JPH04307438A - Optical information recording medium - Google Patents

Abstract

PURPOSE:To suppress the reflection loss of light and to improve signal characteristics and durability by setting the refractive index n of a moistureproof layer between the refractive index n(s) of a substrate and the refractive index n(h) of a hard coat layer. CONSTITUTION:The transparent moistureproof layer is formed on the specular surface of a transparent resin substrate. The value of the refractive index n of this transparent moistureproof layer is set at the value between the refractive index n(s) of the substrate and the refractive index n(h) of the hard coat layer. The transparent moistureproof layer has nearly 0 coefft. of absorption in the use wavelength region of light and the coefft. of moisture vapor permeation thereof is preferably specified to <=5X10<-4>(gmm/m<2> day). The hard coat layer is adequately constituted of a UV curing resin and is more particularly preferably an acrylate system. The (substrate treated) specular surface is preferably subjected to a substrate treatment in order to enhance the adhesion of the transparent moistureproof layer and the substrate. The plasma treatment by O2 is most effective as the substrate treatment.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical information recording medium, and more particularly to an optical information recording medium with low reflection loss of light and excellent signal characteristics and durability.

0002

[Prior Art] In an optical information recording medium in which recording or reproduction is performed by entering light from the mirror side of a transparent substrate, when the substrate material is resin, a signal is generated due to mechanical deformation due to moisture absorption from the mirror side. Deterioration of characteristics has become a problem. Therefore, attempts have been made to form a moisture-proof layer on the mirror surface to prevent moisture absorption (for example, Japanese Patent Laid-Open No. 58-322
Publication No. 38). Alternatively, a technique has also been attempted in which the parts that come into contact with the outside world are covered with a dielectric film (Japanese Patent Laid-Open No. 63-690
Publication No. 46).

However, in the former case, depending on the refractive index of the moisture-proof layer, the reflection loss of incident light is greatly affected by the film thickness, which is disadvantageous in terms of film formation and signal characteristics (recording sensitivity). In addition, when a hard coat layer is provided on the moisture-proof layer from the viewpoint of increasing mechanical strength, this disadvantage becomes even more noticeable. In the latter case, a hard coat layer is also essential from the viewpoint of strength, and in this case, reflectance becomes an issue as in the former case.

[0004] Furthermore, in durability tests under high temperature and high humidity conditions, the adhesion of the moisture-proof layer to the substrate is important, but without surface treatment, the adhesion of the moisture-proof layer is still not sufficient.

[0005]

[Problems to be Solved by the Invention] The present invention provides a method for controlling light by setting the refractive index n of the moisture-proof layer between the refractive index n(s) of the substrate and the refractive index n(h) of the hard coat layer. The purpose of the present invention is to provide an optical information recording medium with low reflection loss and excellent signal characteristics and durability.

[0006] In addition to the above-mentioned objects, the present invention aims to provide an optical information recording medium which has excellent adhesion of a moisture-proof layer and is even more durable.

[0007]

[Means for Solving the Problems] The gist of the present invention to achieve the above object is to provide an optical disc in which a recording layer is formed on the recording surface of a transparent resin substrate, and a moisture-proof layer is formed on the mirror surface of the transparent resin substrate. In the information recording medium, when a hard coat layer is formed on the moisture-proof layer, and the refractive indices of the transparent resin substrate, the moisture-proof layer, and the hard coat layer are n(s), n, and n(h), respectively. , n is between n(s) and n(h). The detailed configuration of the present invention will be explained below.

(Substrate) Here, the transparent resin substrate is made of synthetic resins that can be used as transparent substrates of optical information recording media, such as acrylics such as polycarbonate (PC) and polymethyl methacrylate (PMMA), and epoxy. There is no particular limitation as long as the substrate is Note that the refractive index n(s) of these resins varies depending on the type of resin, but is approximately 1.5 to 1.6.

