JPH01294247A - Optical recording medium - Google Patents

Abstract

PURPOSE:To prevent the deterioration of an optical recording layer and to improve resistance to deterioration with wet heat even in high-temp. high- humidity atmosphere by using a specific UV curing type resin as an adhesive agent. CONSTITUTION:The UV curing resin which consists mainly of a crosslinkable oligomer, multifunctional (meth)acrylate and photopolymn. initiator, has at least 150mol.wt. per acryloyl group of the crosslinkable oligomer and at least 15wt.% content of the tri- or higher functional acrylate and/or methacrylate and has >=50 deg.C softening point of the cured film is used. The optical recording medium having the sufficiently excellent long-term durability (maintenance of high adhesiveness and stability of the recording film) even in the high-temp. high-humidity environment is thereby obtd. The deterioration of the recording film is lessened particularly with the resin having <=1.5 acid value.

Description

Detailed Description of the Invention (Industrial Application Field) The present invention relates to an optical recording medium, more specifically an optical recording medium having a laminated structure in which two plastic substrates are bonded together with an adhesive so that the recording layer is on the inside. Regarding.

(Prior Art) In recent years, optical discs have been actively commercialized and developed as a type of large-capacity memory. Among these, research is being actively conducted to put rewritable magneto-optical disks into practical use.

Typical configurations of recent magneto-optical disks include the following. That is, this is a medium using polycarbonate as a transparent plastic substrate, a TbFeC0 film as a magneto-optical recording layer, and lnS as a dielectric layer between the plastic substrate and the magneto-optical recording layer and a protective film for the magneto-optical recording layer. In this way, the magneto-optical recording film has a structure in which it is protected by a dielectric material from both sides or one side. As a result, the lifetime of the magneto-optical recording film is significantly longer than when the magneto-optical film is exposed to the atmosphere. At the current technical level 5
It is thought to last up to 6 years.

However, considering that a lifespan of at least 10 years is required for practical use, the current technology is insufficient for practical use.

A magneto-optical recording medium having the above-mentioned typical configuration was heated to 60°C and 90%
When subjected to an accelerated RH test, pinholes were generated in the recording film after about 50 hours, and a decrease in C/N and BER (bit error rate) was observed.

Furthermore, if the magneto-optical recording film is stored in contact with the atmosphere, it will be selectively corroded or oxidized by oxygen and water in the atmosphere, making it impossible to record or reproduce information.

Therefore, in general, a protective layer is provided on the surface of the magneto-optical recording film, a transparent plastic substrate is attached to the recording layer side of the medium (single-sided recording medium), or two media are placed so that their recording layers face each other. Attempts have been made to improve durability by adhering the media to the media (double-sided recording media).

However, at present, Sin, S! Even when a moisture-proof inorganic protective layer such as Oz is provided, it is difficult to form a uniform and uniform film, and a protective layer with sufficient moisture-proofing properties is not sufficient to improve the aging deterioration of the magneto-optical recording layer. do not have.

In addition, sufficient moisture resistance cannot be obtained even with a protective coating layer made of a room-temperature curing resin, and at present, it is possible to achieve this by adhering the aforementioned protective transparent plastic substrate or by adhering two magneto-optical recording media together. The main focus is on improving the durability of magneto-optical recording media by preventing moisture and oxygen from permeating into the recording layer. This is a method of laminating so-called transparent plastic substrates.

However, in reality, when trying to obtain a magneto-optical recording medium with a laminated structure by adhesion, there are problems such as distortion such as warping of the medium due to volumetric shrinkage when the adhesive (resin) hardens, and cracks in the recording film due to this. There is.

For example, in the case of bonding using thermosetting resin, due to the long-term heating curing, in addition to thermal deformation (distortion, etc.) of the transparent plastic substrate itself, warpage of the bonding medium due to volumetric shrinkage of the cured resin, In addition, shrinkage of the cured resin causes distortion in the adhering recording film, leading to cracks, etc., which is undesirable.

