JPH09198722A - Manufacture of substrate of optical recording medium and optical recording medium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for manufacturing a substrate of optical recording medium which reduces double refraction and is excellent in transferability. SOLUTION: Molding clamping pressure and/or core compressive force are controlled in plural steps while controlling the molding clamping pressure at a level higher than the core compressive force by which a fused resin within a cavity 24 is compressed during the time from the start of injection and filling until the opening of a mold when the fused resin is injected and filled into the cavity 24 of a molding die 8, to which a stamper 20 is fitted, to form the substrate of the optical recording medium.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a substrate manufacturing method for an optical recording medium and an optical recording medium. More specifically, for example, a phase change rewritable optical recording medium, a magneto-optical recording medium,
Substrate manufacturing method of optical recording medium molded from transparent thermoplastic resin such as polycarbonate resin or polymethylmethacrylate resin used for write-once type optical recording medium, and film deposition on the substrate manufactured by the manufacturing method Optical recording medium.

[0002]

2. Description of the Related Art An optical recording medium capable of reproducing, recording, reproducing, and erasing information by irradiating light is a reproduction-only optical disk commonly called a CD, a CD-ROM, or the like, and a write-once recording / reproduction optical disk. Similarly, there is a rewritable optical disk that can be recorded / reproduced / erased as a rewritable type. Compared to magnetic recording type magnetic discs, optical discs are characterized by having a large capacity, being easy to handle with non-contact type recording and reproduction, and being resistant to scratches and dirt. Demand expansion is expected.

When recording or reproducing information or signals on the optical recording medium, a spindle of a drive is inserted into a drive hole provided at the center of the optical recording medium to rotate the optical recording medium at a high speed (eg, , 2000 RPM) and the optical head follows groups (pits and tracking) for information recording.
Therefore, the grooves and pits are accurately transferred on the substrate of the optical recording medium, and the mechanical characteristics are set within the range of the performance that the optical head can follow, that is, the warp or tilt of the information / signal recording surface is small, and high speed. When rotated, it is required that the generation of axial acceleration or radial acceleration is small. Further, in order to minimize recording / reproducing errors, noise, signal disturbance, etc., it is required to reduce birefringence.

For this reason, the substrate of the optical recording medium is usually molded by injection compression molding, which allows molding of a substrate having low strain and small birefringence, rather than injection molding. That is, the divided surface of the mold is opened by a predetermined compression stroke amount in advance,
A method of compressing and molding the injection-filled molten resin by injection-filling the cavity with resin and then immediately clamping the resin by the compression stroke amount (hereinafter referred to as the injection press method). Molten resin is injected and filled into the cavity of the mold that keeps the mold clamping pressure low, and the mold clamping pressure loses the injection pressure during the filling process to open the split surface of the mold, and remolding is performed after the completion of filling. As a result, a method of compressing and molding the injection-filled molten resin (hereinafter referred to as the Rolinks method) is performed. Alternatively, the core of the mold can be locally pressurized, and the mold is clamped and then resin is injected into the cavity to locally retract the core to a predetermined amount. After filling with, the core part is pressed and moved forward to compress the molten resin for molding (hereinafter, referred to as micromolder method).

In any of the above methods, since the molten resin is injected and filled while the volume of the mold cavity is expanded or after the volume is expanded, the flow resistance of the molten resin in the cavity is reduced and the injection pressure is set low. can do. Further, it is possible to apply a uniform compression force after injection and filling. Therefore, flow orientation and internal strain are reduced, and as a result, it is possible to obtain a substrate for an optical recording medium having a small warpage and a small birefringence.

[0006]

However, in the injection press method or the Rolinks method, it is difficult to precisely control a predetermined compression stroke amount mechanically or hydraulically with good micron order. In other words, in order to transfer the submicron grooves and pits of the stamper precisely and with good reproducibility, it is necessary to apply a certain transfer pressure to the molten resin, but the mold clamping pressure when the resin flows or is compressed If it is low, the transfer is likely to be insufficient. If the mold clamping pressure is simply increased for this improvement, the resin is excessively pressed against the stamper, causing local surface deformation when the substrate is released from the mold, which significantly increases the acceleration component of the substrate. There is a risk.

