Patent Publication Number: US-2010129567-A1

Title: Method for manufacturing information recording medium

Description:
TECHNICAL FIELD 
     The present invention relates to a method for manufacturing an information recording medium used for the purpose of reproduction, or recording and reproduction, and comprising stacked curable resin layers, and more particularly relates to a method for manufacturing an information recording medium having a plurality of information layers. 
     BACKGROUND ART 
     Research has been conducted into optical information recording methods in recent years, and these methods have come to be used in a wide range of industrial and consumer applications. In particular, optical information recording media with which information can be recorded at high density, such as CDs and DVDs, have become very popular. These optical information recording media have a transparent substrate, an information layer, and a protective layer. The transparent substrate has an information face consisting of a bumpy surface, such as guide grooves for tracking recording and reproduction light, or pits that represent an information signal. The information layer is formed from a metal thin film, or a thin film material that allows thermal recording, or the like that is formed over the transparent substrate. The protective layer is formed on the information layer, and consists of a transparent substrate, a resin layer, or the like that protects against moisture in the atmosphere and so forth. Information is reproduced by shining a laser beam on the information layer and detecting the changes in the amount of light that is reflected. 
     In the case of a CD, for example, first an information layer is formed by laminating a metal thin film, a thin film material, or the like over a resin substrate that is approximately 1.1 mm thick and has an information face composed of bumps on one side. This is then coated with a radiation curable resin, typified by a UV curable resin or the like, to form a protective layer. A CD is produced in this way. To reproduce an information signal, a laser beam is directed not from the protective layer side, but from the substrate side. 
     In the case of a DVD, an information layer is formed by laminating a metal thin film, a thin film material, or the like over an information face composed of bumps on a resin substrate that is approximately 0.6 mm thick, after which a separately prepared resin substrate with a thickness of approximately 0.6 mm is affixed with a UV curable resin or the like to produce the DVD. 
     There is a growing need for higher capacity in such optical information recording media, and to this end multiple layers have been used for the information layer in DVDs and the like, and there have been proposals, for example, for optical information recording media with a two-layer structure in which an information layer sandwiches an intermediate with a thickness of a few dozen microns. 
     Also, as digital high-definition broadcasts have become more common in recent years, there has been a need for a next-generation optical information recording medium with higher density and larger capacity than a DVD. For instance, there have been proposals for large-capacity media such as the Blu-ray Disc, in which an information layer is formed by laminating a metal thin film or the like over an information face composed of bumps on a substrate with a thickness of 1.1 mm, and a protective layer with a thickness of approximately 0.1 mm is formed over the information layer. With a Blu-ray Disc, the track pitch of the information layer is narrower and the size of the pits is smaller than with a DVD. Accordingly, the laser spot used to record and reproduce information has to be focused more tightly on the information layer. With a Blu-ray Disc, a special optical head is used to focus the laser beam spot on the information layer. This optical head makes use of a blue-violet laser with a short wavelength of 405 nm, and the objective lens used to focus the laser beam has a numerical aperture (NA) of 0.85. However, when the spot is smaller, the effect of disk tilt tends to be greater, and if the disk tilts even a little, there will be astigmatism in the beam spot, which produces distortion in the focused beam and precludes recording and reproduction. Therefore, with a Blu-ray Disc this drawback is compensated for by reducing the thickness of the protective layer on the side of the disk where the laser is incident to about 0.1 mm. 
     Nevertheless, even with a next-generation optical information recording medium that has large capacity, such as a Blu-ray Disc, there have been proposals to increase the storage capacity by using multiple information layers, just as with a DVD. 
       FIG. 12  is a cross section of a two-layer Blu-ray Disc in which there are two information layers. 
     This two-layer Blu-ray Disc has a molded resin substrate  201 , a first information layer  203 , a resin intermediate layer  204 , a second information layer  206 , and a protective layer  207 . The first information layer  203  and second information layer  206  are composed of a thin film material that allows for thermal recording, or a metal thin film. The resin intermediate layer  204  and protective layer  207  are composed of a resin that is substantially transparent with respect to the recording and reproduction light. 
     A first information face  202  consisting of bumps is formed on the molded resin substrate  201 . The first information layer  203  is laminated over the first information face  202 . The resin intermediate layer  204  is formed over the first information layer  203 . A second information face  205  consisting of bumps is formed over the resin intermediate layer  204 . The second information layer  206  is laminated over the second information face  205 . The protective layer  207  covers the second information layer  206 . 
     The term “substantially transparent” as used here means having transmissivity of at least about 90% with respect to the recording and reproduction light, and “semitransparent” means having transmissivity of at least 10% and no more than 90% with respect to the recording and reproduction light. 
     With this two-layer Blu-ray Disc, the laser beam is incident from the protective layer  207  side, and is focused on either the first or second information layer, whichever is the information layer where recording and reproduction are to be performed, and this allows signals to be recorded and reproduced, etc. 
     The thickness of the molded resin substrate  201  is set to approximately 1.1 mm, the thickness of the resin intermediate layer  204  to approximately 25 μm, and the thickness of the protective layer  207  to approximately 75 μm. 
     A multilayer Blu-ray Disc such as this is generally manufactured by the following method. As an example, a method for manufacturing a two-layer Blu-ray Disc will be described here. 
       FIG. 13  shows the steps for producing a stamper, which is a metal die for producing the molded resin substrate of an information recording medium. First, a photosensitive film  302  is produced by coating a base  301  consisting of a glass plate, a silicon wafer, or the like with a photoresist or another such photosensitive material, and a laser beam, an electron beam, or another such exposure beam  303  is used to expose a pattern such as pits or guide grooves ( FIG. 13   a ). This forms a latent image composed of an exposed part  304  ( FIG. 13   b ). The exposed part  304  is then removed with an alkali developing solution or the like to obtain a recording base  306  comprising a bump pattern  305  formed by a photosensitive material on the base  301  ( FIG. 13   c ). A conductive thin film  307  is formed on the surface of this recording base  306  by sputtering, vapor deposition, or another such method ( FIG. 13   d ). This conductive thin film  307  is used as an electrode to form a metal sheet  308  by metal plating or the like ( FIG. 13   e ). The conductive thin film  307  and the metal sheet  308  are then separated at the interface between the photosensitive film  302  and the conductive thin film  307 . Any photosensitive material remaining on the surface of the conductive thin film  307  is removed with a stripper or the like. Finally, punching is performed to the inside and outside diameters dictated by the molding machine. As a result, a metal stamper  309  is produced ( FIG. 130 . 
     Next, a resin substrate is formed by a resin molding method such as injection molding using the metal stamper  309 . A material such as polycarbonate with excellent moldability is usually used as the substrate material. After this, resin layers are laminated using a resin layer formation process involving spin coating or the like as discussed in Patent Document 1, for example. 
       FIG. 14  shows the steps for producing a two-layer disk, and comprises steps of producing a resin intermediate layer and a protective layer by spin coating. 
     A molded resin substrate  401  is formed by a resin molding method such as injection molding using a metal stamper. The molded resin substrate  401  has on one side a first information face formed by guide grooves or pits consisting of a bumpy surface, and has a thickness of approximately 1.1 mm. Then, a first information layer  402  is formed over the first information face by sputtering, vapor deposition, or another such method from a thin film material that allows thermal recording, or a metal thin film. The molded resin substrate  401  on which the first information layer  402  has been formed is fixed on a rotary stage  403  by vacuum chucking or another such method ( FIG. 14   a ). The first information layer  402  on the molded resin substrate  401  that has been fixed to the rotary stage  403  is coated with a radiation curable resin A  404  from a dispenser and in a concentric pattern of the desired radius ( FIG. 14   b ). The rotary stage  403  is then spun to spread out the radiation curable resin A  404  and form a resin layer  406  ( FIG. 14   c ). The thickness of the resin layer  406  at this point can be controlled as desired by suitably adjusting the viscosity of the radiation curable resin A  404 , the spinning speed, the spinning duration, and the ambient atmosphere in which the spinning is performed (such as its temperature and humidity). After the spinning is stopped, the resin layer  406  is cured by radiation from a radiation emitter  405 . 
     Next, a transfer stamper  407  for forming a second information face is formed by injection molding using the metal stamper shown in  FIG. 13   f . This transfer stamper  407  is fixed by vacuum chucking or the like onto a rotary stage  408 . The transfer stamper  407  placed on the rotary stage  408  is coated with a radiation curable resin B  409  from a dispenser and in a concentric pattern of the desired radius ( FIG. 14   d ). The rotary stage  408  is then spun to spread out the radiation curable resin B  409  and form a resin layer  411  ( FIG. 14   e ). The thickness of the resin layer  411  can be controlled as desired as described above. After the spinning is stopped, the resin layer  411  is cured by radiation from a radiation emitter  410 . 
     Next, the molded resin substrate  401  and the transfer stamper  407  on which the resin layers  406  and  411  have been respectively formed are put together so that the resin layers  406  and  411  are opposite each other, and with a radiation curable resin C  412  interposed between them ( FIG. 140 . The radiation curable resin C is spread out by spinning a rotary stage  413  in this integrated state. After the formation of a resin layer  414  that has been adjusted to the desired thickness, this is irradiated with radiation from a radiation emitter  415  to cure the resin layer  414  ( FIG. 14   g ). After the molded resin substrate  401  and the transfer stamper  407  have been integrated by the resin layer  414 , the transfer stamper  407  is removed from the interface between the transfer stamper  407  and the resin layer  411 , which forms a second information face on the molded resin substrate  401  ( FIG. 14   h ). A second information layer  416  is formed over this second information face by sputtering, vapor deposition, or another such method from a thin film material that allows thermal recording, or a metal thin film. After this, a radiation curable resin D is applied by the same spin coating method and subjected to radiation curing, which forms a protective layer  417  ( FIG. 14   i ). In some cases, another layer such as a hard coating layer for preventing defects in the protective layer surface due to scratches or fingerprints may be formed over the protective layer. This completes a two-layer Blu-ray Disc. 
     The radiation curable resin A  404  used here is a material that has good adhesion to the first information layer  402  and the resin layer  414 , and the material of the resin layer  411  is one that will readily separate from the transfer stamper  407  and has good adhesion to the resin layer  414 . These radiation curable resins A, B, C, and D are resins that are substantially transparent to the wavelength of the recording and reproduction light. Also, what was described here was the process of producing a resin intermediate layer using three types of radiation curable resin, but there is also a simpler method in which the number of types of radiation curable resin is reduced by controlling the separability from the radiation curable resin and the like by proper selection of the transfer stamper material, and so forth. 
     Also, as shown in Patent Document 2, a four-layer information recording medium has been proposed that has four information recording layers. With a four-layer information recording medium, the thickness of the various resin intermediate layers must be varied to minimize the effect of interference from other layers. With spin coating, as discussed above, the desired thickness can be obtained by suitably adjusting the viscosity of the radiation curable resin, the spinning speed, the spinning duration, and the ambient atmosphere in which the spinning is performed (such as its temperature and humidity). Accordingly, spin coating has generally been the method employed to form resin layers of different thickness as in a four-layer information recording medium. 
     Patent Document 1: Japanese Laid-Open Patent Application 2002-092969 
     Patent Document 2: Japanese Laid-Open Patent Application 2004-213720 
     DISCLOSURE OF INVENTION 
     Nevertheless, when a resin intermediate layer is formed by spin coating, the following problems are encountered, mainly due to factors such as that the resin is supplied only to a certain region, or that the centrifugal force used for spreading varies with the radial position. In other words, it is difficult to form a radiation curable resin layer with a uniform thickness, and the resin ends up reaching all the way to the outer peripheral end face of the molded resin substrate, so the effect of surface tension at the end face causes the resin layer to build up at the outermost peripheral part. 
     Also, when spin coating is used, applying one coating of radiation curable resin takes somewhere around 10 seconds, and this is one of the things that lowers production efficiency in the manufacture of a multilayer information recording medium. Also, with spin coating, since the resin layers are formed while part of the resin dropped onto the substrate is spun off, more resin has to be dropped than is actually necessary for the information recording layers that are to be formed on the substrate. Consequently, the resin that is spun off either ends up being wasted, or has to be reused after going through an additional process such as recycling. This is another factor in reducing productivity. 
     Furthermore, in the manufacture of a multilayer information recording medium having three or four information layers, or in the formation of protective layers, coatings are applied over the information recording layers that have been formed before. Accordingly, when a coating is applied over a resin intermediate layer that has already been cured, the applied resin does not conform as well as when the coating is applied to the substrate. In particular, the contact angle is larger, and there is pronounced build-up of the resin layer at the innermost peripheral region or the outermost peripheral region (the ends of the coating region). 
     It is an object of the present invention to produce a plurality of resin layers having different thicknesses, and to manufacture a multilayer information recording medium having good signal characteristics, without reducing productivity. 
     A coating method involving an inkjet method in which non-contact coating can be performed, without requiring any special mask or the like in the desired coating region, is proposed as one means for solving these problems. 
     The method for manufacturing an information recording medium pertaining to the present invention is a method for manufacturing an information recording medium produced by the lamination of a substrate, a plurality of information layers, and a plurality of resin layers of different thickness that separate the information layers. With this method, the resin layers are formed by an inkjet coating method in which a curable resin is discharged at the substrate while either the substrate or an inkjet head is moved relative to the other. The inkjet coating is performed in a coating pattern in which the amount of resin dropped onto the substrate per unit of surface area varies for each of the regions that are aligned in the radial direction of the substrate. 
     Of the coating regions, the amount of resin dropped per unit of surface area in the innermost peripheral region and/or the outermost peripheral region is less than the amount of resin dropped per unit of surface area in an adjacent coating region that is adjacent to the innermost peripheral region and/or the outermost peripheral region. 
     The ratio of the amount of resin dropped per unit of surface area in the innermost peripheral region and/or the outermost peripheral region to the amount of resin dropped per unit of surface area in the adjacent coating region may satisfy the following conditions. Specifically, of the plurality of resin layers, this ratio in the resin layer applied adjacent to the substrate is same as or greater than the ratio in the resin layers applied over said resin layer. 
     The above-mentioned ratio is preferably changed according to the thickness of the resin layers. 
     The amount of resin dropped per unit of surface area can be varied by using either of the following two methods. Preferably, this is a method in which the amount of resin droplets discharged from the inkjet head is varied, or a method in which the coating resolution in the relative movement direction of the substrate with respect to the inkjet head, or a direction perpendicular to the relative movement direction, is varied. 
     The inkjet head preferably has a structure with which the curable resin is discharged according to a signal pattern applied to the inkjet head. The signal pattern may be a multipulse pattern corresponding to a single droplet, and a pattern in which this multipulse pattern is repeated at a specific discharge period. 
     The droplet amount may be changed by changing the pulse number of the multipulse pattern. 
     The droplet amount may be changed by changing the pulse amplitude of the multipulse pattern. 
     The coating resolution may be changed by changing the discharge period. 
     The inkjet head may have a piezoelectric element, and the curable resin may be discharged according to the signal pattern applied to the piezoelectric element. 
     The inkjet head may have a heater, and the curable resin may be discharged according to the signal pattern applied to the heater. 
     The discharge width of the curable resin with the inkjet head may be at least the width of the substrate in a perpendicular relation to the travel direction of the inkjet head. 
     The curable resin may be a radiation curable resin. 
     The radiation curable resin may be a UV curable resin. 
     ADVANTAGEOUS EFFECTS 
     With the present invention, resin layers of different thickness can be formed by using an inkjet coating method in which a curable resin is discharged at the substrate while either the substrate or an inkjet head is moved relative to the other. Furthermore, the inkjet coating is performed in a coating pattern in which the amount of resin dropped onto the substrate per unit of surface area varies for each of the regions that are aligned in the radial direction of the substrate, which has the following effect. The influence of build-up at the ends of the coating region that occurs in the production of a multilayer information recording medium composed of a plurality of information layers is eliminated, and a resin intermediate layer having a uniform film thickness can be achieved. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  illustrates an example of the resin coating region obtained with an inkjet coating apparatus in Embodiment 1 of the present invention; 
         FIG. 2  is a cross section illustrating an example of the structure of a multilayer information recording medium in Embodiment 1 of the present invention; 
         FIG. 3  illustrates an example of the step of transferring an information face to a resin intermediate layer in Embodiment 1 of the present invention; 
         FIG. 4  illustrates an inkjet coating apparatus in Embodiment 1 of the present invention; 
         FIG. 5  is a cross section of a typical structural example of an inkjet nozzle; 
         FIG. 6  illustrates an example of the nozzle layout with an inkjet head; 
         FIG. 7  illustrates the structure of the inkjet head in Embodiment 1 of the present invention; 
         FIG. 8  illustrates the relationship between the substrate and the inkjet nozzle in Embodiment 1 of the present invention; 
         FIG. 9  illustrates a multipulse pattern inputted to the inkjet head in Embodiment 1 of the present invention; 
         FIG. 10  illustrates an example of the shape of the build-up at the end face of the resin intermediate layer that is formed; 
         FIG. 11  is a cross section illustrating an example of the structure of a multilayer information recording medium in Embodiment 2 of the present invention; 
         FIG. 12  is a cross section of a conventional two-layer Blu-ray Disc; 
         FIG. 13  illustrates a conventional stamper production process; and 
         FIG. 14  illustrates a conventional process for producing a two-layer disk consisting of steps for producing a protective layer and a resin intermediate layer using spin coating. 
     