(Objective of the Invention) An object of the present invention is to provide an optical recording medium in which deterioration of the optical recording layer is prevented even in a high-temperature, high-humidity atmosphere, and which has excellent moisture and heat deterioration resistance.

More specifically, the object of the present invention is to protect the recording layer from moisture and oxygen by adhesively bonding a transparent plastic substrate to the optical recording layer or adhesively bonding optical recording media to each other. Regarding optical recording media with a laminated structure, the adhesive that comes into contact with the optical recording layer remains stable against the recording layer for a long period of time without causing thermal distortion of the plastic substrate due to heat curing at high temperatures and for a long time. It is an object of the present invention to provide an optical recording medium having a laminated structure, which has an adhesive strength even under a humid heat atmosphere.

(Structure of the Invention) The present invention consists of the above-mentioned laminated structure, that is, two transparent plastic substrates, a recording layer is laminated on at least one of them, and the transparent plastic substrate is attached with an adhesive so that the recording layer is on the inside. In an optical recording medium having a bonded laminated structure, the adhesive mainly consists of (A) a crosslinkable oligomer, (B) a polyfunctional acrylic ester and/or methacrylic ester, and (C) a photopolymerization initiator. type resin, (1) the molecular weight per acroyl group of the crosslinkable oligomer is at least 150, and (2) the content of trifunctional or higher functional acrylic ester and/or methacrylic ester is at least 15% by weight. (3) The optical recording medium is characterized in that the softening point of the film after curing is 50'C or higher.

In the present invention, the crosslinkable oligomer used in the ultraviolet curable resin has a molecular weight per acroyl group of at least 150. It is preferably 350 or more, particularly preferably 1,000 or more.

Here, if the molecular weight per acroyl group is less than 150, the physical properties of the crosslinked film upon irradiation with ultraviolet rays will be low elongation and brittle. As a result, the bonding adhesive strength becomes weak, and furthermore, it deteriorates significantly in a moist heat atmosphere, making it unsuitable for practical use.

From the viewpoint of the toughness of the crosslinked film and the volume shrinkage during curing, it is more desirable that the molecular weight per acroyl group of the crosslinkable oligomer is large.

In order to minimize media distortion (such as lifting of the recording film and warping of the medium) caused by the adhesive cured film following deformation of the substrate in a moist heat atmosphere, etc., and by curing shrinkage caused by ultraviolet light during lamination, The molecular weight per acroyl group of the crosslinkable oligomer is preferably 350 or more, more preferably i,ooo or more.

The crosslinkable oligomer used in the present invention refers to an addition polymerizable compound having at least one ethylenically unsaturated bond in the molecule, and representative examples include the following 7 acrylates and/or methacrylates (hereinafter referred to as per(meth) acrylate′
(sometimes abbreviated as ) can be exemplified.

Polyester (meth)acrylate, polyether (meth)acrylate, polyurethane (meth)acrylate, epoxy (meth)acrylate.

silicone (meth)acrylate, etc. As specific examples of these, the following can be briefly mentioned.

polybutylene adipate diacrylate, polyethylene glycol dimethacrylate, polypropylene glycol diacrylate, diacrylate of polyurethane (consisting of polyester glycol and isocyanate),
Spiroglycol urethane diacrylate, bisphenol A type epoxy acrylate, bisphenol F type epoxy methacrylate, phenol novolac type epoxy acrylate, cresol novolac type epoxy methacrylate, polydimethylsiloxane dimethacrylate, etc.

These acrylates are useful as crosslinkable oligomers with a lot of practicality, but other crosslinkable oligomers include unsaturated polyesters, allyl resins such as dap resin, vinyl resins such as styrene copolymers, and side chain oligomers. Acrylic acid ester-modified resins such as polyamides, polycretanes, polyesters, polysulfones, polyethersulfones, polyphenylene oxides, and the like having active groups can also be used satisfactorily.

