JP4232025B2 - Optical recording medium - Google Patents

Description

The present invention, the light to form a light transmission layer using an effective optical recording medium curable resin composition in the case of forming a light transmitting transparent protective layer on the laminated successively reflective layer and a recording layer on a plastic substrate The present invention relates to a recording medium.

  In recent years, with the spread of computers, high-definition television broadcasts for home use, digital cameras, and the like, a medium for storing enormous digital information such as music, images, and images for a long period of time has become necessary. Optical recording media are rapidly developing as a technology capable of recording such a large volume of data with high density. Optical recording media have different capacities and recording / reproducing systems depending on the application and method, but what is becoming mainstream is a data recording method that uses a difference in reflectance of laser light represented by CD and DVD. The structure of the medium, the material of the data recording layer, and the like vary depending on the wavelength of the laser beam used and whether it is a once-write type or a rewritable type. It became so.

On the other hand, the capacity required for the optical recording medium is increasing rapidly as the application expands. In particular, recently, there is a demand for a large-capacity medium that can record a digital high-definition television broadcast for two hours or more. As such a high-density recording method, as represented by a Blu-ray disc, it has been proposed to shorten the wavelength of laser light to 500 nm or less and further increase the numerical aperture (NA) of the optical lens. For example, when a blue laser with a wavelength of 405 nm and a lens with an aperture number of 0.60 or more are used, it is necessary to make the light transmission layer provided on the recording layer thin in order to reduce coma generated by the tilt of the disk. is there. In general, it is necessary to form a cover layer having a constant thickness of about 100 μm.
As a method for forming this light transmission protective layer, a method of bonding a transparent sheet with an adhesive and a method of applying and curing a liquid curable resin composition flatly have been reported.

  In the former method, a commercially available transparent sheet can be used, so there is no need to newly develop a material. However, there are many disadvantages, such as difficulty in cutting sheets, bonding technology, investment for the apparatus, and low productivity. On the other hand, the latter method has many merits such that a conventional spin coating / curing apparatus can be used and the productivity of film formation is high. However, when a conventionally known curable resin coating is applied and cured at a desired thickness, the volume shrinkage before and after curing is large, causing a problem that the substrate warps and distortion occurs. Therefore, development of a novel curable resin coating composition with little cure shrinkage suitable for forming this light transmission layer is required.

Japanese Patent Application Laid-Open No. 11-191240 (Patent Document 1) discloses that a cationic polymerization type photocurable resin is used for a light transmission layer of an optical disc. This is because the cationic polymerization type cured resin can suppress the volume shrinkage before and after curing than the radical polymerization type, and even when the light transmission layer is formed with a thickness of 3 to 177 μm, the skew due to the warpage can be suppressed to be small. it can. However, these compositions are not practical because they lack volume shrinkage and light transmittance around 400 nm.
Japanese Unexamined Patent Publication No. 2002-92948 (Patent Document 2) discloses a composition containing a photopolymerization initiator having an absorbance at a laser wavelength of 370 to 430 nm of 0.05 or less. This is a technique for improving the laser beam transparency of the cured layer of the cationic polymerization resin and increasing the reliability during reading. In this cured product, although the absorbance of the photopolymerization initiator is suppressed, the warpage due to volume shrinkage before and after curing, the transparency of the cured layer in the laser beam region, and the durability against degradation by laser beam are also observed. Is not taken into account, and it cannot be said that it can sufficiently withstand practicality.
JP-A-4-21454 (Patent Document 3) discloses a resin composition for an optical disk comprising a silicone resin which may have a glycidoxy group and a curing catalyst. This is an organic peroxide. It was heat-cured by the above and was extremely inferior in workability.

JP 11-191240 A JP 2002-92948 A JP-A-4-21454

The present invention has been made in view of the above circumstances, and in an optical recording medium for recording digital information using laser light, by applying and curing a liquid curable resin composition with little volume shrinkage before and after curing. , and to provide an optical recording medium to form a light transmission layer using an effective optical recording medium curable resin composition in forming the light transmissive layer.

