JP2002170280A - Information recording carrier - Google Patents

Abstract

PROBLEM TO BE SOLVED: To stably reproduce a signal with a high NA reproducer by reducing the double refraction of an information recording carrier. SOLUTION: The information recording carrier reads an information signal by an optical means, is constituted of at least a support body 13, a recording layer 12 which is formed on the support body 13 and records the information signal and a light transmissive layer 11 which is formed on the recording layer 12 and transmits a light. The light transmissive layer 11 is a cellulose ester acetate.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an information recording carrier for use in a reproducing apparatus for reading out information by making a relative movement with respect to the information recording carrier, and more particularly to an information recording carrier for recording and / or reproducing by optical means. It is about.

[0002]

2. Description of the Related Art Conventionally, there is a system for reading out information by relative movement of an information record carrier, and this system uses a disc-like, card-like or tape-like information record carrier. Among them, disc-shaped information recording carriers, particularly systems for recording and / or reproducing data by optical means, have penetrated deeply into daily life. For example, as a read-only type information recording carrier using light having a wavelength of λ = 650 nm, a DVD video in which image information is recorded in advance, a DVD-ROM in which a program or the like is recorded in advance, and music information are recorded in advance. DVD audio,
SACD and the like are known.

Further, DVD-R is a recordable / reproducible information recording carrier using a dye, and DVD-RAM, DVD is a recordable / reproducible information recording carrier using a phase change.
-RW and DVD + RW include ASMO, iD, and GIGAMO as recordable / reproducible information record carriers using magneto-optics.

[0004] Further, in order to increase the recording density of an information recording carrier, research on shortening the wavelength of a laser has been continued for many years. A gallium nitride based compound semiconductor light emitting device (described in, for example, Japanese Patent No. 2778405) and a second harmonic oscillation device, which have been recently invented, emit light in the vicinity of λ = 350 to 450 nm. It can be a light emitting element.

Further, the design of an objective lens corresponding to the wavelength in the vicinity of this is also progressing. In particular, a lens whose NA (numerical aperture) exceeds 0.7 used in DVD and is 0.7 or more is under development. It is. Specifically, single lens (single lens)
NA 0.7, 0.75, 0.78, 0.8, 0.
Lenses of 85 or the like and lenses with NAs of 0.8, 0.85, 0.9, and 0.95 by two-group lenses (two-lens combination lens) are under study.

As described above, an information record carrier reproducing apparatus in which λ is reduced and NA is 0.7 or more is being developed, and an optical disk system far exceeding the current DVD recording capacity is developed by using these techniques. It can be expected to develop.

[0007]

By using such a high NA exceeding that of the DVD, an information recording carrier having a remarkably high recording density can be designed. However, since the aberration when the information recording carrier is tilted becomes extremely large, the thickness of the transmission layer through which light is transmitted is set to be smaller than that of the DVD.
Information recording carriers that are much thinner than those have been proposed.

FIG. 7 is a schematic sectional view showing a basic structure of such an information recording carrier 100. As shown in FIG. Support 103,
An adhesive is filled between the recording layer 102 and the light transmitting layer 101 to form an adhesive layer 104. The support 103 has
Pits or grooves 120 are carved. Recording layer 1
Light used for recording or reproduction on the light-transmitting layer 02 enters from the light-transmitting layer 103 side. Here, the thickness of the light transmitting layer 103 is, for example, 0.1 mm, and a polycarbonate resin sheet is used. In the case of a CD or DVD, light enters from the support 103 side, and the thickness of the support 101 is 1.2 mm.
(CD) or 0.6 mm (DVD) was used. Further, polycarbonate resin has been used as the material.

The present inventor has proposed an information recording carrier 1 having the structure shown in FIG.
00 and a blue-violet laser (λ = 350-450n
m, for example, 400 to 435 nm), and a recording / reproducing experiment was actually performed using a high NA objective lens. As a result, it was found that fluctuations were observed in the reproduced signal output. This fluctuation has two wave components (frequency of 2 Hz) per rotation. However, since the reproduction output fluctuation is large, stable focusing and
This was an obstacle to stable tracking. These triggers also increased the jitter of the recording / reproducing signal.

