JP2008087476A - Optical recording medium - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical recording medium which is excellent in jitter characteristics, has good recording/reproducing characteristics, and carries out very high density recording. <P>SOLUTION: The optical recording medium 20 comprises: a substrate 21 on which a guiding groove is formed; a layer 23 having an optical reflection function on the substrate21; a recording layer 22 having a specific porphyrin compound as a main component; and a cover layer 24 for transmitting recording reproducing light being incident to the recording layer 22, in this order. When a guiding groove part on a remote side from the surface where the recording/reproducing light beam is incident to the cover layer 24 is employed as a recording groove, the reflection light intensity of a recording pit part formed on the recording groove part is higher than a reflection light intensity in the recording pit part in the no-record state. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an optical recording medium, and more particularly to an optical recording medium having a recording layer containing a dye.

  In recent years, blue lasers capable of ultra-high density recording have been rapidly developed, and write-once type optical recording media corresponding thereto have been developed. In particular, development of a dye-coated write-once medium that enables efficient production at a relatively low cost is strongly desired. In a conventional dye-coated write-once optical recording medium, a recording layer made of an organic compound containing dye as a main component is irradiated with laser light, and optical (refractive index / absorption) changes due to decomposition and alteration of the organic compound. Recording pits are formed mainly by generating them. The recording pit portion is not only optically changed, but is usually accompanied by deformation due to volume change of the recording layer, formation of a mixed portion of the substrate and dye due to heat generation, substrate deformation (mainly rising due to substrate expansion), and the like (see, for example, Patent Document 1) ).

  The optical behavior of the organic compound used in the recording layer with respect to the laser wavelength used for recording / reproducing, and the thermal behavior such as decomposition / sublimation and heat generation associated with it are important factors for forming good recording pits. . Therefore, it is necessary to select a material having an appropriate optical property and decomposition behavior for the organic compound used for the recording layer.

  In the first place, in a conventional write-once medium, particularly a CD-R or DVD-R, a read-only recording medium (ROM) in which a reflective film such as Al, Ag, Au is coated on a concave pit formed in advance on a substrate. The purpose is to maintain reproduction compatibility with the medium), and to achieve a reflectivity of approximately 60% or higher and, similarly, a high degree of modulation exceeding approximately 60%. First, in order to obtain a high reflectance in an unrecorded state, the optical properties of the recording layer are defined. Usually, a refractive index n of about 2 or more and an extinction coefficient of about 0.01 to 0.3 are required in an unrecorded state (see, for example, Patent Document 2).

  In a recording layer containing a dye as a main component, it is difficult to obtain a high degree of modulation of 60% or more only by such a change in optical properties due to recording. That is, since the amount of change in the refractive index n and the extinction coefficient k is limited in the case of an organic pigment, the change in reflectance in a planar state is limited.

Therefore, a method of apparently increasing the change in reflectivity (decrease in reflectivity) at the recording pit part is used by using the interference effect of the reflected light from both parts due to the phase difference between the reflected light at the recorded pit part and the unrecorded part. Has been. That is, the same principle as that of a phase difference pit such as a ROM medium is used, and in the case of an organic recording layer whose refractive index change is smaller than that of an inorganic substance, it is rather advantageous to mainly use a change in reflectance due to the phase difference. Has been reported (see Patent Document 3). In addition, a study that comprehensively considers the above-described recording principle has been performed (see Non-Patent Document 1).
Hereinafter, a portion recorded as described above (sometimes referred to as a recording mark portion) is referred to as a recording pit, a recording pit portion, or a recording pit portion regardless of its physical shape.

  FIG. 1 is a diagram for explaining a write-once medium (optical recording medium 10) having a recording layer mainly composed of a dye having a conventional configuration. As shown in FIG. 1, an optical recording medium 10 is formed by forming at least a recording layer 12, a reflective layer 13, and a protective coating layer 14 in this order on a substrate 11 in which grooves are formed. A recording / reproducing light beam 17 is incident through 11 and irradiates the recording layer 12. The thickness of the substrate 11 is usually 1.2 mm (CD) or 0.6 mm (DVD). Further, the recording pit is formed in a portion of the substrate groove portion 16 called a normal groove on the side close to the surface 19 on which the recording / reproducing light beam 17 is incident, and is not formed in the substrate groove portion 15 on the far side.

  In these known documents described above, the refractive index change before and after recording of the recording layer 12 containing the dye is made as large as possible, while the shape change of the recording pit portion, that is, the recording pit portion formed in the groove Thus, the groove shape changes (the substrate 11 swells or sinks and the groove depth changes equivalently), and the film thickness changes (the film thickness is transparent due to expansion and contraction of the recording layer 12). It is also reported that the (change) effect contributes to the phase difference change.

  In the recording principle as described above, in order to increase the reflectance at the time of non-recording and to decompose the organic compound by laser irradiation and cause a large refractive index change (this can obtain a large degree of modulation), Normally, the recording / reproducing light wavelength is selected so as to be located at the bottom of the long wavelength side of the large absorption band. This is because the bottom of the large absorption band on the long wavelength side is a wavelength region having an appropriate extinction coefficient and a large refractive index.

  However, no material has been found that has a conventional optical property with respect to the blue laser wavelength. In particular, in the vicinity of 405 nm, which is the center of the oscillation wavelength of a blue semiconductor laser currently in practical use, an organic compound having an optical constant comparable to the optical constant required for the recording layer of a conventional write-once optical recording medium is present. There are few, and it is still in the search stage. Furthermore, in a write-once optical recording medium having a conventional dye recording layer, since the main absorption band of the dye exists in the vicinity of the recording / reproducing light wavelength, the wavelength dependence of the optical constant increases (the optical constant varies greatly depending on the wavelength). Recording characteristics such as recording sensitivity, modulation, jitter (jitter), error rate, reflectivity, etc. greatly change with respect to fluctuations in recording / reproducing light wavelength due to individual differences of lasers, environmental temperature changes, etc. There is a problem.

  For example, the idea of recording using a dye recording layer having absorption in the vicinity of 405 nm has been reported. However, the dyes used therein are required to have the same optical characteristics and functions as in the past. (See, for example, Patent Document 4). Next, in the write-once type optical recording medium 10 using the conventional recording layer 12 mainly composed of a dye as shown in FIG. 1, the groove shape and the thickness of the substrate groove portion 16 and the substrate groove portion 15 of the recording layer 12 are shown. It has been reported that the distribution of the above must be properly controlled (see, for example, Patent Document 5).

That is, as described above, only a dye having a relatively small extinction coefficient (about 0.01 to 0.3) with respect to the recording / reproducing light wavelength can be used from the viewpoint of securing a high reflectance. Therefore, it is impossible to reduce the film thickness of the recording layer 12 in order to obtain light absorption necessary for recording in the recording layer 12 and to increase a change in phase difference before and after recording. As a result, the film thickness of the recording layer 12 is usually about λ / (2n _s ) (n _s is the refractive index of the substrate 11), and the dye used for the recording layer 12 is buried in the groove to cause crosstalk. In order to reduce this, it is necessary to use the substrate 11 having a deep groove. Since the recording layer 12 containing a dye is usually formed by a spin coating method (coating method), it is more convenient to fill the dye in a deep groove to increase the thickness of the recording layer 12 in the groove. On the other hand, in the coating method, there is a difference in the recording layer thickness between the substrate groove portion 16 and the substrate groove portion 15, and this difference in the recording layer thickness is generated even when a deep groove is used. It is effective in obtaining.

That is, the groove shape defined by the surface of the substrate 11 in FIG. 1 and the groove shape defined by the interface between the recording layer 12 and the reflective layer 13 are not recorded at the proper values unless both are maintained at appropriate values. Both the signal characteristics and the tracking signal characteristics cannot be maintained well. The depth of the groove usually needs to be close to λ / (2n _s ) (λ is the wavelength of the recording / reproducing light beam 17 and n _s is the refractive index of the substrate 11). In R, the range is about 150 nm. The formation of the substrate 11 having such a deep groove becomes very difficult, which is a factor of deteriorating the quality of the optical recording medium 10.

  In particular, in an optical recording medium using blue laser light, if λ = 405 nm, a deep groove close to 100 nm is required, while the track pitch is set to 0.2 μm to 0.4 μm for high density. Many. It is even more difficult to form such a deep groove with such a narrow track pitch, and in practice, mass production is almost impossible with conventional polycarbonate resins. That is, a medium using blue laser light is likely to be difficult to mass-produce with the conventional configuration.

  Further, many of the embodiments in the above publication are examples in FIG. 1 showing a conventional disk configuration, but in order to realize high-density recording using a blue laser, a configuration called so-called film surface incidence is noted. A configuration using an inorganic material recording layer such as a phase change recording layer has been reported (see Non-Patent Document 2). In a configuration called film surface incidence, contrary to the prior art, at least a reflective film, a recording layer, and a cover layer are formed in this order on a substrate on which grooves are formed, and for recording and reproduction via the cover layer. Is incident on the recording layer. The thickness of the cover layer is usually about 100 μm in a so-called Blu-ray disc (Non-Patent Document 3). The recording / reproducing light is incident from such a thin cover layer side to the objective lens for focusing thereof with a higher NA (numerical aperture, usually 0.7 to 0.9, 0. 85). When a high NA objective lens is used, a thickness of about 100 μm is required to reduce the influence of aberration due to the thickness of the cover layer. Many examples of such blue wavelength recording and film surface incident layer configurations have been reported (see Non-Patent Document 4, for example, Patent Document 6). There are also many reports on related technologies (see Non-Patent Document 5 to Non-Patent Document 8, for example, Patent Documents 7 to 9).

“Proceedings of International Symposium on Optical Memory” (USA), Vol. 4, 1991, p. 99-108 “Proceedings of SPIE” (USA), Volume 4342, 2002, p. 168-177 "Optical Disc Dismantling New Book", Nikkei Electronics, Nikkei BP, 2003, Chapter 3 “Japanese Journal of Applied Physics” (Japan), vol. 42, 2003, p. 1056-1058 Heitaro Nakajima and Hiroshi Ogawa, “Compact Disc Reader” revised edition, Ohmsha, 1996, p. 168 “Japanese Journal of Applied Physics” (Japan), vol. 42, 2003, p. 914-918 “Japanese Journal of Applied Physics” (Japan), 39, 2000, p. 775-778 “Japanese Journal of Applied Physics” (Japan), vol. 42, 2003, p. 912-914 Japanese Patent Laid-Open No. 3-6943 JP-A-2-132656 JP-A-57-501980 JP 2002-301870 A JP-A-4-182944 JP 2004-30864 A JP 2003-266554 A JP 2001-331936 A JP 2005-504649 A International Publication No. 06/009107 Pamphlet

  By the way, in a film surface incident type phase change medium that has been developed in advance, a recording mark is formed in the groove of the cover layer as viewed from the incident light side. This is the same as recording on a substrate groove on a conventional substrate when viewed from the incident light side, and means that it can be realized with almost the same layer configuration as CD-RW and DVD-RW. Has been obtained. On the other hand, in the case of a recording layer containing a dye as a main component, particularly a coating type, recording in the cover layer groove is not easy. This is because, usually, spin coating on a substrate tends to collect a dye in a groove portion on the substrate. Even if a dye is applied to the substrate groove portion with an appropriate film thickness, since a considerable amount of the dye usually accumulates in the substrate groove portion, the recording pits (record marks) formed in the cover layer groove portion are covered with the cover layer. Since it is easy to protrude into the groove portion, the crosstalk becomes large and the track pitch cannot be reduced, so that there is a limit to increasing the density.

  However, most of the known documents mentioned above mainly focus on the fact that the reflected light intensity is reduced by recording in the cover layer groove on the side closer to the incident light side as in the past. Alternatively, attention is paid to the decrease in reflectance that occurs in a flat state without considering the change in the phase of the reflected light due to the step of the groove. Alternatively, it is assumed that a change in reflectance in a planar state in which a phase difference is not used as much as possible is used. Under such preconditions, the problem of crosstalk in cover layer groove recording cannot be solved, and the recording layer forming process by solution coating does not suit. In other words, it cannot be said that the phase change is effectively utilized to realize good recording characteristics in the cover layer groove portion. In particular, in mark length modulation recording, there has been no example that has a practical recording power margin with respect to all mark lengths from the shortest mark length to the longest mark length, and has realized good jitter characteristics. Some of the inventors have developed an optical recording medium in which reflected light intensity is increased by recording on a substrate groove portion on the side far from the incident light side in Patent Document 10, but all of jitter, recording sensitivity, etc. In order to satisfy the above characteristics, further improvement was necessary.

  As described above, a film surface incident type write-once medium that has a recording layer mainly composed of a high-performance, low-cost dye comparable to conventional CD-R and DVD-R is not yet known. is the current situation.

  Further, a result of investigation on a film surface incident type medium for blue laser having a recording layer mainly composed of a porphyrin dye having a large extinction coefficient of about 0.5 to 1.3 (Japanese Patent Laid-Open No. 2004-160742). However, with respect to recording characteristics, there is no example that realizes good values for jitter and push-pull signals, which are practical indicators. The reason is as follows.

Here, the optical characteristics of the recording layer in an unrecorded state (before recording) at the recording / reproducing light wavelength λ are represented by a complex refractive index n _d ^* = n _d −i · k _d, where the real part n _d represents the refractive index, imaginary The part k _d is called an extinction coefficient. Recording pit part, i.e., after the recording, n _d is 'a = n _d -δn _d, k _d is k _d' n _d is assumed to vary in = k _d -δk _d.

  Furthermore, the distinction between the two terms “reflectance” and “reflected light intensity” used below will be described. The reflectance is the ratio of the reflected energy light intensity to the incident energy light intensity in the reflection of light generated between two substances having different optical characteristics in a planar state. Even if the recording layer is planar, the reflectance changes if the optical characteristics change. On the other hand, the reflected light intensity is the intensity of light that returns to the detector when the recording medium surface is read through the focused recording / reproducing light beam and the objective lens.

  In the ROM medium, since the pit portion and the unrecorded portion (pit peripheral portion) are covered with the same reflective layer, the reflectance of the reflective film is the same between the pit portion and the unrecorded portion. On the other hand, due to the phase difference between the reflected light generated at the pit portion and the reflected light from the unrecorded portion, the reflected light intensity appears to change (usually appears to decrease) due to the interference effect. . Such an interference effect is caused when the recording pit is locally formed and the recording / reproducing light beam diameter includes the recording pit portion and the surrounding unrecorded portion. The reflected light is caused by interference due to the phase difference. On the other hand, in a recording medium in which some optical change occurs in the recording pit portion, a change in reflectance occurs due to a change in complex refractive index of the recording film itself even in a flat state without irregularities. This is referred to as “reflectance change occurring in a planar state” in the present embodiment. In other words, this is the change in reflectance that occurs in the recording film depending on whether the entire recording film plane is the complex refractive index before recording or the complex refractive index after recording. This is a change in reflected light intensity that occurs even without it. On the other hand, when the optical change of the recording layer is a local pit part, two-dimensional interference of reflected light occurs when the phase of the reflected light of the recording pit part and the phase of the reflected light of the peripheral part are different. The reflected light intensity appears to change locally around the recording pit.

Thus, in this embodiment, the reflected light intensity change that does not take into account two-dimensional interference of reflected light with different phases is referred to as “reflected light intensity change that occurs in a planar state” or “reflected light intensity change in a planar state”. The reflected light intensity change taking into account the two-dimensional interference of the reflected light with different phases between the recording pit and its peripheral portion is “(local) reflected light intensity change caused by phase difference” or “reflected light intensity due to phase difference” “Change” is considered separately.
In general, when a sufficient reflected light intensity change, that is, an amplitude (or optical contrast) of a recording signal is obtained by “a change in reflected light intensity due to a phase difference”, a change in the refractive index of the recording layer 22 itself occurs. Must be very big. For example, in CD-R and DVD-R, the real part of the refractive index before recording of the dye recording layer is 2.5 to 3.0, and after recording, it is required to be about 1 to 1.5. It imaginary part k _d of the recording before the complex refractive index of the dye recording layer is less than about 0.1 has been considered preferable for obtaining a high reflectance ROM compatibility in the unrecorded state. In addition, the recording layer 22 needs to be as thick as 50 nm to 100 nm. Without such a thickness, most of the light passes through the recording layer 22 and sufficient reflected light intensity change and light absorption necessary for pit formation cannot occur. In such a thick dye recording layer, the local phase change due to deformation at the pit portion is merely used as an auxiliary. On the other hand, in the above-mentioned ROM medium, it is considered that there is no local refractive index change at the recording pit portion and only “reflected light intensity change due to phase difference” is detected. In order to obtain good recording quality, when the reflected light intensity change at the recording pit portion occurs by mixing the above two kinds of reflected light intensity changes, it is desirable to strengthen both. The fact that the two types of reflected light intensity changes are strengthened means that the direction of the reflected light intensity change that occurs in each, that is, whether the reflected light intensity increases or decreases.

