Waterborne latex coatings of color: II. Surfactant influences on color development and viscosity

A matrix of coating variables, nonassociative versus associative thickeners, different latex median particle sizes, individual surfactants and colorants [carbon black (CB), red, and yellow pigments], was examined for their influence on variances in coatings rheology and color development. Within the different coating groups, the variable of interest in this study was the surfactant added to the colorant formulation. In all three colorant formulations, sodium dodecyl sulfate (an anionic surfactant) provided poorer color development (CD) than in applied formulations containing an equivalent nonylphenol oxyethylene (EO) surfactant. In CB formulations, nonionic surfactants with higher EO content provide improved color development at low (2 mM) concentrations, but near equality in CD is achieved with low EO surfactants at higher concentrations. In contrast to CB formulations, red and yellow colorants exhibit good color development with high EO content nonionic surfactants only at low nonionic surfactants concentrations. This variance appears to be related to the interactions of surfactants with inorganic pigments (talc and laponite) in the colorant formulation. The coating’s rheology is related to latex, thickeners, and surfactant components of the paint, as has been noted in previous studies, but not to the nature of the color pigment. The viscosity of the hydroxyethyl cellulose (nonassociative type) and HEUR (associative type) thickened paint decreased with colorant addition due to dilution effects. There were no unusual deviations with the NP(EO)_x surfactants, except when a large hydrophobe nonionic surfactant [e.g., C₁₈H₃₇(EO)₁₀₀] is added. In HEC thickened coatings, the viscosity decreases when C₁₈H₃₇-(EO)₁₀₀ is in the colorant due to that surfactant inhibiting depletion flocculation. In the C₁₈H₃₇(EO)₁₀₀ coatings containing the HEUR thickener, significant increases in viscosity were observed, above the dilution values observed with the colorant addition. This is related to the viscosity maximum in the low concentration of HEUR with the C₁₈H₃₇(EO)₁₀₀ surfactant. Color development is independent of the viscosity profile of the coating. Presented in part at the 81st Annual Meeting of the Federation of Societies for Coatings Technology, November 13–14, 2003 in Philadelphia, PA.     

Waterborne latex coatings of color: III. Triblock polyether influences on color development and viscosity

Oxyethylene (PEO)/oxypropylene (PPO) triblock polymers are added to colorant formulations to determine the influence of molecular weight and other structural variances on the rheology and color development of tinted latex paints. Waterborne coatings are a matrix of many coating components. In this study, a 108- or a 600-nm latex was thickened with a nonassociative thickener, hydroxyethyl cellulose, or an associative telechelic HEUR thickener. Triblock polymers with internal PPO segments and PEO terminal segments added as a dispersant to colorant packages, lead to better color development than PPO/PEO/PPO triblocks dispersants in carbon black (CB) tinted paints. The increase in color development with high molecular weight (MW) triblocks starts at a very low concentration (2 mM) and plateaus in a Langmuir-type adsorption isotherm. Lower molecular weight triblock polymers also exhibit this behavior in CB-, red-, and yellow-tinted latex coatings; however, increasing the terminal PEO segment sizes leads to better color development only in the CB-tinted coatings. With large PEO terminal units red and yellow tints are high only at very low concentrations (2 mM) of the triblock. This parabolic response in color development, in contrast to CB-tinted formulations, is attributed to the high surface area and porosity of CB that limits the amount of large PEO segments interacting with the talc particle present at twice the volume fraction of the colorant. With the lower surface areas of the red and yellow colorants, the interaction of the large PEO terminal segments with talc particles accounts for the limited triblock concentration for which good color development is observed. This can be reversed by decreasing or eliminating talc from the formulation.     

Surfactant behavior and its influence on the viscosity of associative thickeners solutions, thickened latex dispersions, and waterborne latex coatings