When the cause of the output fluctuation of the reproduction signal was examined, it corresponded to the one-round fluctuation of the birefringence value of the light transmitting layer 101, and the phase was also coincident. From this, it was found that there was a problem with the birefringence of the polycarbonate sheet constituting the light transmitting layer 101, and it was necessary to reduce it. Although the reduction of birefringence is a problem that has been a concern even in the conventional information recording medium, it has been conventionally solved by devising molding conditions. However, in the case of the information recording carrier 100 having the configuration of FIG.
A polycarbonate sheet (light-transmitting layer 101) of about mm cannot be produced by injection molding or compression molding, and cannot be dealt with by a conventional solution to the problem. The sheet is tensioned to obtain strength in the final step of processing. As a result, a difference in stress occurs in the longitudinal direction and the transverse direction of the sheet, and a birefringence difference occurs. Further, the inventors of the present invention have conducted intensive studies and found that, particularly when a high NA (NA 0.7 or more) objective lens is used, since recording / reproducing light enters the light transmitting layer 101 at a low angle, multiple It was also found that the refraction must be reduced more strictly than before. Specifically, assuming that the refractive index of the light transmitting layer 101 is n, NA = n · sin (90−θ). Therefore, at NA 0.7, about 62 degrees, at NA 0.8, about 58 degrees, At an NA of 0.85, the light is incident at a shallow angle of about 56 degrees, and the birefringence is increased as compared with the case where a conventional low NA (NA of 0.6 or less) is assumed (θ: incident angle, n = about 1.5). Assuming). The present invention is to solve such a problem, and fundamentally reviews the material of the light transmitting layer 101.

[0011]

SUMMARY OF THE INVENTION The present invention is an information recording medium which solves the above-mentioned problems, and has the following arrangement.

An information recording carrier from which an information signal can be read by optical means, comprising a support, a recording layer formed on the support for recording an information signal, and an optical signal formed on the recording layer. And a light-transmitting layer that transmits light, wherein the light-transmitting layer is formed of cellulose acetate.

3. The information recording carrier according to claim 1, wherein said cellulose acetate has two or more esterified hydroxyl groups.

Further, the light transmitting layer has a wavelength λ = 350-45.
3. The information recording carrier according to claim 1, wherein the cellulose acetate ester has a transmittance of 0 nm light of 70% or more.

The information recording carrier according to any one of claims 1 to 3, wherein the support has a fine pattern formed on the surface on which the recording layer is formed. I do.

Further, the information recording carrier according to any one of claims 1 to 4, wherein the recording layer has a highly reflective material.

The information recording carrier according to any one of claims 1 to 4, wherein the recording layer has a coloring material.

The information recording carrier according to any one of claims 1 to 4, wherein the recording layer has a phase change material.

The information recording carrier according to any one of claims 1 to 4, wherein the recording layer comprises a magneto-optical material.

[0020]

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a perspective view of an information recording carrier according to the present invention. FIG. 1 is a sectional view showing the most basic configuration of an information recording carrier 1 according to the present invention. Here, the shape of the information recording carrier 1 may be a disk shape, a card shape, or a tape shape. The shape may be circular, square, or elliptical. Further, a hole may be formed.

Further, the information recording carrier 1 according to the present invention comprises at least a support 13, a recording layer 12, and a light-transmitting layer 11.
Still further, the information recording carrier 1 according to the present invention includes a support 13,
It is desirable that the recording layer 12 and the light transmitting layer 11 are laminated in this order. Here, the support 13 is a base having a function of mechanically holding the recording layer 12 and the light-transmitting layer 11 described later. The constituent material is made of any of synthetic resin, ceramic, and metal. Representative examples of synthetic resins include polycarbonate, polymethyl methacrylate, polystyrene,
Suitable for various thermoplastic resins and thermosetting resins such as polycarbonate / polystyrene copolymer, polyvinyl chloride, alicyclic polyolefin, and polymethylpentene, and various energy ray-curable resins (including examples of ultraviolet-curable resins and visible light-curable resins) Can be used. These may be synthetic resins containing metal powder or ceramic powder. As typical examples of the ceramic, soda lime glass, soda aluminosilicate glass, borosilicate glass, quartz glass, or the like can be used. The thickness of the support 13 is 0.3 to 3 m because of the necessity of mechanical holding.
m, preferably 0.6 to 2 mm is suitably used.