Now, of the complex refractive index of the recording layer, a decrease in the extinction coefficient k _d causes an increase in reflectivity and thus an increase in reflected light intensity in the “planar reflected light intensity change”. In the conventional CD-R and DVD-R, as described above, the change in the extinction coefficient is recorded by using the decrease in the reflected light intensity at the recording pit portion (hereinafter sometimes referred to as HtoL recording). Therefore, it was not preferable. Therefore, there is a tendency that n _d with large k _d in an unrecorded decreases, than it had used way come reproducing light wavelength to the long wavelength side of the main absorption band. Such a method of using a dye requires a large value of n _d of about 2.5 to 3 as described above, but a dye having such a large n _d near 400 nm is practically difficult to obtain. If the conventional recording principle is used as it is, there is a problem that good recording characteristics cannot be obtained.

The present invention has been made to solve such problems.
That is, an object of the present invention is to provide an optical recording medium that is excellent in jitter characteristics and tracking characteristics, has good recording / reproducing characteristics, and is capable of extremely high density recording.

  In view of the above problems, the present inventors have conducted intensive studies on a film surface incident type medium for blue lasers having a recording layer mainly composed of a porphyrin dye having a specific structure. As a result, the guide groove portion on the side farther from the surface on which the recording / reproducing light beam is incident on the cover layer is used as the recording groove portion, and the reflected light intensity of the recording pit portion formed in this recording groove portion is determined when the recording groove portion is unrecorded. It has been found that a film surface incident type medium having good recording characteristics can be obtained by recording so as to be higher than the reflected light intensity (hereinafter sometimes referred to as LtoH recording).

That is, the gist of the present invention is that the substrate on which the guide groove is formed,
A layer having a light reflecting function on the substrate;
A recording layer mainly composed of a porphyrin compound represented by the following general formula [I];
In an optical recording medium comprising in this order a cover layer capable of transmitting recording / reproducing light incident on the recording layer,
The recording / reproducing light wavelength λ is 350 nm to 450 nm,
When the recording / reproducing light beam obtained by converging the recording / reproducing light is a recording groove that is a guide groove on the side far from the surface on which the cover layer is incident,
In the optical recording medium, the reflected light intensity of the recording pit part formed in the recording groove part is higher than the reflected light intensity in the recording groove part when not recorded (claim 1).
(In the general formula [I], Ar ^{a1 to} Ar ^a4 each independently represent an aromatic ring, and each may have a plurality of substituents.
R ^{a1 to} R ^a8 each independently represents a hydrogen atom or an arbitrary substituent,
M ^a represents a divalent or higher valent metal cation. However, when M ^a is trivalent or more, the molecule may further have a counter anion so that the whole molecule is neutral. )

  Further, in the recording pit portion, it is preferable that a cavity is formed in the inside of the recording layer or an interface with a layer adjacent to the recording layer, and the recording layer is accompanied by a shape change that expands toward the cover layer side ( Claim 2).

The recording layer preferably contains a tetraarylporphyrin compound represented by the general formula [II] as a main component (claim 3).
(In the formula [II], X ^{1 to} X ⁴ each independently represent an atom having a valence of 4 or more, and when X ^{1 to} X ⁴ are an atom having a valence of 5 or more, X ^{1 to} X ⁴ are further optional. May have a substituent, and when X ^{1 to} X ⁴ are atoms having a valence of 6 or more, each of them may have two = Q ¹ to = Q ⁴ , in which case the two Q ^{1 to} Q ⁴ may be the same or different.
Q ^{1 to} Q ⁴ each independently represent a group 16 atom of the periodic table.
Ar ^{1 to} Ar ⁴ each independently represent an aromatic ring, and each may have a substituent other than X ^{1 to} X ⁴ .
R ^{1 to} R ⁸ each independently represents an organic group having 20 or less carbon atoms,
R ^{9 to} R ¹⁶ each independently represents a hydrogen atom or an electron-withdrawing substituent,
M represents a divalent or higher valent metal cation. However, when M is trivalent or more, the molecule may further have a counter anion so that the whole molecule is neutral.
R ¹ and R ² , R ³ and R ⁴ , R ⁵ and R ⁶ , R ⁷ and R ⁸ may be bonded to form a ring. )

  Moreover, it is preferable to further provide an interface layer between the recording layer and the cover layer to prevent mixing of the recording layer material and the cover layer material. (Claim 4)

  Further, it is desirable to further provide an intermediate layer between the layer having the light reflection function and the recording layer. (Claim 5)

  Furthermore, the intermediate layer preferably contains at least one element selected from the group consisting of Ta, Nb, V, W, Mo, Cr, and Ti. (Claim 6)

Further, when the interface on the recording layer side of the layer having the light reflecting function is a reflection reference surface, and the guide groove portion not forming the recording pit portion is an inter-recording groove portion, the recording defined by the reflection reference surface The step d _GL between the groove and the recording groove is preferably 30 to 70 nm.

  Thus, according to the present invention, an optical recording medium having excellent jitter characteristics and capable of extremely high density recording can be obtained.

Hereinafter, the best mode for carrying out the present invention (hereinafter, an embodiment of the present invention) will be described. The present invention is not limited to the following embodiments, and various modifications can be made within the scope of the invention.
FIG. 2 is a partial cross-sectional view schematically showing the layer structure of the optical recording medium according to the embodiment of the present invention. An optical recording medium 20 (optical recording medium of the present embodiment) shown in FIG. 2 is a write-once type optical recording medium having a film surface incident configuration, and has a layer (at least a reflective function) on a substrate 21 on which guide grooves are formed. As will be described later with reference to FIG. 2, the reflective layer 23), a recording layer 22 having a light absorption function mainly composed of a dye that absorbs recording / reproducing light in an unrecorded (before recording) state, and a cover layer 24. Are sequentially stacked, and recording / reproduction is performed by entering a recording / reproducing light beam 27 collected from the cover layer 24 via the objective lens 28. In other words, the optical recording medium 20 has a “film surface incidence configuration” (also referred to as a reverse stack). In the following, the layer having a reflection function is simply referred to as “reflection layer 23”, and the recording layer having a light absorption function mainly composed of a dye is simply referred to as “recording layer 22”. As described above, the conventional configuration described with reference to FIG. 1 is referred to as a “substrate incident configuration”.

  When the recording / reproducing light beam 27 is incident on the cover layer 24 side of the film surface incident structure described with reference to FIG. 2, for high-density recording, the numerical aperture (hereinafter referred to as NA) = 0.6-0. An objective lens having a high NA of about 9 is used. In the present invention, the recording / reproducing light wavelength λ is particularly preferably in the wavelength range of 350 nm to 450 nm.

  In this embodiment, in FIG. 2, the guide groove portion (recording / reproducing light beam is incident on the side far from the incident surface (surface 29 on which the recording / reproducing light beam is incident) of the recording / reproducing light beam 27 on the cover layer 24 is incident. The recording groove portion) is used as a recording groove portion, and recording is performed such that the reflected light intensity of the recording pit portion formed in the recording groove portion is higher than the reflected light intensity when the recording groove portion is not recorded. The main mechanism is that an increase in reflected light intensity is due to a decrease in extinction coefficient at the recording pit portion and a phase change of reflected light. The phase change of the reflected light is a change before and after recording of the reciprocal optical path length of the reflected light in the recording groove.

  Here, in the film surface incident type optical recording medium 20, the guide groove portion (coincidence with the groove portion of the substrate 21) far from the incident surface (surface 29 on which the recording / reproducing light beam is incident) of the recording / reproducing light beam 27 on the cover layer 24. The cover layer groove portion (in-groove) 25, the guide groove portion near the surface 29 on which the recording / reproducing light beam 27 is incident (matching the groove portion of the substrate 21), and the cover layer groove portion (on-groove) 26. (The names of on-groove and in-groove are based on Non-Patent Document 2.)

More specifically, the present invention can be realized by devising the following.
(1) Grooves having a depth such that the phase difference Φ between the reflected light from the unrecorded cover layer groove portion and the reflected light from the cover layer groove portion is approximately π / 2 to π are formed on the substrate 21. The thickness of the recording layer in the cover layer groove portion (in-groove) is made to be a thin film that is thinner than the groove depth, while the thickness in the cover layer groove portion (on-groove) is almost zero. A recording layer 22 mainly composed of a thin dye is provided. A recording / reproducing light beam is irradiated to the gap between the cover layers from the cover layer side to cause alteration of the recording layer, and an increase in reflected light intensity due to a phase change is utilized in the recording pit. Thereby, in the film surface incident structure, the performance of the coating type dye medium is greatly improved as compared with the conventional on-groove and HtoL recording. In addition, recording at a high track pitch density (for example, 0.2 μm to 0.4 μm) with small crosstalk becomes possible. Further, it becomes easy to form a groove with such a high track pitch.
In addition, since the dye medium by the coating type (spin coating) has a characteristic that the dye is preferentially collected in the substrate groove portion, the recording layer thickness in the cover layer groove portion (in-groove) is thinner than the groove depth. On the other hand, there is also a process advantage that a very thin dye recording layer in which the film thickness at the cover layer groove (on-groove) is almost zero is easily formed.

(2) For the change of the refractive index in the recording pit portion, the formation of cavities in the recording layer 22 or at the interface portion thereof is used. Inside the cavity, it can be considered that n _d ′ ≈1 and k _d ′ ≈0. In addition, it is preferable to use a deformation that the recording layer 22 swells in the direction of the cover layer 24, and at least the recording layer 22 side of the cover layer 24 is provided with a soft deformation promoting layer made of an adhesive having a glass transition point of room temperature or less. To facilitate the deformation. As a result, the direction of the phase change in which the reflected light intensity increases due to recording is aligned (the distortion of the recording signal waveform is eliminated), and the phase change amount (recording signal amplitude) can be increased even with a relatively small refractive index change. Further, the increase in reflected light intensity due to the change in reflectance caused in the planar state can be used by actively utilizing the decrease in the extinction coefficient of the recording layer.
As described above, as a main component, a substrate on which guide grooves are formed, at least a layer having a light reflection function, and a dye having a light absorption function with respect to a recording / reproducing light wavelength in an unrecorded state are included on the substrate. A recording layer and a cover layer on which recording / reproducing light is incident on the recording layer in this order, and a side far from a surface on which a recording / reproducing light beam obtained by focusing the recording / reproducing light is incident on the cover layer When the recording groove portion is a recording groove portion, an optical recording medium can be realized in which the reflected light intensity of the recording pit portion formed in the recording groove portion is higher than the reflected light intensity of the unrecorded portion in the recording groove portion, It is characterized in that a recording signal having a high modulation degree and no distortion can be obtained from the recording pit portion.

(3) The porphyrin compound represented by the general formula [I] is used as a dye having a light absorption function as a main component of the recording layer.
Since the present porphyrin compound has a very steep and large main absorption band on the longer wavelength side near the recording / reproducing light wavelength of 400 nm, the following advantages are obtained when used as an optical recording medium having a recording / reproducing wavelength of around 400 nm. There is. The present porphyrin compound has a relatively large extinction coefficient before recording of about 0.5 to 1.3, and after recording, it is efficiently decomposed to form a cavity, so that it decreases to nearly zero. That is, the amount of decrease in the extinction coefficient before and after recording is very large. For this reason, the amount of absorbed light is greatly reduced in the recording pit portion, and on the other hand, the reflected light intensity is remarkably increased. Therefore, a large signal amplitude can be easily obtained in a recording method in which the reflected light intensity increases in the recording pit portion after recording. . Furthermore, since the extinction coefficient is large, light is well absorbed at the time of recording, so that the power at the time of recording can be used efficiently, and the recording sensitivity can be improved. On the other hand, there is a feature that a relatively small pigment having a refractive index of about 0.5-1 can be selected. The optical groove depth calculated when the dye is deposited in the recording groove is the product of the absolute groove depth and the refractive index, and this value is the refractive index when the same groove depth is used. It fluctuates with the value of. When the refractive index is small, the optical groove depth can be made small. Therefore, even in a configuration devised to obtain good jitter characteristics, the tracking signal can be easily controlled within a range where tracking is not lost. Therefore, when compared with the tracking signal of a Blu-ray disc using an inorganic material recording layer that has already been put on the market, the same level of signal characteristics can be obtained, and when the recording medium of the present invention is used in an optical recording / reproducing apparatus. Easy to ensure compatibility.
The porphyrin compound having the configuration of the present application is also easily solubilized in fluorine alcohol or the like, and is suitable for a mass production process by a spin coat method.

  Here, a reflection reference plane is defined for the following explanation. As the reflection reference surface, the recording layer side interface (surface) of the reflection layer to be the main reflection surface is taken. The main reflecting surface refers to a reflecting interface that contributes the most to the reflected reflected light. In FIG. 2 showing the optical recording medium 20 to which the present embodiment is applied, the main reflection surface is at the interface between the recording layer 22 and the reflection layer 23. This is because the target recording layer 22 in the optical recording medium 20 to which the present embodiment is applied is relatively thin and has a low absorption rate, so that most of the light energy simply passes through the recording layer 22. This is because the boundary with the reflecting surface can be reached. There are other interfaces where reflection can occur, and the reflected light intensity of the reproduction light is determined by the total contribution of the reflected light intensity from each interface and the phase. In the optical recording medium 20 to which the present embodiment is applied, since the contribution of reflection on the main reflection surface is large, only the intensity and phase of light reflected on the main reflection surface need be considered. For this reason, the main reflection surface is used as a reflection reference surface.

  In the present embodiment, first, pits (marks) are formed in the cover layer inter-groove portion 25 in FIG. This is because the recording layer 22 formed mainly by a spin coating method that is easy to manufacture is used. On the contrary, by using the coating method, the recording layer thickness of the cover layer groove portion (substrate groove portion) 25 is naturally larger than the recording layer thickness of the cover layer groove portion (substrate groove portion) 26. , The thickness is only “a change in reflected light intensity in a flat state”, and it is not thick enough to obtain a sufficient change in reflected light intensity. A large reflected light intensity change (high modulation degree) can be realized at the pit portion formed in the cover layer groove portion 25 with the layer thickness.

  In the present embodiment, when using the change in the phase of the reflected light in the recording pit portion, the step between the cover layer groove portion 25 and the cover layer groove portion 26 formed by the reflection reference surface in FIG. Is characterized by causing a change that appears optically shallower than before recording. At that time, in order to stabilize the tracking servo, first, a phase change that does not cause inversion of the push-pull signal and increases the reflected light intensity after recording compared to the reflected light intensity before recording is performed. It occurs in the recording pit.

  The layer configuration of the optical recording medium 20 having the film surface incident configuration to which the present embodiment shown in FIG. 2 is applied will be described in comparison with the optical recording medium 10 having the substrate incident configuration in FIG. Here, in order to distinguish and explain the layer structure of the optical recording medium 10 shown in FIG. 1 and the optical recording medium 20 shown in FIG. 2 by focusing on the phase of light reflected by the reflection reference plane, FIG. In the case of recording in the groove portion 16, the case of recording in the cover layer groove portion 25 and the cover layer groove portion 26 in FIG. 2 is examined with reference to FIGS. 3, 4, and 5.

FIG. 3 is a diagram for explaining the reflected light of the recording / reproducing light beam 17 incident from the substrate 11 side in the substrate incidence configuration of FIG. 1 which is a conventional configuration.
FIG. 4 is a diagram for explaining the layer structure of the film surface incident type medium (optical recording medium 20) and the phase difference when recording is performed in the cover layer groove portion 25. FIG.
FIG. 5 is a diagram for explaining the layer structure of the film surface incidence type medium (optical recording medium 20) and the phase difference when recording is performed in the cover layer groove 26. FIG.
4 and 5 illustrate the reflected light of the recording / reproducing light beam 27 incident from the incident surface 28 side of the cover layer 24 having the film surface incident structure in the optical recording medium 20 having the film surface incident structure shown in FIG. FIG. 4 forms pits in the cover layer groove portion (substrate groove portion) 25 in the optical recording medium 20 to which the present embodiment is applied. In FIG. 5, for comparison of the effect of the present invention, pits are formed in the cover layer groove portion (inter-substrate groove portion) 26 with the same film surface incidence configuration.

