JPH0330136A - Production of magneto-optical recording medium - Google Patents

Abstract

PURPOSE:To obtain a magneto-optical recording medium having stable mechanical properties with little optical distorsion, no warpage or local deformation by subjecting a polycarbonate disk substrate to heat treatment according to a specified temp. variation program and then providing a magneto-optical recording layer on the polycarbonate substrate. CONSTITUTION:A disk polycarbonate substrate is heated rather slowly at the temp. rising speed of 150-300 deg.C/hour to about 131-132 deg.C which is higher by 10 deg.C than the softening point (121-122 deg.C) of polycarbonate. Then the substrate is maintained at about 131-132 within + or -2 deg.C variation for at least 0.5 hour but shorter than 24 hours, and then cooled slowly at 300-100 deg.C/hour to room temp. about 30 deg.C. By this method, a polycarbonate substrate having little double refraction and little distortion with reduced local deformation in its surface can be obtained at low cost.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a method for manufacturing a magneto-optical recording medium, and in particular a method that makes it possible to provide a magneto-optical recording medium with improved mechanical properties by improving heat treatment of a substrate. It is related to. [Prior art and its problems] Magneto-optical recording has many features such as high density and large capacity, non-contact with the recording/reproducing head, and easy erasing and rewriting. Magnetic recording media have been actively developed and put into practical use in recent years as recording media for high-speed data files and video recording.

The basic structure is generally such that a magneto-optical recording layer made of a thin film such as a dielectric protective layer or a thin film mainly made of rare earth metals, transition metals, etc. is provided on a substrate.

As the substrate of the magneto-optical recording medium, glass or resin such as polycarbonate, polymethyl methacrylate, or epoxy is used.

Although the glass substrate has excellent optical properties, surface properties, and chemical stability, it has problems such as low mass production processability, being easily broken and difficult to handle, and being expensive.

On the other hand, the resin substrates have advantages such as high mass production processability, easy handling, and relatively low cost, and are currently being extensively developed mainly using resin substrates.

Among the resin substrates, polymethylmethac1. IL,
The sheet metal has several problems, such as its high water absorption rate, which causes it to warp over time, and its heat resistance, which is relatively low, which makes it susceptible to thermal deformation.

On the other hand, JP-A-62-252546, JP-A-62-2-6-4-4-6-3, JP-A-63
The polycarbonate substrate disclosed in Japanese Patent No. 97627 and the like has excellent light transmittance, low hygroscopicity, good heat resistance, and low cost, and is seen as a promising substrate for magneto-optical recording media.

The resin substrate for the magneto-optical recording medium described above is generally manufactured by forming a resin material into a disk of specified dimensions using an injection molding method or the like. However, polycarbonate substrates have inherent optical distortions associated with the molding process, which behaves as so-called birefringence and often lowers the C/N of the magneto-optical recording medium.

In order to remove this optical distortion, for example, JP-A-62-13
A method of heat treatment at a temperature below the thermal deformation temperature of a polymer substrate as disclosed in Japanese Patent Laid-Open No. 7747, JP-A-62-2
As disclosed in Publication No. 62248, a method of heat-treating a polycarbonate group + fabric at a temperature of 130°C or less, and furthermore, "Plastic Materials Course 5" (authored by Mikio Matsugane)
Nikkan Kogyo Shinkaisha, first edition published September 30, 1960) proposes a method of removing concentrated stress by heat treating polycarbonate at 130° C. for 20 days.

However, an incidental problem associated with the temporary production of polycarbonate i is that the substrate warps due to heat treatment, making the mechanical properties of the substrate unstable. Especially when rotating at high speeds (1,800 rpm, 3,600 rpm, etc.), the stability of tracking and force-singing was impaired, and the so-called vibration acceleration became so large that playback was even impossible. In order to alleviate this problem, methods have been proposed in which the substrate is warped in the opposite direction in advance.

However, with the conventional method described above, it is possible to sufficiently remove optical distortion and obtain a magneto-optical recording medium with a high C/N, and to eliminate warping of the substrate and obtain a magneto-optical recording medium with stable mechanical properties. It was difficult.

In other words, if the heat treatment temperature is too low, the substrate will not warp, but the optical distortion will not be sufficiently removed, and if the heat treatment temperature is too high, the substrate will warp even though the optical distortion can be removed. It was put away. Furthermore, the conventional method hardly takes into account the local deformation of the substrate, that is, the occurrence of unevenness locally even though the substrate as a whole does not warp. This may cause problems such as an increase in surface runout acceleration (measured as the acceleration of the vertical movement of the big up) in the vertical direction of the board, which hinders faithful recording and reproduction. did.

