JPS6326852A - Durable optical disk - Google Patents

Abstract

PURPOSE:To prevent the deterioration in disk characteristics and to extend the life of the disk by specifying the bending modulus as the property of a substrate of the optical disk provided with a recording layer on a transparent substrate to a specific value or above and specifying the coefft. of linear expansion to a specific value or below. CONSTITUTION:The transparent substrate 1 is formed by using a polycarbonate resin and polymethyl methacrylate resin which are different in the bending modulus and coefft. of linear expansion and providing U-shaped tracking guide grooves thereto. The optical disk is formed by laminating a dielectric layer 22 consisting of nitride, a recording carrier layer 21 consisting of an amorphous film and a protective film 3 consisting of a UV curing resin on the substrate 1. These disks are exposed to specific force deterioration conditions and the change in the C/N thereof is measured after the specific number of date. As a result, the deterioration is hardly admitted with the disks for which the substrate 1 having >=2.4X10<4>kg/cm<2> bending modulus and <=6.5X10<-5>cm/cm.K coefft. of linear expansion is used. The deterioration in the characteristics of the disk is prevented and the life thereof is extended if the properties of the substrate are specified in the above-mentioned values.

Description

[Detailed description of the invention] [Industrial application field]

The present invention relates to an optical disc that is used as a video disc, a compact disc, a file memory disc for office use, and is expected to be used as a memory disc for computers, and more particularly to a single-spindle type (write-once type) optical disc, particularly an erasable and re-recordable type optical disc.

[Conventional technology]

Magnetic recording media were initially put into practical use as recording media for information recording, and as the demand for information recording rapidly increased, recording formats became more compact and denser. In other words, the continuous loss type magnetic layer coated with a magnetic paint with magnetic powder suspended in it was replaced by a deposition type magnetic layer by vapor deposition that could meet the demands for higher density, and furthermore, the horizontal recording form of the above-mentioned type was changed. A form of perpendicular recording, in which a magnetic material is magnetized in the thickness direction of the medium, has reached the stage of practical use, and is capable of dramatically increasing recording density. Furthermore, lagging behind magnetic recording, optical disks have been developed and are accelerating their progress in response to the demand for higher densities, with attention paid to their advantages of large recording capacity, non-contact recording, and playback. Optical discs include play-only discs such as compact discs (CDs), discs that are recordable by the user but cannot be erased, and write-once discs that allow only one recording (WORM type). Re
An optical disc called ``ad Many'' has been added, and the variety has also been expanded to include erasing and rewriting type optical discs that allow erasing and rewriting of records. These optical disks are generally of the bit type, in which dense V-shaped or U-shaped spiral grooves or concentric circular grooves are provided on a transparent substrate, and a recording layer is provided, and physical small hole microdots are provided in the recording layer base along the grooves. There are also two types: the magneto-optical type, which has magnetized microdots with magnetization anisotropy, and the phase-change type, which has reflective microdots with different optical reflectances, but information recording is performed at pitches of 1.0 to 1.0. The various microdots are recorded as rows of the various microdots provided along dense tracks formed by the spiral grooves in the 1.2μ pan range. Concerning optical discs having these forms, a wide variety of issues such as their substrates, materials for recording layers, recording methods, means, disc manufacturing methods, etc., are being studied in a variety of ways. For recording, reproducing, and erasing information, an optical head is used that has a servo control system that is precise, reliable, and withstands rapid access and tracking, and focuses the laser beam to a focus of about 1μ, and prevents the optical head from tracking off. Servo control methods such as a bush-pull method, a three-spot method, a wobbling method, and a mark detection method have been proposed depending on the format of the optical disc. While the above-mentioned precise servo control is carried out, there are problems due to physical properties and processing conditions such as surface roughness, surface waviness, eccentricity or water absorption, warping due to heating, deformation, dimensional stability, transparency, and hardness of the substrate. There are still many problems related to highly accurate and durable substrates, which are prerequisites for the smooth operation of optical disks, such as birefringence, bubble abnormality, moldability, mold releasability, and cost. In other words, when considering the environment in which optical disks are used, there are repeated situations such as: ■ High-speed rotation causes stress and distortion; ■ External forces and shocks may be applied when handled by the user; ■ Dimensional changes occur due to temperature changes. This causes the recording layer, which is a thin film of hundreds to thousands of layers, to peel off, resulting in a reduction in the lifespan. (Objective of the Invention) An object of the present invention is to provide an optical disc with high durability and durability using a substrate with excellent environmental resistance.

