JP2007226856A - Protection film for optical disk, and optical disk using it - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a protection film for optical disk which is used so as to protect an information recording layer of an optical disk, especially, a blu-ray disk and has no bad influence on the recording characteristics of the optical disk, and is constrained in corrosion over a metallic reflection film, and an information recording layer, etc. of the optical disk, and also to provide an optical disk which is made by laminating this protection film through an adhesive layer. <P>SOLUTION: The protection film for optical disk comprises: an optical transparent base material film; and an adhesive layer prepared in its one surface, and is characterized in that a refractive index difference of the light transparent base material film and the adhesive layer is ≤0.08, and a gel fraction of the adhesive layer is 5-30 mass%. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a protective film for an optical disc and an optical disc using the same, and more particularly, is used to protect an information recording layer of an optical disc, particularly a Blu-ray disc (BD), and adversely affects the recording characteristics of the optical disc. In addition, the present invention relates to a protective film for an optical disk in which corrosion to a metal reflective film or an information recording layer of the optical disk is suppressed, and an optical disk formed by bonding the protective film on the information recording layer via an adhesive layer.

In recent years, as an optical disk, an information read-only disk such as CD and CD-ROM, a magneto-optical disk called MO or MD, and a writable optical disk called CD-R have been widely used. The recording capacity of these optical disks is about 650 MB (megabytes), but a series of optical disks called DVDs (Digital Versatile Disks) having a larger recording capacity, specifically, DVD-ROMs (read-only DVDs), DVD-s. DVD series such as R (recordable DVD), DVD-RAM (write / read DVD), and DVD-RW (rewritable DVD) have been developed. These DVD series are made by bonding two substrates, with a recording capacity of 4.7 GB (Gigabyte) on one side and 9.4 GB on both sides. A red laser beam of about 650 nm is used.
However, in the current DVD, for example, in the case of a high-definition video, there is a problem that it can record only about 30 minutes on one side. In order to popularize this DVD, it is desirable that high-definition video can be recorded on one side for at least 2 hours. For this purpose, a large-capacity optical disk is required, and in order to realize this, recording / reproduction with a shorter wavelength laser beam is required.

Therefore, at present, the use of blue laser light having a wavelength of about 405 nm is being studied. However, an optical disc having a sufficient recording capacity cannot be obtained by the standard applied to the DVD series in which substrates having a thickness of 0.6 mm are bonded together (total thickness of the substrate is 1.2 mm). Therefore, for example, on the information recording layer provided on the substrate having a thickness of 1.1 mm, a light-transmitting protective film having a thickness of 0.1 mm (including the adhesive layer) made of the same material as the substrate is bonded, Attempts have been made to produce optical discs with larger recording capacities. In this case, as a method for pasting the protective film, a method using an energy ray curable adhesive or a pressure-sensitive adhesive has been studied. However, the adhesive or pressure-sensitive adhesive may interfere with the recording / reproducing function of the optical disk. It is important that there is nothing.
Among the above methods, the method of bonding using an energy ray curable adhesive has a problem that unevenness of thickness tends to occur because a spin coating method is usually employed for applying the adhesive. On the other hand, the method of bonding using an adhesive can achieve high thickness accuracy.

By the way, the protective film for optical discs is bonded to the side on which light for recording and reproduction of the optical disc is incident. However, in the optical disc produced using the conventional protective film for optical discs using an adhesive, the protective film is used. The difference in refractive index between the substrate used for the film and the pressure-sensitive adhesive layer is large (generally, the refractive index of the pressure-sensitive adhesive layer is lower than the refractive index of the substrate). During reflection, refraction or reflection of laser light occurs at the interface between the pressure-sensitive adhesive layer and the substrate film, which adversely affects the signal level as a decrease in signal intensity or noise. Therefore, in the protective film, the difference in refractive index between the base film and the pressure-sensitive adhesive layer is preferably as small as possible (see, for example, Patent Document 1).
However, in general, since the pressure-sensitive adhesive layer has a lower refractive index than the base film, in order to reduce the refractive index difference between the pressure-sensitive adhesive layer and the base film, the pressure-sensitive adhesive constituting the pressure-sensitive adhesive layer includes: It is conceivable to incorporate a high refractive index component. However, a pressure-sensitive adhesive mixed with a high refractive index component may corrode a metal reflective film or an information recording layer as an adherend due to the high refractive index component oozing out under a high temperature and high humidity environment. There is.

