Effect of particle size distribution on stress development and microstructure of particulate coatings

The role of pigment particle size distribution on stress and microstructure development was studied for coatings prepared from aqueous suspensions of ground calcium carbonate (GCC) and latex binder. Stress development was monitored using a modified beam deflection technique under controlled environment. Microstructure was characterized by scanning electron microscopy (SEM) and cryogenic SEM. For coatings containing only GCC particles and no latex, a wide particle size distribution resulted in a significant particle size gradient in the cross-sectional microstructure and irregular stress development. With latex addition, uniform microstructures were observed in coatings with either wide or narrow GCC particle size distribution. GCC/latex coatings prepared using GCC with a wide particle size distribution developed a higher stress than those prepared using GCC with a similar average particle size but a narrow particle size distribution. The higher stress is related to the particle packing that results in smaller pore sizes and larger capillary pressures that drive compaction. In coatings prepared with the same GCC particles but different latex binders, the stress and cracking behavior of the coating depends on the latex properties.     

Correlation of hardness with MFFT and CPVC of latex/ceramic coatings

Hardness, porosity, and microstructure of film-forming in polyvinyl acetate/alumina coatings from aqueous suspensions were investigated with a minimum film formation temperature (MFFT) bar, Vickers hardness tester, and scanning electron microscopy (SEM). The hardness of opaque composite coatings (alumina:latex=1:2 by volume) increased abruptly at the MFFT of the latex, suggesting that the alumina particles did not change the latex film formation behavior and that the hardness measurement is an alterative to the optical criterion. Studies of coatings from latex particles that were smaller or larger than a common size of ceramic particles indicated that the composition of maximum hardness, called critical Vickers hardness concentration (CVHC), matched conventional critical pigment volume concentration (CPVC). More efficient polymer binding in the coatings from the smaller latex gave them higher peak hardness and CPVC. Department of Chemical Engineering & Materials Science, 421 Washington Ave., SE, Minneapolis, MN 55455-0132.     

Sintering of latex particles in pigmented coatings. II. Influence of the latex particle size

The light-scattering coefficient S of coatings formulated from a mixture of an inorganic pigment and polystyrene latex particles may be enhanced significantly when the dry coating is heated in order to cause sintering of the polystyrene spheres. The relative increase in S depends on the size and the amount of the latex particles and the type of the inorganic pigment. Of the latexes examined (0.5, 0.2, 0.1, and 0.03 μm in diameter) the 0.2μm latex is the most effective in blends with platelike delaminated clay. The coatings based on spherelike precipitated calcium carbonate are less responsive to the heat treatment. The gloss of the clay–latex coatings is not significantly altered by the heat treatment up to 20 pph of latex; the gloss of the calcium carbonate coatings generally decreases upon heating.     

Assessment of Novel Water-Borne Coatings Obtained from Composite Latex Particles and Reinforced with TiO2 Nanotubes

Novel, environmentally friendly waterborne coatings were obtained from the filmification of nanostructured latex particles reinforced with inorganic nanotubes. The latex used to form the coatings consists of core-shell particles with a shell functionalized with different amounts of acrylic acid (AA). This external polymer layer was doped, in some cases, with TiO₂ nanotubes at three different concentrations: 100, 500 and 1000 ppm. The composite particles were synthesized in two steps by semi-continuous emulsion polymerization at 75°C. A series of films was prepared by employing core-shell particles with different sizes, core cross-linking and shell functionalization. The coatings obtained were characterized by infrared spectroscopy (FTIR), tapping mode atomic force microscopy (TM-AFM), scanning electron microscopy (SEM), differential scanning calorimetry (DSC) and thermogravimetrical analysis (TGA). Drying rates and tests were also performed to further evaluate these films. It was observed that the addition of small amounts of TiO₂ nanotubes contributes to improve the application properties, mainly adhesion to metallic substrates and water impermeability. The resistance to thermal degradation was also strongly increased, as showed by the DSC and TGA analyses.     

Preparation of encapsulated aluminum pigments by emulsion polymerization and their characterization

An emulsion polymerization-like process for the encapsulation of commercial aluminum pigments with polymer is discussed. A possible application target is the improvement of the performance of aluminum pigment in waterborne coatings. The effect of the treatment on the stability of the aluminum pigments in the presence of alkaline water was examined. Analytical investigations with SEM, TEM, STEM-EDX, XPS, and TOC were performed and revealed a kind of coagulation mechanism of polymer particles on the pigment surface. D-63784 Obernburg, Germany.     

