JP3072736B2 - Optical disk substrate molding equipment - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical disk substrate forming apparatus for forming an optical disk substrate used for a novel magneto-optical disk that records a digital signal compressed to a disk having an outer diameter of less than 80 mm and a size of 130 Mbytes or more.

[0002]

2. Description of the Related Art An optical recording system has features such as recording and reproduction without contact, easy handling, and resistance to scratches and dirt. It has the advantage that the recording capacity can reach tens to hundreds of times, so that it can be used practically as a compact disk that digitally records audio signals or a video disk that records video signals, as well as code information and image information. Is expected to be used for large files.

Meanwhile, an optical recording medium for this optical recording system has an optical information recording layer formed on a transparent substrate formed of a polycarbonate resin or the like. Have been.

For example, there is little birefringence (in this case, the phase shift between the incident light and the reflected light for signal reading of the disk, mainly due to internal distortion of the transparent substrate), and good transferability. , Good surface smoothness, little contamination, little shaking (skew) of the molding surface, and the like.

In particular, in a magneto-optical disk, a minute rotation of the plane of polarization of a laser beam to be irradiated is read as a signal. Therefore, it is essential to reduce birefringence generated in a transparent substrate.

Under these circumstances, injection molding technology has been developed in various fields, and it is possible to mold a substrate having almost no birefringence in a recording area in a current transparent substrate for a compact disk, a video disk, and the like. Has become.

FIG. 6 shows the basic structure of a conventional disk substrate molding die, and an example of an injection molding method which has been performed up to now will be described.

In this disk substrate molding die, the space (cavity) filled with resin is mainly composed of the fixed mirror plate (101) and the movable mirror plate (1).
02) and a sprue (104) at the center of the mold.

The fixed-side mirror plate (101) and the movable-side mirror plate (102) are provided with temperature control mechanisms, for example, heat medium flow paths (105) and (106), respectively. (Usually, hot water or oil) is applied to each of the mirror plates (101), (10).
The temperature control of 2) is performed.

The movable mirror plate (10)
A stamper (not shown) for transferring pits, guide grooves, and the like to the disk signal portion is attached to 2). The stamper can move an inner peripheral portion punched in advance by an inner peripheral stamper retainer (107). It is held by supporting it with the mirror plate (102), and the outer peripheral portion is also supported by the outer peripheral stamper retainer (108).

A die (109) is attached to the center of the fixed mold, and a sprue bush cap (1) is attached.
The sprue bush (111) is fitted and arranged via 10). At the center of the sprue bush (111), there is a sprue (104) for guiding the molten resin in the molding machine cylinder (112) to the disk cavity through the nozzle (113). The molten resin is supplied into the cavity through the section (104).

Between the sprue bush (111) and the sprue bush cap (110), although not shown, a cooling mechanism independent of the temperature control mechanism of each of the mirror plates (101) and (102) is provided. ing. This cooling mechanism is, for example, such that a groove is provided on the outer peripheral surface of a sprue bush (111) to flow a cooling medium, and usually has a structure in which the cooling medium is sealed by an O-ring (114). ing.

The reason for cooling this portion independently is that the sprue portion (104) is thicker than the disc-shaped portion (103), so that it takes a long time to solidify the resin, and the sprue portion (104) is further cooled. Since the structure is elongated and hard to be removed from the mold, the temperature is set lower than that of the mirror plates (101) and (102) to facilitate quick cooling and release of the sprue resin.

On the other hand, an ejector pin (115), a punch (116), a punch sleeve (117), and an ejector sleep (118) are arranged in a complicated combination at the center of the movable mold. Is provided with a cold slug portion (119).

The cold slug portion (119) is a portion where scum of the molten resin, which is likely to be generated at the nozzle tip when the resin is filled, accumulates. The cold slug portion (119) also has the same reason as the sprue portion (104). The temperature is set lower than that of the mirror plates (101) and (102) by a cooling circuit formed between the punch (116) and the punch sleep (117) so that the thick portion is quickly solidified. .