(Recording layer) A recording layer is formed on the recording surface of the transparent resin substrate. The recording layer is not particularly limited as long as it has the recording function of an optical information recording medium, and may be of a magneto-optical type, a phase change type, or a write-once type. For example, in the case of magneto-optical type, for example, TbFeCo, TbFe, TbC
A thin film of GaTbCo or the like is used. The thickness of the recording layer is generally preferably 100 to 1000 Å.

[0010] A protective layer made of a dielectric material such as SiN or SiAlON may be provided with a thickness of 100 to 1000 Å above and below the recording layer, that is, on both sides of the recording layer. Furthermore, a reflective layer made of, for example, Al, Cr, etc. may be provided thereon to a thickness of about 500 Å, and the top layer may be top coated with, for example, an acrylate-based ultraviolet curing resin to a thickness of about 5 μm.

(Transparent moisture-proof layer) In the present invention, a transparent moisture-proof layer is formed on the mirror surface of a transparent resin substrate. In the present invention, the value of the refractive index n of this transparent moisture-proof layer is set to a value between the refractive index n(s) of the substrate and the refractive index n(h) of the hard coat layer described later.

[0012] The transparent moisture-proof layer preferably has an absorption coefficient of approximately 0 in the usable wavelength range of light, and a moisture permeability coefficient of approximately 5 x 10-4 (gmm/m2day) or less. Its constituent materials include, for example, MgO,
Examples include Al2O3, SiTaO, SiZrO, etc., and the film thickness is preferably 1000 to 2000 Å, and 1400 to 2000 Å.
1600 Å is more preferable.

The refractive index n of the transparent moisture-proof layer can be changed by, for example, changing the composition ratio of its constituent materials, and the composition ratio of the constituent materials can be changed by controlling the film-forming conditions. good. That is, for example, when forming a transparent moisture-proof layer by sputtering, by changing the gas pressure of the sputtering gas, or by changing the partial pressure of O2 when the sputtering gas is (Ar + O2), furthermore, by changing the partial pressure of O2, the target This may be done by placing chips of different materials in varying numbers on the surface of the substrate.

(Hard Coat Layer) In the present invention, a hard coat layer is formed on the transparent moisture-proof layer. The hard coat layer is preferably composed of an ultraviolet curable resin,
For example, acrylate-based, epoxy-based, silicon-based, etc. may be mentioned as constituent materials, and acrylate-based is particularly preferred. Its refractive index n(h) is about 1.5, and its thickness is several microns.
m is preferred.

(Base treatment) It is preferable to perform a base treatment on the mirror surface in order to improve the adhesion between the transparent moisture-proof layer and the substrate (Claim 2). Examples of the base treatment include plasma treatment, electron beam irradiation treatment, etc., and plasma treatment is particularly effective. Examples of plasma processing include plasma processing using O2 and plasma processing using Ar, among which plasma processing using O2 is the most effective.

(Method for forming each layer) The recording layer, the protective layer,
The means for forming the reflective layer and the transparent moisture-proof layer is not particularly limited as long as a uniform thickness and composition can be obtained, and for example, vacuum deposition, sputtering, etc. can be applied. The top coat and hard coat layer are not limited as long as they can be formed to have a uniform thickness, but for example, spin coating can be applied.

[0017]

[Example] (Example 1) Various substrates shown below (1) to (2) were prepared, and a transparent moisture-proof layer was formed on the substrates.

■For reflectance measurement: PC board with a thickness of 1.2 mm (refractive index: n
(s) = 1.59) ■For composition ratio/absorption coefficient/refractive index measurement: Si wafer ■For moisture permeability coefficient measurement: 180 μm thick PC sheet ■For optical information recording medium: 3.5 inch PC disk substrate

[0019]
Using Al2O3 as a target, sputtering was performed in an (Ar+O2) atmosphere to form a transparent moisture-proof layer on the substrates ① to ② above. In addition, by changing the O2 partial pressure during sputtering from 0% to 10% to 20%, the composition of the transparent moisture-proof layer was changed. 11
~No. A transparent moisture-proof layer having a refractive index n shown in No. 13 was formed. In addition, the thickness of the transparent moisture-proof layer is No. 11~No. 1
It was set to 1500 Å for all of 3.

