Relation between chip resistance and mechanical properties of automotive coatings

This work addresses the correlation between stone-chip resistance and mechanical properties of automotive solid colour coating systems. Single-impact tests, which are believed to realistically simulate chipping due to stone impact, were performed to investigate eight different coating systems. Additionally, conventional tests on chip resistance currently used in automotive industry were performed. Results were related to mechanical properties of the coatings, measured by dynamic mechanical thermal analysis and double cantilever adhesion test. It is found that coating systems with a low glass transition temperature for the primer have better stone-chip resistance.     

Tuning the mechanical performance and adhesion of polyurethane UV cured coatings by composition of acrylic reactive diluents

An approach to modify the properties of UV curable polyurethane coatings by altering the amount and functionality of acrylic reactive diluents, in order to optimize the coating performance, is demonstrated. Based on the rheology analysis, a model of the rheological behavior of the UV curable materials depending on the amount and type of a reactive diluent in the composition is demonstrated in this study. The relationships between the rheological behavior, the mechanical properties and adhesion of the coatings prepared from polyurethane UV curable compositions containing different amounts and functionalities of acrylic reactive diluents, have been investigated and discussed in this study. Based on the results of the study, the desired properties of UV cured coatings can be modeled and controlled without changing the nature of a particularly selected oligomer, thus maintaining the advantages of its chemical structure in a coating composition.     

Effects of thickness and substrate on the mechanical properties of hard coatings

Nanoindentation technique was employed to characterize the mechanical properties of TiN coatings deposited on high-speed steel and stainless steel substrates. Effects of thickness and substrate on-the mechanical properties were investigated. The results show that TiN coatings exhibit different mechanical properties corresponding to the variation in thickness and substrate.     

Powder coatings and differential scanning calorimetry: the perfect fit

A thermosetting powder coating is the ideal field of application for differential scanning calorimetry (DSC) analysis. A review of the existing techniques is done and a new product characterization approach is discussed in comparison with some traditional methods. Time savings, effectiveness and compliance with the objectives, can be advantageously obtained by using DSC analysis versus alternative methods (gel time, solvent cure test, storage stability, mechanical test, etc.). An attempt is made to provide a quick ‘one shot' analytical test to predict storage stability, curing behaviour, processing conditions and in some way the end-use performance of powder coatings.     

Thermal and radio-oxidation of epoxy coatings

Degradation induced by thermal (50–110 °C) and radio-oxidation of low T_g epoxy-amine networks has been studied. It has been found that oxidation leads mainly to amide groups formation at the vicinity of tertiary amines whatever ageing conditions (thermal or radio-oxidation at 200 Gy h⁻¹). In addition, some species as acids, peracids or formates have been revealed indicating a chain scission process. Physical modifications as T_g decrease and soluble fraction increase due to chain scission process, have been correlated with chemical modifications.     

Scratch resistant clear coats: development of new testing methods for improved coatings

More and more car manufacturers are now demanding clear coats with improved scratch resistance from their paint suppliers. Some motor companies have developed their own tests, some have chosen a test developed by a paint supplier and others are still looking for their optimum test. The opinion prevails that there should be one test which covers all aspects of realistic damage. However, microscopic photographs and reflow experiments show that two kinds of scratches occur in reality, abrasive as well as non-abrasive, renewable ones. Different standard clear coat systems have different sensitivities to both scratch types. In the scratch tests the rating of the clear coats is divergent, because the ratio of both sorts of scratches differs. We have developed a set of two tests, where each test mainly generates one scratch type. These tests, together with physico-chemical measurements (glass transition onset temperature T_g, laser optical profile scanning, indentation depths) lead to a deeper insight into scratch phenomena. One way to develop a clear coat which is resistant against all kinds of scratching damage is described.     

