Infrared light reflecting element, laminated optical film, and optical article

Abstract

The present invention addresses the problem of providing an infrared light reflecting element having high circular polarization purity of reflected light, a laminated optical film, and an optical article. This infrared light reflecting element has an adhesive layer, an optical interference layer, and at least one cholesteric liquid crystal layer, the center wavelength of the reflection band is in the range of 800-2500 nm, and the reflectance of light of the center wavelength is 20% or more. When the refractive index of the adhesive layer is nA and the average refractive index of the cholesteric liquid crystal layer adjacent to the optical interference layer is nL, the refractive index nI of the optical interference layer is (nA×nL)1 / 2-0.03 ≤nI≤(nA×nL)1 / 2+0.03, and the film thickness of the optical interference layer is within the range of ±30% of a λ / 4 condition with respect to the center wavelength λ of the reflection band, or within the range of ±30% of a 3λ / 4 condition.

Description

Infrared light reflecting element, laminated optical film and optical article

[0001] The present invention relates to an infrared light reflecting element, a laminated optical film, and an optical article.

[0002] A reflective polarizer is a polarizer that reflects one polarized light of incident light and transmits the other polarized light. The reflected and transmitted light by the reflective polarizer are polarized in orthogonal directions.

[0003] Known examples of reflective linear polarizers that produce linearly polarized transmitted and reflected light include a film obtained by stretching a dielectric multilayer film as described in Patent Document 1 and a wire grid polarizer as described in Patent Document 2.

[0004] Furthermore, as a reflective circular polarizer in which transmitted light and reflected light become circularly polarized light, for example, a film having a light-reflecting layer in which a cholesteric liquid crystal phase is fixed, as described in Patent Document 3, is known.

[0005] Reflective polarizers are used to extract only specific polarized light from incident light or to split incident light into two polarized lights. For example, in liquid crystal display devices, they are used as brightness enhancement films that reflect and reuse unwanted polarized light from the backlight, thereby improving light utilization efficiency. They are also used as beam splitters in liquid crystal projectors that split light from a light source into two linearly polarized lights and supply each to a liquid crystal panel.

[0006] In recent years, methods have been proposed that use reflective polarizers to reflect a portion of external light and / or light from an image display device to generate a virtual or real image. For example, Patent Document 4 discloses an in-vehicle rearview mirror that uses a reflective polarizer to reflect light from behind. Furthermore, Patent Document 5 discloses a method for generating a virtual image by reflecting light back and forth between a reflective polarizer and a half mirror in order to make the display unit of a virtual reality display device, an electronic viewfinder, or the like smaller and thinner.

[0007] Japanese Patent Application Laid-Open No. 2011-053705 Japanese Patent Application Laid-Open No. 2015-028656 Japanese Patent No. 6277088 Japanese Patent Application Laid-Open No. 2017-227720 Japanese Patent Application Laid-Open No. 7-120679

[0008] According to the inventors' research, when an infrared light reflecting element is placed in the optical path of an image display device such as a virtual reality (VR) head-mounted display to perform sensing such as eye tracking, facial expression recognition, iris authentication, face authentication, and blood flow monitoring, it has been found that with conventional dielectric multilayer reflective polarizers, the phase difference in the visible range can interfere with the correct display of visible light images. In contrast, cholesteric liquid crystals with a reflection band in the infrared range are preferable because they have a small phase difference in the visible range. However, there is room for improvement in the circular polarization purity of the reflected light. Increasing the circular polarization purity can suppress noise in infrared light sensing and increase detection sensitivity.

[0009] The present invention has been made in consideration of the above-mentioned problems, and the problem that the present invention aims to solve is to provide an infrared light reflecting element, a laminated optical film, and an optical article that have a high circular polarization purity of reflected light.

[0010] The present inventors have conducted extensive research into the above-mentioned problems and have found that the above-mentioned problems can be achieved by the following configuration.

[0011] [1] An infrared light reflecting element having an adhesive layer, a light interference layer, and at least one cholesteric liquid crystal layer, the center wavelength of the reflection band being in the range of 800 nm to 2500 nm, and the reflectance of light of the center wavelength being 20% ​​or more, wherein when the refractive index of the adhesive layer is nA and the average refractive index of the cholesteric liquid crystal layer adjacent to the light interference layer is nL, the refractive index nI of the light interference layer is (nA×nL) １／２ −0.03≦nI≦(nA×nL) １／２+0.03, and the film thickness of the light interference layer is within ±30% of the λ / 4 condition or within ±30% of the 3λ / 4 condition with respect to the center wavelength λ of the reflection band. [2] The at least one or more cholesteric liquid crystal layers constitute one or more laminated reflective layers, and the laminated reflective layer includes a reflective layer A containing at least one cholesteric liquid crystal layer formed using a substantially rod-shaped liquid crystal compound and not containing a cholesteric liquid crystal layer formed using a substantially discotic liquid crystal compound, and a reflective layer B containing at least one cholesteric liquid crystal layer formed using a substantially discotic liquid crystal compound and not containing a cholesteric liquid crystal layer formed using a substantially rod-shaped liquid crystal compound, and the adhesive layer, the light interference layer, and the laminated reflective layer are adjacent in this order, and when the refractive index of the adhesive layer is nA and the average refractive index of the reflective layer A and the reflective layer B of the laminated reflective layer adjacent to the light interference layer is nL, the refractive index nI of the light interference layer is (nA x nL) １／２ −0.03≦nI≦(nA×nL) １／２ +0.03, and the film thickness of the optical interference layer is within ±30% of the λ / 4 condition or within ±30% of the 3λ / 4 condition with respect to the center wavelength λ of the reflection band. [3] The infrared light reflecting element according to [2], wherein, in one laminated reflective layer, the direction of rotation of the helical structure of all the cholesteric liquid crystal layers contained in reflective layer A is the same as the direction of rotation of the helical structure of all the cholesteric liquid crystal layers contained in reflective layer B. [4] The infrared light reflecting element according to any of [1] to [3], wherein the optical interference layer is a photo-alignment film. [5] The infrared light reflecting element according to any of [1] to [3], wherein the optical interference layer is a C-plate. [6] The infrared light reflecting element according to any of [1] to [5], wherein the infrared light reflecting element has a transmittance of 80% or more for light with a wavelength of 550 nm. [7] A laminated optical film having the infrared light reflecting element according to any one of [1] to [6] and a retardation layer. [8] An optical article having the infrared light reflecting element according to any one of [1] to [6] and a lens. [9] An optical article having the infrared light reflecting element according to any one of [1] to [6] and a prism or a substrate.

[0012] According to the present invention, it is possible to provide an infrared light reflecting element, a laminated optical film, and an optical article that have a high circular polarization purity of reflected light.

[0013] It is a schematic diagram showing an example of an infrared light reflecting element of the present invention. It is a schematic diagram showing another example of an infrared light reflecting element of the present invention. It is a schematic diagram showing an example of a laminated optical film of the present invention. It is a schematic diagram showing an example of a head-mounted display having the infrared light reflecting element of the present invention.

[0014] The present invention will be described in detail below. The following description of the constituent elements may be based on representative embodiments and specific examples, but the present invention is not limited to such embodiments. In this specification, a numerical range expressed using "to" means a range that includes the numerical values ​​before and after "to" as the lower and upper limits. In this specification, terms such as "the same" include a generally accepted error range in the technical field, for example, a range of ±5%.

[0015] In this specification, "orthogonal" does not mean an angle of exactly 90°, but means 90°±10°, preferably 90°±5°. "Parallel" does not mean an angle of exactly 0°, but means 0°±10°, preferably 0°±5°. "45°" does not mean an angle of exactly 45°, but means 45°±10°, preferably 45°±5°.

[0016] In this specification, "absorption axis" refers to the polarization direction in which absorbance is maximized in a plane when linearly polarized light is incident. "Reflection axis" refers to the polarization direction in which reflectance is maximized in a plane when linearly polarized light is incident. "Transmission axis" refers to the direction perpendicular to the absorption axis or reflection axis in a plane. "Slow axis" refers to the direction in which refractive index is maximized in a plane.

[0017] In this specification, unless otherwise specified, phase difference refers to in-plane retardation, and is referred to as Re(λ). Here, Re(λ) represents the in-plane retardation at a wavelength λ, and unless otherwise specified, the wavelength λ is 550 nm. Furthermore, in this specification, the retardation in the thickness direction at a wavelength λ is referred to as Rth(λ). Unless otherwise specified, the wavelength λ is 550 nm. Re(λ) and Rth(λ) can be values ​​measured at a wavelength λ using an AxoScan OPMF-1 (manufactured by OptoScience). By inputting the average refractive index ((nx + ny + nz) / 3) and film thickness (d (μm)) into AxoScan, the slow axis direction (°) Re(λ) = R0(λ) and Rth(λ) = ((nx + ny) / 2 - nz) × d can be calculated.

[0018] Here, in this specification, "mutually orthogonal polarization states" refers to polarization states located at antipodes on the Poincaré sphere, such as linearly polarized light that is orthogonal to each other. Generally, right-handed circularly polarized light and left-handed circularly polarized light are not referred to as "mutually orthogonal polarization states," but in this specification, right-handed circularly polarized light and left-handed circularly polarized light are also interpreted as being in mutually orthogonal polarization states.

[0019] The infrared light reflecting element of the present invention will be described below.

[0020] [Infrared Light Reflecting Element] The infrared light reflecting element of the present invention has an adhesive layer, a light interference layer, and at least one cholesteric liquid crystal layer, has a central wavelength of a reflection band within a range of 800 nm to 2500 nm, and has a reflectance of light at the central wavelength of 20% or more, wherein when the refractive index of the adhesive layer is nA and the average refractive index of the cholesteric liquid crystal layer adjacent to the light interference layer is nL, the refractive index nI of the light interference layer satisfies (nA×nL)½−0.03≦nI≦(nA×nL)½+0.03, and the film thickness of the light interference layer is within ±30% of the λ / 4 condition or within ±30% of the 3λ / 4 condition with respect to the central wavelength λ of the reflection band.

[0021] The infrared light reflecting element of the present invention preferably transmits visible light. Specifically, the infrared light reflecting element preferably has a transmittance of 50% to 100%, more preferably 80% to 100%, for light with a wavelength of 380 nm or more and less than 780 nm. The transmittance can be measured using a spectrophotometer UV3150 (Shimadzu Corporation).

[0022] The infrared light reflecting element of the present invention will be described with reference to the drawings. Fig. 1 is a schematic cross-sectional view showing an example of the configuration of an infrared light reflecting element 10. In the embodiment shown in Fig. 1, the infrared light reflecting element 10 is composed of a first laminated reflective layer 25, an optical interference layer 27, and an adhesive layer 28, and the first laminated reflective layer 25 is composed of a reflective layer A 21a and a reflective layer B 22b. In the infrared light reflecting element 10 of the embodiment shown in Fig. 1, the adhesive layer 28, the optical interference layer 27, the reflective layer A 21a, and the reflective layer B 22b are laminated in this order.

[0023] 1, the reflective layer A 21a and the reflective layer B 22b each include a cholesteric liquid crystal layer. Therefore, in the example shown in Fig. 1, at least two cholesteric liquid crystal layers are included. In this case, the average refractive index of the cholesteric liquid crystal layer included in the reflective layer A 21a adjacent to the optical interference layer 27 is defined as nL, and the refractive index nI of the optical interference layer 27 satisfies the above formula.

[0024] In a preferred embodiment, the reflective layer A21a includes at least one cholesteric liquid crystal layer formed using a substantially rod-shaped liquid crystal compound (hereinafter also referred to as a first liquid crystal compound) and does not include a cholesteric liquid crystal layer formed using a substantially discotic liquid crystal compound (hereinafter also referred to as a second liquid crystal compound). Therefore, the reflective layer A21a has a positive thickness retardation Rth. On the other hand, the reflective layer B22b includes at least one cholesteric liquid crystal layer formed using a substantially discotic liquid crystal compound and does not include a cholesteric liquid crystal layer formed using a substantially rod-shaped liquid crystal compound. Therefore, the reflective layer B22b has a negative thickness retardation Rth. The reflective layer A and the reflective layer B will be described later.

[0025] In the present invention, the refractive index and film thickness of the optical interference layer are set to satisfy the above relationship, thereby providing an anti-reflection effect. This makes it possible to suppress changes in the rotation direction of circularly polarized light caused by interfacial reflection (for example, right-handed circularly polarized light being converted to left-handed circularly polarized light by interfacial reflection). Since changes in the rotation direction of circularly polarized light caused by interfacial reflection are one of the causes of a decrease in the circular polarization purity, it is believed that suppressing interfacial reflection can suppress a decrease in the circular polarization purity.

[0026] In addition, when the infrared light reflecting element of the present invention has the above-described configuration, since reflective layer A has a positive Rth and reflective layer B has a negative Rth, the Rths of the two layers are offset, which is thought to suppress a decrease in the circular polarization purity even for light incident from an oblique direction. While FIG. 1 illustrates a laminated reflective layer configuration of reflective layer A and reflective layer B, the present invention is not limited to this configuration. The infrared light reflecting element of the present invention may have at least one cholesteric liquid crystal layer. For example, only reflective layer A or only reflective layer B may be used. The reflective layer A or B may preferably be configured as described below. Furthermore, in the case of a laminated reflective layer, at least two cholesteric liquid crystal layers are used. The infrared light reflecting element of the present invention has a reflection band with a center wavelength in the range of 800 nm to 2500 nm, preferably in the range of 820 nm to 1500 nm, and more preferably in the range of 840 nm to 1100 nm. The method for measuring the reflection band center wavelength is the same as the method for measuring the reflection band center wavelength of liquid crystal layer 1 described below. The reflectance of light at the central wavelength is 20% or more, and the reflectance of incident unpolarized (non-polarized) light is preferably 20% to 50%, more preferably 30% to 50%, and most preferably 40% to 50%.

[0027] [Laminated Reflective Layer] The infrared light reflecting element of the present invention preferably has one or more laminated reflective layers each containing one reflective layer A and one reflective layer B, which will be described in detail later. That is, the infrared light reflecting element of the present invention preferably contains one or more reflective layers A and one or more reflective layers B. In the laminated reflective layer, the reflective layer A and the reflective layer B may be in direct contact with each other, or the reflective layer A and the reflective layer B may be laminated via another layer. In particular, the laminated reflective layer is preferably configured such that one reflective layer A and one reflective layer B are in direct contact with each other. The other layers are not particularly limited, but include an adhesion layer (for example, an adhesive layer, a pressure-sensitive adhesive layer, etc.), a refractive index adjustment layer, a resin film, a positive C plate, and an alignment layer.

[0028] The infrared light reflecting element of the present invention preferably includes one or more laminated reflective layers, but may include two or more, or even three or more, laminated reflective layers. That is, the infrared light reflecting element preferably includes one or more reflective layers A and B, but may include two or more, or even three or more, of the reflective layers A and B. The total number of laminated reflective layers included in the infrared light reflecting element is preferably 30 or less, more preferably 20 or less, and even more preferably 10 or less. That is, the total number of reflective layers A and B of the infrared light reflecting element is preferably 60 or less, more preferably 40 or less, and more preferably 20 or less.

