JPH0487039A - Optical disk - Google Patents

Abstract

PURPOSE:To improve the reliability under severe thermal conditions by constituting an adhesive layer of a radiation curing hot melt type adhesive and specifying the glass transition temp., modulus of elasticity and dynamical loss coefft. of this adhesive layer. CONSTITUTION:The adhesive layer 9 is constituted of the radiation curing hot melt type adhesive. This adhesive layer 9 is so formed that the glass transition temp. Tg thereof is <=-10 deg.C, the modulus of elasticity is <=100kgf/mm<2> at -20 deg.C and 10Hz, and the dynamical loss coefft. tandelta is <=0.1 at -20 deg.C and 10Hz. Then, the stresses and strains, etc., generated between a substrate 2 and a substrate 2, between these substrates and respective constituting layers, and further between the constituting layer and the constituting layer, by a temp. change, etc., are absorbed or relieved. The peeling between the substrate 2 and the substrate 2, between these substrates and the respective constituting layers, and between the constituting layer and the constituting layer is completely prevented in this way even in the case of preservation under the severe thermal conditions. The high reliability is thus obtd.

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial Application Field> The present invention relates to optical discs, particularly magneto-optical recording discs, phase change type optical recording discs, read-only optical discs, and the like.

<Prior Art> Among optical discs, especially optical recording discs, a recording layer serving as an information-carrying portion is provided on a substrate. During recording and reproduction, a laser beam or the like is usually irradiated from the substrate side. It is done by doing.

For this reason, the substrate used is made of a transparent material, such as glass or resin.

In this case, a resin substrate has conventionally been used as the substrate for the optical disk in order to reduce the weight of the disk and to facilitate the formation of tracking groups and bits.

In order to prevent mechanical damage to the recording layer due to cracking or the like, a protective substrate is provided on the side of the substrate on which the recording layer is provided, or a pair of substrates are integrated so that the recording layer is encapsulated therein.

In the case of bonding a pair of resin substrates or a substrate and a protective substrate in this way, U.S. Patent No. 4,503,53
Specification No. 1 states that the softening point is 140°C or less, the normal tensile adhesive strength is 1 kg/Cm” or more at 20°C, and the melt viscosity is 16
It has been proposed to bond with a hot melt adhesive of 1000P or less at 0°C.

Furthermore, Japanese Patent Laid-Open No. 1-165050 proposes that a pair of substrates be integrated using a predetermined hot melt adhesive.

Furthermore, JP-A-1-143033 proposes bonding a pair of substrates together using an ultraviolet crosslinkable hot melt adhesive.

The method for manufacturing an optical disk disclosed in this publication involves applying an ultraviolet crosslinkable hot melt adhesive to only one substrate, irradiating it with ultraviolet light, and then bonding the other substrate.

Further, in the embodiment described in the same publication, a read-only optical disk is manufactured by depositing aluminum on a substrate having a bit recording information section.

<Problems to be Solved by the Invention> On the substrate of an optical disk, particularly an optical recording disk, constituent layers made of different materials such as glass and metal are usually formed in a multilayer structure.

For this reason, for example, when an optical disk is stored at high or low temperatures, warping, stress, distortion, etc. occur in the substrate, protective substrate, and constituent layers such as the recording layer, protective coat, and adhesive layer.

Therefore, under severe thermal conditions where the temperature changes at -30 to 65°C at a rate of 20°C/second, substrates, substrates and protective substrates, or these and each constituent layer, or even constituent layers and constituent layers, may It will come off.

Optical discs that are integrated using adhesives used in conventional optical discs have insufficient reliability under severe thermal conditions.

The object of the present invention is to maintain the structure of substrates, substrates and protective substrates, and their respective constituent layers even when stored under severe thermal conditions such as -30 to 65°C and temperature changes of 20°C/second. The object of the present invention is to provide a highly reliable optical disc in which constituent layers do not peel off from each other.

<Means for Solving the Problems> Such objects are achieved by the following inventions (1) to (4).

(1) having a pair of substrates, forming an information carrying part on at least one of the substrates, so that the information carrying part is enclosed;
An optical disc in which the pair of substrates are integrated via an adhesive layer, the adhesive layer being made of a radiation-curable hot melt adhesive, and the adhesive layer having a glass transition temperature Tg of -110 ℃ or less, the elastic modulus is -20℃,
100 kgf/lr+rn" or less at 10Hz, and the mechanical loss coefficient tan δ is 0 at -20℃ and 10Hz.
．． 1 or more.