Even in the method of warping the substrate in advance, it is difficult to adjust the degree of warpage (warp angle), making it difficult to achieve the above-mentioned problem.

[Problems that the invention attempts to solve]

The present invention was made in view of the problems of the prior art described above, and in particular improves the heat treatment method for polycarbonate substrates to create a machine with low optical distortion < high C/N and no warping or local deformation. The purpose is to provide a magneto-optical recording medium with stable characteristics.

[Means for Solving the Problems] The object of the present invention is to increase the softening temperature of the polycarbonate substrate by 10±2 by raising the temperature from room temperature to 150 to 300° C./hour.
℃ temperature, and at that temperature 0. 5 to 24
The magneto-optical recording layer is provided on the polycarbonate substrate after the polycarbonate substrate is held for a period of time and then subjected to heat treatment in a temperature change pattern in which the temperature is lowered to 30°C or less at a cooling rate of 300 to 100°C/hour. This is achieved by a method of manufacturing a magneto-optical recording medium.

[Embodiments of the Invention] In the present invention, a polycarbonate substrate formed by molding polycarbonate into a disk shape with predetermined dimensions prescribed for magneto-optical recording media by injection molding or the like is heated at a rate of 150 to 300 C/hour or less. The temperature was set at a relatively slow temperature increase rate from room temperature to 13I to 132°C, which is approximately 10°C higher than the thermal softening temperature of polycarbonate (121 to 122°C), and adjusted with an accuracy of ±2°C around 131 to 132°C. 300-100°C/
By performing heat treatment to lower the temperature to 30° C. or lower, close to room temperature, at a relatively slow rate, it is possible to remove optical distortion and at the same time obtain a polycarbonate substrate without warping or local deformation.

I can do it.

That is, the present invention provides that local deformation of the substrate due to heat treatment is caused by a problem in the rate of temperature increase from the time the substrate is placed in the heat treatment atmosphere, and that it is necessary to suppress the temperature increase rate within a certain range. There is a threshold temperature for heat treatment to sufficiently remove optical distortion; once a certain temperature is exceeded, the substrate will rapidly warp, and eventually the groups will disappear; If the time is not appropriate, optical distortion cannot be effectively removed, and if it is too long, the substrate will warp. This was done based on the findings of the inventors that if the speed is not set to , local deformation will occur in the polycarbonate substrate and surface runout acceleration will increase.

In the heat treatment of the polycarbonate substrate in the method for manufacturing a magneto-optical recording medium of the present invention, it is preferable that the temperature of the heat treatment atmosphere be raised at a relatively slow rate of 150 to 300° C./hour or less and as constant as possible.

If the temperature increase rate exceeds 300'C/hour, local deformation will occur in the substrate and surface runout acceleration will increase during rotation of the resulting magneto-optical recording medium, which will impede faithful recording and reproduction. So I don't like it.

Moreover, if the temperature increase rate is less than 150° C./hour, the heat treatment will take a long time, which is not preferable in terms of manufacturing cost.

When the set temperature for the heat treatment is higher than 134°C, warping is likely to occur rapidly as the temperature rises;
If the temperature is lower than 0° C., optical distortion cannot be removed sufficiently, which is not preferable.

If the temperature control width is larger than ±2° C., it is not preferable because prevention of warpage and removal of optical distortion are not compatible.

Further, the time for holding the polycarbonate substrate at the temperature is at least 30 minutes or more and 24 hours or less,
Preferably, the time is 30 minutes to 8 hours. If the heat treatment time is too short, optical distortion cannot be removed sufficiently, and if the heat treatment time is too long, mechanical warping may occur.

Furthermore, after holding at the above-mentioned specific temperature,
The cooling rate to reach the temperature of 0℃ is 300 to 100℃
/It is time. If the cooling rate exceeds 300'C/hour, local deformation occurs in the polycarbonate substrate, increasing surface runout acceleration during rotation of the resulting magneto-optical recording medium, which impedes faithful recording and reproduction. I come to do it.

If the temperature decreasing rate is less than 100° C./hour, it takes time to decrease the temperature, which is not preferable in terms of manufacturing cost.

The heat treatment of the polycarbonate substrate in the method of the present invention is usually carried out by leaving it in a constant temperature bath.

In the present invention, after the polycarbonate substrate is heat treated as described above, a magneto-optical recording layer is formed thereon.

The magneto-optical recording layer is usually made by sandwiching a thin recording layer mainly made of transition metals or rare earth metals, and dielectric materials such as oxides, nitrides, and sulfides such as SiOx, SiNxAINx, and ZnS are placed above and below the recording layer. A magneto-optical recording layer is formed on the polycarbonate substrate by laminating thin protective layers.

These films are generally formed by sputtering.

