Clear Coatings Research Articles

Synthesis and incorporation of poly(methyl methacrylate) microspheres with UV stabilizers in wood clear coating binder

The durability of clear coatings is an important problem in the coatings industry. This problem can be partly solved with the addition of UV absorbers (UVAs) in the coating formulation. UVAs can absorb part of the UV radiation and convert it into harmless heat. Organic UVAs are prone to photodegradation and can migrate in the binder of a coating formulation. In this study, commercial UVAs have been encapsulated in poly(methyl methacrylate) microspheres using the internal phase separation method. Microspheres have been incorporated into a clear acrylic binder. The acrylic was then applied on wood panels and was placed into an artificial UV chamber. Efficiency of coatings after aging as well as chemical and physical properties were monitored using a colorimeter, FTIR spectroscopy and transmission electron microscopy. This study presents a comparison between the efficiency of free and encapsulated Tinuvin 1130 and 292 commercial absorbers. Results have shown that the coating efficiency is slightly improved when using the encapsulated products.

Reactive CeO2 nanofluids for UV protective films

We investigate surface modification by organo-trimethoxysilanes of nano-ceria and if such surface-modified nano-ceria can be transformed into solvent-free nanofluids. We also examine whether simultaneous modification with ionic liquid salts and with acrylate groups yields nanofluids suitable for forming UV-protective films and clear coatings by UV-initiated polymerization. Nominally 3nm diameter CeO2 was successfully synthesized and surface decorated with an ionic liquid salt and with acrylate groups to produce a core/shell structured solvent-free nanofluid after ion exchange of chloride for a soft polyoxyethylene sulfonate anion. This room temperature nanofluid melts at about −10°C and exhibits a glass transition at about −71°C. The melting enthalpy, about 19J/g, corresponds approximately to the gain in surface free energy of such nanofluid particles upon transforming from the solid state to liquid state. Robust films were made by UV photoinitiation of this nanofluid in combination with ethylene glycol dimethacrylate and with a polyoxyethylene diacrylate to yield cross-linked films with absorption coefficients α350nm=6.6±0.8cm2/mg and α300nm=24.5±3.5cm2/mg. Average near UV protection over 300–350nm of 1–3 optical density units can be obtained with 0.065–0.19mg/cm2 of CeO2. These materials appear almost three-fold more effective, per unit ceria, than previously reported clearcoats of nanoceria.

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

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.

Evaluation of Hyperspectral Imaging Visible/Near Infrared Spectroscopy as a forensic tool for automotive paint distinction

Spectroscopies have been widely used in forensic science to analyze fingerprints, bloodstains, paints, etc. Hyperspectral chemical imaging is a fast and non-destructive method that provides spatial and spectral chemical information of a particular specimen. Recently, researchers have evaluated the characterization of automotive paints using Principal Components Analysis (PCA) performed on infrared and Raman spectroscopies data. However, to date, there is no report concerning the discrimination power of such trace evidence using Hyperspectral Imaging Visible/Near Infrared Spectroscopy (HSI-UV/VIS/NIR). Therefore, this work evaluated the potential of this technique combined with PCA as a forensic approach to discriminate automotive paints. In total, 38 samples from twelve brands and a variety of colors were analyzed. HSI-UV/VIS/NIR data was acquired directly from the paint chip’s surfaces, which includes the basecoat and clear coat layers. PCA was individually performed in distinct color datasets and could discriminate 100% of the white, silver, red and grey samples collected from different brands or from the same manufacturer with different color/shades. Furthermore, the PCA reliability for the identification of similar paint chips was successfully tested using fragments of silver and grey samples collected from different vehicle sources with common brand, color and shade. In agreement with the literature, the automotive black paints presented a much lower discriminating power (62.5%) because the spectra did not provide enough reflectance suitable for differentiation. These new findings support the idea of using HSI-UV/VIS/NIR as a fast, easy and efficient alternative technique to other spectroscopies for accurate forensic assessment of automotive paints.

