Patent Publication Number: US-2009232930-A1

Title: Disk Molding Mold, Mirror Surface Disk, and Method of Manufacturing Mirror Surface Disk

Description:
TECHNICAL FIELD 
     The present invention relates to a disk molding mold, a mirror surface disk, and a method of manufacturing a mirror surface disk. 
     BACKGROUND ART 
     Conventionally, in an injection molding machine for molding disk substrates, resin melted within a heating cylinder is charged into a cavity in a disk molding mold, and is then cooled and solidified in the cavity so as to obtain a molded disk substrate. 
     For such a molding process, the above-described injection molding machine includes the disk molding mold consisting of a stationary mold and a movable mold; an injection apparatus for charging resin into a cavity; and a mold-clamping apparatus for bringing the movable mold into contact with the stationary mold or separating the movable mold from the stationary mold. The mold-clamping apparatus is operated so as to advance and retreat the movable mold to thereby close, clamp, and open the disk molding mold. When the disk molding mold is clamped, a cavity is formed between the stationary mold and the movable mold. Notably, a mirror surface disk having a mirror-finished surface is disposed on the side facing the cavity, on each of the stationary mold and the movable mold. 
     The injection apparatus includes a heating cylinder; an injection nozzle attached to the front end of the heating cylinder; and a screw disposed within the heating cylinder so that the screw can rotate and can advance and retreat. 
     In a metering step, the screw is rotated, whereby resin is melted and accumulated forward of the screw, and the screw is retreated accordingly. During this period, the disk molding mold is closed and clamped. Subsequently, in an injection step, the screw is advanced, whereby the resin accumulated forward of the screw is injected from the injection nozzle and charged into the cavity. Next, in a cooling step, the resin within the cavity is cooled, whereby a prototype of a disk substrate; i.e., a disk substrate prototype, is formed. Before the resin solidifies completely, punching is performed on the disk substrate prototype, whereby the disk substrate is formed. Subsequently, the disk molding mold is opened, and the disk substrate is removed therefrom. 
     Incidentally, fine pits and projections are formed on a surface of the disk substrate. Therefore, a stamper is attached to, for example, the mirror surface disk of the stationary mold. A pattern composed of a plurality of pits corresponding to the fine recesses and projections is formed on the stamper, and, as a result of molding, the pattern is transferred to the disk substrate. 
     In this case, when the mirror surface disk is formed to have heat insulation properties, the pattern transcription performance can be improved, and the molding cycle can be shortened (see, for example, Patent Document 1). Patent Document 1: Japanese Patent Application Laid-Open (kokai) No. 2003-311798 
     DISCLOSURE OF THE INVENTION 
     Problems to be Solved by the Invention 
     However, in the above-described conventional disk molding mold, it is difficult to uniformly cool resin within a cavity, and, when a very thin disk substrate is formed, warpage may occur with a resultant decrease in quality of the disk substrate. 
     An object of the present invention is to solve the above-mentioned problem in the conventional disk molding mold and to provide a disk molding mold, a mirror surface disk, and a method of manufacturing a mirror surface disk, which can prevent a disk substrate from warping, and can improve the quality of the disk substrate. 
     MEANS FOR SOLVING THE PROBLEMS 
     To achieve the above object, a disk molding mold according to the present invention comprises a first support plate; a first mirror surface disk attached to the first support plate; a second support plate; and a second mirror surface disk attached to the second support plate and facing the first mirror surface disk. 
     At least one of the first and second mirror surface disks includes a first plate, and a second plate disposed to surround at least a front surface of the first plate. 
     The first plate includes a temperature control flow passage formed on a surface thereof facing the first support plate. The second plate includes a heat insulation section formed on a surface thereof facing the first plate such that the heat insulation section corresponds to the temperature control flow passage. 
     EFFECT OF THE INVENTION 
     According to the present invention, there is provided a disk molding mold which comprises a first support plate; a first mirror surface disk attached to the first support plate; a second support plate; and a second mirror surface disk attached to the second support plate and facing the first mirror surface disk. 
