OPTICAL RECORDING MEDIUM AND METHOD FOR MANUFACTURING OPTICAL RECORDING MEDIUM

An optical recording medium includes a first transparent film layer, a second transparent film layer, and a recording material layer sandwiched between the first transparent film layer and the second transparent film layer. The recording material layer includes a hologram recording material.

DETAILED DESCRIPTION OF EMBODIMENTS

Exemplary embodiments of the present technology are described below with reference to the accompanying drawings. Note that descriptions are made in the following order:1. First Exemplary Embodiment (Example of Configuration of Optical Recording Medium), and2. Other Exemplary Embodiments (Modifications).
In addition, in all drawings of the exemplary embodiments, the same reference symbols are used for the same or similar elements.

1. First Exemplary Embodiment

(Example of Configuration of Optical Recording Medium)

An example of the configuration of an optical recording medium according to a first exemplary embodiment of the present technology is described below.FIG. 1is a schematic cross-sectional view of an example of the configuration of the optical recording medium according to the first exemplary embodiment of the present technology. As illustrated inFIG. 1, the optical recording medium has a structure including an adhesion layer12, a first transparent film layer13a, a recording material layer14, and a second transparent film layer13bstacked on a base plate11in this order.

For example, the optical recording medium is a disc-shaped optical recording medium (an optical disk) having an opening at the center. For example, by emitting a laser beam onto the recording material layer14and generating a recording mark, data can be recorded in the optical recording medium. In addition, by emitting a laser beam onto the recording material layer14, the recorded data can be reproduced. For example, the optical recording medium is an optical recording medium used for recording and reproducing data using a hologram technology (holography).

The base plate11, the adhesion layer12, the first transparent film layer13a, the recording material layer14, and the second transparent film layer13bthat constitute the optical recording medium are sequentially described below.

For example, the base plate11has a disc shape, and the disc has an opening at the center. For example, a plastic material (e.g., polycarbonate series resin, polyolefin series resin, or acrylic-type resin) or glass can be used as the material of the base plate11.

One of the two principal surfaces of the base plate11has the following layers formed thereon: the first transparent film layer13a, the second transparent film layer13b,and the recording material layer14sandwiched between the first transparent film layer13aand the second transparent film layer13b.The first transparent film layer13ais bonded to the base plate11with the adhesion layer12therebetween. In this manner, the rigidity of the recording material layer14sandwiched by the first transparent film layer13abonded to the base plate11and the second transparent film layer13bcan be further increased.

The principal surface of the base plate11is, for example, a bumpy surface. Although not illustrated, a reflecting surface is formed on the bumpy surface. The bumpy surface is formed from a guide groove for indicating the recording or reproducing position. The entire guide groove is a variety of forms in shape, such as a spiral or a concentric circle when viewed from the principal surface of the optical recording medium.

The guide groove can be formed as a continuous groove, a pit string, or a combination of a groove and a pit string. In order to stabilize the linear speed and provide address information, such as positional information (e.g., rotation angle information or radius position information), the guide groove may wobble.

Although not illustrated, a selective reflection layer is provided on the side of the bumpy surface of the base plate11. In the optical recording medium according to the present exemplary embodiment, in addition to a recording beam (a first laser beam) for performing mark recording on the recording material layer14, a servo beam (a second laser beam), for example, is emitted onto the selective reflection layer in order to obtain a tracking error signal and a focus error signal on the basis of the guide groove of the base plate11. When a recording beam is emitted and if the recording beam is reflected or absorbed by the selective reflection layer, the amount of recording beam reaching the inside of the recording material layer is attenuated and, thus, the effective recording sensitivity decreases. Accordingly, it is desirable that the selective reflection layer have a selectivity such that a servo beam is reflected and a nearly all the recording beam is transmitted.

For the optical recording medium, for example, laser beams having different wavelengths are used as a recording beam and a servo beam. For example, the selective reflection layer has a selectivity such that light in a wavelength range that is the same as the wavelength range of the servo beam is reflected and light having the other wavelength range (e.g., the recording beam) is transmitted.

For example, a film stack in which a plurality of low refractive index films and a plurality of high refractive index films are alternately stacked can be used as the selective reflection layer. For example, a dielectric film can be used as each of the low refractive index film and the high refractive index film. Examples of the material of the dielectric film include silicon nitride, oxide silicon, tantalum oxide, titanium oxide, magnesium fluoride, and zinc oxide.

