Journal of Coatings Technology and Research

Current research reports and chronological list of recent articles.


The international scientific Journal of Coatings Technology and Research - JCTR - is a forum for the exchange of original research, experience, knowledge and ideas among those with a professional interest in the science, technology and manufacture of functional, protective and decorative coatings including, but not limited to, paints, inks and related coatings and their raw materials.

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Journal of Coatings Technology and Research - Abstracts



Fabrication and characterization of polysiloxane/polyacrylate composite latexes with balanced water vapor permeability and mechanical properties: effect of silane coupling agent

Abstract

In order to improve the water vapor permeability and mechanical properties of latex films, polysiloxane/polyacrylate (PSi/PA) composite latexes were fabricated via seeded emulsion polymerization of methyl methacrylate and butyl acrylate onto PSi latex particles, and the effects of the silane coupling agent 3-methacryloyloxypropyl trimethoxysilane (MATS) on the morphologies of the latex particles and films, as well as the microphase separation degree, the water vapor permeability and the mechanical properties of the latex films were investigated. Results indicated that MATS was essential for obtaining the PSi/PA composite latex particles with PSi as core and PA as shell and made a great contribution to restrict the phase separation. The PSi/PA core/shell latex films showed similar tensile strength and elongation with pure PA film, while exhibiting promising water vapor permeability. It was found that the influences of MATS content on the water vapor permeability and mechanical properties were opposite, and on the premise of the requirements for mechanical properties, lower MATS content could provide the PSi/PA core/shell latex films with better water vapor permeability.


Datum: 15.09.2017


Synthesis of acrylate-based UV/thermal dual-cure coatings for antifogging

Abstract

A dual-cure hydrophilic acrylate polymer was synthesized via radical polymerization with acrylic acid (AA), isophorone diisocyanate (IPDI), 2-acrylamide-2-methylpropane sulfonic acid (AMPS), hydroxyethyl acrylate (HEA), and 3-(trimethoxysilyl)propyl-2-methyl-2-methacrylate (MPS) as monomers, then used as prepolymer for antifog coating with tetraethylorthosilicate (TEOS) as a novel crosslinker. The prepolymer was mixed with crosslinking agent and photoinitiator to form coating formulas. The coating was characterized by nuclear magnetic resonance (NMR), Fourier-transform infrared (FTIR) spectroscopy, and contact angle measurements. The results indicated that the dosage of AMPS and TEOS had great influence on the antifog performance. With an increasing TEOS amount, the hardness, adhesion, water resistance, impact resistance, and thermal stability of the films were improved, at the expense of transparency; with increasing dosage of AMPS, the hydrophilicity of the film increased at the expense of water resistance. Optimum coating properties could be obtained when the amount of AMPS was 7% and that of TEOS was 5.5%. Scanning electron microscopy (SEM) and atomic force microscopy (AFM) results showed that some SiO2 microspheres were formed and microphase separation occurred between the macromolecular segments, yielding the excellent coating properties.


Datum: 12.09.2017


Regression modeling of solid mottle in coated papers

Abstract

The print industry has observed an exponential growth over the last decade. A shift from plastics to paper has been observed in the packaging industry due to its sustainability. The gravure process dominates the packaging industry because of long runs and high print precision. This work focuses on the effect of gravure process parameters on print mottle for 50 GSM (gram/square meters) and 65 GSM (gram/square meters) C1S (coated-one-side) paper. Solid mottle refers to unevenness in print density and occurs due to variations in substrate, ink, and process parameters degrading the print quality, thereby resulting in printed wastage and loss to an organization. The intricate mechanism of ink transfer in the gravure process needs to be studied in depth so as to deliver higher yield and lower print waste. The Stochastic Frequency Distribution Analysis (SFDA) algorithm was used to measure the print mottle. The design of experiments (DOE) was run for gravure process parameters such as line screen, viscosity, press speed, electrostatic assist (ESA) voltage, and air gap (distance between impression roller and charge bar) at varying levels. The experimental data were analyzed through analysis of variance (ANOVA), main plot, and interaction plot. The analysis revealed significance of all process parameters for minimization of solid mottle. The optimized settings showed reduction in solid mottle by 64.68% and 67.78% for 50 GSM and 65 GSM, respectively. A stepwise regression model was developed to predict the print mottle that showed correlation coefficient of 0.912 and 0.938 for 50 GSM and 65 GSM C1S papers. This work could serve as a framework to maintain operating levels of gravure process for minimization of solid mottle.