  3, 4, and 5, (a) is a cross-sectional view including a recording pit before recording and (b) is a recording pit after recording. Hereinafter, a groove or an inter-groove portion that forms a recording pit is referred to as a “recording groove portion”, and a portion between them is referred to as a “recording groove inter-portion”. That is, in FIG. 3 of the conventional configuration, the substrate groove portion 16 is a “recording groove portion”, and the recording groove portion 15 is a “recording groove portion”. In FIG. 4 according to the present invention, the cover layer groove portion 25 is a “recording groove portion”, and the cover layer groove portion 26 is a “recording groove portion”. On the other hand, in FIG. 5 which is a comparative explanation, the cover layer groove portion 26 is a “recording groove portion”, and the cover layer groove portion 25 is a “recording groove portion”.

  First, in obtaining the phase difference between the reflected light of the recording groove and the reflected light of the recording groove, a phase reference plane is defined by A-A ′. 3, 4, and 5, in FIG. 3 (a) in each unrecorded state, AA ′ is the recording layer 12 / substrate 11 interface (FIG. 3 (a)) in the recording groove portion and recording, respectively. This corresponds to the recording layer 22 / cover layer 24 interface (FIG. 4A) in the groove portion and the recording layer 22 / cover layer 24 interface (FIG. 5A) in the recording groove portion. On the other hand, in FIG. 3, (b) of the post-recording state in FIGS. 3, 4 and 5, AA ′ represents the recording layer 12 (mixed layer 16m) / substrate 11 interface in the recording groove (FIG. 3 (b)). )), The recording layer 22 / cover layer 24 interface in the recording groove portion (FIG. 4B), and the recording layer 22 (mixed layer 26m) / cover layer 24 interface in the recording groove portion (FIG. 4B). ing. There is no optical difference depending on the optical path in front of the A-A ′ plane (incident side). Also, the reference reflection surface at the recording groove part before recording is BB ′, and the bottom of the recording groove part of the substrate 21 (FIG. 3) or the cover layer 24 (FIG. 4) before recording (recording layer 12 / substrate 11, recording layer 22 / The cover layer 24 interface) is defined by CC ′. Before the recording of FIGS. 3 and 5, A-A ′ and C-C ′ coincide.

The recording layer thickness at the substrate groove before recording is d _G , the thickness between the substrate grooves is d _L , the step between the recording groove and the recording groove on the reflection reference surface is d _GL , and the recording groove on the substrate surface Let d _GLS be the step in the _space . In the case of FIG. 3, d _GL depends on how the recording layer 12 is filled in the recording groove, and has a value different from d _GLS . In the case of FIGS. 4 and 5, the reflective layer 23 usually has substantially the same film thickness at the recording groove portion and the recording groove portion, although it depends on the covering condition between the recording groove portion and the recording groove portion of the reflection layer 23. Therefore, since the step on the surface of the substrate 21 is reflected as it is, d _GL = d _GLS .

The refractive index of the substrate 11 and 21 n _s, a refractive index of the cover layer 24 and n _c. Generally, the following changes occur due to the formation of recording pits. Recording pit part 16p, 25p, the refractive index of the recording layer 12 and 22 in 26p changes from n _d to _{n d '= n d -δn d} . Further, in the recording pit portions 16p, 25p, and 26p, mixing occurs between the recording layer 12 and the substrate 11 or the substrate 21 and the cover layer 24 material at the incident side interface of the recording layers 12 and 22, thereby forming a mixed layer. The Further, the recording layers 12 and 22 undergo volume change, and the position of the reflection reference plane (recording layer / reflection layer interface) moves. In general, the formation of a mixed layer between the organic substrate 11 or 21 or the cover layer 24 material and the metal reflective layer material is negligible. Therefore, the recording layer 12 / substrate 11 (FIG. 1), the recording layer 22 / cover layer 24 (FIG. 2) mixing of the recording layer 12 and the substrate 11 or recording layer 22 covering layer 24 material is placed between the thickness d _mix The mixed layers 16m, 25m, and 26m are formed. The mixing layer 16m, 25 m, the refractive index of _{26m, n s '= n s} -δn s ( FIG. _{3 (b)), n c} ' = n c -δn c ( FIG. 4 (b), the 5 ( b)).

At this time, the interface of the recording layer 12 / substrate 11 or the recording layer 22 / cover layer 24 moves by d _bmp after recording with reference to CC ′. As shown in FIGS. 3, 4, and 5, d _bmp is positive in the direction of moving into the recording layers 12 and 22. On the contrary, if d _bmp is negative, it means that the recording layers 12 and 22 expand beyond the CC ′ plane. Further, if the recording layer 12 / substrate 11 of FIG. 3, FIG. 4, the case of providing the interface layer that prevents mixing of the two between the recording layer 22 / cover layer 24 in FIG. 5 can be a d _mix = 0. However, the deformation of d _bmp can occur due to the volume change of the recording layers 12 and 22. It is considered that the influence of the refractive index change accompanying the d _bmp deformation of the substrate 21 or the cover layer 24 when the dye mixture does not occur is small and can be ignored.

On the other hand, the amount of movement of the reflection reference surface in the recording groove is defined as d _pit with reference to the position BB ′ of the reflection reference surface before recording. As shown in FIGS. 3, 4, and 5, d _pit is positive in the direction in which the recording layers 12 and 22 contract (the direction in which the reflection reference plane moves into the recording layers 12 and 22). On the contrary, if d _pit is negative, it means that the recording layers 12 and 22 expand beyond the BB ′ plane. The recording layer thickness after recording is
d _Ga = d _G −d _pit −d _bmp (1)
It becomes. Note that d _GL , d _G , d _L , d _mix , n _d , n _c , n _s , and d _Ga do not take negative values due to their definitions and physical characteristics.
A known method was used for modeling such a recording pit and for estimating the phase described below (Non-Patent Document 1).

Now, the phase difference of the reproduction light (reflected light) between the recording groove portion and the recording groove portion on the phase reference plane AA ′ is obtained before and after recording. The phase difference of the reflected light between the recording groove part and the recording groove part before recording is Φb, and after recording, the phase difference of the reflected light between the recording pit parts 16p, 25p, 26p and the recording groove part is Φa, and is generally referred to as Φ. Both
Φ = Φb or Φa
= (Reflected light phase between recording grooves)-(Phase of recording groove (including pit after recording)) (2)
Φ = Φb or Φa
= (2π / λ) · 2 · {(optical path length of recording groove portion) − (optical path length of recording groove portion (including pit portion after recording))} (3)
Define as

Here, the reason why the coefficient 2 is multiplied in the expression (3) is to consider the round-trip optical path length.
In FIG.
Φb ₁ = (2π / λ) · 2 · (n _s · d _GL + n _d · d _L −n _d · d _G )
= (4π / λ) · {n _s · d _GL −n _d · (d _G −d _L )} (4)
_{Φa 1 = (2π / λ)} · 2 · {n s · d GL + n s · (d mix -d bmp) + n d · d L - _{[(n d -δn d) · (} d G -d pit -d _bmp ) + (n _s −δn _s ) · d _mix ]}
= Φb ₁ + ΔΦ (5)
However,
ΔΦ = (4π / λ) {(n _d −n _s ) · d _bmp + n _d · d _pit + δn _s · d _mix + δn _d · (d _G −d _pit −d _bmp )} (6)
It is. Further, since the recording groove portion is in front of the recording groove portion when viewed from the incident side, Φb ₁ > 0.

On the other hand, in FIG.
_{Φb 2 = (2π / λ)} · 2 · {n d · d L - _{[n d · d G + n c} · (d L + d GL -d G) ]}
= (4π / λ) · {(n _c −n _d ) · (d _G −d _L ) −n _c · d _GL } (7)
_{Φa 2 = (2π / λ)} · 2 · {(n d · d L - _{[n c · (d L + d} GL -d G + d bmp -d mix) + (n d -δn d) · (d G - d _pit −d _bmp ) + (n _c −δn _c ) · d _mix ])
= Φb ₂ + ΔΦ (8)
However,
ΔΦ = (4π / λ) {(n _d −n _c ) · d _bmp + n _d · d _pit + δn _c · d _mix + δn _d · (d _G −d _pit −d _bmp )} (9)
It is. Further, since the recording groove portion is behind the recording groove portion when viewed from the incident side, Φb ₂ <0.

Furthermore, in FIG.
Φb ₃ = (2π / λ) · 2 · {n _d · d _G + n _c · (d _L + d _GL −d _G ) −n _d · d _L }
= (4π / λ) · {(n _d −n _c ) · (d _G −d _L ) + n _c · d _GL } (10)
_{Φa 3 = (2π / λ)} · 2 · {n d · d G + n c · (d L + d GL -d G) + n c · (d mix -d bmp) - [(n _d -δn _d) · ( d _L −d _pit −d _bmp ) + (n _c −δn _c ) · d _mix ]}
= Φb ₃ + ΔΦ (11)
However,
ΔΦ = (4π / λ) {(n _d −n _c ) · d _bmp + n _d · d _pit + δn _c · d _mix + δn _d · (d _L −d _pit −d _bmp )} (12)
It is. In addition, since the recording groove portion is in front of the recording groove portion when viewed from the incident side, Φb ₃ > 0.

ΔΦ is a phase change in the pit portion caused by recording, and can be expressed by the same equation in any case except that d _L and d _G are interchanged in equation (12). Hereinafter, Φb ₁ , Φb ₂ , and Φb ₃ are collectively represented by Φb, and Φa ₁ , Φa ₂ , and Φa ₃ are collectively represented by Φa.
The degree of modulation m of the signal produced by ΔΦ is
m∝1−cos (ΔΦ) = sin ² (ΔΦ / 2) (13)
≒ (ΔΦ / 2) ² (14)
It becomes. The rightmost side (14) is an approximation when ΔΦ is small.

  If | ΔΦ | is large, the degree of modulation increases, but normally, the phase change | ΔΦ | due to recording is between 0 and π, and is generally considered to be about π / 2 or less. Actually, such a large phase change has not been reported in conventional dye-based recording layers such as conventional CD-R and DVD-R, and in the blue wavelength region as described above, This is because the phase change tends to be smaller from the general characteristics. Conversely, a change in which | ΔΦ | exceeds π may reverse the force of push-pull before and after recording, and the change in push-pull signal may become too large, which is preferable from the viewpoint of maintaining tracking servo stability. Absent.

  Here, FIG. 6 is a diagram for explaining the relationship between the phase difference between the recording groove portion and the recording groove portion and the reflected light intensity. FIG. 6 shows the relationship between | Φ | and the reflected light intensity at the recording groove before and after recording. Here, for the sake of simplicity, the influence of the absorption of the recording layers 12 and 22 is ignored. In the configurations of FIG. 3 and FIG. 5, Φb> 0 is usually satisfied, and therefore ΔΦ> 0 is the direction in which | Φ | in FIG. 6 increases. That is, Φb increases to become Φa.

  On the other hand, in the configuration of FIG. 4, Φb <0 is usually satisfied, and thus the case where ΔΦ <0 is the direction in which | Φ | of FIG. 6 increases. That is, it corresponds to a value obtained by multiplying the horizontal axis in FIG. 6 by (−1). Therefore, | Φb | increases to | Φa |.

Assuming that the reflectance of the recording groove in the planar state (d _GL = 0) is R 0, as | Φ | The strength decreases. When the phase difference | Φ | becomes equal to π (half wavelength), the reflected light intensity becomes a minimum value. Further, when | Φ | increases beyond π, the reflected light intensity starts to increase, and reaches a maximum value when | Φ | = 2π.

Here, the push-pull signal intensity becomes maximum when the phase difference | Φ | is π / 2, becomes minimum when the phase difference is π / 2, and the polarity is inverted. Thereafter, it increases / decreases again, reaches a minimum at 2π, and reverses the polarity again. Above relationship, in the ROM medium due to the phase pits, it is exactly the same as the depth of the pit part (equivalent to d _GL) and the relationship of the reflectivity (Non-Patent Document 5).

The push-pull signal will be briefly described below.
FIG. 7 is a diagram for explaining the configuration of a quadrant detector that detects a recording signal (sum signal) and a push-pull signal (difference signal). The quadrant detector is composed of four independent photodetectors, and outputs are Ia, Ib, Ic, and Id, respectively. The zero-order diffracted light and the first-order diffracted light from the recording groove portion and the recording groove portion in FIG. The following calculation output is obtained from the signal from the quadrant detector.
Isum = (Ia + Ib + Ic + Id) (15)
IPP = (Ia + Ib) − (Ic + Id) (16)
The operation output is obtained.

FIG. 8 is a diagram illustrating a signal detected after an output signal obtained while actually traversing a plurality of grooves and between grooves is passed through a low-frequency pass filter (cutoff frequency of about 30 kHz).
In FIG. 8, Isum _pp is a signal amplitude of a peak-to-peak of the Isum signal. IPP _pp is the peak-to-peak signal amplitude of the push-pull signal. The push-pull signal strength means IPP _pp and is distinguished from the push-pull signal IPP itself.
The tracking servo performs feedback servo using the push-pull signal (IPP) in FIG. 8B as an error signal. In FIG. 8B, for example, the 0 cross point where the polarity of the IPP signal changes from + to − corresponds to the center of the recording groove, and the 0 cross point where the polarity changes from − to + corresponds to the recording groove portion. When the push-pull polarity is reversed, the sign change is reversed. If the signs are reversed, the servo is applied to the recording groove portion (that is, the focused beam spot is applied to the recording groove portion), but conversely, the servo is applied to the recording groove portion.

The Isum signal when the servo is applied to the recording groove is a recording signal, and in this embodiment, the change increases after recording.
here,
IPP _actual = [{(Ia + Ib) (t)-(Ic + Id) (t)} / {(Ia + Ib) (t) + (Ic + Id) (t)}] _pp
= {IPP (tb) / Isum (tb)}-{IPP (ta) / Isum (ta)}
(Here, ta is the time when the IPP becomes the minimum value, and tb is the time when the IPP becomes the maximum value.) (17)
The calculated output is called standardized push-pull signal strength (IPP _actual ).
In many cases, the push-pull signal used by the optical recording / reproducing apparatus to actually apply the tracking servo is a normalized push-pull signal that is a signal calculated from the values of Isum and IPP measured instantaneously and instantaneously.

  The relationship between the phase difference and reflected light intensity as shown in FIG. 6 is periodic as can be seen from the above equation (13). The change in | Φ | before and after recording, that is, | ΔΦ | is usually smaller than (π / 2) in a medium containing a dye as a main component. Conversely, in this embodiment, it is assumed that the change in | Φ | due to recording is π or less at the maximum. Therefore, if necessary, the recording layer thickness may be reduced appropriately.

Here, when viewed from the phase reference plane AA ′, when the phase (or optical path length) of the reflected light of the recording groove portion becomes smaller than before recording due to the formation of the recording pit portions 16p, 25p, 26p (the phase is lower than before recording). In the case of delay), that is, when ΔΦ> 0, the optical distance (optical path length) of the reflection reference plane decreases as viewed from the incident side, and approaches the light source (or the phase reference plane AA ′). That's right. Therefore, in FIG. 3, there is an effect equivalent to that when the reflection reference surface of the recording groove portion is moved downward ( _dGL increases), and as a result, the reflected light intensity of the recording pit portion 16p decreases. In FIG. 4, there is an effect equivalent to the fact that the reflection reference surface of the recording groove portion moves upward (d _GL decreases), and as a result, the reflected light intensity of the recording pit portion 25p increases. In FIG. 5, there is an effect equivalent to the fact that the reflection reference surface of the recording groove portion has moved upward (d _GL increases), and as a result, the reflected light intensity of the recording pit portion 26p decreases.

On the other hand, when viewed from the phase reference plane AA ′, when the phase (or optical path length) of the reflected light of the recording pit portions 16p, 25p, and 26p is larger than before recording (when the phase is delayed from before recording), ΔΦ When <0, the optical distance (optical path length) of the reflection reference surface increases as viewed from the incident side, and the distance from the light source (or to the phase reference surface AA ′) increases. In FIG. 3, the reflection reference plane of the recording groove part has the same effect has moved upward (d _GL is reduced), the reflected light intensity as a result the recording pit part 16p increases. In FIG. 4, there is an effect equivalent to the fact that the reflection reference surface of the recording groove portion moves downward ( _dGL increases), and as a result, the reflected light intensity of the recording pit portion 25p decreases. In FIG. 5, there is an effect equivalent to that when the reflection reference surface of the recording groove is moved downward (d _GL is decreased), and as a result, the reflected light intensity of the recording pit portion 26p is increased. Here, the direction of change in reflected light intensity, which is whether the reflected light intensity at the recording pit portion decreases or increases after recording, is referred to as the polarity of recording (signal).