  As a result of intensive studies on a curable resin composition for optical recording media capable of forming a light-transmitting protective film, the present inventors have found that cationic curable organopolysiloxanes, particularly epoxy groups, oxetanyl groups, and pentamethyl groups. It has been found that the above object can be achieved effectively by using a cationically curable organopolysiloxane containing a specific equivalent of any of the cyclotrisiloxanyl groups as a cationically polymerizable group, and the present invention has been made. .

Accordingly, the present invention provides a lower Symbol optical recording medium.
[I]
On the reflective layer and the recording layer sequentially laminated on the plastic substrate,
(A) It has at least two cationic polymerizable groups selected from an epoxy group, an oxetanyl group, and a pentamethylcyclotrisiloxanyl group in one molecule, and has a viscosity at 25 ° C. of 20 to 500 Cation-curable organopolysiloxane of 1,000 mPa · s
100 parts by mass,
(B) an optical recording light transmitting transparent protective layer obtained by curing a cationic polymerization initiator 0.01 to 20 parts by weight shall be the essential component for an optical recording medium curable resin composition is formed Medium .
[II]
The (A) component organopolysiloxane has a monovalent hydrocarbon group R ¹ having the cationic polymerizable group, and R ¹ equivalent (mass per mole of R ¹ ) is 180 to 2,000 [I]. the optical recording medium of the described.
[III]
(A) component is the following composition formula (1)
R ¹ _m R ² _n SiO _{(4-mn) / 2} (1)
(In the formula, R ¹ is a monovalent hydrocarbon group having a cationic polymerizable group selected from an epoxy group, an oxetanyl group and a pentamethylcyclotrisiloxanyl group, which may be the same or different from each other, and R ² is a cation. A substituted or unsubstituted monovalent hydrocarbon group which does not have a polymerizable group and may be the same or different from each other, a part of which may be a hydrogen atom, a hydroxyl group or an alkoxy group. Are each an integer of 0 to 3, and m + n is an integer of 0 to 3.)
In consists shown a structural unit, at least two have a R ¹ in a molecule, the average value of m is 0.1 to 1.5, the average value of n is from 0 to 2.2, the average value of m + n There is an organopolysiloxane is 0.5 to 3.0 [I] or [II] an optical recording medium as set forth.
[IV]
Component (B) is a compound which generates an acid when irradiated with light containing ultraviolet [I], [II] or [III] an optical recording medium as set forth.

The curable resin composition used for the optical recording medium of the present invention has the following effects.
(1) The curable resin composition of the present invention has a very low volume reduction rate (measured by a specific gravity method) before and after curing, and can reduce the influence of warpage of the substrate due to volume shrinkage.
(2) The silicon-oxygen bond in the siloxane is less deteriorated by the laser beam used in the present invention than the bond between carbons. Therefore, it is excellent in reliability as a long-term optical recording medium.
(3) Since the curable polyorganosiloxane of the present invention has a lower surface tension than other materials, it tends to spread in the circumferential direction when applied by spin coating, and flatness is easily obtained.
(4) Since the curable polyorganosiloxane is rich in water repellency, it is possible to prevent the recording layer from being corroded or deteriorated due to moisture permeation.
(5) The cured polyorganosiloxane film exhibits surface slipperiness and scratch resistance while maintaining an appropriate hardness.

(A) Cationic curable organopolysiloxane In the present invention, the cationic curable organopolysiloxane of component (A) includes an epoxy group, an oxetanyl group, a pentamethylcyclotrisiloxanyl group, etc. as a cationic polymerizable group. And those containing two or more of these cationically polymerizable groups in one molecule can be used, and in particular, the following composition formula (1)
R ¹ _m R ² _n SiO _{(4-mn) / 2} (1)
(In the formula, R ¹ is a monovalent hydrocarbon group having a cation polymerizable group which may be the same or different, and R ² is a group having no cation polymerizable group, which may be the same or different from each other. A good substituted or unsubstituted monovalent hydrocarbon group, a part of which may be a hydrogen atom, a hydroxyl group or an alkoxy group, m and n are each an integer of 0 to 3, and m + n = 0 to 3 (It is an integer.)
Organo THAT consists shown a structural unit, having at least two of R ¹ in a molecule, i.e., the unit R ¹ m is represented by 1, 2 or 3 contains to have at least two per molecule Polysiloxane is preferred.
In this case, the structure may be linear or branched, or may have a cyclic structure in whole or in part.