[0020] Furthermore, using MgO as a target in an Ar atmosphere, the sputtering gas pressure introduced was set to 0.7 Pa,
By changing the pressure to 2.0 Pa and 3.0 Pa, the composition of the transparent moisture-proof layer was changed. 14~
No. A transparent moisture-proof layer having a refractive index n shown in No. 16 was formed. The thickness of the transparent moisture-proof layer is No. 14~No. It was set to 1500 Å for all 16.

[0021] On the recording surface side of the 3.5-inch PC disk substrate (■), SiN (protective layer)/TbFeCo (recording layer)/SiN (protective layer)/Al (reflective layer) were coated at 80% each.
Films were formed by sputtering to a thickness of 0 Å/300 Å/300 Å/500 Å, and the transparent moisture-proof layer was formed on the mirror surface side to prepare an optical information recording medium.

[0022] Regarding the substrate ① (substrate for reflectance measurement) and the optical information recording medium made using the substrate ②,
After forming the transparent moisture-proof layer, a UV hard coat (Dainippon Ink & Chemicals Co., Ltd. EX/704, acrylate type, n(h) = 1.52) was applied on it by spin coating.
It was formed with a thickness of μm.

[0023] A transparent moisture-proof layer was formed as described above.
The characteristics of each of the items shown in Table 1 were measured for the substrates of ~■. The maximum amount of warpage shown in Table 1 was measured by placing the substrate 2 (optical information recording medium) on which a transparent moisture-proof layer was formed in a high temperature and high humidity environment (60° C., 80% RH).

The measurement results are shown in Table 1. In addition, in Table 1, the reflectance and the amount of warpage are measured by the total amount of the hard coat layer and the transparent moisture-proof layer. In addition, for comparison, the case where no transparent moisture-proof layer is formed (No. 17) and the SiN film that is widely used as a protective film are shown in the above A.
The results obtained when a transparent moisture-proof layer was used instead of the 12O3 film or the MgO film (No. 18) are also shown. Note that when measuring the reflectance, light with a wavelength of λ=830 nm was used.

[0025]

[Table 1] * Value of PC + hard coat layer * Value of PC board + hard coat layer ** Value of recording section 4-layer film/PC board/hard coat layer No.
．． 11-13: Al2O3 film No. 14-16: MgO film No. 17: PC board (no transparent moisture barrier layer) No. 18:
SiN film

[0026] No. in Table 1. Regarding No. 17, the absorption coefficient, refractive index, and moisture permeability coefficient are the values of the PC board itself, the reflectance is the value when a hard coat layer is formed on the PC board, and the amount of warpage is the value of No. 1 on the recording surface side. 11~No. This value is obtained by forming a four-layer film similar to No. 16 and forming only a hard coat layer on the mirror surface side. Also, No. 18 is the value when a SiN film is used instead of the Al2O3 film or the MgO film.

As shown in Table 1, in the case of SiN film (No.
．． Compared to 18), in the case of Al2O3 film or MgO film (
No. 11 to no. 16), it can be seen that the total reflectance is significantly smaller. In particular, in Examples (No. 12, No. 15) of the present invention, the refractive index n of the transparent moisture-proof layer is
is the refractive index n(s) of the substrate and the refractive index n(s) of the hard coat layer
h) (1.59>n>1.52), and P
Multiple reflections at the interfaces between the C substrate and the transparent moisture-proof layer, as well as between the transparent moisture-proof layer and the hard coat layer, are almost zero, suppressing the reflection loss caused by the presence of the moisture-proof layer and making it equivalent to the case without the transparent moisture-proof layer. There is. In addition, Example (No. 1) of the present invention
2, No. 15), the moisture permeability coefficient Q is 4 x 10-4 (g
mm/m2day), and accordingly, the maximum amount of warpage is extremely small, 2 mrad or less.

Next, CNR (carrier-to-noise ratio) was measured as one of the signal characteristics for the optical information recording medium produced using the substrate (2). The results are shown in Figure 1.

