Method for producing cured product for hologram recording medium

Abstract

The present invention relates to a method for producing a cured product for a hologram recording medium, which is a method for producing a cured product for a hologram recording medium by subjecting a composition for a hologram recording medium to a curing reaction, the composition for a hologram recording medium contains a compound (a) having an isocyanate group and a compound (b) having an isocyanate-reactive functional group, and the curing reaction includes a curing step A for curing at less than 35 DEG C, the remaining rate of unreacted isocyanate groups after the curing step A is 10% or less relative to the isocyanate groups in the composition for the hologram recording medium before the curing reaction.

Description

Technical Field

[0001] The present invention relates to a method for producing a cured product for a hologram recording medium by curing a composition for a hologram recording medium. Background Art

[0002] Hologram recording media, which have attracted much attention in recent years, are recording media that utilize the interference and diffraction phenomena of light. A hologram is a recording method that records the interference pattern generated by the interference fringes of two kinds of light (referred to as recording light) called reference light and object light (also referred to as information light or signal light) in three dimensions inside a recording medium. A hologram recording medium includes a photosensitive material in a recording layer, and the photosensitive material undergoes chemical changes according to the interference pattern, and the interference pattern is recorded by locally changing the optical properties.

[0003] Hologram recording media have been developed for storage applications, and as other applications, they are being studied for use in optical components such as light guide plates for AR glasses. In the case of AR glasses, the optical components used for hologram recording in light guide plates are required to have a wide viewing angle, high diffraction efficiency for light in the visible range, and high transparency of the medium.

[0004] Hologram recording media are classified into several types depending on which optical properties are changed. Volume hologram media are media that record by generating a refractive index difference in a recording layer having a thickness greater than a certain value. Volume hologram media can save space and achieve high diffraction efficiency and wavelength selectivity, so they are considered suitable for use in AR glasses light guide plates.

[0005] As an example of a volume hologram recording medium, there is a write-once format that does not require a wet treatment or a bleaching treatment. The composition of the recording layer of the write-once format is usually formed by making the photoactive compound and the matrix resin compatible. For example, it is known that a photopolymer is used as a recording layer, and the photopolymer is obtained by combining a photopolymerization initiator and a polymerizable reactive compound capable of free radical polymerization or cationic polymerization as a photoactive compound with a matrix resin (Patent Documents 1 to 4).

[0006] When recording a hologram, if there is a recording layer composed of a photopolymer in the part where the reference light and the object light intersect to form an interference pattern, then in the part with higher light intensity in the interference pattern, the photopolymerization initiator undergoes a chemical reaction and becomes an active substance, which acts on the polymerizable compound to polymerize the polymerizable compound. At this time, if there is a difference in refractive index between the matrix resin and the polymer generated by the polymerizable compound, the interference pattern becomes a refractive index difference and is fixed in the recording layer. In addition, when the polymerizable compound is polymerized, it causes the polymerizable compound to diffuse from the periphery, and a concentration distribution of the polymerizable compound or its polymer is generated inside the recording layer. Based on this principle, the interference pattern is recorded in the hologram recording medium as a refractive index difference.

[0007] Hereinafter, the process of changing the optical characteristics of the recording layer by exposing the recording layer of the medium under predetermined conditions as described above is referred to as "recording exposure". The case where recording exposure is performed by changing the intersection angle of the reference light and the object light or changing the respective incident angles to overlap different interference patterns at the same position is referred to as "multiple recording exposure".

[0008] Prior art literature

[0009] Patent Literature

[0010] Patent Document 1: Japanese Patent Application Publication No. 2021-12249

[0011] Patent Document 2: Japanese Patent Application Publication No. 2007-34334

[0012] Patent Document 3: Japanese Patent Laid-Open No. 8-160842

[0013] Patent Document 4: Japanese Patent Application Publication No. 2003-156992

[0014] Patent Document 5: Japanese Patent Application Publication No. 2021-162621

[0015] Non-patent literature

[0016] Non-patent document 1: "Physics Series 22 Holography" by Junpei Tsujiuchi Summary of the invention

[0017] When a volume hologram recording medium is used for an AR glasses light guide plate or a head mounted display, multiple recording exposures of a hologram called a reflection are performed. It is known that the diffraction efficiency of a reflected hologram is reduced due to the polarization state of the light (Non-Patent Document 1). That is, there is a problem that the light waveguided in a light guide plate with a higher birefringence index cannot obtain the desired diffraction efficiency because the polarization state is different from the desired state.

[0018] Therefore, similar to conventional resins, when making a cured product for a hologram recording medium, it is necessary to cure the matrix resin in a manner that does not produce birefringence. However, according to the research of the inventors, the following problem has been clarified, that is, if the reaction of curing is accelerated by heat treatment during the curing process of the matrix resin in order to shorten the time consumed before the end of the curing reaction, birefringence will be generated due to cooling after curing. This problem is a topic of light guide plates used for AR glasses light guide plates or head-mounted displays. Therefore, the problem cannot be solved only by the small in-plane phase difference (or two-dimensional birefringence) described in patent document 5.

[0019] The present invention has been made in view of the above-mentioned problems. An object of the present invention is to provide a cured product for a hologram recording medium having a small three-dimensional birefringence.

[0020] According to the research conducted by the present inventors, it is known that a cured material for hologram recording medium having a small three-dimensional birefringence can be produced by slowly curing without heating until the residual ratio of unreacted isocyanate groups of the matrix resin in the cured material for hologram recording medium (hereinafter referred to as the residual NCO ratio) becomes a certain amount or less. Thus, a hologram with a high diffraction efficiency can be obtained without changing the polarization state of light waveguided in the hologram recording medium.

[0021] That is, the present invention takes the following contents as its gist.

[0022] [1] A method for producing a cured product for a hologram recording medium, comprising subjecting a composition for a hologram recording medium to a curing reaction to produce a cured product for a hologram recording medium, the composition for a hologram recording medium comprising a compound (a) having an isocyanate group and a compound (b) having an isocyanate-reactive functional group,

[0023] The curing reaction includes a curing step A of curing at a temperature below 35° C.,

[0024] The residual ratio of unreacted isocyanate groups after the curing step A is 10% or less based on the isocyanate groups in the hologram recording medium composition before the curing reaction.

[0025] [2] The method for producing a cured product for a hologram recording medium according to [1], wherein the curing reaction includes a curing step B of curing at 35° C. or higher.

[0026] [3] The method for producing a cured product for a hologram recording medium according to [2], wherein the temperature in the curing step B is 150° C. or less.

[0027] [4] The method for producing a cured product for a hologram recording medium according to [2] or [3], wherein the composition for a hologram recording medium contains a bismuth-based catalyst as component (f).

[0028] [5] A method for producing a cured product for a hologram recording medium as described in [4], wherein the bismuth-based catalyst is one or more compounds selected from bismuth tris(2-ethylhexanoate), bismuth tribenzoyloxy, bismuth triacetate, bismuth tris(dimethyldithiocarbamate), bismuth hydroxide, triphenylbismuth(V)bis(trichloroacetate), tris(4-methylphenyl)oxybismuth(V) and triphenylbis(3-chlorobenzoyloxy)bismuth(V).

[0029] [6] The method for producing a cured product for a hologram recording medium according to [4] or [5], wherein the content of the component (f) in the composition for a hologram recording medium is 0.001% by mass to 5% by mass.

[0030] [7] The method for producing a cured product for a hologram recording medium according to any one of [1] to [6], wherein the compound (b) having an isocyanate-reactive functional group has one or more hydroxyl groups in one molecule.

[0031] [8] A method for producing a cured product for a hologram recording medium as described in any one of [1] to [7], wherein the compound (b) having an isocyanate-reactive functional group is one or more compounds selected from polyester polyols, polyether polyols and polycarbonate polyols having two or more hydroxyl groups in one molecule.

[0032] [9] A method for producing a cured product for a hologram recording medium as described in any one of [1] to [7], wherein the compound (b) having an isocyanate-reactive functional group is one or more compounds selected from polycaprolactone polyols having two or more hydroxyl groups in one molecule.

[0033]

[10] The method for producing a cured product for a hologram recording medium as described in any one of [1] to [9], wherein the content of the compound (b) having an isocyanate-reactive functional group in the hologram recording medium composition is 10% by mass to 85% by mass.

[0034]

[11] The method for producing a cured product for a hologram recording medium as described in any one of [1] to

[10] , wherein the compound (a) having an isocyanate group is one or more compounds selected from polyisocyanates having an isocyanurate structure.

[0035]

[12] The method for producing a cured product for a hologram recording medium as described in any one of [1] to

[11] , wherein the content of the compound (a) having an isocyanate group in the hologram recording medium composition is 10% by mass to 85% by mass.