It is desirable to use as little as possible the crosslinkable oligomer of the present invention, preferably 15% by weight or more, preferably 25% by weight or more.

The number of these crosslinkable oligomers may be one type, or two or more types may be used in combination.

Trifunctional or higher functional acrylic ester and/or used in the present invention
Or at least 15% by weight of methacrylic acid ester is used. It is preferably 20% by weight or more, particularly preferably 25% by weight or more.

If the amount of trifunctional or higher functional acrylic ester and/or methacrylic ester is less than 15% by weight, the degree of crosslinking of the film cured by ultraviolet rays will be insufficient, resulting in a decrease in initial physical properties such as adhesive strength, as well as poor performance in a moist heat atmosphere. It is impractical because the adhesive strength is significantly reduced.

Trifunctional or higher functional acrylic ester and/or used in the present invention
Alternatively, the following can be mentioned as representative methacrylic esters.

Trimedylolpropane tri(meth)acrylate, tetramethylolmethane 1-(meth)acrylate (trifunctional), tetramethylolmethanetetra(meth)acrylate 2-hexamethylene diisocyanate and glycerin adduct diacrylate/dimethacrylate (Over 4
sensory), dipentaerythritol to cina acrylate,
and triacrylate/trimethacrylate (hexafunctional) represented by the following formula (A).

・・・・・・(A) δ 0 In addition to the above-mentioned trifunctional or higher functional (meth)acrylates, bifunctional (meth)acrylates or monofunctional (meth)acrylates are used in combination with the ultraviolet curable resin actually used. Various acrylic esters can be selected from the viewpoint of adjusting viscosity and optimizing physical properties after curing.

The softening point of the cured film of the present invention obtained by ultraviolet irradiation is 5
Must be above 0°C. The temperature is preferably 80°C or higher, particularly preferably 115°C or higher.

The definition of "softening point" used here is as follows. [Dynamic thermomechanical analyzer (DuPOnt, USA)
Young's modulus loss [I+
The temperature that gives the maximum value of is taken as the softening point of the film cured by crosslinking.

If the softening point of the cured film is lower than 50° C., the heat resistance of the cured film is insufficient, and the adhesive strength in a moist heat atmosphere is significantly reduced, which is not preferable.

Furthermore, repeated instantaneous temperature increases during laser irradiation will promote fatigue of the cured film and promote deterioration over time, so the softening point must be higher than 50°C, preferably 80'C or higher. In particular, if it is 115°C or higher, it has extremely excellent heat resistance.

Generally, the glass transition point (
Tg) is often used.

However, in the case of crosslinked polymers, the segmental motion units are thought to have a fairly large distribution, and therefore changes in the thermal state (such as thermal expansion coefficient) due to temperature changes in the sample polymer are often not clear. It is difficult to obtain the obvious T (I) observed in ordinary chain polymers, etc. Therefore, an example in which the viscoelasticity ratio tan δ (ratio of Young's modulus loss to Young's modulus) of the sample polymer is assumed to be g. However, tan δ is usually higher than Tg, and the higher the measurement frequency, the more tan δ shifts toward the higher temperature side, so this is not a preferable method.

Keeping the above points in mind, the present inventors determined the softening point of the cured film (temperature that gives the maximum value of Young's modulus loss E' of the sample polymer) as defined above as an index of the heat resistance of the crosslinked polymer. Using.

The cured film whose softening point is determined in the present invention was prepared as follows.

Place the ultraviolet curing resin composition to be measured on a clean glass plate, and use a spacer to maintain a film thickness of 0°1 to 0.5m after curing.
It was applied uniformly with a doctor knife so that

Next, a high-pressure mercury lamp (80W) was applied to the top of the resin together with the glass plate.
/cm) to obtain a cured film. The irradiation time was adjusted depending on the film thickness to obtain a cured film that was sufficiently crosslinked and had satisfactory physical properties, and its softening point was measured.

