The challenge of achieving traditional exterior durability performance in low VOC architectural coatings

Over the years the optimization of water-borne emulsion polymers has resulted in water-borne coatings with excellent exterior durability and significantly reduced solvent emissions versus solvent-borne coatings. In recent years, pressure to further reduce emissions has necessitated the use of softer polymer compositions which can negatively impact gloss and tint retention, and dirt pick up resistance. The use of heterogeneous polymer morphologies are addressing these short comings; however care must still be taken not to affect paint durability. The development of low solvent emission thickeners and mildewcides has allowed further reduction in paint emissions.     

Durable ultra‐hydrophobic surfaces for self‐cleaning applications

Self‐cleaning surfaces have received a great deal of attention, both in research studies and commercial applications. Both transparent and non‐transparent self‐cleaning surfaces are highly desirable as they offer many advantages, and their potential applications are endless. The self‐cleaning mechanism can be seen in nature. The Lotus flower, a symbol of purity in Asian cultures, grows in muddy waters, but it stays clean and untouched by dirt, organisms, and pollutants. The Lotus leaf self‐cleaning surface is hydrophobic and rough, showing a multi‐layer morphology of nanoscaled roughness. While hydrophobicity produces a high contact angle, the surface morphology reduces the adhesion of water drops to the surface, which slides easily across the leaf surface carrying the dirt particles with them. Different ultra‐hydrophobic, non‐transparent, and transparent coatings, for potential self‐cleaning applications, were produced on polycarbonate (PC) substrates, using hydrophobic chemistry and different configurations of roughening micro‐ and nano‐particles. However, in most cases, these coatings present low adhesion and durability. The stability and durability of the ultra‐hydrophobic surfaces is of key importance for potential, commercially viable, self‐cleaning applications thus durability and stability enhancement of such coatings was attempted by different methods, evaluated, and eventually improved using a solvent‐bonding technique. Copyright © 2008 John Wiley & Sons, Ltd.     

Literature review on superhydrophobic self‐cleaning surfaces produced by electrospinning

Self‐cleaning surface is potentially a very useful addition for many commercial products due to economic, aesthetic, and environmental reasons. Super‐hydrophobic self‐cleaning, also called Lotus effect, utilizes right combination of surface chemistry and roughness to force water droplets to form high contact angle on a surface, easily roll off a surface and pick up dirt particles on its way. Electrospinning is a promising technique for creation of superhydrophobic self‐cleaning surfaces owing to a wide set of parameters that allow effectively controlling roughness of resulted webs. This article gives a brief introduction to the theory of super‐hydrophobic self‐cleaning and basic principles of the electrospinning process and reviews the scientific literature where electrospinning was used to create superhydrophobic surfaces. The article reviewed are categorized into several groups and their results are compared in terms of superhydrophobic properties. Several issues with current state of the art and highlights of important areas for future research are discussed in the conclusion. © 2012 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2012     

Development of combinatorial chemistry methods for coatings: high-throughput weathering evaluation and scale-up of combinatorial leads

Combinatorial screening of materials formulations followed by the scale-up of combinatorial leads has been applied for the development of high-performance coating materials for automotive applications. We replaced labor-intensive coating formulation, testing, and measurement with a "combinatorial factory" that includes robotic formulation of coatings, their deposition as 48 coatings on a 9x12-cm plastic substrate, accelerated performance testing, and automated spectroscopic and image analysis of resulting performance. This high-throughput (HT) performance testing and measurement of the resulting properties provided a powerful set of tools for the 10-fold accelerated discovery of these coating materials. Performance of coatings is evaluated with respect to their weathering, because this parameter is one of the primary considerations in end-use automotive applications. Our HT screening strategy provides previously unavailable capabilities of (1) high speed and reproducibility of testing by using robotic automation and (2) improved quantification by using optical spectroscopic analysis of discoloration of coating-substrate structure and automatic imaging of the integrity loss of coatings. Upon testing, the coatings undergo changes that are impossible to quantitatively predict using existing knowledge. Using our HT methodology, we have developed several cost-competitive coatings leads that match the performance of more costly coatings. These HT screening results for the best coating compositions have been validated on the traditional scales of coating formulation and weathering testing. These validation results have confirmed the improved weathering performance of combinatorially developed coatings over conventional coatings on the traditional scale.     

