JPH1153771A - optical disk - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a bonded optical disk having a structure bonded by an acrylic pressure-sensitive adhesive sheet and having high bonding reliability. SOLUTION: A protective coat layer material made of an ultraviolet curable resin formed on a thin film is made of a material having a contact angle θ with purified water of 80 ° or less, or a urethane bond, an amide group, a urea bond, an ether bond, or an amino group. An optical disk is manufactured by using a material containing a compound having at least one of a hydroxyl group and a carboxyl group, a material having a Young's modulus of less than 1600 MPa at 30 ° C., or a material having a pencil hardness of 2H or less.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical disk medium having a bonded structure capable of reproducing at least information by a laser beam or the like. The present invention relates to an optical disk having good mechanical accuracy and excellent adhesive strength. To provide.

[0002]

2. Description of the Related Art Optical disks have attracted attention because of their high density and large capacity, and have been used for various purposes. For example, a read-only optical disk includes a compact disk and a CD-ROM dedicated to data reproduction, and is widely used in the music field, computer field, game field, and the like. In addition, write-once optical discs that can be recorded only once are used in document filing systems, data filing systems, and the like, particularly in fields where data security is important.

[0003] Furthermore, rewritable optical discs capable of erasing and re-recording recorded information are expected to contribute to expanding the use of optical discs, because they are capable of restoring and updating data and can be used repeatedly by rewriting. Is done. As such rewritable optical disks, magneto-optical disks and phase-change optical disks have been put to practical use, and are used for data files and the like. In particular, a phase-change optical disc performs recording and erasing of information by using a recording material that reversibly changes in phase between crystalline and amorphous due to a temperature change, and changes the power of a laser beam. It is easy and easy to overwrite to record new information while erasing old information.

In order to further increase the capacity of such an optical disk, it is necessary to increase the density. In order to increase the density, it is effective to reduce the laser spot diameter. The spot diameter is proportional to the laser wavelength and inversely proportional to the numerical aperture (NA) of the objective lens. Therefore, high N
A is an effective means for reducing the spot diameter, but as the NA increases, the aberration tends to increase with respect to the tilt of the disk, and the influence of the tilt angle (Tilt) of the disk increases.

This aberration depends on the thickness of the disk substrate and (NA)
^Since it is proportional to ³ , when the NA is increased, the aberration can be reduced by making the substrate thinner.
For example, the thickness used in conventional CDs is 1.2m
In the case of a substrate of m, if the NA is 0.6 or more, the tilt angle of the disk can only be about 4 mrad, which is not realistic in consideration of the actual use environment or productivity.
However, for example, when a substrate having a thickness of 0.6 mm is used, even if the NA is 0.6, the inclination angle of the disk is 8 m.
rad, which is within a practically usable range (T. Sugaya et a.
l. : Jpn. J. Appl. Phys. 32 (199
3) 5402. , T .; Ohta et al. : Jp
n. J. Appl. Phys. 32 (1993) 521
4. ).

As described above, in order to reduce the influence of Tilt, it is effective to reduce the thickness of the substrate.
The thickness of 0.6 mm is becoming mainstream as a high-density next-generation optical disc substrate. Such a disk using a substrate having a thickness of 0.6 mm is usually used by bonding two optical disks with their recording layer surfaces facing each other.

[0007] As an adhesive used for bonding,
Conventionally, a hot melt adhesive was generally used, as represented by a laser disk or a 130 mm magneto-optical disk. That is, a hot melt adhesive is applied by a roll coater, and two substrates are bonded and pressed so that the surfaces on which the hot melt adhesive is applied are aligned.

[0008] However, in the conventional method using a hot-melt adhesive for bonding a plastic substrate having a thickness of 0.6 mm, the hot-melt adhesive is softened in a high-temperature and high-humidity environment because it is thermoplastic. Therefore, there is a problem that the warp angle of the disk is greatly deteriorated. In particular, digital video discs (DV
In the case of D), since it is necessary to cope with, for example, in-vehicle use, there is a strong demand for an adhesive having high heat resistance.