Intensification of Electrochemical Performance of AA7075 Aluminum Alloys Using Rare Earth Functionalized Water-Based Polymer Coatings.

This work reports the effect of different amounts of ceria nanoparticles on UV resistance and barrier properties of water-based polyurethane (WPU) on glass and AA7075 aluminum alloy substrates. Hybrid coatings were synthesized from an aliphatic WPU–HDI (1,6-hexamethylene di-isocyanate) and cerium oxide nanoparticles (CeO2) with an average particle size distribution of about 25 nm. Different nanoceria amounts (1, 3 and 5 wt %), mixing times (30, 60 and 120 min) and methods to disperse the nanostructures into the polymer matrix (magnetic stirring and sonication) were evaluated. Initially, the dispersion of CeO2 nanoparticles embedded in the polymer matrix and displacement in the corrosion potential (Ecorr) were analyzed by confocal scanning laser microscopy (CLSM) and open circuit potential (Eocp) measurements. According to this behavior, the dispersion and water ratio required during the polymerization process were established. Coated samples obtained after the second stage were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), atomic force microscopy (AFM) and optical light microscopy. In addition, optical measurements on glass substrates were evaluated with UV-vis spectroscopy. The effect of the synthesis parameters on the corrosion behavior of WPU–CeO2/AA7075 systems was investigated with Eocp and electrochemical impedance spectroscopy (EIS) in a 3 wt % NaCl solution. In addition, the films were subjected to 180 h of accelerated weathering. The results show that the combination of specific nanoceria addition with the optimal synthesis parameters enhances optical transparence of WPU as well as barrier properties. From these, the coated specimens prepared with 3 wt % of ceria content and sonicated for 30 min showed a highly dispersed system, which results in a high charge transfer resistance. The observed properties in clear coats deposited on metallic substrates suggested an improvement in the appearance and less deterioration in UV exposure in comparison with pure WPU, enhancing the protective properties of the AA7075 aluminum alloy when exposed to a corrosive medium.

Preparation and characterization of chalcone functional urethane acrylates for coating applications

Abstract New chalcone modified urethane acrylates (CMUA) were synthesized by the reaction of photoactive 4,4′dihydroxychalcone and polyethylene glycol 1000 (PEG-1000) with isophorone diisocyanate (IPDI) and followed by end-capping with 2-hydroxyethyl methacrylate (HEMA). The structure of CMUA oligomers was characterized by FT-IR and 1 H NMR spectroscopies. Photosensitivity of CMUA oligomers was confirmed by using UV–vis absorption spectroscopy. The UV-curable clear coatings were prepared by the incorporation of CMUA oligomers into formulations together with reactive diluents such as dipropylene glycol diacrylate (DPGDA), 1,6-hexanediol diacrylate (HDDA) and photoinitiator and applied on Plexiglas plates and Teflon moulds. The physicochemical, mechanical and thermal properties of UV-cured coatings such as gel content, gloss, chemical-solvent resistance, contact angle, gloss, pendulum hardness, pencil hardness, tensile properties and char yield were investigated. The effect of chalcone modification on UV-cured CMUA coatings was evaluated and determined as the improvement in the properties of UV-cured coatings mainly due to the photocrosslinking ability of 4,4′dihydroxychalcone.

Relative importance of black carbon, brown carbon, and absorption enhancement from clear coatings in biomass burning emissions

