Optical laminate

Abstract

An optical laminate according to the present invention includes: a first layer that is a photopolymer layer containing a hologram; a second layer that is laminated onto the first layer; and a molecular adhesive layer that is interposed between the first layer and the second layer.

Description

optical laminate

[0001] The present disclosure relates to optical laminates.

[0002] Patent Document 1 discloses an optical laminate including a photopolymer layer on which a hologram is recorded by exposure, an adhesive layer bonded to the photopolymer layer, and another layer such as a substrate, which is further bonded to the photopolymer layer. In the configuration of Patent Document 1, a pressure-sensitive adhesive or a hot-melt adhesive such as a polyolefin adhesive or a urethane adhesive is used as the adhesive layer.

[0003] Special table 2015-510526 publication

[0004] According to Patent Document 1, the disclosed configuration can suppress color shift of a hologram, i.e., a change in the color of a hologram in a laminate after bonding from the color of the hologram in the state of the photopolymer layer alone before bonding. However, configurations including the above-mentioned adhesive layer do not sufficiently suppress color shift, and may not be able to meet the high demand for high color quality of holograms in recent years.

[0005] The present disclosure aims to suppress color shift of a hologram before and after bonding in an optical laminate formed by bonding a photopolymer layer containing a hologram to another layer.

[0006] One aspect of the present disclosure is an optical laminate having a first layer that is a photopolymer layer containing a hologram, a second layer laminated to the first layer, and a molecular adhesive layer interposed between the first layer and the second layer.

[0007] According to the present disclosure, in an optical laminate in which a photopolymer layer containing a hologram is bonded to another layer, color shift of the hologram before and after bonding can be suppressed.

[0008] 1 is a schematic diagram showing an optical laminate according to an embodiment of the present disclosure; FIG. 2 is a schematic diagram showing an optical laminate according to a first embodiment; FIG. 3 is a schematic diagram showing an optical laminate according to a second embodiment; FIG. 4 is a schematic diagram of layer configurations of representative examples and comparative examples; FIG. 5 is a transmittance spectrum of the optical laminate of Example 1-1; and FIG. 6 is a transmittance spectrum of the optical laminate of Comparative Example 1.

[0009] Specific embodiments of the present disclosure will be described in more detail below with reference to the drawings. In this specification and the drawings, components having substantially the same functional configurations are designated by the same reference numerals, and redundant description may be omitted.

[0010] 1 shows an optical laminate 10 according to one embodiment of the present disclosure. The optical laminate 10 has a first layer 1 which is a photopolymer layer containing a hologram, a second layer 2 laminated on the first layer 1, and a molecular adhesive layer 3 interposed between the first layer 1 and the second layer 2. In this specification, an optical laminate is a structure having an optical function and formed by laminating multiple layers.

[0011] In the present disclosure, the first layer 1 is a photopolymer layer containing a hologram, but the second layer 2 is not particularly limited. The second layer 2 may be, for example, a substrate for supporting or reinforcing the first layer 1, or may be a photopolymer layer containing a hologram, similar to the first layer 1. The second layer 2 may also be a layer made of a material used in the optical field other than a substrate or a photopolymer layer, and may be a layer having predetermined optical properties, such as a predetermined refractive index and a predetermined transmittance.

[0012] In this embodiment, the first layer 1 and the second layer 2 are bonded together via the molecular adhesive layer 3, thereby suppressing color change (also referred to as color shift) of the hologram contained in the first layer 1. In this specification, suppression of color change of the hologram refers to color change that may occur due to adhesion between layers, and more specifically, it means that the color change of the hologram contained in the optical laminate is reduced or is absent when comparing the state before the first layer 1 and the second layer 2 are bonded to the state after the first layer 1 and the second layer 2 are bonded.

[0013] If the color change of a hologram caused by adhesion between layers is significant, the hologram may not be displayed in the desired color, and in particular, in the case of a multicolor hologram, an appropriate hologram image may not be displayed. In response to this, the inventors have discovered that by using a molecular adhesive layer 3 as the layer bonding the first layer 1 and the second layer 2, color change of the hologram can be effectively suppressed. This allows for high color quality of the hologram to be achieved. This is thought to be because the molecular adhesive layer 3 has little chemical and / or physical effect on the contact layer that comes into contact with the molecular adhesive layer 3. Furthermore, the thickness of the molecular adhesive layer 3 is thinner than the thickness of an adhesive layer formed without a conventional molecular adhesive, and therefore, even if light enters the molecular adhesive layer 3, it is thought to have little effect on the optical properties of the optical laminate.

[0014] The color change of the hologram can be evaluated by measuring the transmittance spectrum of the hologram using a spectrophotometer or the like and comparing the shape of the spectrum before and after bonding the first layer 1 and the second layer 2. For example, the color change can be evaluated by determining the degree to which the wavelength at the apex of a predetermined peak in the transmittance spectrum shifts before and after bonding (the amount of wavelength change), that is, by determining the difference between the wavelength (nm) at the apex of the predetermined peak in the spectrum before bonding and the wavelength (nm) at the apex of the predetermined peak in the spectrum after bonding. With the optical laminate 10 according to the present disclosure, the amount of wavelength change can be suppressed to 20 nm or less, 15 nm or less, 10 nm or less, or 5 nm or less.