[0036] According to the present invention, by slowly curing in the curing step A at a temperature lower than 35°C until the NCO residual rate becomes a certain amount or less, a cured product for a hologram recording medium having a small three-dimensional birefringence can be produced. Thus, a reflective hologram with high diffraction efficiency can be obtained. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] Figure 1 This is a schematic diagram showing the structure of a birefringence measuring apparatus used in Examples. DETAILED DESCRIPTION

[0038] The following will describe the embodiments of the present invention in detail. The articles, methods, etc. exemplified below are examples (representative examples) of the embodiments of the present invention, and the present invention is not limited to these contents unless it deviates from the gist of the present invention.

[0039] The method for producing a cured product for a hologram recording medium of the present invention is a method for producing a cured product for a hologram recording medium by subjecting a composition for a hologram recording medium to a curing reaction, the composition for a hologram recording medium comprising a compound (a) having an isocyanate group and a compound (b) having an isocyanate-reactive functional group, the method for producing a cured product for a hologram recording medium being characterized in that the curing reaction comprises a curing step A of curing at a temperature lower than 35° C., and the residual ratio of unreacted isocyanate groups after the curing step A is 10% or less relative to the isocyanate groups in the composition for a hologram recording medium before the curing reaction.

[0040] It is preferred that the curing reaction in the present invention includes a curing step B of performing curing at 35° C. or higher.

[0041] Hereinafter, the composition for hologram recording medium containing the compound (a) having an isocyanate group (hereinafter sometimes referred to as "component (a)") and the compound (b) having an isocyanate-reactive functional group (hereinafter sometimes referred to as "component (b)") used for curing in the method for producing a cured material for hologram recording medium of the present invention may be referred to as "the composition for hologram recording medium of the present invention". In addition, the cured material for hologram recording medium produced by the method for producing a cured material for hologram recording medium of the present invention may be referred to as "the cured material for hologram recording medium of the present invention".

[0042] [Composition for hologram recording medium]

[0043] The hologram recording medium composition of the present invention comprises a compound (a) having an isocyanate group and a compound (b) having an isocyanate-reactive functional group, and preferably comprises the following components (a) to (e). The hologram recording medium composition of the present invention may further comprise the following component (f).

[0044] Component (a): Compound (a) having an isocyanate group

[0045] Component (b): Compound (b) having an isocyanate-reactive functional group

[0046] Component (c): polymerizable monomer

[0047] Component (d): Photopolymerization initiator

[0048] Component (e): Compound containing nitroxide radical

[0049] Component (f): Curing catalyst

[0050] <Ingredients (a)>

[0051] The compound (a) having an isocyanate group of the component (a) is preferably a component that reacts with the compound (b) having an isocyanate-reactive functional group (component (b)) in the presence of a curing catalyst (component (f)) described below to form a resin matrix.

[0052] The ratio of the isocyanate group in the molecule of the compound (a) with an isocyanate group is preferably less than 50 mass %, more preferably less than 47 mass %, and further preferably less than 45 mass %. Its lower limit is usually more than 0.1 mass %, preferably more than 1 mass %. If the ratio of the isocyanate group is below the above-mentioned upper limit, it is not easy to produce turbidity when the hologram recording medium is made, and optical uniformity is obtained. If the ratio of the isocyanate group is more than the above-mentioned lower limit, the hardness and glass transition temperature of the resin matrix become high, and the record can be prevented from disappearing.

[0053] The ratio of isocyanate groups in the present invention means the ratio of isocyanate groups in the entire compound (a) having isocyanate groups used, and the ratio of isocyanate groups in the compound (a) having isocyanate groups is calculated according to the following formula. The molecular weight of the isocyanate group is 42.

[0054] (42×number of isocyanate groups / molecular weight of compound (a) having an isocyanate group)×100

[0055] The type of the compound (a) having an isocyanate group is not particularly limited, and for example, the compound may have an aromatic, aromatic aliphatic, aliphatic or alicyclic skeleton.

[0056] The compound (a) with isocyanate group may have 1 isocyanate group in the molecule, or may have more than 2 isocyanate groups. As the compound (a) with isocyanate group, it is preferably a polyfunctional isocyanate with more than 2 isocyanate groups. The reason is that, according to the three-dimensional crosslinked matrix obtained by the compound (a) (component (a)) having more than 2 isocyanate groups in the molecule and the compound (b) (component (b)) having more than 3 isocyanate reactive functional groups in the molecule or the compound (a) (component (a)) having more than 3 isocyanate groups in the molecule and the compound (b) (component (b)) having more than 2 isocyanate reactive functional groups in the molecule, it is possible to obtain a recording layer with excellent record retention.

[0057] Examples of the compound (a) having an isocyanate group include isocyanic acid, butyl isocyanate, octyl isocyanate, butyl diisocyanate, hexamethylene diisocyanate (HMDI), isophorone diisocyanate (IPDI), 1,8-diisocyanato-4-(isocyanatomethyl)octane, 2,2,4- or 2,4,4-trimethylhexamethylene diisocyanate, isomers of bis(4,4'-isocyanatocyclohexyl)methane alkanes and mixtures thereof with any desired isomeric content, isocyanatomethyl-1,8-octanediisocyanate, 1,4-cyclohexylene diisocyanate, isomeric cyclohexanedimethylene diisocyanate, 1,4-phenylene diisocyanate, 2,4- or 2,6-toluene diisocyanate, 1,5-naphthalene diisocyanate, 2,4′- or 4,4′-diphenylmethane diisocyanate, triphenylmethane 4,4′,4″-triisocyanate, and the like.

[0058] As the compound (a) having an isocyanate group, there can be used compounds having carbamate, urea, carbodiimide, urea acrylate, isocyanurate, allophanate, biuret, diazinethione, uretdione and / or imine Isocyanate derivatives of diazinedione structure.

[0059] Among them, in order to record a large diffraction efficiency as a hologram recording medium, the matrix resin is preferably low in refractive index. Therefore, as the compound (a) having an isocyanate group, it is preferable to have an aliphatic or alicyclic skeleton. Therefore, hexamethylene diisocyanate (HMDI), isophorone diisocyanate (IPDI), 1,8-diisocyanate-4-(isocyanate methyl) octane, 2,2,4- or 2,4,4-trimethylhexamethylene diisocyanate, isomer bis(4,4'-isocyanate cyclohexyl) methane and a mixture thereof having any desired isomer content, isocyanate methyl-1,8-octanediisocyanate, 1,4-cyclohexylene diisocyanate, isomer cyclohexane dimethylene diisocyanate, and urethanes, ureas, carbodiimides, acrylates, isocyanurates, allophanates, biuret, diazinethione, uretdione and / or imine Polyisocyanate with diazinedione structure.

[0060] Among them, particularly from the viewpoint of miscibility with the compound (b) having an isocyanate-reactive functional group during production, a low-viscosity polyisocyanate having an isocyanurate, allophanate or uretdione structure is more preferred.

[0061] These compounds (a) having an isocyanate group may be used alone or in combination of two or more in any combination and ratio.

[0062] <Ingredient (b)>

[0063] The compound (b) having an isocyanate-reactive functional group as the component (b) is a compound having active hydrogen (isocyanate-reactive functional group) that participates in the chain extension reaction with the compound (a) having an isocyanate group as the component (a).

[0064] As isocyanate-reactive functional groups, for example, hydroxyl, amino, and mercapto groups can be mentioned. The compound (b) having an isocyanate-reactive functional group may have one isocyanate-reactive functional group in the molecule, or may have two or more isocyanate-reactive functional groups. The compound (b) having an isocyanate-reactive functional group preferably has two or more isocyanate-reactive functional groups. When having two or more isocyanate-reactive functional groups, the isocyanate-reactive functional groups contained in one molecule may be one or more.

[0065] In order to improve the compatibility with other components and obtain a record with high diffraction efficiency, the compound (b) having an isocyanate-reactive functional group is preferably a compound having one or more hydroxyl groups in one molecule.

[0066] The number average molecular weight of the compound (b) with isocyanate reactive functional groups is usually more than 50, preferably more than 100, more preferably more than 150, and usually less than 50000, preferably less than 10000, more preferably less than 5000.When the number average molecular weight of the compound (b) with isocyanate reactive functional groups is more than the above-mentioned lower limit, cross-linking density decreases, and recording speed can be prevented from decreasing.When the number average molecular weight of the compound (b) with isocyanate reactive functional groups is less than the above-mentioned upper limit, the compatibility with other components is promoted, cross-linking density rises, and therefore the recorded content can be prevented from disappearing.

[0067] The number average molecular weight of the component (b) is a value measured by gel permeation chromatography (GPC).