The recording layer 12 is a thin film having a function of reading information from the information recording carrier 1 of the present invention or recording or rewriting information. Recording layer 12
In the case where the information recording carrier is a read-only type information recording carrier, a high reflectivity material is used, and in the case of a recording / reproducing type information recording carrier, a dye material, a phase change material, an optical Used by selecting from magnetic materials. Further, the thickness of the recording layer 12 is 2 to 300 nm, particularly 5 to 200 n.
m is preferably used.

As the high reflectance material, a material having a reflectance of 70% or more, preferably 80% or more at the reproduction wavelength λ can be used. For example, aluminum, silver, silicon, titanium, chromium, nickel, tantalum, molybdenum, iron, gold , Copper, or a metal thereof or an alloy thereof (alloys include examples of oxides, nitrides, carbides, sulfides, and fluorides). In particular, an aluminum alloy or a silver alloy can be suitably used.

As specific examples of the recording material for dye recording, cyanine dyes, phthalocyanine dyes, naphthalocyanine dyes, azo dyes, naphthoquinone dyes, fulgide dyes, polymethine dyes, acridine dyes, and the like can be used.

Further, as a recording material for phase change recording,
Indium, antimony, tellurium, selenium, germanium, bismuth, vanadium, gallium, platinum, gold, silver,
Alloys such as copper, tin, and arsenic (alloys include examples of oxides, nitrides, carbides, sulfides, and fluorides) can be used. In particular, GeSbTe, AgInSbTe, and CuAlT
It is preferable to use eSb or the like. The recording layer 12 may be formed using a laminated film of an indium alloy and a tellurium alloy.

As recording materials for magneto-optical recording, terbium, cobalt, iron, gadolinium, chromium, neodymium, dysprosium, bismuth, palladium, samarium, holmium, proseodymium, manganese, titanium,
Alloys such as palladium, erbium, ytterbium, lutetium and tin (alloys are oxides, nitrides, carbides,
(Including examples of sulfides and fluorides), and it is particularly preferable to use a transition metal and rare earth alloy as represented by TbFeCo, GdFeCo, DyFeCo and the like. Further, the recording layer 12 may be formed using an alternately laminated film of cobalt and platinum.

The recording layer 12 has an auxiliary film such as silicon, tantalum, zinc, magnesium, calcium, aluminum, chromium, zirconium or the like for the purpose of improving the reproduction output, the number of rewrites, and improving the storage stability. An alloy (including an oxide, a nitride, or a carbide) or a high-reflection film (aluminum, gold, silver, or the like) may be used and stacked.

The light transmitting layer 11 which is the main point of the present invention is used.
Has a function of physically guiding the converged reproduction light to the recording layer 12, and at the same time, a function of chemically and mechanically protecting the recording layer 12. The light-transmitting layer 11 according to the present invention is made of a layered cellulose derivative, particularly cellulose acetate, which is thinner than the thickness of the support 13. Cellulose is a six-membered ring having the basic molecular structure shown in FIG. 6, and has three hydroxyl groups (OH) in this basic unit. Esterification of the hydroxyl groups of cellulose using glacial acetic acid or acetic anhydride can synthesize cellulose acetate. At this time, some or all of the three hydroxyl groups can be esterified depending on the synthesis conditions. The synthesized material becomes a transparent body having a refractive index of about 1.5. In addition, the material has the characteristic that the intrinsic birefringence of the material is small and the dependence on the light incident angle is small. It should be noted that, depending on the synthesis conditions, yellowing or whitening occurs, and when the information recording carrier 1 is formed using such a material, the reflectance decreases and the reproduction signal output deteriorates. However, it is possible to adjust the synthesis conditions to make the transmittance at λ = 350-450 nm practically transparent (transmittance 70% or more, preferably 80% or more). The light-transmitting layer 11 of the present invention is a layered cellulose derivative configured to be thinner than the thickness of the support 13, and in particular, has a transmittance of λ = 350 to 450 nm and a transmittance of 70.
% Or more.

Among them, cellulose acetate having two or more hydroxyl groups substituted can be processed into a thin sheet by a casting method using a solvent or a melt extrusion method. And while the sheet obtained by applying tension is tough, it inherits the intrinsic birefringence of the material, and the birefringence difference in the longitudinal and transverse directions can be suppressed.

