Image representation using light guide plate

Abstract

To provide an image display light guide plate which minimizes deterioration of a resin base material caused by a hologram layer.SOLUTION: An image display light guide plate 6 provided herein comprises a first resin base material 1, a first protective layer 2 containing an acrylic resin having a polyfunctional acrylate-derived repeating unit, and a hologram layer 3 arranged in the described order in a thickness direction.SELECTED DRAWING: None

Description

[Technical Field]

[0001] This invention relates to a light guide plate for image display. [Background technology]

[0002] In display devices, light guide plates for image display are sometimes used. For example, in display devices using VR (virtual reality) technology, AR (augmented reality) technology, etc., a light guide plate for image display is used in which a hologram layer is supported on a transparent substrate. Holograms with various optical functions, such as wave guidance, reflection, and diffraction, are formed on the hologram layer.

[0003] Many holographic materials used to form the holographic layer are photosensitive compositions containing radical polymerizable monomers, polyhydric acids, and bases such as amines, which can degrade the resin substrate. In particular, if the material gradually erodes the resin substrate over a long period of time, the visibility of the light guide plate is likely to decrease.

[0004] For example, Patent Document 1 describes forming a photosensitive material layer that forms a hologram on an optically transparent resin substrate, and coating the photosensitive material layer with an aqueous polymer protective barrier. Patent Document 1 suggests that the aqueous polymer protective barrier is provided for the purpose of withstanding attacks caused by moisture. For example, Patent Document 2 describes a hologram laminate having a hologram sandwiched between resin substrates via an optical adhesive, wherein the entire outer periphery is covered with a protective coating layer. Patent Document 2 also states that the protective coating layer may be a coating that enhances airtightness and gas barrier properties. Patent Document 3 describes a layer that blocks outgassing from the substrate side using a blocking layer. [Prior art documents] [Patent Documents]

[0005] [Patent Document 1] Japanese Patent Application Publication No. 5-181400 [Patent Document 2] Japanese Patent Application Publication No. 11-184363 [Patent Document 3] Japanese Patent Publication No. 2013-109301 [Overview of the Initiative] [Problems that the invention aims to solve]

[0006] However, the aforementioned related technologies have the following problems. In the technology described in Patent Document 1, a resin substrate is in close contact with the surface of the photosensitive material layer opposite the aqueous polymer protective barrier. Therefore, there is a risk that the photosensitive material may corrode the resin substrate in high-temperature environments. In the technology described in Patent Document 2, the entire outer periphery of the laminate containing the hologram is sealed by a protective coating layer. Therefore, moisture penetration from the outside of the hologram laminate into the interior and degradation of the hologram are suppressed. However, there is a risk that the photosensitive material may corrode the resin substrate. While the technology described in Patent Document 3 can prevent outgassing of the resin substrate with a dielectric film, there is a risk that the resin substrate will deteriorate over time due to the holographic material. In particular, the effect of the holographic material on the resin substrate becomes significant in high-temperature environments. Furthermore, these related technologies do not mention that the resin substrate is degraded by the holographic material, which is a photosensitive resin composition.

[0007] This invention has been made in view of the above-mentioned problems, and aims to provide an image display light guide plate that can suppress the deterioration of the resin substrate by the hologram layer even when a resin substrate is used. [Means for solving the problem]

[0008] To solve the aforementioned problems, the present invention has the following embodiments, for example. [1] An image display light guide plate comprising a first resin substrate, a first protective layer containing an acrylic resin including repeating units derived from a polyfunctional acrylate, and a hologram layer, arranged in this order in the thickness direction. [2] The image display light guide plate according to [1], wherein the elastic modulus of the first protective layer is 2 GPa or more. [3] The image display light guide plate according to [1] or [2], wherein the thickness of the first protective layer is 2 μm or more. [4] The image display light guide plate according to any one of [1] to [3], wherein the first protective layer comprises a first organic material layer containing the acrylic resin and a first inorganic material layer. [5] The image display light guide plate according to [4], wherein the first inorganic material layer comprises at least one inorganic material selected from the group consisting of silicon oxide, silicon nitride, silicon oxide nitride, silicon sulfide, aluminum oxide, aluminum nitride, aluminum oxide nitride, and aluminum sulfide. [6] The image display light guide plate according to [4] or [5], wherein the thickness of the first inorganic material layer is 50 nm or more and 5000 nm or less. [7] The image display light guide plate according to any one of [1] to [6], wherein the first glass layer is disposed on the side of the first resin substrate opposite to the side of the first protective layer. [8] The image display light guide plate according to [7], wherein a first adhesive layer is disposed between the first resin substrate and the first glass layer. [9] The image display light guide plate according to any one of [1] to [8], wherein the hologram layer is made of a single or volume hologram material. [Effects of the Invention]

[0009] According to the present invention, it is possible to provide a light guide plate for image display that can suppress the deterioration of the resin substrate due to the hologram layer. [Brief explanation of the drawing]

[0010] [Figure 1] This is a schematic cross-sectional view showing an example of a light guide plate for image display according to an embodiment of the present invention. [Figure 2]It is a schematic cross-sectional view showing an example of a light guide plate for image display of a first modification of an embodiment of the present invention. [Figure 3] It is a schematic front view for explaining a method of measuring a luminance value and a FOV. [Figure 4] It is a schematic cross-sectional view showing an example of a light guide plate for image display of a second modification of an embodiment of the present invention.

Embodiments for Carrying Out the Invention

[0011] Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. In all the drawings, even if the embodiments are different, the same or corresponding members are denoted by the same reference numerals, and common descriptions are omitted. A numerical range represented by "~" includes the numerical values at both ends of "~". "UV" means ultraviolet rays. "(Meth)acryl" means one or both of acrylic and methacrylic. "(Meth)acrylate" means one or both of acrylate and methacrylate.

[0012] <Light guide plate for image display> The light guide plate for image display of the embodiment of the present invention will be described. The light guide plate for image display of the present embodiment has a first resin base material, a first protective layer, and a hologram layer. The first resin base material, the first protective layer, and the hologram layer are arranged in this order in the thickness direction. The first resin base material and the first protective layer may be arranged on at least one surface of the hologram layer, but may also be arranged on both surfaces of the hologram layer. In this case, the hologram layer is sandwiched between the first protective layer and the second protective layer, the first resin base material is laminated on the other surface of the first protective layer, and the second resin base material is laminated on the other surface of the second protective layer. In the present embodiment, the first resin base material and the second resin base material may be collectively referred to as simply "resin base material" hereinafter. Also, the first protective layer and the second protective layer may be collectively referred to as simply "protective layer" hereinafter.

[0013] One or more transparent layers may be placed between the first resin substrate and the first protective layer, and between the first protective layer and the hologram layer. Examples include adhesive layers, hard coat layers, and anchor coat layers.

[0014] The image display light guide plate has an incident section for receiving image light and a display section for displaying an image using the image light. The hologram layer is positioned between the incident section and the display section. The hologram layer has a diffraction grating pattern formed on it for guiding image light, at least from the incident section, to the display section and for emission from the display section. The diffraction grating pattern in the display section transmits at least a portion of the ambient light incident from outside the image display light guide plate. The ambient light is incident from the side opposite to the display section.

[0015] Image light entering the incident area is guided within the hologram layer and emitted from the display unit to the outside. Meanwhile, ambient light also passes through the resin substrate and the display unit, allowing the observer of the display unit to see both image light and ambient light within their field of view. The image display light guide plate of this embodiment is suitably used in display devices using VR technology, AR technology, and the like. For example, in addition to display applications, the image display light guide plate of this embodiment may be used in devices such as combiners for automotive head-up displays (HUDs) and reflectors for reflective liquid crystal display devices, as well as holographic optical elements (HOEs).

[0016] The following describes the detailed configuration of an example of an image display light guide plate according to this embodiment, based on the example shown in Figure 1. Figure 1 is a schematic cross-sectional view showing an example of an image display light guide plate according to an embodiment of the present invention.

[0017] In the image display light guide plate 6 shown in Figure 1, the first resin substrate 1, the first protective layer 2, the hologram layer 3, the second protective layer 4, and the second resin substrate 5 are arranged in this order in the thickness direction. The planar shape of the image display light guide plate 6 is not particularly limited. For example, the image display light guide plate 6 may be shaped to be attachable to the display device used. For example, the image display light guide plate 6 may be a rectangular plate larger than the shape to be attached to the display device. In this case, the image display light guide plate 6 is molded, for example, by being cut into a shape that can be attached to the display device, before being assembled to the display device. The image display light guide plate 6 may be flat or, if necessary, curved. The following explanation will describe an example where the image display light guide plate 6 consists of a flat plate with a rectangular shape in plan view.