  Therefore, if a phase change that satisfies ΔΦ> 0 occurs in the recording pit portions 16p, 25p, and 26p, in the recording groove portion of FIGS. 3 and 5, “High to Low” (hereinafter referred to as “High to Low”) in which the reflected light intensity decreases due to recording. It is preferable to use a change in polarity of a signal that is simply referred to as HtoL. In the recording groove portion of FIG. 4, “Low to High” (hereinafter simply referred to as LtoH) in which reflected light intensity increases due to recording. It is preferable to use the polarity which becomes. On the other hand, if there is a phase change that satisfies ΔΦ <0, it is preferable to use the polarity that becomes LtoH in the recording groove portion of FIGS. 3 and 5, and the polarity that becomes HtoL in the recording groove portion of FIG. Is preferred. The above relationships are summarized in Table 1. Table 1 shows whether the reflected light intensity change of the polarity of HtoL or LtoH is preferable in the configuration of FIG. 3, FIG. 4, FIG.

(Preferred embodiment of phase change ΔΦ)
In the present invention, in the case of FIG. 4, the objective is to perform LtoH recording that is consistent with the reflected light intensity due to the reduction of the extinction coefficient, and therefore it is preferable that ΔΦ> 0.
In other words, in order for the polarity of the recording signal to be constant regardless of the recording power and the length and size of the recording pits, the “change in reflected light intensity in a flat state” and “change in reflected light intensity considering interference” It is preferable that each reflected light intensity change is uniform.
In the following, a preferred embodiment for realizing ΔΦ> 0 when recording on the cover layer inter-groove portion 25 in FIG. 4 with the dye recording layer medium will be described.
In ΔΦ,
Φ _bmp = (n _d −n _c ) · d _bmp (18)
Φ _pit = n _d · d _pit (19)
Φ _mix = δn _c・ d _mix (20)
_{Φ n = δn d · (d} G -d pit -d bmp) = δn d · d Ga (21)
Φ _bmp is a phase change due to deformation (movement) of the recording layer incident side interface, Φ _pit is a phase change due to deformation (movement) of the recording layer 22 / reflection layer 23 interface, and Φ _mix is a phase due to formation of the mixed layer 25m. The change, Φ _n , corresponds to a phase change due to a change in the refractive index of the recording layer 22. These phase changes are large, and the direction of the change, that is, the signs of Φ _bmp , Φ _pit , Φ _mix , and Φ _n are aligned, the degree of modulation is increased, and the signal waveform of a specific signal polarity is obtained. This is important for obtaining good recording characteristics without distortion.

Among these, in order to align the direction of phase change, control is limited to as few elements as possible rather than accurately controlling all the physical parameters related to Φ _bmp , Φ _pit , Φ _mix , and Φ _n. It is desirable.
First, it is also preferable to set d _mix = 0 by providing an interface layer on the recording layer incident side interface. This is because the change in phase difference due to d _mix cannot be increased so much that it is difficult to use it actively, and its thickness is difficult to control. Therefore, it is preferable to set d _mix = 0 by providing an interface layer at the recording layer incident side interface.

Next, the deformation is preferably concentrated in one place and limited to one direction. This is because better signal quality is more easily obtained by controlling one deformation part more accurately than a plurality of deformation parts.
Therefore, in this embodiment, it is preferable to mainly use either Φ _bmp or Φ _pit and Φ _n .

With respect to d _pit , since the main factor is usually expansion of the substrate or cover layer or volume shrinkage of the recording layer, d _pit > 0 is often obtained. This is advantageous for Φ _pit but disadvantageous for d _Ga , ie Φ _n . On the other hand, the absorption of the recording layer is highest on the incident side interface side from the middle part of the thickness of the recording layer. If a high heat dissipation material is used for the reflective layer, the heat generation effect of the recording layer is mostly concentrated on the incident side interface of the recording layer. In FIG. 4, the heat generation is concentrated on the interface of the recording layer 22 on the cover layer 24 side. Therefore, in the configuration of FIG. 4, deformation occurs at the dye incident side interface, that is, the interface with the cover layer 24. For this reason, since d _pit is naturally reduced, the contribution is small. Unlike the conventional configuration, the influence of the deformation on the substrate 21 side is considered to be small, and in practice, it can be considered that d _pit ≈0. This suggests that it is better to _{collect the} deformation elements to be controlled in _dbmp .

Also, [Phi _n the refractive index change .DELTA.n _d dyes, deformation d _bmp contributes.
In this case, as can be seen from the equation (21), Φ _n is contributed by the refractive index change δn _d of the pigment and the deformation d _bmp , and is the most important factor in the magnitude and sign of ΔΦ.
In the following, the case of Φ _pit ≈ 0 and Φ _max ≈ 0 will be considered.
_{ΔΦ ≒ Φ bmp + Φ n =} (n d -n c) · d bmp + δn d · (d G -d bmp)
= (N _d '-n _c ) · d _bmp + δn _d · d _G (22)
Can be written.

First, considering Φ _bmp , n _d ′ ≈1, and n _c is usually about 1.5 for a resin material, so n _d ′ −n _c <0. Therefore, in order to _satisfy Φ _bmp > 0, d _bmp <0. This preferably causes blistering on the cover layer side 24 side.

Then, [Phi among physical phenomena related to _n, first consider the influence of the recording layer refractive index change .DELTA.n _d. Recording layer thickness d _Ga after recording, because it is the definition d _Ga> 0, the sign of .DELTA.n _d is believed to dominate the sign of [Phi _n. In the present invention, a recording layer containing a dye as a main component is used. The main absorption band of the dye is an absorption band whose strongest absorption wavelength (absorption peak) is in the visible light region (approximately 400 to 800 nm). Suppose there is. When recording / reproduction is performed at a wavelength near the main absorption edge of the main dye, it is considered that the recording layer is usually decomposed by heat generation of the recording layer, and the absorption is greatly reduced. At least in the unrecorded state, in the main absorption band, so-called Kramers-Kronig type anomalous dispersion exists, and it is considered that the wavelength dependence of the refractive index n and the extinction coefficient k exists.

On the other hand, the decomposition temperature of the dye as the main component of the recording layer in the present invention is 500 ° C. or less, and due to the heat generated by the recording light, the dye of the main component of the recording layer is decomposed until the main absorption edge cannot be maintained. Form. In that case, there is no Kramers-Kronig type anomalous dispersion, and it can be considered that n _d ′ = 1 and k _d ′ = 0.

Here, the porphyrin compound used in the present application has a steep and large main absorption band on the long wavelength side of the recording / reproducing light wavelength λ. Therefore, the relationship between the Kramers-Kronig, n _d is about 0.5 to 1.2. Due to the formation of the cavity in the recording pit portion, the refractive index after recording n _d ′ ≈1, and therefore δn _d <0 may occur. In this case, the _{Φ n = δn d · d G} <0. That is, there are some terms that have the same phase change direction as Φ _bmp > 0, such as Φ _n <0. However, by positively increasing d _bmp <0, by making Φ _bmp the main component of ΔΦ, it is possible to practically eliminate the adverse effects of Φ _n and realize ΔΦ> 0.

In order to increase Φ _bmp > 0, in order to promote the deformation of d _bmp <0, it is desirable that a volume expansion pressure due to thermal expansion, decomposition, and sublimation is generated in the thermal alteration of the recording layer 22. Further, it is preferable to provide an interface layer at the interface between the recording layer 22 and the cover layer 24 so as to confine the pressure and prevent leakage to other layers. It is desirable that the interface layer has a high gas barrier property and is more easily deformed than the cover layer 24. In particular, when a dye having a strong sublimation property is used as a main component, a volume expansion pressure is locally generated in the recording layer 22 portion, and a large cavity is easily formed.

On the other hand, considering the advantage of the contribution of Φ _n , since n _d is 0.5 to 1.2, the following conditions can be considered. First, when n _d <1 and Φ _n <0, in order to reduce the contribution of Φ _n as much as possible, it is desirable that the dye film thickness is as thin as possible in order to make d _G smaller. Further, in order to reduce the value of | δn _d | = | n _d −n _d ′ | ≈ | n _d −1 |, it is desirable that n _d is close to 1. Specifically, it is desirably 0.7 or more, and more desirably 0.8 or more. When n _d > 1 and Φ _n > 0, the direction of phase change is aligned, so the value of | δn _d | = | n _d −n _d ′ | ≈ | n _d −1 | In the porphyrin compound used in the present application, the upper limit of n _d is about 2 in general.

Thus, n _d ', to keep the combination of the signs of the magnitude relationship and d _bmp of n _c (direction of deformation) to a specific relationship, to be a nd a specific range, the mark length, a recording signal polarity This is effective in preventing the phenomenon that (HtoL or LtoH) is reversed or mixed (a differential waveform is obtained).

Here, the relationship between the phase change of ΔΦ> 0 and the push-pull signal will be considered. When performing HtoL recording to the cover layer groove part 26 (see Fig. 5) from the analogy of the conventional CD-R and DVD-R, if you want a push-pull signal polarity so as not reversed, as d _GL, the optical path length of the reciprocating 1 larger than the wavelength or (| | Φb _3> 2π become) such deep groove step (referred to as "deep groove"), is almost zero .PHI.b _3, the groove level difference that barely push-pull signal out ( "shallow groove "). In the case of a deep groove, the groove is optically deepened by utilizing the phase change in the direction of the arrow α on the slope of | Φb |> 2π in FIG. In this case, the groove depth that is the starting point of the arrow needs to be about 100 nm at a blue wavelength of around 400 nm. As described above, when the track pitch is narrow, defective transfer is likely to occur during molding, and mass production is difficult. Further, even if a desired groove shape is obtained, noise due to the minute surface roughness of the groove wall is likely to be mixed into the signal. Furthermore, it is difficult to uniformly form the reflective layer 23 on the groove bottom and side walls. The adhesion of the reflective layer 23 itself to the groove wall is also poor, and deterioration such as peeling tends to occur. As described above, when HtoL recording is performed using the phase change of ΔΦ> 0 in the conventional method using the “deep groove”, it is difficult to reduce the track pitch.

  On the other hand, in the case of a shallow groove, the phase change in the direction of arrow β is used on the slope between | Φ | = 0 to π in FIG. 6, and the groove is optically deepened. Become. If a certain push-pull signal intensity is obtained in the unrecorded state, the groove depth is about 20 nm to 30 nm at the blue wavelength. When the recording layer 22 is formed in such a state, the recording layer thickness is easily formed equally in the recording groove portion (in this case, the cover layer groove portion 26) and the groove portion as in the planar state, and the recording pits are formed. It tends to protrude from the recording groove, and diffracted light from the recording pits leaks into the adjacent recording groove, resulting in very large crosstalk. Similarly, if HtoL recording is performed using the phase change of ΔΦ> 0 in the conventional method, it is difficult to reduce the track pitch.

  The inventors of the present invention do not prefer the conventional HtoL recording using the “deep groove”, but the phase change in the direction of the arrow γ in FIG. It was found that a signal having a recording polarity of LtoH using “ That is, the optical recording medium 20 performs recording / reproduction by entering recording / reproducing light from the cover layer 24 side, and the surface on which the recording / reproducing light beam 27 is incident on the cover layer 24 (surface 29 on which the recording / reproducing light beam 27 is incident). When the guide groove portion on the side far from the recording groove portion is a recording groove portion, the reflected light intensity of the recording pit portion formed in the recording groove portion is higher than the reflected light intensity of the recording groove portion when not recorded, and the recording method.

  In the present embodiment, what is important is that the above-described change in the refractive index of the recording layer, the change in the refractive index at the pit due to the formation of a cavity, and the deformation in the recording layer 22 or at the interface thereof are all the main reflection. That is, the incident occurs on the recording / reproducing light incident side of the reflective layer 23 which is a surface.

With the film surface incidence configuration as shown in FIG. 4, when the guide groove portion far from the surface 29 (FIG. 2) on which the recording / reproducing light beam 27 (FIG. 2) is incident is set as the recording groove portion, ΔΦ> 0. LtoH recording is performed using the phase change.
For this purpose, first, in the recording pit portion 25p, the recording layer is accompanied by a shape change that swells to the cover layer side, and a cavity is formed inside the recording layer or at an interface with a layer adjacent to the recording layer. It is desirable that changes occur.
And before recording, in order to maintain the stability of various servos, it is preferable to maintain a reflectance of at least 3% to 30% in both the groove and the groove.
The recording groove portion reflectivity (R _g ) in the unrecorded state here is formed by forming only a reflective film having a known reflectivity (R _ref ) with the same configuration as the optical recording medium 20 shown in FIG. I _ref is the reflected light intensity obtained by irradiating the recording groove portion in focus, and the reflected light intensity obtained by irradiating the recording groove portion with the focused light beam in the optical recording medium 20 shown in FIG. when to the I _s, is obtained as _{R g = R ref · (I} s / I ref). Similarly, after the recording, the recording signal amplitude, recording groove part reflectivity corresponding to low reflected light intensity I _L R _L between recording pits (space part), high reflected light intensity I _H of the recording pit (mark part) The recording groove portion reflectance corresponding to is called R _H.
In the following, when the change in reflected light intensity of the recording groove portion is quantified according to common usage, this recording groove portion reflectance is used.

In the present embodiment, since the phase change due to recording is used, it is preferable to increase the transparency of the recording layer 22 itself. The transmittance when the recording layer 22 is formed alone on a transparent polycarbonate resin substrate is preferably 40% or more, more preferably 50% or more, and further preferably 60% or more. If the transmittance is too high, the recording light energy cannot be absorbed sufficiently. Therefore, it is preferably 95% or less, more preferably 90% or less.
On the other hand, such a high transmittance is maintained because the reflectivity R0 in the planar state is measured at the flat portion (mirror surface portion) in the disc having the configuration shown in FIG. It can be generally confirmed that the reflectance is 40% or more, preferably 50% or more, more preferably 70% or more, in the planar state of the disk having the same configuration with the recording layer thickness being zero.
Thus, in order to maintain moderate permeability, k _d is preferably 2 or less, and more preferably 1.5 or less.

(Preferable embodiments of recording groove depth d _GL , recording layer thickness d _G of the recording groove portion, and recording layer thickness d _L between the recording groove portions)
When the phase change of ΔΦ> 0 is used and LtoH recording is performed on the cover layer groove portion 25, the groove depth is optically changed at the pit portion. It becomes easy to change. Particularly problematic is a phase change that reverses the polarity of the push-pull signal.

In order to perform LtoH recording and not cause a change in the polarity of the push-pull signal, in FIG. 6, the optical change is caused by the phase change in the direction of the arrow γ on the slope of 0 <| Φb |, | Φa | <π. It is preferable to use the phenomenon that a groove becomes shallow. That is, in FIG. 4, a change is made in the recording pit portion 25p so that the optical path length from the phase difference reference surface AA ′ to the reflection reference surface of the recording groove portion becomes small. In the case of FIG. 4, Φb = Φb ₂ <0, Φa = Φa ₂ <0, and ΔΦ> 0, so | Φb |> | Φa |. Since Φb and Φa are negative in the case of FIG. 4 because the phase difference is defined as in equation (2), they are expressed as absolute values.

In particular, when the standardized push-pull signal intensity IPP _actual of Expression (17) is used as the push-pull signal, the average reflectance after recording increases in this embodiment, so that the denominator of Expression (17) is To increase.
In order to keep the normalized push-pull signal intensity IPP _actual after recording sufficiently large, the push-pull signal intensity IPP _pp, which is the numerator of the formula (17), increases after recording or at least maintains a large value. preferable. That is, | Φa | is preferably in the vicinity of π / 2 after recording. On the other hand, in order to ensure a sufficient push-pull signal even before recording, it is desirable that | Φb | is approximately (1/16) π smaller than π. Therefore, it is preferable that | Φb | is in the range of π / 2 to (15/16) π in the path γ.

