Novel techniques to investigate the impact of cellulose esters on the rheological properties and appearance in automotive basecoat systems

The viscous response of a coating formulation changes over several orders of magnitude after application onto a substrate. Furthermore, the performance and application attributes for a refinish basecoat formulation are slightly different from those of an OEM basecoat. The absence of a high temperature baking step during the refinish process necessitates that the paint exhibit very good antisag behavior as well as quick ‘dry to touch’ without compromising the flow and leveling properties of the coating as it dries. As most paint formulations are multicomponent in nature, it is always a challenge to precisely measure the impact of specific formulation components on the collective performance attributes of the applied coating. In this work, the focus has been to develop novel techniques that can be used to demonstrate a more quantitative measure of some of the performance attributes that rheological additives like cellulose esters can provide to automotive coatings. A series of pigmented basecoat formulations were prepared which contained cellulose acetate butyrates (CABs) of varying molecular weights at different levels based on the total solids of the coating formulation. The nonvolatile content of the formulations was also varied. The viscoelastic behavior of a typical automotive basecoat formulation during the drying process was then investigated using a novel rheological technique. Complex viscosity data (including storage and loss moduli as well as tan delta) were determined as a function of drying time and then compared to the macroscopic properties typically associated with a coating film as it dries. Thermogravimetric analysis (TGA) was also used to correlate the rheology of the metallic basecoat formulations with drying behavior of the coating. The final appearance of the coating was investigated by several microscopic techniques such as Laser Scanning Confocal Microscopy, Scanning Electron Microscopy, Atomic Force Microscopy, and Surface Profilometery, and attempts were made to correlate bulk measurements like ‘flop index’ with the microstructure of the coating. Presented at the 2006 FutureCoat! conference, sponsored by the Federation of Societies for Coatings Technology, in New Orleans, LA, on November 1–3, 2006.     

Powder coating of veneered particle board surfaces by hot pressing

The powder coating of veneered particle boards by the sequence electrostatic powder application – powder curing via hot pressing is studied in order to create high gloss surfaces. To obtain an appealing aspect, veneer sheets were glued by heat and pressure on top of particle boards and the resulting surfaces were used as carrier substrates for powder coat finishing. Prior to the powder coating, the veneered particle board surfaces were pre-treated by sanding to obtain good uniformity and the boards were stored in a climate chamber at controlled temperature and humidity conditions to adjust an appropriate electrical surface resistance. Characterization of surface texture was done by 3D microscopy. The surface electrical resistance was measured for the six veneers before and after their application on the particle board surface. A transparent powder top-coat was applied electrostatically onto the veneered particle board surface. Curing of the powder was done using a heated press at 130 °C for 8 min and a smooth, glossy coating was obtained on the veneered surfaces. By applying different amounts of powder the coating thickness could be varied and the optimum amount of powder was determined for each veneer type.     

乘用车车身漆膜橘皮的成因及其预防

在乘用车的车身涂装中,涂层橘皮是最常见和难以控制的缺陷之一,已成为汽车厂家的棘手问题。阐述了影响涂膜流动和外观的因素;介绍了涂层外观漆膜橘皮的检测方法和车身漆膜橘皮的成因及其防治;以及乘用车塑料外饰件涂装受橘皮的影响因素及其控制;同时指出了车身漆膜橘皮的预防措施。     

水性罩光清漆固化反应速率及漆膜性能研究

水性罩光清漆固化反应速率对于以“湿碰湿”工艺施工的水性三涂一烘（3C1B）体系有很大影响,水性罩光清漆的固化反应速率主要由作为交联剂的氨基树脂所控制。本文对 3种不同类型的氨基树脂进行了红外表征（ FT-IR）,分析了其分子结构。分别以上述氨基树脂作为交联剂制备水性罩光清漆,通过旋转流变仪测试清漆在固化过程中剪切储存模量的变化,探究了上述氨基树脂对水性罩光清漆固化反应速率的影响。对比了所制备的水性罩光清漆搭配水性 3C1B中涂和色漆的漆膜性能,分析了氨基树脂对漆膜性能的影响。研究结果表明：以甲醚丁醚混合醚化的氨基树脂作为交联剂的水性罩光清漆的固化速率适用于 3C1B体系,且制备的漆膜性能最佳。     

An investigation of spin coating of electron resists

This paper reports the results of spin coating studies of an electron resist using several different solvents. Two problems which were frequently observed during the spin coating studies were the appearance of orange peel coatings and the formation of cloudy films. The appearance of orange peel is attributed to the rapid drying of low-boiling solvents. The formation of a cloudy film is believed to be caused by the hygroscopic nature of the solvents used. The resist film thickness can be approximated by the relationship l = KC^2.1/ω^0.5, where l is film thickness, C is volume fraction of polymer resist, K is a constant and ω is the rotation speed. The results are compared with the theoretical modelings of Washo (1) and Meyerhofer (2).     

