JP2000123419A - Optical recording medium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To laminate while keeping flatness by forming a protective layer of an insoluble polymer film by crosslinking a reactive resin mixture containing a pressure-sensitive adhesive in a reactive resin component to change the mixture into insoluble, laminating the obtd. protective layer adjacent to an adhesive layer and on the side where a recording layer is formed. SOLUTION: Relating to the pressure-sensitive adhesive, the glass transition temp. of the homopolymers as the main structural polymer included by >=80% of the whole adhesive is preferably <=0 deg.C. Preferably, the reactive resin component of the reactive resin mixture which forms the protective layer comprised of an insoluble polymer film contains 0.1 to 25% of the pressure-sensitive adhesive and >=75 wt.% of the total of urethane diacrylate, satd. alkylene diglycolacrylate having 2-6 carbon atoms, and triacrylate deriv. of trimethylol propane. As for a tackifier, rosin deriv. resin such as abietic acid, pimaric acid and diterpenoide and polyterpene resin such as pinene and limonene can be used.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical recording medium comprising a pair of disc-shaped transparent plastic substrates bonded together with a recording layer provided on at least one of the substrates inside.

[0002]

2. Description of the Related Art When manufacturing optical recording media such as optical disks and magneto-optical disks, an adhesive is applied to a protective coat applied on a recording layer such that the recording layers of two disk substrates are inside, or an adhesive is applied. , And two disks are superimposed on each other and then pressed to be bonded.

[0003]

However, in the conventional laminating method, two discs are superimposed on each other and then pressurized to be laminated, so that the shape of the disc surface of the adherend to be laminated is like a burr. When there is a projection or a step between the recording portion and the non-recording portion, a gap is likely to remain on the surface to be bonded to the applied adhesive or the adhesive of the adhesive tape. Also, the applied adhesive,
Or, when the adhesive force between the discs to be adhered to the adhesive of the adhesive tape is not sufficient, the two discs that have been pasted once are peeled off, and air bubbles easily enter the surface to be pasted where they came off. There is a problem that bonding with a flat surface cannot be achieved.

[0004] In particular, the place to be stuck becomes very noticeable when an optical disc to be stuck from the inner surface on the stamper side of the stamper holder of the stamper inner peripheral mounting portion where the warp easily occurs on the disc surface.

An optical recording medium having a high recording density, such as a rewritable DVD (digital versatile disk), which has pits and grooves and has a high recording density, has a random number generated by circuit components such as a recording drive on the inner and outer circumferences or the surrounding environment. It is necessary to keep the level of the electrical signal noise or the jitter level, which is a slight shift of the transmission signal in time or phase, within a certain range to reduce the occurrence of errors. Therefore, to create a substrate by injection molding,
To maintain the pits and grooves from the inner circumference to the outer circumference in a sharp and constant shape, raise the die temperature during substrate molding, Increase the clamping force,
The transferability of the pit and groove shape of the stamper must be improved.

For this reason, in order to improve the transferability, the resin used for molding enters between the claw of the stamper presser installed in the mold at the inner peripheral mounting portion of the stamper and the surface on the stamper side. In addition, the tendency to generate burrs in the horizontal direction with respect to the substrate increases. In order to remove the substrate from the mold, when the mold is opened, the burr generated in the horizontal direction with respect to the substrate surface from the end facing the stamper side of the stamper presser is used to remove the substrate in the direction perpendicular to the substrate surface. , Which is deformed by receiving a force on the opposite side, a vertical convex is generated from the substrate surface in the vertical direction. Then, the amount of resin entering between the stamper and the claws of the stamper holder increases as the temperature of the resin in the mold increases, so that the convexes on the protrusions protrude higher from the substrate surface, and the two disks are removed. When overlapping each other and then pasting each other, the convex burrs hit each other, so that the gap between the two disks becomes large, and the intrusion of bubbles around the discs increases, making it difficult to perform uniform joining. .

