WO2006051895A1

WO2006051895A1 - Ultraviolet curable resin composition and curing product thereof

Info

Publication number: WO2006051895A1
Application number: PCT/JP2005/020702
Authority: WO
Inventors: Kiyohisa Tokuda; Go Mizutani; Hideaki Kametani; Kazuhiko Ishii; Masahiro Naitoh
Original assignee: Nippon Kayaku Kabushiki Kaisha
Priority date: 2004-11-15
Filing date: 2005-11-11
Publication date: 2006-05-18
Also published as: TW200630392A; JP2008024724A

Abstract

[PROBLEMS] To provide an ultraviolet curable resin composition, or curing product thereof, that excels in transparency and low water absorption and realizes reduced warpage and high durability, which ultraviolet curable resin composition, or curing product thereof, can be used as a protective coating agent, or curing product thereof, for a high-density optical disk, especially an optical disk capable of read and/or write using blue laser. [MEANS FOR SOLVING PROBLEMS] There is provided an ultraviolet curable resin composition of 100 to 5000 mPa s viscosity as measured at 25°C by the use of B-type viscometer comprising component consisting of a di(meth)acrylic ester of pentacyclopentadecanedimethanol (A), photopolymerization initiator (B) and ethylenically unsaturated compound other than the component (A) (C).

Description

Specification

Ultraviolet curable resin composition and cured product thereof

Technical field

TECHNICAL FIELD [0001] The present invention relates to an ultraviolet curable resin composition and a cured product thereof, and more particularly, an ultraviolet curable resin composition and a cured product that are excellent in transparency and durability with low water absorption rate and curing shrinkage rate. And a next generation high density optical disc having the cured product layer.

Background art

[0002] Today, as a general optical disc recording medium that is put into practical use, CD (compact disc), MO (magneto-optical disc), CD—R (write-once compact disc), CD—RW (Rewritable compact disc). These are formed by forming a recording film and a reflective film on a polycarbonate substrate with a thickness of 1.2 mm, and a protective layer made of an ultraviolet curable coating agent for the purpose of protecting them from external factors. Is provided. In recent years, in order to further improve the storage capacity, the thickness of the polycarbonate has been reduced to 0.6 mm, which is half of the conventional thickness, and the two substrates are bonded together. DVD-R, DVD-RW, DVD-RAM, DVD + R, DVD + RW, etc. have been put to practical use that have cleared the problem when the spot diameter is reduced. These are all formed by forming a recording film, a reflective film, etc. on a polycarbonate substrate having a thickness of 0.6 mm. Similarly to the above, an ultraviolet curable protective layer or an adhesive layer is provided for the purpose of protection, adhesion and the like. It is provided.

[0003] However, as a recording medium corresponding to the increase in capacity in the digital broadcasting era, it is said that the capacity of the DVD recording medium is still insufficient. Therefore, as a next-generation high-density optical disc, a recording layer and a transparent layer with a thickness of 100 m are stacked on the substrate, and the transparent cover layer side force that separates from the polycarbonate substrate side is written and read by blue laser light. An optical disc of the type to be performed has been proposed (Patent Document 1) and has already been put into practical use.

[0004] In this case, as a method of forming the cover layer, a method of laminating a transparent film having a thickness of 100 m and a method of forming a layer having a thickness of 100 / zm on the recording film using an ultraviolet curable resin are used. The 2P method and the spin coater method are proposed as methods for forming the UV-curable resin layer. It has been proposed. As such an ultraviolet curable resin for forming a cover layer on a recording film, for example, 2P agents such as the compositions described in Patent Document 2 and Patent Document 3 have been proposed. In addition, protective coating agents such as the compositions described in Patent Document 4, Patent Document 5, and Patent Document 6 have been proposed.

Patent Document 1: Japanese Patent Laid-Open No. 11-273147

Patent Document 2: JP-A-5-059139

Patent Document 3: Japanese Patent Laid-Open No. 5-132534

Patent Document 4: Japanese Patent Laid-Open No. 3-131605

Patent Document 5: Japanese Patent Laid-Open No. 3-172358

Patent Document 6: Japanese Patent Laid-Open No. 2003-268263

Disclosure of the invention

Problems to be solved by the invention

[0005] However, since these ultraviolet curable resin compositions have a high cure shrinkage, they generate warpage when used in a transparent cover layer of a high-density optical disc, and further warp after a durability test. There was a problem (problem) that it would occur.

