JP3472243B2 - Optical recording medium - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical recording medium for multilevel recording of data by irradiating a recording layer by switching the irradiation time of a laser beam in multiple stages according to the data to be recorded.

[0002]

2. Description of the Related Art A conventional CD-R or DVD-R, for example, having a recording layer and a reflective film provided in this order on a light-transmissive substrate.
In optical recording media such as the above, the depth of the reproduction signal (the degree of modulation of the reflection signal) is different from the method of recording data by changing the length of the reproduction signal (the length of the reflection signal modulator) in multiple stages. There have been many studies on a method of recording a plurality of data in each signal of the same length by switching in multiple stages.

According to this optical recording method, a plurality of data can be recorded in the depth direction as compared with the case where binary data is simply recorded depending on the presence or absence of pits. The amount can be increased. Therefore,
Since a linear recording density can be improved, a holographic method and an optical recording method having a plurality of recording layers have been proposed.

Here, the case of recording data in multiple stages by using the depth variation of reflectance is called multi-level recording.

[0005]

In such multi-level recording, it is necessary to shorten the recording mark to improve the recording density.

However, if the recording mark is to be smaller than the beam diameter when the laser used for recording / reading is focused, multilevel recording becomes difficult.

For example, Japanese Unexamined Patent Publication No. 10-134353 discloses that the amount of laser light is adjusted to perform multi-level recording. Here, when the recording medium is a dye film or a phase change film, the reproduction signal is formed by the difference in reflection between the recorded portion and the unrecorded portion. Therefore, JP-A-10-1
In the method of Japanese Patent No. 34353, the unrecorded stage and the recorded stage have a relation of presence or absence of recording, and are not suitable for multi-stage recording.
More specifically, there is no intermediate state between recorded and unrecorded in the phase change film or the dye film.

Up to now, multi-level multi-level recording was possible by adjusting the laser light amount using a dye film or a phase change film as a recording medium. The reason is that the width of the recording mark mainly changes due to the change of the laser power. Because it was.

The focused beam generally has a Gaussian distribution, but when the recording film is a dye film or a phase change film, recording is performed at a portion exceeding a certain threshold. By changing the laser power, the spot size of the focused beam that can be recorded was changed, and the width of the recording mark was changed.

However, when the recording mark length becomes shorter than the focused beam diameter in order to increase the recording density, the method of modulating the laser power to change the mark width is multi-step recording, especially multi-step recording of five steps or more. Will be difficult.
In other words, changing the recording power makes it difficult to change the reflection level during reproduction in five or more steps.

Generally, the diameter of the focused beam is Kλ / NA
(K: constant, λ: laser wavelength, NA: numerical aperture of lens). In the pickup used for CD, λ = 780 nm, NA = 0.45 and diameter is about 1.6μ.
It becomes m. In this case, when the recording mark length becomes 1.6 μm or less, it is difficult to perform multi-level recording in five or more steps by the conventional method of changing the laser power.

Further, as disclosed in, for example, JP-A-1-182846, optical recording in which the absorbance of the reactant in the recording layer changes as a digital amount when the amount of incident light on the recording layer is given as a digital amount. There is a medium.

However, it is presumed that this optical recording medium has a very small absolute value of change in absorbance with respect to laser irradiation amount (number of times), and has not yet been put to practical use.

Further, as disclosed in JP-A-61-211835, the intensity or the number of times of irradiation of light for irradiating the photochromic material is changed so that the recording can be performed at different arbitrary color development density states. There is an optical recording method.

However, this optical recording method has a problem in that the color density state cannot be read in five or more steps when reading by irradiating laser light.

The present inventor has discovered that multi-level recording of five or more steps is possible by changing the laser irradiation time even under the condition that the recording mark length is shorter than the focused beam diameter. Furthermore, it was discovered that a dye material having a gradual change is more suitable as a material for the recording film than a phase change material having a sharp change from unrecorded to recorded with a temperature rise due to laser irradiation.

