Virtual image display device, head-up display system, and transport aircraft

Abstract

Provided are: a virtual image display apparatus configured so as to be mounted to a transport machine and configured so that P-polarized image display light is incident on a projection part, the virtual image display apparatus having an image display device for emitting projection image light, and the virtual image display apparatus having a diffraction reflecting element having a positive optical power, and a 1 / 2 wavelength plate having a front surface retardation of 200-400 nm in the stated order from the image display device side on the optical path in which the projection image light is guided to the projection part; a head-up display system; and a transport machine provided with the virtual image display apparatus and the head-up display system.

Description

Technical Field

[0001] The present invention relates to a virtual image display device, a head-up display system, and a transport vehicle.

Background Art

[0002] A head-up display (hereinafter also referred to as "HUD") system is known that projects an image onto a windshield glass of a vehicle or the like and provides driving support information such as route guidance, driving speed, and warnings to a driver or the like through the windshield glass. With the HUD system, an observer can obtain various driving support information such as route guidance, driving speed, and vehicle status without significantly moving the line of sight or focus while looking at the outside world ahead, enabling safer and less stressful driving. The basic configuration of HUD is generally as follows. First, projection light from an image display device incorporated in the dashboard forms an intermediate image on the surface of an intermediate image screen (diffusion plate). This intermediate image is magnified by a concave mirror (magnifying glass), passes through a transmission window provided in the dashboard, and is reflected by a windshield glass incorporating a half mirror including a cholesteric liquid crystal layer or a dielectric multilayer film or the like, and is guided to a driver or the like. Hereinafter, the configuration from the image display device to the projection onto the windshield is also referred to as a virtual image display device. A driver or the like recognizes this intermediate image as a so-called virtual image in front of the windshield glass. That is, a driver or the like can recognize the driving support information as if it is floating on the road.

[0003] Various proposals have been made regarding virtual image display devices that constitute HUD systems. For example, Patent Document 1 describes a virtual image display device in which a concave mirror is changed to a positive diffractive optical element having a positive optical power (hereinafter also referred to as a positive diffractive reflecting element). According to Patent Document 1, with the virtual image display device having the above configuration, the robustness of visibility associated with the curvature of the virtual image can be improved, and since the diffractive optical element is a flat plate, it is easier to miniaturize compared to a HUD system using a concave mirror, and it is said that the mountability on a vehicle can be improved.

[0004] In general HUD systems, many projection image display devices of the HUD unit emit S-polarized light, and the windshield glass reflects the S-polarized light to allow a driver or the like to visually recognize a virtual image. At this time, since image light is reflected on the front and rear surfaces of the windshield glass, there is a problem that a double image is visually recognized. Also, since the image light is S-polarized light, there is a problem that the virtual image cannot be visually recognized when the driver wears polarized sunglasses. In order to solve these problems, research has also been conducted on HUD systems in which a P-polarized reflection film is incorporated into the windshield glass and the emitted light from the HUD unit is P-polarized light.

[0005] Also, as a technique for displaying a virtual image in multi-focus or 3D, for example, a technique using a light field display as a projection image display device, as described in Patent Document 2, is known. In a light field display, by forming microlenses on the light-emitting pixels, the focus for each light-emitting pixel can be changed, and an image with a large number of foci or a 3D image can be displayed.

Prior Art Documents

Patent Documents

[0006]

Patent Document 1

Patent Document 2

Summary of the Invention

[0007] It is believed that by combining the HUD unit equipped with a positive diffraction reflector described in Patent Document 1 with a windshield incorporating a P-polarizing reflective film, a HUD system can be obtained that is easily mountable in a vehicle and has good visibility of the virtual image display (improved robustness of visibility, elimination of double images, and suitability for polarized sunglasses). However, as a result of further research by the inventors, it has become clear that when a combination is used in which P-polarized light from a HUD unit equipped with a positive diffraction reflector is shone onto a windshield incorporating a P-polarized reflective film, the diffraction efficiency of the positive diffraction reflector is polarization-dependent because the period of the diffraction pattern is not uniform in the vertical and horizontal directions. This results in a problem where the brightness of the virtual image is reduced compared to a HUD unit using a general reflective mirror such as a concave mirror (magnifying mirror). Furthermore, when the light field display described in Patent Document 2 is applied, the number of pixels used for image display is significantly less than that of a single-focus image, resulting in an even darker image. For this reason, there is a need for a virtual image display device that has a configuration with minimal light loss in the optical path guiding the image light, which can increase the brightness of the virtual image even in a HUD system that displays multi-focus or 3D virtual images equipped with a light field display.

[0008] The present invention aims to provide a virtual image display device and a head-up display system equipped with a positive diffraction reflector, configured such that P-polarized image display light is incident on the projection unit, thereby improving the brightness of the virtual image display and enabling good visibility even when wearing polarized sunglasses, as well as a transport vehicle equipped with these. [Means for solving the problem]

[0009] In view of the above problems, the inventors conducted diligent studies and found that the above problems can be solved by configuring the light incident on the positive diffraction reflecting element to be linearly polarized with good diffraction efficiency, and by configuring the reflected light after diffraction to be P-polarized when it is incident on the projection unit, thus leading to the present invention.

[0010] In other words, the problem of the present invention was solved by the following means. [1] A virtual image display device configured to be mounted on a transport aircraft, wherein P-polarized image display light is incident on the projection unit, A virtual image display device having an image display device that emits projected image light, wherein, on the optical path that guides the projected image light to the projection unit, a diffraction reflector with positive optical power and a half-wave plate with a front retardation of 200 nm to 400 nm are provided in order from the image display device side. [2] The virtual image display device according to [1], wherein, on the optical path described above, a half-wave plate with a front retardation of 200 nm to 400 nm is provided between the diffractive reflector element with positive optical power described above and the image display device described above. [3] The virtual image display device according to [1] or [2], wherein the diffractive reflecting element with positive optical power is a reflective hologram element having a refractive index distribution with a fixed photosensitive material. [4] The diffractive reflective element with positive optical power described above has an alignment film and a liquid crystal layer, and has a liquid crystal alignment pattern corresponding to the periodic pattern of the alignment film, and is a diffractive element that has the function of diffracting and reflecting incident light, as described in [1] or [2]. [5] A virtual image display device according to any one of [1] to [4], wherein, on the optical path described above, a transmissive optical element with negative optical power is provided between the diffractive reflective element with positive optical power and the image display device described above. [6] The virtual image display device described in [5], wherein the above-mentioned negative optical power transmissive optical element is a transmissive hologram element having a refractive index distribution with a fixed photosensitive material. [7] The virtual image display device according to [5], wherein the above-mentioned negative optical power transmission optical element is a diffraction element having an alignment film and a liquid crystal layer, and having a liquid crystal alignment pattern corresponding to the periodic pattern of the alignment film, and having the function of diffracting and transmitting incident light. [8] The virtual image display device according to [5], wherein the above-mentioned negative optical power transmission optical element is a lens that refracts the above-mentioned projected image light. [9] The virtual image display device described in any one of [1] to [8] above, wherein the image display device is a light field display.

[10] A head-up display system comprising a windshield glass having a first glass plate, a P polarizing reflective film, and a second glass plate, and a virtual image display device according to any one of [1] to [9].

[11] The head-up display system according to

[10] , wherein the above-mentioned P polarizing reflective film has a layer made of cholesteric liquid crystal.

[12] The head-up display system according to

[10] , wherein the above-mentioned P polarizing reflective film has a layer formed by laminating an optically anisotropic layer and an optically isotropic layer.

[13] A transport aircraft equipped with a head-up display system as described in any one of

[10] to

[12] . [Effects of the Invention]

[0011] The virtual image display device of the present invention is equipped with a positive diffraction reflector and configured such that P-polarized image display light is incident on the projection unit, thereby improving the brightness of the virtual image display and allowing for good visibility even when wearing polarized sunglasses. Therefore, head-up displays and transport devices using the virtual image display device of the present invention have improved brightness of the virtual image display and allow for good visibility even when wearing polarized sunglasses. [Brief explanation of the drawing]

[0012] [Figure 1]This is a schematic diagram illustrating an example of the HUD system of the present invention. [Figure 2] This is a schematic diagram illustrating another example of the HUD system of the present invention. [Figure 3] This is a schematic diagram illustrating yet another example of the HUD system of the present invention. [Figure 4] This is a schematic diagram showing one example of the configuration of a windshield glass having a P-polarizing reflective film containing a layer made of cholesteric liquid crystal, used in the HUD system of the present invention. [Figure 5] This is a schematic cross-sectional view showing one example of the configuration of a windshield glass having a P-polarizing reflective film made of a dielectric multilayer film, used in the HUD system of the present invention. [Figure 6] Figure 5 is a schematic diagram showing the relationship between the refractive index of the P polarizing reflective film when the windshield glass is viewed from the front. [Modes for carrying out the invention]

[0013] In this invention, "~" is used to mean that the numerical values ​​written before and after it are included as the lower and upper limits. For example, when ε1 is between the numerical values ​​α1 and β1, the range of ε1 is the range that includes the numerical values ​​α1 and β1, and in mathematical notation, this is α1 ≤ ε1 ≤ β1. In this invention, the terms "angle" expressed as a specific numerical value such as 60°, and "parallel" and "perpendicular," unless otherwise specified, include an error range generally accepted in the technical field of this invention. For example, this means being within a range of less than ±10° from the exact angle, and the error from the exact angle is preferably 7° or less, and more preferably 5° or less.

[0014] In this invention, when we refer to "sense" in relation to circularly polarized light, we mean whether it is right-handed or left-handed circularly polarized. The sense of circularly polarized light is defined as follows: when light is viewed as if it were traveling towards the viewer, right-handed circular polarization occurs when the tip of the electric field vector rotates clockwise as time increases, and left-handed circular polarization occurs when it rotates counterclockwise.

[0015] In this invention, the term "sense" is sometimes used to refer to the twisting direction of the helix of a cholesteric liquid crystal. When the twisting direction (sense) of the helix of a cholesteric liquid crystal is to the right, it reflects right-circularly polarized light and transmits left-circularly polarized light. When the sense is to the left, it reflects left-circularly polarized light and transmits right-circularly polarized light.

[0016] In this invention, when the term "light" is used, unless otherwise specified, it refers to visible light and natural light (unpolarized). Visible light is electromagnetic radiation with wavelengths visible to the human eye, specifically light in the wavelength range of 380 to 780 nm. Invisible light is light with wavelengths less than 380 nm or greater than 780 nm. Furthermore, although not limited to these, visible light is defined as follows: light in the 420-490 nm wavelength range is blue light (B light), light in the 495-570 nm wavelength range is green light (G light), and light in the 620-750 nm wavelength range is red light (R light). In addition, although not limited to these, infrared light refers to the non-visible light range with wavelengths between 780 nm and 2000 nm.

[0017] In this invention, "visible light transmittance" refers to the visible light transmittance of a light source A as defined in JIS (Japanese Industrial Standards) R 3212:2015 (Test Methods for Automotive Safety Glass). Specifically, it is the transmittance obtained by measuring the transmittance at each wavelength in the range of 380 to 780 nm using a spectrophotometer with a light source A, and then multiplying the transmittance at each wavelength by a weighting coefficient obtained from the wavelength distribution and wavelength spacing of the CIE (International Commission on Illumination) standard relative luminous efficiency adapted to light, and taking a weighted average. Furthermore, when simply referring to "reflected light" or "transmitted light," it is used to include scattered light and diffracted light.

[0018] In this invention, "p-polarization," denoted using the lowercase letter p, refers to polarization that vibrates in a direction parallel to the plane of incidence of light. The plane of incidence is perpendicular to the reflective surface (such as the surface of a windshield glass) and includes both the incident and reflected light rays. In p-polarization, the plane of vibration of the electric field vector is parallel to the plane of incidence. On the other hand, "s-polarization," denoted using the lowercase letter s, refers to polarization that vibrates in a direction perpendicular to the plane of incidence of light. In s-polarization, the plane of vibration of the electric field vector is perpendicular to the plane of incidence. In the present invention, unless otherwise specified, "P-polarization" as expressed using a capital P means linearly polarized light in which the proportion of p-polarized light among the s-polarized and p-polarized light constituting the reflected light exceeds 50%. The proportion of p-polarized light among the s-polarized and p-polarized light constituting the above reflected light is preferably 60% or more, more preferably 80% or more, and even more preferably 90% or more. There is no limit to the above value of the proportion of p-polarized light among the s-polarized and p-polarized light constituting the above reflected light, but it is preferably 100% or less. Similarly, in the present invention, "S-polarization," as denoted by the capital letter S, means linear polarization in which the proportion of s-polarization among the s-polarization and p-polarization constituting the reflected light exceeds 50%. The proportion of s-polarization among the s-polarization and p-polarization constituting the reflected light is preferably 60% or more, more preferably 80% or more, and even more preferably 90% or more. There is no limit to the above value of the proportion of s-polarization among the s-polarization and p-polarization constituting the reflected light, but it is preferably 100% or less.

[0019] In this invention, an optical element with positive optical power means an element where 1 / f > 0 when f is the focal length, and includes light-gathering optical elements such as concave mirrors and convex lenses. A concave mirror gathers reflected light, and a convex lens gathers transmitted light. A diffraction-reflecting element with positive optical power means an optical element with positive optical power that has diffraction-reflecting functionality. On the other hand, an optical element with negative optical power refers to an element where 1 / f < 0 when f is the focal length, and examples include optical elements that diverge light, such as convex mirrors and concave lenses. A convex mirror diverges reflected light, and a concave lens diverges transmitted light. A transmissive optical element with negative optical power refers to an optical element with negative optical power that also has a light-transmitting function.

[0020] In this invention, the front phase difference (front retardation) is a value measured using an AxoScan manufactured by Axometrics. Unless otherwise specified, the measurement wavelength is 550 nm. The front phase difference can also be measured using a KOBRA21ADH or WR (manufactured by Oji Instruments Co., Ltd.) by incident light of a wavelength within the visible light range in the direction normal to the film. When selecting the measurement wavelength, the wavelength selection filter can be manually replaced, or the measured value can be converted using a program or the like.

[0021] In this invention, the birefringence (Δn) of the liquid crystal compound is a value measured according to the method described on page 214 of "Liquid Crystals: Fundamentals (edited by Mitsuji Okano and Shunsuke Kobayashi)". Specifically, Δn at 60°C can be determined by injecting the liquid crystal compound into a wedge-shaped cell, irradiating it with light of a wavelength of 550 nm, and measuring the refraction angle of the transmitted light.

[0022] In this invention, optical isotropy in the "optical isotropic layer" means that it does not exhibit birefringence. On the other hand, optical anisotropy in the "optical anisotropic layer" means that it exhibits birefringence, and in the optical anisotropic layer, as described later, the refractive index n in the slow axis direction in the plane e1 and the refractive index n in the direction perpendicular to this slow phase axis direction in the plane (the phase-advancing phase axis direction in the plane) o2 That is, n e1 >n o2 They are in a relationship.

[0023] In the present invention, "projection image" means an image based on the projection of light from the image display device used. In the virtual image display device and HUD system of the present invention, the projection image is perceived by the observer as a virtual image that appears to float in front of the projection area of ​​the windshield glass. In this invention, "image (screen image)" means an image displayed on the drawing device of a virtual image display device, or an image drawn on an intermediate image screen or the like by the drawing device. In contrast to a virtual image, an image is a real image. The images and projected images may be monochrome, multi-colored (two or more colors), or full-color.

[0024] Furthermore, in this invention, the term "liquid crystal compound" is used to include compounds that no longer exhibit liquid crystal properties due to curing reactions or the like.

[0025] The virtual image display device and HUD system of the present invention are typically used mounted on vehicles such as automobiles and trains, aircraft, and transport vehicles such as ships.

[0026] The virtual image display device of the present invention will be described in detail below in the attached description of a preferred embodiment illustrated in the accompanying drawings, relating to a head-up display system comprising the virtual image display device of the present invention and a windshield glass. Note that the dimensions and scale of parts in the drawings may differ from those of the actual parts for the sake of explanation. Furthermore, the drawings may be schematic in order to facilitate understanding.

[0027] <<Head-Up Display System (HUD System)>> The HUD system of the present invention is a windshield glass having a first glass plate, a P-polarizing reflective film, and a second glass plate, and a virtual image display device of the present invention.

[0028] The virtual image display device of the present invention is configured to be mounted on a transport vehicle and is configured such that P-polarized image display light is incident on the projection unit, This is a virtual image display device that emits projected image light, and in the optical path that guides this projected image light to the projection unit, the following elements are, in order from the image display device side: a diffraction reflector with positive optical power (hereinafter also simply referred to as a "positive diffraction reflector") and a half-wave plate with a front retardation of 200 nm to 400 nm (hereinafter also simply referred to as a "half-wave plate"). As described above, the virtual image display device of the present invention has a configuration in which a half-wave plate is placed in the optical path from the positive diffraction reflector element to the projection unit. When projected image light from the image display device is incident on the positive diffraction reflector element, this incident light is made into S-polarized light, which has excellent diffraction efficiency in the positive diffraction reflector element. At the same time, the polarization state of the diffracted reflected light from the positive diffraction reflector element is changed from S-polarized to P-polarized by the half-wave plate, and it becomes P-polarized when incident on the projection unit. To elaborate on the diffraction reflection of s-polarized and p-polarized light in the positive diffraction reflector element, the vibration plane of the electric field vector of p-polarized light is perpendicular to the diffraction pattern of the positive diffraction reflector element, so the pitch spacing in the diffraction pattern changes depending on the incident angle, resulting in poor diffraction efficiency. In contrast, the vibration plane of the electric field vector of s-polarized light is parallel to the diffraction pattern of the positive diffraction reflector element, so the pitch spacing in the diffraction pattern hardly changes with respect to the incident angle, and even if the incident angle changes, the emission angle does not deviate from the design value, showing excellent diffraction efficiency. As described above, the HUD system of the present invention, which combines the virtual image display device of the present invention with a windshield glass having a P-polarizing reflective film, has a configuration that suppresses light loss in the optical path that guides the projected image light, thereby improving the brightness of the virtual image display and allowing for good visibility even when wearing polarized sunglasses.

[0029] The virtual image display device of the present invention is configured to be mounted on a transport vehicle, and is configured such that P-polarized image display light is incident on the projection unit. To explain using a vehicle as an example, it is mounted on the vehicle by being housed in the vehicle's instrument panel or dashboard, and is arranged and configured so that P-polarized image display light can be incident on the vehicle's windshield glass, which is the projection unit.

[0030] Figures 1-3 show an example of the HUD system of the present invention. The HUD system 20 of the present invention, shown in Figures 1-3, comprises a windshield glass 24 and a virtual image display device 1.