Means for solving the problem

[0006] As a result of intensive studies to solve the above-mentioned problems, the present inventors have found a resin composition suitable for solving the above-mentioned problems, and have reached the present invention based on that.

That is, the present invention relates to

(1) containing a component (A) comprising a di (meth) acrylic ester of pentacyclopentadecane dimethanol, a photopolymerization initiator (B), and an ethylenically unsaturated compound (C) other than component (A), UV curable resin composition having a viscosity of 100 to 5000 mPa's at 25 ° C measured with a B-type viscometer,

(2) Compound (A-1) in which component (A) is represented by the following general formula (1):

[0008] [Chemical 1]

And a compound represented by the following general formula (2) (A

[Chemical 2]

(In each formula, R represents a hydrogen atom or a methyl group.)

The ultraviolet curable resin composition according to (1), which is a mixture of

(3) The ultraviolet curing according to the above (1) or (2), wherein the ethylenically unsaturated compound (C) is a urethane (meth) atrelate having a molecular weight of 400 to 10,000 and Z or an epoxy acrylate having a molecular weight of 500 to 10,000. Mold oil composition,

(4) The ultraviolet ray curable resin composition according to any one of (1) to (3) above, which is a protective coating agent for optical disks,

(5) A cured product of the ultraviolet curable resin composition obtained by curing the ultraviolet curable resin composition according to any one of (1) to (4) above,

(6) Curing of the ultraviolet curable resin composition according to (5) above, wherein the water absorption of the cured product (measurement temperature: 25 ° C) is 2.0% or less and the curing shrinkage is 6% or less. object,

(7) The cured product of the ultraviolet curable resin composition according to (5) or (6) above, wherein the transmittance of the blue laser at a film thickness of 50 to 150 μm is 70% or more,

(8) An optical disc having a cured product layer of the ultraviolet curable resin composition according to any one of (5) to (7) above,

(9) The optical disc according to (8) above, wherein a cured product layer of an ultraviolet curable resin composition is formed on a side on which recording light and Z or reproduction light are incident,

About. BEST MODE FOR CARRYING OUT THE INVENTION

[0010] The present invention is a UV curable resin composition and a cured product thereof, useful as a protective coating agent for high-density optical discs, having excellent durability with low transparency, excellent water absorption, and low warpage. In addition, it can also be applied to materials related to optical applications such as optical finos and optical switching elements.

Hereinafter, the present invention will be described in detail.

[0012] The ultraviolet curable resin composition of the present invention comprises pentacyclopentadecane dimethanol dimer.

Containing component (A) consisting of (meth) acrylic acid ester, photopolymerization initiator (B), and ethylenically unsaturated compound (C) other than component (A), measured at 25 ° C with a B-type viscometer UV curable resin composition having a viscosity at 100 to 5000 mPa's.

[0013] The component (A) contained in the ultraviolet curable resin composition of the present invention contributes to the low water absorption performance and low shrinkage performance of the cured product. For example, pentacyclopentadeca It can be obtained by a method of dehydration condensation of dimethylethanol and (meth) acrylic acid in the presence of an acid catalyst.

[0014] The raw material pentacyclopentadecane dimethanol can be obtained, for example, by hydrogenating formaldehyde of tricyclopentagen and dialdehyde obtained (for example, JP 2001-10999). In this case, tricyclopentagen has a left-right symmetric structure and a left-right asymmetric structure, and usually exists as a mixture thereof. As a result, the component (A) contained in the ultraviolet curable resin composition of the present invention also has a symmetrical structure in which the pentacyclopentadecane dimethanol moiety is represented by the following general formula (1) and the following general formula: There is a left-right asymmetric structure shown in (2), which usually exists as a mixture.

[0015] General formula (1):

[0016] [Chemical 3]

[0017] General formula (2):

[0018] [Chemical 4]

(In the above formulas, R represents a hydrogen atom or a methyl group.)

[0019] The content of the component (A) in the ultraviolet curable resin composition of the present invention is preferably 5 to 98 parts by weight, particularly preferably 10 to 100 parts by weight based on the total amount of the resin composition. 96 parts by weight.

