JP2000030295A - Optical disk - Google Patents

Abstract

PROBLEM TO BE SOLVED: To perform recording and reproduction in the disk proximity type head of a floating head or the like satisfactorily by allowing an optical disk substrate for performing recording and reproduction, by specifying the distance between a recording surface and a recording and reproducing head to be constituted of a material, having the loss tangent of not smaller than a specific value for reducing the vibration of the substrate. SOLUTION: In order to make smaller the amplitude of vibration to be generated when the force of the vibration from the outside or the like is applied to an optical disk, a material which easily absorbs energy of distortion to be applied to the substrate by the vibration of the substrate is used. Then, a loss tangent tan δ at 25 deg.C at a frequency 100 Hz is preferably 0.02 or larger and more preferably 0.05 or larger. When this value is 0.02 or larger, the energy of the vibration can be sufficiently absorbed to make the vibrating amplitude of the substrate smaller. Here, the upper limit of the tan δ is preferably 1.5 or smaller and more preferably 0.8 or smaller.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical disk, and more particularly, to an optical disk used for an apparatus that performs recording and reproduction with a head close to or in contact with a recording layer of the disk.

[0002]

2. Description of the Related Art With the development of computer technology, the capacity of recording devices has been steadily increasing. Conventional optical disks include a read-only type (ROM) and a rewritable type (RA).
M), write-once type, and the like. In these media, an optical head is provided on the side opposite to the recording surface of the optical disk substrate, so that read light or recording light emitted from the optical head passes through the substrate and performs recording. A so-called substrate surface incidence system that reaches a surface is employed. Optical heads are various optical components,
It is composed of an actuator and a light receiving element. Light emitted from a semiconductor laser passes through various optical components and is guided to an objective lens. Light passing through the objective lens is collected, passes through the substrate, and enters the recording surface. This light is reflected on the recording surface, passes through the substrate and the objective lens again, and is guided to a recording data reproducing optical system, a focus error signal generating optical system, and a tracking error signal generating optical system. The focus error signal generating optical system generates a focus error signal proportional to the amount of deviation between the focal position of the collected light and the recording surface in the direction perpendicular to the disk. The tracking error signal generating optical system generates a tracking error signal proportional to the amount of deviation of the light condensed on the recording surface from the track center in the radial direction. The objective lens is supported by an actuator, and is moved in the vertical direction of the disk so that the focus error signal becomes zero, and further moved in the radial direction of the disk so that the tracking error signal becomes zero. As a result, the focus spot and the track shift of the focused spot are always kept free. Normally, the distance (working distance) between the objective lens and the disk is designed to be about 1 mm, and this distance is kept constant by the above function.

On the other hand, in recent years, as a recording / reproducing apparatus having a large capacity and a high-speed access, an apparatus using various existing optical disks as a hard disk has been proposed. That is, one or two or more optical disks fixed coaxially are built in, and an optical head is provided to face each recording surface,
Recording and reproduction are performed by irradiating light from the recording surface side without passing through the substrate, that is, by so-called film surface incidence. In the conventional substrate surface incidence method, the numerical aperture of the objective lens could not be increased because the aberration of the light spot increased due to the inclination of the substrate and errors in the thickness of the substrate. By increasing the numerical aperture and decreasing the light spot, it is possible to increase the capacity of the optical disk and to access the disk at high speed.

FIG. 1 shows an example of such a recording / reproducing apparatus. A plurality of double-sided recording optical disks 11, 11 ', 1
1 "are coaxially fixed, and two optical heads 12, 13, 12 ', 1
3 ', 12 ", and 13" are arranged. These optical heads are arranged on the same support arm 14, fixed coaxially, and move in conjunction. The moving direction of the optical head may be a radial direction or a rotation about an axis on which these heads are supported.