[0031] The virtual image display device 1 shown in Figure 1 comprises an image display device 2, a positive diffraction reflector 3, and a half-wave plate 5A. The virtual image display device 1 shown in Figure 1 has a configuration in which the image display device 2, the positive diffraction reflector 3, and the half-wave plate 5A are arranged in this order on the optical path that guides the projected image light emitted from the image display device 2 to the windshield glass 24, which is the projection unit. The virtual image display device 1 shown in Figure 2 has a configuration in which a half-wave plate 5B is placed between the image display device 2 and the positive diffraction reflector 3 on the optical path shown in the virtual image display device 1 shown in Figure 1. That is, the virtual image display device 1 shown in Figure 2 has a configuration in which the image display device 2, the half-wave plate 5B, the positive diffraction reflector 3, and the half-wave plate 5A are arranged in this order on the optical path that guides the projected image light emitted from the image display device 2 to the windshield glass 24 which is the projection unit. The virtual image display device 1 shown in Figure 3 has a configuration in which a negative transmissive optical element 7 is placed between the half-wave plate 5B and the positive diffraction reflector element 3 on the optical path shown in the virtual image display device 1 shown in Figure 2. That is, the virtual image display device 1 shown in Figure 3 has a configuration in which the image display device 2, the half-wave plate 5B, the negative transmissive optical element 7, the positive diffraction reflector element 3, and the half-wave plate 5A are arranged in this order on the optical path that guides the projected image light emitted from the image display device 2 to the windshield glass 24, which is the projection unit. In Figures 1-3, S represents S-polarization and P represents P-polarization, while in Figures 2 and 3, L represents linear polarization. These represent the types of polarization of the projected image light emitted from the image display device 2 until it reaches the observer D.

[0032] The windshield glass 24 shown in Figures 1-3 is composed of a first glass plate 30, a P-polarized reflective film 10, and a second glass plate 28 in that order. The windshield glass 24 is positioned such that the P-polarized image display light from the virtual image display device 1 is incident on the second glass plate 28 side. The P-polarized light is reflected by the P-polarized reflective film 10, and the image projected onto the windshield glass 24, which is the projection unit, is observed by observer D as a virtual image through the windshield glass 24. The virtual image display device 1 and the windshield glass 24 will be described in order below.

[0033] <Virtual Image Display Device> As shown in Figures 1-3, the virtual image display device 1 comprises an image display device 2, a positive diffraction reflector 3, and a half-wave plate 5A in this order along the optical path that guides the projected image light emitted from the image display device 2 to the windshield glass 24, which is the projection unit.

[0034] [1] Positive diffraction reflector As long as the positive diffraction reflecting element 3 is an optical element that diffracts and reflects projected image light emitted from the image display device 2, any commonly used positive diffraction reflecting element can be used without any particular limitations. As described above, the virtual image display device 1 of the present invention has, in the optical path that guides the projected image light emitted from the image display device 2 to the windshield glass 24 which is the projection unit, a positive diffraction reflecting element 3, a half-wave plate 5A, and the windshield glass 24 which is the projection unit, in order from the image display device 2 side. This configuration allows the light diffracted and reflected by the positive diffraction reflecting element 3 to be S-polarized, which has excellent diffraction efficiency, and the half-wave plate 5A to convert the S-polarized light to P-polarized light, thereby allowing the P-polarized light that is efficiently reflected to be incident on the P-polarized reflective film 10 on the windshield glass 24.

[0035] Examples of positive diffraction-reflecting elements 3 include a reflective hologram element with a fixed refractive index distribution using a photosensitive material (hereinafter also simply referred to as a "positive reflection-type hologram element"), and a diffraction element having an alignment film and a liquid crystal layer, having a liquid crystal alignment pattern corresponding to the periodic pattern of the alignment film, and having the function of diffracting and reflecting incident light (hereinafter also simply referred to as a "positive reflection-type liquid crystal diffraction element").

[0036] (Positive reflective holographic element) A positive reflective holographic element has a refractive index distribution in which high and low refractive indices are periodically distributed, and functions as a positive diffractive reflecting element. As a positive reflective hologram element, for example, as shown in Figure 3 of Japanese Patent Application Publication No. 2020-56880, a volume-type hologram element can be formed in the shape of a thin plate, particularly a flat plate, by sandwiching a hologram layer between a pair of light-transmitting substrate layers. The periodic refractive index distribution in the hologram layer functions as a diffraction structure.

[0037] A pair of translucent substrate layers are formed in the form of thin, translucent plates made of, for example, synthetic resin or glass, to protect and reinforce the hologram layer.

[0038] The hologram layer is formed by pre-recording information about the amplitude and phase of object light as interference fringes with reference light in the hologram material. These interference fringes are those manifested by the periodic refractive index distribution described above. The hologram material can be selectively selected from materials that can record information about the amplitude and phase of object light through spatial modulation of the refractive index, such as synthetic resin-based materials, gelatin-sensitive materials, or silver halide-sensitive materials.

[0039] In a positive reflective hologram element, interference fringes are formed in the hologram layer that focus and diffract the display light. This diffraction primarily utilizes first-order diffracted light, which has the highest diffraction efficiency. Furthermore, positive reflective hologram elements reflect light without polarization properties, resulting in unpolarized reflection.

[0040] A positive reflective hologram element, which achieves positive optical power using first-order diffracted light, achieves chromatic dispersion in the opposite direction to that of a convex refractive lens, which exhibits normal dispersion for visible light. In other words, the magnitude of the deflection angle due to diffraction by a positive reflective hologram element works to be greater for longer wavelength light than for shorter wavelength light.

[0041] Positive reflective holographic elements can be fabricated by conventional methods. For example, by splitting a laser beam into two using a beam splitter for a photosensitive material, and using these two separated laser beams, information about the amplitude and phase of the object light is created as an interference pattern (periodic refractive index distribution) with a reference light. Once the refractive index distribution is formed in the photosensitive material, it is hardened to fabricate a volume-type reflective hologram element. By adjusting the irradiation direction and / or irradiation surface of the laser light to match the size of the windshield glass, the distance between the windshield glass and the virtual image display device, and other optical components, a desired interference pattern can be created to obtain a hologram element that exhibits the desired diffraction reflection.

[0042] (Positive reflection type liquid crystal diffraction element) A positive reflective liquid crystal diffraction element is not particularly limited as long as it has an alignment film and a liquid crystal layer, has a liquid crystal alignment pattern corresponding to the periodic pattern of the alignment film, and has the function of diffracting and reflecting incident light. For example, the optical element described in International Publication No. 2019 / 131966 has little wavelength dependence of the reflection angle and can reflect red, green, and blue light incident from the same direction in almost the same direction, and is therefore preferably used as the positive reflection type liquid crystal diffraction element. Furthermore, a positive reflective liquid crystal diffraction element reflects light with polarization characteristics, specifically circular polarization. Therefore, when incorporating it into the virtual image display device 1 of the present invention, a quarter-wave plate is bonded to the positive reflective liquid crystal diffraction element, and the projected image light from the image display device 2 is incident on the quarter-wave plate side, thereby using it as a positive diffractive reflecting element that reflects linearly polarized light.

[0043] Positive reflection type liquid crystal diffraction elements can be fabricated by conventional methods. For example, a reflective liquid crystal diffraction element can be fabricated by forming an alignment film on a primer layer formed on a support, irradiating this alignment film with laser light, controlling the interference pattern (surface periodic structure) by changing the intersection angle of the two laser beams, curing the film, and then forming a cholesteric liquid crystal layer on the resulting photo-alignment film. For example, one can refer to the method for fabricating optical elements described in International Publication No. 2019 / 131966.

[0044] [2] 1 / 2 wavelength plate As shown in Figures 1 to 3, in the virtual image display device 1 of the present invention, the half-wave plate 5A is positioned between the positive diffraction reflecting element 3 and the windshield glass 24, which is the projection unit, on the optical path that guides the projected image light emitted from the image display device 2 to the windshield glass 24, which is the projection unit. Furthermore, as shown in Figures 2 and 3, the virtual image display device 1 of the present invention may also have a half-wave plate 5B in the optical path between the positive diffraction reflector 3 and the image display device 2, in addition to the half-wave plate 5A. Both the half-wave plates 5A and 5B described above can be used as appropriate for the purpose, without any particular limitations, as long as they are half-wave plates with a front retardation of 200 nm to 400 nm at a wavelength of 550 nm, as measured by the method described above.

[0045] As described above, the virtual image display device 1 of the present invention provides a half-wave plate 5A between a positive diffraction reflecting element 3 and the windshield glass 24, which is the projection unit, in the optical path that guides the projected image light emitted from the image display device 2 to the windshield glass 24, which is the projection unit. This allows the S-polarized light efficiently diffracted and reflected by the positive diffraction reflecting element 3 to be converted into P-polarized light efficiently reflected by the P-polarized reflective film 10 on the windshield glass 24. Furthermore, as shown in Figures 2 and 3, if the virtual image display device 1 of the present invention has a half-wave plate 5B between the positive diffraction reflecting element 3 and the image display device 2 in the optical path, the projected image light emitted from the image display device 2 can be converted into S-polarized light that is diffracted and reflected with high diffraction efficiency by the positive diffraction reflecting element 3. This configuration further reduces optical loss in the optical path that guides the projected image light, thereby improving the brightness of the virtual image display and visibility when wearing polarized sunglasses.

[0046] Examples of half-wave plates 5A and 5B include stretched polycarbonate film, stretched norbornene-based polymer film, transparent film containing and oriented birefringent inorganic particles such as strontium carbonate, thin film in which an inorganic dielectric is obliquely deposited on a support, film in which a polymerizable liquid crystal compound is uniaxially oriented and fixed in orientation, and film in which a liquid crystal compound is uniaxially oriented and fixed in orientation.

[0047] In particular, films in which polymerizable liquid crystal compounds are uniaxially oriented and their orientation fixed are preferably exemplified as half-wave plates 5A and 5B. Such half-wave plates 5A and 5B can be formed, for example, by coating a liquid crystal composition containing a polymerizable liquid crystal compound onto a transparent substrate, a temporary support, or the surface of an alignment layer, forming the polymerizable liquid crystal compound in the liquid crystal composition in a nematic alignment in a liquid crystal state, and then fixing it by curing. In this case, the formation of the half-wave plates 5A and 5B can be carried out in the same manner as the formation of the cholesteric liquid crystal layer described later, except that no chiral agent is added to the liquid crystal composition. However, when nematic orientation is performed after coating the liquid crystal composition, the heating temperature is preferably 50 to 120°C, and more preferably 60 to 100°C.

[0048] The half-wave plates 5A and 5B may be layers obtained by coating a composition containing a polymer liquid crystal compound onto the surface of a transparent substrate, temporary support, or orientation layer, forming a nematic orientation in a liquid crystal state, and then fixing this orientation by cooling.

[0049] The half-wave plates 5A and 5B may be formed by bonding two quarter-wave plates together using highly transparent adhesive transfer tape (OCA tape). As long as the quarter-wave plates can be obtained, there are no particular restrictions on the type of plate used. For example, a quarter-wave plate with a front retardation of 100 nm to 200 nm is preferred.

[0050] There are no restrictions on the thickness of the half-wave plates 5A and 5B, but 0.2 to 300 μm is preferred, 0.5 to 150 μm is more preferred, and 1.0 to 80 μm is even more preferred. Similarly, there are no particular restrictions on the thickness of the half-wave plates 5A and 5B formed from the liquid crystal composition, but 0.2 to 10 μm is preferred, 0.5 to 5.0 μm is more preferred, and 0.7 to 2.0 μm is even more preferred.

[0051] When incorporating the half-wave plates 5A and 5B into the HUD system 20, the slow-phase axis direction of the half-wave plates 5A and 5B is adjusted by rotating them so that the transmitted light has the desired polarization. Specifically, the half-wave plate 5A is positioned as shown in Figures 1-3 so that the transmitted light, i.e., the light incident on the windshield glass 24, is P-polarized. On the other hand, the half-wave plate 5B is arranged so that the transmitted light, i.e., the light incident on the positive diffraction reflector 3, is S-polarized, as shown in Figures 2 and 3. In the virtual image display device 1 shown in Figure 2, the S-polarized light transmitted from the half-wave plate 5B is directly incident on the positive diffraction reflector 3, while in the virtual image display device 1 shown in Figure 3, the S-polarized light transmitted from the half-wave plate 5B passes through the negative transmission optical element 7 while remaining S-polarized, and is incident on the positive diffraction reflector 3 as S-polarized light. Furthermore, if the P polarizing reflective film 10 has a layer made of cholesteric liquid crystal (also referred to as the "cholesteric liquid crystal layer"), and / or if the positive diffraction reflective element 3 is a positive reflective liquid crystal diffraction element, it is preferable to determine the value according to the sense of the helix of the cholesteric liquid crystal layer. The direction of the slow axis of the half-wave plates 5A and 5B can be set, for example, by rubbing the underlying alignment layer if the half-wave plates 5A and 5B consist of cholesteric liquid crystal layers.

[0052] [3] Negative transmission optical element The virtual image display device of the present invention may have a negative optical power transmissive optical element (also simply referred to as a "negative transmissive optical element") between the positive diffraction reflector and the image display device in the optical path described above. In the present invention, if the virtual image display device has a negative transmissive optical element between a positive diffraction reflector and an image display device in the optical path, it is preferable because the combination of a positive diffraction reflector that focuses light and a negative transmissive optical element that diffuses light can improve chromatic aberration. That is, since the direction of color shift caused by the difference in angle of deviation due to diffraction is opposite between the positive diffraction reflector and the negative transmissive optical element, the color shift can be canceled out and chromatic aberration reduced by bringing the value shown in the following equation 1 closer to 0. 1 / (v1·f1)+1 / (v2·f2) (Equation 1) In the above formula, the optical power of the positive diffraction / reflecting element is 1 / f² and the chromatic dispersion coefficient is v², while the optical power of the negative transmission optical element is 1 / f¹ and the chromatic dispersion coefficient is v¹.

[0053] The present invention is not particularly limited in its configuration as a virtual image display device having a negative transmissive optical element, as long as it is positioned between a positive diffractive reflective element and an image display device in the optical path that guides projected image light to the projection unit. For example, as shown in Figure 3, the negative transmissive optical element 7 can be positioned between the image display device 2 and the positive diffraction reflector 3, and between the half-wave plate 5B and the positive diffraction reflector 3. Alternatively, in the virtual image display device 1 of Figure 2, the negative transmissive optical element 7 may be positioned between the image display device 2 and the positive diffraction reflector 3, and between the image display device 2 and the half-wave plate 5B. Furthermore, in the virtual image display device 1 of Figure 1, the negative transmissive optical element 7 may be positioned between the image display device 2 and the positive diffraction reflector 3. Furthermore, from the viewpoint of further improving diffraction efficiency, it is preferable to position the half-wave plate 5B between the image display device 2 and the negative transmission optical element 7, as shown in Figure 3.

[0054] As long as the negative transmission optical element 7 has negative optical power and transmits projected image light emitted from the image display device 2, any commonly used negative transmission optical element can be used without any particular limitations. Examples of negative transmission optical elements 7 include a transmission hologram element with a fixed refractive index distribution using a photosensitive material (hereinafter also simply referred to as a "negative transmission hologram element"), a diffraction element having an alignment film and a liquid crystal layer, having a liquid crystal alignment pattern corresponding to the periodic pattern of the alignment film, and having the function of diffracting and transmitting incident light (hereinafter also simply referred to as a "negative transmission liquid crystal diffraction element"), and a lens that refracts projected image light (hereinafter also simply referred to as a "negative transmission refractive lens").

[0055] (Negative transmission hologram element) A negative transmission hologram element has a refractive index distribution in which high and low refractive indices are periodically distributed, and functions as a negative diffraction transmission element. For negative transmission hologram elements, the description relating to the positive reflection hologram element described above can be applied, except that the optical power is adjusted to be negative (1 / f < 0) instead of positive (1 / f > 0) in the positive reflection hologram element described above. Similarly, the method for manufacturing negative transmission hologram elements can be applied, except that the optical power is adjusted to be negative instead of positive, as described above.

[0056] In the hologram layer of a negative transmission hologram element, interference fringes are formed that transmit display light while simultaneously diffracting and diverging this display light. The primary diffraction light, which has the highest diffraction efficiency, is primarily used for this diffraction.

[0057] Negative transmission hologram elements, which achieve negative optical power using first-order diffracted light, achieve chromatic dispersion in the opposite direction to concave refractive lenses, which exhibit normal dispersion for visible light. In other words, the magnitude of the deflection angle due to diffraction by a negative transmission hologram element works to be greater for longer wavelength light than for shorter wavelength light.

[0058] (Negative transmission liquid crystal diffraction element) A negative transmission liquid crystal diffraction element is not particularly limited, as long as it has an alignment film and a liquid crystal layer, a liquid crystal alignment pattern corresponding to the periodic pattern of the alignment film, and the function of diffracting and transmitting incident light. As a negative transmission liquid crystal diffraction element, the description relating to the positive reflection liquid crystal diffraction element described above can be applied, except that, as in the positive reflection liquid crystal diffraction element described above, a chiral agent is not added to prevent the liquid crystal layer from undergoing cholesteric orientation so that the optical power becomes negative instead of positive. Regarding the method for fabricating negative transmission liquid crystal diffraction elements, the description of the method for fabricating positive reflection liquid crystal diffraction elements described above can be applied, except that chiral agents are not incorporated to prevent cholesteric orientation when forming the liquid crystal layer. For example, the method for fabricating optical elements described in International Publication No. 2020 / 56880 can be referenced. Furthermore, the intersection angle of the laser beam can be adjusted so that it is small at the center of the element and large at the edges of the element, in order to obtain a negative transmission liquid crystal diffraction element exhibiting desired characteristics, depending on the size of the windshield glass, the distance between the windshield glass and the virtual image display device, and other optical components.

[0059] (Negative transmission refractive lens) Unlike the negative diffractive optical elements described above, negative transmissive refractive lenses are formed to be light-transmitting, for example, using synthetic resin or glass that exhibits normal dispersion with respect to visible light, and transmit light while refracting it at their surface.

[0060] Negative transmission refractive lenses have negative optical power and are concave lenses that diverge the displayed light through refraction. Negative transmission refractive lenses, being concave lenses, can be biconcave lenses, plano-concave lenses, or concave meniscus lenses. Negative transmission refractive lenses can be manufactured by conventional methods, adjusting them to exhibit desired optical properties in accordance with the size of the windshield glass, the distance between the windshield glass and the virtual image display device, and other optical components.

[0061] [4] Image display device Image display device 1 is an image display device that emits projected image light (hereinafter also referred to as "projected light"), and includes a "device for projecting a drawn image", and emits projected light carrying the image to be displayed. In the virtual image display device 1 of the present invention, the projected image light emitted by the image display device 1 only needs to be S-polarized so that it can be incident on the positive diffraction reflector element 3, and is preferably linearly polarized. In the virtual image display device 1 shown in Figure 1, since there is no half-wave plate 5B, it is preferable that the projected image light emitted from the image display device 2 is S-polarized. In the virtual image display device 1 shown in Figures 2 and 3, since there is a half-wave plate 5B, the projected image light emitted from the image display device 2 only needs to be linearly polarized such that the light incident on the positive diffraction reflector 3 is S-polarized. Furthermore, in this invention, not only S-polarized light but also image display devices that project linearly polarized light, rotated in azimuth from S-polarized light by an azimuth angle of more than 0° to about 10°, can be preferably used. The azimuth angle refers to the angle by which the vibration axis is rotated in a plane containing the vibration axes of S-polarized and P-polarized light. That is, linearly polarized light rotated in azimuth from S-polarized light by more than 0° to about 10° refers to linearly polarized light having a vibration axis rotated from -10° to 10° relative to the vibration axis of S-polarized light. In the virtual image display device 1, the image display device 2 should be arranged so that S-polarized light is incident on the positive diffraction reflector 3.

[0062] In the HUD system 20, the image display device 2 preferably includes a drawing device and reflects an image (real image) drawn on a small intermediate image screen as a virtual image using a combiner. The image display device 2 can use a standard image display device used in HUD systems, as long as it can emit linearly polarized projected light.

