WO2000071323A1 - System and method for manufacturing specially shaped cd-roms utilizing injection molding - Google Patents

Abstract

A system for manufacturing a CD (3) of any shape that is no larger than a standard round CD (2), wherein the specially shaped CD (3) is manufactured using an injection molding process which only requires enough polycarbonate material as is specifically required to fill the specially shaped CD cavity (34). The injection molding process is made possible by constructing of the mold that also functions as a venting ring (30) within a CD injection molding press. The mold is slightly thinner than those commonly used in the industry. The result is that the build-up of gases is eliminated without having to construct a specialized venting grid.

Description

SYSTEM AND METHOD FOR MANUFACTURING SPECIALLY SHAPED CD- ROMS UTILIZING INJECTION MOLDING

BACKGROUND 1. The Field Of The Invention.

This invention relates generally to manufacturing compact discs (CDs) . More specifically, the invention relates to manufacturing specially shaped CDs. This includes any shape that is not the industry standard round shape that is used for both music CDs and CD-ROM disks used for storing digital data that can be read by a computer.

2. The State Of The Art

The state of the art of CDs is to make a round disk on which digital data can be stored. The digital data can be music, or it can be computer readable data such as a software program that is read using a CD-ROM disk drive. Recently, specially shaped CDs have become popular. There are many reasons that this fact is true. For example, a specially shaped CD can easily function as a promotion or advertisement for a particular product, holiday, event or merchant, to name but a few. Specially shaped CDs are typically any shape into which a normally round CD can be fashioned. For example, specially shaped CD can include any irregular shape or polygon.

It is known in the industry that a CD-ROM disk does not have to be round in order to rest on a tray in a CD-ROM drive. What is essential is that the CD-ROM disk fit within and rest upon a first or a second recess within the tray. Accordingly, it is possible to make a CD-ROM card which is not circular, and yet still be capable of functioning as a medium for digital data storage which can be read by an industry standard CD-ROM drive.

For example, figure 1 is provided as an example of a CD-ROM card 10 in the prior art which is not circular and which still functions in a CD-ROM drive. The CD-ROM card 10 is generally rectangular in shape with corners 12 that have been rounded about a relatively large radius.

Figure 2 is provided as an example of another CD-ROM card 14 in the prior art which is also not circular. This shape 14 is similar to the overall shape of the present invention, but has at least one important difference. Notice that the corners 16 are sharp or come to abrupt, angled corners. The corners 16 are therefore not rounded, but instead come to a distinct point. This aspect of the card 14 of figure 2 is important for several reasons. First, it is observed that a sharp corner on an edge of a CD-ROM card makes the CD-ROM card structurally weaker. Experimental observation has shown that such corners can be brittle, resulting in the corner cracking or even breaking off. Obviously, any foreign object becoming loose inside a CD-ROM drive is potentially dangerous because it can become lodged in a portion of the drive mechanisms. In addition, digital data stored on the CD-ROM card might become unreadable if the break extends into an area of the card where data is recorded. Second, it is observed that if the manufacturing process which created the CD-ROM card includes extruding the card from a mold, a sharp corner complicates the process. For example, it can be difficult to fill the mold all the way to a corner with the polycarbonate material used for the CD-ROM cards. It is the nature of molds and the polycarbonate material used for construction of the CD-ROM cards that it is difficult to entirely fill a mold when they have a relatively sharp corner in them. Another difficulty with having a corner on the molded object is that it is difficult to extract such an object from the mold.

Third, it is noted that the packaging of CD-ROM cards is typically accomplished by slipping the cards into sleeves. The sleeves are typically plastic, and are relatively tight fitting around the CD-ROM cards. The sharp corners 16 on a CD-ROM card such as shown in figure 2 can disadvantageously catch on the sleeve material . This can result in the sleeve becoming torn, and thereby slowing the packaging process. Finally, it is observed that if the CD-ROM card is being used as a business card, the CD-ROM card will be held and passed from hand to hand. It is possible for the sharp corners of a CD-ROM business card to injure those people holding the cards . Given the fact that specially shaped CDs are desirable, and that some shapes are inherently difficult to manufacture using an injection molding process, it would be an advantage over the prior art to provide a process whereby any desired CD shape can be manufactured without having to cut the desired shape from an industry standard round CD. This would result in substantial savings of the polycarbonate material used to manufacture the CDs. It would also be an advantage over the prior art if the manufacturing process was relatively fast, and did not require the process of both manufacturing and cutting.

OBJECTS AND SUMMARY OF THE INVENTION

It is an object of the present invention to provide a system for manufacturing a CD of any shape using an injection molding process

It is another object to provide a system for manufacturing a CD of any shape using an injection molding process that did not waste polycarbonate used for the CD. It is another object to provide a system for manufacturing a CD of any shape using an injection molding process that does not require cutting of the CD after injection molding.

