Optical disk molding apparatus

Abstract: The optical disk molding apparatus is equipped with a cavity side mold assembly (C) and a force side mold assembly (D), temperature control liquid passages (26, 40) which are formed between disc cavity plates (25, 39) and mounting plates (31, 48) of the respective assemblies, and temperature control liquid sealing means which are provided around an inner circumference and an outer circumference of the temperature control liquid passages. The sealing means have annular grooves (29, 30, 32, 33, 43, 44, 49, 50) which are formed between the disc cavity plates and the mounting plates around the inner circumference and the outer circumference of the temperature control liquid passages, rigid rings (27, 28, 41, 42) which are fitted in the annular grooves with a minute clearance therebetween, and a heat resistant sealing filler which is charged between the inner wall surface of the groove and the outer circumference of the metallic ring.

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical disk molding apparatus according to the preamble of the accompanying claim 1. 2. Description of the Related Art Such a molding apparatus is disclosed in US 4437641 A. The sealing means comprise O-rings which are fitted in the annular apertures and which need to be frequently replaced due to the fact that the temperature of the mold is required to be maintained at a high temperature of 100 to 140 degrees centigrade. FIG. 4 is a schematic sectional view illustrative of a further example of an injection mold for optical disk substrates; the injection mold is in a clamped state. In the drawing, one surface of a fixed side disk cavity plate 1 is provided with concentric channel grooves 2 through which hot water for controlling the mold temperature circulates, and grooves 5 and 6 in which O-rings 3 and 4 are fitted for preventing the hot water from leaking out and which are provided in the inner circumferential section and the outer circumferential section thereof. A fixed side mounting plate 7 is provided with a hot water supply port 8, a draining port 9, and a sprue bush 10 through which melted resin material is injected at the center thereof. The outside diameter of the optical disk substrate is defined by a ring mold member 11 provided on the fixed side disk cavity plate 1. The fixed side disk cavity plate 1 and the fixed side mounting plate 7 are assembled with a plurality of mounting bolts 12 to constitute a fixed side mold assembly A. Further, one surface of a movable side disk cavity plate 13 is provided with concentric channel grooves 14 through which hot water for controlling the mold temperature circulates, and grooves 17 and 18 in which O-rings 15 and 16 are fitted for preventing the hot water from leaking out and which are provided in the inner circumferential section and the outer circumferential section thereof. A stamper plate 20 with signals engraved thereon is provided on the other surface of the movable side disk cavity plate 13 by a mounting bush 19. A cutting punch 21 is used for boring the central hole in the optical disk substrate. A movable side mounting plate 22 is provided with a hot water supply port 23 and a draining port 24. The movable side disk cavity plate 13 and the movable side mounting plate 22 are assembled with a plurality of mounting bolts 23 to constitute a movable side mold assembly B. The molding operation performed by the mold is as follows: in the clamped state shown in FIG. 4, the melted resin material, which has been melted by heating to 300 degrees centigrade or more, is charged through a nozzle aperture of the sprue bush 10 under high pressure into a cavity 24 formed by the respective disk cavity plates 1 and 13. The minute signal pattern of the stamper plate 20 is transferred onto an optical disk substrate surface. The central hole is bored, then the movable side mold assembly B is withdrawn to open the mold, and the molded optical disk substrate is removed from the mold. In a typical optical disk, minute signals of a track pitch of 1.6 µm, a width of 0.8 µm, and a depth of 0.4 µm must be accurately transferred from the stamper plate to a surface of the substrate of the optical disk. For this reason, for achieving better transferring performance, the injection mold for optical disks is set to a higher mold temperature than a general resin injection mold temperature. For example, in the case of the DVD or ROM optical disks, it is considered necessary to maintain the mold temperature to about 130 to about 140 degrees centigrade. Accordingly, the temperature of the hot water for controlling the mold temperature ranges from 130 to 140 degrees centigrade. The hot water of 140 degrees centigrade