JP2002307488A - Method for molding data recording disk substrate, and mold therefor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a molding method optimum for molding a thin data recording disk substrate low in double diffraction and excellent in mechanical characteristics, and a mold therefor. SOLUTION: A cylindrical sleeve 40 advancing and retreating with respect to a cavity 20a is provided to a movable mold 31. The cylindrical sleeve 40 is allowed to advance toward a fixed mold before or during injection to protrude the end part of the cylindrical sleeve 40 into the cavity 20a. By this constitution, the flow of a molten resin into the cavity 20a is controlled. After injection, the cylindrical sleeve 40 is allowed to retreat to cool the resin charged in the cavity 20a. The substrate molded by this method is reduced in the double refraction caused by the generation of stress in the substrate and has excellent mechanical characteristics.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a mold for manufacturing a substrate of an information recording disk by injection molding and a molding method using the same, and more particularly, to a method for molding a small and thin substrate. The present invention relates to an optimal mold and an injection molding method using the same.

[0002]

2. Description of the Related Art As an information recording disk of high recording density, D
VD (Digital Versatile Disk) and ASMO (Advanced
Storage Magneto Optical Disk) has been proposed. In these information recording disks, in order to achieve a higher recording density, the wavelength of the laser beam is shortened and the numerical aperture of the lens (Numerical Aperture) is increased to 0.6 or more to reduce the light spot diameter. In these information recording disks, the thickness of the substrate is reduced to suppress coma caused by the inclination of the disk, and the conventional CD-RO
The thickness of the substrate used in optical disks such as M1.2
0.6 mm, which is half of mm. In recent years, to further increase the recording density, it has been studied to increase the NA of the lens and further reduce the thickness of the substrate to 0.5 mm to 0.4 mm.

However, when the thickness of the substrate is reduced, the rigidity of the substrate may be reduced, or optical anisotropy, that is, birefringence may occur in the substrate. Such a decrease in rigidity and the occurrence of birefringence are important issues in substrate molding technology. For example, the birefringence occurs more remarkably as the thickness of the substrate becomes thinner, and particularly remarkable in the inner peripheral portion of the substrate. Birefringence causes fluctuations in the amount of light of the light receiving element when recording and reproducing signals, and causes signal reading errors. Therefore, for practical use in a small disk using the inner peripheral portion of the disk as a recording area. It is a big obstacle. The occurrence of the birefringence is caused by CD-A, C-C which reproduces information by utilizing the difference in light reflectance due to the unevenness of the pits.
Read-only memory such as D-ROM, DVD-ROM, phase-change disk for reproducing information by using the difference between the crystalline and amorphous reflectance of the recording film, and reproducing information by using the magnetic Kerr effect This problem is common to rewritable memories such as magneto-optical disks. In particular, a magneto-optical disk that reproduces information by using the magnetic Kerr effect is very serious because a change in the amount of linearly polarized light due to slight rotation of the polarization direction is detected.

[0004] Further, polycarbonate is mainly used as a substrate material of information recording discs currently put into practical use. Since polycarbonate has a high photoelastic coefficient, there is a problem that birefringence occurs even when a slight stress is present in the substrate. In particular, the substrate thickness on the recording surface is 0.5 m
When polycarbonate is used as the material of the thin substrate of m or less, it is extremely difficult to suppress the occurrence of birefringence.

[0005] In addition, since the rigidity of the thin substrate is reduced due to the reduced thickness, the thin substrate is deformed when the molded substrate is released from the mold at the time of molding, and there is a problem that the mechanical characteristics are deteriorated. Here, the mechanical characteristics indicate deformation in the axial direction of the information recording disk, and are generally called tilt.
In the case of an information recording disk manufactured using a tilted substrate, the laser beam incident on the disk follows the track because it is reflected by the inclined substrate surface and is displaced from the proper position of the light receiving element. An offset is generated in the servo signal for causing the light to pass, and an aberration is generated in the light transmitted through the optical system. In particular, since a reference surface for positioning the disk in the axial direction when the disk is mounted on the drive is formed on the inner peripheral portion of the information recording disk, it is more important to secure the rigidity of the inner peripheral portion of the disk. is there.

By the way, when the direction in which the stress is generated in each part of the thin plate substrate is examined by, for example, subtracting the circumferential stress from the radial stress of the substrate, it shows an extremely negative value in the inner peripheral portion of the substrate. It can be seen that a large circumferential stress is generated in the inner peripheral portion of the substrate. This indicates that in the injection molding of a thin substrate, a circumferential stress is generated in the substrate because the flow of the resin is obstructed during the flow of the resin into the cavity due to the small cavity spacing. In order to prevent the occurrence of such stress, the cavity spacing is widened during injection for the purpose of reducing the flow resistance of the resin, and after the injection is completed, the cavity spacing is adjusted to a desired thickness, A method has been proposed in which the viscosity of the molten resin is reduced by increasing the temperature of the heating cylinder of the machine to suppress the occurrence of stress during the injection process.