Datum: 11.09.2017


Numerical analysis for predicting the operability window of slot-die coating onto porous media

Abstract

The ability to coat porous media is critical for forming composite functional thin films. A major technical concern for accurately predicting this process is that the flow of the coating bead and the penetration process must be considered. These phenomena strongly influence each other. Therefore, both the flow into porous media and the coating-bead flow should be simultaneously treated. In this study, the target is a high-productivity coating system based on a roll-to-roll process using a slot die. Slot-die coating is a premetered, precision coating method. We investigated the coating of porous media to estimate the practical operability window and the penetration depth using two-dimensional numerical analysis. For this purpose, both the coating-bead pressure and the capillary pressure were considered as driving forces of penetration. Moreover, the curvature of the backup roll opposite the slot die was also taken into account to achieve an accurate estimation. We demonstrate that the penetration depth and operability window for defect-free coatings can be well estimated and that the results are consistent with experimental results.


Datum: 01.09.2017


Trailing edge formation during slot coating of rectangular patches

Abstract

Different products, such as adhesives, pharmaceutical patches, batteries, and fuel cell membranes, require coating discrete patches onto moving substrates. For coating rectangular patches, intermittent slot die coating is the preferred method. The patches can be obtained by rapidly starting and stopping the flow out of the coating die. Controlling the flow start-up and shutdown to produce sharp and uniform leading and trailing edges of each patch is challenging. Different ways to control the liquid feeding are used to optimize the process. Even if the start-up and shutdown of the feeding system are well designed, the transient flow in the coating bead contributes to the formation of nonuniform leading and trailing edges of coated patches. In this work, we analyze how the operating conditions, die geometry, and liquid properties affect the coating bead breakup process and the trailing edge configuration. The process is directly related to the contact line dynamics. The results show that the uniformity of the trailing edge of each coated patch can be improved by changing the die shoulder angle and wetting characteristics of the die surface.


Datum: 01.09.2017


Optimization of film-coating formulation containing a novel low molecular weight hypromellose to achieve balanced tablet-coating performance

Abstract

In recent years, a novel low molecular weight hypromellose (hypromellose 2906, VLV hypromellose) was developed to improve tablet-coating process and lower costs in the pharmaceutical industry. Such VLV hypromellose imparted economic, environmental, and performance benefits to the coating process and final products. However, there were still some concerns about this polymer in regard to weak mechanical strength of films and resultant stability issues of film coatings on tablets. In this study, a tablet-coating formulation was optimized using Box–Behnken design via blending conventional hypromellose with VLV hypromellose to achieve balanced coating performance in terms of highly productive coating, no sticking issues under mild coating conditions, and robust tablet film coatings in an accelerated stability study. By addition of only 5 wt% of conventional hypromellose (3.35 wt% HPMC E50 and 1.65 wt% HPMC E3), the film elongation and toughness index of optimized VLV hypromellose formulation increased by 154% and 372%, respectively, while the solution viscosity was still suitable for spray coating. The results of the following tablet-coating trials and stability study revealed that the stability and quality of tablet film coatings were significantly improved using this optimized VLV hypromellose-coating formulation, while a highly productive coating process and mild coating conditions without “sticking” issues were maintained simultaneously to the utmost extent.


Datum: 01.09.2017


Two-step migration of particles in evaporating bimodal suspension films at high Peclet numbers

Abstract

During the drying of bimodal colloidal suspensions containing particles of various sizes, smaller particles preferentially migrate to the top surface under particular drying conditions, leading to undesirable drying defects in batteries and in other coating applications. Despite extensive previous studies, the migration mechanism is far from being understood because few in situ observations are available to support the hypotheses. To remedy this, we use real-time photoluminescence (PL) microscopy to investigate the migration of small fluorescent latex particles co-dispersing with large nonemissive latex particles. Comparing the measured PL intensity with that predicted by a model allows us to determine the quantity of small particles near the evaporating surface. The results reveal that the fluorescent particles segregate in two steps: The primary segregation occurs early in the evaporation stage, whereas the secondary stepwise migration occurs when the air–liquid interface invades the particle consolidation layer. The latter migration is attributed to the flow-induced motion of small particles that move through interstitial spaces between large particles.


