Formulation effects on the distribution of pigment particles in paints

Modern water-borne paints are widely used in different areas of applications ranging from high-gloss lacquers to flat, scrub-resistant interior paints. From this point of view, the pigment volume concentration (PVC) is one key-parameter adjusting the desired application properties. In high-gloss paints, for example, a low PVC is required to accommodate the proper surface roughness to achieve a high gloss. Consequently, a high concentration of TiO₂ is needed to obtain a good hiding power at the same time. Flat paints nonetheless are highly filled due to cost reasons preferentially by CaCO₃ and the pigment binding capacity of the binder is crucial. In this work, paint formulations differing in PVC, and the type of binder or dispersing agent were investigated by various techniques concerning the distribution and aggregation of pigment particles, e.g. TiO₂. To get a detailed insight into the structure of the liquid paints and the corresponding dried paint films, suitable analytical tools were applied for characterization. The structure of the liquid paints was analyzed by remission light spectroscopy (RLS), disc centrifugation, cryogenic-replication transmission electron microscopy (Cryo-replica TEM) and cryogenic-scanning electron microscopy (Cryo-SEM). The pigment distribution in the corresponding dried paint films was examined by means of atomic force microscopy (AFM), TEM and RLS. The tendency of the TiO₂-pigments to form aggregates was found to depend on both: first on the type of binder used in the formulation and second on the employed dispersing agent. It is shown that only by adjusting the properties of the binder in combination with common dispersants, it is possible to get well-distributed TiO₂ particles within the paint. Correlation of application properties, e.g. gloss and blocking to the microscopic structure is presented.     

Synthesis and characterization of comb polycarboxylic acid dispersants for coatings

Comb polycarboxylic acid dispersants (CPCADs) graft acrylic copolymers which consist of hanging methoxy polyethylene glycol chains and carboxylic acid groups on main acrylic chain. The CPCADs have been synthesized by radical polymerization of methacrylic acid and methoxy polyethylene glycol methacrylate as a nonionic unsaturated hydrophilic macromonomer. The CPCADs are polymeric surfactants that can be used as anionic dispersant. Methoxy polyethylene glycol methacrylate has been synthesized by esterification of methacrylic acid and methoxy polyethylene glycol in the presence of methanesulfonic acid as catalyst. These have been characterized with ¹H‐NMR and GPC. Acid values of CPCA dispersants have been determined. The dispersion of CPCA dispersants depends on their molecular weights, length mPEG, and acid values. Dispersion of titanium dioxide in typical solvent‐based paint formulation has been investigated. The physicochemical and mechanical properties of surface coatings having CPCADs such as gloss, hardness, and contrast ratio have been investigated. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Shear rate-dependent structure of polymer-stabilized TiO2 dispersions

Opacity, gloss, stability, color acceptance, and other paint properties depend on the quality of pigment dispersion. We measured the shear rate-dependent structure of titanium dioxide (TiO₂) dispersions stabilized with commercial polymer dispersants in water. Two different MW polyacid dispersants and two different MW acrylate copolymers were used in this study. The experiments were conducted at the NIST Center for Neutron Research on the perfect crystal diffractometer for ultra-high resolution small-angle neutron scattering (USANS) measurements. The results for TiO₂ scattering and rheology show that shear induced dissociation occurs for certain dispersants and shear induced association of TiO₂ clusters is observed for other dispersants. The results suggest new ways to consider dispersant selection for paints and the quality of pigment dispersions.     

An improvement of color electrophoretic paint via ultrafine modified pigment paste

The ultrafine paste used in electrophoretic paint was prepared via ultrasonic method with pigment yellow 83 (P.Y.83), octadecyl dimethyl benzyl ammonium chloride, and deionized water. The average particle size of the ultrafine paste was only 196?nm and zeta potential was 30?mV with ultrasound for 30?min and 2?wt.% cationic dispersant. The conductivity of the paint was improved as the cationic dispersant increased. Centrifugal stability of the paint with ultrafine paste reached the maximum at 2?wt.% cationic dispersant. Compared with the performances of cathodic electrophoretic paint with the ultrafine yellow paste, the anodic film was smooth, uniform, and neat with 0.5?wt.% cationic dispersant in the ultrafine yellow paste. Deposited amount of the anodic film was 27?g/m², which was higher than the cathodic film. The curing property, adhesion, and chemical resistance of the cathodic film were better than the anodic film. Properties of five color cathodic paints (blue, yellow, red, black, and green) were discussed and were compared with the film of electrophoretic paint containing commercial pastes. Except the green film, the blue, yellow, red, and black films were smooth, fine, and uniform, and also provided good L-effect. The deposited amount of these films with excellent adhesive force was about 14–19?g/m². The electrophoretic paints containing modified pigment pastes and commercial pigment pastes present good adhesion and chemical resistance.     