Further, in the micro-moulder method, the compression stroke amount can be set mechanically from the structural aspect,
The precision control is possible, and precise transfer is possible with a relatively low compression force as compared with the injection press method and the Rolinks method. However, if the compressive force (hereinafter referred to as the core compressive force) is excessively increased, the resin is excessively pressed against the stamper to cause local surface deformation when the substrate is released, as in the injection press method and the Rolinks method. It causes the generation of excessive acceleration. Further, in order to prevent such an adverse effect, if the core compression force is released before the mold is opened, the birefringence becomes excessive, or the groove or pit transferred to the substrate is deformed due to the difference in thermal contraction between the substrate and the stamper. It may occur.

Further, in order to prevent the above-mentioned harmful effects, a method of controlling the mold clamping pressure or the core compression force (Japanese Patent Publication No. 6-75888, Japanese Patent Laid-Open No. 62-9926).
However, it is difficult to obtain a substrate having desired characteristics while keeping the compressive force applied to the molten resin in the cavity within the optimum range by controlling only one of them.

An object of the present invention is to control the mold clamping pressure and the core compressing force within the optimum range, thereby providing excellent transferability, capable of reducing birefringence, and exhibiting excellent mechanical properties. The purpose is to provide a recording medium.

[0010]

In order to solve the above-mentioned problems, according to the method of manufacturing an optical recording medium of the present invention, a molten resin is injected and filled into the cavity of a molding die having a stamper mounted thereon, When molding the substrate of (1), the mold clamping pressure and / or the core compressive force are controlled from the start of injection filling to the mold opening while controlling the mold clamping pressure to be higher than the core compressing force for compressing the molten resin in the cavity. The method is characterized by controlling in multiple stages.

The core compression force is 50 to 250 kg · f / cm ² per unit projected area of the substrate in the mold opening / closing direction.
Is desirably within the range. The stroke due to the core compression is preferably in the range of 5% to 70% of the thickness of the substrate.

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION In the method of manufacturing a substrate for an optical recording medium according to the present invention, from the start of injection filling to the opening of the mold,
While controlling the mold clamping pressure to be higher than the core compression force, the mold clamping pressure and the core compression force are controlled in multiple stages. Therefore,
A sufficient compression force is applied to the molten resin in the cavity to transfer the information recording on the stamper well, but the birefringence as a substrate is deteriorated or the mold release property is hindered. Application of compressive force is prevented.

Further, the core compression force is 50 to 250 kg · f / cm per unit projected area of the substrate in the mold opening / closing direction.
By controlling within the range of ² , it is possible to obtain a molded substrate having particularly excellent transferability and mechanical properties.

Next, an example of a substrate manufacturing method for an optical recording medium according to the present invention will be described with reference to the drawings. FIG. 1 schematically shows a manufacturing apparatus for carrying out a method for manufacturing a substrate for an optical recording medium according to the present invention. In the figure, 1 indicates an injection compression molding machine. The injection compression molding machine 1 has a mold clamping mechanism and an injection mechanism (not shown). The stationary platen 2 of the mold clamping mechanism and the pressure receiving plate 3 are connected by a tie bar 4. A movable platen 5 is slidably attached to the tie bar 4. The movable platen 5 has a mold clamping cylinder 6
The mold clamping piston 7 therein is connected. Mold clamping cylinder 6
As the mold clamping piston 7 reciprocates inside, the movable platen 5 slides left and right in FIG.

The mold 8 is composed of a fixed mold 9 and a movable mold 10 with a mold dividing surface (PL) as a boundary. The fixed mold body 11 of the fixed mold 9 is fixed to a fixed mold mounting plate 12, and a fixed guide ring 13 fixed to the fixed mold mounting plate 12 is provided on the outer peripheral portion of the fixed mold body 11. Further, a resin filling hole, a so-called sprue 14, is provided in the center of the fixed mold 9.
Is provided with a sprue bush 15 and a resin runner, a so-called gate 16, is formed on one end side thereof. A fixed side bush 17 is concentrically fixed around the sprue bush 15, and the tip end thereof is formed as a die 18 for gate cutting.

A stamper 20 is held on the movable core 19 of the movable mold 10 by an inner stamper holder 21 at the inner peripheral portion thereof. On the outer periphery of the stamper 20, the fixed mold 1
The cavity link 22 provided on the outer edge of the first member 1 is biased by a spring (not shown).