R ¹ is a monovalent hydrocarbon group having a cationic polymerizable group which may be the same or different from each other. Specifically, epoxy groups such as 3,4-epoxybutyl group, 7,8-epoxyoctyl group, 9,10-epoxydecyl group, glycidyloxypropyl group, 2- (3,4-epoxycyclohexyl) ethyl group, etc. A group containing an oxetanyl group such as a 3-ethyl-3-oxetanylethoxy group, a 3- (3-ethyl-3-oxetanylethoxy) propyl group, a 2-vinyloxyethyl group, a 3-vinyloxypropyl group, Examples thereof include groups having a vinyl ether group such as 2-vinyloxyethoxy group and 4-vinyloxybutoxy group, groups having a polymerizable internal olefin such as 2-butenyloxy group and arenyloxy group. Other examples include groups containing cyclic siloxane such as 2- (pentamethylcyclotrisiloxanyl) ethyl group and 2- (pentamethylcyclotrisiloxanyl) ethoxy group.
More preferably, R ¹ is a glycidyloxypropyl group, a 2- (3,4-epoxycyclohexyl) ethyl group, or a 3-ethyl-3-oxetanylethoxypropyl group from the viewpoints of ease of synthesis and high reactivity. Groups are preferred.

R ² is a group which is bonded to a silicon atom and does not have a cationic polymerizable group, and may be the same or different from each other, and is a substituted or unsubstituted monovalent hydrocarbon group, preferably having 1 to 8 carbon atoms It is. Specifically, linear or branched alkyl groups such as methyl group, ethyl group, propyl group, and butyl group, alkenyl groups such as vinyl group and allyl group, aryl groups such as phenyl group and tolyl group are included. Examples of substituted hydrocarbons in which some of these hydrocarbon groups are substituted by other atoms or groups, for example, substituted hydrocarbons such as chloromethyl group, 3-chloropropyl group, 3,3,3-trifluoropropyl group, etc. Examples are groups. Among these, a methyl group is preferable from the viewpoint of durability against a laser of around 400 nm used for writing and reading digital data, since it can be easily synthesized. A part of R ² may be a hydrogen atom, a hydroxyl group, and an alkoxy group having 1 to 4 carbon atoms such as a methoxy group, an ethoxy group, or a propoxy group.

  M and n in the siloxane unit are each an integer of 0 to 3, and m + n is an integer of 0 to 3. In order to achieve both good film flexibility and mechanical strength, it is preferable to have a linear siloxane unit with m + n = 2 in the entire siloxane unit. Moreover, it is often effective to give a branched horizontal structure by introducing a unit of m + n = 1 in order to control curability and viscosity.

  In this case, the average value of m is preferably 0.1 to 1.5, particularly 0.15 to 1.2, and the average value of n is 0 to 2.2, particularly 0.2 to 2.0. It is preferable that the average value of m + n is 0.5 to 3.0, particularly 1.0 to 2.5.

  The viscosity of component (A) at 25 ° C. is preferably 20 to 500,000 mPa · s, more preferably 20 to 100,000 mPa · s. If it is less than 20 mPa · s or exceeds 500,000 mPa · s, it becomes difficult to perform coating with the current coating machine. This viscosity is a value measured by a rotational viscometer.

(A) The content of the organic radical R ¹ having a cationically polymerizable substituent components, may be represented by R ¹ equivalent is the weight per R 1 ¹ mole, (A) component of the present invention, this R ¹ equivalent is preferably 180 or more and 2,000 or less. If it is less than 180, synthesis may be difficult, or the number of polymerizable groups may be so large that volume shrinkage before and after curing may increase. If it is greater than 2,000, the number of polymerizable groups is too small, and mechanical properties such as curability and cured product hardness may be inferior, so that it is not suitable for the protective film of the optical recording medium of the present invention. Particularly preferably, R ¹ equivalent is 180 or more and 1,000 or less from the viewpoint of achieving both volume shrinkage and hardness and curability of the cured product.