In a preferred embodiment, the present invention is a system for manufacturing a CD of any shape that is no larger than a standard round CD, wherein the specially shaped CD is manufactured using an injection molding process which only requires enough polycarbonate material as is specifically required to fill the specially shaped CD. The injection molding process is made possible by constructing a mold that also functions as a venting ring within a CD injection molding press. The mold is slightly thinner than those commonly used in the industry. The result is that the build-up of gases is eliminated without having to construct a specialized venting grid.

In a first aspect of the invention, a mold is manufactured from a hardened metal such as steel . In a second aspect of the invention, the mold is mounted to a standard CD press in place of an industry standard round mold.

In a third aspect of the invention, a plurality of screws are mounted flush with a surface of the mold so as not to project above and interfere with the injection molding process.

In a fourth aspect of the invention, a thickness of the mold is manufactured to enable "blow by" of gases.

These and other objects, features, advantages and alternative aspects of the present invention will become apparent to those skilled in the art from a consideration of the following detailed description taken in combination with the accompanying drawings .

BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1 is a top view of a generally square shaped CD-ROM card in the prior art.

Figure 2 is a top view of a generally business card shaped CD-ROM card in the prior art which has sharp corners .

Figure 3 is a top view of a specially shaped CD that is used as an example for all specially shaped CDs that can be manufactured using the system of the present invention.

Figure 4 is a top view of a mold of the present invention that is made in accordance with the principles of the presently preferred embodiment so that the mold itself functions as a venting ring.

Figure 5 is a close-up cut-away view of bolts that attach the mold of the preferred embodiment to the mirror of the molding machine. Figure 6 is an example of a mold for another specially shaped CD that can be manufactured using the system of the present invention.

Figure 7 is a top view of a an alternative embodiment that utilizes a customized venting grid. Figure 8 is a side view of the venting grid of figure

7.

DETAILED DESCRIPTION OF THE INVENTION Reference will now be made to the drawings in which the various elements of the present invention will be given numerical designations and in which the invention will be discussed so as to enable one skilled in the art to make and use the invention. It is to be understood that the following description is only exemplary of the principles of the present invention, and should not be viewed as narrowing the claims which follow.

In order to facilitate an understanding pertaining to the manuf cturing of CDs, a review will be presented that explains the fundamental aspects of conventional CD Disc manufacturing. Emphasis will be added where necessary to thereby identify the significant differences in design and function of the respective manufacturing processes being analyzed within the scope of this specification. The intent is to identify the commonality existing in such new manufacturing processes and to present the significant differences in the design and function employed under these respective manufacturing applications.

Before beginning a review of the manufacturing process, a summary is presented of the presently preferred embodiment of the invention. Novel aspects of the present invention are that it includes a mold that has cut out of it the outline of a specially shaped CD. Preferably manufactured from cold rolled steel, the mold function as a venting ring. There are at least two different types of venting rings that can be used. The presently preferred embodiment is designed to have a thickness that enables outgassing. In other words, by providing a mold of a specific thickness, gases that are involved in the injection molding process are allowed to escape from the mold merely because the thickness of the mold enables the gases to squeeze out as the polycarbonate material is injected into the mold to fill it. This breakthrough enables any desired shape to be cut into a mold and manufactured.

Alternatively, a venting ring is manufactured that contains a plurality of holes along an outer edge thereof. The plurality of holes enable outgassing as the polycarbonate is injected into the mold. This alternative process is more difficult to do because the venting ring is generally more complicated to manufacture than simply cutting an outline of the desired shape and utilizing a mold that has the desired thickness. And yet, these techniques are unknown to and not obvious to the industry, as specially shaped CDs continue to be manufactured by cutting them from a completed round CD.

Turning to an explanation of the manufacturing process, it is more readily apparent why the difficulties involved in the overall manufacturing process would hide the novel aspects of the present invention as herein explained.

Beginning with the physical characteristics of the compact disc, a disc diameter of 120 millimeters, a center hole diameter of 15 millimeters, and a thickness of 1.2 millimeters. The innermost part of the disc does not hold data; it provides a clamping area for the player to hold the disc firmly to the spindle motor shaft. Data is recorded on an area 35.5 millimeters wide. A "lead-in" area encircles the innermost data area, and a "lead-out" area encircles the outermost area. The "lead-in" and "lead-out" areas contain non-audio data used to control the player. On many discs, a change in appearance in the reflective data surface marks the end of audio information.

