JPS6326853A - Optical disk having good recording sensitivity - Google Patents

Abstract

PURPOSE:To improve the accuracy of an optical disk provided with a recording layer on a transparent substrate and to increase the lifetime thereof by specifying the heat conductivity and thermal deformation temp. of the substrate stock of the above-mentioned optical disk. CONSTITUTION:The transparent substrate 1 is formed by using 3 kinds of resins which are different in the heat conductivity and thermal deformation temp. and providing U-shaped tracking guide grooves thereto. The optical disk is formed by laminating a dielectric layer 22 consisting of the same stock as for the stock of the substrate 1, a recording carriage layer 21 and a protective layer 3 on said substrate. Such optical disk is subjected to the cycle withstand test to repeat recording, reproducing and erasing of signals at a specific linear speed and frequency and the change in the C/N thereof is measured after the specific number of cycles. As a result, the deterioration in the characteristics is low with the optical disk 1 for which the substrate 1 having >=105 deg.C thermal deformation temp. and <=4.6X10<-4>cal.cm<-1>.sec<-1>.K<-1> heat conductivity is used. The improved accuracy and the increased lifetime are, therefore, obtd. by using the stock having the high thermal deformation temp. and the low heat conductivity.

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 relates to a write-once type optical disc, particularly an erasing and re-recording 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 increased, the compactness of the recording layer and the increase in density were promoted. In other words, magnetic powder! A: The form of a discrete magnetic layer coated with a turbid magnetic paint gave rise to the form of a deposited magnetic layer formed by vapor phase deposition, which could meet the demands for higher densities, and furthermore, from the horizontal recording form of the above-mentioned type, recording became possible. A form of perpendicular recording in which a magnetic material is magnetically energized in the thickness direction of the medium to achieve higher density has reached the stage of practical use. Furthermore, lagging behind magnetic recording, optical disks have been developed and progress has been accelerated in response to the demand for even higher density, with attention focused on the advantages of large recording capacity, non-contact recording, and reproduction. Optical discs include play-only discs such as compact discs (CDs), discs that can be recorded by the user but cannot be erased, and write-once discs that allow only one recording (140RM type; WriLe 0nceRe).
An optical disc called ``ACL Many'' has been added,
Furthermore, the range of types has been expanded to include erasing and re-recording type optical discs that allow erasing and re-recording. These optical disks are generally of the bit type, in which a transparent substrate is provided with dense 7-shaped or 0-shaped spiral grooves or concentric circular grooves and a recording layer, and physical small microdots are provided in the recording layer base along the grooves. There are two types: a magneto-optical type, which has magnetized microdots with magnetization anisotropy, and a phase change type, which has reflective microdots with different light reflectances, but information recording is performed at a pitch of 1.0 to 1. The various micro-hyphens are recorded as rows 1 to 1 of the various micro-hyphens provided along a dense track formed by the spiral grooves and the like in the .2 μm range. Regarding optical discs having these forms. A wide range of issues such as the substrate, the material of the recording layer, the recording method, the means, the method of producing the disk, etc. are being investigated in a mutually exclusive manner. For recording, reproducing, and erasing information, an optical head is used that has a servo control system that is precise, reliable, and durable for quick access and tracking, and that narrows 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, an ob-ring 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 performed, there may be 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 high-precision substrates, which are a prerequisite for the smooth operation of optical disks, such as birefringence, bubble abnormality, moldability, mold releasability, and cost, and there are also demands for improving the characteristics of optical disks, such as recording sensitivity. be. In other words, in order to achieve high reliability as well as high density, recording sensitivity must be improved.Writable optical disks and magneto-optical disks use heat mode recording, so the heat from the recording laser beam is effectively transmitted to the recording layer. must have low thermal conductivity. However, if the thermal conductivity is low, on the other hand, local temperature increases are likely to occur, and the resin substrate is likely to be deformed due to heating, leading to bit errors and tracking deviations, leading to a reduction in reliability and service life.

