JP2000345111A - Adhesive composition and optical disk using the same - Google Patents

Abstract

(57) [Summary] [PROBLEMS] To be useful for direct bonding of an optical disk substrate,
Provided an adhesive composition that can suppress the corrosion of metal films, especially aluminum films, in the durability test of product optical discs under high temperature and high humidity conditions, and also suppressed the corrosion of metal films under high temperature and high humidity. Provide an optical disk. An adhesive composition comprising (1) a urethane acrylate having polytetramethylene glycol as a skeleton, (2) an acrylate having a hydroxyl group in a molecule, and (3) a photopolymerization initiator, An adhesive composition containing 40% by weight or more of the urethane acrylate (1) based on the total weight of the urethane acrylate (1) and the acrylate (2) is used.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to an adhesive composition for an optical disk. More specifically, the present invention provides a DV
Adhesive composition useful for manufacturing an optical disk used as an optical recording medium having a structure provided with at least one reflective metal film, such as D (digital video disk or digital versatile disk), to which a transparent substrate is attached. And an optical disk using the same.

[0002]

2. Description of the Related Art Optical discs such as CDs (compact discs) and DVDs are widely used as recording media in a wide range of fields from recording of music and video to recording related to computers. In such an optical disk, the recorded data is read by detecting a digital signal recorded on the disk as a change in reflection intensity of a semiconductor laser beam emitted from an optical head for recording and reading. These discs include a read-only disc, a recordable and non-erasable disc, and a disc capable of both recording and erasing.

In these optical disks, a very thin (several tens nm) metal thin film layer of aluminum or the like is formed as a reflective film on a surface (signal recording surface) of a transparent substrate such as polycarbonate having pits corresponding to digital signals to be recorded. Is formed by vapor deposition or sputtering. In the case of a CD, a protective layer is further provided on the signal surface. Meanwhile, DVD
In this case, two transparent substrates having a thickness half that of a CD substrate are used, and they are bonded together with the signal recording surface inside. For DVD, attach 2
The signal may be recorded on only one of the substrates or on both substrates. Also, by moving the objective lens of the optical head that reads the recorded signal in the focus direction (radiation direction of the laser beam), it is possible to read the recorded signals on the two signal recording surfaces from one side. It is also possible to provide two recording layers on one substrate. In this case, the reflective film on the first recording surface on which the reading laser light is first incident is formed of a translucent material such as gold. Is done. Therefore, the recording signal reading method for DVD includes a method of reading only one layer from one side, a method of reading one layer each from both sides, a method of reading two layers from one side, and a method of reading two layers each from both sides.

The characteristics of a metal film such as aluminum formed on the signal surface of an optical disk substrate are easily deteriorated by the influence of oxygen or moisture in the atmosphere. Conventionally, thermoplastic resin, acrylate resin,
A resin containing an epoxy resin as a main component has been used as a protective coating agent for a metal film. For example, JP-A-2
JP-A-107630 describes an epoxy-based UV-curable resin composition used for that purpose, and JP-A-4-264166 describes an acrylate-based composition. When such a protective coating agent is used, an adhesive is applied after forming the protective coat on the signal surface of the optical disk substrate, and the substrates are attached to each other. In addition, in the future when the recording density of disks increases and the pits need to be narrowed,
There is a problem that it is difficult to respond.

[0005] As an adhesive for directly bonding substrates on which signal surfaces are formed without such a protective coat, it is possible to obtain an optical disk with less aluminum deterioration.
For example, JP-A-59-71317 and JP-A-63-1
67442, JP-A-9-31416, JP-A-10-8018, JP-A-10-102007, JP-A-10-67997, JP-A-10-1
Japanese Patent No. 30602 is cited.

The adhesive described in JP-A-59-71317 is a photocurable adhesive composition containing a compound having two or more acrylic or methacrylic groups in a predetermined hydrocarbon compound. In addition, the adhesive strength between substrates of an optical disc can be improved.