As shown in FIG. 12 (n=1.
No. 56) has a sensitivity of 2.0 mW and a CNR of about 2 dB compared to the SiN film one (No. 17). 13,N
o. Even when compared to 16 (both n=1.50), the sensitivity is 1.
Since the improvement is about 0 mW, the refractive index n of the moisture-proof layer is calculated by changing the refractive index n of the substrate to the refractive index n(h) of the hard coat layer.
), the deterioration of the signal characteristics due to reflection loss is suppressed to a low level, resulting in a signal closer to a blank.

(Example 2) In this example, SixTayO1 was used instead of the Al2O3 film or MgO film in Example 1.
A transparent moisture-proof layer was formed by the -xy film. The film was formed as follows.

An appropriate number of Ta chips were placed on a SiO2 target, and sputtering was performed in an (Ar+O2) atmosphere to form a transparent moisture-proof layer on the substrates (1) to (4) described in Examples. Note that the O2 partial pressure during sputtering was 20
%, and by changing the number of Ta chips, the composition of the transparent moisture-proof layer (SixTayO1-x-y) was changed to No. 2 in Table 2. 2
1~No. The refractive index n was changed as shown in 23. All film thicknesses were 1500 Å.

As in Example 1, a protective layer and a recording layer are sandwiched on the recording surface side of the 3.5-inch PC disk substrate (2), and a reflective layer is further formed on top of the protective layer to form an optical information recording medium. Created. Note that the thickness of each layer and the film forming method were also the same as in Example 1.

For the substrate (1) (reflectance measurement substrate) and the substrate (2) (optical information recording medium), a hard coat layer similar to that in Example 1 was formed after forming the transparent moisture-proof layer.

[0034] A transparent moisture-proof layer was formed as described above.
In the same manner as in Example 1, the characteristics of each of the items shown in Table 2 were measured for the substrates of ~■. The maximum amount of warpage shown in Table 2 was measured by placing the substrate 2 (optical information recording medium) on which a transparent moisture-proof layer was formed in a high temperature and high humidity environment (80° C., 80% RH).

The measurement results are also shown in Table 2. In addition, in Table 2, the reflectance and the amount of warpage are measured by the total amount of the hard coat layer and the transparent moisture-proof layer. Further, when measuring the reflectance, light having a wavelength of λ=830 nm was used.

[0036]

[Table 2] *Value of PC + hard coat layer** Value of recording section 4-layer film/PC board/hard coat layer No.
．． 21-23: SiTaO film No. 17: PC board (no transparent moisture barrier layer) No. 18:
SiN film

[0037] Note that No. 2 in Table 2. 17, No. 1
8 is No. 8 in Table 1. 17, No. This is a reprint of 18. As shown in Table 2, in the case of SiN film (No.
．． 18), in the case of SiTaO film (No. 21 to No.
．． 23), it can be seen that the total reflectance is significantly smaller. In particular, in Example (No. 22) of the present invention, the refractive index of the transparent moisture-proof layer is the value (1) between the substrate and the hard coat layer.
．． 59>n>1.52), and multiple reflections at the interfaces between the PC board and the transparent moisture-proof layer, as well as between the transparent moisture-proof layer and the hard coat layer, are almost 0, suppressing reflection loss caused by the presence of the transparent moisture-proof layer. , it is equivalent to the case without a transparent moisture barrier layer.

[0038] Furthermore, in the example (No. 22) of the present invention, the moisture permeability coefficient is 5 x 10-4 (gmm/m2day) or less, and accordingly, the maximum amount of warpage is extremely small at 3 mrad or less. .

(Example 3) In this example, the above-mentioned PC board (1) is used, and the mirror surface side thereof is subjected to base treatment (O2 plasma treatment: O2 plasma treatment).
2 gas pressure 2.0 Pa, 300 W, 1 min) was applied. Next, No. 2 in Table 2 was applied to the mirror surface side of the substrate. Sputtering film formation was performed to obtain film compositions of Nos. 21 to 23 (these will be referred to as Nos. 31, 32, and 33). As in Example 1, the film thickness was 1500 Å in all.