The process until the disk substrate is molded by the disk substrate molding die having the above-described structure will be described. First, a resin melted in a heated cylinder (112) (280 to 250 in case of polycarbonate resin) 3
It is set to about 40 ° C. ) Is a molding machine nozzle (11
3) It is injected into the mold from the tip through the sprue (104). At this time, the cooled resin residue at the tip of the nozzle (113) is transferred to the cold slug (11) provided on the movable mold side.
9), most of the other resin is formed in a disk cavity between the fixed mirror plate (101) and the movable mirror plate (102) set at a temperature range of about 100 to 130 ° C., That is, pits, guide grooves, and the like are transferred to the movable resin surface by the stamper while filling the disk-shaped portion (103). After the filling is completed, the punch (116) and the punch sleeve (117) of the movable mold protrude integrally toward the fixed mold to form a center hole of the disk.
The resin in the disk cavity is sealed by the punch sleeve (117), and the resin pressure is maintained during the cooling period, so that it is possible to prevent resin sink, transfer failure, and the like. I have.

After the cooling, the fixed-side mirror plate (10
Air or nitrogen gas is blown out from the gap between 1) and the die (109) to release the disk from the fixed mold.

Subsequently, the entire movable mold is retracted and the mold is opened. At this time, the disk and the sprue portion must be completely separated from the fixed mold and stuck to the movable mold. Next, the normal ejector sleep (11
8) Air is blown out from the gap between the stamper presser (107) and the disc is peeled from the stamper, and at the same time, the disc is ejected by the ejector sleeve (118). Further, the sprue portion is provided with an ejector pin (115).
And ejected from the mold together with the disk.

Thereafter, the entire movable side mold advances, the mold closes, and the next molding cycle starts again.

[0020]

As described above, in the conventional mold, the structure of the central portion on the movable side is particularly complicated, and the sprue bush (111) and the punch (116) are connected to the mirror plate (101), In order to make the temperature lower than (102), the mold temperature of the disk part has a very large temperature distribution, especially on the inner peripheral side. This temperature distribution has a significant effect on the molding of the transparent substrate, and this effect is particularly noticeable as the size of the transparent substrate to be molded becomes smaller, and the birefringence increases in the inner peripheral portion of the substrate, such as light When a magnetic disk is used, the signal quality is impaired. Birefringence of the transparent substrate significantly degrades S / N.

Furthermore, the dimensions of parts such as punches, punch sleeps, injector sleeps, stamper presses, etc. have been gradually reduced, and the mechanical strength or working limit has been reached.

Under such circumstances, the recording area of the conventional optical recording disk is limited to about 60 mm in inner diameter, and there is no known optical disk that records signals up to the area of 50 mm or less in inner diameter.

Therefore, especially in a small-diameter disk, a sufficient recording area cannot be secured, and the recording capacity is limited. For example, when a standard CD format (CD-DA format) or a CD-MO format (format using a recordable magneto-optical disc) as an extended format is adopted, even if the disc diameter is 8 cm, the recording / reproducing time is sufficient. Is 20-22
Minutes, which is very short. If the disk diameter is to be further reduced, the restriction on the recording area at the inner diameter portion becomes a major obstacle, and even if data is compressed, it is almost impossible to secure a recording capacity corresponding to an audio signal for 60 minutes or more.

Accordingly, the present invention has been proposed in view of the above-mentioned conventional circumstances, and is an optical disk capable of ensuring birefringence to the inner peripheral side and securing a sufficient recording area even with a small diameter. It is an object of the present invention to provide an optical disk substrate molding apparatus capable of molding a substrate for use.

[0025]

SUMMARY OF THE INVENTION In order to achieve the above-mentioned object, the present invention comprises a fixed mold and a movable mold, and the center of the fixed mold is provided in a disc-shaped space sandwiched between them. In an optical disc substrate molding apparatus that supplies molten resin from a sprue portion of a sprue bush arranged in a portion and injection-molds an optical disc substrate, the center of the movable mold is
A punch having an ejector pin disposed at the center is attached, and the ejector pin is retracted from the punch, so that the diameter of the punch is 1
A space of about 2 mm is formed as a cold slug portion.

In the optical disk substrate manufactured by the molding apparatus of the present invention, the birefringence of the transparent substrate is guaranteed up to the inner peripheral side of the disk. ± 50n retardation
m.

Therefore, a sufficient recording area for signal recording can be ensured even for a small-diameter disk, and a compressed digital signal of 130 Mbytes or more can be recorded on a disk having an outer diameter of less than 80 m. This is the same as the CD with a track pitch of 1.6 μm and a linear velocity of 1.2 to 1.4 m /
When the data compression rate is 1/4 and the data compression rate is 1/4, the audio signal corresponds to 60 minutes or more.

