JP4080506B2 - Optical information recording medium - Google Patents

Description

  The present invention relates to an optical information recording medium for recording or reproducing information, and more particularly to an optical information recording medium capable of suppressing warpage due to environmental changes.

FIG. 1 is a schematic cross-sectional view showing the configuration of the optical information recording medium. FIG. 8 shows a plan view (a) and a side view (b) of a conventional optical information recording medium.
Conventionally, as shown in FIG. 1, an optical information recording medium 10 has a dielectric film 41, 43 (silicon nitride, etc.) and a recording film 42 (TbFeCo, etc.) on a disk-shaped substrate 20 made of polycarbonate or the like by sputtering or the like. A single or multilayer thin film layer 40 made of a thin film such as a reflective film 44 (Al, etc.) is formed. A thin film protective film 50 made of a resin film or the like is formed on the thin film layer 40, and a substrate protective film 30 made of a resin or the like is formed on the surface of the substrate 20 on the light incident surface side.

  The thickness of each of these layers is about 1.2 [mm] for the substrate 20, the thickness of the single layer or multilayer thin film layer 40 formed by sputtering or the like is 10 to 300 [nm], and the thickness of the thin film protective film 50. The thickness is 1 to 30 [μm], the thickness of the substrate protective film 30 is 0.1 to 30 [μm], and most of the total thickness of the medium is occupied by the polycarbonate substrate 20.

  For this reason, most of the rigidity of the optical information recording medium depends on the polycarbonate substrate 20, and since the polycarbonate substrate 20 is sufficiently thick, deformation due to environmental changes (temperature and humidity changes) is very small and occurs in each layer. There was no need to consider the balance of stress and bending moment.

  However, in recent years, there has been a demand for high-density recording / reproducing of optical information recording media, and there is a tendency to increase the NA of the objective lens and reduce the thickness of the substrate in order to reduce the beam spot diameter for higher density. is there. In particular, the substrate thickness tends to be reduced to half or less from the conventional 1.2 mm thickness to 0.6 mm thickness and 0.5 mm thickness. Naturally, as the substrate becomes thinner, the rigidity of the optical information recording medium 10 decreases.

When the rigidity is reduced in this way, there is a problem that deformation due to stress generated in each layer forming the optical information recording medium 10 increases due to environmental changes (temperature / humidity changes), making it difficult to record and reproduce information. .
Therefore, even when the transparent substrate 20 is thin and the rigidity is lowered, it is required to suppress the deformation of the substrate as much as possible and provide an optical information recording medium having high environmental performance.

As a method for controlling the deformation of the optical information recording medium, Patent Document 1 proposes a method of providing a dielectric film for preventing warpage on the back surface of the substrate (the surface on which the thin film layer is not formed).
FIG. 5 is a sectional view showing the structure of this conventional optical information recording medium. 5 that are the same as those in FIG. 1 are denoted by the same reference numerals. As shown in FIG. 5, here, a dielectric layer 60 is provided on the light incident side of the polycarbonate substrate 20, and the expansion rates of the thin film layer 40 and the dielectric layer 60 located on both sides of the transparent substrate 20 are made equal. Thus, the optical information recording medium has a symmetrical structure with respect to the transparent substrate 20 so that the warp of the optical information recording medium can be prevented.

  Patent Document 2 describes an optical information recording medium in which deformation at the time of environmental change is reduced by forming a substrate protective film having the same configuration as that of FIG. 1 and having a rigidity higher than that of the substrate.

Patent Document 3 describes an information recording medium for the purpose of preventing warpage due to a change in humidity. FIG. 6 shows a cross-sectional view of the configuration of the information recording medium described in Patent Document 3.
This recording medium includes a thin film protective film 50, a thin film layer 40, a substrate 20, and a substrate protective film (dielectric layer) 30, and further, between the substrate 20 and the substrate protective film 30 in order to prevent warpage due to a change in humidity. A moisture permeation preventive film 70 made of SiO ₂ or AlN is provided. In FIG. 6, the same parts are denoted by the same reference numerals.

