JPH0437490B2 - - Google Patents

Description

[Detailed description of the invention]

(Industrial Application Field) The present invention relates to a magnetic thin film recording disk using polycarbonate as a substrate and used in magneto-optical memories, magnetic recording display elements, etc. (Prior art) Vacuum deposition of rare earth-transition metal amorphous layer,
A magneto-optical recording method involves forming an amorphous layer on a substrate by means such as sputtering or ion plating, writing and erasing information using a thermomagnetic effect by applying a laser beam to this amorphous layer, and reading information using the thermomagnetic effect. It is publicly known,
As the substrate for forming the amorphous layer, a glass plate, a transparent plastic plate such as acrylic resin or polycarbonate resin, and a metal plate made of an opaque material such as aluminum or silicon wafer have been proposed. However, while these various substrates have been proposed,
In the case of a glass substrate, it is possible to form an amorphous layer that can be perpendicularly magnetized, but in the case of a magneto-optical recording disk, the weight of the disk increases and there is a risk of damage if it is accidentally dropped.
It is unsuitable for industrial production because it cannot withstand high-speed rotation and cannot directly form guide grooves used for laser beam tracking, which is expensive. On the other hand, metal materials such as aluminum and silicon wafers can also be used to form an amorphous layer that can be perpendicularly magnetized in the same way as glass, but in the case of silicon, which requires surface polishing like glass, it is very expensive. Large area cannot be produced. Since it is opaque, and guide grooves used for laser beam tracking cannot be directly formed, it cannot be written on or reproduced from the substrate like transparent materials. Therefore, there is a drawback that the signal/noise ratio (S/N ratio) is greatly affected by dust or scratches attached to the surface. Furthermore, in the case of transparent plastic materials such as acrylic resin and polycarbonate, the formation technology for amorphous perpendicular magnetization films has not been established, and there are also the following drawbacks: Acrylic resin has sufficient optical performance. However, it has the disadvantage that it absorbs a large amount of moisture, causing deformation due to moisture absorption, and also suffers from large thermal deformation, depending on the molding conditions. Due to these deformations, the perpendicularly magnetized film and the SiO ₂ , TiO ₂ , Al ₂ O ₃ , Ta ₂ formed thereon are
Cracks may occur in the protective film of O ₅ , MgF _2, etc.
These thin films tend to peel off from the substrate. Another drawback is that the adhesion between the thin film and the acrylic resin is very low compared to glass or metal, and even lower than other plastic materials. Although polycarbonate resin has less hygroscopic deformation and thermal deformation than acrylic resin, it has optical disadvantages of high birefringence and low thin film adhesion. There are other transparent plastics, but styrene resins have even higher birefringence than polycarbonate, vinyl chloride resins have problems with thin film corrosion due to residual chlorine and optical performance, and polyester resins have optical transparency and Each of these materials has its own problems with birefringence, and all of these materials have drawbacks as substrates for magneto-optical recording disks, so they have not been put to practical use at present. Therefore, it is strongly desired to establish a technology for producing magneto-optical recording disks by forming a stable perpendicular magnetization film on a plastic substrate, which is excellent in mass productivity and easy to handle. The present inventors have found that among plastic materials, polycarbonate resin has the best overall physical properties, and if the problems of birefringence and adhesion are improved, it will be possible to solve this problem by The present invention was developed based on the belief that it would be possible to produce a magneto-optical recording disk that is as good as or better than an inorganic substrate. The reason why birefringence adhesion is important in a magneto-optical recording disk using a rare earth-transition metal amorphous layer is that the rare earth-transition metal amorphous layer is irradiated with a laser beam and the Polar Kerr effect is used to However, since the Kerr rotation angle θk based on the Kerr effect is very small at approximately 0.1 to 0.5, if the birefringence is large, the boundary of the information point is formed by a minute reversed magnetization with a diameter of approximately 1μ. It is said that there is a close relationship between the strain in the thin film caused by the adhesion between the thin film and the substrate and the perpendicular magnetization characteristics (H. Takagi et al. J.
Appl.Physics 50(3)P1642-1644). (Object of the present invention) Therefore, the object of the present invention is to create a magneto-optical disk using a plastic substrate, which has magneto-optical properties equivalent to or better than those of inorganic materials such as glass, and which is easy to handle and can be mass-produced. It is about providing. (Structure of the Invention) The first feature of the present invention is that in a magneto-optical recording disk in which an amorphous layer of rare earth-transition metal is supported on a transparent plastic substrate, the transparent plastic substrate is made of polycarbonate. Among the polycarbonates currently produced industrially, bis(hydroxyphenyl)alkane polycarbonates are preferred. Bis(hydroxyphenyl)alkane polycarbonate is bis(4-hydroxyphenyl)