For example, a pressure sensitive adhesive (PSA) or a light cure adhesive, such as HPSA (a sheet UV-curable PSA) can be used as an adhesive that forms the adhesion layer12.

The recording material layer14includes a hologram recording material that can record a hologram. A typical example of a hologram recording material is photopolymer. For example, the photopolymer is a photopolymerizable photopolymer. For example, in an initial state, the photopolymerizable photopolymer contains monomers uniformly dispersed in a matrix polymer. Note that the photopolymerizable photopolymer may contain a photopolymerization initiator in addition to the monomers and matrix polymer. A photopolymerizable photopolymer has a characteristic so that if light is emitted, monomers present in a portion onto which the light is emitted polymerize into polymer and, thus, the refractive index varies.

In the recording material layer14, data is recorded using a recording mark, for example. To record data, a negative micro-hologram method can be typically employed. That is, a pre-constructed hologram is erased by emitting a laser beam, and the erased portion serves as a recording mark. In the negative micro-hologram method, before a recording operation starts, an initialization process is performed on the recording material layer14so that a hologram (a fringe pattern) is formed in advance. After the fringe pattern is formed through the initialization process in advance, information is recorded by forming an erase mark. An erase mark is formed by, for example, focusing a laser beam at a desired position in the recording material layer14and emitting the laser beam in accordance with information to be recorded. For example, volumetric recording is performed on the recording material layer14so that a plurality of layers each having an erase mark and serving as a data recording layer are formed.

Note that the data recording method is not limited to a negative micro-hologram method. For example, a variety of recording methods, such as a positive micro-hologram method, can be employed. In a positive micro-hologram method, a hologram (a fringe pattern) that serves as a recording mark is formed in a recording material layer.

(First Transparent Layer and Second Transparent Layer)

The first transparent film layer13aand the second transparent film layer13bsandwich a pair of the principal surfaces of the recording material layer14. Thus, the first transparent film layer13acovers one of the two principal surfaces of the recording material layer14, and the second transparent film layer13bcovers the other principal surface.

By sandwiching the recording material layer14between the first transparent film layer13aand the second transparent film layer13b,deformation of the recording material layer14due to internal stress caused by, for example, hardening and contraction of the recording material layer14can be prevented. Thus, the flatness of the recording material layer14can be maintained. In addition, exposure of the recording material layer14to oxygen can be prevented.

For example, by maintaining the flatness of the recording material layer14and preventing the recording material layer14from being exposed to oxygen before a hologram is formed in the recording material layer14, a stable hologram (a diffracting grating) can be formed. In addition, by maintaining the flatness of the recording material layer14after a hologram is formed in the recording material layer14, deterioration of hologram diffraction efficiency can be reduced. By sandwiching the recording material layer14between the first transparent film layer13aand the second transparent film layer13bin this manner, a stable hologram can be formed and deterioration of a hologram (e.g., deterioration of the diffraction efficiency) can be reduced. As a result, the hologram can have good keeping quality.

In order to more excellently maintain the flatness of the recording material layer14, it is desirable that, for example, the first transparent film layer13aand the second transparent film layer13bhave the same or substantially the same thickness.

If the first transparent film layer13aand the second transparent film layer13bhave the same or substantially the same thickness, deformation of the recording material layer14in the thickness direction can be made more uniform. Accordingly, the flatness of the recording material layer14can be more excellently maintained. That is, the surface of the recording material layer14adjacent to the first transparent film layer13ais bonded and fixed to the base plate11with the first transparent film layer13atherebetween. Accordingly, the deformability is low. In contrast, since the surface of the recording material layer14adjacent to the second transparent film layer13bis not bonded and fixed to the base plate11, the deformability is higher than that of the side of the recording material layer14adjacent to the first transparent film layer13a.However, such a difference in deformability of the recording material layer14in the thickness direction can be eliminated by making the thicknesses of the first transparent film layer13aand the second transparent film layer13bthe same or substantially the same. As a result, the flatness of the recording material layer14can be more excellently maintained.