Furthermore, Patent Document 4 discloses that an optical information recording medium having a thin film protective film 50, a thin film layer 40, a substrate 20, and a substrate protective film 30 as shown in FIG. An optical information recording medium is described in which a warp due to a change in humidity is reduced by forming a film 30.
JP-A-4-195745 Japanese Patent Laid-Open No. 11-16211 JP-A-4-364248 JP 2000-311381 A

  However, both the recording medium described in Patent Document 1 and the recording medium described in Patent Document 3 require that a dielectric layer (60, 30) be provided on the light incident side of the substrate by sputtering or the like. On the other hand, after forming the thin film layer 40 on one surface, it is necessary to turn the substrate over to form the dielectric layer (60, 30) on the opposite surface, which complicates the process and produces production equipment. There is a problem that this leads to an increase in price and leads to an increase in cost.

The method described in Patent Document 2 also has the same problem as Patent Document 1 because it is necessary to form SiO ₂ on the substrate by plasma CVD or the like as a substrate protective film.
Further, the method described in Patent Document 3 also has a problem for the same reason as Patent Document 1 because AlN or SiO ₂ needs to be provided on the substrate light incident side by sputtering or the like.

  Further, in the method described in Patent Document 4, when a substrate 20 made of a transparent resin such as acrylic, polyolefin, or polycarbonate is used, it is made of a resin that expands to a humidity higher than the substrate 20 in most cases when the humidity changes. Further, since the thin protective film 50 exists, there is a problem that the phenomenon of deformation cannot be completely prevented.

  The present invention has been made to solve such problems, and an object of the present invention is to provide an optical information recording medium that can more effectively suppress deformation (warpage) associated with changes in humidity.

The present invention relates to a transparent substrate made of any one of polycarbonate, acrylic resin, and polyolefin resin, a thin film layer formed on one surface of the transparent substrate, and an ultraviolet curable resin formed on the thin film layer An optical information recording medium comprising: a thin film protective film comprising: a thin film protective film; and a substrate protective film made of an ultraviolet curable resin formed on the other surface of the transparent substrate to be thinner than a film thickness of the thin film protective film. The layer is a single layer film or a multilayer film composed of at least one of a dielectric film, a recording film and a reflective film, and the humidity expansion coefficient of the substrate protective film is larger than the humidity expansion coefficient of the thin film protective film, and the humidity changes It is an object of the present invention to provide an optical information recording medium characterized in that the bending moment that the thin film protective film sometimes gives to the transparent substrate balances the bending moment that the substrate protective film gives to the transparent substrate.

According to this, deformation (warpage) at the time of humidity change can be more effectively suppressed.
Here, a substrate protective film having a humidity expansion coefficient of 1.6 × 10 ⁻⁵ (1 /%) or more can be used.

In consideration of expansion due to temperature, it is preferable that the linear expansion coefficient of the substrate protective film is equal to or smaller than the linear expansion coefficient of the transparent substrate.
Further, the substrate protective film has a higher hardness than the transparent substrate, has a higher conductivity than the transparent substrate, and has a transmittance of 80% or more in a short wavelength region. , Any or all of them may be satisfied. Here, the short wavelength region means a wavelength around 405 nm.

  In the invention, the transparent substrate is made of any one of polycarbonate, acrylic resin, and polyolefin resin, and the thin film protective film and the substrate protective film are made of an ultraviolet curable resin.

In the present invention, the humidity expansion coefficient is obtained by converting the amount of elongation per unit length when the relative humidity around the object is increased at a constant temperature (25 ° C.) into a humidity expansion coefficient per 1% humidity. is there.
For example, polycarbonate or polyolefin can be used as the material of the transparent substrate. Further, in order to effectively prevent the warp of the medium, the substrate protective film and the thin film protective film are formed of a material that satisfies the relationship of the above-described humidity expansion coefficient. For example, an ultraviolet (UV) curable resin, In particular, it can be formed of an ultraviolet curable resin mainly composed of polyester acrylate, epoxy acrylate, urethane acrylate, or polyether acrylate.
Moreover, as a material for the substrate protective film, a material containing a lot of hydrophilic components is preferable from the viewpoint of using a material having a humidity expansion coefficient as large as possible.

