JP2008192236A - Mold for molding optical disk substrate and molding method - Google Patents

Abstract

In a mold for forming an optical disk substrate by setting a stamper, an optical disk having good servo characteristics is obtained by allowing the stamper to stably and uniformly extend and contract in the radial direction when the substrate is formed.
A ring-shaped stamper holding jig 20 is attached to an abutting ring 3 concentrically therewith. In the holding jig 20, a plurality of claw-like pieces 20a are intermittently provided on the inner peripheral side and in the circumferential direction. A claw-like piece 20a is made to oppose the outer periphery of the information recording surface of the stamper 1 on the fixed side mirror surface 2 to be a first locking member for the stamper. A portion near the inner peripheral end of the lower surface of the cavity ring 4 is positioned in the vicinity of the information recording surface of the stamper, and the cavity ring is used as a second locking member for the stamper. In the molding step, the clearance is maintained between the locking member and the stamper so that the radial thermal expansion / contraction operation of the stamper accompanying the injection filling / cooling of the molten resin into the cavity 11 proceeds smoothly. .
[Selection] Figure 8

Description

  The present invention relates to an optical disc substrate molding die and molding method, and an optical disc comprising a substrate obtained by this molding method.

  A substrate used for an optical disc such as a DVD is manufactured by molding by an injection molding method or an injection compression molding method. In any of these optical disk substrate molding methods, a melted material resin is filled in a cavity formed by closing a mold. Then, the molten resin is cooled in the mold until it reaches a temperature at which it can be taken out of the mold and solidified to form a predetermined substrate shape. In the cavity for molding this optical disk substrate, a stamper in which necessary information on the optical disk is engraved as pit rows or guide grooves is set. During the process from filling the molten resin into the cavity and solidifying it The necessary information engraved in the stamper is transferred onto the optical disk substrate that is molded in the process. The optical disk substrate molded in the mold is taken out of the mold after the cooling process in the mold is completed, and transferred to the next process after the molding to produce an optical disk.

  In order to accurately read and write information on the optical disk, it is necessary that a fine pit row or groove is accurately transferred onto the optical disk substrate. Therefore, the material resin is melted at a high temperature to improve the fluidity, and at the same time, the resin is filled at high speed so as to be filled into the cavity while maintaining the high fluidity. In addition, the mold temperature is set to a high value in order to avoid a decrease in fluidity.

  When the material resin is melted at a high temperature and injected into the cavity in this way, low molecular components contained in the material resin called oligomers from the material resin and additive components such as release agents are being molded. The gasification phenomenon occurs. Therefore, the generated gas is discharged to the outside through the gas vent.

A conventional example of a molding die for an optical disk substrate will be described.
FIG. 1 is a schematic sectional view showing a molding die having a well-known structure (hereinafter sometimes referred to as a die). In this figure, reference numeral 1 is a stamper, 2 is a fixed side mirror surface, 3 is an abutment ring, 4 is a cavity ring, 5 is a gas vent hole (gas suction groove), 6 is a movable side mirror surface, 7 is a stamper suction groove, and 8 is fixed. Side guide ring (cavity holder), 9 is cavity ring holder, 10 is a movable side guide ring, 11 is a cavity, 12 is a nozzle for molten resin injection and filling, 31 is a fixed side mold (fixed part), 32 is a movable side This is a mold (movable part).
The gas escape hole 5 and the stamper suction groove 7 are connected to a vacuum system by a vacuum generator, and the gas generated from the resin in the cavity in the molding process is exhausted through the gas escape hole 5. Further, the stamper 1 placed on the fixed mirror surface 2 is attracted and held by the suction force from the stamper suction groove 7.

  That is, the optical disk substrate includes (1) a fixing portion 31 including a fixed side mirror surface 2 having a stamper 1 and a stamper suction groove 7, an abutment ring 3, and a fixed side guide ring 8 having a gas escape hole 5; 2) In a mold comprising the cavity ring 4 held by the movable mirror surface 6 and the cavity ring presser 9, and the movable part 32 having the movable guide ring 10, the injection molding method or the injection compression molding method is used. Molded.

  FIG. 2 is an explanatory diagram of the molding process using the mold, and shows the mold open state. FIG. 3 is an explanatory view of the molding process using the mold, and shows the mold clamping / resin injection process continued from FIG. FIG. 4 is an explanatory view of the molding process using the mold, and shows the mold opening process continued from FIG. FIG. 5 is an explanatory view of the molding process using the above-mentioned mold, and shows the substrate take-out step following FIG. FIG. 6 is an explanatory diagram showing the flow of gas generated from the molten resin in the cavity to the outside of the mold in the molding process using the mold. 3 to 5, reference numeral 14 denotes a molded substrate, and 17 denotes a substrate take-out machine for taking out the molded substrate 14. In FIG. 6, reference numeral 15 denotes an exhaust passage (clearance CL), and 15a denotes a gas (gas flow) generated from the injection-filled resin.