Here, as the laser irradiation time increases, the thermal energy absorbed by the recording film increases. When the thermal energy exceeds a certain threshold value, the dye decomposes and deteriorates, and recording is performed on the recording film. The excess thermal energy that exceeds the threshold value is diffused to the surroundings through the reflective film. For example, C
In an optical recording medium such as D-R, if the diffusion of the thermal energy is insufficient, adverse effects such as deformation of the substrate and guide tracks engraved on the substrate will occur.

In view of the above, the present invention utilizes an optical recording medium such as a CD-R that is widely put into practical use, and performs multi-level multi-level recording to obtain good signal quality. Is an optical recording medium that enables the diffusion of thermal energy by laser irradiation sufficiently, and in particular, the deformation of the light-transmissive substrate and the groove for the laser guide engraved on the substrate, and further An object of the present invention is to provide an optical recording medium that prevents deterioration of a recording signal due to deformation of a protective film on a reflective film.

[0019]

Means for Solving the Problems The present inventor has conducted extensive studies on an optical recording medium and found a recording method for performing multi-stage recording on the optical recording medium.
It was confirmed that it is possible to perform high-density multi-level recording with five or more steps. Further, the present inventor has conducted various experiments and found that it is important for heat diffusion to define the material of the light transmissive substrate, the thermal conductivity and the film thickness of the reflective film, and arrived at the present invention. That is, the above-mentioned object can be achieved by the present invention described below.

(1) A recording layer containing a dye as a main component and a reflective film formed in contact with the recording layer are formed on a light transmissive substrate, and a laser beam is irradiated to record on the recording layer. An optical recording medium capable of recording information by forming marks and irradiating the recording marks with a reading laser beam to read the recorded information, wherein the recording layer comprises a laser beam and a recording layer. The recording layer is defined by an arbitrary unit length in the relative movement direction and a unit width in the direction orthogonal to the relative movement direction, and has virtual recording cells continuously set in the movement direction. Is
It is possible to form recording marks of different sizes corresponding to the modulation of the irradiation time of the laser beam in five or more steps, which is based on at least the area ratio of the area ratio of the recording mark to the virtual recording cell and the light transmittance. The light reflectance is modulated to enable multi-level recording of information in five or more steps, and the light transmissive substrate has a glass transition point (Tg) of 8 or less.
It is made of a thermoplastic resin having a temperature of 0 ° C. or higher and 160 ° C. or lower, the reflective film is a metal having a thermal conductivity of 300 W · m ⁻¹ · K ⁻¹ or more, and a film thickness at a recording mark portion is 50 nm or more. An optical recording medium characterized by the above.

(2) The optical recording medium according to (1), wherein the product of the thermal conductivity and the film thickness of the reflective film material is 2 × 10 ⁻⁵ W · K ⁻¹ or more.

[0022] That is the thermal conductivity as a reflective film material 30 0
When a material smaller than W · m ⁻¹ · K ⁻¹ is used, or when the thickness of the reflective film is 50 nm or less, excess heat is deformed on the substrate or the groove for the laser guide engraved on the substrate, Deformation of the protective film on the reflective film causes deterioration of the recording signal.

This effect depends on the glass transition temperature of the substrate material on which the laser guide groove is engraved. When a material having a high glass transition temperature such as glass is used as the material, no deformation due to heat is observed. It was discovered that the use of a material having a glass transition temperature of 80 ° C. or higher and 160 ° C. or lower is greatly affected by this.

It has also been confirmed that the influence of this thermal diffusion is particularly great in multilevel recording in which recording marks are close to each other in the recording direction.

Although the optical recording medium has hitherto been affected by heat at the time of recording, in multi-level recording, since the recording marks in the line direction are close to each other in order to improve the recording density, the influence is further increased. It is presumed that it became easier to receive.

Further, the above optical recording medium may be constructed as follows.

(3) The unit length of the virtual recording cell is set to be substantially equal to the length of a recording mark formed by laser beam irradiation for the maximum irradiation time (1) or (2). Optical recording medium.

(4) A groove for laser beam guide is provided along the recording layer, the virtual recording cell is set in the groove, and the unit width is substantially equal to the width of the groove. (1), characterized in that
The optical recording medium of (2) or (3).

