Ink Receptive Technologies - A Guide to Ink Receptive Coatings for the Digital Ink Markets

Ink receptive technologies (IRT) are those coatings that are designed to enhance the printing surface of any substrate⁽¹⁾ - paper, film or even textiles. Their purpose can be simply esthetic or used to add functionality to the printed material. IRTs have been in existence for a number of years in the printing industry, but have certainly undergone a renaissance in recent years.

Fig. 1: Example of textile printing with and without Ink receptive technologies.⁽¹⁾

(Photo: Courtesy of Lubrizol)

The way they work is by coating the surface of the paper or film with a material that will fill the microscopic voids in the substrate, making it easier for ink to gain adherence. These materials are typically formulated with synthetic silica and polyvinyl alcohol (PVOH). The ink droplets are rapidly absorbed in the micro-pores between the silica particles and this prevents the ink droplet from spreading, thereby creating a sharper image.⁽²⁾
 

Fig. 2: Photomicrograph of a cross-section of a PVOH coated paper after printing.⁽²⁾

In years gone by we would refer to these as simply primers, and in the analog world of gravure and flexographic printing, primers were and are being used to prepare the surface of substrates to improve ink laydown, gloss and even adhesion. But historically this side of the industry isn't big on using primers, and this is due in part to the limited number of print stations that are available for a primer. A typical 8-color press would dedicate 4 colors for CMYK, have 2-3 spot colors and then reserve the last station for an overprint varnish. 

The other deterrent to using a primer was the added cost that this contributed to the finished package, but the biggest reason of all for the lack of interest in primers is that ink systems for gravure and flexo printing tend to be tailored to the specific substrate or end use -  meaning that if a company is printing a food package, like a sandwich wrap, for example, the ink itself will be formulated with colorants that are safe for direct or indirect food contact, the ink binder will be formulated for things like grease and water resistance, and every aspect of the ink will be targeted with the finished package in mind.

In the digital world, things work a lot differently. The inks formulated for inkjet printing are typically made to work with specific print head technologies and printing platforms, as each ink delivery system demands careful attention paid to elements like viscosity, surface tension, particle size, drying speed and many other items. 

The idea of then altering that delicate balance to include components that can improve adhesion, or add flame retardance is a large undertaking and one that most don't want to tackle. Additionally with the wide range of substrates that are being used on a single printing platform, it would soon become very cost prohibitive to have one ink system for each substrate. And this is where IRTs come into the picture.