(2) After applying adhesive to each of the pair of substrates and curing with radiation, the side substrates are integrated.
The optical disc described in 1).

(3) The optical disc according to (1) or (2) above, wherein the information carrying section is a recording layer.

(4) The above (1), wherein the recording layer contains a rare earth metal element, and a protective coat made of resin is provided on the recording layer.
The optical disc according to any one of 3) to 3).

<Function> The optical disc of the present invention is manufactured by bonding a pair of substrates together using an adhesive layer made of a radiation-curable hot-melt adhesive so that the information carrying portion is encapsulated therein.

By using radiation-curable hot-melt adhesives, the slow curing speed that was a problem with epoxy adhesives and urethane adhesives has been improved, and the monomer component that has been a problem with UV-curable adhesives has been improved. There is no fear of corrosion of the recording layer or substrate due to the adhesive, and the problem of low heat resistance, which was a problem with hot melt adhesives, is improved.

The adhesive layer of the optical disc of the present invention has a predetermined glass transition temperature Tg, elastic modulus, and mechanical loss coefficient tanδ.
Therefore, stress or strain, etc. between the substrates, between these and each constituent layer, or between the constituent layers, caused by temperature changes, etc., is absorbed or alleviated by the adhesive layer. Ru.

Therefore, even when the substrates are stored under severe thermal conditions where the temperature changes at -30 to 65°C at a rate of 20°C/second, peeling between the substrates, each constituent layer, and each constituent layer is prevented. It can be completely prevented and high reliability can be obtained.

Note that the information carrying section in the present invention refers to both a section that carries information in advance, as in a read-only disk, and a recording layer that carries information, as in a recording/playback disk.

Specific composition> Hereinafter, the specific configuration of the present invention will be explained in detail.

FIG. 1 shows an example of a magneto-optical recording disk as a preferred embodiment of the optical disk of the present invention.

The magneto-optical recording disk 1 shown in FIG. 1 includes a protective layer 4,
Two substrates 2 on which are sequentially formed an intermediate layer 5, a recording layer 6 as an information bearing section, a protective layer 7 and a protective coat 8,
It has a configuration in which the recording layer 6 is bonded with an adhesive layer 9 so as to be on the inside.

In the present invention, the substrate 2 is transparent to recording light and reproduction light, and is made of resin or glass.

The shape of the substrate 2 is a disk, and its diameter is usually about 50 to 360 mm, and its thickness is about 0.5 to 360 mm.
It is about 2+am.

When the substrate 2 is made of resin, a rigid resin is used.

In this case, the resin used is not limited, but acrylic resin, polycarbonate, epoxy resin, polymethylpentene, polyolefin, etc. are suitable, for example.

The substrate 2 may be manufactured according to a known method.

For example, in the case of a resin substrate, a predetermined pattern such as bits or groups for tracking, addressing, etc. may be simultaneously formed on the substrate surface using injection molding or the like.

When the substrate 2 is made of glass, it is preferably made of tempered glass. By using tempered glass,
Higher rigidity, better weather resistance, and durability can be obtained.

When using the glass substrate 2, it is preferable that a resin layer is provided on the substrate 2.

The resin layer has a predetermined pattern such as bits or groups on its surface for tracking, addressing, and the like. Note that a predetermined pattern may be formed by chemical etching or the like without providing a resin layer.

There is no particular restriction on the resin material constituting the resin layer, and it may be appropriately selected from known resins used in the so-called 2P method.

The formation of such a resin layer may be performed by the well-known 2P method.

The intermediate layer 5 is provided to improve the C/N ratio, and is preferably formed from various dielectric materials, and preferably has a layer thickness of about 30 to 150 nm.
As the layer forming method, it is preferable to use a vapor phase film forming method such as a sputtering method.

Note that such an intermediate layer material may be provided as a protective layer 7 on a recording layer 6 to be described later, and used in combination with the intermediate layer 5. When used together, the compositions of the intermediate layer 5 and the protective layer 7 may be the same or different.