The distance between the optical disk and the head varies depending on the head, but is usually set to 3 μm or less.
By bringing the head closer to the disk in this manner, it is possible to switch the magnetic field of 1500 e or more required for recording and reproduction on the magneto-optical recording medium at a high speed. In the case of a floating head in which a lens, a reflecting mirror, or an optical fiber is installed on a floating slider, in order to maintain this distance, the spring pressure of the arm that presses the slider against the disk,
The area and shape of the slider portion for obtaining the buoyancy required for flying are set. Further, a contact type head in which a slider portion and a disk surface are partially in contact has been proposed. In the case of this method, unlike the case of the substrate surface incidence method, it is not necessary to actively control the distance between the objective lens and the recording surface based on the focus error signal, and the recording and reproducing head can be reduced in size and simplified. As a result, the size of the recording / reproducing apparatus can be reduced, or the capacity of the recording / reproducing apparatus can be increased by providing a plurality of disks and heads. When recording information sent from the outside, each head detects address information (physical position on the substrate) based on a pre-recorded preformat and records the information on a recording layer of an optical disk facing the optical disk. Record the information in Regarding the method of recording information, either one head or both heads may be used at the same time.

When reading information recorded on a disk, the position of the recorded information is searched by a head and read. At this time, each of the heads with respect to the recorded information so as to maximize the reproduction signal strength
Servo adjustment should be performed independently. The head is passively controlled to a predetermined position by the balance between the spring pressure and the buoyancy during the rotation of the disk, but the position of the head when the rotation of the disk is stopped is in a state of contact with the disk as in a so-called CSS system. However, the disk may be close to or in contact with the disk only when the disk is rotating, as in the dynamic loading method, and may be sufficiently away from the disk when the disk is stopped. In the CSS method, the distance between the disk and the head is determined only by the balance between the spring pressure and the buoyancy. When the rotation speed is small and the linear velocity is low, the buoyancy acting on the head is small. Becomes 0 and the head comes into contact with the disk. In the case of this method, since the head at the time of stop may be attracted to the disk, it is necessary to roughen the substrate surface with an average surface roughness of about 100 nm to 150 nm in order to prevent this. Recently, CSS
A zone called a zone in which a bump of about 500 nm is formed to make it difficult for the head to be attracted is provided on the disk, and the head is moved to the CSS zone when the rotation of the disk is stopped.

In the dynamic loading method, when the disk is stopped, a head located sufficiently away from the disk approaches the disk in a vertical direction to a predetermined position when the disk rotates. Alternatively, when the disk is stopped, the head located at a position sufficiently distant from the disk comes close to a predetermined position along the mechanical guide from the oblique direction to the disk as the disk rotates. The latter is also called a ramp loading method. In the dynamic loading method, the head may not contact the disk when the head approaches the disk, but if not, the head collides with the disk during the approach. When the head comes into contact with the disk as described above, if the surface of the disk is soft, the head sinks into the disk and breaks the recording film. Therefore, the surface of the substrate is preferably hard. The surface of the substrate itself may be hard, or the surface of the substrate may be hardened by a recording film or a protective film.

[0008]

According to the study of the present inventors, it has been found that the following problems occur when an optical disk is used in the recording / reproducing apparatus. That is, in the conventional optical disk, the distance between the optical head and the substrate is usually 1 mm or more, and the distance between the objective lens and the recording surface is actively controlled. In this case, the distance between the optical head and the substrate is extremely short, usually within 3 μm, and the distance is passively determined by the balance between spring pressure and buoyancy. Become.

When vibration is applied to the recording / reproducing apparatus from the outside, the substrate itself vibrates at a natural frequency. When the vibration amplitude is large, the relative position between the head and the substrate is slightly shifted or the relative angle is slightly changed due to the vibration of the substrate because the distance between the head and the substrate is short. I do. For this reason, the servo signal is adversely affected, and the track is deviated during recording / reproducing, or a problem is caused in the recording / reproducing of the signal itself, and the signal quality is reduced. In the case of a flying slider head, the flying height of the head becomes unstable, and the head collides with the disk, making it impossible to perform recording and reproduction at the collision portion, or the head is damaged and recording and reproduction cannot be performed at all. . Specifically, when the vibration is applied so that the maximum value of the acceleration becomes 0.5 G at the resonance frequency of the disk, the amplitude of the vibration of the disk exceeds 0.5 mm (that is, 1.0 mm peak-to-peak). It is said that the above-mentioned problem occurs when using the.