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.     

Latex particle size and CPVC

Monodisperse vinyl acetate/butyl acrylate (85/15) latexes were prepared with particle sizes between 200 and 1200 nm. These were used in a simple paint formulation with TiO₂ as the only pigment. Two optical methods were used for determination of the critical pigment volume concentration (CPVC) of these paints. These are specular gloss at an incidence angle of 85 ° and CIE Z (lightness) values of a blue tinted formulation. Both methods gave coincident results for the CPVC as a function of latex particle size. Our data fit the expression X = 1.44Y^2.65 where X = number of latex particles/number of pigment particles, at CPVC and Y = diameter of pigment particles/diameter of latex particles. Earlier, Bowell reported the same exponential relation, with a different pre-exponential factor, for acrylic latexes. The common exponent is explained with a model in which the latex and pigment particles assume a condition close to minimum porosity during packing. CPVC reflects the packing of particles during the initial stages of dryness of the latex. The ‘universal’ relation reported here permits facile prediction of the effects of latex particle size on the CPVC and binding capacity in water-based paints.     

Polymerization of MMA at the surface of inorganic submicron particles

Inorganic submicron particles, such as TiO₂, were modified with titanate coupling agents. The structure and stability of some titanates, both in solution and at the particle surface, were investigated by various methods. The modified titanium dioxide was dispersed in a solution of sodium dodecylsulphate (SDS) in water. The surfactant adsorbs at the now hydrophobic particle surface, thus creating a micellelike structure with an inorganic particle in the centre. In this system an emulsion polymerization of methyl methacrylate was carried out. Product formed at the particle surface is either physically bound by entanglement or chemically bound by covalent bonding to the titanates. In this way a core-shell morphology is obtained with an inorganic core and a polymer shell. The effects of several reaction parameters on the kinetics of the polymerization were studied. The encapsulated TiO₂ particles may offer interesting prospects in those applications where good coupling between polymer matrix and inorganic particles is necessary, such as latex paints and polymer composite materials.     

The influence of substrate absorbency on coating surface chemistry

The composition of the top surface of a coating layer can influence its functional properties or subsequent processing steps. The effect of the substrate absorbency on the coating surface chemistry is reported. Different coating systems containing a kaolin clay pigment, fine or coarse precipitated calcium carbonates, and a common latex binder were examined. The influence of a soluble polymer added into the coating was characterized. The surface chemistry was measured with attenuated total internal reflectance (ATR) and X-ray photoelectron spectroscopy (XPS).

Absorbent substrates generate bulky coatings with high voids and low gloss. Rapid dewatering by the absorbent substrate pulls the small particles, like latex binder, away from the top layers causing a low latex concentration at the surface. On non-absorbent substrates, the addition of the soluble polymer generates coating layers with higher void volume, lower gloss, and lower latex concentrations at the coating surface. However, on absorbent substrates, polymer addition causes coatings with lower void volumes and higher gloss. In this case, the rapid dewatering and mobility of particles is reduced by the polymer, which helps to retain the small particles at the surface. As a result, latex concentration at the surface increases with polymer addition on absorbent substrates.     

Fate of a coalescing aid after latex paint application

Water-based coatings require coalescing aids to achieve properties equivalent to solvent-borne paints. A common coalescing aid in latex paints is 2,2,4-trimethyl-1,3-pentanediol monoisobutyrate (TMPD-MIB). The relatively large quantity of TMPD-MIB used in latex paints has raised concerns regarding its emissions to both indoor and outdoor atmospheres. In this study, a one-dimensional dual (paint and material) layer diffusion model was developed to estimate emissions of TMPD-MIB from two latex paints applied to gypsum board. The paints contained different pigment volume concentrations (PVC) and different amounts of TMPD-MIB. Different modeling approaches were used depending on the PVC of the paint. The proposed model for paint drying and TMPD-MIB emissions was tested with data from previous chamber experiments. Experimental data were first used for purposes of parameter estimation, and the model was then compared against an independent experimental dataset. The diffusion coefficient of the paint layer was adjusted as a function of the water content remaining in the wet paint film. The effective diffusion coefficient of TMPD-MIB in the paint layer was found to be dependent on the PVC and water content of the paint.     