JP 2000-67468 A

  Under such circumstances, the present invention is used to protect an information recording layer of an optical disc, particularly a Blu-ray disc, and does not adversely affect the recording characteristics of the optical disc. It is an object of the present invention to provide a protective film for an optical disc in which corrosion to a layer or the like is suppressed, and an optical disc obtained by bonding the protective film via an adhesive layer.

  As a result of intensive studies to achieve the above object, the inventors of the present invention have a refractive index difference with respect to one surface of the light transmissive substrate film that is less than a certain value, A pressure-sensitive adhesive layer whose fraction is controlled within a certain range, preferably a (meth) acrylic acid ester copolymer having a structural unit derived from an aryloxyalkyl group and / or an arylalkyl group-containing (meth) acrylic acid ester as a resin component It has been found that the object can be achieved by a protective film for an optical disk provided with a pressure-sensitive adhesive layer composed of a pressure-sensitive adhesive. The present invention has been completed based on such findings.

That is, the present invention
(1) A protective film for an optical disc having a light transmissive substrate film and an adhesive layer provided on one surface thereof, wherein a difference in refractive index between the light transmissive substrate film and the adhesive layer is 0.1. A protective film for an optical disk, characterized in that the protective film for an optical disk is characterized in that it is 08 or less and the gel fraction of the pressure-sensitive adhesive layer is 5 to 30% by mass;
(2) The protective film for optical disks according to the above (1), wherein the pressure-sensitive adhesive constituting the pressure-sensitive adhesive layer comprises a (meth) acrylic acid ester copolymer as a resin component,
(3) The protective film for optical disks according to (2), wherein the (meth) acrylic acid ester copolymer has a structural unit derived from an aryloxyalkyl group and / or an arylalkyl group-containing (meth) acrylic acid ester,
(4) The protective film for optical disks according to (2) or (3) above, wherein the (meth) acrylic acid ester copolymer has a weight average molecular weight of 500,000 to 2,000,000,
(5) The protective film for optical disks according to any one of (1) to (4), wherein the light-transmitting base film is a polycarbonate resin film,
(6) The optical film protective film according to any one of the above (1) to (5), wherein the light transmittance at a wavelength of 405 nm is 87% or more, and (7) Information recording provided on at least one surface of the optical disk substrate. An optical disk formed by laminating the protective film for an optical disk according to any one of the above (1) to (6) on the layer via the adhesive layer;
Is to provide.

  According to the present invention, it is used for protecting an information recording layer of an optical disc, particularly a Blu-ray disc, and does not adversely affect the recording characteristics of the optical disc, and also corrodes a metal reflective film or an information recording layer of the optical disc. It is possible to provide a suppressed protective film for an optical disk and an optical disk formed by bonding the protective film via an adhesive layer.

  The protective film for an optical disk of the present invention is for protecting the information recording layer of the optical disk, and is composed of a light-transmitting base film and an adhesive layer provided on one surface thereof. In the present invention, a light-transmitting film is used as the substrate film. The light-transmitting property means that the substrate film is transparent to a laser beam used for an optical disk to which the protective film is applied. Point to. Therefore, in general, a film that transmits visible light in a wavelength range of 380 to 780 nm is used. As such a light-transmitting substrate film, for example, a film made of a transparent resin such as an acrylic resin, a polyolefin resin, a polycarbonate resin, or a norbornene resin can be used, and an optical disc to which the protective film is applied. A substrate having a thermal expansion coefficient approximate to that of the substrate is preferable from the viewpoint of preventing warpage and the like, and a material having the same quality as that of the substrate is usually used. Therefore, since a polycarbonate-based resin is generally used as a resin substrate of an optical disk, a polycarbonate-based resin film is generally used also in this light-transmitting base film.

  The light-transmitting substrate film is preferably one having a surface that is as flat as possible and is less likely to cause birefringence. If birefringence occurs in the base film, the degree of condensing of the condensed laser light is deteriorated, which is not preferable. Further, it is preferable that the thickness unevenness is as small as possible. If the thickness unevenness exists, it causes a reduction in the degree of condensing of the laser light. Furthermore, an anti-scratch layer can be provided on the surface of the base film opposite to the pressure-sensitive adhesive layer as desired so that the optical head of the drive is not easily damaged even if it contacts the film surface. In the present invention, the thickness of the light transmissive substrate film is appropriately selected according to the wavelength of the laser beam used for the optical disc to which the protective film is applied, but generally 50 to 100 μm, Preferably, it is selected in the range of 50 to 90 μm.

