Journal of Coatings Technology and Research最新文献

Nowadays, coatings need to fulfill a variety of requirements such as having excellent mechanical, chemical, and optical properties at low baking temperatures. On a large scale, polyisocyanates, amines or melamines are used as crosslinking agents in the coatings industry. In this work, a new self-crosslinking agent based on a hydroxy functional 6-membered carbonate with high ring tension and thus presumably lower baking temperature was synthesized and the behavior as self-crosslinking agent was compared to the crosslinking agent derived from the commercially available 5-membered glycerol carbonate. The hydroxy functional 6-membered carbonate monomer was synthesized enzymatically under mild reaction conditions from commercially available substances, linked to a hexamethylene diisocyanate trimer and self-polymerized afterward. NMR- and IR-spectroscopy and GC-MS analysis were found to be suitable techniques to characterize monomers and crosslinking agents. DSC measurements were performed to evaluate appropriate reaction parameters for the attachment reaction of the 6-membered cyclic carbonate to the polyisocyanate without ring opening. The progress of self-crosslinking has been followed by characteristic changes in IR spectra as well as time and temperature-dependent changes of storage and loss modulus while oscillating rheological crosslinking. Furthermore, glass transition temperatures of the resulting coating films are determined, and sol gel analysis was performed to estimate the degree of crosslinking. After application on steel, aluminum and glass plates application tests were performed. In addition to excellent mechanical and chemical properties, the coating film showed good adhesion to the surface and was colorless. Combining these properties with relatively low baking temperatures, 6-membered cyclic carbonate crosslinking agents could represent a new technology for the coatings industry.

We experimentally examined the time-evolutions of local compositions in photocurable, monomer-solvent-initiator ternary liquid film coatings using attenuated total-reflectance-Fourier transform infrared spectroscopy. The coatings exhibited phase separation upon UV exposure owing to the inherent partial miscibility between the solvent and the polymer. The solvent concentration at the bottom of the coating increased when exposed to UV light for 1 s from the top, showing a solvent transport along the irradiation direction. The differences in solvent concentration before and after UV exposure showed good agreement with model predictions based on stress-induced non-Fickian solvent mass transport. The solvent concentrations at the bottom remained constant in the case of discrete phase structures, whereas it exponentially decayed over time in bicontinuous phase structures. These results suggest that light-tunable microstructures enable the relaxation of the reaction-driven nonuniformity in solvent concentration distributions.

Thioxanthone derivatives are synthesized as one-component photoinitiators via a simple condensation reaction between thiosalicylic acids and heterocyclic aromatic hydrocarbons in a concentrated sulfuric acid medium. TX-C (Thioxanthrone–carbazole), TX-N-I (Thioxanthrone–N-methylindole) and TX-I (Thioxanthrone–indole) are characterized by ¹HNMR (nuclear magnetic resonance), FTIR (fourier transform infrared spectroscopy), ultraviolet–visible spectrophotometry, fluorescence spectroscopy, elemental analysis and TG (thermal gravimetric analysis). TX-N-I and TX-I both possess an absorption characteristic similar to the parent thioxanthone with a maximum at 397nm (ε = 3240 L mol⁻¹ cm⁻¹) and 395 nm (ε = 1920 L mol⁻¹ cm⁻¹). The introduction of heterocyclic structures makes the maximum absorption peak red-shifted by 10 nm compared to TX. Its capabilities to act as initiator for the photopolymerization of PEGDA (polyethylene glycol diacrylate) and TMPTA (trimethylolpropane triacrylate) in the absence and presence of TEOA (triethanolamine) media are also examined. TX-N-I acts as an efficient initiator in the UV curable ink, whose light curing time is only 12 s.

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We investigate the interface dynamics in an unsteady quasi-capillary channel flow. The configuration consists of a liquid column that moves along a vertical 2D channel, open to the atmosphere and driven by a controlled pressure head. Both advancing and receding contact lines were analyzed to test the validity of classic models for dynamic wetting and to study the flow field near the interface. The operating conditions are characterized by a large acceleration, thus dominated by inertia. The shape of the moving meniscus was retrieved using Laser-Induced Fluorescence-based image processing, while the flow field near was analyzed via Time-Resolved Particle Image Velocimetry (TR-PIV). The TR-PIV measurements were enhanced in the post-processing, using a combination of Proper Orthogonal Decomposition and Radial Basis Functions to achieve super-resolution of the velocity field. Large counter-rotating vortices were observed, and their evolution was monitored in terms of the maximum intensity of the Q-field. The results show that classic contact angle models based on interface velocity cannot describe the evolution of the contact angle at a macroscopic scale. Moreover, the impact of the interface dynamics on the flow field is considerable and extends to several capillary lengths below the interface.

Slot die coating is a state-of-the-art process to manufacture lithium-ion battery electrodes with high accuracy and reproducibility, covering a wide range of process conditions and material systems. Common approaches to predict process windows are one-dimensional calculations with a limited expressiveness. A more detailed analysis can be performed using CFD simulations, which are often based on in-house code or closed-source software. In this study, a two-phase CFD model in two and three dimensions was created in OpenFOAM with the intent to provide a method for more detailed investigations of the slot die coating process with open access to source code and files. A custom boundary condition enables the proper description of the wetting behavior in the two-dimensional model. The combination of standard no-slip boundary conditions at the substrate boundary with the volume-of-fluid solution algorithm leads to a method-related air entrainment, which was prevented by allowing local slip at the dynamic wetting line at the upstream meniscus in the two-dimensional model. Additionally, a load-balancing dynamic refinement algorithm was implemented to minimize the computational effort and increase the ease of use of the simulation environment. The simulation was validated by comparing the simulated process limits to experimental observations, showing good agreement. As a result, this model enables detailed analyses regarding the influences of slot die geometries, material properties, and process parameters on the coating stability and wet-film profile.

