Time and cost effective methods for testing chemical resistance of aluminium metallic pigmented powder coatings

Polyester based powder coatings containing different types of aluminium metallic flake pigments have been investigated with respect to their chemical stability in acid environments. The metallic flakes are made chemically stable by covering them in silica. The degree of silica coverage and the silica morphology are far more important for the chemical stability of the pigments than the silica thickness. The acid resistance of the final powder coating is found to depend on the pigment embedment depth, on the chemical composition and morphology of the powder coating, and on the silica coating of the pigment. The latter being the single most important factor in our study.     

溶胶凝胶工艺制备超亲水耐污秽易清洁涂层的研究

采用溶胶凝胶工艺,与高纯硅溶胶复合制备了不同粒径匹配的超亲水涂层溶液,采用提拉工艺在玻璃基体上制备了超亲水涂层,分析了影响涂层厚度的因素,通过SEM分析了涂层的微观结构和膜层厚度及易清洁的机理,通过椭偏仪测试了涂层的厚度、孔径分布及气孔率、折射率等性能,通过户外自然积污实验测试了涂层的抗灰尘、易清洁性能,结果表明:涂层具有凹凸微纳多孔结构,涂层厚度在150～275 nm之间,气孔率3％～5％,气孔尺寸小于2 nm.通过控制溶胶组成与制备工艺参数,制备的涂层具有超亲水、耐污秽、易清洁性能.     

Microstructured conducting polymer coatings on plastic strip for contact electrodes: Formulation and tuning of sheet resistance

Mechanically strong and flexible strips of cellulose acetate were used to support a thin coating of poly(3,4 ethylenedioxythiophene) : poly(styrene sulfonic acid) PEDOT : PSS, an intrinsically conducting polymer (ICP), formulated with an aqueous dispersion of judiciously chosen copolymer of vinyl acetate and ethylene (VAE), to impart adhesion of the coating onto the substrate. Incorporation of a few drops of an organic acid to the formulation resulted in a substantial reduction of the sheet resistance of the coated surface. When the coated strips were post‐treated with a salt solution, a further fine tuning of the sheet resistance by a factor of 10 was achieved. The coated strips combine high conductivity with flexibility and mechanical strength. The performance of the coated strips has been evaluated in relationship to composition, coating thickness, and sheet resistance for application as contact electrodes. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 104: 234–237, 2007     

A probabilistic model for estimation of ionically permeable inhomogeneities in polymer coatings

The mechanism of ionic conduction through polymer coatings has been investigated. The presence of highly permeable areas in the coating (designated as D type areas), impose an electrochemical inhomogeneity which is identified by change in the ionic resistance as measured by DC method. The effect of coating thickness was studied on D type behaviour of coatings. A structural model is proposed to explain the changes in conduction mechanism by variation of coating thickness. Statistical models based on numerical (simulation-based) and analytical (probabilistic model) analysis of D type areas distribution have been advanced to estimate the number of D areas in any given coating based on the percentage of D type. Using these models the number of permeable (D type) areas can be estimated based on the D type percentage of the coating.     

Thickness-Dependent Mechanical Behaviour of Aluminium-Coated Polyethylene Terephthalate (PET) Films

Mechanical behaviour of aluminium-coated PET films has been investigated through Dynamic Mechanical Analyser. Aluminium is coated on PET substrate by vacuum thermal evaporation method. As thickness of aluminium coating increases from 150 nm to 350 nm, tensile strength decreases from 108.88 MPa to 99.25 MPa. This mechanical behaviour is correlated with microstructure and its evolution with the thickness of aluminium coating. Al-PET film consists of fine globular grains and average grain size increases monotonically with the film thickness. The relative contribution of the grain size to the strength of aluminium thin films is in good agreement with Hall-Patch equation.     