In the optical disk substrate molding process, as shown in FIGS. 2 and 3, the mold is closed from the mold open state (FIG. 2), and at the same time, the cavity ring 4, the movable mirror surface 6 and the fixed mirror surface 2 are sucked and fixed. The molten resin is injected from the nozzle 12 into the cavity 11 formed by the stamper 1 (FIG. 3). When the resin is injected into the cavity 11, the resin flows into a groove on the information recording surface of the stamper 1 (a fine uneven pattern on the stamper surface). Since the temperature of the resin is 300 to 400 ° C., when the resin flows into the stamper, the stamper expands due to the heat of the resin. When the resin spreads in the entire cavity 11, the molding process transfers the stamper groove, so that the pressure holding process, the cooling process, and the process proceed. During the cooling process, the temperature of the resin in the cavity drops to 100 to 150 ° C. As the resin temperature decreases, the stamper contracts as the resin is cooled. Thus, since the stamper expands and contracts during molding, the surface of the fixed-side mirror surface 2 becomes rough, and the life is shortened.
When the molded substrate is molded, the mold is opened (FIG. 4), and the molded substrate 14 is taken out by the substrate take-out machine 17 (FIG. 5).

  However, when the resin is injected and filled into the cavity, gas is generated from the injected resin. When this gas accumulates, the movement of mold parts deteriorates and the quality of the molded substrate is affected. Therefore, conventional injection molding machines have increased gas piping paths so that gas can be efficiently exhausted outside the mold. A mechanism for forcibly exhausting the gas is installed.

  In the mold shown in FIG. 1, the fixed-side mirror surface 2 and the butting ring 3 are generally incorporated as separate parts, so that the fixed-side mirror surface 2 can be easily maintained. Further, there is a structure in which a clearance is formed between the fixed side mirror surface 2 and the abutting ring 3 so as to be easily disassembled. In addition, since gas is generated from the resin injected into the cavity, it is necessary to exhaust the generated gas outside the mold in a general mold structure. Clearance is provided as a passage. As a mold structure, there is a mold structure in which grooves are provided in the upper part and the lower part of the abutting ring 3 to improve the gas escape efficiency.

  By the way, in order to accurately read and write information on the optical disk, it is necessary that a fine pit row or groove is accurately transferred onto the optical disk substrate. As described above, in order to ensure the quality of the molded substrate, it is important to accurately transfer the stamper groove and to smoothly and smoothly peel the molded molded substrate from the mold and the stamper. Come.

  Patent Document 1 listed below discloses an invention relating to an optical disk substrate molding die that can uniformly peel a molded substrate (prevent peeling failure of the molded substrate). In the present invention, a mold structure is adopted in which the outer diameter ring is movable by a piston when the mold is opened.

  In this molding die, before the molded product is released from the fixed side mirror plate and the stamper, the outer diameter surface of the molded product is released in advance, and then supplied by the next mold release from the fixed side mirror plate and the stamper. The compressed air can be spread evenly and easily on both the fixed and movable sides when the mold is opened, and there will be no delay in mold release, so there will be no mold release defects and Does not occur. Therefore, it is possible to improve mold release properties and molding quality.

  In addition, when the stamper groove is accurately transferred, it is also important that the stamper is uniformly expanded and contracted by heat. If the stamper does not expand and contract evenly, distortion occurs when the stamper groove is transferred to the resin, and the substrate characteristics of that portion deteriorate.

  Therefore, in the optical disk substrate molding die described in Patent Document 2 below, as a structure that is uniformly expanded and contracted without causing deformation or distortion in the stamper radial direction at the time of molding, a cut is made in the outer periphery of the stamper side mirror surface. The shrinkage difference between the inner periphery and the outer periphery due to heat is eliminated. That is, in this mold, in the mold for optical disk substrate comprising a fixed mold, a movable mold disposed opposite to the fixed mold, and a ring for attaching the stamper on the mirror surface of the movable mold, A step portion that is concentrically recessed with the stamper is provided on the mirror surface outside the stamper mounting position by the ring.

Japanese Patent No. 2642158 JP-A-7-57306

  In the optical disk substrate molding die as shown in FIG. 1, the stamper 1 is generally firmly fixed to the fixed mirror surface 2 by the suction force from the stamper suction groove 7. However, when the stamper is sucked and fixed in this way, there arises a problem that the stamper does not expand and contract smoothly during molding.