Next, a specific example will be given. DarOC (Jr 1173 () ferck
Inc.) (1.0 wt%) was added, and a cured film was obtained by irradiation with ultraviolet rays according to the above method. The Young's modulus loss (E'') of the cured film measured with a dynamic thermomechanical analyzer (Du Pont, USA, DMA 982 model) was 1.
It had 4 coarse points at 15° C., which was regarded as the softening point of the cured film.

On the other hand, a similar cured film was obtained for Dainippon Ink and Chemicals' product rsD-17J, which is a commercially available ultraviolet curable resin.
When Young's modulus loss (E'') was measured, it did not show a maximum point above room temperature, and the softening point here was below room temperature, indicating low heat resistance.

In addition, in the present invention, when used in a recording film that is easily oxidized such as a magneto-optical recording film containing rare earth metals such as Tb, DV, Nd, etc., especially when used in direct contact with this recording film, prevention of oxidative deterioration of the recording film is required. From this point of view, it is preferable that the ultraviolet curable resin has an oxidation value of 1.5 or less. More preferably it is 0.9 or less, particularly preferably 0.5 or less. If the acid value is greater than 1.5, the recording film is susceptible to oxidative deterioration (corrosion). For example, in the case of the above-mentioned magneto-optical recording film, when kept in a moist heat atmosphere, pinholes initially appear in the recording film and gradually increase. Then, the recording film becomes transparent, and finally the recording film itself disappears. Note that the rtt used in the present invention
#JJ is expressed in milligrams of potassium hydroxide (KOH>) required to neutralize 1 g of sample.

This acid value is measured by the following procedure for a liquid resin before curing.

(a) Weigh the sample precisely.

(a) Transfer to a titration container, and pour the gas (for example, Nz) excluding carbon dioxide into the container.

(1) Add an appropriate amount of a solvent (usually an equal volume mixture of ethanol and water; depending on the sample, use a solvent such as ethylene glycol methyl ether or dioxane) and heat while stirring to dissolve the sample.

(Process) Add phenolphthalein (or thymolphthalein) as an indicator and, if necessary, water that has been boiled to neutralize in advance.

(e) Titrate using N/loo potassium hydroxide (KOH>).

(For titration, a microbiulet graduated to 0.02 m is used.) (Force) M value (Acid Value) is calculated using the following formula.

VXNX56.108X103 Acid value = □ Where, W: Volume of sample [n+o] V: Potassium hydroxide solution used■ [In! ! ] N: The normality of the potassium hydroxide solution and the cured resin after curing are measured in the same manner as procedures (1) to (f) for liquid resins after preparing a sample according to the following procedure.

(a) Thoroughly crush the cured resin to be the sample.

(b) Precisely measure the required amount of the crushed sample.

(1) Transfer to a titration container, and pour gas (for example, N2) excluding carbon dioxide into the container for sufficient replacement.

(1) Add an appropriate amount of a solvent (usually an equal volume mixture of ethanol and water; depending on the sample, use a solvent such as ethylene glycol methyl ether or dioxane), attach a reflux condenser, and reduce the volume. Reflux both for 60 minutes.

In the present invention, the ultraviolet curable resin refers to a cured resin cured by ultraviolet rays in the case of an optical recording medium, and refers to a liquid resin before curing in the manufacturing method.

Incidentally, the degree of acidity (acid value is one indicator) exhibited by the resin cured by ultraviolet rays or the resin cured by ultraviolet irradiation in the present invention depends on the free acid contained in the resin. In other words, unreacted carboxylic acids such as acrylic acid or methacrylic acid contained in acrylic esters or methacrylic esters, inorganic acids such as sulfuric acid commonly used as ester reaction catalysts,
Furthermore, traces of acidic substances (α-, etc.) mixed in during the manufacturing process
is the main thing.