In order to maintain the servo performance, it is desirable that the first transparent film layer13aand the second transparent film layer13bbe low-birefringent transparent resin films. In addition, it is desirable that the first transparent film layer13aand the second transparent film layer13bhave a resistance to the material of the recording material layer14(e.g., the recording material layer14and each of the first transparent film layer13aand the second transparent film layer13bhave low mutual solubility). Furthermore, it is desirable that each of the first transparent film layer13aand the second transparent film layer13bhave high adhesion to the recording material layer14. Still furthermore, it is desirable that each of the first transparent film layer13aand the second transparent film layer13bhave high peelability from a film adhesion layer21aand a film adhesion layer21b(described in more detail below). Yet still furthermore, it is desirable that the first transparent film layer13aand the second transparent film layer13bhave low transmitted wavefront aberration. Yet still furthermore, in order to prevent stray light, it is desirable that a difference in the index of refraction among the first transparent film layer13a, the recording material layer14, and the second transparent film layer13bbe small.

It is more desirable that the first transparent film layer13aand the second transparent film layer13bbe low birefringent and have resistance to the material of the recording material layer14, high adhesion to the recording material layer14, and high peerability from an adhesion layer21during a manufacturing process. An example of each of the first transparent film layer13aand the second transparent film layer13bis a transparent resin film, such as ARTON® film available from JSR Corporation.

Method for Manufacturing Optical Recording Medium First Example of Method for Manufacturing Optical Recording Medium

A first example of a method for manufacturing an optical recording medium according to a first exemplary embodiment of the present technology is described next. For example, the first example of a method for manufacturing an optical recording medium is employed when manufacturing an optical recording medium that uses a negative micro-hologram method as a data recording method.

FIGS. 2A to 2CandFIGS. 3A to 3Dare schematic cross-sectional views illustrating the method for manufacturing an optical recording medium. The method for manufacturing an optical recording medium is described below with reference toFIGS. 2A to 2CandFIGS. 3A to 3D.

(Formation of Transparent Film Layer Base Material)

As illustrated inFIG. 2A, a first transparent film layer forming base material30ais formed first. For example, after an anti-reflection film23ais formed on one of the principal surfaces of a transparent base material22a,the film adhesion layer21ais formed on the other principal surface of the transparent base material22aand, thereafter, the first transparent film layer13ais formed on top of the film adhesion layer21a.In this manner, the first transparent film layer forming base material30ais formed.

Similarly, a second transparent film layer forming base material30bis formed. For example, after an anti-reflection film23bis formed on one of the principal surfaces of a transparent base material22b, the film adhesion layer21bis formed on the other principal surface of the transparent base material22band, thereafter, the second transparent film layer13bis formed on the film adhesion layer21b.In this manner, the second transparent film layer forming base material30bis formed.

Each of the transparent base material22aand the transparent base material22bhas, for example, a disk-shape having an opening at the center. The transparent base material22aand the transparent base material22bare transparent. A material having rigidity that is higher than that of the recording material layer14is selected as the transparent base material22aand the transparent base material22b.In this manner, deformation of the recording material layer14can be prevented. For example, each of the transparent base material22aand the transparent base material22bhas a thickness that is sufficiently greater than that of the recording material layer14and, thus, has rigidity that is higher than that of the recording material layer14. Alternatively, the transparent base material22aand the transparent base material22bare formed from a material having rigidity that is higher than that of the recording material layer14and, thus, have rigidity that is higher than that of the recording material layer14. Still alternatively, each of the transparent base material22aand the transparent base material22bhas a thickness that is sufficiently greater than that of the recording material layer14and, in addition, the transparent base material22aand the transparent base material22bare formed from a material having rigidity that is higher than that of the recording material layer14. In this manner, each of the transparent base material22aand the transparent base material22bcan have rigidity that is higher than that of the recording material layer14. An example of the material of the transparent base material22aand the transparent base material22bis a transparent base material such as a glass base plate. In order to maintain sufficient rigidity, it is desirable that the glass base plate be thicker than the recording material layer14.

For example, each of the film adhesion layer21aand the film adhesion layer21bis formed from a pressure sensitive adhesive (PSA) or a light cure adhesive, such as HPSA (a sheet UV-curable PSA).