[0068] (Compounds having hydroxyl groups)

[0069] The compound having a hydroxyl group as an isocyanate-reactive functional group only needs to have one or more hydroxyl groups in one molecule, and preferably has two or more hydroxyl groups. Examples thereof include glycols such as ethylene glycol, triethylene glycol, diethylene glycol, polyethylene glycol, propylene glycol, polypropylene glycol (PPG), and neopentyl glycol; diols such as butanediol, pentanediol, hexanediol, heptanediol, tetramethylene glycol (TMG), and polytetramethylene glycol (PTMG); bisphenols; triols such as glycerol, trimethylolpropane, butanetriol, pentanetriol, hexanetriol, and decantriol; compounds obtained by modifying these polyfunctional alcohols with polyoxyethylene chains or polyoxypropylene chains; polyfunctional polyoxybutylenes; polyfunctional polycaprolactones; polyfunctional polyesters; polyfunctional polycarbonates; polyfunctional polypropylene glycols, etc.

[0070] These may be used alone or in combination of two or more in any ratio.

[0071] The number average molecular weight of the compound with hydroxyl is usually more than 50, preferably more than 100, more preferably more than 150, and is usually less than 50000, preferably less than 10000, more preferably less than 5000.When the number average molecular weight of the compound with hydroxyl is above the above lower limit, cross-linking density decreases, and recording speed can be prevented from decreasing.When the number average molecular weight of the compound with hydroxyl is below the above upper limit, the compatibility with other components is promoted, cross-linking density rises, and therefore the recorded content can be prevented from disappearing.

[0072] (Compounds having an amino group)

[0073] The compound having an amino group as an isocyanate-reactive functional group may have one or more amino groups in one molecule, and preferably has two or more amino groups. Examples thereof include aliphatic amines such as ethylenediamine, diethylenetriamine, triethylenetetramine, and hexamethylenediamine; alicyclic amines such as isophoronediamine, menthanediamine, and 4,4'-diaminodicyclohexylmethane; and aromatic amines such as meta-xylylenediamine, diaminodiphenylmethane, and meta-phenylenediamine.

[0074] These may be used alone or in combination of two or more in any ratio.

[0075] The number average molecular weight of the compound with amino group is usually more than 50, preferably more than 100, more preferably more than 150, and usually less than 50000, preferably less than 10000, more preferably less than 5000.When the number average molecular weight of the compound with amino group is above the above lower limit, the cross-linking density decreases, and the recording speed can be prevented from decreasing.When the number average molecular weight of the compound with amino group is below the above upper limit, the compatibility with other components is promoted, the cross-linking density rises, and therefore the recorded content can be prevented from disappearing.

[0076] (Compounds having a mercapto group)

[0077] The compound having a mercapto group as an isocyanate-reactive functional group may have one or more mercapto groups in one molecule, and preferably has two or more mercapto groups. Examples thereof include 1,3-butanedithiol, 1,4-butanedithiol, 2,3-butanedithiol, 1,2-benzenedithiol, 1,3-benzenedithiol, 1,4-benzenedithiol, 1,10-decanedithiol, 1,2-ethanedithiol, 1,6-hexanedithiol, 1,9-nonanedithiol, pentaerythritol tetrakis(3-mercaptopropionate), pentaerythritol tetrakis(2-mercaptoacetate), pentaerythritol tetrakis(3-mercaptobutyrate), trimethylolpropane tris(3-mercaptopropionate), dipentaerythritol hexa(3-mercaptopropionate), and 1,4-bis(3-mercaptobutyryloxy)butane.

[0078] These may be used alone or in combination of two or more in any ratio.

[0079] The number-average molecular weight of the compound with sulfydryl is generally more than 50, is preferably more than 100, is more preferably more than 150, and is generally below 50000, is preferably below 10000, is more preferably below 5000.When the number-average molecular weight of the compound with sulfydryl is above the above-mentioned lower limit, cross-linking density descends, and can prevent that recording speed reduces.When the number-average molecular weight of the compound with sulfydryl is below the above-mentioned upper limit, the compatibility with other components promotes, cross-linking density rises, so can prevent that recorded content disappears.

[0080] (Suitable ingredient (b))

[0081] As the component (b), polycaprolactones are preferably used from the viewpoint of stability as a material and flexibility of the structure.

[0082] Examples of the polycaprolactones used as component (b) include polycaprolactone polyols (polycaprolactone diols, polycaprolactone triols, etc.) obtained by ring-opening polymerization of ε-caprolactone in the presence of polyols such as ethylene glycol, diethylene glycol, triethylene glycol, propylene glycol, dipropylene glycol, 1,3-butanediol, 1,4-butanediol, hexanediol, methyl pentanediol, 2,4-diethyl pentanediol, neopentyl glycol, 2-ethyl-1,3-hexanediol, trimethylolpropane, di(trimethylolpropane), pentaerythritol, and dipentaerythritol, or diols such as polypropylene glycol and polytetramethylene glycol (PTMG).

[0083] These may be used alone or in combination of two or more in any ratio.

[0084] <Ingredient (c)>

[0085] The polymerizable monomer of the component (c) is a compound that can be polymerized by the photopolymerization initiator of the component (d) described below.

[0086] Component (c) is a monomer compound that polymerizes during recording and / or post-exposure.

[0087] The type of polymerizable monomer used in the composition for hologram recording medium of the present invention is not particularly limited and can be appropriately selected from known compounds. Examples of polymerizable monomers include cationic polymerizable monomers, anionic polymerizable monomers, free radical polymerizable monomers, etc. Any one of these can be used, and two or more can also be used in combination. Among them, because it is not easy to hinder the reaction of the compound (a) having an isocyanate group and the compound (b) having an isocyanate-reactive functional group to form a matrix, as component (c), it is preferred to use a free radical polymerizable monomer.

[0088] (Cationic polymerizable monomer)

[0089] Examples of the cationic polymerizable monomer include epoxy compounds, oxetane compounds, oxolane compounds, cyclic acetal compounds, cyclic lactone compounds, thiirane compounds, thietane compounds, vinyl ether compounds, spiroorthoester compounds, ethylenically unsaturated bond compounds, cyclic ether compounds, cyclic thioether compounds, vinyl compounds, and the like.

[0090] The above-mentioned cationically polymerizable monomers may be used alone or in combination of two or more kinds in any ratio.

[0091] (Anionic polymerizable monomer)

[0092] Examples of the anionic polymerizable monomer include hydrocarbon monomers and polar monomers.

[0093] Examples of the hydrocarbon monomer include styrene, α-methylstyrene, butadiene, isoprene, vinylpyridine, vinylanthracene, and derivatives thereof.

[0094] Examples of the polar monomer include methacrylates, acrylates, vinyl ketones, isopropenyl ketones, and other polar monomers.

[0095] The anionic polymerizable monomers exemplified above may be used alone or in combination of two or more kinds in any combination and ratio.

[0096] (Free radical polymerizable monomer)

[0097] Examples of the radical polymerizable monomer include compounds having a (meth)acryloyl group, (meth)acrylamides, vinyl esters, vinyl compounds, styrenes, and spiro ring-containing compounds.

[0098] The radical polymerizable monomers exemplified above may be used alone or in combination of two or more kinds in any combination and ratio.

[0099] In this specification, methacrylic acid and acrylic acid are generally referred to as (meth)acrylic acid, and methacryloyl and acryl are generally referred to as (meth)acryloyl.

[0100] Among the above, compounds having a (meth)acryloyl group are more preferred from the viewpoint of steric hindrance during radical polymerization.

[0101] (Molecular weight of polymerizable monomer)

[0102] The polymerizable monomer used in the composition for hologram recording medium of the present invention generally has a molecular weight of 80 or more, preferably 150 or more, more preferably 300 or more, and generally 3000 or less, preferably 2500 or less, more preferably 2000 or less. When the molecular weight is at least the above lower limit, the shrinkage rate accompanying polymerization by light irradiation during information recording of the hologram can be reduced. When the molecular weight is at most the above upper limit, the mobility of the polymerizable monomer in the recording layer using the composition for hologram recording medium becomes high, diffusion is easily caused, and sufficient diffraction efficiency can be obtained.

[0103] (Refractive index of polymerizable monomer)

[0104] The refractive index of the polymerizable monomer at the wavelength of the irradiated light (recording wavelength, etc.) for the hologram recording medium is usually 1.50 or more, preferably 1.52 or more, more preferably 1.55 or more, and usually 1.80 or less, preferably 1.78 or less. If the refractive index is too small, there is a situation where the diffraction efficiency is insufficient and the multiplicity is insufficient. If the refractive index is too large, the refractive index difference with the resin matrix is ​​too large, and the scattering becomes larger, thereby causing the transmittance to decrease, and more energy is required when recording or reproducing.

[0105] It should be noted that the refractive index shows a larger value when evaluated at a shorter wavelength, but a sample showing a relatively large refractive index at a short wavelength also shows a relatively large refractive index at a long wavelength, and the relationship is not reversed. Therefore, the refractive index can be evaluated at a wavelength other than the recording wavelength to predict the refractive index at the recording wavelength.