Surfactants, varying in their chemical composition and hydrophobic behavior, are used in the formulation of a waterborne coating. These differences influence their aggregation in micellar structures, their interaction with associative thickeners, and in particular, the synergies present in their competitive adsorptions on the disperse phases in a waterborne coating. Adsorption of HEUR thickeners on latexes and the ability of surfactants to displace them from those surfaces is an important variable in the dispersion’s viscosity. With large particle latexes, viscosity increases arise primarily from the network built through the interaction of HEURs with surfactants in the aqueous phase. Fluorescence is used to verify the mechanism by which surfactants enhance associative thickener viscosities. That is best achieved with nonionic surfactants, because of their synergies with large hydrophobe HEURs at low concentration. With decreasing latex particle size the adsorbed species is an important contributor to the dispersion’s viscosity through its contribution to the latex’s effective volume fraction increase and when the size of the adsorbed HEUR is matched to the separation distances of the latex at 0.25 volume fraction. Achieving controlled shear-thinning behavior in small particle size latex paints with the economic constraints on the amount of HEUR required to obtain 90 KU viscosities are discussed. Presented at the 80th Annual Meeting of the Federation of Societies for Coatings Technology, October 30–November 1, 2002, in New Orleans, LA. Polymer and Coatings Dept., Fargo, ND 58103.     

水性硬脂酸的制备及性能

采用相反转技术,通过氨化改性自乳化和外加表面活性剂的途径对硬脂酸进行了水性化,发现采用外加表面活性剂的途径能得到稳定性更好的水性硬脂酸。研究了表面活性剂种类、用量和油水比对水性硬脂酸体系的稳定性、黏度以及平均粒径的影响。结果表明,当采用十二烷基二苯醚二磺酸钠(SDD)/平平加(PER)复合表面活性剂,且m(PER)∶m(SDD)=2、搅拌速率为11 000 r/m in时,可得到平均粒径为10~20μm的稳定的水性硬脂酸;改变复合表面活性剂的用量,可有效地控制体系的稳定性、黏度及平均粒径。硬脂酸质量分数在12%以下时,所得产品的黏度较低;超过15%后,体系黏度急剧增加。     

Interactions in associative thickener/220 nm methyl methacrylate latex dispersions

The rheology of commercial associative thickener dispersions containing 220 nm ‘model’ methyl methacrylate (MMA) latices have been examined. These high T_g MMA latices were synthesized by a semicontinuous process with variable percentages of methacrylic acid (MAA). The latex surface without monomer acid segments was only 70% saturated. The latices stabilized with neutralized methacrylic acid segments provided surfactant-saturated surfaces and uniform dispersions when thickened. With the acid-monomer-free latex, the addition of surfactant to saturate the surface of the latex and to increase the free surfactant concentration in the aqueous phase to the level needed to optimize viscosity by intermicellar participation did not effect viscosities equivalent to those noted in associative thickener dispersions containing acid-stabilized latices. These observations support the ion—dipole associative thickener mechanism previously proposed.

The viscoelastic behavior of associative thickener dispersions containing stabilized MMA/MAA latices neutralized with ammonium and alkali metal hydroxides has also been examined. The viscosities of all dispersions containing associative thickeners were highest with NH₄OH-neutralized latices. These results are interpreted in terms of the greater solubilizing power and lower pK_a value of the ammonium salt. The viscosity of hydroxy-ethylcellulose (HEC) thickened dispersions was found to be insensitive to the free surfactant concentration and the nature of the base cation, with only minimal changes in low shear rate viscosities (LSVs) being observed with increasing latex surface acids. These variables notably influence the LSV of the associative thickeners (AT), the magnitude of the latter variations being specific to the AT employed.

In oscillatory experiments, dispersions containing commercial associative thickeners, used predominately with acrylic latices in the U.S. and Australian markets, were observed to exhibit large viscous components. A large elastic component, reflecting thickening via network formation, was noted with commercial associative thickener used largely with commercial vinyl/acrylic latices.     

Rheological and Morphological Evaluation of Natural Rubber Latex-Based PSAs Containing Waterborne Aliphatic Hydrocarbon Tackifier Dispersions

The effect of three waterborne aliphatic hydrocarbon tackifier dispersions each with different softening points (70°C, 85°C, and 95°C) were evaluated with natural rubber latex at two addition levels (25% and 50%) for pressure-sensitive adhesive (PSA) applications. No other additives were incorporated into the PSA formulations so that rheological effects of waterborne aliphatic hydrocarbon tackifier resin dispersions in natural rubber-based PSAs could be clearly understood. Application of these waterborne PSAs was evaluated, in terms of rheology, since flow parameters have a very important influence on the convertibility (coating ability) of such adhesives. Morphological correlations with wet rheology for these waterborne PSA formulations and starting materials revealed that the interaction between the latex particle and tackifier dispersion particle has a major influence in determining the viscosity characteristics at low to medium shear rate, where stirring, pumping, and filtration processes occur. A shear-thinning effect was also predominant in formulations with lower tackifier dispersion levels. The extent of shear-thinning can be correlated well to morphology. Interestingly, all the PSA formulations tend to follow Newtonian behavior above a shear rate of 1000 s^?1 and no shear-thinning or shear-thickening at higher shear rates was observed. The minimal change in viscosity at higher shear rates is a key parameter for high-speed coating techniques such as curtain coating and reverse gravure, since any change in viscosity can affect coating uniformity and the wetting of the substrate surface during coating.     

