Polyurethane Clear Coat Research Articles

Preparation and performance of hydrophobic two-component polyurethane clearcoats based on perfluoro alcohol modified polyisocyanate hardener

In this study, three perfluoro alcohol with different fluoroalkyl chain length, i.e., 3,3,3-trifluoro-1-propanol (TEOH1), 2-perfluorobutyl ethanol (TEOH4), 2-perfluorohexyl ethanol (TEOH6), were first reacted with polyisocyanate to get hardeners bearing various contents and lengths of fluoroalkyl chain. The fluorinated polyisocyanate hardener was then adopted to fabricate hydrophobic two-component polyurethane (2K PU) clearcoats. The highest water contact angles (WCAs) of the hydrophobic 2K PU clearcoats with no haze and non-sticky surface are 91.9°, 101.6° and 106°, achieved at the perfluoro alcohol dosage of 10 %, 20 % and 20 % for TEOH1, TEOH4 and TEOH6, respectively. Accelerated weathering and outdoor exposure tests were adopted to examine the hydrophobicity durability of the perfluoro alcohol-modified coatings, and dirt pick-up resistance (DPUR) outdoors was also monitored. All coatings showed decreased WCAs in weathering tests. Nevertheless, WCAs of coatings with ≥20 % TEOH4 and ≥5 % TEOH6 remained hydrophobicity after 228-day outdoor exposure. Loss of hydrophobicity is attributed to the oxidation of PU matrix, removal of free perfluoro alcohol-modified polyisocyanate and embedding of silicate dirt. Improved DPUR of 2K PU clearcoat was demonstrated outdoors after incorporation of perfluoro alcohol, especially for the cases with TEOH4 and TEOH6 under an adequate dosage. As a whole, longer fluoroalkyl chain favors the acquisition of both higher hydrophobicity, better hydrophobicity durability, and better outdoor DPUR.

Fluoroalkyl trimethoxysilane route to hydrophobic 2K polyurethane clearcoats and their failure mechanism

In this study, three fluoroalkyl trimethoxysilanes (FATMS) with different chain length of fluoroalkyl moiety, i.e., (3,3,3-trifluoropropyl) trimethoxysilane (C1), (1,1,2,2-tetrahydro-nonafluorohexyl) trimethoxysilane (C4), (1,1,2,2-tetrahydro-perfluorooctyl) trimethoxysilane (C6), were incorporated into component A of a two-component polyurethane (2K PU) clearcoat to assure their chemical anchoring with polymer chains, and then cured with polyisocyanate hardener. The hydrophobic durability of FATMS-modified coatings was further examined under various service conditions by water contact angle analyzer, attenuated total reflection Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy and element-mapping. Hydrophobic 2K PU clearcoats could be achieved at FATMS dosage below 5.0 %, 0.5 %, and 0.5 % for C1, C4, and C6 additive, respectively. All coatings maintained their original hydrophobicity after for two years’ ambient storage, immersing in ambient water or mere UV irradiation. But if UV irradiation and/or heat (i.e., high-temperature) were imposed together with water, the coatings would quickly lose their surface hydrophobicity due to the loss of fluoroalkyl groups via hydrolysis break of Si-O-C chemical bond. The UV irradiation-induced synergistic effect on failure of surface hydrophobicity should be resulted from the increased hydrophilicity of PU matrix, which enhanced the affinity of water molecules with the coatings and hence higher hydrolysis probability of Si-O-C bond. Therefore, FATMS route is more suitable for fabrication of hydrophobic 2K PU clearcoats used indoors at room temperature.

Waterborne polyurethane via encapsulated blocked isocyanate crosslinker for 1 K clearcoats