The protective layer 4 and the protective layer 7 are provided to improve the corrosion resistance of the recording layer 6, and at least one of them is
Preferably both are provided. These protective layers are preferably composed of inorganic thin films made of various oxides, carbides, nitrides, sulfides, or mixtures thereof. Further, as described above, the intermediate layer may be formed of the above-mentioned materials. The thickness of the protective layer is 30 to 300
It is preferable that the thickness is about nm from the viewpoint of improving corrosion resistance.

Such a protective layer is preferably formed by various vapor phase deposition methods such as sputtering.

Information is magnetically recorded in the recording layer 6 using a modulated heat beam or a modulated magnetic field, and the recorded information is reproduced by magneto-optical conversion.

The material for the recording layer 6 is not particularly limited as long as it can perform magneto-optical recording, but alloys containing rare earth metal elements, particularly alloys of rare earth metals and transition metals, can be used by sputtering,
It is preferable that the film be formed as an amorphous film by a vapor deposition method or the like.

Rare earth metals include Tb, Dy, Nd, Gd, Sm,
It is preferable to use one or more types of Ce.

As the transition metal, Fe and CO are preferred.

In this case, the total amount of Fe and CO is 65 to 85 at%
It is preferable that

The remainder is substantially rare earth metal.

Composition of the recording layer suitably used are TbFeCo and DyTbFeCo.

Examples include NdDyFeCo and NdGdFeCo.

In addition, the recording layer contains Cr and A in a range of 10 at% or less.
ff, Ti%Pt1S i, Mo, M n .

(2) Ni, Cu, Zn, Ge, Au, etc. may be contained.

In addition, in the range of 10at% or less, Sc, Y, La, Ce
, Pr%Pm, Sm, Eu, Ho, Er, Tm, Yb,
It may also contain other rare earth metal elements such as Lu.

The thickness of such a recording layer 6 is usually 10 to 500 nm.
It is about m.

Such a recording layer may be formed using a dry coating method such as a vapor deposition method, a sputtering method, an ion blating method, or the like.

The protective coat 8 is provided to improve corrosion resistance and scratch resistance, and is preferably composed of various organic substances, but in particular, it is made of a composition containing a radiation-curable compound that is cured by radiation. Preferably, it is made of a material that is

As the composition containing the radiation-curable compound, a composition containing an epoxy resin and a photocationic polymerization catalyst is preferable.

As the epoxy resin, alicyclic epoxy resins are preferred, and those having two or more epoxy groups in the molecule are particularly preferred.

As the alicyclic epoxy resin, 3,4-epoxycyclohexylmethyl-3,4-epoxycyclohexanecarboxylate, bis-(3,4-epoxycyclohexylmethyl) adipate, bis-(3,4-epoxycyclohexyl) adipate, 1 such as 2-(3,4-epoxycyclohexyl-5,5-spiro-3,4-epoxy)cyclohexane-meta-dioxane, bis(2,3-epoxycyclobentyl)ether, vinylcyclohexene dioxide, etc. More than one species is preferred.

Although there is no particular restriction on the epoxy equivalent of the alicyclic epoxy resin, it is preferably from 60 to 300, particularly from 100 to 200, since good curability can be obtained.

Any known cationic photopolymerization catalyst may be used and is not particularly limited.

For example, complexes of one or more metal fluoroborates and boron trifluoride, bis(perfluoroalkylsulfonyl)methane metal salts, aryldiazonium compounds, 6A
Aromatic onium salts of group elements, aromatic onium salts of group 5A elements, dicarbonyl chelates of group 3A to 5A elements, thiopyrylium salts, M F s anions (where M is P
, As or sb), triarylsulfonium complex salts, aromatic iodonium complex salts, aromatic sulfonium complex salts, etc. can be used. In particular, polyarylsulfonium complex salts, aromatic sulfonium salts of halogen-containing complex ions, or iodonium complex salts can be used. salt, group 3A elements, 5
It is preferable to use one or more aromatic onium salts of Group A elements and Group 6A elements.

Further, a photocationic polymerization catalyst containing an organometallic compound and a photodegradable organosilicon compound can also be used. Since such a photocationic polymerization catalyst is non-strongly acidic, it can avoid adverse effects on highly corrosive recording layers of magneto-optical recording disks and the like.