Data is physically recorded as a series of pits which are impressed along a top surface of the disc. The top surface is then covered with a very thin layer of metal (50 to 100 nanometers) . Aluminum, silver, or gold compose the metal make-up. In addition another thin plastic layer (10 to 30 micrometers) protects the metallized pit surface, on top of which the identifying label (5 micrometers) is printed. A laser beam is used to read the data. It is applied from below and passes through the transparent substrate and back again. The beam is focused on the metallized data surface embedded inside the disc.

The physical method of providing data storage in pits on a flat surface is not directly visible to the naked eye. A scanning electron microscope is required to view the pits. A disc contains a track of pits arranged in a continuous spiral running from the inner circumference to the outer. It is advantageous to start the music on the inside because the outer diameter of a disc, in some manufacturing applications, is more generally prone to manufacturing defects. CDs having a shorter playing duration provides an increased manufacturing yield- In addition, by starting from the inside, the adoption of smaller diameter discs (such as 8-centimeter CD-3 discs) or larger discs [such as 20- and 30 -centimeter CD-Video discs) is facilitated.

There are 22,199 revolutions across the disc's signal surface. A pit track might contain 3 billion pits. The construction of pits is so small that its track pitch acts as a diffraction grating, producing a rainbow of colors- Further examination of a pit track reveals that the linear dimensions of the track are the same as the beginning of its spiral as at the end. This means that a CD must rotate with CLV (constant linear velocity) , a condition in which a uniform relative velocity is maintained between the disc and the pickup.

The simple fact that laser beams can travel through the disc substrate provides one of the most significant assets of the CD system. When light passes from one medium to another with a different index of refraction, its wavelength changes and it bends. When the velocity of light slows, the beam is bent and focusing occurs. The laser beam is focused to a point about three times larger than the pit width. Thus the effects of any dust or scratches on the substrate outer surface are minimized because their size and importance, at the data surface, are effectively reduced along with the laser beam. Specifically, any obstruction less than 0-5 millimeters becomes insignificant and causes no error in the readout-

The entire pit surface is metallized. The reflective flat surface, called land, causes almost ninety percent of the laser light to be reduced back into the pickup. When viewed from the laser's perspective (underneath), the pits appear as bumps. The height of the bumps is approximately one-quarter of the laser's wavelength in the substrate. A bump disperses light, reducing the intensity of the reflected light.

As a beam strikes an area between pits, virtually all of its light is reflected, and upon striking a pit, virtually all of its light is canceled, so none is reflected. In practice, the laser spot is larger than required for complete cancellation between pit and land reflections, and the pits are made slightly shallower than the one-quarter wavelength. This yields a better tracking signal, among other things. The presence of pits and land is thus read by the laser beam and the surface modulates the intensity of the light beam. Thus, the data which is physically encoded on the disc can be recovered by the laser and subsequently converted into an electrical signal . Manufacturing processes for compact discs have been refined over the years as the demand for them has grown. Annual worldwide demand for CDs passed the one billion mark in 1991. Established injection molding factories are expanding and new facilities are coming on-line. The first step in the process is pre-mastering. In other words, it is first necessary to integrate digital data codes, error correction codes, and sub-codes. These integrated codes are converted to the CD data format prior to disc mastering. In pre-mastering, the original master tape is copied to a specially prepared tape master, which is used to produce the master disc prior to replication. It is the first step in CD replication. By means of a digital audio processor, the audio program is copied to a U-matic tape referenced with SMPTE timecode. This tape is called the CD master tape. When subcode data is added, it is called a CD tape master. This is the tape used to cut the CD master disc. The digital audio program is recorded on the helical scan video track, sub-code is recorded on longitudinal channel L, and timecode is recorded on longitudinal channel 2. Although mastering facilities will accept master tapes (of various formats) along with required documentation, pre-mastering may be accomplished in a properly equipped recording studio.

While the pertinent facts are contained in the cardinal rules, some points in the pre-mastering process merit further discussion. No matter what the original medium, the de facto standard equipment for CD mastering is the Sony PCM-L630 digital audio processor format, using a 44.1 kHz sampling rate and a U-matic video recorder. Any recording must be auditioned carefully, with special attention to phantom dropouts caused by loose particles moving around the tape . The original master tape is copied to the timecoded CD tape master. The CD master tape is assembled by performing the correct edits and inserting pauses between tracks. When dubbing from noisy analog tapes, fast fade- ins and fade-outs are preferable to tight leadering in order to avoid abrupt transitions in noise level. Of course, the analog tape machine must be aligned to the tape itself.

