Extreme Hard Glass CD



The world's first ever hard glass CD!

Astounding fine NF Crystal-Clear Sounds


The first of a series of music CDs made of hard glass, which delivers astounding, crystal-clear "fine NF" sound.


                N & F Co., Ltd. has been pursuing its dream of making high-quality music and audio recordings. Now that that dream has become a reality, thanks to an epoch-making disc technology we have jointly developed with "Toemi Media Solutions Limited".

                Unlike conventional CDs, which are made of plastic, the Extreme HARD GLASS CD is carefully handmade, piece by piece, from a toughened version of ultrahigh precision optical glass (the same material found in high-grade lenses), using proprietary technologies. Due to excellent physical properties unique to the hard glass disc, it represents the ultimate "dream CD”, featuring high stability and durability, conducive to the permanent preservation of a performance, not to mention the ability to reproduce sound at the high tonal quality inherent to the CD.


[] Six major features of the Extreme HARD GLASS CD (music CD made of high-grade hard glass):

1. Excellent physical properties: No temperature/humidity-induced disc warpage, or deflection due to runout.

2. Excellent optical properties: Since the substrate is glass and there is no birefringence (double refraction), more efficient laser readout and excellent signal-to-noise ratio are achieved.

3. High disc durability: Thanks to the use of toughened glass, permanent constancy is retained.

4. Enhanced precision on the time axis: As the disc has a large mass (33 grams, an upper limit specified in CD standards), rotation is very smooth, by virtue of the flywheel effect.

5. Stable mechanical characteristics (trackability): The servo system (the pickup's focusing and tracking) has better stability, and the reproduction system exhibits increased signal-to-noise ratio.

6. Excellent signal characteristics: Outstanding signal characteristics by dint of a high-precision ultrafine transfer method, made possible by a photocuring technology.

About the Development of HARD GLASS CD Technology

                This glass CD employs disc technology that was originally developed for use in adjustment stages at plants manufacturing optical disc/device products, such as optical disc pickups and optical disc drives.

                Although optical discs are being manufactured inexpensively in large quantities using resin material such as polycarbonate, they are in fact optical parts with very high precision. As with optical lenses, excellent material and superb production technology are required to obtain outstanding characteristics.

                There are two points to note about the manufacture of the HARD GLASS CD: Firstly, chemically toughened optical glass is used for the substrate and, secondly, a signal pit-forming technology, a photopolymer method employing a photosetting resin, is employed (see Fig. 1, illustrating the method of manufacture). In the photopolymer method, an ultraviolet-curing resin is applied onto a metal die (called a stamper) which is made of nickel and on which signals represented in the form of indentations (pits) have been formed. An optical glass plate is then placed on top of the resin coat. With pressure exerted on the glass plate, the ultraviolet-curing resin is hardened by means of ultraviolet irradiation. After the signals carried on the stamper have been transferred, the stamper and the glass plate are separated from each other. The rest of the process is the same as that used for the manufacture of ordinary CDs; a metallic reflective film is formed, a protective layer for the film is formed, and the label side of the CD is printed to complete the process.

                A major feature of the glass CD is that the use of optical glass eliminates the birefringence effect, a drawback of resins (see Fig. 2, illustrating optical properties). Birefringence is ascribed to the resin-hardening process following transfer of signals to molten resin when the disc is injection moulded, where the resin's molecular structure is disturbed. It causes laser light to undergo phase differences within the disc at the time of CD readout, thereby affecting signal-reading operation. Although CD standards require that birefringence be less than 100 nm, theoretically glass is free from birefringence.

                Another important feature is the disc's extreme stability toward environmental changes. With a conventional CD, a metallic reflective layer, a protective layer and a print layer are formed on the resin substrate. Because the thermal expansion coefficients of these layers differ from one another and the resin substrate has hygroscopicity, discs are subject to warpage caused by changes in humidity and temperature (see Fig. 3, showing physical properties). Warpage has a profound effect on the reading of signals. On the other hand, signal pit formation by means of the photopolymer method allows high-precision transfer, as separation from the stamper is accomplished after the ultraviolet-curing resin has fully solidified subsequent to the signal transfer.

                Figure 4 evaluates signal transfer performance in terms of jitter characteristics, comparing a resin disc and a glass disc, both of which have been replicated from the same stamper. CD signals consist of varying combinations of 9 kinds of signal, from 3T to 11T. Comparisons of the jitter characteristics of these individual signals show that the glass CD is superior by 1.5 to 2 nm for all signals. As discussed, the glass CD demonstrates better overall physical properties than resin disc.

                The two major advantages of this disc are the absence of temperature- and humidity-related physical disc deviation, and the use of the photopolymer method which, in contrast to conventional injection moulding, is capable of extremely high-precision transfer for the formation of indentations (pits) representing signals.(see Fig. 4, illustrating the high-precision ultrafine transfer method).