Abstract:
A Blu-ray ray optical disc comprises a base substrate of recycled polycarbonate molded without a data layer on a first surface. The disc further includes a first transmission stack having (a) a data region layer having a first surface adjoining the first surface of the base substrate and a second, opposite surface embossed with data, and (b) a layer of metallization overlying the second surface of the data layer. Lastly, a protective layer overlies the region of metallization of the first transmission stack.

Description:
TECHNICAL FIELD 
       [0001]    This invention relates to optical discs, and more particularly to Blu-ray optical discs. 
       BACKGROUND ART 
       [0002]    Optical discs have emerged as a convenient mechanism for storing large amounts of data, and particularly, video data. Indeed, optical discs remain the media of choice for storing movies for consumer sale and rental. The Blu-ray standard has recently emerged as the preferred standard for high-definition optical discs. A single-layer Blu-ray disc comprises a molded polycarbonate base substrate with a recorded layer on one surface covered by a single transmission stack that includes a metal layer, a clear resin cover layer, and a protective resin layer overlaying the cover layer. The protective layer provides the entrance surface for the optical beam ultimately directed at the recorded layer to read the data carried thereby. (In addition to the single-layer Blu-ray disc, there also exists a dual-layer Blu-ray disc comprised of a base substrate carrying a first data layer (Layer-0) covered by a reflective metal layer which in turn is covered by a spacer-layer of clear resin in which a second data layer (Layer-1) is embossed; the Layer-1 data is covered by a semi-reflective metal layer and a clear resin cover layer and finally a protective resin layer. First and second transmission stacks (i.e., transmission stacks 0 and 1) are formed by the optical path of the reading laser to the respective data layers (i.e. Layer-0 and Layer-1) 
         [0003]    In practice, the base substrate in both single-layer and dual-layer Blu-ray discs comprises polycarbonate and accounts for much of the material cost of the disc. During manufacture of Blu-ray discs, wasted polycarbonate material results from sprues discarded after each molding cycle plus start-up scrap and purging material associated with the injection molding machine reaching temperature and steady-state operating conditions. Presently, optical disc manufacturers re-cycle scrap/wasted polycarbonate such as molding sprues by re-introducing such sprues into the feedstock material for the Layer-1 portion of a DVD, which does not form part of the optical readout path 
         [0004]    Presently, most optical disc manufacturers limit their recycling strictly to scrap molding sprues; upon discarding of the molding sprue, such sprues are immediately ground and re-introduced into the molding process feed material supply by custom equipment designed to minimize exposure and contamination of material. This continuous dynamic process effectively ensures that the percentage of sprue-regrind material introduced into a DVD Layer-1 substrate remains below approximately 10%. There currently exist strict requirements for the cleanliness and percentage of recycled material used in making the Layer 1 portion of DVDs because the Layer-1 disc has molded digital data with strict requirements for material purity. Typically, much of the wasted/scrapped polycarbonate produced during CD/DVD and Blu-ray disc manufacture, other than sprues, lacks the necessary cleanliness for re-cycling in the disc manufacturing process. Indeed, even introducing small amounts of wasted/scrapped polycarbonate other than molded sprues can adversely affect the production of the DVD layer-1 substrates. The unusable scrapped polycarbonate is typically sold at a fraction of the cost of virgin material. While other cheaper materials could be substituted, polycarbonate has the desired mechanical and optical properties required to minimize impact on the manufacturing process. 
         [0005]    Thus, a need exists for an optical disc production process that can make greater use of recycled polycarbonate. 
       BRIEF SUMMARY OF THE INVENTION 
       [0006]    Briefly, in accordance with a preferred embodiment of the present principles, a Blu-ray optical disc comprises a base substrate of recycled polycarbonate molded with or without a data layer on a first surface; such data layer if present shall not be readable by a player and exists to minimize impact on the manufacturing equipment and process. The disc further includes a first transmission stack having (a) a data region having a first surface adjoining the first surface of the base substrate and a second, opposite surface embossed with data, and (b) a layer of metallization overlying the second surface of the data layer covered by a clear resin cover layer and protective resin layer. 
         [0007]    The Blu-ray disc of the present principles makes use of the fact that Blu-ray discs can comprise either single-layer or dual-layer and that the polycarbonate disc substrate does not have strict optical property requirements because the substrate does not form part of the optical path during playback. Rather than require virgin polycarbonate, the Blu-ray disc of the present principles makes use of a substrate molded from recycled polycarbonate material. The molded substrate of recycled polycarbonate does not have readable data molded thereon in contrast to the substrate of a conventional Blu-ray disc. Instead, the Blu-ray disc of the present principles invention makes use of the dual-layer embossing process integrated into today&#39;s Blu-ray manufacturing lines, which allows for creation of a separate first data layer that serves to isolate the substrate, thereby allowing the use of recycled (low grade) polycarbonate material typically deemed unfit for optical disc substrates. Since the Blu-ray disc of the present principles has no readable molded data associated with it, it further allows the use of damaged or non-optimal mold faces that are not deemed suitable for molding data on Blu-ray discs. The utility of the Blu-ray disc of the present principles is to maximize polycarbonate yield which is typically a key process performance indicator for disc manufacturers. 
     
