JP2008226356A - Radiation curing composition for optical recording medium protective layer, and optical recording medium - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide radiation curing composition for an optical recording medium protective layer used for a protective layer of the optical recording medium and capable of giving a cured product suppressing corrosion of a metal layer such as a recording layer made of silver or a silver alloy even under high temperature and high humidity while expected physical properties of transparency, surface hardness, interlayer adhesion, mechanical strength, deformation properties and the like are maintained, and also to provide the optical recording medium having the cured product layer of the curing composition as the protective layer. <P>SOLUTION: The radiation curing composition for an optical recording medium protective layer containing at least (A) a urethane (meth)acrylate compound, (B) a (meth)acrylate compound other than (A) the urethane (meth)acrylate compound, and (C) a polymerization initiator, has ≤20 ppm chlorine atom content, ≤20 ppm sulfur atom content and ≤10 ppm sodium atom content. The protective layer of the optical recording medium is formed by using the cured product of the radiation curing composition. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a radiation curable composition for an optical recording medium protective layer and an optical recording medium using the same.

  Many attempts have been made to use a radiation-curable composition for a protective layer of an information recording layer in an optical recording medium. For example, an oligomer that is at least one of a urethane (meth) acrylate compound and an epoxy (meth) acrylate compound. With active energy ray-curable composition containing components, dioxolanyl group-containing (meth) acrylate compound, and other ethylenically unsaturated compounds, it has adhesion to the substrate, low cure shrinkage, mechanical strength, etc. It is proposed that a cured product in which corrosion of a metal layer such as a recording layer is prevented can be obtained (see Patent Document 1), and a polyisocyanate compound, a polymer polyol, and a (meth) acrylate compound having a hydroxyl group are reacted. Containing urethane oligomers obtained by heating and ethylenically unsaturated compounds Ray curable composition, it is proposed to obtain give further cured product excellent in heat and humidity variations, etc. (see Patent Document 2). However, according to the study by the present inventors, any conventional radiation-curable composition can sufficiently prevent corrosion of a metal layer such as a silver or silver alloy recording layer under high temperature and high humidity. However, it has been found that there are problems inherent in data storage.

On the other hand, the protective layer of the information recording layer in the optical recording medium is made of an inorganic material containing at least one of zinc oxide, indium oxide, tin oxide, niobium oxide, silicon nitride, aluminum nitride, and SiOx. It is known that the corrosion of the Ag light reflection layer can be suppressed by suppressing the content of sulfur and chlorine, which are corrosive substances of Ag, contained as impurities to 0.1% by weight or less (Patent Document 3). reference).
註 6; I refused to be an inorganic protective layer.
JP 2003-231725 A JP 2006-152289 A JP 2005-190642 A

  The present invention has been made in view of the above-described conventional state of the art, and therefore, the present invention provides transparency, surface hardness in the use of a radiation curable composition for a protective layer of an information recording layer in an optical recording medium. Curing capable of suppressing corrosion of metal layers such as silver or silver alloy recording layers even at high temperatures and high humidity while maintaining the desired physical properties such as interlayer adhesion, mechanical strength, and deformability An object of the present invention is to provide a radiation curable composition for an optical recording medium protective layer capable of providing a product, and an optical recording medium having a cured layer of the radiation curable composition as a protective layer.

  As a result of intensive studies to provide a solution to the above-mentioned problems, the present inventors, as a result, radiation curing containing a urethane (meth) acrylate compound, a (meth) acrylate compound other than the urethane (meth) acrylate compound, and a polymerization initiator. In the composition, the content of sodium atoms is important together with the content of chlorine atoms and sulfur atoms, and by suppressing the respective contents of chlorine atoms, sulfur atoms, and sodium atoms below a specific value, In other words, the gist of the present invention is that at least (A) urethane (meth) acrylate compound, (B) said (A) urethane (meta) ) A radiation-curable composition containing a (meth) acrylate compound other than an acrylate compound, and (C) a polymerization initiator. The radiation curable composition for an optical recording medium protective layer having a chlorine atom content of 20 ppm or less, a sulfur atom content of 20 ppm or less, and a sodium atom content of 10 ppm or less in the radiation curable composition. And the protective layer exists in the optical recording medium formed by the hardened | cured material of the said radiation-curable composition for optical recording medium protective layers.

  According to the present invention, when a radiation curable composition is used for a protective layer of an information recording layer in an optical recording medium, desired properties such as transparency, surface hardness, interlayer adhesion, mechanical strength, and deformability are maintained. However, a radiation curable composition for an optical recording medium protective layer capable of providing a cured product capable of suppressing corrosion of a metal layer such as a silver or silver alloy recording layer even under high temperature and high humidity, and the radiation An optical recording medium having a cured layer of the curable composition as a protective layer can be provided.

  Hereinafter, embodiments of the present invention will be described in detail. However, the present invention is not limited to the following embodiments, and can be arbitrarily modified without departing from the gist of the present invention. it can.

1. Radiation curable composition for optical recording medium protective layer The radiation curable composition for optical recording medium protective layer of the present invention comprises (A) urethane (meth) acrylate compound, (B) said (A) urethane (meth) acrylate compound. Other (meth) acrylate compounds and (C) a polymerization initiator may be contained, and other substances may be contained as long as the effects of the present invention are not significantly impaired.

1-1. (A) Urethane (meth) acrylate compound (A) The urethane (meth) acrylate compound is usually obtained by reacting a polyisocyanate compound, a compound containing a hydroxyl group, and a (meth) acrylate compound containing a hydroxyl group. can get. As the (A) urethane (meth) acrylate compound in the present invention, a urethane acrylate compound is preferable from the viewpoint of excellent surface curability as a composition and less stickiness.

1-1-a. Polyisocyanate compound A polyisocyanate compound is a compound having two or more isocyanate groups in the molecule. Specific examples of the polyisocyanate compound include tetramethylene diisocyanate, hexamethylene diisocyanate, and 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. May be used alone, or two or more may be used in combination. Among these, bis (isocyanatomethyl) cyclohexane, cyclohexane diisocyanate, bis (isocyanatocyclohexyl) methane, and isophorone diisocyanate are preferable in that the hue of the resulting urethane oligomer is good.

  The molecular weight of the polyisocyanate compound is preferably 100 or more, more preferably 150 or more in view of the balance between strength and elastic modulus as a cured product of the composition, and 1000 or less, further 500 or less. Is preferred.

