Solus™ Additives for Gravure Inks

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Eastman has developed a new line of products for ink formulators called Solus™, cellulose-based performance additives that improve the durability and visual quality of inks. These additives are soluble in a variety of organic solvents and form clear solutions. When used in gravure ink formulations, Solus™ provides the following performance factors critical to enhancing durability and appearance.

 

• Increased toughness and scratch resistance
• Enhanced adhesion
• Reduced pigment settling and gravure cell clogging
• Improved blocking resistance

Solus™ was evaluated in shrink film ink formulations and lamination inks to quantify the impacts on performance described above.

Solus™ in Shrink Film Inks

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One of the more demanding applications for gravure inks used in packaging is shrink film ink, which is subjected to a higher degree of physical stress than many other ink formulations. In this application, inks are exposed to high heat and shear stress while they are being shrunk. In fact, shrink films may reduce in size by about 40%–80% when treated; thus, cracking or detachment of inks may occur.

Increased Durability

Film Toughness

Nitrocellulose is a common ingredient in solvent-based gravure inks used to provide film formation, improve flow and leveling, and reduce drying times. Solus™ additives are used in a similar fashion in ink formulations, but compared to nitrocellulose, they impart a higher degree of toughness. Below, four test panels were prepared, with four different ink formulations applied. One contained Solus™ and the other three contained one-fourth or one-eighth nitrocellulose (NC). As seen below, the formulation containing Solus™ maintained a good film and did not embrittle upon curing, indicating comparatively better durability. The nitrocellulose formulation that maintained its film structure was the one that contained a plasticizer.

Better Adhesion

Solus™ also helps improve ink adhesion to shrink film substrates under exposure to hot water. The same ink formulations described above, containing one-fourth NC, one-fourth NC plus plasticizer, one-eighth NC, or Solus™, were tested for adhesion on a PVC film under ambient temperature, hot-air shrinkage, and hot-water shrinkage. Below, a score of 5 indicates the best adhesion with no peeling, and a score of 1 indicates the worst adhesion with ink film peeling. The results show that only the ink formulation containing Solus™ withstood shrinkage by hot water and did not exhibit peeling.

Film Toughness

Blocking is a condition that decreases both the appearance and durability of inks. Blocking may occur during shrink film manufacturing steps after ink printing, such as drying and film winding, where pressure and heat are present. Solus™, being a high Tg additive, helps increase the blocking resistance of ink films by increasing heat resistance and lowering dry-to-touch times. Comparing reverse-gravure printed inks containing NC or Solus™ on shrink films, the ink containing Solus™ did not exhibit ink transfer from the film to glass bottles over seven days at room temperature. Comparatively, some NC inks did transfer from the film to the bottles.

Enhanced Abrasion Resistance

Abrasion may occur naturally during the handling and transport of films and finished products. Compared to NC, Solus™ improves the scratch resistance of ink films more significantly. Below, scratch resistance tests were run with the four ink formulations to determine nail scratch resistance, pencil hardness, and pendulum hardness. The results indicate Solus™ improves durability through a higher nail scratch resistance value, pencil hardness, and number of König pendulum oscillations.

Images are presented below of the nail scratch resistance tests, depicting two different samples of Solus™ providing better performance.

 

Improved Appearance

Gravure Cell Clogging

In gravure printing, clogging is an issue stemming from inks drying in the cells of a gravure cylinder, causing uneven print coverage on substrates. Nitrocellulose resins have a propensity to cause clogging; replacing NC with Solus™ can help reduce clogging issues. Tests were made using the one-fourth NC ink and the Solus™ ink, where they were printed using an RK printing proofer. Then, the ink was washed with a solvent blend, revealing several more clogged ink particles deposited on the film in the one-fourth NC sample versus the sample containing Solus™.

 

Pigment Stabilization

Solus™ also helps reduce pigment settling in ink formulations, helping to ensure a more even viscosity and color strength in prints. Below, two different Solus™ samples were able to prevent aggregation of a white ink sample better than one-fourth NC after inks were stored in a 50°C oven for seven days.

 

Solus™ in Lamination Inks

Solus™ also helps improve performance in lamination inks in many of the same ways that it does for shrink film inks. Antiblocking is a key functionality needed in lamination inks to permit higher drying temperatures and winding tensions for increased print throughput. Polyurethane (PU) inks are commonly used in flexible packaging laminates due to their high durability, chemical resistance, and bond strength. On their own, PU inks do not have sufficient antiblocking properties. To test the improvements Solus™ makes to antiblocking properties, magenta and cyan PU inks were prepared with and without Solus™. Below, results indicate higher antiblocking performance in inks containing Solus™ than those without. Also represented in the chart are properties of these inks to show that Solus™ did not have a significant impact on other qualities.

*0 indicates a sample with the highest area blocked, 5 indicates a sample with no blocking

 

Summary

Solus™, a cellulose-based performance additive, provides many performance benefits when incorporated into ink formulations used in gravure printing. It makes inks more durable by improving adhesion, antiblocking properties, resistance to abrasion, and film toughness. These qualities are important for inks such as reverse-gravure printed shrink film inks and polyurethane lamination inks. Solus™ also enhances the visual quality of inks by preventing gravure cell clogging and ink settling. Several Solus™ grades exist that are designed to improve the performance of gravure inks. Click here to explore options, where the Solus™ 1000 series indicates grades made specifically for ink formulations. ChemPoint is here to help you with grade selection, formulation assistance, and samples. Click below to discuss your formulation with us.