Herein, a waterborne polyurethane clearcoat with excellent chemical and physical performance through an encapsulation system has been developed. The encapsulation system in this study incorporated blocked polyisocyanate (b-PIC) as a crosslinker with an acrylic polyol to ensure homogeneous dispersion under water-based conditions. An acrylic polyol was designed to readily disperse into the water phase, fulfill the requirements of a clearcoat, and effectively encapsulate b-PIC. The structure of the core-shell encapsulation system enabled both homogeneous dispersion and close proximity between the acrylic polyol and b-PIC, resulting in a uniform crosslinking clearcoat. Three different clearcoats were prepared: two water-based b-PIC systems with both polyisocyanate encapsulated dispersion (PED) and conventional b-PIC dispersion (CPD) without encapsulation, and a solvent-based (SB) b-PIC dispersion with ethyl cellosolve. Their crosslinking and mechanical properties were characterized. Using dynamic light scattering (DLS), it was confirmed that PED contained synthesized encapsulated particles smaller than 80 nm with a narrow particle size distribution. The cured PED-containing clearcoat exhibited a higher gloss of 73.6 at 20° compared to that of CPD. In addition, the surface mechanical properties of cured PED waterborne clearcoat using pencil hardness, nano-indentation (NI), and micro-scratch testing (MST) were measured. In particular, the PED clearcoat exhibited superb resistance to water penetration, maintaining more than 95 % transmittance using a UV–Vis spectrometer. Finally, the glass transition temperature of PED, CPD, and SB clearcoats was confirmed by dynamic mechanical analysis (DMA) and differential scanning calorimetry (DSC). These indicated that the PED clearcoat system could be utilized in waterborne coatings technology as a useful and inexpensive technology that addresses the need to reduce volatile organic compound (VOC) production for improved environmental protection.

Application of the temperature-sensitive paint method for quantitative measurements in water

In this paper the characteristics of a Europium-based temperature-sensitive paint (TSP) in polyurethane (PUR) clear coat submerged in water are investigated. It is shown that the temperature sensitivity is not affected by water. However, the optical transmission of the PUR is reduced, which reduces the measurable emission of the TSP. Furthermore, a TSP measurement in the laminar water channel at the Institute of Aerodynamics and Gas Dynamics, University of Stuttgart, was set up. In this experiment the skin friction field for two types of roughness elements, i.e. a truncated cylinder and an array of cuboids, in a Blasius-like boundary layer is investigated. Additionally, the temperature field was recorded with sub-millimeter resolution while an artificial heat flux was applied. A modification of the Colburn analogy is used to derive the skin friction from the temperature measurement. Skin friction results derived from velocity measurements are in good agreement with the TSP results. The experimental setup provides a resolution of the temperature and skin friction measurement of K and N m−2 ( skin friction of the undisturbed flow), respectively. Additionally the uncertainty of the temperature and skin friction measurement is analyzed.

Preview the Products on Display at Display Week 2021

Preview the Products on Display at Display Week 2021

Acrylic‐ester‐polyol based novel two‐component polyurethane clear coat: Evaluation of performance characteristics

AbstractIn the current study, a combination of acrylic polyol (AP) and ester polyol (EP) were synthesized and reacted at variable ratios with hexamethylene diisocyanates and isophorone diisocyanates to prepare a transparent two‐component polyurethane (PU) coating formulation. The formations of the polyol system, isocyanate system, and the PU systems were confirmed by 1H nuclear magnetic resonance and Fourier‐transform infrared spectroscopy. Transparency of the coatings was examined using haze, and gloss measurement, which showed acrylic‐ester‐polyurethane (aePU‐5 and aePU‐6) have 91.5% and 91.8% transparency and gloss of 90.3 and 90.7 GU respectively. The thermal properties like Tg and the thermal stability of the coatings were verified using differential scanning calorimetry, and thermogravimetric analysis respectively which was found to increase with increasing EP content and decreasing AP content which may be ascribed to improved compatibility of copolymers, and homogeneity in PU along with enhanced crosslinking density. The degree of adhesion of coating with the substrate was validated from lap‐shear, and cross‐cut tape test which showed improved performance at AP:EP ratio of 60:40. The coatings were found to exhibit resistance toward pencil hardness with aePU‐5 and aePU‐6 having the optimum resistance of 9H. The surface morphology and topography were observed under scanning electron microscopy, and atomic force microscopy, respectively. The outcome confirms the higher smoothness of the surfaces subjected to the increase in EP content. The PU system with 40 wt% AP content and 60 wt% EP designated as aePU‐5 was found to exhibit optimum performance.