[Structure of the invention]

The object of the present invention is to provide an optical disc in which a recording layer is provided on a transparent substrate, wherein the bending elastic modulus of the substrate is 2.4X 10
”Kg/am2 or more and the wire L3 tensile coefficient is 6.5X
This is achieved by an optical disc having three characteristics: 10-'c+*/cm·K or less. Note that R of the present invention is convenient when the recording layer of the optical disk is a magneto-optical recording layer, and it is preferable that the magneto-optical recording layer is a perpendicularly magnetized magnetic layer made of a rare earth transition metal alloy. Further, it is preferable that the recording layer according to the present invention has at least one dielectric layer in contact with the recording layer, and the dielectric layer may be the same or different, and may be provided on both sides. The number of layers may be different. Further, the transparent substrate is preferably made of resin. Further, it is preferable to provide a tracking guide groove for tracking the optical head. Next, the present invention will be explained in detail. The tracking guide groove provided on the transparent substrate of the optical disc of the present invention may be a V-shaped groove or a U-shaped groove, but is preferably a U-shaped groove. The tracking guide groove may be formed by an injection molding method or by a photopolymer method. Both of the above two molding methods use a stamper that can be applied to ultra-precision molding. When molding, it is essential to first select a stamper with high precision as described above, and it is also necessary to keep the molding environment clean and free of dust. In addition, we consider and adjust the physical properties of the base material for the substrate and the transferability and mold releasability related to the physical properties and the surface of the stamper used, and also prevent the occurrence of internal strain under molding conditions. A desired optical disk substrate can be obtained by selecting conditions such as eliminating such occurrence, but in order to satisfy the requirements required for optical disks at the current technological level, it is necessary to experiment with favorable conditions through repeated trial and error. A method is adopted to set the . Specifically, when using resin as the base material, in the injection molding method, resin amount, resin temperature, resin fluidity, stamper temperature,
Standard values such as mold clamping force, the speed at which the standard values are reached, and the speed at which the environmental conditions return The substrate for the optical disk is changed as a series of combinations of the values and the transition conditions between the reference values and the environmental conditions, and the preferable conditions selected through this trial. Similar procedures are followed when using other base materials for substrates. Regardless of the precision or severity of the various considerations mentioned above, the physical and chemical properties of the substrate and other materials have a potential and significant impact on the durability and durability of the optical disc. These are the combined strength of the constituent layers and the physical properties of the substrate material. In the present invention, the physical properties of the substrate material include a bending elastic modulus of 2.
．． 4X 10'Kg/cm2 or more and a expansion coefficient of 6,
Although it is specified that it is 5X 10-'am/cm-K or less, the lower and upper limits of the elastic modulus and expansion coefficient are determined by the actual material. In the present invention, the materials used for the substrate of the optical disc include:
When making a mold with a stamper, it is necessary to have at least plasticity and porosity, and materials such as glass, ceramic inorganic materials such as aluminum oxide, acrylic resins such as PMMA, polycarbonate resins, epoxy resins, polysulfone resins, and polyethersulfone are used. An organic material such as a polycarbonate-polystyrene copolymer resin or a polycarbonate-polystyrene copolymer resin is used. Among the above-mentioned inorganic and organic materials, transparent resin materials are preferred in the present invention from the viewpoint of ease of adjusting molding conditions and the characteristics of the resulting optical disc. For example, if a transparent resin substrate is used instead of glass as a characteristic, the operation The output of the laser beam can be significantly reduced (about 1/4). Additionally, additives such as a polymerization initiator, viscosity modifier, resin stabilizer, antistatic agent, or lubricant may be added to the resin as necessary. The recording layer and other constituent layers are deposited on the optical disk substrate produced as described above using a sputtering method, a vapor deposition method such as a vacuum evaporation method, a plating method, or a coating method depending on the characteristics of the constituent layer materials. It is possible to form a double-sided optical disc by laminating the optical disk, and further bonding the constituent substrates together. The recording material of the recording layer according to the present invention includes Te, Bi, Te-5e alloy (Se, S, Sb, In, Sn, Pb, Bi, etc.), (TeSe, etc.) for the bit type.
) Pb, Te (TiAg) Se, homogeneous materials such as polymer dyes, as well as Te/C, 7e/CS2. Dye/^1. T
Composite materials such as e-alloy/^l and ^U/Pt/diazo-1-hybrid compounds are used, and phase change types include AsTeGe and 5eTe.
Sn. Alloys such as 5elnSn, T eo x (x# 1.2)
Amorphous oxides such as old Te/5bSe,
A composite material such as Si/Rh8 is used. Furthermore, in the magneto-optical type, a magneto-optical recording material with a large Kerr effect and/or Faraday effect is selected, and B15-ε