    
     
       BRIEF SUMMARY OF THE DRAWINGS 
         [0008]      FIG. 1  depicts a prior art dual-layer Blu-ray disc in cross-section along with an accompanying chart describing the properties of the disc layers; and 
           [0009]      FIG. 2  depicts a single layer Blu-ray disc in cross section in accordance with a preferred embodiment of the present principles, along with an accompanying chart describing the properties of the disc layers. 
       
    
    
     DETAILED DESCRIPTION 
       [0010]      FIG. 1  depicts a prior art dual-layer Blu-ray disc  10  in cross-section along with an accompanying chart describing the properties of the disc layers. Within the industry, the term “BD50” often serves to identify this type of disc. The Blu-ray disc  10  of  FIG. 1  includes a base substrate  12  of virgin polycarbonate produced through a well-known molding process so that a first surface  14  of the substrate has molded pits  16  forming a first set of data on the disc  10  for reading via an optical beam  11 . After molding, the base substrate  12  undergoes a sputtering process to deposit a fully reflective layer metallization  18  onto the surface  14  of the substrate. Typically, a silver alloy constitutes the preferred material for sputtering onto the surface  14  of the substrate  12 , although other metals or metal alloys could find application for this purpose, taking into account a variety of factors including but not limited to cost, reflectivity, and reliability. 
         [0011]    The metallization layer  18  has an overlying layer of resin  20 , typically applied by spin coating. This resin layer  20  often bears the designation “base or spacer layer.” A layer of resin  22 , typically applied through spin coating and bearing the designation “pit layer”, overlies the resin layer  20 . The resin layer  22  undergoes embossing to create pits  23  that form a second set of data on the disc  10 . Just as the first surface  14 , with its molded pits  16 , has an overlying metallization layer  18 , the resin layer  22 , with its embossed pits  23 , also has an overlying layer of metallization  24 , typically formed by sputtering a silver alloy. The metallization layer  24  exhibits at least partial reflectivity as compared to the full reflectivity exhibited by the metallization layer  18 . 
         [0012]    The metallization layer  24  has an overlying resin layer  26  applied through spin coating to create a cover layer. The resin layer  26  itself has an overlying resin layer  28 , also typically applied through spin coating, to provide a hard coating to resist scratches. 
         [0013]    The base substrate  12  has a second surface  30  opposite the surface  14  so as to lie outside the path of the optical beam  11 . The surface  30  of the substrate  12  has an overlying layer  32 , typically formed by sputtering an inorganic moisture barrier such as SiN. The layer  32  typically carries a layer of ink  34  formed by offset printing or silk screening for example to create a label for the purpose of identifying the disc  10 . 
         [0014]      FIG. 2  depicts a single layer Blu-ray disc  200  in cross section in accordance with a preferred embodiment of the present principles, along with an accompanying chart describing the properties of the disc layers. The Blu-ray disc  200  of  FIG. 2  includes a base substrate  202  of recycled polycarbonate. To make the base substrate  202 , scrap/wasted polycarbonate is first ground up into pellets approximately the same size as virgin polycarbonate pellets of the type normally use in the molding of the base substrate for conventional dual-layer Blu-ray discs. During the grinding process, contamination, impurities and fine particles are removed. These recycled polycarbonate pellets serve as the raw material during the molding of the base substrate  202  using the conventional molding techniques/machinery used to make substrates for conventional Blu-ray discs. Thus, manufacturing the base substrate  202  of the Blu-ray disc  200  from recycled polycarbonate requires no special techniques and/or machines. 
         [0015]    Like the Blu-ray disc  10  of  FIG. 1  which has a base substrate  12  produced through a molding process, the Blu-ray disc  200  of the present principles likewise has a base substrate  202  also produced through molding. Indeed, the same kind of molding machine that produces the base substrate  12  for the Blu-ray disc  10  of  FIG. 1  can produce the base substrate  202  for the Blu-ray disc  200  of  FIG. 2 , with the following modification. During the molding of the base substrate  12  of the Blu-ray disc  10  of  FIG. 1 , the substrate surface  14  undergoes molding typically by a nickel stamper to create the pits  16  forming the first data set on the disc. In contrast, during the molding of the base substrate  202  of the Blu-ray disc  200  of  FIG. 2 , the base substrate surface  204  will undergo molding with a dummy plain or textured or data stamper that may contain pits but such pits are not be readable on the final disc. In other words, unlike the Blu-ray disc  10  of  FIG. 1  whose substrate carries data, the substrate  202  of the Blu-ray disc  200  of  FIG. 2  carries no data that will be ultimately readable in the finished disc. 