1-1-b. Compound containing a hydroxyl group As the compound containing a hydroxyl group, polyols containing two or more hydroxyl groups are preferable, and specific examples thereof include ethylene glycol, 1,2-propanediol, and 1,3-propane. Diol, 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-octanediol, trimethylolpropane, pentaerythritol , Alkylene polyols such as sorbitol, mannitol, glycerin, 1,2-dimethylolcyclohexane, 1,3-dimethylolcyclohexane, 1,4-dimethylolcyclohexane, and the like.

  Among these, the polyols have an ether bond for forming a multimer or the like, a polyether polyol compound, an ester bond by reaction with a polybasic acid, or an ester bond by ring-opening polymerization of a cyclic ester. A polyester polyol compound and a polycarbonate polyol compound having a carbonate bond by reaction with carbonate are preferred.

  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, and ethylene oxide, propylene oxide of the polyols, Examples include adducts of alkylene oxides such as 1,2-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 ring opening of a cyclic ester such as caprolactone. Examples include polycaprolactone as a polymer.

  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, diphenyl carbonate, 4-methyldiphenyl carbonate, 4- Ethyl diphenyl carbonate, 4-propyl diphenyl carbonate, 4,4′-dimethyl diphenyl carbonate, 2-tolyl-4-tolyl carbonate, 4,4′-diethyl diphenyl carbonate, 4,4′-dipropyl diphenyl carbonate, phenyl toluyl carbonate , Bischlorophenyl carbonate, phenyl chlorophenyl carbonate, phenyl naphthyl carbonate, diaryl carbonate such as dinaphthyl carbonate, or Dialkyl carbonates such as methyl carbonate, 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.

  These polyols may be used individually by 1 type, and may be used in combination of 2 or more type. Among these polyols, polyether polyol compounds are preferable, among which polyalkylene glycol is more preferable, and polytetramethylene glycol is particularly preferable.

  The molecular weights of these polyols are low water absorption and low hygroscopicity as urethane (meth) acrylate, and therefore from the viewpoint of low corrosiveness of the metal layer when used as an optical recording medium as a cured product of the composition. The total number of polyols is preferably 5 mol% or more, more preferably 10 mol% or more, particularly preferably 15 mol% or more, and the number average molecular weight is preferably 200 or more, more preferably 400 or more, It is preferably 1500 or less, more preferably 800 or less.

  Accordingly, the compound containing a hydroxyl group in the present invention 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.

1-1-c. (Meth) acrylate compound containing hydroxyl group The (meth) acrylate compound containing hydroxyl group is a compound having both a hydroxyl group and a (meth) acryloyl group, specifically, hydroxyethyl (meth) acrylate, Examples include hydroxypropyl (meth) acrylate, hydroxybutyl (meth) acrylate, addition reaction product of glycidyl ether compound and (meth) acrylic acid, mono (meth) acrylate body of glycol compound, etc. You may use, and may use it in combination of 2 or more type.

  The molecular weight of the hydroxyl group-containing (meth) acrylate compound is preferably 40 or more, more preferably 80 or more, and preferably 800 or less, more preferably 400 or less.

1-1-d. (A) Method for Producing Urethane (Meth) acrylate Compound (meth) acryloyl is obtained by addition reaction of the polyisocyanate compound, the compound containing the hydroxyl group, and the (meth) acrylate compound containing the hydroxyl group. A (A) urethane (meth) acrylate compound having a group can be produced. At that time, the isocyanate group and the hydroxyl group are charged so as to have a stoichiometric amount. In particular, diols are used as the compound containing a hydroxyl group, and the (A) urethane (meth) acrylate compound having a (meth) acryloyl group has adhesion and surface curing degree as a cured product of the resulting composition. There is an advantage of further increase.

  In addition, when manufacturing (A) urethane (meth) acrylate compound, the usage-amount of the (meth) acrylate compound containing the said hydroxyl group is used for the compound containing this hydroxyl group and the said hydroxyl group (meth). It 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 based on the total amount of the hydroxyl group-containing compound combined with the acrylate compound. Depending on the ratio, the molecular weight of the (A) urethane (meth) acrylate compound obtained can be controlled.

  The addition reaction of these polyisocyanate compounds and (meth) acrylate compounds containing hydroxyl groups can be carried out by any known method. For example, a mixture of a polyisocyanate compound, a (meth) acrylate compound containing a hydroxyl group and an addition reaction catalyst is usually 40 ° C. or higher, preferably 50 ° C. or higher, and usually 90 ° C. or lower, preferably 75 ° C. or lower. Mix under the conditions of As a mixing method at that time, it is preferable to drop a mixture of a hydroxyl group-containing (meth) acrylate compound and an addition reaction catalyst in the presence of a polyisocyanate compound. In addition, as the addition reaction catalyst at this time, for example, dibutyltin laurate, dibutyltin dioctoate, dioctyltin dilaurate, and dioctyltin dioctoate are preferable, and one of these may be used alone, Two or more kinds may be used in combination.

  When the (A) urethane (meth) acrylate compound is produced, in addition to the polyisocyanate compound, the compound containing the hydroxyl group, and the (meth) acrylate compound containing the hydroxyl group, other components are added. You may make it contain.

1-1-e. (A) Properties of Urethane (Meth) acrylate Compound (A) The urethane (meth) acrylate compound is preferably highly transparent, for example, a compound having no aromatic ring. When the urethane (meth) acrylate compound has an aromatic ring, the radiation-curable composition having an aromatic ring and the cured product are colored during storage even if the resulting product is a colored product or is not colored. Or coloring (so-called yellowing). This is considered to be caused by the fact that the double bond part forming the aromatic ring irreversibly changes its structure by energy rays. For this reason, (A) urethane (meth) acrylate compound By having a structure having no ring, there is an advantage that the hue is not deteriorated and the light transmittance is not lowered, and it is particularly suitable for application to an application requiring colorless and transparent such as an optical recording medium.

  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 ( Specific examples of polyisocyanate compounds that can be produced by selecting a (meth) acrylate compound and have no aromatic ring include bis (isocyanatomethyl) cyclohexane, cyclohexane diisocyanate, bis (isocyanatocyclohexyl) methane, and isophorone diisocyanate. Specific examples of the compound containing a hydroxyl group having no aromatic ring include alkylene polyols, alkylene polyesters, alkylene carbonate polyols, etc., and hydroxyl groups having no aromatic ring. Specific examples of a (meth) acrylate compound, a hydroxyalkyl (meth) acrylate.