Examples of organometallic compounds include Ti, V, Cr, Mn, and Fe.
, Co, Ni, Cu, Zn, Aj2, Zr, etc., and a complex compound in which an alkoxy group, phenoxy group, β-diketonato group, etc. is bonded is preferable. Among these, organoaluminum compounds are particularly preferred, and specifically, trismethoxyaluminum, trispropionatoaluminum, tristrifluoroacetylaluminum, and trisethylacetoacetonatoaluminum are preferred.

The photodecomposable organosilicon compound is one that generates silanol upon irradiation with light such as ultraviolet rays, and is preferably a silicon compound having a peroxysilano group, an 0-nitrobenzyl group, an α-ketosilyl group, or the like.

The content of the photocationic polymerization catalyst in the composition is preferably from 0.05 to 0.7 parts by weight, particularly from 0.1 to 0.5 parts by weight, based on 100 parts by weight of the epoxy resin.

Coatings of such compositions are typically spinner coats,
The layer may be formed by combining various known methods such as gravure coating, spray coating, and dipping. The conditions for forming the coating film at this time may be appropriately determined in consideration of the viscosity of the mixture of coating film composition, the intended coating thickness, etc.

The radiation used for curing the coating film may be determined depending on the radiation-curable compound used, but in the case of the above-mentioned compositions, it is preferable to use ultraviolet rays.

The thickness of the protective coat 8 is preferably about 0.1 to 1 oou, more preferably about 5 to 30 mm.

If this film thickness is less than 0.1-, it will not be possible to form a -like film, and the moisture-proofing effect will not be sufficient in a humid atmosphere (and the durability of the recording layer will not improve. If it exceeds this, the shrinkage that accompanies the curing of the resin film will cause warping of the recording medium and cracks in the protective film.

The adhesive layer 9 is made of a radiation-curable hot-melt adhesive.

The glass transition temperature Tg of the adhesive layer 9 is -10°C or lower, preferably -15°C or lower.

If Tg exceeds the above range, the adhesive strength will disappear at low temperatures, for example -10°C or lower.

Note that as Tg decreases, flow point (FP) also decreases. FP is the temperature at which the adhesive flows. With normal hot melt adhesives, if the Tg is less than 160°C, the FP will be low (too high, for example 45 to 60°C).
The adhesive will flow out at temperatures around ℃. On the other hand, in the case of radiation-curable hot-melt adhesives, the Tg hardly changes by radiation irradiation, but the FP greatly improves, so there is no particular lower limit to the Tg, but the Tg is usually -60° C. or higher.

Further, the elastic modulus of the adhesive layer 9 is 100 kgf/a+m" or less at -20°C and 10 Hz, preferably 3 to 1 O
If the above range is exceeded, the stress or strain occurring between the substrates 2, between these and each of the constituent layers such as the protective coat 8, or between the constituent layers may be reduced by using an adhesive. For example, if placed under severe conditions in which the temperature changes from -30 to 65°C at a rate of 20°C/sec, the constituent layers such as the protective coat 8 may be absorbed by the substrate 2 or other layers. In addition, if the elastic modulus is too low, the elastic modulus at high temperatures will further decrease, resulting in a decrease in adhesive strength.

Therefore, the elastic modulus is 3 to 3 as mentioned above. It is preferably 100 kgf/m+a''.

Furthermore, the mechanical loss coefficient tan δ of the adhesive layer is -20
℃, 0.1 or more, preferably 0.2 to 1.
5. If it is less than the above range, the adhesiveness will be low and it will be difficult to obtain sufficient adhesive strength. For example, -30 to 6
If the adhesive layer 9 is placed under severe conditions where the temperature changes at a rate of 5°C and 2°C/sec, the adhesive layer 9 will peel off from the constituent layers such as the substrate 2 or the protective coat 8. Also, if the tan δ is too high, If the substrate 2 is warped or an external stress such as an impact is applied, there is a possibility that a shift will occur between the two substrates.

Therefore, tan δ is preferably 0.2 to 1.5 as described above.

Tg, FP, elastic modulus, and mechanical loss coefficient tanδ are measured as follows.