[0018] [First resin base material 1] The first resin substrate 1 is positioned at the outermost edge in the thickness direction of the image display light guide plate 6. The first resin substrate 1 is positioned on the surface of the image display light guide plate 6 that emits the displayed image. The first resin substrate 1 has a shape similar to the outer shape of the light guide plate 6 for image display. The first resin substrate 1 transmits image light emitted from the hologram layer 3 and ambient light that passes through the second resin substrate 5 and the hologram layer 3, which will be described later. The thickness of the first resin substrate 1 is not particularly limited. For example, the thickness of the first resin substrate 1 may be 0.1 mm or more and 10 mm or less. In this specification, the thickness of the first resin substrate 1 can be measured using a dial gauge with a stylus or a micrometer.

[0019] The material forming the first resin substrate 1 can be any known transparent resin material without any particular limitations. Considering optical properties such as transparency and refractive index, as well as major physical properties such as impact resistance, heat resistance, and durability, the following are used: polyolefin resins such as homopolymers or copolymers of ethylene, propylene, and butene; amorphous polyolefin resins such as cyclic polyolefin resins; polyester resins such as polyethylene terephthalate (PET) and polyethylene naphthalate (PEN); cellulose resins such as triacetylcellulose, diacetylcellulose, and cellophane; polyamide resins such as nylon 6, nylon 66, nylon 12, and copolymerized nylon; ethylene-vinyl acetate copolymer partial hydrolysate (EVOH), polyimide resins, and polyetherimide resins. Examples of organic materials include resins, polysulfone resins, polyethersulfone resins, polyetheretherketone resins, polycarbonate resins, polyvinyl butyral resins, polyarylate resins, fluororesins, poly(meth)acrylic resins, styrene resins such as polystyrene, polyvinyl alcohol, ethylene vinyl alcohol copolymers, polyvinyl chloride, cellulose, acetylcellulose, polyvinylidene chloride, polyphenylene sulfide, polyurethane, phenolic resins, epoxy resins, polynorbornene, styrene-isobutylene-styrene block copolymers (SIBS), allyl diglycol carbonate, and biodegradable resins. The first resin substrate 1 may be formed from two or more materials, or it may be a laminated structure in which two or more materials are laminated. From the viewpoint of transparency, polycarbonate resins, poly(meth)acrylic resins, etc. are more preferable. Furthermore, from the viewpoint of process resistance, poly(meth)acrylic resins, epoxy resins, cyclic polyolefin resins, etc. are more preferable.

[0020] [1st protective layer 2] The first protective layer 2 is positioned between the first resin substrate 1 and the hologram layer 3, which will be described later, and in the configuration shown in Figure 1, it is in close contact with the surfaces of the first resin substrate 1 and the hologram layer 3, respectively.

[0021] The first protective layer 2 contains an acrylic resin that includes repeating units derived from a polyfunctional acrylate. By placing the first protective layer 2 on the surface of the first resin substrate 1, degradation of the first resin substrate 1 by the hologram layer 3 can be prevented, thereby increasing the range of materials that can be used for the first resin substrate 1.

[0022] The acrylic resin of the first protective layer 2 may contain polyfunctional repeating units derived from various (meth)acrylates, or it may contain monofunctional repeating units derived from various (meth)acrylates. A polyfunctional (meth)acrylate refers to a (meth)acrylate that has two or more radical polymerizable functional groups within its molecule. Examples of polyfunctional (meth)acrylates used as raw materials for acrylic resins include polyethylene glycol diacrylate, neopentyl glycol diacrylate, trimethylolpropane triacrylate, pentaerythritol triacrylate, and tricyclodidecanedimethanol dimethacrylate. Examples of monofunctional (meth)acrylates include isobornyl acrylate, tetrahydrofurfuryl acrylate, 2-hydroxy-3-phenoxypropyl acrylate, butoxyethyl acrylate, lauryl acrylate, stearyl acrylate, benzyl acrylate, hexyldiglycol acrylate, 2-hydroxyethyl acrylate, 2-ethylhexyl acrylate, cyclohexyl acrylate, phenoxyethyl acrylate, dicyclopentadiene acrylate, polyethylene glycol acrylate, polypropylene glycol acrylate, and nonylphenoxyethyl cellosolve acrylate. These (meth)acrylates may be used individually, or two or more may be mixed to form a copolymer.

[0023] Furthermore, in addition to the acrylic resin described above, the product may also contain an oligomer made of the polyfunctional (meth)acrylate described above. Examples include oligourethane (meth)acrylate and oligoester (meth)acrylate.

[0024] The aforementioned acrylic resin may have a cross-linked structure due to having repeating units derived from polyfunctional (meth)acrylate, making it possible to obtain a light guide plate that is less prone to swelling with respect to holographic materials, has excellent chemical resistance, and exhibits superior long-term visibility. The method for forming the first protective layer is not particularly limited. For example, it can be formed by applying an acrylic resin composition containing a polyfunctional (meth)acrylate to the surface of the first resin substrate and then curing the acrylic resin composition. Coating methods for acrylic resin compositions include, for example, coating methods such as air doctor coating, blade coating, knife coating, reverse coating, transfer roll coating, gravure roll coating, kiss coating, cast coating, spray coating, slot orifice coating, calender coating, electrodeposition coating, dip coating, and die coating; and printing methods such as relief printing methods like flexographic printing, intaglio printing methods like direct gravure printing and offset gravure printing, lithographic printing methods like offset printing, and stencil printing methods like screen printing.

[0025] The acrylic resin composition may be diluted with various solvents as needed for viscosity adjustment and coating properties improvement. Common organic solvents can be used as such diluents, including, for example, alcohol compounds such as methanol, ethanol, 1-propanol, and 2-propanol; ketone compounds such as acetone and methyl ethyl ketone; ester compounds such as ethyl acetate, propyl acetate, and butyl acetate; and aromatic compounds such as toluene and xylene. These diluents can be used individually or in combination of two or more.

[0026] The acrylic resin composition may optionally contain a photopolymerization initiator. Examples of photopolymerization initiators include benzophenone, acetophenone, benzoin, benzoin isobutyl ether, benzoin isopropyl ether, benzoin ethyl ether, 4,4'-bis(dimethylamino)benzophenone, benzyldimethyl ketal, 2-chlorothioxanthone, 2,4-dimethylthioxanthone, 2,2'-diisopropylthioxanthone, 1-hydroxycyclohexylphenyl ketone, 2-methyl-1-[4-(methylthio)phenyl]-2-morpholinopropan-1-one, and 2,4,6-trimethylbenzoylphenyldiphosphine oxide. These can be used individually or in combination of two or more.

[0027] The acrylic resin composition can be modified by adding a silane coupling agent as needed to adjust the adhesion between the first protective layer and the first resin substrate. Specifically, a silane coupling agent can be used to enhance the adhesion between the first protective layer and the first resin substrate.

[0028] Typical examples of the silane coupling agents mentioned above include aminosilane compounds. Specific examples of aminosilane compounds include γ-aminopropyltriethoxysilane, γ-aminopropyltrimethoxysilane, N-β-(aminoethyl)-γ-aminopropyltrimethoxysilane, γ-ureidopropyltriethoxysilane, and γ-N-phenylaminopropyltrimethoxysilane. These aminosilanes can be used individually or in combination of two or more. Furthermore, coupling agents other than aminosilanes may be used in combination.

[0029] The thickness of the first protective layer 2 is preferably 2 μm or more, and more preferably 5 μm or more. A thickness of 2 μm or more for the first protective layer 2 prevents deterioration of the resin substrate by the hologram layer 3. Furthermore, the thickness of the first protective layer 2 is preferably 15 μm or less, and more preferably 12 μm or less. A thickness of 15 μm or less for the first protective layer 2 increases the elastic modulus of the first protective layer 2. The thickness of the first protective layer 2 can be measured using a non-contact optical interferometer or similar device.

[0030] The elastic modulus of the first protective layer 2 is preferably 2 GPa or higher, and more preferably 5 GPa or higher. An elastic modulus of 2 GPa or higher prevents deterioration of the resin substrate by the hologram layer 3. Furthermore, the elastic modulus of the first protective layer 2 is preferably 20 GPa or lower, and more preferably 15 GPa or lower. An elastic modulus of 20 GPa or lower suppresses warping due to curing shrinkage during protective layer formation. The elastic modulus can be measured using a Shimadzu Dynamic Microhardness Tester, DUH-W201, under the following conditions: Triangular 115, indentation depth of 230-280 nm.

