JPH0973675A - Production of substrate for magneto-optical recording medium and substrate for magneto-optical recording medium formed by using this process - Google Patents

Abstract

PROBLEM TO BE SOLVED: To lessen the fluctuation in the envelope of RF signals and to increase CN by raising mold temp. and heating cylinder temp. at the time of injection molding a polycarbonate substrate, increasing a mold clamping pressure and increasing a resin injection speed. SOLUTION: The mold temp. and heating cylinder temp. are increased, the resin injection speed is increased and further, the cooling time is prolonged at the time of injection molding of the polycarbonate substrate. A magneto- optical recording disk 20 having the structure shown in Fig. is formed on this polycarbonate substrate. Namely, this substrate consists of the structure obtd. by successively depositing SiN 7 as a protective layer at 1100Å, an amorphous perpendicularly magnetized film 8 of GdDyfeCo at 300Å, SiN 7 as the protective layer at 1100Å, the amorphous perpendicularly magnetized film 8 of GdDyfeCo at 300Å, SiN 7 as the protective layer at 500Å, AlTi10 as a reflection layer and commonly used thermal diffusion layer at 500Å and an overcoating layer 11 consisting of a UV curing resin at 10μm on the substrate 6.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a substrate for a magneto-optical recording medium for high density recording and a substrate for a magneto-optical recording medium molded by the manufacturing method.

[0002]

2. Description of the Related Art For recording, erasing and reproducing information using a magneto-optical recording medium, a rare earth-transition metal amorphous layer formed on a substrate is irradiated with a laser beam having a beam diameter of about 1 to 1.5 μm. Then, the thermomagnetic effect is used.
The rare earth-transition metal amorphous layer is formed by a sputtering method, an ion plating method, or the like, and a glass plate, an acrylic resin, a polycarbonate resin, aluminum, or a metal such as a silicon wafer is proposed as a substrate. As a result of considering handleability, functionality, reliability, etc., it is the current situation that polycarbonate is mostly used at present.

To make a disc, it is first necessary to mold a polycarbonate substrate, which is typically molded by injection molding (injection compression molding) as shown in FIG.
The same shall apply hereinafter). As shown in FIG. 1 (a), pelletized polycarbonate resin is heated to a heating cylinder temperature of 4 t.
Is put in the heating cylinder 4 whose temperature is set to 300 to 350 ° C. to produce the dissolved resin 3. Next, as shown in FIG. 1 (b), using the mold clamping cylinder 5, the heating cylinder 4 is touched on the mold 1 while the stamper 1 ′ is compressed to the mold 1 at a pressure of 2 p,
The molten resin 3 is filled in the mold 1 with the screw 3c. Finally, as shown in FIG. 1C, the materials are charged, the mold is opened, and the product 2 is taken out. This is a general injection molding process, in which the temperature of the mold 1 is
t, the injection speed 3'of the molten resin 3, the mold clamping pressure 2p for compressing the stamper 1 ', the heating cylinder temperature 4t, and the cooling time are important factors for the molding of the substrate.

When a recordable optical disk such as a magneto-optical recording disk is manufactured by injection molding, it is preferable to form a groove instead of a pit, as compared with a read-only optical disk such as a compact disk in which information is recorded with uneven pits. As is typical, transfer of this groove to polycarbonate is more difficult than in the case of pits. For example, in the case of a compact disc, the mold temperature is 90 ° C and the mold clamping pressure is 3
0 kg / cm ² (the applied pressure divided by the area of the disk to be molded is defined as the mold clamping pressure. The same applies hereinafter),
The pits can be transferred at 90% or more under the conditions of the heating cylinder temperature of 335 ° C., the injection speed of 150 mm / s, and the cooling time of 3.8 seconds, but when the grooves are transferred under the same conditions, they are hardly transferred. Therefore, the mold temperature 110 is mainly set by increasing the mold temperature, increasing the mold clamping pressure, and further increasing the cooling time.
℃, mold clamping pressure 100kg / cm ² , heating cylinder temperature 350 ℃,
When injection molding is performed under the conditions of an injection speed of 150 mm / s and a cooling time of 7 seconds, a polycarbonate substrate having a groove as shown in FIG. 2 can be molded. FIG. 2 shows the results of measuring the surface of the molded substrate with an atomic force microscope (AFM). When the radii of curvature at the corner of the groove and the corner of the land are calculated from the data in FIG.
It is as large as 00 nm. A magneto-optical disk using a rare earth-transition metal amorphous as a recording layer was prepared on this polycarbonate substrate, and the information recorded on this magneto-optical disk was recorded as D.
As a result of reproduction by C coupling, as shown in FIG. 3, the fluctuation of the envelope of the RF signal was large and the signal / noise ratio (CN ratio) was as small as 42.1 dB. As described above, as a result of investigating the factors in which the fluctuation of the RF signal envelope is large and the CN ratio is small, in addition to the large radius of curvature at the corners, the birefringence of the polycarbonate substrate is large (60
It was found that the fluctuation of birefringence in the circumferential direction was large (30 nm).