Datum: 01.09.2017


Biomimetic synthesis of calcium carbonate films on bioinspired polydopamine matrices

Abstract

We combine the active surface of polydopamine (PDA) with the biomimetic mineralization of CaCO3 to obtain the macroscopically continuous CaCO3 films under mild conditions. In this approach, the organic matrices were adhesive PDA coatings, which were dip-coated on silicon wafers by the self-polymerization of dopamine in an alkaline aqueous solution (pH 8.5). The inorganic layers were CaCO3 films, which were formed in a CaCl2 solution in the presence of poly(acrylic acid) (PAA) via a CO2 diffusion method. During the biomimetic mineralization, amorphous calcium carbonate (ACC) was formed on PDA matrices with the help of PAA, which, subsequently, was transformed into a flat continuous calcite film on the PDA matrices. As the mineralization time increased, a new layer of CaCO3 crystals was formed over the calcite and, as a result, led to continuous CaCO3 films with rough surfaces. The thicknesses of CaCO3 films can be controlled by tuning the mineralization time. Our approach may provide a simple, yet efficient way for the preparation of macroscopically continuous organic–inorganic composite CaCO3 films under mild conditions. Moreover, superhydrophobic surfaces can be successfully achieved via a hydrophobic modification of the rough CaCO3 films, which make them suitable candidates for a variety of superhydrophobic applications, such as self-cleaning surfaces or anticorrosion, antiadhesive coatings.


Datum: 01.09.2017


Substrate temperature-dependent physical properties of nanocrystalline zirconium titanate thin films

Abstract

Nanocrystalline zirconium titanate thin films were deposited by direct current magnetron reactive sputtering on to glass substrates at room temperature and at different substrate temperatures of 423, 473, 523, and 573 K under high vacuum conditions. The deposited films have been characterized to study the physical properties of the films as a function of substrate temperature. Though the film exhibited amorphous characteristics at room temperature the higher temperatures resulted in the evolution of crystallites in the films. The crystallinity increased with temperature from 423 K onwards and the film deposited at 523 K exhibited a high crystallite size of 22 nm. The SEM images of the films revealed the improvement in the crystallinity from 423 to 523 K with dense columnar structure normal to the substrate. Further higher treatment deteriorated the film properties. The films showed a good transmittance of above 80%. A high optical transmittance of 91% and a high packing density of 96% have been observed for the film deposited at 523 K. The thickness of the films remained consistent at ~230 nm (±6 nm). It is noticed that an increase in the substrate temperature enhanced the structural, optical, and electrical properties of the films up to 523 K.


Datum: 01.09.2017


A facile technique for fabricating poly (2-methacryloyloxyethyl phosphorylcholine) coatings on titanium alloys

Abstract

Poly (2-methacryloyloxyethyl phosphorylcholine) (PMPC) has been widely used for surface modification of titanium (Ti) alloys to improve antifouling properties and blood compatibility. To achieve antifouling and anticoagulant capacities via a facile and efficient technique, PMPC coatings were covalently immobilized on a Ti surface simply by a sequential dip-coating method. The Ti surface was first dipped into hydrochloric acid (HCl) solution to remove surface contaminants and acquire a hydroxyl-enriched surface. Then, the surface was dipped into dopamine solution to acquire the surface bearing –NH2 groups. N-acryloxysuccinimide solution was used for introduction of double linkage which could graft with PMPC via in situ free-radical polymerization. Thus, the surface modification processes were under mild conditions and easy scale up. The obtained PMPC coatings endowed the Ti surface with smooth finish and relatively high packing density. Water contact angle measurements showed that the hydrophilicity of the Ti surface was markedly improved by coating PMPC with the water contact angle of 6.2°. Furthermore, the PMPC coatings could effectively resist protein adsorption and suppress platelet adhesion and activation. The facile and efficient method of immobilization of PMPC on a Ti surface could be promising for a variety of cardiovascular applications.