Abstract. A wide range of globally significant biomass fuels were burned during the fourth Fire Lab at Missoula Experiment (FLAME-4). A multi-channel photoacoustic absorption spectrometer (PAS) measured dry absorption at 405, 532, and 660 nm and thermally denuded (250 °C) absorption at 405 and 660 nm. Absorption coefficients were broken into contributions from black carbon (BC), brown carbon (BrC), and lensing following three different methodologies, with one extreme being a method that assumes the thermal denuder effectively removes organics and the other extreme being a method based on the assumption that black carbon (BC) has an Ångström exponent of unity. The methodologies employed provide ranges of potential importance of BrC to absorption but, on average, there was a difference of a factor of 2 in the ratio of the fraction of absorption attributable to BrC estimated by the two methods. BrC absorption at shorter visible wavelengths is of equal or greater importance to that of BC, with maximum contributions of up to 92 % of total aerosol absorption at 405 nm and up to 58 % of total absorption at 532 nm. Lensing is estimated to contribute a maximum of 30 % of total absorption, but typically contributes much less than this. Absorption enhancements and the estimated fraction of absorption from BrC show good correlation with the elemental-carbon-to-organic-carbon ratio (EC ∕ OC) of emitted aerosols and weaker correlation with the modified combustion efficiency (MCE). Previous studies have shown that BrC grows darker (larger imaginary refractive index) as the ratio of black to organic aerosol (OA) mass increases. This study is consistent with those findings but also demonstrates that the fraction of total absorption attributable to BrC shows the opposite trend: increasing as the organic fraction of aerosol emissions increases and the EC ∕ OC ratio decreases.

Weathering performance of surface of thermally modified wood finished with nanoparticles-modified waterborne polyacrylate coatings

In this research the samples of thermally modified (TMT) beech wood samples, finished with waterborne polyacrylate clear coatings modified with nano-sized ZnO and TiO2-rutil were naturally and artificially exposed to weathering conditions. To extend the lifetime of wood and maintain its natural look, the research and development of clear coatings with minimal use of harmful chemicals has become very important. Therefore nano-sized inorganic UV absorbers are increasingly used to enhance the durability of the coating and wood substrate, still retaining the transparency of the coating. During exposure the visual inspection was performed, further the changes of colour, gloss and adhesion were recorded. Interaction of the film with the thermally modified substrate surface were studied. Results showed that the addition of TiO2-rutil and ZnO nanoparticles to the waterborne polyacrylate coating improved the colour stability of thermally modified beech-wood. However, nano-sized ZnO increased the cracking and peeling, and caused the loss in adhesion strength of the film on thermally modified beech wood.

PEMBUATAN DAN KAJIAN SIFAT-SIFAT FISIKOKIMIA, MEKANIKAL, DAN FUNGSIONAL EDIBLE FILM DARI KITOSAN UDANG WINDU

This research aims to develop bioplastic as primary packaging or edible film of chitosan biopolymer derived from tiger prawn shells (Penaeus monodon), and to perform physicochemical and mechanical characteristics. An evaluation of the physicochemical properties of plastic films made from chitosan, by modifying the order of the different treatment processes, namely: a) DPMA (deproteination, demineralization, deacetylation), b) DMKA (demineralization, decoloration, and deacetylation) has conducted. The results of scanning FT-IR of the product shows that chitosan has identical spectrum compare of standard compound. Chitosan product from tiger prawn shells was the used as raw material for the manufacture of bioplastics. Experiments variable on the manufacture of edible film is a study of the effect of the use of different plasticizers (glycerol and sorbitol) and carboxylmethylcelullose (CMC) additives to the physicochemical, mechanical characteristics, and edible film functional. The results showed that all the edible film produced has a clear coat with a thickness between 0.05 to 0.3 mm. Meanwhile, the film density is highest at the DPMA + chitosan edible film sorbitol + CMC with a value of 1.7300 g/cm3. The use of plasticizer sorbitol provides great tensile strength but not too elastic, compared to the glycerol, while an increase in the average CMC can increase tensile strength and %Elongation. The use of different plasticizers and additives CMC does not significantly affect its functional properties, where the value of WVTR (water vapor transmission rate) is relatively the same on both types of edible films, ranging from 3.2409 to 4.8858 g /hr.m2.