Enhancing corrosion resistance of zinc-filled protective coatings using conductive polymers

Organic coatings containing zinc are amply used for the protection of metals, particularly steel structures. Ways to reduce the zinc content in the coating materials are sought for environmental and financial reasons. Our previous work (Kohl, Prog Org Coat 77:512–517, 2014; Kohl and Kalendová, Mater Sci Forum 818: 171–174, 2015a) suggested that one of the options consists in the use of conductive polymers in the formulation of the zinc coatings. The benefits of conductive polymers include nontoxicity, high stability, electric conductivity and redox potential. Previously we focussed on the effect of conductive polymers added to the organic coatings so as to complete the zinc volume concentration to 67%. The anticorrosion efficiency of the organic coatings was found to improve with increasing polyaniline phosphate or polypyrrole concentrations. Zinc content reduction in the system, however, did not attain more than 5%. The present work focusses on systems where the organic coatings are prepared with zinc having a pigment volume concentration PVC = 50%. Zinc content reduction in the system attains up to 20%. This work examines the mechanical and anticorrosion properties of the organic coatings with reduced zinc contents. The present work was devoted to the feasibility of using of conductive polymers in the formulation of coatings with reduced zinc contents. The conductive polymers included polyaniline, polypyrrole and poly(phenylenediamine); these were synthesised and characterised using physico-chemical methods. Polyphenylenediamine as a potential corrosion inhibitor has not been paid adequate attention so far. Subsequently, organic coatings with reduced zinc contents and containing the pigments at 0.5, 1 and 3% volume concentrations were formulated. The coatings were subjected to mechanical tests and accelerated corrosion tests to assess their mechanical and corrosion resistance. The corrosion resistance of the organic coatings was also studied by linear polarisation. The results of the mechanical tests, accelerated corrosion tests and linear polarisation measurements indicate that the organic coating properties get affected by the conductive polymer type as well as by the pigment volume concentration. The important finding is that the use of conductive polymers in coatings with reduced zinc contents was beneficial in all cases.     

Ultrathin polymer coatings by complexation of polyelectrolytes at interfaces: suitable materials,structure and properties

The article presents the state‐of‐the‐art of alternating physisorption of oppositely charged polyelectrolytes, the so‐called “layer‐by‐layer” method or “electrostatic self‐assembly” (ESA), for the preparation of thin polymer coatings. In comparison to other, more established self‐organization techniques, this recent method is distinguished by its simplicity, versatility, and speed. In particular, the tendency for self‐healing is unique. Emphasis is given to the role of the molecular structure of the polyelectrolytes, and to the nature of the support. Also, various parameters for the preparation of multilayer films are highlighted, which are very important due to the kinetic control of the build‐up process. The structure of the resulting coatings, their quality and stability, chemical reactions in the films, and potential applications are discussed.     

Electrodeposited paint-and-varnish nickel–polymer coatings

Specific features of preparation of paint-and-varnish nickel–polymer coatings by joint cathodic electrodeposition of an amine-containing oligomeric electrolyte and nickel were studied. The coatings obtained exhibit layer-by-layer heterogeneity, with the lowest layer constituted by an intermetallic compound of nickel with iron. The coatings are characterized by higher degree of cross-linking compared to the polymer coatings without nickel. A paint-and-varnish formulation based on a nickel–polymer film-forming agent was developed for electrodeposition of corrosion- and wear-resistant coatings.     

