Abstract:
A method of making composite discs continuously, including forming for each disc a first, a second layer, and a third support layer, each support layer being disc shaped and having a first surface with information indicia. An information layer is added to each support layers respectively. The said first and third support layers are positioned in a facing relationship, with the first and third information layers being adjacent. The third support layer is then separated from the third information layer, which thus remains attached to the first support layer. The first and second support layers are then joined. These steps are performed on a manufacturing line with conveyor belts transferring the support layers from station to station.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    A. Field of Invention  
           [0002]    This invention pertains to a method of manufacturing multilayer discs, such as DVD/CD discs and the like, and more particularly, to a method and apparatus in which the various subassemblies or components of multilayer discs are made and assembled in a continuous manner.  
           [0003]    B. Description of the Prior Art  
           [0004]    Early optical discs, such as CD discs, were made with only a single information layer which was readable by a laser beam directed through one surface of the disc. Novel techniques were used to extend the capacity of discs. High capacity discs are now available, which may have several information layers, each layer being readable by a laser from one surface of the disc. These high capacity discs are known as DVDs and are available in several flavors, such as DVD-5, DVD-9 and so forth, indicating a nominal capacity of 5 Gb, 9 Gb, etc.  
           [0005]    Several types of DVDs are also made that are laser readable on both sides including dual layer DVD/single layer DVD (DVD-4); dual layer DVD/dual layer DVD (DVD-8); Single layer/CD (DVD +); and dual layer DVD/CD. These discs are constructed by making two separate substrates, each substrate having at least one information layer (using either a CD or a DVD format) and then bonding the two substrates together, back to back. However, until now all these types of DVDs couls only be made in a batch mode. This operation is slow, labor intensive and therefore expensive.  
         OBJECTIVES AND SUMMARY OF THE INVENTION  
         [0006]    It is an objective of this invention to provide a method of making multilayered discs of the kind having information layer on two sides, wherein said discs are made in a continuous fashion.  
           [0007]    A further objective is to provide a method and apparatus in which mulitlayered discs are made on a continuously moving assembly line.  
           [0008]    Yet another objective is to provide a method for continuously making discs which can be performed without making major and extensive changes in existing equipment.  
           [0009]    Yet a further objective is to provide a method and apparatus that can be used to make different kinds of discs, including DVD/CD discs. DVD/DVD discs, etc.  
           [0010]    Other objectives and advantages of the invention shall become apparent from the following description.  
           [0011]    Briefly, the discs are manufactured using in a continuous manner on a manufacturing line, with each disc being made using the following sequence of steps. The first step includes forming for each composite disc at least three support layers, each support layer having a support layer surface formed with information indicia. Next, an information layer on each of said support layer surfaces. The information layer from one of the support layers is transferred to the information layer of another support layer. Finally, the other support layer (which now has now two information layers) is attached to the third support layer, in a back-to-back relation. A spacer layer is added between the two information layers that are mounted on the same substrate. In addition a protective layer is added on the bottom of some of the information layers. The two support layers of the final disc can then be joined by bonding the surfaces with the protective layers.  
           [0012]    The manufacturing line for manufacturing a plurality of composite discs continuously includes a first injection press adapted to form a plurality of first and second support layers; and a second injection press adapted to form a plurality of third support layers, each of the layers having a top surface with information indicia and a bottom surface. The manufacturing line further includes an information layer station receiving the support layers and forming information layers on the support layers. A joining station is arranged to receive and join the first and third support layers temporarily, with the respective information layers being positioned in a facing relationship. A separating station is adapted to receive the joined support layers and to separate the third layer while leaving the respective information layer of the third layer attached to the first support layer. Finally a bonding station is adapted to receive the first support layers with two information layers and said second support layers and to bond is them into composite disks. Preferably transport means, including conveyor belts, are used to transport the support layers between the stations of the manufacturing line. The line also includes a protective layer station adapted to add a protective layer to the support layers.  