An aromatic hydrocarbon polymer obtained by reacting a hydroxy di(mononuclear or dinuclear aryl) compound such as an alkane with a carbonate precursor such as phosgene, phosmate or carbonate ester, and has the general formula (In the formula, A is a divalent aromatic group of divalent phenol.) Divalent phenol contains two hydroxyl groups as functional groups and is directly bonded to an aromatic carbon atom. A typical example is 2,2-bis-(4-
hydroxyphenyl)-propane, hydroquinone, resorcinol, 2,2-bis-(4-hydroxyphenyl)-pentane, 2,4'dihydroxydiphenylmethane, bis-(2-hydroxyphenyl)-methane, bis- (4-hydroxyphenyl)methane, bis-(4-hydroxy-5-nitrophenyl)-methane, 1,1-bis-(4-hydroxyphenylethane), 3,3-bis-(4-hydroxyphenyl) )-pentane, 2,2'-dihydroxycyenyl, 2,6-dihydroxynaphthalene, bis-(4hydroxyphenyl)sulfone,
2,4'-dihydroxydiphenyl sulfone, 5'-
Chlor-2,4'dihydroxydiphenyl sulfone, bis-(4-hydroxyphenyl)diphenyldisulfone, 4,4'-dihydroxydiphenyl ether, 3'dichlorodiphenyl ether, 4,
4'dihydroxy-2,5-diethoxydiphenyl ether, 2,2(4,4'-dihydroxy-3,
3',5,5'tetrahalodiphenyl)propane. Diphenyl carbonate is advantageously used as the carbonate ester, but dimethyl carbonate, dimethyl carbonate, diethyl carbonate, phenylmethyl carbonate, phenyltolyl carbonate, di(tolyl) carbonate and the like can also be used. When a carbonyl hydride such as phosgene is used as a carbonate precursor, the condensation reaction is carried out in the presence of a free acid scavenger, and when a carbonate ester is used, the polycarbonate is synthesized by transesterification under reduced pressure. be able to. The molecular weight of polycarbonate resin is a balance between mechanical properties and moldability, and the average molecular weight is 14,000 ~
Preferably it is 22000. That is, if the average molecular weight is less than 14,000, mechanical properties such as impact strength are insufficient, and if it exceeds 22,000, the melt viscosity is too high, resulting in a decrease in optical disk substrate properties such as transferability. Although it is possible to add an antioxidant to prevent deterioration and decomposition of the polycarbonate resin during melting, it is desirable to avoid using additives as much as possible in order to eliminate any adverse effects on the recording medium of the optical disk substrate. The magneto-optical recording medium to which the present invention is applicable may be any known rare earth-transition metal amorphous alloy,
For example, Tb-Fe alloy (Special Publication No. 57-20691), Dy
-Fe-based alloy (Special Publication No. 57-20692), Gd-Tb-
Fe-based alloy (JP-A-56-126907), Gd-Tb-Dy
-Fe-based alloys (JP-A-57-94948), Gd-Co (JP-A-54-121719), Tb-Fe-Co, etc. These rare earth-transition metal amorphous layers are preferably formed by methods such as vapor deposition, sputtering, and ion plating. The thickness of this amorphous layer is generally 500-1500 Å. A second feature of the present invention is that the absolute value of birefringence (Δnd) of the polycarbonate plastic substrate is 25 nm or less when measured at room temperature using a He--Ne laser with a wavelength of 632.8 nm. A polycarbonate substrate with a low birefringence as described above can be made by injection molding. In general, when polycarbonate resin is made by injection molding, it has a high birefringence, and a method to prevent this has been proposed in Japanese Patent Application Laid-Open No.
58-126119 and Japanese Patent Application Laid-open No. 58-180553. However, the polycarbonate substrates described in these publications have a small diameter of 130 mm or less, and the injection molding method for polycarbonate substrates with a large diameter exceeding 130 mm is disclosed in Japanese Patent Application No. 59-12565 filed simultaneously by the present applicant. ) (Japanese Patent Publication No. 3-41048), and please refer to the specification of this application for details. The key points of the injection molding method for polycarbonate substrates described in the above patent application No. 1 by the applicant are as follows: Molten polycarbonate resin is injected from the center of the flat annular cavity to form a mold with a thickness d of 1.0 mm. ~
In an injection molding method for a polycarbonate disk substrate for a high-density information recording carrier having a diameter R of 2.0 mm and a radius R of 65 mm or less and 175 mm or less, 1. The average molecular weight of the polycarbonate resin is
14,000 to 22,000 polycarbonate, the injection cylinder temperature T was set to 330 to 400°C, the mold temperature was set to 80 to 130°C, and the residence time of the polycarbonate resin in the injection cylinder (t: unit = min. ) is set so that t≦14-1/10 (T-300) [Here, T is the above-mentioned injection cylinder temperature (unit=°C)]. 2 The injection speed in the injection process, that is, the inflow speed into the cavity (v: unit = ml/sec), is expressed as follows on a semi-logarithmic table with R/d as the horizontal axis of the evenly spaced scale and v as the vertical axis of the logarithmic scale. Select within the range: In the range of 32.5≦R/d≦100, log2/100 (R/d)-1.5log2+1≦log v≦1/10
0(R/d)+1.5 In the range of 100≦R/d≦175, 1/100(R/d)−0.5log2≦log v≦1/100(R
/d)+1.5 3 The total cross-sectional area (S: unit mm ² ) of the gate opening provided near the center of the flat annular cavity is 1/10R/d+10≦S≦2/10R/d+35 (here, R is the radius of the disk, unit = mm, d
