Lupasol® Improves Inkjet Ink Performance

Inkjet printing has recently seen increased adoption within both the consumer and industrial printing segments for several reasons. For consumers, inkjet printers appeal due to their ability to print higher-definition and more color-accurate photos, plus they are relatively cheaper to purchase than laser printers.

Inkjet offers industrial printers greater speed and flexibility to switch print jobs or accept smaller jobs. In offset, flexographic, and gravure processes, these adjustments require ordering or creating a dedicated printing plate, which makes for a lengthy and costly process. The benefits that inkjet provides are not without challenges, however. From an ink formulation perspective, ensuring consistent image quality and durability can be difficult, especially when varying substrates and environmental conditions come into play. BASF has developed Lupasol® polymers for inkjet ink formulators to facilitate higher-definition, water-fast, and more durable prints.

BASF Lupasol® SC-61B

Lupasol® SC-61B is a multifunctional, cationic, branched polyethyleneimine (PEI) additive manufactured by BASF used in dye or pigment-based ink formulations to provide the following benefits to inkjet inks:
 

• Higher waterfastness
• Superior image definition and reduced intercolor bleeding
• Decreased nozzle blockage through better pigment dispersion and stabilization
• Adhesion onto plastic substrates

Structurally, Lupasol® SC-61B is a hydroxyethylated, water-soluble polyethyleneimine made by the reaction of a high–molecular weight PEI with ethylene oxide.

Lupasol® polymer	Ethoxylated Lupasol® SC-61B polymer

Lupasol® SC-61B is infinitely soluble in water and also soluble in aprotic, nonpolar solvents. It carries an extremely high positive charge density that creates a strong affinity and charge-balancing properties for anionic substrates. Hence, Lupasol® is excellent at promoting adhesion between dissimilar materials and substrates, such as ink and paper. This is a key property for inkjet formulations, as it serves to adhere dyes and pigments tightly to the paper substrate and leads to several performance benefits. Below is a depiction of the interaction of Lupasol®, pigment molecules, and paper.

Increased Waterfastness

Inkjet ink formulations for paper commonly consist of surfactants, biocides, dyes and pigments, water-soluble solvents, and water. Typically, dyes and pigments are water insoluble and must use wetting additives and dispersing agents to enter the ink solution. However, once the ink is deposited onto the substrate, the dyes and pigments that have been made water-soluble will readily redissolve, causing the print to lose its integrity. Lupasol® increases the adherence of dyes and pigments to paper, improving the waterfastness of ink formulations to help maintain image quality when exposed to water.

High Image Definition and Low Intercolor Bleeding

Inkjet technologies create precise images on paper by depositing ink droplets in calculated positions. Controlling the spread of dyes and pigments once the ink droplet is deposited onto paper is key to producing sharp, high-definition images. Lupasol® assists by ensuring that more dye and pigment molecules adhere closer and tighter on the paper’s surface. This prevents ink from traveling too deep within the paper or spreading out too widely on the surface, contributing to a loss in image definition. Additionally, intercolor bleeding is reduced.

Since Lupasol® helps improve binding dyes and pigments in ink droplets to the intended location on paper, it also lowers the chance of interspersing with neighboring dyes and pigments. Below is a comparison of ink sets with and without Lupasol®, showing the vast improvements that Lupasol® provides in reducing intercolor bleeding.
 

Ink set without Lupasol®
Ink set with Lupasol®

Better Pigment Dispersion and Reduced Nozzle Blockages

In addition to the pigment-binding properties stated above, Lupasol® also functions as a good cationic dispersing additive for nanoscale-sized solids, like pigments. Therefore, it facilitates better pigment dispersion, providing easier processing and higher color strength. Below is an image demonstrating how Lupasol® improves flowability and workability by reducing the agglomeration of pigments in a solid pigment dispersion.
 

With 0.4 wt% Lupasol®	With 0.2 wt% Lupasol®	No Lupasol®

This property also lowers the chance for pigments to agglomerate when dispersed in inkjet formulations, decreasing the likelihood for pigment agglomerates to block inkjet nozzles, leading to lengthy and costly downtime for cleaning.

Adhesion to Plastic Substrates

One of the newer areas where inkjet technologies are growing is printing and labeling packaged goods. Plastic is often used to construct these packages, both in rigid and flexible formats, and many low surface energy plastics, such as PE, PP, PET, PVDC, and polyamides, are used. Thus, it is difficult to achieve good ink adherence. Since many of these plastics and substrates used in packaging are anionic, the cationic Lupasol® polymer significantly increases ink adhesion by improving the binding of pigments, dyes, and anionic resins to these surfaces. This results in ink formulations that are more durable and versatile, further extending inkjet’s utility beyond creating images on paper.

Summary

From packaging to printed media, inkjet is becoming a more widely adopted printing technique. However, achieving consistency with image quality, durability, and ink adhesion is difficult, especially given the various substrates that can be used and environmental conditions the ink must endure.

BASF’s Lupasol® SC-61B is a highly charged cationic polymer additive that increases adhesion between dissimilar materials. Thus, it increases inkjet ink waterfastness and image definition by improving the adherence of dyes and pigments to their intended locations on paper and reducing bleeding to the surrounding areas. It also enables ink formulations to be applied on a variety of plastic substrates. As an added benefit, Lupasol® serves as an excellent pigment dispersion agent, making ink formulations easier to prepare and decreasing printer downtime from plugging due to pigment agglomeration. Click below to learn more about Lupasol® SC-61B and request a sample today.