Atmospheric plasma sprayed coatings of nanostructured zirconia

Nanostructured zirconia coating has been fabricated by atmospheric plasma spraying. The microstructure of the coating has been characterized with SEM and XRD, and the microhardness has been measured. The results show ZrO₂ coating possessed two kinds of structure. One was the poorly consolidatedly structure, which was composed of nanosized particles. The other was an overlapping structure, which consisted of micrometer size particles. The former was the main structure in the coating. The zirconia coating had the same phase composition as the starting powder and the thickness of coating was quite heterogeneous. The as-sprayed nano zirconia coating had a similar microhardness to sintered ZrO₂, which was much higher than the conventional couterpart.     

Resistance of paint coatings to multiple solid particle impact: effect of coating thickness and substrate material

A novel technique has been developed to determine the resistance of paint coatings to multiple solid particle impact (i.e. solid particle erosion). The effect of paint layer thickness on erosion resistance was evaluated for two acrylic automotive topcoats. These coatings displayed a two-stage response to erosion. Initially, their thickness was reduced progressively, but once a critical thickness was reached the remaining coating was removed by individual impacts. A simple model is proposed to describe this behaviour. A new measure, specific erosion resistance, which takes account of the coating thickness, is defined to allow coatings with different thicknesses to be compared and has been applied to several industrially sprayed automotive clearcoats on both steel and polymer (TPO) substrates. The clearcoats exhibited significantly higher specific erosion resistance when applied to polymer substrates.     

Hydrodynamic analyses of blade coaters

Simple and complete analyses of Newtonian hydrodynamics in a blade coating system are presented in this paper. The coating behavior of the liquid after it has been pumped to the blade lip is studied. A moving web which is to be coated through a constant gap is partially wrapped over a coating roller under tension. In the simple analysis, the coated liquid film thickness is a function of coating gap, liquid surface tension, viscosity and density, and web speed. In the complete analysis, the film thickness is a function of 15 variables (10 geometric, 3 liquid and 2 operational). Three possible separation conditions at the exit are examined. The optimization of the coater for minimizing liquid film thickness to coating gap ratio is carried out for all 15 variables. Available experimental data are compared with the analyses.     

Characterization of epoxy coatings on steel by reflection/absorption fourier transform infrared spectroscopy. I. Effects of film thickness and angle of incidence

Films of amine-cured epoxy coating of varying thicknesses from 100 Å to 2.5 μm on steel have been studied by reflection/absorption Fourier transform infrared spectroscopy (FTIR-RA). The shape and frequency of several strongly absorbed bands of epoxy have been examined as a function of film thickness and angle of incidence. Compared to transmission spectra, reflection/absorption spectra of epoxy coating on steel show band shifts and distortions of the bands at 1510, 1247, and 1040 cm^?1. These effects are more pronounced at increased thickness and at grazing angles. For thin films ( < 100 nm), RA spectral intensity increases with increasing angle of incidence. For thicker films, the relationship is quite complex. The relationship between film thickness and FTIR-RA spectral peak height of an amine-cured epoxy coating on steel has also been established.     

An investigation of scratch testing of silicone elastomer coatings with a thickness gradient

Silicone elastomer coatings are currently being investigated as foul release coatings on ships hulls. Previous tests on silicone duplex elastomer coatings used a progressive load scratch test. It has been shown that the durability of uniform silicone duplex elastomer coatings is a function of thickness, indentation modulus, and stylus and that the failure mechanism depended on coating thickness and stylus. When applying silicone coatings to a ship's hull, there are regions on the ship where the coating is not uniform. This article investigates the effect of a thickness gradient on the durability of a single layer silicone elastomer coating. In these tests, a constant normal load was used as the stylus moved transversely to the surface. It was found that when the scratch test started in the silicone coating and proceeded in the direction of decreasing coating thickness (“Elastomer to Metal”), there was first a scratch tract followed by the initiation of detachment of the coating, then by gross detachment of the coating. When the scratch started on the exposed aluminum surface and proceeded into the silicone in the direction of increasing coating thickness (“Metal to Elastomer”), there was first gross detachment of the coating, followed by recovery (i.e., silicone coating is intact) and a scratch tract into the silicone. It was also found that the coefficient of friction was much higher in the silicone when the scratch test was going in the direction of decreasing coating thickness as opposed to the scratch test going in the opposite direction. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Thermal conductivity of intumescent coating char after accelerated aging