Furthermore, among cationically polymerizable organopolysiloxanes, compounds having an R ¹ equivalent of 180 or more and 500 or less are particularly small in volume shrinkage and excellent in curability. Therefore, it is particularly preferable that at least one compound satisfying this is 70% by mass or more in the total component (A).

  (A) All the well-known methods can be used for the manufacturing method of a component. As an example, a compound obtained by reacting an organohydrogensiloxane having a Si—H group with a compound containing an aliphatic unsaturated group and a cationic polymerizable substituent by a hydrosilylation reaction is preferable. As the organohydrogensiloxane used here, those having a linear structure, a branched structure, a cyclic structure, and a combination thereof can be used. Moreover, as a reaction catalyst of hydrosilylation, well-known transition metal catalysts, such as platinum, palladium, and rhodium, can be used.

Examples of the compound containing an aliphatic unsaturated group and a cationically polymerizable substituent include 4-vinylcyclohexene oxide and allyl glycidyl ether.
As described above, the component (A) is an organopolysiloxane having a cationic polymerizable substituent at the side chain and / or terminal, and specific examples thereof are shown below.
The following are mentioned as a linear structure.

[All R ¹ MeSiO structure]

[R ¹ MeSiO and Me ₂ SiO coexistence]

[Terminal and side chain R ¹ ]

[Terminal R ¹ : Side Chain R ¹ MeSiO and Me ₂ SiO Coexistence]

[Terminal R ¹ : Side Chain Me ₂ SiO]

[Branch end R ¹ ]

（ｃは２〜１０、特に２〜７、ｄは０〜８、特に１〜５の整数である。） Moreover, as a ring structure, what is shown by following formula (2), especially following formula (3) is preferable.

(C is an integer of 2 to 10, particularly 2 to 7, and d is an integer of 0 to 8, particularly 1 to 5.)

（ｎは３〜１０、特に３〜７であることが好ましい。）

(N is preferably 3 to 10, particularly 3 to 7.)

等が挙げられる。 Specific compounds include

Etc.

(B) Cationic polymerization initiator In the present invention, as the cationic polymerization initiator of the component (B), a compound capable of initiating polymerization of a cationic polymerizable substituent by light including ultraviolet rays can be used.
Various known compounds (acid generators) that generate an acid by light including ultraviolet rays can be used without any limitation, and in particular, the following general formula (R ³ ) _x E ⁺ · Y ⁻
Wherein R ³ is selected from a substituted or unsubstituted aromatic carbocyclic group in which an aromatic ring carbon atom is directly bonded to E and an aromatic heterocyclic group, which may be the same or different from each other. E represents a central element selected from I, S, Se and P, Y ⁻ represents BF ₄ ⁻ , PF ₆ ⁻ , AsF ₆ ⁻ , SbF ₆ ⁻ , ClO ₄ ⁻ , HSO ₄ ⁻ and B represents a non-basic and non-nucleophilic anion selected from B (C ₆ F ₅ ) ₄ ^— , and x is 2 when E is I, 3 when S or Se, and 4 when P.) The onium salt represented by these is preferable.

Examples of the aromatic carbocyclic group include monovalent aromatic carbocyclic groups such as phenyl and naphthyl groups, as well as methyl, ethyl, propyl, butyl, octyl, decyl, and dodecyl. Selected from alkyl groups such as alkenyl groups, alkoxy groups such as methoxy groups, ethoxy groups and propoxy groups, halogen atoms such as chlorine atoms and bromine atoms, sulfur-containing groups such as cyano groups, mercapto groups and thiophenyl groups. Illustrative are monovalent aromatic carbocyclic groups substituted by groups. Particularly, E is preferably I or S because of high reactivity, and Y ⁻ is preferably PF ₆ ⁻ , SbF ₆ ⁻ or B (C ₆ F ₅ ) ₄ ⁻ . R ³ is preferably an aromatic carbocyclic group substituted with an alkyl group having 1 to 20 carbon atoms or an alkoxy group having 1 to 10 carbon atoms from the viewpoint of excellent solubility in silicone. .
Among the photoacid generators, diaryl iodonium salt derivatives and triarylsulfonium salt derivatives are preferable.

