Adhesion properties of nanoparticle-coated emulsion aggregation toner

Toner is the key material in printing and copying processes. Fundamental understanding of toner detachment and adhesion during the printing process is critical to improve both the efficiency of toner usage and the quality of print. To control their adhesion property, toner particles can be surface-coated with nanoparticle additives to modify their surface roughness, and consequently, to tune their adhesion properties. In this study, a technique based on the rolling resistance moment of the particle-substrate adhesion bond is used to quantify the effect of nanoparticle surface area coverage (SAC) on the effective work of adhesion of individual toner particles. Nanoparticle-coated model emulsion aggregation (EA) toner microparticles with the specified SAC levels of 0%, 10%, 50% and 100% were studied and the corresponding particle-substrate work of adhesion values were determined and compared. It is quantitatively demonstrated that the work of adhesion between a surface-coated toner particle and a flat silicon substrate decreases significantly with increasing nanoparticle SAC, which provides an effective means to tailor the adhesion performance of the EA toner. Also, based on the experimental data, for a nanoparticle-coated microparticle on a flat substrate, two possible modes of contact formation were identified and discussed.     

Persistent Rocking Motion of Microparticles Under Acoustic Tone-Burst Base Excitation

Abstract

In this work the rocking vibrational response of individual micro-spherical toner particles under a noncontact tone-burst (gated-harmonic) excitation was studied. An unexpected ringing motion which persisted for long periods of time with minimal damping was observed and reported. It was observed that a weak bond, as a result of suspected pure intermolecular (van der Waals) interactions, led to detectable natural frequencies and persistent rocking motion (ringing) observed while the response of a particle with a stronger bond followed closely the substrate surface motion without a relative vibrating motion. For toner particles with a mean diameter of 8.9 μm, a beat phenomenon vibrational behavior was also observed and reported at the tone-burst central frequency of 500 kHz, which was very close to the most dominant observed natural frequency of the particle’s rocking motion of 501.5 kHz. Strong natural frequencies of the rocking motion were observed in three groups lying in the range of 450–525 kHz. The associated work of adhesion for these three observed natural frequency groups was calculated and found to lie in the range between 65 and 82 mJ/m². The ringing mechanism observed and reported here could lead to the development of a very accurate adhesion characterization technique for individual micro-particles. The approach involves no particle detachment and thus allows the studying of the effects of environmental changes on the same bond without bond breakage.     

Nonlinear dynamics of adhesive micro-spherical particles on vibrating substrates

The coupled (rocking and out-of-plane) vibrational dynamics of micro-spherical particles on vibrating flat substrates is studied experimentally, analytically, and computationally. In the experimental spectral responses of some of vibrating particles, in addition to their predicted rocking resonance frequencies, extra resonance peaks at the doubles of these predicted frequencies have been previously observed and reported. To understand and explain the rocking resonance frequency doubling effect, a two-dimensional mathematical model describing the coupled dynamics of a micro-spherical particle in the out-of-plane and rocking coordinates is developed and reported. Previously, the doubling effect was leading to ambiguity in adhesion characterization. It is determined that the frequency doubling observed in the spectral domain responses of particles is caused by nonlinear coupling between the out-of-plane and in-plane modes of motion while the particle is experiencing a whirling-like motion taking place around a nearly stationary axis tilted with respect to the substrate normal (as opposed to the substrate normal itself). In current study, the leaning angles of the rocking motion with whirling of a set of polystyrene latex particles are approximated by utilizing the coupled dynamic model. Also, the work-of-adhesion values extracted from the experimental resonance frequencies of a set of particles using the developed model are compared to those reported in the literature and a good agreement is found. The detection and analysis of the reported motion is relevant to adhesion bond characterization and particle manipulation.     