  Further, since the gas 15a is generated from the resin injected and filled into the cavity 11, it is necessary to exhaust this gas outside the mold in a general mold structure, and a gas exhaust mechanism is provided to increase the exhaust efficiency. ing. As shown in FIG. 6, the gas 15 a is exhausted through the exhaust passage 15. In this case, the gas 15a flows from the inner peripheral side toward the outer peripheral side of the back surface of the substrate being molded (the surface on the side where the concave / convex fine pattern on the stamper 1 surface is not transferred). Next, the gas 15a flows through the clearance CL between the abutment ring 3 and the cavity ring 4, and further, through the gas escape hole 5 formed in the fixed guide ring 8, the clearance CL between the fixed guide ring 8 and the guide ring 10, and the like. Through the mold. Thus, the clearance CL forms an exhaust passage 15 for the gas 15a.

  However, as described above, if the stamper is kept sucked and fixed in the molding process, the stamper radial direction associated with the “stamp heating / cooling” caused by the “resin injection filling / resin cooling” at the time of molding. There is a problem that expansion and contraction is not performed smoothly. Further, the non-uniform adhesion of the gas from the injection-filled resin to the back surface of the stamper also causes the expansion and contraction of the stamper generated during molding to not proceed smoothly at the gas adhesion portion.

  The problem of non-uniform adhesion of the gas to the back surface of the stamper will be further described. As shown in the exhaust passage 15 in FIG. 6, the gas flows from the side surface (outer peripheral edge) of the stamper 1 along the fixed mirror surface 2. In the case of a mold, when the stamper generated during molding expands or contracts, the gas (the solidified product) easily adheres to the back surface of the stamper (surface on the molding substrate 14 side). This gas adhesion generally occurs on the outer periphery of the back surface of the stamper.

  When the gas adheres unevenly to the back surface of the stamper, the stamper 1 that is firmly fixed to the fixed mirror surface 2 by suction becomes uneven in the expansion and contraction operation of the stamper that occurs when forming the molded substrate. The groove track transferred at the gas adhering portion may be distorted. When the track is distorted, the servo performance important for recording / reproducing of the optical disk is lowered. In particular, with respect to a high-speed recording optical disk, this servo performance requirement is strict, and the non-defective product rate is reduced due to a decrease in servo characteristics caused by gas adhering to the back surface of the stamper.

  Therefore, a main object of the present invention is to enable a stamper to stably and uniformly extend and contract during molding of an optical disk substrate in a mold for molding an optical disk substrate by setting a stamper in the mold, thereby improving servo characteristics. It is to stably manufacture a high-quality optical disc.

Hereinafter, the structure will be described for each claim (see FIGS. 6, 8, and 9).
The molding die for the optical disk substrate according to the invention of claim 1 comprises:
In a mold for molding an optical disk substrate by setting a stamper on a stamper mounting surface to form a mold cavity and cooling molten resin injected and filled in the cavity,
A stamper holding jig having a radially inward locking portion for locking the outer periphery of the information recording surface of the stamper set on the stamper mounting surface;
The locking portion of the stamper holding jig is designed to allow the stamper to expand / contract in the radial direction along with injection / filling of molten resin into the cavity / cooling of the resin in the molding process. A clearance is maintained between the outer periphery of the information recording surface and the information recording surface.

  In the molding die according to the first aspect, like the conventional die, it is preferable to provide a stamper suction hole in the die and hold the stamper by the suction force of the stamper suction groove when the stamper is set in the die. Further, in this case, it is desirable to stop the suction operation by the stamper suction groove from the start of the molding process, so that the expansion / contraction in the stamper radial direction in the molding process proceeds smoothly.

According to a second aspect of the present invention, there is provided a molding die for an optical disk substrate according to the first aspect, wherein when the stamper is at a normal temperature, the locking portion of the stamper holding jig and the outer periphery of the information recording surface of the stamper The clearance is 20 to 50 μm.
According to a third aspect of the present invention, there is provided a molding die for an optical disk substrate according to the first or second aspect, wherein the molding die is provided with a cavity ring in the movable side die, and the stamper is a fixed side mirror surface of the fixed side die (this is The information recording surface of the stamper is opposed to the cavity ring, and when the stamper is at room temperature, the cavity ring and the information recording surface outer periphery of the stamper It is characterized by having a clearance of 20 to 50 μm between them.

According to a fourth aspect of the present invention, there is provided a molding die for an optical disk substrate according to any one of the first to third aspects, wherein the stamper holding jig includes a plurality of claw-shaped pieces as the locking portions on the inner peripheral side, and a circular shape. It is characterized in that it is formed in a ring shape intermittently in the circumferential direction, and the claw-like piece is opposed to the outer peripheral portion of the stamper.
In addition, it can replace with the ring-shaped stamper holding jig provided with two or more said nail | claw-shaped pieces, and can also arrange | position several nail | claw-shaped pieces on the same periphery and at intervals suitably.