[0031] Furthermore, the refractive index difference between the first resin substrate 1 and the first protective layer 2 is preferably 0.3 or less, and more preferably 0.2 or less. The refractive index can be measured using commonly used methods such as Abbe refractometers or ellipsometers.

[0032] [Hologram layer 3] The hologram layer 3 is laminated on the surface of the first protective layer 2. The configuration of the hologram layer 3 is not particularly limited. The hologram layer 3 has an appropriate diffraction grating formed on it that corresponds to the functions required for the image display light guide plate 6.

[0033] The material of the hologram layer 3 is not particularly limited and may be a known resin material for hologram formation. Examples include holographic recording materials comprising a thermosetting resin having at least one solvent-soluble and cationically polymerizable ethylene oxide ring in its structural unit, and a radically polymerizable ethylenic monomer (Japanese Patent Publication No. 9-62169, Japanese Patent Publication No. 11-161141, Japanese Patent Publication No. 2002-310932). Specifically, it is preferable that the photosensitive material be formed from an epoxy resin such as a bisphenol-based epoxy resin; a (meth)acrylate such as triethylene glycol diacrylate; a photopolymerization initiator such as 4,4'-bis(tert-butylphenyl)iodonium hexafluorophosphate; a wavelength sensitizer such as 3,3'-carbonylbis(7-diethylamino)coumarin; and an organic solvent such as 2-butanone. In particular, it is preferable that the hologram layer consists of a single or volumetric hologram material.

[0034] [Second protective layer 4] The second protective layer 4 is laminated on the opposite side of the first protective layer 2 via the hologram layer 3. The second protective layer 4 uses the same configuration as exemplified in the description of the first protective layer 2. However, the thickness, material, etc., of the second protective layer 4 may differ from those of the first protective layer 2.

[0035] [Second resin base material 5] The second resin substrate 5 is laminated on the surface of the second protective layer 4. The second resin substrate 5 has the same configuration as exemplified in the description of the first resin substrate 1. However, the thickness, material, etc., of the second resin substrate 5 may differ from those of the first resin substrate 1. In particular, since the second resin substrate 5 is located on the surface of the external light incident side, opposite to the display image emission side of the image display light guide plate 6, a material with higher surface hardness than the first resin substrate 1 may be used.

[0036] [Light guide plate for image display 6] The image display light guide plate 6 has a first protective layer 2 and a second protective layer 4 positioned between the first resin substrate 1 and the hologram layer 3, and between the second resin substrate 5 and the hologram layer 3, respectively. The chemical resistance of the first resin substrate 1 and the second resin substrate 5 varies to some extent depending on the type of resin material, but it is significantly lower than that of glass. For this reason, the first resin substrate 1 and the second resin substrate 5 have lower solvent resistance and hologram resistance than glass. When the first resin substrate 1 and the second resin substrate 5 are in contact with the hologram layer 3, the holographic agent, which is a component of the hologram layer 3, is likely to permeate through the first resin substrate 1 and the second resin substrate 5, or accumulate inside the first resin substrate 1 and the second resin substrate 5. When the first resin substrate 1 and the second resin substrate 5 are exposed to the holographic agent, they deteriorate, making it easier for a decrease in FOV (field of view) and a decrease in clarity to occur. Therefore, in this invention, by providing a first protective layer 2 and a second protective layer 4 between the first resin substrate 1 and the second resin substrate 5 and the hologram layer 3, respectively, the penetration of the hologram agent into the first resin substrate 1 and the second resin substrate 5 is suppressed, thereby preventing deterioration of the resin substrate.

[0037] In particular, if the refractive indices of the first protective layer 2 and the second protective layer 4 are higher than those of the first resin substrate 1 and the second resin substrate 5, as described above, the emission angle of light from the first protective layer 2 toward the first resin substrate 1 becomes larger. Similarly, the emission angle of light incident on the second protective layer 4 from the second resin substrate 5 is narrowed. As a result, light incident from the outside on the second resin substrate 5 side and transmitted through the image display light guide plate 6 is incident over a wider angle range compared to the case without the second protective layer 4, and emitted over a wider angle range compared to the case without the first protective layer 2. Consequently, the field of view of external light is widened, and the field of view on the display side is also widened. Regarding the image light from the hologram layer 3, as described above, the emission angle of light from the first protective layer 2 toward the first resin substrate 1 increases, resulting in a wider field of view (FOV) of the display screen compared to the case without the first protective layer 2 and the second protective layer 4. In particular, in this embodiment, since the first protective layer 2 and the second protective layer 4 are stacked on the hologram layer 3, the diffusion positions of the external light and image light and the diffraction positions of the hologram layer 3 that constitute the display screen are brought closer together. As a result, compared to the case where the first protective layer 2 and the second protective layer 4 are provided at positions far from the hologram layer 3, a clearer image can be observed from a wider range of angles.

[0038] <First variation> A first modification of an embodiment of the present invention will now be described. In this embodiment, the first organic material layer and the second organic material layer may be collectively referred to simply as the "organic material layer" below. Also, the first inorganic material layer and the second inorganic material layer may be collectively referred to simply as the "inorganic material layer" below. Figure 2 is a schematic cross-sectional view showing an example of a light guide plate for image display, which is a first modified embodiment of the present invention. As shown in Figure 2, the first modified image display light guide plate 16 of the embodiment of the present invention is modified in which the first protective layer comprises a first organic material layer and a second inorganic material layer, compared to the image display light guide plate 6 of the basic example of the embodiment of the present invention.

[0039] As shown in Figure 2, it is preferable that the first protective layer 22 comprises a first inorganic material layer 22B on at least one surface of a first organic material layer 22A containing an acrylic resin with repeating units derived from a polyfunctional acrylate. By further having a first inorganic material layer 22B in the first protective layer 22, long-term visibility can be improved.

[0040] [First organic material layer 22A] The organic material used in the first organic material layer 22A is the same as that described as the acrylic resin for the first protective layer 2. The thickness of the first organic material layer 22A is preferably 2 μm or more, and more preferably 5 μm or more. A thickness of 2 μm or more for the first organic material layer 22A prevents deterioration of the resin substrate by the hologram layer 3. Furthermore, the thickness of the first organic material layer 22A is preferably 15 μm or less, and more preferably 12 μm or less. A thickness of 15 μm or less for the first organic material layer 22A increases the elastic modulus of the first organic material layer 22A.

[0041] [First inorganic material layer 22B] Examples of inorganic materials used in the first inorganic material layer 22B include silicon oxide, silicon nitride, silicon oxide nitride, silicon sulfide, aluminum oxide, aluminum nitride, aluminum oxide nitride, or aluminum sulfide. Among these, silicon dioxide, silicon dioxide nitride, aluminum oxide, and aluminum dioxide nitride are preferred. In particular, a low level of alkali oxide components such as sodium and potassium is preferred.

[0042] The thickness of the first inorganic material layer 22B is preferably 50 nm to 5000 nm, and more preferably 50 nm to 3000 nm. A layer thickness of 50 nm or more provides sufficient resistance to holograms. A layer thickness of 5000 nm or less makes it less likely for cracks to form in the protective layer 22, thereby suppressing delamination. A particularly preferred layer thickness is 50 nm to 1000 nm.

[0043] The inorganic material used in the first inorganic material layer 22B may have a higher refractive index than the first resin substrate 1 or the first organic material layer 22A. For example, the refractive index of the first inorganic material layer 22B may be between 1.48 and 3.0. When the first inorganic material layer 22B has a high refractive index, light transmitted through the first protective layer 22 to the first resin substrate 1 passes from the optically dense first inorganic material layer 22B through the optically coarse first organic material layer 22A before entering the first resin substrate 1. As a result, the emission angle of light from the first protective layer 22 toward the first resin substrate 1 increases in proportion to the refractive index difference between the first protective layer 22 and the first resin substrate 1. This allows the field of view (FOV) of the image display light guide plate 6 to be widened.

[0044] The method for forming the first inorganic material layer 22B is not particularly limited. For example, it can be formed by any of the conventionally known methods such as vacuum deposition, sputtering, ion plating, or plasma CVD. When forming the first inorganic material layer 22B with silicon oxide, in order to improve the adhesion between the film-forming surface and the silicon oxide, the film-forming surface may be subjected to corona discharge treatment, low-temperature plasma treatment, or surface treatment such as applying a silane coupling agent or a mixture of saturated polyester and isocyanate. For example, when depositing a silicon oxide thin film by vacuum deposition, silicon, silicon monoxide, silicon dioxide, or a mixture thereof is used as the evaporating material, and 1.0 × 10 -3 Torr~1.0×10 -5 Under Torr vacuum, heating and evaporation are performed using electron beam, resistance heating, or high-frequency heating. Reaction evaporation methods, performed while supplying oxygen gas, can also be employed.

