JP2019124710A - Optical element and manufacturing method thereof - Google Patents

Abstract

To provide an optical element that has excellent image quality and has durability capable of maintaining a high diffraction efficiency for a long term even under a high humidity condition.SOLUTION: In an optical element, at least one of a pair of bonding surfaces of two adjacent transparent optical members has a curved surface, a layer including a volume hologram recording layer including a photopolymer is disposed in at least a partial region of the bonding surface having the curved surface among the pair of bonding surfaces, and a radiation curable adhesive layer is provided to cover the entire bonding surface having the curved surface. The volume hologram recording layer includes polyurethane.SELECTED DRAWING: Figure 3

Description

  The present invention relates to an optical element and a method of manufacturing the same.

  Conventionally, a holographic optical element (HOE; Holographic Optical Element, hereinafter also simply referred to as “HOE”) including a volume phase hologram is used to diffract and reflect the image light from the display element by the HOE and guide it to the pupil of the observer Various image display apparatuses for allowing an observer to observe an image (virtual image) have been proposed. For example, in Patent Document 1, a flat HOE is attached to an eyepiece prism, and the image light emitted from the display element and guided in the eyepiece prism is diffracted and reflected by the HOE, and the image display device leads to the pupil of the observer. It is disclosed.

  In general, HOE has wavelength dependency, and the diffracted direction changes depending on the wavelength. For this reason, as in the technique described in Patent Document 1, the direction in which the image light is reflected by the HOE attachment surface in the eyepiece prism and the direction in which the image light is diffracted by the HOE are the screen center In the configuration in which the center portions substantially coincide with each other, the wavelength of the image light is dispersed in the radial direction from the center of the screen by using a flat HOE. As a result, at a position other than the center of the screen, the displayed point (image) is radially stretched from the center of the screen, resulting in a problem that the image quality is deteriorated.

  As a means to solve the problem of this image quality deterioration, the eyepiece prism surface in contact with the volume phase hologram that diffracts and reflects the image light is a curved surface, and the point (image) is elongated by the HOE wavelength dependency at positions other than the screen center. Restricting the direction can be mentioned. This makes it possible to suppress the deterioration of the image quality of the HOE as compared to the case where a flat HOE is used.

  On the other hand, as an optical element using a hologram recording material that is less susceptible to the influence of external environment such as humidity, Patent Document 2 arranges the hologram recording material between two curved transparent prisms, and uses two transparent prisms made of polyvinyl A laminated structure bonded with butyral (PVB) is disclosed. The laminated structure described in Patent Document 2 is reported to be suitably used for a head-up display and a windshield for an automobile.

Japanese Patent Application Publication No. 2007-11279 JP-A-7-234627

  However, in the technique described in Patent Document 2, desired interference fringes can not be formed in the area of the hologram recording material, and there is a problem that the image quality is degraded.

  Therefore, an object of the present invention is to provide an optical element having good image quality, and having durability that can maintain high diffraction efficiency for a long time even under high humidity conditions.

  The present inventors conducted intensive studies. As a result, at least one of a pair of bonding surfaces of two adjacent transparent optical members has a curved surface, and the volume hologram is disposed in at least a partial region of the bonding surface having a curved surface among the pair of bonding surfaces. It has been found that the above problems are solved by containing polyurethane in the recording layer, and the present invention has been completed.

  That is, according to the present invention, at least one of a pair of bonding surfaces of two adjacent transparent optical members has a curved surface, and at least a partial region of the bonding surface having a curved surface among the pair of bonding surfaces. In the optical element provided with a layer including a volume hologram recording layer and including a radiation curable adhesive layer so as to cover the entire bonding surface having the curved surface, the volume hologram recording layer contains polyurethane.

  According to the present invention, there is provided an optical element having good image quality and having durability capable of maintaining high diffraction efficiency for a long time even under high humidity conditions.

It is a schematic diagram which shows an example of the exposure apparatus used for holography exposure. It is the schematic which shows the partial structure of the optical element by one Embodiment of this invention. FIG. 1 is a schematic view showing a cross-sectional structure of an image display apparatus including an optical element according to an embodiment of the present invention. FIG. 5 is a schematic view showing a more detailed cross-sectional structure of an image display apparatus provided with an optical element according to an embodiment of the present invention. It is the schematic which shows the transparent optical members 11-1 and 11-2 produced in the Example, (a) is a top view of a transparent optical member, (b) and (c) is a side view of a transparent optical member. is there. It is the schematic which shows the transparent optical members 13-1 and 13-2 produced in the Example, (a) is a top view of a transparent optical member, (b) and (c) is a side view of a transparent optical member. is there. It is the schematic which shows the laminated body which laminated | stacked the volume hologram recording layer on the joint surface which has the curved surface produced in the Example, (a) is a top view of a laminated body, (b) and (c) are laminated bodies. Side view of FIG. It is the schematic which shows the virtual image used for evaluation of sharpness.

  Hereinafter, an optical element according to an embodiment of the present invention will be described.

  Hereinafter, a layer containing a polymerizable monomer before holographic exposure (interference exposure) is referred to as a photosensitive layer, and a layer on which a holographic exposure is performed on the photosensitive layer to record a volume hologram is referred to as a volume hologram recording layer. In addition, a polymer obtained by irradiating a photosensitive composition containing a polymerizable monomer, a photopolymerization initiator, a matrix resin, a precursor thereof and the like with light to cause a polymerization reaction is referred to as a photopolymer.

  In the optical element according to the present embodiment, at least one of the pair of bonding surfaces of two adjacent transparent optical members has a curved surface, and at least a partial region of the bonding surface having a curved surface among the pair of bonding surfaces. A layer including a volume hologram recording layer including a photopolymer is disposed, and a radiation curable adhesive layer is provided so as to cover the entire bonding surface having the curved surface. The optical element of the present embodiment having such a configuration has good image quality, and has durability capable of maintaining high diffraction efficiency for a long time even under high humidity conditions.

  The laminated structure described in Patent Document 2 has a hologram recording material disposed between two curved transparent prisms, and the two transparent prisms are bonded with polyvinyl butyral (PVB) to obtain moisture from the external environment such as humidity. It is said that it is unlikely to be affected. However, in the laminated structure described in Patent Document 2, since the thickness of the adhesive layer is different between the region having the hologram recording material and the region having no hologram recording material, a difference occurs in the shrinkage when curing the adhesive layer. As a result, internal stress is generated, and since the joint surface has a curved surface, internal stress is more likely to be generated. Therefore, in the area | region which has a hologram recording material, a desired interference fringe can not be formed and there existed a problem of causing degradation of an image quality.

  On the other hand, in the optical element of the present embodiment, the volume hologram recording layer contains polyurethane. As a result, even if local internal stress occurs due to curing and shrinkage of the adhesive, polyurethane contained in the volume hologram recording layer disperses the internal stress, desired interference fringes are maintained, and good image quality is obtained. It is thought that Further, it is considered that the durability of the volume hologram recording layer under high humidity conditions is improved by containing the polyurethane inside. The above mechanism is based on speculation, and its correctness does not affect the technical scope of the present embodiment.

  Hereinafter, preferred embodiments will be described in more detail, but the present invention is not limited to the following embodiments.

  In the present specification, “X to Y” indicating a range means “X or more and Y or less”. Moreover, unless otherwise indicated, measurement of operation, a physical property, etc. is measured on the conditions of room temperature (20-25 degreeC) / 40 to 50% relative humidity RH.

[Configuration of optical element]
<Transparent optical member>
In two adjacent transparent optical members according to the present embodiment, at least one of the pair of bonding surfaces has a curved surface. Another bonding surface may be flat or may have a curved surface.

  Examples of the shape of the curved surface include a cylindrical shape (cylindrical shape), a spherical shape, a convex lens shape, a concave lens shape and the like, and the shape is not particularly limited. The curvature of the shape of the curved surface is appropriately changed depending on the installation position of the optical element for displaying an image with respect to the pupil, and the curvature becomes larger as the installation position is closer. When the distance between the optical element and the pupil is R, the curvature is preferably equal to or less than 1 / R. In addition, the curvature may be constant or change over the curved surface of the transparent optical member. When changing, it is preferable to become smaller toward the peripheral end of the transparent optical member.

  The material of the transparent optical member may be optically transparent, and a known material can be appropriately selected. In the present specification, "transparent" means that the total light transmittance in the visible light wavelength region is 60% or more. Examples of the material include, for example, inorganic materials such as glass, silicon and quartz; acrylic resin, polycarbonate, polyethylene terephthalate, polybutylene terephthalate, polyethylene naphthoate, polyethylene, polypropylene, amorphous polyolefin, cellulose acetate, cellulose hydrate, cellulose nitrate And organic materials such as cycloolefin polymer, polystyrene, polyepoxide, polysulfone, cellulose acylate, polyamide, polyimide, polymethyl methacrylate, polyvinyl chloride, polyvinyl butyral, polydicyclopentadiene and the like. These materials may be used alone or in combination of two or more. The materials of the pair of transparent optical members may be the same as or different from each other.

  The transparent optical member can be obtained, for example, by subjecting the above-mentioned material to injection molding, extrusion molding or the like under known conditions using a mold.

  There is no restriction | limiting in particular as a magnitude | size of a transparent optical member, According to the use to be used etc., it can select suitably. In addition, a transparent optical member of a suitable size having the above-mentioned curved surface can be manufactured using a known method or by modifying this as appropriate.