After the master tape has been assembled, the music program is fully recorded on the U-matic tape. The next step in the premastering process turns the CD master tape into a CD tape master, ready for mastering. Every CD contains a subcode. Cue editors use user-input information and timecode numbers to generate the subcode. Using the CD subcode processor/editor, the engineer enters the preliminary required data that is requested by the system's menu: album title, artist, record label, catalog number, UPC number, analog or digital source, and mastering engineer's name. All track titles are entered, along with other individual track information, including the ISRC number, copy inhibit, pre-emphasis, and index points •

The design of CD disc mastering systems presented a unique challenge to the development engineers. Although much of the manufacturing chain could be assembled from existing equipment, such as injection molding, metallization, and label printing machines, the first link in the chain required a wholly new system. The precision required of the system is considerable; and defect introduced on the master disc will be replicated on all production discs.

CD mastering begins with a U-matic tape master and a glass disc. The PCM audio data contained on a tape master will be transferred to the glass master, where it will be represented as pits. Three master methods, using photoresist, nonphotoresist , and direct metal mastering, have been developed. Photoresist mastering is most commonly used. All CD's are ultimately derived from the resulting master disc. Disc mastering begins with a glass plate, which is about 240 millimeters in diameter and 5.9 millimeters thick. It is washed, lapped, and polished. An adhesive (chrome film or a saline coupling agent) is applied, followed by a coat of photoresist that is applied by a spinning developer machine . The plate is tested for optical dropouts with a laser; any burst dropouts in reflected intensity are cause for rejection of the plate. The plate is cured in an oven and stored with a shelf life of several weeks after which it is ready for master cutting.

The photoresist mastering process is generally accomplished with a largely automated laser "cutting" machine which exposes the AZ photoresist on the master glass disc, followed by wet development. The encoded signal must meet the CD encoding standard.

The system controller in the control rack provides for automatic system operation. Recording operations are stored on floppy disk. Recording parameters such as linear velocity, master identification number, and program length are entered via controller keyboard. Track pitch, focus offset, and recording intensity can be altered from program defaults if necessary. A video display shows process status . The master glass plate coated with photoresist is placed on the lathe and exposed with a "cutting" laser to form the spiral track, creating the disc contents in real time as the master tape is played through the PCM processor. The channel bit stream is input to an acousto- optical modulator that is used to intensity modulate a laser which creates the cutting signal corresponding to the data on the original audio master tape. Audio data on the tape master is transferred, sample by sample, to the disc. A second laser, which does not affect the photoresist, is used for focus and tracking. A focus monitor is used to confirm accuracy and recording spot quality. The spiral data track extending outward across the disc requires precise motion, for both disc rotation and the linear speed of the sled carrying the cutting and focusing optics. To obtain frictionless motion, air bearings are used for both mechanisms .

Although the optics are similar to those found inside consumer CD players, the mechanisms are built on a larger scale, especially in terms of isolation from vibration. The entire cutting process is accomplished automatically under computer control . Not only are the contents of the CD exposed, but test signals are recorded on the inner and outer diameters of the master disc data area.

After exposure in the master cutter, the glass master is developed by an automatic developing machine. The exposed areas are etched away by the developing fluid, creating pits in the resist surface. During development, a laser monitors pit depth and stops development when proper engraving depth has been reached. The optimum data signal would result when a pit caused an absence of reflected light from the disc, thus distinguishing it from the surrounding reflective land. This is theoretically achieved when the pit- depth is one quarter of the apparent wavelength of the laser pickup, thus bringing about destructive interference, and the pit width is such that the intensity of the light reflected from the pit bottom equals the intensity of the light reflected from the surface. In practice, pit depth and width specifications must be modified slightly to account for pit geometry and to provide a more robust tracking signal.

Following development, a metal coating, usually of silver, is evaporated onto the photoresist layer; the master disc is then ready for electroforming and replication. An important quality control check is performed at this point in order to ascertain the accuracy of the disc formation and pit geometry. The master disc is played on a master player, and test signals are derived to measure the high-frequency signal output. Track pitch and track stability are measured by monitoring the radial tracking signal during playback. In addition, errors are counted and subcode accuracy is verified. Finally, the master disc is auditioned for audio program quality. Most CD mastering facilities will attest to the difficulties involved in mastering. A laser beam mastering facility requires numerous subsystems, including a resist master preparation system, master recording system, developer system, master disc ration system, master recording system, developer system, master disc player system, and disc master electroplating equipment. Other items from a long list include microscopes, ovens, chemical preparation equipment, diagnostic and test equipment, glassware, cleaning and protective materials, desks and hoods, audio monitoring equipment, and dust-

free paper- Site requirements are carefully specified. Clean air is critical. CD pits are among the smallest of all manufactured formations -- about the size of a smoke particle. Thus the entire mastering process must be carried out in a clean room environment with the size and numbers of particles in the air strictly regulated. Clean room classifications specify the number of particles present in the air and their size. Class 100,000 for example, specifies no more than 100,000 particles 0.5 to 5 micrometers in diameter per cubic foot of air per minute. The air inside a CD mastering lathe is specified to be Class 100-

Temperature and humidity, along with ambient air pollution levels, must also be specified. With some systems the glass disc moves from one process stage to the next in a sealed cartridge. With each process step, the disc is automatically removed from the cartridge and then returned. This minimizes manual contact and air exposure, thus reducing the chances for contamination of the disc. Vibration would be disastrous to the cutting process.