Improving the Performance of Clear Coatings on Wood through the Aggregation of Marginal Gains

Remarkable increases in the performance of complex systems can be achieved by a collective approach to optimizing individual factors that influence performance. This approach, termed the aggregation of marginal gains, is tested here as a means of improving the performance of exterior clear-coatings. We focused on five factors that influence clear-coating performance: dimensional stability of wood; photostability of the wood surface; moisture ingress via end-grain; coating flexibility and photostability; and finally coating thickness. We performed preliminary research to select effective wood pre-treatments and durable clear-coatings, and then tested coating systems with good solutions to each of the aforementioned issues (factors). Red oak and radiata pine panels were modified with PF-resin, end-sealed, and thick acrylic, alkyd or spar varnishes were applied to the panels. Panels were exposed to the weather and the level of coating defects was assessed every year over a 4-year period. All of the coatings are performing well on PF-modified pine after 4 years’ outdoor exposure. In contrast, coatings failed after 2 years on unmodified pine and they are failing on PF-modified oak. We conclude that our approach shows promise. Future research will build on the current work by developing solutions to additional factors that influence clear-coating performance.

Studies in Silicone-Polyether Ketone Blend Based High Performance Coating

Silicone polymer although have some exceptional superior properties have limitations when it is exposed to harsh chemicals. Poly Ether Ketone (PEK), a high performance polymer is well known for its resistance towards acid, alkali and many solvents. PEK exhibits good environmental protection with better thermal stability. In the present study, the coatings were prepared using varying ratios of silicone and Poly Ether Ketone (PEK) to study the effect of concentration of PEK on mechanical, chemical, thermal and performance properties. The clear coatings of Silicone/PEK cured films were characterized for TGA, FTIR and evaluated for thermal resistance, corrosion resistance, resistance to 10% acid, alkali, sodium chloride, detergent solution and humidity resistance. The coating films were found to be stable up to 450 °C as indicated by TGA analysis. It is seen that the performance of silicone / PEK coating films increases with increasing concentration of PEK.

Waterborne Casein-Based Latexes with High Solids Content and Their High-Throughput Coating Optimization

Over the past few years casein-based latexes have attracted increasing interest because of their good film-forming properties. This paper investigates the use of acrylic/casein hybrid latexes with a solids content of 35% in a coating application, which involves the evaluation of nonformulated latexes as binders, the high-throughput formulation with different commercial agents (cosolvents, wetting agents, and defoamers) and the formulation optimization using statistic multivariable analysis. Latexes were obtained by emulsifier-free emulsion polymerization of acrylic monomers in the presence of a chemically modified casein containing 10 vinyl bonds per molecule. The optimized clear coats formulated from the hybrid latexes showed a good performance requiring a reduced formulation-agents concentration, which could be an important benefit from an environmental viewpoint. Together the above results demonstrate that the casein biobased latexes represent a promising alternative for the development of a new genera...

Effects of extractives removal on the performance of clear varnish coatings on boards

In this work, the effects of extractives removal on the performance of used varnishes were studied. The experimental samples were prepared using defect-free alder ( Subcordate alnus) and ironwood ( Zelkova carpinifolia) with moisture content of 12% and were coated with polyester and two-part polyurethane (urethane alkyd) varnishes. Removal of extractive materials followed Tappi Test Methods using hot water and ethanol. Variable parameters were based on the solvent type (extraction method), wood species, and varnish type. Other parameters such as moisture content, sanding process, and dimensions were kept constant. Pull-off adhesion and dynamic absorption tests were used to assess adhesion and performance of the two clear varnish coatings. Sanding process was employed prior to coating, which helped prepare surfaces virtually free of damage. In general, the extractive-free samples had better adhesion strength and wettability compared with the untreated (control) ones. Based on the results of this study, it can be pointed out that all the variable parameters, including the type of wood, varnish, and solvent, had significant effect on the adhesion of varnishes, applied on the wood surface. The difference in wettability between extracted and unextracted samples is due to blocking of the free hydroxyl groups by extractive materials. In addition, it was found that the removal of extractives had the effect of increasing the surface wettability of both species, an important consideration for the varnish coating. The highest adhesion was obtained from polyurethane varnish, applied on ironwood specimens. It seems that the diffuse-porous anatomical structure of ironwood along with its high density of 0.79 g/cm3 could be responsible for its higher adhesion strength than alder species.