[0029] The thickness of the laminated reflective layer is preferably 0.2 μm or more, more preferably 0.4 μm or more, and even more preferably 0.6 μm or more. The thickness of the laminated reflective layer is preferably 20.0 μm or less, more preferably 14.0 μm or less, and even more preferably 10.0 μm or less. The thickness of the laminated reflective layer can be measured in the same manner as for the reflective layer A and the reflective layer B described later.

[0030] The laminated reflective layer may be laminated so that the reflective layer A and the reflective layer B are alternately arranged in the infrared light reflecting element, so that the reflective layers A face each other, or so that the reflective layers B face each other. For example, when the infrared light reflecting element has two laminated reflective layers, the layers may be laminated in the order of reflective layer A, reflective layer B, reflective layer A and reflective layer B, or the order of reflective layer A, reflective layer B, reflective layer B and reflective layer A, or the order of reflective layer B, reflective layer A, reflective layer A and reflective layer B, or the order of reflective layer B, reflective layer A, reflective layer B and reflective layer A. However, when the reflective layers A of two adjacent laminated reflective layers in the stacking direction face each other (for example, when the layers are stacked in the order of reflective layer B, reflective layer A, reflective layer A, and reflective layer B), the central wavelengths of the reflection bands of the reflective layers A included in the two adjacent laminated reflective layers are different, and when the reflective layers B of two adjacent laminated reflective layers in the stacking direction face each other (for example, when the layers are stacked in the order of reflective layer A, reflective layer B, reflective layer B, and reflective layer A), the central wavelengths of the reflection bands of the reflective layers B included in the two adjacent laminated reflective layers are different.

[0031] Hereinafter, an infrared light reflecting element in which the reflective layers A of two adjacent laminated reflective layers in the lamination direction face each other will be described with reference to the drawings. The infrared light reflecting element 11 shown in FIG. 2 is composed of a first laminated reflective layer 25, a second laminated reflective layer 26, an optical interference layer 27, and an adhesive layer 28. The first laminated reflective layer 25 is composed of a reflective layer B21b and a reflective layer A22a, and the second laminated reflective layer 26 is composed of a reflective layer A23a and a reflective layer B24b. In the infrared light reflecting element 11 of the embodiment shown in FIG. 2, the adhesive layer 28, the optical interference layer 27, the reflective layer B21b, the reflective layer A22a, the reflective layer A23a, and the reflective layer B24b are laminated in this order. However, the center wavelength of the reflection band of the reflective layer A22a is different from the center wavelength of the reflection band of the reflective layer A23a. In addition, in the infrared light reflecting element 11 shown in FIG. 2 , the reflective layer A 22a is included in the first stacked reflective layer 25, and the reflective layer A 23a is included in the second stacked reflective layer 26. That is, as described in detail below, the reflective layer A may include two or more liquid crystal layers 1 having different central wavelengths of reflected light. However, in the infrared light reflecting element, when two or more liquid crystal layers 1 are arranged consecutively, the reflective layer A and the stacked reflective layer are arranged so that the number of stacked reflective layers is maximized. Similarly, as described in detail below, the reflective layer B may include two or more liquid crystal layers 2 having different central wavelengths of reflection bands. However, in the infrared light reflecting element, when two or more liquid crystal layers 2 are arranged consecutively, the reflective layer B and the stacked reflective layer are arranged so that the number of stacked reflective layers is maximized. Among these, the stacked reflective layer is preferably arranged so that the reflective layer A and the reflective layer B are alternately arranged. That is, a preferred embodiment is one in which the reflective layer A and the reflective layer B are alternately arranged in the thickness direction of the infrared light reflecting element.

[0032] The reflective layer A and the reflective layer B will be described below.

[0033] [Reflective Layer A] The laminated reflective layer included in the infrared light reflecting element of the present invention preferably includes a reflective layer A that includes at least one liquid crystal layer 1 but does not include a liquid crystal layer 2. The liquid crystal layer 1 is a cholesteric liquid crystal layer formed using a first liquid crystal compound that is substantially a rod-shaped liquid crystal compound, and is substantially composed of rod-shaped liquid crystal compounds. Note that the "cholesteric liquid crystal layer formed using substantially rod-shaped liquid crystal compounds" refers to a layer in which the first liquid crystal compound is in a cholesteric liquid crystal phase and the orientation state of the cholesteric liquid crystal phase is fixed. The term "substantially composed of rod-shaped liquid crystal compounds" refers to a layer in which the rod-shaped liquid crystal compounds account for 95% by mass or more of the liquid crystal compounds (first liquid crystal compounds) included in the liquid crystal layer 1. In other words, the term "first liquid crystal compound substantially composed of rod-shaped liquid crystal compounds" means that the content of the rod-shaped liquid crystal compounds is 95% by mass or more relative to the total mass of the first liquid crystal compounds. In particular, the first liquid crystal compound is preferably composed solely of rod-shaped liquid crystal compounds. Furthermore, the liquid crystal layer 2 is a cholesteric liquid crystal layer formed using a second liquid crystal compound that is substantially a discotic liquid crystal compound, and is substantially composed of a discotic liquid crystal compound. The term "cholesteric liquid crystal layer formed substantially using a discotic liquid crystal compound" refers to a layer in which the second liquid crystal compound is in a cholesteric liquid crystal phase and the orientation state of the cholesteric liquid crystal phase is fixed. The term "substantially composed of a discotic liquid crystal compound" refers to the fact that the discotic liquid crystal compound accounts for 95% by mass or more of the liquid crystal compounds (second liquid crystal compounds) contained in the liquid crystal layer 2. In other words, the term "second liquid crystal compound substantially composed of a discotic liquid crystal compound" means that the content of the discotic liquid crystal compound is 95% by mass or more of the total mass of the second liquid crystal compound. It is particularly preferable that the second liquid crystal compound consists solely of a discotic liquid crystal compound.

[0034] The reflective layer A may include one or more liquid crystal layers 1, or may include two or more liquid crystal layers 1. When the reflective layer A includes two or more liquid crystal layers 1, layers other than the liquid crystal layer 2 may or may not be included between the two or more liquid crystal layers 1. Examples of such layers include, but are not limited to, an adhesion layer (e.g., an adhesive layer, a pressure-sensitive adhesive layer, etc.), a refractive index adjustment layer, a resin film, a positive C plate, and an alignment layer. The number of liquid crystal layers 1 included in the reflective layer A is preferably five or fewer, more preferably three or fewer, and even more preferably two or fewer. The number of liquid crystal layers 1 included in the reflective layer A is preferably one. For example, when two liquid crystal layers 1 have different center wavelengths in their reflection bands, they are considered to be two liquid crystal layers 1. Furthermore, when the center wavelengths of the reflection bands of two or more liquid crystal layers 1 are the same, they are considered to be one liquid crystal layer 1, even if they are formed by sequential coating or are separated by the other layers.

[0035] When the reflective layer A includes two or more liquid crystal layers 1, the central wavelength of the reflection band of the reflective layer A is the central wavelength of the reflection band of the entire reflective layer A. The method for measuring the central wavelength of the reflection band will be described later.

[0036] The thickness of the reflective layer A is preferably 0.1 μm or more, more preferably 0.2 μm or more, and even more preferably 0.3 μm or more. The thickness of the reflective layer A is preferably 10.0 μm or less, more preferably 7.0 μm or less, and even more preferably 5.0 μm or less, in order to further suppress the decrease in circular polarization purity. The thickness of the reflective layer A can be measured by preparing a cross-section of the infrared light reflecting element and observing it with a scanning electron microscope. The thickness of the reflective layer A is the value obtained by averaging the thicknesses of the reflective layer A at any five points on the cross-section of the infrared light reflecting element. When the cross-section of the infrared light reflecting element is observed with a scanning electron microscope, the region of the reflective layer A and the region of the reflective layer B described below can be distinguished by the difference in contrast of the captured image. Furthermore, the reflective layer A and the reflective layer B can also be distinguished by using composition analysis in the film thickness direction by time-of-flight secondary ion mass spectrometry (TOF-SIMS).

[0037] The Rth of the reflective layer A is preferably 8 to 800 nm, more preferably 16 to 560 nm, and even more preferably 24 to 400 nm at a wavelength of 550 nm. The Rth of the reflective layer A may be measured by taking out only the reflective layer A from the infrared light reflecting element, or may be measured by measuring the Rth of a layer prepared under the same conditions as when the reflective layer A is prepared.

[0038] The rod-shaped liquid crystal compound contained in the liquid crystal layer 1 is not particularly limited, and known rod-shaped liquid crystal compounds can be used. Furthermore, the liquid crystal layer 1 may be any layer in which the orientation of the rod-shaped liquid crystal compound in a cholesteric liquid crystal phase is maintained. Typically, the liquid crystal layer 1 can be formed by aligning a polymerizable rod-shaped liquid crystal compound having a polymerizable group in a cholesteric liquid crystal phase by adding a chiral agent or the like, and then polymerizing and curing the compound by ultraviolet irradiation, heating, or the like to form a layer with no fluidity. The liquid crystal layer 1 formed as described above may be any layer whose orientation is not affected by external fields, external forces, or the like. It is sufficient for the liquid crystal layer 1 to maintain the optical properties of the cholesteric liquid crystal phase, and the rod-shaped liquid crystal compound in the liquid crystal layer 1 may no longer exhibit liquid crystallinity. For example, the polymerizable rod-shaped liquid crystal compound may be polymerized by a curing reaction and no longer have liquid crystallinity.

[0039] The central wavelength λ of the reflected light of the liquid crystal layer 1 depends on the pitch P (= helical period) of the helical structure in the cholesteric liquid crystal phase, and is expressed by the relationship λ = n × P, where n is the average refractive index of the liquid crystal layer 1. The central wavelength of the reflection band of the liquid crystal layer 1 can be determined as follows. When the reflection spectrum of the reflective layer A is measured from the normal direction of the liquid crystal layer 1 using a spectrophotometer V-670 (manufactured by JASCO Corporation), a spectrum having a peak where the reflectance increases in the region near the central wavelength of the reflection band is obtained. Of these, the value of the wavelength on the shorter wavelength side of the two wavelengths at which the reflectance is half the value of the largest peak is determined as λ ｌ (nm), and the wavelength on the long wavelength side is λ ｈ (nm), the central wavelength λ of the reflection band is calculated by the following formula: λ = (λ ｌ +λ ｈ ) / 2

[0040] The pitch of the cholesteric liquid crystal phase varies depending on the type and concentration of the chiral agent used together with the polymerizable rod-like liquid crystal compound, and a cholesteric liquid crystal phase with a desired pitch can be obtained by adjusting one or more of the above. Regarding the method for measuring the helical direction and pitch, the methods described in "Introduction to Liquid Crystal Chemistry Experiments" edited by the Japanese Liquid Crystal Society, published by Sigma Publishing in 2007, page 46, and "Liquid Crystal Handbook" edited by the Liquid Crystal Handbook Editorial Committee, published by Maruzen, page 196, can be used.

[0041] [Reflective Layer B] The laminated reflective layer included in the infrared light reflecting element of the present invention preferably includes a reflective layer B that includes at least one liquid crystal layer 2 and does not include a liquid crystal layer 1. The definitions of the liquid crystal layer 2 and the liquid crystal layer 1 are as described above.

[0042] The reflective layer B may include one or more liquid crystal layers 2, or may include two or more liquid crystal layers 2. When the reflective layer B includes two or more liquid crystal layers 2, layers other than the liquid crystal layer 1 may or may not be included between the two or more liquid crystal layers 2. Examples of such layers include, but are not limited to, an adhesion layer (e.g., an adhesive layer, a pressure-sensitive adhesive layer, etc.), a refractive index adjustment layer, a resin film, a positive C plate, and an alignment layer. The number of liquid crystal layers 2 included in the reflective layer B is preferably five or fewer, more preferably three or fewer, and even more preferably two or fewer. The number of liquid crystal layers 2 included in the reflective layer B is preferably one. Note that, for example, when two liquid crystal layers 2 have different center wavelengths in their reflection bands, they are considered to be two liquid crystal layers 2. Furthermore, when the center wavelengths of the reflection bands of two or more liquid crystal layers 2 are the same, they are considered to be one liquid crystal layer 2, even if they are formed by sequential coating or are separated by the other layers.

[0043] When the reflective layer B includes two or more liquid crystal layers 2, the central wavelength of the reflection band of the reflective layer B is the central wavelength of the reflection band of the entire reflective layer B. The central wavelength of the reflection band of each liquid crystal layer 2 is measured in accordance with the method for measuring the central wavelength of the reflection band of the liquid crystal layer 1 described above.

[0044] The thickness of the reflective layer B is preferably 0.1 μm or more, more preferably 0.2 μm or more, and even more preferably 0.3 μm or more. The thickness of the reflective layer B is preferably 10.0 μm or less, more preferably 7.0 μm or less, and even more preferably 5.0 μm or less, in order to further suppress the decrease in circular polarization purity. The thickness of the reflective layer B can be measured by preparing a cross section of the infrared light reflecting element and observing it with a transmission electron microscope.

[0045] The Rth of the reflective layer B is preferably −8 to −800 nm, more preferably −16 to −560 nm, and even more preferably −24 to −400 nm at a wavelength of 550 nm. The Rth of the reflective layer B may be measured by extracting only the reflective layer B from the infrared light reflecting element, or may be measured by measuring the Rth of a layer prepared under the same conditions as when the reflective layer B is prepared.

[0046] The discotic liquid crystal compound contained in the liquid crystal layer 2 is not particularly limited, and any known discotic liquid crystal compound can be used. The liquid crystal layer 2 may be any layer in which the alignment of a discotic liquid crystal compound in a cholesteric liquid crystal phase is maintained. Typically, the liquid crystal layer 2 can be formed by aligning a polymerizable discotic liquid crystal compound having a polymerizable group in a cholesteric liquid crystal phase by adding a chiral agent or the like, and then polymerizing and curing the compound by ultraviolet irradiation, heating, or the like to form a non-fluid layer. The liquid crystal layer 2 formed as described above may be any layer whose alignment state is not affected by external fields, external forces, or the like. It is sufficient for the liquid crystal layer 2 to maintain the optical properties of the cholesteric liquid crystal phase; the discotic liquid crystal compound in the liquid crystal layer 2 may no longer exhibit liquid crystallinity. For example, the polymerizable discotic liquid crystal compound may be polymerized by a curing reaction and no longer exhibit liquid crystallinity.

[0047] The central wavelength λ of the reflection band of the liquid crystal layer 2 depends on the pitch of the helical structure in the cholesteric liquid crystal phase, and can be defined in the same way as in the case of the liquid crystal layer 1 and measured in the same way.

[0048] The pitch of the cholesteric liquid crystal phase varies depending on the type and concentration of the chiral agent used together with the polymerizable discotic liquid crystal compound, and a cholesteric liquid crystal phase with a desired pitch can be obtained by adjusting one or more of the above. Note that the above-mentioned literature can be used as a reference for the method of measuring the helical direction and pitch.

[0049] The pitch of the cholesteric liquid crystal phase may also vary in the film thickness direction. The state in which the pitch varies in the film thickness direction is called a pitch gradient, and a layer in which the pitch varies in the film thickness direction is called a pitch gradient layer. The pitch gradient layer can be produced by a known method, for example, by referring to JP 2020-060627 A. In the pitch gradient layer, the helical pitch varies in the film thickness direction, and therefore light in multiple wavelength ranges (wide wavelength ranges) can be reflected.