However, as described above, it is extremely difficult to control the optical characteristics of a molded substrate by adjusting the molding conditions at the time of molding the substrate when molding a substrate having a small thickness. The reason is as follows. Normal,
The cooling time of the substrate during molding is proportional to the square of the thickness of the substrate. For example, a thin substrate having a substrate thickness of 0.6 mm is rapidly cooled in a quarter of the cooling time of a substrate having a substrate thickness of 1.2 mm. For this reason, the cooling time, that is, the time for adjusting the molding conditions in proportion to the substrate thickness is shortened, and the margin for adjusting the optical characteristics of the molded substrate is also reduced. In other words, even if the molding conditions at the time of molding the substrate are adjusted, the margin for adjusting the optical characteristics of the molded substrate is very small, and the optical characteristics of the molded substrate are ultimately determined by the shape and thickness of the substrate. Become.

The present inventors have disclosed in Japanese Patent Application No. 2000-20922.
2 discloses a substrate in which optical anisotropy, that is, birefringence, is reduced by devising the shape of the inner peripheral portion such as reducing the thickness of the inner peripheral portion. Also, Japanese Patent Application No. 11-
In 336946, a substrate is disclosed in which the rigidity of the substrate is increased by devising the shape of the inner peripheral portion, such as providing a step on the inner peripheral portion, and the mechanical deformation is reduced. However, the birefringence and the mechanical characteristics are in a mutually contradictory relationship in a substrate having a thin plate structure, and there has been a demand for a method of forming a substrate that improves the mechanical characteristics while reducing the birefringence.

The present invention has been made in order to meet such a demand, and an object of the present invention is to provide a molding method and a molding die for a thin substrate having good mechanical properties and small birefringence.

[0010]

According to a first aspect of the present invention, there is provided a fixed mold and a movable mold, wherein a cavity is defined between the fixed mold and the movable mold. In a mold for molding an information recording disk substrate filled with a molten resin, a cylindrical sleeve provided coaxially with a center axis of the cavity, and the sleeve is protruded into the cavity before or during filling with the molten resin. And a sleeve moving device for retracting the sleeve from the cavity after filling with the molten resin.

The mold of the present invention includes a cylindrical sleeve protruding into a cavity defined by a fixed mold and a movable mold, coaxially with the center axis of the cavity. The cylindrical sleeve is provided on a fixed mold or a movable mold, and can be advanced and retracted in the central axis direction of the cavity by a sleeve moving device. Such a cylindrical sleeve can be protruded into the cavity by the sleeve moving device before or during filling of the cavity with the molten resin, thereby restricting the flow of the molten resin. That is, the tip of the cylindrical sleeve protruding into the cavity becomes a resistance of the resin flowing into the cavity. After the filling of the molten resin, the cylindrical sleeve is retracted from the cavity by the sleeve moving device. As a result, a thin substrate molded using a mold having such a cylindrical sleeve has excellent mechanical properties and reduced birefringence.

Further, in the present invention, the sleeve moving device may include a biasing means for allowing the cylindrical sleeve to advance and retreat in the direction of the center axis of the cavity. The biasing means include:
For example, an air cylinder using air pressure as shown in FIG. 5 can be used. As shown in FIGS. 5A and 5B, for example, a pneumatic solenoid valve is opened and closed according to a signal from an injection molding machine, and compressed air or negative pressure air supplied from an air compressor is supplied to a first cylinder. By supplying to the cylinder 42 or the second cylinder 43, the cylindrical sleeve 40 can be advanced or retracted in the cavity central axis direction. By designing the stroke of the cylinder such that the amount of protrusion of the cylindrical sleeve 40 into the cavity becomes a desired value, the amount of protrusion of the cylindrical sleeve 40 can always be kept constant.

A compression coil spring 44 as shown in FIG. 6 can also be used as the means for urging the cylindrical sleeve. In this case, before filling with the molten resin, FIG.
As shown in FIG.
Since the cylindrical member 40 protrudes into the cavity 20a due to the urging force of 4, the molten resin is filled with the end of the cylindrical sleeve 40 protruding into the cavity. When the resin is filled in the cavity 20a, the pressure in the cavity increases, and FIG.
As shown in (B), the cylindrical sleeve 40 is pushed back. Here, the spring load of the compression coil spring 44 can be determined, for example, by inserting a pressure sensor into the cavity and measuring the maximum pressure when the molten resin is filled into the cavity with the pressure sensor. Alternatively, the substrate may be actually formed using compression coil springs having various spring loads, and the spring load of the compression coil spring when a desired formed substrate is obtained may be set as the optimum spring load.
As described above, the mold provided with the compression coil spring as the urging means of the cylindrical sleeve does not need to add a special function to the molding apparatus to which the mold is attached, so that the substrate can be molded using the conventional molding apparatus. It has the advantage that.