The adhesive described in Japanese Patent Application Laid-Open No. 63-167442 is a composition composed of a polyurethane containing a hydrocarbon polyol as a main component. The adhesive is made deformable by following the deformation (warpage) of the substrate.

The adhesive described in Japanese Patent Application Laid-Open No. 9-31416 is a photo-curable adhesive comprising a photopolymerization initiator having a mono extinction coefficient of 400 or more at a wavelength of 360 to 450 nm and an ultraviolet curable compound as essential components. A composition.

The adhesive described in JP-A-10-8018 has a maximum molar extinction coefficient of 5 or less at a wavelength of 360 nm or less.
A photopolymerization initiator comprising a combination of a photopolymerization initiator of 000 or more and a photopolymerization initiator having a wavelength of 360 nm or more and a maximum molar extinction coefficient of 500 or more, and an adhesive composition containing an ultraviolet curable resin; It has sufficient adhesive strength and the like.

The adhesive described in Japanese Patent Application Laid-Open No. 10-102007 is a composition having at least a predetermined bisacylphosphine oxide compound and a predetermined acylphosphine oxide compound.

The above-mentioned disclosed adhesives are common in that they can be directly applied to an optical disk substrate and used to bond the substrates, but in particular, the adhesives are particularly corrosive to metal films. No countermeasures were taken.

On the other hand, the adhesive described in Japanese Patent Application Laid-Open No. H10-67977 uses an acrylate having a very expensive fluorene skeleton as a raw material, and the obtained cured product has an extremely high glass transition temperature (Tg). At room temperature because of its high strength. Furthermore, the durability evaluation conditions of the adhesive described in this publication are 70 ° C., 50%
Since the relative humidity was relatively gentle and the time was as short as 96 hours, the durability was not sufficient.

The adhesive composition described in Japanese Patent Application Laid-Open No. Hei 10-130602 comprises a mixture (A) of an unsaturated group-containing compound, an organic peroxide (B), and a curing accelerator (C) as essential components. And the photopolymerization initiator (D) as an optional component. It has been reported that this adhesive composition did not show pinholes or other abnormalities in the aluminum vapor-deposited film even when left at 80 ° C. and 85% relative humidity for 100 hours. However, also in this case, the evaluation time is as short as 100 hours, which is insufficient for durability evaluation. In addition, the curing speed of this adhesive is easily influenced by the combination of the organic peroxide and the curing accelerator, and the curing is difficult. If it is too fast, curing will proceed during mixing and application, and if curing is too slow, it will be necessary to leave it for a considerable time after laminating, so productivity is poor and the thickness of the adhesive layer can not be maintained, so it is difficult to use. there were.

[0014]

Generally, an adhesive used for bonding a substrate of an optical disk has an appropriate adhesive property, physical properties (particularly, transparency, impact properties, applicability to a substrate), and adhesive properties at the time of bonding. Hardness is required, and even if it is used by directly applying it to the recording surface on which a metal film such as aluminum is formed, corrosion does not occur or hardly occurs in the metal film in an environmental resistance test (durability test). Is required. Specifically, an adhesive for bonding a substrate of an optical disk is required to have the following characteristics.

(1) Adhesive properties A cured film having a cured film thickness of 1 to 100 μm, preferably about 50 μm, has a predetermined adhesive strength to the surface of polycarbonate, aluminum, gold or the like which is a constituent material of an optical disk. (2) Impact characteristics In the drop test, the disk base materials shall not peel off from each other. (3) Adhesion-curing properties Within the photo-curing adhesive, within 1 minute, preferably 1 to 3
The substrate can be adhered by UV irradiation for 0 seconds. (4) Transparency Sufficient transparency to laser light (for example, red semiconductor laser light having a wavelength of 650 to 780 nm). (5) Corrosion to metal film The aluminum film having a thickness of about several tens of nm (for example, 50 nm) is not corroded. In particular, in a durability test under an environment of 80 ° C. and 90% relative humidity, corrosion should not occur on the aluminum film for 500 hours or more. (6) applicability to disk substrate 500 to 10000 mPa · s at room temperature without solvent
It preferably has a viscosity of 1000 to 5000 mPa · s, and can form a cured coating film of about 1 to 100 μm by directly applying by spin coating to the surface of a disk substrate provided with a metal layer.