The center of the movable die core 19 is centered on the ejector pin 25 for ejecting the molded sprue 14 and the gate 16, and inside the gate cut punch 23 and die cavity 24 for punching out the molded gate 16. The ejector sleeve 2 that projects the substrate to be molded by the action of the floating mechanism (not shown) of the ejector pin 25.
The inner stamper holder 21 and the inner stamper holder 21 are concentric with each other, and the ejector pin 25, the gate cut punch 23, and the ejector sleeve 26 are combined so as to be movable forward and backward in the axial direction. Movable core 1
The movable side guide ring 28 on the outer periphery of 9 is a movable side mounting plate 29.
Is fixed to. Further, an adjusting spacer 30 having a compression stroke δ is provided between the movable core 19 and the movable side mounting plate 29.
Is provided.

A contact ring 31 is provided on the outer periphery of the movable core 19.
Is provided integrally with the movable mold core 19 and comes into contact with the cavity ring 22 during mold clamping.
The tip of the fixed guide ring 13 is located at the tip of the movable guide ring 28, and the cavity ring 22 and the contact ring 3
By contacting 1 with each other, a cavity 24 is formed as a predetermined space between the fixed mold 19 and the movable mold 10. Then, the cavity 24 is filled with molten resin and cooled to form a substrate for an optical recording medium.

The mold 8 attached to the mold clamping mechanism of the injection compression molding machine 1 includes a mold clamping hydraulic circuit 32 and a mold clamping control means 3.
The mold clamping piston 6 of the mold clamping cylinder 6 is operated by 6 to move the movable platen 5 forward and backward to open and close the mold. Further, in the mold clamping hydraulic circuit 32, oil is supplied from the hydraulic pressure source 33 to the check valve 34 and the servo valve 35.
Is supplied to the mold clamping cylinder 6 via. Mold clamping control means 3
6 is composed of a servo valve control unit 37, a sequence control unit 38, and a program setting machine 39,
The servo valve 35 is controlled by the servo valve control unit 37. The servo valve control unit 37 is connected to the mold clamping cylinder 6 via a pressure sensor 40, and the mold clamping pressure applied to the mold 8 by the operation of the mold clamping piston 7 is detected by the pressure sensor 40. The servo valve control unit 37 is controlled, and the servo valve 35 is feedback-controlled. Further, a sequence control unit 38 and a program setting machine 39 are connected to the servo valve control unit 37, and the servo valve control unit 37 is controlled and operated by these outputs, whereby the mold clamping cylinder 6
By controlling the hydraulic pressure and its operating time, the mold clamping force applied to the movable mold 10 during the molding process, that is, during injection filling, holding pressure and cooling is controlled in multiple stages.

At the connecting portion between the movable platen 5 and the mold clamping piston 7, a core compression cylinder 41 and an ejector cylinder 42 are provided.
The punch cylinder 51 and the punch cylinder 51 are concentrically mounted, and the core compression hydraulic circuit 43 and the core compression control means 44 allow the core compression piston rod 54 of the core compression cylinder 41.
It is possible to apply or release a compressive force to the resin in the mold cavity 24 via the movable mold core 19 by advancing or retreating. In the core compression hydraulic circuit 43, oil is supplied from the hydraulic pressure source 33 to the core compression cylinder 41 via the check valve 34 and the servo valve 48. The core compression control means 44 is a servo valve control section 45,
It is composed of a sequence control unit 46 and a program setting machine 47, and the servo valve 48 is controlled by the servo valve control unit 45. The servo valve control unit 45 is connected to the core compression cylinder 41 via a pressure sensor 49, and the core compression force applied to the movable core 19 by the operation of the core compression cylinder 41 is detected by the pressure sensor 49. The servo valve control unit 45 is controlled by the signal, and the servo valve 48 is feedback-controlled. In addition, the servo valve control unit 4
5 includes a sequence controller 46 and a program setting machine 4
7 is connected, and the servo valve control unit 45 is controlled and operated by these outputs to control the hydraulic pressure of the core compression cylinder 41 and its operating time, and during the molding process, that is, during injection filling, holding pressure and cooling. The core compression force applied to the movable core 19 is controlled in multiple stages.