Incidentally, a mold for molding a substrate is generally
A gate cutter for punching the center hole of the molded substrate is provided at the center. A stamper for forming a concavo-convex pattern as a preformat pattern in an information recording area of a molded substrate is mounted on one of the fixed mold and the movable mold. The cylindrical sleeve is preferably provided between the gate cutter and the information recording area.
That is, it is preferable that the cylindrical sleeve be positioned in the radial direction of the cavity inside the innermost peripheral position of the information recording area of the stamper and outside the outer peripheral position of the gate cutter. Within such a range, it is preferable to be positioned near the information recording area. Thereby, generation of birefringence of the molded substrate can be effectively suppressed.

In the present invention, the width of the cylindrical sleeve is
In order to secure a recording area, it is preferable to make the recording area as small as possible. In order to process a component with high precision, an appropriate thickness is required, so that the thickness can be set to 0.5 mm to 5 mm.

According to a second aspect of the present invention, in a molding method for manufacturing an information recording disk substrate by filling a molten resin into a mold, a fixed mold and a movable mold are used as the mold. Using a mold having a cylindrical sleeve provided coaxially with the center axis of a cavity defined by these molds, and before or during filling of the cavity with the molten resin. A method for forming an information recording disk substrate, comprising: projecting a cylindrical sleeve into a cavity, filling the cavity with substantially molten resin, and then retracting the cylindrical sleeve from the cavity.

In the molding method of the present invention, a mold for molding a substrate is provided so as to be coaxial with the center axis of a fixed mold, a movable mold, and a cavity defined by these molds. And a mold having a cylindrical sleeve. The cylindrical sleeve is provided in a fixed mold or a movable mold. Before or during filling of the mold with the molten resin, the cylindrical sleeve is protruded into the cavity, and the cylindrical sleeve limits the molten resin flowing into the cavity. The amount of protrusion when the cylindrical sleeve is protruded into the cavity is set at 0.0 to prevent the molten resin from flowing into the outer periphery of the cavity significantly.
5 mm to 0.3 mm is preferred. After the molten resin is substantially filled into the cavity, the cylindrical sleeve is retracted from the cavity to prevent the molded substrate from being thinned at the protruding portion of the cylindrical sleeve, and the resin is removed from the cavity. Allow to solidify within. Since a thin substrate obtained by such a molding method has reduced birefringence, an information recording disk manufactured using this substrate is
Noise is reduced and S / N is improved. In particular, since the birefringence of the inner peripheral portion of the substrate can be reduced, the inner peripheral portion having a radius of 16 mm or less can be used as the innermost peripheral position of the recording area. The thin substrate manufactured by the molding method of the present invention is most suitable as a substrate for a small high-density information recording disk.

In the molding method of the present invention, the timing of retracting the cylindrical sleeve protruding into the cavity from the inside of the cavity is from after the molten resin is substantially filled into the cavity to before the molten resin is solidified. If it is, it is arbitrary, for example, during holding pressure or immediately after the start of cooling. When using the compression molding method to prevent sink marks,
The timing of retracting the cylindrical sleeve from the cavity may be after closing the cooling gate, as long as the resin in the cavity is not solidified. It should be noted that “the molten resin is substantially filled in the cavity” means not only that the cavity is filled with the same amount of molten resin as the cavity volume, but also that the amount of the resin is 80% or more of the cavity volume. This includes the case where the molten resin is filled in the cavity. In addition, when the resin corresponding to the cylindrical sleeve of the obtained molded substrate is not sufficiently filled with resin, the timing for retracting the cylindrical sleeve may be advanced to select an appropriate timing that does not cause sink marks or the like.

As the cylindrical sleeve of the mold used in the molding method of the present invention, for example, an ejection mechanism (ejector sleeve) used for releasing the molded substrate from the mold can be used. In this case, the ejector sleeve may be controlled so as to protrude at least twice at any position and timing in the cavity before or during the filling of the molten resin and at the time of releasing the molded substrate. However, in the case of molding a thin substrate, since the thickness of the cavity is thin, it is necessary to control the amount of protrusion of the ejector sleeve into the cavity before or during filling with the molten resin with high precision. If the amount of protrusion is large, the tip of the ejector sleeve may collide with the mold and damage the mold. Therefore, it is desirable to provide a cylindrical sleeve in addition to the ejector sleeve.

