JP4038417B2 - OPTICAL RECORDING MEDIUM AND METHOD FOR PRODUCING LIGHT-TRANSMITTING PROTECTIVE FILM USED FOR THE SAME - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an optical recording medium having an optical recording layer for optically recording information and a method for producing a light-transmitting protective film used therefor.
[0002]
[Prior art]
In recent years, in the field of information recording, research on optical information recording methods has been promoted in various places. This optical information recording method can perform recording and reproduction in a non-contact manner, can achieve a recording density higher by one digit or more than the magnetic recording method, and can be used in read-only, write-once, and rewritable memory formats. A wide range of applications from industrial use to consumer use is being considered as a method that enables the realization of inexpensive large-capacity files.
[0003]
The increase in capacity of optical recording media for the various optical information recording methods described above is mainly achieved by reducing the wavelength of the laser used as the light source for the optical information recording method and adopting a high aperture lens. This has been achieved by reducing the spot size.
[0004]
A conventional optical recording medium, for example, a compact disc (CD) has a laser wavelength of 780 nm, a lens aperture ratio (NA) of 0.45, and a capacity of 650 MB, but a digital versatile disc (DVD) has a capacity of 650 MB. The laser wavelength is 650 nm, the NA is 0.6, and the capacity is 4.7 GB. Further, in the next-generation optical recording medium currently proposed, an optical recording layer is formed on a disk substrate having a thickness of about 1.1 mm, and a light-transmitting protective film (cover layer) having a thickness of, for example, about 0.1 mm is formed thereon. The capacity of the single-sided 22 GB or more is increased by setting the laser wavelength to 405 nm and NA to 0.85.
[0005]
In the structure of the above-mentioned next-generation optical recording medium, land and groove uneven surfaces are formed on at least one surface of a disk substrate having a thickness of about 1.1 mm made of, for example, polycarbonate resin, cyclic olefin resin, and the like. Is provided with an optical recording layer made of a reflective film such as aluminum, silver, or gold, or an organic or inorganic thin film such as a phase change film, and further has a light transmittance of about 0.1 mm on the optical recording layer. The structure is provided with a protective film.
[0006]
[Problems to be solved by the invention]
The optical recording medium is a type of optical recording medium that reads the reflected light by irradiating the optical recording layer with a laser through the light transmissive protective film. The light transmissive protective film requires a high degree of thickness accuracy. ing.
[0007]
A method of forming a protective film by spin-coating an uncured liquid ultraviolet curable resin on a disk of an optical recording medium proposed as the above-described light-transmitting protective film and irradiating ultraviolet light in a nitrogen atmosphere (Patent Document) 1) is a film thickness of about 0.1 mm, and it is difficult to obtain a light-transmitting protective film having a uniform film thickness near the center and the outer periphery.
[0008]
In addition, when a film is produced from an ordinary thermoplastic resin by an extrusion method or a calendar method, the dimensional accuracy in the thickness direction is usually about ± 5%, and even if an expensive precision device is used, it is about ± 3%, and ± 1 It is difficult to achieve the target of about%, and since the film is manufactured while being pulled in the extrusion direction, there is a disadvantage that the birefringence of the film is large.
Therefore, as a method for producing a film with high dimensional accuracy, a casting method (see Patent Document 2) for producing a film by dissolving a thermoplastic resin with a solvent can produce a film satisfying thickness accuracy and birefringence. There is a problem of solvent recovery at the time, the influence of the residual film of the manufactured film on the disc and the generation of bubbles due to the solvent, the productivity is inferior to produce the film to the extent that the residual solvent does not affect The disadvantage is that the cost is very high.
[0009]
Therefore, the present inventors filed as Japanese Patent Application No. 2002-200850 that a resin sheet, which is a cured product of a solvent-free radiation curable coating, is used for the light-transmitting protective film. However, when a thin film is bonded to a disk substrate, there is a drawback that workability is not good because the rigidity of the film is small.