The laser beam recorder is mounted on a massive baseplate, made from materials such as cast iron or granite, with a pneumatic vibration isolation system. Other requirements include a clean electrical system, demineralized and hot water, compressed air, filtered air, nitrogen, and a system ensuring the exhaust of contaminated air.

Electroforming, sometimes called matrixing, bears a close resemblance to the corresponding stages of vinyl record production. The process describes the production of metal impressions from master or submaster CDs that are to be used for disc molding.

The various aspects of electroforming, such as composition of the plating solution, temperature control, solution flow, and plating current distribution, are optimized to obtain a fine surface for CD replication. These adjustments are completely different from those needed for an analog disc. The electroforming plating process ultimately results in metal stampers used to replicate CD's.

Following mastering and developing, a silver or nickel layer is deposited with vacuum evaporation over the photoresist layer. The master is played on a master player system to assess aural and measured quality, or the computer data is evaluated; it also serves as a reference to evaluate the quality of the final production discs. The silvered master is then transferred to the electroforming room. The silvered master disc, which is now electrically conductive, is placed in a galvanic nickel electrolyte bath. The master disc is the cathode (-) of an electric circuit. From a nickel anode (+) a nickel layer is electroformed onto the master disc.

In a typical application, a reservoir holding the electrolyte solution (nickel sulphamate) is located outside the clean room. It is held at a constant temperature, filter for one or two micron maximum particle size, electrolytically purified, ph checked and held at a constant value by adding sulphamic acid, and circulated constantly. The master is placed in a sink and etched (activated) with a solution of sulphamic acid. It is rinsed and put in a holder to ensure uniform current flow over the mater's face. The holder is placed on the shaft of the cathode drive in the plating tank, and the plating process is initiated.

The plating process starts with a low current which increases as the nickel plate grows thicker. The time required for plating depends on the thickness desired. Nominally, a maximum current of one hundred amps produces a part in less than two hours.

After electroforming, the nickel part is separated from the glass matter. It is rinsed in an electrolytic degreasing tank at high temperature, or with a solvent such as acetone, to remove any particles of photoresist. Since the mater's photoresist layer is usually damaged when it is separated from the metal part, masters may be used only once .

Because the disc master has a positive impression of the CD pit track, the resulting nickel copy, called the "father," is a negative impression. In cases of limited production, the father can be used to replicate CD's. Generally, the father is used to galvanically generate a number of positive impression "mothers." Four or five mothers may be made from one father. Each mother is inspected. If a mother is acceptable, it can generate a number of negative impression nickel mold matrices, "sons" or "stampers," by the same process. Stampers are optically checked to ensure quality. When the stamper is separated from its mother, the stamper is rinsed and dried, and a protective layer (either a tape, form, or plastisol) is applied to its face. Next, a backsanding machine is used to polish its back, and it is put in a centering device. Using a reference mark on the stamper, the part is centered to within one micron, and the center hole is punched out. Next, the outside circumference is punched. The stamper is ready for mounting in an injection molding machine. Four or five stampers may be made from one mother. When mounted for a die, stampers are used in the replicating machines to produce CD discs.

The electroplating room requires a Class 1,000 environment. However, the electroplating process is carried out in enclosed electroforming consoles. They are placed in Class 100 laminar flow enclosures to maintain cleanliness. Often a HEPA (High Efficiency Particulate Air) filter and fan are used to circulate filtered air. Submicronic filtration systems are used to ensure that the chemical baths do not became contaminated. Moreover, the electroplating system must be able to produce disc molds that are flat to within +3 microns over the entire disc surface.