An adhesive for bonding an optical disk substrate that satisfies all of these required characteristics has not been known so far, and conventional adhesives are not suitable for corrosiveness of metal films, impact characteristics, curing conditions for bonding. Had a problem in any of the aspects.

For example, the adhesives described in JP-A-10-67977 and JP-A-10-130602 have a short durability test time for corrosion of an aluminum film (JP-A-10-67997). In the case of the gazette, the test conditions themselves are much milder), which is insufficient for durability evaluation. Further, the adhesive described in JP-A-10-67997 is weak against impact at room temperature because the cured product has a very high glass transition temperature (Tg).
The adhesive described in 30602 has difficulty in controlling the curing speed.

In particular, in an environmental resistance test under an environment of 80 ° C. and 90% relative humidity, an adhesive which does not cause corrosion of the aluminum film for 500 hours or more is not found among adhesives for optical discs currently on the market. .

As described above, the conventional adhesive used for directly bonding an optical disk substrate without a protective coating layer of a reflective metal film does not satisfy all of the required characteristics, and in particular, such as aluminum. There is still room for improvement with respect to the corrosiveness of the reflective metal film.

Therefore, the present invention is useful for direct bonding of an optical disk substrate without a protective coating layer of a reflective metal film, and is useful for a long-term durability test of a product optical disk under high temperature and high humidity conditions. In particular, it is an object of the present invention to provide an adhesive composition capable of suppressing corrosion of an aluminum film. It is also an object of the present invention to provide an optical disc in which a substrate is bonded with such an adhesive composition and in which corrosion of a metal film under high temperature and high humidity is suppressed.

[0021]

The adhesive composition of the present invention comprises (1) a urethane acrylate having polytetramethylene glycol as a skeleton, (2) an acrylate having a hydroxyl group in a molecule, and (3) An adhesive composition containing a photopolymerization initiator, wherein the urethane acrylate (1) is contained in an amount of 4 based on the total weight of the urethane acrylate (1) and the acrylate (2).
It is characterized by containing 0% by weight or more.

The optical disk of the present invention is an optical disk including a disk substrate bonded with an adhesive and at least one reflective metal film, wherein the adhesive is (1) a urethane acrylate having polytetramethylene glycol as a skeleton. , (2) an acrylate having a hydroxyl group in the molecule, and (3) an adhesive composition containing a photopolymerization initiator, wherein the urethane acrylate (1) and the acrylate (2) are combined. It is characterized by being obtained by curing an adhesive composition containing 40% by weight or more of the urethane acrylate (1) based on the weight.

Preferably, the urethane acrylate (1) is an oligomer composed of at least a portion derived from tetramethylxylene diisocyanate, hydroxyethyl acrylate, and ethylene glycol in addition to the skeleton portion of polytetramethylene glycol.

Also preferably, the acrylate (2) is one or more of hydroxyethyl acrylate, hydroxypropyl acrylate, hydroxybutyl acrylate and hydroxyphenoxypropyl acrylate.

[0025]

BEST MODE FOR CARRYING OUT THE INVENTION The main component in the adhesive composition of the present invention is a urethane acrylate having a polytetramethylene glycol skeleton. Preferably, the adhesive composition of the present invention, which is useful for suppressing corrosion of a reflective metal film, particularly an aluminum film in a durability test under conditions of high temperature and high humidity when used for bonding optical disc substrates. Urethane acrylate as a component is an oligomer prepared from at least tetramethylxylene diisocyanate, hydroxyethyl acrylate, and an ethylene glycol component in addition to polytetramethylene glycol as a skeleton component. As an example of a urethane acrylate suitable for use in the present invention, the blending molar ratio of polytetramethylene glycol, tetramethylxylene diisocyanate, hydroxyethyl acrylate, and ethylene glycol is about 62: 15: 14: 9, and the weight average molecular weight is Can be mentioned, and such a urethane acrylate oligomer is commercially available from Nippon Gohsei under the trade name of UV-6100B. This urethane acrylate oligomer can be represented by the following general formula.