Datum: 01.09.2017


Introduction to the special issue: 2017


Datum: 01.09.2017


Performance enhancement of the anti-corrosion coating based on Ce 3+ -polyaniline–montmorillonite composite/epoxy-ester system

Abstract

Herein we report on the Ce3+-5-sulfosalicylic acid dihydrate-doped polyaniline/montmorillonite (Ce3+-PANI/MMT) composite prepared via in situ intercalation polymerization and the cation-exchange method. The as-prepared samples were characterized by the scanning electron microscope, transmission electron microscope, X-ray diffraction analysis, and Fourier transform infrared spectrometer. The release of Ce3+ ions was detected by the immersion test and the solution analysis method. The anti-corrosion performance of the coatings was evaluated by the corrosion test, open-circuit potential analysis, the potentiodynamic polarization curve, and electrochemical impedance spectroscopy in 3.5 wt% NaCl aqueous solution. The results showed that the Ce3+-PANI/MMT composite had better anti-corrosion effects along the coating defects.


Datum: 01.09.2017


Potential for carrying dyes derived from spalting fungi in natural oils

Abstract

Wood colored internally by fungi has long been used by woodcrafters and artisans as a substitute for synthetic dyes. Recent advances in the field of spalted wood have led to methods by which the fungal dyes can be extracted from either a fungal solution or colonized wood and then reapplied to clear wood. This takes the “guess work” out of spalting, as well as the time necessary for fungal colonization; however, it requires organic solvents like dichloromethane, which are toxic and not readily available to consumers. Herein, the authors show that the dyes can be successfully carried and blended together (to increase the range of colors) in a range of natural oils. The blue–green dye of Chlorociboria species, called xylindein, carried best in raw linseed oil, the red dye of Scytalidium cuboideum performed best in Danish oil, although more dye could be carried in raw linseed oil, and the yellow dye of Scytalidium ganodermophthorum performed best in walnut oil. The ability to carry and mix these dyes in easily purchased, nontoxic oils opens up their use to woodworkers who seek to follow the traditions of spalted wood, but do not have the skills or time to work with live fungal cultures or fungal dyes suspended in toxic organic solvents.


Datum: 01.09.2017


Investigation of interfacial instabilities with a two-layer slide coating process

Abstract

Organic electronics have been thoroughly investigated due to their broad application potential, ranging from light-emitting diodes to photovoltaics. The processing of organic electronics is trending from vacuum toward wet chemical deposition, which allows fast low-cost mass production of devices with scalable dimension. One of the current challenges of wet film processing is the redissolution of already dried active materials when applying a liquid top layer. Further, increasing overall process efficiency by coating multiple liquid layers in one step raises such challenges as liquid–liquid mixing or dewetting. This article describes the experimental investigation of these instabilities for two-layer flows with organic solvents. A modified slide coating device was chosen where an extended plate after the slot exit allows prolonged observation of the flow while it travels down the plate. During experimentation, stable and unstable two-layer flows as well as different types of instabilities were detected. The key finding is a correlation of flow stability with the spreading coefficient, a combined measure of surface and interfacial tensions. Focusing on fluid properties, this paper succeeds in defining a three-dimensional stability window for a dual-layer flow.


Datum: 01.09.2017


Plant leaves icephobicity

Abstract

Ice adhesion and accumulation are well known to cause serious problems for different structures such as wind turbines, power transmission and distribution systems, and aircraft. Development of coatings that can resist icing can solve many challenges in various areas of industry. This work was inspired by nature and ice resistivity and superhydrophobicity of plants leaves. Kale is a winter plant with superhydrophobic behaviors, which is normally known as an advantage for cleaning the leaves; however, this article reveals that kale leaves have special surface microstructures delaying the ice formation initiation making them good candidates for designing ice-repellent coatings. In-depth experimental analyses, IR thermography, contact angle measurements, and scanning electron microscopy of the leaves were performed to discover how different plants can prevent icing and further find an optimal design for an artificial ice-repellent coating.


Datum: 01.09.2017


A method to model web trajectory and release in forward roll coating

Abstract

The trajectory of the web at the exit of a roll coating operation can influence the quality of the final coating. While methods to model the web trajectory have been given in the literature, these methods are limited in various ways. A method is proposed to describe the web trajectory and the pressure distribution in the fluid at the exit of a forward roll coater. The Reynolds lubrication equations for the fluid are coupled with the web by a force balance on web node points. The fluid pressure in the coating layer generates forces on the web. These forces deflect the web. Integration in time gives the web dynamics. The angle that the web is pulled from the nip and the tension are found to influence the pressure pulse in the divergent section of the nip to a large extent. Low tensions lead to a second pressure pulse followed by a sub-ambient or tack pressure. Pulling the web at various angles from the nip can cause the tack pressure to increase or decrease. Pressure pulses are predicted that are comparable to measurements by a laboratory device.