    
    
     KEY 
     
         
         
           
               101  substrate 
               102  innermost peripheral coating region 
               103  intermediate coating region 
               104  outermost peripheral coating region 
               201  molded resin substrate 
               202  first information face 
               203  first information layer 
               204  resin intermediate layer 
               205  second information face 
               206  second information layer 
               207  protective layer 
               301  base 
               302  photosensitive film 
               303  exposure beam 
               304  exposed part 
               305  bump pattern 
               306  recording base 
               307  conductive thin film 
               308  metal sheet 
               309  metal stamper 
               401  molded resin substrate 
               402  first information layer 
               403  rotary stage 
               404  radiation curable resin A 
               405  radiation emitter 
               406  resin layer 
               407  transfer stamper 
               408  rotary stage 
               409  radiation curable resin B 
               410  radiation emitter 
               411  resin layer 
               412  radiation curable resin C 
               413  rotary stage 
               414  resin layer 
               415  radiation emitter 
               416  second information layer 
               417  protective layer 
               501  discharge liquid 
               502  piezoelectric element or other vibrational element 
               503  heater 
               504  discharge liquid 
               601  molded resin substrate 
               602  first information face 
               603  first information layer 
               604  first resin intermediate layer 
               605  second information face 
               606  second information layer 
               607  second resin intermediate layer 
               608  third information face 
               609  third information layer 
               610  protective layer 
               701  molded resin substrate 
               702  first information layer 
               703  radiation curable resin 
               704  transfer stamper 
               705  center boss 
               706  pressure plate 
               707  vacuum chamber 
               708  vacuum pump 
               709  radiation emitting apparatus 
               710  first resin intermediate layer 
               801  molded resin substrate 
               802  first information layer 
               803  stage 
               804  inkjet head unit 
               805  inkjet head 
               806  micro-droplets of radiation curable resin A 
               807  radiation curable resin 
               901  inkjet nozzle 
               902  inkjet head 
               1001  molded resin substrate 
               1002  specific place 
               1003  inkjet head unit 
               1004  inkjet head unit 
               1101  inkjet nozzle 
               1102  inkjet head 
               1103  molded resin substrate 
               1301  substrate 
               1302  first information layer 
               1303  resin layer 
               1401  molded resin substrate 
               1402  first information face 
               1403  first information layer 
               1404  first resin intermediate layer 
               1405  second information face 
               1406  second information layer 
               1407  second resin intermediate layer 
               1408  third information face 
               1409  third information layer 
               1410  third resin intermediate layer 
               1411  fourth information face 
               1412  fourth information layer 
               1413  protective layer 
           
         
       