Associative polymer/latex dispersion phase diagrams II: HASE thickeners

The colloidal interactions of HASE associative polymers and latexes in the presence of surfactant are complicated and subject to a number of variables. Both bridging and depletion flocculation can occur, in addition to good particle dispersion. Dispersion phase diagrams have been developed to help visualize these interactions. The various dispersion states can have a significant effect on coating formulations and film properties. Examples of dispersion phase diagrams are presented for a model HASE anionic associative thickener and various model latexes in the presence of sodium dodecyl-sulfate and nonionic surfactants. The major variables affecting dispersion behavior are associative polymer concentration, latex particle size, latex surface hydrophobicity, electrolyte concentration, and surfactant concentration. The dispersion phase behavior of the HASE systems is compared to that of HEUR thickened systems reported previously. A significant difference is that much less bridging flocculation is observed in the HASE systems. In addition, nonionic surfactants induced depletion flocculation in the HASE systems but not in the HEUR systems.     

Surface modification of carbon black nanoparticles by dodecylamine: Thermal stability and phase transfer in brine medium

Stable aqueous dispersions of carbon black (CB) nanoparticles were prepared by developing a generic bilayer approach to the CB phase-transfer method using commercial Avanel as a surfactant. CB was oxidized using ammonium persulfate, and dodecylamine (DDA) was grafted onto this carbon core using N,N-dicyclohexylcarbodiimide as a coupling agent. The covalent bond between CB and DDA was confirmed by X-ray photoelectron spectroscopy, Fourier transform infrared spectroscopy, ultraviolet–visible spectroscopy, and thermogravimetric analysis. The average diameter of the primary carbon nanoparticles after chemical modification increased from 15 to 20 nm, as determined by high-resolution transmission electron microscopy. Dispersions of the modified CB was stable in organic solvents and were thermally stable in saline water when Avanel was used as a surfactant. The Avanel coating on the CB particles enabled the design of carbon materials with high colloidal stability, as evidenced by dynamic light scattering measurements and the breakthrough characteristics of the coated material in sandstone rocks.     

Shear-thickening in aqueous surfactant-associative thickener mixtures

Associative thickeners represent an important class of rheology modifiers used in waterborne coatings. Understanding molecular level interactions between associative thickeners and surfactants has been the subject of a number of prior studies. Our recent studies focused on the behavior of a hydrophobically modified, aminoplast ether (HEAT) associative thickener and a highly hydrophobic ethoxylated octylphenol surfactant in aqueous solution. Aqueous blends of these two materials exhibit shear-thinning, as well as rarely reported, transient, shear-induced thickening behavior. In addition, the same compositions exhibit both thixotropy and antithixotropy. The shear-induced thickening is shown to be the result of transient aggregated structures formed under shear. Addition of a third component, β-cyclodextrin—a molecule known to disrupt hydrophobic associations—to the mixture helped us advance the understanding of the nature of associative thickener–surfactant interactions that cause the transient shear-thickening behavior. Results indicate that, while overall viscosity of the HEAT/surfactant mixtures is decreased by β-cyclodextrin, the shear-induced thickening is unaffected. An intermolecular interaction model to describe the transient thickening mechanism is presented.     