[0010]
The present invention has been made in view of the above circumstances, and therefore the object of the present invention is to provide a method for producing a light-transmitting protective film with masking which is excellent in film thickness accuracy and birefringence, and is further excellent. An optical recording medium is provided.
[0011]
[Patent Document 1]
JP-A-9-161333 [Patent Document 2]
Japanese Patent Laid-Open No. 2002-74749
[Means for Solving the Problems]
In order to achieve the above object, an optical recording medium of the present invention comprises a substrate, an optical recording layer formed on at least one surface of the substrate, a light-transmitting protective film bonded on the optical recording layer, The light-transmitting protective film is a resin sheet that is a cured product of a solvent-free radiation-curing paint, and includes an adhesive layer to which the light-transmitting protective film is bonded. A masking film is bonded to the side.
[0013]
The said masking film is a smooth peeling film which apply | coats the solventless type radiation-curing coating material which forms the said light-permeable protective film.
[0014]
The adhesive layer is preferably a transparent acrylic resin adhesive or a radiation curable resin adhesive, and the light-transmitting protective film includes a primer layer on the adhesive layer side of the resin sheet.
More preferably, the resin sheet is a cured product of a solvent-free radiation curable coating composed of a polymerizable oligomer and a polymerizable monomer, and the primer layer is a radiation curable resin composed of a polymerizable oligomer, an acrylic polyol type. It is a dry paint film of at least one kind of solvent-based paint selected from thermoplastic resins consisting of
[0015]
The light-transmitting protective film used in the optical recording medium of the present invention is, for example, a resin sheet obtained by curing a PET film having smooth peelability to a solvent-free radiation-curable coating film by irradiation with radiation, and its resin sheet. A masking film is bonded to the surface side. Moreover, as a preferable form of the light-transmitting protective film, a primer layer which is a dry coating film of at least one solvent-type paint selected from a radiation curable resin made of a polymerizable oligomer and a thermoplastic resin made of an acrylic polyol type And a laminate of a resin sheet cured by radiation irradiation after forming a coating film of a solvent-free radiation curable paint comprising a polymerizable oligomer and a polymerizable monomer on the primer layer, A masking film is bonded to the surface side.
[0016]
The method for producing a light-transmitting protective film used in the optical recording medium of the present invention comprises a coating film forming step in which a solvent-free radiation-curing coating comprising a polymerizable oligomer and a polymerizable monomer is applied to a smooth release film surface When,
A curing molding step for obtaining a cured resin sheet by irradiating the coating film with radiation,
The release film is also used as a masking film.
[0017]
The method for producing a light-transmitting protective film used in the optical recording medium of the present invention comprises a coating film forming step of applying a solvent-free radiation-curing paint comprising a polymerizable oligomer and a polymerizable monomer to a smooth release surface; ,
A curing molding step for obtaining a cured resin sheet by irradiating the coating film with radiation,
A step of bonding a masking film to the resin sheet surface and a peeling step of peeling the resin sheet from the peeling surface;
It is what has.
[0018]
Further, a preferable method for producing a light-transmitting protective film is a primer layer forming step of forming a primer layer by applying and drying a solvent-type paint on a smooth release surface,
On the primer layer, a coating film forming step of applying a solvent-free radiation curable paint composed of an acrylic oligomer and an acrylic monomer,
A curing molding step for obtaining a cured resin sheet by irradiating at least the coating film with radiation, and
Bonding a masking film to the resin sheet surface;
A peeling step of peeling the resin sheet from the peeling surface;
It is what has.
[0019]
As the adhesive used in the optical recording medium of the present invention, a transparent acrylic resin adhesive or ultraviolet or electron beam curable resin adhesive is preferable.