    
     BEST MODE FOR CARRYING OUT THE INVENTION 
     Summary of the Invention 
     The method for manufacturing an information recording medium pertaining to the present invention is a method for manufacturing an information recording medium produced by the lamination of a substrate, a plurality of information layers, and a plurality of resin layers of different thickness that separate the information layers. With this method, the resin layers are formed by an inkjet coating method in which a curable resin is discharged at the substrate while either the substrate or an inkjet head is moved relative to the other. The inkjet coating is performed in a coating pattern in which the amount of resin dropped onto the substrate per unit of surface area varies for each of the regions that are aligned in the radial direction of the substrate. The phrase “for each of the regions that are aligned in the radial direction of the substrate” is illustrated in  FIG. 1 , for example, in which the plurality of coating regions consists of three regions: an innermost peripheral coating region  102 , an intermediate coating region  103 , and an outermost peripheral coating region  104 . 
     Furthermore, the amount of resin dropped per unit of surface area in the innermost peripheral coating region  102  and/or the outermost peripheral coating region  104  is less than the amount of resin dropped per unit of surface area in the intermediate coating region  103 . 
     With the present invention, resin layers of different thickness can be formed by using an inkjet coating method in which a curable resin is discharged at the substrate while either the substrate or an inkjet head is moved relative to the other. Furthermore, the inkjet coating is performed in a coating pattern in which the amount of resin dropped onto the substrate per unit of surface area varies for each of the regions that are aligned in the radial direction of the substrate, which has the following effect. The influence of build-up of the innermost peripheral coating region  102  and/or the outermost peripheral coating region  104  that occurs in the production of a multilayer information recording medium composed of a plurality of information layers is eliminated, and a resin intermediate layer having a uniform film thickness can be achieved. 
     Formation of Resin Layer by Inkjet Printing 
     The formation of a resin layer by inkjet printing as it relates to the method for manufacturing an information recording medium pertaining to the present invention will now be described. Inkjet methods for discharging a resin are divided into two main types: piezo and thermal. There are also many other methods for discharging a resin, but what they all have in common is a structure in which micro-droplets are discharged from a small-diameter inkjet nozzle, so only a discharge liquid with low viscosity can be discharged. This does not refer to the viscosity of the discharge liquid in the liquid tank at normal temperature, and is restricted to the resin viscosity near the discharge openings of the inkjet nozzle. Accordingly, there are times when a method is used in which the discharge liquid viscosity is first lowered by heating (with a heater or the like) the area around the discharge openings in the inkjet nozzle, for example. With the inkjet nozzles that are commonly used or commercially available at present, the viscosity near the discharge openings of a discharge liquid that can be discharged ranges from about a few mPa·s to a few dozen mPa·s. Accordingly, in the production of a resin intermediate layer by inkjet method, a low viscosity resin is discharged, which means that the resin may run, etc., after coating. Also, since only micro-droplets with a volume of about 1 pL to 1 mL can be discharged as mentioned above, it is extremely difficult to apply a resin layer whose thickness is over 10 μm, for instance. Consequently, this method was never used in the manufacture of multilayer information recording media composed of a plurality of resin layers of different thickness. 
     However, the discharge of micro-droplets from an inkjet nozzle is extremely fast, and coating takes less than half the time as with a conventional spin coating method. Also, as mentioned previously, no special mask or the like is necessary, and many different patterns can be applied to the desired coating region. 
     In light of the above, the inventors of the present invention decided to form the resin layers of different thickness that occur in the production of a multilayer information recording medium by using inkjet printing. Furthermore, the inventors of the present invention realized the present invention with the goal of eliminating the influence of the build-up at the end of the coating region that is caused by lamination coating by using inkjet printing. 
       FIG. 5  consists of cross sections of a typical example of the structure of an inkjet nozzle. The liquid tank, the supply path of the discharged liquid, and so forth are not shown in this drawing.  FIG. 5   a  shows a type with which the discharge liquid  501  is discharged by being pushed out by a piezoelectric element or another such vibrational element  502 , and is called a piezo inkjet nozzle.  FIG. 5   b  shows a type with which the discharge liquid is instantly boiled with a heater  503 , so that the volumetric expansion of the discharge liquid  504  near the heater serves as the motive force in discharge, and this is called a thermal type. 
     Embodiment 1 
     In Embodiment 1, a method for manufacturing the three-layer information recording medium (in which there are three information layers) shown in  FIG. 2  will be described as an example. 
     This three-layer information recording medium has a molded resin substrate  601 , a first information layer  603 , a first resin intermediate layer  604 , a second information layer  606 , a second resin intermediate layer  607 , a third information layer  609 , and a protective layer  610 . The first information layer  603 , the second information layer  606 , the second resin intermediate layer  607 , and the third information layer  609  are composed of a metal thin film, or a thin film material that allows thermal recording. The first resin intermediate layer  604 , the second resin intermediate layer  607 , and the protective layer  610  are composed of a resin that is substantially transparent with respect to the recording and reproduction light. 
     A first information face  602  is formed by bumps on the molded resin substrate  601 . The first information layer  603  is laminated over the molded resin substrate  601 . The first resin intermediate layer  604  is formed over the first information layer  603 . A second information face  605  consisting of bumps is formed over the first resin intermediate layer  604 . The second information layer  606  is laminated over the second information face  605 . The second resin intermediate layer  607  is formed over the second information layer  606 . A third information face  608  consisting of bumps is formed over the second resin intermediate layer  607 . The third information layer  609  is laminated over the third information face  608 . The protective layer  610  covers the third information layer  609 . 
     The “substantially transparent” referred to here means having a transmissivity of about 90% or higher with respect to the recording and reproduction light, and “semitransparent” means having a transmissivity of at least 10% but no higher than 90% with respect to the recording and reproduction light. 
     With this three-layer Blu-ray Disc, a laser beam is incident from the protective layer  610  side, and signals can be recorded, reproduced, etc., by focusing the beam on the information layer where recording and reproduction are to be performed (from out of the first, second, and third information layers). 
     The thickness of the molded resin substrate  601  is approximately 1.1 mm, the thickness of the first resin intermediate layer  604  and the second resin intermediate layer  607  is set to approximately 25 μm and approximately 17 μm respectively, and the thickness of the protective layer  610  is set to approximately 58 μm. The resin intermediate layers and protective layer are not limited to these thicknesses, however, which can be set as desired. 
     The molded resin substrate  601  is formed from a disk composed of a polycarbonate or acrylic resin with an outside diameter of 120 mm, a center hole diameter of 15 mm, and a thickness of about 1.0 to 1.1 mm, so as to be interchangeable in terms of shape with CDs, DVDs, and other such optical disks. An information face such as guide grooves formed by bumps on one side is formed on the molded resin substrate  601  by resin molding (such as injection molding) using a metal stamper as shown in  FIG. 13   f . In Embodiment 1, a polycarbonate was used in the production. 
     If the information recording medium is a read-only medium, then the first information layer  603  may have at least the characteristic of reflecting reproduction light, and is formed, for example, by sputtering, vapor deposition, or another such method from a reflective material such as Al, Ag, Au, Si, SiO 2 , or TiO 2 . If the information recording medium is a recordable medium, then it will be necessary to write information by irradiation with recording light, so the medium may include at least a layer composed of a recording material such as phthalocyanine or another such organic dye, or a phase change material such as GeSbTe. If needed, a layer that will enhance the recording and reproduction characteristics may also be included, such as a reflecting layer or an interface layer. The second information layer  606  and the third information layer  609  can be formed in the same way. Since recording and reproduction are carried out by shining recording and reproduction light at the various information layers from the protective layer  610  side, the second information layer  606  and the third information layer  609  are constituted so that their transmissivity with respect to the wavelength of the recording and reproduction light is higher than that of the first information layer  603 . 
     The first resin intermediate layer  604  and the second resin intermediate layer  607  are substantially transparent with respect to the recording and reproduction light, and can be made, for example, from a UV curing resin whose main component is acrylic, a UV curing resin based on epoxy, or another such radiation curable resin. The “substantially transparent” referred to here means having a transmissivity of about 90% or higher with respect to the recording and reproduction light, and a material having a transmissivity of at least 95% is even better. The method for producing the first resin intermediate layer  604  consists of the following two steps. In the first step, the first information layer  603  is coated with a liquid radiation curable resin by the inkjet coating method described below. In the second step, a transfer stamper having an information face such as pits or guide grooves is utilized to transfer the information face to the radiation curable resin. The method for producing the second resin intermediate layer  607  is the same. 
       FIG. 3  illustrates an example of the step of transferring an information face to a resin intermediate layer in Embodiment 1 of the present invention. A molded resin substrate  701  is transported into a vacuum chamber  707 . The molded resin substrate  701  has a first information layer  702  that has been coated with a radiation curable resin  703 . A transfer stamper  704  is also disposed inside the vacuum chamber  707  here ( FIG. 3   a ). 