[0015] Furthermore, because the perceived color of a hologram also changes depending on its transmittance, the color change of the hologram can also be evaluated by determining the amount of change in transmittance before and after bonding. To determine the change in transmittance, the transmittance spectrum of the hologram is measured using a spectrophotometer or the like, as described above, and the spectra are compared before and after bonding the first layer 1 and the second layer 2. Then, for example, the degree to which the transmittance (%) at the apex of the maximum peak in the transmittance spectrum has changed before and after bonding (the amount of change in transmittance) can be determined, i.e., the difference (%pt) between the transmittance (%) at the apex of the maximum peak in the spectrum before bonding and the transmittance (%) at the apex of the maximum peak in the spectrum after bonding can be determined. According to the optical laminate 10 of the present disclosure, such a change in transmittance can be suppressed to 30% or less, 20% or less, 10% or less, or 5% or less.

[0016] If suppressing color change of the hologram is given top priority, it is also possible to form a laminate by directly stacking the first layer 1 and the second layer 2 without interposing an adhesive layer between them. However, in that case, the adhesion between the layers is insufficient, resulting in low strength and no product that can withstand use as an optical laminate. Therefore, more specifically, the optical laminate according to this embodiment has sufficient interlayer adhesion to function as an optical laminate while suppressing color change as described above.

[0017] Furthermore, the optical laminate 10 according to this embodiment has excellent resistance under certain environments, particularly high-temperature resistance. Here, high-temperature resistance refers to excellent color change of the hologram and excellent interlayer adhesion even after high-temperature storage. High-temperature resistance can be evaluated, for example, by storing the optical laminate 10 at a high temperature, specifically at a temperature of 60°C or higher, preferably at a temperature of 80°C or higher, for a predetermined period of time and then evaluating the optical laminate 10.

[0018] (Photopolymer Layer) The first layer 1 is a layer in which a hologram is recorded in a photopolymer layer. The photopolymer layer used in this embodiment is not particularly limited as long as it is composed of a photopolymer capable of recording a hologram. The photopolymer layer may contain, for example, a photopolymerizable monomer, a photopolymerization initiator, and a binder. Alternatively, the photopolymer layer may contain a matrix polymer, a photopolymerizable writing monomer, and a photoinitiator without a binder. In this case, the matrix polymer may be an amorphous thermoplastic resin. Examples of the matrix polymer include acrylic polymers, such as homopolymers or copolymers containing one or more monomers of (meth)acrylic acid, (meth)acrylic acid esters, and derivatives thereof, polybutyl acrylate, polyvinyl acetate, polyvinyl butyrate, gelatin, cellulose ester, cellulose ether, silicone copolymer, polyurethane, polybutadiene, polyisoprene, polyethylene oxide, epoxy resin polyamide, and polycarbonate.

[0019] As the photopolymer layer, for example, a photopolymer film for hologram recording known in the art can be used. Commercially available photopolymer films for hologram recording include the Bayfol (registered trademark) HX series manufactured by Covestro AG, such as Bayfol HX200. Commercially available products including the Bayfol series may be provided in a form in which the photopolymer layer is sandwiched between a cover film and a substrate film. In such a form, in the production of the optical laminate 10 according to this embodiment, the cover film can be peeled off and attached to the second layer 2 when laminating with the second layer 2. In this case, the production process may be carried out with the substrate film remaining bonded to the photopolymer layer. Alternatively, the optical laminate 10 may be configured to include a substrate film.

[0020] The thickness of the photopolymer layer may be, for example, 1 μm or more, preferably 5 μm or more. The thickness of the layers in the optical laminate 10 according to the present disclosure (including the thickness of the molecular adhesive layer 3) can be measured using an optical interference film thickness meter or the like.

[0021] (Molecular Adhesive Layer) The molecular adhesive layer 3 is a layer that bonds the first layer 1 and the second layer 2 to each other. The molecular adhesive layer 3 is formed by interposing a molecular adhesive between the first layer 1 and the second layer 2 and curing it. In other words, the molecular adhesive layer 3 can also be said to be a cured product of the molecular adhesive. Here, the molecular adhesive refers to an adhesive containing a compound having two or more types of reactive functional groups. When the molecular adhesive is interposed between the first layer 1 and the second layer 2, the two or more types of reactive functional groups in the compound contained in the molecular adhesive chemically react with functional groups on the surfaces of the first layer 1 and the second layer 2, which are the adherends, thereby forming a covalent bond between the first layer 1 and the second layer 2 via the compound.

[0022] The molecular adhesive used to form the molecular adhesive layer 3 is not particularly limited, but a silane coupling agent, a triazine-based molecular adhesive, or the like can be used.