Adhesion forces of charged particles

Adhesion forces of toner and polymer particles to aluminum substrates were measured by the centrifugal, detachment field and microelectrode detachment field methods, and factors affecting the adhesion forces are discussed. The adhesion forces of toner particles increased with an increase in either particle size or particle charge. The adhesion force of an irregularly shaped toner was larger than that of a spherical toner. The mean adhesion force of polymer particles to aluminum substrates decreased with an increase in surface roughness of the substrates. The CF₄ plasma treatment of the polymer particles shifted their adhesion force distribution in a smaller direction. It was confirmed that the results by the centrifugal and the detachment field methods were in good agreement with each other. The contribution of van der Waals, electrostatic and water bridging forces to the adhesion forces of toner particles are also discussed.     

Single particle adhesion variability in additive manufacturing powders

ABSTRACT

The adhesion properties of powder particles could profoundly influence the quality of parts made by Additive Manufacturing (AM) processes. Accurate experimental characterization of adhesion and the spatial surface adhesion distribution of a single microparticle has been a significant challenge, due mainly to difficulties associated with the micro-scale handling/manipulation in a controllable manner and uncertainty in the nature of micro/nano-scale contacts. In current work, an approach for determining the spatial energy/adhesion distribution on the surfaces of single microparticles used in AM is introduced and demonstrated using Molybdenum (Mo) metal particles as model particles. Both ultrasonic base and Surface Acoustic Wave (SAW)-based excitation techniques coupled with laser Doppler vibrometry are utilized to excite and acquire the vibrational rocking motion and to drive the rolling motion of single Mo particles on a Silicon (Si) substrate in a controllable manner and, thereby determining the spatial adhesion distribution on the particle surfaces. Spatial surface energy distribution data of microparticles could be utilized in Discrete Element Method (DEM) simulations as a statistical input for simulating local powder bed dynamics with increased accuracy, which would potentially lead to more predictable AM processes.     

Discrete element modeling of the transient heat transfer and toner fusing process in the Xerographic printing of coated papers

In this study, a computer model based on discrete element method is employed to simulate the unsteady state heat transfer from the fuser roll to the toner and coating layer during the Xerography printing of coated papers. The model coating layers consisted of randomly arranged spherical pigment and latex particles with commercially relevant size distributions. Effects of coating characteristics, toner size, multiple toner layers, toner melting energy, toner thermal conductivity, coating layer thermal conductivity, and fuser roll temperature and pressure were investigated. Iso-thermal contours of fusing time were generated to demonstrate the relative importance of different fusing conditions and toner properties. Simulation results showed that temperature variation highly depended on the toner size, toner melting energy and the fuser roll temperature. Moreover, simultaneous coupling of the compressive stress and heat transfer indicated that the pressure exerted by the fuser roll did not significantly affect the rate of heat transfer.     

Vibration of an adhered microbeam under a periodically shaking electrical force

The vibration analysis of an adhered S-shaped microbeam under alternating sinusoidal voltage is presented. The shaking force is the electrical force due to the sinusoidal voltage. During vibration, both the microbeam deflection and the adhesion length keep changing. The microbeam deflection and adhesion length are numerically determined by the iteration method. As the adhesion length keeps changing, the domain of the equation of motion for the microbeam (unadhered part) changes correspondingly, which results in changes of the structure natural frequencies. For this reason, the system can never reach a steady state. The transient behaviors of the microbeam under different shaking frequencies are compared. We deliberately choose the initial conditions to compare our dynamic results with the existing static theory. The paper also analyzes the changing behavior of adhesion length during vibration and an asymmetric pattern of adhesion length change is revealed, which may be used to guide the dynamic de-adhering process. The abnormal behavior of the adhered microbeam vibrating at almost the same frequency under two quite different shaking frequencies is also shown. The Galerkin method is used to discretize the equation of motion and its convergence study is also presented. The model is only applicable in the case that the peel number is equal to 1. Some other model limitations are also discussed.     