In the protective film for optical discs of the present invention, it is necessary that the difference in refractive index between the light transmissive substrate film and the pressure-sensitive adhesive layer is 0.08 or less. If the difference in refractive index is 0.08 or less, reflection at the interface between the pressure-sensitive adhesive layer and the base film is unlikely to occur when laser light is incident or reflected from the recording surface, resulting in a decrease in signal strength. Or adversely affecting the signal level as noise is suppressed. The refractive index difference is preferably 0.07 or less, more preferably 0.065 or less.
Incidentally, the refractive index of the polycarbonate film is about 1.58, and the refractive index of the polymethyl methacrylate film is about 1.49.
In addition, the refractive index difference between the base film and the adhesive layer is irradiated with sodium D line (wavelength: 589.3 nm) using an Abbe refractometer “Abbe refractometer 1T” manufactured by Atago Co., Ltd. It is a value obtained by measuring each refractive index.

In the protective film for optical disks of the present invention, the pressure-sensitive adhesive layer needs to have a gel fraction in the range of 5 to 30% by mass. When the gel fraction is less than 5% by mass, there is a problem that the adhesive sticks out from the end of the optical disk when the optical disk is manufactured. On the other hand, when the content is 30% by mass or less, corrosion of the metal reflective film and the information recording layer in the optical disk can be suppressed and the adhesive film has an appropriate adhesive force even at high temperatures. Can be prevented from peeling off. From the above viewpoint, the gel fraction is preferably in the range of 8 to 20% by mass, and more preferably in the range of 10 to 17% by mass.
The gel fraction is a value measured by the following method.
<Gel fraction of adhesive layer>
The pressure-sensitive adhesive constituting the pressure-sensitive adhesive layer was applied to the release-treated surface of the heavy release film [“SP-PET 381031” manufactured by Lintec Corporation] with a knife coater, followed by heat treatment at 90 ° C. for about 1 minute for crosslinking. An adhesive layer having a thickness of about 25 μm is prepared. A light release film [“SP-PET38GS” manufactured by Lintec Co., Ltd.] is laminated thereon to obtain a sheet sample for gel fraction measurement. The sheet sample is then allowed to stand for 1 week at 23 ° C. and 50% relative humidity, and then the pressure-sensitive adhesive layer is peeled off and extracted using a Soxhlet extractor for about 16 hours with ethyl acetate. Do. The undissolved components are air-dried, dried at 100 ° C. for 10 hours, left to stand at 23 ° C. and 50% relative humidity for 3 hours to adjust the humidity, and then the mass is measured. The fraction was measured.
Gel fraction (%) = (mass of undissolved component after drying / humidification / mass of adhesive before extraction) × 100
This gel fraction can be adjusted by the degree of crosslinking in producing a resin component of the pressure-sensitive adhesive constituting the pressure-sensitive adhesive layer, for example, a (meth) acrylic acid ester copolymer.

Moreover, it is preferable that the storage elastic modulus in the temperature of 25 degreeC of the said adhesive layer is 10 < ⁴ > Pa or more. When the storage elastic modulus is 10 ⁴ Pa or more, the retention property of the protective film bonded to the optical disk becomes good. The upper limit of the storage elastic modulus is not particularly limited, but is usually about 10 ⁶ Pa. The preferred storage modulus at 25 ° C. is in the range of 10 ⁴ to 10 ⁵ Pa.
In addition, the said storage elastic modulus is the value measured by the following method.
<Storage elastic modulus of adhesive layer at 25 ° C.>
The pressure-sensitive adhesive layer was formed to have a thickness of about 600 μm, and measurement was performed at 1 Hz using a viscoelasticity measuring device (“DYNAMIC ANALYZER RDA II” manufactured by Rheometrics).
In the protective film for optical disks of the present invention, an acrylic pressure-sensitive adhesive comprising a (meth) acrylic acid ester copolymer suitable for optical use as a resin component is preferably used as the pressure-sensitive adhesive constituting the pressure-sensitive adhesive layer.

As this (meth) acrylic acid ester copolymer, (A) a structural unit derived from an aryloxyalkyl group and / or arylalkyl group-containing (meth) acrylic acid ester having a function of increasing the refractive index, (B) glass transition An active hydrogen having a function of adjusting the temperature (Tg), a structural unit derived from a (meth) acrylic acid ester having an alkyl group of 1 to 20 carbon atoms in the ester moiety, and (C) a crosslinking point. Preferred examples include a monomer-containing constitutional unit having a functional group and (D) a copolymer containing a constitutional unit derived from another monomer that is optionally introduced.
In this (meth) acrylic acid ester copolymer, as the monomer (a) that forms the structural unit derived from the (A) aryloxyalkyl group and / or arylalkyl group-containing (meth) acrylic acid ester, for example, Formula (I)