Examples of the type of the adhesive having high heat resistance include a radical polymerization ultraviolet curing adhesive, a cationic polymerization ultraviolet curing adhesive and an acrylic pressure-sensitive adhesive sheet. In bonding a plastic substrate having a thickness of 6 mm, it is possible to reduce the deterioration of the disk warpage angle under a high temperature and high humidity environment. At present, the bonding system using these highly heat-resistant adhesives is being actively studied,
Above all, the lamination method using an acrylic pressure-sensitive adhesive sheet does not require an ultraviolet curing process, so the device can be downsized and labor-saving. There is a merit such as easy handling because it is not available, and it is considered to be a promising method for bonding optical disks such as DVDs in the future.

[0010] On the other hand, optical disks before bonding include a read-only ROM, a write-once R or WORM,
In all types of rewritable magneto-optical type and phase change type, usually, at least one or more thin films are formed on a plastic molded substrate obtained by injection molding, and the thin films are further protected by an ultraviolet curing resin or the like. The form is common. The material of the ultraviolet curable resin is usually selected from the viewpoints that the formed thin film has sufficient protection performance and that curing shrinkage is small in order to suppress the warpage of the disk.

[0011]

When an acrylic pressure-sensitive adhesive sheet is used as the bonding adhesive, sufficient adhesive strength can be obtained depending on the combination of the type of the pressure-sensitive adhesive sheet and the type of the ultraviolet curable resin applied on the thin film. It is not possible to apply the pressure-sensitive adhesive sheet on the protective coat made of UV-curable resin on the disc during the lamination process. There was a problem.

The present invention has been made in view of such problems of the prior art, and has as its object to provide a bonded disc having high bonding reliability.

[0013]

Means for Solving the Problems In order to solve the above problems, the present inventors have made intensive studies on the adhesive force between an acrylic pressure-sensitive adhesive sheet and an ultraviolet curable resin, and as a result, have accomplished the present invention. That is, in the invention according to claim 1, at least one layer of a thin film and a protective coat layer made of an ultraviolet curable resin for protecting the thin film are formed on a disk-shaped disk substrate having a center hole, and the protective coat surfaces are separated from each other. In an optical disc having a structure in which an acrylic pressure-sensitive adhesive sheet is interposed therebetween as an adhesive between the protective coat layer and the protective coat layer, the contact angle θ with purified water at the interface where the protective coating layer is in contact with the adhesive is 80.
° or less is provided.

Although there seems to be no clear theory established as to the adhesion theory, from the thermodynamic point of view, the relationship between the wettability of the solid surface and the adhesion has been discussed using the contact angle as a scale. 1) The Young-Dupray equation represented by the equation is well known. _{W A = γ LV (1 +} cosθ) ... (1) where, W _A: work of adhesion, γ _LV: surface tension of the liquid, θ:
According to this formula, it is understood that it is more effective to obtain a large cos θ, that is, to make the contact angle θ as small as possible, in order to obtain a strong adhesive force using the adhesive work as a guide.

[0015] The inventors of the present invention attached two single-sided disks having the structure shown in FIG. 1 with the protective coating made of an ultraviolet curable resin facing each other and using an acrylic adhesive sheet as an adhesive. As a result of examining the relationship between the adhesive strength and the wetting characteristics of the UV-curable resin surface, the present inventors have found that the adhesive strength greatly depends on the contact angle with purified water on the UV-curable resin surface, and have accomplished the present invention.

That is, using the contact angle measurement by the droplet method, the temperature and humidity at the time of measurement were 25 ° C. and 55% RH.
When the contact angle when microliters of purified water is dropped on the surface of the protective coat made of an ultraviolet curable resin is 80 ° or less, the adhesive strength required for the optical disk can be satisfied, and more preferably 70 ° or less. When the contact angle is larger than 80 °, the adhesive strength is not sufficient, so that the optical disk may be peeled off in a drop test (drop it on an env sheet from a height of 76 cm), or during the bonding step,
Problems such as the inability to apply the acrylic pressure-sensitive adhesive sheet uniformly are undesirable.

According to a second aspect of the present invention, there is provided a disk-shaped disk substrate having a center hole, wherein at least one thin film and a protective coating layer made of an ultraviolet curable resin for protecting the thin film are formed. Are disposed opposite to each other and an acrylic pressure-sensitive adhesive sheet is interposed therebetween as an adhesive, and the material used for the protective coating layer is a urethane bond, an amide group, a urea bond, an ether bond, an amino group, a hydroxy group. And an optical disk comprising a material containing a compound having at least one of carboxyl groups.