     The transfer stamper  704  is made from a polyolefin material, which is a material that parts well from a radiation curable resin, and is formed thinner than the molded resin substrate, in a thickness of 0.6 mm, for example. The purpose of this is so that when the transfer stamper is separated from the molded resin substrate, which is approximately 1.1 mm thick, the stiffness difference that results from the different thickness of the substrate can be utilized to bend back and separate the transfer stamper. A polyolefin material makes it easy to produce an information face such as pits or guide grooves formed by bumps on one side by a method such as injection molding using a conventional metal stamper, just as with the molded resin substrate. Also, since polyolefin materials have high transmissivity with respect to radiation such as UV rays, the radiation curable resin can be efficiently cured by irradiation through the transfer stamper. Furthermore, since polyolefin materials have low adhesion to a radiation curable resin that has been cured, they can be easily parted from the interface with the radiation curable resin after curing. 
     A center hole is made in the center of the transfer stamper  704  for eliminating eccentricity with the molded resin substrate  701  via a center boss  705 . The inside of the vacuum chamber  707  is evacuated by a rotary pump, a turbo molecular pump, or another such vacuum chamber  708 , with a vacuum atmosphere being produced in a short time. In Embodiment 1 of the present invention, when the pressure inside the vacuum chamber  707  reaches a degree of vacuum of 100 Pa or less, the transfer stamper  704  is placed over the molded resin substrate  701  ( FIG. 3   b ). A pressure plate  706  that is installed above the transfer stamper  704  applies pressure to the transfer stamper  704  at this point, and the information face on the transfer stamper  704  is transferred to the radiation curable resin  703 . 
     Because the inside of the vacuum chamber  707  is a vacuum atmosphere, the radiation curable resin  703  and the transfer stamper  704  can be stuck together without any bubbles being trapped in between. The molded resin substrate  701  and transfer stamper  704  that have been stuck together are irradiated with radiation through the transfer stamper  704  by a radiation emitting apparatus  709 , either inside the vacuum chamber  707  or after being taken out ( FIG. 3   c ). After this, a wedge is driven between the transfer stamper  704  and the molded resin substrate  701 , or compressed air is blown in, etc., to separate the transfer stamper  704  from the interface with the radiation curable resin  703  ( FIG. 3   d ). This forms a first resin intermediate layer  710  to which an information face has been transferred. 
     Besides what is discussed here, various other methods can also be used for transferring an information face to a radiation curable resin, such as using a metal or other different material as the transfer stamper, or irradiating with radiation from the molded resin substrate side. Whatever the method, it does not limit the effect of the invention in Embodiment 1. 
     The protective layer  610  is substantially transparent with respect to the recording and reproduction light, and can be, for example, a UV curable resin whose main component is acrylic, or a radiation curable resin such as an epoxy-based UV curable resin. The “substantially transparent” referred to here means having a transmissivity of about 90% or higher with respect to the recording and reproduction light, and a material having a transmissivity of at least 95% is even better. The protective layer  610  can be formed by any of various methods, such as spin coating, screen printing, gravure printing, or inkjet printing. Ideally, the same method as that used in the resin intermediate layer formation step is used as the method for forming the protective layer. For example, when the resin intermediate layer is applied by inkjet method, it is best if the protective layer is also produced by inkjet method. Also, coating with a radiation curable resin is not the only method for forming the protective layer, and it may instead be formed, for example, by affixing a sheet of material such as a polycarbonate resin or an acrylic resin, with an adhesive or the like in between. 
     With the multilayer information recording medium in Embodiment 1 of the present invention, recording and reproduction are performed by using a blue-violet laser with a laser beam of 405 nm, and using an objective lens with a NA of 0.85 to focus the beam on each information layer from the protective layer  610  side. The thickness from the surface of the protective layer  610  to the first information layer  603  is set to approximately 0.1 mm to reduce the effect of disk tilt. 
     The thickness setting values of this resin intermediate layer, however, are just an example, and the effect of the present invention will be the same at other thickness setting values. 
     A brief summary was given above of the constitution of and method for manufacturing a multilayer information recording medium in Embodiment 1 of the present invention, but the method for manufacturing a multilayer information recording medium of the present invention is characterized by the method for forming the information recording layer, and therefore the scope of the present invention is not limited by the constitution or manufacturing method of the rest. 
     The method for manufacturing a multilayer information recording medium in Embodiment 1 of the present invention, and particularly the method for producing the resin intermediate layer, will now be described in detail. 
       FIG. 4  illustrates an example of the step of applying a radiation curable resin using an inkjet coating apparatus in Embodiment 1 of the present invention. 
     First, as shown in  FIG. 4   a , a molded resin substrate  801  having a first information layer  802  formed on one side is fixed to a stage  803  by vacuum chucking or the like. An inkjet head unit  804  is disposed above the molded resin substrate  801 . The stage  803  and the inkjet head unit  804  are able to move relative to one another. 
     The method for fixing the inkjet head unit  804  and coating by parallel movement of the stage  803  will now be described. However, the stage  803  and the inkjet head unit  804  need only be moved relatively, so the stage  803  may instead be fixed and the inkjet head unit  804  moved in parallel, or both may be used. 
     The inkjet head unit  804  is moved in parallel with respect to the stage  803  while micro-droplets  806  of the radiation curable resin A are dropped from an inkjet head  805  onto the molded resin substrate  801 . Also, a heater can be provided to the inkjet head  805  to heat and reduce the viscosity of the resin in the inkjet head  805 . 
     After the coating region of the molded resin substrate  801  has been coated with the micro-droplets  806  of the radiation curable resin A, the stage  803  is moved under a radiation curable resin  807 , the stage  803  is moved, the surface is irradiated with radiation, and the coating of radiation curable resin is cured ( FIG. 4   b ). A UV lamp was used as the irradiation means here. There are various kinds of UV lamp, such as metal halide lamps, high-pressure mercury vapor lamps, and xenon lamps, but a xenon lamp was used here. However, the type of lamp is not limited to this, and the wavelength of the radiation, etc., must be selected according to the radiation curable resin being applied. 
     The region irradiated with radiation may be completely cured, but even if it is not completely cured, as long as it is cured to a state corresponding to this, the flow of resin can be suppressed. The phrase “a state corresponding to complete curing” used here refers to a state in which the resin is in the form of a gel or has a viscosity of at least 10,000 mPa·s. 
     When a resin intermediate layer is being produced, the step of transferring the information face to the resin intermediate layer as discussed above comes after this coating step, so the last radiation curable resin layer that is applied is sent to the information face transfer step shown in  FIG. 3  without being cured, or after being cured completely so that the information face can be transferred. 
     If this coating step is the protective layer production step, then no information layer transfer step is necessary, so the last radiation curable resin layer that is applied will also be completely cured. 
     The constitution of the inkjet head  805  will now be described. 
     One or more inkjet nozzles are provided to the inkjet head  805 . These nozzles are the ones generally used in printers used for printing text or drawing. An inkjet nozzle can discharge micro-droplets of ink whose main component is a pigment, dye, etc. With inkjet technology, development has been conducted to make the droplets as small as possible, such as droplets with a volume of about a few picoliters, and to drop these at high precision to achieve printing of higher resolution. Nevertheless, since there is no need with the present invention to form a relatively thick resin layer of 10 μm or more, for example, it is preferable to use an inkjet nozzle that can discharge droplets that are as large as possible. For instance, it is preferable to use an inkjet nozzle capable of discharging large droplets of about a few dozen picoliters. With printer-use inkjet nozzles that are currently readily available, the volume of the micro-droplets is about 5 to 50 pL, the corresponding dischargeable resin viscosity is about 5 to 20 mPa·s around the discharge area, and the operating frequency is about 1 to 20 kHz. 
     An inkjet head that has only one inkjet nozzle is possible, but providing a plurality of inkjet nozzles is a relatively simple matter. For example, as shown in  FIG. 6   a , there is a configuration in which inkjet nozzles  901  are arranged in a row perpendicular to the scanning direction of an inkjet head  902 , and as shown in  FIG. 6   b , there is a configuration in which a plurality of these 5 rows are arranged in the scanning direction. Alternatively, as shown in  FIG. 6   c , there is a configuration in which a plurality of rows are arranged, with the positions of the inkjet nozzles  901  offset slightly from row to row. The configuration of the nozzles in this inkjet head can be expressed by an index called nozzle resolution. Nozzle resolution refers to the number of nozzles provided per unit of length. For example, the number of nozzles per inch can be expressed in units of npi (nozzles per inch). 
     In Embodiment 1 of the present invention, an inkjet head with a nozzle resolution of 600 npi was used as the inkjet head  805 . A piezo system was used to discharge the resin, in which a piezoelectric element is used to push out the resin according to a signal pattern inputted to the piezoelectric element. However, the configuration of the inkjet head need not be the piezo type used in Embodiment 1, and the effect of the invention in Embodiment will be the same with a thermal head. 