[0023] Examples of the silane coupling agent include amino-based silane coupling agents, epoxy-based silane coupling agents, vinyl-based silane coupling agents, acrylic-based silane coupling agents, methacrylic-based silane coupling agents, mercapto-based silane coupling agents, ureido-based silane coupling agents, isocyanate-based silane coupling agents, and combinations thereof. It is preferable to use an amino-based silane coupling agent and an epoxy-based silane coupling agent in combination.

[0024] Specific examples of amino-based silane coupling agents include N-2-(aminoethyl)-3-aminopropylmethyldimethoxysilane, N-2-(aminoethyl)-3-aminopropylmethyldiethoxysilane, N-2-(aminoethyl)-3-aminopropyldimethoxysilane, N-2-(aminoethyl)-3-aminopropyldiethoxysilane, N-2-(aminoethyl)-3-aminopropyltrimethoxysilane, N-2-(aminoethyl)-3-aminopropyltriethoxysilane, 3-aminopropyldimethylmethoxysilane, 3-aminopropylmethyldimethoxysilane, 3-aminopropylmethyldiethoxysilane, 3-aminopropyltrimethoxysilane, 3-aminopropyltriethoxysilane, and hydrochlorides thereof.

[0025] Commercially available amino silane coupling agents include KBM-602, KBM-603, KBM-903, KBE-603, and KBE-903 manufactured by Shin-Etsu Chemical Co., Ltd.; Z-6011, Z-6020, Z-6026, Z-6032, Z-6094, and Z-6610 manufactured by Dow Corning Toray Co., Ltd.; and A-1100, A-1110, A-1120, A-2120, and Y-9669 manufactured by Momentive Performance Materials Japan, LLC.

[0026] Specific examples of epoxy-based silane coupling agents include 2-(3,4-epoxycyclohexyl)ethylmethyldimethoxysilane, 2-(3,4-epoxycyclohexyl)ethylmethyldiethoxysilane, 2-(3,4-epoxycyclohexyl)ethyltrimethoxysilane, 2-(3,4-epoxycyclohexyl)ethyltriethoxysilane, 3-glycidoxypropylmethyldimethoxysilane, 3-glycidoxypropylmethyldiethoxysilane, 3-glycidoxypropyltrimethoxysilane, and 3-glycidoxypropyltriethoxysilane.

[0027] Commercially available epoxy silane coupling agents include KBM-303, KBM-402, KBM-403, KBE-402, and KBE-403 manufactured by Shin-Etsu Chemical Co., Ltd.; SH6040, Z-6040, Z-6042, Z-6043, and Z-6044 manufactured by Dow Corning Toray Co., Ltd.; and A-186, A-187, and A-1871 manufactured by Momentive Performance Materials Japan, LLC.

[0028] The above-mentioned amino-based silane coupling agent and epoxy-based silane coupling agent can be used alone or in combination of two or more.In addition, the molecular adhesive can contain a silane coupling agent other than the amino-based silane coupling agent and the epoxy-based silane coupling agent, or can contain a molecular adhesive other than the silane coupling agent, for example, the above-mentioned triazine-based molecular adhesive.

[0029] The triazine-based molecular adhesive may be, for example, a triazine ring-containing compound having at least reactive group A and reactive group B (reactive group A is an amino group, azide group, diazomethyl group, diazirine group, mercapto group, isocyanate group, ureido group, or epoxy group; reactive group B is at least one functional group selected from the group consisting of silanol groups or groups capable of generating silanol groups by hydrolysis). Specific examples of triazine-based molecular adhesives include 6-(3-triethoxysilylpropyl)amino-1,3,5-triazine-2,4-diazide and N,N'-bis(2-aminoethyl)-6-(3-trihydroxysilylpropyl)amino-1,3,5-triazine-2,4-diamine.

[0030] However, among the above molecular adhesives, it is preferable that the molecular adhesive be a silane coupling agent, and it is more preferable that the molecular adhesive be made of an amino-based silane coupling agent and an epoxy-based silane coupling agent, because this is highly effective in improving the interlayer adhesion between the first layer 1 and the second layer 2, which are photopolymer layers, while suppressing color changes in the hologram that may occur during adhesion.

[0031] When the molecular adhesive for forming the molecular adhesive layer 3 contains an amino-based silane coupling agent and an epoxy-based silane coupling agent, the ratio of the amino-based silane coupling agent to the epoxy-based silane coupling agent may be preferably 20:80 to 80:20 by mass, more preferably 30:70 to 70:30, and even more preferably 60:40 to 40:60. By using the amino-based silane coupling agent and the epoxy-based silane coupling agent in the above ratio, a molecular adhesive layer 3 can be obtained that can improve the adhesion or bonding between layers. Therefore, an optical laminate can be obtained that suppresses hologram color changes that can occur due to adhesion between layers and has high adhesion between the first layer 1 and the second layer 2. When producing an optical laminate, it is preferable to use the silane coupling agent in the form of a solution (described below) as the molecular adhesive.

