Preparation of surface energy controlled automotive clearcoats loaded with functional silicon additives: Studying the resistance against tree gum attack

The aim of this study is enhancing an automotive clearcoat easy-to-clean property against simulated tree gum (Arabic gum) using hydroxyl-functional silicone polyacrylate additives having different hydroxyl contents. The clearcoat surface, mechanical and chemical properties were studied using a contact angle measuring device, dynamic mechanical thermal analysis (DMTA) and Fourier Transform Infrared spectroscopy (FT-IR) respectively. It was found that additive with lower hydroxyl content gave rise to better easy-to-clean properties of the clearcoat against Arabic gum. This additive also resulted in lower contact angles and higher cross-linking density, tensile stress and work of break of the clearcoat.     

Role of surface active additives on reduction of surface free energy and enhancing the mechanical Attributes of easy-to-clean automotive clearcoats: Investigating resistance against simulated tree gum

The objective of this work is enhancing the clearcoat resistance against simulated tree gum (Arabic gum) using surface active additives including hydroxyl-functional polydimethyl siloxane (PDMS) and hydroxyl-functional silicone polyacrylate which are able to reduce gum adhesion to the clearcoat surface by reducing its surface free energy and work of adhesion. Using a contact angle measuring device, the surface free energy, contact angle and work of adhesion were obtained. The mechanical and structural properties of the clearcoats were studied by tensile test, dynamic mechanical thermal analysis (DMTA) and Fourier transform Infrared spectroscopy (FT-IR). Results showed that both additives enhanced the clearcoat easy-to-clean properties and reduced work of adhesion and surface free energy. The decrease in surface free energy and work of adhesion was more pronounced in presence of hydroxyl-functional polydimethyl siloxane. It was found that polydimethyl siloxane could produce contact angles much greater than silicone polyacrylate. Both additives increased clearcoat cross-linking density and toughness by participating in curing reaction. Results showed that the increase in cross-linking density and toughness was more effective when polydimethyl siloxane based additive was used. Results also revealed that additives could significantly improved the clearcoat resistance against Arabic gum by reducing gum adhesion to the surface. Both number of cracks and etched areas were reduced in presence of the additives especially in presence of polydimethyl siloxane. Both the chemical structure and functionality of the additives were found influential parameters which could alter the clearcoat surface cleanability and biological resistance against simulated tree gum.     

Fabrication of low surface free energy automotive clear coats: Mechanical and surface chemistry studies

This work aims at improving the surface chemistry and the mechanical properties of a commercial acrylic–melamine clear coat using a functional siliconized additive. The resistance of films against biological degradation was then investigated using pancreatin (simulated bird droppings) and Arabic gum (simulated tree gum). Variations in the surface and bulk chemical structures, as well as the thermomechanical characteristics of the clear coats at different concentrations of the additive, were investigated by a wide range of techniques inclusive of contact angle measurement, gonio‐spectrophotometery, dynamic mechanical thermal analysis (DMTA), energy‐dispersive spectroscopy, atomic force microscope, optical microscope, and attenuated totalreflectance Fourier transform infrared (ATR‐FTIR) spectroscopy. Negligible effect of additive on color change was revealed. It was shown that even at low loadings of additive it could migrate to the surface, producing hydrophobic films with very low surface free energies with water contact angle exceeding 100°. In addition, it was found by DMTA and ATR‐FTIR studies that the functional additive was covalently attached to the acrylic–melamine chains through its hydroxyl groups. However, phase separation was observed at high concentrations of additive, leading to reduced crosslinking density. The clear coat resistance against pancreatin and Arabic gum was improved using optimum concentrations of the additive. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Investigating the degradation resistance of silicone-acrylate containing automotive clearcoats exposed to bird droppings

This work reports preparation of acrylic/melamine based clearcoats containing various loads of a reactive polysiloxane additive. The additive was incorporated into the clearcoat formulations up to 8 wt% to enhance its resistance against bird droppings. Contact angle measurements, ATR spectroscopy, energy dispersive X-ray analysis, appearance measurements together with different microscopic techniques were utilized to reveal the effects of additive on the properties of the coating prior and after exposure to pancreatin, the synthetic equivalent of natural bird droppings. Appearance measurements, as well as optical microscope images obviously indicated that the additive improved the clearcoats resistance against pancreatin. Results revealed that surface free energy of the films was reduced in the presence of additive. It was also found that at high concentrations of additive, a significant part of it remained in the bulk, forming a second phase. This resulted in a lack of sufficient reactive groups and lead to an under-cure state at the clearcoat surface.     