[0005]

As described above, in injection molding of polycarbonate, which is a substrate for a magneto-optical recording disk using a rare earth-transition metal amorphous as a recording layer, transfer of a groove from a stamper to a polycarbonate substrate is performed. Due to the low ratio, the radius of curvature was large at the bottom corner of the groove and at the land corner. Further, under the conventional conditions, it was not possible to obtain a polycarbonate substrate having a small radius of curvature at the corner of the groove bottom and a corner of the land, a small birefringence of the polycarbonate substrate, and a small fluctuation in the circumferential direction. As a result, the fluctuation of the RF signal envelope during reproduction was increased, and the CN ratio during recording and reproduction was decreased. Further, this problem has become more significant when the track pitch, which indicates the groove formation width, is narrowed from 1.4 μm to 0.8 μm.

Therefore, according to the present invention, in order to solve the above problems which become remarkable when the track pitch is narrow, the radius of curvature at the corner is small, the birefringence of the polycarbonate substrate is small, and the fluctuation in the circumferential direction is small. Provided is a method for manufacturing a small polycarbonate substrate, and a magneto-optical recording disk using the polycarbonate substrate molded by this manufacturing method has a large CN ratio at the time of recording and reproducing, and an RF at the time of reproducing.
It is clarified to reduce the fluctuation of the signal envelope.

[0007]

In order to solve the above-mentioned problems, the mold temperature and the heating cylinder temperature at the time of injection molding of a polycarbonate substrate are made higher, the mold clamping pressure is made stronger, and the resin injection speed is made faster than before. In addition, the cooling time was extended.

[0008]

Embodiments of the present invention will be described with reference to the drawings and tables. For injection molding of a polycarbonate substrate, see Figure 1.
As shown in, the mold temperature 1t, the mold clamping pressure 2p, the resin injection speed 3 ', the heating cylinder temperature 4t, and the cooling time have great influences, but in the present embodiment, the track pitch is 1.4μ.
m, the width of the groove and the land were set to 1: 1 and molding was performed under the conditions of Example 1 in Table 1. When the transfer rate of the molded substrate was expressed by the ratio of the groove depth of the polycarbonate substrate to the groove depth of the stamper, a high transfer rate of 90% or more was obtained. The results of measuring the surface condition of this substrate by AFM are shown in FIG. As a result of calculating the radii of curvature at the corners of the groove and the land from the AFM data of FIG.
Met. The birefringence of this substrate was measured using a He-Ne laser with a wavelength of 633 nm. As a result, the maximum absolute value was 22 nm (double pass), and the fluctuation in the circumferential direction was 8 nm or less.

A magneto-optical recording disk 20 having the structure shown in FIG. 5 was produced on this polycarbonate substrate. That is, 1100Å SiN7 as a protective layer on the substrate 6, GdDyF
eCo amorphous perpendicular magnetization film 8 300 Å, SiN 9 500 Å as a protective layer, Al as a reflection layer and a heat diffusion layer
The structure is such that Ti 10 is 500 Å and an overcoat layer 11 made of an ultraviolet curable resin is sequentially deposited to 10 μm. In addition, each of the layers of SiN 7, 9 and the GdDyFeCo amorphous perpendicular magnetization film 8 and AlTi 10 was deposited by a sputtering method, and the overcoat layer 11 was formed by spin coating. SiN7,9, G as a protective layer
dDyFeCo amorphous perpendicular magnetic film 8, AlTi1
Table 1 shows the sputtering conditions for each layer of No. 0. In the magneto-optical disk manufactured under the conditions shown this time, each layer is deposited reflecting the surface condition of the polycarbonate substrate.
The radius of curvature at the corner of the groove and the corner of the land are used for confirmation.

[0010]

[Table 1]

A laser wavelength of 8 was added to the manufactured magneto-optical disk.
Magneto-optical recording was performed under the conditions of 30 nm, recording linear velocity 2 m / s, recording laser power 4.0 mW, carrier frequency 500 kHz and track pitch 1.4 μm, and the output waveform of the RF output obtained by reproducing the information by DC coupling is shown in FIG. As shown in (1), a uniform envelope waveform was obtained, and the variation rate was within 5%. Also, the CN ratio is 45.2 dB.
This is a value that can be sufficiently used for magneto-optical recording.

