Special ORMOCER^®-based functional coatings

Pure ORMOCER^® coatings have no effect on heat radiation, but infrared-reflecting surfaces can be created through the targeted incorporation of aluminum pigments. This results in a low heat radiation emittivity, which prevents the surface from cooling down too much. At the same time, hydrophobic treatment of the layer prevents moisture or water accumulating on the surface. Depending on the application, e.g. application of facades, this can prevent the growth of microorganisms and mould formation. The surfaces therefore remain clean, while the reflective effect is retained. In this case, ORMOCER^® coatings are characterized by an adjustment of IR absorption, thermal stability and good pigment compatibility.

Due to their inorganic partial character, ORMOCER^® coatings are characterized by a very high temperature resistance (continuous exposure between 220 °C, short-term exposure up to 250 °C). A flame retardant function is possible by targeted additivation. Commercial flame retardant additives (e.g. Rucoflam^®) or Fraunhofer ISC developments (LDH layered silicates) can be used for this purpose.  Incorporated into the ORMOCER^® matrix, these ensure that the barrier effect of the layers against oxygen increases and thus a flame reduction can occur. By incorporating oxygen into the intermediate layers of the silicates, the smoke and harmful gases are reduced.
Applications for such layers include home textiles (upholstery fabrics or floor coverings) or work textiles, but also automotive/public transport panels.

ORMOCER^® flame retardant coatings therefore also prove to be a suitable matrix material for functional additives. Their actual function is supported by the fact that the formulations of the additives can be easily adapted so that they can be incorporated homogeneously. It is also possible to maximize the proportion of additives in such a way that other coating properties, such as thermal stability, also support their main function.

Photocatalytic coatings represent a cross-sectional technology. In addition to antimicrobial properties and superhydrophilic surfaces, they can also create self-cleaning surfaces. The functional additive responsible for this are TiO₂ particles (anatase).

UV radiation causes the formation of oxygen and hydroxyl radicals, which are extremely hydrophilic and leads to immediately spread of water on the surface. This can reduce the contact angle of a coating by up to 70°. These radicals are also able to oxidize and decompose organic substances.

This process takes some time, but continuous UV radiation significantly degrades colorants, aromas, microorganisms, etc. within a few hours. The effectiveness and time dependency depend on the structure of the contaminations. The ORMOCER^® layer acts as a binder system for the anatase particles here. Due to its inorganic content, it offers significantly higher stability against radical-induced degradation compared to purely organic layers, while at the same time chemically fixing the particles.

ORMOCER^® layers are usually very smooth and can have roughnesses of < 2 nm, but they can also be structured. A more random structuring is achieved by incorporating particles. In addition to adjusting the gloss level (from matt to high-gloss), this structure can also contribute to the hydrophobicity of surfaces via the well-known lotus effect. The reactive groups of ORMOCER^® components can also be used to chemically bind the particles and thus achieve better stability.
The adjustment of the gloss level is relevant for automotive or furniture surfaces, for example, while the water-repellent character can also be used for household or technical appliances or textiles.

However, the surface can also be structured by mechanical molding in the sub-micrometer range to create a broadband anti-reflective coating. The layers are hardened using UV light after the actual embossing process. Possible geometries include moth-eye structures, can be realized and are well- known from nature.

Normally, ORMOCER^® hybrid layers mainly have a passive function. However, they can also be designed to take on an active sensor function due to incorporated reactive centers. They prove useful, for example, in CO₂ or SO₂ gas sensor layers for industrial processes (including occupational safety), for monitoring air quality in living and working spaces or for optimizing plant growth. The gases react with a specific functional group in the siloxane structure and form an adduct that differs from the original state, e.g. in its refractive index. This change can be directly detected optically. As the adduct formation is reversible, the drop in the gas concentration can also be tracked visually, so that comprehensive control and monitoring is possible.

The Fraunhofer ISC has also developed a glucose sensor based on an indirect measuring principle. For this purpose, the oxygen consumption of glucose oxidation is detected in the ORMOCER^® layer by an integrated oxygen-sensitive metal complex, which proportion changes depending on the glucose concentration. The changed oxygen concentrations are then detected by changes in the fluorescence spectrum of the metal complex. The application is in the area of monitoring blood glucose levels in diabetics, for clinical research for studies on blood glucose regulation and control or for food quality control.

ORMOCER^® materials are therefore characterized by their strength in adaptability and the possibility of incorporating functional silanes or other functional molecules.

Thanks to their glass-like basic structure, ORMOCER^® coatings have very good adhesion, especially to glass. Silicone structures and the organic content make ORMOCER^® coatings flexible. Optical fiber sensors for measuring pressure, strain or temperature require precisely this property. ORMOCER^® formulations with an adapted modulus of elasticity have been developed for optical strain sensors (e.g. for the medical or optoelectronics sector). They are flexible that small bending radii are possible. The formulations were adapted in such a way that the application process for glass fiber coating could be designed inline and with a simple curing process. Thanks to a low solvent content and UV curing in a matter of seconds, the glass fibers can be coated directly on the fiber drawing tower. They have no negative impact on light conduction and force transmission, e.g. during pressure measurement, and protect the glass surface against mechanical damage and chemical influences.

Particulate additives can be incorporated into the ORMOCER^® formulations to make the layers conductive, for example. The coating acts here as a binder system. However, (bio)ORMOCER^® materials can also be used specifically as crosslinking binders, for example in wet strength additives for corrugated board adhesives. The many reactive cross-linking sites allow other molecules to be covalently linked together. For this purpose, it is important to modify the synthesis so that the silanol groups are still available. Similarly, the drying process should provide sufficient energy for the crosslinking of the ORMOCER^® coating while the layer is drying.