Waterborne Paints Research Articles

Complete corrosion inhibition of lamellar zinc pigment in aqueous alkaline media

Lamellar zinc pigment reacts in aqueous alkaline media (e.g., water-borne paints) with the evolution of hydrogen. This corrosion reaction can be inhibited by 2-nitrophenol (2-NP), 2,4-dinitrophenol (2,4-DNP), 2-hydroxy-3,5-dinitro-benzoic acid (HDNBA) and 2-hydroxy-3-nitro-benzoic acid (2-H-3-NBA) which all have a nitro-group ortho to a hydroxy-group; this structural part of the inhibitors can be considered as a potential chelating group which may explain the corrosion inhibiting effect. As a rule, with triethylamine (TEA) as neutralizing agent corrosion inhibition is slightly better when compared to dimethylethanolamine (DMEA). With TEA there is complete corrosion inhibition with addition of 2,4-DNP at pH 8 and 10; with 2-H-3-NBA there is complete inhibition at pH 10.

Carboxymethylcellulose acetate butyrate in water-based automotive paints

Water-dispersible carboxymethylcellulose acetate butyrate (CMCAB) has been shown to improve flow and levelling, and reduce cratering, picture framing, and other defects in water-borne paints.

New generation decorative paint technology

The growth of waterborne paints in the higher performance decorative paint segments (like in high gloss paints, trim paints and also in stains and varnishes) has been slowed down due to a lack of open time, rheology, film build and scratch resistance. Over the years the improvement of the open time has been an intense area of research, but to date the typical paint rheology and brushing performance of a solvent based paint could not be achieved in a waterborne system. In this paper very low viscosity oligomers are presented as a solution for the open time problem. These oligomers remain liquid even after the evaporation of water and are self-crosslinking to achieve good final properties. The oligomers are combined with a dispersed polymer to reduce tack free times of the resulting coatings and to increase the rate of development of the properties. A model system is described where this effect is demonstrated.

Effects on the pigment distribution in paint formulations

Modern water-borne paints are applied in different areas ranging from high-gloss lacquers to flat, scrub-resistant interior paints. The pigment volume concentration (PVC) is one key-parameter adjusting the application properties. In this work formulations differing in the type of binder and dispersing agent were investigated by various techniques concerning the distribution of pigments in the liquid paints and films. The structure of the paints was analyzed by Remission Light Spectroscopy (RLS), Disc Centrifugation, Cryo-Replica Transmission Electron Microscopy (Cryo-TEM) and Cryo-Scanning Electron Microscopy (Cryo-SEM). The pigment distribution in the films was examined by means of Atomic Force Microscopy (AFM), TEM and RLS. The tendency of the pigments to form aggregates was found to depend on both: the type of binder and the dispersing agent. Only by adjusting the properties of the binder in combination with common dispersants it is possible to get well distributed TiO 2 particles within the paint. Correlation of application properties e.g. gloss and blocking to the microscopic structure is presented.

Powder and waterborne coatings 2000–2010 – is past growth sustainable? New technological developments and the impact on future markets a world overview

Globally, the penetration of POWDER COATINGS in the Industrial Paints sector is 6%. The deepest penetration is in Europe with just over 9%, of which Italy leads, also worldwide, with the highest degree, 15%. Follow Asia-Pacific, North America. In ten years time, global penetration of powder coatings will reach the 10% level. Penetration of powder coatings is much different in the individual European countries. By the year 2010, penetration of WATERBORNE industrial coatings will reach a level of over 30%. The European Waterborne Industrial Coatings Industry was over 500,000 Tonnes in 1999 and will reach the one million Tonnes mark by the year 2010. Overall, the penetration of Waterborne Coatings in the Industrial Paints sector is currently around 20%. When considering individual market segments, penetration varies from 3% to 70%. Selected industrial coatings sectors, having low penetration of 3% in 2000, will reach up to 15% by the year 2010 at the expense of solvent borne paints and other non-environmentally-friendly systems. Main resin systems include: acrylics, epoxies, alkyds/polyesters, polyurethanes, PUDs, 2K-PU, alkyd emulsions and other. The paper will also cover an in-depth analysis of the inter-competition between solvent borne coatings, waterborne, powder coatings, radiation cureables. The increasing use of a combination of environment-friendly technologies such as powders / WB: powders/radcure (UV, EBC) and WB/radcure will be considered. Chemical intermediates and additive manufacturers have been developing novel raw materials both for waterborne paints and powder coatings.