It is considered that the adhesive force between the two bonded objects is mainly caused by van der Waals force and hydrogen bonding. Therefore, an ultraviolet curable resin containing a compound having a functional group that easily causes a hydrogen bond with an acrylic pressure-sensitive adhesive sheet is desirable, and a urethane bond, an amide group, a urea bond, an ether bond, an amino group, a hydroxy group, and a carboxyl group are preferred. At least one polar group,
Alternatively, it is preferable to select a material containing a compound having a bond because the material has a strong adhesive force to the acrylic pressure-sensitive adhesive sheet.

According to a third aspect of the present invention, there is provided a disk-shaped disk substrate having a center hole, wherein at least one layer of a thin film and a protective coating layer made of an ultraviolet curable resin for protecting the thin film are formed. And an optical disk having a structure in which an acrylic pressure-sensitive adhesive sheet is interposed therebetween as an adhesive, wherein the material used for the protective coating layer has a Young's modulus at 30 ° C. of less than 1600 MPa. I do.

According to a fourth aspect of the present invention, there is provided a disk-shaped disk substrate having a center hole, wherein at least one thin film and a protective coating layer made of an ultraviolet curing resin for protecting the thin film are formed. Provided is an optical disk having a structure in which an acrylic pressure-sensitive adhesive sheet is interposed therebetween as an adhesive, and the protective coating layer has a pencil hardness of 2H or less.

Young's modulus and hardness (pencil hardness) of the material
When the value exceeds a certain value, it is considered that when a certain amount of deformation is applied, the internal stress generated inside the material becomes large and peeling is likely to occur, that is, the adhesive strength is reduced. According to the study of the present inventors, it was found that the UV-curable resin 3
It is desirable that the Young's modulus at 0 ° C. is smaller than 1600 MPa. If the Young's modulus is 1600 MPa or more, the adhesive strength is not sufficient, and peeling occurs in a drop test of the optical disc, which is not preferable.

The pencil hardness of the ultraviolet curable resin is preferably 2H or less in a pencil hardness measurement based on JIS K5401, and when the hardness is higher than 2H, the adhesive strength is not sufficient and the optical disc falls. Peeling occurs in the test, which is undesirable. The application method of the ultraviolet-curable resin used in the present invention is generally such that after applying using a spin coating method, the resin is cured by irradiating ultraviolet rays. Usually, as spin coating conditions, rotation is performed at a rotation speed of 2000 to 6000 rpm for 0.5 to 10 seconds, and then as ultraviolet irradiation conditions, a metal halide lamp or a high-pressure mercury lamp is used to obtain an integrated light amount of 200 to 1.
Irradiation of ultraviolet rays of 000 mJ / cm ² is common.

Further, in order to further improve the adhesive strength with the acrylic pressure-sensitive adhesive sheet, a surface treatment such as corona discharge may be applied to the surface of the protective coat made of an ultraviolet curable resin.
The acrylic pressure-sensitive adhesive sheet used in the present invention, cellulose having a pressure-sensitive adhesive, and those having a substrate such as PET,
Either one without a substrate is effective, but more preferably one without a substrate.

Although there is no particular limitation on the material of the disk substrate used for the base material of the present invention, plastic materials such as polycarbonate resin, acrylic resin, epoxy resin, and polystyrene resin are widely used in terms of cost. A polycarbonate resin is generally used in terms of optical and strength. There is no particular limitation on the material of the thin film formed on the disk substrate. In a read-only ROM, an Al alloy, Au,
In the write-once type, cyanine and phthalocyanine dye materials,
In the rewritable type, a phase change material such as GeTeSb or AgInSbTe or a magneto-optical material such as TbFeCo is generally used.

The method for forming these thin films is not particularly limited, and any known method such as vacuum deposition, sputtering,
Methods such as ion beam sputtering, ion beam evaporation, ion plating, electron beam evaporation, and plasma polymerization can be appropriately employed depending on the purpose, material, and the like.