[0050] [Types of Reflective Layer A and Reflective Layer B] The central wavelength of the reflection band of the reflective layer A and the reflective layer B is preferably in the range of 800 nm to 2500 nm, more preferably in the range of 820 nm to 1500 nm, and most preferably in the range of 840 nm to 1100 nm. The method for measuring the central wavelength of the reflection band is as described above. The reflectance when unpolarized light is incident on the reflective layer A and the reflective layer B is preferably 20% to 50%, more preferably 30% to 50%, and most preferably 40% to 50%. The central wavelength of the reflection band of each of the reflective layers A and B may be the same or different. Furthermore, the helical pitch of the reflective layer A and the reflective layer B preferably has the same winding direction (the direction of rotation of the helical structure). By having the same winding direction, the circular polarization purity of the reflected infrared light can be increased.

[0051] When one reflective layer A includes multiple liquid crystal layers 1, the twist directions of the helical structures in the cholesteric liquid crystal phases of the multiple liquid crystal layers 1 may be the same or different. When one reflective layer B includes multiple liquid crystal layers 2, the twist directions of the helical structures in the cholesteric liquid crystal phases of the multiple liquid crystal layers 2 may be the same or different. Therefore, when liquid crystal layers 1 with different twist directions of the helical structures are successively arranged in an infrared light reflecting element, the reflective layer A and the stacked reflective layers are arranged so that the number of stacked reflective layers is maximized. Similarly, when liquid crystal layers 2 with different twist directions of the helical structures are successively arranged in an infrared light reflecting element, the reflective layer B and the stacked reflective layers are arranged so that the number of stacked reflective layers is maximized.

[0052] In the present invention, it is preferable that the reflective layers A and B constituting one laminated reflective layer reflect circularly polarized light having the same rotation direction. That is, in one laminated reflective layer, it is preferable that the rotation direction of the helical structure of all the cholesteric liquid crystal layers contained in the reflective layer A is the same as the rotation direction of the helical structure of all the cholesteric liquid crystal layers contained in the reflective layer B. Furthermore, in a configuration having a plurality of laminated reflective layers, it is sufficient that the circularly polarized light reflected by the reflective layers A and B is the same for each laminated reflective layer. That is, it is sufficient that the reflective layers A and B constituting one laminated reflective layer reflect the same circularly polarized light, and the reflective layers A and B constituting another laminated reflective layer reflect the same circularly polarized light, and the rotation directions of the circularly polarized light reflected by one laminated reflective layer and the circularly polarized light reflected by the other laminated reflective layer may be the same or different.

[0053] In one embodiment of the infrared light reflecting element of the present invention, the reflective layer A has a positive Rth, whereas the reflective layer B has a negative Rth, so that the Rths of the reflective layers are offset. This will be described in detail below. In an infrared light reflecting element having n reflective layers, the reflective layers are arranged in order from the light source side as L １ , L ２ , L ３ , ..., L ｎ (n is an integer of 4 or more), the reflective layer L １ to the reflective layer L ｉThe sum of Rth of each layer up to (i is an integer equal to or less than n) is SRth ｉ Specifically, SRth ｉ is expressed as follows: SRth １ = Rth １ SRth ２ = Rth １ +Rth ２ ... SRth ｉ = Rth １ +Rth ２ +...+Rth ｉ ... SRth ｎ = Rth １ +Rth ２ +...+Rth ｉ +...+Rth ｎ All these SRth ｉ (SRth １ ~SRth ｎ The absolute values ​​of Rth of each layer in the above formula are preferably 0.3 μm or less, more preferably 0.2 μm or less, and even more preferably 0.1 μm or less. ｉ is calculated by the above-described formula for calculating Rth. ｉ By setting the value of the refractive index within the above preferred range, it is believed that the phase difference that occurs when light passes through each reflective layer can be reduced, and the decrease in the purity of circular polarization can be suppressed even for light incident from an oblique direction.

[0054] Furthermore, in the laminated reflective layer, when the reflective layer A and the reflective layer B are configured to be in direct contact with each other, it is preferable to arrange them so that the alignment direction (slow axis direction) of the liquid crystal compound (rod-shaped liquid crystal compound or discotic liquid crystal compound) changes continuously at the interface in order to reduce the difference in refractive index. For example, when the reflective layer A is formed on the reflective layer B, the above-mentioned arrangement can be achieved by directly applying a coating liquid containing a rod-shaped liquid crystal compound onto the reflective layer B, and aligning the slow axis direction so that it is continuous at the interface due to the alignment control force of the discotic liquid crystal compound contained in the reflective layer B.

[0055] The thickness of the infrared light reflecting element of the present invention is preferably 30 μm or less, more preferably 15 μm or less. There is no particular lower limit, but the thickness is, for example, 1 μm or more, preferably 5 μm or more.

[0056] The method for producing the infrared light reflecting element of the present invention will be explained later.

[0057] [Light interference layer] The infrared light reflecting element of the present invention includes a light interference layer. The refractive index of the light interference layer preferably satisfies the following condition. That is, when the refractive index of the adhesive layer adjacent to the light interference layer is nA and the average refractive index of the cholesteric liquid crystal layer adjacent to the light interference layer is nL, the refractive index nI of the light interference layer is (nA x nL). １／２ −0.03≦nI≦(nA×nL) １／２ +0.03, (nA x nL) １／２ −0.02≦nI≦(nA×nL) １／２ +0.02, (nA × nL) １／２ −0.01≦nI≦(nA×nL) １／２ It is more preferable that the refractive index is +0.01. In this case, the refractive index is the refractive index of the central wavelength of the reflection band. For example, if the central wavelength of the reflection band is 900 nm, the refractive index is the value at a wavelength of 900 nm. Furthermore, when at least one or more cholesteric liquid crystal layers are one or more laminated reflective layers, when the refractive index of the adhesive layer adjacent to the optical interference layer is nA, and the average refractive index of the reflective layer A and reflective layer B of the laminated reflective layer adjacent to the optical interference layer is nL, the refractive index nI of the optical interference layer is (nA x nL). １／２ −0.03≦nI≦(nA×nL) １／２ +0.03, (nA × nL) １／２ −0.02≦nI≦(nA×nL) １／２ +0.02 is more preferable, (nA × nL) １／２ −0.01≦nI≦(nA×nL) １／２It is even more preferable that the refractive index is +0.01. Both reflective layer A and reflective layer B of the laminated reflective layer may be adjacent to the optical interference layer. "The average refractive index of the reflective layer A or reflective layer B adjacent to the optical interference layer is nL" means that when reflective layer A is adjacent to the optical interference layer, the average refractive index of reflective layer A is nL, and when reflective layer B is adjacent to the optical interference layer, the average refractive index of reflective layer B is nL. Furthermore, when the reflective layer contains multiple cholesteric liquid crystal layers, the average refractive index of one cholesteric liquid crystal layer adjacent to the optical interference layer is nL. By setting the refractive index of the optical interference layer within this range, the amplitude reflectance on both sides of the optical interference layer can be made approximately equal, which is believed to result in a significant anti-reflection effect. This can suppress changes in the rotation direction of circularly polarized light caused by interfacial reflection (for example, right-handed circularly polarized light is converted to left-handed circularly polarized light by interfacial reflection). Since changes in the rotation direction of circularly polarized light caused by interfacial reflection are one of the causes of a decrease in circular polarization purity, suppressing interfacial reflection is believed to suppress a decrease in circular polarization purity. The refractive indices of the optical interference layer and adhesive layer were measured using an interference film thickness meter (OPTM) (manufactured by Otsuka Electronics, analyzed using the least squares method). The average refractive index of the reflective layer was measured using the following method. First, the reflective layer adjacent to the adhesive layer was peeled off and the cross section of the reflective layer was observed using a scanning electron microscope (SEM) to obtain the helical pitch P. The helical pitch P is two periods of the light and dark stripes that appear in the SEM image. Next, a reflection spectrum (manufactured by JASCO Corporation, UV-Visible-Near-Infrared Spectrophotometer V-750) was measured to obtain the short-wavelength half-maximum wavelength λl and the long-wavelength half-maximum wavelength λh of the reflection band of the reflective layer. Using the helical pitch P and the half-maximum wavelengths λl and λh, the refractive indices of the reflective layer in two directions, nl = λl / P and nh = λh / P, can be obtained. From this, the average refractive index of the reflective layer, nI = (nl + nh) / 2, was obtained.

[0058] Furthermore, the film thickness of the optical interference layer is preferably within ±30% of the λ / 4 condition of the central wavelength of the reflection band, or within ±30% of the 3λ / 4 condition. The λ / 4 condition is a film thickness where the film thickness is expressed by wavelength ÷ 4 ÷ the refractive index at the central wavelength of the reflection band. Similarly, the 3λ / 4 condition is a film thickness where the film thickness is expressed by wavelength ÷ 4 / 3 ÷ the refractive index at the central wavelength of the reflection band. In this case, it is more preferable that the film thickness is within ±20% of the λ / 4 condition or within ±20% of the 3λ / 4 condition, and most preferably within ±10%.

[0059] Furthermore, the infrared light reflecting element preferably has a surface roughness Ra of 100 nm or less. A small Ra can improve the sharpness of images, for example, when the infrared light reflecting element is used in a virtual reality display device or the like. The inventors have estimated that when light is transmitted or reflected by the infrared light reflecting element, if there are irregularities, the angle of the transmitted or reflected light is distorted, leading to image distortion and blurring. The Ra of the infrared light reflecting element is more preferably 50 nm or less, even more preferably 30 nm or less, and particularly preferably 10 nm or less. The infrared light reflecting element of the present invention is fabricated by stacking multiple layers. According to the inventors' studies, it has been found that stacking another layer on an irregular layer can amplify the irregularities. Therefore, in the infrared light reflecting element of the present invention, it is preferable that all layers have a small Ra. Each layer of the infrared light reflecting element of the present invention preferably has an Ra of 50 nm or less, more preferably 30 nm or less, and even more preferably 10 nm or less. The surface roughness Ra can be measured, for example, using a non-contact surface / layer cross-sectional shape measurement system, VertScan (manufactured by Ryoka Systems Co., Ltd.). Since VertScan is a surface shape measurement method that utilizes the phase of reflected light from a sample, when measuring an optical film (the above-mentioned infrared light reflecting element) consisting of a reflective layer with a fixed cholesteric liquid crystal phase, reflected light from within the film may be superimposed, making it impossible to accurately measure the surface shape. In this case, a metal layer may be formed on the surface of the sample to increase the surface reflectance and further suppress reflection from within. A sputtering method, for example, is used to form a metal layer on the surface of the sample. Examples of sputtering materials include Au, Al, and Pt.

[0060] The infrared light reflecting element of the present invention preferably has a small number of point defects per unit area. Since the infrared light reflecting element of the present invention is fabricated by stacking multiple layers, it is preferable that the number of point defects in each layer is also small in order to reduce the number of point defects in the entire infrared light reflecting element. Specifically, the number of point defects in each layer is preferably 20 or less per square meter, more preferably 10 or less, and even more preferably 1 or less. For the entire infrared light reflecting element, the number of point defects is preferably 100 or less per square meter, more preferably 50 or less, and even more preferably 5 or less. Point defects lead to a decrease in the degree of polarization of transmitted light and a decrease in image sharpness, so it is preferable that they are kept small. Here, point defects include foreign matter, scratches, dirt, film thickness fluctuations, poor alignment of liquid crystal compounds, etc. Furthermore, the number of point defects described above is preferably counted as the number of point defects with a size of 100 μm or more, more preferably 30 μm or more, and most preferably 10 μm or more.

[0061] [Material for interlayer photo-alignment film] The optical interference layer preferably contains a material for an interlayer photo-alignment film. This allows liquid crystal alignment when a liquid crystal material is applied onto the optical interference layer, and a structure in which the optical interference layer and the light reflecting layer are adjacent to each other can be formed. As the material for the interlayer photo-alignment film, the photo-alignable polymer described in JP 2021-143336 A can be used.

[0062] Materials for forming the optical interference layer include a hard coat material crosslinked from a monomer, a photo-alignment film, and a C-plate made of a liquid crystal material. Among these, the C-plate is more preferred because it also plays a role in optical compensation adjustment. A positive C-plate is even more preferred. Here, a positive C-plate is a retardation layer having an Re of substantially zero and a negative Rth. A positive C-plate can be obtained, for example, by vertically aligning a rod-shaped liquid crystal compound. Details of the manufacturing method of a positive C-plate can be found in, for example, JP 2017-187732 A, JP 2016-053709 A, and JP 2015-200861 A. The positive C-plate functions as an optical compensation layer to suppress a decrease in the degree of polarization of transmitted visible light when incident at an angle. The positive C-plate can be installed at any location on the infrared light reflecting element, and multiple plates may be installed. In this case, the Re of the C plate is preferably about 10 nm or less, and the Rth is preferably −100 to −1 nm, more preferably −30 to −5 nm.

[0063] [Adhesive Layer] The infrared light reflecting element of the present invention includes an adhesive layer. As the adhesive layer, any known adhesive and / or pressure-sensitive adhesive can be used as appropriate as long as it has a refractive index that satisfies the above-mentioned relational expression. For example, the adhesive and / or pressure-sensitive adhesive used in the laminated optical film described below can be used as appropriate.

[0064] [Method for Producing Infrared Light Reflecting Element] The infrared light reflecting element of the present invention can be produced by a known method, and the method is not particularly limited.

[0065] For example, the manufacturing method of the infrared light reflecting element can be as follows: (1) after forming a light interference layer having liquid crystal alignment function on a substrate, (2) after coating a composition containing a rod-shaped liquid crystal compound on the light interference layer to form a cholesteric liquid crystal phase, the alignment state of the cholesteric liquid crystal phase is fixed to form a first cholesteric liquid crystal layer, and (3) after coating a composition containing a discotic liquid crystal compound on the first cholesteric liquid crystal layer to form a cholesteric liquid crystal phase, the alignment state of the cholesteric liquid crystal phase is fixed to form a second cholesteric liquid crystal layer, and (3) after peeling the substrate at the interface between the substrate and the light interference layer, a pressure-sensitive adhesive sheet is attached as an adhesive layer on the light interference layer. Note that the first cholesteric liquid crystal layer corresponds to the reflective layer A, and the second cholesteric liquid crystal layer corresponds to the reflective layer B.

[0066] Furthermore, when the infrared light reflecting element of the present invention is stretched or molded to be molded into a curved surface for use, the reflection wavelength range may shift toward shorter wavelengths. Therefore, it is preferable to manufacture the infrared light reflecting element in advance, taking into account this wavelength shift. When using an infrared light reflecting element including a layer formed by fixing a cholesteric liquid crystal phase, the infrared light reflecting element may be stretched by stretching, molding, etc., which may result in a smaller helical pitch of the cholesteric liquid crystal phase. Therefore, it is preferable to set the helical pitch of the cholesteric liquid crystal phase to a large value in advance. Furthermore, in anticipation of a short-wave shift in the reflection wavelength range due to stretching, molding, etc., it is also preferable for the infrared light reflecting element to have an infrared light reflective layer with a reflectance of 40% or more at a wavelength of 1000 nm. Furthermore, if the stretching ratio during stretching, molding, etc. is not uniform within the plane, the infrared light reflecting element may be manufactured by selecting an appropriate reflection wavelength range at each location within the plane of the infrared light reflecting element in accordance with the wavelength shift due to stretching. That is, there may be regions within the plane of the infrared light reflecting element where the reflection wavelength range differs. It is also preferable to set the reflection wavelength range wider than the necessary wavelength range in advance, assuming that the stretching ratio will be different at different locations within the plane of the infrared light reflecting element.