is the thickness of the disk (unit = mm). The polycarbonate substrate made by the above molding method has birefringence of 2.5 nm or less in the recording area of 40 to 170 mm on the radius. As shown in FIG. 1, the magneto-optical disk of the present invention can be composed of a polycarbonate substrate 1, an amorphous recording layer 2, and a surface protective layer 3. However, as shown in FIG. According to feature 3, it is preferable to provide a polymer layer 4 between the polycarbonate plastic substrate and the amorphous layer. The polymer layer 4 must have strong adhesion to the polycarbonate substrate, and is preferably the one described in Japanese Patent Application No. 185094/1985 by the present applicant. As described in the applicant's Japanese Patent Application No. 185094/1985, the polymer is preferably a crosslinkable polymer, and specifically, polyallyl compounds, polyfunctional acrylic compounds, thermosetting resins, etc. , alkyl silicate hydrolysates and organopolysiloxanes are preferred. In order to improve the C/N ratio, a reflective layer and/or a dielectric layer can also be provided on the surface of the amorphous layer opposite to the polymer layer. Further, the thickness of the polymer layer is preferably 0.01 to 10μ. By providing the above-mentioned polymer layer, the perpendicular magnetization characteristics of the amorphous recording layer are greatly improved, and as a result, a magneto-optical disk with a practical C/N ratio of 45 dB or more can be obtained. As is clear from the above description, the inventor of the present invention was concerned with a practical problem with magneto-optical recording disks. Signal due to high birefringence (Δnd) /
We have completed a practical magneto-optical disk by solving the problem of a decrease in the noise ratio (C/N) and a decrease in perpendicular magnetization characteristics caused by poor adhesion between the polycarbonate substrate and the magneto-optical recording medium. It is something. The present invention will be described above with reference to Examples. First, methods for measuring the various physical properties described in the Examples will be explained. (a) Birefringence: Expressed as the absolute value of retardation Δnd measured at room temperature using a Senarmont compensator (λ/4 wavelength plate) using a He--Ne laser as a light source. Here, Δn is the birefringence index, and d is the thickness of the substrate. (b) Kerr rotation angle θk and coercive force Hc: Measured using the magneto-optical effect measuring device shown in FIG. That is, a laser beam 10 from a HeNe laser 1 is applied to a sample 5 placed within the electromagnetic field of an electromagnetic coil 4 via a polarizer 2 and a beam splitter 3, and the reflected light is separated by the beam splitter 3 and sent to an analyzer 6. It is detected by a photodetector 7 via an amplifier 8 and recorded by a recorder 9. Note that 11 is a driving means for the electromagnetic coil 4. (c) C/N: Measured under the following conditions using the writing/reproducing/erasing device shown in FIG. Writing laser power 4 to 10 mW Reproduction laser power 0.8 to 1.5 mW Disk rotation speed 900 to 1350 rpm Carrier frequency 1 MHz Resolution bandwidth 30 kHz Applied magnetic field 200 to 1000 Oe In other words, while the magneto-optical disk 1 is rotated by the motor 2, a wavelength of 830 nm is applied to the surface of the magneto-optical disk 1. shine a laser beam on it. This laser light is sent from a semiconductor laser 7 driven by a signal generation circuit 6 via a mirror 8, a polarizer 9, and a half mirror 10. The reflected light from the disk 1 is separated by a half mirror 10, further separated by another half mirror 15, and each polarized light beam is sent to an analyzer 1.
1 and a photodetector 12 into a differential amplifier 13, and the result is sent to a spectrum analyzer 1.
4 will be displayed. Note that 3 is a write-erase electromagnetic coil, and this coil 3 is driven via a drive means 5. (d) Polycarbonate and acrylic resin
MFI: Measured based on JISK-6719. (Load = 3800g, measurement temperature = 230°C) The display is (g)/10 minutes. Examples 1 to 3 Using the method described in Japanese Patent Application No. 59-12565 (Japanese Patent Publication No. 3-41048) filed concurrently by the present applicant,
Polycarbonate resin (MFI = 15) was molded into a disk shape with a diameter of 200 mm and a thickness of 1.2 mm using an injection molding machine. After cleaning this substrate with Freon in a clean room, rare earth sputtering was performed using an RF magnetron sputtering device manufactured by Japan Vacuum Technology Co., Ltd.
A transition metal amorphous perpendicular magnetization film with a thickness of about 1000 Å and a protective film with a thickness of about 1500 Å were formed and used for physical property measurements. The results are shown in Table-1. Example 4 A polycarbonate substrate was molded by the method described in Example 1, and a polyorganosiloxane film manufactured by Daicel Chemical Co., Ltd. described in Example 2 of Japanese Patent Application No. 185094/1982 was applied to it.
After forming 0.2 μm, the amorphous perpendicular magnetization film was formed to a thickness of about 1000 Å and the protective film was formed to a thickness of about 1500 Å, as in Examples 1 to 3.
Table 1 shows the results of measuring the physical properties after formation. Comparative Examples 1-2 A substrate disk was obtained by injection molding polycarbonate resin (MFI-15) according to a conventional method. An amorphous perpendicular magnetization film of about 1000 Å and a protective film of about 1500 Å were formed under the same conditions as in the example.
As described in 1, it was not possible to measure the C/N. Comparative Examples 3 to 4 Injection molded polymethyl methacrylic resin (MFI=2) as a substrate with a diameter of 200 mm and a thickness of 1.2 mm.
A disk substrate was obtained. Separately diameter 200mm thickness 1.2mm
A borosilicate glass disk was prepared. An amorphous perpendicular magnetization film with a thickness of about 1000 Å and a protective film with a thickness of about 1500 Å were formed by sputtering under the same conditions as in Examples, and the physical properties were measured. The results are shown in Table-1.