[0026]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The embodiments of the present invention will be described below by way of specific examples. Formed by injection molding,
On a transparent disk substrate made of polycarbonate having an outer diameter of 120 mm, an inner diameter of 15 mm, and a thickness of 0.6 mm, a thickness of 20 mm
0 nm ZnS-SiO ₂ protective layer, 25 nm thick
Layer of SbTeGe, ZnS 20 nm thick
Protective layer composed of -SiO _2, were laminated in this order by sputtering a reflective layer mainly composed of Al having a thickness of 100 nm. Next, on the formed thin film, a UV-curable resin manufactured by Dainippon Ink and Chemicals, Inc., product names SD-101, SD
-301, SD-318, and a UV curable resin manufactured by Sony Chemical Co., Ltd., applied to a thickness of about 5 μm by spin coating using a product name SK5110, and irradiated with UV light of about 500 mJ / cm ² by a high-pressure mercury lamp. Irradiation and curing were performed to form a protective coat layer, and four types of phase change single-sided disks having protective coat layers made of different ultraviolet curable resin materials were produced.

The two single-sided disks thus produced were bonded together using an acrylic pressure-sensitive adhesive sheet with the protective coating layer on the inside to obtain a phase-change type optical disk having an overall adhesive structure. At the time of bonding, a pressure-sensitive adhesive sheet obtained by punching a product name DA-8310 into a donut shape having a size within the range of the inner and outer diameters of the disk substrate using an adhesive sheet manufactured by Nitto Denko Corporation was used. The thickness of the adhesive sheet is 50 μm
It is. In the bonding process, first, the protective coat layer of one substrate is fixed on the upper side, and the position where the adhesive sheet attached on the PET separator is bonded is adjusted.
An adhesive sheet is attached to the substrate from above the separator using a roller or the like. Next, the separator was peeled off, another substrate was overlapped with the protective coat layer inside, and pressure bonding was carried out with an autoclave or the like, and voids generated at the time of bonding were removed to remove bubbles.

In accordance with the procedure described above, various bonded samples having different UV-curable resin materials for the protective coat layer were prepared, and their adhesive strength was evaluated by a drop test. The conditions of the drop test are as follows.
The bonded disks were dropped vertically from a height of m, and changes in the bonded state were visually observed and evaluated.
The number of samples was N = 5 disks.

The evaluation results are shown in Table 1 below.

[0030]

[Table 1]

From these results, the combination of the acrylic pressure-sensitive adhesive sheet manufactured by Nitto Denko (product name: DA-8310) and SD-101 was insufficient in adhesive strength, and the drop test was not satisfied.

[0032]

Example 1 120 m outside diameter formed by injection molding
m, inner diameter of 15 mm, thickness of 0.6 mm on a disk substrate made of polycarbonate, using UV-curable resin manufactured by Dainippon Ink and Chemicals, product name SD-101, SD
-301, SD-318, and a UV-curable resin manufactured by Sony Chemical Co., Ltd., using a product name SK5110 to form a protective film having a thickness of about 5 μm by a spin coating method, and then using a high-pressure mercury lamp to about 500 mJ / cm. The sample was cured by irradiating ultraviolet rays of No. ² to produce four types of samples having only a transparent substrate and a protective coat layer.

The contact angle between the surface of the UV-curable resin of the sample thus prepared and purified water was measured by a droplet method. Kyowa Interface Chemical Co., Ltd. "CA-S micro 2 type" was used for the measurement device, and the measurement was performed in an environment of a temperature and humidity of 25 ° C and 55% RH at the time of measurement. First, a sample coated with a protective coat made of an ultraviolet curable resin was cut into a rectangle of about 2 cm × 5 cm, and placed on a slide glass with the protective coat applied surface facing upward, and fixed tightly. Next, 5 μl of purified water was collected with a micropipettor and gently dropped on the protective coat surface. As shown in FIG. 2, the angle of a straight line passing through two points, the end of the droplet and the top of the liquid,
That is, an angle of 1/2 of the contact angle θ (here, θ is the contact angle) was measured with a protractor plate, and a value twice as the contact angle θ. The contact angle was measured 10 times for one ultraviolet curable resin material, and the average was taken as the measured value. Table 2 shows the measurement results.

[0034]

[Table 2]

From these results, it was found that SD-101 had the largest contact angle with purified water, that is, the poorest wetting, and a correlation with the result of the aforementioned insufficient adhesion strength. In order to obtain a sufficient adhesive strength satisfying the drop test with the acrylic pressure-sensitive adhesive sheet, it has been found that the contact angle with purified water is desirably 80 ° or less, and more desirably 70 ° or less.