（式中、Ｒ¹は水素原子又はメチル基、Ａは全炭素数が６〜２０の置換基を有していてもよいアリール基又はアリールオキシ基、Ｒ²はヒドロキシル基を有していてもよい炭素数１〜４のアルキレン基を示し、ｎは０又は１以上の整数を示す。）
で表される（メタ）アクリル酸エステルの中から選ばれる少なくとも１種を挙げることができる。

Wherein R ¹ is a hydrogen atom or a methyl group, A is an aryl group or aryloxy group which may have a substituent having 6 to 20 carbon atoms, and R ² may have a hydroxyl group. A good C1-C4 alkylene group is shown, and n shows 0 or an integer greater than or equal to 1.)
At least one selected from (meth) acrylic acid esters represented by the formula:

In the general formula (I), the aryl group or aryloxy group optionally having a substituent having 6 to 20 carbon atoms represented by A is, for example, a carbon atom having 1 to 10 carbon atoms on the ring. Examples thereof include a phenyl group, 1-naphthyl group, 2-naphthyl group, phenoxy group, 1-naphthyloxy group, 2-naphthyloxy group and the like, which may have one or more hydrogen groups. In addition, the alkylene group having 1 to 4 carbon atoms which may have a hydroxyl group represented by R ² may be linear or branched, and specifically includes a methylene group, an ethylene group, propylene. Group, trimethylene group, 2-hydroxytrimethylene group, tetramethylene group and the like. n is preferably about 0 to 10.
Examples of the (meth) acrylic acid ester represented by the general formula (I) include 2-methoxyethyl (meth) acrylate, 2- (2-phenoxyethoxy) ethyl (meth) acrylate, and (meth) acrylic. 2-hydroxy-3-phenoxypropyl acid, 2- (4-isopropylphenoxy) ethyl (meth) acrylate, 2- (1-naphthyloxy) ethyl (meth) acrylate, 2- (2-) (meth) acrylic acid Naphthyloxy) ethyl, benzyl (meth) acrylate, phenethyl (meth) acrylate, 3-phenylpropyl (meth) acrylate, 1-naphthylmethyl (meth) acrylate, 2-naphthylmethyl (meth) acrylate, ( And (meth) acrylic acid paracumylphenoxyethylene glycol. These may be used individually by 1 type, or may be used in combination of 2 or more types, but among these, the glass transition temperature (Tg) of the (meth) acrylic acid ester copolymer obtained is too small. Particularly suitable is 2-phenoxyethyl acrylate, which can increase the refractive index without increasing it.

(B) As the monomer (b) having a function of adjusting Tg and forming a structural unit derived from a (meth) acrylic acid ester having 1 to 20 carbon atoms in the alkyl group of the ester moiety, for example, (meth) Methyl acrylate, ethyl (meth) acrylate, propyl (meth) acrylate, n-butyl (meth) acrylate, iso-butyl (meth) acrylate, pentyl (meth) acrylate, hexyl (meth) acrylate, Cyclohexyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, isooctyl (meth) acrylate, decyl (meth) acrylate, dodecyl (meth) acrylate, myristyl (meth) acrylate, palmityl (meth) acrylate And stearyl (meth) acrylate. These may be used alone or in combination of two or more.
Among these, n-butyl acrylate and / or 2-ethylhexyl acrylate, which can give an appropriate Tg as an adhesive, are particularly suitable.
Moreover, it is preferable to use methyl (meth) acrylate together from the point which provides heat resistance, and it is preferable that the content is the range of 10-60 mass% in (b) component.

  (C) As the monomer (c) that forms a structural unit derived from a monomer having a functional group having an active hydrogen having a function of imparting a crosslinking point, for example, 2-hydroxyethyl (meth) acrylate 2-hydroxypropyl (meth) acrylate, 3-hydroxypropyl (meth) acrylate, 2-hydroxybutyl (meth) acrylate, 3-hydroxybutyl (meth) acrylate, 4-hydroxybutyl (meth) acrylate (Meth) acrylic acid hydroxyalkyl esters such as (meth) acrylamide, N-methyl (meth) acrylamide, (meth) acrylamides such as N-methylol (meth) acrylamide; (meth) acrylic acid monomethylaminoethyl, (meta ) Monoethylaminoethyl acrylate, monomethylaminopropyl (meth) acrylate, monoethylaminopropyl (meth) acrylate (Meth) acrylic acid monoalkyl aminoalkyl such as pills; (meth) acrylic acid, crotonic acid, maleic acid, itaconic acid, ethylenically unsaturated carboxylic acids such as citraconic acid. These monomers may be used independently and may be used in combination of 2 or more type.