[0020] The photopolymerization initiator (B) contained in the ultraviolet curable resin composition of the present invention includes 1-hydroxycyclohexyl phenyl ketone (Irgacure 184; manufactured by Chinoku Specialty Chemicals), 2,2 Dimethoxy-2-phenylacetophenone (Irgacure 651; manufactured by Tinoku Specialty Chemicals), 2-hydroxy-1-2-methyl-1-phenyl-propane-1-one (Darocur 1173; Chinok 1special) Chemicals), 2-Methyl 1— [4- (Methylthio) phenol] 2 Morpholinopropane 1-one (Irgacure 907; Ciba Specialty Chemicals), 2-Benzyl-2-dimethylamino 1- (4 Morpholi Nophenyl) Butane 1-on, 2 Black mouth thixanthone, 2, 4 Dimethylthioxanthone, 2, 4 Diisopropinoretioxanthone, Isopropinorethi And xanthone, 2,4,6-trimethylbenzoyldiphosphine oxide, bis (2,6 dimethoxybenzoyl) -1,2,4,4 trimethylpentylphosphine oxide and the like. These photopolymerization initiators can be used singly or in combination at any ratio, and can also be used in combination with photopolymerization initiators such as amines.

[0021] The content of the photopolymerization initiator (B) in the ultraviolet curable resin composition of the present invention is preferably 0.5 to 20 parts by weight based on 100 parts by weight of the total amount of the resin composition. Particularly preferred is 1 to 10 parts by weight.

[0022] Examples of photopolymerization initiation assistants such as amines that can be used in the present invention include diethanolamine, 2-dimethylaminoethylbenzoate, dimethylaminoacetophenone, and p-dimethyl. Examples include luaminobenzoic acid ethyl ester, P-dimethylaminobenzoic acid isoamyl ester, and the like. When a photopolymerization initiation aid such as amines is used in combination, the content in the ultraviolet curable oil composition of the present invention is 0.05 to 5 parts by weight with 100 parts by weight of the total amount of the resin composition. Particularly preferred is 0.1 to 3 parts by weight.

[0023] Examples of the ethylenically unsaturated compound (C) other than the component (A) that can be used in the ultraviolet curable resin composition of the present invention include an acrylate monomer, an acrylate oligomer, and the like. May be used arbitrarily.

[0024] The acrylate monomer as the ethylenically unsaturated compound (C) includes a monofunctional monomer having one (meth) acrylate group in the molecule and two or more (meth) acrylate groups in the molecule. The polyfunctional monomer can be classified.

[0025] Examples of monofunctional monomers having one (meth) acrylate group in the molecule include tricyclodecane (meth) acrylate, dicyclopentagenoxychetyl (meth) acrylate, dicyclopental ( (Meth) Atarylate, Isovolyl (Meth) Atarylate, Adamantyl (Meth) Atarylate, Ferrochechetyl (Meth) Atarylate, Benzyl (Meth) Atrelate, Tetrahydrofurfuryl (Meth) Atarylate, Morpholine (Meth) Examples include attalylate, ferricglycidyl (meth) acrylate, 2-hydroxyethyl (meth) acrylate, 2-hydroxypropyl (meth) acrylate, ethyl carbitol (meth) acrylate.

[0026] In addition, examples of the (meth) acrylate monomer (C) having two or more (meth) acrylate groups in the molecule include neopentyl dalycol di (meth) acrylate, tricyclodecane dimethylol di ( (Meth) Atalylate, hydroxypivalaldehyde-modified trimethylolpropane di (meth) atalylate, neopentyl glycol di (meth) acrylate, hydroxybivalate, polyethylene glycol di (meth) attalylate, dicyclopenta-ldi (meth) atari 1, 6-Hexanediol di (meth) acrylate, polypropylene glycol di (meth) acrylate, ethylene oxide modified bisphenol A di (meth) acrylate, ethylene oxide modified trimethylolpropane tri (meth) Atalylate, ethylene oxide Sex Pentaerisu Ritorutetora (meth) Atari rate, tris [(meth) Atari port Kishechiru] Isoshianureto, hexa (meth) Atari rate, etc. to E Chirenokishido modified dipentaerythritol.

[0027] These acrylate monomers may be used alone or in any combination of two or more. May be used together. When the acrylate monomer is used, the content in the ultraviolet curable resin composition of the present invention is preferably 1 to 90 parts by weight, particularly preferably 5 to 100 parts by weight based on the total amount of the resin composition. 85 parts by weight.

[0028] The ultraviolet curable resin composition of the present invention has a viscosity at 25 ° C of 10 measured by a B-type viscometer.

It is necessary to be 0 to 5000 mPa · s.