  These photoacid generators are added for the purpose of initiating the reaction of the cationically polymerizable substituent, and may be used alone or in combination of two or more as long as they meet the purpose. Good.

  (B) The compounding quantity of a component should just add the hardening effective amount, Although it does not specifically limit, From a viewpoint of a cure rate and economical efficiency, it is 0.01 with respect to 100 mass parts of (A) component. -20 mass parts is preferable. If the amount is less than 0.01 parts by mass, the curing reactivity due to light irradiation is too low, and the productivity is greatly reduced. If the amount is more than 20 parts by mass, the physical properties such as the mechanical strength of the protective film are extremely lowered, which is not suitable. More preferably, the addition amount is about 0.1 to 10 parts by mass.

Other components For the purpose of increasing the activity of the cationic polymerization initiator of component (B), a photosensitizer may be used in combination with the cationic polymerization initiator. The photosensitizer has a solubility of 0.01 parts by mass or more with respect to 100 parts by mass of the above cationic polymerizable organosiloxane at 25 ° C., and is sensitized to be compatible with the cationic polymerizable organosiloxane. Any agent may be used. For example, when the onium salt compound is an iodonium salt compound or the like, known sensitizers such as 1-naphthol, 2-naphthol, 1-methoxynaphthalene, naphthalene derivatives such as 1,4-dihydroxynaphthalene, 2-ethylanthracene, 9 , 10-dimethoxyanthracene, anthracene derivatives, 9-hydroxyphenanthrene, phenanthrene derivatives such as 9-methoxyphenanthrene, hydroxyacetophenone derivatives, benzoin derivatives, benzophenone derivatives, thioxanthone derivatives, acylphosphine oxide derivatives, benzyldimethyl ketal derivatives, etc. Any material can be used as long as it can be dissolved in the component (A) of the present invention.
About 0.01-5 mass parts is suitable for the addition amount of a photosensitizer with respect to 100 mass parts of (A) component.

  Further, an epoxy compound not containing silicone, an oxetane compound, and a compound having a polymerizable internal olefin may be blended in order to improve curing reactivity, strength, hardness and the like. Specific examples include 9-decene-1-ol oxide and compounds of the following formula.

  In addition, an inorganic filler such as silica, and a wavelength adjusting agent, a dye, a pigment, a flame retardant, a heat-resistant agent, an oxidation-resistant deterioration agent, and the like may be blended as long as the transparency is not affected.

Light transmissive protective film The curable resin composition for optical recording media of the present invention is capable of forming a light transmissive protective film on a substrate.
In this case, an existing transparent organic resin or inorganic material used as an optical recording material can be used for the support substrate. For example, polycarbonate, polyacrylate, polymethacrylate, polystyrene, polyester, polyolefin, epoxy resin, glass and the like are suitable.

  The shape of the support is an existing shape, specifically, a disc shape having a thickness of about 0.5 to 1.5 mm, a diameter of 120 mm or 80 mm, a card shape, and the like, and can be used without particular limitation. A known reflective layer, recording layer, and the like are laminated on the support. The reflective layer and the recording layer can be formed by a known method such as vacuum deposition, sputtering, ion plating, or spin coating as an organic solution.

  The composition of the present invention is applied on the recording layer with a specific film thickness by spin coating or the like. The optimum film thickness varies depending on the refractive index of the film, the laminated structure, etc., but is preferably about 10 to 300 μm, more preferably about 50 to 200 μm. This film preferably has small thickness variations. In particular, the thickness error is preferably ± 5% or less.

A coating film using a photoacid generator as a cationic polymerization initiator is easily cured by irradiation with light containing ultraviolet rays. As a light source for photocuring the composition of the present invention, a low-pressure water source lamp, a medium-pressure mercury lamp, a high-pressure mercury lamp, an ultrahigh-pressure mercury lamp, a metal halide lamp, a xenon lamp, a carbon arc lamp, or the like is used. Moreover, it can be easily cured by a laser beam such as a semiconductor laser, an argon laser, or a He—Cd laser. The amount of irradiation energy is preferably 10 to 3,000 mJ / cm ² , more preferably 50 to 1,000 mJ / cm ² .