In new generations of electroforming equipment, the emphasis is on speed. In some cases the father, mother, and stamper processing can be completed in less than an hour. This time is crucial when large disc runs require a large volume of stampers . Following the mastering and electroforming processes, the disc is ready for replication. Injection molding techniques are commonly used, as molten plastic is injected into a mold cavity, with the stamper on one face producing a clear plastic disc with pits impressed on one side. A polycarbonate plastic resin is used chiefly because of its high transparency, dimensional stability, good impact resistance, accuracy in reproduction of the mold surface, easy processing characteristics, minimum water absorption, and freedom from impurities. However, polycarbonate material has certain inferior specifications, especially when handled by injection molding, which will be discussed later in this section. The molding of compact discs presents great challenges; the disc must be flat and optically pure, and it must retain an accurate impression of the data pits. Furthermore, typical molding practices result in discs with deficient optical properties. To achieve satisfactory results, the disc molding requires minimized plastic resin viscosity for good fluidity. To obtain low viscosity and good fluidity, which results in desirable optical properties, the resin temperature must be raised considerably. However, the resin is easily decomposed, resulting in color change or bubbles. Because the disc volume is small and the amount of resin needed is small, heated resin retained in the typical molding machines can easily be degraded or burned. Furthermore, high-speed passing of resin causes mechanical shearing heat, which is another factor to be controlled, Although problematic, high-speed filling is still desirable in injection molding. High-speed filling prevents a drop in the temperature of the polycarbonate and enables uniform melting temperature in the cavity. This ensures uniform force and density of the molded disc and make possible uniform cooling speed across the entire disc surface, which in turn allows uniform shrinkage. High-speed filling also prevents pressure drop and assures that adequate pressure is applied even at the far edges of the cavity. Distribution of the pressure in the cavity is uniform and molding shrinkage is small . Molding can be performed with lower pressure, resulting in discs with minimum warpage or deformation. Finally, high-speed filling permits molding at lower temperature and faster cycle times.

As cavity filling speed is increased, however, two problems arise- First, it is difficult to accurately control the amount of polycarbonate to be injected. Second, it is difficult to discharge air from inside the cavity. Sophisticated control systems and, in some cases, a vacuum in the cavity can be used to achieve very brief filling periods of 0.01 to 0.1 seconds at low pressure.

Because of these and other problems, use of typical injection molding machines results in discs containing burned plastic, and consequently, contamination or bubbles may result. If the resin temperature is lowered, strain or deformation of the disc after molding may result, along with a high birefringence. After experimentation with various polycarbonate resins, different kinds of injection molding machine designs and mold shapes, techniques for producing a single-piece polycarbonate disc were achieved. As a result, there is a considerable difference between standard polycarbonate and that used for making CD Discs in specifications such as melt flow rate.

The heart of an injection molding machine is its plasticizing unit. Because polycarbonate is a hygroscopic material, it must be dried, stored at a high temperature, and then used without being exposed to ambient air. Thus pellets of polycarbonate (cleaned and dried) are drawn directly through the hopper and into a heating barrel; a screw moves the pellets through a series of heating coils to heat the plastic quickly and uniformly to a high temperature (approximately 350 degrees centigrade) in order to achieve smooth flow properties into the mold cavity during injection. When the molten plastic is injected into the mold cavity at high pressure, it conforms to the stamper's contours, producing a substrate disc with pits. The mold is kept at a temperature of approximately 110 degrees centigrade.

Some systems use an injection-compression molding process. The molten plastic is first injected into the mold, which is not yet completely closed. The actual final shape of the disc is accomplished during the subsequent high compression step. With injection- compression molding, molded-in stress is minimized; however, cycle times are somewhat longer than with conventional injection molding, perhaps ten seconds as compared with five seconds. In most cases, the center hole is formed before the disc is removed from the mold. In other systems, the center hole is punched out of the disc separately, after the outer layer is applied, but before the label is printed. Following molding, the warm disc is subjected to a static charge, eliminating any dust particles in the air which are attracted to the disc. The molding room must be kept at Class 1,000, and special hoods are placed over the molding machines for an even cleaner environment at the Folding head.

In summary, the entire injection molding process requires consideration for environmental cleanliness, nozzle and hopper temperature regulation, mold temperature regulation, adjustment and stability of injection volume and time, removal of flashes from mold surface, and quality of the stampers.

After leaving the molding machine, the disc is wholly formed but transparent, and a player's laser beam could not read the impressed data because there is no reflected beam to convey the information, hence, a reflective layer must be placed over the data pits. This reflective layer, typically aluminum, is very thin, between 50 to 100 nanometers thick. To protect this thin layer from physical damage and oxidation, an acrylic plastic layer is applied over it-

The reflection coefficient of the metal layer, including the polycarbonate substrate (note that the CD player laser must shine through the substrate to the metal layer), is specified between 70% to 90%. In addition, the metal must be chosen to be inert with the polycarbonate substrate. Three cost-effective metals qualify with the required reflectivity and stability: aluminum, copper, and silver. Gold is an expensive alternative. The fact that it is an inert metal may be of use in certain applications. Reflectance values of 80% to 90% apply at the readout wavelength, even with thin layers. Because of the physical appearance of the layer, aluminum and silver are preferred over copper. Metallization requires a clean room of Class 1,000.