As described above, the thickness of the light transmitting layer 11 of the information recording carrier 1 according to the present invention is smaller than the thickness of the support 13. However, considering the aberration that increases when the information recording carrier 1 is tilted, the thickness is 0.050 to 0.300 mm
Is suitable, preferably 0.060 to 0.200 mm,
More preferably, it is 0.070 to 0.120 mm. In addition, the variation in one side of the thickness is ± 0.003m at the maximum.
m, preferably ± 0.002 mm or less. More preferably, it is set to ± 0.001 mm or less. In the information recording carrier having the configuration shown in FIG. 1, when the thickness of the light transmitting layer 11 is within the above range, the birefringence measured from the light transmitting layer 11 can be ± 20 nm or less by a 90 degree (perpendicular) incident double pass. it can. Also, when measured with a 60-degree incident double pass, ± 40
nm or less can be obtained.

The information recording carrier 1 having the most basic configuration of the present invention has been described above with reference to FIG. Note that the present invention is not limited to the information recording carrier 1 shown in FIG. 1, and various modifications in accordance with the gist of the present invention are possible.

FIG. 2 is a sectional view showing the structure of the second information recording carrier 2 according to the present invention. The information recording carrier 2 according to the present invention comprises a support 13, a recording layer 12, and a light transmitting layer 1.
And at least one. As a difference from the first information recording carrier 1, a fine pattern 20 is engraved on the surface of the support 13. More specifically, a pattern on the order of microns to submicrons, such as a pit on which information is recorded, a hologram on which information is recorded, and a groove which acts as an auxiliary during recording, is formed on the side in contact with the recording layer 12. As a pit on which information is recorded, various kinds of modulation signals called so-called (d, k) codes can be handled. Further, either a fixed-length code or a variable-length code can be used. Also, mark edge recording and mark position recording are possible. In particular, mark edge recording is a kind of fixed length code (2.10) RL.
L modulation (for example, D8 / 15 modulation (Japanese Patent Application No. 2000-201)
No. 71), 8/16 modulation, 8/17 modulation), mark edge recording and recording, and a variable length code (2.7).
Modulation or (1.7) modulation is preferably used.

FIG. 3 shows, for example, a sectional view of the structure of the third information recording carrier 3 according to the present invention. The information recording carrier 3 according to the present invention comprises a support 13 having a fine pattern 20 on its surface, a recording layer 12, an adhesive layer 14, and a light transmitting layer 11.
And at least. That is, the difference from the second information recording carrier 2 is that the adhesive layer 14 is interposed between the recording layer 12 and the light transmitting layer 11 of the information recording carrier 1. The adhesive layer 14 is a layer for firmly bonding the recording layer 12 and the light-transmitting layer 11, and includes a thermosetting resin, various energy ray-curable resins (including an ultraviolet ray-curable resin and a visible light-curable resin), an electron beam-curable resin, A moisture-curable resin, a multi-liquid mixed-cured resin, a solvent-containing thermoplastic resin, or the like can be used. If the thickness of the adhesive layer 14 is large, the birefringence of the adhesive layer 14 itself is added to the birefringence of the light transmitting layer 11, which is not desirable. Therefore, 0.04 mm
The following is desirable, and 0.03 mm or less is more desirable. More preferably, it is 0.02 mm, but most preferably 0.01 mm or less in consideration of the warpage of the entire information recording carrier 2.

FIG. 4 is a sectional view showing the structure of a fourth information recording carrier 4 according to the present invention. The information recording carrier 4 according to the present invention comprises a support 13, an adhesive layer 14, and a recording layer 1.
2, and at least a light-transmitting layer 11. The difference from the third information recording carrier 3 is not the surface of the support 13,
That is, the fine pattern 21 is engraved on the light transmitting layer 11. More specifically, a pattern on the order of microns to submicrons, such as a pit on which information is recorded, a hologram on which information is recorded, and a groove which acts as an auxiliary during recording, is formed on the side in contact with the recording layer 12.

