Patent Publication Number: US-2009218718-A1

Title: Manufacturing method for a mold

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application is based upon and claims the benefit of priority of the prior Japanese Patent Application No. 2008-36584 filed on Feb. 18, 2008, the entire contents of which are incorporated herein by reference 
     BACKGROUND 
     1. Field 
     An aspect of the invention relates to a manufacturing method for a mold. The mold is used to make a magnetic medium. 
     2. Description of the Related Art 
     A magnetic medium such as a so-called bit patterned medium is assembled to, for example, a hard disc drive unit (HDD). The bit patterned medium has nano holes on a front surface which are disposed, for example, regularly. Magnetic bodies are buried in the nano holes. For example, one magnetic body constitutes one recording bit. The bit patterned medium greatly contributes to improved recording density. 
     The bit patterned medium is manufactured making use of a mold. Nano-patterns are formed on a front surface of the mold. When an aluminum film is formed on the front surface of the mold, the nano-patterns are transferred onto the aluminum film. The aluminum film is exfoliated from the mold. Thereafter, a front surface of the aluminum film is subjected to an anodic oxidation process. Nano holes are formed on the front surface of the aluminum film. Thereafter, the nano holes are filled with the magnetic bodies. 
     When a contour of the aluminum film is larger than a contour of the magnetic medium, the contour of the aluminum film is cut out along the contour of the magnetic medium. This is a troublesome process. Accordingly, to simplify the manufacturing process, it is preferable that the contour of the aluminum film agree with the contour of the magnetic medium. In other words, it is preferable that a contour of the mold agree with the contour of the magnetic medium. 
     When the mold is formed, a nickel film is formed based on, for example, a front surface of a substrate, by electrolytic plating. The nickel film is removed from the substrate. Nano-patterns of the substrate are transferred onto the nickel film. In general, in the electrolytic plating process, the film thickness of the nickel film is increased toward an outer periphery. However, the film thickness of the nickel film, i.e. the thickness of the mold is uniform. Accordingly, an allowance for punching is previously formed in the nickel film along the outer periphery. The nickel film has a uniform film thickness inside of the allowance for punching. The mold is punched from the nickel film. 
     [Patent Document 1] 
     Japanese Laid-open Patent Publication No. 2005-212428 
     When the mold is punched, a press process, for example, is used. In the press process, a punching surface of a male mold is pressed against a front surface of the nickel film. The nano-patterns are formed on the front surface of the nickel film as described above. Accordingly, the punching surface is pressed against the front surface of the nickel film in a region other than the nano-patterns. As a result, the male mold cannot cause a sufficient load to act on the nickel film. Thus, the nickel film cannot be sufficiently fixed. When the male mold goes into a female mold in this state an outside edge of the mold, for example, is deformed. This mold cannot be used to transfer the nano-patterns. 
     The object and advantages of the invention will be realized and attained by means of the elements and combinations particularly pointed out in the claims. It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory and are not restrictive of the invention, as claimed. 
     SUMMARY 
     According to an aspect of an embodiment, a manufacturing method for a mold includes a step of forming a protection film having fluidity on a front surface of a base material on which concave/convex patterns are partitioned, and a step of punching a mold from the base material by causing a male mold to come into a female mold while overlapping a punching surface of the male mold on a back surface of the base material. 
     Additional objects and advantages of the invention will be set forth in part in the description which follows and, in part will be obvious from the description, or may be learned by practice of the present invention. The object and advantages of the invention will be realized and attained by means of the elements and combinations particularly pointed out in the appended claims. It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the invention, as claimed. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view schematically showing a structure of a mold; 
         FIG. 2  is a side elevational view schematically showing a structure of an overlapping member; 
         FIG. 3  is a side elevational view schematically showing how a protection film is formed on a front surface of the overlapping member; 
         FIG. 4  is a sectional view schematically showing how the overlapping member is disposed on a female mold; 
         FIG. 5  is a sectional view schematically showing how a front surface of a base material is overlapped on the front surface of the overlapping member; 
         FIG. 6  is a sectional view schematically showing how the base material is pressed against the female mold; 
         FIG. 7  is a sectional view schematically showing how the female mold goes into the male mold a mold is punched thereby; 
         FIG. 8  is a sectional view schematically showing how the base material is exfoliated from the overlapping member after the mold is punched; and 
         FIG. 9  is a sectional view schematically showing how the base material is disposed on the female mold. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     An embodiment of the present invention will be explained below referring to the accompanying drawings. 