超细涂料色浆的制备及其稳定性研究

涂料色浆的着色强度和色牢度等性能除了与颜料分子的化学结构、分散性密切相关外,还与涂料色浆微观颗粒的大小与分布有关。颜料粒径越小,其着色强度、光泽和遮盖力越好,因此,超细涂料色浆的制备得到了人们越来越多的关注。本课题研究了超细涂料色浆的制备方法,讨论了分散剂结构及用量、超声波处理时间、超声波处理功率对颜料分散效果的影响,分析表征了所制备涂料色浆的稳定性。研究结果表明分散剂FPE对颜料的分散效果较好,其较佳工艺为:颜料含量15%,分散剂用量占颜料用量的20%,超声波处理时间30 min,处理功率800 W,所制备的超细涂料色浆的粒径可达到150.9 nm,其离心稳定性达93.27%。稳定性实验表明所制备的涂料色浆具有良好的对温度、pH和电解质的稳定性。     

Application of poly(vinyl alcohol) with an alkyl end group containing anionic groups to coal–water slurry as a dispersant

Anionic groups were introduced with copolymerization of corresponding vinyl monomers with vinyl acetate into poly(vinyl alcohol) (PVA) with an alkylthio end group. The polymers were investigated as a dispersant for coal-water slurry (CWM). Anionic groups such as sodium sulfonate and sodium carboxylate enhance remarkably the ability of PVA with an alkylthio end group to disperse coal. Sodium polyacrylic acid with an alkyl end group also showed a good ability of dispersing coal. The order of the ability of dispersing coal in these polymeric dispersants along with sodium napthalene sulfonate formaldehyde condensate (NSF) varied by the kind of coal used. In cases of the polymeric dispersants, the fluidity of coal in terms of dependence of viscosity on shear rate also varied, from dilatency to thixotropy, in accordance with coal used. Impurities in coal as well as surface properties of coal particles might play important roles in the properties of CWM. © 1995 John Wiley & Sons, Inc.     

Film formation from pigmented latex systems: Mechanical and surface properties of ground calcium carbonate/functionalized poly(n‐butyl methacrylate‐co‐n‐butyl acrylate) latex blend films

The mechanical and surface properties of films prepared from model latex/pigment blends were studied using tensile tests, surface gloss measurements, and atomic force microscopy. Functionalized poly(n‐butyl methacrylate‐co‐n‐butyl acrylate) [P(BMA/BA)] and ground calcium carbonate (GCC) were used as latex and extender pigment particles, respectively. The critical pigment volume concentration of this pigment/latex blend system was found to be between 50 and 60 vol % as determined by surface gloss measurement and tensile testing of the blend films. As the pigment volume concentration increased in the blends, the Young's modulus of the films increased. Nielsen's equations were found to fit the experimental data very well. When the surface coverage of carboxyl groups on the latex particles was increased, the yield strength and Young's modulus of the films both increased, indicating better adhesion at the interfaces between the GCC and latex particles. When the carboxyl groups were neutralized during the film formation process, regions with reduced chain mobility were formed. These regions acted as a filler to improve the modulus of the copolymer matrix and the modulus of the resulting films. The carboxyl groups on the latex particle surfaces increased the surface smoothness of the films as determined by surface gloss measurement. When the initial stabilizer coverage of the latex particles was increased, the mechanical strength of the resulting films increased. At the same time, rougher film surfaces also were observed because of the migration of the stabilizer to the surface during film formation. With smaller‐sized latex particles, the pigment/latex blends had higher yield strength and Young's modulus. Higher film formation temperatures strengthen the resulting films and also influence their surface morphology. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 4550–4560, 2006     