[0067] Although the above describes a method of forming a cholesteric liquid crystal layer by applying the composition directly onto each cholesteric liquid crystal layer, the cholesteric liquid crystal layers may be formed by applying the composition to separate substrates, and the cholesteric liquid crystal layers may be laminated via an adhesive layer (e.g., an adhesive layer or a pressure-sensitive adhesive layer).

[0068] Any commercially available adhesive can be used as the adhesive for the adhesive layer. However, from the viewpoint of thinning and reducing the surface roughness Ra of the infrared light reflecting element, the thickness is preferably 25 μm or less, more preferably 15 μm or less, and most preferably 6 μm or less. Furthermore, it is preferable that the adhesive is less likely to outgas. In particular, when performing stretching and molding, a vacuum process and / or a heating process may be used, and it is preferable that the adhesive does not outgas even under these conditions. Any commercially available adhesive can be used as the adhesive for the adhesive layer, and for example, an epoxy resin adhesive or an acrylic resin adhesive can be used. From the viewpoint of thinning and reducing the surface roughness Ra of the infrared light reflecting element, the thickness of the adhesive is preferably 25 μm or less, more preferably 5 μm or less, and most preferably 1 μm or less. Furthermore, from the viewpoint of thinning the adhesive layer and applying the adhesive to the adherend with a uniform thickness, the viscosity of the adhesive is preferably 300 cP or less, more preferably 100 cP or less. Furthermore, when the adherend has surface irregularities, the pressure-sensitive adhesive and / or adhesive can be selected to have an appropriate viscoelasticity or thickness so as to embed the surface irregularities of the layer to be adhered, from the viewpoint of reducing the surface roughness Ra of the infrared light reflecting element. From the viewpoint of embedding the surface irregularities, the pressure-sensitive adhesive and / or adhesive preferably has a viscosity of 50 cP or more. Furthermore, the thickness is preferably greater than the height of the surface irregularities. As a method for adjusting the viscosity of the adhesive, for example, a method using an adhesive containing a solvent can be mentioned. In this case, the viscosity of the adhesive can be adjusted by adjusting the ratio of the solvent. Furthermore, the thickness of the adhesive can be further reduced by applying the adhesive to the adherend and then drying the solvent.

[0069] In a laminated optical film using an infrared light reflecting element, from the viewpoint of reducing reflection at the interface and suppressing a decrease in the degree of polarization of transmitted light, it is preferable that the pressure-sensitive adhesive or adhesive used to bond each layer has a small difference in refractive index with the adjacent layer. When viewed over the entire thickness direction, the cholesteric liquid crystal layer can be considered to have no in-plane retardation, but when viewed in a very thin region near the surface, the refractive index in the fast axis direction and the slow axis direction differ due to the presence of birefringence, and therefore the average refractive index n of the liquid crystal layer is determined by adding the refractive indexes in the fast axis direction and the slow axis direction and dividing the result by 2. ａｖｅ When the refractive index of the adjacent adhesive layer or bonding layer is n ａｖｅ The difference between the refractive index and the refractive index of the adhesive or pressure-sensitive adhesive is preferably 0.075 or less, more preferably 0.05 or less, and even more preferably 0.025 or less. The refractive index of the pressure-sensitive adhesive or adhesive can be adjusted by mixing, for example, titanium oxide fine particles or zirconia fine particles.

[0070] It is also preferable that the adhesive layer between each layer has a thickness of 100 nm or less. When the adhesive layer has a thickness of 100 nm or less, light is less sensitive to refractive index differences, thereby suppressing unnecessary reflection. The thickness of the adhesive layer is more preferably 50 nm or less, and even more preferably 30 nm or less. An example of a method for forming an adhesive layer having a thickness of 100 nm or less is a method of depositing a ceramic adhesive such as silicon oxide (SiOx layer) on the bonding surface. The bonding surface of the bonding member can be subjected to a surface modification treatment such as plasma treatment, corona treatment, or saponification treatment before bonding, or a primer layer can be applied. Furthermore, when there are multiple bonding surfaces, the type and / or thickness of the adhesive layer can be adjusted for each bonding surface. Specifically, an adhesive layer having a thickness of 100 nm or less can be formed, for example, by the following steps (1) to (3). (1) The layers to be laminated are bonded to a temporary support made of a glass substrate. (2) A SiOx layer having a thickness of 100 nm or less is formed on both the surface of the layer to be laminated and the surface of the layer to be laminated by vapor deposition or the like. Vapor deposition can be performed using, for example, a vapor deposition device manufactured by ULVAC (model number ULEYES) using SiOx powder as the vapor deposition source. It is also preferable to subject the surface of the formed SiOx layer to plasma treatment. (3) After the formed SiOx layers are bonded together, the temporary support is peeled off. The bonding is preferably performed at a temperature of, for example, 120°C.

[0071] The coating, adhesion, or lamination of each layer may be performed by roll-to-roll or sheet-fed. The roll-to-roll method is preferred from the viewpoint of improving productivity and reducing axial misalignment of each layer. On the other hand, the sheet-fed method is preferred because it is suitable for small-lot, high-mix production and because it allows the selection of a special adhesion method such as the above-mentioned adhesive layer thickness of 100 nm or less. Furthermore, examples of methods for applying the adhesive to the adherend include known methods such as roll coating, gravure printing, spin coating, wire bar coating, extrusion coating, direct gravure coating, reverse gravure coating, die coating, spraying, and inkjet printing.

[0072] The infrared light reflecting element of the present invention may include a support and an alignment layer, etc., but the support and alignment layer may be a temporary support that is peeled off and removed when producing the laminated optical film described below. When a temporary support is used, the infrared light reflecting element can be thinned by transferring the infrared light reflecting element to another laminate and then peeling off and removing the temporary support, which is preferable because it can eliminate the adverse effect that the retardation of the temporary support has on the polarization degree of transmitted light. The type of support is not particularly limited, but it is preferably transparent to visible light. For example, films such as cellulose acylate, polycarbonate, polysulfone, polyethersulfone, polyacrylate and polymethacrylate, cyclic polyolefin, polyolefin, polyamide, polystyrene, and polyester can be used. Among these, cellulose acylate film, cyclic polyolefin, polyacrylate, or polymethacrylate are preferred. Commercially available cellulose acetate films (e.g., "TD80U" or "Z-TAC" manufactured by Fujifilm Corporation) can also be used. When the support is a temporary support, a support with high tear strength is preferred from the viewpoint of preventing breakage during peeling. For example, polycarbonate and polyester films are preferred. Furthermore, the support preferably has a small retardation from the viewpoint of suppressing adverse effects on the polarization degree of transmitted light. Specifically, the magnitude of Re at 550 nm is preferably 10 nm or less, and the absolute value of the magnitude of Rth is preferably 50 nm or less. Furthermore, even if the support is used as the above-mentioned temporary support, it is preferred that the retardation of the temporary support is small in terms of performing quality inspection.

[0073] Furthermore, when an infrared light reflecting element is used in an optical system of a virtual reality display device, an electronic viewfinder, or the like for purposes such as eye tracking, facial expression recognition, or iris authentication, the infrared light reflecting element is preferably transparent to light in the visible range in order to minimize the impact on the image display of the virtual reality display device, the electronic viewfinder, or the like. The transmittance for visible light (wavelengths of 380 nm or more and less than 780 nm) is preferably 50% to 100%. The transmittance can be measured using a spectrophotometer UV3150 (Shimadzu Corporation).

[0074] [Applications of Infrared Light Reflecting Element] The infrared light reflecting element of the present invention is useful when incorporated into, for example, an image display device, a virtual reality display device such as a head-up display or a head-mounted display, an AR (Augmented Reality) glass, an electronic viewfinder, or the like, and is used as a reflective optical element that reflects only infrared light when optical sensing is performed using infrared light, because it can suppress the generation of noise and achieve high sensing sensitivity.

[0075] [Laminated optical film] The laminated optical film of the present invention has at least an infrared light reflecting element and a retardation layer in this order. The retardation layer is preferably capable of converting circularly polarized infrared light into linearly polarized light. The infrared light reflecting element is the infrared light reflecting element described above. Preferred embodiments of the infrared light reflecting element are as described above.

[0076] An example of the layer structure of the laminated optical film 100 of the present invention is shown in Figure 3. In the laminated optical film 100 shown in Figure 3, an infrared light reflecting element 101 and a retardation layer 102 are arranged in this order. The laminated optical film of the present invention has, in this order, an infrared light reflecting element 101 and a retardation layer 102 that converts circularly polarized light into linearly polarized light. Therefore, the laminated optical film 100 can be used as a linearly polarized light reflecting element that reflects infrared light by converting linearly polarized light incident from the retardation layer 102 side of the laminated optical film 100 into circularly polarized light and then incidenting the circularly polarized light on the infrared light reflecting element. Note that when the laminated optical film is stretched or molded, there is a concern that the slow axis of the retardation layer may be distorted. However, as described above, the infrared light reflecting element maintains a high degree of polarization even after stretching, molding, etc., and also maintains a high degree of polarization as a linearly polarized light reflecting element.

[0077] Furthermore, the laminated optical film of the present invention preferably has a surface roughness Ra of 100 nm or less. A small Ra can improve the sharpness of images, for example, when the laminated optical film is used in a virtual reality display device or the like. The present inventors have estimated that when light is reflected from the laminated optical film, unevenness distorts the angle of the reflected light, leading to image distortion and blurring. The Ra of the laminated optical film is more preferably 50 nm or less, even more preferably 30 nm or less, and particularly preferably 10 nm or less. The laminated optical film of the present invention is produced by laminating multiple layers. According to the inventors' studies, it has been found that laminating another layer on an uneven layer can amplify the unevenness. Therefore, in the laminated optical film of the present invention, it is preferable that all layers have a small Ra. Each layer of the laminated optical film of the present invention preferably has an Ra of 50 nm or less, more preferably 30 nm or less, and even more preferably 10 nm or less.

[0078] [Retardation Layer] The retardation layer used in the laminated optical film of the present invention preferably has the function of converting incident circularly polarized light into approximately linearly polarized light. For example, a retardation layer having an Re of approximately 1 / 4 wavelength at the center wavelength of the reflection band of the infrared light reflecting element can be used. For example, when the center wavelength of the reflection band of the infrared light reflecting element is 900 nm, the in-plane retardation Re (900) is preferably 195 nm to 255 nm, more preferably 205 nm to 245 nm, and even more preferably 215 nm to 235 nm. In addition, a retardation layer having an Re of approximately 3 / 4 wavelength or approximately 5 / 4 wavelength is also preferable because it can convert linearly polarized light into circularly polarized light.

[0079] In addition, the retardation layer used in the laminated optical film of the present invention preferably has reverse dispersion with respect to wavelength. Reverse dispersion is preferable because it makes it possible to convert circularly polarized light into linearly polarized light over a wide wavelength range. Here, having reverse dispersion with respect to wavelength means that the value of the retardation at that wavelength increases as the wavelength increases. A retardation layer having reverse dispersion can be produced by uniaxially stretching a polymer film such as a modified polycarbonate resin film having reverse dispersion, for example, with reference to JP 2017-049574 A. In addition, a retardation layer having reverse dispersion may be produced by substantially having reverse dispersion. For example, as disclosed in Japanese Patent No. 06259925 A, a retardation layer having an Re of approximately 1 / 4 wavelength and a retardation layer having an Re of approximately 1 / 2 wavelength can be produced by laminating them so that their slow axes form an angle of approximately 60 °. In this case, it is known that even if the 1 / 4 wavelength retardation layer and the 1 / 2 wavelength retardation layer each have normal dispersion (the retardation value at the wavelength decreases as the wavelength increases), circularly polarized light can be converted into linearly polarized light over a wide wavelength range, and it can be considered to have substantially reverse dispersion. In this case, it is preferable that the laminated optical film of the present invention has an infrared light reflecting element, a 1 / 4 wavelength retardation layer, and a 1 / 2 wavelength retardation layer in this order.

[0080] In addition, the retardation layer used in the laminated optical film of the present invention preferably has a layer formed by fixing a uniformly aligned liquid crystal compound. For example, a layer in which a rod-shaped liquid crystal compound is uniformly aligned horizontally relative to the in-plane direction, and a layer in which a discotic liquid crystal compound is uniformly aligned perpendicularly to the in-plane direction, etc. can be used. Furthermore, for example, referring to JP-A-2020-084070, a retardation layer having reverse dispersion can also be produced by uniformly aligning and fixing a rod-shaped liquid crystal compound having reverse dispersion.

[0081] In addition, the retardation layer used in the laminated optical film of the present invention also preferably has a layer that is made by fixing the liquid crystal compound that is twisted and aligned with thickness direction as helical axis.For example, as disclosed in Japanese Patent No. 05753922 and Japanese Patent No. 05960743, the retardation layer can also have a layer that is made by fixing the rod-shaped liquid crystal compound or discotic liquid crystal compound that is twisted and aligned with thickness direction as helical axis, and in this case, the retardation layer can be regarded as having substantially reverse dispersion, so it is preferable.

[0082] The thickness of the retardation layer is not particularly limited, but from the viewpoint of thinning, it is preferably 0.1 to 8 μm, more preferably 0.3 to 5 μm.

[0083] The retardation layer may include a support and an alignment layer, but the support and alignment layer may be a temporary support that is peeled off and removed when producing the laminated optical film. When a temporary support is used, the retardation layer is transferred to another laminate, and then the temporary support is peeled off and removed, thereby making it possible to reduce the thickness of the laminated optical film. Furthermore, this is preferable because the adverse effect of the retardation of the temporary support on the polarization degree of transmitted light can be eliminated. The type of support is not particularly limited, but it is preferably transparent to visible light. For example, films such as cellulose acylate, polycarbonate, polysulfone, polyethersulfone, polyacrylate, polymethacrylate, cyclic polyolefin, polyolefin, polyamide, polystyrene, and polyester can be used. Among these, cellulose acylate film, cyclic polyolefin, polyacrylate, or polymethacrylate is preferred. Alternatively, commercially available cellulose acetate films (e.g., "TD80U" or "Z-TAC" manufactured by Fujifilm Corporation) can also be used. When the support is a temporary support, a support with high tear strength is preferred from the viewpoint of preventing breakage during peeling. For example, polycarbonate and polyester films are preferred. Furthermore, the support preferably has a small retardation from the viewpoint of suppressing adverse effects on the polarization degree of transmitted visible light and / or infrared light. Specifically, the magnitude of Re is preferably 10 nm or less, and the absolute value of the magnitude of Rth is preferably 50 nm or less. Furthermore, even if the support is used as the above-mentioned temporary support, it is preferable that the retardation of the temporary support is small in order to perform quality inspection of the retardation layer and / or other laminates in the manufacturing process of the laminated optical film.