  An optical disk substrate molding die according to a fifth aspect of the present invention is the optical disk substrate molding die according to the third or fourth aspect, wherein the stamper holding jig is detachably fixed to an abutment ring provided on the outer peripheral side of the fixed-side mirror surface. It is characterized by being.

  According to a sixth aspect of the present invention, there is provided a molding die for an optical disk substrate according to the fifth aspect of the present invention, wherein the stamper holding jig is provided with a dull hole (a long hole) at a portion for removably fixing the stamper holding jig to the abutting ring. One type) is provided intermittently in the circumferential direction of the stamper holding jig.

  According to a seventh aspect of the present invention, there is provided an optical disk substrate molding method comprising injecting and filling molten resin into a cavity of a molding die according to any one of the first to sixth aspects.

  An optical disc according to an eighth aspect of the invention is manufactured by an optical disc substrate molded by the molding method according to the seventh aspect.

According to a ninth aspect of the present invention, there is provided a method for molding an optical disk substrate, comprising: forming a mold cavity by setting a stamper on a stamper mounting surface; and cooling the molten resin injected and filled in the cavity. ,
A locking means for locking the outer periphery of the information recording surface of the stamper set on the stamper mounting surface is provided,
A clearance is maintained between the locking means and the outer periphery of the stamper information recording surface so that the stamper can freely expand / shrink in the radial direction as the resin is injected and filled into the cavity / cooled. The molding process is advanced.

  In the molding method of the ninth aspect, it is preferable to use a mold provided with a stamper suction groove, as in the conventional case. In this mold, when the stamper is set in the mold and the cavity is formed, the suction operation by the suction groove is performed, but the suction operation by the stamper suction hole is preferably stopped from the start of the molding process. That is, the stamper suction groove is not operated in a process in which the stamper expands or contracts by heating or cooling. Thereby, expansion / contraction of the radial direction of the stamper in the molding process proceeds smoothly.

In the molding die in any one of Claims 1-6, since the said clearance was formed as the said aspect, according to invention of Claim 7 which uses these molding dies, a molding operation is continued continuously. Even so, the expansion and contraction of the stamper that occurs during molding proceeds smoothly. That is, the degree of freedom of the expansion / contraction operation is improved. Therefore, the information recorded on the stamper is accurately transferred to the optical disk substrate.
As a result, according to the invention of claim 7, even if a gas coagulum adheres to the back surface of the stamper, the stamper expansion / contraction operation during molding is not hindered. A high-quality optical disc that can be manufactured is provided. In addition, when the gas coagulum does not adhere to the stamper back surface, the stamper expansion / contraction operation at the time of molding proceeds more smoothly, so that a particularly high quality optical disc is provided.

In the molding dies of claims 2 and 3, since the predetermined clearance is set to 20 to 50 μm, the degree of freedom of the stamper's expansion / contraction operation is remarkably improved, and the level of the tracking error remaining amount in the optical disc is greatly reduced. (Refer to FIG. 11 described later).
In the molding die according to the fourth aspect of the invention, since a predetermined ring-shaped stamper holding jig is used, an effect of improving the flexibility of the stamper expansion / contraction operation can be obtained with a simple die structure. Further, the stamper holding operation can be easily performed.

In the molding die according to the fifth aspect, it is possible to easily suppress the occurrence of burrs on the mirror surface side (the surface fixed to the fixed mirror surface) of the optical disk substrate.
In the molding die according to the sixth aspect, since the darling hole is provided in a predetermined manner, it is possible to easily perform the work when the stamper holding jig is attached to and detached from the abutting ring (for example, with a bolt). Accordingly, the stamper can be easily replaced.

  In the optical disc manufactured by the optical disc substrate according to the molding method of claims 7 and 9 and the optical disc of claim 8, excellent servo characteristics are guaranteed.

  In the embodiment of the present invention, the structure of a molding die will be described with reference to the drawings. FIG. 8 is a cross-sectional view showing the structure of the main part of the molding die, and shows the clamping state of the die. FIG. 9 is a plan view showing the entire structure of the stamper holding jig constituting the mold.

  First, a molding die for forming an optical disk substrate that has been generally used will be described with reference to FIGS. 1 and 6. In this molding die, a stamper suction groove 7 is provided on the fixed mirror surface 2, and this suction die is provided. The stamper 1 is firmly fixed and held by the suction force by the groove. For this reason, the stamper is not easily expanded and contracted during molding.