[0020]
The light-transmitting protective film used in the optical recording medium of the present invention is a resin sheet composed of a cured product of a solventless radiation curable paint. Examples of the radiation curable coating include urethane oligomers, ester acrylate oligomers, epoxy acrylate oligomers, acrylic oligomers such as acrylic resin acrylates, polymerizable oligomer components such as allyl ether oligomers, vinyl ether oligomers, and allyl urethane oligomers. , Hexyl acrylate, 2-ethylhexyl acrylate, isobornyl acrylate, isooctyl acrylate, 1,6-hexanediol diacrylate, neopentyl glycol diacrylate, and other polymerizable monomer components. When cured by ultraviolet rays, a photopolymerization initiator or the like is included.
[0021]
Among the above polymerizable oligomers, preferred acrylic oligomers include aromatic isocyanates such as tolylene diisocyanate and xylene diisocyanate, aliphatics such as hexamethylene diisocyanate, isophorone diisocyanate, and hydrogenated xylene diisocyanate, and alicyclic isocyanates. A urethane acrylate oligomer comprising a high molecular weight isocyanate and an acrylate having a hydroxyl group such as 2-hydroxyethyl acrylate, 2-hydroxypropyl acrylate, and pentaerythritol acrylate is preferred. The weight average molecular weight is usually preferably about 400 to 7000.
Moreover, an acrylic resin acrylate can be mentioned as another acrylic oligomer. This acrylic resin acrylate is obtained by copolymerizing a (meth) acrylate monomer having a functional group such as a carboxyl group, an epoxy group, or a hydroxyl group in advance in an acrylic copolymer resin containing polymethyl methacrylate as a main component. A double bond is introduced by an addition reaction with an acrylate monomer having a functional group that undergoes an addition reaction corresponding to the group.
[0022]
Examples of the solvent-free radiation curable coating containing an aliphatic urethane acrylate oligomer using an aliphatic isocyanate and a polymerizable monomer include “KRM7818”, “KRM7842”, and “KRM7946” manufactured by Daicel UCB. Can do.
[0023]
On the back side of the resin sheet constituting the light-transmitting protective film, dry coating of at least one solvent-type paint selected from a radiation curable resin made of a polymerizable oligomer and a thermoplastic resin made of an acrylic polyol type is performed. A primer layer which is a membrane is preferably provided. Among these polymerizable oligomers, specific examples of radiation curable resins comprising preferred acrylic oligomers include “CSEB5 medium” (urethane acrylate oligomer) and “CSEB12 medium” (acrylic resin acrylate oligomer) manufactured by Showa Ink Industries, Ltd. Examples of the thermoplastic resin made of acrylic polyol include “MKA medium”, “CSEB2 medium”, and “CSEB10 medium” manufactured by Showa Ink Industries, Ltd.
[0024]
The optical recording medium of the present invention is formed by applying the above-mentioned solvent-free radiation-curing paint on a smooth surface such as a peelable PET film or a stainless steel belt on the optical recording layer provided on the substrate and curing the radiation. Since the resin sheet and the masking film, which are cut in a ring shape, are bonded, handling in the bonding process is improved, and damage to the resin sheet that is a light-transmitting protective film can be prevented. The masking film may also be used as the above-described peelable PET film coated with a solventless radiation curable paint. When bonding another masking film, a polyester film, a polyolefin film, a polycarbonate film, or the like provided with a weak adhesive is used. In addition, since the resin sheet constituting the light-transmitting protective film is made of a solvent-free radiation-curing paint, a highly accurate film can be formed, and a thermoplastic resin containing a large amount of a conventional solvent is allowed to flow. Compared to the resin sheet produced by the rolling method, since no solvent is used, there is no problem of residual solvent or bubbles, and a resin sheet excellent in birefringence, transparency and dimensional stability can be obtained.
[0025]
Further, by using electron beam curing as a curing method of the radiation curable coating, additives such as a photopolymerization initiator can be omitted from the solvent-free radiation curable coating, so that transparency due to the decomposition product of the additive can be reduced. It is more preferable because productivity can be improved from the magnitude of the energy of the electron beam without any decrease.
[0026]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, the embodiment of the present invention will be described in more detail.
An optical recording medium according to an embodiment of the present invention is optically recorded on a disk substrate made of, for example, a polycarbonate-based resin, for example, a substrate of about 1.1 mm, using a reflective film such as aluminum or an organic or inorganic thin film such as a phase change type. Forming a layer. On the substrate, land and groove irregularities are formed with a track pitch of 0.32 μm. A composite material is used in which a masking film having a thickness of about 20 to 100 μm is bonded to a light-transmitting protective film made of a resin sheet, which is a cured product of a radiation curable paint, through an adhesive layer on the optical recording layer. Thereafter, the masking film is peeled off when necessary. When the thickness of the masking film is thin, the handling property is not improved, and when it is too thick, it is bulky.
The two layers of the adhesive layer and the light-transmitting protective film are combined to have a thickness of about 100 μm. The optical recording layer may be formed on both sides of a substrate having a thickness of about 1.0 mm. In that case, the light-transmitting protective film is also formed so as to cover both sides.
[0027]
The optical recording medium according to the embodiment of the present invention irradiates the groove portion of the optical recording layer with a blue-violet laser having a laser wavelength of 405 nm through a light-transmissive protective film having a thickness of about 0.1 mm, and reads reflected light. A high aperture ratio can be achieved.
[0028]
The radiation curable resin adhesive for adhering the light-transmitting protective film to the optical recording layer preferably has a low viscosity so as to spread thinly and uniformly on the substrate. For example, an ultraviolet curable resin adhesive, an electron beam curable resin Adhesives are used, and the hardness after curing of this radiation curable resin adhesive is reduced to H or less in pencil hardness, thereby reducing warpage and distortion of the light-transmitting protective film accompanying curing shrinkage of the adhesive This is preferable.
[0029]
The optical recording medium is made of, for example, a thermoplastic resin such as a polycarbonate resin, a cyclic polyolefin resin, or an acrylic resin, and has a thickness of 1.0 to 1.1 mm in which an uneven pattern for an optical recording layer is formed on at least one surface. An optical recording layer is formed by depositing a reflective film such as aluminum or silver or an organic or inorganic phase change thin film on a disk substrate of about a degree by sputtering or the like. Next, on the optical recording layer of the disk substrate, a composite material in which a masking film having a thickness of about 20 to 100 μm is bonded to a light-transmitting protective film made of a resin sheet that is a cured product of a radiation curable paint is cut into a ring shape. Bonding with an adhesive produces an optical recording medium. Thereafter, the masking film is peeled off when necessary.
[0030]
【Example】
Example 1
Solvent-free radiation curable paint ("KRM7818" manufactured by Daicel UCB, urethane acrylate) is applied to a release film made of a smooth PET film by a die coating method, and then a nitrogen gas atmosphere is applied from the applied radiation curable paint. A light transmissive protective film made of a transparent resin sheet was produced on the release film by irradiating and curing an electron beam under conditions of an absorbed dose of 7 Mrad and a passing speed of 50 m / min.
The thickness of the light-transmitting protective film made of the resin sheet peeled from the release film is in the range of 90 μm ± 0.7 μm and is extremely high in accuracy, and a birefringence measuring device (manufactured by KS System Co., Ltd., KOBRA-21SDH) As a result of measuring retardation with a measurement wavelength of 590 nm, it was 1.3 nm, which was an extremely excellent numerical value. Next, a polycarbonate substrate made of polycarbonate resin made by injection molding and having a thickness of about 1.1 mm is manufactured, and an aluminum reflective film, an alloy-based phase change thin film, and an oxide-based protective film are formed on the substrate by sputtering. After forming the optical recording layer, while rotating the disk substrate, supply a liquid UV curable resin adhesive (manufactured by Nagase ChemteX Corporation), and cut the resin sheet that uses the above release film also as a masking film into a ring shape With the light-transmitting protective film overlapped, the disk substrate is rotated at a high speed and the adhesive is uniformly distributed by centrifugal force, the excess adhesive is shaken off, and the cured adhesive is 10 μm thick by irradiating with ultraviolet rays. After bonding with the agent layer, the masking film was removed to prepare an optical recording medium.
Since the masking film was bonded to the light-transmitting protective film in the bonding process, the rigidity was high, the handling was good, and it was possible to manufacture without defects such as scratches.
[0031]
Example 2
Apply a primer of solvent-type acrylic polyol resin (“MKA Medium” manufactured by Showa Ink Industries Ltd., solid content: 40% by weight) to a release film consisting of a smooth PET film with a coater. Formed. Next, a solvent-free radiation curable paint ("KRM7842" manufactured by Daicel UCB, urethane acrylate) is applied on the primer layer by a die coating method, and then absorbed in a nitrogen gas atmosphere from the applied radiation curable paint. A light-transmissive protective film made of a transparent resin sheet was produced by irradiation with an electron beam under conditions of a dose of 7 Mrad and a passing speed of 50 m / min, and then a PET masking film having a thickness of 0.05 mm was joined. Thereafter, the release film was peeled off. The thickness of the light-transmitting protective film made of the resin sheet with the primer layer was in the range of 70 μm ± 0.6 μm, extremely high accuracy, and the retardation was 1.0 nm.
Next, a disk substrate made of polycarbonate resin having a thickness of about 1.1 mm is manufactured by injection molding, and an optical recording layer comprising an aluminum reflective film, an alloy-based phase change thin film, and a dielectric protective film is formed on the substrate by sputtering. Formed. Next, on the optical recording layer of the disk substrate, a light-transmitting protective film obtained by cutting the resin sheet with the primer layer into a ring shape through a double-sided adhesive sheet using a transparent acrylic resin adhesive having a thickness of 30 μm. Bonding was performed with the primer layer side overlapped.
Since the masking film was bonded to the light-transmitting protective film in the bonding process, it was easy to handle and could be manufactured without defects such as scratches.
[0032]
Example 3
As a primer layer of Example 2, a solvent-type acrylic polyol resin (“MKA medium” manufactured by Showa Ink Industry, solid content of 40% by weight) and a solvent-type urethane acrylate oligomer (“CSEB5 medium” manufactured by Showa Ink Industry) In addition, a light-transmitting protective film made of a transparent resin sheet with a primer layer was produced in the same manner as in Example 2 except that the same amount of primer mixed with 40 wt% solid content was used. After bonding a 0.05 mm PET-based masking film, the release film was peeled off. It was. The thickness of the light-transmitting protective film made of the resin sheet with the primer layer was in the range of 70 μm ± 0.6 μm, extremely high accuracy, and the retardation was 1.0 nm.
Next, an optical recording medium was prepared in the same manner as in Example 2.
Since the masking film was bonded to the light-transmitting protective film in the bonding process, it was easy to handle and could be manufactured without defects such as scratches.
[0033]
Example 4
As a primer layer of Example 2, a solvent-type acrylic polyol resin (“MKA medium” manufactured by Showa Ink Industry, solid content: 40% by weight) and a solvent-type acrylic resin acrylate oligomer (“CSEB12” manufactured by Showa Ink Industry Co., Ltd.) A light-transmitting protective film made of a transparent resin sheet with a primer layer was produced in the same manner as in Example 2 except that a primer mixed with the same amount of “medium” and a solid content of 40% by weight was used. After bonding a PET masking film having a thickness of 0.05 mm, the release film was peeled off. The thickness of the light-transmitting protective film made of the resin sheet with the primer layer was in the range of 70 μm ± 0.8 μm, had extremely high accuracy, and the retardation was 1.1 nm.
Next, an optical recording medium was prepared in the same manner as in Example 2.
Since the masking film was bonded to the light-transmitting protective film in the bonding process, it was easy to handle and could be manufactured without defects such as scratches.
[0034]
Example 5
As a primer layer of Example 2, a solvent-type acrylic resin acrylate oligomer (“CSEB12 medium” manufactured by Showa Ink Industries, Ltd., solid content: 40% by weight) was used as a solvent-free radiation-curing paint (“KRM7846” manufactured by Daicel UCB). ”, Except that urethane acrylate type) was used, a light-transmitting protective film made of a transparent resin sheet with a primer layer was produced in the same manner as in Example 2, and then a PET type masking film having a thickness of 0.05 mm After bonding, the release film was peeled off. The thickness of the light-transmitting protective film made of the resin sheet with the primer layer was in the range of 90 μm ± 0,8 μm, and the accuracy was extremely high, and the retardation was 1.1 nm.
Next, an optical recording medium was prepared in the same manner as in Example 1.
Since the masking film was bonded to the light-transmitting protective film in the bonding process, it was easy to handle and could be manufactured without defects such as scratches.
[0035]
【The invention's effect】
Since the optical recording medium of the present invention uses a composite material in which a masking film is bonded to a light-transmitting protective film, the rigidity becomes high and the handling property in the bonding process can be improved, so that the production speed can be increased. Moreover, the manufacturing method of the light-transmitting protective film excellent in optical characteristics, such as handling property, film thickness precision, transparency, and retardation, can be provided.

Claims (10)

A substrate, an optical recording layer formed on at least one side of the substrate, a light-transmitting protective film bonded on the optical recording layer, and an adhesive layer for bonding the light-transmitting protective film, The optically transparent protective film is a resin sheet that is a cured product of a solvent-free radiation-curing paint, and a masking film is bonded to the surface side of the optically transparent protective film. . 2. The optical recording medium according to claim 1, wherein the masking film is a smooth release film on which a solvent-free radiation-curing paint for forming the light-transmitting protective film is applied. The optical recording medium according to claim 1, wherein the adhesive layer is a transparent acrylic resin adhesive or a radiation curable resin adhesive. The optical recording medium according to claim 1, wherein the resin sheet constituting the light-transmitting protective film has a primer layer on the back side. 2. The optical recording medium according to claim 1, wherein the solventless radiation curable coating material comprises a polymerizable oligomer and a polymerizable monomer. 5. The primer layer according to claim 4, wherein the primer layer is a dry coating film of at least one solvent-type paint selected from a radiation curable resin made of a polymerizable oligomer and a thermoplastic resin made of an acrylic polyol. Optical recording medium. A coating film forming step of applying a solvent-free radiation curable coating composed of a polymerizable oligomer and a polymerizable monomer to the smooth release film surface;
And a curing molding step for obtaining a cured resin sheet by irradiating the coating film, and the release film is also used as a masking film. A method for producing a membrane. A coating film forming step of applying a solvent-free radiation-curing paint composed of a polymerizable oligomer and a polymerizable monomer to a smooth release surface;
A curing molding step for obtaining a cured resin sheet by irradiating the coating film with radiation,
Bonding a masking film to the resin sheet surface;
A peeling step of peeling the resin sheet from the peeling surface;
A method for producing a light-transmitting protective film used for an optical recording medium, comprising: A primer layer forming step of forming a primer layer by applying a solvent-type paint on a smooth release surface and drying;
On the primer layer, a coating film forming step of applying a solvent-free radiation curable coating composed of a polymerizable oligomer and a polymerizable monomer;
A curing molding step for obtaining a cured resin sheet by irradiating at least the coating film with radiation, and
Bonding a masking film to the resin sheet surface;
A peeling step of peeling the resin sheet from the peeling surface;
A method for producing a light-transmitting protective film used for an optical recording medium, comprising: 10. The primer layer according to claim 9, wherein the primer layer is a dry coating film of at least one solvent-type paint selected from a radiation curable resin made of a polymerizable oligomer and a thermoplastic resin made of an acrylic polyol. Of manufacturing a light-transmitting protective film.