[0106] When the sample is a liquid, the refractive index of the polymerizable monomer can be measured by the minimum deviation angle method, the critical angle method, the V-block method, etc. When the sample is a solid, the compound can be dissolved in an appropriate solvent to prepare a solution, the refractive index of the solution can be measured, and the refractive index when the compound is 100% can be obtained by extrapolation.

[0107] As the polymerizable monomer having a relatively high refractive index, compounds having a halogen atom (iodine, chlorine, bromine, etc.) or a heteroatom (nitrogen, sulfur, oxygen, etc.) in the molecule are preferred, and compounds having a heterocyclic structure are more preferred.

[0108] (Molar absorption coefficient of polymerizable monomer)

[0109] The molar absorption coefficient of the polymerizable monomer at the recording wavelength of the hologram is preferably 100 L·mol -1 cm -1 Below. The molar absorption coefficient is 100L·mol -1 cm -1 Hereinafter, the transmittance of the medium can be prevented from being reduced, and a diffraction efficiency sufficient for the thickness can be obtained.

[0110] <Ingredient (d)>

[0111] The photopolymerization initiator of component (d) refers to a substance that generates cations, anions, and free radicals that cause chemical reactions by light, and contributes to the polymerization of the above-mentioned polymerizable monomers. The types of various photopolymerization initiators such as cationic photopolymerization initiators, anionic photopolymerization initiators, and free radical photopolymerization initiators are not particularly limited and can be appropriately selected according to the types of polymerizable monomers.

[0112] Any known cationic photopolymerization initiator can be used as the cationic photopolymerization initiator. Examples of cationic photopolymerization initiators include aromatic onium salts and the like. As a specific example, SbF 6 - , BF 4 - , AsF 6 - PF 6 - CF 3 SO 3 - , B(C 6 F 5 ) 4 - Compounds composed of anion components such as iodine, sulfur, nitrogen, phosphorus, etc. and aromatic cationic components containing atoms such as iodine, sulfur, nitrogen, phosphorus, etc. Among them, diaryliodonium salts, triarylsulfonium salts, etc. are preferred.

[0113] The cationic photopolymerization initiators exemplified above may be used alone or in combination of two or more in any ratio.

[0114] Any known anionic photopolymerization initiator can be used as the anionic photopolymerization initiator. Examples of the anionic photopolymerization initiator include amines. Examples of the amines include amino-containing compounds such as dimethylbenzylamine, dimethylaminomethylphenol, and 1,8-diazabicyclo[5.4.0]undecene-7, and their derivatives; imidazole compounds such as imidazole, 2-methylimidazole, and 2-ethyl-4-methylimidazole, and their derivatives.

[0115] The anionic photopolymerization initiators exemplified above may be used alone or in combination of two or more in any ratio.

[0116] Any known free radical photopolymerization initiator can be used as the free radical photopolymerization initiator. Examples of the free radical photopolymerization initiator include phosphine oxide compounds, azo compounds, azide compounds, organic peroxides, organic borates, onium salts, biimidazole derivatives, titanocene compounds, iodonium salts, organic thiol compounds, halogenated hydrocarbon derivatives, and oxime ester compounds.

[0117] The above-exemplified radical photopolymerization initiators may be used alone or in combination of two or more in any combination and ratio.

[0118] Other examples of the photopolymerization initiator include imidazole derivatives or Oxadiazole derivatives, naphthalene, perylene, pyrene, anthracene, coumarin, 4-Bis(2-phenylvinyl)benzene and its derivatives, quinacridone derivatives, coumarin derivatives, Al(C9 H 6 NO) 3 Aluminum complexes, rubrene, 1H-permeabilized 2(3H)-one derivatives, benzopyran derivatives, rhodamine derivatives, benzothioxanthene derivatives, azabenzothioxanthene, phenylpyridine complexes, porphyrin complexes, polyphenylene vinylene materials, etc.

[0119] As the photopolymerization initiator, it is particularly preferred that the molar absorption coefficient at the recording wavelength is 1000 L·mol -1 cm -1 The following compounds. The molar absorption coefficient is 1000 L·mol -1 cm -1 Hereinafter, it is possible to suppress a decrease in the transmittance of the hologram recording medium at a recording wavelength, which would otherwise occur if an amount sufficient to obtain a sufficient diffraction efficiency is mixed.

[0120] <Ingredient (e)>

[0121] As the compound having a nitroxide free radical of component (e), a compound having an isocyanate-reactive functional group and a nitroxide free radical is preferably used. When the composition for hologram recording medium of the present invention includes such a component (e), the isocyanate-reactive functional group of component (e) reacts with the isocyanate group of component (a) to be fixed to the resin matrix, and the nitroxide free radical contained in component (e) can improve the recording sensitivity and achieve a higher Δn.

[0122] The isocyanate-reactive functional group contained in the component (e) may be the same as the isocyanate-reactive functional group contained in the component (b).

[0123] The nitroxide radical contained in the component (e) is preferably a stable radical.

[0124] The type of component (e) is not particularly limited. Specific examples thereof include 4-hydroxy-2,2,6,6-tetramethylpiperidin-1-oxyl (TEMPOL), 4-thio-2,2,6,6-tetramethylpiperidin-1-oxyl, 4-amino-2,2,6,6-tetramethylpiperidin-1-oxyl, 4-mercapto-2,2,6,6-tetramethylpiperidin-1-oxyl, 4-carboxy-2,2,6,6-tetramethylpiperidin-1-oxyl, -1-oxyl, 4-carbamoyl-2,2,6,6-tetramethylpiperidin-1-oxyl, 4-(2,3-epoxypropyloxy)-2,2,6,6-tetramethylpiperidin-1-oxyl, 3-hydroxy-2,2,5,5-tetramethylpyrrolidine-1-oxyl, 3-thio-2,2,5,5-tetramethylpyrrolidine-1-oxyl, 3-amino-2,2,5,5-tetramethylpyrrolidine-1-oxyl, 3-mercapto-2,2,5 ,5-tetramethylpyrrolidine-1-oxyl, 3-carboxy-2,2,5,5-tetramethylpyrrolidine-1-oxyl, 3-carbamoyl-2,2,5,5-tetramethylpyrrolidine-1-oxyl, 3-(2,3-epoxypropoxy)-2,2,5,5-tetramethylpyrrolidine-1-oxyl, 3-hydroxy-2,2,5,5-tetramethylpyrrolidine-1-oxyl, 3-thio-2,2,5,5-tetramethylpyrrolidine-1-oxyl Stable nitroxide free radical compounds include 3-amino-2,2,5,5-tetramethylpyrroline-1-oxyl, 3-mercapto-2,2,5,5-tetramethylpyrroline-1-oxyl, 3-carboxy-2,2,5,5-tetramethylpyrroline-1-oxyl, 3-carbamoyl-2,2,5,5-tetramethylpyrroline-1-oxyl, and 3-(2,3-epoxypropoxy)-2,2,5,5-tetramethylpyrroline-1-oxyl. However, the present invention is not limited to these.

[0125] These may be used alone or in combination of two or more in any ratio.

[0126] Among them, TEMPOL, 4-thio-2,2,6,6-tetramethylpiperidin-1-oxyl, 4-amino-2,2,6,6-tetramethylpiperidin-1-oxyl and 4-mercapto-2,2,6,6-tetramethylpiperidin-1-oxyl are preferably used from the viewpoint of compound stability and reactivity with isocyanate groups, and TEMPOL is particularly preferably used.

[0127] <Ingredients (f)>

[0128] The composition for hologram recording medium of the present invention preferably further comprises a curing catalyst as component (f) that promotes the reaction between the compound (a) having an isocyanate group and the compound (b) having an isocyanate-reactive functional group. As the curing catalyst of component (f), a bismuth-based catalyst that functions as a Lewis acid is preferably used.

[0129] Examples of bismuth-based catalysts include bismuth tris(2-ethylhexanoate), tribenzoylbismuth, bismuth triacetate, bismuth tris(dimethyldithiocarbamate), bismuth hydroxide, triphenylbismuth(V)bis(trichloroacetate), tris(4-methylphenyl)oxybismuth(V), and triphenylbis(3-chlorobenzoyloxy)bismuth(V).

[0130] Among them, trivalent bismuth compounds are preferred in terms of catalyst activity, and bismuth carboxylates and bismuth compounds of the general formula Bi(OCOR) are more preferred. 3 A bismuth compound represented by (R is a linear or branched alkyl group, a cycloalkyl group, or a substituted or unsubstituted aromatic group).

[0131] The bismuth-based catalyst may be used alone or in combination of two or more.

[0132] As the curing catalyst, the above-mentioned bismuth-based catalyst and other curing catalyst may be used in combination in order to adjust the reaction rate.

