The decorative graphics sometimes found on perfume bottles, beer mugs, and baby bottles, etc., are often made of special glasses containing lead oxide, which can be a health hazard.
In order for printing inks to be durable, they must be made of chemically resistant glass, which usually contains a lot of silicon dioxide. This glass is melted above 1600 degrees Celsius — a temperature at which the base glass would normally deform. The added lead oxide lowers the melting temperature to below 600 degrees Celsius, creating viable processing conditions.
In preparation for a future EU Directive to banish potentially unhealthy lead oxide, some manufacturers are replacing lead oxide with bismuth oxide. But bismuth is also dangerous to health and the environment and it increases the cost of imprints. A new development by researchers at the Fraunhofer Institute for Silicate Research (ISC) (Germany) and the Forschungsgemeinschaft Technik und Glas e.V. (Germany) addresses this issue.
Lead-oxide-free colors have a high color brilliance and are chemically resistant.
© Fraunhofer ISC / K. Selsam-Geißler
“We have developed lead-oxide-free decorative paints, which do perfectly well without toxic substances,” says Anika Deinhardt, researcher at the ISC. “They are easy to process, have brilliant color, are chemically resistant, and do not contain rare or expensive elements.”
The basis of these novel decorative paints is a glass that consists of mainly zinc oxide with aluminum oxide, boron oxide, and silicon dioxide (ZABS). Zinc oxide ensures the glass melts below 650 degrees Celsius.
“Through other additives, we are able to modify ZABS further and adapt it to the respective requirements,” explains Deinhardt. So far, the researchers have reduced the melting temperature to 580 degrees Celsius. Work is underway to produce glasses with a processing temperature of 540 degrees Celsius.
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