         [0016]    Since the base substrate  202  of the Blu-ray disc  200  carries no data, molding the substrate surface  204  with a dummy stamper may seem unnecessary. However, present day Blu-ray manufacturing lines carry out molding as a necessary operation. By making use of a dummy stamper with typical Blu-ray pit structure, production of the Blu-ray disc  200  can occur using present-day Blu-ray manufacturing equipment with little modification. 
         [0017]    Instead of relying on the substrate  202  to carry data, as in the case of a conventional Blu-ray disc, the Blu-ray  200  of the present principles makes use a transmission stack  205 , similar to the transmission stack 1 in a conventional dual-layer Blu-ray disc, for carrying data isolated from the substrate  202 . The transmission stack  205  may optionally comprise a first layer  206  of a partially-reflective material, such as a silver alloy or aluminum, sputtered onto the base substrate surface  204  to aid in coverage of a base or spacer resin layer  207  typically spin coated to overlie the metallization layer  206 . In comparison to the prior-art dual-layer Blu-ray disc  10  of  FIG. 1 , the resin layer  207  corresponds to the  20  base layer of the Blu-ray disc  10 . Indeed, the resin layer  207  can be produced in the same manner using present day Blu-ray production equipment. The resin layer  207  has an overlying resin layer  208  typically formed by spin coating corresponding to the pit layer  22  of Blu-ray disc  10 . The layer  208  undergoes embossing to create pits  209  that comprise the Layer-0 or first data set carried by the Blu-ray disc  200  of the present principles. Typically, the embossing of the layer  208  occurs in the same manner using equipment similar to that for embossing the pits  23  on the resin layer  22  of the Blu-ray disc  10  of  FIG. 1 . 
         [0018]    The resin layer  208  has an overlying layer  210  of reflective metallization, typically formed thereon by sputtering a silver alloy corresponding to metal layer  18  of Blu-ray disc  10 . The metallization layer  210  has an overlying resin layer  212  applied through spin coating to create a cover layer. The resin layer  212  itself has an overlying resin layer  214  also typically form through spin coating, to provide a hard coating to resist scratches. The layers  212  and  214  are typically applied through spin coating using techniques similar to those for applying the layers  26  and  28  on the Blu-ray disc  10  of  FIG. 1 . 
         [0019]    The base substrate  202  of the Blu-ray disc  200  of  FIG. 2  has a second surface  230   30  opposite the surface  204  so as to lie outside the path of an optical beam  231  for reading the data carried by the disc. The surface  230  of the substrate  202  has an overlying acrylic layer  232 , typically formed by spin coating to provide a moisture barrier. The layer  232  typically carries a layer of ink  234  formed by offset printing or silk screening for example to create a label for the purpose of identifying the disc  200 . 
         [0020]    The overall process for making the Blu-ray disc  200  of  FIG. 2  comprises the following steps: 
         [0021]    1. Grind and granulate scrap polycarbonate material to the approximate pellet size of virgin polycarbonate material. Eliminate fine particles and metal contaminants by filtering/blowing and magnets etc. 
         [0022]    2. Dry ground/pelletized recycled material to same dew point as virgin material. 
         [0023]    3. Apply dummy stamper (zero data) to molding machine and mold the substrates 202. 
         [0024]    4. Apply BD25 program stamper to Blu-ray line embossing unit. 
         [0025]    5. Adjust Blu-ray replication line process parameters as follows: 
         [0026]    a. Apply very thin metal layer  206  to aid resin coverage for layer  207  (approximately 3-5 nm to provide resin coating dynamics with no reflectivity requirement) 
         [0027]    b. Reduce first resin layer (base resin layer) from typical 22-micron thickness to as low as 5 micron. This thickness can be varied to optimize yield and material usage. 
         [0028]    c. Apply standard second resin layer  208  of a thickness (pit resin) 3-5 micron 
         [0029]    d. Emboss program using typical embossing process parameters. 
         [0030]    e. Create the layer  210  by metallizing the resin layer  208  with a typical Layer-0 silver thickness 30-40 nm. 
         [0031]    f. Adjust dual-layer Blu-ray cover layer  212  thickness (3 rd  resin layer) from 72 microns to 97 microns. 
         [0032]    g. Add final hardcoat layer  214  (4 th  resin layer) using normal process. 
         [0033]    h. Adjust mold temperature differential to give desired radial skew/tilt of finished disc. 
         [0034]    The foregoing describes single-layer Blu-ray disc manufactured from recycled polycarbonate material. As discussed manufacture of the recycled polycarbonate Blu-ray disc of the present principles can occur using the same techniques and machines as used to make conventional dual-layer Blu-ray discs. 
         [0035]    While the recycled polycarbonate Blu-ray disc of the present principles has been described in terms of a single-layer disc, a dual layer recycled polycarbonate disc could be obtained by adding a second transmission stack (not shown) onto the transmission stack  205 . Adding such a second transmission stack would require a different process than the current process used for conventional dual-layer Blu-ray discs.