Pigment dispersion processing, optimization for higher pigmentation
Abstract: One way to make a UV curable ink is to mix a pigment dispersion with monomers, oligomers, photoinitiators and additives. Creating a pigment dispersion is in many cases the first processing step of making a UV curable ink and is of large importance. To process pigment dispersions of Pigment red 2 and Pigment red 122 a premixing step with a dissolver is used followed by a grinding step employing a three-roll mill. The components for the dispersions are a monomer/oligomer blend of acrylates, pigment and a dispersing agent. The optimal monomer/oligomer blend of acrylates were determined by the Daniel flow point method. When processing using a three-roll mill the process time becomes of great importance, alongside with the final viscosity of the dispersion. Each dispersion was passed three times over the three-roll mill and the passing times were recorded to get the processing time. To find a correlation between processing time and viscosity a design of experiment was conducted for the two different pigments. The design of experiment model was of the extreme vertices design type which allows setting upper and lower boundaries for the input variables. From the design of experiment an expected viscosity and processing time could be estimated. For Pigment red 2 the model suggested a processing time of 14.47 grams/min and a viscosity of 44.58 Pa's. The actual processing time came out as 16.46 grams/min with a viscosity of 49.10 Pa's. For Pigment red 122 the estimated processing time was 24.35 grams/min with a viscosity of 43.04 Pa's. The results were a processing time of 22.98 grams/min with a viscosity of 43.80 Pa's. The use of the Daniel flow point method combined with design of experiment allows for an efficient way of screening new pigments and monomer/oligomer optimums for UV curable inks.
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