The optical disk substrate forming apparatus of the present invention has an elongated shape having a diameter of about 1 to 2 m and a small heat storage capacity so that the cold slag portion can be easily cooled. The structure is such that it solidifies quickly without cooling independently of the mold. Therefore, it is not necessary to provide a cooling circuit in the punch unlike the conventional punch, and the configuration of the apparatus is greatly simplified.

[0029]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a partial sectional view showing an example of the configuration of a magneto-optical disk to which an optical disk substrate manufactured by the molding apparatus of the present invention is applied. This magneto-optical disk is recorded on a transparent substrate (1). The layer (10) and the organic protective film (4) are laminated.

The transparent substrate (1) has a thickness of about 1.
A transparent disc-shaped substrate of 2 mm, which is formed by, for example, injection molding a plastic material such as a polycarbonate resin, an acrylic resin, and a polyolefin resin.

The transparent substrate (1) has a birefringence retardation of at least ± 50 nm in an area up to an inner diameter of 32 mm (that is, an area of a diameter of 32 mm or more) in order to secure a recording area even for a small-diameter disk. In this area, high quality signal recording is possible.

Birefringence is a phenomenon that occurs when light passes through a medium (refractive index anisotropic material) having a different refractive index in the same plane depending on the direction. For example, birefringence in a predetermined direction (x direction). Refractive index n _x , direction perpendicular to this (y direction)
If the refractive index of the transmitted light is n _y , a phase shift occurs between the x component (light having a polarization plane parallel to the x direction) and the y component (light having a polarization plane parallel to the y direction) of the transmitted light. . This phase difference is a retardation δ, δ = 2π / λ · (n x -n y) d ··· (I) (λ: wavelength of light, d: distance of the medium the light is transmitted) made by the formula expressed.

It is desirable that the surface (1a) of the transparent substrate (1) on the laser beam incident side is optically sufficiently smooth, and that the surface (1b) on the side on which the recording layer (10) is provided is not necessary. And a pit (3) corresponding to an address code having a guide groove (2) having a depth of about one-fourth of the laser light wavelength to be used. Depending on the recording format, for example, the pit (3) may not be provided.

The recording layer side surface (1) of the transparent substrate (1)
A recording layer (10) is provided on b), and any recording layer of a normal magneto-optical recording medium can be applied to the recording layer (10), and the configuration is arbitrary. For example, as shown in FIG. 2, the first protective dielectric layer (1
1), the recording magnetic layer (12), the second protective dielectric layer (1)
3), and a recording layer (10) having a four-layer structure in which a reflective metal layer (14) is sequentially formed.

In this case, the first protective dielectric layer (11) and the second protective dielectric layer (13) do not transmit oxygen and water molecules, do not contain oxygen, and sufficiently transmit the used laser beam. Is preferable, and silicon nitride, aluminum nitride, or the like is suitable.

The recording magnetic layer (12) is an amorphous ferromagnetic layer having an easy axis of magnetization in a direction perpendicular to the film surface, has a large coercive force at room temperature, and has a Curie temperature around 200 ° C. It is desirable to have points. A TbFeCo-based alloy thin film is suitable for satisfying such conditions. Also,
For the purpose of imparting corrosion resistance, a small amount of a fourth element such as Cr may be added to the TbFeCo-based alloy thin film.

The reflective metal layer (14) laminated on the second protective dielectric layer (13) is a high-reflectance non-magnetic metal layer that reflects laser light at this boundary by 70% or more, and is thermally A good conductor is desirable, and aluminum is suitable for this.

Further, an organic protective film (4) is provided on the reflective metal layer (14). As a material of the organic protective film (4), a photocurable resin (UV light) having excellent waterproof property is used. Cured resin) is suitable.

It is also possible to form a hard protective film (5) having abrasion resistance on the organic protective film (4) so that a magnetic head provided on the recording / reproducing apparatus side is brought into sliding contact. It is.

In the magneto-optical disk having the above-described configuration, the birefringence is guaranteed in the area on the inner peripheral side of the transparent substrate (1), and the recording capacity of the stereo audio signal is 60 to 74 minutes. And, for example, F
A digital signal (ADPCM with a sampling frequency of 37.8 kHz and a quantization number of 4 bits) having a data compression ratio of 1/4, such as a B level stereo mode having a sound quality equivalent to that of M broadcast, is recorded in an amount of about 130 Mbytes or more.

In order to constitute a portable or pocket-sized recording and / or reproducing apparatus, the outer diameter of the disk is set to less than 8 cm. On the other hand, it is desired that the track pitch and the linear velocity be 1.6 μm and the linear velocity are 1.2 to 1.4 m / sec, as in the case of the CD.