  The weight average molecular weight of these (A) urethane (meth) acrylate compounds is preferably 1000 or more, more preferably 1500 or more, from the viewpoint of the balance between the viscosity and the mechanical properties, and is preferably 10,000 or less, more preferably 5000 or less. Is preferred.

  The content of the (A) urethane (meth) acrylate compound in the radiation curable composition for an optical recording medium protective layer of the present invention is preferably 25% by weight or more, more preferably 30% by weight or more. 80% by weight or less, more preferably 70% by weight or less. (A) When there is too little content of a urethane (meth) acrylate compound, the moldability and mechanical strength at the time of forming hardened | cured material will fall, and it will become easy to produce a crack, On the other hand, when too much, hardened | cured material The surface hardness tends to decrease.

1-2. (B) (Meth) acrylate compound other than (A) urethane (meth) acrylate compound As a radiation-curable composition for an optical recording medium protective layer of the present invention, in addition to (A) urethane (meth) acrylate compound, From the aspect of excellent surface curability as a composition and no tack remaining, it is essential to contain (B) the (meth) acrylate compound other than the (A) urethane (meth) acrylate compound, (B) As the (meth) acrylate compound other than (A), any known (meth) acrylate compound can be used as long as the effects of the present invention are not significantly impaired. For example, monofunctional (meth) acrylate Examples thereof include polyfunctional (meth) acrylate compounds.

  Specific examples of the monofunctional (meth) acrylate compound include (meth) acrylamides such as N, N-dimethyl (meth) acrylamide, hydroxyethyl (meth) acrylate, hydroxypropyl (meth) acrylate, and hydroxybutyl (meth). Hydroxyalkyl (meth) acrylates such as acrylate, (meth) acryloylmorpholine, tetrahydrofurfuryl (meth) acrylate, isobornyl (meth) acrylate, cyclohexyl (meth) acrylate, (meth) acrylate having a tricyclodecane skeleton, etc. Examples include alicyclic (meth) acrylates. Among these, alicyclic (meth) acrylates are preferable, and tetrahydrofurfuryl (meth) acrylate and isobornyl (meth) acrylic acid having high hydrophobicity are preferable. Over DOO, cyclohexyl (meth) acrylate, having tricyclodecane skeleton (meth) acrylate.

Examples of the polyfunctional (meth) acrylate compound include alicyclic poly (meth) acrylates, alicyclic poly (meth) acrylates, aromatic poly (meth) acrylates, and the like. , Polyethylene glycol di (meth) acrylate, 1,2-polypropylene glycol di (meth) acrylate, 1,3-polypropylene glycol di (meth) acrylate, polytetramethylene glycol di (meth) acrylate, 1,2-polybutylene glycol Addition of alkylene oxide such as ethylene oxide, propylene oxide, or butylene oxide of bisphenol such as di (meth) acrylate, polyisobutylene glycol di (meth) acrylate, bisphenol A, bisphenol F, or bisphenol S Di (meth) acrylates of hydrogenated derivatives of bisphenols such as di (meth) acrylates, bisphenol A, bisphenol F, or bisphenol S, blocks of various polyether polyol compounds and other compounds, or random copolymer di (Meth) acrylates having a polyether skeleton such as (meth) acrylate, 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) Bifunctional (meth) acrylates such as acryloyloxyethylthio] xylylene, 4,4′-bis [β- (meth) acryloyloxyethylthio] diphenylsulfone, trimethylolpropane tris (meth) acrylate, glycerin tris ( (Meth) acrylate, trifunctional (meth) acrylates such as pentaerythritol tris (meth) acrylate, tetrafunctional (meth) acrylates such as pentaerythritol tetrakis (meth) acrylate, dipentaerythritol hexa (meth) acrylate, etc. Examples include indefinite polyfunctional (meth) acrylates such as pentafunctional or higher functional (meth) acrylates.

Of these, the above-mentioned bifunctional (meth) acrylates are preferable in terms of controllability of the cross-linking reaction. As the bifunctional (meth) acrylates, alicyclic poly (meth) acrylate, alicyclic poly (meth) acrylate, etc. are preferable, and hexanediol di (meth) acrylate, nonanediol di (meth) acrylate, and the like. Bis (hydroxymethyl) tricyclo [5.2.1.0 ^2,6 ] decane = dimethacrylate is preferred. 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, etc. exemplified above, and trifunctional (meth) having an isocyanurate skeleton. ) Acrylate and the like.

  These (B) (meth) acrylate compounds other than (A) may be used singly or in combination of two or more, but at least one monofunctional (meta) It is preferable to use an acrylate compound in combination with at least one polyfunctional (meth) acrylate compound.

  The molecular weight of these (B) (meth) acrylate compounds other than (A) is preferably 50 or more, more preferably 100 or more, from the viewpoint of the balance between the viscosity of the composition and the curing shrinkage. Also, it is preferably 1000 or less, more preferably 500 or less.

  The content of the (meth) acrylate compound other than (B) the urethane (meth) acrylate compound in the radiation curable composition for an optical recording medium protective layer of the present invention is 20% by weight or more, It is preferably 30% by weight or more, more preferably 75% by weight or less, and even more preferably 70% by weight or less. (B) When there is too little content of (meth) acrylate compounds other than said (A), it will become the tendency for the viscosity of a radiation-curable composition to become high, on the other hand, when too large, the mechanical physical property as hardened | cured material will fall. It becomes a trend.

  Further, in the radiation curable composition for an optical recording medium protective layer of the present invention, the (A) urethane (meth) acrylate compound and the (B) (meth) acrylate compound other than the (A) with respect to the total amount of the composition. Is preferably 80% by weight or more, more preferably 90% by weight or more, and more preferably 90% by weight or more from the viewpoints of excellent curing speed and surface curability as a composition and no tack remaining. Preferably it is 95 weight% or more, Most preferably, it is 98 weight% or more.

1-3. (C) Polymerization initiator The radiation-curable composition for an optical recording medium protective layer of the present invention further comprises a polymerization reaction that proceeds by radiation (for example, active energy rays, ultraviolet rays, electron beams, etc.) ( C) Contains a polymerization initiator. (C) As the polymerization initiator, a radical generator which is a compound having a property of generating radicals by light is common, and any known radical generator can be used as long as the effects of the present invention are not significantly impaired. Furthermore, a combined system of a radical generator and a sensitizer may be used.