(1) Since a substrate protective film having a larger coefficient of humidity expansion than that of the thin film protective film is formed on the transparent substrate of the optical information recording medium, it is possible to suppress warpage when the humidity changes and to improve the reliability of recording and reproduction. Can do.
(2) Since the linear expansion coefficient of the substrate protective film is equal to or smaller than the linear expansion coefficient of the transparent substrate, the warpage at the time of humidity change can be suppressed without deteriorating the warpage at the time of temperature change, and recording. The reliability of reproduction can be increased.
(3) By providing a substrate protective film having a hardness higher than that of the transparent substrate, the substrate surface is less likely to be damaged, and the reliability of recording and reproduction can be improved.
(4) By providing a substrate protective film having a conductivity higher than that of the transparent substrate, dust and other dusts are less likely to adhere, and the reliability of recording and reproduction can be improved.
(5) By providing a substrate protective film having a high transmittance in the short wavelength region, a short wavelength laser such as a blue laser can be used during signal recording and reproduction, and high-density recording with high reliability can be achieved.

The present invention will be described in detail below based on the embodiments shown in the drawings. However, this does not limit the present invention.
The optical information recording medium that is the subject of the present invention has an appearance configuration substantially similar to that shown in FIG.

For example, the first and second dielectric films 41 and 43 (silicon nitride, etc.), the recording film 42 (TbFeCo, etc.), the reflection, etc. are sputtered on the transparent substrate 20 made of polycarbonate, acrylic resin, polyolefin resin or the like. A single-layer or multi-layer thin film layer 40 made of a thin film such as a film 44 (Al or the like) is formed, and a thin film protective film 50 mainly composed of a resin is formed on the thin film layer 40, and the transparent substrate 20 In order to protect the transparent substrate 20 on the opposite surface, a substrate protective film 30 mainly composed of a resin is formed.
Here, the transparent substrate 20 has a thickness of 0.5 mm, the thin film layer 40 has a thickness of 48 nm, the thin film protective film 50 has a thickness of 15 μm, and the substrate protective film 30 has a thickness of about 5 μm.

  Since each layer is made of a different material and has a different thickness, the humidity expansion coefficient, which is a physical property value of each layer, is different, and the stress generated in each layer when the humidity is changed is also different. In the case of the configuration of FIG. 1, the humidity expansion coefficient of the substrate protective film 30 and the thin film protective film 50 is generally larger than that of the transparent substrate 20, single layer, or multilayer thin film layer 40. In addition, the expansion of the single-layer or multi-layer thin film layer 40 in the radial direction of the substrate is very small as compared with the other layers.

For this reason, the cause of deformation when the humidity changes is likely to be dominated by the expansion rates and the respective film thicknesses of the substrate protective film 30 and the thin film protective film 50. In addition, since the substrate protective film 30 is on the light incident surface side, the substrate protective film 30 is formed thinner than the thin film protective film 50 because it is subject to various restrictions on the laser transmission and film thickness distribution.
Generally, when the humidity rises, if the material of the film on both surfaces is the same, the thicker the film, the greater the stress generated than the thinner film. Warping occurs.

Therefore, in the present invention, since the substrate protective film 30 is thinner than the thin film protective film 50, the optical information recording medium 10 is perpendicular to the radial direction when the humidity changes as shown in FIG. Warp tends to occur on the side of the surface where the substrate protective film 30 is formed.
In FIG. 2, assuming that the warp angle (θ) when warping in the left direction is a positive (+) direction, the warp occurs in such a manner that the warp angle becomes a negative direction.

Therefore, in order to suppress the warping in the negative direction, in the present invention, both protections are performed so that the humidity expansion coefficient of the thin substrate protective film 30 is larger than the humidity expansion coefficient of the thin film protective film 50. A film is formed. For example, when the humidity expansion coefficient of the thin film protective film 50 is set to about 1.6 × 10 ⁻⁵ [1 /%], the humidity expansion coefficient of the substrate protective film 30 may be a value having a value larger than this. .
According to this, it is possible to balance the bending moment that the thin film protective film 50 gives to the transparent substrate 20 and the reverse bending moment that the substrate protective film 30 gives to the transparent substrate 20 when the humidity changes.

