Plays So Well with Others: New Dispersing Resin Technology Offers Viscosity Control, Compatibility, Efficiency and Higher Pigment Loading

By Kay Sanborn, Rohm & Haas | 06.09.09

For printers, it’s never business as usual. Higher strength inks must roll onto ever finer line screens. Presses speed up as substrates diversify. Large runs split into smaller jobs that require different equipment settings. And through it all, press operators grapple with ever more precise technical specifications from customers expecting photographic impressions that really pop from magazine pages and packaging.

Fortunately, newer, more flexible dispersing resins that yield higher strength dispersions with better viscosity control, improved resolubility and better compatibility are riding to the rescue. In the quest for press runnability, efficiency and cost management, an innovative dispersing technology can be the effective team player that brings new skills to this very competitive arena.

Limitations with Conventional
Dispersing Resins

Pigment dispersing resins necessarily perform several functions. First, they serve to properly wet out dry, powdered or wet presscake pigments during the premix or incorporation step.Next, they adsorb onto the primary pigment particle during the dispersion phase.Last, they provide a stable suspension that ideally resists flocculation, reagglomeration and viscosity increase for an extended period. Attaining desirable rheology, stability and color can be a tricky art dependent on many factors like pigment type, pigment source, pH, temperature, percent pigment, pigment to binder ratios, adjunct surfactant use and even dispersion equipment type.Polymer choice has its own set of variables that include molecular weight and distribution, functionality, composition and solubility in water, to name a few.

Fig. 1: Dispersion viscosity stability with four process colors.
All too frequently, traditional dispersing resins have been inflexible or unforgiving, displaying limitations in pigment loading capacity, instability with offshore pigments and printing difficulties with finer/ higher line screen anilox rolls. Further, inks made with traditional resin dispersions must be monitored on press for changeable parameters, like pH, that affect resin solubility and ink viscosity. For example, even slight drops in pH may substantially increase ink viscosity, leading to the domino effect of adding water, thereby lowering color density and solid content, which may subsequently harm print quality.

In sum, good dispersing resins, while only one component of a dispersion, fill an important role on the dispersion team. They must play well with others – waxes, surfactants, defoamers and the like – and excel in many different games and arenas. To stretch a metaphor further, if you choose a finicky dispersing resin, it just might take its ball and go home, causing the rest of the team to mill about or freeze in confusion. The wrong resin can disrupt the final ink formulation’s viscosity, letdown performance, stability, gloss, transparency, rheology, resolubility, water resistance and dry speed. Selecting the right one is critical to an on-spec final result.

Higher Efficiency Dispersing Resins Offer Range of Advantages

Newer resins may even lend qualities and work-flow efficiencies printers hadn’t dared to hope for. Rohm and Haas, widely known in the graphic arts industry for their emulsion products like Lucidene and Rhoplex, recently rolled out Morcryl 410 and Morcryl 460+, two new styrene acrylic-based dispersing resin products for organic pigments in aqueous media. These new high efficiency polymers allow higher pigment loadings at higher pigment to binder ratios without compromising on color density and viscosity stability.

It seems that older choices often necessitated minimum thresholds like two to four parts pigment to one part binder, while the new Morcryl options allow six to one ratios. Further, the company’s testing and customer experience indicate that the technology allows higher pigment loading. These offerings have made possible dispersions with pigment loadings of more than 40 percent.

The technology’s design also facilitates broader compatibility with pigment types and other additives including conventional and neutral letdowns, an advantage when employing these resins in formulations destined for in-plant dispensing equipment. These characteristics can be expected to expand formulation possibilities.

Printers know well that offshore pigments are lower cost but often contain minerals, salts and other residuals that complicate formulating. This new technology eliminates some of the guesswork and performs well with fewer adjustments for different color requirements; in all, achieving outstanding dispersions with some very challenging pigments where other products fail.

Supplied in liquid form, the flexible new resins allow printers to dial in the desired performance, whether they run neutral, conventional, hybrid or reverse hybrid processes.

Neutral, Conventional,
Or Hybrid?

Soluble at pH 7.0 but suitable to run from pH 7.0 to pH 9.5+, newer dispersing resins offer unique advantages for increasingly popular neutral pH processes. Neutral pH emulsions address typical runnability issues, keeping viscosity stable while offering good resolubility/dry speed balance and excellent transfer properties. Dispersions based on Morcryl 410 and Morcryl 460 can be used with these emulsions and also enhance the finished product, adding benefits such as improved transparency with outstanding trapping, water resistance, and a clarity/gloss that approaches UV shine.

Additionally, customers report lower total print job costs due to reduced clean up and less down time. Rohm and Haas offers a specially developed cost calculator that enables printers or ink formulators to calculate cost savings brought about by these efficient polymers.

Testing, Testing, Testing

Rohm and Haas has tested the mettle of these new products in finished inks in a variety of different applications at customer facilities and print testing centers in the U.S. and Europe. Trials have compared all neutral inks incorporating Morcryl 460+ resin against conventional inks and hybrid inks (a conventional dispersant with a neutral letdown) containing Morcryl 410.

Fig. 2: Neutral pH vs. Conventional Technology pH/viscosity Profile.
Data has revealed that inks prepared with dispersions at higher pigment loadings print more strongly at very thin film applications to produce higher quality detail. Additional results show excellent transparency and gloss with improved transfer when using all neutral pH inks or hybrid type inks.

Testing also vetted the products’ performance on a range of different substrates and equipment types. Surprisingly, shutting presses off and leaving ink in the pan anywhere from four hours to an entire weekend didn’t dry in on anilox rolls or etched cylinders, and even printed well after 60 hours in the pan.

Availability, Supply, Support

Given changes in the graphic arts polymer markets, ink manufacturers and printers are paying particular attention to issues of reliable supply, adequate capacity, product consistency, and of course, supplier responsiveness. Having acquired Morton’s graphic arts expertise some years ago and adding its own R&D capabilities since, Rohm and Haas is fully committed to supply products and innovation with top notch and responsive technical service. The company regularly tests customers’ pigments, ratios and processes to rapidly generate data and recommendations that can apply immediately to their equipment, schedules, and jobs. Loading, ratios, stability and compatibility for every pigment tested thus far have not caused any problems. In addition, these new dispersing resins are reported to be innovative tools that can help both high and low-volume users easily test possible formulations.

Kay Sanborn has worked at Rohm and Haas for 27 years as an applications researcher, technical service manager, product line manager and market developer. She is currently working at the company’s Charlotte Technical Center, specializing in the graphic arts area. Ms. Sanborn has been instrumental in the development of new dispersing resins, Morcryl 410 and 460.

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