<Adjacent layer>
The optical element of this embodiment preferably has an adjacent layer containing a resin in contact with the volume hologram recording layer. The adjacent layer may play a role of protecting the volume hologram recording layer and / or a role of stably holding the volume hologram recording layer.

  The adjacent layer having the above configuration may be provided in contact with both sides of the volume hologram recording layer, or may be provided in contact with only one side. That is, it is preferable that the optical element of this embodiment has at least one adjacent layer containing resin. When adjacent layers are provided on both sides of the volume hologram recording layer, the constituent material and thickness of each adjacent layer may be the same or different.

  As resin contained in an adjacent layer, the well-known resin which has transparency is mentioned. Specific examples of the resin include acrylic resin, polycarbonate, polyethylene terephthalate, polybutylene terephthalate, polyethylene naphthoate, polyethylene, polypropylene, amorphous polyolefin, cellulose acetate, hydrated cellulose, cellulose nitrate, cycloolefin polymer, polystyrene, polyepoxide, Polysulfone, cellulose acylate, polyamide, polyimide, polymethyl methacrylate, polyvinyl chloride, polyvinyl butyral, polydicyclopentadiene and the like can be mentioned. These resins may be used alone or in combination of two or more.

  Among these, polyethylene terephthalate, cycloolefin polymer, cellulose acylate and polymethyl methacrylate are preferable, and cellulose acylate is more preferable, from the viewpoint of optical properties and the like.

  The adjacent layer may contain, for example, an ultraviolet absorber, an antioxidant, an antidegradant, a light stabilizer, a heat stabilizer, a lubricant, an antistatic agent, a flame retardant, a filler, fine particles, an optical property modifier, in addition to the components described above. Etc., may contain other components. The amount of addition of the other components (the total amount when two or more are added) is preferably 0.1 to 29.5% by mass with respect to the total mass of the adjacent layer.

  The thickness of the adjacent layer is not particularly limited, but is preferably 10 to 1000 μm, and more preferably 50 to 200 μm.

  The method for forming the adjacent layer is not particularly limited, and the resin may be molded using a conventionally known method such as melt extrusion, solution casting (solution casting), calendaring, compression molding, etc. It can be mentioned. Among these methods, the melt extrusion method and the solution casting method (solution casting method) are preferable. Moreover, you may use a commercially available resin film as an adjacent layer.

<Volume hologram recording layer>
The volume hologram recording layer is a photosensitive composition containing a polymerizable monomer, a photopolymerization initiator, a polyisocyanate compound and a polyol compound which are precursors of polyurethane, and a matrix resin other than polyurethane optionally contained or a precursor thereof. It is preferable that the product is produced by applying at least holographic exposure to a coating film (photosensitive layer) obtained by, for example, applying it on an adjacent layer and drying it. In this way, a diffraction grating composed of a high refractive index area and a low refractive index area is formed in the photosensitive layer to form a volume hologram recording layer.

  The photosensitive composition used for forming a volume hologram recording layer preferably contains a radical polymerizable monomer, a photopolymerization initiator, and a polyurethane precursor containing a polyisocyanate compound and a polyol compound, and if necessary, other than polyurethane. It may contain a matrix resin or its precursor, a sensitizer, a solvent and the like. Hereinafter, these components will be described.

<< radically polymerizable monomer >>
The radically polymerizable monomer is not particularly limited as long as it has one or more radically polymerizable ethylenic unsaturated bonds in the molecule, but those exhibiting a relatively high refractive index are preferred. Specifically, for example, acrylamide, methacrylamide, methylenebisacrylamide, polyethylene glycol diacrylate, trimethylolpropane triacrylate, pentaerythritol triacrylate, dipentaerythritol hexaacrylate, 2,3-dibromopropyl acrylate, dicyclopentanyl Acrylate, dibromo neopentyl glycol diacrylate, 2-phenoxyethyl acrylate, 2-phenoxymethyl methacrylate, phenol ethoxylate monoacrylate, 2- (p-chlorophenoxy) ethyl acrylate, p-chlorophenyl acrylate, phenyl acrylate, 2-phenylethyl Acrylate, 2- (1-naphthyloxy) ethyl acrylate, o-biphenyl meta Lilate, o-biphenyl acrylate, styrene, methoxystyrene, benzyl acrylate, phenyl acrylate, 2-phenylethyl acrylate, 2-phenoxyethyl acrylate, 2-phenoxyethyl methacrylate, phenol ethoxylate acrylate, methylphenoxyethyl acrylate, nonylphenoxyethyl acrylate 2-hydroxy-3-phenoxypropyl acrylate, phenoxy polyethylene glycol acrylate, 1,4-benzenediol dimethacrylate, 1,4-diisopropenyl benzene, 1,3,5-triisopropenyl benzene, benzoquinone monomethacrylate, 2 -(1-Naphthyloxy) ethyl acrylate, 2,3-naphthalenedicarboxylic acid (acryloxyethyl) Esters, di (3-methacryloxy-2-hydroxypropyl) ether of diphenolic acid, β-acryloxyethyl hydrogen phthalate, 2,2-di (p-hydroxyphenyl) propane diacrylate, 2,3-di (p-) Hydroxyphenyl) propane dimethacrylate, 2,2-di (p-hydroxyphenyl) propane dimethacrylate, polyoxyethylene-2,2-di (p-hydroxyphenyl) propane dimethacrylate, bisphenol-A di (2-methacrylic acid) Roxyethyl) ether, ethoxylated bisphenol-A diacrylate, di (3-acryloxy-2-hydroxypropyl) ether of bisphenol-A, di (2-acryloxyethyl) ether of bisphenol-A, 2,2-bis 4-acryloxy Toxiphenyl) propane, 2,2-bis (4-methacryloxyethoxyphenyl) propane, 2,2-bis (4-acryloxydiethoxyphenyl) propane, 2,2-bis (4-methacryloxydiethoxyphenyl) Propane, bis (4-acryloxydiethoxyphenyl) methane, bis (4-methacryloxydiethoxyphenyl) methane, 2-chlorostyrene, 2-bromostyrene, 2- (p-chlorophenoxy) ethyl acrylate, tetrachloro- Di (3-acryloxy-2-hydroxypropyl) ether of bisphenol-A, di (2-methacryloxyethyl) ether of tetrachloro-bisphenol-A, di (3-methacryloxy-2-hydroxypropyl of tetrabromo-bisphenol-A ) Ether, Tetrabro -Di (2-methacryloxyethyl) ether of bisphenol-A, bis (4-acryloxyethoxy-3,5-dibromophenyl) methane, bis (4-methacryloxyethoxy-3,5-dibromophenyl) methane, 2,2-bis (4-acryloxyethoxy-3,5-dibromophenyl) propane, 2,2-bis (4-methacryloxyethoxy-3,5-dibromophenyl) propane, bis (4-acryloxyethoxyphenyl) ) Sulfone, bis (4-methacryloxyethoxyphenyl) sulfone, bis (4-acryloxydiethoxyphenyl) sulfone, bis (4-methacryloxydiethoxyphenyl) sulfone, bis (4-acryloxypropoxyphenyl-dibromophenyl) Sulfone, bis (4-methacryloxypropoxyphene -Dibromophenyl) sulfone, diethylenedithioglycol diacrylate, diethylenedithioglycol dimethacrylate, triphenylmethyl thioacrylate, 2- (tricyclo [5,2,10 ^2,6 ] dibromodecylthio) ethyl acrylate, S- (1-) Naphthylmethyl) thioacrylates, compounds described in JP-A-2-247205 and JP-A-2-261808 that contain at least two S atoms in the molecule, N-vinylcarbazole, 2-vinyl carbazole (9-carbazolyl) ethyl acrylate, 2- [β- (N-carpathyl) propionyloxy] ethyl acrylate, 2-naphthyl acrylate, pentachlorophenyl acrylate, 2,4,6-tribromophenyl acrylate, 2- (2- Nahu Thiryloxy) ethyl acrylate, N-phenylmaleimide, p-biphenyl methacrylate, 2-vinylnaphthalene, 2-naphthyl methacrylate, 2,3-naphthalenedicarboxylic acid (2-acryloxyethyl) (3-acryloxypropyl-2-hydroxy) 4, diester, N-phenyl methacrylamide, t-butylphenyl methacrylate, diphenic acid (2-methacryloxyethyl) monoester, diphenic acid (2-acryloxyethyl) (3-acryloxypropyl-2-hydroxy) diester 4, 5-phenanthrenedicarboxylic acid (2-acryloxyethyl) (3-acryloxypropyl-2-hydroxy) diester, 2-{{[3- (methylsulfanyl) phenyl] carbamoyl} oxy} ethyl propa-2-enoe And the like.

  Further, those having a 9,9-diarylfluorene skeleton and having at least one ethylenically unsaturated bond in the molecule can be mentioned. Specifically, it is a compound having the following structure.

Here, R ₁ and R ₂ are each independently a radically polymerizable group containing an acryloyl group or a methacryloyl group at the terminal. As a preferable form, it is a group which has an acryloyl group or a methacryloyl group at the terminal, and which can be bonded to the benzene ring of the above compound via an oxyethylene chain, an oxypropylene chain, a urethane bond, an amide bond or the like.

_Further, X 1 to X ₄ are each independently hydrogen atom or a substituent. Specific examples of the substituent include an alkyl group having 1 to 4 carbon atoms, an alkoxy group having 1 to 4 carbon atoms, an amino group, a dialkylamino group, a hydroxyl group, a carboxyl group, a halogen group and the like.