Studying the rheology,optical clarity and surface tension of an acrylic/melamine automotive clearcoat loaded with different additives

Acrylic/melamine based automotive clearcoats were prepared by inclusion of functional and conventional additives. The conventional additives used were based on polysiloxane chains without any reactive groups. On the other hand, the functional additives were based on polyacrylate and polysiloxane backbones. The additives were added to the clearcoat formulations at different concentrations. Surface tension, optical properties and rheological behaviors of the clearcoats were studied by tensiometer, gonio-spectrophotometer, rheometric mechanical spectrometer (RMS) and Brookfield techniques. Results showed that addition of both conventional and functional additives reduced the surface tension of the clearcoat up to a certain value of the additive concentration. It was seen that functional additives could reduce surface tension much greater than the conventional ones. The coating clarity and transparency were not affected in presence of conventional additives. However, the functional additives, especially the one having higher molecular weight, reduced the coating transparency. The clearcoat viscosity was increased using functional additives. A shear thickening behavior of the clearcoats loaded with functional additives was seen. The conventional additives did not change the clearcoat viscosity. It was concluded that the additive functionality, molecular weight and chemical structure were influential parameters affecting the final properties.     

Effects of different silicon-based surface active additives on degradability of clearcoats exposed to bird droppings

A series of clearcoats separately loaded with different concentrations of functional silicon–polyacrylate and polydimethyl siloxane additives were prepared. Optical performances of the cured films were studied by gonio-spectrophotometry. Dynamic mechanical thermal analysis was used in order to investigate viscoelastic properties of the additive-containing films. Contact angle measurements, (FTIR) spectroscopy, scanning electron microscopy equipped with energy-dispersive analysis of X-ray, and atomic force microscopy techniques were utilized to evaluate surface properties of the clearcoats. It was shown that clearcoat surface free energy decreased and its crosslinking density increased in the presence of the additives. Results revealed that addition of both additives to the clearcoat enhanced its resistance against pancreatin (simulated bird droppings). A decrease in surface degradation was observed in the presence of the additives. Results also showed that functional polydimethyl siloxane influenced coating viscoelastic, surface chemistry, and biological resistance more effectively compared to that of the functional silicon–polyacrylate one.     

The role of basecoat pigmentation on the biological resistance of an automotive clearcoat

This work aims to study the effect of various natural and artificial biological compounds on an automotive acrylic/melamine clearcoat applied over silver and black basecoats containing pigments. The visual performance of the coating system was evaluated at different aging conditions. To this end, analytical techniques including optical microscopy, scanning electron microscopy, gonio-spectrophotometery, gloss measurement, ATR-FTIR spectroscopy, and DMTA analysis were utilized to investigate the optical and mechanical response of the system upon exposure to the biological materials. Results indicated different effects produced by gums and bird droppings on both silver and black systems at all aging processes. In addition, a more severe effect of biological attacks was observed on the clearcoat samples applied on the black basecoat which had experienced postaging conditions. However, it was found that pancreatin and bird droppings influence the coating systems more severely compared to the natural and synthetic Arabic gums.     

Effect of polysiloxane additives on the scratch resistance of an acrylic melamine automotive clearcoat

Many attempts have been carried out to increase the scratch resistance of clearcoats using various appropriate additives. These additives may increase surface hardness or surface slippage, and/or enhance the bulk mechanical strength of the clearcoat. In the present study, the influence of various added loads of three differently structured polysiloxane additives on the scratch resistances of an acrylic melamine clearcoat was investigated. A series of analytical instruments, such as a laboratory carwash simulator, a scanning electron microscope, an optical microscope and an attenuated total reflectance Fourier transform infrared spectroscope, and others were used to compare the effects of the various added contents of polysiloxane additives on changes in the viscoelastic properties and scratch morphologies of the resultant clearcoats. The results illustrated that all polysiloxane additives improve the scratch resistance of such clearcoats, yet the optimum load varied for each individual additive. There is also a good indication that polyether-modified polysiloxanes improve scratch resistance by increasing surface hardness, while the fluorocarbon-modified polysiloxane tends to change the viscoelastic properties of the clearcoats. It was also found that scratch resistance varied linearly with Micro-Vickers’ hardness for brittle clearcoats.     

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.     

壳聚糖/结冷胶双层膜制备工艺优化及表征

以壳聚糖（CS）和结冷胶（GG）为原料，采用溶液流延法并结合层层自组装技术制备了CS/GG双层膜，通过单因素和响应面试验优化制备工艺条件，并对双层膜的微观形貌、化学结构、力学性能、光学性能、阻水性能和抗氧化性能进行评价。结果表明，CS质量分数1.7 %、GG质量分数1.5 %、CS与GG成膜液体积比4/6、甘油质量分数25 %条件下双层膜的拉伸强度为38.83 MPa、透湿量为750.76 g/（m²·d）；与单层膜相比，CS/GG双层膜表面光滑、截面致密，红外光谱分析结果表明双层膜具有良好的相容性；双层膜可以有效改善纯CS膜、纯GG膜的力学性能和阻水性能。     