[0045] When forming a layer consisting of silicon nitrogen oxide as the first inorganic material layer 22B, the same configuration as the first inorganic material layer 22B mainly composed of silicon oxide is used, except that silicon oxide is replaced with silicon nitrogen oxide.

[0046] When forming a layer made of aluminum oxide as the first inorganic material layer 22B, it may be formed using only Al2O3, or it may be formed by mixing Al, AlO, Al2O3, etc. The atomic ratio of Al:O in the aluminum oxide layer will vary depending on the manufacturing conditions of the aluminum oxide layer. The aluminum oxide layer that can be used as the first inorganic material layer 22B may contain trace amounts of other components (up to at most 3% of the total components) as long as the density performance is not impaired.

[0047] The thickness of the aluminum oxide layer can be set as needed, such as for chemical resistance. For example, the thickness of the aluminum oxide layer may be between 5 nm and 800 nm.

[0048] The method for forming the first inorganic material layer 22B with aluminum oxide is not particularly limited. For example, the first inorganic material layer 22B may be formed using PVD (physical vapor deposition) methods such as vacuum deposition, sputtering, or ion plating, or CVD (chemical vapor deposition). For example, in vacuum deposition, Al, Al2O3, etc., may be used as the deposition source material, and the heating method of the deposition source may include resistance heating, high-frequency induction heating, electron beam heating, etc. In vacuum deposition, reactive gases such as oxygen, nitrogen, and water vapor may be introduced, or reactive deposition using means such as ozone addition or ion assistance may be used. Furthermore, bias may be applied to the substrate on the deposition surface, or the temperature of the deposition surface may be increased or decreased. The same applies to other film deposition methods such as sputtering and CVD.

[0049] [Second organic material layer 24A] The second organic material layer 24A has the same configuration as exemplified in the description of the first organic material layer 22A. However, the thickness, material, etc., of the second organic material 24A may differ from those of the first organic material layer 22A.

[0050] [Second inorganic material layer 24B] The second inorganic material layer 24B is laminated on the opposite side of the first inorganic material layer 22B via the hologram layer 3. The second inorganic material layer 24B uses the same configuration as exemplified in the description of the first inorganic material layer 22B. However, the thickness, material, etc., of the second inorganic material 24B may differ from those of the first inorganic material layer 22B. The organic material layer preferably does not contain inorganic materials. The inorganic material layer preferably does not contain organic materials.

[0051] [Image display light guide plate 16] The image display light guide plate 16 has a first protective layer 22 and a second protective layer 24 positioned between the first resin substrate 1 and the hologram layer 3, and between the second resin substrate 5 and the hologram layer 3, respectively. The first protective layer 22 comprises a first organic material layer 22A and a first inorganic material layer 22B, and the second protective layer 24 comprises a second organic material layer 24A and a second inorganic material layer 24B. In the first protective layer 22, it is preferable that the first organic material layer 22A is positioned on the side of the first resin substrate 1 and the first inorganic material layer 22B is positioned on the side of the hologram layer 3. Similarly, in the second protective layer 24, it is preferable that the second organic material layer 24A is positioned on the side of the second resin substrate 2 and the second inorganic material layer 24B is positioned on the side of the hologram layer 3. By positioning the first inorganic material layer 22B and the second inorganic material layer 24B in contact with the hologram layer 3 in this way, the resistance to hologram agents is further improved, and long-term visibility can be enhanced.

[0052] <Second variation> A second modification of the embodiment of the present invention will now be described. In this embodiment, the first glass layer and the second glass layer may be collectively referred to simply as the "glass layer" below. Also, the first adhesive layer and the second adhesive layer may be collectively referred to simply as the "adhesive layer" below. Figure 4 is a schematic cross-sectional view showing an example of a light guide plate for image display, which is a second modified embodiment of the present invention. As shown in Figure 4, the image display light guide plate 26 in the second modified embodiment of the present invention is modified from the image display light guide plate 6 of the basic example embodiment of the present invention to have a first glass layer 37 and a first adhesive layer 38 on the outside of the first resin substrate 1, and a second glass layer 40 and a second adhesive layer 39 on the outside of the second resin substrate 5.

[0053] [First glass layer 37] The first glass layer 37 is positioned on the outside of the first resin substrate 1 and, in the configuration shown in Figure 4, is in close contact with the surface of the first resin substrate 1. The first glass layer 37 prevents scratches and prevents gases penetrating from the outside of the image display light guide plate 26 and from the first resin substrate 1 from penetrating the hologram layer 3. For example, the first glass layer 37 is more preferable if it has low oxygen permeability and water vapor permeability. For example, the oxygen permeability of the first glass layer 37 is 1 cm 3 / m 2 • It may be less than one day. For example, the water vapor transmission rate of the first glass layer 37 is 1 g / m³. 2It may be less than 1 day. The water vapor transmission rate of the first glass layer 37 is 0.5 g / m³. 2 It is preferable that it be less than or equal to one day.

[0054] Since it tends to have excellent gas barrier properties as well as mechanical strength, the thickness of the first glass layer 37 is preferably 10 μm or more. More preferably 30 μm or more. Furthermore, since it tends to have excellent optical properties as a light guide plate, such as light transmittance, the thickness of the first glass layer 37 is preferably 200 μm or less. More preferably 100 μm or less, even more preferably 75 μm or less, and particularly preferably 50 μm or less. Examples of materials for the first glass layer 37 include borosilicate glass, alkali-free glass, low-alkali glass, soda-lime glass, sol-gel glass, or glass that has been heat-treated or surface-treated. Particularly preferred is alkali-free glass from the viewpoint of avoiding discoloration due to impurities in the glass material. The method for forming the first glass layer 37 can be appropriately selected, for example, the slot-down draw method, the fusion method, or the float method can be used. Furthermore, the first glass layer 37 may be a commercially available product, or commercially available glass may be polished to the desired thickness. Examples of commercially available glass include Corning's "EAGLE2000," Asahi Glass's "AN100," Nippon Electric Glass's "OA10G," and Schott's "D263."

[0055] [First adhesive layer 38] In the second modified image display light guide plate 26, the first adhesive layer 38 is not essential if the adhesion between the first resin substrate 1 and the first glass layer 37 is good. However, especially when the above-mentioned resin material is used as the first resin substrate 1, it is preferable to use the first adhesive layer 38 in order to maintain excellent adhesion with the first glass layer 37. The material forming the first adhesive layer 38 is not particularly limited as long as it is a material that provides good adhesion between the first resin substrate 1 and the first glass layer 37. For example, preferred materials for the first adhesive layer 38 include curable resin compositions containing heat- and UV-curable resins, such as acrylic resins, urethane resins, epoxy resins, and silicone resins. The resin composition constituting the first adhesive layer 38 may optionally contain silane coupling agents, sensitizers, crosslinking agents, UV absorbers, polymerization inhibitors, surfactants, fillers, mold release agents, and thermoplastic resins, as long as they do not impair the objectives of the present invention. These can be used individually or in combination of two or more as appropriate. Examples of thermoplastic resins include fluororesins, polyethersulfone resins, polycarbonate resins, acrylic resins, silicone resins, cycloolefin resins, thermoplastic polyimide resins, polyamide resins, polyamideimide resins, polyarylate resins, polysulfone resins, polyetherimide resins, polyetheretherketone resins, polyethersilicone resins, polyester resins, and polyphenylene sulfide resins. Since the light guide plate for image display of the present invention can be given an excellent brightness value, it is preferable that the total light transmittance of the first adhesive layer 38 is 80% or more. More preferably, it is 90% or more. Furthermore, since this can be given an excellent brightness value to the light guide plate and tends to prevent color unevenness, it is preferable that the refractive index of the first adhesive layer 38 is n ± 0.20 with respect to the average refractive index n of the first resin substrate 1 and the first glass layer 37. More preferably, it is n ± 0.15, and even more preferably, it is n ± 0.10. Furthermore, since it tends to maintain excellent adhesion between the first resin substrate 1 and the first glass layer 37, the thickness of the first adhesive layer 38 is preferably 1 μm or more. More preferably 5 μm or more. Also, since it tends to suppress color unevenness of the light guide plate, the thickness of the first adhesive layer 38 is preferably 700 μm or less. More preferably 100 μm or less. The first adhesive layer 38 can be formed, for example, by laminating a glass plate onto an adhesive applied to a resin substrate, and then processing this laminate by methods such as pressing, nip rolling, or heat lamination. If the adhesive is a curable resin, the formation of the first adhesive layer 38 may include a curing step for the adhesive.