Next, the track pitch is set to 1.2, 1.0,
The case where the thickness is 0.8 μm is shown. The conditions for producing the polycarbonate substrate are that the track pitch is 1.2, 1.0,
Example 2, Example 3, and Example 4 in Table 2 correspond to 0.8 μm, respectively. In the case of the molded polycarbonate substrate, as in Example 1, 90
The transfer rate was higher than%. Under the same conditions as in Example 1, the protective layer 7 was formed on the polycarbonate substrate prepared under the respective conditions.
9, GdDyFeCo amorphous perpendicular magnetization film 8, Al
As a result of measuring physical properties such as radius of curvature and CN ratio by forming Ti10 and the like, as shown in Table 3, in any case, the radius of curvature is 50 nm or less, the birefringence is 25 nm or less, and the birefringence changes in the circumferential direction. Is 10 nm or less, and the same result as in the case of Example 1 was obtained. In addition, CN representing recording and reproducing characteristics
The ratio is larger than the conventional value, and the RF fluctuation is 5
% Or less.

[0013]

[Table 2]

[0014]

[Table 3]

As described above, by molding under the conditions shown in Table 2, it was possible to achieve the initial purpose in the narrow track pitch region 0.8 to 1.4 μm as shown in Table 3. Further, although Table 3 shows the case where the depth of the groove of the stamper is about 70 nm, the conditions of Table 2 are effective when the depth of the groove of the stamper is in the range of 50 to 140 nm.

The conditions for injection molding of the polycarbonate substrate were examined in addition to the conditions shown in Table 2. The results are shown in Table 4.
In the column of evaluation in Table 4, ◯ means that the radius of curvature at the bottom of the groove and the corner of the land is 50 nm or less, the birefringence of the polycarbonate substrate is 40 nm or less, and the fluctuation of the birefringence in the circumferential direction is 10 nm or less. Indicates that they are satisfied at the same time. Also, x has a radius of curvature of 50 nm or less and a birefringence of 40.
nm or less, and even if the fluctuation of the birefringence is 10 nm or less, it means that at least one exceeds the reference value. Mold temperature is 1
35 ℃, resin injection speed 150mm / s, cooling time 1
In the case of 0 seconds, the mold clamping pressure is 200,250 kg / cm
^{In 2} , the radius of curvature is 50 nm or less, the birefringence is 40 nm or less, the fluctuation of the birefringence is not 10 nm or less at the same time, and 300 kg / cm ² , the radius of curvature is 50 nm or less,
The birefringence is 40 nm or less and the fluctuation of the birefringence is 10 nm or less at the same time. However, even under this condition, when the resin injection speed is increased from 150 mm / s to 300 mm / s, the radius of curvature is 50 nm or less, the birefringence is 40 nm or less, and the variation of the birefringence is 10 nm or less at the same time. Also, the mold temperature is 130 ° C, the resin injection speed is 150 mm /
s, when the cooling time is 9 seconds, when the mold temperature is 135 ° C., the radius of curvature is 50 nm or less, the birefringence is 40 nm or less,
Even if the mold clamping pressure of 250 kg / cm ² where the fluctuation of the birefringence did not satisfy 10 nm or less at the same time, the radius of curvature was 50 n.
m or less, birefringence 40 nm or less, fluctuation of the birefringence is 1
0 nm or less is simultaneously satisfied. However, even in this case, the resin injection speed is changed from 150 mm / s to 200,300 mm / s.
Radius of curvature of 50 nm or less and birefringence of 40 n
m or less, the fluctuation of the birefringence does not simultaneously satisfy 10 nm or less. Further, when the mold temperature is 120 ° C., the resin injection speed is 150 mm / s, and the cooling time is 11 seconds, when the mold temperature is 130 ° C., the radius of curvature is 50 nm or less, the birefringence is 40 nm or less, and the birefringence thereof is Even when the mold clamping pressure is 200 kg / cm ² which does not satisfy the fluctuation of 10 nm or less at the same time, the radius of curvature is 50 nm or less, the birefringence is 40 nm or less, and the fluctuation of the birefringence is 10 nm or less at the same time. Under this condition, even if the cooling time is reduced from 11 seconds to 9 seconds, the radius of curvature is 50 nm or less, the birefringence is 40 nm or less,
The fluctuation of the birefringence simultaneously satisfies 10 nm or less, but if the cooling time is further reduced to 8.5 seconds, the mold clamping pressure becomes 25
Even if it is as strong as 0,300 kg / cm ² , the radius of curvature is 50 n.
m or less, birefringence 40 nm or less, fluctuation of the birefringence is 1
0 nm or less cannot be satisfied at the same time. Mold temperature is 120
℃, resin injection speed 150mm / s, cooling time 9 seconds, the resin injection speed from 150mm / s to 25
Even at a high speed of 0 mm / s, the radius of curvature is 50 nm or less, the birefringence is 40 nm or less, and the variation of the birefringence is 10 nm or less at the same time. At present, at a mold temperature of 110 ° C., there is no condition that the radius of curvature is 50 nm or less, the birefringence is 40 nm or less, and the variation of the birefringence is 10 nm or less at the same time.