  In addition, in order to harden more completely after irradiating the light containing an ultraviolet-ray, you may heat in a thermostat, a heating drying furnace, an infrared heater, and a hot air drying furnace. The heating temperature is not particularly limited, but is preferably about 30 to 180 ° C. and about 0.5 minutes to 240 hours. Further preferable conditions include heating at 40 to 80 ° C. for about 0.5 to 72 hours.

  You may provide the hard-coat layer which has a damage prevention performance in the outermost layer on the light-transmissive protective film of this invention. As the hard coat layer, a conventionally known composition can be used. Examples include radical reactive compounds such as polyfunctional acrylates, organopolysiloxanes containing silanol groups and the like as binders, such as silica and titania. Those containing inorganic oxide fine particles are preferred. The fine particles may be coated with an organosilane hydrolyzate having a polymerizable functional group or an organosilane hydrolyzate not containing a polymerizable functional group. As the curing method, light irradiation including ultraviolet rays and / or heat curing at 40 to 150 ° C. can be used. The film thickness is preferably about 0.1 to 30 μm, more preferably about 0.5 to 20 μm.

  EXAMPLES Hereinafter, although an Example and a comparative example are shown and this invention is demonstrated concretely, this invention is not restrict | limited to the following Example.

（Ｒ¹：３，４−エポキシシクロヘキシルエチル）
（Ｂ）成分の光酸発生剤として、下記式（ｉｉ）に示されるジアリールヨードニウムヘキサフルオロアンチモネート２質量部、

（Ｒ＝Ｒ’＝Ｃ₁₀Ｈ₂₁）
を均一混合し、保護層形成用組成物とした。
この均一に混合した組成物を脱泡後、スピンコート法にて直径１２ｃｍ、厚み１．１ｍｍの円型ポリカーボネート基板へ塗布した。メタルハライドランプによる紫外光を４００ｍＪ／ｃｍ²照射して硬化を行ったところ、タックのない透明膜（膜厚１１６μｍ）を得た。 [Example 1]
As component (A), 100 parts by mass of a cationic curable organopolysiloxane represented by the following formula (i), having a viscosity at 25 ° C. of 17,800 mPa · s and an epoxy equivalent of 230,

(R ¹ : 3,4-epoxycyclohexylethyl)
(B) 2 parts by mass of diaryliodonium hexafluoroantimonate represented by the following formula (ii) as a photoacid generator of component

(R = R ′ = C ₁₀ H ₂₁ )
Were uniformly mixed to obtain a protective layer forming composition.
The uniformly mixed composition was defoamed and then applied to a circular polycarbonate substrate having a diameter of 12 cm and a thickness of 1.1 mm by spin coating. Curing was performed by irradiating 400 mJ / cm ² with ultraviolet light from a metal halide lamp, and a transparent film (thickness: 116 μm) having no tack was obtained.

[Example 2]
1.1 equivalents of 4-vinylcyclohexene oxide are reacted with Si-H groups of hydrogen polysiloxane blocked with trimethylsilyl groups at both ends (average of dimethylsiloxane units is 80 and average of methylhydrogensiloxane units is 20). Thus, an organopolysiloxane having a cyclohexene oxide group in the side chain, a viscosity at 25 ° C. of 5,270 mPa · s, and an epoxy equivalent of 490 was synthesized. Using this as the component (A), 100 parts by mass of the organopolysiloxane and the photoacid generator of the component (B) are diaryl iodonium hexafluoroantimonates (R = R ′ = C ₁₀ ) represented by the above formula (ii). H ₂₁ ) 2 parts by mass were uniformly mixed to obtain a protective layer forming composition.
The uniformly mixed composition was defoamed and then applied to a circular polycarbonate substrate having a diameter of 12 cm and a thickness of 1.1 mm by spin coating. When cured by irradiating 400 mJ / cm ² with ultraviolet light from a metal halide lamp, a transparent film (thickness 110 μm) having no tack was obtained.