[0007] When the stamper is pressed down and fixed by eliminating the gap between the stamper and the claws of the stamper presser, the resin intrusion is reduced. The repetition of the thermal cycle during molding between the temperature of 380 ° C. and the mold control temperature of 120 ° C. causes a temporal difference in the coefficient of thermal expansion at the contact portion, and the stamper presser hits the stamper every molding cycle. It will be transformed into a stamper. The amount of deformation increases with each repetition of molding, and since it is transferred to the substrate shape, the mechanical properties of the optical recording medium gradually deteriorate,
It becomes impossible to maintain the performance of an optical recording medium of a constant quality. From this, it can be seen that the gap between the stamper and the stamper presser cannot be eliminated, and the occurrence of the shape of the convex portion of the recording portion on the stamper side of the inner peripheral portion of the substrate due to the generation of burrs is an inevitable phenomenon.

Therefore, in order to improve the transferability, it is necessary to increase the internal temperature of the mold during molding and the mold clamping force. By increasing the distance between the two substrates, air bubbles are easily taken into many voids, and there is a large tendency that many air bubbles remain even after the defoaming step such as decompression or heating in the subsequent pressing step. . Further, even if the projections are once adhered, the interval between the superposed substrates becomes large at the place where the projections collide with each other, and the substrate is separated again, so that a gap is easily generated, and it is difficult to secure the flatness of the bonded disc.

The effect of the flatness of an optical disk, a magneto-optical disk, or the like is caused by rotating the disk at a high speed when using the disk, irradiating the disk with a laser beam, and reading the reflected light as a captured signal. Decreases, the surface vibration acceleration increases, and it cannot be read as a reliable signal. Therefore, securing planarity in bonding is an important issue.

The present invention solves the problem of the prior art, and when two disks are overlapped, even if there is a convex portion on the inner peripheral portion of the substrate, it is possible to realize the bonding while ensuring the flatness of the disks. The purpose is to obtain a laminated optical recording medium.

[0011]

The optical recording medium of the present invention comprises:
In an optical recording medium formed by bonding a pair of substrates made of a disc-shaped transparent plastic with a recording layer provided on at least one substrate inside and a bonding adhesive layer provided between the pair of substrates, A protective layer consisting of an insoluble polymer film formed by cross-linking and insolubilizing a reactive resin mixture containing a pressure-sensitive adhesive in a reactive resin component is adjacent to the bonding adhesive layer, at least on the side where the recording layer is provided. It is characterized by being prepared for.

The pressure-sensitive adhesive preferably has a glass transition point of 0 ° C. or lower of a homopolymer of a main constituent polymer containing 80% or more of the whole constitution of the pressure-sensitive adhesive. Such a material is preferably one of a rubber type, an acrylic type, and a silicone type.

In the present invention, the reactive resin component of the reactive resin mixture forming the protective layer comprising the insoluble polymer film contains 0.1 to 25% of a pressure-sensitive adhesive, and further comprises urethane diacrylate. And a saturated alkylene diglycol diacrylate having 2 to 6 carbon atoms and a triacrylate derivative of trimethylolpropane in a total amount of 75% by weight or more.

In the present invention, it is preferable to use a coating type adhesive or an adhesive of an adhesive tape for the bonding adhesive layer.

Further, in the present invention, the substrate is formed by an injection molding method using a ring-shaped stamper. When the substrate is formed, the stamper is formed on the inner peripheral side at a stamper holding inner peripheral mounting portion. A recording part is formed on the substrate on the outer peripheral side from the inner peripheral mounting part of the stamper presser, and a non-recording part is formed on the outer peripheral side adjacent to the recording part. Is molded,
It is preferable that the pair of substrates be bonded to each other in a region from the inner periphery of the stamper retainer inner peripheral attachment portion to at least a part of the recording portion and the outer non-recording portion adjacent to the recording portion.

Alternatively, in the present invention, the substrate is formed by injection molding using a ring-shaped stamper.
The substrate is flat at least on the surface on which light used for reading information is irradiated, and the stamper is fixed to the mold of the molding machine at the inner peripheral mounting portion at the inner peripheral side when the substrate is molded. It is preferable that the thickness of the substrate formed on the inner peripheral side of the inner peripheral mounting portion of the stamper retainer is equal to or less than the thickness of the substrate formed on the outer peripheral side of the inner peripheral mount of the stamper retainer.