[0084] Furthermore, in order to minimize the influence on various sensors that use near-infrared light as a light source, such as those for eye tracking, facial expression recognition, and iris authentication, which are incorporated into optical systems such as virtual reality display devices and electronic viewfinders, the retardation layer used in the laminated optical film of the present invention is preferably transparent to near-infrared light. The transmittance for infrared light (wavelength 800 nm to 2500 nm) is preferably 50% to 100%. The transmittance can be measured using a spectrophotometer UV3150 (Shimadzu Corporation).

[0085] [Other Functional Layers] The laminated optical film of the present invention may have other functional layers in addition to the infrared light reflecting element and the retardation layer.

[0086] Furthermore, in order to minimize the impact on various sensors that use near-infrared light as a light source, such as those for eye tracking, facial expression recognition, and iris authentication, which are incorporated into optical systems such as virtual reality display devices and electronic viewfinders, the other functional layers are preferably transparent to near-infrared light. The transmittance for infrared light (wavelength 800 nm to 2500 nm) is preferably 20% to 100%. The transmittance can be measured using a spectrophotometer UV3150 (Shimadzu Corporation).

[0087] <Linear Polarizer> The laminated optical film of the present invention preferably further comprises a linear polarizer. The linear polarizer used in the laminated optical film of the present invention is preferably an absorption-type linear polarizer. An absorption-type linear polarizer absorbs linearly polarized light in the absorption axis direction of incident light and transmits linearly polarized light in the transmission axis direction. A typical polarizer can be used as the linear polarizer. For example, a polarizer obtained by dyeing a dichroic material onto polyvinyl alcohol or other polymer resin and stretching the material to orient the material, or a polarizer obtained by aligning a dichroic material by utilizing the orientation of a liquid crystal compound, may be used. From the viewpoints of availability and increasing the polarization degree, a polarizer obtained by dyeing polyvinyl alcohol with iodine and stretching the material is preferred. The thickness of the linear polarizer is preferably 10 μm or less, more preferably 7 μm or less, and even more preferably 5 μm or less. A thin linear polarizer can prevent cracking and breakage of the film when the laminated optical film is stretched or molded. The single-plate transmittance of the linear polarizer is preferably 40% or more, more preferably 42% or more. The degree of polarization is preferably 90% or more, more preferably 95% or more, and even more preferably 99% or more. In this specification, the single-plate transmittance and degree of polarization of the linear polarizer are measured using an automatic polarizing film measuring device: VAP-7070 (manufactured by JASCO Corporation). The direction of the transmission axis of the linear polarizer preferably coincides with the direction of the polarization axis of light converted into linearly polarized light by the retardation layer. For example, when the retardation layer is a layer having a retardation of 1 / 4 wavelength, the angle between the transmission axis of the linear polarizer and the slow axis of the retardation layer is preferably approximately 45°.

[0088] The linear polarizer used in the laminated optical film of the present invention is also preferably a light-absorbing anisotropic layer containing a liquid crystal compound and a dichroic material. Linear polarizers containing a liquid crystal compound and a dichroic material are preferred because they can be made thin and are less likely to crack or break even when stretched and molded. The thickness of the light-absorbing anisotropic layer is not particularly limited, but from the viewpoint of thinning, it is preferably 0.1 to 8 μm, more preferably 0.3 to 5 μm. Linear polarizers containing a liquid crystal compound and a dichroic material can be produced, for example, with reference to JP 2020-023153 A. From the viewpoint of improving the polarization degree of the linear polarizer, the light-absorbing anisotropic layer preferably has an orientation degree of the dichroic material of 0.95 or more, more preferably 0.97 or more.

[0089] The liquid crystal compound contained in the composition for forming the optically absorptive anisotropic layer is preferably a liquid crystal compound that does not exhibit dichroism in the visible range. Both low-molecular-weight liquid crystal compounds and high-molecular-weight liquid crystal compounds can be used as the liquid crystal compound. Here, "low-molecular-weight liquid crystal compound" refers to a liquid crystal compound that does not have a repeating unit in its chemical structure. Furthermore, "high-molecular-weight liquid crystal compound" refers to a liquid crystal compound that has a repeating unit in its chemical structure. Examples of high-molecular-weight liquid crystal compounds include the thermotropic liquid crystal polymers described in JP 2011-237513 A. Furthermore, high-molecular-weight liquid crystal compounds preferably have a crosslinkable group (e.g., an acryloyl group or a methacryloyl group) at their terminals. The liquid crystal compounds may be used alone or in combination. It is also preferable to use a high-molecular-weight liquid crystal compound and a low-molecular-weight liquid crystal compound in combination. The content of the liquid crystal compound is preferably 25 to 2,000 parts by weight, more preferably 33 to 1,000 parts by weight, and even more preferably 50 to 500 parts by weight, per 100 parts by weight of the dichroic substance in the composition. When the content of the liquid crystal compound is within the above range, the degree of orientation of the polarizer is further improved.

[0090] The dichroic substance contained in the composition for forming an optically absorptive anisotropic layer for forming the optically absorptive anisotropic layer is not particularly limited, and examples thereof include visible light absorbing substances (dichroic dyes), ultraviolet absorbing substances, infrared absorbing substances, nonlinear optical substances, and carbon nanotubes, and any conventionally known dichroic substance (dichroic dye) can be used.

[0091] When the linear polarizer is a light-absorbing anisotropic layer containing a liquid crystal compound and a dichroic substance, the linear polarizer may include a support, an alignment layer, etc., but the support and alignment layer may be a temporary support that is peeled off and removed when producing a laminated optical film. When a temporary support is used, the light-absorbing anisotropic layer is transferred to another laminate, and then the temporary support is peeled off and removed, thereby making it possible to reduce the thickness of the laminated optical film. Furthermore, this is preferable because it is possible to eliminate the adverse effect of the retardation of the temporary support on the polarization degree of transmitted light. The type of support is not particularly limited, but it is preferably transparent to visible light. For example, a support similar to the support used as the retardation layer can be used. Preferred embodiments of the support used in the linear polarizer are the same as those of the support used as the retardation layer.

[0092] <Positive C Plate> The laminated optical film of the present invention preferably further comprises a positive C plate. Here, the positive C plate is a retardation layer having an Re of substantially zero and an Rth of a negative value. The positive C plate can be obtained, for example, by vertically aligning a rod-shaped liquid crystal compound. Details of the manufacturing method of the positive C plate can be found in, for example, JP-A-2017-187732, JP-A-2016-053709, and JP-A-2015-200861. The positive C plate functions as an optical compensation layer to increase the degree of polarization of transmitted light with respect to obliquely incident light. The positive C plate can be disposed at any position in the laminated optical film, and multiple positive C plates may be disposed.

[0093] The positive C plate may be installed adjacent to the infrared light reflecting element or inside the infrared light reflecting element. For example, when a reflective layer formed by fixing a cholesteric liquid crystal phase containing a rod-shaped liquid crystal compound is used as the infrared light reflecting element, the reflective layer has a positive Rth. In this case, when light is incident on the infrared light reflecting element from an oblique direction, the Rth may change the polarization state of the reflected light and transmitted light, resulting in a decrease in the degree of polarization of the transmitted light. Having a positive C plate inside or near the infrared light reflecting element is preferable because it can further suppress changes in the polarization state of obliquely incident light and further suppress a decrease in the degree of polarization of the transmitted light, thereby further suppressing the phase difference. In this case, the Re of the positive C plate is preferably approximately 10 nm or less, and the Rth is preferably -600 to -10 nm, more preferably -400 to -40 nm.

[0094] The positive C plate may be disposed adjacent to or within the retardation layer. For example, when a layer formed by immobilizing a rod-shaped liquid crystal compound is used as the retardation layer, the retardation layer has a positive Rth. In this case, when light is incident on the retardation layer from an oblique direction, the Rth may change the polarization state of the transmitted light, potentially reducing the degree of polarization of the transmitted light. Having a positive C plate within or near the retardation layer is preferable because it can suppress changes in the polarization state of obliquely incident light and reduce the degree of polarization of the transmitted light. According to our investigations, the positive C plate is preferably disposed on the side of the retardation layer opposite the linear polarizer, but may also be disposed elsewhere. In this case, the Re of the positive C plate is preferably approximately 10 nm or less, and the Rth is preferably −90 to −40 nm.

[0095] <Anti-Reflection Layer> The laminated optical film of the present invention preferably has an anti-reflection layer on its surface. The laminated optical film of the present invention has the function of reflecting specific circularly polarized light and transmitting circularly polarized light orthogonal to it. However, reflection on the surface of the laminated optical film generally includes reflection of unintended polarized light, which may reduce the degree of polarization of the transmitted light. Therefore, it is preferable that the laminated optical film has an anti-reflection layer on its surface. The anti-reflection layer may be provided on only one surface of the laminated optical film or on both surfaces. The type of anti-reflection layer is not particularly limited, but from the viewpoint of further reducing the reflectance, a moth-eye film or an AR (anti-reflective) film is preferred. Known moth-eye films and AR films can be used. Furthermore, when the laminated optical film is stretched or molded, a moth-eye film is preferred because it can maintain high anti-reflection performance even if the film thickness changes due to stretching. Furthermore, when the antireflection layer includes a support and is subjected to stretching, molding, etc., the peak temperature of Tg of the support is preferably 170° C. or less, more preferably 130° C. or less, from the viewpoint of facilitating stretching, molding, etc. Specifically, for example, a PMMA film or the like is preferred.

[0096] <Second Retardation Layer> The laminated optical film of the present invention preferably further has a second retardation layer. For example, it may contain an infrared light reflecting element, a retardation layer, a linear polarizer, and a second retardation layer in this order. The second retardation layer preferably converts linearly polarized light into circularly polarized light, and for example, a retardation layer having a ¼ wavelength Re is preferred. The reason for this will be explained below. Light incident on the laminated optical film from the infrared light reflecting element side and transmitted through the infrared light reflecting element, the retardation layer, and the linear polarizer becomes linearly polarized light, and a portion of it is reflected by the outermost surface on the linear polarizer side and then exits again from the surface on the infrared light reflecting element side. Such light is unnecessary reflected light and can be a factor in reducing the degree of polarization of the reflected light, so it is preferable to reduce it. Therefore, there is a method of laminating an antireflection layer to suppress reflection on the outermost surface on the linear polarizer side. However, when the laminated optical film is used by being attached to a medium such as glass or plastic, even if an antireflection layer is provided on the attachment surface of the laminated optical film, reflection on the surface of the medium cannot be suppressed, making it difficult to obtain an antireflection effect. On the other hand, when a second retardation layer that converts linearly polarized light into circularly polarized light is provided, the light that reaches the outermost surface on the linear polarizer side becomes circularly polarized light and is converted into orthogonal circularly polarized light when reflected on the outermost surface of the medium. After that, when the light passes through the second retardation layer again and reaches the linear polarizer, it becomes linearly polarized light in the absorption axis direction of the linear polarizer and is absorbed by the linear polarizer. Therefore, unnecessary reflection can be prevented. From the viewpoint of more effectively suppressing unnecessary reflection, it is preferable that the second retardation layer has substantially reverse dispersion.

[0097] <Support> The laminated optical film of the present invention may further have a support. The support can be installed in any location. For example, when an infrared light reflecting element, a retardation layer, a linear polarizer, or the like is a film to be transferred from a temporary support, the support can be used as the transfer destination. The type of support is not particularly limited, but it is preferably transparent to visible light. For example, films such as cellulose acylate, polycarbonate, polysulfone, polyethersulfone, polyacrylate, polymethacrylate, cyclic polyolefin, polyolefin, polyamide, polystyrene, and polyester can be used. Among these, cellulose acylate film, cyclic polyolefin, polyacrylate, or polymethacrylate is preferred. Commercially available cellulose acetate films (for example, "TD80U" or "Z-TAC" manufactured by Fujifilm Corporation) can also be used. Furthermore, it is preferable that the support has a small retardation from the viewpoint of suppressing adverse effects on the polarization degree of transmitted light and from the viewpoint of facilitating optical inspection of the laminated optical film. Specifically, the magnitude of Re is preferably 10 nm or less, and the absolute value of the magnitude of Rth is preferably 50 nm or less.

[0098] When the laminated optical film of the present invention is to be stretched, molded, or the like, the support preferably has a tan δ peak temperature of 170° C. or less. From the viewpoint of enabling molding at a low temperature, the tan δ peak temperature is preferably 150° C. or less, and more preferably 130° C. or less.

[0099] Here, the method for measuring tan δ will be described. Using a dynamic viscoelasticity measuring device (DVA-200 manufactured by IT Measurement Control Co., Ltd.), E" (loss modulus) and E' (storage modulus) are measured under the following conditions for a film sample that has been previously conditioned for at least 2 hours in an atmosphere at a temperature of 25°C and a humidity of 60% Rh, and tan δ (= E" / E') is the value obtained. Device: DVA-200 manufactured by IT Measurement Control Co., Ltd. Sample: 5 mm, length 50 mm (gap 20 mm) Measurement conditions: Tensile mode Measurement temperature: -150°C to 220°C Heating conditions: 5°C / min Frequency: 1 Hz In general, in optical applications, resin substrates that have been subjected to a stretching treatment are often used, and the peak temperature of tan δ often becomes high due to the stretching treatment. For example, the peak temperature of tan δ for a TAC (triacetyl cellulose) substrate (TG40, manufactured by Fujifilm Corporation) is 180°C or higher.

[0100] As a support having a tan δ peak temperature of 170°C or less, various resin substrates can be used without any particular limitation. Examples include polyolefins such as polyethylene, polypropylene, and norbornene-based polymers; cyclic olefin-based resins; polyvinyl alcohol; polyethylene terephthalate; acrylic resins such as polymethacrylic acid esters and polyacrylic acid esters; polyethylene naphthalate; polycarbonate; polysulfone; polyethersulfone; polyether ketone; polyphenylene sulfide, and polyphenylene oxide. Among these, in terms of easy commercial availability and excellent transparency, cyclic olefin-based resins, polyethylene terephthalate, and acrylic resins are preferred, and cyclic olefin-based resins and polymethacrylic acid esters are particularly preferred.

[0101] Examples of commercially available resin substrates include Technolloy S001G, Technolloy S014G, Technolloy S000, Technolloy C001, and Technolloy C000 (Sumika Acrylic Sales Co., Ltd.), Lumirror U Type, Lumirror FX10, and Lumirror SF20 (Toray Industries, Inc.), HK-53A (Higashiyama Films Co., Ltd.), Teflex FT3 (Teijin DuPont Films Co., Ltd.), S-Cina and SCA40 (Sekisui Chemical Co., Ltd.), Zeonor Film (Optes Co., Ltd.), and Arton Film (JSR Corporation).

[0102] The thickness of the support is not particularly limited, but is preferably from 5 to 300 μm, more preferably from 5 to 100 μm, and even more preferably from 5 to 30 μm.

[0103] The laminated optical film may also have layers other than those described above. Examples of layers other than those described above include an adhesive layer formed with the adhesive described below, an adhesive layer formed with the adhesive described below, and a refractive index adjustment layer. A refractive index adjustment layer having a smaller difference in refractive index between the fast axis and the slow axis than that of the infrared light reflector may be provided between the infrared light reflector and the adhesive, or between the infrared light reflector and the adhesive. In this case, the refractive index adjustment layer preferably has a layer formed by fixing the orientation state of cholesteric liquid crystal. By including a refractive index adjustment layer, interfacial reflection can be further suppressed, and the occurrence of ghosts can be further suppressed. The average refractive index of the refractive index adjustment layer is more preferably smaller than that of the infrared light reflector. The central wavelength of the reflected light from the refractive index adjustment layer may be smaller than 400 nm or larger than 2500 nm, more preferably smaller than 400 nm.