Further, the ejector cylinder 42 is operated by a hydraulic circuit (not shown) and its control device (not shown), and the ejector pin 25 and the ejector sleeve 26 are respectively moved forward and backward via the ejector rod 50.
Can be retracted. Furthermore, the punch cylinder 5
1 is a hydraulic circuit (not shown) and its control device (not shown)
, And the gate cut punch 23 can be moved forward and backward via the punch piston 53.

In the present embodiment, the mold clamping control means 36.
And the mold clamping hydraulic circuit 32 operates the mold clamping piston 7 in the mold clamping cylinder 6, the movable mold 10 attached to the movable platen 5 of the mold 8 advances, and the fixed mold 9 attached to the stationary platen 2 When a predetermined mold clamping pressure is applied to the mold cavity, the molten resin is injected into the mold cavity 24 from the nozzle (not shown) of the injection mechanism, which is in contact with the mold cavity, through the sprue 14 and the gate 16. Is filled. When a polycarbonate resin is used as the resin, a grade having a viscosity average molecular weight of about 15,000 and a release agent and a heat-resistant agent appropriately mixed is used.
It is desirable to heat-melt at ℃ and injection-fill.

Further, in order to faithfully transfer the grooves and pits engraved on the stamper 20, the fixed main body 11 and the movable core 19 are heated from 90 ° C. to 135 ° C. for a rewritable information disc, for example. . The sprue bush 15 and the gate cut punch 23 are heated from room temperature to 100 ° C., if necessary. In some cases, it is also effective to blow air to cool the sprue bush 15 and the gate cut punch 23.

The molten resin is filled in the cavity 24 with the injection. At this time, the compression stroke adjusting spacer 3 is provided between the movable side mounting plate 29 and the movable die core 19.
0, and the core compression force applied to the movable core 19 is set to be slightly smaller than the filling pressure by injection, whereby the compression stroke δ provided between the movable core 19 and the movable side mounting plate 29 is adjusted. The movable mold core 19 is once retracted, and the mold cavity 24 is expanded, that is, the distance between the fixed mold body 11 and the movable mold core 19 is expanded. Therefore, the pressure of the molten resin flowing in the cavity 24 is reduced, the flow strain is reduced, and the birefringence is suppressed. As a result of various experiments conducted by the present inventors, they have found that it is most effective to set the compression stroke δ to be 5% to 70% of the wall thickness of the molded substrate.

Further, the core compression force applied to the movable mold core 19 is slightly smaller than the filling pressure by injection, and the mold clamping pressure applied to the movable mold 10 is made larger than the core compression force to obtain the injection filling pressure. Accordingly, birefringence is further improved by controlling multiple stages such that the initial filling is low, the latter filling is high, and the second filling is low. Acceleration is reduced. By controlling the mold clamping pressure applied to the movable mold 10 in multiple stages according to the filling pressure by injection, the movable mold 10 is temporarily retracted by a small amount, and the mold cavity 24 is further expanded. Therefore, the pressure of the molten resin flowing in the cavity 24 is reduced, the flow strain is reduced, and the birefringence is further reduced. Further, when the molten resin flows in the cavity 24, the flow pressure and thermal expansion thereof cause the stamper 2 to flow.
Although 0 expands and contracts, by properly controlling the mold clamping pressure in multiple stages,
The clearance between the cavity ring 22 and the stamper 20 is secured at a proper amount or more, whereby the stamper 20 freely expands and contracts, and by extension, the micro waviness of the transfer surface and the deformation of the groove are controlled, and the axial direction and the radial direction of the substrate to be molded are controlled. Acceleration is reduced.

When filling the molten resin, the movable mold 10 is used.
Alternatively, when the movable core 19 is retracted, the fixed mold body 11
While the cavity ring 22 at the outer peripheral portion of the stamper 20 abuts on the abutment ring 31 fixed to the movable core 19,
With a certain clearance (usually 10-20 μm)
Move while holding. This prevents the occurrence of burrs on the outer peripheral portion of the molded substrate due to leakage of the molten resin from the cavity 24. When the molten resin filling is completed,
The mold clamping pressure applied to the movable mold 10 and the core compression force applied to the movable mold core 19 are uniformly applied to the entire surface of the molten resin, and as the resin shrinks due to cooling, the fixed mold body 11 and the movable mold core 19 and The gap between the fixed mold 9 and the movable mold 10 is narrowed, the filled resin is compressed, and a molded substrate having a predetermined wall thickness is formed. Then, the punch piston 53 of the punch cylinder 51 is advanced to press the tip of the punch piston 53 against the die 18 at the tip of the fixed side bush 17, whereby the gate 16 is punched out. Then, after cooling for a predetermined time, the movable die 10 is retracted, the substrate is separated from the fixed die body 11 and the stamper 20 by an air blow mechanism (not shown), and then the ejector piston 50 of the ejector cylinder 42 is advanced to eject the ejector pin. 25 and the ejector sleeve 26 are advanced so that the substrate is ejected and the die 8
Remove from