[0029] Examples of the acrylate oligomer as the ethylenically unsaturated compound (C) include urethane (meth) acrylate having a molecular weight of 400 to 10,000 and epoxy acrylate having a molecular weight of 500 to 10,000.

[0030] Urethane (meth) atalylate having a molecular weight of 400 to 10,000 is obtained by a reaction of the following polyhydric alcohol, an organic polyisocyanate, and a hydroxy (meth) atalytoi compound.

[0031] Examples of the polyhydric alcohol include neopentyl glycol, 3-methyl-1,5-pentanediol, ethylene glycol, propylene glycol, 1,4 butanediol, 1,6 hexanediol, trimethylolpropane, pentaerythritol. , Tricyclodecane dimethylol, bis (hydroxymethyl) cyclohexane and the like, and the polyhydric alcohols and polybasic acids (for example, succinic acid, phthalic acid, hexahydrophthalic anhydride, terephthalic acid, adipic acid, azelaic acid, tetrahydro Polyester polyol obtained by reaction with phthalic anhydride, etc., and force prolataton alcohol obtained by reaction of the polyhydric alcohol with _ε -force prolataton, and polycarbonate polyol (eg, 1, 6 to one) Xanthandiol and diphe And polycarbonate polyols such as polyethylene glycol, polypropylene glycol, polytetramethylene glycol, and ethylene oxide-modified bisphenol 得 obtained by reaction with carbonate).

[0032] Examples of the organic polyisobutylene Xia sulfonates, such as isophorone di-iso-Xia sulfonate, to Kisamechiren Jiisoshianeto, tolylene iso Xia sulfonates, xylylene iso Xia sulfonates, Jifuenirumeta Hmm _4, ₄ 'over-di iso Xia sulfonate, dicyclopenta - Ruisoshianeto etc. Is mentioned.

[0033] Examples of the hydroxy (meth) attareito toy compound include hydroxyethyl (meth) acrylate, hydroxypropyl (meth) acrylate, hydroxybutyl (meth) acrylate, dimethylol cyclohexyl mono (meta) ) Atarylate, hydroxycaprolataton (meth) attareido And so on.

[0034] When a urethane (meth) acrylate with a molecular weight of 400 to 10,000 is used, the content of the ultraviolet ray curable resin composition of the present invention is 1 to 100 parts by weight based on the total amount of the resin composition. 90 parts by weight is preferred, with 3 to 85 parts by weight being particularly preferred.

[0035] The molecular weight 500 to be used in the ultraviolet curable resin composition of the present invention is not particularly limited, but it is preferable to use a bisphenol type epoxy acrylate, for example, oil Epoxy Coat Epoxy Coat 802, 1001, 1004, etc., and Epoxy Coat obtained by the reaction of Bisphenol F type epoxy resin, Epicoat 4001, P2, 4003P, etc. with (meth) acrylic acid Atallate is mentioned. Moreover, you may use the alicyclic epoxy acrylate which hydrogenated the above. When epoxy acrylate having a molecular weight of 500 to 10,000 is used, the content in the ultraviolet ray curable resin composition of the present invention is preferably 1 to 90 parts by weight based on 100 parts by weight of the total amount of the resin composition. Particularly preferred is 3 to 85 parts by weight.

[0036] The ultraviolet curable resin composition of the present invention may contain a polyester-based, polycarbonate-based, polyacrylic-based, polyurethane-based, or polybull-based resin as a high-molecular polymer as necessary. it can. Furthermore, additives such as organic solvents, silane coupling agents, polymerization inhibitors, leveling agents, light stabilizers, antioxidants, antistatic agents, surface lubricants, fillers and the like can be used in combination.

[0037] The ultraviolet curable resin composition of the present invention can be obtained by mixing and dissolving the above-mentioned components at 20 to 80 ° C by stirring and mixing, and may be filtered after obtaining the composition. . The cured product of the ultraviolet curable resin composition of the present invention can be obtained by irradiating the ultraviolet curable resin composition of the present invention with light such as ultraviolet rays and visible light by the following method.

[0038] Light irradiation curing of the ultraviolet curable resin composition of the present invention may be performed using any light source as long as it is a lamp that irradiates light in the ultraviolet region to the near ultraviolet region. Examples include low-pressure, high-pressure or ultra-high pressure mercury lamps, metal nitride lamps, (pulse) xenon lamps, and electrodeless lamps.