(5) The unit length in the virtual recording cell is equal to or less than the diameter of the beam waist of the reading laser beam (1) to (4).
Optical recording medium of any of.

(6) The optical recording medium according to any one of (1) to (5), characterized in that information has been multi-level recorded in advance on a part of the recording layer.

(7) Specific information indicating a multi-level recording medium is recorded in at least one of the virtual recording cell and the multi-level recorded portion, (1) to (6) Any optical recording medium.

(8) A groove for laser beam guide is provided along the recording layer, and the groove is partially interrupted, and the light according to any one of (1) to (7) is used. recoding media.

[0033]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, an example of an embodiment of the present invention will be described in detail with reference to the drawings.

The optical recording medium 10 according to the embodiment of the present invention is a CD-R in which a dye is used for the recording layer 12, the light transmitting substrate 14 and one surface of the light transmitting substrate 14. The recording layer 12 containing a dye as a main component, which is coated so as to cover the laser beam guide groove 16 formed on the upper surface (in FIG. 1), and a reflective film formed on the upper side of the recording layer 12 by sputtering or the like. 18 and a protective layer 20 that covers the outside of the reflective film 18.

The transparent substrate 14 has a glass transition point (T
g) is made of a thermoplastic resin having a temperature of 80 ° C. or higher and 160 ° C. or lower, and can be arbitrarily selected from various materials used in conventional optical recording media. For example, polycarbonate resin, polymethylmethacrylate resin, epoxy resin,
Polyolefin resin and polyester resin can be applied. The glass transition point is, for example, JISK7.
121 by differential thermal analysis.

The recording layer 12 provided on the light transmissive substrate 14 is made of an organic dye. As the organic dye, a cyanine dye, a squarylium dye, a croconium dye, an anthraquinone dye, a metal-containing azo dye, a phthalocyanine dye, a naphthalocyanine dye, or the like can be applied.

Solvents for organic dye coating solutions include esters such as butyl acetate and cellosolve acetate; ketones such as methyl ethyl ketone, cyclohexanone and methyl isobutyl ketone; chlorinated hydrocarbons such as dichloromethane, 1,2-dichloroethane and chloroform. Amides such as dimethylformamide; hydrocarbons such as cyclohexane; ethers such as tetrahydrofuran, ethyl ether, dioxane; alcohols such as ethanol, n-propanol, isopropanol, n-butanol, diacetone alcohol; Fluorine-based solvents such as 3,3-tetrafluoropropanol; Glycols such as ethylene glycol monomethyl ether, ethylene glycol monoethyl ether and propylene glycol monomethyl ether Such as over ethers is available,
These solvents can be used alone or in combination in consideration of the solubility of the organic dye used. Various additives such as a singlet oxygen quencher, an antioxidant, a UV absorber, a plasticizer, and a lubricant may be added to the coating liquid depending on the purpose.

The light reflection film 18 on the recording layer 12 has a thermal conductivity of 300 W · m ⁻¹ · K ^{−1 at} room temperature (about 20 ° C.).
The above metals. This metal is gold, silver, copper and their alloys. The light reflection film 18 is formed by a sputtering method or a vacuum evaporation method. Light reflection film 18
Is 50 at the portion where the recording mark (described later) is formed.
nm or more, and preferably 60 to 300 nm. Also, the product of the thermal conductivity and the film thickness of the material of the reflective film 18 is 2 ×
Set it to be 10 ⁻⁵ W · K ⁻¹ or more.

A protective layer 20 is provided on the light reflecting film 18 for the purpose of physically and chemically protecting the organic dye recording layer 12, the light reflecting film 18, and the like. The protective layer may be provided on the side of the light transmissive substrate 14 where the organic dye recording layer 12 is not provided for the purpose of enhancing scratch resistance and moisture resistance.

As a material for the protective layer 20, generally an ultraviolet curable resin is widely used. This UV curable resin is dissolved as it is or in an appropriate solvent to prepare a coating liquid, and then the coating liquid is coated on the light transmissive substrate 14,
The protective layer 20 is formed by irradiating and curing with ultraviolet rays. Various additives such as an antistatic agent, an antioxidant and an ultraviolet absorber may be further added to these coating solutions depending on the purpose. The layer thickness of the protective layer 20 is 0.1 to 100 μm.
It is about m.