In order to remove these, it is common practice to neutralize acidic substances and repeat filtration, but in order to achieve the low acid value that the present invention aims for, it is necessary to use steam swamp (low molecular weight compounds), ion exchange Alternatively, washing with clean water (or water-solvent mixture) is necessary, and it is important to combine these or repeat effective methods.

Furthermore, in actual use, a photopolymerization initiator is used in the ultraviolet curable resin as is well known. Such photopolymerization initiators are mainly acetophenone, benzophenone, and various derivatives thereof, and specific examples thereof include the following.

[)arocur 111B, Darocur 11
73 (and above) Lerck Company).

Vicur 55 (Stauffer), Ir.
gacur651. Irgacur 184 (all manufactured by Ciba-GeigV) and the like.

In addition, it is also possible to use a benzoin ether-based photopolymerization initiator such as benzoin ethyl ether.

These can be used alone or in combination of two or more.

The amount of these photopolymerization initiators used is at least 0.3 parts by weight, preferably 1.0 parts by weight or more, particularly preferably 2.0 parts by weight or more, based on 100 parts of the ultraviolet curable resin composition.

The adhesive layer of the present invention is formed by applying the above ultraviolet curable resin. Among these, spin cords are preferably used in terms of uniformity of film thickness and production. Further, it is preferable to form an adhesive layer on both substrates to be bonded together in advance and then bond them together in order to prevent air bubbles from being mixed in and the like.

From this point of view, the viscosity of the ultraviolet curable resin is 10 to 5,000 cps at 25°C. Preferably - is 50
~2.000 CpS, particularly preferably 100-1,
000 cps required.

If the viscosity is lower than io cps, the resin tends to flow easily and sag during lamination, which is difficult to handle, and when laminated, air bubbles are likely to be generated, resulting in poor workability, which is undesirable.

If it is higher than 5.000 cps, it is difficult to spread to a uniform HE, and large suppression is required when combining.
- Once air bubbles are introduced, it is difficult to defoam. Also, automatic weighing →
It takes time to supply and the workability is not good.

The viscosity is measured by a conventional method using a B type viscosity system BH type (manufactured by Tokyo Keiki).

The present invention described above will be explained below using a magneto-optical recording medium as an example, but the present invention is not limited to a magneto-optical recording medium.
It is clear from its purpose that it can be widely applied to optical recording media that use optical recording layers that undergo deterioration similar to that of magneto-optical recording layers.

FIGS. 1 and 2 are partial side sectional views of typical configuration examples of magneto-optical recording media according to the present invention. FIG. 1 shows an example of a single-sided recording medium in which a simple transparent plastic substrate 1 is bonded to a transparent plastic substrate 1 provided with a magneto-optical recording layer, and the magneto-optical recording layer 3 includes SiO, Ai! A transparent plastic substrate 1° is bonded with an adhesive layer 5 through a protective layer 4 made of N or the like.

FIG. 2 shows an example of a double-sided recording medium, in which the transparent plastic substrates 1 and 1 degrees, on which the magneto-optical recording layers 3 and 3'' are formed with protective layers 4 and 4'', respectively, and the magneto-optical recording layer 3.3 degrees. This is an example of adhesive bonding using the adhesive layer 5 so that the inner side faces.

In the figure, 2, 2' is a dielectric layer.

These adhesive layers 5 are formed on the magneto-optical recording layer 3 (3°) or the protective layer 4 (4°) obtained by sputtering etc.
As described above, it can be provided by coating by spin cord or roll coating, or by interposing it between transparent plastic substrates to be bonded and then pressing and then applying the coating. Coating thickness is 0.5 to 1,000 μm
, preferably 10 to 500 μm. Then, the adhesive can be cured by UV irradiation.

When bonding simple transparent plastic substrates, sufficient curing can be achieved by irradiating ultraviolet rays from the transparent plastic substrate side.