(Formation of Recording Material Layer)

Subsequently, as illustrated inFIG. 2B, a structure31having the recording material layer14sandwiched between the first transparent film layer forming base material30aand the second transparent film layer forming base material30bis formed. For example, the structure31has a disc-shape. Note that the recording material layer14is, for example, 150 μm in thickness. Each of the first transparent film layer13aand the second transparent film layer13bis, for example, 48 μm in thickness. Each of the transparent base material22aand the transparent base material22bis, for example, 0.9 mm to 1.1 mm in thickness.

For example, photopolymer is applied to one of the principal surfaces of the first transparent film layer forming base material30a(the surface adjacent to the first transparent film layer) using a spin coat technique and is dried as necessary. Thus, the recording material layer14is formed on the first transparent film layer13a.Thereafter, one of the principal surfaces of the second transparent film layer forming base material30b(the surface adjacent to the second transparent film layer) is bonded to the recording material layer14formed on the first transparent film layer13a. In this manner, the structure31having the recording material layer14sandwiched between one of the principal surfaces of the first transparent film layer forming base material30aand one of the principal surfaces of the second transparent film layer forming base material30bis formed.

Subsequently, as illustrated inFIG. 2C, continuous parallel light beams L1and L2each having a wavelength of, for example, 405 nm are emitted into the recording material layer14through the two principal surfaces of the structure31in opposite directions. In this manner, a hologram (a fringe pattern) H is formed in the entire or part of recording material layer14.

Subsequently, in a fixing phase, fixing (a light emitting process) is performed so as to stabilize the hologram H.

(De-Bonding of Transparent Base Material)

Subsequently, as illustrated inFIG. 3A, an adhesion interface between the film adhesion layer21aand the first transparent film layer13ais de-bonded. Similarly, an adhesion interface between the film adhesion layer21band the second transparent film layer13bis de-bonded. In this manner, as illustrated inFIG. 3B, a hologram member32can be obtained. The hologram member32is formed by sandwiching the recording material layer14between the first transparent film layer13aand the second transparent film layer13b.

Subsequently, as illustrated inFIG. 3C, the base plate11with a bumpy surface having a reflection layer and a selective reflection layer formed thereon is prepared. The adhesion layer12having a thickness of, for example, 15 μm is formed on the bumpy surface of the base plate11. Thereafter, the hologram member32is bonded to the base plate11with the adhesion layer12therebetween. In this manner, as illustrated inFIG. 3D, a desired optical recording medium can be produced.

Note that when data is recorded in the optical recording medium, an erase mark is formed in the recording material layer14having a fringe pattern formed through the initialization process of the optical recording medium. The erase mark is formed by, for example, focusing a beam at a desired position in the recording material layer14and emitting a laser beam in accordance with data to be recorded. In addition, when information is reproduced and if a reading beam is emitted to a hologram, a reproduction beam is returned. However, if the reading beam is emitted to a portion in which the hologram is destroyed, any reproduction beam is not returned. Thus, recorded 1-bit data (“0” or “1”) can be obtained.

According to the first example of the method for manufacturing the optical recording medium of the present technology, by forming the structure31in a hologram formation stage, the flatness (the planarity) of the recording material layer can be maintained and, thus, desired wavefront aberration can be obtained. In addition, by removing the transparent base material of the structure31, the thickness restriction of the optical recording medium in recording and reproducing data can be overcome. For example, the optical parameters of a BD can be also satisfied.

Since the recording material layer14is sandwiched between base materials (the transparent film layer forming base materials) each having rigidity provided by its sufficient thickness, deformation of the recording material layer14caused by an internal stress and an external stress (significant strain) of the recording material layer14can be prevented and, thus, the flatness of the recording material layer14can be maintained. Accordingly, a stable hologram (a stable diffracting grating) can be formed. In addition, by preventing exposure of the recording material layer14to oxygen until fixing is completed, deterioration of a hologram can be prevented. For example, if the recording material layer14is exposed to oxygen after a hologram is formed and before fixing starts, the hologram is deteriorated.

By forming the structure31having the light cure adhesive (the film adhesion layer) and the transparent film layer, the transparent base material can be smoothly de-bonded. At that time, since the recording material layer14is sandwiched between the first transparent film layer13aand the second transparent film layer13b, plastic deformation of the recording material layer14having a hologram formed therein can be prevented. According to the first example of the method for manufacturing an optical recording medium of the present technology, a stable hologram can be formed at low cost, and the formed hologram can have good keeping quality.