  In addition, urethane acrylate composed of a condensation product of a phenyl isocyanate compound and a compound having a hydroxy group and an acryloyl group in one molecule can also be used. Specifically, it is a compound having the following structure.

  In the above chemical formulas (I) to (III), R each independently represents a group having an ethylenically unsaturated bond, and X each independently represents a single bond, or a linear, branched, Or a cyclic divalent aliphatic hydrocarbon group.

  In addition, compounds having a structure represented by the following chemical formula (IV) can also be used.

In the above chemical formula (IV), R ^{1 to} R ⁵ each independently represent a hydrogen atom, a halogen atom, an alkyl group having 1 to 6 carbon atoms, a trifluoromethyl group, an alkylthio group having 1 to 6 carbon atoms, R ⁶ and R ⁷ are each independently a hydrogen atom or an alkyl group having 1 to 6 carbon atoms. .

  A represents a linear or branched C 1 to C 6 alkylene group, a linear or branched C 2 to C 6 alkenylene group, or a poly having 2 to 6 ethylene oxide units or propylene oxide units It is an alkylene oxide group.

  Among these radically polymerizable monomers, monomers having a substituted or unsubstituted phenyl group, monomers having a substituted or unsubstituted naphthyl group, substituted or unsubstituted heterocyclic aromatic moieties having up to 3 rings The monomer which has, the monomer which has a chlorine atom, and the monomer which contains a bromine atom are preferable since the refractive index is comparatively high.

  The radical polymerizable monomers may be used alone or in combination of two or more.

  The content of the radically polymerizable monomer in the photosensitive composition is preferably 1 to 25% by mass, and more preferably 5 to 20% by mass.

«Photo radical polymerization initiator»
The photo radical polymerization initiator is an agent which starts photopolymerization of a radically polymerizable monomer by irradiation with laser light of a specific wavelength or light with excellent coherence in holographic exposure. As a radical photopolymerization initiator, for example, US Pat. Nos. 4,766,055, 4,868,092, 4,965,171, JP-A-54-151024, JP-A-58-15503, and 58-29803. JP-A-59-189340, JP-A-60-76735, JP-A-1-28715, JP-A-4-239505 and "Procedures of conference on radiation cure curing Asia" The known polymerization initiators described in “PROCEDINGS OF CONFERENCE ON RADIATION ASIA” (pp. 461-477, 1988) and the like can be used, but the invention is not limited thereto.

  Specific examples of the photo radical polymerization initiator include, for example, diaryliodonium salts, 2,4,6-substituted-1,3,5-triazines (triazine compounds), azo compounds, azide compounds, organic peroxides, tetra Organic boronates such as butylammonium triphenylbutylborate, onium salts, halogenated hydrocarbon derivatives, titanocene compounds, monoacylphosphine oxides, bisacylphosphine oxides, combinations of bisacylphosphine oxides and α-hydroxy ketones, etc. Be In addition, a photoradical polymerization initiator system can also be used which is a combination of a hydrogen donor such as a thiol compound and a bisimidazole derivative. These radical photopolymerization initiators may be used alone or in combination of two or more.

  The amount of the photo radical polymerization initiator used is preferably 0.05 to 50 parts by mass, more preferably 0.1 to 30 parts by mass with respect to 100 parts by mass of the radical polymerizable monomer.

«Sensitizer»
The photosensitive composition may contain a sensitizer having a sensitizing function to a photo radical polymerization initiator. Such sensitizers have a maximum absorption wavelength in the range of 400 to 800 nm, in particular 450 to 700 nm. These sensitizers absorb light in the above range, thereby producing a sensitizing effect on the photo radical polymerization initiator.

  Examples of such sensitizers include polymethine compounds such as cyanine dyes and styryl dyes, xanthene compounds such as rhodamine B, rhodamine 6G and pyronine GY, phenazine compounds such as safranin O, cresyl violet, Phenoxazine compounds such as brilliant cresyl blue, phenothiazine compounds such as methylene blue and new methylene blue, diarylmethane compounds such as auramine, triarylmethane compounds such as crystal violet, brilliant green and lissamine green, (thio) pyrylium Salt compounds, squarylium compounds, coumarin dyes, thioxanthene dyes, acene dyes, merocyanine dyes, thiazolium dyes and the like can be mentioned. These sensitizers can be used alone or in combination of two or more.

  1-2000 mass parts is preferable with respect to 100 mass parts of radical photopolymerization initiators, and, as for the usage-amount in the case of using a sensitizer, 20-1500 mass parts is more preferable.

«Chain transfer agent»
The photosensitive composition may contain a chain transfer agent. The chain transfer agent is not particularly limited, and known radical chain transfer agents can be used.

  As chain transfer agents, for example, n-butyl mercaptan, t-butyl mercaptan, t-dodecyl mercaptan, n-octyl mercaptan, n-lauryl mercaptan, 5-chloro-2-mercaptobenzothiazole, 6-ethoxy-2-mercapto Mercaptans such as benzothiazole; Disulfides such as tetramethylthiuradium disulfide and tetraethylthiuradium disulfide; Halogen compounds such as carbon tetrachloride and carbon tetrabromide; and 2-methyl-1-butene, α-methylstyrene dimer, etc. Olefins; and the like. These chain transfer agents can be used alone or in combination of two or more.

  The amount used in the case of using a chain transfer agent is preferably 0.05 to 50 parts by mass, more preferably 0.1 to 30 parts by mass with respect to 100 parts by mass of the radical polymerizable monomer.

«Precursor of polyurethane»
The photosensitive composition according to the present embodiment preferably contains a polyisocyanate compound and a polyol compound which are precursors of polyurethane. These compounds become polyurethane by addition polymerization, and the volume hologram recording layer contains polyurethane. That is, the polyurethane according to a preferred embodiment includes a constituent unit derived from a polyisocyanate compound and a constituent unit derived from a polyol compound.

  When the volume hologram recording layer contains polyurethane, the polyurethane disperses the internal stress even if local internal stress occurs with curing and shrinkage of the adhesive, and the desired interference fringes formed in the volume hologram recording layer It is considered that the image quality is maintained and good image quality is obtained, and the durability of the volume hologram recording layer under high humidity conditions is improved.

  Polyurethane can also play a role as a matrix resin described later.

[Polyisocyanate compound]
The polyisocyanate compound is a compound having two or more isocyanate groups in one molecule, but the type is not particularly limited. The upper limit of the number of isocyanate groups in one molecule is not particularly limited, but is usually 20 or less, preferably 8 or less, and more preferably 4 or less.

  Examples of the polyisocyanate compound used in the present embodiment include, for example, aliphatic polyisocyanate compounds such as butylene diisocyanate, hexamethylene diisocyanate, lysine methyl ester diisocyanate, 2,4,4-trimethylhexamethylene diisocyanate, isophorone diisocyanate, Alicyclic polyisocyanate compounds such as 4,4'-methylenebis (cyclohexyl isocyanate); Aromatic polyisocyanate compounds such as tolylene diisocyanate, 4,4'-diphenylmethane diisocyanate, xylylene diisocyanate, naphthalene-1,5'-diisocyanate And multimers thereof and the like. In addition to these, water, reaction products of polyhydric alcohols such as trimethylol ethane and trimethylol propane with these isocyanates and the like, multimers of hexamethylene diisocyanate, or derivatives thereof can be mentioned. These polyisocyanate compounds may be used alone or in combination of two or more.

[Polyol compound]
The polyol compound is a compound having two or more hydroxy groups in one molecule, but the type is not particularly limited. The polyol compound preferably has an average hydroxy functionality of 1.5 to 6.0 and a number average molecular weight of 1000 to 18500 g / mol, more preferably an average hydroxy functionality of 1.8 to 4.0 and 1000 to 8500 g / mol. And more preferably having an average hydroxy functionality of 1.9 to 3.1 and a number average molecular weight of 1000 to 6500 g / mol.

  Examples of the polyol compound include, for example, polypropylene polyol, polycaprolactone polyol, polyester polyol, polycarbonate polyol, ethylene glycol, propylene glycol, 1,4-butanediol, 1,5-pentanediol, 3-methyl-1,5- Pentanediol, 1,6-hexanediol, neopentyl glycol, diethylene glycol, 1,4-cyclohexanediol, 1,4-cyclohexanedimethanol, decamethylene glycol, trimethylolpropane, polyethylene glycol, polypropylene glycol, polytetramethylene glycol, etc. Can be mentioned. These polyol compounds may be used alone or in combination of two or more.

  A catalyst for addition polymerization (curing) of the polyisocyanate compound and the polyol compound can be blended in the photosensitive composition. It can be cured at room temperature (20-25 ° C.) by using a catalyst, but may be cured by heating. The temperature for heat curing is preferably in the range of 40 to 90 ° C., and the heat curing time is preferably in the range of 1 to 24 hours.

  Examples of the catalyst include conventional urethane reaction catalysts, for example, tin compounds such as dibutyltin dilaurate, dioctyltin dilaurate and dibutyltin dioctoate, and tertiary amine compounds such as triethylamine and triethylenediamine. Among these, tin compounds have good solubility and performance as a medium, and in particular, dibutyltin dilaurate is preferable.