紫外光固化涂料附着力促进剂的研制

为了解决紫外光固化涂料附着力差的问题,以丙烯酸羟乙酯或甲基丙烯酸羟乙酯与五氧化二磷为原料在一定条件下进行亲电加成反应制得可紫外光固化的含磷酸基团的附着力促进剂。采用酸值跟踪测试确定总反应时间为3.5h。对产品进行红外光谱分析,表明反应物中的羟基已经完全反应以及产物中磷酸基团与CC双键的形成。对比了自制产品与市售产品在不同板材上的性能,结果表明这两种产品对紫外光固化涂料与金属、玻璃、木材等极性基材都具有很好的附着促进作用,并确定了自制产品的优势。     

Investigation of accelerated aging behaviour of high performance industrial coatings by dynamic mechanical analysis

Dynamic mechanical analysis (DMA) represents one of the most important methods for understanding mechanical behaviour of surface coatings providing a valuable link between chemistry, morphology, and performance properties. In this work, dynamic mechanical properties of several high performance industrial coatings were studied extensively. Four commercially available topcoats namely alkyd modified polyurethane (PU), economy aliphatic PU, high performance aliphatic PU and epoxy modified polysiloxane were selected based on their cure chemistries, volume solids, and overall performance. DMA was used to determine elastic modulus, glass transition temperature (T_g), crosslink density and creep behaviour of these coatings. DMA data were substantiated with mechanical and performance properties. Among the coatings, epoxy modified polysiloxane showed the highest T_g of 65.6 °C as well as crosslink density value of 2.24 × 10⁻³ mol/cc which was attributed to its superior mechanical and performance properties. In addition, topcoats were also subjected to artificial aging process in accelerated cyclic corrosion cabinet and QUV-weatherometer, respectively. The consequent changes in their physico-mechanical properties post exposure were also evaluated using DMA and correlated with other performance properties. After aging, the T_g increased substantially for all the coatings irrespective of their exposure type. For example, T_g of economy aliphatic PU increases from 38.4 °C to 52.9 °C and 51 °C after cyclic corrosion and UV-B weathering, respectively. However, crosslink densities either increased or decreased depending on the type of exposure and cure chemistries. These changes were corroborated using the Fourier transform infrared spectroscopy findings. The outcome of this study is expected to generate new insights into the behaviour of these coatings under dynamic mechanical stress and its relation with long term performance properties.     

Molecular modeling of crosslinked epoxy polymers: The effect of crosslink density on thermomechanical properties

Molecular dynamics and molecular mechanics simulations are used to establish well-equilibrated, validated molecular models of the EPON 862-DETDA epoxy system with a range of crosslink densities using a united atom force field. Molecular dynamics simulations are subsequently used to predict the glass transition temperature, thermal expansion coefficients, and elastic properties of each of the crosslinked systems. The results indicate that glass transition temperature and elastic properties increase with increasing levels of crosslink density and the thermal expansion coefficient decreases with crosslink density, both above and below the glass transition temperature. The results demonstrate reasonable agreement with thermomechanical properties in the literature. The results also indicate that there may be a range of crosslink densities in epoxy systems beyond which there are limited changes in thermomechanical properties.     

Thermal and dielectric properties of powder coatings based on carboxylated polyester and β-hydroxyalkylamide

Thermal transitions, relaxations and the crosslinking reaction in varnishes and pigmented paints based on carboxylated polyester and β-hydroxyalkylamide (Primid) were studied by differential scanning calorimetry (DSC), temperature modulated DSC (TMDSC), thermogravimetry (TGA) and dielectric analysis (DEA). The effect of the Primid content on the glass transition of the powder coatings before and after crosslinking was analysed. The melting and flow regions were studied by TMDSC and correlated with the loss factor, which was measured by DEA. A comparison of the DSC and TGA scans showed that the crosslinking reaction was masked by the vaporisation of water formed during esterification. The resulting endothermic reaction made it difficult to analyse the crosslinking by DSC. Nevertheless, it was possible to detect the crosslinking reaction by the dielectric measurement of the loss factor and the conductivity.     