DSC evaluation of binder content in latex paints

The estimate by differential scanning calorimetry of the enthalpy of thermal decomposition of the organic fraction in a complex material can be used, in proper conditions, for evaluating the concentration of the organic components. The application of this technique of thermal analysis to latex paints aimed at identification of binder content is discussed in this paper. On the one hand it gives good results on binder content estimate; on the other hand it highlights some aspects of the thermal decomposition of polymers enclosed in an inorganic matrix. The phenomena of thermal decomposition are studied for the main components of latex paints, i.e. for polymers, and for complete paint formulations. The materials considered include widely used binders for the manufacture of latex paints such as vinyl acetate/Versatate copolymers and styrene/acrylic copolymers, rheology modifiers such as cellulose ethers and other standard components of latex paints. Formulations representing typical latex paints with different binder content and simplified polymer/filler systems are considered. Although decomposition paths are very different for different polymers and for the same polymer in different concentrations, the overall heat output is consistent and proportional to the amount of polymer in the sample. Therefore identification by DSC measurements of the binder content in a latex paint appears as a feasible technique.     

Drying and collapse of hollow latex

Hollow latex particles are used as white pigments for paints and paper coatings. In the coating dispersion, each hollow particle is filled with water. As the coating dries, water vacates the latex, leaving an air-filled void sized to scatter light (~0.5 μm) within each particle. Examinations of dried coatings reveal that hollow particles can collapse, decreasing their light scattering efficiency. Cryogenic scanning electron microscopy (cryoSEM) was used to characterize the microstructure of coatings containing hollow latex during drying. Images suggest latex voids empty after air invades into the coating interstitial space and collapse occurs late in the drying process. The effects of temperature (10–60°C), humidity (20–80%), and binder concentration (0–30 wt%) on particle collapse were also studied through SEM of dried coating surfaces. High drying temperature, high humidity, and low binder concentrations promoted collapse. For hollow latex particles with porous shell walls, temperature and humidity had little effect, whereas binder increased collapse. From these results, a theoretical model is proposed. During drying, diffusion of water from the particle creates a vacuum inside the latex. The vacuum is either relieved by nucleation of a gas bubble from the dissolved air in the water-filled particle or it causes the particle to collapse by buckling.     

Study of epoxy and alkyd coatings modified with emeraldine base form of polyaniline

In this work we examine the ability of the emeraldine base form of polyaniline to impart protection against corrosion when it is used as additive of commercial paints. For this purpose, three paints, which are used as primers in marine environments, were checked: two epoxy coatings that differ in the presence or absence of inorganic anticorrosive pigment (zinc) and one alkyd coating. In a first stage, the rheological, structural, thermal and mechanical properties of the three coatings were characterized using viscosity measurements, infrared spectroscopy, thermogravimetric analyses and stress–strain assays, respectively. Furthermore, we observed that the resulting properties were not altered by the addition of a low concentration of polyaniline (0.3%, w/w). Accelerated corrosion tests were performed to compare the degree of protection of both the modified and unmodified paints. The polyaniline did not affect to the protective properties of the epoxy without inorganic anticorrosive pigment nor the alkyd formulations. In opposition, the polyaniline added to the epoxy paint with inorganic anticorrosive pigment induced the formation of a zinc oxide layer, which promoted the corrosion attack.     

耐沾污外墙涂料的研制

利用可反应性大分子乳化剂、功能单体制备了具有良好稳定性的核壳苯丙乳液 ,并通过选择合适的涂料颜料体积浓度 (PVC)制备了有良好柔韧性、低成本和优良耐沾污性能的外墙涂料     

Long-term hydrophobicity and ice adhesion strength of latex paints containing silicone oil microcapsules

Waterborne anti-icing coatings were prepared by embedding silicone oil microcapsules in latex paints. The long-term hydrophobicity and ice adhesion strength of the coatings were examined with a QUV accelerated weathering tester and a pull-off adhesion tester. The effects of silicone oil content and pigment/binder (PB) ratio on the long-term hydrophobicity and the ice adhesion strength of the coatings were investigated. A higher silicone oil content and a PB ratio close to the critical pigment volume concentration favor long-term hydrophobicity of the coatings. An obvious decrease in ice adhesion strength was achieved for coatings with a PB ratio of 5.0 and a silicone oil content of 4.2%. For coatings with the same surface roughness, a higher water contact angle (WCA) led to lower ice adhesion strength. However, for coatings with different surface roughnesses, the ice adhesion strength was found to be dependent on surface roughness rather than on WCA.     