This paper presents the results of an experimental and numerical simulation study to obtain thermal conductivity of intumescent coating after accelerated aging. Two types of intumescent coating were used. The main objective of this research was to check the accuracy of a thermal conductivity model for the fully expanded intumescent coating char, which was assumed to depend on the expansion thickness and the bubble size and distribution. By using the model and the measured expanded thicknesses and average bubble diameters for the two types of intumescent coating after different cycles of accelerated aging, the intumescent coating insulated steel plate temperatures were numerically calculated and compared with measured results. The agreement has been found to be generally satisfactory, suggesting that the thermal conductivity model is acceptable. The measured results of intumescent coating expanded thickness and bubble size show that aging has two detrimental effects on the insulation performance of intumescent coating: reducing the expansion thickness and increasing the bubble size, both leading to increased thermal conductivity. Copyright © 2012 John Wiley & Sons, Ltd.     

双向脉冲电源在镀银中的应用

齿轮齿型面形状复杂,直流电镀银时各处电力线分布不均,造成镀层厚度不均匀,影响齿轮啮合。采用双向脉冲电源镀银,从镀层外观、厚度均匀性等方面进行比较,优选出最佳工艺参数。结果表明:镀层在外观和厚度均匀性上有较大的改善,镀层结合力、纯度及氢脆性均符合AMS 2412的要求。     

Leached Layer Formation on Float Glass Surfaces in the Presence of Acid Interleave Coatings

Acid interleave coatings are routinely used in the float glass industry to inhibit corrosion during transport and storage in hot, humid environments. It is well recognized that acid interleave coatings neutralize surface alkalinity, and thereby delay the onset of etching, dissolution, and permanent staining (so-called Stage II corrosion). However, the effect of acid interleave coatings on leached layer formation (so-called Stage I corrosion) has not been reported. For many applications of float glass, the presence of a shallow leached layer may be of little consequence, but in other applications, there can be nanoscale effects on scratch resistance, optical properties, adsorption, adhesion, and interface stability. In this study, complementary techniques of X-ray photoelectron spectroscopy (XPS) sputter depth profiling and infrared reflection spectroscopy were used to evaluate the thickness of leached layers in float glass samples weathered in a controlled manner, both with and without acid interleave coatings applied. The results reveal that acid interleave coatings do, in fact, enhance leaching during both cyclic and static weathering. This confirms that the acid not only neutralizes the alkaline reaction products of weathering but also reacts with the glass itself by ion exchange. The concentration of acid in the coating influences the thickness of the resultant leached layer, but this effect depends on the weathering conditions (cyclic versus static) and the duration of the exposure; boric acid and adipic acid coatings performed similarly. An excellent correlation was found between the more direct method of XPS depth profiling of the sodium leaching profile and the less direct, but perhaps more convenient, method of infrared reflection spectroscopy.     

Dip-coating of chemically patterned surfaces

For the purpose of solution-based manufacturing of organic electronic devices, we conducted dip-coating experiments on flat, chemically patterned surfaces. The patterns consisted of long wettable lines of varying width or triangles of different base lengths on an otherwise non-wettable surface. The thickness of the coated film has been measured as a function of pattern dimensions and coating speed. For lines of width comparable to the capillary length, i.e. several millimeters, which were oriented with the long axis parallel to the direction of withdrawal, qualitative agreement has been found with analytical results by Landau and Levich [1], Darhuber et al. [5] and Davis [6]. For narrower lines, quantitative agreement was found. Whereas the coating of long lines is essentially a steady-state process, the coating of compact shapes such as circles and squares is intrinsically time-dependent and involves capillary break-up effects. Nevertheless, for equilateral triangles oriented tip-down, the dependence of film thickness on coating speed and pattern dimensions was found to resemble the behavior of long lines.     