着色剂对PET树脂特性粘度的影响

依据色素分子的性质，将着色剂进行了分类，并以此为基础讨论不同着色剂对聚酯特性粘度的影响，通过Mark-Houwink公式，推导了着色剂的加入与聚酯特性粘度之间的关系，发现小分子染料会使聚酯特性粘度迅速下降，聚合染料基本不影响聚酯的特性粘度，而熔融活性着色剂在低浓度范围内对聚酯起着明显的增粘作用，不仅可提高着色牢度，还可以抵消由于热加工而引起的聚酯的热降解。     

On the surface properties of waterborne fluorinated coating polymers

In the present work the results of a study concerning the surface properties of coating materials obtained from fluorinated latices are reported. Better understanding is required regarding the influence of polymer structure, latex composition, and morphology on the surface properties of the resulting films. For this purpose, two commercial fluorinated waterborne polymer dispersions were compared with a model fluorinated acrylic latex purposely synthesized. The surface properties of mold samples, prepared from either the whole solid matter contained in the latices (dried latex) or the purified polymer, were determined by simple contact angle measurements. Two series of homologous liquids, namely H‐bonding alcohols and apolar hydrocarbons, were employed for determining the critical surface tension γ_c according to the method of Zisman. The results of the surface characterization indicate that the degree of fluorination plays a minor role in these materials, suggesting that the threshold above which the polymer surface is virtually saturated by CF₂ or CF₃ groups might have been largely exceeded. On the other hand, the effectiveness of the hydrophobic fluorinated coating resulted substantially unaffected by the presence of amphiphilic low molecular weight additives, such as surfactants and wetting agents, which can actually contribute to the reduction of the surface energy of these materials upon suitable thermal treatment.     

Associative behavior of hydrophobically modified hydroxyethyl celluloses (HMHECs) in waterborne coatings

The associative behavior of hydrophobically modified hydroxyethyl cellulose (HMHEC) in polymer dispersions has been determined as a function of the composition of both the associative thickener (AT) and the latex. How changes in interaction between HMHEC and the latex influence the rheology of the latex thickener systems is discussed. Adsorption of HMHECs onto an acrylic emulsion strongly depends on the hydrophobe type and degree of substitution, as well as on the molecular weight of the associative thickener. The degree of latex adsorption is influenced dramatically by the stabilization system utilized, that is choice and level of surfactant and carboxylic acid content, in addition to the composition of the monomer mix. Rheological measurements demonstrate that HMHECs of specific composition can provide gloss emulsion paints with a balance of rheological properties, combining excellent levelling with sag resistance.     

Surfactants in water-borne paints

The main uses of surfactants in water-borne coatings are discussed. Special attention is put on the use of surfactants in latex polymerization and in post-emulsification of binders, such as alkyd resins. The advantage of polymerizable surfactants as emulsifier is pointed out and the use of atomic force microscopy (AFM) to observe differences in film properties between formulations based on polymerizable surfactants and on conventional surfactants is illustrated. The paper further discusses the problem of competitive adsorption between surfactants and between surfactant and associative thickener in paint formulations.     

Skin Development during the Film Formation of Waterborne Acrylic Pressure-Sensitive Adhesives Containing Tackifying Resin

Tackifying resins (TR) are often used to improve the adhesive properties of waterborne pressure-sensitive adhesives (PSAs) derived from latex dispersions. There is a large gap in the understanding of how, and to what extent, the film formation mechanism of PSAs is altered by the addition of TR. Herein, magnetic resonance profiling experiments show that the addition of TR to an acrylic latex creates a coalesced surface layer or “skin” that traps water beneath it. Atomic force microscopy of the PSA surfaces supports this conclusion. In the absence of the TR, particles at the surface do not coalesce but are separated by a second phase composed of surfactant and other species with low molecular weight. The function of the TR is complex. According to dynamic mechanical analysis, the TR increases the glass transition temperature of the polymer and decreases its molecular mobility at high frequencies. On the other hand, the TR increases the molecular mobility at lower frequencies and thereby promotes the interdiffusion of latex particles to create a skin layer. In turn, the skin layer is a barrier that prevents the exudation of surfactant to the surface. The TR probably enhances the coalescence of the latex particles by increasing the compatibility between the acrylic copolymer and the solids in the serum phase.     