[0104] [Method of Adhesion of Each Layer] The laminated optical film of the present invention is a laminate composed of multiple layers. Each layer can be bonded by any bonding method, for example, a pressure-sensitive adhesive and / or adhesive. Any commercially available pressure-sensitive adhesive can be used as the pressure-sensitive adhesive. However, from the viewpoint of thinning and reducing the surface roughness Ra of the laminated optical film, the thickness is preferably 25 μm or less, more preferably 15 μm or less, and most preferably 6 μm or less. Furthermore, it is preferable that the pressure-sensitive adhesive is one that is less likely to outgas. In particular, when performing stretching and molding, etc., vacuum processes and heating processes may be used, and it is preferable that the pressure-sensitive adhesive does not outgas even under these conditions. Any commercially available adhesive can be used as the adhesive, for example, an epoxy resin-based adhesive or an acrylic resin-based adhesive. From the viewpoint of thinning and reducing the surface roughness Ra of the laminated optical film, the thickness of the adhesive is preferably 25 μm or less, more preferably 5 μm or less, and most preferably 1 μm or less. Furthermore, from the viewpoint of thinning the adhesive layer and applying the adhesive to the adherend with a uniform thickness, the adhesive preferably has a viscosity of 300 cP or less, more preferably 100 cP or less, and even more preferably 10 cP or less. Furthermore, if the adherend has surface irregularities, the pressure-sensitive adhesive and / or adhesive can be selected to have an appropriate viscoelasticity or thickness so as to embed the surface irregularities of the layer to be adhered, thereby reducing the surface roughness Ra of the laminated optical film. From the viewpoint of embedding the surface irregularities, the pressure-sensitive adhesive and / or adhesive preferably has a viscosity of 50 cP or more. Furthermore, the thickness is preferably greater than the height of the surface irregularities. Examples of methods for adjusting the viscosity of the adhesive include using a solvent-containing adhesive. In this case, the viscosity of the adhesive can be adjusted by adjusting the ratio of the solvent. Furthermore, the thickness of the adhesive can be further reduced by drying the solvent after applying the adhesive to the adherend.

[0105] In a laminated optical film, from the viewpoint of reducing unnecessary reflection and suppressing a decrease in the degree of polarization of transmitted light and reflected light, it is preferable that the pressure-sensitive adhesive or adhesive used to bond each layer has a small refractive index difference with adjacent layers. Specifically, the refractive index difference between adjacent layers is preferably 0.1 or less, more preferably 0.05 or less, and even more preferably 0.01 or less. The refractive index of the pressure-sensitive adhesive or adhesive can be adjusted, for example, by mixing titanium oxide fine particles and zirconia fine particles. Furthermore, the infrared light reflecting element, retardation layer, and linear polarizer may have in-plane refractive index anisotropy, but it is preferable that the refractive index difference with adjacent layers is 0.05 or less in all directions in the plane. Therefore, the pressure-sensitive adhesive and / or adhesive may have in-plane refractive index anisotropy.

[0106] It is also preferable that the adhesive layer between each layer has a thickness of 100 nm or less. When the adhesive layer is 100 nm or less, the difference in refractive index is less noticeable, and reflection at the interface can be suppressed. The adhesive layer thickness is more preferably 50 nm or less. An example of a method for forming an adhesive layer having a thickness of 100 nm or less is a method of vapor-depositing a ceramic adhesive such as silicon oxide (SiOx layer) onto the bonding surface. The bonding surface of the bonding member can be subjected to surface modification treatments such as plasma treatment, corona treatment, and saponification treatment before bonding, or a primer layer can be applied. Furthermore, when there are multiple bonding surfaces, the type and thickness of the adhesive layer can be adjusted for each bonding surface. Specifically, an adhesive layer having a thickness of 100 nm or less can be formed, for example, by the following steps (1) to (3): (1) The layer to be laminated is laminated to a temporary support made of a glass substrate. (2) SiOx layers having a thickness of 100 nm or less are formed on both the surface of the layer to be laminated and the surface of the layer to be laminated by vapor deposition or the like. The deposition can be performed using, for example, a deposition apparatus (model number ULEYES) manufactured by ULVAC, Inc., using SiOx powder as a deposition source. It is also preferable to subject the surface of the formed SiOx layer to plasma treatment. (3) After the formed SiOx layers are bonded together, the temporary support is peeled off. The bonding is preferably performed at a temperature of, for example, 120°C.

[0107] The coating, adhesion, or lamination of each layer may be performed by roll-to-roll or sheet-to-sheet. The roll-to-roll method is preferred from the viewpoint of improving productivity and reducing axial misalignment of each layer. On the other hand, the sheet-to-sheet method is preferred because it is suitable for small-lot, high-mix production and because it allows the selection of a special adhesion method such as the above-mentioned adhesive layer thickness of 100 nm or less. Furthermore, methods for applying the adhesive to the adherend include known methods such as roll coating, gravure printing, spin coating, wire bar coating, extrusion coating, direct gravure coating, reverse gravure coating, die coating, spraying, and inkjet printing.

[0108] [Direct Coating of Each Layer] It is also preferable that there is no adhesive layer between the layers of the laminated optical film of the present invention. When forming a layer, the adhesive layer can be eliminated by directly coating the layer on an adjacent layer that has already been formed. Furthermore, when one or both of the adjacent layers contain a liquid crystal compound, it is preferable that the alignment direction of the liquid crystal compound continuously changes at the interface in order to reduce the refractive index difference in all in-plane directions. For example, a retardation layer containing a liquid crystal compound can be directly coated on a linear polarizer containing a liquid crystal compound and a dichroic material, and the liquid crystal compound in the retardation layer can be continuously aligned at the interface due to the alignment regulating force of the liquid crystal compound in the linear polarizer.

[0109] [Lamination Order of Layers] The laminated optical film of the present invention is composed of many layers, but the order of the lamination steps is not particularly limited and can be selected arbitrarily. For example, when transferring a functional layer from a film consisting of a temporary support and a functional layer, wrinkles, cracks, and the like during transfer can be prevented by adjusting the lamination order so that the thickness of the transferred film is 10 μm or more. Furthermore, from the viewpoint of reducing the surface roughness Ra of the laminated optical film, laminating another layer on a layer with large surface irregularities may further amplify the surface irregularities, so it is preferable to laminate the layers in order from the layer with the smallest surface roughness Ra. Furthermore, the lamination order can also be selected from the viewpoint of quality evaluation in the production process of the laminated optical film. For example, layers other than the infrared light reflecting element can be laminated and quality evaluation can be performed using a transmission optical system, and then the infrared light reflecting element can be laminated and quality evaluation can be performed using a reflection optical system. Furthermore, the lamination order can also be selected from the viewpoint of improving the manufacturing yield of the laminated optical film and reducing costs.

[0110] <Molding method> The infrared light reflecting element and laminated optical film of the present invention may be used in a flat form or may be molded into any shape. Here, the infrared light reflecting element and laminated optical film will be collectively referred to as the optical film, and the molding method will be described. The molding method for the optical film includes a step of heating the optical film, a step of pressing the optical film against a mold and deforming it to conform to the shape of the mold, and a step of cutting the optical film.

[0111] [Step of Heating Optical Film] Methods for heating the optical film include heating by contacting it with a heated solid, heating by contacting it with a heated liquid, heating by contacting it with a heated gas, heating by irradiating it with infrared rays, and heating by irradiating it with microwaves. However, heating by irradiating it with infrared rays, which allows heating to be performed remotely immediately before molding, is preferred.

[0112] The wavelength of the infrared rays used for heating is preferably 1.0 μm to 30.0 μm, and more preferably 1.5 μm to 5 μm. Examples of IR (infrared) light sources that can be used include near-infrared lamp heaters with a tungsten filament sealed in a quartz tube and wavelength-controlled heaters with multiple quartz tubes and a mechanism for cooling a portion of the space between the quartz tubes with air. Furthermore, by creating a temperature distribution on the optical film, the physical properties during molding can be controlled according to the purpose. Methods for creating a temperature distribution include creating a distribution of the amount of infrared radiation used for heating, controlling the intensity distribution of cooling air, and controlling the cooling progress due to contact with the mold by controlling the mold temperature and contact time. Examples of methods for creating a distribution of infrared radiation include varying the density of IR light sources and placing a filter with a patterned infrared light transmittance between the IR light source and the optical film. Examples of filters with patterned transmittance include glass with metal vapor deposition, cholesteric liquid crystal layers with a reflection band that is infrared-transformed, dielectric multilayer films with a reflection band that is infrared-transformed, and ink that absorbs infrared. The temperature of the optical film is controlled by the intensity of infrared radiation, and is controlled by the infrared radiation exposure time and / or illuminance of infrared radiation. The temperature of the optical film can be monitored using a non-contact radiation thermometer or thermocouple, and it can be molded at the target temperature.

[0113] [Step of Pressing the Optical Film Against the Mold and Deforming it to Fit the Mold Shape] The method of pressing the optical film against the mold and deforming it to fit the mold shape is to reduce the pressure and / or increase the pressure in the molding space. Alternatively, a mold pressing method can be used.

[0114] [Process for Cutting Optical Film] Cutting the molded optical film into any desired shape can be performed using a cutter, scissors, a cutting plotter, a laser cutter, or the like. <Molding Apparatus> One form of molding apparatus consists of a box 1 with an opening at the top and a box 2 with an opening at the bottom. To form a molding space, the openings of box 1 and box 2 are aligned directly or via other jigs to form a sealed molding space. A mold (also called an adherend) with the shape to be molded and the film to be molded are placed in the molding space. The film acts as a partition to divide the molding space consisting of box 1 and box 2 into two spaces. The mold is placed on the box 1 side, below the film to be molded. Furthermore, the vacuum molding apparatus has multiple heating elements dispersedly arranged to heat the film to be molded. The heating elements may be placed inside the molding space, or they may be placed outside the molding space and heat the film to be molded through a transparent window.

[0115] <Optical Article> One embodiment of the optical article of the present invention is a composite lens comprising a lens and the infrared light reflecting element of the present invention or the laminated optical film of the present invention. A half mirror may be formed on one side of the lens. The lens may be a convex lens or a concave lens. The convex lens may be a biconvex lens, a plano-convex lens, or a convex meniscus lens. The concave lens may be a biconcave lens, a plano-concave lens, or a concave meniscus lens. The lens used in the focusing optical system is preferably a convex meniscus lens or a concave meniscus lens, with a concave meniscus lens being more preferred in terms of minimizing aberration. Lens materials that are transparent to visible light and infrared light, such as glass, crystal, or plastic, can be used. Since birefringence of a lens can cause unevenness and noise, the smaller the birefringence, the more preferable, and zero-birefringence materials are more preferred. The infrared light reflecting element of the present invention or the laminated optical film of the present invention used in the optical article of the present invention may be flat or curved, with a curved surface being preferred in terms of minimizing image distortion and aberration. Another embodiment of the optical article of the present invention comprises a prism or substrate and the infrared light reflecting element of the present invention or the laminated optical film of the present invention. Materials for the prism and substrate may be glass, crystal, plastic, or other materials that are transparent or opaque to visible light and infrared light. Because birefringence of the prism and substrate can cause unevenness and noise, low birefringence is preferable, and zero-birefringence materials are more preferable. A laminate of a lens or prism and an infrared light reflecting element is used in an infrared detection sensor system to focus or reflect infrared light. This enables infrared detection with high sensitivity and a compact configuration.

[0116] [Head-Mounted Display] As described above, the infrared light reflecting element of the present invention can be used as a reflecting optical element for optical sensing using infrared light by being incorporated into, for example, an image display device, a head-up display, a virtual reality display device such as a head-mounted display, an AR glass, an electronic viewfinder, etc. As an example, a head-mounted display (virtual reality display device) having the reflecting optical element of the present invention will be described below.

[0117] The head-mounted display (virtual reality display device) 50 shown in Figure 4 has an optical system known as a reciprocating optical system, a folding optical system, or a pancake lens, which uses polarized light to reciprocate light between a half mirror and a reflective polarizer. The head-mounted display 50 includes an image display element 52, a λ / 4 plate 53, an absorptive linear polarizer 54, a λ / 4 plate 55, a half mirror 56, a support 57, a reflective circular polarizer 58, a λ / 4 plate 59, an absorptive linear polarizer 60, an infrared light reflecting element 61, and a detector 62. The λ / 4 plate 53, the absorptive linear polarizer 54, the λ / 4 plate 55, the support 57, the λ / 4 plate 59, and the absorptive linear polarizer 54 are preferred components of the head-mounted display. The infrared light reflecting element 61 corresponds to the infrared light reflecting element of the present invention described above.

[0118] The image display element 52 emits light (hereinafter also referred to as image light) that becomes an image displayed by the head-mounted display 50. Therefore, the light emitted by the image display element 52 is visible light. A known image display panel can be used as the image display element 52. Examples of such an image display panel include an organic electroluminescence display device, an LED (Light Emitting Diode) display device, a micro LED display device, or other image display panel in which minute self-luminous light emitters are arranged on a transparent substrate. Another example of an image display panel is a liquid crystal display device.

[0119] The λ / 4 plate 53 , the absorbing linear polarizer 54 , and the λ / 4 plate 55 are arranged in this order on the light exit surface (display surface) side of the image display element 52 .

[0120] The half mirror 56 is disposed on the surface of the support 57 facing the image display element 52, and the reflective circular polarizer 58, the λ / 4 plate 59, and the absorbing linear polarizer 60 are disposed in this order on the surface of the support 57 opposite the image display element 52. The support 57 has a convex curved shape facing the image display element 52, and acts as a lens. The laminate of the half mirror 56, the support 57, the reflective circular polarizer 58, the λ / 4 plate 59, and the absorbing linear polarizer 60 is disposed so that the optical axis of this lens is perpendicular to the display surface of the image display element 52.

[0121] The λ / 4 plate 55 (image display element 52) ​​and the half mirror 56 are spaced apart, and the infrared light reflecting element 61 is disposed between the λ / 4 plate 55 (image display element 52) ​​and the half mirror 56. The infrared light reflecting element 61 is disposed obliquely so that the normal to its principal surface intersects with the normal to the display surface of the image display element 52.

[0122] The detector 62 detects the infrared light reflected by the infrared light reflecting element 61, and is disposed at a position where it can detect the infrared light reflected by the infrared light reflecting element 61, depending on the arrangement, angle, etc. of the infrared light reflecting element 61. The detector 62 is disposed at a position away from the optical path of the image light emitted by the image display element 52.

[0123] A photodetector element such as a photodiode or phototransistor that is sensitive to infrared light but not to visible light can be used as the detector 62. Preferably, the detector 62 is a photodiode or phototransistor that is sensitive only to the infrared region and not to the visible light region. An organic photodiode (OPD) or an organic phototransistor (OPT) may also be used as the photodetector element.

