Precision molding is a state-of-the-art technology for the volume production of complex lenses. Generally used mold materials in the molding process exhibit a thermal stability of up to 650°C. However, a variety of so-called low transformation temperature glasses (low Tg glasses) is required for the precision molding process.

According to our definition, low Tg glasses have a Tg not higher than 550°C. Furthermore, the glass compositions of these glasses have been developed to have low tendencies to devitrification and reduced reactions with mold materials at the molding temperature range.

With specially developed compositions and transformation temperatures below 550 °C, low Tg glass can be directly pressed into the required aspherical shape. This leads to:

• Low tendencies to devitrification
• Longer lifetime of molds
• Low tendency to chemical interaction between glass constituents and mold materials within molding temperature range
• Reduced process time

In addition, these low Tg glass types are free of lead and arsenic.

Low Tg glasses for precision molding are often supplied for applications requiring pre-forms with the weight range of 30 mg and 12 g each. Hence, these are suited especially for the precision molding of aspherical lenses and other optical components in consumer products such as:

• Digital Still Cameras (DSC)
• Camcorders
• Camera Phone
• Digital Front Projectors
• Optical Communications

Low Tg glasses are available in various forms of supply, like spherical lenses and discs, precision gobs, rods and pressings. However, the most prominent one is currently the polished ball, which can be offered in a diameter range from about 0.8-14 mm and a surface roughness better then 3nm Ra (roughness average).

• Optical glasses for precision molding are selected based on the refractive index value and Abbe number at a reference annealing rate of 2 K/h.
• Tolerances for refractive index are ±0.0005 and for the Abbe number are ±0.5% (step 3/3 according to the catalog based on a 2 K/h reference annealing rate).
• Customers will receive preforms with a test certificate certifying the refractive index and Abbe number of the batch based on a reference annealing of 2 K/h. The actual refractive index of the glass within the delivery batch will differ from this value but this causes no problem during molding.
• For all P-type glasses (e.g. P-SK57, P-PK53, P-SF8, P-LASF47 and P-SF67) these specifications will be automatically fulfilled.
• For N-FK5, N-FK51A, N-PK52A and N-PK51 “P-quality” grade preforms shall be ordered.

• Polished aspherical lenses
• Precision molded aspherical lenses
• Optical glasses