[0026]

Embedded image

In the urethane acrylate oligomer, the mixing ratio of each constituent component and the molecular weight of the oligomer can be variously changed as long as the above-mentioned various characteristics required for the optical disk are satisfied.

In the adhesive composition of the present invention, in addition to urethane acrylate having a polytetramethylene glycol skeleton as a main component, an acrylic ester having a hydroxyl group in a molecule, which acts as a reactive diluent, is used. Examples of suitable acrylic esters include hydroxyethyl acrylate, 2-hydroxypropyl acrylate, 4-hydroxybutyl acrylate, 2-hydroxy-3-phenoxypropyl acrylate, and the like. More preferred acrylic esters are hydroxyethyl acrylate, 2-hydroxypropyl acrylate, and 4-hydroxybutyl acrylate, which are preferred over the others when mixing the adhesive composition of the present invention in preparing the adhesive composition. This is because the composition uniformity at the time is good and the viscosity of the composition can be easily adjusted.

In the adhesive composition of the present invention, the urethane acrylate having a polytetramethylene glycol skeleton as a main component is at least 40% by weight based on the total weight of the urethane acrylate and the acrylic ester having a hydroxyl group in the molecule. It is necessary to configure 4
If the amount is less than 0% by weight, it cannot withstand a durability test at 80 ° C. and 90% relative humidity for 500 hours or more. On the other hand, when the urethane acrylate having the polytetramethylene glycol skeleton is present in an amount exceeding 90% by weight based on the total weight of the urethane acrylate and the acrylic ester having a hydroxyl group in the molecule, the viscosity becomes too high. This makes application difficult and poor adhesion to the metal film, which is not preferable. A more preferred amount of the urethane acrylate having a polytetramethylene glycol skeleton is 50 to 80% by weight based on the total weight of the urethane acrylate and the acrylic ester having a hydroxyl group in the molecule.

The adhesive composition of the present invention can be cured by photopolymerization using a photopolymerization initiator or by thermal polymerization using a thermal polymerization initiator to form an adhesive layer of an optical disk. it can. In the curing by photopolymerization, unlike the thermal polymerization, it is possible to avoid adverse effects such as deformation (mainly warpage) of the disk substrate caused by heating in the curing process, and therefore, it is preferable to use curing by photopolymerization. As the photopolymerization initiator, generally, a commercially available photopolymerization initiator can be used. As a typical example of such a commercially available photopolymerization initiator, Darocure 1173 manufactured by Ciba-Geigy can be mentioned.

The adhesive composition of the present invention can be considered as an embodiment used as a second-generation acrylic adhesive SGA. In this case, an organic peroxide and a curing accelerator are used. In the SGA, the mixture of the urethane acrylate (1) and the acrylic ester (2) is divided into two,
One of which is supplemented with an organic peroxide (here, "A
Liquid) and the other with a curing accelerator (“B
Liquid)) and mix them when used as an adhesive. Alternatively, one of the above compositions (for example, solution A) may be applied to one disk substrate, and the other (for example, solution B) may be applied to the other disk substrate, and then these disk substrates may be bonded together.

The adhesive composition of the present invention may further contain, if necessary, a thickener, a plasticizer, a dispersant, a flame retardant, a filler, a coloring agent, an antioxidant, a heat aging inhibitor, an ultraviolet absorber, and a silane. Various additives generally used in the adhesive composition, such as a coupling agent, may be contained.

The adhesive composition of the present invention comprises a urethane acrylate having a polytetramethylene glycol as an essential component as a skeleton, an acrylate having a hydroxyl group in a molecule, a photopolymerization initiator, and optionally other components. It can be easily prepared by uniformly mixing the optional components using a usual mixing means.