Investigation of factors impacting the in-service degradation of aerospace coatings

The impact of in-service environmental stressors on the durability of exterior decorative aerospace coating systems was investigated using accelerated weathering for a high-gloss polyurethane-based monocoat with and without clearcoat. Color, gloss, surface roughness, hardness, and chemical composition changes were studied by varying UV irradiance, temperature, thermal extremes, particulate matter, and acid environment while using constant moisture condensation conditions. The use of a clearcoat was found to enhance the resistance to gloss loss regardless of the stressors applied; however, the clearcoat system also produced a larger increase in hardness under all experimental conditions and a larger color shift for all stressors except for the particulate matter and particulate matter combined with acid. A correlation between color shift and chemical degradation was established by monitoring changes in amide and carbonyl functional groups as a function of UV irradiance, temperature, and thermal extremes. The particulate matter, with or without acid was found not to affect chemical degradation, but produced large color shifts for both coating systems and some loss of gloss at high radiant exposures for the clearcoat system. For the accelerated tests studied here, only the highest UV irradiance and temperature level, with or without additional stressors, produced changes in the clearcoat relative to the monocoat system without clearcoat that correlate with in-service performance observations.     

Studying the effects of the chemical structure of an automotive clearcoat on its biological degradation caused by tree gums

The effects of artificial and natural tree gums on the mechanical, chemical, and aesthetic performances of two automotive acrylic/melamine clearcoats were studied. To this end, two clearcoats with different acrylic/melamine ratios were investigated. Biological experiments were performed under post-aging conditions using an accelerated weathering test. Analytical techniques including optical microscopy, scanning electron microscopy (SEM), gloss measurement, FTIR, and DMTA analyses were utilized to reveal the responses of the coating system upon exposure to the aforementioned biological materials. Contact angle measurements were also conducted to estimate the surface energy of the coatings. Greater crosslinking density, together with a higher T _g and damping behavior of the clearcoat, indicative of a greater degree of cure, were obtained as the ratio of melamine crosslinker increased. It was shown that both Arabic and natural tree gums could strongly attach to the clearcoats’ surface, imposing a significant stress during the drying process, thereby leading to a physical failure. In addition, the acidic nature of these biological materials leads to a chemical alteration in the clearcoats’ structure. The greater crosslinking density and lower hydrophilicity of the clearcoats containing higher melamine crosslinker were responsible for the weaker interaction of gums with the surface. This showed a greater capability for stress damping. Small surface cracks with fracture morphology on the coatings exposed to biological materials at higher exposure times (in the xenon test) were also observed. This is discussed based on the adhesion of the coatings to gums at longer exposure times, because of significant stress.     

Improving the mechanical resistance of waterborne wood coatings by adding cellulose nanofibres

In the present study, microfibrillated cellulose (MFC) and nanocrystalline cellulose (NCC) were applied as additives for a waterborne acrylate/polyurethane-based wood coating in order to improve the mechanical resistance of coated wood surfaces. Coating mixtures containing up to 5 wt% nanocellulose were prepared by high-shear mixing and applied to wood substrates. The optical, mechanical and chemical properties of cured coatings were characterized. Surface roughness, gloss, scratch resistance, abrasion resistance and resistance against chemicals were determined according to the relevant European standards. Additionally, nanoindentation (NI) was used to assess the micromechanical properties of modified and unmodified coatings. Owing to a higher surface roughness, cellulose-filled coatings showed significantly lower levels of gloss than the unmodified coating indicating that nanocellulose acts as a matting agent. NI experiments revealed a slightly positive effect of nanocellulose addition on the hardness and modulus of the coatings. While scratch resistance improved consistently with increasing nanocellulose addition, abrasion resistance was found to improve only sporadically. Tensile tests on free-standing coating films revealed a significantly higher tensile strength and modulus for cellulose-filled coatings. Overall, the results suggest that the addition of cellulose nanofibres primarily improves the internal cohesion of the coating layer whereby MFC was more effective than NCC.     

Investigation of char strength and expansion properties of an intumescent coating exposed to rapid heating rates

An efficient and space saving method for passive fire protection is the use of intumescent coatings, which swell when exposed to heat, forming an insulating char layer on top of the virgin coating. Although the temperature curves related to so-called cellulosic fires are often referred to as slow heating curves, special cases where the protective char is mechanically damaged and partly removed can cause extremely fast heating of the coating. This situation, for a solvent based intumescent coating, is simulated using direct insertion of free films into a muffle oven. The char formed is evaluated with respect to the mechanical resistance against compression, degree of expansion, and residual mass fraction. Experimental results show that when using this type of shock heating, the mechanical resistance of the char against compression cannot meaningfully be correlated to the expansion factor. In addition, char properties, measured at room temperature, were dependent on the preceding storage conditions (in air or in a desiccator). The char was found to have the highest mechanical strength against compression in the outer crust facing the heat source. For thin (147 μm) free coating films, a tendency to contract in the horizontal plane was observed. The experimental approach is relevant for testing of intumescent coatings used in buildings where moving or falling objects may damage the char during a fire.     