[0032] The thickness of the molecular adhesive layer 3 is thinner than the thickness of conventional adhesive layers formed using pressure-sensitive adhesives, hot-melt adhesives, etc. This reduces the effect of the thickness of the adhesive layer interposed between the first layer 1 and the second layer 2. Furthermore, the thin molecular adhesive layer 3 allows the entire optical laminate 10 to be configured thin, making it applicable to a variety of applications. The thickness of the molecular adhesive layer 3 can be less than 1 μm, 500 nm or less, 100 nm or less, or 50 nm or less.

[0033] The hologram contained in the first layer 1, which is a photopolymer layer, is preferably a volume hologram, and may be a reflection hologram or a transmission hologram. The hologram can be formed by exposing a layer of a hologram recording medium material, which is a precursor of the first layer 1, to an interference pattern, for example by irradiating it with ultraviolet light.

[0034] The optical laminate 10 according to this embodiment can be configured to be thin and small, and therefore can be suitably used in small display devices. For example, it can be particularly suitably used in augmented reality (AR) devices, such as AR glasses such as smart glasses, head-mounted displays (HMDs), and the like.

[0035] Next, more specific embodiments of the present disclosure will be described.

[0036] 2 is a schematic diagram of an optical laminate 10A according to a first embodiment. In the first embodiment, the second layer 2 serves as a substrate supporting the first layer 1, which is a photopolymer layer. That is, the laminate 10A according to the first embodiment includes the first layer 1, which is a photopolymer layer containing a hologram, the second layer 2A, which serves as a substrate, laminated on the first layer 1, and the molecular adhesive layer 3 interposed between the first layer 1 and the second layer 2A.

[0037] Since the second layer is the substrate 2A, the first layer 1 can be reinforced to prevent damage to the first layer 1, thereby improving the mechanical strength or mechanical robustness of the entire optical laminate 10A. The substrate 2A is preferably a transparent substrate. The substrate 2A may also contain one or more of glass and resin, and is preferably composed of glass or resin. When the substrate 2A is a resin, it may be a thermosetting resin or a thermoplastic resin, such as a poly(meth)acrylate resin, a polycarbonate resin, a polyurethane resin, an epoxy resin, a polyamide resin, a polyimide resin, a polyolefin resin, a (meth)acrylic resin, a cyclic polyolefin resin (norbornene-based resin), a polyarylate resin, a polystyrene resin, a polyvinyl alcohol resin, a cellulose resin such as a triacetyl cellulose-based resin film, a polyester resin, a polyethersulfone resin, or a polysulfone resin.

[0038] The thickness of the substrate 2A may be 1 μm or more, preferably 5 μm or more.

[0039] According to this embodiment, it is possible to suppress a change in the color of the hologram contained in the first layer 1 before and after bonding to the base material 2A.

[0040] Second Embodiment Fig. 3 shows an optical laminate 10B according to a second embodiment. In the optical laminate 10B, the first layer 1 is a photopolymer layer containing a hologram, and the second layer 2 is also a photopolymer layer containing a hologram. That is, the laminate 10B according to the second embodiment includes a first layer 1 which is a photopolymer layer containing a hologram, a second layer 2B which is a photopolymer layer containing a hologram and is laminated on the first layer 1, and a molecular adhesive layer 3 interposed between the first layer 1 and the second layer 2B. In other words, the optical laminate 10B has a configuration in which photopolymer layers having two holograms are laminated.

[0041] Here, the photopolymer layer used in the first layer 1 and the photopolymer layer used in the second layer 2B may be the same as or different from each other. That is, the composition and thickness of the photopolymer layer in the second layer 2B may be the same as or different from those of the photopolymer layer in the first layer 1. For example, the same commercially available product of the above-mentioned hologram recording photopolymer film may be used for both the first layer 1 and the second layer 2B.

[0042] 3 can further include a photopolymer layer containing a hologram. Thus, the number of photopolymer layers containing a hologram included in the optical stack 10B may be 3 or more and 100 or less. When the optical stack 10B includes an additional photopolymer layer containing a hologram, the additional photopolymer layer can be adhered to the first layer 1 or the second layer 2 via an additional molecular adhesive layer.

[0043] In this configuration in which photopolymer layers containing multiple holograms are stacked, light of different wavelengths can be guided to each photopolymer layer separately for each color, allowing a color image to be displayed.

[0044] (Other Embodiments) Furthermore, unlike the first and second embodiments, the second layer 2 ( FIG. 1 ) may be a layer having a function other than that of a substrate and a photopolymer layer containing a hologram. For example, the second layer 2 may be a layer having specific optical properties. The specific optical properties may be a specific refractive index, transmittance, reflectance, etc. Preferably, the second layer 2 is a layer having a specific refractive index, and more preferably a low refractive index layer.