[Purpose of the invention] An object of the present invention is to obtain an optical disk with high recording sensitivity and high reliability by using a substrate with low thermal conductivity and high thermal deformation temperature. [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, in which the thermal deformation temperature of the substrate is 105°C or higher and the thermal conductivity is 4.6X 10-'ca1.cwh.
This is achieved by an optical disc characterized in that -'.sec-' -1 or less. Note that the recording sensitivity (Sn+) referred to in the present invention is given by the following equation. Also, heat distortion temperature is JIS K7207-+ss
This is a value specified by the sB method. The embodiment of the present invention is advantageous 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, the recording layer according to the present invention preferably has at least one dielectric layer in contact with the recording layer, and the dielectric layer may be the same or different, and furthermore, the dielectric layer is provided in contact with both surfaces and 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 square-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 environmental conditions return * value and transition conditions between the reference value and environmental conditions, and the substrate for the optical disk is changed as a series of combinations of preferable conditions selected through this trial. Similar procedures are followed when using other base materials for substrates. Regardless of the precision and roughness of the above considerations, the physical and chemical properties of the substrate and other materials potentially and overtly affect the durability, durability, and recording sensitivity of the optical disc, and especially the recording sensitivity. In contrast, the thermal characteristics of the constituent layers and substrate materials are a problem. In the present invention, the thermal deformation temperature is 1 as a characteristic of the substrate material.
05℃ or higher, thermal conductivity 4.8X 10-'cal-am
-'・sec"'・K-' However, the lower and upper limits of the thermal deformation temperature and thermal conductivity are determined by the actual material. In the present invention, the substrate of the optical disk The materials used for
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. Organic materials such as olefin-based resins or polycarbonate-polystyrene copolymer-based resins are 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. For the optical disk substrate produced as described above, the recording layer and its constituent layers are formed by sputtering, vapor deposition such as vacuum evaporation, plating, or coating according to the characteristics of the constituent layer materials. A double-sided optical disk can be produced by laminating the constituent substrates together. As the recording material of the recording layer according to the present invention, for the bit type, Te, Bi or Te-5e alloy (Se, 8S, Sb, In, Sn, Pb, Di, etc.), (TeSe,
) Pb, Te (TiAg) Se, homogeneous materials such as polymer dyes, as well as Te/C, Te/CS2. Dye/^N,
Te alloy/^1. Composite materials such as ^u-Pt/G-Pt compounds are used, and phase change types include ^5TeGe and 5eTe.
Sn. Alloys such as 5elnSn, amorphous materials such as oxides such as TeOx (×ζ1.2), and [1iTe/5bSe, S
A composite material such as i/Rh[1] 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 B15iE
Single crystal films such as rCa iron garnet, MnA1? Ge. Polycrystalline films such as Eu0Fe, CoCr, GdCo, G
dFe1li, 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 Ni, 1M represents an inert element (such as He), a halogen element (CC1, etc.), lanthanide, actinide. and most of the elements except hydrogen, and may also be oxides, carbides, borides, fluorides, sulfides, or phosphides of these elements. Also, for × and so (1, 1≦×≦0, 4.0≦y≦
A value in the range of 0.4 can be accommodated. 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 optimally selected depending on the design specifications of the optical disk. Further, the characteristics of the composition M may be adjusted by varying the concentration in the recording layer thickness direction using a multi-source sputtering method or the like. Next, the compositional elements in the above general formula, RE and TM. Specific examples of combinations of M will be given, and the composition ratios of X, y, etc. are optimally selected. The composition M is marked following the 10 sign after the RE and TM elements. DyCoFe, DyGdCoFe, DyGdTbF
