Stability Of Pigment Dispersions Research Articles

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

AbstractThe 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.

Role of surfactants on stability of iron oxide yellow pigment dispersions

Iron oxide yellow pigment (PY42) dispersion was prepared using the mixture of dispersing agents (surfactants) alkyl aryl sulphonates (S1), lecithin (mixture of phospholipids) (S2), alkoxylated fatty alcohols (S3), and polyoxyethylene tri-decyl ether phosphate (S4). Evaluation of this pigment dispersion in an aqueous paint resulted in acceptable coloristic properties. However, stability of the dispersion with respect to a significant increase in viscosity and settling behaviors when subjected to accelerated stability test (at 55 °C for 30 days) was observed. Rheology profiles have been used to characterize the pigment dispersions. Role of various combinations of surfactants on rheology of pigment dispersion was studied. It was found that, certain surfactants played a crucial role on stability of pigment dispersions during accelerated stability. Elimination of surfactant S3 or S4 resulted in an acceptable viscosity at ambient conditions. However, in the accelerated stability test pigment dispersion without S3 showed significantly high viscosity whereas, dispersion without S4 showed no increase in viscosity. From the physical examination, viscosity measurements and analysis of rheology profiles it can be concluded that polyoxyethylene tri-decyl ether phosphate (S4) is the key contributor for the viscosity pickup and settling behavior during the accelerated stability test. Moreover, the rheology study is of great help in predicting the relative stability of the samples.

Encapsulation of Pigment Red 122 into UV‐curable resins via a mini‐emulsion technique

PurposeThe purpose of this paper is to encapsulate aqueous dispersions of nano‐scale CI Pigment Red 122 prepared through ball milling into UV‐curable resins, 1,6 hexanediol diacrylate (HDDA, monomer), and polyester acrylate (oligomer) using the mini‐emulsion technique.Design/methodology/approachThe encapsulation of pigment is achieved by mixing a surfactant‐stabilised pigment dispersions and a monomer/oligomer mini‐emulsions and subjecting both to mini‐emulsification conditions. A film of encapsulated pigment mini‐emulsion is finally UV cured using water‐soluble initiator. Efficient encapsulation is proven by ultra‐centrifugal sedimentation, scanning electron microscopy and thermogravimetric analysis (TGA). The stability of pigment dispersions and also the encapsulation process are investigated.FindingsTGA and ultracentrifuge sedimentation results showed that CI Pigment Red 122 is successfully encapsulated into polyester acrylate/HDDA resins. The oligomer (polyester acrylate) in the presence of organic pigment could stabilise the mini‐emulsion droplets without introducing any other hydrophobes (co‐stabiliser) in the formulation. In addition, the encapsulation percentage and suspension stability of mini‐emulsion are best when the polyester acrylate/HDDA weight ratio is 3:2.Research limitations/implicationsThe UV‐curable resins used in the present context are 1,6 HDDA and polyester acrylate. Besides, various oligomer/monomer composition types could be used and its impact on encapsulation efficiency could be also studied.Practical implicationsThis method of encapsulation is practically effective for modification of organic pigments for use in UV‐curable ink‐jet printing inks.Originality/valueThe developed method is novel from a literature point of view and can be of a great benefit to achieve the required properties of pigmented UV‐curable system in inkjet printing of textiles. In addition, it could find numerous applications in surface coating.

Effects of Ethanol on the Stability of Pigment Colloidal Dispersion

The effects of ethanol on the thickness and ionization of adsorbed polymer layer on pigment were investigated. The results showed that the thickness of adsorbed polymer layer decreased with the increase of the ethanol concentration, and then the pigment particles aggregated when the concentration of ethanol is higher than 40%. The zeta potentials became more negative with the increasing of the ethanol concentration, and then changed reversely when the ethanol concentration was higher than 16%. The thickness and structure of adsorbed polymer layer on the particle determined the stability of pigment dispersion.

Photocurable inkjet ink for printing on metallic and plastic substrates

A novel vinyl ether monomer was employed to improve curing properties of photocurable inkjet ink. A cationic polymerization system was used and the improved curing properties using a novel vinyl ether monomer with cyclic ether compounds were demonstrated. The cured UV ink film showed good adhesion on metallic substrates such as stainless steel, copper, aluminum and also plastic substrates. The stability of pigment dispersion in the ink was improved by controlling zeta-potential of the ink. The higher zeta-potential value resulted in stable particle size of the pigment and viscosity of the ink.

The effect of polymer molecular weight in the adsorption process

The stability of pigment dispersions, which governs most of the film properties of paints, depends on the type and the extent of polymer species adsorbed by a pigment. The adsorption dependency with respect to molecular weight of the polymer and concentration of its solution was studied using epoxy esters of different molecular weights as adsorbates and anatase titanium dioxide as adsorbent. The amount of polymer adsorbed was determined by infrared spectroscopy. The type of molecular weight species adsorbed from unfractionated binder, the competitive adsorption in presence of more than one molecular weight species, and displacement of one molecular weight species by the other at different concentrations of the resin solutions were followed by gel permeation chromatography. The hiding power of paint and the gloss of the paint film, which are dependent on the degree of dispersion, were examined and the results correlated with the types of molecular weight species used in paint formulations. The type of molecular weight species adsorbed was found to be concentration dependent: the lower the concentration, the higher the molecular weight species adsorbed. The dispersions of pigment in the solution of higher-molecular-weight species were found to be more stable than those derived from lower-molecular-weight resin solutions. The TiO 2 paint derived from higher-molecular-weight epoxy resins had better gloss and hiding power.

顔料の分散安定性

顔料の分散安定性

高分子の吸着と顔料の分散安定性 (III)

高分子の吸着と顔料の分散安定性 (III)

高分子の吸着と顔料の分散安定性 (I)

高分子の吸着と顔料の分散安定性 (I)

高分子の吸着と顔料の分散安定性.II

高分子の吸着と顔料の分散安定性.II

Adsorption of polymers and the stability of pigment dispersions

The stabilization of dispersions of titanium dioxide and iron oxide pigments in benzene by polyesters of adipic acid and neopentyl glycol terminated with different functional groups has been studied. Adsorption of the polyesters corresponded to approximately a close-packed monolayer, being somewhat lower for the hydroxyl-terminated polyester. Stability of the pigment dispersions was high in solutions of carboxyl- or hydroxyl/carboxyl terminated polyesters, but extremely low with hydroxyl-terminated polyesters. Interaction of the ester groups with the pigment surface was found to occur at low surface concentrations, but not at higher concentrations, suggesting that at low concentrations the polyester molecules lie flat on the surface, while at higher concentrations the polymer lies on the surface in random coils. The dispersed pigments were found to be uncharged, and stabilization by an adsorbed layer mechanism is postulated.