Evaluation of flow properties of toner powder using conical rotor

In order to accurately evaluate the dynamic flow properties of toner powder, a new rotary shearing tester with a conical rotor was developed. This instrument was equipped with an automatic pressing system to compress toner powder. The tester could simultaneously measure torque and compression load during the intrusion and rotation of the conical rotor into the same packed toner powder. The optimum rotational speed and intrusion rate of the conical rotor for the characterization of the flow properties of toner powder were discussed based on test results; their values were calculated as 0.017 s^− 1 and 0.083 mm/s, respectively. The torque of toner powder changed in proportion to the cube of the depth of intrusion in the toner powder bed. The surfaces of toner powder samples prepared from polymer resin and carbon pigment particles were coated with fine particles (SiO₂, TiO₂) under a different condition. The flow characteristics of toner powder with a different particle surface were evaluated based on the relationship between the shearing torque and the void fraction of packed toner. In the present case, the Rumpf model was applied to estimate the shearing force H at the contact point between two particles of toner powder. The value of H for toner powder with a rough particle surface, which was covered with fine particles (SiO₂, TiO₂), was 41 nN, while that for toner powder with a smooth particle surface, which was not covered with fine particles, was 357 nN. Further the effects of the particle shape of the toner on the torque of toner powder after compression under the same conditions were investigated. The torque of toner powder decreased with an increase in circularity.     

Adhesion of charged particles

The adhesion properties of charged particles are of considerable importance in the electrophotographic process. Measurements on irregularly-shaped, pigmented particles, called toner in the electrophotographic industry, show that adhesion increases with toner charge but that the magnitude is much larger than expected from a simplified electrostatic image force model. An enhanced electrostatic adhesion is also seen in electric field detachment measurements on spherical charged particles. In both cases, this unexpected large adhesion can be attributed to a nonuniform distribution of charge on the surfaces of the particles.     

Effects of moisture and temperature ageing on reliability of interfacial adhesion with black copper oxide substrate

The reliability of adhesion performance of bare Cu, as-deposited and surface-hardened black oxide coatings on Cu substrates was studied. The interfacial adhesion with a polyimide adhesive tape and an epoxy moulding compound was measured using the button shear and tape peel tests after hygrothermal ageing in an autoclave, high temperature ageing and thermal cycles. Moisture adsorption and desorption studies at different aging times suggested that the black oxide coating was effective in reducing the moisture adsorption. The bond strengths for all substrates remained almost unchanged after thermal ageing at 150°C for 8 h. Thermal cycling between ?50°C and 150°C for 500 cycles reduced by about 20% the button shear strength of the as-deposited black oxide substrate, but it did change much the bonding performance of the bare Cu substrate. Hygrothermal ageing at 121°C/100% RH in an autoclave was most detrimental to adhesion performance because of the combined effect of elevated temperature and high humidity. The reduction in button shear strength after the initial ageing for 48 h was 50–67%, depending on the type of coating. In all accelerated ageing tests, the residual interfacial bond strengths were consistently much higher for the black-oxide-coated substrates than the bare Cu surface, confirming a higher reliability of black oxide coating. Fracture surfaces analysis of tape-peeled bare copper substrates after 500 cycles of thermal loading revealed a transition in failure mechanism from interfacial to cohesive failure. In contrast, the failure mechanism remained unchanged for black-oxide-coated substrates. The observations made from the button shear and tape peel tests were generally different because of the different fracture modes involved.     

Particle adhesion and removal in electrophotography

Particle adhesion and removal is often controlled by the interplay of electrostatic forces, related to electrical charges on the particles, and electrodynamic forces, such as those arising from van der Waals interactions. In addition, when electrostatically detaching a charged particle from a substrate, the manner in which the electric field is applied can alter the charge on the particle, thus changing both the attractive and detachment forces. The effects are clearly illustrated in the transfer of a toned image from the photoconductor in an electrophotographic engine. This paper reviews present day understanding of the interplay between electrostatic and electrodynamic interactions, as they occur within the electrophotographic process, and presents the results of previous studies in a unified manner.     