In the present invention, before the magneto-optical recording layer is provided on the polycarbonate substrate, the polycarbonate substrate is heat-treated under the conditions described above, so there is no increase in noise level due to birefringence of the substrate, and warpage of the substrate is prevented. Since the occurrence of is also suppressed, a magneto-optical recording medium with a high C/N and stable mechanical properties can be obtained.

There are no particular limitations on the size or dimensions of the disk-shaped polycarbonate substrate used in the method of the present invention.

Further, the effects of the method of the present invention are not limited to polycarbonate substrates, and similar effects can be obtained with other transparent resin substrates with large birefringence. That is, approximately 10°C lower than the thermal softening temperature of the resin.
A similar effect is expected by heat treatment at a high set temperature.

The thickness of the magneto-optical recording layer of the magneto-optical recording medium to which the present invention is applied is as follows: 2.
The thickness of the thin film of the dielectric protective layer is preferably from 500 to 2,000 thick.

As the material for the recording layer of the magneto-optical recording layer of the magneto-optical recording medium applied in the present invention, thin films of magnetic substances of various oxides and metals including the aforementioned transition metals and rare earth metals can be used. For example, MnBi MnAIGe
, crystalline materials such as MnCuBi, GdJG, BiSmE
Single crystal materials such as rGalG, BiSmYbCoGe IG, as well as GdCo, GdFe, TbFe Dy
Fe, GdFeBi, GdTbFe, GdTbCo, T
It is a thin film using non-quality materials such as bFeCo and TbFeNi. Among these, a recording layer mainly composed of rare earth metals or transition metals is most preferable in terms of sensitivity, C/N, etc. [Effects of the invention] The temperature is raised to the thermal softening temperature of the polycarbonate substrate +10±2°C at a heating rate within a specific range, and after being held at that temperature for a specific period of time, the temperature is lowered to near room temperature at a rate within a specific range. Accordingly, a polycarbonate substrate with low birefringence, low warpage, and reduced local deformation of the surface can be obtained at low manufacturing cost.

Furthermore, the mechanical properties of a magneto-optical recording medium using a polycarbonate substrate heat-treated by the method of the present invention can be improved.

The novel effects of the present invention will be explained based on the following examples and comparative examples.

[Example-1] A polycarbonate substrate injection molded to a size of 130φ and a thickness of 1.2mm was placed in a thermostatic oven (clean oven manufactured by Yamato Kagaku ■) at room temperature (23°C), and then heated at 220°C/hour. After reaching the specified temperature, the temperature was raised at a rate of
) to complete the heat treatment of the polycarbonate substrate.

At that time, changing the set temperature and temperature control as shown in Table 1, 6al! for samples a to e! A sample of polycarbonate substrate was fabricated.

[Comparative Example-1] Sample f was prepared as a sample of a polycarbonate substrate that was left at room temperature without being heat-treated.

On the polycarbonate substrates obtained in Example-1 and Comparative Example-1 above, a dielectric insulator of SiNx with a thickness of 900 mm was deposited by magnetron sputtering.
A thin film of TbFeCo with a thickness of 1,000 thick, a thin film of a dielectric protective layer of SiNX with a thickness of 1,000 thick were sequentially formed in this order on the polycarbonate substrates from sample a to sample f. Samples A to F of magneto-optical recording media provided with a 3N magneto-optical recording layer were obtained. The birefringence and warpage of each sample of the polycarbonate substrate obtained as described above were measured under the following conditions. Further, the C/N of each sample of the magneto-optical recording medium was measured under the following conditions.

Birefringence measurement method: He-Ne laser (λ=632.8
Measurements were made from the disk reflected light using a parallel beam of 100 nm).

Warpage measurement method: N. A. =0.55, λ-830
The amount of pick-anop movement by a nm focused beam was measured as capacitance. Radial warpage and circumferential warpage at a radius of 60mm
The square root of the sum of the products was taken as the warpage value.

C/N measurement method: Magneto-optical disk tester equipped with a differential optical system (N.A. = 0.55, λ = 8 3 0
nm) was used.

Note that the thermal softening temperature of the polycarbonate substrate is AST
Load 18. by MD648. 6 kg/c
When measured by applying i, the temperature was 122°C.

The results of each measurement are shown in Table 2.

As is clear from Table 1 and Table 2, Sample C has a temperature control width of ±2°C when heat treated at a set temperature of 132°C, which is the thermal softening temperature (122'c) of the polycarbonate substrate + 10°C.
With this substrate, both birefringence and warpage are smaller than in other cases.
The C/N of the magneto-optical recording medium produced using this substrate was also a good value.