[0045] When the second layer 2 is a low-refractive index layer, one embodiment of the present disclosure is an optical laminate having a first layer that is a photopolymer layer containing a hologram, a second layer that is a low-refractive index layer laminated on the first layer, and a molecular adhesive layer interposed between the first and second layers. Even in this embodiment, the color change of the hologram before and after bonding between the layers is suppressed, allowing the hologram to be displayed in an appropriate color, and the function of the low-refractive index layer, i.e., its low refractive index, is not impaired. When the second layer 2 is a low-refractive index layer, the refractive index of the second layer 2 is preferably 1.05 or more and 1.25 or less, more preferably 1.08 or more and 1.20 or less, and even more preferably 1.10 or more and 1.18 or less. Materials for constituting the low-refractive index layer include, for example, materials described in International Publication No. 2004 / 113966, JP 2013-254183 A, and JP 2012-189802 A. Specific examples of materials constituting the low refractive index layer include silicon compounds, organic polymers, polymerizable monomers, and curable resins. These may be used alone or in combination of two or more. Among these, it is preferable that the material constituting the low refractive index layer contains a silicon compound.

[0046] (Method for manufacturing optical laminate) A method for manufacturing the above-mentioned optical laminate 10 (including optical laminates 10A and 10B) may include, for example, preparing a first layer that is a photopolymer layer on which a hologram is recorded (S1), applying a molecular adhesive to one surface of the first layer (S2), laminating a second layer 2 on the surface on which the molecular adhesive has been applied (S3), and curing the second layer 2 (S4).

[0047] In the step (S2) of applying the molecular adhesive to one surface of the first layer, the molecular adhesive can be used in the form of a solution, preferably in the form of an aqueous solution. By dissolving the molecular adhesive in a solvent to form a solution, a low-viscosity coating solution can be obtained, allowing the molecular adhesive layer 3 to be distributed evenly between the first layer 1 and the second layer 2 with as few gaps as possible. Furthermore, the thickness of the molecular adhesive layer 3 in the resulting optical laminate 10 can also be reduced. When using a molecular adhesive solution, the concentration of the molecular adhesive solution may preferably be 0.01% by mass or more and 30% by mass or less, more preferably 0.05% by mass or more and 20% by mass or less, and even more preferably 0.1% by mass or more and 10% by mass or less. A reverse coater, gravure coater (direct, reverse, or offset), bar reverse coater, roll coater, die coater, bar coater, rod coater, spin coater, spray coater, etc. can be used to apply the molecular adhesive or the molecular adhesive solution.

[0048] In addition, when the photopolymer layer is obtained in a form sandwiched between a cover film and a base film, in the step (S2) of applying the molecular adhesive, the cover film is peeled off to expose one side of the photopolymer layer, and the molecular adhesive is applied to that exposed surface.

[0049] At least one of the first and second layers may be subjected to a surface treatment, preferably a hydrophilization treatment or a wettability improvement treatment, such as a corona treatment or a plasma treatment, on the surface that will come into contact with the molecular adhesive before contacting the molecular adhesive.

[0050] The curing step (S4) may be performed immediately after the lamination step (S3). However, pressure may be applied in the thickness direction (lamination direction) to the laminate formed by laminating the first layer and the second layer via the molecular adhesive. For example, a roller such as a hand roller may be used. By applying pressure, the molecular adhesive can be spread between the layers without any gaps, thereby improving interlayer adhesion.

[0051] The curing step (S4) is a step for promoting the reaction between the molecular adhesive and the materials of the first layer 1 and the second layer 2 by heat, light, or the like. For example, the curing step (S4) may be heating at 60°C or higher and 120°C or lower.

[0052] The step (S1) of preparing a first layer, which is a photopolymer layer having a hologram recorded thereon, may include a hologram recording step (S1a) of recording a hologram in the first photopolymer layer. In the hologram recording step (S1a), a known means for recording a hologram in a photopolymer layer may be used. Recording a hologram can be performed, for example, by irradiating the photopolymer layer with laser light of a predetermined wavelength using a known hologram recording laser device to form an interference pattern. When there are two or more photopolymer layers, for example, when both the first and second layers are photopolymer layers, a hologram is recorded in each layer. The hologram may be a volume hologram, and may be a reflection hologram or a transmission hologram. The hologram may be a monochromatic hologram or a multicolor hologram.

[0053] Furthermore, the hologram recording step (S1a) may not be included in the step (S1) of preparing the first layer, and may be performed after the curing step (S4) or before the curing step (S4).

[0054] The present disclosure will be described below based on examples.

[0055] <Materials used in sample preparation> Hologram recording medium material (photosensitive material): "Bayfol (registered trademark) HX200" manufactured by Covestro AG (three-layer structure of polyethylene cover layer / photopolymer layer / triacetyl cellulose (TAC) layer) Glass substrate: "EAGLEXG (registered trademark)" manufactured by Corning Inc.