In manufacturing the optical recording medium of the present invention, a method of bonding a pair of substrates is not particularly limited, but for example, a bonding method using a press, a hand roller, a rubber roller, or the like is used. Is preferably performed under pressure, and there are some burr-like convex portions on the inner peripheral portion of the substrate,
Even if there is a gap in the inner circumference of the disk, by increasing the adhesive force between the protective film on the outermost layer on the optical disk recording surface side, which is the adherend, and the adhesive used for bonding and the adhesive of the adhesive tape. In this way, it is possible to realize bonding while ensuring the flatness of the disk.

That is, the outermost protective film used in the present invention is formed by a crosslinking reaction of a reactive resin mixture.
The main component is tolylene diisocyanate, isophorone diisocyanate, diphenylmethane diisocyanate, dicyclohexylmethane diisocyanate, or
One of isocyanate derivatives selected from diphenyl ether diisocyanate, or a mixture thereof and the isocyanate derivative in a stoichiometric excess of 2 carbon atoms
Urethane diacrylate obtained by diacrylate of urethane diol obtained by reaction with a saturated alkylene diglycol having from 6 to 6, a saturated alkylene diglycol diacrylate having 2 to 6 carbon atoms, and a triacrylate derivative of trimethylolpropane. It is a resin mixture, and an intended mixture can be obtained by adding an acrylate ester component to the resin mixture.

As the pressure-sensitive adhesive added to the mixture, the homopolymer of the main constituent monomer containing 80% or more has a glass transition point of 0 ° C. or less, for example, natural rubber, styrene-butadiene copolymer rubber. Rubber-based pressure-sensitive adhesives having a saturated hydrocarbon fatty acid group having 2 to 8 carbon atoms and a silicone-based pressure-sensitive adhesive having a siloxane bond based on a methyl group or a phenyl group. Can be

Further, as a tackifier, abietic acid,
Pimalic acid, rosin derivative resins such as diterpenoids, pinene, polyterpene resins such as limonene and piperylene,
A petroleum resin such as styrene, indene or dicyclopentadiene may be used in combination.

In the present invention, the method of applying and bonding the adhesive to the DVD substrate includes polyethylene, PVA,
Roll coating method using hot melt adhesive such as polyamide, polyester resin, etc., spin coating method using UV curing adhesive such as radical polymerization type acrylic resin, UV curing type adhesion such as cationic polymerization type epoxy resin And a method using an adhesive tape such as a rubber-based, silicone-based, or acrylic-based resin.

Here, in the case of a double-sided DVD-RAM or the like, since the recording layer or the reflective layer hardly transmits ultraviolet light, an ultraviolet curing adhesive such as a radical polymerization type acrylic resin which is irradiated with ultraviolet light after laminating the discs is spun. Rather than using a coating method, a method using a roll coating method using a hot melt adhesive, a cationic polymerization slow curing UV
A method using a screen printing machine method and a method using a pressure-sensitive adhesive tape are suitable for the curable adhesive.

In the present invention, as a configuration of a rewritable optical recording medium, for example, a first dielectric layer, a recording layer, a second dielectric layer, and a reflective layer are provided in this order on one transparent substrate, and It is obtained by laminating a resin protective layer such as a UV-curable resin layer containing a pressure-sensitive adhesive on top of it, providing a bonding adhesive layer, and bonding this to another substrate.

When recording / erasing is performed from the substrate side, it is preferable to use a material through which laser light is transmitted. For example, a polymer such as a polycarbonate resin, a polymethyl methacrylate resin, an epoxy resin, and a polyamorphous olefin resin is preferably used. Resin or inorganic glass is used.