In this embodiment, the mold clamping pressure is always kept higher than the core compression force, both pressures are controlled in a plurality of stages, and the pressure per unit projected area of the substrate in the mold opening / closing direction is 50 to 250 kg / cm ² . The core compression force is controlled within the range, and the mold clamping pressure and the core compression force are applied from immediately before the start of injection to the mold opening. If the core compressive force is too low, the transferability becomes insufficient. On the contrary, if the core compressive force is too high, the molten resin is likely to adhere to the stamper 20 and the molded substrate becomes the stamper 2.
At the time of peeling from 0, micro waviness deformation of the transfer surface occurs, thereby increasing axial acceleration and the like. As a result of various studies by the present inventors, the core compression force was 50 kg / cm ^{2 to} 25 per unit projected area of the substrate in the mold opening / closing direction.
It has been found that a molded substrate having excellent transferability and mechanical properties can be obtained by setting the range to 0 kg / cm ² . In addition, the mold clamping pressure and the core compressive force are applied from just before the injection is started until the mold is opened. When the mold clamping pressure and the core compressive force are released before the mold is opened, the birefringence is extremely increased, the This is because the deformation of the grooves and pits, which is considered to be due to the difference in heat shrinkage of the stamper, occurs, and the desired molded substrate of good quality cannot be obtained. The mold clamping pressure is always higher than the core compression force, and these are controlled in multiple stages together. This control can be carried out by applying the above-mentioned hydraulic circuit and its control circuit, but the control means is not limited at all.

The substrate manufactured by the method of manufacturing a substrate for an optical recording medium according to the present invention can be molded from a resin composition containing polycarbonate as a main component. Polycarbonates are transparent, for example, obtained by the reaction of a dihydric phenol with a carbonate precursor. Examples of the dihydric phenol include hydroquinone, 4,4'-dioxydiphenyl, bis (hydroxyphenyl) alkane, bis (hydroxyphenyl) cycloalkane, bis (hydroxyphenyl) ether, bis (hydroxyphenyl) ketone, bis (hydroxyphenyl). Sulfide,
Bis (hydroxyphenyl) sulfone and substituted products thereof such as lower alkyl and halogen can be used.

The viscosity average molecular weight of the above polycarbonate resin composition must be in the range of 13,000 to 18,000. If it is less than 13,000, the strength of the substrate to be molded becomes insufficient, and practical strength as an optical recording medium cannot be obtained. On the other hand, when it exceeds 18,000, the fluidity of the resin at the time of molding is reduced, and problems such as transferability and optical distortion are likely to occur.

A predetermined recording layer is provided on the information surface of the molded substrate. For the recording layer, first provide a protective layer on the substrate,
You may make it formed on it. Various layers such as a protective layer and a reflective layer may be further provided on the formed recording layer.

In the recording layer, for example, Te-Ge-Sb is used.
-Pd alloy, Te-Ge-Sb-Pd-Nb alloy, Nb
-Ge-Sb-Te alloy, Pt-Ge-Sb-Te alloy, Ni-Ge-Sb-Te alloy, Ge-Sb-Te alloy, Co-Ge-Sb-Te alloy, In-Sb-Te alloy, In -Se alloys and alloys containing these as main components are used. Especially Te-Ge-Sb-Pd alloy, T
The e-Ge-Sb-Pd-Nb alloy is preferable because deterioration is unlikely to occur even when recording / erasing / reproduction is repeated and thermal stability is excellent. A particularly desirable recording film composition is, for example, in the range represented by the following formula, from the viewpoint of excellent thermal stability and repetition stability. M _z (Sb _x Te _(1-x) ) _1-yz (Ge _0.5 Te _0.5 ) _y 0.35 ≦ x ≦ 0.5 0.20 ≦ y ≦ 0.5 0 ≦ z ≦ 0.05 where M Is at least one metal selected from palladium, niobium, platinum, silver, gold, and cobalt, Sb is antimony, Te is tellurium, and Ge is germanium. Also,
x, y, z and numerals represent the number of atoms of each element (the number of moles of each element). In particular, palladium and niobium preferably contain at least one kind. In this case, z is 0.
It is preferably at least 0005. These alloys are applied on the first protective layer provided on the substrate by, for example, sputtering to form a recording layer.