Next, the structural points of the molding die according to this embodiment will be described (see FIGS. 8 and 9).
A ring-shaped stamper holding jig 20 is attached to the abutting ring 3 concentrically with the abutting ring 3. In the holding jig 20, a plurality of claw-like pieces 20a are intermittently provided on the inner peripheral side and in the circumferential direction. The claw-shaped piece 20a is opposed to the stamper 1 on the fixed side mirror surface 2 in the vicinity of the outer periphery of the information recording surface to form a first locking member for the stamper. A portion near the inner peripheral end of the lower surface of the cavity ring 4 is positioned in the vicinity of the information recording surface of the stamper, and the cavity ring is used as a second locking member for the stamper.
Then, in the molding step, the thermal expansion / contraction operation in the stamper radial direction accompanying the injection filling / resin cooling of the molten resin into the cavity 11 proceeds smoothly, and between the first locking member and the stamper, and A clearance is maintained between the second locking member and the stamper.

In the present invention, the stamper holding jig 20 shown in FIG. 9 is attached in the form shown in FIG. 8, and the stamper outer peripheral portion is locked by the claw-like piece 20 a provided on the inner peripheral side of the stamper holding jig 20. When the stamper 1 is set on the fixed mirror surface 2, the inner periphery of the stamper is fixed by a stamper holder (not shown) having a well-known configuration.
The stamper is sucked and fixed in advance by the stamper suction groove 7, and in this state, the outer periphery of the stamper is held by the stamper holding jig 20. Then, the stamper suction operation by the stamper suction groove 7 is stopped from the start of the molding process (for an example of the structure and arrangement of the stamper holder, refer to FIG. 1 of Japanese Patent Application Laid-Open No. 2003-181883 and its description) See).
In addition, although the stamper suction groove 7 is provided in the mold of FIG. 8, a mold in which this is not formed can also be used. In any case, the stamper outer peripheral portion is held by the stamper holding jig 20 at the time of stamper setting and molding.

The structure of FIG. 8 will be further described. In the movable side mold (movable part) 32, the cavity ring 4 is detachably attached to the outer peripheral side of the movable side mirror surface 6 with a bolt or the like. A movable guide ring 10 is provided on the outer peripheral side of the cavity ring 4. The cavity 11 is formed by the inner peripheral end face of the cavity ring 4 together with other members.
On the other hand, in the fixed-side mold (fixed portion) 31, the butting ring 3 is detachably attached to the outer peripheral side of the fixed-side mirror surface 2 with a bolt or the like. Further, the stationary guide ring 8 is disposed on the outer peripheral side of the abutting ring 3. Further, a stamper suction groove 7 is formed in the fixed side mold 31 and connected to a vacuum system (not shown).

  When forming the optical disk substrate, the stamper 1 is placed on the fixed mirror surface 2, the inner peripheral end of the stamper 1 is held by a stamper holder (not shown), and then on the inner peripheral portion of the abutting ring 3. The stamper holding jig 20 is placed and attached detachably with bolts or the like. Thereby, the clearance CL is set and maintained between the outer peripheral surface of the stamper (more precisely, the outer peripheral portion of the stamper information recording surface). Next, the movable mold 32 is brought close to the fixed mold (fixed portion) 31 and the mold is clamped to obtain the state shown in FIG.

  In FIG. 8, the inner peripheral end surface of the cavity ring 4 faces the cavity 11, but the portion near the inner peripheral end of the lower surface of the cavity ring 4 is located in the immediate vicinity of the outer peripheral surface of the stamper 1. The clearance CL between 1 and the cavity ring 4 is in the range of 20 to 50 μm when the stamper is at room temperature (Claim 3). As is clear from FIG. 8, a sufficient gap is formed between the lower surface of the cavity ring 4 and the stamper 1 and the stamper holding jig 20 on the outer peripheral side of the lower surface near the inner peripheral end. ing.

  As described above, in the molding die of FIG. 8, the stamper outer peripheral end portion of the stamper information recording side surface is locked to the stamper holding jig 20, and the stamper information recording side surface of the stamper inner recording side, that is, the cavity 11 nearest portions are locked by the cavity ring 4, and the clearance CL of these locking portions is in the range of 20 to 50 μm when the mold is at room temperature. Further, as described above, the entire surface of the stamper opposite to the information recording side is held by the fixed mirror surface 2.

Since the stamper holding jig 20 is detachably fixed to the abutting ring 3 provided on the outer peripheral side of the fixed-side mirror surface 2, the mirror surface side of the optical disk substrate (the surface fixed to the fixed-side mirror surface 2) ) Can be easily suppressed.
In the state of FIG. 8, an exhaust passage similar to the exhaust passage 15 shown in FIG. 6 is formed in this mold, but this is omitted in this figure.

  As shown in FIG. 9, the stamper holding jig 20 has an annular shape as a whole, and is configured by providing a plurality of claw-like pieces 20a on the inner peripheral side, intermittently in the circumferential direction at equal pitches. Yes. The claw-shaped piece 20a faces the upper surface of the stamper outer peripheral portion (FIG. 8). Further, the stamper holding jig 20 has a plurality of dart holes 20b as a dart-shaped through-hole in a portion for removably fixing the stamper holding jig 20 to the abutting ring 3 in the circumferential direction of the stamper holding jig. Are provided intermittently. As described above, when the mold temperature in FIG. 8 is normal temperature (before the molding process is started), the claw-like piece 20a that is a stamper locking portion of the stamper holding jig 20 and the information recording surface of the stamper 1 The clearance CL between the outer peripheral portion is 20 to 50 μm.

