What's next for CD molding?

Despite constant emphasis on improving cycle times and quality, injection molding of compact discs has changed relatively little since disc replication moved from the clean room to the monoline some years ago. During that time, the most significant new technology for improving productivity was twin-cavity molds. But even the pressures of heavy competition and excess capacity in the marketplace have not yet caused its widespread adoption, owing to doubts about quality control.

A review of current trends in CD manufacturing with most key equipment suppliers turned up two other developments that could create new excitement in the CD business. Soon, the expected opening up of the market for high-density compact discs (HDCDs) will create new business and require disc replicators to establish new quality/productivity parameters. While HDCD may not require much new technology, the even newer concept of multilevel CDs will be a different story.

TWIN-CAVITY STILL RARE

Although technology to manufacture CDs using twin-cavity molds has been around for at least five years, few replicators have yet adopted it. Only a few molding machines can handle tooling to mold two discs at the same time with different stampers. Other than Robi System Inc. in Cherry Hill, N.J., and Marubeni America Corp. in Southfield, Mich. (both of which offer complete replication systems with twin-cavity capability), most machinery manufacturers and integrators have not developed twin-cavity molding systems because, they say, the technology is still "experimental."

"The technology has been around since the mid-1980s but there are a lot of technical risks," says Michael Hill, president of Multimedia Machinery Inc., Charlotte, N.C., which supplies masters, stampers, and integrated production systems. "We are among many in the industry watching to see whether this technology proves itself."

However, Digital Audio Disc Corp. (DADC), Terre Haute, Ind., has been using dual-cavity molding since 1988. According to Mike Mitchell, manager of process and R&D engineering, "We have never had a problem with the technology. Certainly, there can be an imbalance between the two cavities, but we have the engineering resources at our facility to ensure continued success with this type of molding technology. The majority of molding capacity in our original plant is dual-cavity. We even use this technology for extremely small orders of less than 200 discs. We modified our original single-mold machinery and increased productivity while virtually doubling efficiency - all at minimal cost." DADC has even produced CD-ROMs on the dual-cavity system.

Robi System engineering manager Jim Keating claims Robi's dual-cavity "Rondo Line" cuts per-disc cycle time to less than 3 sec (the twin-cavity injection molding cycle is about 5 sec), and two different titles can be produced at the same time. "We are even able to maintain the 3-sec cycle with CD-ROM discs that are well within Yellow Book specifications," Keating says, referring to the technical standard developed by Philips of the Netherlands.

Keating adds, "Twin-cavity molding is the most cost-effective way to manufacture CDs, since only one CD fine is required to manufacture over 7 million discs/yr. Down stream equipment is best utilized this way without the need to purchase dual process equipment." (CIRCLE 18)

Robi's Rondo line incorporates molding machines from Netstal Machinery Inc., Fitchburg, Mass. Netstal introduced a twin-cavity molding system in 1992 utilizing a standard "Disc 60" molding machine and a mold from GPT Axxicon of the Netherlands. But Robert Hayes, Netstal's manager of CD market development, does not believe that twin-cavity molding systems are suitable for everyone. "Netstal recommends the twin-cavity system to experienced replicators with longer title runs of 10,000 or more," Hayes says. "A center-gated disc in a single cavity is nearly an ideal part for moldability. Two cavities become more complicated with respect to dynamic balance in the mold, and require a tighter process window."

Marubeni, the other major supplier of twin-cavity molding systems (for about five years), also qualifies its recommendation of this approach. Marubeni supplies optical-disc manufacturing equipment as well as integrated replication systems utilizing Meiki injection machines from Japan. Twin-cavity systems are offered for both 3.5-in. CD singles and standard 5-in. discs. Toshio Koike, Marubeni's director of sales, says a twin-cavity mold should be run in 50- or 70-ton injection machines because 25-ton presses are not big enough to mount this type of tool. Koike points out that it is technically possible to run two titles simultaneously in a dual mold, "but it is not recommended due to title mix-ups by human error, as well as other economic considerations."

Like Netstal's Hayes, Koike recommends dual-cavity molds for runs of at least a couple of thousand discs. "Also, batch systems are more reasonable than in-line or monoline systems. With batch systems, if the number of molds and downstream equipment is well matched, the downstream equipment can remain operational while stampers are being changed. However, with monoline or in-line systems, downstream equipment always stops whenever the dual-cavity mold is down. This means double the amount of downtime for downstream equipment. This is not economical."