     At least one of the first and second mirror surface disks includes a first plate, and a second plate disposed to surround at least a front surface of the first plate. 
     The first plate includes a temperature control flow passage formed on a surface thereof facing the first support plate. The second plate includes a heat insulation section formed on a surface thereof facing the first plate such that the heat insulation section corresponds to the temperature control flow passage. 
     In this case, since the first plate includes a temperature control flow passage formed on a surface thereof facing the first support plate and the second plate includes a heat insulation section formed on a surface thereof facing the first plate such that the heat insulation section corresponds to the temperature control flow passage, the distribution of heat in the first and second plates is made uniform. Accordingly, a molding material within the cavity can be cooled uniformly. As a result, when a very thin disk substrate is formed, the disk substrate does not warp, whereby the quality of the disk substrate can be improved. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS  
         FIG. 1  is a sectional view of a mirror surface disk according to an embodiment of the present invention. 
         FIG. 2  is a sectional view of a disk molding mold according to the embodiment of the present invention. 
     
    
    
     DESCRIPTION OF SYMBOLS 
     
         
           10 : disk molding mold 
           15 : base plate 
           16 ,  36 : disk plate 
           40 : intermediate plate 
           68 : void 
           71 ,  73 : first mold plate 
           72 ,  74 : second mold plate 
           93 ,  94 : first and second temperature control flow passages 
       
    
     BEST MODE FOR CARRYING OUT THE INVENTION 
     An embodiment of the present invention will next be described in detail with reference to the drawings. In this case, a disk molding mold, which serves as a mold apparatus, will be described. 
       FIG. 1  is a sectional view of a mirror surface disk according to an embodiment of the present invention.  FIG. 2  is a sectional view of a disk molding mold according to the embodiment of the present invention. 
     In these drawings, reference numeral  10  denotes a disk molding mold. The disk molding mold  10  includes a stationary mold (a first mold; a stationary-side mold assembly)  12 , and a movable mold (a second mold; a movable-side mold assembly)  32 , which is disposed to face the stationary mold  12 . 
     An unillustrated injection apparatus is disposed adjacent to the disk molding mold  10 . The injection apparatus includes a heating cylinder (a cylinder member); an injection nozzle (an injection member) attached to the front end of the heating cylinder; a screw disposed within the heating cylinder so that the screw can rotate and can advance and retreat; a metering motor (a drive section for metering) for rotating the screw; an injection motor (a drive section for injection) for advancing and retreating the screw; etc. 
     An unillustrated mold-clamping apparatus is provided so as to close, clamp, and open the disk molding mold  10 . The mold-clamping apparatus includes a stationary platen, which serves as a first holding member for holding the stationary mold  12 ; a movable platen, which serves as a second holding member for holding the movable mold  32 ; a base plate which is disposed to face the stationary platen with the movable platen intervening therebetween; a toggle mechanism disposed between the movable platen and the base plate; a mold-clamping motor (a drive section for mold-clamping) for operating the toggle mechanism; etc. 
     The stationary mold  12  includes a base plate (a first support plate)  15 ; a disk plate (a first mirror surface disk)  16  having a circular shape and attached to the base plate  15  by means of unillustrated bolts; a locating ring  23  disposed in the base plate  15  in such a manner as to face the stationary platen and adapted to position of the base plate  15  with respect to the stationary platen; and a sprue bush  17  disposed adjacent to the locating ring  23 . The base plate  15  and the disk plate  16  function as a first mold main body. 
     The disk plate  16  includes a first mold plate (a first plate; a lower plate)  71 , and a second mold plate (a second plate; an upper plate)  72  disposed to surround at least a front surface of the first mold plate  71 . The first mold plate  71  has a function of cooling an unillustrated resin (a molding material) charged into a cavity C. The second mold plate  72  has a function of suppressing excessive lowering of the temperature of the resin and making the temperature of the resin uniform. 
     The first and second mold plates  71  and  72  are formed of the same metal; in the present embodiment, stainless steel, and are united together by means of diffusion bonding. Notably, the first and second mold plates  71  and  72  may be formed of different materials whose coefficients of thermal expansion are the same. Further, the first and second mold plates  71  and  72  may be used as separate members, without being united. 