Organic Thickeners for Water-Borne Paints

Thickeners are used in paint systems to achieve particular rheological properties such as shear-rate dependent behavior, to control the viscosity at low and high shear rates, sag resistance and application viscosity. This contribution addresses the use and application of thickeners in water-borne paints.Examples of successfully used types of thickeners are the cellulose and PUR-thickeners. Specific compositions, features and benefits of both types are explained in detail.

2K waterborne clearcoat—a competition between crosslinking and side reactions

The combination of OH-functional polymers with di- or trifunctional polyisocyanates is widely used as crosslinking chemistry in high-performance two component clearcoats. This curing chemistry had always been limited by strong side reactions. Thus use of solvents in formulation was limited to non-OH-/NH-functional components. Some years ago Bayer came up with the strange idea to formulate 2K isocyanate waterborne paints. They carried out a lot of investigations to establish the proportion of crosslinking and side reactions. Nevertheless the formulation of two-component waterborne PUR paint remains a highly sophisticated task. This presentation shows the basic evaluation carried out and communicated by Bayer [Aqueous two-component polyurethane systems for coatings, in: Proceedings of the IUPAC Symposium, Warsaw, July 2000; Aqueous 2-Pack Polyurethane Coatings for Automotive Refinish and Transportation, Bayer Publication; Prog. Org. Coat. 40 (2000) 99] and additional experiences we have gathered in DuPont Performance Coatings [DE 19 607 672, EP 654 051, EP 654 053, EP 654 055, EP 358 979, EP 542 105, EP 578 940, EP 669 352, EP 751 179, EP 469 389, EP 456 210, etc.]. The focus of DuPont experiments is on a high-performance waterborne clearcoat system for car refinish. Especially, the demands of refinish customers have led us to focus on miscibility, sprayability and pot life issues. Kinetic as well as thermodynamic effects are discussed. Finally, a formulation is described which fulfils most of our customer needs.

PREPARATION AND CHARACTERIZATION OF SOME ACRYLIC ACID CHELATING COPOLYMERS BY EMULSION TECHNIQUE

ABSTRACT Binary chelating copolymers were prepared by emulsion copolymerization of acrylic acid (AA) with butyl acrylate (BuA), butylmethacrylate (BuMA) and styrene (St) using potassium persulphate/sodium meta bisulphite as a redox initiation system and sodium dodecylbenzene sulfonate as an emulsifier. It was found that the rate of copolymerization was decreased with increasing AA content. Based on the copolymerization data of (BuA/AA), (BuMA/AA) and (St/AA) in emulsion polymerization process, the reactivity ratios of the systems were calculated and discussed. The structures of the designed chelating copolymers were characterized and investigated via spectrophotometric measurements and thermal analysis. Some of the best stable copolymeric emulsions having enhanced physico-mechanical properties were introduced in water-borne paint formulations. The prepared chelating copolymers showed semiconducting properties at room temperature.

Synthesis and some properties of functionalized film-forming latexes

Semi-continuous emulsion copolymerization was used for preparation different colloid copolymers containig hydroxyl, carboxyl and amide functional groups. Copolymerization of hydroxyethyl methacrylate with styrene and butyl acrylate was investigated. Molecular weight increase in the copolymerization of methacrylamide indicated an extensive branching of macromolecules. Functionalized latexes have been used as binders in water borne paints. In addition to the crosslinking ability the hydrophilic functional monomers positively affect the film formation. The effect of dissociated carboxylic groups on lowering the minimum film forming temperature was much more pronounced if the polymer chains were more polar and softer. Some relationships between the latex flow properties and the film forming ability have been illustrated in this paper.

