JPH04254927A - Optical recording medium - Google Patents

Abstract

PURPOSE:To prevent the deterioration in recording characteristic by protecting the recording layer with an org. protective layer. CONSTITUTION:This optical recording medium is provided with at least a substrate, a recording layer and an org. protective layer, the protective layer is formed with the cured layer of the actinic ray-curing resin composition consisting essentially of a polymerizable monomer, and the elongation of the protective layer is controlled to >=10%.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to optical recording media.

0002

[Prior art] Recording, reproducing information, etc. by irradiating laser light,
As recording media for erasing, media in which a recording layer is formed on a substrate such as glass or plastic are known.

[0003] When forming such a recording medium,
In addition to developing materials for the recording layer, we are developing an organic protective layer that has good adhesion with the recording layer, prevents deterioration of the recording layer due to oxidation, prevents mechanical damage, and prevents deterioration of the signal quality of the recording medium. Development is extremely important. At present, recording media provided with an organic polymer protective layer include those in which a layer of ultraviolet curable resin is provided on the surface of the recording layer.
360, Japanese Patent Laid-Open No. 61-133067, etc. are known. In optical disks capable of double-sided recording, reproduction, and erasing, two substrates each having a recording layer and having an organic protective layer are used in a structure in which these two substrates are placed facing each other and bonded together with an adhesive.

0004

[Problems to be Solved by the Invention] However, when an optical recording medium made using a conventional organic protective layer is irradiated with a laser beam for recording and reproduction, bit errors, which are important for the signal quality of the recording medium, occur. There was a problem that recording characteristics deteriorated, such as an increase in rate and the occurrence of errors, making it not necessarily practical.

[0005] That is, although JP-A-61-120360 specifies the residual stress of radiation-curable paint,
The key point is to improve adhesion. However, it is difficult to say that improved adhesion is necessarily effective as a protective material for a practical medium, and even in the examples, nothing is disclosed about the bit error rate, which is a practical characteristic for an actual medium.

[0006] Furthermore, JP-A-61-133067 claims that radiation-curable compounds are cured by ultraviolet rays to prevent deterioration caused by moisture and oxygen, and are limited to use in magneto-optical materials. be. However, the patent emphasizes that all UV curable materials exhibit good properties. However, it is difficult to say that it is practical as a media protection material simply because it is an ultraviolet curable material. Further, although the specific example illustrates the C/N characteristic, nothing is disclosed about the error rate for determining whether or not a bit error actually occurs.

The present invention was devised in view of the various drawbacks of the conventional techniques, and its purpose is to provide an optical recording medium comprising an organic protective layer with excellent protection for the recording layer. .

[0008]

[Means for Solving the Problems] The purpose of the present invention is to
An optical recording medium comprising at least a substrate, a recording layer, and an organic protective layer, the organic protective layer being a cured layer of an actinic radiation-curable resin composition containing a polymerizable monomer as a main component, This is achieved by an optical recording medium characterized in that the elongation of the protective layer is 10% or more.

The substrate and recording layer used in the present invention are not particularly limited, and known ones can be used.

The substrate is polymethyl methacrylate,
Plastics such as polycarbonate and epoxy resin, glass, etc. can be used, and the thickness is usually 10 μm ~
The range is 5mm. The substrate is usually used in the form of a disk, but it can also be used in the form of a tape, sheet, or card.

Examples of the recording layer include, but are not limited to, those listed below.

(1) A Te compound recording film or a magneto-optical recording film is directly formed on a substrate, (2) A SiO
, SiO2, SIALON, Si3 N4, Ta2
After forming an inorganic protective film such as O2, GeO2, ZnS and MgO, the above-mentioned recording film is formed.
(3) An inorganic protective film, a recording film, and an inorganic protective film are formed on a substrate in this order.

(4) After forming an inorganic protective film, a recording film and an inorganic protective film on the substrate, Al, Ni, Cr, Au
A reflective film made of metals such as , Ti, Ta, or alloys thereof.

The recording layer can be formed by a known method, such as a vacuum deposition method, a sputtering method, or an ion plating method.

The thickness of the recording film can range from 10 nm to 100 nm, and is preferably from 10 to 50 nm in order to obtain higher recording sensitivity. Further, the thickness of the inorganic protective film and the reflective film can generally be used within a range of 10 nm to 1000 nm.

The recording medium of the present invention performs recording by causing a thermally or optically detectable change in physical properties or a change in form in the recording film by irradiation with recording light such as a semiconductor laser or strobe light. It is something that can be done.