     A die  28  is formed at the front end of the sprue bush  17  so that the die faces the cavity C. A sprue  26  is formed in the sprue bush  17  and communicates with the die  28 . Resin injected from the injection nozzle passes through the sprue  26 . A stamper-holding bush  14  is disposed radially outward of a front half portion of the sprue bush  17 . The stamper-holding bush  14  serves as a holding member for holding an inner circumferential edge of an unillustrated stamper, which serves as a cavity insert. Notably, an unillustrated air blow bush, etc. are also disposed in the stationary mold  12 . In the present embodiment, the stamper is disposed on the stationary mold  12  side; however, the stamper may be disposed on the movable mold  32  side. 
     Further, an annular abutment ring  18  is attached to the outer circumferential edge of the disk plate  16  by means of a bolt b 1 , and an annular first peripheral ring  27  is disposed on the radially outer side of the disk plate  16  and the abutment ring  18  and attached to the base plate  15 . Notably, the disk plate  16  is positioned in relation to the first peripheral ring  27 . 
     The movable mold  32  includes a base plate  35 ; an intermediate plate (a second support plate)  40  having a circular shape and attached to the base plate  35  by means of a bolt b 2 ; a disk plate (a second mirror surface disk)  36  attached to the intermediate plate  40  by means of a bolt b 3 ; a cylinder  44  which is disposed within the base plate  35  such that the cylinder  44  faces the movable platen and is attached to the intermediate plate  40  by means of a bolt b 4 ; and a cut punch (a member of processing)  48  which is advanced and retreated along the cylinder  44  and has a shape corresponding to the die  28 . Notably, the base plate  35 , the disk plate  36 , and the intermediate plate  40  function as a second mold main body. 
     The disk plate  36  includes a first mold plate (a first plate; a lower plate)  73 , and a second mold plate (a second plate; an upper plate)  74  disposed to surround at least a front surface of the first mold plate  73 . The first mold plate  73  has a function of cooling the resin charged into the cavity C. The second mold plate  74  has a function of suppressing excessive lowering of the temperature of the resin and making the temperature of the resin uniform. 
     The first and second mold plates  13  and  74  are formed of the same metal; in the present embodiment, stainless steel, and are united together by means of diffusion bonding. Notably, the first and second mold plates  73  and  74  may be formed of different materials whose coefficients of thermal expansion are the same. Further, the first and second mold plates  73  and  74  may be used as separate members, without being united. 
     An annular cavity ring  37  is disposed along the outer circumferential edge of the disk plate  36  and in opposition to the abutment ring  18 . A second peripheral ring  38  is disposed radially outward of the disk plate  36  and the cavity ring  37  and in opposition to the first peripheral ring  27 , and is attached to the intermediate plate  40 . Notably, the disk plate  36  is positioned in relation to the second peripheral ring  38 . The cavity ring  37  is attached to a rod  41  by means of a bolt b 5 , and disposed such that it can move in relation to the intermediate plate  40  via the rod  41 . A cavity-ring holder  39  is in engagement with the outer circumferential edge of the cavity ring  37 , and is attached to the second peripheral ring  38  by means of an unillustrated bolt. The cavity ring  37  projects from the front end surface of the disk plate  36 . The inner circumferential surface of the cavity ring  37  forms the outer circumferential edge of a disc substrate. 
     In the injection molding machine having the above-described configuration, in a metering step, the screw is rotated, whereby the resin is melted and accumulated forward of the screw, and the screw is retreated. During this operation, the disk molding mold  10  is closed and clamped. Subsequently, in an injection step, the screw is advanced, whereby the resin accumulated forward of the screw is injected from the injection nozzle, and charged into the cavity C. Next, in a cooling step, the resin within the cavity C is cooled, whereby a disk substrate prototype is molded. 
     Before the resin within the cavity C solidifies completely, punching is performed on the disk substrate prototype, whereby a central hole is formed in the disk substrate. 