     In Embodiment 1 of the present invention, it is preferable if the coating can be done in a length of 120 mm, which is the diameter of the molded resin substrate  801  that is the object of coating, in a single pass. In view of this, it is possible to arrange one or more rows of nozzles perpendicular to the scanning direction of the inkjet head, in a straight line and in a width of at least 120 mm. 
     As shown in  FIG. 7   a , it is also possible to apply the coating with an inkjet head unit  1003 , whose discharge width is narrower than the length of the coating object in a direction perpendicular to the scanning direction of the inkjet head (here, 120 mm, which is the diameter of the molded resin substrate  1001  serving as the coating object). In  FIG. 7   a , coating is commenced from a specific location  1002  of the molded resin substrate  1001 . However, the coating region cannot be coated in a single scan of the inkjet head. Also, the following problems are encountered if coating is performed by scanning the inkjet head a number of times over the substrate while shifting the scan by the width of the inkjet head each time. The seams between coated coating regions may have uneven thickness distribution, and resin applied subsequently may splatter onto the previously coated coating regions. 
     Accordingly, as shown in  FIG. 7   b , a preferable configuration is one in which an inkjet head unit  1004  is longer than the diameter of the molded resin substrate  1001 . 
     In view of this, with the inkjet coating apparatus in Embodiment 1 of the present invention, the molded resin substrate  1103  is coated using inkjet nozzles with a drive frequency of 7 hKz. More specifically, as shown in  FIG. 8 , 1000 inkjet nozzles  1101  are arranged in a straight line, perpendicular to the scanning direction and at a pitch of 141 μm, and three of these rows are used, with each row offset by 42.3 μm. Furthermore, an inkjet head  1102  provided with 3000 nozzles and an inkjet head length of 127 mm is used. This inkjet head configuration corresponds to a nozzle resolution of 600 npi. The discharge of resin can be selectively controlled for each of the inkjet nozzles. When all of the nozzles are used for discharge the resin, the resin can be dropped at a resolution of 600 dpi (dots per inch). For example, when resin is dropped using 1000 nozzles arranged in a single row, the resin is dropped at a resolution of 200 dpi. Thus selecting as desired the number of inkjet nozzles that drop the resin makes it possible to set as desired the resolution at which the resin is dropped. This is a method for changing the coating resolution in a direction perpendicular to the relative movement direction of the substrate with respect to the inkjet head, and is one way to change the coating resolution. 
     When resin is dropped from the inkjet head, a signal pattern consisting of the multipulse pattern shown in  FIG. 9   a  is inputted to the inkjet head, whereupon the resin is pushed out from the inkjet nozzles and dropped onto the substrate. This is because the resin is efficiently discharged from the inkjet nozzles filled with resin by utilizing the mechanical resonance produced when the force of pushing out the resin from the nozzles is applied to the head by a heater, a piezoelectric element, or the like provided to the head. For example, the multipulse pattern consisting of four pulses shown in  FIG. 9   a  is set to a pulse period with a frequency close to the mechanical resonance around the inkjet nozzles filled with resin. Four resin droplets discharged according one pulse are discharged from the nozzle openings, after which they merge in the air before reaching the substrate, and are dropped onto the substrate in the form of a single droplet. Therefore, if the amplitude of this multipulse pattern is changed, the amount of resin pushed out from the nozzles by the pulse varies, and changing the pulse number from four to five results in the amount of resin droplet increasing to 1.25 times. By thus changing the amplitude of the multipulse pattern, or setting the number of pulses that make up the multipulse pattern as desired, the amount of resin in one drop discharged from the inkjet nozzles can be changed. This functions as a droplet amount change method for changing the amount of resin dropped onto the substrate. 
     Also, the use of this multipulse pattern makes it possible for the inkjet nozzle to discharge resin stably in an amount of about 15 pL per drop, as long as the resin viscosity is about 5 to 20 mPa·s. 
     In dropping the resin onto the substrate, the resin is preferably dropped continuously onto the substrate while the substrate or the inkjet head is moved relatively. However, the coating resolution in the relative movement direction of the substrate with respect to the inkjet head is determined by the relative movement speed of the substrate with respect to the inkjet head and the timing at which the resin discharged from the inkjet head is dropped. The timing at which the resin discharged from the inkjet head is dropped is adjusted by repeating the multipulse pattern discussed above at a specific discharge period, as shown in  FIG. 9   b . The discharge period can be set as desired to vary the coating resolution in the relative movement direction of the substrate with respect to the inkjet head. Of course, if the multipulse pattern is eliminated at this discharge period timing, the resin will not be dropped, so it is possible to drop the resin at the desired coating locations. This is one way to vary the coating resolution in the relative movement direction of the substrate with respect to the inkjet head. 
     Working Example 1 
     Working Example 1 will now be described. As shown in  FIG. 1 , Working Example 1 is an experiment, and the results thereof, in which the coating region was divided into a plurality of regions, the resin drop amount per unit of surface area was varied for each coating region, and the conditions that eliminated build-up at the coating end faces shown in  FIG. 10  were examined. The “plurality of coating regions” comprised three regions: the innermost peripheral coating region  102 , the intermediate coating region  103 , and the outermost peripheral coating region  104 . 
     The three-layer information recording medium shown in  FIG. 2  was produced using the above-mentioned inkjet coating apparatus. With inkjet coating, unlike spin coating or other such methods, there is no need for a special mask or the like for limiting the coating region, and resin can be dropped in the desired amount per unit of surface area in the desired region. 
     In Working Example 1, when the first resin intermediate layer  604  in  FIG. 2  was applied, it was applied by changing the amount of resin dropped in regions partitioned into concentric circles, using the center of the substrate  101  as a reference as shown in  FIG. 1 . Here, the coating region was divided into three regions (the innermost peripheral coating region  102 , the intermediate coating region  103 , and the outermost peripheral coating region  104 ) partitioned into concentric circles, using the center of the substrate  101  as a reference, and coating was performed in different drop amounts per unit of surface area for the various regions. The resin used here was a UV curable acrylic resin, and its viscosity at a temperature of 25° C. was approximately 10 mPa·s. 
     First, the first resin intermediate layer  604  shown in  FIG. 2  was formed in a thickness of 25 μm. 
     In general, the following problem is encountered when regions partitioned into concentric circles are coated without varying the amount of resin dropped per unit of surface area. The first resin intermediate layer is formed over the first information layer formed on the substrate. The first information layer is not formed over the entire surface of the substrate, from its innermost diameter to its outermost diameter, and the substrate surface is exposed near its inside and outside diameters, and the first resin intermediate layer is formed so as to cover and hide the first information layer. Therefore, the radiation curable resin touches the substrate surface at the innermost and outermost peripheral parts of the resin coated region. Accordingly, the resin coated end faces rise up at a contact angle determined by the surface properties of the substrate, the surface tension of the resin, and other such factors, and it can be seen in  FIG. 10  how resin builds up at the end faces. In  FIG. 10 , a first information layer  1302  is formed over a substrate  1301 . A resin layer  1303  completely covers the first information layer  1302 , and also covers the exposed outer peripheral end of the substrate  1301 . The outer peripheral end of the resin layer  1303  rises up more than the flat portion further inward, and then drops off toward the outer peripheral side. 
     Out of the coating region, the innermost peripheral coating region  102  was the region from a diameter of 22 mm to a diameter of 24 mm, the intermediate coating region  103  was the region from a diameter of 24 mm to a diameter of 117 mm, and the outermost peripheral coating region  104  was the region from a diameter of 117 mm to a diameter of 119 mm. 
     The thickness of the first resin intermediate layer  604  was measured as follows. Using a laser with a wavelength of 405 nm as the light source, the beam was focused with a lens, and the lens was moved by an actuator while the beam was focused on the information layer formed on the molded resin substrate surface or the resin intermediate layer surface. A thickness gauge was used to measure the thickness from the amount this actuator was driven. 
     Table 1 shows the results of measuring build-up at the coated end face and the amount of resin dropped per unit of surface area for each region. Condition numbers 4 and 5 are working examples pertaining to the present invention, while condition numbers 1 to 3 and 6 to 8 are comparative examples. 
     Here, the inkjet head was fixed and coating was performed while the substrate was moved underneath at a constant speed of 120 mm/s. The coating resolution perpendicular to the relative movement direction of the substrate and the inkjet head was 600 dpi, and the amount of resin dropped per unit of surface area was varied by varying the coating resolution in the relative movement direction of the substrate and the inkjet head. Changes in the coating resolution were achieved by varying the discharge period of the multipulse pattern. After the substrate had passed under the inkjet head, the resin was irradiated with UV rays approximately one second later using a radiation emitting apparatus (a xenon UV lamp was used here), to effect semi-curing. Build-up at the end face was evaluated as follows. The thickness differences between the average thickness near a radius of 40 mm of an information recording medium with a diameter of 120 mm and the maximum or minimum value for thickness at a radius of 12 mm (the innermost peripheral end face), and between the average thickness and the maximum or minimum value for thickness at a radius of 58 mm (the outermost peripheral end face) were found. The acceptability standard was that the thickness differences were in the range of ±1 μml. 
     The discharge period was set to 70.6 μs for the intermediate coating region  103 , and the coating resolution in the relative movement direction of the substrate and the inkjet head was set to 3000 dpi. In contrast, the discharge period was changed to 235.2 us for the innermost peripheral coating region  102  and the outermost peripheral coating region  104 , and the coating resolution was changed to 900 dpi. 
     