[0020]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, a method for molding an information recording disk substrate and a mold therefor according to the present invention will be specifically described, but the present invention is not limited thereto.

[0021]

Embodiment 1 Embodiment 1 of the present invention will be described with reference to FIGS. FIG. 1 is a schematic sectional view of an information recording disk. The information recording disk 1 includes a molded substrate 2 as a base.
And a hub 3. The hub 3 is mounted on the inner peripheral portion of the information recording disk 1. A center hole 8 is formed in the center of the information recording disk 1, and an information recording surface 6 is formed on the upper surface of the information recording disk. The information recording disk 1 is mounted on a turntable 9 provided in a driving device (not shown), and is driven to rotate by a rotation shaft 10. A magnet 11 is fitted in the turntable 9, and the information recording disk 1 is mounted on the turntable 9.
When the hub 3 is mounted, the hub 3 is magnetically attracted by the magnet 11, thereby preventing the information recording disk 1 from coming off the turntable 9. At the time of recording / reproducing, a recording or reproducing laser beam is condensed by the objective lens 12, enters the laser incident surface 7, transmits through the molded substrate 2, and focuses on the information recording surface 6 on the information recording disk 1. Are connected, and signal recording and reproduction are performed.

FIG. 2 shows a cross-sectional structure of the molded substrate 2 shown in FIG. The molded substrate 2 is formed from a polycarbonate resin, and is manufactured by injection molding using a mold described later. The molded substrate 2 has an outer diameter of 50 mm and 11 mm.
mm inside diameter. In FIG. 2, the upper surface of the molded substrate 2 is an information recording surface 6, the lower surface is a laser beam incident surface 7, and the information recording surface 6 has an information recording area 5. The thickness of the substrate in the information recording area 5 is 0.6 mm. On the information recording surface 6, a plurality of grooves and a plurality of concave and convex marks on which address information is recorded are formed. A recess 4 for accommodating the hub 3 shown in FIG. 1 is formed on the inner peripheral side of the information recording area 5.

FIG. 3 shows an injection mold 20 according to the present invention.
2 shows a cross-sectional structure in a fastened state. FIG. 4 shows an enlarged cross section of the inner peripheral portion of the cavity 20a of the injection mold 20 shown in FIG. As shown in FIG.
No. 0 is configured by combining the fixed mold 21 and the movable mold 31 coaxially (on the X axis).

The fixed die 21 includes a fixed die set 22, a sprue bush 26, a fixed bush 27, and a stamper suction bush 2 sequentially inserted on the center axis (X axis).
5, a fixed mirror 23 and a stamper 24 for forming a signal surface of the molded substrate 2 are provided. The sprue bush 26 is connected to a molding machine nozzle (not shown) for flowing molten resin into a mold during injection molding. The fixed bush 27
The sprue bush 26 is a cylindrical insertion piece inserted into the outer peripheral side. The fixed bush 27 forms the concave portion 4 into which the hub of the substrate 2 to be molded is inserted, and a female mold used when a gate cutter 34 described later advances to the stationary mold side and punches the center hole 9 of the molded substrate 2. Has the role of.
On the stamper 24, a plurality of grooves formed on the information recording surface 6 of the molded substrate 2 and an inverted concavo-convex pattern corresponding to a plurality of concavo-convex marks recording address information are formed. The stamper 24 has a stamper suction bush 25 at its inner periphery.
The outer peripheral portion is vacuum-sucked by a stamper negative-pressure suction hole 23 a provided on the fixed mirror 23, and is closely attached to the fixed mirror 23. . Fixed mirror 2
The surface of the fixed mirror 23 is mirror-finished in order to attach the stamper 24 in close contact with it, and expands and contracts repeatedly due to heat generated during molding. DLC
(Diamond-like carbon), TiN, TiC, T
Hard coating such as iCN is PVD (Physical Vapor Depos)
ition) and plasma CVD (Chemical Vapor Depositio)
n).

On the other hand, the movable die 31 is
2, and an ejector pin 38, a gate cutter 34, and an ejector pin sequentially inserted on the central axis (X axis) thereof.
Sleeve 36, movable bush 35, cylindrical sleeve 40,
It comprises a movable mirror 33 and a cavity ring 37 forming the outer diameter of the molded substrate. The ejector pins 38
A sprue (not shown), which is an unnecessary part of the molded substrate cooled in the mold, can be released. The ejector sleeve 36 is inserted movably in the center axis direction into an ejector driving cylindrical cylinder 36a formed in the movable die set 32, and moves the molded substrate 2 into the cavity 20.
a can be released from the mold. The movable mirror 33 is for forming the laser light incident surface 7 of the molded substrate 2 and is mirror-finished so that the laser light is not diffracted on the laser light incident surface and the transmittance is not impaired. The gate cutter 34 has a role of a male die when punching the center hole 9 of the molded substrate 2. After filling the cavity 20 a with the molten resin, the gate cutter 34 advances to the fixed mold side to form a center hole in the molded substrate 2. . A cylindrical sleeve 40 is provided between the movable bush 35 and the movable mirror 33, and the cylindrical sleeve 40 is positioned inside the information recording area of the substrate to be formed.