  Specific examples of such radical generators include benzophenone, 2,4,6-trimethylbenzophenone, 4,4-bis (diethylamino) benzophenone, 4-phenylbenzophenone, methylorthobenzoylbenzoate, thioxanthone, diethylthioxanthone, and 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, and among them, the curing speed is high and the crosslinking density can be sufficiently increased. Therefore, benzophenone, 2-hydroxy-2-methyl-1- Phenylpropan-1-one, 1-hydroxycyclohexyl fe Luketone, 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, 1-hydroxycyclohexyl phenyl ketone, 2,4,6-trimethylbenzoyldiphenylphosphine oxide, and 2-hydroxy-1- [4- [4- (2-hydroxy-2-methyl) More preferred is -propionyl) -benzyl] -phenyl] -2-methyl-propan-1-one.

  In addition, when the cured product of the radiation curable composition for the protective layer of the optical recording medium of 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 is sufficiently obtained. It is preferable to select and use the type and amount of the radical generator so as to pass through the cured product layer. In this case, it is particularly preferable to use a short wavelength photosensitive radical generator in which the obtained cured product 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 -2-methyl-1-phenylpropan-1-one, benzyl dimethyl ketal, 1-hydroxycyclohexyl phenyl ketone, benzoin methyl ether, benzoin ethyl ether, benzoin isopropyl ether, benzoin isobutyl ether, methyl benzoyl formate, etc. Among them, those having a hydroxyl group such as 1-hydroxycyclohexyl phenyl ketone are particularly preferable.

  In addition, these radical generators may be used individually by 1 type, and may be used in combination of 2 or more type. Moreover, the addition amount of the radical generator is usually 0.1 with respect to a total of 100 parts by weight of the (A) urethane (meth) acrylate compound and the (B) (meth) acrylate compound other than the (A). It is at least 1 part by weight, preferably at least 1 part by weight, more preferably at least 2 parts by weight, and usually at most 10 parts by weight, preferably at most 9 parts by weight, more preferably at most 7 parts by weight. If the amount added is too small, the radiation curable composition tends not to be cured sufficiently, while if too large, the polymerization reaction proceeds rapidly, causing not only an increase in optical distortion but also a hue. It tends to get worse.

  In addition to these radical generators, for example, known sensitizers such as methyl 4-dimethylaminobenzoate, ethyl 4-dimethylaminobenzoate, amyl 4-dimethylaminobenzoate, 4-dimethylaminoacetophenone, etc. are used in combination. May be. A sensitizer may be used individually by 1 type and may be used in combination of 2 or more type.

1-4. Auxiliary components The radiation-curable composition for an optical recording medium protective layer of the present invention may contain auxiliary components such as additives as 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 or / And oligomers thereof, or curing agents necessary for the synthesis of inorganic components, catalysts, curing accelerators, and the like. These auxiliary components may be used alone or in combination of two or more. It 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.

  Among these, silica as fillers will be described in detail. In the radiation curable composition of the present invention, silica refers to silicon oxide in general, and it does not matter whether the ratio of silicon and oxygen 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 these, when used in the radiation curable composition of the present invention, silica particles dispersed in a solvent or silica particles derived and synthesized from a raw material such as alkoxysilane, because of ease of mixing and dispersion. Is preferred.

  The particle diameter of the silica particles is arbitrary, but 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 40 nm or less, still more preferably 30 nm or less, particularly preferably 15 nm or less, and most preferably 12 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.

1-5. Production method and characteristics of radiation curable composition for optical recording medium protective layer 1-5-a. Method for producing radiation curable composition for optical recording medium protective layer The radiation curable composition for optical recording medium protective layer of the present invention comprises the (A) urethane (meth) acrylate compound, the (B) the (A) urethane. The (meth) acrylate compound other than the (meth) acrylate compound, the (C) polymerization initiator, and the auxiliary component used as necessary are prepared by stirring and mixing uniformly while blocking radiation. The The order of addition of each compound at that time is not particularly limited, but it is preferable to add a high viscosity liquid component and / or a solid component to a low viscosity liquid component and stir, and the polymerization initiator is , Preferably added last.

  The stirring conditions at that time are not particularly limited, but the stirring temperature is usually room temperature, but it may be heated to a temperature of usually 90 ° C. or lower, preferably 70 ° C. or lower. The 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 more, preferably 3 hours or more, and usually 24 hours or less.

1-5-b. Characteristics of radiation curable composition for optical recording medium protective layer In the present invention, the radiation curable composition for optical recording medium protective layer has a chlorine atom content of 20 ppm or less, a sulfur atom content in the radiation curable composition. It is essential that the content is 20 ppm or less and the content of sodium atoms is 10 ppm or less, the content of chlorine atoms is 18 ppm or less, further 10 ppm or less, the content of sulfur atoms is 15 ppm or less, and further 10 ppm or less. And the sodium atom content is preferably 8 ppm or less, more preferably 5 ppm or less. Here, the respective contents of chlorine atom, sulfur atom and sodium atom can be measured by a known method such as ion chromatogram.

  If any of the chlorine atom content, sulfur atom content, and sodium atom content in the radiation curable composition exceeds the above range, the cured product of the radiation curable composition is used as an information recording layer in an optical recording medium. In the protective layer, it is difficult to suppress corrosion of a metal layer such as a silver or silver alloy recording layer under high temperature and high humidity. In the present invention, the reason why it is difficult to suppress corrosion of the metal layer when the content of chlorine atom, content of sulfur atom, or content of sodium atom in the radiation curable composition exceeds the above range is obvious. However, it is estimated as follows for each of a chlorine atom, a sulfur atom, and a sodium atom.

As for chlorine atoms, when the surface of metal begins to corrode, a passive film mainly composed of oxide is formed on the surface, and the corrosion reaction is often suppressed. When chlorine atoms enter there, they form a salt with the metal, and the salt dissolves in water to produce hydrochloric acid, which dissolves the passive film. For example, when an iron atom is taken as an example, it is presumed that the following reactions proceed sequentially and promote corrosion of the metal layer.
(1) 2Cl ⁻ + Fe ²⁺ → FeCl ₂
(2) FeCl ₂ + 2H ₂ O → Fe (OH) ₂ + 2HCl
(3) HCl dissolves the passive film and promotes corrosion

As for sulfur atoms, metal elements, particularly metal elements such as silver, easily form salts with sulfur atoms by the following reaction to dissolve the metal layer.
(1) S ²⁺ + 2Ag → Ag ₂ S
Therefore, when the content of sulfur atoms is large, the probability that the sulfide ions S ²⁺ move to the vicinity of the metal element is increased, and it is easy to come into contact with the metal element. As a result, the metal layer is dissolved and corrosion is promoted. It is estimated to be.