  The amount of the catalyst used is preferably 0.0001% by mass or more, more preferably 0.001% by mass or more, and preferably 10% by mass or less, with respect to the total amount of the polyisocyanate compound and the polyol compound, and 5% by mass The following are more preferable. In addition, when using these catalysts, it is preferable to apply a photosensitive composition within 10 minutes after adding a catalyst from a viewpoint of ensuring the uniformity of a photosensitive layer coating film.

  By using a polyisocyanate compound having three or more isocyanate groups in one molecule and / or a polyol compound having three or more hydroxy groups in one molecule, it is possible to obtain a polyurethane having a crosslinked structure after addition polymerization. When the volume hologram recording layer contains a polyurethane having a crosslinked structure, a high-intensity volume hologram recording layer can be obtained.

  The content of the polyisocyanate compound in the photosensitive composition is preferably 0.02 to 0.5% by mass, and more preferably 0.05 to 0.3% by mass. Further, the content of the polyol compound in the photosensitive composition is preferably 5 to 35% by mass, and more preferably 10 to 30% by mass.

The volume hologram recording layer comprises a polyurethane, the volume hologram recording layer is dissolved in an organic solvent which is not component of the Fourier transform infrared spectrophotometer (Fourier transform infrared spectrometer: FT- IR) by analyzing, 2270 cm-derived isocyanate groups ^{- 1} of the absorption, and can be confirmed by the presence of absorption of 1690 cm ^-1 and 1470 cm ^-1 derived from an amide group.

<Matrix resin or precursor thereof>
The matrix resin has the function of improving the uniformity of the film thickness of the volume hologram recording layer, the heat resistance, the mechanical properties and the like, and stabilizing the hologram formed by the holographic exposure. In addition, at the time of formation of the volume hologram recording layer, it may have a function of not inhibiting or efficiently expressing the diffusion and migration phenomenon of the polymerizable monomer or the photopolymer. The polyurethane can play a role as a matrix resin described in this section.

  As a matrix resin other than polyurethane, for example, any of thermoplastic resin, thermosetting resin, active energy ray curable resin, etc. can be used without limitation. In addition, those resins modified with a polysiloxane chain or a perfluoroalkylene chain can also be used. The matrix resins can be used alone or in combination of two or more.

  Examples of the thermoplastic resin include, for example, polyvinyl acetate, polyvinyl butyrate, polyvinyl formal, polyvinyl carbazole, polyacrylic acid, polymethacrylic acid, polymethyl acrylate, polymethyl methacrylate, polyethyl acrylate, polybutyl acrylate, polymethacrylic resin Nitrile, polyethyl methacrylate, polybutyl methacrylate, polyacrylonitrile, poly-1,2-dichloroethylene, ethylene-vinyl acetate copolymer, syndiotactic polymethyl methacrylate, poly-α-vinyl naphthalate, polycarbonate, cellulose acetate, Cellulose triacetate, cellulose acetate butyrate, polystyrene, poly-α-methylstyrene, poly-o-methylstyrene, poly-p-me Chilstyrene, poly-p-phenylstyrene, poly-2,5-dichlorostyrene, poly-p-chlorostyrene, poly-2,5-dichlorostyrene, polyarylate, polysulfone, polyether sulfone, styrene-acrylonitrile copolymer Styrene-divinylbenzene copolymer, styrene-butadiene copolymer, styrene-maleic anhydride copolymer, ABS resin, polyethylene, polyvinyl chloride, polypropylene, polyethylene terephthalate, polybutylene terephthalate, polyethylene naphthalate, polyvinyl pyrrolidone, Polyvinylidene chloride, hydrogenated styrene-butadiene-styrene copolymer, polytetrafluoroethylene, polyvinylidene fluoride, tetrafluoroethylene, hexafluoroethylene and vinyl alcohol, Copolymers with nyl ester, vinyl ether, vinyl acetal, vinyl butyral, etc., copolymer of (meth) acrylic acid cyclic aliphatic ester and methyl (meth) acrylate, polyvinyl acetate, methyl methacrylate-ethyl acrylate-acrylic acid co-polymer Polymer etc. are mentioned.

  As a thermosetting resin, unsaturated polyester resin, acrylic urethane resin, epoxy modified acrylic resin, epoxy modified unsaturated polyester resin, alkyd resin, phenol resin etc. are mentioned.

  As an active energy ray curable resin, epoxy acrylate, urethane acrylate, acrylic modified polyester etc. are mentioned. These active energy ray curable resins can include other monofunctional or polyfunctional monomers, oligomers and the like as described below for the purpose of adjusting the crosslinking structure, viscosity and the like. For example, monofunctional monofunctional (meth) acrylates such as tetrahydrofurfuryl (meth) acrylate, hydroxyethyl (meth) acrylate, vinylpyrrolidone, (meth) acryloyloxyethyl succinate, (meth) acryloyloxyethyl phthalate, etc. When classified by the framework structure, polyol (meth) acrylate (epoxy modified polyol (meth) acrylate, lactone modified polyol (meth) acrylate etc.), polyester (meth) acrylate, epoxy (meth) acrylate, urethane (meth) acrylate, other polybutadiene type Is a poly (meth) acrylate having a skeleton such as isocyanuric acid, hydantoin type, melamine type, phosphoric acid type, imide type and phosphazene type, and is UV and electron beam curable Monomers, oligomers, polymers may be utilized such.

  When using the above-mentioned thermoplastic resin, thermosetting resin, or active energy ray curable resin, metal soap such as cobalt naphthenate and zinc naphthenate, organic peroxide such as benzoyl peroxide, methyl ethyl ketone peroxide, and benzophenone A heat or active energy ray curing agent such as acetophenone, anthraquinone, naphthoquinone, azobisisobutyronitrile or diphenyl sulfide can be contained in the photosensitive composition.

  In the case of using a thermosetting resin or an active energy ray curable resin, after forming the photosensitive layer, curing can be performed by heating or active energy ray irradiation. Curing may take place before or after holographic exposure.

  Moreover, you may use a cationically polymerizable monomer as another precursor of matrix resin. A matrix resin made of a cationically polymerizable monomer enables production of a volume hologram recording layer excellent in film strength.

  Specific examples of such cationically polymerizable monomers include diglycerol polyglycidyl ether, pentaerythritol polyglycidyl ether, 1,4-bis (2,3-epoxypropoxyperfluoroisopropyl) cyclohexane, sorbitol polyglycidyl ether, trimethylolpropane poly Glycidyl ether, resorcine diglycidyl ether, 1,6-hexanediol diglycidyl ether, polyethylene glycol diglycidyl ether, phenyl glycidyl ether, para-t-butylphenyl glycidyl ether, adipic acid diglycidyl ester, orthophthalic acid diglycidyl ester, dibromo Phenyl glycidyl ether, dibromo neopentyl glycol diglycidyl ether, 1,2,7,8-diepoxy Cutane, 1,6-dimethylol perfluorohexane diglycidyl ether, 4,4'-bis (2,3-epoxypropoxyperfluoroisopropyl) diphenyl ether, 3,4-epoxycyclohexylmethyl-3 ', 4'-epoxycyclohexane Carboxylate, 3,4-epoxycyclohexyloxirane, 1,2,5,6-diepoxy-4,7-methanoperhydroindene, 2- (3,4-epoxycyclohexyl) -3 ', 4'-epoxy-1 , 3-dioxane-5-spirocyclohexane, 1,2-ethylenedioxy-bis (3,4-epoxycyclohexylmethane), 4 ′, 5′-epoxy-2′-methylcyclohexylmethyl-4,5-epoxy- 2-Methylcyclohexanecarboxylate, ethylene glycol -Bis (3,4-epoxycyclohexanecarboxylate), bis- (3,4-epoxycyclohexylmethyl) adipate, di-2,3-epoxycyclopentyl ether, vinyl-2-chloroethyl ether, vinyl-n-butyl ether, Triethylene glycol divinyl ether, 1,4-cyclohexane dimethanol divinyl ether, trimethylol ethane trivinyl ether, vinyl glycidyl ether and the like can be mentioned. These cationically polymerizable monomers may be used alone or in combination of two or more.

  When using the said cationically polymerizable monomer, you may add a photocationic polymerization initiator and a thermal cationic polymerization initiator in a photosensitive composition.

  Specific examples of the cationic photopolymerization initiator include, for example, iodonium salts and triarylsulfonium salts. Specific examples of iodonium salts include tetrafluoroborate of iodonium, hexafluorophosphate, hexafluoroarsenate, hexafluoroantimonate, trifluoromethanesulfonate, 9,10-dimethoxyanthracene-2-sulfonate and the like. Specific examples of triarylsulfonium salts include triarylsulfonium, triphenylsulfonium, 4-t-butyltriphenylsulfonium, tris (4-methylphenyl) sulfonium, tris (4-methoxyphenyl) sulfonium, 4-thiophenyltrinium. Examples thereof include tetrafluoroborate of sulfonium such as phenylsulfonium and the like, hexafluorophosphate, hexafluoroarsenate, hexafluoroantimonate, trifluoromethanesulfonate, 9,10-dimethoxyanthracene-2-sulfonate and the like. These photocationic polymerization initiators can be used alone or in combination of two or more.