Current state of the theory of metal corrosion inhibition

The general regularities of the action of metal corrosion inhibitors are analyzed. It is noted that the creation of inhibitors is a big scientific problem, requiring that achievements of many fields of physical chemistry be used. The limitations involved in application of adsorption inhibitors, whose theory of action has been developed most thoroughly, are considered. The importance and theoretical aspects of the development of composite materials and inhibiting hydrophilic monomers, that undergo polymerization following adsorption on metal surface, are discussed. The search for ways to manage the polymerization of inhibitors in thin adsorption layers can become a new efficient direction of corrosion inhibition. Special cases of inhibition, which cannot be rationalized in terms of the adsorption theory and which require that complexation be taken into account, are discussed. As the theory of corrosion inhibition develops, the scope of inhibitors expands. Besides the combination of cathodic protection with corrosion inhibitors, the latter are used more and more widely in conversion coatings and in water-borne paints. The strict technological and environmental requirements that are applied to inhibitors in this case do not prevent the progress of this scientific direction and do not diminish its prospects.

Corrosion inhibition of aluminium and zinc pigments by saccharides

Both aluminium and zinc pigments react in aqueous alkaline media (e.g., water-borne paints) with the evolution of hydrogen which can be measured gas volumetrically. The hydrogen corrosion of aluminium pigment can be inhibited with addition of the reducing saccharides fructose and mannose as well as with addition of the reducing ascorbic acid whereas the non-reducing saccharose did not inhibit this corrosion reaction. With increasing addition of fructose or ascorbic acid the hydrogen volumes evolved increase; this observation leads to the assumption that reaction products of aluminium and fructose or ascorbic are the actual corrosion inhibitors. The hydrogen corrosion of zinc pigment is inhibited by ascorbic acid only. So, the most efficient of the examined natural corrosion inhibitors both for aluminium and zinc pigment is ascorbic acid. But corrosion inhibition of ascorbic acid on zinc pigment is much less effective when compared to aluminium.

Alternative environmentally friendly coatings for mild steel and electrogalvanized steel to be exposed to atmospheres

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Zinc pigments and waterborne paint resins

Zinc pigments corrode in aqueous alkaline paint media (e.g., waterborne anticorrosive paints) with the evolution of hydrogen. Paint resins inhibit this corrosion reaction at a pH value of 8 more effectively than at pH10. An increase of resin addition effects a decrease of hydrogen evolution (i.e., corrosion inhibition increases). The corrosion reaction of spherical zinc dust can be nearly completely inhibited with the addition of a certain epoxy ester resin (EPE 1). The epoxy ester resin looses its corrosion inhibiting properties after film formation, because of loosing its mobility, which seems to a be requirement for corrosion inhibition. So, zinc dust is inhibited in the liquid waterborne paint but still shows its sacrificial action in the solid primer coating.

Effect of dispersion agent on the degradation of a water borne paint on steel studied by scanning acoustic microscopy and impedance

Scanning acoustic microscopy (SAM) was used as a complementary method to electrochemical impedance spectroscopy to characterize delamination processes at a water borne epoxy coating/steel interface. The nature of the dispersing agent incorporated in the water borne epoxy coating was found to have a strong influence on the coating performance. SAM results supported the impedance data, the same ranking of the specimens being obtained. SAM observations also gave complementary information on the initiation sites of the delamination, on the morphology of the blisters and qualitatively on their growth rate.

Test methods for a reliable assessment of water-borne paints for exterior wood protection

Water-borne paint systems, which are applied in a relatively wet season, may cause an accumulation of water in the wooden substrate. This is exacerbated by an increase in moisture-barrier properties due to the leaching of water-soluble components, and is further promoted by the increasing barrier properties under relatively dry external conditions. Recent tests with four commercially available paint systems show an increase in μ-value with a factor 2.4 to 3.8, after a leaching period of only two weeks. Existing test methods and standards do not take sufficient consideration of the effects of leaching on the moisture barrier properties. The reliable assessment of the quality of water-borne paint systems for exterior wood protection needs new or modified test methods and standards. Mathematical models have to be developed to translate laboratory test results in to different practical conditions, climates and timber dimensions.