FIG. 5, for example, shows the structure of a fifth information recording carrier 5 according to the present invention in a sectional view. The information recording carrier 5 according to the present invention comprises a support 13, a pattern layer 1.
5, at least a recording layer 12, an adhesive layer 14, and a light transmitting layer 11. And the difference from the third information recording carrier 3 is that
The surface of the support 13 is flat, and the fine pattern 22 is carved on the pattern layer 15 in contact with the support 13. Here, the pattern layer 15 is a fine pattern 22
Is a very thin film for providing The material of the pattern layer 15 is selected from metals and their alloys (alloys include examples of oxides, nitrides, carbides, sulfides, and fluorides) and resins, and the thickness is selected from about 5 nm to 20 μm. . Representative examples of the resin include an energy ray-curable resin (for example, an acrylic UV-curable resin) and a novolak-based UV-sensitive resin that can be alkali-developed.

The information recording carriers 1 to 5 according to the present invention have been described in detail above. The components described in the description may be interchanged or combined with each other as long as the content of the invention is not hindered. For example, although not shown, the information recording carriers 1 to 5
May be prepared, and the support members 1 may be attached to each other so as to face each other. Further, the recording layer 20 and the light-transmitting layer 4 may be further stacked on the light-transmitting layer 11 of the information recording carriers 1 to 5 as a set. By preparing two information recording carriers 1 to 5, the capacity of the information recording carrier 10 can be approximately doubled. Although not shown, a known antistatic layer, a lubricating layer, a protective layer, and the like may be formed on the side of the light transmitting layer 11 opposite to the recording layer 12. Although not shown, label printing may be performed on the side of the support 13 opposite to the recording layer 12. Further, the information recording carriers 1 to 5 may be mounted inside the cartridge. Further, in the case of a disc-shaped information recording carrier, its size is not limited.
It can take various sizes from 0 to 300mm and has a diameter of 3
2, 51, 65, 80, 88, 120, 130, 20
It may be 0, 300 mm, or the like.

Next, the content of the present invention will be further described based on a prototype example.

(Example 1) As a read-only information recording carrier, a disc-shaped information recording carrier 2 having an outer diameter of 120 mm and an inner diameter of 15 mm having the configuration shown in FIG. 2 was prepared. As the support 13, a polycarbonate injection molding machine made of a thermoplastic resin having a thickness of 1.1 mm is used, and on the surface thereof, as a fine pattern 20, 8-16 modulation signals (pit lengths 3T to 11T and 1 pit length).
4T) is formed in a spiral shape. Note that the shortest pit (3T) length of the fine pattern 20 is 0.24 μm, and the interval between the spirals in the radial direction is 0.341 μm. Then, aluminum was formed as the high reflectance recording layer 12 on the fine pattern 20 by DC sputtering. Then, as the light-transmitting layer 11, a 0.100 mm sheet made of cellulose acetate ester obtained by esterifying 2.9 of the three hydroxyl groups in FIG. 6 and having a transmittance of λ = 350 to 450 nm of 70% or more is prepared. (Wavelength 405 nm
Has a refractive index of 1.48). This translucent layer 11 was thermally fused onto the recording layer 12 to complete the information recording carrier 2.

The birefringence of the information recording carrier 2 is determined by
When light was incident from one side and measured 360 degrees around the circumference, 90
It was -5 to +5 nm in the degree (normal) incidence double pass. When measured with a 60-degree incident double pass, -6
−−15 nm.

The information recording carrier 2 was mounted on a reproducing apparatus having a pickup composed of a blue-violet laser emitting at λ = 405 nm and an objective lens having a numerical aperture of NA 0.7 to reproduce signals. Then, when the 14T top level (I14H) of the signal modulation was measured, the level unevenness during 360 degrees in one round was about 2%. The signal reproduction jitter was 11%, which was a sufficiently satisfactory level.

Example 2 As a read-only information recording carrier, a disk-shaped information recording carrier 3 having an outer diameter of 120 mm and an inner diameter of 15 mm having the configuration shown in FIG. 3 was prepared. As the support 13, a polycarbonate injection molding machine made of a thermoplastic resin having a thickness of 1.1 mm is used, and a fine pattern 20 is formed on its surface as a 8 to 16 modulation signal (pit lengths 3T to 11T and 1P).
4T) is formed in a spiral shape. Note that the shortest pit (3T) length of the fine pattern 20 is 0.24 μm, and the interval between the spirals in the radial direction is 0.341 μm. Then, aluminum was formed as the high reflectance recording layer 12 on the fine pattern 20 by DC sputtering. The light transmitting layer 11 is made of the cellulose acetate ester of 2.9 pieces used in Example 1 and has a thickness of 0.100 m.
An m-sheet is prepared and an adhesive layer 14 made of an ultraviolet curing resin is prepared.
(Thickness: 2 μm), and the information recording carrier 3
Was completed.