[0063] The virtual image display device 1 of the present invention is preferably one in which the imaging distance of the virtual image, that is, the imaging position of the virtual image, is variable. Methods for changing the imaging distance of a virtual image in a virtual image display device include, for example, moving the image generation surface (screen) (see Japanese Patent Publication No. 2017-21302), switching between multiple optical paths with different optical path lengths (see WO2015 / 190157), changing the optical path length by inserting and / or moving a mirror, changing the focal length by using a lens assembly as an imaging lens, moving the image display device, switching between multiple image display devices with different virtual image imaging distances, and using a variable focus lens (see WO2010 / 116912).

[0064] The virtual image display device may be one that can continuously change the imaging distance of the virtual image, or one that can switch the imaging distance of the virtual image at two or three or more points. Here, it is preferable that at least two of the virtual images projected by the virtual image display device have different image formation distances of 1 m or more. Therefore, if the virtual image display device is capable of continuously changing the image formation distance of the virtual images, it is preferable that the image formation distance of the virtual images can be changed by 1 m or more. Using such a virtual image display device is preferable because it can suitably handle situations where the driver's line of sight differs greatly, such as when driving at normal speeds on ordinary roads and when driving at high speeds on expressways.

[0065] In the virtual image display device 1 of the present invention, a light field display can also be used as the image display device 2. A light field display refers to an image display device having light-emitting pixels and microlenses, with microlenses formed on the light-emitting pixels. As mentioned above, a light field display can change the focus of each light-emitting pixel, allowing it to display multi-focus and / or 3D images. However, since the number of pixels used for image display is significantly less than that for single-focus images, the brightness of the image decreases. In contrast, the virtual image display device of the present invention has a configuration that suppresses light loss in the optical path that guides the projected image light, thereby improving the brightness of the virtual image display and visibility when wearing polarized sunglasses. Any commonly used light field display can be used as the light field display without any particular limitations. For example, the light field display described in Japanese Patent Publication No. 2020-160296 can be cited.

[0066] (Drawing device) The drawing device may be a device that displays an image itself, or it may be a device that emits light capable of drawing an image. In a drawing device, the light from a light source should be adjusted by a drawing method such as an optical modulator, laser luminance modulation means, or optical deflection means for drawing. A drawing device means a device that includes a light source and further includes an optical modulator, laser luminance modulation means, or optical deflection means for drawing, depending on the drawing method.

[0067] (light source) There are no particular restrictions on the light source that constitutes the image display device 2; commonly used light sources for image display devices, drawing devices, and displays, such as LEDs (light-emitting diodes), organic light-emitting diodes (OLEDs), discharge tubes, and laser light sources, can be used. Of these, LEDs and discharge tubes are preferred because they are suitable as light sources for drawing devices that emit linearly polarized light, and LEDs are particularly preferred. This is because LEDs have an emission wavelength that is not continuous in the visible light region, making them suitable for combination with combiners that use a cholesteric liquid crystal layer that exhibits selective reflection in a specific wavelength range, as will be described later.

[0068] (Drawing method) The drawing method can be selected according to the laser light source and is not particularly limited. Examples of drawing methods include methods using fluorescent display tubes, LCD (Liquid Crystal Display) and LCOS (Liquid Crystal on Silicon) methods utilizing liquid crystals, DLP (Registered Trademark) (Digital Light Processing) methods, and, for example, scanning methods utilizing lasers. The display method may also be one that uses a fluorescent display tube integrated with the light source. An LCD display method is preferred.

[0069] In LCD and LCOS systems, light of each color is modulated and combined by an optical modulator, and the light is emitted from the projection lens. DLP (Digital Light Projection) is a display system that uses a DMD (Digital Micromirror Device), where micromirrors equal to the number of pixels are arranged to create the image, and light is emitted from the projection lens.

[0070] The scanning method involves scanning a light ray across a screen and creating an image using the afterimage of the eye. For example, see the descriptions in Japanese Patent Publication No. 7-270711 and Japanese Patent Publication No. 2013-228674. In the scanning method using a laser, it is sufficient that luminance-modulated laser light of each color, such as red, green, and blue light, is combined into a single light ray using a multiplexing optical system or a focusing lens, and that the light ray is scanned by a light deflection means and drawn on an intermediate image screen, which will be described later. In the scanning method, for example, the brightness modulation of red, green, and blue laser light may be performed directly as a change in the intensity of the light source, or it may be performed by an external modulator. Examples of optical deflection means include galvanometer mirrors, a combination of galvanometer mirrors and polygon mirrors, and MEMS (Micro Electro Mechanical Systems), of which MEMS is preferred. Examples of scanning methods include random scanning and raster scanning, of which raster scanning is preferred. In raster scanning, the laser light can be driven, for example, at the resonant frequency in the horizontal direction and with a sawtooth wave in the vertical direction. Since the scanning method does not require a projection lens, it is easy to miniaturize the device.

[0071] As mentioned above, the light emitted from the drawing device should be adjusted so that S-polarized light is incident on the positive diffraction reflector 3, and linear polarization is preferred. In drawing devices using LCD or LCOS drawing methods, and in drawing devices using laser light sources, the emitted light is essentially linearly polarized. In drawing devices where the emitted light is linearly polarized and the emitted light contains light of multiple wavelengths (colors), it is preferable that the polarization direction (transmission axis direction) of the light of multiple wavelengths is the same. It is known that some commercially available drawing devices have non-uniform polarization directions in the wavelength ranges of red, green, and blue light (see Japanese Patent Publication No. 2000-221449). Specifically, there are known examples where the polarization direction of green light is orthogonal to the polarization directions of red light and blue light. In the HUD system 20 of the present invention, the projected light emitted by the virtual image display device 1 is P-polarized.

[0072] (Intermediate image screen) As described above, the drawing device may use an intermediate image screen. The "intermediate image screen" is a screen on which an image is drawn. That is, when the light emitted from the drawing device is not yet visible as an image, the drawing device uses this light to form a visible image on the intermediate image screen. The image drawn on the intermediate image screen may be projected onto the combiner by light passing through the intermediate image screen, or it may be projected onto the combiner after being reflected from the intermediate image screen.

[0073] Examples of intermediate image screens include scattering films, microlens arrays, and screens for rear projection. When a plastic material is used as the intermediate image screen, if the intermediate image screen has birefringence, the polarization plane and light intensity of the polarized light incident on the intermediate image screen are disturbed, which can easily cause color unevenness in the combiner (P polarized reflective film 10). However, this problem of color unevenness can be reduced by using a phase difference film with a predetermined phase difference. As an intermediate image screen, one that has the function of spreading and transmitting incident light rays is preferable, because it enables magnified display of the projected image. Examples of such intermediate image screens include screens composed of a microlens array. Microarray lenses used in HUD systems are described, for example, in Japanese Patent Publication No. 2012-226303, Japanese Patent Publication No. 2010-145745, and Japanese Patent Publication No. 2007-523369. The projector may include a reflector or the like that adjusts the optical path of the projected light formed by the drawing device.

[0074] For HUD systems using windshield glass as a reflective film, refer to Japanese Patent Publication No. 2-141720, Japanese Patent Publication No. 10-96874, Japanese Patent Publication No. 2003-98470, U.S. Patent No. 5013134, and Japanese Patent Publication No. 2006-512622, etc.

[0075] Windshield glass is particularly useful in HUD systems that use image display devices such as lasers, LEDs, and OLEDs (organic light-emitting diodes) as light sources, where the emission wavelength is not continuous in the visible light region. This is because the center wavelength of selective reflection of the cholesteric liquid crystal layer can be adjusted to match each emission wavelength. It can also be used for projection of displays such as LCDs (liquid crystal displays) where the display light is polarized.

[0076] [Projection light (incident light)] It is preferable that the light incident on the windshield glass 24 from the virtual image display device 1 of the present invention is incident at an oblique angle of 45° to 70° with respect to the normal of the P-polarized reflective film 10. The Brewster angle at the interface between glass with a refractive index of about 1.51 and air with a refractive index of 1 is about 56°, and by incidenting P-polarized light within the above-mentioned angle range, the amount of reflected light from the surface of the windshield glass 24 on the viewing side is reduced relative to the selective reflective layer of the P-polarized reflective film 10 for projected image display, making it possible to display an image with less double image influence. The angle mentioned above is preferably 50° to 65°. In this case, the projected image can be observed on the incident side of the projected light at an angle of 45° to 70°, preferably 50° to 65°, on the opposite side from the incident light, with respect to the normal of the selective reflective layer of the P-polarized reflective film 10.

[0077] The incident light may enter the windshield glass 24 from any direction, such as above, below, left, or right, and should be determined in accordance with the viewing direction. For example, a configuration in which the light enters from below at the oblique angle described above is preferred. In the present invention, the P-polarized reflective film 10 in the windshield glass 24 is arranged to reflect incident p-polarized light.

[0078] As described above, in the HUD system 20 of the present invention, the image display light (projected light) emitted from the virtual image display device 1 of the present invention and incident on the projection unit is P-polarized. As described above, when using a virtual image display device 1 in which the polarization direction of the emitted light is not uniform in the wavelength ranges of red, green, and blue light, it is preferable to selectively adjust the polarization direction to allow P-polarization to occur in the wavelength ranges of all colors.

[0079] As described above, the HUD system 20 may be a projection system that allows for variable virtual image formation position. By allowing for variable virtual image formation position, the driver can view the virtual image more comfortably and conveniently. The virtual image formation position is the position from which the vehicle driver can see the virtual image, for example, a position at least 1000 mm away from the driver, beyond the windshield glass.

[0080] In Figures 1-3, the vertical direction Y of the windshield glass 24 refers to the long axis direction of the windshield glass 24 on the plane of the paper. This direction corresponds to the vertical direction of the vehicle, etc., on which the windshield glass 24 is installed, with the ground side being the bottom and the opposite side being the top. Note that when the windshield glass 24 is installed on a vehicle, etc., it may be installed at an angle for structural or design reasons. In this case, the vertical direction Y will be along the surface of the windshield glass 24. The surface is the outer side of the vehicle.

[0081] In the HUD system 20, the virtual image display device 1 emits P-polarized projected light onto the second glass plate 28 of the windshield glass 24. By using P-polarized projected light emitted by the virtual image display device 1 onto the windshield glass 24, reflection of the projected light by the first glass plate 30 and the second glass plate 28 of the windshield glass 24 can be significantly reduced, thereby suppressing problems such as the observation of double images. Preferably, the virtual image display device 1 emits P-polarized projected light onto the windshield glass 24 at a Brewster angle. This eliminates reflection of the projected light from the first glass plate 30 and the second glass plate 28, enabling the display of a clearer image.

[0082] <Windshield glass> In Figures 1-3, the windshield glass 24 is a windshield glass having a first glass plate 30, a P polarizing reflective film 10, and a second glass plate 28 in that order.

[0083] Windshield glass refers to the windows and windshields of vehicles such as cars and trains, airplanes, ships, motorcycles, and amusement rides. Windshield glass is preferably used as the front windshield and windshield located in the direction of travel of the vehicle.

[0084] The windshield glass 24A shown in Figure 4 comprises, in this order, a second glass plate 28, a heat-seal layer 38, a P-polarizing reflective film 10A, an interlayer 36, and a first glass plate 30. In Figure 4, the P polarizing reflective film 10A is arranged such that the polarization conversion layer 14 is on the first glass plate 30 side and the phase difference layer 16 (transparent substrate 18) is on the second glass plate 28 side. The windshield glass 24B shown in Figure 5 comprises, in this order, a second glass plate 28, an interlayer 36, a P-polarizing reflective film 10B, another interlayer 36, and a first glass plate 30.

[0085] When the above-mentioned windshield glass is used in a vehicle, curved glass is often used for the second glass plate 28 and the first glass plate 30. In that case, if the second glass plate 28 is on the inside of the vehicle and the first glass plate 30 is on the outside of the vehicle, the second glass plate 28 is positioned with its convex side facing the first glass plate 30, and the first glass plate 30 is positioned with its concave side facing the second glass plate 28.

[0086] When the second glass plate 28 and the first glass plate 30 are curved glass, in the example shown in Figure 4, the polarization conversion layer 14 and the selective reflection layer 11 are arranged in that order from the concave side of the first glass plate 30 toward the second glass plate 28. The phase difference layer 16 is also arranged between the selective reflection layer 11 and the second glass plate 28.

[0087] From a legal regulatory standpoint, the visible light transmittance of the windshield glass is preferably 70% or higher, more preferably over 70%, even more preferably 75% or higher, and particularly preferably 80% or higher. The above-mentioned visible light transmittance is preferably satisfied at any position on the windshield glass, and is particularly preferably satisfied at the position where the P polarizing reflective film is present. As described later, the P polarizing reflective film can increase the visible light transmittance, and the above-mentioned visible light transmittance can be satisfied regardless of which type of glass commonly used for windshield glass is used.

[0088] There are no restrictions on the shape of the windshield glass; it is determined appropriately depending on the object in which the windshield glass is installed. The windshield glass may be, for example, flat, or it may have a three-dimensional shape with curved surfaces such as concave or convex. For windshield glass molded for applicable vehicles, the sides that are normally facing upwards, the observer side, the driver side, and the viewer side (such as the inside of the vehicle) can be specified.

[0089] In the case of windshield glass, the P polarizing reflective film only needs to be provided on the projected image display area (projected image reflective area) of the windshield glass. The windshield glass 24 used in the HUD system 20 of the present invention has a laminated glass structure, and the P polarizing reflective film 10 is protected by being placed between two glass plates (a first glass plate 30 and a second glass plate 28) that make up the laminated glass. Furthermore, a windshield glass 24 may be used in which the P polarizing reflective film 10 is provided on the outer surface of the laminated glass constituting the windshield glass. In this case, the P reflective film 10 may be provided inside the vehicle (on the incident side of the projected image) or on the outside, but it is preferable that it be provided inside.

[0090] As described above, the P-polarized reflective film 10 is a component for displaying a projected image by reflecting the projected image. Therefore, the P-polarized reflective film 10 should be placed in a position where the projected image projected from the virtual image display device 1 can be displayed in a visible manner. In other words, in the HUD system 20 of the present invention, the P-polarized reflective film 10 functions as a combiner of the HUD system. In a HUD system, a combiner is an optical element that can display an image projected from a virtual image display device in a visible manner, and when the combiner is observed from the incident surface side of the projected image, it is possible to simultaneously observe information on the side opposite to the incident surface of the projected light, such as a landscape. In other words, the combiner has the function of an optical path combiner that displays the ambient light and the light of the projected image in superimposition.

[0091] The P polarizing reflective film may be provided over the entire surface of the windshield glass, or it may be provided on a part of the surface of the windshield glass, but it is preferable that it is provided on a part. When a P-polarizing reflective film is provided on a portion of the windshield glass, the P-polarizing reflective film may be provided at any position on the windshield glass, but it is preferable that it be provided in a position where the virtual image is easily visible to observers such as the driver when used as a HUD system. For example, the position on the windshield glass where the P-polarizing reflective film is provided can be determined based on the relationship between the position of the driver's seat in a vehicle equipped with a HUD system and the position where the virtual image display device is installed. The P-polarizing reflective film may be flat or curved. Furthermore, the P-polarizing reflective film may have an overall concave or convex shape, and may enlarge or reduce the projected image for display.

[0092] [1] P polarizing reflective film In the HUD system of the present invention, the P-polarized reflective film means a reflective film that has the function of reflecting p-polarized light. The P-polarized reflective film 10 has a selective reflective layer that has the function of reflecting p-polarized light.

[0093] [Selective reflection layer] The windshield glass used in the HUD system of the present invention preferably has a selective reflection layer including the following three wavelengths as the selective reflection center wavelengths at a light incident angle of 60°: λ B , λ G and λ R . 400 nm ≤ λ B < 500 nm 500 nm ≤ λ G < 600 nm 600 nm ≤ λ R ≤ 700 nm

[0094] In the present invention, the selective reflection center wavelength of the selective reflection layer and the half-value width of the reflection peak having this selective reflection center wavelength are obtained as follows. As described in detail in the examples described later, when a reflection spectrum at a desired (for example, 60°) light incident angle with respect to the normal direction of the selective reflection layer is measured using a spectrophotometer (for example, manufactured by JASCO Corporation, trade name: V-670), a maximum peak of reflectance can be seen in the selective reflection band. Among the two wavelengths that are the intermediate (average) reflectance between the maximum reflectance of this peak and the minimum reflectance at the base of the maximum peak, if the value of the wavelength on the short wavelength side is λ l (nm) and the value of the wavelength on the long wavelength side is λ h (nm), the selective reflection center wavelength λ and its half-value width Δλ can be expressed by the following formula. λ = (λ l + λ h ) / 2 Δλ = (λ h − λ l ) The selective reflection center wavelength obtained as described above substantially coincides with the wavelength at the center of gravity of the reflection peak of the circular polarization reflection spectrum measured at a desired light incident angle with respect to the normal direction of the selective reflection layer when the selective reflection layer is made of cholesteric liquid crystal. Also, in the present invention, the natural light reflectance at the selective reflection center wavelength of the selective reflection layer is also determined by the method described in the examples described later. The reflection spectrum of the selective reflective layer was measured in the state of the windshield glass including the selective reflective layer, as described in the examples below.

[0095] Examples of P-polarization reflective films including the aforementioned selective reflective layer include, for example, a P-polarization reflective film including a cholesteric liquid crystal layer having the function of reflecting circularly polarized light, and a P-polarization reflective film including a selective reflective layer (hereinafter also referred to as a "dielectric multilayer film") having the function of reflecting P-polarized light, which is formed by laminating an optically anisotropic layer and an optically isotropic layer. The following will explain the P-polarized reflective films in order, based on the P-polarized reflective film 10A in the windshield glass 24A shown in Figure 4, and the P-polarized reflective film 10B in the windshield glass 24B shown in Figure 5. The cholesteric liquid crystal layer and dielectric multilayer film will be explained separately in the descriptions of each P-polarized reflective film.

[0096] [1-1] P polarized reflective film containing a cholesteric liquid crystal layer Figure 4 is a schematic diagram showing an example of a windshield glass 24 used in the present invention, and the P polarizing reflective film 10A contained in this windshield glass 24 has a polarization conversion layer 14, a selective reflective layer 11, a phase difference layer 16, and a transparent substrate 18 in this order.

[0097] When the windshield glass 24A includes a P-polarized reflective film 10A as shown in Figure 4, the P-polarized reflective film 10A first converts the projected p-polarized light incident from the second glass plate 28 side into circularly polarized light via the phase difference layer 16. Next, the selective reflective layer 11 (cholesteric liquid crystal layer 12) selectively reflects this circularly polarized light and re-incidentates it to the phase difference layer 16. Furthermore, the phase difference layer 16 converts the circularly polarized light back into p-polarized light. As a result, the P-polarized reflective film 10A reflects the incident p-polarized projected light while maintaining its p-polarized state. Therefore, the phase difference layer 16 is set to convert the incident p-polarized light into circularly polarized light in the direction of rotation that the selective reflection layer 11 (cholesteric liquid crystal layer 12) reflects, according to the sense of circularly polarized light that the selective reflection layer 11 (cholesteric liquid crystal layer 12) selectively reflects. That is, if the selective reflection layer 11 selectively reflects right-handed circularly polarized light, the phase difference layer 16 is set to convert the incident p-polarized light into right-handed circularly polarized light. Conversely, if the selective reflection layer 11 selectively reflects left-handed circularly polarized light, the phase difference layer 16 is set to convert the incident p-polarized light into left-handed circularly polarized light.