In the mold shown in FIG. 8, when the stamper is at room temperature, a clearance CL of 20 to 50 μm is formed between the inner peripheral surface of the cavity ring 4 and the stamper surface. In a portion other than the peripheral portion, a sufficient gap is formed between the cavity ring 4 and the stamper 1 as is apparent in FIG.
Instead of the ring-shaped stamper holding jig 20 provided with a plurality of the claw-shaped pieces 20a, a plurality of claw-shaped pieces may be arranged on the same circumference with an appropriate interval between the claw-shaped pieces. it can.

  As described above, in the molding die of the present invention, if the stamper holding jig 20 and the stamper 1 come into contact with each other, the stamper 1 cannot be smoothly expanded and contracted in the molding process. A predetermined clearance is formed between the stampers 1. Thereby, the expansion / contraction operation of the stamper generated when the molten resin is injected into the cavity 11 and cooled can be improved.

  In the molding die currently under examination shown in FIG. 7, the stamper 1 is held by the cavity ring 4, and the cavity ring 4 is installed in the fixed side die 31. In the case of this mold structure, when the cavity is formed, resin enters the boundary between the cavity ring 4 and the movable mirror surface 6 to generate burrs, and this burr control becomes very difficult. Therefore, it is desirable that the cavity ring 4 be installed on the movable mold 32 and the stamper holding jig be a separate structure.

In the molding die shown in FIG. 8, the abutting ring 3 and the stamper holding jig 20 can be integrated as desired. However, the stamper replacement operation when producing the optical disk substrate may not be simple. For this reason, as shown in FIG. 8, the abutting ring 3 and the stamper holding jig 20 are separate members, and the stamper holding jig 20 is easily attached to and detached from the abutting ring 3 so that the stamper can be easily removed. To do.
As described above, in the present embodiment, the stamper holding jig 20 shown in FIG. 9 is used, and bolts are inserted into the dart hole 20b to fix the stamper holding jig 20 to the abutting ring 3, The jig 20 can be easily attached and removed.

FIG. 10 is a graph showing the servo characteristics of the optical disc (track signal at the time of on-track), that is, a tracking error signal at the time of on-track. Reference symbol A is a track jump signal.
When distortion occurs in a track, the track of that portion cannot be tracked, and a waveform like symbol B (a portion that cannot track) is obtained. In this case, the tracking error signal remaining amount was obtained by the ratio of b to a, that is, b / a. Here, a indicates the amount of signal obtained when the track jumps, and b indicates the amount that the track cannot be tracked. That is, if the track of the disk can be completely tracked, the tracking error signal remaining amount is zero, and this value increases as the portion of the track that cannot be tracked increases.

  The tracking error signal remaining amount is an alternative value of the servo characteristic that is important for recording and reproduction of the optical disk. If the track can be tracked completely, the tracking error signal remaining amount is 0, and the portion where the track cannot be tracked The larger the value, the larger this value. As the evaluation method, DDU1000 manufactured by Pulstec is used. The wavelength of the laser is 650 ± 5 nm, and NA is 0.60 ± 0.01. The optical disk is rotated at 3000 rpm with CAV (constant angular velocity), focused and tracked, and the track signal during on-track is evaluated. Also, as a setting, a setting is made such that after one rotation, the track returns to the previous track (track jump). At this time, an on-track tracking error signal as shown in FIG. 10 is obtained.

  FIG. 11 is a graph showing the relationship between the clearance CL between the cavity ring 4 and the stamper 1 in the molding die shown in FIG. 8 (value when the die is at room temperature) and the tracking error signal remaining amount. When the thickness is about 30 μm, the remaining amount is minimized. It has been confirmed that the clearance CL between the claw-shaped piece 20a and the stamper 1 (value when the mold is at room temperature) has the same relationship as in FIG.

The result of FIG. 11 will be further described. When the clearance is in the range of 30 to 50 μm, if the clearance between the stamper 1 and the cavity ring 4 is wide, the tracking error signal remaining amount increases, and as the clearance decreases, this value decreases. If the clearance is too narrow, such as around 10 μm, when the stamper tries to expand and contract during molding, this clearance becomes resistance and the stamper's expansion / contraction operation does not proceed smoothly, and distortion occurs in the stamper.
However, if the clearance is widened too much, resin enters the clearance and this resin portion becomes a burr after the optical disk molded substrate is molded. When the optical disc substrates are bonded to each other, the burrs may collide with the mating substrate surface to generate distortion, which causes deterioration of the tracking error signal remaining amount. From FIG. 11, it can be said that the optimum clearance is about 30 μm.
From the above results, it is desirable that both the clearance between the stamper holding jig and the stamper and the clearance between the cavity ring and the stamper (both at normal temperature) be 20 to 50 μm. Telescopic movement can be freely performed.

