Polyurethane-based glass coatings offer attractive design alternatives to molten glass
Glass bottles, transparent or frosted windows, decorative elements in household furniture and fittings – glass is very much a part of our everyday lives, and has been for centuries. Now polyurethane-based coatings are opening up new perspectives for colored glass – as an attractive alternative to coloring molten glass.
Conventional colored glass is expensive and frequently contains toxic heavy metals, which makes recycling tricky. If glass is colored by means of an organic coating instead of the traditional tinting method, only one transparent glass melt is required instead of a separate melt for each color. Another advantage is that specific colors can be produced in small batches without using heavy metal salts. Moreover, coatings make a greater variety of colors and surface textures possible. Last but not least, coated glass is easier to recycle because there is no need for sorting. When the glass is melted down, any organic material in the coating’s binder is simply combusted.
Functional benefits
The polyurethane-based coatings used to color glass can also perform functional tasks such as making glass more shatter- or dishwasher-proof and increasing its scratch or internal stress resistance. A coating just a few microns thick significantly improves the internal stress resistance of lightweight glass bottles. Trials with mineral water bottles have proved that polyurethane-based coatings prolong their working life through improved scratch and burst protection. Besides enhancing resistance to abrasion and chemicals, PU-based coatings can also produce special effects such as frosted, metallic, pearl or soft-feel glass. In the case of frosted glass this avoids the use of harmful chemicals.
Attractive alternative
These aqueous organic glass coatings are made up of two components: an OH-functional polyol with an adhesion enhancing siloxane additive and the respective coloring agent; and a waterthinnable blocked polyisocyanate. The formulation is highly stable in storage and can be handled and applied like any 1K product. Once the water has evaporated, the coating is baked for 20-30 min. at around 170° C. At these high temperatures the isocyanates are unblocked and cross-link with the polyol. The aqueous dispersions are marketed under the Bayhydrol® and the polyisocyanate crosslinkers under the Bayhydur® brand name. Although originally designed for bottles and glasses, coated colored glass is increasingly being used for decorative purposes in kitchens or furniture, and we have products for every segment – from low-price to high-end.
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