（Ｒ¹：３，４−エポキシシクロヘキシルエチル）
（Ｂ）成分の光酸発生剤として、下記式（ｉｖ）に示されるジアリールヨードニウムテトラキス（ペンタフルオロフェニル）ボレート２質量部

を均一混合し、保護層形成用組成物とした。
この均一に混合した組成物を脱泡後、スピンコート法にて直径１２ｃｍ、厚み１．１ｍｍの円型ポリカーボネート基板へ塗布した。ＵＶを４００ｍＪ／ｃｍ²照射して硬化を行ったところ、タックのない透明膜（膜厚１０７μｍ）を得た。 [Example 3]
As the component (A), 100 parts by mass of a cationic curable organopolysiloxane represented by the following formula (iii), having a viscosity of 3,010 mPa · s at 25 ° C. and an epoxy equivalent of 184,

(R ¹ : 3,4-epoxycyclohexylethyl)
(B) 2 parts by mass of diaryliodonium tetrakis (pentafluorophenyl) borate represented by the following formula (iv) as a photoacid generator of component

Were uniformly mixed to obtain a protective layer forming composition.
The uniformly mixed composition was defoamed and then applied to a circular polycarbonate substrate having a diameter of 12 cm and a thickness of 1.1 mm by spin coating. When cured by irradiation with UV at 400 mJ / cm ² , a tack-free transparent film (film thickness 107 μm) was obtained.

[Example 4]
100 parts by mass of a cationic curable organopolysiloxane represented by the following formula (v), having a viscosity at 25 ° C. of 890 mPa · s and an epoxy equivalent of 561,
R ¹ (CH ₃ ) ₂ SiO — [(CH ₃ ) ₂ SiO] ₁₀ —Si (CH ₃ ) ₂ R ¹ (v)
(R ¹ : 3,4-epoxycyclohexylethyl)
As a photoacid generator for component (B), 2 parts by mass of diaryliodonium tetrakis (pentafluorophenyl) borate were uniformly mixed to obtain a composition for forming a protective layer.
The uniformly mixed composition was defoamed and then applied to a circular polycarbonate substrate having a diameter of 12 cm and a thickness of 1.1 mm by spin coating. When cured by irradiation with UV at 400 mJ / cm ² , a tack-free transparent film (film thickness: 92 μm) was obtained.

[Example 5]
100 parts by mass of a cationic curable organopolysiloxane represented by the following formula (vi), having a viscosity at 25 ° C. of 2,280 mPa · s and an epoxy equivalent of 239,
_{(CH 3) 3 SiO- [R} 1 (CH 3) SiO] 3 -Si (CH 3) 3 (vi)
(R ¹ : 3,4-epoxycyclohexylethyl)
As a photoacid generator for component (B), 2 parts by mass of diaryliodonium tetrakis (pentafluorophenyl) borate were uniformly mixed to obtain a composition for forming a protective layer.
The uniformly mixed composition was defoamed and then applied to a circular polycarbonate substrate having a diameter of 12 cm and a thickness of 1.1 mm by spin coating. When cured by irradiation with UV at 400 mJ / cm ² , a tack-free transparent film (film thickness 101 μm) was obtained.

[Comparative Example 1]
UV curable acrylic resin material (Aronix M-8060, viscosity at 25 ° C. is 9,070 mPa · s, manufactured by Toagosei Co., Ltd.), 100 parts by mass, photopolymerization initiator (Darocur-1173, Ciba Specialty Chemicals ( Co., Ltd.) 2 parts by mass were uniformly mixed to form a protective layer forming composition.
The uniformly mixed composition was defoamed and then applied to a circular polycarbonate substrate having a diameter of 12 cm and a thickness of 1.1 mm by spin coating. When cured by irradiation with UV at 400 mJ / cm ² , a tack-free transparent film (film thickness 108 μm) was obtained.