For example, the adhesive is applied onto release paper using a roll coater or the like to a thickness of 100 to 500 μm. Next, it is irradiated with radiation such as ultraviolet rays under the same conditions as when producing the optical disk, and is cured. After curing, the adhesive is peeled off from the release paper to obtain an adhesive layer sample. For this sample, using a viscoelasticity measuring device, an excitation frequency of 10H was measured using the forced vibration method.
Measurement is performed between -50 and 80°C using z (sine wave). In this case, Tg is determined from the temperature at which the loss modulus E'' peaks, and FP is determined from the temperature at which the elastic modulus E' sharply decreases on the high temperature side of 7 g or higher.

The radiation-curable hot-melt adhesive used in the present invention preferably contains a hot-melt resin base polymer, a radiation-curable component, and a photopolymerization initiator.

The hot-melt resin base polymer is not particularly limited as long as it has tackiness at room temperature, but it is preferable to use a thermoplastic block copolymer elastomer.

As the block component of the thermoplastic block copolymerized elastomer, polystyrene, polybutadiene, polyisoprene, ethylene-butylene copolymer, etc. are preferable, and it is preferable to use one or more of these.

Particularly preferred is a block copolymer elastomer of polystyrene with a molecular weight of about 2,000 to 12,500 and polybutadiene, polyisoprene, or ethylene-butylene copolymer with a molecular weight of about 1,000 to 250,000. In addition, the molecular weight of the block copolymer elastomer is 30
It is preferable that it is about 000,000 to 500,000.

In addition to these thermoplastic block copolymer elastomers, hot-melt resin base polymers include synthetic rubbers such as inbrene rubber, styrene rubber, butadiene rubber, butyl rubber, polyolefins such as polyethylene, polypropylene, and ethylene-vinyl acetate copolymers. It is preferable that one or more types of polyolefin copolymers and the like are contained as necessary.

As the radiation-curable component, an oligomer of a saturated hydrocarbon resin having at least one acryloyl group having a double bond exhibiting radiation sensitivity in one molecule is preferable.

Examples of such oligomers include acrylates, urethane acrylates of saturated hydrocarbon resin oligomers containing at least one hydroxyl group or carboxyl group in one molecule, such as hydrogenated polybutadiene, polybutene, hydrogenated polyisoprene, and polyisobutylene. Epoxy acrylate or ester acrylate is preferred, and it is preferred to use one or more of these.

The ratio of the hot melt type resin base polymer and the radiation curable component in the adhesive is 5 to 100 parts by weight of the radiation curable component per 100 parts by weight of the hot melt type resin base polymer.
It is preferably 10 to 40 parts by weight, particularly 10 to 40 parts by weight.

When the radiation-curable component is less than the above range, the heat resistance of the adhesive tends to be insufficiently improved, and when it exceeds the above range, the adhesiveness tends to be insufficient.

As the photopolymerization initiator, a normal photopolymerization initiator that generates radicals when irradiated with radiation such as ultraviolet rays may be used.
For example, benzoin ethers such as benzoin isopropyl ether and benzoin isobutyl ether, benzophenones such as benzophenone, p-methoxybenzophenone, and p-bromobenzophenone, benzyl methyl ketal, 2,2-jethoxyacetophenone, l, 1-
Examples include acetophenone types such as dichloroacetophenone, thioxanthone types such as 2-chlorothioxanthone, quinone types such as anthraquinone and phenanthraquinone, and sulfide types such as benzyl disulfide and tetramethylthiuram monosulfide.

The amount of the photopolymerization initiator is preferably 0.5 to 5% by weight based on the total of the hot-melt resin base polymer and the radiation-curable component.

Furthermore, in addition to these, it is preferable that a tackifier is contained. As the tackifier, one or more of rosin resin, coumaron resin, hydrogenated petroleum resin, hydrogenated terpene resin, phenol resin, etc. is preferable. Hydrogenated tackifiers have good compatibility, do not adversely affect thermal stability, and have low water absorption, so they have good corrosion resistance.

The content of the tackifier is 5 to 300 parts by weight, particularly 10 to 300 parts by weight, per 100 parts by weight of the hot-melt resin base polymer.
Preferably it is 150 parts by weight.

Furthermore, it is preferable that a softener is further contained as needed. As the softener, one or more of process oil, paraffin oil, polybutene, polyisobutylene, etc. is preferred.