Flexible clear coats—Effect of curing conditions

The effect of curing at different conditions was investigated for flexible model clear coat films for coil coating applications. Based on a commercial polyester binder two formulations with isocyanate based crosslinking agents (hexamethylene diisocyanate (HDI), isophorone diisocyanate (IPDI)) were prepared. The clear coats were baked at laboratory (145 °C) and industrial processing (300 °C) conditions. While for high temperature curing the baking time was kept constant at 30 s, the curing time at 145 °C, which is above the deblocking temperature of the crosslinking agents, was varied from 10 to 90 min. The clear coat films were characterized as to their thermomechanical and mechanical properties by dynamic mechanical analysis (DMA) and by tensile testing. Regarding DMA loading in tensile and penetration mode was performed.     

A new approach to investigate relationships between certain instrumentally measured appearance parameters and their visually perceived equivalents in the automotive industry

Appearance control has continuously been a major challenge to the automotive industry. In order to implement a consistent control on the appearance of automotive finishes, objective measurement of various appearance attributes such as gloss, distinctness of image, orange peel, etc., is indispensable to the automotive manufacturers. In the present study, attempts were made to find the correlation between visually perceived and instrumentally measured appearance of achromatic automotive finishes. To this end, three physical scales of appearance attributes, namely specular gloss, distinctness of image, and orange peel were prepared using a series of metallic black, metallic gray, metallic silver, and solid white automotive finishes. The samples were visually evaluated by a panel of 16 observers, by utilizing an also prepared lightness scale, in a light cabinet having a 45/0 illumination/observation geometry. The innovative use of a common lightness scale in the present study showed that there is a surprisingly good correlation between instrumentally measured specular gloss, distinctness of image, and Wave scan LW and Wd parameters, and the corresponding visually evaluated data at the four investigated achromatic levels.     

溶剂及施工工艺对3C1B水性面漆外观影响研究

水性 3C1B（三涂一烘）工艺是以湿碰湿的方式喷涂水性中涂、水性面漆和清漆,并一次性烘干的工艺,可以显著降低能源损耗,提高生产效率。涂层外观是评价涂料质量和涂装效果的重要指标之一,而湿碰湿工艺的这种特殊的施工方式对涂层的外观表现更为敏感。本文以水性白实色涂料为例,从中涂、面漆的材料配方及施工工艺等方面对水性 3C1B汽车涂料的外观改进进行了研究,并识别出了关键影响因素,结果表明：水性面漆对漆膜整体外观的影响大于中涂;配方的干湿及喷涂雾化后的干湿对漆膜流平、流挂等影响较大,进而会影响漆膜的外观表现。     

Glass–ceramics as oxidation resistant bond coat in thermal barrier coating system

Thermal barrier coating (TBC) system consisting of yttria stabilized zirconia (YSZ) top coat, glass–ceramic bond coat and nickel base superalloy substrate was subjected to static oxidation test at 1200 °C for 500 h in air. Oxidation resistance of this TBC system was compared with the conventional TBC system under identical heat treatment condition. Both the TBC systems were characterized by SEM as well as EDX analysis. No TGO layer was found between the bond coat and the top coat in the case of glass–ceramic bonded TBC system while the conventional TBC system exhibited a TGO layer of about 16 μm thickness at the bond coat-top coat interface region.     

基于双旋杯工艺的水性3C1B复合涂层的研发

在3C1B(三涂一烘)的工艺下,通过树脂、助溶剂、颜料的合理搭配制备了一款水性双组分中涂和一款水性双组分底色漆,中涂采用旋杯喷涂,底色漆采用两遍旋杯的喷涂方式,该配套组合能够满足产品对于多种性能的要求.同时探究了在上述工艺条件下,漆膜厚度变化以及漆雾对漆膜外观的影响,结合抗紫外穿透测试,找出了施工的最佳膜厚.结果表明:...     

Evaluation of the weathering performance of basecoat/clearcoat automotive paint systems by electrochemical properties measurements

The aim of the present study was to investigate the possibility of evaluating the weathering performance of a basecoat/clearcoat automotive paint system through the determination of its electrochemical properties. To this end, the electrochemical properties of a basecoat/clearcoat automotive paint in a 3.5% solution of NaCl in deionized water were measured at different weathering exposure times. A constant phase element (CPE) was used for describing the electrochemical behavior of the coatings under test. The values of the CPE parameters, i.e. Y₀ (the CPE constant) and n (the CPE power) were subsequently correlated to the extent of photo-oxidation (as measured by appearance, surface roughness, FTIR, surface tension and adhesion measurements) of clearcoat at the surface, in the bulk and at the interface between the basecoat and the clearcoat. The result showed that the electrochemical parameters Y₀ and n provide ready means for comparing the weathering performances of basecoat/clearcoat automotive paint systems. Increases in the value of Y₀ together with decreases in the value of n with increasing weathering exposure times suggest increased possibilities for the onset of cracking in the clearcoat itself in addition to its propagation towards the basecoat. Additionally, sudden variations in the values of Y₀ and n are indicative of increases for the clearcoat to peel off.     