Minimizing Corrosion of Outdoor Metalworks Using Dispersed Chemically Stabilized Nanoclays in Polyvinylidene Fluoride Latex Coatings.

Nanoclays are small enough to appear optically transparent, yet they have large surface-to-volume and high aspect ratios that can significantly inhibit water diffusion when incorporated into protective coatings. Clear coatings, which minimally affect the aesthetics of metalworks, are commonly applied to outdoor metalworks, such as sculptures, to prevent and slow corrosion. In recent years, waterborne clear coatings, rather than solvent-based clear coatings, are increasingly used in many applications to reduce the quantity of volatile organic components in the formulation, yet the performance of dry films produced from waterborne colloidal suspensions is generally poorer. In this work, we aim to improve the barrier properties of a highly weatherable waterborne acrylic/polyvinylidene fluoride emulsion by adding a synthetic nanoclay, Laponite, into the formulation. To improve clay–polymer compatibility, the clay was covalently modified using an acetoxy or perfluoroalkyl silane monomer that is reactive with the hydroxyl groups at the edges of the Laponite platelets. Cation exchange on the clay faces using phosphorylcholine was conducted to increase the stability in water and characterized by zeta potential. Resulting changes in barrier properties of the polymer nanocomposite films were characterized by gravimetry, colorimetry, and electrochemical impedance spectroscopy. Surface ablation after accelerated artificial weathering was monitored by attenuated total internal reflectance Fourier transform infrared microspectroscopy and Raman microspectroscopy, thin film X-ray diffraction (TF-XRD) and gloss and thickness measurements. The composite films showed many improved properties: reduced water sensitivity and ultraviolet-induced polymer degradation, which increased the barrier properties and reduced the diffusion constants over both short- and long-term weathering studies compared with films without nanoclays. The diffusion constant measured for the highest performing composite film showed that the performance gap between relevant water- and solvent-borne coatings used to protect outdoor metals was narrowed by half.

Self‐Cleaning Coatings: Clear and Durable Epoxy Coatings that Exhibit Dynamic Omniphobicity (Adv. Mater. Interfaces 14/2016)

Guojun Liu and co-workers describe the design and synthesis of a graft copolymer in article 1600001. This polymer is used to introduce 4.0 wt% or more poly(dimethyl siloxane) into epoxy formulations to yield transparent coatings. On tilting these coatings, all tested laboratory liquids with surface tension above 22 mN m−1 cleanly slide down. In addition, the coatings shrink paint and ink even after extensive wear which further demonstrate their practical value.

Properties of powder clear coatings systems modified with hydrotalcites

Properties of powder clear coatings systems modified with hydrotalcites

Forensic analysis of automotive paints using a pattern recognition assisted infrared library searching system: Ford (2000–2006)

A prototype infrared (IR) library search system for the paint data query (PDQ) database has been further developed to determine the make, line and model of an automotive vehicle from the clear coat, surfacer-primer, and e-coat layers in an effort to improve discrimination capability in automotive paint comparisons involving intact paint chips. Search prefilters for the IR spectral library of PDQ were developed from the clear coat, surfacer-primer and e-coat layers for 1179 manufacturer paint systems within a limited production year range (2000–2006) to identify vehicle manufacturer (Ford, Chrysler, and General Motors). For each make (i.e., manufacturer), search prefilters were developed to identify the assembly plant of the vehicle using a hierarchical classification scheme. A cross correlation library search algorithm that performed both forward and backward searching was then used to identify the line and model of the vehicle from the truncated IR spectral library of PDQ identified by the search prefilters. Samples assigned to the same line and model by both a forward and backward search of the IR spectral data were always correctly matched, always correlated well on an individual basis to a specific library sample and were well represented in the truncated PDQ spectral library identified by the search prefilters. The performance of the prototype IR library searching system (search prefilters and cross-correlation library search algorithms) for the PDQ database was benchmarked against commercial library searching algorithms. Only the results for Ford are reported here.