Tetrafunctional acrylates based on β-hydroxy alkyl amides as crosslinkers for UV curable coatings

Ultraviolet (UV) curable coating formulations were prepared from novel crosslinking acrylates synthesized from β-hydroxy alkyl amides. Variations were done with respect to the nature of the monomer backbone by introducing aliphatic, aromatic and cycloaliphatic structures in between the amide groups. The synthesized multifunctional alcohols and acrylates were subjected to IR and NMR analysis for structure confirmation. The acrylates were dissolved in chloroform and the UV–vis spectrum was recorded to substantiate the presence of carbonyl group conjugated to the vinyl group. The new acrylates were added to basic formulation and exposed to UV radiation to get transparent films. The dynamic mechanical properties of the films cast from the formulations were assessed and studies on the effect of the synthesized crosslinking acrylate content and their nature on the viscoelastic properties of the films were carried out. Improvements in glass transition temperature (T_g) were observed with increasing percentage of crosslinker. Acrylates based on aromatic acid amides showed higher T_g than aliphatic acid amides. The storage modulus (E′) increased up to 10% and further increases in the crosslinker percentage led to a decrease in the modulus. The rubbery modulus depended on percentage of crosslinker and not on crosslinker structure.     

Characterization and conductive property of polyurushiol/silver conductive coatings prepared under UV irradiation

Polyurushiol/silver (PU/Ag) composite conductive coatings were prepared from urushiol and AgNO₃ under UV irradiation by using in situ radical reduction approach. The effects of the silver nitrate loading and the irradiation time on the surface resistivity of polyurushiol/silver (PU/Ag) composite films were investigated. The result from XRD analysis showed that the formation of Ag particles, and the surface resistivity of polyurushiol/silver (PU/Ag) composite films reached the value of 0.26 Ω cm, when the content of Ag particles in composite films was 23.8 wt%, and the irradiation time 90 s. Additionally, Ag particles were well dispersed in the composite films. And the films had good thermo-stability.     

Enhancing the performance of exterior waterborne coatings for wood by inorganic nanosized UV absorbers

Enhancing the durability of the architectural wood coatings is essential for a successful commercialization of the forest products. Therefore, this paper is focused on UV resistant waterborne nanocomposites coatings for exterior uses of wood, which were improved with inorganic UV absorbers such as zinc oxide and titanium dioxide nanoparticles. The performance of such nanocomposites coatings applied on black spruce boards was demonstrated trough accelerated weathering. Artificial aging behavior of the coatings was followed by color, gloss and thickness changes. Scanning electron microscopy and transmission electron microscopy was used to investigate nanoparticles dispersion in nanocomposite dry films. Fourier Transform Infrared Spectroscopy was used to characterize the chemical modification of the weathered coatings surface. The results have shown significant improvement in UV-shielding of the nanocomposites coatings. Depending of aging criteria, a selection of the best nanocomposite coatings formulations for exterior wood could be done.     

涂料树脂的相容性

讨论了涂料用共混树脂的相容性以及提高其相容性的主要途径,对部分相容树脂的形态及其对性能的影响作了介绍。     

Synthesis of fluorinated/methacrylated epoxy based oligomers and investigation of its performance in the UV curable hybrid coatings

Organic–inorganic hybrid coatings based on fluorinated/methacrylated soybean oil and bisphenol A/F epoxy methacrylate were obtained by combining photopolymerization and sol–gel process. Hard and transparent hybrid coatings were prepared on polycarbonate panels and their physical and mechanical properties such as gel content, hardness, adhesion, gloss, contact angle as well as tensile strength were measured. Results from the mechanical measurements showed that the properties of hybrid coatings improved with the increase in fluorine and sol–gel precursor contents. Thermo gravimetric analysis results demonstrated that fluorine and silica incorporations significantly enhanced the thermal oxidative stability of the hybrid coating materials. The surface morphology was also characterized by scanning electron microscopy (SEM). SEM studies indicated that inorganic particles were dispersed homogenously throughout the organic matrix.     