As shown in FIGS. 5A and 5B, the cylindrical sleeve 40 has a first outer diameter portion 40a and a second outer diameter portion 40b having an outer diameter smaller than the first outer diameter portion 40a. ,
A third having an outer diameter larger than the outer diameter of the first outer diameter portion 40a
And an outer diameter portion 40c. Second outer diameter portion 40b
A first cylinder 42 is defined by the outer peripheral wall of the movable mirror 33 and the inner peripheral wall of the movable mirror 33, and the end of the cylindrical sleeve 40 on the third outer diameter side, the outer peripheral wall of the movable bush 35, and the inner peripheral wall of the movable mirror 33. A second cylinder 43 is defined. The protrusion amount of the end of the cylindrical sleeve 40 on the first outer diameter side is 0.
The stroke of the cylindrical sleeve 40 was designed to be 2 mm.

Here, the operation of the cylindrical sleeve 40 will be described. To advance the cylindrical sleeve 40, a signal is sent at a desired timing from a molding machine (not shown) to a pneumatic solenoid valve (not shown), and an air compressor (not shown) is sent.
From the second through the forward drive port 41a.
The solenoid valve is opened to be supplied to the cylinder 43. Thereby, the cylindrical sleeve 40 receives the air pressure of the compressed air supplied to the second cylinder 43, and advances in a direction approaching the cavity 20a as shown in FIG. On the other hand, to retract the cylindrical sleeve 40, the supply of the compressed air to the second cylinder 43 is stopped, and the solenoid valve is controlled so that the compressed air is supplied to the first cylinder 42 through the retreat drive port 41b. Thereby, the cylindrical sleeve 40 receives the air pressure of the compressed air supplied to the first cylinder 42, and retreats in a direction away from the cavity 20a as shown in FIG. 5B.

Here, compressed air is supplied to the second cylinder 43 to advance the cylindrical sleeve 40, and compressed air is supplied to the first cylinder 42 to retract the cylindrical sleeve 40. It is also possible to advance the cylindrical sleeve by applying pressure, and to retract the cylindrical sleeve by applying negative pressure to the second cylinder 43. Alternatively, while supplying compressed air to the second cylinder 43, the first cylinder
By setting the cylinder 42 to a negative pressure, the cylindrical sleeve 4
0 may be advanced, and the cylindrical sleeve may be retracted by making the second cylinder 43 a negative pressure while supplying compressed air to the first cylinder 42.

As shown in FIG. 3 or FIG. 4, a fixed release air passage 27a is provided between the fixed bush 27 and the stamper suction bush 25, and the movable bush 35 and the cylindrical sleeve 40 are movable. A release air channel 35a is provided. By sending air from the fixed release air flow path 27a and the movable release air flow path 35a, the substrate molded at high temperature can be uniformly released from the cavity. The thickness of the gate 34a is smaller than the cavity interval and 0.3 m so as not to hinder the flow of the molten resin.
m.

The fixed mold 21 and the movable mold 31 are supported by four rods (not shown) parallel to the central axis (X axis) before being mounted on the molding machine. The upper part is slidable and can move in the direction of the central axis (X axis). As shown in FIG.
1 is integrated with the fixed mold 21, the fixed bush 27, the stamper 24, the stamper suction bush 25, and the movable mirror 3
3. The cavity 20a is defined by the cavity ring 37, the movable bush 35 and the ejector sleeve 36.

Next, the injection mold 20 shown in FIG.
Was mounted on an injection molding machine DISK3 (not shown) manufactured by Sumitomo Heavy Industries, Ltd. using bolts (not shown), and FIG.
The substrate having the structure shown in was manufactured. Hereinafter, a method of manufacturing a substrate will be described.

First, the mold temperature of the fixed mold 21 and the movable mold 31 was adjusted to 125 ° C., and the cylinder temperature was adjusted to 380 ° C., respectively. Next, after pressing the molding machine nozzle (not shown) against the sprue bush 26, the fixed mold 21 and the movable mold 31 were clamped by a mold clamping mechanism (not shown) of the injection molding machine with a mold clamping force of 10 tonf. Next, the cylindrical sleeve 40 is advanced to protrude the tip of the cylindrical sleeve into the cavity 20a by 0.2 mm and melted polycarbonate resin (Teijin Kasei Panlite AD550)
3) was injected into the cavity 20a of the injection mold 20. After the cavity 20a was filled with the resin, the pressure was maintained for a certain period of time to replenish the volume contraction of the resin due to cooling. During this pressure holding operation, the cylindrical sleeve 40 was retracted.