changes from a liquid phase to a water vapor phase of 3.685 kgf/cm 2 in pressure, adversely affecting the heat transfer between mold wall surfaces; therefore, the hot water must be circulated in the liquid phase. This requires that a pressure of 7 to 8 kgf/cm 2 be applied beforehand so that the hot water may be circulated forcibly through the channel grooves. The inventor has carried out the aforesaid molding operation by using the injection molding apparatus for optical disk substrates shown in FIG. 4 to study the operation of each section, especially the durability of O-rings. The fixed side O-rings 3 and 4 for preventing the leakage of the hot water in the apparatus are subject to the hot water of high temperature which flows through the very small clearance between the surfaces of the disk cavity plate 1 and the mounting plate 7. The same applies to the movable side O-rings 15 and 16. As shown in FIG. 5, the O-ring 15 is pressed against a surface of the fitting groove by the hot water pressure and plastically deformed and the cross-sectional shape thereof becomes rectangular. Generally, O-rings are less resistant to hot water vapor; therefore, hotter water accelerates the deterioration of the O-rings. It has been observed that, as the O-rings deteriorate, they turn into nonelastic hardened fragile materials until they finally lose the sealing function thereof. The optical disk substrate mold employing the 0-rings as the means for sealing the hot water provides an advantage in that the simple structure thereof permits easy manufacture; however, it has a serious drawback in maintenance and control in that the O-rings need to be frequently replaced. As an alternative to obviate the use of O-rings, there has been a method wherein the groove surfaces of the disk cavity plate and the mounting plate are connected by silver soldering. The silver soldering requires an operating temperature of approximately 700 degrees centigrade; therefore, the disk cavity plate and the mounting plate must be heated to that temperature. It is important to provide a disk cavity plate with wear resistance; therefore, a typical disk cavity plate uses SUS440C type martensite stainless steel which has been subject to heat treatment and the plate is further provided with coating. More specifically, SUS440C type martensite stainless steel is heated to approximately 1100 degrees centigrade and quenched to harden it, then tempered at about 500 to 515 degrees centigrade so as to refine to a hardness of H R C 58 to 60. After that, the cavity surface is provided with Ti-N coating to generate a cured film having a hardness ranging from MHv 1800 to 2000. The SUS440C type martensite stainless steel has such a temperature characteristic that its hardness suddenly drops when the tempering temperature rises higher than 550 degrees centigrade and at the operating temperature of about 700 degrees centigrade for silver soldering, it goes back completely to the hardness before quenching. Hence, the silver soldering must be performed prior to the heat treatment for hardening, presenting a difficulty in manufacture that the disk cavity plates and the mounting plates which have deformed during the hardening process need to be corrected in shape. There has been another serious manufacturing problem in that no correcting means has been available for unevenly silver-soldered portions. SUMMARY OF THE INVENTION Accordingly, it is an object of the present invention to provide an optical disk molding apparatus which has improved sealing means for preventing hot water for controlling the temperature of mold assemblies from leaking out. To this end, the optical disk molding apparatus according to the present invention comprises the features of the accompanying claim 1. The aforesaid annular aperture may be formed by combining annular grooves which are formed on the disk cavity plate and the mounting plate, respectively. The aforesaid annular aperture may be provided around the inner and outer circumferences of the aforesaid temperature control liquid passage. The fitting surface of the aforesaid annular aperture may be provided with a chamfered section. The aforesaid rigid ring may be a metallic ring. The aforesaid heat resistant sealing filler may be silicone resin. BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a sectional view illustrative of an embodiment of an optical disk molding apparatus in accordance with the present invention; FIG. 2 is an explanatory enlarged view showing an assembly process of a temperature control liquid sealing means of the embodiment; FIG. 3 is an explanatory enlarged view showing the temperature control liquid sealing means of the embodiment which has been completely