The price of a twin-cavity mold is almost twice that of a single-cavity mold, according to Koike, because "the dual-cavity mold needs a hot-runner system and a single-cavity system does not." (CIRCLE 19)

Netstal's Hayes agrees: "Theoretically, twin-cavity molding systems appear to be a good use of capital. A twin-cavity system costs 28% more than a single-cavity system, and at 90.2% efficiency (95% uptime x 95% yield) it will produce 48% more discs per hour. As a practical matter, however, with a tighter process window, efficiency rates from twin cavities will probably be less than from a single cavity, particularly at higher q-c levels."

Hayes adds, "We believe that for smaller manufacturers with shorter title runs and a diversity of products, an inline system - such as Netstal's Uniline 2000 - with a single-cavity mold is the safest and most practical method of production. What really counts is how many good discs can be shipped at the end of each day with no risk of title mix-ups." (CIRCLE 20)

MAKE WAY FOR HDCD

Before video CD can really be viable, HDCDs will have to become commonplace. High-density discs pack in much more data, but their market introduction has been delayed by the lack of an industry standard. One such standard is being developed jointly by Philips, Matsushita and Sony and is expected to be released soon. A "Blue Book" standard was submitted in April by Optical Disc Corp. of Los Angles to the International Electrotechnical Commission in Geneva, Switzerland. It is based on the IEC 908 specification for standard CDs and allows for a range of densities up to four times standard CD density on a 12-cm disc. The standard is also designed to be "backward-compatible" to allow HDCD players to play standard CDs or any intermediate density between one and four times standard CD density.

When HDCDs finally hit the market, will replicators have to buy new production machinery? Machinery manufacturers believe that most of the difference between a conventional CD and an HDCD will be in the mastering stage. It appears unlikely that the molding machinery will change, even though pit sizes will be different. There will probably be no change in the coating or metalizing process.

"A higher-density disc intended for blue-laser playback will require pits half the depth of those on today's CDs," says Adrian Farmer, deputy chairman at Nimbus Engineering and Technology, a disc manufacturer in Monmouth, England. "Cycle times on presses will be longer since the pits will be more difficult to mold accurately." Tests by Nimbus indicate that high-quality discs of 4X density cannot be molded in a 6-sec cycle on less than a 60-ton press. Future developments in mold design, polycarbonate resin, and presses with higher injection speeds may ultimately permit reductions in tonnage. But it may still be difficult for facilities geared to short-cycle, low-tonnage CD audio production to produce HDCDs on the same equipment.

Machinery manufacturers such as Optical Disc Manufacturing Equipment (ODME) in Eindhoven, the Netherlands; Nobler Technologies in Boston; Toolex Alpha in Stockholm, Sweden; and Marubeni generally assert that today's production systems can make HDCDs. For example, ODME product manager Rob van Dorp says, "Our machinery can at least handle up to six times the current density." (CIRCLE 21)

A Toolex Alpha spokesman agrees: "Present equipment is sufficient for double-density discs. However, the molds are hotter and the cycle times will be slower." (CIRCLE 22)

Krauss-Maffei Corp., Florence, Ky., already has an 80-ton injection machine available for HDCDs (model KM80/190 C2-H2), according to business manager Artie Riegger. "It is identical to our 40-ton series for traditional CDs except for a higher clamp tonnage and longer cycle time necessary to achieve HDCD quality," he says. (CIRCLE 23)

Art Leblanc, president of First Light Technology in Saco, Me. (a monoline equipment producer that works with Netstal), says Netstal's standard Uniline 2000 can produce HDCDs because all key process variables are under closed-loop control and can be altered either through the Uniline 2000 host computer or through the Netstal Sycap controller. (CIRCLE 24)

NEXT: MULTILEVEL DISCS

If IBM Corp.'s concept for multi-layer HDCDs becomes a standard, however, new machinery may have to be developed. Scientists at IBM's Almaden Research Center in San Jose, Calif., have demonstrated two- to six-level optical discs that are capable of up to 10 times the density of conventional discs. That's 6.5 billion bytes of information, equivalent to more than a million pages of printed text, according to IBM spokesman Michael Ross.

Multilevel discs will be created by gluing individual layers together into a stack with spacers providing a gap between discs, according to Hal J. Rosen, manager of Novel Recording Studies at Almaden. Data are contained on all disc surfaces inside the stack. Movable lenses allow laser light to be focused on any of the data surfaces. "Discs containing four or more surfaces would probably be made thinner than today's optical discs to keep the stack from becoming too thick," he adds. Likely materials would include glass or plastic films.

IBM researchers have demonstrated that this type of molding is feasible, but before this process becomes commercially viable, the company will have to work with disc and machinery manufacturers. Rosen notes that although the process may sound costly, when one disc can replace the need for many discs, there will be a proportionate reduction in packaging, which accounts for a big portion of today's disc prices.