Optically transparent and environmentally durable superhydrophobic coating based on functionalized SiO2 nanoparticles

Optical surfaces such as mirrors and windows that are exposed to outdoor environmental conditions are susceptible to dust buildup and water condensation. The application of transparent superhydrophobic coatings on optical surfaces can improve outdoor performance via a ‘self-cleaning’ effect similar to the Lotus effect. The contact angle (CA) of water droplets on a typical hydrophobic flat surface varies from 100° to 120°. Adding roughness or microtexture to a hydrophobic surface leads to an enhancement of hydrophobicity and the CA can be increased to a value in the range of 160°–175°. This result is remarkable because such behavior cannot be explained using surface chemistry alone. When surface features are on the order of 100 nm or smaller, they exhibit superhydrophobic behavior and maintain their optical transparency. In this work we discuss our results on transparent superhydrophobic coatings that can be applied across large surface areas. We have used functionalized silica nanoparticles to coat various optical elements and have measured the CA and optical transmission between 190 and 1100 nm on these elements. The functionalized silica nanoparticles were dissolved in a solution of the solvents, while the binder used was a polyurethane clearcoat. This solution was spin-coated onto a variety of test glass substrates, and following a curing period of about 30 min, these coatings exhibited superhydrophobic behavior with a static CA ≥ 160°.

Preparation and characterization of polyurethane clearcoats and investigation into their antigraffiti property

A type of antigraffiti polyurethane clearcoat was prepared and characterized. Polymethylsiloxane grafted by fluorocarbon side chains (PSF) was first synthesized through hydrosilylation of polymethylhydrosiloxane with dodecafluoroheptyl acrylate. Hydroxyl fluoroacrylate resins with different hydroxyl contents were synthesized via free radical-initiated solution polymerization and further applied to prepare polyurethane clearcoats. The synthesized polymers were structurally characterized by using Fourier transform infrared and 1H nuclear magnetic resonance. The prepared polyurethane clearcoats underwent contact angle measurement, dynamic thermal mechanical analysis, nanoscratch experiments, and atomic force microscopy. The results reveal that low surface energy, high crosslink density, low coefficient of friction, and low roughness were jointly beneficial to antigraffiti properties. Antigraffiti testing was carried out on the clearcoat with 8.0 wt% PSF and 2.0 wt% active silicone fluid, and this clearcoat showed high resistance to acrylic spray paint, permanent markers, and other graffiti materials.

Polyurethane nanocomposite films containing nano-cerium oxide as UV absorber; Part 2: Structural and mechanical studies upon UV exposure

Degradation of a water-based polyurethane clear coat containing nano-sized cerium oxide was investigated. Nanoparticles at different concentrations were dispersed in a water-reducible polyol polyacrylate dispersion resin, followed by mixing with polyisocayanate hardener from which wet films of 90μm thick were prepared. Samples were exposed to 700h of accelerated artificial weathering (QUV).Their performances were then accessed by DMTA and ATR–FTIR spectroscopy. It was revealed that the glass transition temperature (Tg) of films systematically increased with increase in nano ceria content. Due to UV absorption and decrease in photo-oxidation and chain scission reactions, the storage moduli of clear coats containing nano ceria were shown higher than that of the blank polyurethane after UV exposure. Tg for both pure blank polyurethane and nano-ceria embedded clear coats increased with increase in degradation time. Most of variations in Tgs occurred in the first 150h of exposure. ATR–FTIR spectra also proved these results by showing depreciation in intensities of CH and NH peaks. It was seen that the surface of the clear coats as analyzed by ATR–FTIR was polyurea-rich and contained urea functionality at least as much as polyurethane. During weathering, the photo-oxidation of CH groups to carbonyl groups occurred.

Investigating the antigraffiti properties of a polyurethane clearcoat containing a silicone polyacrylate additive

In this study, a polyurethane clearcoat was modified using a silicone polyacrylate antigraffiti additive and its surface free energy and mechanical properties were evaluated by various analytical techniques. The results showed that surface free energy decreased by replacing the polyol resin with the additive up to 10 mol%. Dynamic mechanical thermal analysis (DMTA) showed that the presence of the additive increased the storage modulus of the samples at ambient temperature. Evaluation of stainability of the coatings containing the additive revealed that a spray paint would be repelled from the surface showing a proper antigraffiti behavior. The additive did not affect the surface roughness of the films, indicating that the antigraffiti properties resulted from changes in surface chemistry due to migration of the additive to the surface.