  Specific examples of the thermal cationic polymerization initiator include, for example, cationic or protic acid catalysts such as triflic acid salt, boron trifluoride etherate, boron trifluoride and the like, and preferable thermal cationic polymerization initiators , Triflate. Specific examples thereof include diethylammonium triflate, triethylammonium triflate, diisopropylammonium triflate, ethyldiisopropylammonium triflate, etc., which are available from 3M, and the like (many of which are manufactured by R.R. Alm in 1980 Listed in the October issue of Modern Coatings. Further, among aromatic onium salts which are also used as an active energy ray cationic polymerization initiator, there are some which generate cationic species by heat, and these can also be used as a thermal cationic polymerization initiator. As examples of commercially available products, "San-Aid (registered trademark) SI-60L", "San-Aid (registered trademark) SI-80L" and "San-Aid (registered trademark) SI-100L" (manufactured by Sanshin Chemical Industries, Ltd.) is there. When a cationically polymerizable monomer is used as a matrix resin, the amount of the photocationic polymerization initiator or thermal cationic polymerization initiator used is preferably 0.05 to 50 parts by mass with respect to 100 parts by mass of the cationically polymerizable monomer. -30 mass parts are more preferable.

  The content of the matrix resin other than polyurethane or the precursor thereof is preferably 1 to 30% by mass, more preferably 1 to 28% by mass, and 5 to 25% by mass in the photosensitive composition. Is more preferred.

<Solvent>
At the time of coating, a solvent may be added to the photosensitive composition as needed. However, when the photosensitive composition contains a component which is liquid at normal temperature, the solvent may not be added.

  Examples of the solvent include aliphatic solvents such as n-pentane, n-hexane, n-heptane, n-octane, cyclohexane and methylcyclohexane; ketone solvents such as methyl ethyl ketone (2-butanone), acetone and cyclohexanone; diethyl Ether, isopropyl ether, tetrahydrofuran, dioxane, ethylene glycol dimethyl ether, ethylene glycol diethyl ether, diethylene glycol dimethyl ether, diethylene glycol diethyl ether, propylene glycol monomethyl ether, ether solvents such as anisole, phenetole; ethyl acetate, butyl acetate, ethylene glycol diacetate, etc. Ester solvents; aromatic solvents such as toluene and xylene; methyl cellosolve and ethyl celloso Cell solvents such as butyl cellosolve; alcohol solvents such as methanol, ethanol, propanol and isopropyl alcohol; ether solvents such as tetrahydrofuran and dioxane; halogen solvents such as dichloromethane and chloroform; nitriles such as acetonitrile and propionitrile Solvents: Polar solvents such as N-methyl-2-pyrrolidone, N-ethyl-2-pyrrolidone, N, N-dimethylformamide, N, N-dimethylacetamide and the like can be mentioned. These solvents may be used alone or in combination of two or more.

<Additives>
The photosensitive composition may, if necessary, be a plasticizer, a compatibilizer, a polymerization inhibitor, a surfactant, a silane coupling agent, an antifoaming agent, a release agent, a stabilizer, and an oxidation as long as the above effects are not impaired. The composition may further contain additives such as inhibitors, flame retardants, optical brighteners, and ultraviolet light absorbers.

[Method of preparing photosensitive composition]
The photosensitive composition can be obtained by collectively or sequentially mixing each component mentioned above. As an apparatus used at the time of mixing, stirring or mixing apparatuses, such as a magnetic stirrer, a homodisper, a quick homomixer, a planetary mixer, etc. are mentioned, for example. The obtained photosensitive composition may be used after filtration, if necessary.

Radiation curable adhesive layer
The radiation-curable adhesive layer is a layer obtained by applying a radiation-curable adhesive and then curing it with radiation such as visible light, ultraviolet light, and electron beam, that is, a layer containing a cured product of the radiation-curable adhesive. . Examples of the material of the radiation curable adhesive include, for example, (meth) acrylic monomers, photopolymerization initiators, photosensitizers, additives and the like.

  As the (meth) acrylic monomer, for example, 2-hydroxyethyl (meth) acrylate, 2-hydroxypropyl (meth) acrylate, 4-hydroxybutyl (meth) acrylate, 4-hydroxycyclohexyl (meth) acrylate, 5-hydroxycyclo Octyl (meth) acrylate, 1,3-butanediol (meth) acrylate, 1,4-butanediol (meth) acrylate, 1,6-hexanediol (meth) acrylate, 3-methylpentanediol (meth) acrylate, di Cyclopentenyl acrylate, 2-hydroxy-3-phenoxypropyl acrylate, 2-isocyanate ethyl (meth) acrylate, 1,1-bis (acryloyloxymethyl) ethyl isocyanate and the like. These may be used alone or in combination of two or more.

  Examples of the photopolymerization initiator include benzoin compounds, acetophenone compounds, acyl phosphine oxide compounds, titanocene compounds, thioxanthone compounds, and oxime ester compounds. Examples of photosensitizers include amine compounds and quinone compounds.

  As other additives, silane coupling agents such as γ-glycidoxypropyltrimethoxysilane, vinylpropyltrimethoxysilane, γ-methacryloxypropyltrimethoxysilane, and maleic anhydride adducts of isoprene polymers Examples thereof include oligomers such as esters with hydroxyethyl methacrylate.

  The thickness of the radiation curable adhesive layer in the region where the volume hologram recording layer is present is not particularly limited, but is preferably 5 to 50 μm, and more preferably 10 to 40 μm.

  The method of forming the radiation curable adhesive layer is not particularly limited. For example, after a radiation curable adhesive is applied to cover the bonding surface having a curved surface on which the volume hologram recording layer is provided, the adhesive is irradiated with radiation. There is a method of curing the

  As a method of applying a radiation curable adhesive, conventionally known methods can be used, and specific examples thereof include a spray method, a spin coating method, a wire bar method, a dip coating method, an air knife coating method, and a roll coating Methods, blade coating methods, doctor roll coating methods and the like.

Examples of light sources used for radiation irradiation include light sources that emit ultraviolet light such as ultrahigh pressure mercury lamps, high pressure mercury lamps, carbon arc lamps, xenon arc lamps, and metal halide lamps. As an irradiation energy amount in the case of performing ultraviolet irradiation, 100-2000 mJ / cm < ² > is preferable.

[Method of Manufacturing Optical Element]
The method for producing the optical element is not particularly limited, but a layer including a volume hologram layer is produced in at least a partial region of a junction surface having a curved surface among a pair of junction surfaces, and the layer including the volume hologram recording layer is disposed. Applying a radiation curable adhesive so as to cover the entire joint surface having the curved surface, and curing the radiation curable adhesive using radiation to form a radiation curable adhesive layer preferable.

Specifically, the manufacturing method is
(1) A process of forming a photosensitive layer on an adjacent layer (2) A photosensitive layer and one transparent optical member whose bonding surface has a curved surface are bonded, and a photosensitive layer is formed on at least a partial region of the bonding surface having a curved surface. (3) a step of producing a layer including a volume hologram recording layer by holographically exposing the photosensitive layer (4) covering the entire bonding surface having a curved surface on which the volume hologram recording layer is disposed As described above, a step of applying a radiation curable adhesive and bonding another transparent optical member (5) curing the radiation curable adhesive using radiation to form a radiation curable adhesive layer.

  Hereinafter, such a manufacturing method will be described.

(1) Step of Forming Photosensitive Layer on Adjacent Layer The method for forming the photosensitive layer on the adjacent layer is not particularly limited. For example, the photosensitive composition described above is directly coated on the adjacent layer. The method of drying is mentioned.

  The material of the adjacent layer, the manufacturing method, and the like are as described above, and thus the description thereof is omitted here.

  As a method of applying the photosensitive composition on the adjacent layer, conventionally known methods can be used, and specific examples include a spray method, a spin coat method, a wire bar method, a dip coat method, an air knife coat method , Roll coating method, blade coating method, doctor roll coating method and the like.

  For drying, various methods known in the art using a hot plate, an oven, a belt furnace or the like can be employed. The drying temperature can be selected in a range that does not impair the photosensitivity of the photosensitive composition described above, for example, in the range of 10 to 80 ° C., and the drying time is also not particularly limited, for example, in the range of 1 to 60 minutes.

  When the photosensitive composition contains a polyisocyanate compound and a polyol compound which are precursors of polyurethane, addition polymerization (curing) of these compounds is carried out in this step. The catalyst used for curing, curing conditions and the like are as described above.

  The thickness of the photosensitive layer may be appropriately set so as to be within the preferable thickness range of the volume hologram recording layer described later.

(2) A process of bonding a photosensitive layer and one transparent optical member having a curved bonding surface, and producing a layer including a photosensitive layer in at least a part of the bonding surface having a curved surface The bonding surface bonds together with one transparent optical member having a curved surface. As a method of bonding, for example, a method using a laminator can be mentioned.

(3) Step of Holographic Exposure to the Photosensitive Layer to Produce a Layer Including a Volume Hologram Recording Layer By conducting holographic exposure to the photosensitive layer, the polymerization reaction of the polymerizable monomer in the photosensitive layer proceeds. The area of the photocured photopolymer generated by the polymerization reaction and the area of the other component are formed as the same pattern as the interference wave irradiated by the holographic exposure.

〔Recording method〕
There is no particular limitation on the method of performing holographic exposure on the photosensitive layer and recording (writing) a volume hologram as a volume hologram recording layer, and the method of reproducing (reading) a volume hologram, for example, the following method may be mentioned. .

  First, at the time of recording information, light capable of causing a chemical change of the polymerizable monomer, that is, polymerization and density change thereof is used as recording light (also called object light).