Surface modification of p-Si by a polyethylenimine coating: influence of the surface pre-treatment. Application to a potentiometric transducer as pH sensor

p-Si electrodes coated with linear polyethylenimine (L-PEI) allow the fabrication of a pH sensitive film for potentiometric transducers. The coating is realized in one step through the anodic oxidation of pure ethylenediamine (EDA) charged with 0.1 M LiCF₃SO₃ (Lithium Triflate). Such an electrochemical procedure leads to the thickness control of the coating. The best silicon surface pre-treatment before any coating is obtained with potassium dichromate in sulfuric acid, which leads to OH-terminated p-Si. This pre-treatment allows a uniform thin coating. In this work, the thickness is 2.6 nm. The pH response is high and close to 50 mV per pH unit.     

The effect of polymer additives on the performance of a two-roll coater

The effect of polymer additives on the performance of a two-roll coater has been examined experimentally. The coater consists of a rigid steel roll and a deformable roll with polyurethane surface. Newtonian coating solutions and solutions with polymer additives were used as test fluids. Both forward and reverse coating operations were studied. It was found that for the forward coating operation, the shear-thinning behavior of the polymer solutions can reduce the coating thickness, but the fluid elasticity can increase the coating thickness significantly and can also destabilize the coating flow. For the reverse coating operation, a small amount of polymer additives can effectively increase the wipe ratio.     

Simulation of the photopolymerization gradient inside a pigmented coating: Influence of TiO2 concentration on the gradient

The UV light behavior crossing a thick scattering and absorbing paint film has been modelled by a four-flux radiative transfer theory. For all that, the scattering characteristics of the coating as well as the calculation of the UV intensity decay through the coating thickness were measured versus TiO₂ pigment concentration. Thanks to these results, the conversion profiles in the coating thickness were obtained by numerical modeling and the influence of TiO₂ pigment concentration on these conversion profiles was discussed.     

Control of Interfacial Properties through Fiber Coatings: Monazite Coatings in Oxide–Oxide Composites

Fiber pushout tests were used to quantify the effects of fiber coating thickness on the mechanical properties of two model composite systems: a monazite-coated (LaPO₄-coated) alumina (Al₂O₃) fiber in an Al₂O₃ matrix and a LaPO₄-coated yttrium aluminum garnet (YAG) fiber in an Al₂O₃ matrix. Interface properties were quantified using the Liang and Hutchinson (LH) pushout model and mechanistically rationalized by considering the change in residual thermal stresses with changes in the coating thickness. Measures of the pure Mode II interfacial fracture energy, the coefficient of friction, and a radial clamping pressure are extracted by fitting the LH equations to the experimental results. Using the approach that has been developed herein, a methodology is available for measuring the interfacial properties, predicting the effect of coating thickness, and selecting the coating thickness to     

铝合金直流电阳极氧化膜电解着色的研究

以工业纯铝L2为实验材料,采用硫酸直流电阳极氧化-电解着色工艺在铝合金表面制备黑色膜层.着重分析着色电压对黑色膜层表观颜色、厚度、硬度的影响.通过SEM表征、EDS测试及性能测试表明:在优化后的电解着色工艺条件下可以获得与工业纯铝L2基体结合力良好,且耐蚀性、耐热性、吸光性均较好的黑色膜层.     

Finite Element Analysis of Thickness Dependent Debonding Forces of Elastomer Coatings

Adhesion tests consisting of cylindrical studs to be pulled off from a soft elastomer coating on a substrate have been widely performed in the literature to characterize various biofouling and adhesive situations. These experiments have shown that the pull-off forces are strongly dependent on the coating thickness. To understand this thickness dependence on the debonding forces, a detailed analysis is performed by the finite element method, applying the virtual crack closure technique. In these simulations, coating thickness, elastic modulus, and initial geometries have been varied to study their influence on the debonding forces. The effect of these factors on the debonding forces is discussed with respect to experimental pull-off results of silicone coatings.