JPH02173959A - Production of magneto-optical recording medium - Google Patents

Abstract

PURPOSE:To obtain the recording medium which is small in optical strain, is high in C/N, is free from camber and local deformation and is stable in mechanical characteristics by providing a magneto-optical recording layer on a polycarbonate substrate after subjecting the substrate to a heat treatment. CONSTITUTION:The polycarbonate substrate formed to a disk shape is placed in a heat treatment atmosphere and is heated up to the (thermal softening temp. of the polycarbonate substrate +10)+ or -2 deg.C at <=300 deg.C/hour heating up rate of the heat treatment atmosphere. After the substrate is heat-treated for 30 minutes to 24 hours at this temp., the magneto-optical recording layer is provided on the polycarbonate substrate. Namely, the polycarbonate substrate is subjected to the heat treatment before the magneto-optical recording layer is provided on the substrate and, therefore, the increase of a noise level by the double refraction of the substrate is obviated. Since the generation of the warpage of the substrate is suppressed, the C/N is high. The magneto-optical recording medium having stable mechanical characteristics is obtd. in this way.

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, to a method for manufacturing a magneto-optical recording medium, which improves characteristics by improving heat treatment of a substrate, thereby making it possible to provide a multi-magnetic recording medium. It's about how to do it.

[Prior art and its problems]

The magneto-optical recording method has many features such as high density and large capacity, no contact with the recording/reproducing head, and easy erasing and rewriting. Therefore, the magneto-optical recording medium is suitable for high-speed data files and As a recording medium for video recording, its development and practical application have been actively promoted in recent years.

The general form is that a magneto-optical recording layer made of a thin film such as a protective layer for a visiting body 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 glass substrates have excellent optical properties, surface properties, and chemical stability, they have problems such as low mass production processability, being easily broken and difficult to handle, and being expensive.

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

Among resin substrates, polymethyl methacrylate has several problems, such as its high absorption rate, which causes it to warp over time, and its heat resistance temperature, which is relatively low, which makes it susceptible to thermal deformation.

On the other hand, JP-A-42-2J Ko! Hirotsu Publication, JP-A No. 1986-27T, JP-A-63-27T
The polycarbonate substrate disclosed in Publication No. 27 and the like has excellent light transmittance, low hygroscopicity, good heat resistance, and low cost, and is considered to be a promising substrate for magneto-optical recording media.

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

For example, Japanese Patent Application Laid-Open No. 62-1/3 is used for rounding to remove this optical distortion.
A method of heat treatment at a temperature below the thermal deformation temperature of a polymer substrate as disclosed in Publication No. 77≠7, JP-A-42-2
A method of heat treating a polycarbonate substrate Q/at a temperature of 30°C or less as disclosed in Publication No. 62λ≠j,
In addition, “Plastic Materials Course!” (written by Mikio Matsugane)
Nikkan Kogyo Shimbun, Showa 4L≠First edition published on February 3Q, 2013) proposes a method of removing concentrated stress by heat treating polycarbonate at f/30°C for λ0 days.

However, an incidental problem associated with the manufacture of polycarbonate substrates is that the substrate warps due to heat treatment, making the mechanical properties of the substrate unstable. During high-speed rotation (/I0Orpm, JAOOrpm, etc.), tracking stability is impaired, so-called surface runout acceleration increases, and reproduction may even become impossible.

In order to completely alleviate this problem, methods have been proposed, such as forming the substrate with a reverse warp in advance.

However, in the conventional method described above, it is difficult to remove optical distortion into optical components to obtain a magneto-optical recording medium with a high C/H, and to obtain a magneto-optical recording medium with stable mechanical properties by eliminating warping of the substrate. It was difficult to achieve both.

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, even if the optical distortion can be removed, the substrate will warp. I had left it behind. 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 is not distorted, and especially when the heating rate is increased, Local deformation is likely to occur, and the image blur acceleration in the vertical direction of the board (the acceleration of the vertical movement of the pickup is
It is added. ), problems that impede faithful recording and playback have arisen.

Even in a method in which the substrate is pre-scored, it is difficult to adjust the degree of the warp (reverse angle), making it difficult to achieve the above-mentioned problem.

[Problem that the invention seeks to solve]

The present invention has been made in view of the above-mentioned problems of the prior art, and in particular improves the heat treatment method for polycarbonate substrates to achieve low optical distortion, high C/N, and no distortion or local deformation. The purpose of the present invention is to provide a magneto-optical recording medium with stable mechanical properties.

[Means for solving problems]

The object of the present invention is to place a polycarbonate substrate molded into a disk shape in a heat treatment atmosphere, and increase the temperature of the heat treatment atmosphere at a heating rate of 300'C/hour so that the polycarbonate substrate has a thermal softening temperature of 110±λ degrees. After raising the temperature to (℃) and heat-treating at that temperature for 30 minutes to 2 hours,
This is achieved by a method for manufacturing a magneto-optical recording medium characterized by providing a magneto-optical recording layer on the polycarbonate substrate.