Next, the resin in the cavity is compressed while increasing the mold clamping force to 15 tonf, and at the same time, the gate cutter 34 is protruded toward the fixed bush 27 on the fixed mold 21 side, and the gate 34a is cut to start cooling. . While maintaining the mold clamping force at 15 tonf, a cooling time of 6 seconds was passed. Then, mold release air was flowed from the fixed mold release air flow path 27a on the fixed mold side, and the mold was opened while uniformly peeling the molded substrate 2 from the stamper 24. Next, mold release air is flowed from the movable mold release air flow path 35a on the movable mold side to uniformly peel the molded substrate 2 from the movable mirror 33, and eject the ejector sleeve 36 and the ejector pins 38 to form the molded substrate 2. 2 and the sprue were released from the cavity. Thus, a molded substrate made of polycarbonate resin having a diameter of 50 mm as shown in FIG. 2 was obtained.

[0034]

Embodiment 2 In this embodiment, the thickness of the information recording area 5 of the molded substrate 2 shown in FIG.
The thickness of the mold cavity is set to 0.1 more than that of the first embodiment.
A molded substrate made of a polycarbonate resin was manufactured in the same manner as in Example 1 except that the amount of resin filling the cavity was reduced by the amount corresponding to the thickness of the cavity and the thickness of the cavity.

[0035]

Example 3 In this example, a molded substrate made of a polycarbonate resin was produced in the same manner as in Example 1 except that the mold shown in FIG. 7 was used in order to make the shape of the molded substrate a flat plate structure. . The thickness of the information recording area of the molded substrate is 0.6 m
m, the substrate outer diameter was 65 mm, and the filling amount of the resin in the cavity was adjusted according to the cavity volume.

[0036]

Embodiment 4 In this embodiment, an air cylinder as shown in FIG.
6, except that a mold having a compression coil spring 44 as the means for urging the cylindrical sleeve was used as shown in FIG. Was formed.

FIG. 6A shows a state where the cylindrical sleeve 40 has moved forward, and FIG. 6B shows a state where the cylindrical sleeve 40 has receded. A biasing force acts on the compression coil spring 44 in a direction in which the cylindrical sleeve is advanced (right side in the figure). During injection of the molten resin, as shown in FIG. 6A, the cylindrical sleeve 40 advances toward the cavity by the urging force of the compression coil spring 44, and the end of the cylindrical sleeve 40 projects into the cavity by a predetermined amount. Sticking out. After the cavity is filled with the resin, if the pressure in the cavity increases due to the holding pressure and becomes larger than the urging force of the compression coil spring 44, as shown in FIG.
Is pushed back. As described above, the mold provided with the compression coil spring 44 does not need to control the forward and backward movement of the cylindrical sleeve 40 by the molding machine. The stroke of the cylindrical sleeve 40 was designed to be 0.2 mm as in the case of the first embodiment.

[0038]

Comparative Example A In order to confirm the effects of the present invention, a substrate was prepared in the same manner as in Examples 1, 2 and 3 except that the holding and cooling were performed without retracting the cylindrical sleeve protruding into the cavity. Molded. The obtained molded substrates are referred to as Comparative Examples A1, A2 and A3, respectively.

[0039]

Comparative Example B A substrate was formed in the same manner as in Examples 1, 2, and 3, except that the cylindrical sleeve was not protruded into the cavity when the cavity was filled with the polycarbonate resin. The obtained molded substrates were compared with Comparative Examples B1 and B2, respectively.
And B3.

[Evaluation of Molded Substrate]
3. The optical characteristics of the molded substrates of Comparative Examples A1 to A3 and Comparative Examples B1 to B3 were evaluated. In the evaluation of the optical characteristics, in-plane retardation (optical phase difference), which is most commonly measured and managed as the optical characteristics, was determined. A commercially available birefringence measuring device manufactured by Mizojiri Optical Co., Ltd. was used as the evaluation device. This device converts parallel light having a beam diameter of φ1 mm emitted from a He-Ne laser light source having an oscillation wavelength of 633 nm into λ /
After being polarized by a four-wavelength plate and transmitted through the substrate, the retardation of the wavelength is calculated by obtaining the ellipticity of circularly polarized light after transmission through the substrate by a photodetector via a rotating analyzer. The retardation here is the product of the in-plane birefringence and the thickness of the substrate. In addition, evaluation was performed using a value when light was transmitted through a transparent substrate generally defined as a single pass. The evaluation result was obtained as an average value measured at 12 points in the rotation direction of the disk as a value of each radius.

