Dry Paint Film Research Articles

Three-Dimensional Direct Numerical Simulation of Surface-Tension-Gradient Effects on the Leveling of an Evaporating Multicomponent Fluid

Mathematical and numerical modeling of drying coating layers is of interest to both industrial and academic communities. Compositional changes that occur during the drying process make the implementation of practical and efficient numerical models rather difficult. In this paper we present a three-dimensional mathematical and numerical model based on the lubrication approximation for the flow of drying paint films on horizontal substrates. The paint is modeled as a multicomponent liquid with one nonvolatile and one volatile component, termed the “resin” and the “solvent” respectively. Our model includes the effects of surface tension and gravitational forces as well as surface tension gradient effects which arise due to solvent evaporation. The dependence of viscosity, diffusivity, and evaporation rate on resin concentration is also incorporated in the model. A closed-form linearized solution has been found for coating layers that are of almost uniform thickness. The numerical solution agrees closely with the linear solution in the appropriate limit. A model simulation demonstrates the effect of surface tension gradients due to compositional changes in a three-dimensional flow field, and we suggest methods by which these gradients may be used to obtain a more uniform final coating layer.

Pigment/dispersant interactions in water-based coatings

By using non-ionic dispersants it is possible to produce titanium dioxide pigment suspensions that have full steric stabilisation. Water-based pigment dispersions thus stabilised can show greater resistance to flocculation in both the wet and dry phases. This can result in better stability and compatibility of paints as well as higher opacity in dry paint films.

Direct VOC analysis of water-based coatings by gas chromatography and solid-phase microextraction

Solvents in water-based coatings may be determined by sampling the coating head space using solid phase microextraction and gas chromatographing the extract. Several water-based coatings of known composition were analyzed by direct capillary gas chromatography and excellent agreement with theoretical VOC values was obtained. Fifty-two water-based architectural and industrial maintenance coatings were analyzed by a combination of SPME/GC and direct GC of solutions in methanol or dimethyl-formamide and the results compared with reported values. The SPME/GC method appears to be especially suitable for the analysis of low VOC content water-based coatings, for which EPA Method 24 often gives poor results. The identification and quantitation of exempt solvents may be performed easily with this method. Residual solvent in dried paint films may be determined by SPME/GC.

Étude expérimentale du séchage infrarouge et convectif de peintures automobiles modèle sur supports plastiques ou métalliques

This work aims to study car paint drying and to better understand the complex physico-chemical transformations which occur during this process. Two different model painting systems were studied: • - a water-based epoxy-amine paint applied on steel support; • - a solvent based polyurethane paint applied either on sheet molding compound support (SMC) or on steel support. In these two cases, drying is an important step and determines significantly the final paint film quality. Indeed, water is a solvent which is difficult to evaporate and SMC supports are plastic and porous materials which can induce the apparition of bubbles on the dry paint film. After the description of the two paint systems and of the near infrared and convective laboratory drier, we will sum up the different results obtained for different experimental conditions, in terms of drying kinetics and dry paint film quality. These experiments show the influence of the physical process parameters (air temperature and velocity), of the infrared flux density, of the paint system (film thickness, chemical properties...) and of the supports properties.

Effects of the loadings and type of copper powder on the electrical resistivity of copper powder-polymer paint films

Conductive behaviour in copper powder-filled paint films was subdivided into three regions, I, II, and III, with copper loading. Paint films were insulators in Region I. In Region II, resistivity decreased linearly in proportion to the cube root of the volume concentration, V, of the copper powders, reaching a minimum value at a certain V, which is the critical volume concentration, Vc, of copper powders. Vc, increased linearly in proportion to the bulk density of branched copper powders. This suggests that conductivity in the region is dependent upon the packing state of the copper particles. Vc, and resistivity at Vc, decreased with decrease in the grain size of isotropic branched and spherical copper powders, although they increased for flake copper powders. In Region III, resistivity increased with increase in copper loading. The increase in resistivity was due to the decrease in the apparent density of dry paint films.

Marine anticorrosion paints

Four paint compositions were prepared, two of them based on vinyl copolymer as a binder and the other contain boiled oil in presence or absence of soluble resin material. Boiled oil based paints meet the most anticorrosion action and film property. Also, the anticorrosion potential of the paints depend on the type of ingredients and their ratio in the dry paint films.