紫外固化粉末涂料的合成及固化研究

用E-12、E-20环氧树脂与丙烯酸反应,合成了可紫外光固化的环氧丙烯酸酯预聚物,并对产物进行固化研究。讨论了催化剂的种类、反应温度、反应时间等对合成产物的影响,光引发剂的种类、光照时间等对固化产物的影响。结果表明:环氧树脂与丙烯酸以甲苯为溶剂、四丁基溴化铵为催化剂,在110℃下反应180 min为较适宜的反应条件;环氧丙烯酸酯以TPO为引发剂,120 w/cm的紫外灯光照15 s为较宜适的固化条件。     

Effect of silane modified nano ZnO on UV degradation of polyurethane coatings

Nanosized ZnO modified by 2-aminoethyl-3-aminopropyltrimethoxysilane (APS) was prepared using the precipitation method. Modified nano ZnO by silane (ZnO-APS) was characterized by XRD, SEM, TEM and UV–vis measurements. The degradation of the polyurethane coating, the polyurethane coatings containing 0.1 wt% nano ZnO and the polyurethane coatings containing nano ZnO-APS at two concentrations (0.1 and 0.5 wt%) during QUV test was evaluated by gloss measurement and electrochemical impedance spectroscopy. The coating surface after QUV test was observed with SEM. The results show that nano ZnO-APS has spherical structure with particle size around 10–15 nm. Nano ZnO improved the UV resistance of the PU coating and surface treatment by APS enhanced the effect of nano ZnO. The presence of nano ZnO-APS at 0.1 wt% concentration significantly improved the UV resistance of polyurethane coating.     

The effect of morphology on the corrosion inhibition and mechanical properties of hybrid polymer coatings

The durability and mechanical properties of epoxy ester coatings and films has been improved by blending with rigid aromatic polyurea (PU). The interaction of PU and epoxy ester was enhanced by coupling the polymers with polymethylhydrosiloxane. The reactions between various entities are analyzed by Fourier transform infrared spectroscopy and the change in physical and mechanical properties are studied by a dynamic mechanical analyzer. The corrosion resistance of the hybrid coatings was measured by direct current polarization method, direct current polarization (DCP). The addition of polymethylhydrosiloxane enhances the corrosion properties in the hybrid coatings. The surface morphology was analyzed by scanning electron microscopy. The glass transition temperature of the films increases with increasing PU concentration and a wide glass rubber transition range for hybrid coatings was achieved which confirms the higher impact strength of the hybrid coatings and films. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Effect of the hard segment on the properties of UV curable waterborne blocked polyurethanes

Two types of UV curable waterborne blocked polyurethanes (PUs) were obtained from 2,4-tolylene diisocyanate(TDI) and isophorone diisocyanate (IPDI), which had the same soft segments and different hard segments. The PUs contained both the UV curable C=C bond and the blocked NCO groups which could be de-blocked when heated. Effect of the hard segment on the properties of the two types of PUs was investigated. The FTIR spectra method was employed to confirm the structure of the PUs. The photo-DSC was used to study the photo-polymerization rate of the PUs under UV irradiation in the presence of a photo-initiator and the C=C conversion behaviors. Heating-up IR analysis was used to track the de-blocking process and the heat curing process. The thermal degradation analysis (TGA) was employed to investigate the thermal stability of the UV cured films before and after heat curing process. Dynamic mechanical properties of the UV and heat cured films were investigated by the dynamic mechanical thermal analysis (DMTA).     

HPLC法测定UV固化涂料中光引发剂含量

建立了高效液相色谱法测定UV固化涂料中光引发剂的组分及其含量的方法。样品经定容过滤后进行色谱分析,采用的色谱条件:色谱柱NUCLEODUR C18 Isis 250mm×4.6mm,5μm;流动相:A液为乙腈,B液为超纯水;流速1.0mL/min,柱温25℃,UV检测器。采用该方法测定二苯甲酮、TPO、光引发剂1173、光引发剂819、苯甲酰甲酸甲酯5种组分的回收率均高于99.98%,相对标准偏差(n=7)小于0.44%,线性相关系数R2大于0.9999。该方法已应用于UV固化涂料生产控制中。