[0056] [Second adhesive layer 39] In the second modified image display light guide plate 26, the second adhesive layer 39 is not essential if the adhesion between the second resin substrate 5 and the second glass layer 40 is good. However, especially when the above-mentioned resin material is used as the second resin substrate 5, it is preferable to use the second adhesive layer 39 in order to maintain excellent adhesion with the second glass layer 40. The second adhesive layer 39 is configured in the same way as illustrated in the description of the first adhesive layer 38. However, the thickness, material, etc., of the second adhesive layer 39 may differ from those of the first adhesive layer 38.

[0057] [Second glass layer 40] The second glass layer 40 is positioned on the outside of the second resin substrate 5 and, in the configuration shown in Figure 4, is in close contact with the surface of the second resin substrate 5. The second glass layer 40 is configured in the same way as illustrated in the description of the first glass layer 37. However, the thickness, material, etc., of the second glass layer 40 may differ from those of the first glass layer 37.

[0058] [Image display light guide plate 26] The image display light guide plate 26 has a glass layer, a resin substrate, a protective layer, and a hologram layer. In the image display light guide plate 26, the glass layer, resin substrate, protective layer, and hologram layer are arranged in this order in the thickness direction. An adhesive layer may be placed between the glass layer and the resin substrate, as needed. From the viewpoint of suppressing scratches on the surface of the image display light guide plate, it is preferable that the glass layer be the outermost layer on at least one side of the image display light guide plate, and more preferably the outermost layer on both sides of the image display light guide plate.

[0059] One or more transparent layers may be placed on at least one surface of the glass layer. One or more transparent layers may be placed between the glass layer and the resin substrate. Examples of the types of transparent layers include a hard coat layer or an anchor coat layer.

[0060] The following describes the detailed configuration of an example of the image display light guide plate of this embodiment, based on Figure 4. Figure 4 is a schematic cross-sectional view showing an example of a light guide plate for image display according to a second modified example of the present invention. In the image display light guide plate 26 shown in Figure 4, the first glass layer 37, first adhesive layer 38, first resin substrate 1, first protective layer 2, hologram layer 3, second protective layer 4, second resin substrate 5, second adhesive layer 39, and second glass layer 40 are arranged in this order in the thickness direction.

[0061] The image display light guide plate 26 of this embodiment is the same as the basic example of the present invention, except that it has a first glass layer 37 and a first adhesive layer 38 on the outside of the first resin substrate 1, and a second glass layer 40 and a second adhesive layer 39 on the outside of the second resin substrate 5. Therefore, the configurations of the first resin substrate 1, first protective layer 2, hologram layer 3, second protective layer 4, and second resin substrate 5 in this embodiment are the same as those exemplified in the description of the first resin substrate 1, first protective layer 2, hologram layer 3, second protective layer 4, and second resin substrate 5 in the basic example of the embodiment of the present invention. The first glass layer 37 and the second glass layer 40, as well as the first adhesive layer 38 and the second adhesive layer 39, will be described below.

[0062] The first glass layer 37 and the second glass layer 40 are positioned on the outermost edges in the thickness direction of the image display light guide plate 26, which prevents scratches on the surface of the image display light guide plate 26 and protects the first resin substrate 1 from gases outside the image display light guide plate 26.

[0063] <Manufacturing method for light guide plates for image display> The light guide plate 6 for image display can be manufactured, for example, as follows. A first resin substrate 1 and a second resin substrate 5 are prepared ([Substrate preparation step]), and a first protective layer 2 and a second protective layer 4 are formed on the surfaces of the first resin substrate 1 and the second resin substrate 5, respectively ([Protective layer formation step]). As for the manufacturing method of the first protective layer 2 and the second protective layer 4, an appropriate manufacturing method is selected depending on the materials of the first protective layer 2 and the second protective layer 4. For example, a photosensitive material for hologram formation is applied to the surface of the first protective layer 2 on a first resin substrate 1 on which the first protective layer 2 is formed. At this time, a transparent sealing layer of the same thickness as the hologram layer 3 may be provided on the outer periphery of the first protective layer 2. The sealing layer seals the outer periphery of the hologram layer 3 after the hologram layer 3 has been formed. The sealing layer is made of a transparent material, such as epoxy resin, silicone resin, or ethylene thiol resin. After this, the second resin substrate 5, on which the second protective layer 4 has been formed, is placed on the photosensitive material with the second protective layer 4 facing the photosensitive material ([light guide plate manufacturing process]). However, the above manufacturing sequence is just one example. For example, the photosensitive material may be applied to the second resin substrate 5 on which the second protective layer 4 is formed, and then the first resin substrate 1 on which the protective layer 2 is formed may be placed on the hologram layer 3. Subsequently, a laminate consisting of a first resin substrate 1, a first protective layer 2, a hologram layer 3, a second protective layer 4, and a second resin substrate 5 is bonded together by a vacuum press. Subsequently, interference fringes corresponding to the diffraction pattern are formed on the photosensitive material of the laminate, and a diffraction grating is formed within the photosensitive material. In this way, the light guide plate 6 for image display is manufactured.

[0064] The image display light guide plate 16 can be manufactured, for example, as follows. A first resin substrate 1 and a second resin substrate 5 are prepared ([Substrate preparation step]), and a first organic material layer 22A and a second organic material layer 24A are formed on the surfaces of the first resin substrate 1 and the second resin substrate 5, respectively ([Organic material layer formation step]). A first inorganic material layer 22B and a second inorganic material layer 24B are formed on the surfaces of the first organic material layer 22A and the second organic material layer 24A of the intermediate, which consists of the resin substrate and the organic material layer (Inorganic material layer formation step). A photosensitive material for hologram formation is applied to the surface of the first inorganic material layer 22B. At this time, a transparent sealing layer with the same thickness as the hologram layer 3 may be provided on the outer periphery of the first inorganic material layer 22B. In this case, the photosensitive material is applied to the recess formed by the sealing layer. The sealing layer seals the outer periphery of the hologram layer 3 after its formation. Subsequently, the second resin substrate 5, on which the second protective layer 24 is formed, is placed on the photosensitive material with the second protective layer 24 facing the photosensitive material ([light guide plate manufacturing process]).

[0065] When the inorganic material is silicon oxide, the inorganic material layer can be formed as follows. An intermediate consisting of a resin substrate and an organic material layer is placed in a vacuum deposition apparatus, after which silicon oxide is vacuum deposited. The ultimate vacuum level in the chamber of the vacuum deposition apparatus is 3 × 10⁻⁶. -3 It is preferable to keep the Torr value below 1 / 2. Under this vacuum, 99.9% pure silicon monoxide is heated and evaporated using a high-frequency induction heating method to form a silicon oxide thin film on the surface of the resin substrate. This yields an intermediate with a silicon oxide thin film layer formed on it. Subsequently, the image display light guide plate 16 is formed in the same manner as the light guide plate manufacturing step in the manufacturing method of the image display light guide plate 6.

[0066] When the inorganic material is alumina, the inorganic material layer can be formed as follows. An intermediate consisting of a resin substrate and an organic material layer is placed inside the electron beam deposition apparatus, and an appropriate amount of alpha alumina particles with a purity of 99.999% and a particle size of 0.5 to 5 mm is placed as the deposition source, and the apparatus is evacuated. Preferably, the distance from the deposition source to the shutter is approximately 3 to 15 cm, and the distance from the deposition source to the surface of the resin substrate is approximately 5 to 50 cm. The pressure of the electron beam deposition apparatus is 3 × 10 -3After reaching a temperature below Torr, the electron beam filament current is increased to 25-50 mA, the shutter is opened, and alumina film deposition is performed. When the temperature of the wall inside the apparatus exceeds 45°C, the shutter is closed and the electron beam filament current is stopped. After cooling to below 35°C, the electron beam filament current is increased to 25-50 mA to heat the deposition source, the shutter is opened, and alumina film deposition is performed. This process is repeated to deposit alumina films. This yields an intermediate with a thin alumina film layer deposited. Subsequently, the image display light guide plate 16 is formed in the same manner as the light guide plate manufacturing step in the manufacturing method of the image display light guide plate 6.