Therefore, for example, when the disk outer diameter is 64 m
m, the outer diameter of the data recording area is 61 mm, the inner diameter of the data recording area is 32 mm, and the inner diameter of the lead-in area is 30 m.
m, center hole 9-11mm (eg 10mm)
And it is sufficient. This magneto-optical disk is 70 mm long and short.
If it is stored in a disk caddy of × 74 mm and supplied to the market, recording and reproduction on the disk can be performed by a recording / reproducing device of about pocket size.

In the above 1/4 data compression mode, 7
The dimensional range of the inner and outer diameters of the data recording area of the disk for enabling recording and reproduction for about 2 minutes to 76 minutes is from an outer diameter of 60 to 62 mm when the inner diameter is 32 mm to an inner diameter of 50 mm. The diameter may be set appropriately within the range of 71 to 73 mm.

When manufacturing the above-described magneto-optical disk, there is a problem how to guarantee birefringence on the inner peripheral side of the transparent substrate. Accordingly, an example of a mold structure capable of suppressing birefringence to the inner peripheral side and an example of a method of forming a substrate will be described.

FIG. 3 shows an example of a mold structure for ensuring birefringence up to the inner peripheral side of the substrate.

Also in this disk substrate molding die,
The space (cavity) filled with the resin is mainly composed of the fixed mirror plate (21) and the movable mirror plate (2).
A disc-shaped portion (23) sandwiched by 2) and a sprue portion (24) at the center of the mold.

The fixed-side mirror plate (21) and the movable-side mirror plate (22) are provided with temperature control mechanisms, for example, heat medium flow paths (25) and (26), respectively. The temperature of each of the mirror plates (21) and (22) is controlled by (usually, hot water or oil).

The movable mirror plate (22)
A stamper (27) for transferring pits, guide grooves, and the like to the disk signal portion is attached to the stamper. The stamper (27), as shown in FIG. 28), it is held by being sandwiched between the movable mirror plate (22) and the outer peripheral portion is also supported by the outer peripheral stamper retainer (29).

The structure of the fixed mold is the same as that of the conventional mold shown in FIG. 6. A die (30) is attached to the center of the mold and a sprue bush (32) is inserted through a sprue bush cap (31). Are fitted and arranged.

At the center of the sprue bush (32),
There is a sprue section (24) for guiding the molten resin in the molding machine cylinder (33) to the disk cavity section via the nozzle section (34).
The molten resin is supplied through the cavity into the cavity.

Between the sprue bush (32) and the sprue bush cap (31), although not shown, a cooling mechanism independent of the temperature control mechanism of each of the mirror plates (21) and (22) is provided. ing. This cooling mechanism is, for example, such that a groove is provided on the outer peripheral surface of a sprue bush (32) to flow a cooling medium, and usually has a structure in which the cooling medium is sealed by an O-ring (35). ing.

On the other hand, the structure of the movable mold is simplified as compared with the conventional mold.
Only an ejector pin (36), a punch (37) and an ejector sleeve (38) are provided. And
A cold slag portion (39) is provided at the center thereof. The cold slag portion has an elongated shape with a diameter of about 1 to 2 mm so that the cold slag portion is easily cooled, and has a small heat storage capacity. 37) is quickly solidified without cooling independently of the movable mirror plate (22). Accordingly, the punch (37) is not provided with a cooling circuit unlike the conventional one.

As a result, the temperature distribution in the mold becomes more uniform, and an increase in the substrate birefringence on the inner peripheral side can be suppressed. Further, since the punch (37) is not cooled independently, it is not necessary to have a complicated double structure including a cooling circuit for the punch and the punch sleeve, and a disk having a smaller diameter is formed even in consideration of mechanical strength and the like. It has a structure suitable for. In addition, the base of the cold slug (39) has a slightly overhanging shape with a large diameter, so that when the mold is opened, it comes out of the sprue quickly. ing.

The process until the disk substrate is molded by the disk substrate molding die having the above-described structure is almost the same as in the case of the conventional injection molding. First, the disk substrate is melted in the heated cylinder (33). The resin (in the case of a polycarbonate resin, set at about 280 to 340 ° C.) is injected into the mold from the tip of the molding machine nozzle (34) through the sprue portion (24).