Specifically, in FIG. 4, in order to set | Φb ₂ | = (4π / λ) | ψb ₂ | to a range of π / 2 to (15/16) π,
| Ψb ₂ | = | (n _c −n _d ) · (d _G −d _L ) −n _c · d _GL |
= | (N _d −n _c ) · (d _G −d _L ) + n _c · d _GL |
Is preferably in the range of λ / 8 to (15/64) · λ.
When the groove depth d _GL at that time is d _G = d _L and the recording / reproducing light wavelength λ = blue wavelength of 350 to 450 nm, from the equation (7),
_{| Ψb 2 | = n c ·} d GL (7a)
It becomes. Similar equations can be obtained with n _d ≈n _c . The value of a typical polymeric materials n _c, when the order of 1.4 to 1.6, the groove depth d _GL is normally 30nm or more, preferably more than 35 nm. On the other hand, the groove depth d _GL is normally 70nm or less, preferably 65nm or less, more preferably 60nm or less. A groove having such a depth is referred to as an “intermediate groove”. Compared to the case of using the “deep groove” in FIGS. 3 and 5 described above, there is an advantage that the formation of the groove and the covering of the reflection film on the cover layer groove portion 25 are greatly facilitated.

In general, when a recording layer is formed by spin coating, the recording layer tends to accumulate in the substrate groove portion, so that d _G > d _L naturally occurs. Further, when the amount of the dye to be applied is reduced and the film thickness of the recording layer is made thin as a whole, d _L ≈0 can be obtained. ).

In this case, equation (7) becomes
| Ψb ₂ | = | (n _c −n _d ) · d _G −n _c · d _GL |
= | (N _d −n _c ) · d _G + n _c · d _GL | (7b)
Therefore, correction for the above-mentioned preferable range of the groove depth with respect to (7a) is required by | (n _c −n _d ) · d _G |. In the present application, since it is n _d <n _c, resulting in deeper slightly preferred. Conversely, if a groove shape of n _d · d _GL is given, | Φb ₂ | becomes smaller as n _d is smaller than n _c, and the reflected light intensity of the groove increases from FIG. This means that when the dye recording layer is confined in the recording groove portion in order to suppress crosstalk, the optical groove depth can be reduced even if a deep groove of 40 to 60 nm is used.

The recording layer thickness is preferably smaller than the groove depth and d _G <d _GL . This is because even if the recording pits are accompanied by deformation as described later, the effect of suppressing at least the width within the groove width is obtained, and crosstalk can be reduced. For this reason, it is preferable to _satisfy (d _G / d _GL ) ≦ 1, more preferably (d _G / d _GL ) ≦ 0.8, and (d _G / d _GL ) ≦ 0.7. Is more preferable.

That is, in the optical recording medium 20 to which this embodiment is applied, it is preferable that the recording layer 22 is formed by coating so that d _GL > d _G > d _L. More preferably, d _L / d _G ≦ 0.5 is set so that the recording layer 22 is practically hardly deposited on the portion between the recording grooves. On the other hand, since d _L is preferably substantially zero as will be described later, the lower limit value of d _L / d _G is ideally zero.

As described above, when d _GL is 30 to 70 nm, d _G is preferably 5 nm or more, and more preferably 10 nm or more. This can be accomplished by the d _G or more 5 nm, can be increased a phase change, because it is possible to absorb the light energy required for recording pit formation. On the other hand, d _G is preferably less than 50 nm, more preferably 45 nm or less, and even more preferably 40 nm or less. This is because, as described above, the reflectance during reproduction is 3 to 30%, so that the recording layer is kept at a suitable transmittance.
Furthermore, the thinner the recording layer 22, it is possible to suppress the deformation at the recording pit portion from becoming too large or protruding from the recording groove portion.

In the present invention in which recording pits are formed between the cover layer grooves, the above-described “intermediate groove” depth is used, and d _G / d _L ≦ 1, and the recording layer 22 is thinned to form an “intermediate groove”. The confinement in the recording groove having a depth is more preferable when the formation of a cavity in the recording pit portion and the bulging deformation toward the cover layer are positively used as will be described later. Also in this respect, the present invention is superior in the effect of suppressing crosstalk as compared with the case where the recording is performed in the groove of the cover layer and the cavity is formed to perform the HtoL recording. Furthermore, the present invention dyes, since k _d can be as large as about 1, be thinner recording layer thickness, sufficient light absorption is performed, can be kept low recording light power required for recording pit formation. In general, when the recording layer thickness is small, the “reflected light intensity change that occurs in the planar state” tends to be small. However, in this recording layer, the difference between k _d and k _d ′ is large, so sufficient reflected light An intensity change is obtained. For this reason, k _d is preferably 1 or more.

Thus, the recording pit is almost completely confined in the recording groove, and the leakage (crosstalk) of the diffracted light of the recording pit portion 25p in FIG. 4 into the adjacent recording groove can be extremely reduced. . In other words, LtoH recording for recording in the cover layer groove portion 25 is not only an advantageous combination of phase change of ΔΦ> 0 and recording in the cover layer groove portion 25 but also a narrow track pitch. This makes it easier to obtain a configuration suitable for high density recording. Furthermore, when d _L is almost zero, the contribution of the term (n _c −n _d ) · d _G can be maximized in | ψb ₂ | in the equation (7b), and d _GL should be made slightly shallower. And groove formation becomes easier.

(Concerning preferred embodiments of specific layer structure and materials)
In the following, regarding the specific materials and aspects of the layer structure shown in FIGS. 2 and 4, considering the situation where the development of the blue wavelength laser is progressing, especially when the wavelength λ of the recording / reproducing light beam 27 is around 405 nm An explanation will be given assuming this.

(substrate)
The substrate 21 may be made of plastic, metal, glass or the like having an appropriate workability and rigidity in a film surface incident configuration. Unlike conventional substrate incidence configurations, there are no restrictions on transparency or birefringence. The guide groove is formed on the surface. However, in the case of metal or glass, it is necessary to provide a light or thermosetting thin resin layer on the surface and to form the groove there. In this respect, it is preferable in terms of manufacturing to use a plastic material and to form the shape of the substrate 21, particularly the disk shape, and the surface guide groove all at once by injection molding.

  As the plastic material that can be injection-molded, polycarbonate resin, polyolefin resin, acrylic resin, epoxy resin, and the like conventionally used in CDs and DVDs can be used. The thickness of the substrate 21 is preferably about 0.5 mm to 1.2 mm. The total thickness of the substrate and the cover layer is preferably 1.2 mm, which is the same as that of a conventional CD or DVD. This is because cases and the like used in conventional CDs and DVDs can be used as they are. In the Blu-ray disc, the substrate thickness is 1.1 mm and the cover layer thickness is 0.1 mm. (Non-Patent Document 3)

A tracking guide groove is formed in the substrate 21. In the present embodiment, the track pitch at which the cover layer groove portion 25 becomes the recording groove portion is 0.1 μm to 0.6 μm in order to achieve higher density than CD-R and DVD-R. Preferably, it is more preferable to set it as 0.2 micrometer-0.4 micrometer. As described above, the groove depth depends on the recording / reproducing light wavelengths λ, d _GL , d _G , d _{L and the} like, but is preferably in the range of approximately 30 nm to 70 nm. Within the above range, the groove depth is appropriately optimized in consideration of the recording groove portion reflectance R _g in an unrecorded state, the signal characteristics of the recording signal, the push-pull signal characteristics, the optical characteristics of the recording layer, and the like. In the present embodiment, since the interference due to the phase difference of the reflected light in the recording groove portion and the recording groove portion is used, it is necessary that both exist in the focused light spot. For this reason, the recording groove width (width of the cover layer groove portion 25) is preferably smaller than the spot diameter (diameter in the groove transverse direction) of the recording / reproducing light beam 27 on the recording layer 22 surface. In an optical system having a recording / reproducing light wavelength λ = 405 nm and NA (numerical aperture) = 0.85, when the track pitch is 0.32 μm, it is preferably in the range of 0.1 μm to 0.2 μm. Outside these ranges, it is often difficult to form grooves or inter-groove portions.

  The shape of the guide groove is usually rectangular. In particular, when forming a recording layer by coating described later, it is desirable that the dye is selectively accumulated on the substrate groove in several tens of seconds until the solvent of the solution containing the dye is almost evaporated. For this reason, it is also preferable that the shoulder between the substrate grooves of the rectangular groove is rounded so that the dye solution easily falls and accumulates in the substrate groove portion. Such a groove shape having a round shoulder can be obtained by etching the surface of a plastic substrate or stamper by exposing it to plasma or UV ozone for several seconds to several minutes. Etching with plasma is suitable for obtaining the shape of the shoulder of the rounded groove portion because the sharp portion such as the shoulder of the groove portion of the substrate (edge of the groove portion) is selectively cut away.

  The guide groove is usually added by groove modulation, groove modulation such as groove meandering, groove depth modulation, or irregular pits due to intermittent or intermittent recording grooves, in order to give additional information such as addresses and synchronization signals. Have a signal. For example, in a Blu-ray disc, a wobble address method using two modulation methods, MSK (minimum-shift-keying) and STW (saw-tooth-wobbles), is used. (Non-Patent Document 3)

(Layer with light reflection function)
The layer having the light reflection function (reflective layer 23) preferably has a high reflectance with respect to the recording / reproducing light wavelength and a reflectance of 70% or more with respect to the recording / reproducing light wavelength. Examples of visible light used as a recording / reproducing wavelength, particularly those exhibiting high reflectivity in the blue wavelength region, include Au, Ag, Al, and alloys containing these as main components. More preferably, it is an alloy mainly composed of Ag having a high reflectance at λ = 405 nm and a small absorption. Mainly composed of Ag, Au, Cu, rare earth elements (particularly Nd), Nb, Ta, V, Mo, Mn, Mg, Cr, Bi, Al, Si, Ge, etc. 0.01 atomic% to 10 atomic% By adding, the corrosion resistance against moisture, oxygen, sulfur and the like can be improved, which is preferable. In addition, a dielectric mirror in which a plurality of dielectric layers are stacked can be used.

The film thickness of the reflective layer 23 is preferably equal to or thinner than _dGL in order to maintain the groove step on the surface of the substrate 21. Similarly, when the recording / reproducing light wavelength λ = 405 nm, as described above, d _GL is preferably 70 nm or less. Therefore, the thickness of the reflective layer is preferably 70 nm or less, more preferably 65 nm or less. . Except for the case where a two-layer medium described later is formed, the lower limit of the reflective layer thickness is preferably 30 nm or more, more preferably 40 nm or more. The surface roughness Ra of the reflective layer 23 is preferably 5 nm or less, and more preferably 1 nm or less. Ag has a property that flatness is increased by the addition of an additive. In this sense, the content of the additive element is preferably 0.1 atomic% or more, more preferably 0.5 atomic% or more. The reflective layer 23 can be formed by sputtering, ion plating, electron beam evaporation, or the like.

Groove depth d _GL is defined by the step of the reflection reference plane is equal to the groove depth d _GLS almost substrate 21 surface. The groove depth can be directly measured by observing the cross section with an electron microscope. Alternatively, it can be measured by a probe method such as an atomic force microscope (AFM). In the case where the groove or the inter-groove portion is not completely flat, d _GL is defined by the difference in height at the center between the groove and the groove. Similarly, the groove width refers to the width of the groove portion where the recording layer 22 actually exists after the formation of the reflective layer 23. A surface groove width value can be used. Moreover, the width | variety in the half depth of a groove depth is employ | adopted for a groove width. Similarly, the groove width can be directly measured by observing the cross section with an electron microscope. Alternatively, it can be measured by a probe method such as an atomic force microscope (AFM). Note that the depth and width of any groove defined in the optical recording medium 10 can be measured in the same manner as described herein.

(Middle layer)
An intermediate layer is preferably provided between the reflective layer 23 and the recording layer 22. By providing the intermediate layer, it is possible to improve the jitter characteristics.

  The intermediate layer usually contains an element selected from the group consisting of Ta, Nb, V, W, Mo, Cr, and Ti from the viewpoint of improving jitter characteristics. Especially, it is preferable to contain either Ta, Nb, Mo, and V, and it is preferable to contain either Ta or Nb. In addition, the intermediate | middle layer may contain any one of these elements independently, and may contain 2 or more types by arbitrary combinations and compositions. Since the above elements have low reactivity and solid solubility with silver or silver alloys widely used as a reflective layer, an optical recording medium with excellent storage stability can be obtained by using these elements as an intermediate layer. It becomes possible.

  It is preferable to contain the said element as a main component of an intermediate | middle layer. In the present specification, the “main component of the intermediate layer” means that the above elements are contained in an amount of 50 atomic% or more among the elements constituting the intermediate layer. Among them, the element is preferably contained in an amount of 70 atomic% or more, more preferably 90 atomic% or more, further preferably 95 atomic% or more, and particularly preferably 99 atomic% or more. preferable. Ideally, the element is contained at 100 atomic%. In addition, when the intermediate | middle layer contains 2 or more types of the said element, it is preferable that the total ratio satisfy | fills the said range.

  The mechanism by which the effect of improving the jitter is obtained by inserting the intermediate layer is not clear. However, according to the study by the present inventors, the intermediate layer is composed of an element having a higher hardness than Ag or Al, which is usually used as the material of the reflective layer 23, and / or light at the recording / reproducing wavelength. It was found that the jitter tends to be improved by using an element having a large absorption as the intermediate layer. For this reason, it is presumed that the above condition is easily satisfied by forming the intermediate layer using the above elements.

  Note that the intermediate layer may contain an element other than the above elements as an additive element or an impurity element in order to impart desired characteristics. Examples of such additive elements or impurity elements include Mg, Si, Ca, Mn, Fe, Co, Ni, Cu, Y, Zr, Pd, Hf, and Pt. One of these additive elements or impurity elements may be used alone, or two or more thereof may be used in any combination and ratio. The upper limit of the concentration of these additive elements or impurity elements in the intermediate layer is usually about 5 atomic% or less.

  If the film thickness of the intermediate layer is at least formed as a film, the effect can be exhibited, but the lower limit of the film thickness is usually 1 nm or more. On the other hand, if the film thickness of the intermediate layer becomes too large, the light absorption of the intermediate layer increases, causing a decrease in recording sensitivity and a decrease in reflectivity. Therefore, it is usually 15 nm or less, preferably 10 nm or less, more preferably 5 nm or less. When the film thickness is within the above range, a jitter improvement effect and appropriate reflectance and recording sensitivity can be obtained at the same time.

  The intermediate layer can be formed by a sputtering method, an ion plating method, an electron beam evaporation method, or the like.

(Recording layer)
The recording layer 22 contains, as a main component, a dye having a light absorption function with respect to the recording / reproducing light wavelength in an unrecorded (before recording) state. Specifically, the dye contained as a main component in the recording layer 22 is an organic compound having a remarkable absorption band due to its structure in the visible light (and its vicinity) wavelength region of 400 nm to 800 nm. It is an organic compound having an absorption band peak on the longer wavelength side than the reproduction light wavelength λ. In such an unrecorded (before recording) state, an optical component having absorption at the wavelength λ of the recording / reproducing light beam 27, which is altered by recording and can be detected in the recording layer 22 as a change in the reflected light intensity of the reproducing light. A pigment that causes a change is referred to as a “principal component pigment” in the present specification. One type of main component dye may be used, but a mixture of a plurality of dyes may exhibit the above functions.

  The content of the main component dye in the recording layer 22 is usually 50% by weight or more, preferably 80% by weight or more, and more preferably 90% by weight or more. As the main component dye, it is preferable that a single dye absorbs with respect to the wavelength λ of the recording / reproducing light beam 27 and is altered by recording to cause the above optical change. It may be functionally shared so as to indirectly change the other dye and cause an optical change by generating heat. In addition to this, a dye as a so-called quencher for improving the temporal stability (temperature, humidity, light stability) of a dye having a light absorption function may be mixed with the main component dye. Examples of the content of the recording layer 22 other than the main component dye include a binder (binder) made of a low-polymer material and a dielectric.

The film thickness of the recording groove portion of the recording layer 22 is usually 70 nm or less, preferably 50 nm or less, more preferably 40 nm or less, and further preferably 30 nm or less.
The recording layer thickness when the recording groove is not recorded is usually 0 nm or more, and usually 10 nm or less, preferably 7 nm or less, more preferably 5 nm or less. This is because if the recording layer film thickness when the recording groove is not recorded is in the above range, the width of the recording pit in the lateral direction exceeds the recording groove width, and the influence on crosstalk can be reduced. Therefore, it is particularly preferable that the thickness of the recording layer when the recording groove is not recorded is 10 nm or less, which is a range that can be regarded as substantially zero.