Acid etch resistance of automotive clearcoats. I: Laboratory test method development

This paper reports on the development of a laboratory test procedure for the evaluation of the environmental etch resistance of clearcoats. The test evaluates the bulk acid hydrolysis resistance of clearcoats by gravimetrically following material weight loss as a function of exposure time to a sulfuric acid solution, under conditions that simulate outdoor exposure. The bulk hydrolysis resistance of five production clearcoat technologies including acrylic melamine, acrylic melamine-silane, carbamate, acrylic urethane, and epoxy acid were evaluated. Results from the weight loss measurements were consistent with those anticipated based on the coating systems bulk chemistry and inherent hydrolysis resistance, for clearcoat systems processed under nominal processing conditions. The relative rankings from the laboratory test were found to correlate with field etch ratings. The test method is inexpensive, quantitative, and generates repeatable results that are not subject to environmental variations associated with current field etch testing. Ford Research Laboratory, Dearborn, MI 48121-2053.     

WATER-BORNE,LOW-TEMPERATURE CURABLE POLYACRYLATE COATINGS

A water-borne, low-temperature curable polyacrylate (PA) coating was developed by introducing crosslinkages in polymer chains with a polyfunctional comonomer. The effect was investigated of amount of comonomer on the properties of coating latex, such as mechanical properties, solvent resistance, Tg, and surface morphology of polymer. The particle size, size distribution, and the dispersion stability were also measured. Comparisons of the product were carried out with some coatings available from the market.     

蜡助剂在水性木器涂料中的应用

蜡助剂是水性木器涂料中使用的一种功能性助剂，本文研究了不同种类的蜡助剂在水性木器涂料中的使用对漆膜性能的影响。采用复配法将水性蜡助剂加入到水性木器涂料中，蜡助剂在涂料成膜时均匀地分散在整个涂层中，蜡助剂的加入能够显著提高漆膜的抗回粘性和耐刮伤性能，但是大粒径的蜡助剂会引起漆膜光泽的下降。     

纳米氧化锌表面改性及其复合水性聚氨酯涂膜性能的研究

以异丙醇为介质,用钛酸酯偶联剂对纳米ZnO进行表面改性,制备改性纳米ZnO/WPU(水性聚氨酯)复合涂膜。通过涂膜的力学性能来评价纳米ZnO的改性效果,讨论了改性纳米ZnO添加量对涂膜的力学性能、耐摩擦性能及耐水性能的影响。结果表明:当偶联剂用量为2%(质量分数),搅拌时间为70 min,反应温度为50℃时,纳米ZnO改性效果最好,当改性纳米ZnO添加量为0.3%(质量分数)时涂膜的综合性能最佳。     

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.     

High‐solids mar resistant clearcoats prepared from an isophthalate‐based oligoester and a melamine resin. Study and characterization of mar resistance with scanning probe microscopy method

A new series of high‐solids [low‐VOC (volatile organic compound)content] mar resistant clearcoats (CL‐series) were prepared upon crosslinking of a new‐synthesized hydroxyl‐terminated isophthalate‐based liquid oligoester (L‐311) with an hexakis(methoxymethylol)melamine (HMMM) resin, via an acid‐catalyzed etherification reaction. The chemical, physical, and mechanical properties of the CL‐clearcoats were compared to those of a reference clearcoat (CRO). An attempt was made to investigate the effect that the amounts of catalyst and melamine resin had on the clearcoats' physical, chemical, and mechanical properties, and moreover, to correlate these properties to the films chemical structures. The new‐formulated high‐solids clearcoats (CL‐series) presented enhanced processability and higher NVW values (lower VOC content) than the reference clearcoat CRO, and their properties (pencil hardness, knoop hardness, adhesion, impact resistance, solvent and gasoline resistance, mar resistance, and flexibility) were better or comparable to those of the CRO. More specifically, the mar resistance of the CL‐clearcoats series was investigated by applying both the crockmeter test and a novel method that employed a modified scanning probe microscope. In addition, we identified and characterized the different responses of the CRO and certain CL‐clearcoats to marring stress. The experimental data regarding the mar resistance of the new‐formulated clearcoats fully justified our polymer design strategy, verifying our expectations for the possibility of preparing glossy, high‐solids mar‐resistant clearcoats that could present enhanced processability and solvent resistance, relatively high pencil hardness, and at the same time very good elastic recovery to marring stress. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 83: 1317–1333, 2002