Comparative study between galvanised steel and three duplex systems submitted to a weathering cyclic test

Two types of samples, uncoated galvanised steel (UGS) and galvanised steel coated with chlorinated rubber paint (DS1), alkyd paint (DS2) and water-borne acrylic paint (DS3) were tested in a weathering cyclic chamber. The behaviour evolution of these systems was tracked using electrochemical impedance spectroscopy. For the duplex system, regardless of the type of paint, high impedance values were obtained, even at long exposure time. The UGS samples exhibited lower impedance values. Such behaviours could be interpreted in terms of different nature of the corrosion products generated on zinc surface. Using scanning electron microscopy, energy dispersive X-ray and X-ray diffraction techniques the identification of those compounds was possible. The main corrosion product generated on UGS was hydrozincite, Zn 5(CO 3) 2(OH) 6, in the case of the duplex systems, the corrosion product formed was zincite, ZnO. Such difference suggests that the zinc oxide formed under the coating is the responsible of the better duplex system behaviour and so, it leads a better passivation of zinc surface than the obtained with hydrozincite, which is the main corrosion product formed on UGS. In that sense, the coating acts as a selective membrane, avoiding the CO 2 uptake and so, hydrozincite formation is inhibited. This behaviour was observed even for coatings with poor barrier properties, such as water-borne acrylic one.

Effect of some formulation parameters on the penetration and adhesion of water-borne primers into wood

In the context of recent environmental laws, the paint industry received a new impulse to introduce novel water-borne and high solid paints on the market. Although intensive comparative research has already been performed, the influence of certain physical parameters on the natural weathering resistance of these new products still remains questionable. Penetration in close connection with adhesion of the coating is, in this perspective, one of the characteristics at issue. In this paper the impact of certain formulation parameters of the paints on their penetrating ability is assessed. In a further stage the influence of the average penetration depth on the adhesive strength of these paints is investigated.

Stabilization of aluminum pigment in waterborne paints

The corrosion of aluminum pigments in aqueous alkaline paint media, which results in the evolution of hydrgen, can be inhibited by certain substances. The combination of noninhibiting paint resins with three corrosion inhibitors (salicylic acid, a fluorinated phosphate surfactant, and an epoxy ester resin) has been studied. The presence of the resins does not significantly affect the stabilization of the aluminum pigment at pH 10 by the corrosion inhibitors. With the addition of corrosion inhibitors, the hydrogen volume evolved from aqueous aluminum pigment dispersions is surprisingly reduced by stirring. However, when heated to +40°C aqueous aluminum pigment dispersions with inhibitors evolve more hydrogen; at pH 8 the results are still satisfactory even at +40°C.

Application of dynamic speckle interferometry to the drying of coatings

In this work a new tool to study the drying of paints, based on an optical technique known as dynamic speckle interferometry is presented. The basic concepts of the technique are described and applied to the drying process of white solvent-borne and white water-borne paints (latex paint) following the time evolution of the activity of dynamic speckle patterns. For processing the data an alternative method based on the use of the second-order moment of the modified co-occurrence matrix of the time history of its intensity was used. The experimental results obtained were compared with the gravimetric technique and the resulting curves from the speckle-time evolution compared favorably with gravimetric drying curves. The results were also discussed on the basis of the knowledge of the coating drying process and factors related with the surface properties. Dynamic speckle interferometry seems to be a useful technique for assessing the time evolution of surfaces and, its sensitivity to refractive index changes helps to determine the start of different stages during the drying of latex paints. The dynamic speckle method tests mainly the activity on the surface and the measurements seem to confirm that the initial stage of drying is like a pure solvent. Finally, the study of different aspects of the drying process using this technique is proposed.

The impact of rheological modifiers on water-borne coatings

While low volatile organic components (VOC) architectural coatings like interior wall or exterior façade paints are accepted to a large extent by the end-users, conventional solvent based alkyds are dominating in the area of high performance laquers. The lower acceptance of water-borne coatings corresponds to aesthetic problems like lower gloss, poorer flow and leveling as well as application disadvantages like shorter open-time, lower brush drag and limited weather conditions. To solve these problems it is mandatory to understand dispersions rheology and the different ways to adjust rheological properties of water-borne paints and laquers by special modifiers. In this paper a short review is given about the thickening mechanisms of three main groups of rheological modifiers (cellulose ethers HEC and HMHEC, acrylics ASE and HASE, and urethanes HEUR) in the presence of an acrylic and a polyurethane dispersion. Furthermore measurements on two model coatings are presented. These results allow a discussion about several factors which influence the coatings rheology and performance.