Performance of finish coated galvanized steel sheets for automotive bodies

High performance and cost reduction are principal concerns for vehicle manufacturers. In addition to shape, the exterior finish is the first thing a consumer sees when looking at a vehicle. The quality and durability of the finish is a reflection of the quality and durability of the vehicle itself. In this work, the behavior of two finish coat systems was studied. Finish coat system 1 included a powder coat, a waterborne base coat and a clear coat, and finish coat system 2 included the same powder coat, a solvent-based base coat and a clear coat. These finish coats were applied on unprimed and pre-primed electrogalvanized, hot dip galvanized and galvannealed steel. Before application, for each finish coat two activation treatments were considered: a conventional zinc phosphate for automotive industry and an experimental pretreatment. Three primers were considered. Primer 1 is an organic zinc rich silicate with a low thickness (near 4 μm), primer 2 is a very thin (near 2 μm) water-based primer filled with graphite and primer 3 is a conventional electrophoretic applied primer system.     

重型车车身涂装桔皮缺陷案例解析

随着汽车工业的发展,完美的涂装外表已不仅仅局限于轿车行业,很多重型车制造商为了满足顾客的更高要求、提升竞争力,对其表面质量越来越重视。通过对驾驶室涂装中出现严重桔皮的故障排除,浅析了桔皮的成因机理及测定方法,并根据在现场生产中对车身板材、涂装用漆、喷涂环境及操作工技术等产生桔皮因素的监测和整改,为在生产中控制桔皮缺陷提供了必要依据。     

减少车身橘皮提高涂膜外观的工艺实践

通过调整喷涂工艺参数如油漆黏度、喷涂距离、湿碰湿喷涂闪干时间及流平时间等来减少由工艺参数不当引起的橘皮、涂膜失光发乌 另外,调整油漆流平及鲜映性等外观性来减少由油漆本身的外观性能不良产生的橘皮、涂膜失光发乌等问题,最终使车身涂膜外观得到改善。     

Mechanical properties of MWPECVD diamond coatings on Si substrate via nanoindentation

The mechanical properties of polycrystalline diamond coatings with thickness varying from 0.92 to 44.65 μm have been analysed. The tested samples have been grown on silicon substrates via microwave plasma enhanced chemical vapour deposition from highly diluted gas mixtures CH₄-H₂ (1% CH₄ in H₂). Reliable hardness and elastic modulus values have been assessed on lightly polished surface of polycrystalline diamond films.The effect of the coating thickness on mechanical, morphological and chemical-structural properties is presented and discussed. In particular, the hardness increases from a value of about 52 to 95 GPa and the elastic modulus from 438 to 768 GPa by varying the coating thickness from 0.92 to 4.85 μm, while the values closer to those of natural diamond (H = 103 GPa and E = 1200 GPa) are reached for thicker films (> 5 μm). Additionally, the different thickness of the diamond coatings permits to select the significance of results and to highlight when the soft silicon substrate may affect the measured mechanical data. Thus, the nanoindentation experiments were made within the range from 0.65% to 10% of the film thickness by varying the maximum load from 3 to 80 mN.     

Assembly of 8YSZ nanoparticles into gas-tight 1-2 μm thick 8YSZ electrolyte layers using wet coating methods

The application of a thin film electrolyte layer with a thickness in the micrometer range could greatly improve current solid oxide fuel cells (SOFCs) in terms of operating temperature and power output. Since the achievable minimal layer thickness with conventional powder coating methods is limited to ∼5 μm, a variety of thin film methods have been studied, but results on regular large-scale anode substrates are still lacking in the literature. In this paper, a wet coating process is presented for fabricating gas-tight 1-2 μm thick 8YSZ electrolyte layers on a regular NiO/8YSZ substrate, with a rough surface, a high porosity and a large pore size. These layers were deposited in a similar way as conventional suspension based layers, but the essential difference includes the use of coating liquids (nano-dispersion, sol) with a considerably smaller particle size (85 nm, 60 nm, 35 nm, 6 nm). Successful deposition of such layers was accomplished by means of an innovative coating process, which involves the preparation of a hybrid polyvinyl alcohol/8YSZ membrane by dip-coating or spin-coating and subsequently burning out the polymer part at 500 °C. Results from He leak tests confirmed that the sintered layers posses a very low number of defects and with values in the range 10⁻⁴-10⁻⁶ (hPa dm³)/(s cm²) the gas-tightness of the thin film layers is satisfactory for fuel cell operation. Moreover, preliminary results have also indicated a potential reduction of the sintering temperature from 1400 °C to the range 1200-1300 °C, using the presented coating process.     