In order to measure the mechanical characteristics of the substrate with the same device, the molded substrate having a different shape is used. The displacement in the direction was measured. From the measured values, the maximum value of the runout runout and the maximum tangential tilt in the axial direction were obtained. The maximum tangential tilt value was the maximum value obtained by dividing one rotation into 512 and calculating the inclination angle from the displacement difference between each division point.

[Evaluation Results and Discussion] FIG.
In the comparative examples A1 and B1, the change of the in-plane retardation with respect to the disk radius of the molded substrate having the substrate thickness of 0.6 mm in the information recording area produced was shown. FIG. 9 shows the change of the in-plane retardation with respect to the disk radius of the molded substrate having a thickness of 0.5 mm in the information recording area prepared in Example 2 and Comparative Examples A2 and B2, and FIG. The changes in the in-plane retardation with respect to the disk radius of the molded substrates having the flat plate structures manufactured in Example 3 and Comparative Examples A3 and B3 are shown. From the graphs of FIGS. 8 to 10, in the molded substrates of Examples 1 to 3 and the molded substrates of Comparative Examples Al to A3, the absolute value of the in-plane retardation was smaller than 30 nm, and Comparative Example B
It turns out that it is better than the molded substrates of Nos. 1, B2 and B3. This indicates that when molding the substrate, the in-plane retardation of the substrate can be reduced by advancing the cylindrical sleeve of the injection mold and injecting the resin while projecting the tip of the cylindrical sleeve into the cavity. In particular, the effect is more remarkable in the inner circumference.

As can be seen from the graphs of FIGS. 8 and 10, regardless of whether the molded substrate has a stepped structure or a flat plate structure, the substrate molded by the molding method of the present invention reduces the retardation. The effect is obtained. Further, as can be seen from the graph of FIG. 9, even when the substrate thickness is as thin as 0.5 mm, the effect of reducing the retardation is obtained.

FIG. 11 shows the in-plane retardation of a substrate formed using a mold having a compression coil spring as a biasing means for the cylindrical sleeve 40 with respect to the disk radius. The substrate molded using a mold having a compression coil spring also had good in-plane retardation over the entire surface of the disk, and was confirmed to have an effect of reducing the retardation.

Table 1 shows Examples 1-4 and Comparative Examples Al-A
3 and the measurement results of the mechanical properties of the molded substrates of Comparative Examples Bl to B3 are shown.

[0046]

[Table 1] As can be seen from this table, Examples 1-4 and Comparative Example Bl
The substrates B3 to B3 have a maximum axial runout runout of 31.
μm or less, maximum tangential tilt ± 0.0
It is within 7 deg., Which is better than the substrates of Comparative Examples Al to A3. This is because, in the substrates of Comparative Examples Al to A3 in which the cylindrical sleeve of the injection molding die was advanced and the tip of the cylindrical sleeve was protruded into the cavity, and the injection molding was performed, the plate thickness at the inner peripheral portion was locally increased. It is considered that deformation occurred at the time of mold release because the thickness was reduced, and it can be considered that the difference in plate thickness is reflected in this result. From the results in Table 1, the molding method of the present invention has an effect of improving mechanical properties even when the thickness of the molded substrate is as thin as 0.5 mm, or even when the substrate has a flat plate structure or a stepped structure. Obtained. Further, it can be seen that even when a compression coil spring is used as the urging means of the cylindrical sleeve 40, there is an effect of improving the mechanical characteristics of the molded substrate.

From the above results, it can be seen that the molded substrates produced in Examples 1 to 4 are excellent in both in-plane retardation and mechanical properties.

[0048]

The mold of the present invention has a cylindrical sleeve which projects into the cavity before or during the injection and retracts from the cavity after the injection, so that the birefringence is small and the machine characteristics are good. A thin information recording disk substrate can be manufactured.

According to the molding method of the present invention, before or during injection of the molten resin into the mold, the cylindrical sleeve is protruded into the cavity to control the flow of the resin into the cavity, thereby filling the molten resin. Since the cylindrical sleeve is retracted after the process and before the resin is solidified, the birefringence of the substrate to be molded can be reduced. In particular, since the birefringence of the inner peripheral portion of the substrate can be reduced, it is most suitable as a method for molding a relatively small-sized information recording disk substrate having an outer diameter of 65 mm or less. Furthermore, since a polycarbonate resin can be used as a substrate material, a thin substrate can be manufactured at low cost and with high productivity.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view showing a state where an information recording disk is inserted into a driving rotary shaft.

FIG. 2 is a schematic sectional view of a molded substrate manufactured in Example 1.

FIG. 3 is a schematic sectional view of an injection mold according to the present invention.