Second Example of Method for Manufacturing Optical Recording Medium

A second example of the method for manufacturing an optical recording medium according to the first exemplary embodiment of the present technology is described next. For example, the second example of a method for manufacturing an optical recording medium is employed when manufacturing an optical recording medium that uses a positive micro-hologram method as a data recording method.

(Formation of Transparent Film Layer Base Material)

As illustrated inFIG. 4A, a first transparent film layer forming base material50ais formed first. For example, by forming the film adhesion layer21aon one of the principal surfaces of a base material42aand forming the first transparent film layer13aon top of the film adhesion layer21a, the first transparent film layer forming base material30ais formed.

Similarly, a second transparent film layer forming base material50bis formed. For example, by forming the film adhesion layer21bon one of the principal surfaces of a base material42band forming the second transparent film layer13bon the film adhesion layer21b,the second transparent film layer forming base material30bis formed.

Each of the base material42aand the base material42bhas, for example, a disk shape. In addition, a material having rigidity that is higher than that of the recording material layer14is selected as the base material42aand the base material42b. In this manner, deformation of the recording material layer14can be prevented. For example, each of the base material42aand the base material42bhas a thickness that is sufficiently greater than that of the recording material layer14and, thus, has rigidity that is higher than that of the recording material layer14. Alternatively, the base material42aand the base material42bare formed from a material having rigidity that is higher than that of the recording material layer14and, thus, have rigidity that is higher than that of the recording material layer14. Still alternatively, each of the base material42aand the base material42bhas a thickness that is sufficiently greater than that of the recording material layer14and, in addition, the base material42aand the base material42bare formed from a material having rigidity that is higher than that of the recording material layer14. Thus, each of the base material42aand the base material42bcan have rigidity that is higher than that of the recording material layer14. Note that the base material42aand the base material42bmay be transparent, such as a glass base plate. However, the base material42aand the base material42bmay be non-transparent.

(Formation of Recording Material Layer)

As illustrated inFIG. 4B, the recording material layer14is formed between one of the principal surfaces of the first transparent film layer forming base material50a(the surface adjacent to the first transparent film layer) and one of the principal surfaces of the second transparent film layer forming base material50b(the surface adjacent to the second transparent film layer). In this manner, a disc-shaped structure51having the recording material layer14sandwiched between one of the principal surfaces of the first transparent film layer forming base material50aand one of the principal surfaces of the second transparent film layer forming base material50bis formed.

(De-Bonding of Base Material)

As illustrated inFIG. 4C, an adhesion interface between the film adhesion layer21aand the first transparent film layer13ais de-bonded. Similarly, an adhesion interface between the film adhesion layer21band the second transparent film layer13bis de-bonded. In this manner, a hologram member32can be obtained. The hologram member32is formed by sandwiching the recording material layer14between the first transparent film layer13aand the second transparent film layer13b.

Subsequently, a base plate11with a bumpy surface having a reflection layer and a selective reflection layer formed therein is prepared. The adhesion layer12is formed on the bumpy surface of the base plate11. Thereafter, the hologram member32is bonded to the base plate11with the adhesion layer12therebetween. In this manner, a desired optical recording medium can be produced.

Note that when data is recorded in the optical recording medium, a fringe pattern of light is locally formed in a portion of the recording material layer14in which data is to be recorded. In this manner, the fringe pattern is formed as a record mark of a hologram. In addition, when information is reproduced and if a reading beam is emitted to a hologram, a reproduction beam is returned. However, if the reading beam is emitted to a portion other than a hologram, any reproduction beam is not returned. Thus, recorded 1-bit data (“0” or “1”) can be obtained.

According to the second example of the method for manufacturing the optical recording medium of the present technology, since the recording material layer14is sandwiched by base materials (the transparent film layer forming base materials) having rigidity provided by its sufficient thickness, deformation of the recording material layer14caused by an internal stress and an external stress (significant strain) of the recording material layer14can be prevented and, thus, the flatness of the recording material layer14can be maintained. Accordingly, a stable hologram can be formed.

By forming the structure51having the light cure adhesive (the film adhesion layer) and the transparent film layer, the base material can be smoothly de-bonded. At that time, since the recording material layer14is sandwiched between the first transparent film layer13aand the second transparent film layer13b,plastic deformation of the recording material layer14having a hologram formed therein can be prevented.