[0040]No. created in this way. 31～No
．． Sample 33 (with surface treatment) and Example 2
No. created in 21~No. A total of 6 types of samples, 23 samples (without surface treatment), were subjected to a tape peel test to evaluate the adhesion.
00, Test method No. 6: Test on long-term performance of paints and coating films.

[0041] Initial and durability test (80°C, 90%RH
, 200 hours) are shown in Table 3. In Table 3, (0/100) means that out of 100 squares in which the film was cut with a knife, the number of squares in which the film remained completely in the tape peel test was 0. For comparison, measurement data on Al2O3 and MgO films without surface treatment are also shown as examples of thin films with excellent durability. Note that in order to evaluate the adhesion of the film itself, no hard coating was applied to any of the samples.

[0042]

[Table 3] By applying the base treatment, the adhesion strength especially after the durability test was significantly improved, and even the SiTaO film showed the same adhesion as the highly durable Al2O3 and MgO films. Recognize.

(Example 4) An optical information recording medium using a SiTaO film as a moisture-proof layer was produced. The substrate is a 3.5-inch PC, and the recording surface side is SiN/TbFeCo/SiN/A.
1 was formed by sputtering to a thickness of 800 Å/300 Å/300 Å/500 Å, respectively. The mirror side is undercoated (O2
Plasma treatment: O2 gas pressure 2.0 Pa, 300 W, 1 m
In), SiTaO was added to No. 2 in Table 2. 21~N
o. A film was formed by sputtering under the conditions of 23, and then a 5 μm hard coat (ex-704 described above) was applied by spin coating.
) were applied (these were No. 41, 42, 43, respectively).
). In addition, after surface treatment on the mirror side, SiTaO
A similar optical information recording medium was prepared using a SiN film instead of the film (this sample was designated as No. 48), and the CNR was measured. The results are shown in FIG. In addition, in FIG. 2, N
o. The data for No. 17 (a similar optical information recording medium with only a hard coat layer on the specular side without any base treatment or moisture barrier layer) is also shown again.

As shown in FIG. 2, No. 2 is an embodiment of the present invention. No. 42 (n=1.53) has a sensitivity of 2.0 mW and a CNR of about 2 dB compared to the SiN film one.
41 (n=1.4), No. 43 (n = 1.66), the sensitivity has improved by about 1.0 mW, so by setting the refractive index of the moisture barrier layer to a value between the substrate and the hard coat layer, the signal due to reflection loss can be reduced. Keeping deterioration of characteristics to a low level,
It can be seen that the image is closer to a blank.

[0045]

According to the present invention, by forming a transparent moisture-proof layer and a hard coat layer on the mirror surface side of the substrate, deformation of the substrate due to moisture absorption can be prevented and scratch resistance can also be imparted. Further, by subjecting the substrate to a base treatment, the adhesion of the moisture-proof layer is improved, and the durability under high temperature and high humidity conditions is improved. Furthermore, by controlling the refractive index of the moisture-proof layer to a value between that of the substrate and the hard coat layer, the reflection loss of light incident from the mirror side is kept low, resulting in improved signal characteristics.

[Brief explanation of drawings]

[Figure 1] CNR of the optical information recording medium in Example 1
Graph showing characteristics.

[Figure 2] CNR of the optical information recording medium in Example 4
Graph showing characteristics.

Claims (2)

[Claims] Claim 1: A recording layer is formed on one surface of a transparent resin substrate (hereinafter referred to as the "recording surface"), and a recording layer is formed on the surface of the transparent resin substrate opposite to the recording surface (hereinafter this opposite surface). of"
In an optical information recording medium in which a moisture-proof layer is formed on a mirror surface, a hard coat layer is formed on the moisture-proof layer, and the refractive index of the transparent resin substrate, the moisture-proof layer, and the hard coat layer are set to n. An optical information recording medium characterized in that, where (s), n, and n(h), the value of n is between n(s) and n(h). 2. The optical information recording medium according to claim 1, wherein the mirror surface is a surface that has been subjected to a base treatment.