[0039] The ultraviolet curable resin composition of the present invention has a curing shrinkage rate of 6% or less when cured, and a water absorption rate (measurement temperature 25 ° C) of the cured product is 2.0% or less. Is preferred. [0040] The protective coating agent for optical disks using the ultraviolet curable resin composition of the present invention may be applied by any coating method as long as the film thickness can be 50-100 μm. Examples of the method include spin coating, 2P, roll coating, and screen printing.

[0041] In addition, since a blue laser with a wavelength of about 400 nm is used for reading and Z or writing for the next generation high-density optical disc, the transmittance around 400 to 500 nm is 70 in a cured product with a film thickness of 50 to 150 m. % Or more is preferable.

[0042] Furthermore, the optical disk according to the present invention having a cured product layer of the above-described ultraviolet curable resin composition, and the ultraviolet curable adhesive on the side on which recording light and Z or reproduction light are incident. The thing in which the hardened | cured material layer of the fat composition is formed is mentioned as a suitable thing.

Example

Hereinafter, specific embodiments of the present invention will be described in more detail using examples.

[0044] (Synthesis Example 1)

In a reactor equipped with a reflux condenser, stirrer, thermometer, temperature controller, and water separator, 39.4 g (0.15 mol) pentacyclopentadecanedimethanol, 25.9 g (0.36 mol) acrylic acid, Noratorenens Norehon 0.518 g, Noid, Pquinone 0.197 g, Tolene 22.9 g, Cyclohexane 9.8 g were charged, and the product water was azeotroped with the solvent at a reaction temperature of 95-105 ° C. The reaction was carried out while distilling off, and the reaction was terminated when the amount of produced water reached 5.4 ml. After adding 83.8 g of toluene and 35.9 g of cyclohexane to the reaction mixture, the reaction mixture was neutralized with 25 wt% aqueous sodium hydroxide solution and then washed 3 times with 30 g of 15 wt% brine. The solvent was distilled off under reduced pressure, and 54.2 g of pentacyclopentadecane dimethanol ditalylate (A-3) consisting of a mixture of the following structural formula (3) and the following structural formula (4) was obtained as a pale yellow liquid. (Yield 97.5%) was obtained.

[0045] Structural Formula (3):

[0046] [Chemical 5]

(3)

[0047] Structural formula (4):

[0048] [Chemical 6]

α

(Examples 1-3 and Comparative Examples 1-2)

Using the compound (A-3) obtained in Synthesis Example 1, an ultraviolet curable resin composition having the composition shown in Table 1 was prepared by a conventional method. Table 1 shows the evaluation results of the obtained ultraviolet curable resin composition. The parts in Table 1 are parts by weight.

[0050] [Table 1] Table 1

Example 1 Example 2 Example 3 Comparative Example 1 Example Ingredient (A) (Part)

A— 3 100 60 70

Ingredient (C) (part)

UX-6101 10 20 20 50

R-604 30 80

PEG—40 ODA 50

LA 10 Inore Gacure 184 5 5 5 5

BP- 100 5

EPA 3 Viscosity 2045 3500 2300 1700 2000

(tifa · s / 25.C)

Curing shrinkage (%) 4. 8 5. 3 5. 0 7. 1 6. 7 Water absorption (%) 0. 3 0. 5 0. 5 1. 0 3. 1 Permeability (%) 80 80 80 80 80 Warpage 〇〇〇 XX Durability 〇〇〇〇 X The abbreviations of each component shown in the table are as follows.

UX-6101: Polyester urethane acrylate (molecular weight; 2700 ± 500), Nippon Kayaku Made by company.

R-604: Hydroxypivalaldehyde-modified trimethylolpropane di (meth) acrylate, manufactured by Enomoto Kayaku Co., Ltd.

PEG—400DA: Polyethylene glycol ditalylate, manufactured by Nippon Kayaku Co., Ltd.

LA: Lauryl acrylate, manufactured by NOF Corporation.

Irgacure 184: 1-Hydroxycyclohexylphenyl ketone, photopolymerization initiator manufactured by Tinoku 'Specialty' Chemicals.

BP—100: Benzophenone, manufactured by Nippon Kayaku Co., Ltd.

EPA: 4-dimethylaminoethyl benzoate, manufactured by Nippon Kayaku Co., Ltd.

[0051] In the present invention, the viscosity was measured with a B-type viscometer.