[0098] The selective reflection layer 11 preferably includes three cholesteric liquid crystal layers (12R, 12G, 12B). The three cholesteric liquid crystal layers have different selective reflection center wavelengths at an incident angle of 60° of light, and each has a selective reflection center wavelength λ at an incident angle of 60° of light, as described later. B A cholesteric liquid crystal layer 12B having the following characteristics, and the selective reflection center wavelength λ at an incident angle of light of 60° (described later). G A cholesteric liquid crystal layer 12G having the following, and the selective reflection center wavelength λ at an incident angle of light of 60° (described later). R This corresponds to the cholesteric liquid crystal layer 12R having the following properties. In the illustrated example, the cholesteric liquid crystal layer 12R, cholesteric liquid crystal layer 12G, and cholesteric liquid crystal layer 12B are present in this order. In the illustrated example, each cholesteric liquid crystal layer is in direct contact with any of the other cholesteric liquid crystal layers.

[0099] Although not shown in Figure 4, it is also preferable from the viewpoint of suppressing reflected color to include, in addition to the three cholesteric liquid crystal layers (12R, 12G, 12B) described above, a cholesteric liquid crystal layer having a selective reflection center wavelength of 300 nm or more and less than 400 nm at an incident light angle of 60° (hereinafter referred to as the cholesteric liquid crystal layer UV). By providing a cholesteric liquid crystal UV layer, when the windshield glass is configured to include the cholesteric liquid crystal layer and phase difference layer described later, the color (especially yellowish) observed when the windshield glass is viewed under ambient light can be suppressed.

[0100] As is well known, a cholesteric liquid crystal layer is a layer in which a liquid crystal compound is fixed in the orientation of a helical structure of the cholesteric liquid crystal phase. It reflects light at a selective reflection center wavelength corresponding to the pitch of the helical structure and transmits light in other wavelength ranges. Furthermore, a cholesteric liquid crystal layer exhibits selective reflectivity for either left- or right-handed circularly polarized light at specific wavelengths.

[0101] In a selective reflective layer having a cholesteric liquid crystal layer, the reflected wavelength and reflectivity can be adjusted by the selective reflection center wavelength and thickness (number of helical pitches) of the cholesteric liquid crystal layer.

[0102] Here, as shown in Figure 4, it is preferable that each cholesteric liquid crystal layer is in direct contact with any other cholesteric liquid crystal layer. For example, in the example shown in Figure 4, the selective reflection center wavelength λ at an incident angle of light of 60° R A cholesteric liquid crystal layer 12R having a selective reflection center wavelength λ at an incident angle of light of 60° G The cholesteric liquid crystal layer 12G having the following properties is in contact with each other, and the selective reflection center wavelength λ at an incident angle of light of 60° is also present. G A cholesteric liquid crystal layer 12G having a selective reflection center wavelength λ at an incident angle of light of 60° B A cholesteric liquid crystal layer 12B having the above properties is in contact with each other.

[0103] When cholesteric liquid crystal layers are spaced apart, the interlayer thickness increases, making it difficult to obtain the interference effect of light reflected by each cholesteric liquid crystal layer. In contrast, by configuring the cholesteric liquid crystal layers to be in contact with each other, the wavelength bandwidth can be narrowed by the interference effect of light reflected by each cholesteric liquid crystal layer. In particular, when the thickness of each cholesteric liquid crystal layer is thinner than the wavelength of light (visible light 380nm to 780nm), the interference effect becomes even more pronounced.

[0104] In this invention, the cholesteric liquid crystal layers are not limited to being in direct contact with each other, but may be laminated via an adhesive layer or the like.

[0105] Here, each cholesteric liquid crystal layer has the aforementioned λ as its selective reflection center wavelength at an incident angle of light of 60°. B , λ G and λ R It is sufficient that the cholesteric liquid crystal layer has at least one selective reflection center wavelength among the three wavelengths, and at least one layer of the cholesteric liquid crystal layer may have two or more selective reflection center wavelengths. A cholesteric liquid crystal layer having two or more selective reflection center wavelengths is achieved by a helical structure in which the helical pitch changes in the thickness direction.

[0106] Furthermore, although the illustrated example shows that the selective reflection layer 11 has a configuration having three cholesteric liquid crystal layers with different selective reflection center wavelengths, it is not limited to this configuration. The selective reflection layer 11 may have one cholesteric liquid crystal layer, or it may have two or four or more cholesteric liquid crystal layers.

[0107] From the viewpoint of exhibiting high transmittance while showing sufficient natural light reflectance due to the selective reflective layer 11, the total thickness of the selective reflective layer 11 is preferably 0.5 to 30 μm, and more preferably 1 to 15 μm.

[0108] In the P-polarized reflective film shown in Figure 4, the selective reflective layer, which consists of a cholesteric liquid crystal layer, reflects circularly polarized light. Therefore, in a P-polarized reflective film, it is preferable to have a layer that converts P-polarized light incident on the P-polarized reflective film into circularly polarized light. Examples of layers that convert the polarization state of light include a polarization conversion layer and a phase difference layer.

[0109] The polarization conversion layer exhibits optical rotation and birefringence with respect to visible light, and converts the polarization state of incident light. In this invention, the polarization conversion layer consists of a layer of birefringent material, such as a liquid crystal compound, oriented with a twist of 360° or less. A phase difference layer alters the state of incident polarization by introducing a phase difference (optical path difference) between two orthogonal polarization components. In this invention, the phase difference layer is a layer in which birefringent materials such as liquid crystal compounds are arranged in the same direction, and does not possess optical activity.

[0110] By configuring the above-mentioned P-polarized reflective film to have a polarization conversion layer or a phase difference layer on the side of the selective reflective layer where light is incident, the P-polarized light incident on the P-polarized reflective film can be converted into circularly polarized light, the selective reflective layer reflects the circularly polarized light, and the polarization conversion layer or phase difference layer converts the reflected circularly polarized light into P-polarized light before emission.

[0111] In the example of the windshield glass shown in Figure 4, the P polarizing reflective film 10A has a polarization conversion layer 14 on one side of the selective reflective layer 11 and a phase difference layer 16 on the other side, with the phase difference layer 16 on the second glass plate 28 side facing the interior of the vehicle, and the polarization conversion layer 14 on the first glass plate 30 side facing the exterior of the vehicle.

[0112] In this case, the phase difference layer 16 has the function of converting the projected p-polarized light into circularly polarized light that is reflected by the cholesteric liquid crystal layer of the selective reflection layer 11. On the other hand, the polarization conversion layer 14 has an optical compensation function for light incident from the outside of the windshield glass. For example, when s-polarized light incident from the outside of the windshield glass passes through the phase difference layer 16, its polarization state changes, and a p-polarized component becomes mixed in. Since polarized sunglasses cut out s-polarized light, this p-polarized component passes through the polarized sunglasses. As a result, the function of polarized sunglasses in cutting out glare from reflected light, which is mainly composed of s-polarized light, is impaired, causing problems that interfere with driving. In contrast, by having a polarization conversion layer 14 and providing optical compensation with the polarization conversion layer 14, the suitability of polarized sunglasses can be improved.

[0113] In the example shown in Figure 4, the P polarizing reflective film 10A is configured such that the polarization conversion layer 14 is on the side of the first glass plate 30 facing the outside of the vehicle, and the phase difference layer 16 is on the side of the second glass plate 28 facing the inside of the vehicle. However, the configuration is not limited to this. The P polarizing reflective film 10A may also be configured such that the polarization conversion layer 14 is on the side of the second glass plate 28 facing the inside of the vehicle, and the phase difference layer 16 is on the side of the first glass plate 30 facing the outside of the vehicle.

[0114] In this case, the polarization conversion layer 14 has the function of converting the projected p-polarized light into circularly polarized light that is reflected by the cholesteric liquid crystal layer of the selective reflection layer 11. On the other hand, the phase difference layer 16 has an optical compensation function for light incident from the outside of the windshield glass, and by performing optical compensation with the phase difference layer 16, the suitability for polarized sunglasses can be improved.

[0115] Furthermore, the P polarizing reflective film 10A may have a polarization conversion layer on both sides of the selective reflective layer 11, or it may have a phase difference layer on both sides. In this case, the polarization conversion layer or phase difference layer placed on the inside of the vehicle should be configured to have the function of converting the projected p-polarized light into circularly polarized light that is reflected by the cholesteric liquid crystal layer of the selective reflection layer 11. On the other hand, the polarization conversion layer or phase difference layer located on the outside of the vehicle may be configured to have an optical compensation function for light incident from the outside of the windshield glass. The polarization conversion layer and phase difference layer will be described in detail later.

[0116] The following describes in detail the cholesteric liquid crystal layer, polarization conversion layer, phase difference layer, and transparent substrate, which are components of the P polarizing reflective film 10A including the cholesteric liquid crystal layer.

[0117] [Cholesteric liquid crystal layer] The cholesteric liquid crystal layer has the aforementioned λ as its selective reflection center wavelength at an incident light angle of 60°. B , λ G and λ R It is preferable to include these three wavelengths. In the present invention, the cholesteric liquid crystal layer refers to a layer in which a cholesteric liquid crystal phase is fixed. A cholesteric liquid crystal layer is a layer in which the orientation of the liquid crystal compound in the cholesteric liquid crystal phase is maintained. Typically, a cholesteric liquid crystal layer is formed by polymerizing and curing a polymerizable liquid crystal compound in the orientation of the cholesteric liquid crystal phase by ultraviolet irradiation and heating, thereby forming a non-fluid layer that simultaneously changes in orientation to a state that does not change due to external fields or external forces. In addition, it is sufficient that the optical properties of the cholesteric liquid crystal phase are maintained within the layer, and the liquid crystal compound in the layer does not need to exhibit liquid crystalline properties anymore. For example, a polymerizable liquid crystal compound may have its molecular weight increased by the curing reaction and may no longer have liquid crystalline properties.

[0118] Cholesteric liquid crystal phases are known to exhibit selective circular polarization reflection, which selectively reflects circularly polarized light of either right-circularly polarized or left-circularly polarized light, while transmitting circularly polarized light of the other sense. Many films formed from compositions containing polymerizable liquid crystal compounds have been conventionally known as films containing a layer on which a cholesteric liquid crystal phase exhibiting selective circular polarization reflectivity is fixed, and prior art can be referenced for the cholesteric liquid crystal layer.

[0119] The center wavelength λ of selective reflection in a cholesteric liquid crystal layer at an incident light angle of 5° depends on the pitch P (=period of the helix) of the helical structure (helical orientation structure) in the cholesteric liquid crystal phase, and follows the relationship n = n × P with respect to the average refractive index of the cholesteric liquid crystal layer. As can be seen from this equation, the center wavelength of selective reflection can be adjusted by adjusting the n value and / or the P value. The pitch P of a helical structure (one helical pitch) is, in other words, the length in the helical axis direction for one turn of the helix, that is, the length in the helical axis direction for a 360° rotation of the director (long axis direction in the case of a rod-shaped liquid crystal) of the liquid crystal compound constituting the cholesteric liquid crystal phase. The helical axis direction of a typical cholesteric liquid crystal layer coincides with the thickness direction of the cholesteric liquid crystal layer.

[0120] In the aforementioned head-up display system, by using it so that light is incident on the windshield glass at an oblique angle, the reflectivity on the surface of the glass plate on the side where the projected light is incident can be reduced. At this time, light is also incident at an oblique angle on the cholesteric liquid crystal layer that constitutes the selective reflective layer 11 of the P-polarized reflective film 10A. For example, light incident at an angle of 45° to 70° to the normal of the P-polarized reflective film 10A in air with a refractive index of 1 will pass through the cholesteric liquid crystal layer with a refractive index of approximately 1.61 at an angle of approximately 26° to 36°. In this case, the reflected wavelength shifts to the shorter wavelength side. In a cholesteric liquid crystal layer where the selective reflection center wavelength for light with an incident angle of 5° is wavelength λ, when the light ray passes through the cholesteric liquid crystal layer at an angle θ² with respect to the normal direction of the cholesteric liquid crystal layer (the direction of the helical axis of the cholesteric liquid crystal layer), the selective reflection center wavelength λd is expressed by the following equation. λd = λ × cosθ²

[0121] Therefore, for example, a cholesteric liquid crystal layer having a center wavelength of selective reflection in the range of 650 to 780 nm when θ2 is 26° to 36° can reflect projected light in the range of 520 to 695 nm. Because this wavelength range is a wavelength range with high visual sensitivity, it contributes significantly to the brightness of the projected image, resulting in the achievement of a high-brightness projected image.

[0122] The helical pitch of the cholesteric liquid crystal phase depends on the type of chiral agent used with the polymerizable liquid crystal compound and its concentration; therefore, the desired pitch can be obtained by adjusting these factors. For methods of measuring the helical sense and pitch, the methods described in "Introduction to Liquid Crystal Chemistry Experiments" edited by the Japanese Liquid Crystal Society, Sigma Publishing, 2007, p. 46, and "Liquid Crystal Handbook" edited by the Liquid Crystal Handbook Editorial Committee, Maruzen, p. 196, can be used.

[0123] Each cholesteric liquid crystal layer used is one in which the helical sense is either right-handed or left-handed. The sense of circularly polarized light reflected by the cholesteric liquid crystal layer (the direction of rotation of the circularly polarized light) coincides with the helical sense. When there are multiple cholesteric liquid crystal layers with different selective reflection center wavelengths, the helical senses of each cholesteric liquid crystal layer may all be the same, or they may include different ones. However, it is preferable that the multiple cholesteric liquid crystal layers all have the same helical sense.

[0124] Furthermore, if the P-polarizing reflective film 10A has multiple cholesteric liquid crystal layers as the selective reflective layer 11, it is preferable not to include cholesteric liquid crystal layers with different helical senses as cholesteric liquid crystal layers that exhibit selective reflection in the same or overlapping wavelength ranges. This is to avoid the transmittance in a specific wavelength range decreasing to, for example, less than 50%.

[0125] The half-width Δλ (nm) of the selective reflection band exhibiting selective reflection depends on the birefringence Δn of the liquid crystal compound and the pitch P described above, following the relationship Δλ = Δn × P. Therefore, the width of the selective reflection band can be controlled by adjusting Δn. Δn can be adjusted by changing the type or mixing ratio of the polymerizable liquid crystal compound, or by controlling the temperature during orientation fixation. To form a single type of cholesteric liquid crystal layer with the same central wavelength for selective reflection, multiple cholesteric liquid crystal layers with the same pitch P and the same helical sense may be stacked. By stacking cholesteric liquid crystal layers with the same pitch P and the same helical sense, circular polarization selectivity can be increased at a specific wavelength.

[0126] When stacking multiple cholesteric liquid crystal layers in the selective reflective layer 11, the separately prepared cholesteric liquid crystal layers may be stacked using an adhesive or the like, or a liquid crystal composition containing a polymerizable liquid crystal compound or the like may be directly applied to the surface of the cholesteric liquid crystal layer formed by the method described later, and the orientation and fixing steps may be repeated, the latter being preferred. This is because forming the next cholesteric liquid crystal layer directly on the surface of the previously formed cholesteric liquid crystal layer causes the orientation of the liquid crystal molecules on the air interface side of the previously formed cholesteric liquid crystal layer to match the orientation of the liquid crystal molecules on the underside of the cholesteric liquid crystal layer formed on top of it, resulting in good polarization characteristics of the cholesteric liquid crystal layer laminate. Furthermore, interference irregularities that may arise from thickness variations in the adhesive layer are not observed.

[0127] The thickness of the cholesteric liquid crystal layer is preferably 0.2 to 10 μm, more preferably 0.3 to 8 μm, and even more preferably 0.4 to 5 μm.

[0128] (Method for fabricating a cholesteric liquid crystal layer) The following describes the materials and methods for fabricating the cholesteric liquid crystal layer. Materials used to form the cholesteric liquid crystal layer described above include liquid crystal compositions containing polymerizable liquid crystal compounds and chiral agents (optically active compounds). If necessary, the above-mentioned liquid crystal composition, which has been mixed with a surfactant and a polymerization initiator and dissolved in a solvent, can be applied to a support, an alignment layer, or a lower cholesteric liquid crystal layer. After cholesteric alignment maturation, the liquid crystal composition can be fixed by curing to form the cholesteric liquid crystal layer.

[0129] (Polymerizable liquid crystal compound) The polymerizable liquid crystal compound may be a rod-shaped liquid crystal compound or a disc-shaped liquid crystal compound, but a rod-shaped liquid crystal compound is preferred. Examples of rod-shaped polymerizable liquid crystal compounds that form a cholesteric liquid crystal layer include rod-shaped nematic liquid crystal compounds. Preferred rod-shaped nematic liquid crystal compounds include azomethines, azoxys, cyanobiphenyls, cyanophenyl esters, benzoic acid esters, cyclohexanecarboxylic acid phenyl esters, cyanophenylcyclohexanes, cyanosubstituted phenylpyrimidines, alkoxysubstituted phenylpyrimidines, phenyldioxanes, trans, and alkenylcyclohexylbenzonitriles. Not only low molecular weight liquid crystal compounds but also high molecular weight liquid crystal compounds can be used.

[0130] Polymerizable liquid crystal compounds are obtained by introducing polymerizable groups into liquid crystal compounds. Examples of polymerizable groups include unsaturated polymerizable groups, epoxy groups, and aziridinyl groups, with unsaturated polymerizable groups being preferred and ethylenically unsaturated polymerizable groups being particularly preferred. Polymerizable groups can be introduced into the molecules of liquid crystal compounds by various methods. The number of polymerizable groups in a polymerizable liquid crystal compound is preferably 1 to 6 per molecule, more preferably 1 to 3. Examples of polymerizable liquid crystal compounds include compounds described in Makromol. Chem., Vol. 190, p. 2255 (1989), Advanced Materials, Vol. 5, p. 107 (1993), U.S. Patent No. 4,683,327, U.S. Patent No. 5,622,648, U.S. Patent No. 5,770,107, WO95 / 22586, WO95 / 24455, WO97 / 00600, WO98 / 23580, WO98 / 52905, Japanese Patent Publication No. 1-272551, Japanese Patent Publication No. 6-016616, Japanese Patent Publication No. 7-110469, Japanese Patent Publication No. 11-080081, and Japanese Patent Publication No. 2001-328973, etc. Two or more polymerizable liquid crystal compounds may be used in combination. Using two or more polymerizable liquid crystal compounds in combination can lower the orientation temperature.

[0131] Furthermore, the amount of polymerizable liquid crystal compound added to the liquid crystal composition is preferably 80 to 99.9% by mass, more preferably 85 to 99.5% by mass, and particularly preferably 90 to 99% by mass, relative to the solid content mass (mass excluding solvent) of the liquid crystal composition.

[0132] To improve visible light transmittance, the cholesteric liquid crystal layer may have a low Δn. Low-Δn cholesteric liquid crystal layers can be formed using low-Δn polymerizable liquid crystal compounds. The following describes low-Δn polymerizable liquid crystal compounds in detail.

[0133] (Low Δn polymerizable liquid crystal compound) A cholesteric liquid crystal phase can be formed using a low-Δn polymerizable liquid crystal compound, and a film on which this phase is fixed can be obtained to acquire a narrow-band selective reflective layer. Examples of low-Δn polymerizable liquid crystal compounds include those described in WO2015 / 115390, WO2015 / 147243, WO2016 / 035873, Japanese Patent Publication No. 2015-163596, and Japanese Patent Publication No. 2016-053149. For liquid crystal compositions that provide a selective reflective layer with a small full width at half maximum, refer to the description in WO2016 / 047648, and polymerizable compounds represented by formula (I) described in WO2016 / 047648 are also preferred.