Additionally, additives such as plasticizers, waxes, ultraviolet absorbers, fillers, and anti-aging agents may be added as necessary.

By appropriately selecting and combining these adhesive constituents, the physical properties of the adhesive layer can be controlled within the ranges described above.

When bonding substrates together using the radiation-curable hot-melt adhesive described above, it is preferable to use the following method.

The adhesive is applied to the substrate surface in a molten state using a roll coater for hot melt adhesives or the like.

The adhesive may be applied to only one or both of the pair of substrates, but is preferably applied to both. This is because it is difficult to make the adhesive coating surface smooth.

In other words, if adhesive is applied to only one substrate and bonded to the other substrate after curing with radiation, the substrate is likely to become distorted due to the unevenness existing on the surface of the adhesive layer (this distortion may cause the disc to be used as an optical disc). The surface runout acceleration is large (
Become.

However, when adhesive is applied to both substrates, there are still unevenness on the surface of the adhesive layer of each substrate, but when these are bonded together, the unevenness on the surface of the adhesive coating is absorbed by both adhesive layers. It has little negative effect on the board, and therefore the surface runout acceleration can be kept small.

After applying the adhesive to the substrate, it is irradiated with radiation.

Although it is preferable to use ultraviolet rays as the radiation, electron beams may also be used.

The ultraviolet irradiation conditions are 300 to 5000 in cumulative irradiation amount.
mJ/c+++". By carrying out ultraviolet curing under such conditions, an adhesive layer having the above-mentioned physical properties can be easily obtained.

After curing, the side substrates are stacked together, e.g. 0.2~20k
Adhesive by pressing with a pressure of about gf/Cm,
Get an optical disc.

The thickness of the adhesive layer 9 is 10 to 100μ, especially 50 to 80μ
- is preferable. When the thickness of the adhesive layer is less than the above range, the adhesive force tends to be insufficient, and when it exceeds the above range, the durability tends to decrease.

In the present invention, by adhering with an adhesive layer having the physical properties described above, the recording layer 6 and the protective coat 8 as an information carrying part are bonded together.
It becomes possible to firmly bond the substrates 2 on which the respective constituent layers such as the above are formed.

In other words, the adhesive layer 9 absorbs or relieves the stress and strain between the substrates 2 and 2 and between each constituent layer caused by thermal expansion or the like.

For this reason, for example, the magneto-optical recording disk 1 of the present invention can be
Even when stored under severe thermal conditions in which the temperature changes from 0 to 65°C at a rate of 20°C/sec, peeling between the substrates 2 and each constituent layer can be prevented.

Although the case where the optical disk of the present invention is applied to a double-sided recording type magneto-optical recording disk has been described above, the present invention can also be applied to a single-sided recording type magneto-optical recording disk.

A single-sided recording type magneto-optical recording disk has a structure in which a substrate 2 having each of the constituent layers described above and a protective substrate are bonded together so that the recording layer is on the inside.

In this case as well, the same effects as those of the above-mentioned double-sided recording type magneto-optical recording disk can be obtained.

The protective substrate is provided to effectively prevent damage to the recording layer.

The protective board may be made of resin or glass (
, may be opaque.

In the case of a glass protective substrate, it is preferable to use the above-mentioned tempered glass, especially chemically strengthened glass.

Further, for the resin protective substrate, a rigid resin such as polycarbonate, acrylic resin, polyolefin, etc. is suitable.

The thickness of the protective substrate is 0.5 to 2 to ensure rigidity.
．． It is preferable to set it to about On+m.

The shape of the protective substrate may be matched to the shape of the substrate 2.

The present invention can also be applied to optical recording disks that have a so-called phase change type recording layer and perform recording and reproduction by changing reflectance.

As such a recording layer, for example,
Te described in No. 902, Patent No. 1004835, etc.
Se-based alloy, JP-A-58-54338, Patent No. 974
No. 257, Patent No. 974258, Patent No. 974257
Te oxide system described in the above issue, various other chalcogen systems mainly composed of Te and Se, alloys that cause amorphous-crystalline transition such as Ge-3n and 5i-3n, Ag-Zn, Ag-Aj2-Cu, Cu -Aj
Alloys that change color due to changes in crystal structure, such as In
There are alloys that cause changes in crystal grain size, such as -5b.