The birefringence of the information recording carrier 3 is determined by
When light was incident from one side and measured 360 degrees around the circumference, 90
It was -5 to +5 nm in the degree (normal) incidence double pass. When measured with a 60-degree incident double pass,
6 to -15 nm.

The information recording carrier 3 was mounted on a reproducing apparatus having a pickup composed of a blue-violet laser emitting at λ = 405 nm and an objective lens having a numerical aperture of 0.7 to reproduce signals. Then, when the 14T top level (I14H) of the signal modulation was measured, the level unevenness during 360 degrees in one round was about 2%. The signal reproduction jitter was 11%, which was a sufficiently satisfactory level.

Example 3 As a read-only type information recording carrier, a disk-shaped information recording carrier 3 having an outer diameter of 120 mm and an inner diameter of 15 mm having the configuration shown in FIG. 3 was prepared. A polycarbonate injection molding machine, which is a thermoplastic resin having a thickness of 1.1 mm, is used for the support 13, and a D8 / 15 modulation (pit length 3T to 12T) is spirally formed as a fine pattern 20 on the surface thereof. ing. Note that the shortest pit (3T) length of the fine pattern 20 is 0.24 μm, and the spiral spacing in the radial direction is 0.341 μm. And the fine pattern 20
The high reflectance recording layer 12 is formed on the
A6061 aluminum alloy was formed as a film. Then, 2.5% of the three hydroxyl groups in FIG.
Consisting of cellulose acetate which is esterified,
A 0.07 mm sheet having a transmittance of λ = 350 to 450 nm of 70% or more was prepared (the refractive index at a wavelength of 405 nm was 1.50). The translucent layer 11 was thermally bonded via an adhesive layer 14 (thickness 30 μm) made of a solvent-containing thermoplastic resin to complete the information recording carrier 3.

The birefringence of the information recording carrier 3 is determined by
When light was incident from one side and measured 360 degrees around the circumference, 90
It was -6 to +6 nm in the degree (normal) incidence double pass. When measured with a 60-degree incident double pass, -7
−−17 nm.

The information recording carrier 3 was mounted on a reproducing apparatus having a pickup composed of a blue-violet laser emitting at λ = 405 nm and an objective lens having a numerical aperture of NA 0.7 to reproduce signals. Then, when the 12T top level (I12H) of the signal modulation was measured, the level unevenness during 360 degrees in one round was about 3%. The signal reproduction jitter was 12%, which was a sufficiently satisfactory level.

Example 4 As a recording / reproducing type information recording carrier, a disk-shaped information recording carrier 3 having an outer diameter of 120 mm and an inner diameter of 15 mm having the configuration shown in FIG. 3 was prepared. As the support 13, a polycarbonate injection molding machine made of a thermoplastic resin having a thickness of 1.1 mm is used, and grooves (continuous grooves) having a width of 0.15 μm are spirally formed as fine patterns 20 on the surface thereof. . The spiral groove pitch in the radial direction is 0.40 μm. Then, DC is placed on the fine pattern 20.
And the phase change recording layer 12 using AgPdCu / ZnSSiO / AgInSeTe /
A laminated film made of ZnSSiO was formed. The light transmitting layer 11 is made of cellulose triacetate of 0.100 m.
An m-sheet is prepared and an adhesive layer 14 made of an ultraviolet curable resin is prepared.
(Thickness: 5 μm), and the information recording carrier 3
Was completed.

The birefringence of the information recording carrier 3 is determined by
When light was incident from one side and measured 360 degrees around the circumference, 90
It was -5 to +5 nm in the degree (normal) incidence double pass. When measured with a 60-degree incident double pass, -6
−−15 nm.