[0056] The following adhesives were prepared. Molecular adhesive A: An amino-based silane coupling agent ("KBM-903" manufactured by Shin-Etsu Chemical Co., Ltd., 3-aminopropyltriethoxysilane, molecular weight 179.3) and an epoxy-based silane coupling agent ("KBM-403" manufactured by Shin-Etsu Chemical Co., Ltd., 3-glycidoxypropyltrimethoxysilane, molecular weight 236.3) were added to distilled water in a mass ratio of 50:50, and the molecular adhesive solution was adjusted so that the total silane coupling agent concentration (also simply referred to as the silane coupling agent concentration) was a predetermined value. Molecular adhesive solutions with silane coupling agent concentrations of 0.1%, 1%, and 10% by mass were prepared, respectively.

[0057] Molecular adhesive B: An amino-based silane coupling agent (Shin-Etsu Chemical Co., Ltd. "KBM-603", N-2-(aminoethyl)-3-aminopropyltriethoxysilane, molecular weight 222.4) and an epoxy-based silane coupling agent (Shin-Etsu Chemical Co., Ltd. "KBM-403", 3-glycidoxypropyltrimethoxysilane, molecular weight 236.3) were added to distilled water in a mass ratio of 50:50, and the molecular adhesive solution was adjusted so that the concentration of the total silane coupling agent (also simply referred to as the silane coupling agent concentration) was a predetermined value. Note that molecular adhesive solutions with silane coupling agent concentrations of 0.1% by mass, 1% by mass, and 10% by mass were prepared, respectively.

[0058] Molecular adhesive C: An amino-based silane coupling agent ("X-12-972F" manufactured by Shin-Etsu Chemical Co., Ltd.) and an epoxy-based silane coupling agent ("KBM-403" manufactured by Shin-Etsu Chemical Co., Ltd., 3-glycidoxypropyltrimethoxysilane, molecular weight 236.3) were added to distilled water in a mass ratio of 50:50, and the molecular adhesive solution was adjusted so that the total silane coupling agent concentration (also simply referred to as the silane coupling agent concentration) was a predetermined value. Note that molecular adhesive solutions with silane coupling agent concentrations of 0.1% by mass, 1% by mass, and 10% by mass were prepared, respectively.

[0059] Adhesive a: Optical transparent adhesive sheet "LUCIACS CS986 UAS (thickness 25 μm)" manufactured by Nitto Denko Corporation

[0060] <Preparation of Laminate> The following laminates were prepared using the materials described above. Schematic diagrams of the laminates prepared in Examples 1-1 and 2-1, and Comparative Examples 1 and 2 are shown in FIG.

[0061] (Example 1-1) A hologram (holographic diffraction grating) was recorded in the photopolymer layer from the triacetyl cellulose (TAC) layer side of the above hologram recording medium material by two-beam interference exposure using a semiconductor laser (Verdi G series, manufactured by Coherent, peak wavelength 532 nm). Subsequently, light from a xenon lamp light source was irradiated onto the entire surface from the glass substrate side to cause discoloration. The polyethylene cover layer was peeled off from the material with the recorded hologram to expose the photopolymer layer (first layer). The exposed surface of this photopolymer layer was subjected to corona treatment (treatment conditions: 1000 W min / m ２ Separately, one side of the glass substrate (second layer) was also subjected to corona treatment (treatment conditions: 1000 W·min / m ２ ), and then a 10% by mass aqueous solution of molecular adhesive A was applied to the entire treated surface. A photopolymer layer was then laminated so that the corona-treated surface of the photopolymer layer was in contact with the aqueous solution of molecular adhesive A, yielding a laminate. Pressure was then applied to the entire laminate using a hand roller. This stretched the intervening molecular adhesive, ensuring that the molecular adhesive was distributed over the entire surface between the photopolymer layer and the glass substrate. The laminate was then heated in an oven at 90°C for 5 minutes to promote the reaction of the molecular adhesive. This resulted in an optical laminate measuring 50 mm x 50 mm, having a structure in which a photopolymer layer having a triacetyl cellulose (TAC) layer and a glass substrate were bonded via a molecular adhesive layer.

[0062] Example 1-2 An optical laminate was obtained in the same manner as in Example 1-1, except that a 1.0 mass% aqueous solution of molecular adhesive B was used instead of the 10 mass% aqueous solution of molecular adhesive A used in Example 1-1.

[0063] Example 1-3 An optical laminate was obtained in the same manner as in Example 1-1, except that a 0.1% by mass aqueous solution of molecular adhesive C was used instead of the 10% by mass aqueous solution of molecular adhesive A used in Example 1-1.