  In the case where the interface layer described later is used, if the recording layer thickness when the recording groove portion is not recorded is within the above range, the interface layer and the reflective layer 23 are in contact with each other at the recording groove portion. . At this time, for example, when a material containing sulfur (for example, ZnS) is used for the interface layer and Ag is used for the reflective layer 23, the sulfur and the reflective layer 23 react to cause corrosion of the reflective layer 23. There is. In the case where such corrosion can occur, the intermediate layer suppresses the interface layer and the reflective layer 23 from being in direct contact with each other, so that the effect of suppressing the corrosion phenomenon is exerted.

(Dye compound that is the main component of the recording layer)
The dye compound as the main component of the recording layer of the optical recording medium of the present invention is a porphyrin compound represented by the following general formula [I].
In the general formula [I], Ar ^{a1 to} Ar ^a4 each independently represent an aromatic ring, and each may have a plurality of substituents.
In general formula [I], R ^{a1 to} R ^a8 each independently represents a hydrogen atom or an arbitrary substituent, and among them, a hydrogen atom is preferable.
Further, in the general formula [I], M ^a represents a divalent or higher metal cation. However, when M ^a is trivalent or more, the molecule may further have a counter anion so that the whole molecule is neutral.

This porphyrin compound is preferably a tetraarylporphyrin compound represented by the following general formula [II].
(In the formula [II], X ^{1 to} X ⁴ each independently represent an atom having a valence of 4 or more, and when X ^{1 to} X ⁴ are an atom having a valence of 5 or more, X ^{1 to} X ⁴ are further optional. May have a substituent, and when X ^{1 to} X ⁴ are atoms having a valence of 6 or more, each of them may have two = Q ¹ to = Q ⁴ , in which case the two Q ^{1 to} Q ⁴ may be the same or different.
Q ^{1 to} Q ⁴ each independently represent a group 16 atom of the periodic table.
Ar ^{1 to} Ar ⁴ each independently represent an aromatic ring, and each may have a substituent other than X ^{1 to} X ⁴ .
R ^{1 to} R ⁸ each independently represents an organic group having 20 or less carbon atoms,
R ^{9 to} R ¹⁶ each independently represents a hydrogen atom or an electron-withdrawing substituent,
M represents a divalent or higher valent metal cation. However, when M is trivalent or more, the molecule may further have a counter anion so that the whole molecule is neutral.
R ¹ and R ² , R ³ and R ⁴ , R ⁵ and R ⁶ , R ⁷ and R ⁸ may be bonded to form a ring. )

In the recording layer forming dye of the present invention, one type of tetraarylporphyrin compound according to the present invention may be included alone, or two or more types may be mixed and included.
Hereinafter, the tetraarylporphyrin compound represented by the general formula [II] will be described in detail.

{X ¹ (= Q ¹ ) to X ⁴ (= Q ⁴ )}
[II] In the formula, NX ¹ (= Q ¹ ) to NX ⁴ (= Q ⁴ ) each independently represents an amide structure for the reason of significantly improving the solubility of the porphyrin compound of the present invention in a solvent. To express.
^{X 1 (= Q 1) ~X} 4 constituting the amide structure (= Q ⁴⁾ of, X ¹ to X ⁴ valence each independently represents 4 or more atoms, X ¹ to X ⁴ are valence of 5 In the case of the above atoms, X ^{1 to} X ⁴ may further have an arbitrary substituent, and when X ^{1 to} X ⁴ are atoms having a valence of 6 or more, each of = Q ¹ to = Q ⁴ is 2 In this case, the two Q ^{1 to} Q ⁴ may be the same or different.
Examples of X ^{1 to} X ⁴ are each independently C, S, P, etc., and C and S are particularly preferable. When X ^{1 to} X ⁴ are atoms having a valence of 5 or more, the substituents that X ^{1 to} X ⁴ may further correspond to specific examples of R ^{9 to} R ¹⁶ described later.
Q ^{1 to} Q ⁴ of X ¹ (= Q ¹ ) to X ⁴ (= Q ⁴ ) constituting the amide structure each independently represent a group 16 atom of the periodic table, and preferably O or S.
Specific examples of X ¹ (= Q ¹ ) to X ⁴ (= Q ⁴ ) include the following. Note that these structures are each at the site of a is bonded to Ar ¹ to Ar ^4, attached to the nitrogen atom at the site of b. R ¹⁷ represents a substituent, and specific examples thereof correspond to specific examples of R ^{9 to} R ¹⁶ described later.

Among these, X ¹ (= Q ¹ ) to X ⁴ (= Q ⁴ ) are carbonyl groups (that is, NX ¹ (= Q ¹ ) to NX ⁴ (= Q ⁴ ) are carbamoyl groups N—C, respectively. (= O)) or a sulfonyl group (that is, N—X ¹ (= Q ¹ ) to N—X ⁴ (= Q ⁴ ) is a sulfamoyl group N—C (═S)). It is preferable in terms of ease of handling. Furthermore, X ¹ (= Q ¹ ) to X ⁴ (= Q ⁴ ) are each preferably a carbonyl group from the viewpoint of improving solubility, but a sulfonyl group is preferable from the viewpoint of improving sensitivity due to a decrease in thermal decomposition temperature. preferable. Further, X ¹ (= Q ¹ ) to X ⁴ (= Q ⁴ ) are preferably different from the viewpoint of improving the film properties of the compound, but the same is preferable for the reason of synthesis.
As for the substitution position of X ¹ (= Q ¹ ) to X ⁴ (= Q ⁴ ) with respect to Ar ^{1 to} Ar ⁴ , it is preferable to substitute at a position overlapping with a porphyrin ring in terms of improving solubility and film properties. , It is preferable to be separated for reasons of synthesis.

{Ar ^{1 to} Ar ⁴ }
<Ask structure of Ar ^{1 to} Ar ⁴ >
[II] In the formula, Ar ^{1 to} Ar ⁴ each independently represents an aromatic ring optionally having a substituent. In the present invention, the aromatic ring means a ring having aromaticity, that is, a ring having a (4n + 2) π electron system (n is a natural number). The skeleton structure is usually an aromatic ring consisting of a 5- or 6-membered monocyclic ring or a 2-6 condensed ring. The aromatic ring includes an aromatic hydrocarbon ring, an aromatic heterocyclic ring, and an anthracene ring. , Condensed rings such as a carbazole ring and an azulene ring are also included.
Specific examples of the skeleton structure of Ar ^{1 to} Ar ⁴ include a furan ring, a thiophene ring, a pyrrole ring, an imidazole ring, a thiazole ring, an oxadiazole ring as a 5-membered monocyclic ring, a benzene ring as a 6-membered monocyclic ring, and pyridine. Examples of the ring, pyrazine ring, and condensed ring include a naphthalene ring, a phenanthrene ring, an azulene ring, a pyrene ring, a quinoline ring, an isoquinoline ring, a quinoxaline ring, a benzofuran ring, a carbazole ring, a dibenzothiophene ring, and an anthracene ring. Of these, a monocyclic ring is preferable for reasons of synthesis, a 6-membered monocyclic ring is more preferable, and a benzene ring is particularly preferable.
Ar ^{1 to} Ar ⁴ are preferably different from the viewpoint of solubility and improvement in film properties when forming the recording layer, but the same is preferable from the viewpoint of synthesis.

<Substituents Ar ^{1 to} Ar ⁴ have>
Ar ^{1 to} Ar ⁴ may have a substituent in addition to X ^{1 to} X ⁴ , respectively. The substituents Ar ^{1 to} Ar ⁴ have other than X ^{1 to} X ⁴ include an alkyl group, an alkenyl group, an alkynyl group, a hydrocarbon ring group, a heterocyclic group, an alkoxy group, an alkylcarbonyl group, and a (hetero) aryloxy group. , (Hetero) aralkyloxy group, and optionally substituted amino group, nitro group, cyano group, ester group, halogen atom, hydroxyl group and the like. Preferably, an alkyl group having 1 to 20 carbon atoms, an alkenyl group having 2 to 20 carbon atoms, an alkynyl group having 2 to 20 carbon atoms, a hydrocarbon ring group having 3 to 20 carbon atoms, a 5- or 6-membered monocyclic ring, or A heterocyclic group derived from a 2-6 condensed ring, an alkoxy group having 1 to 9 carbon atoms, an alkylcarbonyl group having 2 to 18 carbon atoms, a (hetero) aryloxy group having 2 to 18 carbon atoms, a 3 to 18 carbon atoms ( Hetero) aralkyloxy group, amino group, alkylamino group having 2 to 20 carbon atoms, (hetero) arylamino group having 2 to 30 carbon atoms, nitro group, cyano group, ester group having 2 to 6 carbon atoms, halogen atom, Such as a hydroxyl group.

Examples of the alkyl group having 1 to 20 carbon atoms include methyl group, ethyl group, propyl group, isopropyl group, butyl group, iso-butyl group, sec-butyl group, tert-butyl group, hexyl group and octyl group. Can be mentioned.
Examples of the alkenyl group having 2 to 20 carbon atoms include vinyl group, propenyl group, butenyl group, 2-methyl-1-propenyl group, hexenyl group, octenyl group and the like.
Examples of the alkynyl group having 2 to 20 carbon atoms include ethynyl group, propynyl group, butynyl group, 2-methyl-1-propynyl group, hexynyl group, octynyl group and the like.
Examples of the hydrocarbon ring group having 3 to 20 carbon atoms include a cyclopropyl group, a cyclohexyl group, a cyclohexenyl group, a tetradecahydroanthranyl group, a phenyl group, an anthranyl group, a phenanthryl group, and a ferrocenyl group.

Heterocyclic groups derived from 5- or 6-membered monocyclic or 2-6 condensed rings include pyridyl, thienyl, benzothienyl, carbazolyl, quinolinyl, 2-piperidinyl, 2-piperazinyl, octahydroxy Examples include a nolinyl group.
Examples of the alkoxy group having 1 to 9 carbon atoms include methoxy group, ethoxy group, propoxy group, isopropoxy group, butoxy group, iso-butoxy group, sec-butoxy group, tert-butoxy group, hexyloxy group, octyloxy Groups and the like.
Examples of the alkylcarbonyl group having 2 to 18 carbon atoms include a methylcarbonyl group, an ethylcarbonyl group, an isopropylcarbonyl group, a tert-butylcarbonyl group, a cyclohexylcarbonyl group, and the like.

Examples of the (hetero) aryloxy group having 2 to 18 carbon atoms include aryloxy groups such as phenoxy group and naphthyloxy group, and heteroaryls such as 2-thienyloxy group, 2-furyloxy group, and 2-quinolyloxy group. An oxy group etc. are mentioned.
Examples of the (hetero) aralkyloxy group having 3 to 18 carbon atoms include aralkyloxy groups such as benzyloxy group, phenethyloxy group, naphthylmethoxy group, 2-thienylmethoxy group, 2-furylmethoxy group, 2-quino Heteroaralkyloxy groups such as a rylmethoxy group.
Examples of the alkylamino group having 2 to 20 carbon atoms include an ethylamino group, a dimethylamino group, a methylethylamino group, a dibutylamino group, and a piperidyl group.

Examples of the (hetero) arylamino group having 2 to 30 carbon atoms include arylamino groups such as diphenylamino group, dinaphthylamino group, naphthylphenylamino group, and ditolylamino group, di (2-thienyl) amino group, and di Examples include heteroarylamino groups such as (2-furyl) amino group and phenyl (2-thienyl) amino group.
Examples of the ester group having 2 to 6 carbon atoms include methoxycarbonyl group, ethoxycarbonyl group, propoxycarbonyl group, isopropoxycarbonyl group, tert-butoxycarbonyl group and the like.
Examples of the halogen atom include a fluorine atom, a chlorine atom, a bromine atom, and an iodine atom.

When Ar ^{1 to} Ar ⁴ each have two or more substituents other than X ^{1 to} X ⁴ , the substituents may be bonded to each other to form a cyclic structure. For example, when Ar ^{1 to} Ar ⁴ are groups derived from a benzene ring, the following (a-1) and (a-2) are examples in which substituents of the benzene ring are bonded to form a cyclic structure. ), (A-3). In the following, the part a is the bonding position to the porphyrin ring, and the part b is the bonding position to X ^{1 to} X ⁴ .
Ar ^{1 to} Ar ⁴ preferably have these substituents in addition to X ^{1 to} X ⁴ from the viewpoint of improving the film properties, but those having no substituent are preferable from the viewpoint of synthesis. .

<Molecular weight of Ar ^{1 to} Ar ⁴ >
The molecular weight of Ar ^{1 to} Ar ⁴ is 3,000 or less in total, including N, N-disubstituted amide structural groups and other substituents, from the viewpoint of preventing a decrease in recording sensitivity due to a decrease in absorbance. It is preferable that
{N, N-disubstituted amino group}

<Organic group of R ^{1 to} R ⁸ >
R ^{1 to} R ⁸ which are substituents of the N, N-disubstituted amino group moiety contained in the N, N-disubstituted amide structural group each independently represents an organic group having 20 or less carbon atoms.
Examples of the organic group represented by R ^{1 to} R ⁸ include an alkyl group, an alkenyl group, an alkynyl group, a hydrocarbon ring group, a heterocyclic group, an alkoxy group, an alkylcarbonyl group, a (hetero) aryloxy group, a (hetero) aralkyloxy group, An ester group etc. are mentioned. Preferably, it is an alkyl group having 1 to 20 carbon atoms, an alkenyl group having 2 to 20 carbon atoms, an alkynyl group having 2 to 20 carbon atoms, a hydrocarbon ring group having 3 to 20 carbon atoms, a 5- or 6-membered monocyclic ring, or A heterocyclic group derived from a 2-6 condensed ring, an alkoxy group having 1 to 9 carbon atoms, an alkylcarbonyl group having 2 to 18 carbon atoms, a (hetero) aryloxy group having 2 to 18 carbon atoms, a 3 to 18 carbon atoms ( A hetero) aralkyloxy group, an ester group having 2 to 6 carbon atoms, and the like.

In addition, as those specific examples, the C1-C20 alkyl group, C2-C20 alkenyl group, carbon number mentioned as the substituent which Ar < ¹ > -Ar < ⁴ > may have was mentioned. 2-20 alkynyl groups, C3-C20 hydrocarbon ring groups, 5- or 6-membered monocyclic or heterocyclic groups derived from 2-6 condensed rings, C1-C9 alkoxy groups, C2 Specific examples such as an alkylcarbonyl group having 18 to 18 carbon atoms, a (hetero) aryloxy group having 2 to 18 carbon atoms, a (hetero) aralkyloxy group having 3 to 18 carbon atoms, and an ester group having 2 to 6 carbon atoms are applicable.

R ¹ and R ² , R ³ and R ⁴ , R ⁵ and R ⁶ , R ⁷ and R ⁸ may be bonded to each other to form a cyclic structure. For example, the following structures (R-1), (R-2), and (R-3) are exemplified as N, N-disubstituted amino groups in which R ¹ and R ² are bonded to form a 6-membered ring. .
R ^{1 to} R ⁸ are preferably different from each other in terms of improving solubility and film property, but the same is preferable for the reason of synthesis. In addition, R ^{1 to} R ⁸ are preferably not sterically bulky with respect to the nitrogen atom of each amide structural group in terms of preventing the solubility of the compound from decreasing, specifically, an n-alkyl group, an n-alkenyl group, An n-alkynyl group, an alkoxy group, an alkylcarbonyl group and the like are preferable, and an n-alkyl group and an alkoxy group are particularly preferable.

<Molecular weight of R ¹ to R ^8>
In order to prevent a decrease in recording sensitivity due to a decrease in absorbance, the molecular weights of R ^{1 to} R ⁸ are preferably 3,000 or less in total.

{R ^{9 to} R ¹⁶ }
R ^{9 to} R ¹⁶ each independently represents a hydrogen atom or an electron-withdrawing substituent for reasons of synthesis and stability of the compound.
Examples of the electron-withdrawing substituent include an alkylcarbonyl group having 2 to 18 carbon atoms, an ester group having 2 to 6 carbon atoms, a halogen atom, a cyano group, and a nitro group. Specific examples thereof include those described above. Specific examples such as an alkylcarbonyl group having 2 to 18 carbon atoms, an ester group having 2 to 6 carbon atoms, and a halogen atom, which are exemplified as the substituents that Ar ^{1 to} Ar ⁴ may have, correspond.

Among these, it is preferable that the R ⁹ to R ¹⁶ reasons of synthesis are each a hydrogen atom or a halogen atom, R ⁹ to R ¹⁶ are each a halogen atom is particularly preferred from the viewpoint of improving light resistance However, from the viewpoint of synthesis, R ^{9 to} R ¹⁶ are each particularly preferably a hydrogen atom.
The molecular weights of R ^{9 to} R ¹⁶ are preferably 1,000 or less in total from the viewpoint of preventing a decrease in recording sensitivity due to a decrease in absorbance.