Even when the recording / reproducing apparatus is stationary, the substrate vibrates at a natural frequency due to the resistance of air when the disk rotates at a high speed inside. The self-excited vibration of the substrate is known as flutter. If the amplitude of the vibration exceeds 0.5 μm (that is, 1.0 μm peak-to-peak), the above-described disturbance of the servo signal and the quality of the recording / reproducing signal may occur. The problem of degradation occurs. As described above, in the recording / reproducing apparatus of the above-mentioned method, the object of the present invention, in which the vibration of the optical disk substrate is required to be extremely small as compared with the related art, is to solve these problems and to be suitable for use in such a recording / reproducing apparatus. To provide an optical disk.

[0011]

SUMMARY OF THE INVENTION The gist of the present invention is to provide an optical disk for performing recording and reproduction with a recording surface provided on a substrate and a distance between the recording surface and the recording and reproducing head being within 3.0 μm. The substrate is at a temperature of 25 ° C. for 100 hours.
An optical disc characterized by comprising a material having a loss tangent tan δ at z of 0.02 or more.

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in more detail. The optical disk used in the present invention is not particularly limited as long as it has a writable recording layer, and specific examples include a disk using a magneto-optical system and a phase change system that can be repeatedly rewritten. . The magneto-optical method is excellent in rewriting durability,
It can be rewritten 100,000 times. The phase change method has an advantage that the optical system can be simplified because the read signal is a method of modulating the intensity of the reflected light. Also, using a dye etc. as a write-once method that can be written only once,
Alternatively, there is a writing method using deformation. Particularly preferably, a magneto-optical method is adopted because it is easy to perform high-speed and high-density recording.

The optical disk is provided with a preformat including information accessible by a head for reading and writing. Specifically, the address information includes address information such as a track address and a sector address, rotation synchronization information, and tracking servo information. The preformat used for the existing optical disc may be used as it is. The preformat may be provided on both sides as long as it is a double-sided recording type optical disc, or may be provided on only one side,
It suffices if at least each recording / reproducing device is provided on one optical disk recording surface. At the time of manufacturing a disc, usually, a mold containing addresses and tracking information is created, a preformatted substrate is created using the mold, and layers such as a recording layer are formed as necessary to obtain an optical disc. .

There are various methods for producing a substrate, such as an injection molding method, a casting molding method, a press molding method, and a method using a photo-curable resin. Is most preferable because it can be shortened most. Burnishing may be performed in order to reduce protrusions on the substrate surface. In the case of a double-sided recording type optical disk, the two disks may be bonded together with an adhesive with the substrate inside. Alternatively, a substrate such as a recording layer may be formed on both sides as needed after preparing a substrate that has been preformatted simultaneously on both sides by using two molds.

FIG. 2 shows an example of the layer structure of the optical disk of the present invention.
Shown in Lubricating layer 5 / protective layer 4 / recording layer 3 / protective layer 2 / substrate 1 / adhesive layer 6 / substrate 1 '/ protective layer 2' / recording layer 3 '/
This is a double-sided optical disc comprising a protective layer 4 '/ lubricating layer 5'. The substrate generally has a thickness of about 1.2 mm to 0.6 mm. The recording layer is a magneto-optical recording film such as TbFeCo or GdFeCo, or a phase change recording film such as GeSbTe or AgInSbTe, and may be composed of a plurality of layers when a super-resolution method or the like is employed. In general, a dielectric such as SiN, TaOx, SiO ₂ , or ZnS is used as the protective layer. As the adhesive layer, a photocurable adhesive, a hot melt adhesive, or the like is used. Further, a reflective heat radiation layer may be provided between the protective layer 2 and the substrate 1 (the protective layer 2 ′ and the substrate 1 ′).