[0064] Example 2-1: A laminate was obtained in the same manner as in Example 1-1, except that the above-described hologram recording medium material was used as the second layer instead of a glass substrate. That is, a laminate was produced in which two photopolymer layers were bonded via a molecular adhesive. More specifically, a hologram was recorded on each of the two hologram recording medium materials and faded in the same manner as in Example 1-1. The polyethylene cover layer was then peeled off from each of the hologram-recorded medium materials to expose the photopolymer layer, and the exposed surfaces of the photopolymer layers were subjected to a corona treatment similar to the corona treatment applied to the photopolymer layer in Example 1-1. A 10% by mass aqueous solution of molecular adhesive A was applied to the corona-treated surface of one photopolymer layer, and the other photopolymer layer was laminated so that the corona-treated surfaces of the photopolymer layer were in contact. Furthermore, an adhesive (optically clear adhesive (OCA) tape, 25 μm thick) was placed on the triacetyl cellulose layer of one photopolymer layer, and the corona-treated glass substrate used in Example 1-1 was then laminated thereon. Pressure was applied to the laminate obtained in this manner and heating was performed under the same conditions as in Example 1-1, thereby obtaining an optical laminate having a structure in which two photopolymer layers each having a triacetyl cellulose (TAC) layer and a molecular adhesive layer were bonded together, the structure being 50 mm x 50 mm in size.

[0065] Example 2-2 A laminate was produced and a hologram was recorded in the same manner as in Example 2-1, except that a 0.1% by mass aqueous solution of molecular adhesive B was used instead of the 10% by mass aqueous solution of molecular adhesive A used in Example 2-1, to obtain an optical laminate.

[0066] Example 2-3 A laminate was produced and a hologram was recorded in the same manner as in Example 2-1, except that a 10% by mass aqueous solution of molecular adhesive C was used instead of the 10% by mass aqueous solution of molecular adhesive A used in Example 2-1, to obtain an optical laminate.

[0067] Comparative Example 1 A laminate including a hologram was obtained in the same manner as in Example 1-1, except that the adhesive a was used instead of the aqueous solution of the molecular adhesive A. More specifically, the adhesive a (adhesive tape) was applied to the corona-treated surface of the glass substrate, and then a photopolymer layer was laminated on the corona-treated exposed surface of the photopolymer layer so that it was in contact with the adhesive a, thereby obtaining an optical laminate.

[0068] Comparative Example 2 A laminate was obtained in the same manner as in Example 1-1, except that the glass substrate and the photopolymer layer were laminated by directly contacting the corona-treated surface of the photopolymer layer with the corona-treated surface of the glass substrate without using any adhesive or pressure-sensitive adhesive.

[0069] <Evaluation> The optical properties and interlayer adhesion of the obtained laminate samples were evaluated as follows.

[0070] (Optical Properties) The optical properties were evaluated by determining (i) the change in diffraction wavelength before and after bonding, (ii) the change in transmittance before and after bonding, (iii) (i) after high-temperature storage, and (iv) (ii) after high-temperature storage.

[0071] (i) Change in Diffraction Wavelength For each laminate obtained as described above, i.e., a laminate (bonded sample) including a photopolymer layer on which a hologram was recorded, the transmittance spectrum was measured using a method conforming to JIS Z8791:2011. More specifically, a spectrophotometer (UH4150 manufactured by Hitachi High-Tech Science) was used to obtain a transmittance spectrum in the range of 400 nm to 700 nm. The wavelength (nm) at the apex of the transmittance peak was then recorded as the diffraction wavelength of the sample. Meanwhile, in each example, a laminate (unbonded sample) was also prepared by directly laminating the photopolymer layer and the second layer (glass substrate or photopolymer layer) without adhesive, resulting in a hologram recorded in the photopolymer layer, i.e., a laminate without an adhesive layer. The transmittance spectrum was measured in the same manner as above, and the diffraction wavelength was also recorded. The diffraction wavelength of the unbonded sample was defined as λn (nm), and the diffraction wavelength of the bonded sample was defined as λa (nm), where λa - λn (nm) was the change in diffraction wavelength. The unbonded laminates in Examples 1-1 and 2-1 to 2-9, in which the second layer was a glass substrate, were equivalent to the laminate produced in Comparative Example 4.

[0072] (ii) Change in transmittance The transmittance (%) at the apex of the peak in the transmittance spectrum obtained as described above was recorded as the transmittance of the sample. The transmittance of the unbonded sample was Tn (%), and the diffraction wavelength of the bonded sample was Ta (%), and the change in transmittance was calculated as Ta - Tn (%pt).

[0073] (iii) Change in diffraction wavelength after high-temperature storage The diffraction wavelength of the bonded sample was measured after storing it in an environment at a temperature of 80°C for 240 hours using the same method as described in "(i) Change in diffraction wavelength." The diffraction wavelength of the unbonded sample was λn, and the diffraction wavelength of the bonded sample after high-temperature storage was λa. Ｈ As a result, λa Ｈ −λn (nm) was defined as the amount of change in the diffraction wavelength after high-temperature storage.

[0074] (iv) Change in transmittance after high-temperature storage The transmittance of the bonded sample was measured after storing it in an environment at a temperature of 80° C. for 240 hours using the same method as described in “(ii) Change in transmittance.” The transmittance of the unbonded sample was Tn, and the diffraction wavelength of the bonded sample after high-temperature storage was Ta. Ｈ As Ta Ｈ −Tn (% pt) was defined as the amount of change in transmittance after high-temperature storage.