  For example, when information is recorded as a volume hologram, object light is irradiated to the photosensitive layer together with the reference light so that the object light and the reference light are interfered in the photosensitive layer. Thereby, the interference light causes the polymerization and concentration change of the polymerizable monomer in the photosensitive layer, and as a result, the interference fringes cause the refractive index difference in the photosensitive layer, and the interference fringes recorded in the photosensitive layer It is recorded as a volume hologram and becomes a volume hologram recording layer.

  It is preferable to use a visible light laser having excellent coherence as the recording light (the wavelength in the parentheses is shown) used for recording the volume hologram, for example, argon ion laser (458 nm, 488 nm, 514 nm), krypton ion laser (647) Helium-neon laser (633 nm), YAG laser (532 nm), etc. can be used.

The amount of irradiation energy (exposure amount) at the time of hologram recording is not particularly limited, but is preferably in the range of 10 to 250 mJ / cm ² .

  In addition, as a hologram recording method, there are a polarization collinear hologram recording method, a reference light incident angle multiplex type hologram recording method, and the like, and any recording method can provide good recording quality.

  The exposure apparatus is not particularly limited, but, for example, an exposure apparatus of a type whose schematic configuration is shown in FIG. 1 can be used. In the exposure apparatus shown in FIG. 1, the light beam (recording light) emitted from the laser light source 201 is directed to a suitable position of the exposure system by beam steerers 202a and 202b consisting of two pairs of mirrors. A shutter 203 controls ON / OFF of a light beam (recording light). A beam expander 204 has a function of expanding the light beam diameter and changing the aperture ratio (NA) according to the exposure area of the photosensitive layer.

  The light beam (recording light) having passed through the beam expander 204 is split into two light beams by a beam splitter 205. The divided light beams (recording light) are guided to spatial filters 211 and 212 by mirrors 206 and 207 and mirrors 209 and 208, respectively. The spatial filters 211 and 212 are composed of a lens and a pinhole. The lens condenses a light beam (recording light) and guides the light beam (recording light) to the manufacturing optical system 213 through the pinhole.

  The manufacturing optical system 213 can set and fix a sample such as a glass prism provided with a photosensitive layer to be a volume hologram recording layer at a suitable position so that the reflection angle of the light beam of the optical element can be controlled.

  The photosensitive layer provided in the prism fixed to the manufacturing optical system 213 is divided into two light beams, and holographic exposure (interference exposure) is performed by light beams (recording light) guided through the spatial filters 211 and 213, respectively. Ru.

  An example of holographic exposure (interference exposure) on the photosensitive layer fixed to the manufacturing optical system 213 is shown in FIG. In the example shown in FIG. 2, holographic image exposure on the photosensitive layer is performed by irradiating the laminated body 15 of the first transparent optical member 11 and the photosensitive layer (volume hologram recording layer) 12 with laser light from two directions. It will be. Of the laser beams from two directions, one is the object beam 31 and the other is the reference beam 32.

  Note that although only one light source is shown in FIG. 1, when holographic exposure is performed using a plurality of laser light sources having different wavelengths, a glonic mirror is inserted in the light path in front of the shutter 203 and a plurality of light sources The emitted laser beams may be combined stepwise.

After recording the volume hologram, the volume hologram recording layer can be appropriately subjected to processing such as whole surface exposure with ultraviolet light and heating in order to promote refractive index modulation and complete the polymerization reaction (fixing). As a light source used in the entire surface exposure, for example, a light source emitting ultraviolet light such as an ultra-high pressure mercury lamp, a high pressure mercury lamp, a carbon arc lamp, a xenon arc lamp, and a metal halide lamp can be used. As an irradiation energy amount in the case of performing whole surface exposure by an ultraviolet-ray, 50-200 J / cm < ² > is preferable. Moreover, as for the temperature at the time of heat-processing, 50-150 degreeC is preferable, and, as for processing time, 30 minutes-3 hours are preferable.

  When the entire surface exposure and the heat treatment are performed together, the order is not particularly limited, and the entire surface exposure may be performed first, or the heat treatment may be performed first.

  In the present embodiment, the thickness of the volume hologram recording layer is preferably 5 to 100 μm, and more preferably 5 to 40 μm from the viewpoint of durability.

(4) A step of applying a radiation curable adhesive so as to cover the entire bonding surface having a curved surface on which the volume hologram recording layer is disposed, and bonding other transparent optical members. In this step, it was prepared in the above (3) A radiation curable adhesive is applied to cover the entire bonding surface having a curved surface on which the volume hologram recording layer is disposed, and another transparent optical member is bonded.

  When the adjacent layer is not provided, the adjacent layer is peeled off from the volume hologram recording layer before the radiation curable adhesive is applied, and the radiation curable adhesive is applied directly on the volume hologram recording layer. If an adjacent layer is to be installed, apply a radiation curable adhesive onto the adjacent layer.

  The coating method, coating thickness and the like of the radiation curable adhesive are as described above.

(5) Step of curing a radiation curable adhesive using radiation to form a radiation curable adhesive layer In this step, the radiation curable adhesive is cured using radiation to form a radiation curable adhesive layer Do. The light source used for radiation irradiation, the irradiation conditions, and the like are as described above.

[Other layer]
The optical element of the present embodiment may have other layers such as a protective layer, a reflective layer, an antireflective film, an ultraviolet ray absorbing layer, etc. in addition to the above.

  The protective layer is a layer for preventing the influence such as deterioration of storage stability of the volume hologram recording layer. There is no restriction | limiting in the specific structure of a protective layer, It is possible to apply a well-known thing arbitrarily. For example, a layer formed of a water-soluble polymer, an organic / inorganic material or the like can be formed as a protective layer. The formation position of the protective layer is not particularly limited. For example, between the volume hologram recording layer and the radiation curable adhesive layer, between the adjacent layer and the radiation curable adhesive layer, and between the volume hologram recording layer and the transparent optical member Etc.

  The reflective layer is formed when the optical element is configured to be reflective. In the case of a reflective optical element, the reflective layer is usually formed on the outer surface of the adjacent layer. The reflective layer can be applied with reference to conventionally known ones as appropriate. For example, a thin film of metal can be used.

  Furthermore, in any of the transmissive and reflective optical elements, an antireflective film may be provided on the side where the object light and the reproduction light are incident and / or emitted. The antireflective film works to improve the light utilization efficiency and to suppress the generation of ghost images. The material and shape of the antireflective film can be applied with appropriate reference to conventionally known ones.

  When the volume hologram recorded in the volume hologram recording layer is to be reproduced, predetermined reproduction light (usually, reference light) is irradiated to the volume hologram recording layer. The irradiated reproduction light is diffracted in response to the interference fringes. Since this diffracted light contains the same information as that of the volume hologram recording layer, the information recorded in the volume hologram recording layer can be reproduced by reading the diffracted light by an appropriate detecting means. The wavelength regions of the object light, the reproduction light and the reference light are arbitrary according to the respective applications, and may be a visible light region or an ultraviolet light region.

[Video display device]
The optical element of this embodiment is suitably used for image display apparatuses, such as a head mounted display (HMD), a head up display (HUD), and an optical see-through display. In the following, an example of an image display apparatus including an optical element will be described. FIG. 3 shows a schematic cross-sectional structure of an image display apparatus 1 including an optical element 10 and a display element 20. In the optical element 10 of FIG. 3, the first transparent optical member 11 having a curved surface and the second transparent optical member 13 which makes a pair with the first transparent optical member 11 are joined so as to sandwich the volume hologram recording layer 12. It has the following structure.

  As the volume hologram recording layer 12 obtained by holography (interference) exposure is sandwiched between two transparent optical members 11 and 13, a first transparent optical member 11 having a curved surface and a pair with the first transparent optical member 11 By bonding the second transparent optical member 13 to the second transparent optical member 13 with the adhesive 14, the optical device 10 in a state capable of reproducing a hologram can be obtained. In the hologram reproduction, as shown in FIG. 3, when the image light (reproduction illumination light) 41 is incident on the optical element 10, the reproduction image light 42 is diffracted and reflected. The reproduced image light 42 enters the observer's eye EY together with the external image light 43 transmitted through the optical element 10. Therefore, the observer can observe the external image as well as the display image.

  The volume hologram recording layer 12 is attached to the first transparent optical member 11 having a curved surface, and the radiation provided between the first transparent optical member 11 and the second transparent optical member 13 as a pair. The first transparent optical member 11 and the second transparent optical member 13 are bonded together with the curable adhesive layer 14 so as to sandwich the volume hologram recording layer 12. Since the volume hologram recording layer 12 is provided on the bonding surface between the first transparent optical member 11 and the second transparent optical member 13 having a curved surface, the see-through property of the external image through the bonding surface is ensured. .

  As shown in FIG. 3, the image display apparatus 1 includes, in addition to the optical element 10, a display element 20 for displaying an image. Examples of the display device 20 include a reflective or transmissive liquid crystal display (LCD), a digital micromirror device, and an organic electro-luminescence (EL) display. . Furthermore, a lighting device for lighting the display element 20 may be disposed. Examples of the illumination device include those provided with a light source such as an LED (light emitting diode), an illumination device including a condensing optical element (lens, mirror, etc.), and the like.

  A more detailed configuration of the video display device 1 shown in FIG. 3 is shown in FIG. FIG. 4 shows an optical path from the light source 21 to the optical pupil EP in the image display device 1 provided with the illumination device and the like. The image display apparatus 1 includes a polarizing plate 24, a polarization beam splitter 25, a display element 20, and an optical element 10 functioning as an eyepiece optical system, in addition to the illumination device.