Grafting. IV. Graft tercopolymers as antifouling resin

AbstractA graft tercopolymer CLR‐g‐(MMA–TBTMA) based on chlorinated rubber as the backbone and binary copolymer of methyl methacrylate and tributyltin methacrylate as grafted chains has been synthesized. This graft copolymer has been used for the formulation of controlled‐release antifouling paints, and leaching rate behavior of toxin from such paints has been studied. The data have been compared with those obtained using controlled‐release antifouling paint based on linear chain copolymer of methyl methacrylate and tributyltin methacrylate. The paint based on grafted copolymer is characterized by having a lower leaching rate and reduced time for attainment of steady‐state leaching. Raft exposure studies indicate longer antifouling life compared to that of linear chain copolymer‐based paint both having the same dry paint film thickness.

Organic soot pigmented paint for solar panels: Formulation, optical properties and industrial application

Abstract Black paint was formulated from phenoxy resin and organic soot (5 μm) pigment (Degussa FW2). The paint is suitable for industrial application on chromated aluminium foil with thickness up to 0·5 μm (coil coating process). Thickness of a dry paint film is 4·5 μm and makes the paint/aluminium tandem spectrally selective with solar absorbance ( α s = 0·92) and thermal emittance ( e T ) = 0·52 Dispersion properties of the paint were enhanced due to addition of aerosol particles (Degussa 380) into the paint. Excellent weather stability, chemical resistance and mechanical properties of the paint were achieved. Benefits of the technical process of application using coil coating technique is discussed.

Quantitative Analysis of Platelike Pigments by X-Ray Diffraction

X-ray diffraction has been shown to provide an accurate qualitative and quantitative determination of the pigment composition of paint films. This analysis, however, is frequently complicated by the presence of pigments with plate-like crystallites which show a marked tendency to orient in preferred directions in drying paint films. The variability in the degree of orientation causes line intensity variations not attributable to pigment concentration.A technique based on a summation of the intensities of many lines has been used to correct for the effects of preferred orientation in the analysis of retained austenite in certain steels. This method is shown to be applicable to the quantitative analysis of mica in paint films.

Instrumentation and painting quality control

Any suggestion that the use of instruments in the inspection of painting and its allied operation of surface preparation is a substitute for the visual and critical inspection carried out by an inspector experienced in the work involved would be a serious disservice to the quality control of painting. Broadly speaking, the experienced inspector knows the problems associated with achieving a predetermined result, he knows how the operator may react to problems of access and other difficulties and is familiar with the short cuts that are sometimes taken. He can, by concentrating his attention on these higher risk areas, do much to prevent bad work and to eliminate the premature breakdown which too frequently mars the finished job. As each successive operation will tend to obscure any faults in the work already done, it is only when the inspector is at hand to see the work actually in progress, and at the completion of each stage, that a sufficiently high degree of security is achieved. This said, it must be added that it is only in conjunction with the use of instruments that the quality of the work can be correctly assessed. In fact the case for the introduction of instrumentation into painting quality control is particularly strong. But great care is required in the interpretation of individual measurements. Many of the tests for physical properties of the dry paint film are empirical, and need to be carried out under controlled conditions if reproducible results are to be obtained.

Collaborative Study of the Determination of Lead in Alkyd and Latex Paints

Abstract A collaborative study was conducted on the determination of lead in alkyd and latex paints by atomic absorption spectrophotometry after nitric acid digestion. Fourteen samples of blank paints and paints with known additions of lead were analyzed by 10 collaborators. Coefficients of variation from 4 to 16% were obtained for 0.33 to 0.02% lead in the paint solids. The statistical analysis indicates minimal bias and adequate precision for the analysis of lead in paints at the current regulatory limit (0.5% in the paint solids or dry paint film). The method has been adopted as official first action.

On convection cells induced by surface tension

A mechanism is proposed by which cellular convective motion of the type observed by H. Bénard, which hitherto has been attributed to the action of buoyancy forces, can also be induced by surface tension forces. Thus when a thin layer of fluid is heated from below, the temperature gradient is such that small variations in the surface temperature lead to surface tractions which cause the fluid to flow and thereby tend to maintain the original temperature variations. A small disturbance analysis, analogous to that carried out by Rayleigh and others for unstable density gradients, leads to a dimensionless number B which expresses the ratio of surface tension to viscous forces, and which must attain a certain minimum critical value for instability to occur. The results obtained are then applied to the original cells described by Bénard, and to the case of drying paint films. It is concluded that surface tension forces are responsible for cellular motion in many such cases where the criteria given in terms of buoyancy forces would not allow of instability.

A Study of Vapors from Drying Paint Films.

A Study of Vapors from Drying Paint Films.