  (D) Examples of the monomer (d) that forms a constituent unit derived from another monomer introduced as desired include vinyl esters such as vinyl acetate and vinyl propionate; olefins such as ethylene, propylene, and isobutylene Halogenated olefins such as vinyl chloride and vinylidene chloride; Styrene monomers such as styrene and α-methylstyrene; Diene monomers such as butadiene, isoprene and chloroprene; Nitrile monomers such as (meth) acrylonitrile; N, N -N, N-dialkyl-substituted (meth) acrylamides such as dimethyl (meth) acrylamide. These may be used alone or in combination of two or more.

In the acrylic pressure-sensitive adhesive, the content of each structural unit in the (meth) acrylic acid ester copolymer used as the resin component is the desired refractive index, gel fraction, and pressure-sensitive adhesive in the pressure-sensitive adhesive layer to be formed. Is selected as appropriate depending on the desired Tg of (A) 0 to 99.9% by mass, (B) 0 to 99.9% by mass, (C) 0.1 to 20% by mass and (D) ) Units 0-5% by mass, preferably (A) units 40-90% by mass, (B) units 10-60% by mass, (C) units 0.1-5% by mass and (D) units 0-0. 5% by mass.
In the acrylic pressure-sensitive adhesive, the (meth) acrylic acid ester copolymer used as a resin component is not particularly limited with respect to the copolymerization form, and may be any of random, block, and graft copolymers. . The molecular weight is preferably in the range of 500,000 to 2,000,000 in terms of weight average molecular weight from the viewpoint of ensuring the reliability of the optical disk without adversely affecting the optical disk. In addition, the said weight average molecular weight is the value of polystyrene conversion measured by the gel permeation chromatography (GPC) method.
In addition, the content of the low molecular weight copolymer in the uncrosslinked component in the (meth) acrylic acid ester copolymer is preferably small from the viewpoint of inhibiting corrosion on the metal reflective film, the information recording layer, and the like in the optical disk. More specifically, the ratio of the component having a molecular weight of 10,000 or less in the uncrosslinked component is preferably 30% by mass or less, particularly preferably 25% by mass or less, based on the uncrosslinked component. Here, the uncrosslinked component in the (meth) acrylic acid ester copolymer means a component extracted into ethyl acetate in the above-described gel fraction measurement.

The Tg of the (meth) acrylic acid ester copolymer is usually about −60 to −10 ° C., preferably −50 to −20 ° C.
In this invention, this (meth) acrylic acid ester copolymer may be used individually by 1 type, and may be used in combination of 2 or more type.
The polymerization of the (meth) acrylic acid ester copolymer in the present invention can be performed by a conventional method. Examples of the solvent include ethyl acetate and toluene, and examples of the polymerization initiator include azobisisobutyronitrile and benzoyl peroxide. It does not specifically limit regarding polymerization conditions, Usually, it carries out on the conditions for 2 to 30 hours at 50-90 degreeC.

The acrylic pressure-sensitive adhesive used in the present invention may contain a crosslinking agent. The crosslinking agent is not particularly limited, and those conventionally used as crosslinking agents in acrylic pressure-sensitive adhesives such as polyisocyanate compounds, epoxy resins, melamine resins, urea resins, dialdehydes, methylol polymers, metal chelate compounds, The metal alkoxide, metal salt, and the like are appropriately selected depending on the type of the reflective film and the information recording layer of the optical disk to which the protective film is applied. Although there is no restriction | limiting in particular in content of this crosslinking agent, Usually, 0.01-10 mass parts with respect to 100 mass parts of (meth) acrylic acid ester copolymer, Preferably it is 0.01-1 mass part, More preferably Is 0.02 to 0.1 parts by mass (all in terms of solid content).
Further, in the present invention, it is preferable to contain an antioxidant in the acrylic pressure-sensitive adhesive from the viewpoint of suppressing corrosion of the metal reflective film of the optical disk, and the content thereof is in the range of 0.005 to 10% by mass. It is preferable that When the content of the antioxidant is 0.005% by mass or more, the corrosion-inhibiting effect of the metal reflective film and the information recording layer is sufficiently exhibited, and even if the content exceeds 10% by mass, May not be improved and may be economically disadvantageous. The more preferable content of the antioxidant is in the range of 0.01 to 5% by mass, further in the range of 0.01 to 3% by mass, and particularly in the range of 0.01 to 2% by mass.

  The antioxidant is not particularly limited, and may be arbitrarily selected from conventionally known hindered phenol-based antioxidants, amine-based antioxidants, sulfur-based antioxidants, phosphorus-based antioxidants, quinone-based antioxidants, and the like. Can be appropriately selected and used, but a hindered phenolic antioxidant is preferably used. Specific examples include 2,6-di-tert-butyl-p-cresol, butylhydroxyanisole and stearyl β- (3,5-di-tert-butyl-4-hydroxyphenyl) as monocyclic phenolic antioxidants. ) Propionate or the like as a bicyclic phenolic antioxidant, 4,4′-butylidenebis (3-methyl-6-tert-butylphenol) and 3,6-dioxaoctamethylenebis [3- (3-tert-butyl) -4-hydroxy-5-methylphenyl) propionate] and the like, 1,1,3-tris (2-methyl-4-hydroxy-5-tert-butylphenyl) butane as a tricyclic phenolic antioxidant, Tetrakis [methylene-3- (3 ′, 5′-di-tert-butyl-4′-hydroxy] as a tetracyclic phenolic antioxidant Ciphenyl) propionate] methane and the like can be preferably mentioned. These antioxidants may be used individually by 1 type, and may be used in combination of 2 or more type.

  Furthermore, the total content of residual solvent and residual monomer is 100 from the viewpoint of suppressing the corrosion of the protective film for optical disks of the present invention to the base film and the substrate of the optical disk, or the corrosion to the metal reflective film and information recording layer of the optical disk. An acrylic pressure-sensitive adhesive having a mass ppm or less is preferred. If the total content of the residual solvent and residual monomer is 100 ppm by mass or less, erosion of the protective film to the base film or the substrate of the optical disk is sufficiently suppressed, and corrosion of the metal reflective film or information recording layer of the optical disk is suppressed. Is sufficiently suppressed. The total content of the residual solvent and residual monomer is more preferably 50 ppm by mass or less, and particularly preferably 20 ppm by mass or less.

  In the protective film for an optical disk of the present invention, the acrylic pressure-sensitive adhesive may be directly applied to one side of the light-transmitting substrate film to provide a pressure-sensitive adhesive layer, or an acrylic pressure-sensitive adhesive may be applied on the release sheet. Then, after the pressure-sensitive adhesive layer is provided, the pressure-sensitive adhesive layer may be transferred by sticking it to one side of the base film. In this case, the release sheet may be adhered as it is without being peeled off if desired, and may be peeled off when the protective film is used. The thickness of the pressure-sensitive adhesive layer provided on one side of the base film is usually 5 to 60 μm, preferably about 10 to 30 μm. Examples of the release sheet include paper substrates such as glassine paper, coated paper, cast coated paper, laminated paper obtained by laminating a thermoplastic resin such as polyethylene on these paper substrates, or polyethylene terephthalate, polybutylene terephthalate, polyethylene naphthalate. Examples thereof include a polyester film such as phthalate or a plastic film such as a polyolefin film such as polypropylene or polyethylene and a release agent such as a silicone resin applied thereto. Although there is no restriction | limiting in particular about the thickness of this peeling sheet, Usually, it is about 20-150 micrometers.

Also, when applying an acrylic adhesive on one side of a light-transmitting substrate film or on a release sheet, it is usually applied after adding a solvent such as ethyl acetate or toluene, and then dried to form an adhesive layer However, it is preferable to heat and dry at 70 ° C. or higher, preferably 80 to 150 ° C. for about 10 seconds to 10 minutes.
The protective film for optical discs of the present invention thus obtained is applied to optical discs, particularly Blu-ray discs, so that the light transmittance at a wavelength of 405 nm is preferably 87% or more. If the light transmittance is 87% or more, the transmission of the laser light incident on the information recording surface of the Blu-ray disc and the reflected light from the recording surface is good. The light transmittance is more preferably 89% or more.

  The protective film for optical discs of the present invention is used for protecting the information recording layer of an optical disc, particularly a Blu-ray disc, and does not adversely affect the recording characteristics of the optical disc, and also includes a metal reflective film, an information recording layer, etc. Therefore, it is possible to provide a highly reliable optical disc without causing any trouble in the information recording / reproducing function of the optical disc.

Next, the optical disk of the present invention is an optical disk formed by laminating the protective film for an optical disk via an adhesive layer on an information recording layer provided on at least one surface of an optical disk substrate.
The substrate in the optical disk of the present invention is not particularly limited as long as it is used for a normal optical disk, but in general, a polycarbonate resin substrate is used. The thickness of the substrate is appropriately selected according to the standard of the total thickness of the optical disc, the thickness of the protective film provided on the information recording layer, etc., but is usually in the range of 1.05 to 1.15 mm. The structure of the functional layer provided on the substrate is not particularly limited as long as it is an ordinary optical disk layer structure. For example, in the case of a read-only type, it is only necessary to provide a reflective metal film as an information recording layer by sputtering or the like. A layer structure in which an information recording layer comprising a dielectric layer, the recording material layer, and a dielectric layer is provided on the film can be exemplified. Here, as the reflective film, for example, a silver alloy film, aluminum, an aluminum alloy film, or the like is used. As the recording material in the information recording layer, TeOx, Te-Ge, Sn-Te-Ge, Bi-Te-Ge, Sb-Te-Ge, Pb-Sn-Te, etc. are magneto-optical types as phase change types. Tb-Fe, Tb-Fe-Co, Dy-Fe-Co, Tb-Dy-Fe-Co, etc. are used. Further, the dielectric layer in the information recording layer, for example SiN, SiO, etc. _{SiO 2, ZnS-SiO 2,} Ta 2 O 5 is used. The optical disk of the present invention can use blue laser light, and is particularly suitable for a Blu-ray disk series such as a high-capacity BD-ROM, BD-R, and BD-RAM.

EXAMPLES Next, although an Example demonstrates this invention further in detail, this invention is not limited at all by these examples.
In addition, the various characteristics in each example were calculated | required according to the method shown below.
(1) Refractive index of pressure-sensitive adhesive layer In the produced protective film for an optical disk, an Abbe refractometer [manufactured by Atago Co., Ltd., “Abbe Refractometer 1T”] was used, and sodium D line (wavelength 589. 3 nm), and the refractive index of the pressure-sensitive adhesive layer was measured.
(2) Gel fraction of adhesive layer It measured according to the method of the statement text.
(3) Adhesive strength After peeling and removing the release sheet from the protective film for optical disks produced in Examples and Comparative Examples, soda lime glass as a test plate (“Soda Lime Glass” manufactured by NSG Precision Co., Ltd.) The TiO ₂ coating was not applied to the surface of the tin surface, and was left for 24 hours in an environment of 23 ° C. and a relative humidity of 65%, and then measured by a 180-degree peeling method according to JIS Z0237 (room temperature). Here, the tin surface side refers to the surface on the side in contact with the molten tin in the glass produced by the float process.
Further, after being allowed to stand for 24 hours and then allowed to stand in an environment of 80 ° C. for 1 hour, it was measured by a 180 degree peeling method in accordance with JIS Z0237 in an environment of 80 ° C. (high temperature).
(4) Light transmittance at a wavelength of 405 nm of the protective film for an optical disk The produced protective film for an optical disk was measured using an ultraviolet-visible spectrophotometer [trade name “UV-3100PC” manufactured by Shimadzu Corporation] with a wavelength of 405 nm. Measure light transmittance.
(5) Corrosion test After the release film of the produced protective film for optical disks was peeled off and attached to the silver alloy film via the adhesive layer, it was left in an environment of 80 ° C. and 90% relative humidity for 100 hours. Thereafter, the silver alloy film was visually observed and evaluated according to the following criteria.
○ No change in appearance × Discoloration or pinholes were observed

Example 1
In a monomer mixture consisting of 59 parts by mass of 2-phenoxyethyl acrylate, 28 parts by mass of 2-ethylhexyl acrylate, 10 parts by mass of methyl methacrylate and 3 parts by mass of acrylic acid, 150 parts by mass of ethyl acetate as a solvent and azo as a polymerization initiator 0.1 parts by mass of bisisobutyronitrile was added, polymerization was performed at 60 ° C. for 17 hours in a nitrogen atmosphere, and a 2-phenoxyethyl acrylate / 2-ethylhexyl acrylate / methyl methacrylate / acrylic acid copolymer solution was obtained. Obtained. Next, an aluminum chelate compound [manufactured by Soken Chemical Co., Ltd., trade name “M-5A”] as a cross-linking agent with respect to 100 parts by mass of the solid content of the copolymer solution (0.05 mass in terms of solid content). Part) was added to prepare an adhesive coating solution.
The copolymer had a weight average molecular weight of 1,20,000.
Next, this pressure-sensitive adhesive coating solution was applied to the release-treated surface of the release film [manufactured by Lintec Corporation, trade name “SP-PET381031”] with a knife coater so that the thickness after drying was 20 μm. Then, after drying at 90 ° C. for about 1 minute, it was laminated on a polycarbonate film having a thickness of 80 μm as a light-transmitting substrate film to produce a protective film for optical disk having a thickness of about 100 μm. The various properties of this protective film are shown in Table 1.

Example 2
In Example 1, it replaced with the aluminum chelate compound which is a crosslinking agent, polyisocyanate type crosslinking agent [The Toyo Ink Mfg. Co., Ltd. make, brand name "BHS-8515"] 0.125 mass part (0.0% in solid content conversion). 047 parts by mass) was added in the same manner as in Example 1 except that an adhesive coating solution was prepared.
Next, using this pressure-sensitive adhesive coating solution, an optical disk protective film having a thickness of about 100 μm was produced in the same manner as in Example 1. The various properties of this protective film are shown in Table 1.

Comparative Example 1
In Example 1, a monomer mixture consisting of 59 parts by mass of 2-phenoxyethyl acrylate, 38 parts by mass of n-butyl acrylate and 3 parts by mass of acrylic acid was used as a monomer mixture, and an aluminum chelate compound [Soken Chemical Co., Ltd.] as a crosslinking agent was used. Coated with adhesive in the same manner as in Example 1 except that the content of “M-5A” manufactured by Co., Ltd. was changed to 2.5 parts by mass (0.125 parts by mass in terms of solid content). A liquid was prepared.
The copolymer had a weight average molecular weight of 900,000.
Next, using this pressure-sensitive adhesive coating solution, an optical disk protective film having a thickness of about 100 μm was produced in the same manner as in Example 1. The various properties of this protective film are shown in Table 1.

Comparative Example 2
In Example 1, a copolymer solution was obtained in the same manner as in Example 1 except that the monomer mixture was changed to 77 parts by mass of ethyl acrylate, 20 parts by mass of butyl acrylate, and 3 parts by mass of acrylic acid. Next, for 100 parts by mass of the solid content of the copolymer solution, 10 parts by mass of aluminum chelate compound [manufactured by Soken Chemical Co., Ltd., trade name “M-5A”] as a crosslinking agent (0.5 in terms of solid content). Part by mass) was added to prepare an adhesive coating solution.
The copolymer had a weight average molecular weight of 890,000.
Next, using this pressure-sensitive adhesive coating solution, an optical disk protective film having a thickness of about 100 μm was produced in the same manner as in Example 1. The various properties of this protective film are shown in Table 1.

Comparative Example 3
In Example 1, the content of the aluminum chelate compound (trade name “M-5A”, manufactured by Soken Chemical Co., Ltd.), which is a cross-linking agent, was 7.5 parts by mass (0.375 parts by mass in terms of solid content). Except for this, an adhesive coating solution was prepared in the same manner as in Example 1.
Next, using this pressure-sensitive adhesive coating solution, an optical disk protective film having a thickness of about 100 μm was produced in the same manner as in Example 1. The various properties of this protective film are shown in Table 1.

  The protective film for optical discs of the present invention is used for protecting the information recording layer of optical discs, particularly Blu-ray discs, and does not interfere with the information recording / reproducing function of optical discs, and provides a highly reliable optical disc. Can do.

Claims (7)

  A protective film for an optical disc having a light transmissive substrate film and an adhesive layer provided on one surface thereof, wherein a difference in refractive index between the light transmissive substrate film and the adhesive layer is 0.08 or less. A protective film for optical disks, wherein the pressure-sensitive adhesive layer has a gel fraction of 5 to 30% by mass.   The protective film for an optical disk according to claim 1, wherein the pressure-sensitive adhesive constituting the pressure-sensitive adhesive layer comprises a (meth) acrylic acid ester copolymer as a resin component.   The protective film for optical disks according to claim 2, wherein the (meth) acrylic acid ester copolymer has a structural unit derived from an aryloxyalkyl group and / or an arylalkyl group-containing (meth) acrylic acid ester.   The protective film for optical disks according to claim 2 or 3, wherein the (meth) acrylic acid ester copolymer has a weight average molecular weight of 500,000 to 2,000,000.   The protective film for optical disks according to claim 1, wherein the light transmissive substrate film is a polycarbonate-based resin film.   The optical film protective film according to claim 1, which has a light transmittance of 87% or more at a wavelength of 405 nm.   An optical disk comprising an optical disk protective film according to any one of claims 1 to 6 bonded via an adhesive layer on an information recording layer provided on at least one surface of an optical disk substrate.