[Comparative Example 2]
100 parts by mass of a commercially available alicyclic epoxy compound represented by the following structural formula, as a photoacid generator of the component (B), diaryl iodonium hexafluoroantimonate (R = R ′ = C) represented by the above formula (ii) ₁₀ H ₂₁ ) 2 parts by mass were uniformly mixed to form a protective layer forming composition.
The uniformly mixed composition was defoamed and then applied to a circular polycarbonate substrate having a diameter of 12 cm and a thickness of 1.1 mm by spin coating. When cured by irradiation with UV at 400 mJ / cm ² , a tack-free transparent film (film thickness 99 μm) was obtained.

[Comparative Example 3]
100 parts by mass of a commercially available epoxy resin material (Epototo YD-128, manufactured by Toto Kasei Co., Ltd.) and 2 parts by mass of diaryliodonium hexafluoroantimonate (R = R ′ = C ₁₀ H ₂₁ ) represented by the above formula (ii) Were uniformly mixed to obtain a composition for forming a protective layer.
The uniformly mixed composition was defoamed and then applied to a circular polycarbonate substrate having a diameter of 12 cm and a thickness of 1.1 mm by spin coating. When cured by irradiation with UV at 400 mJ / cm ² , a tack-free transparent film (film thickness 105 μm) was obtained.
The evaluation results are shown in Table 1.

Volume shrinkage: Calculated from the change rate of liquid specific gravity and solid specific gravity after curing Warpage: Visual evaluation of warpage of substrate after irradiation with metal halide lamp 400 mJ / cm ² Pencil hardness: JIS K5600-5-4 scratch hardness (pencil method) The coating film for measuring pencil hardness is a bar coater (No. 46) coating / curing light resistance test on a polished steel plate: decrease rate of 400 nm transmittance 72 hours after irradiation with a metal halide lamp (140 MJ / m ² ): 10% Less than ×: 10% or more

From the above results, it can be seen that the volume shrinkage obtained from the specific gravity is smaller than the composition of the comparative example. Therefore, when used as a light-transmitting protective layer of an optical recording medium, the internal distortion is small and the warpage of the substrate over time can be suppressed. Moreover, it turns out that the coating film of an Example has moderate hardness from the result of pencil hardness. In the weather resistance test that examined the degree of photodegradation of the resin by irradiating light containing intense ultraviolet light, the organosiloxanes described in the examples showed a small decrease in light transmission and excellent light resistance. I understand.

Claims (4)

On the reflective layer and the recording layer sequentially laminated on the plastic substrate,
(A) It has at least two cationic polymerizable groups selected from an epoxy group, an oxetanyl group, and a pentamethylcyclotrisiloxanyl group in one molecule, and has a viscosity at 25 ° C. of 20 to 500 Cation-curable organopolysiloxane of 1,000 mPa · s
100 parts by mass,
(B) an optical recording light transmitting transparent protective layer obtained by curing a cationic polymerization initiator 0.01 to 20 parts by weight shall be the essential component for an optical recording medium curable resin composition is formed Medium . The organopolysiloxane as component (A) has a monovalent hydrocarbon group R ¹ having the cationic polymerizable group, and R ¹ equivalent (mass per mole of R ¹ ) is 180 to 2,000. the optical recording medium of the described. (A) component is the following composition formula (1)
R ¹ _m R ² _n SiO _{(4-mn) / 2} (1)
(In the formula, R ¹ is a monovalent hydrocarbon group having a cationic polymerizable group selected from an epoxy group, an oxetanyl group and a pentamethylcyclotrisiloxanyl group, which may be the same or different from each other, and R ² is a cation. A substituted or unsubstituted monovalent hydrocarbon group which does not have a polymerizable group and may be the same or different from each other, a part of which may be a hydrogen atom, a hydroxyl group or an alkoxy group. Are each an integer of 0 to 3, and m + n is an integer of 0 to 3.)
In consists shown a structural unit, at least two have a R ¹ in a molecule, the average value of m is 0.1 to 1.5, the average value of n is from 0 to 2.2, the average value of m + n There is an organopolysiloxane is 0.5 to 3.0 according to claim 1 or 2 optical recording media material according. Component (B), the optical recording medium of claim 1, 2 or 3 wherein the compound which generates acid by irradiation of light including ultraviolet rays.