Recording on the optical recording medium 10 thus obtained is carried out by the following optical recording device 30, for example, as a recording light having a wavelength in the range of 770 to 790 nm or 630 to 6 nm.
Using a semiconductor laser beam having a wavelength in the range of 60 nm, the organic dye recording layer 12 is irradiated with a laser beam suitable for it while rotating the optical recording medium 10 at a constant linear velocity or a constant angular velocity to alter the organic dye. It is done by letting. The reproduction is performed by reading the difference in the reflected light amount of the laser light between the portion where the organic dye is denatured and the portion where it is not.

The optical recording device 30 is a CD-R recorder, and a spindle motor 32 rotates a optical recording medium (disk) 10 through a spindle servo 31 at a constant linear velocity, and a laser beam from a laser 36. Information is recorded on the recording layer 12 formed as described above on the optical recording medium (disk) 10.

According to the information to be recorded, the laser 36 causes the laser driver 38 to irradiate the laser beam per one virtual recording cell (details described later) 40 shown in FIGS. 1 and 3, for example, laser pulse. The number is controlled.

Reference numeral 42 in FIG. 2 is a recording optical system including an objective lens 42A and a half mirror 42B. Focus tracking control is performed on the objective lens 42A by the focus tracking servo 44 so that the laser beam is focused on the recording layer 12. The objective lens 42A and the half mirror 42B are controlled by the feed servo 46 to move from the inner peripheral side to the outer peripheral side at a predetermined speed in synchronization with the rotation of the disk 10.

The spindle servo 31, laser driver 38, focus tracking servo 44, and feed servo 46 are controlled by a controller 50. Recording layer 12
The data (information) to be recorded in is input to the control device 50.

Next, the virtual recording cells 40 and the recording marks recorded in the virtual recording cells 40 will be described.

This virtual recording cell is defined by a unit width in the radial direction and a unit length in the rotating direction of the recording medium. The unit width is equal to or smaller than the beam waist diameter of the laser beam, and is a width that can be arbitrarily selected such as the track pitch and the group width of the disk 10.

Virtual recording cell 40 of the example of this embodiment
As shown in FIG. 1, a length (circumferential length) shorter than the beam diameter (beam waist diameter) D in the groove 16 in the rotation direction of the disc 10, that is, in the circumferential direction.
And the width is defined to be equal to that of the croup 16 and is continuously assumed in the circumferential direction.
By irradiating the laser beam for each, the recording marks 48A to 48G schematically illustrated in FIG. 3 are formed according to the information to be recorded.

Here, the beam diameter D of the laser beam emitted from the laser 36 at the position of the recording layer 12 is
Recording marks 48A to 48G having different diameters are formed in the central portion of the laser beam by selecting the material of the recording layer 12, which is larger than the virtual recording cell 40. (Although the laser beam has a circular shape, the laser beam is emitted while the optical recording medium 10 is being rotated, so the recording mark becomes an elliptical shape depending on the irradiation time).

Because the focused laser beam generally has a Gaussian distribution, the recording layer 12
In the above, since recording is performed only in a portion where the irradiation energy of the laser beam exceeds a certain threshold value, the recording layer 12 is changed by changing the irradiation time of the laser beam.
The spot size of the recordable laser beam changes, which allows the formation of seven-step recording marks 48A to 48G as shown in FIG. 3, for example.

In this case, the size of each of the recording marks 48A to 48G is set so that the light reflectance of the reflected light when the virtual recording cell 40 is irradiated with the reading laser beam has seven levels. The light reflectance increases as the recording mark becomes smaller, and becomes the maximum reflectance in the virtual recording cell in which no recording mark is formed and the minimum reflectance in the virtual recording cell in which the maximum recording mark 48G is formed.

More specifically, the light reflectance is set in consideration of the area ratio of each recording mark 48A to 48G to the virtual recording cell 40 and the light transmittance of the recording mark itself.

