Effects of Binders and Additives on Inkjet Coating Pigment Pore Structures, 2011 PaperCon Conference

Please Note: This document will be available in PDF format in the "My Electronic Documents" link on the home page once your order has been completed. Please make sure you have the latest version of Acrobat Reader. Click on the Acrobat Reader icon to check for the latest version, it’s FREE. To print a hardcopy of a PDF file correctly you must have a postscript printer. If you are not sure if your printer is a postscript printer please refer to your owner’s manual.

Purchase of electronic (downloadable) documents made at www.tappi.org by credit cards, followed by instant download CANNOT be cancelled. We do not offer refunds on electronic download documents.

This study considers the evidence for pore volume loss, studied by mercury intrusion porosimetry, of inkjet coating structures when using certain binder types and polymer additives. It is shown that starch is particularly disadvantageous as it not only prevents access, when film formed, to the crucially absorbing pores, but is itself non-absorbing. Polyvinyl alcohol (PVOH) on the other hand does absorb up to ~30 % of its own weight of water, but if present in pores acts also to limit the absorption rate by reducing it to the interpolymer matrix diffusivity, and reduces the volume according to the loss of pore space by the presence of the PVOH. It is also shown that latex particulate binder can be used to allow continued access to the nanopore region within the porous pigment particles by choosing the right glass transition temperature, Tg, and chemistry of the synthetic polymer. Similarly, the permeability can also be maintained to a large extent when adopting particulate binder. Depending on ink type, pigmented or dye-based, the coating can be dispersed either anionically or cationically for pigmented inks, but the coating must be cationic to enable the development of water fastness when considering anionic ink dyes. This requirement adds another source of pore volume loss, and hence degraded printability, as the added cationic polymer, such as PolyDadmac, used to achieve cationising, itself reduces the available pore volume for absorption by distributing itself on the pigment surfaces and within pores. Linking this pore volume loss to increased feathering and intercolour bleed supports the need to re-consider carefully the use of water soluble polymers and binders, and indicates that coating formulation optimisation for the future, when using cost-effective porous pigments in inkjet coatings, points to the minimising of charge conversion requirements and the development of improved particulate binders.