[0134] Examples of polymerizable compounds represented by formula (I) described in WO2016 / 047648 include, in addition to the compounds described in paragraphs 0051 to 0058 of WO2016 / 047648, compounds described in Japanese Patent Publication No. 2013-112631, Japanese Patent Publication No. 2010-070543, Japanese Patent No. 4725516, WO2015 / 115390, WO2015 / 147243, WO2016 / 035873, Japanese Patent Publication No. 2015-163596, and Japanese Patent Publication No. 2016-053149.

[0135] (Chiral agents: optically active compounds) Chiral agents have the function of inducing a helical structure in the cholesteric liquid crystal phase. Since different chiral compounds induce different helical senses or helical pitches, they should be selected according to the purpose. There are no particular restrictions on the chiral agent, and commonly used compounds can be used. Examples of chiral agents include compounds described in the Liquid Crystal Device Handbook (Chapter 3, Section 4-3, Chiral Agents for TN and STN, p. 199, edited by the 142nd Committee of the Japan Society for the Promotion of Science, 1989), Japanese Patent Publication Nos. 2003-287623, 2002-302487, 2002-080478, 2002-080851, 2010-181852, and 2014-034581, among others.

[0136] Chiral agents generally contain an asymmetric carbon atom, but axially asymmetric or planar asymmetric compounds that do not contain an asymmetric carbon atom can also be used as chiral agents. Examples of axially asymmetric or planar asymmetric compounds include binaphthyl, helicene, paracyclophane, and their derivatives. The chiral agent may have polymerizable groups. When both the chiral agent and the liquid crystal compound have polymerizable groups, a polymerization reaction between the polymerizable chiral agent and the polymerizable liquid crystal compound can form a polymer having repeating units derived from the polymerizable liquid crystal compound and repeating units derived from the chiral agent. In this embodiment, it is preferable that the polymerizable groups of the polymerizable chiral agent are of the same type as the polymerizable groups of the polymerizable liquid crystal compound. Therefore, the polymerizable groups of the chiral agent are preferably unsaturated polymerizable groups, epoxy groups, or aziridinyl groups, more preferably unsaturated polymerizable groups, and even more preferably ethylenically unsaturated polymerizable groups. Furthermore, the chiral agent may be a liquid crystal compound.

[0137] As chiral agents, isosorbide derivatives, isomannide derivatives, and binaphthyl derivatives can be preferably used. As isosorbide derivatives, commercially available products such as LC756 (trade name) manufactured by BASF may be used. In the liquid crystal composition, the chiral agent content is preferably 0.01 to 200 mol%, and more preferably 1 to 30 mol%, of the polymerizable liquid crystal compound.

[0138] Furthermore, as mentioned above, the cholesteric liquid crystal layer of the selective reflective layer of the P-polarized reflective film may have two or more selective reflection center wavelengths. A cholesteric liquid crystal layer having two or more selective reflection center wavelengths is achieved by changing the pitch of the helical structure in the thickness direction. A cholesteric liquid crystal layer in which the pitch of the helical structure changes in the thickness direction can be fabricated by changing the amount of light irradiation in the thickness direction when forming the cholesteric liquid crystal layer using a chiral agent whose helical twisting power (HTP) changes upon light irradiation.

[0139] Chiral agents whose HTP changes upon light irradiation include those that undergo reverse isomerization, dimerization, and isomerization and dimerization upon light irradiation. When the chiral agent has a photoisomerizing group, the photoisomerizing group is preferably the isomerization site of a photochromic compound, an azo group, an azoxy group, or a cinnamoyl group. Specific compounds that can be used include those described in Japanese Patent Publication No. 2002-080478, 2002-080851, 2002-179668, 2002-179669, 2002-179670, 2002-179681, 2002-179682, 2002-338575, 2002-338668, 2003-313189, and 2003-313292, etc.

[0140] (Polymerization initiator) The liquid crystal composition preferably contains a polymerization initiator. In the embodiment in which the polymerization reaction is carried out by ultraviolet irradiation, the polymerization initiator used is preferably a photopolymerization initiator that can initiate the polymerization reaction by ultraviolet irradiation. Examples of photopolymerization initiators include α-carbonyl compounds (described in U.S. Patent Nos. 2,367,661 and 2,367,670), acyloin ether compounds (described in U.S. Patent No. 2,448,828), α-hydrocarbon-substituted aromatic acyloin compounds (described in U.S. Patent No. 2,722,512), polynuclear quinone compounds (described in U.S. Patent Nos. 3,046,127 and 2,951,758), combinations of triarylimidazole dimers and p-aminophenyl ketones (described in U.S. Patent No. 3,549,367), acridine and phenazine compounds (described in Japanese Patent Publication No. 60-105,667 and U.S. Patent No. 4,239,850), and acylphosphorus compounds. Phenoxide compounds (Japanese Patent Publication No. 63-040799, Japanese Patent Publication No. 5-029234, Japanese Patent Publication No. 10-095788, Japanese Patent Publication No. 10-029997, Japanese Patent Publication No. 2001-233842, Japanese Patent Publication No. 2000-080068, Japanese Patent Publication No. 2006-342166, Japanese Patent Publication No. 2013-114249, Japanese Patent Publication No. 201 Examples include JP 4-137466, Japanese Patent No. 4223071, Japanese Unexamined Patent Publication No. 2010-262028, and Japanese Patent Publication No. 2014-500852), oxime compounds (as described in Japanese Unexamined Patent Publication No. 2000-066385 and Japanese Patent No. 4454067), and oxadiazole compounds (as described in U.S. Patent No. 4,212,970). For example, paragraphs 0500 to 0547 of Japanese Unexamined Patent Publication No. 2012-208494 can also be considered.

[0141] It is also preferable to use acylphosphine oxide compounds or oxime compounds as polymerization initiators. As an acylphosphine oxide compound, for example, IRGACURE 810 (trade name, compound name: bis(2,4,6-trimethylbenzoyl)-phenylphosphine oxide) manufactured by BASF Japan Ltd. can be used. As an oxime compound, commercially available products such as IRGACURE OXE01 (trade name, manufactured by BASF), IRGACURE OXE02 (trade name, manufactured by BASF), TR-PBG-304 (trade name, manufactured by Changzhou Strong Electronic New Materials Co., Ltd.), ADEKA Arclus NCI-930 (trade name, manufactured by ADEKA), and ADEKA Arclus NCI-831 (trade name, manufactured by ADEKA) can be used. A single polymerization initiator may be used, or two or more may be used in combination. The content of the photopolymerization initiator in the liquid crystal composition is preferably 0.1 to 20% by mass, and more preferably 0.5 to 5% by mass, relative to the content of the polymerizable liquid crystal compound.

[0142] (Crosslinking agent) The liquid crystal composition may optionally contain a crosslinking agent to improve the film strength and durability after curing. Suitable crosslinking agents include those that cure with ultraviolet light, heat, or moisture. There are no particular restrictions on the crosslinking agent, and it can be appropriately selected according to the purpose. Examples of crosslinking agents include polyfunctional acrylate compounds such as trimethylolpropane tri(meth)acrylate and pentaerythritol tri(meth)acrylate; epoxy compounds such as glycidyl(meth)acrylate and ethylene glycol diglycidyl ether; aziridine compounds such as 2,2-bishydroxymethylbutanol-tris[3-(1-aziridinyl)propionate] and 4,4-bis(ethyleneiminocarbonylamino)diphenylmethane; isocyanate compounds such as hexamethylene diisocyanate and biuret-type isocyanate; polyoxazoline compounds having an oxazoline group in the side chain; and alkoxysilane compounds such as vinyltrimethoxysilane and N-(2-aminoethyl)3-aminopropyltrimethoxysilane. In addition, a commonly used catalyst can be used depending on the reactivity of the crosslinking agent, which can improve productivity in addition to improving film strength and durability. These may be used individually or in combination of two or more. The crosslinking agent content in the liquid crystal composition is preferably 3 to 20% by mass, and more preferably 5 to 15% by mass, relative to the solid content mass (mass excluding solvent) of the liquid crystal composition. By setting the crosslinking agent content to 3% by mass or more, the effect of improving crosslink density can be obtained, and by setting the crosslinking agent content to 20% by mass or less, a decrease in the stability of the cholesteric liquid crystal layer can be prevented. Note that "(meth)acrylate" is used to mean "either acrylate or methacrylate, or both."

[0143] (Orientation control agent) An orientation control agent may be added to the liquid crystal composition to contribute to the stable or rapid formation of a planar-oriented cholesteric liquid crystal layer. Examples of orientation control agents include fluorine (meth)acrylate polymers described in paragraphs

[0018] to

[0043] of Japanese Patent Application Publication No. 2007-272185, compounds represented by formulas (I) to (IV) described in paragraphs

[0031] to

[0034] of Japanese Patent Application Publication No. 2012-203237, and compounds described in Japanese Patent Application Publication No. 2013-113913. Furthermore, one type of orientation control agent may be used alone, or two or more types may be used in combination.

[0144] The amount of orientation control agent added to the liquid crystal composition is preferably 0.01 to 10% by mass, more preferably 0.01 to 5% by mass, and particularly preferably 0.02 to 1% by mass, relative to the total mass of the polymerizable liquid crystal compound.

[0145] (Other additives) Furthermore, the liquid crystal composition may contain at least one additive selected from various sources, such as surfactants for adjusting the surface tension and uniformity of the coating film, and polymerizable monomers. Additionally, polymerization inhibitors, antioxidants, ultraviolet absorbers, light stabilizers, colorants, and metal oxide fine particles may be added to the liquid crystal composition as needed, within limits that do not degrade optical performance.

[0146] A cholesteric liquid crystal layer can be formed by dissolving a liquid crystal composition, which consists of a polymerizable liquid crystal compound, a polymerization initiator, and optionally added chiral agents, surfactants, etc., in a solvent, onto a transparent substrate, a phase difference layer, an alignment layer, or a previously prepared cholesteric liquid crystal layer, drying it to obtain a coating film, and then irradiating this coating film with active light to polymerize the cholesteric liquid crystal composition, thereby forming a cholesteric liquid crystal layer with fixed cholesteric regularity. Furthermore, a laminated film consisting of multiple cholesteric liquid crystal layers can be formed by repeatedly performing the above-described manufacturing process for the cholesteric liquid crystal layer.

[0147] (solvent) There are no particular restrictions on the solvent used in preparing the liquid crystal composition, and it can be appropriately selected depending on the purpose, but organic solvents are preferably used. There are no particular restrictions on the organic solvent, and it can be appropriately selected depending on the purpose. Examples include ketones, alkyl halides, amides, sulfoxides, heterocyclic compounds, hydrocarbons, esters, and ethers. These may be used individually or in combination of two or more. Among these, ketones are particularly preferred when considering the environmental impact.

[0148] (Coating, orientation, polymerization) There are no particular restrictions on the method of coating the liquid crystal composition onto the transparent substrate, alignment layer, underlying cholesteric liquid crystal layer, etc., and a suitable method can be selected depending on the purpose. Examples of coating methods include wire bar coating, curtain coating, extrusion coating, direct gravure coating, reverse gravure coating, die coating, spin coating, dip coating, spray coating, and slide coating. Alternatively, the liquid crystal composition can be applied to a support separately and then transferred. The liquid crystal molecules are oriented by heating the coated liquid crystal composition. The heating temperature is preferably 200°C or lower, and more preferably 130°C or lower. This orientation treatment yields an optical thin film in which the polymerizable liquid crystal compound is twisted and oriented so that it has a helical axis substantially perpendicular to the film surface.

[0149] The liquid crystal composition can be cured by further polymerizing the oriented liquid crystal compound. Polymerization can be carried out by thermal polymerization or photopolymerization using light irradiation, but photopolymerization is preferred. For light irradiation, ultraviolet light is preferred. The irradiation energy is 20 mJ / cm². 2 ~50J / cm 2 Preferably, 100-1,500 mJ / cm² 2 This is preferable. To promote the photopolymerization reaction, light irradiation may be carried out under heating conditions or in a nitrogen atmosphere. The irradiation ultraviolet wavelength is preferably 350 to 430 nm. From the viewpoint of stability, a higher polymerization reaction rate is preferable, specifically, 70% or more is preferred, and 80% or more is more preferred. The polymerization reaction rate can be determined by measuring the consumption rate of polymerizable functional groups in the infrared absorption spectrum.

[0150] [Polarization conversion layer] The polarization conversion layer 14 is a layer in which the helical orientation structure of the liquid crystal compound is fixed, and it is preferable that the number of pitches x of the helical orientation structure and the thickness y of the polarization conversion layer (in μm) satisfy all of the following relational expressions (a) to (c). 0.1≦x≦1.0 ··· Formula (a) 0.5≦y≦3.0 ··· Formula (b) 3000≦(1560×y) / x≦50000 ··· Formula (c) Note that one pitch in the helical structure of a liquid crystal compound corresponds to one turn of the helix. In other words, a pitch of 1 is defined as a state where the director (the long axis direction in the case of a rod-shaped liquid crystal) of a spirally oriented liquid crystal compound is rotated 360°.

[0151] If the polarization conversion layer has a helical structure of a liquid crystal compound, it will exhibit optical rotation and birefringence with respect to visible light, which has a wavelength shorter than the reflection peak wavelength in the infrared region. Therefore, polarization in the visible region can be controlled. By setting the pitch number x of the helical orientation structure of the polarization conversion layer and the film thickness y of the polarization conversion layer within the above range, it is possible to impart a function of optical compensation for visible light by the polarization conversion layer, or a function of converting P-polarized light incident on the P-polarized reflective film into circularly polarized light.

[0152] The polarization conversion layer exhibits optical activity and birefringence with respect to visible light because the liquid crystal compound has a helical structure that satisfies relational equations (a) to (c). In particular, by setting the pitch P of the helical structure of the polarization conversion layer to a length corresponding to the pitch P of the cholesteric liquid crystal layer, whose selective reflection center wavelength is in the long-wavelength infrared region, high optical activity and birefringence are exhibited with respect to short-wavelength visible light.

[0153] The relationship (a) is '0.1 ≤ x ≤ 1.0'. If the pitch number x of the helical structure is less than 0.1, problems such as insufficient optical rotation and birefringence will occur. Furthermore, if the pitch number x of the helical structure exceeds 1.0, excessive optical rotation and birefringence occur, leading to problems such as the inability to obtain the desired elliptical polarization.

[0154] The relationship (b) is '0.5 ≤ y ≤ 3.0'. If the thickness y of the polarization conversion layer is less than 0.5 μm, the film thickness is too thin, resulting in problems such as insufficient optical rotation and birefringence. If the thickness y of the polarization conversion layer exceeds 3.0 μm, excessive optical rotation and birefringence occur, resulting in problems such as the inability to obtain the desired circular polarization, a higher likelihood of orientation defects, and other undesirable aspects for manufacturing.

[0155] The relationship (c) is '3000 ≤ (1560 × y) / x ≤ 50000'. If "(1560 × y) / x" is less than 3000, problems such as excessive optical rotation and inability to obtain the desired polarization will occur. If "(1560 × y) / x" exceeds 50,000, optical rotation becomes insufficient, leading to problems such as the inability to obtain the desired polarization.

[0156] In the present invention, the pitch number x of the helical structure of the polarization conversion layer is more preferably 0.1 to 0.8, and the film thickness y is more preferably 0.6 μm to 2.6 μm. Furthermore, "(1560 × y) / x" is more preferably 5000 to 13000.

[0157] In other words, it is preferable that the polarization conversion layer has a long helical structure pitch P and a small number of pitches x. Specifically, it is preferable that the polarization conversion layer has a helical pitch P equivalent to that of a cholesteric liquid crystal layer whose selective reflection center wavelength is in the long-wavelength infrared region, and a small number of pitches x. More specifically, it is preferable that the polarization conversion layer has a helical pitch P equivalent to that of a cholesteric liquid crystal layer whose selective reflection center wavelength is 3000 to 10000 nm, and a small number of pitches x. Such a polarization conversion layer exhibits the optical rotation and birefringence for visible light described above more favorably because the selective reflection center wavelength corresponding to the pitch P is much longer than that of visible light.

[0158] Such polarization conversion layers can be formed in essentially the same way as conventional cholesteric liquid crystal layers. However, when forming the polarization conversion layer, it is necessary to adjust the liquid crystal compound used, the chiral agent used, the amount of chiral agent added, and the film thickness so that the number of pitches x of the helical structure in the polarization conversion layer and the film thickness y [μm] satisfy all of the relationships (a) to (c).

[0159] <Layer with fixed helical orientation structure (helical structure) of liquid crystal compound> A layer in which the helical orientation structure (helical structure) of a liquid crystal compound is fixed is a so-called cholesteric liquid crystal layer, meaning a layer in which the cholesteric liquid crystal phase is fixed. A cholesteric liquid crystal layer is a layer in which the orientation of the liquid crystal compound in the cholesteric liquid crystal phase is maintained. Typically, a cholesteric liquid crystal layer is formed by polymerizing and curing a polymerizable liquid crystal compound in the orientation of the cholesteric liquid crystal phase by ultraviolet irradiation and heating, thereby forming a non-fluid layer that simultaneously changes in orientation to a state that does not change due to external fields or external forces. In addition, it is sufficient that the optical properties of the cholesteric liquid crystal phase are maintained within the layer, and the liquid crystal compound in the layer does not need to exhibit liquid crystalline properties anymore. For example, a polymerizable liquid crystal compound may have its molecular weight increased by the curing reaction and may no longer have liquid crystalline properties.

[0160] As mentioned above, the center wavelength λ of selective reflection by the cholesteric liquid crystal layer depends on the pitch P (=period of the helix) of the helical structure (helical orientation structure) in the cholesteric liquid crystal phase, and follows the relationship between the average refractive index n of the cholesteric liquid crystal layer and λ = n × P. As can be seen from this equation, the center wavelength of selective reflection can be adjusted by adjusting the n value and / or the P value.

[0161] The helical pitch of the cholesteric liquid crystal phase depends on the type of chiral agent used with the polymerizable liquid crystal compound and its concentration; therefore, the desired pitch can be obtained by adjusting these factors. As mentioned above, the cholesteric liquid crystal layer used as a polarization conversion layer has its helical pitch adjusted so that the selective reflection center wavelength is in the long-wavelength infrared region. The method for forming the cholesteric liquid crystal layer as a polarization conversion layer is basically the same as the method for forming the cholesteric liquid crystal layer described above.

[0162] [Retardation layer] A phase difference layer alters the state of incident polarization by introducing a phase difference (optical path difference) between two orthogonal polarization components.

[0163] If the phase difference layer is located on the outside of the vehicle and is optically compensated for, the frontal phase difference of the phase difference layer should be such that it can be optically compensated for. In this case, the phase difference layer preferably has a front retardation of 50 nm to 160 nm at a wavelength of 550 nm. Furthermore, when a windshield glass having a P polarizing reflective film is mounted on a vehicle, it is preferable that the angle of the lagging axis is 10° to 50° or -50° to -10°, with the direction corresponding to the vertically upward direction of the surface of the second glass plate being defined as 0°.

[0164] Furthermore, if the phase difference layer converts P-polarized light into circularly polarized light, the front phase difference of the phase difference layer is preferably configured to give λ / 4, or it may be configured to give 3λ / 4 as the front phase difference. Also, the angle of the slow axis should be arranged so as to be in the direction that converts the incident P-polarized light into circularly polarized light.