Coatings have been used since time immemorial for decorative and protective purposes. During the initial periods, when not much information was available regarding the health impact of the raw materials, there was no thought given or restrictions put on use of any ingredients in coatings. Some of the raw materials like white lead (lead carbonate), red lead (lead oxide), hexavalent chromium compounds, and other similar compounds were being used in large quantities to get specific paint film properties. This not only affected human health but also with no effective effluent treatment contaminated soil and water resources. With progress in technology and diagnostics, lead and chromium compounds have been identified as carcinogens. The developed countries (Europe and USA) were the first to ban the use of lead in their products in the 1970s and 1980s, but due to mainly economic reasons, these are still being used in the developing countries. As the long-term health impact is too much to bear, regulations/legislations have been enacted by the governments restricting use of lead/chrome in paints. The Global Alliance to Eliminate Lead Paint (GAELP), a joint association formed under the United Nations Environment programme, and World Health Organization have agreed to phase out manufacture and sale of paints containing lead by 2020. Similar restrictions exist for many other compounds used in coatings. The article attempts to present a synopsis of the history of coatings composition, impact of the heavy metals on health and environment, and the options available for shifting to safer coating composition. As major focus of the world is on lead elimination, it has been covered in more detail, but the article also provides information on other metals, namely cadmium, chromium, mercury, arsenic, antimony, tin, nickel, manganese, cobalt, etc., and their current status.

Stretchable, nanocarbon heaters were screen-printed onto a stretchable film to create a passive heat maintenance device for elite sport. The heat uniformity and the temperature performance of these lightweight, large area electrothermal heaters were evaluated over a range of applied voltages using thermal imaging. The heaters provided a uniform heat over the 15 × 4 cm area with temperatures of 39°C, 54°C, and 72°C at 10, 15, and 20 V, respectively, within 150 s of being switched on. Tensile testing was used to examine the performance of the heaters under strain. At 20% nominal strain, the heaters gave a uniform heat output and a temperature of 44°C at 15 V, making it a promising candidate for wearable applications. The heaters were capable of maintaining temperatures of 40°C over 10 cyclic strains up to 10% nominal strain. The heaters were integrated into a proof-of-concept stretchable base-layer garment, with the effect of the heaters on skin temperature measured and thermal sensation evaluated during a simulated training session in an environmental chamber at an ambient temperature 0°C. The printed heaters maintained skin temperature and thermal sensation when compared with an unheated control.

The curing process of polydimethylsiloxane (PDMS) coating was systematically investigated by nonisothermal differential scanning calorimeter (DSC), and accordingly, the thermodynamic as well as kinetic parameters were obtained. Meanwhile, effect of structural factors, including different divinyl-terminated polydimethylsiloxane (^ViPDMS^Vi), divinyl-terminated polymethylvinylsiloxane (^ViPMVS^Vi), polymethylhydrosiloxane (PMHS), and reinforcing filler content, on mechanical and thermal properties of coating was studied. The results demonstrated that platinum compounds could significantly accelerate the hydrosilylation and reduce the curing temperature and activation energy. The viscosity, vinyl/hydrogen sites, and quantities of ^ViPDMS^Vi, ^ViPMVS^Vi, and PMHS were important factors to influence mechanical and thermal properties. Low viscosity ^ViPDMS^Vi and PMHS with side hydrogen atoms could increase crosslinking density, and then enhance the tensile strength and heat resistance. ^ViPMVS^Vi with higher viscosity and vinyl content could dramatically improve tensile strength while maintaining breaking elongation. Reinforcing filler was another vital factor to enhance strength and thermostability. 550% improvement in tensile strength occurred when reinforcing filler content was 40 wt%. All aforementioned results provided a comprehensive guidance for the preparation and property regulation of PDMS coating. This kind of PDMS coating can be applied in synthetic leather manufacturing.

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In the era of sustainability, direct-to-metal coatings have proven to be a promising solution as it eliminates the need for underneath primer coating layers. In the present study, two coating systems, viz. acrylic polyurethane and acrylic-polyester hybrid polyurethane nano-composite coatings, were prepared by addition of nano-silica in various loadings for direct-to-metal coating applications. The addition of nano-silica along with selected resin systems enables to meet desired mechanical properties, chemical resistance along with weathering and corrosion resistance of DTM coating system. Incredible improvement in the overall mechanical properties of the coating including pencil hardness and scratch resistance has been observed by the addition of nano-silica. SEM technique was employed to evaluate the nano-silica dispersion into the coating system along with its morphology. SEM studies revealed thorough dispersion of the nanoparticles within the coating matrix for both the coating systems. Thermal properties were studied by thermogravimetric analysis along with structural characterization by Fourier transform infrared spectroscopy. Thermal stability of both the coating systems increased with the addition of nano-silica; however, acrylic-polyester hybrid polyurethane coatings revealed better thermal stability at 8% nano-silica loading. Color and gloss changes were studied before and after 500 h exposure to a QUV chamber. Anticorrosive properties were evaluated by salt spray exposure for 700 h. At 8% nano-silica loading, acrylic-polyester hybrid polyurethane coatings revealed better weathering performance along with anticorrosive properties and chemical resistance owing to the presence of hybrid polymer chains.