Controlling particle dispersion in latex paints containing associative thickeners

Latex paints contain several types of particles including polymer binder, primary pigment, extenders, and colorants. When the paints contain associative thickeners, control of particle dispersion can be very complicated due to the interaction of the particles with dispersants, surfactants, and the associative thickener itself. In particular, dispersion of the pigments can act independently of dispersion of the binder particles. The consequences of this situation are manifested in the physical properties of the paint and of the films it forms. This paper describes these interactions in terms of their colloid chemistry and shows the consequences of additive choices on the particle dispersion and also the optical properties of model paint films. Presented at the 2006 FutureCoat! conference, sponsored by the Federation of Societies for Coatings Technology, in New Orleans, LA, on November 1–3, 2006.     

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.     

Flow and film properties of coatings containing microgels

Microgels have been prepared via an emulsion polymerization process involving the use of the amphiphilic oligosoap, ZEO. The particle sizes of these microgels were < 100 nm and particle properties such as crosslink density, copolymer composition and functionality could be varied over a wide range. Their versatility and usefulness as coating modifiers has been demonstrated.

Dispersions of the microgels are stable in both aqueous and organic media. Furthermore, solid powdered microgels can be produced by drying emulsions. These powdered microgels are generally added to photoreactive coatings or can be redispersed in the above media.

Such microgels may be applied in various other fields besides coatings because of the diversity of their form and properties.     

Study of the rheology of aqueous radiation curable polyurethane dispersions modified with associative thickeners

The chemistry of radiation curable polyurethane dispersions is outlined with an emphasis on the microstructure of the aqueous polymer dispersion and the possible interactions with associative thickeners. The steady-shear flow was studied for two model dispersions prepared from the same unsaturated polyurethane but showing significantly different particle size distributions. A hydrophobically modified ethoxylated urethane (HEUR) associative thickener with a linear structure was incorporated at different amounts to the dispersions with varying particle volume fractions. The steady-state viscosity at 25 and 10 °C was always reached quickly after instant flow rate changes so that no significant thixotropic effects were reported within the experimental timescale. Without thickener, the flow curves of the two model dispersions exhibited a Newtonian behavior except at the highest volume fractions where shear thinning became apparent. The maximum packing values determined from the Krieger–Dougherty relationship were essentially the same for the two systems. In the presence of thickener, the flow curves were characterized by a Newtonian plateau followed by a marked shear thinning region even at low particle volume fractions. This behavior typically suggests the formation of a physical network between polyurethane particles and thickener molecules partly adsorbed onto the polymer surface. The zero-shear viscosity of the two dispersions was compared with respect to: (i) particle volume fraction and (ii) particle surface area at different HEUR concentrations. At a given volume fraction, the particle size affects the viscosity of thickened models. As a corollary, a relationship is found between the particles size and the level of thickener required to reach a target viscosity. This study offers practically relevant data in terms of application conditions and provides a better insight into the thickening protocol.     

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.     

Evolution of the film properties of 3-methacryloxypropyl trimethoxysilane containing waterborne acrylic coatings during storage

The use of alkoxysilane monomers is one of the most attractive methods to obtain one-pot self-crosslinkable latexes for coating applications. The copolymerization kinetics shows that the alkoxysilane monomer is effectively incorporated into the copolymer. However, the hydrolysis and condensation reactions that give the latex the self-crosslinking ability can also prematurely happen. As a result, the microstructure of the latex, and consequently of the dried polymer film, will change during the storage. Herein, the evolution of key film properties, such as, water uptake and tensile strength as a function of the storage time of latexes with different alkoxysilane monomer loadings is presented. As storage time increases, there is an improvement on the mechanical properties, obtaining a harder polymer as the result of the development of the hydrolysis and condensation reactions during the first 4 weeks. However, for more extended storage periods (17 weeks) there is a significant decrease in the mechanical performance, because the crosslinking in the latex has developed enough to hinder the film formation.     

Synthesis and characterization of block-copolymer surfactants with specific interactions with associative thickeners

It has been theorized that, in order to get some positive interaction with the associative thickeners, the surfactants should have, at the end of the hydrophilic sequence, a short hydrophobic group. On the other hand, in order to control the hydrophilic lipophilic balance (HLB), it is wise to use well controlled polymerization procedures to build the block-copolymer. Then, the safer and simplest way to reach such goal is to use the ring-opening living anionic polymerization of butylene oxide (hydrophobic sequence) and then ethylene oxide (hydrophilic sequence); this living block-copolymer is then killed using an alkyl or aryl chloride (or bromide). However, because such surfactants include at the end of the hydrophilic sequence a hydrophobic group, they tend to adopt, when adsorbed onto hydrophobic latex particles, a back-folded conformation. In order to get for them an extended conformation, the hydrophilic sequence should have charges able to repel each other. This was achieved upon preparing block-copolymers of acrylic acid and butylacrylate, using a controlled radical polymerization with reversible addition fragmentation transfer (RAFT) agents, starting with the poly(acrylic acid) (PAA) sequence. Then, the radical fragment coming from the RAFT agent is at the end of the PAA sequence. A few rheological data actually confirm the interest of the concept.     