[0124] Although not shown, the head-mounted display 50 also includes an infrared light source that irradiates the eyes of the user U with infrared light. The location of the infrared light source is not particularly limited. For example, the infrared light source may be disposed on the back side of the image display element 52, near the side of the image display element 52, or near the side of the support 57. Alternatively, the infrared light source may be configured to irradiate infrared light from some pixels of the image display element 52. From the viewpoint of increasing the accuracy of sensing using infrared light, it is desirable for the infrared light source to irradiate infrared light from a direction close to the front of the user's eyes. Furthermore, the infrared light source is not limited to a configuration in which it is disposed so as to directly irradiate the eyes of the user U with infrared light. It may also be disposed so that the infrared light is reflected by the infrared light reflecting element 61 and irradiated onto the eyes of the user U. The wavelength of the infrared light emitted by the infrared light source is the wavelength reflected by the infrared light reflecting element 61. A laser light source or the like can be used as the infrared light source.

[0125] The following describes the operation of the head-mounted display 50. Image light emitted from the image display element 52 passes through the λ / 4 plate 53, the absorbing linear polarizer 54, and the λ / 4 plate 55 in this order, where it is converted into circularly polarized light and enters the infrared light reflecting element 61. In the following, the explanation will be given assuming that the light has been converted into right-handed circularly polarized light R, as an example.

[0126] Since the infrared light reflecting element 61 transmits visible light, the right-handed circularly polarized light R passes through the infrared light reflecting element 61 and enters the half mirror 56 .

[0127] Here, the infrared light reflecting element 61 is disposed obliquely with respect to the display surface of the image display element 52. Therefore, the right-handed circularly polarized light R passes through the infrared light reflecting element 61 in an oblique direction.

[0128] In the case of conventional infrared light reflecting elements, when polarized visible light is transmitted at an oblique angle, it is subjected to a phase difference and the degree of polarization decreases, which may result in a decrease in the amount of light passing through the appropriate path described below, or a change in the ratio of the amount of light for each wavelength, which may cause problems such as changes in the color and brightness of the displayed image.

[0129] In contrast, a preferred embodiment of the infrared light reflecting element of the present invention has a reflective layer A including a cholesteric liquid crystal layer formed using a rod-shaped liquid crystal compound and a reflective layer B including a cholesteric liquid crystal layer formed using a discotic liquid crystal compound, and therefore the Rths of the two layers are offset, and polarized visible light transmitted in an oblique direction can be transmitted without imparting a phase difference. This makes it possible to suppress a decrease in the degree of polarization of polarized visible light, and enables the display image to be displayed correctly without affecting the color, brightness, etc. of the displayed image.

[0130] A portion of the right-handed circularly polarized light R that enters the half mirror 56 passes through the half mirror 56, passes through the support 57, and enters the reflective circular polarizer 58. In the example shown in FIG. 4 , the reflective circular polarizer 58 reflects right-handed circularly polarized light R and transmits left-handed circularly polarized light, so the incident right-handed circularly polarized light R is reflected by the reflective circular polarizer 58 and enters the half mirror 56 again. A portion of the right-handed circularly polarized light R that enters the half mirror 56 is reflected by the half mirror 56 toward the reflective circular polarizer 58. At this time, the rotation direction of the circularly polarized light is reversed by reflection by the half mirror 56, so that the right-handed circularly polarized light R is converted into left-handed circularly polarized light L. The left-handed circularly polarized light L that enters the reflective circular polarizer 58 passes through the λ / 4 plate 59 and the absorbing linear polarizer 60, is converted into linearly polarized light, and is irradiated toward the user U. As a result, the video (image) displayed by the image display element 52 is visually recognized by the user U as a virtual image.

[0131] Next, optical sensing using infrared light performed by the head mounted display 50 having the infrared light reflecting element of the present invention will be described.

[0132] A head-mounted display 50 having an infrared light reflecting element of the present invention irradiates infrared light IR from an infrared light source onto the eye of a user U. The infrared light IR reflected by the eye of the user U passes through an absorptive linear polarizer 60, a λ / 4 plate 59, a reflective circular polarizer 58, a support 57, and a half mirror 56, and is incident on an infrared light reflecting element 61. The infrared light reflecting element 61 reflects the infrared light IR toward a detector 62. The infrared light IR reflected by the infrared light reflecting element 61 is incident on and detected by the detector 62. By detecting the infrared light IR with the detector 62, it is possible to detect or recognize the three-dimensional shape of an object, the surface condition of the object, and the user's eye movement, eye position, facial expression, facial shape, vein pattern, blood flow, pulse, blood oxygen saturation, fingerprint, iris, etc.

[0133] Here, in the various types of infrared light sensing described above, it is preferable to use polarized light in order to remove noise caused by surface reflected light and / or stray light and to improve detection contrast, etc. In infrared light sensing using polarized light, if the circular polarization purity of the reflected light decreases when infrared light is reflected by an infrared light reflecting element, there is a risk of a problem in that noise increases and detection sensitivity decreases. In contrast, as described above, the infrared light reflecting element of the present invention can increase the circular polarization purity of the reflected light, thereby suppressing noise and increasing detection sensitivity during the various types of infrared light sensing described above.

[0134] Furthermore, in the head-mounted display 50, the infrared light reflecting element 61 is disposed on the path of the image light, i.e., in the front direction of the user U, thereby improving the accuracy of sensing using infrared light.

[0135] The absorbing linear polarizer 54 and the λ / 4 plate 55, which are arranged on the light exit surface (display surface) side of the image display element 52, are intended to convert light emitted by the image display element 52 into circularly polarized light. The λ / 4 plate 53 and the absorbing linear polarizer 54, which are arranged on the light exit surface (display surface) side of the image display element 52, function as anti-reflection layers that prevent stray light incident on the image display element 52 from being reflected on the surface of the image display element. The λ / 4 plate 59 and the absorbing linear polarizer 60, which are arranged on the surface of the reflective circular polarizer 58 opposite to the half mirror 56, are intended to prevent stray light that has passed through the reflective circular polarizer 58 from emitting from the head-mounted display 50.

[0136] Therefore, the λ / 4 plates 53, 55, and 59 may be retardation layers having a phase difference of λ / 4 with respect to visible light, and conventionally known retardation layers may be used as appropriate. The absorbing linear polarizers 54 and 60 may be retardation layers that function as absorbing linear polarizers with respect to visible light, and conventionally known linear polarizers may be used as appropriate.

[0137] The reflective circular polarizer 58 may be any polarizer that reflects circularly polarized light in the visible light range emitted by the image display element 52, and may be a cholesteric liquid crystal layer having a selective reflection center wavelength in the visible light range. The reflective circular polarizer 58 may have a plurality of cholesteric liquid crystal layers with different selective reflection center wavelengths. The reflective circular polarizer having a cholesteric liquid crystal layer may have the same configuration as a conventionally known reflective circular polarizer used in a head-mounted display.

[0138] Since the cholesteric liquid crystal layer has wavelength selective reflectivity, the reflective circular polarizer 58 can be made not to reflect infrared light.

[0139] The half mirror 56 is a conventionally known half mirror that transmits approximately half of the incident light and reflects the remaining half. The transmittance of the half mirror is preferably 50±30%, more preferably 50±10%, and most preferably 50%. The half mirror is configured to have a reflective layer made of a metal such as silver or aluminum on a substrate made of, for example, a transparent resin such as polyethylene terephthalate (PET), cycloolefin polymer (COP), or polymethyl methacrylate (PMMA), or glass. The reflective layer made of a metal such as silver or aluminum is formed on the surface of the substrate by vapor deposition or the like. The thickness of the reflective layer is preferably 1 to 20 nm, more preferably 2 to 10 nm, and even more preferably 3 to 6 nm. The substrate preferably does not have a phase difference. From this perspective, the substrate of the half mirror is preferably cycloolefin polymer (COP), polymethyl methacrylate (PMMA), or glass. A half mirror with a reflective layer made of metal functions as a half mirror for both visible light and infrared light. On the other hand, there is also a configuration that has a dielectric multilayer film in which multiple thin layers with different refractive indices are laminated on a substrate made of the aforementioned resin or glass. A reflective layer made of a dielectric multilayer film is formed on the surface of the substrate by sputtering or vapor deposition. By appropriately selecting the material and film thickness of the dielectric multilayer film, it is possible to fabricate a half mirror that functions as a half mirror for visible light but transmits infrared light.

[0140] Furthermore, it is preferable that the half mirror 56 has high transmittance to infrared light. The transmittance of the half mirror to infrared light is preferably 30% or more, more preferably 50% or more, and even more preferably 80% or more.

[0141] Here, in the example shown in Figure 4, the infrared light reflecting element 61 is configured to be placed between the image display element 52 (λ / 4 plate 55) and the half mirror 56, but this is not limited to this and the infrared light reflecting element 61 may be placed at any position on the path of the image light emitted by the image display element 52.

[0142] The angle between the perpendicular to the main surface of the infrared light reflecting element 61 and the perpendicular to the display surface of the image display element 52 is preferably 20° to 70°, more preferably 30° to 60°, and even more preferably 40° to 50°.

[0143] Note that the configuration of the head-mounted display other than the infrared light reflecting element can be any of various conventionally known head-mounted display configurations. For example, in the example shown in Fig. 4, a reflective circular polarizer is used as the reflective polarizer, but this is not limited thereto, and a reflective linear polarizer may also be used. Furthermore, in the example shown in Fig. 4, the half mirror 56 and the reflective circular polarizer 58 are arranged in this order from the image display element 52 side, but this is not limited thereto, and the reflective circular polarizer 58 and the half mirror 56 may also be arranged in this order from the image display element 52 side.

[0144] The above describes in detail the infrared light reflecting element, laminated optical film, and optical article of the present invention, but the present invention is not limited to the above examples, and various improvements and modifications may be made within the scope of the present invention.

[0145] The features of the present invention will be explained in more detail below with reference to examples. Note that the materials, amounts used, ratios, processing details, processing procedures, etc. shown below can be changed as appropriate without departing from the spirit of the present invention. Furthermore, configurations other than those shown below can also be used without departing from the spirit of the present invention.

[0146] [Preparation of Coating Solution for Reflective Layer]

[0147] <Reflective layer coating solution R-1> The composition shown below was stirred and dissolved in a container kept at 70° C. to prepare a reflective layer coating solution R-1, where R represents a coating solution using a rod-like liquid crystal compound.

[0148] -------------------------------------------------- Coating liquid R-1 for reflective layer -------------------------------------------------- Methyl ethyl ketone 120.9 parts by mass Cyclohexanone 21.3 parts by mass Mixture X of rod-shaped liquid crystal compounds shown below 100.0 parts by mass Photopolymerization initiator B shown below 1.00 part by mass Chiral agent A shown below 2.20 parts by mass Surfactant F1 shown below 0.1 part by mass

[0149] Mixture X of rod-shaped liquid crystal compounds

[0150] In the above mixture X, the numerical values ​​are in mass %. R is a group bonded via an oxygen atom. Furthermore, the average molar absorption coefficient of the above rod-shaped liquid crystal compound in the wavelength range of 300 to 400 nm was 140 / mol cm.

[0151] Chiral agent A

[0152] Surfactant F1

[0153] Photopolymerization initiator B

[0154] Chiral agent A is a chiral agent whose helical twisting power (HTP) is reduced by light.

[0155] <Reflective Layer Coating Solution R-2> This was prepared in the same manner as Reflective Layer Coating Solution R-1, except that the amount of chiral agent A added was changed as shown in Table 1 below.

[0156] Table 1. Amount of chiral agent in coating solution containing rod-shaped liquid crystal compound

[0157]

[0158] <Reflective layer coating solution D-1> The composition shown below was stirred and dissolved in a container kept at 50° C. to prepare a reflective layer coating solution D-1, where D represents a coating solution using a discotic liquid crystal compound.

[0159] -------------------------------- Coating liquid D-1 for reflective layer -------------------------------------------------- 80 parts by mass of discotic liquid crystal compound (A) below 20 parts by mass of discotic liquid crystal compound (B) below 10 parts by mass of polymerizable monomer E1 below 0.3 parts by mass of surfactant F2 below 3 parts by mass of photopolymerization initiator (Irgacure 907, manufactured by BASF) 2.67 parts by mass of the above chiral agent A 290 parts by mass of methyl ethyl ketone 50 parts by mass of cyclohexanone ------------------------------------------------

[0160] Discotic Liquid Crystal Compound (A)

[0161] Discotic Liquid Crystal Compound (B)

[0162] Polymerizable Monomer E1

[0163] Surfactant F2

[0164] <Reflective Layer Coating Solution D-2> A reflective layer coating solution was prepared in the same manner as Reflective Layer Coating Solution D-1, except that the amount of chiral agent A added was changed as shown in Table 2 below.

[0165] Table 2. Amount of chiral agent in coating solution containing discotic liquid crystal compound

[0166]

[0167] <Coating Solution PA-1 for Light Interference Layer> The composition shown below was stirred and dissolved in a container kept at 60° C. to prepare Coating Solution PA-1 for light interference layer.

[0168] -------------------------------- Coating liquid for optical interference layer PA-1 ---------------------------------- Methyl isobutyl ketone 3011.0 parts by mass Mixture X of the above rod-shaped liquid crystal compound 100.0 parts by mass Photopolymerization initiator C described below 5.1 parts by mass Photoacid generator described below 3.0 parts by mass Hydrophilic polymer described below 2.0 parts by mass Vertical alignment agent described below 1.9 parts by mass Viscosity reducer described below 4.2 parts by mass Material for interlayer photoalignment film described below 8.0 parts by mass Stabilizer described below --------------------------------

[0169] Photopolymerization initiator C

[0170] Photoacid generator

[0171] hydrophilic polymer

[0172] Vertical alignment agent

[0173] Viscosity reducer

[0174] Materials for interlayer photo-alignment films

[0175] stabilizers

[0176] [Preparation of infrared light reflective element 1] A 100 μm thick PET (polyethylene terephthalate) film (A4160, manufactured by Toyobo Co., Ltd.) was prepared as a temporary support, and the surface of the PET film without the easy-adhesion layer was subjected to a rubbing treatment. The reflective layer coating solution R-1 prepared above was applied using a wire bar coater, and then dried at 110°C for 72 seconds. Thereafter, the reflective layer was subjected to a rubbing treatment at 100°C under a low-oxygen atmosphere (100 ppm or less) with an illuminance of 80 mW / cm. ２, irradiation amount 500mJ / cm ２ The coating was cured by irradiating it with light from a metal halide lamp (1000 W / m²), thereby forming an infrared light reflective layer (first light reflective layer, corresponding to reflective layer A) made of a cholesteric liquid crystal layer. The light irradiation was carried out from the cholesteric liquid crystal layer side in all cases. The coating thickness was adjusted so that the film thickness of the first light reflective layer after curing would be 2.5 μm.

[0177] Next, the first light-reflecting layer surface was subjected to a discharge of 150 W·min / m ２ After corona treatment, the reflective layer coating solution D-1 was applied to the corona-treated surface using a wire bar coater. Subsequently, the coating film was dried at 70°C for 2 minutes, and after the solvent was evaporated, it was heat-aged at 115°C for 3 minutes to obtain a uniform alignment state. Thereafter, this coating film was kept at 45°C and irradiated with ultraviolet light (300 mJ / cm) using a metal halide lamp under a nitrogen atmosphere. ２ ) and curing the coating, thereby forming a second light-reflecting layer (corresponding to reflective layer B) on the first light-reflecting layer, and producing infrared light reflecting element 1. Light irradiation was performed from the cholesteric liquid crystal layer side in all cases. At this time, the coating thickness was adjusted so that the film thickness of the second light-reflecting layer after curing would be 2.5 μm.