Control of rheology of water-borne paints using associative thickeners

Water-borne decorative topcoats generally show inferior leveling and open time compared to solvent-based paints. Basically, this behavior is caused by the divergent viscosity–solid content relationship for dispersions and emulsions and by the relatively high evaporation rate of water. Employment of associative thickeners may improve leveling and open time of latex paints only if they introduce a substantial amount of ‘network viscosity,' characterized by a short relaxation time and little dependence on solid content. This network viscosity enables one to formulate a paint with sufficient high-shear viscosity at a particle-packing density far below the value where low-shear viscosity starts to diverge. Addition of an associative thickener not only affects rheology, but also the interaction between latex particles: Associative HEUR thickeners may induce undesired phase separation by strong bridging between the latex particles. The influence of HEUR thickeners on latex particle interaction has been studied by turbidity measurements. The experimental results could qualitatively be interpreted very well by two-particle interaction potentials computed using the Self-Consistent-Field theory of Scheutjens and Fleer. It is demonstrated how viscosity, created by the addition of an associative thickener to a highly concentrated latex, can be split up into a polymer network viscosity and a contribution to (relative) dispersion viscosity. According to these analyses, reduction of the molecular weight of tri-block HEUR thickeners yields an increase of the favorable network viscosity and a reduction of the unfavorable dispersion viscosity. However, reduction of the molecular weight of the HEUR thickener is limited by the introduction of undesired phase separation (bridging flocculation) below a certain molecular weight.     

Polyurethane macromers—new building blocks for acrylic hybrid emulsions with outstanding performance

Emulsion polymerization is an efficient process to produce waterborne binders. It has been observed that films prepared from traditional latices do not show high performance especially concerning humidity and stone chip resistance. Polymeric emulsifiers are promising alternatives to low molecular weight surfactants. Polyurethanes are an interesting polymer class. The structure of the polymer backbone can be varied in a wide range by using different building blocks. The synthesis of copolymerizable polyurethanes, which have an amphiphilic structure similar to traditional surfactants, and their use in aqueous polymerization is discussed in detail. This process leads to polymer emulsions with structured particle morphology. The resulting films show outstanding properties. The polyurethane–polyacrylic dispersions can be used as binders for high performance waterborne coating formulations.     

Skin Development during the Film Formation of Waterborne Acrylic Pressure-Sensitive Adhesives Containing Tackifying Resin

Tackifying resins (TR) are often used to improve the adhesive properties of waterborne pressure-sensitive adhesives (PSAs) derived from latex dispersions. There is a large gap in the understanding of how, and to what extent, the film formation mechanism of PSAs is altered by the addition of TR. Herein, magnetic resonance profiling experiments show that the addition of TR to an acrylic latex creates a coalesced surface layer or “skin” that traps water beneath it. Atomic force microscopy of the PSA surfaces supports this conclusion. In the absence of the TR, particles at the surface do not coalesce but are separated by a second phase composed of surfactant and other species with low molecular weight. The function of the TR is complex. According to dynamic mechanical analysis, the TR increases the glass transition temperature of the polymer and decreases its molecular mobility at high frequencies. On the other hand, the TR increases the molecular mobility at lower frequencies and thereby promotes the interdiffusion of latex particles to create a skin layer. In turn, the skin layer is a barrier that prevents the exudation of surfactant to the surface. The TR probably enhances the coalescence of the latex particles by increasing the compatibility between the acrylic copolymer and the solids in the serum phase.     

Waterborne Coatings Based on Renewable Oil Resources: an Overview

Polyurethane dispersions are gaining in importance due to their environmentally friendly coating system, versatile coating properties and ease of application. An enormous amount of research is focused on waterborne coatings such as waterborne alkyds, water-reducible alkyds, alkyd–acrylic hybrids, oil modified polyurethane dispersions and their composite latexes. This review gives a comprehensive compilation of recent studies on the synthesis and applications of waterborne coatings. The article specifically covers all of the research work carried out in the field of waterborne alkyd–acrylics, polyurethane dispersions and their hybrid latexes systematically.     

Synthesis and properties of hybrid alkyd–acrylic dispersions and their use in VOC-free waterborne coatings

Hybrid waterborne alkyd–acrylic dispersions with solid content of 40%, free from any surfactant and exempt of any organic solvent, were successfully synthesized by a melt co-condensation reaction between an acrylic prepolymer bearing carboxylic groups and a long-oil alkyd resin. Spontaneous emulsification of the ensuing hybrid resin was achieved by the addition of an aqueous ammonia solution that neutralized the carboxylic functions. The key role of the carboxylic groups on the stabilization process and on the storage stability of the dispersion was assessed and it was shown that the insertion of anhydride moieties within the acrylic prepolymer ensured the efficient coupling between the acrylic and the alkyd resin and prevented the phase separation. These dispersions are easy to implement and might be used to prepare high quality zero VOC coatings in terms of drying time, stability and gloss. The most stable dispersion was also used in the formulation of air-drying waterborne lacquers and their coating properties were evaluated.