Impact of functional group distribution on the adsorption of a polymeric dispersant

Binder polymers functionalized with a small amount of polar groups satisfy both the dispersion quality of paints and the mechanical strength of coating films. For industrial-grade polydisperse dispersant polymers, functional groups are not evenly distributed among the polymer chains. The functional group distribution in polyurethane dispersant polymers was investigated by statistical estimation and an adsorption experiment. The polymeric dispersants had a broad functional group distribution and contained a significant amount of nonfunctionalized chains. By considering the existence of these ineffective chains, the dispersion behavior of the paint was more clearly explained. The described method can be a useful tool to analyze the structure and the properties of polydisperse functionalized polymers for various applications. Science and Technology Research Center, Yokohama, Kanagawa, 227-8502, Japan     

Synthesis of polymeric dispersants from renewable DCO fatty acid and their multifunctional behavior in waterborne flat paint

Copolymers containing 50% dehydrated castor oil fatty acids (DCOFA) derived from renewable resources, were synthesized via free radical solvents less polymerization with maleic anhydride, styrene, and butyl acrylate. The copolymer was crosslinked further with polyethylene glycol 400 (PEG 400) to increase its molecular weight. The copolymers with and without crosslinking were then neutralized with sodium hydroxide to prepare polymeric dispersants DFCD1 and DFCD2 respectively in aqueous medium. It was observed via surface-tension measurement that both DFCD1 and DFCD2 transfer to the air–water interface before forming any aggregates, and the ease of forming the aggregates is in the order of DFCD1 > DFCD2. The efficacy of these dispersants was examined in the dispersion of the titanium dioxide pigment and conventional extenders like calcite, talc, and china clay using flow point and zeta potential measurements. The results reveal that DFCD2 improved the dispersing ability for the pigment and extenders studied. The performance of these polymeric dispersants was also studied and compared in waterborne flat paint as a rheology modifier and pigment-dispersing agent. The paint rheology profile and dE data indicate the superior performance of the paint containing dispersant DFCD2. When used in combination with conventional styrene-acrylic latex, DFCD1 and DFCD2 reduced the minimum film-forming temperature (MFFT) of the polymer latex.     

A new concept for dispersing agents in aqueous coatings

After a short overview about the development of synthetic dispersing agents for solvent-borne coatings up to the actual state of technique, analogous concepts of polymeric additives for water-borne coatings are introduced. The performance of these polyfunctional dispersants will be critically reviewed and described in comparison to dispersing agents based on new concepts. With these new concepts using mono- and difunctional oleochemical agents or a combination of them it is often possible to reach better performance than with polyfunctional polymers. During our study different physicochemical methods (Zeta potential, adsorption, desorption) and paint application tests including numerous binders and pigments were done. These investigations lead to the discussion of new models for the dispersing of pigments in water-borne coatings and to more knowledge about the design of a dispersant to reach high gloss, optimal rub-out and high color-strength. Furthermore the formulation of solvent- and resin-free water-borne pigment pastes is possible using dispersing agents selected by the new concepts.     

A Quantitative study of polymeric dispersant adsorption onto oxide-coated titania pigments

Polyacrylic acid salts and similar copolymers are used extensively in the coatings industry to disperse oxide-coated titania pigments. The effect of polymer adsorption onto the pigment can vary widely depending on polymer composition, pigment surface treatment, and solution properties such as pH and ionic strength. This investigation examines the effect of molecular weight on the adsorbed layer thickness and stabilizing action of polyacrylic acid dispersants. In order to understand the stabilization mechanism, a DLVO model was used in which the surface treatment layer of the pigment and the adsorbed layer thickness of the dispersant were taken into account. It was found that only this level of detail could account for the degree of stability found in pigment suspensions. Layer thickness and adsorption isotherms indicate that the dispersant molecules do not adsorb completely flat to the pigment surface but with enough loops and tails to provide some electrosteric stabilization.     