assembled; FIG. 4 is a sectional view showing an optical disk molding apparatus which has a temperature control liquid sealing means employing an O-ring; and FIG. 5 is an enlarged view illustrating a problem with the temperature control liquid sealing means shown in FIG. 4. DESCRIPTION OF THE PREFERRED EMBODIMENT The present invention will now be described in more detail with reference mainly to the accompanying drawings. FIG. 1 is a sectional view illustrative of an embodiment of an optical disk injection molding apparatus in accordance with the present invention. One surface of a fixed side disk cavity plate 25 is provided with concentric channel grooves 26 through which hot water for controlling the mold temperature circulates, and grooves 29 and 30 in which metallic cylindrical rings 27 and 28 are fitted for preventing the hot water from leaking out and which are provided in the inner circumferential area and the outer circumferential area thereof, respectively. One surface of a fixed side mounting plate 31 is provided with grooves 32 and 33 in which the metallic cylindrical rings 27 and 28 are fitted. The fitting surfaces of the annular grooves are chamfered in a similar way to that shown in FIG. 2 which will be discussed later. Hot water introduced through a hot water supply port 34 is circulates through the concentric channel groove 26 and drained through a draining port 35. A melted resin material is injected into the mold through the center of a sprue bush 36 for injection. A ring mold member 37 forms the outside diameter of an optical disk substrate. An appropriate amount of a heat resistant sealing filler such as silicone resin is applied to the respective fitting grooves 29, 30, 32, and 33 for the metallic cylindrical rings 27 and 28 of the fixed side disk cavity plate 25 and the fixed side mounting plate 31, then the metallic cylindrical rings 27 and 28 are inserted therein. The groove surfaces of the fixed side disk cavity plate 25 and the fixed side mounting plate 31 are opposed to each other and brought in close contact, then they are assembled using a plurality of mounting bolts 38 to constitute a fixed side mold assembly C as illustrated. One surface of a movable side disk cavity plate 39 is provided with concentric channel grooves 40 through which hot water for controlling the mold temperature circulates, and grooves 43 and 44 in which metallic cylindrical rings 41 and 42 are fitted for preventing the hot water from leaking out and which are provided in the inner circumferential area and the outer circumferential area thereof. A stamper plate 46 with engraved signals to be transferred is supported on a cavity surface, i.e. the other surface of the movable side disk cavity plate 39, by a mounting bush 45. A cutting punch 47 is used for punching the central hole in an optical disk substrate. One surface of a movable side mounting plate 48 is provided with fitting grooves 49 and 50 for the metallic cylindrical rings 41 and 42, respectively. The hot water is introduced from a supply port 51 into the concentric channel groove 40 of the movable side mold assembly and drained through a draining port 52. FIG. 2 is an explanatory enlarged view illustrative of an assembly process for assembling the movable side of a temperature control liquid sealing means of the embodiment. Almost the same assembly process applies to the fixed side assembly. FIG. 3 is an explanatory enlarged view illustrative of the temperature control liquid sealing means of the embodiment which has been completely assembled. The fitting grooves 43, 44, 49, and 50 of the metallic cylindrical rings 41 and 42 of the movable side disk cavity plate 39 and the movable side mounting plate 48 are provided with, for example, skirted or chamfered sections 43a and 49a on the fitting surfaces thereof as shown in FIG. 2. An appropriate amount of a heat resistant sealing filler 54 such as silicone resin is applied to the respective fitting grooves 43, 44, 49, and 50 (see FIG. 2), then the metallic cylindrical rings 41 and 42 are inserted in the grooves. The grooved surfaces of the movable side disk cavity plate 39 and the movable side mounting plate 48 are opposed to each other and brought in close contact to connect the two plates with a plurality of mounting bolts 53 so as to constitute a fixed side mold assembly D. The description of the basic operation of the molding apparatus will be omitted because it has already been given in conjunction with FIG. 4; the function of the sealing means will be described. As shown in FIG. 3, the hot water pressure from the channel groove 40 passes through a clearance S between the disk cavity plate 39 and the mounting plate 48 and reaches an inner