The application of the adhesive composition to the optical disk substrate is preferably performed by a spin coating method. To perform spin coating, the viscosity of the coating solution should be 500 to 10,000 m
Pa · s, preferably 1000 to 5000 mPa ·
It is preferable to make adjustment so as to be about s. When the above-mentioned UV-6100B available from Nippon Synthetic Chemical Company or its equivalent is used as the urethane acrylate (1) having a polytetramethylene glycol skeleton, an acrylic ester having a hydroxyl group in the molecule (2) By using hydroxyethyl acrylate, 2-hydroxypropyl acrylate, 4-hydroxybutyl acrylate, or a mixture thereof,
This appropriate range of viscosity can be obtained more easily.
The method for applying the adhesive composition is not limited to the spin coating method, and other methods may be used.

The thickness of the cured adhesive layer formed by the adhesive composition is suitably from 1 to 100 μm.
For example, for the DVD 9, the thickness of the adhesive layer is defined as 55 ± 15 μm according to the standard defined in the DVD book.

The bonding of the disk substrate after the application of the adhesive composition is preferably performed under vacuum defoaming. this is,
This is because gas can be degassed in a short time from the applied adhesive composition, which is effective for preventing bubbles from remaining between base materials of the product optical disc.

The optical disk of the present invention includes a disk substrate bonded with an adhesive and at least one reflective metal film. As schematically shown in FIG. 1, in its simplest form, the optical disc 10 of the present invention comprises two disc substrates 11, 11 'made of a transparent plastic material and a signal recording surface of one disc substrate 11. Including a reflective metal film 12 made of metal such as aluminum formed on 11R,
The disk substrates 11 and 11 ′ have a structure in which the reflective metal film 12 is disposed inside and bonded via an adhesive layer 13 formed from the adhesive composition of the present invention. On the surface (signal recording surface 11R) of the substrate 11 which is in contact with the reflective metal film 12, there are minute pits (not shown) formed corresponding to the digital signals to be recorded, and from the direction of arrow A in the figure. By detecting the presence or absence of the reflected reading laser light from the reflective metal film 12 with an objective lens (not shown), the presence or absence of a pit corresponding to the recorded digital signal can be read. The optical disc of this aspect corresponds to the above-described one for reading only one layer from one side.

In the embodiment shown in FIG. 1, a pit and a reflective metal layer similar to those provided on the substrate 11 are also provided on the substrate 11 ', and a laser beam is applied to the substrate 11' from the opposite direction as indicated by A in FIG. It can be easily understood that, if the light is irradiated on the optical disk, the optical disk can be read one layer at a time from each of the two surfaces described above.

FIG. 2 shows another embodiment of the optical disk. The optical disk 20 of this embodiment is provided on two disk substrates 21 and 21 ′, a translucent film 22 made of gold or the like provided on one disk substrate 21, and provided on another disk substrate 21 ′. An adhesive layer formed from the adhesive composition of the present invention, comprising a reflective metal film 24 made of aluminum, and having both disk substrates 21 and 21 ′ disposed inside the translucent film 22 and the reflective metal film 24, respectively. 25 are bonded together. In this embodiment, pits (not shown) corresponding to digital signals to be recorded are provided on a signal recording surface 21R in contact with the translucent film 22 of the substrate 21 and on a surface (signal recording surface) of the adhesive layer 25 in contact with the reflective metal film 24. 25
R). The reflected light from the translucent film 22 is detected by moving the objective lens (not shown) of the optical head that reads the recorded signal in the focus direction (the direction of emission of the laser light indicated by A in the figure). As a result, the signal recorded on the (signal recording surface 21R) can be read, and the signal recorded on the (signal recording surface 25R) is detected by detecting the reflected light transmitted through the translucent film 22 and reflected from the reflective metal film 24. The signal can be read. As described above, in this embodiment, signals of the two recording layers formed on the optical disc 20 can be read from one side, that is, the optical disc of this embodiment corresponds to the above-described one for reading two layers from one side.