In the present invention, the recording surface is 3.0
A recording / reproducing head is provided at a distance of not more than μm. In this case, the head does not have to be in contact with the recording surface.
The head is for recording and reproducing information recorded on the recording surface, and various types of heads are used according to the recording and reproducing method. As a method for maintaining the distance between the head and the recording surface, various methods such as a method using an actuator and a method for generating buoyancy in the head by designing the shape and area of the slider portion can be adopted. If
Since the slider is pressed against the recording surface by the spring pressure, the effect of the magnitude of the vibration of the medium is greater, and in that respect, the effect of the present invention is remarkable.

In the present invention, it is important to reduce the amplitude of vibration generated when a force such as vibration is externally applied to the optical disk substrate. For that purpose, it was found that a material that easily absorbs the energy of the strain applied to the substrate due to the vibration of the substrate as an internal loss should be used. Specifically, the loss tangent tan δ at a temperature of 25 ° C. and 100 Hz is preferably set to 0.02 or more, and more preferably, the loss tangent t
It was found that setting an δ to 0.05 or more was good.
If it is 0.02 or more, the vibration energy can be sufficiently absorbed, and the vibration amplitude of the substrate can be reduced. The upper limit of tan δ is usually 1.5 or less, preferably 0.8 or less. If the value of tan δ is too large, the substrate is likely to be deformed, and dimensional and shape accuracy cannot be maintained.

The optical disk of the present invention is suitable for a film-incident system in which light is irradiated from the recording surface side. Thus, the optical properties of the substrate are not important and need not be transparent. In the case where two substrates are bonded to each other, there is not much problem even if the water absorption is large. Examples of the substrate material that can satisfy these conditions include an acrylic resin, a norbornene-based resin, a liquid crystal polymer, and the like. ZEONEX (Zeon Corporation)
Norbornene-based cyclic olefin ring-opening polymer hydrogenated product), and aromatic polyester-based liquid crystal polymer.
It should be noted that the value of tan δ also changes depending on these molding conditions and the like. The value of tan δ can be measured by cutting a sample piece from a molded disk and using a dynamic viscoelasticity measuring device.

Polymethyl methacrylate has a low heat distortion temperature and is excellent in transferability. Since ARTON has a glass transition temperature and a heat deformation temperature close to each other, it is possible to achieve both transferability and shape stability during molding. ZEONEX has low water absorption and is particularly good in shape and dimensional stability. A plurality of different resins may be blended and used. In this case, it is not always necessary to use the above resins, and the above resin and another resin may be blended, or the other resins may be blended and used. Generally, when a resin is blended, cloudiness occurs depending on the combination. However, as described above, the substrate of the present invention can be used because the optical characteristics are not important. Further, tan δ is 0.02 even when the resin is a single resin or a blend of a plurality of resins.
The value of tan δ can be changed by changing the resin molding conditions (mold temperature, resin temperature, mold clamping force, etc.) and the mixing ratio of the resin.

Further, in the present invention, it is preferable that the roughness of the substrate is small to some extent. This is because, if there are irregularities on the disk, a collision with the floating head or the contact head is likely to occur. Also, if a highly crystalline resin is used as the substrate, fine crystals can be formed on the substrate surface during molding,
It is preferable to use a resin having relatively low crystallinity because it causes an increase in roughness. Usually, it is preferable that the maximum value Rmax of the surface roughness of the disk is not more than 1/2 of the working distance between the head and the disk. However, in the case of the CSS system, the center line average surface roughness Ra is 0.5 n
It is more preferably larger than m.