       FIG. 1  schematically shows a structure of an object, i.e. a mold  11  according to a specific example. The mold  11  is formed in, for example, a disk-shape. The mold  11  is formed of a metal material, for example, nickel. The mold has a thickness of, for example, about 0.2 mm to 0.3 mm. The mold  11  has the same diameter as that of a magnetic medium as a manufacturing object. The diameter of the mold  11  is set to, for example, 1 inch. A center hole  12  of the mold  11  is formed at the center of the mold  11 . The center hole  12  passes through the mold  11  from a front surface to a back surface. The axis of the center hole  12  agrees with the axis of the mold  11 . 
     Nano-patterns i.e. concave/convex patterns (not shown) to be described later are partitioned on a front surface of the mold  11 . The concave/convex patterns partition predetermined concaves and convexes according to, for example, a shape of recording tracks of a magnetic medium. A difference in height of the concaves and convexes is set to, for example, about 100 nm. The concave/convex patterns are formed based on, for example, an electrolytic plating method. When the concave/convex patterns are formed, a nickel film is formed on a substrate on a front surface on which, for example, the concave/convex patterns are previously formed. After the nickel film is formed, it is exfoliated from the substrate. With this operation, the concave/convex patterns are transferred onto a front surface of the nickel film. However, the transferred patterns may be formed by, for example, radiating an electron beam. 
     The mold  11  described above is used when a magnetic storage medium such as a so-called discrete track medium and a so-called bit patterned medium, i.e. a magnetic medium is manufactured. When the magnetic medium is manufactured, first, an aluminum film is formed to a uniform film thickness on the front surface of the mold  11 . When the aluminum film is formed, a well-known sputtering method is executed. A glass substrate, for example, is bonded on a back surface of the aluminum film. An adhesive is used to bond the glass substrate. The aluminum film is exfoliated from the mold  11  together with the glass substrate. With this operation, the concave/convex patterns are transferred onto the front surface of the aluminum film. 
     Thereafter, the front surface of the aluminum film is subjected to an anodic oxidation process. The front surface of the aluminum film is oxidized by the anodic oxidation process. As a result, so-called nano holes grow from the concave/convex patterns. The front surface of the aluminum film is changed to an alumina film. The nano holes formed as described above are filled with magnetic bodies. After the magnetic bodies are filled, the front surface of the aluminum film is subjected to a polishing process. Thereafter, a DLC film and a lubricating film are formed on the front surface of the aluminum film. The magnetic medium is manufactured as described above. 
     Next, a method of manufacturing the mold  11  will be explained. As shown in  FIG. 2 , in the manufacture of the mold  11 , first, a disk-shaped overlapping member  15 , for example, is prepared. The diameter of the overlapping member  15  is set larger than that of the mold  11 . The overlapping member  15  is formed somewhat larger than that of the mold  11 . That is, the overlapping member  15  is provided with an allowance for punching. Here, the overlapping member  15  has a diameter of, for example, about 50 mm. The overlapping member  15  has a uniform thickness. The overlapping member  15  is formed of a solid. Here, the overlapping member  15  is formed of a metal material, for example, nickel. 
     A resin material, i.e. a thermoplastic material is coated on the front surface of the overlapping member  15 . A spin coating method, for example, is executed to coat the resin material. Thermoplastic resin such as polymethylmethacrylate resin (PMMA) is used as the resin material. When the spin coating method is executed, the resin material is heated to a predetermined temperature. As a result, as shown in  FIG. 3 , a protection film  16  having a uniform film thickness is formed on the front surface of the overlapping member  15 . The protection film  16  has a film thickness larger than the difference in height of the concaves and convexes partitioned on the front surface of the mold  11  described above. Here, the protection film  16  has a film thickness of, for example, about 150 nm. 
     Subsequently, as shown in  FIG. 4 , a press machine  21  is prepared. The press machine  21  has a die plate  22 . The die plate  22  has a female mold  23 . A front surface of the female mold  23  is formed in a flat surface. A columnar guide hole  24  is formed to the female mold  23 . The guide hole  24  extends in a vertical direction orthogonal to the front surface of the female mold  23 . The guide hole  24  has a diameter of, for example, 1 inch. The guide hole  24  has an opening  24   a  on the front surface of the female mold  23 . A columnar receiving member  25  is disposed to the opening  24   a  of the guide hole  24 . The receiving member  25  is exposed to the front surface of the female mold  23  through the opening  24   a . The guide hole  24  guides movement of the receiving member  25  in a vertical direction. 