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0013]    [0013]FIG. 1 a  shows a somewhat diagrammatic cross-sectional view of a composite DVD/CD disc constructed in accordance with this invention, with the DVD substrate being a multi-layered substrate;  
         [0014]    [0014]FIG. 1 b  shows a somewhat diagrammatic cross-sectional view of a composite DVD/DVD disc constructed in accordance with this invention, with at least one of the DVD substrates being a multi-layered substrate;  
         [0015]    [0015]FIG. 2 shows a block diagram of an assembly line used to make composiute DVD/CD discs of the type shown in FIG. 1 a;    
         [0016]    [0016]FIGS. 3 a - 3   g  show cross sectional views of various intermediate discs during the manufacturing process; and  
         [0017]    [0017]FIG. 4 shows a flow chart describing the process used to generate continuously a plurality of composite discs, each disc being similar to the one shown in FIG. 1 a.   
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0018]    [0018]FIG. 1 a  shows a DVD/CD composite disc  10 . Disc  10  has a diameter of about 12 cm and is formed of two substrates  12  and  14  joined by a bonding layer  16 . In the embodiment of FIG. 1 a , substrate  12  is the CD substrate, substrate  14  is the DVD substrate. The CD substrate  12  is about 1000 microns thick and the bonding glue is about 50 microns thick. The thickness of the DVD component depends on its number of information layers. A DVD-5 substrate has only a single information layer and is about 600 microns thick resulting in a disc having an overall thickness of about 1,650 microns (obviously FIG. 1 a  is not to scale). This thickness is compatible with most DVD and CD players, and, accordingly, a disc with a DVD-5 substrate can be played by most of these players. However, a standard DVD-9 substrate has a thickness of about 1200 microns. If such a substrate were used for a composite disc, the overall thickness of the disc would be 2250 microns, which would not be useable in most CD or DVD players. Accordingly, in the present invention, the DVD substrate  14  is a dual layer DVD-9 substrate having a special structure as disclosed in U.S. Pat. No. 6,117,284 (the &#39;284 patent), incorporated herein by reference. The resulting composite disc is only 1680 microns, still well within the limits of most players.  
         [0019]    Therefore preferably, the DVD substrate  14  is a high data capacity, i.e., it&#39;s a DVD-9 or higher, but has the special structure disclosed in the &#39;384 patent.  
         [0020]    As shown in FIG. 1 a , CD substrate  12  is formed of a transparent support layer  20 , an information layer  22  and a protective layer  24 . The information layer  22  is formed with various surface pits and land areas in accordance with the standard CD specifications, and referred to herein as information indicia. These indicia have been omitted for the sake of clarity.  
         [0021]    The DVD substrate  14  is formed of the following layers:  
         [0022]    a transparent support layer  26 ;  
         [0023]    a first information layer  28 ;  
         [0024]    a spacer layer  30 ;  
         [0025]    a second information layer  32 ; and  
         [0026]    a protective layer  34 .  
         [0027]    Information layers  28  and  32  also information indicia formed in accordance with standard DVD specifications, which again have been omitted for the sake clarity. Information layer  28  is semi-transparent, to allow a laser beam (not shown) to read the second information layer  32 .  
         [0028]    The two transparent support layers  20 ,  26  allow a laser beam to be directed to the respective information layers in a manner well known in the art.  
         [0029]    The spacer layer  30  is also an adhesive layer used to secure the information layer  32  during manufacturing, as discussed in more detail below.  
         [0030]    [0030]FIG. 2 shows schematically the elements of a disc manufacturing line  100  used to make a dual layer disc in accordance with this invention. The manufacturing line consists of several stations, each station being provided with apparatus designed to perform a specific function. Discs are transported from one station to another by conveyor belts or other similar means known in the art. In the following description, the means for transporting discs are referred to as conveyor belts for convenience, it being understood that the transporting means may involve other mechanisms as well, including rotating wheels with slots for receiving discs, etc.  