Evidential significance of automotive paint trace evidence using a pattern recognition based infrared library search engine for the Paint Data Query Forensic Database

A prototype library search engine has been further developed to search the infrared spectral libraries of the paint data query database to identify the line and model of a vehicle from the clear coat, surfacer-primer, and e-coat layers of an intact paint chip. For this study, search prefilters were developed from 1181 automotive paint systems spanning 3 manufacturers: General Motors, Chrysler, and Ford. The best match between each unknown and the spectra in the hit list generated by the search prefilters was identified using a cross-correlation library search algorithm that performed both a forward and backward search. In the forward search, spectra were divided into intervals and further subdivided into windows (which corresponds to the time lag for the comparison) within those intervals. The top five hits identified in each search window were compiled; a histogram was computed that summarized the frequency of occurrence for each library sample, with the IR spectra most similar to the unknown flagged. The backward search computed the frequency and occurrence of each line and model without regard to the identity of the individual spectra. Only those lines and models with a frequency of occurrence greater than or equal to 20% were included in the final hit list. If there was agreement between the forward and backward search results, the specific line and model common to both hit lists was always the correct assignment. Samples assigned to the same line and model by both searches are always well represented in the library and correlate well on an individual basis to specific library samples. For these samples, one can have confidence in the accuracy of the match. This was not the case for the results obtained using commercial library search algorithms, as the hit quality index scores for the top twenty hits were always greater than 99%.

Characterization of automotive paint by optical coherence tomography

Automotive paint is common trace evidence that plays a significant role in many vehicle-related criminal cases. However, the conventional methods of obtaining tomographic images tend to damage the samples. Optical coherence tomography (OCT) is a novel method to obtain high-resolution and cross-sectional images of the automotive paints in a non-destructive, and high-speed manner. In this study, OCT was applied to image and analyze the automotive paint, using scanning electron microscope (SEM) as reference. Eight automotive paint samples of different brands were examined. The images of multi-layer structures provided by OCT system with 5μm depth resolution were consistent with those by SEM. To distinguish different paints with similar visual appearance, we extracted internal structural features from the images using peak analysis and optical attenuation fit. Six characterized parameters were found to distinguish the samples including the optical path length (OPL) of base coat, the optical attenuation coefficient (OAC) of base coat, the OPL of clear coat, the back-scattering ratio (BSR) of clear coat and base coat, the OPL of primer surfacer, and the BSR of base coat and primer. Statistical differences were evaluated by an independent t-test with p<0.05. OCT was applied to analyze repainted paint as well. Three-dimensional OCT reconstruction of the paints was also implemented to create en face (transverse section) images for morphology examination and comparison. These results suggest that OCT imaging can provide additional new features for analyzing the automotive paints and thereby may be a promising supplement to traditional methods. Meanwhile, the OCT system is favorable for achieving in-situ and real-time examination at the scene of crime.

Clear and Durable Epoxy Coatings that Exhibit Dynamic Omniphobicity

A graft copolymer is designed, synthesized, and used to introduce 4.0 wt% or more poly(dimethyl siloxane) into epoxy formulations to yield transparent coatings. On tilting these coatings, all tested laboratory liquids with surface tension above 22 mN m−1 cleanly slide down. In addition, the coatings shrink paint and ink even after extensive wear. These coatings are of practical value. As a service to our authors and readers, this journal provides supporting information supplied by the authors. Such materials are peer reviewed and may be re-organized for online delivery, but are not copy-edited or typeset. Technical support issues arising from supporting information (other than missing files) should be addressed to the authors. Please note: The publisher is not responsible for the content or functionality of any supporting information supplied by the authors. Any queries (other than missing content) should be directed to the corresponding author for the article.