In addition, the present invention is also applicable to read-only optical discs. However, the optical disc on which the present invention is highly effective is
Among the above optical recording disks, the information carrying portion is a recording layer, and the most effective optical disk is an optical recording disk having a recording layer containing a highly corrosive metal such as a rare earth metal element.

Note that when bonding the substrates 2 together via the protective coat 8, the protective coat 8 absorbs the stress and strain that occurs in addition to the adhesive layer 9, so the storage stability at high and low temperatures is extremely high. This effect appears.

Furthermore, if the protective coat 8 is made of the above-mentioned radiation-curable resin, the adhesive force with the adhesive layer also made of the radiation-curable resin will be increased.

The optical disc of the present invention is driven at a rotational speed of 100 rpm or more for recording and reproduction.

At this time, recording and reproduction may be performed according to a known method.

<Example> Hereinafter, the present invention will be explained in further detail by giving specific examples of the present invention.

[Example 1] A magneto-optical recording disk as shown in FIG. 1 was manufactured.

First, a glass protective layer 4, an SiNx intermediate layer 5, a TbFeCo recording layer 6, and an SiNx protective layer 71 are placed on a resin substrate 2.
3 and protective coat 8 were sequentially formed.

The resin substrate 2 was made of polycarbonate and had a disk shape with an outer diameter of 130 mm and a thickness of 1.2 mm.

The substrate 2 was manufactured by injection molding, and at the same time, tracking groups were formed on its surface.

Further, a sputtering method was used to form the protective layer 4, intermediate layer 5, recording layer 6, and protective layer 7.

The protective coat 8 was formed to a thickness of 10 μm by applying a composition containing an alicyclic epoxy resin and a cationic photopolymerization catalyst, and then irradiating it with ultraviolet rays to crosslink and cure the composition.

Next, the two substrates thus obtained were bonded together so that the recording layer was on the inside.

When adhering, first apply the protective coat 8 surface of both substrates.
Adhesive A below was applied to the same thickness. A roll coater was used for application.

Next, after irradiating the adhesive with ultraviolet rays under the following condition A,
The substrates were overlapped and bonded by pressing at 1.0 kgf/cm''.

(Adhesive A composition) Polystyrene-polybutadiene copolymer 30 parts by weight Isobutylene 10 parts by weight acryloyl hydrogenated butadiene oligomer at both ends 20 parts by weight Hydrogenated rosin resin tackifier 30 parts by weight Benzophenone photopolymerization initiator 3 parts by weight ( Ultraviolet irradiation conditions A) Cumulative irradiation dose: 1000 mj/cm'' Substrate transport speed: 1,5 m/win The thickness of the adhesive layer existing between the two substrates was 70-cm.

The magneto-optical recording disk thus obtained was designated as Sample A.

Glass transition temperature Tg of adhesive layer 9 of sample A, -20
Elastic modulus and mechanical loss coefficient tan δ at ℃, 10 Hz
is as shown in Table 1.

Note that the glass transition temperature Tg, elastic modulus, and mechanical loss coefficient tan δ were measured as follows.

Apply adhesive onto release paper to a thickness of 300 mm using a roll coater.
Apply it so that
hardened. Peel the obtained adhesive layer from the release paper,
Measurement was performed using a viscoelastic spectrometer manufactured by Script Seisakusho at an excitation frequency (sine wave) of 10 Hz at a temperature of -50 to 80°C.

Sample A was subjected to the following tests and measurements.

(Thermal shock test) The sample was placed in an atmosphere of -30°C and stored for 30 minutes.
Thereafter, the temperature of the atmosphere is raised to 65° C. for 5 seconds with the sample still inside. Then, 30
After storing for 5 minutes, cool to -30°C for 5 seconds.

The above was considered as one cycle, and 20 cycles were performed.

(Cycle test) The sample is placed in an atmosphere at a temperature of -30°C and stored for 4.5 hours. Afterwards, the temperature of the atmosphere was raised to 65°C at a rate of 10°C/hour with the sample still in it, and the humidity was reduced to 80%R.
Keep it at H. After being stored in an atmosphere of 65° C. and 80% RH for 4.5 hours, it was cooled to -30° C. at a rate of 10° C./hour.