In the dynamic loading method, the head may not contact the disk when the head approaches the disk. In many cases, the head collides with the disk during the approach. When the head collides with the disk as described above, if the surface of the disk is soft, the head sinks into the disk and breaks the recording film. Therefore, the surface of the substrate is preferably hard. The surface of the substrate itself may be hard, or the surface of the substrate may be hardened by a recording film or a protective film.
In the present invention, the hardness of the substrate surface is HB or more in pencil hardness, more preferably 2H or more.

The flexural modulus of the resin substrate is usually 20,
4,000 kg / cm ² to 40,000 kg / cm ² , but it is 10 kg for a special resin substrate such as a liquid crystal polymer.
Some of them exceed 000 kg / cm ² . Since the amount of vibration of the substrate is inversely proportional to the half power of the flexural modulus, the flexural modulus is preferably large, preferably 24,000.
0 kg / cm ² or more, more preferably 28,000 k
g / cm ² . However, since the flexural modulus of the resin substrate varies at most about 10 times, the vibration characteristic changes only by a factor of 1/2, that is, about 3 times. As will be described later, the loss tangent tan δ greatly changes depending on the resin, and by changing this, the vibration characteristic becomes 1
/ 10 or less, and the loss tangent tan
δ is a very important parameter for suppressing the vibration characteristics of the substrate.

The loss tangent of a polycarbonate resin generally used as a substrate for an optical disk is usually smaller than 0.02.

[0024]

EXAMPLES Examples 1 to 3 A donut-shaped disc having a diameter of 130 mm, an inner diameter of 15 mm, and a thickness of 1.2 mm was prepared using polymethyl methacrylate (PMMA).
It was produced by injection molding using ARTON and ZEONEX. For molding, PMMA mold temperature 60 ° C, resin temperature 2
At 00 ° C, ARTON is mold temperature 110 ° C, resin temperature 3
At 20 ° C., ZEONEX was molded at a mold temperature of 110 ° C. and a resin temperature of 320 ° C. The loss tangent t at this time
When the value of an δ was measured using a dynamic viscoelasticity measuring device (Toyo Baldwin Co., Ltd., RHEO-VIBRON), PMMA was 0.078, ARTON was 0.028,
ZEONEX was 0.026.

The center of these disks is attached to the vibrator with the outer diameter.
Fix with 35mm brass fixing jig,
Frequency (PMMA 207Hz, ARTON 122H
z, ZEONEX 109Hz,)
The disk was vibrated to 0.5 G. Of this vibration
Using a laser Doppler speedometer and FFT analyzer
To determine the maximum amplitude at the disk edge.
As a result, PMMA is 0.04mm, ARTON is 0.34m
m, ZEONEX are 0.43mm and both are 0.50m
Below m, good results were obtained. Where the flexural modulus and
And the center line average surface roughness Ra was 3 for PMMA.
5,000kg / cm^Two, 0.3 nm, ARTON is 2
9,000 kg / cm ^Two, 0.5 nm, ZEONEX
24,000kg / cm^Two, 0.3 nm.

Examples 4 to 7 In addition to the disk prepared in Example 1, a diameter of 130 m
A donut-shaped disk having a diameter of m, an inner diameter of 15 mm and a thickness of 1.2 mm was produced by injection molding using a polyester-based liquid crystal polymer. Molding temperature 110 ° C, resin temperature 370 ° C
And a loss tangent tan in the same manner as in Example 1.
When the value of δ was measured, it was 0.366. The disk prepared in Example 1 and the above disk were fixed to a spindle motor with a stainless steel fixing jig having an outer diameter of 35 mm, and were rotated at 7200 rpm to perform laser displacement measurement and FFT.
The vibration amplitude at the resonance frequency was determined by an analyzer. The amplitude of each substrate is 0.08 μm for PMMA and ARTON
Is 0.36 μm, ZEONEX is 0.48 μm, and polyester liquid crystal polymer is 0.06 μm, which is 0.5
Good results were obtained at 0 μm or less. Here, the bending elastic modulus and the center line average surface roughness Ra of the polyester-based liquid crystal polymer were 130,000 kg / cm ² and 7 nm.