       
         
           
               
               
               
               
               
               
               
               
             
               
                 TABLE 1 
               
               
                   
               
               
                   
                   
                   
                   
                   
                 Build-up 
                   
                 Build-up 
               
               
                   
                   
                   
                   
                   
                 at 
                   
                 at 
               
               
                   
                   
                   
                   
                   
                 peripheral 
                   
                 outer 
               
               
                   
                 Drop amount 
                 Drop amount 
                 Drop amount 
                 Drop amount 
                 inner 
                 Drop amount 
                 peripheral 
               
               
                 Condition 
                 in region 102 
                 in region 103 
                 in region 104 
                 ratio, regions 
                 end face 
                 ratio, regions 
                 end face 
               
               
                 number 
                 (L/m 2 ) 
                 (L/m 2 ) 
                 (L/m 2 ) 
                 102 and 103 
                 (μm) 
                 104 and 103 
                 (μm) 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
               
               
               
               
               
               
            
               
                 1 
                 16.2 
                 16.2 
                 16.2 
                 1.0 
                 5.2 
                 X 
                 1.0 
                 4.9 
                 X 
               
               
                 2 
                 14.6 
                 16.2 
                 14.6 
                 0.9 
                 3.1 
                 X 
                 0.9 
                 2.5 
                 X 
               
               
                 3 
                 13.0 
                 16.2 
                 13.0 
                 0.8 
                 1.3 
                 X 
                 0.8 
                 1.1 
                 X 
               
               
                 4 
                 11.3 
                 16.2 
                 11.3 
                 0.7 
                 0.2 
                 ◯ 
                 0.7 
                 −0.1 
                 ◯ 
               
               
                 5 
                 9.7 
                 16.2 
                 9.7 
                 0.6 
                 −0.9 
                 ◯ 
                 0.6 
                 −1.0 
                 ◯ 
               
               
                 6 
                 8.1 
                 16.2 
                 8.1 
                 0.5 
                 −2.1 
                 X 
                 0.5 
                 −2.4 
                 X 
               
               
                 7 
                 6.5 
                 16.2 
                 6.5 
                 0.4 
                 −3.0 
                 X 
                 0.4 
                 −3.2 
                 X 
               
               
                 8 
                 4.9 
                 16.2 
                 4.9 
                 0.3 
                 −4.3 
                 X 
                 0.3 
                 −4.3 
                 X 
               
               
                   
               
            
           
         
       
     
     As shown in Table 1, the following results were obtained when the drop amount ratio between the innermost peripheral coating region  102  and its adjacent region (the intermediate coating region  103 ), and the drop amount ratio between the outermost peripheral coating region  104  and its adjacent region (the intermediate coating region  103 ) were between 0.6 and about 0.7. More specifically, in condition number 4 (ratio 0.7) and condition number 5 (ratio 0.6), the thickness difference was within ±1 μm with respect to the average thickness near a radius of 40 mm. 
     Thus, it was found that there is less build-up at the coating end face when the amount of resin dropped per unit of surface area in the innermost peripheral region or the outermost peripheral region is reduced with respect to the adjacent coating region. 
     Furthermore, it was found that the coating end face ends up being concave if the amount of resin dropped per unit of surface area in the innermost peripheral region or the outermost peripheral region is reduced too much. 
     In this working example, the change in the amount of resin dropped per unit of surface area was achieved by changing the discharge period, but how the dropped amount is changed is not limited to this. The drop amount may be reduced by leaving the discharge period constant and changing the signal amplitude of the multipulse pattern inputted to the inkjet head, or the number of pulses of the multipulse pattern may be varied. 
     Also, a piezo head in which the resin was pushed out by a piezoelectric element was used as the inkjet head in this working example, but a thermal head may be used instead, in which the resin is pushed out by a heater. 
     Next, the first resin intermediate layer  604  was formed under the conditions of condition number 4 in Table 1, after which the second resin intermediate layer  607  was formed by going through an information face transfer step and then a step of forming the second information layer  606 . 
     The build-up at the coating end face in the formation of the second resin intermediate layer  607  was evaluated under the same conditions as in the formation of the first resin intermediate layer  604  above. The drop amount per unit of surface area was varied in three regions partitioned into concentric circles in the innermost peripheral coating region  102 , the intermediate coating region  103 , and the outermost peripheral coating region  104 . 
     Here again, an experiment was conducted in which the coating resolution perpendicular to the relative movement direction of the substrate and the inkjet head was 600 dpi, the coating resolution in the relative movement direction of the substrate and the inkjet head was varied by changing the discharge period, and the resin drop amount per unit of surface area was changed. Table 2 shows the results of this experiment. Condition numbers 4 and 5 are working examples pertaining to the present invention, while condition numbers 1 to 3 and condition number 6 are comparative examples. 
     
       
         
           
               
               
               
               
               
               
               
               
             
               
                 TABLE 2 
               
               
                   
               
               
                   
                   
                   
                   
                   
                 Build-up 
                   
                 Build-up 
               
               
                   
                   
                   
                   
                   
                 at 
                   
                 at 
               
               
                   
                   
                   
                   
                   
                 inner 
                   
                 outer 
               
               
                   
                 Drop amount 
                 Drop amount 
                 Drop amount 
                 Drop amount 
                 peripheral 
                 Drop amount 
                 peripheral 
               
               
                 Condition 
                 in region 102 
                 in region 103 
                 in region 104 
                 ratio, regions 
                 end face 
                 ratio, regions 
                 end face 
               
               
                 number 
                 (L/m 2 ) 
                 (L/m 2 ) 
                 (L/m 2 ) 
                 102 and 103 
                 (μm) 
                 104 and 103 
                 (μm) 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
               
               
               
               
               
               
            
               
                 1 
                 11.3 
                 11.3 
                 11.3 
                 1.0 
                 4.1 
                 X 
                 1.0 
                 3.8 
                 X 
               
               
                 2 
                 9.7 
                 11.3 
                 9.7 
                 0.9 
                 2.6 
                 X 
                 0.9 
                 2.3 
                 X 
               
               
                 3 
                 8.1 
                 11.3 
                 8.1 
                 0.7 
                 1.4 
                 X 
                 0.7 
                 1.3 
                 X 
               
               
                 4 
                 6.5 
                 11.3 
                 6.5 
                 0.6 
                 0.2 
                 ◯ 
                 0.6 
                 0.1 
                 ◯ 
               
               
                 5 
                 4.9 
                 11.3 
                 4.9 
                 0.4 
                 −0.8 
                 ◯ 
                 0.4 
                 −0.8 
                 ◯ 
               
               
                 6 
                 3.2 
                 11.3 
                 3.2 
                 0.3 
                 −1.6 
                 X 
                 0.3 
                 −1.8 
                 X 
               
               
                   
               
            
           
         
       
     