Other techniques for application of the reflective layer include vacuum evaporation, sputtering, wet silvering, and spin coating.

To ensure that all CDs successfully play on all CD players or in CD-ROM drives, a large range of optical, mechanical, and electrical criteria have been established for the CD system. The co-inventors and license holders of the compact disc, Philips and Sony, have published these specifications in the Red Book, the reference on standards available to all CD licensees. Some disc tolerances, such as disc eccentricity, have been established empirically; they represent a compromise between practicalities of manufacturing discs on one hand and those of manufacturing players and drivers on the other. Additional specifications, such as error flags, are strictly theoretically determined. However, the implementation of this aspect and the number of errors permitted on any particular disc, again represent a compromise between media and players- Molded disc are checked for correct dimensions, lack of flash and burns, birefringence, reflectivity, flatness (skew angle) and general appearance. The pit surface is checked for correct pit depth, correct pit volume, form and dimensions. The metallized coating is checked far pinholes and uneven thickness . As many manufacturers have discovered, one of the easiest ways to detect dust in the clean room is the appearance of pinholes in the discs. Birefringence can be checked with a circularly polarized light used to convert the phase change to an intensity variation measured with a photodiode . The disc can be scanned, creating a map of birefringence versus radius .

Angle deviation measures the normal angle formed as the disc plays in the radial direction. This angle is critical because any deviation causes the reflected laser beam too deviate from its return path through the objective lens. This angle deviation could result from improper manufacturing methods. Specifications call for a maximum angle of 0.5 degrees. Because warpage could be introduced later in the field (for example the extreme temperatures found in a car interior might cause bending) , the specification allows a safety factor of 0-3 degrees. Disc eccentricity measures the deviation from circularity of the pit track and the positioning of the center hole. The electroforming and molding processes introduce some eccentricity in the shape of the pit track. In addition, the player's or the drive's positioning of the disc in the drive might introduce eccentricity. If it is excessive, it could exceed the ability of the radial tracking servo of the player. Tolerances for deviation from circularity call for maximum eccentricity of 140 micrometers ^• Disc eccentricity must also account for alignment of the center hole. Specifications call for a center hole tolerance of 0-4 millimeters. A hole that is off center would lead to disc imbalance, noise and resonance errors. In practice, an eccentricity of only one millimeter would result in significant imbalance.

Figure 3 is a description of one particular specially shaped compact disc 20 that measures 80 mm in diameter, with perpendicular sides 57 mm apart from each other. This specially shaped CD 20 is known as the business card shaped CD, and is used as the example in the figures to follow. It should be remembered that any specially shaped CD can be substituted, and using the techniques of the present invention, it can be manufactured.

In the presently preferred embodiment, the four points or rounded corners 22 have an 8 mm radius. The purpose for this design is to enable an easy fit of the disc into an 80 mm CD ROM or CD audio carrier tray. Having 8 mm rounded edges accomplishes two objectives: (1) the card 20 will not hang-up when inserted and removed from the carrier; and (2) the disc will stay balanced during the ramp-up or ramp-down of the spindle motor in the player drive .

Figure 4 is a top view of a mold 30 for the business card shaped CD 20 of figure 3. The mold 30 is injected with polycarbonate. This presents an initial problem because gases build up and become trapped in the mold cavity. These gases must be released or deformities in the disc will result. As a solution to prevent the build- up of gases, a piece of metal 30 has been designed which bolts 32 around the milled-out section 34 of the mold 30. It is crucial to note that a standard mold has a thickness of approximately 1.20 mm. In the present invention, the mold 30 is thinner, thus enabling out-gassing when the polycarbonate is injected into the mold. The industry has not previously attempted this design for a mold.

To overcome the problem of gas build-up in the mold 30, the inventor utilized a mold 30 having a thickness that is slightly less than an industry standard mold. The result is that the gases have sufficient time to leave the mold as the polycarbonate fills it. Experimentation was necessary in order to determine if the design would work. In essence, the preferred embodiment is for the mold 30 itself to function as a venting ring. This is accomplished by using a mold that is approximately 0.002" thinner than a standard mold.

This discovery of making the mold a fraction of an inch thinner in order to perform out-gassing was very unexpected, and yet results in obtaining specially shaped CDs that have the quality necessary to function as a CD for either audio purposes, or for storage of computer readable data. When extracting the business card shaped CD, the mold easily punches out the sprue and card without experiencing sticking or hanging-up of either piece.