Light stability in cyan and magenta tones using standard and highly chromatic toner particles

An increasing requisite regarding the reproduction quality of electrophotographic printing machines demands improvement of new electrophotographic toner formulation, especially used pigments. The subject of this paper is a comparison of prints realised by depositing high chroma (HC) and standard emulsion aggregation (EA) toner on gloss fine art paper. HC toner has a different composition of the cyan and magenta tones compared with the corresponding standard EA toner tones and therefore behaves differently under real conditions. The patches used for this experiment were cyan and magenta tone prints with tone values (TVs) of 0, 20, 60 and 100%. Ultraviolet (UV) degradation was measured over time intervals of 0, 6, 12, 24, 48, 96, 144 and 240 h for all patches. Results (laboratory values) were calculated using colorimetric difference. Values were plotted as a function of time in tonal degradation graphs. A model was created using non‐linear regression‐based modelling. The experiment demonstrates that magenta patches are more susceptible to degradation in comparison with cyan patches. With the increase in tonal value, it is noticeable that the colorimetric difference is higher. Colorimetric differences calculated using HC magenta toner and standard EA cyan toner (100% TV) were higher than ?E = 5, starting to appear after 6 h of exposure to UV radiance. After 12 h of exposure, colorimetric differences of standard magenta tones that were greater than ?E = 5 also started to appear. Cyan patches (100% TV) printed with HC toner were more stable than the other patches, and after 240 h of exposure had not crossed the boundary of ?E = 5.     

The role of surface modification in digital printing on polymer‐coated packaging boards

Digital printing is increasingly being used for package printing. One of the major techniques of digital printing is dry‐toner electrophotography. This paper evaluates the printability of three different extrusion coatings used for packaging boards: low‐density polyethylene (PE‐LD), ethylene methyl acrylate (E/MA) and polyethylene terephthalate (PET). Extrusion coatings in general have an impervious, chemically inert, nonporous surface with low surface energies that cause them to be non‐receptive to bonding with toners. The most common methods used in improving the adhesion properties of polymer coatings are different surface treatments. These increase the surface energy and also provide the polar molecular groups necessary for good bonds between the toner and polymer molecules. The polymer coatings have been modified with electrical corona discharge treatment. The effects of corona on polymer surfaces and the correlation between surface modification and print quality have been evaluated. Results show that sufficiently high surface energy and surface‐charge uniformity are necessary for even print quality and toner adhesion. E/MA and PET have the required surface‐energy level without the corona treatment, but PE‐LD needs surface modification in order to succeed in the electrophotographic process. E/MA also has exceptional surface‐charge properties compared with PET and PE‐LD. Polym. Eng. Sci. 44:2052–2060, 2004. © 2004 Society of Plastics Engineers.     

Evaluation of the particle-particle interactions in a toner by colloid probe AFM

In order to evaluate the particle-particle interactions in a toner particle with a high accuracy, the changes in the adhesion force between a toner particle glued to an AFM cantilever tip and a particle in a compressed layer of toner powder was measured by colloid probe atomic force microscopy. Toner particle layers compressed by a pressure of 54.9 MPa were used as the substrate in this study. The effects of the scan rate, particle diameter, humidity, and surface coating of silica nanoparticles on the adhesion force were discussed on the base of measurement results. The adhesion force between the toner surfaces decreased with an increase in the AFM scan rate; it then reduced to a constant value at 1.95 Hz. The adhesion force between the toner particles increased proportionally with approximately the second power law of the particle diameter; it exhibited a change that differs from the force characteristic that was directly proportional to the first power law of the particle diameter, as given in van der Waals expression. Next, the additives that consisted of SiO₂ were glued on to the surface of the toner particle, and the influence of the surface coverage of SiO₂ on the particle-particle interactions was examined. The particle-particle interactions consequently decreased in inverse proportion with a surface coverage of SiO₂ 26% or less. Moreover, when the SiO₂ surface coverage was 26%, almost no changes were observed in the particle-particle interactions at 80% R.H. It was confirmed that the influence of humidity reduced by coating the toner particle with SiO₂. The relationships between the particle-particle interactions and the flow properties were examined by using a rotary shear tester with a conical rotor. When the mean particle diameters were identical, a first strong positive correlation between the particle-particle interaction and the shearing torque that crossed the zero point was observed. When the shearing force H was calculated from the torque of the conical rotor method by using Rumpf's equation, a first strong positive correlation between the particle-particle interaction Fa and the shearing force H that crossed the zero point was observed.     