     For such punching operation, a flange  51  formed integrally with the cut punch  48  is disposed within the cylinder  44  such that it can advance and retreat. The rear end  51   a  of the flange  51  is received by the above-described cylinder  44 . Further, a cut-punch return spring  52  is disposed ahead of the flange  51 . The cut-punch return spring  52  urges the flange  51  rearward. 
     When the flange  51  is advanced in a mold clamped state by supply of oil to an unillustrated drive cylinder, the cut punch  48  is caused to advance and enter the die  28 . As a result, a center hole can be formed in the disk substrate. 
     Subsequently, mold opening is performed, and the disk substrate is removed. Notably, an unillustrated ejector bush for ejecting the disk substrate is disposed radially outward of a front half portion of the cut punch  48 ; and an air blow bush  47  for jetting compressed air to the disk substrate so as to separate the disk substrate from the disk plate  36  is disposed radially outward of the ejector bush. Further, an ejector pin and other components are disposed within the movable mold  32 . 
     Notably, guide posts  84  are attached, through press fitting, to the first peripheral ring  27  such that they are arranged along a circle concentric with the stationary mold  12  and project toward the movable mold  32 , and are connected to the base plate  15  by means of bolts b 7 . Meanwhile, guide bushes  88 , which serve as guide members, are attached to the second peripheral ring  38  and the intermediate plate  40 . The guide bushes  88  can guide the guide posts  84 . 
     Incidentally, first and second temperature control flow passages  93  and  94  are formed in the disk plates  16  and  36 , respectively, in a predetermined pattern, and a temperature control medium of a predetermined temperature from a temperature controller is supplied to the first and second temperature control flow passages  93  and  94 , whereby the disk plates  16  and  36  are cooled, and the resin within the cavity C is cooled. 
     The first temperature control flow passage  93  is formed by forming a spiral groove in the first mold plate  71  such that the groove is open to a surface of the first mold plate  71  facing the base plate  15  and has a predetermined depth, and closing the opening of the groove by the base plate  15 . The second temperature control flow passage  95  is formed by forming a spiral groove in the first mold plate  73  such that the groove is open to a surface of the first mold plate  73  facing the intermediate plate  40  and has a predetermined depth, and closing the opening of the groove by the intermediate plate  40 . 
     Since each of the first and second temperature control flow passages  93  and  94  is formed by groove, temperature differences arise in the first mold plates  71  and  73  between respective portions in close proximity to the first and second temperature control flow passages  93  and  94  and respective portions separated away from the first and second temperature control flow passages  93  and  94 . If uniform cooling of the resin within the cavity C becomes difficult, when a very thin disk substrate is molded, the disk substrate may warp, with a resultant decrease in the quality of the disk substrate. 
     In order to cope with such a problem, a heat transmission restraining section for restraining transmission of heat is provided in the vicinity of a surface of the second mold plate  72  facing the first mold plate  71 , and void  68 , which serves as a heat insulation section, is formed in the heat transmission restraining section. The void  68  is formed by a spiral groove which is formed at the position corresponding to that of the groove constituting the first temperature control flow passage  93  in the same pattern as the first temperature control flow passage  93  to has a predetermined depth. In this case, the void  68  is formed such that the distance xl between the void  68  and a front surface S 1  of the second mold plate  72  is not less than 4 mm but not greater than 12 mm. Notably, when the distance x 1  is short, the thickness of the second mold plate  72  as measured to the void  68  is insufficient, so that the strength of the second mold plate  72  decreases, and a sufficient strength against resin pressure cannot be maintained. Accordingly, the distance x 1  is desirably at least 4 mm. Further, when the distance x 1  is long, the thickness of the second mold plate  72  as measured to the void  68  becomes excessively large, so that the heat capacity of the second mold plate  72  increases. As a result, the cooling performance of the disk molding mold lowers. Moreover, since the distance between the front surface S 1  of the second mold plate  72  and a rear surface S 2  of the first mold plate  71  is set to 20 mm, if the distance x 1  is long, it becomes impossible to sufficiently secure the first temperature control flow passage  93 , and the cooling performance lowers. Therefore, the distance x 1  is desirably set to 12 mm at the maximum. 