     As shown in Table 2, the following results were obtained when the drop amount ratio between the innermost peripheral coating region  102  and its adjacent region (the intermediate coating region  103 ), and the drop amount ratio between the outermost peripheral coating region  104  and its adjacent region (the intermediate coating region  103 ) were between 0.4 and about 0.6. More specifically, in condition number 4 (ratio 0.6) and condition number 5 (ratio 0.4), the thickness difference was within ±1 μm with respect to the average thickness near a radius of 40 mm. Thus, it was found that there is less build-up at the coating end face when the amount of resin dropped per unit of surface area in the innermost peripheral region or the outermost peripheral region is reduced with respect to the adjacent coating region. 
     It was also found that the thickness standard was met under conditions when the drop amount ratio was lower with the second resin intermediate layer  607  as compared to the results of Table 1 in which the first resin intermediate layer  604  was formed. 
     The reason is as follows as to why unfavorable results were obtained with condition number 3 (ratio 0.7) in Table 2 despite the fact that condition number 3 (ratio 0.7) in Table 2 had the same ratio as condition number 4 (ratio 0.7) in Table 1. Since the molded resin substrate  601  was coated with the first resin intermediate layer  604 , build-up was less likely to be large, whereas since the first resin intermediate layer  604  was coated with the second resin intermediate layer  607 , build-up was more likely to be large. Accordingly, with the first resin intermediate layer  604 , the drop amount ratio between the intermediate coating region  103  and the innermost peripheral coating region  102  and outermost peripheral coating region  104  has to be set large. By contrast, with the second resin intermediate layer  607 , the build-up will be too large if the drop amount ratio between the intermediate coating region  103  and the innermost peripheral coating region  102  and outermost peripheral coating region  104  is set large. 
     The above tells us that the ratio of the drop amount per unit of surface area for the plurality of resin layers of the resin intermediate layer is preferably larger (or at least the same) with the resin layers coating the substrate than with other resin layers. 
     The reason is as follows as to why build-up was more likely to occur at the end face with the second resin intermediate layer  607  than with the first resin intermediate layer  604 . The first resin intermediate layer  604  was formed by dropping resin onto the molded resin substrate  601 , but the second resin intermediate layer  607  was formed over the cured first resin intermediate layer  604 . Although it depends on the properties of the resin material, in general, with a UV curing acrylic resin with a viscosity of about 10 mPa·s, the resin will separate more easily when dropped onto a cured UV curing acrylic resin than when dropped onto a polycarbonate substrate. Also, this creates a tendency for the build-up to be larger at the end face. Actually, when the drop amount per unit of surface area for the innermost peripheral coating region  102  and the drop amount per unit of surface area for the outermost peripheral coating region  104  are set to be the same with respect to the drop amount in the adjacent intermediate coating region  103  (condition number 1 in Table 1), the following result is obtained. The amount of build-up at the end face corresponds to approximately 25% with respect to the average thickness near a radius of 40 mm. Also, this amount is larger than the approximately 20% that is the amount of build-up at the end face with respect to the average thickness near a radius of 40 mm in the case of the first resin intermediate layer dropped onto the substrate (condition number 1 in Table 1). 
     Changing the drop amount per unit of surface area here was accomplished by changing the discharge period, but how the drop amount is changed is not limited to this. For instance, drop amount may be reduced by leaving the discharge period constant and changing the signal amplitude of the multipulse pattern inputted to the inkjet head, or the number of pulses of the multipulse pattern may be varied. 
     Also, a piezo head in which the resin was pushed out by a piezoelectric element was used as the inkjet head in this working example, but a thermal head may be used instead, in which the resin is pushed out by a heater. 
     Working Example 2 
     A four-layer information recording medium is shown in  FIG. 11  as Embodiment 2 pertaining to the present invention. 
     This four-layer information recording medium has a molded resin substrate  1401 , a first information layer  1403 , a second information layer  1406 , a third information layer  1409 , a fourth information layer  1412 , and a protective layer  1413 . The four-layer information recording medium further has a first resin intermediate layer  1404 , a second resin intermediate layer  1407 , and a third resin intermediate layer  1410 . The first information layer  1403 , the second information layer  1406 , the third information layer  1409 , and the fourth information layer  1412  are composed of a thin-film material that allows thermal recording, or a metal thin film. The first resin intermediate layer  1404 , the second resin intermediate layer  1407 , the third information layer  1409 , the third resin intermediate layer  1410 , the fourth information layer  1412 , and the protective layer  1413  are composed of a resin that is substantially transparent with respect to the recording and reproduction light. 
     A first information layer  1402  is formed in a bumpy shape over the molded resin substrate  1401 . The first information layer  1403  is laminated over the first information face  1402 . The first resin intermediate layer  1404  is formed over the first information layer  1403 . A second information face  1405  is formed in a bumpy shape over the first resin intermediate layer  1404 . The second information layer  1406  is laminated over the second information face  1405 . A second resin intermediate layer  1407  is formed over the second information layer  1406 . A third information face  1408  is formed in a bumpy shape over the second resin intermediate layer  1407 . The third information layer  1409  is formed over the third information face  1408 . The third resin intermediate layer  1410  is formed over the third information layer  1409 . A fourth information face  1411  is formed in a bumpy shape over the third resin intermediate layer  1410 . The fourth information layer  1412  is laminated over the fourth information face  1411 . The protective layer  1413  covers the fourth information layer  1412 . 
     The thicknesses of the first resin intermediate layer  1404 , the second resin intermediate layer  1407 , the third resin intermediate layer  1410 , and the protective layer  1413  are set to 15 μm, 19 μm, 11 μm, and 55 μm, respectively. 
     Working Example 2 
     An experiment was conducted into this four-layer information recording medium under the same conditions as in Working Example 1. 
     Table 3 shows the results of measuring build-up or depression at the coated end face and the resin drop amount per unit of surface area in each region in the formation of the first resin intermediate layer  1404 . Condition numbers 2 and 3 are working examples pertaining to the present invention, while condition numbers 1 and 4 to 6 are comparative examples. 
     
       
         
           
               
               
               
               
               
               
               
               
             
               
                 TABLE 3 
               
               
                   
               
               
                   
                   
                   
                   
                   
                 Build-up 
                   
                 Build-up 
               
               
                   
                   
                   
                   
                   
                 at 
                   
                 at 
               
               
                   
                   
                   
                   
                   
                 inner 
                   
                 outer 
               
               
                   
                 Drop amount 
                 Drop amount 
                 Drop amount 
                 Drop amount 
                 peripheral 
                 Drop amount 
                 peripheral 
               
               
                 Condition 
                 in region 102 
                 in region 103 
                 in region 104 
                 ratio, regions 
                 end face 
                 ratio, regions 
                 end face 
               
               
                 number 
                 (L/m 2 ) 
                 (L/m 2 ) 
                 (L/m 2 ) 
                 102 and 103 
                 (μm) 
                 104 and 103 
                 (μm) 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
               
               
               
               
               
               
            
               
                 1 
                 9.4 
                 9.4 
                 9.4 
                 1.0 
                 2.4 
                 X 
                 1.0 
                 2.3 
                 X 
               
               
                 2 
                 8.5 
                 9.4 
                 8.5 
                 0.9 
                 0.7 
                 ◯ 
                 0.9 
                 0.6 
                 ◯ 
               
               
                 3 
                 7.5 
                 9.4 
                 7.5 
                 0.8 
                 −0.1 
                 ◯ 
                 0.8 
                 −0.3 
                 ◯ 
               
               
                 4 
                 6.6 
                 9.4 
                 6.6 
                 0.7 
                 −1.2 
                 X 
                 0.7 
                 −1.3 
                 X 
               
               
                 5 
                 5.6 
                 9.4 
                 5.6 
                 0.6 
                 −1.8 
                 X 
                 0.6 
                 −2.0 
                 X 
               
               
                 6 
                 4.7 
                 9.4 
                 4.7 
                 0.5 
                 −2.5 
                 X 
                 0.5 
                 −2.8 
                 X 
               
               
                   
               
            
           
         
       
     
     As is clear from the table, under condition numbers 2 (ratio 0.9) and 3 (ratio 0.8), in which the drop amount ratio between the intermediate coating region  103  and the innermost peripheral coating region  102  and outermost peripheral coating region  104  was set relatively high, build-up or depression was sufficiently reduced at the inner peripheral end face and the outer peripheral end face. On the other hand, under condition number 1 (ratio 1.0), condition number 4 (ratio 0.7), condition number 5 (ratio 0.6), and condition number 6 (ratio 0.5), build-up or depression was too large at the inner peripheral end face and the outer peripheral end face. These are examples in which the drop amount ratios between the intermediate coating region  103  and the innermost peripheral coating region  102  and between the intermediate coating region  103  and the outermost peripheral coating region  104  were set even higher, or were set relatively low. 
     The reason as to why favorable results were obtained when the drop amount ratios between the intermediate coating region  103  and the innermost peripheral coating region  102  and between the intermediate coating region  103  and the outermost peripheral coating region  104  were set relative high is as follows. Since the molded resin substrate  1401  is coated with the first resin intermediate layer  1404 , it is less likely that the build-up or depression will be large. Accordingly, the depression will be too large unless the drop amount ratios between the intermediate coating region  103  and the innermost peripheral coating region  102  and between the intermediate coating region  103  and the outermost peripheral coating region  104  are set relatively high. 
     Table 4 shows the results of measuring build-up or depression at the coated end face and the resin drop amount per unit of surface area in each region in the formation of the second resin intermediate layer  1407 . Condition numbers 4 and 5 are working examples pertaining to the present invention, while condition numbers 1 to 3 and 6 are comparative examples. 
     