Atomic force microscopy of coated glasses

Atomic force microscopy has been used to investigate the topology of alkoxide gel dip coatings on different substrates. Results of SiO(2) - TiO(2) - ZrO(2) (STZ) coatings are presented on float glass, on polished fused silica, on commercially coated insulating flat glass, and on PtRh. Consolidated STZ coatings display the so-called glass pattern with ripples equal or less than 2 nm high. The same pattern is seen on partially dense STZ coatings, as soon as the surface is stiff enough for scanning, and also on the bottom of a 50 nm deep sputtering crater in the consolidated coating. The vitreous STZ coating on the fire side of the float glass is as flat as the float glass itself. It has the same tendency to contamination. 100 nm wide and 50 nm deep polishing grooves on fused silica have been filled up with the 80 nm thick coating, only dips of a few nm remain. The trenches between the SnO(2) crystallites on the insulating flat glass were filled up and the roughness of the substrate was partially reduced. PtRh sheet remained rough even after the coating. On the partially densified STZ coating, sputtering generates a grained surface.     

Cerium hybrid silica coatings on stainless steel AISI 304 substrate

AISI 304 Stainless Steel is widely used in different industrial fields because of its mechanical and corrosion properties. However, its tendency to corrosion in presence of halide ions limits the applications. One strategy to improve the corrosion resistance is the use of coatings barriers containing corrosion inhibitors in their formulation. The lanthanides present attractive green and corrosion properties for the substitution of chromates, which are the most common substances used as corrosion protection. However, these compounds are highly toxic, and an intense effort is being undertaken to replace them. Cerium is a good alternative because of its relatively low cost and abundance. It fulfils the basics requirements for being considered an alternative inhibitor: the ions form insoluble hydroxides and they present low toxicity. Inorganic and hybrid sol-gel coatings have been developed to increase the corrosion resistance of metals and they provide an excellent vehicle for the incorporation of secondary phases including particles and metal ions as cerium ions. The aim of this work was to study the influence of the incorporation of cerium ions in hybrid silica sol-gel coatings deposited on AISI 304 stainless steel as substrate as a potential replacement of chromate treatments. This system should combine the barrier protection effect of silica coating with the corrosion inhibitor effect of the cerium ions inside the coatings. After 7 days of immersion in NaCl, coated substrates showed lower current densities than the bare steel, although the coatings produced from Ce (III) salts experience a slight weakening in time and those obtained from Ce (IV) chemicals evidence an enhance in the coating performance, probably due to the plugging of corrosion products in the defective areas of the film.     

Carrier gas UV laser ablation sensitizers for photopolymerized thin films

Designed carrier gas UV laser ablation sensitizers were synthesized and proved to greatly enhance the UV laser ablation of photopolymerized thin films. Polymers containing dense ester groups are reported to have better laser ablation performance because of the tendency of the ester groups to decompose into gaseous products (“carrier gases”) during the ablation process. In order to introduce this mechanism to cationic UV curable coatings for better laser ablation, a series of “carrier gas” sensitizers were synthesized by reacting hydroxyl containing reactive diluents such as oxetane and polyester polyols with monomethyl oxalyl chloride or dimethyl oxalate; the oxalyl group is considered a “carrier gas” generating moiety. Furthermore, a UV absorbing chromophore, naphthalene, is either chemically bound to the oxalyl containing molecules or blended with the synthesized oxalyl containing compounds to produce a synergistic effect. The “carrier gas” sensitizers were added into a typical cationic UV curable formulation to form sensitized coatings, which were then characterized by thermogravimetric analysis, real time FTIR and ablated by a 355 nm laser. The ablation vias were examined using optical profilometry and SEM. Compared to the control, the sensitized coatings were found to have similar thermal decomposition temperatures and higher functional group conversion during photopolymerization. All of the sensitized coatings containing the “carrier gas” sensitizers exhibited better UV laser ablation performance than the control. The combination of naphthalene derivatives and the oxalyl group gave a better ablation result, suggesting a synergistic effect. The chemical combination of the naphthalene and oxalyl group exhibited better ablation sensitization than their blends, suggesting a more efficient intramolecular laser energy utilization process.     