2. Other Exemplary Embodiments

It should be understood that this technology is not intended to be unduly limited by the above-described embodiments, but various modifications may be made without departing from the spirit and scope of the technology.

For example, the values, the structures, the shapes, the materials, the raw materials, and the manufacturing processes described in the embodiments above are only illustrative. Different values, structures, shapes, materials, raw materials, and manufacturing processes may be employed as necessary.

In addition, the configuration, the methods, the processes, the shapes, the materials, and the values described in the embodiments above can be combined in any way without departing from the spirit and scope of the technology.

Note that the stacking structure of an optical disk is not limited to that described above. For example, any stacking structure that includes the stacking structure of the present technology (i.e., the stacking structure having the recording material layer14sandwiched between the first transparent film layer13aand the second transparent film layer13b) can be employed. Furthermore, an additional layer may be provided as necessary.

The present technology can have the following configurations:

(1) an optical recording medium including a first transparent film layer, a second transparent film layer, and a recording material layer sandwiched by the first transparent film layer and the second transparent film layer, where the recording material layer includes a hologram recording material,

(2) the optical recording medium described in (1), in which a thickness of the first transparent film layer is the same or substantially the same as a thickness of the second transparent film layer,

(3) the optical recording medium described in one of (1) or (2) further including a base plate having one of principal surfaces having the first transparent film layer, the second transparent film layer, and the recording material layer thereon,

(4) the optical recording medium described in (3), in which the first transparent film layer is bonded to the one of the principal surfaces of the base plate with an adhesion layer therebetween,

(5) the optical recording medium described in any one of (1) to (4), in which the hologram recording material is photopolymer,

(6) the optical recording medium described in any one of (1) to (5), in which the first transparent film layer and the second transparent film layer are low refractive index transparent resin films having a resistance to the recording material layer and high adhesion to the recording material layer,

(7) the optical recording medium described in (6), in which the transparent resin film is an Arton film,

(8) a method for manufacturing an optical recording medium, including forming a first transparent film layer forming base material by bonding a first transparent film layer to one of principal surfaces of a first base material with a first adhesion layer therebetween, forming a second transparent film layer forming base material by bonding a second transparent film layer to one of principal surfaces of a second base material with a second adhesion layer therebetween, forming a recording material layer including a hologram recording material between a principal surface of the first transparent film layer forming base material adjacent to the first transparent film layer and a principal surface of the second transparent film layer forming base material adjacent to the second transparent film layer, forming, after the recording material layer is formed, a member having the recording material layer formed between the first transparent film layer and the second transparent film layer by de-bonding a first adhesion interface between the first transparent film layer and the first adhesion layer and de-bonding a second adhesion interface between the second transparent film layer and the second adhesion layer, and bonding the member to one of principal surfaces of a base plate,

(9) the method for manufacturing an optical recording medium described in (8), in which a thickness of the first transparent film layer is the same or substantially the same as a thickness of the second transparent film layer,

(10) the method for manufacturing an optical recording medium described in (8) or (9), in which the first base material and the second base material are transparent, and each of the first adhesion interface and the second adhesion interface is de-bonded after a hologram is formed in the recording material layer,

(11) the method for manufacturing an optical recording medium described in any one of (8) to (10), in which each of the first base material and the second base material serves as a base plate having rigidity higher than rigidity of the recording material layer,

(12) the method for manufacturing an optical recording medium described in (11), in which the base plate has a thickness greater than a thickness of the recording material layer,

(13) the method for manufacturing an optical recording medium described in any one of (8) to (12), in which each of the first base material and the second base material is a glass base plate,

(14) the method for manufacturing an optical recording medium described in any one of (8) to (13), in which each of the first transparent film layer and the second transparent film layer is a low refractive index transparent resin film having a resistance to the recording material layer, high adhesion to the recording material layer, and high peelability from the adhesion layer,

(15) the method for manufacturing an optical recording medium described in (11), in which the transparent resin film is an Arton film, and

(16) the method for manufacturing an optical recording medium described in any one of (8) to (15), in which a material of each of the first adhesion layer and the second adhesion layer is a light cure adhesive.

The present disclosure contains subject matter related to that disclosed in Japanese Priority Patent Application JP 2012-176227 filed in the Japan Patent Office on Aug. 8, 2012, the entire contents of which are hereby incorporated by reference.