[0165] In this case, the phase difference layer preferably has a front phase difference in the range of 100 to 450 nm at a wavelength of 550 nm, and more preferably in the range of 120 to 200 nm or 300 to 400 nm. Furthermore, the direction of the slow axis of the phase difference layer is preferably determined according to the incident direction of the projected light for displaying the projected image when the P-polarized reflective film 10 is used in a head-up display system, and the sense of the helix of the cholesteric liquid crystal layer constituting the selective reflective layer.

[0166] The phase difference layer is not particularly limited and can be appropriately selected depending on the purpose. Examples of phase difference layers include stretched polycarbonate film, stretched norbornene-based polymer film, transparent film containing and oriented inorganic particles having birefringence such as strontium carbonate, thin film in which an inorganic dielectric is obliquely deposited on a support, film in which polymerizable liquid crystal compounds are uniaxially oriented and fixed in orientation, and film in which liquid crystal compounds are uniaxially oriented and fixed in orientation.

[0167] In particular, a film in which a polymerizable liquid crystal compound is uniaxially oriented and its orientation fixed is a suitable example of a phase difference layer. Such a phase difference layer can be formed, for example, by applying a liquid crystal composition containing a polymerizable liquid crystal compound to a transparent substrate, a temporary support, or the surface of an alignment layer, forming the polymerizable liquid crystal compound in the liquid crystal composition in a nematic orientation in a liquid crystal state, and then fixing it by curing. In this case, the formation of the phase difference layer can be carried out in the same manner as the formation of the cholesteric liquid crystal layer described above, except that a chiral agent is not added to the liquid crystal composition. However, when nematic orientation is performed after coating the liquid crystal composition, the heating temperature is preferably 50 to 120°C, and more preferably 60 to 100°C.

[0168] The phase difference layer may be a layer obtained by applying a composition containing a polymer liquid crystal compound to the surface of a transparent substrate, temporary support, or orientation layer, forming a nematic orientation in a liquid crystal state, and then fixing this orientation by cooling.

[0169] There are no restrictions on the thickness of the phase difference layer, but it is preferably 0.2 to 300 μm, more preferably 0.5 to 150 μm, and even more preferably 1.0 to 80 μm. Similarly, there are no particular restrictions on the thickness of the phase difference layer formed from the liquid crystal composition, but it is preferably 0.2 to 10 μm, more preferably 0.5 to 5.0 μm, and even more preferably 0.7 to 2.0 μm.

[0170] The phase difference layer has a slow phase axis set at an angle α, for example, with respect to an axis in any direction of the phase difference layer. The direction of the slow phase axis can be set, for example, by rubbing the alignment film that forms the layer below the phase difference layer.

[0171] The above-mentioned P-polarized reflective film may have layers other than the selective reflective layer, polarization conversion layer, and phase difference layer described above. For example, the above-mentioned P-polarized reflective film may have a transparent substrate, an adhesive layer, etc. For example, in the example shown in Figure 4, the P-polarized reflective film 10A has a transparent substrate 18 positioned on the opposite side of the phase difference layer 16 from the selective reflective layer 11. The transparent substrate 18 supports the phase difference layer 16, the selective reflective layer 11 (cholesteric liquid crystal layer), and the polarization conversion layer 14. The transparent substrate 18 may also be used as a support when forming the phase difference layer 16, the selective reflective layer 11 (cholesteric liquid crystal layer), and the polarization conversion layer 14.

[0172] The above-mentioned P-polarizing reflective film may be in the form of a thin film or sheet. Before being used in the windshield glass, the above-mentioned P-polarizing reflective film may be in the form of a roll of thin film.

[0173] It is preferable that both the transparent substrate (support) and the adhesive layer are transparent in the visible light region. Furthermore, it is preferable that both the transparent substrate and the adhesive layer have low birefringence. Low birefringence means that in the wavelength range in which the selective reflective layer contained in the windshield glass used in the present invention exhibits reflection, the front phase difference is 10 nm or less. It is preferable that this front phase difference is 5 nm or less. Moreover, it is preferable that both the support and the adhesive layer have a small difference in refractive index from the average refractive index (in-plane average refractive index) of the selective reflective layer.

[0174] [Transparent base material] The transparent substrate can also be used as a substrate when forming the selective reflective layer. The transparent substrate used for forming the selective reflective layer may be a temporary support that is peeled off after the selective reflective layer is formed. Therefore, the finished P polarizing reflective film and windshield glass do not necessarily contain the transparent substrate. If the finished P polarizing reflective film or windshield glass contains the transparent substrate, rather than being peeled off as a temporary support, it is preferable that the transparent substrate is transparent in the visible light region.

[0175] There are no restrictions on the material of the transparent substrate. Examples of transparent substrates include plastic films such as polyethylene terephthalate (PET) and other polyesters, polycarbonates, acrylic resins, epoxy resins, polyurethanes, polyamides, polyolefins, cellulose derivatives, and silicones. In addition to the plastic films mentioned above, glass may also be used as a temporary support.

[0176] The thickness of the transparent substrate can be approximately 5.0 to 1000 μm, preferably 10 to 250 μm, and more preferably 15 to 90 μm.

[0177] In this case, if the transparent substrate is positioned on the outside of the vehicle relative to the selective reflective layer, it is preferable that the transparent substrate contains an ultraviolet absorber. By including an ultraviolet absorber in the transparent substrate, the degradation of the P polarizing reflective film (selective reflective layer) due to ultraviolet light can be suppressed.

[0178] [1-2] P-polarized reflective film containing dielectric multilayer film Figure 5 is a schematic diagram showing an example of a windshield glass used in the present invention. The P-polarizing reflective film 10B contained in this windshield glass 24B consists of a selective reflective layer (dielectric multilayer film) in which optically anisotropic layers (13Ra, 13Ga, 13Ba) and optically isotropic layers (13Rb, 13Gb, 13Ba) are alternately laminated. In the illustrated example, the P-polarizing reflective film 10B has a first laminated portion 13R in which optically anisotropic layer 13Ra and optically isotropic layer 13Rb are alternately laminated, a second laminated portion 13G in which optically anisotropic layer 13Ga and optically isotropic layer 13Gb are alternately laminated, and a third laminated portion 13B in which optically anisotropic layer 13Ba and optically isotropic layer 13Bb are alternately laminated. The above dielectric multilayer film has the following λ as its selective reflection center wavelength at an incident angle of light of 60°: B , λ G and λ R It is preferable to include these three wavelengths.

[0179] When the windshield glass 24 includes a windshield glass 24B containing a P-polarizing reflective film 10B as shown in Figure 5, the P-polarizing reflective film 10B selectively reflects the projected p-polarized light incident from the second glass plate 28 side while retaining its p-polarization.

[0180] The first laminated section 13R, the second laminated section 13G, and the third laminated section 13B have different thicknesses for the optically anisotropic layer and the optically isotropic layer. Furthermore, the number of layers, refractive index, etc., may also differ.

[0181] Furthermore, in the above P polarizing reflective film 10B, the refractive index n in the slow axis direction of the optical anisotropy layer e1 The refractive index n of the optically isotropic layer o2 exceeding (i.e., n e1 >n o2 ), refractive index n in the direction perpendicular to the slow axis of the optical anisotropy layer o1 The refractive index n of the optically isotropic layer o2 It is essentially the same as this. Multiple optically anisotropic layers are stacked so that their respective slow phase axes are parallel. Therefore, as shown in Figure 6, in one direction (the vertical direction in Figure 6), the refractive index (n e1 ) is a layer with a high refractive index (n o2 This results in a stacked state with layers having a low refractive index. On the other hand, in the direction perpendicular to this direction (left-right direction in Figure 6), layers with the same refractive index are stacked. When placing the P polarizing reflective film 10B on the HUD system 20 shown in Figures 1-3, it is positioned so that the axis P of the P polarizing reflective film 10B shown in Figure 6 coincides with the vertical direction Y of the windshield glass 24.

[0182] A film in which layers with low refractive index (low refractive index layers) and high refractive index (high refractive index layers) are alternately laminated is known to reflect light of specific wavelengths due to structural interference between numerous low and high refractive index layers. Therefore, the P-polarization reflective film 10B shown in Figures 5 and 6 reflects P-polarized light in the vertical direction and transmits P-polarized light in the horizontal direction in Figure 6.

[0183] Here, the dielectric multilayer film used in the HUD system of the present invention has the selected reflection center wavelength at an incident angle of light of 60° as the aforementioned λ. B , λ G and λ R It is preferable to include these three wavelengths.

[0184] In dielectric multilayer films, the selective reflection center wavelength and reflectivity can be adjusted by the refractive index difference between the low-refractive-index layer and the high-refractive-index layer, thickness, number of layers, etc. In the example shown in Figure 5, the first layer 13R mainly controls the selective reflection center wavelength λ at an incident angle of 60° of light. R This achieves a reflection having the following properties, and the second stacked portion 13G provides the aforementioned selective reflection center wavelength λ at an incident angle of 60° of light. G This achieves a reflection having the following properties, and the third stacked portion 13B provides the aforementioned selective reflection center wavelength λ at an incident angle of 60° of light. B It achieves a reflection that possesses this property.

[0185] In the above dielectric multilayer film, the reflection peak having the selective reflection center wavelength obtained by the above method is a maximum value having a difference of 2% or more from an adjacent minimum value, and has a half-value width of 10 to 200 nm.

[0186] As described above, the selective reflection center wavelength and reflectance in the dielectric multilayer film can be adjusted by the refractive index difference, thickness, stacked layers, etc. between the low refractive index layer and the high refractive index layer. Specifically, the selective reflection center wavelength can be adjusted by setting the thickness d of the low refractive index layer and the high refractive index layer to d = λ / (4×n) from the wavelength λ of the reflected light and the refractive index n. Also, since the reflectance increases as the number of stacked layers of the low refractive index layer and the high refractive index layer increases, the reflectance can be adjusted by adjusting the number of stacked layers. Further, the half-value width of the reflection peak having this selective reflection center wavelength can be adjusted by the refractive index difference between the low refractive index layer and the high refractive index layer.

[0187] Here, the half-value width of the reflection peak having each selective reflection center wavelength depends on the difference between the refractive index in the slow axis direction of the optically anisotropic layer and the refractive index of the optically isotropic layer, and the larger the refractive index difference, the larger the half-value width. Also, if reflection peaks with low reflectance are at wavelengths close to each other, interference occurs and the reflection peak becomes too strong or too weak. From the viewpoints of appropriately adjusting the half-value width of the reflection peak having each selective reflection center wavelength to improve the luminance of the display image while increasing the transmittance, and reducing the influence of interference with adjacent reflection peaks, the difference between the refractive index in the slow axis direction of the optically anisotropic layer and the refractive index of the optically isotropic layer is preferably 0.03 to 0.20, more preferably 0.05 to 0.14, and even more preferably 0.05 to 0.10.

[0188] Also, the dielectric multilayer film has a light reflection layer having the above λ as the selective reflection center wavelength at an incident angle of light of 60°, a light reflection layer having the above λ B and a light reflection layer having the above λ G and these light reflection layers preferably contact each other. For example, in the example shown in FIG. 5, the selective reflection center wavelength λ at an incident angle of light of 60° R and these light reflection layers preferably contact each other. For example, in the example shown in FIG. 5, the selective reflection center wavelength λ at an incident angle of light of 60°R A first laminated part 13R having G and a second laminated part 13G having a selective reflection center wavelength λ at an incident angle of light of 60° are in contact with each other, and also, the selective reflection center wavelength λ at an incident angle of light of 60° G A second laminated part 13G having and a third laminated part 13B having a selective reflection center wavelength λ at an incident angle of light of 60° are in contact with each other. The first laminated part 13R, the second laminated part 13G, and the third laminated part 13B are light reflection layers that constitute a dielectric multilayer film (selective reflection layer) used in the HUD system of the present invention. B Although not shown in FIG. 5, in addition to the three laminated parts 13R, 13G, and 13B, from the viewpoint of suppressing the reflected color tone, it is also preferable to include a selective reflection layer (hereinafter referred to as a light reflection layer UV) formed by laminating an optically anisotropic layer and an optically isotropic layer, which has a selective reflection center wavelength at an incident angle of light of 60° in the range of 300 nm or more and less than 400 nm.

[0189] When the windshield glass includes the cholesteric liquid crystal layer and the retardation layer described above and is configured with the light reflection layer UV provided, the color tone (especially yellowish color) confirmed when the windshield glass is observed under external light can be suppressed. When the light reflection layers having the respective selective reflection center wavelengths at an incident angle of light of 60° are separated from each other, the film thickness between the layers becomes thick, and it becomes difficult to obtain the effect of interference of light reflected by each light reflection layer. On the other hand, by adopting a configuration in which the light reflection layers are in contact with each other, the half-value width of the reflection peak having each selective reflection center wavelength can be narrowed by the effect of interference of light reflected by each light reflection layer.

[0190] The P-polarized light reflection film may be in the form of a thin film, such as a film or a sheet. Before being used for the windshield glass, the P-polarized light reflection film may be in the form of a roll as a thin film. <​​​​​​For example, materials and methods for fabricating dielectric multilayer films can be those described in Japanese Patent Publication No. 9-506837. Specifically, dielectric multilayer films can be formed using a wide variety of materials by processing under conditions selected to obtain the refractive index relationship. Generally, it is necessary that the first material has a different refractive index from the second material in a selected direction. This difference in refractive index can be achieved by various methods, including stretching, extrusion, or coating during or after film formation. Furthermore, it is preferable that the two materials have similar rheological properties (e.g., melt viscosity) so that they can be extruded simultaneously.

[0193] Materials particularly suitable for use in dielectric multilayer films include PEN (polyethylene naphthalate) and PET (polyethylene terephthalate) as materials for the optically anisotropic layer, and (isotropically adjusted) PEN, PET, and PMMA (polymethyl methacrylate resin) as materials for the optically isotropic layer.

[0194] As described above, the P-polarized reflective film (dielectric multilayer film) used in the HUD system of the present invention has the aforementioned λ as the selective reflection center wavelength at an incident angle of light of 60°. B , λ G and λ R To achieve a configuration having three wavelengths, it is preferable to have three laminated sections with different thicknesses for the optically anisotropic layer and the optically isotropic layer. In the present invention, the three laminated sections can be formed by stretching, extrusion molding, etc. as described above, and then the laminated sections can be bonded together to produce a P-polarized reflective film (dielectric multilayer film). Alternatively, the thickness before processing can be adjusted so that three laminated sections of different thicknesses are formed, and the three laminated sections can be integrally formed by stretching, extrusion molding, etc.

[0195] The thickness of the dielectric multilayer film is preferably 2.0 to 50 μm, and more preferably 8.0 to 30 μm.

[0196] A P-polarization reflective film containing a dielectric multilayer has a selective reflective layer (dielectric multilayer) formed by laminating an optically anisotropic layer and an optically isotropic layer. In addition to the dielectric multilayer, the P-polarization reflective film may also include a phase difference layer, a polarization conversion layer, a support, and an adhesive layer.

[0197] The phase difference layer, polarization conversion layer, support (transparent substrate), and adhesive layer used in the above-mentioned P-polarized reflective film can be described in the terms of the phase difference layer, polarization conversion layer, transparent substrate (support), and adhesive layer used in the P-polarized reflective film including the cholesteric liquid crystal layer described above.

[0198] Below, we will describe, in order, the components of the windshield glass other than the P polarizing reflective film mentioned above: the glass plate (laminated glass), the intermediate layer, and the heat-seal layer (adhesive layer).

[0199] [2] Laminated glass The windshield glass may have a laminated glass structure. The windshield glass used in the HUD system of the present invention is preferably laminated glass, and preferably has the above-mentioned P polarizing reflective film between the first glass plate and the second glass plate. The windshield glass may be configured such that a P-polarizing reflective film is placed between a first glass plate and a second glass plate. However, it is preferable that the windshield glass is configured such that an interlayer (interlayer sheet) is provided between the first glass plate and the P-polarizing reflective film, and between the P-polarizing reflective film and the second glass plate. In the windshield glass, as an example, as shown in Figures 1-3, the first glass plate 30 is positioned on the side opposite to the viewing side of the image in the HUD system (outside the vehicle), and the second glass plate 28 is positioned on the viewing side (inside the vehicle). In the windshield glass used in the HUD system of the present invention, the designations "first" and "second" in the first and second glass plates have no technical significance and are merely provided for convenience to distinguish between the two glass plates. Therefore, the second glass plate may be on the outside of the vehicle and the first glass plate on the inside. For the first and second glass plates, etc., glass plates commonly used for windshield glass can be used. For example, glass plates with a visible light transmittance of 80% or less, such as 73% and 76%, such as heat-shielding green glass, may be used. Even when using glass plates with low visible light transmittance in this way, by using the P polarizing reflective film described above, it is possible to produce windshield glass that has a visible light transmittance of 70% or more even at the position of the P polarizing reflective film.

[0200] There are no particular restrictions on the thickness of the glass plate, but it should be approximately 0.5 to 5.0 mm, preferably 1.0 to 3.0 mm, and more preferably 2.0 to 2.3 mm. The material or thickness of the first glass plate and the second glass plate may be the same or different.

[0201] Windshield glass having a laminated glass structure can be manufactured by the conventional method for producing laminated glass. Generally, laminated glass can be manufactured by sandwiching an interlayer film between two glass plates, repeating heat treatment and pressure treatment (such as treatment using rubber rollers) several times, and finally performing heat treatment under pressure using an autoclave or the like.

[0202] A windshield glass having a laminated glass structure with a P polarizing reflective film and an interlayer may, for example, be manufactured by first forming the P polarizing reflective film on the surface of a glass plate and then using the laminated glass manufacturing method described above, or by using the laminated glass manufacturing method described above with an interlayer for laminated glass containing the P polarizing reflective film described above. When forming a P-polarizing reflective film on the surface of a glass plate, the glass plate on which the P-polarizing reflective film is attached may be either a first glass plate or a second glass plate. In this case, the P-polarizing reflective film may be bonded to the glass plate, for example, with an adhesive (heat-seal layer).

[0203] [3] interlayer The interlayer 36 prevents the glass from penetrating the vehicle and shattering in the event of an accident. In the examples shown in Figures 1-3, the P polarizing reflective film 10 is bonded to the first glass plate 30; in the example shown in Figure 4, the P polarizing reflective film 10A is bonded to the first glass plate 30; and in the example shown in Figure 5, the P polarizing reflective film 10B is bonded to the second glass plate 28 and the first glass plate 30.

[0204] Any interlayer commonly used as an interlayer (interlayer sheet) in laminated glass can be used as the interlayer (interlayer sheet). For example, a resin film containing a resin selected from polyvinyl butyral (PVB), ethylene-vinyl acetate copolymer, and chlorine-containing resin can be used. The above-mentioned resin is preferably the main component of the interlayer. The main component refers to a component that accounts for 50% or more by mass of the interlayer.

[0205] Of the resins mentioned above, at least one of polyvinyl butyral and ethylene-vinyl acetate copolymer is preferred, with polyvinyl butyral being more preferred. The resin is preferably a synthetic resin. Polyvinyl butyral can be obtained by acetalizing polyvinyl alcohol with butyraldehyde. The preferable lower limit of the acetalization degree of the above-mentioned polyvinyl butyral is 40% or more, the preferable upper limit is 85% or less, the more preferable lower limit is 60% or more, and the more preferable upper limit is 75% or less.