The metal layer (particularly the aluminum layer) of the optical disk of the present invention has a small corrosion when evaluated by a durability test under high temperature and high humidity conditions such as 80 ° C. and 90% relative humidity. If the adhesive used to attach the disc substrates contains trace amounts of impurity ions derived from the raw materials, etc., these may cause corrosion of thin metal films such as aluminum, so a protective coat is required on the metal reflective film. Become. The adhesive composition of the present invention is characterized in that it has a small corrosive effect on a metal thin film even if it contains a small amount of impurity ions or the like mixed during synthesis of raw materials or handling. Further, the adhesive layer formed from the adhesive composition of the present invention is different from the one formed from the composition used for a general protective coating agent, and is made of various materials used for manufacturing optical discs such as aluminum, gold, and polycarbonate. In addition to exhibiting a strong adhesive force to the optical disk, the optical disk has a high shock absorbing ability against an impact such as a drop of the optical disk, so that it is possible to provide an optical disk that is not easily broken by the impact. In addition, the adhesive composition of the present invention satisfies the above-mentioned various properties required for bonding an optical disc substrate.

[0041]

Next, the present invention will be further described with reference to examples, but it goes without saying that the present invention is not limited to these examples.

In these examples, the following acrylate oligomers, acrylate monomers, and photopolymerization initiators were used.

Oligomer Oligomer A: Polytetramethylene glycol urethane acrylate (UV-6100 manufactured by Nippon Synthetic Chemical Co., Ltd.)
B) Oligomer B: Polyester urethane acrylate (UV-3000B manufactured by Nippon Gohsei) Oligomer C: Polycaprolactone urethane acrylate (UX-4101 manufactured by Nippon Kayaku) Oligomer D: Propylene oxide-modified bisphenol A diacrylate (Kyoeisha Chemical) Oligomer E: Polycarbonate urethane acrylate (UN-9200A manufactured by Negami Engineering Co., Ltd.)

Monomer HPA: 2-hydroxypropyl acrylate (light ester HOP-A manufactured by Kyoeisha Chemical Co., Ltd.) PEA: phenoxyethyl acrylate (Biscoat # 192 manufactured by Osaka Organic Chemical Co., Ltd.) HBA: 4-hydroxybutyl acrylate (manufactured by Mitsubishi Chemical Corporation) 4-hydroxybutyl acrylate) HPPA: 2-hydroxy-3-phenoxypropyl acrylate (Epoxyester M-6 manufactured by Kyoeisha Chemical Co., Ltd.)
00A) IBA: isobornyl acrylate (light acrylate IB-XA manufactured by Kyoeisha Chemical Co., Ltd.)

Photopolymerization initiator D1173: Darocure 1173 manufactured by Ciba-Geigy

Each of the adhesives of Examples 1 to 6 and Comparative Examples 1 to 9 blended with the compositions shown in Tables 1 and 2 (for example, in the composition of Example 1 shown in Table 1, "oligomer A / HPA
/ D1173 = 80/20/1 "means that oligomer A, HPA and D1173 were blended in a weight ratio of 80: 20: 1), and a DVD9 half disk (aluminum was sputtered on a polycarbonate substrate). The opaque substrate and the translucent substrate obtained by sputtering gold on a polycarbonate substrate) are spin-coated on each of the sputtered films and bonded together by a DVD bonding apparatus DLB-9900 manufactured by Sumitomo 3M Limited to provide a gold thin film. UV light is irradiated from the disk side by a high-pressure mercury UV lamp (UV illuminance at 360 nm: about 30 mW /
cm ² , 20 seconds) to cure the adhesive.