  As for the sodium atom, the sodium atom has high mobility in an environment where water is present, and forms salts with many negative substances. For this reason, when a chemical reaction related to corrosion occurs in a certain local area, the sodium atom easily moves to the local area and forms an anion and a salt there, thereby lowering the chemical potential of the system in the vicinity of the local area, It is estimated that the chemical reaction energy is lowered to promote the reaction, and as a result, the corrosion of the metal layer is promoted.

  In order to make the contents of chlorine atom, sulfur atom and sodium atom in the radiation curable composition for optical recording medium protective layer of the present invention within the above range, (1) each atom is washed by washing the composition. And (2) a method of producing a composition by selecting a raw material having a low content of each atom.

  Regarding the method (1), chlorine atoms, sulfur atoms, and sodium atoms often exist as water-soluble salts, while the composition of the present invention tends to be oil-soluble and hardly soluble in water. Utilizing the composition, after mixing a large amount of water-soluble solvent into the composition, it is allowed to stand to separate into an aqueous phase and an oil phase, and by separating the aqueous phase, chlorine atoms, sulfur atoms, sodium in the aqueous phase Atoms can be removed from the composition. In addition, when there are components having both oil solubility and water solubility in the components of the composition, a hydrophobic solvent is mixed with the water soluble solvent so that the water soluble component is dissolved on the hydrophobic solvent side. , Decreasing the dissolution in the aqueous phase to separate the water phase and the oil phase, and then removing the hydrophobic solvent.

  In this case, the water-soluble solvent is preferably water, more preferably pure water containing no chlorine atom, sulfur atom, sodium atom or the like, and even more preferably ultrapure water. The oil-soluble solvent is preferably a general organic solvent having a relatively low water solubility, such as tetrahydrofuran, methyl ethyl ketone, methyl isobutyl ketone, butanol, methoxy butanol, propylene glycol monomethyl ether, propylene glycol monomethyl ether acetate, Examples include toluene and xylene.

  The amount of water-soluble solvent used is 5 to 500% by volume of the composition, and the amount of oil-soluble solvent used is 5 to 100% by volume of the composition. Are preferred. The mixing time of these solvents is preferably 15 minutes or longer, more preferably 1 hour or longer. Moreover, as a container used for separation operation, a separatory funnel is preferable. After the separation and removal of the aqueous phase, it may be heated at a temperature of 150 ° C. or lower, or may be depressurized at a pressure of 0.1 Torr or higher.

  In the method (2), chlorine atoms, sulfur atoms, and sodium atoms are often derived mainly from chlorine atoms, sulfur atoms, and sodium atoms contained in the raw material. These impurities are contained in the distillation raw material for synthesizing the raw material compound, mixed in the raw material compound synthesis process, for example, those adhering to the inside of the reactor, mixed in what was contained in the solvent used for the synthesis. In addition, there are those due to contamination such as contamination of gas introduced during or in contact with the reaction.

  Therefore, it is preferable to quantitatively analyze chlorine atoms, sulfur atoms, and sodium atoms contained in the raw materials, and to select and use those raw materials with few. On the other hand, if there is no raw material with a low content of chlorine atoms, sulfur atoms, or sodium atoms, the composition can be changed by changing the raw material to another low-impurity-containing compound or by reducing the blending amount of the raw material. The content of chlorine atoms, sulfur atoms and sodium atoms in the product can be reduced. The method (2) is preferably employed when it is difficult to achieve a reduction in the initial impurity content by the method (1) or when it is desired to avoid disadvantages in terms of economy. The

  It is known that many of commercially available urethane (meth) acrylate raw materials, particularly polyisocyanate compounds, contain chlorine atoms. This chlorine atom is presumed to be mixed during the polyisocyanate synthesis process. For example, for isophorone diisocyanate, a chlorine atom-containing compound such as phosgene is used in the production process, so that chlorine atoms are likely to remain even after the purification process. The chlorine atom finally contained in the urethane (meth) acrylate is preferably 40 ppm or less, more preferably 20 ppm or less, and still more preferably 10 ppm or less. The sulfur atom contained in the urethane (meth) acrylate is preferably 40 ppm or less, more preferably 30 ppm or less, and still more preferably 20 ppm or less. Furthermore, the sodium atom contained in urethane (meth) acrylate is preferably 20 ppm or less, more preferably 15 ppm or less, and still more preferably 10 ppm or less.

  Further, commercially available products of (meth) acrylate often contain sulfur atoms derived from raw materials or manufacturing processes. For example, the transesterification reaction, which is one of important reactions in the (meth) acrylate production process, may use a sulfonic acid-based catalyst such as a sulfonate, and in that case, even after passing through a purification process. Sulfur atoms are likely to remain. The sulfur atom contained in this (meth) acrylate is preferably 200 ppm or less, more preferably 150 ppm or less, and still more preferably 100 ppm or less. Moreover, the chlorine atom contained in this (meth) acrylate becomes like this. Preferably it is 50 ppm or less, More preferably, it is 30 ppm or less, More preferably, it is 10 ppm or less. Furthermore, the sodium atom contained in this (meth) acrylate becomes like this. Preferably it is 50 ppm or less, More preferably, it is 20 ppm or less, More preferably, it is 10 ppm or less.

  Moreover, in the commercially available photopolymerization initiator, the origin is unknown, but chlorine atoms and / or sodium are often contained in the atoms. Of these, the chlorine atom contained in the photopolymerization initiator is preferably 50 ppm or less, more preferably 30 ppm or less, and even more preferably 10 ppm or less. Furthermore, the sodium atom contained in a photoinitiator becomes like this. Preferably it is 50 ppm or less, More preferably, it is 20 ppm or less, More preferably, it is 10 ppm or less. The sulfur atom contained in the photopolymerization initiator is preferably 200 ppm or less, more preferably 150 ppm or less, and still more preferably 100 ppm or less.

  On the other hand, the radiation curable composition for an optical recording medium protective layer of the present invention has a viscosity at 25 ° C. of 1000 centipoise or more as measured by an E-type viscometer, a B-type viscometer, or a vibration-type viscometer. Is preferably 1300 centipoise or more, more preferably 5000 centipoise or less, and still more preferably 4000 centipoise or less. When the viscosity is too small, it tends to be difficult to form a cured product having a thickness of 50 μm or more. On the other hand, when the viscosity is too large, it becomes difficult to form a cured product having a smooth surface. Note that 1 centipoise = 1 mPa · s.