By the way, when the linear expansion coefficient of the substrate protective film 30 is larger than that of the transparent substrate 20, when the temperature changes, compared to when the substrate protective film 30 is not present, the direction opposite to the humidity change (the warp angle is positive). Warp easily).
Considering this point, the linear expansion coefficient of the substrate protective film 30 is preferably equal to or smaller than the linear expansion coefficient of the transparent substrate 20. For example, when the linear expansion coefficient of the transparent substrate 20 is 6.6 × 10 ⁻⁵ [1 / ° C.], the linear expansion coefficient of the substrate protective film 30 is about 6.3 × 10 ⁻⁵ [1 / ° C.]. That's fine.

In addition, although it is a necessary condition for fulfilling the original role of the substrate protective film 30, it is preferable to make the hardness of the substrate protective film 30 higher than that of the transparent substrate 20 in order to prevent the surface from being damaged.
In addition, the substrate protective film 30 preferably has higher conductivity than the transparent substrate 20 in order to prevent dust and other dust from adhering.
Further, in the case of high density recording, a short wavelength laser is mainly used. However, in order to ensure sufficient reliability of high density recording, a high transmittance (for example, 80%) in the region of a short wavelength laser having a wavelength of about 405 nm. It is preferable to use a substrate protective film 30 having a degree of

  Therefore, in order to suppress the warpage when the humidity changes without adversely affecting the warp due to the temperature change, the humidity expansion coefficient of the substrate protective film 30 is made larger than the humidity expansion coefficient of the thin film protective film 50, and further It is preferable to satisfy the conditions of the linear expansion coefficient, hardness, conductivity, and transmittance in the short wavelength region of the substrate protective film 30.

Next, an embodiment of the optical information recording medium of the present invention will be described.
As described above, an optical information recording medium according to an embodiment of the present invention was manufactured having the same layer structure as shown in FIG. That is, the substrate protective film 30, the transparent substrate 20, the thin film layer 40 (the dielectric film 41, the recording film 42, the dielectric film 43, the reflective film 44), and the thin film protective film 50 are stacked in this order when viewed from the light irradiation direction. The prepared media was produced.
For comparison, a medium 1 that does not use the substrate protective film 30 and a medium 2 that is an embodiment of the present invention in which the substrate protective film 30 is formed were produced.
FIG. 7 shows the material and thickness of the constituent members of both media.

  Here, a UV curable resin having a film thickness of about 15 μm, which is considered to have a relatively small humidity expansion coefficient and a small amount of change in the warping angle due to a change in humidity, is used for the thin film protective film 50. For the transparent substrate 20, a polyolefin resin having a thickness of about 0.5 mm was used. The thin film layer 40 can also be formed as a multilayer film as described above. However, since the dielectric films 41 and 43 have the greatest influence as a cause of warping, in this embodiment, a single layer made of AlN having a film thickness of about 48 nm is used. A layer film was used.

Both the thin film protective films 50 of the media 1 and 2 used the UV curable resin 1 made of the same material. As the substrate protective film 30 of the medium 2, the UV curable resin 2 having a humidity expansion coefficient different from that of the thin film protective film 50 is used. In particular, as described above, the humidity expansion coefficient of the substrate protective film 30 is preferably larger than that of the thin film protective film 50. Therefore, here, the humidity expansion coefficient of the UV curable resin 1 of the thin film protective film 50 is 1.6 ×. 10 ⁻⁵ [1 /%], and the humidity expansion coefficient of the UV curable resin 2 of the substrate protective film 30 is 2.5 × 10 ⁻⁵ [1 /%].

Furthermore, the linear expansion coefficient of the polyolefin resin that is the transparent substrate 20 is 6.6 × 10 ⁻⁵ [1 / ° C.], and the linear expansion coefficient of the UV curable resin 2 that is the substrate protective film 30 is slightly smaller than that of the transparent substrate 20. 6.3 × 10 ⁻⁵ [1 / ° C.].
Both media 1 and 2 were circular media having an inner diameter of 7 mm and an outer diameter of 50 mm.

FIG. 3 shows a graph comparing the temporal change of the warp angle (θ) with respect to the humidity change for these two media.
This is a graph when the temperature and humidity are changed from (23 ° C., 50%) to (38 ° C., 90%). Further, the measured warp angle (θ) is at the outer peripheral portion of the medium, that is, at a position of a radius (r =) 22 mm from the center. In this graph, the black circle is an actual measurement value of the warp angle (θ) of the medium 2 of the present invention, and the white circle is an actual measurement value of the warp angle (θ) of the medium 1. The solid line is temperature, and the broken line is humidity.