The dielectric layer is used to prevent deformation of the substrate and the recording layer due to heat caused by recording due to heat, thereby deteriorating the recording / erasing characteristics, to protect the recording layer from moisture, heat and oxidation, and to protect the recording layer. It plays the role of a diffusion prevention layer for preventing diffusion of atoms from the recording layer to the reflection layer. Examples of such a dielectric layer include ZnS, SiO ₂ , Ta ₂ O ₅ , IT
An inorganic film such as O, Si ₃ N ₄ , TiO _2, or a mixed film thereof can be used. In particular, a mixed film of ZnS and SiO ₂ is preferable because it has excellent wet heat resistance and suppresses deterioration of the recording layer due to repeated recording / erasing.

As the recording layer, one having a high crystallization rate is preferable as a phase-change optical recording medium for performing recording / erasing, and examples thereof include a GeSbTe-based thin film and an InSbTe-based thin film. GeS with excellent repeatability
A recording layer containing bTe is preferred.

The reflective layer facilitates the formation of amorphous marks by facilitating thermal diffusion from the dielectric layer and increasing the cooling rate of the recording layer melted during recording. In addition, there is an effect of preventing the protective layer and the like from being thermally deformed, and an effect of improving the contrast of a reproduced signal due to optical interference. As such a reflective layer, a mixture of a metal or a metal oxide, a metal nitride, a metal carbide, or the like, which has light reflectivity and absorptivity at the wavelength of laser light and has higher thermal conductivity than the protective layer. For example, Zr, Hf, Ti, Ta, Mo, S
Metals such as i, Al, Au, Cr and the like, alloys thereof, and mixtures thereof with Si oxides, Si nitrides, Al oxides and the like can be used. In particular, Al, Au, Ta, alloys thereof, and the like have high light reflectivity and high thermal conductivity by selecting a material.

[0028]

Embodiment 1 First, a phase change type light having a structure of a transparent substrate / first dielectric layer / recording layer / second dielectric layer / reflection layer / ultraviolet curing type protective layer containing a pressure-sensitive adhesive. A recording medium was produced.

For this purpose, a polycarbonate resin (trade name: AD550) manufactured by Teijin Chemicals Ltd. is used as a raw material on the transparent substrate.
3) was used. Then, an injection molding machine (model name: MO40D3H) manufactured by Nissei Plastic Industry Co., Ltd.
mm, a disk diameter of 120 mm and a storage capacity of 2.6 GB D
VD Specifications for DVD
-RAM (Version 1.0. July 199)
7) A format stamper was attached to form a transparent substrate having pits and grooves for tracking.

By smoothing the flow from the gate of the mold,
In order to reduce residual stress and maintain good substrate performance represented by birefringence, the inner non-recording portion of the stamper holding portion of this substrate is set to be lower by 10 μm than the outer recording portion, In addition, since the mold temperature is set as high as about 120 ° C. in order to improve the transferability of the stamper pattern, burrs of 1 to 100 μm are generated in the circumferential direction of the inner presser of the stamper.

The first transparent dielectric layer is made of ZnS—SiO ₂
(Film thickness: 150 nm) and formed on a transparent substrate by magnetron sputtering. The recording layer is Ge ₂ S
b ₂ Te ₅ (film thickness 25 nm). The second transparent dielectric protective layer, a ZnS-SiO ₂ (film thickness 50 nm). The reflective layer is made of Al (100 nm thick).

The organic protective layer is a UV-curable reactive resin composed of urethane diacrylate composed of dilen glycol and tolylene diisocyanate, pentaerythritol tetraacrylate, neopentyl glycol diacrylate, and trimethylolpropane triacrylate. A UV-curable protective layer having a thickness of 10 μm is formed by a spin coating method using a coating liquid in which 10% by weight of isooctyl acrylate is added as a pressure-sensitive adhesive to the resin component. Formed. At that time, a 3KW high-pressure mercury lamp was used for curing, and the irradiation time was 15 minutes.
Performed in seconds.

The medium thus obtained was bonded to another substrate. For that purpose, first, a 50 μm-thick base polymer, isooctyl acrylate, acrylic acid,
An adhesive prepared using trimethylolpropane triacrylate as a crosslinking agent was attached using an adhesive tape. Further, an organic protective layer to which a pressure-sensitive adhesive is added is applied by spin coating to a transparent substrate (the dielectric layer, the recording film layer and the reflective layer are not sputtered) formed by the same method as above, and cured by ultraviolet light. This was performed by laminating the discs just as they were and pressing them with a hand roller.