[0067] The image display light guide plate 26 can be manufactured, for example, as follows. A first resin substrate 1 and a second resin substrate 5 are prepared ([Substrate preparation step]), and a first protective layer 2 and a second protective layer 4 are formed on the surfaces of the first resin substrate 1 and the second resin substrate 5, respectively ([Protective layer formation step]). As for the manufacturing method of the first protective layer 2 and the second protective layer 4, an appropriate manufacturing method is selected depending on the materials of the first protective layer 2 and the second protective layer 4. A first adhesive layer 38 and a second adhesive layer 39 are formed on the surface of the first resin substrate 1 on which the first protective layer 2 is formed, opposite to the side with the first protective layer 2, and on the surface of the second resin substrate 5 on which the second protective layer 4 is formed, opposite to the side with the second protective layer 4 ([Adhesive layer formation step]). A first glass layer 37 is formed on the surface of the first adhesive layer 38, and a second glass layer 40 is formed on the surface of the second adhesive layer 39 ([glass layer formation step]). For example, a photosensitive material for hologram formation is applied to the surface of the first protective layer 2 on a first resin substrate 1 on which the first protective layer 2 is formed. At this time, a transparent sealing layer of the same thickness as the hologram layer 3 may be provided on the outer periphery of the first protective layer 2. The sealing layer seals the outer periphery of the hologram layer 3 after the hologram layer 3 has been formed. The sealing layer is made of a transparent material, such as epoxy resin, silicone resin, or ethylene thiol resin. After this, the second resin substrate 5, on which the second protective layer 4 has been formed, is placed on the photosensitive material with the second protective layer 4 facing the photosensitive material ([light guide plate manufacturing process]). However, the above manufacturing sequence is just one example. For example, the photosensitive material may be applied to the second resin substrate 5 on which the second protective layer 4 is formed, and then the first resin substrate 1 on which the first protective layer 2 is formed may be placed on the hologram layer 3. Subsequently, a laminate consisting of a first glass layer 37, a first adhesive layer 38, a first resin substrate 1, a first protective layer 2, a hologram layer 3, a second protective layer 4, a second resin substrate 5, a second adhesive layer 39, and a second glass layer 40 is bonded together by a vacuum press. Subsequently, interference fringes corresponding to the diffraction pattern are formed on the photosensitive material of the laminate, and a diffraction grating is formed within the photosensitive material. In this way, the image display light guide plate 26 is manufactured.

[0068] <Brightness value and FOV> Here, we will briefly explain an example of a method for measuring the luminance value and FOV in the image display light guide plate 6. Figure 3 is a schematic front view illustrating the measurement method for luminance values ​​and FOV.

[0069] As shown in Figure 3, in order to measure the brightness value and FOV of the image display light guide plate 6, the display device 10 is manufactured using the image display light guide plate 6. The display device 10 includes an image light projection unit 13 and an incident optical system 12, in addition to the image display light guide plate 6. The image light projection unit 13 projects image light to be displayed on the image display light guide plate 6 in accordance with the image signal sent from a controller (not shown). The incident optical system 12 includes, for example, a prism. The incident optical system 12 directs the image light emitted from the image light projection unit 13 into an incident unit 6a provided on the surface of the image display light guide plate 6. For example, the incident unit 6a is provided on the surface on the resin substrate 1 side. Image light incident on the incident section 6a passes through the waveguide diffraction grating section 3b formed in the hologram layer 3 and reaches the display diffraction grating section 3c of the hologram layer 3. In the display diffraction grating section 3c, the image light is diffracted at positions corresponding to each display pixel. The diffracted light is emitted to the outside from the display section 6d on the surface of the image display light guide plate 6. In the example shown in Figure 2, the display section 6d is formed on the surface on the resin substrate 1 side at a position spaced apart from the incident section 6a.

[0070] The brightness value and FOV of the image display light guide plate 6 are measured by placing the display device 10 on the measuring device 15. The measuring device 15 comprises a holding stand (not shown), a luminance meter 14, and a goniometer stage (not shown). The holder holds the display device 10. The luminance meter 14 measures the luminance value of the received light. The oscillating stage supports the luminance meter 14 so that it can swing on a circumference centered on its rotation center. The distance d between the luminance meter 14 and the display surface 3a is the distance corresponding to the position of the user's eyes when the display device 10 is worn. For example, if the display device 10 is a head-mounted display, d is set to 15 mm.

[0071] The luminance value of the image display light guide plate 6 is measured by placing the luminance meter 14 at a position with an oscillation angle of 0° (see the solid line luminance meter 14 in Figure 2). The display device 10 is positioned by a holder so that the center of the display surface 3a is on the measurement optical axis of the luminance meter 14 and faces the luminance meter 14. The luminance value is the luminance measured by the luminance meter 14 when the display device 10 displays a white image with maximum luminance. The brightness value is preferably 1000 nits or higher, and more preferably 1200 nits or higher. In measuring the field of view (FOV) of the image display light guide plate 6, the brightness is measured by changing the oscillation angle θ while displaying a white image with maximum brightness on the display device 10. The brightness corresponding to the point at which the white image becomes invisible is used as a threshold, and the angle range in which brightness above the threshold can be obtained is determined. If brightness above the threshold can be obtained in the range from -θ1 to +θ2, the FOV is θ1 + θ2. The field of view (FOV) of the image display light guide plate 6 is more preferably 24° to 160°, and even more preferably 35° to 160°. A larger FOV expands the viewing angle of the image, increasing the amount of information in the image and broadening the range of applicable applications. Conversely, a FOV smaller than the upper limit tends to result in a larger amount of light being extracted per unit area, making the image brighter, which is preferable.

[0072] For example, the closer the distance between the first protective layer 2 and the second protective layer 4 and the hologram layer 3, the more the field of view (FOV) can be improved by about 10° or more. The distance is preferably 1000nm or less, more preferably 500nm or less, and most preferably 100nm or less. [Examples]

[0073] The present invention will be described more specifically below with reference to examples and manufacturing examples. However, the present invention is not limited to these examples and manufacturing examples.

[0074] [Example 1] The resin substrate material used will be PMMA ("Acrylite®," manufactured by Mitsubishi Chemical Corporation). The resin substrate will be a rectangular plate with dimensions of 60 mm in width, 60 mm in length, and 1 mm in thickness. DCP (tricyclodidecanedimethanol dimethacrylate, manufactured by Shin-Nakamura Chemical Co., Ltd.) is used as the material for the protective layer.

[0075] Using the above materials, a resin substrate (hereinafter also referred to as an "intermediate") with a protective layer is prepared by performing the substrate preparation process and protective layer formation process described below.

[0076] [Substrate preparation process] In the substrate preparation process, the resin substrate is washed and dried. The resin substrate is ultrasonically cleaned for 5 minutes while immersed in a 5% surfactant aqueous solution of Semiclean (registered trademark) M-LO (product name; manufactured by Yokohama Oil & Fat Industry Co., Ltd.), a neutral cleaning agent. Thereafter, the resin substrate is ultrasonically cleaned for 5 minutes while being immersed in ultrapure water. Further, the resin substrate is rinsed with ultrapure water, and after air drying, it is dried in an oven at 80°C under a nitrogen atmosphere. Thereafter, the air-dried evaluation sample B is subjected to UV ozone cleaning for 1 minute using a UV ozone cleaner. Thus, the substrate preparation process is completed.

[0077] [Protective layer formation process] In the protective layer formation process, an organic material layer is formed on the surface of the resin substrate. To 100 parts by weight of DCP (manufactured by Shin-Nakamura Chemical Co., Ltd., tricyclodecane dimethanol dimethacrylate), 5 parts by weight of Irgacure 184 (manufactured by BASF Japan) is added as an initiator, and a high-pressure mercury lamp (integrated light quantity: 200 mJ / cm 2 ) is irradiated to form an organic material layer such that the thickness after curing is 5 μm, thereby obtaining an intermediate of Example 1. Thus, the protective layer formation process is completed.

[0078] [Example 2] Example 2 is the same as Example 1 except that an inorganic material layer formed of silicon oxide with a thickness of 100 nm is formed on the organic material layer of Example 1, and an intermediate is produced. Hereinafter, the protective layer formation process of Example 2 will be mainly described with respect to the differences from Example 1.

[0079] In the protective layer formation process of this example, after forming an organic material layer on the resin substrate in the same manner as in Example 1, a silicon oxide thin film layer is formed on the surface of the organic material layer. After the intermediate composed of the resin substrate and the organic material layer is placed in a vacuum deposition apparatus, vacuum deposition of silicon oxide is performed. The ultimate vacuum degree of the chamber of the vacuum deposition apparatus is set to 1.0×10 -4 Torr. Under this vacuum, silicon monoxide with a purity of 99.9% is heated and evaporated by a high-frequency induction heating method to form a silicon oxide thin film with a thickness of 100 nm on the surface of the resin substrate. Thereby, an intermediate of Example 2 with a silicon oxide thin film layer formed thereon is obtained.