The influence of different components on interpenetrating polymer network's (IPN's) characteristics as automotive top coats

The aim of this study was to investigate the influence of different components of interpenetrating polymer networks (IPNs) on their behavior in dual curing automotive applications. Dual curing is one of possible ways to obtain fast curing, scratch resistant coatings for use in OEM and car refinish applications. Dual curing systems, upon hardening, represent interpenetrating networks (IPNs) [1]. IPN's were obtained using novel acrylate-terminated hyperbranched polyester with high functionality and compared to classical 2-pack polyurethane clear coat. In our previous manuscript [1] we investigated the influence of the acrylated hyperbranched polyester (HBP(A)) content in dual curing systems. In this article we studied the influence of the reactive diluent on dual curing compositions. To this end, we have chosen IPN with 50/50 weigth ratio of polyurethane (PU) and polyacrylic (PA) component. In order to determine more clearly the role of the HBP(A) in one IPN HBP(A) was changed with hexane diol diacrylate (HDDA), keeping the same ratio with EHA. The IPNs were characterized by dynamic-mechanical analysis (DMA), differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). The mechanical properties of the IPNs were also investigated. The IPN with HDDA as reactive diluent, had the best performance. IPN with HBP(A) had the highest glass transition temperature Tg and the highest crosslink density, but it did not have the highest hardness.

Investigating the changes in properties when a hydrophobic nanosilica is added to a two-pack polyurethane clear coat

Various concentrations of a hydrophobic nanosilica were employed to prepare a series of two-pack acrylic polyol polyurethane nanocoatings in order to study the changes in the properties of the resultant coatings. Furthermore, the morphological, mechanical, rheological, thermal and optical properties of such coatings were investigated. The morphological properties were carried out by the aid of a transmission electron microscope (TEM); whereas, the rheological properties were determined by a rotaviscometer. The optical properties were determined by UV-Visible spectrophotometric and turbidimetric techniques. The static mechanical properties were acquired by the aid of an Instron testing machine. The glass transition temperature (Tg) of the nanocoatings were obtained by DSC analyses. The results showed that coatings containing hydrophobic nanosilica exhibit excellent dispersion and compatibility of nanoSiO2 within the polyurethane matrix. Additionally, such coatings also exhibited improved mechanical properties, especially increases in the scratch resistance. In the fluid state, these coatings showed a shear thinning behaviour. In addition, the nanocomposites' Tg decreased compared to the pure polyurethane clear coat. The optimum range of adding hydrophobic nanosilica to the two-pack acrylic polyol polyurethane clear coat in order to achieve optimum mechanical, rheological and optical properties was determined to be within the range of 4-8%: by weight.

Investigating changes in electrochemical properties when nano-silica is incorporated into an acrylic-based polyurethane clearcoat

Two different types of nano-silica (i.e., hydrophilic Aerosil 200 and hydrophobic Aerosil R805) were employed in the preparation of 2-pack acrylic polyol polyurethane nano-coatings so that the electrochemical properties of the resultant coatings could be investigated. Electrochemical impedance spectroscopy was used to evaluate the corrosion performances of such nano-coatings applied onto mild steel substrates that were immersed in 3.5% (w/w) NaCl solutions. It was observed coatings that contained nano-silica increased the barrier properties of the binder, as well as the coatings’ electrochemical resistance compared with pure polyurethane coatings. The surface tension of pure polyurethane was measured by a tensiometer. Rheological properties were also determined at various shear rates by a rotaviscometer. Results showed that the surface tension of hydrophobic nano-silica is very close to the pure polyurethane matrix, giving the better compatibility of the two. This was further confirmed by transmission electron microscopy and by the fact that the hydrophobically filled nano-silica coatings showed shear thinning behavior in the fluid state. Also observed was better corrosion performance of the resultant hydrophobic nano-coatings compared to coatings embedded with hydrophilic nano-silica.