The stone decay of monuments in relation to atmospheric environment

In order to explain why different forms of decay are present on a building facade some samples were taken from different areas of many monuments. Macroscopic observations of the forms of decay were correlated with quantitative analytical data in order to build up a simple model which was able to explain in a general way the decay phenomena. This simplified model was tested on several Venetian monuments and the features visible on stone surfaces correspond to different degree of deterioration. The quantitative analytical data were associated with the different forms of decay, which were defined as white washing, dirt accumulation and dirt washing. The results obtained showed that the features visible on stone surfaces corresponded to different degree of deterioration and the sulphate formation is greatest in the black dendrite-shaped crusts which are generally formed at the interface between the white washing areas and the sheltered ones, which were defined as dirt washing area.     

Binders for exterior coatings exhibiting low soiling tendency

Elastomeric coatings protect building facades and flat roofs from moisture and weather exposure. As a drawback, these coatings are prone to dirt-pickup due to the low glass transition temperature of the used polymeric binders. Strategies to overcome this enhanced soiling tendency are discussed, and the results of laboratory and outdoor soiling tests are compared. A novel method for the assessment of wet soiling tendency is presented.     

Atomic force microscopy of coated glasses

Atomic force microscopy has been used to investigate the topology of alkoxide gel dip coatings on different substrates. Results of SiO₂ – TiO₂ – ZrO₂ (STZ) coatings are presented on float glass, on polished fused silica, on commercially coated insulating flat glass, and on PtRh.· Consolidated STZ coatings display the so-called glass pattern with ripples equal or less than 2 nm high. The same pattern is seen on partially dense STZ coatings, as soon as the surface is stiff enough for scanning, and also on the bottom of a 50 nm deep sputtering crater in the consolidated coating.· The vitreous STZ coating on the fire side of the float glass is as flat as the float glass itself. It has the same tendency to contamination. 100 nm wide and 50 nm deep polishing grooves on fused silica have been filled up with the 80 nm thick coating, only dips of a few nm remain. The trenches between the SnO₂ crystallites on the insulating flat glass were filled up and the roughness of the substrate was partially reduced. PtRh sheet remained rough even after the coating.· On the partially densified STZ coating, sputtering generates a grained surface.     

涂液浓度对Ru-Ti-Ir氧化物阳极涂层性能的影响

应用热分解法制备了由不同浓度涂液形成的Ru-Ti-Ir氧化物阳极涂层,SEM,EDX,XRD、强化电解寿命、极化曲线、循环伏安和电化学阻抗等测试表明,涂液浓度对阳极涂层的表面形貌有着很大的影响,但不甚影响其析氯极化过程.随着涂液浓度的增加,阳极涂层的伏安电量和双电层电容都出现先降低后增加的变化趋势.     

Polymeric isocyanates by nontoxic routes. II. Nucleophilic displacement reaction on chloromethyl pendant groups by alkali cyanates

The environmental regulations regarding the solvent emissions have given impetus to the formulation of powder coatings and high solids coatings which require oligomeric or polymeric crosslinkers of desired functionality. We are exploring nontoxic routes for the preparation of polymeric isocyanates and isocyanate precursors. In this article, we report nucleophilic displacement of polymer-bound alkyl halides by cyanate ion as a novel route to polymeric isocyanate crosslinkers with no intermediacy of either phosgene or low molecular weight isocyanates. The effects of solvent and phase-transfer catalyst on the selectivity of the reaction are discussed. © 1992 John Wiley & Sons, Inc.     

UV-cured coatings for functional protection

Photopolymerizing formulations of urethane-acrylate and epoxy-acrylate oligomers with active diluents of varied functionality and molecular mass were studied. It was found that the functionality of the monomers strongly affects the mechanism by which protective properties of a coating are formed. The limits of the range of optimal concentrations of the active monomers were found. It was confirmed that the maximum protective properties of the coatings are observed when unifunctional and bifunctional active diluents are used in the mixture formulation in a stoichiometric or nearly so ratio. The possibility of creating formulations with nanosize particles of functional additives determining the purpose of a formulation (anticorrosive, decorative) was revealed and substantiated.     