[0206] Polyvinyl alcohol is usually obtained by saponifying polyvinyl acetate, and polyvinyl alcohol with a saponification degree of 80 to 99.8 mol% is generally used. In addition, the preferable lower limit of the polymerization degree of the above-mentioned polyvinyl alcohol is 200 or more, and the preferable upper limit is 3000 or less. When the polymerization degree of polyvinyl alcohol is 200 or more, the penetration resistance of the obtained laminated glass is unlikely to decrease. When it is 3000 or less, the formability of the resin film is good, and moreover, the rigidity of the resin film does not become too large and the processability is good. The more preferable lower limit is 500 or more, and the more preferable upper limit is 2000 or less.

[0207] Also, there is no limitation on the thickness of the intermediate film 36, and the thickness according to the forming material etc. may be set in the same way as the intermediate film of a conventional windshield glass.

[0208] In FIGS. 1 to 3, the windshield glass 24 has a heat seal layer 38 provided between the P-polarized light reflection film 10 and the second glass plate 28, and the P-polarized light reflection film 10 and the first glass plate 30 are adhered with the intermediate film 36, but it is not limited thereto. That is, a configuration in which a heat seal layer is provided between the P-polarized light reflection film 10 and the first glass plate 30, and an intermediate film is provided between the P-polarized light reflection film 10 and the second glass plate 28 may also be used. Also, a configuration in which the windshield glass 24 does not have the intermediate film 36, and the heat seal layer 38 is used for adhering the P-polarized light reflection film 10 and the second glass plate 28, and for adhering the P-polarized light reflection film 10 and the first glass plate 30 may also be used. The description of this paragraph regarding the heat seal layer 38 and the intermediate film 36 is similarly applicable in FIGS. 4 and 5.

[0209] (Interlayer containing P-polarizing reflective film) An interlayer for laminated glass containing a P-polarizing reflective film can be formed by laminating the P-polarizing reflective film to the surface of the aforementioned interlayer. Alternatively, the P-polarizing reflective film can be formed by sandwiching it between two of the aforementioned interlayers. The two interlayers may be the same or different, but it is preferable that they be the same. For bonding the P polarizing reflective film and the interlayer, a standard bonding method can be used, and lamination is preferred. The lamination is preferably carried out under certain heating and pressurizing conditions to prevent the laminate (P polarizing reflective film) and the interlayer from peeling off after processing. To ensure stable lamination, the surface temperature of the interlayer on the bonding side is preferably 50-130°C, and more preferably 70-100°C. Pressurization is preferable during lamination. There are no restrictions on the pressurization conditions, but 2.0 kg / cm² is preferable. 2 Preferably less than 196 kPa, and between 0.5 and 1.8 kg / cm³. 2 (49-176 kPa) is more preferable, and 0.5-1.5 kg / cm³ 2 (49-147 kPa) is even more preferable.

[0210] Furthermore, if the P-polarizing reflective film has a support (transparent substrate), the support may be peeled off simultaneously with lamination, immediately after lamination, or immediately before lamination. In other words, the P-polarizing reflective film attached to the interlayer obtained after lamination may not have a support. An example of a method for manufacturing an interlayer containing a P-polarized reflective film is: (1) A first step of laminating a P-polarized reflective film onto the surface of a first interlayer to obtain a first laminate, and (2) A second step of laminating a second interlayer to the side of the P polarizing reflective film in the first laminate that is opposite to the side to which the first interlayer is laminated. For example, in the first step, the P-polarizing reflective film and the first interlayer are bonded together without the support and the first interlayer facing each other. Next, the support is peeled off the P-polarizing reflective film. Furthermore, in the second step, the second interlayer is bonded to the surface from which the support was peeled off. This makes it possible to manufacture an interlayer containing a P-polarizing reflective film that does not have a support. In addition, by using this interlayer containing a P-polarizing reflective film, laminated glass in which the P-polarizing reflective film does not have a support can be easily manufactured. To ensure stable and damage-free peeling of the support, the temperature of the support when peeling it from the P-polarizing reflective film is preferably 40°C or higher, and more preferably 40-60°C.

[0211] [4] Heat seal layer (adhesive layer) The heat-seal layer (adhesive layer) 38 is, for example, a layer made of a coating-type adhesive. In the example shown in Figure 4, the P polarizing reflective film 10A is attached to the second glass plate 28 by the heat-seal layer 38. In the windshield glass used in the present invention, instead of the heat-seal layer 38, the P polarizing reflective film 10A may be attached to the second glass plate 28 by an interlayer. Also, if the P polarizing reflective film 10A is smaller than the interlayer 36 that attaches the first glass plate 30 and the P polarizing reflective film 10A, the P polarizing reflective film 10A may be attached to the second glass plate 28 by the interlayer 36.

[0212] There are no restrictions on the heat seal layer 38; any commonly used coating-type adhesive can be used as long as it can ensure the transparency required for the windshield glass 24 and adhere the P polarizing reflective film 10 to the glass with the necessary adhesive strength. The heat seal layer 38 may be the same as the interlayer 36, such as PVB. In addition, adhesives such as acrylate-based adhesives can also be used for the heat seal layer 38, as described below.

[0213] The heat seal layer 38 may be formed from an adhesive. Adhesives can be classified into hot-melt type, thermosetting type, photocuring type, reaction-curing type, and pressure-sensitive adhesive type that does not require curing, from the perspective of curing method. Furthermore, regardless of the type of adhesive, compounds selected from acrylate-based, urethane-based, urethane-acrylate-based, epoxy-based, epoxy-acrylate-based, polyolefin-based, modified olefin-based, polypropylene-based, ethylene vinyl alcohol-based, vinyl chloride-based, chloroprene rubber-based, cyanoacrylate-based, polyamide-based, polyimide-based, polystyrene-based, and polyvinyl butyral-based materials can be used as the material. From the viewpoint of workability and productivity, a photocuring type is preferred as the curing method, and from the viewpoint of optical transparency and heat resistance, it is preferable to use a compound selected from acrylate-based, urethane acrylate-based, and epoxy acrylate-based materials.

[0214] The heat-seal layer 38 may be formed using a highly transparent adhesive transfer tape (OCA tape). As the highly transparent adhesive transfer tape, commercially available products for image display devices, especially commercially available products for the surface of the image display part of an image display device, may be used. Examples of commercially available products include adhesive sheets manufactured by Panac Corporation (product name, PD-S1, etc.) and adhesive sheets of the MHM (product name) series manufactured by Nichiei Kako Co., Ltd.

[0215] There are no restrictions on the thickness of the heat seal layer 38. Therefore, depending on the material used to form the heat seal layer 38, a thickness that provides sufficient adhesion can be set as appropriate. If the heat seal layer 38 is too thick, it may not be possible to adhere the P polarizing reflective film 10 to the second glass plate 28 or the first glass plate 30 while maintaining sufficient flatness. Considering this point, the thickness of the heat seal layer 38 is preferably 0.1 to 800 μm, and more preferably 0.5 to 400 μm.

[0216] The present invention is basically configured as described above. Although the virtual image display device and HUD system of the present invention have been described in detail above, the present invention is not limited to the embodiments described above, and various improvements or modifications may be made without departing from the spirit of the present invention. [Examples]

[0217] The present invention will be described in more detail below based on examples. The materials, amounts used, proportions, processing content, and processing procedures shown in the following examples can be modified as appropriate without departing from the spirit of the present invention. Therefore, the scope of the present invention should not be interpreted as being limited by the specific examples shown below. In the following examples, "parts" and "%" used to express composition refer to mass unless otherwise specified. Room temperature is assumed to be 25°C.

[0218] <Preparation of coating solution> (1) Coating solution for forming a cholesteric liquid crystal layer For multiple coating solutions for forming cholesteric liquid crystal layers (B1, G1, R1) whose selective reflection center wavelengths are the desired wavelengths shown in Table 1 below, the following components were mixed to prepare coating solutions for forming cholesteric liquid crystal layers with the following compositions. ·Mixture 1 100 parts by mass • Fluorine-based horizontal orientation agent 1 (orientation control agent 1) 0.05 parts by mass • Fluorine-based horizontal orientation agent 2 (orientation control agent 2) 0.02 parts by mass • Right-rotating chiral agent Paliocolor LC756 (trade name, BASF) (Manufactured in Italy) Adjusted to match the reflection wavelength. • Polymerization initiator IRGACURE OXE01 (product name, manufactured by BASF) 1.0 parts by mass • Solvent (methyl ethyl ketone): Amount sufficient to achieve a solute concentration of 20% by mass.

[0219] Mixture 1: [ka]

[0220] Orientation control agent 1: [ka]

[0221] Orientation control agent 2: [ka]

[0222] (Reflective properties of the cholesteric liquid crystal layer) Using the cholesteric liquid crystal layer forming coating solutions prepared above, single-layer cholesteric liquid crystal layers (layers cured by polymerization reaction) with a thickness of approximately 3 μm were fabricated on a temporary support in the same manner as the fabrication of cholesteric liquid crystal layers described later. All fabricated cholesteric liquid crystal layers were confirmed to be right-circularly polarized reflective layers, and their selective reflection center wavelength (center wavelength) was confirmed to be the wavelength shown in Table 1 below. Note that the selective reflection center wavelengths listed in Table 1 are values ​​measured by the reflection spectrum measurement of the [Evaluation α] selective reflection layer described later.

[0223] [Table 1]

[0224] (2) Coating solution for forming a phase difference layer The following components were mixed in the composition ratio shown below to prepare a coating solution for forming a phase difference layer. ·Mixture 1 100 parts by mass • Fluorine-based horizontal orientation agent 1 (orientation control agent 1) 0.05 parts by mass • Fluorine-based horizontal orientation agent 2 (orientation control agent 2) 0.01 parts by mass • Polymerization initiator IRGACURE OXE01 (product name, manufactured by BASF) 1.0 parts by mass • Solvent (methyl ethyl ketone): Amount sufficient to achieve a solute concentration of 20% by mass.

[0225] (3) Coating solution for forming a polarizing layer The following components were mixed in the composition ratio shown below to prepare a coating solution for forming a polarizing layer. ·Mixture 1 100 parts by mass • Fluorine-based horizontal orientation agent 1 (orientation control agent 1) 0.05 parts by mass • Fluorine-based horizontal orientation agent 2 (orientation control agent 2) 0.02 parts by mass • Right-rotating chiral agent Paliocolor LC756 (trade name, BASF) (manufactured by) 0.26 parts by mass • Polymerization initiator IRGACURE OXE01 (product name, manufactured by BASF) 1.0 parts by mass • Solvent (methyl ethyl ketone): Amount sufficient to achieve a solute concentration of 20% by mass.

[0226] (Polarization characteristics of the polarization conversion layer) The selective reflection center wavelength λ of the polarization conversion layer obtained from the polarization conversion layer forming coating solution prepared above was 10,000 nm at an incident angle of light of 5°. The selective reflection center wavelength λ at an incident angle of 5° of light was measured by FTIR (Fourier Transform Infrared Spectroscopy, PerkinElmer, product name: Spectrum Two) after fabricating a single layer of cholesteric liquid crystal with a thickness of approximately 3 μm on a temporary support using the polarization conversion layer forming coating solution prepared above. Furthermore, in a cholesteric liquid crystal layer, the thickness d of the helical structure is expressed as "pitch P of the helical structure × number of pitches". As mentioned above, the pitch P of the helical structure refers to the thickness of the layer when the helically oriented liquid crystal compound rotates 360°. Also, in a cholesteric liquid crystal layer, the selective reflection center wavelength λ at an incident angle of light of 5° is equal to "pitch P of the helical structure × average refractive index n in the plane" (λ = P × n). Therefore, the pitch P of the helical structure becomes "selective reflection center wavelength λ at an incident angle of light of 5° / average refractive index n in the plane" (P = λ / n).

[0227] [Examples] [1] Preparation of P polarizing reflective film <1-1> Fabrication of a selective reflective layer consisting of a cholesteric liquid crystal layer (1) Preparation of saponified cellulose acylate film In the preparation of the cellulose acylate film described in Example 20 of International Publication No. 2014 / 112575, a cellulose acylate film with a thickness of 40 μm was prepared in the same manner as described in the International Publication No. 2014 / 112575, except that instead of 2 parts by mass of the ultraviolet absorber described in paragraph

[0277] of International Publication No. 2014 / 112575, a core layer cellulose acylate dope was used, which consisted of 3 parts by mass of the ultraviolet absorber UV-531 (trade name) manufactured by Teisei Chemicals Co., Ltd., per 100 parts by mass of cellulose acetate (excluding ester oligomer A). The prepared cellulose acylate film was passed through a dielectric heating roll at a temperature of 60°C to raise the film surface temperature to 40°C. Then, an alkaline solution with the composition shown below was applied to one side of the film using a bar coater at a rate of 14 mL / m². 2 The mixture was applied in this manner and then left under a steam-type far-infrared heater (manufactured by Noritake Co., Ltd.) heated to 110°C for 10 seconds. Next, using the same bar coater, add 3 mL / m² of pure water. 2 It was applied in this manner. Next, the cellulose acylate film (transparent support) was prepared by repeating the process of washing with a fountain coater and draining with an air knife three times, followed by drying in a 70°C drying zone for 5 seconds. The in-plane phase difference of a saponified cellulose acylate film was measured using AxoScan (Axometrics, trade name) and was found to be 1 nm.

[0228] ------------------------------------------------------------------ Composition of alkaline solution ------------------------------------------------------------------ • Potassium hydroxide 4.7 parts by mass ·Water 15.7 parts by mass Isopropanol 64.8 parts by mass • Surfactants (C 16 H 33O(CH2CH2O) 10 H) 1.0 parts by mass • Propylene glycol 14.9 parts by mass ------------------------------------------------------------------

[0229] (2) Formation of the orientation film Apply an orientation film-forming coating solution with the composition shown below to the saponified surface of a saponified cellulose acylate film (transparent support) using a wire bar coater at a rate of 24 mL / m². 2 The material was applied in this manner and dried with 100°C hot air for 120 seconds to form an oriented film.

[0230] ------------------------------------------------------------------ Composition of coating solution for aligning film formation ------------------------------------------------------------------ • 28 parts by mass of the modified polyvinyl alcohol shown below • Citrate ester (product name: AS3, manufactured by Sankyo Chemical Co., Ltd.) 1.2 parts by mass • Photoinitiator (Product name: Irgacure 2959, manufactured by BASF) 0.84 parts by mass Glutaraldehyde 2.8 parts by mass ·Water 699 parts by mass • Methanol 226 parts by mass ------------------------------------------------------------------

[0231] Modified polyvinyl alcohol: [ka]

[0232] (3) Fabrication of a laminate of a phase difference layer, a selective reflection layer, and a polarization conversion layer (3-1) Fabrication of the phase difference layer A cellulose acylate film with an orientation film formed on it was used as a support (transparent substrate). The orientation film surface of the support was subjected to rubbing in a direction rotated 45° clockwise from the long side of the support. Specifically, a rayon cloth was used, and the procedure was performed under the following conditions: pressure: 0.1 kgf (0.98 N), rotation speed: 1000 rpm (revolutions per minute), conveying speed: 10 m / min, and number of cycles: 1 round trip.

[0233] The phase difference layer forming solution prepared above was applied to the rubbed surface of the orientation film on the support using a wire bar, and then dried. Next, place it on a hot plate at 50°C and, in an environment with an oxygen concentration of 1000 ppm or less, use a Fusion UV Systems electrodeless lamp "D-bulb" (60 mW / cm²). 2 The liquid crystal phase was fixed by irradiating it with ultraviolet light for 6 seconds. This resulted in obtaining a phase difference layer whose thickness was adjusted to achieve the desired front phase difference, i.e., the desired retardation. The retardation of the fabricated phase difference layer was measured using AxoScan (Axometrics, product name) and found to be 126 nm.

[0234] (3-2) Fabrication of selective reflective layer The cholesteric liquid crystal layer (B1) forming solution prepared above was applied to the surface of the obtained phase difference layer using a wire bar at room temperature so that the film thickness after drying was as shown in Table 3 below, thereby obtaining a coated layer. The coated layer was dried at room temperature for 30 seconds, then heated in an 85°C atmosphere for 2 minutes. Afterwards, it was heated in an environment with an oxygen concentration of 1000 ppm or less at 60°C using a Fusion D valve (60 mW / cm²). 2 The cholesteric liquid crystal phase was fixed by irradiating it with ultraviolet light at 60% output for 6 to 12 seconds using a lamp, and a cholesteric liquid crystal layer B1 with the film thickness described in Table 3 below was obtained. Next, cholesteric liquid crystal layer G1 and cholesteric liquid crystal layer R1 were laminated on the surface of the obtained cholesteric liquid crystal layer B1 in the order shown in Table 3 below, to obtain a laminate in which three cholesteric liquid crystal layers were laminated on top of the phase difference layer. Each cholesteric liquid crystal layer G1 and R1 was fabricated one layer at a time, in the same manner as when fabricating cholesteric liquid crystal layer B1, except that the corresponding coating solution for each cholesteric liquid crystal layer (G1 and R1) was used instead of the coating solution for forming cholesteric liquid crystal layer (B1).

[0235] (3-3) Fabrication of the polarization conversion layer Next, the polarization conversion layer-forming coating solution prepared above was applied to the outermost surface of the cholesteric liquid crystal layer of the obtained laminate to a thickness of 1.7 μm to form a polarization conversion layer (twisted layer). The polarization conversion layer was formed in the same manner as in the preparation of the cholesteric liquid crystal layer described above, except that the polarization conversion layer-forming coating solution was used instead of the cholesteric liquid crystal layer-forming coating solution. The resulting polarization conversion layer was a twisted layer with a selective reflection center wavelength λ10000nm and a pitch of 0.265. In this manner, a laminate (also referred to as a "P-polarized reflective film") was fabricated by stacking a phase difference layer, a selective reflective layer, and a polarization conversion layer in that order on a support (transparent substrate).

[0236] <1-2> Fabrication of a P-polarized reflective film consisting of a selective reflective layer (dielectric multilayer film) Based on the method described in Japanese Patent Publication No. 9-506837, a P-polarized reflective film consisting of a direct-selective reflective layer (dielectric multilayer film) was fabricated as follows.

[0237] 2,6-Polyethylene naphthalate (PEN) and a copolyester (coPEN) consisting of 70 mol% naphthalate and 30 mol% terephthalate were synthesized in a standard polyester resin synthesis kettle using ethylene glycol as the diol. The obtained single-layer films of PEN and coPEN were extruded, stretched at approximately 150°C with a stretch ratio of 5:1, and heat-treated at approximately 230°C for 30 seconds. As a result of this stretching and heat treatment, the refractive index of the PEN film was approximately 1.86 along the slow axis (orientation axis), and the refractive index along the transverse axis was 1.64. It was confirmed that the coPEN film was isotropic and had a refractive index of approximately 1.64.

[0238] Next, by adjusting the stretching ratio, the refractive index of the PEN film with respect to the slow axis became approximately 1.71, and the refractive index with respect to the transverse axis became 1.64. It was confirmed that the coPEN film is isotropic and has a refractive index of approximately 1.64. In other words, the difference Δn between the refractive index of the optically anisotropic layer, the PEN film, in the direction of the slow axis, and the refractive index of the optically isotropic layer, the coPEN film, is 0.07.