  Next, FIG. 12 is a graph showing the tracking error signal remaining amount of the optical disc manufactured by the conventional mold according to the comparative example shown in FIG. FIG. 13 is a graph showing the tracking error signal remaining amount of the optical disc manufactured by the mold according to the embodiment of the present invention shown in FIGS. 8 and 9. In these comparative examples and examples, the tracking error signal remaining amount of the optical disk obtained from these substrates was confirmed for each number of molded optical disk substrates.

In this case, in the comparative example, the stamper was always sucked and fixed to the fixed mirror surface during the molding process.
In the embodiment, when assembling the mold, the clearance between the stamper 1 and the cavity ring 4 was set to 20 μm, and the clearance between the stamper 1 and the stamper holding jig 20 was set to 30 μm. In this embodiment, when the stamper is placed on the fixed-side mirror surface 2, the inner peripheral portion of the stamper is held by a not-shown stamper holder, and the stamper is fixed to the fixed-side mirror surface by the stamper suction groove 7. After holding the outer periphery of the stamper with the holding jig, the stamper suction operation by the stamper suction groove 7 was stopped.

  As is apparent from FIG. 12, in the optical disk manufactured by the optical disk substrate using the molding die of FIG. 1 in which the stamper is sucked and fixed to the fixed mirror surface, the tracking error signal remaining amount increases as the number of molded optical disk substrates increases. is doing. On the other hand, in FIG. 13, even when the number of molded optical disk substrates increases, the tracking error signal remaining amount does not increase, and the effect of the present invention was confirmed.

In the present invention, a molding die having both the configuration of FIG. 8 and the configuration of the exhaust passage shown in FIG. That is, an optical disk substrate molding die having the configuration of claim 1 and also having the following configuration can be employed (see FIGS. 6 and 8).
A cavity 11 is formed by the stamper 1 set on the fixed side mirror surface 2, the movable side mirror surface 6, and the cavity ring 4 surrounding the outer periphery of the movable side mirror surface 6, and the cavity ring 4 (as shown in FIG. 8). The fixed-side mirror surface 2 side tip surface is brought into contact with an abutment ring 3 provided on the fixed-side mirror surface 2 side, and a fixed-side guide ring (cavity presser) 8 is provided on the outer peripheral side of the abutment ring 3. In an optical disk substrate molding die in which movable guide rings 10 are respectively arranged on the outer peripheral side of the cavity ring 4,
A first exhaust passage is formed by a facing gap between the cavity ring 4 and the butting ring 3, a second exhaust passage is formed by a facing gap between the movable side guide ring 10 and the fixed side guide ring 8, and the fixed side guide ring. 8 are formed with third exhaust passages (through holes),
A substantial amount of the gas generated from the resin in the cavity 11 during molding is allowed to flow along the surface of the flat resin in the cavity and radially outward of the resin under reduced pressure, and then the first A molding die for an optical disc substrate, characterized in that after passing through the exhaust passage, it is caused to flow down through the second exhaust passage and the third exhaust passage and discharged out of the die.

In an example of a method for molding an optical disk substrate using this molding die, a cavity is filled with a molten resin, and a gas generated from the molten resin is sucked and exhausted outside the die through the first to third exhaust passages. While proceeding with the molding process.
In the mold shown in FIG. 6, the gas 15a from the molten resin in the cavity branches after flowing through the gap between the cavity ring 4 and the abutting ring 3, and one of them is the movable side guide ring 10 and the fixed side guide. The opposite gap between the rings 8 is sucked and discharged through the gas vent hole 5 formed in the other through the stationary guide ring 8.

According to the molding die having the above configuration, the following effects can be obtained.
(1) In the process of injecting and filling resin into the mold cavity and cooling to mold the optical disk substrate, the stamper tries to expand and contract in the diametrical direction in accordance with the temperature change. be able to. That is, the stamper can freely expand and contract in the molding process.
(2) In the molding process of the optical disk substrate, the gas generated from the molten resin in the cavity is molded while being exhausted out of the mold through the first to third exhaust passages. Since the adhesion of the gas coagulum is suppressed, the degree of freedom of the stamper's expansion and contraction operation is greatly increased.
(3) Therefore, it is possible to stably provide an optical disc having particularly good servo characteristics.