On the other hand, when bonding transparent plastic substrates on which magneto-optical recording layers are formed, the recording layer part is not transparent like the substrates, so it is difficult for ultraviolet rays to pass through. It is difficult to cure in a short period of time due to the small size of UV rays.For this reason, a primer solution containing a photopolymerization catalyst is applied to one or both of the bonded surfaces in advance, and an adhesive layer is placed on top of that. After lamination, the curing reaction can be completed in a short time by irradiation with ultraviolet rays.As a photopolymerization catalyst, benzoyl peroxide (J
Peroxides such as ions, metal ions such as iron and nickel, or redox catalytic agents Is are often used.

The structure of the above-mentioned magneto-optical recording medium is not particularly limited except for the adhesive layer, and any known structure can be applied as is. For example, the transparent substrate may be a transparent plastic substrate such as polycarbonate resin or acrylic resin, and the dielectric layer may be Z.
From nS, Sin, AiN, etc., F is used as a magneto-optical distribution BB.
Examples include FcTb alloys such as eTbCo and FeTbGd alloys, and F(1'Nd alloys).
Great effect on CO alloys, etc. These dielectric layers and magneto-optical recording layers are formed by conventional methods such as physical vapor deposition methods such as sputtering methods.

Examples of the above-mentioned magneto-optical recording medium according to the present invention will be described in detail below, but the present invention is not limited in any way by these examples.

Examples 1-4. Comparative Examples 1 and 2 A magneto-optical recording medium having the laminated structure shown in FIG. 1 was produced as follows. In FIG. 1, 1 and ] are transparent plastic substrates, and 2 is a dielectric layer.

3 is a magneto-optical recording layer, 4 is an inorganic protective layer, and 5 is an adhesive layer.

That is, a high-frequency magnetron sputtering device (5PF manufactured by Nichiden Anelva ■) capable of mounting 83 targeters was used to attach a substrate 1 made of polycarbonate resin (PC) having a diameter of 130 mm, a thickness of 1.2 mm, and groups of 1.6 μm pitch. -430 type) in a vacuum chamber of 4 x 10
-7 Torr or less. Note that during film formation, the substrate 1 was water-cooled and rotated at 15 rpm.

Next, intoxication gas was introduced into the vacuum chamber, and the pressure was 5.3 x 10-
The flow rate of Ar gas was adjusted to 3 rorr, a ZnS disk with a diameter of 100 mm and a thickness of 5 mm was targeted, the discharge power was 100 W, and the discharge frequency was 13.56 MH.
2, high frequency sputtering was performed to deposit 650 ZnS films as dielectric layer 2.

Next, the recording layer 3 was changed to TI) 23F 86gcOa alloy (the suffix indicates the composition (atomic %)), Ar gas was introduced into the vacuum chamber, and TbFcCo was used under the same discharge conditions as above.
800 people deposited alloy films. Furthermore, as the inorganic protective layer 4, the target is AJ! Ar gas was introduced into the vacuum chamber instead of N, and 500 AiN films were deposited under the same discharge conditions as described above.

After uniformly applying an adhesive layer 5 made of an ultraviolet curable resin containing a crosslinkable oligomer and a polyfunctional acrylate shown in Table 1 to a thickness of about 50 μm using a spin coater,
A simple transparent plastic substrate 1' made of the same polycarbonate was bonded together without introducing air bubbles, and
At least the side surfaces of the recording layer 3 were coated with the ultraviolet curable resin.

Next, 804/cm from the side of the transparent plastic substrate 1゛
The single-sided recording medium with the laminated structure shown in Fig. 1 with side coatings was bonded by irradiating ultraviolet rays with a high-pressure mercury lamp to harden the resin.
An accelerated deterioration test was conducted in an atmosphere of 0'C and 90% RH.

On the other hand, as mentioned above, an ultraviolet curable resin having the composition shown in Table 1 was applied onto a glass plate, a cured film was obtained by irradiation with ultraviolet rays, and a dynamic thermomechanical analyzer (DNA 982 model) was used.
The softening point of each cured film was measured. The acid value was also measured.