surface J of the metallic cylindrical ring 41. The pressure, however, is received and blocked by the side surface of the metallic cylindrical ring which is highly rigid. It has been found that, if the minute clearance between the metallic cylindrical ring 41 and the fitting grooves 43, 49 is set to about 0.05 mm to about 0.1 mm and the silicone charging length is set to about 9 mm, then only the inner surface J (see FIG. 3) is deteriorated by the hot water and the remainder of the part filled with silicone is hardly affected under a condition where the temperature of the hot water is 140 degrees centigrade, the hot water pressure is 10 kgf/cm 2 , and the test time is 2000 hours. As described in conjunction with FIGs. 1, 2, and 3, in the optical disk molding apparatus according to the present invention, the hot water sealing mechanism is designed to receive and block the hot water pressure by the highly rigid metallic cylindrical ring which is inserted and fitted together with the silicone resin sealant in the fitting groove provided on the disk cavity plate and the mounting plate. The hot water is completely sealed by the silicone resin sealant which has been charged in the lengthy fitting clearance. Hence, the optical disk molding apparatus in accordance with the present invention permits easy manufacture because of its simple structure and it also provides high reliability over a prolonged period of time. The optical disk molding apparatus according to the present invention has solved the problem with the experimental example described previously wherein the half of the outer circumferential surface of the O-ring deforms due to the hot water pressure applied, causing the sealing function to be easily lost. The conventional sealing method based on silver soldering described previously has manufacturing difficulty in that the deformation of the disk cavity plates and the mounting plates has to be corrected; it also has a serious manufacturing difficulty in that no correcting means is available if an unevenly silver-soldered spot results. The hot water sealing mechanism in accordance with the present invention is free from such manufacturing restrictions or difficulties, providing such advantages as reduced manufacturing cost and shorter time required. Various other modifications of the embodiment which has been described in detail can be made without departing from the scope of the present invention.

Claims: An optical disk molding apparatus comprising: a fixed side mold assembly (C) and a movable side mold assembly (D); a temperature control liquid passage (26, 40) which is formed by disk cavity plates (25, 39) and mounting plates (31, 48) of said respective assemblies (C, D); and temperature control liquid sealing means (27-30, 32, 33, 41-44, 49, 50) which is provided around an inner circumference or an outer circumference of said temperature control liquid passage (26, 40); wherein said temperature control liquid sealing means has an annular aperture (29, 30, 32, 33, 43, 44, 49, 50) which is formed between said disk cavity plate (25, 39) and said mounting plate (31, 48) around the inner circumference or the outer circumference of said temperature control liquid passage (26, 40), characterized in that said temperature control liquid sealing means has further a rigid ring (27, 38, 41, 42) which is fitted in said annular aperture with a minute clearance therebetween, and a heat resistant sealing filler (54) which is charged between the inner wall surface of said annular aperture and the outer circumference of said rigid ring. An optical disk molding apparatus according to claim 1, wherein said annular aperture is formed by combining annular grooves (29, 30, 32, 33, 43, 44, 49, 50) which are formed on said disk cavity plate (25, 39) and said mounting plate (31, 48), respectively. An optical disk molding apparatus according to claim 1 or 2, wherein said annular apertures (29, 30, 32, 33, 43, 44, 49, 50) are provided around the inner and outer circumference, respectively, of said temperature control liquid passage (26, 40). An optical disk molding apparatus according to any of claims 1 to 3, wherein the surface of said annular aperture (29, 30, 32, 33, 43, 44, 49, 50) is provided with a chamfered section (43a, 49a). An optical disk molding apparatus according to any of claims 1 to 4, wherein said rigid ring (27, 28, 41, 42) is a metallic ring. An optical disk molding apparatus according to any of claims 1 to 5, wherein said heat resistant sealing filler (54) is silicone resin.

Inventors: TAKAHASHI MITSUO, TAKAHASHI, MITSUO
Applicants: SEIKO GIKEN KK, SEIKOH GIKEN CO., LTD.
Application year: 1997
Main classification: B29D17
IPC codes: B29C33, B29C45, B29L17