The Success Story

Printable mirrors

Working in cooperation with BYK, ECKART has developed a procedure for creating extremely thin, high-quality metallic pigments

The packaging is attractive and the paper a mirror-like gold. It looks really classy – yet if you peel off the adhesive strip, the golden printing ink comes off with it. And that does not look good. This kind of effect is bad for the image, especially with branded products in high-quality packaging, for example high-end perfumes or expensive cosmetics.

MIRRORGOLD and PLATINVARIO, two new types of effect pigments, do not flake off. The special advantage of ECKART's products is that the extremely thin metal particles (mean thickness ~ 30 nm) create an absolutely sharp and brilliant image – a mirror-like effect – because they arrange themselves horizontally to the substrate within the layer of paint or coating. This allows the surfaces already printed in gold or silver to be overprinted, for instance with lettering or another ink, which is a key requirement for printing inks used in packaging for high-end branded articles.

The two highly brilliant pigment types have yet another important advantage over other effect pigments. They have a much longer shelf life, i.e. twelve months instead of only six.

First ALTANA Innovation Award

Both of these properties are based on a manufacturing process developed by ECKART in cooperation with BYK. The team of developers from the two companies received the first Innovation Award ever presented by ALTANA. That was back in 2009.

"Four years later, our sales of these high-quality mirror-effect pigments are in the millions of Euros," says a delighted Dieter Prölss, Global Head of R&D Technology & Process Development. Now the developing team wants to score again: the manufacturing process is to be expanded to cover more applications. Once again ECKART and BYK are working closely together. But let's look at one thing at a time.

New milling process

When ECKART and BYK launched their project in 2006, the established milling processes for manufacturing metal-based effect pigments could indeed generate the familiar metallic effects, but not mirror-like effects. In this process either aluminum or brass powder is ground up in mills with a range of different grinding bodies, and formed into metal flakes with an average thickness of approximately 200 nm. To prevent them from agglomerating, a lubricant based on fatty acids is added during milling.

Yet these fats then prove to be a disadvantage in the pigment paste because they oxidize over time; high temperatures and high humidity accelerate this process. The pigments become unusable. "This was a major disadvantage for exporting our products to the booming markets in Southeast Asia and Latin America," says Dr. Stephan Roth, Senior Project Manager, summarizing the situation. "Often almost half of their product lifetime was over when they reached the customer."

Alternatives to fatty acids

So ECKART's developers started looking for an alternative lubricant. First of all, the ideal candidate should markedly extend the shelf-life of the products and, second, it should demonstrate a better lubricating effect during milling, to improve shaping of the pigment particles. The goal was to achieve extremely thin pigments that align themselves perfectly within the layer of ink or coating. Third, the lubricant should guarantee the "non-leafing effect." This is essential for embedding the ultra-thin pigments properly into the primer surface to make them split-proof.

With these requirements in mind, the ECKART developers contacted BYK, where Bärbel Gertzen, head of the product group "plastic and process additives," and Dr. Wolfgang Pritschins, head of synthesis development for wetting and dispersion agents, took on the job of developing the new product. BYK's approach could be described as "a different company, different chemistry and new perspectives."

Separating and encapsulating

The additive manufacturer has a wealth of experience with distributing and separating the smallest particles in the most varied systems and quickly focused on the following question: how to ensure that the metal particles were indeed well encapsulated, but are also properly separated from one another at the same time?

Bärbel Gertzen rapidly hit on the solution: "We needed a process additive with the right modification to achieve a balance between 'separation and stabilization.' We had to adjust the molecular weight of the polymer we were using. The molecular chain of the additive acting as a spacer must not be either too long or too short."

On this basis, the two teams then gradually narrowed down the structure and formulation of the additive, tested it on a larger scale in the BYK pilot plant, and finally developed it to product maturity. The result is a high molecular weight AB block copolymer based on renewable raw materials and with a specifically adapted molecular weight.

Roth, Prölss and Gertzen all agreed, "We have rarely experienced such intensive and transparent cooperation as in this project." The frank discussion of formulations and their effects sets an example for collaboration between the divisions within ALTANA, they said. "We managed to develop a common language," Gertzen emphasized, and continued, "That was crucial to our cooperation."

Three patents now protect the results from this development project. "This ensures that ECKART remains the only manufacturer producing mirror-effect pigments based on a number of different metals using an optimized procedure," Roth stressed.

Industrial application

MIRRORGOLD and PLATINVARIO are used in printing inks for the graphic arts industry, for example on labels or packaging for cosmetics or foodstuffs. SILVERSHINE S has been created for especially high-quality industrial coatings. It was developed from PLATINVARIO using somewhat coarser pigments. One example of its uses is application of a silver company logo to the backs of smartphones and tablet PCs.

The fact that these pigments are selling well is due not least to ECKART's marketing strategy. "We are in close contact with the major brands in the food and cosmetics industries," Roth says, adding: "This means that if necessary, we can provide direct support in the implementation of their design ideas."

The aim is to increase the proportion of effect pigments in the market for printing inks. At present it is around two percent. "Every new gold or silver-colored area on the label or packaging of a branded product increases our sales considerably," Prölss points out.

Alongside the mirror-effect pigments, ECKART also uses the newly developed additive for manufacturing all its finer pigments that are sold in Asia. There it is added after the traditional milling process, to improve the shelf-life of the products. That now gives ECKART pigments a major competitive advantage on the Asian market.

Further development for migration-free applications

Prölss and Roth want to apply the procedure to more additive recipes. To start with, they are planning an additive for stabilizing mirror-effect pigments in environmentally friendly, water-based coatings. After that they want to create an additive to render all of ECKART's pigments that are suitable for food packaging migration-free.

In fact the pigments already satisfy the legal food compatibility requirements in all the regions where they are used. But now the aim is to ensure that no substances of any kind can migrate from the packaging into the food, which adversely impact on its quality or affect the health of consumers. Initial tests for the new additive are already under way, Roth explains. It should be ready for market launch in 2014.