Development of combinatorial chemistry methods for coatings: high-throughput adhesion evaluation and scale-up of combinatorial leads

Coupling of combinatorial chemistry methods with high-throughput (HT) performance testing and measurements of resulting properties has provided a powerful set of tools for the 10-fold accelerated discovery of new high-performance coating materials for automotive applications. Our approach replaces labor-intensive steps with automated systems for evaluation of adhesion of 8 x 6 arrays of coating elements that are discretely deposited on a single 9 x 12 cm plastic substrate. Performance of coatings is evaluated with respect to their resistance to adhesion loss, because this parameter is one of the primary considerations in end-use automotive applications. Our HT adhesion evaluation provides previously unavailable capabilities of high speed and reproducibility of testing by using a robotic automation, an expanded range of types of tested coatings by using the coating tagging strategy, and an improved quantitation by using high signal-to-noise automatic imaging. Upon testing, the coatings undergo changes that are impossible to quantitatively predict using existing knowledge. Using our HT methodology, we have developed several coatings leads. These HT screening results for the best coating compositions have been validated on the traditional scales of coating formulation and adhesion loss testing. These validation results have confirmed the superb performance of combinatorially developed coatings over conventional coatings on the traditional scale.     

Effects of sodium laurylsulfate on crystal structure of calcite formed from mixed solutions

This paper presents a solvent-based, mild method to prepare superhydrophobic, carbon nanofiber/PTFE-filled polymer composite coatings with high electrical conductivity and reports the first data on the effectiveness of such coatings as electromagnetic interference (EMI) shielding materials. The coatings are fabricated by spraying dispersions of carbon nanofibers and sub-micron PTFE particles in a polymer blend solution of poly(vinyledene fluoride) and poly(methyl methacrylate) on cellulosic substrates. Upon drying, coatings display static water contact angles as high as 158° (superhydrophobic) and droplet roll-off angles of 10° indicating self-cleaning ability along with high electrical conductivities (up to 309 S/m). 100 μm-thick coatings are characterized in terms of their EMI shielding effectiveness in the X-band (8.2-12.4 GHz). Results show up to 25 dB of shielding effectiveness, which changed little with frequency at a fixed composition, thus indicating the potential of these coatings for EMI shielding applications and other technologies requiring both extreme liquid repellency and high electrical conductivity.     

Complexation of an acrylic resin by tertiary amines: synthesis and characterisation of new binders for antifouling paints

Antifouling coatings are the most reliable way to prevent biofouling of immersed surfaces. As concerning the high toxicity of organotin paints, the tendency is the development of coatings, which do not present environmental risks. In this work, we prepare binders from modification of acrylic copolymers containing free carboxylic acid groups. Biocides chosen are tertiary ammonium salts; alkyl chain substituents with different length are considered. The chemical modifications of resins are carried out via a single step reaction. Modification extents are monitored through proton nuclear magnetic resonance and thermogravimetric analysis and the modified resins are characterised by Fourier transform infrared spectroscopy. The glass transition temperature of the acrylate systems is assessed by dynamical mechanical analysis (pin point method) and compared with data obtained by differential scanning calorimetry. The erosion and antifouling properties of the binders are followed during an exposure to marine environment by a visual observation.     

Thermal and neutron shielding properties of 10B containing UV cured hybrid coatings

¹⁰B containing organic–inorganic hybrid coating material based on a UV-curable formulation was prepared via anhydrous sol–gel technique. UV curable coatings were applied on Plexiglas (PMMA) substrates. The molecular structure of the coating material was analyzed by ATR-FTIR spectroscopy technique. The characterization of the UV-curable coating was evaluated by various techniques such as gel content, abrasion resistance, chemical resistance, pencil hardness, pendulum hardness, MEK rubbing test, contact angle, cross-cut test, gloss, transmittance test, neutron absorption, Limiting Oxygen Index and stress–strain tests. Hybrid coatings showed a significant enhancement in radiation shielding properties. The thermal behavior of coatings was also evaluated. It is observed that the thermal stability of coatings mainly depends on their boron and silicate contents. Results of all analysis conducted on hybrid films, and coatings were discussed.