Sophisticated surfaces

Glass that doesn’t go blind in sand-storms or change color when viewed from different angles is fascinating.  This is made possible by coatings and surface modifications that result in stable processes for innovative customer solutions.

Inkjet printers enable high design flexibility. SCHOTT’s know-how lies in the chemistry of ceramic inks.

Glass that doesn’t go blind in sand-storms or change color when viewed from different angles is fascinating.  This is made possible by coatings and surface modifications that result in stable processes for innovative customer solutions.

Our motivation is to develop new properties and solve puzzles,” says Dr. Eveline Rudigier-Voigt. This is not so much about conventional puzzles as it is about scientific and technical issues: how can glass that is exposed to stresses such as corrosion, wear and tear, and many other effects be improved by altering its surfaces? How can glass surfaces, in particular, be manipulated in such a way, for example, that light reflects differently or not at all? What processes can be used for this and how can stable and economical processes be achieved in addition to new properties? This is precisely what interests the team in the Coating and Surface Modification competence area.

In order to solve such challenges and to modify surfaces to precisely meet customer requirements, the experts at SCHOTT Research have a toolbox at their disposal for implementing various property profiles. “Our ‘superficial’ approach requires a deep and detailed understanding of the materials of glass and glass-ceramics,” explains Dr. Rudigier-Voigt who has been at SCHOTT for 12 years. After all, layers must not only adhere to glass optimally but also be able to survive temperature cycles or sterilization processes, for example, without damage depending on the subsequent application. Besides the traditional coatings, surfaces can also be modified in a targeted manner by doping, activating or leaching, for example. These types of functionalizations often need to fulfill not only one property or requirement, but must also combine several of them.

 

Innovative processes for different (layer) designs

The traditional methods of enhancing glass surfaces are no secret: here, a distinction is made between plasma-assisted and direct gas-phase technology, as well as liquid coating technologies. These technologies are then adapted and optimized for a wide variety of glasses or glass-ceramics.

Key technologies for gas-phase coating include PVD (physical vapor deposition) and CVD (chemical vapor deposition), in which the coating materials are applied by the gas phase. The advantages of such vacuum processes are high precision and the deposition of extremely thin layers, from a few micrometers to a few 10 nanometers. These technologies are constantly being questioned, optimized and adapted with regard to their future viability and competitiveness. With plasma-assisted chemical vapor deposition processes, such as PICVD (Plasma Impulsed Chemical Vapor Deposition), a plasma pulsed in a few µs ensures a homogeneous special coating of complex 3D geometries, for the inside of pharmaceutical containers, for example.

Typical liquid coating technologies that SCHOTT uses include screen printing, inkjet and dipping processes, which can be used to apply a wide variety of coating mate-rials – also available in a structured form. As a comparatively new technology for glass and glass-ceramic coating, inkjet combines the advantages of high design flexibility with the possibility of economically realizing small batch sizes up to batch size one, making it an important component for future product developments, in the home appliance area, for example. The glass can be of various shapes and geometries: from flat and ultra-thin glass to tubes and formed pharmaceutical containers.

The main components for the respective functionality are the coating materials that are produced and applied using the previously mentioned processes. The process and synthesis go hand in hand. These materials can be organic,  hybrid or inorganic. The layer design, on the other hand, can consist of a single material, a gradient, a nano-composite or several layers (multilayers) depending on the functionality needed. Processes that achieve a change in the glass surface without direct coating are yet another component of realizing functionalities. The main emphasis is on developing wet chemical processes, from cleaning to etching. Experts on the team of Dr. Markus Kuhr, Head of Analytics, are responsible for this. Recently, however, the coating experts have also started researching modification processes that can be realized via the gas phase and especially through plasma processes.

First product tests are carried out on prototype systems. With the inkjet printer, different geometries – from flat glass to thin glass up to pharmaceutical containers – can be individually printed.
In the multi-process plant, functional coating materials with nanometer-sized particles can be produced.

Toolbox for every requirement

The easiest way to describe an overview of the functionalities that can be achieved by coating and surface modification (see graphic for examples) is to use a toolbox system. For example, coatings can be used to achieve optical, decorative, scratch-resistant, protective, tribological, electrically conductive or switchable properties, as well as surfaces with bio-relevant functionality such as protein-repellent properties.

The respective SCHOTT products range from optical glasses and filters, decorative flat glasses and glass-ceramic cooktop panels to pharmaceutical packaging and diagnostic slides. “There are always a number of fascinating questions for us: What is the best way to meet the customer’s requirements? What is really needed and how can the target functionality be best described? Are familiar solutions already sufficient or do we have to tinker around and develop something new?” says Dr. Rudigier-Voigt.

Top coating innovations

The coating team recently broke its own functionality re-cords with an innovation. Together with the Home Tech Business Unit, they developed the world’s first and only scratch-resistant glass-ceramic cooktop panel. The surface of CERAN Miradur® has a degree of hardness close to that of a diamond! Practically speaking, this means 95 percent fewer scratches from sand and 70 percent fewer scratches from abrasive sponges. The special coating meets all of the respective thermal, mechanical and chemical requirements and can be used with various heating technologies. The innovative lighting solutions of CERAN EXCITE®, which are also implemented by means of underside coatings, allow for new design options, by replacing the decor with light, for example – and at the same time increase user comfort through precise, visual feedback.

Microscopically thin double-sided Low-E coatings enable the oven doors of pyrolytic baking ovens to remain below 70° Celsius on the outside – and this during pyrolysis processes lasting up to five hours at temperatures of up to 400° Celsius. This is ensured by specially developed, highly efficient heat-reflective coatings that also shorten the heating up phase for the self-cleaning process.

With their innovative coating on the outer surface, EVERIC™ smooth pharmaceutical vials help eliminate a problem in filling pharmaceuticals: the outer glass surface is protected by this layer, which means that during processing on a filling line, the vials can be additionally protected against defects such as scratches. The transparent coating on the outer wall of the vials creates a low-friction surface while maintaining the optimized container strength. The result: an 80 percent improvement in the coefficient of friction for a smooth filling process. Side effect: cosmetic defects can be reduced by up to 95 percent.

A PICVD inner coat-ing enables highly efficient, transparent barrier layers for pharmaceutical packaging.
Coating gives glasses and glass-ceramics a variety of additional functionalities.

What does the future hold for coatings?

Comprehensive material know-how, a detailed overview of the portfolio, internal synergies, analyses and product tests, from which we learn time and again, coupled with the observation of worldwide technological trends, enable the experts at SCHOTT’s central research center to develop perfect and customized solutions for customers.

Other challenging puzzles that need to be solved are currently in the development of magnetic layers in the context of quantum sensor technology and glass as a functional (sensory) component. In addition, coated glass plays an important role in digitalized processes and products: glass can ‘communicate,’ for example, through functionalization with RFIDs or sensor elements that can register surface changes. Current trends such as sustainability, health and environmental protection are also increasingly important for the development of new surface functionalities. For example, future coatings will have to meet increasingly stringent requirements in terms of performance and service life, as well as regulatory guidelines. Researchers are committed to the creative design of surfaces and evaluate, among other things, the applicability of self-healing layers, functional layers with a defined morphology, or biomimetic surfaces for our SCHOTT products. No wonder that the puzzle-cracking among the coating experts is so successful and effective.

February 10, 2021

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Dr. Eveline Rudigier-Voigt
Research & Development
SCHOTT AG

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