This information recording carrier 3 is mounted on a recording / reproducing apparatus having a pickup composed of a blue-violet laser emitting at λ = 405 nm and an objective lens having a numerical aperture of NA 0.7, and the shortest pit (3T) length is set. Recording and reproduction of a D8 / 15 modulation signal set to 0.24 μm were performed. Then, when the 12T top level (I12H) of the signal modulation was measured, the level unevenness during 360 degrees in one round was about 2%. The signal reproduction jitter was 11%, which was a sufficiently satisfactory level.

(Comparative Example) An information recording carrier 3 was completed in the same manner as in Example 4 except that the light transmitting layer 11 was a 0.100 mm sheet made of polycarbonate.

The birefringence of the information recording carrier 3 is determined by
When light was incident from one side and measured 360 degrees around the circumference, 90
It was -90 to +90 nm in the degree (normal) incidence double pass. When measured with a 60-degree incident double pass,
It was 110-130 nm.

The information recording carrier 3 is mounted on a recording / reproducing apparatus having a pickup composed of a blue-violet laser emitting at λ = 405 nm and an objective lens having a numerical aperture NA of 0.7, and the shortest pit (3T) length is set. Recording and reproduction of a D8-15 modulated signal set to 0.24 μm were performed. When the 12T top level (I12H) of the signal modulation was measured, the level unevenness during 360 degrees of the circumference was as high as 24%. The signal reproduction jitter was 17%, which exceeded the reproduction jitter of 15% at which the error rate increased rapidly. It was an information record carrier with remarkably many errors, and a practical level could not be obtained.

[0053]

As described in detail above, by using the cellulose acetate ester for the light-transmitting layer of the information recording carrier, the birefringence of the information recording carrier can be reduced, and stable signal reproduction in a high NA reproducing device can be achieved. To Further, the birefringence of the information recording carrier can be reduced even with a blue-violet laser by making the light transmitting layer of the information recording carrier according to the present invention a cellulose acetate ester having a transmittance of 70% or more of light having a wavelength of λ = 350 to 450 nm. This enables stable signal reproduction in a high NA reproducing apparatus.

[Brief description of the drawings]

FIG. 1 is a sectional view showing a first embodiment of an information recording carrier according to the present invention.

FIG. 2 is a sectional view showing a second embodiment of the information recording carrier according to the present invention.

FIG. 3 is a sectional view showing a third embodiment of the information recording carrier according to the present invention.

FIG. 4 is a sectional view showing a fourth embodiment of the information recording carrier according to the present invention.

FIG. 5 is a sectional view showing a fifth embodiment of the information recording carrier according to the present invention.

FIG. 6 is a diagram showing a basic molecular structure of cellulose.

FIG. 7 is a sectional view showing a conventional information recording carrier.

[Explanation of symbols]

 1-5 Information recording carrier 11 Translucent layer 12 Recording layer 13 Support 14 Adhesive layer

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) G11B 11/105 531 B41M 5/26 W F term (Reference) 2H111 EA03 EA04 EA22 EA23 EA25 EA27 EA32 FA11 FA30 FB03 FB05 FB09 FB12 FB21 FB42 4J038 BA051 GA03 NA01 NA18 PB11 5D029 HA07 LA03 LB01 LC04 NA12 5D075 EE05 FG04

Claims (8)

[Claims] 1. An information recording carrier capable of reading an information signal by optical means, comprising: a support; a recording layer formed on the support, for recording an information signal; and a recording layer formed on the recording layer. And a light-transmitting layer that transmits light, wherein the light-transmitting layer is formed of cellulose acetate. 2. The information recording carrier according to claim 1, wherein the cellulose acetate has two or more esterified hydroxyl groups. 3. The light-transmitting layer has a wavelength λ = 350 to 450 nm.
The information recording carrier according to claim 1 or 2, wherein the light transmittance of the cellulose acylate is 70% or more. 4. The support according to claim 1, wherein a fine pattern is formed on the side of the recording layer.
An information recording carrier according to any one of claims 3 to 3. 5. The information recording carrier according to claim 1, wherein said recording layer comprises a highly reflective material. 6. The information recording carrier according to claim 1, wherein said recording layer has a coloring material. 7. The information recording carrier according to claim 1, wherein said recording layer comprises a phase change material. 8. The information recording carrier according to claim 1, wherein said recording layer comprises a magneto-optical material.