[Embodiments of the Invention] In the present invention, a polycarbonate substrate formed by injection molding or the like into a disk shape having predetermined dimensions prescribed for a magneto-optical recording medium is made of 3009.
Thermal softening temperature of polycarbonate from room temperature to the temperature (1/2 to 2/2) at a relatively slow heating rate of 67 hours.
It is also almost 10℃ higher/3λ℃ and 13℃ higher.
By performing heat treatment within a specific range at a temperature adjusted with an accuracy of ±2°C around , it is possible to remove optical distortion and at the same time obtain a polycarbonate substrate free from warping and local deformation.

In other words, local deformation of the substrate due to heat treatment is due to a problem with the temperature increase rate after the substrate is placed in the heat treatment atmosphere, and it is necessary to keep the temperature increase rate within a certain range. It was found that there is a threshold temperature for heat treatment to sufficiently remove optical distortion, and that when a certain temperature is exceeded, warping rapidly occurs on the substrate, and eventually the groups disappear.

Furthermore, it was found that there is an appropriate processing time to remove the υ optical distortion by heat treatment at this threshold temperature, and if the processing time is not long, warping will occur on the substrate.

Based on the above study results, it was found that the above heat treatment conditions are the most preferable for achieving the object of the present invention.

In the heat treatment of the polycarbonate substrate in the present invention, it is desirable to raise the temperature of the atmosphere at a relatively slow rate of 3oo0c/hour or less and as constant as possible, and more preferably at a rate of JOO~/! It is desirable to increase the temperature at a constant temperature increase rate selected within the range of 0°C/hour.

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 obtained magneto-optical recording medium, which will impede faithful recording and reproduction. Undesirable.

Moreover, if the temperature increase rate is less than 1ro0c7 hours, 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 /3≠℃, reaction υ tends to occur rapidly as the temperature rises, and /3
If the temperature is lower than 0°C, optical distortion cannot be removed sufficiently, which is not preferable.

If the temperature during the temperature control exceeds ±2''C, it is not preferable because prevention of warpage and removal of optical distortion are not compatible with each other.

Further, the heat treatment time of the polycarbonate substrate is preferably at least 30 minutes or more and 2 hours or less,
Preferably, the time is 30 minutes to 30 minutes. If the heat treatment time is too short, optical distortion cannot be removed sufficiently, and if it is too long, mechanical cracks may occur.

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 sandwiched between a thin film of a recording layer mainly composed of transition metals or rare earth metals, and layers of, for example, SiOx or SiNx are placed above and below the recording layer.

A magneto-optical recording layer is formed on the polycarbonate substrate by laminating and providing thin films of a protective layer for a current visiting body made of oxides such as A I N x and ZnS, nitrides, and sulfides.

A sputtering method is generally used to form these thin films.

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 that there is no increase in noise level due to birefringence of the substrate, and there is no increase in the noise level due to the birefringence of the substrate. Since the occurrence of scratches 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 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 set temperature.

The thickness of the magneto-optical recording layer of the magneto-optical recording medium to which the method of the present invention is applied is as follows:
It is preferably from 00 to 2000^. The thickness of the thin film of the dielectric protective layer is ! It is preferably between 00 and 2000^.

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, MnB i , MnAlGe
, crystalline materials such as MnCuBi, GdIG, I3iS
Single crystal materials such as mFrGaIG, BiSmYbCoGeIG, and also GdCo, GdFe, TbFe
, DYFe , GdFeB i , GdTbFe , G
It is a thin film using an amorphous material such as dTbCo, TbFeCo, or Tb)'eNi. Among these, a recording layer mainly composed of rare earth metals or transition metals is most preferable in terms of sensitivity, C/N, etc.

〔Effect of the invention〕

By heat treatment according to the method of the present invention, it is possible to obtain a polycarbonate substrate with low birefringence and low antireflection, and furthermore, local deformation of the surface can be reduced.

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-7] A polycarbonate substrate injection-molded to a size of /30φ, thickness /, 2m771 was placed in a constant temperature oven (clean oven manufactured by Yamato Scientific Co., Ltd.) at room temperature (23°C), and then
The temperature was raised at a temperature increase rate of 20,067 hours, and after reaching a predetermined temperature, it was left for 2 hours to complete the heat treatment of the polycarbonate substrate.

At that time, four types of polycarbonate substrate samples from sample a to et were prepared by changing the temperature setting and temperature control as shown in Table 1.

[Comparative Example-7] Sample f was prepared as a sample of a polycarbonate substrate that was left at room temperature without being heat-treated.

A thin film of a dielectric protective layer of SiNx with a thickness of 200 mm and a recording layer of TbFeCo with a thickness of 1 mm were deposited on the polycarbonate substrates obtained in the above Examples and Comparative Examples by magnetron sputtering. A thin film of a dielectric protective layer of SiNx with a thickness of 7000 mm was sequentially formed in this order, and a three-layer magneto-optical recording layer was provided on the polycarbonate substrates from sample a to sample f. Samples A to F of magnetic recording media 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: Birefringence was measured from the reflected light of the disk using parallel light from a He-Ne laser.