[0133] As a catalyst that can be used in combination, there is no particular limitation as long as it does not violate the purpose of the present invention, but in order to obtain the synergistic effect of the catalyst, it is preferred to use a compound having an amino group in a part of the structure. Examples of compounds having an amino group in a part of the structure include triethylamine (TEA), N,N-dimethylcyclohexylamine (DMEDA), N,N,N',N'-tetramethylethylenediamine (TMEDA), N,N,N',N'-tetramethyl-1,3-propylenediamine (TMPDA), N,N,N',N'-tetramethyl-1,6-hexanediamine (TMHMDA), N,N,N',N",N"-pentamethyldiethylenetriamine (PMDETA), N,N,N',N",N"-pentamethyl Amine compounds such as dipropylene triamine (PMDPTA), triethylene diamine (TEDA), N,N'-dimethylpiperazine (DMP), N,-methyl, N'-(2-dimethylamino)-ethylpiperazine (TMNAEP), N-methylmorpholine (NMMO), N-(N',N'-dimethylaminoethyl)-morpholine (DMAEMO), bis(2-dimethylaminoethyl) ether (BDMEE), ethylene glycol bis(3-dimethyl)-aminopropyl ether (TMEGDA), and diisopropylethylamine (DIEA).

[0134] These may be used alone or in combination of two or more in any ratio.

[0135] <Other ingredients>

[0136] The composition for hologram recording media of the present invention may contain other components in addition to the above-mentioned components (a) to (f) unless such components violate the gist of the present invention.

[0137] Other components include: solvents, plasticizers, dispersants, leveling agents, defoaming agents, adhesion promoters, etc. for preparing the recording layer of the hologram recording medium; or chain transfer agents, polymerization terminators, compatibilizers, reaction aids, sensitizers, antioxidants, etc. for controlling the recording reaction.

[0138] These components may be used alone or in combination of two or more in any combination and ratio.

[0139] <Composition ratio of each component in the composition for hologram recording medium>

[0140] The content of each component in the composition for hologram recording media of the present invention may be any content as long as it does not violate the gist of the present invention. However, the content of each component is preferably in the following range.

[0141] The content of component (a) in the hologram recording medium composition of the present invention is usually 10% by mass or more, preferably 20% by mass or more, more preferably 30% by mass or more, and is usually 85% by mass or less, preferably 75% by mass or less, more preferably 65% ​​by mass or less.

[0142] When the content of the component (a) is at least the above lower limit, the component (a) can be easily mixed with the component (b). When the content of the component (a) is at most the above upper limit, the component (b) can be easily mixed with the component (b).

[0143] The content of component (b) in the hologram recording medium composition of the present invention is usually 10% by mass or more, preferably 20% by mass or more, more preferably 30% by mass or more, and is usually 85% by mass or less, preferably 75% by mass or less, more preferably 65% ​​by mass or less.

[0144] When the content of the component (b) is at least the above lower limit, the component (b) can be easily mixed with the component (a). When the content of the component (b) is at most the above upper limit, the component (b) can be easily mixed with the component (a).

[0145] The total content of component (a) and component (b) in the composition for hologram recording medium of the present invention is usually 20% by mass or more, preferably 25% by mass or more, more preferably 30% by mass or more, and further preferably 35% by mass or more. In addition, it is usually 99.9% by mass or less, preferably 99% by mass or less, and more preferably 98% by mass or less.

[0146] When the total content of components (a) and (b) is equal to or greater than the above lower limit, the recording layer can be easily formed. When the total content of components (a) and (b) is equal to or less than the above upper limit, the contents of other essential components can be ensured.

[0147] In the composition for hologram recording medium of the present invention, the ratio of the number of isocyanate reactive functional groups of component (b) to the number of isocyanate groups of component (a) is preferably 0.1 or more, more preferably 0.5 or more. In addition, the ratio is usually 10.0 or less, preferably 2.0 or less. When the ratio is within the above range, there are fewer unreacted functional groups and storage stability is improved.

[0148] The content of component (c) of the composition for hologram recording medium of the present invention is usually 0.1% by mass or more, preferably 1% by mass or more, more preferably 2% by mass or more. In addition, it is usually 80% by mass or less, preferably 50% by mass or less, more preferably 30% by mass or less. By making the content of component (c) above the above lower limit, sufficient diffraction efficiency is obtained. By making the content of component (c) below the above upper limit, the compatibility of the recording layer is maintained.

[0149] The content of component (d) of the composition for hologram recording medium of the present invention is usually 0.1% by mass or more relative to the content of component (c), preferably 0.2% by mass or more, and more preferably 0.3% by mass or more. In addition, it is usually 20% by mass or less, preferably 18% by mass or less, and more preferably 16% by mass or less. By making the content of component (d) above the lower limit, sufficient recording sensitivity is obtained. If the content of component (d) is below the upper limit, the sensitivity reduction caused by the generation of excessive free radicals causing bimolecular termination reaction can be suppressed.

[0150] The content of component (e) in the hologram recording medium composition of the present invention is preferably such that the molar ratio of component (e) to component (d) (component (e) / component (d)) is usually 0.1 or more, particularly preferably 0.2 or more, especially 0.3 or more, and is usually 10 or less, particularly preferably 8 or less, especially 6 or less.

[0151] If the ratio of component (e) / component (d) is not less than the above lower limit, the effect of improving Δn due to the inclusion of component (e) can be effectively obtained. If the ratio of component (e) / component (d) is not more than the above upper limit, a free radical polymerization reaction can be carried out during exposure for recording, and the refractive index modulation required for forming a diffraction grating can be obtained, thereby obtaining sufficient recording sensitivity.

[0152] The content of component (f) in the hologram recording medium composition of the present invention is preferably determined in consideration of the reaction rates of components (a) and (b), and is usually 5% by mass or less, preferably 4% by mass or less, and more preferably 1% by mass or less. The content of component (f) in the hologram recording medium composition of the present invention is preferably 0.001% by mass (10 ppm) or more.

[0153] The total content of the components other than the components (a) to (f) in the hologram recording medium composition of the present invention may be 30% by mass or less, preferably 15% by mass or less, and more preferably 5% by mass.

[0154] <Method for producing cured product for hologram recording medium>

[0155] In the method for producing a cured product for hologram recording media of the present invention, the above components (a) to (e), preferably components (a) to (f) are mixed to produce the composition for hologram recording media of the present invention, and the mixture is cured.

[0156] When producing the composition for hologram recording media of the present invention, components (a) to (e), preferably components (a) to (f) may be mixed in any combination and order, and other components may be mixed in combination at this time.

[0157] The mixture of the produced hologram recording medium composition is usually applied onto the support described below and cured according to the method for producing a hologram recording medium described below.

[0158] By increasing the content of component (f), the mixture of the hologram recording medium composition can quickly undergo a curing reaction even at room temperature. As the curing proceeds, the fluidity of the mixture decreases, so it takes a long time to cure at room temperature until the reaction is completed. Therefore, it is preferred to perform a heat treatment as a post-treatment.

[0159] In the present invention, the curing reaction of the hologram recording medium composition is carried out by the curing step A of carrying out the curing reaction at less than 35° C. Preferably, the curing reaction in the present invention includes the curing step A and the curing step B of carrying out the curing at 35° C. or higher, and the curing step B is preferably carried out after the curing step A.

[0160] In the method for producing a cured product for hologram recording medium of the present invention, curing is performed by curing step A until the NCO residual rate of the hologram recording medium composition becomes 10% or less. That is, in curing step A, the NCO residual rate is reduced to 10% or less, and curing step B is preferably performed thereafter, thereby obtaining a cured product for hologram recording medium with a small three-dimensional birefringence.

[0161] The NCO residual rate in the present invention is expressed as the percentage of the concentration of unreacted isocyanate groups (NCO) relative to the concentration of NCO that can react in the composition for hologram recording media before the curing reaction, that is, immediately after the production. For example, in the case of a composition in which isocyanate groups are present in excess, such as the ratio of the number of isocyanate-reactive functional groups of component (b) to the number of isocyanate groups of component (a) being 0.5, not all of the isocyanate groups can react, but half of the isocyanate groups in the composition for hologram recording media can react, and the remaining half are NCO that cannot react in the first place. Therefore, the NCO that cannot react is not included in the calculation of the NCO residual rate.

[0162] There is a tendency that the lower the NCO residual rate after the curing step A in the present invention is, the lower the three-dimensional birefringence after the subsequent curing step B is. The reason for this is as follows.

[0163] If curing process B is performed as post-treatment under the condition that the NCO residual rate of the composition for hologram recording medium is relatively high, the curing reaction of the matrix resin is terminated under high temperature environment. However, it is cooled to room temperature thereafter, so thermal shrinkage will occur. At this time, at least one side of the matrix resin is bonded to the substrate material of the support as described below, so in the surface direction of the bonding surface, only thermal shrinkage following the substrate material occurs. On the other hand, in the thickness direction, a larger thermal shrinkage including the amount in the plane direction will occur. At this time, a part of the components of the curing reaction under the high temperature state in the curing process B is arranged in the thickness direction as stress relaxation. Therefore, the refractive index becomes different in the thickness direction and the surface direction, and the three-dimensional birefringence becomes larger. The larger the NCO residual rate before the curing process B is performed after the curing process A, the greater the tendency.