The light transmittances of the recording marks 48A to 48G themselves are changed when the material forming the recording layer 12 is decomposed and altered by the irradiation of the laser beam and the refractive index is changed, or when the recording layer 12 is changed in the thickness direction. It depends on the quantity. If the formed recording mark portion has a light transmittance of zero, this need not be taken into consideration.

At this time, as described above, a material having a thermal conductivity of 300 W · m ⁻¹ · K ⁻¹ or more is used as the material of the light reflecting film 18, and the thickness of the light reflecting film 18 is 50 nm or more. In addition, the light-transmissive substrate 14 has a glass transition temperature of 80
Since a material having a temperature of ℃ or more and 160 ℃ or less is used, excess heat due to laser beam irradiation is engraved on the light-transmissive substrate 14 or the light-transmissive substrate 14 for the laser guide group 16
Moreover, the protective layer 20 on the light reflection film 18 is not deformed. Therefore, the recording signal is not deteriorated.

In the above embodiment, the optical recording medium 10 is the CD-
However, the present invention is not limited to this, and is generally applied to other optical recording media including DVD-R.

Further, although the example of the above-mentioned embodiment is for the optical recording medium 10 in which information such as data is not recorded, the present invention is not limited to this, and the information is divided into five or more stages. It is also applied to an optical recording medium in which is recorded in multilevel.

Furthermore, the size of the virtual recording cell 40 set on the recording layer 12 when the recording mark is formed by the optical recording device 30 is not limited to the example of the embodiment, but the laser beam is used. The beam waist diameter can be any length or less. Further, in the optical recording medium having no groove 16, the size of the virtual recording cell 40 can be set arbitrarily, but the irradiation energy at the longest irradiation time of the laser beam is set to a threshold value that changes the recording layer 12. It is advisable to set the virtual recording cell 40 to a length substantially equal to the recording mark formed when it exceeds.

Further, the laser beam is circular at the position of the recording layer 12, which is formed by using, for example, a cylindrical lens 42C in addition to the objective lens 42A as shown in FIG. However, the recording medium 10 may have an elliptical shape or a linear shape that is short in the feeding direction and long in the orthogonal direction. In this case, since the recording mark 49 becomes short, the virtual recording cell can be further shortened. That is, the recording density can be improved.

Further, as shown by reference numeral 52 in FIG. 1, the optical recording medium 10 has a plurality of pits having different reflectances in advance according to the number of stages of signal modulation, or the optical recording medium 10 concerned. By performing the multi-level recording on a part of the recording medium in advance as described above, the plurality of pits 52 and / or the recording marks 54 of the multi-level recorded part individually identify the recording medium, and the multi-level recording light. It has specific information such as information for identifying a recording medium, information for determining the power of a laser beam for recording / reproducing the recording medium, and the specific information is used for reproducing the optical recording medium and / or By reading at the time of recording, it can be surely identified that it is an optical recording medium for multilevel recording, and further it can be identified individually. It is possible or to determine the number of stages of the laser beam power in response to beforehand that is recorded in the number of stages of the pits, it is possible to perform more reliable multi-level recording. Alternatively, as shown by the reference numeral 56 in FIG. 1, the same effect can be obtained by providing a groove interruption part that partially interrupts the groove for the laser beam guide. These methods can be used alone or in combination.

[0060]

EXAMPLES Examples 1 to 6 of the present invention will be compared with Comparative Examples 1 to 4 below.
Will be described in comparison with. Here, a multi-level recording experiment was conducted using a CD-R having a recording layer 12 containing a dye as the recording medium 10.

[0061]

Example 1 A cyanine dye was dissolved in a fluorinated alcohol to prepare a 2% coating liquid for forming a recording layer, and the coating liquid was used to form a spiral pre-groove (track pitch:
1.6 μm, pre-groove width: 0.35 μm, pre-groove depth: 0.18 μm polycarbonate formed by injection molding (manufactured by Teijin Chemicals: Panlite AD)
Rotation speed of 200 rp on the surface of the pre-groove side of the light transmissive substrate having a diameter of 120 mm and a thickness of 1.2 mm made of 5503).
It is applied by spin coating while changing from m to 5000 rpm, and the thickness from the bottom in the pre-groove is about 2
An organic dye recording layer of 00 nm was formed. The glass transition temperature of polycarbonate was 140 ° C.