[0052] In the present invention, the curing shrinkage is a value calculated from the following formula (1) from the liquid specific gravity before curing at 25 ° C and the film specific gravity at 25 ° C obtained by curing.

Formula (1):

Curing shrinkage = (Membrane specific gravity Liquid specific gravity) Z Membrane specific gravity X 100 (1)

In the present invention, the water absorption is a value obtained by a method according to JIS K-7209 7.2.1.

[0053] Further, the transmittance is measured by applying a resin to a polycarbonate substrate by spin coating to a thickness of 100 ± 10 μm, and after UV curing, measure the transmittance at 405 nm using the polycarbonate substrate as a reference. It went by.

In the present invention, a DVD substrate on which aluminum was sputtered was used for warpage evaluation. Each of the compositions shown in Table 1 was applied onto an aluminum sputtered DVD substrate by a spin coater to form a coating film having an average film thickness of 100 m. As a coating film set UV irradiator (Japan Storage Battery Co. CS- 30L, 80wZcm high pressure mercury lamp) lamps height of the 10 cm, and cured at an energy amount of integrated light quantity 1 OOOmiZcm ^2. The obtained test piece was allowed to stand for 24 hours and then placed on a glass plate, and the warpage was evaluated according to the following criteria.

[0055] Evaluation criteria for warpage

○ · · 'Almost no warpage.

△ · · · When one side of the specimen is pressed with a finger, the opposite side is lifted, but it is 2 mm or less. X ··· When one side of the specimen is pressed with a finger, the opposite side is lifted by 5 mm or more.

For the durability evaluation in the present invention, the test piece used for the evaluation of the warp was used and left for 500 hours in an environment of 80 ° C. and 85% RH. The state of the reflective film was visually observed, and the durability was evaluated according to the following criteria.

[0057] Durability evaluation criteria

○ · · · Immediately after bonding No change is seen in the reflective film.

△ · · 'Slight discoloration or pinholes can be seen in the reflective film.

X · · 'Large discoloration or pinholes in the reflective film.

Industrial applicability

[0058] The ultraviolet curable resin composition and the cured product thereof according to the present invention are excellent in transparency, low water absorption, and have high durability with little warpage, and the cured product thereof. It can be used as a protective coating agent for high-density optical discs, and is extremely useful when applied to optical discs that perform reading and Z or writing using a blue laser. It is.

[0059] The ultraviolet curable resin composition and the cured product thereof according to the present invention include a protective coating agent for optical discs and a force that provides the cured product, and other materials related to optical applications such as optical finos and optical switching elements. It can also be applied to.

Claims

The scope of the claims

[1] containing a component (A) comprising a di (meth) acrylic ester of pentacyclopentadecane dimethanol, a photopolymerization initiator (B), and an ethylenically unsaturated compound (C) other than component (A), An ultraviolet curable resin composition having a viscosity of 100 to 5000 mPa's at 25 ° C measured with a B-type viscometer.

[2] Compound (A-1) in which component (A) is represented by the following general formula (1):

[Chemical 7]

And a compound (A-2) represented by the following general formula (2):

[Chemical 8]

(In each formula, R represents a hydrogen atom or a methyl group.)

The ultraviolet curable resin composition according to claim 1, which is a mixture of

[3] The ultraviolet curable resin according to claim 1 or 2, wherein the ethylenically unsaturated compound (C) is urethane (meth) acrylate with a molecular weight of 400 to 10,000 and epoxy acrylate with Z or a molecular weight of 500 to 10,000. Fat composition.

[4] The ultraviolet curable resin composition according to any one of claims 1 to 3, which is a protective coating agent for optical disks.

[5] A cured product of the ultraviolet curable resin composition obtained by curing the ultraviolet curable resin composition according to any one of claims 1 to 4.

[6] The water absorption of the cured product (measuring temperature 25 ° C) is 2.0% or less and the cure shrinkage is 6% or less.

A cured product of the ultraviolet curable resin composition according to claim 5. [7] The cured product of the ultraviolet curable resin composition according to claim 5 or 6, wherein the transmittance of the blue laser at a film thickness of 50 to 150 μm is 70% or more.

[8] An optical disc having a cured product layer of the ultraviolet curable resin composition according to any one of claims 5 to 7.

9. The optical disc according to claim 8, wherein a cured product layer of an ultraviolet curable resin composition is formed on a side on which recording light and Z or reproduction light are incident.