[0164] For the above reasons, the NCO residual rate after the curing step A in the present invention is 10% or less, preferably 6% or less. With such a state of NCO residual rate, even if the curing step B of curing at 35° C. or above is subsequently performed, a cured product for hologram recording medium with a small three-dimensional birefringence can be obtained.

[0165] There is no particular restriction on the lower limit of the NCO residual rate. However, if the NCO residual rate is to be reduced by the curing reaction in the curing step A at a temperature lower than 35°C, a long time is required, which is not only inefficient, but also there is a situation where the NCO residual rate no longer decreases even if the time of the curing step A is extended. Therefore, it is usually preferably set to 0.1% or more, and particularly preferably set to 1% or more.

[0166] The NCO residual ratio can be measured by the method described in the following Examples.

[0167] In the present invention, the temperature condition in the curing step A is less than 35° C. From the viewpoint of efficiently reducing the NCO residual rate, the lower limit of the temperature condition under non-heating in the curing step A is preferably 10° C. or more, more preferably 15° C. or more.

[0168] From the viewpoint of reducing the three-dimensional birefringence, the upper limit of the temperature condition in the curing step A is preferably 30° C. or lower, and more preferably 25° C. or lower.

[0169] The curing step A is usually performed without heating.

[0170] When the room temperature during the curing reaction in the curing step A is too high, the temperature can be adjusted to the above-mentioned temperature range by cooling as necessary.

[0171] As described above, the implementation time of the curing step A is a time for making the NCO residual ratio 10% or less, preferably 6% or less, and 0.1% or more, preferably 1% or more.

[0172] The time of the curing step A varies depending on the amount of the curing catalyst in the hologram recording medium composition and is not particularly limited, but is generally about 0.1 to 240 hours.

[0173] In the present invention, the temperature in the curing step B after the curing step A is preferably 35° C. or higher. From the viewpoint of the time required for the reaction to be completed and the suppression of the degradation of the matrix resin itself, the lower limit of the treatment temperature in the curing step B after the curing step A is preferably 35° C. or higher, more preferably 50° C. or higher, and further preferably 65° C. or higher. In addition, the upper limit of the treatment temperature in the curing step B after the curing step A is preferably 150° C. or lower, more preferably 120° C. or lower, and further preferably 100° C. or lower.

[0174] Therefore, in the curing step B, heating is performed so as to reach the above-mentioned appropriate temperature.

[0175] As for the treatment time in the curing step B, the shorter the better if the manufacturing cycle time is taken into consideration, but if it is too short, a sufficient effect cannot be obtained as a post-treatment. Therefore, the treatment time of the curing step B is preferably 15 minutes or more, more preferably 1 hour or more, further preferably 6 hours or more, and usually 72 hours or less.

[0176] The NCO residual rate after the curing step B is preferably 1% or less, particularly preferably 0 to 0.4%.

[0177] The cured product for a hologram recording medium of the present invention can also be used to produce a hologram recording medium according to the method for forming a recording layer in the method for producing a hologram recording medium described below.

[0178] [Hologram recording medium]

[0179] By subjecting the cured product for a hologram recording medium of the present invention to interference exposure, a hologram recording medium can be obtained.

[0180] Hereinafter, a hologram recording medium using the cured product for a hologram recording medium of the present invention may be referred to as a hologram recording medium of the present invention.

[0181] Hereinafter, preferred embodiments of the hologram recording medium of the present invention will be described.

[0182] The hologram recording medium of the present invention comprises a recording layer, and at least a support and other layers. Usually, the hologram recording medium has at least one support, and the recording layer and other layers are stacked on the support to form the hologram recording medium. Examples of other layers include: a protective layer, a reflection layer, an anti-reflection layer (anti-reflection film), etc.

[0183] <Recording layer>

[0184] The recording layer of the hologram recording medium of the present invention is a layer formed of the cured product for hologram recording medium of the present invention, and is a layer for recording information. The information is usually recorded in the form of a hologram. As described in detail in the recording method described below, the polymerizable monomer contained in the recording layer is a component of which a part undergoes chemical changes such as polymerization by hologram recording, etc. Therefore, in the hologram recording medium after recording, a part of the polymerizable monomer is consumed and exists as a reacted compound such as a polymer.

[0185] The thickness of the recording layer is not particularly limited and can be appropriately determined in consideration of the recording method, etc. Generally, it is usually 1 μm or more, preferably 10 μm or more and usually 3000 μm or less, preferably 2000 μm or less. By setting the thickness of the recording layer to be above the lower limit, the selectivity of each hologram becomes higher during multiple recording in the hologram recording medium, and the degree of multiple recording can be improved. By setting the thickness of the recording layer to be below the upper limit, the entire recording layer can be uniformly formed, and multiple recording with uniform diffraction efficiency of each hologram and high S / N ratio can be performed.

[0186] The shrinkage rate of the recording layer due to exposure during recording and reproduction of information is preferably 0.5% or less.

[0187] <Support body>

[0188] The details of the support are not particularly limited as long as they have the strength and durability required for the medium, and any support may be used.

[0189] The shape of the support is not limited, but is usually formed in a flat plate shape or a film shape.

[0190] The material constituting the support is also not limited, and may be transparent or opaque.

[0191] When the material of the transparent support is mentioned, there can be mentioned organic materials such as acrylic acid, polyethylene terephthalate, polyethylene naphthalate, polycarbonate, polyethylene, polypropylene, amorphous polyolefin, polystyrene, cellulose acetate, etc.; inorganic materials such as glass, silicon, quartz, etc. Among them, polycarbonate, acrylic acid, polyester, amorphous polyolefin, glass, etc. are preferred, and polycarbonate, acrylic acid, amorphous polyolefin, and glass are more preferred.

[0192] On the other hand, examples of materials for the opaque support include metals such as aluminum, and materials obtained by coating the above-mentioned transparent support with metals such as gold, silver, and aluminum, or dielectrics such as magnesium fluoride and zirconium oxide.

[0193] The thickness of the support is not particularly limited, and is usually preferably set in the range of 0.05 mm to 1 mm. If the thickness of the support is above the lower limit, the mechanical strength of the hologram recording medium can be obtained, and the warping of the substrate can be prevented. If the thickness of the support is below the upper limit, the light transmittance can be maintained, and the cost increase can be suppressed.

[0194] The surface of the support may also be subjected to a surface treatment. The surface treatment is usually performed to improve the adhesion between the support and the recording layer. Examples of surface treatment include subjecting the support to a corona discharge treatment or pre-forming an undercoat layer on the support. Here, compositions of the undercoat layer include halogenated phenols, partially hydrolyzed vinyl chloride-vinyl acetate copolymers, polyurethane resins, and the like.

[0195] The surface treatment of the support may be performed for purposes other than improving adhesion. Examples thereof include: reflective coating treatment for forming a reflective coating made of metal such as gold, silver, and aluminum; dielectric coating treatment for forming a dielectric layer such as magnesium fluoride or zirconium oxide, etc. These layers may be formed as a single layer or as two or more layers.

[0196] These surface treatments may also be performed for the purpose of controlling the gas or water permeability of the substrate. For example, by making the support sandwiching the recording layer also have the function of suppressing the gas or water permeability, the reliability of the medium can be further improved.

[0197] The support may be disposed only on either the upper side or the lower side of the recording layer of the hologram recording medium of the present invention, or may be disposed on both sides. When the support is disposed on both the upper and lower sides of the recording layer, at least one of the support is configured to be transparent so that active energy rays (excitation light, reference light, regeneration light, etc.) can pass through.

[0198] In the case of a hologram recording medium having a support on one or both sides of the recording layer, a transmission type or reflection type hologram can be recorded. In addition, when a support having a reflective property is used on one side of the recording layer, a reflection type hologram can be recorded.

[0199] The support may be provided with a pattern for data address. The patterning method is not limited, and for example, the support itself may be provided with concavoconvex shapes, a pattern may be provided on the reflective layer described below, or a combination of these methods may be used.

[0200] <Protective layer>

[0201] The protective layer is a layer for preventing the recording layer from being affected by oxygen or moisture, such as a decrease in sensitivity or degradation of storage stability. The specific composition of the protective layer is not limited, and any known composition can be applied. For example, a layer composed of a water-soluble polymer, an organic / inorganic material, etc. can be formed as the protective layer.

[0202] The protective layer may be formed at any position without particular limitation, and may be formed, for example, on the surface of the recording layer, between the recording layer and the support, or on the outer surface of the support. The protective layer may also be formed between the support and other layers.

[0203] <Anti-reflective film>

[0204] For both transmissive and reflective hologram recording media, an antireflection film may be provided on the incident and emitting sides of the object light and the reading light, or between the recording layer and the support. The antireflection film improves the light utilization efficiency and suppresses the generation of ghost images.