     Similarly, a heat transmission restraining section for restraining transmission of heat is provided in the vicinity of a surface of the second mold plate  74  facing the first mold plate  73 , and the void  68 , which serves as a heat insulation section, is formed in the heat transmission restraining section. The void  68  is formed by a spiral groove which is formed at the position corresponding to that of the groove constituting the second temperature control flow passage  94  in the same pattern as the second temperature control flow passage  94  to has a predetermined depth. In this case, the void  68  as formed such that the distance x 2  between the void  68  and a front surface S 3  of the second mold plate  74  is not less than 4 mm but not greater than 12 mm. 
     In this case, when the distance x 2  is short, the thickness of the second mold plate  74  as measured to the void  68  is insufficient, so that the strength of the second mold plate  74  decreases, and a sufficient strength against resin pressure cannot be maintained. Accordingly, the distance x 2  is desirably at least 4 mm. Further, when the distance x 2  is long, the thickness of the second mold plate  74  as measured to the void  68  becomes excessively large, so that the heat capacity of the second mold plate  74  increases. As a result, the cooling performance of the disk molding mold lowers. Moreover, since the distance between the front surface S 3  of the second mold plate  74  and a rear surface S 4  of the first mold plate  73  is set to 20 mm, if the distance x 2  is long, it becomes impossible to sufficiently secure the second temperature control flow passage  94 , and the cooling performance lowers. Therefore, the distance x 2  is desirably set to 12 mm at the maximum. 
     Accordingly, even when, in the first mold plates  71  and  73 , temperature differences arise between respective portions in close proximity to the first and second temperature control flow passages  93  and  94  and respective portions separated away from the first and second temperature control flow passages  93  and  94 , the resin within the cavity C can be cooled uniformly. Specifically, the first and second temperature control flow passages  93  and  94  and the cavity C are thermally insulated from each other by the void  68 , whereby the transmission of heat therebetween is restrained. Further, portions where the first and second temperature control flow passages  93  and  94  are not formed and the cavity C are not thermally insulated from each other by the void  68 , whereby the transmission of heat therebetween is not restrained. 
     As a result, the distribution of heat within each of the second mold plates  72  and  74  becomes uniform, so that the resin within the cavity C can be cooled uniformly. Consequently, when a very thin disk substrate is molded, the disk substrate hardly warps, and, thus, the quality of the disk substrate can be improved. 
     In the present embodiment, the void  68  is formed as a heat insulation section, and air is accommodated in the groove. However, the heat insulation section may be formed by filling the entirety or portions of the groove constituting the void  68  with a heat insulating material which is lower in thermal conductivity than the first mold plates  71  and  73 . The heat insulating material may be formed by, for example, mixing a metal into resin. In this case, since the first mold plates  71  and  73  are formed of stainless steel and have a thermal conductivity of 25 W/m·° K, the thermal conductivity of the heat insulating material charged into the groove is set to a predetermined value less than 25 W/m·° K by adjusting the amount of the metal mixed into the resin. Notably, the thermal conductivity of air is also smaller than 25 W/m·° K. When the heat insulating material is used, the thermal conductivity can be changed depending on the position along the groove. 
     In the present embodiment, the second mold plates  72  and  74  each have a flat-plate like shape. However, the second mold plates may be formed to have a box-like shape. 
     In the present embodiment, the disk plate  16  is composed of the first and second mold plates  71  and  72 , and the disk plate  36  is composed of the first and second mold plates  73  and  74 . However, the embodiment may be modified such that only one of the disk plates  16  and  36  is composed of the first and second mold plates. 
     The present invention is not limited to the above-described embodiments. Numerous modifications and variations of the present invention are possible in light of the spirit of the present invention, and they are not excluded from the scope of the present invention. 
     INDUSTRIAL APPLICABILITY 
     The present invention can be applied to a disk manufacturing apparatus for manufacturing disks.