     A front surface of the receiving member  25  is formed in a flat surface. Accordingly, when the receiving member  25  is positioned at, for example, a reference position, the front surface of the receiving member  25  is made flush with the front surface of the female mold  23 . At that time, a flat surface  22   a  is formed by the female mold  23  and the receiving member  25 . A contour on the front surface of the receiving member  25  is formed in the shape of a contour of the mold  11 . The receiving member  25  is formed of, for example, a metal material. A heater (not shown) is assembled to the receiving member  25 . The heater can increase the temperatures of the receiving member  25  and the female mold  23  by the heat generated thereby. The heater may be formed of, for example, an electrically heating wire. 
     The press machine  21  has a press mechanism  26 . The press mechanism  26  can relatively move along the axial center of the guide hole  24  with respect to the die plate  22 . The press mechanism  26  has a support block  27 . A lower surface of the support block  27  is formed in a flat surface. A columnar guide hole  28  is formed to the support block  27 . The guide hole  28  extends in the vertical direction orthogonal to the flat surface  22   a  of the die plate  22 . The guide hole  28  has a diameter of, for example, 1 inch. A columnar male mold  29  is received by the guide hole  28 . The male mold  29  is exposed to the lower surface of the support block  27 . The guide hole  28  guides movement of the male mold  29  in the vertical direction. 
     An extreme end surface, i.e. a punching surface  29   a  of the male mold  29  is formed in a flat surface. Accordingly, when the male mold  29  is positioned to for example, the reference position, the lower surface of the support block  27  and the punching surface  29   a  of the male mold  29  are made flush with each other. At that time, a flat surface  27   a  is formed by the lower surface of the support block  27  and the punching surface  29   a  of the male mold  29 . The flat surface  27   a  spreads in parallel with the flat surface  22   a  of the die plate  22 . The male mold  29  and the receiving member  25  define a contour along a column drawn by the same bus. The punching surface  29   a  has a diameter of, for example, 1 inch. With this arrangement, the male mold  29  can come into the female mold  23 , i.e. into the guide hole  24 . 
     The die plate  22  has the overlapping member  15  disposed at a predetermined position of the flat surface  22   a . When the overlapping member  15  is disposed, the axis of the overlapping member  15  is aligned with the axis of the receiving member  25 . The heater of the receiving member  25  heats the receiving member  25  and female mold  23 . Heat is transmitted to the overlapping member  15 . The temperatures of the overlapping member  15  and the protection film  16  are increased. The temperature of the protection film  16  is set to, for example, about 100° C. to 120° C. As a result, the protection film  16  is softened on the front surface of the overlapping member  15 . The protection film  16  has fluidity. The fluidity of the protection film  16  is maintained by the temperature of the heater. 
     At the time, as shown in  FIG. 5 , the front surface of the overlapping member  15  is overlapped with a disk-shaped nano pattern member, i.e. a front surface of a base material  31 . Concave/convex patterns  32  are formed on the front surface of the base material  31 , i.e. a nano pattern forming surface. The concave/convex patterns  32  are formed on the front surface of the base material  31  inward of the allowance for punching. The base material  31  is formed of simple nickel. The contour of the base material  31  is caused to conform with, for example, the contour of the overlapping member  15 . Here, the base material  31  has a diameter of, for example, about 50 mm. Thus, an allowance for punching is formed in the base material  31  similar to that of the overlapping member  15 . Here, a mold lubricant (not shown) is coated on the front surface of the base material  31  before the base material  31  is overlapped with the overlapping member  15 . 
     When the base material  31  is overlapped with the overlapping member  15 , the protection film  16  is clamped between the front surface of the overlapping member  15  and the front surface of the base material  31  by the action of the fluidity of the protection film  16 . When the base material  31  is overlapped with the overlapping member  15 , the environment in the periphery of the press machine  21  is set to a pressure lower than the atmospheric pressure. Here, the pressure is set to, for example, about one tenth the atmospheric pressure. As a result, the protection film  16  sufficiently comes into intimate contact with the concave/convex patterns  32  of the base material  31  and with the overlapping member  15 . Air is expunged from between the protection film  16  and the base material  31  and the overlapping member  15 . 
     As shown in  FIG. 6 , the press mechanism  26  presses the base material  31  against the die plate  22  through the flat surface  27   a . The male mold  29  is received and stopped on the back surface of the base material  31  by the punching surface  29   a . With this arrangement, the base material  31  and the overlapping member  15  are clamped between the punching surface  29   a  and the front surface of the receiving member  25 . The lower surface of the support block  27  is received and stopped by the base material  31  in the periphery of the punching surface  29   a . With this arrangement, the base material  31  and the overlapping member  15  are clamped by the flat surface  22   a  and the flat surface  27   a . At that time, it is sufficient for the environment in the periphery of the press machine  21  to be set to the atmospheric pressure. The press force is set to, for example, about several hundreds of [Pa] to several tens of [kPa]. 