[0032]

【Example】

Example 1, Comparative Examples 1 to 4 An appropriate amount of a release agent and a heat-resistant agent were mixed, and the average molecular weight was 150.
00 polycarbonate optical grade, 1.2mm pitch with 1.2μm pitch on one side, 1.2mm thick substrate, cylinder temperature 350 ℃, mold temperature, 120 ℃, injection filling time The mold clamping pressure and the core compressive force were changed as shown in Table 1 under the conditions of 0.3 seconds and holding time of 0.2 seconds, and injection molding was performed. The characteristics of the obtained substrate were evaluated and the results shown in Table 2 were obtained.

As is clear from Tables 1 and 2, in the conventional molding methods shown in Comparative Examples 1, 2, 3 and 4, the transfer rate, birefringence and A substrate satisfying both mechanical characteristics has not been easily obtained. On the other hand, according to the method for manufacturing a substrate for an optical recording medium of the present invention shown in Example 1, a substrate satisfying the above main characteristics was easily obtained.

[0034]

[Table 1]

[0035]

[Table 2]

[0036]

As described above, according to the method for manufacturing a substrate for an optical recording medium of the present invention, the mold clamping pressure and the core compressive force are controlled in multiple steps from the start of injection filling to the mold opening. Since the optimum compressive force is always applied to the molten resin in the cavity, birefringence is reduced and a substrate having improved transferability can be obtained. Further, by forming a film on the substrate, an optical recording medium having excellent mechanical characteristics can be obtained.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram of a manufacturing apparatus for carrying out a method of manufacturing a substrate of an optical recording medium according to an embodiment of the present invention.

[Explanation of symbols]

 1 Injection compression molding machine 2 Fixed side platen 3 Pressure receiving plate 4 Tie bar 5 Movable platen 6 Clamping cylinder 7 Clamping piston 8 Mold 9 Fixed type 10 Movable type 11 Fixed type main body 12 Fixed type mounting plate 13 Fixed type guide ring 14 Spool 15 Spool Bush 16 Gate 17 Fixed Bush 18 Die 19 Movable Core 20 Stamper 21 Inner Stamper Holder 22 Cavity Ring 23 Gate Cut Punch 24 Cavity 25 Ejector Pin 26 Ejector Sleeve 28 Movable Side Guide Ring 29 Movable Side Mounting Plate 30 Adjusting Spacer 31 Contact ring 32 Clamping hydraulic circuit 33 Hydraulic pressure source 34 Check valve 35, 48 Servo valve 36 Clamping control means 37, 45 Servo valve control section 38, 46 Sequence control section 39, 47 Program setting Machine 40, 49 pressure sensor 41 core compression cylinder 42 the ejector cylinder 43 the core compression hydraulic circuit 44 core compression control unit 50 the ejector rod 51 punch cylinder 52 the nozzle touch part 53 punch piston

Claims (4)

[Claims] 1. When a molten resin is injection-filled into a cavity of a molding die in which a stamper is mounted and a substrate of an optical recording medium is molded, a mold clamping pressure is applied between the start of injection filling and the mold opening. A method for manufacturing a substrate for an optical recording medium, wherein the mold clamping pressure and / or the core compression force is controlled in a plurality of steps while controlling the compression pressure higher than the core compression force for compressing the molten resin therein. 2. The core compression force is 50 to 250 kg · f / cm per unit projected area of the substrate in the mold opening / closing direction.
^The method of manufacturing a substrate for an optical recording medium according to claim 1, wherein the substrate is in the range of ² . 3. The method of manufacturing a substrate for an optical recording medium according to claim 1, wherein the stroke due to the core compression is in the range of 5% to 70% of the thickness of the substrate. 4. An optical recording medium film-coated on a substrate manufactured by the method according to claim 1.