According to FIG. 3, in the medium 2 of the present invention, there is almost no change in the warp angle even when the humidity changes, but in the medium 1 without the substrate protective film 30, the warp angle also changes greatly when the humidity increases greatly. You can see that The change amount Δθ1 of the warp angle of the medium 1 is about 4 [mrad], whereas the change amount Δθ2 of the warp angle of the medium 2 of the present invention is substantially equal to 0 and is 0.5 [mrad] at most.
That is, it can be seen from FIG. 3 that the formation of the substrate protective film 30 having a large humidity expansion coefficient can suppress the warpage compared to the case where it is not formed at all.

FIG. 4 shows a graph comparing mainly the change with time of the warp angle (θ) with respect to the temperature change for these two media.
This is a graph when the temperature and humidity are changed from (23 ° C., 45%) to (65 ° C., 25%). Moreover, the measurement site | part of curvature angle ((theta)) is the same as FIG.

According to FIG. 4, it can be seen that even when the temperature changes greatly, the amount of change in the warp angle (θ) is almost the same in either medium.
The fact that there is almost no difference in the amount of change in the warp angle (θ) is the same even when the linear expansion coefficients of the substrate protective film 30 and the transparent substrate 20 are made equal.
That is, in the medium 2 of the present invention, since the substrate protective film 30 having a linear expansion coefficient equal to or smaller than that of the transparent substrate 20 is used, it can be understood that the warp is not deteriorated by the temperature change.

  From the above results, in the present invention, a substrate protective film having a humidity expansion coefficient larger than that of the thin film protective film and having a linear expansion coefficient equal to or smaller than that of the transparent substrate is formed on the transparent substrate. Therefore, it can be seen that the warp angle at the time of humidity change can be reduced without deteriorating the change of the warp angle due to temperature change.

It is sectional drawing which shows the structure of the optical information recording medium of this invention. It is explanatory drawing of the deformation | transformation state of an optical information recording medium. It is a comparison figure of the time-dependent change of the curvature angle at the time of the humidity change of two media. It is a comparison figure of the time-dependent change of the curvature angle at the time of the temperature change of two media. It is sectional drawing which shows the structure of the conventional optical information recording medium. It is sectional drawing which shows the structure of the conventional optical information recording medium. It is a comparison figure of the material and thickness of the structural member of two media. It is the top view and side view of the conventional optical information recording medium.

Explanation of symbols

10: Optical information recording medium 20: Substrate 30: Substrate protective film 40: Thin film layer 41: First dielectric film 42: Recording film 43: Second dielectric film 44: Reflective film 50: Thin film protective film 60: Dielectric film 70: Moisture permeation prevention film

Claims (5)

Transparent substrate made of polycarbonate, acrylic resin or polyolefin resin , thin film layer formed on one surface of transparent substrate, and thin film protection made of UV curable resin formed on the thin film layer An optical information recording medium comprising a film and a substrate protective film made of an ultraviolet curable resin formed on the other surface of the transparent substrate to be thinner than the film thickness of the thin film protective film,
The thin film layer is a single layer film or a multilayer film composed of at least one of a dielectric film, a recording film, and a reflective film, and the humidity expansion coefficient of the substrate protective film is larger than the humidity expansion coefficient of the thin film protective film, An optical information recording medium characterized in that the bending moment given to the transparent substrate by the thin film protective film when the humidity changes is balanced with the bending moment given to the transparent substrate by the substrate protective film.   2. The optical information recording medium according to claim 1, wherein a linear expansion coefficient of the substrate protective film is equal to or smaller than a linear expansion coefficient of the transparent substrate.   The optical information recording medium according to claim 1, wherein the substrate protective film has a hardness higher than that of the transparent substrate.   The optical information recording medium according to claim 1, wherein the substrate protective film has higher conductivity than the transparent substrate.   2. The optical information recording medium according to claim 1, wherein the substrate protective film has a transmittance of 80% or more in a short wavelength region.

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