Single crystal films such as rGa iron garnet, MnAfGe. Polycrystalline films such as Eu0Fe, CoCr, GdCo, C
dFe[li, TbFeC. In the present invention, the preferred magneto-optical recording material in the magneto-optical optical disk is a rare earth transition metal alloy represented by the following general formula. In the formula, RE represents a rare earth transition metal (cerium group and yttrium group), TM represents a triad of Fe, Co, and N1, and 0M represents an inert element (such as He), a halogen element (such as C1), or a lanthanide. , actinides, and most elements other than hydrogen, and may also be oxides, carbides, borides, fluorides, sulfides, or phosphides of these elements. Also, x and y are 0.1≦ ×≦0.4.0≦y≦0
．． It can take values in the range of 4. Furthermore, RE, TM, and M may each be two or more types, and a multi-component alloy is preferable to a binary alloy. Since the magneto-optical properties of the alloy vary depending on the compositional elements and their composition ratios, they can be appropriately selected depending on the design specifications of the optical disk. Further, the characteristics of the composition M may be adjusted by changing the concentration in the thickness direction of the recording layer using a multi-source sputtering method or the like. Next, the compositional elements in the above general formula, RE and TM. A specific example of the combination of M will be given, and the composition ratio of x, y, etc. will be returned to the optimum. The composition M is marked following the 10 sign after the RE and TM elements. DyCoFe, DyGdCoFe, DyGclTb
Fe, DyGdTbCoFe. DyGdTbCoFe+Ti, DyTbCo, Dy
TbFe, DyTbCoFe. EuTbFe, GdNdFe, GdSmTbFe,
GdS+++TbCoFe, GdTbFe, (:
dTbFeTbFeNiTbFe+Cr, GdNd
Fe+C, GdNdFe+Si, GclTbCoF
e, GdTbCoFe+Cr, GdTbFeFe+
(Ni+Cr), GdTbCoFe+Si, [;d
TbCoFeNi, SmTbC. Fe, TbCoFe, TbCoFeNi, TbCoFe
Ni, TbCoNi. TbFeCu, TbFeNi, TbCoFeN
i etc. Note that the present invention is not limited to these. The magnetized dots applied to the recording layer made of the magneto-optical recording material may be provided in concave portions or convex portions of tracks formed of clear material. As mentioned above, it is possible to improve the performance of an optical disk by increasing the number of compositional elements of the magneto-optical recording material.
Furthermore, the function of the recording layer may be divided into a multilayer structure consisting of a recording/writing layer, a recording/reproducing layer, etc. each having its own function. Alternatively, a method may be adopted in which a reflective layer is provided to reflect and reuse the light that has passed through the recording layer. Furthermore, in the present invention, at least one dielectric layer is provided in contact with the recording layer to minimize the reflectance of the recording layer.
It is preferable to define the thickness and cause enhancement to increase the Kerr effect. If the reflectance of the recording layer is R and the Kerr rotation angle is θ, then C/
N is C/N engineering θ? The dielectric material can be improved by at least twice according to the relationship .
F2. Examples include fluorides such as LaF* and CaF2, and sulfides such as ZnS. Note that the dielectric layer may be a plurality of layers, and the dielectric material of each layer may be different, and when provided on both sides of the recording layer, the dielectric layers may be of the same dielectric material or may be different. Good too. On the other hand, since rare earth transition metals and metal alloys are easily oxidized, a protective layer may be provided early after forming the recording layer. Materials for the protective layer include SiN, SiO, or resins such as ultraviolet curable resin 5DI7 (manufactured by Dainippon Ink) and non-adhesive hot melt agent PK441 (manufactured by He〇! Japan).
etc. are used. Note that the protective layer may be regulated so as to contribute to the enhancement. FIG. 1 shows an optical disc of the present invention constructed as described above. Figure (a) is a partially cutaway perspective view of a portion of the optical disc. 1 is a transparent substrate, 2 is a recording layer, and 3 is a protective layer. Further, FIG. 2B is an enlarged sectional view of the tracking guide groove portion. 21 is a recording carrier layer, and 22 is a dielectric layer. [Example] Next, the present invention will be explained with reference to Examples. Example 1 An optical disk having the configuration shown in FIG. 1 was prepared using a transparent substrate having the following physical properties, and forced deterioration was performed on it by repeating the pattern shown in FIG. 2, and the change in C/N was observed. Substrate + (1,2mm) Flexural modulus Linear expansion coefficient (
xlO'Kycw-2) (xlO-'cm-c+s-'
・K-') A polycarbonate 2.5
6.5B Polycarbonate 2.1 6.5 Dielectric layer: 81N, 800N Magnetic N: TbFeNi, 1,000N Organic protective layer: 5D17 (manufactured by Dainippon Ink), 5μm The above forced deterioration conditions (900- 1,800r, I), m,
Table 1 shows the changes in C/H of the three types of magneto-optical disks that were subjected to a 24-hour rotation-temperature cycle of 25-60°C. ■/S,
A signal recorded at a recording frequency of IMHz was measured again at a linear velocity of 4III/s only during reproduction, and the value immediately after the first recording was used as a reference (○ dB). The disc had a diameter of 120 mm, and was stored in and removed from a commercially available compact disc case three times every 24 hours. Table 1 shows that disk A, which has excellent bending modulus and coefficient of linear expansion, shows almost no deterioration, while disks B and C deteriorate by more than 6 dB after 100 days.
Long-term reliability is extremely low. That is, unless a substrate with a sufficiently large flexural modulus and a sufficiently low 1-meter tensile modulus is used, a disk with rapid deterioration of characteristics and a short life will be obtained.