It is a schematic sectional drawing which shows the prior art example of an optical disk substrate shaping die. It is explanatory drawing of the shaping | molding process by the metal mold | die of FIG. 1, Comprising: A mold open state is shown. It is explanatory drawing of the shaping | molding process by the metal mold | die of FIG. 1, Comprising: The mold clamping and resin injection process following FIG. 2 are shown. It is explanatory drawing of the shaping | molding process by the metal mold | die of FIG. 1, Comprising: The mold opening process following FIG. 3 is shown. It is explanatory drawing of the shaping | molding process by the metal mold | die of FIG. 1, Comprising: The board | substrate taking-out process following FIG. 4 is shown. FIG. 2 is an explanatory diagram showing a flow of gas generated from a molten resin in a cavity to the outside of the mold in the molding process using the mold of FIG. 1. It is a schematic sectional drawing which shows the shaping die currently under examination. It is sectional drawing which shows the principal part structure of the shaping die concerning embodiment of this invention. It is a top view which shows the whole structure of the stamper holding jig which comprises the metal mold | die of FIG. 3 is a graph showing the servo characteristics of an optical disc (track signal at the time of on-track). FIG. 9 is a graph showing a relationship between a clearance between a cavity ring and a stamper and a tracking error signal left in the molding die of FIG. 8. 6 is a graph showing the tracking error signal remaining amount of an optical disc manufactured with a mold according to Comparative Example 1; It is a graph which shows the tracking error signal remaining amount of the optical disk produced with the metal mold | die which concerns on the Example of this invention.

Explanation of symbols

1: Stamper 2: Fixed mirror surface 3: Abutting ring 4: Cavity ring 5: Gas suction groove (gas vent hole)
6: Movable mirror surface 7: Stamper suction groove 8: Fixed side guide ring (cavity presser)
9: Cavity ring retainer 10: Movable guide ring 11: Cavity 12: Nozzle 14: Molded substrate 15: Exhaust passage 15a: Gas 17: Substrate take-out machine 20: Stamper holding jig 20a: Claw-shaped piece 20b: Daruma hole 31: Fixed mold (fixed part)
32: Movable mold (movable part)
A: Todrug jump signal B: The part that could not follow the track CL: Clearance

Claims (9)

In a mold for molding an optical disk substrate by setting a stamper on a stamper mounting surface to form a mold cavity and cooling molten resin injected and filled in the cavity,
A stamper holding jig having a radially inward locking portion for locking the outer periphery of the information recording surface of the stamper set on the stamper mounting surface;
The locking portion of the stamper holding jig is designed to allow the stamper to expand / contract in the radial direction along with injection / filling of molten resin into the cavity / cooling of the resin in the molding process. A clearance is maintained between the outer periphery of the information recording surface,
An optical disk substrate molding die characterized by the above.   The clearance between the engaging portion of the stamper holding jig and the outer periphery of the information recording surface of the stamper is 20 to 50 µm when the stamper is at room temperature. Mold for optical disk substrate.   The mold has a cavity ring on the movable mold, the stamper is set on the fixed mirror surface of the fixed mold, the information recording surface of the stamper faces the cavity ring, and the stamper is at room temperature. 3. The molding die for an optical disk substrate according to claim 1 or 2, wherein a clearance of 20 to 50 [mu] m is provided between the cavity ring and the outer periphery of the information recording surface of the stamper.   The stamper holding jig is configured by a plurality of claw-shaped pieces as the locking portions on the inner peripheral side and intermittently provided in the circumferential direction, and the whole is a ring-shaped piece. 4. A molding die for an optical disk substrate according to claim 1, wherein a piece faces the outer peripheral portion of the stamper.   5. The molding die for an optical disk substrate according to claim 3, wherein the stamper holding jig is detachably fixed to an abutting ring provided on the outer peripheral side of the fixed-side mirror surface.   The stamper holding jig has a plurality of harpoon-shaped through holes (hereinafter referred to as daruma holes) in a portion for removably fixing the stamper holding jig to the abutting ring, and intermittently in the circumferential direction of the stamper holding jig. The molding die for an optical disk substrate according to claim 5, wherein the molding die is provided on the optical disk substrate.   7. A method for molding an optical disk substrate, comprising injecting and filling molten resin into a cavity of a molding die according to claim 1.   An optical disc manufactured by an optical disc substrate molded by the molding method according to claim 7. In a method of forming an optical disk substrate by setting a stamper on a stamper mounting surface to form a mold cavity and cooling molten resin injected and filled in the cavity,
A locking means for locking the outer periphery of the information recording surface of the stamper set on the stamper mounting surface is provided,
A clearance is maintained between the locking means and the outer periphery of the stamper information recording surface so that the stamper can freely expand / shrink in the radial direction as the resin is injected and filled into the cavity / cooled. A molding method of an optical disk substrate, wherein the molding process is advanced.

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