[0080] [Example 3] Example 3 is prepared in the same manner as Example 2, except that the thickness of the organic material layer is 10 μm and the inorganic material layer is formed from alumina with a thickness of 500 nm. The following section will describe the protective layer formation process in Example 3, focusing on the differences from Example 1.

[0081] In the protective layer formation step of this embodiment, an organic material layer is formed on a resin substrate in the same manner as in Example 1, and then an alumina thin film layer is formed on the surface of the organic material layer. An intermediate consisting of a resin substrate and an organic material layer is placed inside the electron beam deposition apparatus. An appropriate amount of alpha alumina particles with a purity of 99.999% and a particle size of 2 mm is placed as the deposition source, and the apparatus is evacuated. The distance from the deposition source to the shutter is approximately 8 cm, and the distance from the deposition source to the surface of the resin substrate is approximately 35 cm. The pressure of the electron beam deposition apparatus is 3 × 10 -3 After reaching Pa, the electron beam filament current is increased to approximately 35 mA, the shutter is opened, and alumina film deposition is performed. When the temperature of the wall surface inside the apparatus reaches 50°C, the shutter is closed and the electron beam filament current is stopped. After cooling to below 30°C, the electron beam filament current is increased to approximately 35 mA to heat the deposition source, the shutter is opened, and alumina film deposition is performed. This is repeated to deposit an alumina film with a thickness of 40 nm. This yields the intermediate of Example 3 in which an alumina thin film layer has been deposited.

[0082] [Example 4] Example 4 is an embodiment corresponding to the image display light guide plate 26 of the second modified example (see Figure 4). As shown in Table 1, Example 4 is the same as Example 1 except that a glass layer is placed on the outermost surface. The following section will focus on explaining the differences from Example 1.

[0083] The image display light guide plate 26 of Example 4 has the following layers stacked in this order: first glass layer 37, first adhesive layer 38, first resin substrate 1, first protective layer 2, hologram layer 3, second protective layer 4, second resin substrate 5, second adhesive layer 39, and second glass layer 40 (see Figure 4).

[0084] [Glass layer bonding process] In the glass layer bonding process, the glass layers 37 and 40 are bonded to the opposite side of the protective layer side of the resin substrates 1 and 5 (intermediates obtained in the same manner as in Example 1), where the protective layers 2 and 4 are formed, via adhesive layers 38 and 39. A heat- and UV-curable epoxy resin (product name "KRX-690-5", manufactured by ADEKA Corporation) is applied to resin substrates 1 and 5 using a bar coater, so that the thickness after curing is 3 μm, as the uncured adhesive layer 38 and 39. Furthermore, thin glass sheets (product name "OA-10G", thickness: 50 μm, manufactured by Nippon Electric Glass Co., Ltd.) are laminated onto resin substrates 1 and 5, respectively, using a hand roll (hardness: 90°) with the adhesive layer 38 and 39 facing the coated surface. A high-pressure mercury lamp (cumulative luminous intensity: 370 mJ / cm²) is used. 2 The heat and UV-curable resin composition is cured by irradiating it with a UV-curable light, and then heat-treating it in a hot air circulating dryer at 150°C for 30 minutes to obtain adhesive layers 38 and 39. The glass layers 37 and 40, the adhesive layers 38 and 39, and the resin substrates 1 and 5 are arranged so that their outer dimensions (edges) coincide. This results in a resin substrate (hereinafter also referred to as the "intermediate laminate") with the glass layer bonded to the side opposite to the protective layer side of the intermediate.

[0085] [Comparative Example 1] As shown in [Table 1], Comparative Example 1 is the same as Example 1 except that it consists only of a resin substrate and lacks a protective layer.

[0086] [Comparative Example 2] As shown in [Table 1], Comparative Example 2 is the same as Example 3 except that it has no organic protective layer and only an inorganic material layer.

[0087] [Comparative Example 3] As shown in [Table 1], the method is the same as in Example 1, except that BZA (manufactured by Osaka Organic Chemical Industry Co., Ltd., benzyl acrylate, trade name "Viscoat #160"), a monofunctional monomer, is used as the material for the protective layer.

[0088] <Measurement of elastic modulus> Intermediate samples from each example and comparative example were used as measurement samples, and the elastic modulus of the protective layer was measured using a Shimadzu Dynamic Microhardness Tester DUH-W201 under the measurement conditions: Triangular 115, indentation depth 230-280 nm.

[0089] Table 1 below shows the configuration and measurement results for each example and comparative example.

[0090] [Table 1]

[0091] Next, we will describe manufacturing examples of light guide plates for image display using intermediates from each embodiment and comparative example. The light guide plates for image display can be manufactured by following the light guide plate manufacturing process described below.

[0092] [Manufacturing Example 1] Manufacturing Example 1 involves using the intermediate from Example 1 to produce the image display light guide plate 6 of the embodiment. For the photosensitive material for the hologram layer 3, a mixture of 100 parts by weight of bisphenol epoxy resin jER(registered trademark) 1007 (degree of polymerization n=10.8, epoxy equivalent: 1750-2200, manufactured by Mitsubishi Chemical Corporation), 50 parts by weight of triethylene glycol diacrylate, 5 parts by weight of 4,4'-bis(tert-butylphenyl)iodonium hexafluorophosphate, and 0.5 parts by weight of 3,3'-carbonylbis(7-diethylamino)coumarin, dissolved in 100 parts by weight of 2-butanone (hereinafter also referred to as "photosensitive material A") is used.

[0093] [Light guide plate manufacturing process] In the light guide plate manufacturing process of Manufacturing Example 1, the image display light guide plate 6 is manufactured using two intermediates from Example 1. A sealing layer with a width of 5 mm and a thickness of 5 μm is applied to the periphery of the protective layer of the intermediate. The sealing layer is made of a transparent material and is not particularly limited as long as it is a material that can bond the intermediate protective layers together. However, in Example 1, the photo-adhesive Hardlock® OP-1045K (product name; manufactured by Denka Co., Ltd.) is used. This prepares an intermediate substrate with a stepped seal layer, in which the opening surrounded by the seal layer has dimensions of 50 mm x 50 mm. Next, the photosensitive material A, used as a hologram photopolymer material, is applied to this intermediate substrate by spin coating. The photosensitive material is applied so that its thickness after drying is 5 μm. Next, the other intermediate substrate is laminated onto the seal layer and photosensitive material so that its protective layer faces the protective layer of the intermediate substrate with the seal layer, and then press-bonded under reduced pressure. The press-bonding conditions are an absolute pressure of 5 kPa, a temperature of 70°C, and a press pressure of 0.04 MPa. Next, a diffraction grating is recorded onto the photosensitive material of the press-bonded laminate. During this process, the temperature of the laminate is maintained at 20°C. The diffraction grating is created by irradiating the laminate with two laser beams and adjusting the irradiation angle and intensity of each beam to form interference fringes that create the desired diffraction pattern. This records the diffraction grating onto the photosensitive material. Specifically, the diffraction grating is designed to diffract the red, green, and blue wavelength light incident as image light at the incident point, forming a color display diffraction grating that is emitted from the display unit at positions corresponding to the pixels of the image light. After this, the laminate is kept at 20°C and exposed to ultraviolet light (wavelength 365nm, irradiance 80W / cm²). 2 The entire surface of the laminate is irradiated with ultraviolet light from one side for 30 seconds. A high-pressure mercury lamp is used as the source of ultraviolet light. This causes the sealing layer to harden, and the image display light guide plate 6 from manufacturing example 1 is produced.

[0094] [Manufacturing Example 2] Manufacturing Example 2 involves using the intermediate from Example 2 to produce the image display light guide plate 16 of the embodiment. The image display light guide plate 16 of Manufacturing Example 2 is produced in the same manner as in Manufacturing Example 1, except that the intermediate from Example 2 is used.

[0095] [Manufacturing Example 3] Manufacturing Example 3 involves producing the image display light guide plate 16 of the embodiment using the intermediate from Example 3. The image display light guide plate 16 of Manufacturing Example 3 is produced in the same manner as in Manufacturing Example 1, except that the intermediate from Example 3 is used.