From the direction of the transparent substrate of the double-sided disk obtained by continuously forming and bonding, it was visually inspected for the presence or absence of air bubbles between the disks caused by the bonding failure. Only two sheets could be observed, and no air bubbles were observed in the other eight sheets.

[0035]

Comparative Example 1 A laminated disk was prepared in the same manner as above except that isooctyl acrylate as a pressure-sensitive adhesive was not added to the organic protective layers on both the upper and lower substrates to be bonded. From the direction of the transparent substrate of the double-sided disk obtained by continuously forming and bonding, when ten sheets were visually inspected for the presence or absence of bubbles between the disks due to the bonding failure, no bubbles were observed. With only two sheets, bubbles were observed on the other eight sheets, and bubbles having a size on the order of millimeters were observed on many substrates.

[0036]

By adding a pressure-sensitive adhesive to the organic protective layer, it is possible to increase the adhesive force of the adhesive when used for bonding with the organic protective layer of the disc to be bonded. Thus, it is easy to prepare a disk with reduced bubbles, and it is possible to maintain good mechanical properties and to bond a DVD disk with good flatness.

Claims (8)

[Claims] An optical system comprising a pair of substrates made of a disc-shaped transparent plastic and bonded by a bonding adhesive layer provided between the pair of substrates with a recording layer provided on at least one of the substrates inside. In the recording medium,
A reactive resin mixture containing a pressure-sensitive adhesive in a reactive resin component was crosslinked and insolubilized. A protective layer formed of an insoluble polymer film was formed adjacent to the bonding adhesive layer, and at least a recording layer was provided. An optical recording medium provided on the side. 2. The optical recording medium according to claim 1, wherein the glass transition point of the homopolymer of the main constituent polymer containing 80% or more of the whole constitution of the pressure-sensitive adhesive is 0 ° C. or lower. 3. The pressure-sensitive adhesive according to claim 2, wherein the pressure-sensitive adhesive is one of a rubber type, an acrylic type and a silicone type.
The optical recording medium according to the above. 4. A reactive resin component of a reactive resin mixture forming a protective layer composed of an insoluble polymer film contains 0.1 to 25% of a pressure-sensitive adhesive, and further comprises urethane diacrylate and carbon number. The optical recording medium according to any one of claims 1 to 3, wherein the total content of the saturated alkylene diglycol diacrylate of 2 to 6 and the triacrylate derivative of trimethylolpropane is 75% by weight or more. 5. The optical recording medium according to claim 1, wherein the bonding adhesive layer is made of a coating type adhesive. 6. The optical recording medium according to claim 1, wherein the bonding adhesive layer is made of a pressure-sensitive adhesive of a pressure-sensitive adhesive tape. 7. The substrate is formed by an injection molding method using a ring-shaped stamper, and when the substrate is formed, the stamper presses the inner peripheral side of the molding machine at an inner peripheral mounting portion of a stamper presser. A recording portion is formed on the substrate on the outer peripheral side of the stamper retainer inner peripheral mounting portion, and a non-recording portion is formed on the outer peripheral side adjacent to the recording portion. In a region from the inner periphery of the stamper retainer inner periphery attachment portion to at least a part of the recording portion and the non-recording portion on the outer peripheral side adjacent to the recording portion, the pair of substrates is bonded to each other. The optical recording medium according to claim 1. 8. A substrate is formed by an injection molding method using a ring-shaped stamper, and at least a surface of the substrate on which light used for reading out information is irradiated is flat.
Further, when the substrate is formed, the stamper is fixed to the mold of the molding machine at the inner peripheral side at the stamper retainer inner peripheral mounting portion, and is formed on the inner peripheral side of the stamper retainer inner peripheral mounting portion. 8. The optical recording medium according to claim 1, wherein the thickness of the substrate is equal to or less than the thickness of the substrate formed on the outer peripheral side of the inner peripheral mounting portion of the stamper retainer.