The organic protective film according to the present invention is composed of a cured layer of an actinic radiation-curable resin composition containing a polymerizable monomer as a main component, and the elongation of the organic protective layer is determined by the tensile test according to JIS K6301. Consisting of 10% or more,
More preferably it is 30% or more. If it is less than 10%, the reliability of the medium decreases, such as an increase in bit error rate, and sufficient protection cannot be obtained. On the other hand, there is no particular restriction on the upper limit of the elongation, but in cases where sufficient protection against mechanical damage is important, it is preferable to set it to 300% or less.

An example of the polymerizable monomer used in the present invention is a compound having one polymerizable double bond in one molecule.

As these compounds, compounds having an acryloyloxy group or a methacryloyloxy group (hereinafter, both groups are collectively referred to as a (meth)acryloyloxy group) are preferably used, and specific examples thereof are as follows. The following acrylates can be mentioned. That is, (meth)acrylic acid esters having a (meth)acryloyloxy group of a monohydric alcohol: methyl (meth)acrylate, ethyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, benzyl (meth)acrylate, isobornyl (meth)acrylate, tetrahydrofurfuryl (
Examples include meth)acrylate, (meth)acrylate of a tetrahydrofurfuryl derivative, and 1H.1H.5H-octafluoropentyl (meth)acrylate.

Further, for the purpose of improving the curability of the organic protective layer and adjusting the elongation, other monomers that can be copolymerized with the above-mentioned monomers can be used in combination. Examples of these copolymerizable monomers include compounds having two or more polymerizable double bonds in one molecule. Specific examples thereof include the following (meth)acrylates (a) to (f).

(a) One molecule obtained by reacting a terminal isocyanate group-containing compound obtained by reacting a diisocyanate compound and a compound having two or more alcoholic hydroxyl groups in advance with an alcoholic hydroxyl group-containing (meth)acrylate. Urethane (meth)acrylates having two or more (meth)acryloyloxy groups in them: Specific examples include Artosidine UN-6060P, UN-1101T, and UN-5, which are trade names manufactured by Negami Kogyo Co., Ltd.
200, UN-1255, UN-9000PEP, UN
-9000H, etc. (b) (meth)acrylic acid diesters of alkylene glycol having 2 to 12 carbon atoms: ethylene glycol di(meth)acrylate, propylene glycol di(meth)acrylate, 1,4-butanediol di(meth) acrylate, neopentyl glycol di(meth)acrylate, 1,6-hexanediol di(
(meth)acrylate, etc.

(c) (meth)acrylic acid diesters of polyoxyalkylene glycol: diethylene glycol di(meth)acrylate, triethylene glycol di(meth)acrylate, tetraethylene glycol di(
(d) having two or more (meth)acryloyloxy groups of a polyhydric alcohol, such as meth)acrylate, dipropylene glycol di(meth)acrylate, polyethylene glycol di(meth)acrylate, polypropylene glycol di(meth)acrylate, etc. meth)acrylic acid polyesters: pentaerythritol di(meth)acrylate, pentaerythritol tri(meth)acrylate, pentaerythritol tetra(meth)acrylate, dipentaerythritol tri(meth)acrylate, dipentaerythritol tetra(meth)acrylate, etc. (e) (meth)acrylic acid diesters of bisphenol A or bisphenol A hydride adducts with ethylene oxide and propylene oxide.

(f) Epoxy (meth)acrylate having two or more (meth)acryloyloxy groups in the molecule obtained by reacting a compound having two or more epoxy groups in the molecule with acrylic acid or methacrylic acid. kind.

As mentioned above, the organic protective layer of the present invention has J
This is an actinic radiation curable resin composition that requires an elongation of 10% or more in the ISK6301 tensile test. From this point of view, a compound having two (meth)acryloyloxy groups in one molecule can be used as a copolymerizable monomer that provides sufficient elongation. Urethane (meth)acrylates can also be used as a group of compounds that exhibit particularly excellent adhesion to the recording layer. As for the ratio of blending these copolymerizable monomers, the monomer having two (meth)acryloyloxy groups in one molecule is used in an amount of at least 5% by weight or more of the total amount of polymerizable monomers in the blended composition. It is preferable. More preferably, it is used in an amount of 10% by weight or more. A particularly preferred blending example of the acrylic monomer is 2-hydroxypropyl acrylate or benzyl acrylate 90, which has one (meth)acryloyloxy group in one molecule.
Art resin UN-6060P 10 to 40% by weight in urethane (meth)acrylate of group (a) having 2 (meth)acryloyloxy groups in one molecule and 60% by weight
A mixed system of

One or more photopolymerization initiators may be added to the actinic radiation-curable resin composition used in the present invention. Conventionally known photopolymerization initiators can be used, such as ketones such as acetophenone, benzophenone, and p-dimethylaminopropiophenone, benzoin, benzoin methyl ether, and benzoin ethyl ether.
benzoin series such as ter, benzoin isopropyl ether, sulfide series such as tetramethylthiuram monosulfide and tetramethylthiuram disulfide, thioxane series such as thioxane and 2-methylthioxane, and peroxides such as benzoin peroxide and di-t-butyl peroxide. Examples include systems. The amount of photopolymerization initiator used is 0 with respect to 100 parts by weight of the polymerizable monomer composition.
．． 01 to 10 parts by weight is suitable.

The actinic radiation-curable resin composition used in the present invention also contains hydroquinone, hydroquinone monomethyl ether, 2,5-t-butylhydroquinone, etc. in order to prevent thermal polymerization during production and dark reaction during storage. A known thermal polymerization inhibitor can be added. The amount added is preferably 0.001 to 0.1% by weight based on the total weight of the polymerizable compound. When using electron beams or gamma rays as a curing method,
It is not always necessary to use a polymerization initiator.

[0027] The actinic radiation-curable resin composition used in the present invention may contain a leveling material such as a silicone material to improve coating properties, and may also contain other additives such as an antistatic agent, if necessary. Agents can also be added. Furthermore, organic solvents such as alcohol solvents, acetate ester solvents, ketone solvents, etc. can also be blended to improve workability during coating and control coating film thickness.

The cured layer of the actinic radiation-curable resin composition of the present invention is prepared by applying actinic radiation, ie, ultraviolet rays, electron beams, gamma rays, etc., onto a recording layer formed on a substrate by applying the composition in a conventional manner. It is cured by irradiation with active energy rays.

The curable composition may be applied by any known method, such as spin coating, bar coating, roll coating, spray coating, gravure coating, slit die coating, etc.

[0030] The thickness of the hardened layer is 0.5 μm to 30 μm.
The range of m is preferable, and more preferably 1 μm to 10 μm.
It is.

Next, a method for manufacturing one example of the structure of the optical recording medium of the present invention will be explained. That is, first, an inorganic protective film, a recording film, an inorganic protective film, and a reflective film are sequentially formed on a substrate by sputtering or the like. Next, an actinic radiation-curable resin composition containing the polymerizable monomer of the present invention as a main component is uniformly applied onto the reflective film, and then the coated surface is irradiated with ultraviolet rays using an ultraviolet lamp to cure the composition. By doing so, an optical recording medium is obtained. [Evaluation of elongation by JIS K6301 tensile test]
■Preparation of test piece An actinic radiation curable resin composition with a strength of 140 in an N2 atmosphere
For each composition, four test pieces were prepared by curing with a high-pressure mercury lamp of 0 mJ/cm2, each having a tumble-shaped shape, a No. 3 shape, and a parallel portion thickness of 0.3 mm.

■Measurement and calculation method of elongation JISK63
I followed 01.

[Method for evaluating recording characteristics] The recording method is 2-7.
Modulation position recording, repetition rate is 1.5T (3.7MH
A single signal of z) was repeatedly overwritten 10,000 times, and then a 2-7 random pattern was overwritten once to measure the bit error rate. The measurement conditions are as follows.

Substrate: ISO standard format disk, 130mmφ
Optical system of evaluation machine: λ = 830 nm, N = 0.53 Substrate rotation speed: 1800 rpm Recording power: 20 mW Erasing power: 10 mW Recording pulse width: 50 nS

[0035]

[Examples] The present invention will be explained below with reference to Examples, but the present invention is not limited thereto.

Example 1 Test pieces of the following actinic radiation curable resin composition were prepared in order to measure the elongation according to the tensile test according to JIS K6301. The elongation of the obtained test piece was 130%.

[Composition of actinic radiation curable resin composition] 1-hydroxy added to a liquid mixture of 30 parts by weight of Artresin UN-6060P (urethane acrylate manufactured by Negami Kogyo Co., Ltd.) and 70 parts by weight of 2-hydroxypropyl acrylate. 5 parts by weight of cyclohexyl phenyl ketone (Irgacure 184, manufactured by Ciba Geigy) were mixed and dissolved to obtain an ultraviolet curable resin protective layer composition.

Example 2 A test piece for measuring elongation was prepared in exactly the same manner as in Example 1, except that the following composition was used in place of the ultraviolet curable resin protective layer composition used in Example 1. The elongation of the obtained test piece was 180%.

[Composition of actinic radiation curable resin composition] Art Resin UN6060P
30 parts by weight benzyl acrylate (Viscoat 160, manufactured by Osaka Organic Chemical Industry Co., Ltd.)

70 parts by weight Irgacure 1
84
5 parts by weight Example 3 A polycarbonate substrate with spiral groups having a thickness of 1.2 mm, a diameter of 13 cm, and a pitch of 1.6 μm is processed at 3 parts per minute.
The following recording layer forming substrate laminate was prepared by sputtering while monitoring the film thickness with a crystal resonator under the condition of 0 rotation and argon gas pressure of 0.5 Pa.

That is, on the substrate, a 200 nm mixed layer of ZnS and SiO2 (molar ratio 80:20), a 20 nm mixed layer of Pd3 Sb17Te50Ge30,
A mixed layer of ZnS and SiO2 (molar ratio 80:20),
A recording layer forming substrate laminate was obtained by sequentially forming 80 nm Al layers. Next, the ultraviolet curable resin composition prepared in Example 1 was applied onto the obtained recording layer forming substrate laminate so that the film thickness after curing was 8 μm, and the strength was 1400 mJ/cm2 in an N2 atmosphere. The protective layer was completely cured by irradiation with a high-pressure mercury lamp to create an optical recording medium.

When the bit error rate of the obtained optical recording medium was measured, a value of 10 -5 or less was obtained. This value can be said to be sufficient for an optical recording medium. After being left in an environment of 80 DEG C. and 80% relative humidity for 200 hours, it was taken out and the same measurement was performed again. The bit error rate was also below 10@-5 and no deterioration was observed.

Example 4 An optical recording medium was prepared in exactly the same manner as in Example 3, except that the ultraviolet curable resin composition prepared in Example 2 was used as a protective layer.

When the bit error rate of the obtained optical recording medium was measured, a value of 10 -5 or less was obtained. This value can be said to be sufficient for an optical recording medium. After being left in an environment of 80 DEG C. and 80% relative humidity for 200 hours, it was taken out and the same measurement was performed again. The bit error rate was also below 10@-5 and no deterioration was observed.

Comparative Example 1 A test piece for measuring elongation was prepared in exactly the same manner as in Example 1, except that the following composition was used in place of the ultraviolet curable resin composition prepared in Example 1. The elongation of the obtained test piece was 3%.
Met.

[Composition of actinic radiation curable resin composition] Art Resin UN6060P
30 parts by weight neopentyl glycol diacrylate (light acrylate NP-A, manufactured by Kyoeisha Yushi Kagaku Kogyo Co., Ltd.)

20 parts by weight 2-hydroxypropyl acrylate
50 parts by weight Irgacure 184

5 parts by weight Comparative Example 2 A test piece for measuring elongation was prepared in exactly the same manner as in Example 1, except that the following composition was used instead of the ultraviolet curable resin composition used in Example 1. The elongation of the obtained test piece was 5%.
Met.

[Composition of actinic radiation curable resin composition] Art Resin UN6060P
30 parts by weight Light acrylate NP-A
20 parts by weight Viscoat 160
50 parts by weight Irgacure 184

5 parts by weight Comparative Example 3 An optical recording medium was prepared in exactly the same manner as in Example 3, except that the ultraviolet curable resin composition prepared in Comparative Example 1 was used as a protective layer. When the bit error rate of the obtained optical recording medium was measured, it was significantly degraded to 10-2, and it was impossible to reproduce the recorded signal. From the above, it is clear that in the UV-curable resin protective layer composition not according to the present invention, signal deterioration due to repetition is large.

Comparative Example 4 An optical recording medium was prepared in exactly the same manner as in Example 3, except that the ultraviolet curable resin composition prepared in Comparative Example 2 was used. When the bit error rate of the obtained optical recording medium was measured, it was significantly degraded to 10-2, and it was impossible to reproduce the recorded signal. From the above, it is clear that in the UV-curable resin protective layer composition not according to the present invention, signal deterioration due to repetition is large.

[0048]

Effects of the Invention As described above, the present invention provides excellent protection for the recording layer and good signal quality by providing a recording layer and a protective layer made of an actinic radiation-curable resin composition having an elongation of 10% or more. The optical recording medium shown in FIG.

Claims (1)

[Claims] 1. An optical recording medium comprising at least a substrate, a recording layer, and an organic protective layer, the organic protective layer being a cured layer of an actinic radiation-curable resin composition containing a polymerizable monomer as a main component. An optical recording medium characterized in that the organic protective layer has an elongation of 10% or more.