[0096] [Manufacturing Example 4] Manufacturing Example 4 involves fabricating the image display light guide plate 26 of the embodiment using the intermediate laminate of Example 4. The image display light guide plate 26 of Manufacturing Example 4 is fabricated in the same manner as in Manufacturing Example 1, except that the intermediate laminate of Example 4 is used instead of the intermediate.

[0097] [Comparative Manufacturing Example 1] Comparative Manufacturing Example 1 involves manufacturing an image display light guide plate using the resin substrate of Comparative Example 1. The image display light guide plate of Comparative Manufacturing Example 1 is manufactured in the same manner as in Manufacturing Example 1, except that the resin substrate of Comparative Example 1 is used instead of the intermediate of Example 1.

[0098] [Comparative Manufacturing Example 2] Comparative Manufacturing Example 2 involves manufacturing an image display light guide plate using the intermediate from Comparative Example 2. The image display light guide plate for Comparative Manufacturing Example 2 is manufactured in the same manner as in Manufacturing Example 1, except that the intermediate from Comparative Example 2 is used.

[0099] [Comparative Manufacturing Example 3] Comparative Manufacturing Example 3 involves manufacturing an image display light guide plate using the intermediate of Comparative Example 3. The image display light guide plate of Comparative Manufacturing Example 3 is manufactured in the same manner as in Manufacturing Example 1, except that the intermediate of Comparative Example 3 is used.

[0100] <Evaluation Method> Next, we will explain the evaluation methods for each manufacturing example. The evaluation includes FOV evaluation and display image clarity evaluation.

[0101] [FOV measurement] For measuring luminance values, prepare a sample that has not undergone humidification testing (labeled "Initial" in [Table 2]). The humidification test will be conducted using a small environmental tester, SH-241 (product name; manufactured by ESPEC Corporation). The test conditions for the humidification test are 40°C, 90% RH, and 100 hours. In the embodiment, the luminance value of the measurement sample is measured based on the measurement method described above. Each measurement sample is assembled into the display device described above. In the embodiment, the FOV is measured based on the measurement method described above. The luminance meter 14 used is the BM-8 (product name; manufactured by Topcon Corporation). The measurement angle is 1°. The distance d from the display surface 3a is 15 mm. If the brightness value is 1000 nits or higher and the FOV is 45° or higher, it is judged as very good (indicated as "S" in [Table 2]). If the brightness value is 1000 nits or higher and the FOV is between 35° and 45°, it is judged as good (indicated as "A" in [Table 2]). If the brightness value is 1000 nits or more and the FOV is between 24° and 35°, it is judged as fair (indicated as "B" in [Table 2]). If the brightness value is 1000 nits or less and the FOV is less than 24°, it is judged as unacceptable (no good, indicated as "C" in [Table 2]).

[0102] [Image clarity evaluation] The clarity of the displayed image is evaluated using a display device used for FOV measurement. The input images used for evaluation are white images and images displaying text. The evaluation is performed by visually determining how the white image and the displayed text image appear. The text image displayed will be "ABCDE" within a 10mm x 100mm area. If no rainbow colors are visible in a white image, and the text is clearly visible in an image displaying text, it is judged as good (indicated as "A" in [Table 2]). If a slight rainbow color is visible in a white image, but the text is clearly visible in an image displaying text, it is judged as acceptable (fair, indicated as "B" in [Table 2]). If rainbow colors are visible in at least a portion of a white image, and the outlines of the characters appear blurred in an image displaying text, it is judged as unacceptable (no good, indicated as "C" in [Table 2]).

[0103] Table 2 below shows the composition and evaluation results for each manufacturing example.

[0104] [Table 2]

[0105] <Evaluation Results> As shown in [Table 2], the FOV of manufacturing examples 1, 2, 3, and 4 can be evaluated as "good" or "very good," respectively. In contrast, the FOV of comparative manufacturing examples 1, 2, and 3 can each be evaluated as "acceptable". This is thought to be because the protective layer in manufacturing examples 1, 2, 3, and 4 prevents the holographic agent from eroding the resin substrate. In contrast, comparative manufacturing examples 1, 2, and 3 lack a protective layer containing an acrylic resin with repeating units derived from polyfunctional acrylate, resulting in erosion of the hologram layer into the resin substrate and a decrease in FOV. The reason why the FOV of manufacturing examples 2 and 3 is even better than that of manufacturing examples 1 and 4 is thought to be due to the presence or absence of an inorganic material layer in the protective layer. The inorganic material layer further prevents erosion by the hologram agent, and because the inorganic material layer has a higher refractive index than the resin substrate layer and the organic material layer, the FOV is increased and improved.

[0106] The clarity of the display images in manufacturing examples 1, 2, 3, and 4 (referred to as "Clarity" in Table 2) can all be judged as "Good" both initially and after humidity resistance. In contrast, the clarity of the display images in comparative manufacturing examples 1, 2, and 3 is "Acceptable" initially, but after the humidity resistance test, they can all be judged as "Unacceptable (C)". The reason for this is thought to be the same as the reason for the differences in brightness value evaluation described above. In other words, in manufacturing examples 1, 2, 3, and 4, the protective layer prevents erosion of the hologram layer into the resin substrate, even after the initial and humidity resistance tests, resulting in the observation of a clear image. In contrast, comparative manufacturing examples 1, 2, and 3 lack a protective layer containing an acrylic resin with repeating units derived from polyfunctional acrylate. As a result, erosion of the hologram layer into the resin substrate occurs, and a clear image cannot be observed.

[0107] Preferred embodiments, modifications, examples, and manufacturing examples of the present invention have been described above, but the present invention is not limited to these embodiments, modifications, examples, and manufacturing examples. Additions, omissions, substitutions, and other modifications to the configuration are possible without departing from the spirit of the present invention. Furthermore, the present invention is not limited by the foregoing description, but is limited only by the appended claims. [Industrial applicability]

[0108] The image display light guide plate of the present invention can suppress the degradation of the hologram layer even when using a resin substrate, and is useful for display devices in VR and AR applications, for example. For example, the image display light guide plate of the present invention is useful for display devices such as head-up displays, wearable displays, and head-mounted displays. [Explanation of Symbols]

[0109] 1 First resin base material 2, 22 First protective layer 3 Hologram layer 3a Display surface 3b Waveguide diffraction grating section 3c Diffraction grating section for display 4, 24 Second protective layer 5 Second resin base material 6, 16, 26 Light guide plate for image display 6a Inlet section 6d display 10 Display device 12 Input optical system 13 Image light projection section 14. Luminance meter 15 Measuring device 22A 1st organic material layer 22B 1st inorganic material layer 24A 2nd organic material layer 24B 2nd inorganic material layer 37. First glass layer 38. First adhesive layer 39. Second adhesive layer 40. Second glass layer

Claims

1. An image display light guide plate comprising a first resin substrate containing polymethyl methacrylate, a first protective layer containing an acrylic resin containing repeating units derived from tricyclodidecanedimethanol dimethacrylate, a hologram layer, and a second protective layer containing an acrylic resin containing repeating units derived from tricyclodidecanedimethanol dimethacrylate, arranged in this order in the thickness direction.

2. The image display light guide plate according to claim 1, wherein the elastic modulus of the first protective layer is 2 GPa or more.

3. The image display light guide plate according to claim 1 or 2, wherein the thickness of the first protective layer is 2 μm or more.

4. The image display light guide plate according to any one of claims 1 to 3, wherein the first protective layer comprises a first organic material layer containing the acrylic resin and a first inorganic material layer.

5. The image display light guide plate according to claim 4, wherein the first inorganic material layer comprises at least one inorganic material selected from the group consisting of silicon oxide, silicon nitride, silicon oxide nitride, silicon sulfide, aluminum oxide, aluminum nitride, aluminum oxide nitride, and aluminum sulfide.

6. The image display light guide plate according to claim 4 or 5, wherein the thickness of the first inorganic material layer is 50 nm or more and 5000 nm or less.

7. The image display light guide plate according to any one of claims 1 to 6, wherein the first glass layer is disposed on the side of the first resin substrate opposite to the side of the first protective layer.

8. The image display light guide plate according to claim 7, wherein a first adhesive layer is disposed between the first resin substrate and the first glass layer.

9. The image display light guide plate according to any one of claims 1 to 8, wherein the hologram layer is made of a volume hologram material.

10. The image display light guide plate according to claim 1 or 2, wherein the hologram layer is made of a photosensitive material.

11. The image display light guide plate according to claim 10, wherein the photosensitive material comprises a bisphenol epoxy resin, triethylene glycol diacrylate, 4,4'-bis(tert-butylphenyl)iodonium hexafluorophosphate, and 3,3'-carbonylbis(7-diethylamino)coumarin.

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