[0017]

[Table 4]

In an actual disc, uniformity within one disc is important. Therefore, the uniformity of the transfer rate during the molding of a polycarbonate substrate, which greatly affects the characteristics of the disc, was investigated. The diameter of the disk used is 120 mmΦ. Regarding the transfer rate in the present invention, when the radius is 22 mm, the variation in the circumferential direction is 3.0%, the radius is 38 mm, the variation in the circumferential direction is 3.1%, and the radius is 50 mm.
The variation in the circumferential direction was 2.9%, and the variation in the radial direction was 5% or less in the radius range of 25 to 55 mm. Next, Table 5 shows variations in the birefringence of the polycarbonate substrate in the present invention and the conventional example in the respective radii in the circumferential direction. In Table 5, the fluctuation value was obtained by measuring the fluctuation value at eight points in the circumferential direction at a certain radius. In the present invention, a radius of 23-5
It was found that the variation was 11 nm or less in the region of 4 mm, which was about half that of the conventional example.

As described above, according to the present invention, a polycarbonate substrate having excellent uniformity can be injection molded.

[0020]

[Table 5]

[0021]

According to the present invention, in order to increase the CN ratio during recording and reproducing of a magneto-optical recording disk using a rare earth-transition metal amorphous as a recording layer, and to reduce the fluctuation of the RF signal envelope during reproducing. The required radius of curvature at the bottom corner of the groove and the corner of the land is 50
nm, the polycarbonate substrate has a birefringence of 40 nm or less, and the variation in the circumferential direction thereof is 10 nm or less. The track pitch is 0.8 to 1.4 μm.
It can be manufactured in the range of. Further, in the magneto-optical recording disk using the polycarbonate substrate according to the present invention, it is possible to increase the CN ratio at the time of recording and reproducing and reduce the fluctuation of the envelope of the RF signal at the time of reproducing. Further, a polycarbonate substrate for a disc having a diameter of 120 mm and excellent in uniformity can be injection-molded.

[Brief description of drawings]

FIG. 1 is a diagram illustrating a process of injection molding.

FIG. 2 is a result of AFM measurement of a polycarbonate substrate under conventional conditions.

FIG. 3 is a diagram showing an RF signal when reproducing from a conventional magneto-optical recording disk.

FIG. 4 is a polycarbonate substrate AFM according to the present invention.
It is a measurement result.

FIG. 5 is a diagram showing a cross-sectional structure of a magneto-optical recording disk according to the present invention.

FIG. 6 is a diagram showing an RF signal during reproduction of the magneto-optical recording disk of the present invention.

[Explanation of symbols]

 1 ・ ・ Mold 1t ・ ・ ・ Mold temperature 1 '・ ・ ・ Stamper 2 ・ ・ ・ ・ Polycarbonate substrate 2p ・ ・ ・ Pressure 3 ・ ・ ・ ・ ・ ・Molten resin 3c ・ ・ ・ Screw 3 '・ ・ ・ ・ ・ Resin injection speed 4 ・ ・ ・ ・ Heating cylinder 4t ・ ・ ・ Heating cylinder temperature 5 ・ ・ ・ ・ ・ Mold clamping cylinder

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Office reference number FI technical display location B29C 45/74 9350-4F B29C 45/74 45/77 7365-4F 45/77

Claims (2)

[Claims] 1. An injection molding device comprising a groove forming stamper, a heating cylinder for melting polycarbonate, an injection port for injecting the melted resin, and means for applying a mold clamping pressure for mold clamping is used. In the method of molding a substrate for a magneto-optical recording medium, the mold temperature is 118 to 135 ° C., the mold clamping pressure is 200 to 300 kg / cm ² , the resin injection speed is 150 to 200 mm / s, and the heating cylinder temperature is 310 to 340. A method for producing a substrate for a magneto-optical recording medium, characterized in that the cooling time is 9 to 16 seconds. 2. An injection molding device comprising a groove forming stamper, a heating cylinder for melting polycarbonate, an injection port for injecting the melted resin, and means for applying a mold clamping pressure for mold clamping. In the method of molding a substrate for a magneto-optical recording medium, the mold temperature is 118 to 135 ° C., the mold clamping pressure is 200 to 300 kg / cm ² , the resin injection speed is 150 to 200 mm / s, and the heating cylinder temperature is 310 to 340. A substrate for a magneto-optical recording medium, which is formed by using a method for manufacturing a substrate for a magneto-optical recording medium, the temperature of which is 9 ° C. and the cooling time is 9 to 16 seconds.