疏水缔合型两性聚丙烯酰胺增稠剂的制备及性能研究

以司班-80、OP-10为复配乳化体系,N,N′-亚甲基双丙烯酰胺(甲叉)为交联剂,丙烯酸十八酯(ODA)为长碳链疏水单体,用过硫酸钾引发丙烯酰胺(AM)、丙烯酸(AA)、甲基丙烯酰氧乙基三甲基氯化铵(DMC)进行反相乳液聚合,制备了疏水缔合型两性增稠剂。探讨了增稠剂的交联结构、交联剂用量、长碳链疏水单体用量,DMC用量以及所得产品的耐盐性、流变性和耐稀释性。结果表明:当交联剂占单体量0.17%,长链疏水单体为0.6%,DMC为13.8%时,其综合增稠效果最佳。     

Dispersion and film properties of carbon nanofiber pigmented conductive coatings

The use of multi-walled carbon nanotubes and nanofibers for coatings applications has been quite limited because of problems associated with obtaining dispersions of individual tubes/fibers. The potential for unique properties associated with these materials, such as obtaining electrical conductivity at very low volume concentrations, is dependent upon exploiting their very large geometric aspect ratios. Therefore, dispersion quality has a direct relationship to performance. We have developed a novel dispersion technique that appears to yield high quality dispersions without significant damage to the nanofiber properties. This technique involves the exfoliation of an aklylamine hectorite clay in the presence of nanofiber agglomerates, forming a stable gel, followed by stabilization with a suitable dispersant. We hypothesize that the size of the clay platelets is appropriate to penetrate the pores of the nanofiber agglomerates to assist in dispersive forces. Several thermoplastic acrylic coating formulations were prepared at various nanofiber volume concentrations utilizing this dispersion method. The onset of DC electrical conductivity was observed at only 4% volume concentration, indicative of high aspect ratios. Conductivity increases as a power law function of nanofiber volume concentration, resulting in 1.0 S/cm values at 12% volume.     

Properties of powdered associative alkali‐swellable acrylics thickeners synthesized by precipitation polymerization

Powdered alkali‐swellable acrylics thickener (ASAT) was synthesized by precipitation polymerization with acrylic acid (AA) and stearyl acrylate (SA) as monomer, allyl sucrose ether (ASE) as crosslink agent and lauroyl peroxide (LPO) as initiator in the solvent of ethyl acetate. The powders were normal distribution in the range 1–80 μm and showed sensitive to pH in water. Before pH 7, both of the viscosity and the light transmittance of the APAT emulsion increased with enhancing pH value. ASE and SA played an important role in the properties of ASAT. When the amount of ASE was increased, the crosslink degree in the ASAT molecule increased. As the result, the viscosity of its emulsion increased firstly and then decreased, but the light transmittance of the emulsion decreased monotonously. Introduction of SA led to formation of an associative ASAT. Therefore, both of the viscosity and light transmittance of ASAT emulsion increased firstly and then decrease with increasing the amount of SA. Meanwhile, the associative ASAT emulsion showed shear thinning behavior, good salt tolerate, and less sensitivity to temperature. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40512.     

Phase behaviors of comb-like liquid crystalline polysiloxanes containing fluorinated mesogenic units

Several liquid crystalline polysiloxanes (Pa-Pf) bearing fluorinated mesogenic units were synthesized using poly(methylhydrogeno)siloxane, 4′-(4-undec-10-enoyloxy-benzoyloxy)-biphenyl-4-yl 4-fluoro-benzoate and 4′-propionyloxy-biphenyl-4-yl 4-allyloxy-benzoate, and effect of fluorinated mesogenic units on phase behaviors of the fluorinated LC polysiloxanes was studied as well. The samples Pa and Pb showed single nematic mesophase when they were heated and cooled, but Pc, Pd, Pe and Pf exhibited both smectic and nematic phases. The glass transition temperature and smectic A-nematic mesophase transition temperature of polymers increased slightly with increase of fluorinated units in the polymer systems, but mesophase-isotropic phase transition temperature decreased slightly. In XRD curves, the intensity of sharp reflections at low angle increased with increase of fluorinated mesogenic units in the polymers' systems, indicating that the longer spacer and the fluorophobic effect of fluorinated mesogenic units could lead to a significant stabilization and even to modifications of smectic mesophases.     

Characterization and corrosion protection properties of epoxy powder coatings containing nanoclays

Two types of nanoclays, montmorillonite nanoflakes and halloysite nanotubes, at various concentrations were tested as nanofillers in epoxy powder coatings applied on an aluminum foil and a steel panel. The produced coatings were separated from the aluminum foil, enabling determination of peel strength, and mechanical properties and water permeability were determined for the obtained free films. Coated steel panels were characterized in terms of microstructure and corrosion protection properties in 0.5 M NaCl solution.     

Effect of crosslinker reaction rate on film properties for thermoset coatings

With thermoset coatings that employ room temperature crosslinkers, there is often a competition between film formation and crosslinking. In order to meet the early use/handling requirements for the coated substrate, formulators sometimes need to use crosslinkers with very fast room temperature reaction rates. However, when the coatings are based on aqueous latex resins, sufficient time must be allowed for latex particle coalescence to occur prior to crosslinking, or the resulting films will be partially or completely precross-linked, which is detrimental to many coatings properties. In this paper the effect of the crosslinker reaction rate on various film properties of coatings based on acrylic and acrylic/styrene latex resins will be investigated using several model carbodiimide-functional crosslinkers which have different reaction rates. Presented at the 76th Annual Meeting of the Fedeation of Societies for Coatings Technology on October 14–16, 1998, in New Orleans, LA. 727 Norristown Rd., Spring House, PA 19477, E-mail: RSCWTB@rohmhaas.com.     

水性易分散环保颜料的制备

以颜料合成后经过洗涤的滤饼为母体,通过添加颜料衍生物、组合分散剂然后进过特殊干燥或者易分散环保颜料。该颜料系列可以用于水性各种用途,包括水性涂料、油墨以及其他水性分散体。