Imaging in evaluation of polymer coatings adhesion to glass at high humidity

Adhesion reduction occurring after polymer coated glass was immersed in water was studied in a variety of UV-cured urethane acrylate coatings containing alkyloxysilane adhesion promoting additives. It was observed that water accumulated under the coating surface in drops and formed ‘blisters’ in the glass-polymer interface. A non-destructive imaging technique was developed to measure the average size of the water blisters. The size of the water blisters within the interface was correlated with the wet adhesion force measured by coating resistance to 180° peel. The force of coating resistance to 180° peel off glass surface decreased non-linearly with the increase of the average size of the water blisters. It was concluded that the decrease in adhesion between the coating and glass was a result of stretching and breaking of the silane bridging bonds and polymer fibrils by water condensing on the glass surface within the polymer-glass interface. The mathematical model relating coating wet peel resistance force with the size of the debonding produced by water accumulation was presented.     

Effect of surface microstructure on the hydrophobicity of coatings

In this paper, coatings adopted SiO₂ nanoparticles ranging from 1 wt% to 7 wt% were in situ polymerized with low surface energy polymer, and different surface microstructures were built automatically during painting film. Copper microstructure surface was also achieved by chemical etching method and then was modified by low surface energy resin as contrast. The contact angle and the peel strength between the coating and bio-gooey simulacrum were studied. The results showed that the hydrophobicity of the coating was remarkably affected by the surface microstructure. The coating containing 5 wt% SiO₂ nanoparticles was covered with micro- and nano-scale salience and holes, and had the maximum contact angle and the minimum peel strength. Copper slices presented uniform micron and sub-micron structure surface when etching for 15 min and the contact angle reached a maximum of 125° after being modified.     

Synthesis and characterization of silicone-modified polyester as a clearcoat for automotive pre-coated metals

Four types of silicone-modified polyester resins were synthesized for cleanable characteristics with silicone intermediate, which has a long chain, to extend the polymer chains of the resins. These resins were formulated to make polyester/melamine heat-cured coatings to control the formability. The characteristics, viscoelastic behavior and flexibility of the resins were measured by DMA and tensile test. The contact angle measurement can be measured by the water repellence of the coating surface, which is a standard method to evaluate cleanable characteristics. The surface free energy was calculated by the contact angle measurement, and the surface analysis of each cured coating was evaluated using an XPS. Silicone-modified polyester coatings were coated on the cold rolled steel sheets to verify their formability, using a deep drawing test. Results showed that the storage modulus decreased, and the glass transition temperature shifted to a lower temperature with increasing contents of silicone intermediate. So, silicone intermediate provides lower stiffness and higher softness to polyester coating. To analyze the formability, we calculated F_U (the forming coefficient based on strain energy) and F_? (the forming coefficient based on strain). When F_U and F_? are both larger than 1, the polyester coatings have good formability. CSiPE-3 and CSiPE-5 had good formability. Also, CSiPE-5, which had the highest amount of silicone intermediate, had 93.5° of water contact angle, and had 26.5 mN/m of surface free energy and had 5.5 N/25 mm of the peel strength. So, it is implied that silicone intermediate can give a low surface energy and peel strength to polyester coatings. From those tests, the polyester/melamine coating of CSiPE-5 that had 0.5 mol of silicone intermediate had good formability and low peel strength, which are semi-removable characteristics. So, it would be an appropriate coating as a clearcoat for automotive pre-coated metals.     

Preparation and properties of PVDF-fabric composite membrane for membrane distillation

The flat sheet PVDF-fabric composite membrane used for membrane distillation was prepared by coating and wet phase inversion process. The composite membrane consisted of a PVDF porous membrane layer and a fabric layer. The thin polyester filament woven fabric with water-and-oil repellent finish was used as the support of composite membrane. The effects of fabric texture, PVDF concentration in casting solution and functional finishing of fabric on the preparation and properties of the composite membrane were investigated. The experimental results showed that fabric texture, PVDF concentration and functional finishing of fabric had great influence on the preparation and properties of the composite membrane. When the PVDF concentration in casting solution was 10-12% and the support fabric, with 435 warps/10 cm and 273 wefts/10 cm and the area weight of 79 g/m², was finished with 2 g/L water-and-oil repellent agent FK-501, the prepared composite membrane exhibited better performance in tensile strength, peeling strength and water vapor permeability, with mean pore size of 0.63 μm and overall porosity of 57.6%.