  As a method of adjusting the viscosity as a radiation curable composition, (A) Urethane (meth) acrylate compound, and (B) The method of adjusting the molecular weight of (meth) acrylate compounds other than said (A), and addition amount Furthermore, there are methods such as mixing a diluent, a solvent, a thickener, a rheology control agent, etc., among others (A) urethane (meth) acrylate compound, and (B) other than (A) ( A method of adjusting the amount of addition of the (meth) acrylate compound is particularly preferable.

  The radiation curable composition for the optical recording medium protective layer of the present invention preferably contains substantially no solvent. This is to prevent bubbles from remaining and hindering reading and writing of information. “Contains substantially no solvent” means a state in which the content of a so-called organic solvent having volatility or a low boiling point is very low, and the solvent content in the radiation curable composition is usually 5% by weight or less. Preferably, it is 3% by weight or less, particularly preferably 1% by weight or less, and particularly preferably 0.1% by weight or less. For simplicity, it means a state in which no odor of the organic solvent is observed.

2. 2. Cured product of radiation curable composition for optical recording medium protective layer 2-1. Method for producing cured product of radiation-curable composition for protective layer for optical recording medium The cured product of radiation-curable composition for protective layer for optical recording medium in the present invention is polymerized by irradiation with radiation (active energy rays or electron beams). It is obtained by so-called “radiation curing” which initiates the reaction. There is no restriction | limiting in the form of a polymerization reaction, For example, well-known polymerization forms, such as radical polymerization, anionic polymerization, cationic polymerization, and coordination polymerization, can be used. Among these polymerization modes, the most preferable polymerization mode is radical polymerization. The reason for this is not clear, but it is presumed to be due to the homogeneity of the product due to the initiation of the polymerization reaction being homogeneous and proceeding in a short time within the polymerization system.

  Here, the term “radiation” refers to electromagnetic waves (gamma rays, X-rays, ultraviolet rays, visible rays, infrared rays, micro rays, which act on a polymerization initiator that initiates a necessary polymerization reaction to generate chemical species that initiate the polymerization reaction. Wave) or particle beam (electron beam, α-ray, neutron beam, various atomic beams, etc.). Examples of radiation preferably used in the present invention are preferably ultraviolet rays, visible rays, and electron beams, and most 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 (C). At this time, you may use a sensitizer together as needed. The wavelength of the ultraviolet rays 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 at a distance of 30 cm or more, and usually 80 cm or less, preferably 60 cm or less, because the light deterioration, thermal deterioration, thermal deformation, etc. of the irradiated object are small.

  The radiation-curable composition for an optical recording medium protective layer of the present invention 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 the advantage that (C) the use of a polymerization initiator can be omitted and the polymerization is not inhibited by oxygen, and therefore the surface hardness is good. There is. 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 usually 20 J / cm ² or less, preferably 10J / cm ² or less, more preferably 5 J / cm ² or less, more preferably 3J / cm ² or less, particularly preferably irradiated with 2J / 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 in terms of promoting the reaction and productivity. When the irradiation energy or irradiation time of radiation is extremely small, the heat resistance and mechanical properties of the cured product may not be sufficiently exhibited due to incomplete polymerization. On the other hand, when it is extremely excessive, deterioration such as deterioration of hue due to light such as yellowing may occur.

  The radiation may be irradiated in one stage or 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 radiation-curable composition shaped in the mold is fixed and stationary or conveyed by a conveyor. It is also possible to use a radiation curable composition as a coating liquid film on a suitable substrate (for example, resin, metal, semiconductor, glass, paper, etc.) and to cure the coating liquid film by irradiating it with radiation. .

2-2. Properties of cured product of radiation-curable composition for optical recording medium protective layer The cured product of the radiation-curable composition for optical recording medium protective layer of the present invention usually exhibits insoluble and infusible properties in a solvent or the like, and is a thick film. Even if it is a case, it is preferable that it has the property advantageous for the use of an optical member, and is excellent in adhesiveness and surface hardening degree. Specifically, it exhibits low optical distortion (low birefringence), high light transmittance, mechanical strength, dimensional stability, high adhesion, high surface hardness, and a certain level of heat and humidity resistance. preferable. Further, the smaller the curing shrinkage, the better.

  The film thickness of the cured product of the radiation curable composition for an optical recording medium protective layer of the present invention is usually 10 μm or more, preferably 20 μm or more, more preferably 30 μm or more, still more 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. This is because the balance between the influence on the reading and writing of information by dust and the transmittance is good.

  The light transmittance of the cured product of the radiation-curable composition for the protective layer for an optical recording medium of the present invention is such that the light transmittance per optical path length of 0.1 mm at a wavelength of 550 nm is usually 80% or more, preferably 85% or more. More preferably, it is 89% or more, and there is no upper limit. When the light transmittance is too low, the transparency as a cured product is poor. Therefore, when used in an optical recording medium, errors tend to increase when reading recorded information. Further, the light transmittance per optical path length of 0.1 mm at a wavelength of 400 nm is preferably 80% or more, more preferably 85% or more, and particularly preferably 89% or more. The light transmittance can be measured at room temperature by a known method using, for example, an HP8453 type ultraviolet / visible absorptiometer manufactured by Hewlett-Packard Company.

  In order to set the light transmittance of the cured product of the radiation curable composition for an optical recording medium protective layer of the present invention within the above range, it is preferable to use a material having a high light transmittance as each component constituting the radiation curable composition. preferable. Furthermore, those having a small amount of impurities such as colored substances and decomposed substances in each component are preferred. Moreover, the thing with little catalyst amount at the time of manufacture is preferable. These are effective in order not to reduce the light transmittance in the visible light region. Furthermore, it is preferable to select an aliphatic or alicyclic skeleton having no aromatic ring in each component. These are effective in order not to reduce the light transmittance in the ultraviolet region.

  The hardness of the cured product of the radiation curable composition for an optical recording medium protective layer of the present invention is a surface hardness according to a pencil hardness test in accordance with JIS K5400, and is usually B or more, preferably HB or more.

3. Optical Recording Medium In the optical recording medium of the present invention, a protective film is formed on a surface on which a dielectric film, a recording film, a reflective film, etc. (hereinafter, these layers are collectively referred to as a recording / reproducing functional layer) is formed on a substrate. If it is, it will not be specifically limited. However, a next generation high density optical recording medium using a blue laser is preferable. In the present invention, the next-generation high-density optical recording medium refers to a protective film on a surface on which a dielectric film, a recording film, a reflective film, etc. (hereinafter these layers are collectively referred to as a recording / reproducing functional layer) are formed. Is an optical recording medium using a laser beam having a wavelength of 380 to 800 nm, preferably a laser beam having a wavelength of 450 to 350 nm.