         [0031]    As indicated in FIG. 4, the first step  200  in the process is the making of support three layers: support layer  20  for the CD substrate  12 , support layer  26  for the DVD substrate  14  and intermediate support layer  40  which is not incorporated in the final dual layer disc. These support layers are depicted in FIGS. 3 a ,  3   b  and  3   c , respectively. Each of these support layers has a respective top surface that has information pit and land areas as described above. The support layers  20  and  26  are made of a transparent plastic material, such as polycarbonate (PC) while intermediate support layer  40  is made of polymethyl methacrylate (PMMA) or other similar material which does not bond well with materials used for the information layers, such as aluminum. The support layers  20 ,  26  are made in an injection press  102 , which makes use of multi-cavity type device using two molds using techniques well known in the art. Intermediate support layer  40  is made by a separate injection press  104 . Details of how these layers are made can be found in above-mentioned U.S. Pat. No. 6,117,284.  
         [0032]    The support layers from injection press  102  are deposited on a conveyor belt  106  while the support layers  40  are deposited on a conveyor belt  108 . Next, in step  204  the information layers  22 ,  28  and  32  are deposited on support layers  20 ,  26 ,  40 , respectively, as shown in FIGS. 3 a - 3   c , resulting in intermediate discs I 1 , I 2  and I 3 , as shown. In FIG. 2, step  204  is accomplished by passing the support layers  20 ,  26  under a metalizer  110  by conveyor belt  106 . Similarly, support layer  40  is passed under a metalizer  112  by conveyor belt  108 . The metalizers  110 ,  112  deposit a reflective metallic layer, made for instance of aluminum, using sputtering or other similar techniques.  
         [0033]    The metallized layers are shown in FIGS. 3 a - 3   b  and are designated as intermediate discs I 1 , I 2  and I 3 .  
         [0034]    Next, the intermediate discs are fed to a sequencer  114 . The purpose of the sequencer  114  is to align the intermediate discs in a particular sequence (step  206 ) on two separate conveyor belts  116 ,  118 . Conveyor belt  116  is used to carry intermediate discs I 2  and conveyor belt  118  carries intermediate discs I 1  and I 3 .  
         [0035]    Discs I 1  and I 3  are fed to a bonding station  120  where the two discs are joined (step  208 ). For this purpose, the spacer layer  30  is applied to the layer  28  of each disc I 1  resulting in an intermediate disc I 4 . Before the material of this layer is set, or hardens, the intermediate disc I 3  is applied to or pressed against I 1  with the spacer layer  30  being in intimate contact with layer  32 , as shown in FIG. 3 d . The resulting intermediate disc I 5  has five layers as shown in FIG. 3 e . Discs I 5  are carried to the next station, which is a surface transfer module, by a conveyor belt  122 .  
         [0036]    Surface transfer module  124  is used to finalize the transfer of information layer  32  so that it remains joined to the spacer layer  30  (step  210 ). This process is facilitated by the material of support layer  40  which does not stick to the metallic layer  32 . Between steps  204  and  210 , information layer  32  is maintained on support layer  40  by adhesion caused by molecular roughness at the interface between these layers. In step  210 , the intermediate support layer  40  is separated and pulled away from information layer  32 , as shown in FIG. 3 e . The support layer can now be discarded, or reused to make and carry another information layer. The result is a four-layer intermediate disc  16  which is deposited on conveyor belt  116 .  
         [0037]    Next, in step  212  protective layers  24  and  34  are added to intermediate discs I 2 ,I 6  using protective layer station  126 . The resulting intermediate discs I 7 ,I 8 , shown in FIGS. 3 f  and  3   g  respectively.  
         [0038]    In step  214  the discs I 7 ,I 8  are provided to a rebonding station  128 . At this station, the two intermediate discs I 7  and I 8  are joined by bonding layer  16 . The end result of step  214  is dual layer disc  10 . From station  128  the discs  10  are transferred to other stations(not shown) for labeling (step  216 ) and/or other finishing processes. Thus, the manufacturing line  100  is capable of producing dual layer discs having the structure indicated in FIG. 1 a  in a continuous manner. Obviously other types of discs may be made as well, using a manufacturing line having the appropriate stations, as required. For example, FIG. 1 b  shows a cross-sectional view similar to FIG. 1 b  with a composite DVD/DVD disc. In this case, the discs made of PC are made by one injection press similar to press  102 , PMMA discs are made by a second injection press similar topress  104 , all the discs are coated with a reflective material, and then joined as described above.  
         [0039]    Obviously numerous modifications can be made to this invention without departing from its scope as defined in the appended claims.