The optical disk sample thus obtained is
After being left at room temperature for more than half a day, the sample was placed in an oven at 80 ° C. and 90% relative humidity, taken out after 100 hours, 250 hours, and 500 hours, and observed for appearance to evaluate the durability of the sample. The evaluation was as follows: も の: no change was observed in the aluminum film, △: the aluminum film became slightly rough, and ×: the aluminum film was severely deteriorated. did. Table 1 shows the evaluation results.
And Table 2.

[0048]

[Table 1]

[0049]

[Table 2]

From these tables, it can be seen that the polytetramethylene glycol urethane acrylate of the oligomer A and the acrylic monomer having a hydroxy group (HPA, HBA, H
PPA), the content of the oligomer A occupying 40% or more of the total weight of the oligomer and the acrylic monomer. It can be seen that there was no visible change in the aluminum film even after the accelerated durability test at 500% relative humidity for 500 hours.

On the other hand, a disk using the adhesive composition of Comparative Example 1 containing oligomer A and acrylic monomer HPA, wherein the content of oligomer A is less than 40% of the total content of this oligomer and acrylic monomer Then 5
After the test for 00 hours, the aluminum film was slightly roughened. In addition, as in Comparative Examples 2 and 3, those containing a polytetramethylene glycol-based urethane acrylate (oligomer A) but not containing an acrylic monomer having a hydroxy group, and those containing a hydroxy group as in Comparative Examples 4, 5, 6, and 8 Composition containing an acrylic monomer having no but having no polyether-based urethane acrylate (oligomer A), and an adhesive composition containing neither a polyether-based urethane acrylate (oligomer A) nor an acrylic monomer having a hydroxy group as in Comparative Example 7 In the disk made of the material, corrosion of the aluminum film was observed in an accelerated test at 80 ° C. and 90% relative humidity for 250 hours or less. Further, the disk of Comparative Example 9 manufactured using one of the typical commercially available optical disk substrate adhesives is also a commercially available DVD.
Also in the disk of Comparative Example 10 which is 9 products, corrosion was recognized in a part of the aluminum film by visual inspection after 250 hours in the same accelerated durability test.

[0052]

As described above, according to the present invention, the optical disk substrate can be directly bonded, and the durability of the product optical disk for 500 hours under high temperature and high humidity conditions of 80 ° C. and 90% relative humidity. In the test, it is possible to use an adhesive composition capable of suppressing corrosion of a metal film, particularly an aluminum film. By using this adhesive composition, it is possible to provide an optical disk in which the corrosion of the metal film is suppressed under high temperature and high humidity. The present invention is not limited to optical disks such as DVDs, but can also be applied to magneto-optical (MO) disks and the like.

[Brief description of the drawings]

FIG. 1 is a diagram illustrating an optical disc according to one embodiment of the present invention.

FIG. 2 is a diagram illustrating an optical disc according to another embodiment of the present invention.

[Explanation of symbols]

 10, 20 optical disk 11, 11 ', 21, 21' disk substrate 12, 24 reflective metal film 13, 25 adhesive layer 22 translucent film

Claims (4)

[Claims] 1. An adhesive composition comprising (1) a urethane acrylate having polytetramethylene glycol as a skeleton, (2) an acrylate having a hydroxyl group in a molecule, and (3) a photopolymerization initiator. An adhesive composition comprising 40% by weight or more of the urethane acrylate (1) based on the total weight of the urethane acrylate (1) and the acrylate (2). 2. The urethane acrylate (1) is an oligomer composed of at least a portion derived from tetramethylxylene diisocyanate, hydroxyethyl acrylate, and ethylene glycol in addition to a skeleton portion of polytetramethylene glycol. Item 1
The adhesive composition as described in the above. 3. The adhesive according to claim 1, wherein the acrylate (2) is one or more of hydroxyethyl acrylate, hydroxypropyl acrylate, hydroxybutyl acrylate, and hydroxyphenoxypropyl acrylate. Composition. 4. An optical disk comprising a disk substrate bonded with an adhesive and at least one reflective metal film, wherein the adhesive is any one of claims 1 to 3. An optical disc characterized by being obtained by curing of an optical disc.