Datum: 01.09.2017


Transient response of slot coating flows of shear-thinning fluids to periodic disturbances

Abstract

Slot coating is a popular coating method, in which the film thickness is precisely controlled by adjusting the flow rate and production speed. When the coating flow undergoes small-scale disturbances generated by rotating elements such as motors, pumps, or uneven rolls, the downstream meniscus fluctuates, which causes film thickness variation in the flow direction. Although most coating liquids including polymeric and particulate solutions exhibit a shear-thinning rheological property, their effect on transient coating flow behaviors is not deeply understood. Here, the effect of shear-thinning property on film thickness variation under different disturbances is investigated using a computer-aided analysis of transient slot coating flow. In this study, the Carreau model is used to describe the shear-thinning property, and four different disturbances are considered.


Datum: 01.09.2017


Preparation of fluoroalkyl end-capped vinyltrimethoxysilane oligomeric silica/phosphonic acids nanocomposites possessing superoleophobic/superhydrophilic and superoleophilic/superhydrophobic characteristics: application of these nanocomposites to the separation of oil and water

Abstract

Fluoroalkyl end-capped vinyltrimethoxysilane oligomer [RF–(CH2CHSi(OMe)3) n –RF; RF = fluoroalkyl group; n = 2, 3] can undergo the sol–gel reactions in the presence of a variety of phosphonic acid derivatives such as 1-hydroxyethylidene-1,1-diphosphonic acid, nitrilotris(methylene phosphonic acid), and 2-phosphonobutane-1,2,4-tricarboxylic acid under alkaline conditions to provide the corresponding fluorinated oligomeric silica/phosphonic acids nanocomposites. Interestingly, it was demonstrated that the modified glasses and filter papers treated with these obtained fluorinated nanocomposites can exhibit the superoleophobic/superhydrophilic and superoleophilic/superhydrophobic characteristics on their surfaces, respectively. More interestingly, the modified filter papers treated with these nanocomposites were applied to the separation of the mixture of oil and water.

Graphical Abstract


Datum: 01.09.2017


Slot die-coated blue SMOLED multilayers

Abstract

The key challenge in solution-processing efficient OLEDs is to realize the multilayer device architecture. We demonstrate that slot die coating is applicable to deposit small-molecule (SM) layers on top of each other without dissolving the underlying layer. A stack for a blue SMOLED is chosen comprising slot die-coated PEDOT:PSS, an SM emissive layer (EML) as well as an SM electron transport layer (ETL). The devices are fabricated in a sheet-to-sheet coating process with a slot die table coater under ambient conditions. While keeping the processing parameters constant for PEDOT:PSS and the EML, the composition of the ETL is varied. The choice of solvent for coating the ETL is crucial regarding wetting and dissolution of the underlying layer, solubility, surface roughness, and device efficiencies. Average roughness values down to 0.38 nm and peak to valley values around 10 nm were measured. Comparing device efficiencies of devices with and without ETL, an increase in efficiency with a factor up to 42 was achieved. In total, we show 135 blue SMOLEDs to demonstrate reproducibility.


Datum: 01.09.2017


Cellulose nanocrystal (CNC)-based nanocomposites for UV curable high-solid coating systems

Abstract

Demand for durable clear wood coatings is on the rise. Cellulose nanocrystals (CNC) constitute an organic nanomaterial widely studied in polymer composites for its reinforcing effect. In this study, CNC was used to enhance the performance of a UV curable high-solid content coating system intended for indoor environments. The CNC surface was modified by a cationic surfactant since the coating system was hydrophobic resin-based requiring hydrophobic nanomaterial reinforcement. Modified CNC was mixed with the coating system using a high-speed mixer and the ultrasonication technique. Mechanical, thermal and morphological properties and curing behavior of the newly developed UV-curing coatings were assessed. Inclusion of CNC in the coating increased the mechanical properties (hardness and reduced modulus) of the coating system to a large extent. Thermal stability of the coating system was also improved by CNC addition. The CNC did not affect the curing behavior of the coating, in contrast to most inorganic nanomaterials. The CNC dispersed well in the matrix at 1% loading. Results of this study show that CNC can be used successfully with high-solid content coating systems.


Datum: 01.09.2017






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