Structured latex particles with improved mechanical properties

Structured polymer latex particles are prepared by a swelling emulsion polymerization process, in which the initial particles are first swollen by ethylenically unsaturated monomers and the polymerization of the latter is then carried out. This special polymerization process leads to multi-phase particle morphology. Instead of a thermodynamically more favorable large-scale phase-separation, we obtain multiple, near-spherical domains dispersed within the particles. TEM analysis after selective staining reveals the size and distribution of the microdomains. Dynamic mechanical analysis of the polymer films confirms the absence of a distinct, large second phase and indicates that such microdomains interfere at the molecular level with the segmental mobility of the dispersing phase. We present examples of soft polymers as the continuous phase and hard polymers as the dispersed phase. The inclusion of hard microdomains into soft continuous phase increases dramatically both the films tensile strength and elongation, which means improved cohesive strength of the polymer material. The increase in tensile strength of the polymer film correlates directly with the hardness of the dispersed phase. Improvement in tensile strength and elongation is important in a number of industrial applications of polymers, such as flexible coatings, coalescent-free paints and pressure sensitive adhesives (PSAs). Examples are presented which demonstrate the potential applications of the swelling emulsion polymerization process.     

Structure of polymer within the coating: an atomic force microscopy and small angle neutrons scattering study

Synthetic latex is widely used as a binder in waterbased paints. Upon dehydration of the dispersion, latex particles are brought into contact with mineral pigments: this process results in coating structuration and consolidation. This composite layer is described as a porous mineral structure, whose pores are covered by latex particles. Therefore, it is of fundamental interest to study the ordering of binder particles in the coating, and the wetting of pigments by polymer particles, toward understanding properties of coating such as: optical properties, adhesion, cohesion, sensitivity to water, etc. In this regard, we have used small angle neutron scattering and atomic force microscopy to study the ordering, the spreading, and the adhesion of latex particles on calcium carbonate within the coating. We discuss the structure of the coating.     

Fluorinated additives for stain-resistant matt latex paints

Latex paints are often preferred over solvent-based paints due to their good gloss and color retention, ease of handling, and lower volatile organic contents. However, matt latex paints tend to show poor stain resistance since they develop highly porous and rough surfaces. In recent years, matt latex paints have been improved in their stain resistance with resulting better cleanability, by adding hydrocarbon acrylic polymers and fluorine-containing compounds. In this work, we prepared fluorinated acrylic emulsions of the copolymer of butyl acrylate (BA) and perfluorobutylethylene (PFBE), which were introduced in latex paint compositions. The properties of the modified paints were evaluated by performing stain resistance tests with several domestic products. It was observed that they had good stain release properties, thus conferring good properties to the final painting system. They contain the self-cleaning behavior typical of fluorinated coatings, which have been proven by the decrease of their surface energies. Since the cleaning procedures of a matt paint film can also impart some gloss increase, the wet and dry burnishes were also evaluated. The results have shown improvements in stain resistance and cleanability of the modified matt latex paints with the maintenance of their stability and the coatings gloss as required.     

Properties of calcined kaolins in anticorrosion paints depending on PVC,chemical composition and shape of particles

The properties of calcined kaolins in paints were identified in relation to their pigment volume concentration (PVC). The study involved three kinds of kaolin exhibiting different development of the lamellar structure of primary particles as well as different distribution of particle size. Kaolins also displayed varying contents of a glassy phase – mullite and quartz. Prepared model paints were formulated with the increasing content of kaolins, with PVC ranging from 5 to 40% up to a maximum critical pigment concentration (CPVC), i.e. up to a point where PVC = CPVC. The properties of paints were tested by means of laboratory corrosion tests in the environments of neutral salt mist and of condensed humidity. It was the aim of the study to identify the effect of kaolin's PVC on the mechanical and corrosion resistance of coatings based on water-borne epoxy resin.     

建筑涂料领域中影响电脑配色准确性的因素

电脑配色在涂料行业是一门新兴技术,颜色配方的准确性一直是配色师关注的问题。从色浆数据库的建立、基漆数据库的建立、颜色配方的设计、色浆与基漆的匹配、色浆/基漆批次稳定性等方面来阐述影响电脑配色精度的因素。