Figure 5 is a close-up cut-away view of a bolt 32 that is holding the mold 32 to a portion 40 of the molding machine referred to as a mirror 36. The number of bolts and the size of the bolts utilized to hold the mold in place can vary. It is suggested, however, that a bolt that is 9.4 mm in diameter be used. Furthermore, at least four bolts 32 should be used to secure the mold 32 to the mirror 36.

Figure 6 is simply offered as an example of another specially shaped CD that can be manufactured using the system of the present invention. Specifically, the mold will produce a CD having the shape of a pumpkin.

Figure 7 is an alternative embodiment of the present invention. Specifically, a mold is now used that has the same thickness as the molds used in the industry. Thus, the mold itself does not vent the gases. Now, a venting grid 40 is provided in the mold 42. The venting grid 40 vents gases through a plurality of holes 44 that are drilled around its surface. This prevents the disc from flashing or rejecting the polycarbonate.

Figure 8 is provided as an edge view of the venting grid 40 and its placement within the mold 40. The embodiment of figures 7 and 8 also produces specially shaped CDs. However, the cost of having to manufacture the venting grid 40 as opposed to just milling out the shape from a mold as in the preferred embodiment does not make the alternative embodiment as attractive from a perspective of time or money.

Metallization of the polycarbonate disc is accomplished through a specially designed mask which is composed of either copper or steel. The metal is cut-out with a milling machine to the basic size of a business card, hence the name identification of a business card shaped CD. In most instances, the mask is one to two millimeters smaller than the actual size of the business card shaped CD. This keeps unwanted debris from falling onto the disk during metallization. The mask is easily removed far cleaning and/or replacement •

Through applying the processes of injection molding- coupled with the added design modifications to the mold as described above, the result is an injection molded design that will produce 5 to 2.5 second cycle times per CD. This will drastically increase production quantities as compared to cutting specialty shapes, and result in a substantial reduction in the overall cost of producing the discs.

It is to be understood that the above-described arrangements are only illustrative of the application of the principles of the present invention. Numerous modifications and alternative arrangements may be devised by those skilled in the art without departing from the spirit and scope of the present invention. The appended claims are intended to cover such modifications and arrangements .

Claims

CLAIMSWhat is claimed is:

1. A system for manufacturing specially shaped compact discs, wherein the specially shaped compact discs are not circular, said system comprising a mold, wherein the mold comprises : a plurality of holes therethrough for receiving bolts therein, wherein the bolts couple the mold to a mirror of a molding machine; an outline of the specially shaped compact disk that is cut out of the mold, wherein plastic is injected into the mold to thereby manufacture the specially shaped compact disc, such that the plastic will fill the outline when injected into the mold; and wherein the mold is manufactured to be uniformly thinner with respect to thickness of industry standard molds, thereby enabling outgasing of gases that can buildup during injection molding.

2. The system for manufacturing as defined in claim 1 wherein the mold is approximately .002 mm thinner than the industry standard molds .

3. The system for manufacturing as defined in claim 1 wherein the outline is milled from the mold.

4. The system for manufacturing as defined in claim 1 wherein the mold is manufactured from cold rolled steel.

5. A system for manufacturing specially shaped compact discs, wherein the specially shaped compact discs are not circular, said system comprising: a mold, wherein the mold includes an outline of the specially shaped compact disk that is cut out of the mold, wherein plastic is injected into the mold to thereby manufacture the specially shaped compact disc, such that the plastic will fill the outline when injected into the mold; and a venting grid disposed within the outline of the mold, wherein the venting grid includes a plurality of holes therethrough which enable outgasing of gases during injection molding.

6. A method for manufacturing specially shaped compact discs, wherein the specially shaped compact discs are not circular, said method comprising the steps of:

(1) providing a mold, wherein the mold includes a plurality of holes therethrough for receiving bolts therein, wherein the bolts couple the mold to a mirror of a molding machine, and an outline of the specially shaped compact disk that is cut out of the mold, wherein the mold is manufactured to be uniformly thinner with respect to thickness of industry standard molds, thereby enabling outgasing of gases that can build-up during injection molding; and

(2) injecting plastic into the outline of the mold using the molding machine, wherein the plastic fills the outline when injected into the mold.

7. The method as defined in claim 6 wherein the method further comprises the step of fashioning the mold to be approximately .002 mm thinner than industry standard molds .

8. A method for manufacturing specially shaped compact discs, wherein the specially shaped compact discs are not circular, said method comprising the steps of: (1) providing a mold, wherein the mold includes an outline of the specially shaped compact disk that is cut out of the mold;

(2) providing a venting ring which is disposed within the outline in the mold, wherein the venting includes a plurality of holes therethrough which enable gases to escape from the mold during injection molding; and

(3) injecting plastic into the outline of the mold using the molding machine, wherein the plastic fills the outline when injected into the mold.