Next, Ag (the thermal conductivity of silver is 427 W · m ⁻¹ · K ⁻¹ ; science chronology) was sputtered on the organic dye recording layer to a thickness of 50 nm to form a light reflecting film. . Further, an ultraviolet curable resin (Dainippon Ink and Chemicals, Inc .: SD318) was spun on the light reflection film at a rotation speed of 300 rpm to 4000.
It was applied by spin coating while changing to rpm. After coating, ultraviolet rays were irradiated from above the coating film by a high pressure mercury lamp to form a protective layer having a layer thickness of 10 μm.

Multilevel recording was performed using the optical recording medium thus obtained. Multi-level recording is performed by irradiating an optical recording medium rotated at a constant linear velocity with a laser beam while changing the irradiation time in 6 steps, and recording is performed at 1 mW while rotating at a constant linear velocity. Reproduction was performed by irradiating a laser beam and detecting the reflected light. The recording / evaluating apparatus used was DDU (recording wavelength: 784 nm) manufactured by Pulstec, and the laser beam power during recording was 14 mW. At this time, the recording linear velocity is 4.8 m / s, and the recording clock frequency is 4
It was set to MHz (250 nsec).

Laser irradiation time during recording on this medium was (1) 50 nsec, (2) 80 nsec, and (3) 110, respectively.
nsec, (4) 140 nsec, (5) 170 nsec, (6) 2
Multi-level recording was performed at 00 nsec. Each single signal was recorded over one round of the disc.

Recording was carried out in this manner, and the jitter value of the recorded signal was measured by Le Croy Digital Oscilloscope LC-
When it was taken into 534EL and measured, the fluctuation due to the difference in laser beam irradiation time during recording was small and good.

Considering the case of recording by the conventional binary recording / reproducing method, it is possible to judge that the jitter value measuring device used this time is good if the jitter value is 10% or less.

[0067]

Example 2 An optical recording medium was prepared in the same manner as in Example 1 except that the thickness of the Ag light reflection film was changed to 100 nm.
Multi-level recording was done. The recording conditions were the same as in Example 1. The jitter value of the recorded signal was measured in the same manner.

[0068]

Example 3 The light reflecting film material is Au (the thermal conductivity of gold is 31
8 W · m ⁻¹ · K ⁻¹ ; science chronology), an optical recording medium was prepared in the same manner as in Example 1, and multilevel recording was performed. The recording conditions were the same as in Example 1. The jitter value of the recorded signal was measured in the same manner.

[0069]

Example 4 An optical recording medium was prepared in the same manner as in Example 3 except that the light reflection film thickness was 100 nm, and multilevel recording was performed. The recording conditions were the same as in Example 1. The jitter value of the recorded signal was measured in the same manner.

[0070]

[Embodiment 5] The light reflecting film material is made of Cu (the thermal conductivity of copper is 40
1 W · m ⁻¹ · K ⁻¹ ; science chronology), an optical recording medium was prepared in the same manner as in Example 1, and multilevel recording was performed. The recording conditions were the same as in Example 1. The jitter value of the recorded signal was measured in the same manner.

[0071]

Example 6 An optical recording medium was prepared in the same manner as in Example 1 except that the light transmissive substrate material was polyolefin (ZEONEX 280 manufactured by Nippon Zeon Co., Ltd.), and multilevel recording was performed.

The glass transition temperature of this polyolefin was 123 ° C.

The recording conditions were the same as in Example 1.

The jitter value of the recorded signal was measured in the same manner.

[0075]

Comparative Example 1 Example 1 except that the Ag film thickness was changed to 40 nm.
An optical recording medium was prepared in the same manner as described above, and multilevel recording was performed.

When the jitter value of the recorded signal was measured in the same manner, it was found that there was a problem in the signal quality especially when the laser irradiation time was long.