  The illumination device illuminates the display element 20, and includes a light source 21, an illumination mirror 22, and a diffusion plate 23. The light source 21 is configured of an LED that emits light in a wavelength band of, for example, 520 nm. Although the light source 21 shown in FIG. 4 has only one wavelength, when the volume hologram recording layer diffracts a plurality of different wavelengths, it is composed of an integrated LED emitting light of a plurality of different wavelength bands. It is also good. The illumination mirror 22 reflects light (illumination light) emitted from the light source 21 toward the diffusion plate 23, and bends the illumination light such that the optical pupil EP and the light source 21 become substantially conjugate (for example, It is a free-form surface mirror). The diffusion plate 23 diffuses the illumination light from the light source 21 and the degree of diffusion differs depending on the direction (for example, it is a unidirectional diffusion plate having a diffusion action only in the lateral direction).

  A diffusion plate 23 is bonded and held on the surface of the polarizing plate 24. Among the light incident through the diffusion plate 23, light of a predetermined polarization direction is transmitted and guided to the polarization beam splitter 25. The direction of the polarizing beam splitter 25 is aligned so that the polarized light transmitted through the polarizing plate 24 is reflected by the polarizing beam splitter 25. While the polarization beam splitter 25 reflects the light transmitted through the polarizing plate 24 in the direction of the reflective display element 20, of the light reflected by the display element 20, a light corresponding to the image signal ON (a polarizing plate 24 The transmitted light is a flat plate-like polarization separation element that transmits light having orthogonal polarization directions), and is attached to the surface 11c of the transparent optical member 11 having the first curved surface.

  The display element 20 is a display element that modulates the light from the illumination device (that is, the light reflected by the polarization beam splitter 25) to display an image IM. In this image display device 1, a reflective liquid crystal display element is used. It is assumed. In the case of expressing a plurality of different wavelength regions, the display element 20 may be configured to have a color filter, or may be configured to be driven by time division for each different wavelength region.

  The display element 20 is disposed so that light incident substantially perpendicularly from the polarization beam splitter 25 is reflected substantially perpendicularly and directed to the polarization beam splitter 25. This facilitates optical design to increase the resolution as compared with a configuration in which light is incident on a reflective display element at a large incident angle. The display element 20 is disposed on the same side as the light source 21 with respect to the light path from the illumination mirror 22 to the polarization beam splitter 25. Thereby, the whole optical system from a lighting installation to the display element 20 can be comprised compactly. The display element 20 may be supported by the same substrate as the light source 21 or may be supported by a separate substrate.

  The optical element 10 includes a first transparent optical member 11 having a curved surface, a second transparent optical member 13 paired with the first transparent optical member 11, and a volume hologram recording layer 12, and the transparent optical member 11 and 13 are made of, for example, plastic (more specifically, acrylic resin, polycarbonate, cycloolefin resin, etc.). The optical element 10 has non-axisymmetric (non-rotationally symmetric) positive optical power, and thereby functions as an eyepiece optical system for guiding the image light from the display element 20 to the optical pupil EP. The transparent optical member 11 guides the image light incident from the display element 20 through the polarization beam splitter 25 inside, and transmits the light of the external image (external light), and the upper end of the parallel flat plate The portion is thicker toward the upper end and thinner at the lower end toward the lower end.

  In the first transparent optical member 11 having a curved surface, the surface 11 c to which the polarization beam splitter 25 is attached is an optical surface on which image light from the display element 20 first enters. Further, the two surfaces 11a and 11b positioned substantially parallel to the optical pupil EP and facing each other are total reflection surfaces that guide the image light by total reflection. Among them, the surface 11 a on the optical pupil EP side also serves as an emission surface of image light diffracted and reflected by the volume hologram recording layer 12.

  The first transparent optical member 11 having a curved surface is a second transparent optical member that forms a pair with the first transparent optical member 11 with the adhesive 14 so as to sandwich the volume hologram recording layer 12 disposed at the lower end thereof. It is joined with 13 to form a substantially parallel plate. By bonding the second transparent optical member 13 to the first transparent optical member 11, the refraction when external light passes through the lower end of the first transparent optical member 11 is referred to as the second transparent optical member 13. It is possible to prevent the distortion of the observed external image from occurring. The volume hologram recording layer 12 is provided in contact with the surface 11 d of the first transparent optical member 11, and is a volume phase type that diffracts and reflects the image light guided inside the first transparent optical member 11 and is reflected. It is an optical element that is a mold. The diffraction wavelength of the volume hologram recording layer 12 substantially corresponds to the wavelength of the image light (the emission wavelength of the light source 21).

  In the above configuration, light emitted from the light source 21 of the illumination device is reflected by the illumination mirror 22 and diffused only in one direction by the diffusion plate 23, and then only light of a predetermined polarization direction is To Penetrate. Then, the light transmitted through the polarizing plate 24 is reflected by the polarization beam splitter 25 and enters the display element 20. In the display element 20, the incident light is modulated according to the image signal. At this time, the image light corresponding to the image signal ON is converted by the display element 20 into light whose polarization direction is orthogonal to that of the incident light and emitted, so that it is transmitted through the polarization beam splitter 25 and the first transparent optics The light enters the inside of the first transparent optical member 11 from the member surface 11 c. On the other hand, since the image light corresponding to the image signal OFF is emitted without the polarization direction being converted by the display element 20, the image light is blocked by the polarization beam splitter 25 and does not enter into the first transparent optical member 11. .

  In the first transparent optical member 11, the incident image light is totally reflected once by each of the two opposing surfaces 11 a and 11 b of the first transparent optical member 11 and then enters the volume hologram recording layer 12. In the volume hologram recording layer 12, only light of a specific wavelength is diffracted and reflected, and exits from the surface 11a to reach the optical pupil EP. Therefore, the observer can observe the image IM displayed on the display element 20 at the position of the optical pupil EP as a virtual image. On the other hand, since the first transparent optical member 11, the second transparent optical member 13, and the volume hologram recording layer 12 transmit almost all the external light, the observer can observe the external image in a see-through manner. Therefore, the virtual image of the image IM displayed on the display element 20 is observed to overlap with a part of the external image.

  As described above, in the optical element 10, the image of the display element 20 is an external image through the volume hologram recording layer 12 between the joined first transparent optical member 11 and second transparent optical member 13. It functions as an eyepiece optical system that projects and displays the display image as a virtual image on the observer's eye EY (see FIG. 3) as a virtual image so as to overlap. Therefore, the volume hologram recording layer 12 is preferably a volume phase reflection type hologram. Since the volume phase type reflection type hologram has a high light transmittance of the external image, if the volume phase type reflection type hologram is used as the volume hologram recording layer 12, the observer should clearly observe the external image together with the display image. Becomes possible.

  As shown in FIGS. 3 and 4, since the volume hologram recording layer 12 is used in a state of being held between the first transparent optical member 11 and the second transparent optical member 13 having curved surfaces, humidity, oxygen, etc. Hardly affected by the external environment of the The optical element as an eyepiece optical system which totally reflects the image light provided from the display element 20 inside the transparent optical member 11 and guides it to the volume hologram recording layer 12 by the configuration embedded in the transparent optical members 11 and 13 It becomes possible to adopt ten. And, by optimizing the shape of the transparent optical members 11 and 13 and the shape of the volume hologram recording layer 12, the see-through property (combiner function) of the external image is maintained while maintaining the optical performance of the volume hologram recording layer 12. be able to.

  As described above, the image display apparatus 1 shown in FIGS. 3 and 4 has the optical element 10 and the display element 20 for displaying an image, and the volume hologram recording layer 12 is the image light from the display element 20. It is preferable to diffract light of a specific wavelength among them. Such a configuration enables see-through display in which a high quality image is superimposed on an external image. Therefore, it becomes possible to observe a high quality image provided from the optical element 10 through the optical element 10, and at the same time to observe an external image through the optical element 10 in a see-through manner.

  The first transparent optical member 11 having a curved surface that constitutes the optical element 10 is configured to totally reflect the image light from the display element 20 inside and guide it to the volume hologram recording layer 12 as shown in FIGS. 3 and 4. It is preferable to have With such a configuration, it is possible to provide an observer with a bright image by using the video light provided from the display element 20 without waste. In addition, the display element 20 can be disposed at a position distant from the optical element 10, and a wide view of the observer with respect to the external world can be secured.

  Hereinafter, specific examples and comparative examples will be described. However, the technical scope of the present invention is not limited to the following examples. Moreover, in the following operation, unless otherwise specified, measurement of operation, physical properties, etc. was performed under the conditions of room temperature (20 to 25 ° C.) / Relative humidity 40 to 50% RH.

  Transparent optical members 11-1 and 11-2 having cemented surfaces having curved surfaces were produced. The outline of the shape is shown in FIG. In FIG. 5, (a) is a plan view of the transparent optical member, and (b) and (c) are side views of the transparent optical member. As shown in FIG. 5, the curved surface of the transparent optical member 11-1 is a convex surface of a cylindrical shape (cylindrical shape), and the curved surface of the transparent optical member 11-2 is a convex lens shape (convex spherical surface). .

  In addition, a transparent optical member 13-1 whose bonding surface has a curved surface opposite to the bonding surface of the transparent optical member 11-1, and a transparent optical device whose bonding surface has a curved surface reverse to the bonding surface of the transparent optical member 11-2. The member 13-2 was also produced (refer FIG. 6).