These results are shown in Table 1. In addition, in Table 1, PHR (Parts pe
r (undred Resin) refers to parts by weight added to 100 parts of resin.

The chemical structural formula of the crosslinkable oligomer shown in Table 1, the (meth)acrylic acid ester, and the photopolymerization initiator No. 118 are as follows.

・Trifunctional or higher functional (meth)acrylate TMPTA: Trimethylolpropane triacrylate CH20COCH=CH2 DPEHA Nidipentaerythritol hexaacrylate ・Other (meth)acrylates NPG-DA: Neobentyl glycol diacrylate HD-DM: 1.6- Hexanethiol dimethacrylate/photopolymerization initiator D: Darocure 1173 (manufactured by Merck & Co.) = Bicure 55 (manufactured by Stouft Chemical) B: Benzophenone (
In Examples 1 to 4 of the present invention (manufactured by Wako Tsumugi Yakuhin Co., Ltd.), compared to Comparative Examples 1 and 2, the softening points of the ultraviolet-cured films were all higher than 50°C, and the durability of the lamination medium in a moist heat atmosphere was lower. The sexual results are also very good. That is, even after 1000 hours at 60°C and 90% RH, there was no warping of the medium, the adhesion at the bonded area was strong, and there were no signs of peeling at all, and there were no pinholes or pinholes in the recording film of the medium.
No deterioration such as pitting corrosion is observed. This has an acid value of 1.5
It is thought that the following small points also contributed.

On the other hand, in Comparative Example 1, the molecular weight per acroyl group of the crosslinkable oligomer was as small as 107, and the softening point of the cured film was 20.
℃ and the acid value is higher than 1.5, a wet heat deterioration test of the laminated media showed that the medium warped significantly and the adhesive part peeled off, and the recording film suffered significant oxidative deterioration and was unable to withstand use. do not have.

In addition, since Comparative Example 2 contains only 10 wt% of trimethylolpropane triacrylate (hereinafter abbreviated as TMPTA), which is a (meth)acrylate with trifunctional or higher functionality, the crosslinking density of the cured film is insufficient, and the initial adhesive strength is In addition to the fact that the softening point (40°C) was lower than 50°C and the acid value was higher than 1.5, the wet heat aging test results showed partial peeling of the medium and deterioration of the recording film. .

Examples 5-8. Comparative Example 3 A TbFeCo alloy target was used in the same manner as Examples 1 to 4 using a magnetron sputtering device.

Using an In203 target and a Ti target, In is deposited on a transparent plastic substrate 1 made of polycarbonate.
22 dielectric layers bFec consisting of 203 (650 people)
.

(500) and magneto-optical recording layer 3 consisting of Ti (550)
Films were formed in the order of the protective layer 4 consisting of the following:

An adhesive layer 5 made of an ultraviolet curable resin containing a crosslinkable oligomer and a polyfunctional acrylate shown in Table 2 was applied to both the protective layer 4 of the laminate and the transparent polycarbonate substrate to be bonded thereto in Examples 1 to 2. Similarly to 4, each layer was formed to a thickness of 25 μm using a spin coater, and then a transparent polycarbonate substrate was stacked on top of the other, and then irradiated with ultraviolet rays.
A single-sided recording medium having a laminated structure shown in FIG. 1 was obtained. It has been found that by forming the adhesive layer 5 on both adhesive surfaces prior to overlapping in this way, it is possible to effectively prevent air bubbles from being mixed in during overlapping. An accelerated deterioration test was conducted on each of the obtained media in an atmosphere of 60° C. and 90% RH.

Furthermore, the softening point and acid value of the cured film of the ultraviolet curable resin having the composition shown in Table 2 were also measured.

These results are shown in Table 2.

The chemical structural formulas of the crosslinkable oligomers and the abbreviations of the (meth)acrylic esters shown in Table 2 are as follows. Other abbreviations are the same as in Table 1.