[0205] As the antireflection film, any known antireflection film can be used.

[0206] <Method for producing hologram recording medium>

[0207] The method for producing the hologram recording medium of the present invention is not limited, and can be produced, for example, by coating the hologram recording medium composition of the present invention on a support without a solvent and subjecting it to a curing reaction according to the present invention to form a recording layer.

[0208] Any method may be used to apply the composition for hologram recording media, and specific examples thereof include spraying, spin coating, wire bar coating, dipping, air knife coating, roll coating, blade coating, and blade roll coating.

[0209] When forming a recording layer, especially when forming a thick recording layer, a method of placing the composition for hologram recording media of the present invention in a mold to form the composition or a method of applying the composition on a release film and punching the mold can be used.

[0210] The hologram recording medium composition of the present invention can also be mixed with a solvent or an additive to prepare a coating liquid, which is applied to a support and dried to form a recording layer. In this case, any method can be used as a coating method. For example, the same method as described above can be used.

[0211] The solvent used in the coating liquid is not limited, but it is usually preferred to use a solvent that has sufficient solubility for the components used, imparts good coating properties, and does not damage a support such as a resin substrate.

[0212] Examples of solvents include ketone solvents such as acetone and methyl ethyl ketone; aromatic solvents such as toluene and xylene; alcohol solvents such as methanol and ethanol; ketone alcohol solvents such as diacetone alcohol; ether solvents such as tetrahydrofuran; halogen solvents such as dichloromethane and chloroform; cellosolve solvents such as methyl cellosolve and ethyl cellosolve; propylene glycol solvents such as propylene glycol monomethyl ether and propylene glycol monoethyl ether; ester solvents such as ethyl acetate and methyl 3-methoxypropionate; perfluoroalkyl alcohol solvents such as tetrafluoropropanol; highly polar solvents such as dimethylformamide and dimethyl sulfoxide; chain hydrocarbon solvents such as n-hexane; cyclic hydrocarbon solvents such as cyclohexane and cyclooctane; or mixed solvents thereof.

[0213] These solvents may be used alone or in combination of two or more in any combination and ratio.

[0214] The amount of the solvent used is not limited. From the viewpoint of coating efficiency and workability, it is preferred to prepare a coating liquid having a solid content concentration of about 1 to 1000% by mass.

[0215] The hologram recording medium manufactured in this way can be in the form of a vertical flat plate or disk, and can be used in three-dimensional image display devices or diffractive optical elements, large-capacity storage devices, and other devices.

[0216] In particular, the hologram recording medium of the present invention using the cured product for hologram recording medium with a small three-dimensional birefringence manufactured according to the present invention as a recording layer can have a higher Δn, reduce color unevenness and improve brightness, and can be used as a light guide plate for AR glasses.

[0217] <Application of large-capacity storage>

[0218] Both writing (recording) and reading (reproducing) information on the hologram recording medium of the present invention are performed by irradiation with light.

[0219] When recording information, light that can chemically change a polymerizable monomer, that is, polymerize the monomer and cause a concentration change, is used as object light.

[0220] For example, when recording information in the form of a volume hologram, object light and reference light are irradiated to the recording layer together, so that the object light and the reference light interfere with each other in the recording layer. As a result, the interference light causes the polymerizable monomer in the recording layer to polymerize and change its concentration, and as a result, interference fringes generate a refractive index difference in the recording layer, and the information is recorded in the recording layer in the form of a hologram through the interference fringes recorded in the recording layer.

[0221] When reproducing the volume hologram recorded in the recording layer, a predetermined reproducing light (usually a reference light) is irradiated to the recording layer. The irradiated reproducing light is diffracted according to the interference fringes. The diffracted light is light containing the same information as the recording layer, so by reading the diffracted light using an appropriate detection device, the information recorded in the recording layer can be reproduced.

[0222] The wavelength range of the object light, the regeneration light, and the reference light can be any wavelength range according to their respective uses, and can be the visible light range or the ultraviolet range. Examples of suitable light among these lights include ruby, glass, Nd-YAG, Nd-YVO 4 Solid-state lasers such as GaAs, InGaAs, and GaN; diode lasers such as helium-neon, argon, krypton, excimer, and CO 2 Gas lasers such as lasers with pigments; lasers with excellent monochromaticity and directivity such as dye lasers with pigments, etc.

[0223] There is no limitation on the irradiation amount of the object light, the regenerated light, and the reference light, and the irradiation amount may be any irradiation amount as long as it is within the range that allows recording and regeneration. When the irradiation amount is too small, the chemical change of the polymerizable monomer is too incomplete, and the heat resistance and mechanical properties of the recording layer may not be fully exhibited. On the contrary, when the irradiation amount is too large, the components of the recording layer (components of the hologram recording medium composition) may deteriorate. Therefore, the object light, the regenerated light, and the reference light are usually 0.1 J / cm according to the composition of the hologram recording medium composition used to form the recording layer, the type and amount of the photopolymerization initiator, etc. 2 ~20J / cm 2 range for irradiation.

[0224] As hologram recording methods, there are polarization collinear hologram recording methods, reference light incident angle multiplex hologram recording methods, etc. However, when the hologram recording medium of the present invention is used as a recording medium, any recording method can provide good recording quality.

[0225] <Application of light guide plates for AR glasses>

[0226] The hologram recording medium of the present invention records a volume hologram in the same manner as in the above-mentioned mass storage application.

[0227] For the volume hologram recorded in the recording layer, the specified regeneration light is irradiated to the recording layer. The irradiated regeneration light is diffracted according to the above-mentioned interference fringes. At this time, even if the wavelength of the regeneration light is inconsistent with the wavelength of the recording light, diffraction is generated as long as the above-mentioned interference fringes and Bragg conditions are met. Therefore, as long as the corresponding interference fringes are recorded in advance according to the wavelength and incident angle of the regeneration light to be diffracted, the regeneration light in a wider wavelength range can be diffracted, which can expand the display color gamut of the AR glasses.

[0228] As long as the corresponding interference fringes are recorded in advance according to the wavelength and diffraction angle of the regenerated light, the regenerated light incident from the outside of the hologram recording medium can be waveguided into the inside of the hologram recording medium, or the regenerated light waveguided inside the hologram recording medium can be reflected, split, enlarged, or reduced, or the regenerated light waveguided inside the hologram recording medium can be emitted to the outside of the hologram recording medium, thereby expanding the viewing angle of the AR glasses.

[0229] The wavelength region of the object light and the regeneration light is any wavelength region according to their respective uses, and can be the visible light region or the ultraviolet region. As suitable ones among these lights, the above-mentioned laser etc. can be exemplified, but as the regeneration light, it is not limited to the laser etc., and display devices such as liquid crystal display (LCD) and organic electroluminescent display (OLED) can also be exemplified as suitable options.

[0230] There is no limitation on the irradiation amount of the object light, the regenerated light, and the reference light, and the irradiation amount may be any irradiation amount as long as it is within the range that allows recording and regeneration. When the irradiation amount is too small, the chemical change of the polymerizable monomer is too incomplete, and the heat resistance and mechanical properties of the recording layer may not be fully exhibited. On the contrary, when the irradiation amount is too large, the components of the recording layer (components of the hologram recording medium composition) may deteriorate. Therefore, the object light, the regenerated light, and the reference light are usually 0.1 J / cm according to the composition of the hologram recording medium composition of the present invention used to form the recording layer, the type and amount of the photopolymerization initiator, etc. 2 Above 20J / cm 2 The following ranges are irradiated.

[0231] <Three-dimensional birefringence>

[0232] In the present invention, the three-dimensional birefringence δn shown in the following formulas (1) to (3) is used as an index of the three-dimensional birefringence. The smaller the δn, the less the polarization component of the waveguide light remains unchanged, and the diffracted light intensity of the hologram recording desired as the AR glasses light guide plate can be obtained. Therefore, δn is preferably 2.1×10 -4 Below, more preferably 1.0×10 -4Here, δn may become a negative integer depending on the tilting method of measuring the polarization angle of the incident light, but in the present invention, the magnitude of δn is important, so the tilting method of the polarization angle is selected to make δn>0.

[0233]

[0234] (where Δ is the phase difference; d is the distance the measured light passes through; λ is the wavelength of the measured light; T is the thickness of the optical element; n 0 is the absolute refractive index of air; n 1 is the absolute refractive index of the optical element; φ is the incident angle of the incident light for measurement; θ is the polarization angle of the measurement light after passing through the optical element; ψ represents the ellipticity of the measurement light after passing through the optical element; θ and ψ are measured by the following birefringence difference measurement device.

[0235] Example

[0236] Hereinafter, the present invention will be described in more detail by way of examples. The present invention is not limited to the following examples unless it deviates from the gist thereof.

[0237] [Raw materials used]

[0238] The composition raw materials used in Examples and Comparative Examples are as follows.

