Optimizing dispersion in sublimation inkjet inks: unveiling the role of sodium naphthalene sulfonate formaldehyde condensate as a co-dispersant

Abstract

The primary challenge in the development of sublimation inkjet inks lies in achieving a uniform, low particle size, and stable dispersion of pigments. This study addresses this issue by exploring the incorporation of sodium naphthalene sulfonate formaldehyde polymer (SNF) as a co-dispersant. Sublimation inkjet inks must maintain a particle size below 200 nm to ensure optimal printing behavior. The investigation focuses on the impact of SNF incorporation in the dispersion process of direct red 60 pigment and its optimum usage level. Results indicate that the presence of SNF in the formulation, at a concentration of 20% by weight of dye, optimizes ink behavior during dispersion. Comprehensive analysis techniques such as rheological characterization, turbidity monitoring over time, UV–Vis spectroscopy, filterability measurement, and dynamic light scattering analysis demonstrate the superior performance of the SNF-treated sample with SNF to dye weight ratio of 20% in achieving stable, uniform, and low particle size dispersion of pigment in the ink as well as flowability and rheological properties. However, further evaluation from the perspectives of printability and transfer yields unexpected findings. Contrary to the conventional assumption that inkjet inks with better dispersion exhibit superior overall performance in the final printing product, the SNF-treated sample with the tiniest and most uniform particle size and the highest flowability shows inferior performance in the transfer process. Colorimetric analysis of printed samples on transfer paper and polyester fabric reveals that sample with the tiniest particle sizes and the highest flowability penetrates deeper into the transfer paper, hindering their effective transfer to the fabric, especially at low transfer temperatures. In other words, while SNF exhibits a desirable effect on sublimation inkjet ink formulation, its optimal usage level must be carefully optimized, considering not only dispersion quality but also the colorimetric aspects of the final printed product. This underscores the importance of a nuanced approach to formulation optimization to achieve optimal printing performance in sublimation inkjet printing on polyester fabrics.