The above was considered as one cycle, and 14 cycles were performed.

(Measurement of surface runout acceleration) The disk rotation speed was 1800 rpm, and measurements were made at 5II 1 m intervals within a radius of 30 to 60 mm from the center of the disk. The number of measurement samples was three, and the average value of the maximum surface runout acceleration is shown in Table 1.

The surface runout acceleration is expressed by the acceleration of light pickup during focusing servo, and indicates the flatness of the substrate on which the tracking group is formed. This value is
According to the ISO standard, in the case of a magneto-optical recording disk with an outer diameter of 130 cm, the speed is preferably 20 m/s" or less, particularly 10 m/s2 or less.

The results of these tests and measurements are shown in Table 1.

[Comparative Example 1] Magneto-optical recording disk sample B was produced in the same manner as in Example 1 except that the following B was used as the adhesive and ultraviolet irradiation was performed under the following conditions B.

(Adhesive B composition) Urethane polymer 50 parts by weight Urethane acrylate oligomer 10 parts by weight Coumarone resin tackifier 30 parts by weight Benzophenone photopolymerization initiator 2 parts by weight (Ultraviolet irradiation condition B) Cumulative irradiation dose 600 mj/ca+" Substrate conveyance speed: 1.5 m/win Tests and measurements similar to those of Example 1 were performed on this sample B.

The results are shown in Table 1.

[Example 2] Magneto-optical recording disk sample C was produced in the same manner as in Example 1 except that adhesive A was applied to only one substrate.

The same tests and measurements as in Example 1 were performed on this sample C.

The results are shown in Table 1.

From the results shown in Table 1, the effects of the present invention are clear.

When a single-sided recording type magneto-optical recording disk in which a resin substrate and a resin protective substrate were integrated was also tested, the same results as in the above example were obtained.

<Effects of the Invention> In the optical disc of the present invention, since the pair of substrates are integrated so that the information bearing part is enclosed, damage to the information bearing part, for example, the recording layer, can be sufficiently prevented.

Furthermore, since the adhesive layer is made of a radiation-curable hot-melt adhesive, the working time is short, the heat resistance is good, and there is little adverse effect on the substrate.

In the optical disc of the present invention, the substrates have a predetermined glass transition temperature Tg, elastic modulus, and mechanical loss coefficient t.
They are integrated by an adhesive layer with an δ.

For this reason, even when stored under severe thermal conditions where the temperature changes at -30 to 65°C and 20°C/sec, it is possible to maintain the temperature between the substrates, or between them and each constituent layer such as a protective coat. The stress, strain, etc. that occur between the layers and between the constituent layers are absorbed or relaxed by the adhesive layer, and peeling between the layers can be prevented.

Furthermore, if the adhesive is applied to the surfaces of both substrates when applying the adhesive, an optical disk with low surface runout acceleration can be obtained.

Thus, according to the present invention, a highly reliable optical disc is realized.

[Brief explanation of the drawing]

FIG. 1 is a sectional view showing an example of the configuration of a magneto-optical recording disk which is a preferred embodiment of the optical disk of the present invention. IG Code explanation 1...Magneto-optical recording disk 2...Substrate 4...Protective layer 5...Intermediate layer 6...Recording layer 7...Protective layer 8...Protective coat 9...・Adhesive layer

Claims (4)

[Claims] (1) having a pair of substrates, forming an information carrying part on at least one of the substrates, so that the information carrying part is enclosed;
An optical disc in which the pair of substrates are integrated via an adhesive layer, wherein the adhesive layer is made of a radiation-curable hot-melt adhesive, and the adhesive layer has a glass transition temperature Tg of -10. ℃ or less, the elastic modulus is 100kgf/mm^2 or less at -20℃ and 10Hz, and the mechanical loss coefficient t
An optical disc characterized in that an δ is 0.1 or more at −20° C. and 10 Hz. (2) The optical disc according to claim 1, wherein an adhesive is applied to each of the pair of substrates and cured by radiation, and then the two substrates are integrated. (3) Claim 1 or 2, wherein the information carrying section is a recording layer.
The optical disc described in . (4) The optical disc according to any one of claims 1 to 3, wherein the recording layer contains a rare earth metal element, and a resin protective coat is provided on the recording layer.