Influence of different dispersants on the quality and stability of aqueous quinacridone magenta pigment dispersion for ink-jet applications

The stability of water-based pigment dispersions is a key factor in determining their utility in ink-jet applications, and the appropriate choice of dispersant plays a special role. Among the pigment formulations tested to date, literature data on magenta pigments are very limited. Thus, the goal of this work was to study the influence of the type and loading of dispersants on the quality and stability of quinacridone magenta pigment dispersions. Three different commercially available dispersants were tested: (1) a cationic styrene-maleic anhydride copolymer, (2) an anionic polyacrylate, and (3) a nonionic alkyl ethoxylate. Pigment and dispersing agents were analysed using the Fourier Transform–infrared method. The stability of pigment dispersions was determined by comparative studies of changes in the pigment particle size, viscosity, pH, filtration time, optical density and gloss during the accelerated ageing test. Moreover, Turbiscan AGS and LUMiFuge analysers were used for evaluations of the instability of the dispersions. The properties of each dispersing agent affected the performances of the different dispersants. The highest stability for the pigment formulations was provided using the nonionic dispersant (small particle size, < 60 nm; the lowest viscosity < 60 mPa·s at the optimal dispersant content; favourable results of the filtration test; the highest pigment dispersability, proven by optical density and gloss). The Turbiscan AGS and LUMiFuge results indicated that the stability of all tested quinacridone magenta pigment dispersions was excellent (Turbiscan Stability Index values below three, and no significant differences in transmission profiles, respectively). However, it was found that the measurement results were influenced by the viscosity of the formulations.     

Stability of pigment and resin dispersions in waterborne paint

The stability of a colloidal dispersion in a waterborne paint system, which consists of dispersed pigment and polymeric particles (dispersion or emulsion) along with a water-soluble acrylic polymer, was investigated. It was found that adsorption of appropriate ultrafine particles to the relevant particles could stabilize these particles against flocculation, leading to lower viscosity and yield value. The gloss and smoothness of the resultant films are notably improved. As the stability of the colloidal particles in an aqueous system is strongly dependent on the electrostatic effect, the effect was evaluated by measuring the ζ-potentials of the relevant colloidal particles. The ζ-potential is the electric potential on the outside of the surface layer, which includes the counterions around the particle. The ζ-potentials of a series of pigments in a solution of a water-soluble polymer were determined. By arranging the pigments according to their ζ-potentials, an order of basicity-acidity was established for pigments in a waterborne system, and the order was found to be different from that of solventborne systems, thought to be due to adsorbed counterions. After dispersing the pigment sufficiently with an appropriate polymer dispersant, ultrafine particles (of size under 0.05 μm) of lower refractive indexes were adsorbed to the surface of the pigments and polymeric particles. The adsorption layer of ultrafine particles can modulate the ζ-potentials of various colloidal particles to bring them into a certain range, so that the co-flocculation tendency between different colloids is remarkably diminished providing quite stable paint compositions by both electrostatic and steric hindrance effects.     

Pigment/dispersant interactions in water-based coatings

Conclusions  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.     

Associative polymer/particle dispersion phase diagrams III: Pigments

The colloidal interactions of both HEUR and HASE associative polymers with pigments in the presence of dispersant are complicated and subject to a number of variables. The objective of this work was to clarify the conditions needed to achieve good pigment dispersion in associative thickener systems by characterizing particle dispersion behavior. This had previously been done for latex particles, but not for pigments such as TiO₂. Good dispersion leads to optical properties, such as gloss and hiding, that are superior to nonassociative thicknener systems. Pigment dispersion phase diagrams represent a good way to visualize the complex interactions among pigments, dispersant, and thickener. The two most important variables were found to be pigment type (i.e., surface composition) and dispersant composition. Associative thickners can yield good pigment dispersion or flocculation, depending on the correct matching of dispersants and pigment type. Because of the hydrophobic functional groups governing associative thickner behavior, dispersants having some hydrophobic character yielded the best pigment dipersions and optical properties because they could couple the pigment particles with the associative thickener network. Interior-grade TiO₂ tended to yield better dispersions and optical properties than exterior-grade TiO₂. Optimized associative thickner systems generally had improved optical properties over comparable nonassociative systems. Optical properties correlated well with particle dispersion behavior as displayed by the dispersion phase diagrams. Presented at the Tess Symposium of the 230th American Chemical Society National Meeting, Aug. 28–Sept. 1, 2005, in Washington, D.C.     