Comparative Example 1 A donut disk having a diameter of 130 mm, an inner diameter of 15 mm, and a thickness of 1.2 mm was prepared by injection molding using commercially available polycarbonate. The molding was performed under the conditions of a mold temperature of 110 ° C. and a resin temperature of 320 ° C. The value of loss tangent tan δ measured by the same method as in Example 1 was 0.017. This disk was vibrated by a vibrator in the same manner as in Example 1, and the amplitude of the disk was measured.
16Hz, vibration amplitude 0.70mm, amplitude 0.50m
m or less. Here, the flexural modulus of elasticity and the center line average surface roughness Ra of the polycarbonate are 2
It was 3,000 kg / cm ² and 0.2 nm.

Comparative Example 2 The same polycarbonate disk as in Comparative Example 1 was used in Example 4.
In the same manner as in the above, it was fixed to a spindle motor and rotated at 7200 rpm, and the vibration amplitude of the resonance frequency was obtained using a laser displacement meter and an FFT analyzer. The vibration amplitude of the substrate is 0.6
At 6 μm, the standard with an amplitude of 0.50 μm or less could not be satisfied.

Example 8 A magneto-optical recording film for film surface incidence was formed on the ARTON substrate manufactured in Example 1, and a lubricant was applied to perform a dynamic loading test. The membrane was not broken. The structure of the magneto-optical recording film for incidence on the film surface is such that a reflection layer (AlTa alloy: film thickness 100
nm), an interference layer (Si nitride: 33 nm in thickness), a recording layer (TbFeCo: 28 nm in thickness), a protective layer (Si nitride:
100 nm). The pencil hardness of the ARTON substrate was 2H when measured.

Comparative Example 3 On the PC substrate manufactured in Comparative Example 1, the same magneto-optical recording film for film surface incidence as in Example 8 was formed, a lubricant was applied, and a dynamic loading test was performed. The recording film was cracked upon impact. The pencil hardness of the PC board was measured to be B.

[0031]

As described above, according to the present invention, there is provided a disk-shaped optical recording medium in which the vibration of the substrate is small and the recording / reproduction with a disk proximity type optical head such as a flying head can be performed well. be able to.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram of an example of a recording / reproducing apparatus using an optical disk of the present invention

FIG. 2 is an explanatory diagram of an example of a layer configuration of the optical disc of the present invention.

[Explanation of symbols]

 1, 1 'substrate 2, 2' protective layer 3, 3 'recording layer 4, 4' protective layer 5, 5 'lubricating layer 6 adhesive layer 11, 11', 11 "optical disk 12, 12 ', 12" optical head 13 , 13 ', 13 "optical head 14 support arm

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) G11B 11/10 506 G11B 11/10 506Z 511 511A

Claims (8)

[Claims] 1. An optical disk having a recording surface provided on a substrate and performing recording and reproduction with a distance between the recording surface and the recording / reproducing head being within 3.0 μm.
The loss tangent tan δ at a temperature of 25 ° C. and 100 Hz is 0.0
An optical disc comprising at least two materials. 2. The optical disk according to claim 1, wherein the substrate is an injection-molded thermoplastic resin substrate. 3. The optical disk according to claim 1, wherein the substrate is an injection-molded acrylic resin substrate. 4. The optical disk according to claim 1, wherein said substrate is a norbornene-based resin substrate formed by injection molding. 5. The optical disk according to claim 1, wherein said substrate is an injection-molded liquid crystal polymer substrate. 6. The optical disk according to claim 1, wherein the recording / reproducing head is a floating head, and a distance from the recording surface is kept constant. 7. A light beam is irradiated from the recording surface side.
7. The optical disc according to any one of claims 1 to 6, 8. The optical disk according to claim 1, wherein information is recorded and reproduced by a magneto-optical method.