Short timescale inkjet ink component diffusion: An active part of the absorption mechanism into inkjet coatings

The polar liquid (water) diffuses into the polymer network of hydrophilic binder polymer (polyvinyl alcohol, PVOH) and partially fixes there acting as a swelling agent. The water molecule diffusion opens the PVOH polymer network and the colourant of inkjet ink follows into the PVOH polymer matrix. In the case of styrene acrylate latex, the hydrophobic nature of latex prevents the diffusion of the polar liquid into the polymer network of the binder and there exists only a surface diffusion. The colourant of inkjet ink remains on the top of binder. [Display omitted] ► The polar liquid diffuses into the PVOH causing swelling and causing closure of some pores. ► The swelling of PVOH reduces pore diameters and pore volume of coating layer. ► At the beginning of liquid uptake, the small pores dominate the inkjet ink vehicle imbibition. ► The hydrophobic nature of latex prevents the diffusion of the polar liquid into the polymer. ► The polar liquid diffusion on the styrene acrylic latex is a surface diffusion. The structures of inkjet coatings commonly contain a high concentration of fine diameter pores together with a large pore volume capacity. To clarify the interactive role of the porous structure and the coincidentally occurring swelling of binder during inkjet ink vehicle imbibition, coating structures were studied in respect to their absorption behaviour for polar and non-polar liquid. The absorption measurement was performed using compressed pigment tablets, based on a range of pigment types and surface charge polarity, containing either polyvinyl alcohol (PVOH) or styrene acrylic latex (SA) as the binder, by recording the liquid uptake with a microbalance. The results indicate that, at the beginning of liquid uptake, at times less than 2 s, the small pores play the dominant role with respect to the inkjet ink vehicle imbibition. Simultaneously, water molecules diffuse into and within the hydrophilic PVOH binder causing binder swelling, which diminishes the number of active small pores and reduces the diameter of remaining pores, thus slowing the capillary flow as a function of time. The SA latex does not absorb the vehicle, and therefore the dominating phenomenon is then capillary absorption. However, the diffusion coefficient of the water vapour across separately prepared PVOH and SA latex films seems to be quite similar. In the PVOH, the polar liquid diffuses into the polymer network, whereas in the SA latex the hydrophobic nature prevents the diffusio