At this time, the cooled resin residue at the tip of the nozzle (34) is transferred to the cold slug (3) provided on the movable mold side.
Although the cold slag portion (39) is elongated and has a small heat storage capacity, it is quickly solidified without a cooling circuit.

On the other hand, most of the other resins are about 1%.
Fixed-side mirror plate (21) and movable-side mirror plate (22) set in a temperature range of about 00 to 130 ° C.
Disc cavities between the disc-shaped portions (2
3) The pits and the guide grooves are simultaneously transferred to the movable resin surface by the stamper.

After the filling is completed, the movable mold punch (37)
Projecting toward the fixed mold side, a center hole of the disk is formed, the resin in the disk cavity is sealed by the punch (37), and the resin pressure is maintained during the cooling period. It is possible to prevent sink marks and transfer failure of the resin.

After the cooling, the fixed mirror plate (2)
Air or nitrogen gas is blown out from the gap between 1) and the die (30) to release the disk from the fixed mold.
Subsequently, the entire movable mold retreats and the mold opens, but at this time, the disk and the sprue part are completely separated from the fixed mold,
It must be stuck to the movable mold.

Next, a normal ejector sleeve (38)
Air is blown out from a gap between the stamper and the stamper retainer (28) to peel the disc from the stamper and simultaneously eject the disc by the ejector sleeve (38). Further, the sprue portion is pushed out by the ejector pin (36) and taken out of the mold together with the disk.

Thereafter, the entire movable mold moves forward, the mold closes, and the next molding cycle starts again.

FIG. 5 shows the magnitude of the birefringence retardation at each position in the radial direction of the transparent substrate (polycarbonate substrate) formed by the above-described forming method.

As is apparent from FIG. 5, by using the mold having the above structure, the center hole diameter is 10 mm, the disk outer diameter is 64 mm, and the polycarbonate resin is used.
It is possible to mold a small disc whose innermost circumference of the recording area is reduced to 30 mm,
In m), the birefringence was also controlled within the allowable value of ± 50 nm.

[0064]

As is clear from the above description, according to the molding apparatus of the present invention, at least the inner diameter of the transparent substrate is at least 32.
± 50 nm birefringence retardation in the region up to m
Within. Therefore, by using the obtained optical disk substrate, it is possible to sufficiently secure a recording area even with a small-diameter magneto-optical disk,
It is possible to provide a novel magneto-optical recording system which is smaller than ever and which allows a user to freely write, for example, an audio signal for 60 minutes or more.

Further, in the optical disk substrate molding apparatus of the present invention, since the heat storage capacity of the cold slag portion is small and solidifies quickly without a cooling circuit, for example, a complicated slag including a cooling circuit with a punch and a punch sleeve is provided. It is not necessary to have a double structure, and it is possible to greatly simplify the device configuration.

[Brief description of the drawings]

FIG. 1 is a schematic perspective view of a main part of a configuration example of a magneto-optical disk, partially cut away.

FIG. 2 is an enlarged sectional view of a main part showing a configuration example of a recording layer.

FIG. 3 is a schematic sectional view showing an example of a mold for suppressing birefringence in an inner peripheral portion of a disk.

FIG. 4 is a schematic cross-sectional view of a main part, showing the vicinity of a stamper retainer in an enlarged manner.

5 is a characteristic diagram showing the relationship between the substrate radius and the magnitude of birefringence of a polycarbonate substrate molded using the mold shown in FIG.

FIG. 6 is a schematic sectional view showing an example of a conventional disk substrate molding die.

[Explanation of symbols]

21 fixed side mirror plate, 22 movable side mirror plate, 24 sprue section, 36 ejector pin, 3
7 Punch, 39 Cold slug

──────────────────────────────────────────────────続 き Continued on the front page (58) Fields investigated (Int. Cl. ⁷ , DB name) G11B 7/26 521 B29C 45/00 B29C 45/27 G11B 11/105 546

Claims (2)

(57) [Claims] A fixed-side mold and a movable-side mold are provided, and molten resin is supplied from a sprue portion of a sprue bush disposed at a central portion of the fixed-side mold to a disk-shaped space interposed therebetween. In the optical disk substrate molding apparatus for injection molding an optical disk substrate, a punch having an ejector pin disposed at the center is attached to the center of the movable mold, and the ejector pin is retracted from the punch. An optical disc substrate forming apparatus, wherein a space having a diameter of 1 to 2 mm is formed as a cold slug portion facing the sprue portion. 2. The optical disc substrate forming apparatus according to claim 1, wherein said punch has a non-cooling structure.