{M}
M represents a divalent or higher valent metal cation. Any metal element can be used as long as it can coordinate to the center of the porphyrin ring. Specific examples include Mg, Al, Si, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Mo, Ru, Rh, Pd, Ag, Pt, Au, Er, etc. are mentioned.
It is preferable that M is a divalent or higher metal cation to improve the stability of the compound, and that the metal corresponding to M does not exhibit diamagnetism from the viewpoint of improving the recording sensitivity of the compound. Ni, Cu are preferred.

When M is a trivalent or higher metal ion, M may be further bonded to a counter anion. Thereby, the whole molecule | numerator of the compound represented by general formula [II] becomes neutral. The types of counter anions include alkoxy ions, (hetero) aryloxy ions, (hetero) aralkyloxy ions, and optionally substituted cyano ions, ester ions, halogen ions, hydroxy ions, oxygen ions, etc. Examples thereof include alkoxy ions having 1 to 9 carbon atoms, (hetero) aryloxy ions having 2 to 18 carbon atoms, and (hetero) aralkyloxy ions having 3 to 18 carbon atoms. Specific examples thereof include , Ar ¹ to Ar ⁴ alkoxy group having 1 to 9 carbon atoms, which is exemplified as the substituent which may be possessed by the above-described C2-18 (hetero) aryl group, having 3 to 18 carbon atoms ( It corresponds to a specific example such as (hetero) aralkyloxy group replaced by an ion.
The counter anion having a smaller molecular weight is preferred in terms of improving the sensitivity of the compound, and in particular, those having a molecular weight of 200 or less such as acetoxy ion, cyano ion, chlorine ion, oxygen ion are preferred.

{Molecular weight}
The compound represented by the general formula [II] described above usually has a molecular weight of 6,000 or less, particularly preferably 3,000 or less, from the viewpoint of preventing sensitivity from being reduced due to a decrease in absorbance.
The compound represented by the general formula [II] is usually preferably insoluble in water.

{Concrete example}
Specific examples of the compound represented by the general formula [II] are illustrated below, but the present invention is not limited thereto. In the following, Et is an ethyl group.

{Synthesis method}
The compound represented by the general formula [II] can be easily synthesized by the method described in, for example, “Bioorg. Med. Chem., 2002 (10 volumes), 3013-3021”.
For example, X ¹ (= Q ¹ ) to X ⁴ (= Q ⁴ ) are all carbonyl groups (that is, NX ¹ (= Q ¹ ) to NX ⁴ (= Q ⁴ ) are carbamoyl groups N—C (= In the case of O)), a tetraarylporphyrin compound having a N, N-disubstituted carbamoyl group is obtained by heating a tetraarylporphyrin compound having a commercially available carboxyl group under thionyl chloride mixing conditions and further reacting with a disubstituted amine. be able to. A tetraarylporphyrin metal complex having an N, N-disubstituted carbamoyl group can be obtained by reacting the resulting tetraarylporphyrin compound and a metal salt in the presence or absence of a solvent at room temperature or under heating conditions.
A tetraarylporphyrin compound having X ¹ (= Q ¹ ) to X ⁴ (= Q ⁴ ) other than the carbonyl group can be synthesized in the same manner by changing the tetraarylporphyrin compound as a starting material. it can.

(Recording layer formation method)
Examples of the method for forming the recording layer 22 include a coating method, a vacuum deposition method, and the like, and it is particularly preferable to form the recording layer 22 by a coating method. That is, the coating liquid for the recording layer 22 is prepared by dissolving the dye as a main component and other components such as a binder and a quencher in an appropriate solvent, and the above-described reflective layer 23 or the intermediate layer on the reflective layer. Apply to. The concentration of the main component pigment in the solution is usually 0.01% by weight or more, preferably 0.1% by weight or more, more preferably 0.2% by weight or more, and usually 10% by weight or less, preferably 5% by weight. % Or less, more preferably 2% by weight or less. Thereby, the recording layer 22 is usually formed to a thickness of about 1 nm to 100 nm. In order to make the thickness 50 nm or less (preferably less than 50 nm), the dye concentration is preferably less than 1% by weight, and more preferably less than 0.8% by weight. It is also preferable to further adjust the number of rotations of coating.

  Solvents for dissolving materials such as main component dyes include alcohols such as ethanol, n-propanol, isopropanol, n-butanol and diacetone alcohol; fluorinations such as tetrafluoropropanol (TFP) and octafluoropentanol (OFP). Hydrocarbon solvents; glycol ethers such as ethylene glycol monomethyl ether, ethylene glycol monoethyl ether and propylene glycol monomethyl ether; esters such as butyl acetate, ethyl lactate and cellosolve acetate; chlorinated hydrocarbons such as dichloromethane and chloroform; dimethylcyclohexane Hydrocarbons such as tetrahydrofuran, ethers such as ethyl ether and dioxane, and ketones such as methyl ethyl ketone, cyclohexanone and methyl isobutyl ketone Door can be. These solvents can be appropriately selected in consideration of the solubility of a pigment material or the like that is a main component to be dissolved. In addition, any one of these solvents may be used alone, or two or more thereof may be mixed and used.

As the binder, organic polymers such as cellulose derivatives, natural polymer substances, hydrocarbon resins, vinyl resins, acrylic resins, polyvinyl alcohol, and epoxy resins can be used. Further, the recording layer 22 can contain various dyes or anti-fading agents other than the dyes in order to improve light resistance. As the antifading agent, a singlet oxygen quencher is generally used. The amount of the anti-fading agent such as a singlet quencher is usually 0.1% by weight or more, preferably 1% by weight or more, more preferably 5% by weight or more, and usually 50% by weight with respect to the recording layer material. % Or less, preferably 30% by weight or less, more preferably 25% by weight or less.
Examples of the coating method include a spray method, a spin coating method, a dip method, and a roll coating method. In particular, in a disk-shaped optical recording medium, the uniformity of the film thickness is ensured and the defect density is reduced. The spin coating method is preferable because it can be reduced.

(Interface layer)
In the present embodiment, in particular, by providing an interface layer between the recording layer 22 and the cover layer 24, it is possible to effectively utilize the swelling of the recording layer 22 toward the cover layer 24, d _bmp <0. it can. The thickness of the interface layer is more preferably 1 nm to 50 nm. More preferably, the upper limit is 30 nm. The lower limit is preferably 5 nm or more. It is desirable that the reflection at the interface layer be as small as possible. This is because the phase change of the reflected light from the reflection layer 23 which is the main reflection surface is selectively used. It is not preferable in the present embodiment that the interface layer has a main reflection surface. For this reason, it is desirable that the difference in refractive index between the interface layer and the recording layer 22 or between the interface layer and the cover layer 24 is small. The difference is preferably 1 or less, more preferably 0.7 or less, and still more preferably 0.5 or less.

  It should be noted that the interface layer is used to suppress the formation of the mixed layer 25m as shown in FIG. 4, to prevent corrosion due to an adhesive when the cover layer 24 is stuck on the recording layer 22 in the reverse configuration, The effect of preventing the elution of the recording layer 22 by the solvent when applying the coating 24 is known, and in the present embodiment, such an effect can be used as appropriate. The material used for the interface layer is preferably a material that is transparent to the recording / reproducing light wavelength and is chemically, mechanically, and thermally stable. Here, “transparent” means that the transmittance with respect to the recording / reproducing light beam 27 is 80% or more, and more preferably 90% or more. The upper limit of the transmittance is 100%.

The interface layer is preferably a dielectric compound such as a metal, an oxide such as a semiconductor, a nitride, a carbide, a sulfide, a fluoride such as magnesium (Mg), calcium (Ca), or a mixture thereof. As described above, the refractive index of the interface layer preferably has a difference from the refractive index of the recording layer or the cover layer of 1 or less, and the value is preferably in the range of 1 to 2.5. Depending on the hardness and thickness of the interface layer, the deformation of the recording layer 22, in particular, the bulging deformation (d _bmp <0) toward the cover layer 24 can be promoted or suppressed. In order to effectively utilize the bulging deformation, a dielectric material having a relatively low hardness is preferable, and in particular, ZnO, In ₂ O ₃ , Ga ₂ O ₃ , ZnS, sulfides of rare earth metals, other metals, A material in which a semiconductor oxide, nitride, or carbide is mixed is preferable. A sputtered plastic film or a plasma polymerized film of hydrocarbon molecules can also be used. Even if the interface layer is provided, if the thickness and refractive index are uniform in the recording groove portion and the inter-groove portion and do not change remarkably by recording, the optical path lengths and equations in Equations (2) and (3) Expressions (7) to (9) hold as they are.

(Cover layer)
The cover layer 24 is made of a material that is transparent to the recording / reproducing light beam 27 and has a small amount of birefringence. It is formed by curing with heat or the like. The cover layer 24 preferably has a transmittance of 70% or more and more preferably 80% or more with respect to the wavelength λ of the recording / reproducing light beam 27.

  The plastic used as the sheet material is polycarbonate, polyolefin, acrylic, cellulose triacetate, polyethylene terephthalate, or the like. For adhesion, light, radiation curing, thermosetting resin, or pressure sensitive adhesive is used. As the pressure-sensitive adhesive, pressure sensitive adhesives made of acrylic, methacrylate, rubber, silicon, and urethane polymers can be used.

  For example, after the photocurable resin constituting the adhesive layer is dissolved in a suitable solvent to prepare a coating solution, this coating solution is applied onto the recording layer 22 or the interface layer to form a coating film, Overlay the polycarbonate sheet. Thereafter, the coating liquid is further stretched and developed by rotating the medium in a superposed state as necessary, and then cured by irradiating ultraviolet rays with a UV lamp. Alternatively, a pressure sensitive adhesive is applied to the sheet in advance, the sheet is overlaid on the recording layer 22 or the interface layer, and then pressed and pressed with an appropriate pressure.

  The pressure-sensitive adhesive is preferably an acrylic or methacrylate polymer pressure-sensitive adhesive from the viewpoint of transparency and durability. More specifically, 2-ethylhexyl acrylate, n-butyl acrylate, iso-octyl acrylate and the like are used as main component monomers, and these main component monomers are used as acrylic acid, methacrylic acid, acrylamide derivatives, maleic acid, hydroxyl ethyl acrylate, A polar monomer such as glycidyl acrylate is copolymerized. Glass transition temperature Tg, tack performance (adhesive force immediately formed when contacted at low pressure), peel strength by adjusting the molecular weight of the main monomer, mixing its short chain components, and adjusting the crosslink point density with acrylic acid The physical properties such as shear holding power can be controlled (Alphonsus V. Pocius, written by Hiroshi Mizumachi, Hirokuni Ono, "Introduction to Adhesives and Adhesive Technology", Nikkan Kogyo Shimbun, 1999, Chapter 9 ). As the solvent for the acrylic polymer, ethyl acetate, butyl acetate, toluene, methyl ethyl ketone, cyclohexane and the like are used. The pressure-sensitive adhesive preferably further contains a polyisocyanate-based crosslinking agent.

The pressure-sensitive adhesive is made of the above-mentioned material. A predetermined amount is uniformly applied to the surface of the cover layer sheet material in contact with the recording layer side, and the solvent is dried. If it has, it is cured by applying pressure to the surface) with a laminating roller or the like. When the cover layer sheet material coated with the pressure-sensitive adhesive is bonded to the surface of the recording medium on which the recording layer is formed, it is preferably bonded in a vacuum so as not to entrain air and form bubbles.
Also, after applying the above-mentioned pressure-sensitive adhesive on the release film and drying the solvent, the cover layer sheet is bonded, and the release film is further peeled off to integrate the cover layer sheet and the pressure-sensitive adhesive layer, and then the recording medium You may paste together.

  When the cover layer 24 is formed by a coating method, a spin coating method, a dip method, or the like is used. In particular, a spin coating method is often used for a disk-shaped medium. Similarly, as the cover layer 24 material by application, urethane, epoxy, acrylic resin, or the like is used, and after application, it is cured by irradiating with ultraviolet rays, electron beams, or radiation to accelerate radical polymerization or cationic polymerization.

Here, in order to use the deformation of d _bmp <0, at least the recording layer 22 of the cover layer 24 or the layer on the side in contact with the interface layer (at least in a range equal to or thicker than d _GL ) It is desirable to easily follow the bulging deformation. Thus, d _bmp is preferably in the range of 1 to 3 times d _G. Rather, it is desirable to actively use a large deformation of 1.5 times or more. The cover layer 24 preferably has an appropriate softness (hardness). For example, when the cover layer 24 is made of a resin sheet material having a thickness of 50 μm to 100 μm and is bonded with a pressure-sensitive adhesive, the adhesive Since the glass transition temperature of the layer is as low as −50 ° C. to 50 ° C. and is relatively soft, the deformation of d _bmp <0 is relatively large. Particularly preferred is that the glass transition temperature is not more than room temperature. The thickness of the adhesive layer made of an adhesive is usually preferably 1 μm to 50 μm, and more preferably 5 μm to 30 μm. It is preferable to provide a deformation promoting layer that controls the thickness of the adhesive layer material, the glass transition temperature, and the crosslinking density to positively control the amount of swelling deformation. Alternatively, the cover layer 24 formed by a coating method is also applied in multiple layers by dividing it into a relatively low hardness deformation promoting layer having a thickness of 1 μm to 50 μm, more preferably 5 μm to 30 μm, and the remaining thickness. Is preferable for controlling the deformation amount d _bmp .

  As described above, when a deformation promoting layer made of an adhesive, an adhesive, a protective coating agent, or the like is formed on the recording layer (interface layer) side of the cover layer, a glass transition temperature Tg of 25 is given to give a certain flexibility. It is preferably not higher than ° C., more preferably not higher than 0 ° C., and further preferably not higher than −10 ° C. The glass transition temperature Tg here is a value measured after curing of the pressure-sensitive adhesive, adhesive, protective coating agent, and the like. A simple method for measuring Tg is differential scanning calorimetry (DSC). It can also be obtained by measuring the temperature dependence of the storage modulus with a dynamic viscoelasticity measuring device (Alphonsus V. Pocius, Hiroshi Mizumachi, Hirokuni Ono, "Introduction to Adhesives and Adhesive Technology") "Nikkan Kogyo Shimbun, 1999, Chapter 5).

Promoting the deformation of d _bmp <0 has the advantage that not only the signal amplitude of LtoH can be increased, but also the recording power required for recording can be reduced. On the other hand, if the deformation is too large, the crosstalk becomes large or the push-pull signal becomes too small. Therefore, it is preferable that the deformation promoting layer keeps an appropriate viscoelasticity even at the glass transition temperature or higher.

The cover layer 24 may further be provided with a layer having a thickness of about 0.1 μm to 50 μm on the surface in order to impart functions such as scratch resistance and fingerprint resistance to the incident light side surface. The thickness of the cover layer 24 depends on the wavelength λ of the recording / reproducing light beam 27 and the NA (numerical aperture) of the objective lens 28, but is preferably in the range of 0.01 mm to 0.3 mm, and 0.05 mm to 0.15 mm. A range is more preferred. It is preferable that the entire thickness including the thickness of the adhesive layer, the hard coat layer, and the like be in an optically acceptable thickness range. For example, in a so-called Blu-ray disc, it is preferable to control to about 100 μm ± 3 μm or less.
Incidentally, as in the case of providing the deformation facilitating layer, if provided layers having different refractive index in the recording layer side of the cover layer, as a cover layer refractive index n _c of the present invention, refers to the value of the recording layer side of the layer To do.

(Other configurations)
Note that the optical recording medium of the present embodiment may have an arbitrary layer in addition to the above-described layers as long as it does not depart from the spirit of the present invention. For example, in addition to the interface between the recording layer 22 and the cover layer 24 described above, between the substrate 21 and the reflective layer 23, in order to prevent mutual contact / diffusion of the layers, and to adjust the phase difference and reflectance, An interfacial layer can be inserted.