On the other hand, even if the set temperature is 132°C, which is the same as that of sample C, the substrate of sample D, whose controlled temperature range is ±5°C, which is larger than ±2°C, has a relatively small birefringence but a large warpage. ．． In addition, the set temperature is 122°C (sample A), which is lower than 132°C.
), 127°C (sample B), the temperature control width is ±2
℃, the warpage was small, but the birefringence value increased, and the C/N of the magneto-optical recording medium obtained using it increased.
was not very high.

Furthermore, if the set temperature is 137"C higher than 132"C
In the case (sample E), even if the heat treatment was performed with a temperature control range of ±2° C., the birefringence could be reduced, but the warpage became large.

The substrate of Sample F, which was not heat-treated, had a large birefringence, and the C/N of the magneto-optical recording medium produced using it did not become very large.

[Example 2] Example except that a polycarbonate substrate with a heat softening temperature of 125°C was heat treated at the set temperature and control temperature range shown in Table 3.
A heat treatment was carried out under the same conditions as in Example 1, and a magneto-optical recording medium was produced.

The results obtained are shown in Table 4.

Table 3, Table 4 Thermal softening temperature 1 2 5 + l O'C Even if the set temperature was lower or higher than C, the polycarbonate a plate did not have desirable birefringence or warpage.

[Example-3] Example except that a polycarbonate substrate with a thermal softening temperature of 122°C was set at a temperature of 132°C, a controlled temperature range of ±2°C, and the processing time under the set temperature was set to the conditions shown in Table 5. Polycarbonate substrates from sample j to sample r were obtained by heat treatment under the same conditions as in -1, and magneto-optical recording media were created using these substrates. (Sample J-R) The obtained results are also shown in Table 5.

Table 5 Samples J and R whose substrate processing time does not reach 30 minutes after reaching the set temperature have large birefringence values, and the C/N of magneto-optical recording media made using these substrates is low. It didn't get high.

Further, in samples Q and R for which the processing time exceeded 24 hours, the warpage of the substrate became large.

[Example-4] A polycarbonate substrate was placed in a constant temperature oven (Yamato Scientific Clean Oven) at room temperature (23°C), and then heated to 132°C at the rate shown in Table 6. The substrates were heat-treated under the same conditions as in Example-1 except that the temperature was set at a control temperature of ±2"C to obtain substrates from samples S to y, and these substrates were used for magneto-optical recording. A medium was prepared (Sample S-X).
When the temperature in the constant temperature bath reached the set temperature, a polycarbonate substrate was suddenly inserted and heat treated to prepare Sample Z.

In addition, the surface runout acceleration of each sample of the magneto-optical recording medium was prepared under the following conditions.

Measuring method of surface runout acceleration: The number of rotations of the magneto-optical recording medium is 18
The maximum value of the surface runout acceleration at the positions where the radius from the center of the substrate to the outer circumference of the substrate is divided into eight equal parts from 30 degrees to the outer circumference with 0 Orpm is the surface runout acceleration of the magneto-optical recording medium (the vertical dimension of the substrate). stability).

Table 6 shows the measurement results of the heat-treated substrate and the surface runout acceleration of the magneto-optical recording medium made using the substrate. When the heating rate was relatively slow, within 300"C/hour, the surface runout acceleration was relatively small at 2.0m/sec or less, but when it exceeded 300"C/hour, it became considerably large. Ta.

In addition, in sample Y that did not undergo the temperature raising process, the surface runout acceleration was considerably large, and local deformation of the substrate surface could be observed with the naked eye.

[Example-5] A 130φ, 1.2-inch thick polycarbonate substrate was placed in a constant temperature oven (clean oven manufactured by Yamato Scientific ■) at room temperature (23°C), and then heated at 220°C/hour. After reaching 132°C, the temperature was maintained at that temperature for 2 hours, and then the temperature was lowered to room temperature (23°C) at the cooling rate shown in Table 7. Heat treatment was performed, and then a magneto-optical recording layer was formed on each of the obtained polycarbonate substrates under the same conditions as in Example-1 to form samples α, β, γ, δ, and ε of magneto-optical recording media. I got it.

The rate of temperature decrease was controlled by providing a thermocouple inside the thermostatic chamber and rotating a fan to circulate air inside the thermostatic chamber.

7 table

Claims (1)

[Claims] A polycarbonate substrate formed into a disk shape is heated from room temperature at a heating rate of 150 to 300 °C/hour to a temperature of its softening temperature + 10 ± 2 °C, and held at that temperature for 0.5 to 24 hours. Then 300 to 100℃/
A method for manufacturing a magneto-optical recording medium, comprising providing a magneto-optical recording layer on the polycarbonate substrate after performing heat treatment in a temperature change pattern that lowers the temperature to a temperature of 30° C. or less at a cooling rate per hour.