  The recording / playback functional layer is a rewrite that can repeat recording and erasure when the optical recording medium is a read-only medium (ROM medium), or a write-once medium that can be recorded only once (Write Once medium). Depending on the case of a possible type medium (Rewritable medium), it is possible to adopt a layer structure corresponding to each purpose.

  For example, in a read-only medium, the recording / playback functional layer is usually composed of a single layer containing a metal such as Al, Ag, or Au. In the write-once medium, the recording / reproducing functional layer is usually configured by providing a reflective layer containing a metal such as Al, Ag, Au, etc. and a recording layer containing an organic dye on the substrate in this order. The Furthermore, in a rewritable medium, the recording / reproducing functional layer is usually formed of a reflective layer containing a metal such as Al, Ag, Au, a dielectric layer, a recording layer, and a dielectric layer in this order. It is configured by providing on top.

  FIG. 1 is a cross-sectional view for explaining an example of the recording / reproducing functional layer 5 in the rewritable optical recording medium 10. The recording / reproducing functional layer 5 is provided so as to sandwich the reflective layer 51 formed of a metal material directly provided on the substrate 1, the recording layer 53 formed of a phase change material, and the recording layer 53 from above and below. And two dielectric layers 52 and 54.

  The protective layer 3 is formed of a cured product obtained by spin-coating the radiation-curable composition for the optical recording medium protective layer of the present invention and radiation-curing the composition. The protective layer 3 is provided in contact with the recording / reproducing functional layer 5 and has a planar annular shape. have. The protective layer 3 is made of a material that can transmit laser light used for recording and reproduction. The transmittance of the protective layer 3 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 3 is sufficiently transparent to laser light in the vicinity of a wavelength used for recording / reproducing of an optical disk, and protects the recording layer 53 formed on the substrate 1 from water and dust. It is desirable to have properties. In addition, the surface hardness of the protective layer 3 is preferably B or more according to a pencil hardness test in accordance with JIS K5400. If the hardness is too small, the surface tends to be damaged. There is no problem with the hardness being too large, but the cured product tends to become brittle, and cracks and peeling tend to occur.

  Furthermore, it is preferable that the adhesion between the protective layer 3 and the recording / reproducing functional layer 5 is high. Furthermore, it is preferable that the adhesiveness with time is high, and the ratio of the adhesive area between the protective layer 3 and the recording / reproducing functional layer 5 after being placed in an environment of 80 ° C. and 85% RH 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 3 is usually 10 μm or more, preferably 20 μm or more, more preferably 30 μm or more, still more preferably 70 μm or more, particularly preferably 85 μm or more, and usually 300 μm or less, preferably 130 μm or less, more preferably 115 μm. It is as follows. When the film thickness is in such a range, the influence of dust and scratches attached to the surface of the protective layer 3 can be reduced, and the thickness sufficient to protect the recording / reproducing functional layer 5 from moisture of the outside air. It can be. 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 3 is preferably formed with a uniform film thickness in a range covering the recording / reproducing functional layer 5.

  In addition, although illustration was abbreviate | omitted in FIG. 1, the hard-coat layer may be further formed on the said protective layer 3, and the hard-coat layer in that case is, for example, (meth) acryloyl group, vinyl group, and Using a radiation curable composition containing a radiation curable monomer or / and oligomer having a functional group selected from the group consisting of mercapto groups, a fluorine compound, a silicone compound, and the aforementioned silica particles, etc. It is preferable to form such that the light transmittance at a wavelength of 550 nm is 80% or more, the contact angle with water is 90 ° or more, and the surface hardness is B, more preferably HB or more.

  The optical recording medium obtained as described above may be used as a single plate, or two or more may be bonded together. Further, if necessary, a hub may be attached and incorporated into the cartridge.

Preparation of urethane acrylate composition liquid A A 4-necked flask was charged with 222 g of isophorone diisocyanate produced by the phosgene method and 60 mg of dibutyltin laurate, heated to 70-80 ° C. in an oil bath, and gently stirred until the temperature became constant. To do. When the temperature becomes constant, a mixture of 45 g of 1,4-butanediol and 142 g of polytetramethylene glycol is added dropwise with a dropping funnel and stirred for 2 hours while maintaining the temperature at 80 ° C. After the temperature was lowered to 70 ° C., a mixture of 79 g of hydroxyethyl acrylate and 0.3 g of methoquinone was dropped with a dropping funnel, and when the dropping was completed, the temperature was kept at 80 ° C. and stirred for 10 hours to synthesize a urethane acrylate oligomer. . To the synthesized urethane acrylate oligomer, 195 g of tetrahydrofurfuryl acrylate (produced by Osaka Organic Chemical Co., Ltd.) was added and diluted to prepare urethane acrylate composition liquid A.

Preparation of urethane acrylate composition liquid B Into a four-necked flask, add 222 g of isophorone diisocyanate produced by the urea method and 60 mg of dibutyltin laurate, heat to 70-80 ° C. in an oil bath, and gently stir until the temperature becomes constant. To do. When the temperature becomes constant, a mixture of 45 g of 1,4-butanediol and 142 g of polytetramethylene glycol is added dropwise with a dropping funnel and stirred for 2 hours while maintaining the temperature at 80 ° C. After the temperature was lowered to 70 ° C., a mixture of 79 g of hydroxyethyl acrylate and 0.3 g of methoquinone was dropped with a dropping funnel, and when the dropping was completed, the temperature was kept at 80 ° C. and stirred for 10 hours to synthesize a urethane acrylate oligomer. . To the synthesized urethane acrylate oligomer, 195 g of tetrahydrofurfuryl acrylate (produced by Osaka Organic Chemical Co., Ltd.) was added and diluted to prepare urethane acrylate composition liquid B.