・Trifunctional or higher functional (meth)acrylate U-48A: urethane dimethacrylate to diacrylate (abbreviations of other acrylates and photoinitiators are from Example 1)
Same as 4. ) In Examples 5 to 8 of the present invention, compared to Comparative Example 3, the softening points of the UV-cured films were all higher than 50°C, and the durability test of the lamination medium under a moist heat atmosphere gave excellent results. be.

That is, even after 1000 hours at 60° C. and 90% RH, the bonded portion had strong adhesion and no peeling was observed, and no deterioration of the recording film occurred. This is thought to be due to the small acid value of 1.5 or less.

On the other hand, in Comparative Example 3, since the molecular species per acroyl group of the crosslinkable oligomer is as small as 121, the medium warps, which is thought to be caused by shrinkage of the cured film after UV curing, and is a practical problem. Roughly speaking, the softening point of the cured film is as low as 20°C or lower, and the acid value is higher than 1.5, so 60°C and 90% R
Durability results under H atmosphere also showed adhesive layer peeling and recording film deterioration.

(Effects of the Invention) As is clear from the above, according to the present invention,
In the optical recording medium with a laminated structure, the adhesive mainly consists of (A) a crosslinkable oligomer (8) a polyfunctional (meth)acrylic acid ester (C) a photopolymerization initiator; (1) an acroyl of the crosslinkable oligomer; The molecular weight per group is at least 150, (2) the content of trifunctional or higher functional acrylic ester and/or methacrylic ester is at least 15% by weight, and (3) the softening point of the cured film is 50. If you use an ultraviolet curable resin that is resistant to temperatures above ℃,
An optical recording medium with sufficiently excellent long-term durability (maintenance of high adhesion, stability of recording film) even in a high temperature and high humidity atmosphere is obtained. Particularly, those having an acid value of 1.5 or less are advantageous against deterioration of the recording film.

Therefore, the present invention is particularly useful in magneto-optical recording media that use magneto-optical recording films made of alloy films of rare earth metals and transition metals, such as TbFeCo alloys or NdDyFeCo alloys, where recording film deterioration is a problem as described above. Qin effect. As described above, the present invention greatly contributes to improving the durability of optical recording media, especially magneto-optical recording media.

[Brief explanation of the drawing]

FIG. 1 is a partial schematic sectional view of an example of a magneto-optical recording medium for single-sided recording in which a simple transparent plastic substrate according to the present invention is laminated. FIG. 2 is a partial schematic sectional view of an example of double-sided recording in which the simple transparent plastic substrate of FIG. 1 is laminated with a recording layer instead. 1.1°: Transparent plastic substrate, 2,2°: Dielectric layer, 3.3': Magneto-optical recording layer, 4.4': Protective layer, 5
: Adhesive layer

Claims (1)

[Claims] Consisting of one or two disk-shaped transparent plastic substrates, a recording layer is laminated on at least one of them, and the transparent plastic substrates are adhered with an adhesive so that the recording layer is on the inside. In the optical recording medium with a laminated structure, the adhesive is an ultraviolet curable resin mainly consisting of (A) a crosslinkable oligomer, (B) a polyfunctional acrylic ester and/or methacrylic ester, and (C) a photopolymerization initiator. (1) the molecular weight per acroyl group of the crosslinkable oligomer is at least 150, and (2) the content of trifunctional or higher functional acrylic ester and/or methacrylic ester is at least 15% by weight. (3) An optical recording medium characterized in that the softening point of the film after curing is 50°C or higher. 2. The optical recording medium according to claim 1, wherein the oxidation of the ultraviolet curable resin is 1.5 or less. 3. The optical recording medium according to claim 1 or 2, wherein the recording layer is a magneto-optical recording layer. 4. The optical recording medium according to claim 1, 2 or 3, wherein a dielectric layer is provided on the substrate side of the recording layer, and a protective layer is provided on the adhesive side of the recording layer.