[0075] (Interlayer Adhesion) The interlayer adhesion of the laminate containing the hologram obtained in each example was evaluated by a cross-cut test based on JIS K5400-8.5:1999. More specifically, 11 vertical and horizontal incisions were made at 1 mm intervals on the triacetyl cellulose (TAC) layer side of the obtained laminate using a cutter knife, forming a total of 100 grids. Cellophane adhesive tape was applied over a length of approximately 50 mm to cover the incised surface, and the tape was rubbed with an eraser to adhere the tape. After leaving the tape for 1 to 2 minutes, the edge of the cellophane adhesive tape was lifted perpendicular to the surface and then instantly peeled off, and the number of grids that remained on the cellophane adhesive tape and were not removed was counted. The number of grids that were not removed out of 100 was recorded. For example, if the number of grids that were not removed was 10, it was expressed as 10 / 100.

[0076] The results are shown in Table 1.

[0077]

[0078] 5 shows the change in transmittance spectrum of the optical laminate of Example 1-1 when unbonded, after bonding, and after high-temperature storage after bonding. Similarly, FIG. 6 shows the change in transmittance spectrum of the optical laminate of Comparative Example 1 when unbonded, after bonding, and after high-temperature storage after bonding.

[0079] 5, it was found that in the optical laminates (Examples 1-1 to 1-3) in which a hologram-containing photopolymer layer and a substrate were bonded via a molecular adhesive layer, and in the optical laminates (Examples 2-1 to 2-3) in which hologram-containing photopolymer layers were bonded together via a molecular adhesive, the changes in wavelength and transmittance before and after bonding were suppressed, and color shift was suppressed (good optical properties were obtained). It was also found that these optical laminates exhibited high interlayer adhesion.

[0080] On the other hand, the optical properties of the optical laminates (Comparative Examples 1 to 3) including an adhesive layer that was not a molecular adhesive layer were lower than those of Examples 1-1 to 1-3. Furthermore, in the case of a configuration produced without using an adhesive, although optical properties equivalent to those of Examples 1-1 to 1-3 were exhibited, the interlayer adhesion was poor and the laminate was not durable for normal use in optical laminates.

[0081] Further aspects of the present disclosure are as follows, for example.

[0082] <1> An optical laminate having a first layer that is a photopolymer layer containing a hologram, a second layer laminated on the first layer, and a molecular adhesive layer interposed between the first layer and the second layer.

[0083] <2> The optical laminate according to <1>, wherein the second layer is a substrate containing at least one of glass and resin.

[0084] <3> The optical laminate according to <1>, wherein the second layer is a photopolymer layer containing a hologram.

[0085] <4> The optical laminate according to any one of <1> to <3>, wherein the molecular adhesive layer contains a cured product of a molecular adhesive, and the molecular adhesive contains a silane coupling agent.

[0086] <5> The optical laminate according to <4>, wherein the molecular adhesive contains an amino-based silane coupling agent and an epoxy-based silane coupling agent.

[0087] <6> The optical laminate according to <5>, wherein the ratio of the amino-based silane coupling agent to the epoxy-based silane coupling agent is 20:80 to 80:20 by mass.

[0088] <7> A method for producing an optical laminate, comprising: preparing a first layer that is a photopolymer layer having a hologram recorded thereon; applying a molecular adhesive to one surface of the first layer; and laminating a second layer on the surface to which the molecular adhesive has been applied; and curing the second layer.

[0089] <8> The method for producing an optical laminate according to <7>, wherein the molecular adhesive contains a silane coupling agent.

[0090] <9> The method for producing an optical laminate according to <7> or <8>, wherein the molecular adhesive is applied in the form of a solution of 0.01% by mass or more and 30% by mass or less.

[0091] This application claims priority based on Japanese Patent Application No. 2024-069481, filed on April 23, 2024, the entire contents of which are incorporated herein by reference.

[0092] REFERENCE SIGNS LIST 1 First layer (photopolymer layer) 2 Second layer 2A Second layer (substrate) 2B Second layer (photopolymer layer) 3 Molecular adhesive layer 10, 10A, 10B Optical laminate

Claims

1. An optical laminate comprising: a first layer that is a photopolymer layer containing a hologram; a second layer laminated to the first layer; and a molecular adhesive layer interposed between the first layer and the second layer.

2. The optical laminate according to claim 1, wherein the second layer is a substrate containing at least one of glass and resin.

3. The optical laminate according to claim 1, wherein the second layer is a photopolymer layer containing a hologram.

4. The optical laminate according to claim 1 or 2, wherein the molecular adhesive layer contains a cured product of a molecular adhesive, and the molecular adhesive contains a silane coupling agent.

5. The optical laminate according to claim 4, wherein the molecular adhesive comprises an amino-based silane coupling agent and an epoxy-based silane coupling agent.

6. The optical laminate according to claim 5, wherein the ratio of the amino-based silane coupling agent to the epoxy-based silane coupling agent is 20:80 to 80:20 by mass.

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