FIG. 4 is a partially enlarged cross-sectional view of an inner peripheral portion of a cavity of the injection mold shown in FIG.

FIG. 5 is a conceptual diagram when an air cylinder is used as a biasing means of a cylindrical sleeve of an injection molding die according to the present invention, and FIG. 5 (A) shows a state when the cylindrical sleeve is advanced; FIG. 5B shows the state when the cylindrical sleeve is retracted.

FIG. 6 is a conceptual diagram when a compression coil spring is used as a biasing means of the cylindrical sleeve of the injection molding die according to the present invention, and FIG. 5 (A) shows a state when the cylindrical sleeve is advanced; FIG. 5B shows the state when the cylindrical sleeve is retracted.

FIG. 7 is a schematic sectional view of an injection molding die for molding a substrate having a flat plate structure used in Example 3.

FIG. 8 is a graph of in-plane retardation with respect to the disk radius of the formed substrate having a thickness of 0.6 mm manufactured in Example 1, Comparative Examples A1 and B1.

FIG. 9 is a graph of in-plane retardation with respect to the disk radius of the formed substrate having a thickness of 0.5 mm manufactured in Example 2, Comparative Examples A2 and B2.

FIG. 10 is a graph of in-plane retardation with respect to the disk radius of the flat substrate formed in Example 3 and Comparative Examples A3 and B3.

FIG. 11 is a graph of in-plane retardation with respect to a disk radius of a molded substrate manufactured in Example 4.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Information recording disk 2 Mold substrate 3 Hub 4 Depression 5 Information recording area 6 Information recording surface 7 Laser incidence surface 8 Center hole 9 Turntable 10 Rotation axis 11 Magnet 12 Objective lens 20 Injection mold 20a Cavity 21 Fixed mold 22 Fixed Die set 23 Fixed mirror 23a Stamper negative pressure suction hole 23b Stamper negative pressure suction groove 24 Stamper 25 Stamper suction bush 26 Sprue bush 27 Fixed bush 27a Fixed mold release air channel 31 Movable mold 32 Movable die set 33 Movable mirror 34 Gate Cutter 34a Gate 35 Movable bush 35a Movable mold release air flow path 36 Ejector sleeve 36a Ejector driving cylindrical cylinder 37 Cavity ring 38 Ejector pin 40 Cylindrical sleeve 40a First outer diameter portion 40b 2nd outer diameter part 40c 3rd outer diameter part 41a Forward drive port 41b Retreat drive port 41c Cylindrical cylinder 42 First cylinder 43 Second cylinder 44 Compression coil spring

Claims (9)

[Claims] 1. An information recording disk substrate molding mold comprising a fixed mold and a movable mold, wherein a molten resin is filled in a cavity defined between the fixed mold and the movable mold. A cylindrical sleeve provided coaxially with the center axis of the cavity, and for projecting the sleeve into the cavity before or during filling with the molten resin, and for retracting the sleeve from the cavity after filling with the molten resin. And a sleeve moving device. 2. The information recording disk substrate molding die according to claim 1, wherein the moving device includes an urging means for urging the sleeve in a direction of a center axis of the cavity. 3. The mold includes a gate cutter for forming a center hole of the substrate, and a stamper for forming an information recording area of the substrate, wherein the sleeve is perpendicular to a central axis of the cavity. 3. The mold for forming an information recording disk substrate according to claim 1, wherein the metal mold is present between the gate cutter and the information recording area of the stamper in the direction. 4. The information recording disk substrate molding die according to claim 1, wherein the amount of protrusion of the sleeve into the cavity is 0.05 mm to 0.3 mm. . 5. The apparatus according to claim 3, further comprising a cylindrical ejector sleeve between the gate cutter and the sleeve for projecting the formed substrate and removing the substrate from the mold. The information recording disk substrate molding die described in the above. 6. The mold for forming an information recording disk substrate according to claim 2, wherein said urging means is a compression coil spring. 7. The information recording disk substrate molding die according to claim 2, wherein said urging means is an air cylinder for supplying compressed air or negative pressure air. 8. A molding method for manufacturing an information recording disk substrate by filling a mold with a molten resin, wherein the mold is defined by a fixed mold, a movable mold, and these molds. Using a mold having a cylindrical sleeve provided so as to be coaxial with the center axis of the cavity, and projecting the cylindrical sleeve into the cavity before or during filling the molten resin into the cavity, After filling the cavity with the molten resin,
A method for forming an information recording disk substrate, wherein the cylindrical sleeve is retracted from a cavity. 9. A projection amount of the cylindrical sleeve when projecting into the cavity is 0.05 mm to 0.3 mm.
The method for forming an information recording disk substrate according to claim 8, wherein: