JP2009140588A - Optical recording medium - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical recording medium with high surface durability, having less deformation even when an environment humidity changes. <P>SOLUTION: The optical recording medium has at least the substrate, transparent resin layer (b) and transparent resin layer (a) stacked in this order, wherein the elastic modulus of the transparent resin layer (a) is ≥1,000 MPa and ≤2,500 MPa, while the elastic modulus of the transparent resin layer (b) ≥100 MPa and ≤1,300 MPa. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an optical recording medium such as a recording / reproducing disk. More specifically, the present invention provides an optical recording medium that can cope with changes in environmental humidity, has excellent surface durability, and can be used for high-density optical discs and the like.

  In recent years, optical information media such as read-only optical discs and optical recording discs have been widely used as information recording media for recording or storing vast amounts of information such as moving image information. As one of them, for example, a high-density optical disc (so-called Blu-ray disc, hereinafter also referred to as “Blu-ray disc” as appropriate) using a laser beam having a wavelength of 400 nm has been proposed (see Patent Document 1).

  The Blu-ray disc is an optical recording medium having layers such as a resin substrate, a reflective layer, a recording layer, and a protective layer. However, the disc surface requires durability against local pressure and scratches. On the other hand, for the entire disk, it is required that the deformation of the disk is small even if the temperature and humidity are suddenly changed so that information can be stably read and written even if the environment such as temperature and humidity changes. .

  Patent Document 2 discloses a radiation curable composition (a radiation curable composition containing urethane acrylate) that is excellent in transparency, abrasion resistance, recording film protection, mechanical properties, and also excellent in heat resistance and moisture deformation resistance. ), And an optical recording medium using this radiation-curable composition has been proposed. Patent Document 2 describes that the optical recording medium is less deformed after being stored at high temperature and high humidity for a long time and then returned to room temperature and stored for a long time.

Japanese Patent Laid-Open No. 11-273147 JP 2003-263780 A

  However, the optical recording media described in Patent Documents 1 and 2 are insufficient in suppressing the deformation of the disk when the temperature and humidity are suddenly changed, and at the same time, further withstand the local pressure on the surface. It was difficult to satisfy sex.

  The present invention has been made in view of the above-described problems. That is, an object of the present invention is to provide an optical recording medium that has little deformation and high surface durability even when the environmental humidity changes.

  As a result of intensive research by the present inventors, in the protection of optical recording media, a layer having a relatively low elastic modulus and a layer having a relatively high elastic modulus are formed into a two-layer structure, thereby suppressing deformation against environmental humidity changes. The inventors have found that high surface durability can be achieved, and have completed the present invention.

  That is, the gist of the present invention is an optical recording medium in which at least a substrate, a transparent resin layer b, and a transparent resin layer a are laminated in this order, and the elastic modulus of the transparent resin layer a is 1000 MPa to 2500 MPa, and transparent The elastic modulus of the resin layer b is in the range of 100 MPa to 1300 MPa (claim 1).

  At this time, the elastic modulus of the transparent resin layer a is preferably larger than the elastic modulus of the transparent resin layer b (Claim 2).

  The film thickness ratio of the transparent resin layer a to the film thickness of the transparent resin layer b is preferably 10/90 or more and 60/40 or less (Claim 3).

  The transparent resin layer a is a cured product of the radiation curable composition α, and the radiation curable composition α is (A) a urethane (meth) acrylate compound, and (C) (A) a urethane (meth). The polyfunctional (meth) acrylate compound other than the acrylate compound is contained, and the content of the polyfunctional (meth) acrylate compound other than the (C) (A) urethane (meth) acrylate compound in the radiation curable composition α is It is preferable that it is 15 to 90 weight% (Claim 4).

  At this time, it is preferable that the polyfunctional (meth) acrylate compound other than the (C) (A) urethane (meth) acrylate compound includes a trifunctional or higher functional (meth) acrylate compound.

  The transparent resin layer b is a cured product of a radiation curable composition β, and the radiation curable composition β is (A) urethane (meth) acrylate compound, (B) (A) urethane (meth) acrylate. A monofunctional (meth) acrylate compound other than the compound, and a polyfunctional (meth) acrylate compound other than the (C) (A) urethane (meth) acrylate compound (B) in the radiation curable composition β (B) ( A) The content of the monofunctional (meth) acrylate compound other than the urethane (meth) acrylate compound is preferably 10% by weight or more and 70% by weight or less (Claim 6).

  At this time, it is preferable that the (A) urethane (meth) acrylate compound contains a polyether skeleton (Claim 7).

  The optical recording medium is preferably reproduced using a blue laser (claim 8).

  According to the present invention, an optical recording medium that can be used stably and has excellent surface durability can be obtained because deformation is small even when the environmental humidity changes.

  Hereinafter, the present invention will be described in detail, but the present invention is not limited to the following examples, and various modifications can be made without departing from the spirit of the present invention.

  "(A) Urethane (meth) acrylate compound", "(B) (A) Monofunctional (meth) acrylate compound other than urethane (meth) acrylate compound", and "(C) (A) Urethane (meth)" (A), (B), and (C) attached to the beginning of the “polyfunctional (meth) acrylate compound other than acrylate compound” are only symbols for identifying each compound.

  Currently, optical recording media that are generally used include read-only media (ROM media), write-once media that can be recorded only once (Write Once media), or rewritable media that can be repeatedly erased. Media (Rewritable media).

These optical recording media can adopt a layer structure corresponding to each purpose. For example, in a read-only medium, it is preferable that a reflective layer containing a metal such as aluminum, silver, or gold is usually formed on a substrate surface on which unevenness for reproduction is formed.
In the write once optical recording medium, it is preferable that a protective film is formed on the surface on which the recording / reproducing functional layer is formed. The recording / reproducing functional layer is usually configured by providing a reflective layer containing a metal such as aluminum, silver and gold and a recording layer containing an organic dye on the substrate in this order.
Also in the rewritable optical recording medium, it is preferable that a protective film is formed on the surface on which the recording / reproducing functional layer is formed. The recording / reproducing functional layer is usually configured by providing a reflective layer containing a metal such as aluminum, silver, and gold, a dielectric layer, a recording layer, and a dielectric layer in this order on the substrate.

  On the other hand, the wavelength of a laser for recording / reproducing of an optical recording medium (hereinafter sometimes referred to as “recording / reproducing light” as appropriate) is a light having an optimum wavelength depending on the standard such as CD, DVD, Blu-ray disc, HDDVD, etc. Can be used. Along with the popularization of rich contents in recent years, research for using a blue laser with a shorter wavelength has been actively carried out as the demand for higher density and higher capacity of optical recording media is increasing.

  An optical recording medium using this blue laser for recording and reproduction is referred to as a “next-generation high-density optical recording medium” in this specification. Specifically, the next-generation high-density optical recording medium is a substrate formed with a dielectric film, a recording film, a reflective film, and the like (hereinafter, these layers may be collectively referred to as “recording / reproducing functional layer” as appropriate). An optical recording medium in which a protective film is formed on the coated surface, and an optical recording medium using recording / reproducing light having a wavelength of usually 350 nm or more, preferably 380 nm or more, and usually 450 nm or less, preferably 430 nm or less.

  The optical recording medium of the present invention can be applied to any of the above types of optical recording media. In other words, the present invention can be applied to any of ROM media, White Once media, and Rewritable media. Further, the wavelength of the recording / reproducing light used in the optical recording medium of the present invention is arbitrary as long as the effects of the present invention are not significantly impaired. Among them, it is preferable to use a blue laser because of the demand for high density and high capacity. That is, it is preferably applied to the next generation high density optical recording medium.

The optical recording medium of the present invention is an optical recording medium in which at least a substrate, a transparent resin layer b, and a transparent resin layer a are laminated in this order. In addition to these layers, other layers such as a reflective layer and a recording layer may be provided.
The configuration of these layers is not limited as long as it is a layer configuration normally used as an optical recording medium. Accordingly, another layer may be provided between the substrate and the transparent resin layer b, or another layer may be provided between the transparent resin layer b and the transparent resin layer a. You may have another layer on the opposite side to the transparent resin layer a of the resin layer b.

Here, as an example of a typical layer configuration, there is a layer configuration in which layers are formed in the order of a substrate, a reflective layer, a recording layer, a transparent resin layer b, and a transparent resin layer a. This layer structure is preferably used for a write once or rewritable optical recording medium.
As another example of the layer configuration, there is a layer configuration in which layers are formed in the order of a substrate, a recording layer, a reflective layer, a transparent resin layer b, and a transparent resin layer a. This layer structure is preferably used for a read-only optical recording medium.

Further, for example, a two-layered structure having two recording layers and two reflective layers may be employed. In the case of a two-layer structure, the layers may be sequentially stacked on the substrate, but two layers of a recording layer and a reflective layer may be laminated to form a laminate. When bonding, an adhesive layer may be provided on the surfaces to be bonded. Further, it may have a layer structure of three or more layers.
Furthermore, if necessary, a hub may be attached and incorporated into the cartridge.

  Hereinafter, in the optical recording medium of the present invention, each of the above layers will be described in detail.

[1. Transparent resin layer a / transparent resin layer b]
The transparent resin layer b is formed using a material for the transparent resin layer b. The material for the transparent resin layer b is preferably a liquid compound having radiation curability. As the material for the transparent resin layer b, one type may be used alone, or two or more types may be used in any combination and ratio.
Examples of the method for forming the transparent resin layer b include a method in which a radiation curable composition β in which a plurality of types of materials for the transparent resin layer b are mixed is applied by spin coating and then irradiated with radiation.

The transparent resin layer a is formed using a material for the transparent resin layer a. The material for the transparent resin layer a is preferably a liquid compound having radiation curability. As the material for the transparent resin layer a, one type may be used alone, or two or more types may be used in any combination and ratio.
As a method for forming the transparent resin layer a, for example, a method of irradiating with radiation after applying a radiation curable composition α mixed with a plurality of types of transparent resin materials a by a spin coating method, like the transparent resin layer b Etc.

  The transparent resin layer b and the transparent resin layer a may be collectively referred to as a protective layer. Hereinafter, these layers will be described in detail.

<1-1. Protective layer>
The protective layer in the optical recording medium of the present invention is configured by combining the transparent resin layer b and the transparent resin layer a.

  The elastic modulus at 25 ° C. of the transparent resin layer b constituting the protective layer is usually 100 MPa or more, preferably 200 MPa or more, more preferably 400 MPa or more, and usually 1300 MPa or less, preferably 1000 MPa or less. More preferably, it is 800 MPa or less, More preferably, it is 600 MPa. As a result, it is possible to reduce the deformation of the optical recording medium when the environmental temperature changes.

The elastic modulus at 25 ° C. of the transparent resin layer a constituting the protective layer is usually 1000 MPa or more, preferably 1350 MPa or more, more preferably 1500 MPa or more, and usually 2500 MPa or less, preferably It is 2200 MPa or less, more preferably 2000 MPa or less. Thereby, it is possible to prevent the signal characteristics of the surface on the protective layer side of the optical recording medium from being deteriorated due to deformation with respect to local pressure.
The elastic modulus means an elastic modulus when a 0.1 mm thick film is formed and a tensile test is performed at a tensile speed of 1 mm / min using a tensile strength tester.

  The elastic modulus of the transparent resin layer a is preferably larger than the elastic modulus of the transparent resin layer b. Specifically, the difference in elastic modulus is 200 MPa or more, preferably 400 MPa or more, and more preferably 600 MPa or more.

  In addition, the transparent resin layer a which comprises a protective layer is the surface hardness by the pencil hardness test based on JISK5400, and is 6B or more normally, Preferably it is 4B or more, More preferably, it is B or more, Preferably it is HB or more.

  The protective layer usually has a planar annular shape and is formed of a material that can transmit laser light used for recording and reproduction. The transmittance of the protective layer is usually 80% or more, preferably 85% or more, more preferably 89% or more at the wavelength of light used for recording / reproduction. Within such a range, loss due to absorption of recording / reproducing light can be minimized. On the other hand, the transmittance is most preferably 100%, but is usually 99% or less in view of the performance of the material used.

Such a protective layer is sufficiently transparent to laser light in the vicinity of the wavelength used for optical disc recording / reproduction, and has a property of protecting the recording layer formed on the substrate from water and dust. Is desirable.
In addition, the surface hardness of the protective layer is preferably B or higher according to a pencil hardness test in accordance with JIS K5400. If the hardness is too small, the surface may be easily scratched. On the other hand, if the hardness is too high, the cured product may become brittle, and cracks and peeling may easily occur. When the surface hardness of the protective layer is insufficient, a hard coat layer described later can be formed on the transparent resin layer a to compensate for the shortage.

  Furthermore, it is preferable that the protective layer has high adhesion to the layer in contact therewith. Furthermore, it is preferable that the adhesiveness with time is higher, and the ratio of the contact area between the protective layer and the layer in contact with the protective layer after being placed in an environment of 80 ° C. and 85% relative humidity for 100 hours, more preferably 200 hours is It is preferable to hold 50% or more of the contact area, more preferably 80% or more, and particularly preferably 100%.

  The thickness of the protective layer is arbitrary as long as the effect of the present invention is not significantly impaired, but is usually 10 μm or more, preferably 20 μm or more, more preferably 30 μm or more, further preferably 70 μm or more, particularly preferably 85 μm or more, Usually, it is 300 μm or less, preferably 130 μm or less, more preferably 115 μm or less. When the film thickness is in such a range, the influence of dust and scratches attached to the surface of the protective layer can be reduced, and the thickness is sufficient to protect the recording layer and the reflective layer from moisture in the outside air. be able to. In addition, a uniform film thickness can be easily formed by a general coating method used in spin coating or the like. The protective layer is preferably formed with a uniform thickness in a range covering the recording layer and the reflective layer.

  The film thickness ratio of the transparent resin layer a to the film thickness of the transparent resin layer b constituting the protective layer is preferably 10/90 or more, more preferably 25/75 or more, and preferably 60/40 or less. More preferably, it is 40/60 or less. If the film thickness ratio of the transparent resin layer a is too high, the amount of deformation of the optical recording medium with respect to the environmental temperature and humidity increases, which may hinder information reproduction and recording. On the other hand, if the film thickness ratio of the transparent resin layer b is too high, the surface strength decreases, and when the local force is applied for a certain time or more, creep deformation is likely to occur, and the surface smoothness is impaired, which is the cause. This may interfere with the playback and recording of information.

  In addition, the protective layer may have layers other than the transparent resin layer b and the transparent resin layer a in arbitrary positions, unless the effect of this invention is impaired remarkably.

<1-2. Transparent resin layer b>
Hereinafter, the material for the transparent resin layer b and the radiation curable composition β will be described. In addition, about the manufacturing method of the transparent resin layer b using the radiation curable composition (beta), it is <1-4. The method for forming the protective layer is described below.

<1-2-1. Material for transparent resin layer b>
Any material can be used as the material for the transparent resin layer b as long as the effects of the present invention are not significantly impaired. In order to form the transparent resin layer b, it is preferable to use a liquid composition (a radiation curable composition β) in which a material for the transparent resin layer b having radiation curability is mixed.

  As the material for the transparent resin layer b, (A) a radiation curable compound containing a urethane (meth) acrylate compound is preferable. Furthermore, as the material for the transparent resin layer b, (B) (A) a monofunctional (meth) acrylate compound other than the urethane (meth) acrylate compound (hereinafter sometimes referred to as “(B) monofunctional acrylate compound”) and It is preferable to use a polyfunctional (meth) acrylate compound other than (C) (A) urethane (meth) acrylate compound (hereinafter sometimes referred to as “(C) polyfunctional acrylate compound” as appropriate). Moreover, the other component may be contained.

<(A) Urethane (meth) acrylate compound>
The (A) urethane (meth) acrylate compound as the transparent resin layer b material according to the present invention can be obtained by any method as long as the effects of the present invention are not significantly impaired. It is obtained by reacting a compound containing a group with a (meth) acrylate compound containing a hydroxyl group. (A) As a urethane (meth) acrylate compound, a urethane acrylate compound is preferable. This is because the surface curability is excellent and tack is difficult to remain.
(A) A urethane (meth) acrylate compound may be used individually by 1 type, and may use 2 or more types by arbitrary combinations and a ratio.

(A. Polyisocyanate compound)
A polyisocyanate compound is a polyisocyanate compound having two or more isocyanate groups in the molecule. By using this compound, the advantage that the optical recording medium of the present invention is excellent in mechanical properties can be obtained.

  Any compound can be used as the polyisocyanate compound as long as the effects of the present invention are not significantly impaired. For example, tetramethylene diisocyanate, hexamethylene diisocyanate, trimethylhexamethylene diisocyanate, bis (isocyanatomethyl) cyclohexane, cyclohexane diisocyanate. Bis (isocyanatocyclohexyl) methane, isophorone diisocyanate, tolylene diisocyanate, xylylene diisocyanate, diphenylmethane diisocyanate, m-phenylene diisocyanate, naphthalene diisocyanate, and the like, and multimers thereof.

Especially, since the hue of the urethane oligomer obtained is favorable, tetramethylene diisocyanate, hexamethylene diisocyanate and its multimer, bis (isocyanatomethyl) cyclohexane, cyclohexane diisocyanate, bis (isocyanatocyclohexyl) methane, and isophorone diisocyanate are preferable.
A polyisocyanate compound may be used individually by 1 type, and may be used 2 or more types by arbitrary ratios and combinations.

  The molecular weight of the polyisocyanate compound is usually 100 or more, preferably 150 or more, and usually 1000 or less, preferably 500 or less. When the molecular weight is in this range, an advantage that the balance between strength and elastic modulus is good can be obtained.

(B. Compound containing a hydroxyl group)
Any compound containing a hydroxyl group can be used as long as the effects of the present invention are not significantly impaired. Among these, polyols containing two or more hydroxyl groups are preferable, and specific examples thereof include ethylene glycol, 1,2-propanediol, 1,3-propanediol, 2-methyl-1,3-propanediol, 1,3-butanediol, 1,4-butanediol, 1,5-pentanediol, 2-methyl-1,5-pentanediol, neopentyl glycol, 3-methyl-1,5-pentanediol, 2,3 , 5-trimethyl-1,5-pentanediol, 1,6-hexanediol, 2-ethyl-1,6-hexanediol, 2,2,4-trimethyl-1,6-hexanediol, 1,8-octane Diol, trimethylolpropane, pentaerythritol, sorbitol, mannitol, glycerin, 1,2-dimethylol Cyclohexane, 1,3-dimethylolcyclohexane, alkylene polyols such as 1,4-dimethylol cyclohexane. As the compound containing a hydroxyl group, one kind may be used alone, and two kinds or more may be used in optional ratio and combination.

  Among them, the above-mentioned polyols have a polyether polyol compound having an ether bond for forming a multimer, etc .; a polyester having an ester bond by reaction with a polybasic acid or an ester bond by ring-opening polymerization of a cyclic ester Polyol compound; or a polycarbonate polyol compound having a carbonate bond by reaction with carbonate is preferable.

  Specific examples of the polyether polyol compound include polytetramethylene glycol as a ring-opening polymer of a cyclic ether such as tetrahydrofuran in addition to the multimers of the polyols; ethylene oxide, propylene oxide, 1, Examples include adducts of alkylene oxides such as 2-butylene oxide, 1,3-butylene oxide, 2,3-butylene oxide, tetrahydrofuran and epichlorohydrin;

  Specific examples of the polyester polyol compound include a reaction product of the polyol and a polybasic acid such as maleic acid, fumaric acid, adipic acid, sebacic acid, and phthalic acid, and a ring-opening polymer of a cyclic ester such as caprolactone. And polycaprolactone.

  Specific examples of the polycarbonate polyol compound include the polyols and alkylene carbonates such as ethylene carbonate, 1,2-propylene carbonate, and 1,2-butylene carbonate, or diphenyl carbonate, 4-methyldiphenyl carbonate, and 4-ethyldiphenyl. Carbonate, 4-propyldiphenyl carbonate, 4,4′-dimethyldiphenyl carbonate, 2-tolyl-4-tolyl carbonate, 4,4′-diethyldiphenyl carbonate, 4,4′-dipropyldiphenyl carbonate, phenyltoluyl carbonate, bis Diaryl carbonates such as chlorophenyl carbonate, phenyl chlorophenyl carbonate, phenyl naphthyl carbonate, dinaphthyl carbonate, Dialkyl carbonates such as dicarbonate, diethyl carbonate, di-n-propyl carbonate, diisopropyl carbonate, di-n-butyl carbonate, diisobutyl carbonate, di-t-butyl carbonate, di-n-amyl carbonate, diisoamyl carbonate, etc. Examples include reactants.

  Among these polyols, polyether polyol compounds capable of introducing a polyether skeleton are preferable, and polyalkylene glycol is more preferable. Of the alkylene glycols, tetramethylene glycol is particularly preferable.

  These polyols may be used individually by 1 type, and may be used 2 or more types by arbitrary ratios and combinations.

  Further, the number average molecular weight of the polyols is usually at least a part of the polyols, preferably 15 mol% or more of the total polyols, more preferably 30 mol% or more of the total polyols, preferably 200 or more, more preferably 400. In addition, it is preferably 1500 or less, more preferably 800 or less. When the number average molecular weight of the polyols is within this range, the water absorption and hygroscopicity as a monomer having a urethane bond is lowered, and the corrosion of the recording layer when used as an optical recording medium as a cured product can be suppressed. Is obtained.

  Therefore, the compound containing a hydroxyl group is preferably a polyalkylene glycol having a number average molecular weight of 800 or less, and particularly preferably a polytetramethylene glycol having a number average molecular weight of 800 or less.

(C. (Meth) acrylate compound containing hydroxyl group)
The (meth) acrylate compound containing a hydroxyl group is a compound having both a hydroxyl group and a (meth) acryloyl group. Any compound can be used as long as the effect of the present invention is not significantly impaired. For example, hydroxyethyl (meth) acrylate, hydroxypropyl (meth) acrylate, hydroxybutyl (meth) acrylate, glycidyl ether compound and (meth) acrylic. Examples include addition reaction products with acids and mono (meth) acrylates of glycol compounds. These (meth) acrylate compounds containing a hydroxyl group may be used alone or in combination of two or more in any ratio and combination.

  The molecular weight of the (meth) acrylate compound containing a hydroxyl group is usually 40 or more, preferably 80 or more, and usually 800 or less, preferably 400 or less. If the molecular weight is too small, curing shrinkage may increase, and if it is too large, the viscosity may increase.

(D. (A) Method for producing urethane (meth) acrylate compound)
A (A) urethane (meth) acrylate compound having a (meth) acryloyl group is produced by addition reaction of a polyisocyanate compound, a hydroxyl group-containing compound, and a hydroxyl group-containing (meth) acrylate compound. be able to. In that case, it is preferable that the amount of the raw material used is charged so that the isocyanate group and the hydroxyl group are stoichiometrically equivalent. In particular, by using a diol as a compound containing a hydroxyl group, the (A) urethane (meth) acrylate compound obtained has an advantage that the adhesion and the degree of surface hardening of the cured product are further increased.

  In addition, when manufacturing (A) urethane (meth) acrylate compound, the usage-amount of the (meth) acrylate compound containing a hydroxyl group, the compound containing the said hydroxyl group, and the (meth) acrylate compound containing the said hydroxyl group Is usually 20% by weight or more, preferably 40% by weight or more, and usually 80% by weight or less, preferably 60% by weight or less. Depending on the ratio, the molecular weight of the (A) urethane (meth) acrylate compound obtained can be controlled. If the amount used is too small, curing shrinkage may increase. Moreover, when there is too much usage-amount, a viscosity may increase remarkably.

  The addition reaction between the polyisocyanate compound and the hydroxyl group-containing (meth) acrylate compound can be carried out by any known method as long as the desired (A) urethane (meth) acrylate compound can be produced. For example, a polyisocyanate compound and a (meth) acrylate compound containing a hydroxyl group are usually reacted at 40 ° C. or higher, preferably 50 ° C. or higher, and usually 90 ° C. or lower, preferably 75 ° C. or lower. If the temperature is too low, the desired (A) urethane (meth) acrylate compound may not be produced. If the temperature is too high, the raw material may be decomposed.

  In this case, a catalyst is used as necessary, but this catalyst is preferably mixed with a (meth) acrylate compound containing a hydroxyl group in advance.

  The reaction time is arbitrary as long as the desired (A) urethane (meth) acrylate compound can be produced, but is usually 30 minutes or longer, preferably 1 hour or longer, more preferably 3 hours or longer, and usually 48 hours or shorter, Preferably it is 24 hours or less, More preferably, it is 18 hours or less. If the reaction time is too short, the desired (A) urethane (meth) acrylate compound may not be produced. Moreover, when reaction time is too long, the possibility of coloring and gelling increases.

  As the heating operation, the raw material mixture may be heated to a predetermined temperature, or each raw material and the catalyst used as necessary may be heated to a predetermined temperature alone or in a mixture of two or more. In addition, the heated raw material and a catalyst used as necessary may be mixed. At this time, the heating method, conditions, apparatus, and the like can be arbitrarily determined as long as the effects of the present invention are not significantly impaired.

  The mixing method is arbitrary as long as the effects of the present invention are not significantly impaired. Among them, a mixture of a (meth) acrylate compound containing a hydroxyl group and an addition reaction catalyst is dropped in the presence of a polyisocyanate compound. Is preferred.

  The catalyst for the addition reaction is optional as long as the desired (A) urethane (meth) acrylate compound can be produced. Examples thereof include dibutyltin laurate, dibutyltin dioctoate, dioctyltin dilaurate, and dioctyltin dioctoate. Is preferred. One of these may be used alone, or two or more thereof may be used in any ratio and combination.

  (A) When manufacturing a urethane (meth) acrylate compound, in addition to the above-mentioned materials, other components may be included as long as the effects of the present invention are not significantly impaired. Further, conditions other than those described above can be arbitrarily determined as long as the effects of the present invention are not significantly impaired.

(E. Other)
(A) The urethane (meth) acrylate compound is preferably a highly transparent material. As the highly transparent compound, any compound can be used as long as the effects of the present invention are not significantly impaired. For example, a compound having no aromatic ring is preferable. The radiation-curable composition β and its cured product containing an aromatic ring are colored or intensely colored during storage even if the resulting compound is colored or initially uncolored (so-called yellowing) ) This is considered to be because the double bond part forming the aromatic ring irreversibly changes its structure by the energy rays. For this reason, (A) urethane (meth) acrylate compounds have a structure that does not have an aromatic ring, so there is no deterioration in hue and light transmittance, and there is no need for colorless and transparent applications such as optoelectronics. There are advantages that are particularly suitable for applications in the required applications.

  The (A) urethane (meth) acrylate compound having no aromatic ring contains a polyisocyanate compound having no aromatic ring, a compound containing a hydroxyl group having no aromatic ring, and a hydroxyl group having no aromatic ring ( It can be produced by addition reaction with a (meth) acrylate compound.

  Specific examples of the polyisocyanate compound having no aromatic ring include tetramethylene diisocyanate, hexamethylene diisocyanate, bis (isocyanatomethyl) cyclohexane, cyclohexane diisocyanate, bis (isocyanatocyclohexyl) methane, and isophorone diisocyanate. One of these may be used alone, or two or more thereof may be used in any ratio and combination.

  Specific examples of the compound containing a hydroxyl group having no aromatic ring include alkylene polyol, alkylene polyester, alkylene carbonate polyol and the like. One of these may be used alone, or two or more thereof may be used in any ratio and combination.

  Specific examples of the (meth) acrylate compound containing a hydroxyl group having no aromatic ring include hydroxyalkyl (meth) acrylate and the like. One of these may be used alone, or two or more thereof may be used in any ratio and combination.

  The weight average molecular weight of the (A) urethane (meth) acrylate compound obtained by reacting the above raw materials is usually 1000 or more, preferably 1500 or more, and usually 10,000 or less, preferably 5000 or less. This is because when the weight average molecular weight is within this range, the balance between viscosity and mechanical properties is good.

  Moreover, it is preferable that content of (A) urethane (meth) acrylate compound is 25 weight% or more in the radiation-curable composition (beta), More preferably, it is 30 weight% or more. Moreover, it is preferable that the upper limit is 95 weight% or less, More preferably, it is 90 weight% or less. When there is too little content, the moldability and mechanical strength at the time of forming hardened | cured material will fall, and it may become easy to produce a crack. When there is too much content, the surface hardness of hardened | cured material may fall.

<(B) (A) Monofunctional (meth) acrylate compound other than urethane (meth) acrylate compound>
Monofunctional (meth) acrylate compounds other than (B) (A) urethane (meth) acrylate compounds (hereinafter, simply referred to as “(B) monofunctional acrylate compounds”) as the material for the transparent resin layer b according to the present invention. As for ()) other than the above-mentioned (A) urethane (meth) acrylate compound, any known monofunctional (meth) acrylate compound can be used as long as the effects of the present invention are not significantly impaired. A functional acrylate compound is preferable in that it has excellent surface curability and no tack remains.
Here, the monofunctional is defined as a compound containing one (meth) acryloyl group in the molecule.

  Specific examples of monofunctional (meth) acrylate compounds include (meth) acrylamides such as N, N-dimethyl (meth) acrylamide, hydroxyethyl (meth) acrylate, hydroxypropyl (meth) acrylate, and hydroxybutyl (meth) acrylate. Such as hydroxy (meth) acrylates, (meth) acryloylmorpholine, tetrahydrofurfuryl (meth) acrylate, isobornyl (meth) acrylate, cyclohexyl (meth) acrylate, and (meth) acrylate having a tricyclodecane skeleton And formula (meth) acrylates.

  Among them, (meth) acryloylmorpholine, tetrahydrofurfuryl (meth) acrylate, isobornyl (meth) acrylate, cyclohexyl (meth) acrylate, alicyclic (meth) acrylate such as (meth) acrylate having a tricyclodecane skeleton is preferable, Furthermore, tetrahydrofurfuryl (meth) acrylate, isobornyl (meth) acrylate, cyclohexyl (meth) acrylate, and (meth) acrylate having a tricyclodecane skeleton having high hydrophobicity are preferable.

  One of these (B) monofunctional acrylate compounds may be used alone, or two or more thereof may be used in any ratio and combination.

  The molecular weight of the (B) monofunctional acrylate compound is arbitrary as long as the effect of the present invention is not significantly impaired, but is usually 50 or more, preferably 100 or more, more preferably 150 or more, and usually 1000 or less, preferably 500 or less. When the molecular weight is within this range, there is an advantage that the balance between viscosity and shrinkage is good.

  Further, the content of the (B) monofunctional acrylate compound is preferably 10% by weight or more, more preferably 15% by weight or more, and 70% by weight or less in the radiation curable composition β. More preferably, it is 50 weight% or less, Most preferably, it is 40 weight% or less. If the amount of these (B) monofunctional acrylate compounds is too small, the viscosity of the radiation curable composition β may increase. Moreover, when there are too many, the mechanical physical property as a hardened | cured material (transparent resin layer b) of the radiation-curable composition (beta) may fall.

  The content of the (B) monofunctional acrylate compound with respect to 100 parts by weight of the sum of the (A) urethane (meth) acrylate compound, the (B) monofunctional acrylate compound, and the later-described (C) polyfunctional acrylate compound is usually It is 10 parts by weight or more, preferably 20 parts by weight or more, more preferably 30 parts by weight or more, and usually 70 parts by weight or less, preferably 50 parts by weight or less, more preferably 40 parts by weight or less. (B) When there are few monofunctional acrylate compounds, while a viscosity will rise and workability | operativity will fall remarkably, there exists a tendency for a cure rate to fall and for a tack | tuck to remain easily. On the other hand, if the amount is too large, the mechanical properties of the optical recording medium of the present invention tend to deteriorate.

<(C) (A) Polyfunctional (meth) acrylate compound other than urethane (meth) acrylate compound>
Polyfunctional (meth) acrylate compounds other than (C) (A) urethane (meth) acrylate compounds (hereinafter referred to simply as “(C) polyfunctional acrylate compounds”) as the material for the transparent resin layer b according to the present invention. .) Can be any known polyfunctional (meth) acrylate compound other than the (A) urethane (meth) acrylate compound as long as the effects of the present invention are not significantly impaired. An acrylate compound is preferable from the viewpoint of excellent surface curability.
Here, polyfunctionality is defined as a compound containing two or more (meth) acryloyl groups in the molecule.

  Specific examples of the (C) polyfunctional (meth) acrylate compound include alicyclic poly (meth) acrylate, alicyclic poly (meth) acrylate, and aromatic poly (meth) acrylate.

(C) Specific examples of polyfunctional (meth) acrylate compounds include polyethylene glycol di (meth) acrylate, 1,2-polypropylene glycol di (meth) acrylate, 1,3-polypropylene glycol di (meth) acrylate, polytetra Methylene glycol di (meth) acrylate, 1,2-polybutylene glycol di (meth) acrylate, polyisobutylene glycol di (meth) acrylate, bisphenol A, bisphenol F, or bisphenol S such as ethylene oxide, propylene oxide, or Di (meth) acrylates of alkylene oxide adducts such as butylene oxide, hydrogenated derivatives of bisphenols such as bisphenol A, bisphenol F, or bisphenol S ) Acrylate, block of various polyether polyol compounds and other compounds, or (meth) acrylates having a polyether skeleton such as di (meth) acrylate of random copolymer, and hexanediol di (meth) acrylate, Nonanediol di (meth) acrylate, decanediol di (meth) acrylate, 2,2-bis [4- (meth) acryloyloxyphenyl] propane, 2,2-bis [4- (2- (meth) acryloyloxyethoxy) ) Phenyl] propane, bis (hydroxymethyl) tricyclo [5.2.1.0 ^2,6 ] decane = dimethacrylate, p-bis [β- (meth) acryloyloxyethylthio] xylylene, 4,4′-bis 2 such as [β- (meth) acryloyloxyethylthio] diphenylsulfone (Meth) acrylates, trimethylolpropane tris (meth) acrylate, glycerol tris (meth) acrylate, trivalent (meth) acrylates such as pentaerythritol tris (meth) acrylate, pentaerythritol tetrakis (meth) acrylate, etc. Indefinite polyvalent (meth) acrylates such as tetravalent (meth) acrylates, pentavalent or higher (meth) acrylates such as dipentaerythritol hexa (meth) acrylate, and the like.

Among these, the above-mentioned divalent (meth) acrylates are preferable in terms of controllability of the cross-linking formation reaction. As specific examples of the divalent (meth) acrylates, alicyclic poly (meth) acrylate, alicyclic poly (meth) acrylate and the like are preferable. Furthermore, hexanediol di (meth) acrylate, nonanediol di ( Preferred are (meth) acrylate and bis (hydroxymethyl) tricyclo [5.2.1.0 ^2,6 ] decane = dimethacrylate.

  Trifunctional or higher functional (meth) acrylates are preferably used for the purpose of improving the heat resistance of the cross-linked structure of the cured product and the surface hardness. Specific examples thereof include trimethylolpropane tris (meth) acrylate, pentaerythritol tris (meth) acrylate, dipentaerythritol hexa (meth) acrylate and the like exemplified above and trifunctional (meth) having an isocyanurate skeleton. ) Acrylate and the like.

  The molecular weight of these (C) polyfunctional acrylate compounds is arbitrary as long as the effect of the present invention is not significantly impaired, but is usually 50 or more, preferably 100 or more, and usually 1000 or less, preferably 500 or less. When the molecular weight is within this range, there is an advantage that the balance between viscosity and shrinkage is good.

  Moreover, it is preferable that content of (C) polyfunctional acrylate compound is 1 weight% or more in the radiation-curable composition (beta), More preferably, it is 1.5 weight% or more. The upper limit is usually preferably 30% by weight or less, more preferably 15% by weight or less, and particularly preferably 7% by weight or less. If the amount of these (C) polyfunctional acrylate compounds is too small, the elastic modulus of the radiation curable composition β may be too low. If the amount is too large, the deformation of the optical recording medium may be significantly increased.

  In addition, (C) a polyfunctional acrylate compound may be used individually by 1 type, and may be used 2 or more types by arbitrary ratios and combinations.

  The content of the (C) polyfunctional acrylate compound with respect to 100 parts by weight of the sum of the (A) urethane (meth) acrylate compound, (B) monofunctional acrylate compound, and (C) polyfunctional acrylate compound is preferably 1 Part by weight or more, more preferably 5 parts by weight or more, preferably 30 parts by weight or less, more preferably 20 parts by weight or less. (C) If the polyfunctional acrylate compound is small, the surface hardness of the optical recording medium tends to decrease, and if it is too large, the deformation of the optical recording medium with respect to changes in environmental temperature and humidity may be remarkably increased.

<Polymerization initiator>
The radiation curable composition β preferably contains a polymerization initiator in order to initiate a polymerization reaction that proceeds by radiation (for example, active energy rays, ultraviolet rays, electron beams, etc.). Especially, when a radiation is an active energy ray and an ultraviolet-ray, it is especially preferable that a polymerization initiator is included. As the polymerization initiator, a radical generator that is a compound having a property of generating radicals by light is generally used, and any known radical generator can be used as long as the effects of the present invention are not significantly impaired. .

  Specific examples of such radical generators include benzophenone, 2,4,6-trimethylbenzophenone, 4,4-bis (diethylamino) benzophenone, 4-phenylbenzophenone, methylorthobenzoylbenzoate, thioxanthone, diethylthioxanthone, isopropylthioxanthone. Chlorothioxanthone, 2-ethylanthraquinone, t-butylanthraquinone, diethoxyacetophenone, 2-hydroxy-2-methyl-1-phenylpropan-1-one, benzyldimethyl ketal, 1-hydroxycyclohexyl phenyl ketone, benzoin methyl ether, Benzoin ethyl ether, benzoin isopropyl ether, benzoin isobutyl ether, methylbenzoyl formate, 2-methyl-1- [4 (Methylthio) phenyl] -2-morpholinopropan-1-one, 2,6-dimethylbenzoyldiphenylphosphine oxide, 2,4,6-trimethylbenzoyldiphenylphosphine oxide, bis (2,6-dimethoxybenzoyl) -2,4 , 4-Trimethylpentylphosphine oxide, bis (2,4,6-trimethylbenzoyl) phenylphosphine oxide, 2-hydroxy-1- [4- [4- (2-hydroxy-2-methyl-propionyl) -benzyl]- Phenyl] -2-methyl-propan-1-one and the like.

  Among them, 1-hydroxycyclohexyl phenyl ketone, 2,4,6-trimethylbenzoyldiphenylphosphine oxide, and 2-hydroxy-1- [4- [4- (2-hydroxy-2-methyl-propionyl) -benzyl]- Phenyl] -2-methyl-propan-1-one is preferred.

  Further, since the curing speed is high and the crosslinking density can be sufficiently increased, among the above radical generators, benzophenone, 2-hydroxy-2-methyl-1-phenylpropan-1-one, 1-hydroxycyclohexylphenyl Ketone, 2-hydroxy-1- [4- [4- (2-hydroxy-2-methyl-propionyl) -benzyl] -phenyl] -2-methyl-propan-1-one, 2,4,6-trimethylbenzoyl Diphenylphosphine oxide is particularly preferred.

  When the cured product of the radiation curable composition β according to the present invention is used for an optical recording medium using a laser having a wavelength of 380 to 800 nm as a light source, the laser beam necessary for reading sufficiently passes through the light transmitting layer. Thus, it is preferable to select and use the type and amount of the radical generator. In this case, it is particularly preferable to use a short-wavelength photosensitive radical generator in which the obtained light transmission layer hardly absorbs laser light.

  Among the above radical generators, such short wavelength photosensitive radical generators include benzophenone, 2,4,6-trimethylbenzophenone, 4-phenylbenzophenone, methylorthobenzoylbenzoate, diethoxyacetophenone, 2-hydroxy Examples include 2-methyl-1-phenylpropan-1-one, benzyldimethyl ketal, 1-hydroxycyclohexyl phenyl ketone, benzoin methyl ether, benzoin ethyl ether, benzoin isopropyl ether, benzoin isobutyl ether, and methyl benzoyl formate. Among them, those having a hydroxyl group such as 1-hydroxycyclohexyl phenyl ketone are particularly preferable.

  In addition, a radical generator may be used individually by 1 type, and may be used 2 or more types by arbitrary ratios and combinations.

  Moreover, the usage-amount of a radical generator with respect to the sum total of 100 weight part of (A) urethane (meth) acrylate compound, (B) monofunctional acrylate compound, and (C) polyfunctional acrylate compound is 0.1 weight normally. Part or more, preferably 1 part by weight or more, more preferably 2 parts by weight or more, and usually 10 parts by weight or less, preferably 9 parts by weight or less, more preferably 7 parts by weight or less. If the amount used is too small, the radiation curable composition β may not be sufficiently cured. Moreover, when there is too much usage-amount, a superposition | polymerization reaction will advance rapidly and it may not only increase an optical distortion but a hue may also deteriorate.

  Any component may be used in combination with these radical generators as long as the effects of the present invention are not significantly impaired. For example, known sensitizers such as methyl 4-dimethylaminobenzoate, ethyl 4-dimethylaminobenzoate, amyl 4-dimethylaminobenzoate and 4-dimethylaminoacetophenone can be used in combination. A sensitizer may be used individually by 1 type and may be used 2 or more types by arbitrary ratios and combinations.

  When a benzophenone-based polymerization initiator is used as the polymerization initiator, the benzophenone-based compound is added to 100 parts by weight of the total of (A) urethane (meth) acrylate compound, (B) monofunctional acrylate compound, and (C) polyfunctional acrylate compound. The amount of the polymerization initiator used is usually 0.5 parts by weight or more, preferably 2 parts by weight or less, more preferably 1 part by weight or less. When the amount of the benzophenone-based polymerization initiator is large, the volatile components in the cured product increase, and the film thickness under a high temperature and high humidity environment may decrease.

  In addition, when starting a polymerization reaction with an electron beam as radiation, although the said radical generator can also be used, it is preferable not to use a radical generator and other polymerization initiators. This is because sufficient curing can be achieved without using a polymerization initiator.

Examples of the polymerization initiator other than the radical generator include an oxidizing agent.
One of these polymerization initiators may be used alone, or two or more thereof may be used in any ratio and combination.

  The polymerization initiator may contain impurities such as a chlorine atom, a sulfur atom, a phosphorus atom, and a sodium atom, but such an impurity content is preferably small. Each content is preferably 100 ppm or less, more preferably 50 ppm or less. If the amount of impurities is too large, a cured product of the desired radiation curable composition β may not be obtained.

<Compound containing epoxy group>
For the purpose of improving the signal characteristics of the optical recording medium of the present invention, the radiation curable composition β may contain a compound containing one or more epoxy groups. The epoxy group may be contained in any form and method.

  The compound containing at least one epoxy group according to the present invention is not particularly limited as long as it is a compound having an epoxy group. Specific examples include polyphenols such as bisphenol A, bisphenol F, bisphenol S, phenol or alkylphenol novolacs; glycols; glycidyl ether type epoxy resins obtained by glycidylation of polyhydric alcohols such as trimethylolpropane; adipic acid Glycidyl ester type epoxy resins obtained by glycidylation of polycarboxylic acids such as phthalic acid; glycidyl amine type epoxy resins obtained by glycidylation of polyamines such as diaminodiphenylmethane, diaminodiphenylsulfone and isocyanurate; aminophenols, aminoalkylphenols, etc. Glycidylaminoglycidyl ether type epoxy resin obtained by glycidylation of 3,4-epoxy-6-methylcyclohexyl-3,4-epoxy 6-methyl cyclohexyl carboxylate, alicyclic epoxides such as 3,4-epoxycyclohexylmethyl-3,4-epoxycyclohexyl carboxylate; and the like.

  The compound which contains 1 or more of these epoxy groups in a molecule | numerator may be used individually by 1 type, and may be used 2 or more types by arbitrary ratios and combinations.

<Auxiliary component>
The radiation curable composition β according to the present invention may contain an auxiliary component such as an additive, if necessary, as long as the effects of the present invention are not significantly impaired.
Specific examples of the auxiliary components include stabilizers such as antioxidants, heat stabilizers, or light absorbers; glass fibers, glass beads, silica, alumina, zinc oxide, titanium oxide, mica, talc, kaolin, metal fibers, fillers metal powders and the like; carbon fiber, carbon black, graphite, carbon nanotube, a carbon material such as fullerene such as C ₆₀ (fillers, referred to as an inorganic component are collectively a carbon material such.); charge Modifiers such as inhibitors, plasticizers, mold release agents, antifoaming agents, leveling agents, anti-settling agents, surfactants, thixotropy imparting agents; colorants such as pigments, dyes, hue modifiers; monomers and And / or oligomers thereof, or curing agents, catalysts, curing accelerators, and the like necessary for the synthesis of the inorganic component. These auxiliary components may be used alone or in combination of two or more. These ratios and combinations may be used. The content of these auxiliary components is usually 20% by weight or less, preferably 10% by weight or less, more preferably 5% by weight or less of the radiation curable composition β.

  Among these, silica as fillers will be described in detail. The silica used for the radiation curable composition β refers to silicon oxide in general, and it does not matter whether it is a ratio of silicon and oxygen or whether it is crystalline or amorphous. Examples of the silica particles include industrially produced silica particles dispersed in a solvent, or powdered silica particles; silica particles derived and synthesized from raw materials such as alkoxysilanes, and the like. Can do. Among them, when used in the radiation curable composition β, silica particles dispersed in a solvent or silica particles derived and synthesized from a raw material such as alkoxysilane are used for ease of mixing and dispersion. preferable.

  Although the particle diameter of the silica particles is arbitrary, the number average particle diameter measured by morphological observation using a TEM (transmission electron microscope) or the like is preferably 0.5 nm or more, more preferably 1 nm or more, Further, it is preferably 50 nm or less, more preferably 30 nm or less, further preferably 15 nm or less, particularly preferably 10 nm or less, and particularly preferably 6 nm or less. The silica particles are preferably ultrafine particles, but if they are too small, the cohesiveness of the ultrafine particles is extremely increased, and the transparency and mechanical strength of the cured product tend to be extremely decreased. This is because the characteristics tend not to be remarkable.

<1-2-2. Method for producing radiation curable composition β>
The radiation curable composition β includes the (A) polyisocyanate compound, (B) monofunctional acrylate compound, and (C) polyfunctional acrylate compound, and the polymerization initiator and auxiliary components used as necessary. It is prepared by stirring and mixing uniformly while blocking radiation.

  The order of mixing the components at that time is not limited, but it is preferable to add the high viscosity liquid component and / or solid component to the low viscosity liquid component and stir. The polymerization initiator is preferably added last.

Moreover, the stirring conditions in that case are not limited. The stirring temperature is usually normal temperature, but may be heated to a temperature of usually 90 ° C. or lower, preferably 70 ° C. or lower.
The stirring speed is usually 100 rpm or more, preferably 300 rpm or more, and usually 1000 rpm or less.
The stirring time is usually 10 seconds or longer, preferably 3 hours or longer, and usually 24 hours or shorter.

<1-3. Transparent resin layer a>
Hereinafter, the material for the transparent resin layer a and the radiation curable composition α will be described. In addition, about the manufacturing method of the transparent resin layer a using the radiation curable composition (alpha), it is <1-4. The method for forming the protective layer is described below.

<1-3-1. Material for transparent resin layer a>
Any material can be used as the material for the transparent resin layer a as long as the effects of the present invention are not significantly impaired. In order to form the transparent resin layer a, it is preferable to use a liquid composition (radiation curable composition α) in which a material for the transparent resin layer a having radiation curability is mixed, as in the transparent resin layer b. .

  The material for the transparent resin layer a is preferably a radiation curable compound containing the (A) urethane (meth) acrylate compound. Furthermore, although the (B) monofunctional acrylate compound may be used as the material for the transparent resin layer a, it is preferable not to use the (B) monofunctional acrylate compound or to reduce it as much as possible. Moreover, it is preferable to use the said (C) polyfunctional acrylate compound as a material for transparent resin layer a. Moreover, the other component may be contained.

<(A) Urethane (meth) acrylate compound>
The (A) urethane (meth) acrylate compound as the material for the transparent resin layer a according to the present invention is usually a polyisocyanate compound, a compound containing a hydroxyl group, and a hydroxyl group, like the material for the transparent resin layer b. It is obtained by reacting with a (meth) acrylate compound containing (A) As a urethane (meth) acrylate compound, a urethane acrylate compound is preferable. This is because the surface curability is excellent and tack is difficult to remain.
(A) A urethane (meth) acrylate compound may be used individually by 1 type, and may use 2 or more types by arbitrary combinations and a ratio.

(A. Polyisocyanate compound)
As the polyisocyanate compound, the same compound as the transparent resin layer b can be used. Among them, a compound containing an isocyanate skeleton that is a multimer such as tetramethylene diisocyanate and hexamethylene diisocyanate is an optical recording medium of the present invention. This is preferable because the signal characteristics are less likely to deteriorate.
A polyisocyanate compound may be used individually by 1 type, and may be used 2 or more types by arbitrary ratios and combinations.

(B. Compound containing a hydroxyl group)
As the compound containing a hydroxyl group, the same compound as that of the transparent resin layer b can be used. Among them, a polyether polyol compound capable of introducing a polyether skeleton and a polyester polyol compound capable of introducing a polyester skeleton are preferable.
The compound containing a hydroxyl group may be used individually by 1 type, and may be used 2 or more types by arbitrary ratios and combinations.

(C. (Meth) acrylate compound containing hydroxyl group)
As the (meth) acrylate compound containing a hydroxyl group, the same compound as the transparent resin layer b can be used.
As the (meth) acrylate compound containing a hydroxyl group, one type may be used alone, or two or more types may be used in any ratio and combination.

(D. (A) Method for producing urethane (meth) acrylate compound)
The (A) urethane (meth) acrylate compound as the material for the transparent resin layer a according to the present invention is the same method as the (A) urethane (meth) acrylate compound as the material for the transparent resin layer b according to the present invention. Can be manufactured.

(E. Other)
(A) The urethane (meth) acrylate compound is preferably a highly transparent material. As the highly transparent compound, any compound can be used as long as the effects of the present invention are not significantly impaired. For example, it is a compound having no aromatic ring in the same manner as the material for the transparent resin layer b. preferable.
The weight average molecular weight of the (A) urethane (meth) acrylate compound is usually 500 or more, preferably 800 or more, and usually 5000 or less, preferably 2000 or less. This is because when the weight average molecular weight is within this range, both low cure shrinkage and high surface durability can be achieved.

<(B) (A) Monofunctional (meth) acrylate compound other than urethane (meth) acrylate compound>
(B) As the monofunctional acrylate compound, the same compound as the transparent resin layer b can be used, but the content is small or preferably not contained. (B) One type of monofunctional acrylate compound may be used alone, or two or more types may be used in any combination and ratio.
Specifically, the preferred content is usually 30 weights per 100 parts by weight of the total of (A) urethane (meth) acrylate compound, (B) monofunctional acrylate compound, and (C) polyfunctional acrylate compound described later. Part or less, preferably 20 parts by weight or less, more preferably 10 parts by weight or less, and still more preferably 0 parts by weight. When the content of (B) is too large, the surface of the optical recording medium on the protective layer side tends to be deformed with respect to local pressure, and the signal characteristics tend to deteriorate due to the influence.

<(C) (A) Polyfunctional (meth) acrylate compound other than urethane (meth) acrylate compound>
(C) As a polyfunctional acrylate compound, the compound similar to the said transparent resin layer b can be used.
Among them, polyalkylene glycol skeletons such as polyethylene glycol di (meth) acrylate, 1,2-polypropylene glycol di (meth) acrylate, 1,3-polypropylene glycol di (meth) acrylate, polytetramethylene glycol di (meth) acrylate, etc. (Meth) acrylate, hexanediol di (meth) acrylate, nonanediol di (meth) acrylate, bis (hydroxymethyl) tricyclo [5.2.1.0 ^2,6 ] decane = dimethacrylate, trimethylolpropane tri (meta ) Aliphatic (meth) acrylates such as acrylate, pentaerythritol tetrakistri (meth) acrylate, pentaerythritol tetrakistetra (meth) acrylate, dipentaerythritol hexa (meth) acrylate, etc. Over preparative and these polyalkylene glycol modified products are particularly preferred.
(C) One type of polyfunctional acrylate compound may be used alone, or two or more types may be used in any combination and ratio.

  Particularly in the radiation curable composition α, the (C) polyfunctional (meth) acrylate preferably contains a trifunctional or higher functional (meth) acrylate compound. Specifically, aliphatic (meth) such as trimethylolpropane tri (meth) acrylate, pentaerythritol tetrakistri (meth) acrylate, pentaerythroletetrakistetra (meth) acrylate, dipentaerystol hexa (meth) acrylate, etc. Acrylates and their modified polyalkylene glycols. The content of the trifunctional or higher functional (meth) acrylate compound is preferably 10% by weight or more, more preferably 20% by weight or more, and preferably 90% by weight or less, more preferably 80% in the polyfunctional (meth) acrylate. % By weight or less.

  In addition, (C) a polyfunctional acrylate compound may be used individually by 1 type, and may be used 2 or more types by arbitrary ratios and combinations.

  Moreover, it is preferable that content of (C) polyfunctional acrylate compound is 15 weight% or more in the radiation-curable composition (alpha), More preferably, it is 20 weight% or more, More preferably, it is 25 weight% or more. The upper limit is usually preferably 90% by weight or less, more preferably 70% by weight or less, still more preferably 50% by weight or less, and particularly preferably 35% by weight or less. If the amount of these (C) polyfunctional acrylate compounds is too small, the surface of the protective layer side of the optical recording medium tends to be deformed with respect to local pressure, and the signal characteristics tend to deteriorate due to the influence. On the other hand, if the amount is too large, there is a possibility that the deformation of the optical recording medium with respect to environmental temperature and humidity changes will increase significantly.

  The content of (C) polyfunctional acrylate compound with respect to the sum of (A) urethane (meth) acrylate compound, (B) monofunctional acrylate compound, and (C) polyfunctional acrylate compound is preferably 15 parts by weight or more. More preferably, it is 20 parts by weight or more, more preferably 25 parts by weight or more, preferably 90 parts by weight or less, more preferably 70 parts by weight or less, still more preferably 50 parts by weight or less, particularly preferably 35 parts by weight or less. is there. If the polyfunctional acrylate compound is small, the surface hardness of the optical recording medium tends to decrease. If the polyfunctional acrylate compound is too large, the deformation of the optical recording medium with respect to changes in environmental temperature and humidity may be remarkably increased.

<Polymerization initiator>
The radiation curable composition α according to the present invention preferably contains a radical generator as a polymerization initiator in order to initiate a polymerization reaction that proceeds by radiation. Specific examples of the radical generator include compounds similar to the compounds that can be used for the transparent resin layer b.
One type of polymerization initiator may be used alone, or two or more types may be used in any combination and ratio.

  The amount of radical generator used is usually 0.1 parts by weight or more relative to 100 parts by weight of the total of (A) urethane (meth) acrylate compound, (B) monofunctional acrylate compound, and (C) polyfunctional acrylate compound. 1 part by weight or more, preferably 10 parts by weight or less, preferably 6 parts by weight or less, more preferably 4 parts by weight or less, particularly preferably 2.5 parts by weight or less. If the amount used is too small, the radiation curable composition α may not be sufficiently cured. In addition, if the amount used is too large, the polymerization reaction proceeds rapidly and not only increases optical distortion, but also the hue deteriorates, or the surface of the protective layer side of the optical recording medium is not subjected to local pressure. Therefore, the signal characteristics tend to be deteriorated easily.

<Compound containing epoxy group>
For the purpose of improving the signal characteristics of the optical recording medium of the present invention, the radiation curable composition α may contain a compound containing one or more epoxy groups. The epoxy group may be contained in any form and method.

Specific examples of the compound containing one or more epoxy groups in the molecule according to the present invention include compounds similar to the compounds that can be used for the transparent resin layer b.
A compound containing one or more epoxy groups in the molecule may be used alone, or two or more may be used in any ratio and combination.

<1-3-2. Method for producing radiation curable composition α>
The radiation curable composition α can be produced by the same method as the radiation curable composition β.

<1-4. Method for forming protective layer>
The manufacturing method of a protective layer is arbitrary as long as a desired protective layer can be formed. For example, the transparent resin layer b material (radiation curable composition β) is applied onto a substrate of an optical recording medium, and a polymerization reaction is started by irradiating with radiation (active energy rays or electron beams). It can be manufactured by performing “radiation curing” and subsequently applying and radiation curing the material for the projection resin layer a (radiation curable composition α). There is no restriction | limiting in the said coating method, For example, it can be set as general methods, such as a spin coat method.

  In addition, after forming a reflective layer and a recording layer on a board | substrate, you may form said transparent resin material a, and form another layer between the transparent resin layer a and the transparent resin layer b. Also good. Even in such a case, it is preferable to cure the transparent resin layer a and the transparent resin layer b using a polymerization reaction by irradiating radiation.

  There is no limitation on the type of polymerization reaction of the radiation curable composition α and the radiation curable composition β (hereinafter, these two types may be simply referred to as “radiation curable composition”). Known polymerization formats such as radical polymerization, anionic polymerization, cationic polymerization, and coordination polymerization can be used. Among these examples of polymerization modes, a particularly preferable polymerization mode is radical polymerization. This is because in radical polymerization, it is presumed that the homogeneity of the product is increased by starting the polymerization reaction in the polymerization system in a uniform and short time.

  Here, the radiation refers to an electromagnetic wave (gamma ray, X-ray, ultraviolet ray, visible ray, infrared ray, which acts on a polymerization initiator that initiates a necessary polymerization reaction and generates a chemical species that initiates the polymerization reaction. Microwave, etc.) or particle beam (electron beam, α-ray, neutron beam, various atomic beams, etc.). An example of the radiation preferably used in the present invention is preferably ultraviolet rays, visible rays, and electron beams, and particularly preferably ultraviolet rays and electron beams because energy and a general-purpose light source can be used.

  When ultraviolet rays are used as radiation, it is preferable to use a photo radical generator that generates radicals by ultraviolet rays as the polymerization initiator. At this time, you may use a sensitizer together as needed. The wavelength of the ultraviolet ray is usually 200 nm or more, preferably 240 nm or more, and usually 400 nm or less, preferably 350 nm or less.

  As a device for irradiating ultraviolet rays, a known device such as a high-pressure mercury lamp, a metal halide lamp, or an ultraviolet lamp having a structure for generating ultraviolet rays by microwaves can be preferably used. The output of the apparatus is usually 10 W / cm or more, preferably 30 W / cm or more, and usually 200 W / cm or less, preferably 180 W / cm or less. The apparatus is usually 5 cm or more, preferably Is preferably set at a distance of 30 cm or more, and usually 80 cm or less, preferably 60 cm or less, because there is little light deterioration, thermal deterioration, thermal deformation, etc. of the irradiated object.

  The radiation curable composition can be cured preferably by an electron beam, and a cured product having excellent mechanical properties, particularly tensile elongation properties, can be obtained. When an electron beam is used, the light source and the irradiation device are expensive, but there are advantages that the use of a polymerization initiator can be omitted and that the polymerization is not hindered by oxygen and therefore the surface hardness is good. An electron beam irradiation apparatus used for electron beam irradiation is not particularly limited, and examples thereof include a curtain type, an area beam type, a broad beam type, and a pulse beam type. The acceleration voltage upon electron beam irradiation is usually 10 kV or more, preferably 100 kV or more, and usually 1000 kV or less, preferably 200 kV or less.

These radiation, the irradiation intensity, usually 0.1 J / cm ² or more, preferably 0.2 J / cm ² or more, and generally 20 J / cm ² or less, preferably 10J / cm ² or less, more preferably 5 J / Irradiation is performed at cm ² or less, more preferably 3 J / cm ² or less, and particularly preferably ² J / cm ² or less. If irradiation intensity is in this range, it can select suitably by the kind of radiation-curable composition.

  The irradiation time of radiation is usually 1 second or longer, preferably 10 seconds or longer, and usually 3 hours or shorter, and preferably 1 hour or shorter from the viewpoint of reaction promotion and productivity. When the irradiation energy or irradiation time of radiation is extremely small, the heat resistance and mechanical properties of the protective layer may not be sufficiently exhibited due to incomplete polymerization. On the other hand, when it is extremely excessive, deterioration such as yellowing caused by light deterioration may occur.

  The irradiation with the radiation may be performed in one stage or may be performed in a plurality of stages. As the radiation source, a diffusion radiation source in which radiation spreads in all directions is usually used. The irradiation of radiation is usually carried out with the radiation source fixed and stationary in a state where the disk coated with the radiation curable composition is fixed and stationary or conveyed by a conveyor.

The elastic modulus of the transparent resin layer b and the transparent resin layer a is controlled by (A) the molecular chain length of the compound containing the hydroxyl group constituting the urethane (meth) acrylate compound, and (C) the polyfunctional acrylate compound. The content can be changed by changing the number of functional groups and the number of functional groups.
In order to increase the elastic modulus, (A) the molecular chain of the hydroxyl group-containing compound constituting the urethane (meth) acrylate compound is shortened, (C) the content of the polyfunctional acrylate compound is increased, (C ) This is made possible by increasing the number of functional groups in the polyfunctional acrylate compound. Conversely, in order to lower the elastic modulus, (A) the molecular chain of the compound containing the hydroxyl group constituting the urethane (meth) acrylate compound is lengthened. Or (C) by reducing the content of the polyfunctional acrylate compound, or (C) by reducing the number of functional groups of the polyfunctional acrylate compound.

[2. Hard coat layer]
In the optical recording medium of the present invention, a hard coat layer may be further formed on the protective layer. The hard coat layer in this case is not limited as long as the surface hardness is B or more, and a known hard coat layer in a general optical recording medium can be used. The surface hardness of the hard coat layer in the present invention is preferably B or more, more preferably HB or more, further preferably F or more, and particularly preferably H or more.
The surface hardness can be measured by a pencil hardness test in accordance with JIS K5400.

  The light transmittance of the hard coat layer at a wavelength of 550 nm is usually 80% or more, preferably 85% or more, more preferably 88% or more. Moreover, the contact angle with respect to water is 90 degrees or more, More preferably, it is 100 degrees or more. Thereby, the antifouling property of the optical recording medium can be increased. The measurement of the contact angle with respect to water can be carried out by a known method using a contact angle meter or the like.

  The thickness of the hard coat layer is arbitrary as long as the effect of the present invention is not significantly impaired, but is usually 0.5 μm or more, preferably 1 μm or more, more preferably 1.5 μm or more. Moreover, it is 5 micrometers or less normally, Preferably it is 3 micrometers or less, More preferably, it is 2 micrometers or less. If the film thickness is too thin, the surface hardness may decrease, and if it is too thick, cracks may easily occur.

  The hard coat layer according to the present invention preferably has antifouling properties such as a high contact angle with water. As a material for the hard coat layer having antifouling properties (hereinafter sometimes referred to as “hard coat agent” as appropriate), any known material can be used as long as the effects of the present invention are not significantly impaired. Among these, a radiation curable composition containing a silicone compound and / or a fluorine compound and an inorganic component such as a polyfunctional (meth) acrylate monomer, an epoxy compound, and inorganic nanoparticles is preferably used as a stain resistance imparting agent. Specific examples of the stain resistance imparting agent include, for example, a polymer having a silicone skeleton such as an organopolysiloxane skeleton, a radiation curable compound having a silicone skeleton and an acrylic group, and a silicone compound such as a silicone surfactant. , Fluorine-containing polymers, radiation-curable compounds having fluorine atoms and acrylic groups, and fluorine compounds such as fluorine-based surfactants. As the stain resistance imparting agent, one kind may be used alone, and two kinds or more may be used in optional ratio and combination.

  However, in the case of a high recording density medium such as an optical recording medium using a blue laser, since the laser spot diameter is small, it is sensitive to dirt such as fingerprints, dust, and dust. In particular, for dirt containing organic substances such as fingerprints, if the dirt adheres to the surface on the laser beam incident side of the medium, there is a possibility of causing a great influence such as a recording / reproducing error by the laser, and it is difficult to remove it. Sometimes. Accordingly, the hard coat agent that can be used in the present invention is an active energy ray-curable hard coat agent containing a silicone compound and / or a fluorine compound as a stain resistance imparting agent (hereinafter, referred to as “hard coat agent” as appropriate). In particular, it is preferable to contain the antifouling agent having active energy ray curability. The silicone compound is preferably polysiloxane.

  Preferable specific examples of the hard coat agent include, for example, (1) a hard coat agent containing an active energy ray-curable silicone compound and / or a fluorine compound at the terminal and not containing an inorganic component, and (2) active energy ray cure. Hard coat agent containing a polymer containing a functional group and a silicone unit and / or an organic fluorine group unit, (3) a hard containing a silicone compound and / or a fluorine compound having an active energy ray-curable group in the side chain Coating agents. In addition, these hard coat agents may be used individually by 1 type, and may be used 2 or more types by arbitrary ratios and combinations.

  In addition, the coating method of the material used for forming a hard-coat layer is not limited, For example, it can be set as general coating methods, such as a spin coat method. Moreover, it does not limit about the radiation used for hardening of said radiation-curable material etc., For example, it can carry out similarly to the radiation used in the case of formation of a protective layer.

[3. Back layer]
The optical recording medium of the present invention may have a back layer formed on the surface opposite to the recording / reproducing functional layer when viewed from the substrate. The back layer used in the present invention can be arbitrarily formed as long as the effects of the present invention are not significantly impaired, but the elastic modulus at 25 ° C. is preferably within a predetermined range, and specifically, the upper limit is It is 2000 MPa or less, preferably 1500 MPa or less. Moreover, although there is no restriction | limiting in a minimum, it is preferable that it is higher than the elasticity modulus of a protective layer. If the elastic modulus of the back layer is too high, the optical recording medium may be deformed excessively with respect to temperature changes. The method for measuring the elastic modulus can be the same as the method for measuring the elastic modulus of the protective layer, and can be measured by a method based on JIS K7127.

  The film thickness of the back layer is not limited as long as the effect of the present invention is not significantly impaired, but is usually 3 μm or more, preferably 5 μm or more, more preferably 10 μm or more, and usually 50 μm or less, preferably 30 μm or less, more preferably 20 μm. Hereinafter, it is more preferably 15 μm or less. If the thickness of the back layer is too small, the effect of suppressing deformation of the optical recording medium due to the back layer formation tends to be hardly exhibited. On the other hand, if the recording medium is too large, the optical recording media may be easily brought into contact with each other when stored, and the appearance may be impaired, and an error may easily occur during reading of the recording.

  The material used for forming the back layer is not limited as long as the effects of the present invention are not significantly impaired. Specifically, generally known materials can be used for the back layer, and for example, the same material as the above-described protective layer can be used, but a material capable of obtaining the elastic modulus is selectively used. It is preferable. As such a material, it is particularly preferable to use a radiation-curable compound used for forming the protective layer.

  In addition, the coating method of the said radiation-curable compound used when forming a back layer is not limited, For example, it can be set as general coating methods, such as a spin coat method. Moreover, it is not limited about the radiation used for hardening of the compound which has the said radiation curing property, For example, it can carry out similarly to the radiation used in the case of formation of a protective layer.

  In the optical recording medium of the present invention, a thin film such as an inorganic layer is formed on the surface opposite to the recording / reproducing functional layer of the substrate by a technique such as sputtering for the purpose of suppressing deformation of the optical recording medium with respect to temperature change. However, it is preferably not formed from the viewpoint of cost.

[4. substrate]
There is no restriction | limiting about the resin substrate used for this invention, A well-known thing can be used arbitrarily as a resin substrate of an optical recording medium. The shape of the resin substrate of the optical recording medium is arbitrary, but is usually formed in a disc shape.

  Further, the material of the resin substrate is not limited as long as it is a light transmissive material. That is, it can be formed of any material that can transmit light having a wavelength used for recording and reproducing optical information. Specific examples thereof include thermoplastic resins such as polycarbonate resin, polymethacrylate resin, and polyolefin resin. Among these, polycarbonate resin is particularly widely used in CD-ROMs and the like, and is particularly preferable because it is inexpensive. In addition, the material of a resin substrate may be used individually by 1 type, and may use 2 or more types together by arbitrary combinations and a ratio.

Further, the dimensions of the resin substrate are not limited and are arbitrary. However, the thickness of the resin substrate is usually 0.1 mm or more, preferably 0.3 mm or more, more preferably 0.5 mm or more, and usually 20 mm or less, preferably 15 mm or less, more preferably 3 mm or less. Among them, a resin substrate having a thickness of about 1.2 ± 0.2 mm is often used. The outer diameter of the resin substrate is generally about 120 mm.
Moreover, although there is no restriction | limiting in the manufacturing method of a resin substrate, it is arbitrary, For example, it can manufacture by injection molding of a light transmissive resin, etc.

[5. Reflective layer / recording layer]
The reflective layer of the optical recording medium of the present invention is formed by sputtering a material containing a metal such as aluminum, silver, or gold.
The recording layer of the optical recording medium of the present invention is preferably a concavo-convex layer formed on a substrate, or a layer containing a phase change material or an organic dye.
A plurality of other layers such as the reflective layer and the recording layer may be present, or may be present in the transparent resin layer b or the transparent resin layer a. For example, as an example of a layer configuration of an optical recording medium in which two reflective layers and two recording layers exist, a substrate, a reflective layer, a recording layer, a part of a transparent resin layer b, a reflective layer, a recording layer, and a transparent resin layer b The remaining part of the layer structure is a transparent resin layer a.

[6. Advantages of the present invention and mechanisms for obtaining the effects of the present invention]
According to the present invention, it is possible to provide an optical recording medium with little deformation and high surface durability even when the environmental humidity changes.

  However, it is not clear why such an effect is obtained. The inventor infers this as follows.

  Conventionally, radiation curable compositions have been developed that excel in transparency, abrasion resistance, recording film protection, mechanical properties, and heat resistance and moisture deformation resistance. The suppression of deformation of the optical recording medium at that time was insufficient. Furthermore, at the same time, the durability against local pressure on the surface was not satisfactory.

  For example, if it is attempted to satisfy the durability against local pressure, the elastic modulus of the protective layer is increased. However, when the elastic modulus is increased, the optical recording medium is likely to be deformed when the temperature and humidity are suddenly changed, and the optical recording medium is warped over time even if the humidity is not suddenly changed. Becomes stronger. Although the warp of the optical recording medium over time can be adjusted by the curing conditions and the like, deformation due to a rapid change in humidity cannot be avoided, and there is a trade-off relationship with durability against local pressure.

  Therefore, a transparent resin layer a having a high elastic modulus for improving durability against local pressure, and a transparent resin layer b having a low elastic modulus for suppressing warpage of the optical recording medium due to a sudden change in humidity. A protective layer was formed by laminating.

Here, the force that causes the optical recording medium to warp due to a sudden change in humidity is determined by the following equation.
Force = stress σ x cross-sectional area A
= (Dehydration shrinkage ε × elastic modulus E) × cross-sectional area A
That is, in order to suppress warping due to a rapid change in humidity, it is preferable to reduce the cross-sectional area of the transparent resin layer a having a high elastic modulus as much as possible (thickness as thin as possible).

  Therefore, by maintaining the durability to local pressure by the transparent resin layer a having a high elastic modulus, the thickness is reduced, and the transparent resin layer b having a low elastic modulus is further laminated, thereby rapidly changing the humidity. It is considered that the warp of the optical recording medium due to the is suppressed.

  EXAMPLES Hereinafter, although this invention is demonstrated in detail using an Example, this invention is not limited to a following example, unless it deviates from the summary.

(Preparation of radiation curable composition α)
Into a four-necked flask equipped with a stirrer, reflux condenser, dropping funnel and thermometer, 41.9 g of isophorone diisocyanate and 40 mg of dibutyltin laurate are placed and heated to 70-80 ° C. in an oil bath to keep the temperature constant. Gently stirred until

  When the temperature became constant, a mixture of 11.1 g of 1,6-hexanediol and 88.0 g of hexamethylenediamine trimer (“Tronate HDT” manufactured by Rhodia) was added dropwise with a dropping funnel, and the temperature was adjusted to 80 ° C. And stirred for 2 hours.

  After the temperature is lowered to 70 ° C., a mixture of 33.9 g of hydroxyethyl acrylate and 0.2 g of methoquinone is added dropwise with a dropping funnel. When the addition is completed, the temperature is kept at 80 ° C. and stirred for 10 hours to obtain a urethane acrylate oligomer. Was synthesized.

  After the temperature was lowered to 50 ° C., 25.0 g of tetrahydrofurfuryl acrylate (manufactured by Kyoeisha Chemical Co., Ltd.) was added, and the mixture was further stirred for 3 hours to obtain a uniform liquid urethane acrylate oligomer diluent A.

72 g of this urethane acrylate oligomer diluent A was taken in another beaker, 28.0 g of nonanediol diacrylate (manufactured by Shin-Nakamura Chemical Co., Ltd.), and 3.0 g of 1-hydroxycyclohexyl phenyl ketone (manufactured by Ciba Specialty Chemicals) were added. The mixture was stirred at room temperature for 3 hours using a stirring blade to obtain a radiation curable composition α.
The content of the monofunctional acrylate compound in this composition is 8.7% by weight, and the content of the polyfunctional acrylate compound is 27.2% by weight.

This composition was applied to a PET film affixed on a glass plate to a thickness of 100 μm by spin coating, and using a high-pressure mercury lamp (manufactured by JATEC; J-cure 100), an irradiation amount of 1000 mJ / cm at a wavelength of 365 nm. After being cured by irradiating with ultraviolet rays of ^2, the film was peeled from the PET film to obtain a film of a cured product of the radiation curable composition α.
Five strips of 10 mm × 100 mm strips were cut out from this film, and a tensile test was performed using a tensile strength tester to determine the elastic modulus. The average value was 1750 MPa. .

(Preparation of radiation curable composition β)
Into a four-necked flask equipped with a stirrer, reflux condenser, dropping funnel and thermometer, 59.5 g of isophorone diisocyanate and 40 mg of dibutyltin laurate are placed, and heated to 70-80 ° C. in an oil bath to keep the temperature constant. Gently stirred until

  When the temperature became constant, a mixture of 11.3 g of 1,6-hexanediol and 24.6 g of polytetramethylene glycol (manufactured by Mitsubishi Chemical Co., Ltd .; number average molecular weight 650) was dropped with a dropping funnel, and the temperature was changed to 80 ° C. And stirred for 2 hours.

  After the temperature is lowered to 70 ° C., a mixture of 31.1 g of hydroxyethyl acrylate and 0.2 g of methoquinone is added dropwise with a dropping funnel. When the addition is completed, the temperature is kept at 80 ° C. and stirred for 10 hours to obtain a urethane acrylate oligomer. Was synthesized.

  After the temperature was lowered to 50 ° C., 73.5 g of tetrahydrofurfuryl acrylate (manufactured by Kyoeisha Chemical Co., Ltd.) was added and further stirred for 3 hours to obtain a uniform liquid urethane acrylate oligomer diluent B.

98 g of this urethane acrylate oligomer diluent B is taken in another beaker, and 2.0 g of nonanediol diacrylate (manufactured by Shin-Nakamura Chemical Co., Ltd.) and 3.0 g of 1-hydroxycyclohexyl phenyl ketone (manufactured by Ciba Specialty Chemicals) are added. The mixture was stirred at room temperature for 3 hours using a stirring blade to obtain a radiation curable composition β.
The content of the monofunctional acrylate compound in this composition is 35.0% by weight, and the content of the polyfunctional acrylate compound is 1.9% by weight.

This composition was applied to a PET film affixed on a glass plate to a thickness of 100 μm by spin coating, and using a high-pressure mercury lamp (manufactured by JATEC; J-cure 100), an irradiation amount of 1000 mJ / cm at a wavelength of 365 nm. After being cured by irradiating with ultraviolet rays of ^2, the film was peeled from the PET film to obtain a cured film of the radiation curable composition β.
Five strips of 10 mm × 100 mm strips were cut out from this film, and a tensile test at a test speed of 1 mm / min was performed using a tensile strength tester to determine the elastic modulus. The average value was 530 MPa. .

<Example 1>
(Preparation of test disc)
An Ag—Cu—Au reflective layer having a thickness of 100 nm was formed by sputtering on a smooth polycarbonate resin substrate surface having a diameter of 120 mm and a thickness of 1.1 mm.
The surface of this reflective layer was coated with a radiation curable composition β so as to have a thickness of 80 μm using a spin coater, and using a high-pressure mercury lamp (manufactured by JATEC; J-cure 100), an irradiation amount of 1000 mJ / cm at a wavelength of 365 nm. ^The resin was cured by irradiating the ultraviolet ray ² to obtain a transparent resin layer b. Next, the radiation curable composition α was applied with a spin coater so as to have a thickness of 20 μm and cured in the same manner to obtain a transparent resin layer a, a protective layer was formed, and a test disk was obtained. A total of two test disks were obtained by the same operation.

(Humidity disk deformation evaluation test)
One of the manufactured discs was allowed to stand for 3 days in an environment set at 25 ° C. and 45% RH (relative humidity), and then this disc was placed in a constant temperature and humidity chamber set at 25 ° C. and 90% or more RH. Left for days. Thereafter, the disk is taken out in an environment set to 25 ° C. and 45% RH, and the warp d ₀ of the disk immediately after the removal is measured at a position 35 mm from the center of the disk by a displacement sensor (manufactured by Keyence Corporation; model number “LT-9010”). It was determined by measuring the displacement. However, the case of concave warpage on the protective layer side was positive, and the case of convex warpage was negative.
Thereafter, the warp d ₁ d ₂ d ₄ d ₆ of the disc for 1 hour, 2 hours, 4 hours and 6 hours after the removal was obtained by measurement, and D _{1 to} D ₆ were calculated by the following equations.

D ₁ = | d ₁ -d ₀ |
D ₂ = | d ₂ −d ₀ |
D ₄ = | d ₄ -d ₀ |
D ₆ = | d ₆ -d ₀ |

The maximum value among D ₁ , D ₂ , D ₄ , and D ₆ is the “humidity deformation value” of this disc, and when this value is 0.06 mm or more, “x”, 0.03 or more and less than 0.06 The case of “Δ” was judged as “Δ”, the case of 0.015 or more and less than 0.03 was judged as “◯”, and the case of less than 0.015 was judged as “◎”. The results are shown in Table 1.

(Surface durability test)
Place the remaining protective layer on the surface plate with the remaining protective layer on top of the manufactured disk, and lay a sandblasted 100 mm square, 5 mm thick glass plate on the protective layer surface. Weighed 630 g) and allowed to stand for 1 day. Thereafter, the cork base and the glass plate were gently removed, and immediately the surface of the protective layer was observed visually and with a polarizing microscope.

  When the surface of the protective layer is visually observed in 75% or more of the total area, “X” is indicated, and when it is visually observed in less than 75% of the entire area, “△” is indicated. When it was observed at ◯, it was judged as “◯”, and when it was not observed by visual observation or a polarizing microscope, it was judged as “◎”. The results are shown in Table 1.

<Example 2>
A test disk was produced in the same manner as in Example 1 except that the thickness of the transparent resin layer b was 75 μm and the thickness of the transparent resin layer a was 25 μm in the production of the test disk of Example 1. Table 1 shows the humidity disk deformation evaluation test and the surface durability test.

<Example 3>
A test disk was produced in the same manner as in Example 1 except that the thickness of the transparent resin layer b was 70 μm and the thickness of the transparent resin layer a was 30 μm in the production of the test disk of Example 1. Table 1 shows the humidity disk deformation evaluation test and the surface durability test.

<Example 4>
A test disk was prepared in the same manner as in Example 1 except that the thickness of the transparent resin layer b was set to 60 μm and the thickness of the transparent resin layer a was set to 40 μm. Table 1 shows the humidity disk deformation evaluation test and the surface durability test.

<Example 5>
A test disk was produced in the same manner as in Example 1 except that the thickness of the transparent resin layer b was 50 μm and the thickness of the transparent resin layer a was 50 μm in the production of the test disk of Example 1. Table 1 shows the humidity disk deformation evaluation test and the surface durability test.

<Example 6>
A test disk was prepared in the same manner as in Example 1 except that the thickness of the transparent resin layer b was 85 μm and the thickness of the transparent resin layer a was 15 μm. Table 1 shows the humidity disk deformation evaluation test and the surface durability test.

<Example 7>
A test disk was produced in the same manner as in Example 1 except that the thickness of the transparent resin layer b was 45 μm and the thickness of the transparent resin layer a was 55 μm in the production of the test disk of Example 1. Table 1 shows the humidity disk deformation evaluation test and the surface durability test.

<Comparative Example 1>
A test disk was prepared in the same manner as in Example 1 except that the thickness of the transparent resin layer b was set to 100 μm and the transparent resin layer a was not formed. Table 1 shows the humidity disk deformation evaluation test and the surface durability test.

<Comparative example 2>
A test disk was produced in the same manner as in Example 1 except that the thickness of the transparent resin layer a was 100 μm and the transparent resin layer b was not formed in the production of the test disk of Example 1. Table 1 shows the humidity disk deformation evaluation test and the surface durability test.

  From these results, it was found that the optical recording medium of the present invention has little deformation and high surface durability even when the environmental humidity changes.

  The optical recording medium of the present invention has little deformation and high surface durability even when the environmental humidity changes. Therefore, the present invention can be suitably used for optical recording media including next-generation high-density optical recording media such as Blu-ray discs.

Claims (8)

An optical recording medium in which at least a substrate, a transparent resin layer b, and a transparent resin layer a are laminated in this order,
The elastic modulus of the transparent resin layer a is 1000 MPa to 2500 MPa,
An optical recording medium, wherein the transparent resin layer b has an elastic modulus of 100 MPa to 1300 MPa. 2. The optical recording medium according to claim 1, wherein the elastic modulus of the transparent resin layer a is larger than the elastic modulus of the transparent resin layer b. The film thickness ratio of the film thickness of the transparent resin layer a to the film thickness of the transparent resin layer b is 10/90 or more and 60/40 or less, The claim 1 or 2, Optical recording medium. The transparent resin layer a is a cured product of the radiation curable composition α,
The radiation curable composition α contains a polyfunctional (meth) acrylate compound other than (A) urethane (meth) acrylate compound and (C) (A) urethane (meth) acrylate compound,
The content of the polyfunctional (meth) acrylate compound other than (C) (A) urethane (meth) acrylate compound in the radiation curable composition α is 15% by weight or more and 90% by weight or less. The optical recording medium according to any one of claims 1 to 3. The optical recording medium according to claim 4, wherein the polyfunctional (meth) acrylate compound other than the (C) (A) urethane (meth) acrylate compound contains a trifunctional or higher functional (meth) acrylate compound. The transparent resin layer b is a cured product of the radiation curable composition β,
The radiation curable composition β is composed of (A) urethane (meth) acrylate compound, (B) (A) monofunctional (meth) acrylate compound other than urethane (meth) acrylate compound, and (C) (A) urethane (meth) ) Containing polyfunctional (meth) acrylate compounds other than acrylate compounds,
The content of the monofunctional (meth) acrylate compound other than (B) (A) urethane (meth) acrylate compound in the radiation curable composition β is 10% by weight or more and 70% by weight or less. The optical recording medium according to any one of claims 1 to 5. The optical recording medium according to claim 6, wherein the (A) urethane (meth) acrylate compound contains a polyether skeleton. The optical recording medium according to any one of claims 1 to 7, wherein reproduction is performed using a blue laser.