Adhesion between rubber compounds and ternary-alloy-coated steel cords,Part I: effect of cobalt plating amount in ternary-alloy-coated steel cords

The adhesion between a rubber compound and ternary-alloy-coated steel cords with different cobalt plating amounts (0, 2 and 4 wt%) was investigated to understand the role of cobalt in stabilizing adhesion to the rubber compound. The adhesion property of ternary alloy coated steel cords to the rubber compound did show significant enhancement after cure for the ternary alloy coated steel cord with 2 wt% cobalt plating. Further increase of cobalt plating in ternary-alloy-coated steel cord was responsible for the poor adhesion to the rubber compound. An improvement in adhesion durability after aging in various hostile environments was shown for the ternary-alloy-coated steel cord with 2 wt% cobalt plating. The interphase between the ternary-alloy-coated steel cords and the rubber compound studied using AES showed a stable adhesion interphase by optimum cobalt plating, resulting in enhancement of adhesion retention.     

Uniaxial compaction behavior of filled polymer powders

A simple method is described to obtain rheological data on filled polymeric materials in the form of powders. The powder is compacted in a cylindrical chamber by a plunger driven by the cross-head in an Instron testing machine and the load-displacement curve is recorded. Further information is obtained by compressing the powder to a fixed load and measuring the load decay with time (stress-relaxation). The tests are illustrated by application to “monocomponent toner” powders used in dry copying or nonimpact printing processes. It is shown that compaction and stress-relaxation data are able to differentiate between different toners and facilitate the prediction of their relative performances in terms of pressure fusing. A mechanical spring-dashpot-slider model is effective in describing the rheological behavior of these powders and its dependence on the loading of a hard filler (magnetic pigment). The latter affects the “slider” yield stress in the model but has no influence on the relaxation times.     

Electropolymerised acrylic coatings for polymer-metal adhesion enhancement

Electrochemical polymerisation (ECP) of acrylic monomers produces thin coatings on metal substrates and is a potentially useful method for forming adhesion promoting tie-layers at a polymer-metal interface. Uniform, passive films of poly (methyl methacrylate) and poly (glycidyl acrylate) have been formed via a cathodic free radical mechanism on stainless steel electrodes from aqueous electrolytes. The thickness of these films was found to increase with electrolysis time and the passive nature has been demonstrated by cyclic voltammetry studies. Adhesion tests were performed to compare the adhesion strength and failure mechanisms of various adhesives to coated and uncoated stainless steel substrates. The results indicate that ECP tie-layers can significantly increase the adhesive bond strength and alter the failure mechanisms observed. Electropolymerised acrylic coatings on metal substrates are thus seen as a promising approach for pretreatment of metals for adhesion enhancement.     

Adhesion of underfill and components in flip chip encapsulation

The underfill material is a polymeric adhesive used in flip chip packaging. It encapsulates the solder joints by filling the gap between a silicon die and an organic substrate or board. Within a typical flip chip structure, there are interfaces between the various components, namely, substrate, solder mask, flux residue, underfill encapsulant and die passivation layer, etc. Maintaining a good adhesion condition, both as-made and after temperature/humidity aging, is vital for these interfaces because of the expected performance of the flip chip device, where the underfill material is employed to enhance the reliability of the flip chip interconnect. We have studied the adhesion strength between the various components for different process variables as measured with the lap shear and die shear test configurations. The effects of the assembly factors, i.e. solder mask, flux residue, underfill, and die passivation, etc., were evaluated and the adhesion strength was found to depend greatly on these factors. The die shear strength of a passivated die assembled onto an organic board coated with a solder mask was much higher after using a no-clean flux on the solder mask than for the assembly without such a no-clean flux. The influence of some accelerated aging tests on the adhesion durability was also investigated. A die passivation layer of benzocyclobutene exhibited better capability in retaining the die shear strength than a passivation layer of silicon nitride or polyimide, especially for the initial aging period. The knowledge obtained in this study should provide insights into the interfacial adhesion in the flip chip assembly structure.