e, DyGdTbCoFe. [1yGdτbcoFe+Ti, DyTbCo,
DyTbFe, DyTbCoFe. Eu'TbFe, 'GdNdFe, GdSmTbFe
, Gds+TbcoFe, GdTbFe, GdS
bFe+B, CdTbFe+Cr,' GdTbF
e+ C, GdTbFe+ Si, GdTbCoF
e, GdTbC6Fe+ Cr, GdTbC6
Fe+(Ni+Cr), GdTbC6Fe+Si,
GdTbCoFeNi, SmTbC. Fe, TbCoF'e, TbCoFeNi, Tb
CoFe+C1TbCoNi. TbFeNiu, TbFeNi, TbCoFeNi
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 by grooves. 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, it may be a multilayer structure consisting of a recording/writing layer, a recording/reproducing layer, etc., each of which has its own function by dividing the function of the recording layer. 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, it is preferable to provide at least one dielectric layer in contact with the recording layer and to define the layer thickness so that the reflectance of the recording layer is minimized to cause enhancement and increase the Kerr effect. If the reflectance of the recording layer is R and the Kerr rotation angle is θ, then C/
N can be improved by at least a factor of two depending on the relationship to C/N (X: θ. The dielectric material may include nitrides such as ^lN, SiJ, etc., S
Oxides such as iO2, Sin, Tie□, MgF2.
Examples include fluorides such as LaF, 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. As the material for the protective layer, SiN, SiO, resin such as ultraviolet curable resin 5DI7 (manufactured by Dainippon Ink), non-adhesive hot melt agent PK441 (manufactured by C 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. The figure (IL) is a partially cutaway perspective view of a part of the optical disc. 61 is a transparent substrate, 2 is a recording layer, and 3 is a protective layer. Furthermore, FIG. 2(b) is an enlarged sectional view of the l/racking guide groove portion. 21 is a recording carrier layer, and 22 is a dielectric layer. Figure 2 shows the relationship between recording sensitivity and thermal conductivity. Thermal conductivity 4.6x IQ-4cal-c+a-' ・s
It has been shown that the recording sensitivity drops sharply from around ec-'4-'. [Example] Next, the present invention will be explained with reference to Examples. Example-1 Three types of resin substrate materials with different thermal properties shown in Table 1 below were used as A.
, B and C, an optical disk having a tracking guide groove having the configuration shown in FIG. 1 was prepared, and a cycle durability test was conducted by repeating the "recording-reproducing-erasing" cycle. Table 1 1 - Racking guide groove specifications "Pitch 1.6μ theory L; R depth 700 people yJ
Configuration "Substrate: 1.2 μm, above A, B or CL
Protective layer: 5 μs, 5D17 (manufactured by Dainippon Ink),
The three types of magneto-optical disks created in this way have a linear velocity of 4-/
s, record a signal at a frequency of IMHz, play it back and convert it to C
/N is measured. After that, erase is performed at a linear speed of 1 m/s.
A cycle durability test was carried out with the above-mentioned recording-(reproducing)-(erasing) as one cycle. Table 2 shows the reduction rate after the durability test @100 cycles and after 1,000 cycles based on the disc A. Table 2 Disk B has a heat deformation temperature of 105°C, and disk A
There is no difference in the rate of decrease in C/H due to the cycle test compared to disk A, but disk C with a heat distortion temperature of 100°C (recording sensitivity is low) has a significant decrease in C/H and is extremely reliable compared to disk A. descend. From the above results, the thermal conductivity is 4.8x 10-cal-e
Unless the heat distortion temperature is as low as s-'・s-l・K-' and as high as 105"C or higher, only disks with low recording sensitivity and significant performance deterioration as the number of uses increases will be obtained. Therefore, it can be seen that the precision required for the recording and reproducing apparatus is required, and that the life span of the disk is also short.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 shows an optical disc of the present invention, and FIG. 1(a) is a partially cutaway perspective view. FIG. 2 is a graph showing the relationship between recording sensitivity and thermal conductivity.゛Applicant Konishiroku Photo Industry Co., Ltd. Figure 1 1111111, (b)

Claims (6)

[Claims] (1) In an optical disc in which a recording layer is provided on a transparent substrate, the thermal deformation temperature of the substrate is 105°C or higher, and the thermal conductivity is 4.6 × 10^-^4 cal·cm^-^1·sec.
＾-＾1・K＾-＾1 or less. (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.