Effects of morphology and surface treatment of inorganic pigments on waterborne coating properties

Inorganic pigments in aqueous coatings are investigated using atomic force microscopy and microprobe analysers. The first method characterises the topography at a very high resolution. The findings obtained using the second method reveal the distribution of the pigment in the paint film. Taking selected titanium dioxide and iron oxide pigments, the effects of particle morphology as well as inorganic and organic surface treatment on the dispersibility and flocculation stability are shown. These two phenomena are factors in gloss, hazing, hiding power, tinting strength and viscosity – key quality parameters in waterborne coatings.     

Impact of cooling method and incoming sheet quality on final part surface quality in thick sheet paint film thermoformed parts

Thick sheet, “dry paint” film parts were thermoformed using different cooling methods and sheet temperatures to determine whether these two parameters had a direct effect on the surface quality of the final part. Although some thermoformers have claimed that applying chilled air after forming “dry paint” film parts improves the gloss of the parts, the data from this study showed that application of chilled air did not have an effect on either the parts' initial gloss or their gloss after time‐dependent hazing. The critical factor in maintaining surface quality in these parts was the maximum temperature reached by the “dry paint” film during heating. In addition, analysis of the data taken on the sheet prior to forming versus that taken on the part after forming demonstrated the importance of validating the surface quality of the as‐received sheet prior to conducting process versus appearance experiments. On the basis of these findings, a recommendation is made for incoming sheet surface quality levels for both process development studies and production applications. POLYM. ENG. SCI., 2009. © 2008 Society of Plastics Engineers     

Flooding and floating in latex paint

Flooding and floating are problems in many paint applications. If pigment concentration is uniform on the surface but not through the thickness of the film, one refers to ‘flooding’ (horizontal separation). If, however, concentration differences are visible across the surface of the paint film, one refers to ‘floating’ (vertical separation). In this article, the influence of pigment, filler, additives, and processing conditions on the flooding and floating of colored latex paint were investigated. It was discovered that too broad a distribution of pigment and filler particle size can lead to flooding and floating. Different levels of pigment (TiO₂) or filler (kaolin) loading cause diverse degrees of flooding and floating. Waterborne coatings that do not exhibit flooding or floating may show these conditions when diluted. Using dispersants or thickeners with hydrophobic constituents, increasing viscosity, reducing surface tension, etc., all help to prevent or reduce flooding and floating. Comparison tests revealed little influence of processing conditions on flooding or floating.     

活性聚合物型颜料分散剂

活性聚合物型颜料分散剂是由专利的活性聚合方法制得，具有其他类型颜料分散剂无法比拟的优点，使难以稳定的颜料具有很好的分散稳定性，可满足汽车涂料等高装饰性涂料的要求，介绍了毕克化学公司的活性聚合物型颜料分散剂的作用原理及应用实例。     

Structure and properties of multiphase particles and their impact on the performance of architectural coatings

Aqueous dispersions used as binders in low-pigmented solvent-free paint formulations have to cope with the challenge to simultaneously guarantee an excellent film formation and appearance as well as good block resistance and hardness. One strategy to fulfill these contradictory requirements is the employment of multiphase particles.

In this work it is proved that the structure of latex particles, synthesized by a two-stage emulsion polymerization process, can be correlated to the morphology and properties of the dispersion films as well as to the application properties of the corresponding paint films.

Two sets of model dispersions were made. In the first set, the hard/soft ratio was varied, in the second set the amount of the AA. The structure of the particles was determined by TEM, and a morphology map was derived. AFM demonstrated a clear correlation between the particle structure and the morphology of the latex film. Dynamic mechanical analyses verified the presence of two distinct polymers with the hard phase acting as a transparent filler. For the hard/soft series, the properties of the dispersion films such as block resistance, gloss and hardness could be attributed to their structure. A closer look on the block behavior revealed that it can be related to the tack and surface roughness of the dispersion film, but not to its internal strength. Solvent free emulsion gloss paints were formulated, and application tests performed. The properties of the paint films correlated very well with those of the dispersion films. The test results clearly show that dispersions of multiphase particles enable the formulation of solvent free paints with excellent film-forming ability in combination with high block resistance, hardness and gloss.