[0077]

[Comparative Example 2] Example 5 except that the Cu film thickness was changed to 40 nm.
An optical recording medium was prepared in the same manner as described above, and multilevel recording was performed. The jitter value of the recorded signal was measured in the same manner.

[0078]

Comparative Example 3 An optical recording medium was prepared in the same manner as in Example 2 except that the reflective film was changed to Al (the thermal conductivity of aluminum was 237 W · m ⁻¹ · K ⁻¹ ; chronology of science). Multi-level recording was done.

The jitter value of the recorded signal was measured in the same manner.

[0080]

Comparative Example 4 An optical recording medium was prepared in the same manner as in Comparative Example 1 except that glass was used as the substrate material, and multilevel recording was performed.

The shape of the pre-groove on the glass was the same as in Example 1, and the plasma etching method was used as the method of forming the groove. The recording conditions were the same as in Example 1. The jitter value of the recorded signal was measured in the same manner.

Table 1 shows the relationship between the jitter value, the light reflection film characteristics and the laser irradiation time in the above results.

[0083]

[Table 1]

[0084]

EFFECT OF THE INVENTION An optical recording medium having a dye recording layer is irradiated with a laser beam by changing the irradiation time of the laser beam in five stages or more to record data to be recorded in a multi-level recording method. 5 in the depth direction of reflectance change
It became possible to record more than one level.
At this time, it was possible to prevent the deformation of the translucent substrate and the groove due to the extra heat accompanying the laser beam irradiation, and to prevent the deterioration of the recording signal.

[Brief description of drawings]

FIG. 1 is a partial cross-sectional perspective view showing an essential part of an optical recording medium according to an example of an embodiment of the invention.

FIG. 2 is a block diagram showing an optical recording device for recording information on the optical recording medium by using a laser beam.

FIG. 3 is a schematic diagram showing the relationship between a recording mark, a virtual recording cell, and its light reflectance when a recording mark is formed on a recording layer by the optical recording device.

FIG. 4 is a schematic perspective view showing a case where the laser beam for irradiating the virtual recording cell has another shape.

[Explanation of symbols]

10 ... Optical recording medium 12 ... Recording layer 14 ... Translucent substrate 16 ... groove 18 ... Light reflection film 20 ... Protective layer 30 ... Optical recording device 32 ... Spindle 34 ... Disc 36 ... Laser 38 ... Laser driver 40 ... Virtual recording cell 42 ... Recording optical element 42A ... Objective lens 42B ... Half mirror 42C ... Cylindrical lens 44 ... Focus servo circuit 46 ... Feed servo circuit 48A to 48G, 49, 54 ... recording marks 52 ... Pit 56 ... Groove interruption D ... Beam diameter

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁷ Identification code FI B41M 5/26 G11B 7/0045 A // G11B 7/0045 B41M 5/26 Y

Claims (2)

(57) [Claims] 1. A recording mark having a recording layer containing a dye as a main component on a light-transmissive substrate, and a reflective film formed in contact with the recording layer, the recording layer being irradiated with a laser beam. An optical recording medium capable of recording information by forming a recording medium, and irradiating the recording mark with a reading laser beam to read the recorded information, the recording layer comprising:
It is defined as an arbitrary unit length in the relative movement direction of the laser beam and the recording layer and a unit width in the direction orthogonal to this, and has virtual recording cells continuously set in the movement direction. The recording layer in the virtual recording cell is capable of forming recording marks having different sizes in accordance with the modulation of the irradiation time of the laser beam in five or more steps, whereby the area ratio of the recording mark to the virtual recording cell and the optical recording layer. The light reflectance based on at least the area ratio of the transmittance is modulated to enable multi-level recording of five or more levels of information, and the light transmissive substrate has a glass transition point (Tg) of 80 ° C.
Made of a thermoplastic resin having a temperature of 160 ° C. or lower, and the reflective film is a metal having a thermal conductivity of 300 W · m ⁻¹ · K ⁻¹ or higher,
An optical recording medium having a recording mark portion having a film thickness of 50 nm or more. 2. The optical recording medium according to claim 1, wherein the reflective film material has a product of thermal conductivity and film thickness of 2 × 10 ⁻⁵ W · K ⁻¹ or more.