JP4523575B2 - Structure and optical recording medium using the same - Google Patents

Description

  The present invention relates to a structure applicable to electronic materials, optical materials and the like, and an optical recording medium using the same.

Introducing a nanometer-sized functional material into a polymer to form a composite can yield a functional composite material that exhibits new functions such as electronic properties, conductive properties, optical properties, and magnetic properties. It is an important technology.
Conventionally, metal-organic composite materials using metal fine particles (metal nanoclusters) as functional materials have been researched and developed. Research and development of nanometer-sized dye materials and polymers that can be expected to have unlimited material flexibility and functionality are also underway. However, in a functional composite material using a polymer, the glass transition point and the softening point are low, and the created nanometer-size pattern may collapse.

  On the other hand, in the optical memory field, CD-R, DVD-R, DVD + R, and the like that are recordable according to the CD standard and the DVD standard, which are optical recording media having a reflective layer on a substrate, have been commercialized. In the future, in such an optical recording medium, further recording capacity and downsizing are desired, and further improvement in recording density is required. Elemental technologies for improving the recording capacity in the current system include a recording pit miniaturization technology and an image compression technology represented by MPEG2. In order to reduce the recording / reproducing light wavelength and increase the diffraction limit, the recording pit miniaturization technology has been studied to increase the numerical aperture NA of the optical system, but recording / reproduction exceeding the diffraction limit is not possible. Is possible. Thus, super-resolution technology capable of recording / reproduction exceeding the diffraction limit and optical memory systems using near-field light have attracted attention as promising means, but they have not yet been put into practical use due to the high technical hurdles.

Examples in which the microphase separation structure is applied to a recording medium are disclosed in Patent Documents 1 to 3 listed below.
JP 2003-89269 A JP 2004-347978 A JP 2005-112934 A

  The present invention provides a novel structure having a structure in which a functional material of nanometer size is dispersed in a polymer, and the structure is applied to a recording layer of an optical recording medium to provide a conventional optical disk. Therefore, an object of the present invention is to provide an optical recording medium that can be recorded / reproduced at a recording density exceeding the diffraction limit of a pickup lens, and that can stabilize the structure simultaneously with optical recording.

  As a result of various investigations, the present inventor can obtain the structure intended by the present invention by using the microphase separation phenomenon of the block copolymer and incorporating a component capable of photocrosslinking in one phase. did it. Further, by utilizing the structure as an optical recording medium, recording / reproduction at a recording density exceeding the diffraction limit of the laser pickup can be performed.

The invention according to claim 1 has a microphase separation structure formed by a block copolymer in which polymer chains that are incompatible with each other are bonded, and at least one separated phase of the microphase separation structure has a light phase. The structure is characterized in that a cross-linking group is chemically bonded.
The invention according to claim 2 is the structure according to claim 1, wherein the microphase-separated structure is spherical, columnar, or a structure similar to each of the shapes.
According to a third aspect of the present invention, in the structure according to the first or second aspect, the photocrosslinking group is contained in the spherical, columnar, or structural portion similar to each of the shapes. is there.
The invention according to claim 4 is the structure according to any one of claims 1 to 3, wherein the photocrosslinking group is photodimerized.
A fifth aspect of the present invention is an optical recording medium comprising the structure according to any one of the first to fourth aspects as a recording layer on a substrate.
The invention according to claim 6 is the optical recording medium according to claim 5, wherein the diameter of the cross-section of the microphase-separated structure having a spherical shape, a columnar shape, or a structure similar to each shape is smaller than the recording wavelength. It is.
The invention according to claim 7 is the optical recording medium according to claim 5 or 6, wherein a groove is formed on the substrate and the structure is formed thereon.

  ADVANTAGE OF THE INVENTION According to this invention, the structure which has the structure where the functional material of nanometer size which the application as an electronic material and an optical material was anticipated disperse | distributed in the polymer can be provided. Further, according to the present invention, the structure can be applied to the recording layer of an optical recording medium, and can be recorded / reproduced at a recording density exceeding the diffraction limit of a pickup lens, which cannot be realized with a conventional optical disk. A recording medium can be provided. Since the optical recording medium of the present invention undergoes a crosslinking reaction simultaneously with optical recording, the structure can also be stabilized.

Hereinafter, the present invention will be described in more detail.
The structure of the present invention comprises a block copolymer in which polymer chains incompatible with each other are bonded as a main component, and a group that is photocrosslinked to at least one separated phase of a microphase-separated structure formed by the copolymer. Are chemically bonded. Since the photocrosslinking group is chemically bonded to the block copolymer in advance, the photocrosslinking reaction becomes a reaction between the polymers and is easy to stabilize, thereby contributing to the stabilization of the structure.

In the structure of the present invention, the photocrosslinking group is present in a highly ordered manner in the polymer matrix at nanometer size. The micro phase separation phenomenon of the block copolymer is used as the driving force. As the microphase separation structure, a spherical structure (sea-island structure) as shown in FIG. 1 (a), a columnar structure as shown in FIG. 1 (b), or a similar structure is preferable. The photocrosslinking group is preferably contained in the spherical, columnar or similar structure portion. When a diblock copolymer having two components is used as the block copolymer, a spherical structure (sea-island structure) as shown in FIG. 1 (a) and a columnar structure as shown in FIG. 1 (b) are obtained. In addition, only four types of lamellar and co-continuous structures can be made. However, when a block copolymer having three or more components is used, the type of microphase separation structure of the structure is, for example, as shown in FIG. As shown in (d), it spreads almost infinitely. Further, in order to control the structure, other polymers (including block copolymers and the like) and low molecules may be mixed. Moreover, as a group which carries out a photocrosslinking, what photodimerizes especially is preferable. By photodimerization, the structure of the polymer side chain is greatly changed, so that a function as an optical functional site such as a change in refractive index can be expected. At the same time, the high molecular weight of the material occurs, and the stability of the structure increases.

The block copolymer in the present invention can be synthesized by combining polymers that are incompatible with each other. It may be a combination of two or more polymers. As a synthesis method of the block copolymer used in the present invention, as a monomer, for example, polysilanes, styrene, isoprene, α-methylstyrene, chloromethylstyrene, 2-vinylpyridine, aminostyrene, 4-vinylpyridine, and acrylates. , Methacrylates, ε-caprolactone, butadiene, vinyl methyl ether, 1,3-cyclohexanediene, ethylene oxide and derivatives thereof, and the like, a living polymerization method (anionic polymerization, living The polymer can be synthesized by a polymerization method such as radical polymerization), living polymerization synthesized from the center of the chain (anionic polymerization), or a synthetic method (anionic polymerization, living radical polymerization, etc.) in which terminal ends of terminal functional polymers are bonded. The photocrosslinking group may be chemically bonded to the monomer before polymerization, or may be chemically bonded to one component of the polymer after polymerization of the polymer.

Examples of the group capable of photo-dimerization, cinnamoyl group, cinnamylidene group, a chalcone group, a coumarin group, isocoumarin group, a stilbene group, styryl pyridinium group, thymine group, uracil group, a maleimide group, an anthracene group, and a pyrone group, benzophenone group . Kumari down group, thymine group, uracil group, anthracene emission group, photo-dimerization is the use of the reversibly progressive group, a rewritable media when used as an optical recording medium. Further, a sensitizer may be added to increase the efficiency of photodimerization or to change the irradiation light wavelength.

Next, an optical recording medium in which the structure is applied as a recording material (recording layer) will be described.
A conventional optical recording medium includes a recording layer composed of a continuous recording material (a layer in which the recording material exists). The recording layer is irradiated with a laser beam, and some change corresponding to the shape of the laser beam ( (Physical and chemical changes accompanying optical changes) are formed on the recording material and recorded. Therefore, since the size of the minimum recording pit depends on the laser beam diameter determined by the oscillation wavelength of the optical system and the NA of the lens, in the conventional recording / reproducing system, the increase in density is basically the laser oscillation wavelength or lens. Has been influenced by the practical technology of NA.

  Also, because the beam shape is a Gaussian distribution and there is almost no material that changes with a clear threshold for heat or light as a recording material, the size and change of the outermost circumference of the pits formed The amount is not uniform, and there is always a variation factor in the quality of the reproduced signal, and there is a limit to obtaining high quality signal characteristics.

  The optical recording medium of the present invention is an optical recording medium having a new structure that overcomes the problems of the conventional optical recording medium. That is, in the optical recording medium to which the structure of the present invention is applied, recording dots that are highly ordered exist in a continuous layer in a discontinuous manner through a matrix. In addition, the recording dots are formed in a uniform nanometer size (10 to 500 nm). Therefore, the size of the minimum recording pit is not determined only by the laser oscillation wavelength or the NA of the lens, but is determined by the recording layer dots to be formed, and an optical recording medium having an arbitrary recording density can be designed. Furthermore, since the outermost edge of the pit is also determined by this micro phase separation structure, it is possible to obtain high-quality signal characteristics without pit variations by recording the entire recording layer dot to change. It becomes.

The configuration of the optical recording medium of the present invention and the necessary physical properties thereof will be described below.
<Recording medium configuration>
In the optical recording medium of the present invention, a recording layer containing the structure is provided on a substrate. If necessary, an undercoat layer, a metal reflection layer, a protective layer, a substrate surface hard coat layer, and the like are provided as constituent layers. The configuration of the constituent layers can be selected according to the purpose and required characteristics. The optical recording medium of the present invention will be described with reference to the drawings.

The optical recording medium of the present invention has a configuration such as the example shown in the schematic cross-sectional views of FIGS. 2 (a) to 2 (d) and FIGS. 3 (a) to 3 (e).
The optical recording medium shown in FIG. 2 (a) has a configuration in which a recording layer 2 is provided on a substrate 1; the optical recording medium shown in FIG. 2 (b) has an undercoat layer 3 and a recording layer 2 on the substrate 1. The optical recording medium shown in FIG. 2C has a configuration in which a protective layer 4 is further provided on the recording layer 2 in the layer configuration shown in FIG. 2B; The optical recording medium shown in d) has a configuration in which the substrate surface hard coat layer 5 is provided on the back surface of the substrate 1 in the layer configuration shown in FIG. The optical recording medium shown in FIGS. 2A to 2D shows an example in which a metal reflection layer is not provided on a substrate.

  The optical recording medium shown in FIG. 3A has a configuration in which a recording layer 2 and a metal reflection layer 6 are sequentially provided on a substrate 1; the optical recording medium shown in FIG. The optical recording medium shown in FIG. 3C is provided with a protective layer 4 on the metal reflective layer 6 in the layer configuration shown in FIG. The optical recording medium shown in FIG. 3D has a configuration in which an undercoat layer 3 is provided between the substrate 1 and the recording layer 2 in the layer configuration shown in FIG. The optical recording medium shown in FIG. 3E has a configuration in which the substrate surface hard coat layer 5 is provided on the back surface of the substrate 1 in the layer configuration shown in FIG. The optical recording medium shown in FIGS. 3A to 3E shows an example in which a metal reflective layer is provided on a substrate.

  The configuration of the optical recording medium of the present invention may be a write-once optical disc structure (a so-called air sandwich structure in which two recording layers are provided on a substrate), or a CD-R structure (recording on a substrate). Providing a layer, a reflective layer, and a protective layer), or a DVD structure in which a CD-R structure is bonded. The above configuration is an example for describing the embodiment, and other configurations may be used. Hereinafter, each constituent layer of the optical recording medium will be described.

<substrate>
The substrate used for the optical recording medium of the present invention must be transparent to the laser used only when recording / reproducing is performed from the substrate side, and when recording / reproducing is performed from the recording layer side (opposite side of the substrate). The substrate need not be transparent.
As the substrate material, for example, plastic such as polyester, acrylic resin, polyamide, polycarbonate resin, polyolefin resin, phenol resin, epoxy resin, polyimide, glass, ceramic, or metal can be used. Note that a guide groove for tracking, a guide pit, and a preformat such as an address signal may be formed on the surface of the substrate.

  The guide groove for tracking can also be used for the arrangement of the micro phase separation structure, and the form in that case is shown in FIG. In FIG. 4, a spherical structure as a microphase separation structure is applied in a guide groove so as to be aligned in a line. The thickness of the guide groove can be adjusted so that the structures are arranged in a line as shown in FIG.

<Recording layer>
The recording layer causes some optical change by irradiation with laser light, and information can be recorded and reproduced by the change. The recording layer has polymer chains that are incompatible with each other as described above. The structure of the present invention has a microphase separation structure formed by a bonded block copolymer, and a photocrosslinking group is chemically bonded to at least one separated phase of the microphase separation structure. Become. As the optical characteristics of the photocrosslinking group , it is preferable to control the wavelength so as to have the maximum absorption wavelength in the vicinity of the laser wavelength when reproducing using the change in the absorption characteristic with respect to the recording / reproducing laser wavelength, When reproduction is performed using the change in refractive index with respect to the recording / reproducing laser wavelength, it is preferable to control the wavelength so that the maximum refractive index is provided in the vicinity of the laser wavelength. At that time, the wavelength may be controlled using a sensitizer or the like.
In the present invention, it is desirable that the diameter of the cross-section of the microphase-separated structure in a spherical shape, a columnar shape, or a structure similar to each shape is smaller than the recording wavelength.

<Underlayer>
The undercoat layer consists of (1) improved adhesion, (2) a barrier such as water or gas, (3) improved storage stability of the recording layer, (4) improved reflectance, and (5) a substrate from a solvent. And (6) formation of guide grooves, guide pits, and preformats.
For the purpose of (1), polymer materials such as ionomer resins, polyamide resins, vinyl resins, natural resins, natural polymers, silicones, various rubber compounds such as liquid rubber, and silane coupling agents. Can be used. For the purpose of (2) or (3), there are inorganic compounds other than the above polymer materials, for example, SiO, MgF, SiO ₂ , TiO, ZnO, TiN, SiN, etc., and further metals or semi-metals such as Zn, Cu, Ni, Cr, Ge, Se, Au, Ag, Al, or the like can be used. For the purpose of (4), metals such as Al, Au, and Ag, and pigments having metallic luster such as methine dyes and xanthene dyes can be used. For the purpose of (5) or (6), an ultraviolet curable resin, a thermosetting resin, a thermoplastic resin, or the like can be used.
The thickness of the undercoat layer is 0.01 to 30 μm, preferably 0.05 to 10 μm.

<Metal reflective layer>
The metal reflective layer is used when necessary according to the required reflectance.
As the metal reflection layer, a metal or a semi-metal that is highly resistant to corrosion and is not easily corroded is used, and examples of such materials include Au, Ag, Cr, Ni, Al, Fe, and Sn. It is done. Among these materials, Au, Ag, and Al are most preferable from the viewpoint of reflectance and productivity. These metals and metalloids may be used alone or as two kinds of alloys.
Examples of the method for forming the metal reflective layer include, but are not limited to, vapor deposition and sputtering. The thickness of the reflective layer is preferably from 50 to 5000 mm, more preferably from 100 to 3000 mm.

<Protective layer, hard coat layer on substrate surface>
The protective layer and the hard coat layer on the substrate surface are (1) protecting the recording layer (reflection / absorption layer) from scratches, dust, dirt, etc. (2) improving the storage stability of the recording layer (reflection / absorption layer), (3 ) Used for the purpose of improving the reflectance. For these purposes, the materials shown in the undercoat layer can be used.
In addition, SiO, SiO ₂ or the like can be used as the inorganic material, and polymethyl acrylate, polycarbonate, epoxy resin, polystyrene, polyester resin, vinyl resin, cellulose, aliphatic hydrocarbon resin, natural rubber, styrene butadiene as the organic material. Thermosoftening and heat melting resins such as resins, chloroprene rubber, waxes, alkyd resins, drying oils and rosins can also be used.
The most preferable example among the above materials is an ultraviolet curable resin excellent in productivity. The film thickness of the protective layer or the substrate surface hard coat layer is 0.01 to 30 μm, preferably 0.05 to 10 μm.

  In the present invention, the undercoat layer, the protective layer, and the substrate surface hard coat layer have the same stabilizers, dispersants, flame retardants, lubricants, antistatic agents, surfactants, plasticizers, etc. as in the recording layer. Can be contained.

  EXAMPLES Hereinafter, although an Example and a comparative example further demonstrate this invention, this invention is not limited to the following example.

Example 1
A block comprising a polymer comprising styrene (St) and a compound comprising a repeating unit represented by the general formula (I), having a number average molecular weight of 100,000, and a volume ratio of the compound represented by the general formula (I) being 21% The copolymer was dissolved in toluene and further cast on a quartz substrate to form a structure. Furthermore, when this thin film was heat-treated at 120 ° C. for 12 hours, the phase separation structure was confirmed to be a spherical structure (sea-island structure) having a diameter of 20 nm by AFM observation, TEM observation, and SAXS measurement.

Example 2
A block copolymer comprising a polymer comprising methyl methacrylate (MMA) and a compound comprising a repeating unit represented by the general formula (II), and having an average molecular weight of 150,000 and a volume ratio of the compound represented by the general formula (II) of 30%. The polymer was dissolved in chloroform and cast on a quartz substrate to form a structure. Furthermore, when this thin film was heat-treated at 120 ° C. for 12 hours, the phase separation structure was confirmed to be a columnar structure having a diameter of 30 nm by AFM observation, TEM observation, and SAXS measurement.

Example 3
A block comprising a polymer comprising 4-vinylpyridine (4VP) and a compound comprising a repeating unit represented by the general formula (III), and having an average molecular weight of 200,000 and a volume ratio of the compound represented by the general formula (III) of 19% The copolymer was dissolved in toluene and cast on a quartz substrate to form a structure. Furthermore, when this thin film was heat-treated at 120 ° C. for 12 hours, the phase separation structure was confirmed to be a spherical structure having a diameter of 30 nm by AFM observation, TEM observation, and SAXS measurement.

Example 4
A block copolymer consisting of a polymer composed of St and a compound composed of a repeating unit represented by the general formula (IV), having an average molecular weight of 150,000 and a volume ratio of the compound represented by the general formula (IV) of 28% in chloroform. It was melted and cast on a quartz substrate to form a structure. Furthermore, when this thin film was heat-treated at 120 ° C. for 12 hours, the phase separation structure was confirmed to be a columnar structure having a diameter of 30 nm by AFM observation, TEM observation, and SAXS measurement.

Comparative Example 1
A block copolymer consisting of a polymer consisting of St and a polymer consisting of 2-hydroxyethyl methacrylate (HEMA), having an average molecular weight of 100,000 and a HEMA volume ratio of 18%, is dissolved in chloroform and cast onto a quartz substrate. A structure was formed. Furthermore, when this thin film was heat-treated at 120 ° C. for 12 hours, the phase separation structure was confirmed to be a spherical structure having a diameter of 20 nm by AFM observation, TEM observation, and SAXS measurement.

Example 5
The structures prepared in Examples 1 to 4 and Comparative Example 1 were irradiated with light having wavelengths as shown in Table 1. Regarding Example 4, it is also known that the side chain structure irradiates short wavelength light, thereby causing a reverse reaction of photodimerization. Therefore, after irradiating 365 nm, 254 nm light is irradiated to the same location of the same sample. Was irradiated. As the light source, a high pressure mercury lamp was used at 365 nm and a low pressure mercury lamp was used at 254 nm. The irradiated part and the non-irradiated part were measured for reflectance and transmittance by the microspectroscopic method. The results are shown in Table 1.

Example 6
In Example 1, a structure was formed in exactly the same manner except that the substrate was formed by forming a groove having a width of 90 nm and a depth of 30 nm on a Si wafer. When the surface structure of the film was observed with an AFM, it was confirmed that island-like structures of microphase separation were neatly arranged in the grooves as shown in FIG.

From the results in Table 1, it has been clarified that the structures of Examples 1 to 4 change in transmittance and reflectance when irradiated with a specific wavelength. Therefore, it is clear that the structure of the present invention can be used as an optical recording medium. The fourth embodiment can be used as a rewritable medium. Moreover, since the comparative example 1 did not contain the group which photocrosslinks, even if it irradiated with light, it turned out that a transmittance | permeability and a refractive index cannot be changed.
In this experiment, since recording was performed with a light source having a large beam diameter (1 μm or more) compared to the functional material dot diameter (several tens of nm), a large number of functional material dots were recorded at once. It is obvious that the recording between the functional material dots and the dots can be performed individually by recording with the same beam diameter as that between the functional material dots and the dots.

  As described above, the structure of the present invention is useful for a recording layer of an optical recording medium, and can be recorded and reproduced at a recording density exceeding the diffraction limit of a pickup lens, which cannot be realized by a conventional optical disk. Can be provided.

It is the figure which represented typically the micro phase-separation structure of the structure of this invention. It is sectional drawing for demonstrating the layer structural example of the optical recording medium of this invention. It is sectional drawing for demonstrating the layer structural example of the optical recording medium of this invention. It is a top view for demonstrating the form which arranged the structure of this invention on the board | substrate which has a groove | channel.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Substrate 2 Recording layer 3 Undercoat layer 4 Protective layer 5 Substrate surface hard coat layer 6 Metal reflective layer

Claims (7)

It has a microphase-separated structure formed by a block copolymer in which polymer chains that are incompatible with each other are bonded, and a photocrosslinking group is chemically bonded to at least one separated phase of the microphase-separated structure. A structure characterized by   2. The structure according to claim 1, wherein the microphase separation structure is a spherical shape, a columnar shape, or a structure similar to each shape. The structure according to claim 1, wherein the photocrosslinking group is contained in the spherical, columnar, or structural portion similar to each of the shapes. The structure according to claim 1, wherein the photocrosslinking group is photodimerized.   An optical recording medium comprising the structure according to claim 1 as a recording layer on a substrate.   6. The optical recording medium according to claim 5, wherein a diameter of a cross section of the micro phase separation structure having a spherical shape, a column shape, or a structure similar to each of the shapes is smaller than a recording wavelength.   7. The optical recording medium according to claim 5, wherein a groove is formed on the substrate, and the structure is formed thereon.

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