Example 1
In a 200 cc flask, 70 g of the urethane acrylate composition liquid A prepared above, 10 g of tetrahydrofurfuryl acrylate (produced by Osaka Organic Chemical Co., Ltd.), 10 g of tetrahydrofurfuryl acrylate (produced by Kyoeisha Chemical Co., Ltd.), tricyclodecane dimethanol diacrylate (Daicel Cytec) 10 g), 1 g of 1-hydroxycyclohexyl phenyl ketone (manufactured by Ciba Specialty Chemicals), and 4 g of 1-hydroxycyclohexyl phenyl ketone (manufactured by Nippon Siebel Hegner) were mixed for 5 hours at room temperature using a stirring blade. A uniform liquid radiation-curable composition for an optical recording medium protective layer was obtained. About this radiation-curable composition, the chlorine atom content, sulfur atom content, and sodium atom content are measured by the method shown below, and further, after the environmental resistance test as a cured product by the method shown below. The corrosiveness to the metal layer and the wet heat ray transmittance were evaluated, and the results are shown in Table 1.

<Chlorine atom content and sulfur atom content in the composition>
Quantified using combustion absorption-IC analysis.
<Sodium atom content in the composition>
Quantified using wet digestion-AAS analysis.

<Environmental resistance test>
A silver layer is sputtered to a thickness of 0.1 μm on a 1.1 mm thick polycarbonate substrate and a ZnS—SiO ₂ inorganic layer is sputtered to a thickness of 0.05 μm, and the prepared composition is applied thereon using a spin coater. A composition layer having a thickness of 100 ± 5 μm was formed and cured by irradiation with a high-pressure mercury lamp at 1 J / cm ² to prepare a test sample as a cured product. After storing this test sample in a constant temperature and humidity chamber set at 55 ° C. and 80% RH for 24 hours, the degree of corrosion of the silver layer was observed at a magnification of 20 times using a differential interference reflection optical microscope. 10 points of view were randomly selected, the number of point defects observed in each view was counted, and the average number was used as the degree of corrosion. However, the number of point defects of 5 μm or more was calculated by converting the number of the defects to twice. For example, when 5 point defects of less than 5 μm and 2 point defects of 5 μm or more can be observed in a certain visual field, the point defects observed in the visual field are calculated as follows.
5 (number of point defects less than 5 μm) +2 (number of point defects of 5 μm or more) × 2 = 9 (pieces)
Furthermore, after the environmental resistance test, after storing for 200 hours in a constant temperature and humidity chamber set at 90 ° C. and 85% RH, the composition layer was peeled off, and the light transmittance at 550 nm was measured using a spectrometer. The moisture-resistant heat ray transmittance was determined.

Example 2
In Example 1, 84 g of the urethane acrylate composition liquid B prepared above, 11 g of tetrahydrofurfuryl acrylate (manufactured by Osaka Organic Chemical Co., Ltd.), 5 g of tricyclodecane dimethanol diacrylate (manufactured by Daicel Cytec Co., Ltd.), 1-hydroxycyclohexylphenyl This was carried out in the same manner except that 5 g of ketone (manufactured by Nippon Shibel Hegner) was used to obtain a uniform liquid radiation-curable composition for an optical recording medium protective layer. For this radiation curable composition, the chlorine atom content, the sulfur atom content, and the sodium atom content were measured in the same manner as in Example 1, and the corrosion on the metal layer after the environmental resistance test as a cured product was measured. The moisture resistance and heat ray transmittance were evaluated, and the results are shown in Table 1.

Comparative Example 1
In Example 1, 84 g of the urethane acrylate composition A prepared above, 11 g of tetrahydrofurfuryl acrylate (manufactured by Osaka Organic Chemicals), 5 g of tricyclodecane dimethanol diacrylate (manufactured by Daicel Cytec), 1-hydroxycyclohexyl phenyl ketone This was carried out in the same manner except that 2.5 g (manufactured by Ciba Specialty Chemicals) and 2.5 g of 1-hydroxycyclohexyl phenyl ketone (manufactured by Nippon Siebel Hegner) were used. Obtained. For this radiation curable composition, the chlorine atom content, the sulfur atom content, and the sodium atom content were measured in the same manner as in Example 1, and the corrosion on the metal layer after the environmental resistance test as a cured product was measured. The moisture resistance and heat ray transmittance were evaluated, and the results are shown in Table 1.

Comparative Example 2
In Example 1, 84 g of the urethane acrylate composition B prepared above, 9 g of tetrahydrofurfuryl acrylate (manufactured by Osaka Organic Chemical Co., Ltd.), 5 g of tricyclodecane dimethanol diacrylate (manufactured by Daicel Cytec), ditrimethylolpropane tetraacrylate ( This was carried out in the same manner except that 2 g of Shin-Nakamura Chemical Co., Ltd. and 5 g of 1-hydroxycyclohexyl phenyl ketone (manufactured by Nippon Siebel Hegner) were used to obtain a uniform liquid radiation-curable composition for an optical recording medium protective layer. For this radiation curable composition, the chlorine atom content, the sulfur atom content, and the sodium atom content were measured in the same manner as in Example 1, and the corrosion on the metal layer after the environmental resistance test as a cured product was measured. The moisture resistance and heat ray transmittance were evaluated, and the results are shown in Table 1.

It is sectional drawing which shows one Example of the optical recording medium of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1; Substrate 3; Protective layer 5; Recording / reproducing functional layer 51; Reflective layer 52; Dielectric layer 53; Recording layer 54; Dielectric layer 10;

Claims (6)

  A radiation curable composition containing at least (A) a urethane (meth) acrylate compound, (B) a (meth) acrylate compound other than the (A) urethane (meth) acrylate compound, and (C) a polymerization initiator. In the protective layer for an optical recording medium, the chlorine content in the radiation curable composition is 20 ppm or less, the sulfur atom content is 20 ppm or less, and the sodium atom content is 10 ppm or less. Radiation curable composition.   The optical recording according to claim 1, wherein the (A) urethane (meth) acrylate compound comprises a product obtained by reacting a polyisocyanate compound, a polyether polyol compound, and a (meth) acrylate compound containing a hydroxyl group. A radiation curable composition for a medium protective layer.   The radiation curable composition for an optical recording medium protective layer according to claim 2, wherein the polyether polyol compound is polytetramethylene glycol having a number average molecular weight of 800 or less.   The radiation curable composition for an optical recording medium protective layer according to any one of claims 1 to 3, wherein (C) the polymerization initiator contains 1-hydroxycyclohexyl phenyl ketone.   The radiation for an optical recording medium protective layer according to any one of claims 1 to 4, wherein a chlorine atom content is 18 ppm or less, a sulfur atom content is 15 ppm or less, and a sodium atom content is 8 ppm or less. Curable composition.   An optical recording medium, wherein the protective layer is formed of a cured product of the radiation curable composition for an optical recording medium protective layer according to any one of claims 1 to 5.

Images