     As described above, the protection film  16  has fluidity. As a result, the protection film  16  comes securely into the concaves and convexes of the concave/convex patterns  32  of the base material  31  by the press force. The protection film  16  sufficiently comes into intimate contact with the overlapping member  15  and the base material  31 . With this arrangement, the base material  31  and the overlapping member  15  are securely held at a predetermined position between the flat surface  22   a  and the flat surface  27   a . Since the base material  31  and the overlapping member  15  are clamped between the flat surfaces  22   a ,  27   a , they are prevented from being deformed. Moreover, since the film thickness of the protection film  16  is larger than the concaves and convexes of the concave/convex patterns  32 , the concave/convex patterns  32  of the base material  31  do not come into contact with the overlapping member  15 . Thus, damage to the concave/convex patterns  32  can be avoided. 
     At that time, as shown in  FIG. 7 , the male mold  29  instantly falls toward the female mold  23  in a direction orthogonal to the front surface of the base material  31 , i.e. in parallel with a direction in which the base material  31  and the overlapping member  15  are laminated. The male mold  29  punches a punching component  33  from the base material  31  and the overlapping member  15  along a contour of the punching surface  29   a . The male mold  29  goes into the guide hole  24  of the female mold  23 . After the punching component  33  is punched, it is taken out from the press machine  21 . The punching component  33  is cooled to room temperature. As a result, the protection film  16  is hardened. Thereafter, as shown in  FIG. 8 , the base material  31  after it is punched, i.e. the mold  11  is taken away from the protection film  16 . Since the mold lubricant is coated on the front surface of the base material  31 , taking out the mold  11  can be easily executed. The mold  11  is manufactured as described above. 
     According to the manufacturing method of the mold  11 , the protection film  16  having the fluidity is clamped between the base material  31  and the overlapping member  15 . As a result, the male mold  29  can press the base material  31  against the flat surface  22   a  through the entire punching surface  29   a  formed by the flat surface. The base material  31  is securely held at a predetermined position. Moreover, a press force, which acts from the punching surface  29   a  when the punching component  33  is punched, is absorbed by the protection film  16 . Deformation of the base material  31  is suppressed. Damage to the concave/convex patterns  32  of the base material  31  is avoided. The mold  11  is manufactured with pinpoint accuracy. Since the mold  11  is simply punched as described above, high mass productivity is sufficiently realized. Moreover, since the protection film  16  is clamped between the base material  31  and the overlapping member  15 , the protection film  16  is not adhered to the male mold  29 , the female mold  23 , and the receiving member  25 . 
     In the manufacturing method of the mold  11  described above, when the base material  31  is overlapped with the overlapping member  15 , the base material  31  may be disposed on the flat surface  22   a  of the die plate  22  first as shown in  FIG. 9 . It is sufficient for the front surface of the overlapping member  15  to be overlapped with the front surface of the base material  31 . Thus, the flat surface  27   a  of the press mechanism  26  is received and stopped by a back surface of the overlapping member  15 . The male mold  29  punches the overlapping member  15  and the base material  31  in this order. The mold  11  may be manufactured as described above. With this operation, the same operation/working-effect as that described above can be realized. 
     Further, the overlapping member  15  may use a metal material softer than, for example, nickel. The metal material includes, for example, copper, aluminum, and brass. When the mold  11  is manufactured by the overlapping member  15  made of the soft metal material, it can be deformed prior to the base material  31  formed of nickel. As a result, the overlapping member  15  can absorb the press force acting from the male mold  29  in addition to the protection film  16 . Accordingly, the deformation of the base material  31  is further avoided, and the mold  11  is manufactured with a more pinpoint accuracy. 
     As described above, according to the present invention, there is provided a manufacturing method of an object having a pinpoint accuracy. 
     All examples and conditional language recited herein are intended for pedagogical purposes to aid the reader in understanding the invention and the concepts contributed by the inventor to furthering the art, and are to be construed as being without limitation to such specifically recited examples and conditions, nor does the organization of such examples in the specification relate to a showing of the superiority and inferiority of the invention. Although the embodiment(s) of the present inventions have been described in detail, it should be understood that the various changes, substitutions, and alterations could be made hereto without departing from the spirit and scope of the invention.