Deterministic performance parameters for an automotive polyurethane clearcoat loaded with hydrophilic or hydrophobic nano-silica

In this study, two different nano-silica particles (hydrophilic, Aerosil TT600 and hydrophobic, Aerosil R972) were selected in order to provide the most transparent, UV-absorbent nano-clearcoats. These nano-silica particles were used to improve and optimize properties of 2-pack polyurethane clearcoats based on acrylic polyol. Micro-PIXE analysis was employed to illustrate distribution of nano-silica in the polyurethane matrix. Physical and chemical degradations were investigated via spectrophotometry and FTIR spectroscopy. Additionally, thermal stability and the ability of the clearcoats to resist simulated car wash conditions were also studied. Contrary to belief, coatings loaded with hydrophilic nano-silica which are more UV-absorbent had less durability in UV-B/H 2O accelerated tests.

Surface modification of TiO2 nano-particles with silane coupling agent and investigation of its effect on the properties of polyurethane composite coating

Surface modification and characterization of TiO2 nano-particles as an additive in a polyurethane clear coat were investigated. For the improvement of nano-particles dispersion and increasing possible interactions between nano-particles and polymeric matrix, the surface of the nano-particles was modified with amino propyl trimethoxy silane (APS). Equivalent amount of APS for monolayer formation on the nano-particles surface was determined by means of elemental analysis (CHN). The grafting of APS on the TiO2 nano-particles surface was characterized with TGA and FTIR techniques. Mechanical properties of coatings containing various amount of TiO2 nano-particles were evaluated with DMA technique and tensile strength measurement. UV–vis spectroscopy was employed to evaluate the absorbance and transmittance of the nano-TiO2 composite coatings in the wavelength range of 230–700nm.The results showed that surface treatment of TiO2 nano-particles with APS improves nano-particles dispersion, mechanical properties and UV protection of the urethane clear coating.

Investigating the variations in properties of 2-pack polyurethane clear coat through separate incorporation of hydrophilic and hydrophobic nano-silica

In the present study, a 2-pack polyurethane clear coat curable at ambient conditions was selected. Two different types of nano-silica (i.e. hydrophilic and hydrophobic nano-silica) were employed as fillers in order to vary the properties of the resultant nano-composite polyurethane coatings. Various morphological, mechanical, rheological and optical properties of such coatings were investigated. The results showed that coatings based on hydrophilic nano-silica gave a less transparent more UV absorbent coating. However, coatings based on hydrophobic nano-silica gave more miscible, transparent coating having improved mechanical properties especially scratch resistance. In the fluid state these coatings showed shear thinning behavior. The optimum range of adding 4–8% by weight of hydrophobic nano-silica to the chosen 2-pack acrylic polyol polyurethane clear coat gave optimal morphological, rheological, mechanical and optical properties to the final nano-composite coatings.

Comparison of different commercial pretreatment methods for hot-dip galvanized and Galfan coated steel

Abstract The performance of different pretreatment methods for hot-dip galvanized (HDG) and Galfan coated steel has been studied by treating both substrates with three different commercial pretreatment systems. Conventional chromate based pretreatment, zinc phosphating pretreatment and zirconium based pretreatment systems were studied. The chemically pretreated substrates were characterized by using electron spectroscopy for chemical analysis (ESCA), glow discharge optical emission spectroscopy (GD-OES) and atomic force microscopy. The pretreated surfaces were coated with a polyurethane clear coat and the corrosion resistance of the coated panels was tested by a prohesion test. ESCA results show that chromium from the chromate final rinses in the conventional chromate based and the zinc phosphating pretreatment is adsorbed of equal amount. ESCA results also show that there is a difference in surface composition of the zirconic acid rinsed samples prepared with two different techniques. According to the GD-OES results the galvanized steel strip materials react to a different degree in the chromate and zirconium based pretreatments. According to the prohesion test results of the clear coated pretreated HDG samples the zirconic acid rinse pretreatment is similar in corrosion performance to the two other pretreatments studied. The prohesion test result also show that the untreated Galfan coated steel strip has better corrosion resistance than the untreated HDG steel strip.

High performance Polyurethane Clearcoats for Automotive OEM

High performance Polyurethane Clearcoats for Automotive OEM

Star oligomers with different reactivity in low VOC polyurethane coatings: Part II

In this paper the effects of the reactivity of hydroxyl functional oligomers with a polyisocyanate crosslinking agent have been demonstrated by comparing the potlife/hardness of a 3.5 VOC two-component polyurethane clear coat based on a low TG, high reactive against a high TG, low reactive oligomer.