[Brief explanation of the drawing]

FIG. 1 shows an optical disc of the present invention, and FIG. 1(a) is a partially cutaway perspective view. FIG. 2 is a diagram showing a pattern of a forced deterioration test. Applicant Roku Konishi Photo Industry Co., Ltd. Figure 1 1111~ (1)) Figure 2 IflJJ4:24hr Humidity, t: 60zp-H

Claims (6)

[Claims] (1) In an optical disc in which a recording layer is provided on a transparent substrate, the bending elastic modulus of the substrate is 2.4×10^4Kg/cm^2
or more, and the coefficient of linear expansion is 6.5 x 10^-^5cm
1. An optical disc characterized in that it is less than /cm·K. (2) The optical disc according to claim 1, wherein the recording layer of the optical disc is a magneto-optical recording layer. (3) The optical disk according to claim 2, wherein the magneto-optical recording layer is a perpendicularly magnetized magnetic layer made of a rare earth transition metal alloy. (4) Claim 1, characterized in that at least one dielectric layer is provided in contact with the recording layer of the optical disc.
2. The optical disc according to item 2, item 3, or item 3. (5) The optical disc according to any one of claims 1 to 4, wherein the transparent substrate is a resin substrate. (6) The optical disc according to any one of claims 1 to 5, characterized in that a tracking guide groove is provided on the substrate.