonstrated that the molecular weight and degree of substitution of the starches might be adjusted to control the flocculation behavior.

The mechanisms of adsorption and association for sodium carboxymethylcellulose (NaCMC) in calcium carbonate suspensions have been determined from isothermal calorimetry and adsorption measurements. The equilibrium adsorption isotherms were determined by two different methods of separation; a depletion method and a serum exchange method. The enthalpy of dilution for NaCMC was determined on supernatants obtained from the calcium carbonate suspensions in order to investigate the interaction between NaCMC and dissolved species from the mineral. For comparison, NaCMC was injected into CaCl(2) solutions in order to determine the role of calcium ions in the adsorption process. The initial part of the adsorption isotherm showed a quasi-infinite slope indicating a high affinity for the NaCMC to the calcium carbonate surface, which was significantly reduced when anionic sodium polyacrylate was preadsorbed onto the calcium carbonate implying competitive adsorption. An endothermic enthalpy change was observed between the NaCMC and the calcium carbonate surface, suggesting attachment of the carboxylic acid groups onto the hydrated calcium sites. A similar endothermic enthalpy was observed when NaCMC was injected into CaCl(2) solutions or supernatants obtained from the calcium carbonate suspensions, indicating a complexation of carboxylic acid groups and hydrated calcium ions. It was concluded that the mechanisms of interaction of NaCMC in calcium carbonate suspensions are primarily an association between NaCMC and Lewis acid sites on the calcium carbonate surface and the formation of NaCMC-Ca(2+) complexes in the bulk solution, both of which will be affected by the amount of anionic sodium polyacrylate present.

The temperature-dependence of the electrical and dielectric properties of paper substrates was studied using experimental papers with different NaCl contents, different thicknesses, and different grammages. Physical processes related to the charging potential, charge decay rate, conductivity, dielectric constant, and dielectric loss of papers are dependent on thermal energy, and this dependence on temperature can be described by exponential expressions. The ion content of paper not only determines the level of these properties at a given temperature, as expected but also influences their temperature-dependence. Frequency analysis of the dielectric loss confirms that new structures are formed in paper by the addition of NaCl. The results may be applicable to the design of materials and equipment, e.g., for the electrophotographic printing processes.

t. The electrical and dielectric properties of paper are important parameters in electrophotography influencing both toner transfer and runnability in laser printers and in digital printing machines. These parameters are dependent on the ionic content and moisture content of the substrate. The effects of NaCI content of the substrate and the ambient relative humidity (RH) on the direct current resistivity in different electric fields and on the real part of the dielectric constant and dielectric loss factor at different frequencies have been investigated with experimental papers of different grammages. A physical model of electrical conductivity in papers with ionic addition is proposed, based on the hypothesis that ionic addition not only increases the number of available free ions but also changes the water state and the paper structure, which influence the ionic motion in an electric field. This model is supported by the dependencies of the real part of the dielectric constant and the dielectric loss factor on the NaCI content, RH, and frequency.

Toner transfer efficiency in electrophotography and the resulting image quality are influenced by the resistivity of the substrate. Resistivity measurements are, however, often made using electric fields that are lower than those used in the transfer of toner in electrophotography. The dependence of surface and volume resistivity on electric field strength, including fields similar to those utilized in the toner transfer of electrophotographic printers, has been studied. Resistivities of paper samples with differences in grammage, filler content, and calendering were evaluated utilizing electrodes with a geometry in accordance with the ASTM D257 (volume resistivity) and raker-type electrodes (surface resistivity) applying electric fields of between 10 2 and 105 V/cm. The surface resistivity and especially the volume resistivity of paper were found to be strongly dependent on the electric field strength, the characteristics of this dependence being influenced by paper properties. The study of the field dependence further indicated that the Poole-Frenkel type of hopping drift of ions could be applied to conduction in paper, although the electric field dependence was overlapped by paper compression effects. Shottky's model was considered also, but it seems that the role of contact effects is small.

The demands for high electrophotographic color print quality emphasize the importance of the paper surface. This work demonstrates the effects of the surface roughness and coating layer characteristics of low grammage coated papers on print mottle. Samples were prepared using different coating techniques, different coating formulations and different coat weights and by changing the calendering conditions to give different surface morphological properties. Print mottle was strongly dependent on substrate roughness. The impact of the surface topography was further demonstrated at different transfer voltages, and when the moisture content or resitivity of the paper was changed, where significant differences were found in print mottle especially when the paper was rough. Surface topography can be optimized by a suitable combination of surface treatment and finishing parameters to give a surface texture with good toner-recipient properties.

Scanning probe microscopy (SPM) was utilized to study the thermal behavior of latex films dried under different conditions. Using the SPM probe resonance frequency method, the resonance frequency (ω) of the oscillating probe above the sample surface was followed as a function of temperature (T). Two different approaches for detecting thermal transitions were used and compared. In the heating-by-the-sample approach, the SPM probe acts as a thermal sensor detecting the heat dissipated by the heated sample. In the heating-by-the-probe approach, the SPM probe is utilized simultaneously as an actuator and a sensor: the heated probe both dissipates heat and detects the heat reflected from the sample surface. Thermal transitions in the polymer films could be observed in the Δω-T curves. The results were consistent with those observed by differential scanning calorimetry, but also additional information about the characteristics of the transitions was obtained. The heating-by-the-probe method showed higher surfac...

Dispersion coating layers consisting of hydroxypropylated starch, 0–30 pph of barrier-grade talc and 0–10 pph of styrene-butadiene latex were subjected to both positive and negative direct-current corona treatments utilizing a specially developed dynamic treatment unit. The effects of the surface composition (barrier coating) on the response to the direct current corona treatment were evaluated by measuring contact angles and determining the surface energy. The effects of corona treatment on the properties of the barrier coating were further determined by measuring the contact angle of rapeseed oil and the grease resistance. It was found that the grease resistance of the corona-treated barrier coatings was substantially lower than that of untreated samples, which was ascribed to holes caused by corona discharge strike-through and to chemical changes on the treated surfaces. The corona treatment lowered the surface energy of the coatings, as indicated by an increase in the contact angles of water and rapeseed oil. Changes in the dispersion part of the surface energy were recorded, particularly after positive treatment voltage, whereas a negative discharge led to greater changes in the polar part of the surface energy. X-ray photoelectron spectroscopy (XPS) tests revealed an increase in the proportion of talc at the surface after corona treatment, which indicates a migration caused by the applied electric field. The peak force tapping mode of an atomic force microscope revealed moderate topographical changes in the coatings and a decrease in surface elasticity, supporting the migration of talc particles. In addition, significant changes in the physicochemical properties of the untreated reverse side were observed.