       
         
           
               
               
               
               
               
               
               
               
             
               
                 TABLE 4 
               
               
                   
               
               
                   
                   
                   
                   
                   
                 Build-up 
                   
                 Build-up 
               
               
                   
                   
                   
                   
                   
                 at 
                   
                 at 
               
               
                   
                   
                   
                   
                   
                 inner 
                   
                 outer 
               
               
                   
                 Drop amount 
                 Drop amount 
                 Drop amount 
                 Drop amount 
                 peripheral 
                 Drop amount 
                 peripheral 
               
               
                 Condition 
                 in region 102 
                 in region 103 
                 in region 104 
                 ratio, regions 
                 end face 
                 ratio, regions 
                 end face 
               
               
                 number 
                 (L/m 2 ) 
                 (L/m 2 ) 
                 (L/m 2 ) 
                 102 and 103 
                 (μm) 
                 104 and 103 
                 (μm) 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
               
               
               
               
               
               
            
               
                 1 
                 11.9 
                 11.9 
                 11.9 
                 1.0 
                 4.3 
                 X 
                 1.0 
                 4.0 
                 X 
               
               
                 2 
                 10.7 
                 11.9 
                 10.7 
                 0.9 
                 2.6 
                 X 
                 0.9 
                 2.5 
                 X 
               
               
                 3 
                 8.3 
                 11.9 
                 8.3 
                 0.7 
                 1.6 
                 X 
                 0.7 
                 1.3 
                 X 
               
               
                 4 
                 7.1 
                 11.9 
                 7.1 
                 0.6 
                 0.5 
                 ◯ 
                 0.6 
                 0.5 
                 ◯ 
               
               
                 5 
                 4.8 
                 11.9 
                 4.8 
                 0.4 
                 −0.6 
                 ◯ 
                 0.4 
                 −0.7 
                 ◯ 
               
               
                 6 
                 3.6 
                 11.9 
                 3.6 
                 0.3 
                 −1.4 
                 X 
                 0.3 
                 −1.8 
                 X 
               
               
                   
               
            
           
         
       
     
     As is clear from the table, under condition numbers 4 (ratio 0.6) and 5 (ratio 0.4), build-up or depression was sufficiently reduced at the inner peripheral end face and the outer peripheral end face. These are examples in which the drop amount ratios between the intermediate coating region  103  and the innermost peripheral coating region  102 , between the outermost peripheral coating region  104  and the intermediate coating region  103 , and between the innermost peripheral coating region  102  and the outermost peripheral coating region  104  were set relatively low. On the other hand, under condition number 1 (ratio 1.0), condition number 2 (ratio 0.9), condition number 3 (ratio 0.7), and condition number 6 (ratio 0.3), build-up or depression was too large at the inner peripheral end face and the outer peripheral end face. These are examples in which the drop amount ratios between the intermediate coating region  103  and the innermost peripheral coating region  102  and outermost peripheral coating region  104  were set even higher, or were set even lower. 
     It was also found that the thickness standard was met under conditions when the drop amount ratio was lower as compared to the results of Table 4 in which the first resin intermediate layer  1404  was formed. 
     The reason is as follows as to why unfavorable results were obtained despite the fact that condition number 2 (ratio 0.9) in Table 4 had the same ratio as condition number 2 (ratio 0.9) in Table 3. Since the molded resin substrate  1401  was coated with the first resin intermediate layer  1404 , build-up was less likely to be large, whereas since the first resin intermediate layer  1404  was coated with the second resin intermediate layer  1407 , build-up was more likely to be large. Accordingly, with the first resin intermediate layer  1404  the drop amount ratio between the intermediate coating region  103  and the innermost peripheral coating region  102  and outermost peripheral coating region  104  has to be set high. By contrast, with the second resin intermediate layer  1407 , the build-up will be too large if the drop amount ratio between the intermediate coating region  103  and the innermost peripheral coating region  102  and outermost peripheral coating region  104  is set high. 
     The above tells us that the ratio of the drop amount per unit of surface area for the plurality of resin layers of the resin intermediate layer is preferably larger (or at least the same) with the resin layers coating the substrate than with other resin layers. 
     Table 5 shows the results of measuring build-up at the coated end face and the resin drop amount per unit of surface area in each region in the formation of the third resin intermediate layer  1410 . Condition numbers 3 and 4 are working examples pertaining to the present invention, while condition numbers 1, 2, 5, and 6 are comparative examples. 
     
       
         
           
               
               
               
               
               
               
               
               
             
               
                 TABLE 5 
               
               
                   
               
               
                   
                   
                   
                   
                   
                 Build-up 
                   
                 Build-up 
               
               
                   
                   
                   
                   
                   
                 at 
                   
                 at 
               
               
                   
                   
                   
                   
                   
                 inner 
                   
                 outer 
               
               
                   
                 Drop amount 
                 Drop amount 
                 Drop amount 
                 Drop amount 
                 peripheral 
                 Drop amount 
                 peripheral 
               
               
                 Condition 
                 in region 102 
                 in region 103 
                 in region 104 
                 ratio, regions 
                 end face 
                 ratio, regions 
                 end face 
               
               
                 number 
                 (L/m 2 ) 
                 (L/m 2 ) 
                 (L/m 2 ) 
                 102 and 103 
                 (μm) 
                 104 and 103 
                 (μm) 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
               
               
               
               
               
               
            
               
                 1 
                 6.9 
                 6.9 
                 6.9 
                 1.0 
                 3.0 
                 X 
                 1.0 
                 3.3 
                 X 
               
               
                 2 
                 6.2 
                 6.9 
                 6.2 
                 0.9 
                 2.3 
                 X 
                 0.9 
                 2.1 
                 X 
               
               
                 3 
                 5.5 
                 6.9 
                 5.5 
                 0.8 
                 0.8 
                 ◯ 
                 0.8 
                 0.5 
                 ◯ 
               
               
                 4 
                 4.8 
                 6.9 
                 4.8 
                 0.7 
                 −0.6 
                 ◯ 
                 0.7 
                 −0.6 
                 ◯ 
               
               
                 5 
                 4.1 
                 6.9 
                 4.1 
                 0.6 
                 −1.6 
                 X 
                 0.6 
                 −1.8 
                 X 
               
               
                 6 
                 2.8 
                 6.9 
                 2.8 
                 0.4 
                 −2.6 
                 X 
                 0.4 
                 −2.7 
                 X 
               
               
                   
               
            
           
         
       
     
     As is clear from the table, under condition numbers 3 (ratio 0.8) and 4 (ratio 0.7), build-up or depression was sufficiently reduced at the inner peripheral end face and the outer peripheral end face. These are examples in which the drop amount ratios between the intermediate coating region  103  and the innermost peripheral coating region  102  and outermost peripheral coating region  104  were set to a medium level. On the other hand, under condition number 1 (ratio 1.0), condition number 2 (ratio 0.9), condition number 5 (ratio 0.6), and condition number 6 (ratio 0.4), build-up or depression was too large at the inner peripheral end face and the outer peripheral end face. These are examples in which the drop amount ratios between the intermediate coating region  103  and the innermost peripheral coating region  102  and outermost peripheral coating region  104  were set even higher, or were set even lower. 
     It was also found that the thickness standard was met under conditions when the drop amount ratio was lower as compared to the results of Table 3 in which the first resin intermediate layer  1404  was formed, and that the thickness standard was met under conditions when the drop amount ratio was higher as compared to the results of Table 4 in which the second resin intermediate layer  1407  was formed. 
     The reason why unfavorable results were obtained with condition number 2 (ratio 0.9) in Table 5 despite the fact that condition number 2 (ratio 0.9) in Table 5 had the same ratio as condition number 2 (ratio 0.9) in Table 3 is as discussed in the explanation of Table 4. 
     The reason is as follows as to why unfavorable results were obtained despite the fact that condition number 5 (ratio 0.6) and condition number (ratio 0.4) in Table 5 had the same ratio as condition number 4 (ratio 0.6) and condition number 6 (ratio 0.4) in Table 4. Since the second resin intermediate layer  1407  was thick (with a thickness of 19 μm), build-up was more likely to be large at the coated end face, whereas since the third resin intermediate layer  1410  was thin (with a thickness of 11 μm), build-up was less likely to be large at the coated end face. Accordingly, with the second resin intermediate layer  1407  the drop amount ratio between the intermediate coating region  103  and the innermost peripheral coating region  102  and outermost peripheral coating region  104  has to be set low. By contrast, with the third resin intermediate layer  1410 , the depression at the coated end face will be too large if the drop amount ratio between the intermediate coating region  103  and the innermost peripheral coating region  102  and outermost peripheral coating region  104  is set low. 
     Because of this, the drop amount ratios per unit of surface area for a plurality of resin layers is preferably varied according to the thickness of the plurality of resin layers, and more specifically, it was found that the greater is the thickness, the better it is to lower the ratio. 
     Other Embodiments 
     Embodiments of the present invention will described above, but the present invention is not limited to the above-mentioned embodiments, and various modifications are possible without departing from the gist of the invention. 
     In the above embodiments, the coating of the intermediate region between the outermost peripheral coating region and the innermost peripheral coating region was all performed under the same conditions, but the present invention is not limited to this. For example, the intermediate coating region may be further divided into a plurality of regions, and the coating conditions made different for each one. 
     In the above embodiments, the outermost peripheral coating region, the innermost peripheral coating region, and the intermediate coating region were formed as concentric circles, but the present invention is not limited to this. For example, as long as each region is annular in shape, the edges of the regions need not be circular. 
     INDUSTRIAL APPLICABILITY 
     The inkjet coating method of the present invention is useful as a way to form resin layers such as resin intermediate layers in a multilayer information recording medium, and in particular can be used in the resin layer lamination process for Blu-ray Discs and the like.