[0239] Next, a P-polarized reflective film was fabricated by stretching and heat-treating a laminate obtained by simultaneously extruding PEN and coPEN. The thickness of this P-polarized reflective film is approximately 18.6 μm, and it has the P-polarized reflective layers (1) to (6) shown in Table 2 below in that order. Each P-polarized reflective layer is a layer having 16 alternating layers of PEN and coPEN with the thicknesses shown in each row of P-polarized reflective layers. Specifically, using a 32-slot supply block equipped with a standard extrusion die, under the same conditions as described in Example 1 of Japanese Patent Publication No. 9-506837, each pre-stretched laminate corresponding to the P-polarized reflective layers (1) to (6) in Table 2 below was prepared by adjusting the extrusion speeds of PEN and coPEN so that the thickness was one-quarter of the optical wavelength of the desired selective reflection center wavelength (5°). Then, the laminate formed by stacking all of these layers was uniaxially stretched at approximately 150°C with a stretch ratio of 5:1, and the stretched laminate was heat-treated in an air oven at approximately 230°C for 30 seconds to produce a P-polarized reflective film. Note that the selective reflection center wavelengths listed in Table 2 are values ​​measured by the reflection spectrum measurement of the [Evaluation α] selective reflection layer described later.

[0240] [Table 2]

[0241] [2] Fabrication of windshield glass <2-1> Fabrication of windshield glass having a selective reflective layer made of a cholesteric liquid crystal layer Using the laminate prepared above, in which a support (transparent substrate), a phase difference layer, a selective reflection layer, and a polarization conversion layer are stacked in that order, a laminate was prepared in which a first glass plate, an interlayer, a polarization conversion layer, a selective reflection layer (cholesteric liquid crystal layer), a phase difference layer, a support (transparent substrate), a heat seal layer, and a second glass plate are stacked in that order. In the above-mentioned laminate, the heat-seal layer was formed by applying a heat-seal layer forming solution to the support (transparent substrate) side of the selective reflective layer, which consists of a cholesteric liquid crystal layer, using a wire bar, drying it, and then heating it at 50°C for 1 minute to form a heat-seal layer with a thickness of 1 μm. The resulting laminate was held at 90°C and 10kPa (0.1 atm) for one hour, and then heated in an autoclave (manufactured by Kurihara Seisakusho) at 115°C and 1.3MPa (13 atm) for 20 minutes to remove air bubbles, thereby obtaining a windshield glass A having a selective reflective layer made of a cholesteric liquid crystal layer.

[0242] <2-2> Fabrication of windshield glass having a selective reflective layer made of dielectric multilayer film Using the P-polarized reflective film made of the dielectric multilayer film prepared as described above, a laminate was fabricated in which a second glass plate, an interlayer, a selective reflective layer (dielectric multilayer film), an interlayer, and the first glass plate were stacked in this order. The obtained laminate was held at 90°C and 10kPa (0.1 atm) for one hour, and then heated in an autoclave (manufactured by Kurihara Seisakusho) at 115°C and 1.3MPa (13 atm) for 20 minutes to remove air bubbles and obtain windshield glass B. In this case, the P-polarized reflective film was laminated such that the P-polarized reflective layer (1) was on the second glass plate side and the P-polarized reflective layer (6) was on the first glass plate side.

[0243] The windshield glass described above was used by cutting each layer to the same shape as the first and second glass plates described above. The glass plate, interlayer, and heat-sealing layer forming solution used in the production of the above-mentioned windshield glass are as follows: For the first and second glass plates, we used glass plates measuring 120mm in length x 100mm in width and 2mm in thickness (manufactured by Central Glass Co., Ltd., FL2, visible light transmittance 90%). Furthermore, a 0.38mm thick PVB (polyvinyl butyral) film manufactured by Sekisui Chemical Co., Ltd. was used as an interlayer. Furthermore, to prepare the heat seal layer, a coating solution for forming a heat seal layer was used, which was prepared by mixing the following components in the composition ratio shown below. (Coating liquid for forming a heat seal layer) • PVB sheet pieces (manufactured by Sekisui Chemical Co., Ltd., Esrec Film) 5.0 parts by mass • Methanol 90.25 parts by mass • Butanol 4.75 parts by mass

[0244] Table 3 below summarizes the configuration of the selective reflective layer in windshield glass A and B. In the design of the HUD system described later, the image display light was positioned so that it was incident on the second glass plate side of each windshield glass.

[0245] [Table 3]

[0246] [3] Fabrication of a positive diffraction reflector element <3-1> Fabrication of reflective liquid crystal diffraction elements An alignment film was formed on a primer layer created on a support, and this alignment film was irradiated with laser light. By changing the intersection angle of the two laser beams, the interference pattern (surface periodic structure) was controlled and cured. A reflective liquid crystal diffraction element was fabricated by forming a liquid crystal layer on the obtained photo-alignment film. Specifically, in the fabrication of a reflective liquid crystal diffraction element described in Example 2 of International Publication No. 2019 / 131966, the only difference was that the intersection angle of the two laser beams used to expose the alignment film with the exposure apparatus shown in Figure 5 of International Publication No. 2019 / 131966 was changed to obtain the desired diffraction reflection shown in Table 4 below. In this manner, a reflective liquid crystal diffraction element was fabricated in which the B reflective layer, G reflective layer, and R reflective layer were bonded together in this order with an adhesive (manufactured by Soken Chemical Co., Ltd., product name: SK Dyne 2075). Note that the selective reflection center wavelengths listed in Table 4 are values ​​measured by measuring the reflection spectrum of the [Evaluation α] selective reflection layer described later, and one period refers to the length of a 180° rotation of the optical axis originating from the liquid crystal compound.

[0247] [Table 4]

[0248] The reflective liquid crystal diffraction element fabricated as described above has polarization characteristics in its reflection and diffracts and reflects circularly polarized light. Therefore, in the design of the HUD system described later, the R-reflective layer side of the reflective liquid crystal diffraction element was bonded to a quarter-wave plate (Teijin Corporation, product name: PureAce WR-S, polycarbonate film, front retardation of 126 nm), and the element was positioned so that light from the image display device was incident on the side of this quarter-wave plate, thereby using it as a diffraction reflecting element that reflects P-polarized light.

[0249] <3-2> Fabrication of reflective holographic elements For dichromate gelatin, a photosensitive material, laser light was split into two beams using a beam splitter. Using these two separated laser beams, information about the amplitude and phase of the object light was created as an interference pattern (periodic refractive index distribution) with a reference light. Once the refractive index distribution was formed in the photosensitive material, it was cured to fabricate a volume-type reflective hologram element exhibiting the desired diffraction reflection shown in Table 5 below. In the obtained volume-type reflective hologram element, the period of the refractive index distribution on its surface acts as a diffraction grating.

[0250] [Table 5]

[0251] The volumetric reflective hologram element fabricated as described above does not possess polarization properties for reflection, but diffracts and reflects unpolarized light.

[0252] [4] Fabrication of half-wave plate A half-wave plate was fabricated by laminating two quarter-wave plates (Teijin Corporation, product name: PureAce WR-S, polycarbonate film, front retardation of 126 nm) using OCA tape (Nichiei Chemical Co., Ltd., product name: MHM-UVC15, thickness 15 μm). In the design of the HUD system described later, the half-wave plate was rotated and positioned to align the direction of the slow axis so that the transmitted light would have the desired polarization.

[0253] [5] Fabrication of negative transmission optical elements <5-1> Fabrication of a transmissive liquid crystal diffraction element An alignment film was formed on a primer layer created on a support, and this alignment film was irradiated with laser light. By changing the intersection angle of the two laser beams, the interference pattern (surface periodic structure) was controlled and cured. A transmissive liquid crystal diffraction element was fabricated by forming a liquid crystal layer on the obtained photo-alignment film without twisting the rod-shaped liquid crystal (without incorporating a chiral agent). Specifically, a transmissive liquid crystal diffraction element was fabricated according to the method for fabricating a transmissive optical anisotropic element (transmissive liquid crystal diffraction element) described in Example 2 of International Publication No. 2020 / 022513. The length (one period) over which the optical axis derived from the liquid crystal compound rotates by 180° was designed to be approximately 10 μm at the center of the element and approximately 1 μm at the edges of the element. In the design of the HUD system described later, the transmissive liquid crystal diffraction element fabricated above was used as is, positioned so that light from the image display device was incident on the liquid crystal layer side.

[0254] <5-2> Fabrication of transparent hologram elements A volume-type transmissive hologram element was fabricated in the same manner as described in <3-2> above, except that the interference pattern was adjusted to be transmissive. In the obtained volume-type reflective hologram element, the period of the refractive index distribution on its surface acts as a diffraction grating.

[0255] <5-3> Concave lens Concave lenses with the required curvature were fabricated using conventional methods, taking into account the size of the windshield glass, the distance between the windshield glass and the virtual image display device, and other optical components used in the HUD system.

[0256] [Design of a Head-Up Display System (HUD System)] Using the windshield glass, positive diffraction reflector, half-wave plate, and negative transmission optical element fabricated as described above, and the image display device described below, we designed HUD systems No. 101-107 and c11 shown in Table 6. HUD system No. 101 was arranged to have the configuration shown in Figure 1, HUD systems No. 102 to 104 to have the configuration shown in Figure 2, and HUD systems No. 105 to 107 to have the configuration shown in Figure 3. Note that HUD system No. 104 has a configuration in which an interlayer is used instead of the heat-seal layer, as shown in Figure 2. These HUD systems No. 101 to 107 are HUD systems equipped with the virtual image display device of the present invention. On the other hand, HUD system No. c11 shown in Table 6 is a HUD system equipped with a virtual image display device for comparison, designed using the positive diffraction reflector and negative transmission optical element fabricated above, along with the image display device and glass described below. HUD system No. c11 is arranged in the same configuration as in Figure 3, except that it does not have the half-wave plates 5A and 5B and uses glass instead of the windshield glass 24.

[0257] A light field display was used as the image display device. Furthermore, the polarization of the light emitted from the image display device was linearly polarized, and its polarization direction was rotated by approximately 10° from S-polarization. In addition, for HUD systems No. 101-107, the placement angles and other factors were adjusted so that the light incident on the positive diffractive reflector becomes S-polarized light, which has good diffraction efficiency, and becomes P-polarized light when it enters the windshield glass. In the No.c11 HUD system, the windshield glass is wedge-shaped glass, and even when reflecting S-polarized light, it is sometimes designed so that the HUD image can be seen to some extent even when wearing polarized sunglasses by using linearly polarized light whose polarization direction is rotated by about 10° from the aforementioned S-polarized light. Therefore, in the No.c11 HUD system, the above-mentioned HUD system was reproduced, and the arrangement angles were adjusted so that linearly polarized light whose polarization direction is rotated by about 10° from S-polarized light is incident on the positive diffraction reflector element, and linearly polarized light whose polarization direction is rotated by about 10° from S-polarized light is incident on the glass.

[0258] Brightness, brightness when wearing polarized sunglasses, and chromatic aberration were evaluated visually from a position 1 m away from the windshield glass (corresponding to the position of observer D in Figures 1-3). These results are summarized in Table 6 below.

[0259] [Evaluation α] Measurement of the reflectance spectrum of the selective reflector layer Of the fabricated windshield glass panels, a black PET (polyethylene terephthalate) film (light absorber) was laminated to the back surface of the first glass panel. Using a spectrophotometer (manufactured by JASCO Corporation, product name: V-670), P-polarized or S-polarized light was incident from a second glass plate of the windshield glass at a desired angle relative to the normal direction of the windshield glass surface, and the reflection spectra of P-polarized and S-polarized light in the wavelength band of 300 to 800 nm were measured. The average value (average reflection spectrum) of the measured P-polarized and S-polarized reflection spectra was calculated. In this invention, the selective reflection center wavelength (60°) is calculated based on the reflection spectrum measured when light is incident at an angle of 60° with respect to the normal direction of the windshield glass surface, and the selective reflection center wavelength (5°) is calculated based on the reflection spectrum measured when light is incident at an angle of 5° with respect to the normal direction of the windshield glass surface. Note that the average of the P-polarized and S-polarized reflection spectra is equivalent to the reflection spectrum when natural light is incident.

[0260] [Evaluation 1] Brightness evaluation An image of white text on a black background was displayed using an image display device, and the brightness was evaluated by applying the following evaluation criteria to the visual appearance of the text. - Evaluation Criteria (Brightness) - A: The text is readable outdoors in sunny conditions, and also readable under indoor lighting. A - The text is somewhat difficult to read outdoors in bright sunlight, but readable under indoor lighting. B: The text is somewhat difficult to read outdoors in bright sunlight, and also somewhat difficult to read under indoor lighting. C: The text is difficult to read outdoors, and somewhat difficult to read under indoor lighting.

[0261] [Evaluation 2] Evaluation of brightness when wearing polarized sunglasses White text on a black background was displayed using an image display device, and the brightness when wearing polarized sunglasses was evaluated by applying the following evaluation criteria to the appearance of the text as observed visually. In this exam, a score of "A" to "B" is considered a passing level. - Evaluation criteria (brightness when wearing polarized sunglasses) - A: The text is readable outdoors in sunny conditions, and also readable under indoor lighting. A - The text is somewhat difficult to read outdoors in bright sunlight, but readable under indoor lighting. B: The text is somewhat difficult to read outdoors in bright sunlight, and also somewhat difficult to read under indoor lighting. C: The text is invisible outdoors and also invisible under indoor lighting.

[0262] [Evaluation 3] Evaluation of chromatic aberration Photographs of buildings were displayed on a black background using an image display device, and chromatic aberration was evaluated by applying the visually observed color shifts (i.e., positional shifts of red, blue, and green images) to the evaluation criteria below. In this test, evaluations "A" and "B" indicate good chromatic aberration and are at a favorable level. - Evaluation Criteria (Chromatic Aberration) - A: The color shift is barely noticeable. B: A slight color shift is visible at the edge of the building. C: The color shift is clearly visible.

[0263] [Table 6]

[0264] (Notes in the table) The windshield glass, positive diffraction reflector, half-wave plate, and negative transmission optical element were fabricated as described above. Among positive diffraction reflecting elements, the polarization of reflected light from a reflective liquid crystal diffraction element is linear because it uses a stack of quarter-wave plates. Of the half-wave plates, the half-wave plate described in the first column is positioned on the optical path that guides the projected image light to the projection unit, between a diffraction reflector with positive optical power and a windshield glass. On the other hand, the half-wave plate described in the second column is positioned on the optical path that guides the projected image light to the projection unit, between the image display device and a transmissive optical element with negative optical power, or, if there is no negative transmissive optical element, between the image display device and a positive diffraction reflector.

[0265] The results in Table 6 show the following: As described in Patent Document 1, in the virtual image display device of HUD system No. c11, which does not include a half-wave plate as defined in the present invention, and in which projected image light from an image display device is diffracted by a diffraction reflector element with positive optical power and S-polarized image display light is incident on the projection part, when used in combination with a windshield glass equipped with an S-polarization reflector function, the projected characters were difficult to read outdoors and somewhat difficult to read under indoor lighting, and were invisible both outdoors and under indoor lighting when wearing sunglasses, and the brightness was poor. In contrast, in the virtual image display devices in HUD systems No. 101 to 107, which are equipped with a half-wave plate as defined in the present invention and in which projected image light from an image display device is diffracted by a diffraction reflector with positive optical power and P-polarized image display light is incident on the projection area, when used in combination with a windshield glass equipped with a P-polarization reflector function, the projected characters can be read regardless of whether sunglasses are being worn (the brightness evaluations in evaluations 1 and 2 are both "A" to "B"), and showed superior brightness compared to the virtual image display device in HUD system No. c11. Furthermore, HUD systems No. 101 to 107 equipped with the virtual image display device of the present invention also showed a good level of chromatic aberration.

[0266] Although we have described the present invention along with its embodiments, we do not intend to limit our invention in any detail of the description unless specifically designated, and we believe that it should be interpreted broadly without contradicting the spirit and scope of the invention as set forth in the appended claims.

[0267] This application claims priority based on Japanese Patent Application No. 2021-181368, filed in Japan on November 5, 2021, the contents of which are incorporated herein by reference as part of this specification. [Explanation of symbols]

[0268] 1. Virtual Image Display Device 2 Image display device 3. Positive diffraction reflector 5A, 5B 1 / 2 wavelength plate 7. Negative transmission optical elements 10 P polarizing reflective film 10A P polarizing reflective film 10B P polarizing reflective film 11 Selective Reflection Layer 12 Cholesteric liquid crystal layer 12R Selective reflection center wavelength λ at an incident angle of light of 60° R Cholesteric liquid crystal layer having 12G Selective reflection center wavelength λ at an incident angle of light of 60° G Cholesteric liquid crystal layer having 12B Selective reflection center wavelength λ at an incident angle of light of 60° B Cholesteric liquid crystal layer having 13R Selective reflection center wavelength λ at an incident angle of light of 60° R First laminate having 13G Selective reflection center wavelength λ at an incident angle of light of 60° G Second laminate having 13B Selective reflection center wavelength λ at an incident angle of light of 60° B Third laminate having 13Ra, 13Ga, 13Ba optically anisotropic layer 13Rb, 13Gb, 13Bb optically isotropic layer 14 Polarization conversion layer 16 Retardation layer 18 Transparent base material 20. Head-Up Display System (HUD System) 24, 24A, 24B Windshield Glass 28. Second glass plate 30 First glass plate 36 Interlayer 38 Adhesive layer (heat seal layer) D Observer L linear polarization PP Polarization SS Polarization n e1 Refractive index in the slow phase axis direction of the optically anisotropic layer n o1 Refractive index in the direction perpendicular to the slow axis of the optical anisotropy layer no2 Refractive index of an optically isotropic layer

Claims

1. A virtual image display device configured to be mounted on a transport aircraft, wherein P-polarized image display light is incident on the projection unit, A virtual image display device having an image display device that emits projected image light, wherein, on the optical path that guides the projected image light to the projection unit, a diffraction reflector with positive optical power and a half-wave plate with a front retardation of 200 nm to 400 nm are provided in order from the image display device side.

2. The virtual image display device according to claim 1, wherein, on the optical path, between the diffraction reflecting element having positive optical power and the image display device, there is a half-wave plate with a front retardation of 200 nm to 400 nm.

3. The virtual image display device according to claim 1 or 2, wherein the diffraction reflecting element with positive optical power is a reflective hologram element having a refractive index distribution with a fixed photosensitive material.

4. The virtual image display device according to claim 1 or 2, wherein the diffraction reflecting element having positive optical power is a diffraction element having an alignment film and a liquid crystal layer, having a liquid crystal alignment pattern corresponding to the periodic pattern of the alignment film, and having the function of diffracting and reflecting incident light.

5. The virtual image display device according to claim 1 or 2, wherein, on the optical path, a transmissive optical element with negative optical power is provided between the diffractive reflective element with positive optical power and the image display device.

6. The virtual image display device according to claim 5, wherein the aforementioned negative optical power transmissive optical element is a transmissive hologram element having a refractive index distribution with a fixed photosensitive material.

7. The virtual image display device according to claim 5, wherein the aforementioned negative optical power transmission optical element is a diffraction element having an alignment film and a liquid crystal layer, having a liquid crystal alignment pattern corresponding to the periodic pattern of the alignment film, and having the function of diffracting and transmitting incident light.

8. The virtual image display device according to claim 5, wherein the aforementioned negative optical power transmissive optical element is a lens that refracts the projected image light.

9. The virtual image display device according to claim 1 or 2, wherein the image display device is a light field display.

10. A head-up display system comprising a windshield glass having a first glass plate, a P-polarizing reflective film, and a second glass plate, and a virtual image display device according to claim 1 or 2.

11. The head-up display system according to claim 10, wherein the P-polarized reflective film has a layer made of cholesteric liquid crystal.

12. The head-up display system according to claim 10, wherein the P polarizing reflective film has a layer formed by laminating an optically anisotropic layer and an optically isotropic layer.

13. A transport aircraft equipped with the head-up display system described in claim 10.

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