Hereinafter, the present invention will be described in more detail with reference to examples. However, the present invention is not limited to the following examples.
(Example 1)
An alloy target having a composition of Ag _98.1 Nd _1.0 Cu _0.9 on a polycarbonate resin substrate on which a guide groove having a track pitch of 0.32 μm, a groove width of about 0.18 μm and a groove depth of about 55 nm is formed (the composition is atomic% The reflective layer having a thickness of about 70 nm was formed by sputtering. An intermediate layer having a thickness of about 2 nm was formed by sputtering Nb on the reflective layer. Further, a dye represented by the following structural formula was dissolved in octafluoropentanol (OFP), and the resulting solution was formed on the intermediate layer by a spin coating method.
This structural formula had a refractive index of 1.08 and an extinction coefficient of 1.15. The refractive index and extinction coefficient were measured by ellipsometry (polarization analysis) using an ellipsometer “MEL-30S” manufactured by JASCO Corporation (Patent Document 45, Hiroyuki Fujiwara, “Spectroscopic Ellipsometry”, Maruzen Publishing Co., Ltd.) , 2003, Chapter 5). The absorption spectrum of the recording layer alone applied on the polycarbonate resin substrate was measured using a spectrophotometer (manufactured by Shimadzu Corporation, UV-3150).

Furthermore, the groove depth and groove width of the substrate were measured using an atomic force microscope (AFM: NanoScope IIIa manufactured by Digital Instruments).
FIG. 9 shows the absorption spectrum of the recording layer alone coated on the polycarbonate resin substrate and the wavelength dependence of n _d and k _d .

The conditions for the spin coating method are as follows. That is, a solution in which the above dye is dissolved in OFP at a concentration of 0.66% by weight is applied in the form of a ring of 1.5 g in the vicinity of the center of the disk (the reflection layer and the intermediate layer formed on the substrate). The dye solution was stretched at 120 rpm for about 4 seconds and 1200 rpm for about 3 seconds, and then applied at 9200 rpm for 3 seconds to shake off the dye solution. After the application, the disc was kept in an environment of 100 ° C. for 1 hour, and the recording layer was formed by evaporating and removing the OFP as the solvent.
Thereafter, an interface layer made of ZnS—SiO ₂ (molar ratio 80:20) was formed on the recording layer to a thickness of about 16 nm by sputtering. A transparent cover layer having a total thickness of 100 μm composed of a polycarbonate resin sheet having a thickness of 75 μm and a pressure-sensitive adhesive layer having a thickness of 25 μm is bonded to the optical recording medium (the optical recording medium of Example 1). Recording medium).

(Example 2)
An alloy target having a composition of Ag _98.1 Nd _1.0 Cu _0.9 on a polycarbonate resin substrate on which a guide groove having a track pitch of 0.32 μm, a groove width of about 0.18 μm, and a groove depth of about 60 nm is formed. The reflective layer having a thickness of about 65 nm was formed by sputtering. A dye represented by the following structural formula was dissolved in octafluoropentanol (OFP) on the reflective film, and the obtained solution was formed on the intermediate layer by a spin coating method.

The refractive index of this structural formula was 0.98, and the extinction coefficient was 1.22. FIG. 10 shows the absorption spectrum of the recording layer alone coated on the polycarbonate resin substrate and the wavelength dependence of n _d and k _d .

The subsequent steps such as the spin coating method and the recording layer forming method are the same as those in the first embodiment.
Thereafter, an interface layer made of ZnS—SiO ₂ (molar ratio 80:20) was formed on the recording layer to a thickness of about 16 nm by sputtering. A transparent cover layer having a total thickness of 100 μm composed of a polycarbonate resin sheet having a thickness of 75 μm and a pressure-sensitive adhesive layer having a thickness of 25 μm is bonded to the optical recording medium (the optical recording medium of Example 1). Recording medium).

(Comparative Example 1)
An alloy target having a composition of Ag _98.1 Nd _1.0 Cu _0.9 on a polycarbonate resin substrate on which a guide groove having a track pitch of 0.32 μm, a groove width of about 0.18 μm, and a groove depth of about 60 nm is formed. The reflective layer having a thickness of about 65 nm was formed by sputtering. On the reflective film, an azo dye represented by the following structural formula was dissolved in octafluoropentanol (OFP), and the resulting solution was formed on the intermediate layer by spin coating.

The refractive index of the dye material having the above structural formula was 1.24, and the extinction coefficient was 0.24. The subsequent steps such as the spin coating method and the recording layer forming method are the same as those in the first embodiment.
Thereafter, an interface layer made of ZnS—SiO ₂ (molar ratio 80:20) was formed on the recording layer to a thickness of about 20 nm by sputtering. A transparent cover layer having a total thickness of 100 μm composed of a polycarbonate resin sheet having a thickness of 75 μm and a pressure-sensitive adhesive layer having a thickness of 25 μm is bonded to the optical recording medium (the optical recording medium of Comparative Example 1). Recording medium).

(Evaluation conditions)
The recording / reproduction evaluation with respect to the optical recording media of Examples 1 and 2 was performed by recording / reproducing light wavelength λ = 406 nm, NA (numerical aperture) = 0.85, and a focused beam spot diameter of about 0.42 μm (1 / e ^{2 of} center intensity). This was performed using an ODU1000 tester manufactured by Pulstec Corp. having an optical system of Recording / reproduction was performed on the substrate groove (in-groove).

  The recording was performed by setting the linear velocity to 4.92 m / s to 1 × speed and rotating to 1 × speed or 2 × speed to record a (1, 7) RLL-NRZI modulated mark length modulation signal (17PP). The reference clock period T is 15.15 nsec. (Channel clock frequency 66 MHz) and 7.58 nsec. (Channel clock frequency 132 MHz). Recording conditions such as recording power and recording pulse were adjusted so that the following jitter was minimized. Reproduction was performed at 1 × speed, and jitter and reflectance were measured.

Jitter measurement was performed according to the following procedure. That is, the recording signal was waveform-equalized by a limit equalizer and then binarized. Thereafter, a time difference distribution σ between the rising edge and falling edge of the binarized signal and the rising edge of the channel clock signal was measured by a time interval analyzer. Then, with the channel clock period as T, jitter (%) was measured by σ / T (data to clock jitter).
Since the reflectance is proportional to the voltage output value of the reproduction detector, the value was obtained by normalizing this voltage output value with a known reflectance R _ref . In both the examples and comparative examples, the reflectance increased by recording.

In the recording signal, the reflectance of the highest reflectance part (9T mark) and the lowest reflectance part (9T space) are R _H and R _L , respectively.
m = (R _H −R _L ) / R _H
The degree of modulation m was calculated by
For the push-pull signal, the value of the standardized push-pull signal intensity (IPP _actual ) was measured.

(Evaluation results)
FIG. 11 is a transmission electron micrograph of the cross section of the disk used in Example 1. FIG. 11A is a transmission electron microscope (TEM) photograph of the cross section of the unrecorded disk, and FIG. 11B is a transmission electron microscope (TEM) photograph of the cross section of the recorded disk. The cross-sectional sample was produced as follows. When the adhesive tape is applied to the cover layer and pulled, the peeled surface at the partially exposed interface layer / cover layer interface is taken out. W (tungsten) is deposited on the peeled surface for protection. Further, from the upper part of the peeled surface coated with W, sputtering is performed by irradiating high-speed ions in a vacuum to form holes. What formed the cross section in the side surface of the hole was observed with the transmission electron microscope.

In the cross-sectional images of FIG. 11A and FIG. 11B, the recording layer is an organic substance, so that it transmits electrons and thus appears whitish. It can be seen that the recording layer thickness d _L is substantially zero in the recording groove portion (cover layer groove portion), and the recording layer thickness d _G is about 29 nm in the recording groove portion. Further, the groove depth d _GL defined by the step of the reflection reference surface is about 53 nm, which is almost the same as that measured on the substrate surface by AFM. In the recording pit portion, it can be seen from the shape of the interface layer that the recording layer is deformed so as to swell toward the cover layer (that is, d _bmp <0 in FIG. 4). Furthermore, since it is whitish compared to an unrecorded recording layer, it is considered that a cavity (that is, n _d '= 1) is formed. It can also be seen that the recording pit is confined in the groove without protruding from the recording groove.

Note that the height of the cavity after recording from the reflection reference plane is about 88 nm, and d _bmp = 59 nm. It was also confirmed that d _{pit ≈d mix ≈0} because no alteration or deformation was observed at the reflective layer / substrate interface. Now, these values and n _d = 1.08, n _c = 1.5, δn _d = 1.08−1 = 0.08 (where the refractive index in the cavity is 1), λ = 406 nm, Using d _G ≈29 nm, d _L ≈0 nm, and d _GL ≈53 nm, the value of each phase in the present embodiment is estimated as follows.

Φb in equation (7) is
Φb = (4π / 406) × (0.42 × 29−1.5 × 53) ≈−0.66π
Therefore, | Φb ₂ | <π.
ΔΦ in equation (9) is
ΔΦ = (4π / 406) × (0.42 × 59 + 0.08 × 88) ≈0.31π
Therefore, ΔΦ normally satisfies the assumption that it is equal to or less than (π / 2).
In addition, Φa in Equation (8) is
Φa≈ (−0.66 + 0.31) π = −0.35π
And | Φb |> | Φa |.

It has been clarified that the phase change depends on the refractive index change accompanied by the cavity formation by the recording pit portion, and that the recording layer swells to the cover layer side at the recording pit portion. Although δn _d <0, it can be seen that the recording using the phase change of ΔΦ> 0 can be performed by actively using d _bmp <0.
Further, since the polarity of the push-pull signal did not change, it can be said that LtoH recording is performed by the phase change of 0 <| Φa | <| Φb | <π.
In Example 2 as well, the formation of cavities in the recording pit portion and the deformation expanding to the cover layer side were confirmed.

The jitter σ, reflectivity R _H , R _L , and modulation degree m in the optical recording medium of Example 1 are as follows: σ = 5.1%, R _H = 34.2%, R _L = 17.5 in 1 × speed recording. %, M = 0.49, and in double speed recording, σ = 6.1%, R _H = 33.4%, R _L = 17.4%, and m = 0.48.
Further, the normalized push-pull strength was 0.54 before recording, 0.26 after recording at 1 × speed, and 0.32 after 2 × recording. The power during recording was 5.6 mW at 1 × speed and 7.0 mW at 2 × speed.
As a result of studies, the present inventors have found that the jitter in a Blu-ray disc is 7.0% or less, the recording power is 7.0 mW or less, and the normalized push-pull signal intensity is 0.21 to 0.60. If it is within the range, it is considered that the characteristics are practically sufficient. It can be seen that the above numerical values of Example 1 satisfy these criteria.

The jitter σ, reflectivity R _H , R _L , and modulation degree m in the optical recording medium of Example 2 are as follows: σ = 6.1%, R _H = 38.8%, R _L = 21.9 for 1 × speed recording. %, M = 0.44. The normalized push-pull signal strength was 0.50 before recording and 0.32 after recording at 1 × speed. In Example 2, the standard of the Blu-ray disc is substantially satisfied while recording at 1 × speed.
The jitter σ and reflectance R _H in the optical recording medium of Comparative Example 1 are σ = 7.8% and R _H = 30.8% in 1 × speed recording, and σ = 11.8% in 2 × speed recording. , R _H = 31.2%. The recording power was 6.6 mW at 1 × speed and 8.0 mW at 2 × speed. In the optical recording medium of Comparative Example 1, it can be seen that the jitter value and the recording power value at double speed cannot satisfy the standard of the Blu-ray Disc.
From the above results, it can be seen that the present invention can provide an excellent optical recording medium that satisfies the Blu-ray Disc standard for both 1 × speed recording and 2 × speed recording.

  The present invention is particularly suitable for use in film surface incident type blue laser compatible optical recording media and the like.

It is a figure explaining the write-once type medium (optical recording medium) which has a recording layer which has the pigment of the conventional composition as a main component. It is a figure explaining the write-once type medium (optical recording medium) of the film surface incidence composition which has the recording layer which has the pigment as a main component to which this embodiment is applied. It is a figure for demonstrating the reflected light of the recording / reproducing light beam which injects from the board | substrate side of the board | substrate incident structure of FIG. 1 which is a conventional structure. It is a figure explaining the phase difference in the case of recording in the layer structure of a film surface incident type medium, and a cover layer groove part. It is a figure explaining the phase difference in the case of recording on the layer structure of a film surface incident type medium, and a cover layer groove part. It is a figure explaining the relationship between the phase difference of a recording groove part and a recording groove part, and reflected light intensity. It is a figure explaining the structure of the 4 division | segmentation detector which detects a recording signal (sum signal) and a push pull signal (difference signal). It is a figure which shows the signal detected after actually passing the low frequency pass filter (cutoff frequency about 30kHz) through the output signal obtained crossing a some groove part and a groove part. 6 is a graph showing the absorption spectrum of the recording layer dye of Example 1 and the wavelength dependence of nd and kd. 6 is a graph showing the absorption spectrum of the recording layer dye of Example 2 and the wavelength dependence of nd and kd. 2 is a transmission electron micrograph of the cross section of the disk used in Example 1. FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10, 20 ... Optical recording medium, 11, 21 ... Substrate, 12, 22 ... Recording layer, 13, 23 ... Reflective layer, 14 ... Protective coat layer, 15 ... Substrate groove part, 16 ... Substrate groove part, 16m, 25m, 26m ... mixed layer, 16p, 25p, 26p ... recording pit portion, 17, 27 ... recording / reproducing light beam, 18, 28 ... objective lens, 24 ... cover layer, 25 ... cover layer groove portion, 26 ... cover layer groove portion, 19, 29... Surface on which the recording / reproducing light beam is incident

Claims (7)

A substrate on which guide grooves are formed;
A layer having a light reflecting function on the substrate;
A recording layer mainly composed of a porphyrin compound represented by the following general formula [I];
In an optical recording medium comprising in this order a cover layer capable of transmitting recording / reproducing light incident on the recording layer,
The recording / reproducing light wavelength λ is 350 nm to 450 nm,
When the recording / reproducing light beam obtained by converging the recording / reproducing light is a recording groove that is a guide groove on the side far from the surface on which the cover layer is incident,
An optical recording medium, wherein a reflected light intensity of a recording pit portion formed in the recording groove portion is higher than a reflected light intensity in an unrecorded state in the recording groove portion.
(In the general formula [I], Ar ^{a1 to} Ar ^a4 each independently represent an aromatic ring, and each may have a plurality of substituents.
R ^{a1 to} R ^a8 each independently represents a hydrogen atom or an arbitrary substituent,
M ^a represents a divalent or higher valent metal cation. However, when M ^a is trivalent or more, the molecule may further have a counter anion so that the whole molecule is neutral. ) The recording pit portion is characterized in that a cavity is formed inside the recording layer or at an interface with a layer adjacent to the recording layer, and the recording layer is accompanied by a shape change that expands toward the cover layer. Item 4. The optical recording medium according to Item 1. The optical recording medium according to claim 1, wherein the porphyrin compound is a tetraarylporphyrin compound represented by the following general formula [II].
(In the formula [II], X ^{1 to} X ⁴ each independently represent an atom having a valence of 4 or more, and when X ^{1 to} X ⁴ are an atom having a valence of 5 or more, X ^{1 to} X ⁴ are further optional. May have a substituent, and when X ^{1 to} X ⁴ are atoms having a valence of 6 or more, each of them may have two = Q ¹ to = Q ⁴ , in which case the two Q ^{1 to} Q ⁴ may be the same or different.
Q ^{1 to} Q ⁴ each independently represent a group 16 atom of the periodic table.
Ar ^{1 to} Ar ⁴ each independently represent an aromatic ring, and each may have a substituent other than X ^{1 to} X ⁴ .
R ^{1 to} R ⁸ each independently represents an organic group having 20 or less carbon atoms,
R ^{9 to} R ¹⁶ each independently represents a hydrogen atom or an electron-withdrawing substituent,
M represents a divalent or higher valent metal cation. However, when M is trivalent or more, the molecule may further have a counter anion so that the whole molecule is neutral.
R ¹ and R ² , R ³ and R ⁴ , R ⁵ and R ⁶ , R ⁷ and R ⁸ may be bonded to form a ring. ) 4. An interface layer for preventing mixing of the recording layer material and the cover layer material is further provided between the recording layer and the cover layer. The optical recording medium according to Item. The optical recording medium according to claim 1, further comprising an intermediate layer between the layer having the light reflection function and the recording layer. The optical recording medium according to claim 5, wherein the intermediate layer contains at least one element selected from the group consisting of Ta, Nb, V, W, Mo, Cr, and Ti. When the interface on the recording layer side of the layer having the light reflection function is a reflection reference surface, and the guide groove portion that does not form the recording pit portion is a recording groove portion, the recording groove portion defined by the reflection reference surface; step d _GL between the recording land part, characterized in that a 30 to 70 nm, an optical recording medium according to any one of claims 1 to 6.