[0036]

Embodiment 2 Outer diameter 120m formed by injection molding
m, inner diameter of 15 mm, thickness of 0.6 mm on a disk substrate made of polycarbonate, using UV-curable resin manufactured by Dainippon Ink and Chemicals, product name SD-101, SD
-301, SD-318, and a UV-curable resin manufactured by Sony Chemical Co., Ltd., using a product name SK5110 to form a protective film having a thickness of about 5 μm by a spin coating method, and then using a high-pressure mercury lamp to about 500 mJ / cm. The sample was cured by irradiating ultraviolet rays of No. ² to produce four types of samples having only a transparent substrate and a protective coat layer.

The pencil hardness of the ultraviolet curable resin surface of the sample thus prepared was measured. The measurement was carried out in accordance with JIS K5401, and the measuring device used was manufactured by Nihonn Rigaku Kogyo, and the pencil used was HI-UNI manufactured by Mitsubishi Pencil Co., Ltd. The temperature and humidity environment at the time of measurement was 25 ° C. and 55% RH. Table 3 shows the measurement results.

[0038]

[Table 3]

From the above measurement, the hardest result was obtained in which the pencil hardness of SD-101 was 3H. This result corresponds to the result of the above-mentioned drop test in which the adhesive strength is insufficient, and it can be said that the pencil hardness is desirably 2H or less. In addition, UV-curable resin manufactured by Dainippon Ink and Chemicals, Inc., with product names SD-101, SD-301 and SD-318.
Table 4 shows the Young's modulus at 0 ° C.

[0040]

[Table 4]

From the viewpoint of Young's modulus, SD-101 is the largest, and this result also corresponds to the above-mentioned drop test result with insufficient bonding strength.
It can be said that it is desirable to be smaller than 0 MPa.

[0042]

According to the present invention, at least one layer of a thin film and a protective coating layer made of an ultraviolet curable resin for protecting the thin film are formed, and the protective coating surfaces are arranged to face each other, and an acrylic adhesive is used as an adhesive therebetween. An optical disc with a structure in which an acrylic adhesive sheet is interposed has excellent adhesive strength between an acrylic adhesive sheet and an ultraviolet curable resin, and provides a stable bonding process and a highly reliable optical disc even in acceleration tests such as drop tests. be able to.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view schematically showing a disc form before bonding according to the present invention.

FIG. 2 is a schematic diagram showing a contact angle by a droplet method.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Plastic substrate 2 Thin film 3 Protective coating layer (ultraviolet curing resin) 4 Solid 5 Liquid 6 Straight line passing through two points of a drop end and a vertex 7 Tangent line 8 Angle of straight line passing through two points of a drop end and a vertex (contact angle θ 1/2) 9 Contact angle θ

Claims (4)

[Claims] 1. A disk-shaped disk substrate having a center hole, at least one thin film and a protective coating layer made of an ultraviolet-curing resin for protecting the thin film are formed, and the protective coating surfaces are arranged to face each other. An optical disk having a structure in which an acrylic pressure-sensitive adhesive sheet is interposed as an adhesive, wherein a contact angle θ with purified water at an interface where the protective coating layer contacts the adhesive is 80 ° or less. 2. A disk-shaped disk substrate having a center hole, at least one layer of a thin film and a protective coating layer made of an ultraviolet-curing resin for protecting the thin film are formed, and the protective coating surfaces are disposed so as to face each other. In an optical disc having a structure in which an acrylic pressure-sensitive adhesive sheet is interposed as an adhesive, the material used for the protective coat layer is a urethane bond, an amide group, a urea bond, an ether bond, an amino group,
An optical disc comprising a compound having at least one of a hydroxy group and a carboxyl group. 3. A disk-shaped disk substrate having a center hole, at least one layer of a thin film and a protective coating layer made of an ultraviolet-curing resin for protecting the thin film are formed, and the protective coating surfaces are opposed to each other. In an optical disc having a structure in which an acrylic pressure-sensitive adhesive sheet is interposed as an adhesive, the protective coat layer has a Young's modulus at 30 ° C. of 160.
An optical disc characterized by being smaller than 0 MPa. 4. A disk-shaped disk substrate having a center hole, at least one thin film and a protective coating layer made of an ultraviolet curable resin for protecting the thin film are formed, and the protective coating surfaces are arranged to face each other. An optical disc having a structure in which an acrylic adhesive sheet is interposed as an adhesive, wherein the pencil hardness of the protective coating layer is 2H or less.