  Transparent optical members 11-1, 11-2, 13-1 and 13-2 are pellets of polymethyl methacrylate resin heated to 220 ° C. using an injection molding machine (product name; ACRYPET (registered trademark) VH; Mitsubishi Rayon Co., Ltd.) was poured into a dedicated mold maintained at 100 ° C., clamped at a load of 50 tons, then taken out of the mold and cooled to 25 ° C. to produce a molded article.

Example 1 Preparation of Optical Element 1
<Photosensitive composition 1 for preparation of volume hologram recording layer>
The following components were charged into a container in the dark and stirred at room temperature (25 ° C.) for 30 minutes to obtain a solution. The resulting solution was filtered through a mesh to give mixture 1.

Hexamethylene diisocyanate 0.1 part by mass Polypropylene glycol 10.0 parts by mass
(Molecular weight 4000, hydroxy value 25.3 mg KOH / g)
2-{{[3- (methylsulfanyl) phenyl] carbamoyl} oxy} ethyl prop-2-enoate 3.0 parts by mass tetrabutylammonium triphenylbutyl borate
(Organic boronate polymerization initiator, manufactured by Showa Denko KK)
0.01 parts by mass Safranin O (sensitizing dye, manufactured by Tokyo Chemical Industry Co., Ltd.)
0.1 parts by mass N-ethyl-2-pyrrolidone 0.5 parts by mass Ethyl acetate 25.0 parts by mass 0.01 parts by mass of dibutyltin dilaurate is added to the obtained mixture 1 to prepare a volume hologram recording layer After obtaining the photosensitive composition 1, 5 minutes after that, the photosensitive composition 1 for producing the above volume hologram recording layer is coated on one side of a 50 μm thick polyethylene terephthalate (PET) film (adjacent layer) with a blade coater. It applied using. Thereafter, it was dried for 30 minutes in an environment of 20 ° C. and 50% RH, and further heat treatment was carried out at 60 ° C. for 2 hours to obtain a photosensitive layer 25 μm in thickness. The PET film coated with the photosensitive layer was cut, and the photosensitive layer and the transparent optical member 11-1 were made to face each other, and laminated (adhered) as shown in FIG.

An exposure apparatus (light source: argon laser, exposure wavelength: 514 nm) having the same basic structure as that of FIG. 1 is used to adjust the photosensitive layer so that a virtual image with a field angle of 25 ° appears 1 m ahead, on the photosensitive layer surface Holographic exposure was performed so that the amount of irradiation energy was 24 mJ / cm ² .

  After holographic exposure was performed, the whole surface was exposed to ultraviolet light by standing for 60 minutes at a position of 15 cm from a high pressure mercury lamp (illuminance 100 W) to obtain a volume hologram recording layer.

Thereafter, an acrylate system containing dicyclopentenyl acrylate, 2-hydroxy-3-phenoxypropyl acrylate, and γ-glycidoxypropyltrimethoxysilane so as to cover the entire bonding surface having a curved surface on which the volume hologram recording layer is disposed. Adhesive (radiation-curable adhesive), using a dispenser, the thickness of the part with the volume hologram recording layer is 15 μm thick and the part without the volume hologram is the thickness including the thickness of the volume hologram recording layer and the adjacent layer Each was applied at 80 μm. Furthermore, the second transparent optical member 13-1 is pasted on the applied adhesive, ultraviolet rays are irradiated from a high pressure mercury lamp (illuminance 100 W / cm ² ) (irradiation amount: 200 mJ / cm ² ), and the adhesive is It was cured to obtain an optical element KO-1.

(Example 2)
In the same manner as in Example 1 except that the transparent optical member 11-1 is changed to the transparent optical member 11-2 as shown in FIG. 5 and the transparent optical member 13-1 is changed to the transparent optical member 13-2. , Optical element KO-2.

(Comparative example 1)
An optical element KO-21 was obtained in the same manner as Example 1, except that the photosensitive composition was prepared as follows using the photosensitive composition 2 for producing a volume hologram recording layer described below.

<Photosensitive composition 2 for preparation of volume hologram recording layer>
Hexyl isocyanate 0.1 part by mass Polypropylene glycol 10.0 parts by mass (molecular weight 4000, hydroxy value 25.3 mg KOH / g)
2-{{[3- (methylsulfanyl) phenyl] carbamoyl} oxy} ethyl prop-2-enoate 3.0 parts by mass tetrabutylammonium triphenylbutyl borate
(Organic boronate polymerization initiator, manufactured by Showa Denko KK)
0.01 parts by mass Safranin O (sensitizing dye, manufactured by Tokyo Chemical Industry Co., Ltd.)
0.1 parts by mass N-ethyl-2-pyrrolidone 0.5 parts by mass Ethyl acetate 25.0 parts by mass The obtained photosensitive composition 2 for producing a volume hologram recording layer is a 50 μm thick polyethylene terephthalate (PET) film The resultant was coated using a blade coater and dried for 30 minutes in an environment of 20 ° C. and 50% RH to obtain a photosensitive layer with a thickness of 20 μm. The obtained photosensitive layer was allowed to stand for 5 days in an environment of 20 ° C. and 50% RH. After standing, the PET film coated with the photosensitive layer was cut, and the photosensitive layer and the transparent optical member 11-1 were made to face each other to be laminated (adhered) as shown in FIG.

(Comparative example 2)
In the same manner as Comparative Example 1 except that the transparent optical member 11-1 is changed to the transparent optical member 11-2 as shown in FIG. 5 and the transparent optical member 13-1 is changed to the transparent optical member 13-2. , Optical element KO-22.

(Comparative example 3)
After obtaining the volume hologram recording layer of Example 1, an optical element KO-23 was obtained in the same manner as in Example 1 except that the second transparent optical member 13-1 was not laminated.

  The sharpness of the initial virtual images of the obtained optical elements KO-1, KO-2, and KO-21, and the diffraction efficiency after the initial and moisture resistance tests were measured by the following methods.

(Sharpness of virtual image)
The optical element manufactured above was disposed on the image display apparatus as shown in FIG. 4 so that the concave curved surface faced the pupil side, and the observer observed the virtual image of the image IM displayed on the display element 20. Specifically, the positions of nine points of the image as shown in FIG. 8 were observed, and ten observers scored according to the following criteria, and calculated the average value. The average score values are shown in Table 1:
5: A virtual image can be clearly seen over the entire surface 4: 1 to 2 points, visible, but slightly reduced, the sharpness of the virtual image 3: 3 to 5 points, visible, although slightly, a virtual image The sharpness is degraded 2: 1 to 2 points, the virtual image is unclear, some parts can not be seen 1: 3 points or more, the virtual image is not clear, some parts can not be seen.

(Evaluation)
<Diffraction efficiency>
About the obtained optical element, the transmittance | permeability was measured on condition of the following using spectrophotometer U-3900 (made by Hitachi, Ltd.).

Scan range 800 nm to 400 nm
Scanning speed 600 nm / min
A baseline was calculated from the transmittance at a wavelength of 600 nm to 460 nm of the obtained transmittance data, and the diffraction efficiency was calculated by the following equation from the values of the transmittance T at a wavelength of 521 nm and the baseline transmittance B:
Diffraction efficiency = [(B−T) / T] × 100 (%).

<Diffraction efficiency measurement after moisture resistance test>
The obtained optical element is exposed for 500 hours under an environment of 30 ° C. and 80% RH, and left for 24 hours under a low humidity condition (30 ° C., 4.7% RH) containing silica gel, and thereafter in the same manner as described above The diffraction efficiency was calculated.

  The evaluation results of Examples 1 to 2 and Comparative Examples 1 to 3 are shown in Table 1 below.

  As is clear from Table 1 above, the optical elements of the examples have good sharpness of the virtual image (image quality) and have durability capable of maintaining high diffraction efficiency for a long time even under high humidity conditions. I understand.

1 video display element,
10 optical elements,
11 first transparent optical member,
12 volume hologram recording layer,
13 second transparent optical member,
14 radiation curable adhesive layer,
15 stacks,
20 display elements,
21 light sources,
22 illumination mirrors,
23 diffusers,
24 polarizers,
25 polarization beam splitters,
31 object light,
32 reference lights,
41 image light,
42 reproduced image light,
43 outside image light,
201 laser light source,
202 beam steerer,
203 shutter,
204 beam expander,
205 beam splitters,
206, 207, 208, 209, 210 mirrors,
211, 212 spatial filter,
EP optical pupil,
EY observer eye,
IM picture.

Claims (2)

  At least one of a pair of bonding surfaces of two adjacent transparent optical members has a curved surface, and the volume hologram recording layer includes a photopolymer in at least a part of the bonding surface having a curved surface among the pair of bonding surfaces. An optical element having a radiation-curable adhesive layer disposed to cover the entire bonding surface having the curved surface, wherein the volume hologram recording layer comprises polyurethane. At least one of a pair of bonding surfaces of two adjacent transparent optical members has a curved surface, and the volume hologram recording layer includes a photopolymer in at least a part of the bonding surface having a curved surface among the pair of bonding surfaces. An optical element having a radiation-curable adhesive layer disposed to cover the entire bonding surface having the curved surface, wherein the volume hologram recording layer includes polyurethane.
A layer including a volume hologram layer is produced in at least a partial region of a bonding surface having a curved surface among a pair of bonding surfaces, and the entire bonding surface having the layer including the volume hologram recording layer is covered. And applying a radiation curable adhesive thereto, and curing the radiation curable adhesive using radiation to form a radiation curable adhesive layer.