Measurement method of anti-shi: N, Ni, = OM, λ = t30nm
The amount of pickup movement by the focused beam was measured as capacitance.

The square root of the λ-th power sum of the radial direction and the circumferential direction at a position of 4Qrnm radius was taken as the value of the inverse.

C/N measurement method: Magneto-optical disk tester equipped with a differential optical system (N, A, = 0.!j.

Remember to use λ = r j On m).

Note that the thermal softening temperature of the polycarbonate substrate is AST
M-f)6111 load/r, A Kg/
When measured by applying cm2, the temperature was 722°C.

The measurement results were as shown in Table 2.

As is clear from Table 1 and λ Table 2, the thermal softening temperature of the polycarbonate substrate (122°C) +/(132°C which is 7'C)
The substrate of sample C, which has a temperature control width of ±2°C when heat treated at a set temperature of
/N was also a good value.

On the other hand, even if the set temperature is the same as sample C/3λ℃, the control temperature range is still as large as ±2℃! Although the birefringence of the sample substrate at ℃ was relatively small, the anti-reflection became large.

In addition, for lco-00 (sample A) and 727°C (sample B) where the equipment temperature was lower than 132°C, the warpage was small even when the temperature control width was ±2°C, but the birefringence value was As a result, the C/N of the magneto-optical recording medium obtained using it was not very high.

Furthermore, the set temperature is 737°C higher than 132°C.
In the case of (sample E), even if the heat treatment was performed with a temperature control width of 2°C, the birefringence could be reduced, but the reciprocity became large.

The substrate of Sample F, which was not subjected to heat treatment, had a large birefringence, and the C/N of the magneto-optical recording medium prepared using it did not increase significantly.

[Example 2] Example except that a polycarbonate substrate with a heat softening temperature of 121°C was heat treated at the set temperature and control temperature range shown in Table 3.
The heat treatment and magneto-optical recording medium were produced under the same conditions as /.

The results obtained are shown in Table V.

Table 3: Thermal Softening Temperature/2j'+10°C Even if the set temperature was low or high, a polycarbonate substrate with neither birefringence nor anti-reflection was obtained.

[Example 3] A polycarbonate substrate with a thermal softening temperature of 722°C was projected at a temperature of 1 &:/32°C, a controlled temperature range of ±λ°C, and a processing time under the set temperature under 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 Example No. 2, and magneto-optical recording media were produced using these substrates. (Sample J-It) The obtained results are also shown in Table 3.

Table 5 Samples J and R whose substrate processing time does not reach 3Q minutes after reaching the set temperature have large birefringence values, and the C/N of magneto-optical recording media made using these substrates is small. It didn't get high.

In addition, in samples Q and R for which the processing time exceeded 2≠ hours, the warp of the substrate became large.

[Example-Hiroshi]

The polycarbonate substrate was placed in a constant temperature oven (manufactured by Yamato Scientific Co., Ltd.)
After placing it in a clean oven at room temperature (23°C),
The substrate was heat-treated under the same conditions as in Example-/, except that the temperature was raised to 132 °C at the temperature increase rate shown in Table 6, and the temperature was set as the control temperature ±2 °C. Substrates of samples S to y were obtained by using these substrates, and a magneto-optical recording medium was created using these substrates. (Sample 5-X) For comparison, the sample was heated to 13λ℃ without going through the specified heating process.
When the temperature in the thermostatic oven reached the set temperature, a polycarbonate substrate was suddenly heated by nine people 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 rotation speed of the magneto-optical recording medium is /I0Orpm, and the radius J is measured from the center of the substrate to the outer circumference.
The maximum value of the direction acceleration at a position r equally divided between Qmm and 4Qrnm was taken as the plane acceleration (dimensional stability of the substrate in the vertical direction) of the magneto-optical recording medium.

Table 1 shows the measurement results of the heat-treated substrate and the measurement results of the surface runout acceleration of the magneto-optical recording medium prepared using the substrate.

Table 6 Under relatively moderate conditions where the temperature increase rate is within 3006C/hour, the surface excavation acceleration showed a relatively small value of less than λ,Qm/sec, but when it exceeded 3006C/hour, it became quite large. It is had.

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

Patent Applicant: Fujisha X Film Co., Ltd. 1, Incident Display 1988 Patent Application No. 321667 2. Name of the invention Manufacturing method of magneto-optical recording medium 3. Person who makes corrections Relationship with the incident

Claims (1)

[Claims] A polycarbonate substrate formed into a disk shape is placed in a heat treatment atmosphere and the temperature of the heat treatment atmosphere is increased to 300°C/
After increasing the temperature to the thermal softening temperature of the polycarbonate substrate +10±2 degrees (°C) at a heating rate of 1 hour, and heat-treating at that temperature for 30 minutes to 24 hours, a magneto-optical recording layer is provided on the polycarbonate substrate. A method for manufacturing a magneto-optical recording medium characterized by: