JP2023141380A - optical disk - Google Patents

Abstract

To provide an optical disk capable of surely recognizing a recording layer.SOLUTION: An optical disk comprises a plurality of recording layers for recording data and a resin layer between the recording layers. The resin layer is UV cured with fluorine by a polymerization initiator. The polymerization initiator is a radical polymerization type acetophenone type. A carbon at an α-position of a carbonyl group of the structure is bonded to one oxygen or one nitrogen atom, and two non-cycloalkane alkyl groups, and a phenyl group containing the carbon at the other α-position is bonded to a non-substituted or -NC4H8O functional group.SELECTED DRAWING: Figure 4

Description

The present disclosure relates to optical discs.

The amount of digital data used is increasing year by year due to the spread of the Internet and the digitalization of broadcasting. Under such an environment, an optical disk, which is an optical information recording medium, is composed of multiple recording layers for recording data and a resin layer as an intermediate layer between the recording layers, and is irradiated with laser light. As a highly reliable information recording medium suitable for long-term storage, data can be recorded and played back, and as the amount of information increases, storage capacity continues to increase.

In order to realize an optical disc with even higher capacity, it is essential to increase the number of recording layers. However, the recording layer of an optical disc is mainly composed of inorganic compounds, and the transmittance of inorganic compounds is low, and it takes too much man-hours, so it has been difficult to create multiple recording layers composed of inorganic compounds. . Therefore, a technique of multilayering recording layers made of organic compounds is also being considered, but there is a problem that the recording layer cannot be recognized unless there is a difference in refractive index between the recording layer and the resin layer.

Japanese Patent Application Publication No. 2008-137190

In Patent Document 1, a curable resin containing fluorine is used for the purpose of water and oil repellency (stain resistance) in a material layer whose low refractive index is technically important. However, although Teflon (registered trademark) contains a large amount of fluorine and has a low refractive index, it has high crystallinity and low transparency, so there is a problem in that it is difficult to transmit laser light.

The inventors focused on low refractive index resins that have a chemical structure that contains a large amount of fluorine and has low crystallinity, and in particular, focused on ultraviolet curable resins that can be layered through common processes such as spin coating. However, even if 3 parts of a polymerization initiator was added to 2,2,2-trifluoroethyl acrylate, which is an ultraviolet curable resin containing a large amount of fluorine, and the resin was cured with ultraviolet light, a layer with a low refractive index could not be obtained. It was found that fluorine was desorbed (reduced) from the layers in which a low refractive index layer could not be obtained.The cause of fluorine desorption was estimated, and a polymerization initiator capable of obtaining a low refractive index layer was discovered. did. Furthermore, since the recording layer is recognized by detecting the interface reflection on the incident side of the laser beam, the interface reflection on the opposite side causes crosstalk. They have also discovered that in order to reduce this crosstalk, the recording layer can be made thin and the resin layer thick enough to reduce the difference between the interface reflection of the recording layer and the interface reflection on the opposite side.

The optical disc according to the present disclosure is an optical disc composed of a plurality of recording layers for recording data and a resin layer between the recording layers, and the resin layer is cured by ultraviolet rays containing fluorine using a polymerization initiator. The polymerization initiator is a radical polymerizable acetophenone type, and the carbon at the α-position of the carbonyl group in the structure is bonded to one oxygen or nitrogen atom, two alkyl groups that are not cycloalkanes, and It is characterized in that the phenyl group containing one carbon at the α-position is unsubstituted or bonded to a -NC ₄ H ₈ O functional group.

In the optical disc according to the present disclosure, the recording layer can be reliably recognized.

Schematic cross-sectional diagram of an optical recording disk Diagram showing the three-dimensional structure of each polymerization initiator Energy and 3D structure diagram of cyclohexane Diagram showing the relationship between α’ carbon activity and functional group

Hereinafter, embodiments will be described in detail with reference to the drawings as appropriate. However, more detailed explanation than necessary may be omitted. For example, detailed explanations of well-known matters or redundant explanations of substantially the same configurations may be omitted. This is to avoid unnecessary redundancy in the following description and to facilitate understanding by those skilled in the art. The accompanying drawings and the following description are provided to enable those skilled in the art to fully understand the present disclosure, and are not intended to limit the subject matter recited in the claims.
(Embodiment)
FIG. 1 shows an optical disc 100 according to this embodiment. An embodiment of the optical disc 100 will be described below. The optical disc 100 includes a binder 101, which is an example of a recording layer, and a binder 102, which is an example of a resin layer, which are alternately laminated in many layers. The binder 101 includes a recording material that can record information by irradiation with a recording laser beam. The binder 102 does not contain a recording material and functions as an intermediate layer. The recording material is a two-photon absorption compound, and is not particularly limited as long as it is excited or changed to the ground state by irradiation with the recording laser beam, and optically changes with the recording and reading laser beam, such as fluorescence. Examples include fluorescent compounds that have absorption in the wavelength region of the laser light. Examples include phenylamine derivatives, cyclopentane derivatives, azulene derivatives, and porphyrin derivatives.

The cover layer 104 is provided on the outermost surface of the optical disc 100 for the purpose of scratch resistance and the like. A servo layer 106 is optionally provided on the surface of the base material 105 for tracking. Tracking may be performed by forming a groove shape only on the servo layer 106 and using a laser beam capable of tracking the groove shape of the servo layer 106 in addition to the recording laser beam, or by using a laser beam that can track the groove shape of the servo layer 106. A groove may be provided in a similar manner.

The base material 105 serves as a support for the optical disc 100, and may be a relatively thick film of several hundred μm to several mm, or a film of several hundred μm or less, as long as it has a thickness that functions as a support.

The binder 101 and the binder 102 are usually used for the purpose of improving the film formation stability, uniformity of film thickness/density, and storage stability of the composition, so they have excellent compatibility with the composition and are compatible with the composition. A film that can form a uniform film and has high storage stability is preferable, and thermoplastic resins, curable resins, etc. can be used alone or in combination, and additives such as mold release agents and dispersants can be used. It can be used as needed.

The binder 101 is a layer that can record information by optically changing the recording material such as fluorescence by excitation or changing to the ground state by laser beam irradiation and readout laser beam. If possible, the film thickness is not particularly limited. That is, when the binder 101 contains a recording material, the film thickness must be thicker than when the recording material is used alone, but the film thickness may be sufficient as long as it can record information.
The thickness of the binder 102 is not limited as long as the binder 101 can be recognized, but the intensity of the reflected light for layer recognition and, for example, the laser beam in an optical disc in which about 30 layers of the binder 101 and the binder 102 are laminated in total are not limited. When considering access to the layer farthest from the light irradiation surface, the difference in refractive index between the binder 101 and the binder 102 is preferably 0.15 or more, preferably about 0.2.

In order to make it easier to recognize the binder 101 in the depth direction with the recording laser beam, the optical disc 100 is made of binders that are transparent in the wavelength range of the recording laser beam and have a different refractive index for each unit, as shown in FIG. 101 and binder 102 are used.

The binder 101 uses a resin that is transparent and has a high refractive index in the wavelength region of the recording laser beam. The binder 101 is not particularly limited as long as it has a difference in refractive index of 0.15 or more with the binder 102, which is a resin that is transparent and has a low refractive index in the wavelength region of the recording laser beam. The resin used for the binder 101 can be a thermoplastic resin such as a polymer or copolymer of styrene, ester, vinyl, polycarbonate, polyethylene naphthalate, acrylate, methacrylate, urethane, amide, etc. As the resin, resins that harden by irradiation with active energy such as ultraviolet rays, and thermosetting resins such as phenol, epoxy, ester, urethane, and imide can be used.

The binder 102 is a resin that is transparent and has a low refractive index in the wavelength region of the recording laser beam. The binder 102 is not particularly limited as long as it has a refractive index difference of 0.15 or more with the binder 101, which is transparent in the wavelength region of the recording laser beam and has a high refractive index. Polymers and copolymers of systems such as vinyl alcohol, polylactic acid, polyolefins, and silicones can be used, and as the curable resin, in addition to the above, resins of systems such as acrylates, methacrylates, and olefins can be used. However, in order to be transparent in the wavelength region of the recording laser beam and to ensure a difference in refractive index, a resin containing fluorine in its structure is preferable.

The material of the cover layer 104 is not particularly limited, but is preferably transparent to the recording/reading laser beam.

The servo layer 106 is provided to control tracking of laser light irradiated during recording and reading.

In this embodiment, the refractive index difference between binder 101 and binder 102 in the wavelength region of the recording laser beam is 0.15 or more. That is, when the refractive index of the resin used for the binder 101 having a high refractive index is 1.7, the refractive index of the binder 102 having a low refractive index is 1.55 or less. As a resin with a low refractive index, a resin containing fluorine in its structure has excellent transparency.

In order to obtain the binder 101 with a high refractive index, it is necessary to use optical polyester resin (OKP) manufactured by Osaka Gas Chemical Co., Ltd., fluorene-based acrylate (OGSOL), or polyester resin, which can be easily processed into a disk shape by spin coating or the like. (1-naphthyl methacrylate), Taisei Fine Chemical's high refractive index coating material (8DK), and other resins can be used. OKP, which is a thermoplastic resin, can be spin-coated by dissolving it in a volatile solvent to adjust the viscosity of the coating solution, and UV-curable OGSOL, etc., can be applied by adding about 3 parts of a polymerization initiator such as Irgacure 184, and A binder 101 with a high refractive index can be obtained by spin-coating a coating liquid to which a volatile solvent is added if necessary, and irradiating the coating film with ultraviolet rays. The volatile solvent used is a solvent that has good compatibility with the resin material, can adjust the viscosity, does not corrode the coated surface, and evaporates after spin coating. The high refractive index binder 101 disperses the recording material in the high refractive index resin. It may be formed by coating with a coating liquid in which a recording material and a resin are dispersed. For dispersion, general methods such as stirring and ultrasonic waves can be used.

As the binder 102, in order to obtain the binder 102 with a low refractive index, a resin with a low refractive index is used, and when an ultraviolet curable resin is used, an optimal polymerization initiator is used.The method for obtaining the binder 101 is used, except that can. As the thermoplastic resin with a low refractive index, DYNEON THV powder type manufactured by 3M can be used. As the ultraviolet curable resin having a low refractive index, 2,2,2-trifluoroethyl acrylate or the like can be used.

The chemical structure of the polymerization initiator that is most suitable for obtaining the ultraviolet curable binder 102 with a low refractive index will be explained. The polymerization initiator is selected depending on the monomer, and as in this embodiment, an acrylic or methacrylic monomer is used as a monomer that is required to be colorless and transparent in addition to the refractive index. Radical polymerization initiators are used as such monomers, and among them, acetophenone-based and benzophenone-based polymerization initiators are often used. When an acetophenone-based polymerization initiator is irradiated with ultraviolet rays, the space between the carbonyl group and the α-position carbon of the carbonyl group is excited to generate radicals. In this embodiment, the α-position carbon bonded to one oxygen or nitrogen atom is expressed as the α-position carbon, and the other α-position carbon is expressed as the α′-position carbon.

ラジカルの発生し易さは、化１におけるカルボニルの炭素～α位炭素間、カルボニルの炭素～α’位炭素（フェニル環）間、に及ぼす電子共鳴によって決まり、主にα位炭素、α’位炭素（フェニル環）が結合している官能基及び官能基数、立体構造が大きく影響していると言われている。

The ease with which radicals are generated is determined by the electronic resonance between the carbonyl carbon and the α-position carbon in Chemical formula 1, and between the carbonyl carbon and the α'-position carbon (phenyl ring). It is said that the functional group to which carbon (phenyl ring) is bonded, the number of functional groups, and the three-dimensional structure have a large influence.

In Figure 2, the α-position carbon is bonded to an electron-donating heteroatom, a benzene ring, etc. (for example, the hydroxyl group of 2-hydroxy-2-methyl-1-phenylpropanone, the 1-hydroxycyclohexyl- It is said that the hydroxyl group of phenylketone strengthens the electronic resonance and ensures radical activity as a radical polymerization initiator. Furthermore, it is said that when the functional group is located close to the carbonyl carbon to the α-position carbon, the electronic resonance becomes even stronger (for example, 2-hydroxy-2-methyl-1-phenyl in Figure 1). The positional relationship between the hydroxyl group of propanone and the α-position carbon is always the same, but the hydroxyl group and the α-position carbon of 1-hydroxycyclohexyl-phenyl ketone are 2-hydroxy- (closer than 2-methyl-1-phenylpropanone).

On the other hand, from FIG. 4, the chemical activity of the α'-position carbon (phenyl ring) changes depending on the functional group bonded to the phenyl ring (for example, , the order of functional groups is halogen < alkyl < hydroxyl group, and the order of chemical activity is benzene < toluene), and the electronic resonance at the same position is also said to change.

Here, the cause of the problem that the refractive index of the binder layer changes depending on the polymerization initiator is that the amount of fluorine in the polymer film (binder) differs depending on the polymerization initiator. Therefore, it was assumed that fluorine in the monomer would be easily eliminated during polymerization, and elemental analysis and refractive index measurements were conducted on polymer films in which the chemical structure of the polymerization initiator was changed.

The monomer was 2,2,2-trifluoroethyl acrylate, the amount of polymerization initiator added was 3 parts, and all other formulation conditions and light irradiation conditions were the same. For elemental analysis, the mass % of F (fluorine) and C (carbon) in the polymer film was measured using a JEOL SEM (JSM-6700F) and EDS (JED-2300F), and F [mass %] / C [mass %] was used as a polymerization initiator that could maintain a large amount of fluorine, and a polymer film that had a small value was used as a polymerization initiator that could eliminate a large amount of fluorine (Table 1).

The refractive index at the recording/reproducing wavelength, etc. was determined by measuring the film thickness in direct measurement mode using a fine shape measuring machine ET4000A manufactured by Kosaka Laboratory Co., Ltd. A. Measurement was performed using Alpha-SE and Complete EASE6 manufactured by Woollam Co., Standard mode, Sample Alignment-Robust, Angle: 65°, 70° (Table 1).

表１より、重合開始剤の化学構造により、重合膜に含まれるフッ素量は、異なる事が分かった。

From Table 1, it was found that the amount of fluorine contained in the polymer film differed depending on the chemical structure of the polymerization initiator.

2-hydroxy-2-methyl-1-phenylpropanone has -OH containing an oxygen atom bonded to αC, two -CH ₃ bonds as an alkyl group that is not a cycloalkane, and a phenyl group containing α'C is free. It is a replacement. 2-benzyl-2-(dimethylamino)-4'-morpholinobutyrophenone is an alkyl group in which -N(CH ₃ ) ₂ is not a bonded cycloalkane containing nitrogen at αC -C ₂ H ₅ , -CH ₂ -C ₆ H ₆ is bonded, and the phenyl group containing α'C is bonded to -NC ₄ H ₈ O.
(Example)
The binder 102 is not particularly limited as long as it can sufficiently transmit recording and reproducing light and contains fluorine. For example, radical polymerizable acrylic compounds, methacrylic compounds, etc. can be used.
<Preparation>
The binder 102 may be a mixture, but is not particularly limited as long as at least one monomer contains fluorine in its chemical structure. In order to confirm the difference in the polymerization initiator, the monomer was 2,2,2-trifluoroethyl acrylate, and only the chemical structure of the compound as a polymerization initiator (added amount: 3 parts) was changed. Each binder was obtained through the steps described below.
<Film formation method>
The method for manufacturing the optical disc 100 is not particularly limited, but spin coating, which is a simple and inexpensive coating, was used. As the spin coating device, an Opticoat spin coater (MS-B200) manufactured by Mikasa Co., Ltd. was used.
<Ultraviolet irradiation>
When using a radical polymerizable monomer as the binder 102, the binder 102 was obtained by irradiating with ultraviolet rays. For ultraviolet irradiation, a lamp manufactured by Panasonic Corporation (ANUF82001T) was used as a light source.
<Film thickness measurement>
The thickness of the binder 102 was measured in direct measurement mode using a fine shape measuring machine ET4000A manufactured by Kosaka Institute Co., Ltd.
<Optical measurement>
The refractive index of the binder 102 at the recording/reproducing wavelength, etc. is determined by J. A. Measurement was performed using Alpha-SE and Complete EASE6 manufactured by Woollam Co., Standard mode, Sample Alignment-Robust, Angle: 65°, 70°.

By configuring the binder 102 as described above, the binder of the optical information disc can be recognized by the optical recording/reproducing device.

The resin layer according to the present disclosure is a colorless and transparent low refractive index resin layer, and can be used as a binder for optical recording discs.

100 optical disc 101, 102 binder 104 cover layer 105 base material 106 servo layer

Claims (6)

An optical disc comprising a plurality of recording layers for recording data and a resin layer between the recording layers,
The resin layer is cured by ultraviolet rays containing fluorine using a polymerization initiator,
The polymerization initiator is a radical polymerizable acetophenone type, and the carbon at the α-position of the carbonyl group in the structure is bonded to one oxygen or nitrogen atom, two alkyl groups that are not cycloalkanes, and the other An optical disc characterized in that a phenyl group containing carbon at the α-position is unsubstituted or bonded to a -NC ₄ H ₈ O functional group. 2. The optical disc according to claim 1, wherein the difference between the refractive index of the recording layer and the refractive index of the resin layer is 0.15 or more. 3. The optical disc according to claim 1, wherein the resin layer has a light transmittance of 80% or more. 4. The optical disc according to claim 1, wherein the recording layer has a thickness of 0.01 to 0.5 μm, and the resin layer has a thickness of 1 to 15 μm. 5. The optical disc according to claim 1, wherein the ratio of the thickness of the recording layer to the thickness of the resin layer is 1:10 to 1:150. 6. The optical disc according to claim 1, wherein the resin layer contains 1 to 20 wt% or more of a two-photon absorbing material.

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