[Table] As is clear from Table 1, a magneto-optical disk with a good C/N ratio can be obtained only when the polycarbonate substrate of the present invention having a birefringence of 25 nm or less is used. The C/N ratio can be further improved by interposing a layer.

[Brief explanation of drawings]

FIG. 1 is a schematic diagram of a disk configuration according to an embodiment of the present invention. FIG. 2 is a schematic diagram of a disk configuration according to another embodiment of the present invention. FIG. 3 is a schematic diagram of the magneto-optical constant measuring device. FIG. 4 is a configuration diagram of a magneto-optical disk writing/reproducing/erasing device. Symbols in the figure, 1... polycarbonate substrate, 2...
...Amorphous recording layer, 3...Surface protection layer, 4...
...polymer layer.

Claims (1)

[Claims] 1. In a magneto-optical recording disk in which an amorphous layer of rare earth-transition metal is supported on a transparent polycarbonate substrate, the absolute value of the birefringence (Δnd) of the polycarbonate plastic substrate is He- with a wavelength of 632.8 nm. Ne
A magneto-optical recording disk characterized by a diameter of 25 nm or less when measured using a laser at room temperature. 2. The magneto-optical recording disk according to claim 1, wherein a polymer layer is provided between the polycarbonate plastic substrate and the amorphous layer. 3. The magneto-optical recording disk according to claim 1, wherein the polycarbonate plastic substrate is injection molded under the following conditions: (a) using polycarbonate having an average molecular weight of 14,000 to 22,000; (b) an injection cylinder; The temperature T was set at 330-400℃, the mold temperature was set at 80-130℃, and the residence time (t: unit = minutes) of the polycarbonate resin in the injection cylinder was set at t≦14-1/10 (T −300) (where T is the injection cylinder temperature (unit =
(c) The injection speed in the injection process, that is, the inflow speed into the cavity (v: unit = ml/sec), where R/d is the horizontal axis of the evenly spaced scale, and v is the horizontal axis of the logarithmic scale. Select within the following range on the semi-logarithm table with the vertical axis: In the range of 32.5≦R/d≦100, log2/100R/d−1.5log2 +1≦log v≦1/100R/d+1.5 100≦ In the range of R/d≦175, 1/100R/d−0.5log2≦log v≦1/100R/d+1.5 (d) Total cross-sectional area of the opening of the gate provided near the center of the flat annular cavity (s : Unit md) is set to 1R/10d+10≦S≦2/10R/d+35 (where R is the radius of the disk, unit = mm, and d is the thickness of the disk, unit = mm).