[0178] Next, UV adhesive UVX6282 (manufactured by Toagosei Co., Ltd., refractive index after curing n 1.49) was applied to a thickness of 2 μm on the PMMA substrate using a wire bar coater. The second light-reflecting layer was then attached to the UV adhesive using a laminator so that it was in contact with the UV adhesive. After purging with nitrogen in the purge box until the oxygen concentration was 100 ppm or less, the PMMA substrate was irradiated with ultraviolet light from a high-pressure mercury lamp and cured. The illuminance was 25 mW / cm. ２ , the irradiation dose is 1000 mJ / cm ２ Next, the 100 μm thick PET film serving as a temporary support was peeled off, and then a 5 μm thick adhesive was attached as an adhesive layer onto the first light-reflecting layer. The refractive index nA of the adhesive used at this time was 1.49. In this way, infrared light-reflecting element 1 was obtained.

[0179] Table 3 shows the central reflection wavelength and film thickness for each reflective layer of the infrared light reflective element 1 produced. Here, the central reflection wavelength is used to define the characteristics of a light reflective film having a reflection band using cholesteric liquid crystal, and refers to the midpoint of the spectral band reflected by the film. Specifically, it was obtained by calculating the average value of the wavelengths on the short wavelength side and the long wavelength side that show half the peak reflectance. The central reflection wavelength (central wavelength of the reflection band) was confirmed by producing a film coated with only a single layer. The film thickness was confirmed using an SEM.

[0180] [Preparation of Infrared Light Reflecting Element 2] A 60 μm thick tack (triacetyl cellulose) film (TG60, manufactured by Fujifilm Corporation) was prepared as a temporary support.

[0181] The coating solution for optical interference layer PA-1 prepared above was applied to the tack film described above using a wire bar coater, and then dried at 80°C for 60 seconds. Thereafter, the coating solution was dried in a low-oxygen atmosphere (100 ppm) at 78°C with an irradiation dose of 300 mJ / cm. ２ The liquid crystal compound was cured by irradiating it with light from a 365 nm ultraviolet LED lamp, simultaneously cleaving the cleavage group of the interlayer photo-alignment film material. The film was then heated at 115°C for 25 seconds to remove the fluorine-containing substituents. This resulted in the formation of a positive C-plate layer with a cinnamoyl group on the outermost surface and a film thickness of 140 nm. The refractive index nI at a wavelength of 900 nm measured using an OPTM interference film thickness meter (manufactured by Otsuka Electronics, analyzed using the least squares method) was 1.55. Since the central wavelength λ of the reflection band was 900 nm and the refractive index nI was 1.56, the film thickness under the λ / 4 condition was determined to be 144 nm. Therefore, the film thickness of 140 nm was within ±30% of the λ / 4 condition. Furthermore, the Rth at a wavelength of 550 nm measured using an Axoscan (manufactured by Axometrics) was -15 nm.

[0182] Next, the illuminance is 7 mW / cm ２ , irradiation amount 7.9mJ / cm ２Polarized UV (wavelength 313 nm) was irradiated from the positive C-plate side. The 313 nm polarized UV was obtained by passing ultraviolet light emitted from a mercury lamp through a bandpass filter having a transmission band at wavelength 313 nm and a wire grid polarizer. A reflective layer was formed on the photo-alignment film thus obtained under the same conditions as for infrared light reflective element 1, thereby producing infrared light reflective element 2 having an optical interference layer.

[0183] Next, UV adhesive UVX6282 (manufactured by Toagosei Co., Ltd., refractive index after curing n 1.49) was applied to a thickness of 2 μm on the PMMA substrate using a wire bar coater. The second light-reflecting layer was then attached to the UV adhesive using a laminator so that it was in contact with the UV adhesive. After purging with nitrogen in the purge box until the oxygen concentration was 100 ppm or less, the PMMA substrate was irradiated with ultraviolet light from a high-pressure mercury lamp and cured. The illuminance was 25 mW / cm. ２ , the irradiation dose is 1000 mJ / cm ２ Next, the 100 μm thick PET film serving as a temporary support was peeled off, and then a 5 μm thick adhesive was attached as an adhesive layer onto the light interference layer. The refractive index nA of the adhesive used at this time was 1.49. In this way, an infrared light reflecting element 2 was obtained.

[0184] [Preparation of infrared light reflecting element 3] In the process of preparing infrared light reflecting element 2, the film thickness of the first light reflecting layer was changed to 5.0 μm, and the process of preparing the second light reflecting layer was omitted, thereby preparing infrared light reflecting element 3 having only one light reflecting layer and a total thickness of the light reflecting layer of 5.0 μm.

[0185] [Preparation of infrared light reflecting element 4] Infrared light reflecting element 4 was prepared by further forming a third light reflecting layer (corresponding to reflective layer A) using reflective layer coating liquid R-2 and a fourth light reflecting layer (corresponding to reflective layer B) using reflective layer coating liquid D-2 on infrared light reflecting element 2, and the remaining steps were the same as in the preparation of infrared light reflecting element 2. Table 3 shows the reflection center wavelength and film thickness of each reflective layer of infrared light reflecting element 4.

[0186] The structures and characteristics of the reflective layers of the fabricated infrared light reflective elements 1 to 4 are shown in Table 3 below.

[0187] Table 3. Fabricated infrared light reflecting elements 1 to 4

[0188]

[0189] [Fabrication of Infrared Light Reflecting Elements 5 to 10] Infrared light reflecting elements 5 to 10 were fabricated in the same manner as infrared light reflecting element 2, except that the film thickness of the optical interference layer was changed as shown in Table 4 below.

[0190] [Fabrication of Infrared Light Reflecting Element 11] The infrared light reflecting element 11 was fabricated in the same manner as the infrared light reflecting element 2, except that a photo-alignment layer was formed as a light interference layer by the following process.

[0191] <Formation of Photo-Alignment Layer> The alignment layer-forming coating solution PA2 described below was continuously applied onto a 60 μm-thick tack (triacetyl cellulose) film (TG60, manufactured by Fujifilm Corporation) using a wire bar. The support on which the coating film was formed was dried with hot air at 140° C. for 120 seconds, and then the coating film was irradiated with polarized ultraviolet light (10 mJ / cm ２ A photo-alignment layer having a thickness of 150 nm was formed by irradiating the substrate with light (using an ultra-high pressure mercury lamp).

[0192] ------------------------------------------------------------------ (Coating liquid PA2 for forming alignment layer) ------------------------------------------------------------------ Polymer M-PA-1 (shown below) 100.00 parts by mass Acid generator PAG-1 (shown below) 5.00 parts by mass Acid generator CPI-110TF (shown below) 0.005 parts by mass Xylene 3660.00 parts by mass Methyl isobutyl ketone 366.00 parts by mass

[0193] Polymer M-PA-1

[0194] Acid generator PAG-1

[0195] Acid generator CPI-110TF

[0196] The characteristics of the optical interference layers of the fabricated infrared light reflecting elements 1 to 11 are shown in Table 4 below.

[0197] Table 4. Fabricated infrared light reflecting elements 1 to 11

[0198]

[0199] [Preparation of Optical Articles] The prepared infrared light reflecting elements 1 to 11 were transferred onto a glass plate via the adhesive layer, with the adhesive layer side facing the glass plate, to prepare optical articles 1 to 11. As described above, the refractive index nA of the pressure-sensitive adhesive used as the adhesive layer was 1.49. Meanwhile, the average refractive index nL of the cholesteric liquid crystal layer was 1.62. The square root of the product of these values ​​((nA × nL) １／２ ) is 1.56, the refractive index of the light interference layer used in the infrared light reflecting elements 2 to 10 is 1.55, and the refractive index of the light interference layer used in the infrared light reflecting element 11 is 1.53. Therefore, the refractive index nI of the light interference layer of the infrared light reflecting elements 2 to 11 is (nA×nL) １／２ −0.03≦nI≦(nA×nL) １／２ The condition of +0.03 is satisfied. On the other hand, the infrared light reflecting element 1 does not have a light interference layer.

[0200] Furthermore, the infrared light reflecting elements 2 to 4, 6 to 7, and 10 to 11 have optical interference layer thicknesses within the range of ±30% of the λ / 4 condition or ±30% of the 3λ / 4 condition, relative to the central wavelength λ of the reflection band. On the other hand, the infrared light reflecting elements 5, 8 to 9 have optical interference layer thicknesses that do not satisfy the above ranges. Therefore, the infrared light reflecting elements 2 to 4, 6 to 7, and 10 to 11 are considered preferable for imparting antireflection properties to the infrared light reflecting elements.

[0201] Infrared light reflecting elements 2 to 3 and 5 to 10, which have a central wavelength of 900 nm and a refractive index of the optical interference layer of 1.55, have a film thickness of 145 nm under the λ / 4 condition and a film thickness of 435 nm under the 3λ / 4 condition. Infrared light reflecting element 4, which has a central wavelength of 950 nm and a refractive index of the optical interference layer of 1.55, have a film thickness of 153 nm under the λ / 4 condition. Infrared light reflecting element 11, which has a central wavelength of 900 nm and a refractive index of the optical interference layer of 1.53, have a film thickness of 147 nm under the λ / 4 condition.

[0202] Therefore, infrared light reflecting elements 2 to 4, 6 to 7, and 10 to 11 correspond to examples of the present invention, and infrared light reflecting elements 1, 5, and 8 to 9 correspond to comparative examples. Infrared light reflecting elements 2 to 4, 6 to 7, and 10 to 11 were examples 1 to 7, and infrared light reflecting elements 1, 5, and 8 to 9 were comparative examples 1 to 4.

[0203] [Evaluation of Circular Polarization Purity] The central wavelength of the reflection band of the prepared infrared light reflecting elements 1 to 11 was evaluated using the aforementioned spectrophotometer V-670 (manufactured by JASCO Corporation). Furthermore, to evaluate the degree of circular polarization purity of the reflected light of the prepared infrared light reflecting elements 1 to 11, a circular polarizer (linear polarizer + retardation layer) was placed on the detection side of the spectrophotometer V-670 and evaluation was performed. The circular polarizer was placed so that the surface on the retardation layer side faced the sample. The circular polarizer was prepared by combining a retardation plate whose thickness was adjusted to have a phase difference of ¼ of the central wavelength of the reflection band with a polarizer (wire grid polarizer WP25L-UB manufactured by Thorlabs) that functions as a linear polarizer in the infrared range, to prepare right-handed circularly polarized and left-handed circularly polarized circular polarizers, respectively. The right-handed and left-handed circularly polarized components of the reflected light when unpolarized infrared light was incident were evaluated.

[0204] The results are shown in Table 5. In Table 5, the item of refractive index condition is that the refractive index nI of the optical interference layer is (nA × nL) １／２ −0.03≦nI≦(nA×nL) １／２ +0.03 is satisfied, and if satisfied, it is marked A, and if not, it is marked C. The film thickness condition item is an item that indicates whether the film thickness of the optical interference layer satisfies the condition that it is within the range of ±30% of the λ / 4 condition or the range of ±30% of the 3λ / 4 condition with respect to the central wavelength λ of the reflection band, and if satisfied, it is marked A, and if not, it is marked C.

[0205] As a result, in the infrared light reflecting elements of Examples 1 to 7, the ratio of left-handed circularly polarized light to right-handed circularly polarized light at an incident angle of 25° at the center wavelength of the reflection band was small, at approximately 0.8% or less. On the other hand, the ratio of left-handed circularly polarized light to right-handed circularly polarized light in Comparative Examples 1 to 4 was large, at 1.0% or more. In other words, the infrared light reflecting elements of Examples 1 to 7 had a high circular polarization purity of reflected light. The above results clearly demonstrate the effects of the present invention.

[0206] Table 5. Types of infrared light reflecting elements used in Examples and Comparative Examples, and evaluation results of the ratio of right-handed circularly polarized light to left-handed circularly polarized light

[0207]

[0208] 10-11 Infrared light reflecting element 21a, 22a, 23a Reflecting layer A 21b, 22b, 24b Reflecting layer B 25 First laminated reflective layer 26 Second laminated reflective layer 27 Light interference layer 28 Adhesive layer 50 Head-mounted display (virtual reality display device) 52 Image display element 53, 55, 59 λ / 4 plate 54, 60 Absorptive linear polarizer 56 Half mirror 57 Support 58 Reflective circular polarizer 61 Infrared light reflecting element 62 Detector 100 Laminated optical film 101 Infrared light reflecting element 102 Retardation layer

Claims

1. An infrared light reflecting element having an adhesive layer, an optical interference layer, and at least one cholesteric liquid crystal layer, the central wavelength of the reflection band being within the range of 800 nm to 2500 nm, and the reflectance of light of the central wavelength being 20% ​​or more, wherein the refractive index of the adhesive layer is nA, and the average refractive index of the cholesteric liquid crystal layer adjacent to the optical interference layer is nL, the refractive index nI of the optical interference layer is (nA x nL). １／２ −0.03≦nI≦(nA×nL) １／２ +0.03, and the thickness of the optical interference layer is within the range of ±30% of the λ / 4 condition or within the range of ±30% of the 3λ / 4 condition with respect to the central wavelength λ of the reflection band.

2. The at least one cholesteric liquid crystal layer constitutes one or more laminated reflective layers, the laminated reflective layer includes a reflective layer A including at least one cholesteric liquid crystal layer formed substantially using a rod-shaped liquid crystal compound and not including a cholesteric liquid crystal layer formed substantially using a discotic liquid crystal compound, and a reflective layer B including at least one cholesteric liquid crystal layer formed substantially using a discotic liquid crystal compound and not including a cholesteric liquid crystal layer formed substantially using a rod-shaped liquid crystal compound, the adhesive layer, the optical interference layer, and the laminated reflective layer are adjacent to each other in this order, the refractive index of the adhesive layer is nA, and the average refractive index of the reflective layer A and the reflective layer B adjacent to the optical interference layer is nL, the refractive index nI of the optical interference layer is (nA x nL). １／２ −0.03≦nI≦(nA×nL) １／２ 2. The infrared light reflecting element according to claim 1, wherein the thickness of the optical interference layer is within a range of ±30% of the λ / 4 condition or within a range of ±30% of the 3λ / 4 condition with respect to a central wavelength λ of the reflection band.

3. An infrared light reflecting element as described in claim 2, wherein in one of the stacked reflective layers, the direction of rotation of the helical structures of all the cholesteric liquid crystal layers contained in the reflective layer A is the same as the direction of rotation of the helical structures of all the cholesteric liquid crystal layers contained in the reflective layer B.

4. The infrared light reflecting element according to claim 1, wherein the optical interference layer is a photo-alignment film.

5. The infrared light reflecting element according to claim 1, wherein the optical interference layer is a C plate.

6. The infrared light reflecting element according to claim 1, wherein the infrared light reflecting element has a visible light transmittance of 50% or more.

7. A laminated optical film comprising the infrared light reflecting element according to any one of claims 1 to 6 and a retardation layer.

8. An optical article comprising an infrared light reflecting element according to any one of claims 1 to 6 and a lens.

9. An optical article comprising the infrared light reflecting element according to any one of claims 1 to 6, and a prism or a substrate.

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