[0239] In the following examples and comparative examples, a composition for hologram recording media containing only component (a), i.e., a compound (a) having an isocyanate group, component (b), i.e., a compound (b) having an isocyanate-reactive functional group, and component (f), i.e., a curing catalyst, was prepared. However, the purpose of the composition is to study the three-dimensional birefringence affected by thermal shrinkage during the curing reaction. As a composition for hologram recording media for actual use, it is preferred to contain the above-mentioned components (a) to (e), especially components (a) to (f).

[0240] (Compound (a) having an isocyanate group)

[0241] DURANATE TM TSS-100: Hexamethylene diisocyanate polyisocyanate (NCO 17.6%) (manufactured by Asahi Kasei Corporation)

[0242] · TAKENATE 600: Aliphatic diisocyanate (NCO 43.3%) (Made by Mitsui Chemicals)

[0243] (Compound (b) Having an Isocyanate-Reactive Functional Group)

[0244] PLACCEL PCL-305: Polycaprolactone triol (molecular weight 550) (manufactured by Daicel)

[0245] Capa2047A: Polycaprolactone diol (molecular weight 400) (manufactured by INGEVITY)

[0246] (Curing Catalyst)

[0247] Bismuth tris(2-ethylhexanoate)octanoate solution (active ingredient content 56% by mass)

[0248] [Examples 1 to 12, Comparative Examples 1 to 3]

[0249] <Preparation of composition for hologram recording medium>

[0250] DURANATE TM TSS-100: 2.1119 g, TAKENATE 600: 0.3727 g, Capa2047A: 2.2639 g, and PCL-305: 0.2515 g were mixed (the amount of isocyanate-reactive functional groups was 1.0 times the amount of isocyanate groups) (the obtained mixed solution was referred to as the "initial mixed solution"), and an octanoic acid solution of bismuth tri(2-ethylhexanoate) was added in an amount of a curing catalyst as shown in Table 1, and the mixture was stirred and mixed to obtain a mixed solution of a composition for a hologram recording medium.

[0251] <Manufacturing of cured product for hologram recording medium>

[0252] The mixed liquid of the composition for hologram recording medium was poured onto a slide glass having spacers of 1.0 mm thickness placed on both opposite side edges, and the slide glass was placed thereon, and the periphery was fixed with a clamp.

[0253] As shown in Table 1, when the amount of the curing catalyst was 40ppm, 80ppm, 120ppm, 160ppm, 200ppm, and 240ppm, the curing time at room temperature (24°C) before the heat treatment was set to 24, 96, and 168 hours to perform the curing step A to form a cured product A having a thickness of 1.0 mm. After the NCO residual rate (NCO residual rate after the curing step A) of the formed cured product A was measured by the method described below, the curing step B was performed at 80°C for 24 hours to complete the curing. The three-dimensional birefringence index of the obtained cured product B was measured by the following method.

[0254] <Measurement of NCO residual rate>

[0255] The NCO residual rate of the cured product A before the heat treatment at 80°C for 24 hours was determined by using the method disclosed in Non-Patent Document 1. TM iS TM5 (manufactured by THERMO FISHER SCIENTIFIC), with a wavelength of 2859 cm derived from the CH bond that does not change due to curing -1 Based on the absorption peak of the isocyanate group, the wavelength of 2267cm -1 The residual NCO ratio is 100%, and the isocyanate group intensity ratio of the initial mixed solution before the curing reaction without adding a curing catalyst within 30 minutes of the initial mixed solution preparation is calculated.

[0256] <Measurement of three-dimensional birefringence>

[0257] exist Figure 1 2 is a schematic diagram of a birefringence measuring apparatus for measuring three-dimensional birefringence. Figure 1 S is the cured material (cured material B) for the hologram recording medium produced, and is tilted so that the incident angle of the measuring light becomes 70°. LED is a measuring LED light source with a central wavelength of 455nm (M455L4 manufactured by ThorLab). P is a polarizing plate, and is configured so that the incident light of the measuring light becomes a linear polarization of 45°. PD represents a birefringence measurement sensor (PAX1000VIS manufactured by ThorLab). Based on the measurement results, the three-dimensional birefringence δn is calculated using the above formulas (1) to (3).

[0258] <Evaluation Results>

[0259] Table 1 shows the NCO residual rate of the cured product A and the three-dimensional birefringence δn of the cured product B. Table 1 also shows the results of evaluation of the three-dimensional birefringence δn according to the following criteria.

[0260] <Judgment Criteria>

[0261] Based on the three-dimensional birefringence δn, evaluation was performed according to the following criteria.

[0262] ◎:δn<1.0×10 -4

[0263] ○:1.0×10 -4 ≤δn≤2.1×10 -4

[0264] ×: 2.1×10 -4 <δn

[0265] [Table 1]

[0266]

[0267] <Investigation>

[0268] It is known from the above-mentioned Examples and Comparative Examples that by performing the curing step A so that the NCO residual rate of the cured product A becomes 10% or less, the three-dimensional birefringence of the cured product B obtained in the subsequent curing step B becomes significantly smaller. In particular, it is known that under the condition that the NCO residual rate after the curing step A becomes 6% or less, the three-dimensional birefringence becomes even smaller.

[0269] Industrial Applicability

[0270] The method for producing a cured product for a hologram recording medium of the present invention is particularly useful as a method for reducing the three-dimensional birefringence in an optical element for recording a hologram.

[0271] Although the present invention has been described in detail using specific embodiments, it will be apparent to those skilled in the art that various modifications can be made within the scope of achieving the effects of the invention.

[0272] This application is based on Japanese Patent Application No. 2022-181979 filed on November 14, 2022, the entire contents of which are incorporated herein by reference.

[0273] Explanation of symbols

[0274] S: Cured material for hologram recording medium

[0275] P: Polarizing plate

[0276] LED: LED light source for measurement

[0277] PD: Birefringence sensor

Claims

1. A method for manufacturing a cured product for a holographic recording medium, which is a method for manufacturing a cured product for a holographic recording medium by subjecting a composition for a holographic recording medium to a curing reaction. The composition for a holographic recording medium contains a compound (a) having an isocyanate group and a compound (b) having an isocyanate-reactive functional group. The curing reaction includes a curing step A carried out at a temperature lower than 35°C. The residual rate of the unreacted isocyanate groups after the curing step A is 10% or less relative to the isocyanate groups in the composition for a holographic recording medium before the curing reaction.

2. The method for manufacturing a cured product for a holographic recording medium according to claim 1. Wherein, The curing reaction includes a curing step B carried out at a temperature of 35°C or higher.

3. The method for manufacturing a cured product for a holographic recording medium according to claim 2. Wherein, The temperature of the curing step B is 150°C or lower.

4. The method for manufacturing a cured product for a holographic recording medium according to claim 1. Wherein, The composition for a holographic recording medium contains a bismuth-based catalyst as component (f).

5. The method for manufacturing a cured product for a holographic recording medium according to claim 4. Wherein, The bismuth-based catalyst is one or more compounds selected from bismuth tris(2-ethylhexanoate), bismuth tribenzoyloxide, bismuth triacetate, bismuth tris(dimethyldithiocarbamate), bismuth hydroxide, bismuth(V) triphenyl bis(trichloroacetate), bismuth(V) tris(4-methylphenyl)oxo and bismuth(V) triphenyl bis(3-chlorobenzoyloxy).

6. The method for manufacturing a cured product for a holographic recording medium according to claim 4. Wherein, The content rate of the component (f) in the composition for a holographic recording medium is 0.001% by mass to 5% by mass.

7. The method for manufacturing a cured product for a holographic recording medium according to claim 1. Wherein, The compound (b) having an isocyanate-reactive functional group has one or more hydroxyl groups in one molecule.

8. The method for manufacturing a cured product for a holographic recording medium according to claim 1. Wherein, The compound (b) having an isocyanate-reactive functional group is one or more compounds selected from polyester polyols, polyether polyols and polycarbonate polyols having two or more hydroxyl groups in one molecule.

9. The method for manufacturing a cured product for a holographic recording medium according to claim 1. Wherein, The compound (b) having an isocyanate-reactive functional group is one or more compounds selected from polycaprolactone polyols having two or more hydroxyl groups in one molecule.

10. The method for manufacturing a cured product for a holographic recording medium according to claim 1. Wherein, The content rate of the compound (b) having an isocyanate-reactive functional group in the composition for a holographic recording medium is 10% by mass to 85% by mass.

11. The method for manufacturing a cured product for a holographic recording medium according to claim 1. Wherein, The compound (a) having an isocyanate group is one or more compounds selected from polyisocyanates having an isocyanurate structure.

12. The method for producing a cured product for a hologram recording medium according to claim 1, wherein, the content of the compound (a) having an isocyanate group in the composition for a hologram recording medium is 10% by mass to 85% by mass.

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